JPH04329894A - Painting method - Google Patents

Abstract

PURPOSE:To greatly improve the chipping resistance, corrosion preventiveness, etc., of electrodeposition coated films and multilayered coated films contg. finish coated films. CONSTITUTION:This painting method consists in applying a cationic electrodeposition coating material which contains an epoxy cationic electrodepositable resin having 40 to 60dyne/cm surface tension and a film formable resin having 25 to 45dyne/cm surface tension and 0 to -95 deg.C static glass transition temp. of the foamed coated film respectively within a weight range of 70:30 to 98:2 and has the surface tension of the epoxy cationic electrodepositable resin larger than the surface tension of the film formable resin, then curing the coating by heating and executing finish coating.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for painting steel materials, particularly the outer panels of automobile bodies, and more specifically, it greatly improves the chipping resistance and corrosion resistance of multilayer coatings including electrodeposited coatings and topcoats. The present invention relates to a painting method that can be improved.

0002

[Prior art and its problems] In recent years, in the automobile industry,
There is a growing demand for improved durability of car body outer panels in corrosive environments (for example, rock salt spraying in cold regions), and for this reason, each automobile manufacturer is using corrosion-resistant materials in addition to conventional cold-rolled steel sheets as the material for vehicle body outer panels. Galvanized steel sheets, which have excellent properties, have been adopted. In addition, car bodies with these outer panel materials are
There is often a problem that when rock salt particles or pebbles collide with the coating surface during driving, the coating layer peels off, causing so-called "chipping." Particularly in low-temperature environments, the coating film becomes hard and loses its elasticity, making it unable to absorb the impact, and the impact is applied directly to the steel sheet beneath the coating film. peeling is more likely to occur. In particular, in the case of galvanized steel sheets, the weight of the galvanized coating is large, so peeling is likely to occur, and there is an urgent need to consider countermeasures against chipping in low-temperature environments.

[0003] To counter this problem, the applicant proposed a coating method in which a chipping sealer with a low static glass transition temperature is applied to the object to be coated after electrodeposition, and then a conventional intermediate coat and top coat are applied ( For example, Japanese Patent Laid-Open No. 62-65767, etc.). However, the coating thickness of the chipping sealer is
A particularly preferable range is 5 to 10 μm; below this range, the chipping resistance effect cannot be expected much, and above this range, the finished appearance after the top coat tends to deteriorate; however, in the commonly used spray painting method, It is difficult to control such film thickness, and there are problems in dealing with it on a mass production painting line. Furthermore, increasing the step of applying a chipping sealer to the conventional painting step is counterproductive from the viewpoint of process saving, and cannot be said to be economically preferable.

0004

[Means for Solving the Problems] As a result of intensive studies to solve the above-mentioned problems, the present inventors have developed an epoxy-based electrodepositable resin having a surface tension within a specific range, and an epoxy-based electrodepositable resin having a surface tension lower than that of the resin and forming The above purpose can be achieved by applying a cationic electrodeposition paint mixed with a film-forming resin whose static glass transition temperature is within a specific range, curing with heat, and then applying a top coat. Chipping resistance,
The present inventors have discovered that it is possible to form a coating film with excellent anti-corrosion properties, and have completed the present invention.

That is, the present invention provides (A) a surface tension of 40
Epoxy-based cationic electrodepositable resin having a surface tension of ~60 dyne/cm, and (B) a surface tension of 25 to 45 dyne/cm.
and the static glass transition temperature of the formed coating film is 0 to -9
Resin (A): Resin (B) = film-forming resin at 5°C
A cationic electrodeposition paint containing a weight ratio in the range of 70:30 to 98:2 and in which the surface tension of the resin (A) is higher than that of the resin (B) is applied, and after curing by heating, the coated surface is then coated. To provide a coating method characterized by coating a top coat with a top coat.

[0006] In the method of the present invention, in the step of sequentially applying an electrodeposition paint and a top coat to an object to be coated, resin components having different surface tensions in the electrodeposition paint cause the formation of the electrodeposition paint film due to the difference in surface tension. A concentration gradient is generated within the coating film during formation, and the surface layer of the electrodeposited coating film has excellent chipping resistance, making it possible to achieve the same function without using a conventional chipping primer.

