JP3196497B2 - Paint for pre-coated steel sheet, pre-coated steel sheet and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention is applied to the outermost layer of a pre-coated steel sheet requiring high hardness, high workability and high sharpness.
The present invention relates to a thermosetting paint , a precoated steel sheet using the paint, and a method for producing the same. The coated steel sheet obtained by the present invention is suitable for, for example, home appliances and building materials, and may be used for automobiles.

[0002]

2. Description of the Related Art In recent years, steel plates used for home appliances and the like have been coated by a post-coating method in which coating is performed after forming, in order to streamline the coating line, save labor, and reduce environmental issues. It has shifted to the precoat method of forming. The paint used for the precoated steel sheet is required to have a high degree of workability to withstand the forming process when forming the coating film. In addition, paints for pre-coated steel sheets include not only workability but also hardness, stain resistance, chemical resistance, water resistance, corrosion resistance,
Many characteristics such as weather resistance and sharpness are required. Among them, hardness and workability, which are important features, are mutually exclusive properties.
Yes, but the required level is high. Workability here means that the coating film is less damaged in the process of bending, cutting, squeezing, etc. when making various shapes from a flat metal plate, and the elongation and flexibility of the coating film itself The higher the degree, the better. On the other hand, the hardness is desirably as high as possible from the viewpoint of improving the durability of the coating film, but acts in the direction of reducing the workability.

Conventionally, polyester resin and epoxy resin have been mainly used as the undercoat paint for the outer surface and the backcoat material as the paint for the precoated steel sheet, and polyester, acrylic and vinyl paints have been used as the outer paint. ing. The most common outer surface top coating is a polyester resin coating composed of a combination of a polyester resin (main component) and a melamine compound (curing agent). In this case, the polyester resin provides workability and the melamine compound obtains hardness. I have. However, the performance of pre-coated steel sheets, which are strictly required, is not always sufficient, especially for home appliances, and improvements have been desired.

For example, Japanese Patent Application Laid-Open No. Sho 59-11370 discloses that terephthalic acid, isophthalic acid, and aliphatic dicarboxylic acid are used as acid components, and ethylene glycol and neopentyl glycol are used as glycol components. There is disclosed a coating resin composition in which different kinds of linear polyesters are combined and further blended with a methoxymelamine compound and a butoxymelamine compound.

JP-A-62-195057 discloses a urethane polymer in which a urethane bond is contained in a resin obtained by polycondensing a copolymerized polyester resin having a hydroxyl group and a polyisocyanate compound, a copolymerized polyester resin having a hydroxyl group, A coating composition for a precoated steel sheet comprising an alkyletherified melamine resin is disclosed.

[0006] Japanese Patent Application Laid-Open No. 209997/1990 discloses an acid component having an aromatic dicarboxylic acid (or an ester thereof) as an essential component and a glycol component composed of a low addition product and a high addition product of an alkylene oxide of bisphenol A. A coating composition for a coated steel sheet comprising a saturated polyester resin and an alkyl etherified formaldehyde resin is disclosed.

Japanese Unexamined Patent Publication (Kokai) No. 62-236817 discloses a paint comprising a polyester polyol containing an alicyclic glycol such as 1,4-cyclohexanedimethanol as a glycol component and a blocked prepolymer having a terminal NCO group. Useful resin compositions are disclosed.

JP-A-63-108081 discloses a polyester polyol comprising an aromatic dicarboxylic acid containing terephthalic acid as an acid component and an aliphatic carboxylic acid and a polyol component comprising ethylene glycol and 1,4-cyclohexanedimethanol as a polyol component. A coating composition comprising a curing agent is disclosed.

Further, in the technique disclosed in Japanese Patent Publication No. 56-18032, the processing strain is relaxed by dispersing rubber particles in an acrylic resin composition.

Further, Japanese Patent Application No. 05-024147 discloses that a polyester resin is reacted with a melamine resin which has been given orientation by modification as a curing agent.
Attempts have been made to obtain a coating film that satisfies both flexibility and coating film hardness at a high level.

