JPS5928231B2 - Thermosetting high solids paint - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermosetting high solids coating composition that can be spray coated at a coating temperature of about 70° C. or less.

Recently, due to serious air pollution and global resource shortages, countermeasures have been required in the paint industry as well. Increasing the concentration of paint is an extremely effective means of solving these two problems at the same time.

This is because increasing the concentration of paint significantly reduces the amount of solvent (organic solvent, hereinafter referred to as organic solvent) that evaporates into the atmosphere during the coating film formation process, and at the same time reduces the amount of solvent that does not become a component of the final coating film. Since the amount used is extremely small, it also greatly contributes to resource conservation of paint. As a result of repeated research aimed at increasing the concentration of paint, the present inventors have found that by applying a paint composition as described in the claims above, the performance of currently used thermosetting paints can be improved to some extent. It has been found that the amount of solvent used can be reduced by about 1/2 to 1/7 without any loss in performance.

In other words, when spray painting currently used thermosetting paints, a solvent is added to 100 parts by weight of vehicle solids in the paint in order to achieve a viscosity of 100 to 50 centistokes, which is suitable for spray painting at the painting temperature. 1
Whereas it is necessary to use 50 parts by weight or more, in the composition of the present invention, it is 80 to 20 parts by weight, making it possible to reduce the amount of solvent used to about 1/2 to 1/7. It is.

Furthermore, by using the coating composition of the present invention, it is possible to reduce the amount of solvent used in the so-called painting and setting process, which is the process of forming a coating film and before the coating is applied and the object to be coated is placed in a baking oven. It has the effect of extremely reducing the amount of volatilization.
This means that the exhaust air volume is large, and volatile solvents are incinerated, adsorbed, and
Since the amount of solvent can be drastically reduced in processes that are difficult to treat by absorption methods, etc., this together with the reduction in the absolute amount of solvent makes the effects of the present invention even greater. Furthermore, since the composition of the present invention has good thermal stability, it is easy to apply hot solenoid, which is known as an extremely effective means for applying paints at high concentrations. One possible way to increase the concentration of a paint is to lower the molecular weight of the resin component in the vehicle used, but it is true that it is possible to achieve a high concentration of a paint by simply lowering the molecular weight alone. However, it lacks curing properties, and it is not possible to obtain a thermosetting paint that exhibits sufficient performance.

As a result of intensive research on increasing the concentration of paint, the present inventors found that the number average molecular weight of conventionally used acrylic resins is 150,000 to 150,000, whereas the number average molecular weight of conventionally used acrylic resins is 10,000 to 50,000.
By having a fairly low molecular weight of 0 to 6,000 and introducing about twice as many functional hydroxyl groups into the resin as compared to conventional ones, it is possible to obtain a resin with curability comparable to conventional ones. I found out. That is, the present invention provides a compound represented by (a) (i) general formula (R1 represents H or a C1-2 alkyl group, R2 represents H or CH3) 20 to 35% by weight (b) acrylic acid or Methacrylic acid 4% by weight or less (to) Carbon number of methacrylic acid is 1
One or more types selected from ~4 alkyl esters, cyclohexyl esters of acrylic acid or methacrylic acid, styrene, α-methylstyrene, and alkylated styrene substituted with an alkyl group having 1 to 4 carbon atoms. Compound 20-55% by weight and (d) C1-18 alkyl ester of acrylic acid, C5-18 alkyl ester of methacrylic acid, general formula (R3 is a C1-17 alkyl group, R4 is H or CH
3) and the compound represented by the general formula (R3 and R4 are the same as above, R5 is H or C1-
2 alkyl group, R6 or [ 1! 15 to 6 of one or more selected from the compounds represented by
Acrylic copolymer 6 with a number average molecular weight of 1500 to 6000 obtained by copolymerizing 0% by weight in the presence of a polymerization initiator
5 to 20% by weight (b) A melamine resin whose main component is hexakizalkoxymethylmelamine, in which in the chemical formula below, an average of 2 to 6 R's are alkyl groups having 2 to 4 carbon atoms, and the remainder are methyl groups. 20-40% by weight) Compounds 15-15 with a molecular weight of 250-1000 that simultaneously contain one or more double bonds and one or more primary or secondary hydroxyl groups in one molecule
If additionally required for 60% by weight, 1) carbon number 1 in which bound formaldehyde is 5.5 mol or less per 1 mol of melamine;
The alcohol-denatured melamine resin of ~4 above (b
1/2% by weight or less of the above components (a) and (b).
0.05 to 1.00 parts by weight of (e) aliphatic or aromatic sulfonic acid or its amine salt per 100 parts by weight of the mixture obtained by adding component (c) and component (d), and ( f) A coating material containing 80 to 20 parts by weight of an organic solvent capable of simultaneously dissolving each of the above components at a temperature of about 7.
The present invention relates to a thermosetting high solids coating composition that can be spray coated at temperatures below 0°C.

