U.S. patent application number 09/798118 was filed with the patent office on 2001-11-29 for polyester-based aqueous coating composition.
Invention is credited to Kitabatake, Michiharu.
Application Number | 20010047057 09/798118 |
Document ID | / |
Family ID | 26586609 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010047057 |
Kind Code |
A1 |
Kitabatake, Michiharu |
November 29, 2001 |
Polyester-based aqueous coating composition
Abstract
Polyester-based aqueous coating compositions comprising a
mixture of a carboxyl-functional polyester resin (A), a
water-insoluble epoxy resin (B), and a hydrophobic solvent (C), the
mixture being neutralized with neutralizer (D) and dispersed or
dissolved in water. The compositions have excellent film forming
and processing characteristics, and are particularly useful in
coating the interior surface of cans and as automobile
coatings.
Inventors: |
Kitabatake, Michiharu;
(Ota-ku, JP) |
Correspondence
Address: |
Donald W. Huntley
Huntley & Associates
1105 North Market Street
PO Box 948
Wilmington
DE
19899-0948
US
|
Family ID: |
26586609 |
Appl. No.: |
09/798118 |
Filed: |
March 2, 2001 |
Current U.S.
Class: |
525/107 |
Current CPC
Class: |
C09D 167/00 20130101;
C09D 163/00 20130101; C09D 163/00 20130101; C09D 167/00 20130101;
C08L 2666/18 20130101; C08L 63/00 20130101 |
Class at
Publication: |
525/107 |
International
Class: |
C08F 008/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 2, 2000 |
JP |
57141/2000 |
Mar 2, 2000 |
JP |
57145/2000 |
Claims
I Claim:
1. A polyester-based aqueous coating composition comprising a
mixture of carboxyl-functional polyester resin (A) which is a
condensation product of at least one polyalcohol of which ethylene
glycol comprises at least about 60 mol % based on the total
polyalcohol component and at least one polybasic acid of which
polyvalent aromatic carboxylic acid comprises at least about 80 mol
% based on the total polybasic acid component, and which has a
number average molecular weight of about from 1,000 to 20,000 and
an acid value of about from 10 to 170 mgKOH/g; a water-insoluble
epoxy resin (B); and hydrophobic solvent (C); the mixture being
neutralized with neutralizer (D) and dispersed or dissolved into
water.
2. An aqueous coating composition according to claim 1 wherein the
carboxyl-functional polyester resin (A) has a hydroxyl value of
about 10 mgKOH/g or less.
3. An aqueous coating composition according to claim 1 wherein the
water-insoluble epoxy resin (B) consists essentially of Novolac
based epoxy resin.
4. An aqueous coating composition according to claim 1 wherein the
water-insoluble epoxy resin (B) is selected from alicyclic
epoxy-functional resins and glycidyl-functional acrylic resins.
5. An aqueous coating composition according to claim 1 wherein an
equivalent ratio of the carboxyl group of the polyester resin (A)
and the epoxy group of the epoxy resin (B) is about from 1/0.3 to
1/1.5.
6. An aqueous coating composition according to claim 1 wherein the
hydrophobic solvent (C) consists essentially of cyclohexanone.
7. An aqueous coating composition according to claim 1 comprising
about from 1 to 200 parts by weight of the hydrophobic solvent (C)
per 100 parts by weight of the total resin solids.
8. An aqueous coating composition according to claim 1 comprising
about from 0.05 to 3 parts by weight of a curing catalyst per 100
parts by weight of total solids of the polyester resin (A) and the
epoxy resin (B).
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to crosslinkable aqueous coating
compositions which exhibit excellent film-forming and curing
characteristics, in terms of processability and safety. The
compositions can be used for coating the interior surfaces of cans.
Moreover, these crosslinkable aqueous coating compositions are
capable of forming films having excellent hardness, and accordingly
can be used as primers or finish coats for automotive or industrial
applications.
[0003] 2. Description of the Prior Art
[0004] In the past, aqueous coating compositions have been made
from the reaction product of a high acid value acrylic resin and a
high molecular weight bisphenol A based epoxy resin. These
compositions have been used for coating the interior surface of
cans. However, recently questions have been raised about bisphenol
A, and effort has been directed to coating compositions in which
bisphenol A does not elute.
[0005] Polyester resins have previously been proposed for use as a
base resin in aqueous coatings. Japanese Laid-Open Patent
Application No. 61-37811 discloses a thermosetting resin
composition prepared by emulsifying a water-soluble polyester resin
and an epoxy resin. The composition contains hydrophilic solvent
for polyester resin, and exhibits increased dispersion power.
