JPH09241891A - Coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating method by which the coating process is shorten and a coating film is made excellent in appearance, peformance and so on. SOLUTION: A thermosetting cation electrodeposition coating material is applied on a metal to be coated to form a primary electrodeposition coating film. Then, the electrodeposition coating film is washed with water, and next, is drained and dried to form an unhardened electrodeposition coating film having a moisture content of <=5wt.%. A thermosetting powder coating, whose hardening starting time is slower than that of the unhardened electrodeposition coating film and whose surface tension is higher than that of the unhardened electrodeposition coating film, is applied by electrostatic powder coating on the metal to form a powder-coating film. Then, baking is performed to harden the electrodeposition coating film and the powder-coating film at the same time.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel coating method.

[0002]

2. Description of the Related Art Conventionally, a metal coating object such as an automobile body is subjected to undercoat electrodeposition coating, washing with water, baking, polishing, washing with water, drying, intermediate coating, baking, overcoating, baking and undercoating to overcoating. A film is formed. However, after baking, polishing, washing with water, and drying after the undercoat electrodeposition coating is applied in the coating step, the baking is performed because the intermediate coating is applied.
The cost of equipment, installation and operation of the drying process becomes high, and contaminants such as dust and lumps easily enter, and the appearance of the coating film deteriorates. For this reason, in the field of automobiles and the like, improvement of these painting processes is required. Further, there has been a problem that an organic solvent type paint has been conventionally used as an intermediate coating, and the paint generates an organic solvent during the coating work, which is not preferable in terms of environmental hygiene.

[0003]

SUMMARY OF THE INVENTION The present invention aims to shorten the conventional coating process and to develop a coating system containing no organic solvent.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the surface of an uncured electrodeposition coating film having a water content of 5% by weight or less is specified. We have found that this is a method in which the conventional problems can be ameliorated by applying a powder coating, and have completed the present invention.

That is, according to the present invention, a thermosetting cationic electrodeposition coating composition is applied to a metal object to form an undercoat electrodeposition coating film, the electrodeposition coating film is washed with water, and then drained and dried. The water content is 5% by weight
The following uncured electrodeposition coating film is formed, and a thermosetting powder coating which is slower than the curing start time of the uncured electrodeposition coating film and smaller than the surface tension of the uncured electrodeposition coating film is electrostatic powder. The present invention relates to a coating method characterized in that after coating to form a powder coating film, baking is performed to simultaneously cure the electrodeposition coating film and the powder coating film.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The metal coating object used in the coating method of the present invention can be any metal coating object conventionally used for coating automobile bodies, parts and the like without particular limitation. Is a wide range of metal materials such as aluminum, alumite, iron and steel, and metal materials obtained by plating the surface of the metal material with zinc, tin, chromium, aluminum, etc., or those obtained by subjecting the surface of these metal materials to chemical conversion with chromic acid, phosphoric acid, etc. There are various metallic materials.

As the cationic electrodeposition coating used in the coating method of the present invention, conventionally known cationic electrodeposition coatings can be used, and in particular, an electrodeposition coating containing an epoxy resin as a base resin can be preferably used. As the cationic electrodeposition paint, for example, amine-added epoxy resin or amine-added polyester-modified epoxy resin is used as a base resin and a cross-linking agent of block polyisocyanate is added to or neutralized with water. Dispersed ones can be used. A pigment, an organic solvent, a curing catalyst, a surfactant, and the like can be added to the cationic electrodeposition coating as needed.

As a cationic electrodeposition coating method, a conventionally known coating method can be used. For example, it can be carried out by using a cationic electrodeposition coating as an electrodeposition bath, a metal coated object as a cathode, and a metal elution-free material (carbon plate or the like) as an anode, and applying current. The energizing condition is that the electrodeposition coating film thickness is about 10
It is desirable to do in the range of -40 microns, preferably about 15-30 microns. After electrodeposition coating, washing with ultrafiltration filtrate, ultrafiltrate, tap water, etc. is performed.

