JP6791628B2 - Powder coating for non-conductive members and coating method for non-conductive members - Google Patents

Description

The present invention relates to a powder coating material and a coating method, and more particularly to a powder coating material that can be applied to a non-conductive member and a method for coating a non-conductive member.

Resin and glass members are used in various fields, including housings for mobile devices. The surface of these members is usually required to be coated with a coating film for the purpose of improving cosmeticity and durability. For coating metal materials and the like, electrostatic coating such as corona charging type or trivo charging type is performed. Electrostatic coating is widely used as an effective method from the viewpoints of production efficiency, working environment, and reuse of paint.

However, it is not possible to directly electrostatically coat a non-conductive molded product (member) such as resin or glass. Therefore, a method has been proposed in which the surface of the non-conductive member is coated with a conductive film in advance and then electrostatically coated.
In Patent Document 1, a white conductive primer (A) is coated on a plastic molded product so as to have a dry film thickness of 5 to 30 μm, and a white non-conductive color base (B) is coated with a dry film thickness while remaining uncured. After electrostatic coating to 15 to 50 μm and baking as needed, electrostatically coat the interference color base paint (C) to a dry film thickness of 10 to 25 μm as needed. Disclosed is a method for forming a high-white pearl-like multi-layer coating film, which comprises electrostatically coating and baking a clear paint (D) with a dry film thickness of 20 to 50 μm after baking. There is. In the method of Patent Document 1, when coating a plastic molded product, the film thickness of the conductive primer can be suppressed to be thin, which not only significantly reduces the cost but also can form a multi-layer coating film having a high whiteness. Are listed.

Japanese Unexamined Patent Publication No. 2004-262988

As described above, by using the conductive primer, electrostatic coating on the non-conductive member becomes possible. However, by going through the plurality of steps in this way, the cost and time required for painting increase. In particular, when the conventionally conductive member is changed to non-conductive by changing the material, a drastic change in the manufacturing process is required, which is not preferable.
Therefore, an object of the present invention is to provide a powder coating capable of electrostatically coating a non-conductive member and a method for coating the non-conductive member without increasing the number of coating steps.

As a result of diligent research in view of the above problems, the present inventors have made a direct non-conductive member by electrostatic coating without using a conductive primer by using a powder coating material containing or supporting a polarization material. We have found that a coating film can be formed on the surface, and came up with the present invention. That is, the powder coating material for non-conductive members of the present invention is characterized by containing or supporting a polarization material.
The polarization material is preferably at least one of a metal oxide, a metal sulfide, a conductive polymer, and a carbon material.
Further, the polarization material preferably contains at least one of graphite, barium titanate, strontium titanate, and calcium titanate.

The non-conductive member of the present invention is characterized by being coated with the above-mentioned powder coating material for a non-conductive member.

The method for coating a non-conductive member of the present invention is characterized by including a step of coating a positively or negatively charged powder coating material and a polarized polarization material on a surface to be coated.

According to the powder coating material for non-conductive members and the coating method of the present invention, a good coating film for cosmetics, durability, rust prevention, etc. can be directly applied to the non-conductive members.

Embodiments of the present invention will be described in detail below.
In the present invention, the non-conductive member or the insulating member means a member having a volume resistivity of 1 MΩ · cm or more.
Further, in the description other than the examples of the present specification, unless otherwise specified, the term "powder coating material" simply means a powder coating material excluding the polarization material, and when the polarization material is contained. Is described as "powder coating material containing a polarization material", "powder coating material supporting a polarization material ", "powder coating material for non-conductive members", or "powder coating material containing a polarization material".

The powder coating material for a non-conductive member of the present invention is characterized by containing or supporting a polarization material. With such a powder coating material for non-conductive members, a good coating film for cosmetics, durability, rust prevention, etc. can be directly applied to the non-conductive members.
In the present specification, "encapsulating the polarization material" means a state obtained by mixing the polarization material with at least a part of the constituent components of the powder coating material in a liquid state such as melt mixing, and is a part of the polarization material. Also includes those exposed on the surface of the powder coating material or protruding from the surface of the powder coating material.
Further, "supporting the polarization material" means a state in which the powder coating material is mixed with the polarization material without going through the melting step of the powder coating material, and the surface of the powder coating material is coated with the polarization material, the powder coating material. Includes a mixture of powder and polarization material powder.
The details of the powder coating material of the present invention will be described below.