However, the film forming ability and processability for coating
the interior surface of cans is inadequate. In addition, attempts
to improve processability often result in reduction of the
stability of an emulsion of this type.
[0006] Compositions for coating substrates other than cans have
been prepared from polyester resin obtained by using hydrophilic
materials such as those having sulfonic acid metal salt,
polyalkylene glycol, aliphatic dicarboxylic acid and the like.
These compositions exhibit good solubility and dispersibility in
water. However, the water resistance of the resulting coating was
not satisfactory. Japanese Laid-Open Patent Application No.
57-40525 and No. 61-37811 disclose a technique to raise water
dispersion capacity in which a hydrophilic solvent is used in the
polyester resin having a content of hydrophilic material reduced.
However, the hardness and physical properties of the resulting
coating were inadequate.
[0007] Aqueous coating compositions have also been proposed
containing a polyester resin having hydroxyl group and carboxyl
group, an alicyclic epoxy resin and a quaternary ammonium compound.
These are described in Japanese Laid-Open Patent Application No.
4-359075. These compositions provided good storage stability and
film properties. Continuing effort has been directed toward further
improvement of stain resistance and scratch resistance in the final
finish. In addition, it has been difficult to provide a good
balance between a high hardness in the coating s made using the
polyester resin and emulsion stability after dispersion in
water.
SUMMARY OF THE INVENTION
[0008] The present invention is provides polyester-based aqueous
coating compositions which exhibit good emulsion stability after
dispersing in water, excellent processability, film forming
ability, and cost performance when used in coating the interior
surface of cans.
[0009] The invention also provides polyester-based aqueous coating
compositions which exhibit good emulsion stability after dispersing
in water, excellent curability, film forming ability and film
hardness when used as either an undercoating or finish coating on
automobile bodies or industrial products.
[0010] Specifically, the present invention provides a
polyester-based aqueous coating composition comprising a mixture of
carboxyl-functional polyester resin (A) which is a condensation
product of at least one polyalcohol of which ethylene glycol
comprises at least about 60 mol % based on the total polyalcohol
component and at least one polybasic acid of which polyvalent
aromatic carboxylic acid comprises at least about 80 mol % based on
the total polybasic acid component, and which has a number average
molecular weight of about from 1,000 to 20,000 and an acid value of
about from 10 to 170 mgKOH/g;
DETAILED DESCRIPTION OF THE INVENTION
[0011] The carboxyl-functional polyester resin (A) used in the
present invention is a condensation product of a polyalcohol
component comprising at least about 60 mol ethylene glycol, based
on the total polyalcohol components, and a polybasic acid component
comprising at least about 80 mol %, based on the total polybasic
acid components, of a polyvalent aromatic carboxylic acid, and
contains carboxyl groups in the resin. The polyester resin has a
number average molecular weight of about from 1,000 to 20,000 and
an acid value of about form 10 to 170 mgKOH/g.
[0012] The polyester resin can be prepared by any of the following
methods (1), (2), or (3). Method (1) involves esterifying polybasic
acid components and polyalcohol components using an excess of the
former over the latter. Method (2) involves reacting an acid
anhydride with a polyester polyol which is obtained by reaction of
polybasic acid components and polyalcohol components with a molar
excess of the polyalcohol components. Method (3) involves a first
step of preparing a hydroxyl-functional polyester by alcoholysis of
a high molecular weight polyester such as polyethylene
terephthalate or polybutylene terephthalate; then esterifying the
resulting hydroxyl-functional polyester with polybasic acid
components, and if necessary, polyalcohol components, under
conditions in which the polybasic acid components are in molar over
the hydroxyl-functional components.
[0013] Examples of polybasic acids which can be used in the present
invention, mainly in the preparation of the polyester resin,
include dicarboxylic acids such as phthalic acid, phthalic
anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic
acid, tetrahydrophthalic anhydride, hexahydrophthalic acid,
hexahydrophthalic anhydride, hexahydroisophthalic acid,
hexahydroterephthalic acid, 4-carbonylhexahydrophthalic acid,
4-carbonylhexahydrophthalic anhydride, 3-carbonyltetrahydrophthalic
acid, 3-carbonyltetrahydrophthalic anhydride, succinic acid,
succinic anhydride, fumaric acid, adipic acid, azelaic acid,
sebacic acid, maleic acid, maleic anhydride and lower alkyl esters
of these dicarboxylic acids. In addition to these dicarboxylic
acids, monobasic acids such as benzoic acid, crotonic acid,
p-t-butyl benzoic acid and other various fatty acids can be used.
