JP2005146026A - Epoxy resin powder coating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an epoxy resin powder coating which is excellent in shelf stability and coating appearance, without deteriorating its basic characteristics as a powder coating. <P>SOLUTION: The epoxy resin powder coating contains an epoxy resin, a phenol resin and an imidazole compound, wherein the phenol resin and the imidazole compound are melted and mixed. The imidazole compound preferably has a melting point of ≤160°C and is preferably 2-phenylimidazole. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an epoxy resin powder coating.

  Epoxy resin powder coatings have excellent electrical, mechanical, and thermal properties. Compared to conventional solvent-based coatings, the epoxy resin powder coating does not contain any solvent. Electronic parts, OA equipment, home appliances, building materials, automobile parts, etc. due to advantages such as being excellent, being usable immediately after painting, being relatively inexpensive, and being able to collect and use excess paint during painting In recent years, there is a high demand for coatings for insulation protection decoration.

Many curing agents or curing accelerators used in epoxy resin powder coatings are solid (powder, granular, flake, etc.) at room temperature.
For this reason, conventionally, these curing agents and the like, and epoxy resins, fillers, pigments, and various additives are melt-kneaded with an apparatus such as an extruder and then pulverized (for example, see Patent Document 1) or cured. An agent and an epoxy resin were dissolved and mixed, melted and kneaded with an extruder or the like together with other components, and then pulverized to obtain a powder coating material.

However, the former production method can disperse the curing agent and the like to some extent, but it is difficult to disperse uniformly. This tendency is particularly remarkable in the case of a curing accelerator in which the blending amount is small. In addition, when a solution obtained by dissolving and mixing a curing agent or the like and an epoxy resin is used as in the latter production method, the reaction proceeds depending on these types, and the storage stability may be lowered.
For this reason, if the curing agent is not blended in a larger amount with respect to the epoxy resin, the curability is not sufficient, and when used in a powder coating, a large amount of unreacted curing agent remains in the cured coating film, It may affect the moisture resistance of the coating film. Further, in the case of a curing accelerator, there is a problem of causing poor coating appearance and lowering storage stability due to poor dispersion.

For such problems, it has been proposed to use a novolac type phenol resin obtained by dispersing and mixing a powdered imidazole compound in a softened or melted novolac type phenol resin as a curing catalyst used in an epoxy resin powder coating. (For example, refer to Patent Document 2).
This method has an effect of preventing the storage stability of the powder coating material from being lowered, but in particular when the blending amount of the curing catalyst is small, the uniform dispersibility may still not be sufficient.

Japanese Patent Laid-Open No. 2002-275412 JP 2002-020683 A

  The present invention provides an epoxy resin powder coating excellent in storage stability and coating appearance without impairing the basic characteristics as a powder coating.

Such an object is achieved by the following present inventions (1) to (4).
(1) An epoxy resin powder coating material containing an epoxy resin, a phenol resin, and an imidazole compound, wherein the phenol resin and the imidazole compound are melt-mixed. Body paint.
(2) The epoxy resin powder coating according to (1), wherein the imidazole compound has a melting point of 160 ° C. or lower.
(3) The epoxy resin powder coating according to (1) or (2), wherein the imidazole compound is 2-phenylimidazole.
(4) The epoxy resin powder coating according to any one of (1) to (3) above, containing 5 to 40% by weight of the imidazole compound based on the total of the phenol resin and the imidazole compound.

The present invention is an epoxy resin powder coating material comprising an epoxy resin, a phenol resin, and an imidazole compound, wherein the phenol resin and the imidazole compound are melt-mixed.
When the imidazole compound is used as a curing agent or a curing accelerator, the epoxy resin powder coating of the present invention can improve the uniform dispersibility even if the amount of the imidazole compound in the powder coating is small. it can. As a result, an epoxy resin powder coating excellent in storage stability and coating appearance can be obtained without impairing the basic characteristics of the powder coating.

Hereinafter, the epoxy resin powder coating of the present invention will be described in detail.
The epoxy resin powder coating of the present invention is an epoxy resin powder coating containing an epoxy resin, a phenol resin, and an imidazole compound, and is obtained by melt-mixing the phenol resin and the imidazole compound. It is characterized by.
First, raw material components used in the epoxy resin powder paint of the present invention (hereinafter sometimes simply referred to as “powder paint”) will be described.

