JP2009013364A - Powder coating composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a powder coating composition superior in low temperature hardenability, and superior in moisture resistance and boiling water resistance of a coating film provided by coating, without volatilizing an organic solvent in the atmosphere. <P>SOLUTION: This powder coating composition includes a carboxy group-including branch type polyester resin, a β-hydroxyalkyl amide cross-linking agent, calcium carbonate as an extender pigment and precipitating barium sulfate. In the powder coating composition, an acid value of the carboxy group-including branch type polyester resin falls within a range of 20-60 mg/KOH. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a powder coating composition having excellent low-temperature curability and water resistance.

Powder paints are attracting attention as low-pollution paints because organic solvents do not volatilize into the atmosphere during painting. In particular, a polyester resin powder coating using a combination of a polyester resin and a crosslinking agent is known as a coating applied to metal products.

  Known crosslinking agents for polyester resin powder coatings include triglycidyl isocyanurate (hereinafter sometimes abbreviated as “TGIC”), blocked polyisocyanate, and the like. TGIC has problems in its use from the viewpoint of skin irritation and toxicity, and blocked polyisocyanate is a volatile organic compound when the blocking agent is a PRTR target substance and further desorbed during the baking reaction of the coating film. There was a problem of (VOC).

  Conventionally, hydroxylalkylamide has been put to practical use as a crosslinking agent that solves such problems. In Patent Document 1, as a powder coating composition excellent in weather resistance, secondary adhesion and corrosion resistance in a chemical conversion treated steel sheet, a normal temperature solid carboxyl group-containing polyester resin, hydroxylalkylamide, calcium carbonate, and tripolyphosphate A thermosetting powder coating composition characterized by containing hydrogen aluminum is disclosed.

  However, when the baking temperature of the coating film was set to 160 ° C., crosslinking was insufficient, and moisture resistance and boiling water resistance could not be obtained.

JP 2004-25068 A

An object of the present invention is to provide a powder coating composition which is excellent in low-temperature curability and excellent in moisture resistance and boiling water resistance of a coating film obtained by coating.

The present invention
1. A powder coating composition containing a carboxyl group-containing branched polyester resin, a β-hydroxyalkylamide crosslinking agent and calcium carbonate and barium sulfate as extender pigments.
2. 2. The powder coating composition according to item 1, wherein the acid value of the carboxyl group-containing branched polyester resin is in the range of 20 to 60 mg / KOH.

The powder coating composition of the present invention contains a carboxyl group-containing branched polyester resin, a β-hydroxyalkylamide curing agent and a specific extender pigment, so that the organic solvent does not volatilize in the atmosphere and is low temperature curable. It is to provide a coated article excellent in moisture resistance and boiling water resistance of a coating film obtained by coating.

The powder coating composition of the present invention contains a carboxyl group-containing branched polyester resin as a vehicle forming component.

  Specifically, the carboxyl group-containing branched polyester resin in the present invention is a polycondensation reaction by an ordinary method using an acid component mainly composed of a polyvalent carboxylic acid and an alcohol component mainly composed of a polyhydric alcohol as raw materials. Can be obtained.

  In the powder coating composition of the present invention, in particular, a branched carboxyl group-containing polyester resin synthesized by using a bifunctional component and a trifunctional component in combination is used from the viewpoint of low temperature curability. Here, the low temperature curability means that excellent coating film performance is obtained by heating and drying at 140 ° C. to 160 ° C. for 10 to 20 minutes.

  The acid component is not particularly limited. For example, phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, succinic acid, fumaric acid, adipic acid, azelaic acid, sebacic acid, dodecanic acid Dibasic acids such as maleic anhydride, itaconic acid and dimer acid, and polybasic acids having three or more valences such as lower alkyl esterified products of these acids, trimellitic anhydride, methylcyclocentricarboxylic acid, pyromellitic anhydride, etc. Can be used.

  Moreover, it does not specifically limit as a polyhydric alcohol component, For example, ethylene glycol, diethylene glycol, propylene glycol, 1, 4- butanediol, neopentyl glycol, 3-methylpentanediol, 1, 4-hexanediol, 1, Use dihydric alcohols such as 6-hexanediol, cyclohexanedimethanol, hydrogenated bisphenol A, and ethylene oxide adducts of bisphenol A, and trihydric or higher polyhydric alcohols such as glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol. be able to. These polyhydric alcohols can be used alone or in admixture of two or more.