Further, trivalent or higher polycarboxylic acids such as
trimellitic acid, trimellitic anhydride, methylcyclohexene
tri-carboxylic acid, pyromellitic acid, pyromellitic anhydride and
butane tricarboxylic acid can also be used. Among these polybasic
acids, it is important that the polyvalent aromatic carboxylic acid
comprise at least about 80 mol %, preferably more than 90 mol %,
based on the total polybasic acid components. This high
concentration of the polyvalent aromatic carboxylic acid has been
found to contribute good hydrolysis stability resistance.
[0014] Examples of the polyalcohols which can be used in the
present invention, mainly in the preparation of the polyester
resin, include dihydric alcohols including aliphatic glycols such
as ethylene glycol, diethylene glycol, triethylene glycol,
propylene glycol, 1,2 butanediol, 1,3-butanediol, 1,4-butanediol,
neopentyl glycol, 2-methylpropane diol, 3-methylpentane diol,
1,4-hexane diol, 1,6-hexane diol, 1,5-pentane diol, 1, 9 -nonane
diol, diethyl pentane diol, and 2 - butyl ethyl propanediol;
alicyclic glycols such as cyclohexane dimethanol and spiro glycol;
aromatic glycols such as ethylene oxide or propylene oxide addition
product of bisphenol compound; polyether polyol such as
polyethylene glycol, polypropylene glycol, polybutylene glycol;
polyurethane polyol obtained by the reaction of glycol and
polyisocyanate compound. In addition to these dihydric alcohols,
trivalent or higher polyhydric alcohol such as glycerin,
trimethylolethane, trimethylolpropane, pentaerythritol and the like
can be used. These polyalcohols can be used singly or as a mixture
of two or more. Further, a glycol including ester functionality in
the molecular structure such as bishydroxyethyl terephthalate can
be used. Among these polyalcohols, ethylene glycol should comprise
at least about 60 mol %, preferably more than about 70 mol %, based
on the total polyalcohol components. This high concentration of
ethylene glycol provides good film hardness and, in the coating to
cans, flavor-retaining ability. Further, it is preferred that
butylene glycol be used in combination with ethylene glycol. This
combination results in excellent physical properties in the
resulting film, such as processability. It is assumed that molar
quantity of glycol including ester function in molecular adds with
mole ratio of minimum unit monomer. In a bishydroxyethyl
terephthalate, for example, it calculates as terephthalic acid 1
mol and ethylene glycol 2 mol.
[0015] The condensation or transesterification of both
above-mentioned components can be performed by known methods to
form the polyester resin (A).
[0016] In the first method, the polyester resin (A) can be obtained
by means of direct condensation or transesterification of the
polybasic acid component and the polyalcohol component, with the
polybasic acid being in molar excess over the polyalcohol. In that
case, to provide the best processability, it is preferable that the
amount of trivalent or higher component based on a total of the
polybasic acid component and the polyalcohol component be less than
about 12 mol %, preferably less than 7 mol %.
[0017] In the second method for preparing polyester resin (A), the
polyester polyol can be prepared by means of the direct
condensation or transesterification of the polybasic acid component
and the polyalcohol component on the condition that the polyalcohol
is in moar excess of the acid. In the case of the preparation of
the polyester polyol, to provide the best processability, it is
preferable that the amount of the trivalent or higher component
based on the total of the polybasic acid component and the
polyalcohol component be less than about 12 mol %, preferably less
than 7 mol %. The polyester resin (A) can be obtained by the
reaction of an acid anhydride to the polyester polyol. Examples of
acid anhydrides which can be used include phthalic anhydride,
succinic anhydride, maleic anhydride, hexahydro phthalic anhydride,
and trimellitic anhydride.
[0018] In the third method, polyester resin (A), the polyester
resin (A) can be obtained by first preparing a hydroxyl-functional
polyester by alcoholysis of a high molecular weight polyester as a
starting material and a second step of directly esterifiying or
transesterifying the hydroxyl-functional polyester thus obtained,
polybasic acid component and, if necessary, the polyalcohol
component, provided that the polybasic acid component is in molar
excess over the hydroxyl-functional components. In this case, to
provide the best processability, it is preferable that the amount
of the trivalent or higher component based on the total of the
polybasic acid component and the polyalcohol component be less than
about 12 mol %, preferably less than 7 mol %.
