JP3128342B2 - Transparent anticorrosive thick film coating composition and method for forming transparent coating film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a road surface made of an aluminum alloy and applied to a metal background to prevent corrosion of the metal without impairing the transparency of the metal background before the application and to prevent adhesion by external impact. The present invention relates to a transparent anticorrosive thick-film coating composition capable of preventing inhibition and making a coating surface smoother than a metal background surface, and a method for forming a transparent coating film.

[0002]

2. Description of the Related Art In recent years, the proportion of automobile parts such as wheels, brake cylinders, radiators, and the like made of aluminum-based light alloys has been increasing in accordance with the demand for reducing the body weight. In particular, the so-called aluminum wheels in which the wheels are formed of an aluminum-based alloy have been remarkably popularized and widely used.

Generally, an aluminum wheel is formed into a wheel shape by means of casting, forging, or the like of an aluminum alloy. A small piece of metal, such as a stainless steel alloy, is struck against a molded aluminum-based alloy for the purpose of removing the mold release agent and oxide film remaining on the surface and uniformizing the surface roughness (hereinafter, abbreviated as a shot step, and is referred to as an aluminum-based alloy formed in the shot step) The surface of the alloy is called a shot surface). Then, necessary parts are cut for mounting on the axle, mounting of tires, and design (hereinafter, abbreviated as a cutting process, and a surface for the design generated in the cutting process is referred to as a cut surface).

[0004] When coating an aluminum wheel that has undergone a cutting step, the surface of the aluminum wheel is usually subjected to chromate chromate treatment in order to improve the adhesion of the paint and to enhance the corrosion resistance of the painted surface. While the corrosion resistance of chromate chromate treatment is strong, the chromate treatment of aluminum wheels that use the metallic luster of the cut surface for design is suppressed to the extent that it does not visually discolor because the aluminum wheel surface is colored. Since chromate chromate treatment of an aluminum wheel that does not use the metallic luster of the cut surface for design is also performed under the same treatment conditions, there is a limit in ensuring the corrosion resistance of the painted surface of the aluminum wheel by the chromate chromate treatment.

[0005] An aluminum wheel that has been subjected to chromate chromate treatment is coated on the entire surface or a part of the aluminum wheel in order to impart corrosion resistance, cosmetics, and weather resistance.

[0006] The shot surface is usually coated with a thermosetting synthetic resin enamel paint (hereinafter abbreviated as a colored paint) containing a color pigment, a metal powder pigment, a rust preventive pigment, an extender pigment, etc., and then thermally cured.

[0007] The cut surface is painted depending on whether the metallic luster is used for a design (hereinafter referred to as a brilliant specification and the surface is referred to as a brilliant surface) or not (hereinafter referred to as a colored specification and the surface is referred to as a colored surface). And the coating process used are different.

[0008] In the case of a colored specification, a colored paint is usually applied at the same time as the shot surface and then heat-cured, and thereafter, a thermosetting synthetic resin clear paint (hereinafter referred to as a clear paint) containing a surface conditioner, an antioxidant, an ultraviolet absorber and the like. (Abbreviated as paint) is applied once and thermally cured.

In the case of the brilliant specification, an acute portion (hereinafter abbreviated as an edge portion) formed at the boundary between the shot surface and the cut surface in the cutting process is covered with a coating film so as to provide corrosion resistance, aesthetics, and weather resistance. As a method of applying the transparent paint to be applied, for example,
Japanese Patent Publication Nos. 64-70175 and 3-74147 and JP-A-64-4660 and JP-A-1-149868 as coating compositions.
No. 2,250,999, etc., and as a coating film, Japanese Patent Publication No. 2-7980, etc., and these transparent paints are masked on the cut surface and the shot surface is painted with a colored paint. Then, after being thermally cured, the cut surface and the shot surface are painted and thermally cured. (This transparent paint is hereinafter abbreviated as rust-proof clear paint)

[0010]

In recent years, the direction of an aluminum wheel design adapted to the performance and shape of a vehicle is such that the shot surface is equal to or larger than the area of the cut surface, and the body is used in a colored specification and a bright specification. Higher appearance painting of aluminum wheels is required along with higher appearance of painting.

"High appearance" means that visible light is not irregularly reflected on the surface of the coating film and the image reflected on the surface of the coating film is clear. As the former evaluation method, the reflectance when the incident angle and the reflection angle in JIS K-5400 7.6 specular glossiness are each 20 °, and as the latter evaluation method, the visible light is projected onto the coating film through a comb-shaped pattern, and the There are instruments NSIC and NSIC ^* that measure the degree of bleeding of a comb pattern obtained as reflected light, that is, a mathematical coefficient when a light intensity curve is converted into a Fourier series based on trigonometric functions. However, since the surface of the aluminum wheel is actually a three-dimensional curved surface, it is difficult to measure with the above method that requires a constant horizontal area, and it is determined visually based on the above evaluation with a test plate that can secure a horizontal plane. You.

In order to enhance the appearance of the shot surface by conventional coating, a method of reducing the surface roughness of the shot surface in the shot process is considered. However, in order to remove the release agent and the oxide film, the surface of the shot metal piece is removed. Even if a certain size is necessary, and even after incorporating a shot process only for the purpose of reducing the surface roughness, in order to separate the metal pieces to be beaten from the scraped aluminum pieces and reuse the metal pieces, The metal pieces need to have a certain size, and there is a limit to reducing the surface roughness of the shot surface in the shot process.

In order to make the shot surface have a high appearance by painting, it is necessary to thicken the coating film. After applying a colored paint on the shot surface, heat-curing, and then applying a clear paint once or twice,
When the film is thickened by thermosetting, the appearance of the shot surface seen through the clear coating film can be obtained even though the smoothness of the coated surface is obtained, but the colored paint directly applied to the shot surface is almost comparable to the surface roughness of the shot surface It is a well-known fact that surface roughness appears to be low, and it is necessary to form a smooth coating film on the shot surface before applying a colored paint on the shot surface.

When a colored paint is applied on a shot surface after forming a smooth paint film and cured by heat, it is necessary to apply a clear paint on the colored paint film and heat cure it to protect the colored paint film. The appearance is considered to be effective for colored specifications as a high appearance.

