JPS6360774B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a cationizable coating resin. In particular, the present invention is a resin obtained by reacting a polyurethane prepolymer with a hydroxyl group contained in an epoxy resin, and reacting the epoxy resin with a compound capable of cationizing the base material. The present invention relates to a method for producing a cationizable paint resin that can provide a coating film with excellent adhesion, flexibility, corrosion resistance, etc.

In recent years, cationic electrodeposition paints made from epoxy resins have come to be widely used as primers for automobiles and the like. Such cationic electrodeposition paints are produced by reacting the epoxy group in the epoxy resin with a compound having a reactive group and a cationizable group, and neutralizing the reaction product with an acid or the like to form a curing agent. Conventionally, cationic electrodeposition paints made from epoxy resins provide superior coating properties than anionic electrodeposition paints, but they have poor adhesion and poor adhesion.
It cannot be said that it is possible to form a coating film that is completely satisfactory in terms of flexibility, corrosion resistance, impact resistance, surface smoothness, etc.

The present inventors focused on this point, and further improved the adhesion and
The present invention was achieved as a result of intensive research in order to produce a coating resin suitable for cationic electrodeposition coatings and the like with improved flexibility, corrosion resistance, impact resistance, surface smoothness, etc. from epoxy resin.

That is, the present invention relates to a method for producing a cationizable coating resin suitable for, for example, cationic electrodeposition coatings, and the method for producing a cationizable coating resin of the present invention includes a polyisocyanate and a molecular weight of 300 to 300.
3000, a polyurethane prepolymer having a terminal isocyanate group obtained by reacting with a bifunctional or higher-functional polyhydroxy compound having a hydroxyl equivalent of 200 to 1500 and a hydroxyl equivalent of 150 to 1500 and an epoxy equivalent of 150 to
Epoxy resin and isocyanate group with 1500/
The ratio of hydroxyl groups (hereinafter referred to as NCO/OH ratio) is
This method is characterized by reacting the epoxy group so that the epoxy group is 0.05 to 1.0, and further reacting with a compound that is reactive with an epoxy group and has a cationizable group.

The polyisocyanates used in the method for producing the cationizable coating resin of the present invention include aliphatic, alicyclic, aromatic, and aliphatic-aromatic polyisocyanates having two or more isocyanate groups in the molecule. Isocyanates, such as aliphatic polyisocyanates such as hexamethylene diisocyanate, for example isophorone diisocyanate, hydrogenated 4,4'-diphenylmethane diisocyanate, hydrogenated paraxylylene diisocyanate, and other aromatic compounds as described below. Alicyclic polyisocyanates such as polyisocyanates obtained by hydrogenating aromatic rings contained in group polyisocyanates, such as 2,4-toluylene diisocyanate, 2,6-toluylene diisocyanate, 1,4-naphthylene diisocyanate , 1,5-naphthylene diisocyanate,
1,3-phenylene diisocyanate, 1,4-
phenylene diisocyanate, 1-isopropylbenzole-2,4-diisocyanate, ω,
ω'-diisocyanate-1,2-dimethylbenzole, 4,4'-diphenylmethane diisocyanate, 2,2'-dimethyldiphenylmethane-4,
4'-diisocyanate, diphenyldimethylmethane-4,4'-diisocyanate, 3,3'-dichlorodiphenyldimethylmethane-4,4'-diisocyanate, biphenyl-2,4'-diisocyanate, 3,3'-dimethyl Aromatic diisocyanates such as biphenyl-4,4'-diisocyanate and diphenylsulfone-4,4'-diisocyanate;
For example, benzene-1,2,4-triisocyanate, 2,4,6-triisocyanate toluene, 4,4',4''-triphenylmethane triisocyanate, 2,4,4'-triisocyanate diphenyl ether , aromatic polyisocyanates such as polymethylene polyphenyl isocyanate obtained by phosgenating a condensation product of an aromatic amine and formaldehyde.