[0019] In the methods (1), (2), and (3) above, the reaction of the
direct condensation or transesterification can be promoted by
operating under pressure or reduced pressure, or flowing inert gas.
Further, an organometallic catalyst such as di-n-butyl tin oxide
can be used as a condensation catalyst. Of these three methods,
method (1) is preferred on the basis of ease of control of
molecular weight and acid value.
[0020] The carboxyl-functional polyester resin (A) has a number
average molecular weight of about from 1,000 to 20,000, preferably
about from 2,000 to 10,000, and an acid value of about from 10 to
170 mg KOH/g, preferably about from 25 to 75 mg KOH/g. These
characteristics provide good processability, flavor-retaining
ability, curability and stability. The ratio of the acid and
alcohol components, and the specific kind of each component can be
adjusted, according to factors known in the art, so that a
polyester resin having above property values is provided. In
addition, for good dispersibility and curability, the
carboxyl-functional polyester resin (A) should have a hydroxyl
value of about 10 mg KOH/g or less, preferably 5 mg KOH/g or less,
and have a glass transition temperature of about 0.degree. C. or
more, and preferably about from 20 to 80.degree. C.
[0021] The water-insoluble epoxy resin (B) is used as a curing
agent and has at least two epoxy groups in a molecule. Examples of
the epoxy resin which can be used include glycidyl ether compounds
such as 2-glycidylphenyl glycidyl ether, 2,6-diglycidyphenyl ether;
glycidyl ester of aliphatic alcohol and alicyclic alcohol;
bisphenol based epoxy resin which is prepared by reaction of
epichlorohydrin with bisphenol compound such as bisphenol F,
bisphenol A, and 1,1 -bis (4hydroxyphenyl) ethane; Novolac based
epoxy resin such as phenol Novolac type epoxy resin, creosol
Novolac type epoxy resin; epoxidized polybutadiene; alicyclic
epoxy-functional resin such as alicyclic epoxyfunctional compound
(e.g., 3, 4-epoxycyclohexylmethyl -3,4-epoxycyclohexane
carboxylate), alicyclic epoxy-functional copolymer which is
obtained by copolymerizing a polymerizable unsaturated monomer
having an alicyclic epoxy-group (e.g., 3,4-epoxy cyclohexyl
(meta)acrylate) with other polymerizable unsaturated monomers;
glycidylfunctional acrylic resin which is obtained to use a
polymerizable unsaturated monomer having a glycidyl group (e.g.,
glycidyl (meta)acrylate, glycidyl allyl ether). It is preferable
that an epoxy resin which does not include free bisphenol A be used
for coating the interior surface of cans. Further, the Novolac
based epoxy resin is preferred from point of food hygiene and film
properties. When free bisphenol A is completely removed by
purification, even in coating the interior surface of cans, the
bisphenol A type epoxy resin prepared by the reaction with
bisphenol A and epichlorohydrin can be employed. On the other hand,
the alicyclic epoxy-functional resin or the glycidyl-functional
acrylic resin is preferred for use in finish coatings.
[0022] The epoxy resin (B) can be compounded in the manner that an
equivalent ratio of the carboxyl group of the polyester resin (A)
and the epoxy group of the epoxy resin (B) is in the range of about
from 1/0.3 to 1/1.5, preferably about from 1/0.5 to 1/1.0.
[0023] The hydrophobic solvent (C) works as a viscosity controller
in mixing and dispersing, an inhibitor of crystallization of resin,
and a film forming auxiliary for use in formation of continuous
film. Examples of the hydrophobic solvent (C) which can be used
include aromatic hydrocarbons such as toluene, and xylene; ketones
such as butanone, and methyl isobutyl ketone; cyclic ketones such
as cyclohexanone, and isophorone; alcohol ethers such as ethylene
glycol monohexyl ether, ethylene glycol monophenyl ether, and
propylene glycol phenyl ether; alcohols such as 2-ethylhexyl ethyl
alcohol, butyl alcohol, hexyl alcohol, and benzyl alcohol;
petroleum solvents such as "Swasol 1500" (product of Cosmo Oil Co.,
Ltd.), "Solvesso 150" (product of Etsuso Sekiyu KK); "Texanol"
(ester alcohol, product of Eastman Chemical Japan Ltd.), "Kyowanol
M" (product of Kyowa Hakko Kogyo Co., Ltd.).
