JP2003181368A - Method for forming multilayer coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide physical property values giving excellent chipping resistance and a coating material having excellent chipping resistance in a method for forming a multilayer coating film by 3C1B. <P>SOLUTION: In the method for forming a coating film by coating a first color base coating (A), a second color base coating (B), and a clear coating (C) by the wet on wet method, and then crosslinking and curing the multilayer coating film comprising the three layers by heating the layers at the same time, the cured coating film at -20 of the first color base paint (A) has a Young's modulus (a) of 3,000 MPa or more and a breaking energy (b) of 2×10<SP>-3</SP>J or more. In the physical property values of the first color base coating (A), the molecular weight between crosslinks (c) is 300 g/mol or less, and the bond strength (d) between the first color base coating (A) and an undercoating film is 13-18 N. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the formation of a 3C1B automobile coating film in which a colored first base paint, a colored second base paint, and a clear paint are sequentially applied to an object to be coated,
The present invention relates to a method for forming a multilayer coating film, which has good chipping resistance, interlayer adhesion, and finish.

[0002]

2. Description of the Related Art As a method for forming a coating film on an automobile body, after electrodeposition coating is applied to an object to be coated, a colored first base paint, a colored second base paint, and a clear paint are applied by wet-on-wet. As a method for simultaneously baking and curing an uncured coating film composed of three layers to form a coating film, a 3-coat 1-bake method (3C1B) is widely known. (For example, JP-A-10-328615, 1
(See JP-A 1-10067, JP-A-11-10081, etc.) Since this 3-coat 1-bake method requires one baking of the coating film, it has an energy-saving effect such as omission of drying equipment, and is suitable for many automobile coating lines. Is expected to be applied. But,
Since three layers of paint are applied and baking is performed once, chipping peeling (peeling) is likely to occur between layers of the coating film when pebbles or the like are flipped up while the vehicle is running, and in particular, Delamination between the colored first base paint and the electrodeposition coating film was observed.

There has been a demand for improvement in the chipping resistance, but it is not possible to ascertain the specific characteristics of these multilayer coating films that have good chipping resistance, and the paint formulation (base resin, curing agent, A lot of time was spent investigating factors such as types and amounts of additives, catalysts and pigments.

Therefore, in the line to which the 3C1B multi-layer coating film is applied, line conditions (for example, baking temperature and time, direct drying furnace or indirect drying furnace, exhaust equipment in dryer, setting time, etc.) and vehicle type of automobile body Due to (differences in heat capacity, types of steel plates, thicknesses of steel plates, etc.), the chipping resistance may not be as expected or may vary. Therefore, it has been demanded to easily find a multilayer coating film having good chipping resistance and develop a coating material having the performance.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in order to achieve the above-mentioned target, and as a result, in the coloring first base (A) in the coating process of 3C1B, the coating film physical property values are within the following ranges. It was found that a coating film having good chipping resistance can be obtained by setting the above.

That is, the present invention is as follows: The colored first base paint (A), the colored second base paint (B) are applied, and the clear paint (C) is applied wet-on-wet, and then a multilayer coating film consisting of three layers is simultaneously heated and crosslinked. In the method of forming a coating film for curing, -2
A colored first base paint (A) having a Young's modulus (a) of the cured coating film of the colored first base paint (A) at 0 ° C. of 3000 MPa or more and a breaking energy (b) of 2 × 10 ⁻³ J or more. 1. A method for forming a multi-layer coating film for coating, Further, in the coating film physical property value of the colored first base coating material (A), the multilayered coating film formation according to item 1, wherein the colored first base coating material (A) having an inter-crosslinking molecular weight (c) of 300 g / mol or less is applied. Method, 3. Furthermore, in the coating film physical property value of the colored first base coating material (A), a colored first base coating material (A) having an adhesion strength (d) between the colored first base coating material (A) and the undercoat coating film of 13 to 18 N is used. 3. The method for forming a multilayer coating film according to item 1 or 2 for coating; The base resin in the colored first base paint (A) has an acid value of 5 to 100 mgKOH / g and a hydroxyl value of 10 to 150.
Colored first base paint (A) in the range of mgKOH / g
4. The method for forming a multilayer coating film according to any one of 1 to 3 above, wherein 5. The colored first base paint (A) contains any one of the addition products of at least one or more 2-hydroxyethyl (meth) acrylate and caprolactone in a monomer component constituting a resin. 5. The method for forming a multilayer coating film according to item 6. The method for forming a multilayer coating film according to any one of items 1 to 5, wherein the colored first base coating material (A) contains talc in the formulation.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the present invention, in the multi-layer coating film in 3-coat 1-bake (3C1B) having good chipping resistance, the coating physical properties of the colored first base coating material (A) should be within the ranges shown by the following. Found that can be obtained by.