The cationic electrodeposition coating film is washed with water as described above and then drained and dried so that the water content of the cationic electrodeposition coating film is 5
The water content is adjusted to be not more than 5% by weight, preferably not more than 3% by weight. Water content of the cationic electrodeposition coating film is 5% by weight
Beyond the above, the water vaporized and diffused from the electrodeposition coating layer is not compatible with the powder coating film, so that a large amount of water will be present at the interface between the electrodeposition coating film and the powder coating film. The appearance and adhesion of the powder coating are deteriorated, and the moisture is difficult to permeate through the powder coating, so that it tends to remain as bubbles in the coating. There is a drawback that it lowers. The cationic electrodeposition coating film after draining and drying is an uncured coating film. The uncured coating film may be a partially cured coating film. The uncured coating film had a gel fraction (the coating film was peeled off, placed in a 300 mesh mesh container made of stainless steel, and extracted with an acetone solvent in a Soxhlet extractor at a reflux temperature for 2 hours. Fraction = (weight of sample after extraction / weight of sample before extraction) × 100) is in the range of about 10% by weight or less, preferably about 5% by weight or less.

When a cured cationic coating film after draining is used, the adhesion of the cationic electrodeposition coating film and the powder coating film, the smoothness of the powder coating film, the appearance of the coating film such as gloss, etc. It is not preferable because the number of baking and hardening steps increases and the number of baking and hardening steps increases. The water-drying drying conditions may be appropriately determined depending on the size, heat capacity, material, etc. of the metal coated object, the air volume of the drier, etc., and the water content of the electrodeposition coating film is 5% by weight or less and curing of the coating film does not start. Usually, it is about 40 to 120 ° C, preferably about 50 to 100 ° C for about 5 to 30 minutes, preferably about 5 to 2
It is a range of 0 minutes.

The powder coating material used in the coating method of the present invention has a curing start time (same baking temperature condition as that of the electrodeposition coating film) of the powder coating material, and the curing start of the cationic electrodeposition coating film after draining and drying. It is necessary that the time is slower than the time and the surface tension of the powder coating is smaller than that of the cationic electrodeposition coating film. If the curing start time of the powder coating is the same as that of the cationic electrodeposition coating, or if the powder coating is faster (shorter) than the cationic electrodeposition coating, the appearance of the powder coating (smoothness, stripes, etc.) ) Becomes worse, which is not preferable. The curing start time of the powder coating is, for example, in the baking temperature range of about 140 to 180 ° C., compared with that of the cationic electrodeposition coating film.
It is preferable that the time is from 1 second to 15 minutes long. The curing start time of the powder coating material and the electrodeposition coating film can be adjusted, for example, by the resin composition used, the crosslinking agent, the catalyst, and the like.

The curing start time of the powder coating material and the cationic electrodeposition coating film is determined by a rigid pendulum type viscoelasticity measuring apparatus [eg polyfile. Vol31. No362 (1994) 26-2
Recent surface and interface evaluation techniques described on page 8, Color Materials Association magazine. 51 (1978) pp. 403-409, viscoelasticity type measurement in the process of coating film formation by free damping vibration of a rigid pendulum, and viscosity of a paint which changes viscoelasticity with heat and time as described in Japanese Utility Model Laid-Open No. 6-56757. Elasticity measurement], and the time (corresponding to the baking time) due to the heat
Then, the vibration period (viscoelasticity) of the pendulum of the coating film is measured, and the curing start time can be obtained from the inflection point (time) of the vibration period.

Further, in the surface tension of the above-mentioned paint,
If the surface tension of the powder coating (powder coating) is the same as that of the cationic electrodeposition coating or if the powder coating is larger than the cationic electrodeposition coating, the appearance of the powder coating (smoothness, cissing, dents,
It is not preferable because the surface gloss of the coating film) deteriorates. The surface tension of the powder coating is usually in the range of 25 to 45 dynes / cm, preferably 25 to 40 dynes / cm as the powder coating, and the surface tension of the cationic electrodeposition coating is usually 30 to
50 dynes / cm, preferably 35-45 dynes / cm
And the difference in surface tension between the powder coating and the electrodeposition coating is less than about 5 dynes / cm for the powder coating, especially about 7 to 30 dynes / cm. It is preferably smaller by cm. The surface tension of powder coating and electrodeposition coating is
For example, it can be adjusted depending on the base resin, crosslinking agent, additive, etc. used.

