JP2892357B2 - Paint composition for painted steel sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a coating composition for producing a coated steel sheet usually called PCM (pre-coated metal).

2. Description of the Related Art Painted steel sheets (PCM) are widely used in industrial and consumer applications.

Paint for PCM is required to have properties such as press workability, adhesion to steel sheets, corrosion resistance, and solvent resistance.

Conventionally, alkyd resins, acrylic resins or polyester resins have been used as paints for PCM. As a reference when a polyester resin is used, see
JP-A-54-16537, JP-A-54-16538, JP-B-62
No. 5467 (JP-A-56-167767).

In particular, JP-B-62-5467 discloses that (1) a dicarboxylic acid containing at least 70 mol% of an aromatic dicarboxylic acid; (Wherein, R ₁ and R ₂ are hydrogen or a methyl group, and m and n are each a number of 1 or more and at the same time satisfy 2 ≦ m + n ≦ 6). Propylene oxide adduct 20-100
Mole% and an aliphatic glycol having about 2 to 6 carbon atoms
It is disclosed that a polyester resin consisting of mol% is used as a paint for PCM.

Problems to be Solved by the Invention Alkyd resins used as paints for PCM are inherently poorly flexible, so they are one of the important properties even if other required properties are satisfied. There is room for improvement in the bending workability during press working.

In this regard, PCM coatings using polyester resins are of interest because the lack of flexibility, which is a disadvantage of alkyd resins, has been improved, but pigment dispersibility is not always good, and thick film coating is not possible. There is also a problem that it is not easy.

In this regard, the polyester resin described in Japanese Patent Publication No. Sho 62-5467 described above has a well-balanced property as a paint for PCM as compared with other resins, but the bending workability during press working, especially There is a strong demand to further increase the corrosion resistance of the processed part.

The present invention has been made in view of the above circumstances, and has as its main object to provide a polyester-based coating material having further improved properties as a coating material for PCM, especially workability and corrosion resistance.

Means for Solving the Problems The coating composition for a coated steel sheet of the present invention comprises an acid component having an aromatic dicarboxylic acid (or an ester thereof) as an essential component and a glycol component, and 10 to 60 of the glycol component.
Mol% is a general formula Wherein R is an alkylene group having 2 to 3 carbon atoms, m and n are 1
The above number is a low alkylene oxide adduct of bisphenol A represented by 2 ≦ m + n ≦ 4), and 0.5 to 10 mol% of the glycol component is represented by the general formula: (Wherein, R is an alkylene group having 2 to 3 carbon atoms, p and q are 1
The saturated polyester (X) having a reduced viscosity of 0.2 to 0.75 dl / g and comprising an alkylene oxide adduct of bisphenol A represented by 7 ≦ p + q ≦ 16) represented by 7 ≦ p + q ≦ 16), and an alkyl etherified formaldehyde resin (Y) And characterized by the following.

 Hereinafter, the present invention will be described in detail.

<Saturated polyester (X)> The saturated polyester (X) is composed of an acid component having an aromatic dicarboxylic acid (or an ester thereof) as an essential component and a glycol component.

Acid component As aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, phthalic anhydride, phthalic acid, 1,4-naphthalic acid, 1,5-naphthalic acid, diphenic acid, 4,4′-oxybenzoic acid, diglycol Acid, 4,4'-sulfonyldibenzoic acid, 2,5-naphthalenedicarboxylic acid and the like are used,
Use of terephthalic acid is particularly preferred from the viewpoint of coating film properties. As the ester of the aromatic dicarboxylic acid, one having 1 carbon atom
About to 4 alkyl esters, usually methyl esters, are used.

The proportion of the aromatic dicarboxylic acid (or ester thereof) in the acid component is desirably 40 mol% or more. Most preferably, the proportion of terephthalic acid (or its ester) in the acid component is 40 to 100 mol%, and the balance is other aromatic dicarboxylic acids (or its esters).
Is the case.

