JP2002038100A - Abrasion resistant coating film and method for forming the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abrasion resistant coating film and a method for forming the coating film wherein the coating film is used as a clear coating film applied to finishing coating processes for automobiles or the like, shows excellent abrasion resistance and excellent properties at thermal cycle testing, and can maintain excellent surface appearance characteristics for a long time. SOLUTION: In this abrasion resistant coating film, there is formed a 1-20 μm thick clear coat as a surface layer comprising a cross-linked resin with a cross-linking density of 5×10-3-5×10-2 mol/cm3. Preferably, a 20-80 μm thick clear undercoat or solid coat comprising a cross-linked resin with a cross-linking density of 5×10-4-5×10-3 mol/cm3 is formed under the clear coat.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating film for exterior use applied to a top coat of an automobile or the like, and particularly to a scratch-resistant coating film having excellent scratch resistance (hardness to be damaged by car washing or the like) and a method for forming the same. Things.

[0002]

2. Description of the Related Art The abrasion resistance of a clear coating film used for finishing automobiles and the like is one of the important quality characteristics required for a final product. In recent years, it has improved dramatically. The clear coatings currently in practical use have achieved satisfactory scratch resistance, but they have not yet reached a level where they are not damaged at all. Seeking.

It has been confirmed that the scratch resistance of a clear coating film is improved by increasing the crosslink density of a crosslinkable resin constituting the coating film. And it is generally adopted as a technique for increasing the crosslink density,
A method of increasing the cross-linking reactive functional group of the base resin,
Among them, a resin having a crosslinking reactive functional group such as a hydrolyzable silyl group or a silanol group in a molecule constituting the resin has a high crosslinking density improving effect, and therefore, a resin for forming a scratch-resistant coating film. It is known to be useful as a material.

However, when the crosslink density of the clear coating film is increased to improve the scratch resistance, the internal stress of the coating film is increased when subjected to repeated temperature changes of cold and heat, and the clear coating film is liable to crack. (This phenomenon is generally evaluated as “cooling / heat repeatability”).

That is, in order to satisfy the required properties as a finished clear coating film, it is necessary to secure sufficient performance with respect to the repetition of cooling and heating as well as the improvement of the scratch resistance. However, in conventional clear coatings, the effect of crosslinking density on scratch resistance has only been qualitatively confirmed, but the quantitative relationship between the two has not been clarified. What is the specific effect of the thermal repeatability due to internal stress, and what specific measures should be taken to achieve both abrasion resistance and thermal repeatability? Pursuit is not enough.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its object is to provide a clear coating film which is applied to finish coating for automobiles and the like. An object of the present invention is to provide an abrasion-resistant coating film which exhibits excellent abrasion performance and also has excellent performance in terms of repetition of cooling and heating, and which can maintain excellent surface appearance characteristics for a long period of time, and a method for forming the same.

[0007]

The abrasion-resistant coating film according to the present invention, which has achieved the above-mentioned objects, comprises a crosslinked layer having a crosslink density of 5 × 10 ^{−3 to} 5 × 10 ⁻² mol / cm ³ as a skin layer. A clear coat layer having a thickness of 1 to 20 μm containing a resin is formed, and has a gist in that it has both excellent scratch resistance and repetition of cooling and heating.

In the scratch-resistant coating film of the present invention, 1) a crosslink density of 5 × 10 5
^{-4 to} 5 × 10 ^-3 mol / cm ³ thickness including cross-linked resin 20
A clear undercoat layer of ~ 80 µm is formed, or a base coat layer is further formed under the clear base coat layer, or 2) a crosslink density of 5 × 10
^{-4 to} 5 × 10 ^-3 mol / cm ³ thickness including cross-linked resin 20
A coating film on which a solid coat layer having a thickness of about 80 μm is formed is preferred because it has more excellent scratch resistance and repetition of cooling and heating.

As a constituent material of the clear coat layer constituting the coating film of the present invention, a polyfunctional acrylic resin and / or an organosiloxane resin is recommended as a particularly preferable one.