[0011]

SUMMARY OF THE INVENTION Japanese Patent Application Laid-Open No. 62-2368
The technique disclosed in Japanese Patent Application Laid-Open No. 17-175173 has insufficient bending workability, and the technique disclosed in Japanese Patent Application Laid-Open No. 63-108081 has insufficient xylol resistance.

Although the technique disclosed in Japanese Patent Publication No. 56-18032 attempts to reduce working strain, it cannot be said that the balance between elongation and hardness as a precoated steel sheet is sufficiently achieved.

According to the technique disclosed in Japanese Patent Application No. 05-024147, the process of synthesizing a modified melamine compound is long, and it has not been possible to produce a practical resin.

As described above, the prior art often attempts to improve the hardness and workability of the coating film by devising the resin as the main component. However, in general, the hardness and workability of a coating film are contradictory, and a coating film having high hardness and excellent workability cannot be easily obtained by the conventional technique.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides an excellent prepainted steel plate paint which satisfies both workability and coating film hardness in a simpler manner than before. The purpose is to gain.

[0016]

Means for Solving the Problems The inventors of the present invention have studied to solve the above-mentioned problems and to obtain a paint for a precoated steel sheet having excellent performance. As a result, the present inventors have found that a polyol is used as a main component and an isocyanate compound and / or an amino resin compound are used. In a paint compounding system as a curing agent, 1,4-cyclohexanedicarboxylic acid or dicarboxylic acid containing lower alkyl ester thereof or lower alkyl ester thereof is converted to alcohol component.
By adding minutes polyester compound obtained by reacting, processability and a high degree of both was found that the coating film that satisfies is obtained at high, it was possible to achieve the above object. Further, in the coating film thus obtained, improvements in not only workability and hardness but also various properties such as weather resistance were observed.

[0017] That is precoated steel sheet coating material of the present invention, the polyester polyol (excluding the following polyester compound (c)), selected from among acrylic polyol
Polyols and main resin (a) and that, the resin of an isocyanate compound and / or an amino resin curing agent (b)
For the composition , the general formula

Embedded image Represented by, a styrene-equivalent number average molecular weight of the polyester compound (c) of 2000 or less , the main resin (a), the curing agent (b)
And the solid content in the polyester compound (c) is 2-3
It is a paint for a pre-coated steel sheet characterized by containing 0 % by weight.

[0018]

Further , the precoated steel sheet of the present invention and its production
The coating method is to apply the above paint on the steel plate surface to form a coating film.
It is characterized by that.

Polyester that can be used in the present invention
The compound (c) is a polyester compound obtained from 1,4-cyclohexanedicarboxylic acid and / or a lower alkyl ester thereof as an acid component and an alcohol component.

Further, a polyester compound in a paint
The compounding amount of (c) depends on the main resin (a), the curing agent (b) and the polyester resin.
The solid content in the tellurium compound (c) is 2 to 30% by weight.
You.

When the blending amount of the polyester compound is within the above lower limit,
When the amount is smaller than the amount, the effect of improving the coating film performance is not remarkable, and the superiority over the comparative material may be slight. On the other hand, the amount of the polyester compound described above
When the amount is larger than the upper limit , the coating film performance, particularly the flexibility, decreases.

The dicarboxylic acid used as the acid component in the present invention is mainly 1,4-cyclohexanedicarboxylic acid and / or its lower alkyl ester, and a part thereof is terephthalic acid, isophthalic acid, naphthalene-2, 6-dicarboxylic acid, naphthalene-2,7-
Dicarboxylic acids can be replaced by such a dicarboxylic acid or lower alkyl esters of dicarboxylic acids, such as diphenyl dicarboxylic acid. Examples of the lower alkyl ester include a methyl ester having 1 to 2 carbon atoms and an ethyl ester. In this case, the main 1,4-cyclohexanedicarboxylic acid accounts for 85 mol% of the whole acid component.
As described above, it is desirable that the proportion of other compounds that can be replaced be less than 15 mol%.