That is, the electrodeposition coating film formed by the method of the present invention has a resin having excellent anticorrosion properties and adhesion properties mainly distributed on the surface side of the object to be coated in one electrodeposition coating; This can result in a multilayer coating film having a concentration gradient such that the resin with excellent chipping resistance is mainly distributed in the surface layer of the film. Therefore, the surface layer of the electrodeposited coating where the film-forming resin having a static glass transition temperature within a specific range is localized is flexible and has unique viscoelasticity, so it resists external impact through the surface of the top coat. It is possible to achieve good chipping resistance. Therefore, the method of the present invention can omit the conventional process of applying a chipping primer, simplifying the painting process and lowering the painting cost.

The cationic electrodeposition paint used in the present invention comprises (A) an epoxy cationic electrodeposition resin having a surface tension of 40 to 60 dyne/cm, and (B) a surface tension of 25 to 45 dyne/cm. and contains a film-forming resin whose static glass transition temperature of the formed coating is 0 to -95°C in a weight ratio within the range of resin (A):resin (B) = 70:30 to 98:2. In addition, the present invention is a cationic electrodeposition paint for forming a multilayer film in which the surface tension of the resin (A) is higher than that of the resin (B).

[0009] The above epoxy cationic electrodepositable resin (A)
is a water-solubilized or water-dispersed product of a polyamine resin such as an acine-added epoxy resin that has been conventionally used in the field of cationic electrodeposition coatings, and includes, for example, (1) polyepoxide, primary mono- and polyamine, secondary Adducts with polyamines or mixed primary and secondary polyamines (see, for example, U.S. Pat. No. 3,984,299); (2) polyepoxide compounds and secondary mono- and polyamines having ketiminated primary amine groups; (3) a reaction product obtained by etherification of a polyepoxide compound with a hydroxy compound having a ketiminated primary amino group (see, for example, JP-A-59-1999); 43013) etc. can be used. These polyamine resins can be cured, if necessary, using a polyisocyanate compound blocked with alcohol or the like as a curing agent.

[0010] Furthermore, amine-added epoxy resins that can be cured without using the above-mentioned crosslinking agent can also be used.
9-155470); a type of resin that can be cured by transesterification (for example, JP-A-55-80);
436); resins in which blocked isocyanate groups are introduced into the base resin can be used.

Furthermore, as the resin (A), a cationic electrodepositable resin having a hydroxyl group, such as the above-mentioned polyamine resin having a hydroxyl group, is used, and as a curing agent,
Those using epoxy resins having an average of two or more epoxy group-containing functional groups per molecule, which are formed by bonding epoxy groups to an alicyclic skeleton and/or a bridged alicyclic skeleton (e.g., JP-A-2-255874) ) can be used. As such a resin having a hydroxyl group, for example, a resin obtained by reacting a polyepoxide compound with an alkanolamine such as diethanolamine to have a primary hydroxyl group is preferably used.

The above-mentioned polyepoxides used in the production of the resin (A) include, for example, polyglycidyl ethers of polyphenols which can be produced by reacting polyphenols with epichlorohydrin in the presence of an alkali, and such polyepoxides Representative examples include bis(4-hydroxyphenyl)-2,2-propane, bis(4-hydroxyphenyl)-1,1-ethane, bis(4-hydroxyphenyl)-methane, 4,
Glycidyl ethers of polyphenols such as 4'-dihydroxydiphenyl ether, 4,4'-dihydroxydiphenyl sulfone, phenol novolak, and cresol novolac, and polymers thereof are included.

