U.S. patent application number 09/852623 was filed with the patent office on 2001-09-27 for method of producing aqueous dispersions as a base for hot sealing adhesives.
This patent application is currently assigned to ROEHM GMBH CHEMISCHE FABRIK. Invention is credited to Elser, Wilhelm, Foelsch, Karl, Scheuermann, Hubert, Tessmer, Dieter, Wicke, Michael.
Application Number | 20010025077 09/852623 |
Document ID | / |
Family ID | 26034432 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010025077 |
Kind Code |
A1 |
Scheuermann, Hubert ; et
al. |
September 27, 2001 |
Method of producing aqueous dispersions as a base for hot sealing
adhesives
Abstract
Poly(meth)acrylate dispersions, comprised of: (A) 50-90 wt. %
methacrylic acid esters; (B) 5-30 wt. % acrylic acid alkyl esters
[lit., "acrylic acid acrylic esters"]; (C) 2-10 wt. % of another
functionalized monomer; (D) 2-10 wt. % of a radically polymerizable
carboxylic acid or a polycarboxylic acid or a partially esterified
polycarboxylic acid; and (E) 0-40 wt. % of a monomer which is
copolymerizable with components (A) to (D).
Inventors: |
Scheuermann, Hubert; (Marl,
DE) ; Tessmer, Dieter; (Darmstadt, DE) ;
Foelsch, Karl; (Mainz, DE) ; Elser, Wilhelm;
(Riedlingen, DE) ; Wicke, Michael;
(Seeheim-Jugenheim, DE) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
ROEHM GMBH CHEMISCHE FABRIK
Kirschenallee
Darmstadt
DE
D-64275
|
Family ID: |
26034432 |
Appl. No.: |
09/852623 |
Filed: |
May 11, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09852623 |
May 11, 2001 |
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09685594 |
Oct 11, 2000 |
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09685594 |
Oct 11, 2000 |
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09033607 |
Mar 3, 1998 |
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6194514 |
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Current U.S.
Class: |
524/458 ;
428/520; 524/558; 524/561; 524/833 |
Current CPC
Class: |
Y10T 428/31699 20150401;
C08F 265/06 20130101; Y10T 428/31928 20150401; Y10S 525/902
20130101; C08F 265/06 20130101; C09J 151/003 20130101; C08F 2/22
20130101 |
Class at
Publication: |
524/458 ;
524/833; 524/558; 524/561; 428/520 |
International
Class: |
C08F 265/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 1997 |
DE |
197 08 412.5 |
Feb 6, 1998 |
DE |
198 04 613.8 |
Claims
1. Aqueous poly(meth)acrylate dispersions, comprising: a
particulate poly(meth)acrylate comprising the following components:
(A) 50-90 wt. % of methacrylic acid alkyl esters; (B) 5-30 wt. % of
an acrylic acid alkyl ester having a glass transition temperature
Tg in the range c. -20 to 50.degree. C. and having formula I:
4wherein R.sub.1 represents an alkyl, aryl, or alkaryl group having
2-10 C atoms; (C) 2-10 wt. % of a functionalized monomer of formula
II: 5wherein R.sub.2 represents hydrogen or methyl; and R.sub.3
represents a glycidyl group 6or an alkyl group which has 2-6 C
atoms and is substituted with at least one hydroxyl group; (D) 2-10
wt. % of at least one radically polymerizable carboxylic acid or a
polycarboxylic acid or a partially esterified polycarboxylic acid;
and (E) 0-40 wt. % of other monomers which are copolymerizable with
(A) to (D); wherewith, in the process of preparation, a first
polymerization stage (Process Step 1) is conducted with monomers of
groups (A) to (C) and optionally (E), and in a second
polymerization stage (Process Step 2), monomers of groups (A), (B),
(D), and optionally (E) are copolymerized; and wherewith the sum of
the amounts of monomers (A) to (E) is 100 wt. %.
2. The aqueous poly(meth)acrylate dispersion of claim 1, wherein
the monomer of formula I is n-butyl acrylate.
3. The aqueous poly(meth)acrylate dispersion of claim 1, wherein
the monomer of formula II is glycidyl (meth)acrylate, or
hydroxyethyl (meth)acrylate.
4. The aqueous poly(meth)acrylate dispersion of claim 1, wherein
the monomer(s) of group (E) is(are) styrene,
(C.sub.1-C.sub.4)-alkylstyrene or cycloalkyl (meth)acrylate.
5. Aqueous poly(meth)acrylate dispersions, comprising: a
particulate poly(meth)acrylate comprising the following components:
(A) 60-80 wt. % of methacrylic acid alkyl esters; and (B) 10-20 wt.
% of an acrylic acid alkyl ester having a glass transition
temperature Tg in the range of about -20 to 50.degree. C., of
formula I: 7where R1 represents an alkyl, aryl, or alkaryl group
having 2-10 C atoms; and (C) 3-10 wt. % of a functionalized monomer
of formula II: 8where R2 represents hydrogen or methyl, and R3
represents a glycidyl group 9or an alkyl group which has 2-6 C
atoms and is substituted with at least one hydroxyl group; and (D)
3-10 wt. % of at least one radically polymerizable carboxylic acid
or a polycarboxylic acid or a partially esterified polycarboxylic
acid; and (E) 0-40 wt. % of other monomers which are
copolymerizable with (A) to (D); wherewith, in the process of
preparation,a first polymerization stage (Process Step 1) is
conducted of monomers of groups (A) to (C) and optionally (E), and
in the second polymerization stage (Process Step 2), monomers of
groups (A), (B), (D), and optionally (E) are copolymerized; and
wherewith the sum of the amounts of monomers (A) to (E) is 100 wt.
