JP2000129201A - Rust inhibiting primer coating for aluminum die casting part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rust inhibiting primer for an aluminum die casting part having a sufficient corrosion resistance and being capable of forming a film which is hard to melt under pressure even if fastening a bolt. SOLUTION: This rust inhibiting primer for an aluminum die casting part comprises (1) an urethane-modified epoxy resin having a number average mol.wt. of 2,000-12,000, a glass transition temp. (Tg) of 40-100 deg.C and a hydroxyl group value of 150-300, (2) a melamine resin, (3) a non-chromium type rust inhibiting pigment, and (4) an extender pigment. A film of the rust inhibiting primer coating is formed on the surface of an aluminum die casting part, over which a film of a top coat is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rust-preventive primer paint and a rust-preventive coating film for a structural material part (hereinafter, referred to as an aluminum die-cast part) made of an aluminum die-cast alloy for an outboard motor of a boat with an engine. It relates to a forming method.

[0002]

2. Description of the Related Art Aluminum die-cast parts for outboard motors are:
The outer part of the engine, which is mounted on the hull and serves as a power source for the ship, or forms part of the drive system.It is necessary to protect the engine and its interior from heat, light, water, seawater, etc. (Rust prevention) is required.

[0003] Generally, it is considered that metal corrosion is a chemical reaction between an environmental substance and a metal, and that the environmental substance that has permeated and diffused into a coating film reaches a substrate and acts on the metal. In other words, even in the coating of aluminum die-cast parts, a large amount of chromium-based rust-preventive pigments have been used for the purpose of preventing corrosion-inducing substances from reaching the metal material surface and at the same time providing a passivation layer on the metal material surface. Solvent-type epoxy paints and the like.

[0004] However, since the chromium-based rust-preventive pigment contains a large amount of chromium, it may adversely affect the environment. Although there is a coating method using a rust-preventive paint containing no chromium, there is a problem that the passivation of the material and the separation of the corrosive environment from the metal material (separation of corrosive environmental substances) become insufficient.

[0005] Further, in the assembling process, the aluminum die-cast part is press-fitted and tightened (bolted) with the painted surface of the part aligned with the painted surface. It is generally known that when a component is clamped with a coating film therebetween, the coating film is pressed and melted. That is, even if the parts are once bolted with optimum strength, the coating film sandwiched between the parts becomes thinner due to compression melting, and the bolts are loosened. When the bolt is loosened, it is necessary to retighten the bolt, which requires an extra step than when the bolt is not loosened. As a result, the workability of assembling the parts is significantly deteriorated. In addition, if retightening is neglected, there is a fear that parts may fall off.

On the other hand, when coating is performed using a conventional rust preventive paint, it is necessary to apply the rust preventive paint thickly in order to ensure sufficient corrosion protection performance. For this reason, the coating film thickness was inevitably increased, and the coating film was likely to be pressed and melted.

In Japanese Patent Application Laid-Open No. 10-204686, an outboard motor made of an aluminum die-cast alloy is used to form an anodized film in a sulfuric acid electrolytic bath, and a non-chrome type urethane-modified epoxy ether resin-based primer is applied. hand,
A sample is obtained by applying a metallic paint and a clear paint thereon, but no specific study has been made on a rust-preventive primer paint.

In Japanese Patent Application Laid-Open No. Hei 7-26199, a rust-preventive primer coating composition contains a polyol resin as a main component, a benzoguanamine resin having an alkoxymethyl group and a carboxyl group as a crosslinking agent, an epoxy resin, and a strong acid catalyst. As an essential ingredient, apply a color coat,
Although a clear coat is applied to the outermost surface, no consideration has been given to the problem of a decrease in workability in assembly due to compression melting of the coating film.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a sufficient rust-proofing and corrosion-proofing property even without containing a chromium-based rust-proofing pigment. Another object of the present invention is to provide a rust-preventive primer coating for aluminum die-cast parts, which forms a coating film that is hardly pressed and melted even when bolted.

