JPH0255465B2 - - Google Patents

Description

[Detailed description of the invention]

Background and Problems of the Present Invention Electrodeposition paints are widely used as undercoats with anticorrosive properties because of their workability regardless of shape and their safety. Electrodeposition paints are in the form of resins dispersed or dissolved in water as a medium, so safety and control of throwing power by energization are necessary to stabilize the coating line. Regarding its performance as a coating film, coating films with high film thickness and high performance physical properties are desired, particularly in fields where high corrosion resistance and pitting resistance are required, such as automotive coating systems. In addition, as consumers have recently become more conscious of high-quality products, there has been a strong desire for high-quality paint films, and there is a strong need for paint films that have higher definition and higher gloss than ever before. It is conventionally known to add minute resin particles (microgel) made of internally crosslinked polymers of ethylenically unsaturated monomers to electrodeposition paints. In other words, Japanese Patent Application Laid-Open No. 58-93762 describes an emulsion of an internally crosslinked polymer consisting of a polyfunctional vinyl monomer and a monofunctional vinyl monomer and a thermosetting water-soluble polymer as a method for obtaining a washable coating film that is difficult to obtain with normal methods. The internally crosslinked emulsion is uniformly distributed and cured in the uniformly cured product with the thermosetting resin for the electrodeposition paint, and as a result, the light rays are hardened. The diffused reflection creates a fading effect. This technology is related to electrodeposition paints whose surface has unevenness that causes diffused reflection, and because of the unevenness, it is not intended to obtain a coating film with a high appearance by applying an intermediate coat or top coat on top of it. Not yet. An erasable electrodeposition paint for aluminum or aluminum alloy based on the same principle is disclosed in Japanese Patent Application Laid-Open No. 56-49766.
It is also stated. As described above, the use of conventional erasable electrodeposition paints containing microgels is limited to erasable transparent paints for aluminum or aluminum alloys, and not only is it not versatile, but the microgels tend to settle during paint storage. Moreover, if it is added in an amount that provides a sufficient erasing effect, it tends to impair electrodeposition workability. Therefore, an object of the present invention is to provide an erasable electrodeposition paint that can form a smooth coating film without impairing the stability of the paint or the workability of electrodeposition. Solution The above problem is solved by adding internally crosslinked fine resin particles whose refractive index difference from the aqueous resin is within a certain range to an aqueous dispersion of an electrodepositable aqueous resin (base resin). be done. Therefore, in the present invention, (a) an aqueous dispersion of an aqueous resin that can be electrodeposited, and (b) a refractive index difference of 0.02 that is uniformly dispersed in the aqueous dispersion of the aqueous resin and that the aqueous resin has a refractive index difference of 0.02. ~
Provided is an erasable electrodeposition coating composition characterized in that it contains internally crosslinked fine resin particles having a molecular weight of 0.3 as an essential component. The fine resin particles are held in a coating film formed by electrodeposition and curing, and because there is a difference in refractive index between the resin and the water-based resin that forms the matrix, light is diffusely reflected at the interface, creating an quenching effect. It is something that causes Therefore, the erasing effect does not depend on the unevenness of the paint film surface, so a smooth paint film can be obtained, and the particle size is such that it can be stably dispersed in an aqueous dispersion of an aqueous resin, which improves the stability of the paint. Furthermore, since the minute resin itself becomes part of the film forming component, it does not adversely affect the performance of other coating films. Detailed Discussion Electrodepositable Aqueous Resins The present invention is applicable to both cationic and anionic electrodeposition coatings. Electrodepositable aqueous resins (base resins) are generally film-forming resins that have functional groups that provide the charge and hydrophilicity necessary for electrodeposition. They are classified into aqueous solution type, dispersion type, emulsion type, and suspension type, mainly depending on their form when dispersed in water, and they are collectively referred to herein as aqueous resin. Various types of water-based resins are known for use in electrodeposition paints, and any of these known water-based resins can be used in the present invention. The water-based resin used in anionic electrodeposition paints has anionic functional groups such as carboxyl groups in order to give the resin the negative charge and hydrophilicity