  Further, if necessary, monobasic acids such as benzoic acid, crotonic acid, and pt-butylbenzoic acid, and monovalent alcohols such as methyl alcohol, ethyl alcohol, and butyl alcohol can be used in combination.

  The esterification or transesterification reaction between the acid component and the alcohol component can be performed by a method known per se, for example, obtained by condensation polymerization of the acid component and the alcohol component at a temperature of 100 to 250 ° C. be able to.

  In the present invention, after obtaining a polyester resin having a hydroxyl group from the acid component and the alcohol component, to the hydroxyl group of the obtained polyester resin, maleic acid, maleic anhydride, phthalic anhydride, trimellitic anhydride, You may use what made the carboxyl group-containing polyester resin by introduce | transducing a carboxyl group in resin by making polybasic acids, such as hexahydro phthalic anhydride and tetrahydro phthalic anhydride, react.

  The acid value of the carboxyl group-containing branched polyester resin in the present invention is preferably in the range of 10 to 100 mgKOH / g, more preferably 15 to 80 mgKOH / g, and still more preferably in the range of 20 to 60 mgKOH / g. is there.

  When the acid value is less than 10 mgKOH / g, the curability may be lowered and the mechanical properties may be lowered. On the other hand, when the acid value is more than 100 mgKOH / g, the appearance of the coating film obtained by coating is significantly reduced. There is a case. The carboxyl group-containing branched polyester resin preferably has a glass transition temperature (Tg) of 40 ° C. or higher. When glass transition temperature is lower than 40 degreeC, storage stability may fall.

  The powder coating composition of the present invention contains β-hydroxyalkylamide as a crosslinking agent for the carboxyl group-containing branched polyester resin. As β-hydroxyalkylamide, those having two or more functional groups per molecule are particularly preferred from the viewpoint of low-temperature curability and the moisture resistance of a coating film obtained by coating. For example, β-hydroxyalkylamide represented by the following formula can be used. (Here, n means an integer of 1 or more. From the viewpoint of low temperature curability and blocking resistance of the powder coating material, n is preferably in the range of 3 to 8, more preferably 4 to 4. Within the range of 6.)

  The blending ratio of the β-hydroxyalkylamide and the carboxyl group-containing polyester resin is arbitrary, but the equivalent ratio of the carboxylic acid group and the hydroxyalkylamide group is 1 / 0.7 to 0.7 / 1. It is preferable from the viewpoint of moisture resistance and boiling water resistance of the coating film obtained by coating, and more preferably in the range of 1 / 0.9 to 0.9 / 1.

  The powder coating composition of the present invention contains calcium carbonate and barium sulfate from the viewpoint of moisture resistance and boiling water resistance of a coating film obtained by painting as an extender pigment.

  Calcium carbonate includes precipitated calcium carbonate (light tancal) obtained by chemical synthesis, and naturally produced calcium carbonate (heavy tancal) obtained by pulverizing marble, limestone, thorn skin, animal fossils and the like. Any of these can be used in the present invention.

  Barium sulfate includes pulverized barite minerals (barite powder) called natural barite and precipitated barium sulfate produced by chemical reaction. Precipitated barium sulfate can be used that allows the particle size to be selected.

  If the powder coating contains calcium carbonate as an extender pigment and does not contain barium sulfate, the coating film obtained by coating may have the disadvantage of lowering the gloss of the coating film when subjected to moisture and water resistance. There is. Further, when barium sulfate is contained but calcium carbonate is not contained, there may be a disadvantage that the secondary adhesion is lowered when subjected to moisture resistance and water resistance load.

  In the powder coating composition of the present invention, hydrous magnesium silicate (talc), magnesium carbonate, calcium sulfate (gypsum), diatomaceous earth, mica (mica powder), clay (kaolin), silica and the like are further used as extender pigments. May be.

  As the extender, those having an average particle diameter of 0.01 to 30 μm are usually preferable, and those having an average particle diameter of 0.5 to 10 μm are more preferable. If the average particle size is larger than 30 μm, the appearance may be poor when the film is thin, and if it is smaller than 0.1 μm, melt dispersion may be difficult. The maximum particle size is preferably 200 μm or less, more preferably 50 μm or less.