[0015] When the cut surface is masked with a brilliant specification to form a smooth coating film and a colored coating film on the shot surface, and then coated with a rust-preventive clear paint and thermally cured, the smooth coating film is formed on the shot surface. As much as possible, the unevenness of the coating film on the masking part reduces the appearance of the entire aluminum wheel painted surface, so it is necessary to form a smooth coating film formed on the shot surface over the entire aluminum wheel painted surface including the cutting surface There is.

When a smooth coating film is formed on the entire aluminum wheel coating surface, if the coating film has a coating performance higher than that of the rust-preventive clear paint, the colored specification is formed by adding the colored paint and the clear paint on top of each other. Coating and heat curing may be performed. For the bright specification, the cut surface is masked and colored paint is applied to the shot surface, and after heat curing, the cut surface and the shot surface are subjected to clear coating.

As described above, in order to obtain a high appearance by increasing the thickness of the coating film, it is necessary to apply the coating material repeatedly, and for this purpose, the adhesion between the coating films and between the shot surface and the cut surface is ensured. This is very important.

In North America, traveling at a temperature of -20 ° C. is usually in winter, and chipping with crushed stone used to prevent slippage due to freezing is sufficiently considered. An aluminum wheel with a thick coating film and a high appearance can be obtained. In this case as well, damage to the coating film due to chipping must be small, and floating of the coating film in which corrosion progresses must not occur between the shot surface, the cut surface and the coating film.

For example, using a colored paint and a clear paint,
Although the colored coating film that has been coated and thermally cured satisfies the high appearance on the shot surface, in the chipping test assuming North America, remarkable damage and lifting of the coating film are recognized, it is obtained by the present invention A smooth paint film requires a paint, a paint film, and a design concept different from the conventional one.

[0020]

Means for Solving the Problems A transparent anticorrosive thick film coating composition according to the present invention for attaining the above object is characterized by sharing functions in the following (A) and (B). Primer for preventing rust on shot surface, cut surface, and edge (A) Low-temperature chipping applied to the cut surface for the purpose of smoothing the coating on the shot surface and assisting the cover with the coating on the edge Thick film primer with excellent properties (B)

The primer (A) is applied to the entire aluminum wheel coating surface and heat-dried (the coating composition does not have many crosslinkable functional groups, and mainly the solvent contained in the coated paint is evaporated by heat. In this manner, a film that forms a coating film is called thermal drying, which is distinguished from thermal curing), or is coated with the primer (B) over the entire aluminum wheel coated surface without thermal drying, and is thermally cured. Thereafter, the conventional colored paint and clear paint are applied and heat-cured, respectively. When the shot surface has a large surface roughness and a high appearance cannot be obtained, a high appearance can be obtained by further adding the coating film (B) before applying the colored paint. When applying a colored paint, it can be divided into a colored specification and a bright specification depending on whether or not the cut surface is masked.

The primer (A) comprises the following component (1)
(4) as a main component. (1) Acrylic resin (2) Epoxy resin (3) Powdered silica (4) Crosslinked polymer particles

Component (1) is a compound having two or more radically polymerizable ethylenically unsaturated groups in the molecule: (a): hydroxylmethyl (meth) acrylate, hydroxylethyl (meth) acrylate, ( Ethylene monomers having a hydroxyl group such as hydroxylpropyl (meth) acrylate, hydroxylbutyl (meth) acrylate, and N-methylolacrylamine (b): (meth) acrylic acid, crotonic acid, itaconic acid, fumaric acid, and maleic acid Ethylenic monomers having a carboxyl group such as (c): methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl acrylate, n-propyl acrylate, n-butyl acrylate, Isobutyl acrylate, 2-ethylhexyl acrylate, n-acrylate (D): an ethylenic monomer copolymerizable with (a) and (b), such as octyl and alkyl (meth) acrylates such as n-dodecyl acrylate; and (e): (meth) acrylonitrile , Which can be polymerized from a monomer such as styrene by an ordinary method and has a weight average molecular weight (hereinafter abbreviated as Mw) of 70,000.
-100,000, glass transition temperature (hereinafter abbreviated as Tg) -10 ° C. to 0 ° C., hydroxyl value (hereinafter abbreviated as OHV) theoretically calculated from the glass transition temperature of the homopolymer of each monomer.
An acrylic resin having an acid value of 10 to 30 and an acid value (hereinafter abbreviated as AV) of 25 to 40.

The component (2) is a general-purpose epoxy resin comprising a compound containing two or more epoxy groups in one molecule. Specifically, for example, bisphenol A, bisphenol F, 1,1 Glycidyl ether epoxy resins of polyphenol compounds such as 2,2,2-tetrakis (4'-hydroxyphenyl) ethane; catechol;
Glycidyl ether-based epoxy resins of polyhydric phenols such as resorcin, hydroquinone, phloroglucin; glycidyl ether-based epoxy resins of polyhydric alcohols such as ethylene glycol, butanediol, glycerol, erythritol, polyoxyalkylene glycol; Cycloaliphatic epoxy resins such as vinylcyclohexene dioxide, limonene dioxide and dicyclopentadiene dioxide; polyglycidyl ester epoxy resins of ester condensates of polycarboxylic acids such as phthalic acid and cyclohexane-1,2-dicarboxylic acid A polyglycidylamine-based epoxy resin and the like. Here, the epoxy equivalent is 210-1,000
The glycidyl ether-based epoxy resin or cycloaliphatic epoxy resin is preferred.

The component (3) has a number average diameter of primary particles (hereinafter referred to as a number average diameter).
7 to 9 nm, specific surface area by BET method (constant pressure / capacity method using nitrogen gas using gas adsorption) (hereinafter referred to as B
ET) 200-380 m ² / g powdered silica.

The component (4) is prepared, for example, by subjecting a monomer having two or more radically polymerizable ethylenically unsaturated groups in the molecule to 0.1% by weight or more in the total blend to carry out emulsion polymerization or solution polymerization. Is obtained, dn
Are 50-80 nm crosslinked polymer particles . Specifically,
The method for producing crosslinked polymer fine particles (microgel) described in JP-A-62-79873 and the like can be mentioned.

With respect to the component (1), the smaller the Mw, the lower the rust prevention effect, and the larger the Mw, the lower the coating workability.
The higher the Tg, the lower the self-chipping resistance at low temperatures, and the lower the Tg, the better the rust-preventive effect, the self-chipping resistance at low temperatures, and the adhesion to the coating film (B). The lower the OHV, the lower the adhesion to the coating film (B), and the higher the OHV, the lower the rust-preventive effect. The higher and lower the AV, the lower the self-chipping resistance at low temperatures.