necessary for electrodeposition. Typical such resins are maleated natural or synthetic drying oils, maleated polybutadiene, half esters, half amides thereof, and the like. The water-based resin used in cationic electrodeposition paints has cationic functional groups such as amino groups to give it positive charge and hydrophilicity. Various types of resins such as epoxy resins, polyether resins, polyester resins, polyurethane resins, polyamide resins, and polybutadiene resins are known as examples of such resins. Depending on the mechanism of the curing reaction, these resins can be classified into self-crosslinking types that are cured by themselves through radical polymerization or oxidative polymerization, and those that are cured with a curing agent such as melamine resin or blocked polyisocyanate compound. There are curing agent types that harden when used in combination, and types that use both in combination. Furthermore, according to the type of curing energy, it can be classified into types such as room temperature curing, heat curing, and radiant energy curing such as ultraviolet rays and electron beams. Furthermore, for the purpose of improving coating film performance, resins that do not have functionality that imparts charge and hydrophilicity, such as epoxy acrylate resins, are used in combination with the hydrophilic resins in the form of emulsions. In the present invention, a system in which such a curing agent is used in combination with a resin having no hydrophilic functional group is also referred to as an aqueous resin. Such electrodepositable aqueous resins are well known to those skilled in the art and do not require further explanation as such do not form part of the present invention. Micro resin particles Various methods have been proposed to produce micro resin particles, one of which involves suspension polymerization or emulsion polymerization of an ethylenically unsaturated monomer with a crosslinkable copolymer in an aqueous medium. This method creates a dispersion of fine resin particles, and then removes water by solvent replacement, azeotropy, centrifugation, drying, etc. to obtain fine resin particles.
Ethylenically unsaturated monomers and crosslinkable copolymers are co-coated in organic solvents or non-aqueous organic solvents that dissolve monomers but do not dissolve polymers, such as high SP organic solvents such as esters, ketones, and alcohols. Polymerize and disperse the resulting micro resin particle copolymer
This method is called the NAD method or precipitation method. The fine resin particles of the present invention may be produced by any of the above methods. Examples of ethylenically unsaturated monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)allylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Alkyl esters of acrylic acid or methacrylic acid and other monomers having ethylenically unsaturated bonds that can be copolymerized with them, such as styrene,
Examples include α-methylstyrene, vinyltoluene, t-butylstyrene, ethylene, propylene, vinyl acetate, vinyl propionate, acrylonitrile, methacrylonitrile, dimethylaminoethyl (meth)acrylate, and the like. Two or more types of these monomers may be used. The crosslinkable copolymerizable monomer is a monomer having two or more radically polymerizable ethylenically unsaturated bonds in the molecule and/or two types of ethylenically unsaturated monomers each carrying groups that can react with each other. Contains group-containing monomers. Examples of monomers having two or more radically polymerizable ethylenic unsaturations in the molecule include polymerizable unsaturated monocarboxylic acid esters of polyhydric alcohols, polymerizable unsaturated alcohol esters of polybasic acids, and monomers having two or more radically polymerizable ethylenic unsaturations in the molecule. There are aromatic compounds substituted with the above vinyl groups, examples of which include the following compounds. Ethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 1,4-butanediol dimethacrylate acrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate,
Pentaerythritol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol dimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, glycerol dimethacrylate,
Glycerol diacrylate, glycerol allyloxy dimethacrylate, 1,1,1-trishydroxymethylethane diacrylate, 1,1,
1-trishydroxymethylethane triacrylate, 1,1,1-trishydroxymethylethane dimethacrylate, 1,1,1-trishydroxymethylethane trimethacrylate, 1,1,
1-trishydroxymethylpropane diacrylate, 1,1,1-trishydroxymethylpropane triacrylate, 1,1,1-trishydroxymethylpropane dimethacrylate, 1,
1,1-trishydroxymethylpropane trimethacrylate, triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, diallyl terephthalate, diallyl phthalate and divinylbenzene. In addition, two groups each carrying a group that can react with each other
Examples of monomers having ethylenically unsaturated groups include epoxy group-containing ethylenically unsaturated monomers such as glycidyl acrylate and glycidyl methacrylate, and carboxyl group-containing ethylenically unsaturated monomers such as acrylic acid, methacrylic acid, and crotonic acid. Monomers are the most representative, but mutually reactive groups are not limited to these.