Among the above-mentioned polyepoxides, those having a number average molecular weight of at least about 380, preferably within the range of about 800 to 2,000, and those having an epoxy equivalent weight of 190 to 2,000 are particularly preferred from the viewpoint of cost and anticorrosion properties. 2,000, preferably 4
It is a polyglycidyl ether of polyphenol within the range of 00 to 1,000, especially the following general formula:

[Chemical formula 1] It is a polyepoxide represented by

When the above-mentioned cationic electrodepositable resin having a hydroxyl group is used as the resin (A), the epoxy resin containing an alicyclic skeleton and/or a bridged alicyclic skeleton used as a curing agent includes those known per se. can be used,
Commercial products such as EHPE-3150 and EHPE-1
150 [both manufactured by Daicel Chemical Industries, Ltd., trade names], which is an epoxy resin having the following structural formula and having a cyclohexane skeleton synthesized using 4-vinylcyclohexene-1-oxide.

[Case 2]

In the present invention, the resin (A) is one in which the above-mentioned epoxy resin containing an alicyclic skeleton and/or a bridged alicyclic skeleton is used as a curing agent to form a cured coating film through an addition reaction between an epoxy group and a hydroxyl group. Therefore, since there is almost no volumetric shrinkage of the coating film, the adhesion of the coating film is very excellent, and it is also particularly suitable from the point of view of forming multiple layers.

The resin used as the above-mentioned resin (A) can be water-dispersed or water-solubilized by neutralizing the resin with a water-soluble organic acid such as formic acid, acetic acid, or lactic acid.

In the present invention, the resin (A) has a surface tension of 40 to 60 dyne/cm, preferably 45 to 55 dyne/cm.
It is necessary to be within the range of e/cm. When the surface tension is lower than 40 dyne/cm, the film-forming resin described below (
If the compatibility with B) becomes too good, it becomes difficult to form a multilayer film having a desired temperature gradient, and the coating film tends to have poor weather resistance and corrosion resistance. On the other hand, when the surface tension exceeds 60 dyne/cm, the temperature gradient becomes extreme and resin (A) and resin (B) completely separate into two layers. ) tends to result in poor interlayer adhesion.

[0018] In this specification, the "surface tension" of the epoxy cationic resin (A) and the film-forming resin (B) described below was measured as follows:
Resin (A) or resin (B) is diluted with a solvent and coated on a degreased smooth tin plate using a bar coater to form a dry film for 10 minutes.
Paint to a thickness of μm. Let the paint film air dry at room temperature for one day.
Further dry at 50°C/0.1 atm for 1 hour, and then dry at room temperature for 10 min.
After leaving it for a minute, take the next measurement. Deionized water is added dropwise to measure the contact angle (θ) with the dry resin. Next, SeLL and Neumann's empirical formula

[Equation 1] In the formula, γL: surface tension of water (72.8 dyne/cm
), γS: Surface tension of resin (A) or resin (B) (
The surface tension of resin (A) or resin (B) is determined by dyne/cm).

The film-forming resin (B) used in the cationic electrodeposition paint in the present invention has a surface tension of 25 to 45 d.
yne/cm and the static glass transition temperature of the formed coating film is 0 to -95°C, there is no particular restriction, and either thermosetting resin or thermoplastic resin may be used, and it does not matter whether it is nonionic or cationic. However, from the viewpoint of multilayer formation and chipping resistance, nonionic thermoplastic resins are suitable, and specific examples include the following.