In the component (1) of the present invention, Mw
Is suitably 70,000-100,000, preferably 80,000-90,0
The Tg is suitably from -10 ° C to 0 ° C, preferably from -10 ° C to
-4 ° C, OHV is suitably 10 to 30, preferably 10 to 20,
AV is suitably from 25 to 40, and preferably from 25 to 35.

As for the component (2), the lower the epoxy equivalent, the lower the self-chip resistance at low temperatures, and the higher the epoxy equivalent, the lower the water resistance.

For component (2), the epoxy equivalent is 210
1,0001,000 is suitable, preferably 2702701,000.

The mixing ratio (parts by weight) of the components (1) and (2) is suitably (1) / (2) as 100/5 to 100/20.
Preferably it is 100/5 to 100/15. When the compounding ratio of the component (1) exceeds 100/5, the water-resistant adhesion decreases, and when it is lower than 100/20, the self-chipping resistance at low temperatures decreases.

The characteristics and the mixing ratio of the components (1) and (2) determine the physical properties of the coating film after heat drying. The coating film (A) excluding the components (3) and (4) obtained after thermal drying because it affects chipping resistance and adhesion to the coating film (B). Is characterized by being in a certain range with respect to the physical properties thereof.

(A) As a measurement of the viscoelasticity of the coating film, a constant vibration strain and a temperature rise are given to the coating film (hereinafter abbreviated as dynamic viscoelasticity measurement), and the ratio of viscosity to elasticity (hereinafter abbreviated as tan δ). At the temperature at which the maximum value is reached,
Abbreviated). (B) Strength at which the coating film breaks when the coating film is pulled at a constant speed under a constant temperature condition. (C) The elongation of the coating film at the time of breaking (b).

The Tm is preferably 35 to 70 ° C. when 11 Hz, 2 g weight vibration strain and a temperature rise of 2 ° C./min are applied in the length direction of the coating film (A) having a length of 10.0 mm and a width of 4.0 mm. And preferably 35
The breaking strength when pulled at 5mm / min at -20 ° C in the length direction of a coating film (A) of ~ 45 ° C, length 50.0mm, width 10.0mm is 500 ~
1,000 kg / cm ² is suitable, preferably 650 to 1,000 kg / cm ² ,
The elongation at that time is suitably 4 to 7%, preferably 4 to 6%.
%.

The primer (A), excluding the components (3) and (4) having the above-mentioned characteristics, was subjected to heat drying at a cutting surface of 10 to 20%.
Painted on the entire painted surface of the aluminum wheel to a thickness of μm, and finally heat-dried to provide low-temperature self-chipping resistance to shot and cut surfaces and adhesion to the coating film (B). And a coating film having excellent corrosion resistance can be obtained.

The components (3) and (4) are obtained by coating the primer (A) on an aluminum wheel and finally forming a coating film (A) on the edge portion when heat-dried. It is a component that controls the fluidity of the coating film (A) until the end of thermal drying.

Components (3) and (4) were used as primers (A)
An important point when using the components (1) and (2) is that the characteristics of the coating film (A) before using the components (3) and (4) as components are not impaired. )
The amount (parts by weight) of component (3) is 5 to 100
20 is suitable, preferably 5 to 10, similarly to the component (4).
Is suitably 1 to 10, preferably 1 to 5. The film thickness on the cut surface after thermal drying of the coating film (A) is 10-30μ
m is preferred.

Component (3) is an organic solvent or component (1),
It can be easily dispersed in (2) and components (1) and (2).

Since the component (4) is in a state of being dispersed in an organic solvent, the components (1), (2) and (3) may be added to a place where the components are stirred.

The kind and amount of the organic solvent for dissolving and dispersing the primer (A) and the primer (A)
The type and amount of the organic solvent that dilutes the component (1),
It is sufficient that the components (1) to (4) react with (2) and (4), or after coating and before the end of thermal drying, do not separate or aggregate to impair the characteristics of the coating film (A). Select the type and amount of the organic solvent which can sufficiently bring out the effects of (3) and (4) and does not inhibit the coated surface of the coating film (A) from smoothing the coating film (B) according to various coating methods and methods. It is desirable to do.

The primer (B) comprises the following components (5) to
(8) is a main component. (5) Acrylic resin (6) Blocked polyisocyanate compound (7) Powdered silica (8) Crosslinked polymer particles

The component (5) is obtained in the same manner as the component (1), and has a Mw of 5,000 to 40,000 and a Tg of -44 ° C. to -20.
It is an acrylic resin having an OHV of 80 to 160 ° C.

Component (6) is a blocked polyisocyanate, hexamethylene diisocyanate, ethylene diisocyanate, propylene diisocyanate, tetramethylene diisocyanate, decamethylene diisocyanate, metaphenylene diisocyanate, triphenylmethane triisocyanate, cyclohexyl isocyanate, phenylene diisocyanate, triene Range isocyanate (TDI), xylylene diisocyanate (XDI), isophorone diisocyanate (IPDI)
Various diisocyanates such as, and adducts, hydrates, condensates, and the like with these polyols, phenol-based, lactam-based, active methylene-based, which is unblocked by heat,
Alcohol, amine, oxime, urea and imine blocking agents are added. Here, the reaction start temperature due to the difference in the blocking agent (the temperature at which the elastic modulus changes from decreasing (thermoplastic) to increasing (thermosetting) when a certain temperature rise is given in the process of curing the paint as a coating film, Using a polyisocyanate having an onset temperature of 120 to 150 ° C., a ratio (%) of isocyanate groups (hereinafter abbreviated as NCO) in component (6) to 100 parts by weight of component (6) (hereinafter referred to as NCO group content) 9)
16% blocked polyisocyanate compound.

The component (7) is the same as the component (3) of the primer (A).

Component (8) is a crosslinked polymer having a dn of 50 to 80 nm obtained in the same manner as the component (4) of the primer (A).
Particles .