Component (a) of the acrylic copolymer (5) in the present invention includes, for example, 2-hydroxyethyl acrylate:
Examples include 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl acrylate, and 2-hydroxybutyl methacrylate.

Examples of H→components include methyl, ethyl, i-propyl, n-propyl, n-butyl, i-butyl, t-butyl, and cyclohexyl methacrylate; cyclohexyl acrylate; styrene; α-methylstyrene; butylstyrene ; Vinyltoluene, etc.

(d) Components include amyl, hexyl, 2-ethylhexyl, and lauryl esters of acrylic acid or methacrylic acid; methyl, ethyl, i-propyl, n-propyl, n-butyl, i-butyl, and t-butyl esters of acrylic acid. ; Furthermore, an adduct of glycidyl acrylate or glycidyl methacrylate and a fatty acid having 2 to 18 carbon atoms; an adduct of methacrylic acid or acrylic acid and a glycidyl ester having an aliphatic chain having 2 to 18 carbon atoms; component α a) above; Addition of a glycidyl ester containing an aliphatic side chain having 2 to 18 carbon atoms to a half-esterified product of a compound and a dicarboxylic anhydride such as phthalic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, or succinic anhydride. Things can be given.

Acrylic copolymers comprising such components can be produced by methods such as solution polymerization, cloud polymerization, and bulk polymerization in the same manner as conventional methods for producing acrylic resins, but solution polymerization is most advantageous. Acrylic copolymers having a number average molecular weight of 1,500 or less require the use of an extremely large amount of initiator or the reaction at an extremely low concentration, making them impractical from an economic standpoint.

On the other hand, if it is 6,000 or more, the viscosity is too high even if the monomer composition is capable of imparting appropriate hardness and flexibility to the coating film, and the object of the present invention cannot be achieved. In addition, in order to maintain the hardness and flexibility of the cured coating film at a sufficiently practical level, the hard monomer components and soft monomer components in the acrylic copolymer composition should be It is necessary to adjust the body (c) component to within the above range.

That is, if the amount of carbon is too large, the viscosity of the copolymer will be high, and the coating film obtained will be brittle and have poor flexibility. If the amount of component (d) is too large, the resulting coating film will be too soft and the surface will remain sticky. The melamine resin (component (b)) which is a curing agent is a melamine resin modified with mixed alcohol.
It can be easily synthesized by ether exchange with an alcohol having 2 to 4 carbon atoms.

