JPH1180610A - Powder coating and film forming method using said powder coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a powder coating which can easily form a highly insulating film even in a small thickness without sacrificing the mechanical strength of the film and the storage stability of the powder coating by incorporating particles of a resin powder contg. an insulating flat powder, a noncrystalline resin, and a crystalline resin. SOLUTION: An insulating flat powder, such as a mica powder, a glass powder, a ceramic powder, or a plastic powder, having an average particle diameter of 5 to 30 μm, pref. 10 to 30 μm, in an amt. of 10 to 50 wt % is mixed with particles of a resin powder having a particle diameter of not more than 5 μm comprising 90 to 60 wt.% noncrystalline resin having a softening point of 100 deg.C or below and 10 to 40 wt.% crystalline resin having an m.p. of 120 deg.C or above to obtain a powder coating. The powder coating M and an object W with a pressure-sensitive adhesive layer formed thereon are placed in an annular space 1d of a container 1. A decentered weight 2d is rotated through a motor 2c of a vibrating device 2, and the container 1 is vibrated through a vertical shaft 2e attached to a diaphragm 2b, thereby adhering particles constituting the powder coating onto the pressure-sensitive layer of the object W through the film-forming medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder coating used in a method for forming a film on various articles and a method for forming a film using the powder coating.

[0002]

2. Description of the Related Art The inventors of the present invention apply vibration to a mixture of a powder coating material, a film forming medium, and an article forming a film (hereinafter, simply referred to as "object to be coated") by a vibration device. Proposed a method for forming a film on an object to be coated on which an adhesive layer was formed. In order to enhance the insulating property of the film formed by the above film forming method, it is necessary to reduce pinholes and irregularities on the film surface (eliminating extremely thin portions). Thick film coating is applied to make it thicker.

[0003] An example of a method of forming a film using a film forming apparatus to which the above-described method of forming a film is applied will be outlined below with reference to FIG.

[0004] Reference numeral 1 denotes a bowl-shaped container made of a hard material such as a hard synthetic resin or metal, and has an opening 1a formed at an upper portion thereof. Further, the central portion of the bottom portion 1b is bulged upward almost to the height of the opening portion 1a to form the columnar portion 1c, whereby an annular space 1d is formed around the columnar portion 1c.

[0005] Reference numeral 2 denotes a vibration device. The vibration device 2 has a vibration plate 2b provided on a machine base 3 and supported by a plurality of coil springs 2a. A motor 2c is hung at a lower central portion of the diaphragm 2b, and a weight 2d is eccentrically attached to an output shaft 2c 'of the motor 2c extending downward. Also, in the upper central part of the diaphragm 2b,
A vertical axis 2e is attached, and at the upper end of the vertical axis 2e,
The upper part of the columnar part 1c of the container 1 is attached. Therefore,
By rotating the motor 2c, the eccentric weight 2
d is rotated so that the vertical axis 2e mounted on the diaphragm 2b
, The container 1 is vibrated.

[0006] In the annular space 1d of the container 1, a granular film forming medium formed of rubber, synthetic resin, ceramics, metal, or the like, a powder coating material described later, or a coloring agent, a spreading agent, a foaming agent, if necessary. A mixture M made of an appropriate additive such as an inhibitor and a curing accelerator, and an object to be coated W having an adhesive layer formed on the surface thereof with an uncured resin, a liquid material, or the like are put in advance.
Next, when the vibration device 2 is driven, the particles constituting the powder paint (hereinafter, particles constituting the powder paint are simply referred to as “powder”) on the adhesive layer of the workpiece W via the film-forming medium. (Referred to as “body particles”). The attached powder particles are
The powder particle layer is formed by being beaten to the film-forming medium and firmly pressed or pressed into the adhesive layer. Further, by repeatedly being beaten to the film forming medium, the pressure-sensitive adhesive is extruded from the surface of the powder particle layer adhered thereto. Adheres. In this way, the formation of a film on the surface of the object to be coated proceeds. Then, the film formation on the surface of the object to be coated ends when the pressure-sensitive adhesive is no longer extruded from the surface of the powder particle layer even if the powder particle layer is hit by the film forming medium. . By subjecting the object on which the powder particle layer is formed as described above to heat treatment, a film is formed.

