JPH0557310B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention has excellent processability and weather resistance, and has gloss and
The present invention relates to a coating composition for coated steel plates that exhibits a coating film appearance with excellent image clarity. The first characteristics required for painted steel sheets are:
It has excellent workability such as press working.
There are many paints currently in use, such as alkyd resin, vinyl resin, and silicone resin paints, but if you place emphasis on processability, all of them inevitably have drawbacks in other properties, and there are restrictions on their use. The current situation is what we are receiving. When trying to obtain good workability with the alkyd resin or acrylic resin paints that are currently most commonly used, the paint film becomes considerably soft and lacks hardness. On the other hand, if an attempt is made to obtain a coating film with high hardness, it becomes impossible to obtain a coating film with sufficient workability. Generally used alkyd resins include dicarboxylic acids such as orthophthalic acid and adipic acid as acid components, glycols such as ethylene glycol, propylene glycol, and neopentyl glycol as alcohol components, and trivalent resins such as trimethylolpropane and pentaerythritol. It is a polyester resin containing at least 20 mol% of the total alcohol component or total acid component of the above polyalcohol or trivalent or higher polycarboxylic acid such as trimellitic acid. However, products that use orthophthalic acid as the main raw material and also contain large amounts of trifunctional or higher-functional polyols or polycarboxylic acids lack flexibility and flexibility when hardness exceeds a certain level, resulting in so-called hard and brittle coatings. It was difficult to form a coating film with excellent workability. The present inventors have already applied alkyl etherified aminoformaldehyde resin to various copolymerized polyesters in order to obtain coated steel sheets with excellent processability, stain resistance, solvent resistance, adhesion, and a high degree of gloss. After further research into improving this, we found that by blending an alkyl etherified amino formaldehyde resin with a specific copolymerized polyester, we not only further improved processability but also improved weather resistance. We have discovered that this is the case, and have arrived at the present invention. That is, the present invention uses isophthalic acid as the acid component.
40 to 90 mol%, 0 to 40 mol% of aromatic dicarboxylic acids other than isophthalic acid, 0 to 30 mol% of aliphatic dicarboxylic acids having 4 to 12 carbon atoms, and 0 to 5 mol% of trivalent or higher polycarboxylic acids. , neopentyl glycol 20-80 mol% as polyol components, neopentyl glycol hydroxypivalate 20-80
Mol% and trivalent or higher polyol 0-8 mol%
95 to 70 parts by weight of a polyester resin consisting of 95 to 70 parts by weight of a polyester resin and 5 parts of an alkyl etherified amino formaldehyde resin
This is a coating composition for painted steel sheets, characterized in that it contains ~30 parts by weight. The polyester resin of the present invention has an acid component of 40 to 90 mol% of isophthalic acid, preferably 50 to 70 mol%, and 0 of aromatic dicarboxylic acids other than isophthalic acid.
~40 mol%, preferably 10-30 mol%, carbon number 4
~12 aliphatic dicarboxylic acids 0 to 30 mol%, preferably 10 to 30 mol%, and trivalent or higher polycarboxylic acids, and the polyol component is neopentyl glycol 20 to 80 mol%, preferably 30 to 60 mol% neopentyl Consists of 20 to 80 mol% of glycol hydroxypivalate, preferably 35 to 65 mol%, and 0 to 8 mol% of trihydric or higher polyol, and has a reduced viscosity of 0.15 to 0.15 to 80 mol%.
0.80, preferably in the range of 0.30 to 0.60. Aromatic dicarboxylic acids other than isophthalic acid used in the present invention include terephthalic acid, orthophthalic acid, 2,
Examples include 6-naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, and carbon atoms having 4 to 4 carbon atoms.
Examples of the 12 aliphatic dicarboxylic acids include succinic acid, adipic acid, azelaic acid, sedicic acid, and dodecanedioic acid, and examples of trivalent or higher polycarboxylic acids include trimellitic acid and pyromellitic acid. Examples of polyols having a valence of 3 or more include trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol. The acid components used in the polyester resin of the present invention include 40 to 90 mol% of isophthalic acid, 0 to 40 mol% of aromatic dicarboxylic acids other than isophthalic acid, and 4 carbon atoms.
~12 aliphatic dicarboxylic acids 0-30 mol% and 3
It consists of 0 to 5 mol% of a polycarboxylic acid having a value higher than that of the polycarboxylic acid.
If isophthalic acid is 40 mol% or less and other aromatic dicarboxylic acids, such as terephthalic acid, exceeds 40 mol%, some crystalline substances will be formed, so the solution after dissolving the polyester resin in a solvent will become cloudy. Alternatively, the gloss of the resulting coating film may be reduced, and the weather resistance may also be adversely affected. Additionally, if the aliphatic dicarboxylic acid content exceeds 30 mol%, the resulting coating film will become too soft and easily scratched.
Weather resistance also deteriorates. The polyol components used in the polyester resin of the present invention include 20-80 mol% of neopentyl glycol, 20-80 mol% of neopentyl glycol hydroxypivalate, and 0-80 mol% of trivalent or higher polyol.
It is 8 mol%. If neopentyl glycol hydroxypivalate is less than 20 mol%, the resulting coating film will have poor flexibility, and conversely, if neopentyl glycol hydroxypivalate exceeds 80 mol%, the resulting coating film will be too soft. Therefore, it becomes easily damaged. Also, 0 to 5 mol% of trivalent or higher polycarboxylic acid
(in the acid component) and/or 0 to 8 mol% (in the polyol component) of a polyol having a valence of 3 or higher, but in any case, if the upper limit is exceeded, the resulting coating film becomes flexible. It loses its flexibility and becomes less flexible. Although it is possible to use a trivalent or higher polycarboxylic acid and a trivalent or higher polyol together,
Considering the flexibility of the coating film, the sum of both is