With respect to the component (5), the higher or lower the Tg, the better the chipping resistance at a low temperature. The higher the Mw, the lower the appearance, and the lower the Mw, the lower the chipping resistance at a low temperature. The higher the OHV, the better the chipping resistance at low temperatures and the adhesion to the coating film (A). The lower the OHV, the lower the water resistance and the adhesion to the coating film (A).

In the component (5) of the present invention, Mw is 5,0
00 to 40,000 is suitable, preferably 7,000 to 30,000, Tg
Is suitably -44 ° C to -20 ° C, preferably -44 ° C to -30 ° C.
C. and OHV are suitably from 80 to 160, preferably from 120 to 160.
It is.

With respect to the component (6), the higher the reaction initiation temperature, the lower the water resistance, and the lower the temperature, the more the coating film undergoes a significant yellowing and the lower the low-temperature chipping resistance. The lower the NCO group content, the lower the water resistance, and the higher the NCO group content, the lower the chipping resistance at low temperatures.

Regarding the component (6), the reaction starting temperature is from 120 to
The temperature is suitably 150 ° C., preferably 130 to 150 ° C., the skeleton of the polyisocyanate is preferably an aliphatic type, and the NCO group content is preferably 10 to 15%.

The compounding ratio of the components (5) and (6) is a value obtained by substituting the OHV of the component (5) and the NCO group content of the component (6) by the NCO value (hereinafter abbreviated as NCOV).
The ratio OHV / NCOV is 1.0 / 0.9 to 1.0 / 1.1, and preferably 1.0 / 0.9 to 1.0 / 1.0. NCOV
If NCOV is less than 0.9, the water resistance decreases, and if NCOV exceeds 1.1, chipping resistance at low temperatures decreases.

The characteristics and the mixing ratio of the components (5) and (6) affect the physical properties of the coating film after thermosetting, and the physical properties include chipping resistance at a low temperature and adhesion to the coating film (A). sex,
Further, the coating (B) obtained after thermosetting has an effect on the adhesion with the coating (B) when the primer (B) is applied and the adhesion with the colored coating and the clear coating. ), The physical properties (a) to (c) are within a certain range.

When the measurement conditions of the physical properties (a) to (c) are the same as those for the coating film (A), Tm is suitably 35 to 125 ° C.
Preferably 35 to 80 ° C., the breaking strength is 300 to 600 kg / cm ² is suitable, preferably 400 to 600 kg / cm ² The growth rate in the 2 to 25% of suitable, preferably 10% to 25% is there.

The primer (B) excluding the components (7) and (8) having the above characteristics is heat-cured so that the thickness of the layer becomes 20 to 60 μm on the cut surface after heat curing. Regardless, the coating surface of the aluminum wheel coated with the coating film (A) is coated once or twice and heat-cured to give the shot surface and cut surface the adhesion with the coating film (A) and the coating film (B) Comrade adhesion,
It is possible to obtain a smooth coating film which has an adhesive property with a colored paint and a clear paint and has excellent chipping resistance at a low temperature.

When the primer (B) is applied to an aluminum wheel, the components (7) and (8) are used to coat the primer (B) on the vertical surface from the end of coating to the end of thermosetting (hereinafter referred to as “flow-off property”).
Regardless of whether or not the edge portion is thermally dried, the coating (A) is applied and then the coating (B) is formed. Is a component that controls the fluidity of the coating film (B).

Components (7) and (8) were used as primers (B)
An important point when using the components (5) and (8) is that the characteristics of the coating film (B) before the components (7) and (8) are not impaired. Compounding amount of component (7) when 6) is taken as 100 (parts by weight)
Is suitably 5 to 20, preferably 5 to 10, and similarly, the compounding amount of the component (8) is suitably 1 to 10, and preferably 1 to 10.
5 The layer thickness of the coating (B) on the cut surface after thermosetting is preferably 40 to 100 μm.

The component (7) can be a component of the primer (B) in the same manner as the component (3).

The component (8) can be used as a component of the primer (B) in the same manner as the component (4).

The kind and amount of the organic solvent for dissolving and dispersing the primer (B) and the primer (B)
The type and amount of the organic solvent that dilutes the component (5),
Reacts with (6) and (8) or separates and aggregates components (5) to (8) from after coating to the end of heat curing to form a coating film (B)
Any type of organic solvent that does not impair the characteristics of the coated film (A) regardless of the effects of the components (7) and (8) and whether or not it is thermally dried It is desirable to select the compounding amount according to various coating methods and methods.

The primers (A) and (B) are commonly or separately provided with additives such as a surface conditioner, a reaction catalyst, an antioxidant and an ultraviolet absorber as primers for forming a coating film. Is desirably added within a range that does not impair the characteristics of.

[0060]

[Function] The effect of imparting corrosion resistance to light alloy materials is mainly to prevent the generation of rust. However, when considering from the viewpoint of paint resin, the prevention of rust is considered to be O ₂ , H ₂ O, and ion. To reduce the permeability, enhance the adhesion with the substrate, increase the film thickness, and tough coating film with high Young's modulus
Requirements such as reducing the internal stress are required.

When the chipping resistance at a low temperature is considered from the viewpoint of the coating resin, in the portion in contact with the base material, (a) the adhesion to the base material is enhanced against the impact energy that could not be absorbed by the upper layer. And (b) the requirement for a tough coating film with high breaking strength is required. On the other hand, in the surface of the coating film which is directly impacted, impact energy is dispersed and absorbed in the horizontal direction. It is necessary to have requirements such as making the coating film having a high rate of tenacity, (d) lowering Tm and improving the efficiency of (c) of the coating film to be chipped.

The object of the present invention is to smooth the metal surface (shot surface of an aluminum wheel) including the above, and the composition of the primer (A) is intended to prevent the yarn rust by suppressing the internal stress of the coating film and the adhesion. The synergistic effect with the suppression of the amount of functional groups at the interface and the effect of preventing the chipping can be effectively achieved by making good use of the direction of the yarn rust prevention.

Since the internal stress of the coating film causes a distortion in the adhesion between the material and the coating film, the coating film having a larger internal stress including the environmental conditions with the passage of time tends to cause deterioration of adhesion and facilitate the progress of thread rust. In the present invention, increasing the Mw of the component (1) is a requirement to reduce the amount of functional groups per molecular weight and to suppress an increase in internal stress due to crosslinking by a condensation reaction.