The forming method of the present invention is a method capable of efficiently forming a coating film having particularly excellent scratch resistance among the above-mentioned coating films, and a) forming a coating film on a base coat layer formed on a substrate surface. After the clear base coat layer forming agent is wet-on-wet coated so as to have a dry film thickness of 20 to 80 μm, the clear coat layer forming agent is coated on the clear base coat layer with a dry film thickness of 1 to 80 μm.
Wet-on-wet coating to a thickness of about 20 μm and then baking and drying, or b) apply a solid coat layer forming agent on the substrate surface to a dry film thickness of 2 μm.
After wet-on-wet coating to a thickness of 0 to 80 μm, a clear coat layer forming agent is wet-on-wet coated on the solid coat layer so that the dry film thickness is 1 to 20 μm. The point is to bake and dry.

In carrying out the above coating film forming method, particularly preferably used as the clear coat layer forming agent is
A polyfunctional acrylic resin and / or an organosiloxane resin having a cross-linking reactive functional group of 5 to 20 mol / kg resin and a number average molecular weight of 1,000 to 50,000; Particularly preferably used as a clear base coat layer forming agent or a solid coat layer forming agent is a resin having a crosslinking reactive functional group of 0.5 to 5 mol / kg resin and having a number average molecular weight of 1,000 to 50, 000 reactive oligomers and / or reactive polymers.

Further, particularly preferably used as the base coat layer forming agent is a resin having a hydroxyl group of 0.5 to 3 mol / kg and a number average molecular weight of 1,000 to 50,000.
No. 00 containing an acrylic resin and an aminoplast resin as a curing agent.

The crosslink density, the number of crosslinkable functional groups, the number average molecular weight, the number of hydroxyl groups (hydroxyl value) and the acid value defined in the present invention mean values determined by the following methods.

Crosslink density: The dynamic viscoelasticity of the coating film is measured, and the temperature (T) at which the coating film reaches the rubber region and the elastic modulus (E ') at the temperature (T) are determined. E ′ / 3RT [where E ′ is the elastic modulus (dyne / cm ² ), and R is 8.3]
14 × 10 ⁷ (erg / deg · mol), and T represents a temperature (K)].

The number of crosslinking reactive functional groups: It is determined by calculation from the amount of functional groups of the acrylic monomer or silane monomer having a functional group and the mixing ratio thereof.

Number average molecular weight: It is determined by gel permeation chromatography based on the number average molecular weight in terms of polystyrene measured by a conventional method.

Number of hydroxyl groups (hydroxyl value): Calculated in the same manner as the above-mentioned number of crosslinking reactive functional groups.

Acid value: The acid value is the number of mg of potassium hydroxide required to neutralize 1 g of the resin.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, in the conventional clear top coat, the scratch resistance is improved by increasing the crosslink density, but on the other hand, a decrease in the thermal repetition property cannot be avoided. As shown in FIG.

That is, FIG. 1 is a graph showing the relationship between the scratch resistance (gloss retention) of the clear coating film and the crosslink density on the thermal repetition property. The scratch resistance rapidly rises with the increase in the crosslink density. The crosslinking density is, for example, 5 × 10 ⁻³ mol /
If the level is raised to the level of cm ³ or more, the clear coating film becomes high in quality and exhibits a high level of scratch resistance. However, the thermal repeatability of the clear coating film shows a sharp tendency to decrease with an increase in the crosslink density, particularly when the crosslink density exceeds the level of 10 × 10 ⁻³ mol / cm ³ .

This is considered to be due not only to the brittleness of the clear coating film due to an excessive increase in the crosslinking density, but also to an increase in internal stress when subjected to repeated temperature history of cooling and heating. Therefore, while improving the scratch resistance of the clear coating film and improving the thermal repeatability thereof, not only unnecessarily increasing the crosslink density of the coating film components, but also controlling the crosslink density to an appropriate range, It is necessary to reduce the internal stress generated when the cooling / heating temperature history is repeated.

The inventors of the present invention have conducted intensive studies from this viewpoint, and as a result, have found that the crosslink density of the clear coat layer formed as the skin layer (outermost layer) of the clear coating film is 5 × 10 ⁻³ to 5 × 10 ^−3.
By controlling the thickness of the clear coat layer in the range of 1 to 20 μm while controlling the thickness in the range of × 10 ^-2 mol / cm ³ , both the scratch resistance and the thermal repetition property are improved, and the excellent appearance characteristics and It has been confirmed that the durability can be significantly increased.