[0009]. The Young's modulus (a) of the cured coating film of the colored first base coating material (A) is 3000 MPa or more, and the breaking energy (b) is 2 × 10 ⁻³ J or more. ． More preferably, the cured cross-linked molecular weight (c) of the colored first base coating material (A) is 300 g / mol or more. ． More preferably, the adhesion strength (d) between the colored first base coating material (A) and the undercoat coating film is in the range of 13 to 18N.

A three-coat one-bake (3C1B) coated automobile body is formed by galvanizing a steel sheet or a cold-rolled steel sheet, press-molding it, and then degreasing and chemical-converting it. After coating and forming an electrodeposition coating film, a colored first base paint (A) and a colored second base paint (B) are applied thereon, and further a clear paint (C) is applied wet-on-wet By baking and drying, a multi-layer coating film consisting of three layers can be obtained. This 3
The C1B process has been used in many automobile coating line processes from the viewpoint of energy saving in terms of the baking process being required only once and obtaining a new design property.

Further, chipping is a phenomenon in which a coating film is peeled off from a plated surface of a steel plate or between layers of the coating film when a stone thrown up by a wheel of an automobile collides with a vehicle body, and the plated surface is exposed. By doing so, rust may be generated on the vehicle body to promote corrosion. Regarding the improvement of the chipping property, a three-layer coating consisting of a colored first base coating (A), a colored second base coating (B), and a clear coating (C) formed on an electrodeposition coating is a stone. When a shock such as is received from the outside, a coating with good chipping property by absorbing the shock (shock absorption type) or a film with good chipping property by spreading the shock between the coatings (shock diffusion) Type).

As a result of earnest studies for improving the chipping resistance, the impact absorption effect and the impact diffusion are determined by defining the coating film physical properties (coating viscoelasticity, adhesion) of the colored first base coating material (A). It has been found that an effective coating film can be obtained.

Physical Properties of Coating Film (Viscoelasticity and Adhesiveness of Coating Film ) Information obtained by measuring the physical properties of the coating film is related to not only the mechanical strength of the coating film but also the adhesion and corrosion resistance of the coating film. Wide range. Furthermore, in recent years, since improvement in chipping resistance has been demanded in coating films as well,
It has become important to measure physical properties of coatings (viscous elasticity and adhesive strength of coatings).

Viscoelasticity measurement is classified into a static measurement method and a dynamic measurement method. As a static measurement method, a tensile tester known by a trade name such as Tensilon or Autograph is used.
As a dynamic measurement method, FT Rheospectr DVE-V4 manufactured by Rheology Co., Ltd. is mentioned as a trade name. In addition, as a measure of the adhesiveness of the coating film, SAI by the circus method
CAS BN-1 (manufactured by Daipla Wintes Co., Ltd.
Product names, surface-interface physical property analyzers, etc. may be mentioned.

1. Young's modulus (a), breaking energy
(B) As a static viscoelasticity measuring method, Tensilon UTM-II (100 g to 20 kg) manufactured by Orientec Co., Ltd., Autograph AG2000B manufactured by Shimadzu Corporation, or the like can be used. The device consists of a chuck that moves up and down by two feed screws. The two chuck sample coatings are fixed, and one of the chucks moving up and down is moved at a constant speed to extend the sample. From the relationship between stress and strain at this time, Young's modulus (A), Young's module
s is required.

