JPH11246796A - Powder coating for pcm, powder coating process for pcm and pcm steel plate obtained thereby - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an extremely practical powder coating for PCM which exerts a high opacifying effect of a film and smoothness of a film, even when the film is thinned to yield a high bending processibility, a powder coating process for PCM and a PCM steel plate obtained thereby. SOLUTION: A powder coating for PCM contains a film-forming component, and its volume average particle size is from 3 to 30 μm. This powder coating for PCM contains, e.g. a thermosetting resin and a hardener as the film-forming component. In a powder coating process for PCM, a powder coating for PCM wherein the volume average particle size is adjusted to from 3 to 30 μm is blown against a steel plate through electrostatic spray coating using a powder coating gun. A PCM steel plate comprises a steel plate and a film which is formed on at least one surface of the steel plate, wherein the film is a film which is obtained by curing a powder coating for PCM wherein the volume average particle size is adjusted to from 3 to 30 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a powder coating for PCM, a method for coating powder for PCM, and a PCM steel sheet obtained by the method.

[0002]

2. Description of the Related Art The application of PCM (pre-coated metal) by electrostatic coating of powder coating has been applied to a wide variety of applications such as home electric appliances, building materials, steel products, and vehicle parts. PCM means that instead of painting on the assembled work, it is painted on a sheet-like steel plate in advance or painted while rewinding a coiled steel plate, and the painted steel plate is painted in a predetermined composition. It means a method of cutting, molding and commercializing. In the case of PCM, powder is used because it does not contain any organic solvent and does not cause environmental pollution problems, and it is possible to recover and reuse paint that has not been applied to the object to be coated during coating. Paint is often used. By the way, the painted PCM steel sheet is generally processed into a complicated shape after painting, so that high bending workability is required. In addition, home appliances also require a high coating smoothness. However, in order to satisfy the high bending workability, when the coating film of the PCM steel sheet is made thinner, the use of the conventional powder coating for PCM causes uneven coating, thereby hiding the coating film and the coating film. The smoothness decreases.

On the other hand, in the case of a PCM steel sheet, in order to maintain the concealing property of the coating film and to obtain a high smoothness of the coating film, the thickness of the coating film must be 30 μm or more, especially when the coating color is light color such as white. Needs to be thicker than 50 μm. Therefore, it has been difficult for conventional powder coating materials for PCM to achieve both high bending workability, high concealment of the coating film, and high smoothness of the coating film.

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a coating film having good concealing properties and good coating smoothness even when the coating film is made thinner in order to obtain high bending workability. Extremely practical powder coating for PCM, PCM
An object of the present invention is to provide a powder coating method for use and a PCM steel sheet obtained by the method.

[0005]

A powder coating for PCM according to the present invention is a powder coating for PCM containing a film-forming component, and has a volume average particle diameter of 3 to 30 μm. It is a powder paint. Here, the powder coating material for PCM contains, for example, a thermosetting resin and a curing agent as film-forming components. Further, for example, the thermosetting resin is a polyester resin, and the curing agent is a blocked isocyanate. In addition, the powder coating for PCM is, for example, a pigment of 5%.
５５55% by weight.

The powder coating method for PCM according to the present invention is characterized in that a powder coating for PCM having a volume average particle diameter of 3 to 30 μm is prepared by coating a steel sheet with an electrostatic powder coating method using a powder coating gun. This is a PCM powder coating method that is sprayed on the PCM. The PCM steel sheet according to the present invention is a PCM steel sheet comprising a steel sheet and a coating film formed on at least one side of the steel sheet, wherein the coating film has a volume average particle diameter of 3 to 30 μm.
It is a PCM steel plate which is a coating film formed by curing a powder coating for use.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Powder Coating for PCM The powder coating for PCM of the present invention contains a film-forming component. A thermosetting tree can be used as the film-forming component. As the thermosetting resin, those which are solid at room temperature are preferably used, and specific examples thereof include polyester resins, polyester resins mixed with acrylic resins, polyester resins mixed with epoxy resins, epoxy resins, and fluororesins.