Preferred among such polyisocyanates are alicyclic or aromatic polyisocyanates having 2 to 3 isocyanate groups in the molecule.

Further, the polyhydroxy compound used in the production of the coating resin of the present invention is a bifunctional or higher functional polyhydroxy compound having a molecular weight of 300 to 3000 and a hydroxyl equivalent of 200 to 1500. Examples of such polyhydroxy compound include ethylene glycol, , dihydric alcohols such as propylene glycol; trihydric alcohols such as glycerin, trimethylolpropane; other polyhydric alcohols such as pentaerythritol, sorbitol; e.g. hydrogenated 2,2-bis(4-hydroxyphenyl); ) Alicyclic polyhydric alcohols such as propane (common trade name: bisphenol A); for example, 2,2-bis(4-
Polyhydric phenols such as (hydroxyphenyl)propane, polyhydroxy compounds such as hydroxyl group-containing esters such as castor oil and castor oil fatty acid esters, and these polyhydroxy compounds are reacted with alkylene oxides such as ethylene oxide and propylene oxide, or tetrahydrofuran. polyether polyols and polytetramethylene glycols obtained by Polyether polyols obtained by reacting alkylene oxides such as ethylene oxide and propylene oxide with amine compounds such as group amines, the aforementioned dihydric alcohols, trihydric alcohols, alicyclic polyhydric alcohols, polyhydric phenols, and polyethers. Polyols such as adipic acid, succinic acid, suberic acid, sebacic acid, oxalic acid, methyladipic acid, glutaric acid, pimelic acid, azelaic acid, maleic acid,
Polymerization of polyester polyols or polyester-ether polyols and lactones obtained by reacting with polycarboxylic acids such as fumaric acid, citraconic acid, itaconic acid, thiodipropionic acid, phthalic acid, terephthalic acid, isophthalic acid, and benzenetricarboxylic acid. Examples include polylactone glycols obtained by.

Preferred examples of such polyhydroxy compounds include di- to trifunctional hydroxyl group-containing esters, polyether polyols, polyester polyols, and polylactone polyols.

The epoxy resin used in the production of the paint resin of the present invention has a hydroxyl equivalent of 150 to 1500 and an epoxy equivalent of 150.
-1500, and a typical group of such epoxy resins are epoxy resins having an average of more than one substituted or unsubstituted glycidyl ether group in the molecule. Such epoxy resins include aromatic polyhydric phenols, polyhydroxy compounds to which alkylene oxide is added, and aliphatic, alicyclic, or heterocyclic polyhydroxyl compounds that do not contain an aromatic nucleus. The polyhydroxyl compound and epihalohydrin are treated with a basic catalyst such as sodium hydroxide or triethylamine in a conventional manner.
Alternatively, it may be reacted in the presence of boron trifluoride or the like and simultaneously or finally converted into glycidyl ether by reaction with a basic compound such as sodium hydroxide.

The aromatic polyhydric phenols mentioned here include mononuclear polyhydric phenols such as resorcinol and 2,7-dihydroxynaphthalene, as well as 2,2-bis-(p-hydroxyphenyl) commonly referred to as bisphenol A. ) propane, 2,
Bis(hydroxyphenyl)alkanes such as 4'-dihydroxydiphenylmethane, dihydroxybiphenyls such as 4,4'-dihydroxybiphenyl, 4,4'-dihydroxyoctachlorobiphenyl, bis-(4 -di(hydroxyphenyl) sulfones such as -hydroxyphenyl) sulfone, di(hydroxyphenyl) sulfones such as bis(4-hydroxyphenyl) ether, and di(hydroxyphenyl) ether such as 4,4'-dihydroxy-2,6-dimethyldiphenyl ether. enyl) ethers, 1,1-bis(p-hydroxyphenyl)-2-phenylethane, 2,
4-bis(p-hydroxyphenyl)-4-methylpentane, 1',4-bis(p-hydroxybenzyl)benzene, 1,4-bis(p-hydroxybenzyl)tetramethylbenzene, 1,4-bis Initial condensates of polynuclear divalent phenols such as (p-hydroxycumyl)benzene, such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethanephenols and carbonyl compounds (e.g., phenolic resin condensation condensation reaction product of phenol and acrolein, condensation reaction product of phenol and gluoxal, condensation reaction product of phenol and pentanediallyl, condensation reaction product of resorcinol and acetone, xylene-phenol-formalin initial condensate), Other aromatic polyhydric phenols include condensation products of phenols and polychloromethylated aromatic compounds (eg, condensation products of phenol and bischloromethylxylene).