%.
6. The aqueous poly(meth)acrylate dispersion of claim 5, wherein
the monomer of formula I is n-butyl acrylate.
7. The aqueous poly(meth)acrylate dispersion of claim 5, wherein
the monomer of formula II is glycidyl (meth)acrylate, or
hydroxyethyl (meth)acrylate.
8. The aqueous poly(meth)acrylate dispersion of claim 5, wherein
the monomer(s) of group (E) is(are) styrene,
(C.sub.1-C.sub.4)-alkylstyrene or cycloalkyl (meth)acrylate.
9. A hot-sealable coated substrate prepared by a process,
comprising: applying the poly(meth)acrylate dispersion of claim 1
to a substrate comprising metal or plastic as a primer layer, which
is then dried; and applying, on said dried primer layer, a second
layer comprised of an aqueous poly(meth)acrylate dispersion
comprised of: (i) at least 70 wt. % of at least one
C.sub.1-C.sub.4-alkyl ester of methacrylic acid; and (ii) an
appreciable amount of acrylamide, methacrylamide, aminoalkyl
acrylate, aminoalkyl methacrylate or combinations thereof, which
applied second layer is then dried.
10. The process of claim 9, wherein, in the first stage, the extent
of monomer polymerization is 60.+-.20 wt %
11. The process of claim 9, wherein, in the first stage, the extent
of polymerization of monomer of formula I in the monomers
polymerized is 30.+-.10 wt %.
12. The process of claim 9, wherein, in the first stage, the extent
of polymerization of monomer of formula II in the monomers
polymerized is about 10.+-.5 wt %.
13. A method of preparing the polymer dispersion of claim 1,
comprising, in a two-stage process: copolymerizing monomers of
groups (A) to (C) and optionally (E) in the first stage, and in the
second process stage, copolymerizing monomers of groups (A), (B),
(D), and optionally (E).
14. The process of claim 13, wherein, in the first stage, the
extent of monomer polymerization is 60.+-.20 wt %
15. The process of claim 13, wherein, in the first stage, the
extent of polymerization of monomer of formula I in the monomers
polymerized is 30.+-.10 wt %.
16. The process of claim 13, wherein, in the first stage, the
extent of polymerization of monomer of formula II in the monomers
polymerized is about 10.+-.5 wt %.
17. The method according to claim 13; wherein the ratio of the
amount in the first polymerization stage to the amount of the
second polymerization stage ranges from 30:70 to 70:30 parts by
weight.
18. A method of priming metal surfaces, comprising: applying the
aqueous polymer dispersion according to claim 1 on the surfaces of
metals.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to aqueous dispersions based
on poly(meth) acrylates, produced in a multi-state emulsion
polymerization process, and to the use of such dispersions to
prepare adhesives (bonding compositions) which are susceptible to
hot-sealing.
[0003] 2. Description of the Background
[0004] In the past, hot-sealing compositions have been devised for
the packaging industry, which compositions fully meet the
applicable technical criteria, but which contain substantial
amounts of organic solvents. E.g., Eur. Pat. 129,178 describes a
hot-sealable coating composition comprised of a film-forming
dispersion of at least two different polymer types with different
adhesion properties in an organic solvent system, wherewith the
dispersion contains polymers of the two types and in addition
contains a polymer comprised of units corresponding to the two
polymer types. Vinylidene chloride polymers have also been used
widely in the past as hot-sealable compositions.
[0005] Coating compositions for sealing metal substrates are of
particular practical and economic importance; in particular,
compositions for providing seals between aluminum and plastics such
as polystyrene, polypropylene, and polyvinyl chloride, or between
aluminum and glass. (See Ullmanns Enzyklopaedie der techn. Chemie,
6th Ed., 1985 ff., Vol 16, pub. Verlag Chemie, pp. 101-103.)
[0006] Ger. Pat 4,209,651 (to BASF AG) describes an aqueous
dispersion containing a copolymer A in the presence of which a
polymerization is carried out to produce a copolymer B. Copolymer A
is produced by bulk polymerization, and is not a core-and-shell
product. The product materials are used in sealing PVC to paper
board.
[0007] Jap. Pat. 08-231729 A (Derwent No. 96-461419/46). The
products comprise core-and-shell polymers produced by emulsion
polymerization followed by spray drying. The shell has larger
amounts of carboxyl-group-containing monomers which improve the
re-dispersibility of the product in water.
[0008] Rising awareness of environmental issues has created a trend
away from solvent-containing formulations and toward aqueous
dispersions such that when, e.g., a coating or adhesive is applied
to a surface, organic compounds are not emitted into the
environment. Also significant is the trend away from
chlorine-containing products, and, perhaps to a lesser extent,
aromatic compounds.
[0009] Technology has been able to adjust, to some extent, to these
more stringent requirements. Thus, as disclosed in Ger. 29 06 118,
polymers of vinylidene chloride, used as hot sealing adhesives, may
be applied in the form of aqueous dispersions. In order to improve
adhesion to un-primed plastic and metal sheets, special "anchoring
agents" may be added to the composition. Suitable such additives
are water-soluble polymers of functionally substituted acrylamides
and/or methacrylamides, or copolymers of these monomers with
acrylamide and/or methacrylamide, which (co)polymers are present as
species dissolved in the aqueous phase of the dispersion.