[0024] These solvents can be used alone, or as a mixture of two or
more thereof. Of these, Cyclohexanone is particularly
preferred.
[0025] The amount of hydrophobic solvent (C) should be present in
quantities of about from 1 to 200 parts by weight per 100 parts by
weight of the total resin solid. If the amount is less than 1 part
by weight, it results in poor film forming ability and smoothness
of coating film, while amounts higher than 200 parts by weight
causes instability on emulsifying. When the hydrophobic solvent (C)
is used in quantities higher than this range, for example, to
facilitate te preparation of a mixture before water dispersion, it
can be adjusted to the range indicated above by conventional
methods such as azeotropy or reduced pressure in the emulsion after
water dispersion.
[0026] A water miscible organic solvent can be admixed with the
hydrophobic solvent (C) before water dispersion, if necessary.
Water miscible organic solvents which can be used include, for
example, butyl cellosolve, monomethyl carbitol, dimethyl carbitol,
monoethyl carbitol, propylene glycol monomethyl ether, acetone,
methanol, ethanol, and isopropanol. It is desirable that the amount
of water miscible organic solvent is less than about 40 % by
weight, preferably 20 % by weight, based on the total solvent
content.
[0027] In the present invention, the mixture of the
carboxyl-functional polyester resin (A), the water-insoluble epoxy
resin (B) and the hydrophobic solvent (C) is neutralized with
neutralizer (D) and dispersed into water.
[0028] A basic compound such as an amine or ammonia can be used for
neutralizer (D).
[0029] Examples of the amines which can be used include alkylamines
such as trimethylamine, triethylamine, and tributyl amine;
alkanolamines such as dimethylethanolamine, methyldiethanolamine,
diethanolamine, and aminomethyl propanol; cyclic amines such as
morpholine, alkyl morpholine, methylpiperazine, and ethyl
piperazine. The triethylamine and dimethylethanolamine are
preferred among these. The neutralization degree is generally in
the range of about from 0. 2 to 1 -0 equivalent, preferably about
from 0.1 to 2. 0 equivalent, per one equivalent of the carboxyl
group in the resin (A).
[0030] The mixture including carboxyl-functional polyester resin
(A) is neutralized and dispersed into water by ordinary techniques.
For example, the mixture including the carboxyl-functional
polyester resin (A) can be doped by degrees, with agitating, in
aqueous medium containing the neutralizer (D). In another method,
the mixture including the carboxyl-functional polyester resin (A)
is neutralized with basic compound, and, while agitating, the
resulting neutralized mixture can be poured into water, or water
can be poured into the neutralized mixture. Further, the solvent
content in coating can be adjusted by removing solvent with water
under reduced pressure.
[0031] The aqueous coating compositions of the present invention
can optionally include curing catalysts, antifoaming agents,
lubricants, reforming resins, pigments, flocculation inhibitors,
leveling agents, rheology control agents, odorants, and cissing
inhibitors or anti-cratering agents. The solvents above mentioned
can be combined as a surfactant after water dispersion.
[0032] The curing catalyst promotes the reaction with the
carboxyl-functional polyester resin (A) and the water-insoluble
epoxy resin (B). The curing catalysts include, for example,
water-soluble quaternary ammonium salts such as choline chloride;
nicotinamide, organic metal carboxylate, imidazole compound, and
metal chelate compound. The amount of the curing catalyst used is
generally in the range of about from 0.05 to 3 parts by weight per
100 parts by weight of the total solid of the resin (A) and resin
(B).
[0033] The aqueous coating compositions of the present invention
can be applied to a variety of substrates.
[0034] Examples of the substrates include treated or nontreated
metal plates such as aluminum plate, steel plate, and tin plate;
plates obtained so that a primer such as epoxy-type or vinyl-type
is applied to these metal plates; polyethylene terephthalate (PET)
sheet; cans or bottles processed by using these metal plates and
PET; and those bearing a primer to facilitate electrodeposition.
Known coating techniques can be used, such as roll coating, spray
coating, dip coating, and electrodeposition coating.
[0035] The present invention is explained more fully in the
following Examples and Comparative Examples, in which parts and
percentages are all by weight.