For example, various compounds have been proposed, such as amine and carbonyl, epoxide and carboxylic acid anhydride, amine and carboxylic acid chloride, alkyleneimine and carbonyl, organoalkoxysilane and carboxyl, hydroxyl and isocyanate, etc., and the present invention broadly encompasses these. It is something to do. The micro resin particles are composed of a monomer having two or more radically polymerizable ethylenically unsaturated bonds in the molecule and/or two types of ethylenically unsaturated group-containing monomers each carrying a group capable of reacting with each other. body 1
~100 parts by weight of monofunctional ethylenically unsaturated monomer
It is preferable to contain 99 to 0 parts by weight. Fine resin particles produced in an aqueous medium or a water-insoluble organic medium are isolated by methods such as filtration, spray drying, and freeze drying, and then directly processed.
Alternatively, it can be used by pulverizing it to an appropriate particle size using a mill or the like, and the synthesized dispersion can be used as it is or by replacing the medium with the solvent. The fine resin particles obtained by the above synthesis method generally have a particle size of 0.01 to 20μ. Generally, it is desirable to control the particle size of the particles obtained by the polymerization method. 0.01
For particles of ~0.6 μ, emulsion polymerization method and NAD method are
Precipitation polymerization is suitable for particles larger than 0.2. The refractive index (nDb) of the internally crosslinked microscopic resin particles must be in the range of 0.02≦|nDa−nDb|≦0.3 with respect to the refractive index (nDa) of the aqueous resin. If it exceeds this level, it will not have a sufficient erasing effect. The refractive index (nDa) of the aqueous resin was measured using an Abbe Refractometer (manufactured by ATAGO Corporation) after forming a film with a thickness of 30 to 50 μm using α-bromnaphthalene as a medium.
Measured at 20°C. The internally crosslinked microscopic resin (nDb) can be measured by actually measuring it as a film, but it can also be determined by calculation using the following formula. nDb=ΣC ₁ n ₁ , C ₂ n ₂ ...Cm nm However, C ₁ , C ₂ ...Cm are the weight fractions of each monomer constituting the micro resin particles (C ₁ +C ₂ +...Cm=1) Yes, n ₁ , n ₂ …nm is the individual polymer of each monomer.
It is the refractive index at 20℃. In order to maintain a stable dispersion state in the paint and the electrodeposition bath, the fine resin particles themselves preferably have ionizable groups having the same polarity as the aqueous resin that is the base resin. That is, in the case of anionic electrodeposition, it is preferable to support an anionic group such as a carboxyl group or a sulfonic acid group, and in the case of cationic electrodeposition, it is preferable to support a cationic group such as an amino group or a quaternary ammonium group. To achieve this, monomers having an ethylenically unsaturated bond and a carboxyl group, such as acrylic acid and methacrylic acid, and monomers having an ethylenically unsaturated bond and a basic group, such as dimethylaminoethyl (Meth)acrylates, vinylpyridines, etc. are added to the monomer mixture during the synthesis of minute resin particles, or the monomer mixture is polymerized using an initiator that provides a cationic end for the synthesis of minute resin particles. There is a way. If the polymer itself that makes up the micro resin particles is non-polar, use an appropriate emulsifier during synthesis of the micro resin particles, especially oligosoaps, polysoaps, or reactive emulsifiers that have amphoteric ionic groups to stably disperse the micro resin particles. You can also do so. These emulsifiers having zwitterionic groups were disclosed in Japanese Patent Application Laid-Open No.