The content is preferably 10 mol% or less. In addition, if the sum of both is less than 1 mol% of the total components, the reactivity with the alkyl etherified aminoformaldehyde resin will be low, and the performance of the resulting coating film, such as solvent resistance, will tend to be somewhat low. , and desirably the sum of both is 1 to 10 mol % of the total components. The copolyester of the present invention is produced by a conventional method for producing high molecular weight polyesters, such as a transesterification method or a direct esterification method. The alkyl etherified amino formaldehyde resin used in the present invention is, for example, formaldehyde or paraformaldehyde that has been alkyl etherified with an alkyl alcohol having 1 to 4 carbon atoms such as methanol, ethanol, n-propanol, isopropanol, and n-butanol. It is a condensation product of urea, N,N-ethylene urea, dicyandiamide, aminotriazine, etc., and specifically, methoxylated methylol-N,N-ethylene urea, methoxylated methylol dicyandiamide, methoxy Examples include methoxylated methylolmelamine, methoxylated methylolbenzoguanamine, butoxylated methylolmelamine, butoxylated methylolmelamine, butoxylated methylolbenzoguanamine, but from the viewpoint of processability, methoxylated methylolmelamine or butoxylated methylolmelamine is preferable. Each can be used alone or in combination. In the coating composition of the present invention, the ratio of the copolymerized polyester to the alkyl etherified aminoformaldehyde resin is preferably 95-70:5-30 (weight ratio). The proportion of the copolymerized polyester is
If it exceeds 95% by weight, the desired solvent resistance (xylene resistance) and coating hardness will be insufficient, which is undesirable.
Moreover, if it is less than 70% by weight, processability will be poor, which is not preferable. To the coating composition of the present invention, p-toluenesulfonic acid, monoalkyl phosphoric acid ester, or amine salt of p-toluenesulfonic acid may be added as a curing catalyst. The amount of the catalyst used is 0 to 5% by weight based on the formaldehyde resin. The coating composition of the present invention is generally used in the form of a solution in an organic solvent. Examples of organic solvents include toluene, xylene, and sorbet.
150, ethyl acetate, butyl acetate, cellosolve, butyl cellosolve, cellosolve acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, butanol, octanol, butyl carbitol, diethyl carbitol, tetrahydrofuran, etc., depending on its solubility and evaporation rate. can be selected. In many cases, in the production of coated steel sheets, high-speed painting and high-temperature short-time baking are performed, so the boiling point is
It is desirable to use a mixture of two or three kinds of solvents having a temperature of 100°C or higher. Generally aliphatic hydrocarbon 90
It is desirable to use polar solvents such as esters, ketones and ethers in a proportion of 10 to 70% by weight. Note that the coating composition of the present invention exhibits sufficient performance even if it is applied to a steel plate and baked.
If further improvement in corrosion resistance is required, use epoxy resin as a primer coating agent, such as commercially available Epicoat #1001, #1004, etc.
#1007 (manufactured by Ciel Chemical Co., Ltd.), Araldite 6084 (manufactured by Ciba Geigy), etc. are used. The baking temperature of the coating composition of the present invention may be arbitrarily selected depending on the size and thickness of the steel plate, the capacity of the baking furnace, the hardenability of the coating material, etc. Mixing machines such as roll kneaders, ball mills, blenders, etc. are used to manufacture coating compositions. For painting, roller painting, roll coater, spray painting, electrostatic painting, etc. are selected as appropriate. The coating composition of the present invention may contain pigments such as titanium oxide, glass fiber, silica, etc. depending on the purpose and use.
Additives such as wax can be added. The coating composition of the present invention has excellent workability after being applied to a steel plate, and the coated surface has excellent solvent resistance, adhesion, and high weather resistance, as well as high gloss and sharpness. have The present invention will be explained below using examples. In the examples, the term "part" simply indicates part by weight, and the term "%" indicates weight %. Each measurement item was measured according to the following method. (1) Reduced viscosity ηsp/e (dl/g) 0.10 g of polyester resin was dissolved in a mixed solvent of phenol/tetrachloroethane (volume ratio 6/4)25
cc and measured at 30°C. (2) Hardness (Pencil Hardness) The painted surface of the steel plate was measured according to JIS K-5400 using a high-grade pencil specified in JIS S-6006. (3) Gloss Reflectance at 60°C was measured. (4) Flexibility A coated steel plate was bent 180 degrees and cracks that occurred at the bends were observed and determined using a 10x magnifying glass. 3T refers to the case where three boards of the same thickness are sandwiched at the bending part, and OT is 180 without sandwiching the boards.
Refers to the case where it is bent. (5) Xylol resistance It was expressed by the number of times gauze was spread around a cork stopper, the xylene was soaked through, and the coated surface was rubbed until the bare surface came out. (6) Weather resistance Expressed as gloss retention after 1000 hours of irradiation using accelerated weather resistance tester QUV. QUV irradiation conditions
One cycle consisted of 8 hours of UV 60°C x 4 hours and dew condensation 50°C x 4 hours, and 62.5 cycles were performed. Example 1 349.2 parts of dimethyl isophthalate, 174.6 parts of dimethyl terephthalate, neopentyl glycol
390.0 parts, neopentyl glycol hydroxypivalate 459.0 parts, trimethylolpropane 20.1 parts
and 0.26 parts of zinc acetate at 160°C to 220°C.
The transesterification reaction was carried out over a period of 4 hours. Next, 43.8 parts of adipic acid was added and the temperature was raised from 200°C to 240°C over 2 hours to perform an esterification reaction. Next, reduce the pressure to 20-25 mmHg over 30 minutes,
Further, a polycondensation reaction was carried out at 260°C for 60 minutes. As a result of composition analysis such as NMR, the obtained copolymerized polyester component (A) has an acid component in a molar ratio of terephthalic acid/isophthalic acid/adipic acid = 30/60/10, and a glycol component in a molar ratio of neopentyl. The glycol/neopentyl glycol hydroxypivalate/trimethylolpropane ratio was 30/65/5, and the reduced viscosity ηsp/c was 0.374. Similarly, the polymer compositions are shown in Tables 1-1 and 1-2.
Copolymerized polyester resins (B) to (L) shown in the table were synthesized.