This is because by setting the crosslink density within an appropriate range, the clear coat layer is given the hardness necessary for improving the scratch resistance, the brittleness is minimized, and the film thickness is controlled within the appropriate range. By doing so, the minimum film thickness required for abrasion resistance is secured, and the internal stress when subjected to repeated cooling and heating history is minimized, ensuring excellent cooling and heating repetition. I believe.

Incidentally, the crosslink density of the clear coat layer is 5
× 10^-3Mol / cm^ThreeIf less than, it is insufficient hardness
Hard to obtain good scratch resistance, and the crosslink density is 5 ×
10 ^-2Mol / cm^ThreeBecomes too large beyond
Hardening makes the coating layer brittle, and
Increase in internal stress when subjected to repeated temperature history
As a result, satisfactory cooling / heating repeatability cannot be obtained. Ma
When the clear coat layer is thinner than 1 μm,
Layer itself becomes insufficient in strength and cannot withstand frictional force
On the contrary, if the thickness exceeds 20 μm and becomes excessively thick, scratch resistance
Improves, but receives repeated cold / heat temperature history
It is difficult to suppress the internal stress of
It cannot be secured.

In consideration of such a tendency of the skin layer, the lower limit of the crosslink density of the clear coat layer constituting the skin layer is more preferably 10 × 10 ⁻³ mol / cm ³ , and still more preferably 20 × 10 ⁻³ mol / cm ³ .
× 10 ⁻³ mol / cm ³ , the upper limit of which is 50 × 10 ⁻² mol / cm ³ .
cm ³ , more preferably 40 × 10 ^-2 mol / cm ³ . A more preferred lower limit of the thickness of the coat layer is 2 μm.
m, more preferably 5 μm, more preferably 15 μm.
m, more preferably 10 μm.

In the present invention, both the abrasion resistance and the heat-and-heat repetition property are achieved by specifying the crosslinking density and the thickness of the clear coat layer constituting the skin layer (uppermost layer) of the finished coating film as described above. However, in order to exhibit these characteristics more effectively, it is desirable to consider the configuration of the layer formed below the clear coat layer.

The preferred layer structure is as follows: 1) Under the clear coat layer, a crosslink density of 5 × 10
^{-4 to} 5 × 10 ^-3 mol / cm ³ thickness including cross-linked resin 20
A layered coating structure in which a base coat layer is formed on a clear undercoat layer having a thickness of ~ 80 µm,
Or 2) a crosslink density of 5 × 10 below the clear coat layer
^{-4 to} 5 × 10 ^-3 mol / cm ³ thickness including cross-linked resin 20
A laminated coating structure in which a solid coat layer having a thickness of up to 80 μm is formed.

The clear undercoat layer in the above 1) is a hard undercoat layer.
As a base layer for the clear and thin clear coat layer,
Demonstrates the effect of reducing the internal stress of the coat layer
In order for these effects to be exhibited effectively,
The crosslink density is 5 × 10 ^-Four~ 5 × 10^-3Mol / c
m^Three20-80 μm thick containing cross-linked resin
It is desirable.

The undercoat layer has a crosslink density of 5
× 10^-FourMol / cm^ThreeIf it is less than 10%, the hardness is insufficient and
All of the above effects tend to be insufficient, and conversely 5 × 10^-3Mol /
cm ^ThreeIs exceeded, the undercoat layer itself becomes cold and heat repeatable.
Insufficient cooling / heat repeatability as a whole coating film
It is difficult to obtain. Considering these points, the base coat
The lower limit of the more preferred crosslink density of the layer is 10 × 10^-FourMol /
cm^Three, More preferably 15 × 10^-FourMol / cm^Three,Than
Preferred upper limit is 4 × 10^-3Mol / cm^Three, More preferably
Is 3 × 10^-3Mol / cm^ThreeIt is. The undercoat layer
The lower limit of the thickness is more preferably 23 μm, and further preferably
25 μm, more preferably upper limit is 60 μm, still more preferably
Is 40 μm.

