JPS6245381A - Method for coating steel plate - Google Patents

Abstract

PURPOSE:To enhance the chipping resistance and corrosion resistance of a composite film, by applying electrodeposition paint to a steel plate and subsequently applying org. solvent type barrier coat having a specific composition and properties to the electrodeposition paint film prior to applying intermediate coat. CONSTITUTION:The composition applied to an anionic electrodeposition paint film contains a modified polyolefin resin forming a film with static glass transition temp. of -30--60 deg.C and an org. solvent as main components. Because the barrier coat film formed by this composition has flexibility and peculiar viscoelasticity, the surface physical damage of the intermediate coat film and the top coat film formed through said film is reduced to a large extent and the generation of rust and corrosion of the steel plate due to chipping is also prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating method for forming a composite coating film having excellent chiaping resistance, corrosion resistance and physical performance on a steel plate, particularly an automobile body.

In the automobile industry, emphasis is being placed on the durability of paint films, particularly the decline in corrosion resistance of paint films due to impact peeling and the slowing of the progression of corrosion on steel plates. Particularly in the cold regions of Europe and the United States, to prevent road surfaces from freezing during the winter, concrete gravel is often mixed with large amounts of relatively coarsely crushed rock salt, and cars driving on these types of roads are often covered with gravel. Rock salt particles and pebbles thrown up by the wheels collide with the coating surface, and the impact often causes the coating to be partially peeled off from the vehicle body, resulting in so-called "chipping." Due to this phenomenon, the metal surface of the impact area on the outer surface of the car body is exposed (rust quickly develops and corrosion progresses. Paint peeling due to chipping usually occurs at the bottom of the car body and the footrest area, but it does not occur on the hood and roof. It is known that localized corrosion occurs in about 6 months to 1 year and becomes quite noticeable.

In order to prevent this chipping and the progress of corrosion caused by it, various studies have been made on chemical conversion treatments for the surface of the external metal base of the car body, as well as electrodeposition paints, intermediate coats, and top coats.

For example, in chemical conversion treatments, the use of iron phosphate coatings and zinc phosphate coatings with different crystal forms has been considered, but it is difficult to sufficiently improve the adhesion of coatings on impact areas with such chemical conversion treatments. be. In addition, various studies have been conducted on the resin and/or cuticle pigments contained in the paints and top coats, but so far no one has been found that has a sufficient adhesion-improving effect to withstand chipping. Not yet reached.

In addition, sericite powder, which is an inorganic foil-like pigment, is contained in the intermediate coating composition, thereby mitigating and/or dispersing the impact force caused by shearing in the intermediate coating film layer due to the inorganic foil-like pigment. or locally cause peeling only within the intermediate coating layer or at the interface between the electrocoated paint surface and the intermediate coating film, thus preventing damage to the electrocoating coating film, and The aim is to ensure that the scratch-free electrodeposition paint film maintains its anti-corrosion function, but the impact force applied to the outside surface of the car body is not constant and can be quite large, so these methods require intermediate coating. If an impact force that exceeds the mitigation and dispersion ability due to shear within the coating layer is applied, the impact force cannot be stopped at the intermediate coating layer and the affected area will damage all coatings, including the electrodeposited coating. There is a drawback that the entire coating film peels off from the surface of the metal substrate, and as a result, the affected area quickly develops rust and corrosion progresses.

Therefore, the inventors of Zero devised a method to improve the above-mentioned problems.
A composite coating with excellent chipping resistance, physical properties, and corrosion resistance that is at least equivalent to the finished appearance obtained by a steel plate coating system consisting of ordinary anion static paint, intermediate coat paint, and single-coat paint. As a result of extensive research aimed at providing a coating method for forming a film, the present invention was finally completed.

That is, according to the present invention, a steel plate is coated with an anionic electrodeposition paint, and then a static glass transfer film is formed on the coated surface.
Provided is a method for coating a steel plate, characterized in that after coating an organic solvent-based barrier foot mainly composed of a modified polyolefin resin with a temperature of -30 to -60°C, an intermediate coat and a top coat are sequentially applied. be done.