A functional group is required for the adhesion of the coating film to the substrate, but if there is an excess of functional groups at the interface beyond contributing to the adhesion, the film penetrates the coating film in a corrosive environment and reaches the interface. Water is supplemented, and the progress of thread rust is facilitated.
The decrease in the amount of the functional group per molecular weight in this increase in Mw is a requirement for suppressing a decrease in adhesion due to water retention of the adhesion interface of the coating film in a corrosive environment.

On the other hand, it is known that the higher the molecular weight, the higher the tensile strength and the impact strength, which satisfy the chipping resistance (b) for preventing rust resistance.

Further, lowering the Tg of the component (1) leads to lowering the Tm of the coating film (A), and (c) and (d)
Similarly to the relationship, there is an effect of improving the efficiency of (b).

The primer (A) is formed by adding the component (2) to the component (1) because the reaction of the component (2) has a small curing shrinkage and the component (2) has excellent adhesion to a substrate. Can be raised. Regarding the component (2), the epoxy equivalent is specified because even if the three-dimensional structure of the molecules forming the coating film is dense, the target is not achieved if the internal stress is large. In order not only to prevent the prevention but also to reduce the water resistance, the components (1) and (2)
Is also an important requirement to achieve this goal.

Since the composition of the primer (A) imparts anticorrosive properties and the low-temperature chipping resistance of the portion in contact with the substrate, the coating of the coating (A) is used in the composition of the primer (B).
This is effectively achieved by suppressing the reactivity and synergizing the curing properties of thick film coatings for the purpose of chipping resistance at low temperatures and smoothing the skin without hindering the properties of the coating film surface. Things.

In the case of spray coating, the smoothness of the unevenness after coating of the coating film when the coating particles adhere to the object to be coated depends on the fluidity of the coating film given by the solvent remaining after coating from coating to curing. In the process of curing the paint as a coating film, it is due to the thermoplasticity shown before the reaction starts, but in order to obtain the smoothness of the coating film in thick film coating, if the former is selected, the seasonal variation factor will cause painting Since the workability is narrowed, the smoothness tends to vary.

In the latter case, it is possible to improve the smoothness of the coating film by adjusting the thermoplastic state by suppressing the reaction starting temperature and the reactivity, and it is possible to improve the blocking agent dissociation temperature of the component (6) and the polyisocyanate. It is a requirement to improve the smoothness of a thick film by adjusting the reactivity of the film at a specified heat curing temperature and time within a range that does not affect subsequent workability or coating film performance.

On the other hand, lowering the Tg of the component (5) leads to lowering the Tm of the coating film (B), thereby improving the efficiency of (c) and improving the smoothness of a thick film by thermoplasticity. is there.

In the present invention, the polyisocyanate used for the purpose of reducing the reactivity is preferably an aliphatic skeleton in the direction of giving flexibility to the coating film (B).
It is very effective in forming (c).

When a coating system is formed by two or more coating films, the difference in internal stress between the layers causes deterioration in adhesion or poor adhesion between the layers as well as distortion in the adhesion between the material and the coating film. ,
Significantly, the paint that adheres to the material may be distorted.
Since the function sharing of the coatings (A) and (B) in this case is a contradictory coating formation technique, in the dynamic viscoelasticity measurement, the curing properties of the primers (A) and (B) from liquid to solid are measured. The difference affects the characteristics of the coatings (A) and (B).

The direction of lowering the Tg of the component (5) and the suppression of the reactivity of the component (6) are in the direction of bringing the curing characteristics of the primer (B) closer to the curing characteristics of the primer (A).
This is an important requirement to derive the characteristics of the coating films (A) and (B).

[0075]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but it goes without saying that the scope of the present invention is not limited to these Examples. In the following examples, parts show parts by weight.

Comparative Examples 1-21 and Examples 1-18 Various (1) were used to determine the characteristics of the primer (A).
Acrylic resin, (2) epoxy resin, (3) powdered silica and (4) crosslinked polymer particles were blended in the amounts shown in Table 1 (parts by weight of solid content), and the parts by weight of components (3) and (4) were: The amounts are shown in terms of parts by weight of the solids when the parts by weight of the components (1) and (2) are 100. The types of the components indicated by the symbols in Table 1 are as follows.

(1) Acrylic resin A-1: Acrylic resin (Dianal LR576: manufactured by Mitsubishi Rayon Co., Ltd.) A-2 to 10: 〃 (Mw, Tg, AV modified product of A-1: Mitsubishi Rayon Co., Ltd.) )) A-11: ヤ (Dianal LR578: manufactured by Mitsubishi Rayon Co., Ltd.) A-12: M (Mw, Tg, AV modified product of Dianar SE5102: manufactured by Mitsubishi Rayon Co., Ltd.) A-13-21 : 〃 (Tg of A-12, OHV changed: Mitsubishi Rayon Co., Ltd.)

(2) Epoxy Resin B-1: Glycidyl Ether Epoxy Resin (Epototo YD134: manufactured by Toto Kasei Co., Ltd.) B-2: 〃 (DYD011: 〃) B-3: 〃 (〃YD014: 〃) B-4: Polyfunctional cyclic aliphatic epoxy resin (Eporide GT302: manufactured by Daicel Chemical Industries, Ltd.) B-5: 〃 (〃 GT400: 〃) B-6: 〃 (〃 GT401: 〃) B-7: 〃 (〃 GT403: 〃)

(3) Powdered silica C-1: Ultrafine powdered silica (Aerosil 200: manufactured by Nippon Aerosil Co., Ltd.) C-2: 〃 (〃300: 〃) C-3: 〃 (〃380: 〃)

(4) Crosslinked polymer particles D-1: Production examples are shown below.

I Preparation Example of Microgel Preparation of Zwitterionic Group-Containing Polyester A 2-liter kolben equipped with a stirrer, nitrogen inlet tube, temperature controller, condenser, decanter, 134 parts of bishydroxyethyltaurine, neopentyl glycol 1
30 parts, 236 parts of azelaic acid, 186 parts of phthalic anhydride and 27 parts of xylene are charged and heated. Water generated by the reaction is removed by azeotropic distillation with xylene.

The temperature was raised to 190 over about 2 hours from the start of reflux.
℃, continue stirring and dehydration until the acid value equivalent to carboxylic acid reaches 145, and then cool to 140 ° C. Then 140 ° C
Is maintained, and 314 parts of "Kajura E10" (glycidyl versatate ester manufactured by Shell Co.) are added dropwise over 30 minutes, and then stirring is continued for 2 hours to complete the reaction. The obtained polyester resin had AV59, OHV90 and Mn (number average molecular weight) of 1054.