When the strain is further increased, the strength of the coating film reaches its limit and is destroyed, resulting in a fracture stress (Tensile).
strength) is required. The fracture energy (b) is obtained from the area of the stress-strain curve.

Here, as the physical property value of the coating film having good chipping resistance, the cured coating film of the colored first base coating material (A) is -20.
It was found that the Young's modulus (a) measured at 0 ° C. was 3000 MPa or more and the breaking energy (b) was 2 × 10 ⁻³ J or more. The higher the Young's modulus (a), the greater the impact absorption, and the larger the breaking energy (b), the greater the effect of dispersing the impact.

The Young's modulus (a) and the breaking energy (b) are measured by coating a paint on a tin plate to a thickness of 30 μm and then applying a predetermined condition, for example, at 140 ° C. for 30 minutes.
The coating film cured by heating for a minute was peeled off from the tin plate by an amalgam method, and at -20 ° C, a Tensilon meter manufactured by Orientec Co., Ltd. or an autograph AG manufactured by Shimadzu Corporation.
It was measured using 2000B.

2. Molecular weight between crosslinks (c) Young's modulus (a) and breaking energy (b) are physical properties of the coating film with good chipping resistance in a multilayer coating film of 3C1B.
In addition, it is more preferable that the cured coating film of the colored first base coating material (A) has a molecular weight (c) between crosslinks of 300 g / mol or less.

Here, as a dynamic measuring method of coating film viscoelasticity,
It is possible to know the mechanical damping term of the coating as a viscous body by applying a periodic microstrain to the coating and measuring the response to it. When a cyclic strain is applied to the coating film, if it is a perfect elastic body, there will be no time delay in response to it, and it will appear in the same phase. But,
The presence of viscous elements delays the response. The strain and stress with the time delay are expressed as a complex elastic modulus G ^* , and are separated into a real part and an imaginary part on the complex plane. The real part G'is the elastic modulus (storage elastic modulus) of the sample, the imaginary part G "represents the dynamic loss (loss elastic modulus) due to the viscous element, and its ratio is the loss tangent (Loss tangent).
, G ^* = G '+ G "and tan δ = G" / G'.

For example, as an instrument capable of measuring dynamic viscoelasticity, FT Rheospectra DVE-V4 manufactured by Rheology Co., Ltd.
The strain cycle may be 0.1 to 999 Hz, and the temperature range is −150 ° C. to 40 ° C.
The measurement can be continuously performed while changing the temperature in an arbitrary temperature range of 0 ° C. and also changing the frequency. The result measured at a constant frequency (for example, 110 Hz) is displayed as a change in elastic modulus with temperature.

When the polymer main chain in the coating film starts thermal vibration, the storage elastic modulus decreases, and the maximum value of the loss tangent (tan δ), which is a viscous element, is obtained for the elastic modulus. The dynamic Tg can be known as the inflection point from the glass region to the rubber region at the measurement frequency. Further, the molecular weight between crosslinks (c) is obtained from the minimum value of the storage elastic modulus in the rubber region by the equation (1) obtained by applying the glass transition temperature (Tg) value to the following theoretical formula of rubber viscoelasticity such as Flory. You can Molecular weight between crosslinks (c) = 3ρ RT / E _min Formula (1) (where R = 8.13 × 10 ⁷ (evg / Kmol), T =
Temperature (K) at the minimum elastic modulus, ρ = density (g / cm) of the sample coating film, generally 0.5, E _min = minimum elastic modulus (dyne / cm) in the high temperature region. ).

3. Adhesive strength (d) The adhesive strength (d) was measured according to the SAICAS method. (Evaluation of adhesion strength of adherend by SAICAS method (1) Coating technology, 34, 4, 123 (1995), S
Adhesive strength evaluation of adherend by AICAS method (2) Coating technology, 34,5,129 (1995) or above, written by Itsuo Nishiyama
(See Fig. 1)
It is composed of a cutting blade that displaces in the vertical direction, a vertical displacement meter, and a horizontal force detector.

