U.S. patent application number 16/342873 was filed with the patent office on 2019-08-15 for acrylic polymers and compositions containing such polymers.
This patent application is currently assigned to SWIMC LLC. The applicant listed for this patent is SWIMC LLC. Invention is credited to Marie Braillon, Joseph DeSousa, Sebastien Gibanel, Nusrah Hussain, Jason S. Ness, Robert M. O'Brien, Samuel Puaud, Kailas Sawant.
Application Number | 20190249029 16/342873 |
Document ID | / |
Family ID | 62018867 |
Filed Date | 2019-08-15 |
United States Patent
Application |
20190249029 |
Kind Code |
A1 |
Gibanel; Sebastien ; et
al. |
August 15, 2019 |
ACRYLIC POLYMERS AND COMPOSITIONS CONTAINING SUCH POLYMERS
Abstract
A coating composition is provided that is preferably
substantially free of bisphenol A. The coating composition is
useful in coating metal substrates such as, for example, interior
and/or exterior surfaces of food or beverage cans. In some
embodiments, the coating composition is formulated using an acrylic
polymer that is formed form ingredients that do not include
styrene.
Inventors: |
Gibanel; Sebastien; (Givry,
FR) ; Braillon; Marie; (Tournus, FR) ; Puaud;
Samuel; (Tournus, FR) ; Hussain; Nusrah;
(Gibsonia, PA) ; Sawant; Kailas; (Mars, PA)
; DeSousa; Joseph; (Pittsburgh, PA) ; O'Brien;
Robert M.; (Monongahela, PA) ; Ness; Jason S.;
(Woodbury, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SWIMC LLC |
Cleveland |
OH |
US |
|
|
Assignee: |
SWIMC LLC
Cleveland
OH
|
Family ID: |
62018867 |
Appl. No.: |
16/342873 |
Filed: |
October 19, 2017 |
PCT Filed: |
October 19, 2017 |
PCT NO: |
PCT/US2017/057432 |
371 Date: |
April 17, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62410255 |
Oct 19, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B65D 51/00 20130101;
B65D 23/02 20130101; C09D 133/08 20130101; B05D 7/227 20130101;
B05D 7/14 20130101; C08F 220/18 20130101; B05D 1/02 20130101; B65D
25/14 20130101; C09D 133/02 20130101; B05D 2520/05 20130101; C08F
2/22 20130101; C09D 125/14 20130101; C09D 7/65 20180101; C09D
133/10 20130101; C08L 33/06 20130101; C08F 220/1804 20200201; B05D
2202/25 20130101; C09D 5/024 20130101 |
International
Class: |
C09D 133/08 20060101
C09D133/08; B05D 7/22 20060101 B05D007/22; B05D 7/14 20060101
B05D007/14; C08F 220/18 20060101 C08F220/18 |
Claims
1. An inside spray coating composition comprising: an acid- or
anhydride-functional acrylic polymer comprising an acid- or
anhydride-functional latex that is substantially free of styrene
and has a glass transition temperature of greater than 40.degree.
C.; and a nitrogen-containing carboxyl-reactive crosslinker;
wherein the coating composition is an aqueous coating composition
that is suitable for use in forming a food-contact coating of a
metal food or beverage can and is substantially free of bisphenol
A.
2-40. (canceled)
41. The coating composition of claim 1, wherein the
nitrogen-containing carboxyl-reactive crosslinker includes hydroxyl
groups and at least one amide group.
42. The coating composition of claim 41, wherein the
nitrogen-containing carboxyl-reactive crosslinker includes a
hydroxyl group that is located beta relative to the nitrogen atom
of at least one amide group.
43. The coating composition of claim 1, wherein the
nitrogen-containing carboxyl-reactive crosslinker comprises one or
more groups capable of forming an intermediate having an
oxazolinium structure.
44. The coating composition of claim 1, wherein the
nitrogen-containing carboxyl-reactive crosslinker comprises:
##STR00004##
45. The coating composition claim 1, wherein the
nitrogen-containing carboxyl-reactive crosslinker includes one or
more aziridine, diimide, or oxazoline groups.
46. The coating composition of claim 1, wherein the coating
composition includes at least one weight percent, based on total
resin solids, of the nitrogen-containing carboxyl-reactive
crosslinker, and wherein the coating composition includes at least
50 weight percent, based on total resin solids, of the acid- or
anhydride-functional latex.
47. The coating composition of claim 1, wherein the acid- or
anhydride-functional latex has an acid number of at least 20 mg
KOH/g resin.
48. The coating composition of claim 1, wherein at least a portion
of the acid- or anhydride-functional latex is formed from an
emulsion polymerized ethylenically unsaturated monomer component
including at least one monomer having (i) a Tg of more than
40.degree. C. and (ii) one or more groups selected from cyclic
groups, branched organic groups, or a combination thereof.
49. The coating composition of claim 48, wherein at least one
branched organic group is present, and the at least one monomer
having (i) and (ii) has the following structure:
(R.sup.3).sub.2--C.dbd.C(R.sup.4)--W.sub.n--Y, wherein: R3 is
independently selected from hydrogen or an organic group; R4 is
selected from hydrogen or an alkyl group; W, if present, is a
divalent linking group; n is 0 or 1; and Y comprises a branched
organic group including one or more branching atoms.
50. The coating composition of claim 49, wherein Y is a branched
organic group of the following structure:
--C(CH.sub.3).sub.t(R.sup.5).sub.3-t wherein: t is 1; each R.sup.5
comprises an alkyl group that may optionally be itself branched;
two or more R.sup.5 may optionally form a cyclic group with one
another; and the total number of carbon atoms in both R.sup.5
groups is 6, 7, or 8.
51. The coating composition of claim 48, wherein the emulsion
polymerized ethylenically unsaturated monomer component includes at
least 10 weight percent of one or more branched or cyclic
monomers.
52. The coating composition of claim 1, wherein one or both of: (i)
the acid- or anhydride-functional latex polymer and (ii) the
coating composition are substantially free of each of bisphenols
and halogenated monomers.
53. The coating composition of claim 1, wherein the acid- or
anhydride functional latex is formed from ingredients including an
emulsion polymerized ethylenically unsaturated monomer component
that includes a multi-ethylenically unsaturated monomer.
54. The coating composition of claim 1, wherein the emulsion
polymerized ethylenically unsaturated monomer component includes at
least 20 weight percent of methyl methacrylate.
55. The coating composition of claim 1, wherein the coating
composition includes, based on total resin solids, from 1 to 20
weight percent of the nitrogen-containing carboxyl reactive
crosslinker and from 50 to 99 weight percent of the acid- or
anhydride-functional latex.
56. The coating composition of claim 1, wherein the coating
composition includes both the nitrogen-containing carboxyl reactive
crosslinker and a resole phenolic crosslinker.
57. The coating composition of claim 17, wherein the coating
composition includes, based on total resin solids, 2 to 10 weight
percent of a beta-hydroxyalkylamide crosslinker and 1 to 10 weight
percent of a resole phenolic crosslinker.
58. The coating composition of claim 1, wherein the acid- or
anhydride-functional latex is a reaction product of a
multi-ethylenically unsaturated monomer component emulsion
polymerized in the presence of a non-polymeric surfactant.
59. The coating composition of claim 1, wherein the coating
composition exhibits an elongation at break of at least 1% when
tested pursuant to the Elongation at Break test disclosed
herein.
60. A method of coating a food or beverage can, comprising the
steps of: spray applying the coating composition of claim 1 on an
interior surface of a food or beverage can, or a portion thereof,
and curing the coating composition on the metal substrate to form a
continuous cured coating having an average film thickness of from
about 2 to about 15 micrometers and a metal exposure value after
drop damage of less than 10 mA when tested pursuant to the Metal
Exposure after Drop Damage test disclosed herein.
61. A food or beverage can, or a portion thereof, having an
interior food-contact coating having an overall average dry coating
thickness of from 2 to 15 micrometers, wherein: the interior
food-contact coating is formed from a spray applied aqueous coating
composition of claim 1; and the interior food-contact coating has a
metal exposure value after drop damage of less than 10 mA when
tested pursuant to the Metal Exposure after Drop Damage test
disclosed herein.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/410,255 filed on Oct. 19, 2016 and entitled
"STYRENE-FREE ACRYLIC POLYMERS AND COMPOSITION CONAINING SUCH
POLYMERS," which is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] There is a desire to reduce or eliminate the use of certain
bisphenol A-derived polymers in food or beverage container
coatings. Although a number of replacement coating compositions
made without bisphenol A have been proposed, some replacement
compositions have exhibited insufficient coating properties such as
insufficient corrosion resistance on metal substrates, insufficient
flexibility or insufficient toughness.
[0003] In recent years styrene has also come under greater
scrutiny. Although the balance of scientific evidence indicates
that coatings containing polymerized styrene are safe for
food-contact end uses, there is a desire by some to eliminate
styrene from such end uses. Styrene, however, brings advantageous
properties that contribute to the overall performance of food or
beverage can coatings and can be difficult to replicate using other
materials.
[0004] Coatings for use on food or beverage containers should avoid
unsuitably altering the taste of the packaged food or beverage
products, and should also avoid flaking or chipping into the
packaged products. The coatings should also resist chemically
aggressive food or beverage products (which can have a complex
chemical profile, including salts, acids, sugars, fats, etc.) for
extended periods of time (e.g., years). Food or beverage container
coatings should also have good adhesion to the underlying substrate
and remain sufficiently flexible after curing to survive subsequent
fabrication and/or denting during transportation, storage or use
that causes the metal substrate to deform and the coating to flex.
Some brittle coatings have been observed to crack during flexure,
thereby exposing the container metal to the packaged products,
which can cause contamination of the packaged product and even
cause a leak in the container. Even a low probability of coating
failure may cause a significant number of containers to leak, given
the large number of manufactured food and beverage containers.
[0005] Accordingly, it will be appreciated that what is needed in
the art are improved coating compositions that are made without
intentionally using bisphenol A and/or styrene, but which exhibit
the stringent balance of coating properties to permit the use of
such coating compositions on food or beverage containers.
SUMMARY
[0006] In one aspect, the invention provides a free-radical
polymerized polymer that is preferably an acrylic polymer, more
preferably an acrylic polymer that is substantially free of
styrene. In preferred embodiments, the polymer preferably: (i) has
a glass transition temperature of greater than 40.degree. C., more
preferably from greater than 40.degree. C. to less than 100.degree.
C., and more preferably from greater than 50.degree. C. to less
than 80.degree. C. and/or (ii) is formed from ingredients including
an ethylenically unsaturated monomer component that includes one or
both of a monomer having a cyclic group or a monomer having a
branched organic group. An acid- or anhydride-functional acrylic
latex is preferred in some embodiments.
[0007] In another aspect, the invention provides an acrylic coating
composition that is preferably substantially free of each of
styrene (and preferably also substantially free of halogenated
monomers) and bisphenol A (and preferably substantially free of
each of bisphenol A, bisphenol F, and bisphenol S, including
epoxides thereof), and exhibits an enhanced elongation at break
that is preferably comparable to a conventional styrene-containing
acrylic coating. In preferred embodiments, the coating composition
exhibits a sufficient amount of flexibility when cured to be
suitable for use as an interior or exterior coating on an aluminum
beverage can.
[0008] In one embodiment, the invention provides a coating
composition that exhibits an elongation at break of at least 1%
when suitably cured and tested as a free film. The coating
composition preferably includes an emulsion polymerized latex
polymer that is substantially free of each of styrene and
halogenated monomers and preferably has a glass transition
temperature of greater than 40.degree. C. The coating composition
is preferably an aqueous coating composition that is suitable for
use in forming a food-contact coating of a metal food or beverage
can (e.g., an inside spray coating of an aluminum beverage can) and
is substantially free of bisphenol A (and preferably substantially
free of each of bisphenol A, bisphenol F, and bisphenol S,
including epoxides thereof).
[0009] In yet another aspect, the invention provides a coating
composition that includes an acid- or anhydride-functional acrylic
polymer (more preferably an acid or anhydride-functional acrylic
latex) that is preferably substantially free of styrene and
preferably has a glass transition temperature of greater than
40.degree. C. The coating composition preferably includes a
carboxyl-reactive crosslinker, and more preferably a
nitrogen-containing carboxyl-reactive crosslinker. The coating
composition preferably includes a liquid carrier that includes one
or both of water and an organic solvent. In preferred embodiments,
the coating composition is a coating composition suitable for use
in forming a food-contact coating of a metal food or beverage can
and is substantially free of bisphenol A (and preferably
substantially free of each of bisphenol A, bisphenol F, and
bisphenol S, including epoxides thereof).
[0010] In yet another aspect, the invention provides a coating
composition that includes an acid- or anhydride-functional acrylic
polymer that is optionally substantially free of styrene (some
embodiments may include styrene). The acid- or anhydride-functional
acrylic polymer is preferably an acid- or anhydride-functional
latex formed by emulsion polymerizing ethylenically unsaturated
monomers comprising more than 5 wt- %, more than 6 wt- %, more than
7 wt- %, more than 8 wt- %, more than 9 wt- %, more than 10 wt- %,
more than 11 wt- %, more than 12 wt- %, more than 13 wt- %, or more
than 14 wt- % of multi-ethylenically unsaturated monomer. The
coating composition preferably includes a carboxyl-reactive
crosslinker (e.g., a nitrogen-containing carboxyl-reactive
crosslinker). In preferred embodiments, the coating composition is
an aqueous coating composition that is suitable for use in forming
a food-contact coating (e.g., inside spray beverage can coating) of
a metal food or beverage can and is substantially free of bisphenol
A (and preferably substantially free of each of bisphenol A,
bisphenol F, and bisphenol S, including epoxides thereof).
[0011] In yet another aspect, the invention provides a method of
coating a food or beverage can, or a portion thereof, including
receiving a coating composition described herein and applying the
coating composition on a metal substrate prior to, or after,
forming the metal substrate into a food or beverage can or a
portion thereof In some embodiments, the method includes spray
applying the coating composition to an interior portion of a food
or beverage can.
[0012] In yet another aspect, the invention provides an inside
spray beverage can coating composition that comprises an aqueous
coating composition that is preferably substantially free of each
of styrene and halogenated monomers and is also preferably
substantially free of bisphenol A (and more preferably
substantially free of each of bisphenol A, bisphenol F, and
bisphenol S, including epoxides thereof). The coating composition
preferably includes, based on total resin solids, at least 50 wt- %
of an emulsion polymerized latex. In preferred embodiments, the
inside spray beverage can coating composition, when spray applied
onto an interior of a standard 12-ounce two-piece drawn and ironed
aluminum 211 diameter beverage can at a dry film weight of 120
milligrams per can and cured at an oven temperature of at least
188.degree. C. to achieve a dome peak temperature of at least
199.degree. C., gives a metal exposure of less than 20 mA, less
than 10 mA, or less than 3.5 mA when tested pursuant to the Metal
Exposure after Drop Damage test disclosed herein.
[0013] In yet another aspect, the invention provides an article
having a metal substrate, wherein at least a portion of the metal
substrate has a coating disposed thereon formed from a coating
composition of the present invention. In some embodiments, the
article is a food or beverage can or a portion thereof. In certain
preferred embodiments, the article is an aluminum beverage can
having an inside spray coating disclosed herein on an interior
surface.
[0014] The above summary of the present invention is not intended
to describe each disclosed embodiment or every implementation of
the present invention. The description that follows more
particularly exemplifies illustrative embodiments. In several
places throughout the application, guidance is provided through
lists of examples, which can be used in various combinations. In
each instance, the recited list serves only as a representative
group and should not be interpreted as limiting or as an exclusive
list.
[0015] The details of one or more embodiments of the invention are
set forth in the description below. Other features, objects, and
advantages of the invention will be apparent from the description
and from the claims.
Selected Definitions
[0016] Unless otherwise specified, the following terms as used
herein have the meanings as provided below.
[0017] As used herein, the term "organic group" means a hydrocarbon
group (with optional elements other than carbon and hydrogen, such
as oxygen, nitrogen, sulfur, and silicon) that is classified as an
aliphatic group, a cyclic group, or combination of aliphatic and
cyclic groups (e.g., alkaryl and aralkyl groups).
[0018] A group that may be the same or different is referred to as
being "independently" something. Substitution on the organic groups
of the compounds of the present invention is contemplated. As used
throughout this application, the terms "group" and "moiety" are
used to differentiate between chemical species that allow for
substitution or that may be substituted and those that do not allow
or may not be so substituted. Thus, when the term "group" is used
to describe a chemical substituent, the described chemical material
includes the unsubstituted group and that group with O, N, Si, or S
atoms, for example, in the chain (as in an alkoxy group) as well as
carbonyl groups or other conventional substitution. Where the term
"moiety" is used to describe a chemical compound or substituent,
only an unsubstituted chemical material is intended to be included.
For example, the phrase "alkyl group" is intended to include not
only pure open chain saturated hydrocarbon alkyl substituents, such
as methyl, ethyl, propyl, t-butyl, and the like, but also alkyl
substituents bearing further substituents known in the art, such as
hydroxy, alkoxy, alkylsulfonyl, halogen atoms, cyano, nitro, amino,
carboxyl, etc. Thus, "alkyl group" includes ether groups,
haloalkyls, nitroalkyls, carboxyalkyls, hydroxyalkyls, sulfoalkyls,
etc. On the other hand, the phrase "alkyl moiety" is limited to the
inclusion of only pure open chain saturated hydrocarbon alkyl
substituents, such as methyl, ethyl, propyl, t-butyl, and the like.
As used herein, the term "group" is intended to be a recitation of
both the particular moiety, as well as a recitation of the broader
class of substituted and unsubstituted structures that includes the
moiety.
[0019] The term "ethylenically unsaturated" refers to a
carbon-carbon double or triple bond capable of participating in a
free-radical initiated polymerization reaction, and is not intended
to encompass the carbon-carbon double bonds present in aryl groups
such as, for example, the phenyl group of styrene. Thus, for
example, dodecyl benzene sulfonic acid is not considered to include
an ethylenically unsaturated group.
[0020] The term "branched organic group" refers to a
carbon-containing group that has a branching atom (e.g., carbon,
nitrogen, silicon, or phosphorus) that is attached to at least
three other atoms other than hydrogen, more typically at least
three carbon-containing groups (e.g., --CR.sub.3, --OCR.sub.3,
--NH--C(O)--O--CR.sub.3, and the like, where each R is
independently any suitable atom or group such as a halogen, a
hydrogen, an organic group, or a non-carbon-containing group (e.g.,
--OH, --NH.sub.2, etc.)), and even more typically at least three
carbon atoms of at least three carbon-containing groups.
[0021] The term "branched alkyl group" refers to an alkyl group,
which optionally includes one or more heteroatoms (e.g., O, N, P,
Si, etc.), that includes at least one carbon-containing substituent
group in place of a hydrogen (e.g., --CR.sub.3, --O--CR.sub.3,
--NH--C(O)--O--CR.sub.3 and the like where each R is as described
above). The term "branched alkyl moiety" refers to a branched alkyl
group that does not include any heteroatoms.
[0022] The term "on" when used in the context of a coating applied
on a surface or substrate, includes both coatings applied directly
or indirectly to the surface or substrate. Thus, for example, a
coating applied to a primer layer overlying a substrate constitutes
a coating applied on the substrate.
[0023] Unless otherwise indicated, the term "polymer" includes both
homopolymers and copolymers (e.g., polymers of two or more
different monomers). Similarly, unless otherwise indicated, the use
of a term designating a polymer class such as, for example,
"acrylic" is intended to include both homopolymers and copolymers
(e.g., polyether-acrylate copolymers).
[0024] The term "monomer" includes any reactant molecule used to
produce a polymer, and encompasses both single-unit molecules
(e.g., an acrylic molecule) and multi-unit molecules (e.g., an
acrylic oligomer).
[0025] A group that may be the same or different is referred to as
being "independently" something. The term "group" also encompasses
single atom moieties. Thus, for example, a halogen atom can be a
group.
[0026] The terms "acrylate" and "acrylic" are used broadly (and
interchangeably) herein and encompass materials prepared from, for
example, one or more of acrylic acid, methacrylic acid, or any
acrylate or methacrylate compound. Thus, for example, a homopolymer
consisting entirely of polymerized (meth)acrylic acid would still
be an "acrylate" polymer even though no (meth)acrylate monomer was
employed.
[0027] The term "(meth)" as used in "(meth)acrylate",
"(meth)acrylic acid", and the like is intended to indicate that
either a hydrogen or methyl group may be attached to the pertinent
carbon atom of the monomer. For example "ethyl (meth)acrylate"
encompasses both ethyl acrylate and ethyl methacrylate, as well as
mixtures thereof.
[0028] The term "substantially free" when used with respect to a
coating composition, or polymer or other composition, that may
contain a particular compound means that the referenced composition
contains less than 1,000 parts per million (ppm) of the recited
compound whether the compound is mobile in the composition or bound
to a constituent of the composition (e.g., as a structural unit of
a polymer). The term "essentially free" when used with respect to a
coating composition, or polymer or other composition, that may
contain a particular compound means that the referenced composition
contains less than 100 parts per million (ppm) of the recited
compound. The term "essentially completely free" when used with
respect to a coating composition, or polymer or other composition,
that may contain a particular compound means that the referenced
composition contains less than 5 parts per million (ppm) of the
recited compound. The term "completely free" when used with respect
to a coating composition, or a polymer or other composition, that
may contain a particular compound means that the referenced
composition contains less than 20 parts per billion (ppb) of the
recited compound. When the phrases "free of" (outside the context
of the aforementioned phrases), "does not include any" and the like
are used herein, such phrases are not intended to preclude the
presence of trace amounts of the pertinent structure or compound
which may be present, e.g., as environmental contaminants.