[0010]

The present invention provides (1) a compound having a number average molecular weight of 2,000 to 12,000, a glass transition temperature (Tg) of 40 to 100 ° C., and a hydroxyl value of 150 to 3;
A rust-preventive primer coating for aluminum die-cast parts, comprising: a urethane-modified epoxy resin of No. 00, (2) a melamine resin, (3) a chromium-free rust-preventive pigment, and (4) an extender pigment. This achieves the above object.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a rust-preventive primer paint is applied to an aluminum die-cast part for an outboard motor,
Further, a coating film of a top coating material is sequentially formed to form a rust preventive coating film.

As the aluminum die-cast part for the outboard motor, for example, ADC 12 or ADC 10 according to JIS standard has high mechanical strength and is easy to die-cast, so that it can be made of other die-cast alloys. ADC 12 is particularly easy to die-cast and has high strength, and is widely used for outboard motors. However, in this aluminum die-cast alloy, 1.5 to
Since it contains 4.0% of copper, it has a disadvantage that it is easily corroded. In addition, there can be mentioned those produced by containing metals such as iron and magnesium.

The rust-preventive primer coating composition of the present invention contains a urethane-modified epoxy resin in order to add rust-preventing power, anti-corrosion power, and assembly workability after coating.

The epoxy resin constituting the urethane-modified epoxy resin is not particularly limited. For example, an epoxy resin obtained by glycidyl etherification of bisphenol A, bisphenol F, novolak, or the like, or glycidyl ether obtained by adding propylene oxide or ethylene oxide to bisphenol A. An etherified epoxy resin or the like can be used. In addition, aliphatic epoxy resins, alicyclic epoxy resins, and polyether-based epoxy resins can also be used, and two or more of these epoxy resins can be used in combination. An acrylic epoxy resin, an ether epoxy resin, an ester epoxy resin, and the like can be given. Preferably, it is a glycidyl ether type epoxy resin.

As such an epoxy resin, a modified epoxy resin obtained by modifying an epoxy resin with a polyfunctional carboxylic acid or a polyfunctional amine is most preferable in terms of corrosion resistance and adhesion. Generally, a modified epoxy resin is obtained by reacting a glycidyl group of an epoxy resin with a polyfunctional carboxylic acid or a polyfunctional amine.

Examples of the polyfunctional carboxylic acid or polyfunctional amine include those having two or more active hydrogens in one molecule, and two or more of these carboxylic acids or amines can be used in combination.

The polyfunctional carboxylic acids include succinic acid, adipic acid, sebacic acid, maleic acid, itaconic acid, phthalic acid, trimellitic acid, tetrahydrophthalic acid, hexahydrophthalic acid, pyromellitic acid and the above monomers. Examples include polyfunctional carboxylic acids such as anhydrides. Examples of the polyfunctional amine include primary alkanolamines such as ethanolamine, propanolamine, isopropanolamine, and butanolamine, and primary alkyls such as propylamine, butylamine, octylamine, and decylamine. Examples include polyfunctional amines such as amine, ethylenediamine, diethylenetriamine, tetraethylenepentamine, xylenediamine, aminoethylpiperazine, norbornanediaminomethyl, and the like.

The carboxylic acid or amine active hydrogen is excessive relative to the glycidyl group, and the carboxylic acid or amine active hydrogen is present in the modified epoxy resin. Then, by reacting the active hydrogen with the diisocyanate, chain elongation is carried out, which has the effect of further improving the corrosion resistance.

Examples of the diisocyanate constituting the urethane-modified epoxy resin include aliphatic isocyanates such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate, xylylene diisocyanate, 2,4-tolylene diisocyanate, and 2,6-tolylene diisocyanate. Alicyclic isocyanates such as aromatic isocyanate, isophorone diisocyanate and norbornane diisocyanate methyl, and mixtures thereof can be used.