In the measurement, as shown in FIG. 1, when the cutting blade is moved while being pressed against the surface of the coated surface with a predetermined load, the cutting blade cuts inward from the surface of the coated surface. When the cutting edge reaches the vicinity of the interface, the cutting edge is locked or the balance load is adjusted to separate the coating film from the substrate. The graph obtained by the measurement shows the horizontal force (F _H : cutting force or peeling force) and vertical displacement (D _H ) of the cutting edge.
v) From the data, the F _H pattern shown in FIG. 2 is obtained. Shear strength is obtained at the cutting step in FIG. 2, and adhesion strength (d) is obtained at the coating film separating step.

In the present invention, in addition to Young's modulus (a) and breaking energy (b), the peel strength (P) of the colored first base paint (A) is more preferable as the physical properties of the coating film having good chipping resistance. The adhesion strength (d) is 13 to
The range is 18N.

The peel strength by the SAICAS method is a force required for separating (peeling) the coating film per blade width, and is represented by the formula (2). P = F _H / w Formula (2) (P: Peel strength (N / m), F _H : Horizontal force (N), w:
Blade Width (m)) Saicus BN-1 (manufactured by Daipla Wintes Co., trade name, surface-interface physical property analyzer) was used for the measurement of the present invention, on an Electron GT-10LF electrodeposition coating film of 20 μm. Then, apply the colored first base paint (A) to 30 μm and
What was baked at 40 ° C. for 20 minutes was measured. Next, each coating material for forming a multilayer coating film, particularly the colored first base coating material, which is a feature of the present invention, will be described.

Colored First Base Paint (A) The colored first base paint (A) is a multi-layer coating film consisting of three layers.
It is a colored paint that is applied on the electrodeposition surface and can be used in either organic solvent type or water-based, and known thermosetting paints containing resin component, curing component, pigment and organic solvent or water are applied. it can. As the resin component, at least one substrate selected from acrylic resin, vinyl resin, polyester resin, alkyd resin, urethane resin, etc., having a crosslinkable functional group (eg, hydroxyl group, epoxy group, carboxyl group, alkoxysilane group, etc.) Resin, the base resin has an acid value of 5 to 1
00 mgKOH / g, preferably 20-80 mgKOH
/ G, a hydroxyl value of 10 to 120 mgKOH / g, preferably 30 to 90 mgKOH / g in terms of chipping resistance.

As the monomer constituting the resin, a hydroxyl group-containing unsaturated monomer is, for example, a monoester of acrylic acid or methacrylic acid such as hydroxyethyl (meth) acrylate or hydroxypropyl acrylate and glycols having 2 to 10 carbon atoms. And the like. These can be used alone or in combination of two or more. The carboxyl group-containing unsaturated monomer is, for example, acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid,
Further, among these, half monoalkyl (suitably having 1 to 10 carbon atoms) ester of dicarboxylic acid and the like can be mentioned, and these can be used alone or in combination of two or more.

Other unsaturated monomers can be used without particular limitation as long as they can be copolymerized with the above monomers. Specifically, an addition product of 2-hydroxyethyl (meth) acrylate and caprolactone,
(For example, as trade names of Daicel Chemical Industries, Ltd., Praxel FA, Praxel FM2, Praxel F
It is preferable to include FM series such as M3) for improving the physical properties of the coating film, that is, for improving the chipping resistance.