An organic solvent-based paint capable of forming a composite coating film that achieves the objective f of the present invention is referred to as a "barrier coat."

A feature of the present invention is that in a composite coating process in which anionic electrodeposition paint, intermediate coat paint, and top coat paint are sequentially applied to a steel plate,
After applying the electrodeposited paint and before applying the intermediate paint, an organic solvent-based barrier coat with a specific composition and properties is applied to the electrodeposited surface in advance.As a result, chipping resistance and corrosion resistance are achieved. It was possible to form a composite coating film with significantly superior physical properties.

In other words, a barrier coating film with a static glass transition temperature adjusted to -30 to -60°C is more flexible than a pre-coated film for the purpose of improving the above-mentioned chipping resistance, and is more flexible due to the modified polyolefin resin. It has a unique viscoelasticity. Then, even if a strong impact force from rock salt, pebbles, etc. is applied to the surface of the intermediate coat to top coat film formed through the next barrier coat film layer that has such physical properties, the Most or all of the impact energy is absorbed within the barrier coat film and does not spread to the underlying electrodeposited film, and both the top coat and intermediate coat are virtually free from physical damage. It was done. . In other words, the above-mentioned barrier coating film layer exhibits a buffering effect against external impact forces, significantly improving chipping resistance, and preventing the occurrence of corrosion of the steel plate due to chipping. This also eliminates the deterioration of the topcoat film due to collisions such as collisions.

Below is a detailed explanation of how to paint V, Zero, and J.
] fru.

There are no restrictions on the material as long as it is a material to be coated by the method of Steel Sheet Nirei Hatsuho and has a metal surface that can be coated by anionic electrodeposition. Examples include iron, copper, aluminum, tin, zinc, alloys of these containing gold F, and plated or vapor-deposited products of these metals and alloys, and specifically passenger cars made of these. There are vehicle bodies such as cars, trucks, zufari cars, and motorcycles. Also, before applying paint to the anion type plate, it is best to chemically treat it with phosphate or chromic acid/salt in advance.

Anion type electrodeposition paint
A known coating fPl can be used. Anionic electrodeposition paints are anodic electrodeposition paints that are mainly based on resins with carboxyl groups and are neutralized with basic compounds and made water-soluble (water-dispersed).
F: Painting using steel material (subject) as an anode (+Resins with carboxyl groups can be applied by adding maleic anhydride to drying oil (linseed oil, dehydrated oil, tung oil, etc.). Nen maleated oil and fat;
(4) Polyhydric alcohol (molecular weight approx. 1000 or more, including partial esters of epoxy resins and styrene/allyl alcohol copolymers), polybasic acids (anhydrous trimeri, 7
Resin obtained by adding toric acid, malefinized fatty acid, male, insulin oil, etc.); ■Carboxyl group-containing polyester resin (including fatty acid modified type): ■ Carboxyl group-containing acrylic resin; ■Glycidyl or a hydroxyl group-containing polymerizable unsaturated monomer and an unsaturated fatty acid. It is generally suitable that the content t is in the range of about 30 to 200 based on the acid value. As a neutralizing agent for neutralizing the carboxyl groups in these carboxyl foundation-1111 resins and making the resin water soluble (dispersed), for example, alkanols such as monoethanolamine, jetanolamine, dimethylaminoethanol, etc. Alkylamines such as diethylamine and triethylamine; inorganic alkalis such as potassium hydroxide and sodium hydroxide can be used. The amount of these neutralizing agents used is approximately 0 of the theoretical neutralization equivalent to the acid value of the resin.
．． A range of 1 to 1.0 times equivalent (preferably 0.4 to 0.8 times equivalent) is suitable.

