JPH08323288A - Method for applying powder coating material - Google Patents

Abstract

PURPOSE: To form an undercoating free from defects such as pinhole in a stable manner in a method for applying powder coating material to the surface of an item to be coated through an undercoating film by specifying compositions of epoxy resin powder compositions for constituting an undercoating film. CONSTITUTION: When a powder coating material is applied to the surface of an item to be coated such as electric and electronic parts, etc., through an undercoating film, epoxy resin powder compositions are used for an undercoating film. That is, the epoxy resin powder compositions are prepared from a powder of a mixture containing, as indispensable compositions, an epoxy resin in the form of solid at room temperature containing 55-95wt.% bivalent phenol diglycidyl ether crystalline epoxy resin having m.p. of 115 deg.C or higher and having steric hindrance groups in bonding neighboring position of glycidyl ether groups and a curing agent exhibiting a solid form at room temperature. The mixture is used as a molten mixture and an agent containing partially crystalline curing agent is used as the curing agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating an object to be coated such as electric / electronic parts with a powder coating material.

[0002]

2. Description of the Related Art It has been widely practiced to apply an electrically insulating powder coating such as an epoxy resin powder coating on the outer surface of an electric article to be coated. In such powder coating, since a coating film defect such as a pinhole is likely to occur in the coating film formed on the surface of the object to be coated, prior to the powder coating, an undercoat layer is formed on the object to be coated, Powder coating is generally performed through the undercoat layer. As the undercoating method, a method of coating and drying a curable resin such as a phenol resin, a urethane resin, or an epoxy resin in a liquid state as an undercoating agent is carried out so that a film defect such as a pinhole does not occur in the undercoating film. ing. However, in the case of the undercoating method using such a liquid resin, resin damage, sagging, etc. occur below the object to be coated, resulting in a non-uniform coating film. When these phenomena are large, a step of removing them is required, the yield is low, and this causes variations in characteristics. Since the liquid resin is unstable, the surplus resin remaining after the undercoating operation cannot be reused and must be discarded, which is unsatisfactory from the economical point of view.

[0003]

DISCLOSURE OF THE INVENTION The present invention is a method of coating a powder coating on a surface of an object to be coated through an undercoating coating film, which comprises a defect-free undercoating coating film as an undercoating agent for forming an undercoating coating film. It is an object of the present invention to provide a method of using a curable resin powder composition to be given.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the present invention, in a method of coating a powder coating material on the surface of an object to be coated through an undercoat coating film, the undercoat coating film is formed from an epoxy resin powder composition, The resin powder composition has a sterically hindering group adjacent to the glycidyl ether group bonding point, melting point 115.
Powder of a mixture containing, as essential components, an epoxy resin containing 55 to 95% by weight of a dihydric phenol diglycidyl ether type crystalline epoxy resin having a temperature of ℃ or more and showing a solid state at room temperature, and a curing agent showing a solid state at room temperature An epoxy resin powder composition comprising (i) the mixture is a melt mixture, (ii) the curing agent contains a crystalline curing agent in at least a part thereof, (iii) in the mixture The amount of the non-crystalline substance contained in the mixture is 0 to 50% by weight based on the total amount of the crystalline substance and the non-crystalline substance contained in the mixture, (iv) the powder of the mixture is A method for coating a powder coating material, which is characterized by being non-adhesive. Further, according to the present invention, in a method of coating a powder coating material on a surface of an object to be coated through an undercoating coating film, the undercoating coating film is formed from an epoxy resin powder composition. The resin powder composition contains 55 to 50 of a dihydric phenol diglycidyl ether-based crystalline epoxy resin having a steric hindrance group at a position adjacent to a bond of a glycidyl ether group and having a melting point of 115 ° C. or higher.
An epoxy resin which is solid at room temperature and contains 100% by weight;
An epoxy resin powder composition comprising a powder of a mixture containing, as an essential component, a curing agent that is solid at room temperature, (i) the mixture is a molten mixture, and (ii) the curing agent is At least a part thereof contains trimellitic anhydride and / or a trimellitic anhydride derivative, (ii
i) The amount of the non-crystalline substance contained in the mixture is 0 to 50% by weight based on the total amount of the crystalline substance and the non-crystalline substance contained in the mixture, (iv) A method for coating a powder coating is provided, characterized in that the powder of the mixture is non-tacky.