Conventionally, in order to enhance the insulation of a product on which a film has been formed by the above-described method of forming a film, a powder coating is required to have at least an excellent insulating property with resin powder particles which are melted during heat treatment. What consists of flat powders, such as mica, is known. As described above, as the powder coating for the film forming method, a powder coating composed of resin powder particles that are melted during heat treatment and flat powder of mica or the like having excellent insulating properties is used to coat the object to be coated. On the surface, a film layer composed of resin powder particles and flat powder arranged in parallel to the film is formed, and then heat-treated to melt the resin powder particles, and the resin is placed between the insulating flat powders. Will be formed.

[0008]

However, when a thick film is applied to enhance the insulating property, the amount of powder paint used increases, which is uneconomical. Due to space restrictions, thin film coating is often required, and there is a problem that it is difficult to perform thick film coating.

In addition, using a powder coating composed of resin powder particles that melt during heat treatment and insulating flat powder, the resin powder particles and the coating are arranged in parallel on the surface of the object to be coated. A coating layer made of the flattened powder is formed, and then heat-treated to melt the resin powder particles to form a coating in which a resin is interposed between the insulating flat powders.
By using such flat powder and arranging the flat powder horizontally with respect to the film, pinholes of the film can be reduced and the surface of the film can be smoothed by the flat powder. However, in the conventional powder coating, at the time of heat treatment, due to poor fluidity of the molten resin, the surface of the insulating flat powder is not sufficiently dispersed with the molten resin,
Due to the poor wettability (adhesion) between the molten resin and the insulating flat powder, the electric current passes through the front surface of the insulating flat powder to the back surface, and thus the withstand voltage is reduced. there were. It is conceivable to use a low molecular weight resin to increase the fluidity when molten, but low molecular weight resins are
It is not preferable because storage stability is poor.

An object of the present invention is to solve the problems of the above-mentioned conventional powder coating and the method of forming a film using the powder coating.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention firstly provides a method of forming a powder coating material on a workpiece having an adhesive layer formed on its surface in advance via a film forming medium. Powder coating used in a method of forming a film to adhere particles, wherein the powder coating comprises insulating flat powder, and resin powder particles containing at least an amorphous resin and a crystalline resin. Second, the softening point of the non-crystalline resin is set to 100 ° C. or less, and the melting point of the crystalline resin is set to 12 ° C.
Thirdly, after the resin powder particles are dry-mixed with at least a composition comprising an amorphous resin and a crystalline resin, the softening point of the amorphous resin is higher than or equal to 0 ° C. After being melt-kneaded under a temperature condition equal to or lower than the melting point of the crystalline resin, it is obtained by pulverization and classification.Fourth, the non-crystalline resin and the crystalline resin are epoxy resins, Fifth, the insulating flat powder is mica powder, and sixth, the weight ratio between the non-crystalline resin and the crystalline resin is 90:10 to 60:40. 7 is a method for forming a pressure-sensitive adhesive layer on a surface of an object to be coated, and applying the powder coating particles to the obtained object to be coated via a film-forming medium. Item 1
To 6 using a powder coating.

[0012]

Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments unless it departs from the gist of the present invention.

