JPH07206956A - Water-based resin and its production and water-based thermosetting coating composition containing the same - Google Patents

Abstract

PURPOSE:To obtain a low-viscosity water-based resin excellent in water dilutiveness, stability and film coating workability, useful for e.g. water-based thermosetting coatings, by mixing an aldehyde with an organic solvent in the presence of a specific copolymer followed by addition of an amino compound and then conducting a condensation reaction and by neutralizing the product followed by conversion into the water- based final product. CONSTITUTION:In the presence of a copolymer produced by copolymerization between the essential raw materials, an alpha, beta-ethylenically unsaturated carboxylic acid such as (meth)acrylic acid and an ethylenic unsaturated monomer having functional group reactive with amino resin (e.g. 2-hydroxymethyl acrylate), an aldehyde such as formaldehyde is mixed with an organic solvent followed by addition of an amino compound such as urea and then conducting a condensation reaction under heating, and at least part of the product is neutralized with a basic compound such as ammonia followed by conversion into a water-based product, thus affording the aimed water-based resin. It is preferable that the acid value of the copolymer be 20-150. And, a wate based thermosetting coating composition can be obtained by designing its composition so as to contain >=5wt.% of this water-based resin on a solid basis.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel and useful aqueous resin, a method for producing the aqueous resin, and an aqueous thermosetting coating composition containing the aqueous resin, that is, an aqueous thermosetting coating. Regarding

More specifically, the present invention is carried out in the presence of a copolymer containing an unsaturated carboxylic acid and an ethylenically unsaturated monomer having a functional group capable of reacting with an amino resin as essential raw material components. , An aqueous resin obtained by reacting an aldehyde with an amino compound, neutralizing with a basic substance, and making it aqueous; and a method for producing the aqueous resin; and an aqueous thermosetting composition containing the aqueous resin It relates to a coating composition.

[0003]

2. Description of the Related Art In recent years, it has been considered that organic solvents emitted from paints are one of the causes of air pollution in coatings in general. Recently, conventional solvent-based paints are gradually converted into water-soluble paints. The study to do is being actively conducted.

For such water-soluble paint, acrylic resin,
It is inevitable that amino resins are required to be used appropriately as the thermosetting component since a hydrated material such as polyester resin and epoxy resin is used.

Generally, there is a method for imparting a hydrophilic group by adding formaldehyde to an amino group bonded to a triazine ring to make it a methylol for the purpose of making an amino resin aqueous, but too much methylol is used. If there are many groups, problems such as poor water resistance of the cured coating film and deterioration of workability due to the odor of deformalin accompanying the curing reaction will inevitably occur.

By the way, an amino resin in which a methylolated amino resin is modified with an alkyl ether by a lower alcohol is used as a cross-linking agent for an aqueous paint.

However, even in such a case, the water resistance is poor, and in addition, if the concentration of the amino resin is increased, then a problem occurs in water solubility or water dispersibility. When using an alkyl etherified amino resin in a water-based paint, the type and amount of compound in the resin composition,
Not a little, you will be limited. Also,
A method of making it aqueous by using an emulsifier can be considered, but such a method is very inferior in water resistance.

[0008] Therefore, as another method of making water-soluble, several patents have been filed so far, in which a water-soluble resin is co-condensed with an alkyl etherified amino resin to make it water-soluble.

For example, a water-soluble resin synthesized in advance,
There is a method in which an alkyl etherified amino resin is blended under heating and co-condensed. (JP-A-3
-182543)

However, although the amino resin obtained by such a method is water-dispersed or water-solubilized, anyway, its water dilutability is insufficient, and thus the viscosity at the time of coating becomes high, The reality is that stability will deteriorate.

[0011] In recent years, there is an increasing trend toward lowering VOC (volatile organic compounds) of water-based paints, and when the water dilutability is insufficient, such VOCs are quite possible.
However, it is not possible to reduce the number of times, and at the same time, in terms of coating workability, it cannot reach the stage of practical application.

[0012]

However, in view of the various drawbacks of the prior art as described above, the present inventors, in addition, in order to meet the urgent needs of the industry, in particular, the curability and the like. In search of an excellent so-called water-based amino resin, the research was earnestly started.

