JP2012201859A - Coating composition and coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder coating composition allowing for obtaining a uniform coating film with a high deposition efficiency and an excellent appearance even with a high-speed coating, as well as a powder coating method and a coated article using the same.SOLUTION: In the powder coating composition used with a flat conveying device with a conveyance speed being at least 15 m/min, a volume average particle size is 20-40 μm, a proportion of particles with 11 μm or less size is less than 12%, a true specific gravity is 1.3-2.0, and the maximum particle size is 180 μm or less. The powder coating method and the coated article using the same are also provided.

Description

  The present invention relates to a powder coating composition capable of high-speed coating, a powder coating method, and a coated product.

  Unlike conventional solvent-based paints, powder paints are said to be environmentally friendly because they do not use organic solvents, and are widely used industrially. In a user painting line using powder paint, it is common to hang an object to be coated on a conveyor and apply it in the form of an automatic gun, a hand gun or a powder fluidized bed. In addition, in a special user in which the object to be coated is limited to only a flat plate, the object to be coated is placed on a flat conveying device such as a belt conveyor and painted.

  However, in the method of coating the object to be hung on the conveyor, if the conveying speed is too fast, the object to be swayed from side to side will not be able to be applied uniformly and the film thickness will vary depending on the position of the object to be coated. Since there is a harmful effect such that it comes out, the coating efficiency of the paint decreases, and the amount of waste paint and recovered paint increases, there is a limit to the conveying speed in the painting line.

  Further, even in a coating method using a flat conveying device as disclosed in Patent Document 1, when coating is performed at a high speed, there is a range (paint cloud) in which the paint blown from the normal coating gun spreads in the space. A coating film having high coating efficiency, uniform and high appearance could not be obtained because it was covered with an object to be passed at high speed.

JP-A-6-343904

  An object of the present invention is to provide a powder coating composition, a powder coating method, and a coated product, which can obtain a coating film having high coating efficiency, uniform and good appearance even in high-speed coating.

  According to the present invention, there is provided a powder coating composition for use in a flat transport device having a transport speed of 15 m / min or more, wherein the volume average particle diameter is 20 to 40 μm, and the ratio of the particle diameter is 11 μm or less is less than 12%. A powder coating composition having a specific gravity of 1.3 to 2.0 and a maximum particle size of 180 μm or less is provided.

  Further, according to the present invention, a powder coating material having a volume average particle diameter of 20 to 40 μm, a ratio of the particle diameter of 11 μm or less is less than 12%, a true specific gravity of 1.3 to 2.0, and a maximum particle diameter of 180 μm or less. There is provided a powder coating method characterized by having a coating process by a flat transport apparatus having a transport speed of 15 m / min or more for the composition.

  Furthermore, according to the present invention, there is provided a coated product obtained by using the above powder coating method.

  According to the present invention, a powder coating composition capable of obtaining a uniform and high-appearance coating film with a high coating efficiency of 90% or more even in high-speed coating with a conveying speed of 15 m / min or more, its powder coating method and coating It became possible to provide things.

  Hereinafter, the present invention will be specifically described.

  By controlling the volume average particle diameter, the ratio of fine powder region, the ratio of coarse particles, the specific gravity and the melt viscosity of the powder coating, the present inventors have high coating efficiency and uniform and high appearance in flat transportation high speed coating. It was found that an excellent coating film can be obtained.

  As the powder coating composition used in the present invention, a composition usually used for a thermosetting powder coating, for example, a resin, a curing agent, a pigment, an additive and the like can be used without any particular limitation. I can do it.

  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 epoxy resins, epoxy-polyester curable resins, polyester-urethane curable resins, polyester-primid curable resins, acrylic resins, acrylic-polyester resins, fluororesins, and acrylic resins. -Urethane curing resin, acrylic-melamine curing resin, polyester-melamine curing resin, alkyd resin, fluorine resin, silicone resin, amide resin, ABS resin, novolac resin, phenoxy resin, ketone resin, polyester resin, rosin, etc. These resins can be used, and 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, and hydroxyalkylamides. Typical curing agents 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, and cyclohexene 1,2-dicarboxylic acid.