It is considered that the inclusion of the FM series monomer in the resin contributes to the improvement of the crosslink density of the coating film formed and the adhesion to the substrate. In addition, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, pentyl acrylate, pentyl methacrylate, hexyl acrylate, hexyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, lauryl Monoesters of acrylic acid or methacrylic acid such as acrylate and lauryl methacrylate with monoalcohols having 1 to 24 carbon atoms, glycidyl acrylate and radically polymerizable unsaturated monomer containing glycidyl group, acrylonitrile, acrylamide, N-methylacrylamide , N-methylol acrylamide, N-butoxymethyl acryl And dimethyl aminoethyl nitrogen-containing radical-polymerizable unsaturated monomers such as methacrylate, styrene, phenyl ethyl (meth) acrylate, vinyl acetate, vinyl chloride, and the like. These can be used alone or in combination of two or more.
Alternatively, it may be polymerized with a crosslinkable monomer such as allyl methacrylate or 1,6-hexanediol diacrylate.
As the curing component, one or more crosslinking agent components selected from alkyl etherified melamine resin, urea resin, guanamine resin, polyisocyanate compound which may be blocked, epoxy compound, carboxyl group-containing compound and the like are used. And the resin component is 5 based on the total weight of both components.
It is preferable to use 0 to 90% and the curing component together in a ratio of 50 to 10%.

As the pigment, usual paint pigments can be used, for example, titanium oxide, zinc white, carbon black,
Cadmium red, molybdenum red, chrome yellow,
Inorganic or organic solid color pigments such as chromium oxide, Prussian bull, cobalt bull, azo pigment, phthalocyanine pigment, quinacridone pigment, isoindoline pigment, slene pigment, and perylene pigment; scaly aluminum, mica, Metallic pigments such as mica and mica-like iron oxide surface-coated with metal oxides;

In the pigment component, talc (Mg ₃ Si ₄
It was found that the inclusion of O ₁₀ (OH) ₂ was effective in improving the chipping resistance. It has been found that the physical properties of the coating film also fall within the range described above as being effective for improving the chipping resistance of 1-3. The reason for this is that talc has a flaky shape, which is thought to have an effect of absorbing impact and dispersing impact.

The addition amount of talc in the colored first base coating material is preferably in the range of 0.1 to 20 parts with respect to the resin solid content, and when it exceeds 20 parts, the coating film formed becomes hard, so that chipping resistance is obtained. May decrease, which is not preferable.

Further, the colored first base coating material (A), if necessary, a light interference pigment, an extender pigment, a dispersant, an anti-settling agent,
Specific examples of organic solvents, catalysts for urethanization reaction (such as organotin compounds), defoamers, thickeners, rust preventives, UV absorbers, surface conditioners, and curing catalysts for promoting crosslinking reactions Examples include tin octylate, dibutyltin di (2-ethylhexanoate), dioctyltin di (2-ethylhexanoate), dioctyltin diacetate, dibutyltin dilaurate, dibutyltin oxide, monobutyltin trioctate, 2-ethylhexyne. Organometallic compounds such as lead acid and zinc octylate can be appropriately blended. The amount of these curing catalysts used can be arbitrarily selected,
0.005 to 5 per total solid content of resin component and curing component
A range by weight, especially 0.01 to 3% by weight, is suitable.

To apply the colored first base paint (A), the viscosity of the colored first base paint (A) is 13 to 16 seconds (for
(Dup cup # 4/20 ° C), the solid content is adjusted to 20 to 40% by weight, and the solid content is adjusted by airless spray, air spray, electrostatic coating, etc. Directly or undercoat paint such as cationic electrodeposition paint on the metal or plastic object to be coated, and then on the cured surface to be coated.
Colored second base paint (B) for further forming a second colored coating film in a state of standing at 100 ° C. for several minutes or in an uncured state
To paint.

[0036] As colored coating of the colored second base paint (B) colored second base paint (B), solid color - coating and the like metallic coating film and the like, coloring either it through coating film No. (1) A colored transparent coating film having a transparency such that the solid color of the base coating film or the metallic coating film surface can be visually recognized.

Second colored film for forming a second colored coating film
As the base paint (B), a known thermosetting paint containing a resin component, a color pigment and a solvent as main components can be applied. As these resin components, color pigments and solvents, those exemplified in the above-mentioned colored first base coating material (A) can be preferably used.