Production of crosslinked polymer particles After stirring, 232 parts of deionized water, 10 parts of the polyester resin obtained above and 0.75 part of dimethylethanolamine were charged into a 1-liter reaction vessel equipped with a cooler and a temperature controller. Then, the mixture is dissolved under stirring at a temperature of 80 ° C., and a solution prepared by dissolving 4.5 parts of azobiscyanovaleric acid in 45 parts of deionized water and 4.3 parts of dimethylethanolamine is added. Then, a mixed solution comprising 70.7 parts of methyl methacrylate, 94.2 parts of n-butyl acrylate, 70.7 parts of styrene, 30 parts of 2-hydroxyethyl acrylate and 4.5 parts of ethylene glycol dimethacrylate is added dropwise over 60 minutes.
After dropping, add 1.5 parts of azobiscyanovaleric acid to deionized water.
A solution dissolved in 15 parts and 1.4 parts of dimethylethanolamine was added, and stirring was continued at 80 ° C. for 60 minutes to complete the reaction.

Xylene was added to the obtained crosslinked polymer particle emulsion, water was removed by azeotropic distillation under reduced pressure, and the medium was replaced with xylene to form a crosslinked polymer particle having a solid content of 40% by weight.
A child xylene solution (D-1) was obtained.

Production Examples Comparative Examples 1 to 21 and Examples 1 to 18 were prepared by the following methods.
Primer (A) was produced.

A mixed solvent (hereinafter abbreviated as mixed solvent) having a mixing ratio of hydrocarbon solvent / ester solvent (parts by weight) of 1/1 was prepared. Add a powdered silica based on Table 1 and an acrylic resin varnish to a mixed solvent so as to obtain a 4/10 mixture, and use a batch type dispersing machine using glass beads to make a gauge of 5 μm or less (JISK
Disperse the powdered silica until -5400 4.7.1). The dispersion was taken out to another container, and an epoxy resin varnish based on Table 1 was added thereto with stirring, and then a crosslinked polymer particle solution was similarly added thereto to produce a primer (A).

In the comparative example where powdered silica does not enter, it is only necessary to add the acrylic resin varnish while stirring the mixed solvent. In the case where the crosslinked polymer particles do not enter, the step of adding the varnish is omitted. According to the production example.

In order to evaluate the performance of the coating films of Comparative Examples and Examples, composite coating films were formed in the following manner.

A metal piece (SUS430 0.6 mm cut wire manufactured by Toyo Seiko Co., Ltd.) leaving half of the cut surface after the entire cutting process
Alloy plate (AC4C (V) 150 × 70
× 6mm: Nippon Route Service Co., Ltd.) was degreased (Surf Cleaner 53: Nippon Paint Co., Ltd.) and chromate chromate treatment (Alsurf 1000: Nippon Paint Co., Ltd.)
Then, the paints of Comparative Examples 1 to 20 and Examples 1 to 18 are air-sprayed on the entire surface of the cut surface after heat drying so as to have a film thickness of 20 μm and baked (the surface temperature of the aluminum alloy plate is reduced). The temperature was raised to 140 ° C. and maintained for 20 minutes, hereinafter abbreviated as baking) and dried by heat.

Then, the paint of Example 31 described later was air-sprayed on the entire surface of the cut surface after heat curing so that the coating film had a thickness of 60 μm, and baked to be heat-cured.

Further, a colored paint (Super Luck 5000 Silver: manufactured by Nippon Paint Co., Ltd.) was temporarily masked on the cut surface after heat curing so that the coating film had a thickness of 20 μm, and only the shot surface was formed. It was air-sprayed, baked after removing the masking, and thermally cured.

Finally, clear paint (Super Lak 5000
Clear: Nippon Paint Co., Ltd.) was heat-cured by air spray painting and baking the entire surface of the cut surface after thermosetting so that the coating film had a thickness of 30 μm.

The resulting composite coating film was evaluated for the specular glossiness of the shot surface, the rust resistance, the low-temperature chipping resistance, the adhesion, and the water resistance of the cut surface and the shot surface. Table 1 shows the results. Was.

The evaluation method is as follows.

Specular gloss of shot surface The reflectance (%) was measured when the incident angle and the reflection angle were respectively 20 ° according to JIS K-5400 7.6. (The results in Table 3 were made simultaneously with the aluminum alloy plate of Example 1,
evaluated. ) ×… Less than 70 △… More than 70 and less than 80 ○… More than 80

After making a straight cut of 5 cm reaching the alloy surface with a thread rust resistant cutter knife, sodium chloride was immersed in 1N hydrochloric acid solution (35 ° C.) containing 5% by weight for 15 minutes, and then taken out to be taken indoors. Dry until no water drops adhere. Next, the temperature is 40-45 ° C and the humidity is 70
Removed 240 hours in a bath maintained at ~ 75% RH.

The maximum length and the number of rusts generated at the cut portion from the cut were measured. ○… No rust at all or only spot rust less than 1 mm △… 1 mm or more and 2 mm or less and 20 yarns or less ×… Not applicable

Low-temperature chipping resistance : Placed in a bath at -22 ° C. to -18 ° C. for 1 hour, taken out and immediately 500 g of No. 6 crushed stone (JIS A-5001) gravelometer (stepping stone tester: Toyo Rika Kogyo Co., Ltd.) Compressed air pressure 4
The surface was hit with a kg / cm ² on the coated surface, and the damage caused by the impact and its surroundings were observed and measured. ○… only scratches caused by impact △… The maximum width from the scratch on the part where the coating film is lifted or removed between the alloy surface or coating layer from the scratch part is less than 0.5 mm △ ×… △ Same as above with a maximum width of 0.5mm or more and 1mm or less ×… Not applicable

Eleven straight cuts of 2 cm or more reaching the alloy surface are made in parallel with the adhesive cutter knife at intervals of 2 mm, and 11 cuts are made in the same direction at right angles to the cuts, and the cut is inserted into the cut. Make 100 squares, 2 mm wide and 2 mm wide, stick cellophane adhesive tape (cellophane: Nichiban Co., Ltd.) to that part, peel off this quickly in the direction perpendicular to the painted surface, The peeling was observed and measured. ○… The square coating film does not come off or is only due to the cut. △… Even if the square coating film comes off, the number is within 10 or the peeling from the cut is 0.5 mm or less between the cuts. Not applicable to the above

[0100] Immerse in a constant temperature water bath with a water resistance temperature of 38 to 42 ° C for 240 hours and take out.
After time, the adhesion was evaluated. However, blistering, decrease in gloss, and change in color are observed by visual observation immediately after removal.
And

In order to determine the characteristics of the coating film (A) together with the evaluation of the composite coating film, the physical properties of the coating films of Comparative Examples 1 to 21 and Examples 1 to 18 were measured by the following method. Table 1 shows the results.