(1) Polarizing Material As described above, the powder coating material for non-conductive members of the present invention contains or supports a polarization material.
The polarization material used in the present invention is not particularly limited, and metal oxides, metal sulfides, conductive polymers, carbon materials and the like can be used.
As the metal oxide, in addition to cobalt oxide, manganese oxide, vanadium oxide, nickel oxide, molybdenum oxide and the like, composite metal oxides such as barium titanate, strontium titanate and calcium titanate can be used.
Examples of the metal sulfide include molybdenum sulfide, titanium sulfide, vanadium sulfide and the like.
Conductive polymers include polyaniline, polyacetylene and its derivatives, polyparaphenylene and its derivatives, polypyrrole and its derivatives, polythienylene and its derivatives, polypyridinediyl and its derivatives, polyisothianaftenylene and its derivatives, polyfurylene and its derivatives. Examples thereof include derivatives, polyselenophenes and derivatives thereof, polyarylene vinylenes such as polyparaphenylene vinylenes, polythienylene vinylenes, polyfurylene vinylenes, polynaphthenylene vinylenes, polyselenophenene vinylenes, polypyridinediylbinenes, and derivatives thereof. Be done.
Examples of carbon materials include natural graphite, artificial graphite, vapor-phase graphite, graphite such as fluorographite (graphite), nanocarbon such as fullerene, carbon nanotubes, and graphene, and amorphous (microcrystals) such as carbon book and activated carbon. Examples include carbon.
Among these, graphite, barium titanate, strontium titanate, and calcium titanate are preferable.
The relative permittivity of the polarization material is preferably 8 or more, and more preferably 10 or more. The average particle size of the polarization material is preferably 0.02 μm to 50 μm, more preferably 1 μm to 30 μm.

(2) Powder coating The powder coating of the present invention is not particularly limited, and is appropriately selected depending on the application of coating and the like. Specific examples thereof include known powder coating materials such as epoxy powder coating materials, polyester powder coating materials, acrylic powder coating materials, and epoxy-polyester hybrid powder coating materials.
The powder coating material containing or supporting the polarization material of the present invention can be obtained by adding the polarization material to the powder coating material by the method shown below.

(3) Method of Adding Polarizing Material In the present invention, the method for producing a powder coating material for non-conductive members is not particularly limited, but the method of adding a polarizing material can be divided into two methods, an internal addition method and an external addition method. .. Each will be described below.
(A) Internal addition method A polarization material is added to a resin material such as an epoxy resin and a curing catalyst, and melt-kneading is performed. If necessary, fillers and various additives can be added. An extruder or the like can be used for melt-kneading. The temperature at the time of melt-kneading depends on the resin material and the like, but is preferably in the range of 90 ° C. to 120 ° C. The melt-kneading time is preferably 10 minutes or less, more preferably 5 minutes or less, and even more preferably 60 seconds or less.
As described above, all the raw materials can be melt-kneaded at once, but some raw materials can be melt-mixed in advance. A kneader, a planetary mixer, or the like can be used for melt mixing.
After melt-kneading, it is cooled and solidified, and the obtained mixture is finely pulverized and classified to obtain a powder coating material containing a polarization material.
The content of the polarization material is preferably 1% to 20%, more preferably 3% to 10% of the total mass of the powder coating material containing the polarization material.

(B) External Addition Method The polarization material is supported on the powder coating material produced by the above method, except that the polarization material is not added. Examples of the supporting method include a dry blend method. In this method, a powder coating material carrying a polarization material can be obtained by mixing the powder coating material and the polarization material using a Henschel mixer, a V blender, a Nauter mixer or the like.
Further, a powder coating material supporting the polarization material can also be obtained by immersing the powder coating material in a liquid in which the polarization material is dispersed, mixing and stirring the mixture, and then drying the powder coating material.
In the case of the external addition method, the content of the polarization material is preferably 0.1% to 10%, more preferably 1% to 5% of the total mass of the powder coating material containing the polarization material.

(4) Coating method of powder coating The coating method of the powder coating for non-conductive members of the present invention is not particularly limited, and a known coating method can be applied. Specifically, electrostatic coating such as a friction charge method (trivo type) or an external charge method (corona type) can be used.
In the case of tribo-type electrostatic coating, a positively charged powder coating material and a polarized polarization material are attached to the surface to be coated. On the other hand, in the case of corona type electrostatic coating, a negatively charged powder coating material and a polarized polarization material are adhered to the surface to be coated.
In the following description, the "powder coating material" simply refers to a powder coating material excluding a polarization material, for example, an epoxy-based powder coating material, a polyester-based powder coating material, or an acrylic-based powder coating material that does not contain a polarization material. , Epoxy-polyester hybrid powder paint, etc.
In the tribo type electrostatic coating, the powder coating is positively charged. Here, since the non-conductive member to be coated is grounded via the conductive member, the surface to be coated is slightly negatively charged. Excellent adhesion is realized by effectively depositing the positively charged powder coating material on such a surface to be coated via the polarized material.
On the other hand, in the corona type electrostatic coating, the powder coating is negatively charged. Here, since the non-conductive member to be coated is grounded via the conductive member, the surface to be coated is slightly positively charged. Excellent adhesion is realized by effectively depositing a negatively charged powder coating material on such a surface to be coated via a polarized material.
By the above method, a coating film can be obtained by applying a powder coating material for a non-conductive member on the surface of a member to be coated and then curing the coating film. The curing temperature and curing time are not particularly limited, but it is preferable to cure at 150 ° C. to 250 ° C. for 10 minutes to 2 hours. It is also possible to improve the adhesion of the coating film by subjecting the member to be coated to a surface treatment in advance, if necessary.
The film thickness of the coating film obtained from the powder coating material for non-conductive members of the present invention is not particularly limited, but is preferably 10 μm or more and 300 μm or less.