Examples of aliphatic, alicyclic, or heterocyclic polyhydroxyl compounds that do not contain an aromatic nucleus include ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, dibutylene glycol, glycerin, and pentyl glycol. polyhydric alcohols such as erythritol, and polyhydroxyl compounds in which alkylene oxide is added to these polyhydric alcohols or other active hydrogen-containing compounds (for example, compounds with groups such as amino groups, carboxyl groups, and thiohydroxyl groups); Aliphatic polyhydroxyl compounds such as polyether polyols, alicyclic polyhydroxy compounds obtained by hydrogenating the aromatic nucleus of the above-mentioned aromatic polyhydric phenols and polyhydroxyl compounds obtained by adding alkylene oxide thereto, and oxazolidinones. Polyhydroxyl compounds containing one or more rings, furan rings, dioxane rings, imidazoline rings, imidazole rings, hydantoin rings, triazine rings, etc., such as polyhydroxyl compounds obtained by adding alkylene oxide or formaldehyde to the secondary amino group of hydantoin. Examples include heterocycle-containing polyhydroxy compounds such as hydroxy compounds.

In addition, the epihalohydrin has the general formula (Here, Z is a hydrogen atom, a methyl group, an ethyl group,
X is a halogen atom), and examples of such epihalohydrin include epichlorohydrin, epibromohydrin,
Examples include 1,2-epoxy-2-methyl-3-chloropropane and 1,2-epoxy-2-ethyl-3-chloropropane.

In addition, as another representative group of epoxy resins,
There are epoxy resins that have on average one or more substituted or unsubstituted glycidyl ester groups in their molecules. Such epoxy resins include aliphatic polycarboxylic acids or aromatic polycarboxylic acids (e.g. phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, hexahydrophthalic acid, methylhexahydrophthalic acid, endomethylenetetrahydrophthalic acid). Phthalic acid, methylendomethylenetetrahydrophthalic acid, maleic acid, phthalic acid, itaconic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dimer fatty acid, trimellitic acid, trimesic acid , pyromellitic acid, cyclopentanetetracarboxylic acid, and halogen-substituted compounds thereof, as well as terminal carboxyl polyester oligomers obtained from these polyhydric carboxylic acids and polyhydric alcohols), such as epihalohydrin and methacrylate. Epoxy resins such as those obtained by polymerizing glycidyl methacrylate synthesized from acids, heterocyclic-containing polycarboxylic acids such as dicarboxylic acids having a hydantoin ring, polycarboxylic acids containing a bridged hydrocarbon ring, such as those of the formula Examples include polyglycidyl esters of polycarboxylic acids having the following structure.

In addition, as another group of epoxy resins, the formula (In the formula, Z is hydrogen, methyl group, ethyl group) N-substituted or unsubstituted 1,2
-There are epoxy resins that have an average of more than one epoxypropyl group in the molecule.