On the lower layer side of the clear undercoat layer, a colored layer is usually provided as an overcoat layer, and a base coat layer is formed to improve the design of the coating film. The cross-link density and thickness are not particularly limited, since they have almost no effect on the scratch resistance and the heat / heat repetition property.

In the present invention, a solid coat layer having an arbitrary coloring may be formed instead of the clear undercoat layer and the base coat layer. In this case, it is necessary to effectively act the solid coat layer as a support layer for the clear coat layer. In this case, the cross-link density and the thickness of the solid coat layer are determined by the thickness of the clear base coat layer. For substantially the same reason that the preferable crosslink density and thickness are determined, the crosslink density of the constituent resin is set to 5 × 10 ⁻⁴ to 5 × 10 ^−4.
× 10 ^-3 mol / cm ^3, it is desirable to set the thickness in a range of 20 to 80 [mu] m. Their more preferable range is, for the same reason, the lower limit of the more preferable crosslink density is 10 × 10
^-4 mol / cm ³ , more preferably 15 × 10 ^-4 mol / c
m ³ , a more preferred upper limit is 4 × 10 ⁻³ mol / cm ³ , still more preferably 3 × 10 ⁻³ mol / cm ³ , a more preferred lower limit for the thickness is 23 μm, still more preferred 25 μm, and a more preferred upper limit is 60 μm. More preferably, it is 40 μm.

The type of the substrate on which the coating film is formed is not particularly limited, but the most common type is a metal plate such as a steel plate or an aluminum alloy, or a hard resin (including a fiber reinforced resin such as FRP) plate. It is. In the above metal plate,
Of course, a metal plate subjected to a surface treatment such as a galvanizing treatment, a phosphate treatment, and a chromate treatment is also included.

Next, a method for forming the scratch-resistant coating film will be described.

This method is positioned as a method capable of forming a scratch-resistant coating film more efficiently as described above. Specifically, i) a method for forming a scratch-resistant coating film on a base coat layer formed on a substrate surface; After the clear base coat layer forming agent is wet-on-wet coated so as to have a dry film thickness of 20 to 80 μm, the clear coat layer forming agent is coated on the clear base coat layer with a dry film thickness of 1 to 80 μm.
A method of wet-on-wet coating to a thickness of about 20 μm, followed by baking and drying; and ii) a solid coat layer forming agent on the surface of the base material, a wet-on-wet method of a dry film thickness of 20 to 80 μm. After coating, wet the clear coat layer forming agent on the solid coat layer so that the dry film thickness is 1 to 20 μm.
A method of performing on-wet painting and then baking and drying is adopted.

In carrying out this method, the thicknesses of the clear undercoat layer, the solid coat layer and the clear coat layer were determined to be 20 to 80 μm and 1 to 20 μm, respectively, in terms of the dry film thickness. This is based on the same reason as the thickness of each of the constituent layers is determined. In addition, wet coat
What we decided to form by on-wet painting is
In addition to enhancing the smoothness of the finished coating film to enhance the appearance of the coating film, the adhesion between the base coat layer, the clear undercoat layer, and the clear coat layer, or between the solid coat layer and the clear coat layer, is improved, and the resistance of the finished coating film is improved. In order to enhance the abrasion resistance and the repetition of cooling and heating, the dry and wet coating makes the adhesion between the above layers insufficient, and the support effect of the clear undercoat layer and the solid coat layer on the clear coat layer Is difficult to be effectively exhibited. Here, the wet-and-wet coating refers to a method in which an upper-layer coating film forming agent is applied before the lower-layer coating film is baked and hardened, and thereafter, the two layers are simultaneously baked and hardened by heating. At this time, the lower coating film when applying the upper coating film forming agent may be in an undried state or a pre-dried state before baking and curing.

Next, the forming agent (coating material) of each coat layer used when performing the above-mentioned coating film forming method will be described.

First, as the base coat layer forming agent, an aesthetic paint containing a pigment, a vehicle, a solvent, and the like is used, and a particularly preferable vehicle is one containing an acrylic resin and a curing agent. As the acrylic resin, an alkyl ester of acrylic acid or methacrylic acid and, in some cases, another ethylenically unsaturated monomer copolymerizable therewith or a monomer having a functional group capable of reacting with a crosslinking agent A polyfunctional polymer copolymerized by an ordinary method is used.