  The above extender is a fine particle but has a strong surface activity and easily forms agglomerates, so that it has been surface-treated for the purpose of preventing aggregation and increasing affinity with vehicle-forming components. May be used. Surface treatment includes fatty acids and their salts, resin acids, other organic carboxylic acids and their salts and surfactants alone or in combination, treatment with titanate and silane coupling agents, inorganic acids, alkalis, Examples of the surface treatment include silica, alumina, and zinc compounds.

  In particular, in order to prepare a powder coating composition for forming a high-gloss coating without adjusting gloss, an extender usually has an average particle size in the range of 0.01 to 10 μm. It is preferable for obtaining gloss when the smoothness and gloss adjustment of the coating film are not performed.

  Although content of the said extender is not specifically limited, From the smoothness point of the coating film obtained, it is 5-40 mass parts with respect to a total of 100 mass parts of the said carboxyl group-containing polyester resin and the said crosslinking agent. It is preferably 10 to 25 parts by mass.

  The powder coating composition of the present invention may further contain a rust preventive pigment. As the rust preventive pigment, conventionally known pigments can be used for paints, and for example, aluminum phosphomolybdate, aluminum tripolyphosphate, zinc oxide (zinc white), and the like can be used. In particular, aluminum dihydrogen triphosphate can be used from the viewpoint of rust prevention and storage stability of the paint. Further, a pigment whose surface is treated with a compound such as zinc, calcium, sodium, manganese, tin, or titanium may be used.

  In this invention, when using a rust preventive pigment, the compounding quantity is 1 with respect to a total of 100 mass parts of the said carboxyl group-containing polyester resin and the said crosslinking agent from the point of the rust prevention property of a coating film, and smoothness. It is preferably ˜20 parts by mass, and more preferably 3 to 10 parts by mass.

  The powder coating composition of the present invention may further contain a color pigment. As the colored pigment, conventionally known pigments for ink and paint can be used alone or in combination of two or more. Specific examples of color pigments include metal oxide pigments such as titanium oxide and iron oxide, composite metal oxide pigments such as titanium yellow, carbon black, azo pigments, quinacridone pigments, diketopyrrolopyrrole pigments, and perylene pigments. Perinone pigments, benzimidazolone pigments, isoindoline pigments, isoindolinone pigments, metal chelate azo pigments, phthalocyanine pigments, indanthrone pigments, dioxane pigments, indigo pigments, and the like. .

  The blending amount of the color pigment is within a range of 1 to 150 parts by mass with respect to a total of 100 parts by mass of the carboxyl group-containing polyester resin and the crosslinking agent from the viewpoint of coloring power and finished appearance of the resulting coating film. It is preferable that it exists, More preferably, it exists in the range of 3-100 mass parts.

  In addition to the above components, the powder coating composition of the present invention includes glitter pigments, fluidity regulators, anti-blocking agents, ultraviolet absorbers, and ultraviolet stabilizers used in ordinary powder coatings as necessary. , A surface conditioner, an anti-bacterial agent, a charge control agent, a curing accelerator, an epoxy resin, and the like.

  The powder coating composition of the present invention can be produced by a known method. For example, the above-mentioned carboxyl group-containing branched polyester resin, a β-hydroxyalkylamide crosslinking agent, an extender pigment, and a component to be blended as necessary. It can manufacture by cooling and grind | pulverizing after melt-mixing.

  Specifically, after mixing and dispersing the above components, using an extrusion kneader, uniaxial or biaxial extruder, etc., usually melt-mixed at about 80 to 150 ° C. to form a pellet and then cooled To do. This can be manufactured by finely pulverizing and classifying with an impact pulverizer, an airflow pulverizer or the like.

  The particle size of the powder coating composition of the present invention is adjusted so that the volume average particle size is within a range of 10 μm to 80 μm. It is preferable from the point, and it is further more preferable to set it in the range of 20 micrometers-45 micrometers.

Next, an Example is given and this invention is demonstrated more concretely. Here, “parts” and “%” mean “parts by mass” and “% by mass”, respectively.

Production Example 1
A reactor equipped with a thermometer, a stirrer, a pressurizing device and a rectifying column was charged with 517 parts of neopentyl glycol, and the temperature was raised to 130 ° C. with stirring, and after the liquid became transparent, monobutyltin oxide 0 .12 parts and 860 parts of isophthalic acid were added and the temperature was raised to 180 ° C. Subsequently, the content was heated from 180 ° C. to 240 ° C. over 4 hours, and kept at 240 ° C. for 90 minutes after the temperature was raised. Thereafter, the rectifying column was replaced with a water separator, 60 parts of xylene was charged into the reaction apparatus, xylene was also charged into the water separator, and water and xylene were azeotroped to remove condensed water. The acid value was measured every 10 minutes from 30 minutes after the addition of xylene, and after 2 hours and 30 minutes from the addition of xylene, the acid value became 34.8 mgKOH / g, so the heating was stopped.

