JP2013249397A - Resin for coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin for a coating material affording various good coated film properties such as water resistance, weatherability and chemical resistance for various articles to be coated such as nylon, polyethylene terephthalate, an ABS resin, polycarbonate, aluminum, iron and mortar.SOLUTION: A resin for a coating material is obtained by reacting a mixture of 100 pts.wt. of a mixture (A) of (a) 50-99.9 pts.wt. (meth)acrylic acid alkyl ester and (b) 0.1-50 pts.wt. another vinylic monomer, and 0.02-20 pts.wt. of a polymerization initiator (B), where the reaction rate of the mixture (A) is 90% or above, the weight-average molecular weight of (A) is 5,000-200,000, and the content of fraction less than 1,000 molecular weight is less than 10 wt.%.

Description

  The present invention is a coating resin having various coating performances such as water resistance, weather resistance, chemical resistance and the like for various coated objects such as nylon, polyethylene terephthalate, ABS resin, polycarbonate, aluminum, iron and mortar. About.

  Acrylic resins are abundant in the types of acrylic monomers that can be used as raw materials and monomers that can be copolymerized therewith. Adhesion, adhesion, hardness, transparency, and light resistance can be selected by selecting these monomers. It is widely used as a resin for paints because it can arbitrarily control physical properties and chemical properties such as heat resistance, weather resistance and chemical resistance.

  In recent years, resin for coating materials is required to satisfy both cost and performance. Especially for paints used in bridges, ships, containers, etc. where repainting is indispensable, there is a need for room-temperature drying paints that are easy to construct, maintain a certain level of coating film performance, and are low in cost. Is expensive.

  As an example of such a paint, a method of improving the weather resistance by copolymerizing a polymerizable UV-stable monomer has been devised (see Patent Document 1). However, in general, the polymerizable UV-stable monomer itself is expensive and has insufficient weather resistance.

  A one-pack type resin composition for paint that can be cured at a low temperature has been devised (see Patent Document 2). The one-pack type resin composition for paints requires a tight control of molecular weight and residual monomer in order to improve the stability of the paint and exhibit good film performance, and is at a level where it can be put to practical use. Absent.

  Furthermore, in order to reduce the odor at the time of construction, the coating material which uses a certain alkyl (meth) acrylate and a hydrocarbon solvent is devised (refer patent document 3). A paint using a specific alkyl (meth) acrylate and a hydrocarbon solvent must remove the residual monomer, which is one of the causes of odor, and requires a lot of work in the manufacturing process.

JP 2001-172551 A JP 2002-88296 A JP-A-6-184490

  The present invention is low in cost and has various film performances such as water resistance, weather resistance, chemical resistance and the like for various coated objects such as nylon, polyethylene terephthalate, ABS resin, polycarbonate, aluminum, iron, and mortar. The object is to provide a good resin for paints.

  As a result of diligent research on low-cost and various coating resins that have good coating film performance for various types of coatings, we found a method for producing coating resins with very few residual monomers and low molecular components, It has been found that the coating resin produced thereby has good coating film performance.

  That is, the present invention is a mixture of (a) 50 to 99.9 parts by weight of (meth) acrylic acid alkyl ester and (b) 0.1 to 50 parts by weight of other copolymerizable vinyl monomers ( A) A coating resin obtained by reacting a mixture of 100 parts by weight and a polymerization initiator (B) 0.02 to 20 parts by weight, wherein the reaction rate of the mixture (A) is 90% or more, and the weight average It is a resin for coating materials having a molecular weight of 5,000 to 200,000 and a molecular weight of less than 1,000 and less than 10% by weight.

  The coating resin of the present invention has various coating film performances such as water resistance, weather resistance, and chemical resistance against various coated objects such as nylon, polyethylene terephthalate, ABS resin, polycarbonate, aluminum, iron, and mortar. . The coating resin of the present invention is low in cost.

  The present invention is a mixture (A) of (a) 50 to 99.9 parts by weight of (meth) acrylic acid alkyl ester and (b) 0.1 to 50 parts by weight of other copolymerizable vinyl monomers. A resin for coating obtained by reacting a mixture of 100 parts by weight and a polymerization initiator (B) 0.02 to 20 weights, wherein the reaction rate of the mixture (A) is 90% or more, and the weight average molecular weight is 5 It is a resin for coatings having a content of less than 1,000 to 200,000 and a molecular weight of less than 1,000.