Preparation of Carboxyl-functional Polyester Resin
Preparation Example 1
[0036] A stainless flask equipped with a stirrer, heater,
thermometer, nitrogen gas inlet tube, fractionating unit and
distillant storage was charged with 8.3 parts of terephthalic acid,
91.3 parts of isophthalic acid, 9.7 parts of trimellitic anhydride,
88.9 parts of bishydroxyethyl terephthalate, 26 parts of neopentyl
glycol, and 0.1 part of dibutyl tin dioxide per 100 parts of total
of above materials as catalyst. The mixture was heated to
240.degree. C. with agitation under nitrogen. After the temperature
was raised to 240.degree. C. while distilling off condensed water,
the temperature was kept at 240.degree. C. and the reaction was
allowed to proceed. When distillation water stopped at one or two
hours, xylene was added due to promote the reaction. The
polycondensation reaction was continued until an acid value of 45
was attained. The carboxyl-functional polyester resin (A-1) thus
obtained had a number average molecular weight of 3,000.
Preparation Examples 2 to 8
[0037] The carboxyl-functional polyester resins (A-2) to (A-8) were
prepared in the same manner as in Preparation Example 1, except
that the formulation of polyester materials was charged as shown in
Table 1. Table 1 also shows acid value and number average molecular
weight of each polyester resin (A-2) to (A-8).
1 TABLE 1 Preparation Example 1 2 3 4 5 Polyester resin A-1 A-2 A-3
A-4 A-5 Terephthalic Acid 8.3 16.6 16.6 Isophthalic acid 91.3 49.8
99.6 74.7 41.5 Adipic acid 29.2 29.2 43.8 Trimellitic anhydride 9.7
19.4 19.4 9.7 9.7 Benzoic acid 6.1 Bishydroxyethyl 88.9 101.6 76.2
50.8 76.2 terephthalate Ethylene glycol 24.2 6.0 Neopentyl glycol
26 58.2 26 1,4-butandiol 13.5 Acid value 45 65 50 40 45 Number
average 3000 2000 2500 3500 3000 molecular weight Preparation
Example 6 7 8 Polyester resin A-6 A-7 A-8 Terephthalic acid 8.3
Isophthalic acid 66.4 91.3 58.1 Adipic acid 14.6 87.6 Trimellitic
anhydride 19.4 9.7 9.7 Benzoic acid Bishydroxyethyl terephthalate
101.6 88.9 Ethylene glycol 43.4 Neopentyl glycol 27 26
1,4-butandiol 13.5 Acid value 65 56 45 Number average molecular
weight 2500 2500 3000
Production of Aqueous Coating Composition
Example 1
[0038] A reaction vessel was charged with the polyester resin (A-1)
obtained in Preparation Example 1 and cooled until 1 50.degree. C.
50 parts of cyclohexanone per 100 parts of the resin was added and
the mixture was cooled to 100.degree. C. When the temperature was
100.degree. C., 10 parts of "ECN1299"(manufactured by Asahi Kasei
Epoxy Co., Ltd., creosol Novolac phenol epoxy resin) as a curing
agent was added and the mixture was dissolved in uniformity.
Subsequently, 5 parts of dimethylethanolamine was added, and the
mixture was neutralized and diluted with 275 parts of deionized
water to obtain a transparent or opaque white water dispersion
having a solid content of 25 %. The water dispersion had good
emulsion appearance without precipitating after the storage at
20.degree. C. for one month.
[0039] The resulting water dispersion was mixed with 0.25 parts of
choline chloride as a curing catalyst and 10 parts of isopropanol a
surfactant, followed by stirring to obtain an aqueous coating
composition.
Examples 2 to 4 and Comparative Examples 1 to 4
[0040] The general procedure of Example 1 was repeated, except that
the compositions shown in Table 2 were used, to obtain aqueous
coating compositions having a solids content of 25%. But, in the
composition of Comparative Example 2, water dispersion could not be
performed, and therefore the aqueous coating composition was not
obtained.
Performance Test
[0041] The aqueous coating compositions obtained Examples and
Comparative Examples were applied to aluminum sheets with a bar
coater to form coating films having a thickness of 15 .mu.m (when
dried), followed by baking at 230.degree. C. for 10 minutes. Each
coating film was subjected to the following performance tests; The
results are summarized in Table 3.
[0042] (* 1) Film surface condition: The surface of the film was
visually evaluated according to the following criteria.
