JPH02390B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a thermosetting water-based coating composition with good scuff resistance. In recent years, the demand for water-based paints has rapidly increased from the viewpoints of work safety, non-pollution, and resource conservation issues. In particular, there has been a remarkable move toward water-based thermosetting paints in industrial painting lines, such as those for automobiles. However, in thermosetting water-based paints, the main component of the medium is water, and due to the low boiling point of this water, paint film defects (hereinafter referred to as "flanks") occur due to foaming during heat curing. It becomes more noticeable when the film thickness is around 30 to 40μ compared to current solvent-based paints. However, the standard film thickness for intermediate and top coats in car body painting is generally 30 to 40 microns, and a film thickness of 50 microns is applied to some parts of the body. For this reason, there has been a problem in that paint film defects may occur partially or entirely on the automobile body due to the armpits. However, this problem is
This can be improved by adding a large amount of a high-boiling point organic solvent, but this will impair the safety (non-hazardous material), which is the most important feature of water-based paints, so other solutions are needed. It was getting worse. Therefore, the present inventors conducted intensive research to improve the above-mentioned problems, and found that by adding a small amount of benzoin derivative without using the above-mentioned high boiling point organic solvent, the generation of underarms was suppressed, and the underarm film thickness was The present invention has been completed based on the discovery that it is possible to further improve the performance. Thus, according to the present invention, an alkyl etherified product of benzoin having 1 to 4 carbon atoms (hereinafter sometimes abbreviated as "benzoin derivative") is added to the resin solid content (weight) in a thermosetting water-based coating composition. of
There is provided a thermosetting water-based coating composition with good scuff resistance, characterized in that it is blended in an amount of 0.1 to 10% by weight, preferably 1 to 5% by weight. The water-based resin used in the thermosetting water-based coating composition in the present invention has an acid value of 20 to 100 and a hydroxyl value of 20.
200-200. Representative examples of the aqueous resin include the following. (1) Carboxyl group-containing polymerizable unsaturated monomers such as (meth)acrylic acid, maleic acid, fumaric acid, itaconic acid, hydroxyalkyl (meth)acrylates (the number of carbon atoms in the alkyl group is 2 to 4,
For example, hydroxyl group-containing polymerizable unsaturated monomers such as (meth)acrylic acid (2-hydroxyethyl, -2-hydroxypropyl, -2-hydroxybutyl, etc.) and other polymerizable unsaturated monomers that can be copolymerized with these. Preferably a number average molecular weight of 5,000 to 40,000 obtained by copolymerizing with a saturated monomer
acrylic resin or vinyl resin. (2) Ethylene glycol, diethylene glycol, propylene glycol, butanediol,
Polyhydric alcohols such as pentanediol, 2,2-dimethylpropanediol, glycerin, trimethylolpropane, pentaerythritol, and monohydric alcohols used in combination as necessary, or monoepoxy compounds having one glycidyl group in the molecule (e.g. , Karjiura E
(Product name, manufactured by Ciel Chemical Co., Ltd.)" as an alcohol component, phthalic anhydride, isophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, maleic anhydride, succinic anhydride, adipic acid, sebacic acid, trimerizanhydride. An oil obtained by condensing the above alcohol component and the above acid component with a polybasic acid such as acid, pyromellitic anhydride, and a monobasic acid such as benzoic acid or t-butylbenzoic acid used in combination as necessary. Free alkyd resin, or in addition to the above alcohol component and the above acid component, castor oil, dehydrated castor oil, tung oil, safflower oil, soybean oil, linseed oil, tall oil, coconut oil, etc., and one type of fatty acid thereof. Or an oil-modified alkyd resin obtained by adding an oil component which is a mixture of two or more types to the above acid component and an alcohol component and reacting the three components, and preferably has a number average molecular weight of 500 to 10,000. . (3) A graft copolymer obtained by grafting an acrylic resin or a vinyl resin onto an alkyl resin, preferably having a number average molecular weight of 5,000 to 20,000, for example, an