[0029] As used herein, the term "styrene-free" indicates that
styrene was not intentionally used, although trace amounts of
contaminating styrene may be present (e.g., due to environmental
contamination).
[0030] The terms "preferred" and "preferably" refer to embodiments
that may afford certain benefits, under certain circumstances.
However, other embodiments may also be preferred, under the same or
other circumstances. Furthermore, the recitation of one or more
preferred embodiments does not imply that other embodiments are not
useful, and is not intended to exclude other embodiments from the
scope of the invention.
[0031] The terms "comprises" and variations thereof do not have a
limiting meaning where these terms appear in the description and
claims.
[0032] As used herein, "a," "an," "the," "at least one," and "one
or more" are used interchangeably. Thus, for example, a coating
composition that comprises "a" surfactant can be interpreted to
mean that the coating composition includes "one or more"
surfactants.
[0033] Also herein, the recitations of numerical ranges by
endpoints include all numbers subsumed within that range (e.g., 1
to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). Furthermore,
disclosure of a range includes disclosure of all subranges included
within the broader range (e.g., 1 to 5 discloses 1 to 4, 1.5 to
4.5, 4 to 5, etc.).
DETAILED DESCRIPTION
[0034] The present invention provides an acrylic coating
composition that provides a good balance of coating properties for
food and beverage container coatings. Such properties include, for
example, good adhesion, good flexibility, and good corrosion
resistance. In preferred embodiments, the coating composition is
formulated using an acrylic polymer that is styrene-free. In such
preferred embodiments, the coating composition is also preferably
styrene-free. In some embodiments, the acrylic resin system, and
preferably also the coating composition, is also substantially free
of substituted styrene compounds (e.g., alpha-methyl styrene,
methyl styrenes (e.g., 2-methyl styrene, 4-methyl styrene, vinyl
toluene, and the like), dimethyl styrenes (e.g., 2,4-dimethyl
styrene), trans-beta-styrene, divinylbenzene, and the like).
[0035] Nonetheless, the various embodiments disclosed herein may
optionally also, or alternatively, include styrene, although it is
not presently preferred.
[0036] The use of styrene in can coating compositions, including
inside spray beverage can coating compositions, has been
advantageous for a variety of reasons, including, for example,
because styrene possesses both a high level of hydrophobicity and a
relatively high glass transition temperature ("Tg") and can
contribute to substrate adhesion, which can positively affect
coating flexibility. Prior attempts to replace styrene in acrylic
food or beverage can coatings have often resulted in coating
systems that either exhibit an unsuitable balance of coating
properties for such end uses or exhibit one or more coating
properties that are substantially diminished relative to
conventional styrene-containing acrylic coating systems.
[0037] Acrylic can coatings have often suffered from flexibility
problems and have generally been regarded as relatively inflexible
as compared to other can coatings such as bisphenol-A-based epoxy
can coatings. The relative inflexibility of acrylic resin systems
tends to worsen with increasing Tg and, therefore, most
conventional "high" Tg acrylics are unsuitable for use in can
coatings, including inside spray beverage can coatings, due to
insufficient flexibility for the end use. Moreover, omitting
styrene from such "high" Tg acrylics further exacerbates the
flexibility problems. The use of "high" Tg acrylic polymers,
however, can be beneficial for purposes of achieving one or both of
(i) decreased flavor scalping by the cured coating and (ii)
enhanced chemical resistance by the cured coating. Surprisingly,
preferred acrylic coating compositions of the present invention are
capable of simultaneously exhibiting good adhesion, good
flexibility (e.g., sufficient flexibility for use as an inside
spray coating of a drawn and ironed aluminum beverage can), good
corrosion resistance, and reduced flavor scalping without the use
of any styrene and at "high" Tg's (e.g., acrylic polymers having a
Tg>40.degree. C. or >60.degree. C.).
[0038] To achieve such improved coating properties without the use
of styrene, in preferred embodiments, the acrylic coating
composition of the present invention includes one or both of: (i) a
carboxyl reactive crosslinker, more preferably a
nitrogen-containing carboxyl-reactive crosslinker and (ii) an
ethylenically unsaturated monomer having a cyclic group or a
branched organic group.
[0039] In the discussion that follows, emphasis is placed on
acrylic latexes and latex-based coatings, and particularly
styrene-free acrylic latexes and latex-based coatings. It should be
understood, however, that the teachings and disclosure contained
herein may also be applied to acrylic polymers, and especially
styrene-free acrylic polymers, that are not latexes and acrylic
coatings that are not latex-based. Examples of such acrylic
polymers that may not be latexes include organic-solution
polymerized acrylics, which may or may not be
water-dispersible.
[0040] While not intending to be bound by any theory, it is
believed that the use of one, and more preferably both of, the
above (i) and (ii) can result in a styrene-free acrylic coating,
including a "high" Tg styrene-free acrylic latex based coating,
capable of exhibiting enhanced elongation at break properties that
can correlate to improved flexibility in food or can coating end
uses, and particularly improved flexibility for inside spray
beverage can coatings. Assuming that other requisite coating
properties are present (e.g., suitable coating adhesion), it is
believed that a suitably high elongation at break can correlate to
suitable coating flexibility in end use specific food or beverage
can coating tests such as the "Metal Exposure after Drop Damage"
test described herein. Thus, in some embodiments, the styrene-free
acrylic latex based coatings of the present invention preferably
exhibit an elongation at break value that is comparable to that of
a reference styrene-containing acrylic latex based coating. An
example of such a reference styrene-containing acrylic latex based
coating is Comparative Example 5 in the Examples section below.
[0041] Moreover, it is contemplated that the use of, for example,
one or more preferred crosslinkers provided herein may even result
in a styrene-free coating having an improved elongation at break
relative to such a reference styrene-containing coating.
[0042] While it is contemplated that the styrene-free coatings of
the present invention can exhibit any suitable elongation at break
values, in some embodiments, the coatings, when evaluated as
suitable cured free films, preferably exhibit an elongation at
break percent of at least 1%, more preferably at least 1.5%, even
more preferably at least 2%, and even more preferably at least 3%.
In some embodiments, the elongation at break of the coating
compositions, when evaluated as suitable cured free films, are
greater than 5%, greater than 10%, and in some instances even 15%
or more (e.g., .gtoreq.15%, >20%, or .gtoreq.30%). The
elongation at break is not restricted on the upper end, but may be,
for example, less than 100%, 80%, 50%, 40%, 30%, or 20%. A suitable
methodology for assessing elongation at break is disclosed later
herein.
[0043] While not wishing to be bound by any theory, it is believed
that the beneficial effects of the above (i) (e.g.,
nitrogen-containing carboxyl-reactive crosslinker) may
alternatively be achieved using certain internal crosslinking
moieties within the polymer itself to achieve suitable flexibility
improvements at high "Tg" without requiring the use of styrene.
Thus, for example, it is believed that a coating composition that
exhibits the above minimum elongation break values can be achieved
without using a nitrogen-containing carboxyl-reactive crosslinker
described herein if suitable internal cross-link density is built
into the polymer. For example, monomers such as allyl methacrylate,
glycidyl methacrylate, multi-ethylenically unsaturated monomers
(e.g., di(meth)acrylates), etc. may be useful in creating such
internal crosslinks.
[0044] The polymer is preferably a free-radical polymerized polymer
formed from ingredients including an ethylenically unsaturated
monomer component, which may be polymerized in one or more stages,
which may be of a same or different monomer composition. More
preferably, the polymer is an acrylic polymer such as, for example,
an organic solution polymerized acrylic polymer (which may
optionally be water-dispersible) or an acrylic latex polymer, and
more preferably an acrylic latex polymer that may optionally
include a water-dispersible polymer such as, for example, a
water-dispersible organic solution polymerized acrylic polymer. In
a preferred embodiment, the polymer is a latex polymer formed by
emulsion polymerizing an ethylenically unsaturated monomer
component in the presence of a water-dispersible polymer (e.g., a
polymeric surfactant).
[0045] The inventors have surprisingly discovered that the use of
certain nitrogen-containing carboxyl-reactive ("NCCR") crosslinkers
can substantially improve the flexibility of acrylic food or
beverage can coatings, including acrylic coatings having a
relatively "high" Tg (e.g., Tg greater than 60.degree. C.). This
was surprising because conventional crosslinkers used in can
coatings are generally not capable of providing large improvements
in coating flexibility when used to formulate acrylic coatings.
Consistent with this, the substantial improvement in coating
flexibility was not observed for other more conventional
crosslinkers. For example, resole phenolic crosslinkers, which are
often used to formulate acrylic can coatings, were not capable of
yielding a comparable flexibility improvement. In addition, the use
of NCCR crosslinkers such as, e.g., hydroxyalkylamide crosslinkers
allows for production of a formaldehyde-free acrylic coating
composition having sufficient flexibility for use as an interior or
exterior coating of a food or beverage can.
[0046] The NCCR crosslinker can have any suitable combination of
one or more carboxyl-reactive functional groups, and more
preferably includes two or more such groups. Hydroxyl groups are
preferred carboxyl-reactive groups. Other suitable
carboxyl-reactive groups may include thiol groups. In some
embodiments, the NCCR includes two or more, three or more, or four
or more hydroxyl groups.
[0047] The NCCR crosslinker can include any suitable number of
nitrogen atoms, although it will typically include two or more
nitrogen atoms, and, in some embodiments, two total nitrogen atoms.
In some embodiments, one or more (and more preferably two or more)
nitrogen atoms are present in an amide group, an aziridine group,
an imide group, a diimide group, an oxazoline group, a urethane
group, or a combination thereof. In a preferred embodiment, the
NCCR crosslinker includes two or more amide groups. It is
contemplated, however, that the NCCR crosslinker may contain a
single amide group such as, for example, a poly-substituted amide
group having two or more hydroxyl groups.
[0048] In certain preferred embodiments, the NCCR crosslinker
includes one or more, and more preferably two or more, groups
having the structure of the below Formula (I):
HO--R.sup.1--N(R.sup.2)--C(.dbd.O)--
wherein each R.sub.1 is independently an organic group, and each
R.sub.2 is independently hydrogen or an organic group.
[0049] As shown in Formula (I), the depicted hydroxyl group can be
a primary hydroxyl group, secondary hydroxyl group, or tertiary
hydroxyl group depending on the structure of R.sup.1. In some
embodiments, the hydroxyl group is a primary hydroxyl group.
[0050] R.sup.1 can include any suitable number of carbon atoms, but
will typically include from 2 to 10 carbons atoms, more typically
from 2 to 8 carbon atoms, more typically from 2 to 6 carbons atoms,
and even more typically from 2 to 4 carbon atoms. le will typically
include at least two carbon atoms in a chain connected on one end
to the depicted nitrogen atom and on the other end to the depicted
hydroxyl group. In an embodiment, the depicted hydroxyl group is
attached directly to a first carbon atom, which is attached
directly to a second carbon, which is in-turn attached directly to
the depicted nitrogen atom. In some embodiments R.sup.1, is
--(CH.sub.2).sub.2--.
[0051] In some embodiments, R.sup.1 is an alkylene group preferably
containing from 1 to 5 carbon atoms (e.g., methylene, ethylene,
n-propylene, sec-propylene, n-butyl, sec-butylene, tert-butylene,
pentylene, etc.).
[0052] In some embodiments R.sup.2 is an organic group that
includes a hydroxyl group. In some such embodiments, R.sup.2 is of
the formula HO--R.sup.1--, wherein le is as described above.
Examples of such R.sup.2 groups include hydroxyl alkyl groups
preferably having from 1 to 5 carbon atoms (e.g., hydroxy-ethyl,
3-hydroxy-propyl, 2-hydroxy-propyl, 4-hydroxy-butyl,
3-hydroxy-butyl, 2-hydroxy-2-propyl-methyl, 5-hydroxy-pentyl,
4-hydroxy-pentyl, 3-hydroxy-pentyl, 2-hydroxy-pentyl and the pentyl
isomers). An example of an NCCR crosslinker including such an
R.sup.2 group is provided below (which is believed to be the
structure of the PRIMID XL-552 product commercially available from
EMS):
##STR00001##
[0053] In some embodiments, the NCCR crosslinker is a compound
having the structure of the below Formula (II):
(HO--R.sup.1--N(R.sup.2)--C(.dbd.O)).sub.n--X,
wherein:
[0054] R.sup.1 and R.sup.2 are as described above,
[0055] n is 2 or more, and
[0056] X is a polyvalent organic group.
[0057] In some embodiments, X is an alkylene group. In some
embodiments, X is a --(CH.sub.2).sub.m-- group wherein (i) m is 1
or more, 2 or more, 3 or more, 4 or more, and more typically from 2
to 10 and (ii) one or more hydrogens may be replaced with
substituent groups (e.g., organic substituent groups). In an
embodiment, X is --(CH.sub.2).sub.4--.
[0058] In certain preferred embodiments, the hydroxyl group is
located "beta" relative to a nitrogen atom, more preferably a
nitrogen atom of an amide bond. Thus, for example, in certain
preferred embodiments the NCCR crosslinker is a
beta-hydroxyalkylamide compound. Some examples of such compounds
include: bis[N,N-di(.beta.-hydroxy-ethyl)]adipamide,
bis[N,N-di(.beta.-hydroxy-propyl)]succinamide,
bis[N,N-di(.beta.-hydroxy-ethyl)]azelamide,
bis[N,N-di(.beta.-hydroxy-propyl)]adipamide,
bis[N-metil-N-(.beta.-hydroxy-ethyl)]oxamide, and mixtures thereof.
The PRIMID QM-1260 product commercially available from EMS is an
example of a preferred beta-hydroxyalkylamide crosslinker. The
structure believed to correspond to the PRIMID QM-1260 product is
provided below:
##STR00002##
[0059] Without intending to be bound by theory, the use of
beta-hydroxyalkylamides is preferred in certain embodiments due to
the formation of an oxazolinium intermediate that is believed to
occur and result in enhanced reactivity of the crosslinker with
carboxyl groups. Thus, in some embodiments, the NCCR crosslinker is
preferably capable of forming an oxazolinium intermediate or other
carbon-nitrogen heterocyclic intermediate having enhanced
reactivity with carboxyl groups. Preferably, such reactive
intermediates are formed under typical food or beverage can coating
thermal cure conditions. For example, for beverage inside spray
coatings, such reactive intermediates are preferably formed at oven
bake conditions of from 188 to 199.degree. C. during an oven
residence time of 30 to 85 seconds.
[0060] The NCCR crosslinker is preferably formed from reactants
that do not include formaldehyde.
[0061] Although in presently preferred embodiments the NCCR
crosslinkers described herein are used in combination with a
styrene-free acrylic resin system (e.g., a styrene-free acrylic
latex), it is also contemplated that the NCCR may be used in
conjunction with styrene-containing acrylic resin systems (not
presently preferred) to improve one or more coating properties of
coatings formulating using such styrene-containing resin
systems.
[0062] As previously discussed, in some embodiments, one or more
branched or cyclic monomers are used in place of styrene, alone or
in combination with one or more other monomers (e.g., one or more
non-branched or non-cyclic (meth)acrylates) to provide a
styrene-free acrylic polymer that, when suitably formulated,
provides comparable coating properties in food or beverage can
coatings to conventional styrene-containing acrylic formulations.
For purposes of convenience, hereinafter an ethylenically
unsaturated monomer having a branched organic group is referred to
as a "branched monomer" and an ethylenically unsaturated monomer
having a cyclic group is referred to as a "cyclic monomer." An
ethylenically unsaturated monomer that, when incorporated into the
acrylic polymer, does not provide a pendant branched group is not
considered a branched monomer. Thus, as used herein, methyl
methacrylate is not considered to be a branched monomer because it
does not provide a pendant branched group when incorporated into an
acrylic polymer. Stated otherwise, methyl methacrylate is not
considered herein to be a branched monomer because it does not
provide a pendant group having at least one branching atom that is
not present in the polymer backbone.
[0063] In some embodiments, an ethylenically unsaturated monomer
component used to form the acrylic polymer includes both one or
more branched monomers and one or more cyclic monomers. Similarly,
in some embodiments, the ethylenically unsaturated monomer
component includes one or more monomers that include both a
branched group and a cyclic group.
[0064] The branched and/or cyclic monomer can be any suitable
monomer. Preferably, the monomer is capable of being incorporated
into a polymer, such as, for example, an acrylic polymer, via a
free-radical polymerization process.
[0065] In some embodiments, the branched and/or cyclic monomer is a
vinyl ester monomer.
[0066] A branched and/or cyclic monomer having any suitable Tg may
be used. The selection of a branched or cyclic monomer having a
particular Tg value may be influenced by a variety of factors
including the end use of the coating composition (e.g., whether the
coating is intended for an exterior or interior of a can) and the
Tg of the other monomers selected. Typically, the branched and/or
cyclic monomer will have a Tg greater than -10.degree. C., more
typically greater than 0.degree. C.
[0067] In some embodiments, branched monomers having Tg's as low as
about -3.degree. C. (e.g., the VeoVa 10 monomer product
commercially available from Hexion) or even as low as about
-40.degree. C. (e.g., the VeoVa 11 monomer product commercially
available from Hexion) may be used. If used, such "low" Tg monomers
will typically be used in combination with one or more "high" Tg
monomers, such as one or more "high" Tg branched or cyclic monomers
(e.g., Tg>40.degree. C.).
[0068] In embodiments in which the branched and/or cyclic monomer
is intended as at least a partial replacement for styrene, such as
for an interior food-contact can coating, the branched and/or
cyclic monomer preferably has a glass transition temperature ("Tg")
that is sufficiently high to offset the replaced styrene. Thus, in
some embodiments, the branched and/or cyclic monomer preferably has
a Tg >40.degree. C., more preferably >50.degree. C., even
more preferably >60.degree. C. , and optimally >70.degree. C.
Although the upper Tg is not restricted, in some embodiments, the
branched and/or cyclic monomer has a Tg <110.degree. C.,
<95.degree. C., <85.degree. C., or <75.degree. C. For
branched and/or cyclic monomers specifically referenced herein, any
Tg values provided herein for such monomers should be used for
comparison relative to the above Tg thresholds. For a branched
and/or cyclic monomers not having a reported Tg value herein, in
the absence of a reliable Tg value reported by a manufacturer of
the monomer, the Tg of the monomer may be determined by making a
homopolymer having a number average molecular weight of at least
about 4,000 and a suitable polydispersity index (e.g., preferably
less than 3 and ideally as low as possible) and measuring the Tg of
the homopolymer using a suitable procedure such as the procedure
included in the test methods section below.
[0069] Any suitable cyclic monomer or combination of cyclic
monomers may be used including, for example, vinyl aromatics
compounds, vinyl alicyclic compounds, and combinations thereof. If
a vinyl aromatic monomer is used, it preferably is not styrene or a
substituted styrene. In some embodiments, the coating composition
is substantially free of vinyl aromatic compounds. In some
embodiments, the acrylic polymer (e.g., emulsion polymerized
acrylic latex) is substantially free of cyclic-group-containing
vinyl monomers (e.g., certain embodiments such as, e.g., certain
embodiments when methyl (meth)acrylate is employed).
[0070] The cyclic monomers may include any suitable number of
cyclic groups, which may be monocyclic groups or polycyclic groups
and may be saturated or unsaturated. The atoms in the ring(s) of
the one or more cyclic groups may be all carbon atoms or may
include one or more heteroatoms (e.g., N, O, P, Si, etc.).
Similarly, the rings may be of any suitable size and may, for
example, include 3 to 13 atoms in the ring, more typically 4 to 9
atoms in the ring, and even more typically 4 to 6 atoms in the
ring. In some embodiments, the ring of the cyclic group is a C4
ring (e.g., cyclobutane), a C5 ring (e.g., cyclopentane), or a C6
ring (e.g., cyclohexane). Cyclohexane groups, which may optionally
include one or more substituents in place of hydrogen, are
preferred cyclic groups in some embodiments.
[0071] Examples of suitable cyclic monomers may include benzyl
(meth)acrylate, cyclohexyl (meth)acrylate, isobornyl
(meth)acrylate, phenyl (meth)acrylate, substituted variants thereof
(e.g., 3,3,5-trimethylcyc1ohexyl (meth)acrylate and
4-tert-butylcyclohexyl (meth)acrylate), and mixtures thereof.
Cyclohexyl methacrylate is a preferred cyclic monomer, and may be
used to replace styrene in some embodiments.
[0072] Any suitable branched monomer or combination of branched
monomers may be used. Preferred branched monomers include branched
organic groups such as, for example, branched hydrocarbon groups,
with branched alkyl groups being preferred in certain embodiments.
The branched organic group may optionally include one or more
heteroatoms (e.g., O, N, P, Si, etc.). In certain preferred
embodiments, the branched organic group includes one or more, two
or more, or even three or more branching atoms (preferably tertiary
or quaternary carbon atoms). Although the branched organic group
(inclusive of any carbon branching atoms) can include any suitable
number of carbon atoms, typically it will include 3 or more, 4 or
more, 5 or more, or 6 or more total carbon atoms. While the upper
number of carbon atoms is not restricted, typically the branched
organic group will include 18 or less, 13 or less, or 10 or less
carbon atoms (see, e.g., branched organic group "Y" of Formula
(III)) described herein). If the branched organic group is
connected to the ethylenically unsaturated group via a
heteroatom-containing linkage (e.g., linkages including at least
one or more heteroatoms such as N, O, P, S, etc.) the carbon atoms
of the heteroatom-containing linkage are not counted as being part
of the branched organic group. Examples of suitable
heteroatom-containing linkages include, for example, those formed
by reacting two complimentary reactive functional groups (e.g.,
--OH and --COOH) such as are used, for example, to produce
condensation linkages and the like. Example of suitable heteroatom
containing-linkages include amide, carbonate ester, ester, ether,
urea, and urethane linkages.