In the present invention, it is used as an alcohol component.
It is primarily diols. As the diol , an aliphatic diol and an alicyclic diol can be used. Ethylene glycol, propylene glycol, 1,
4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, and the like.

These components react with the acid component, and are used in the present invention.
The polyester compound used is produced. This polyester compound can be obtained by a usual polyester production method such as a transesterification method or a direct esterification method. Usually, the acid component and the diol component react at a molar ratio of 1: 2. In order to carry out the reaction efficiently, it is desirable to add the acid component and the diol component in a molar ratio as close as possible to 1: 2.

The molecular weight of the polyester compound is determined by gel permeation chromatography (hereinafter abbreviated as GPC).
Is preferably 2,000 or less, more preferably 1,000 or less, in terms of the number average molecular weight in terms of styrene, as measured by the method described above. When the styrene-equivalent number average molecular weight exceeds 2,000, the effect of the polyol compound is not remarkable, and the appearance, hardness, and processability of the coating film are insufficient.

There is no problem in practicing the present invention even if a trihydric or higher polyhydric alcohol is used in addition to the diol as the alcohol component . Polyhydric alcohols include triethylene glycol, glycerin, pentaerythritol,
Trimethylolpropane, trimethylolethane and the like.

Polyols which can be used as the base resin (a) in the present invention include polyester polyols and acrylic polyols.

The polyester polyol has at least two hydroxyl groups in one molecule and has a number average molecular weight of 10
The compound is not particularly limited as long as it is from 00 to 50,000. Also, this polyester polyol is preferred
The number average molecular weight is from 1500 to 30,000, more preferably from 2,000 to 20,000 . The hydroxyl group in the molecule of the polyester polyol may be at either the terminal or the side chain in the molecule. When the number average molecular weight of the polyester polyol is less than 1,000, processability is significantly reduced. On the other hand, when the number average molecular weight exceeds 50,000, an excessive diluting solvent is required because of high viscosity,
A sufficient coating film cannot be obtained because the proportion of the resin in the coating material decreases. Further, the compatibility with other compounding components is significantly reduced. The number average molecular weight of the polyester polyol is a molecular weight in terms of polystyrene measured by GPC.

The polyester polyol is a copolymer obtained by heating and reacting a polybasic acid component and a polyhydric alcohol component by a known method. As the polybasic acid component, phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic anhydride, maleic acid, adipic acid, fumaric acid and the like can be used. On the other hand, examples of the polyhydric alcohol component include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, and 1,4.
-Butanediol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, glycerin, pentaerythritol, trimethylolpropane,
And trimethylolethane.

Commercially available products such as Almatex (registered trademark of Mitsui Toatsu Chemical Co., Ltd.), alkynol (registered trademark of Sumitomo Bayer Urethane Co., Ltd.), desmophen (registered trademark of Sumitomo Bayer Urethane Co., Ltd.), and Byron (registered trademark of Toyobo Co., Ltd.) Can also be used.

The acrylic polyol has at least two hydroxyl groups in one molecule and has a number average molecular weight of 500 to 500.
There is no particular limitation as long as the compound is 50,000. Also, the preferred number average amount of this acrylic polyol
The number of particles is 1,000 to 30,000, more preferably 1500
~ 20,000 . Hydroxyl groups are randomly arranged in the main chain of the acrylic polyol, and when the number average molecular weight of the acrylic polyol is less than 500, processability is significantly reduced. On the other hand, when the number average molecular weight exceeds 50,000, an excessive dilution solvent is required because of high viscosity, and a sufficient coating film cannot be obtained because the ratio of the resin in the coating material decreases. Further, the compatibility with other compounding components is significantly reduced. The number average molecular weight of the acrylic polyol is a molecular weight in terms of polystyrene measured by GPC.

The acrylic polyol is a copolymer obtained by subjecting an acrylic monomer having a hydroxyl group and an acrylic ester to a heat reaction by a known method. As the acrylic monomer, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, and the like can be used. On the other hand, examples of the acrylate include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, and acrylic acid.
2-ethylhexyl and the like.

