U.S. patent application number 10/614731 was filed with the patent office on 2004-04-15 for dip, spray, and flow coating process for forming coated articles.
Invention is credited to Hutchinson, Gerald A., Lee, Robert A..
Application Number | 20040071885 10/614731 |
Document ID | / |
Family ID | 30119132 |
Filed Date | 2004-04-15 |
United States Patent
Application |
20040071885 |
Kind Code |
A1 |
Hutchinson, Gerald A. ; et
al. |
April 15, 2004 |
Dip, spray, and flow coating process for forming coated
articles
Abstract
This invention relates to methods and apparatus for making
coated articles with one or more layers by dip, spray or flow
coating. In one aspect, this invention relates to an apparatus and
method for making coated containers, preferably comprising
polyethylene terephthalate, from coated preforms. In preferred
embodiments, the apparatus and method permit the coated container
or preform to be made in an energy-efficient manner that reduces
the danger of coating damage and thus increases the efficacy of the
final container.
Inventors: |
Hutchinson, Gerald A.; (Coto
de Caza, CA) ; Lee, Robert A.; (Bowdon Cheshire,
GB) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
30119132 |
Appl. No.: |
10/614731 |
Filed: |
July 3, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60394092 |
Jul 3, 2002 |
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60422251 |
Oct 28, 2002 |
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60441718 |
Jan 21, 2003 |
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Current U.S.
Class: |
427/385.5 ;
118/400; 118/416; 118/426; 118/501; 118/58; 427/407.1;
428/35.7 |
Current CPC
Class: |
B05D 7/546 20130101;
B29C 2049/026 20130101; C08J 7/048 20200101; Y10T 428/1352
20150115; C08J 7/043 20200101; B05D 7/544 20130101; Y10S 118/04
20130101; C08J 7/046 20200101; B05D 1/18 20130101; C08J 2433/04
20130101 |
Class at
Publication: |
427/385.5 ;
428/035.7; 427/407.1; 118/400; 118/416; 118/426; 118/501;
118/058 |
International
Class: |
B65D 001/00; B05D
001/36; B32B 001/08; B05C 021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 3, 2003 |
WO |
PCT/US03/22333 |
Claims
What is claimed is:
1. A process for making thermoplastic resin coated articles, the
process comprising: applying an aqueous solution or dispersion of a
first thermoplastic resin on the outer surface of an article
substrate by dip, spray, or flow coating; withdrawing the article
from the dip, spray, or flow coating at a rate so as to form a
first coherent film; curing/drying the coated article until the
first film is substantially dried so as to form a first coating;
optionally applying an aqueous solution or dispersion of a second
thermoplastic resin on the outer surface of an article substrate by
dip, spray, or flow coating; withdrawing the article from the dip,
spray, or flow coating at a rate so as to form a second coherent
film; curing/drying the coated article until the second film is
substantially dried so as to form a second coating; wherein at
least one of the first and second thermoplastic resins comprises a
thermoplastic epoxy resin.
2. The process of claim 1 wherein the curing/drying of the coating
comprising a thermoplastic epoxy resin is performed so as to form
an article that exhibits substantially no blushing or whitening
when exposed to water.
3. The process of claim 1 further comprising the application of one
or more additional coating layers to said article.
4. The process of claim 1 wherein at least one coating layer is
crosslinked to provide chemical or mechanical abuse resistance.
5. The process of claim 1, wherein the article substrate comprises
a polymer selected from the group consisting of polyesters,
polyolefins, polycarbonates, polyamides and acrylics.
6. The process of claim 5, wherein the article substrate comprises
amorphous and/or semi crystalline polyethylene terephthalate.
7. The process of claim 5, wherein said article comprises a
preform.
8. The process of claim 1 which further comprises the removal of
any excess material between the coating and curing/drying
steps.
9. The process of claim 1 wherein said curing/drying source is
selected from one or more of the group consisting of infrared
heating, electron beam processing, forced air, flame curing, gas
heaters, UV radiation, such that the coating is formed without
undesirably heating the article substrate.
10. The process of claim 9 wherein said curing/drying source is
infrared heating and forced air.
11. The process of claim 10 wherein the temperature of the forced
air is between about 10.degree. C. to about 50.degree. C. and
sufficient to prevent undesirable shrinkage of article while
maximizing the removal of liquids without prematurely sealing the
article's outer surface so as to entrap unexpelled liquid.
12. The process of claim 9 wherein said curing/drying source is
infrared heating.
13. The process of claim 1 wherein said article is rotated to
achieve consistent coating and curing/drying.
14. The process of claim 1 wherein said thermoplastic resin
coatings comprise one or more of the following characteristics:
gas-barrier protection, UV protection, scuff resistance, blush
resistance, and/or chemical resistance.
15. The process of claim 1 wherein said thermoplastic epoxy resin
coating comprises phenoxy resins.
16. The process of claim 15 wherein said phenoxy resin coating
comprises hydroxy-phenoxyether polymers.
17. The process of claim 16 wherein said hydroxy-phenoxyether
polymer coating comprises polyhydroxyaminoether copolymers made
from resorcinol diglycidyl ether, hydroquinone diglycidyl ether,
bisphenol A diglycidyl ether, or mixtures thereof.
18. The process of claim 15 wherein said solution or dispersion of
the thermoplastic epoxy resin comprises organic acid salts made
from the reaction of polyhydroxyaminoethers with phosphoric acid,
lactic acid, malic acid, citric acid, acetic acid, glycolic acid
and/or mixtures thereof.
19. The process of claim 3 wherein said third coating is an
acrylic, phenoxy, latex, or epoxy coating that is crosslinked
during the drying process.
20. An apparatus for making coated articles comprising: a conveyor
that transports said articles through a flow coating system; and a
flow coating system comprising: a first flow coating unit which
comprises: a tank or vat containing an aqueous solution/dispersion
coating material wherein said tank or vat is in fluid communication
with a fluid guide; a fluid guide wherein said coating material
flows off of said fluid guide forming a sheet or falling shower
curtain; a coating material collector which receives unused coating
material; a first curing/drying unit which comprises: an oven or
chamber in which a curing/drying source is located; wherein said
articles are moved through the oven or chamber by the article
conveyor; a second flow coating unit which comprises: a tank or vat
containing an aqueous solution/dispersion coating material wherein
said tank or vat is in fluid communication with a fluid guide; a
fluid guide wherein said coating material flows off of said fluid
guide forming a sheet or falling shower curtain; a coating material
collector which receives unused coating material; and a second
curing/drying unit which comprises: an oven or chamber in which a
curing/drying source is located; wherein said articles are moved
through the oven or chamber by the article conveyor; wherein at
least one of the aqueous solution/dispersion coating materials
comprises a thermoplastic epoxy resin.
21. The apparatus of claim 20 wherein a third flow coating unit and
a third curing/drying unit are included.
22. The apparatus of claim 20 wherein a single integrated
processing line comprises two or more flow coating units and two or
more curing/drying units wherein the article conveyor transports
the articles through the processing line.
23. The apparatus of claim 20 comprising one or more coating
modules and an article conveyor; wherein each coating module
comprises: a self-contained processing line comprising one or more
flow coating units and one or more curing/drying units; and wherein
the article conveyor can transport the articles into, within, and
between coating modules and eject the article from the system.
24. The apparatus of claim 20 wherein said article conveyor rotates
said articles while transporting them through the system.
25. The apparatus of claim 20 wherein said fluid guide is
angled.
26. The apparatus of claim 20 wherein said coating material
collector is in fluid communication with said tank or vat thereby
recycling and reusing any excess material.
27. The apparatus of claim 20 wherein the tank or vat of the first
and second flow coating units is a single, common tank or vat.
28. The apparatus of claim 20 wherein the oven or chamber of the
first and second curing/drying units is a single, common oven or
chamber.
29. The apparatus of claim 20 further comprising a drip remover
positioned between said coating material collector and said
curing/drying unit.
30. The apparatus of claim 29 wherein said drip remover comprises
one or more of the following: rotation, gravity, wiper, brush,
sponge roller, air knife or air flow.
31. The apparatus of claim 20 wherein the curing/drying source
comprises one or more sources selected from infrared heating lamp,
electron beam processing source, forced air, flame, gas heater, or
UV radiation source.
32. The apparatus of claim 31 wherein said curing/drying source
comprises infrared heating and forced air.
33. The apparatus of claim 32 wherein the temperature of the forced
air is between 10 C to about 50 C.
34. The apparatus of claim 32 wherein the temperature of the forced
air is sufficient to prevent undesirable shrinkage of the article
while maximizing the removal of liquids without prematurely sealing
the surface and entrapping unexpelled liquid.
35. The apparatus of claim 20 wherein said article is a
preform.
36. The apparatus of claim 35, wherein the preform comprises a
material selected from the group consisting of polyesters,
polyolefins, polycarbonates, polyamides and acrylics.
37. The apparatus of claim 35, wherein the preform comprises
amorphous or semi crystalline polyethylene terephthalate.
38. A multilayer article comprising: a substrate having at least
one layer comprising thermoplastic epoxy resin coating material
disposed on at least a portion of said substrate to form a coated
article, wherein the coated article exhibits substantially no
blushing or whitening when exposed to water.
39. The article of claim 38, wherein the article comprises a
thermoplastic material selected from the group consisting of
polyester, polypropylene, polyethylene, polycarbonate, polyamides
and acrylics.
40. The article of claim 38 wherein the substrate comprises
polyethylene terephthalate.
41. The article of claim 38, further comprising one or more layers
of thermoplastic resin coating material disposed on said
substrate.
42. The article of claim 38, wherein the article is a preform or
bottle having a body portion and a neck portion, and said coating
is disposed substantially only on the body portion of the preform
or bottle.
43. The article of claim 38, wherein the coated article has
substantially no distinction between coating layers.
44. The article of claim 38, wherein the coating layers are applied
by dip, spray, or flow coating.
45. The article of claim 38, wherein the exposure to water occurs
for about 24 hours and with the water at a temperature of about
0.degree. C. to about 25.degree. C.
46. A multilayer container preform or bottle having a body portion,
end cap, and neck portion, said preform or bottle comprising: a
first substrate comprising a thermoplastic material said
thermoplastic material chosen from the chosen from the group
consisting of polyesters, polyolefins, polycarbonates, polyamides
and acrylics; one or more layers of thermoplastic resin coating
material disposed on said substrate; wherein one or more layers
contain one or more of the following characteristics: gas-barrier
protection, UV protection, scuff resistance, blush resistance,
chemical resistance; wherein the coating is disposed substantially
only on the body portion of the preform; and wherein the finished
product has substantially no distinction between layers.
47. A preform or bottle of claim 46 wherein the coating layers
comprise: an O.sub.2 scavenger inner coating layer; a CO.sub.2
scavenger intermediate layer; an UV protection intermediate layer;
and an outer layer of partially or highly cross-linked
material.
48. A preform or bottle of claim 46 wherein the coating layers
comprise: an inner coating layer of UV protection material; and an
outer layer of partially or highly cross-linked material.
49. The preform or bottle of claim 46 wherein the preform or bottle
substrate comprises amorphous or semi crystalline polyethylene
terephthalate.
50. The preform or bottle of claim 46 wherein the coating layers
are applied by dip, spray, or flow coating.
51. The preform of claim 46 wherein successive layers of coating
material decrease in amount of coating material required to
thoroughly coat the preform.
Description
RELATED APPLICATION DATA
[0001] This application claims priority under 35 U.S.C. 119(e) from
provisional applications Serial No. 60/394,092 filed Jul. 3, 2002,
Ser. No. 60/422,251 filed Oct. 28, 2002, and Ser. No. 60/441,718
filed Jan. 23, 2003, and is a continuation of PCT/US03/______,
entitled DIP, SPRAY, AND FLOW COATING PROCESS FOR FORMING COATED
ARTICLES filed Jul. 3, 2003, the disclosures of which are
incorporated in their entirety herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to methods and apparatus for making
coated articles with one or more layers by dip, spray or flow
coating. In one aspect, this invention relates to an apparatus and
method for making coated containers, preferably comprising
polyethylene terephthalate, from coated preforms.
[0004] 2. Description of the Related Art
[0005] Preforms are the products from which containers are made by
blow molding. Unless otherwise indicated the term "container" is a
broad term and is used in its ordinary sense and includes, without
limitation, both the preform and bottle container therefrom. A
number of plastic and other materials have been used for containers
and many are quite suitable. Some products such as carbonated
beverages and foodstuffs need a container, which is resistant to
the transfer of gases such as carbon dioxide and oxygen. Coating of
such containers has been suggested for many years. A resin now
widely used in the container industry is polyethylene terephthalate
(PET), by which term we include not only the homopolymer formed by
the polycondensation of [beta]-hydroxyethyl terephthalate but also
copolyesters containing minor amounts of units derived from other
glycols or diacids, for example isophthalate copolymers.
[0006] The manufacture of biaxially oriented PET containers is well
known in the art. Biaxially oriented PET containers are strong and
have good resistance to creep. Containers of relatively thin wall
and light weight can be produced that are capable of withstanding,
without undue distortion over the desired shelf life, the pressures
exerted by carbonated liquids, particularly beverages such as soft
drinks, including colas, and beer.
