JPS62129363A - Resin composition for water-based low-temperature baking paint - Google Patents

Abstract

PURPOSE:To provide the titled composition composed mainly of a base resin having epoxy group, hydroxyl group and amino group as functional groups wherein at least a part of the amino group is protonated with an acid and a polyurethane resin as a curing resin, having excellent solvent-resistance, etc., and especially suitable for cationic electrodeposition coating. CONSTITUTION:The objective composition can be produced by mixing (A) a resin having epoxy group, hydroxyl group and amino group as functional groups wherein at least a part of the amino group is protonated with an acid and (B) a polyurethane resin devoid of free NCO group and composed of a polyisocyanate and monophenol consisting of a polyphenol and, if necessary, monophenol and dispersing the mixture in water. The resin A is preferably produced by reacting an amine compound with a polyepoxide composed of a polyphenol polyglycidyl ether and an epoxidized polybutadiene polymer and protonating then amino group with a water-soluble organic carboxylic acid such as formic acid, acetic acid, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resin composition for low-temperature baking type water-based paint,
More specifically, for thermoplastic materials such as plastics and rubber that must be baked at low temperatures,
The present invention relates to a resin composition for low-temperature baking type water-based paints, which is suitable for the removal of goods and clothing of small objects, and is especially suitable for cationic electrodeposition coating.

Conventionally used cationic electrodeposition paints include, for example, bisphenol-epic-alhydrin-type epoxy I (consisting of a water-soluble product of a fat-like epoxy resin and an aromatic polyisocyanate compound blocked with an alcohol). This is a typical example, and this one is electroplated,
For example, the coating film obtained by curing at 170°C has excellent corrosion resistance, but the curing temperature is high, so it is possible to integrate the coated material made of thermoplastic resin such as plastics or rubber and metal such as zinc phosphate treated plate. Painting, casting, etc. at room temperature or 130℃
It is unsuitable for applications requiring curing in the temperature range of °C. Therefore, in order to obtain electrodeposition paints that can be cured at low temperatures, attempts have been made to use large amounts of catalysts that dissociate isocyanate compounds blocked with alcohols at low temperatures, but this still requires high temperatures and has not yet been solved. .

If you want to cure at a low temperature of 130℃ or higher,
-Pro 1. Tertiary amines having hydroxyl groups, caprolactams, active methylene compounds, etc. may be used, but when these blocking agents are used in water-based paints, the following may occur. Problems include at least one of the following problems: ■ Toxicity of the blocking agent, ■ Insufficient compatibility with the base resin, ■ Generation of smoke or tar during baking, and ■ Instability of the blocked product, especially at 130°C. When performing the following low TM baking,
These blocking agents remain in the paint film even after baking, reducing corrosion protection and causing defects such as bleeding and yellowing.In addition, the remaining blocking agents themselves are harmful (toxic,
It is difficult to put it into practical use because of the large odor (odor).

Therefore, as a method for solving these problems, the present inventors first developed (A) a resin having a hydroxyl group and a cationic group, and (B) a polyphenol containing at least two 7-7-yl groups and an isocyanate group. We have proposed a low-temperature baking type water-based paint resin composition containing as a main component a polyurethane tree with a heptad-enol group at the end, which is a reaction product with a polyisocyanate containing at least two of (See application specification).

This material is suitable for curing at low temperatures of 130°C or less, and almost all of the solids in the resin composition, excluding water and volatile solvents, participate in the formation of a cured film, resulting in a film with good film performance. This is a resin composition that provides the following properties. However, the heat-cured coating film obtained in this way still contains free polyphenols. That is, among the polyisocyanate and polyphenol components that form the polyurethane resin that is the curing resin, when the polyisocyanate is bonded to the base resin by a curing reaction, the polyphenol that is left behind is present alone in the coating film. Although this polyphenol does not have an adverse effect on the water resistance, slip spray resistance, etc. of the coating film, there is a problem in that it has a somewhat adverse effect on the solvent resistance, other physical properties, etc. Therefore, the present inventors have developed a cationic electrodeposition coating that does not have these problems, that is, has excellent low-temperature curing suitability at 130°C or less, and has excellent not only water resistance and corrosion resistance, but also solvent resistance and other physical properties. As a result of extensive research in order to obtain a resin composition for low-temperature baking water-based paints suitable for j (II) As an alternative to (A), as a functional group reactive with a polyphenol containing at least two phenol groups produced by thermal decomposition of a polyurethane resin and mo/phenol added as necessary, By using as the first component (A) 01 fat having an epoxy group, a hydroxyl group, and an amino group, and at least a part of the amino group being protonated with an acid, it is cured at a low temperature of 130 ° C or less, A coating film that has excellent solvent resistance and other physical properties, and almost all of the solids in the resin composition, excluding water and volatile solvents, participate in the formation of a cured coating film, and has good anticorrosive coating performance. The present inventors have discovered that a coating resin composition can be obtained that provides the following properties, and have completed the present invention.

