JP3196496B2 - 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]

BACKGROUND OF THE INVENTION The present invention, high hardness, precoated steel sheets as well as with high processability and thermosetting coating material and the coating material is applied to the outermost layer of the precoated steel sheet high sharpness and the like are required It relates to a manufacturing method. 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 There are many characteristics required for paints for precoated steel sheets, such as high hardness, high workability, stain resistance, chemical resistance, water resistance, and high definition. Hardness and workability is inter alia important feature is the opposite properties to each other
However, the required level is high. Workability here means
Bending when making various shapes from a flat metal plate,
In a process such as cutting or squeezing, it means that the coating film is less damaged, and the larger the degree of elongation and flexibility of the coating film itself, 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, JP-A-59-11370 discloses that terephthalic acid, isophthalic acid, and aliphatic dicarboxylic acid are used as an acid component, and ethylene glycol and neopentyl glycol are used as a glycol component. There is disclosed a coating resin composition in which two kinds of linear polyesters having different compositions are combined and further mixed with a methoxymelamine compound and a butoxymelamine compound.

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

Japanese Unexamined Patent Publication (Kokai) No. 2-209797 discloses a glycol composed of an acid component containing an aromatic dicarboxylic acid (or an ester thereof) as an essential component and a low- or high-alkylene oxide adduct of bisphenol A. There is disclosed a coating composition for a coated steel sheet comprising a saturated polyester resin comprising the above components and an alkyl etherified formaldehyde resin.

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.

Japanese Patent Application Laid-Open No. 3-550544 discloses an acrylic or polyester polymer having a low glass transition point covalently bonded to a mesogen group, which is formed by a reaction with a curing agent such as an amino resin. Is disclosed.

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.

[0010]

Problems to be Solved by the Invention Japanese Patent Publication No. 56-1803
Although the technique disclosed in Japanese Patent Application Publication No. 2002-115699 attempts to alleviate the processing strain, it cannot be said that the balance between the elongation and the hardness of the precoated steel sheet is sufficiently secured.

The technique disclosed in Japanese Patent Publication No. 3-550544 is excellent in hardness and impact resistance, but requires a complicated and complicated process for synthesizing a polymer modified by a mesogen group. Further, it is difficult to apply the composition as a paint for a pre-coated steel sheet from the viewpoint of the coating film composition, the curing conditions, and the like. Furthermore, there is no mention of bending workability.

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.
The present invention has been made in order to solve the above problems, and has as its object to obtain a paint for a pre-coated steel sheet having a good balance between workability and coating film hardness by a simpler method than before. .

[0014]

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, naphthalene-2,6-dicarboxylic acid or a dicarboxylic acid containing a lower alkyl ester thereof or a lower alkyl ester thereof is converted into an alcohol component.
It has been found that by adding a polyester compound obtained by reacting with the above , a coating film satisfying both workability and hardness at a high level can be obtained, and the above object can be achieved. Further, the coating film obtained in this way also improved various properties such as glossiness.

That is, the first invention of the present application relates to a number average molecule.
Polyester polyol with an amount of 1500 to 50,000
(However, excluding the following polyester compound (c)), number average
Acrylic polyol having a molecular weight of 1500 to 50,000
The base resin (a) is a polyol selected from the group consisting of
Anate compound and / or amino resin as curing agent (b)
General formula for the resin composition

Embedded image Polyester compound (c) represented by the main resin (a), hard
It is a paint for a pre-coated steel sheet , wherein 2 to 10% by weight of a solid content in the agent (b) and the polyester compound (c) is blended.

[0016]

The second invention of the present application relates to the first invention.
It is a pre-coated steel sheet, characterized in that to form a coating film by coating the coating material on the steel sheet surface. A third invention of the present application is a method for manufacturing a precoated steel sheet, comprising manufacturing a precoated steel sheet by applying the paint according to the first invention on a steel sheet surface to form a coating film.