[0013] Therefore, the problem to be solved by the present invention is, in particular, excellent in curability, and
Moreover, it is a highly practical water-soluble amino resin that is not only a dispersion of an amino resin that also has excellent water resistance and chemical resistance, but also has excellent water dilutability and that it can exist stably. And a method for producing the resin, which is one of the basic objects of the present invention.

Still another object of the present invention is to use, as a water-based resin, a water-soluble thermosetting amino resin which is used as a solvent-type thermosetting coating, and which is particularly excellent in processability and is substantially water-insoluble. Water resistance, hardness, and processing of coated materials from the point that it is stable and has good compatibility with other resins, and therefore can be added in a high concentration state. The object is to provide a low-viscosity water-based thermosetting coating composition which can improve the properties and the like, and which has good coating workability.

[0015]

Therefore, the present inventors have
First, as described above, focusing on the problem to be solved by the invention, as a result of earnestly studying, the method of co-condensing the same aqueous resin is also different in that the synthesis method is different. We thought that controlling the degree of co-condensation and changing the molecular weight and hydrophilicity would lead to an improvement in water dilutability.

The inventors of the present invention subsequently made essential raw materials an α, β-ethylenically unsaturated carboxylic acid and an α, β-ethylenically unsaturated monomer having a functional group capable of reacting with an amino resin. As a component, an aldehyde is mixed in a copolymer obtained by copolymerizing these in the presence of an organic solvent, and further,
By adding an amino compound and subjecting it to a co-condensation reaction under heating, then neutralizing at least a portion with a basic substance, and adding it to water, the viscosity is easily low, and the water dilutability is excellent. The present invention has been completed by finding that a water-soluble product or aqueous dispersion of the amino resin can be obtained.

Here, first, of the α, β-ethylenically unsaturated carboxylic acids used in the present invention, only typical ones will be exemplified. (Meth) acrylic acid, maleic acid, fumaric acid, etc. , Various carboxyl group-containing vinyl monomers and the like. The amount used is appropriately in the range of about 2 to about 30% by weight, preferably in the range of 5 to 20% by weight, based on the total ethylenically unsaturated monomer.

Next, only the particularly representative ethylenically unsaturated monomers having a functional group capable of reacting with the amino resin described above will be exemplified, and a hydroxyl group, an imino group and an N-methylol group will be given. Or various functional groups such as N-alkyl etherified methylol groups,
Such compounds may be included in at least a part of them.

As a representative example of the amino resin-reactive functional group-containing ethylenically unsaturated monomer, specifically, 2-
Hydroxymethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate,
2-hydroxyamyl acrylate or 2-hydroxyhexyl acrylate; or various hydroxyl group-containing vinyl monomers such as their corresponding methacrylates,

Various acrylamides or derivatives thereof, such as acrylamide, N-methylol acrylamide, N-methoxymethyl acrylamide, N-isobutoxymethyl acrylamide, N-butoxymethyl acrylamide or diacetone acrylamide;

Alternatively, various methacrylamides or their derivatives corresponding to these may be mentioned, but the compounds are by no means limited to these compounds.
Of course, these various monomers may be used alone or in combination of two or more kinds.

Of course, other ethylenically unsaturated monomers may be copolymerized depending on the purpose of use and the required performance of the aqueous resin and coating composition.

As typical examples of such copolymerizable monomers, only ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate or cyclohexyl acrylate can be given.

Various alkyl acrylates or methacrylic acid alkyl esters represented by methyl methacrylate, ethyl methacrylate, butyl methacrylate, stearyl methacrylate, cyclohexyl methacrylate, etc .;

Alternatively, various aromatic vinyl monomers represented by styrene, vinyltoluene, α-methylstyrene and the like are used, but the compounds are not limited to these compounds.

Of course, these monomers may be used alone or in combination of two or more kinds. As mentioned above, the copolymerization reaction of various monomers is carried out in a nitrogen atmosphere by using various radical polymerization initiators such as peroxide radical polymerization initiators and azo radical polymerization initiators. In the presence of an organic solvent in the presence of a temperature range of about 60 to about 130 ° C.