[0007] Thin-walled PET containers are permeable to some extent to
gases such as carbon dioxide and oxygen and hence permit loss of
pressurizing carbon dioxide and ingress of oxygen which may affect
the flavor and quality of the bottle contents. In one method of
commercial operation, preforms are made by injection molding and
then blown into bottles. In the commercial two-liter size, a shelf
life of 12 to 16 weeks can be expected but for smaller bottles,
such as half liter, the larger surface-to-volume ratio severely
restricts shelf life. Carbonated beverages can be pressured to 4.5
volumes of gas but if this pressure falls below acceptable product
specific levels, the product is considered unsatisfactory.
[0008] It is therefore desirable to provide the container with a
layer of a barrier material which has a low vapor and gas
permeability. Barrier layers may be provided by a variety of
techniques, including coinjection, chemical vapor deposition,
plasma coating with amorphous carbon and/or SiOx, etc., so as to
form a laminar coated container. Other examples involve the use of
an aqueous dispersion of barrier polymers, and have included
dispersions made from vinylidene chloride with acrylonitrile and/or
methyl acrylate, optionally containing units derived from other
monomers such as methyl methacrylate, vinyl chloride, acrylic acid,
or itaconic acid, dispersions made from EVOH and MXD6, etc. The
dispersions typically contained surfactants such as sodium alkyl
sulphonates.
SUMMARY OF THE INVENTION
[0009] In one aspect, this invention relates to methods and
apparatus for making articles, preferably plastic articles, having
coatings comprising one or more layers. These layers may comprise
thermoplastic materials with good gas-barrier characteristics as
well as layers that provide UV protection, scuff resistance, blush
resistance, chemical resistance, and/or active properties such as
O.sub.2 or CO.sub.2 scavenging.
[0010] In a preferred embodiment, there is provided a process for
the production of a coated article. The process comprises providing
an article, preferably a container or preform comprising
polyethylene terephthalate; applying to said article a coating of
an aqueous dispersion of a thermoplastic epoxy resin to the
article; and curing/drying the coating. In embodiments where the
article is a preform, the method preferably further comprises a
blow molding operation, preferably including stretching the dried
coated preform axially and radially, in a blow molding process, at
a temperature suitable for orientation, into a bottle-container. In
the process the thermoplastic epoxy coating is applied by dip,
spray, or flow coating of the article and the coating and drying is
applied in more than one pass such that the coating properties are
increased with each coating layer. The volume of coating deposition
may be altered by the article temperature, the article angle, the
solution/dispersion temperature, the solution/dispersion viscosity
and the number of layers. The multiple coatings of preferred
processes result in multiple layers with substantially no
distinction between layers, improved coating performance and/or
reduction of surface voids and coating holidays. In addition, a
preferred multiple coating process results in successive layers
requiring decreasing amounts of coating material to thoroughly coat
the article.
[0011] In preferred embodiments, the coating and drying process
results in enhanced surface tension properties. Furthermore, in
preferred processes, the drying process of articles has a repairing
effect on surface defects of the finished article. In addition, in
preferred processes, the drying/curing process produces articles
which exhibit substantially no blushing.
[0012] In accordance with one embodiment, there is provided a
process for making thermoplastic resin coated articles, the process
comprising: applying an aqueous solution or dispersion of a first
thermoplastic resin on the outer surface of an article substrate by
dip, spray, or flow coating; withdrawing the article from the dip,
spray, or flow coating at a rate so as to form a first coherent
film; curing/drying the coated article until the first film is
substantially dried so as to form a first coating. Optionally, the
method may further include applying an aqueous solution or
dispersion of a second thermoplastic resin on the outer surface of
an article substrate by dip, spray, or flow coating; withdrawing
the article from the dip, spray, or flow coating at a rate so as to
form a second coherent film; curing/drying the coated article until
the second film is substantially dried so as to form a second
coating. In preferred embodiments, at least one of the first and
second thermoplastic resins comprises a thermoplastic epoxy resin,
and the first and second resins may be the same or different.
[0013] In accordance with a preferred embodiment, a method for dip
coating articles is provided comprising the steps of: a) dipping
the article into an aqueous coating solution/dispersion contained
either in a static vat or in a flow coater with the article
rotating to achieve full exposure to the flow; b) withdrawing the
article from the static vat or flow coater below the rate at which
a coherent film is observed; and c) exposing the article and film
to infrared heaters until the film is substantially dried,
optionally while cooling the article with air.
[0014] In accordance with a preferred embodiment, an apparatus for
dip coating articles is provided comprising: an article conveyor
that transports the articles through a dip coating system; a tank
or vat containing an aqueous solution/dispersion coating material
wherein the conveyor draws or dips the articles through the tank or
vat; and a curing/drying unit which comprises an oven or chamber in
which a curing/drying source is located, wherein the articles are
moved through the oven or chamber by the conveyor. The
curing/drying unit is optionally coupled with a fan or blower for
cooling the article with air. A preferred apparatus may further
comprise a second tank or vat of coating material and a second
curing/drying unit. In another preferred apparatus, the conveyor
transports the articles back through the tank and/or the
curing/drying unit to provide a second coating on the article. A
preferred apparatus may optionally include one or more drip
removers positioned between the coating tank or vat and the
curing/drying unit, or elsewhere before the curing/drying unit.
[0015] In accordance with another preferred embodiment, a method
for coating articles is provided comprising the steps of: a) spray
coating the article with an aqueous coating solution/dispersion
with the article rotating to achieve full exposure to the flow, b)
spraying the article at a rate which a coherent film is observed;
and c) exposing the article and film to infrared heaters until the
film is substantially dried; optionally while cooling the article
with air.
[0016] In accordance with a preferred embodiment, an apparatus for
spray coating articles is provided comprising: an article conveyor
that transports the articles through a spray coating system; one or
more spray nozzles is in fluid communication with an aqueous
solution/dispersion of coating material, such as may be contained
in a tank or vat; a coating material collector which receives
unused coating material; and a curing/drying unit which comprises
an oven or chamber in which a curing/drying source is located,
wherein the articles are moved through the oven or chamber by the
conveyor. The curing/drying unit is optionally coupled with a fan
or blower for cooling the article with air. A preferred apparatus
may further comprise a second tank or vat of coating material, a
second grouping of one or more spray nozzles, and/or a second
curing/drying unit, or, in providing a second coating, one or more
components of the first spray coating system may be used. A
preferred apparatus may optionally include one or more drip
removers positioned between the sprayer and the curing/drying unit,
or elsewhere before the curing/drying unit.
[0017] In accordance with another preferred embodiment, a method
for flow coating articles is provided comprising the steps of: a)
flow coating the article with an aqueous coating
solution/dispersion with the article rotating to achieve full
exposure to the flow, b) withdrawing the article from sheet of the
flow coating at a rate which a coherent film is observed; c)
exposing the article and film to infrared heaters until the film is
substantially dried; and optionally d) cooling the article with
air.
[0018] In accordance with a preferred embodiment, an apparatus for
flow coating articles is provided comprising: an article conveyor
that transports the articles through a flow coating system; a tank
or vat containing an aqueous solution/dispersion of coating
material that is in fluid communication with a fluid guide, wherein
the coating material flows off of the fluid guide forming a sheet
or falling shower curtain; a coating material collector which
receives unused coating material; and a curing/drying unit which
comprises an oven or chamber in which a curing/drying source is
located, wherein the articles are moved through the oven or chamber
by the conveyor. The curing/drying unit is optionally coupled with
a fan or blower for cooling the article with air. A preferred
apparatus may further comprise a second tank or vat of coating
material, a second fluid guide, and/or a second curing/drying unit,
or, in providing a second coating, one or more components of the
first flow coating system may be used. A preferred apparatus may
optionally include one or more drip removers positioned between the
coating tank or vat and the curing/drying unit, or elsewhere before
the curing/drying unit.
[0019] In one embodiment, a preferred apparatus includes means for
entry of the article into the system; dip, spray, or flow coating
of the article; optionally removal of excess material; drying or
curing; optionally, cooling, during and/or after drying/curing, and
ejection from the system. In one embodiment the apparatus is a
single integrated processing line that contains multiple stations
wherein each station coats the article thereby producing a article
with multiple coatings. In another embodiment, the system is
modular wherein each processing line is self-contained with the
ability to handoff to another line, thereby allowing for single or
multiple coatings depending on how many modules are connected
thereby allowing maximum processing flexibility.
[0020] In accordance with one embodiment, there is provided a
multilayer article comprising: a substrate, and at least one layer
comprising thermoplastic epoxy resin coating material disposed on
at least a portion of said substrate to form a coated article,
wherein the coated article preferably exhibits substantially no
blushing or whitening when immersed in water or otherwise directly
exposed to water. In preferred embodiments, such articles also
exhibit substantially no blushing or whitening when exposed to high
humidity, including humidity of about 70% or higher. Such exposure
or immersion to water or high humidity may occur for several hours
or longer, including about 6 hours, 12 hours, 24 hours, 48 hours,
and longer and/or may occur at temperatures around room temperature
and at reduced temperatures. In one embodiment, the coated articles
exhibit substantially no blushing or whitening when immersed in or
otherwise exposed directly to water at a temperature of about
0.degree. C to 30.degree. C., including about 5.degree. C.,
10.degree. C., 15.degree. C., 20.degree. C., 22.degree. C., and
25.degree. C. for about 24 hours. In preferred embodiments, the
substrate comprises a polymeric material, preferably a
thermoplastic material chosen from the group consisting of
polyester, polypropylene, polyethylene, polycarbonate, polyamides
and acrylics. In embodiments wherein the article is a preform or
bottle having a body portion and neck portion, the coating is
preferably disposed substantially only on the body portion of the
preform. In a preferred embodiment, one or more additional coating
layers are disposed on the article. In such three or more layer
embodiments, preferably there is substantially no distinction
between coating layers, and/or one or more additional layers
comprise thermoplastic materials. The coating layer(s) may contain
one or more of the following characteristics in preferred
embodiments: gas-barrier protection, UV protection, scuff
resistance, blush resistance, chemical resistance.
[0021] In accordance with a preferred embodiment a multilayer
container is produced, preferably a preform or bottle having a body
portion and neck portion. Preferably the container, preform or
bottle comprises a thermoplastic material substrate and one or
moore, layers of thermoplastic resin coating material. Preferably
the thermoplastic substrate material is chosen from the chosen from
the group consisting of polyesters, polyolefins, polycarbonates,
polyamides and acrylics. Preferably the coating layers contain one
or more of the following characteristics: gas-barrier protection,
UV protection, scuff resistance, blush resistance, chemical
resistance. Preferably the coating is disposed substantially only
on the body portion of the preform. In addition, the finished
product preferably has substantially no distinction between
layers.
[0022] In a preferred embodiment, the coated article or container
formed from a coated preform shows substantially no blushing or
whitening when exposed to water or high humidity at room
temperature or reduced or elevated temperatures (with respect to
room temperature) for a period of several hours or longer. In one
embodiment, the coated article or container exhibits substantially
no blushing when immersed in or otherwise exposed to water. In
related embodiments, the infrared heating is replaced with flame
curing, gas heaters, electron beam processing, or UV radiation
optionally followed by or combined with cooling with air.
[0023] All of these embodiments are intended to be within the scope
of the invention herein disclosed. These and other embodiments of
the present inventions will become readily apparent to those
skilled in the art from the following detailed description of a
preferred embodiments having reference to the attached figures, the
invention not being limited to any particular preferred
embodiment(s) disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is an uncoated preform as is used as a starting
material for preferred embodiments.
[0025] FIG. 2 is a cross-section of a preferred uncoated preform of
the type that is coated in accordance with a preferred
embodiment.
[0026] FIG. 3 is a cross-section of one preferred embodiment of a
coated preform.
[0027] FIG. 4 is an enlargement of a section of the wall portion of
a coated preform.
[0028] FIG. 5 is a cross-section of another embodiment of a coated
preform.
[0029] FIG. 6 is a cross-section of a preferred preform in the
cavity of a blow-molding apparatus of a type that may be used to
make a preferred coated container of an embodiment of the present
invention.
[0030] FIG. 7 is a coated container prepared in accordance with a
blow molding process.
[0031] FIG. 8 is a cross-section of one preferred embodiment of a
coated container having features in accordance with the present
invention.
[0032] FIG. 9 is a three-layer embodiment of a preform.
[0033] FIG. 10 there is a non-limiting flow diagram that
illustrates a preferred process.
[0034] FIG. 11 is a non-limiting flow diagram of one embodiment of
a preferred process wherein the system comprises a single coating
unit.
[0035] FIG. 12 is a non-limiting flow diagram of a preferred
process wherein the system comprises multiple coating units in one
integrated system.
[0036] FIG. 13 is a non-limiting flow diagram of a preferred
process wherein the system comprises multiple coating units in a
modular system.
[0037] FIG. 14 is a non-limiting top view of one embodiment of a
preferred process wherein the system comprises a single flow
coating unit.
[0038] FIG. 15 is a non-limiting front view of one embodiment of a
preferred process wherein the system comprises a single flow
coating unit.
[0039] FIG. 16 is a non-limiting cross section view of one
embodiment of a preferred process wherein the system comprises a
single flow coating unit.
[0040] FIGS. 17A and 17B depict non-limiting views of one
embodiment of a preferred IR drying/curing unit.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
A. General Description of Preferred Embodiments
[0041] Methods and apparatus for coating articles comprising one or
more layers are described herein. These layers may comprise
thermoplastic materials with good gas-barrier characteristics as
well as layers or additives that provide UV protection, scuff
resistance, blush resistance, chemical resistance, and/or active
properties for O.sub.2 and/or CO.sub.2 scavenging.