Examples of the alkyl ester include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isobutyl acrylate, isobutyl methacrylate, n-butyl acrylate, and n-butyl acrylate. -Butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate,
Examples thereof include 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, and glycidyl methacrylate.

The monomers copolymerizable with these alkyl esters include acrylic acid, methacrylic acid, maleic anhydride, itaconic acid, fumaric acid, crotonic acid, N-
Methylolacrylamide, α-methylstyrene, o-
Methyl styrene, m-methyl styrene, p-methyl styrene, p-tert-butyl styrene, etc .; and acrylic acid, methacrylic acid, 2- (or 3-) hydroxyethyl methacrylate blocked with ethyl vinyl ether, trimethylsilyl chloride, etc. monomer;
Examples thereof include vinyltrimethoxysilane, vinyltriethoxysilane, and α-methacryloxypropyltrimethoxysilane. The above-mentioned alkyl ster and other copolymerizable monomers can be used alone, respectively, and of course, two or three or more kinds can be copolymerized as needed.

The copolymerization is carried out by a general method, for example, by adding each of the above monomer components at a predetermined ratio to a solvent such as toluene, xylene, mineral spirit, ethyl acetate, butyl acetate, etc., and adding azobisisobutyl nitrile or di-t The reaction can be carried out by a heat reaction using a conventional radical polymerization initiator such as -butyl peroxide.

Among the acrylic resins comprising the above copolymer, particularly preferred for forming the base coat layer are:
0.5-3 mol / kg resin, more preferably 0.5-2
It has hydroxyl groups of mol / kg resin and has a number average molecular weight of 1,0.
00 to 50,000, more preferably 2,000 to 2,000
000 acrylic resin, in addition to these,
Those containing an aminoplast resin as a curing agent are particularly preferred.

Examples of the aminoplast resin include a melamine resin, a urea resin and a benzoguanamine resin. Among them, melamine resin is particularly preferable, and specifically, a condensation polymerization reaction product of melamine and formaldehyde,
N etherified with a monohydric alcohol having about 1 to 4 carbon atoms
-Butylated melamine resin, isobutylated melamine resin and the like. It is also possible to include a small amount of an isocyanate-based prepolymer for adjusting the crosslinking density.

A preferred compounding ratio of the acrylic resin and the aminoplast resin preferably compounded as a curing agent is 90 to 40 parts by mass, more preferably 80 to 40 parts by mass.
The latter 10 to 60 parts, more preferably 20 to 50 parts
It is in the range of ~ 50 parts.

A vehicle that satisfies the preferred number of hydroxyl groups, acid value, number average molecular weight of the acrylic resin preferably used as a constituent component of the base coat layer forming agent, and also a preferred compounding ratio with the aminoplast resin is used as the base coat layer. It is recommended as providing a base film having very excellent characteristics required in particular, especially water resistance and chipping resistance.

The base coat layer forming agent used in the present invention contains, in addition to the above-mentioned vehicle components, coloring agents such as titanium oxide, carbon black, organic pigments and metal flakes, and extenders such as calcium carbonate and barium sulfate. It may further contain an ultraviolet absorber or a light stabilizer, a surface conditioner, a viscosity control agent, a catalyst, a dispersant, an antifoaming agent, an antistatic agent, an anti-settling agent, and the like, if necessary. I do not care.

Next, the clear base coat layer forming agent comprises a vehicle and a solvent as basic components, and a paint containing a coloring component is used if necessary. Particularly preferably used as a vehicle is one containing the same acrylic resin and curing agent as those exemplified for the base coat layer forming agent. As the acrylic resin, an alkyl ester of acrylic acid or methacrylic acid and, in some cases, another ethylenically unsaturated monomer copolymerizable therewith or a monomer having a functional group capable of reacting with a crosslinking agent Polyfunctional polymers copolymerized by a conventional method can be used in the same manner.