Further, commercially available acrylic polyols such as Almatex (registered trademark of Mitsui Toatsu Chemicals, Inc.) and desmophen (registered trademark of Sumitomo Bayer Urethane Co., Ltd.) can also be used.

Polyol (a) and polyester compound
(c) forms a cured coating film by reaction with a curing agent. Polyol (a) and polyester compound (c) used in the present invention
As the curing agent, an isocyanate compound and / or an amino resin can be used.

The isocyanate compound of the present invention includes
An isocyanate compound obtained by a general production method is used. Considering application as a paint for pre-coated steel sheet,
A compound blocked with a blocking agent such as phenol, cresol, aromatic secondary amine, tertiary alcohol, lactam, oxime and the like, which can be used as a one-pack type paint, is desirable. More preferably, non-yellowing hexamethylene diisocyanate (hereinafter abbreviated as HDI) and its derivative, tolylene diisocyanate (hereinafter abbreviated as TDI) and its derivative, 4,4'-diphenylmethane diisocyanate (hereinafter abbreviated as MDI) and Derivatives, xylylene diisocyanate (hereinafter abbreviated as XDI) and its derivatives, isophorone diisocyanate (hereinafter abbreviated as IPDI) and its derivatives, trimethylhexamethylene diisocyanate (hereinafter abbreviated as TMDI) and its derivatives, etc. Can be.

Further, commercially available isocyanate compounds such as Sumidur (registered trademark of Sumitomo Bayer Urethane Co., Ltd.), Desmodur (registered trademark of Sumitomo Bayer Urethane Co., Ltd.) and Coronate (registered trademark of Nippon Polyurethane Co., Ltd.) can also be used.

The ratio (NCO / OH) of the isocyanate group of the isocyanate compound to the hydroxyl group of the polyester compound and the polyol is preferably 0.75 to 1.25 (molar ratio). Preferably 0.85 to 1.15
Is desirable. If the compounding ratio of (NCO / OH) is less than 0.75, the coating film is insufficiently cured, and the expected hardness and strength of the coating film cannot be obtained. When the mixing ratio of (NCO / OH) is more than 1.25, a side reaction occurs between excess isocyanate groups or with urethane bonds, and the processability of the coating film is reduced.

The amino resin used in the present invention includes:
A resin obtained by the reaction of urea, benzoguanamine, melamine, etc. with formaldehyde, and alkyl etherified with an alcohol such as methanol or butanol is also used. Specifically, methylated urea resin, n-butylated benzoguanamine resin, methylated melamine resin,
Examples thereof include an n-butylated melamine resin and an iso-butylated melamine resin.

Further, Cymel (registered trademark of Mitsui Cyanamid Co., Ltd.), Uban (registered trademark of Mitsui Toatsu Chemical Co., Ltd.), Sumimar (registered trademark of Sumitomo Chemical Co., Ltd.), Melan (registered trademark of Hitachi Chemical Co., Ltd.), etc. Commercially available amino resins can also be used.

The compounding weight ratio (solid content ratio) of the amino resin to the polyester resin and the polyol is (polyester resin and polyol) / (amino resin) in the range of 95 to 65 /
It is good to mix at a ratio of 5 to 35, preferably 90 to 75/10 to 25.

The paint is used after being dissolved in an organic solvent.
Examples of the organic solvent include methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, Solvesso 10
0, Solvesso 200, toluene, xylene, methyl cellosolve, butyl cellosolve, cellosolve acetate,
Butyl cellosolve acetate, carbitol, ethyl carbitol acetate, butyl carbitol acetate, ethyl acetate, butyl acetate, petroleum ether, petroleum naphtha and the like.

The paint of the present invention has p-type according to the purpose and use.
Curing catalyst such as toluenesulfonic acid, tin octoate, dibutyltin dilaurate, lead 2-ethylhexoate, and calcium carbonate, kaolin, clay, titanium oxide, talc, barium sulfate, mica, red iron oxide, manganese blue, carbon black, etc. And various additives such as an antifoaming agent and a flow control agent can be selected and blended.