As a crosslinking agent for the above resin, low molecular weight melamine resins such as Gen 1, hexakismethoxymethylmelamine, butoxylated methylmelamine, and ethoxylated methylmelamine can be used as necessary. M paint contains pigments (W color pigment, extender pigment, anti-rust pigment, etc.) The blending aim of @Kan is to have an impact solid content of 10.
0 parts by weight can be less than 40 parts by weight),
Add a hydrophilic solvent, water, additives, etc. as necessary, adjust the solid content concentration to approximately 5 to 40% by weight with deionized water, etc., maintain the pH in the range of 7 to 9, and use it for anionic electrodeposition coating. be able to. Anion electrodeposition coating can be carried out according to a conventional method, for example, at a bath temperature of 15 to 35°C and a load voltage of 1
The coating can be carried out under the conditions of 00 to 350 V using the object to be coated as an anode. There is no particular limit to the coating film thickness, but usually,
A range of 10 to 40 microns is preferred based on the cured coating.

Anionic electrodeposited coatings are cured by heating to a temperature in the range of 100 to 200°C, preferably 140 to 200°C. can also be dried at room temperature.

Barrier coat: A composition applied to anionic electrodeposition coating, in which the static glass transition temperature of the formed coating is -30 to -6
It is a paint whose main components are a modified polyolefin resin and an organic solvent at a temperature of 0°C, preferably -40 to -55°C. In other words, a modified polyolefin (t7) (for example, a propylene-ethylene copolymer (preferably a molar ratio of about 40 to 80:60 to 20%) and a chlorinated polyolefin (chlorination rate of about 1 ~60%), 1 to 50 parts by weight, preferably 10 to 20 parts by weight (both 100% by weight)
0.1 to 50 parts by weight of maleic acid or maleic anhydride to 100 parts by weight of the above-mentioned propylene-ethylene copolymer; Examples include resins grafted with 0.3 to 20 parts by weight.

Any organic solvent may be used as long as it can dissolve or disperse the above-mentioned modified polyolefin resin, such as aromatic hydrocarbons such as alcoholic acid, tonolenine, xylene, aliphatic carbonates such as hexane, heptane, octane, and decane. Hydrogen, chlorinated hydrocarbons such as trichlorethylene, perchlorethylene, dichloroethylene, citalolethane, dichlorobenzene, methyl ethyl ketone, diacetone alcohol fx, etc. (D': r-ton type, ethanol,
Examples include alcohols such as propatool and butanol, and cellosolves such as butyl cellosolve.

In the present invention, if the modified polyolefin resin itself has a static glass transition temperature within the above range, it can be used as a barrier coat by itself, but if it deviates from the above range or has a static glass transition temperature within the above range, However, if the static glass transition temperature is to be slightly adjusted, a viscosity imparting agent may be added as necessary. Examples of the viscosity imparting agent include those having good compatibility with the modified polyolefin resin, such as Logici, petroleum resin (coumaron), ester gum, polybutadiene, epoxy-modified polybutadiene, low molecular weight aliphatic epoxy resin, and low molecular weight aliphatic bisphenol type. Examples include epoxy resin, polyoxytetramethylene glycol, and vinyl acetate-modified polyethylene, and the blending amount thereof is preferably 1 to 50 parts by weight per 100 parts by weight of the above-mentioned modified polyolefin resin.

In the present invention, regarding the formed coating film of the barrier coat,
It is essential that the static glass transition temperature is within the above range, but furthermore, the tensile strength elongation rate at break of the coating film is 200 to 1000%, particularly 300 to 1000%, in an atmosphere of -20°C.
Preferably it is 700%. If the static glass transition temperature of the formed coating film is higher than -30°C, the above object of the present invention cannot be achieved, and if it is 11' higher than -60°C, the performance of the coating film, especially water resistance, adhesion, etc. will deteriorate. This is not preferable because it reduces the Furthermore, even if extender pigments, coloring pigments (excluding anticorrosive pigments), etc. are added to the barrier coat, no change is made. The blending amount of these pigments is preferably 1 to 150 parts by weight, especially 100 parts by weight of the modified polyolefin resin.

