Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
The present invention relates to an aqueous coating
resin composition. More particularly, the invention
relates to an aqueous coating resin composition useful
for forming a coating directly on a tinplate, on aluminum
plate, a treated steel plate or the like, or on an under-
coating layer of a phenol-epoxy or epoxy-amino paint,
which is formed on such metal substrate, particularly the
inner surface of a metal can or can closure.
For metal cans, there have heretofore been used a
phenol-epoxy or epoxy-amino paint as a base coat paint to
be a~plied on the inner surface and a thermoplastic copolymer
composed mainly of vinyl chloride and vinyl acetate as a
topcoat-forming material. When the base coat alone is
applied, the flavor of the content is degraded, and when
only the topcoat of a copolymer composed mainly of vinyl
chloride and vinyl acetate is formed, the adhesion to the
metal substrate and the resistance are insufficient.
Since this copolymer is readily decomposed under heat,
the temperature range for the baking treatment is very
narrow. Furthermore, since conventional topcoat-forming
paints are of the non-aqueous type and contain considerable
quantities of organic solvents, polIution of the working
atmosphere and other problems are caused and the use of
these paints involves a risk of occurrence of a fire.
As means for solving these problems, there have been
proposed various aqueous coating compositions to be used
instead of the conventional vinyl chloride-vinyl acetate
paints. For example, the specification of United States Patent
No. 4,021,396 discloses an aqueous coating composition
obtained by neutralizing an epoxy resin and an acrylic
- 2 -
copolymer formed by copolymerizing 0.5 to 10% of an
unsaturated carboxylic acid with other specific monomers,
with ammonium or an amine. From experiments made by us,
it was found that this aqueous coating composition is poor
in the storage stability, particularly at a high temperature
(about 50C) and gelation is readily caused at such
high temperature, and that at the baking step, there is
caused a problem that the physical properties of the
resulting coatings vary widely depending on the difference
of the baking temperature.
Japanese Patent Application Laid-Open Specification
No. 1228/78 proposes a paint formed by grafting an unsatu-
rated carboxylic acid-containing monomer to the aliphatic
skeleton of an epoxy resin, neutralizing a mixture of this
graft polymer and a carboxylic acid-modified functional
addition polymer with ammonium or an amine and dispersing
the neutralization product in an aqueous medium. Further-
more, Japanese Patent Applica~ion Laid-Open Specification
No. 1285/78 dlscloses an improvement of the above-mentioned
technique, in which the epoxy group of an epoxy resin is
reacted with a stopping agent to improve the resistance to
hydrolysis.
The proposals made in these Japanese Patent Applica-
tion Laid-Open Specifications still involve problems ~o
be solved. For example, since it is necessary to effect
graft polymerization, expensive and dangerous benzoyl
peroxide or a corresponding free radical initiator should
be used in large quantities. Moreover, the molecular
weight of the addition polymer is reduced, resulting in
degradation of the physical properties of the resulting
,~
~8'~8
coatingS. Therefore, there are caused various disadvan-
tages with respect to physical properties, adaptability
to operations and manufacturing and running costs. Still
further, scattering of properties in products is readily
caused according to reaction conditions adopted for the
graft polymerization.
The most important role of a composition for coating
the inner surface of a metal can is to sanitarily protect
the content. If dissolution of components of the coating
into the content is advanced at the s~erilizing step or
during long-time storage, the flavor of the content is
degraded and a sanitarily undesirable phenomenon is caused
by the extracted components. Accordingly, the coating
formed on the inner face of the metal can should have
such a characteristic that dissolution of components o
the content into the content should be reduced to a level
as low as possible under treatment conditions which the
metal can actually undergo. ~Ordinarily, dissolution
of components of the coating into the content is evaluated
depending on the ratio of extraction of the components in
water from the coating). All of the aqueous coating
compositions according to the above-mentioned proposals
are still insufficient in this point. It is therefore a
primary object of the present invention to provide an
aqueous coating composition which is excellent in the
stability and can give coatings having excellent physical
properties and in which dissolution of components of the
coating into the content can be controlled to a very low
level.
From experiments made by us, it was found that in an
aqueous coating composi-tion comprising an acrylic resin
and an epoxy resin 7 if the molecular weight of the epoxy
resin used is low~ the ratio o:~ extraction of the components
in water from -the re~sulting coating tend,, to increase.