[0043] A: Excellent smoothness with no foaming over the entire
film
[0044] B: Slight unevenness with small foam all over the film
[0045] C: Slight unevenness with large foam all over the film
[0046] (*2) Gel fraction ratio: The aqueous coating composition was
applied to a weight of W1 of tin plate to obtain a coated plate
having a weight of W2. A flask equipped with reflux condenser is
charged with the coated plate having a weight of W2 and methyl
ethyl ketone so that the coating area to the amount of methyl ethyl
ketone may be 100 cm2 to 100 cc, followed by heating to reflux for
1 hour. Thereafter the coated plate was picked up and dried at
120.degree. C. for 30 minutes.
[0047] The coated plate was cooled down until room temperature and
a weight of W3 of the coated plate was measured. The gel fraction
ratio (%) was pursued by means of the following formula.
Gel fraction ratio (%){(W3-W1) / (W2-W1) }* 100
[0048] (*3) Processability: A coated plate was folded into two
equal parts in such a way that the film was outside. A 1-kg iron
load was dropped on the bent portion of the coated plate from a
height of 50 cm. A length of crack of the bent portion of the
coated plate was measured and evaluated according to the following
criteria.
[0049] A: Less than 5mm
[0050] B: 5mm or more and less than 20mm
[0051] C: 2mm or more
[0052] (*4) Water resistance: A coated plate was treated at
125.degree. C. for 35 minutes in an autoclave followed by dipping
into water to evaluate visually a degree of blushing of the film
according to the following criteria.
[0053] A: No blushing
[0054] B: Slight degree of blushing
[0055] C: Remarkable degree of blushing
[0056] (*5) Adhesion: Squares were formed by effecting 11 cuts
respectively in length and width at about 1.5 mm intervals on a
film of a test plate by using a knife. An adhesive cellophane tape
having a width of 24 mm was adhered to the squares, followed by
strongly peeling the tape to evaluate the adhesion properties of
the squares according to the following criteria.
[0057] A: No peeling
[0058] B: Slight degree of peeling
[0059] C: Remarkable degree of peeling
[0060] (*6) Adhesion after water resistance test: A coated plate
was treated at 125 V for 35 10 minutes in an autoclave followed by
dipping into water. Squares were formed by effecting 11 cuts
respectively in length and width at about 1.5 mm intervals on the
film of the coated plate by using a knife. An adhesive cellophane
tape having a width of 24 mm was adhered to the squares, followed
by strongly peeling the tape to evaluate the adhesion properties of
the squares according to the above (*5) criteria.
[0061] (*7) Corrosion resistance: The aqueous coating compositions
obtained Examples and Comparative Examples were applied to the
inside surface of steel two-piece cans having capacity of 250 cc by
a hot air spray coating to form coating films 15 .mu.m (when
dried), followed by baking at 215.degree. C. for 60 seconds to
obtain the coated two-piece can bodies. 10 % pineapple juice was
heated at 98.degree. C. and packed into the coated two-piece can,
followed by hermetically sealing the can. After storage at
37.degree. C. for 6 months, the can was opened and the degree of
corrosion of the inside of, the can was visually evaluated
according to the following criteria.
[0062] A: No change
[0063] B: Slight corrosion
[0064] C: Remarkable corrosion
[0065] (*8) Flavor-retaining ability: Tap water (250 cc) treated
with activated carbon was packed into the coated two-piece can
obtained similarly as above (*7). The can was hermetically sealed
and treated for sterilization at 100.degree. C. for 30 minutes.
After storage at 37.degree. C. for 6 months, the liquid in the can
was tested for flavor-retaining ability and evaluated according to
the following criteria.
[0066] A: No change in flavor
[0067] B: Slight change in flavor
[0068] C: Remarkable change in flavor
2 TABLE 2 Example Comparative Example 1 2 3 4 1 2 3 4 Polyester
resin kind A-1 A-2 A-1 A-3 A-1 A-1 A-4 A-5 Amount 100 100 100 100
100 100 100 100 Cyclohexanone 50 50 30 50 50 50 Solvesso 1500 20
Butylcellosolve 50 Propylene glycol 50 monomethyl ether Novolac
epoxy resin 10 10 10 10 10 10 10 10 Dimethylethanol-amine 5.0 7.2
5.0 5.5 5.0 5.0 4.4 5.0 Neutralization equivalent 0.7 0.7 0.7 0.7
0.7 0.7 0.7 0.7 Deionized water 275 273 275 275 275 275 276 275
Total amount 440 440 440 440 440 440 440 440 Emulsion appearance
Good Good Good Good Good -- Good Good Storage stability Good Good
Good Good * -- Good Good (40.degree. C. .times. 1 month)
*Sedimentation/ separation
[0069]
3 TABLE 3 Example Comparative Example 1 2 3 4 1 3 4 Film surface
condition .smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. .smallcircle. Gel fraction ratio 85 87
84 86 83 84 83 Processability .smallcircle. .smallcircle.