[0073] In some embodiments, the branched organic group is a
branched C3 to C13 alkyl group or moiety, more preferably a
branched C4 to C10 alkyl group or moiety.
[0074] The branched organic group may optionally include one or
more cyclic groups. In some embodiments, the branched organic group
includes one or more branching atoms (e.g., tertiary or quaternary
carbon atoms) in a ring of the cyclic group or in a location other
than the ring. Some examples of such compounds include
3,3,5-trimethylcyclohexyl (meth)acrylate (branching atom, in the
form of a quaternary carbon atom, included in an aliphatic ring)
and 4-tert-butylcyclohexyl (meth)acrylate (branching atom, in the
form of quaternary carbon atom, attached to an aliphatic ring).
[0075] In some embodiments, the branched organic group (and
optionally the branched monomer) does not include any cyclic
groups. Thus, in some embodiments, the branched organic group is a
branched, open-chain alkyl group (e.g., isopropyl, sec-butyl,
isobutyl, tert-butyl, etc).
[0076] In some embodiments, the ethylenically unsaturated monomer
component includes one or more branched and/or cyclic monomers of
the below Formula (III):
(R.sup.3).sub.2--C.dbd.C(R.sup.4)--W.sub.n--Y,
wherein: [0077] R.sup.3 is independently selected from hydrogen or
an organic group; [0078] R.sup.4 is selected from hydrogen or an
alkyl group; [0079] W, if present, is a divalent linking group;
[0080] n is 0 or 1, more typically 1; and [0081] Y is: (i) a
branched organic group including one or more branching atoms, more
typically one or more branching carbon atoms, (ii) a cyclic group
(e.g., any of the cyclic groups disclosed herein), or (iii) a
combination of (i) and (ii) (e.g., such as present in
4-tert-butylcyclohexyl (meth)acrylate).
[0082] The branched and/or cyclic monomer of Formula (III) can be
either a vinyl monomer or an olefin monomer depending upon the
R.sup.3 and R.sup.4 selections. In preferred embodiments, the
monomer of Formula (III) is a vinyl monomer (e.g., a (meth)acrylate
or vinyl ester) and both R.sup.3 are hydrogen.
[0083] In preferred embodiments, R.sup.4 is hydrogen, a methyl
moiety (--CH.sub.3), or an ethyl moiety, more preferably hydrogen
or a methyl moiety.
[0084] When present, W is typically a heteroatom-containing linkage
such as, for example, any of those previously discussed. Examples
of suitable such linkages include amide, carbonate, ester, ether,
urea, and urethane. Ester linkages of either directionality
(--C(O)--O-- or --O--C(O)--) are preferred such linkages. In some
embodiments, W is an ester linkage and the carbonyl carbon of the
ester is attached to a carbon atom of Y.
[0085] In some embodiments, Y is a branched organic group having
the structure of the below Formula (IV):
--C(CH.sub.3).sub.t(R.sup.5).sub.3-t
wherein: [0086] t is 0 to 3; [0087] each R.sup.5, if present, is
independently an organic group that may optionally be itself
branched, more typically an alkyl group that may optionally include
one or more heteroatoms (e.g., N, O, P, Si, etc.); and [0088] two
or more R.sup.5 may optionally form a cyclic group with one
another.
[0089] In some embodiments, t is 3. Tert-butyl acrylate and
tert-butyl methacrylate are two examples of a branched monomer of
Formula (III) in which "Y" has a structure of Formula (IV) and t is
3.
[0090] In some embodiments, t is 1 and the total number of carbon
atoms present in both R.sup.5 groups is 6, 7, or 8. Examples of
such branched monomers include the VEOVA 9 (Tg 70.degree. C.),
VEOVA 10 (Tg -3.degree. C.), and VEOVA 11 (Tg -40.degree. C.)
monomers commercially available from Hexion.
[0091] In some embodiments in which the monomer of Formula (III)
includes a Y group of Formula (IV), t is 0, 1, or 2, and Y includes
at least one R.sup.5 group that is itself a branched organic group,
more typically a branched alkyl group. Thus, for example, in some
embodiments, at least one R.sup.5 is present that includes a
tertiary or quaternary carbon atom. The VEOVA 9 monomer is an
example of such a branched monomer.
[0092] Additional examples of suitable branched monomers may
include isopropyl methacrylate, isobutyl methacrylate, sec-butyl
methacrylate, and mixtures thereof.
[0093] In certain preferred embodiments, Y includes at least one
carbon atom that functions as a branching point (e.g., the leftmost
carbon atom depicted in Formula (IV)). Nonetheless, it is
contemplated that the branched organic group may include a
branching atom(s) other than carbon such as, for example, P, Si, or
N. Such a branching heteroatom may be used in place of, or in
addition to, a branching carbon atom in Y.
[0094] In some embodiments, the branched organic group is provided
by neodecanoic acid and/or neononanoic acid. In one embodiment, the
branched monomer is a vinyl ester of neodecanoic acid or
neononanoic acid.
[0095] The ethylenically unsaturated monomer component (e.g., an
ethylenically unsaturated monomer component polymerized in the
presence of a polymeric and/or non-polymeric surfactant(s) to form
a latex) can include any suitable amount of one or more branched
and/or cyclic monomers. The amount of branched and/or cyclic
monomer employed can vary depending upon a variety of factors such
as, for example, the other monomer(s) present, the desired Tg, and
the desired end use including, e.g., the desired amount of coating
flexibility and/or corrosion resistance. In some embodiments, one
or both of: (i) the ethylenically unsaturated monomer component or
(ii) an acrylic-containing resin system formed, at least in part,
from the ethylenically unsaturated monomer component (e.g., a latex
formed by emulsion polymerizing the ethylenically unsaturated
component in the presence of a water-dispersible polymer) includes
at least 10 weight percent ("wt- %"), more preferably at least 20
wt- %, even more preferably at least 30 wt- %, and in some
embodiments 40 wt- % or more of one or more branched and/or cyclic
monomers. Although the upper amount of branched and/or cyclic
monomers is not restricted, typically the ethylenically unsaturated
monomer component will include less than 90 wt- %, more typically
less than 70 wt- %, more typically less than 60 wt- %, and even
more typically less than 50 wt- % of one or more branched and/or
cyclic monomers. In some such embodiments, one or more branched
monomers are present in an above recited amount, while either no
cyclic monomers are present or one or more cyclic monomers are
present in an additional amount. In some such embodiments, one or
more cyclic monomers are present in an above recited amount, while
either no branched monomers are present or one or more branched
monomers are present in an additional amount.
[0096] In some embodiments in which the polymer is an emulsion
polymerized latex, the overall latex particle or polymer preferably
includes an amount of one or more branched and/or cyclic monomers
pursuant to the amounts disclosed in the preceding paragraph. For
example, in certain embodiments where the ethylenically unsaturated
monomer component is polymerized in the presence of a
water-dispersible acrylic polymer (e.g., an acid- or
anhydride-functional organic solution polymerized acrylic polymer),
the overall latex particle or polymer includes an amount of one or
more branched and/or cyclic monomers in such amounts.
[0097] It is contemplated that, in some embodiments, the
ethylenically unsaturated monomer component may not include one or
more branched and/or cyclic monomers, but rather, may include a
reactive functional group through which a branched and/or cyclic
organic group may be subsequently grafted. For example, a polymer
having pendant reactive groups could be post-modified with a
branched and/or cyclic reactive compound (e.g., a compound
including a "Y" branched and/or cyclic group and a reactive
functional group capable of forming a "W" divalent linkage) to
include one or more branched organic groups disclosed herein. For
example, the hydroxyl groups of a latex polymer could be reacted
with neodecanoic acid and/or neononanoic acid to provide branched
organic groups thereon.
[0098] As previously discussed, in certain preferred embodiments,
the polymer is a latex polymer. The latex polymer is preferably
formed by emulsion polymerizing the ethylenically unsaturated
monomer component in an aqueous medium. The latex can be a
single-stage latex or a multi-stage latex. The ethylenically
unsaturated monomer component is typically emulsion polymerized in
the aqueous medium in the presence of at least one surfactant (or
emulsifier), which can be polymeric, non-polymeric, or a blend
thereof.
[0099] The latex polymer may be of any suitable molecular weight.
In some embodiments, the latex polymer has a number average
molecular weight (M.sub.n) of at least about 30,000, at least about
100,000, at least about 200,000, or at least about 300,000. The
upper range of the M.sub.n of the latex polymer is not restricted
and may be 1,000,000 or more. In certain embodiments, however, the
M.sub.n of the latex polymer is less than about 1,000,000, less
than about 600,000, or less than about 400,000. Because in some
embodiments the molecular weight may be too high to measure (e.g.,
via GPC analysis using polystyrene standards), it may be necessary
to determine the number average molecular weight via theoretical
calculation.
[0100] Preferably, at least 5 wt- %, more preferably at least 25
wt- %, even more preferably at least 40 wt- %, even more preferably
at least 50 wt- %, and even more preferably at least 55 wt- % or at
least 60 wt- %, of the ethylenically unsaturated monomer component
is used in making the latex polymer. In some embodiments, the
ethylenically unsaturated monomer component may comprise up to
about 100 wt- %, up to 98 wt- %, up to 95 wt- %, up to 80 wt- %, or
up to 70 wt- % of the latex polymer. Such percentages are based on
the total combined weight of the ethylenically unsaturated
component and any polymeric or polymerizable surfactant used to
make the latex.
[0101] In embodiments in which a water-dispersible polymer is used
to facilitate emulsion polymerization of the latex polymer (e.g.,
as a "polymeric surfactant"), preferably no greater than 95 wt- %,
more preferably no greater than 90 wt- %, and even more preferably
no greater than 85 wt- % of the ethylenically unsaturated monomer
component is used in making the latex polymer. Such percentages are
based on the total weight of ethylenically unsaturated monomer
component and water-dispersible polymer used to make the latex.
[0102] In preferred embodiments, the ethylenically unsaturated
monomer component is a mixture of monomers, more preferably a
mixture of monomers that that includes at least one (meth)acrylate
monomer. Any combination of one or more (meth)acrylates may be
included in the ethylenically unsaturated monomer component,
including, for example, combinations of one or more branched and/or
cyclic (meth)acrylate monomers and one or more other (meth)acylate
monomers (e.g., "linear" alkyl (meth)acrylates) optionally in
combination with one or more non-(meth)acrylate monomers.
[0103] Suitable (meth)acrylates include any of those referenced
herein, as well as those having the structure:
CH.sub.2.dbd.C(R.sup.6)--CO--OR.sup.7 wherein R.sup.6 is hydrogen
or methyl, and R.sup.7 is an alkyl group preferably containing one
to sixteen carbon atoms, a cycloaliphatic group, an aryl group, a
silane group, or a combination thereof. If desired, R.sup.7 may
optionally be substituted with one or more (e.g., one to three)
moieties such as hydroxy, halo, phenyl, and alkoxy, for example.
Examples of suitable (meth)acrylates (including, e.g., suitable
alkyl (meth)acrylates) include methyl (meth)acrylate, ethyl
(meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate,
butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl
(meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate,
2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, decyl
(meth)acrylate, isodecyl (meth)acrylate, benzyl (meth)acrylate,
phenyl (meth)acrylate, lauryl (meth)acrylate, isobornyl
(meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate,
hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and the
like, substituted variants thereof (e.g., ring substituted variants
of benzyl (meth)acrylate or phenyl (meth)acrylate), and isomers and
mixtures thereof.
[0104] Typically, (meth)acrylates will constitute a substantial
portion of the ethylenically unsaturated monomer component. In some
embodiments, (meth)acrylates may constitute at least 20 wt- %, at
least 30 wt- %, at least 50 wt- %, at least 70 wt- %, at least 95
wt- %, or even 99 wt- % or more of the ethylenically unsaturated
monomer component. The aforementioned weight percentages include
all (meth)acrylates monomers present in the ethylenically
unsaturated monomer component, regardless of whether one or more of
the monomers may also qualify as a branched monomer, a cyclic
monomer, or both.
[0105] In preferred embodiments, the ethylenically unsaturated
monomer component includes at least one "linear" alkyl
(meth)acrylate having a linear (e.g., non-branched) alkyl group.
Examples of such linear groups include the following moieties:
methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, etc. Preferred
such monomers include one or more of methyl (meth)acrylate, ethyl
(meth)acrylate, n-propyl (meth)acrylate, and n-butyl
(meth)acrylate, with acrylate forms thereof being particularly
preferred in certain embodiments. In some embodiments, the
ethylenically unsaturated monomer component includes at least 10
wt- %, more preferably at least 15 wt- %, and even more preferably
at least 20 wt- % of one or more linear alkyl (meth)acrylates. When
present, linear alkyl (meth)acrylates preferably constitute less
than 90 wt- %, more preferably less than 80 wt- %, and even more
preferably less than 70 wt- % of the ethylenically unsaturated
monomer component.
[0106] One or more multi-functional monomers may optionally be
included in the ethylenically unsaturated monomer component.
Examples of preferred multi-functional monomers include
multi-ethylenically unsaturated monomers such as
multi-ethylenically-unsaturated (meth)acrylates. Examples of
multi-ethylenically unsaturated (meth)acrylates include polyhydric
alcohol esters of acrylic acid or methacrylic acid, such as
ethanediol di(meth)acrylate, propanediol di(meth)acrylate (e.g.
1,2-propanediol di(meth)acrylate and 1,3-propanediol
di(meth)acrylate), butanediol di(meth)acrylate (e.g.,
1,3-butanediol di(meth)acrylate and 1,4-butanediol
di(meth)acrylate), heptanediol di(meth)acrylate, hexanediol
di(meth)acrylate, trimethylolethane tri(meth)acrylate
trimethylolpropane tri(meth)acrylate, trimethylolbutane
tri(meth)acrylate, trimethylolheptane tri(meth)acrylate,
trimethylolhexane tri(meth)acrylate, tetramethylol methane
tetra(meth)acrylate, dipropylene glycol di(meth)acrylate,
trimethylol hexane tri(meth)acrylate, pentaerythritol
tetra(meth)acrylate, isosorbide di(meth)acrylate, allyl
(meth)acrylate, glycerol dimethacrylate, isomers thereof, and
mixtures thereof. Examples of multi-ethylenically-unsaturated
monomers other than (meth)acrylates include diallyl phthalate,
divinylbenzene, divinyltoluene, divinylnaphthalene, and mixtures
thereof
[0107] In one embodiment, 1,4-butane diol di(meth)acrylate is
included in the ethylenically unsaturated monomer component.
[0108] In some embodiments, the ethylenically unsaturated monomer
component includes at least 5%, at least 6%, at least 7%, at least
8%, at least 9%, at least 10%, at least 11%, at least 12%, at least
13%, or at least 14% by weight of multi-ethylenically unsaturated
monomer. If used, such multi-ethylenically unsaturated monomers
will typically be included in the ethylenically unsaturated monomer
component in an amount of less than about 25 wt- %, more typically
less than about 20 wt- %, and even more typically less than about
17.5 wt- %. In some embodiments, di(meth)acrylates are preferred
multi-ethylenically unsaturated monomers.
[0109] In some embodiments, the ethylenically unsaturated monomer
component includes at least one oxirane-functional monomer, more
preferably at least one oxirane-functional alpha, beta-unsaturated
monomer. The ethylenically unsaturated monomer component preferably
contains no greater than 30 wt- %, more preferably no greater than
20 wt- %, even more preferably no greater than 10 wt- %, and
optimally no greater than 9 wt- %, of the oxirane group-containing
monomer. In some embodiments, the ethylenically unsaturated monomer
component includes more than 1 wt- %, more than 2 wt- %, more than
3 wt- %, or 5 or more wt- % of oxirane-group containing
monomer.
[0110] Suitable oxirane-functional monomers include monomers having
a reactive carbon-carbon double bond and an oxirane (viz., a
glycidyl) group. Typically, the monomer is a glycidyl ester of an
alpha, beta-unsaturated acid, or anhydride thereof (viz., an
oxirane group-containing alpha, beta-ethylenically unsaturated
monomer). Suitable alpha, beta-unsaturated acids include
monocarboxylic acids or dicarboxylic acids. Examples of such
carboxylic acids include, but are not limited to, acrylic acid,
methacrylic acid, alpha-chloroacrylic acid, alpha-cyanoacrylic
acid, beta-methylacrylic acid (crotonic acid), alpha-phenylacrylic
acid, beta-acryloxypropionic acid, sorbic acid, alpha-chlorosorbic
acid, angelic acid, cinnamic acid, p-chlorocinnamic acid,
beta-stearylacrylic acid, itaconic acid, citraconic acid, mesaconic
acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid,
tricarboxyethylene, maleic anhydride, and mixtures thereof.
[0111] Specific examples of suitable monomers containing a glycidyl
group are glycidyl (meth)acrylate (viz., glycidyl methacrylate and
glycidyl acrylate), mono- and di-glycidyl itaconate, mono- and
di-glycidyl maleate, and mono- and di-glycidyl formate. It also is
envisioned that allyl glycidyl ether and vinyl glycidyl ether can
be used as the oxirane-functional monomer. Preferred monomers are
glycidyl acrylate and glycidyl methacrylate ("GMA"), with GMA being
particularly preferred in some embodiments.
[0112] In embodiments in which the ethylenically unsaturated
monomer component includes an oxirane-functional monomer, it may be
advantageous to employ an amine, more preferably a tertiary amine,
in preparing the latex or other acrylic polymer. Without intending
to be bound by theory, under preferred conditions an acid group
(e.g., present in the ethylenically unsaturated monomer component
and/or a water-dispersible polymer), an oxirane group, and an amine
(particularly a tertiary amine) are believed to form a quaternary
salt linkage. This linkage is favored, as it not only links the
polymers but promotes water dispersibility of the joined polymer
and can enhance the mechanical properties of a coating composition
including the latex polymer. It should be noted that an acid group
and an oxirane group may also form an ester. Some of this reaction
is possible, though this linkage is less desirable when water
dispersibility is sought.
[0113] In some embodiments, the ethylenically unsaturated monomer
component does not include any monomers having oxirane groups.
[0114] In some embodiments (e.g., when the ethylenically
unsaturated monomer component is emulsion polymerized), the
ethylenically unsaturated monomer component may include a minority
amount (e.g., less than 30 wt- %, less than 25 wt- %, less than 20
wt- %, less than 15 wt- %, less than 10 wt- %, less than 5 wt- %,
less than 2 wt- %, or less than 1 wt- %) of acid- or
anhydride-functional ethylenically unsaturated monomer. Examples of
suitable such acid- or anhydride-functional monomers may include
any of those disclosed herein. When present, the acid- or
anhydride-functional monomer are typically present in an amount of
more than 1 wt- %, more than 2 wt- %, more than 3 wt- %, more than
5 wt- %, or even more than 10 wt- %, based on the total weight of
the ethylenically unsaturated monomer component.
[0115] The ethylenically unsaturated monomer component may also
include any other suitable monomers. For example, suitable other
ethylenically unsaturated monomers (e.g., olefinic or vinyl
monomers other than (meth)acrylates) may include isoprene,
diallylphthalate, conjugated butadiene, vinyl naphthalene,
acrylonitrile, (meth)acrylamides (e.g., acrylamide, methacrylamide,
N-isobutoxymethyl acrylamide, N-butoxymethyl acrylamide, etc.),
methacrylonitrile, vinyl acetate, vinyl propionate, vinyl butyrate,
vinyl stearate, and the like, and variants and mixtures thereof
[0116] The ethylenically unsaturated monomer component may
optionally include one or more vinyl aromatic compounds, including
styrene. In preferred embodiments, however, the ethylenically
unsaturated monomer component is not intentionally formulated to
include styrene. Suitable vinyl aromatic compounds may include
styrene (not preferred), substituted styrene compounds (not
preferred in some embodiments), and/or other types of vinyl
aromatic compounds (e.g., any of the aryl-group-containing
ethylenically unsaturated monomers described herein, including aryl
(meth)acrylates such as, e.g., benzyl (meth)acrylate). In some
embodiments, the ethylenically unsaturated monomer component
includes, if any, less than 20 wt- %, less than 10 wt- %, less than
5 wt- % or less than 1 wt- % of vinyl aromatic compounds. In some
embodiments, the ethylenically unsaturated monomer component, and
preferably the final polymer, is substantially free of such
compounds.
[0117] In presently preferred embodiments, the ethylenically
unsaturated monomer component, and preferably the final polymer,
does not include any acrylamide-type monomers (e.g., acrylamides or
methacrylamides).
[0118] In embodiments in which one or more surfactants are used to
prepare a latex polymer, the surfactant can be an anionic, a
cationic or a zwitterionic surfactant, or a mixture thereof, and
also preferably includes one or more salt groups. In preferred
embodiments, the surfactant includes one or more neutralized acid
or anhydride groups. Examples of suitable neutralized acid groups
may include carboxylate groups (--COO.sup.-), sulfate groups
(--OSO.sub.3.sup.-), sulfinate groups (--SOO.sup.-), sulfonate
groups (--SO.sub.2O.sup.-), phosphate groups (--OPO.sub.3.sup.-),
phosphinate groups (-POO.sup.-), phosphonate groups
(--PO.sub.3.sup.-), and combinations thereof.