[0042] As presently contemplated, one embodiment of a coated
article is a preform of the type used for beverage containers.
Alternatively, embodiments of the coated articles of the present
invention could take the form of jars, tubes, trays, bottles for
holding liquid foods, medical products, or other products sensitive
to gas exposure. However, for the sake of simplicity, these
embodiments will be described herein primarily as articles or
preforms.
[0043] Furthermore, the articles described herein may be described
specifically in relation to a particular substrate, polyethylene
terephthalate (PET), but preferred methods are applicable to many
other thermoplastics of the polyester type. As used herein, the
term "substrate" is a broad term used in its ordinary sense and
includes embodiments wherein "substrate" refers to the material
used to form the base article that is coated. Other suitable
article substrates include, but are not limited to, various
polymers such as polyesters, polyolefins, including polypropylene
and polyethylene, polycarbonate, polyamides, including nylons, or
acrylics. These substrate materials may be used alone or in
conjunction with each other. More specific substrate examples
include, but are not limited to, polyethylene 2,6- and
1,5-naphthalate (PEN), PETG, polytetramethylene 1,2-dioxybenzoate
and copolymers of ethylene terephthalate and ethylene
isophthalate.
[0044] In one embodiment, PET is used as the polyester substrate
which is coated. As used herein, "PET" includes, but is not limited
to, modified PET as well as PET blended with other materials. One
example of a modified PET is "high IPA PET" or IPA-modified PET.
The term "high IPA PET" refers to PET in which the IPA content is
preferably more than about 2% by weight, including about 2-10% IPA
by weight.
[0045] One or more layers of a coating material are employed in
preferred methods and processes. The layers may comprise barrier
layers, UV protection layers, oxygen scavenging layers, carbon
dioxide scavenging layers, and other layers as needed for the
particular application. As used herein, the terms "barrier
material," "barrier resin," and the like are broad terms and are
used in their ordinary sense and refer, without limitation, to
materials which, when used to coat articles, preferably adhere well
to the article substrate and have a lower permeability to oxygen
and carbon dioxide than the article substrate. As used herein, the
terms "UV protection" and the like are broad terms and are used in
their ordinary sense and refer, without limitation, to materials
which, when used to coat articles, preferably adhere well to the
article substrate and have a higher UV absorption rate than the
article substrate. As used herein, the terms "oxygen scavenging"
and the like are broad terms and are used in their ordinary sense
and refer, without limitation, to materials which, when used to
coat articles, preferably adhere well to the article substrate and
have a higher oxygen absorption rate than the article substrate. As
used herein, the terms "carbon dioxide scavenging" and the like are
broad terms and are used in their ordinary sense and refer, without
limitation, to materials which, when used to coat articles,
preferably adhere well to the article substrate and have a higher
carbon dioxide absorption rate than the article substrate. As used
herein, the terms "crosslink," "crosslinked," and the like are
broad terms and are used in their ordinary sense and refer, without
limitation, to materials and coatings which vary in degree from a
very small degree of crosslinking up to and including fully cross
linked materials such as a thermoset epoxy. The degree of
crosslinking can be adjusted to provide the appropriate degree of
chemical or mechanical abuse resistance for the particular
circumstances.
[0046] Once a suitable coating material is chosen, an apparatus and
method for commercially manufacturing a coated article is
necessary. One such method and apparatus is described below.
[0047] Preferred methods provide for a coating to be placed on an
article, specifically a preform, which is later blown into a
bottle. Such methods are, in many instances, preferable to placing
coatings on the bottles themselves. Preforms are smaller in size
and of a more regular shape than the containers blown therefrom,
making it simpler to obtain an even and regular coating.
Furthermore, bottles and containers of varying shapes and sizes can
be made from preforms of similar size and shape. Thus, the same
equipment and processing can be used to coat preforms to form
several different types of containers. The blow-molding may take
place soon after molding and coating, or preforms may be made and
stored for later blow-molding. If the preforms are stored prior to
blow-molding, their smaller size allows them to take up less space
in storage. Even though it is often times preferable to form
containers from coated preforms, containers may also be coated.
[0048] The blow-molding process presents several challenges. One
step where the greatest difficulties arise is during the
blow-molding process where the container is formed from the
preform. During this process, defects such as delamination of the
layers, cracking or crazing of the coating, uneven coating
thickness, and discontinuous coating or voids can result. These
difficulties can be overcome by using suitable coating materials
and coating the preforms in a manner that allows for good adhesion
between the layers.
[0049] Thus, preferred embodiments comprise suitable coating
materials. When a suitable coating material is used, the coating
sticks directly to the preform without any significant delamination
and will continue to stick as the preform is blow-molded into a
bottles and afterwards. Use of a suitable coating material also
helps to decrease the incidence of cosmetic and structural defects
which can result from blow-molding containers as described
above.
[0050] One common problem seen in articles formed by coating using
coating solutions or dispersions is "blushing" or whitening when
the article is immersed in (which includes partial immersion) or
exposed directly to water or high humidity (which includes at or
above about 70% relative humidity). In preferred embodiments, the
articles disclosed herein and the articles produced by methods
disclosed herein exhibit minimal or substantially no blushing or
whitening when immersed in or otherwise exposed directly to water
or high humidity. Such exposure may occur for several hours or
longer, including about 6 hours, 12 hours, 24 hours, 48 hours, and
longer and/or may occur at temperatures around room temperature and
at reduced temperatures, such as would be seen by placing the
article in a cooler containing ice or ice water. Exposure may also
occur at an elevated temperature, such elevated temperature
generally not including temperatures high enough to cause an
appreciable softening of the materials which form the container or
coating, including temperatures approaching the Tg of the
materials. In one embodiment, the coated articles exhibit
substantially no blushing or whitening when immersed in or
otherwise exposed directly to water at a temperature of about
0.degree. C. to 30.degree. C, including about 5.degree. C,
10.degree. C., 15.degree. C., 20.degree. C., 22.degree. C., and
25.degree. C. for about 24 hours. The process used for curing or
drying coating layers appears to have an effect on the blush
resistance of articles.
B. Detailed Description of the Drawings
[0051] Referring to FIG. 1, a preferred uncoated preform 1 is
depicted. The preform is preferably made of an FDA approved
material such as virgin PET and can be of any of a wide variety of
shapes and sizes. The preform shown in FIG. 1 is a 24 gram preform
of the type which will form a 16 oz. carbonated beverage bottle,
but as will be understood by those skilled in the art, other
preform configurations can be used depending upon the desired
configuration, characteristics and use of the final article. The
uncoated preform 1 may be made by injection molding as is known in
the art or by other suitable methods.
[0052] Referring to FIG. 2, a cross-section of a preferred uncoated
preform 1 of FIG. 1 is depicted. The uncoated preform 1 has a neck
portion 2 and a body portion 4. The neck portion 2, also called the
neck finish, begins at the opening 18 to the interior of the
preform 1 and extends to and includes the support ring 6. The neck
2 is further characterized by the presence of the threads 8, which
provide a way to fasten a cap for the bottle produced from the
preform 1. The body portion 4is an elongated and cylindrically
shaped structure extending down from the neck 2 and culminating in
the rounded end cap 10. The preform thickness 12 will depend upon
the overall length of the preform 1 and the wall thickness and
overall size of the resulting container. It should be noted that as
the terms "neck" and "body" are used herein, in a container that is
colloquially called a "longneck" container, the elongate portion
just below the support ring, threads, and/or lip where the cap is
fastened would be considered part of the "body" of the container
and not a part of the "neck".
[0053] Referring to FIG. 3, a cross-section of one type of coated
preform 20 having features in accordance with a preferred
embodiment is depicted. The coated preform 20 has a neck portion 2
and a body portion 4 as in the uncoated preform 1 in FIGS. 1 and 2.
The coating layer 22 is disposed about the entire surface of the
body portion 4, terminating at the bottom of the support ring 6. A
coating layer 22 in the embodiment shown in the figure does not
extend to the neck portion 2, nor is it present on the interior
surface 16 of the preform which is preferably made of an FDA
approved material such as PET. The coating layer 22 may comprise
one layer of a single material, one layer of several materials
combined, or several layers of at least two materials. The overall
thickness 26 of the preform is equal to the thickness of the
initial preform plus the thickness 24 of the coating layer or
layers, and is dependent upon the overall size and desired coating
thickness of the resulting container.
[0054] FIG. 4 is an enlargement of a wall section of the preform
showing the makeup of the coating layers in one embodiment of a
preform. The layer 110 is the substrate layer of the preform while
112 comprises the coating layers of the preform. The outer coating
layer 116 comprises one or more layers of material, while 114
comprises the inner coating layer. In preferred embodiments there
may be one or more outer coating layers. As shown here, the coated
preform has one inner coating layer and two outer coating layers.
Not all preforms of FIG. 4 will be of this type.
[0055] Referring to FIG. 5, another embodiment of a coated preform
25 is shown in cross-section. The primary difference between the
coated preform 25 and the coated preform 20 in FIG. 3 is that the
coating layer 22 is disposed on the support ring 6 of the neck
portion 2 as well as the body portion 4. Preferably any coating
that is disposed on, especially on the upper surface, or above the
support ring 6 is made of an FDA approved material such as PET.
[0056] The coated preforms and containers can have layers which
have a wide variety of relative thicknesses. In view of the present
disclosure, the thickness of a given layer and of the overall
preform or container, whether at a given point or over the entire
container, can be chosen to fit a coating process or a particular
end use for the container. Furthermore, as discussed above in
regard to the coating layer in FIG. 3, the coating layer in the
preform and container embodiments disclosed herein may comprise a
single material, a layer of several materials combined, or several
layers of at least two or more materials.
[0057] After a coated preform, such as that depicted in FIG. 3, is
prepared by a method and apparatus such as those discussed in
detail below, it is subjected to a stretch blow-molding process.
Referring to FIG. 6, in this process a coated preform 20 is placed
in a mold 28 having a cavity corresponding to the desired container
shape. The coated preform is then heated and expanded by stretching
and by air forced into the interior of the preform 20 to fill the
cavity within the mold 28, creating a coated container 30. The blow
molding operation normally is restricted to the body portion 4 of
the preform with the neck portion 2 including the threads, pilfer
ring, and support ring retaining the original configuration as in
the preform.
[0058] Referring to FIG. 7, there is disclosed an embodiment of
coated container 40 in accordance with a preferred embodiment, such
as that which might be made from blow molding the coated preform 20
of FIG. 3. The container 40 has a neck portion 2 and a body portion
4 corresponding to the neck and body portions of the coated preform
20 of FIG. 3. The neck portion 2 is further characterized by the
presence of the threads 8 which provide a way to fasten a cap onto
the container.
[0059] When the coated container 40 is viewed in cross-section, as
in FIG. 8, the construction can be seen. The coating 42 covers the
exterior of the entire body portion 4 of the container 40, stopping
just below the support ring 6. The interior surface 50 of the
container, which is made of an FDA-approved material, preferably
PET, remains uncoated so that only the interior surface 50 is in
contact with the packaged product such as beverages, foodstuffs, or
medicines. In one preferred embodiment that is used as a carbonated
beverage container, a 24 gram preform is blow molded into a 16
ounce bottle with a coating ranging from about 0.05 to about 0.75
grams, including about 0.1 to about 0.2 grams.
[0060] Referring to FIG. 9 there is shown a preferred three-layer
preform 76. This embodiment of coated preform is preferably made by
placing two coating layers 80 and 82 on a preform 1 such as that
shown in FIG. 1.
[0061] Referring to FIG. 10 there is shown a non-limiting flow
diagram that illustrates a preferred process and apparatus. A
preferred process and apparatus involves entry of the article into
the system 84, dip, spray, or flow coating of the article 86,
removal of excess material 88, drying/curing 90, cooling 92, and
ejection from the system 94.
[0062] Referring to FIG. 11 there is shown a non-limiting flow
diagram of one embodiment of a preferred process wherein the system
comprises a single coating unit, A, of the type in FIG. 10 which
produces a single coat article. The article enters the system 84
prior to the coating unit and exits the system 94 after leaving the
coating unit.
[0063] Referring to FIG. 12 there is shown a non-limiting flow
diagram of a preferred process wherein the system comprises a
single integrated processing line that contains multiple stations
100, 101, 102 wherein each station coats and dries or cures the
article thereby producing an article with multiple coatings. The
article enters the system 84 prior to the first station 100 and
exits the system 94 after the last station 102. The embodiment
described herein illustrates a single integrated processing line
with three coating units, it is to be understood that numbers of
coating units above or below are also included.
[0064] Referring to FIG. 13 there is shown a non-limiting flow
diagram of one embodiment of a preferred process. In this
embodiment, the system is modular wherein each processing line 107,
108, 109 is self-contained with the ability to handoff to another
line 103, thereby allowing for single or multiple coatings
depending on how many modules are connected thereby allowing
maximum flexibility. The article first enters the system at one of
several points in the system 84 or 120. The article can enter 84
and proceed through the first module 107, then the article may exit
the system at 118 or continue to the next module 108 through a hand
off mechanism 103 known to those of skill in the art. The article
then enters the next module 108 at 120. The article may then
continue on to the next module 109 or exit the system. The number
of modules may be varied depending on the production circumstances
required. Further the individual coating units 104 105 106 may
comprise different coating materials depending on the requirements
of a particular production line. The interchangeability of
different modules and coating units provides maximum
flexibility.