As the powder coating material used in the coating method of the present invention, conventionally known thermosetting powder coating materials can be used without particular limitation as long as they satisfy the above-mentioned conditions. Examples of the thermosetting powder coating material include epoxy resin, polyester resin (containing a functional group such as hydroxyl group and carboxyl group), acrylic resin (hydroxyl group,
A resin containing a functional group such as a carboxyl group or an epoxy group is used as a base resin, and a cross-linking agent (block polyisocyanate, tetramethoxymethyl glycoluril, etc. as a cross-linking agent that reacts with a hydroxyl group) reacts with a carboxyl group. As a crosslinking agent, polyepoxide, β-hydroxyalkylamide, etc., as a crosslinking agent that reacts with epoxy groups, polycarboxylic compound, polycarboxylic acid polyester resin, acid anhydride, phenol resin, dicyandiamide, organic acid dihydrazide, aromatic sulfonium salt cation A thermosetting powder coating composition containing a polymerization catalyst etc.) can be preferably used.

In the thermosetting powder coating material, in addition to the above-mentioned components, for example, a coloring pigment, a filler, a fluidity adjusting agent, an antiblocking agent, a surface adjusting agent, an anti-arming agent, an antioxidant, a curing accelerator, Other compounds such as resins may be blended as necessary. As the powder primer, those which have passed through about 150 mesh can be preferably used.

The thermosetting powder coating material is prepared by a conventionally known method for producing a thermosetting powder coating material, for example, a base resin, a cross-linking agent and, if necessary, other compounds, and then dry blending. , Then melt blending, then cooling,
It can be manufactured by performing coarse pulverization, fine pulverization, and filtration.

The thermosetting powder coating can be applied by a known electrostatic powder coating method such as a corona charging method or a friction charging method. The film thickness of the thermosetting powder coating is usually about 20 to 100 microns, preferably about 3
A range of 0-60 microns is preferred. Baking of the thermosetting powder coating material can be carried out under a temperature condition where it can be cured simultaneously with the cationic electrodeposition coating film, and specifically, for example, it is preferably at about 140 to 180 ° C. for about 20 to 40 minutes.

On the surface of the coating film on which the thermosetting powder coating film has been formed, a curable top coating composition such as a powder coating composition, an organic solvent coating composition and a non-aqueous dispersion coating composition can be applied. As these paints, paints conventionally used in the automobile field can be used without particular limitation. The top coating may be, for example, one coat, two coat, one bake system, two coat, two bake system, or three coat, two bake system. Further, the top coat may be any finish such as solid finish, metallic finish and pearl finish.

[0019]

EXAMPLES The present invention will be described in detail below with reference to examples.

Example 1 Thickness 0.8 × length 300 × width 1 after zinc phosphate conversion treatment
Cationic electrodeposition paint (using amine-added epoxy resin as a base resin and a crosslinking agent of block polyisocyanate and a tin catalyst) on a 00 (mm) dull steel plate, curing start time 720 seconds "160 ℃ ”, surface tension 42
Dyne / cm) was subjected to cationic electrodeposition coating so that the dry film thickness was about 20 microns, washed with ultrafiltration filtration water, and dried at 160 ° C. for about 10 minutes to give a water content of about 3% by weight. An uncured dry electrodeposition coating film of was obtained. Then, on the surface of the electrodeposition coating film, an epoxy polyester thermosetting resin powder coating material (Finedec M-8860 "Dainippon Ink & Co., Inc., trade name, high acid value polyester powder resin with acid value 32" / Epico- To 1002 "made by Yuka Shell Co., Ltd.,
Trade name, Bisphenol A type epoxy resin = 70
/ 30 weight ratio of poly n-butyl acrylate "comprising surface tension reducing agent, curing start time 840 seconds" 160
℃ ", surface tension 32 dynes / cm) electrostatic powder coating to a film thickness of about 60 microns and baking at 160 ° C for 30 minutes to simultaneously cure the electrodeposition coating and powder coating, and electrodeposition A coating film and a powder coating film were formed.

Examples 2 to 4 Table 1 shows the curing start time (adjusted by the amount of tin catalyst) of the cationic electrodeposition coating, and the surface tension (adjusted by the amount of poly n-butyl acrylate) of the powder coating. The electrodeposition coating films and powder coating films of Examples 2 to 4 were formed in the same manner as in Example 1 except that the results shown in Table 1 were used.