Examples of such epoxy resins include epoxy resins obtained from aromatic amines (e.g. aniline or aniline having an alkyl substituent in the nucleus) and the above-mentioned epihalohydrins, precondensates of aromatic amines and aldehydes (e.g. aniline -Formaldehyde initial condensate, aniline-phenol-
Examples include epoxy resins obtained from formaldehyde initial condensates) and epihalohydrin, as well as triglycidyl isocyanurate and diglycidyl hydantoin compounds. Furthermore, other epoxy resins include epoxidized oils (e.g., epoxidized linseed oil, epoxidized soybean oil, epoxidized safflower oil, epoxidized tung oil, epoxidized eno oil, epoxidized dehydrated castor oil, epoxidized oiticica oil, epoxidized toll). oil, etc.), epoxidized fatty acids, epoxidized cyclic olefin compounds [e.g. vinyl cyclohexene dioxide, 1-(1
-Methyl-1,2-epoxyethyl)-3,4-
Epoxy-4-methylcyclohexane, 3,4-
Epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-6-methylcyclohexylmethyl-3,
4-epoxy-6-methylcyclohexanecarboxylate, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, dicyclopentadiene dioxide, dipentene dioxide, tetrahydroindene dioxide, or these rings are divalent [Aralddite CY-175 (manufactured by Ciba), etc.], epoxidized products of conjugated diene polymers (e.g., epoxidized polybutadiene, epoxidized polypentadiene,
epoxidized styrene-butadiene copolymer, epoxidized acrylonitrile-styrene copolymer), epoxidized polymers containing unsaturated bonds (e.g. epoxidized polypropylene, epoxidized polyisobutyne), polyglycidyl polysiloxane Ethers, such as epoxy resins in which an epoxy group is bonded to the oxazolidinone ring via a carbon atom, polyepoxy compounds obtained from imidazolines substituted with a polyunsaturated alkenyl group at the 2-position, and other heterocycle-containing epoxy resins. Conventionally known epoxy resins include various epoxy resins such as those described in "Production and Application of Resins" (edited by Hiroshi Kakiuchi).

Among such epoxy resins, a preferred group of epoxy resins are polyglycidyl ethers of polynuclear dihydric phenols and polyhydroxy compounds obtained by adding alkylene oxide to them, or those in which the aromatic nucleus contained therein is hydrogenated. is an alicyclic polyglycidyl ether.

Compounds that are reactive with an epoxy group and have a cationizable group used in the production of the paint resin of the present invention include a group that is reactive with an epoxy group and a cationizable group. Any primary amines such as methylamine, ethylamine, propylamine, butylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, methylbutylamine or secondary amines such as ethanolamine, propanol can be used. Hydroxylamines such as amines, diethanolamine, diisopropanolamine, other amine compounds such as piperazine, N-methylpiperazine, etc., such as diethyl sulfide, dipropyl sulfide, dibutyl sulfide, diphenyl sulfide, dicyclohexyl sulfide, tetramethylene sulfide, thiodiethanol, thio Amines containing a carboxyl group, such as those obtained by reacting a sulfide such as dipropanol, an acid anhydride such as succinic anhydride, phthalic anhydride, or maleic anhydride with an alkanolamine such as dimethylethanolamine or methyldiethanolamine. Examples include boric acid triesters in which at least one of the organic groups is substituted with an amino group, such as phosphine compounds such as trimethylphosphine, triethylphosphine, diphenylmethylphosphine, etc.
Preferred among these are water-soluble amine compounds, and particularly preferred is hydroxylamine containing a hydroxyl group.

In the method for producing a coating resin of the present invention, first, the above-mentioned polyisocyanate has a molecular weight of 300 to 300.
3,000 and a difunctional or more functional polyhydroxy compound having a hydroxyl equivalent of 200 to 1,500 to produce a polyurethane prepolymer having terminal isocyanate groups. This reaction is carried out by using an amount of the above-mentioned reaction components such that the ratio of the hydroxyl groups of the polyhydroxy compound to the isocyanate groups of the polyisocyanate is less than 1, preferably 0.7 to 0.2.
This may be carried out with stirring for about 6 hours.

