JPH05179197A - Polyester coating composition and coated steel sheet - Google Patents

Abstract

PURPOSE:To obtain the title composition excellent in hardness, processability, staining resistance, gloss, etc., and useful as a coating material for automobiles and general industries by mixing a specified polyester resin with an aminoaldehyde resin or a blocked polyisocyanate. CONSTITUTION:The title composition comprises 95-50 pts.wt. (in terms of solid matter) polyester resin which is a condensate of an acid component containing below 85mol%, based on the whole acid component, aromatic dicarboxylic acids with an alcohol component containing 20-100mol%, based on the whole alcohol component, disphenol S/alkylene oxide adduct of the formula (wherein R is H or methyl; and n and m are each 1-8) and containing below 30mol% aliphatic glycols having a side chain, and 5-50 pts.wt. (in terms of solid matter) aminoaldehyde resin and/or blocked polyisocyanate.

Description

Detailed Description of the Invention

[0001] BACKGROUND and problems present invention relates to coated steel sheet of the polyester-based coating composition and the coating composition formed by baking finish.

A coating composition comprising a polyester resin and a curing agent such as a melamine resin or a blocked polyisocyanate compound is used for precoat metal, automobile,
It is used as a paint for other general industries. In particular, paints for precoat metals used indoors and outdoors for home appliances and building materials are required to have excellent stain resistance and sharpness (gloss) in addition to the contradictory characteristics of processability and hardness. Conventionally, these properties were controlled by the glass transition temperature of the resin, the molecular weight, the monomer composition, the skeleton structure such as the functional group concentration, the type and blending amount of the curing agent and the catalyst, but processing while maintaining high hardness. It was difficult to obtain a coating having excellent properties, particularly workability at low temperatures, stain resistance and gloss.

The object of the present invention is to overcome such difficulties and to be excellent in properties such as hardness, workability, stain resistance and gloss, and useful not only for precoat metal but also for automobiles and other general industrial coatings. Another object of the present invention is to provide a novel polyester coating composition and a coated steel sheet obtained by baking coating the coating composition.

[0004] To resolve the above problems, the present invention, A. The proportion of aromatic dicarboxylic acid in all acid components is 85
The acid component, which is less than mol%, and the total alcohol component, the formula

[Chemical 2] (In the formula, R is hydrogen or a methyl group, and n and m are 1 to 8
Means an integer of. 20% to 100% by mole of the bisphenol S alkylene oxide adduct of 4) and an alcohol component in which the proportion of the aliphatic glycol having a side chain is less than 30% by mole, and a polyester resin as a condensation product as a solid content. 95-50 parts by weight, B.I. A polyester-based coating composition comprising an aminoaldehyde resin and / or a blocked polyisocyanate compound in a solid content of 5 to 50 parts by weight. The present invention also provides a coated steel sheet obtained by baking-coating the above polyester-based coating composition.

Preferred Embodiment As is well known, a polyester resin is a polycondensation product of an acid component mainly containing a polycarboxylic acid and an alcohol component mainly containing a polyhydric alcohol.

As the acid component, terephthalic acid, isophthalic acid, phthalic acid or its anhydride, aromatic dicarboxylic acid such as 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid and its anhydride, and succinic acid. And aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. Further, lactones such as γ-butyrolactone and ε-caprolactone and corresponding hydroxycarboxylic acids, and aromatic oxymonocarboxylic acids such as p-oxyethoxybenzoic acid and p-oxybenzoic acid, trimellitic acid, trimezic acid, and pyromellitic acid. A small proportion of trivalent or higher polycarboxylic acids such as acids can be included.

In the present invention, the aromatic carboxylic acids mentioned at the beginning should not amount to 85 mol% of the total acid component.
In other words, the acid component other than the aromatic dicarboxylic acid accounts for 15 to 100 mol% of the total acid component. When the aromatic dicarboxylic acid content in all the acid components is 85 mol% or more, the flexibility of the coating film,
In particular, it does not reach a satisfactory level at low temperature, which deteriorates the workability of the precoated steel sheet.

As the alcohol component, the bisphenol S alkylene oxide adduct represented by the above formula is used as an essential component, and in addition, 1,2-propanediol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol. , 2,3-butanediol, 1,2-pentanediol, 2,3-pentanediol, 1,4-pentanediol, 1,4-hexanediol, 2,5-hexanediol, 3-methyl-1,5 -Pentanediol,
Aliphatic glycols having side chains such as 1,2-dodecanediol and 1,2-octadecanediol, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6 A diol other than the bisphenol S alkylene oxide adduct such as hexane diol, diethylene glycol, triethylene glycol, 1,4-cyclohexane diol, 1,4-cyclohexane dimethanol, and bisphenol A alkylene oxide adduct and a branched chain aliphatic glycol. Can be used. Further, the alcohol component may contain a small proportion of a polyhydric alcohol having 3 or more valences such as trimethylolethane, trimethylolpropane, glycerin and pentaerythritol.