56-24461, 57-21927, 57-40522, etc. The fine resin particles are obtained by polymerizing the above-mentioned monofunctional ethylenically unsaturated monomer and crosslinkable monomer by solution polymerization or bulk polymerization, crushing the resulting polymer, and then classifying it to a predetermined particle size. You can also get it. As another method, in the case of fine resin particles such as epoxy resin, melamine resin, alkyd resin, etc., a liquid resin is emulsified and dispersed in water, and the emulsified resin dispersion is spray-dried to obtain a fine resin having a predetermined particle size. Alternatively, if the resin is solid, it can be pulverized and classified to form a fine resin with a predetermined particle size. Electrodeposition Coating Composition The electrodeposition coating composition of the present invention contains the electrodepositable aqueous resin and the fine resin particles as essential components. The ratio of aqueous resin and fine resin particles is 1 to 50% by weight of the former as solid content.
It is. If the amount of fine resin particles added is too small, there will be no effect, and if it is too large, the stability of the paint and the workability of electrodeposition will be impaired. Depending on the type of aqueous resin used, auxiliary curing agents such as melamine resin, benzoguanamine resin, phenol resin, and blocked polyisocyanates, and metal compounds such as manganese, cobalt, copper, lead, and tin may be included as catalysts. can. These components are dispersed in an aqueous medium containing a base for anionic electrodeposition and an acid for cationic electrodeposition. These acids and bases are used to neutralize the electrodepositable water-soluble resin. Examples of the base used for neutralization include ammonia, diethanolamine, triethanolamine, methylethanolamine, diethylamine,
Examples include morpholine and potassium hydroxide. As the acid, phosphoric acid, acetic acid, propionic acid, lactic acid, etc. are used. The aqueous medium is water or a mixture of water and a water-miscible organic solvent. If necessary, the aqueous medium may contain a water-immiscible organic solvent. Examples of water-miscible organic solvents include ethyl cellosolve, propyl cellosolve, butyl cellosolve, ethylene glycol dimethyl ether, diacetone alcohol, 4-
Examples include methoxy-4-methylpentanone-2 and methyl ethyl ketone. Examples of water-immiscible organic solvents include xylene, toluene, methyl isobutyl ketone, and 2-ethylhexanol. The coating composition of the present invention has a non-volatile content of the coating of 10 to 10%.
Adjust to about 20%, electrodeposit to a dry film thickness of 15 to 30μ,
Depending on the type of resin, it can be cured by room temperature curing, heat curing, ultraviolet curing, electron beam curing, etc. Production examples, examples and comparative examples of the present invention are shown below. Parts and percentages in these examples are by weight. Production Example 1 Production of Anionic Fine Resin Particles 216 parts of deionized water was charged into a reaction vessel equipped with a stirrer, and while stirring and maintaining the temperature at 80°C, 4.5 parts of azobiscyanovaleric acid, 4.9 parts of triethylamine and deionized water were added. A mixed solution consisting of 45 parts of ionized water was added. Then, at the same temperature, N-dodecyl-N-
6 parts of vinylbenzyl taurine, triethylamine
A first mixed solution consisting of 2.4 parts and 90 parts of deionized water and a second mixed solution consisting of 156 parts of methyl methacrylate, 135 parts of n-butyl acrylate, and 3 parts of ethylene glycol methacrylate were simultaneously dropped over 60 minutes each. did. After dripping,
Furthermore, at the same temperature, a mixed solution consisting of 1.5 parts of azobiscyanovaleric acid, 1.6 parts of triethylamine, and 15 parts of deionized water was added, and stirring was continued for 60 minutes, resulting in a non-volatile content of 45%, a pH of 7.8, a viscosity (25°C) of 108 cps, An emulsion with a particle size of 132 nm was obtained. Refractive index: 1.479 Production Example 2 Production of fine resin particles 426 parts of deionized water was placed in a flask equipped with a stirrer and a thermometer, and the temperature was heated to 80°C. An aqueous solution consisting of 1 part of ammonium persulfate and 20 parts of deionized water was added dropwise under a nitrogen stream. In addition, 5 parts of styrene,
After adding a monomer mixture consisting of 4.5 parts of n-butyl acrylate and 0.5 parts of neopentyl glycol dimethacrylate and reacting for 10 minutes, an aqueous solution consisting of 1 part of ammonium persulfate and 20 parts of deionized water and 10 parts of methyl methacrylate, n - A monomer mixture consisting of 10 parts of butyl methacrylate, 60 parts of styrene, and 10 parts of ethylene glycol dimethacrylate was added dropwise over 60 minutes. The reaction was further kept at 80° C. for 2 hours to complete the reaction. The resulting emulsion had a particle size of 208 nm.