Example 5 White top coat paint (Magiclon 1000, Kansai Paint Co., Ltd., trade name, thermosetting acrylic resin paint) on the surface of the powder coating film of the electrodeposition coating film and the powder coating film obtained in Example 1. )
Was spray-coated to a dry film thickness of about 60 microns and baked at about 140 ° C. for 30 minutes to form a top coat film.

Comparative Examples 1 to 4 Comparative Examples 1 to 1 were carried out in the same manner as in Examples 1 and 5 except that the water content of the electrodeposition coating film, the curing time and the surface tension of the electrodeposition coating film and the powder coating material are shown in Table 1. 4 electrodeposition coating film and powder coating film were formed.

The results of Examples and Comparative Examples are shown in Table 1.

[0025]

[Table 1]

In Table 1, the curing start time, surface tension, coating film appearance and coating film performance are as follows.

Curing start time: Rhovibron DDV-O
It was measured using a viscoelasticity measuring device of PAIII (manufactured by Orientec Co., Ltd.). The curing start time of the electrodeposition coating film and powder coating material of Example 1 is shown in FIG. FIG. 1 shows the relationship between the vibration period of the pendulum and the heating time at the reference point. From the inflection point of the vibration period of the pendulum at 160 ° C. in FIG. Approximately 840 seconds (1
4 minutes). The curing start times of Examples 2 to 5 and Comparative Examples 1 to 4 were determined by the same method as above. In addition, in the difference in the curing start time, − indicates that the electrodeposition coating film is slower than the powder coating material.

Surface tension: The surface tension of the electrodeposition coating film and the powder coating material was measured as follows. The contact angle (θ) was measured by dropping deionized water on the surface of the cured coating film (baked at 160 ° C. for 30 minutes) of the electrodeposition coating material and the powder coating material. Then Se
ll and Neumann's empirical formula

[0029]

[Equation 1]

In the formula, γ _L : surface tension of water (72.8 dyne / cm) γ _S : surface tension of electrodeposition coating or powder coating (dyne / c
m).

In the difference in surface tension, -indicates that the electrodeposition coating film is smaller than the powder coating material.

Appearance of coating film Repelling: Repelling on the surface of the coating film was visually evaluated. ○: good with no cissing, △: poor with cissing, ×
Remarkably causes cratering and is extremely inferior. Waki: The wrinkle on the coating surface was visually evaluated. ◯ is good with no cracks, Δ is poor with cracks, and × is markedly poor with cracks Smoothness: The smoothness of the coating film surface was visually evaluated. ◯ indicates that the smoothness is good, Δ indicates that the smoothness is inferior, and x indicates that the smoothness is significantly inferior. Gloss: The specular reflectance described in JIS K5400 was measured.

Coating Performance Interlayer adhesion between electrodeposition coating and powder coating: goggles cutter
Then, 25 2 mm squares were formed on the coated surface, cellophane tape was brought into close contact with the surface and strongly separated, and then evaluated according to the following criteria. ○: No peeling at all, Δ: Some peeling is observed, ×: Many peeling are observed Interlayer adhesion between powder coating film and topcoat coating film: Tested by the same adhesion test method as above.

[0034]

The coating method of the present invention can omit the steps of baking, polishing, washing with water and drying after electrodeposition coating, as compared with the conventional coating system. As the powder coating material containing no organic solvent is used as the above, there is a feature that there is no fear of polluting the environment. Further, usually, even if a powder coating is applied to the surface of the electrodeposition-washed coating film, the appearance and performance of the coating film are deteriorated, but in the present invention, the appearance and performance thereof are good.

[Brief description of drawings]

FIG. 1 shows the curing start time of an electrodeposition coating film and a powder coating material of Example 1 of the present invention.

Front page continuation (72) Inventor Shinichi Ueda Kansai Paint Co., Ltd. 4-17-1, Higashi-Hachiman, Hiratsuka City, Kanagawa Prefecture

Claims (1)

[Claims] 1. A metal coating material is coated with a thermosetting cationic electrodeposition coating composition to form an undercoat electrodeposition coating film, which is then washed with water and then drained and dried to obtain a water content. Is 5% by weight
The following uncured electrodeposition coating film is formed, and a thermosetting powder coating which is slower than the curing start time of the uncured electrodeposition coating film and smaller than the surface tension of the uncured electrodeposition coating film is electrostatic powder. After coating to form a powder coating film, baking is performed to simultaneously cure the electrodeposition coating film and the powder coating film, which is a coating method.