In the present invention, an epoxy resin powder composition is used as the undercoat. The epoxy resin in this case contains a dihydric phenol diglycidyl ether-based crystalline epoxy resin (hereinafter, also referred to as crystalline epoxy resin A) having a steric hindrance group at a position adjacent to the bond of the glycidyl ether group and having a melting point of 115 ° C. or higher. It is a thing. Such crystalline epoxy resin A includes those represented by the following general formula (1).

Embedded image In the above formula, R ¹ represents a sterically hindered group, R ² represents a lower alkyl group or a halogen atom, G represents a glycidyl group,
m shows the number of 0-3, n shows the number of 0 or 1. The sterically hindered group includes an iso-propyl group, an iso-butyl group,
An iso-alkyl group having 3 to 6 carbon atoms such as an iso-amyl group, an iso-hexyl group, a tert-butyl group, a tert-amyl group, and a tert-hexyl group, and a carbon number of 4 to 6
Tert-alkyl groups and the like are included. Examples of the lower alkyl group include an alkyl group having 1 to 6 carbon atoms, for example, methyl, ethyl, propyl, butyl, amyl, hexyl and the like, and the lower alkyl group may be the sterically hindered group. . Examples of the halogen atom include chlorine and bromine.

The crystalline epoxy resin represented by the general formula (1) is described in, for example, JP-A-6-145293.
JP-A-6-298902 and the like. Further, other examples of the crystalline epoxy resin include those represented by the following general formula (2).

Embedded image In the above formula, R ¹ , R ² and m have the same meaning as described above.

In the present invention, the crystalline epoxy resin A is used in the form of a mixture with an epoxy resin having a fast curing reaction. As such a quick-curing epoxy resin,
A normal epoxy resin which does not have a sterically hindering group adjacent to the bond of the glycidyl ether group and which is solid at room temperature is used. Such quick-curing epoxy resin includes general-purpose crystalline epoxy resin and non-crystalline epoxy resin. The crystalline epoxy resin has a melting point lower than 115 ° C., for example, tetramethylbiphenol diglycidyl ether (melting point: 105 ° C.), tetramethylbisphenol A diglycidyl ether (“ESLV-80XY”,
Nippon Steel Chemical Co., Ltd., melting point 78 ° C.), bis (4-hydroxyphenyl) ether diglycidyl ether (“ESLV
-80DE ", Nippon Steel Chemical Co., melting point 79 ° C), formula

Embedded image (In the formula, G represents a glycidyl group) (“ESLV-90CR”, Nippon Steel Chemical Co., Ltd., melting point 89 ° C.) and the like. Examples of the fast-curing non-crystalline epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, biphenyl type epoxy resin, 1,1,2,2-tetrabis (glycidyloxyphenyl) ethane, and phenol novolac type. , Alkylphenol novolac type, bisphenol A novolac type novolac type epoxy resin, cyclopentadiene / phenol type epoxy resin (“DCE400”,
Sanyo Kokusaku Pulp Co., Ltd., softening point 65 ° C.), trifunctional aromatic epoxy resin [“Epicoat YL933”, (softening point 60 ° C., Yuka Shell Epoxy Co., Ltd.), “VG310
1 "(manufactured by Mitsui Petrochemical Co., Ltd., softening point 61 ° C.), etc.] Tetrafunctional aromatic epoxy resin (“ Epicoat 1031S ”, manufactured by Yuka Shell Epoxy Co., Ltd., softening point 92 ° C., etc.), tetrafunctional or higher polyfunctional Aromatic epoxy resin ("Epicoat 103
2 ”, manufactured by Yuka Shell Epoxy Co., Ltd., softening point 92 ° C., etc.) and the like. In the present invention, it is preferable to use a trifunctional or higher functional polyfunctional epoxy resin, particularly a tetrafunctional or higher functional epoxy resin.