Hidden-ζAccording to the present invention, (A) a resin having an epoxy group, a hydroxyl group, and an amino group as functional groups, and at least a portion of the amino groups being protonated with an acid; (B) at least two phenol groups; 'i!, which is a reaction product of a phenol compound obtained by adding polyphenol containing polyphenol and heptanophenol as necessary, and a polyisocyanate containing at least 62 isocyanate groups. A resin composition for a low-temperature baking type water-based paint is provided, which is characterized by containing as a main component a polyurethane resin having no L-separating isocyanate groups.

In the present invention, an epoxy group, a "resin J (A) having an epoxy group, a hydroxyl group, and an amino group as functional groups, and at least a part of the amino group is protonated with an acid" (hereinafter referred to as "base resin") A)) is a polyphenol containing at least two phenol groups produced by thermal decomposition of polyurethane resin (B) and an epoxy group that is reactive with a monophenol added as necessary. and contains a hydroxyl group capable of reacting with an isocyanate group, and further has a sufficient number of amino groups to form a stable aqueous dispersion, and at least some of the amino groups are protonated with an acid. Resin can be used. Examples of the mononuclear base resin (A) include reaction products obtained by reacting polyepoxide (k) with an amine compound and protonating at least a portion of the amino groups with an acid.

The polyepoxide resin generally contains at least 2 t) (1, preferably 4 t) of epoxy groups.
00~so,ooo, more preferably 800~2゜0
Those having a number average molecular weight within the range of 0.00 are suitable. As such epoxide compounds, those known per se can be used, and examples thereof include the following.

i) Included are polyglycidyl ethers of polyphenols which can be prepared by reacting poly7enol with epichlorohydrin in the presence of an alkali. Boria 2/-oles that can be used here include, for example,
bis(4-hydroxy7enyl)-2,2-propane,
4.4'-nohydroxybenzophenone, bis(4-bitroxyphenyl) 1,1-ethane, bis-(4-hydroxyphenyl)-1,1-isobutane, bis(4-hydroxy-1ert-butyl-phenyl) -2,2-propane, bis(2-hydroxynaphthyl)methane, 1.
5-nohydro-a-xinaphthalene, bis(2,4-nohydroxyphenyl)methane, tetra(4-hydroxyphenyl)-1,1,2°2-ethane, 4.4'-nohydroxydiphenyl ether, 4.4' ii) Natural fats and oils such as linseed oil, tung oil, soybean oil and dehydrated castor oil; Polyepoxide obtained by epoxidizing stand oil obtained by heat-treating natural oils and fats (for example, see Japanese Patent Application Laid-Open No. 16048/1983)
1ii) polymers of conjugated diolefins such as butadiene, isoprene and piperylene and/or copolymers of these conjugated diolefins; one of said conjugated diolefins;
Polyepoxides obtained by epoxidizing copolymers of one or more species with vinyl monomers having ethylenically unsaturated groups, such as imbutylene, styrene, vinyltoluene, acrylonitrile, etc.
5466); iv) ethylenically unsaturated polymerizable epoxy group-containing moamer, such as butadiene monoepoxide, 4-vinylcyclohexene mo7 epoxide, etc. or two or more thereof, and the conjugated diolefin and/or ethylenically unsaturated Copolymers with vinyl monomers having saturated groups (for example, JP-A-54
(Refer to Japanese Patent Laid-open No. 15935 and Japanese Patent Application Laid-open No. 139147/1983).