[0119] Anionic surfactants are preferred in some embodiments.
[0120] Examples of suitable anionic surfactants include any of the
following surfactants, which preferably have been at least
partially neutralized with a suitable base (e.g., any of the bases
disclosed herein): any of the acid- or anhydride-functional
polymeric surfactants disclosed herein, dodecylbenzene sulfonic
acid, dinonylnaphthalene sulfonic acid,
dinonylnaphthylenedisulfonic acid, bis(2-ethylhexyl)sulfosuccinic
acid, dioctyl sulfosuccinic acid, sodium lauryl sulfate, sodium
dodecyl sulfate, sodium laureth sulfate, fatty acid (ester)
sulfonate, polyaryl ether phosphate acid or sulfonate acid, and the
like, including mixtures thereof.
[0121] In some embodiments, it may be useful to use a surfactant
that is a "strong acid" surfactant prior to neutralization.
Examples of "strong acid" surfactants include surfactants having a
pK.sub.a of less than 4 prior to neutralization.
[0122] Although any suitable base may be used to neutralize or
partially neutralize polymeric or non-polymeric surfactants to form
anionic salt groups, amines are preferred bases, with tertiary
amines being particularly preferred. Some examples of suitable
tertiary amines are trimethyl amine, dimethylethanol amine (also
known as dimethylamino ethanol), methyldiethanol amine, triethanol
amine, ethyl methyl ethanol amine, dimethyl ethyl amine, dimethyl
propyl amine, dimethyl 3-hydroxy-1-propyl amine, dimethylbenzyl
amine, dimethyl 2-hydroxy-1-propyl amine, diethyl methyl amine,
dimethyl 1-hydroxy-2-propyl amine, triethyl amine, tributyl amine,
N-methyl morpholine, and mixtures thereof. Most preferably triethyl
amine or dimethyl ethanol amine is used as the tertiary amine.
[0123] Some additional examples of neutralizing bases for forming
anionic salt groups include inorganic and organic bases such as
sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium
hydroxide, and mixtures thereof.
[0124] Some examples of neutralizing compounds for neutralizing
base groups present on the surfactant and forming cationic salt
groups include organic and inorganic acids such as formic acid,
acetic acid, hydrochloric acid, sulfuric acid, and combinations
thereof.
[0125] Although the surfactant may optionally include one or more
ethylenically unsaturated groups (e.g., if the surfactant is a
polymerizable non-polymeric surfactant), in some embodiments, the
surfactant is a saturated surfactant. By way of example,
amine-neutralized dodecylbenzenesulfonic acid is considered to be a
saturated surfactant. Although amine-neutralized
dodecylbenzenesulfonic acid includes an aryl group that includes
carbon-carbon double bonds, it does not include any ethylenically
unsaturated groups.
[0126] The surfactant can be any suitable type of surfactant and
may, for example, be a "lower" molecular-weight surfactant (e.g., a
surfactant that is non-polymeric and/or has a number average
molecular weight of less than about 1,000 Daltons, more typically
less than about 750 Daltons, and even more typically less than
about 500 Daltons).
[0127] In certain preferred embodiments, a polymeric surfactant is
used which has, for example, a number average molecular weight
greater than about 2,000 Daltons or even greater than about 4,000
Daltons. It is generally preferable to use a polymeric surfactant
and/or a polymerizable surfactant to, for example, minimize or
eliminate the possibility of surfactant migrating out of the cured
coating and into the packaged product. Examples of suitable
polymeric surfactants may include water-dispersible polymers of the
acrylic, alkyd, polyester, polyether, polyolefin, or polyurethane
type, including copolymers thereof (e.g., polyether-acrylic
copolymers), and mixtures thereof. Typically, such
water-dispersible polymers include one or more salt groups to
facilitate stable dispersion into water. Examples of suitable such
polymer salts are disclosed in U.S. Pat. No. 8,092,876; U.S.
Application Ser. No. 62/362,729 filed on Jul. 15, 2016 and entitled
"Latex Coating Composition Having Reduced Flavor Scalping
Properties" (corresponds to International Application No.
PCT/US2017/041858) and U.S. Pub. No. 2016/024325 (which describes
the use of certain (poly)ethylene (meth)acrylic acid
copolymers).
[0128] An example of a specific water-dispersible polymer for use
as a "polymeric surfactant" is a "higher" acid number
acid-functional polymer (e.g., acid number greater than about 40,
more preferably greater than about 100 milligrams KOH per gram
polymer). In a preferred embodiment, an acrylic polymer having such
an acid number is solution polymerized in organic solvent and then
inverted into water (e.g., via at least partial neutralization with
a suitable base such as, e.g., an amine or any of the other bases
disclosed herein) and used to support emulsion polymerization of
the ethylenically unsaturated monomer component. In some
embodiments, the acid- or anhydride-functional organic solution
polymerized acrylic polymer is formed from an ethylenically
unsaturated monomer component that includes an acid- or anhydride
functional monomer, a branched and/or cyclic monomer, and
optionally any other suitable ethylenically unsaturated monomer. In
some such embodiments, the acrylic polymer is styrene-free.
[0129] A variety of acid- or anhydride-functional monomers, or
salts thereof, can be used; their selection is dependent on the
desired final polymer properties. Preferably, such monomers are
ethylenically unsaturated, more preferably, alpha,
beta-ethylenically unsaturated. Suitable ethylenically unsaturated
acid- or anhydride-functional monomers include monomers having a
reactive carbon-carbon double bond and an acidic or anhydride
group, or salts thereof. Preferred such monomers have from 3 to 20
carbons, at least 1 site of unsaturation, and at least 1 acid or
anhydride group, or salt thereof
[0130] Suitable acid-functional monomers include ethylenically
unsaturated monobasic and dibasic acids, as well as anhydrides and
monoesters of dibasic acids. The selected monomers preferably are
readily copolymerizable with any other monomer(s) used to prepare
the water-dispersible polymer. Illustrative monobasic acids include
those represented by the formula CH.sub.2.dbd.C(R.sup.8)--COOH,
where R.sup.8 is hydrogen or an alkyl group of 1 to 6 carbon atoms,
more typically hydrogen or methyl (--CH.sub.3).
[0131] Examples of useful ethylenically unsaturated acid-functional
monomers include acids such as, for example, acrylic acid,
methacrylic acid, alpha-chloroacrylic acid, alpha-cyanoacrylic
acid, crotonic acid, alpha-phenylacrylic acid,
beta-acryloxypropionic acid, fumaric acid, maleic acid, sorbic
acid, alpha-chlorosorbic acid, angelic acid, cinnamic acid,
p-chlorocinnamic acid, beta-stearylacrylic acid, citraconic acid,
mesaconic acid, glutaconic acid, aconitic acid, tricarboxyethylene,
2-methyl maleic acid, itaconic acid, 2-methyl itaconic acid,
methyleneglutaric acid, and the like, or mixtures thereof.
Preferred unsaturated acid-functional monomers include acrylic
acid, methacrylic acid, crotonic acid, fumaric acid, maleic acid,
2-methyl maleic acid, itaconic acid, 2-methyl itaconic acid, and
mixtures thereof. More preferred unsaturated acid-functional
monomers include acrylic acid, methacrylic acid, crotonic acid,
fumaric acid, maleic acid, itaconic acid, and mixtures thereof.
Most preferred unsaturated acid-functional monomers include acrylic
acid, methacrylic acid, maleic acid, crotonic acid, and mixtures
thereof If desired, aqueous salts of the above acids may also be
employed.
[0132] Examples of suitable ethylenically unsaturated anhydride
monomers include compounds derived from the above acids (e.g., as a
pure anhydride or mixtures of such). Preferred anhydrides include
acrylic anhydride, methacrylic anhydride, and maleic anhydride.
[0133] Examples of suitable polymerizable surfactants include those
disclosed in U.S. Publication No. 2002/0155235; and those
commercially available under the tradename "REASOAP" from Adeka
Corporation, Tokyo, Japan; under the tradenames "NOIGEN" and
"HITENOL" from Da-Ichi Kogyo Siyyaku Co., Ltd., Tokyo, Japan; and
under the tradename "SIPOMER" from Solvay Rhodia, Brussels,
Belgium.
[0134] In some embodiments, a non-ionic surfactant is included in
the reaction mixture used to make the latex polymer. Any suitable
non-ionic surfactant may be employed. Examples of suitable
non-ionic surfactants include ethoxylated compounds. In some
embodiments, the non-ionic compound is a sucrose ester, sorbitan
ester, alkyl glycoside, glycerol ester, or mixture thereof. In some
embodiments, a non-ionic surfactant is used that includes hydroxyl
groups. Non-ionic surfactants that comprise, or are derived from,
polysorbate compounds may be used in some embodiments.
[0135] In some embodiments, a surfactant or mixture of surfactants
as described in U.S. App. No. 62/387,129 entitled "Latex Polymer
Made Using Metallic-Base-Neutralized Surfactant and Blush-Resistant
Coating Compositions Containing Such Polymers" may be used. For
example, one or more anionic or zwitterionic surfactant (e.g.,
non-polymeric surfactant) having an acid group neutralized with a
metallic base may be used (e.g., a metallic base including
aluminum, calcium, lithium, magnesium, sodium, or potassium). An
example of such a surfactant is dioctyl sodium sulfosuccinate.
[0136] The latex polymer or other acrylic polymer of the present
invention may exhibit any suitable glass transition (Tg) value(s).
In this context, the Tg value refers to the Tg value of the latex
polymer (or other acrylic polymer) alone (e.g., prior to
formulating a coating composition with additional optional
ingredients such as co-resins, crosslinkers, etc.). In some
embodiments, it may be desirable that the latex polymer (or other
acrylic polymer) has a relatively "high" Tg, such as interior can
coatings that will be exposed to sensitive flavor products (e.g.,
certain colas in which certain flavorants are present at very low
concentrations) and/or chemically aggressive food or beverage
products (e.g., high acid, high salt, and/or high fat). While not
intending to be bound by any theory, such a "high" Tg can be
beneficial from one or more of the following perspectives: (i)
decreased flavor scalping by the cured coating and/or (ii) enhanced
chemical resistance exhibited by the cured coating. In such
embodiments, preferred glass transition temperatures for the latex
polymer (or other acrylic polymer) include those greater than
40.degree. C., more preferably greater than 50.degree. C., even
more preferably greater than 60.degree. C., and in some embodiments
greater than 70.degree. C. or greater than 80.degree. C. Preferred
glass transition temperatures for the latex polymer (or other
acrylic polymer) include those less than 120.degree. C., more
preferably less than 115.degree. C., even more preferably less than
110.degree. C., and in some embodiments, less than 100.degree. C.
or less than 80.degree. C. The term "latex polymer" is used broadly
in the above Tg discussion and is also intended to include latex
particles that include, for example, two polymers that are not
covalently attached. An example of such a latex particle is one
that includes a polymeric surfactant and a polymer resulting from
emulsion polymerization of the ethylenically unsaturated component,
wherein the two polymers are not covalently attached to one
another.
[0137] In some embodiments, the Tg of the latex polymer or other
acrylic polymer may be less than that described above, such as, for
example, less than 40.degree. C., 0 to 40.degree. C., or 20 to
40.degree. C.
[0138] Differential scanning calorimetry (DSC) is an example of a
useful method for determining the Tg of the latex polymer/particle,
with a representative DSC methodology provided in the tests method
section described below.
[0139] It should be noted that it may not be possible to measure a
discrete Tg for certain latex polymers. For example, this may be
the case for a gradient Tg latex polymer, which can contain an
almost infinite number of Tg stages. For example, one may start
with a high Tg monomer composition and then at a certain point in
the polymerization start to feed a lower Tg stage monomer
composition into the high Tg stage monomer feed. The resulting
multistage latex polymer will have a gradient Tg from high to low.
A "power feed" process may be used to prepare such compositions. A
gradient Tg polymer may also be used in conjunction with multiple
multistage Tg polymers. As an example, one may prepare a high Tg
monomer feed (F1) and a low Tg monomer feed (F2). One would begin
to feed F1 into the latex reactor vessel and initiate
polymerization. At a certain period during the F1 feed, one would
then feed F2 into F1 wherein the F2 feed rate is faster than the
overall feed rate of F1 +F2 into the reactor vessel. Consequently,
once the F2 feed into F1 is complete, the overall Tg of the F1+F2
monomer feed blend will be a lower Tg "soft stage" monomer
composition. For such gradient Tg latex polymers, the Fox equation
may be used instead of DSC to calculate Tg. If the monomers used to
produce such a latex polymer include one or more monomers not
having a homopolymer Tg (e.g., because the monomer does not
homopolymerize), then a non-gradient reference latex can be made,
in a non-power feed method, using the same overall monomer
composition and used to measure Tg.
[0140] The overall latex polymer (or other acrylic polymer) may
have any suitable acid number so long as the polymer is preferably
capable of being stably dispersed into water. While not intending
to be bound by any theory, it is believed that the presence of at
least some acid groups in the latex polymer is desirable, for
example, to enhance the liquid stability of the varnish and
crosslinking of the resin system. In embodiments in which a
carboxyl-reactive crosslinker is used (e.g., a
beta-hydroxyalkylamide compound), the latex polymer (or other
acrylic polymer) preferably has an acid number of at least 8 more
preferably at least 15, even more preferably at least 20, and
optimally at least 30 mg KOH per gram of the polymer. Preferably,
the acid number is less than 200, more preferably less than 120,
even more preferably less than 100, and optimally less than 80 mg
KOH per gram of the polymer. Acid numbers can be measured pursuant
to BS EN ISO 3682-1998 standard. The above acid numbers are
inclusive of any acid- or anhydride-functional polymeric
surfactant(s) incorporated into the latex polymer/particle,
regardless of whether the polymeric surfactant(s) are covalently
attached to the emulsion polymerized ethylenically unsaturated
monomer component. The above acid numbers do not include any
non-polymeric and non-polymerizable surfactant that may have been
used to produce the polymer. Neutralized dodecyl benzene sulfonic
acid is an example of such a non-polymeric and non-polymerizable
surfactant.
[0141] When hydroxyl-functional monomer is used, the latex polymer
may have any suitable hydroxyl number to achieve the desired
result.
[0142] Any suitable process or materials may be employed in making
the latex polymer (or other acrylic polymer). In preferred
embodiments, the latex polymer is prepared using a single-stage or
multi-stage emulsion polymerization process. The emulsion
polymerization process may be conducted in a variety of manners.
For example, the emulsion polymerization reaction of the
ethylenically unsaturated monomer component can occur as a batch,
intermittent, or continuous operation.
[0143] In some embodiments, the emulsion polymerization process
uses an optional pre-emulsion monomer mixture in which some or all
of the reactant components and one or more surfactants are
dispersed in the aqueous carrier under agitation to form a stable
pre-emulsion.
[0144] In other embodiments, the ethylenically unsaturated monomer
component is polymerized without the use of a pre-emulsion
step.
[0145] A portion of the surfactant(s) and a portion of the aqueous
carrier may also be introduced into a reactor, and are preferably
heated, agitated, and held under nitrogen sparge to assist in the
subsequent polymerization reactions. Preferred temperatures for
heating the surfactant dispersion include temperatures greater than
about 65.degree. C., and more preferably from about 70.degree. C.
to about 90.degree. C.
[0146] The monomer pre-emulsion or non-pre-emulsified ethylenically
unsaturated monomer component may be fed to the heated aqueous
dispersion in the reactor incrementally or continuously over time.
Alternatively, in certain embodiments a batch or semi-batch process
may be used to polymerize the reactant monomers in the aqueous
dispersion, as described in, for example, U.S. Pat. No. 8,092,876.
In further embodiments, the polymerization process can occur in a
classic two-stage (or multiple stage) "core-shell" arrangement.
Alternatively, the polymerization process can occur in a multiple
stage "inverse core-shell" arrangement as discussed in
International Publication No.WO2015/002958.
[0147] With regard to the conditions of the emulsion
polymerization, the ethylenically unsaturated monomer component is
preferably polymerized in aqueous medium with a water-soluble free
radical initiator.
[0148] The temperature of polymerization is typically from
0.degree. C. to 100.degree. C., preferably from 50.degree. C. to
90.degree. C., more preferably from 70.degree. C. to 90.degree. C.,
and even more preferably from about 80.degree. C. to about
85.degree. C. The pH of the aqueous medium is usually maintained at
a pH of 5 to 12.
[0149] In embodiments in which the acrylic polymer is a latex, the
free radical initiator can be selected from one or more
water-soluble peroxides which are known to act as free radical
initiators. Examples include hydrogen peroxide and t-butyl
hydroperoxide. Redox initiator systems well known in the art (e.g.,
t-butyl hydroperoxide, erythorbic acid, and ferrous complexes) can
also be employed.
[0150] Further examples of polymerization initiators which can be
employed include polymerization initiators which thermally
decompose at the polymerization temperature to generate free
radicals. Examples include both water-soluble and water-insoluble
species. Further examples of free radical initiators that can be
used include persulfates, such as ammonium or alkali metal
(potassium, sodium or lithium) persulfate; azo compounds such as
2,2'-azo-bis(isobutyronitrile),
2,2'-azo-bis(2,4-dimethylvaleronitrile), and
1-t-butyl-azocyanocyclohexane; hydroperoxides such as t-butyl
hydroperoxide, hydrogen peroxide, t-amyl hydroperoxide, methyl
hydroperoxide, and cumene hydroperoxide; peroxides such as benzoyl
peroxide, caprylyl peroxide, di-t-butyl peroxide, ethyl
3,3'-di(t-butylperoxy) butyrate, ethyl 3,3'-di(t-amylperoxy)
butyrate, t-amylperoxy-2-ethyl hexanoate, and t-butylperoxy
pivilate; peresters such as t-butyl peracetate, t-butyl
perphthalate, and t-butyl perbenzoate; as well as percarbonates,
such as di(1-cyano-1-methylethyl)peroxy dicarbonate; perphosphates,
and the like; and combinations thereof.
[0151] Polymerization initiators can be used alone or as the
oxidizing component of a redox system, which also preferably
includes a reducing component such as ascorbic acid, malic acid,
glycolic acid, oxalic acid, lactic acid, thiogycolic acid, or an
alkali metal sulfite, more specifically a hydrosulfite, hyposulfite
or metabisulfite, such as sodium hydrosulfite, potassium
hyposulfite and potassium metabisulfite, or sodium formaldehyde
sulfoxylate, benzoin and combinations thereof. The reducing
component is frequently referred to as an accelerator or a catalyst
activator.
[0152] The initiator and accelerator (if any) are preferably used
in proportion from about 0.001% to 5% each, based on the weight of
monomers to be copolymerized. Promoters such as chloride and
sulfate salts of cobalt, iron, nickel or copper can be used in
small amounts, if desired. Examples of redox catalyst systems
include tert-butyl hydroperoxide/sodium formaldehyde
sulfoxylate/Fe(II), and ammonium persulfate/sodium bisulfate/sodium
hydrosulfite/Fe(II).
[0153] Chain transfer agents can be used to control polymer
molecular weight, if desired.
[0154] After the polymerization is completed, at least a portion of
the carboxylic acid groups and/or anhydride groups of the latex
polymer (or other salt-forming groups such as, e.g., other
neutralizable acid groups and/or neutralizable base groups) may be
neutralized or partially neutralized with a suitable basic compound
(or other suitable neutralizing compound) to produce
water-dispersing groups. The basic compound used for neutralization
can be a metallic base, a fugitive base (e.g., ammonia and primary,
secondary, and/or tertiary amines), or a mixture thereof In
preferred embodiments, the base is a fugitive base, more preferably
an amine. The degree of neutralization may vary considerably
depending upon the amount of acid or base groups included in the
latex polymer, and the degree of dispersibility that is
desired.
[0155] Coating compositions of the present invention preferably
include at least a film-forming amount of the latex polymer or
other acrylic polymer described herein. In preferred embodiments,
the coating composition includes at least about 50 wt- %, more
preferably at least about 65 wt- %, and even more preferably at
least about 80 wt- % or at least about 90 wt- % of the latex
polymer (or other acrylic polymer described herein), based on the
total resin solids weight of the coating composition. The coating
composition includes 100 wt- % or less, more typically less than
about 99 wt- %, and even more typically less than about 95 wt- % of
the latex polymer (or other acrylic polymer described herein),
based on the total resin solids weight of the coating composition.
The above weight percentages of latex polymer are inclusive of any
surfactant(s) (e.g., polymeric and/or non-polymeric surfactant)
used to make the latex polymer, regardless of whether the
surfactant(s) are covalently attached to the emulsion polymerized
ethylenically unsaturated monomer component.
[0156] The coating composition may be formulated from the latex
polymer and/or other acrylic polymer described herein, optionally
with the inclusion of one or more additives. In embodiments in
which the coating composition includes one or more additives, the
additives preferably do not adversely affect the latex emulsion or
other polymer described herein, or a cured coating formed from the
coating composition. For example, such optional additives may be
included in the coating composition to enhance composition
aesthetics, to facilitate manufacturing, processing, handling, and
application of the composition, and to further improve a particular
functional property of the coating composition or a cured coating
resulting therefrom.
[0157] Such optional additives include, for example, catalysts,
dyes, pigments, toners, extenders, fillers, lubricants,
anticorrosion agents, flow-control agents, thixotropic agents,
dispersing agents, antioxidants, adhesion promoters, light
stabilizers, curing agents, co-resins, organosilicon materials, and
mixtures thereof. Each optional additives is preferably included in
a sufficient amount to serve its intended purpose, but not in such
an amount to adversely affect the coating composition or a cured
coating resulting therefrom.
