JP2871409B2 - Method of forming a coating film on a casting for cutting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a coating film which does not generate burrs on the coating film by cutting, and a casting for coating formed by this method.

[0002]

2. Description of the Related Art Conventionally, castings have been coated with a solvent type paint. In recent years, powder paints have been used to improve the working environment in the coating process. However, when a powder coating is applied, the coating film thickness is large and the coating film strength is large, so the coating film at the cutting location remains in a burr-like state in the casting cutting work after coating, so that a coating deburring step to remove it. Was needed.

Therefore, a powder coating film is formed on a casting,
A method was studied in which a coating film deburring step after cutting was omitted.

[0004] First, a study was made to reduce the powder particle size of the powder coating material to make it thinner. However, in the case of coating a three-dimensional casting having a complicated shape, the film thickness is widely varied, so that the film is made uniform. However, it is difficult to omit the deburring step because the coating film remains in the form of burrs when a thick film portion is cut.

[0005] Further, it was studied to mix a large amount of extender pigment in order to reduce the coating strength of the powder coating film and to make the coating film brittle and improve the cutting workability. However, calcium carbonate, barita, clay, silica and the like were examined. Even if a general extender is blended, the effect is small, and in order to obtain the effect, it is necessary to blend a large amount so that the continuous film forming property of the paint is extremely reduced. In order to form a coating film, a thick film is required, and the obtained coated surface has a very large unevenness, which is not practical.

Accordingly, the present inventors have conducted intensive studies on a method for forming a powder coating film capable of forming a coating film having a film thickness of 60 μm or less and having excellent finishability and good cutting workability with a continuous coating film. As a result, the minimum value of the dynamic elastic modulus (E ') of the cured coating film was set to 5 × 1 by combining the specific epoxy resin and the curing agent.
By the 0 ⁸ dyne / cm ² or more was achieved the present invention found that can achieve the above coating film forming method.

[0007]

That is, according to the present invention, a softening point of 75 to 135 ° C. and an epoxy equivalent of 600 to 280 are used.
Bisphenol A type epoxy resin (A) 90
Novolak-type epoxy resin (B) having 50% by weight, a softening point of 30 to 120 ° C. and an epoxy equivalent of 150 to 250.
A curing agent (C) is added to the base resin component consisting of 10 to 50% by weight.
A powder coating mainly composed of a composition comprising imidazole and / or acid anhydride is applied to a casting for cutting, and then heat-cured to form a coating film on the casting for cutting. The present invention relates to a method for forming the casting, and a casting for forming a coating film obtained by the method.

[0008]

In the powder coating used in the present invention,
Epoxy equivalent of 600 to 2.8 at softening point of 75 to 135 ° C
The bisphenol A type epoxy resin (A) of No. 00 can be obtained, for example, by reacting bisphenol A [2,2-bis (4-hydroxyphenyl) propane] with epihalohydrin such as epichlorohydrin. Examples of commercially available epoxy resins include Epicoat 1002, 1004, and 1007 manufactured by Shell Chemical Co., Ltd.

If the softening point of the epoxy resin is less than 75 ° C., the powder particles tend to fuse together during storage of the powder coating, while if it exceeds 135 ° C., the melt viscosity tends to increase, and a continuous coating film is formed. Becomes difficult. When the epoxy equivalent of the epoxy resin is less than 600, the molecular weight is generally small and the softening temperature is low. On the other hand, when it exceeds 2,800, the molecular weight generally increases and the softening temperature increases.

The novolak epoxy resin (B) having a softening point of 30 to 120 ° C. and an epoxy equivalent of 150 to 250 used in the present invention can be obtained by reacting novolak resin with epichlorohydrin. Commercially available products of the epoxy resin (B) include, for example, Araldite-ECN1235, ECN
1273, 1280, and 1299.

The epoxy resin (B) contains more crosslinkable functional groups and has a higher aromatic content such as a benzene ring than the bisphenol A type epoxy resin (A), so that it has excellent heat resistance and reactivity. The feature is that. That is, the component (B), which is an essential component because it improves the crosslinkability of the coating film required during cutting, is used in combination with the bisphenol A type epoxy (A). During storage, the powder particles tend to fuse together, while if it exceeds 120 ° C., the melt viscosity tends to increase, making it difficult to form a continuous coating film.

When the epoxy equivalent of the epoxy resin (B) is less than 150, the molecular weight is generally small and the softening temperature is low. On the other hand, if it exceeds 250, the molecular weight generally increases and the softening temperature increases. Furthermore, since the reactivity is too large, the finish is inferior.