In -this case 9 -the epoxy group of ~the low--molecular weight
epoxy resin chemically reac-ts in the aqueous medium ~uring
storage 9 resulting in increase of the viscosity or ocour-
rence of gelation. The coating formed by using such
composition having an increased viscosity or such gelled
composition is inferior in various physical properties.
On the other hand 7 when a high-molecular-weight epoxy resin
having a number average molecular weight exceeding 19400
is employed9 -the wa-ter extraction ratio is considerably
reduced 7 but the level of the water ex-traction ratio is not
so low as -the level attainable by the conventional vinyl
chloride copol~mer paintO Although chemical reaction of
the epoxy group of the high-molecular-weight epoxy group
during storage is reduced~ -the compatibi~ity of the epoxy
resin with the acrylic resin is poor and the epoxy resin
tends to separate from the acrylic resin during storage.
~urthermore9 in the resul-ting coating9 whitening is readily
caused owing to -this poor compatibility 9 and a coating having
satisfactory physical properties cannot be obtained~
We made researches with a view to solving the foregoing
problems and as a resul-t9 we succeeded in developing a
novel aqueous coating resin composition in which the ratio
of extraction of the components in water from the coating9
that is9 consumption of potassium permanganate 7 iS remar-
kably reduced9 an excellent flavor retaining property
can be attained 7 the s-toage stability in the form of a
-- 5 --
32~8
paint is very good and the resulting coating is excellent in
various physical properties such as the resistance to
boiling water and the processability. Thus, we have now
completed the present invention.
More specifically, in accordance with the present
invention, there is provided an aqueous coating resin
composition which comprises an aqueous dispersion of a
carboxyl group-excessive epoxy resin-acrylic resin partial
reaction product in the presence of ammonia or an amine in
an amount sufficient to maintain the pH value of the
composition between 5 and 11, said carboxyl group-excessive
epoxy resin-acrylic resin partial reaction product being
formed by reacting ~A) an alkali-neutralizable acrylic
resin having a number average molecular weight of from
5,000 to 100,000, which is obtained by copolymerl~ing 12
to 50% by weight of acrylic acid or methacrylic acid with
50 to 88% by weight of at least one member selected from
the group consisting of styrene, methylstyrene, vinyltoluene
and alkyl esters of acrylic acid and methacrylic acid having
1 to 8 carbon atoms in the alkyl group, with (B) an aromatic
epoxy group having 1.1 to 2.0 epoxy groups on the average
in one molecule and a number average molecular weight of
at least 1,400.
The characteristic features of the aqueous coating
resin composition of the present invention are as follows
(1I Since a high-molecular-weight epoxy resin is used
and this high-molecular-weight epoxy resin is chemically
bonded to an acrylic resin, the ratio of extraction of the
components in water from the resulting coating is very low.
Accordingly, the flavor-retaining property under treatment
~ - 6 -
~8Z~38
conditions which the metal can pract:ically undergo is
very good and consumption of potassium permanganate is
remarkably reduced.
(2) Since a high-molecular-weight epoxy resin is
used, increase of the viscosity of the paint or gelation
owing to chemical reaction of the epoxy group is not caused
during storage.
(3) Since a high-molecular-weight epoxy resin and
an acrylic resin, between which the compatibility is very
low, are chemically bonded to form a carboxyl group-excessive,
self-emulsifiable epoxy resin-acrylic resin partial reaction
product, the phase separation is not caused in the paint
during storage.
(~) Since there are present epoxy groups left at the
terminals, the above-mentioned partial reaction product has
a self-crosslinking property, and by virtue of not only
this self-crosslinking property and a good film-forming
property inherent of the acrylic resin, a coating having
excellent physical properties can be obtained.
(5) An aqueous coating resin composition including
an aromatic epoxy resin having 1.1 to 2.0 epoxy groups in
one molecule and a number average molecular weight of
2,000 to 10,000, which is obtained by heating an aromatic
epoxy resin having 2 epoxy groups in one molecule and a
number average molecular weight of 1,~00 to 5,000 in the
presence or absence of an epoxy group-modifying agent has
a very industrially advantageous property that variation
of properties in the resulting coating, which is due to
the variation of the baking temperature at the coating
forming step, is drastically reduced. This aqueous coating
,~
~4~
resin composition is excellent over aqueous coating Tesin
compositions including an aromatic epoxy resin which has
not been subjected to the heat treatment, with respect to
other properties of the coating.
