JP4191024B2 - Powder coating composition and powder coating - Google Patents

Description

  The present invention relates to a powder coating composition and an article to be coated with the composition. In particular, the present invention relates to a powder coating composition in which the covering property of the coated product edge portion is improved in order to suppress the occurrence of rust and corrosion from the edge portion, and a powder coated product obtained by coating the composition. .

  A powder coating material forms a coating film by coating an object to be coated in a powder state, and applying heat to melt and cure. Usually, the material of the object is the most metal. In the case of iron, a cold rolled steel plate or a hot rolled steel plate is used in addition to cast iron, and powder coating is performed after processing into the desired shape of the object to be coated.

  In the case of a cold-rolled steel sheet or a hot-rolled steel sheet, burrs are unavoidable at the edge part because cutting is performed with a mechanical cutting machine.

  Even if powder coating is applied to this burr portion, the coating film is pulled by surface tension during baking, and when fully cured, the powder coating film is very thin and close to the bare state in the state of a metal burr. Become.

  Of course, such an object to be coated also has a reduced commercial value due to the generation of rust from the burrs and the progress of corrosion. In order to prevent this, by removing the burrs after machine cutting and then applying the coating, a method to minimize the generation of surface tension due to baking after powder coating and cover the edge part with a powder coating as much as possible is performed. In this case, however, the machining cost increases because the number of machining steps increases by one.

  Recently, a powder coating material has been developed that can form a powder coating film on the burr portion thicker than conventional powder coatings even when burrs remain on the object to be coated. This powder coating increases the melt viscosity of the powder by increasing the pigment content, so that even if a force pulling from the burr portion due to surface tension is generated, it is a high-viscosity powder that has the property of not being pulled. It was a body paint.

  However, powder coating is generally performed by electrostatic coating by air conveyance, and as the pigment content increases, the specific gravity increases, which not only makes air conveyance difficult, but also reduces the charging characteristics of the paint itself. As a result, there is a problem that electrostatic repulsion is likely to occur and the coating workability is remarkably lowered.

  Furthermore, in order to solve this problem, there has been an attempt to suppress the concentration of the pigment by using very fine silica or alumina having a large oil absorption amount to suppress the deterioration of the air conveyance property and the charging property.

  However, although it was possible to prevent the air transportability and the charging characteristics from being deteriorated, the workability during the production of the powder coating material may be greatly reduced. In the powder coating manufacturing process, the raw materials are usually mixed and stirred with a Nauter mixer or Henschel mixer, kneaded with a thermal kneader, so-called extruder, and pulverized after cooling, but very fine silica and alumina have an apparent specific gravity. It is light and floats at the top of the mixer in the raw material stirring process and cannot be uniformly dispersed, and the addition of such pigments also reduces the total specific gravity of the raw materials, leading to a decrease in the transportability of the stirred raw materials. There were problems such as difficulty in biting into the entrance.

  Accordingly, the present invention relates to a powder coating composition and an object to be coated with the composition, and a powder coating having improved edge coverage of the coated object in order to suppress rust generation and corrosion from the edge part. An object is to provide a composition and a powder coating obtained by coating the composition.

As a result of intensive studies to solve the above problems, the present inventors have found that an alkyl acetalized polyvinyl alcohol containing a polyester resin and having an average molecular weight (Mw) of 40000 or less with respect to 100 parts by weight of the powder coating composition. A powder coating composition containing 0.1 to 10 parts by weight of a coating material and a coated object coated with the composition are covered with an edge portion of the coated material in order to suppress rust generation and corrosion from the edge portion. I found that sex improved.

That is, the powder coating composition of the present invention contains a polyester resin, and 0.1 to 10 parts by weight of an alkyl acetalized polyvinyl alcohol having an average molecular weight (Mw) of 40000 or less with respect to 100 parts by weight of the powder coating composition. It is characterized by becoming.

  The powder coating composition of the present invention and the powder coating obtained by coating the composition improve the coating coverage of the edge of the coating to suppress the occurrence of rust and corrosion from the edge. be able to.

  Hereinafter, the present invention will be described in detail.

  In the powder coating composition of the present invention, it is possible to use a compound usually used for a thermosetting powder coating, for example, a resin, a curing agent, a pigment, an additive and the like without particular limitation.

  As the resin used for the powder coating material, various resins conventionally used in the production of powder coating materials can be used. Examples of such resins include polyester-urethane curing resins, epoxy-polyester curing resins, epoxy resins, acrylic resins, acrylic-polyester resins, fluorine resins, acrylic-urethane curing resins, acrylics. -Melamine curable resin, polyester-melamine curable resin, alkyd resin, fluororesin, silicon resin, amide resin, ABS resin, novolac resin, modified resin such as phenoxy resin, ketone resin, polyester resin, rosin, etc. These resins can be used alone or in combination of two or more.

  As the curing agent, for example, various curing agents usually used for thermosetting resins can be used without particular limitation. Examples of such curing agents include amide compounds, acid anhydrides, dibasic acids, glycidyl compounds, aminoplast resins, blocked isocyanates, uretdione isocyanates, hydroxyalkylamides, and the like. Typical curing agents Examples thereof include dicyandiamide, acid hydrazide, triglycidyl isocyanurate, and isophorone diisocyanate block. For example, as dibasic acid, adipic acid, pimelic acid, suberic acid, sebacic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,20-eicosanedicarboxylic acid, hexahydrophthalic acid Maleic acid, phthalic acid, cyclohexene 1,2-dicarboxylic acid and the like.

  Examples of the pigment include titanium dioxide, bengara, iron oxide, zinc powder, carbon black, phthalocyanine blue, phthalocyanine green, quinacridone pigment, azo pigment, isoindolinone pigment, various calcined pigments, silica , Talc, barium sulfate, calcium carbonate, extender pigments such as glass flakes, aluminum pigments, aluminum powders such as aluminum paste, bright magenta pigments called white mica or silver mica showing white to silver turbid colors, and the like.

  Examples of other additives include sagging inhibitors, surface conditioners, ultraviolet absorbers, light stabilizers, antioxidants, and the like, which can be optionally blended as necessary.

  In the present invention, the alkyl acetalized polyvinyl alcohol having an average molecular weight (Mw) of 40000 or less needs to be blended in an amount of 0.1 to 10 parts by weight with respect to 100 parts by weight of the powder coating composition, and 0.5 to 5 weights. It is preferable to blend parts. When the blending amount of the alkyl acetalized polyvinyl alcohol having an average molecular weight (Mw) of 40000 or less is less than 0.1 part by weight, the viscosity characteristic of the paint is not improved, and a desired powder paint having good edge cover properties is obtained. I can't. On the other hand, when the amount exceeds 10 parts by weight, the melt viscosity of the coating material is remarkably increased and the appearance of the coating film is lowered. On the other hand, if the average molecular weight of the alkyl acetalized polyvinyl alcohol exceeds 40,000, the softening point and Tg increase, and it cannot be dispersed at the kneading temperature of the conventional powder coating by an extruder, which adversely affects the coating film appearance. The average molecular weight is preferably 8000 or more. The glass transition point is preferably 65 ° C. or lower.

  Powder coating materials are mixed at room temperature using a mixer such as a Nauter mixer or Henschel mixer, and then kneaded using a melt kneader commonly used in the production of powder coating materials such as monoaxial or biaxial extruders. To do. The pellets formed by kneading are pulverized using a pulverizer such as a pin mill or a jet mill, and adjusted to an arbitrary particle size distribution using a sieve or the like.

  The average particle size of the powder coating material containing 0.1 to 10 parts by weight of alkyl acetalized polyvinyl alcohol having an average molecular weight (Mw) of 40000 or less is preferably 20 to 150 μm, and more preferably 25 to 120 μm. . When the average particle size is smaller than 20 μm, the surface area of the particles of the powder coating to be electrostatically coated becomes large, and the amount of charge per unit volume of the powder increases, so there is a tendency to generate electrostatic repulsion even in a relatively thin film. . Once electrostatic repulsion occurs in the edge part, the powder easily falls from the part due to the phenomenon of electricity release, making it difficult to form a powder coating on the edge part, and the target edge cover is sufficiently It is not preferable because it cannot be achieved. On the other hand, when the average particle size exceeds 150 μm, the appearance of the coating film tends to deteriorate and the unevenness tends to increase. As a result, a concave portion is also generated at the edge portion, and the powder coating film is partially thinned. This is not preferable because rust is easily generated and corrosion proceeds easily.

  The obtained powder coating is applied to the object by electrostatic coating, and is heated and cured in a hot air oven, infrared furnace, induction heating furnace, etc. so as to reach an object temperature of 120 to 250 ° C. A film can be formed.

  Hereinafter, the present invention will be described in more detail with reference to the following examples and comparative examples. In the examples, “parts” and “%” are based on weight. The components used in the following examples and comparative examples are as follows.

<Example 1>
30 parts of thermosetting polyester resin “Iupica Coat GV230: made by Nippon Iupika Co., Ltd.” with an acid value of 53 mg KOH / g, 30 parts of bisphenol A type epoxy resin “Epicoat 1004: made by Japan Epoxy Resin Co., Ltd.” with an epoxy resin equivalent of 920 g / eq, additive As silica adsorbed acrylic acid oligomer "Modaflow Powder 2000: Monsanto Co., Ltd." 1 part, 0.3 parts of benzoin as defoamer, 1 part of carbon black as pigment, 30 parts of barium sulfate, 5 parts of titanium oxide, alkylacetalization As polyvinyl alcohol, 2 parts of “ESREC BL-10: Sekisui Chemical Co., Ltd. (average molecular weight 15000, glass transition point 59 ° C.)” were stirred with a Henschel mixer, kneaded with an extruder, pulverized, and classified with 180 mesh to obtain an average particle size Create a 35μm powder coating .

<Example 2>
Addition of 10 parts of IPDI (isophorone diisocyanate) ε-caprolactam block polyisocyanate resin “Vestagon B-1530: manufactured by HULS” to 50 parts of a thermosetting polyester resin having a hydroxyl value of 36 mgKOH / g Silica adsorbed acrylic acid oligomer “Modaflow Powder 2000: manufactured by Monsanto Co.” as an agent, 0.3 part of benzoin as a defoamer, 1 part of carbon black as a pigment, 30 parts of barium sulfate, 5 parts of titanium oxide, alkyl acetal 2 parts of “S-Lec BL-10: Sekisui Chemical Co., Ltd. (average molecular weight 15000, glass transition point 59 ° C.)” as a modified polyvinyl alcohol is stirred with a Henschel mixer, kneaded with an extruder, pulverized and classified with 180 mesh Diameter 35μm The powder coating was made.

<Comparative Example 1>
30 parts of thermosetting polyester resin “Iupica Coat GV230: made by Nippon Iupika Co., Ltd.” with an acid value of 53 mg KOH / g, 30 parts of bisphenol A type epoxy resin “Epicoat 1004: made by Japan Epoxy Resin Co., Ltd.” with an epoxy resin equivalent of 920 g / eq, additive As a silica adsorbed acrylic acid oligomer "Modaflow Powder 2000: manufactured by Monsanto Co., Ltd." 1 part, 0.3 parts of benzoin as a defoaming agent, 1 part of carbon black as a pigment, 30 parts of barium sulfate, 5 parts of titanium oxide in a Henschel mixer After stirring, the mixture was kneaded with an extruder, pulverized, and classified with 180 mesh to prepare a powder coating having an average particle size of 35 μm.

<Comparative example 2>
20 parts of thermosetting polyester resin "Iupica Coat GV230: made by Nippon Iupika Co., Ltd." with an acid value of 53 mgKOH / g, 20 parts of bisphenol A type epoxy resin "Epicoat 1004: made by Japan Epoxy Resin Co., Ltd." with an epoxy resin equivalent of 920 g / eq, additive 1 part of silica adsorbed acrylic acid oligomer “Modaflow Powder 2000: manufactured by Monsanto”, 0.3 part of benzoin as defoaming agent, 1 part of carbon black as pigment, 50 parts of barium sulfate, 5 parts of titanium oxide by Henschel mixer After stirring, the mixture was kneaded with an extruder, pulverized, and classified with 180 mesh to prepare a powder coating having an average particle size of 35 μm.

<Comparative Example 3>
30 parts of thermosetting polyester resin “Iupica Coat GV230: made by Nippon Iupika Co., Ltd.” with an acid value of 53 mg KOH / g, 30 parts of bisphenol A type epoxy resin “Epicoat 1004: made by Japan Epoxy Resin Co., Ltd.” with an epoxy resin equivalent of 920 g / eq, additive 1 part of silica adsorbed acrylic acid oligomer “Modaflow Powder 2000: manufactured by Monsanto”, 0.3 part of benzoin as defoaming agent, 1 part of carbon black as pigment, 30 parts of barium sulfate, 5 parts of titanium oxide, hydrophobic fine powder Silica “Aerosil RY200 (average particle size 12 nm): manufactured by Nippon Aerosil Co., Ltd.” 1 part was stirred with a Henschel mixer, kneaded with an extruder, pulverized and classified with 180 mesh to prepare a powder coating with an average particle size of 35 μm .

<Comparative example 4>
30 parts of thermosetting polyester resin “Iupica Coat GV230: made by Nippon Iupika Co., Ltd.” with an acid value of 53 mg KOH / g, 30 parts of bisphenol A type epoxy resin “Epicoat 1004: made by Japan Epoxy Resin Co., Ltd.” with an epoxy resin equivalent of 920 g / eq, additive As silica adsorbed acrylic acid oligomer "Modaflow Powder 2000: Monsanto Co., Ltd." 1 part, 0.3 parts of benzoin as defoamer, 1 part of carbon black as pigment, 30 parts of barium sulfate, 5 parts of titanium oxide, alkylacetalization As polyvinyl alcohol, 0.05 part of “S Lec BL-10: Sekisui Chemical Co., Ltd. (average molecular weight 15000, glass transition point 59 ° C.)” was stirred with a Henschel mixer, kneaded with an extruder, pulverized, and classified with 180 mesh. Powder coating with an average particle size of 35μm It was created.

<Comparative Example 5>
30 parts of thermosetting polyester resin “Iupica Coat GV230: made by Nippon Iupika Co., Ltd.” with an acid value of 53 mg KOH / g, 30 parts of bisphenol A type epoxy resin “Epicoat 1004: made by Japan Epoxy Resin Co., Ltd.” with an epoxy resin equivalent of 920 g / eq, additive As silica adsorbed acrylic acid oligomer "Modaflow Powder 2000: Monsanto Co., Ltd." 1 part, 0.3 parts of benzoin as defoamer, 1 part of carbon black as pigment, 30 parts of barium sulfate, 5 parts of titanium oxide, alkylacetalization As polyvinyl alcohol, 15 parts of “ESREC BL-10: Sekisui Chemical Co., Ltd. (average molecular weight 15000, glass transition point 59 ° C.)” were stirred with a Henschel mixer, kneaded with an extruder, pulverized, classified with 180 mesh, and averaged Made powder paint with a diameter of 35μm It was.

<Comparative Example 6>
30 parts of thermosetting polyester resin “Iupica Coat GV230: made by Nippon Iupika Co., Ltd.” with an acid value of 53 mg KOH / g, 30 parts of bisphenol A type epoxy resin “Epicoat 1004: made by Japan Epoxy Resin Co., Ltd.” with an epoxy resin equivalent of 920 g / eq, additive As silica adsorbed acrylic acid oligomer "Modaflow Powder 2000: Monsanto Co., Ltd." 1 part, 0.3 parts of benzoin as defoamer, 1 part of carbon black as pigment, 30 parts of barium sulfate, 5 parts of titanium oxide, alkylacetalization As polyvinyl alcohol, 2 parts of “S-REC BH-6: Sekisui Chemical Co., Ltd. (average molecular weight 92000, glass transition point 67 ° C.)” were stirred with a Henschel mixer, kneaded with an extruder, pulverized, classified with 180 mesh, and averaged Create a powder coating with a diameter of 35μm .

<Reference Example 1>
30 parts of thermosetting polyester resin “Iupica Coat GV230: made by Nippon Iupika Co., Ltd.” with an acid value of 53 mg KOH / g, 30 parts of bisphenol A type epoxy resin “Epicoat 1004: made by Japan Epoxy Resin Co., Ltd.” with an epoxy resin equivalent of 920 g / eq, additive As silica adsorbed acrylic acid oligomer "Modaflow Powder 2000: Monsanto Co., Ltd." 1 part, 0.3 parts of benzoin as defoamer, 1 part of carbon black as pigment, 30 parts of barium sulfate, 5 parts of titanium oxide, alkylacetalization As polyvinyl alcohol, 2 parts of “S-Rec BL-10: Sekisui Chemical Co., Ltd. (average molecular weight 15000, glass transition point 59 ° C.)” was stirred with a Henschel mixer, kneaded with an extruder, pulverized, classified with 300 mesh, and averaged Create a powder coating with a diameter of 18μm It was.

<Reference Example 2>
30 parts of thermosetting polyester resin “Iupica Coat GV230: made by Nippon Iupika Co., Ltd.” with an acid value of 53 mg KOH / g, 30 parts of bisphenol A type epoxy resin “Epicoat 1004: made by Japan Epoxy Resin Co., Ltd.” with an epoxy resin equivalent of 920 g / eq, additive As silica adsorbed acrylic acid oligomer "Modaflow Powder 2000: Monsanto Co., Ltd." 1 part, 0.3 parts of benzoin as defoamer, 1 part of carbon black as pigment, 30 parts of barium sulfate, 5 parts of titanium oxide, alkylacetalization As polyvinyl alcohol, 2 parts of “S-Rec BL-10: Sekisui Chemical Co., Ltd. (average molecular weight: 15000, glass transition point: 59 ° C.)” were stirred with a Henschel mixer, kneaded with an extruder, pulverized, and classified with 40 mesh. Create a powder coating with a diameter of 175μm It was.

  All the paints prepared in the above Examples, Comparative Examples and Reference Examples were degreased with 150 x 70 mm plate thickness 0.8 mm SPCC-B (manufactured by Nippon Test Panel Co.) with xylene and not subjected to chemical conversion treatment, etc. Using a body coating machine (PG-1 type, manufactured by Asahi Sunac Co., Ltd.), double-side coating was performed at a voltage of −60 kV so that the coating film thickness was 60 μm. Thereafter, it was heated and cured in an electric furnace at a material temperature of 200 ° C. for 20 minutes to prepare a test plate.

  Thereafter, various tests described below were performed, and the results are shown in Tables 1 to 3.

<State of coating film>
The state of the coating film is visually determined.

○: Good ×: Bad

<Weight drop resistance> Based on JIS K5600-5-3 (DuPont type) Evaluate resistance to weight drop. Evaluate the weight drop height that does not cause cracking or peeling of the coating film.

<Rust test from edge>
The test plate was put into a neutral-resistant salt spray tester for 96 hours, and the number of rust generated from the edge portion and a peel test using a cellophane tape were performed to obtain the peel width from the edge portion.

<Edge cover rate>
(i) The test plate was cut and polished, so that the situation where the edge portion was covered with the coating film could be confirmed with a microscope, and the film thickness of the edge portion was measured with a microscope.

  (ii) The film thickness of the normal part was measured with a film thickness meter at 10 mm from the edge part.

  Edge coverage ratio (%) = (i) Edge part film thickness / (ii) Normal part film thickness × 100

<Specific gravity of paint>
Calculated from catalog value data of raw materials.

<Conveyance test with screw feeder>
A transportability test was performed using an SFC screw feeder manufactured by Asahi Sunac Corporation. The material to be conveyed was a raw material before kneading in which each raw material was stirred with a Henschel mixer, and was carried out under the condition that the raw material of Comparative Example 1 was conveyed at 100 g / min. As a result, it was used as an index of transportability during paint production, penetration into the extruder, and production efficiency.

Claims (5)

It includes a polyester resin, to powder coating 100 parts by weight of the composition, average molecular weight (Mw) of the powder coating composition according to claim 40000 that is formed by an alkyl acetalized polyvinyl alcohol 0.1 to 10 parts by weight blended object.   The powder coating composition according to claim 1, wherein the glass transition point of the alkyl acetalized polyvinyl alcohol is 65 ° C or lower. The powder coating composition according to claim 1 or 2, wherein the compounding amount of the alkyl acetalized polyvinyl alcohol is 0.5 to 5 parts by weight based on 100 parts by weight of the powder coating composition. The powder coating composition according to any one of claims 1 to 3, wherein the powder coating has an average particle size of 20 to 150 µm. The powder coating composition in which the powder coating composition in any one of Claims 1-4 is coated.