  Examples of the (meth) acrylic acid alkyl ester used in the present invention include methyl acrylate, ethyl acrylate, normal propyl acrylate, isopropyl acrylate, normal butyl acrylate, isobutyl acrylate, tertiary butyl acrylate, and acrylic acid. Cyclohexyl, 2-ethylhexyl acrylate, isobornyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, normal butyl methacrylate, tertiary butyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, methacryl Examples thereof include linear, branched and cyclic alkyl esters having 1 to 18 carbon atoms of (meth) acrylic acid such as acid isobornyl. These may be used alone, but various properties can be obtained by using two or more of them in combination.

  In particular, the alkyl group of the (meth) acrylic acid alkyl ester used in the present invention is preferably an alkyl group having 4 or more carbon atoms, more preferably an isobutyl group, a tertiary butyl group, A branched alkyl group such as 2-ethylhexyl group and a cyclic alkyl group such as cyclohexyl group and isobornyl group are preferred.

  The usage-amount of the (meth) acrylic-acid alkylester used by this invention is 50-99.9 weight part in 100 weight part of mixtures (A).

  Other copolymerizable vinyl monomers used in the present invention include, for example, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, and monoacrylate of cyclohexanedimethanol. , 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, monomethacrylate of cyclohexanedimethanol, Daicel Chemical Industries, Ltd. Plaxel F series (FM2D, FM3, FM5, FA1DDM, FA2D, FA10L) and the like, carboxyl group-containing monomers such as methacrylic acid and acrylic acid, glycidyl methacrylate, glycidyl acrylate, 3,4-epoxycyclohexylmethyl acrylate, 3, 4 Epoxy group-containing monomers such as epoxycyclohexylmethyl methacrylate, alkoxy group-containing monomers such as 3-methacryloyloxypropyltrimethoxysilane, 3-methacryloyloxypropyltriethoxysilane, 3-methacryloyloxypropylmethyldimethoxysilane, acrylamide, Acrylamide monomers such as diacetone acrylamide, diacetone methacrylamide, N-butoxymethyl acrylamide, N-butoxymethyl methacrylamide, 2- [2'-hydroxy-5 '-(methacryloyloxymethyl) phenyl] -2H- Benzotriazole, 2- [2′-hydroxy-5 ′-(methacryloyloxyethyl) phenyl] -2H-benzotriazole, 2- [2′-hydroxy-5 ′-(methacryloylio) Cyclopropyl) phenyl] -2H-benzotriazole and other benzotriazole-based UV-absorbing unsaturated monomers (R-UVA), 4-methacryloylamino-2,2,6,6-tetramethylpiperidine, 4-methacryloyl Hindered amine light-stable unsaturated monomers (R-HALS) such as oxy-1,2,2,6,6-pentamethylpiperidine, styrene, vinyl acetate, tetrahydrofurfuryl (meth) acrylate, butadiene, Vinyl monomers such as tetrafluoroethylene, trichlorofluoroethylene, dichlorofluoroethylene, monochlorofluoroethylene, butyl vinyl ether and cyclohexyl vinyl ether can be raised. These other copolymerizable vinyl monomers may be used alone or in combination of two or more.

  The amount of other copolymerizable vinyl monomers used in the present invention includes (a) (meth) acrylic acid alkyl ester, and (b) other copolymerizable other vinyl monomers. In 100 parts by weight of the mixture (A), 0.1 to 50 parts by weight.

  In the present invention, the reaction rate of (a) (meth) acrylic acid alkyl ester, (b) other copolymerizable monomer (A) and mixture (A) is 90% or more, Preferably, it is 93% or more, more preferably 95% or more.

  As the polymerization initiator (B) used in the present invention, various polymerization initiators can be used. For example, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4 -Dimethylvaleronitrile), azo-based initiators such as 2,2'-azobis (2-methylbutyronitrile), 2-tert-butylperoxybenzoate (TBPB), tert-butyl hydroperoxide (TBHPO), 2 Peroxide based initiators such as tert-butyl peroxide (DTBP) are used. These initiators may be used alone or in combination of two or more. These polymerization initiators (B) are used in an amount of 0.02 to 20 parts by weight, preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the mixture (A). When the amount of the polymerization initiator used is less than 0.02 parts by weight, the polymerization reaction does not proceed sufficiently, the molecular weight of the resin to be produced varies, the quality is not constant, and when it exceeds 20 parts by weight, the polymerization initiator ( The water resistance and weather resistance of the coating film deteriorate due to the influence of the decomposition product of B).