The epoxy resin blended in the powder coating material of the present invention can be one that is solid at room temperature, and is not particularly limited. For example, bisphenol A type epoxy resin, novolac type epoxy resin, biphenyl type epoxy resin, etc. These may be used alone or in combination.
Among these, when a bisphenol A type epoxy resin is used, the coating film is preferable because it has excellent mechanical and electrical characteristics.

  The molecular weight and epoxy equivalent of the epoxy resin are not particularly limited, and may be appropriately selected according to the formulation of the powder coating and the required properties. For example, when a bisphenol A type epoxy resin is used, it is preferable to use one having an epoxy equivalent of 450 to 2000 because the paintability of the powder coating is excellent.

Further, the amount of the epoxy resin in the powder coating is not particularly limited, but when a curing agent component is used in addition to the imidazole compound and the phenol resin, 25 to 60 wt. %, More preferably 35 to 55% by weight. Thereby, the coating property of a powder coating material can be made favorable.
If the blending amount is less than the above lower limit value, the smoothness of the coating film may be reduced. On the other hand, if it is greater than the above upper limit value, appearance defects such as sagging or toggling may occur during firing, which is a curing step after coating. is there.

  The powder coating material of the present invention contains a phenol resin and an imidazole compound. Here, the phenol resin and the imidazole compound are characterized by being melt-mixed (hereinafter referred to as “phenol resin molten imidazole compound”).

As the phenol resin used in the powder coating material of the present invention, those that are solid at room temperature can be preferably used, and the type thereof is not particularly limited, and examples thereof include novolak type phenol resins and resol type phenol resins. In addition to these ordinary phenol resins, various modified phenol resins can also be used.
Although it is not particularly limited as a modified phenolic resin, for example, phenols such as cresol, alkylphenol, resorcin, various animal and vegetable oils such as cashew oil, tall oil, linseed oil, unsaturated fatty acid, rosin, alkylbenzene resin, aniline, A phenol resin modified with melamine, rubber or the like can be used alone or in combination of two or more.

  Among these, when a novolac type phenol resin is used, melt mixing with an imidazole compound can be performed in a wide temperature range. In addition, the powder coating is preferable in view of the coating appearance, storage stability, heat resistance, and the like, since no substantial deterioration is observed.

  When the novolac type phenol resin is used, the melting point thereof is not particularly limited, but, for example, those having a temperature of 70 to 140 ° C. can be suitably used. Thereby, melt mixing with the imidazole compound mentioned later can be easily performed in a relatively low temperature range.

  Moreover, about the imidazole compound used by the powder coating material of this invention, the well-known thing generally used as a hardening | curing agent for epoxy resins can be used. For example, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-methylimidazole isocyanuric acid adduct 1-cyanoethyl-2-phenylimidazolium trimellitate, 1-cyanoethyl-2-undecylimidazolium trimellitate and the like, and these can be used alone or in combination.

Among the imidazole compounds, those having a melting point of 160 ° C. or less are preferably used. Thereby, melt mixing with a phenol resin can be easily performed in a relatively low temperature range.
Examples of such imidazole compounds include 2-methylimidazole, 2-phenylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-methylimidazole isocyanuric acid adduct 1-cyanoethyl-2-undecylimidazolium. Trimeritate and the like.
Among these, 2-phenylimidazole is particularly preferable. Thereby, in addition to the said effect, the storage stability and sclerosis | hardenability of a powder coating material can be made excellent.

In the powder coating of the present invention, the amount of the imidazole compound is not particularly limited, but when used as a curing agent, it is preferably 1 to 8% by weight with respect to the epoxy resin. Moreover, when using a hardening | curing agent separately and using as a hardening accelerator, it is preferable to set it as 0.1 to 1.0 weight% similarly. Thereby, favorable sclerosis | hardenability can be provided to a powder coating material.
If the amount of the imidazole compound is less than the above lower limit, curing may take time and the curability may not be sufficient. Moreover, when the said upper limit is exceeded, the moisture resistance of a coating film may fall.