[0065] Referring to FIGS. 14, 15, and 16 there are shown alternate
views of non-limiting diagrams of one embodiment of a preferred
process. In this embodiment, the top view of a system comprising a
single flow coater 86 is shown. The preform enters the system 84
and then proceeds to the flow coater 86 wherein the preform 1
passes through the coating material waterfall. The coating material
proceeds from the tank or vat 150 through the gap 155 in the tank
down the angled fluid guide 160 where it forms a waterfall (not
illustrated) as it passes onto the preforms. The gap 155 in the
tank may be widened or narrowed to adjust the flow of the material.
The material is pumped from the reservoir (not illustrated) into
the vat or tank at a rate that maintains the coating material level
above that of the gap 155. Advantageously, this configuration
ensures a constant flow of coating material. The excess amount of
material also dampens any fluid fluctuations due to the cycling of
the pump. As the preform passes out of the coating waterfall,
excess material drips off into the material collection reservoir
170. The coating material collector (not illustrated) receives any
unused coating waterfall and returns the material back to the
coating tank or vat. The excess material is then removed from the
bottom of the preform 88. The preform then moves toward the
drying/curing unit 90 before being ejected from the system 94. As
shown here, the preforms are allowed to rest before ejection to
cool. The collection reservoir and coating material collector
preferably empty into the reservoir that feeds the tank or vat so
as to allow for reduction of waste from the system.
[0066] Referring to FIG. 17A and 17B there are shown non-limiting
views of one embodiment of a preferred IR drying/curing unit 90. As
shown in FIG. 17A the unit 90 is open. The arrow at the bottom of
the unit indicates how the unit would close. On one side of the
processing line there is shown a series of ten lamps 200. Below the
preforms there is shown an angled reflector 210 which reflects heat
towards the bottom of the preforms for more thorough curing.
Opposite to the lamps is a semicircular reflector 230 which
reflects the IR heat back onto the preforms allowing for a more
thorough and efficient cure. Reflectors of other shapes and sizes
may also be used.
[0067] Referring to FIG. 17B there is an enlarged section detailing
the lamp placement in one embodiment of a preferred IR
drying/curing unit 90. The lamps in this embodiment are adjustable
220 and may be moved closer to or farther away from the preform
allowing for maximum drying/curing flexibility.
[0068] A preferred method and apparatus for making coated articles,
more specifically preforms, is discussed in more detail below.
C. Physical Characteristics of Preferred Coating Materials
[0069] The following physical characteristics are described in
terms of a preferred material, PET. However, those of skill in the
art will understand that other suitable substrates, as mentioned
previously, may be used.
[0070] The glass transition temperature (Tg) is a property relating
to the transition of a polymer from a glassy form to a plastic
form. In a range of temperatures above its Tg, a material will
become soft enough to allow it to flow readily when subjected to an
external force or pressure, yet not so soft that its viscosity is
so low that it acts more like a liquid than a pliable solid. The
temperature range above Tg is a preferred temperature range for
performing a blow-molding process, as the material is soft enough
to flow under the force of the air blown into the preform to fit
the mold but not so soft that it breaks up or becomes uneven in
texture. Thus, when materials have similar glass transition
temperatures, they will have similar preferred blowing temperature
ranges, allowing the materials to be processed together without
compromising the performance of either material.
[0071] In the blow-molding process to produce a bottle from a
preform, the preform is heated to a temperature slightly above the
Tg of the preform material so that when air is forced into the
preform's interior, it will be able to flow to fill the mold in
which it is placed. If one does not sufficiently heat the preform
the preform material will be too hard to flow properly, and would
likely crack, craze, or not expand to fill the mold. Conversely, if
one heats the preform to a temperature well above the Tg, the
material would likely become so soft that it would not be able to
hold its shape or it would crystallize and would process
improperly.
[0072] If the material which forms a coating layer has a Tg similar
to that of the chosen substrate material, it will have a blowing
temperature range similar to the substrate. For example, if a PET
preform is coated with such a material, a blowing temperature can
be chosen that allows both materials to be processed within their
preferred blowing temperature ranges. If the coating were to have a
Tg dissimilar to that of PET, it would be difficult, if not
impossible, to choose a blowing temperature suitable for both
materials. When coating materials comprise polymers having a Tg
similar to PET (or the chosen substrate material), the coated
preform behaves during blow molding substantially as if it were
made of one material, expanding smoothly and creating a
cosmetically appealing container with an even thickness and uniform
coating of the material where it is applied.
[0073] The glass transition temperature of PET occurs in a window
of about 75-85.degree. C., depending upon how the PET has been
processed previously. Therefore, the Tg for preferred coating
materials to coat PET preferably range from about 55 to about
140.degree. C., more preferably from about 90 to about 110.degree.
C., including about 60, 65, 70, 80, 95, 100, 105, 115, 120, and
130. One should note that if the coating is applied to a container,
such as a bottle, the Tg of the coating material is greatly
diminished in importance because the need for blow molding is
absent.
[0074] Another factor which has an impact on the performance of
coated preforms during blow molding is the state of the material.
It is preferred that coating materials be amorphous rather than
crystalline. This is because materials in an amorphous state are
easier to form into bottles and containers by use of a blow molding
process than materials in a crystalline state. PET can exist in
both crystalline and amorphous forms. However, in certain
embodiments of the present invention, it is preferred that the
crystallinity of the PET be minimized and the amorphous state
maximized in order to create a semicrystalline state which, among
other things, aids interlayer adhesion and in the blow molding
process. In other embodiments, such as when the article coated is a
container such that there is no subsequent blow molding or when
crystallinity is desired, such as for hot-fill containers, having
amorphous substrates and/or coatings is not important, and may even
be contraindicated.
[0075] Preferred coating materials may have tensile strength and
creep resistance similar to PET or the chosen substrate material.
If so, they may act as a structural component of the container,
allowing the coating material to displace some of the polyethylene
terephthalate in the preform without sacrificing preform
performance. Similarity in tensile strength between PET and the
coating materials helps the container to have structural integrity
while similarity in creep resistance between PET and the coating
materials helps the container to retain its shape. Creep resistance
relates to the ability of a material to resist changing its shape
in response to an applied force. Although certain preferred
embodiments may have coatings that provide structural integrity,
other preferred embodiments may not.
[0076] For applications where optical clarity is of importance,
preferred coating materials have an index of refraction similar to
that of PET or the chosen substrate material. When the refractive
index of the PET and the coating material are similar, the preforms
and, perhaps more importantly, the containers blown therefrom are
optically clear and, thus, cosmetically appealing for use as a
beverage container where clarity of the bottle is frequently
desired. If, however, the two materials have substantially
dissimilar refractive indices when they are placed in contact with
each other, the resulting combination may have visual distortions
and may be cloudy or opaque, depending upon the degree of
difference in the refractive indices of the materials.
[0077] Polyethylene terephthalate has an index of refraction for
visible light within the range of about 1.40 to 1.75, depending
upon its physical configuration. When made into preforms, the
refractive index is preferably within the range of about 1.55 to
1.75, and more preferably in the range of 1.55-1.65. After the
preform is made into a bottle, the wall of the final product, may
be characterized as a biaxially-oriented film since it is subject
to both hoop and axial stresses in the blow molding operation. Blow
molded PET generally exhibits a refractive index within the range
of about 1.40 to 1.75, usually about 1.55 to 1.75, depending upon
the stretch ratio involved in the blow molding operation. For
relatively low stretch ratios of about 6:1, the refractive index
will be near the lower end, whereas for high stretch ratios, about
10:1, the refractive index will be near the upper end of the
aforementioned range. It will be recognized that the stretch ratios
referred to herein are biaxial stretch ratios resulting from and
include the product of the hoop stretch ratio and the axial stretch
ratio. For example, in a blow molding operation in which the final
preform is enlarged by a factor of 2.5 in the axial direction and a
factor of 3.5 diametrically, the stretch ratio will be about 8.75
(2.5.times.3.5).
[0078] Using the designation n.sub.i to indicate the refractive
index for PET and n.sub.o to indicate the refractive index for the
coating material, the ratio between the values n.sub.i and n.sub.o
is preferably 0.8-1.3, more preferably 1.0-1.2, most preferably
1.0-1.1. As will be recognized by those skilled in the art, for the
ratio n.sub.i/n.sub.o=1 the distortion due to refractive index will
be at a minimum, because the two indices are identical. As the
ratio progressively varies from one, however, the distortion
increases progressively.
D. Preferred Coating Materials
[0079] In a preferred embodiment, the coating materials comprise
thermoplastic epoxy resins (TPEs). A further preferred embodiment
includes "phenoxy" resins which are a subset of thermoplastic epoxy
resins. Phenoxy resins, as that term is used herein, include a wide
variety of materials including those discussed in WO 99/20462. A
further subset of phenoxy resins, and thermoplastic epoxy resins,
are preferred hydroxy-phenoxyether polymers, of which
polyhydroxyaminoether copolymers (PHAE) is a further preferred
material. See for example, U.S. Pat. Nos. 6,455,116; 6,180,715;
6,011,111; 5,834,078; 5,814,373; 5,464,924; and 5,275,853; see also
PCT Application Nos. WO 99/48962; WO 99/12995; WO 98/29491; and WO
98/14498.
[0080] Preferably, the thermoplastic epoxy resins, more
specifically the phenoxy resins, used as coating materials in the
present invention comprise one of the following types:
[0081] (1) hydroxy-functional poly(amide ethers) having repeating
units represented by any one of the Formulae Ia, Ib or Ic: 1
[0082] (2) poly(hydroxy amide ethers) having repeating units
represented independently by any one of the Formulae IIa, IIb or
IIc: 2
[0083] (3) amide- and hydroxymethyl-functionalized polyethers
having repeating units represented by Formula III: 3
[0084] (4) hydroxy-functional polyethers having repeating units
represented by Formula IV: 4
[0085] (5) hydroxy-functional poly(ether sulfonamides) having
repeating units represented by Formulae Va or Vb: 5
[0086] (6) poly(hydroxy ester ethers) having repeating units
represented by Formula VI: 6
[0087] (7) hydroxy-phenoxyether polymers having repeating units
represented by Formula VIII: 7
[0088] and
[0089] (8) poly(hydroxyamino ethers) having repeating units
represented by Formula VIII: 8
[0090] wherein each Ar individually represents a divalent aromatic
moiety, substituted divalent aromatic moiety or heteroaromatic
moiety, or a combination of different divalent aromatic moieties,
substituted aromatic moieties or heteroaromatic moieties; R is
individually hydrogen or a monovalent hydrocarbyl moiety; each
Ar.sub.1 is a divalent aromatic moiety or combination of divalent
aromatic moieties bearing amide or hydroxymethyl groups; each
Ar.sub.2 is the same or different than Ar and is individually a
divalent aromatic moiety, substituted aromatic moiety or
heteroaromatic moiety or a combination of different divalent
aromatic moieties, substituted aromatic moieties or heteroaromatic
moieties; R.sub.1 is individually a predominantly hydrocarbylene
moiety, such as a divalent aromatic moiety, substituted divalent
aromatic moiety, divalent heteroaromatic moiety, divalent alkylene
moiety, divalent substituted alkylene moiety or divalent
heteroalkylene moiety or a combination of such moieties; R.sub.2 is
individually a monovalent hydrocarbyl moiety; A is an amine moiety
or a combination of different amine moieties; X is an amine, an
arylenedioxy, an arylenedisulfonamido or an arylenedicarboxy moiety
or combination of such moieties; and Ar.sub.3 is a "cardo" moiety
represented by any one of the Formulae: 9
[0091] wherein Y is nil, a covalent bond, or a linking group,
wherein suitable linking groups include, for example, an oxygen
atom, a sulfur atom, a carbonyl atom, a sulfonyl group, or a
methylene group or similar linkage; n is an integer from about 10
to about 1000; x is 0.01 to 1.0; and y is 0 to 0.5.
[0092] The term "predominantly hydrocarbylene" means a divalent
radical that is predominantly hydrocarbon, but which optionally
contains a small quantity of a heteroatomic moiety such as oxygen,
sulfur, imino, sulfonyl, sulfoxyl, and the like.
[0093] The hydroxy-functional poly(amide ethers) represented by
Formula I are preferably prepared by contacting an
N,N'-bis(hydroxyphenylamido)alka- ne or arene with a diglycidyl
ether as described in U.S. Pat. Nos. 5,089,588 and 5,143,998.
[0094] The poly(hydroxy amide ethers) represented by Formula II are
prepared by contacting a bis(hydroxyphenylamido)alkane or arene, or
a combination of 2 or more of these compounds, such as
N,N'-bis(3-hydroxyphenyl) adipamide or
N,N'-bis(3-hydroxyphenyl)glutarami- de, with an epihalohydrin as
described in U.S. Pat. No. 5,134,218.
[0095] The amide- and hydroxymethyl-functionalized polyethers
represented by Formula III can be prepared, for example, by
reacting the diglycidyl ethers, such as the diglycidyl ether of
bisphenol A, with a dihydric phenol having pendant amido,
N-substituted amido and/or hydroxyalkyl moieties, such as
2,2-bis(4-hydroxyphenyl)acetamide and 3,5-dihydroxybenzamide. These
polyethers and their preparation are described in U.S. Pat. Nos.
