JP2002348528A - Epoxy resin powder coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an epoxy resin powder coating having an improved edge- covering rate without loosing excellent properties of epoxy resin powder coatings. SOLUTION: The epoxy resin powder coating contains an epoxy resin (A), a curing agent (B) and an inorganic filler (C) as essential components. The coating is further compounded with a positively chargeable inorganic powder (D) and a negatively chargeable inorganic powder (E). The positively chargeable inorganic powder (D) is preferably alumina.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an epoxy resin powder coating.

[0002]

2. Description of the Related Art Epoxy resin powder coatings have electrical properties,
Excellent in mechanical and thermal properties.Compared with conventional solvent-based paints, it does not contain solvents in paints, so it has low pollution and excellent work environment. Because of the advantages of being able to do so, being able to apply multiple layers and increasing the thickness of the coating film, being relatively inexpensive, and being able to collect and use excess paint during coating, electronic components, OA equipment, home appliances, building materials, In recent years, demand has been high as a coating for insulation protection decoration of automobile parts and the like.

[0003] In the case of micro motors for OA equipment, which is one of the uses of epoxy resin powder coating, in recent years it has been necessary to increase the number of turns of copper wires in order to reduce the size and increase the output. There is a strong demand for paints that can be made thinner in order to make the film as thin as possible. Generally, the method of reducing the particle size of the powder coating is used to make the insulating coating thinner. However, when forming a coating on a component having a complicated shape, usually, the edge portion is more thinner than the flat portion. The film thickness becomes thin, and it is difficult to form a uniform coating film over the entire exterior part. For this reason, if the particle size of the powder coating is made too fine, it becomes impossible to form an insulating film having a required thickness on the edge portion.

[0004] Such a shortage of the coating film at the edge causes not only a decrease in the protection performance by the coating film but also a problem peculiar to each application. For example, when used for painting a micromotor, there is a risk that insulation failure occurs at the edge. In addition, when used in a multilayer film capacitor, which is one of the electronic components, when the coated multilayer film capacitor is immersed in a high-temperature solder bath after mounting on the board, the moisture absorbed by the coating film instantaneously becomes water vapor. This causes a so-called steam explosion, which blows out, and the thin edge portion of the coating film may be destroyed. To solve this problem, attempts have been made to improve the strength of the coating film by increasing the degree of curing of the resin and to alleviate the stress by imparting flexibility to the resin, but these methods are still satisfactory. Is not obtained.

[0005] Therefore, there is a demand for a powder coating material that can obtain a required film thickness at the edge portion of a part to be coated and can form a thinner insulating film at a flat portion than before. Usually, the ratio of the film thickness at the edge portion to the film thickness at the flat portion of the part to be coated is called an edge coverage, and there is an increasing need for a powder coating material having a high edge coverage.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an epoxy resin powder coating having an improved edge coverage without impairing the excellent properties of the epoxy resin powder coating.

[0007]

This and other objects are achieved by the present invention described in the following (1) to (6). (1) In an epoxy resin powder coating material containing an epoxy resin (A), a curing agent (B) and an inorganic filler (C) as essential components, positively chargeable inorganic particles (D) and negatively chargeable inorganic particles ( E) and an epoxy resin powder coating characterized by comprising: (2) The epoxy resin powder coating according to the above (1), wherein the positively chargeable inorganic particles (D) are alumina. (3) The epoxy resin powder coating according to the above (1) or (2), wherein the negatively chargeable inorganic particles (E) are silica. (4) Any of the above (1) to (3), wherein the weight ratio (E / D) of the positively chargeable inorganic particles (D) to the negatively chargeable inorganic particles (E) is 2 to 8. The epoxy resin powder coating according to the above. (5) Both the positively chargeable inorganic particles (D) and the negatively chargeable inorganic particles (E) have an average primary particle diameter of 0.001 to 0.1.
The epoxy resin powder coating according to any one of the above (1) to (4), which has a thickness of μm. (6) The total amount (D + E) of the positively chargeable inorganic particles (D) and the negatively chargeable inorganic particles (E) is 0.3 to 2.0% by weight based on the whole powder coating material. (1) to (5)
The epoxy resin powder coating according to any one of the above.

Hereinafter, the epoxy resin powder coating of the present invention will be described in detail. The epoxy resin powder coating composition of the present invention is obtained by adding positively chargeable inorganic particles (D) to an epoxy resin powder coating composition containing an epoxy resin (A), a curing agent (B) and an inorganic filler (C) as essential components. And negatively chargeable inorganic particles (E).