In the powder coating of the present invention, the melt mixing ratio of the phenol resin and the imidazole compound is not particularly limited, but the imidazole compound may be 5 to 40% by weight with respect to the total of the phenol resin and the imidazole compound. preferable. More preferably, it is 10 to 30% by weight.
If the mixing ratio of the imidazole compound is less than the above lower limit value, the amount of the phenol resin required for blending a predetermined amount of the imidazole compound into the powder coating becomes relatively large. May affect film adhesion. On the other hand, when the above upper limit is exceeded, the amount of the phenol resin molten imidazole compound to be blended in the powder coating is reduced, and the dispersion accuracy of the imidazole compound in the powder coating may be lowered.

  In the powder coating material of the present invention, the amount of the phenol resin is not particularly limited, but is preferably 0.5 to 10% by weight based on the epoxy resin. Thereby, it is possible to improve the dispersion and mixing accuracy of the imidazole compound in the powder coating material, and it is possible to substantially eliminate the influence on the properties of the powder coating material and the coating film due to the blending of the phenol resin.

The method for preparing the phenol resin molten imidazole compound is not particularly limited. For example, a reaction apparatus having a stirring device prepared by mixing a phenol resin and an imidazole compound at a predetermined ratio and thoroughly mixing them with a Henschel mixer or the like, It can be prepared by melt mixing in a temperature range where the phenol resin and the imidazole compound melt using a stirring and mixing device equipped with a temperature control device, a twin screw extrusion kneading device such as an extruder, and the like. In particular, the use of a reaction apparatus having a stirrer, a stirrer / mixer equipped with a temperature controller, etc. is preferable because it can improve the uniformity of the phenol resin molten imidazole compound.
A phenol resin molten imidazole compound can be obtained by melt-mixing by the above method, cooling to room temperature, and pulverizing to a predetermined particle size. Although it does not specifically limit as this particle size, It is preferable to set it as 300 micrometers or less. Thereby, the dispersion | distribution precision in a powder coating material can be made favorable.

In the powder coating material of the present invention, the following effects can be imparted by using a phenol resin molten imidazole compound.
When an imidazole compound is blended with a powder coating material containing an epoxy resin as a main component, particularly when used as a curing accelerator, the blending amount is usually very small. For this reason, in the conventional manufacturing method, the uniform dispersibility of the imidazole compound in the powder coating material may not be sufficient.
On the other hand, in the powder coating of the present invention, by using a phenol resin molten imidazole compound, the apparent mixing ratio with respect to the whole powder coating can be increased, and in the phenol resin molten imidazole compound, Since the compound can be in a form in which the compound is dispersed at a molecular level or substantially close thereto, the uniform dispersibility of the imidazole compound in the powder coating can be improved. Thereby, the uneven distribution of the imidazole compound component in the powder coating material can be prevented, and as a result, the curability and the coating appearance can be improved.

In addition, since the phenol resin and the imidazole compound usually do not substantially react with each other, both the phenol resin and the imidazole compound are mixed at a melting temperature or higher, and the phenol resin molten imidazole compound or a powder coating obtained by blending the phenol resin is good. It can have storage stability.
And since the phenol resin used for a phenol resin molten imidazole compound itself functions as a hardening | curing agent of an epoxy resin, it also has the advantage that it is hard to influence basic characteristics, such as the mechanical strength of a coating film, and adhesiveness.
For these reasons, storage stability and paint appearance can be improved without substantially impairing the basic properties of conventional epoxy resin powder coatings.

In the powder coating of the present invention, the above-mentioned phenol resin molten imidazole compound can be used alone as a curing agent component, but it can also be used in combination with other curing agents and curing accelerators as necessary. Such curing agents and curing accelerators are not particularly limited, and known ones that are generally used as curing agents for epoxy resins can be used.
For example, dicyandiamide, adipic acid, an amine curing agent, an aromatic acid anhydride, and the like can be given. Among these, when a bisphenol A type epoxy resin is used as the epoxy resin, it is preferable to use dicyandiamide or an acid anhydride because of excellent curability, adhesion, heat resistance, and the like. The blending amount of the curing agent is not particularly limited, and may be appropriately set in consideration of the type of epoxy resin to be used, the type of curing agent, and the like.

In addition to the above epoxy resin and curing agent, an inorganic filler can be blended in the powder coating of the present invention. Thereby, while being able to adjust the fluidity | liquidity of a powder coating material, mechanical strength and heat resistance can be provided to the coating film after hardening.
Although it does not specifically limit as an inorganic filler mix | blended here, For example, a silica, calcium carbonate, aluminum hydroxide, aluminum oxide, a calcium silicate, a talc etc. are mentioned, These can be used individually or in mixture.