In the present invention, these barrier coats are applied to the anionic electrodeposition coating surface, but the coating method is not limited, and examples include spray coating, brush coating, dipping coating, melt coating, electrostatic coating, etc. The coating thickness is preferably 1 to 20 microns, particularly 5 to 10 microns, including the formed coating film.

The static glass transition temperature of the coating film used in the present invention was measured using a differential scanning calorimeter (DS manufactured by Daini Seitamasha Co., Ltd.).
C-10 type), and the tensile strength elongation at break is the bond measured using a universal tensile tester with a constant temperature bath (Shimabara Autograph S-D), and the length of the sample. is 2
The test was carried out at a tensile rate of 20 min/min. The samples used for these measurements were coated on a tin plate to a thickness of 25 μm with the barrier coat added to the formed coating film.
After baking for 30 minutes at 0.degree. C., the sample was isolated by removing the mercury amalgam and used.

When applying an intermediate coat to the barrier coat surface, it is preferable to bake the barrier coat in advance, but it is also okay to apply the intermediate coat with a wet-on-queue method without baking. do not have. The baking temperature of the barrier coating film is 80 to 160℃, especially 80 to 13℃.
0°C is suitable.

Intermediate paint: A paint to be applied to the barrier coated surface, and any known intermediate paint with excellent adhesion, smoothness, sharpness, overbake resistance, weather resistance, etc. can be used. Specifically, thermosetting intermediate coatings whose vehicle main component is a short oil having an oil length of 30% or less, an ultra-short oil alkyd resin, or an oil-free polyester are mentioned. These alkyd resins and polyester resins are
Hydroxyl value 60-140, acid value 5-200, 1, it is preferable to use unsaturated oil (unsaturated fatty acid) as the modified oil,
5) Etherified sitamelamine resin, urea resin beshisoguanamine resin, etc. are suitable. The blending ratio of these is preferably 80% alkyd fM and/or oil-free polyester and 35 to 15% amine resin, particularly 30 to 20, based on solid weight. Furthermore, at least a portion of the above amino ginger fat can be replaced with a polyisocyanate compound or a blocked polyisocyanate compound.

Although the form of the intermediate coating paint is most preferably an organic solution type, it may also be a non-aqueous liquid type, a high solid type, an aqueous solution type, an aqueous dispersion type, etc. using the above-mentioned vehicle components. In the present invention, the hardness of the intermediate coating film (pencil hardness)
It is preferably in the range of id3B or higher (20°C). Furthermore, extender pigments, young paints, other paint additives, and the like can be blended into the intermediate paint as necessary.

In the present invention, the intermediate coating paint is applied to the surface of the barrier coat by the same method as the barrier coat, and the coating thickness is preferably in the range of 10 to 50μ even for the cured coating. The curing temperature of the coating film varies depending on the vehicle component, and when curing by heating, it is 80 to 170°C, especially 1
It is preferable to heat at a temperature of 20 to 150°C.

Top coat: A paint applied to the intermediate coated surface, which imparts cosmetic properties to the object to be coated.

Specifically, the finished appearance (sharpness, smoothness, gloss, etc.)
, weather resistance (glossy retention, color retention, chalking resistance, etc.), chemical resistance, water resistance, moisture resistance, curing properties, etc. All well-known paints are used to form a full fc coating. For example, paints whose vehicle main component is an amino-acrylic oil type, an amino-alkyd resin type, an amino-polyester resin type, etc. can be mentioned. The form of these paints is not particularly limited, and organic solution type, non-aqueous dispersion type, aqueous (dispersion) liquid type, powder type, high tree type, etc. can be used.

Drying and curing of the coating film is carried out by drying at room temperature, drying by heating, irradiation with active energy rays, etc. In the present invention, the coating film formed by the stiff top coat has a pencil hardness of 2B to 3H.
(20℃) lol! The top coating used in the present invention should preferably be within the range 4. The top coating used in the present invention uses the above-mentioned vehicle main component. It is classified as a clear coating Fl-, which contains almost no pigment.The following methods can be mentioned, for example, to form a topcoat film using these coatings: ■ Metallic pigment and, if necessary, A metallic paint containing a coloring agent, sweet f!:, is a metallic paint containing a coloring agent 1
．． A method of applying solid color paint and curing it by heating (1 coat) Baking method for metallic finish (solid color finish button).