The coating of the colored second base coating material (B) has a viscosity of the colored second base coating material (B) of 13 to 16 seconds (Food cup # 4/20 ° C.) and a solid content of 20 to 40 weight. % To the airless spray, air spray,
It is applied to the uncured colored first base coating film surface so that the thickness of the cured coating film is about 10 to about 20 μm by electrostatic coating,
After leaving for several minutes at room temperature to 100 ° C. as necessary, or in an uncured state, a clear paint (C) for forming a clear coating film is applied.

Clear paint (C) : The clear paint is a paint which does not substantially contain a coloring pigment, and a solid color of a colored first coating film and a colored second coating film through the coating film. Alternatively, it is a colorless transparent coating film having a transparency that allows the metallic coating film surface to be visually recognized.

As the clear coating material (C) for forming a clear coating film, known thermosetting clear coating materials containing a resin component and a solvent as main components can be applied, but in particular, acid resistance, stain resistance, and scratch resistance. It is preferable to use a paint having excellent properties. As the resin component and the solvent, those shown in the colored first base coating material (A) can be preferably used.

The clear paint (C) has a viscosity of 20 to 40 seconds (fod cup # 4/20 ° C.) and a solid content of 40.
-60% by weight, and apply it to the uncured second colored coating film surface by airless spray, air spray, electrostatic coating, etc. so that the thickness of the cured coating film is about 30 to about 60 μm. Then, after leaving at room temperature to 100 ° C for several minutes, if necessary, about 100 to about 180 ° C, preferably about 120 to about 1
By heating at 60 ° C. for about 10 to about 40 minutes, the colored first coating film, the colored second coating film and the clear coating film are simultaneously cross-linked and cured (3C1).
By carrying out B), a multilayer coating film consisting of three layers is formed.

The baking condition of the coating film after coating is that it can be heated and cured at a temperature of about 80 to about 170 ° C., preferably about 120 to about 160 ° C. for about 20 to about 40 minutes,
As a heating method, a commonly used method, for example, hot air heating, infrared heating, high frequency heating or the like is used.

[0043]

EFFECTS OF THE INVENTION In a 3C1B multilayer coating film obtained by applying the first colored base coating material (A), the second colored base coating material (B), and the clear coating material (C) wet-on-wet, chipping resistance is improved. As a good condition, it was found that the coating properties of the first colored base coating material (A) are as follows. ． Young's modulus (a) of the cured coating film of the colored first base coating material (A) at −20 ° C. is 3000 MPa or more, and breaking energy (b) is 2 × 10 ⁻³ J or more. ． Further, the molecular weight (c) between crosslinks is 300 g / mol or less. ． Further, the adhesion strength (d) between the colored first base coating material (A) and the undercoat coating film is in the range of 13 to 18N. Satisfying these coating film physical property values is proof that the coating film has the ability to absorb impact when an external force such as pebbles is applied to the automobile coating film, or to diffuse the impact. Therefore, it is considered that the chipping resistance is good.

[0044]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to this. "Parts" and "%" mean "parts by weight" and "% by weight".

Acrylic resin solution No. Production Example 1 of Example 1 To 60 parts of butyl cellosolve heated to 120 ° C., the monomer component 1 was added for 3 hours and copolymerized to give an acid value of 40.
mgKOH / g, hydroxyl value 52 mgKOH / g, and number-average molecular weight about 10,000, acrylic resin solution No. 70 having a solid content of 70%. Got 1. "Monomer component 1" Methyl methacrylate 30 parts Ethyl methacrylate 23 parts Butyl methacrylate 30 parts Hydroxyethyl methacrylate 12 parts Methacrylic acid 5 parts FM-3 (Note 1) 15 parts α, α'-azobisisobutyronitrile 2 parts (Note 1) FM-3 (manufactured by Daicel Chemical Industries, Ltd., trade name,
Addition product of 2-hydroxyethyl (meth) acrylate and caprolactone).