[0013] In the base resin component comprising the component (A) and the component (B) in the powder coating used in the present invention, the composition ratio of these components is determined based on the total amount of both components. The component (B) is 90 to 50% by weight, and the component (B) is 10 to 50% by weight. When the amount of the component (A) is more than 90% by weight, the degree of crosslinking of the cured coating film is small, and burrs are likely to occur during cutting. On the other hand, if it is less than 50% by weight, the degree of crosslinking is too high, and the smoothness of the coating film is undesirably reduced.

In the powder coating of the present invention, imidazole and / or acid anhydride are used as the curing agent (C) for the base resin.

Examples of the imidazole include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl -2-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 2-phenyl-4-benzylimidazole,
1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-isopropylimidazole, 1-cyanoethyl-2-phenylimidazole, 1 -Cyanoethyl-
2-methylimidazolium trimellitate, 1-cyanoethyl-2-ethyl-4-methylimidazolium trimellitate, 1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate Melitate, 2,4 diamino-6
-[2'-methylimidazolyl- (1) ']-ethyl-
S-triazine, 2,4 diamino-6- [2'-ethyl-4-methylimidazolyl- (1) ']-ethyl-S-
Triazine, 2,4 diamino-6- [2′-undecylimidazolyl- (1) ′]-ethyl-S-triazine,
2-methylimidazolium isocyanuric acid adduct, 2-
Phenylimidazolium isocyanuric acid adduct, 2,
4-dicyano-6- [2'-methylimidazolyl- (1)
'] -Ethyl-S-triazine-isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenyl-4-benzyl-5- Hydroxymethylimidazole, 4,4'-methylene-bis- (2-ethyl-5-methylimidazole), 1-aminoethyl-2-methylimidazole, 1-cyanoethyl-2-phenyl-4,5-di (cyanoethoxy Methyl) imidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, and the like, and these may contain one kind or two or more kinds. Among these, it is particularly preferable to use 2-heptadecylimidazole, 1-cyanoethyl form, 1-cyanoethyl form, trimellitate and triazine compound which are excellent in storage stability.

As the acid anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenonetetracarboxylic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, endomethylenetetrahydrophthalic anhydride, methylendomethylenetetrahydrophthalic anhydride,
Hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylcyclohexenedicarboxylic acid copolymer,
Alkyl styrene-mynic anhydride copolymer, chlorendic anhydride, HT901, HT903 manufactured by Ciba-Geigy,
HY905, HY906, HT907, HY920, X
B3380 and the like, and these may contain one kind or two or more kinds.

Further, imidazole and an acid anhydride can be used in combination.

The curing agent (C) has an equivalent ratio of 0.5 to the total epoxy group of the components (A) and (B).
To 3.0, preferably 0.6 to 2.0. The resin component is a resin that can react with the epoxy resins (A) and (B), such as a phenol / formaldehyde resin and a carboxyl group-containing polyester resin; an epoxy resin other than the epoxy resins (A) and (B); If necessary, a resin or the like can be blended in an amount of 50 parts by weight or less based on 100 parts by weight of the bisphenol A type epoxy resin (A).

The powder coating material used in the present invention contains 3 parts of the inorganic filler (D) based on 100 parts by weight of the base resin component.
It is contained in an amount of 0 to 200 parts by weight, preferably 60 to 120 parts by weight. Examples of the inorganic filler include extenders such as calcium carbonate, barita, clay, silica , and talc .

When the compounding amount of the filler is 200 parts by weight or more, the cutting workability is improved, but the continuous coating film thickness is 60 μm.
Beyond m becomes impractical. If the amount is less than 30 parts by weight, the machinability is insufficient.

In the powder coating used in the present invention, in addition to the above-mentioned filler (D), titanium white, red iron oxide, red organic pigment, titanium yellow, yellow organic pigment, phthalocyanine blue, phthalocyanine green, carbon black, various calcined A coloring pigment such as a coloring pigment; a rust preventive pigment such as zinc chromate, strontium chromate, and basic lead silicate may be contained as necessary.

In the present invention, it is essential that the minimum value of the dynamic elastic modulus (E ') of the cured coating film of the above powder coating material is 5 × 10 ⁸ dyne / cm ² or more. The measurement of the minimum value of the dynamic elastic modulus (E ') is performed by the following method.

The thickness of the tin plate based on the cured coating film is 80 μm.
m, and heat-cured under the conditions of 150 ° C. for 20 minutes. Next, a free film is made using mercury. It is cut into a size of 5 mm x 20 mm to obtain a sample piece. Using DVE Leo Spectra -DVE-V4 ((Ltd.) Rheology Co.), temperature range 0 to 2 5 0 ° C., a frequency of 1
Determine the minimum value of the dynamic elastic modulus (E ′) at 200 ° C. when measured at 10 Hz.