  In this invention, Preferably, 0.01-20 weight part of compounds (C) which have a thiol group with respect to 100 weight part of mixtures (A) are contained.

  Various compounds (C) having a thiol group used in the present invention are selected. For example, alkyl such as 1-butanethiol, 1-heptanethiol, 1-decanethiol, 1-dodecanethiol, etc. Thiols, thioglycolic acid, 2-mercaptopropionic acid, 2-mercaptoethanol, 3-mercapto-2-butanol, etc. can be raised and may be used alone or in combination of two or more. it can. By using the compound (C) having a thiol group, the terminal structure of the resin is controlled, and a resin having high weather resistance can be synthesized.

  The amount of the compound (C) having a thiol group used is preferably 0.01 to 20 parts by weight, more preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the mixture (A). Is done.

  In the present invention, the weight average molecular weight of the coating resin is set in the range of 5000 to 200,000, more preferably 10,000 to 100,000. If it is less than 5000, sufficient film performance such as weather resistance and chemical resistance cannot be obtained. If it is 200,000 or more, the viscosity of the paint is high, and the coating workability is remarkably lowered.

  Furthermore, the molecular weight dispersity (weight average molecular weight / number average molecular weight) of the coating resin is preferably set in the range of 1.9 to 3.0. By setting within this range, it is possible to obtain a coating film with good workability in which sagging of the paint is suppressed and a good finished appearance.

  In the present invention, the coating resin has a molecular weight of less than 1,000 and a content of less than 10% by weight. Preferably, it is less than 9% by weight, more preferably less than 8% by weight.

  The coating resin in the present invention includes pigments such as titanium oxide, calcium carbonate, carbon black, silica sol, titania sol, bitumen and iron oxide, leveling agents, thickeners, pigment dispersants, antifoaming agents, ultraviolet absorbers, and light stabilizers. Paint additives such as antioxidants (HALS), antioxidants, fluororesin, silicone, butyl rubber, chlorinated rubber, isoprene rubber, polyurethane rubber, rubber-modified epoxy resin, alkyd resin, polyester resin, epoxy resin, chlorinated polyolefin resin, A coating material can be prepared by appropriately blending a coating resin such as an acrylic resin and a curing agent such as epoxy, isocyanate, melamine, and hydrolyzable silicone.

  In the method for producing a coating resin according to the present invention, (a) 50 to 99.9 parts by weight of (meth) acrylic acid alkyl ester, and (b) 0.1 to 50 parts by weight of other copolymerizable vinyl monomers. A resin for coating obtained by reacting a mixture of 100 parts by weight of the mixture (A) and 0.02 to 20 parts by weight of the polymerization initiator (B), wherein the reaction rate of the mixture (A) is 90% or more. The coating resin having a weight average molecular weight of 5,000 to 200,000 and a molecular weight of less than 1,000 is less than 10% by weight is reacted at a reflux temperature and aging at a reflux temperature or lower. To manufacture.

  In the present invention, the reaction at the reflux temperature means a method of reacting the mixture (A) under reflux or a method of reacting under a reflux of a mixture of the mixture (A) and a solvent. Among these, the method of reacting the mixture of the mixture (A) and the solvent under reflux makes it easy to control the polymerization reaction, suppresses the runaway polymerization, and can produce a high-quality resin.