Figure 1 is a chart showing the molecular weight
distribution determined according to GPC just after mixing
(A) a carboxyl group-containing acrylic resin with (B) an
epoxy resin solution at room temperature in Example 1.
Figure 2 is a chart showing the molecular weight
distribution determined according to GPC when the above-men-
tioned mixture has been cooked at 80C for 1 hour.
The alkali-neutralizable acrylic resin (A) that is
used in the present invention may be obtained by copolymeriz-
ing 12 to 50% by weight of acrylic acid or methacrylic
acid with 50 to 88% by weight of at least one member
selected from the group consisting of styrene, methylstyrene,
vinyltoluene and alkyl esters of acrylic acid and methacrylic
acid having 1 to 8 carbon atoms in the alkyl group in a
hydrophilic organic solvent having a boiling point of 70
to 230 C, such as ethyleneglycol monoethyl ether or ethylene-
glycol monobutyl ether in the presence of a radical poly-
merization initiator such as azobisisobutyronitrile or a
peroxide at a temperature of 80 to 150C. If the amount
of acrylic acid or methacrylic acid used for this
copolymerization is smaller than 12% by weight, the
dispersion stability of the resulting aqueous coating resin
composition is poor. If the amount of acrylic acid or
methacrylic acid is larger than 50% by weight, the water
resistance of the resulting coating is degraded.
As the alkyl ester of acrylic acid or methacrylic
acid, there can be mentioned, for example, methyl acrylate
or methacrylate, ethyl acrylate or methacrylate, isopropyl
acryla-te or methacrylate, n-butyl acrylate or methacrylate,
isobutyl acrylate or methacrylate, n-amyl acrylate or
methacrylate, isoamyl acrylate or methacrylate, n-hexyl
acrylate or methacrylate, 2-ethylhexyl acrylate or methacryl-
ate and n-octyl acrylate or methacrylate.
From the viewpoint of the sanitary effect of the
inner coating of a metal can on the content food, it is
preferred that the monomer combination for formation of the
above-mentioned copolymer be selected from (1) methyl
methacrylate/2-ethylhexyl acrylate/acrylic acid, (2)
styrene/methyl methacrylate/ethyl acrylate/methacrylic
acid and (3) styrene/ethyl acrylate/methacrylic acid.
The alkali-neutralizable acrylic resin (A) has a
number molecular weight of 5,000 to 100,000, preferably
20,000 to 40,000. Furthermore, it is preferred that the
acid value of the alkali-neutralizable acrylic resin (A) be
in the range of from 80 to 350 as calcula~ed as the solid.
Epichlorohydrin/bisphenol type epoxy resins are
used in the present invention as the aromatic epoxy resin
having 1.1 to 2.0 epoxy groups on the average in the molecule
and a number average molecular weight of at least 1,400. For
example, there can be mentioned "Epikote* 1004", "Epikote
1007" and~"Epikote 1009" manufactured and sold by Shell
Chemical Co. and "Epiclon* 4050" and "Epiclon 7050" manu-
factured by Dainippon Ink Chemicals Co. These commer-
cially available products have two epoxy groups in one
molecule and a number average molecular weight of 1,400
to 5,000. In the present invention, a high-molecular-
*Trademark - 9 -
38
weight aromatic epoxy resin obtained by heating and modifying
an unmodified aromatic epoxy resin such as mentioned above
in the presence or absence of an epoxy group-modifying
agent. The resulting modified aromatic epoxy resin has an
elevated molecular weight and the aqueous coating resin
composition obtained by using such modified aromatic epoxy
resin provides a coating having a much reduced water extrac-
tion ratio. When the modified epoxy resin obtained by
conducting the heat treatment in the presence of an epoxy
group-modifying agent is used, the water extraction ratio
is further reduced, as compared with the case where the modi-
fied epoxy resin obtained by conducting the heat treatment
in the absence of an epoxy group-modifying agent is used.