Polyester that can be used in the present invention
Compound (c) comprises naphthalene-2,6-dicarboxylic acid and / or a lower alkyl ester thereof as an acid component,
It is a polyester compound obtained from an alcohol component. In addition, blending of polyester compound (c) in paint
Amounts are main resin (a), curing agent (b) and polyester compound
The content of solids in (c) is 2 to 10% by weight. Also,
More preferable compounding amount of the polyester compound (c) is 3 to 8 layers.
%. If the amount is less than the lower limit ,
The effect of improving the performance of the coating film is not remarkable, and the advantage over the comparative material is slight. On the other hand, when the blending amount is larger than the upper limit amount , solubility in a solvent and a polyol,
The compatibility with a curing agent or the like becomes insufficient, and the appearance and performance of the coating film are reduced.

The dicarboxylic acid used as the acid component in the present invention is mainly naphthalene-2,6-dicarboxylic acid and / or its lower alkyl ester, and a part thereof is terephthalic acid, isophthalic acid, or naphthalene-2. , 7-dicarboxylic acid, may also 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 naphthalene-2,6-dicarboxylic acid is preferably at least 85 mol% of the entire acid component, and the proportion of other compounds that can be replaced is desirably 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, an alicyclic diol, or the like can be used. Ethylene glycol, propylene glycol,
1,4-butanediol, 1,6-hexanediol,
Neopentyl glycol, 1,4-cyclohexane dimethanol and the like can be mentioned. Also, polyoxyalkylene glycols, particularly polyoxyalkylene glycols having an average molecular weight of 1200 or less, desirably having an average molecular weight of 1
Polyethylene glycol (hereinafter abbreviated as PEG) of 000 or less or polytetramethylene glycol (hereinafter abbreviated as PTG) having an average molecular weight of 1000 or less can also be used. Further, these may be used as a mixture.

[0021] These components react with the acid component, and 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 polyester compound may be used alone or
Any combination of more than one type can be used.

[0022] The polyester compound, when observed with a polarizing microscope, shows liquid crystallinity. In the coating film containing such a polyester compound, the toughness of the coating film can be attained by the action of the orientation and the like, which are the characteristics of the liquid crystal compound, even in the coating film after baking. As a result, high hardness, high processability of the coating film Re obtain et al
It believed to be that.

In addition, when the PEG or PTG is used,
In this case, it is desirable that the compound formed by the reaction of this with the acid component has a reduced viscosity of 0.20 dl / g or less. When the reduced viscosity exceeds 0.20 dl / g, the solubility in a solvent and the compatibility with a polyol, a curing agent and the like are remarkably reduced, and the coating film performance is insufficient. Note that the reduced viscosity was measured using a sample of phenol / tetrachloroethane (60/40 weight ratio).
And the value measured at 25 ° C. using an Ubbelohde viscometer. For this compound, flexible toughness crosslinking structure by a combination of the polyether chain and rigid naphthalene skeleton is given, as a result, high hardness, high formability of the coating film is considered to be obtained al.

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.

In the present invention, it can be used as the base resin (a).
Polyols 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 gel permeation chromatography (hereinafter abbreviated as 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, polyhydric alcohol components include, for example, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,4
-Butanediol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, glycerin, pentaerythritol, trimethylolpropane,
And trimethylolethane.

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.), Byron (registered trademark of Toyobo Co., Ltd.), etc. 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 acid 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 (b) , an isocyanate compound and / or an amino resin can be used.

As the isocyanate compound, an isocyanate compound obtained by a general production method is used. Pheno which can be preferably used as a one-pack type paint
, Cresol, aromatic secondary amine, tertiary alcohol
Compounds blocked with blocking agents such as lactam, lactam and oxime. By using the blocked isocyanate compound, storage with one liquid becomes possible, and application as a paint for a pre-coated steel sheet becomes possible. 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, referred to as “4,4′-diphenylmethane diisocyanate”)
MDI) and its 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 derivatives thereof.