Particularly suitable polyepoxides in the present invention are those in which a polyglycyl ether of a polyphenol and an epoxidized polybutadiene polymer and V/or copolymer are used in a weight ratio of 95:5 to 50:50. These may be simply mixed, but poly7 ether,
polycarboxylic acid, polyamine, polyamide polyamine,
It is preferable to use one or more of polyols, polyether polyols, polyester polyols, polyisocyanates, etc. reacted together.

Particularly preferred polyglycidyl ethers of the above polyphenols have a number average molecular weight of at least about 3110.
, preferably about 800-2,000, and epoxy equivalent force f190-2.000, preferably 380-1, OOO
On the other hand, particularly suitable epoxidized polybutanoene (co)polymers have an iodine value of 100 to 500, preferably 200 to +50, and a number average molecular weight of 200 or more. , preferably 1,000 to 4,000 carbon-carbon divalent bonds of the polybutadiene (co)polymer, e.g. 0 to 10
Conventionally known methods of reacting with peracetic acid at a temperature of 0°C (for example, Japanese Patent Publication No. 37-15107, Japanese Patent Publication No. 38-82
It is a compound having 2 or more, preferably 5 to 20, epoxy groups in one molecule, which is obtained by epoxidation according to No. 89), and generally has 200 or more, preferably 400 to 400.
50,000, more preferably 1.000 to 4.0
Those having a number average molecular weight in the range of 0.00 are suitable.

On the other hand, examples of the amine compound to be reacted with the polyepoxide compound include aliphatic or Jiff ring group or aromatic-aliphatic primary or secondary amines. These react with epoxy groups to form amine groups. Furthermore, a tertiary amino monoisocyanate obtained by the reaction of a tertiary amino alcohol and a diisocyanate can be reacted with a hydroxyl group of an epoxy resin to form an amino group.

Examples of the amine compounds include the following.

(1) 7nalamine, ethylamine, ■1- or 1
Primary amines such as so-propylamine, monoethanolamine, ■1 or 1so-propafuramine; (
2) Secondary amines such as diethylamine, noethanolamine, di-n- or lso-propanolamine, N-methylnitinolamine, N-ethylethanolamine; (3) ethylenediamine, ethylenetriamine, hydroxyethylaminoethylamine, ethyl Polyamines such as aminoethylamine, methylamino/propylamine, dimethylaminoethylamine, dimethylamino/propylamine.

Among these, alkali/amiso compounds having a hydroxyl group are preferred. These amines may be reacted with epoxy groups as they are, but preferably the primary amino group or N-hydroxyalkyl secondary amino group is blocked by reacting with a ketone, aldehyde, or carboxylic acid in advance to form an aldimine or ketimine. , oxacillinone, or imigzoline group, and then reacted with an epoxy group using the remaining active hydrogen.

Furthermore, other than the above-mentioned amine compounds, basic compounds such as ammonia, hydroloxylamine, hydranone, and hydroxyethylhydranone can also be used. The basic groups formed using these compounds are protonated with acids, particularly preferably water-soluble organic carboxylic acids such as formic acid, acetic acid, lactic acid.

The epoxy group content of the base resin (A) used in the present invention is:
The number of epoxy groups (equivalent number) is determined by the curing resin (B
) of the total number (equivalent number) of unreacted phenol groups and isocyanate groups and phenol groups that have already reacted. preferable.

In this case, polyurethane fil (poly7 ether dissociated from l1ff and optionally added 7) is used during curing.
Since the 7-7-el binds with the base resin (A) in the coating film and does not volatilize and scatter, the use of mono-7-7-ols becomes +1 (functionality). The epoxy group based on the (co)polymer is particularly desirable because it coexists stably with the amino group in water.The hydroxyl group content generally has a hydroxyl value of about 10 to 400, particularly from the viewpoint of reactivity with polyisocyanate. The content of amino groups is preferably in the range of 20 to 200.The content of amino groups is desirably a small amount that allows the base resin (A) to be stably dispersed in water;
HCl (6 g/g solid content) is generally preferably in the range of 5 to 160, particularly 10 to 80. However, even when the amino group content is 5 or less, it is possible to use aqueous dispersion using a surfactant etc., but the p I-1 of the aqueous dispersion composition is preferably 4 to 9, preferably 6 to 7 (it is desirable to arrange one amino group in one order so that

Next, the polyurethane resin (B) having no free isocyanate groups, which is used in combination with the base resin (A), will be explained.