alkyd resin having a polymerizable unsaturated group, a vinyl monomer and/or Or a graft copolymer obtained by reacting acrylic monomers. (4) Other phenolic resins and epoxy resins with an acid value of 20 to 100 and a hydroxyl value of 20 to 200. etc. can also be used. When the acid value of these hydroxyl group-containing polycarboxylic acid resins is less than 20, water solubility is insufficient, and when the hydroxyl value is less than 20, the curing of the coating film is insufficient. If it exceeds 200, the water resistance and chemical resistance of the coating film decreases, which is not preferable. A basic substance is added to these hydroxyl group-containing polycarboxylic acid resins to neutralize 50% or more of the carboxyl groups and make them water-soluble. Examples of basic substances used here include ammonia, methylamine,
Examples include ethylamine, dimethylamine, diethylamine, trimethylamine, triethylamine, dimethylethanolamine, diethanolamine, and triethanolamine. In the present invention, the water-soluble amino resin used as the crosslinking agent for the water-based resin described above has various structures, such as di-, tri-,
Examples include tetra-, penta-, and hexa-methylolmelamine, methyl etherified products thereof, urea-formaldehyde condensates, and urea-melamine cocondensates. In the present invention, the water-soluble amino resin is added in an amount of 5 to 70 parts by weight per 100 parts by weight of the hydroxyl group-containing polycarboxylic acid resin. If the proportion of the water-soluble amino resin deviates from this range, water resistance, chemical resistance, solvent resistance, etc. will decrease. Examples of benzoin derivatives that are added to the aqueous coating composition of the present invention and have the effect of suppressing the formation of wrinkles during heat curing of the coating film and increasing the critical thickness of the coating film include benzoin methyl ether, benzoin ethyl ether, and benzoin n- propyl ether,
Examples include benzoin iso-propyl ether, benzoin n-butyl ether, and benzoin iso-butyl ether. These benzoin derivatives can be used alone or in combination of two or more, and if the amount added is less than 0.1% by weight based on the solid content (weight) of the aqueous resin, the effect will not be recognized.
On the other hand, when the amount is more than 10% by weight, no further improvement in the armpit improving effect is observed and the gloss of the painted surface is reduced. Furthermore, if the alkyl ether compound of benzoin has 5 or more carbon atoms in the alkyl group, no armpit improvement effect will be observed. The method of adding the benzoin derivative to the aqueous coating composition is (1) adding it at the time of pigment dispersion. (2) Add to the base aqueous resin solution at room temperature or under heating and stir and mix. (3) There are methods such as adding it during the synthesis of water-based resin, and there is no effect on the underarm improvement effect using either method of addition, but in general, the pigment content in the paint and the melting point of the benzoin derivative are taken into consideration. It is determined. The aqueous coating composition of the present invention can be used in any form, either as a clear coating or as a pigment-containing coating. When blending pigments, the amount added is within the range of 300 PHR or less. It is also possible to use a solvent, for example alcoholic solvents such as methyl alcohol, ethyl alcohol, isopropyl alcohol, butyl alcohol; ethers such as methyl cellosolve, cellosolve, butyl cellosolve, methyl carbitol, carbitol, butyl carbitol. Solvents that are freely miscible with water are used, such as alcohol solvents; ester solvents such as methyl cellosolve acetate and cellosolve acetate; ketone solvents such as acetone. These solvents can be used in an amount of 20% by weight or less based on the solid content (weight) of the aqueous resin. The aqueous coating composition thus obtained is used after being diluted with water to a viscosity suitable for coating, if necessary. Further, the coating composition may appropriately contain commonly used coating film surface conditioners such as ultraviolet absorbers and anti-repellent agents, if necessary. The aqueous coating composition can be applied in accordance with conventional methods, such as air spray coating, electrostatic air spray coating, electrostatic airless coating, and curtain flow coater. Baking is done in accordance with conventional methods, such as using an electric hot air dryer, indirect hot air oven, direct hot air oven, far infrared oven, etc.