MoreoverJ by the use of such modified aromatic epoxy resin,
there can be attained an effect that variation of the water
extraction ratio or physical properties of the coating owing
to the variation of the baking temperature at the coating-
forming step can be remarkably reduced.
As the epoxy group-modifying agent, there can be
used, for example, bisphenols such as bisphenol A and bisphenol
B, and vegetable oil fatty acids such as dehydrated castor
oil, soybean oil fatty acid, cotton seed oil fatty acid,
safflower oil fatty acid, tall oil -fatty acid, linseed oil
fatty acid, castor oil fatty acid, coconut oil fatty acid
and palm oil fatty acid, and mixtures thereof. If necessary,
aromatic carboxylic acids such as benzoic acid and p-tert~
butyl benzoate may be used in combination with the above
modifiers. Theoretically, the amount of the epoxy group-
modifying agent may be up to 45 equivalent % based on the
epoxy group of the unmodified aromatic epoxy resin. However,
- 10 -
~.
~48Z~
since heating is ordinarily necessary for this modification
reaction and self-condensation is caused in the aromatic
epoxy resin under heating, a modified aromatic epoxy resin
having 1.1 to 2.0 epoxy groups in one molecule and a number
average molecular weight of 2,000 to 10,000 is practically
obtained by using the epoxy group-modifying agent in an
amount of 0.5 to 10 equivalent %.
Conditions to be adopted for the heating reaction
between the unmodified aromatic epoxy resin and the epoxy
group-modifying agent will now be described.
When a bisphenol is used as the modifying agent,
predetermined amounts of the epoxy resin and bisphenol are
charged in a stirrer-equipped reaction vessel, the inside
atmosphere of which has been replaced by nitrogen, and the
mixture is cooked in the absence of a solvent or in a
hydrophilic organic solvent such as ethyleneglycol monobutyl
ether at 150 to 170C for about 5 hours. When a fatty
acid is used as the modifying agent, predetermined amounts
of the epoxy resin and fatty acid and, if necessary, a small
amount of sodium carbonate as the alkali catalyst, are changed
in the same stirrer-equipped, nitrogen-substituted reaction
vessel as described above, and the mixture is cooked in the
absence of a solvent or in a hydrophllic organic solvent
such as ethyleneglycol monobutyl ether at 140 to 170C
for about 5 hours. The heat treatment not using an epoxy
group-modifying agent is carried out under similar condi-
tions. More specifically, heating is conducted in the absence
of a solvent or in a hydrophilic organic solvent such as
ethyleneglycol monobutyl ether at 140 to 170C for several
hours, if desired, in ~he presence of a catalyst such as
sodium carbonate.
The modification reaction of unmodified aromatic epoxy
resins can be controlled by measuring the content of oxirane
according to the hydrobromic acid/acetic acid method
described by, for example, "Determination of Epoxide Groups"
written by B. Dobinsonl W. Hofmann and B. P. Stark.
In the present invention, a carboxyl group-excessive
epoxy resin-acrylic resin partial reaction product obtained
by reacting the above-mentioned alkali-neutralizable acrylic
resin (A) with the above-mentioned aromatic epoxy resin
(B) is used. Reaction condltions adopted for formation of
this partial reaction product will now be described.
The two components (A) and (B) are stirred in a hydro-
philic organic solvent such as ethyleneglycol monobutyl
ether in the presence or absence of ammonia or an amine
as described hereinafter at 60 to 170C for 10 minutes
to 2 hours, if necessary, under pressure. The reaction
can be controlled by measuring the content of oxirane,
examining increase of the viscosity or checking the molecular
weight distribution according to gel permeation chromatography
(GPC) as described in detail in Example 1 given hereinafter.
In the present invention, the weight ratio (A)/(B) of
the alkali-neutrali~able acrylic resin (A) to the aromatic
epoxy resin (B) is preferably adjusted in the range of from
4/1 to 1/5. When the amount of the component (A) exceeds
beyond this range, a tendency of degradation of physical
properties of the resulting coati-ng is observed. On the
other hand, when the amount of the component (B) is too
large, the ratio of extraction of the components in water
from the coating is increased and the stability of the
- 12 -
2~
aqueous coating resin composi~ion tends to decrease. It
is preferred that the weight ratio (A)/(B) be adjusted so
that the amount of excessive carboxyl groups in the aqueous
coating resin composition is such as will provide an acid
value of 30 to 200 (as calculated as the solid).