[0010] Two methods of coating of aluminum foils and sheets are in
widespread use:
[0011] In the case of relatively aggressive filler materials, first
a primer coat of about 2 microns in thickness is applied to the
aluminum foil. This primer is comprised of a
vinyl-chloride-containing solution polymer. A finish coating
comprised of a methacrylate resin of 4-8 micron thickness is then
provided over the primer coat.
[0012] For cases of less aggressive filler materials, a single-coat
system is used, employing a hot-sealable coating of thickness of
about 5-10 microns comprising a mixture of the abovementioned
polymers.
[0013] Still unsolved is the problem of providing a
non-chlorinated, hot-sealing adhesive in the form of an aqueous
dispersion with adequate adhesion. Ger. 27 27 914 (U.S. Pat. No.
4,291,090) and Ger. 28 55 147 disclose hot-sealing adhesives based
on polyacrylate which can be applied as aqueous dispersions. In
some cases, these adhesives are not comprised exclusively of esters
of (meth)acrylic acid. That is, they may contain one or more
comonomers, employed, e.g., for the purpose of modifying the
melting temperature, hardness, or adhesion properties of the
adhesive. Suitable comonomers include, inter alia,
(meth)acrylamide, and aminoalkyl esters of acrylic acid and/or of
methacrylic acid. The specific effects which these comonomers have
on the properties of the polymers is not disclosed.
[0014] Ger. 39 30 743 (Can. Pat. App. 2,025,368.1) describes an
aqueous polyacrylate dispersion, which is useful as a hot-sealing
adhesive, based on at least 70 wt. % of a polyacrylate comprised of
units of lower alkyl methacrylates and also containing polymerized
(meth)acrylamide or aminoalkyl (meth)acrylate. Other publications
relate to aqueous dispersions of copolymers of olefins and/or vinyl
acetate, which copolymers contain units of chlorinated monomers and
are produced in a single-stage process. The described dispersions
exhibit poor adhesion to aluminum substrates.
[0015] Polymer dispersions, which are prepared from polymer
particles having a core-and-shell structure, which are described in
the literature, either contain chlorinated monomers or are not
suitable for bonding plastics to aluminum.
[0016] Eur. Pat. 574,803 describes aqueous polymer dispersions of
5-80 wt. % of a copolymer (A), having a glass transition
temperature of 50-150.degree. C., and 95-20 wt. % of a copolymer
(B), having a glass transition temperature of -50 to +50.degree.
C., the two copolymers in the composition havingwith a temperature
difference of 20.degree. C. There is no specific indication in this
publication that the proposed products are suitable for bonding
plastics to aluminum.
[0017] Further, no appropriate two-coat methods are described in
the cited state of the art references.
[0018] A two-coat coating is proposed in Jap. Pat. App. 54-161,684
(Chem.Abstr. 92:199427x). First, an aluminum foil is coated with
the aqueous dispersion of a monomer and then with a mixture of an
ethylene-vinyl acetate copolymer, colophony, and wax, to a
thickness of 20 microns.
[0019] In connection with the object of formulating chlorine-free
aqueous polymer dispersions for use as hot-sealing adhesives,
another problem exists which is the problem of compatibility with
the state of the art apparatus employed. This problem is
particularly significant in the large-scale coating of aluminum
foils and sheets. In particular, one should be able to use
customary methods of applying polymers as thin films (see Polymer
Handbook, 2nd Ed., pub. Hanser Verlag), and the films employed
should not be sticky at ordinary temperatures.
[0020] A requirement imposed on means of hot sealing an adhesive to
a suitable substrate is that good adhesion for bonding the two
materials (e.g. aluminum and polystyrene) must be achieved in a
short time and at temperatures which are not excessive and which
are about, e.g., 180-220.degree. C.
[0021] The proposed packaging methods are also intended for used
with foodstuffs. In such applications, the monomers and the
adjuvants must be selected such that the regulations governing food
packaging (German Federal Health Office guidelines BGA 14, and the
corresponding US FDA guidelines) are complied with.
[0022] In Ger. 39 30 743 an aqueous dispersion is proposed which
has adequate adhesion to an aluminum foil substrate coated with a
vinyl chloride copolymer as a primer. Efforts to modify such
dispersions by incorporating units of adhesion-promoting monomers
in order to provide a variant which can be applied to un-primed
aluminum have not been successful. Thus the reference does not
provide a solution to the problem of replacing chlorinated primers.
Other efforts using similar approaches, using polymers with simple
particle structures, have not been successful.
SUMMARY OF THE INVENTION
[0023] Accordingly, one object of the present invention is to
provide an aqueous polymer dispersion of improved hot-sealing and
adhesion characteristics to plastic and metal substrates.
[0024] Another object of the present invention is to provide
aqueous poly(meth) acrylate dispersions PD, which are produced by
emulsion polymerization and which have at least a two-stage
particle structure, for use as hot-sealing adhesives.