■ Styrene-butadiene copolymer: The content of styrene is about 1 to 80% by weight, preferably 10 to 80% by weight.
40% by weight copolymer, number average molecular weight approximately 10,00
Preferably, it ranges from 0 to about 1,000,000. (2) Butadiene resin: This is a polymer obtained by polymerizing in (1) above without using styrene. ■ Acrylonitrile-butadiene copolymer: acrylonitrile content of 1 to 50% by weight, preferably 10%
~40% by weight copolymer, number average molecular weight approximately 10,0
A range of 00 to about 1,000,000 is suitable. ■ Acrylic resin: Main component is acrylic acid ester and/or methacrylic acid ester, and optionally contains functional monomers such as acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxypropyl methacrylate, and/or other polymerizable monomers. It is obtained by polymerizing a vinyl monomer component that is a mixture of unsaturated monomers. Examples of the acrylic esters include ethyl acrylate, propyl acrylate, n-butyl acrylate, iso-butyl acrylate, 3-pentyl acrylate, hexyl acrylate, 2-heptyl acrylate, octyl acrylate, 2-octyl acrylate, nonyl acrylate, lauryl acrylate, 2-
Ethylhexyl acrylate, 2-ethylbutyl acrylate, etc. are particularly preferred, and as the methacrylic acid ester, for example, pentyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate, lauryl methacrylate, stearyl methacrylate, etc. are particularly preferred. The static glass transition temperatures of the homopolymers derived from these acrylic esters and methacrylic esters illustrated here are all 0°C or lower, and one or more acrylic monomers selected from these monomers are used. Acid esters and methacrylic esters are suitable as monomers for forming the acrylic resin. Preferably, the acrylic resin has a number average molecular weight in the range of about 5,000 to 1,000,000. ■ Polybutene: Mainly made of isobutylene, mixed with normal butylene if necessary, and obtained by low-temperature polymerization. The number average molecular weight of the resin preferably ranges from about 1,000 to about 500,000. ■ Modified polyolefin resin: For example, chlorinated polyolefin (for example, polypropylene with a chlorination rate of about 1 to 60% by weight) is added to a propylene-ethylene copolymer (the molar ratio is preferably about 40 to 80:60 to 20). 1 to 50 parts by weight, preferably 10 to 20 parts by weight (
Examples include mixtures containing 100 parts by weight of the copolymer. It is generally preferred that the number average molecular weight of these copolymers, chlorinated polyolefins and graft polymers range from about 5,000 to about 300,000. In the present invention, among the above, ■ and ■
Particularly suitable are the following resins. The resins listed above can be used alone or in combination of two or more.

It is important for the above resin (B) that the static glass transition temperature (Tg) of the coating film to be formed is in the range of 0 to -95°C, preferably -30 to -75°C; 0
If the temperature is higher than ℃, the chipping resistance, corrosion resistance, physical performance, etc. of the electrodeposited multilayer film will not be improved, while if it is lower than -95℃, the water resistance, adhesion, etc. of the electrodeposited multilayer film will decrease. Undesirable.

Further, the resin (B) has a surface tension of 25 to 45
dyne/cm, preferably within the range of 28 to 40 dyne/cm. Surface tension is 25dyn
If it is smaller than e/cm, interlayer adhesion between the coating film to be formed and the top coat film will be reduced, and resin (A) and resin (B) will be completely separated into two layers, resulting in poor interlayer adhesion. On the other hand, if the surface tension exceeds 45 dyne/cm, the compatibility with the resin (A) will be too good, making it difficult to form a multilayer film with the desired concentration gradient, and the chipping resistance and corrosion resistance of the coating film will deteriorate. Both results are inferior.

In the present invention, the surface tensions of the resin (A) and the resin (B) used in the cationic electrodeposition paint are within the above-mentioned specific ranges, and the surface tension of the resin (A) is the same as that of the resin (
If the surface tension is larger than that of resin (B), a multilayer film with a concentration gradient can be formed, but preferably the difference in surface tension between resin (A) and resin (B) is 5 dyne/cm or more, more preferably It is practical to select and combine both components so that they fall within the range of 10 to 20 dyne/cm, as it is easy and quick to form a multilayer film. Further, in order to further facilitate the formation of a multilayer film, a combination in which the compatibility between the resin (A) and the resin (B) is incompatible or poorly compatible may be selected. Resin (A) and resin (B)
The compatibility between "incompatible" or "poorly compatible" means the following. That is, resin (A) and resin (B)
were mixed in equal parts by weight, dissolved in an organic solvent, etc., and uniformly air-sprayed onto a Teflon plate to a film thickness of about 70 microns, and then heated at a constant temperature between 160 and 220°C for 15 minutes. When measuring the light transmittance of the isolated film obtained by baking for a certain period of ~60 minutes and cooling it, it was found that ultraviolet rays (wavelength of about 300 millimicrons) and visible light (wavelength of about 500 millimeters) were measured. micron)
This means that the transmittance for each of these values is 0 to about 70%.