Polyurethane a(II) without free isocyanate groups used in the present invention? (13) (hereinafter referred to as 1
The polyisocyanate used in the production of the curable resin (also referred to as (+3)J) is a polyisocyanate containing at least two isocyanate groups. The polyisocyanate has a total of 2 to 3 incyane I
- It is preferable to have a group and have a molecular weight in the range of 150 to 600. Representative examples of such polyisocyanates are:
Aromatic isocyanates such as 4,4'-diphenylmethane diisocyanate; aliphatic diisocyanates such as hexamethylene diisocyanate and gimaric acid diisocyanate; diisocyanates containing cycloalkylene rings such as 1,4-dicyclohexylmethane diisocyanate and isophorone diisocyanate;...- or p-
Aromatic-aliphatic diisocyanates such as xylylene diisocyanate, etc. Suitable polyisocyanates include cycloaliphatic polyisocyanates having excellent weather resistance and low volatility suitable for use in 2-foot finishing primer coatings. '-dicyclohexylmethane diisocyanate.

A curing resin (B ) can be generated.

The polyphenol preferably has a total of 2 to 3 727-l groups and a molecular weight in the range of 100 to GOO. Representative examples of such polyphenols include bis(4-hydroxyphenyl)-2,2-propane, 4,4'-nohydroxybenzophenone, and bis(4-hydroxyphenyl)-2,2-propane, 4,4'-nohydroxybenzophenone,
4-hydroxyphenyl)-1゜1-ethane, bis(4
-hydroquinphenyl)-1,1-isobutane, bis(
4-hydroxyphenyl)-2゜2-isobutane, bis(4-hydroxy-tert-butylphenyl)-2,
2-propane, bis(2-hydroxynaphthyl)methane, 1,5-dihydroxynaphthalene, /Borafuku 7/
Bis(4-hydroxyphenyl)-2,2-
Propane and/or borac phenolic resins are preferred.

Furthermore, as the heptophenol, one having a molecular weight in the range of 90 to 600 is preferable. Typical examples of such monophenols include nonyl-7ethyl, α- or β-su7tol, p-tert-octylphenol, and o- or p-phenylphenol, which are industrially easily available and easy to handle. Nonylphenol, which is easy to prepare, is suitable.

The reaction for producing a polyurethane resin (B) having no free isocyanate groups from such polyisocyanate, polyphenol, and optionally added monophenol can be carried out in the absence of a solvent or in the presence of, for example, toluene,
Generally in the presence of an inert organic solvent such as xylene, nooxane, methyl ethyl ketone, ethyl acetate, etc.
It can be carried out at 0°C. The reaction may be carried out in the presence of a urethanization catalyst such as butyltin diacetate, butyltin nolaurate, etc., if necessary. The amount of polyphenol and optionally added monophenol relative to the polyisocyanate is more than one equivalent (less than two equivalents, more preferably a ratio of less than two equivalents) of the isocyanate groups of the polyisocyanate. Poly7z/ corresponding to the amount of 17% of 7E/-
- amount of monophenol added as needed.

Both ends of the polyurethane resin may be phenol groups,
Further, if necessary, the increase in molecular weight may be stopped with monomers. The molecular weight of the curing resin (B) thus obtained is usually in the range of 400 to 3,000, preferably in the range of i,ooo to 2,000.

The amount of the curing resin (B) used when combining the curing resin (B) with the base resin (A) depends on the base resin (A) used.
Depending on the type, the amount can be varied from the minimum amount necessary for the resulting coating to be self-curing or thermosetting, to the maximum amount that does not impair the stability of the aqueous dispersion coating.
In general, the number of isocyanate groups (equivalent number) reacted with the phenol groups in the curing resin (B) is the IJf for the substrate.
It is preferable that the amount is about % to equal equivalents of the total amount (number of equivalents) of functional groups having active hydrogen in f (A).

In this way, 11H (A '') for the substrate and the curing resin ([
1> can be used as a 1M component for water-based paints that can be baked at low temperatures of 130° C. or lower.

