JPS6134754B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coating composition for coated steel plates that has excellent workability and solvent resistance. The first performance required for painted steel sheets is excellent workability such as press working.
Many of the paints currently used for painted steel sheets have insufficient machining performance, so they cannot be used for high-machining applications, and even if they are used, the paint film cracks on the processed parts, causing rust. There is. Currently, there are alkyd resin, acrylic resin, and silicone resin paints as paints used as paints for painted steel plates, but there is a demand for improvement in processability of all of these paints. On the other hand, solution type vinyl resin,
Although vinyl chloride organosol or vinyldene fluoride resin paints have excellent processability, they do not have sufficient coating hardness, solvent resistance, or gloss.
Another problem is that the paint is expensive. Generally, processing performance is closely related to the flexibility of the paint film, and in the case of acrylic resin and alkyd resin paints, in order to obtain good workability, the paint film needs to be considerably soft, and the hardness is insufficient. I'll come.
On the other hand, if high hardness is attempted, a coating film with sufficient workability cannot be obtained. Commonly used alkyd resins contain isophthalic acid, orthophthalic acid, adipic acid, etc. as acid components, ethylene glycol, neopentyl glycol, etc. as glycol components, and trifunctional or higher functional components such as glycerin, trimethylolpropane, pentaerythritol, trimerite. It was difficult to achieve both hardness of the painted surface and workability when it was used as the main raw material along with acids. Taking these current circumstances into account, the present inventors have developed a method that has excellent workability and hardness, as well as solvent resistance, stain resistance, adhesion, and
The present invention was achieved through intensive research into paints for coated steel plates with excellent gloss and the like. That is, the present invention comprises 30 to 80 mol% of terephthalic acid as a dibasic acid component and 70 to 20 mol% of an aromatic dicarboxylic acid other than terephthalic acid, and 1,5-pentanediol and/or as a glycol component.
or a copolymerized polyester resin consisting of 30 to 75 mol% of 1,6-hexanediol and 70 to 25 mol% of aliphatic glycol having 2 to 4 carbon atoms and having a reduced viscosity of 0.15 to 0.80; This is a coating composition for painted steel sheets, characterized by comprising an aminoformaldehyde resin etherified with an alkyl alcohol. The coating composition of the present invention uses a copolymerized polyester resin with a novel composition, so that it is superior to conventional copolymerized polyester resins in both the workability of the steel plate after painting and the hardness of the coated surface. The copolyester resin of the present invention consists of terephthalic acid and an aromatic dicarboxylic acid other than terephthalic acid as a dibasic acid component. Aromatic dibasic acids other than terephthalic acid include isophthalic acid, orthophthalic acid, 2,6-naphthalene dicarboxylic acid, 4,
Examples include 4'-diphenyldicarboxylic acid. Furthermore, the glycol component of the copolyester resin of the present invention consists of 1,5-pentanediol and/or 1,6-hexanediol and an aliphatic glycol having 2 to 4 carbon atoms. Examples of aliphatic glycols having 2 to 4 carbon atoms include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, and 1,2-butane. Examples include diol. The molar ratio of terephthalic acid and aromatic dicarboxylic acid other than terephthalic acid is terephthalic acid/aromatic dicarboxylic acid other than terephthalic acid = 30-80/70-20, but especially terephthalic acid/aromatic dicarboxylic acid other than terephthalic acid. = 40-70/60-30 is preferable; when terephthalic acid exceeds 80 mol%, the obtained polyester resin has poor solvent solubility and is difficult to form into a paint, and when it is less than 30 mol%, the obtained polyester resin The coating film has insufficient flexibility and cannot be used for highly processed applications. In addition, the molar ratio of the glycol component is 1,5-pentanediol and/or 1,6-hexanediol/aliphatic glycol having 2 to 4 carbon atoms = 30 to
70/75 to 25, and when 1,5 pentanediol and/or 1,6-hexanediol exceeds 75 mol%, the resulting coating will be soft and easily scratched, and when it is less than 25 mol% The resulting coating is stiff and has insufficient flexibility to be used in highly processed applications. The reduced viscosity of the copolymerized polyester resin of the present invention is
It is 0.15 to 0.80, preferably 0.25 to 0.55. When the intrinsic viscosity of the copolyester resin is less than 0.15, the resulting coating film has poor flexibility and is not suitable for highly processed applications. Further, when the intrinsic viscosity exceeds 0.80, the reactivity between the copolyester resin and the curing agent decreases, and the properties such as boiling water resistance and solvent resistance will not be sufficient. The copolymerized polyester resin of the present invention is essentially a linear saturated copolymerized polyester resin, and unlike known oil-free alkyd resins, it does not contain a trifunctional or higher-functional polycarboxylic acid or polyol. It is not preferable to copolymerize a large amount of polycarboxylic acids or polyols having trifunctionality or more, since the flexibility decreases. The curing agent for the copolyester resin in the present invention is an aminoformaldehyde resin etherified with an alkyl or alcohol having 1 to 4 carbon atoms. For example, the amino formaldehyde resin etherified with alcohol has 1 to 4 carbon atoms.
There are main condensation products of formaldehyde or paraformaldehyde that has been alkyl etherified with an alcohol, and urea, N,N'-ethylene urea, dicyandiamide, aminotriazine, etc. Specifically, methoxylated methylol urea, methoxylated methylol urea, etc. -N,N'-ethylene urea, methoxylated methylol dicyandiamide, methoxylated methylol melamine, methoxylated methylol benzoguanamine, butoxylated methylol melamine, butoxylated methylol benzoguanamine and the like. Further, as the catalyst, acids such as hydrochloric acid, phosphoric acid monoalkyl ester, p-toluenesulfonic acid, and salts of these acids and tertiary amines or secondary amine compounds are used as necessary. The amount used is 0 to 10% by weight based on the amino formaldehyde resin. In the present invention, the blending ratio of copolyester resin (1) and curing agent (2) is (1)/(2)=95-50/5-50
(weight ratio). When the weight ratio of (1)/(2) exceeds 95 to 5, the desired hardness, solvent resistance, boiling water resistance, and stain resistance of the coating film will be insufficient. Also, the weight ratio of (1)/(2) is
When it is less than 50/50, flexibility and flexibility are insufficient,
Workability deteriorates. In particular, the molar ratio of copolyester resin (1) and curing agent (2) is (1)/(2) = 95 ~
It is preferable that it is 70/5 to 30. The coating composition of the present invention exhibits sufficient performance by itself, but when particularly required to improve corrosion resistance etc., epoxy resins such as commercially available Epicoat 1001, 1004, 1007, 1009 (manufactured by Ciel Chemical Co., Ltd.) may be used. ), Araldite 6097 (manufactured by Ciba Geigy)
Add. These epoxy resins can also be used as primer coating agents. Furthermore, an acrylic resin may be used as a top coating agent in order to further improve stain resistance. In this case, it is preferable to adopt a two-coat/two-bake method. The coating composition of the present invention is used in the form of a solution in an organic solvent. Examples of organic solvents include toluene, xylene, Sorbetsuso 100, 150, ethyl acetate, butyl acetate, methyl cellosolve, ethyl cellosolve, butyl cellosolve, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethylene glycol monoacetate, carbitol acetate, methyl cellosolve. It can be arbitrarily selected from acetate, methoxybutyl acetate, diacetone alcohol, butanol, octanol, etc. depending on its solubility and evaporation rate. In many cases, the coated steel sheets that are the object of the present invention are coated at high speed and baked at high temperatures for short periods of time, so solvents with a boiling point of 100°C or higher are used to prevent paint film defects such as pinholes from occurring in the paint film. It is desirable to use a mixture of 2 to 3 or more types, and generally aliphatic hydrocarbons or aromatic hydrocarbons 80 to 10
Polar solvents such as esters, ketones, ethers, etc. are used at a ratio of 20 to 90% by weight, but are not limited to this range, depending on baking temperature, curing time, size of steel plate, baking furnace It can be arbitrarily selected depending on the ability of the paint, the hardenability of the paint, etc. Mixing machines such as roll kneaders, ball mills, and high-speed mixers are used to manufacture paints. For painting, roller painting, roller 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 processability after being applied to a steel plate, has a coated surface with high hardness, excellent solvent resistance and adhesion, and has a high gloss. The present invention will be explained below using examples. In the examples, parts simply indicate parts by weight, and %
% indicates weight %. Each measurement item was measured according to the following method. (1) Reduced viscosity ηsp/c (dl/g) 0.10 g of copolyester resin was dissolved in 25 c.c. of a mixed solvent of phenol/tetrachloroethane (volume ratio 6/4) and measured at 30°C. (2) Hardness (Pencil Hardness) The painted surface of the steel plate was measured in accordance with JIS K-5400 using a high-grade pencil specified in JIS S-6006. (3) Gloss 60° reflectance was measured. (4) Dupont impact value Using a Dupont impact tester, load 1.0Kg (1/
2)" was dropped onto the paint film from a specified height and the maximum height without cracking the paint surface was taken as the measured value (JIS K5460). (5) Flexibility The painted steel plate was bent 180 degrees and the bent part 〇 indicates no abnormality. A straight line was drawn on the book, and the central part was extruded using an Erichsen tester, and the length of extrusion (mm) until peeling was measured. Example 1 485 parts of dimethyl terephthalate, 485 parts of dimethyl isophthalate, 478 parts of ethylene glycol,
390 parts of 1,6-hexanediol and zinc acetate
A reaction vessel was charged with 0.44 parts of antimony trioxide and 0.43 parts of antimony trioxide, and the transesterification reaction was carried out from 140°C to 220°C over 3 hours. Then, over 30 minutes, 0.5
The pressure was reduced to mmHg, and the polycondensation reaction was further carried out at 250°C and 0.2 mmHg for 45 minutes. As a result of composition analysis such as NMR, the obtained copolymerized polyester resin (A) has an acid component in a molar ratio of terephthalic acid/isophthalic acid = 50/50, and a glycol component in a molar ratio of ethylene glycol/isophthalic acid.
It was 1,6-hexanediol = 50/50, and was pale yellow and transparent with a reduced viscosity of 0.420 dl/g. Copolymerized polyester resins (B) to (H) whose compositions are shown in Table 1 were synthesized in the same manner.