The aqueous coating resin composition of the present
invention can be prepared by dispersing the above-mentioned
epoxy resin-acrylic resin partial reaction product in an
aqueous medium containing ammonia or an amine in such an
amount that the pH value of the final coating composition
is in the range of from 5 to 11. As the amine, there can
be used, for example, alkylamines such as trimethylamine,
triethylamine and butylamine, alcohol amines such as
2-dimethylaminoethanol, diethanolamine, triethanolamine,
aminomethylpropanol and dimethylaminomethylpropanol, and
morpholine. Furthermore, polyvalent amines such as
ethylene-diamine and diethylene-triamine can be used.
By the term "aqueous medium" used herein are meant
water and a mixture of water and a hydrophilic organic solvent
in which the content of water is at least 10% by weight.
As the hydrophilic solvent, there can be mentioned, for
example, alkylalcohols such as methanol, ethanol, n-propanol,
isopropanol, n-butanol, sec-butanol, tert-butanol and iso-
butanol, ather alcohols such as methyl cellosolve*, ethyl
cellosolve, propyl cellosolve, butyl cellosolve, methyl
carbitol and ethyl carbitol, ether esters such as methyl
cellosolve acetate and ethyl cellosolve acetate, and dioxane,
dimethylformamide, diacetone alcohol and tetrahydrofurfuryl
alcohol.
The aqueous coating resin composition of the present
*Trademark - 13 -
invention may be applied to a metal plate such as a tinplate,
an aluminum plate or a treated steel plate directly or after
application of an undercoat or forming processing according
to known coating means such as brush coating, spray coating,
dip coating, roll coating or electric deposition coating.
The thickness of the coating is not particularly critical,
so far as the entire surface of the metal plate is uniformly
coated, but ordinarily, the thickness of the coating is
adjusted in the range of from 1 to 20 microns.
~Vhen the aqueous coating resin composition is applied
to a me-tal plate such as a tinplate, an aluminum plate or
a treated steel plate directly or after formation of under-
coating of an epoxy-amino resin or the like, a very good
adhesion to the metal substrate can be attained, and
especially when the aqueous coating resin composition of
the present invention is applied to the inner surface of
a metal can, the water extraction ratio can be drastically
reduced and a coating excellent in the flavor-retaining
property, adhesion, resistance to boiling water and
processability can be obtained. Moreover, the aqueous
coating resin composition of the present invention may be
used for the manufacture of aqueous varnishes for dispersing
pigments or anticorrosives therein, metal paints and printing
inks, and if the kind of the acrylic resin is appropriately
chosen, the composition of the present invention may be used
as an adhesive, a fiber-processing agent or the like.
The present invention will now be described in detail
with reference to the following Examples that by no means
limit the scope of the invention. In these Examples, all
of "%" and "parts" are by weight.
- 14 -
z~
Example 1
(A) Preparation of Carboxyl Group-Containing Acrylic Resin
Solution:
Styrene 300.0 parts
Ethyl acrylate 210.0 parts
Methacrylic acid 90.0 parts
Ethyleneglycol monobutyl ether 388.0 parts
Benzoyl peroxide 12.0 parts
1/4 of a mixture having the above composition was charged
in a 4-neck flask, the inside atmosphere of which had been
replaced by nitrogen, and the temperature was elevated to
80 to 90C by heating. While the temperature was being
maintained at this level, remaining 3/4 of the mixture
was gradually added dropwise over a period of 2 hours.
After completion of the dropwise addition, the reaction
mixture was stirred at the above temperature for 2 hours
and was then cooled to obtain a carboxyl group-containing
acrylic resin solution having an acid value of 93 as calculated
as the solid (all the acid values mentioned hereinafter
are those as calculated as the solid), a solid content of
59.7% and a viscosity of 4,100 cps as measured at 25C ~all
the viscosity values mentioned hereinafter are those as
measured at 25C).