Acrylic resin solution No. Production Example 2 of 2 To 50 parts of Swazol # 1000 (manufactured by Maruzen Petroleum Co., Ltd., trade name, organic solvent) heated to 120 ° C., “monomer component 2” was added for 3 hours and copolymerized to give an acid value of 40 m.
gKOH / g, hydroxyl value 130 mgKOH / g, and number-average molecular weight about 6000, solid content 70% acrylic resin solution No. Got 2. "Monomer component 2" Styrene 30 parts Butyl acrylate 35 parts 2-Ethylhexyl methacrylate 10 parts 2-Hydroxyethyl acrylate 25 parts α, α'-azobisisobutyronitrile 4 parts

[0047]

[Table 1]

(Note 6) Cymel 325: Mitsui Cytec Co., Ltd., trade name, imino group-containing melamine resin) (Note 7) Duranate MF-K60X: Asahi Kasei Corporation, trade name, 60% urethane resin (Note 8) Leocon Agent: Acrylic resin microgel, particle size of about 80 nm (Note 9) CR-95: Ishihara Sangyo Co., Ltd., trade name, Titanium White MICRO ACE S-3: Nippon Talc Co., Ltd., trade name,
Talc (Note 11) Carbon MA-100: trade name, carbon black manufactured by Mitsubishi Chemical Corporation.

Production Example of Colored Second Base Paint 75 parts (solid content) of hydroxyl group-containing acrylic resin (hydroxyl value 70, acid value 14, number average molecular weight 30000), 25 parts of methyl-butylated mixed ether melamine resin (solid) Min), C
30 parts of AB (solid content) and 10 parts of flaky aluminum flakes coated with a phosphoric acid group-containing compound (Note 12) (solid content) are mixed and dispersed in toluene / xylene (equal weight mixture) to obtain a viscosity. For 10 seconds (Forward cup # 4/20
C.) and the solid content was adjusted to 5 to 8% to obtain an organic solvent type colored second base paint. (Note 12): Phosphate group-containing compound in 100 parts of flaky aluminum flakes having a thickness of 0.03 to 0.1 μm, an aspect ratio of 150 to 250, and a longitudinal dimension of 10 to 20 μm.

Clear paint (C) Magiclon MG # 7100 clear (manufactured by Kansai Paint Co., Ltd.,
A commercial product, acrylic resin-melamine-curable organic solvent type clear paint) was used and applied over the colored first base paint and the colored second base paint.

Examples and Comparative Examples Example 1 Preparation of isolated film: No. 1 colored base paint prepared in Production Example. 1 to coat the film thickness to 30μm, 140
It was baked and dried at 30 ° C. for 30 minutes. The coating film was peeled from the tin plate by the mercury amalgam method to obtain a coating film for physical properties of the coating film. Preparation of multi-layer coating film: Electron GT-10LF gray (manufactured by Kansai Paint Co., Ltd., trade name, cation) using cold-rolled steel plate that has been subjected to Palbond # 3020 (trade name, manufactured by Nippon Parkerizing Co., Ltd., zinc phosphate chemical conversion treatment) Electrodeposition coating) is applied to a film thickness of 20 μm, and 170
It was heated at 0 ° C. for 20 minutes to be crosslinked and cured to obtain a coating object. On top of that, the colored first base paint No. 1 was applied to 30 μm. Further, after leaving the coated plate at room temperature for 3 minutes, the colored second base paint No. 1 was applied to 20 μm.
Next, MagiClone MG # 7100 was applied to a film thickness of 40 μm, and baked and dried at 140 ° C. for 30 minutes to form a multi-layer coating film consisting of three layers.

Comparative Examples 1 to 4 In the same manner as in Example 1, the combinations shown in Table 2 were used to prepare isolated films for coating film physical properties and multilayer coating films. The test results are also shown.

[0053]

[Table 2]

(Note 13) Tensilon (Young's modulus, breaking energy): Tensilon UTM-II (manufactured by Orientec Co., trade name , Tensile tester) 3
Apply a load of 9.2 N (4 kgf) to pull the coating film,
Young's modulus and breaking energy were measured.