This emulsion was dried by spray drying to obtain fine resin particles with an average size of 5 μm. Refractive index 1.547 Production example 3 Nisseki Polybutadiene B-1500 (*1) 1000g Antigen 6C (*2) 10g Maleic anhydride 250g Deionized water 20g Diethylamine 0.5g Propylene glycol 100g Ethyl cellosolve 340g (*1) Nippon Petrochemical Co., Ltd. ) Made: Mn1500, vinyl
65%, trans 14%, cis 16% (*2) Manufactured by Sumitomo Chemical Co., Ltd.: N-methyl-N'-1,
3-dimethylbutyl), p-phenylenediamine Charge 1000 g of Nisseki Polybutadiene B-1500 into a 2-kolben equipped with a cooling tube, and add 10 g of Antigen 6C and 250 g of maleic anhydride. While stirring,
The addition reaction of maleic acid to polybutadiene is carried out while maintaining the internal temperature at 190 to 200°C. Approximately 5 hours after the temperature was raised, it was confirmed that the reaction was completed by a dimethylaniline color reaction. After that, the internal temperature is cooled to 100℃,
A mixture of 20 g deionized water and 0.5 g diethylamine is added dropwise over about 30 minutes. Further, stirring was continued for about 1 hour after the completion of the dropwise addition, and the acid value was confirmed to be 140.
Then add 100g of propylene glycol and heat to 110℃.
The mixture was reacted for 3 hours and the total acid value was confirmed to be 125. Then add 340g of ethyl cellosolve and add 80g of ethyl cellosolve.
After stirring at °C for about 1 hour, the synthesis was completed. Non-volatile content 80% Production example 4 Epotote YD-014 (*3) 950g Ethyl cellosolve 240g Hydroquinone 10g Acrylic acid 65g Dimethylbenzylamine 5g (*3) Manufactured by Tobu Kasei Co., Ltd., epoxy resin, epoxy equivalent 950 2 Kolben with cooling tube Epotote YD−014
Add 950g and 240g of ethyl cellosolve and gradually
Uniformly dissolve YD-014 while stirring to 120℃. Then add 10 g of hydroquinone, and further add 65 g of acrylic acid and 5 g of dimethylbenzylamine. After reacting at 120°C for 4 hours, it was confirmed that the post-acid value was 1 or less. Non-volatile content 80% Example 1 125g of varnish from Production Example 3, 75g of varnish from Production Example 4
g, butylated melamine (50% non-volatile content), 40 g of resol type phenolic resin (50% non-volatile content) were collected, 2 g of nonionic surfactant and 3 g of cobalt naphthenate were added thereto, stirred uniformly, and 13 g of triethylamine was collected. and then deionized water 707
47g of the fine resin particle dispersion of Production Example 1 was added, and the solid content concentration was approximately 20% (the solid content of fine resin particles in the paint was approximately 20%).
%) paint bath was prepared. Refractive index of matrix resin nDa = 1.41 Refractive index of minute resin particles nDb = 1.479 |△nD | = 0.069 A double steel plate treated with zinc phosphate is immersed in a paint bath, and the object to be coated is used as an anode at 150V for 3 minutes. Electrodeposition painted. Thereafter, the surface of the object to be coated was washed with water and baked in a baking oven at 140°C for 30 minutes to obtain a coated plate with a film thickness of about 20μ. Table 1 shows the results of testing the performance of the obtained coating film. Production example 5 Nisseki polybutadiene B-2000 (number average molecular weight
2000, 1, 2 bonds (65%) was epoxidized using peracetic acid to produce epoxidized polybutadiene with an oxirane oxygen content of 6.4%. After charging 1000 g of this epoxidized polybutadiene and 354 g of ethyl cellosolve into two autoclaves, 62.1 g of dimethylamine was added, and the mixture was heated to 150°C.
