JPH0819374B2 - Paint composition for painted steel plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention has a coated steel sheet having excellent workability and weather resistance, a coating film appearance excellent in gloss and image clarity, and excellent stain resistance. The present invention relates to a coating composition for use.

(Prior Art) The first requirement for a coated steel sheet is excellent workability such as press working. There are many paints currently in use, such as alkyd resin, vinyl resin, and silicone resin paints. However, if focus is placed on processability, it will inevitably cause defects in other performances, and there are restrictions on use. The current situation is that they are receiving it.

At present, when trying to obtain good processability with the alkyd resin or acrylic resin paints that are most often used,
The coating film becomes considerably soft and lacks in hardness. On the contrary, if a coating film having high hardness is to be obtained, a coating film having sufficient workability cannot be obtained. Alkyd resins that are commonly used include dicarboxylic acids such as orthophthalic acid and adipic acid as acid components, and glycols such as ethylene glycol, propylene glycol and neopentyl glycol as alcohol components, and trivalent trimethylolpropane and pentaerythritol. A polyester resin containing the above polyalcohol or tricarboxylic or higher polycarboxylic acid such as trimellitic acid in at least 20 mol% of all alcohol components or all acid components.

(Problems to be solved by the invention) However, the main raw material is orthophthalic acid, and
When a large amount of functional polyol or polycarboxylic acid is contained, when the hardness exceeds a certain level, flexibility and flexibility are insufficient, so-called hard and brittle coating surface is formed, and a coating film excellent in processability is formed. It was difficult to form.

On the other hand, as a coating resin having both processability and weather resistance, the inventors of the present invention have variously studied a polyester resin containing a minimum amount of a trifunctional component, and found a resin having both weather resistance and processability. Probably because such a resin has a low cross-linking density, it has a drawback that the coated surface is soiled by dust and soot in the air, which is a serious problem in practical use.

In view of these problems, the present inventors have arrived at the present invention as a result of diligent studies on a coating resin that is not only excellent in workability and weather resistance, but also does not become soiled by soot in the air.

(Means for Solving the Problems) That is, the present invention provides an aromatic dicarboxylic acid as an acid component.
70-90 mol%, C4-12 aliphatic dicarboxylic acid 30-
It comprises 10 mol% and 0 to 5 mol% of a polycarboxylic acid having a valence of 3 or more, and as a polyol component, the following general formula (1)
95 mol% or more (wherein at least one of the alkyl groups R _{1 and} R _{2 in} the general formula (1) is 20 mol% or more of a glycol component having 2 to 4 carbon atoms) and a polyol having a valency of 3 or more. 95 to 60 parts by weight of a polyester resin having a reduced viscosity of 0.20 to 0.80 and an alkyl etherified aminoformaldehyde resin 5
A coating composition for a coated steel sheet, characterized in that the coating composition contains 40 to 40 parts by weight.

General formula (However, R ₁ and R ₂ are each an alkyl group having 1 to 4 carbon atoms.) In the polyester resin of the present invention, the acid component is 70 to 90 mol% of aromatic dicarboxylic acid, preferably 70 to 85 mol%, Carbon number 4
~ 12 aliphatic dicarboxylic acid 30 to 10 mol%, preferably 30
To 15 mol% and 0 to 5 mol% of a polycarboxylic acid having a valence of 3 or more, and a polyol component having the following general formula (1) is 95 mol% or more (and the alkyl in the general formula (1) is included therein). A glycol component in which at least _{one of the} groups R ₁ or R ₂ has 2 to 4 carbon atoms is 20 mol% or more) and a polyol having a valence of 3 or more is composed of 0 to 5 mol%, and a reduced viscosity is 0.20 to 0.80, preferably 0.30 to It is in the range of 0.60.

Examples of the aromatic dicarboxylic acid used in the present invention include isophthalic acid, terephthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, and 4,4'-diphenyldicarboxylic acid, which have 4 to 12 carbon atoms. As the aliphatic dicarboxylic acid, succinic acid, glutaric acid, adipic acid,
Examples thereof include azelaic acid, sebacic acid, dodecanedioic acid, and the like, and examples of the trivalent or higher polycarboxylic acid include trimellitic acid and pyromellitic acid. Also, as the trivalent or higher polyol, trimethylolethane,
Trimethylolpropane, glycerin, pentaerythritol and the like can be mentioned. Further, among the compounds represented by the general formula (1), which are the main glycol components of the present invention, either of the alkyl groups (R ₁ , R ₂ ) has 2 to 4 carbon atoms.
2-ethyl-2-methyl-1,3-propanediol, 2-methyl-2-n-propyl-1,3
-Propanediol, 2-n-butyl-2-methyl-1,
3-propanediol, 2,2'-diethyl-1,3-propanediol, 2-ethyl-2-n-propyl-1,3-propanediol, 2-ethyl-2-n-butyl-1,3-
Propanediol, 2,2'-di-n-propyl-1,3-propanediol, 2-n-butyl-2-n-propyl-
1,3-Furopandiol, 2,2'-n-dibutyl-1,3-
Examples thereof include propanediol. Further, neopentyl glycol can be mentioned as a compound represented by the general formula (1) in which both alkyl groups are methyl groups.