[0158] One preferred optional additive is a catalyst to increase
the rate of cure. Examples of catalysts, include, but are not
limited to, strong acids (e.g., dodecylbenzene sulfonic acid
(DDBSA, available as CYCAT 600 from Cytec), methane sulfonic acid
(MSA), p-toluene sulfonic acid (pTSA), dinonylnaphthalene
disulfonic acid (DNNDSA), and triflic acid), quaternary ammonium
compounds, phosphorous compounds, and tin, titanium, and zinc
compounds. Specific examples include, but are not limited to, a
tetraalkyl ammonium halide, a tetraalkyl or tetraaryl phosphonium
iodide or acetate, tin octoate, zinc octoate, triphenylphosphine,
and similar catalysts known to persons skilled in the art.
[0159] If used, the catalyst is preferably present in an amount of
at least about 0.01% by weight, and more preferably at least about
0.1% by weight, based on the total solids weight of the coating
composition. Furthermore, if used, the catalyst is also preferably
present in a non-volatile amount of no greater than about 3% by
weight, and more preferably no greater than about 1% by weight,
based on the total solids weight of the coating composition.
[0160] Another useful optional ingredient is a lubricant (e.g., a
wax), which facilitates manufacture of metal closures and other
fabricated coated articles by imparting lubricity to coated metal
substrate. Preferred lubricants include, for example, Carnauba wax
and polyethylene-type lubricants. If used, a lubricant is
preferably present in the coating composition in an amount of at
least about 0.1% by weight, and preferably no greater than about 2%
by weight, and more preferably no greater than about 1% by weight,
based on the total solids weight of the coating composition.
[0161] Another useful optional ingredient is an organosilicon
material, such as a siloxane-based and/or polysilicone-based
materials. Representative examples of suitable such materials are
disclosed in International Publication Nos. WO/2014/089410 and
WO/2014/186285.
[0162] Another useful optional ingredient is a pigment, such as
titanium dioxide. If used, a pigment is present in the coating
composition in an amount of no greater than about 70% by weight,
more preferably no greater than about 50% by weight, and even more
preferably no greater than about 40% by weight, based on the total
solids weight of the coating composition.
[0163] As previously discussed, preferred embodiments of the
coating composition include a carboxyl-reactive crosslinker, more
preferably a NCCR crosslinker, and even more preferably a
beta-hydroxyalkylamide crosslinker. In addition, or alternatively,
the coating may include one or more additional curing agents such
as, for example, any of the crosslinkers described below. Preferred
crosslinkers are substantially free of each of BPA, BPF, BPS,
including glycidyl ether compounds thereof (e.g., BADGE), and epoxy
novolacs.
[0164] Any of the well-known, hydroxyl-reactive curing resins can
be used. For example, phenoplast, blocked isocyanates, and
aminoplast curing agents may be used, as well as combinations
thereof.
[0165] Phenoplast resins include the condensation products of
aldehydes with phenols. Formaldehyde and acetaldehyde are preferred
aldehydes. Various phenols can be employed such as phenol, cresol,
p-phenylphenol, p-tert-butylphenol, p-tert-amylphenol, and
cyclopentylphenol. Resole phenolics, particularly resole phenolics
not made using BPA, BPF, or BPS, are preferred phenoplasts.
[0166] Aminoplast resins are the condensation products of aldehydes
such as formaldehyde, acetaldehyde, crotonaldehyde, and
benzaldehyde with amino or amido group-containing substances such
as urea, melamine, and benzoguanamine. Examples of suitable
aminoplast crosslinking resins include benzoguanamine-formaldehyde
resins, melamine-formaldehyde resins, esterified
melamine-formaldehyde, and urea-formaldehyde resins.
[0167] As examples of other generally suitable crosslinkers are the
blocked or non-blocked aliphatic, cycloaliphatic or aromatic di-,
tri-, or poly-valent isocyanates, such as hexamethylene
diisocyanate (HMDI), cyclohexyl-1,4-diisocyanate, and the like.
Further examples of generally suitable blocked isocyanates include
isomers of isophorone diisocyanate, dicyclohexylmethane
diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate,
phenylene diisocyanate, tetramethyl xylene diisocyanate, xylylene
diisocyanate, and mixtures thereof.
[0168] The total amount of one or more crosslinkers included in the
coating composition may depend on the type of crosslinker, the time
and temperature of the bake, and molecular weight. If used, the one
or more crosslinkers are typically present in an amount of up to
about 50 wt- %, preferably up to about 30 wt- %, more preferably up
to about 15wt- %. If used, the crosslinker is typically present in
an amount of at least about 0.1 wt- %, more preferably at least
about 1 wt- %, and even more preferably at least about 2 wt- %.
These weight percentages are based on the total resin solids weight
of the coating composition.
[0169] In preferred embodiments, the coating composition includes
at least 1 wt- %, more preferably at least 2 wt- %, and even more
preferably at least 3 wt- % of one or more NCCR crosslinkers, based
on total resin solids of the coating composition. Although the
upper amount is not restricted, the coating composition preferably
includes less than 20 wt- %, more preferably less than 15 wt- %,
and even more preferably less than 10 wt- % of one or more NCCR
crosslinkers, based on total resin solids of the coating
composition. In certain preferred embodiments, the coating
composition includes from 4 to 8.5 wt- % of one or more NCCR
crosslinkers (e.g., Primid QM1260 crosslinker), more preferably
from 5 to 7.5 wt- % of one or more NCCR crosslinker, based on the
total resin solids of the coating composition. In some embodiments,
the coating composition includes at least the above amount of one
or more beta-hydroxyalkylamide crosslinkers.
[0170] In embodiments in which excellent "hard-to-hold"
food-contact coating performance is desired (e.g., the ability to
withstand the corrosive properties of packaging food or products
having particularly challenging chemical profiles such as, e.g.,
certain alcoholic cider beverages), it has been discovered that it
can be beneficial to use both an NCCR crosslinker and a phenoplast
crosslinker. The use of certain such crosslinker combinations has
been observed to result in interior can coatings that have
increased chemical resistance when challenged with certain
"hard-to-hold" products (e.g., alcoholic ciders), as indicated, for
example, by reduced instances of coating blush and reduced aluminum
pickup. A preferred combination of such crosslinkers is the
combination of one or more beta-hydroxyalkylamides (e.g., the
PRIMID QM 1260 crosslinker) with one or more resole phenolic
crosslinkers (more preferably one or more resole phenolics that are
not intentionally made with BPA, BPF, or BPS as a starting
ingredient). Thus, in some embodiments, the coating composition
includes, based on total resin solids: (i) 2 to 10 wt- %, 4 to 8.5
wt- %, or 5 to 7.5 wt- % of NCCR crosslinker (more preferably a
beta-hydroxyalkylamide crosslinker); and (ii) 1 to 10 wt- %, 3 to 8
wt- %, or 4 to 6 wt- % of a phenoplast crosslinker (more preferably
a resole phenolic crosslinker).
[0171] In some embodiments, the coating composition may be cured
without the use of an external crosslinker. Additionally, the
coating composition may be substantially free of formaldehyde and
formaldehyde-containing materials, essentially free of these
compounds, essentially completely free of these compounds, or even
completely free of these compounds. In preferred embodiments, the
coating composition is also substantially free, essentially free,
essentially completely free, or completely free of each of BPA,
BPF, and BPS, including any diepoxides thereof (e.g., diglycidyl
ethers thereof such as the diglycidyl ether of BPA ("BADGE")). In
some embodiments, the coating composition is substantially free or
completely free of bisphenol compounds.
[0172] In preferred embodiments, the coating composition is also
substantially free, essentially free, essentially completely free,
or completely free of one or both of styrene and substituted
styrene compounds.
[0173] In preferred embodiments, the coating composition is
substantially free or completely free of halogenated monomers
(whether free or polymerized), such as chlorinated vinyl
monomers.
[0174] In some embodiments, such as for certain spray coating
applications (e.g., aqueous inside spray for food or beverage cans
including, e.g., aluminum beverage cans), the coating composition
may have a total solids weight greater than about 5%, more
preferably greater than about 10%, and even more preferably greater
than about 15%. In these embodiments, the coating composition may
also have a total solids weight less than about 40%, more
preferably less than about 30%, and even more preferably less than
about 25%. In some of these embodiments, the coating composition
may have a total solids weight ranging from about 18% to about 22%.
The liquid carrier (e.g., aqueous carrier) may constitute the
remainder of the weight of the coating composition.
[0175] If desired, the coating composition may also include one or
more other optional polymers, such as, for example, one or more
acrylic polymers, alkyd polymers, epoxy polymers, polyolefin
polymers, polyurethane polymers, polysilicone polymers, polyester
polymers, and copolymers and mixtures thereof.
[0176] In aqueous embodiments, the aqueous carrier of the coating
composition preferably includes water and may further include one
or more optional organic solvents (e.g., one or more water-miscible
solvents). In some embodiments, water constitutes greater than
about 20% by weight, more preferably greater than about 35% by
weight, and even more preferably greater than about 50% by weight
of the total weight of the aqueous carrier. In some embodiments,
water constitutes 100% or less, less than about 95% by weight, or
less than about 90% by weight of the total weight of the aqueous
carrier.
[0177] While not intending to be bound by theory, the inclusion of
a suitable amount of an organic solvent in the aqueous carrier can
be advantageous in some embodiments. Accordingly, in certain
embodiments, the one or more organic solvents may constitute
greater than 0%, more preferably greater than about 5%, and even
more preferably greater than about 10% by weight of the aqueous
carrier. In these embodiments, the organic solvents may also
constitute less than about 80%, more preferably less than about
65%, and even more preferably less than about 50% or less than
about 40% by weight of the aqueous carrier.
[0178] In some embodiments, the coating composition is a
solvent-based coating composition that preferably includes no more
than a de minimus amount (e.g., 0 to 2 wt- %) of water. For
example, in some embodiments, the coating composition is a
styrene-free, organic-solvent-based food or beverage can coating
composition that includes a styrene-free organic solution
polymerized acid- or anhydride-functional acrylic polymer (e.g.,
acid number>20 mg KOH/g resin) preferably in combination with
one or more NCCR described herein. Such organic solution
polymerized acid- or anhydride acrylic polymers can have any
suitable number molecular weight (Mn) such as, for example, greater
than 3,000, greater than 4,000, greater than 5,000, or even as high
as or greater than 30,000 Mn if viscosity can be suitably
controlled.
[0179] The coating composition preferably has a viscosity suitable
for a given coating application. In some embodiments (e.g., aqueous
inside spray for food or beverage cans), the coating composition
may have an average viscosity greater than about 5 seconds, more
preferably greater than 10 seconds, and even more preferably
greater than about 15 seconds, based on the Viscosity Test
described below. In some embodiments e.g., aqueous inside spray for
food or beverage cans), the coating composition may also have an
average viscosity less than about 40 seconds, more preferably less
than 30 seconds, and even more preferably less than about 25, based
on the Viscosity Test described below.
[0180] The coating composition of the present invention may be
applied to a variety of different substrates using a variety of
different coating techniques (e.g., spray coating, roll coating,
wash coating, dipping, etc.). In certain preferred embodiments, the
coating composition is applied as an inside spray coating. As
briefly described above, cured coatings formed from the coating
composition are particularly suitable for use on metal food and
beverage cans (e.g., two-piece cans, three-piece cans, and the
like). Two-piece cans (e.g., two-piece beer or soda cans and
certain food cans) are typically manufactured by a drawn and
ironing ("D&I") process. The cured coatings are also suitable
for use in food or beverage contact situations (collectively
referred to herein as "food-contact"), and may be used on the
inside or outside of such cans.
[0181] The disclosed coating compositions may be present as a layer
of a mono-layer coating system or as one or more layers of a
multi-layer coating system. The coating composition can be used as
a primer coat, an intermediate coat, a top coat, or a combination
thereof. The coating thickness of a particular layer, and of the
overall coating system, will vary depending upon the coating
material used, the substrate, the coating application method, and
the end use for the coated article. Mono-layer or multi-layer
coating systems including one or more layers formed from the
disclosed coating composition may have any suitable overall coating
thickness, but will typically have an overall average dry coating
thickness of from about 1 to about 60 micrometers and more
typically from about 2 to about 15 micrometers. Typically, the
overall average dry coating thickness for rigid metal food or
beverage can applications will be about 3 to about 10 micrometers.
Coating systems for use on closures (e.g., twist-off metal
closures) for food or beverage containers may have an overall
average dry coating thickness up to about 15 micrometers. In
certain embodiments in which the coating composition is used as an
interior coating on a drum (e.g., a drum for use with food or
beverage products), the overall average dry coating thickness may
be approximately 25 micrometers.
[0182] The metal substrate used in forming rigid food or beverage
cans, or portions thereof, typically has an average thickness in
the range of about 125 micrometers to about 635 micrometers.
Electro-tinplated steel, cold-rolled steel and aluminum are
commonly used as metal substrates for food or beverage cans, or
portions thereof. In embodiments in which a metal foil substrate is
employed in forming, e.g., a packaging article, the thickness of
the metal foil substrate may be even thinner that that described
above.
[0183] The disclosed coating compositions may be applied to a
substrate either prior to, or after, the substrate is formed into
an article such as, for example, a food or beverage container or a
portion thereof In one embodiment, a method of forming food or
beverage cans is provided that includes: applying a coating
composition described herein to a metal substrate (e.g., applying
the composition to the metal substrate in the form of a planar coil
or sheet), hardening the composition, and forming (e.g., via
stamping or other deformation process) the substrate into a
packaging container or a portion thereof (e.g., a food or beverage
can or a portion thereof). For example, two-piece or three-piece
cans or portions thereof such as riveted beverage can ends (e.g.,
soda or beer cans) having a cured coating of the disclosed coating
composition on a surface thereof can be formed in such a method. In
another embodiment, a method of forming food or beverage cans is
provided that includes: providing a packaging container or a
portion thereof (e.g., a food or beverage can or a portion
thereof), applying a coating composition described herein to the
inside, outside or both inside and outside portions of such
packaging container or a portion thereof (e.g., via spray
application, dipping, etc.), and hardening the composition.
[0184] After applying the coating composition onto a substrate, the
composition can be cured using a variety of processes, including,
for example, oven baking by either conventional or convectional
methods, or any other method that provides an elevated temperature
suitable for curing the coating. The curing process may be
performed in either discrete or combined steps. For example,
substrates can be dried at ambient temperature to leave the coating
compositions in a largely uncrosslinked state. The coated
substrates can then be heated to fully cure the compositions. In
certain instances, the disclosed coating compositions may be dried
and cured in one step.
[0185] The cure conditions will vary depending upon the method of
application and the intended end use. The curing process may be
performed at any suitable temperature, including, for example, oven
temperatures in the range of from about 100.degree. C. to about
300.degree. C., and more typically from about 177.degree. C. to
about 250.degree. C. If a metal coil is the substrate to be coated,
curing of the applied coating composition may be conducted, for
example, by heating the coated metal substrate over a suitable time
period to a peak metal temperature ("PMT") of preferably greater
than about 177.degree. C. More preferably, the coated metal coil is
heated for a suitable time period (e.g., about 5 to 900 seconds) to
a PMT of at least about 218.degree. C.
[0186] In some embodiments, the coating composition is an inside
spray coating composition capable of being spray applied on an
interior of a food or beverage can (e.g., a 2-piece steel or
aluminum food or beverage can) to effectively, and evenly, coat the
substrate and form a continuous cured coating (e.g., a coating that
exhibits a suitable initial metal exposure value, thereby
indicating that the substrate has been effectively coated and is
free of unsuitable pores or gaps in the coating).
[0187] For interior food-contact coatings, and interior coatings
for soda beverage cans in particular, preferred Tg for the cured
coating include those greater than about 50.degree. C., more
preferably greater than about 60.degree. C., even more preferably
greater than about 70.degree. C., and in some embodiments, greater
than about 80.degree. C. Preferred Tg for the cured coating include
those less than about 120.degree. C., more preferably less than
about 115.degree. C., even more preferably less than about
110.degree. C., and in some embodiments, less than about
100.degree. C. An example of a suitable DSC methodology is provided
below.
[0188] In some embodiments, the cured coating preferably exhibits
desired properties for use as an interior food-contact coating
(e.g., inside spray coating) for food and beverage cans. For
example, the cured coating preferably gives a global extraction of
less than about 25 parts-per-million (ppm), and more preferably
less than about 10 ppm, and even more preferably less than about 1
ppm, pursuant to the Global Extraction test below. Additionally,
the cured coating preferably exhibits a metal exposure less than
about 5 milliamps (mA), more preferably less than about 2 mA, and
even more preferably less than about 1 mA, pursuant to the Initial
Metal Exposure test below. In addition, the cured coating is
preferably free of or substantially free of blush (e.g., exhibits a
blush rating of at least 8, more preferably at least 9, and
optimally 10) pursuant to the Blush Resistance test described
below. For inside spray beverage can coating compositions,
preferred cured coatings give metal exposure values after drop
damage of less than 30 mA, more preferred values of less than 20
mA, even more preferred values of less than 10 mA, even more
preferred values of less than 3.5 mA, even more preferred values of
less than 2.5 mA, and even more preferred values of less than 1.5
mA pursuant to the Metal Exposure After Drop Damage test below
[0189] The coating composition of the present disclosure may also
offers utility in other coating applications. These additional
applications include, but are not limited to, wash coating, sheet
coating, and side seam coatings (e.g., food can side seam
coatings). Other commercial coating application and curing methods
are also envisioned, for example, electrocoating, extrusion
coating, laminating, powder coating, and the like. The coating
composition may also be useful in medical or cosmetic packaging
applications, including, for example, on surfaces of metered-dose
inhalers ("MDIs"), including on drug-contact surfaces.
[0190] Because the balance of coating requirements for food or
beverage can coatings are particularly stringent and difficult to
achieve, it is believed the coating compositions of the present
invention may also be suitable for a multitude of other coatings
areas, which generally have less stringent coating requirements.
For example, the coating compositions of the present invention may
be particularly suitable for non-packaging-related coil coating
operations (e.g., "industrial" coil coatings). The coating
composition may be applied to planar metal stock such as is used,
for example, for lighting fixtures; architectural metal skins
(e.g., gutter stock, window blinds, siding and window frames);
interior or exterior steel building products; HVAC applications;
agricultural metal products; industrial coating applications (e.g.,
appliance coatings); packaging coating applications (e.g., food or
beverage cans, drug cans, etc.) and the like. The coating
composition may be particularly suited for a coil coating operation
where the composition is applied on rapidly moving planar metal
coil substrate and then baked at elevated temperatures (e.g.,
>100.degree. C.) as the coated substrate travels toward an
uptake coil winder.
Exemplary Embodiments
[0191] Embodiment 1 is a coating composition comprising: [0192] an
acid- or anhydride-functional acrylic polymer that is substantially
free of styrene; [0193] a nitrogen-containing carboxyl-reactive
crosslinker; and [0194] liquid carrier that includes one or both of
water and an organic solvent; [0195] wherein the coating
composition is a food or beverage can coating composition suitable
for use in forming a food-contact coating of a metal food or
beverage can and is substantially free of bisphenol A, including
epoxides thereof.
[0196] Embodiment 1' is the coating composition of Embodiment 1
wherein the coating composition is substantially free of, more
preferably essentially free of, each of bisphenol A, bisphenol F,
and bisphenol S, including epoxides thereof.
[0197] Embodiment 2 is the coating composition of any preceding
embodiment, wherein the coating composition is an aqueous coating
composition.
[0198] Embodiment 3 is a coating composition comprising: [0199] an
acid- or anhydride-functional acrylic polymer comprising an acid-
or anhydride-functional latex that is substantially free of styrene
and has a glass transition temperature of greater than 40.degree.
C., greater than 50.degree. C., or greater than 60.degree. C.; and
[0200] a nitrogen-containing carboxyl-reactive crosslinker; [0201]
wherein the coating composition is an aqueous coating composition
that is suitable for use in forming a food-contact coating of a
metal food or beverage can and is substantially free of bisphenol
A.
[0202] Embodiment 3' is the coating composition of Embodiment 3
wherein the coating composition is substantially free of, more
preferably essentially free of, each of bisphenol A, bisphenol F,
and bisphenol S, including epoxides thereof.
[0203] Embodiment 4 is a coating composition comprising: [0204] an
acid- or anhydride-functional acrylic polymer comprising an acid-
or anhydride-functional latex that is optionally substantially free
of styrene (i.e., some embodiments may include styrene), the acid-
or anhydride-functional latex formed by emulsion polymerizing
ethylenically unsaturated monomers comprising more than 5 wt- %,
more than 6 wt- %, more than 7 wt- %, more than 8 wt- %, more than
9 wt- %, more than 10 wt- %, more than 11 wt- %, more than 12 wt-
%, more than 13 wt- %, or more than 14 wt- % of multi-ethylenically
unsaturated monomer; [0205] a carboxyl-reactive crosslinker (e.g.,
a nitrogen-containing carboxyl-reactive crosslinker); [0206]
wherein the coating composition is an aqueous coating composition
that is suitable for use in forming a food-contact coating of a
metal food or beverage can and is substantially free of bisphenol
A.
[0207] Embodiment 4' is the coating composition of Embodiment 4
wherein the coating composition is substantially free of, more
preferably essentially free of, each of bisphenol A, bisphenol F,
and bisphenol S, including epoxides thereof.