The reaction was carried out for 5 hours. After distilling off the unreacted amine, it was cooled to 120°C, a mixture of 79.3g of acrylic acid, 7.6g of hydroquinone and 26.4g of ethyl cellosolve was added, and the reaction was further carried out at 120°C for 3 hours and 45 minutes to obtain the resin solution (A). Manufactured. This amine value is
85.2 mmol/100g, acid value 100 mmol/100
g, and the solid content concentration was 75.0% by weight. Production Example 6 1000 g of bisphenol type epoxy resin with an epoxy equivalent of 950 [trade name Epicote 1004, manufactured by Yuka Ciel Epoxy Co., Ltd.] was mixed with ethyl cellosolve 343.
Dissolved in g, 76.3 g of acrylic acid, hydroquinone
Add 10g and 5g of N,N-dimethylaminoethanol, heat to 100°C and react for 5 hours,
A resin solution (B) was synthesized. Solid content concentration 75% Production example 7 Nisseki polybutadiene B-1000 (number average molecular weight
1000, 1, 2 bonds 60%) 1000g, maleic anhydride
265.8 g, xylene 10 g, and Antigen 6C (Sumitomo Chemical brand name) 1 g were placed in two separable flasks equipped with a reflux condenser and heated at 190°C under a nitrogen stream for 50 minutes.
Allowed time to react. Next, unreacted maleic anhydride and xylene were distilled off under reduced pressure, and the acid value was 214 mmol/100.
g maleated polybutadiene was synthesized. Next, 1000 g of maleated polybutadiene and 212.4 g of ethyl cellosolve were charged into a two-separable flask equipped with a reflux condenser and reacted with stirring at 120°C for 2 hours to produce a half-esterified product (C) of maleated polybutadiene. Solid content concentration 98% Example 2 400 g of (A) produced in Production Example 5, 240 g of (B) produced in Production Example 6, and 19.2 g of (C) produced in Production Example 7
were mixed until homogeneous. Refractive index of varnish nDa = 1.43 8.1 g of acetic acid was added and thoroughly stirred to neutralize. After adding 200 g of the fine resin particles of Production Example 2 to this varnish and uniformly dispersing it with a disper, 1835 g of deionized water was gradually added to obtain an emulsion with a solid content concentration of about 20%. Next, deionized water was gradually added to prepare an aqueous solution having a solid content of 20% (the solid content of the fine resin particles in the paint bath was about 3%). Cathode deposition type electrodeposition coating was carried out using the above electrodeposition coating solution at 100V for 3 minutes using the carbon electrode as the anode and the zinc phosphate treated plate as the cathode. Baking at 175℃ x 30 minutes.
The test results are shown in Table-1. Comparative Example 1 The same procedure as in Example 1 was carried out except that 47 g of the fine resin particles of Production Example 1 were not added.
(Coating voltage: 100 V) Comparative Example 2 The same procedure as in Example 2 was carried out except that 200 g of the fine resin particles of Production Example 2 were not added.
(Painting voltage 80V)

【table】

【table】

Claims (1)

[Scope of Claims] 1. A difference in refractive index between (a) an aqueous dispersion of an aqueous resin capable of electrodeposition, and (b) an aqueous resin that is uniformly dispersed in the aqueous dispersion of the aqueous resin. is 0.02~
1. An erasable electrodeposition paint composition comprising as an essential component internally crosslinked fine resin particles having a molecular weight of 0.3. 2. The erasable electrodeposition coating composition according to item 1, wherein the aqueous dispersion of the electrodepositable aqueous resin is an emulsion. 3 The aqueous resin has a cationic group.
3. The erasable electrodeposition coating composition according to item 1 or 2. 4 The aqueous resin has a first aqueous resin having an anionic group.
3. The erasable electrodeposition coating composition according to item 1 or 2. 5 Items 1 to 4, wherein the amount of the fine resin particles is 1 to 50% by weight of the solid content of the aqueous resin.
3. The erasable electrodeposition paint composition according to any one of the above items.