[0025] Briefly, these objects and other objects of the present
invention as hereinafter will become more readily apparent can be
attained by aqueous poly(meth)acrylate dispersions, comprising:
[0026] a particulate poly(meth)acrylate comprising the following
components:
[0027] (A) 50-90 wt. % of methacrylic acid alkyl esters;
[0028] (B) 5-30 wt. % of an acrylic acid alkyl ester having a glass
transition temperature Tg in the range c. -20 to 50.degree. C. and
having formula I: 1
[0029] wherein R.sub.1 represents an alkyl, aryl, or alkaryl group
having 2-10 C atoms;
[0030] (C) 2-10 wt. % of a functionalized monomer of formula II:
2
[0031] wherein R.sub.2 represents hydrogen or methyl; and R.sub.3
represents a glycidyl group 3
[0032] or an alkyl group which has 2-6 C atoms and is substituted
with at least one hydroxyl group;
[0033] (D) 2-10 wt. % of at least one radically polymerizable
carboxylic acid or a polycarboxylic acid or a partially esterified
polycarboxylic acid; and
[0034] (E) 0-40 wt. % of other monomers which are copolymerizable
with (A) to (D); wherewith, in the process of preparation, a first
polymerization stage (Process Step 1) is conducted with monomers of
groups (A) to (C) and optionally (E), and in a second
polymerization stage (Process Step 2), monomers of groups (A), (B),
(D), and optionally (E) are copolymerized; and wherewith the sum of
the amounts of monomers (A) to (E) is 100 wt. %.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] The sum of the percentages of monomer units from groups (A)
to (E) is 100 wt. %. The preferred monomer of formula I is n-butyl
acrylate. Preferred monomers of formula II include glycidyl
(meth)acrylate and hydroxyethyl (meth)acrylate.
[0036] Suitable monomers for group (E) monomers include styrene,
(C.sub.1to C.sub.4)-alkylstyrene compounds, cycloalkyl
(meth)acrylates, and the like. Data on glass transition
temperatures TG may be found in, e.g., Kirk and Othmer, 1978,
"Encyclopedia of Chemical Technology", 3rd Ed., pub. J. Wiley, Vol.
1, pp. 387-389.
[0037] The ratio of the materials in the first polymerization stage
to the masterials in the second polymerization stage ranges from
30:70 to 70:30 parts by weight (pbw). A recommended rule for the
proportioning of the polymerization stages is that the amounts
should not differ by more than a factor of 2.5.
[0038] Additional preferred embodiments of the reaction include the
following:
[0039] (i) The methacrylate content of the monomers polymerized in
the first stage should be about 60.+-.20 wt. %.
[0040] (ii) The content of monomers of formula I in the monomers
polymerized in the first stage should be about 30.+-.10 wt. %.
[0041] (iii) The content of monomers of formula II in the monomers
polymerized in the first stage should be about 10.+-.5 wt. %.
[0042] (iv) The remainder of the monomers to complete 100 wt. % of
the monomers in the first stage is the monomer of group (E).
[0043] Still further preferences include:
[0044] (i) The content of methyl methacrylate and/or monomers of
group (E) in the monomers polymerized in the second stage should be
c. 20.+-.10 wt. %.
[0045] (ii) The content of (meth)acrylic acid in the monomers
polymerized in the second stage should be about 12.+-.8 wt. %.
[0046] For each stage of polymerization, the sum of the percentages
of all the monomers is 100 wt. %.
[0047] The molecular weights of the poly(meth)acrylates in the
dispersion PD are generally in the range >20,000 g/mol. The
polymer content of the dispersions is generally in the range 20-65
wt. %; and the particle sizes are generally in the range 60-250 nm,
preferably 80-160 nm, particularly preferably 100-140 nm
(determined by photon correlation spectroscopy).
[0048] The poly(meth)acrylate dispersion PD of the invention is
produced by emulsion polymerization in the aqueous phase in the
presence of anionic, cationic, or nonionic emulsifiers, which
emulsifiers are per se known, and in the presence of at least one
radical-forming initiator, in a two-stage reaction (see
Rauch-Puntigam, H., and Voelker, Th., 1967, "Acryl- und
Methacrylverbindungen", pub. Springer-Verlag, pp. 217-230).
[0049] It should be noted that certain advantageous properties,
e.g. resistance to peeling, as specified in food packaging
regulations (BGA 14 guidelines, and the corresponding US FDA
guidelines), can be achieved with the use of additives.
[0050] The first stage may be conducted as a controlled-feed
process: A suitable reaction vessel equipped with a stirrer and
heater is initially charged with deionized water and emulsifier(s).
Subsequently, after a certain temperature is reached, the initiator
preferably dissolved in water, is added. The initiator may be,
e.g., an inorganic peroxide such as potassium peroxydisulfate (KPS)
or ammonium peroxydisulfate (APS). It is recommended that the
content of initiator in the mixture at this point be in the
neighborhood of 0.8 wt. %, based on the weight of the monomers
reacted in Process Step 1.
[0051] Suitable ionic emulsifiers, which are used in amounts of
0.01-2.0 wt. %, based on the total weight of monomers, include
anionic emulsifiers such as Aerosol OT75(R) of Cyanamid BV and
"Dowfax 2A1" of Dow Europa SA.
[0052] The addition of the above-described mixture for Process Step
1 is a controlled feed over a prescribed period of time, e.g. 2 hr,
in the first stage. As an example, the feed mixture for Process
Step 1 may comprise 20-60 wt. % of the total water to be used, plus
the monomers of groups (A) to (C) and optionally (E).
[0053] Advantageously, the mixture is then mixed for an additional
period of time, e.g. 1 hr, at elevated temperature, e.g. 80.degree.
C., following which it is allowed to cool, e.g. to 30.degree. C.
The monomers described above in connection with "Process Step 2"
are then added dropwise over a relatively short period of time,
e.g. 30 min, and the mixture is then allowed to stand for an
appreciable period of time, e.g. 4 hr.
[0054] The resulting aqueous monomer/polymer mixture is then heated
slightly, e.g. to 40.degree. C., and additional radical initiator,
preferably a redox-type initiator, e.g. comprised of
peroxydisulfate, dithionite, and iron(II) sulfate, is added in
water, and further polymerization is initiated.
[0055] After the maximum temperature is reached, advantageously the
temperature is controlled, e.g. at 80.degree. C., and the mixture
is stirred for an additional period, e.g. 2 hr, to complete the
polymerization.