5,115,075 and 5,218,075.
[0096] The hydroxy-functional polyethers represented by Formula IV
can be prepared, for example, by allowing a diglycidyl ether or
combination of diglycidyl ethers to react with a dihydric phenol or
a combination of dihydric phenols using the process described in
U.S. Pat. No. 5,164,472. Alternatively, the hydroxy-functional
polyethers are obtained by allowing a dihydric phenol or
combination of dihydric phenols to react with an epihalohydrin by
the process described by Reinking, Barnabeo and Hale in the Journal
of Applied Polymer Science, Vol. 7, p. 2135 (1963).
[0097] The hydroxy-functional poly(ether sulfonamides) represented
by Formula V are prepared, for example, by polymerizing an
N,N'-dialkyl or N,N'-diaryldisulfonamide with a diglycidyl ether as
described in U.S. Pat. No. 5,149,768.
[0098] The poly(hydroxy ester ethers) represented by Formula VI are
prepared by reacting diglycidyl ethers of aliphatic or aromatic
diacids, such as diglycidyl terephthalate, or diglycidyl ethers of
dihydric phenols with, aliphatic or aromatic diacids such as adipic
acid or isophthalic acid. These polyesters are described in U.S.
Pat. No. 5,171,820.
[0099] The hydroxy-phenoxyether polymers represented by Formula VII
are prepared, for example, by contacting at least one
dinucleophilic monomer with at least one diglycidyl ether of a
cardo bisphenol, such as 9,9-bis(4-hydroxyphenyl)fluorene,
phenolphthalein, or phenolphthalimidine or a substituted cardo
bisphenol, such as a substituted bis(hydroxyphenyl)fluorene, a
substituted phenolphthalein or a substituted phenolphthalimidine
under conditions sufficient to cause the nucleophilic moieties of
the dinucleophilic monomer to react with epoxy moieties to form a
polymer backbone containing pendant hydroxy moieties and ether,
imino, amino, sulfonamido or ester linkages. These
hydroxy-phenoxyether polymers are described in U.S. Pat. No.
5,184,373.
[0100] The poly(hydroxyamino ethers) ("PHAE" or polyetheramines)
represented by Formula VIII are prepared by contacting one or more
of the diglycidyl ethers of a dihydric phenol with an amine having
two amine hydrogens under conditions sufficient to cause the amine
moieties to react with epoxy moieties to form a polymer backbone
having amine linkages, ether linkages and pendant hydroxyl
moieties. These compounds are described in U.S. Pat. No. 5,275,853.
For example, polyhydroxyaminoether copolymers can be made from
resorcinol diglycidyl ether, hydroquinone diglycidyl ether,
bisphenol A diglycidyl ether, or mixtures thereof.
[0101] The phenoxy thermoplastics commercially available from
Phenoxy Associates, Inc., PAPHEN 25068-38-6 as one example, are
suitable for use in the present invention. These
hydroxy-phenoxyether polymers are the condensation reaction
products of a dihydric polynuclear phenol, such as bisphenol A, and
an epihalohydrin and have the repeating units represented by
Formula IV wherein Ar is an isopropylidene diphenylene moiety. The
process for preparing these is described in U.S. Pat. No.
3,305,528, incorporated herein by reference in its entirety.
[0102] Generally, preferred TPE, including phenoxy and PHAE,
coating materials form stable aqueous based solutions or
dispersions. Preferably, the coating properties of the
solutions/dispersions are not adversely affected by contact with
water. Preferred coating materials range from about 10% solids to
about 50% solids, including about 15%, 20%, 25%, 30%, 35%, 40% and
45%, and ranges encompassing such percentages. Preferably, the
coating material used dissolves or disperses in polar solvents.
These polar solvents include, but are not limited to, water,
alcohols, and glycol ethers. See, for example, U.S. Pat. Nos.
6,455,116, 6,180,715, and 5,834,078 which describe some preferred
TPE solutions and/or dispersions.
[0103] One preferred thermoplastic epoxy coating material is a
polyhydroxyaminoether copolymer (PHAE), represented by Formula
VIII, dispersion or solution. The dispersion or solution, when
applied to a container or preform, greatly reduces the permeation
rate of a variety of gases through the container walls in a
predictable and well known manner. One dispersion or latex made
thereof comprises 10-30 percent solids. A PHAE solution/dispersion
may be prepared by stirring or otherwise agitating the PHAE in a
solution of water with an organic acid, preferably acetic or
phosphoric acid, but also including lactic, malic, citric, or
glycolic acid and/or mixtures thereof. These PHAE
solution/dispersions also include organic acid salts produced by
the reaction of the polyhydroxyaminoethers with these acids.
[0104] The following PHAE solutions are examples of suitable TPE
solutions. One suitable material is BLOX.RTM. experimental barrier
resin, for example XU-19061.00 made with phosphoric acid
manufactured by Dow Chemical Corporation. This particular PHAE
dispersion is said to have the following typical characteristics:
30% percent solids, a specific gravity of 1.30, a pH of 4, a
viscosity of 24 centipoise (Brookfield, 60 rpm, LVI, 22.degree.
C.), and a particle size of between 1,400 and 1,800 angstroms.
Other suitable materials include BLOX.RTM. 599-29 resins based on
resorcinol have also provided superior results as a barrier
material. This particular dispersion is said to have the following
typical characteristics: 30% percent solids, a specific gravity of
1.2, a pH of 4.0, a viscosity of 20 centipoise (Brookfield, 60 rpm,
LVI, 22.degree. C.), and a particle size of between 1500 and 2000
angstroms. Other variations of the polyhydroxyaminoether chemistry
may prove useful such as crystalline versions based on hydroquinone
diglycidylethers. Other suitable materials include
polyhydroxyaminoether solutions by Imperial Chemical Industries
("ICI," Ohio, USA) more specifically coded EXP12468 and EXP12468-4B
including cross-linked materials which exhibit high chemical
resistance, low blushing and low surface tension. Other suitable
solutions are disclosed in U.S. patent application Ser. No.
10/______, filed ______, 2003, including one based upon BLOX.RTM.
5000 resin that is a proprietary material available from ICI, which
comprises ICI-coded components PXR-15700, E6039, and F3473, which
exhibits good cross-linking, chemical resistance and does not
exhibit excessive foaming. Other suitable materials include
BLOX.RTM. 5000 resin dispersion intermediate, BLOX.RTM. XUR 588-29,
BLOX.RTM. 0000 and 4000 series resins. The solvents used to
dissolve these materials include, but are not limited to, polar
solvents such as alcohols, water, glycol ethers or blends
thereof.
[0105] In one embodiment, preferred thermoplastic epoxies are
soluble in aqueous acid. A polymer solution/dispersion may be
prepared by stirring or otherwise agitating the thermoplastic epoxy
in a solution of water with an organic acid, preferably acetic or
phosphoric acid, but also including lactic, malic, citric, or
glycolic acid and/or mixtures thereof. In a preferred embodiment,
the acid concentration in the polymer solution is preferably in the
range of about 5% -20%, including about 5% -10% by weight based on
total weight. In other preferred embodiments, the acid
concentration may be below about 5% or above about 20%; and may
vary depending on factors such as the type of polymer and its
molecular weight. The amount of dissolved polymer in a preferred
embodiment ranges from about 0.1% to about 40%. A uniform and free
flowing polymer solution is preferred. In one embodiment a 10%
polymer solution is prepared by dissolving the polymer in a 10%
acetic acid solution at 90.degree. C. Then while still hot the
solution is diluted with 20% distilled water to give an 8% polymer
solution. At higher concentrations of polymer, the polymer solution
tends to be more viscous.
[0106] Examples of preferred copolyester coating materials and a
process for their preparation is described in U.S. Pat. No.
4,578,295 to Jabarin. They are generally prepared by heating a
mixture of at least one reactant selected from isophthalic acid,
terephthalic acid and their C.sub.1 to C.sub.4 alkyl esters with
1,3 bis(2-hydroxyethoxy)benzene and ethylene glycol. Optionally,
the mixture may further comprise one or more ester-forming
dihydroxy hydrocarbon and/or bis(4-.beta.-hydroxyethoxyphen-
yl)sulfone. Especially preferred copolyester coating materials are
available from Mitsui Petrochemical Ind. Ltd. (Japan) as B-010,
B-030 and others of this family.
[0107] Examples of preferred polyamide coating materials include
MXD-6 from Mitsubishi Gas Chemical (Japan). Other preferred
polyamide coating materials are blends of polyamide and polyester,
including those comprising about 1-10% polyester by weight, where
the polyester is preferably PET or a modified PET. The blends may
be ordinary blends or they may be compatibilized with an
antioxidant or other material. Examples of such materials include
those described in U.S. patent application Ser. No. 10/395,899,
filed Mar. 21, 2003, which is hereby incorporated by reference in
its entirety. Polyamide materials may also be used as substrate
materials.
[0108] Other preferred coating materials include polyethylene
naphthalate (PEN), PEN copolyester, and PET/PEN blends. PEN
materials can be purchased from Shell Chemical Company.
E. Additives to Enhance Coating Materials
[0109] An advantage of preferred methods disclosed herein are their
flexibility allowing for the use of multiple functional additives.
Additives known by those of ordinary skill in the art for their
ability to provide enhanced CO.sub.2 barriers, O.sub.2 barriers, UV
protection, scuff resistance, blush resistance, impact resistance
and/or chemical resistance may be used.
[0110] Preferred additives may be prepared by methods known to
those of skill in the art. For example, the additives may be mixed
directly with a particular coating solution/dispersion, they may be
dissolved/dispersed separately and then added to a particular
coating solution/dispersion, or they may be combined with a
particular coating prior to addition of the solvent that forms the
solution/dispersion. In addition, in some embodiments, preferred
additives may be used alone as a single coating layer.
[0111] In preferred embodiments, the barrier properties of a
coating layer may be enhanced by the addition of different
additives. Additives are preferably present in an amount up to
about 40% of the coating solution/dispersion, also including up to
about 30%, 20%, 10%, 5% and 1% of the coating solution/dispersion.
Further, additives are preferably stable in aqueous conditions. For
example, derivatives of resorcinal (m-dihydroxybenzene) may be used
in conjunction with coating materials. The higher the resorcinol
content the greater the barrier properties of the coating. Another
additive that may be used are nanoparticles or nanoparticular
materials. These nanoparticles are tiny particles of materials
which enhance the barrier properties of a material by creating a
more tortuous path for migrating oxygen or carbon dioxide. One
preferred type of nanoparticular material is a microparticular
clay-based product available from Southern Clay Products.
[0112] In preferred embodiments, the UV protection properties of
the coating may be enhanced by the addition of different additives.
In a preferred embodiment, the UV protection coating material used
provides UV protection up to about 350 nm or greater, preferably
about 370 nm or greater, more preferably about 400 nm or greater.
The UV protection material may be used as an additive with layers
providing additional functionality or applied separately as a
single coat. Preferably additives providing enhanced UV protection
are present in the coating solution/dispersion from about 1 to 20%,
but also including about 3%, 5%, 10%, and 15%. Preferably the UV
protection material is added in a form that is compatible with
aqueous based solutions/dispersions. For example, a preferred UV
protection material is Milliken UV390A clear shield. UV390A is an
oily liquid for which mixing is aided by first blending the liquid
with water, preferably in roughly equal parts by volume. This blend
is then added to the TPE solution, for example, BLOX.RTM. 599-29,
and agitated. The resulting solution contains about 10% UV390A and
provides UV protection up to 400 nm when applied to a PET preform.
As previously described, in another embodiment the UV390A solution
is applied as a single coating.
[0113] In preferred embodiments, CO.sub.2 scavenging properties can
be added to the coating. In one preferred embodiment such
properties are achieved by including an active amine which will
react with CO.sub.2 forming a high gas barrier salt. This salt will
then act as a passive CO.sub.2 barrier. The active amine may be an
additive or it may be one or more moieties in the thermoplastic
resin material of one or more layers.
[0114] In preferred embodiments, O.sub.2 scavenging properties can
be added to the coating by including O.sub.2 scavengers such as
anthroquinone and others known in the art. In other embodiments,
these O.sub.2 scavengers may also be used alone as a separate
coating. These O.sub.2 scavenging materials must first be activated
by UV which can be done prior to the drying/curing process.
[0115] In another preferred embodiment, a top coat is applied to
provide chemical resistance to harsher chemicals. Preferably these
top coats are aqueous based polyesters or acrylics which are
optionally partially or fully cross linked. A preferred aqueous
based polyester is polyethylene terephthalate, however other
polyesters may also be used. A preferred aqueous based acrylic is
ICI PXR 14100 Carboxyl Latex.
[0116] A preferred aqueous based polyester resin is described in
U.S. Pat. No. 4,977,191 (Salsman), incorporated herein by
reference. More specifically, U.S. Pat. No. 4,977,191 describes an
aqueous based polyester resin, comprising a reaction product of
20-50% by weight of waste terephthalate polymer, 10-40% by weight
of at least one glycol an 5-25% by weight of at least one
oxyalkylated polyol.