  In the case of the method of reacting the mixture (A) and the solvent, various solvents are used. Solvents include, for example, aromatic solvents such as toluene, xylene and ethylbenzene, acetate solvents such as ethyl acetate, normal butyl acetate, isobutyl acetate, normal propyl acetate, isopropyl acetate and amyl acetate, methyl isobutyl ketone, methyl ethyl ketone and diisobutyl. Ketone solvents such as ketone, acetone, alcohol solvents such as methanol, ethanol, isopropyl alcohol, normal propyl alcohol, normal butyl alcohol, isobutyl alcohol, tertiary butyl alcohol, benzyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, propylene Glycols such as glycol, glycols such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether Ruether solvents, acetate solvents such as methyl cellosolve acetate, methoxypropyl acetate, hydrocarbon solvents such as normal hexane, cyclohexane, methylcyclohexane, heptane, ExxonMobil's Solvesso 100, Solvesso 150, Maruzen Petroleum Corporation Naphtha solvents such as Swazol 1000, Swazol 1500, Swazol 1800, Ipsol 100 and Ipsol 150 from Idemitsu Kosan Co., Ltd. These solvents can be used alone or in combination of two or more, but two or more solvents having different boiling points may be appropriately used in combination so that the target reaction temperature becomes the reflux temperature. preferable.

  Examples of the method of reacting the mixture of the mixture (A) and the solvent under reflux include, for example, a method in which the mixture (A) and the solvent are collectively charged and reacted, a part of the mixture (A) is charged in the solvent, and the rest Various methods of supplying the mixture (A) to the solvent, such as a method of reacting the mixture (A) by dividing or dropping the mixture, a method of reacting all of the mixture (A) by dividing or dropping the mixture (A) There is.

  In the method for producing a coating resin according to the present invention, the temperature in the case of reacting at the reflux temperature is preferably set in the range of −20 to + 20 ° C. with the 1-hour half-life temperature of the polymerization initiator (B) as the center. . If the temperature is lower than this, unreacted initiator remains, and the performance such as water resistance and weather resistance of the coating film deteriorates.If the temperature is higher than this, the initiator is decomposed too early, so that the molecular weight increases. Or there is a tendency for residual monomer to increase. Furthermore, the reaction temperature is preferably set in the range of 50 to 200 ° C, more preferably in the range of 70 to 180 ° C.

  In the method for producing a coating resin of the present invention, the step of aging at a reflux temperature or lower is a step of reacting the mixture (A) at the reflux temperature, and the reaction rate of the mixture (A) is 70% or more, more preferably When the temperature reaches 90% or higher, the reaction temperature is lowered to a temperature at which reflux is stopped, and the reaction is continued in that state.

  In the method for producing a coating resin according to the present invention, it is preferable to additionally add a polymerization initiator (B) in the step of aging at a reflux temperature or lower. In the step of aging at the reflux temperature or lower, the polymerization can be completed in a short period of time by additionally adding a polymerization initiator (B). Also in this case, it is preferable to select a polymerization initiator such that the one-hour half-life temperature of the polymerization initiator (B) is in the range of −20 to + 20 ° C. with respect to the reaction temperature.

  In the method for producing a coating resin of the present invention, the weight average molecular weight and the degree of molecular weight dispersion include the temperature at which the mixture (A) is reacted under reflux, the type and amount of the polymerization initiator (D), and the thiol group. It can be adjusted by appropriately combining conditions such as the type and amount of the compound (C) and the method of supplying the mixture (A) to the solvent. In particular, when the weight average molecular weight is 40,000 to 200,0000 and the dispersity is 2.3 to 2.6, the sagging property can be improved.

  The coating material using the coating resin in the present invention can be applied by various coating methods applied to general coating materials. For example, methods such as spray coating, roll coating, curtain coating, brush coating, electrostatic coating, anion, cationic electrodeposition coating, and dipping can be applied. Furthermore, it can be applied to various coating film configurations such as primer (adhesive layer), base coat (normally colored paint with intermediate coating), top coat (surface finish coating), and one coat.

  As the base material (coating material) to which the paint using the paint resin in the present invention can be applied, polystyrene resin, acrylic resin, acrylonitrile-styrene-butadiene resin (ABS), polypropylene, ethylene-propylene resin, polycarbonate resin, noryl. Resin, nylon resin, epoxy resin, polyester resin plastic, and composite materials blended with fillers, reinforcing materials such as glass fiber and carbon fiber, inorganic materials such as glass, mortar, cement slate and rock, iron ( And alloys), copper (and alloys), aluminum (and alloys), magnesium (and alloys), paper, vinyl cloth, and the like.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

(Measurement of weight average molecular weight and number average molecular weight)
Relative molecular weight based on polystyrene by gel permeation chromatography (instrument: Tosoh Corporation, HLC-8220GPC, column: TSKgel SuperHZM-N, guard column: TSKGuardcolumn SuperHZ-L, solvent: tetrahydrofuran, hereinafter abbreviated as GPC) Asked.