[0056] Alternatively, the second stage can be carried out as
another controlled-feed "semicontinuous" step, with addition of a
monomer emulsion gradually over a period of, e.g., 2 hr.
[0057] The mixture is cooled to about 30.degree. C., and
advantageously a suitable preservative is added, e.g. Acticid
SPX(R) of Thor Chemie GmbH, along with a small amount of ammonia
(as 25% ammonia in water).
[0058] One may also add 0-5% of nonionic emulsifiers, e.g.
ethoxylated alcohols, or methacrylate esters of methoxypolyethylene
glycols, e.g. "Carbowax 550", or alkylphenols, and also an
additional amount of an anionic emulsifier.
[0059] As a rule, the polymer dispersion (PD) may be used directly
for coating. In certain cases limited amounts of thickeners or
film-forming agents may be employed. The coating may be applied by
spraying, brushing, pouring, dipping, blade-coating, or
roll-coating. Generally the coating is applied in a thickness such
that the dried coating has a thickness such that the dried coating
layer is 2-10 microns thick.
[0060] Advantageously, the coated articles are dried in a drying
oven or by continuously conveying the coated articles through a
drying tunnel, possibly at reduced pressure and at temperatures in
the range 100-200.degree. C.
[0061] In general, the higher the drying temperature, the shorter
the drying time. Drying times are, e.g., in the range 5 sec to 5
min. It is possible to apply the coating in multiple coats.
Preferably, the substrate to which the polymer dispersion (PD) is
applied has a non-porous and continuous ("closed") surface, e.g.
the surface of a plastic film or sheet, or particularly of a metal
foil or sheet, e.g. aluminum foil or iron.
[0062] As stated above, one advantage of using the present
poly(meth)acrylate dispersions (PD) as hot-sealing adhesives is
that they solve the important and urgent problem of formulating a
hot-sealable composition based on an aqueous acrylate dispersion,
e.g. the type of dispersion disclosed in Ger. 39 30 74, which
composition adheres strongly to substrates, particularly metal
foils or sheets, and in particular aluminum foils or sheets.
[0063] Accordingly, the principal embodiment of the present
invention is hot-sealable coated substrates, particularly of metal
or plastic, coated with the present poly(meth)acrylate
dispersion(s) (PD) as a primer layer, with a second layer applied
over the primer layer comprised of an aqueous poly(meth)acrylate
dispersion comprised of:
[0064] at least 70 wt. % of at least one C.sub.1-C.sub.4-alkyl
ester of (meth)acrylic acid; and
[0065] an appreciable amount of (meth)acrylamide and/or aminoalkyl
(meth)acrylate; wherewith the second layer is applied over the
dried primer layer, and then dried.
[0066] For details beyond those provided in the example embodiments
described below reference is made to the disclosure of Ger. 39 30
743. A representative such dispersion and the means of its
application are described hereinbelow (see Part II of the Example
section).
[0067] In hot-sealing, the temperature in the coating must exceed
the glass transition temperature of the poly(meth) acrylate. The
temperature of the hot contact members which effect the sealing
must exceed the required sealing temperature by an amount which
increases as the contact time is decreased and as the heat
conduction through the substrate layer is decreased. A thin metal
foil has very good heat conduction, enabling the hot contact
members to be at a temperature which is only slightly above the
melting temperature of the poly(meth)acrylate. However, in practice
the fastest possible sealing is desired, necessitating
substantially higher temperatures of the hot contact members, e.g.
120-220.degree. C. In the case of a plastic substrate, the hot
contact member temperature may have to be limited because of the
glass transition temperature of the plastic. To obtain a seal of
high strength, the pressure exerted by the hot contact members
should be at least 1 kp/cm.sup.2, preferably 3-6 kp/cm.sup.2.
[0068] The effective peeling resistance of hot-sealing samples from
the Examples was tested in the customary fashion (sealing seam
strength according to DIN 51 221).
[0069] The objective was to demonstrate that, e.g., the use of the
present poly(meth)acrylate dispersions as primers on aluminum foils
or sheets, along with the use of the aqueous dispersions of Ger. 39
30 743, as an outer hot-sealable layer provides adhesive properties
equivalent to those provided with primers based on
solvent-containing and/or chlorinated polymers.
[0070] Having now generally described the invention, a further
understanding can be obtained by reference to certain specific
examples which are provided herein for purpose of illustration only
and are not intended to be limiting unless otherwise specified.
[0071] The production and testing of hot-sealed samples is
described hereinbelow, and a table of the strengths of the seals is
be presented.
COMPARATIVE EXAMPLES
[0072] To produce the comparative samples, a 10 wt. % solution of a
commercial vinyl chloride/vinyl acetate/maleic acid copolymer
("Vinylite VMHC", supplied by Union Carbide) in ethyl acetate was
applied with a spiral blade applicator to a 40 micron thick soft
aluminum foil, in a thickness such that after drying 1 min at
180.degree. C., a primer of thickness 2 micron was produced. The
present poly(meth)acrylate dispersions (PD) were applied with a
blade applicator, and, to form a film, were immediately placed in a
circulating air drying cabinet preheated to 180.degree. C. before
the water had evaporated from the dispersion coating. The
applicator was selected such that the layer of dried hot-sealable
adhesive had thickness of 0.5-3.0 micron.
[0073] The poly(meth)acrylate dispersions of Ger. 39 30 743 can be
applied by a similar technique, after drying of the
poly(meth)acrylate dispersions (PD).
[0074] The coated aluminum foils were sealed to polystyrene films
and PVC films, respectively, on edge regions 1 cm wide, using a
laboratory-scale hot sealing apparatus (manufactured by Brugger).