In the present invention, it is important to set the minimum value of the dynamic elastic modulus (E ') of the cured coating film of the powder coating material to 5 × 10 ⁸ dyne / cm ² or more. In cutting,
Since the coating film is cut in a heated state, a hard and brittle coating film is required even in a relatively high temperature range. It is important that the coating has a high degree of crosslinking and does not soften even in a high temperature range. Due to this necessity, a novolak resin (B) having a large number of functional groups and a large amount of aromatic content, and a curing agent (C) selected from imidazole and / or acid anhydride, which have high reactivity and structurally high crosslink density, are used. Is preferred. If the minimum value of the dynamic elastic modulus (E ′) is less than 5 × 10 ⁸ dyne / cm ² , burrs of the coating film remain by cutting.

The powder coating used in the present invention includes:
In addition to the resin component and the pigment component, powder coating additives such as a surface conditioner, a curing accelerator, and a slipperiness imparting agent may be blended. It is usually 10 parts by weight or less for 100 parts by weight.

In the method of the present invention, a coating film is formed by applying the powder coating material to a casting for cutting and baking it. The casting for cutting may be subjected to a pre-painting treatment such as a shot blast treatment before painting. The casting for cutting described above is a casting that needs to be processed into a predetermined shape with a predetermined accuracy after painting. This casting includes, for example, brake drums, engine blocks,
Examples include gearboxes and cast steel pipe joint parts that require threading.

The coating thickness of the powder coating is usually 60 to 200 μm.
m, which is applied by electrostatic powder spray coating, fluid immersion coating, etc. The conditions for baking the coating film are usually about 150 to 200 ° C. for about 5 to 20 minutes. By forming a coating film on the casting for cutting as described above, it is possible to obtain a casting for cutting having a coating film with good appearance and good cutting workability.

[0028]

The present invention will be described more specifically with reference to the following examples. Hereinafter, “parts” are based on weight.

Manufacture of Powder Coating Manufacture Example 1 Epicoat 1004 [(Note 1) 90 parts of bisphenol A type epoxy resin manufactured by Shell Chemical Co., Ltd., softening point of about 98 ° C., epoxy equivalent of about 925], ECN1273 [Ciba Geigy Co., Ltd. ) Cresol novolak resin, softening point about 70
° C, epoxy equivalent about 220] 10 parts, C ₁₁ Z-Azin
e2 part, Polyflow-S [manufactured by Kyoeisha Yushi Kagaku Kogyo Co., Ltd.
Surface conditioner] 1 part, Mitsubishi carbon black MA-100
[Mitsubishi Chemical Industries, Ltd., carbon black, oil absorption 1
00] 2 parts and 80 parts of S talc (Note 11)
The mixture was melt-kneaded by an extruder, cooled, pulverized by a turbo mill, and coarse particles were separated by a 100-mesh sieve to obtain a powder coating.

Production Examples 2 to 12 and Production Examples 13 to 17 (for comparison) Powder coatings of the respective examples were obtained in the same manner as in Production Example 1 except that the composition was as shown in Tables 1 and 2 below.

Example 1 A gray cast iron member for cutting (100 × 300 × 2)
0mm) with a shot blasting process and SSPC SP
-5 white metal. One of this white metal
The powder coating obtained in Production Example 1 was electrostatically coated on a surface of 00 × 300 mm so as to have a film thickness of 120 μm.
Baking at 50 ° C. for 20 minutes formed a cured coating film.

Examples 2 to 12 and Comparative Examples 1 to 5 The same procedures as in Example 1 were carried out except that the powder coatings of the respective production examples shown in Table 1 or Table 2 were used as the powder coatings. A cast member on which a film was formed was obtained.

The cast members having the coating film obtained in each of the examples and comparative examples were tested for cutting workability and finishability. The test results are shown in Tables 1 and 2 below.
The test was performed according to the following test method.

Cutting workability: The coating film surface on the casting member surface is vertically cut with a milling machine, and the state of the coating surface at the cut portion is evaluated. The blade of the milling machine used was a roughing blade for casting, and the peripheral speed of the blade was 100 km / h and the casting speed was 1,200.
Cutting was performed under the conditions of mm / min and a cutting depth of 3 mm. ：: No coating film burr is observed. Δ: Despite considerable coating film burrs, finish coating with the finishing blade (cutting conditions are the same as above) does not allow coating film burrs. ×: Many coating film burrs are observed, and even when the finishing blade is used for finish cutting (the cutting conditions are the same as above), considerable coating film burrs are observed.