The blending ratio of resin (A) and resin (B) is resin (A):resin (B) = 70:30 to 98:2 by weight;
Preferably, it is essential that the ratio be within the range of 70:30 to 95:5; if it is outside this range, a multilayer film with an effective concentration gradient will not be obtained, resulting in poor chipping resistance and corrosion resistance. Become.

[0025] In addition to the resin (A) and resin (B), the cationic electrodeposition paint may contain coloring pigments, anticorrosion pigments, extender pigments, additives, A curing catalyst etc. can be added.

The thickness of the coating film obtained by electrodepositing the cationic electrodeposition paint thus prepared on a suitable substrate (object to be coated) is not strictly limited, but in general,
Based on the cured coating, a range of 5 to 50μ, preferably 10 to 35μ is suitable;
C., preferably at a temperature between 120.degree. C. and 180.degree.

[0027] The method of forming an electrodeposited film on a substrate using such a cationic electrodeposition paint is not particularly limited, and can be carried out using ordinary cationic electrodeposition coating conditions. For example, resin (A) and resin (B) are dispersed in water, then pigments, curing catalysts, and other additives are added as necessary, and the bath concentration (solid content concentration 5 to 40% by weight, preferably A cationic electrodeposition bath is prepared with a concentration of 10 to 25% by weight and a bath pH of 5 to 8, preferably 5.5 to 7. This electrodeposition bath is then used to deposit a 5 cm x 15 cm, e.g.
A carbon plate with a size of ×1 cm is used as an anode, and
When using a zinc phosphate treated steel plate with dimensions of cm x 15 cm x 0.7 mm as a cathode, electrodeposition can be performed under the following conditions. Bath temperature: 20-35℃, preferably 25℃
~30°C DC current Current density: 0.005~2A/cm2, preferably 0.01~1A/cm2 Voltage: 10~
500V, preferably 100-300V, energizing time: 0.
After electrodeposition coating for 5 to 5 minutes, preferably 2 to 3 minutes, the object to be coated is pulled out of the electrodeposition bath and washed with water, and then the moisture contained in the electrodeposition coating can be removed by drying means such as hot air. .

The electrodeposited coating film formed as described above is coated with epoxy resin (A
) has a multilayer structure in which the film-forming resin (B) is preferentially distributed on the surface side.

In the present invention, a top coat may be applied directly to the surface of the electrodeposited coating, but if an excellent finished appearance is required, an intermediate coating may be applied to the surface of the electrodeposition coating. It is preferable to apply a top coat.

[0030] As the intermediate coating, any known intermediate coating that has excellent adhesion, smoothness, sharpness, overbake resistance, weather resistance, etc. can be used. Specifically, an organic solution type thermosetting intermediate coating material whose vehicle main components are a short oil or ultra-short oil alkyd resin with an oil length of 30% or less or an oil-free polyester resin and an amino resin can be mentioned. These alkyd resins and polyester resins have a hydroxyl value of 60 to 140 and an acid value of 5 to 20.
Moreover, it is preferable to use unsaturated oil (or unsaturated fatty acid) as the modified oil, and suitable amino resins include alkyl (1 to 5 carbon atoms) etherified melamine resin, urea resin, benzoguanamine resin, etc. There is. The blending ratio of these should be 65-85% by weight, especially 70-80% by weight of alkyd resin and/or oil-free polyester resin, and 35-15% by weight, especially 30-20% by weight of amino resin, based on the solid weight. is preferred. Furthermore, the above amino resin can be replaced with a polyisocyanate compound or a blocked polyisocyanate compound.

The form of the intermediate coating is preferably an organic solution type, but it may also be a non-aqueous dispersion type, a high solid type, an aqueous solution type, an aqueous dispersion type, etc. using the above vehicle component. In the present invention, the hardness (pencil hardness) of the intermediate coating film is preferably in the range of 3B to 2H. Furthermore, extender pigments, coloring pigments, other paint additives, and the like can be added to the intermediate paint as necessary.