[0208] Embodiment 5 is the coating composition of any of
embodiments 1, 1', 2, 2', 4 or 4', wherein the acid- or
anhydride-functional acrylic polymer has a glass transition
temperature of greater than 40.degree. C., greater than 50.degree.
C., or greater than 60.degree. C.
[0209] Embodiment 6 is the coating composition of any preceding
embodiment, wherein the carboxyl-reactive crosslinker (e.g.,
nitrogen-containing carboxyl-reactive crosslinker) is not formed
from reactants including formaldehyde.
[0210] Embodiment 7 is the coating composition of any preceding
embodiment, wherein the nitrogen-containing carboxyl-reactive
crosslinker (e.g., nitrogen-containing carboxyl-reactive
crosslinker) includes hydroxyl groups.
[0211] Embodiment 8 is the coating composition of any preceding
embodiment, wherein the nitrogen-containing carboxyl-reactive
crosslinker includes two or more nitrogen atoms.
[0212] Embodiment 9 is the coating composition of any preceding
embodiment, wherein the carboxyl-reactive crosslinker includes at
least one amide group, and optionally two or more amide groups.
[0213] Embodiment 10 is the coating composition of any preceding
embodiment, wherein the nitrogen-containing carboxyl-reactive
crosslinker includes a hydroxyl group that is located beta relative
to the nitrogen atom of an amide bond.
[0214] Embodiment 11 is the coating composition of any preceding
embodiment, wherein the nitrogen-containing carboxyl-reactive
crosslinker includes two or more groups of the following
structure:
HO--R.sup.1--N(R.sup.2)--C(.dbd.O)-- [0215] wherein each R.sub.1 is
independently an organic group, and each R.sub.2 is independently
hydrogen or an organic group.
[0216] Embodiment 12 is the coating composition of embodiment 11,
wherein each R independently includes from 2 to 10 carbon
atoms.
[0217] Embodiment 13 is the coating composition of embodiment 12,
wherein the depicted hydroxyl group is attached directly to a first
carbon atom that is attached directly to a second carbon, and
wherein the depicted nitrogen atom is attached directly to the
second carbon atom.
[0218] Embodiment 14 is the coating composition of any of
embodiment 11 to 13, wherein each R.sup.2 is independently an
organic group that includes a hydroxyl group.
[0219] Embodiment 15 is the coating composition of any preceding
embodiment, wherein the nitrogen-containing carboxyl-reactive
crosslinker comprises one or more groups capable of forming an
intermediate having an oxazolinium structure.
[0220] Embodiment 16 is the coating composition of any of
embodiment 11 to 15, wherein the nitrogen-containing
carboxyl-reactive crosslinker comprises a compound having the
following structure:
(HO--R.sup.1--N(R.sup.2)--C(.dbd.O)).sub.n--X [0221] wherein:
[0222] n is 2 or more, and [0223] X is a polyvalent organic
group.
[0224] Embodiment 17 is the coating composition of embodiment 16,
wherein Xis an alkylene group.
[0225] Embodiment 18 is the coating composition of embodiment 17,
wherein the alkylene group is --(CH.sub.2).sub.4--.
[0226] Embodiment 19 is the coating composition of any preceding
embodiment, wherein the nitrogen-containing carboxyl-reactive
crosslinker comprises:
##STR00003##
[0227] Embodiment 20 is the coating composition of any of
embodiments 1 to 18, wherein the nitrogen-containing
carboxyl-reactive crosslinker is selected from
bis[N,N-di(.beta.-hydroxy-ethyl)]adipamide,
bis[N,N-di(.beta.-hydroxy-propyl)]succinamide,
bis[N,N-di(.beta.-hydroxy-ethyl)]azelamide,
bis[N,N-di(.beta.-hydroxy-propyl)]adipamide,
bis[N-metil-N-(.beta.-hydroxy-ethyl)]oxamide, or a mixture
thereof.
[0228] Embodiment 21 is the coating composition of any of
embodiments 1 to 18, wherein the nitrogen-containing
carboxyl-reactive crosslinker comprises a beta-hydroxyalkylamide
crosslinker.
[0229] Embodiment 22 is the coating composition of any of
embodiments 1 to 8, wherein the carboxyl-reactive crosslinker
includes one or more aziridine, diimide, or oxazoline groups.
[0230] Embodiment 23 is the coating composition of any preceding
embodiment, wherein the coating composition includes at least I wt-
%, at least 2 wt- %, at least 3 wt- %, at least 4 wt- %, or at
least 5 wt- %, based on total resin solids, of the
carboxyl-reactive crosslinker (e.g., nitrogen-containing
carboxyl-reactive crosslinker).
[0231] Embodiment 24 is the coating composition of any preceding
embodiment, wherein the coating composition includes at least 50
weight percent, based on total esin solids, of the acid- or
anhydride-functional acrylic polymer.
[0232] Embodiment 25 is the coating composition of any preceding
embodiment, wherein the coating composition includes one or more
water-miscible organic solvents.
[0233] Embodiment 26 is the coating composition of any preceding
embodiment, wherein the coating composition, when thermally cured,
has a glass transition temperature of at least 40.degree. C., at
least 50.degree. C., or at least 60.degree. C.
[0234] Embodiment 27 is the coating composition of any preceding
embodiment, wherein the acid- or anhydride-functional acrylic
polymer has a glass transition temperature of from 50 to 80.degree.
C.
[0235] Embodiment 28 is the coating composition of any preceding
embodiment, wherein the acid- or anhydride-functional acrylic
polymer has a number average molecular weight of at least
3,000.
[0236] Embodiment 29 is the coating composition of any preceding
embodiment, wherein the acid- or anhydride-functional acrylic
polymer has a number average molecular weight of more than
30,000.
[0237] Embodiment 30 is the coating composition of any preceding
embodiment, wherein the acid- or anhydride-functional acrylic
polymer has an acid number of at least 20 mg KOH/g resin.
[0238] Embodiment 31 is the coating composition of any of
embodiments 3 to 30, wherein the acid- or anhydride-functional
latex is a reaction product of an ethylenically unsaturated monomer
component emulsion polymerized in the presence of an aqueous
dispersion of a water-dispersible polymer.
[0239] Embodiment 32 is the coating composition of embodiment 31,
wherein the water-dispersible polymer comprises an acrylic polymer,
a polyether polymer, a polyolefin polymer, a polyester polymer, or
a mixture or copolymer thereof.
[0240] Embodiment 33 is the coating composition of embodiment 32,
wherein the water-dispersible polymer comprises an at least
partially neutralized acid- or anhydride-functional acrylic
polymer.
[0241] Embodiment 34 is the coating composition of embodiment 32 or
33, wherein the acrylic polymer is an organic solution polymerized
acrylic polymer.
[0242] Embodiment 35 is the coating composition of any preceding
embodiment, wherein at least a portion of the acid- or
anhydride-functional acrylic polymer is formed an ethylenically
unsaturated monomer component including at least one monomer having
(i) a Tg of more than 40.degree. C. and (ii) one or more groups
selected from cyclic groups, branched organic groups, or a
combination thereof.
[0243] Embodiment 36 is the coating composition of embodiment 35,
wherein at least one cyclic group is present.
[0244] Embodiment 37 is the coating composition of embodiment 36,
wherein the at least one cyclic group is selected from one or more
of substituted or unsubstituted: cyclobutane groups, cyclopentane
groups, cyclohexane groups, phenylene groups, norbornene groups,
norbornane groups, tricyclodecane groups, or a combination
thereof.
[0245] Embodiment 38 is the coating composition of embodiment 35,
wherein at least one branched organic group is present.
[0246] Embodiment 39 is the coating composition of embodiment 38,
wherein the at least one branched organic group is present in a
monomer selected from isopropyl methacrylate, isobutyl
methacrylate, sec-butyl methacrylate, or a mixture thereof.
[0247] Embodiment 40 is the coating composition of embodiment 35,
wherein the at least one monomer having (i) and (ii) has the
following structure:
(R.sup.3).sub.2--C.dbd.C(R.sup.4)--W.sub.n--Y, [0248] wherein:
[0249] R.sup.3 is independently selected from hydrogen or an
organic group; [0250] R.sup.4 is selected from hydrogen or an alkyl
group; [0251] W, if present, is a divalent linking group; [0252] n
is 0 or 1; and [0253] Y is: (a) a branched organic group including
one or more branching atoms, (b) a cyclic group, or (c) a
combination of (a) and (b).
[0254] Embodiment 41 is the coating composition of embodiment 40,
wherein Y is a branched organic group of the following
structure:
--C(CH.sub.3).sub.t(R.sup.5).sub.3-t [0255] wherein: [0256] t is 0
to 3; [0257] each R.sup.5, if present, is independently an organic
group that may optionally be itself branched and may optionally
include one or more heteroatoms; and [0258] two or more R.sup.5 may
optionally form a cyclic group with one another.
[0259] Embodiment 42 is the coating composition of embodiment 41,
wherein t is 1, each R.sup.5 comprises an alkyl group, and the
total number of carbon atoms in both R.sup.5 groups is 6, 7, or
8.
[0260] Embodiment 43 is the coating composition of embodiment 41,
wherein t is 0, 1, or 2 and at least one R.sup.5 is a branched
organic group.
[0261] Embodiment 44 is the coating composition of any one of
embodiments 41 to 43, wherein at least one R.sup.5 includes a
tertiary or quaternary carbon atom.
[0262] Embodiment 45 is the coating composition of any preceding
embodiment, wherein the acid- or anhydride-functional polymer
(e.g., acid- or anhydride-functional latex) is formed by
polymerizing (e.g., emulsion polymerizing in an aqueous media) an
ethylenically unsaturated monomer component comprising at least 10
wt- %, at least 20 wt- %, at least 30 wt- %, and in some
embodiments 40 wt- % or more of one or more branched and/or cyclic
monomers.
[0263] Embodiment 46 is the coating composition of any preceding
embodiment, wherein one or both of: (i) the acid- or
anhydride-functional acrylic polymer and (ii) the coating
composition are substantially free of each of bisphenols and/or
halogenated monomers.
[0264] Embodiment 47 is the coating composition of any of
embodiments 3 to 46, wherein the acid- or anhydride functional
latex is formed from ingredients including an emulsion polymerized
ethylenically unsaturated monomer component that includes a
multi-ethylenically unsaturated monomer, and wherein the emulsion
polymerized ethylenically unsaturated monomer component is
optionally substantially free of oxirane-group-containing
monomers.
[0265] Embodiment 48 is the coating composition of Embodiment 47,
wherein multi-ethylenically unsaturated monomer comprise more than
5 wt- %, more than 6 wt- %, more than 7 wt- %, more than 8 wt- %,
more than 9 wt- %, more than 10 wt- %, more than 11 wt- %, more
than 12 wt- %, more than 13 wt- %, or more than 14 wt- % of the
total weight of emulsion polymerized ethylenically unsaturated
monomers used to form the acid- or anhydride-functional latex.
[0266] Embodiment 49 is the coating composition of any of
embodiments 4 to 48, wherein the multi-ethylenically unsaturated
monomer comprises 1,4-butandiol di(meth)acrylate.
[0267] Embodiment 50 is the coating composition of any of
embodiments 3 to 49, wherein methyl (meth)acrylate comprises at
least 20 wt- %, at least 25 wt- %, at least 30 wt- %, or at least
40 wt- % of the ethylenically unsaturated monomers used to form the
acid- or anhydride-functional latex.
[0268] Embodiment 51 is the coating composition of any of
embodiments 3 to 50, wherein methyl methacrylate comprises at least
20 wt- %, at least 25 wt- %, at least 30 wt- %, or at least 40 wt-
% of the emulsion polymerized ethylenically unsaturated monomers
used to form the acid- or anhydride-functional latex.
[0269] Embodiment 52 is the coating composition of any of
embodiments 3 to 51, wherein the ethylenically unsaturated monomer
component used to form the acid or anhydride-functional latex
includes methyl methacrylate and ethyl acrylate.
[0270] Embodiment 53 is the coating composition of any of
embodiment 52, wherein the ethylenically unsaturated monomer
component include a hydroxyl-functional (meth)acrylate (e.g.,
hydroxyethyl methacrylate).
[0271] Embodiment 54 is the coating composition of any of
embodiments 47 to 53, wherein an acid- or anhydride-functional
acrylic latex has a glass transition temperature of greater than
40.degree. C., greater than 50.degree. C., or greater than
60.degree. C.
[0272] Embodiment 55 is the coating composition of any preceding
embodiment, wherein the coating composition includes, based on
total resin solids, from 1 to 20 wt- % (e.g., 2 to 10 wt- %, 4 to
8.5 wt- %, or 5 to 7.5 wt- %) of the nitrogen-containing carboxyl
reactive crosslinker and from 50 to 99 wt- % of the acid- or
anhydride-functional acrylic polymer.
[0273] Embodiment 56 is the coating composition of any preceding
embodiment, wherein the coating composition is an inside spray
beverage can coating composition.
[0274] Embodiment 57 is a method of coating a food or beverage can,
comprising: [0275] applying the coating composition of any
preceding embodiment on a metal substrate prior to, or after,
forming the metal substrate into a food or beverage container or a
portion thereof.
[0276] Embodiment 58 is the method of embodiment 57, wherein the
coating composition is spray applied on the metal substrate.
[0277] Embodiment 59 is the method of embodiment 57, wherein the
coating composition is spray applied on an interior surface of an
aluminum beverage can.
[0278] Embodiment 60 is the method of any one of embodiments 57 to
59, and further comprising curing the coating composition on the
metal substrate to form a continuous cured coating having an
average film thickness of from 2 to 15 microns.
[0279] Embodiment 61 is a food or beverage can, or a portion
thereof, resulting from the method of any of embodiments 57 to
60.
[0280] Embodiment 62 is food or beverage can, or a portion thereof,
having a metal substrate with a cured coating formed from the
coating composition of any of embodiments 1 to 56 applied on an
interior surface, an exterior surface, or both.
[0281] Embodiment 63 is the food or beverage can, or portion
thereof, of embodiments 61 or 62, wherein the cured coating has a
Tg of at least 50.degree. C., at least 60.degree. C., or at least
70.degree. C.
[0282] Embodiment 64 is a food or beverage can, or a portion
thereof, having an interior food-contact coating having an overall
average dry coating thickness of from 2 to 15 micrometers, wherein:
[0283] the interior food-contact coating is formed from a spray
applied aqueous coating composition that is substantially free of
each of styrene and halogenated monomers and is also substantially
free of bisphenol A, and wherein the coating composition includes,
based on total resin solids, at least 50 wt- % of an emulsion
polymerized latex; and [0284] the interior food-contact coating has
a metal exposure value after drop damage of less than 10 mA when
tested pursuant to the Metal Exposure after Drop Damage test
disclosed herein.
[0285] Embodiment 64' is the s a food or beverage can, or a portion
thereof, of embodiment 64, wherein the coating composition is
substantially free of, more preferably essentially free of, each of
bisphenol A, bisphenol F, and bisphenol S, including epoxides
thereof.
[0286] Embodiment 65 is the food or beverage can, or a portion
thereof, of embodiment 64 or 64', wherein the can comprises an
aluminum beverage can and the interior food-contact coating has a
metal exposure value after drop damage of less than 3.5 mA.
[0287] Embodiment 66 is the food or beverage can, or portion
thereof, of any of embodiments 64 to 65, wherein the emulsion
polymerized latex comprises the emulsion polymerized latex of any
one of embodiments 3 to 56.
[0288] Embodiment 67 is the food or beverage can, or portion
thereof, of any of embodiments 64 to 66, wherein the coating
composition includes any of the features recited in embodiments 3
to 56.
[0289] Embodiment 68 is an inside spray beverage can coating
composition, wherein the coating composition comprises an aqueous
coating composition that is substantially free of each of styrene
and halogenated monomers and is also substantially free of
bisphenol A; and wherein the coating composition includes, based on
total resin solids, at least 50 wt- % of an emulsion polymerized
latex; and wherein the inside spray beverage can coating
composition, when spray applied onto an interior of a standard 12
ounce two-piece drawn and ironed aluminum 211 diameter beverage can
at a dry film weight of 120 milligrams per can and baked for 50
seconds at an oven temperature of at least 188.degree. C. to
achieve a dome peak metal temperature of at least 199.degree. C.,
gives a metal exposure of less than 20 mA, less than 10 mA, or less
than 3.5 mA when tested pursuant to the Metal Exposure after Drop
Damage test disclosed herein.
[0290] Embodiment 68' is the inside spray beverage can coating
composition of embodiment 68, wherein the coating composition is
substantially free of, more preferably essentially free of, each of
bisphenol A, bisphenol F, and bisphenol S, including epoxides
thereof.
[0291] Embodiment 69 is the inside spray beverage can coating
composition of embodiment 68 or 68', wherein the emulsion
polymerized latex comprises the emulsion polymerized latex of any
one of embodiments 3 to 56.
[0292] Embodiment 70 is the inside spray beverage can coating
composition of any of embodiments 68 to 70, wherein the coating
composition includes any of the features recited in embodiments 3
to 56.
[0293] Embodiment 71 is the inside spray beverage can coating
composition of any of embodiments 68 to 70, wherein the emulsion
polymerized latex has a Tg of greater than 40.degree. C., greater
than 50.degree. C., or greater than 60.degree. C.
[0294] Embodiment 72 is the inside spray beverage can coating
composition of any of embodiments 64 to 71, wherein the emulsion
polymerized latex polymer is formed from ingredients including an
ethylenically unsaturated monomer component including at least one
monomer having (i) a Tg of more than 40.degree. C. and (ii) one or
more groups selected from cyclic groups, branched organic groups,
or a combination thereof.
[0295] Embodiment 73 is a coating composition comprising: [0296] an
emulsion polymerized latex polymer that is substantially free of
each of styrene and halogenated monomers and preferably has a glass
transition temperature of greater than 40.degree. C., greater than
50.degree. C., or greater than 60.degree. C.; [0297] wherein the
coating composition is an aqueous coating composition that is
suitable for use in forming a food-contact coating of a metal food
or beverage can and is substantially free of bisphenol A; and
[0298] wherein the coating composition exhibits an elongation at
break of at least 1%, when tested as described herein.
[0299] Embodiment 73' is the coating composition of embodiment 73,
wherein the coating composition is substantially free of, more
preferably essentially free of, each of bisphenol A, bisphenol F,
and bisphenol S, including epoxides thereof
[0300] Embodiment 74 is the coating composition of embodiment 73 or
73' comprising any of the features recited in embodiments 3 to
56.
[0301] Embodiment 75 is a food or beverage can, or a portion
thereof, having an interior food-contact coating formed from the
coating composition of any of embodiments 73 to 74.
[0302] Embodiment 76 is the food or beverage can, or portion
thereof, of embodiment 75 wherein the can comprises an aluminum
beverage can, and wherein the interior food-contact coating is an
inside spray coating.
[0303] Embodiment 77 is the coating composition, method, or can of
any preceding embodiment, wherein the coating composition is
substantially free of styrene, and optionally substantially free of
substituted styrene compounds.
[0304] Embodiment 78 is the coating composition, method, or can of
any preceding embodiment, wherein the coating composition is made
without using any polyolefin polymer.
[0305] Embodiment 79 is the coating composition, method, or can of
any of embodiments 3 to 78, wherein the acid- or
anhydride-functional latex is made without using any non-polymeric
surfactant.
[0306] Embodiment 80 is the coating composition, method, or can of
any preceding embodiment, wherein the coating composition is made
without using a phosphorus acid compound.
[0307] Embodiment 81 is the coating composition, method, or can of
any of embodiments 3 to 80, wherein the acid- or
anhydride-functional latex is made without using a surfactant that
is a polymerizable with at least one ethylenically unsaturated
monomer.
[0308] Embodiment 82 is the coating composition, method, or can of
any preceding embodiment, wherein the coating composition includes
both the NCCR crosslinker (more preferably a beta-hydroxyalkylamide
crosslinker) and a phenoplast crosslinker (more preferably a resole
phenolic crosslinker).
[0309] Embodiment 83 the coating composition, method, or can of any
preceding embodiment, wherein the coating composition includes,
based on total resin solids: [0310] 2 to 10 wt- %, 4 to 8.5 wt- %,
or 5 to 7.5 wt- % of NCCR crosslinker (more preferably a
beta-hydroxyalkylamide crosslinker); and [0311] 1 to 10 wt- %, 3 to
8 wt- %, or 4 to 6 wt- % of phenoplast crosslinker (more preferably
a resole phenolic crosslinker).
[0312] Polymers and coating compositions such as those described in
the Examples may be evaluated using a variety of tests
including:
1. Viscosity Test
[0313] This test measures the viscosity of a latex emulsion or
coating composition for rheological purposes, such as for
sprayability and other coating application properties. The test is
performed pursuant to ASTM D1200-88 using a Ford Viscosity Cup #4
at 25.degree. C. The results are measured in the units of
seconds.
2. Curing Conditions
[0314] For beverage inside spray bakes, the curing conditions
typically involve maintaining the temperature measured at the can
dome at 188.degree. C. to 199.degree. C. for at least 30
seconds.
3. Initial Metal Exposure
[0315] This test method determines the amount of the inside surface
of the can that has not been effectively coated by the sprayed
coating. This determination is made through the use of an
electrically conductive solution (1% NaC1 in deionized water). The
interior "inside spray" coating is typically applied using a high
pressure airless spray. The following film weights are typically
used: 1.6 grams per square meter ("gsm") for a beer can, 2.3 gsm
for a soda can, and 3.4 gsm for a can intended for use in packaging
a "hard-to-hold" product.