The epoxy resin powder coating of the present invention (hereinafter referred to as “the epoxy resin powder coating”)
Epoxy resin (A) blended in "powder coating")
Is not particularly limited. For example, bisphenol A
Type epoxy resin, novolak type epoxy resin, biphenyl type epoxy resin and the like can be used, and these may be used alone or in combination. Among these, the use of bisphenol A type epoxy resin is preferable because the coating film has excellent mechanical and electrical properties. The molecular weight and epoxy equivalent of these epoxy resins are not particularly limited, and may be appropriately selected according to the composition of the powder coating and the required properties. For example, when a bisphenol A type epoxy resin is used, it is preferable to use a resin having an epoxy equivalent of 450 to 2,000 because the coating properties of the powder coating are excellent. The amount of the epoxy resin (A) is not particularly limited, but is 30 to 6 with respect to the whole paint together with the curing agent (B) described later.
0% by weight, more preferably 40% by weight.
~ 55% by weight. By setting the amount of the epoxy resin (A) in such a range, the coatability of the powder coating can be improved. If the blending amount is less than the lower limit, the smoothness of the coating film may be reduced, while if it is greater than the upper limit, appearance defects such as sagging and rubbing may be caused during firing which is a curing step after coating. is there.

The curing agent (B) to be blended in the powder coating of the present invention is not particularly limited, and a known curing agent generally used as a curing agent for an epoxy resin can be used. For example, dicyandiamide, adipic acid, imidazole compounds, amine-based curing agents, aromatic acid anhydrides and the like can be mentioned. Among these, when a bisphenol A type epoxy resin is used, the use of dicyandiamide, an imidazole compound, or an acid anhydride is preferred because of excellent curability, adhesion, heat resistance and the like. The amount of the curing agent (B) is not particularly limited.
What is necessary is just to set suitably in consideration of the kind of hardener, etc.

The inorganic filler (C) blended in the powder coating of the present invention is not particularly limited.
Examples thereof include calcium carbonate, aluminum hydroxide, aluminum oxide, calcium silicate, and talc, which can be used alone or in combination. The amount of the inorganic filler (C) is not particularly limited, but is preferably from 40 to 70% by weight, more preferably from 45 to 60% by weight, based on the entire powder coating composition. By setting the amount of the inorganic filler (C) in such a range, the coatability of the powder coating can be improved. If the amount is less than the lower limit, appearance defects such as sagging and scumming may occur during firing, while if it is more than the upper limit, the smoothness of the coating film may be reduced. The particle size of the inorganic filler (C) is not particularly limited, but usually, the average particle size is 10 to 30 μm. By using an inorganic filler having such an average particle size, good fluidity and strength of the coating film can be imparted to the powder coating.

The powder coating of the present invention contains positively chargeable inorganic particles (D) in order to improve the edge coverage at the time of coating.
And negatively chargeable inorganic particles (E). The positively chargeable inorganic particles (D) blended in the powder coating of the present invention are not particularly limited, and examples thereof include alumina, magnesia, magnesium hydroxide, aluminum hydroxide, zinc oxide, titanium oxide, and calcium carbonate. And these can be used alone or in combination. Among these, alumina is particularly preferable because it has strong positive chargeability and a large effect can be obtained. The negatively chargeable inorganic particles (E) are not particularly limited, but include, for example, silica, glass, talc, clay and the like, and these can be used alone or in combination. Among these, silica is particularly preferred because it has a strong negative chargeability and a large thickening effect can be obtained when used in combination with the alumina.

The amount of the positively chargeable inorganic particles (D) and the negatively chargeable inorganic particles (E) is not particularly limited. 2.
It is preferably 0% by weight, more preferably 0.1% by weight.
9 to 1.3% by weight. By blending in such a range, the edge coverage can be set to an optimum level without impairing the appearance of the coating film. If the amount is less than the lower limit, the effect of improving edge coverage may not be sufficient.On the other hand, if the amount exceeds the upper limit, the leveling property at the time of melting may be reduced depending on the composition of the coating, and a coating film may be formed. In some cases, the surface may not be finished cleanly.

The mixing ratio of the positively chargeable inorganic particles (D) and the negatively chargeable inorganic particles (E) is not particularly limited, but the weight ratio (E / D) is preferably 2 to 8. Preferably, it is 3-6 more preferably. By using such a mixing ratio, the paint can be effectively thickened at the time of melting, and the edge cover property can be improved. If the compounding ratio exceeds the upper limit or is less than the lower limit, the effect of improving the edge cover property may not be sufficient.

The particle diameters of the positively chargeable inorganic particles (D) and the negatively chargeable inorganic particles (E) are not particularly limited either.
μm, more preferably 0.01 μm.
0 to 0.050 μm. When the particle size is larger than the upper limit, the specific surface area of the inorganic particles becomes small, so that it becomes difficult for the inorganic particles to be charged efficiently, and the thickening effect may not be sufficient. On the other hand, if it is less than the lower limit, the workability at the time of melting and mixing may decrease.

The powder coating of the present invention is characterized in that positively chargeable inorganic particles and negatively chargeable inorganic particles are blended in order to improve the edge coverage. In particular, when alumina is used in combination with the positively chargeable inorganic particles and silica is used as the negatively chargeable inorganic particles, the effect becomes more remarkable. The mechanism by which these types of inorganic particles are mixed to improve the edge coverage of the paint is not clear, but they are positively and negatively charged when the epoxy resin in the powder paint is melted, respectively. It is considered that the thixotropy of the molten paint is improved by binding by electrostatic force in the resin. For this reason, when applied to the coating of electronic components having sharp edges, it is possible to prevent the melted paint from moving from the edge to the flat portion of the component and to reduce the amount of paint at the edge. The thickness of the film can be secured. In addition, since both are inorganic particles, it is considered that they hardly hinder the curing of the epoxy resin or affect the properties after the curing. For this reason, there is also an advantage that there is no particular limitation on the type of resin used and the composition of the powder coating.

The coating composition of the present invention may contain, in addition to the above-mentioned compounds, titanium oxide, as long as the object of the present invention is not impaired.
A coloring pigment such as iron oxide and carbon black, a leveling agent, a curing accelerator and the like may be added.

In the present invention, the method for producing the powder coating is not particularly limited, and a general method can be used. As an example, after the raw material components mixed in a predetermined composition ratio are sufficiently homogeneously mixed with a Henschel mixer, and then melt-mixed with a kneading device such as an extruder,
Then, it is pulverized to an appropriate particle size by a pulverizer and classified. Further, with respect to the powder coating of the present invention, the surface of the powder coating particles can be coated with a fine powder such as silica in order to improve the fluidity of the powder. As a method of performing such treatment, there are pulverization mixing in which fine powder is added during pulverization and mixing, or dry mixing using a Henschel mixer or the like.

[0019]

The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited by these examples. The amounts of the raw materials described in Tables 1 and 3 indicate "parts by weight".

1. Powder coating for motor (1) Preparation of powder coating The raw material components were mixed at the mixing ratio shown in Table 1 with a Henschel mixer for 20 minutes, and kneaded using an extruder.
It was pulverized by a pulverizer to obtain an epoxy resin powder coating having an average particle size of 40 to 60 μm. (2) Preparation of sample for evaluation: steel rod (12.5 × 12.5 ×
50 mm) by using an electrostatic coating apparatus so that the thickness of the insulating film is about 250 μm in the flat part,
It was cured by heating to 230 ° C. in 120 seconds with a high frequency of 0 kHz. Table 2 shows the evaluation results of the obtained samples.

[0021]

[Table 1] (3) Raw materials used Epoxy resin: bisphenol A type epoxy resin (Epicoat 105 manufactured by Japan Epoxy Resin Co., Ltd.)
5, epoxy equivalent 850) Curing agent: dicyandiamide Curing accelerator: 2-phenylimidazole Inorganic filler: Calcium carbonate (manufactured by Maruo Calcium Co., Ltd., Tankal N-35, average particle size 22 μm) Positively charged inorganic particles: Alumina fine Powder (Nippon Aerosil Co., Ltd., alumina oxide C, primary average particle size: 15 nm) Negatively charged inorganic particles: silica fine powder (Tokuyama Co., Ltd., Reolosil, primary average particle size: 12 nm)

[0022]

[Table 2] (4) Test method Edge coverage: Take a cross section of the sample, measure 4 points at the center of each side as the thickness of the flat portion, and 4 points at each corner as the thickness of the edge, calculate the average value of each, The edge coverage was calculated by the following equation. Edge coverage (%) = (average thickness of edge part coating / average thickness of flat part coating) × 100 Gelation time: Measured by a needle method at 200 ° C. using a 0.1 g sample. Flowability: 0.5 g of powder coating is placed in a mold and placed at room temperature for 10
It was shaped into a tablet having a diameter of mmφ and heated in a dryer at 150 ° C. for 30 minutes. Measure the tablet diameter (mm) after heating,
It was calculated from the change in tablet diameter before and after heating according to the following equation. Flow rate (%) = (diameter of tablet after heating / 10) × 100 Appearance of coating film: Observing the surface of the coating film of the sample after coating. A sample that was not so good but had no problem was rated as “good”.

The powder coatings of Examples 1 to 5 contain two types of inorganic particles having a chargeability together with an epoxy resin, a curing agent, and an inorganic filler, so that any of them has no problem in the appearance of the coating film. Thus, a product excellent in edge cover property was obtained. In particular, in Example 1, the compounding amount of the two kinds of inorganic particles having chargeability and the compounding ratio of the two were optimal, so that the characteristic balance was most excellent. On the other hand, Comparative Example 1 did not use positively chargeable inorganic particles, and Comparative Example 2 did not use both types of chargeable inorganic particles.

2. Powder coatings for laminated film capacitors (1) Preparation of powder coatings
After mixing for 0 minutes, the mixture was kneaded using an extruder, and after cooling, pulverized material was classified with a 150 mesh to obtain an average particle size of 5.
A powder coating of 0 μm was obtained. (2) Preparation of evaluation sample: multilayer film capacitor element 1 as shown in FIG. 1 (cross section 3 × 2 mm)
Then, the coating film 2 was coated with a fluid immersion coating machine so as to have a thickness of 0.6 mm, and then cured at 120 ° C. for 1 hour.
Table 4 shows the evaluation results of the obtained samples.

[0025]

[Table 3] (3) Raw materials used Epoxy resin: Epicoat EP1002 (manufactured by Japan Epoxy Resin Co., Ltd., bisphenol A type epoxy resin: epoxy equivalent: 600 to 700) Curing agent: 2-phenylimidazole Inorganic filler: hydrated aluminum oxide (Alcoa Chemical Co., Ltd.) B-325) Positively chargeable inorganic particles: fine alumina powder (Alumina oxide C, manufactured by Nippon Aerosil Co., Ltd., primary average particle size: 15 nm) Negatively chargeable inorganic particles: fine silica powder (manufactured by Tokuyama Corporation, Reolosil, (Primary average particle size 12nm)

[0026]

[Table 4] (4) Test method Evaluation of edge coverability: As shown in FIG. 2, the film thickness of the edge portions a, b, c, and d of the element cross section was measured for ten samples, and the average of the edge portion coating film thickness was measured. Values were calculated. “a” and “b” indicate the upper side during dip coating, and “c” and “d” indicate the lower side. Oil dip test: The sample was subjected to 60 ° C./95% RH, 7
After the treatment for 2 hours, the film was immersed in an oil bath at 170 ° C. for 2 minutes, and the occurrence of cracks in the coating film and the generation of bubbles from the coating film were observed (n = 40). Appearance of coating: The surface of the coating film of the element after coating was observed. ◎ indicates that the coating film surface was excellent in smoothness, and ○ indicates that the smoothness was slightly inferior but had no practical problem.

The powder coatings of Examples 6 to 10 contain two kinds of inorganic particles having a chargeability together with an epoxy resin, a curing agent and an inorganic filler, so that any of them has no problem in the appearance of the coating film. Also, a sufficient coating film thickness could be obtained for the edge portion. In particular, Example 1 has a chargeable property of 2
Since the blending amounts of the kinds of inorganic particles and the blending ratio of the two were optimal, the characteristic balance was most excellent. On the other hand, Comparative Examples 4 to 6 did not use both or one of the chargeable inorganic particles, all had a thin coating film at the edge portion, and the oil dip test results were inferior to those of the examples. became.

[0028]

According to the present invention, an epoxy resin, a curing agent and an inorganic filler are essential components, and positively chargeable inorganic particles and negatively chargeable inorganic particles are contained in predetermined amounts and ratios. The epoxy resin powder coating of the present invention, the powder coating of the present invention has a high edge coverage at the time of coating, and forms a sufficiently thick coating film on the edge even when used for coating a component having a complicated shape. be able to. Therefore, the powder coating of the present invention is useful as an epoxy resin powder coating capable of forming a stable insulating film.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view after the coating of the present invention is applied to a laminated film capacitor.

Fig. 2 Measurement position of coating film thickness of multilayer film capacitor

[Explanation of symbols]

 1 multilayer film capacitor 2 coating thickness

Claims (6)

[Claims] 1. An epoxy resin powder coating material comprising an epoxy resin (A), a curing agent (B) and an inorganic filler (C) as essential components, comprising positively chargeable inorganic particles (D) and negatively chargeable inorganic particles. An epoxy resin powder coating characterized by being blended with particles (E). 2. The epoxy resin powder coating according to claim 1, wherein the positively chargeable inorganic particles (D) are alumina. 3. The epoxy resin powder coating according to claim 1, wherein the negatively chargeable inorganic particles (E) are silica. 4. The method according to claim 1, wherein the weight ratio (E / D) of the positively chargeable inorganic particles (D) to the negatively chargeable inorganic particles (E) is 2 to 8. Epoxy resin powder coating. 5. The positively chargeable inorganic particles (D) and the negatively chargeable inorganic particles (E) both have an average primary particle diameter of 0.001.
The epoxy resin powder coating according to any one of claims 1 to 4, wherein the thickness is from 0.1 to 0.1 µm. 6. The total blending amount (D + E) of the positively chargeable inorganic particles (D) and the negatively chargeable inorganic particles (E) is 0.3 to 2.0% by weight based on the whole powder coating material. The epoxy resin powder coating according to any one of claims 1 to 5.