  Finally, xylene was removed under reduced pressure to obtain a polyester resin 1 having a heating residue of 100%. The acid value was measured by titrating with 1/10 N alcoholic KOH solution using pyridine as a solvent.

Production Example 2
519 parts of neopentyl glycol and 30 parts of trimellitic acid were charged into a reaction apparatus equipped with a thermometer, a stirrer, a pressurizing device and a rectifying column, and the temperature was raised to 130 ° C. while stirring, so that the transparent liquid became Thereafter, 0.12 part of monobutyltin oxide and 824 parts of isophthalic acid were added, and the temperature was raised to 180 ° C. Subsequently, the content was heated from 180 ° C. to 240 ° C. over 4 hours, and kept at 240 ° C. for 90 minutes after the temperature was raised. Thereafter, the rectifying column was replaced with a water separator, 60 parts of xylene was charged into the reaction apparatus, xylene was also charged into the water separator, and water and xylene were azeotroped to remove condensed water. The acid value was measured every 10 minutes from 30 minutes after the addition of xylene. After 2 hours and 30 minutes from the addition of xylene, the acid value became 34.3 mgKOH / g, so the heating was stopped. Finally, xylene was removed under reduced pressure to obtain polyester resin 2 having a heating residue of 100%.

Production Example 3
494 parts of neopentyl glycol and 21 parts of trimethylolpropane were charged into a reaction apparatus equipped with a thermometer, a stirrer, a pressurizing device and a rectifying column, and the temperature was raised to 130 ° C. with stirring to become a transparent liquid. Thereafter, 0.12 part of monobutyltin oxide and 863 parts of isophthalic acid were added, and the temperature was raised to 180 ° C. Subsequently, the content was heated from 180 ° C. to 240 ° C. over 4 hours, and kept at 240 ° C. for 90 minutes after the temperature was raised. Thereafter, the rectifying column was replaced with a water separator, 60 parts of xylene was charged into the reaction apparatus, xylene was also charged into the water separator, and water and xylene were azeotroped to remove condensed water. The acid value was measured every 10 minutes from 30 minutes after the addition of xylene, and after 2 hours and 30 minutes from the addition of xylene, the acid value became 33.8 mgKOH / g, so the heating was stopped. Finally, xylene was removed under reduced pressure to obtain polyester resin 3 having a heating residue of 100%.

The powder coating composition of the composition shown in Examples and Comparative Examples <br/> Table 1 (parts by mass) were charged high-speed mixer (trade name, Fukae Kogyo Co., Ltd., 2 liter), the agitator 500rpm The mixture is stirred and mixed uniformly at a chopper of 4000 rpm, and then melt-kneaded using an extrusion kneader (trade name, Busconyder PR46, manufactured by Busus) at a temperature of 80 ° C. to 100 ° C. After finely pulverizing with a mechanical impact pulverizer, classification was performed with a 200-mesh wire mesh to produce a powder coating having an average particle size of 35 μm.

  The obtained powder coating material was treated with zinc phosphate using Palbond # 3118, a base material (Nippon Parkerizing Co., Ltd.) using an electrostatic coating machine PG-1 (trade name, manufactured by Matsuo Sangyo Co., Ltd.). SPCC steel plate) is coated with electrostatic powder so that the cured film thickness is 60 μm, and is dried by heating under the conditions of maintaining the material temperature at 150 ° C. for 20 minutes and maintaining the material temperature at 160 ° C. for 20 minutes. For each of the comparative examples, two levels of test plates were obtained. The evaluation results of the coating film performance of the obtained test plate are shown in Table 2.

The powder coating composition of the present invention can be applied to home appliances, steel furniture, building materials, road materials, automobile parts, and the like.

Claims (2)

A powder coating composition comprising a carboxyl group-containing branched polyester resin, a β-hydroxyalkylamide crosslinking agent, and calcium carbonate and barium sulfate as extender pigments. The powder coating composition according to claim 1, wherein the acid value of the carboxyl group-containing branched polyester resin is in the range of 20 to 60 mg / KOH.