[0032] The coating method for the intermediate coating is not particularly limited, and any known method can be used, such as spray coating, brush coating, dipping coating, electrostatic coating, etc., and the coating film thickness is Generally 10-5 based on cured coating
A range of 0μ, particularly 20 to 30μ, is preferred. The curing method of the intermediate coating film varies depending on its composition, but for example, about 8
Preferably, curing is performed by heating to a temperature of 0 to about 160°C.

[0033] The top coat applied to the surface of the cationic electrodeposition coating or intermediate coating according to the present invention is a coating that imparts cosmetic properties to the object to be coated, and specifically improves the finished appearance (
(image clarity, smoothness, gloss, etc.), weather resistance (gloss retention, color retention, chalking resistance, etc.), chemical resistance, water resistance, moisture resistance,
Any topcoating paint known per se that forms a coating film with excellent curability etc. can be used. Specifically, paints whose vehicle main component is an amino acrylic resin, an amino alkyd resin, an amino polyester resin, or the like are 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 solid type, etc. can be used. The curing of the coating film is
This can be carried out by drying at room temperature, drying by heating, irradiation with active energy rays such as electron beams and ultraviolet rays, and the like. In the present invention, the paint film formed by these top coats preferably has a pencil hardness of 2B or more.

[0034] The top coat used in the present invention is a metallic paint or a solid color finishing paint, which is a paint using the above-mentioned vehicle main component mixed with a metallic pigment and/or a colored pigment, and a clear paint that does not contain any or almost any of these pigments. (Including color clear paint)
are categorized. Then, as a method of forming a top coat film using these paints, for example, ■ Applying a metallic paint containing a metallic pigment, a colored pigment if necessary, or a solid color paint containing a colored pigment. , heated and cured (metallic or solid color finish using one coat, one bake method). ■ After applying metallic paint or solid color paint and curing with heat, apply clear paint and heat harden again (metallic or solid color finish using 2-coat, 2-bake method). ■ After applying metallic paint or solid color paint and then applying clear paint, heat and cure both coatings at the same time (2 coats, 1 coat).
Metallic or solid color finish by baking method).

[0035] These top coatings are preferably applied by spray coating, electrostatic coating, or the like. In addition, the coating film thickness is 25 to 40μ in the above (■) and 25 to 40μ (in the above) based on the dry coating film.
, (2), metallic paints and solid color paints preferably have a thickness of 10 to 30μ, and clear paints preferably have a thickness of 25 to 50μ. Heating conditions can be arbitrarily selected depending on the vehicle components, the material of the object to be coated, etc., but generally it is preferably about 60 DEG to about 140 DEG C., particularly 80 DEG to 140 DEG C., for 10 to 40 minutes.

[0036]

[Effects of the Invention] As described above, the method of the present invention allows the painting process to be simplified, and the resulting paint film has excellent chipping resistance and corrosion resistance, making it suitable for automobiles, motorcycles, etc. It can be widely used in painting.

Next, the present invention will be explained in more detail with reference to Examples. In the present invention, "part" means "part by weight", and "%" means "% by weight". Production Example (A) Production of epoxy cationic electrodepositable resin Production Example 1 Bisphenol A type epoxy resin with an epoxy equivalent weight of 950 [trade name "Epicote 1004", Shell Chemical Co., Ltd.
1,900 parts of butyl cellosolve were dissolved in 993 parts of butyl cellosolve,
After dropping 210 parts of diethanolamine at 80 to 100°C, the mixture was kept at 100°C for 2 hours to obtain an epoxy resin solution (solid content: 68%, primary hydroxyl equivalent: 528, amine value: 53).
A-1) was obtained. The surface tension of the resin is 53 dyne/c
It was m.

Preparation Example 1 To 100 parts of the resin solution (A-1) (solid content: 68 parts),
A resin solution (D-
1).

Preparation Example 2 110 parts of the epoxy resin solution (A-1) (solid content 75
8 parts) of EHPE3150 (epoxy equivalent: 175 to 195, manufactured by Daicel Chemical Industries, Ltd., trade name) as a curing agent.
A resin solution (D
-2).