As an example of synthesizing a urethane-modified epoxy resin, an active hydrogen of a polyfunctional carboxylic acid or a polyfunctional amine is mixed with the glycidyl group of the epoxy resin in an amount equivalent to 1.1 to 1.8 times equivalent, and both are mixed. 70 ~ 150 ℃ 4 ~
After reacting for 10 hours, diisocyanate is added to active hydrogen of the remaining polyfunctional carboxylic acid or amine in an amount of 0.
1 to 0.9 times equivalent, 30 to 100 ° C
To continue the reaction.

The urethane-modified epoxy resin has a number average molecular weight of 2,000 to 12,000, a glass transition temperature (Tg) of 40 to 100 ° C., and a hydroxyl value of 150 to 3
00. The acid value is preferably substantially absent, and more preferably 3 or less. When the number average molecular weight of the urethane-modified epoxy resin is less than 2,000, assembly workability and storage stability are deteriorated.
The effect of blocking the entry of water and corrosive environmental substances into the coating film is reduced, and the anticorrosion property is deteriorated. More preferably, 3000 to 110
00, more preferably 3000 to 8000.

When the glass transition temperature (Tg) is less than 40 ° C., the adhesiveness and workability of the coating film are reduced, and when it exceeds 100 ° C., the appearance of the coating film is deteriorated. More preferably, 6
0-90 ° C. When the hydroxyl value is less than 150, the crosslinkability and anticorrosion of the coating film decrease, and when it exceeds 300, the flexibility of the coating film decreases. More preferably, 180 to 2
80, and more preferably 210 to 270.

The compounding amount of the urethane-modified epoxy resin in the solid content of the paint is 20 to 80% by weight. If it is less than 20% by weight, the function of the resin as a binder becomes insufficient, and the organic film becomes brittle, so that the paint adhesion and the corrosion resistance are poor. On the other hand, if it exceeds 80% by weight, the workability of assembling after painting is inferior. Further, in order to satisfy even higher corrosion resistance and assembly workability, the range of 30 to 70% by weight is preferable.

The second component of the rust preventive primer coating used in the present invention is a melamine resin. The melamine resin is not particularly limited, and for example, a resin composition comprising a melamine formaldehyde resin (hereinafter abbreviated as melamine resin) obtained by reacting melamine with formaldehyde and further modifying with alcohol. As the melamine resin, generally, one or more of methyl etherified melamine resin, butyl etherified melamine resin and mixed alkyl etherified melamine resin can be used in combination.

The amount of the melamine resin curing agent is 3 to 45 parts by weight based on 100 parts by weight of the solid content of the urethane-modified epoxy resin. If the amount is less than 3 parts by weight, the curing is insufficient and the object of the present invention cannot be achieved. If the amount is more than 45 parts by weight, the storage stability of the rust preventive coating composition is reduced and a smooth surface is obtained. Therefore, it is limited to the above range. Preferably, it is 5 to 30 parts by weight.

The third component of the rust preventive primer coating used in the present invention is a chromium-free rust preventive pigment. The chromium-free rust preventive pigment is not particularly limited as long as it does not contain chromium. The choice of active pigments that act on metal passivation is important, for example basic lead sulfate (1.5% water soluble), zinc molybdate (1.2% water soluble),
Use fine powders such as aluminum tripolyphosphate (water-soluble content 1.5%), aluminum phosphomolybdate (water-soluble content 0.4%), zinc phosphate (water-soluble content 0.1%), etc. be able to.