This material has a significantly lower viscosity than ordinary melamine resins, and is preferred for increasing the concentration of paints. On the other hand, the conventionally well-known hexakizmethoxymethyl melamine has a large cohesive force when combined with the above-mentioned acrylic copolymer, and it is difficult to use because it tends to cause coating defects such as repellent dents on the coated surface. However (
It has been found that by substituting the = part of the methoxy group with an alcohol having 2 to 4 carbon atoms as in component b), this drawback can be compensated for and the viscosity can be reduced. However, this melamine resin (component (b)) has low reactivity and requires a curing catalyst, and the conventional alkyd resins have poor stability when heated, and paints cannot be used at high concentrations. Although hot spray, which is an effective method for spray painting, cannot be applied, by using it in combination with an acrylic copolymer such as the one of the present invention, stability during heating can be improved, and curability can be improved. In order to improve the results, even when a conventionally used melamine resin (component (d) above) is used within the scope of the present invention, sufficient hot spraying can be achieved at a temperature of 70'C or less. Examples of reactive diluents that can be used as component (c) include glycidyl acrylate or glycidyl methacrylate and aliphatic or aromatic mono- or dicarboxylic acids or anhydrides thereof (for example, fatty acids having 12 to 18 carbon atoms, p-t- butylbenzoic acid, phthalic acid and its anhydrides, tetrahydrophthalic acid and its anhydrides, etc.); mono- or Diepoxide compound (
For example, Cardilla E1 Epicote 828, 1001 (
(all are product names manufactured by ShellChem), phenyl glycidyl ether, diglycidyl phthalate, glycidyl isononaate, etc.), monoesterified products with glycol, or trivalent or higher polyvalent products such as trimethylolpropane, glycerin, etc. Mono- or diesterified products with alcohols; monoesters and monoesters of compounds represented by the general formula (R1: H or C1-2 alkyl group R2: H or CH3) and aliphatic or aromatic dicarboxylic acids or their anhydrides; or adducts with diepoxide compounds, monoesters with glycols, or mono- or diesterified products with trihydric or higher polyhydric alcohols such as trimethylolpropane; glycol monoallyl ether; mono- or diallyl ether of polyoxymethylene glycol, acrylic acid Or methacrylic acid esters, etc., which have an average of one or more hydroxyl groups in one molecule,
Molecular weight 250-1000 containing one or more unsaturated bonds
It can be used as Seishu c) if it is a compound of Those reacted in a molar or less quantity can also be used.

These reduce the viscosity of the paint without reducing the non-volatile content. Furthermore, the melamine resin which is the component (d) used in the present invention includes most of the melamine resins that have been used conventionally, and although this is not always necessary, especially when it is desired to lower the baking temperature. It is an effective means, and the above-mentioned effects will not be impaired if the amount used is within the scope of the present invention.

As the curing catalyst (component αe above), sulfonic acids such as alkylsulfonic acids having 2 to 18 carbon atoms, alkylbenzenesulfonic acids having 1 to 18 carbon atoms, benzenesulfonic acids, and organic amine salts thereof are used. However, sulfonic acids, which are particularly strong acids, are particularly effective.

The appropriate amount of component (e) to be used is 0.05 to 1.00 parts by weight per 100 parts by weight of the mixture consisting of the above (a), (b), (c) and, if necessary, component (d). be. That is 0
．． If the amount is less than 0.5 parts, the curing properties will be poor, and if it is more than 1.00 parts, the heating stability will be poor, making it difficult to apply hot spray. The solvent (component (f)) is not particularly limited as long as it can simultaneously dissolve each component used in the present invention, and is no different from those used in conventional American paints.

That is, aromatic hydrocarbons, alicyclic hydrocarbons, aliphatic hydrocarbons, alcohols, esters, glycol ethers,
One kind or a mixture of two or more kinds of ketones can be used. The coating composition of the present invention can be used as a clear coating or colored with appropriate dyes and pigments, just like conventional coatings.

Additionally, additives such as flowability modifiers and color separation inhibitors can be used in the same manner as in conventional paints. Next, production examples and examples of the acrylic copolymer and melamine resin (component (b)) in the present invention will be shown.

The following parts and % represent parts by weight and % by weight. Preparation of Acrylic Copolymer A 1000 parts of ethylene glycol monoethyl ether acetate is charged into a reaction vessel equipped with a thermometer, a stirrer, and a backflow condenser dropping device, and heated to its reflux temperature.

While maintaining the reflux state, from a dropping device, add 250 parts of 2-hydroxyethyl methacrylate, 20 parts of acrylic acid, 500 parts of n-butyl methacrylate, 130 parts of i-butyl acrylate, 100 parts of lauryl methacrylate, and 50 parts of azobisisovaleronitrile. 10 parts of t-dotesylmercaptan were added dropwise over a period of 3 hours. One hour after the completion of the dropwise addition, 10 parts of azobisisovaleronitrile was mixed with 10 parts of ethylene glycol monoethyl ether acetate over a period of 3 hours.
The solution (additional catalyst) dissolved in 0 parts was added dropwise and kept at the same temperature for 1 hour. Next, the solvent was distilled off under reduced pressure below 15°C and concentrated to obtain a copolymer solution with a solid content of 80%. The number average molecular weight of this copolymer was 3,000.