In the present invention, in all alcohol components,
The above-mentioned bisphenol S alkylene oxide adduct constitutes 20 to 100 mol%, and when present, the branched chain aliphatic glycol should not exceed 30 mol%. When the amount of the bisphenol S alkylene oxide adduct is less than 20 mol%, a cured coating film having satisfactory flexibility and stain resistance, especially at low temperatures, is not formed. When the branched chain aliphatic glycol exceeds 30 mol%, the flexibility of the cured coating film at low temperature is not satisfied.

The polyester resin can be obtained by polycondensing the above-mentioned acid component and alcohol component according to a conventional method at a ratio and conditions at which a polyester having a molecular weight of at least 500, usually 2,000 to 25,000 can be obtained.

Examples of aminoaldehyde resins include melamine, urea, acetoguanamine, benzoguanamine,
Examples thereof include condensates of amine components such as stearoganamin and spiroguanamine with aldehyde components such as formaldehyde, paraformaldehyde, acetaldehyde and glyoxal, and etherified products thereof with a lower alkanol such as butanol and methanol. Melamine formaldehyde resin and its etherified products are common.

The blocked polyisocyanate compound is
Tolylene diisocyanate, xylylene diisocyanate, polymethylene polyphenylene polyisocyanate,
It is a polyisocyanate compound such as hexamethylene diisocyanate and isophorone diisocyanate blocked with a free isocyanate function by a blocking agent well known in the art. Blocked products such as non-yellowing hexamethylene diisocyanate and isophorone diisocyanate are preferred. Examples of commercially available products include Coronate 2515 manufactured by Nippon Polyurethane Industry Co., Ltd., Barnock D-550 manufactured by Dainippon Ink and Chemicals Inc., Takenate R-815M manufactured by Takeda Pharmaceutical Co., Ltd., Aditel UXL-80 manufactured by Hoechst Co., Ltd. There is.

The blending ratio of the polyester resin to the aminoaldehyde resin and / or the blocked polyisocyanate compound is 95 to 50/5 to 50, preferably 90 to 60/10 to 40 in terms of solid content weight ratio. When the aminoaldehyde resin and / or the blocked polyisocyanate compound is insufficient, the curability is deteriorated and the coating film hardness, stain resistance and solvent resistance are insufficient, and when it is used excessively, the workability is not satisfied.

The coating composition of the present invention is generally used in the form of being dissolved in an organic solvent. Examples of the organic solvent include toluene, xylene, Solvesso 100, Solvesso 15
0, ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, butanol, octanol, diacetone alcohol, carbitol acetate, methoxybutyl acetate, etc. can be selected in consideration of solubility and evaporation rate.

The coating composition of the present invention thus obtained exerts sufficient performance just by directly applying it to a galvanized steel sheet and baking it, but especially for applications requiring corrosion resistance. Apply the primer in advance,
It is preferable to employ the 2-coat 2-bake system.

The coating composition of the present invention may, of course, contain a coloring pigment such as titanium dioxide or an extender pigment, and various additives depending on the purpose and application. Alternatively, a system containing an aminoaldehyde resin is a system containing a blocked polyisocyanate compound with an acid catalyst such as dodecylbenzene sulfonic acid or its amine salt, paratoluene sulfonic acid or its amine salt, and phosphoric acid monoalkyl ester. Alternatively, a tin-based catalyst such as dibutyltin oxide may be included.

In preparing the coating composition, a usual dispersing machine such as a sand grind mill, a ball mill, a blender or a kneader can be used. For the coating, roll coating, curtain flow coating, airless spray coating, electrostatic spray coating and other ordinary coating methods are used, and cold-rolled steel sheet, galvanized steel sheet, aluminum-zinc plated steel sheet, stainless steel sheet, tin plate, etc. A wide range of coating applications such as baking on aluminum plates, indoor equipment such as audio equipment, refrigerators, washing machines, heaters and other electrical equipment, partitions, curtain rails and other indoor building materials, metal embossed boards, and high-performance building materials. Suitable for

The baking temperature of the coating composition of the present invention may be appropriately selected depending on the size and thickness of the steel sheet, the capacity of the baking furnace, the curability of the coating, and the like. Hereinafter, the present invention will be illustrated by examples and comparative examples. In them, "parts" and "%" are by weight unless otherwise specified.

Synthetic Example 4.0 moles of terephthalic acid, 4.0 moles of isophthalic acid, 2.0 moles of adipic acid, 2 moles of bisphenol S ethylene oxide adduct (BSE-20 manufactured by Sanyo Kasei Co., Ltd.)
0 mol, 4.0 mol of 1,6-hexanediol and 6.0 mol of ethylene glycol were placed in a reaction vessel, and dibutyltin oxide was added as a polymerization catalyst in an amount of 0.05% with respect to the total amount charged. The esterification reaction was performed over time. Next, 1mmH over 1 hour
decompress to g, and further under reduced pressure of 0.3 mmHg at 260 ° C
The reaction was continued for 3 hours to obtain the polyester resin of A in Table 1. According to the above procedure, polyester resins B to O in Table 1 and P to Y in Table 2 were produced in the same manner.