■ Metallic I coating F+ is a method of applying solid color paint, heating and curing, then applying clear paint and heating and curing again (metallic TI solid color finish using 2-coat, 2-base method).

■Paint with metallic paint or solid color paint,
A method in which a clear paint is then applied and then heated to cure both coatings at the same time (metallic or solid color finish using the 2-coat 1-beta method).

These top coat paints are preferably applied by spray painting, electrostatic painting, or the like. However, the coating film thickness is 25 to 40μ in the above (■), based on the dry coating film, and the above (■) and (■).
So, metallic paint and solid color paint are 1
The preferred thickness is 0 to 30μ, and the preferred clear paint is 25 to 50μ. Heating conditions can be arbitrarily selected depending on the vehicle components, but it is preferable to heat at 80 to 170°C, particularly 120 to 150°C.

``Pencil hardness'' of the above intermediate and top coats: Painted on a glass plate and cured (Hard coating thickness: 30μ) The test plate was held at 20℃, the tip of the thinner was sharpened flat, and the corner was sharpened. (Mitsubishi drafting pencil ``Uni'') held at a 45 degree angle,
About 1 hour while pressing firmly against the painted surface so that the thin film does not break.
The value was evaluated using the hardness of the hardest pencil that leaves no trace of scratches caused by the pencil after moving c1n (3 seconds/fold).

As described above, the steel plate is coated with anion electrodeposition coating, barrier coating coating, intermediate coating coating, top coating coating, and outer coating (for example,
(smoothness, gloss, sharpness, etc.), water resistance, weather resistance, etc.
The e+internal properties have been significantly improved.

Next, examples and comparative examples related to the present invention will be described.

■Sample (]) Steel plate: Steel plate chemically treated with Bonderite + 3030 (manufactured by Nippon Barker Rising ■, zinc phosphate system) (size 300 x 90 x O, 8 cabinets) (2)
Anionic electrodeposition coating T+: 325 parts by weight of fAl Epon #1001 (manufactured by Ciel Togakusha, epoxy tallow), 270 itf15 epoxy ester obtained by reacting 525 parts by weight of oil fatty acid and 17,575 parts by weight of dehydrated castor oil fatty acid with 1. Add 1 part by weight of 2-polybutadiene carboxylic acid, 40 parts by weight of 1.4-polybutadiene, and 75 parts by weight of maleic anhydride to make 200'
The resin obtained by reacting with C, -+ -+ and then opening the anhydride group had a total acid value of 85.

The resin was neutralized in a caustic oven, 25% by weight of hexakismethoxymethylmelamine (crosslinking agent) was added based on the total weight of the 5f-Eil fraction, and then water was added to give a solids content of 13% by weight. % anionic electrodeposition paint.

(B linseed oil fatty acid modified epoxy resin is reacted with maleic anhydride, the acid value after ring opening is 90, then neutralized with triethylamine, partial butoxymethylmelamine (crosslinking agent) is added to this, the total of both components Based on the weight, 25% by weight was added, and then water was added to obtain an anionic electrodeposition paint with a solids content of 13% by weight.

(3) Barrier coat (A: Propylene-ethylene copolymer is graft-polymerized with maleic acid and then resin organic liquid (static glass transition temperature -43°C, tensile strength elongation at -20°C 4)
10%), (B: Organic liquid of resin mixed with 100 parts by weight of the above resin and 10 parts by weight of rosin (static glass transition temperature -5)
Tensile breaking strength elongation rate at 2°C and -20°C 7 (10
%).

(○: Organic liquid of a resin made by graft polymerizing maleic acid to a propylene-ethylene copolymer (static glass transition temperature +5°C).