(Note 14) Molecular weight between crosslinks: FT Rheospectra DVE-V4 (trade name, dynamic viscoelasticity measuring device, manufactured by Rheology Co., Ltd.) was used, and the strain cycle was 110.
The cross-linking molecular weight was determined by the equation (1) obtained by applying the value of the glass transition temperature (Tg) to Flory's theoretical theory of rubber viscoelasticity while changing the Hz and the temperature range from 20 ° C. to 200 ° C. Molecular weight between crosslinks (c) = 3ρRT / E _min Formula (1).

(Note 15) Adhesion strength:
The peel strength (F _H ) measured using SAICAS BN-1 (manufactured by Daipla Wintes Co., Ltd., trade name, surface-interface physical property analyzer) was taken as the adhesion strength.

(Note 16) Finishability: Evaluated visually.
The case where the gloss and smoothness were excellent was evaluated as ◯, and the case where these were inferior was evaluated as Δ.

(Note 17) Chipping resistance: US QP
ANEL Co., Q-G-R Gravelometer (chipping test device) with a test plate installed on the sample holder, -20 ℃
In this case, 100 g of crushed granite stone with a grain size of 7 was sprayed on the coated surface with compressed air of 0.392 MPa (4 kgf / cm ² ) and the degree of occurrence of scratches on the coating film due to this was visually observed and evaluated. Is small, and the coating film of the colored first base paint is exposed. △: The size of the scratch is small, but the base steel plate is exposed. ×: The size of the scratch is considerably large and the base steel plate is also exposed. is doing.

(Note 18) Impact resistance: Using a Du Pont impact tester, load of 500 g, 1/2 inch (about 1
The test was carried out with a hitting point of 2.7 mm). The drop height at which the coating film was cracked at that time was measured.

[0060]

[Brief description of drawings]

[Figure 1] Model diagram of Saikas measurement equipment

[Fig. 2] Circus measurement chart

[Explanation of symbols]

1. Vertical displacement meter 2. Horizontal force (F _H ) 3. Vertical displacement (Dv) 4. Coating film 1 5. Coating film 2 6. Cutting direction 7. Peeling force 8. Cutting step 9. Paint film separation stage

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4D075 AE12 BB26Z BB91Z CA03                       CA04 CA13 CA33 CB06 DA06                       DC12 EA43 EB14 EB15 EB19                       EB20 EB22 EB32 EB33 EB35                       EB38 EB45 EB55 EC01 EC11                 4J038 CD001 CG001 CG142 CH122                       CH162 DD001 DG001 GA03                       GA06 HA536 NA11 PA19                       PB03 PB07 PC02

Claims (6)

[Claims] 1. A colored first base paint (A), a colored second base paint (B) are applied, and a clear paint (C) is applied wet-on-wet. In the coating film forming method of simultaneously heating and crosslinking curing, Young's modulus (a) of the cured coating film of the colored first base coating material (A) at −20 ° C. is 3000 MPa or more, and breaking energy (b) is 2 × 10 ^−. Coloring 1 that is ³ J or more
A method for forming a multilayer coating film, which comprises coating a base coating material (A). 2. In the coating film physical properties of the colored first base coating material (A), the molecular weight between crosslinks (c) is 300 g / mo.
The method for forming a multilayer coating film according to claim 1, wherein the colored first base coating material (A) having a ratio of 1 or less is applied. 3. The colored first base, wherein the adhesion strength (d) between the colored first base paint (A) and the undercoat is 13 to 18 N in the coating film physical property value of the colored first base paint (A). The method for forming a multilayer coating film according to claim 1 or 2, wherein the coating material (A) is applied. 4. The acid value of the base resin in the colored first base coating material (A) is 5 to 100 mgKOH / g, and the hydroxyl value is 1.
The method for forming a multilayer coating film according to any one of claims 1 to 3, wherein the colored first base coating material (A) in the range of 0 to 150 mgKOH / g is applied. 5. The colored first base coating composition (A) contains an addition product of at least one or more 2-hydroxyethyl (meth) acrylate and caprolactone in a monomer component constituting a resin. 5. The method for forming a multilayer coating film according to any one of 4 above. 6. The method for forming a multilayer coating film according to claim 1, wherein the colored first base coating material (A) contains talc in the composition.