In preparing the coating material , an ordinary dispersing machine or kneading machine such as a sand grind mill, a ball mill, or a blender may be selectively used and blended.

The paint is useful for the production of pre-coated steel sheets, and includes cold-rolled steel sheets, hot-dip galvanized steel sheets, electro-galvanized steel sheets, composite galvanized steel sheets, chrome-coated steel sheets (T
FS) or the like, which has been subjected to a chemical conversion treatment such as a phosphate treatment or a chromate treatment. By coating on the steel sheet that has been subjected to the chemical conversion treatment, the adhesion to the steel sheet is improved and the corrosion resistance is also improved. Also,
At the time of painting, a primer coat to which a rust-preventive pigment is added can be applied to improve the adhesion between the paint and the steel sheet and increase the corrosion resistance. Epoxy or polyester coatings are suitable as such primer coats.

The coating method is not particularly limited. Preferably, it is applied by a method such as roll coater coating or curtain flow coating. After the application, the coating film is baked by a heating means such as hot-air drying, infrared heating, or induction heating to crosslink the resin to obtain a cured coating film. The baking temperature during heat curing is 2
It is carried out at 00 to 250 ° C. for about 40 seconds to 3 minutes. The thickness of the cured coating film thus formed is about 15 to 25 μm, but is not particularly limited.

The present coating material is a two-coat two-bake system or a three-coat system.
It is preferable to use it as a top coat of a coat-3 bake system. 3 If you want to use in the coat-3-bake system, the present
Between paint and primer coat, normal 3 coats / 3
Apply the intermediate coat used in baking.

[0048]

Next, the present invention will be described with reference to examples. In addition,
Parts and% in the examples mean parts by weight and% by weight, respectively, unless otherwise specified.

Synthesis Example 1 of Polyester Compound 1,4-cyclohexanedicarboxylic acid dimethyl ester (trans isomer ratio: 20%, manufactured by Towa Kasei Kogyo Co., Ltd.) was placed in a reaction vessel equipped with a heating device, a stirrer, a rectification column and a thermometer. ) 200 parts, ethylene glycol 130 parts,
0.84 parts of titanium tetra-n-butoxide was charged, and the reaction temperature was gradually increased to 240 ° C.
Over time, 64 parts of methanol was distilled off to complete the reaction. Thus, a polyester compound (1) was obtained. At room temperature (23 ° C.), the polyester compound (1)
It was a white waxy solid and had a number average molecular weight (Mn) of 512 as determined by GPC.

Synthesis Example 2 of Polyester Compound A dimethyl ester of 1,4-cyclohexanedicarboxylic acid (trans isomer ratio: 99%, manufactured by Towa Chemical Industry Co., Ltd.) was placed in a reaction vessel equipped with a heating device, a stirrer, a rectification column, and a thermometer. ) 200 parts, ethylene glycol 130 parts,
0.53 parts of titanium tetra-n-butoxide were charged, and the reaction temperature was gradually increased to 200 ° C.
Over time, 64 parts of methanol was distilled off to complete the reaction. Thus, a polyester compound (2) was obtained. At room temperature (23 ° C.), the polyester compound (2)
It was a white crystalline solid, and the number average molecular weight (Mn) determined by GPC was 326.

Synthetic Example 3 of Polyester Compound A dimethyl ester of 1,4-cyclohexanedicarboxylic acid (trans isomer ratio 20%, manufactured by Towa Kasei Kogyo Co., Ltd.) was placed in a reaction vessel equipped with a heating device, a stirrer, a rectification tower and a thermometer. ) In 200 parts and 1,6-hexanediol in 24
8 parts, 0.53 parts of titanium tetra-n-butoxide were charged, and the reaction temperature was gradually increased to 240 ° C.
It took about 5 hours to distill out 64 parts of methanol to complete the reaction. Thus, a polyester compound (3) was obtained. Compound (3) is a white waxy solid at room temperature (23 ° C.), and has a number average molecular weight (Mn) determined by GPC.
Was 618.