The polyurethane prepolymer having terminal isocyanate groups thus obtained is then reacted with an epoxy resin having a hydroxyl equivalent weight of 150 to 1500 and an epoxy equivalent weight of 150 to 1500.

The reaction between epoxy resin and polyurethane prepolymer having terminal isocyanate groups is NCO/OH
The above compounds are mixed so that the ratio is 0.05 to 1.0, preferably 0.3 to 0.9, and the
This can be done for 10 hours with stirring.

If necessary, unreacted substances and the like are removed from the reaction product thus obtained, and then the reaction product is reacted with a compound having reactivity with an epoxy group and a cationizable group. Although this reaction can occur simply by mixing at room temperature, it is preferable to conduct the reaction by heating to 50°C to 130°C, preferably 70°C to 100°C, in order to complete the reaction.

In a compound having a group that is reactive with an epoxy group and can be cationized, the ratio of the group that is reactive with an epoxy group to the epoxy group contained in the reaction product is 0.2 to 1.0, preferably 0.5 to 1.0. 1.0
It is preferable to use such an amount that the compound is added gradually to the reaction product in order to prevent rapid heat generation. In order to facilitate the reaction, a solvent may be used, such as alcohols such as isopropanol, isobutanol, and ethyl cellosolve, such as methyl ethyl ketone,
In addition to ketones such as methyl isobutyl ketone and cyclohexanone, various other solvents can be used.

The cationizable coating resin thus obtained according to the invention can be used, for example, with organic acids such as formic acid, acetic acid, propionic acid, lactic acid, or with inorganic acids such as phosphoric acid, hydrochloric acid, boric acid, sulfuric acid, etc. The aqueous liquid containing the coating resin may optionally be simply mixed with water to form an aqueous emulsion or solution of the coating resin.

In addition, when reacting a compound that is reactive with the above-mentioned epoxy group and has a group that can be cationized, the above-mentioned acid is added at the same time, and after the reaction is completed, water is added to react in the same manner. , an aqueous emulsion or an aqueous solution of a coating resin. The amount of acid is preferably at least the amount necessary to solubilize or disperse the resin in water and not more than the equivalent of the cationizable groups contained in the resin.

The coating resin obtained by the present invention can be used in combination with various curing agents to coat the object to be coated by coating, dipping, electrodeposition, etc., and then cured to provide excellent adhesion, flexibility, and corrosion resistance. Provides a coating film with properties.

As the curing agent, for example, blocked isocyanates, partially capped organic polyisocyanates, melamine resins, guanamine resins, urea resins, etc. can be used, and blocked isocyanates and partially capped organic polyisocyanates are particularly preferred.

The coating resin obtained in the present invention can be solubilized or dispersed in water without the need for a surfactant, but a surfactant may be used in some cases, and the solvent has an affinity for water. You may use it if it is available.
When the coating resin obtained in the present invention is used with various curing agents, for example, tertiary amines, alkyl metal salts, etc. can be used as curing accelerators in order to make curing occur more quickly and completely. .
Further, the coating resin obtained according to the present invention may be used with a pigment added thereto, and the pigment preferably does not have reactivity with acids.

It is also possible to mix other neutral or cationic resins within a range that is compatible with the coating resin obtained in the present invention.

The coating resin obtained in the present invention has better adhesion, flexibility, corrosion resistance, surface smoothness, and impact resistance than conventional cationizable coating resins used in cationic electrodeposition coatings. It provides an excellent coating film and is particularly suitable for electrodeposition coatings.

The present invention will be explained in detail with reference to Examples below. Note that parts in the examples are based on weight.

[Example 1] Polyethylene glycol (average molecular weight = 1500)
50 parts and 12 parts of 2,4-toluylene diisocyanate were stirred at 85°C for 3 hours to obtain a polyurethane prepolymer terminated with isocyanate groups.