(B) Preparation of Epoxy Resin Solution:
Epikote 1,007 500 parts
Ethyleneglycol monobutyl ether 333.3 parts
All of a mixture having the above composition was charged
in a 4-neck flask, the inside atmosphere of which had been
replaced by nitrogen, and the inside temperature was elevated
to 100C by gradual heating and the mixture was stirred for
- 15 -
`~
B~
1 hour to completely dissolve the epoxy resin. Then, the
solution was cooled to 80C to form an epoxy resin solution
having a solid content of 60%.
~C) Preparation of Aqueous Coating Resin Composition:
(1) Carboxyl group-containing acrylic 100 parts
resin solution (A)
Epoxy resin solution (B)50 parts
(2) 2-Dimethylaminoethanol9.3 parts
(3) Deionized water 290.7 parts
All of the mixture (1) was charged in a 4-neck flask,
and the component (2) was added thereto under stirring to
neutralize the contained carboxyl groups substantially
equimolarly. Then, the inside temperature was elevated to
80 C and stirring was conducted at this temperature for
30 minutes. Then, the mixture was cooled to room temper-
ature. The ratio of decrease of the oxirane content
was 63.5%, and the viscosity was 1.5 times the viscosity
before this cooking treatment.
The molecular distribution before cooking, determined
according to GPC, is shown in the chart of Figure l. As is
seen from Figure 1, there are present two peaks of the high-
molecular-weight acrylic resin and the low-molecular-weight
epoxy resin. In the molecular weight distribution after
cooking, shown in the chart of Figure 2, the peak of the low-
molecular-weight epoxy resin is not observed. Accordingly,
it was confirmed that the epoxy resin was rendered pendant
from the acrylic resin.
After the above-mentioned cooking treatment, the
component (3) was gradually added under agitation to obtain
a slightly milky white dispersion having a solid content
~ - 16 -
/ ~
of 19.8% and a viscosity of 360 cps. When the resulting
dispersion was stored at 50C for 1 month, no change was
observed.
Example 2
(B) Preparation of Fatty Acid-Modified Epoxy Resin Solution:
~1) Epikote 1,007 500.0 parts
Coconut oil fatty acid 2.6 parts
Sodium carbonate 0.2 part
E~hyleneglycol monobutyl ether125.4 parts
(2) Ethyleneglycol monobutyl ether 209.4 parts
The mixture (1) was charged in a 4-neck flask, the
inside atmosphere of which had been replaced by nitrogen,
and the inside temperature was elevated to 160 C and
cooking was carried out for 4 to 5 hours. The ratio of
decrease of the oxirane content was 14%. Then, the reac-
tion mixture was cooled to 80C and the component (2)
was added thereto to obtain a modified epoxy resin solution
having a solid content of 60%.
(C) Preparation of Aqueous Coating Resin Composition:
(1) Carboxyl group-containing acrylic 100.0 parts
resin solution (A) prepared in
Example 1
Modified epoxy resin solution (B) 50.0 parts
t2) 2-Dimethylaminoethanol 9.3 parts
(3) Deionized water 290.7 parts
All of the mixture (1) was charged in a 4-neck flask,
and the component (2) was added thereto under agitation to
neutralize 90 mole % of the contained carboxyl groups. Then,
the inside temperature was elevated to 100C and cooking
was carried out at this temperature for 30 minutes. The
ratio of decrease of the oxirane content was found to be
X
83.5%.
The component (3) was gradually added to the reaction
mixture under agitation to obtain a milky white dispersion
having a solid content of 20.1% and a viscosity of 500 cps.
When this dis~ersion was stored at 50C for 1 month, no
change was observed.
Examples 3 to 7 and Compa~ative Examples 1 to 6
(A) Preparation of Carboxyl Group-Containing Acrylic Resin
Solution:
A carboxyl group-containing acrylic resin solution
was prepared according to a recipe shown in Table 1 in the
same manner as described in Example 1.