In addition to aromatic dicarboxylic acids (or their esters),
Tetrahydrophthalic anhydride, 2,5-norbornanedicarboxylic acid, heptic acid, oxalic acid, malonic acid, dimethylmalonic acid, succinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, dodecanedicarboxylic acid, pimelic acid , Suberic acid, azelaic acid, sebacic acid, 1,3-
Cyclohexanedicarboxylic acid and esters thereof can also be used in combination. In addition, a carboxylic acid having three or more functional groups, for example, trimellitic acid, pyromellitic acid, butanetetracarboxylic acid, and the like can be used in a small amount. Further, a small amount of unsaturated dicarboxylic acid such as maleic anhydride, maleic acid, itaconic anhydride, itaconic acid, fumaric acid and the like can be used in combination.

Glycol Component The first essential component of the glycol component constituting the saturated polyester (X) is represented by the general formula Wherein R is an alkylene group having 2 to 3 carbon atoms, m and n are 1
The above number is a low alkylene oxide adduct of bisphenol A represented by 2 ≦ m + n ≦ 4), and its proportion in the glycol component is set in the range of 10 to 60 mol%. If the proportion is out of this range, it has a negative effect on the balance of properties as a paint for PCM.

The second essential component of the glycol component constituting the saturated polyester (X) has a general formula (Wherein, R is an alkylene group having 2 to 3 carbon atoms, p and q are 1
In the above number, bisphenol A is a highly adduct of alkylene oxide represented by 7 ≦ p + q ≦ 16), and its proportion in the glycol component is set in the range of 0.5 to 10 mol%. If the ratio is out of this range, it also has a negative effect on the balance of properties as a paint for PCM.

The balance of the glycol component is normal aliphatic diols, such as ethylene glycol, diethylene glycol,
Triethylene glycol, polyethylene glycol, 1,
2- or 1,3-propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,3-, 1,4- or 2,3-butylene glycol, 1,5-pentanediol, 1,6-hexane Diol,
2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, polytetramethylene glycol, bisphenol A, hydrogenated bisphenol A, etc. are used. . A small amount of a trifunctional or more functional alcohol such as trimethylolethane, trimethylolpropane, glycerin, 1,3,6-hexanetriol, pentaerythritol, and bisphenoldioxypropyl ether can also be used.

Saturated polyester (X) The ratio between the acid component and the glycol component is usually set to be approximately equimolar, but either one can be used in a slight excess.

The saturated polyester (X) is produced by condensing the above components in an inert gas atmosphere at a temperature of about 150 to 250 ° C. in a conventional manner, and further performing polycondensation at about 220 to 280 ° C. under reduced pressure. As the condensation reaction catalyst, dibutyltin oxide, zinc acetate, or the like is used. As the polycondensation reaction catalyst, antimony trioxide, germanium oxide, tetrabutyl titanate, dibutyltin oxide, or the like is used. The polycondensation reaction catalyst can be added together with the condensation reaction catalyst during the condensation reaction.

The saturated polyester (X) has a reduced viscosity of 0.2 to 0.75 dl /
It is necessary to determine the condensation conditions and the polycondensation conditions so that the value of g is obtained. If the conditions are outside these ranges, optimal results cannot be obtained. For example, if the reduced viscosity is less than 0.2 dl / g, the flexibility of the coating film is impaired, and the film cannot sufficiently withstand a high degree of bending or deep drawing.

<Alkyl etherified formaldehyde resin (Y)> As the alkyl etherified formaldehyde resin (Y), a melamine-based compound is useful.

Examples of the melamine-based compound include melamine and derivatives thereof, for example, those in which most of the hydrogen of a free amino group is substituted with a methylol group, such as hexamethylol melamine,
And alkoxymethyl melamine having 1 to 6 carbon atoms, that is, the above-mentioned hexamethylol melamine obtained by alkoxylating most of the methylol groups, such as hexamethoxymethyl melamine, hexaethoxymethyl melamine, hexapropoxymethyl melamine, hexabutoxymethyl melamine, Hexapentyloxymethyl melamine, hexahexyloxymethyl melamine, or a mixed etherified melamine obtained by combining these two types can be used.

In the case of hexamethoxymethylmelamine, for example, in the case of hexamethoxymethylmelamine, hexamethylolmelamine obtained by reacting melamine with formaldehyde is etherified with methanol, and most of it is converted to a methoxymethyl group.

In addition to the above, a methyl ether compound or a butyl ether compound of metronated benzoguanamine can also be used.