[0117] Another preferred aqueous based polymer is a sulfonated
aqueous based polyester resin composition as described in U.S. Pat.
No. 5,281,630 (Salsman), herein incorporated by reference.
Specifically, U.S. Pat. No. 5,281,630 describes an aqueous
suspension of a sulfonated water-soluble or water dispersible
polyester resin comprising a reaction product of 20-50% by weight
terephthalate polymer, 10-40% by weight at least one glycol and
5-25% by weight of at least one oxyalkylated polyol to produce a
prepolymer resin having hydroxyalkyl functionality where the
prepolymer resin is further reacted with about 0.10 mole to about
0.50 mole of alpha, beta-ethylenically unsaturated dicarboxylic
acid per 100 g of prepolymer resin and a thus produced resin,
terminated by a residue of an alpha, beta-ethylenically unsaturated
dicarboxylic acid, is reacted with about 0.5 mole to about 1.5 mole
of a sulfite per mole of alpha, beta-ethylenically unsaturated
dicarboxylic acid residue to produce a sulfonated-terminated
resin.
[0118] Yet another preferred aqueous based polymer is the coating
described in U.S. Pat. No. 5,726,277 (Salsman), incorporated herein
by reference. Specifically, U.S. Pat. No. 5,726,277 describes
coating compositions comprising a reaction product of at least 50%
by weight of waste terephthalate polymer and a mixture of glycols
including an oxyalkylated polyol in the presence of a glycolysis
catalyst wherein the reaction product is further reacted with a
difunctional, organic acid and wherein the weight ratio of acid to
glycols in is the range of6:1 to 1:2.
[0119] While the above examples are provided as preferred aqueous
based polymer coating compositions, other aqueous based polymers
are suitable for use in the products and methods describe herein.
By way of example only, and not meant to be limiting, further
suitable aqueous based compositions are described in U.S. Pat. No.
4,104,222 (Date, et al.), incorporated herein by reference. U.S.
Pat. No. 4,104,222 describes a dispersion of a linear polyester
resin obtained by mixing a linear polyester resin with a higher
alcohol/ethylene oxide addition type surface-active agent, melting
the mixture and dispersing the resulting melt by pouring it into an
aqueous solution of an alkali under stirring Specifically, this
dispersion is obtained by mixing a linear polyester resin with a
surface-active agent of the higher alcohol/ethylene oxide addition
type, melting the mixture, and dispersing the resulting melt by
pouring it into an aqueous solution of an alkanolamine under
stirring at a temperature of 70-95.degree. C., said alkanolamine
being selected from the group consisting of monoethanolamine,
diethanolamine, triethanolamine, monomethylethanolamine,
monoethylethanolamine, diethylethanolamine, propanolamine,
butanolamine, pentanolamine, N-phenylethanolamine, and an
alkanolamine of glycerin, said alkanolamine being present in the
aqueous solution in an amount of 0.2 to 5 weight percent, said
surface-active agent of the higher alcohol/ethylene oxide addition
type being an ethylene oxide addition product of a higher alcohol
having an alkyl group of at least 8 carbon atoms, an
alkyl-substituted phenol or a sorbitan monoacylate and wherein said
surface-active agent has an HLB value of at least 12.
[0120] Likewise, by example, U.S. Pat. No. 4,528,321 (Allen)
discloses a dispersion in a water immiscible liquid of water
soluble or water swellable polymer particles and which has been
made by reverse phase polymerization in the water immiscible liquid
and which includes a non-ionic compound selected from C.sub.4-12
alkylene glycol monoethers, their C.sub.1-4 alkanoates, C.sub.6-12
polyakylene glycol monoethers and their C.sub.1-4 alkanoates.
[0121] The coating materials may be cross-linked to enhance thermal
stability of coatings for hot fill applications. Inner layers may
comprise low-cross linking materials while outer layers may
comprise high crosslinking materials or other suitable
combinations. For example, the inner coating on the PET surface may
utilize non or low cross-linked material, such as the BLOX.RTM.
599-29, and the outer coat may utilize material, such as EXP
12468-4B, capable of cross linking to ensure maximum adhesion to
the PET. Suitable additives capable of cross linking may be added
to the coating layer. Suitable cross linkers can be chosen
depending upon the chemistry and functionality of the resin to
which they are added. For example, amine cross linkers may be
useful for crosslinking resins comprising epoxide groups.
Preferably cross linking additives, if present, are present in an
amount of about 1% to 10% of the coating solution/dispersion,
preferably about 1% to 5%, also including 2%, 3%, 4%, 6%, 7%, 8%,
and 9%.
[0122] In some embodiments, the coating material solutions or
dispersions form foam and/or bubbles which can interfere with the
coating process. One way to avoid this interference, is to add
anti-foam/bubble agents to the coating solution/dispersion.
Suitable anti-foam agents include, but are not limited to, nonionic
surfactants, alkylene oxide based materials, siloxane based
materials, and ionic surfactants. Preferably anti-foam agents, if
present, are present in an amount of about 0.01% to about 0.3% of
the coating solution/dispersion, preferably about 0.01% to about
0.2%, but also including about 0.02%, 0.03%, 0.04%, 0.05%, 0.06%,
0.07%, 0.08%, 0.09%, 0.1%, 0.25%, and ranges encompassing these
amounts.
[0123] An advantage of the present invention is the ability to
handle many types of additives and coatings in an aqueous based
system. This makes the present invention easy to use and economical
as compared to other systems. For example, since the present
invention is aqueous based, there is no need for expensive systems
to handle VOC's used in other systems such as epoxy thermosets. In
addition, most of the solvents can contact human skin without
irritation allowing for ease of use in manufacturing.
F. Preferred Articles
[0124] Generally, preferred articles herein include preforms or
containers having one or more coating layers. The coating layer or
layers preferably provide some functionality such as barrier
protection, UV protection, impact resistance, scuff resistance,
blush resistance, chemical resistance, antimicrobial properties,
and the like. The layers may be applied as multiple layers, each
layer having one or more functional characteristics, or as a single
layer containing one or more functional components. The layers are
applied sequentially with each coating layer being partially or
fully dried/cured prior to the next coating layer being
applied.
[0125] A preferred substrate is a PET preform or container as
described above. However, other substrate materials may also be
utilized. Other suitable substrate materials include, but are not
limited to, polyesters, polypropylene, polyethylene, polycarbonate,
polyamides and acrylics.
[0126] For example, in one multiple layer article, the inner layer
is a primer or base coat having functional properties for enhanced
adhesion to PET, O.sub.2 scavenging, UV resistance and passive
barrier and the one or more outer coatings provide passive barrier
and scuff resistance. In the descriptions herein with regard to
coating layers, inner is taken as being closer to the substrate and
outer is taken as closer to the exterior surface of the container.
Any layers between inner and outer layers are generally described
as "intermediate" or "middle". In other embodiments, multiple
coated articles comprise an inner coating layer comprising an
O.sub.2 scavenger, an intermediate active UV protection layer,
followed by an outer layer of the partially or highly cross-linked
material. In another embodiment, multiple coated preforms comprise
an inner coating layer comprising an O.sub.2 scavenger, an
intermediate CO.sub.2 scavenger layer, an intermediate active UV
protection layer, followed by an outer layer of partially or highly
cross-linked material. These combinations provide a hard increased
cross linked coating that is suitable for carbonated beverages such
as beer. In another embodiment useful for carbonated soft drinks,
the inner coating layer is a UV protection layer followed by an
outer layer of cross linked material. Although the above
embodiments have been described in connection with particular
beverages, they may be used for other purposes and other layer
configurations may be used for the referenced beverages.
[0127] In a related embodiment, the final coating and drying of the
preform provides scuff resistance to the surface of the preform and
finished container in that the solution or dispersion contains
diluted or suspended paraffin or wax, slipping agent, polysilane or
low molecular weight polyethylene to reduce the surface tension of
the container.
G. Methods and Apparatus for Preparation of Coated Articles
[0128] Once suitable coating materials are chosen, the preform is
preferably coated in a manner that promotes adhesion between the
two materials. Although the discussion which follows is in terms of
preforms, such discussion should not be taken as limiting, in that
the methods and apparatus described may be applied or adapted for
containers and other articles. Generally, adherence between coating
materials and the preform substrate increases as the surface
temperature of the preform increases. Therefore it is preferable to
perform coating on a heated preform, although preferred coating
materials will adhere to the preform at room temperature.
[0129] Plastics generally, and PET preforms specifically, have
static electricity that results in the preforms attracting dust and
getting dirty quickly. In a preferred embodiment the preforms are
taken directly from the injection-molding machine and coated,
including while still warm. By coating the preforms immediately
after they are removed from the injection-molding machine, not only
is the dust problem avoided, it is believed that the warm preforms
enhance the coating process. However, the methods also allow for
coating of preforms that are stored prior to coating. Preferably,
the preforms are substantially clean, however cleaning is not
necessary.
[0130] In a preferred embodiment an automated system is used. A
preferred method involves entry of the preform into the system,
dip, spray, or flow coating of the preform, optional removal of
excess material, drying/curing, cooling, and ejection from the
system. The system may also optionally include a recycle step. In
one embodiment the apparatus is a single integrated processing line
that contains two or more dip, flow, or spray coating units and two
or more curing/drying units that produce a preform with multiple
coatings. In another embodiment, the system comprises one or more
coating modules. Each coating module comprises a self-contained
processing line with one or more dip, flow, or spray coating units
and one or more curing/drying units. Depending on the module
configuration, a preform may receive one or more coatings. For
example, one configuration may comprise three coating modules
wherein the preform is transferred from one module to the next, in
another configuration, the same three modules may be in place but
the preform is transferred from the first to the third module
skipping the second. This ability to switch between different
module configurations allows for flexibility. In a further
preferred embodiment either the modular or the integrated systems
may be connected directly to a preform injection-molding machine
and/or a blow-molding machine. The injection molding machine
prepares preforms for use in the present invention.
[0131] The following describes a preferred embodiment of a coating
system that is fully automated. This system is described in terms
of currently preferred materials, but it is understood by one of
ordinary skill in the art that certain parameters will vary
depending on the materials used and the particular physical
structure of the desired end-product preform. This method is
described in terms of producing coated 24 gram preforms having
about 0.05 to about 0.75 total grams of coating material deposited
thereon, including about 0.07, 0.09, 0.10, 0.15, 0.20, 0.25, 0.30,
0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, and 0.70 grams. In the
method described below, the coating solution/dispersion is at a
suitable temperature and viscosity to deposit about 0.06 to about
0.20 grams of coating material per coating layer on a 24 gram
preform, also including about 0.07, 0.08, 0.09, 0.1, 0.11, 0.12,
0.13, 0.14, 0.15, 0.16. 0.17, 0.18, and 0.19 grams per coating
layer on a 24 gram preform. Preferred depostion amounts for
articles of varying sizes may be scaled according to the increase
or decrease in surface area as compared to a 24 gram preform.
Accordingly, articles other than 24 gram preforms may fall outside
of the ranges stated above. Furthermore, in some embodiments, it
may be desired to have a single layer or total coating amount on a
24 gram preform that lies outside of the ranges stated above.
[0132] The apparatus and methods may also be used for other
similarly sized preforms and containers, or may adapted for other
sizes of articles as will be evident to those skilled in the art in
view of the discussion which follows. Currently preferred coating
materials include, TPEs, preferably phenoxy type resins, more
preferably PHAEs, including the BLOX resins noted supra. These
materials and methods are given by way of example only and are not
intended to limit the scope of the invention in any way.
1. ENTRY INTO THE SYSTEM
[0133] The preforms are first brought into the system. An advantage
of one preferred method is that ordinary preforms such as those
normally used by those of skill in the art may be used. For
example, 24 gram monolayer preforms of the type in common use to
make 16 ounce bottles can be used without any alteration prior to
entry into the system. In one embodiment the system is connected
directly to a preform injection molding machine providing warm
preforms to the system. In another embodiment stored preforms are
added to the system by methods well known to those skilled in the
art including those which load preforms into an apparatus for
additional processing. Preferably the stored preforms are
pre-warmed to about 100.degree. F. to about 130.degree. F.,
including about 120.degree. F., prior to entry into the system. The
stored preforms are preferably clean, although cleaning is not
necessary. PET preforms are preferred, however other preform and
container substrates can be used. Other suitable article substrates
include, but are not limited to, various polymers such as
polyesters, polyolefins, including polypropylene and polyethylene,
polycarbonate, polyamides, including nylons, or acrylics.
2. DIP, SPRAY, OR FLOW COATING
[0134] Once a suitable coating material is chosen, it can be
prepared and used for either dip, spray, or flow coating. The
material preparation is essentially the same for dip, spray, and
flow coating. The coating material comprises a solution/dispersion
made from one or more solvents into which the resin of the coating
material is dissolved and/or suspended.
[0135] The temperature of the coating solution/dispersion can have
a drastic effect on the viscosity of the solution/dispersion. As
temperature increases, viscosity decreases and vice versa. In
addition, as viscosity increases the rate of material deposition
also increases. Therefore temperature can be used as a mechanism to
control deposition. In one embodiment using flow coating, the
temperature of the solution/dispersion is maintained in a range
cool enough to minimize curing of the coating material but warm
enough to maintain a suitable viscosity. In one embodiment, the
temperature is about 60.degree. F.-80.degree. F., including about
70.degree. F. In some cases, solutions/dispersions that may be too
viscous to use in spray or flow coating may be used in dip coating.