- 18 -
~:~L4~
~¦ [same as in Example 1]
~¦ [same as in Example 3]
zO
~ ~¦ [same as in Example 3]
x
~ ~¦ [same as in Comparative Example 2]
h
t~ O ~ 00 q~ N cr, O
0~ t~ ~0 11) ~ oOo ~ `'
[same as in Example 1]
~> I O O O 00 O Cl O L~
~ ~ o o o oo ~ n O
E-' ~`1 N t~
00
~¦ [same as in Example 1]
, ~
o
z ~ [same as in Example 4]
~ I o 000 o oo ~ o o o
00 u'
o o o co ~ cr~ o so
~D
h `-- ,_
~ ~ Vl
v, ~ ~ a~
~ I~
O ~ C ~ O
~ ~ ~ ::C ¢ ~ ~ O ~ V~
O ~-- ~ X tL~ ¢ ~ ¢ ~ O 1~ 0 rl
- 19 -
z~
In Table 1, abbreviations have the following meaning:
St: Styrene
h~lA: methyl methacrylate
2EHA: 2-ethylhexyl acrylate
EA: ethyl acrylate
hlAA: methacrylic acid
AA: acrylic acid
BP0: benzoyl peroxide
(B) Preparation of Epoxy Resin Solution and Modified Epoxy
Resin Solution:
An epoxy resin or modified epoxy resin solution was
prepared according to a recipe shown in Table 2. All the
starting materials other than ethyleneglycol monobutyl
ether for dilution were charged in a 4-neck flask, and the
temperature was elevated to a predetermined level and cooking
was carried out for a predetermined time. Then, the reaction
mixture was cooled to ab ut 80 C and ethyleneglycol
monobutyl ether for dilution was added thereto.
- 20 -
.fL3L~
~ol [ samt-~ as in Exar.lple 1 ~
O O t\l 1~ cr~ r I
O u~ O ~O O ~D O t~, O O Lr~
~; O t\l r I u~ D
u~ r I t \I r~r~
~ ~1
X o N r~ ~o u~ ~D u~
:~ LS~ r~ t\J r
t~
~ ~ [ sam~ as in Example 5 ]
s~
'~ '`~¦ [ same as in Example 1 ]
v o o ~ c,~
r~ ¦ O u~ cO u~ ~o r~
u~ rl t\l rl
o u~ t\~ ~ ~ O
~I o t~J o u; G; ~ O O u~
o t~ o r~ ~O ~D
r~ r~ t\l r~
O O ~ 1~
t~l ~Dl o u; co' ~ o' o u-~
r~ u~ rY t\l r~
,n o
E~ ~; I O ~ ~ r~
tL~ I r~ 3 r-l u~ t~ ~0 t~ o u~
r~ t\l o r I u~ ~o
~ I r~ r~ t\J r~
x I t~ ~o c~ u~ c~
~ o Lr~ co r~ I ~ O r~
O U~ ~r.~ ~, u~
u~ r I t~l r~
[ samS as in F,xampl.~ 1. ]
r~ r~
r~ ~ -1~ ~ C)
~ O o rl !~ O ~ tl)
+~ ~ tl) E~
t~ r~l ~ ~0 tL) O r~ h tS~ ~ t~
._ O O O <J r~ ,n ~ h ~d tt,, +~ tv ~: E3
tn O O ~1 h r~ h r-l h ~ O ~ tu ~1
~ r~ r~ r~ r--l t~ 1~ ~ t~l~ ~ r~
tLI ti) tL) tL~ O tL) b10 t~,O
O O ,~ r~ h r I h O 0
, O ~rl ~ t~ rl ,~ ,~
o , , . rn t~ o O O
,Q t~ tl~ tU tL~ t~ tl) ~ O u~ t~ o
B
(C) Preparation of Aqueous Coating Resin Composition:
In all the Examples and Comparative Examples, except
Comparative Example 6, aqueous coating resin compositions
were prepared according to recipes shown in Table 3 in
the same manner as described in Example 1. In Comparative
Example 6, the operation was conducted in the same manner
as described in Example 1 except that the carboxyl group-
containing acrylic resin solution and epoxy resin solution
were not cooked but were merely mixed at 25C.
- 22 -
.
~8
~¦ [~ame as in ~ .--
Example 1]
~1 [same as Compara-
z ~ive Example 4] N ~
C~ .,
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X~ I O O ~ O 11'~
Ul
[same as Compara-
I ~ive Example 2]
~: o o o o ~
o ~ I o o u~
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[same as in O O
Example 1]
I o o In ,.