From the viewpoint of corrosion resistance, phosphate-based pigments, such as zinc phosphate, form a chemical conversion film by depositing phosphate ions on a metal surface and reacting with the metal ions in an alkaline environment,
Zinc molybdate has strong oxidation of molybdate ions,
It is preferable because the metal surface is oxidized to form a passive film. Aluminum phosphomolybdate is the above-mentioned zinc phosphate and a pigment having the characteristics of aluminum phosphate and zinc molybdate, and is more preferable because it exhibits an anticorrosive effect as a corrosion inhibitor. However, in general, if the water-soluble content is large, ions are easily dissolved in water and effective for corrosion, but if the water-soluble content is too large, the ions tend to swell due to the coating film.
It is preferably at most 2.0%, more preferably at most 1.0%.

The amount of the rust preventive pigment is 10 to 85 parts by weight based on 100 parts by weight of the resin solid content. If the amount is less than 10 parts by weight, the purpose of the present invention cannot be achieved due to insufficient anticorrosion properties. If the amount is more than 85 parts by weight, a smooth surface cannot be obtained.
Preferably, it is 15 to 55 parts by weight.

The fourth component of the rust-preventive primer coating composition of the present invention is an extender pigment. The extender is not particularly limited, and those having a pH in the range of 4 to 8, those having a flake-like shape, and those having a lower electric conductivity are more likely to cause water and corrosive environmental substances to enter the coating film. Excellent blocking effect, improves the water resistance of the coating, and thus the corrosion resistance.

The extender is not particularly limited, and examples thereof include scaly clay. The extender having a specific gravity of 2.5 to 3.0 has a PWC (pigment weight content) of 30 to 60%.

When the content of the extender is less than 30%,
If sufficient assembling workability cannot be obtained, and if it exceeds 60%, the gloss of the surface is lowered and a smooth surface cannot be obtained, so that it is limited to the above range. Preferably, 40 to 5
5%.

If necessary, other additives, coloring agents and the like may be added to the rust preventive paint as long as the constitution of the present invention is not impaired. As the above additives,
For example, a general low-molecular-weight acrylic ester-based surface conditioner, a flat pigment excellent in the effect of blocking the entry of water and corrosive environmental substances into the coating film, such as flaky silica, and the like, for example, epoxy resin 100 1 to 5 parts by weight
About part by weight can be added. Examples of the colorant include color pigments such as carbon black and titanium, and the amount of the colorant can be selected within a range that does not hinder practical use.

The coating formed by the rust-preventive primer coating of the present invention described above has a thickness of 5 to 30 μm. If the film thickness is less than 5 μm, sufficient corrosion resistance cannot be expected. On the other hand, if it exceeds 30 μm, the coating film tends to be pressed and melted, and assembling workability is reduced. Further, in order to satisfy even higher corrosion resistance and assembly workability, 10-25 μm
Is preferred.

In the method for forming a rust-preventive coating film of the present invention, as a method of applying a rust-preventive primer coating to an aluminum die-cast part, a usual coating method can be applied, for example, airless coating, spray coating, static coating, or the like. An electrospray coating method can be used.

Thereafter, the layer of the rust-preventive primer coating formed on the surface of the aluminum die-cast part is heated and cured to form a coating of the rust-preventive primer coating. Heating is generally performed at a temperature of 110 to 150 ° C., preferably 120 to 13 ° C.
It is carried out at a temperature of 0 ° C. for 15 to 60 minutes, preferably for 20 to 30 minutes.

An overcoat is applied on the rust-preventive primer coating thus formed. As the topcoat paint, all paints usually used for painting members for use in contact with water or seawater can be used. The method of application may be appropriately selected according to the type of the top coat selected. Thereafter, the layer of the top coating is generally cured by heating to form a coating film of the top coating.

The rust-preventive primer coating composition of the present invention adjusts the amount of the urethane-modified epoxy resin, the curing agent, the water-soluble content of the rust-preventive pigment, the shape or pH of the extender pigment, and the weight content (PWC) of the pigment. Therefore, when powder coating is applied to aluminum die-cast parts using the rust-preventive primer paint of the present invention, it is possible to obtain a coating film with a smooth surface that is difficult to compress and melt, and the workability of assembling aluminum die-cast parts is also improved. improves.
Further, the coating film formed by the rust-preventive primer coating of the present invention,
Despite not using a chrome-based rust-preventive pigment, it has the same or better rust-preventive power as a chromium-based rust-proof pigment-containing coating film.