Production of acrylic copolymer B-L Using a reaction vessel similar to that used for producing copolymer A, the same reaction procedure was performed to produce acrylic copolymer B-L with the composition shown in Table 1. I got it.

(The numbers in (d) in Table 1 indicate the blended parts.) Table 2 shows the reaction conditions according to the above composition, and the solid content % and number average molecular weight of the obtained acrylic copolymer.

Production of melamine resin A Cymel #300 (Anle
ricanCyanamidCO. Hexakizmethoxymethylmelamine (purity 95-97% or less) 39
0 parts (1 mol), ethanol 184 parts (4 mol) 60%
Charge 2.8 parts of nitric acid.

The temperature of the reaction system is gradually increased to 60° C., and at the same time the pressure inside the system is reduced to 50 to 60 mmHg. The reaction is carried out at 60° C. for 5 hours while removing methanol by-produced during the reaction from the system. After the reaction was completed, the pH was adjusted to 8.0 with a 30% aqueous solution of caustic soda.
2, the neutralized solution was heated to its boiling point and unreacted ethanol was removed under reduced pressure. The concentrate is filtered to remove neutralized salts. What was obtained (solid content 99.7%)
Gardna-Folso foam viscosity θ/25°C Its chemical structure was determined by gas chromatography analysis of a phosphoric acid decomposition product to be a mixed alkyl methyl and ethyl group containing 2.3 ethoxy groups per melamine nucleus and no free methylol groups. It was recognized as etherified methylolmelamine.

Production of melamine resin B Cymel #3 was placed in a reaction vessel similar to the production method of melamine resin A.
00390 parts (1 mol), n-butanol 518 parts (7
Mol), 4.2 parts of 60% nitric acid were prepared in the same manner, and the solid content was 99.2% Gardner-Holtz foam viscosity L/25°C contained 4.1 butoxy groups per melamine nucleus and free methylol groups. A methylolmelamine containing almost no methyl and n-butyl mixed alkyl ether was obtained.

Production of Melamine Resin C 126 parts (1.00 mol) of melamine was placed in a reaction vessel equipped with a stirrer, a thermometer, a water separator, and a backflow condenser.
Butanol formalin (contains 40% formaldehyde)
Prepare 450 parts (6 moles as formaldehyde) 1
Heat under reflux for half an hour (during this time, adjust the pH to 7 with caustic soda.
.

Next, add 500 parts of n-butanol, adjust the pH to 7.5 with phthalic anhydride, dehydrate through a water separator for 3 hours, and then bring the temperature of the contents to 117°C. The butanol-water-formaldehyde mixture was distilled off until it rose.

Furthermore, the solids content is 60% with a mixture of butanol/xylene.
I adjusted it so that The resulting product had a Gardner-Holtz foam viscosity of K/25° C., and the amount of bound formaldehyde per melamine nucleus was 5.1 mol. Melamine resin A.
B can be used as component (b) and C can be used as component (6).

Example 0. A paint having the composition shown in Table 3 was spray-coated on a panel made of a mild steel plate of 8mTn thickness and coated with an epoxy primer, and then cured at 160°C.

・Heat for 20 minutes North ) indicates the solid content ratio.

The measured solids content indicates the proportion of the residue after heating the sample at 150° C. for 60 minutes, and the blended solids content is theoretically calculated based on the sample blend.

sample. 46.1 to 6 are compositions of the present invention, and the others are comparative examples.

That is, 7 has insufficient hydroxyl group content in the acrylic copolymer (
(A) has a small amount of component) and has poor curability; conversely, 8 has an excess of hydroxyl groups and has poor thermal stability; and although the curability is the same as in Examples, the flexibility of the coating film is poor.

No. 9 is a case in which the number average molecular weight of the acrylic copolymer is too small, and the curability is clearly insufficient, and defects such as repellency and smearing are likely to occur in the coating film.

On the other hand, the number average molecular weight of No. 10 is too high, the viscosity is high, the thermal stability is poor, and it is difficult to apply hot spray.

No. 11 has a high viscosity because the acrylic copolymer is too hard, and the flexibility of the coating film is also poor.

On the contrary, in No. 12, the acrylic copolymer was too soft, the coating film hardness was poor, the coating film remained somewhat sticky, and the gasoline resistance was also poor.

No. 13 is an example lacking the q component (reactive diluent), has high viscosity, and has slightly poor thermal stability.

No. 14 is a case where the amount of component (c) is too large, and the solvent resistance and curing properties are poor, and the coating film is prone to repelling and dirt ('015 is a case where the amount of catalyst (component (e)) is small. This is an example, and it is clearly insufficiently cured.

No. 16 is an example in which the amount of catalyst is large, and the thermal stability is poor, making it difficult to apply hot spray. The flexibility of the coating film is poor.

No. 17 is a case in which a component (c) having a molecular weight that is too small is used, and most of it evaporates during the curing process and does not work effectively.

In this case, the volatile content is 100 to 100 of the component that effectively forms a coating film. It is undesirable for such oligomer substances to be baked in the baking oven. No. 18 is a case where a component (c) having an excessively large molecular weight is used, and the viscosity increases and the crosslinking density decreases, resulting in deterioration of solvent resistance.

The paint obtained in the O-gel fraction example was applied onto a 2 mm thick glass plate using a 4 mH doctor blade, and heated at a predetermined temperature for 30 minutes.
Baked for 0 minutes.

Peel off the cured coating film obtained in this way, put about 0.5y in a cylindrical P paper #5A, soak it in acetone as an extraction solvent, extract it in an extractor for 10 hours, and then reach a constant weight at 60°C in a vacuum dryer. until dry. The weight of the cured coating film before and after extraction was measured, and the weight was included in the following formula to calculate the solvent-insoluble portion. Erichsen test: This was conducted in accordance with JISZ-2247, and the higher the test result value, the better the flexibility.

. Gloss value: JISK-5400) 6.70 Gasoline resistance: After being immersed in Nisseki Silver gasoline at 20° C. for 24 hours, the degree of swelling and elution of the coating film in the immersed area of the pulled-up coated plate was evaluated.

Claims (1)

[Claims] 1 (a) (a) General formula ▲ Numerical formula, chemical formula, table, etc. ▼ (R_1 is H or an alkyl group of C_1 to_2, R_2
represents H or CH_3) Compounds 20-3
5% by weight (b) 4% by weight or less of acrylic acid or methacrylic acid (c) alkyl ester of methacrylic acid having 1 to 4 carbon atoms;
Cyclohexyl ester of acrylic acid or methacrylic acid, styrene, α-methylstyrene and carbon number 1-4
20 to 55% by weight of one or more compounds selected from alkylated styrenes substituted with alkyl groups, and (d) alkyl esters of acrylic acid having 1 to 18 carbon atoms, and methacrylic acid having 1 to 18 carbon atoms. General formula of 5 to 18 alkyl esters ▲ Numerical formulas, chemical formulas, tables, etc. are available ▼ (R_3 is an alkyl group of C_1 to _1_7, R_4 is H
or CH_3), and the general formula ▲mathematical formula, chemical formula, table, etc. ,
Obtained by copolymerizing 15 to 60% by weight of one or more of the compounds shown in Tables ▼ or ▲Mathematical formulas, chemical formulas, tables, etc.) in the presence of a polymerization initiator. 65 to 20% by weight of a copolymer having a number average molecular weight of 1,500 to 6,000 (b) In the chemical formula below, an average of 2 to 6 of R is an alkyl group having 2 to 4 carbon atoms, and the remainder is a methyl group. Melamine resin whose main component is 20-40% by weight ▲Mathematical formulas, chemical formulas, tables, etc.▼ (c) One or more double bonds and one primary or secondary hydroxyl group in one molecule Molecular weight: 250 to 10
If 15 to 60% by weight of compound 00 is additionally required, (d
) melamine resin modified with an alcohol having 1 to 4 carbon atoms in which the amount of bound formaldehyde is 5.5 mol or less per 1 mol of melamine is added in an amount of 1/2% by weight or less of the component (b) above; Per 100 parts by weight of the mixture formed by adding components b) and (c) or further adding component (d), (
e) 0 aliphatic or aromatic sulfonic acid or its amine salt
．． 05 to 1.00 parts by weight, and (f) 80 to 20 parts by weight of an organic solvent capable of dissolving each of the above-mentioned components at the same time.A thermosetting high solid that can be sprayed at a coating temperature of about 70°C or less. Parting paint composition.