When the crystalline epoxy resin A is mixed with the quick-curing epoxy resin, the curing reactivity of the mixed epoxy resin is improved and the gelation time is shortened. Among the fast-curing epoxy resins, it is particularly preferable to use an aromatic epoxy resin containing 3 or more, particularly 4 or more glycidyl ether groups in the molecule. By mixing this with the crystalline epoxy resin A, It is possible to obtain a mixed epoxy resin exhibiting high curing reactivity. The content of the crystalline epoxy resin A in all the epoxy resins is at least 55% by weight or more.
In addition to impairing the expression of the low melt viscosity of the above, the cooling and solidifying rate of the mixture after melt mixing becomes slow, and it takes a long time to become a pulverizable solidified product. From the viewpoint of low melt viscosity, improvement of curing reactivity, and solidification by cooling, crystalline epoxy resin A in all epoxy resins is used.
Content of 55 to 95% by weight, preferably 65 to 95
%, More preferably 70 to 95% by weight. The mixing ratio of the crystalline epoxy resin A is adjusted so that the mixed epoxy resin has a solid state without tackiness at room temperature. The minimum content for this is determined by the type of epoxy resin mixed with the crystalline epoxy resin A, but is usually 55% by weight or more.

The curing agent used for the epoxy resin has a solid state at room temperature and contains a crystalline curing agent in at least a part thereof. Examples of the crystalline curing agent include bisphenol A (melting point 157 ° C.), bisphenol F, bisphenol S (melting point 245 ° C.), tetrabromobisphenol A (melting point 180 ° C.), and the like; 5 (2,5-dioxotetrahydrofloryl) ) -3-Methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride (“Epiclone B-4400”, manufactured by Dainippon Ink and Chemical Co., melting point 165 ° C.), tetrahydrophthalic anhydride (melting point 101 ° C.), nadic acid Anhydrides, trimellitic anhydride (melting point 165 ° C), derivatives of trimellitic anhydride, pyromellitic anhydride, acid anhydrides such as benzophenonetetracarboxylic anhydride; diaminodiphenylmethane, isophoronediamine, metaphenylenediamine, diamino In addition to diamino compounds such as diphenyl sulfone, Acid hydrazide, dicyandiamide, and the like. In the present invention, the melting point is 90 ° C. or higher, preferably 100.
It is preferable to use a crystalline curing agent having a temperature of ℃ or higher.

Among the crystalline hardeners, the bisphenol compound, which is a high melting point substance, is a hardener which is preferably applicable to the present invention. Since the bisphenol compound has a high melting point and an excellent low melt viscosity, an epoxy resin powder composition having no stickiness and an excellent low melt viscosity by being melt-mixed with the crystalline epoxy resin A. Give things. Of the crystalline hardeners, trimellitic anhydride and
The trimellitic anhydride derivative is a curing agent preferably applicable to the present invention. In this case, the trimellitic anhydride derivative means a compound in which a free carboxyl group bonded to trimellitic anhydride reacts with another reactive compound. Such reactive compounds include monohydric alcohols that give fatty acid esters, alcohols such as glycols (ethylene glycol, propylene glycol, etc.), triols (glycerin, etc.), and phenols, alkylphenols, polyhydric phenols, etc. that give aromatic esters. Is mentioned. Surprisingly, such a trimellitic anhydride or a trimellitic anhydride derivative reacts with the crystalline epoxy resin A having low curing reactivity at a high speed,
It was found that its gelling time was very short.
The content of the trimellitic anhydride and / or its derivative is at least 5% by weight, preferably 1%, based on the total curing agent.
It is 0 to 100% by weight. The trimellitic anhydride and / or its derivative can be preferably used as a mixture with a bisphenol compound. In this case, the proportion of trimellitic anhydride and / or its derivative is 20 to 60% by weight, preferably 30%, based on the total weight of both.
~ 50% by weight.

The curing agent used for the epoxy resin may contain an amorphous curing agent. As such an amorphous hardener, a conventionally known one that is solid at room temperature, for example, a phenol novolac type resin (“Tamanol # 75
9 ", manufactured by Arakawa Chemical Co., Ltd., softening point 100 ° C, ortho-cresol novolak type resin (" OCN90 ", manufactured by Nippon Kayaku Co., softening point 120 ° C), bisphenol A novolac type resin (" Epicure YLH-129 ", oil). And a softening point of 115 ° C., aminopolyamide resin, polysulfide resin, etc. The content of the crystalline curing agent in the curing agent is at least 5% by weight, and preferably 50% by weight.
１００100% by weight.