[0038]

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.

Example 1 Urethane-modified epoxy resin (Epokey 8 manufactured by Mitsui Chemicals, Inc.)
11) 46.8 parts by weight, 2.6 parts by weight of melamine resin (Sumimar M-40S, manufactured by Sumitomo Chemical Co., Ltd.), aluminum phosphomolybdate-based rust preventive pigment (Kikuchi Color Co., Ltd., L
F Bowsei PM308) 5.0 parts by weight, scaly pigment (Translink # 37 manufactured by Tsuchiya Kaolin Co., Ltd.) 20.0
Parts by weight, titanium white pigment (Titanium R-96, manufactured by Sakai Chemical Co., Ltd.)
0) 6.06 parts by weight, black pigment (manufactured by Mitsubishi Carbon Corporation, carbon MA-100), flaky silica (manufactured by Nippon Aerosil Co., Ltd., Aerosil R-972) 3.1 parts by weight, solvent 44.
The pigment was blended with 0 in a conventional manner, dispersed to 5 μm or less, dissolved in a resin and a solvent, and added with other components to produce a rust-preventive primer coating.

Examples 2 to 6 and Comparative Examples 1 to 2 Rust-preventive primer coatings were produced in the same manner as in Example 1 using the components listed in Table 1.

Evaluation method of coating film (1) Assembly workability (easiness of compression melting of coating film) Alkaline degreasing (surf cleaner 53, manufactured by Nippon Paint Co., Ltd.) as a pretreatment for aluminum die-cast parts of JIS ADC-12 ) And a chemical treatment (Nippon Paint Co., Ltd.
Alsurf C5N-2) was performed. Next, the rust-preventive primer coating composition of Example 1 previously diluted to a coating viscosity was spray-coated so as to have a dry film thickness of 15 μm, left for 10 minutes, and kept at 120 ° C. for 20 minutes. Was formed. After cooling, apply 5 gauze on the primer coating.
The sheets were stacked, and a 1 kg weight previously heated to the ambient temperature was placed thereon, and left in a 100 ° C. constant temperature bath for 10 minutes. Thereafter, the gauze was removed, and the gauze marks on the coating film were visually evaluated to obtain a substitute test for the loosening of the bolt generated after the step of crimping and tightening the parts (bolting).

-Evaluation Criteria- 5: No trace of cloth is observed on the coating film. 4: Slight traces are observed in the coating film. 3: Traces of cloth are slightly observed in the coating film. 2: A clear cloth mark is observed in the coating film. 1: A cloth mark is observed on the coating film in a grid pattern.

(2) Solution Diffusivity Test The diffusivity of a water / methanol mixed solution is evaluated by a change in electric resistance of the coating film by a method of judging the permeability of water and corrosive substances in the coating film. For detailed measurement methods, see Kawai Hitoshi, Yamamoto Takashi,
Amako Hiroshi, "Coloring Materials", 47 (1974), page 396, left column, line 24 to page 398, left column, line 12.

First, a coating plate similar to the coated plate prepared for the method of evaluating the assembling workability was prepared. As shown in FIG. 1, a silicone rubber packing 10
The platinum ring-shaped electrode 103 and the Teflon (registered trademark) ring 104 are fixed via the second and second 102 '. Put this device in an air thermostat, 35 ℃ with accuracy within ± 0.1 ℃
The temperature was adjusted. Water / methanol mixed at a volume ratio of 9/1 was put into the ring, a DC voltage of 5 volts was applied between the substrate to be coated 105 and the platinum electrode 103, and the current change from this point was measured at 610 ° C. by Keithley. Electrometer 106
And recorded by recorder 107. The surface temperature of the painted plate is determined by a copper-constantan thermocouple (PHILIPS, PR
6452A) (not shown).