The blending amount of the inorganic filler is not particularly limited, but is preferably 30 to 70% by weight, more preferably 35 to 60% by weight with respect to the whole powder coating material. Thereby, the coating property of a powder coating material can be made favorable.
If the blending amount is less than the above lower limit value, defects in appearance such as sagging or toggling may occur during firing, whereas if it exceeds the above upper limit value, the smoothness of the coating film may be deteriorated.

  Moreover, the particle diameter of the inorganic filler is not particularly limited, but usually an average particle diameter of 10 to 30 μm is preferably used. Thereby, the favorable fluidity | liquidity and the mechanical strength of a coating film can be provided to a powder coating material.

  In addition to the powder coating material of the present invention, a flame retardant usually used for an epoxy resin powder coating material can be blended as necessary. Examples of such flame retardants include halogen compounds such as brominated epoxy resins, phosphorus compounds containing inorganic red phosphorus, and organic phosphates.

  In addition, in order to improve the flame retardancy of powder coating materials, flame retardants such as silicone resin, melamine resin and other cyanuric ring skeletons, antimony trioxide, zinc borate, expandable graphite, etc. It can be suitably used as an auxiliary agent. Furthermore, additives such as various pigments, leveling agents, and coupling agents can be appropriately blended as necessary.

  The powder coating material of the present invention can be blended with other components within a range not impairing the object of the present invention. Examples of such components include a color pigment, a leveling agent, a curing accelerator, and the like. For example, titanium oxide, iron oxide, carbon black, and the like are used as the color pigment.

  The method for producing the powder paint of the present invention is not particularly limited, and a general method for producing a powder paint can be used. As an example, an epoxy resin, a phenol resin, a molten imidazole compound, a curing agent, an inorganic filler, and the like are blended at a predetermined composition ratio, mixed sufficiently with a Henschel mixer, and then melt-mixed with a kneader such as an extruder. And then pulverized and classified to an appropriate particle size by a pulverizer.

  In 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. A method for performing such a treatment is not particularly limited. For example, there is a method such as pulverization mixing in which a fine powder such as silica is added at the time of pulverization of a powder coating, or dry mixing using a Henschel mixer.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. However, the present invention is not limited to these examples.

-Preparation of phenol resin molten imidazole compound 1.1 The raw material components were mixed at the blending ratio shown in Table 1 and stirred while heating to 165 ° C in a reaction kettle, and melt mixed for 1 hour. Then, it cooled to normal temperature and grind | pulverized to 300 micrometers or less, and the phenol resin molten imidazole compound was obtained.

1.2 Raw materials used (1) Phenolic resin: Novolac type phenolic resin (manufactured by Sumitomo Bakelite, PR-53195, weight average molecular weight = 3000, melting point 110 ° C.)
(2) Imidazole compound 1: 2-phenylimidazole (manufactured by Shikoku Chemicals Co., 2PZ, melting point: 137 to 147 ° C.)
(3) Imidazole compound 2: 2-undecylimidazole (Shikoku Kasei Co., Ltd., C17Z, melting point 90 ° C.)

2. Production of powder coating 2.1 Examples 1 to 5
Using the phenol resin molten imidazole compound obtained in 1 above, the raw materials having the blending ratios shown in Table 2 were mixed for 20 minutes with a Henschel mixer, kneaded with an extruder, and then pulverized with a pulverizer to obtain an average particle size. An epoxy resin powder coating of 40-60 μm was obtained.
2.2 Comparative Examples 1-2
The raw materials having the blending ratios shown in Table 2 were mixed for 20 minutes with a Henschel mixer, kneaded with an extruder, and then pulverized with a pulverizer to obtain an epoxy resin powder coating having an average particle size of 40 to 60 μm.
2.3 Comparative Example 3
Phenol resin (manufactured by Sumitomo Bakelite Co., Ltd., PR-53195): Compounded in a ratio of imidazole compound 1 = 80: 20, kneaded with a roll kneader at 90 ° C., cooled to room temperature, ground to 300 μm or less, and phenol A resin / imidazole kneaded product was obtained.
Using this phenol resin / imidazole kneaded material, the raw materials having the blending ratios shown in Table 2 were mixed for 20 minutes with a Henschel mixer, kneaded with an extruder, and then pulverized with a pulverizer to have an average particle size of 40 to 60 μm. An epoxy resin powder coating was obtained.