(B) Production of film-forming resin (B) Production Example 2 A component containing styrene and butadiene in a weight ratio of 30:70 was subjected to emulsion polymerization according to a conventional method to obtain a resin (
B-1) was obtained. The surface tension of this resin is 33dyne/
cm, and the static glass transition temperature was -48°C. Production Example 3 A resin (B-2) was obtained by emulsion polymerization of a component containing acrylonitrile and butadiene in a weight ratio of 30:70 according to a conventional method. The surface tension of this resin is 35d
yne/cm, the static glass transition temperature was -50°C.

Production Example 4 A butadiene homopolymer was produced according to a conventional method, and a resin (B
-3) was obtained. The surface tension of this resin is 31 dyne/c
The static glass transition temperature was -80°C. Production Example 5 Resin (B-4) was obtained by emulsion polymerization of components consisting of 60 parts of nonyl acrylate, 20 parts of 2-ethylhexyl acrylate, 15 parts of methyl acrylate, and 5 parts of hydroxyethyl acrylate according to a conventional method. This resin had a surface tension of 35 dyne/cm and a static glass transition temperature of -48°C.

Production Example 6 Resin (B-5) was obtained by emulsion polymerization of components consisting of 60 parts of hexadecyl acrylate, 20 parts of 2-ethylhexyl acrylate, 15 parts of methyl acrylate, and 5 parts of hydroxyethyl acrylate according to a conventional method. This resin had a surface tension of 35 dyne/cm and a static glass transition temperature of +4°C.

Production of Pigment Paste Production Example 7 4.4 parts of 10% formic acid are added to 14.8 parts of the epoxy resin solution (A-1), and 15 parts of deionized water is added while stirring. Furthermore, 20 parts of titanium white, 1 part of carbon, and 2.5 parts of basic lead silicate were added, and after dispersion in a ball mill for 24 hours, deionized water was added to obtain a paste (P-1) with a solid content of 50%. Production Example 8 Produced in the same manner as Production Example 7 except that 3 parts of dioctyltin oxide was added to the formulation in Production Example 7 above, and the solid content was 5.
A 0% paste (P-2) was obtained.

Preparation of cationic electrodeposition paint bath A cationic electrodeposition paint was prepared using the resin components (A) and (B) and pigment paste obtained in the production example. First, the resin (A) obtained in the preparation example
A resin solution containing resin (B) and resin (B) are mixed based on the mixing ratio (solid content) shown in Table 1, and pigment paste etc. are added to the emulsion obtained by neutralizing with a 10% formic acid aqueous solution as shown in the table. After blending, deionized water was added to obtain a cationic electrodeposition paint bath with a solids content of 20%. Incidentally, all the blending amounts in Table 1 are expressed as solid content.

Examples and Comparative Examples The cationic electrodeposition paint bath obtained above was used to coat an alloy hot-dip galvanized steel sheet treated with zinc phosphate at a bath temperature of 28°C.
Electrodeposition was performed at 00V for 3 minutes and baked at 170°C for 30 minutes to obtain a cured coating film of about 20μ. Next, an intermediate coating material [manufactured by Kansai Paint Co., Ltd., "Amilac N-2 Sealer" (polyester resin paint)] was applied to the surface of the electrodeposited film to a thickness of 25 to 35 μm based on the cured film thickness. 3 at 140℃
It was cured by heating for 0 minutes. This process is referred to as "M-1". Note that the intermediate coating may be omitted. Furthermore, when the electrodeposited coating surface was directly coated or an intermediate coat was applied, a top coat was applied to the intermediate coated surface. This top coat is divided into solid color finish and metallic finish. First, for the solid color finish, use "Magiclon #200 White" [manufactured by Kansai Paint Co., Ltd., product name, thermosetting acrylic resin/amino resin topcoat paint] to a thickness of 30 to 40 μm based on the cured coating. It was coated and cured by baking at 140°C for 30 minutes (one coat, one bake method). This process is referred to as "S". In addition, the metallic finish is "Magicron #300 Silver" [manufactured by Kansai Paint Co., Ltd., trade name, thermosetting acrylic resin/melamine resin/cellulose acetate butyrate resin metallic paint] based on the cured coating film, 15 to 20 μm. Then, without curing the metallic coating film, apply "Magicron #300 Clear" [manufactured by Kansai Paint Co., Ltd., trade name, thermosetting acrylic resin/melamine resin based clear] to the painted surface. 35 to 4 based on the cured coating film
After coating to a thickness of 0 μm, both coatings were cured simultaneously by heating at 140° C. for 30 minutes (two-coat one-bake method). This process is designated as "M". Table 1 also shows the performance test results of the coating film obtained as described above.