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 0.8 to 1.2 (molar ratio). Preferably it is 0.90 to 1.10. When the compounding ratio of (NCO / OH) is smaller than 0.8, curing of the coating film is insufficient, and the expected hardness and strength of the coating film cannot be obtained. If the compounding ratio of (NCO / OH) is larger than 1.2, a side reaction between excessive isocyanate groups or a urethane bond occurs, and the processability of the coating film deteriorates.

The amino resin used in the present invention includes:
Resins obtained by the reaction of urea, benzoguanamine, melamine and the like with formaldehyde and those obtained by alkyl etherification with alcohols such as methanol and butanol can be 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.), Sumimar (registered trademark of Sumitomo Chemical Co., Ltd.), Melan (registered trademark of Hitachi Chemical Co., Ltd.)
Commercially available amino resins such as can be used.

The compounding weight ratio (solid content ratio) of the amino resin to the polyester compound and the polyol is (polyester compound and the polyol) / (amino resin) in the range of 95 to 6.
It is good to mix at a ratio of 5/5 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 can 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 floor 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
Perform for about 1-3 minutes at 00-250 ° C. The thickness of the cured coating film thus formed is about 15 to 25 μm, but is not particularly limited.

The present paint 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.

[0045]

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.

Polyester Compound Synthesis Example 1 Dimethyl naphthalene-2,6-dicarboxylate was placed in a reaction vessel equipped with a heating device, a stirrer, a rectification column, and a thermometer.
Ter (hereinafter abbreviated as 2,6-NDCM) is 1.0 mo
1, 2.1 mol of ethylene glycol, 200 ° C
Was heated and melted. Then manganese acetate was added as a catalyst
6-NDCM was added at 0.03 mol%, the reaction temperature was gradually increased to 230 ° C., and when 64 g (2.0 mol) of the theoretical amount of methanol had been distilled off, trimethyl phosphate was added to 2,6 mol%. 0.03mo for 6-NDCM
1% was added to terminate the reaction. Thus, the compound (1)
I got The reduced viscosity was 0.05 dl / g. The onset temperature range of the liquid crystallinity measured by a polarizing microscope was about 130 to 190 ° C. when the temperature was rising, and 140 ° C. to room temperature when the temperature was falling. The measurement method is a method in which a sample is thinly sandwiched between two slide glasses, set on a polarizing microscope equipped with a temperature control function, and observed while heating or cooling under polarized light. The range was defined as a liquid crystal expression range.

Synthesis Example 2 of Polyester Compound A reaction vessel equipped with a heating device, a stirrer, a rectification column and a thermometer was charged with 0.5 mol of 2,6-NDCM and 1.02 mol of 1,4-butanediol, It was heated and melted at 200 ° C. Thereafter, as a catalyst, titanium tetra-n-butoxide was added at 0.06 mol% to 2,6-NDCM, and the reaction temperature was gradually increased to 240 ° C. to obtain a theoretical amount of 32 g (1.0 mol) of methanol. When distilling off, the reaction was terminated. Thus, compound (2) was obtained. The reduced viscosity was 0.04 dl / g. The liquid crystallinity developing temperature range measured using a polarizing microscope in the same manner as in Synthesis Example 1 was about 90 to 180 ° C. when the temperature was rising, and 1 when the temperature was falling.
60 ° C. to room temperature.

Synthesis Example 3 of Polyester Compound In a reaction vessel equipped with a heating device, a stirrer, a rectification column and a thermometer, 0.5 mol of 2,6-NDCM and 1,4-cyclohexanedimethanol (trans 70 %) To 1.0
2 mol was added and the mixture was heated and melted at 200 ° C. Thereafter, titanium tetra-n-butoxide was used as a catalyst in 2,6-ND.
0.06 mol% was added to CM, and the reaction temperature was increased stepwise to 270 ° C. to obtain a theoretical amount of methanol 32.
The reaction was terminated when g (1.0 mol) was distilled off. Thus, compound (3) was obtained. The reduced viscosity was 0.05 dl / g. The liquid crystal development temperature range measured by a polarizing microscope in the same manner as in Synthesis Example 1 was around 140 to 280 ° C. when the temperature was rising, and 240 ° C. to room temperature when the temperature was falling.

Polyester Compound Synthesis Example 4 A reaction vessel equipped with a heating device, stirrer, rectification tower and thermometer was charged with 0.5 mol of 2,6-NDCM and 1.05 mol of neopentyl glycol, and heated at 200 ° C. Melted. Then, calcium acetate was used as a catalyst in 2,6-ND.
0.03 mol% was added to CM, and the reaction temperature was increased stepwise to 240 ° C. to obtain a theoretical amount of methanol 32.
When g (1.0 mol) was distilled off, trimethyl phosphate was added at 0.03 mol% to 2,6-NDCM to terminate the reaction. Thus, compound (4) was obtained.
The reduced viscosity was 0.04 dl / g. The liquid crystallinity manifestation temperature range measured using a polarizing microscope in the same manner as in Synthesis Example 1 was about 100 to 180 ° C. when the temperature was rising, and 19 when the temperature was falling.
0 ° C. to room temperature.

Synthesis Example 5 of Polyester Compound (Comparative Example) In a reaction vessel equipped with a heating device, a stirrer, a rectification tower and a thermometer, 1.0 mol of dimethyl terephthalate (hereinafter abbreviated as DMT), ethylene glycol -2.1m
and melted by heating at 180 ° C. Thereafter, 0.03 mol% of manganese acetate was added to DMT as a catalyst, and the reaction temperature was gradually increased to 220 ° C. When 64 g (2.0 mol) of the theoretical amount of methanol was distilled, phosphoric acid was added. Trimethyl was added to DMT at 0.03 mol
1% was added to terminate the reaction. Thus, compound (5)
I got The reduced viscosity was 0.04 dl / g. The liquid crystallinity developing temperature range measured using a polarizing microscope in the same manner as in Synthesis Example 1 was around 80 to 120 ° C. when the temperature was rising, and was not observed when the temperature was falling.

Synthesis Example 1a of Polyester Compound 0.5 mol of 2,6-NDCM and 1.05 mol of diethylene glycol were placed in a reaction vessel equipped with a heating device, a stirrer, a rectification column and a thermometer, and heated and melted at 200 ° C. . Thereafter, as a catalyst, titanium tetra-n-butoxide was added in an amount of 0.10 mol% with respect to 2,6-NDCM, and the reaction temperature was gradually increased to 240 ° C., and 32 g (1.0 mol) of a theoretical amount of methanol was distilled. The reaction was terminated when it was released. Thus, compound (6) was obtained. The reduced viscosity was 0.05 dl / g.

Polyester Compound Synthesis Example 2a In a reaction vessel equipped with a heating device, stirrer, rectification column, and thermometer, 0.5 mol of 2,6-NDCM and polyethylene glycol having an average molecular weight of 200 (PEG @ 200) were added. 1.02 mol was added, and the mixture was heated and melted at 200 ° C. Thereafter, titanium tetra-n-butoxide was used as a catalyst in 2,6.
0.06 mol% was added to -NDCM, the reaction temperature was gradually increased to 270 ° C, and it took 3 hours from the addition of the catalyst to distill out 30 g of methanol corresponding to 95% of the theoretical amount. Thus, compound (7) was obtained. The reduced viscosity was 0.08 dl / g.

Polyester Compound Synthesis Example 3a 0.5 mol of 2,6-NDCM and polyethylene glycol having an average molecular weight of 600 (PEG @ 600) were placed in a reaction vessel equipped with a heating device, a stirrer, a rectification column and a thermometer. 1.02 mol was added and the mixture was heated and melted at 200 ° C. Thereafter, titanium tetra-n-butoxide was used as a catalyst in 2,6.
0.06 mol% was added to NDCM, the reaction temperature was increased stepwise to 270 ° C., and 4 hours and 10 minutes after the addition of the catalyst, methanol 2 equivalent to 92% of the theoretical amount was added.
9 g were distilled off. Thus, compound (8) was obtained. The reduced viscosity was 0.07 dl / g.

Polyester Compound Synthesis Example 4a In a reaction vessel equipped with a heating device, a stirrer, a rectification column and a thermometer, 0.5 mol of 2,6-NDCM and polytetramethylene glycol having an average molecular weight of 650 (PTG♯65) were added.
0) was added and melted by heating at 200 ° C.
Thereafter, 0.06 mol% of titanium tetra-n-butoxide as a catalyst was added to 2,6-NDCM, and the reaction temperature was gradually increased to 270 ° C., and it took 4 hours from the catalyst addition to reach the theoretical amount. Methanol 3 equivalent to 93%
0 g were distilled off. Thus, compound (9) was obtained. The reduced viscosity was 0.07 dl / g.

Compound Synthesis Example 5a (Comparative Example) In a reaction vessel equipped with a heating device, a stirrer, a rectification column and a thermometer, 0.5 mol of DMT and polytetramethylene glycol having an average molecular weight of 650 (PTG @ 650) 1.
02 mol was added and heated and melted at 170 ° C. Thereafter, titanium tetra-n-butoxide was added as a catalyst in an amount of 0.06 mol% with respect to DMT, and the reaction temperature was gradually increased to 24.
The temperature was raised to 0 ° C., and it took 4 hours and 20 minutes from the addition of the catalyst to distill 29 g of methanol corresponding to 92% of the theoretical amount. Thus, compound (10) was obtained. The reduced viscosity was 0.07 dl / g.

Synthesis Example 1 of Polyester Polyol 174.6 parts of DMT, 213.4 parts of dimethyl isophthalate, ethylene glycol in a reaction vessel equipped with a heating device, a stirrer, a rectification column, a decompression device and a thermometer. 93.0
Parts, 52.0 parts of neopentyl glycol and 1.5 parts of a manganese acetate catalyst, 180-210 parts in a nitrogen atmosphere.
A transesterification reaction was performed at ℃ to distill methanol. Further, 6.1 parts of trimethylolpropane was added, and
The polymerization reaction was carried out by gradually reducing the pressure to 10 mmHg while heating to 50 ° C., and the nonvolatile content was adjusted to 70% with a cyclohexanone solution. Thus, a polyester polyol (1) was obtained. The resulting polyester polio
(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.

Polyester Polyol Synthesis Example 2 The same operation was performed under the same conditions as in Polyester Polyol Synthesis Example 1 except that the polymerization reaction time was changed. The obtained polyester polyol (2) has a nonvolatile content of 60%,
The number average molecular weight (Mn) determined by GPC is 4000,
The hydroxyl value determined by the phthalic anhydride-pyridine method is 45.0.
mg KOH / g.

[0058]

Examples 1-3 According to the composition shown in Table 1, 40 parts of cyclohexanone was added to the compound (1) obtained in Synthesis Example 1 of the polyester compound, and the mixture was stirred for 12 hours. At this time, the compound (1) used was pulverized to 250 microns or less by a pulverizer.
To the cyclohexanone dispersion of the compound (1) thus obtained, the polyester polyol 1 obtained in the polyester polyol synthesis example 1 and the blocked isocyanate (Desmodur BL317
5: HDI isocyanurate, manufactured by Sumitomo Bayer Urethane Co., Ltd., NCO content 11.1%, nonvolatile content 75
%), Rutile-type titanium oxide, dibutyltin dilaurate (hereinafter abbreviated as DBTDL) 10% cyclohexanone solution, and acronal 4F (manufactured by BASF) 50% cyclohexanone solution, and then a sand mill containing glass beads having a diameter of about 1 mm. And dispersed for 1 hour.
Further, cyclohexanone was added to adjust the nonvolatile content to 60%, and paints 1 to 3 were obtained. The ratio of compound 1 in the resin composition was 5.0 in Examples 1, 2, and 3, respectively.
8.0 and 12.0% by weight. The paints 1 to 3 are chromate-treated and polyester-based primer (film thickness 4
μm) electrogalvanized steel sheet (thickness: 0.5m)
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 210 ° C. for 150 seconds. Thus, a precoated steel sheet was obtained. The coating performance of the obtained precoated steel sheet was evaluated by the method described below. Table 1 shows the results.

Example 4 A blocked isocyanate (Desmodur XP7001: hydrogenated MDI prepolymer manufactured by Sumitomo Bayer Urethane KK, NCO content: 8.9%, nonvolatile content: 75%) was used as a curing agent, and is shown in Table 1. The same operation as in Example 1 was performed with the above composition to obtain a paint . The paint was applied to a steel plate, baked, and evaluated in the same manner as in Example 1. Table 1 shows the results
Shown in

[0061]

Example 5 To a cyclohexanone dispersion of the compound (1) obtained in the same manner as in Example 1, 125.0 parts of the polyester polyol 2 obtained in Polyester Polyol Synthesis Example 2 was added.
20.0 parts of methylated melamine (Cymel 300: manufactured by Mitsui Cyanamid Co., Ltd.) and 8 parts of rutile-type titanium oxide
After blending 0.0 part and 0.5 part of p-toluenesulfonic acid,
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 .
The prepared paint was applied to a steel sheet in the same manner as in Example 1,
Baking and evaluation were performed. Table 1 shows the results.

Example 6 To a cyclohexanone dispersion of the compound (1) obtained in the same manner as in Example 1, an acrylic polyol (desmophen A365: manufactured by Sumitomo Bayer Urethane Co., Ltd., 2.8% hydroxyl group content, non-volatile 98.0 parts)
Blocked isocyanate (Desmodur BL317
5) 48.4 parts, rutile type titanium oxide 80.0 parts,
Dibutyltin dilaurate (hereinafter abbreviated as DBTDL) 1
10 parts of 0% cyclohexanone solution, Acronal 4F
After mixing 4.4 parts of a 50% cyclohexanone solution (manufactured by BASF Corporation), 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 . The paint was applied to a steel plate, baked, and evaluated in the same manner as in Example 1. Table 1 shows the results.

[0064]

[Table 1]

Example 7 As the polyester compound, the compound (2) obtained in Synthesis Example 2 of the polyester compound was used. Otherwise, in the same combination as in Example 1, the same operation as in Example 1 was performed with the composition shown in Table 2 to obtain a paint . The paint was applied to a steel plate, baked, and evaluated in the same manner as in Example 1. Table 2 shows the results.

Example 8 As the polyester compound, the compound (3) obtained in Polyester Compound Synthesis Example 3 was used. Otherwise, in the same combination as in Example 1, the same operation as in Example 1 was performed with the composition shown in Table 2 to obtain a paint . The paint was applied to a steel plate, baked, and evaluated in the same manner as in Example 1. Table 2 shows the results.

Example 9 As the polyester compound, the compound (4) obtained in Polyester Compound Synthesis Example 4 was used. Otherwise, in the same combination as in Example 1, the same operation as in Example 1 was performed with the composition shown in Table 2 to obtain a paint . The paint was applied to a steel plate, baked, and evaluated in the same manner as in Example 1. Table 2 shows the results.

Example 10 As the polyester compound, the compound (6) obtained in Polyester Compound Synthesis Example 1a was used. Otherwise, in the same combination as in Example 1, the same operation as in Example 1 was performed with the composition shown in Table 2 to obtain a paint . The paint was applied to a steel plate, baked, and evaluated in the same manner as in Example 1. Table 2 shows the results.

Example 11 As the polyester compound, the compound (7) obtained in Polyester Compound Synthesis Example 2a was used. Otherwise, in the same combination as in Example 1, the same operation as in Example 1 was performed with the composition shown in Table 2 to obtain a paint . The paint was applied to a steel plate, baked, and evaluated in the same manner as in Example 1. Table 2 shows the results.

Example 12 As the polyester compound, the compound (8) obtained in Synthesis Example 3a of a polyester compound was used. Otherwise, in the same combination as in Example 1, the same operation as in Example 1 was performed with the composition shown in Table 2 to obtain a paint . The paint was applied to a steel plate, baked, and evaluated in the same manner as in Example 1. Table 2 shows the results.

Example 13 As the polyester compound, the compound (9) obtained in Polyester Compound Synthesis Example 4a was used. Otherwise, in the same combination as in Example 1, the same operation as in Example 1 was performed with the composition shown in Table 2 to obtain a paint . The paint was applied to a steel plate, baked, and evaluated in the same manner as in Example 1. Table 2 shows the results.

[0072]

[Table 2]

Comparative Example 1 99.7 parts of polyester polyol 1 and 40.000 of blocked isocyanate (Desmodur BL3175).
3 parts, 80.0 parts of rutile type titanium oxide, DBTDL1
After mixing 10.0 parts of a 0% cyclohexanone solution and 4.4 parts of a 50% cyclohexanone solution of Acronal 4F (manufactured by BASF Corporation), 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 . The prepared paint was applied on a galvanized steel sheet (thickness: 0.5 mm) that had been subjected to chromate treatment and a polyester-based primer (thickness: 4 μm) using a bar coater so that the dry film thickness was 15 to 18 μm. The printing was performed in a hot air drying oven at 210 ° C. for 150 seconds. Thus, a precoated steel sheet was obtained. The coating performance of the obtained precoated steel sheet was evaluated by the method described below. Table 3 shows the results.

[0074] In Comparative Example 2 Comparative Example 2, a polyester polyol 1 as a polyol, a curing agent to blocked isocyanate (Death
Using the module XP7001) , the same operation as in Comparative Example 1 was performed with the composition shown in Table 3 to obtain a coating material . The paint was applied to a steel plate, baked and evaluated in the same manner as in Comparative Example 1. Table 3 shows the results.

Comparative Examples 3 and 4 In Comparative Examples 3 and 4 , polyester polyol 2 and acrylic polyol (desmophen A36) were used as polyols.
5) as a curing agent, methylated melamine (Cymer 3
00), blocked isocyanate (Desmodur B
L3175). The same operation as in Comparative Example 1 was performed with the composition shown in Table 3 to obtain a paint . These paints were applied to a steel sheet, baked, and evaluated in the same manner as in Comparative Example 1. Table 3 shows the results.

[0076]

[Table 3]

Comparative Examples 5 to 7 As the polyester compound, the compound (5) obtained in Polyester Compound Synthesis Example 5 was used. Otherwise, in the same combination as in Examples 1, 5, and 6 , the same operation as in Example 1 was performed with the composition shown in Table 4 to obtain a paint . These paints were applied to a steel plate, baked and evaluated in the same manner as in Example 1. Table 4 shows the results.

Comparative Examples 8 to 10 As compounds, compound (10) obtained in compound synthesis example 5a
It was used. Otherwise, in the same combination as in Comparative Examples 5 to 7 , the same operation as in Example 1 was performed with the composition shown in Table 4,
Paint was obtained. These paints were applied to a steel plate, baked and evaluated in the same manner as in Example 1. Table 4 shows the results.