[Table] Copolymerized polyester resins (A) to (H) were each dissolved in a mixed solvent of cyclohexanone/Sorbetsuso-150 (weight ratio 50/50), and the nonvolatile content was adjusted to 40%. 100 parts of the above copolyester resin (A) solution, 40 parts of titanium oxide, methyl ether right methyl roll melamine (trade name: Sumimaru M-40S, non-volatile content)
10 parts of 80% (manufactured by Sumitomo Chemical Industries, Ltd.), 0.5 parts of p-toluenesulfonic acid solution (benzyl alcohol 20wt% solution) and 0.20 parts of Polyflow S (manufactured by Kyoeisha Yushi Kagaku Kogyo Co., Ltd.) were kneaded for one day and night in a ball mill and then painted. A coating composition for steel plates was prepared. Replace copolymerized polyester resin (A) with copolymerized polyester resins (B) to (H), or use methylated methylol melamine as alkyl etherified aminoformaldehyde resin, such as methylated melamine resin, methylated benzoguanamine resin, butylated melamine resin. Instead, coating compositions shown in Table 2 were obtained in the same manner. The obtained coating composition was 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 15 to 20 μ.
Baking was performed at 210°C for 2 minutes. The test results of the obtained coated steel plate are shown in Table 2. For comparison, the measurement results of steel plates coated with commercially available solution-type vinyl resin paints and amino oil-free alkyd resin paints are also listed.