Synthesis Example 4 of Polyester Compound (Comparative Example) In a reaction vessel equipped with a heating device, a stirrer, a rectification tower and a thermometer, 194 parts of dimethyl terephthalate (hereinafter abbreviated as DMT) and 130 parts of ethylene glycol were added. Put, 180
Heated and melted at ℃. Thereafter, 0.074 part of manganese acetate was added as a catalyst, and the reaction temperature was gradually increased to 220 ° C. When 64 parts of methanol was distilled off, 0.042 part of trimethyl phosphate was added to terminate the reaction. Thus, a polyester compound (4) was obtained. Polyester compound (4) was a white solid at room temperature (23 ° C.), and had a reduced viscosity of 0.04 dl / g. The reduced viscosity was determined by using a sample of phenol / tetrachloroethane (60 /
(40 weight ratio) and measured at 25 ° C. using an Ubbelohde viscometer.

Synthesis Example 1 of Polyester Polyol 174.6 parts of DMT, 213.4 parts of dimethyl isophthalate and 933.4 parts of ethylene glycol were placed in a reaction vessel equipped with a heating device, a stirrer, a rectification column, a decompression device, and a thermometer. .
0 parts, 52.0 parts of neopentyl glycol and 1.5 parts of a manganese acetate catalyst, and 180 to 21 in a nitrogen atmosphere.
Transesterification was carried out at 0 ° C. to distill off methanol. Further, 6.1 parts of trimethylolpropane was added,
While heating to 250 ° C., the polymerization reaction was performed by gradually reducing the pressure to 10 mmHg, and a cyclohexanone solvent was used.
The nonvolatile content was adjusted to 70%. Thus, a polyester polyol (1) was obtained. The obtained polyester polyol (1) had a number average molecular weight (Mn) determined by GPC of 3000, and a hydroxyl value determined by a phthalic anhydride-pyridine method of 60.0 mgKOH / g.

Synthesis Example 2 of Polyester Polyol Synthesis was performed in the same manner as in Synthesis Example 1 of Polyester Polyol while changing the polymerization reaction time to obtain Polyester Polyol (2). Obtained polyester polyol (2)
Has a nonvolatile content of 60%, a number average molecular weight (Mn) determined by GPC of 4000, and a hydroxyl value determined by a phthalic anhydride-pyridine method of 45.0 mgKOH / g.

Examples 1-3 The polyester compounds (1) obtained in the synthesis example 1 of the polyester compound, the polyester polyols (1) obtained in the synthesis example 1 of the polyester polyol, with the formulations shown in Examples 1 to 3 of Table 1, Blocked isocyanate (Desmodur B
L3175: HDI, manufactured by Sumitomo Bayer Urethane Co., Ltd.
Isocyanurate, NCO content 11.1%, nonvolatile content 75%), rutile-type titanium oxide, dibutyltin dilaurate (hereinafter abbreviated as DBTDL) 10% cyclohexanone solution, Acronal 4F (manufactured by BASF Corporation) 50
% Cyclohexanone solution, and then dispersed for 1 hour using a sand mill containing glass beads having a diameter of about 1 mm. Further, by adding cyclohexanone, the nonvolatile content becomes 60%.
% To obtain a paint. The resulting paint is
Electrogalvanized steel sheet (thickness: 0.5 m) with chromate treatment and polyester-based primer (4 μm thickness)
m) was coated with a bar coater so as to have a dry film thickness of 15 to 18 μm, and baked in a hot air drying furnace at 230 ° C. for 50 seconds. Thus, a precoated steel sheet was obtained. The coating performance of the obtained precoated steel sheet was evaluated by the method described below. These Examples 1-3 Ri example der of changing the blending ratio of the polyester compound (1), a resin component
The amount of the polyester compound (1) in Example 1, 2, 3
5.0% by weight, 10.0% by weight, 22.0% by weight
%. Table 1 shows the results.