As the above-mentioned alkyl ester, those exemplified as the constituent material of the base coat layer forming agent are exemplified again, and the same copolymerizable monomer can be used as a monomer copolymerizable with these alkyl esters. And a crosslinkable polymerizable silane compound. These alkylsters and other copolymerizable monomers can be used alone, respectively, and it is of course possible to copolymerize two or three or more kinds as necessary. The copolymerization may be carried out by a conventional method using a usual radical polymerization initiator such as azobisisobutylnitrile and di-t-butyl peroxide.

Among the acrylic resins made of the above-mentioned copolymer, particularly preferred for forming a clear undercoat layer is 0.5 to 5 mol / kg resin, more preferably 0.5 to 5 mol / kg resin.
４4 mol / kg resin having a cross-linking reactive functional group, and having a number average molecular weight of 1,000-50,000, more preferably 1,
000 to 30,000 reactive oligomers and / or reactive polymers.

The amount of the cross-linking reactive functional group contained in the reactive oligomer or the reactive polymer is 0.5.
If the amount is less than 5 mol / kg resin, the bake-hardened film is unlikely to increase to a preferable crosslink density of 5 × 10 ⁻⁴ mol / cm ³ or more, and the support effect tends to be insufficient as a clear undercoat layer. The base amount is 5 × 10 ^-3 mol / c
If the amount exceeds m ³ , the crosslink density of the baked cured film will excessively exceed 5 × 10 ⁻³ mol / cm ^3, and the cooling / heat repeatability as a clear undercoat layer will deteriorate.

In the case of a low molecular weight product having a number average molecular weight of less than 1,000, imperfect resin having no reactive functional group is liable to be mixed, resulting in insufficient weather resistance.
If the molecular weight is more than 0 and the molecular weight is excessively high, the fluidity of the resin at the time of coating is reduced, and the finish of the coated film is deteriorated.

It is particularly preferable that the clear base coat layer forming agent also contains, as a curing agent, an aminoplast resin as exemplified as a component of the base coat layer forming agent. It is also effective to include a small amount of an isocyanate-based prepolymer for adjusting the crosslink density.

The clear base coat layer forming agent used in the present invention may be a colorless and transparent one comprising the above-mentioned vehicle component and a solvent, but if necessary, in addition to these, titanium oxide, carbon black, organic pigment Colorants such as metal flakes, extenders such as calcium carbonate and barium sulfate may be included, and further, if necessary, ultraviolet absorbers and light stabilizers, surface conditioners, viscosity control agents, catalysts,
It may contain a dispersant, an antifoaming agent, an antistatic agent, an antisettling agent, and the like.

Next, as the solid coat layer forming agent, a paint comprising a coloring component, a vehicle and a solvent as basic components is used. Particularly preferably used as a vehicle is one containing the same acrylic resin and curing agent as those exemplified for the base undercoat layer forming agent. As the acrylic resin, an alkyl ester of acrylic acid or methacrylic acid and, in some cases, another ethylenically unsaturated monomer copolymerizable therewith or a monomer having a functional group capable of reacting with a crosslinking agent Polyfunctional polymers copolymerized by a conventional method can be used in the same manner.

As the alkyl ester, those exemplified as the constituent material of the base coat layer forming agent are exemplified again, and the same copolymerizable monomer may be used as a monomer copolymerizable with these alkyl esters. And a crosslinkable polymerizable silane compound. These alkylsters and other copolymerizable monomers can be used alone, respectively, and it is of course possible to copolymerize two or three or more kinds as necessary. The copolymerization may be carried out by a conventional method using a usual radical polymerization initiator such as azobisisobutylnitrile and di-t-butyl peroxide.

Among the acrylic resins made of the above copolymer, particularly preferred for forming a solid coat layer is 0.5 to 5 mol / kg resin, more preferably 0.5 to 5 mol / kg resin.
４4 mol / kg resin having a cross-linking reactive functional group, and having a number average molecular weight of 1,000-50,000, more preferably 1,
000 to 30,000 reactive oligomers and / or reactive polymers.