62 parts of this polyurethane prepolymer contains 2,2-
Add 100 parts of polyglycidyl ether (epoxy equivalent = 450, hydroxyl equivalent = 1050) of bis(4-hydroxyphenyl)propane propylene adduct, and add 95
The mixture was stirred at ℃ for 6 hours to obtain a reaction product having an epoxy equivalent weight of 730. After adding 40 parts of methyl isobutyl ketone to this reaction product to obtain a solvent solution (A), 14 parts of diethylamine were gradually added at 60°C, and the mixture was heated again to 90°C and held for an additional 3 hours. Blocked isocyanate of the coating resin of the present invention thus obtained (B-1065, manufactured by Fueva, isophorone diisocyanate lactam mask product, NCO content = 11%) 45
After thoroughly mixing and dissolving, 115 parts of 10% acetic acid was gradually added, and then 115 parts of 10% acetic acid was added.
After stirring for a period of time until the mixture becomes homogeneous, add 1170 parts of deionized water. The paint resin solution thus obtained containing 15% non-volatile matter had a pH of 6.3. Apply this to a degreased steel plate as an electrodeposition bath.
Electrodeposition was performed at 250V for 2 minutes, and the resulting coating was heated at 200℃ for 20 minutes.
After baking for minutes, a coating film with a thickness of 17 μm and a pencil hardness of 3H was obtained. The performance of this coating film was as follows.

Impact resistance (1Kgr x 50cm) Corrosion resistance (250 hours) with no abnormality Surface smoothness Excellent Erichsen resistance 8mm or more [Example 2] Obtained by the dehydration reaction of hydrogenated bisphenol A and adipic acid. 50 parts of polyester polyol (average molecular weight = 2200) and 10 parts of methylene bisphenyl diisocyanate were stirred at 85°C for 3 hours to obtain an isocyanate-terminated urethane prepolymer.

To 60 parts of this urethane prepolymer, 50 parts of polyglycidyl ether of 2,2-bis(4-hydroxycyclophenyl)propane (epoxy equivalent = 320, hydroxyl equivalent = 1250) was added and stirred at 85°C for 7 hours, resulting in an epoxy equivalent of 720. A reaction product was obtained. To this reaction product, 25 parts of methyl ethyl ketone was added to form a solvent solution, and then 8 parts of diisopropanolamine was gradually added at 50°C. It was heated again to 90°C and held for an additional 4 hours. Add 30 parts of partially capped isocyanate (methyl ethyl ketoxime partially masked product of tolylene diisocyanate/trimethylolpropane adduct, NCO content 15%) to the coating resin of the present invention thus obtained, and thoroughly mix and dissolve. After that, lower the temperature to 50℃ and add 10% acetic acid 105
After stirring for 2 hours, 580 parts of deionized water was added to the mixture until the mixture became homogeneous. The paint solution thus obtained containing 18% non-volatile matter had a pH of 5.9. This product was used as an electrodeposition bath to electrodeposit on a degreased steel plate at 220V for 3 minutes. The resulting coating film was baked at 170° C. for 30 minutes to obtain a coating film with a thickness of 15 μm and a pencil hardness of 2H. The performance of this coating film was as follows.

Impact resistance (1Kg/50cm) No abnormality Corrosion resistance (250 hours) Surface smoothness Excellent Erichsen resistance 7mm [Example 3] Polylactone polyol (average molecular weight = 1200)
50 parts and 17 parts of tolylene diisocyanate at 90℃
The mixture was stirred for hours to obtain a polyurethane prepolymer with isocyanate group terminals.

67 parts of this polyurethane prepolymer contains 2,2-
70 parts of bis-(4-hydroxyphenyl)propane diglycidyl ether (epoxy equivalent = 625, hydroxyl equivalent = 525) and 35 parts of methyl isobutyl ketone were added and stirred at 85°C for 8 hours to form a reaction product with an epoxy equivalent of 1250. A solvent solution was obtained. To this solution, 7 parts of diethylamine was gradually added at 60°C, and then again at 95°C.
The mixture was heated to a temperature of 100.degree. C. and held for an additional 3 hours.