Finishability: Cold rolled dull steel sheet for automobiles (100
× 300 × 0.8 mm) and the film thickness is 4 in the length direction of 30 cm.
The powder coating obtained in each of the production examples was subjected to slant coating so that the temperature gradually changed from 0 μm to 100 μm.
For 20 minutes.

The film thickness of 80 μm was evaluated according to the following criteria. A: Smooth coated surface without unevenness. ：: Smooth coated surface with some irregularities. Δ: There are considerable unevenness and poor smoothness. X: The unevenness is remarkable and the smoothness is extremely poor.

In Tables 1 and 2, (Note) is as follows. (Note 1) Epicoat 1004: a bisphenol A type epoxy resin manufactured by Shell Chemical Co., Ltd., having a softening point of about 98 ° C. and an epoxy equivalent of about 925 . (Note 2) DX517: Yuka Shell Chemical Co., Ltd., softening point
A phenol novolak type epoxy resin having an epoxy equivalent of about 220 at about 70 ° C. and a softening point of about 98 ° C.
Carboxymethyl about equivalent to about 925 bisphenol A type epoxy resin
A mixture consisting of 80% by weight . (Note 3) ECN1235: manufactured by Nippon Ciba Geigy Co., Ltd.
Cresol novolak type resin, softening point about 38 ° C, epoxy equivalent about 215. (Note 4) ECN1273: manufactured by Japan Ciba Geigy Co., Ltd.
Cresol novolak resin, softening point about 70 ° C, epoxy equivalent about 220. (Note 5) C ₁₁ Z-Azine: Shikoku Chemicals Co., Ltd., 2,
4-diamino-6- [2'undecylimidazolyl-
(1) ']-ethyl-S-triazine, melting point about 186
° C. (Note 6) C ₁₇ Z: Shikoku Chemicals Co., Ltd., 2-heptadecyl imidazole, melting point about 88 ° C. (Note 7) BTDA: GULF Oil Chem. C
o. Benzophenonetetracarboxylic acid, melting point about 2
23 ° C. (Note 8) PMDA: Furukawa Electric Co., Ltd., pyromellitic anhydride, melting point 286 ° C. (Note 9) ADH: Japan Hydrazine Industry Co., Ltd., adipic dihydrazide, melting point 180 ° C. (Note 10) HT2844: manufactured by Japan Ciba Geigy Co., Ltd.
Dicyandiamide derivative, mp 145 ° C. (Note 11) S-talc: manufactured by Nippon Taishi Smelting Co., Ltd., oil absorption 2
5 talc. (Note 12) Mica powder B-31: mica powder manufactured by Yamaguchi Mica Co., Ltd. (Note 13) Hydrocab: manufactured by Hoechst Synthesis Co., Ltd.
Calcium carbonate.

[0038]

According to the method of the present invention, it is possible to obtain a casting for cutting which does not generate burrs on the coating film during the cutting process and has a coating film having a good finish. Can be omitted. Further, since a powder coating is used for coating in the method of the present invention, the working environment in the coating process can be improved.

[0039]

[Table 1]

[0040]

[Table 2]

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C09D 5/03 C09D 163/00-163/10 B05D 7/14 B05D 7/24 B22D 29/00

Claims (4)

(57) [Claims] 1. A bisphenol A type epoxy resin (A) having a softening point of 75 to 135 ° C. and an epoxy equivalent of 600 to 2,800 (A) at 90 to 50% by weight and a softening point of 30 to 12
A novolak-type epoxy resin (B) having an epoxy equivalent of 150 to 250 at 0 ° C. is imidazole and / or a curing agent (C) added to a base resin component consisting of 10 to 50% by weight.
Mainly composed of a composition containing acid anhydride and cured
The minimum value of the dynamic elastic modulus (E ') of the coating film is 5 × 10 ⁸ dyne
/ Cm ² or more powder coatings which have a value, and painted for cutting castings, a method of forming a coating film on cutting castings, characterized by heat curing. 2. The method according to claim 1, wherein the powder coating further contains 30 to 200 parts by weight of an inorganic filler (D) per 100 parts of the total of the components (A) and (B). 3. The compounding amount of the curing agent (C) in the powder coating composition is set to 0.1 based on the equivalent ratio to the total epoxy group of the bisphenol A type epoxy resin (A) and the novolak type epoxy resin (B). 3. The method according to claim 1, wherein the amount is from 5 to 3.0. 4. The method of claim 1 to 3 coating film formed for cutting castings obtained by the method according to any one of.