The alkyl etherified formaldehyde resin (Y) is
Each may be used alone, or two or more kinds may be used in combination.

<Blending ratio> The blending ratio of the alkyl etherified formaldehyde resin (Y) to 100 parts by weight of the saturated polyester (X) is as follows:
It is desirable that the content be 5 to 45% by weight, particularly 10 to 35% by weight. If the compounding ratio of the alkyl etherified formaldehyde resin (Y) is not too small, the solvent resistance and stain resistance of the coating film will be reduced, while if the compounding ratio is too large, the coating film will be too hard, resulting in press working. It cannot withstand the high bending and deep drawing at the time.

<Coating method> The coating composition of the present invention is composed of a blend of the above-mentioned saturated polyester (X) and alkyl etherified formaldehyde resin (Y). When coating on a steel sheet, toluene, xylene, methyl ethyl ketone is used as a solvent. , Methyl isobutyl ketone, cyclohexanone, isophorone, methyl cellosolve, butyl cellosolve, cellosolve acetate, butyl cellosolve acetate, carbitol, ethyl carbitol acetate, butyl carbitol acetate, methanol, isopropanol, butanol, octanol, diacetone alcohol, ethyl acetate, butyl acetate Dissolved in a solvent such as petroleum ether, petroleum naphtha or the like at an appropriate concentration.

In this case, fillers (calcium carbonate, kaolin, clay, alumina, silica, titanium oxide, talc, barium sulfate, lithopone, mica, gypsum, perlite, dolomite, etc.) generally used in paints, coloring agents ( Bengala, manganese blue, carbon black, iron black, ultramarine blue, chrome yellow, chrome green, aniline black, cyanine blue, phthalocyanine blue, quinacridone red, etc., rust preventive pigments (strontium chromate, etc.), leveling agents (silicone, cellulose) Acetate butyrate, etc.), a curing catalyst (p-toluenesulfonic acid and its salt, monoalkyl phosphate, curing catalyst for melamine resin, etc.) and the like are blended as required.

As a coating method, various methods such as a spray coating method, a roll coating method, a flow coating method, an electrostatic coating method, an electrodeposition coating method, and a dip coating method are employed.

Action and Effects of the Invention The coating composition for PCM of the present invention has a PCM
Properties required for paint for coating (bending workability during press working,
It has a good balance of adhesion to steel sheets, corrosion resistance, moisture resistance, and solvent resistance).

Furthermore, the combined use of the low addition product (I) and the high addition product (II) of the alkylene oxide of bisphenol A in the above-mentioned ratios improves the workability in particular, and the corrosion resistance of the processed portion is remarkably improved. It can fully respond to market demands.

EXAMPLES Next, the present invention will be further described with reference to examples. Hereinafter, “parts” and “%” are expressed on a weight basis, excluding the reflection gloss retention (%).

The reduced viscosity was 0.1 g of the saturated polyester in a volume ratio of phenol to tetrachloroethane of 6 to 4 in a mixed solvent of 25 ml.
And measured at 30 ° C.

<Production of Saturated Polyester (X)> Production Example 1 166.4 parts of terephthalic acid, 166.4 parts of isophthalic acid, and ethylene oxide 2 of bisphenol A were placed in a reaction vessel equipped with a stirrer, a rectification column, a nitrogen inlet tube, a vacuum device, and a thermometer. Mole adduct (New Pole, manufactured by Sanyo Chemical Industries, Ltd.)
BPE20) 121.7 parts, 8 mol of ethylene oxide adduct of bisphenol A (BA-8 glycol manufactured by Nippon Emulsifier Industry Co., Ltd.) 49.0 parts, 155.2 parts of ethylene glycol, and 0.15 part of di-n-butyltin oxide as a reaction catalyst,
0.15 parts of antimony trioxide was charged and an esterification reaction was carried out from 160 ° C. to 240 ° C. for 5 hours. Subsequently, the pressure was reduced to 1 mmHg over 30 minutes, and further reduced to 0.1 to 0.8 mmHg under 220 to 220 mmHg.
The polycondensation reaction was performed at 280 ° C. for 2 hours. Thereby, a pale yellow transparent saturated polyester having a reduced viscosity of 0.56 dl / g was obtained.