.smallcircle. .smallcircle. .smallcircle. X .smallcircle. Water
resistance .smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. .tangle-solidup. Adhesion .smallcircle.
.smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. Adhesion after water resistance
.smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. .tangle-solidup. test Corrosion
resistance .smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. .smallcircle. Flavor-retaining ability
.smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. X
Production of Aqueous Coating Composition
Example 5
[0070] The flask was charged with the polyester resin (A-1)
obtained in Preparation Example 1 and cooled until 150.degree. C.
50 parts of cyclohexanone per 100 parts of the resin was added and
the mixture was cooled until 100.degree. C. When the temperature
was 100.degree. C., 10 parts of "EHPE-3150, (manufactured by Daicel
Chemical Industries, Ltd., alicyclic epoxy resin) as a curing agent
was added and the mixture was dissolved in uniformity.
Subsequently, 5 parts of dimethylethanolamine was added, and the
mixture was neutralized and diluted with 275 parts of deionized
water to obtain a transparent or opaque white water dispersion
having a solid content of 25 %. The water dispersion had good
emulsion appearance without precipitating after the storage at
40.degree. C. for one month.
[0071] The resulting water dispersion was mixed with 1 part of
choline chloride as a curing catalyst and 10 parts of isopropanol a
surfactant, followed by stirring to obtain an aqueous coating
composition.
[0072] Example 6, 7 and Comparative Example 5 to 8
[0073] The general procedure of Example 5 was repeated, except that
the compositions shown in Table 4 were used, to obtain aqueous
coating compositions having a solid content of 25 %. But, in each
composition of Comparative Example 6 and 7, water dispersion could
not be performed, and therefore the aqueous coating composition was
not obtained.
Performance Test
[0074] The aqueous coating compositions obtained Example 5 to 7 and
Comparative Example 5 to 8 were applied to tin plates with a bar
coater to form coating films 10 .mu.m (when dried), followed by
baking at 230.degree. C. for 10 minutes. Each coating film was
subjected to the following performance tests. The result is
summarized in Table 5.
[0075] (*1) Film surface condition: The surface of the film was
visually evaluated according to the following criteria.
[0076] A: Excellent smoothness with no foaming over the entire
film
[0077] B: Slight unevenness with small foam all over the film
[0078] C: Slight unevenness with large foam all over the film
[0079] (*2) Adhesion: Squares were formed by effecting 11 cuts
respectively in length and width at about 1 mm intervals on a film
of a coated plate by using a knife according to JIS K-5400. An
adhesive cellophane tape was adhered to the squares, followed by
strongly peeling the tape to measure a number of remaining squares
per 100 squares.
[0080] (*3) Pencil hardness: A pencil hardness of the coated plate
was measured by pencil scratch examination of JISK-5400.
[0081] (*4) Bending resistance: A coated plate was placed at
20.degree. C. atmosphere and bent in a right angle in two or three
seconds in such away that the film was outside. A peeling condition
of the bent portion of the coated plate was evaluated according to
the following criteria.
[0082] A: No change
[0083] B: Peeling and cracking was found
4 TABLE 4 Example Comparative Example 5 6 7 5 6 7 8 Polyester resin
kind A-1 A-6 A-1 A-1 A-1 A-7 A-8 Amount 100 100 100 100 100 100 100
Cyclohexanone 50 50 30 50 50 Solvesso 1500 20 Butylcellosolve 50
Propylene glycol 50 monomethyl ether Novolac epoxy resin 10 10 10
10 10 10 10 Dimethylethanol-amine 5.0 7.2 5.0 5.0 5.0 4.4 5.0
Neutralization equivalent 0.7 0.7 0.7 0.7 0.7 0.7 0.7 Deionized
water 275 273 275 275 275 276 275 Total amount 440 440 440 440 440
440 440 Emulsion appearance Good Good Good Good -- -- Good Storage
stability Good Good Good * -- -- Good (40.degree. C. .times. 1
month) *Sedimentation/ separation
[0084]
5 TABLE 5 Comparative Example Example 5 6 7 5 8 Film surface
condition .largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. Adhesion 100/100 100/100 100/100 100/100 100/100
Pencil hardness 2H H 2H 2H B Bending resistance .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
* * * * *