[0046]

[Table 1]

[0047] Each test in Table 1 was conducted according to the following method. (*1) Smoothness of electrodeposited surface: The finish of the electrodeposited surface was visually evaluated. ○: Good △: Slightly good

(*2) Chipping resistance: The following chipping resistance test was conducted on a test plate coated according to the method of the present invention, and the salt water spray resistance test was further conducted on the test plate. For chipping resistance test, test equipment: Q-G
-R Gravelometer (product of Q Panel Company); Stone to be sprayed: Crushed stone with a diameter of approximately 15 to 20 m/m; Temperature during test: Attach the test piece to a test piece holding stand under conditions of approximately 20°C. Approximately 500 at a blowing air pressure of approximately 4kg/cm2
After firing ml of crushed stone onto a test piece, the coating surface condition and salt water spray resistance were evaluated. The condition of the painted surface was visually observed and evaluated using the following standard a, and the salt spray resistance was evaluated using the JIS standard.
A salt spray test was conducted using Z2371 for 720 hours, and then an adhesive cellophane tape was applied to the painted surface, and after rapid peeling, the appearance of rust, corrosion state, and peeling of the paint film from the impacted area was visually observed. The following standard b was followed. a. Painted surface condition ◎ (very good): Some scratches on the top coat due to impact,
Alternatively, only slight peeling was observed between the top coat and intermediate coat, and no peeling of the electrodeposited coat was observed at all. ○ (Good): There is some peeling between the top coat and intermediate coat, and very slight peeling of the electrodeposition coat itself is observed. Δ (slightly poor): A lot of peeling was observed between the top coat and intermediate coat or between the electrodeposition coating, and peeling of the electrodeposition coating itself was also observed here and there. × (Poor): The top coat and intermediate coat were considerably peeled off, and the electrodeposition coat itself was significantly peeled off. b. Salt spray resistance ◎: No rust, corrosion, or peeling of the paint film is observed. ○: Rust, corrosion, and paint peeling are slightly observed. Δ: Slightly more rust, corrosion, and peeling of the paint film are observed. ×: Significant rust, corrosion, and paint peeling occurred.

(*3) Water resistance: The coated surface is evaluated after being immersed in water at 40°C for 10 days. ◎
There is no abnormality. (*4) Corrosion resistance: Cross-cut scratches are made on the coating film with a knife to reach the base material, and then
) The extent of rust and blisters from knife scratches was measured after 480 hours of testing using a salt spray tester similar to that used in the above. ○: less than 1.0 mm △: 1.0 to less than 3.0 mm ×: 3.0 mm or more

Claims (3)

[Claims] Claim 1: (A) Surface tension is 40 to 60 dyne
/cm of epoxy cationic electrodepositable resin, and (B
) A film-forming resin having a surface tension of 25 to 45 dyne/cm and a static glass transition temperature of the formed coating film of 0 to -95°C is used as resin (A): resin (B) = 70:30 to 9.
A cationic electrodeposition paint containing a weight ratio within the range of 8:2 and in which the surface tension of the resin (A) is higher than that of the resin (B) is applied, and after curing by heating, a top coat is applied to the coated surface. A painting method characterized by painting. 2. The cationic electrodeposition paint comprises a resin (A).
Contains an epoxy resin having an average of two or more epoxy group-containing functional groups per molecule, in which an epoxy group is bonded to an alicyclic skeleton and/or a bridged alicyclic skeleton, as a curing agent. The coating method according to claim 1. 3. After applying the cationic electrodeposition paint according to claim 1 or 2, and then applying an intermediate paint to the coated surface,
A painting method characterized by applying a top coat to the intermediate coated surface.