A feature of the present invention is that the insulating flat powder is contained in a powder coating, and the insulating flat powder includes mica powder, glass powder, ceramic powder, plastic powder, rubber powder, and other powder. Powders of inorganic compounds and the like may be mentioned, and one kind or a mixture of two or more kinds may be used. Among them, mica powder which has a particularly large aspect ratio, has a thin and wide shape, and is laminated and superposed on the surface of the object to be coated, thereby obtaining an object to be coated having high insulating property is preferable. In addition, the surface of the insulating flat powder is typified by a coupling treatment, a hydrophobic treatment, a resin coating, or the like, for the purpose of improving adhesion with resin powder particles, or improving corrosion resistance or weather resistance. Various surface treatments may be applied. The insulating flat powder has a shape in which a three-dimensional object is crushed between surfaces, and the average particle diameter of the opposing flat surface is 5 to 5.
The size is preferably in the range of 30 μm, and more preferably 1 μm.
It is preferably from 0 to 30 μm. When the average particle size of the insulating flat powder is less than 5 μm, the direction of the insulating flat powder is not correct in the film on the surface of the workpiece because the resin powder particles are relatively larger than the insulating flat powder. It is not preferable because the insulating property tends to be low because it is formed uniformly and does not form a laminated structure. Further, if the average particle diameter of the insulating flat powder is larger than 30 μm, it becomes large and heavy, so that the transportability becomes poor,
It is difficult to uniformly adhere to the adhesive layer formed on the surface of the object to be coated, and is easily separated from the adhesive layer and the film-forming medium and stays on the bottom surface in the coating machine. As a result, the ratio of the flat powder in the powder coating material decreases, and it becomes difficult to uniformly adhere the flat powder to the surface of the object to be coated. The average particle size of the insulating flat powder was measured using Nikkiso Co., Ltd.'s Microtrack, after sufficiently dispersing the flat powder in water to which a surfactant was added using an ultrasonic disperser. is there. In addition, the flat surface refers to a flat surface as compared with a spherical object or an irregular-shaped object, and may be a flat surface due to deformation due to distortion, warping, bending of a bowl, or unevenness. The surfaces do not necessarily have to be parallel. Further, the content of the insulating flat powder in the powder coating can be added at a ratio of 10 to 50% by weight. If the amount is less than 10% by weight, no improvement in the withstand voltage is observed, and the insulating property is low.

Another feature of the present invention is that it has a crystal structure,
Since it has a low molecular weight and a narrow molecular weight distribution, it melts instantly when it reaches its melting point, and has a very low viscosity above the melting point. It was added to. The melting point is 1
It is preferable to use a crystalline resin having a temperature of 20 ° C. or higher and an amorphous resin having a softening point of 100 ° C. or lower. Here, the melting point refers to a peak of heat absorption in differential scanning calorimetry (DSC), and the softening point refers to a value measured by a ring and ball method according to JIS K 7234. In addition, as the crystalline resin, a resin having a crystal structure such as an epoxy resin, a polyester resin, and an acrylic resin can be used. Among them, an epoxy resin is particularly preferable because of its high insulating property. In addition, as the non-crystalline resin, epoxy resin, acrylic resin, phenol resin, xylene resin, urea resin, melamine resin,
Resins such as polyester resin, polyethylene resin, silicone resin and polyurethane resin are used alone or in combination. Among them, particularly when the crystalline resin is an epoxy resin, an epoxy resin having excellent compatibility with the crystalline resin is preferable.

When a thermosetting resin is used as the non-crystalline resin or the crystalline resin, it is preferable to use a curing agent having a functional group capable of undergoing a cross-linking reaction with the functional group of the thermosetting resin. Examples of the curing agent include amines, amides, dicyandiamide, carboxylic acids such as dodecane diacid,
A curing agent such as an acid anhydride, isocyanate, polysulfide, acid hydrazide, imidazole or the like is used alone or in combination.

When the crystalline resin and the non-crystalline resin are melt-kneaded at a temperature not lower than the melting point and the softening point of both, they are compatible with each other and the crystal structure is impaired, resulting in a resin having only a low softening point. The storage stability of the powder coating deteriorates. for that reason,
After dry-mixing a composition consisting of a crystalline resin having a melting point of 120 ° C. or more and a non-crystalline resin having a softening point of 100 ° C. or less so that the two are not compatible, the softening point of the non-crystalline resin As described above, after melt-kneading under a temperature condition equal to or lower than the melting point of the crystalline resin, by pulverizing and classifying, the resin powder particles can be produced without impairing the crystallinity of the crystalline resin in the resin powder particles. Can be.

The proportion of the crystalline resin and the non-crystalline resin constituting the resin powder particles is preferably such that the resin powder particles contain 10 to 40% by weight of the crystalline resin. This amount is 1
When the amount is less than 0% by weight, the wettability (adhesion) with the insulating flat powder is insufficient due to the insufficient amount of addition, and the withstand voltage is low. In addition, a crystalline resin having a low molecular weight and a high crosslink density has a large curing shrinkage. When the weight ratio exceeds 40%, fine cracks are easily generated in the film, so that the withstand voltage and the mechanical strength of the film are increased. Is undesirably reduced.

It is preferable that the volume ratio of the resin powder particles having a particle diameter of 5 μm or less is large because the directionality and coating properties of the insulating flat powder are good, and particles having a particle diameter of 5 μm or less are preferable.
Preferably, it is contained in an amount of 10% by weight or more. In addition,
The particle shape of the resin powder particles is Coulter Multisizer II
Can be measured.

Further, the resin powder particles may have, if necessary,
Various fillers such as calcium carbonate, barium sulfate, and talc; various thickeners such as silica, alumina and aluminum hydroxide; various colorants such as copper phthalocyanine, azo pigments and condensed polycyclic compounds; and butyl acrylate Acrylic oligomers, various spreading agents such as silicones, various foaming inhibitors such as benzoin, further curing accelerators, waxes,
Various additives such as a coupling agent and an antioxidant and various functional materials can be appropriately added. For example, the resin powder particles are dry-mixed using a mixer or a blender or the like, and the resulting mixture is melt-kneaded using a kneader or the like, and the resulting kneaded material is cooled. afterwards,
It can be obtained by pulverizing using a mechanical or airflow type pulverizer and then classifying.

The powder coating of the present invention can be obtained by mixing the above-mentioned insulating flat powder and resin powder particles. For this mixing, dry mixing using a mixer or a blender or the like is preferable from the viewpoint of productivity and uniform mixing of the powder coating. Incidentally, the powder coating of the present invention, for the purpose of improving the mixing and dispersing properties of the insulating flat powder and the resin powder particles, improving the fluidity and storage stability of the powder coating, as necessary,
Inorganic fine particles such as silica fine particles and alumina fine particles, crosslinked resin particles such as methyl methacrylate, and a fluidity imparting agent such as metal soap such as zinc stearate may be appropriately added by dry mixing.

Examples and Comparative Examples The compositions of the powder coating compositions used in Examples and Comparative Examples are as follows. The following epoxy resins were used as the crystalline resin and the non-crystalline resin. Non-crystalline resin: YD-014, softening point 95 ° C (manufactured by Toto Kasei) Crystalline resin: YDC-1312, melting point 140 ° C (manufactured by Toto Kasei) Curing agent: dicyandiamide (manufactured by Ube Industries) Agent: imidazole (manufactured by Shikoku Chemicals) spreading agent: polyacrylic acid butyl ester (manufactured by BASF) foaming inhibitor: benzoin (manufactured by Midori Kagaku) After dry-mixing the powder coating composition having the above composition, 1
After melt-kneading and cooling at a temperature of 00 ° C., the mixture was pulverized and classified so that the volume ratio of particles having a particle diameter of 5 μm or less was 50% to obtain resin powder particles. On the other hand, mica powder (Daimo UV-50: average particle diameter 6 μm (manufactured by Topy Industries)) was used as the insulating flat powder, and
3 and Comparative Examples 1 and 2, resin powder particles and mica powder
The powder coating was obtained by dry mixing at a ratio of 0:30.

A film is formed by the above-described method for forming a film, and a liquid epoxy resin (YD-1) is used as an adhesive.
28 (manufactured by Toto Kasei Co., Ltd.) and imidazole (C ₁₁ Z (manufactured by Shikoku Kasei Co., Ltd.)) were mixed at a ratio of 95: 5 and diluted with acetone to 5%, and the object to be coated was washed. Also, after the object to be coated was immersed in the adhesive, it was dried with hot air to form an adhesive layer on the object to be coated. As the film forming medium, a zirconia sphere coated with rubber and having a diameter of 1 mm is used, and 1 kg of the film forming medium and 40 g of powder coating material are charged into a container 1 having the same volume as in FIG.
After the container 1 is vibrated for 5 minutes and uniformly mixed, an object to be coated (a steel plate having a size of 40 mm × 40 mm × 0.8 mm (thickness)) is charged, and the film thickness after heat treatment on the object becomes 20 μm. After forming a powder layer as described above, at 180 ° C for 20 minutes,
Heat treatment was performed using a hot air drying furnace to form a film.

In Comparative Example 5, a jig also serving as a ground was attached to one end of the object on which the adhesive layer was formed, and an electrostatic spray gun (G × -108) manufactured by Nippon Parker Rising Co., Ltd. was used. Voltage is -60 KV and film thickness after heat treatment is 20
After a powder layer was formed so as to have a thickness of μm, heat treatment was performed at 180 ° C. for 20 minutes using a hot-air drying furnace to form a film.

[0024]

[Table 1]

A steel sheet of 40 mm × 40 mm × 0.8 mm (thickness) coated with the powder coating shown in Table 1 so that the average film thickness after heat treatment was 20 μm was used. The voltage was measured as follows. A part of the film is polished with a file, a test lead (black) of a withstand voltage tester (manufactured by Kikusui Electronics Co., Ltd., trade name: TOS-5030) is attached to the portion, and the test lead (red) is brought into contact with the film surface. In this state, the applied voltage was gradually increased, and the withstand voltage of the film was evaluated. In this test, conduction was considered when a current of 0.5 mA or more flowed, and the average value of 10 points measured at 5 points / 1 sheet was taken as the withstand voltage (volt, per 10 μm). Are shown in Table 2. Further, for each of the two steel plates, a bending resistance test was performed using a mandrel having a diameter of 4 mm according to JIS-K540, 8.1, and the mechanical strength of the coating was examined. Table 2 shows the results. ○ indicates that the bending resistance is good, and x indicates that the bending resistance is poor.

[0026]

[Table 2]

Examples 1 to 3 are all excellent in withstand voltage and bending resistance. Comparative Example 1 is inferior in both withstand voltage and bending resistance. Comparative Examples 2 to 5
Has good bending resistance but poor withstand voltage.

50 g of the powder coatings of Examples 1 to 3 were put into a 200 cc polyethylene bottle, left in a constant temperature bath at 35 ° C. for 2 weeks, taken out, and the storage stability of the powder coatings was visually checked. However, caking and the like did not occur, and the storage stability was good.

[0029]

Since the present invention has the above-described structure, the following effects can be obtained.

Since the powder coating is composed of insulating flat powder and resin powder particles containing at least an amorphous resin and a crystalline resin, the mechanical strength of the film and the storage stability of the powder coating are A film having high insulation properties can be easily formed even with a thin film without damaging the film.

By setting the softening point of the non-crystalline resin to 100 ° C. or lower and the melting point of the crystalline resin to 120 ° C. or higher, the crystallinity of the crystalline resin in the resin powder particles is not impaired. Powder particles can be produced.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view of a film forming apparatus to which the present invention is applied as an example.

[Explanation of symbols]

 1 ···· Container 2 ···· Vibration device W ····· Coating object

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Osamu Itaya 1-2-1 Eripart 2 401, Matsumuro-Ojocho, Nishikyo-ku, Kyoto-shi, Kyoto (72) Inventor Akira Fujiwara For Shizuoka-shi, Shizuoka No.3-1 Sompocho In the Chemical Products Division of Hamakawa Paper Mill Co., Ltd.

Claims (7)

[Claims] 1. An object to be coated having an adhesive layer formed on its surface in advance,
A powder coating used in a film forming method for adhering particles of the powder coating via a film forming medium, the powder coating comprising an insulating flat powder, at least an amorphous resin and a crystalline resin. And a resin powder particle containing the following. 2. The powder coating according to claim 1, wherein the softening point of the non-crystalline resin is 100 ° C. or lower, and the melting point of the crystalline resin is 120 ° C. or higher. 3. The resin powder particles are prepared by dry-mixing at least a composition comprising an amorphous resin and a crystalline resin, and then subjected to a temperature condition between the softening point of the amorphous resin and the melting point of the crystalline resin. The powder coating material according to claim 1, wherein the powder coating material is obtained by melt-kneading, and then pulverizing and classifying. 4. The powder coating according to claim 1, wherein the non-crystalline resin and the crystalline resin are epoxy resins. 5. The powder coating according to claim 1, wherein the insulating flat powder is mica powder. 6. The powder coating according to claim 1, wherein the weight ratio of the non-crystalline resin to the crystalline resin is from 90:10 to 60:40. 7. A film forming method for forming an adhesive layer on the surface of an object to be coated and adhering particles of the powder coating to the obtained object to be coated via a film forming medium, wherein:
A method for forming a film, comprising using the powder coating material according to claim 1.