[Table 1]

[Table 2] Note 1) Bisphenol S ethylene oxide 2 mol adduct Note 2) Bisphenol S ethylene oxide 4 mol adduct

Examples 1 to 15 and Comparative Examples 1 to 10 Polyester resins A to Y were dissolved in cyclohexanone to a concentration of 40%, and then each resin solution 200
Part, Sumimar M40S (Sumitomo Chemical Co., Ltd. methylated melamine resin, nonvolatile content 80%) 25 parts, Taipaque CR-9
7 (Titanium dioxide pigment manufactured by Ishihara Sangyo Co., Ltd.) 100 parts, Catalyst 6000 (dodecylbenzene sulfonic acid solution manufactured by Mitsui Toatsu Co., Ltd.) 1 part, Cyclohexanone / Solvesso 150
115 parts of (1: 1) mixed solvent was placed in a container, stirred and mixed until uniform, transferred to a paint shaker, and dispersed for 1 hour. Each paint was applied by a roll coater to a zinc-plated steel sheet having a thickness of 0.5 mm, which had been previously treated with zinc phosphate, and baked at 250 ° C. for 1 minute to obtain a coated galvanized steel sheet having a dry film thickness of 16 μ. The coating film performance of each coated steel sheet is shown in Tables 3 and 4.

Examples 16 to 30 and Comparative Examples 11 to 20 Polyester resins A to Y were dissolved in cyclohexanone to a concentration of 40%, and then each resin solution 200
Parts, Sumimar M40S (Sumitomo Chemical Co., Ltd. methylated melamine resin, nonvolatile content 80%) 12.5 parts, Coronate 25
15 (manufactured by Nippon Polyurethane Company, blocked polyisocyanate, non-volatile content 80%) 12.5 parts, Typake CR
-97 (Titanium dioxide pigment manufactured by Ishihara Sangyo Co., Ltd.) 100 parts, Catalyst 6000 (dodecylbenzene sulfonic acid solution manufactured by Mitsui Toatsu Co., Ltd.) 1 part, cyclohexanone / Solvesso 1
Take 115 parts of 50 (1: 1) mixed solvent in a container, stir to mix until uniform and transfer to a paint shaker,
Dispersed for 1 hour. Each paint was applied by a roll coater to a zinc-plated steel sheet having a thickness of 0.5 mm, which had been previously treated with zinc phosphate, and baked at 250 ° C. for 1 minute to obtain a coated galvanized steel sheet having a dry film thickness of 16 μ. The coating film performance of each coated steel sheet is shown in Table 5.
And shown in Table 6.

Examples 31 to 45 and Comparative Examples 21 to 30 Polyester resins A to Y were dissolved in cyclohexanone to a concentration of 40%, and then each resin solution 200 was prepared.
Part, Coronate 2515 (blocked polyisocyanate made by Nippon Polyurethane Company, non-volatile content 80%) 25 parts, Taipaque CR-97 (titanium dioxide pigment made by Ishihara Sangyo Co., Ltd.)
100 parts, cyclohexanone / Solvesso 150 (1:
1) 115 parts of the mixed solvent was placed in a container, stirred and mixed until uniform, transferred to a paint shaker, and dispersed for 1 hour. Each paint was previously treated with zinc phosphate to a thickness of 0.
Apply to a 5mm galvanized steel plate with a roll coater and
It was baked at 50 ° C. for 1 minute to obtain a coated galvanized steel sheet having a dry film thickness of 16 μm. The coating film performance of each coated steel sheet is shown in Table 7 and Table 8.
Shown in.

Coating Film Evaluation Method Hardness (Pencil Hardness): The coated surface on the steel sheet is JIS S-6
JIS-K-54 using the high-grade pencil specified in 006.
00 was measured. Flexibility: The coated steel sheet was bent 180 degrees, cracks generated in the bent portion were determined, and the minimum T number that did not cause the cracks was noted. 2T means a case where two sheets having the same plate thickness are sandwiched at the time of bending. Stain resistance: Oil-based ink (red) coated surface 0.5 cm x 2 cm
The sample was applied to the test piece, left standing at 20 ° C. for 24 hours, and then wiped off with ethanol-impregnated gauze to measure the degree of stain. ○: good, △: slightly bad, ×: bad Gloss (vividness): 60 ° reflectance was measured.

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

[Table 5]

[0027]

[Table 6]

[0028]

[Table 7]

[0029]

[Table 8]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location C08L 67/02 LPK 8933-4J C09D 175/06 PHQ 8620-4J

Claims (2)

[Claims] 1. A. In the acid component in which the proportion of the aromatic dicarboxylic acid in the total acidic component is less than 85 mol%, and in the total alcohol component, the formula: (In the formula, R is hydrogen or a methyl group, and n and m are 1 to 8
Means an integer of. 20% to 100% by mole of the bisphenol S alkylene oxide adduct of 4) and an alcohol component in which the proportion of the aliphatic glycol having a side chain is less than 30% by mole, and a polyester resin as a condensation product as a solid content. 95-50 parts by weight, B.I. A polyester-based coating composition comprising an aminoaldehyde resin and / or a blocked polyisocyanate in a solid content of 5 to 50 parts by weight. 2. A coated steel sheet obtained by baking coating the polyester coating composition according to claim 1.