[0316] The coated can is filled with this room-temperature
conductive solution, and an electrical probe is attached in contact
to the outside of the can (uncoated, electrically conducting). A
second probe is immersed in the salt solution in the middle of the
inside of the can.
[0317] If any uncoated metal is present on the inside of the can, a
current is passed between these two probes and registers as a value
on an LED display of a suitable measurement apparatus. The LED
displays the conveyed currents in milliamps (mA). The current that
is passed is directly proportional to the amount of metal that has
not been effectively covered with coating. The goal is to achieve
100% coating coverage on the inside of the can, which would result
in an LED reading of 0.0 mA. Preferred coatings give metal exposure
values of less than 3 mA, more preferred values of less than 2 mA,
and even more preferred values of less than 1 mA. Commercially
acceptable metal exposure values are typically less than 2.0 mA on
average.
4. Can Formation
[0318] This is a flexibility test for a coating, and correlates to
how an inside-spray coating will withstand a can formation process
(e.g., necking steps). In this test, the coated can undergoes a can
formation process, including a necking step and bottom dome
reformation. The formed can is then tested in the electrically
conductive solution following the same steps discussed above in the
Initial Metal Exposure test.
5. Metal Exposure After Drop Damage
[0319] Drop damage resistance measures the ability of the coated
container to resist cracks after being in conditions simulating
dropping of a filled can. The ability of a coating to withstand
drop damage without rupturing can also be indicative of the ability
of the coating to withstand post-coating fabrication steps such as
dome reformation and necking. The presence of cracks is measured by
passing electrical current via an electrolyte solution, as
previously described in the Initial Metal Exposure section. A
coated container is filled with the electrolyte solution (1% NaCl
in deionized water) and the initial metal exposure is recorded. The
electrolyte solution is removed and the can is then filled with
room-temperature tap water. For two-piece "inside spray" beverage
cans, the film weights described in the Initial Metal Exposure test
can be used.
[0320] The water-filled can, which does not include a "top" can
end, is dropped through a vertical cylindrical tube having a 2 and
7/8 inch (7.3 centimeter) internal diameter, can bottom down, onto
two opposing impact wedges (each wedge provides an inclined plane
angled upwards at 33 degrees relative to a horizontal plane
orthogonal to the vertical cylindrical tube, with the inclined
planes angled outward relative to one another). The impact wedges
are positioned relative to the cylindrical tube such that two dents
are formed opposite one another in the rim area where the can
bottom end meets the sidewall (typically referred to as the "chime"
of a beverage can). The water-filled can is dropped through the
tube from a 24-inch (61 centimeter) height (as measured between the
can bottom and the point of impact on the impact wedges) onto the
inclined planes.
[0321] Water is then removed from the can and metal exposure is
again measured as described above. If there is no damage, no change
in current (mA) will be observed relative to the Initial Metal
Exposure value. Typically, an average of 6 or 12 container runs is
recorded. The metal exposures results for before and after the drop
are reported as absolute values. The lower the milliamp value, the
better the resistance of the coating to drop damage. Preferred
coatings give metal exposure values after drop damage of less than
3.5 mA, more preferred values of less than 2.5 mA, and even more
preferred values of less than 1.5 mA.
6. Adhesion
[0322] Adhesion testing is performed to assess whether the coating
adheres to the coated substrate. The adhesion test is performed
according to ASTM D 3359 - Test Method B, using SCOTCH 610 tape,
available from 3M Company of Saint Paul, Minn. Adhesion is
generally rated on a scale of 0-10 where a rating of "10" indicates
no adhesion failure (best), a rating of "9" indicates 90% of the
coating remains adhered, a rating of "8" indicates 80% of the
coating remains adhered, and so on. Adhesion ratings of 10 are
typically desired for commercially viable coatings.
7. Blush Resistance
[0323] Blush resistance measures the ability of a coating to resist
attack by various solutions. Typically, blush is measured by the
amount of solution (e.g., water) absorbed into a coated film. When
the film absorbs water, it generally becomes cloudy or looks white.
Blush is generally measured visually using a scale of 0-10 where a
rating of "10" indicates no blush (best) and a rating of "0"
indicates complete whitening of the film (worst). Blush ratings of
7 or higher are typically desired for commercially viable coatings,
and optimally 9-10.
[0324] To assess blush, the coating composition to be assessed is
spray applied using an airless sprayer to a standard aluminum
beverage can.
8. Corrosion Resistance
[0325] These tests measure the ability of a coating to resist
attack by solutions of different levels of aggressiveness. Briefly,
a given coating is subjected to a particular solution, as described
below, and then measured for adhesion and blush resistance (or
whitening), each also described below. For each test, a result is
given using a scale of 0-10, based on the Adhesion Resistance
and/or Blush Resistance, where a rating of "10" is best and a
rating of "0" is worst.
A. Acetic Acid Solution
[0326] A 3% solution of acetic acid (C.sub.2H.sub.4O.sub.2) in
deionized water is prepared and heated to 100.degree. C. Coated
panels are immersed in the heated solution for 30 minutes and then
removed, rinsed, and dried. Samples are then evaluated for adhesion
and blush, as previously described.
B. Citric Acid Solution
[0327] A 2% solution of citric acid (C.sub.6H.sub.8O.sub.7) in
deionized water is prepared and heated while subjected to a
pressure sufficient to achieve a solution temperature of
121.degree. C. Coated panels are immersed in the heated solution
for 30 minutes and then removed, rinsed, and dried. Samples are
then evaluated for adhesion and blush, as previously described.
[0328] 9. Pasteurization
[0329] The Sterilization or pasteurization test determines how a
coating withstands the processing conditions for different types of
food products packaged in a container. Typically, a coated
substrate is immersed in a water bath and heated for 5-60 minutes
at temperatures ranging from 65.degree. C. to 100.degree. C. For
the present evaluation, the coated substrate was immersed in a
deionized water bath for 45 minutes at 85.degree. C. The coated
substrate was then removed from the water bath and tested for
coating adhesion and blush as described above. Commercially viable
coatings preferably provide adequate pasteurization resistance with
perfect adhesion (rating of 10) and blush ratings of 5 or more,
optimally 9-10.
10. Glass Transition Temperature ("Tg")
[0330] Samples for differential scanning calorimetry ("DSC")
testing may be prepared by first applying the liquid resin
composition onto aluminum sheet panels. The panels are then baked
in a Fisher Isotemp electric oven for 20 minutes at 300.degree. F.
(149.degree. C.) to remove volatile materials. After cooling to
room temperature, the samples are scraped from the panels, weighed
into standard sample pans and analyzed using the standard DSC
heat-cool-heat method. The samples are equilibrated at -60.degree.
C., then heated at 20.degree. C. per minute to 200.degree. C.,
cooled to -60.degree. C., and then heated again at 20.degree. C.
per minute to 200.degree. C. Glass transitions are calculated from
the thermogram of the last heat cycle. The glass transition is
measured at the inflection point of the transition.
11. Global Extraction
[0331] The global extraction test is designed to estimate the total
amount of mobile material that can potentially migrate out of a
coating and into food packed in a coated can. Typically coated
substrate is subjected to water or solvent blends under a variety
of conditions to simulate a given end use. Acceptable extraction
conditions and media can be found in 21 CFR .sctn. 175.300
paragraphs (d) and (e). The allowable global extraction limit as
defined by the FDA regulation is 50 parts per million (ppm).
[0332] The extraction procedure used in the current invention is
described in 21 CFR .sctn. 175.300 paragraph (e)(4)(xv) with the
following modifications to ensure worst-case scenario performance:
(1) the alcohol (ethanol) content is increased to 10% by weight,
and (2) the filled containers are held for a 10-day equilibrium
period at 37.8.degree. C. (100.degree. F.). These conditions are
per the FDA publication "Guidelines for Industry" for preparation
of Food Contact Notifications.
[0333] The coated beverage can is filled with 10% by weight aqueous
ethanol and subjected to pasteurization conditions (65.6.degree.
C., 150.degree. F.) for 2 hours, followed by a 10-day equilibrium
period at 37.8.degree. C. (100.degree. F.). Determination of the
amount of extractives is determined as described in 21 CFR .sctn.
175.300 paragraph (e) (5), and ppm values are calculated based on
surface area of the can (no end) of 44 square inches with a volume
of 355 milliliters. Preferred coatings give global extraction
results of less than 50 ppm, more preferred results of less than 10
ppm, even more preferred results of less than 1 ppm. Most
preferably, the global extraction results are optimally
non-detectable.
12. Elongation at Break
[0334] Elongation at break can be an indicator of flexibility for a
cured coating. A cured coating sample suitable for testing can be
prepared using a #12 bar to apply liquid coating to release paper,
which is then baked in an oven so that the temperature of the
coating reaches 380.degree. F. for 45 seconds with a maximum
temperature between 390-400.degree. F. An initial indicator of
sample flexibility can be obtained if one is able to remove the
sample from the free film. Samples that are too brittle to be
tested or removed from the release paper to be tested are noted as
too brittle. A sample is then cut from the free film using an
ASTM-D638 Type V die using a manual die press. The elongation at
break of the cured free-film coating sample can be assessed using a
test procedure similar to ASTM-D638-10 "Standard Test Method for
Tensile Properties of Plastics". A TA Instruments RSA-G2 with
free-film geometry can be used in conjunction with TA Instruments
TRIOS software package to analyze experimental measurements for
measured behaviors. A sample width of 3.18 millimeters ("mm") and
gage length of 7.62 mm can be used. Sample dimensions are entered
into the software and the sample is loaded into the film-fiber
tension clamp of the instrument. The sample is tested at room
temperature and elongated at a Hencky strain rate of 10% per minute
to measure the tensile properties of the cured film and determine
the elongation at break.
13. Necking Test
[0335] This test measures the flexibility and adhesion of the film
following commercial necking process. Necking is done to facilitate
the application of a container end that allows sealing the
container. The test involves applying the coating to the container
at a recommended film thickness and subjecting the container to a
recommended bake (see above can, coating, and bake specifications
for items 2-4). Prior to the necking process, sample cans typically
will have a metal exposure value of <1.0 mA (average of 12 cans)
when evaluated using an electrolyte solution as described above.
After the necking process, the cans should display no increase in
metal exposure compared to the average for 12 non-necked cans.
Elevated mA values indicate a fracture in the film which
constitutes film failure.
EXAMPLES
[0336] The following examples are offered to aid in understanding
of the present invention and are not to be construed as limiting
the scope thereof. It is to be understood that the particular
examples, materials, amounts, and procedures are to be interpreted
broadly in accordance with the scope and spirit of the inventions
as set forth herein. Unless otherwise indicated, all parts and
percentages are by weight.
Example 1: Styrene-Free Acid-Functional Acrylic Emulsifier
[0337] A premix of 336.35 parts glacial methacrylic acid, 723.15
parts ethyl acrylate (EA), 622.25 parts cyclohexyl methacrylate
("CHMA"), 20.22 parts n-butanol, and 36.99 parts Luperox 26
initiator was prepared in a monomer premix vessel. To a reaction
vessel equipped with a stirrer, reflux condenser, thermocouple,
heating and cooling capability, and inert gas blanket, 737.64 parts
n-butanol and 42.89 parts deionized water were added. With
agitation and an inert blanket, the reaction vessel was heated to
97.degree. C. to 102.degree. C. with reflux occurring. Once within
the temperature range, 5.74 parts Luperox 26 initiator was added.
Five minutes after the Luperox 26 initiator addition, the
monomer-initiator premix was added to the reaction vessel over two
and a half hours maintaining the temperature range of 97.degree. C.
to 102.degree. C. with reflux and cooling as needed. After the
premix additions, the monomer-initiator premix vessel was rinsed
with 83.33 parts n-butanol going into the reaction vessel.
Immediately after rinsing, a second initiator premix of 7.33 parts
Luperox 26 initiator and 60.67 parts n-butanol was added to the
reaction vessel over thirty minutes maintaining the temperature
range of 97.degree. C. to 102.degree. C. At the end of the
addition, the premix vessel was rinsed with 15.5 parts n-butanol
and the rinse was added to the reaction vessel. Thirty minutes
after rinsing the initiator premix vessel, 1.43 parts Luperox 26
initiator was added to the reaction vessel and rinsed with 40.44
parts n-butanol. The ingredients where allowed to react an
additional two hours, at which time 202.22 parts n-butanol and 6.74
parts deionized water were added and the reaction vessel was cooled
to less than 60.degree. C. This process gave an acrylic polymeric
emulsifier with solids (i.e. non-volatile or "NV") of .about.58.0%,
with an acid number of .about.125 mg KOH/g resin, a Brookfield
viscosity of .about.25,000 centipoise at 80.degree. F., an Mn of
10,680, a Mw of 37,240, and polydispersity index (PDI) of 3.5. The
Tg using DSC was 55.degree. C.
Example 2: Styrene-Free Latex
[0338] To a reaction vessel equipped with a stirrer, reflux
condenser, thermocouple, heating and cooling capability, and inert
gas blanket, 111.96 parts of deionized water and 483.35 parts of
the acid-functional acrylic polymeric emulsifier of Example 1 were
added to the reaction vessel. Next, 32.79 parts dimethyl ethanol
amine ("DMEOA") was added over 5-10 minutes while the temperature
of the reaction mixture was allowed to increase. The DMEOA addition
vessel was rinsed with 6.32 parts deionized water, and the rinse
was added to the reaction vessel. Next, 850.30 parts deionized
water was added over 30-45 minutes while heating the reaction
vessel to 50.degree. C. In a separate vessel, 287.76 parts CHMA,
94.20 parts butyl acrylate, and 38.56 parts glycidyl methacrylate
were premixed and stirred until uniform. This monomer premix was
then added over 20-25 minutes. When the premix vessel was empty, it
was rinsed with 412.61 parts deionized water and the rinse was
added to the reaction vessel. The reaction vessel was stirred for
15 minutes to make the contents uniform. Next, 0.811 parts Trigonox
TAHP-W85 initiator was added and rinsed with 5.69 parts deionized
water. The reaction mixture was stirred for five minutes after
which a premix of 0.60 parts erythorbic acid, 51.36 parts deionized
water, 0.60 parts DMEOA, and 0.058 parts iron complex was added
over one hour. The reaction vessel was allowed to increase in
temperature to a maximum of 84.degree. C. When the premix addition
was complete, the premix vessel was rinsed with 14.86 parts
deionized water and allowed to react for 60 minutes while the
temperature allowed to drift down to 55.degree. C. After the 60
minute time, 0.09 parts Trigonox TAHP-W85 initiator was added and
rinsed with 0.63 parts deionized water followed by a premix of 0.07
parts erythorbic acid, 5.71 parts deionized water, and 0.07 parts
DMEOA rinsed with 1.38 parts deionized water and allowed to react
for 60 minutes. The reaction mixture was held for one hour at
55.degree. C. before cooling to below 38.degree. C. This process
yielded a latex material containing .about.28% solids, a #4 Ford
viscosity of 21 seconds at 80.degree. F., an acid number of 53 mg
KOH/g resin, a pH of 7.4, and a particle size of 0.12 microns.
Example 3: Styrene-Free Acid-Functional Acrylic Emulsifier
[0339] A premix of 132.24 parts glacial methacrylic acid, 165.3
parts butyl acrylate, 130.5 parts VeoVa 9 vinyl ester monomer
(commercially available from Hexion), 115.7 parts of methyl
methacrylate, 12.76 parts Luperox 26 initiator, 54.62 parts
butanol, and 4.65 parts deionized water was prepared in a monomer
premix vessel. To a reaction vessel equipped with a stirrer, reflux
condenser, thermocouple, heating and cooling capability, and inert
gas blanket, 206.71 parts butanol and 10.10 parts deionized water
were added. With agitation and an inert blanket, the reaction
vessel was heated to 97.degree. C. to 102.degree. C. with reflux
occurring. Once within the temperature range, 2.00 parts Luperox 26
initiator was added. Five minutes after the Luperox 26 initiator
addition, 14.5 parts VeoVa 9, 6.96 parts methacrylic acid, 6.09
parts methyl methacrylate, and 8.70 parts butyl acrylate were
added. After the addition, the monomer-initiator premix was added
to the reaction vessel over two and a half hours maintaining the
temperature range of 97.degree. C. to 102.degree. C. with reflux
and cooling as needed. After the premix additions, the
monomer-initiator premix vessel was rinsed with 13.92 parts butanol
going into the reaction vessel. Immediately after rinsing, a second
initiator premix of 2.53 parts Luperox 26 initiator and 20.92 parts
butanol was added to the reaction vessel over thirty minutes
maintaining the temperature range of 97.degree. C. to 102.degree.
C. At the end of the addition, the premix vessel was rinsed into
the reaction vessel with 5.35 parts butanol. Thirty minutes after
rinsing the initiator premix vessel, 0.49 parts Luperox 26
initiator was added to the reaction vessel and rinsed with 13.95
parts butanol. The ingredients were allowed to react an additional
two hours. After the two hour time, 0.49 parts Luperox 26 initiator
was added and allowed to react for 60 minutes. After the 60 minute
time, 2.32 parts deionized water and 69.73 parts butanol was added
and the reaction vessel cooled to less than 60.degree. C. This
process yielded acrylic polymeric emulsifier with solids of
.about.56.0% NV, an acid number of 163 mg KOH/g resin, a Brookfield
viscosity of 52,000 centipoise at 26.7.degree. C., an Mn of 9,100,
an Mw of 30,070, and PDI of about 3.3. The Tg using DSC was
88.degree. C.
Example 4: Styrene-Free Latex
[0340] To a reaction vessel equipped with a stirrer, reflux
condenser, thermocouple, heating and cooling capability, and inert
gas blanket, 93.30 parts of deionized water and 402.79 parts of the
acid-functional acrylic polymeric emulsifier of Example 3 were
added to the reaction vessel. Next, 27.32 parts DMEOA was added
over 5-10 minutes while the temperature of the reaction mixture was
allowed to increase. The DMEOA addition vessel was rinsed with 5.26
parts deionized water and the rinse was added to the reaction
vessel. Next, 708.58 parts deionized water was added over 30-45
minutes while heating the reaction vessel to 50.degree. C. In a
separate vessel, 239.80 parts of VeoVa 9 vinyl ester monomer, 78.50
parts butyl acrylate, and 32.13 parts glycidyl methacrylate were
premixed and stirred until uniform. This monomer premix was added
to the reaction vessel over 20 minutes. When the premix vessel was
empty it was rinsed with 343.84 parts deionized water and the rinse
was added to the reaction vessel. The reaction vessel was stirred
for 15 minutes to make the contents uniform. Next, 0.680 parts
Trigonox TAHP-W85 initiator was added and rinsed with 2.36 parts
deionized water. The reaction vessel was stirred for five minutes
after which a premix of 0.50 parts erythorbic acid, 42.80 parts
deionized water, 0.50 parts DMEOA, and 0.05 parts iron complex was
added over one hour. The reaction vessel was allowed to increase in
temperature to a maximum of 62.degree. C. When the premix addition
was complete, the premix vessel was rinsed with 12.38 parts
deionized water and allowed to react for 60 minutes while the
temperature allowed to drift down to 55.degree. C. After the 60
minute time, 0.08 parts Trigonox TAHP-W85 initiator was added and
rinsed with 0.53 parts deionized water followed by a premix of 0.06
parts erythorbic acid, 4.76 parts deionized water, and 0.06 parts
DMEOA and allowed to react for 60 minutes. After the 60 minute
time, 0.08 parts Trigonox TAHP-W85 initiator was added and rinsed
with 0.53 parts deionized water followed by a premix of 0.06 parts
erythorbic acid, 4.76 parts deionized water, and 0.06 parts DMEOA
rinsed with 1.38 parts deionized water. The material was held for
one hour at 55.degree. C. before cooling to below 38.degree. C.
This process yielded a latex material with .about.28% solids, a #4
Ford viscosity of 29 seconds at 26.7.degree. C., an acid number of
.about.67 mg KOH/g resin, a pH of 7.3, and a particle size of 0.2
microns.
Comparative Example A: Styrene-Containing Acid-Functional Acrylic
Emulsifier
[0341] A premix of 115.982 parts glacial methacrylic acid, 249.361
parts ethyl acrylate, 214.567parts styrene, 47.649 parts butanol,
and 4.649 parts deionized water was prepared in a monomer premix
vessel. In a separate vessel, an initiator premix of 12.756 parts
Luperox 26 initiator and 6.973 parts butanol was prepared. To a
reaction vessel equipped with a stirrer, reflux condenser,
thermocouple, heating and cooling capability, and inert gas
blanket, 206.71 parts butanol and 10.14 parts deionized water were
added. With agitation and an inert blanket, the reaction vessel was
heated to 97.degree. C. to 102.degree. C. with reflux occurring.
Once within the temperature range, 1.979 parts Luperox 26 initiator
was added. Five minutes after the Luperox 26 initiator addition,
the monomer premix and the initiator premix was added
simultaneously to the reaction vessel over two and a half hours
maintaining the temperature range of 97.degree. C. to 102.degree.
C. with reflux and cooling as needed. After the premix additions,
the monomer premix vessel was rinsed with 10.46 parts butanol and
the initiator premix vessel was rinsed with 3.487 parts butanol,
and both rinses were added to the reaction vessel. Immediately
after rinsing, a second initiator premix of 2.528 parts Luperox 26
initiator and 20.919 parts butanol was added to the reaction vessel
over thirty minutes maintaining the temperature range of 97.degree.