The epoxy resin powder composition used in the present invention may contain a curing accelerator, if necessary.
Examples of the curing accelerator include conventionally known ones, such as tertiary amine, quaternary ammonium salt, phosphine compound, phosphonium salt, and imidazole compound. The composition may contain conventional adjunct ingredients.
Such auxiliary components include, for example, organic or inorganic fillers, flame retardants, silane coupling agents, colorants, release agents and the like. The epoxy resin powder composition used in the present invention is produced by a melt mixing method which has been generally adopted conventionally. In this case, the curing agent and the curing accelerator may be preliminarily melt-mixed with each other. When two or more epoxy resins are used, the epoxy resins may be mutually pre-melted and mixed. it can. That is, it is produced by melt-mixing each compounding component, cooling the resulting melt-mixture, and pulverizing to a required particle size. The melt mixing in this case means at least one of the components other than the crystalline epoxy resin A.
It means a mixture in which two components, preferably a non-crystalline substance (such as a non-crystalline epoxy resin and a curing agent) are present in a molten state. In the case of the above composition, the crystalline epoxy resin A having poor reactivity is a mixed resin with a fast curing reactive epoxy resin, or trimellitic anhydride and / or
Alternatively, since the derivative thereof is used, it can be easily cured by heating. As the heat curing conditions, usually, a heating temperature of 110 to 180 ° C. and a heating time of 2 to 0.5 hours can be adopted.

In the epoxy resin powder composition, since the respective compounding components are firmly bonded by the melt mixing method,
Even if external force such as stirring force or vibration force is applied, each component does not easily peel off. In addition, since the surface of the powder is non-adhesive (there is no surface tackiness), this composition does not stick to each other, and is very excellent in handleability and workability. . Furthermore, since this composition contains a specific crystalline epoxy resin A and a crystalline curing agent, it has a characteristic that the viscosity at the time of melting is very low, and the melt has a property of impregnating into fine voids. It is excellent in (penetration) and film forming ability, and gives a coating film without defects such as pinholes on the surface of the object to be coated.

In order to apply the powder coating material to an object to be coated according to the present invention, an undercoat coating film is first formed on the surface of the object to be coated using the above-mentioned epoxy resin powder composition as an undercoating agent. This undercoat film can be formed by a conventionally known powder coating method, for example, a sprinkling method, a fluid immersion coating method, an electrostatic coating method, or the like. In the fluid immersion coating method, the epoxy resin powder composition is fluidized by a gas such as air or nitrogen gas, and the heated article to be coated is placed in the fluidized epoxy resin powder composition, At the same time that the epoxy resin powder composition is melted on the surface of the object to be coated, the melt is adhered to the surface of the object to be coated.
The heating temperature of the object to be coated may be a temperature at which the epoxy resin powder composition is completely melted, and generally 110 to 18
0 ° C. In this way, an undercoat coating film having no defects such as pinholes can be formed on the surface of the object to be coated.

On the other hand, in the electrostatic coating method, a pre-charged epoxy resin powder composition is attached to the surface of an object to be coated by utilizing the electrostatic adsorption force by the charging, and then the epoxy resin powder is obtained. Heat to the complete melting temperature of the composition.
In this way, an undercoat film having no defects such as pinholes can be formed on the surface of the article to be coated. The thickness of the undercoat coating film formed on the surface of the article to be coated is 50 to 300 μm,
It is preferably 100 to 200 μm. Further, this undercoat coating film can be further heat-treated and cured, if necessary.