Further, trivalent or higher polycarboxylic acid 0 to 5 mol% (in the acid component) and / or trivalent or higher polyol 0 to 5 mol%
Although (in the polyol component) is used, in any case, when the content exceeds the upper limit, the coating film obtained loses flexibility and becomes poor in flexibility. It is possible to use a polycarboxylic acid having a valence of 3 or more and a polyol having a valence of 3 or more, but when the flexibility of the coating film is taken into consideration, the sum of the two is in all components,
It is preferably 10 mol% or less. Further, if the sum of the two is less than 1 mol% in all the components, the opposition to the alkyl etherified aminoformaldehyde resin will be low, and the performance of the resulting coating film, such as solvent resistance, will tend to be rather low. Desirably, the sum of both is 1 to 5 mol% in all components.

The copolyester of the present invention is produced by a usual method for producing a high molecular weight polyester by a transesterification method or a direct esterification method.

The alkyl etherified aminoformaldehyde resin used in the present invention includes, for example, methanol, ethanol, n
-Condensation products of formaldehyde or paraformaldehyde alkylated with an alkyl alcohol having 1 to 4 carbon atoms such as propanol, isopropanol, n-butanol and the like with urea, N, N-ethylene urea, dicyandiamide, aminotriazine, etc. Specifically, methoxylated methylol urea, methoxylated methylol-N, N-ethylene urea, methoxylated methylol dicyandiamide, methoxylated methylol melamine, methoxylated methylol benzoguanamine, butoxylated methylol melamine, butoxylated methylol melamine, butoxylated. Methylol benzoguanamine and the like can be mentioned, but from the viewpoint of processability, methoxylated methylol melamine or butoxylated methylol melamine is preferable, and each of them is In combination can be used.

The coating composition of the present invention has a ratio of the copolymerized polyester and the alkyl etherified aminoformaldehyde resin.
It is preferably 95 to 60: 5 to 40 (weight ratio). If the proportion of the copolymerized polyester exceeds 95% by weight, the desired solvent resistance (xylol resistance) and coating film hardness are insufficient, which is not preferable. On the other hand, if it is less than 60% by weight, the workability is poor, which is not preferable.

To the coating composition of the present invention, a p-toluenesulfonic acid, a monoalkyl phosphate ester, or an 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 dissolved in an organic solvent. As the organic solvent, for example,
Toluene, xylene, Solvesso 150, ethyl acetate, butyl acetate, cellosolve, butarcelsolve, cellosolve acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclolohexanone, isophorone, butanol,
It can be arbitrarily selected from octanol, butyl carbitol, diethyl carbitol, tetrahydrofuran and the like depending on its solubility and evaporation rate.

In many cases, high-speed coating and high-temperature short-time baking are performed in the manufacture of coated steel sheets, so 2-3 or more solvents with boiling points of 100 ° C or higher are used to prevent coating film defects such as pinholes from occurring. It is desirable to use them as a mixture. Generally, it is desirable to use 90 to 30% by weight of aliphatic hydrocarbons and 10 to 70% by weight of polar solvents such as esters, ketones and ethers.

The coating composition of the present invention is itself applied to a steel plate,
Although it shows sufficient performance just by baking, when it is required to further improve the corrosion resistance, an epoxy resin as a primer coating agent, for example, commercially available Epicoat # 1001, # 1004, # 1007 (Shell Chemical Co., Ltd. Manufactured by Ciba Geigy) and the like.

The baking temperature of the coating composition of the present invention may be arbitrarily selected depending on the size and thickness of the steel sheet, the ability of the baking furnace, the curability of the coating, and the like. A mixer such as a roll kneader, a ball mill and a blender is used for producing the coating composition.
For coating, roller coating, roll coater, spray coating, electrostatic coating, etc. are selected as appropriate.

To the coating composition of the present invention, pigments such as titanium oxide and additives such as glass fiber, silica and wax can be added depending on the purpose and application. The coating composition of the present invention has excellent workability after being coated on a steel sheet, and the coated surface has excellent solvent resistance and adhesiveness, has high weather resistance, and has high gloss and sharpness. Have.

(Example) Hereinafter, the present invention will be described using examples. In the examples, "parts" means "parts by weight" and "%" means "% by weight". Each measurement item followed the following method.

(1) Reduced viscosity η SP / c (dl / g) 0.10 g of polyester resin was dissolved in 25 cc of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (volume ratio 6/4) and measured at 30 ° C. .

(2) Hardness (Empty hardness) The coated surface of the steel plate was measured according to JIS K-5400 using a high-grade pencil defined in JIS S-6006.

(3) Gloss The reflectance at 60 ° C. was measured.

(4) Flexibility Bending the coated steel sheet 180 degrees
It was observed and judged with a double magnifying glass.

3T refers to the case where three bent sheets with the same plate thickness are sandwiched, and OT refers to the case where the plate is folded 180 degrees without clipping.