  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 And extender pigments such as talc, barium sulfate, calcium carbonate, and glass flakes, aluminum powders, aluminum powders such as aluminum paste, and bright pigments called white mica or silver mica showing white to silver turbid colors.

  Examples of other additives include a sagging inhibitor, a surface conditioner, an ultraviolet absorber, a light stabilizer, and an antioxidant, and can be arbitrarily blended as necessary.

  The thermosetting powder coating composition of the present invention has a volume average particle diameter of 20 to 40 μm, a ratio of the particle diameter of 11 μm or less is less than 12%, a true specific gravity of 1.3 to 2.0, and a maximum particle diameter. Is suitably 180 μm or less. When the volume average particle diameter is smaller than 20 μm or the true specific gravity is smaller than 1.3, the ratio of the powder discharge amount particles being blown off to the discharge air from the coating gun is increased and the coating efficiency is lowered. On the other hand, if the true specific gravity is larger than 2.0, when the conveying speed of the object to be coated is 15 m / min or more, the paint discharged from the coating gun is covered with the object to be passed at a high speed and the coating efficiency is lowered. . When the volume average particle diameter is larger than 40 μm or the maximum particle diameter is larger than 180 μm, the coating film appearance is deteriorated in addition to the decrease in the coating efficiency due to the tilt of the object to be coated. Further, when the ratio of the particle size of 11 μm or less is 12% or more, the paint tends to accumulate at the tip of the coating gun, and spits are likely to occur. In addition, said particle size measurement is the numerical value which measured the volume average particle diameter on the conditions which measure a normal powder coating material with a dry-type particle size distribution analyzer.

  The powder coating composition in the present invention preferably has a minimum melt viscosity of 400 Pa · S or less when the temperature is raised from 100 ° C. to 10 ° C./min. If it exceeds 400 Pa · S, a sufficient melt force cannot be obtained during baking and melting, and the appearance of the powder coating film is deteriorated. The melt viscosity in the present invention is a cone plate type viscosity measuring apparatus equipped with a temperature program controller (for example, Mettler-Toledo Co. (currently Waters Technologies Corporation / TA Instruments Co., Ltd.) equipped with Shimaden's temperature program controller FP21). It is a numerical value measured with a rheometer RM260 (numerical calculation software SWR-37) of a cone plate type viscosity measuring apparatus.

  The above-mentioned powder coating composition can form a coating film by being applied to an object by electrostatic coating or preheating coating and heated and cured so as to have an object temperature of 120 to 250 ° C. It is desirable to have a baking process using a baking hardening apparatus capable of baking and hardening in a short time with near infrared or induction heating. Unless these baking and curing devices are used in a short time, the heating furnace becomes very large on the high-speed conveying device of 15 m / min or more in the present invention, which is not economical. Alternatively, a batch method can be used, but there is a disadvantage that the production efficiency is lowered, which is also not economical. As described above, the upper limit of the conveying speed is that, as described above, if the conveying speed becomes very high, the coating efficiency of the powder coating material may be lowered due to the passing workpiece, and the heating furnace is very large. The upper limit speed is practically about 80 m / min because the scale becomes less economical.

  Moreover, in the said coating method, a coating film with a higher external appearance can be obtained if it has a process of preheating and holding the object to be coated at 100 ° C. to 130 ° C. within 60 seconds after coating and before baking and curing. If the heating and holding temperature is lower than 100 ° C, it is not sufficient to melt-flow the powder coating material. Conversely, if the temperature is higher than 130 ° C or if heated and held for more than 60 seconds, the curing reaction proceeds partially, which is good. Appearance is difficult to obtain.

  Hereinafter, the present invention will be described in more detail with reference to examples. In principle, “parts” means parts by mass.

<Example 1>
40 parts of a thermosetting polyester resin having a hydroxyl value of 50 mgKOH / g “Iupica Coat GV560: manufactured by Nippon Iupika” and a polyisocyanate resin “Alcure 4470: Eastman Chemical: IPDI (isophorone diisocyanate) 1,2,4-triazole block as a curing agent 7 parts, silica adsorbed acrylic acid oligomer "Polyflo-PW-95: manufactured by Kyoeisha" 1 part, benzoin 0.3 parts as defoaming agent, carbon black 1 part as pigment, precipitated barium sulfate 30 Parts and 20 parts of titanium oxide were stirred with a Henschel mixer, kneaded with an extruder, pulverized, and classified with 180 mesh to prepare a powder coating material having a volume average particle size of 30 μm. The powder coating was applied at a conveying speed of 15 m / min using a flat conveying device.

<Example 2>
The materials blended in the same manner as in Example 1 were stirred with a Henschel mixer, kneaded with an extruder, pulverized, and classified with 200 mesh to prepare a powder coating material having a volume average particle size of 27 μm. The powder coating was applied at a conveying speed of 15 m / min using a flat conveying device.

<Example 3>
Thermosetting polyester resin having a hydroxyl value of 34 mgKOH / g “Iupika Coat GV150: manufactured by Nippon Yupica” in 50 parts, polyisocyanate resin “Vestagon B-1530: manufactured by EVONIK Degussa” of IPDI (isophorone diisocyanate) ε-caprolactam block as a curing agent 9 parts, silica adsorbed acrylic acid oligomer "Polyflo-PW-95: manufactured by Kyoeisha" as an additive, 1 part, benzoin as a defoaming agent, 0.3 part, carbon black as a part, titanium oxide 5 parts, calcium carbonate 30 The parts were stirred with a Henschel mixer, kneaded with an extruder, pulverized, and classified with 180 mesh to prepare a powder coating material having a volume average particle size of 30 μm. The powder coating was applied at a conveying speed of 15 m / min using a flat conveying device.

<Example 4>
The materials blended in the same manner as in Example 3 were stirred with a Henschel mixer, kneaded with an extruder, pulverized, and classified with 150 mesh to prepare a powder coating material having a volume average particle size of 36 μm. The powder coating was applied at a conveying speed of 15 m / min using a flat conveying device.

<Comparative Example 1>
The material blended in the same manner as in Example 3 was stirred with a Henschel mixer, kneaded with an extruder, pulverized, and classified with 300 mesh to prepare a powder coating material having a volume average particle diameter of 19 μm. The powder coating was applied at a conveying speed of 15 m / min using a flat conveying device.

<Comparative example 2>
The materials blended in the same manner as in Example 3 were stirred with a Henschel mixer, kneaded with an extruder, pulverized, and classified with 120 mesh to prepare a powder coating material having a volume average particle size of 45 μm. The powder coating was applied at a conveying speed of 15 m / min using a flat conveying device.

<Comparative Example 3>
The materials blended in the same manner as in Example 3 were stirred with a Henschel mixer, kneaded with an extruder, pulverized, and classified with 270 mesh to prepare a powder coating material having a volume average particle diameter of 21 μm. The powder coating was applied at a conveying speed of 15 m / min using a flat conveying device.

<Comparative example 4>
Thermosetting polyester resin having a hydroxyl value of 34 mg KOH / g “Iupica Coat GV150: manufactured by Iupika Nippon, Japan” 80 parts IPDI (isophorone diisocyanate) 1,2,4-triazole block polyisocyanate resin “Alcure 4470: Eastman Chemical Co., Ltd. 14 parts, 1 part silica adsorbed acrylic acid oligomer “Polyflo-PW-95: manufactured by Kyoeisha” as additive, 0.3 part benzoin as defoaming agent, 1 part carbon black as pigment, 3 parts titanium oxide in Henschel After stirring with a mixer, the mixture was kneaded and pulverized with an extruder and classified with 180 mesh to prepare a powder coating material having a volume average particle size of 30 μm. The paint was applied at a transfer speed of 15 m / min using a flat transfer apparatus.

<Comparative Example 5>
Thermosetting polyester resin having a hydroxyl value of 50 mgKOH / g “Iupika Coat GV560: manufactured by Iupika Nippon” 35 parts as a curing agent IPDI (isophorone diisocyanate) ε-caprolactam block polyisocyanate resin “Vestagon B-1530: manufactured by EVONIK Degussa” 9 1 part of silica adsorbed acrylic acid oligomer “Polyflo-PW-95: manufactured by Kyoeisha” as additive, 0.3 part of benzoin as defoaming agent, 1 part of carbon black as pigment, 30 parts of precipitated barium sulfate, titanium oxide 20 parts were stirred with a Henschel mixer, kneaded with an extruder, pulverized, and classified with 180 mesh to prepare a powder coating material having a volume average particle size of 30 μm. The powder coating was applied at a conveying speed of 15 m / min using a flat conveying device.

<Comparative Example 6>
Except for the point that precipitated barium sulfate was used instead of calcium carbonate, the material blended in the same manner as in Example 3 was stirred with a Henschel mixer, kneaded with an extruder, pulverized, and classified with a 120 mesh. A powder coating material having an average particle diameter of 40 μm was prepared. The powder coating was applied at a conveying speed of 15 m / min using a flat conveying device.

  Table 1 shows the results of evaluating the appearance and coating efficiency of the obtained molded product. The appearance and coating efficiency of the coating film were evaluated according to the following evaluation methods.

<Appearance of coating film>
The unevenness of the coating film was visually evaluated according to the following criteria.
A: The coating film is smooth and smooth.
○: Slightly uneven coating.
Δ: The coating film has irregularities.
X: The unevenness of the coating film is remarkable, and the skin is distorted.

<Coating property>
The coating efficiency was calculated by the following calculation method.
Coating efficiency (%) = (weight of object after painting−weight of object before painting) / (discharge amount × painting time) × 100

<Example 5>
The powder coating prepared in Example 1 is used, and the powder coating is applied at a transfer speed of 15 m / min using a flat transfer apparatus, and the bake hardening is performed by combining a near-infrared generator and a hot-air circulating heating furnace. went.

<Example 6>
The powder paint produced in Example 3 is used, and the powder paint is applied at a transport speed of 15 m / min using a flat transport device, and the bake hardening is performed by combining a near-infrared generator and a hot air circulation heating furnace. went.

<Example 7>
The powder paint produced in Example 1 was used, and the powder paint was applied at a transport speed of 15 m / min using a flat transport device, and the bake curing was performed after preheating and holding at 100 ° C. for 30 seconds. This was performed by combining a near-infrared generator and a hot-air circulating heating furnace.

<Example 8>
The powder coating material produced in Example 3 was used, and the coating of the powder coating material was performed at a transport speed of 15 m / min using a flat transport device, and the bake hardening was performed after preheating and holding at 100 ° C. for 30 seconds. This was performed by combining a near-infrared generator and a hot-air circulating heating furnace.

<Example 9>
The powder paint produced in Example 3 was used, and the powder paint was applied at a transport speed of 60 m / min using a flat transport device, and the bake hardening was performed after preheating and holding at 100 ° C. for 30 seconds. This was performed by combining a near-infrared generator and a hot-air circulating heating furnace.
<Example 10>
The powder coating material produced in Example 3 was used, and the coating of the powder coating material was performed at a transport speed of 15 m / min using a flat transport device, and the bake curing was performed after preheating and holding at 110 ° C. for 60 seconds. This was performed by combining a near-infrared generator and a hot-air circulating heating furnace.

  Table 2 shows the results of evaluating the appearance and coating efficiency of the obtained molded body in the same manner as described above.

Claims (6)

A powder coating composition for use in a flat conveying device having a conveying speed of 15 m / min or more,
A powder coating composition having a volume average particle diameter of 20 to 40 μm, a ratio of the particle diameter of 11 μm or less is less than 12%, a true specific gravity of 1.3 to 2.0, and a maximum particle diameter of 180 μm or less. object.   The powder coating composition according to claim 1, wherein the minimum melt viscosity when heated from 100 ° C to 10 ° C / min is 400 Pa · s or less.   The conveyance speed of the powder coating composition having a volume average particle size of 20 to 40 μm, a particle size of 11 μm or less is less than 12%, a true specific gravity of 1.3 to 2.0, and a maximum particle size of 180 μm or less. A powder coating method comprising a coating process using a flat conveying device of 15 m / min or more.   Furthermore, the powder coating method of Claim 3 which has a baking process by the baking hardening apparatus provided with far infrared rays, near infrared rays, or induction heating after coating the said powder coating composition.   5. The powder coating method according to claim 3, further comprising a step of preheating and holding the object to be coated at 100 ° C. to 130 ° C. within 60 seconds before baking and curing.   A coated article obtained by using the powder coating method according to any one of claims 3 to 5.