This can be carried out by maintaining the temperature between 120° C. and about 180° C. for about 15 minutes to about 45 minutes. The coating film obtained by heating and drying the aqueous coating composition of the present invention does not cause any wrinkles up to a dry film thickness of about 40 to 60 μm, and does not impair other coating properties, so it can be used for automobile bodies and other applications. It is extremely suitable for painting metal moldings. Hereinafter, the present invention will be explained in more detail with reference to Examples. In the examples, "parts" and "%" indicate "parts by weight" and "% by weight" unless otherwise specified. Production Example 1 Preparation of water-soluble alkyd resin Neopentyl glycol 31 parts Trimethylolpropane 7 Phthalic anhydride 24 Tetrahydrophthalic anhydride 17 Trimellitic anhydride 5 Tall oil fatty acid 15 were added to a reaction vessel and reacted at 200 to 230°C for 5 hours. After that, 8 parts of phthalic anhydride was added and further reacted at 130℃ for 1 hour to obtain a molecular weight of 5600, an acid value of 45, and a hydroxyl value.
32 alkyd resins were obtained. 10 parts of methyl carbitol and 6.7 parts of diethanolamine were added to 100 parts of the alkyd resin to neutralize all carboxyl groups in the resin. Production Example 2 Preparation of water-soluble acrylic resin Styrene 30 parts n-butyl acrylate 38 2-hydroxyethyl methacrylate 25 acrylic acid 7 azobisisobutyronitrile 3 20 parts of butyl cellosolve heated to 120°C in a reaction vessel was added dropwise and polymerized for 7 hours.
Acrylic resin D (83% butyl cellosolve solution) having an acid value of 54, a hydroxyl value of 107, and a molecular weight of 20,000 was obtained. To 120 parts of this solution, 9.8 parts of dimethylaminoethanol was added to neutralize all the carboxyl groups in the resin, and 22 parts of water was added to obtain an aqueous solution with a solid content of 66%. Production Example 3 Preparation of water-dispersed acrylic resin 68.0 parts of deionization, 0.2 parts of ammonium persulfate, and 1.5 parts of Triton X-200 ⁽¹⁾ were added to a reaction vessel.
Heat to 95°C. Separately, the following monomer composition Styrene 30.0 parts Butyl methacrylate 50.0 Hydroxypropyl methacrylate 18.0 Acrylic acid 2.0 ⁿ -octyl mercaptan 0.6 Ammonium persulfate 0.4 Triton Surfactant (2) Manufactured by Kao Atlas A nonionic surfactant is mixed to form an aqueous emulsion of acrylic monomer. Then, this aqueous emulsion was added dropwise to the solution heated to 95° C. over a period of 3 hours. Meanwhile, the temperature is maintained at 95°C. After the monomer addition is complete, the reaction mixture is held at 95° C. for about 2 hours under stirring, then allowed to cool to 35° C. and 0.5 parts dimethylethanolamine and 4 parts deionized water are added. A stable milky white dispersion with a solids content of 45% was thus obtained. Example 1 22.5 parts of the 66% water-soluble alkyd resin obtained in Production Example 1, 80 parts of Rutile Titanium White ⁽³⁾ , 20 parts of Baryta #100 ⁽⁴⁾ , 0.4 parts of Carbon Black ⁽⁵⁾ , and Nobuko were placed in a Pebble Mill.