Air spray coating was performed on a polypropylene plate (Noblen MH-8: manufactured by Nippon Test Panel Co., Ltd.) so that the film thickness after drying was 60 μm, and the surface temperature of the polypropylene plate was raised to 140 ° C. for 20 minutes. Hold and form a dry coating.

(A) A coating film was cut to a length of 15 mm and a width of 4.0 mm with a cutter knife, and the coating film was peeled off from a polypropylene plate using tweezers to measure the viscoelasticity of the coating film (Reo Vibron: Orientec Co., Ltd.) ) Is set so as to have a film length of 10.0 mm, and Tm is measured by giving 11 Hz, 2 g weight vibration strain and a temperature rise of 2 ° C./min in the length direction.

(B) As in (a), length 70 mm, width 10.0 mm
Is set in a stress-strain measuring device (Tensilon: Orientec Co., Ltd.) in a constant temperature room at -20 ° C so that the film length becomes 50.0 mm. Strength at 5mm / min in the length direction 10 minutes after the temperature reaches -20 ° C

(C) (b) Elongation of coating film at break when measured

[0106]

[Table 1]

[0107]

[Table 2]

[0108]

[Table 3]

[0109]

[Table 4]

[0110]

[Table 5]

[0111]

[Table 6]

[0112]

[Table 7]

Comparative Examples 22 to 32 and Examples 19 to 39 To determine the characteristics of the primer (B), various (5)
Table 2 shows acrylic resin, (6) blocked polyisocyanate compound, (7) powdered silica, and (8) crosslinked polymer particles.
In the amounts shown in Table 1. About the component (6), the component (5)
The NCOV value of the component (6) when the OHV of the solid content part 100 is 1.0 (that is, OHV / NCOV O
NCOV value when HV = 1.0) is defined as the NCOV ratio
In Table 2, the parts by weight of the components (7) and (8) are indicated by parts by weight of the respective solids when the weight of the solids of the components (5) and (6) is 100. The types of the components indicated by symbols in Table 2 are as follows.

(5) Acrylic resin E-1: Acrylic resin (Dianal AS-6699: manufactured by Mitsubishi Rayon Co., Ltd.) E-2 to 7: 〃 (Mw, Tg, OHV of Dianal AS-6699 modified products: E-8: 〃 (Hitaroid A204: manufactured by Hitachi Chemical Co., Ltd.) E-9: 〃 (〃 3533: 〃) E-10: 〃 (〃 3635-1: 〃) E -11: 〃 (〃3635-2: 〃)

(6) Blocked Polyisocyanate Compound F-1: Aromatic Polyisocyanate Compound (Desmodur BL4165: manufactured by Sumitomo Bayer Urethane Co., Ltd.) F-2: Aliphatic 〃 (〃 BL3175: 〃) F-3 : 〃 〃 (〃 GA1048: 〃) F-4: Aromatic 〃 (IPDI B1299: manufactured by Daicel Huls Co., Ltd.) F-5: Aliphatic 〃 (Coronate 2507: manufactured by Nippon Polyurethane Co., Ltd.) F- 6: 〃 デ ス (Death module TPLS2759: manufactured by Sumitomo Bayer Urethane Co., Ltd.)

(7) Powdered silica G-1: Same as C-1 G-2: Same as C-2 G-3: Same as C-3

(8) Crosslinked polymer particles H-1: Production examples are shown below.

Production of amphoteric group-containing polyester In a reaction vessel equipped with a stirring and heating device, a thermometer, a nitrogen inlet tube, a cooling tube and a decanter, 213 parts of bishydroxyethyl taurine, 208 parts of neopentyl glycol, 296 parts of phthalic anhydride And 376 parts of azelaic acid and 30 parts of xylene were charged and heated. Water generated by the reaction was removed by azeotropic distillation with xylene. It takes about 3 hours from the start of reflux
The temperature was raised to 210 ° C., and stirring and dehydration were continued until the acid value corresponding to the carboxylic acid reached 135. After cooling the liquid temperature to 140 ° C., 500 parts of “Cajura-E10” (Gercidyl versatate ester manufactured by Shell) was dropped in 30 minutes,
Thereafter, stirring was continued for 2 hours to complete the reaction. The obtained polyester resin had AV55, OHV91 and a number average molecular weight of 12
It was 50.

Production of Crosslinked Polymer Particles 141 parts of deionized water was charged into a reactor equipped with a stirring and heating device, a thermometer, a nitrogen inlet tube and a cooling tube, and the temperature was raised to 80 ° C.
15 parts of the above polyester resin, 107 parts of deionized water and 1.5 parts of dimethylethanolamine were charged into a stainless steel beaker, and 100 parts of the following monomer mixture (A) was added thereto, and the mixture was vigorously stirred with a stirrer to form a monomer suspension. . Simultaneously add 21.64 parts of this monomer suspension and 21.64 parts of an aqueous initiator solution (60)
The reaction was continued over 90 minutes to complete the reaction. Xylene was added to the obtained crosslinked polymer particle emulsion, water was removed by azeotropic distillation under reduced pressure, the medium was replaced with xylene, and the crosslinked polymer particles having a solid content concentration of 30% by weight were added.
A child xylene solution (H-1) was obtained.