Since the powder coating material for non-conductive members of the present invention can be effectively applied to non-conductive members, it is effective for coating various plastic members, glass members, ceramic members, or composite materials thereof. Can be used. Specific examples thereof include housings for mobile devices, electronic / electrical device members such as substrates and capacitors, and automobile members such as bumpers and door mirror covers.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the examples, unless otherwise specified, "%" and "part" indicate mass% and parts by mass. Further, in the description of the following examples, the "powder coating material" refers to the powder coating material produced by the methods described in each Example and Comparative Example, and those containing a polarization material also include a polarization material. It shall include those that do not exist.

(Example 1)
Bisphenol A type epoxy resin, 2,4-diamino-6- [2- (2-methyl-1-imidazolyl) ethyl] -1,3,5-triazine and scaly graphite (graphite) in the mass ratio shown in Table 1. Powders (relative permittivity 12 to 13) were blended and melt-kneaded at 100 ° C. to 150 ° C. using an extruder. The kneading time at this time was 30 seconds or less. After the mixture was cooled and solidified, it was finely pulverized to obtain a powder coating material containing scaly graphite powder. This powder coating was applied to a gypsum board attached to a cold-rolled steel plate (SPCC) using a trivo-charged electrostatic coating gun (manufactured by Asahi Sanac Co., Ltd.) (voltage: course). The painting time was 10 seconds. Then, the obtained coating film was cured at 190 ° C. for 20 minutes.
Table 1 shows the results of evaluating the adhesion state of the powder coating material of Example 1 after coating by the method shown below.

(Example 2)
Extruder containing bisphenol A type epoxy resin and 2,4-diamino-6- [2- (2-methyl-1-imidazolyl) ethyl] -1,3,5-triazine in the mass ratio shown in Table 1. The mixture was melt-kneaded at 100 ° C. to 150 ° C. The kneading time at this time was 30 seconds or less. The mixture was cooled and solidified, and then finely pulverized to obtain a powder coating material. The powder coating material and scaly graphite powder (relative permittivity 12 to 13) were blended at the ratios shown in Table 1 and dry-blended for 5 minutes. Using a tribo-charged electrostatic coating gun, the powder coating material supporting the obtained scale-like graphite powder was applied to a gypsum board attached to a cold-rolled steel plate (SPCC). The painting time was 10 seconds. Then, it was cured at 190 degreeC for 20 minutes to obtain a coating film.
Table 1 shows the results of evaluating the adhesion state of the powder coating material of Example 2 after coating by the method shown below.

(Comparative Example 1)
Bisphenol A type epoxy resin and 2,4-diamino-6- [2- (2-methyl-1-imidazolyl) ethyl] -1,3,5-triazine were blended in the blending ratio (mass) shown in Table 1. , Melt and kneaded at 100 ° C to 150 ° C with an extruder. The kneading time at this time was 30 seconds or less. The mixture was cooled and solidified, and then finely pulverized to obtain a powder coating material. This powder coating was applied to a gypsum board attached to a cold-rolled steel plate (SPCC) using a trivo-charged electrostatic coating gun. The painting time was 10 seconds. Then, it was cured at 190 degreeC for 20 minutes to obtain a coating film.
Table 1 shows the results of evaluating the adhesion state of the powder coating material of Comparative Example 1 after coating by the method shown below.