A pigment dispersion paste was obtained by dispersing 1.5 parts of DF122NS ⁽⁶⁾ and 30 parts of deionized water for 20 hours. Then, benzoin methyl ether, benzoin ethyl ether, benzoin n-propyl ether, benzoin iso-propyl ether, benzoin n-butyl ether and benzoin iso-
Six types of benzoin derivatives of butyl ether were individually stirred and mixed with the water-soluble alkyd resin of Production Example 1 at a ratio of 2% based on the resin solid content in the paint to prepare six types of resin solutions. Next, 100 parts of the water-soluble alkyd resin solution obtained in Production Example 1 and 88% water-soluble melamine resin (CY-370,
Mitsui Toatsu) 22.4 parts, ethyl carbitol 10
1.0 parts of anti-cissing agent and 50 parts of deionized water were added and mixed with stirring using a disper to obtain six types of thermosetting water-based coating compositions. The coating composition thus obtained was diluted with deionized water in a food cup No. 4 (20°C) for 20 seconds, and coated under the following coating conditions to measure the critical underarm film thickness. The results are shown in Table 1. [Paint conditions] Object to be coated: 0.8mm steel plate pre-coated with solvent-based paint Spray gun: Iwata W-71 Kapgun (manufactured by Iwata Painting Co., Ltd.) Coating method: Thickness gradient coating Booth conditions: 25℃, 70~ 75%RH Baking conditions: Set in the booth for 10 minutes after painting, then bake at 160℃ for 20 minutes Note (3) Manufactured by Teikoku Kako Co., Ltd., product name: R-602 (4) Extender pigment, manufactured by Sakai Chemical Co., Ltd. (5) Manufactured by Mitsubishi Kasei Corporation, product name: Mitsubishi Carbon Black M-100 (6) Antifoaming agent manufactured by Sannopco Example 2 30 parts of the 66% water-soluble acrylic resin obtained in Production Example 2 in a peplum mill, rutile type titanium white ⁽³⁾ 100 parts, butyl carbitol 10 parts, Nopco DF-122NS ⁽⁶⁾ 1.5 parts,
A pigment dispersion paste was prepared by dispersing 40 parts of deionized water and benzoin ethyl ether at a ratio of 2% based on the resin solid content in the resulting paint for 20 hours. Next, 66 obtained in Production Example 1 was added to the above dispersion paste.
% water-soluble alkyd resin 37.9 parts, 45 obtained in Production Example 3
% water-dispersed acrylic resin, 25 parts of 100% water-dispersed melamine resin, 0.1 part of anti-cissing agent, and 30 parts of deionized water were added and mixed with stirring using a disk bar to obtain a thermosetting water-based coating composition. Example 1 of this paint
It was diluted and painted in the same manner as above, and the critical underarm film thickness was measured. The results are shown in Table 2. Example 3 In Example 1, the blending amount of benzoin ethyl ether was 0.2% and 0.5%, respectively, based on the resin solid content.
3 in the same manner as in Example 1 except that it was changed to % and 5%.
Various types of thermosetting water-based paint compositions were prepared and the critical underarm film thickness was measured. The results are shown in Table 3. Comparative Example 1 A paint was prepared in exactly the same manner as in Example 1 except that the benzoin ether compound was not blended, and the coating was applied to measure the critical underarm film thickness. The results are shown in Table 1. Comparative Example 2 A paint was prepared in exactly the same manner as in Example 2 except that the benzoin ethyl ether compound was not blended, and the coating was applied to measure the critical underarm film thickness. The results are shown in Table 2.

【table】

【table】

[Table] Measurement of underarm film thickness.
When baking and drying is then carried out, wrinkles occur from the thickest parts to the thinnest parts, but the film thickness of the parts where there are no coating surface abnormalities caused by these wrinkles is measured using an electromagnetic micro-thickness meter.

Claims (1)

[Claims] 1 The carbon content of benzoin is calculated based on the resin solid content (weight) in a thermosetting water-based coating composition containing a hydroxyl group-containing polycarboxylic acid resin and an amino resin as binder components having an acid value of 20 to 100 and a hydroxyl value of 20 to 200. 0.1 to 10% by weight of alkyl ether compounds of numbers 1 to 4
A thermosetting water-based paint composition with good underarm resistance.