Examples 4 and 5 Coatings were prepared according to the formulations shown in Examples 4 and 5 in Table 1.
Examples 4 and 5 are examples in which the polyester compound (1) was used, and the polyol, the curing agent, and the additives and catalysts associated therewith were changed. Of these, Example 4 is an example in which an amino resin is used as a curing agent. Example 5 is an example in which acrylic polyol was used as the polyol. The coating, baking, and evaluation methods of the obtained paint were performed under the same conditions as in Example 1. Table 1 shows the results.

[0057]

[Table 1]

Examples 6 to 11 Coatings were prepared according to the formulations shown in Examples 6 to 11 in Table 2. Examples 6 to 8 are examples in which the polyester compound (2) obtained in the polyester compound synthesis example 2 was used instead of the polyester compound (1) in Examples 1 to 3. Example
9 to 11 are polyester compounds (1) of Examples 1 to 3.
In this example, the polyester compound (3) obtained in Synthesis Example 3 of the polyester compound was used instead of The obtained paint was painted, baked and evaluated under the same conditions as in Example 1. Table 2 shows the results.

[0059]

[Table 2]

Comparative Example 1 99.7 parts of polyester polyol (1) and 4 parts of blocked isocyanate (Desmodur BL3175)
0.3 parts, 80.0 parts of rutile titanium oxide, DBTD
After mixing 10.0 parts of L10% cyclohexanone solution and 4.4 parts of Acronal 4F 50% cyclohexanone solution, they were dispersed for 1 hour using a sand mill containing glass beads having a diameter of about 1 mm. Further, cyclohexanone was added to adjust the nonvolatile content to 60% to obtain a paint . The obtained paint was applied and baked under the same conditions as in Example 1 to evaluate the coating film performance. Table 3 shows the results.

COMPARATIVE EXAMPLES 2 AND 3 Paints were prepared by changing the polyol, the curing agent and the additives and catalysts associated therewith in Comparative Example 1. The coating, baking, and evaluation of the paint were performed under the same conditions as in Example 1. Table 3 shows the results.

[0062]

[Table 3]

Comparative Examples 4 and 5 In Comparative Examples 4 and 5, the amount of the polyester compound (1) was adjusted.
Examples are 0.5 parts (% by weight) and 35 parts ( % by weight) , respectively , and the method of preparing the paint is the same as in Example 1. The coating, baking, and evaluation methods of the obtained paint were performed under the same conditions as in Example 1. Table 4 shows the results.

Comparative Examples 6 to 8 In Comparative Example 6, cyclohexanone was added to 5.0 parts of the polyester compound (4) obtained in Polyester Compound Synthesis Example 4.
0 parts were added and stirred for 12 hours. At this time, the compound (4) used was pulverized to 250 microns or less by a pulverizer. The polyester polyol (1) was added to the cyclohexanone dispersion of the compound (4) thus obtained.
88.4 parts, blocked isocyanate (Desmodur BL3175) 44.2 parts, rutile type titanium oxide 80.0 parts, DBTDL 10% cyclohexanone solution 10.0 parts, acronal 4F50% cyclohexanone solution 4.4 parts. After blending, the mixture was dispersed for 1 hour using a sand mill containing glass beads having a diameter of about 1 mm. further,
Cyclohexanone was added to adjust the nonvolatile content to 60% to obtain a paint . In Comparative Examples 7 and 8, the blending ratio of the polyester compound (4) was changed, and paints were obtained in the same manner. The obtained paint was coated under the same conditions as in Example 1,
Baking was performed and the coating film performance was evaluated. Table 4 shows the results.