The temperature of the hot contact members was 180.degree. C., the
sealing pressure was 6 kp/cm.sup.2, and the sealing time was 1
sec.
[0075] Seal strength was measured by the procedure described in DIN
51 221. The samples were first stored in a standard atmosphere
(23.degree. C., 50% relative humidity). Strips 15 mm wide were cut
transversely to the seal seam, folded outward, and tested in a
tensile testing machine, with one of the holding clamps gripping
the free end of the aluminum foil and the other gripping the free
end of the plastic film, wherewith the tensile force was exerted
approximately transversely to the sealing seam on the test strip.
The seal seam strength was taken to be the force required to
advance the separation of the foil and film to the extent of 15
mm.
[0076] To test water resistance of the seal seam, the sample strips
were stored 48 hr in water at room temperature, then tested for
seal strength in the wet state by the above-described method.
Examples 1-20 (Table 1):
[0077] Ia. General method of producing poly(meth)acrylate
dispersions PD with emulsion polymerization:
[0078] Process variants:
[0079] (Iaa) Controlled feed ("semicontinuous") process.
[0080] (Iab) Controlled feed followed by batch.
[0081] (Iac) Controlled feed followed by controlled feed.
[0082] Into a round-bottom flask equipped with a stirrer, contact
thermometer, and heater, were charged deionized water and an
emulsifier (Aerosol OT75(R)), and heating was begun. After the
temperature reached 90.degree. C., ammonium peroxydisulfate (APS)
dissolved in water was added as an initiator, and Process Step 1
was begun.
[0083] (Iaa) For variant Iaa, the feed was added gradually over 240
min, followed by stirring at 80.degree. C. for an additional 2 hr,
to allow completion of the polymerization.
[0084] (Iab) For variant Iab, the feed for Process Step 1 was added
gradually over 120 min, followed by stirring at 80.degree. C. for
an additional 1 hr, and cooling at 30.degree. C. Then the feed for
Process Step 2 was added dropwise over 30 min, following which the
mixture was allowed to stand 4 hr. The monomer/polymer mixture was
then heated to 40.degree. C. and a redox initiator was added. After
the maximum temperature was reached, the temperature was maintained
at 80.degree. C. and stirring was continued for an additional 2 hr,
to allow completion of the polymerization.
[0085] (Iac) For variant Iac, the feed for Process Step 1 was added
gradually over 120 min, followed by stirring at 80.degree. C. for
an additional 40 min. Then the feed for Process Step 2 was added
gradually over 2 hr, following which the mixture was stirred for an
additional 2 hr to allow completion of the polymerization.
[0086] In all three variants (Iaa) to (Iac), a preservative in
water was then added (for amounts, see Table 3).
[0087] The data for Examples 1- 19 are presented in Tables 1 and 3.
Table 1 gives the monomer compositions, amounts of emulsifier, and
amounts of water, for Process Step 1 and Process Step 2. Table 3
gives the amounts of various additives.
[0088] Ib. Production of the poly(meth)acrylate dispersions by
emulsion polymerization in a process comprising a batch process
followed by a controlled feed process:
[0089] Into a round-bottom flask equipped with a stirrer, contact
thermometer, and heater, were charged the materials for the batch
preparation (Process Step 1). The monomer mixture was the heated to
40.degree. C. and a redox-type initiator was added, to initiate the
polymerization. After the maximum temperature was reached, the
temperature was maintained at 80.degree. C. and stirring was
continued for an additional 40 min. Then the feed for the
controlled feed process (Process Step 2) was added gradually over a
period of 2 hr, following which the mixture was stirred for an
additional 1 hr to allow completion of the polymerization. The
preservative was then added at 30.degree. C.
[0090] For example 20, Table 1 gives the monomer compositions,
amounts of emulsifier, and amounts of water, for Process Step 1 and
Process Step 2, and Table 3 gives the amounts of various
additives.
[0091] II. Production of an aqueous polyacrylate dispersion
(according to Ger. 39 30 743, "Coating for use as a sealant"):
[0092] In a 1-liter round-bottom flask equipped with a stirrer,
contact thermometer, and heater, 60 pbw of fully desalinated water
and 0.05 pbw of sodium diisooctylsulfosuccinate were heated to
80.degree. C. with stirring, and 2.4 pbw of a 10 wt. % solution of
ammonium peroxydisulfate (APS) was added. Thereafter, the following
were added dropwise over a period of 4 hr, also at 80.degree.
C.:
[0093] (i) An emulsion comprised of 240 pbw completely desalinated
water, 4 pbw sodium diisooctyl sulfosuccinate, 1 pbw APS, 320 pbw
butyl methacrylate, 72 pbw methyl methacrylate, and 8 pbw
methacrylic acid amide, along with
[0094] (ii) A regulator comprising 0.4 g dodecyl mercaptan. After
another 2 hr at 80.degree. C., the mixture was cooled to room
temperature. A stable, coagulate-free dispersion was obtained. The
solids content was about 50 wt. %. Mean particle diameter was 340
nm. The viscosity was 40 mPa-sec, as determined with a Brookfield
viscosimeter.
[0095] III. Testing of the hot sealing properties:
[0096] For examples 1-20 (with Examples 1-3 being comparative
examples), a coating 1.5 micron thick comprised of the respective
poly(meth)acrylate dispersion (PD) was applied to an untreated
aluminum foil, followed by drying 1 min at 180.degree. C. Then a
coating 7 micron thick comprised of the dispersion of Sec. II was
applied, again followed by drying 1 min at 180.degree. C. Strips 15
mm wide comprised of the thus treated aluminum foils were sealed
against a polystyrene film. Sealing duration was 1 sec, with the
hot contact members being at 180.degree. C. and exerting a pressure
of 6 kp/cm.sup.2.