(Example 3)
Extruder containing bisphenol A type epoxy resin and 2,4-diamino-6- [2- (2-methyl-1-imidazolyl) ethyl] -1,3,5-triazine in the mass ratio shown in Table 2. The mixture was melt-kneaded at 100 ° C. to 150 ° C. The kneading time at this time was 30 seconds or less. The mixture was cooled and solidified, and then finely pulverized to obtain a powder coating material. The powder coating material and carbon black (relative permittivity 8 to 12) were blended at the ratios shown in Table 2 and dry-blended for 5 minutes. The obtained powder coating material supporting carbon black was applied to a gypsum board attached to a cold-rolled steel sheet (SPCC) using a trivo-charged electrostatic coating gun. The painting time was 10 seconds. Then, it was cured at 190 degreeC for 20 minutes to obtain a coating film.
Table 2 shows the results of evaluating the adhesion state of the powder coating material of Example 3 after coating by the method shown below.

(Example 4)
A powder coating material carrying barium titanate was prepared and coated in the same manner as in Example 2 except that barium titanate (relative permittivity 1200) was used instead of the scaly graphite powder. Table 2 shows the results of evaluating the adhesion state of the powder coating material of Example 4 after coating by the method shown below.

(Comparative Example 2)
A powder coating material supporting dimethylsilicone-treated fumed silica, as in Example 2, except that dimethylsilicone-treated fumed silica (relative permittivity 2.0 to 2.7) was used instead of scaly graphite powder. Was made and painted. Table 2 shows the results of evaluating the adhesion state of the powder coating material of Comparative Example 2 after coating by the method shown below.

(Comparative Example 3)
A powder coating material carrying acrylic particles was prepared and coated in the same manner as in Example 2 except that acrylic particles (relative permittivity 2.7 to 4.5) were used instead of the scaly graphite powder. Table 2 shows the results of evaluating the adhesion state of the powder coating material of Comparative Example 3 after coating by the method shown below.

(Evaluation of adhesion state of powder paint)
As described above, after the powder coatings of Examples and Comparative Examples were applied to the gypsum board using a trivo-charged electrostatic coating gun, the coated surface was visually observed to evaluate the adhesion state of the powder coating. The evaluation result is represented by the following three stages.
⊚: Adhesion of powder paint is observed over the entire area of the painted surface with a predetermined thickness. ◯: Adhesion of powder paint is observed in a region of 30% or more of the painted surface.
X: Adhesion of powder paint is observed in the area of less than 30% of the painted surface, or adhesion of powder paint is not observed.

As shown in Table 1, Comparative Example 1 obtained from bisphenol A type epoxy resin and 2,4-diamino-6- [2- (2-methyl-1-imidazolyl) ethyl] -1,3,5-triazine. However, almost no adhesion of powder coating was observed due to trivo-charged electrostatic coating. On the other hand, the scaly graphite powder was melt-kneaded with bisphenol A type epoxy resin and 2,4-diamino-6- [2- (2-methyl-1-imidazolyl) ethyl] -1,3,5-triazine. In Example 1 obtained and Example 2 obtained by dry-blending the scale-like graphite powder with the powder coating material of Comparative Example 1, it was found that the powder coating material having a sufficient thickness adhered to the entire coated surface. It was.
From the above results, it was found that the powder coating material containing the scaly graphite powder or the powder coating material supporting the scaly graphite powder can efficiently perform electrostatic coating even on the non-conductive member.

As shown in Table 2, in Comparative Example 2 in which dimethyl silicone-treated fumed silica was supported and Comparative Example 3 in which acrylic particles were supported, adhesion of the powder coating material by trivo-charged electrostatic coating was hardly observed. On the other hand, in Example 3 in which carbon black was supported, adhesion of the powder coating material was observed. Further, in Example 4 in which barium titanate was supported, it was found that a powder coating material having a sufficient thickness adhered to the entire coated surface as in Example 2 in which scaly graphite powder was supported.
From the above results, a powder coating material carrying a non-polarizing powder having a low relative permittivity cannot be applied to a non-conductive member, but a powder coating material carrying a powder of a polarization material having a high relative permittivity cannot be applied. It was confirmed that the non-conductive member can be effectively coated by electrostatic coating. It is considered that the relative permittivity of the polarization material is preferably 8 or more.
It has been confirmed that a powder coating material containing a polarization material having a high relative permittivity other than the scaly graphite powder also has good adhesiveness.

Claims (3)

A powder coating material for non-conductive members that contains or supports a polarization material.
The polarization material, scaly graphite and barium titanate, strontium titanate, among calcium titanate, looking contains at least one,
The powder coating material is a powder coating material for non-conductive members containing an epoxy resin as a main component . A non-conductive member characterized by being coated with the powder coating material for a non-conductive member according to claim 1. A method of coating a non-conductive member, which comprises a step of coating a surface to be coated with a powder coating material containing or supporting a polarization material .
The polarization material, scaly graphite and barium titanate, strontium titanate, among calcium titanate, looking contains at least one,
The powder coating is a method for coating a non-conductive member containing an epoxy resin as a main component .