(4) Intermediate paint: Amirac N-2 Sealer (manufactured by Kansai Paint ■, amine polyester resin intermediate paint) (5) Top coat (A) Near Mirac White (manufactured by Kansai Paint ■, amino alkyd resin-based top coat paint, 1 coat 1 coat white paint, pencil hardness H (20℃) (20°C)) (0: Magiklon Clear (manufactured by Kansai Paint ■, amino acrylic resin top coat paint, clear paint for 2 coats and 1 coat, pencil hardness H (20°C)) ■ Example Comparative example The above sample Apply anionic paint, barrier coat, intermediate coat paint, and top coat paint to the steel plate using the steps shown in Table 1.

The anionic electrodeposition coating conditions were: bath solid content concentration 12%, bath temperature 30°C, pH 7.8, and load voltage approximately 200V.

Power on for 180 seconds. Electric! @Wash with water after installing. The coating film thickness is 20 μm even for the cured film.The barrier coat is I'WL with an air spray machine, and the film thickness is at least 8 μm for the dry film.
μ.

Both the intermediate coating and the heat coating are spray-painted using an electrostatic coating machine, and the film thickness of the intermediate coating is at least 25 μm for the cured coating.In the top coating system, r ICIBJ is This is a coating system in which topcoat A is applied and then baked at 140°C for 30 minutes, and r2cIBJ is a coating system in which topcoat B and C are coated with Couette-on-Quette and then baked at 140℃ for 30 minutes to cure both coatings at the same time. It is a system that encourages

I. Performance Test Results A coating film performance trial was conducted using a coated plate coated in the above Examples and Comparative Examples. The results are shown in Table 2. 0, [M, h method] (*1) @Chipping property: O) Test equipment: Q-G-R gravelometer (product of Q Panel Company) c2) Stone to be sprayed : Diameter approx. 15-20 m/m
■Capacity of crushed stone: Approx. 5 (temperature during lot test: approx. 20°C) The sample was attached to a test piece holder, and the blast of approx. 4 KIi/d was performed using air pressure to test approx. After spraying on a piece, evaluate its coated surface condition and salt spray resistance.

The condition of the painted surface was visually observed and evaluated using the following criteria. For salt spray resistance, test pieces were subjected to a salt spray test for 240 hours in accordance with JIS Z2371, and then adhesive cellophane tape was attached to the painted surface and peeled off rapidly. Check for rust, corrosion, peeling of paint, etc. from the impact area afterward.

■ Painted surface condition (0 (Good) There are very few scratches due to impact on some parts of the second top coat, and there is no evidence of peeling of the electrodeposited paint.

△ (Slightly unsatisfactory) There are not many scratches caused by impact on the second and intermediate coats, and there are some peelings of the electrodeposited coatings.

× (Poor): Most of the top coat and intermediate coat have peeled off, and the droplet film on the impacted area and its surrounding area has peeled off.

■ Salt water spray resistance (Fu: No rust, corrosion, peeling of paint, etc.).

○: No rust, corrosion, or peeling of the paint film observed.

△: Slightly more rust, corrosion, and paint peeling are observed. ×: Significant rust, corrosion, and peeling of the coating occurred.

(*2) Citrus & Grain: Performed in an atmosphere at 0°C according to JIS K54no-19796, 13, 3B method. Weight 5 (1(
Drop a +9 Omogen from a height of 50 degrees and check for damage to the paint film.

(i-4: No abnormality C: Slight cracking and peeling ×: Significant cracking and peeling (*3) Adhesion: Based on JIS K5400-1979 6.15, the size of the paint film is 1 x 1 m + 100 squares. Make one piece, stick adhesive cellophane tape on its surface, and suddenly peel it off r%
Check the remaining number of Goban eyes @model.

(*4) Submersible: The coated surface was evaluated after being immersed in water at 40°C for 10 days.

Claims (1)

[Claims] A steel plate is coated with an anionic electrodeposition paint, and then an organic solvent-based barrier coat mainly composed of a modified polyolefin resin whose static glass transition temperature is -30 to -60°C is applied to the coated surface. A method for coating a steel plate, which comprises applying an intermediate coat and a top coat after coating.