Next, the powder coating is applied to the surface of the object to be coated on which the undercoating film has been formed as described above through the undercoating film. In this case, a conventionally known powder coating can be used, and a conventionally known powder coating method can be adopted. As the powder coating material, a thermosetting material can be preferably used. These include epoxy resin powder coatings, silicone resin powder coatings, melamine resin powder coatings, polyimide resin powder coatings, and the like. As a powder coating material for electric / electronic parts, it is particularly preferable to use an epoxy resin powder coating material. This epoxy resin-based powder coating material has been widely used in the past and is composed of an epoxy resin and a curing agent, and if necessary, a curing accelerator, a pigment,
It contains auxiliary components such as a filler. As the powder coating method, a conventional method such as a fluid immersion coating method or an electrostatic coating method is adopted. The thickness of the outer coating film formed by the powder coating is 100 to 800 μm, preferably 400 to 800 μm.
It is 600 μm.

As described above, the article to be coated having the exterior coating film of the powder coating material formed on the surface thereof through the undercoat coating film is heat-treated by using a heating furnace or the like. In this case, the heat treatment condition may be a heating temperature and time at which both the undercoating film and the exterior coating film on the upper surface thereof are melt-cured. When the exterior coating film is formed of an epoxy resin-based powder coating material, the heating temperature is generally 90 to 180 ° C, preferably 100 to 150 ° C. The heating time is
Generally, it is 120 to 30 minutes, preferably 45 to
70 minutes.

The article to be coated used in the present invention is generally
Although it is an electric / electronic component such as a capacitor, a resistor, a coil, or a hybrid IC, it may be a cold rolled steel plate, a galvanized steel plate, an aluminum plate, or the like, and the type thereof is not particularly limited.

[0019]

EXAMPLES Next, the present invention will be described in more detail by way of examples.

Reference Example 1 Epotote YDC-1312 (2,5-di-t-butylhydroquinone diglycidyl ether, manufactured by Tohto Kasei Co., Ltd.,
The epoxy resin shown in Table 1 was mixed with an epoxy equivalent of 175 and a melting point of 145 ° C.) at a temperature at which at least a part of Epototo YDC-1312 was not melted, and the epoxy resin shown in Table 1 was completely melted, and the mixture was cooled (14 (° C) solidified. The properties of the solidified product thus obtained and the solidification time upon cooling are shown in Table 1.
Shown in In this case, the cooling and solidifying time means the time for the mixture to be mixed in a molten state and for the cooled (14 ° C.) mixture to solidify to a hardness at which it can be finely pulverized. The symbols shown in Table 1 indicate the following contents. Epotote YD-7011: Bisphenol A type epoxy resin (non-crystalline), epoxy equivalent: 475, softening point: 65 ° C, Toto Kasei Epotote YDCN-701: cresol novolac type epoxy resin (non-crystalline), epoxy equivalent: 215, softening point: 65 ° C., manufactured by Tohto Kasei Co., Ltd. EOCN-103: cresol novolac type epoxy resin (non-crystalline), epoxy equivalent: 220, softening point: 82
C., Nippon Kayaku Co., Ltd. Epicoat YL-6350: Tetrabromobisphenol A diglycidyl ether (crystalline), epoxy equivalent:
335, melting point 115 ° C, made by Yuka Shell Epoxy Co., Ltd.

[0021]

[Table 1]

As can be seen from the results shown in Table 1, when the crystalline epoxy resin A specified in the present invention is melt-mixed with another rapidly curable epoxy resin and the mixture is cooled and solidified, the cooling and solidifying time is fast. Moreover, the solidified product obtained is a crystalline mixed epoxy resin which is crystalline, has a sufficiently high melting point, is non-tacky on the surface, and has excellent handleability.
Therefore, such a crystalline mixed epoxy resin gives a good powder composition having a low viscosity.

Comparative Reference Example 1 70 parts by weight of Epicoat YX-4000 was melt mixed with 30 parts by weight of Epicoat YD-7011, and the mixture was allowed to cool and solidify at room temperature.
In addition to requiring a long period of time or more, the surface of the solidified product obtained was tacky. Therefore, this solidified product is unsuitable as a raw material epoxy resin for forming a powder composition.