[0097] The adhesive strengths of these bonded structures are given
in Table 4. If the bond failed a hand separation test, the
measurement was not performed. The first value of resistance to
peeling given is the value for the dry bond; the second is the
value after storing 48 hr in water.
[0098] Results:
[0099] The results demonstrate that by a rational selection of the
monomers and the production process, aqueous polymer dispersions of
the invention can be produced which yield primer layers on aluminum
foil which primers provide adhesive properties equivalent to those
provided with primers based on solvent-containing and/or
chlorinated polymers.
[0100] IV. Testing of adhesion of primers to various metallic
substrates:
[0101] A variety of metal plates ("BM") comprised of aluminum or
iron were cleaned with ethyl acetate. The dispersion being tested
was applied to the desired site by means of a film drawing
apparatus, with gap heights of 20 micron, 80 micron, and 100
micron. Also, dispersions to which 4% butyldiethylene glycol
acetate ("BDGA") had been added were applied, using gap heights of
100 micron and 200 micron. The adhesion was measured by a
grid-cutting test (with an a added Tesa film-peeling test),
evaluated visually.
[0102] Results:
[0103] In all instances, the films adhered well.
[0104] Table 1 (parts 1 and 2 of 2):
[0105] Dispersions (PD) prepared according to variant methods Iaa,
Iab, Iac, and Ib:
[0106] [For Table 1 parts 1 and 2, see 2 pages following the
text.]
[0107] KEY to Table 1:
[0108] Columns:
[0109] (a) Process;
[0110] Examples 1-3. (comparison examples). [Method variant]
Iaa;
[0111] Examples 4-17. [Method variant] Iab, first process step is
controlled feed process, second process step is batch;
[0112] Examples 18-19. [Method variant] Iab, first process step is
controlled feed process, and second process step is controlled feed
process.
[0113] Examples 20. [Method variant] Ib [lit., "Iab"],
[0114] first process step is batch, and second process step is
controlled feed process.
[0115] Rows:
[0116] (b) First process step (controlled feed for Examples 1-19;
batch for Example 20).
[0117] (c) VINYLITE VMHC=Vinyl Chloride/Vinyl Acetate/Maleic Acid
Copolymer (supplied by Union Carbide), dissolved in ethyl
acetate.
1 Iaa Iaa Iaa Iab Iab Iab Iab Iab Iab Iab Ex- Process Example 1
Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example
8 Example 9 ample 10 First Step Semicon- Semicon- Semicon- Semicon-
Semicon- Semicon- Semicon- Semicon- Semicon- Semicon- tinuous
tinuous tinuous tinuous tinuous tinuous tinuous tinuous tinuous
tinuous Water 533.7 531 531 509.7 509.7 510.6 509.7 509.7 509.7
509.7 Aerosol 8.5 8.55 8.55 8.55 8.55 8.55 8.55 8.55 8.55 8.55
OT75(R) Methyl 39.5 360 270 270 270 292.5 281.25 292.5 270
Methacrylate Butyl Acrylate 35 135 135 135 135 135 135 135 135 135
Glycidyl 45 Methacrylate Hydroxyethyl 45 45 45 45 22.5 33.75 22.5
45 Acrylate Butyl 697.5 Methacrylate Methacrylamide 18 Methacrylic
22.5 Acid Acrylic Acid 22.5 45 45 Butyl 315 315 Methacrylate First
Step Semicon- Semicon- Semicon- Semicon- Semicon- Semicon- Semicon-
Semicon- Semicon- Semicon- tinuous tinuous tinuous tinuous tinuous
tinuous tinuous tinuous tinuous tinuous Styrene 360 Dodecyl 0.45
Mercaptan Second Step Example Example Example Example Example
Example Example Butyl 315 315 315 315 315 315 315 Methacrylate
Methyl 90 90 112.5 101.25 90 112.5 Methacrylate Acrylic Acid 45 45
45 22.5 33.75 45 22.5 Styrene 90 Polycarboxylic Acid* Aerosol
OT75(R) Water Ammonium Peroxydisulfate Table 1: (Continued)
Dispersions PD Prepared According to Variant Methods Iaa, Iab, lac,
and Ib: Iab Iab Tab Iab Iab Iab Iab Iab Iab Ib Example Example
Example Example Example Example Example Example Example Example
Process 11 12 13 14 15 16 17 18 19 20 First Step Semicon- Semicon-
Semicon- Semicon- Semicon- Semicon- Semicon- Semicon- Semicon-
Semicon- tinuous tinuous tinuous tinuous tinuous tinuous tinuous
tinuous tinuous tinuous Water 482.2 482.2 482.2 482.2 814.3 482.2
370.4 266.9 361.5 629.2 Aerosol 8.55 8.55 8.55 8.55 3.43 8.55 10.3
4.28 3 0.9 Methyl 270 270 270 270 198 270 324 270 270 270
Methacrylate Butyl Acrylate 135 135 135 135 54 135 162 135 135 135
