Note: Descriptions are shown in the official language in which they were submitted.
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WATER SOLUBLE EPOXY ESTER COPOLYMERS FOR
~ S~NITARY CAN USE
Technical Field
The present invention relates to water soluble
epoxy ester copolymers which are particulaxly adapted
to sanitary can use where good resistance to extraction
by hot water and good odor and flavor characteristics
are essential.
Backgro~und Art
1~ Water solution coating compositions have been
employed for diverse purposes, but it has been difficult
to obtain the good resistance to extraction by hot water -
and good odor and flavor characteristics which are
important to enable application of the coatings to
15 sanitary cans.
Disclosure of Invention
In this invention, a relatively low molecular
weight polyepoxide having an average molecular weight
of about 300 to about 1100 (by calculation) and a
20 1,2-epoxy equivalency of about 1.4 to about 2.0 is
; esterified with an at least approximately stoichio-
metric proportion, based on epoxide functionality, of
monocarboxylic acid selected from benzoic acid, a Cl-C8
alkyl substituted benzoic acld, or a C6-Cl~ alkanoic
25 acid to produce an ester derivative substantially free
of epoxy functionality. This esterification reaction
~ is continued to an acid number of less than 20. The
; resulting hydroxy functional epoxy ester is then poly-
esterified with a monoethylenic dicarboxylic acid which
- 30 resists homopolymerization, preferably fumaric acid.
From 1.5-8% of the diacid is used in the polyesterifica-
tion reaction, based on the weight of the epoxy ester,
so the hydroxy groups in the epoxy ester are present l.n
stoichiometric excess, and the polyesterification is
35 continued to an acid number of less than 20 to provide
an ethylenically unsaturated hydroxy functional poly-
,'' ~
ester. This unsaturated polyester is then copolymerizedwith from 15~/, to 70% of monoethylenic monomers, based
on the weight of the copolymer, to provide a copolymer
product. These monomers include monoethylenic carhoxyl-
ic acid, such as methacrylic acid or fumaric acid, toprovide an acid number of from 20-100 in the final
copolymer so that amine and water can be added to pro-
vide a water dispersion which is either a solution or a
colloidal dispersion. Reactive monomers, such as
10 hydroxyèthyl acrylate or N-methylol acrylamide or its
ether, such as the butyl ether, may be used. Alterna-
tively, an aminoplast, such as hexamethoxy methyl
melamine, or a water soluble or dispersible phenoplast,
or a mixture thereof, may be used for cure.
The polyepoxides preferably have a l,2-epoxy
equivalency of about 1.4 to about 2.0 and the best
properties are obtained using diglycidyl ethers of a
bisphenol, such as bisphenol A. The preferred molecular
weight of the polyepoxides, which may be provided by
20 the use of mixtures, is from 350 to 800.
The saturated monocarboxylic acid used to consume
the epoxy functionality may be benzoic acid or a Cl-C8
. alkyl substituted benzoic acid or a C6-C10 alkanoic
acid, but para tertiary butyl benzoic acid is particu-
25 larly preferred. The C6-C10 alkanoic acids are less
, preferred and are illustrated by hexoic acid or pelar-
. gonic acid. These saturated monocarboxylic acids
: uniquely provide maximum impermeability in the combina-
tion of this invention.
The esterification reaction is wholly conventional,
simple heating to a hot melt, desirably in the presence
of a trace of amine catalyst, being all that is needed.
The acid is used in at least approximately stoichiomet-
- ric proportion and the reaction is continued to consume
35 most of the acid, an acid number of less than about 20,
. preferably less than 10, being contemplated.
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Significant residual epoxy functionality yields
instability and should be avolded. Some excess acid
will simply react with the hydroxy functionality on the
epoxy ester. It is here noted that polyepoxides fre-
quently contain hydroxy groups, and even if they do not,the carboxy-epoxy reaction produces hydroxy groups, so
the epoxy ester which is formed is hydroxy functional.
Substantially stoichiometric proportions are preferred.
The.monoethylenically unsaturated dicarboxylic
10 acid should resist homopolymerization so that its acid-
ity can be substantially consumbed in the production of
a polyester with the hydroxyl functional epoxy ester
without consuming the unsaturation. The preferred
dicarboxylic acid is fumaric acid, but maleic acid or
15 maleic anhydride can also be used. An acid number of
less than 20, preferably less than 10, indicates the
desired complete reaction.
This polyester now contains polymerizable unsat-
uration and it is copolymerized with monoethylenic
20 monomers, the bulk of which (at least about 50% by
~- weight) are nonreactive. This means that, aside from
their polymerizable unsaturation, they do not react
- under the conditions of polymerization and use which are
contemplated. A similar statement is that there are no
25 functional groups except the polymerizable ethylenic
group. Styrene and vinyl toluene are particularly
contemplated, though methyl methacrylate, methyl acryl-
ate, ethyl acrylate, acrylonitrile and vinyl acetate
will further illustrate the useful materials. Styrene
30 and vinyl toluene are especially i~portant for two
- reasons. First, they copolymerize better with the di-
carboxylic acids used fur polyesterification. Second,
they produce higher molecular weight copolymers which
provide higher viscosity aqueous solutions at low solids
3~-content, and this provides spray solutions which better
resist the formation of bubbles, blisters and foams.
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A monoethylenic carboxylic acid of any desired
type should be employed to provide an ac-id number of
from 20-100 in the final copolymer. Fumaric acid and
maleic acid are preferred because these are F.D.A
approved, but acrylic acid, methacrylic acid, crotonic
acid and itaconic acid are all useful, and one cannot
know which acids-will be a-proved for sanitary can use
in t~e future. Maleic anhydride is useful at the
small~r proportion of use. The preferred acidity should
10 not exceed 60. While more acid polymers can be used,
sanitary can use requires maximum water resis~ance and
good resistance to water extraction, and these are best
at low acid value. The copolyme~s herein are well
adapted to disperse in water at low acid value.
` 15 Other reactive monoethylenic monomers may be
included in an amount up to about 20% of the total
polymerizable monomers. These are illustrated by
hydroxy monomers, such as 2-hydroxyethyl acrylate,
amide monomers, such as acrylamide, ~-methylol function-
; 20 al monorners, such as N-methylol acrylamide or ethers
thereof like the butyl ether.
The copolymerization is itself conventional being
carried out in organic solvent solution using a free
radical generating polymerization catalyst. These are
25 well known and are illustrated in the Example.
The aminoplast and phenoplast resins which may
be used for cure are also well known and will be illus-
trated by hexamethoxymethyl melamine. This class of
water soluble and water dispersible materials useful
30 for curing hydroxy functional resins is a ma-tter of
common knowledge in the art. They are used in an amount
of 5-40% of total resin solids.
An amine, including ammonia, is added to allow
the acidic copol~mer to be dispersed in water. This is
35 again conventional, and is illustrated using dimethyl
ethanol amine.
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The resulting aqueous solutions cure to provide
films characterized by superior resistance to extrac-
tion and they resist absorbing odor and flavor compo-
nents of the foods and beverages which are packaged.
- 5 They can be applied to any metal can interior, such as
aluminum, steel and tin plated steel. Spray appication
and cure by baking at 400F. or 3 minutes are particu-
- larly contemplated. Films of about 0.2-0.3 mil are
formed~. Good adhesion is obtained on all of these
10 surfaces.
Best Mode for Carrying Out the Invention
The invention is illustrated in the following
example of preferred operation, all parts herein being
' by weight except where otherwise noted.
Example 1
(1) Para tertiary butyl benzoic acid) 210
CIBA 6010 ) 230
Heat to 100C. to melt.
: (2) Dimethyl ethanol amine
Add (2). Watch for exotherm which heats the mixture
to 225C. and hold for acid value less than 5. Then
cool to 1~0C.
(3) Fumaric acid ) 15
Xylol ~ 30
Add (3). Heat to 225C. and remove water of esteri-
- 25 fication and hold for acid value less than 7. ~ol
- to 170C.
- (4) Butyl cellosolve ) 460
- (5) Fumaric acid ) 40
~dd (4) and (5). Hold 30 minutes to dissolve the
fumaric acid and then cool to 125C.
(6) Styrene ) 160
Cumene Hydroperoxide ) 25
Premix (6) and add over 2 hrs. at 125C. and
hold 1 hr.
35 (7) Cumene hydroperoxide ) 5
Add (7) and hold 1 hr.
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(8) Cumene hydroperoxide ) 5
Add (8) hold 1 hr., and cool to 70C.
(9) Dimethyl ethanol amine ) 75
(10) Hexamethoxymethyl melamine )165
Add (9) and ~10)
(11) Deionized water )1400
Add (11) slowly over 30 minutes.
The final product is a milky dispersion having
the following characteristics: Nonvolatile solids -
10 30. l~/o~ Acid value of solids - 33.5.
This dispersion has been successfully sprayed on
aluminum and steel can interiors and cured by baking
at 400F. for 3 minutes. Extractables are low and
good flavor and color properties are obtained.
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