The determination of whether or not the powder surface shown above is non-adhesive was made by the following method. Temperature 2
Under an atmosphere of 5 ° C. and a humidity of 70% RH, 50 g of powder that passed through a 60-mesh sieve was placed in a cylindrical container having an inner diameter of 5 cm, and a load of ² g / cm ² was applied, and the mixture was left for 3 hours. Next, the powder was taken out from the cylindrical container, and the powder of 60 mesh attached to the low-taper type shaker φ200A (sieve rotation number 290 times / minute, impulse number 165 times / minute) manufactured by Iida Seisakusho It was placed on a sieve and shaken for 30 minutes.
If 95% by weight or more of the powder passes through a 60-mesh sieve by the shaking, it is determined that the powder is non-adhesive, and if not, the powder is not non-adhesive (adhesive Yes).

Reference Example 2 A powder mixture having the composition shown in Table 2 was prepared as YDC-13.
At least a part of 12 did not melt but showed a solid state and was melt-kneaded under a temperature condition in which other components were melted, and this kneaded product was cooled (14 ° C.) to be solidified and pulverized. The gel time of this powder composition was evaluated. The results are shown in Table 2. Gel time is measured according to JIS C 21 at 150 ° C.
It was measured according to 04. The symbols shown in Table 1 mean the following contents. BPA: Bisphenol A (melting point 157 ° C.) THPA: Tetrahydrophthalic anhydride (melting point 1
01 ° C.) YLH-129: Bisphenol A novolac type resin (“Epicure YLH129”, softening point 115 ° C., manufactured by Yuka Shell Epoxy Co., Ltd.) DAM: diaminodiphenylmethane (melting point 9
0 ° C.) TMA: trimellitic anhydride (melting point 165
C) TBA: tetrabromobisphenol A (melting point 180 ° C) TPP: triphenylphosphine 2MZ-A: 2,4-diamino-6-6 [2-methylimidazolyl (1)]-ethyl S-triazine BTDA: benzophenone tetracarboxylic. acid dianhydride TMEG-500: trimellitic anhydride derivative ( "RIKACID TMEG-500", manufactured by New Japan Chemical Co., Ltd.) Sb ₂ 0 _3: antimony trioxide ( "Pirogado A
N-850 ", manufactured by Dai-ichi Kogyo Co., Ltd. Al (OH) ₃ : Aluminum hydroxide (" Hidilite H-32 ", manufactured by Showa Denko KK) XK-21: Acrylic ester oligomer (" Nicalite XK-21 ", (Made by Nippon Carbite Co., Ltd.)

[0026]

[Table 2]

As can be seen from the results shown in Table 2, as the epoxy resin, only the crystalline epoxy resin A containing no fast-curing epoxy resin and having poor curing reactivity is used, and the curing agent containing no TMA. In the case of using (Experiment No. 9), it can be seen that the curing reactivity of the composition is very poor. On the other hand, when the one containing TMA is used as the curing agent (Experiment No. 3 to No. 5), the curing reactivity of the composition is very good, and it is understood that the composition is rapidly cured by heating. Moreover, in this case, when only the crystalline epoxy resin A having poor curing reactivity is used (Experiment N
o. It can be seen that even in the case of 3), the curing rate of the composition is high.

Example 1 A PET film capacitor was used as an article to be coated, and an undercoat coating film and an exterior coating film were formed on the surface thereof as follows. (1) Formation of undercoat coating film As an epoxy resin powder composition, Experiment N in Table 3 was performed.
o. The compositions 10 to 13 were melt-kneaded, and the kneaded material was cooled (14 ° C.) to be solidified and pulverized. This was applied to the surface of a PET film capacitor as follows. The pre-heated (120 ° C., 60 minutes) PET film capacitor was coated with the epoxy resin powder composition so that the coating film thickness was 100 μm on each side, and was cured by heating. Experiment No. 1
The composition of No. 4, that is, a commercially available epoxy resin liquid composition (“Epiform E-8501”, manufactured by Somar) was applied to a preheated (120 ° C., 60 minutes) PET film capacitor so that the coating thickness was 50 μm on each side. And was cured by heating (120 ° C., 60 minutes). In addition, in Experiment No. 3 using only the non-crystalline epoxy resin. 1
The composition of 6 was melt-kneaded, solidified by cooling (14 ° C), and pulverized, and applied to a preheated (120 ° C, 60 minutes) PET film capacitor so that the coating thickness would be 100 μm on each side, and heat-cured. did. (2) Formation of outer layer coating film After forming the undercoating film, a commercially available epoxy resin powder composition (“Epiform F-255”, manufactured by Somar Co., Ltd.) was applied so that the coating thickness would be 500 μm on each side, and heating ( 120
(° C, 50 minutes) cured. Evaluation method Moisture resistance A PET film capacitor (test piece) having an outer coating film was left standing at room temperature for 24 hours. Next, the test piece is placed in an atmosphere of a temperature of 60 ° C. and a relative humidity of 90% for 25
After forcibly humidifying for 0 hours, measure the capacitance (μF) with an impedance analyzer (Yokogawa Hewlett-Packard) and obtain the rate of change (%) with the capacitance (μF) of the test piece before the forced humidification test. The moisture resistance was evaluated as follows. The capacitance (μF) change rate (%) of less than 3% was rated as ◎ 3 to less than 4% as ○ 4 to less than 5% as Δ 5% or more as x.