Glycidyl Methacrylic Hydroxyethyl 45 45 45 45 18 45 54 45 45 45
Acrylate Butyl Methacrylate Methacrylamide Methacrylic Acid Acrylic
Acid Butyl Methacrylate Styrene First Step Semicon- Semicon-
Semicon- Semicon- Semicon- Semicon- Semicon- Semicon- Semicon-
Semicon- tinuous tinuous tinuous tinuous tinuous tinuous tinuous
tinuous tinuous tinuous Dodecyl Mercaptan Second Step Example
Example Example Example Example Example Example Semicon- Semicon-
Semicon- tinuous tinuous tinuous Butyl 315 315 315 315 126 315 378
315 315 315 Methacrylate Methyl 90 90 36 90 108 90 Methacrylate
Acrylic Acid 45 45 45 45 18 54 45 45 45 Styrene 90 90 90 90
Polycarboxylic 112.5 Acid* Aerosol 4.28 3 7.88 Water 266.9 261.5
210.4 Ammonium 0.9 0.9 0.9 Peroxydisulfate *Polycarboxylic Acid -
Rohagil SL 140
[0118]
2TABLE 2 Amounts of Additives Second Process Step (but first
process step in Example 20) After Initial Charge to Reactor Sodium
Polymerization Aerosol Ammonium Ammonium Hydroxymethyl Acticid SPX
Example Water OT75(R) Peroxydisulfate.sup.a Peroxydisulfate.sup.a
Fe.sub.2(SO.sub.4).sub.3.sup.- b Na.sub.2S.sub.2O.sub.5.sup.c
Sulfinate.sup.d in 10 g water NH.sub.3.sup.e 1 340 0.255 2.7 1.8
0.34 2 340 0.225 2.7 1.8 0.34 3 340 0.225 2.7 1.8 0.34 4 340 0.225
2.7 0.72 0.0009 0.36 1.8 0.34 5 340 0.225 2.7 0.72 0.0009 0.36 1.8
0.34 6 340 0.225 2.7 0.72 0.0009 0.36 1.8 0.34 7 340 0.225 2.7 0.72
0.0009 0.36 1.8 0.34 8 340 0.225 2.7 0.72 0.0009 0.36 1.8 0.34 9
340 0.225 2.7 0.72 0.0009 0.36 1.8 0.34 10 340 0.225 2.7 0.72
0.0009 0.36 1.8 0.34 11 340 0.045 2.7 0.72 0.009 0.504 1.8 0.34 12
340 1.8 2.7 0.72 0.009 0.504 1.8 0.34 13 340 0.045 2.7 0.72 0.009
0.504 1.8 0.34 14 340 1.8 2.7 0.72 0.009 0.504 1.8 0.34 15 556
0.091 1.08 0.288 0.0043 0.202 0.72 0.135 16 340 0.225 2.7 0.72
0.009 0.504 1.8 0.34 17 268 0.27 3.24 0.864 0.011 0.605 2.16 0.41
18 340 0.225 2.7 1.8 0.34 19 340 0.3 0.9 1.8 0.34 20 0.72 0.009
0.504 1.8 0.34 .sup.aAmmonium Peroxydisulfate dissolved in 20 g
water .sup.bFe.sub.2(SO.sub.4).sub.3 dissolved in 10 g water
.sup.cNa.sub.2S.sub.2O.sub.5 dissolved in 20 g water .sup.dSodium
Hydroxymethyl Sulfinate dissolved in 20 g water .sup.e20% Ammonia
in 5 g water
[0119]
3TABLE 4 Measurements of resistance to peeling: Peeling Strength,
N, for 15 mm strip width: Seal between aluminum and Seal between
polystyrene ("PS") aluminum and PVC Example After 48 hr in Normal
After 48 hr in Number Normal pressed water Pressed water 1 Value
too low 2 4.8 1.7 2.1 1.1 3 5.7 3.7 3.1 1.7 4 6.9 8.0 6.7 5.8 5 8.1
4.3 5.1 2.5 6 7.0 6.0 3.8 2.4 7 Value too low 8 Value too low 9
Value too low 10 Value too low 11 6.9 4.7 3.4 2.9 12 5.0 6.2 3.3
3.3 13 4.7 2.3 2.3 2.3 14 7.6 7.4 4.8 3.7 15 4.2 6.8 1.9 2.4 16 4.2
4.9 1.9 2.1 17 5.9 1.9 3.9 2.9 18 2.0 0.6 1.3 0.7 19 8.1 8.0 6.9
5.6 20 3.8 4.3 2.4 2.6
[0120]
4TABLE 5 Results of adhesion tests of Example 9 sample, using
grid-cutting test. (Data are the number of fields loosened in the
test.) Film according to Example 19 + 4% butyldiethylene glycol
acetate ("BDGA"), applied to solid metal plates ("BM") Drying
180.degree. C., 1 Drying 180.degree. C., 2 Film according to
Example 19 minute; application minutes; application Drying
180.degree. C., 1 minute; Drying 180.degree. C., 2 minutes; with
film-drawing with film-drawing application with film-drawing
application with film-drawing apparatus; column apparatus; column
apparatus; column headings are apparatus; column headings are
headings are gap headings are gap gap height (micron) gap height
(micron) height (micron) height (micron) 20 .mu.m 60 .mu.m 100
.mu.m 20 .mu.m 60 .mu.m 100 .mu.m 100 .mu.m 200 .mu.m 100 .mu.m 200
.mu.m Actual coating thickness 12-19 14-28 15-27 14-18 13-17 12-33
15-28 33-46 20-30 -40 (micron) (measured on the Fe plate) Iron
plate 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 Aluminum plate
2/4)*** 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 ***Drying was not
optimal for this [failing] test.
[0121] German priority application 197 08 412.5 filed Mar. 3, 1997
is hereby incorporated by reference into the present
application.
[0122] Obviously, numerous modifications and variations of the
present invention are possible in light of the above teachings. It
is therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *