JPH0565452A - Paint composition and thinner composition - Google Patents

Abstract

(57) [Summary] [Structure] A polyester resin having a specific number average molecular weight and molecular weight distribution, a butoxy group having an average degree of polymerization of 1.5 to 3,
A coating composition containing as a main component a mixed solvent of a methylol group and an imino group with a specific ratio of butylated melamine resin, a non-polar solvent, a high boiling point solvent, and a low boiling point alcohol solvent. [Effect] Good suitability for roll coating of precoated steel sheet,
The storage stability of the paint is good, and by improving the non-volatile content, the amount of volatile solvent at the time of baking the coating film can be reduced, and productivity can be improved and environmental measures can be taken.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a coating composition and a thinner composition. More specifically, it relates to a coating composition and a thinner composition used for a coating material for precoat metal.

[0002]

2. Description of the Related Art In recent years, pre-coated metal has been widely used for home electric appliances and general building materials, etc., and the coating film has improved weather resistance and processability of the coating film, and improved productivity during pre-coating. Due to environmental issues, various performances such as suppression of volatile components during painting are required.

A coating composition prepared by blending a polyester resin with a melamine resin as a cross-linking agent is widely used as a coating film having excellent weather resistance and processability, and such a polyester resin is blended with a melamine resin. Improving productivity is one of the performance requirements for coating compositions. A means of improving productivity is to enable high-speed coating, but current paints cannot perform high-speed coating due to the limited capacity of volatile solvent treatment during drying and baking. Therefore, it is required to suppress volatile components in the paint, that is, to increase the ratio of non-volatile components in the paint.

Generally, in a coating composition, the viscosity of the coating composition increases as the proportion of non-volatile components increases, and the coating film thickness controllability during roll coating, which is usually used for precoat metal coating, The so-called drawability deteriorates, and streaky appearance defects such as roll eyes occur, which makes it difficult to put into practical use.

As means for solving these problems, as the polyester resin used, the molecular weight distribution of the polyester resin is sharpened and no unnecessary additives are used ("pre-coated steel sheet application material", industrial materials, 1
989, Vol. 37, No. 7, pp. 27-32) and the like, and as the melamine resin, "About amino resins for paints", Journal of Color Materials, 1990, 63.
Vol. 1, No. 1, pp. 19-28 describes melamine resins that give various characteristics. By blending these melamine resins with the above polyester resins in accordance with the required performance, a coating composition having a high proportion of non-volatile components is provided. You can get things. Although such a coating composition improves the controllability of the coating film thickness, the appearance of the coating film, etc. to some extent, the present situation is that satisfactory results have not yet been obtained.

Further, in order to increase the ratio of the non-volatile components, the mixing ratio of the volatile internal solvent is decreased, the appearance of the coating film such as the glossiness of the coating film is further improved, and the conditions of the polyester resin described above are used. Since it is required to use no additive, a cross-linking agent such as a melamine resin is inevitably a self-curing type which cures without using a catalyst such as an acid catalyst. Thus, when the blending ratio of the internal solvent is lowered or when the self-curing melamine resin is used, there is a problem in storage stability such that the viscosity is increased during storage and it cannot be used as a paint.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to increase the proportion of non-volatile components in a coating composition without causing an increase in viscosity.
An object of the present invention is to provide a coating composition having good workability and at the same time excellent storage stability.

Another object of the present invention is to provide a thinner composition which has good curing properties of the coating material and at the same time excellent storage stability.

[0009]

Means for Solving the Problems As a result of studies by the present inventors, control of the coating film by controlling the high shear viscosity (Hishare viscosity) of the coating material to 3 poise (shear rate: 10 ⁵ / sec) or less. The present inventors have found that a coating composition having good properties and having a high proportion of non-volatile components, which has improved coating film appearance and storage stability, can be obtained by devising an internal solvent, leading to the present invention.

That is, the above-mentioned various purposes are as follows: (a) number average molecular weight of 1,000 to 4,000, molecular weight distribution (Mw / M
n) is a polyester resin having 1-2, (b) an average degree of polymerization of 1.5-3, and an average of 3 butoxy groups per melamine nucleus.
˜4.5, a methylol group on average 0.05 to 1 and an imino group on average 0.5 to 2 and a butyl etherified melamine resin and (c) a non-polar solvent / polar solvent having a boiling point of 150 ° C. or higher / The alcohol-based solvent having a boiling point of less than 150 ° C. is in a weight ratio of 25 to 60/10 to 30/20 to 6, respectively.
It is achieved by a coating composition characterized by containing an organic solvent blended in a ratio of 5.

Further, the above-mentioned various purposes are as follows. The organic solvent composition in the coating composition is 25 to 60/10 in weight ratio of nonpolar solvent / polar solvent having a boiling point of 150 ° C. or more / alcohol solvent having a boiling point of less than 150 ° C., respectively. It is also achieved by a coating composition characterized by being blended in a ratio of -30 / 20-65.

Further, the above-mentioned objects are as follows: Nonpolar solvent / polar solvent having a boiling point of 150 ° C. or higher / alcoholic solvent having a boiling point of less than 150 ° C. in a weight ratio of 25 to 60/10 to 30, respectively.
It is also achieved by a thinner composition characterized by containing an organic solvent blended in a ratio of / 20 to 65.

[0013]

The present invention will be described in detail below.

In the coating composition of the present invention, (a) the polyester resin as the main resin has a number average molecular weight of 1,000 to
4,000, a polyester resin having a molecular weight distribution (Mw / Mn) of 1 to 2 and (b) a melamine resin as a cross-linking agent having an average degree of polymerization of 1.5 to 3 and an average of 3 to butoxy groups per melamine nucleus. 4.5, an average of 0.05 to 1 methylol groups
Butyl etherified melamine resin having an average of 0.5 to 2 imino groups and (c) a paint internal solvent, a non-polar solvent / a polar solvent having a boiling point of 150 ° C. or higher / a boiling point of 15
The weight ratio of alcoholic solvents below 0 ° C is 25 to
It is characterized by containing an organic solvent blended in a ratio of 60/10 to 30/20 to 65.

First, the polyester resin (a), which is the main resin of the coating composition, has a number average molecular weight of 1,000 to 4,0.
00, preferably 1,500 to 2,500, more preferably 1,800 to 2,200, and the molecular weight distribution (Mw
/ Mn and Mw are weight average molecular weights, and Mn is number average molecular weight)
Is 1 to 2, preferably about 1.5. If the number average molecular weight is less than 1,000, chemical resistance and boiling water resistance cannot be obtained, and if it exceeds 4,000, the non-volatile component ratio is lowered and the viscosity is increased. On the other hand, when the molecular weight distribution is less than 1, synthesis is difficult and unsuitable, and when the molecular weight distribution is more than 2, a large amount of the large molecular weight is mixed and the content of non-volatile components becomes low, which causes an increase in viscosity, which is not preferable.

The polyester resin used in the present invention is
As long as it satisfies the above conditions, it may be one that is usually used as a coating composition and is not particularly limited, but one that is synthesized from a polyhydric alcohol and a polybasic acid (synthesized by an ester condensation reaction) is preferable. .. Specifically, for example,
As the polyhydric alcohol component, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1 , 4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropio Nate (BASHPN), N, N-bis (2-hydroxyethyl) dimethylhydantoin, polytetramethylene ether glycol, polycaprolactone polyol, glycerin, sorbitol, annitol, trimethylolethane, Examples include trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol, tris (hydroxyethyl) isocyanate and 1,9-nonanediol. Use of two or more of these polyhydric alcohols in combination. You can also Further, as the polybasic acid, phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyltetrahydrophthalic acid, methyltetrahydrophthalic anhydride, hymic acid anhydride, trimetic acid , Trimetic acid anhydride, pyromellitic acid, pyromellitic acid anhydride, isophthalic acid, terephthalic acid, maleic acid,
Maleic anhydride, fumaric acid, itaconic acid, adipic acid,
Azelaic acid, sebacic acid, succinic acid, succinic anhydride,
Lactic acid, dodecenyl succinic acid, dodecenyl succinic anhydride,
Examples thereof include cyclohexane-1,4-dicarboxylic acid and endo acid anhydride, and two or more kinds of these polybasic acids may be used in combination. Further, as the modifier for the polyester resin, for example, long-chain monoepoxide (trade name: Cardura E, manufactured by Shell Co., Ltd.), AOEX24 (manufactured by Daicel Corporation), or the like may be used.

The melamine resin (b) used in the present invention has an average degree of polymerization of melamine resin of 1.5 to 3, preferably 1.5 to 2, and an alkyl ether per melamine nucleus (triazine ring). The degree of chemical conversion of butoxy groups is 3 to
4.5, preferably 3-4, an average of 0.05-1 methylol groups, preferably 0.4-0.8, and 0.5-2 imino groups, preferably 0.8- It is 1.5.

Here, the average degree of polymerization of the melamine resin is 1.5.
If it is less than 3, curing may be insufficient, scratching may be defective, etc.
When it exceeds, the ratio of non-volatile components becomes small and the viscosity becomes high, which is not preferable. The degree of alkyl etherification per melamine nucleus (triazine ring) is less than 3 butoxy groups, the non-volatile content is small and the viscosity is high, and when it exceeds 4.5, insufficient curing or scratching occurs. When the methylol group is less than 0.05, insufficient curing or defective scratching occurs, and when it exceeds 1, the non-volatile component ratio becomes small and the viscosity becomes high, and the imino group is less than 0.5. If it is, curing will be insufficient, and if it exceeds 2, the content of non-volatile components will be small and the viscosity will be high.

Next, the (c) paint internal solvent used in the present invention is a non-polar solvent, a polar solvent having a boiling point of 150 ° C. or higher (hereinafter referred to as a high boiling point solvent), and an alcohol solvent having a boiling point of less than 150 ° C. (hereinafter , Simply called alcohol solvent)
The non-polar solvent is 25-60, preferably 25-40, more preferably 2
5 to 35, high boiling point solvent 10 to 30, preferably 10 to 2
5, more preferably 15 to 21, alcohol solvent 20
-65, preferably 30-50, more preferably 30-
It is a mixture of 40.

This mixing ratio is such that the ratio of the nonpolar solvent is 25.
If the amount is less than the above, the viscosity of the coating material increases if the amount of the other solvent increases, and if it exceeds 60 and the amount of the other solvent decreases, the leveling property decreases and the storage stability also decreases, which is not preferable. If the proportion of the high boiling point solvent is less than 10 and the amount of other solvent is large, the leveling property after coating is deteriorated, and if it exceeds 30, the viscosity of the coating material is increased, which is not preferable. If the proportion of the alcohol-based solvent is less than 20 and the amount of the other solvent is large, the viscosity of the paint during storage is increased and the storage stability is lowered, and if it exceeds 65 and the amount of the other solvent is decreased, the viscosity of the paint is increased, which is not preferable.

Here, the non-polar solvent and the alcohol solvent contribute to the storage stability of the paint. Generally paints, especially polyester resin-melamine resin based paints,
Simply put, the coating is cured by addition polymerization or condensation polymerization and self-crosslinking of melamine resin or crosslinking between polyester and melamine to form a coating film, but this self-crosslinking or crosslinking occurs during paint storage, When the so-called gelation phenomenon occurs, it exceeds the usable area as paint, and when this progresses,
Even if it is diluted with a solvent after that, it cannot be used as a paint at all. Therefore, the non-polar solvent is intended to stabilize the viscosity of the paint by suppressing the reaction due to the interaction between the solvent and the resin, and the alcohol-based solvent is the equilibrium with the crosslinking reaction due to the hydrolysis reaction of alcohol in the paint. Is maintained to suppress the increase in the molecular weight, in other words, to suppress the increase in the molecular weight, thereby enhancing the storage stability.

The non-polar solvent is an aromatic hydrocarbon or an aliphatic hydrocarbon containing a methylene group, which does not have a polar atomic group. For example, aromatic hydrocarbons such as benzene, toluene, xylene and ethylbenzene, Examples thereof include aliphatic hydrocarbons such as cyclohexane, ethylcyclohexane, and perchloroethylene, and generally commercially available aromatic hydrocarbon mixtures such as Solvesso 1
00, Solvesso 150 (manufactured by Exxon Chemical Co., Ltd.) and the like can also be used. The alcohol solvent is a hydroxy compound obtained by substituting a hydrogen atom of a chain or alicyclic hydrocarbon having a boiling point of 150 ° C. or less with a hydroxyl group (OH group), and examples thereof include methanol, ethanol, n-propanol, n-butanol, isobutanol, n-amyl alcohol, isoamyl alcohol, methylamyl alcohol, isopropanol, secondary butanol, tertiary
Butanol, activated amyl alcohol, secondary amyl alcohol, fusel oil, 3-pentanol, 2-ethyl-1
-Butanol, tertiary amyl alcohol and the like can be mentioned.

The high boiling point solvent is for controlling the solvent evaporation speed at the time of coating the paint. Generally, in the paint for precoat metal, the solvent evaporation speed is increased in order to improve productivity, and the solvent evaporation is started immediately after coating. Further, in the case of roll coating, since the baking is carried out immediately after the roll coating in a continuous process, the coating becomes a sufficiently uniform state on the object to be coated, so that time for so-called leveling cannot be taken Baking is performed with the roll eyes (roping) remaining. In order not to leave this roping, it is necessary to slow down the line speed or lengthen the distance between the coater and the printing device. If the interval is lengthened, there is a problem that the equipment becomes large and a large space is required. In particular, in the case of a coating material having a high non-volatile content, if solvent evaporation starts immediately after coating, more time is required for leveling, and with conventional equipment, roping will remain and the appearance of the coating film will deteriorate.

In order to solve such a problem, it is suitable to use a solvent which does not start evaporation of the solvent immediately after roll coating, that is, at room temperature and has a good leveling property, and which evaporates rapidly at a high temperature after entering the printing apparatus. As such a solvent,
A ketone solvent having a boiling point of 150 ° C. or higher, an alcohol solvent, a polyhydric alcohol and a polyhydric alcohol derivative are suitable. Specifically, for example, as the ketone solvent, cyclohexanone, isophorone, diacetone alcohol, alcohol, etc. As the system solvent, n-hexanol, n
-Heptanol, 2-heptanol, 3-heptanol, n-octanol, 2-octanol, 2-ethylhexanol, 3,5,5-trimethylhexanol,
Nonanol, n-decanol, undecanol, tetradecanol, cyclohexanol, benzyl alcohol, furfuryl alcohol, abietinol, and the like, polyhydric alcohols such as ethylene glycol, propylene glycol, butyl diglycol, diacetone alcohol,
Diethylene glycol, dipropylene glycol, trimethylene glycol, 1,3-butanediol, 2,3
-Butanediol, 1,4-butanediol, 3,4-
Examples of polyhydric alcohol derivatives such as hexylene glycol and 1,2,6-hexanetriol are ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, ethylene glycol monobutyl ether, ethylene glycol dibutyl ether, ethylene glycol isoamyl ether, ethylene glycol. Monophenyl ether, ethylene glycol monohexyl ether, ethylene glycol monoacetate, ethylene glycol diacetate, diethylene glycol monoethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol Butyl ether, diethylene glycol monoacetate, propylene glycol monobutyl ether, propylene glycol monoacetate, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, 1-butoxyethoxy propanol, carbitol acetate, etc., isophorone, butyl diglycol, acetic acid as a high boiling solvent Carbitol is preferred, and the amount of such a high boiling point solvent may be appropriately determined in view of the leveling property and the evaporation speed required within the above range.

In the present invention, the above-mentioned non-polar solvent, high boiling point solvent and alcohol solvent can be used alone or in combination of two or more kinds. Needless to say, it is necessary to determine the thinner composition so as not to impair the solubility of the resin composition by the thinner composition.

Since the internal solvent used in the coating composition of the present invention exhibits the above-mentioned characteristics, not only the polyester resin-melamine resin-based coating composition but also other coating compositions have an organic solvent component. Can be used as

Other coating compositions are generally used and are not particularly limited. Specific examples include, for example, aminoalkyd resin-based coatings, nitrocellulose-based coatings, aminoacrylic resin-based coatings. Examples include paints, polyurethane-based paints, epoxy resin-based paints, and the like.

Further, the internal solvent of the present invention can be used as a thinner composition for diluting a coating material,
When the paint is diluted and used, the solvent evaporation amount can be controlled, workability is improved, and good coating characteristics are brought about.

(A) Polyester resin of the present invention, (b)
The coating composition comprising the melamine resin and the internal solvent (c) is blended in a blending ratio used as a general coating material, and is not particularly limited. Specifically, in the case of such a paint, usually, a polyester resin as a main resin / a melamine resin as a cross-linking agent (weight ratio) =
90/10 to 50/50, preferably 85/15 to 60 /
40, more preferably 80/20 to 70/30, and the amount of the internal solvent is such that the nonvolatile content of the coating composition is 70% or more, preferably 70 to 90%, more preferably 70 to 80%. ..

Further, the coating composition of the present invention includes a pigment and
If desired, various additives used in general coating compositions may be used.

As the pigment, those which can be usually used in the field of paints, titanium dioxide, iron oxide (red rust, yellow), carbon black, yellow chromate, phthalocyanine blue, phthalocyanine green, quinacridone,
Indanthrone, isoindolinone, perylene, anthrapyrimidine, benzimidazolone, various organic and inorganic color pigments such as graphite, precipitated calcium carbonate, barium sulfate, aluminum silicate, kaolin, talc, clay, white carbon, etc. Pigments, zinc chromate, strontium chromate, calcium chromate, barium chromate, magnesium chromate, red lead, lead suboxide, basic lead chromate, cyanamide lead, calcium lead phosphate, zinc phosphate, aluminum phosphate, calcium phosphate, metallic zinc powder And anticorrosion pigments such as a mixture of glass flake powder, flake-shaped aluminum powder paste for giving a metallic feeling, titanium coating mica powder or aluminum foil, bronze foil, tin foil, gold foil,
Silver foil, titanium metal foil, stainless steel foil, alloy foil such as nickel-copper, metal foil coated with plastic, bright pigment such as metal foil pigment such as foil phthalocyanine blue,
Specific pigments such as various fluorescent agents used in fluorescent paints and the like, antifouling pigments such as cuprous oxide and the like can be mentioned. Further, in order to improve the lubricity of the coating film, a wax and a lubricant such as polyethylene or fluorinated polyethylene powder or molybdenum difluoride can be added, if necessary. Pigments and lubricants can be added depending on the purpose within the range of the critical pigment constitutional concentration or less.

As various additives which can be used in the present invention, those which are usually used in the field of paints, such as curing catalysts of dodecylbenzenesulfonic acid, UV absorbers of benzophenol type, phenol type, sulfide type, etc. Antioxidants, surface modifiers such as silicones and organic polymers, anti-sagging agents, thickeners, lubricants, etc., rust preventives such as fumed silica, etc. It is possible to improve the coating performance and the coating performance by blending in an amount of not more than parts by weight. However, if the blending amount of these is too large, repellency may occur during coating film formation, or the adhesion of the article to be coated (metal plate, etc.) may deteriorate, as is the case with general paints, which is not preferable. ..

To disperse and mix the respective components of the coating composition of the present invention, a device such as a paint shaker, a dissolver, a ball mill, a sand grind mill, a kneader or the like which is usually used in the production of coating materials is used.

The coating composition which can be coated with the coating composition of the present invention includes not only steel sheets but also cold rolled steel sheets, galvanized steel sheets, alloy-plated steel sheets such as zinc-aluminum and zinc-nickel, stainless steel sheets, Metal plates such as aluminum plate, copper plate, brass plate, plastic products such as FPR, polyethylene, polypropylene, polyamide, polyacryl, vinyl chloride, vinylidene chloride, polycarbonate, polyurethane, various rubbers, etc. It may be in the form of a coil or a sheet.

The coating composition of the present invention is for precoating, to obtain suitability for roll coating in which an object to be coated is coated while passing it between an applicator roll and a backup roll. It can also be used for air spray coating, spray coating, electrostatic coating, gravure coating, curtain coating, extrusion coating of die coater, etc.

When the coating composition of the present invention is applied, first, the coating composition is adjusted to a desired viscosity. Viscosity is the value used during normal painting, 35-70 seconds / # 4
Ford cup (25 ° C) is good. The coating film thickness varies depending on the hue, but is 5 to 50 μm, preferably 10 to 2
About 5 μm (dry film thickness) is preferable. The baking temperature of the coating is preferably about 200 to 250 ° C. at the maximum reached plate temperature.

[0037]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Reference Example 1 Production of Polyester Resin Varnish In a 3 liter reaction vessel equipped with a heating device, stirring device, reflux device, water separator, rectification column and thermometer, 158 parts by weight of trimethylolpropane and neopentyl glycol were added. 27
9 parts by weight, 316 parts by weight of 1,6-hexanediol, 512 parts by weight of isophthalic acid, 450 parts by weight of adipic acid and 4 parts by weight of dibutyltin oxide are charged, and the reaction temperature is raised to 170 ° C. When water of reaction condensation starts to be generated, the temperature is raised to 220 ° C. over 3 hours at a uniform rate while distilling water out of the system, and the reaction is continued for 2 hours at the same temperature. Then, 2 parts by weight of xylol was added to the reaction vessel, the condensation reaction was continued by the xylol refluxing method, and when the resin acid value reached 15, the reaction was terminated, and after cooling, it was diluted with cellosolve acetate to give a nonvolatile content of 70%. A polyester resin varnish having a cell viscosity of Z3 was obtained.

This polyester resin varnish was fractionated by molecular weight using liquid chromatography (LC-908, manufactured by Nippon Analytical Industry Co., Ltd.) and the low molecular weight portion was fractionated to obtain a molecular weight of 1,000 to 4,000. Molecular weight distribution 1-2
The polyester resin varnish of was prepared.

Reference Example 2 Production of Melamine Resin Varnish 600 parts by weight of 40% formalin-n-butanol solution (Hormite NB, manufactured by Koei Chemical Co., Ltd.) in a four-necked flask equipped with a stirrer, a reflux condenser and a thermometer. 740 parts by weight of n-butanol and 126 parts by weight of melamine were weighed, triethylamine was added to adjust the pH to 9 to 9.5, and methylolation reaction was performed for 20 minutes under reflux, and then paratoluene sulfonic acid was adjusted to pH 3. The mixture was added to 2 and reacted for 20 minutes under reflux, and then a mixed solvent consisting of 168 parts by weight of n-butanol, 126 parts by weight of xylol, and 28 parts by weight of ion-exchanged water was added to carry out reflux dehydration for 3 hours, This was concentrated under reduced pressure to obtain a melamine resin varnish A having a nonvolatile component of 80%. Melamine resin varnishes BF were prepared in the same manner by adjusting the blending amount of n-butanol. Table 1 shows the structural characteristics of the obtained melamine resin.

[0041]

[Table 1]

The molecular weights and molecular weight distributions of the polyester resins and melamine resins of Reference Examples 1 and 2 were measured by GPC (column: SHOD) manufactured by Tosoh Corporation.
EXKF803, solvent: tetrahydrofuran) was used to measure polystyrene equivalent. The functional group in the melamine resin was nitrogen in the usual Keltal method, and total bound formaldehyde was phosphoric acid decomposition method (JJLevenson Ing.Eng.Chem.Anal.E).
d. 12, 332 (1940)), the free hydroxymethyl group is an iodine method (Miyauchi, Kogaku, 20, 46 , (1963)), and the alkoxy group (butoxy group) is a part of the phosphoric acid decomposition distillate. Was measured by a colorimetric assay using a p-dimethylaminobenzaldimide color former (Miyauchi, Kogaku, 20, 42 , (1963)).

Examples 1 to 10 and Comparative Examples 1 to 9 The polyester resin varnish and melamine resin varnish obtained in Reference Examples 1 and 2 above, and a commercially available melamine resin and an internal solvent were mixed in the mixing ratio shown in Table 2. Prepare a paint, and adjust the viscosity with a thinner that has the same composition as the internal solvent of the paint.
Ford cup viscosity, drawability (controllability of coating film thickness), storage stability, chemical resistance, non-volatile components during coating and appearance were evaluated. The measurement results are shown in Table 3 for the examples and Table 4 for the comparative examples.

Evaluation method 1. High shear viscosity (high-speed shear viscosity) High-speed extrusion type viscosity analyzer (Capillerizer CP-R
M2, manufactured by Rheology Co., Ltd.) to measure the high shear viscosity.

2. Ford cup viscosity It was measured at 25 ° C. using a Ford cup (FC) of # 4 (see JIS 54004.5).

3. Drawability (controllability of coating film thickness) The amount of coating film adhered is measured by a gravimetric method. The evaluation criteria are that the adhesion amount is less than 31 g / m ² : ◯, and the adhesion amount is 31 g / m ² or more: ×. The gravimetric method is as follows: coated steel plate (10 x 10c)
m) was weighed (W ₀ g), then Neo River SP
The coating film is peeled off using 751 (manufactured by Sansai Kako Co., Ltd.),
The weight (W ₁ g) of the steel sheet was measured, and the adhesion amount was calculated by the following formula. Coating weight ^{(g / m 2) = {} (W 0 -W 1) × 100} - 5 * * subbing coating weight: a 5 g / ^{m 2.}

4. Storage stability The paint is stored in a sealed state at 20 ° C for 4 weeks, and the change in viscosity with time is measured. The evaluation standard is that the change in viscosity is ± the above Ford cup viscosity.
Less than 40 seconds: ○ ± 40 seconds or more: x

5. Chemical resistance 5% Hydrochloric acid is soaked at 20 ° C. for 24 hours and the appearance (planar portion) is visually inspected. The evaluation criteria are that there is no abnormality in the appearance of the coating film (no blister formation): ○ Blister formation: ×.

6. Non-volatile components during coating 70% or more: ○ (105 ° C, 3 hours) less than 70%: × 7. Appearance Visually observe the presence of rolls. The evaluation criteria were that there was no abnormality (good leveling): ◯ Roll eyes occurred (poor leveling): ×.

Further, the article to be coated and the coating conditions are as follows. Substrate: 0.27 (thickness) x 400 (width) x 2,500
(Length) mm galvanized steel sheet.

Coating device: roll coater applicator roll (AR) and pickup roll
It consists of two rolls of (PR) and is supported by a backup roll.

Paint Topcoat: Paints of Examples 1-10 and Comparative Examples 1-9 Basecoat: Superlac D1F P-01 Primer,
Nippon Paint Co., Ltd. Coating amount 5 g / m ² Coater condition: Topcoat coating Undercoat coating Backup roll peripheral speed (LS) 110 m / min 110 m / min AR peripheral speed ratio (AR / LS) 1.1 1.1 PR peripheral speed ratio (PR / LS) 0.6 0.7 AR rotation direction Reverse natural PR immersion depth 25 mm 25 mm AR and PR linear pressure (air pressure) 8 kg / cm 8 kg / cm Baking conditions (maximum plate temperature) 220 ° C × 30 seconds 200 ° C × 30 seconds Paint viscosity during coating 45 to 50 seconds 70 seconds (depending on Ford cup viscosity above)

[0053]

[Table 2]

[0054]

[Table 3]

[0055]

[Table 4]

[0056]

The number average molecular weight (a) of the present invention is 100
0 to 4,000, a polyester resin having a molecular weight distribution (Mw / Mn) of 1 to 2, (b) an average degree of polymerization of 1.5 to 3.0 and an average of 3 to 4.5 butoxy groups per melamine nucleus. Individual,
A butyl etherified melamine resin having an average of 0.05 to 1 methylol groups and an average of 0.5 to 2 imino groups, and (c) a non-polar solvent / polar solvent having a boiling point of 150 ° C. or higher / a boiling point of less than 150 ° C. A thinner composition having the same composition as the coating composition and the internal solvent of the present invention, wherein the alcohol-based solvent contains an organic solvent blended in a weight ratio of 25 to 60/10 to 30/20 to 65, respectively. Since the ratio of non-volatile components at the time of coating can be reduced, the amount of volatile solvent at the time of baking can be reduced, and (1) the production amount can be increased (the limit due to the explosion limit of the oven is eliminated), 2) It becomes an environmental measure by reducing the amount of volatile solvent. In addition, (3) low-molecular-weight polyethylene and melamine having a low degree of polymerization are expected to improve the pin limit, and (4) low-molecular-weight polyester resin improves the sharpness. 5) Thick film coating workability by the extrusion coating method is also improved.

Claims (3)

[Claims] 1. (a) Number average molecular weight of 1,000 to 4,
000, a polyester resin having a molecular weight distribution (Mw / Mn) of 1 to 2, (b) an average degree of polymerization of 1.5 to 3 and a melamine nucleus 1
The average is 3 to 4.5 butoxy groups, the average is 0.05 to 1 methylol groups, and the average is 0.5 to 2 imino groups per piece.
Butyl etherified melamine resin and (c) non-polar solvent / polar solvent having a boiling point of 150 ° C. or higher / boiling point of 15
Alcoholic solvent below 0 ° C is 25-60 / 1 by weight ratio
A coating composition comprising an organic solvent blended in a ratio of 0 to 30/20 to 65. 2. The organic solvent composition in the coating composition comprises a nonpolar solvent / polar solvent having a boiling point of 150 ° C. or higher / alcoholic solvent having a boiling point of less than 150 ° C. in a weight ratio of 25 to 60/1, respectively.
A coating composition, which is blended in a ratio of 0 to 30/20 to 65. 3. An organic compound in which a non-polar solvent / a polar solvent having a boiling point of 150 ° C. or higher / an alcohol solvent having a boiling point of less than 150 ° C. are blended in a weight ratio of 25 to 60/10 to 30/20 to 65, respectively. A thinner composition comprising a solvent.