The composition of this saturated polyester was analyzed by NMR, atomic absorption, gas chromatography and the like. The results are shown in Table 1.

Production Examples 2 to 10 According to Production Example 1, saturated polyesters having the compositions and reduced viscosities shown in Table 1 were produced.

 The results are shown in Table 1.

Comparative Production Examples 1 to 6 According to Production Example 1, saturated polyesters having the compositions and reduced viscosities shown in Table 1 were produced.

The results are shown in Table 1. The units of the acid component and the glycol component in Table 1 are “mol”.

When Comparative Production Examples 1 to 4 lack the alkylene oxide high adduct of bisphenol A represented by the general formula (II), Comparative Production Examples 5 to 6 include the low adduct represented by the general formula (I) and the general formula (I) This is the case where the ratio of the latter high-addition product is excessive although the high-addition product shown in (II) is used in combination.

<Preparation of Paint> Example 1, Examples 4 to 10, Comparative Examples 1 to 6 The saturated polyester obtained above was used in a weight ratio of cyclohexanone / solvesso # 150 (aromatic solvent manufactured by Esso Standard Oil Co.) / Isophorone. Dissolved in a mixed solvent of 50/30/20 to make a solution with a non-volatile content of 40%. Using this solution, mix each component according to the following formulation and disperse and knead in a disper for 1 hour to obtain a coating composition for PCM. Was prepared.

Example 2 In place of methyl etherified methylolmelamine, Sumimal M504C manufactured by Sumitomo Chemical Co., Ltd. (nonvolatile content: 96%)
Was used in the same manner as in Example 1 except that 15 parts of was used to prepare a coating composition for PCM.

Example 3 Instead of methyl etherified methylol melamine, Nikarac MS-11 manufactured by Nippon Carbide Industry Co., Ltd.
PCM in the same manner as in Example 1 except that 15 parts of 60%) were used.
A coating composition for use was prepared.

<Coating test> The PCM coating composition prepared above was dried on a 0.3 mm thick zinc phosphate treated mild steel plate (Bond # 144 treated plate manufactured by Japan Test Panel Co., Ltd.) to a dry film thickness of 17 to 20 μm. So that the final temperature of the mild steel sheet is 230 ° C.
Baking was performed with a hot air drier for 2 seconds.

With respect to the obtained coated steel sheet (PCM), physical properties of the coating film were measured by the methods described below. The results are shown in Table 2 below.

<Measurement of physical properties of coating film> Gloss 60 ° -60 ° Reflective gloss retention was measured.

Pencil hardness The coated surface of the coated steel plate was measured using a high-grade pencil specified in JIS S-6006 in accordance with JIS K-5400.

Workability (T-bend workability) Insert a mild steel plate of the same thickness as the test piece in the bent part bent to about 2φ mandrel, and perform final scissor bending using a vice, until cracks do not enter the bent part. Workability was evaluated by the number of sandwiched plates. nT for n sheets
It was expressed as

The determination of cracks was made by observing the bent portion with a 30-power loupe.

Corrosion resistance According to JIS K-5400 (salt spray test), the state of the flat portion (cross cut portion), the 0T bent portion and the 2T bent portion of the coated steel plate after 1000 hours of the salt spray test was observed.

Continuation of front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C09D 167/00-167/08 C09D 161/00-161/34 C08G 63/00-63/91

Claims (1)

(57) [Claims] 1. An acid component comprising an aromatic dicarboxylic acid (or an ester thereof) as an essential component and a glycol component, wherein 10 to 60 mol% of the glycol component is represented by the general formula: Wherein R is an alkylene group having 2 to 3 carbon atoms, m and n are 1
The above number is a low alkylene oxide adduct of bisphenol A represented by 2 ≦ m + n ≦ 4), and 0.5 to 10 mol% of the glycol component is represented by the general formula: (Wherein, R is an alkylene group having 2 to 3 carbon atoms, p and q are 1
The saturated polyester (X) having a reduced viscosity of 0.2 to 0.75 dl / g and comprising an alkylene oxide adduct of bisphenol A represented by 7 ≦ p + q ≦ 16) represented by 7 ≦ p + q ≦ 16), and an alkyl etherified formaldehyde resin (Y) And a coating composition for a coated steel sheet.