(5) Xylol resistance The gauze was sprinkled on a cork stopper, the xylol was bleeded, and the coated surface was rubbed.

(6) Weather resistance It was shown by the retention rate of gloss after irradiation for 2000 hours by using an accelerated weather resistance tester QUV. QUV irradiation conditions UV60 ℃ x 4 hours, condensation 5
250 cycles were carried out with one cycle consisting of 8 hours at 0 ° C. × 4 hours.

(7) Stain resistance After the coated steel sheet was exposed on the outdoor exposure table for one year, the adhesion of dust on the coated steel sheet was visually determined. The criteria for judgment are as follows.

Good: No dust adhesion Somewhat good: Small amount of dust adhesion Poor: Excessive dust adhesion Example of polyester resin production Dimethyl isophthalate 566.5 parts, neopentyl glycol 561.6 parts, 2-n-butyl-2-methyl 1,3-propanediol 384.8 Part, trimellitic anhydride 15.4 parts and titanium tetrabutoxide 0.41 part were charged, 160 ° C to 220
The transesterification reaction was carried out to 4 ° C. for 4 hours. Then, 146.0 parts of adipic acid was added and the temperature was raised from 200 ° C. to 240 ° C. over 2 hours to carry out an esterification reaction. Then, the pressure was reduced to 20 to 25 mmHg over 30 minutes, and the polycondensation reaction was further performed at 260 ° C. for 60 minutes.

As a result of composition analysis such as NMR, the obtained copolyester resin (A) was found to have an acid component in a molar ratio of isophthalic acid / adipic acid / trimellitic acid = 73/25/2 and a glycol component in a molar ratio of neo. Pentyl glycol / 2-n-butyl-
2-Ethyl-1,3-propanediol pan = 50/50 and reduced viscosity ηSP / c = 0.567. In the same manner, copolymerized polyester resins (B) to (L) having polymer compositions shown in Tables 1-1 and 1-2 were synthesized.

Examples (1) to (6), Comparative Examples (1) to (8) Copolyester resins (A) to (F) and (G)
To (L) were each dissolved in a cyclohexanone / Solvec 150 mixed solvent (weight ratio 50/50) to adjust the nonvolatile content to 50%.

Titanium oxide 62.5 parts, methyl etherified methylol melamine (trade name: Sumimar M-40S, nonvolatile content 80%, manufactured by Sumitomo Chemical Co., Ltd.) 15.6 parts, p-toluenesulfonic acid solution in 100 parts of the above copolymerized polyester resin (A) solution 1.25 parts (10% by weight solution of benzyl alcohol) and 0.25 parts of Polyflow S (produced by Kyoeisha Yushi-Kagaku Kogyo Co., Ltd.) were added, and the pigment was dispersed for 4 hours with a glass bead type high-speed shaker to obtain a coating composition for coated steel sheet.

Methyl etherified methylol melamine (trade name: Sumimar M100, manufactured by Sumitomo Chemical Co., Ltd.), butyl etherified melamine (commodity), replacing the copolyester resin (A) with (B) to (N) or as an alkyl etherified amino formaldehyde resin Name: Super Beckamine J-
820-60, manufactured by Dainippon Ink and Chemicals, Inc.
The coating compositions shown in Table -1 and Table 2-2 were obtained in the same manner.

These coating compositions were applied to a zinc iron plate (JIS G-
3302) was treated with a zinc phosphate solution, and a film thickness of 18-
After coating so as to have a thickness of 22 μ, it was baked at 260 ° C. for 2 minutes. The test results of the obtained coated steel sheet are shown in Table 2-1 and Table 2-2.

As a result, the present invention has excellent workability and weather resistance from Examples and Comparative Examples, and a coating composition for a coated steel sheet having excellent stain resistance and exhibiting a coating film appearance excellent in gloss and image clarity. I know there is.

(Effect of the Invention) The coating composition for a coated steel sheet of the present invention has excellent workability and weather resistance, exhibits an excellent coating appearance, and provides a coated steel sheet having excellent stain resistance. it can.

Claims (1)

[Claims] 1. An acid component comprising 70 to 90 mol% of an aromatic dicarboxylic acid and 30 to 10 mol% of an aliphatic dicarboxylic acid having 4 to 12 carbon atoms,
A glycol component comprising 0 to 5 mol% of a polycarboxylic acid having a valence of 3 or more and a polyol component having the following general formula (1):
95 mol% or more (however, 20 mol% or more of a glycol component in which at least one of the alkyl groups R ₁ or R _{2 in} the general formula (1) has 2 to 4 carbon atoms) and a trivalent or more polyol are 0 to
A coating composition for coated steel sheet, which comprises 5 to 40 parts by weight of a polyester resin having a reduced viscosity of 0.20 to 0.80 and having a reduced viscosity of 0.20 to 0.80, and 5 to 40 parts by weight of an alkyl etherified aminoformaldehyde resin. General formula (However, R ₁ and R ₂ are each an alkyl group having 1 to 4 carbon atoms.)