Here, as the polyester resin, for example, a polyhydric alcohol such as ethylene glycol, diethylene glycol or neopentyl glycol and a carboxylic acid such as terephthalic acid, isophthalic acid, adipic acid or sebacic acid are polymerized according to a conventional method. Is used.

Examples of the acrylic resin used in the acrylic resin mixed polyester resin include styrene, acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, iso-butyl acrylate, and tert-butyl acrylate. And monomers obtained by polymerizing monomers such as glycidyl acrylate, glycidyl methacrylate and 2-methyl glycidyl methacrylate according to a conventional method. These acrylic resins are used by being mixed with the polyester resin described above.

Further, as the epoxy resin used for the polyester resin mixed with the epoxy resin, for example, a compound having two or more glycidyl groups (including oxirane) in one molecule is preferably used. Resins, glycidyl ether type resins such as condensation products of bisphenol A and epichlorohydrin, and condensation products of bisphenol F and epichlorohydrin, alicyclic epoxy resins, aliphatic epoxy resins, and bromide epoxy resins Phenol novolak type epoxy resin, cresol novolak type epoxy resin and the like are used. These epoxy resins are used by being mixed with the polyester resin described above. These epoxy resins can be used alone without being mixed with the polyester resin.

Further, as the fluororesin, those containing a hydroxyl group as a functional group are preferable, and a fluoromonomer,
A polymer obtained by polymerizing a hydroxyl group-containing alkyl monomer and a monomer used for the above-mentioned acrylic resin in accordance with a conventional method is used. Specifically, a brand name “Lubron L-2” manufactured by Daikin Industries, Ltd. can be exemplified.

Among such thermosetting resins, it is particularly preferable to use a polyester resin from the viewpoint of high mechanical strength and bending workability. This polyester resin
From the viewpoints of curability, bending workability, and smoothness of the coating film, those having a number average molecular weight of 2,000 to 8,000 and a hydroxyl value of 25 to 100 are preferable.

When the above-mentioned thermosetting resin is used, a curing agent is generally used in combination. This curing agent is included in the film-forming component. As the curing agent, various known ones can be used depending on the functional group of the thermosetting resin to be used. Specifically, blocked isocyanates (for example, trade name “Cleran U” manufactured by Sumitomo Bayer Urethane Co., Ltd.)
I "), aliphatic polycarboxylic acids such as sebacic acid, aliphatic acid anhydrides, aminoplast resins, epoxy resins, triglycidyl isocyanates, polyamide-based curing agents, hydroxyalkylamides (for example, products manufactured by Rohm and Haas Co.) Name "Primid XL552"), glycoluril curing agent (for example, trade name "Powderlink 1174" manufactured by Scitech), amine curing agent, triglycidyl isocyanurate, dicyandiamide, phenolic resin, imidazoles, imidazolines and the like. can do. In particular, when a polyester resin is used as the thermosetting resin, it is preferable to use a blocked isocyanate as a curing agent from the viewpoint of high mechanical strength and bending workability.

The weight ratio between the thermosetting resin and the curing agent is preferably in the range of 60:40 to 90:10 from the viewpoint of curability. Further, the above-mentioned thermosetting resin and curing agent may be used as a mixture of two or more kinds.

In view of the concealing property of the coating film, the bending property, the smoothness of the coating film, and the physical properties of the coating film, the powder coating 10
The film-forming component is preferably contained in an amount of 45 to 95 parts by weight based on 0 parts by weight. In addition, a thermoplastic resin can also be used as a film-forming component.

In the powder coating for PCM of the present invention, the pigment is added in an amount of from 5 to 5.
It may contain 55% by weight. When the content is less than 5% by weight, the concealing property of the coating film is inferior. Specific pigments include titanium dioxide, red iron oxide, yellow iron oxide, carbon black, phthalocyanine blue, phthalocyanine green, quinacridone pigments, coloring pigments such as azo pigments, talc, silica, calcium carbonate, precipitated barium sulfate and the like. An extender and the like can be exemplified.