[0029]

[Table 3]

[0030]

According to the present invention, since the epoxy resin powder composition containing the specific crystalline epoxy resin A and the crystalline curing agent is used as the undercoating agent, the coating film formed by the undercoating agent is , High quality with no coating defects such as pinholes and craters. Therefore, by coating the powder coating material through this undercoating film, it is possible to form a coating film excellent in moisture resistance, insulation property, adhesion property, heat cycle resistance property, etc. on the surface of the object to be coated. . Further, since the undercoating agent used in the present invention is a powder, the excess undercoating agent remaining after the undercoating operation can be reused.

Claims (7)

[Claims] 1. A method of coating a powder coating material on the surface of an article to be coated with an undercoat coating film, wherein the undercoat coating film is formed from an epoxy resin powder composition. The composition comprises a dihydric phenol diglycidyl ether type crystalline epoxy resin having a steric hindrance group at a position adjacent to the bond of the glycidyl ether group and having a melting point of 115 ° C. or higher.
An epoxy resin which is solid at room temperature and contains about 95 wt%
An epoxy resin powder composition comprising a powder of a mixture containing, as an essential component, a curing agent that is solid at room temperature, (i) the mixture is a molten mixture, and (ii) the curing agent is At least a part thereof contains a crystalline curing agent, (iii) the amount of the non-crystalline substance contained in the mixture is
The content of the crystalline substance and the non-crystalline substance contained in the mixture is 0 to 50% by weight, and (iv) the powder of the mixture is non-adhesive. Powder coating method. 2. The crystalline epoxy resin is 2,5-di-
The method of claim 1 which is tert-butyl hydroquinone diglycidyl ether. 3. The method according to claim 1, wherein the crystalline curing agent is at least one selected from bisphenol compounds, trimellitic anhydride and trimellitic anhydride derivatives. 4. The melting point of the epoxy resin is 115 ° C., which does not have a sterically hindering group adjacent to the glycidyl ether group bonding position.
The method according to any one of claims 1 to 3, which comprises a lower crystalline epoxy resin and / or a non-crystalline epoxy resin having 3 or more glycidyl ether groups. 5. The method of claim 4, wherein the non-crystalline epoxy resin is a novolac type epoxy resin. 6. The method according to claim 1, wherein the powder coating material is an epoxy resin powder coating material. 7. A method of coating a powder coating on a surface of an object to be coated through an undercoat coating film, wherein the undercoat coating film is formed from an epoxy resin powder composition. The composition comprises a dihydric phenol diglycidyl ether type crystalline epoxy resin having a steric hindrance group at a position adjacent to the bond of the glycidyl ether group and having a melting point of 115 ° C. or higher.
An epoxy resin powder composition comprising a powder of a mixture containing, as essential components, an epoxy resin containing 100% by weight to 100% by weight of a solid state at room temperature and a curing agent showing a solid state at room temperature. The mixture is a molten mixture, (ii)
The curing agent contains trimellitic anhydride and / or trimellitic anhydride derivative in at least a part thereof,
(Iii) The amount of the non-crystalline substance contained in the mixture is 0 to 50% by weight based on the total amount of the crystalline substance and the non-crystalline substance contained in the mixture, (iv) A powder coating method, wherein the powder of the mixture is non-adhesive.