From various ethylenically unsaturated monomers mainly composed of the above-mentioned α, β-ethylenically unsaturated carboxylic acid and ethylenically unsaturated monomer containing an amino resin reactive functional group, The acid value of the obtained copolymer is appropriately in the range of about 20 to about 150,

When the amount exceeds about 150, the coating performance tends to be deteriorated due to the influence of the residual carboxyl groups. On the other hand, when the amount is less than about 20, hydrophilicity is inevitably caused. From where it is easy to become insufficient,
Either case is not preferable.

Regarding the molecular weight of the copolymer, first, the number average molecular weight is about 2,000 to about 20,000.
It can be said that the range of about 3,000 to about 30,000 by weight average molecular weight is suitable.

Examples of the above-mentioned aldehydes used in the present invention include formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, acrolein, and the like. Use is desirable.

As the above-mentioned amino compounds used in the present invention, only typical ones are exemplified, and examples thereof include urea, melamine, acetoguanamine, benzoguanamine, cyclohexanecarboguanamine, steroguanamine or spiroguanamine. , One or more selected from the group consisting of the various compounds listed above.

Of these, urea, melamine or benzoguanamine are preferably used alone or in combination from the viewpoints of cost and crosslinkability.

The amino compound may be initially charged all at once, may be charged in a divided manner over a certain period of time, or may be continuously charged for a certain period of time. Good.

The above-mentioned organic solvent used in the present invention is particularly necessary for stabilizing the reaction product of the amino compound and the aldehyde. As the organic solvent, only typical ones are specifically exemplified. Methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butanol or tert-. Butyl alcohol, etc.

Any of them is usually used alone or as a mixture. Among them, it is particularly preferable to use methyl alcohol, ethyl alcohol, n-butyl alcohol, isobutyl alcohol or isopropyl alcohol.

In the present invention, α and β as described above are used.
-Based mainly on ethylenically unsaturated carboxylic acid- and amino resin-reactive functional group-containing ethylenically unsaturated monomers,
The copolymer obtained by using various ethylenically unsaturated monomers is converted into an acid value with respect to 1 gram (g) of an amino compound at a ratio of about 20 to about 200 equivalents. It is desirable to use

On the other hand, it is desirable that the aldehydes are used in a ratio of about 1 to about 4 mol per 1 mol of the amino compound, and the organic solvent is, inter alia, for example, The alcohols are preferably used in a ratio of about 3 to about 10 mol per 1 mol of the amino compound.

In the present invention, the temperature during the condensation reaction is appropriately within the range of about 80 to about 150 ° C., preferably within the range of 95 to 120 ° C. 2 to 4 depending on temperature
Allow the reaction to continue over time.

What is obtained at the end of this condensation reaction is considered to be a partial condensate of an amino resin and a carboxyl group-containing resin. To make the condensate aqueous, the carboxyl group in the resin is used. With a volatile base,
It may be completely neutralized or partially neutralized and dissolved or dispersed in an aqueous medium.

In this case, excess organic solvent may be distilled off under reduced pressure from the solution of the copolymer, followed by neutralization to dissolve or disperse it in an aqueous medium, or Neutralization may be carried out, in an aqueous medium, after being dissolved or dispersed, the excess organic solvent may be distilled off under reduced pressure together with water,

Further, the solvent may be removed after the neutralization is performed in advance, and the neutralization may be performed again, if necessary, before being dissolved or dispersed in the aqueous medium. .

In this case, only typical examples of volatile bases are ammonia, ammonia,
Various amines such as monoethanolamine, dimethylamine, diethylamine, triethylamine, triethanolamine, diethylethanolamine, dimethylethanolamine or morpholine, etc., but as a degree or degree of neutralization by the volatile base. Is most preferably about 80 to 100%.

The aqueous medium referred to herein includes water and a mixture of water and a water-soluble solvent. Such water-soluble solvents, that is, various typical ketones, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, or diacetone alcohol, are listed only as typical water-soluble solvents.

Or ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether or diethylene glycol monoethyl ether

Alternatively, diethylene glycol diethyl ether, diethylene glycol monobutyl ether,
Various glycols such as triethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol dimethyl ether or dipropylene glycol dimethyl ether;

Furthermore, isopropyl alcohol, n-
Various alcohols such as butyl alcohol, isobutyl alcohol or 3-methoxybutanol, 3-methyl-3-methoxybutanol, etc. may be used alone or in combination of two or more kinds. However, if necessary, it is also possible to use a mixture of a small amount of another so-called water-insoluble solvent.

The aqueous thermosetting coating composition of the present invention thus obtained usually contains the above-mentioned amino resin in the resin solid content in an amount of about 5% by weight or more. And if it is less than 5% by weight,
Inevitably, it becomes impossible to impart sufficient thermosetting property, which is not preferable.

The water-based thermosetting coating composition of the present invention comprises a water-based resin which is a basic component constituting the water-based thermosetting coating composition, that is, a water-based amino resin, which is used as a heat treatment. Although it can be used as a curable paint,

Of course, various other water-based resin components such as water-based acrylic resin, water-based polyester resin, water-based epoxy resin or water-based urethane resin may be added, if necessary. is there.

The aqueous thermosetting coating composition of the present invention may further contain, if necessary, an acid catalyst such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid or dinonylnaphthalene disulfonic acid, or an amine thereof. As a so-called curing aid, a salt is used in an amount of about 0.1 to about 1.0 part by weight per 100 parts by weight of the solid content of the aqueous resin, which is a basic component of the aqueous coating composition. Of course, it may be added in such a proportion that

Similarly, various well-known conventional additives such as leveling agents, defoaming agents, lubricants or pigments are added to the aqueous thermosetting coating composition of the present invention. It is also possible to blame.

The aqueous coating composition of the present invention is prepared by a dipping method,
It can be applied by a variety of known and conventional methods, such as brushing, spray painting or roll coating, among others wood, paper, fibers, plastics, ceramics, inorganic cement substrates, ferrous or non-ferrous metals and the like. , Can be coated on the surface of various base materials,

Then, the aqueous coating composition of the present invention is
Usually, in a temperature range of about 100 to about 250 ° C.,
Moreover, baking can be performed under heating conditions of about 5 seconds to about 30 minutes.

[0054]

EXAMPLES Next, the present invention will be explained more specifically with reference to Synthesis Examples, Reference Examples, Examples and Comparative Examples, but the present invention is by no means limited to these Examples. Not a thing. In the following, all parts and% are based on weight unless otherwise specified.

Synthesis Example 1 50 parts of isobutyl alcohol were charged into a flask equipped with a stirrer, a reflux condenser for purging water, a thermometer and an inert gas introducing tube, and heated to 105 ° C.,
20 parts of 2-hydroxyethyl acrylate, 5 parts of acrylic acid, 25 parts of ethyl acrylate and "Perbutyl O" [tert-butyl (Nippon Yushi Co., Ltd.)
Ethyl hexanoate)]

Dropwise over 4 hours, and then at 105 ° C.
Then, by reacting for 3 hours, a solution of a copolymer having a nonvolatile content (solid content) of 50.2% was obtained.
Hereinafter, this is abbreviated as resin a.

Next, this resin a was added with "Hormite I
B "[a mixture of formaldehyde / isobutanol / water = 40/50/10 (weight ratio) manufactured by Koei Chemical Industry Co., Ltd.] and 160 parts of isobutanol were added, and the mixture was heated to 100 ° C. Then, 100 parts of benzoguanamine was charged, and the reaction was carried out at a temperature of 95 to 105 ° C. for 3 hours.

After that, isobutanol was removed under reduced pressure, and the solvent was replaced with butyl cellosolve. Then, the solution was neutralized with dimethylethanolamine until the pH became 8.5, and the nonvolatile content was 69.5. % Resin solution was obtained. Finally, it was diluted with ion-exchanged water so that the nonvolatile content became about 40%. The resin solution thus obtained is abbreviated as resin A hereinafter.

Synthesis Example 2 A flask equipped with a stirrer, a reflux condenser for expelling water, a thermometer and an inert gas introducing tube was charged with 50 parts of isobutyl alcohol, and then heated to 105 ° C.

20 parts of 2-hydroxyethyl methacrylate, 5 parts of acrylic acid, 10 parts of n-butyl acrylate, 5 parts of ethyl acrylate and n methacrylate.
A mixed solution consisting of 10 parts of butyl and 3 parts of "perbutyl O",

Dropwise over 4 hours, and then at 105 ° C.
Then, the reaction was carried out for 3 hours, and the nonvolatile content was 51.
A 4% solution of the copolymer was obtained. Hereinafter, this is referred to as resin b
Is abbreviated.

Then, the resin b was added with "Hormite I
After adding 50 parts of "B" and heating to 100 ° C, 10 parts of benzoguanamine was charged, and 1 hour after that, 10 parts of this benzoguanamine was added again, and further 1 hour later, another 10 parts were added. A total of 30 parts of the benzoguanamine was charged. Furthermore, the reaction was continued for 2 hours, and the condensation reaction was carried out at a temperature of 95 to 105 ° C. for a total of 4 hours.

After that, isobutanol was removed under reduced pressure, and the solvent was replaced with butyl cellosolve. Then, the solution was neutralized with dimethylethanolamine until the pH reached 8.5, and the nonvolatile content was 70.2. % Resin solution was obtained. Finally, so that the nonvolatile content is about 40%,
It was diluted with deionized water. The resin solution thus obtained will be abbreviated as resin B hereinafter.

Reference Example 1 (Preparation Example of Butylated Benzoguanamine Resin) In a flask equipped with a stirrer, a reflux condenser for expelling water and a thermometer, 187 parts of benzoguanamine, 300 parts of “Hormite IB” and 294 parts of isobutanol were added. After adding 3 parts and heating to 95 ° C. for 3 hours, 0.9 part of formic acid was added and the mixture was brought to reflux for 1 hour.

Next, the reaction was carried out for 4 hours under this reflux condition, and then isobutanol was removed under reduced pressure to obtain a solution of a butylated benzoguanamine resin having a nonvolatile content of 80%. Hereinafter, this is abbreviated as amino resin F.

Synthesis Example 3 100 parts of Amino Resin F and Resin a obtained in Synthesis Example 1
Was charged into a flask equipped with a stirrer, a temperature control device, and a reflux condenser for purging water, and heated to 80 ° C.
Then, after heating and stirring for 2 hours, the viscosity increased from Y to ZZ ₁ .

Then, the isobutanol was removed under reduced pressure, the solvent was replaced with butyl cellosolve, and the mixture was neutralized with dimethylethanolamine until the pH reached 8.5, whereby the non-volatile content was 68. A 9% resin solution was obtained. Finally, it was diluted with ion-exchanged water so that the nonvolatile content was about 40%. Less than,
The resin solution thus obtained is abbreviated as resin C.

Synthesis Example 4 94 parts of benzoguanamine and 150 parts of "Hormite IB" were added to a flask equipped with a stirrer, a reflux condenser for expelling water, and a thermometer, and heated at 95 ° C for 3 hours. After stirring, 290 parts of Resin b obtained in Synthesis Example 2 was added, and the reaction was allowed to continue under reflux for 4 hours.

Then, the isobutanol was removed under reduced pressure, the solvent was replaced with butyl cellosolve, and the mixture was neutralized with dimethylethanolamine until the pH reached 8.5, whereby the non-volatile content was 65. A 3% resin solution was obtained. Finally, it was diluted with ion-exchanged water so that the nonvolatile content became about 40%. The resin solution thus obtained is abbreviated as resin D below.

Reference Example 2 (preparation example of water-soluble acrylic resin) 450 parts of butyl cellosolve were charged into a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a nitrogen gas introducing pipe and a dropping tank, and the temperature was raised to 120 ° C. Warmed. While maintaining this temperature, 87 parts of ethyl acrylate, 87 parts of n-butyl acrylate, 75 parts of styrene, 30 parts of 2-hydroxyethyl acrylate, 21 parts of acrylic acid were added from the dropping tank.
Part and 18 parts of benzoyl peroxide,
It dripped continuously over 4 hours.

One hour after the completion of dropping, "perbutyl
3 parts of "O" were added and the reaction was allowed to continue for a further 2 hours. The resin solution thus obtained was then evaporated under reduced pressure to remove 375 parts of solvent and neutralized with 20 parts of dimethylethanolamine. Furthermore, by diluting with 200 parts of ion-exchanged water, a so-called acrylic resin aqueous solution was obtained. Hereinafter, this is abbreviated as acrylic resin E.

Examples 1 and 2 and Comparative Examples 1 to 3 The respective resins obtained in Synthesis Examples 1 to 4 and Reference Examples 1 and 2 were mixed in the proportions shown in Table 1 (solid content weight ratio). Thus, various water-based paints were prepared by blending, mixing and dispersing.

Then, after the respective components were blended, butyl cellosolve and water were added to make the amount of the organic solvent in the obtained coating composition 20% and the nonvolatile content 65%.

Thereafter, 0.1% of paratoluenesulfonic acid and 0.1% of a silicon-based leveling agent were added to each of them, and the desired water-based thermosetting paint and the control were respectively added. A waterborne thermosetting paint for use was obtained.

Next, each of the water-based paints was applied onto a tin plate with a bar coater so that the dry coating film thickness was 10 microns (μm), and was applied at 180 ° C. for 10 minutes. Baking was performed to cure the coating film.

After that, various performance evaluations were conducted on each of the cured coating films thus obtained. The results are collectively shown in Table 2.

[0077]

[Table 1]

[0078]

[Table 2]

[0079]

[Table 3]

<< Footnote in Table 2 >> The criteria for evaluation and determination of each performance are as follows.

∘ ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ ×. … It can't be put to practical use

Water dilutability: until a certain amount of paint becomes cloudy,
It was diluted with water and judged by the amount of water when it became cloudy.

Viscosity: The viscosity was measured using a B type viscometer.

Boiling resistance ... After being immersed in boiling water for 30 minutes, the degree of whitening of the coated surface was visually determined.

Pencil hardness: It was conducted according to JIS K-5400 "Pencil scratch test".

Adhesion: The coating film is cut with a cutter / knife in a grid pattern at 1 mm intervals for convenience.
Make 100 squares, peel off with cellophane tape, divide the number of remaining squares by the original number (100), multiply by 100, the so-called percentage ("%") Was displayed.

[0087]

By using the water-based resin of the present invention and the water-based thermosetting coating composition of the present invention, or by using the water-based resin obtained by the method of the present invention, the curability is particularly excellent. For the first time, it is possible to develop a novel aqueous amino resin component into an aqueous paint.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area C09D 161/32 PHH

Claims (6)

[Claims] 1. An α, β-ethylenically unsaturated carboxylic acid and an ethylenically unsaturated monomer having a functional group capable of reacting with an amino resin as essential raw material components and obtained by copolymerizing them. Aldehydes and amino compounds are reacted in an organic solvent in the presence of a copolymer, and then
An aqueous resin obtained by neutralizing at least a part of a basic substance to make it aqueous. 2. The aqueous resin according to claim 1, wherein the copolymer has an acid value within the range of 20 to 150. 3. A copolymer obtained by copolymerizing an α, β-ethylenically unsaturated carboxylic acid and an ethylenically unsaturated monomer having a functional group capable of reacting with an amino resin as essential raw material components. In the presence of a polymer, aldehydes and an organic solvent are mixed, an amino compound is further added, a condensation reaction is performed under heating, and then at least a part of the mixture is neutralized with a basic substance to form an aqueous solution. A method for producing an aqueous resin, characterized by comprising: 4. The method for producing an aqueous resin according to claim 3, wherein the copolymer has an acid value within the range of 20 to 150. 5. An α, β-ethylenically unsaturated carboxylic acid and an ethylenically unsaturated monomer having a functional group capable of reacting with an amino resin are contained as essential raw material components in a resin solid content.
In the presence of a copolymer obtained by copolymerizing these, aldehydes and amino compounds are reacted in an organic solvent, and then at least a part is neutralized with a basic substance to make it aqueous. The resulting aqueous resin is used as an indispensable base resin component, and the solid content of the aqueous resin is 5% by weight.
A water-based thermosetting coating composition, characterized in that it is contained as described above. 6. The aqueous thermosetting coating composition according to claim 5, wherein the copolymer has an acid value within the range of 20 to 150.