[0065]

[Table 4]

Test Method (1) Gloss Based on JIS, K5400, 60 ° specular reflectance (%) was measured. (2) Pencil hardness It was performed based on JIS, K5400 using Mitsubishi Uni. (3) Flexibility (Bending workability) After bending a previously painted steel plate with a bending vise specified in 6.15 (flexibility) of JIS, K5400, n identical sample plates are sandwiched inside, It was bent by a press. The bent portion was observed with a 30-fold loupe, and the minimum number of sandwiches that did not cause cracks in the coating film was evaluated as an evaluation value.
The number is displayed with T added as in T, 2T, 3T. (4) Adhesion (gobang peeling) test 10 minutes at 1 mm intervals on the cured coating film using a cutter knife.
After cutting 100 pieces of squares into a range of mm × 10 mm, the cellophane tape was pressed and peeled off vigorously, the peeled state of the squares was observed, and evaluated by 100− (number of peeled squares). (5) Impact resistance Using a DuPont impact tester, apply a load of 1.0 kg or 1.5 kg to a maximum of 50 cm based on JIS, K5400.
Was dropped on the coating film from the height of the sample, and the value obtained by multiplying the load by the maximum height at which no crack was observed on the coating film surface when observed with a 30-fold loupe was used as the evaluation value. (6) Solvent resistance test Using a gauze impregnated with methyl ethyl ketone, the coating film surface is rubbed under a load of 1.0 kg. One reciprocation was defined as one time, and the number was represented by the number of times until the primer was exposed. However, the upper limit was set to 100 times. (7) Weather Resistance The sunshine weatherometer was used to evaluate the gloss retention (720 ° specular reflectance (%)) after 720 hours.

From the above Examples and Comparative Examples, Examples 1 to 1
The performance of the precoat film obtained from the paint shown in No. 1 is
Comparative Examples 1 to 1 containing no polyester compound having the structure of the above general formula (polyester compounds 1 to 3)
In comparison with No. 3 , the coating film hardness and accelerated weather resistance were improved, and the impact resistance and bending workability were also greatly improved. Also, in comparison with Comparative Examples 6 to 8 including the polyester compound 4 having a terephthalic acid skeleton in place of the polyester compounds 1 to 3, a large difference is observed in the weather resistance and bending workability.

[0068]

As is clear from the above Examples and Comparative Examples, the paint for precoated steel sheet of the present invention has improved coating film hardness and accelerated weather resistance as compared with Comparative Examples, and further has impact resistance and bending work. The sex is also greatly improved. Thus, the paint for a precoated steel sheet of the present invention satisfies both the contradictory properties of workability and coating film hardness, which were the problems of the conventional precoated steel sheet, at a high level, and provides a precoated steel sheet having excellent performance. Can be provided.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-39377 (JP, A) JP-A-52-7729 (JP, A) JP-A-5-17682 (JP, A) JP-A-1- 272517 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09D 1/00-201/10 B05D ⁷ /00-7/26

Claims (5)

(57) [Claims] 1. A polyester polyol (excluding the following polyester compound (c)), the acrylic polyol
A polyol selected from the group consisting of a main resin (a) and an isocyanate compound and / or an amino resin as a curing agent (b)
Relative to the resin composition of the general formula ## STR1 ## Represented by, a styrene-equivalent number average molecular weight of the polyester compound (c) of 2000 or less , the main resin (a), the curing agent (b)
And the solid content in the polyester compound (c) is 2-3
A paint for a pre-coated steel sheet, wherein 0 % by weight is blended. 2. The paint for a precoated steel sheet according to claim 1, wherein the polyester compound (c) has a number average molecular weight in terms of styrene of 1,000 or less. 3. The polyester resin as the main resin (a) is a polyester polyol having at least two hydroxyl groups in one molecule and having a number average molecular weight of 1,000 to 50,000, and the main resin (a). The paint for a pre-coated steel sheet according to claim 1 or 2, wherein the acrylic polyol is an acrylic polyol having at least two hydroxyl groups in one molecule and having a number average molecular weight of 500 to 50,000. 4. A pre-coated steel sheet wherein the paint according to claim 1, 2 or 3 is applied on a steel sheet surface to form a coating film. 5. A method for producing a precoated steel sheet, comprising applying the paint according to claim 1, 2 or 3 on a steel sheet surface to form a coating film.