[0079]

[Table 4]

[0080] The compound obtained in Comparative Example 11 to 16 Polyester Compound Synthesis Example 1 (1), poly
Using the compound (5) obtained in the ester compound synthesis example 5 ,
A paint was prepared according to the formulation shown in Table 5, which was then painted and baked to obtain a precoated steel sheet. In Comparative Example 11 , the mixing ratio of the polyester compound (% by weight in the resin component) was 0.5.
%, In Comparative Examples 12, 14, and 16, of the polyester compound
Compounding ratio (% by weight in resin component) was 18%, Comparative Example 13,
In No. 15, the compounding ratio of the polyester compound (the resin component
(% By weight) was 25% . As the polyol , polyol 2 was used in Comparative Examples 14 and 15 ,
Except for Comparative Examples 14 and 16, Polyol 1 was used. As the curing agent , methylated melamine (Cymer 300) was used in Comparative Examples 14 and 15, and blocked isocyanate (Desmodur BL3175) was used in all other than Comparative Examples 14 and 15 . Adjustment of the paint, painting, baking was performed in the same manner as in Example 1. The coating performance of the obtained precoated steel sheet was evaluated by the method described below. Table 5 shows the results. Comparative Examples 12 to 16
Now, as the amount of polyester compound increases,
Dispersibility in the coating is reduced, and
It did not reach the level as a coated steel sheet.

[0081]

[Table 5]

The glass transition temperature of the coating film containing the compounds (1) and (2) obtained in the synthesis examples of the polyester compound (the coating films of the compositions of Examples 1 and 7 and Comparative Example 1) was measured using a thermomechanical tester. Was measured. Table 6 shows the results. The coating films of Examples 1 and 7 containing the polyester compound were Comparative Example 1
The glass transition temperature was higher than that of. Generally, the higher the transition temperature, the higher the hardness. In the experimental results of the pencil hardness, Example 1 was H, Example 7 was 2H, and Comparative Example 1 was F, which coincided with the results of the transition temperature. On the other hand, the bending workability did not decrease, which is considered to be an action unique to the polyester compound in the present invention. Furthermore, the higher the transition temperature, the better the stain resistance, blocking resistance and chemical resistance of the coating film. Therefore, the polyester resin of the present invention also improved other properties in addition to hardness and workability.

[0083]

[Table 6]

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 cracking of 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 The cured coating film was cut at 1 mm intervals using a cutter knife.
After cutting 100 pieces of the 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 with a load of 1.0 kg. One reciprocation was defined as one time, and the number was expressed as the number of times until the primer was exposed. However, the upper limit was set to 100 times. (7) Glass transition temperature measurement Thermomechanical tester TMA120 manufactured by Seiko-Electronic Industry Co., Ltd.
It was used. While raising the temperature at a rate of 1 ° C./min, the glass transition temperature of the coating film cured on the steel plate was measured.

[0085]

As is clear from the above Examples and Comparative Examples, the paint for precoated steel sheet of the present invention has greatly improved workability and coating film hardness. Also, for the precoated steel sheet of the present invention
The paint satisfies both conflicting properties of workability and coating film hardness, and can provide a precoated steel sheet having excellent performance .

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shoichi Osuga 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-1-272517 (JP, A) JP-A-5 -17682 (JP, A) JP-A-52-72729 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09D 1/00-201/10 B05D ⁷ /00-7/26

Claims (3)

(57) [Claims] (1) a number average molecular weight of from 1500 to 50,000
Polyester polyol (however, the following polyester compound
Product (c)), number average molecular weight of 1500 to 50,000
Mainly selected from acrylic polyols
Agent resin (a), and isocyanate compound and / or
For a resin composition using an amino resin as a curing agent (b), a general formula: Polyester compound (c) represented by the main resin (a), hard
A paint for a pre-coated steel sheet, which is blended in an amount of 2 to 10% by weight based on a solid content in the agent (b) and the polyester compound (C) . 2. A precoated steel sheet, wherein the paint according to claim 1 is applied on a steel sheet surface to form a coating film. 3. A method for manufacturing a precoated steel sheet, comprising coating the coating material according to claim 1 on a steel sheet surface to form a coating film.