2.3 Used raw materials (1) Epoxy resin: Bisphenol A type epoxy resin (Japan Epoxy Resin, Epicoat 1055, epoxy equivalent 850)
(2) Aromatic acid anhydride curing agent: trimellitic anhydride (3) Phenol resin fused imidazole compound prepared in 1 above (4) Inorganic filler: Crystalline silica (SQ-H25, manufactured by Sumitomo Coal Mining Co., Ltd.) (Average particle size 25 μm) (5) phenol resin: novolac type phenol resin (manufactured by Sumitomo Bakelite Co., Ltd., PR-53195)
(6) Imidazole compound: 2-phenylimidazole (manufactured by Shikoku Kasei Co., Ltd., 2PZ)

  The following evaluations were performed using the powder coating materials obtained in the examples and comparative examples. The evaluation results are shown in Table 3.

3. Test method
(1) Gelation time: A 0.1 g sample was measured by a 200 ° C. needle method.
(2) Flow rate: 0.5 g of powder coating material was put in a mold, formed into a 10 mmφ tablet mold at room temperature, and heated in a drying apparatus at 150 ° C. for 30 minutes. The tablet diameter (mm) after heating was measured and calculated from the change in tablet diameter before and after heating by the following formula.
Flow rate (%) = (tablet diameter after heating / 10) × 100
(3) Coating appearance: It was coated on a SPCC (1.6 mm × 70 mm × 100 mm) using a fluid dip coating apparatus and a static current dip coating apparatus so that the thickness of the coating film was about 250 μm at the flat part. Curing conditions were fluidized immersion coating apparatus / preheating 250 ° C. for 30 minutes + post-curing 200 ° C. for 30 minutes, static current immersion coating apparatus / 250 ° C. high frequency heating. The coating surface was observed. Each code is as follows.
◎: The coating film surface was excellent in smoothness. ○: The coating film surface smoothness was slightly inferior to ◎, but there was no practical problem. △: No skin-like unevenness on the coating film surface. Slightly generated x: No surface roughness on the surface of the coating film (4) Storage stability: The powder coating was treated in a constant temperature bath at 40 ° C. for 3 days. In accordance with JIS C 2161 “Test Method for Powder Coating for Electrical Insulation”, the horizontal melt flow rate before and after the treatment was measured, and the retention rate of the melt flow rate was calculated by the following formula.
Retention rate of melt flow rate (%) = (melt flow rate after treatment / melt flow rate before treatment) × 100
(5) Moisture resistance of coating film Measure the insulation resistance value after processing a ceramic capacitor with lead wire (φ12mm) coated with powder coating to 0.6mm thickness with a pressure cooker at 121 ° C for 2 hours. What was 10 < ¹² > (ohm) or more was set as (circle).

Examples 1 to 5 were all powder coatings of the present invention in which a phenol resin molten imidazole compound was blended, and could be excellent in storage stability and coating appearance. In particular, in Examples 1 to 3, the type of the imidazole compound used and the melt mixing ratio of the imidazole compound in the phenol resin molten imidazole compound were optimal, so that the balance was best with other characteristics. I was able to.
In Comparative Example 1, an imidazole compound was used, and in Comparative Example 2, an imidazole compound and a phenol resin were used without being previously melt-mixed.
Moreover, although the comparative example 3 used the phenol resin and imidazole kneaded material, a slight fall was seen in the coating external appearance.

  The present invention is an epoxy resin powder coating that can improve storage stability and coating appearance without impairing basic properties as a powder coating, such as electronic components, OA equipment, home appliances, building materials, It can be suitably used as a coating for insulation protection decoration of automobile parts and the like.

Claims (4)

An epoxy resin powder paint containing an epoxy resin, a phenol resin, and an imidazole compound, wherein the phenol resin and the imidazole compound are melt-mixed. The epoxy resin powder paint according to claim 1, wherein the imidazole compound has a melting point of 160 ° C or lower. The epoxy resin powder paint according to claim 1 or 2, wherein the imidazole compound is 2-phenylimidazole. The epoxy resin powder coating material according to any one of claims 1 to 3, comprising 5 to 40% by weight of the imidazole compound with respect to the total of the phenol resin and the imidazole compound.