E~1~ O o o o cn o
O O N 00
a~
[same as in
I Example 1]
o
z I o ooo
~ In O O ~ L~ O
7 ~o o
o oo~ ~ o
Ul ~ I O O ~ ~ o L~
o ~ oo ~ ~C)
o o.,, L~ ~
c~) o o u, ~ o n
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o ~ ~ o R h ~ o
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O & ~ O &~ O ~S '~ ~o ~
- 23 -
~'~
2~
Each of the aqueous coating resin cor,lpositions
prepared in Examples 1 through 7 and Comparative Examples
1 through 6 was subjec~ed to the stability test. Further-
more, after each composition had been allowed to stand
still at room temperature for 5 hours, the composition was
roll-coated on a tinplate having an undercoating of an
epoxy-urea resin, so that the thickness of the dry coating
was 10 to 12 ~, and baking was carried out at 160 or 200 C
for 5 minutes to form a test panel. The so obtained test
panel was subjected to various resistance tests. Results
of the stability and resistance tests are shown in Table 4.
Each of the above-mentioned coating compositions was
spray-coated on the inner surface of a 3-piece tinplate can
having an inner diameter of 52.5 mm, a top and bottom lap
seam height of 132.8 mm and an inner capacity of 268 cc, and
baking was carried out at 160 or 200C for 5 minutes.
Physical properties of the resulting inner surface-coated
metal can were tested to obtain results shown in Table 5.
With respect to the results of the resistance tests,
there was found no substantial difference between the case
where the untreated tinplate was used and the case where
the undercoated tinplate was used. Therefore, only
results of the resistance tests made on the untreated
tinplate are shown.
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+~ G) ~) ~J (I) O a) a) a) ~T5 0 ~5 a) ~ 5 q) ~
H ~~C r-l r-l r-l r-l r-i r-l r-l h r-l h r~l h r~l> I r~l h r-l h r~l
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-- 26 --
The tests mentioned in Tables 4 and 5 were carried out
in the following manners.
(1) Adhesion:
Cut lines having a width of about 1.5 mm were formed
on the coating by a knife. Namely, cut squares were formed
by forming 11 of such cut lines in the lengthwise direction
and 11 of such cut lines in the widthwise direction. Then,
an adhesive cellophane* tape was applied to the coating and
bonded thereto, and the tape was strongly peeled. The
10 number of the unpeeled squares is indicated in the numerator.
(2) Resistance to Boiling Water:
The coating was treated in boiling water at 100 C for
30 minutes, and the resistance was evaluated by the visual
observation and the above--mentioned adhesion test using
an adhesive cellophane tape.
(3) Processability:
A sample having the lower portion folded in two was
set at a special folding type Du Pont impact tester, and an
iron weight of 1 Kg having a flat contact surface was let to
20 fall down on the sample from a height of 50 cm and the
length of the crack formed on the folded portion of the
coating was measured.
O : 0 to 10 mm
: 10 to 20 mm
X : longer than 20 n~n
(4) Storage Stability of Paint:
A sarnple was stored in an incubator maintained at
50 C, and the appearance and resistance to boiling water
were examined at predetermined intervals during a period of
1 month.
~ *Trademark - 27 -
-
2~3~
O : good storage stability
X : abnormal changes in the dispersion, such as gela-
tion, precipitation and phase separation
5) Potassium Permanganate Consumption:
250 mQ of deionized water was filled in an inner face-
coated metal can, and after lap seaming, the can was
treated at 60C for 30 minutes or at 100C for 30 minutes.
I`he potassium permanganate consumption was determined
according to the method described in the Food Sanitation Act.
~6) Flavor-Retaining Property:
250 mQ of deionized water was filled in an inner face-
coated can, and after lap seaming, sterilization was
; carried out at 100C for 30 minutes and the can was
stored at 50C for 6 months. The content was subjected
to the flavor test.
; O : no change
: slight change
X : considerable change
(7) Water Extraction Ratio:
250 mQ of deionized water was filled in an inner face-
coated can, and after lap seaming, the can was treated at
60 C for 30 minutes or at 100C for 30 minutes. The
content was evaporated by a rotary evaporator and the can
was dried in vacuo. The weight of the residue was measured
and expressed in terms of the ratio (ppm) to the volume of
the content.
- 28 -
-