Similarly, because the coating material may spend less time at an
elevated temperature in spray coating, higher temperatures than
would be recommended for dip or flow coating because of curing
problems may be utilized in spray coating. In any case, a solution
or dispersion may be used at any temperature wherein it exhibits
suitable properties for the application. In preferred embodiments,
a temperature control system is used to ensure constant temperature
of the coating solution/dispersion during the application process.
In certain embodiments, as the viscosity increases, the addition of
water may decrease the viscosity of the solution/dispersion. Other
embodiments may also include a water content monitor and/or a
viscosity monitor that provides a signal when viscosity falls
outside a desired range and/or which automatically adds water or
other solvent to achieve viscosity within a desired range.
[0136] In a preferred embodiment, the solution/dispersion is at a
suitable temperature and viscosity to deposit about 0.06 to about
0.2 grams per coat on a 24 gram preform, also including about 0.07,
0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16. 0.17, 0.18,
and 0.19 grams per coating layer on a 24 gram preform. Preferred
deposition amounts for articles of varying sizes may be scaled
according to the increase or decrease in surface area as compared
to a 24 gram preform. Accordingly, articles other than 24 gram
preforms may fall outside of the ranges stated above. Furthermore,
in some embodiments, it may be desired to have a single layer on a
24 gram preform that lies outside of the ranges stated above.
[0137] In one embodiment, coated preforms produced from dip, spray,
or flow coating are of the type seen in FIG. 3. The coating 22 is
disposed on the body portion 4 of the preform and does not coat the
neck portion 2. The interior of the coated preform 16 is preferably
not coated. In a preferred embodiment this is accomplished through
the use of a holding mechanism comprising an expandable collet or
grip mechanism that is inserted into the preform combined with a
housing surrounding the outside of the neck portion of the preform.
The collet expands thereby holding the preform in place between the
collet and the housing. The housing covers the outside of the neck
including the threading, thereby protecting the inside of the
preform as well as the neck portion from coating.
[0138] In preferred embodiments, coated preforms produced from dip,
spray, or flow coating produce a finished product with
substantially no distinction between layers. Further, in dip and
flow coating procedures, it has been found that the amount of
coating material deposited on the preform decreases slightly with
each successive layer.
a. Dip Coating
[0139] In a preferred embodiment, the coating is applied through a
dip coating process. The preforms are dipped into a tank or other
suitable container that contains the coating material. The dipping
of the preforms into the coating material can be done manually by
the use of a retaining rack or the like, or it may be done by a
fully automated process. Although the apparatus shown in FIG. 14
depicts one embodiment of an automated flow coating unit, in
certain embodiments utilizing automated dip coating, the position
of the flow coater 86 would represent the positioning of the dip
coating tank or other suitable container containing the coating
material.
[0140] In a preferred embodiment, the preforms are rotating while
being dipped into the coating material. The preform preferably
rotates at a speed of about 30 -80 RPM, more preferably about 40
RPM, but also including 50, 60, and 70 RPM. This allows for
thorough coating of the preform. Other speeds may be used, but
preferably not so high as to cause loss of coating material due to
centrifugal forces.
[0141] The preform is preferably dipped for a period of time
sufficient to allow for thorough coverage of the preform.
Generally, this ranges from about 0.25 to about 5 seconds although
times above and below this range are also included. Without wishing
to be bound to any theory, it appears that longer residence time
does not provide any added coating benefit.
[0142] In determining the dipping time and therefore speed, the
turbidity of the coating material should also be considered. If the
speed is too high the coating material may become wavelike and
splatter causing coating defects. Another consideration is that
many coating material solutions or dispersions form foam and/or
bubbles which can interfere with the coating process. To avoid this
interference, the dipping speed is preferably chosen to avoid
excessive agitation of the coating material. If necessary
anti-foam/bubble agents may be added to the coating
solution/dispersion.
b. Spray Coating
[0143] In a preferred embodiment, the coating is applied through a
spray coating process. The preforms are sprayed with a coating
material that is in fluid connection with a tank or other suitable
container that contains the coating material. The spraying of the
preforms with the coating material can be done manually with the
use of a retaining rack or the like, or it may be done by a fully
automated process. Although the apparatus shown in FIG. 14 depicts
one embodiment of an automated flow coating unit, in certain
embodiments utilizing automated spray coating, the position of the
flow coater 86 would represent the positioning of the spray coating
apparatus.
[0144] In a preferred embodiment, the preforms are rotating while
being sprayed with the coating material. The preform preferably
rotates at a speed of about 30 -80 RPM, more preferably about 40
RPM, but also including about 50, 60, and 70 RPM. Preferably, the
preform rotates at least about 360.degree. while proceeding through
the coating spray. This allows for thorough coating of the preform.
The preform may, however, remain stationary while spray is directed
at the preform.
[0145] The preform is preferably sprayed for a period of time
sufficient to allow for thorough coverage of the preform. The
amount of time required for spraying depends upon several factors,
which may include the spraying rate (volume of spray per unit
time), the area encompassed by the spray, and the like.
[0146] The coating material is contained in a tank or other
suitable container in fluid communication with the production line.
Preferably a closed system is used in which unused coating material
is recycled. In one embodiment, this may be accomplished by
collecting any unused coating material in a coating material
collector which is in fluid communication with the coating material
tank. Many coating material solutions or dispersions form foam
and/or bubbles which can interfere with the coating process. To
avoid this interference, the coating material is preferably removed
from the bottom or middle of the tank. Additionally, it is
preferable to decelerate the material flow prior to returning to
the coating tank to further reduce foam and/or bubbles. This can be
done by means known to those of skill in the art. If necessary
anti-foam/bubble agents may be added to the coating
solution/dispersion.
[0147] In determining the spraying time and associated parameters
such as nozzle size and configuration, the properties of the
coating material should also be considered. If the speed is too
high and/or the nozzle size incorrect, the coating material may
splatter causing coating defects. If the speed is too slow or the
nozzle size incorrect, the coating material may be applied in a
manner thicker than desired. Suitable spray apparatus include those
sold by Nordson Corporation (Westlake, Ohio). Another consideration
is that many coating material solutions or dispersions form foam
and/or bubbles which can interfere with the coating process. To
avoid this interference, the spraying speed, nozzle used and fluid
connections are preferably chosen to avoid excessive agitation of
the coating material. If necessary anti-foam/bubble agents may be
added to the coating solution/dispersion.
c. Flow Coating
[0148] In a preferred embodiment, the coating is applied through a
flow coating process. The object of flow coating is to provide a
sheet of material, similar to a falling shower curtain or
waterfall, that the preform passes through for thorough coating.
Advantageously, preferred methods of flow coating allow for a short
residence time of the preform in the coating material. The preform
need only pass through the sheet a period of time sufficient-to
coat the surface of the preform. Without wishing to be bound to any
theory, it appears that longer residence time does not provide any
added coating benefit.
[0149] Referring to FIGS. 14, 15, and 16 there are shown alternate
views of non-limiting diagrams of one embodiment of a preferred
flow coating process. In this embodiment, the top view of a system
comprising a single flow coater 86 is shown. The preform enters the
system 84 and then proceeds to the flow coater 86 wherein the
preform 1 passes through the coating material waterfall (not
illustrated). The coating material proceeds from the tank or vat
150 through the gap 155 in the tank down the angled fluid guide 160
where it forms a waterfall as it passes onto the preforms. Other
embodiments may have fluid guides that are substantially
horizontal. The gap 155 in the tank 150 may be widened or narrowed
to adjust the flow of the material. The material is pumped from the
reservoir (not illustrated) into the vat or tank 150 at a rate that
maintains the coating material level above that of the gap 155.
Advantageously, this configuration ensures a constant flow of
coating material. The excess amount of material also dampens any
fluid fluctuations due to the cycling of the pump.
[0150] In order to provide an even coating the preform is
preferably rotating while it proceeds through the sheet of coating
material. The preform preferably rotates at a speed of about 30 -80
RPM, more preferably about 40 RPM, but also including 50, 60, and
70 RPM. Preferably, the preform rotates at least about two full
rotations or 720.degree. while being proceeding through the sheet
of coating material. In one preferred embodiment, the preform is
rotating and placed at an angle while it proceeds through the
coating material sheet. The angle of the preform is preferably
acute to the plane of the coating material sheet. This
advantageously allows for thorough coating of the preform without
coating the neck portion or inside of the preform. In another
preferred embodiment, the preform 1 as shown in FIG. 16 is
vertical, or perpendicular to the floor, while it proceeds through
the coating material sheet. It has been found that as the coating
material sheet comes into contact with the preform the sheet tends
to creep up the wall of the preform from the initial point of
contact. One of skill in the art can control this creep effect by
adjusting parameters such as the flow rate, coating material
viscosity, and physical placement of the coating sheet material
relative to the preform. For example, as the flow increases the
creep effect may also increase and possibly cause the coating
material to coat more of the preform than is desirable. As another
example, by decreasing the angle of the perform relative to the
coating material sheet, coating thickness may be adjusted to retain
more material at the center or body of the perform as the angle
adjustment decreases the amount of material removed or displaced to
the bottom of the preform by gravity. The ability to manipulate
this creep effect advantageously allows for thorough coating of the
preform without coating the neck portion or inside of the
preform.
[0151] The coating material is contained in a tank or other
suitable container in fluid communication with the production line
in a closed system. It is preferable to recycle any unused coating
material. In one embodiment, this may be accomplished by collecting
the returning waterfall flow stream in a coating material collector
which is in fluid communication with the coating material tank.
Many coating material solutions or dispersions form foam and/or
bubbles which can interfere with the coating process. To avoid this
interference, the coating material is preferably removed from the
bottom or middle of the tank. Additionally, it is preferable to
decelerate the material flow prior to returning to the coating tank
to further reduce foam and/or bubbles. This can be done by means
known to those of skill in the art. If necessary anti-foam/bubble
agents may be added to the coating solution/dispersion.
[0152] In choosing the proper flow rate of coating materials,
several variables should be considered to provide proper sheeting,
including coating material viscosity, flow rate velocity, length
and diameter of the preform, line speed and preform spacing.
[0153] The flow rate velocity determines the accuracy of the sheet
of material. If the flow rate is too fast or too slow, the material
may not accurately coat the preforms. When the flow rate is too
fast, the material may splatter and overshoot the production line
causing incomplete coating of the preform, waste of the coating
material, and increased foam and/or bubble problems. If the flow
rate is too slow the coating material may only partially coat the
preform.
[0154] The length and the diameter of the preform to be coated
should also be considered when choosing a flow rate. The sheet of
material should thoroughly cover the entire preform, therefore flow
rate adjustments may be necessary when the length and diameter of
preforms are changed.
[0155] Another factor to consider is the spacing of the preforms on
the line. As the preforms are run through the sheet of material a
so-called wake effect may be observed. If the next preform passes
through the sheet in the wake of the prior preform it may not
receive a proper coating. Therefore it is important to monitor the
speed and center line of the preforms. The speed of the preforms
will be dependant on the throughput of the specific equipment
used.
3. REMOVAL OF EXCESS MATERIAL
[0156] Advantageously preferred methods provide such efficient
deposition that virtually all of the coating on the preform is
utilized (i.e. there is virtually no excess material to remove).
However there are situations where it is necessary to remove excess
coating material after the preform is coated by dip, spray or flow
methods. Preferably, the rotation speed and gravity will work
together to normalize the sheet on the preform and remove any
excess material. Preferably, preforms are allowed to normalize for
about 5 to about 15 seconds, more preferably about 10 seconds. If
the tank holding the coating material is positioned in a manner
that allows the preform to pass over the tank after coating, the
rotation of the preform and gravity may cause some excess material
to drip off of the preform back into the coating material tank.
This allows the excess material to be recycled without any
additional effort. If the tank is situated in a manner where the
excess material does not drip back into the tank, other suitable
means of catching the excess material and returning it to be
reused, such as a coating material collector or reservoir in fluid
communication with the coating tank or vat, may be employed.
[0157] Where the above methods are impractical due to production
circumstances or insufficient, various methods and apparatus, such
as a drip remover 88, known to those skilled in the art may be used
to remove the excess material. See e.g. FIGS. 14, 15, and 16. For
example, suitable drip removers include one or more of the
following: a wiper, brush, sponge roller, air knife or air flow,
which may be used alone or in conjunction with each other. Further,
any of these methods may be combined with the rotation and gravity
method described above. Preferably any excess material removed by
these methods is recycled for further use.
4. DRYING AND CURING
[0158] After the preform 1 has been coated and any excess material
removed 88, the coated preform is then dried and cured 90. The
drying and curing process is preferably performed by infrared (IR)
heating 90. See FIGS. 14, 15, 17A, and 17B. In one embodiment, a
1000 W quartz IR lamp 200 is used as the source. A preferred source
is a General Electric Q1500 T3/CL Quartzline Tungsten-Halogen lamp.
This particular source and equivalent sources may be purchased
commercially from any of a number of sources including General
Electric and Phillips. The source may be used at full capacity, or
it may be used at partial capacity such as at about 50%, about 65%,
about 75% and the like. Preferred embodiments may use a single lamp
or a combination of multiple lamps. For example, six IR lamps may
be used at 70% capacity.