The specific resistance (Ω · cm) of the coating film was converted to the time (mi)
n), the permeability of the coating film was evaluated based on the time (minutes) required for the specific resistance value to decrease to a steady value.

-Evaluation criteria- Large: less than 5 minutes Medium: 5 minutes or more and less than 10 minutes Small: 10 minutes or more

(3) Composite Environment Acceleration Test (CCT) As shown in FIG. 2A, a JIS ADC having a bolt tightening hole 201 at a position 25 mm from the end of the part and having a space for a 30 mm cross cut. Twelve aluminum die-cast parts were subjected to alkaline degreasing (Surf Cleaner 53, manufactured by Nippon Paint Co., Ltd.) as a pretreatment, and a chemical conversion treatment (Alsurf C5N-2, manufactured by Nippon Paint Co., Ltd.). Next, the rust-preventive primer coating composition of Example 1 previously diluted to a coating viscosity was spray-coated so as to have a dry film thickness of 15 μm, left for 10 minutes, and kept at 120 ° C. for 20 minutes. Was formed.

Next, an acrylic / melamine resin-based metallic paint is spray-coated so that the total dry film thickness of the base coating film and the clear coating film is 35 μm, left for 10 minutes, and kept at 120 ° C. for 20 minutes. Then, a laminated coating film having a metallic coating film as an overcoat was formed.

Next, as shown in FIG. 2B, stainless steel bolts (SUS # 304M10)
2 and a cross cut 202 reaching a 30 mm long base with a cutter knife as shown in FIG.
Was put.

Using a composite environmental promotion tester manufactured by Itabashi Rika Kogyo Co., Ltd., immersed in a 5% sodium chloride aqueous solution at 50 ° C. for 2 hours, and dried at 80 ° C. in a dry atmosphere.
The solution was spray-irradiated with a 5% aqueous sodium chloride solution at 50 ° C. for 1 hour, and kept at 80 ° C. in a dry atmosphere for 1 hour.
1 hour in a 95% humidified state at 95 ° C
Continuous operation was performed as a cycle, and the corrosion degree of the coated plate after 30 days was measured.

-Evaluation Criteria- 5: Some rusting started around the bolt and the cross cut. 4: Traces of corrosion progressing around the bolt and the cross cut were observed in a dot-like manner. 3: Traces of increased corrosion are observed in the coating film around the bolt and the cross cut. 2: Rust marks are observed on the entire coating film around the bolt and the cross cut. 1: A clear rust mark is observed on the entire coating film around the bolt and the cross cut.

(4) Seawater Exposure Test The same pool (see FIG. 2) as that prepared for the Combined Environment Acceleration Test (CCT) was used for a pool filled with seawater constantly drawn from the shore. , Soak 1
Applying 2 hours and drying 12 hours as one cycle, 30
After a day, the degree of corrosion was measured.

-Evaluation Criteria- 5: Slight rusting around bolts and cross cuts was observed. 4: Traces of corrosion progressing around the bolt and the cross cut were observed in a dot-like manner. 3: Traces of increased corrosion are observed in the coating film around the bolt and the cross cut. 2: Rust marks are observed on the entire coating film around the bolt and the cross cut. 1: A clear rust mark is observed on the entire coating film around the bolt and the cross cut.

(5) Corrosion Acceleration Test (Corrosion Rate Meter) A coating prepared for a complex environmental acceleration test (CCT) using a corrosion rate meter ACS type (a device for measuring corrosion phenomena of painted metal) manufactured by Nippon Paint Co., Ltd. Using the same composite coating as the plate, the corrosion of the coating was evaluated.