Monomer mixed solution (a) 15 parts of methyl methacrylate 25 parts of styrene 15 parts of n-butyl acrylate 40 parts of ethylene glycol dimethacrylate 4 parts of 2-ethylhydroxy methacrylate 1 part of dimethylaminoethyl methacrylate

Aqueous initiator solution (a) Azobiscyanovaleric acid 1.0 part Deionized water 20 parts Dimethylethanolamine 0.64 parts

Production Examples In Comparative Examples 22 to 32 and Examples 19 to 39, a primer (B) was produced by the following method. Batch-type dispersion using glass beads by adding powdered silica and acrylic resin varnish based on Table 2 to the mixed solvent so that the mixing ratio (parts by weight) of the same mixed solvent as the primer (A) / each acrylic resin varnish is 6/10. The powdered silica is dispersed by a machine until the gauge becomes 5 μm or less. The dispersion was taken out to another container, and a varnish of the blocked polyisocyanate compound based on Table 2 was added thereto with stirring, and then a crosslinked polymer particle solution was similarly added thereto to produce a primer (B).

In order to evaluate the performance of the coating films of Comparative Examples and Examples, composite coating films were formed by the following methods.

On the same treated plate as that used in Comparative Examples and Examples of the primer (A), the primer (A) of Example 2 was used.
Was subjected to air spray coating on the entire surface so as to have a film thickness of 20 μm on the cut surface after the heat drying, baking, and heat drying.

Further, Comparative Examples 22 to 31 and Examples 19 to 39
On the cut surface after thermosetting, the coating was applied by air spray coating over the entire surface so as to have a film thickness of 60 μm, and baked to be thermoset.

Subsequently, a composite coating film was formed in the same manner as in Example 1,
The obtained composite coating film was evaluated for coating film performance by the same evaluation method for the same evaluation items as in Example 1, and the results are shown in Table 2.

In order to determine the characteristics of the coating film (B) together with the evaluation of the composite coating film, the physical properties of the coating films of Comparative Examples 22 to 32 and Examples 19 to 39 were determined in the same manner as in Example 1. The measurement was performed and the results are shown in Table 2.

[0128]

[Table 8]

[0129]

[Table 9]

[0130]

[Table 10]

[0131]

[Table 11]

[0132]

[Table 12]

[0133]

[Table 13]

Examples 40 to 53 and Comparative Examples 33 to 35 The primers (A) in Table 1 and the primers (B) in Table 2
The composite coating film was formed by the following method in order to evaluate the coating film performance in the combinations shown in Table 3 among the above.

An aluminum road wheel (manufactured by Toyota Motor Corporation) was treated in the same manner as in Example 1, and the primer (A) was air spray-coated on the entire surface so that the cut surface after heat drying had a thickness of 20 μm. I do. At this time, two aluminum road wheels are painted, one is baked and heat dried, and the other is not.

The primer (B) was air-coated by spraying on the entire surface of the cut surface after heat curing so that the coating film had a thickness of 60 μm, and baked to be heat-cured.

Subsequently, a composite coating film was formed in the same manner as in Example 1,
With respect to the obtained composite coating film, coating film performance was evaluated by the same evaluation method for the same evaluation items as in Example 1, and the results are shown in Table 3. In each case, when the evaluation was different depending on the presence or absence of thermal drying of the primer (A), the worse result was shown. In the evaluation of the thread rust resistance, rust was not observed at the edge of the aluminum road wheel. And those which were recognized were evaluated as x.

[0138]

[Table 14]

[0139]

As described above, according to the present invention, it is possible to prevent corrosion and prevent adhesion by an external impact by coating a metal background without impairing the transparency of the metal background before coating. In addition, it is possible to provide a coating composition and a coating film forming method capable of making a painted surface smoother than a metal background surface. Therefore, it is useful for the purpose of coating bright and colored specifications that require high corrosion resistance, high chipping resistance and high appearance of wheels made of aluminum-based light alloy materials.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI C09D 163/00 C09D 163/00 175/04 175/04 (72) Inventor Toru Tanaka 1st Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Vehicle (56) References JP-A-1-103671 (JP, A) JP-A-64-4660 (JP, A) JP-A-1-223169 (JP, A) JP-A-61-249576 (JP, A A) JP-A-3-215578 (JP, A) JP-A-60-90270 (JP, A) JP-A-5-51552 (JP, A) JP-A-4-202260 (JP, A) JP-A-6060 -92365 (JP, A) JP-A-61-42579 (JP, A) JP-A-4-18473 (JP, A) JP-A-61-42580 (JP, A) JP-A-6-506154 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) C09D 133/02 C09D 5/08 C09D 133/08 C09D 133/14 C09D 163/00 C09D 17 5/04

Claims (3)

(57) [Claims] (1) Weight average molecular weight 70,000 to 100,00
0, glass transition point -10 ° C to 0 ° C, hydroxyl resin value of 10 to 30, and acid value of 25 to 40 per 100 parts by weight of an acrylic resin solid content (2) epoxy equivalent of 210 to 1,000 epoxy resin solid content of 5 to 20 Parts by weight, and the above components (1) and (2)
(3) 5 to 20 parts by weight of powdered silica having a number average diameter of primary particles of 7 to 9 nm and a specific surface area (BET method) of 200 to 380 m ² / g based on 100 parts by weight of solid content of An anticorrosion coating composition which forms a transparent coating film containing 1 to 10 parts by weight of crosslinked polymer particles having a number average diameter of 50 to 80 nm. (5) a weight average molecular weight of 5,000 to 40,000,
Glass transition point -44 ° C to -20 ° C and hydroxyl value of 80 to 160 (6) For the solid content of acrylic resin, the reaction initiation temperature is 120 to
Blocked polyisocyanate compound NCO in the solid content is 9-16% of the block polyisocyanate compound solids acrylic resin solids of a hydroxyl value for the compound 100 parts by weight of a solid content with a 0.99 ° C. blocking agent (OHV) / Block NCO value (NCO
V) The ratio OHV / NCOV is adjusted to be 1.0 / 0.9 to 1.0 / 1.1, and (7) the number average of the primary particles with respect to 100 parts by weight of the solid content of the components (5) and (6). 5 to 20 parts by weight of powdered silica having a diameter of 7 to 9 nm and a specific surface area (BET method) of 200 to 380 m ² / g and (8) a number average diameter of primary particles
A thick-film coating composition for forming a transparent coating film containing 1 to 10 parts by weight of crosslinked polymer particles of 50 to 80 nm. 3. A method for forming a transparent coating film, which comprises applying the anticorrosion coating composition according to claim 1 and then applying the thick coating composition according to claim 2.