(Measurement of molecular weight less than 1000)
From the histogram data obtained from GPC, the cumulative value with a molecular weight of less than 1000 was used.

(Measurement of reaction rate)
It was set as the percentage of the theoretical heating residue which assumed the reaction rate of 100% of the mixture (A) with respect to the measurement heating residue. That is, it calculated | required with the following formulas.
{(Measured overheating residue (%)) ÷ (Theoretical overheating residue (%) assuming a reaction rate of 100% of the mixture (A))} × 100.
In addition, the measurement of the heating residue was based on JISK5601-1-2.

(Cross cut tape test)
The steel sheet was spray-coated to a dry film thickness of 40μ, and the test piece baked at 80 ° C for 10 minutes was cooled to room temperature, and in accordance with JIS K5400 (discontinued in 1999), a cross-cut tape test was conducted. Judgment was made according to the following criteria.

90-100 / 100: good 80-89 / 100: somewhat good 79 or less / 100: bad

(Specular gloss test)
After spray coating the steel sheet to a dry film thickness of 40μ and baking for 10 minutes at 80 ° C, the test piece was cooled to room temperature, and in accordance with JIS Z8741, a 60 ° specular gloss test was conducted. Judgment was made as follows.

45 or more: Good 40-45: Slightly good Less than 40: Defect.

(Water resistance test)
A test piece that was spray-coated on a steel sheet to a dry film thickness of 40 μm and baked at 80 ° C. for 10 minutes was cooled to room temperature and immersed in warm water set to 40 ° C. ± 1 ° C., and the test piece was taken out after 7 days. . The test piece taken out was completely wiped off moisture and visually judged according to the following criteria.

No change in appearance: Good Slightly whitened / partially whitened: Slightly good Entirely whitened, partially peeled, completely peeled: Poor.

(Accelerated weather resistance test)
A test piece that was spray-coated on a steel sheet to a dry film thickness of 40 μm and baked at 80 ° C. for 10 minutes was cooled to room temperature and subjected to a Q-UV irradiation tester (lamp: UVB-313, BPT: 63 ° C., illuminance: 60 ° specular gloss retention after irradiation time of 500 hours at 0.67 W / m 2, rainfall conditions: 18/120 minutes (no irradiation during rain)), measured by Nippon Denshoku Industries VG2000, viewing angle 60 ° did. The 60 ° specular gloss retention was determined according to the following criteria.

60 ° specular gloss retention 50% or more: good 60 ° specular gloss retention 40-50%: somewhat good 60 ° specular gloss retention less than 40%: poor.

(Sag test)
After coating on a steel sheet using a sagging property tester tag tester, the test piece was set up vertically and the limit film thickness of the coating film was measured and judged according to the following criteria.

Coating film thickness of 14 mils or more: Good Coating film thickness of 11 to 14 mils: Slightly good Coating film thickness of less than 10 mils: Poor

Example 1
A four-necked flask equipped with a thermometer, a dropping funnel, a condenser, and a stirrer was charged with 15 parts by weight of Solvesso 100 (manufactured by ExxonMobil) and 34 parts by weight of xylene as the solvent. After purging with nitrogen, the solvent was brought to reflux. It heated in the oil bath until it became. The reflux temperature at this time was 138-142 degreeC. Next, 37 parts by weight of methyl methacrylate, 62 parts by weight of normal butyl methacrylate, 1 part by weight of methacrylic acid, and 0.6 parts by weight of perbutyl D (manufactured by NOF Corporation, ditertiary butyl peroxide) are weighed and mixed well. After that, the dropping funnel was charged. This mixture was added dropwise in refluxing solvent over 3 hours. The reaction rate at the end of dropping was measured and found to be 87%. Next, the temperature in the four-necked flask is adjusted to 90 ° C., the reflux of the solvent is stopped, this state is maintained for 2.5 hours, and then cooled, and 50 parts by weight of Solvesso 100 is added to add the coating resin solution. Obtained. The coating resin thus obtained has a weight average molecular weight of 47,000, a number average molecular weight of 18,000, a molecular weight dispersity (weight average molecular weight / number average molecular weight) of 2.6, a content of less than 1000 molecular weight, and a reaction rate of 8.3%. 92%.