A 3% aqueous solution of sodium chloride was used as a corrosive liquid, and conditions were set at 35 ° C. by continuous immersion.
Make a scratch on the flat part of the composite coating with a cutter knife to reach a base of 5 mm length, set the cell of the corrosion rate meter there, and use a potentiostat to reduce the material to -700 mV.
Next, the anodic polarization of Ag / AgCl was performed, and the corrosion degree of the coated plate was measured 30 days after the anodic polarization.

The corrosion degree was evaluated by the value of the current flowing when the anode polarization was stopped and the potential was changed in a direction 100 mV lower than the corrosion potential after 5 minutes.

By the above method, Examples 1 to 6 and Comparative Examples 1 to 2
Was evaluated for corrosion resistance and assembly workability. The results are shown in Table 1.

[0058]

[Table 1]

Table 2 shows the characteristic values of the compounds shown in Table 1.

[0060]

[Table 2] EPOKEY 811 (solid content 40%) Urethane-modified epoxy resin manufactured by Mitsui Chemicals (number average molecular weight 10600, glass transition temperature 89 ° C, hydroxyl value 220) EPOKEY 813 (solid content 45%) Urethane-modified by Mitsui Chemicals Epoxy resin (number average molecular weight 4900, glass transition temperature 85 ° C, hydroxyl value 220) Epoki 863 (solid content 45%) Urethane-modified epoxy resin manufactured by Mitsui Chemicals, Inc. (number average molecular weight 3100, glass transition temperature 68 ° C, hydroxyl value 265) Sumimar M-40S (solid content 80% of butylated melamine resin manufactured by Sumitomo Chemical Co., Ltd.) LF BOSEI PM308 Aluminum phosphomolybdate pigment manufactured by Kikuchi Color (0.4% water soluble) LF BOSEI ZP-N Phosphoric acid manufactured by Kikuchi Color Zinc pigment (water-soluble content 0.1%) K White # 105 Aluminum tripolyphosphate pigment manufactured by Teica (water-soluble content 1.5%) Translink # 3 Tsuchiya Kaolin Co. scaly clay pigment (pH 6.6, conductivity 2.3Ω ^-1 · m ^-1) Titanium R-960 manufactured by Sakai Chemical Industry Co., Ltd. titanium white pigments carbon MA-100 Mitsubishi Carbon Co. Black Pigment

[0061]

The method for forming a rust-preventive coating film on an aluminum die-cast part of the present invention and the rust-preventive primer coating used do not contain a chromium pigment which has a bad influence on the environment, and the separation of corrosive environmental substances and metal materials is possible. It has sufficient corrosion resistance. Moreover, since the coating film formed using this primer coating is hard to be pressed and melted even when bolted, it is excellent in assembly workability after coating and baking.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing one embodiment of a method for measuring the solution diffusivity of a coating film.

FIG. 2 is a top view and a side view showing the shape of an aluminum die-cast component used for evaluation of a coating film.

[Explanation of symbols]

 Reference Signs List 100: painted plate, 101: coating film, 102, 102 ': silicon rubber packing, 103: platinum ring electrode, 104: Teflon ring, 105: substrate to be coated, 106: electrometer, 107: recorder, 201 ... bolt tightening holes, 202 ... cross cut, 203 ... stainless steel bolts.

Continuation of the front page F term (reference) 4D075 CA33 DB02 DC16 EA05 EA41 EB33 EB38 EB45 EB52 EB53 EB55 EC13 4J038 PC02

Claims (2)

[Claims] (1) a number average molecular weight of 2,000 to 120
A urethane-modified epoxy resin having a glass transition temperature (Tg) of 40 to 100 ° C. and a hydroxyl value of 150 to 300, (2) a melamine resin, (3) a chromium-free rust preventive pigment, and (4) A rust-preventive primer paint for aluminum die-cast parts, characterized by containing an extender pigment. 2. A rust-preventive coating film comprising a step of forming a coating film of the rust-preventive primer coating material according to claim 1 on the surface of an aluminum die-cast component; and a step of forming a coating film of a top-coating paint thereon. Forming method.