C. to 102.degree. C. At the end of the addition, the premix vessel
was rinsed with 5.346 parts butanol and the rinse was added to the
reaction vessel. Thirty minutes after rinsing the initiator premix
vessel, 0.494 parts Luperox 26 initiator was added to the reaction
vessel and rinsed with 13.946 parts butanol. The ingredients were
allowed to react an additional two hours when 69.73 parts butanol
and 2.324 parts deionized water were added and the reaction vessel
was cooled to less than 60.degree. C. This process yielded an
acrylic polymeric emulsifier with solids of 58.0% NV, an acid
number of .about.130 mg KOH/g resin, a Brookfield viscosity of
about 22,000 centipoise at 26.7.degree. C., an Mn of 12,000, a Mw
of 29,500, and PDI of about 2.5. The Tg using DSC was 68.degree.
C.
Comparative Example B: Styrene-Containing Latex
[0342] To a reaction vessel equipped with a stirrer, reflux
condenser, thermocouple, heating and cooling capability, and inert
gas blanket, 201.394 parts acid-functional acrylic polymeric
emulsifier of Comparative Example A and 46.65 parts deionized water
were added to the reaction vessel. Next, 13.661 parts DMEOA was
added over 5-10 minutes with the temperature of the material
allowed to increase. The DMEOA was rinsed with 2.632 parts
deionized water and the rinse was added to the reaction vessel.
Next, 354.29 parts deionized water was added over 30-45 minutes
while heating the reaction vessel to 50.degree. C. In a separate
vessel, 119.898 parts styrene, 39.248 parts butyl acrylate, and
16.067 parts glycidyl methacrylate were premixed and stirred until
uniform. This monomer premix was then added to the reaction vessel
over 20-25 minutes. When the premix vessel was empty it was rinsed
with 171.92 parts deionized water and the rinse was added to the
reaction vessel. The reaction vessel was stirred for 15 minutes to
make the contents uniform. Next, 0.338 parts Trigonox TAHP-W85
initiator was added and rinsed with 2.369 parts deionized water.
The reaction mixture was stirred for five minutes after which a
premix of 0.248 parts erythorbic acid, 21.398 parts deionized water
0.248 parts DMEOA, and 0.024 parts iron complex were added over one
hour. The reaction vessel was allowed to increase in temperature to
a maximum of 84.degree. C. When the premix addition was complete,
the premix vessel was rinsed with 6.19 parts deionized water and
allowed to react for 60 minutes while the temperature was allowed
to drift down to 55.degree. C. After the 60 minute time, 0.038
parts Trigonox TAHP-W85 initiator was added and rinsed with 0.263
parts deionized water followed by a premix of 0.028 parts
erythorbic acid, 2.378 parts deionized water and 0.028 parts DMEOA
rinsed with 1.69 parts deionized water. The material was held for
60 minutes at 55.degree. C. before cooling to below 38.degree. C.
This process yielded latex materials containing 28.2-30.2% solids,
a #4 Ford viscosity of 15-100 seconds, an acid number of 40-60 mg
KOH/g resin, a pH of 7.2-8.2, and a particle size of about
0.07-0.14 microns.
Example 5: Inside Spray Coating Compositions
[0343] Inside spray coating compositions were prepared using the
ingredients provided below in Table 1, with the ingredients added
under agitation in order as provided below in Table 1. DMEOA was
used as needed to adjust for final viscosity.
TABLE-US-00001 TABLE 1 Composition Ex. 5, Ex. 5, Ex. 5, Ex. 5,
Comparative (Weight Parts) Run 1 Run 2 Run 3 Run 4 Example 5
Example 2 Latex 67.8 65.8 0 0 0 Example 4 Latex 0 0 72.0 69.8 0
Comparative 0 0 0 0 68.1 Example B Latex PRIMID QM1260 0 2.0 0 2.0
0 Crosslinker Deionized Water 18.2 18.1 14.7 14.8 17.6
Water-Miscible 10.7 10.9 10 10 10.5 Organic Solvents Resole
Phenolic 0 0 0 0 0.5 Crosslinker Deionized Water 3.0 3.0 3.0 3.0
3.0 DMEOA As Needed As Needed As Needed As Needed As Needed
Formulation Solids 20% 20% 20% 20% 20% Viscosity #2 Ford 51 52 65
60 50 Cup (seconds)
[0344] The formulations in Table 1 were sprayed at typical
laboratory conditions at 110 mg/can to 130 mg/can (per 12-ounce
can) coating weight into the interior of industry standard 12-ounce
aluminum beverage cans. The inside-spray coated cans were cured at
188.degree. C. to 199.degree. C. (measured at the can dome) for 30
to 60 seconds through a gas oven conveyor at typical heat schedules
for this application. Pertinent application and film coating
properties in a beverage can inside spray end use are shown below
in Table 2.
TABLE-US-00002 TABLE 2 Coating Properties Ex. 5, Ex. 5, Ex. 5, Ex.
5, Comparative Coating Run 1 Run 2 Run 3 Run 4 Example 5 Initial
1.2 mA 1.2 mA 2.7 mA 1.7 mA 0.9 mA Metal Exposure Metal 223.2 mA
208.9 mA 166.5 mA 5.6 mA 1.3 mA Exposure After Drop Damage Blister
Commercially Commercially Commercially Commercially Commercially
Resistance Acceptable Acceptable Acceptable Acceptable Acceptable
Wetting Pass Pass Pass Pass Pass Adhesion Pass Pass Pass Pass Pass
Boiling Pass Pass Pass Pass Pass Water Resistance 2% Citric Pass
Pass Pass Pass Pass Acid Resistance
[0345] As shown in the data of Table 2, the styrene-free inside
spray coatings of Example 5, Runs 1 and 3 formulated without Primid
QM1260 crosslinker exhibited poor flexibility upon drop can
challenge. In contrast, the styrene-free inside spray coating of
Example 5, Run 4 exhibited both a good initial metal exposure after
spray application and a satisfactory metal exposure after drop
damage. In addition, the Example 5, Run 4 coating exhibited good
blister resistance, substrate wetting, substrate adhesion, boiling
water resistance, and 2% citric acid resistance. Thus, the coating
of Example 5, Run 4 exhibited a good balance of coating properties
for an inside spray beverage can end use. It is believed the drop
can damage resistance could be improved by further optimization of
the coating formulation such that it is comparable to that of the
styrene-containing control (Comparative Example 5).
[0346] As for Example 5, Run 2, the metal exposure after drop can
damage was not suitable for an inside spray application. It is
unclear why the inside spray coating of Example 5, Run 2 exhibited
poor flexibility even when using PRIMID QM1260 crosslinker.
Notably, styrene-free latexes having good flexibility, including
sufficient flexibility for interior beverage can coatings, were
successfully developed using CHMA (see, e.g., Table 6 below). Thus,
it is clear that suitable styrene-free latexes may be successfully
synthesized using CHMA.
Example 6: Preparation of a Styrene-Free Latex
[0347] A styrene-free latex emulsion was prepared using the
ingredients provided in the below Table 3.
TABLE-US-00003 TABLE 3 Weight Weight % Reactor A1 Water 1280.00
37.21 Polyethylene glycol sorbitan 1.92 0.0558 monolaurate
(Glycosperse L-20 KFG surfactant) Dioctyl sodium sulfosuccinate
2.40 0.0698 (AEROSOL OT 70 surfactant) Iron sulfate heptahydrate
0.0045 0.0001 Water 45.00 1.31 Part B1 Cyclohexyl methacrylate
(CHMA) 406.55 11.82 Ethyl Acrylate 363.64 10.57 Acrylic Acid 116.36
3.38 Hydroxy Ethyl Methacrylate 105.45 3.07 1,4-Butanediol
dimethacrylate 176.00 5.12 Part B2 Polyethylene glycol sorbitan
9.28 0.27 monolaurate (Glycosperse L-20 KFG surfactant) Dioctyl
sodium sulfosuccinate 12.80 0.37 (AEROSOL OT 70 surfactant) Water
544.00 15.81 Tertioamyl Hydroperoxide 1.60 0.0465 (LUPEROX TAH 85)
Initiator C Isoascorbic acid 0.90 0.0262 DMEAO (dimethyl ethanol
amine) 0.45 0.0131 Water 147.20 4.28 Part D WATER FLUSH 160.00 4.65
Spike redox (E) Tertioamyl Hydroperoxide 0.64 0.0186 (LUPEROX TAH
85) Isoascorbic acid 0.3200 0.0093 DMEAO 0.16 0.0047 Iron sulfate
heptahydrate 0.0032 0.0001 Water 32.00 0.9303 Spike redox (E2)
Tertioamyl Hydroperoxide 0.64 0.0186 (LUPEROX TAH 85) Isoascorbic
acid 0.3200 0.0093 DMEAO 0.16 0.0047 Iron sulfate heptahydrate
0.0032 0.0001 Water 32.00 0.9303 Total 3439.80 100.00
Process
[0348] 1. Monomer Pre-Emulsion Preparation:
[0349] First, a premix was prepared from all the constituents of
part B2. Slow agitation was required at this stage to avoid
formation of foam. Once homogeneous, the monomers (part B1) were
added under vigorous agitation at room temperature and stirred for
20 minutes. The medium turned white and liquid.
[0350] 2. Latex preparation:
[0351] The ingredients of Part A1 were loaded in the 6L reactor
equipped with a reflux condenser, thermometer, mechanical stirred,
two metering pumps and nitrogen sparge and the reactor was heated
up to 80.degree. C., under moderate agitation.
[0352] The stable monomer pre-emulsion (resulting from Parts B1 and
B2) and the initiator solution (premix part C) were then added in
the reactor with two separate lines at a constant rate over 180
minutes at 80.degree. C. and under agitation (120 -150 revolutions
per minute). Once the monomer addition was completed, Part D1 was
added and the mixture held for one hour at 80.degree. C. to reach
complete conversion.
[0353] The redox package (Part E) was then added in the reactor to
reduce as much as possible the level of free monomers in the resin
and then the mixture was held for an additional hour. At this
stage, a post-neutralization of the final latex can be envisaged to
improve the stability and/or increase the viscosity of the
latex.
[0354] The reactor was then slowly cooled down to 40.degree. C. and
filtered to collect the resulting latex emulsion. The final latex
had a non-volatile content ("NVC") of 34 to-35% (1 g/30 min/
180.degree. C.). The resulting latex emulsion is referred to as
Example 6, Run 1. Additional latexes were prepared in a similar
manner using methyl methacrylate in place of CHMA (Example 6, Run
2).
Example 7: Preparation of Styrene-Free Latexes
[0355] Additional latex emulsions were prepared using the process
and ingredients of Example 6, with the composition of the monomer
premix part B1 employed for each of Runs 1-4 noted below in Table
4. Otherwise the process and materials used were the same as in
Example 6. The measured Tg value for each latex is also provided in
Table 4. All of the ingredient amounts indicated in the below Table
4 are weight parts.
TABLE-US-00004 TABLE 4 Example 7 Latexes Run 1 Run 2 Run 3 Run 4
Monomers premix part B1 VeoVa 9 MMA (methyl methacrylate) 30 CHMA
34.83 41.7 VeoVa 9 34.83 Ethyl acrylate (EA) 31.13 34.7 22 31.13
Acrylic acid (AA) 9.96 15 11.11 9.96 Hydroxy ethyl methacrylate
9.02 10.3 10.19 9.02 (HEMA) 1,4-Butanediol dimethacrylate 15.06 10
15 15.06 (BDDMA) Tg range (DSC) .degree. C. 60-65 60-65 85-90
55-60
Example 8: Preparation of Styrene-Free, Acid-Functional Acrylic
[0356] This preparation was used in some of the coating
compositions as an additive to improve substrate wetting
performance.
[0357] A premix of 647.22 parts glacial acrylic acid (GAA), 359.5
parts ethyl acrylate (EA), 431.28 parts methyl methacrylate (MMA),
436.26 parts Butyl CELLOSOLVE, and 48.29 parts deionized water was
prepared in a monomer premix vessel. In a separate vessel, an
initiator premix of 86.34 parts LUPEROXTM 26 initiator from Arkema
and 240 parts butyl CELLOSOLVE was prepared. To a reaction vessel
equipped with a stirrer, reflux condenser, thermocouple, heating
and cooling capability, and inert gas blanket, 512.75 parts butyl
CELLOSOLVE and 25.15 parts deionized water were added. With
agitation and an inert blanket, the reaction vessel was heated to
97 to 102.degree. C. with reflux occurring. Once within the
temperature range, 13.40 parts LUPEROX 26 initiator was added. Five
minutes after the initiator addition, the monomer premix and the
initiator premix were added simultaneously to the reaction vessel
over three hours while maintaining the temperature range at 97 to
102.degree. C. with reflux and cooling as needed. The ingredients
were allowed to react an additional two hours. If the monomer
conversion is not achieved at this stage, an additional initiator
premix can be added to the vessel over one hour maintaining the
temperature range of 97.degree. C. to 102.degree. C. Sixty minutes
after the addition of the second initiator premix, the reaction
vessel was cooled to less than 60.degree. C. under agitation. This
process yielded an acrylic emulsifying polymer (viz., an acrylic
polymeric emulsifier) with solids of .about.55.0% NVC, an acid
number of .about.300 mg KOH/g resin.
Example 9: Preparation of Styrene-Free, Acid-Functional Acrylic
[0358] This preparation was used in some of the coating
compositions as an additive to improve substrate wetting
performance.
[0359] A premix of 647.22 parts glacial acrylic acid (GAA), 359.5
parts ethyl acrylate (EA), 431.28 parts cyclohexyl methacrylate
(CHMA), 436.26 parts Butyl CELLOSOLVE, and 48.29 parts deionized
water was prepared in a monomer premix vessel. In a separate
vessel, an initiator premix of 86.34parts LUPEROX.TM. 26 initiator
from Arkema and 240 parts butyl CELLOSOLVE was prepared. To a
reaction vessel equipped with a stirrer, reflux condenser,
thermocouple, heating and cooling capability, and inert gas
blanket, 512.75 parts butyl CELLOSOLVE and 25.15 parts deionized
water were added. With agitation and an inert blanket, the reaction
vessel was heated to 97 to 102.degree. C. with reflux occurring.
Once within the temperature range, 13.40 parts LUPEROX 26 initiator
was added. Five minutes after the initiator addition, the monomer
premix and the initiator premix were added simultaneously to the
reaction vessel over three hours while maintaining the temperature
range at 97 to 102.degree. C. with reflux and cooling as needed.
The ingredients were allowed to react an additional two hours. If
the monomer conversion is not achieved at this stage, an additional
initiator premix can be added to the vessel over one hour
maintaining the temperature range of 97.degree. C. to 102.degree.
C. Sixty minutes after the addition of the second initiator premix,
the reaction vessel was cooled to less than 60.degree. C. under
agitation.
[0360] This process yielded an acrylic emulsifying polymer (viz.,
an acrylic polymeric emulsifier) with solids of .about.55.0% NVC,
an acid number of .about.300 mg KOH/g resin.
Examples 10-18: Inside Spray Coating Compositions
[0361] The coating compositions of Examples 10-18 were prepared
from the latex emulsions of Example 7, Runs 1-4 using the
ingredients and amounts indicated in the below Table 5. The acrylic
polymeric emulsifiers of Examples 8 and 9 were added in additive
levels to improve application of the coating to substrate. Coating
compositions were spray applied to the inside of aluminum beverage
containers, cured, and evaluated. The coating composition
ingredients were added in the order shown in Table 5 with
agitation. Ingredients 2 and 3 were premixed before addition.
Ingredient 7 was added as needed to obtain a desired final
viscosity. All of the ingredient amounts indicated in the below
Table 5 are weight parts.
TABLE-US-00005 TABLE 5 Inside Spray Coating Compositions Spray
Coating Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex.
18 Notable "High" Tg CHMA CHMA CHMA MMA MMA CHMA CHMA VeoVa 9 VeoVa
9 Monomer Latex Tg (.degree. C.) range, DSC 60-65 60-65 60-65 60-65
60-65 80-90 80-90 55-60 55-60 Crosslinker None Primid Phenolic None
Primid None Primid None Primid Ingredient 1 Ex. 7, Run 1500.0
1500.0 1500.0 1 Latex Ex. 7, Run 2 1500.0 1500.0 Latex Ex. 7, Run
1500.0 1500.0 3 Latex Ex. 7, Run 1540.0 1540.0 4 Latex Ingredient 2
Deionized 900.0 900.0 940 1140.0 1140.0 930.0 930.0 1065.0 1065.0
water Ingredient 3 DMEOA 10.0 10.0 7.0 6.0 6.0 10.3 10.3 4.6 4.6
Ingredient 4 Water- 349 349 149 3500 350 349 349 356.4 356.4
Miscible Organic Solvents Ingredient 5 Resole 66.0 Phenolic
Crosslinker Primid QM 92.0 92.0 91.0 92 1260 Crosslinker (EMS)
Ingredient 6 Example 8 41.0 41.0 33.0 33.0 33.0 33.0 Acrylic
Emulsifier Example 9 33.0 33.0 33.0 Acrylic Emulsifier Ingredient 7
DMEOA As As As As As As As As As Viscosity in needed needed needed
needed needed needed needed needed needed seconds 40 40 37 48 48 40
40 38 38 using ASTM #2 cup at ambient temperature
[0362] The coating compositions of Table 5 were sprayed into the
interior of 33 cl (330 milliliter) aluminum beverage cans using
typical laboratory conditions and a 100 to 140 mg/can dry coating
weight (120 mg/can dry coating weight target), and cured at 180 to
200.degree. C. (as measured at the can dome) for 30 to 60 seconds
through a gas oven conveyor from Greenbank Technology Ltd. at
typical heat schedules for this application. The application and
film properties are shown in Table 6 below.
TABLE-US-00006 TABLE 6 Inside Spray Coating Properties Comp. Ex. 10
Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18 Ex. C
Notable CHMA CHMA CHMA MMA MMA CHMA CHMA VeoVa 9 VeoVa 9 CHMA
"High" Tg high Tg high Tg Monomer Latex Tg .degree. C. 60-65 60-65
60-65 60-65 60-65 80-90 80-90 55-60 55-60 80-90 range, DSC
Crosslinker None Primid Phenolic None Primid None Primid None
Primid None Initial Metal <1 mA <1 mA <1 mA <1 mA <1
mA <1 mA <1 mA <1 mA <1 mA 1.3 mA Exposure Metal
>200 mA 0.5 mA 39.6 mA >200 mA 0.3 mA >200 mA 20.5 mA
>200 mA 2.6 mA >200 mA Exposure after Drop Damage (from
initial) Necking Fail Pass Fail No Data No data Fail Fail No Data
No data No data Dome Fail Pass Fail No Data No Data Fail Fail No
Data No Data No data Reforming Water Pass Pass Pass Fail Pass Pass
Pass Pass Pass Pass Pasteurization 3% Boiling Pass Pass Pass Fail
Pass Pass Pass Fail Pass Fail Acetic acid
[0363] The data in Table 6 illustrates that the use of Primid QM
1260 crosslinker allows for production of a styrene-free latex
coating composition yielding sufficient flexibility for use as an
interior coating of an aluminum beverage can. As illustrated by
Example 12, while the use of resole phenolic crosslinker helped to
improve drop can damage resistance relative to Example 10 which
lacked crosslinker, the use of resole phenolic crosslinker was not
capable of yielding a styrene-free latex coating composition having
acceptable flexibility for an inside spray aluminum beverage can
coating.
[0364] Table 6 also includes Comparative Example C, which is a
reproduction of Example 6 of U.S. Publication No. 2016/0009941
formulated for beverage can inside spray application using the same
solvent package as the other Examples. Although Comparative Example
6 demonstrated a satisfactory initial metal exposure value after
spray application, the coating was inflexible and did not exhibit
any meaningful drop can damage resistance. As such, the coating is
unsuitable for use as a beverage can coating.
[0365] A coating composition similar to that of Example 14 was
tested for elongation at break pursuant to the Elongation at Break
test method. (The latex in the sample tested was prepared using all
of the same monomers as the Example 7, Run 2 latex employed in the
coating formulation of Example 14, with the main difference being
that it included 15 wt- % of BDDMA, as opposed to 10 wt- % BDDMA,
and had a lower acid number.) When the sample was tested in tensile
elongation it exhibited a linear region of deformation before
yielding and then further stretched before breaking, as defined in
ASTM-D638-10. The latex by itself (i.e., without formulation) could
not be tested in tensile elongation without further formulation.
For example, when a formulation similar to Example 14 was tested
without any Primid QM1260 crosslinker, it was too brittle to be
tested and could not be removed from the release paper. This
representation of the sample, without the Primid QM1260
crosslinker, was deemed to be highly inflexible with a low
elongation to break. It is believed that the addition of the Primid
crosslinker to the sample gives the coating mechanical strength and
flexibility in reacting with the latex to form a strong film that
can be removed from the release paper in addition to be tested in
tensile elongation. The tensile elongation at break of the
aforementioned fully formulated coating composition similar to
Example 14 exhibited an elongated at break ranging from between 5
and 10%, which met or exceeded the tensile elongation at break of a
commercial styrene-containing latex coating standard.
[0366] The complete disclosure of all patents, patent applications,
and publications (including material safety data sheets, technical
data sheets and product brochures for the raw materials and
ingredients used in the Examples), and electronically available
material cited herein are incorporated herein by reference as if
individually incorporated. The foregoing detailed description and
examples have been given for clarity of understanding only. No
unnecessary limitations are to be understood therefrom. The
invention is not limited to the exact details shown and described,
for variations obvious to one skilled in the art will be included
within the invention defined by the claims. The invention
illustratively disclosed herein suitably may be practiced, in some
embodiments, in the absence of any element which is not
specifically disclosed herein.
* * * * *