(Example 2)
The reaction was carried out under the same apparatus, blending and reflux temperature conditions as in Example 1. The reaction rate at the end of dropping was measured and found to be 87% as in Example 1. Adjust the temperature in the four-necked flask to 90 ° C., stop the reflux of the solvent, then prepare a slurry of 0.8 parts by weight of 2,2′-azobisisobutyronitrile and 10 parts by weight of Solvesso 100. This was divided into four portions every 30 minutes, and then aging was continued for another 1.5 hours. The inside of the four-necked flask was cooled, and 50 parts by weight of Solvesso 100 was added to obtain a coating resin solution. The coating resin thus obtained has a weight average molecular weight of 46000, a number average molecular weight of 22,000, a molecular weight dispersity (weight average molecular weight / number average molecular weight) of 2.1, a content of less than 1000 molecular weight of 0.8%, and a reaction rate of It was 98%.

(Example 3)
In the same apparatus as in Example 1, the solvent was charged in the same composition, and the same conditions and reflux temperature were obtained. Next, 37 parts by weight of methyl methacrylate, 62 parts by weight of normal butyl methacrylate, 1 part by weight of methacrylic acid, 0.01 part by weight of n-dodecyl mercaptan, perbutyl D (manufactured by NOF Corporation, ditertiary butyl peroxide) 6 parts by weight were weighed and mixed well, and then charged into a dropping funnel. This mixture was added dropwise in refluxing solvent over 3 hours. The reaction rate at the end of dropping was measured and found to be 87% as in Example 1. The temperature in the four-necked flask was adjusted to 90 ° C., the reflux of the solvent was stopped, and then 0.8 parts by weight of 2,2′-azobisisobutyronitrile and 10 parts by weight of Solvesso 100 (solid content adjusting solvent (Part of 50 parts by weight) of the slurry was prepared, and divided into 4 portions every 30 minutes, and then aging was continued for another 1.5 hours. The interior of the four-necked flask was cooled, and 40 parts by weight of the solid content adjusting solvent Solvesso 100 (the remainder excluding the slurry formulation) was added to obtain a resin solution for coating. The coating resin thus obtained has a weight average molecular weight of 45,000, a number average molecular weight of 21,000, a molecular weight dispersity (weight average molecular weight / number average molecular weight) of 2.1, a content of less than 1000 molecular weight, and a reaction rate of 0.8%. It was 98%.

(Examples 4 to 13)
When the compound (D) having a thiol group is not used under the conditions and composition as shown in Tables 1 and 2, the same operation as in Example 2 is performed, and the compound (D) having a thiol group is used. The same operation as in Example 3 was performed to obtain a coating resin. The evaluation results of each resin are shown in Tables 4-5.

(Comparative Example 1)
In Example 1, the same operation was performed except that the aging temperature was maintained at a reflux state of 140 ° C. to obtain a coating resin. The evaluation results are shown in Table 6.

(Comparative Examples 2 to 4)
A coating resin was obtained by performing the same operation as in Example 4 except that the formulation was as shown in Table 3. The evaluation results for each resin are shown in Table 6.

Claims (4)

(A) 50 to 99.9 parts by weight of (meth) acrylic acid alkyl ester, (b) 100 parts by weight of a mixture of 0.1 to 50 parts by weight of other copolymerizable vinyl monomers (A) and A resin for coating obtained by reacting a mixture of 0.02 to 20 weight with a polymerization initiator (B), wherein the reaction rate of the mixture (A) is 90% or more, and the weight average molecular weight is 5,000 to 200. Resin for coating materials whose content of less than 1,000 and molecular weight less than 1,000 is less than 10% by weight. (A) Mixture of (meth) acrylic acid alkyl ester and (b) other copolymerizable vinyl monomer (A) 100 parts by weight of compound (C) having a thiol group with respect to 100 parts by weight The resin for paints according to claim 1 containing 01 to 20 parts by weight. The method for producing a coating resin according to claim 1 or 2, comprising a step of reacting at a reflux temperature and a step of aging at or below the reflux temperature. The method for producing a coating resin according to claim 3, wherein the polymerization initiator (B) is additionally added in the step of aging at the reflux temperature or lower.