【table】

[Table] Example 2 Copolymerized polyester resins (I) and (J) shown in Table 3 were synthesized in the same manner as in Example 1.

[Table] Copolymerized polyester resins (I) and (J) were each dissolved in a mixed solvent of cyclohexanone/Solvetsu-150 (weight ratio 50/50), and the nonvolatile content was adjusted to 50%. When the dissolved product was stored at 20°C for one month and its appearance was observed, no change had occurred in the solution of copolymerized polyester resin (I), but the solution of copolymerized polyester resin (J) was white and cloudy. It was on. The above copolymerized polyester resin (I) or (J)
80 parts of the solution, 40 parts of titanium oxide, 10 parts of methyl etherified methylolmelamine, 0.5 part of p-toluenesulfonic acid solution and 0.20 part of Polyflow S were kneaded in a ball mill for one day and night to prepare a coating composition for painted steel sheets. The obtained coating composition was applied to a test piece prepared by treating a 0.3 mm thick galvanized iron plate with a zinc phosphate solution in a film thickness of 15 to 20 μm.
After painting it so that it looked like this, it was baked at 210℃ for 2 minutes. Table 4 shows the test results of the obtained coated steel plate.

[Table] When each of the above coating compositions was left to stand for one month and then painted, in the case of copolymerized polyester resin (I),
Although no difference from the above initial characteristic values was observed, in the case of copolymerized polyester (J), foreign matter-like substances were observed in the coating film here and there.

Claims (1)

[Claims] 1 30 to 80 mol% of terephthalic acid and aromatic dicarboxylic acids other than terephthalic acid as dibasic acid components
It consists of 70 to 20 mol%, and contains 1,5-pentanediol and/or 1,6 as a glycol component.
- 30-75 mol% hexanediol and 2 carbon atoms
Consisting of 70-25 mol% of aliphatic glycol of ~4,
1. A coating composition for painted steel sheets, comprising a copolyester resin having a reduced viscosity of 0.15 to 0.80 and an aminoformaldehyde resin etherified with an alkyl alcohol having 1 to 4 carbon atoms.