[0159] Preferred embodiments may also use lamps whose physical
orientation with respect to the preform is adjustable. As shown in
FIGS. 17A and 17B, the lamp position 200 may be adjusted 220 to
position the lamp closer to or farther away from the preform. For
example, in one embodiment with multiple lamps, it may be desirable
to move one or more of the lamps located below the bottom of the
preform closer to the preform. This advantageously allows for
thorough curing of the bottom of the preform. Embodiments with
adjustable lamps may also be used with preforms of varying widths.
For example, if a preform is wider at the top than at the bottom,
the lamps may be positioned closer to the preform at the bottom of
the preform to ensure even curing. The lamps are preferably
oriented so as to provide relatively even illumination of all
surfaces of the coating.
[0160] In other embodiments reflectors are used in combination with
IR lamps to provide thorough curing. In preferred embodiments lamps
200 are positioned on one side of the processing line while one or
more reflectors 210 230 are located on the opposite side of or
below the processing line. This advantageously reflects the lamp
output back onto the preform allowing for a more thorough cure.
More preferably an additional reflector 210 is located below the
preform to reflect heat from the lamps upwards towards the bottom
of the preform. This advantageously allows for thorough curing of
the bottom of the preform. In other preferred embodiments various
combinations of reflectors may be used depending on the
characteristics of the articles and the IR lamps used. More
preferably reflectors are used in combination with the adjustable
IR lamps described above.
[0161] FIG. 17 depicts a view of one non-limiting embodiment of a
preferred IR drying/curing unit. On one side of the processing line
there is shown a series of lamps 200. Below the preforms there is
shown an angled reflector 210 which reflects heat towards the
bottom of the preforms for more thorough curing. Opposite to the
lamps is a semicircular reflector 230 which reflects the IR heat
back onto the preforms allowing for a more thorough and efficient
cure. FIG. 17B is an enlarged section of the lamp which
demonstrates an embodiment where the lamp placement is adjustable
220. The lamps may be moved closer to or farther away from the
preform allowing for maximum drying/curing flexibility.
[0162] In addition, the use of infrared heating allows for the
thermoplastic epoxy (for example PHAE) coating to dry without
overheating the PET substrate and can be used during preform
heating prior to blow molding, thus making for an energy efficient
system. Also, it has been found that use of IR heating can reduce
blushing and improve chemical resistance.
[0163] Although this process may be performed without additional
air, it is preferred that IR heating be combined with forced air.
The air used may be hot, cold, or ambient. The combination of IR
and air curing provides the unique attributes of superior chemical,
blush, and scuff resistance of preferred embodiments. Further,
without wishing to be bound to any particular theory, it is
believed that the coating's chemical resistance is a function of
crosslinking and curing. The more thorough the curing, the greater
the chemical resistance.
[0164] In determining the length of time necessary to thoroughly
dry and cure the coating several factors such as coating material,
thickness of deposition, and preform substrate should be
considered. Different coating materials cure faster or slower than
others. Additionally, as the degree of solids increases, the cure
rate decreases. Generally, for IR curing, 24 gram preforms with
about 0.05 to about 0.75 grams of coating material the curing time
is about 5 to 60 seconds, although times above and below this range
may also be used.
[0165] Another factor to consider is the surface temperature of the
preform as it relates to the glass transition temperature (T.sub.g)
of the substrate and coating materials. Preferably the surface
temperature of the coating exceeds the T.sub.g of the coating
materials without heating the substrate above the substrate T.sub.g
during the curing/drying process. This provides the desired film
formation and/or crosslinking without distorting the preform shape
due to overheating the substrate. For example, where the coating
material has a higher T.sub.g than the preform substrate material,
the preform surface is preferably heated to a temperature above the
T.sub.g of the coating while keeping the substrate temperature at
or below the substrate T.sub.g. One way of regulating the
drying/curing process to achieve this balance is to combine IR
heating and air cooling, although other methods may also be
used.
[0166] An advantage of using air in addition to IR heating is that
the air regulates the surface temperature of the preform thereby
allowing flexibility in controlling the penetration of the radiant
heat. If a particular embodiment requires a slower cure rate or a
deeper IR penetration, this can be controlled with air alone, time
spent in the IR unit, or the IR lamp frequency. These may be used
alone or in combination.
[0167] Preferably, the preform rotates while proceeding through the
IR heater. The preform preferably rotates at a speed of about 30
-80 RPM, more preferably about 40 RPM. If the rotation speed is too
high, the coating will spatter causing uneven coating of the
preform. If the rotation speed is too low, the preform dries
unevenly. More preferably, the preform rotates at least about
360.degree. while proceeding through the IR heater. This
advantageously allows for thorough curing and drying.
[0168] In other preferred embodiments, Electron Beam Processing may
be employed in lieu of IR heating or other methods. Electron Beam
Processing (EBP) has not been used for curing of polymers used for
and in conjunction with injection molded performs and containers
primarily due to its large size and relatively high cost. However
recent advances in this technology, are expected to give rise to
smaller less expensive machines. EBP accelerators are typically
described in terms of their energy and power. For example, for
curing and crosslinking of food film coatings, accelerators with
energies of 150-500 keV are typically used.
[0169] EBP polymerization is a process in which several individual
groups of molecules combine together to form one large group
(polymer). When a substrate or coating is exposed to highly
accelerated electrons, a reaction occurs in which the chemical
bonds in the material are broken and a new, modified molecular
structure is formed. This polymerization causes significant
physical changes in the product, and may result in desirable
characteristics such as high gloss and abrasion resistance. EBP can
be a very efficient way to initiate the polymerization process in
many materials.
[0170] Similar to EBP polymerization, EBP crosslinking is a
chemical reaction, which alters and enhances the physical
characteristics of the material being treated. It is the process by
which an interconnected network of chemical bonds or links develop
between large polymer chains to form a stronger molecular
structure. EBP may be used to improve thermal, chemical, barrier,
impact, wear and other properties of inexpensive commodity
thermoplastics. EBP of crosslinkable plastics can yield materials
with improved dimensional stability, reduced stress cracking,
higher set temperatures, reduced solvent and water permeability and
improved thermomechanical properties.
[0171] The effect of the ionizing radiation on polymeric material
is manifested in one of three ways: (1) those that are molecular
weight-increasing in nature (crosslinking); (2) those that are
molecular weight-reducing in nature (scissioning); or (3), in the
case of radiation resistant polymers, those in which no significant
change in molecular weight is observed. Certain polymers may
undergo a combination of (1) and (2). During irradiation, chain
scissioning occurs simultaneously and competitively with
crosslinking, the final result being determined by the ratio of the
yields of these reactions. Polymers containing a hydrogen atom at
each carbon atom predominantly undergo crosslinking, while for
those polymers containing quaternary carbon atoms and polymers of
the --CX.sub.2--CX.sub.2-- type (when X=halogen), chain scissioning
predominates. Aromatic polystyrene and polycarbonate are relatively
resistant to EBP.
[0172] For polyvinylchloride, polypropylene and PET, both
directions of transformation are possible; certain conditions exist
for the predominance of each one. The ratio of crosslinking to
scissioning may depend on several factors, including total
irradiation dose, dose rate, the presence of oxygen, stabilizers,
radical scavengers, and/or hindrances derived from structural
crystalline forces.
[0173] Overall property effects of crosslinking can be conflicting
and contrary, especially in copolymers and blends. For example,
after EBP, highly crystalline polymers like HDPE may not show
significant change in tensile strength, a property derived from the
crystalline structure, but may demonstrate a significant
improvement in properties associated with the behavior of the
amorphous structure, such as impact and stress crack
resistance.
[0174] Aromatic polyamides (Nylons) are considerably responsive to
ionizing radiation. After exposure the tensile strength of aromatic
polyamides does not improve, but for a blend of aromatic polyamides
with linear aliphatic polyamides, an increase in tensile strength
is derived together with a substantial decrease in elongation.
[0175] EBP may be used as an alternative to IR for more precise and
rapid curing of TPE coatings applied to preforms and
containers.
[0176] It is believed that when used in conjunction with dip,
spray, or flow coating, EBP may have the potential to provide lower
cost, improved speed and/or improved control of crosslinking when
compared to IR curing. EBP may also be beneficial in that the
changes it brings about occur in solid state as opposed to
alternative chemical and thermal reactions carried out with melted
polymer.
[0177] In other preferred embodiments, gas heaters, UV radiation,
and flame may be employed in addition to or in lieu of IR or EPB
curing. Preferably the drying/curing unit is placed at a sufficient
distance or isolated from the coating material tank and/or the flow
coating sheet as to avoid unwanted curing of unused coating
material.
5. COOLING
[0178] The preform is then cooled. The cooling process combines
with the curing process to provide enhanced chemical, blush and
scuff resistance. It is believed that this is due to the removal of
solvents and volatiles after a single coating and between
sequential coatings.
[0179] In one embodiment the cooling process occurs at ambient
temperature. In another embodiment, the cooling process is
accelerated by the use of forced ambient or cool air.
[0180] There are several factors to consider during the cooling
process. It is preferable that the surface temperature of the
preform is below the T.sub.g of the lower of the T.sub.g of the
preform substrate or coating. For example, some coating materials
have a lower T.sub.g than the preform substrate material, in this
example the preform should be cooled to a temperature below the
T.sub.g of the coating. Where the preform substrate has the lower
T.sub.g the preform should be cooled below the T.sub.g of the
preform substrate.
[0181] Cooling time is also affected by where in the process the
cooling occurs. In a preferred embodiment multiple coatings are
applied to each preform. When the cooling step is prior to a
subsequent coating, cooling times may be reduced as elevated
preform temperature is believed to enhance the coating process.
Although cooling times vary, they are generally about 5 to 40
seconds for 24 gram preforms with about 0.05 to about 0.75 grams of
coating material.
6. EJECTION FROM SYSTEM
[0182] In one embodiment, once the preform has cooled it will be
ejected from the system and prepared for packaging. In another
embodiment the preform will be ejected from the coating system and
sent to a blow-molding machine for further processing. In yet
another embodiment, the coated preform is handed off to another
coating module where a further coat or coats are applied. This
further system may or may not be connected to further coating
modules or a blow molding-machine.
7. RECYCLE
[0183] Advantageously, bottles made by, or resulting from, a
preferred process described above may be easily recycled. Using
current recycling processes, the coating can be easily removed from
the recovered PET. For example, a polyhydroxyaminoether based
coating applied by dip coating and cured by IR heating can be
removed in 30 seconds when exposed to an 80.degree. C. aqueous
solution with a pH of 12. Additionally, aqueous solutions with a pH
equal to or lower than 4 can be used to remove the coating.
Variations in acid salts made from the polyhydroxyaminoethers may
change the conditions needed for coating removal. For example, the
acid salt resulting from the acetic solution of a
polyhydroxyaminoether resin can be removed with the use of an
80.degree. C. aqueous solution at a neutral pH. Alternatively, the
recycle methods set forth in U.S. Pat. No. 6,528,546, entitled
Recycling of Articles Comprising Hydroxy-phenoxyether Polymers, may
also be used. The methods disclosed in this application are herein
incorporated by reference.
8. EXAMPLE
[0184] A lab scale flow coating system was used to coat 24 gram PET
preforms. A system, as illustrated in FIGS. 14 through 16 was used,
and comprised a single flow coating unit with an IR curing/drying
unit. The preforms were manually loaded onto the processing line.
The collets used to hold the 24 gram preforms were spaced 1.5" on
center from each other. It was found that this distance provided
the proper spacing to avoid any wake effect while the preforms
passed through the coating waterfall or sheet. The coating material
was pumped into a tank using a non-shearing pump. The coating
material then flowed out of the tank forming a waterfall or sheet
that coated the preforms as they passed through the sheet. The
preforms moved along the line at a rate of three inches per second
in order to ensure two full rotations while passing through the
coating sheet. Once through the sheet the line speed allowed the
preforms to drip for approximately 10 seconds before passing over a
sponge roller to remove an excess coating material from the bottom
of the preform. The preforms then moved into the IR curing/drying
unit. Five 1000 W General Electric Q1500 T3/CL Quartzline
Tungsten-Halogen lamps at 60% capacity were used as the source. The
lamps were positioned at 0.6 inches on the centerline. The preforms
remained in the IR curing/drying unit for about 10 seconds. As the
preforms moved out of the curing/drying unit they were cooled for
about 10 seconds with forced ambient air before being removed from
the system.
[0185] The coating material used in this example was a PHAE
dispersion, BLOX.RTM. XUR 588-29 (from The Dow Chemical Company),
having 30% solids. The average deposition (single layer on a 24
gram preform) was about 97 mg.
[0186] The various methods and techniques described above provide a
number of ways to carry out the invention. Of course, it is to be
understood that not necessarily all objectives or advantages
described may be achieved in accordance with any particular
embodiment described herein.
[0187] Furthermore, the skilled artisan will recognize the
interchangeability of various features from different embodiments.
Similarly, the various features and steps discussed above, as well
as other known equivalents for each such feature or step, can be
mixed and matched by one of ordinary skill in this art to perform
methods in accordance with principles described herein.
[0188] Although the invention has been disclosed in the context of
certain nd examples, it will be understood by those skilled in the
art that the invention the specifically disclosed embodiments to
other alternative embodiments obvious modifications and equivalents
thereof. Accordingly, the invention is be limited by the specific
disclosures of preferred embodiments herein.
* * * * *