The PCM powder coating of the present invention may contain various additives in addition to the above-mentioned film-forming components and pigments. Specifically, silicones such as dimethylsilicone and methylsilicone, surface modifiers such as acrylic oligomers, foam inhibitors such as benzoins such as benzoin and benzoin derivatives, curing accelerators (or curing catalysts), plasticizers , An antistatic agent, an antioxidant, a pigment dispersant, a flame retardant, a flow imparting agent, and the like.

Here, examples of the fluidity-imparting agent include “AEROSIL 13” manufactured by Nippon Aerosil Co., Ltd.
0 ”,“ AEROSIL 200 ”,“ AEROS ”
IL 300 ”,“ AEROSIL R-972 ”,
"AEROSIL R-812", "AEROSI"
LR-812S "," Titanium dioxide T-805 ",
"Titanium dioxide P-25", "Aluminium"
Oxide C "and the product name" Carplex FPS-1 "manufactured by Shionogi & Co., Ltd. can be exemplified.

The amount of the fluidizing agent to be added is set to 0.05 to 2.0% by weight in the powder coating from the viewpoint of the effect to be imparted, the smoothness of the coating film and the coating efficiency. Is preferred.

When the powder coating for PCM of the present invention is applied by being charged by a triboelectric charging method, it may contain a charge control agent for imparting triboelectric charging. As such a charge control agent, for example, inorganic fine particles such as aluminum oxide,
Alternatively, nitrogen compound-based organic fine particles and the like can be used, but it is preferable to use aluminum oxide fine particles in that chargeability and powder fluidity can be further improved.

The amount of the charge control agent to be added is preferably 0.03% in the powder coating in view of the effect to be imparted and the coating efficiency.
It is preferably set to 1.0% by weight.

The powder coating for PCM of the present invention can be produced through a step of making fine particles in addition to a conventional method for producing a powder coating. Specifically, the above-mentioned film-forming component, further, a pigment and other additives are mixed at a predetermined ratio,
This is melt-kneaded, cooled and coarsely pulverized. After the thus obtained coarsely pulverized particles are further finely pulverized, fine particles and coarse particles are removed as required using a classifier.

The powder coating for PCM of the present invention produced through such a process has a volume average particle diameter of 3 to 30 μm,
Preferably 10-30 μm, more preferably 20-30
μm. The volume average particle diameter used in the present invention can be determined by a particle diameter measuring device using a laser light scattering method generally used in the field of powder coatings.

When the volume average particle diameter is less than 3 μm, the process of producing the coating material is often complicated, and the efficiency of applying the powder coating material to the object to be coated may be reduced. Conversely, when the volume average particle diameter exceeds 30 μm, coating unevenness occurs at the time of thin film, and the concealing property of the coating film and the smoothness of the coating film decrease.

Powder Coating Method for PCM The powder coating method for PCM of the present invention has a volume average particle diameter of 3
PCM spraying powder paint set to ~ 30μm onto steel plate by electrostatic powder coating method using powder coating gun
Powder coating method.

The powder coating used in the powder coating method for PCM of the present invention has a volume average particle diameter of 3 to 30 μm. As such a powder coating, the above-mentioned powder coating for PCM can be used.

The PCM powder coating method of the present invention utilizes an electrostatic powder coating method using a powder coating gun. Examples of the powder coating gun include a corona charging coating gun and a friction charging coating gun. The corona charging type coating gun is a corona discharge treatment of powder coating and sprays it.
The triboelectric coating gun sprays a powder coating by triboelectric treatment.

The object to be coated used in the powder coating method for PCM of the present invention is not particularly limited as long as it is a steel plate used for PCM. In the powder coating method for PCM of the present invention, an object to be coated is usually grounded, and a powder coating for PCM is sprayed on the object using a powder coating gun.

At this time, the discharge rate of the powder coating for PCM from the powder coating gun is preferably set to 50 to 200 g / min. The distance from the tip of the gun portion of the powder coating gun to the object to be coated is 150 to 40 from the viewpoint of coating efficiency.
Preferably, it is set to 0 mm.

When the powder coating for PCM is discharged from the corona charging type coating gun and applied, the applied voltage applied to the components constituting the powder coating by corona discharge treatment is -50 to-
100 KV, and -60 from the viewpoint of coating efficiency and appearance.
It is preferable to set to -80 KV.

On the other hand, when the powder coating for PCM is discharged from the triboelectric coating gun to perform coating, the current value generated inside the powder coating is 1.0 to 8 from the viewpoint of coating efficiency and appearance. .
It is preferable to perform a triboelectric charging treatment so as to be 0 μA.

In the industrial implementation of the powder coating method for PCM of the present invention by forming an electrostatic coating line, for example, a grounded conductive horizontal belt for installing an unpainted steel plate and grounding the steel plate is used. A conveyor is laid in the coating room, and a gun is installed above the coating room. Here the painting pattern width is 50 ~
500 mm, the operation speed of the gun is preferably 1 to 30 m / min, and the conveyor speed is preferably 1 to 50 m / min. Appropriate conditions may be selected from these ranges according to the purpose. The steel sheet thus obtained is 170-260 ° C
For a predetermined time. In industrial practice, it is preferable to process from the input to the discharge of the baking furnace within 5 minutes.

The PCM steel sheet according to the present invention comprises a steel sheet and a coating film formed on at least one side of the steel sheet, and the coating film is formed by curing a PCM powder coating material having a volume average particle size of 3 to 30 μm. It is a PCM steel plate comprising a coating film. This PCM steel sheet can be formed by the PCM powder coating method using the above-described PCM powder coating.

The thickness of the coating film of the PCM steel sheet according to the present invention varies depending on the coating color.
5 to 40 μm, dark colors such as black have an average film thickness of 15 to 3
It can be 0 μm. If the thickness of the coating film exceeds these values, the bending property of the PCM steel sheet will not be improved. Here, the light-colored paint color is L ^* a ^* b ^* measured by a chromaticity measuring device ^.
The average value of the L ^* values of the color system chromaticity is 70 or more, and the average value of the dark color paint is less than 70. Regarding the smoothness of the coating film, the average Ra value of the coating film of the PCM steel sheet according to the present invention is preferably 0.6 or less.

Incidentally, the average film thickness is defined as 20 times within a PCM steel sheet.
It is the average value of the film thickness measured in several places, and the average L value is PC
This is the average of L ^* values measured at 20 locations in a M steel plate using a chromaticity meter. The average Ra value is an average value of Ra values measured at 20 locations in a PCM steel sheet using a surface roughness shape measuring instrument.

[0036]

Example 1 Production of powder coating for PCM with a deep coating color Fine Dick M-8076 60.0 parts by weight (polyester resin manufactured by Dainippon Ink and Chemicals, Inc.) Cleran UI 20.0 parts by weight (Sumitomo) (Block isocyanate manufactured by Bayer Urethane Co.) Titanium dioxide 20.0 parts by weight Carbon black 1.5 parts by weight Calcium carbonate 5.0 parts by weight Benzoin 0.3 parts by weight Irganox 1010 0.5 parts by weight (antioxidant manufactured by Ciba Geigy) CF-1056 0.1 parts by weight (Silicone-based surface conditioner manufactured by Toshiba Silicone Co., Ltd.)

Using the above components as raw materials, the mixture was mixed for about 3 minutes using a supermixer (manufactured by Nippon Spindle Co., Ltd.), and was further melt-kneaded at about 100 ° C. using a melt kneader (kneader, Buss). Thereafter, the obtained melt-kneaded material was cooled to room temperature, coarsely pulverized using a pulverizer atomizer (manufactured by Fuji Paudal), and further finely pulverized by a jet mill IDS-2 type (manufactured by Nippon Pneumatic). And pulverized. The obtained powder was classified using an airflow classifier DS-2 (manufactured by Nippon Pneumatic Industries, Ltd.) to remove fine particles and coarse particles. As a result, a gray polyester resin-based powder coating for PCM having a volume average particle diameter of 25 μm, which is a dark-colored coating color, was obtained.

The volume average particle size and the particle size distribution are values measured using a particle size analyzer Microtrac HRAX-100 (manufactured by Nikkiso Co., Ltd.). For this measurement,
As an analysis program, MICRO TRAC D. H.
S. X100 DataHandling Syst
em SD-9300PRO-100 (manufactured by Nikkiso Co., Ltd.) and "Particle Trans"
The parameter “parameter” was set to “reflect.” The measurement sample was polyoxyethylene (1) in a sample bottle.
0) 0.1% by weight aqueous solution of octyl phenyl ether 50
g and 0.5 g of the powder coating material to be measured are added, and the sample bottle is placed in an ultrasonic cleaner SILENTSONIC UT.
Powdered paint dispersed water immersed in water subjected to ultrasonic vibration with -105 (manufactured by Sharp Corporation) for 3 minutes was used.

[0039] except that not performed grinding with Comparative Example 1 mill, by the same procedure as in Example 1, the volume average particle diameter is determined in 40 [mu] m, gray polyester resin system is a dark color paint color P
A powder coating for CM was obtained.

Example 2 A powder coating method for PCM and a dark-colored PCM steel sheet to be coated obtained by the method were as follows.
A steel plate having a thickness of 0.8 mm and a phosphoric acid-treated steel plate having a thickness of 600 mm × 300 mm (hereinafter referred to as a steel plate) is grounded so that the plane of the steel plate is perpendicular to the coating direction. It was installed on a horizontal belt conveyor. The coating gun was installed so that the distance from the tip of the gun head of the corona charged coating gun PG-1 (manufactured by GEMA) to the steel plate was 300 mm, and was obtained in Example 1 while moving the steel plate at a constant conveyor moving speed. The PCM powder coating was applied at a set film thickness of 20 to 25 μm. The coating conditions were as follows. Horizontal belt conveyor moving speed 3.0m / min Painting gun applied voltage -80KV

Next, the obtained steel sheet was baked and hardened in a hot air baking drying oven at 230 ° C. for 2 minutes to obtain a PCM steel sheet. With respect to the coating film of the PCM steel sheet, the actual coating film thickness, average Ra value, average L value, concealment variation, and bending workability were evaluated. Table 1 shows the results of these evaluations. The evaluation method is as follows.

<Actual coating film thickness> Electromagnetic film thickness meter LX-2
Using 00 (manufactured by Kett Scientific Research Institute), the film thickness was measured at 20 places in the coated steel plate. The average film thickness was an average value of the measured film thicknesses at 20 locations. <Average Ra value of coating film> Surfcom 470, a surface roughness measuring instrument
A (manufactured by Tokyo Seimitsu Co., Ltd.) under the measurement conditions of cut-off 2.5 mm, R
The a value was measured, and the average value was obtained and defined as the average Ra value. When the Ra value is 0.6 or less, the coating film has good smoothness. <Average L value of coating film, variation in concealment of coating film> Chromaticity measuring device SM Color Computer SM-7 (manufactured by Suga Test Instruments Co., Ltd.)
The L value was measured at 20 points in a steel plate coated with reflection under the measurement conditions, and the average value was determined as the average L value, and the difference between the maximum value and the minimum value was determined as the concealment variation.
When the value of this variation is 0.40 or less, the hiding power of the coating film is good. (Compliant with JISZ 8722-4-2) <Bending workability> When a painted steel plate is directly bent 180 degrees without sandwiching anything, the cracks in the coating film generated at the bent portion are visually and visually evaluated with a loupe. did. ◎… No cracks are observed even with a loupe ○… No cracks are visually observed, but fine cracks are observed with a loupe

Example 3 A PCM steel sheet was obtained in the same procedure as in Example 2, except that the set film thickness was 30 to 40 μm. Table 1 shows the evaluation results.

Comparative Example 2 A PCM steel sheet was obtained in the same procedure as in Example 2, except that the one obtained in Comparative Example 1 was used as the powder coating for PCM.
Table 1 shows the evaluation results.

Comparative Example 3 A PCM steel sheet was obtained in the same procedure as in Example 2 except that the powder coating obtained in Comparative Example 1 was used as a powder coating for PCM, except that the set film thickness was 30 to 40 μm. Table 1 shows the evaluation results.

[0046]

[Table 1]

Example 4 Production of PCM Powder Coating of Light Color Coating Color A PCM powder coating was produced in the same procedure as in Example 1 except that the blending amount of carbon black was 0.1 part by weight. As a result, a white polyester resin-based PC having a light-colored coating color with a volume average particle diameter of 25 μm was determined.
A powder coating for M was obtained.

Example 5 A powder coating method for PCM and a light-colored PCM steel sheet obtained by using the powder coating obtained in Example 4 and having a set film thickness of 30 were used.
PC by the same procedure as in Example 2 except that
An M steel plate was obtained. Table 2 shows the evaluation results.

Example 6 A PCM steel sheet was obtained in the same procedure as in Example 2 except that the powder coating obtained in Example 4 was used as the powder coating for PCM and the set film thickness was 40 to 50 μm. Table 2 shows the evaluation results.

Comparative Example 4 A white polyester resin-based PCM having a light-colored coating color, which was determined to have a volume average particle diameter of 40 μm, in the same procedure as in Example 4 except that pulverization by a pulverizer was not performed.
Powder coating was obtained.

Comparative Example 5 A PCM steel sheet was obtained by the same procedure as in Example 2 except that the powder coating obtained in Comparative Example 4 was used as the PCM powder coating material, and the set film thickness was 30 to 40 μm. Table 2 shows the evaluation results.

Comparative Example 6 A PCM steel plate was obtained by the same procedure as in Example 2 except that the powder coating obtained in Comparative Example 4 was used as the PCM powder coating material, and the set film thickness was 40 to 50 μm. Table 2 shows the evaluation results.

[0053]

[Table 2]

[0054]

The powder coating material for PCM according to the present invention has a volume average particle diameter of 3 to 30 μm. Therefore, even when the coating film is made thin, high bending workability and concealing property of the coating film can be obtained. High smoothness of the coating film can be achieved at the same time.

In particular, in the case of light-colored coating colors,
Where the coating film thickness could not be ensured unless the coating film thickness was 50 μm or more, even if a thin film of 40 μm or less by using the powder coating for PCM according to the present invention,
It is possible to maintain the concealing property of the coating film and the high smoothness of the coating film, and to obtain a PCM steel sheet having extremely good bending workability.

The powder coating method for PCM according to the present invention can reduce the amount of powder coating used in the powder coating line by thinning, so that the production cost of PCM steel sheets can be suppressed. It is pollution-free and fits for resource saving.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C09D 5/03 C09D 5/03 175/06 175/06

Claims (11)

[Claims] 1. A PCM powder coating material containing a film-forming component, wherein the volume average particle diameter is set to 3 to 30 μm. 2. The powder coating for PCM according to claim 1, wherein the film-forming component comprises a thermosetting resin and a curing agent. 3. The powder coating for PCM according to claim 2, wherein said thermosetting resin is a polyester resin and said curing agent is a blocked isocyanate. 4. The powder coating material for PCM according to claim 1, which contains 5 to 55% by weight of a pigment. 5. A powder coating method for PCM, wherein a powder coating material having a volume average particle size of 3 to 30 μm is sprayed on a steel sheet by an electrostatic powder coating method using a powder coating gun. 6. A powder coating method for PCM according to claim 5, wherein said coating gun is a corona charging type coating gun capable of performing corona discharge treatment. 7. The powder coating method for PCM according to claim 5, wherein said coating gun is a triboelectric charging gun capable of triboelectric charging. 8. A PCM steel sheet comprising a steel sheet and a coating film formed on at least one surface of the steel sheet, wherein the coating film is formed by curing a PCM powder coating material having a volume average particle size of 3 to 30 μm. PCM steel plate which is a coating film consisting of 9. The PCM steel sheet according to claim 8, wherein the coating has an average thickness of 15 to 40 μm. 10. The PC according to claim 8, wherein said coating has an average L value of less than 70 and an average film thickness of 15 to 30 μm.
M steel plate. 11. The PCM steel sheet according to claim 8, wherein said coating has an average Ra value of 0.6 or less.