For the aqueous coating composition of the present invention (for preparing the fat composition, the base resin (A) is preferably protonated with an acid in advance).
After mixing the curing resin (B), it is stably dispersed in water, and then, if necessary, coloring pigments such as carbon black, titanium white, benzene, extender pigments such as clay and talc, and chromium are added. This is done in addition to the addition of anti-corrosion pigments such as strontium oxide, lead chromate; or additional additives. Other additives that may be included include, for example, a small amount of nonionic surfactant as a dispersant or anti-foaming agent for the painted surface; hardening accelerators (such as lead, bismuth,
salts of metals such as tin, zinc, iron, aluminum, and/or
or imidacillin compounds, imidazoles, phosphines, quaternary phosphonium salts), and the like.

The 1,000M fat composition for water-based paints prepared in this way can be made of, for example, a cationic compound. Can be used for ftjM painting. The coating film obtained by electrodeposition on a suitable substrate is
For example, it can be cured by heating at 130°C or lower, preferably from 8°C to 130°C, but if desired, it can also be cured at room temperature. The reason for this is that the resin composition, which had been neutralized with acid, is removed by electrodeposition and the deposited film has a high
This is because the curing reaction is accelerated by +-[. This also applies when other coating methods useful for water-based paints for room temperature drying or low temperature baking are used.

The low-temperature curing aqueous coating composition of the present invention is advantageously used for integral coating of objects made of thermoplastic substances such as plastics and rubber and metals, coating of castings, etc., particularly for cationic electrodeposition coating thereof. be able to.

Next, the present invention will be further explained by examples. All parts in the examples are 1-part by weight, and 1 part % is 1 part by weight.
”.

In addition, the coating compositions obtained in the following examples were measured by the following methods: This is what I did.

(1) Throwing property test method (pipe method) JP-A-55-9
The method is based on the method described in Publication No. 0566.

(2) Creep spray resistance Tested according to JIS Z28'71, cut < m-shaped cut)
7 cracks of the coating film within I6 Ifi and other than the cut part are 8
If it is less than or equal to 1'(As1' M ), it is considered to be a pass.

(3) Impact resistance (DuPont method) After placing the test plate in a constant temperature and humidity room with a temperature of 20 ± 1 °C and a humidity of ° 75 ± 2% for 24 hours, place it on a pedestal of the specified size in a DuPont impact tester. Attach the impact center and place the test plate with the painted surface facing upward, sandwich it between them, then drop a weight of the specified weight onto the impact center from the specified height, and crack the paint film due to the G8 impact.
If there is no difference, it will be considered a pass.

(4) Resistance 17 (bending test) After the plate was placed in a constant temperature and humidity room at a temperature of 20±1°C and a temperature of 75±2% for 24 hours, it was bent at a right angle for 1 to 2 seconds.

A hardened coating film was applied to the front and back surfaces of the test board. If there is no abnormality on both sides of the folded part, the product is considered to be passed, and if there is any abnormality such as cracks or scratches on at least one side, it is considered to be rejected.

(5) If no scratches remain even after 15 times wiping back and forth with a 1ittB agent containing methyl imbutyl ketone, it is considered to be a pass, and if it cannot withstand it, it is judged to be a fail.

Example 1 Bis7enol A22.8 was added to 20 parts of epoxidized polybutadiene (trade name E-1000, manufactured by Nippon Petrochemical Co., Ltd.) with an epoxy equivalent of 200 and a viscosity of 700 voids at 25°C.
of epoxy and reacted at 140°C for 2 hours to bring the epoxy equivalent to 25
After changing it to 3, the bisphenol A type epoxy tree Jffi (trade name Koko Pico) 828EL, manufactured by Yuka Shell Epoxy Co., Ltd., has an epoxy weight of 380.
57.0 parts, methyl in butyl ketone 10.0711S
and 0.45 parts of diethylamine were added and reacted at ζ140°C for 4 hours to obtain a polyepoxide compound having an epoxy equivalent of 517 and a solid content of 90.9.

Next, 103 parts of noethylenetriamine and 225 parts of methyl isobutyl ketone were heated to 120'C, 360 parts of condensed water was removed by distant flow, and the temperature was raised to 150°C to produce diethylenetriamine ketimine with a purity of 91.4%. get.