The isocyanate partially capped in the coating resin of the present invention thus obtained (ethyl cellosolve partial mask of tolylene diisocyanate,
Add 20 parts of NCO content (24%), mix and dissolve thoroughly, lower the temperature to 50℃, gradually add 70 parts of a 10% propionic acid aqueous solution, stir for 2 hours, and when the mixture becomes homogeneous, deionize. Added 590 parts of water.
The paint solution thus obtained containing 20% non-volatile matter had a pH of 6.1. This product was used as an electrodeposition bath to electrodeposit on a degreased steel plate at 200V for 2 minutes, and the resulting coating film was baked at 210°C for 30 minutes to obtain a coating film with a thickness of 20μ and a pencil hardness of 3H. The performance of this coating film was as follows.

Impact resistance (1Kg x 50cm) No abnormality Corrosion resistance (250 hours) Surface smoothness Excellent Erichsen resistance 8mm or more [Example 4] Solvent solution of the reaction product with an epoxy equivalent of 730 obtained in Example 1 (A ) 200 parts diethylamine 14
The mixture was gradually added at 60° C., heated again to 90° C., and held for an additional 3 hours to obtain a coating resin of the present invention.
Then, methylated melamine resin (Cymel 370,
Add 30 parts (manufactured by Mitsui Toatsu, equivalent weight = 225-325), mix and dissolve thoroughly, and gradually add 115 parts of 10% acetic acid.
A coating solution containing 60% non-volatile matter was obtained. Apply this solution to a degreased steel plate and bake it at 180℃ for 30 minutes.
A coating film with a thickness of 25μ and a pencil hardness of 4H was obtained. The performance of this coating film was as follows.

Impact resistance (1Kg x 50cm) No abnormality Corrosion resistance (250 hours) Surface smoothness Excellent Erichsen resistance 8mm or more [Comparative example 1] 2,2-bis-(4-hydroxyphenyl) propane diglycidyl ether (epoxy Equivalent =
625) was mixed and dissolved in 30 parts of methyl ethyl ketone, 10 parts of diethylamine was gradually added at 60°C, and the mixture was heated again to 110°C and held for another 2 hours to produce a coating resin. Isocyanate partially capped in this paint resin (ethyl cellosolve partial mask product of tolylene diisocyanate,
After thoroughly mixing and dissolving 45 parts (NCO content 24%), the temperature was lowered to 50°C, and 100 parts of a 10% aqueous propionic acid solution was gradually added. Thereafter, the mixture was stirred for 2 hours, and when the mixture became uniform, 810 parts of deionized water was added. Paint resin solution containing 15% non-volatile matter is
The pH was 5.8. This product was used as an electrodeposition bath to electrodeposit on a degreased steel plate at 220V for 2 minutes. The obtained coating film is 210
A coating film with a thickness of 15μ and a pencil hardness of 4H was obtained by baking at ℃ for 30 minutes. The performance of this coating film is as follows.

Impact resistance (1Kg/20cm) No cracking Corrosion resistance (250 hours) No abnormality Surface smoothness Poor smoothness with cracks and pinholes.

Erichsen resistance value 2mm

Claims (1)

[Claims] 1. A polyurethane prepolymer having a terminal isocyanate group obtained by reacting a polyisocyanate with a bifunctional or higher polyhydroxy compound having a molecular weight of 300 to 3000 and a hydroxyl equivalent of 200 to 1500 and a hydroxyl equivalent of 150 to 1500 and an epoxy equivalent of 150 to 1500. A cation characterized by reacting an epoxy resin having an isocyanate group/hydroxyl group such that the ratio of isocyanate groups to hydroxyl groups is 0.05 to 1.0, and further reacting a compound having a group that is reactive with an epoxy group and can be cationized. A method for producing paint resin that can be used as a coating material.