【table】

[Table] Copolymerized polyester resins (A) to (G) and (H) to (N) were each dissolved in a cyclohexanone/Solbetsuso-150 mixed solvent (weight ratio 50/50), and the nonvolatile content was adjusted to 40%. To 100 parts of the above copolyester resin (A) solution, 40 parts of titanium oxide, methyl etherified methylolmelamine (trade name: Sumimaru M-40S, non-volatile content: 80 parts)
%, manufactured by Sumitomo Chemical Industries) 10 parts, p-toluenesulfonic acid solution (20% by weight solution of benzyl alcohol)
and 0.2 parts of Polyflow S (manufactured by Kyoeisha Yushi Kagaku Kogyo) were added, and the pigment was dispersed for 2 hours using a glass bead type high-speed shaker to obtain a coating composition for painted steel plates. Instead of copolymerized polyester resin (A) with (B) to (N), or as an alkyl etherified aminoformaldehyde resin, methyl etherified methylolmelamine (product name: Sumimaru M100, manufactured by Sumitomo Chemical), butyl etherified melamine (product name: Sumimaru M100, manufactured by Sumitomo Chemical), Name: Super Betsucomin J-820-60, manufactured by Dainippon Ink and Chemicals) Table 2-1 and 2-2
The coating compositions shown in the table were obtained in the same manner. These coating compositions were applied to a test piece of a 0.3 mm thick galvanized iron plate (JIS G-3302) treated with a zinc phosphate solution to a film thickness of 18 to 22 μ, and then baked at 230°C for 2 minutes. I went there. The test results of the obtained coated steel sheets are shown in Tables 2-1, 2-2, and 2-2.

【table】

【table】

[Table] As is clear from Tables 2-1 and 2-2, the coating composition of the present invention has excellent coating film properties such as flexibility (processability) and weather resistance.

Claims (1)

[Claims] 1 As acid components, 40 to 90 mol% of isophthalic acid, 0 to 40 mol% of aromatic dicarboxylic acids other than isophthalic acid, 0 to 30 mol% of aliphatic dicarboxylic acids having 4 to 12 carbon atoms, and 0 to 3 or more valent polycarboxylic acids ~5 mol%, with 20-80 mol% neopentyl glycol, 20-80 mol% neopentyl glycol hydroxypivalate, and 3 as polyol components.
1. A coating composition for painted steel sheets, comprising 95 to 70 parts by weight of a polyester resin comprising 0 to 8 mol% of a polyol having a polyol or higher, and 5 to 30 parts by weight of an alkyl etherified aminoformaldehyde resin.