To 110.25 parts of the above polyepoxy l' compound, 8.8 parts of diethylenetriamine cheminate, 6.8 parts of diethalamine and 34.8 parts of ethyl cellofulve were added to 85°C.
Reacted for 2 hours at C, solid content 72.1%, amine value 64.
, a polyepoxide-amine adduct of epoxy 1287 is obtained. This polyepoxide-amine adduct 160.7
The mixture was cooled to room temperature and neutralized by adding 3.1 parts of acetic acid to obtain 163.8 parts of base resin neutralized product (A). Next, 4,4'-nocyclohexylmethane diisocyanate) 11.7ff
12.6 parts of bis(4-hydroxyphenyl)-2,2-propane were dissolved in 12.2 parts of methyl isobutyl ketone and 1 drop of cypnaltinnolaurate was added to give 120.
After reacting at °C for 12 hours, the mixture was cooled to room temperature to synthesize the curing resin (B).

While thoroughly stirring 163.8 parts of the base resin neutralized product (A) and 36.5 parts of the curing resin (B) solution, 503.6 parts of deionized water was added. Make an electric λ1 bath with a solid content of 20% and 1) H6, [3.

Using this electrodeposition bath, mold deposition was carried out at 27°C and 200V for 3 minutes using a zinc phosphate treated plate as a cathode, and then at 120°C for 30 minutes.
A coating film with a thickness of 24 μm and a pencil hardness of 1-1 was obtained by baking for a few minutes. The performance of this coating film is as follows.

(1) Impact resistance (% inch, 11(Hi, 50cII+)
Pass (2) Tsuruto spray resistance (240 hours) Pass (3
) Throwing ability 17c+++ (4)
Bending resistance Pass (5) Solvent resistance Pass Example 2 Epoxidized polybutadiene (trade name: ['(-45EP11
11 parts of bisphenol A to 30 parts of Idemitsu Petrochemical Co., Ltd.
．． Add 4 parts and react at 140'C for 2 hours to change the epoxy equivalent to 306, then add Bis71/-L A type epoxy tree III (trade name Ebicor) 1001, Shell Chemical Co., Ltd. fJl having an epoxy equivalent of 925. )92.5
29.4 parts of butyl cellosolve were added and dissolved at 100°C, and then heated at 90°C. 6.8 parts of jetanolamine, prepared in Example 1.
．． 711F.

was added and reacted at 90°C for 2 hours, then 29.41% of butyl cellosolve was added, cooled to below 50°C, and neutralized by adding 3.2 parts of acetic acid to give an amine value of 54 and an epoxy equivalent of 11.
21. Neutralized base resin with solid content of 70.6% and acid value of 20 (
A) Obtain 214.5 parts.

Next, 16 parts of bis(4-hydroxyphenyl)methane was dissolved in 2.13 parts of methyl imbutyl ketone, and 1.1 part of hexamethylene diisocyanate was added thereto at 140°C.
After reacting for 5 hours with methyl isobutyl ketone 7.8
36.5 parts of the curing resin was synthesized by adding 1.5 parts of the resin and cooling, and this was added to 214.5 parts of the above base resin neutralized product (A), and while stirring thoroughly, 932 parts of deionized water was added. ,
Create an electrodeposition bath with approximately 15% solids and pH 6.4 parts. Using this electrodeposition bath, a zinc phosphate treated plate was used as a cathode and 27
℃, 200 V''c for 3 minutes to obtain a coating film.
Baking at 0° C. for 30 minutes yields a coating film with a thickness of 24 μm and a pencil hardness of H. The properties of this coating film are as follows.

(1) Passed impact resistance (% inch, lk, 50cm) (2) Passed spray resistance (240 hours) (3)
Throwing property: 16 parts w + (4) Flexibility: Passed (5) Solvent resistance
1 letter of amendment to successful procedure) January 10, 1985, Patent Office, Uga Michibu, 3 Relationship with the case of the person making the amendment Patent applicant 4, agent 〒107・4th episode 585-2256 ( 6 others) +11
On page 5, lines 9-10 of the specification, the phrase ``There is an epoxy group as a functional group'' has been corrected to ``At least one epoxy group is contained as a functional group.''

(2) Delete the phrase "epoxy group" on page 6, line 11.

that's all

Claims (1)

[Scope of Claims] (A) a resin having an epoxy group, a hydroxyl group, and an amino group as functional groups, and at least a portion of the amino groups being protonated with an acid; and (B) containing at least two phenol groups. A polyurethane resin having no free isocyanate groups, which is a reaction product of a phenol compound obtained by adding a monophenol to the polyphenol as required, and a polyisocyanate containing at least two isocyanate groups. A low-temperature baking type water-based paint resin composition characterized by: