JP5317400B2 - Epoxy resin powder coating - Google Patents

Description

  The present invention relates to a powder coating, an insulating method using the powder coating, and a metal coating with an insulating layer in which the powder coating is thermally cured to form an insulating layer.

  Powder paints that do not contain an organic solvent in the composition are attracting attention as paints that meet recent VOC (volatile organic compound) emission regulations, and the amount of use tends to increase remarkably. Typical applications include powder coatings for slot insulation of micromotors used in hard disks, DVDs, CD-ROMs, etc., and insulation of various parts used in digital home appliances such as various portable devices. Things are widely done. The powder coating material for slot insulation of a micromotor generally has an average particle size of about 50 μm, and the thickness of the insulating coating after curing is about 100 μm. In recent years, with the miniaturization of objects to be coated such as micro motors used in hard disks and the like, it has been eagerly desired by the industry to reduce the thickness of the insulating coating to 50 μm or less. In addition, with the achievement of higher functionality of information home appliances described above, there is a demand for reducing the size and weight of components used and reducing the thickness of the insulating layer.

  The powder coating used in the above-mentioned fields of use generally has a thermosetting resin as a main component, and is usually electrostatically attached to a grounded object by electrostatic coating through a coating gun. Later, it is heated and melted to form a coating film. As the electrostatic coating method, a corona charging method and a friction charging method are known.

  In the electrostatic coating described above, in order to form a uniform coating film on a metal object, it is necessary to uniformly apply a charged powder coating material to the entire object. In general, a sufficiently uniform coating film can be formed on a flat object, but powder coating particles are difficult to enter on non-planar parts (particularly concave and convex parts), and adhere to non-planar parts. In many cases, the amount of body paint is reduced compared to other parts. In this case, since the film thickness of the coating film formed on the non-planar part becomes thinner than the film thickness of other parts, it is difficult to obtain a uniform coating film. This phenomenon is noticeable in the corona charging method, and is caused by the Faraday cage effect. The Faraday cage effect is a phenomenon in which an electric field (lines of electric force) is not formed in a concave portion of an object to be coated but concentrated on the convex portion. Further, since the coating material itself is granular as compared with the case of the liquid coating material, it is difficult to smooth the unevenness on the surface of the coating film even by melting and baking after coating.

The following methods have been proposed as means for solving these problems.
As a first method, after the powder coating is applied to the flat surface by conventional means, a uniform coating film cannot be formed by powder coating. A method has been proposed (for example, Patent Document 1). In this method, since the electrodeposition coating is performed after the powder coating, it is difficult to apply the electrodeposition coating to the coated surface of the powder coating, and the boundary portion between the powder coating and the electrodeposition coating is difficult. In some cases, a sufficient film thickness could not be ensured, and a portion with poor corrosion resistance was generated.
As a second method, a powder coating material has been proposed in which the average particle size of the powder coating material is reduced and an upper limit is set for the ratio of particles having a small particle size (for example, Patent Document 2).
As a third method, it has been proposed to use a powder coating material having an average particle size of 20 to 50 μm and a particle size distribution standard deviation of 20 μm or less (for example, Patent Document 3).
As a fourth method, the applicant of the present application previously described an epoxy resin having a specific property mainly composed of a bisphenol A type epoxy resin, an inorganic resin having a specific particle size range together with polyvinyl butyral, a catalyst curing agent, and an acrylate oligomer. It has been proposed to use an epoxy resin composition containing a filler (Patent Document 4).
Each of the second to fourth methods aims to improve the smoothness of the coating film by making the particle diameter uniform. In other words, the original purpose is to remove small or large particles by classification.

However, in the second to fourth methods, it is merely disclosed that it is not preferable to include particles having a small particle size in the homogenization of the particle size. For example, specific disclosure of particles of 5 μm or less is provided. Not at all.
Since the metal object to be used was further downsized, the smoothness of the coating film was not yet satisfactory only by removing the small particle diameter and making the particle diameter uniform.

JP-A-49-111947 Japanese Patent Laid-Open No. 5-98193 JP-A-8-41384 JP-A-10-265714

An object of this invention is to provide the powder coating material which can form the coating film of the high external appearance by thinning and smoothing a coating film.
Another object of the present invention is to provide a method for insulating a metal object to be formed with an insulating layer using the powder coating material, and a metal object with an insulating layer obtained by the method.

  As a result of intensive studies to solve the above problems, the present inventors have found that the average particle diameter is at a specific range in a powder coating containing at least an epoxy resin, a curing agent and a filler, and 5 μm. In order to complete the present invention, it has been found that when a predetermined amount of the following particles (hereinafter also referred to as particles having a small particle size) is contained, a coating film thermally cured after powder coating can have a high appearance. It came.

（２）前記充填剤を、エポキシ樹脂１００重量部当たり２０〜１５０重量部含むことを特徴とする特徴とする前記（１）に記載の粉体塗料。
（３）電子部品の表面に絶縁層を形成する絶縁方法であって、該絶縁層は、前記（１）または（２）に記載の粉体塗料を金属製被塗物に静電塗装した後に熱硬化することにより塗膜を形成することを特徴とする絶縁方法。
（４）電子部品の表面に絶縁層を形成した絶縁層付き金属製被塗物であって、該絶縁層は、前記（３）に記載の方法により形成された塗膜であることを特徴とする絶縁層付き金属製被塗物。
That is, the present invention provides the following powder coating, an insulating method using the powder coating, and a metal object with an insulating layer in which the powder coating is thermally cured to form an insulating layer.
(1) A powder paint containing an epoxy resin, a curing agent and a filler , wherein the filler contains fused silica and crystalline silica, and the powder paint has an average particle size of 10 is 30 .mu.m, particles below 5μm viewed 3.0-6.0 vol% free, and put powder coating 1.0g tablet shaping mold having an inner diameter of diameter of 16 mm, the pressure for 60 seconds pressurizes 90MPa When the diameter of the tablet formed in this way is (A), the tablet is placed on a slide glass and left in a hot air drying oven at 140 ° C. for 10 minutes and the diameter of the tablet is (B), it can be obtained from the following formula (I). A powder coating material having a horizontal flow rate of 1.0 to 5.0% ;

(2) The powder coating material as described in (1) above , wherein the filler is contained in an amount of 20 to 150 parts by weight per 100 parts by weight of the epoxy resin .
(3) An insulating method for forming an insulating layer on the surface of an electronic component, wherein the insulating layer is formed by electrostatically applying the powder coating according to (1) or (2) on a metal object. An insulating method comprising forming a coating film by thermosetting.
(4) A metal article with an insulating layer in which an insulating layer is formed on the surface of an electronic component, wherein the insulating layer is a coating film formed by the method described in (3) above. Metal object to be coated with an insulating layer.

The powder paint of the present invention has an average particle diameter in a specific range and contains a predetermined amount of particles having a small particle diameter, so that the difference between the film thickness after electrostatic coating and the film thickness after curing is determined. Can be reduced. For this reason, the smoothness of a cured coating film can be improved and a coating film having a high appearance can be formed.
In addition, the powder coating having a horizontal flow rate in a specific range is excellent in terms of stable shape of the coating film.
Furthermore, the present invention provides an insulating method for forming a coating film having a high appearance by electrostatic coating using the powder coating, followed by thermosetting, and a metal coating with an insulating layer formed with the coating method. Things are provided.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described below, but the present invention is not limited to the following embodiment, and is based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention. Those in which the following embodiments are appropriately modified and improved are also within the scope of the present invention.

  The powder coating material of the present invention is a powder coating material containing an epoxy resin, a curing agent and a filler.

As the epoxy resin used in the present invention, a conventionally known epoxy resin can be appropriately used depending on the purpose of use. For example, a compound having two or more oxirane groups in the molecule can be preferably used. Examples of such epoxy resins include glycidyl ester resins, bisphenol type epoxy resins, and the like. Specific examples include bisphenol A type epoxy resins, bisphenol F type epoxy resins, alicyclic epoxy resins, aliphatic epoxy resins, bromines. Bisphenol A type epoxy resin, phenol-novolak type or cresol-novolak type epoxy resin, brominated novolak type epoxy resin, hydrogenated bisphenol A type or AD type epoxy resin, propylene glycol diglycidyl ether, pentaerythritol polyglycidyl ether Aliphatic epoxy resins such as epoxy resins obtained from aliphatic or aromatic amines and epichlorohydrin, epoxy resins obtained from aliphatic or aromatic carboxylic acid epichlorohydrin, complex Epoxy resins, may be used biphenol type epoxy resin or the like. These epoxy resins may be used alone or in combination of two or more.
Among these, when used for electronic parts such as capacitors, it is preferable to contain a brominated epoxy resin from the viewpoint of flame retardancy.
Moreover, when using for micro motors, it is preferable to contain a bisphenol A type epoxy resin from the viewpoint of coating film adhesion and toughness.

  Various conventionally known materials can be selected as the curing agent used in the present invention. For example, acid anhydrides, amines, imidazoles, dihydrogins, Lewis acids, Bronsted acid salts, polymercaptons, isocyanates, blocked isocyanates, dicyandiamide, carboxylic acid dihydrazide, melamine resins, polycarboxylic acids, etc. Can be used.

  The proportion of the curing agent used in the present invention is preferably such that the equivalent number of functional groups in the curing agent is 0.3 to 1.2 equivalents relative to 1 equivalent of the functional group contained in the epoxy resin. The ratio is preferably 0.4 to 0.8 equivalent.

As the filler used in the present invention, for example, an inorganic compound such as fused silica, crystalline silica, alumina, calcium carbonate, calcium silicate, mica, talc, clay, titanium white, silicon nitride, and silicon carbide is used. Can do.
The filler preferably has a lower linear expansion coefficient from the viewpoint of improving heat cycle resistance, and in order to lower the linear expansion coefficient, it is preferable to use fused silica. These fillers may be used alone or in combination of two or more. Two or more kinds of the same type of filler may be used. In these fillers, the average particle size is preferably 0.1 to 20 μm, more preferably 0.1 to 10 μm, and further preferably 0.5 to 3 μm. The blending amount is preferably 20 to 150 parts by weight, more preferably 40 to 100 parts by weight per 100 parts by weight of the epoxy resin. If the blending amount of the filler is less than 20 parts by weight, there is a problem that the fluidity in the melt-curing process of the powder composition becomes too large to form a coating film uniformly. On the other hand, if it exceeds 150 parts by weight, the fluidity of the powder coating in the melt-curing process becomes too small to obtain sufficient adhesion with the object to be coated, and there is a problem that sufficient adhesion strength cannot be obtained. Because there is.

  In addition to the above-mentioned components, conventional auxiliary components such as a catalyst, a spreading agent, a flame retardant, a pigment, a coupling agent, and an antifoaming agent can be appropriately added to the epoxy resin composition of the present invention.

Next, the method for producing a powder coating will be described.
For powder coatings, either an epoxy resin or a filler such as an inorganic filler is melt-kneaded with a kneader or the like, or melt-mixed with an extruder or the like, and then the mixture is cooled and solidified, coarsely crushed, The pulverized product is dry-mixed with a curing agent and, if necessary, a curing accelerator and auxiliary components. After the mixture is melt-mixed, the mixture is cooled and solidified, finely pulverized, classified, and an average particle size of 10 to 10%. It can be obtained by adjusting to 30 μm. In the present invention, it is necessary to contain a predetermined amount of particles of 5 μm or less, but the particles may be classified so as to be contained in a predetermined amount at the time of classification, or by a method of containing a predetermined amount in the particles from which particles of 5 μm or less have been removed during classification. Also good.

  In the present invention, the average particle size of the powder coating material is 10 to 30 μm, more preferably 15 to 25 μm. By making the average particle size of the powder coating material smaller than the average particle size (about 50 μm) of conventionally known powder coating materials, it is possible to reduce the thickness of the formed coating film. When the average particle size of the particles in the powder coating composition is less than 10 μm, the manufacturing process becomes complicated, and the particles having a size of 5 μm or less that tend to aggregate relatively increase. This is because the efficiency of adhering to the article to be coated is lowered, so that the yield is poor and the productivity is lowered. This is because if the average particle diameter of the powder coating exceeds 30 μm, it becomes difficult to make the cured coating film 50 μm or less.

  As described above, the powder coating material in the present invention needs to have an average particle diameter of 10 to 30 μm. In addition to this, particles of 5 μm or less are added to 3.0 to 6 particles in the powder coating material. This is an important feature because it is contained in an amount of 0.0% by volume, more preferably 3.5 to 5.0% by volume. If the content of the particles of 5 μm or less is less than 3.0% by volume, it is insufficient for small particles to enter the gaps between the particles. This is because the thickness is significantly reduced compared with the film thickness, and the surface smoothness is impaired. In addition, if the content is more than 6.0% by volume, there is a problem that the fluidity of the powder coating material is lowered because the number of particles of 5 μm or less that easily aggregate is increased.

In the present invention, the horizontal flow rate of the powder coating is preferably 1.0 to 5.0%, more preferably 2.0 to 4.5%. If it is less than 1.0%, the paint will not flow at the time of melting, so that coating hole defects such as pinholes are likely to occur. If it exceeds 5.0%, so-called sagging occurs in the process of melting to curing when a cured film is obtained. This is because a phenomenon called “occurs” and a desired film thickness cannot be formed.
The horizontal flow rate indicates the meltability of the powder coating material when heated. If this value is large, it indicates that the coating material flows easily because the viscosity is low at the time of melting. This indicates that the paint is difficult to flow.
A method for measuring the horizontal flow rate will be described later.

  The shape of the metal object to be coated with the powder coating material of the present invention is not particularly limited, but the powder coating material of the present invention is particularly suitable for a three-dimensional structure having a non-planar portion, and the effect of the present invention. Is effectively demonstrated. That is, since the powder coating material of the present invention has good followability with respect to uneven shapes, for example, a box-shaped object, corrugated sheet-shaped object, bag-shaped object, cylindrical object, rod-shaped object, perforated It is also preferably used for a shape or the like.

  The powder coating of the present invention is applied to a target metal object by electrostatic coating. The electrostatic coating method may be either a corona charging method or a friction charging method. In the corona charging method, either the external charging method or the internal charging method may be used.

As the coating method in the present invention, an electrostatic fluidized bed method is also preferable. The electrostatic flow method is based on the following principle.
First, fluidized air is ionized by a charged electrode placed in a fluidizing chamber or more usually a plenum chamber below a porous air distribution membrane. The ionized air then charges the powder coating, thereby causing the similarly charged particles to begin an upward motion to cause electrostatic repulsion. A cloud of charged powder particles is formed on the surface of the fluidized bed. By introducing a metallic object into the cloud, the powder particles adhere to the surface by electrostatic attraction. is there.
For this reason, when the particle diameter is small, the particles are aggregated, so that the above-described upward movement is unlikely to occur and the particles are not fluidized.

  Next, in the present invention, the powder coating is heat-cured after coating by the above method. The thickness of the cured coating film is preferably 20 to 60 μm. This is because if the thickness is less than 20 μm, a coating film defect occurs and insulation cannot be secured. Moreover, it is because the request | requirement of film thickness will not be satisfied when it exceeds 60 micrometers.

Hereinafter, the powder coating of the present invention, after coating this on a metal object, the formation of a coating film by heating and curing, and the formed coating film (hereinafter referred to as a cured coating film) are specifically described using examples. However, the powder coating, the formation of the cured coating, and the cured coating of the present invention are not limited by these examples.
In addition, about the powder coating material of the Example and the comparative example, volume average particle diameter and particle size distribution, horizontal flow rate, and fluidity | liquidity were evaluated, and the film thickness and external appearance were evaluated about the cured coating film.

<Volume average particle size and particle size distribution>
The volume average particle size and the particle size distribution are values measured using a laser diffraction particle size distribution measuring device (manufactured by SYMPATEC, trade name HELO SandRODOS analysis software WINDOWX5). Specifically, after adding 1.0 g of powder coating material, the dispersion pressure of the disperser was measured under the condition of 2.0 bar.

<Horizontal flow rate>
For the horizontal flow rate, 1.0 g of powder coating material is placed in a tablet shaping die having an inner diameter of 16 mmφ, a pressure of 90 MPa is applied for 60 seconds to form a tablet, and the diameter (A) of the tablet is measured. Next, the tablet was placed on a slide glass, left in a hot air drying oven at 140 ° C. for 10 minutes and then taken out, and the diameter (B) of the tablet was measured. The horizontal flow rate is measured from the following formula (I).

<Coating test>
The powder coating materials obtained in Examples 1 to 5 and Comparative Examples 1 to 4 which will be described later are each applied to a coating bar (manufactured by Eifu Co., Ltd.) on a 3.0 mm × 3.0 mm × 30 mm square bar (hereinafter also referred to as a test piece). , MODEL-380), and powder coating was performed under the conditions of a voltage of 52 kV, an air pressure of 0.4 kgf / cm ² , and a coating time of 1.5 seconds. At this time, the powder coating material put into the coating machine is 1 kg each. Next, this square bar was suspended and placed in a drying furnace, heated to 150 ° C. at a speed of 1 ° C. per minute, and then heated for 1 hour to obtain a cured coating film.

<Appearance and film thickness difference>
The appearance of the cured coating film obtained by the above-described coating test was evaluated by sagging properties and glossiness based on the following criteria. The film thickness difference referred to in the sagging property is the film thickness (C) of the cured coating film at 5 mm from the upper end of the test piece and the film thickness (D) of the cured coating film at 5 mm from the lower end of the test piece. Measure with a caliper. The film thickness difference is calculated from the following formula (II).
Sagging property ○: Difference in film thickness of test piece is 5 μm or less Δ: Difference in film thickness of test piece is larger than 5 μm and 10 μm or less ×: Glossiness where difference in film thickness of test piece is larger than 10 μm ○: Gloss is visually observed, In addition, the surface has no roughness. △: The gloss is visually observed, but the surface is rough. ×: The gloss is not visually observed, and the surface is rough.

<Fluidity>
The fluidity was evaluated based on the following criteria from the behavior of the powder coating in the coating machine in the coating test.
○: The powder paint is flowing and adhering to the test piece ×: The powder paint is not flowing and not adhering to the test piece

Example 1
40 parts by mass of bisphenol A type epoxy resin (epoxy equivalent 630), 60 parts by mass of brominated epoxy resin (epoxy equivalent 660), 35 parts by mass of fused silica (average particle size 2.3 μm), crystalline silica (average particle size 1. 4 μm) 45 parts by mass, hardener BTDA (JAYHAWK FINE CHEMICALS INK., Trade name BTDA) 12.5 parts by weight, castor oil additive (RHEOX. INC, trade name THIXCIN R) 2 parts by weight, silane cup 1 part by mass of a ring agent (manufactured by Chisso Corp., trade name: Silaace S-510) and 10 parts by mass of a flame retardant aid (manufactured by Suzuhiro Co., Ltd., trade name: Fire Cut AT-3) are mixed, and PCM-45 manufactured by Ikegai Seisakusho Co., Ltd. What was melt-mixed in an extruder, cooled, solidified, and coarsely pulverized was ACM-10 Pulverizer manufactured by Hosokawa Micron Co., Ltd., disk rotation speed 4000 rpm, separator rotation speed 1800 rpm, supply amount 50 After grinding under the conditions of g / hr, subjected to classification treatment to remove fine particles and coarse particles. The average particle diameter of the obtained powder coating material was 19 μm, and the content ratio of particles having a particle diameter of 5 μm or less was 4% by volume. The physical properties of this product are shown in Table 1.

Example 2
A powder coating material was produced in the same manner as in Example 1 except that the average particle size was changed to 25 μm. The physical properties of this product are shown in Table 1.

Example 3
A powder coating material was manufactured in the same manner as in Example 1 except that the amount of fused silica was changed to 45 parts by mass and the amount of crystalline silica was changed to 35 parts by mass. The physical properties of this product are shown in Table 1.

Reference example 1
A powder coating material was produced in the same manner as in Example 1 except that the amount of fused silica was changed to 15 parts by mass and the amount of crystalline silica was changed to 65 parts by mass. The physical properties of this product are shown in Table 1.

Reference example 2
A powder coating material was produced in the same manner as in Example 1 except that the amount of fused silica was changed to 65 parts by mass and the amount of crystalline silica was changed to 15 parts by mass. The physical properties of this product are shown in Table 1.

Comparative Example 1
In Example 1, a powder coating material was produced in the same manner as in Example 1 except that no crystalline silica was added and 80 parts by mass of fused silica was blended. The physical properties of this product are shown in Table 1.

Comparative Example 2
A powder coating material was produced in the same manner as in Example 1 except that the pulverization conditions were changed to a disk rotation speed of 3500 rpm and a separator rotation speed of 2200 rpm. The physical properties of this product are shown in Table 1.

Comparative Example 3
A powder coating material was produced in the same manner as in Example 1 except that the pulverization conditions were changed to a disk rotation speed of 4500 rpm and a separator rotation speed of 1800 rpm. The physical properties of this product are shown in Table 1.

Comparative Example 4
A powder coating material was produced in the same manner as in Example 1 except that the pulverization conditions were changed to a disk rotation speed of 4000 rpm and a separator rotation speed of 1500 rpm. The physical properties of this product are shown in Table 1.

From Table 1, it can be seen that when the average particle diameter exceeds 30 μm, the cured coating film becomes as thick as 80 μm and cannot be thinned. It can be seen that when the average particle size is smaller than 10 μm, it does not fluidize and therefore does not adhere to the object to be coated. It can be seen that the flowability of the powder deteriorates when particles of 5 μm or less are contained in an amount exceeding 6% by volume. It can be seen that sagging occurs when the horizontal flow rate exceeds 5%. It can be seen that the gloss is lowered when the horizontal flow rate is less than 1%.
From these results, when the average particle diameter is 10 to 30 μm and a predetermined amount of particles of 5 μm or less is included in an amount of 3.0 to 6.0% by volume, it is possible to improve the film thickness and smoothness. It is understood that there is. As a result, a uniform film thickness can be obtained and stable insulation can be obtained.

The powder coating material of the present invention can improve the film thickness and smoothness of the coating film by setting the content of particles having an average particle size and a small particle size within a predetermined range. For this reason, it becomes possible to respond to miniaturization of various precision equipment parts mounted on information home appliances, and the obtained cured coating film can contribute to improvement of insulation. The application fields applicable to the present invention include resistance networks, collective integrated circuits, inductor coil micromotors, various capacitors, automotive electrical components, and the like.

Claims (4)

A powder paint containing an epoxy resin, a curing agent and a filler , wherein the filler contains fused silica and crystalline silica, and the powder paint has an average particle size of 10 to 30 μm. There, 5 [mu] m seen below contains particles 3.0-6.0 vol%, and placed in a powder coating 1.0g tablet shaping mold having an inner diameter of diameter of 16 mm, it was molded by applying pressure to pressure 60 seconds 90MPa When the tablet diameter is (A), the tablet is placed on a slide glass and left in a hot air drying oven at 140 ° C. for 10 minutes and the tablet diameter is (B), the horizontal flow rate obtained from the following formula (I) Is a powder coating material characterized by being 1.0 to 5.0% .

The powder coating material according to claim 1, wherein the filler is contained in an amount of 20 to 150 parts by weight per 100 parts by weight of the epoxy resin .   An insulating method for forming an insulating layer on a surface of an electronic component, the insulating layer being applied by electrostatically coating the powder coating material according to claim 1 or 2 on a metal object and then thermally curing the coating material. An insulating method comprising forming a film.   A metal article with an insulating layer in which an insulating layer is formed on the surface of an electronic component, wherein the insulating layer is a coating film formed by the method according to claim 3. Metal substrate.