Incidentally, the amount of the crosslinking reactive functional group contained in the reactive oligomer or the reactive polymer is 0.5.
If the amount is less than 5 mol / kg resin, the bake-hardened film is unlikely to increase to a preferable crosslink density of 5 × 10 ⁻⁴ mol / cm ³ or more, and the supporting effect as a base layer of the clear coat layer tends to be insufficient. When the amount of the reactive functional group exceeds 5 × 10 ⁻³ mol / cm ³ , the crosslink density of the baked cured film excessively increases beyond 5 × 10 ⁻³ mol / cm ³ , and the solid coat layer is cooled and heated. Poor repeatability.

In the case of low molecular weight compounds having a number average molecular weight of less than 1,000, imperfect resins having no reactive functional groups are liable to be mixed, resulting in insufficient weather resistance.
If the molecular weight is more than 0 and the molecular weight is excessively high, the fluidity of the resin at the time of coating is reduced, and the finish of the coated film is deteriorated.

It is particularly preferable that the solid coat layer forming agent further contains an aminoplast resin as a curing agent as exemplified as a component of the base coat layer forming agent. It is also effective to include a small amount of an isocyanate-based prepolymer for adjusting the crosslink density.

The solid coat layer forming agent used in the present invention contains a coloring agent in addition to the above-mentioned vehicle component and solvent, and includes a coloring agent such as titanium oxide, carbon black, organic pigment, metal flake and the like. Agents, extenders such as calcium carbonate and barium sulfate are exemplified as preferred. The solid coat layer forming agent may also contain an ultraviolet absorber, a light stabilizer, a surface conditioner, a viscosity control agent, a catalyst, a dispersant, an antifoaming agent, an antistatic agent, and an anti-settling agent, if necessary, for the same purpose as described above. Agents and the like can be contained.

The clear coat layer forming agent, which is the most important component in the present invention, is an essentially transparent paint essentially containing a vehicle and a solvent, and a particularly preferred vehicle is a polyfunctional coating. It contains an acrylic resin and / or an organosiloxane resin and a curing agent.

Examples of the polyfunctional acrylic resin used herein include, among those exemplified as the constituent resin of the base coat layer forming agent, polyfunctional acrylic acid or methacrylic acid alkyl ester, or various monomers copolymerizable therewith. (Co) polymers are exemplified. Among these, an acrylic resin containing vinyltrimethoxysilane or vinyltriethoxysilane as a monomer component is particularly preferred.

As the organosiloxane-based resin,
Trimethylmethoxysilane, triethylethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, methyltrimethoxysilane, tetramethoxysilane, methyltriethoxysilane, tetraethoxysilane, methyldimethoxysilane, methyldiethoxysilane, dimethylethoxysilane, diphenyldimethoxy silane, phenyl trimethoxy silane, diphenyl diethoxy silane, but phenyltriethoxysilane and the like, particularly preferable among these are the siloxane-based resin using dimethyl dimethoxy silane or tetramethoxysilane and the like as a monomer component.

Among the above-mentioned polyfunctional acrylic resins and / or organosiloxane resins, particularly preferred for forming a clear coat layer are 5 to 20 mol / kg resin,
More preferably, a cross-linking reactive functional group (hydroxyl group, carboxyl group, glycidyl group, alicyclic epoxy group, block carboxyl group, hydrolyzable silyl group, acid anhydride group, block hydroxyl group, silanol group) of 10 to 20 mol / kg resin And a number average molecular weight of 1,000 to 50,000.
0, more preferably 2,000 to 30,000 resins.

If the amount of reactive functional groups in these resins is less than 5 mol / kg, the clear coat layer after baking and curing has a crosslink density of 5 × 10 ⁻³ mol / cm ³ or more due to insufficient functional groups. And the abrasion resistance of the clear coat layer becomes insufficient. On the other hand, when the amount of the functional group exceeds 20 mol / kg resin and becomes excessively large, the crosslink density of the clear coat layer after baking and curing becomes insufficient. It becomes more than 5 × 10 ^-2 mol / cm ³ , and the repetition of cooling and heating deteriorates. In consideration of these points, it is desirable that the more preferable amount of the reactive functional group of these resins is 10 mol / kg resin or more.

The resin has a number average molecular weight of 1,000.
If the molecular weight is less than 5 × 10 ⁻³ mol / cm ³ , it becomes difficult to increase the crosslink density to 5 × 10 ⁻³ mol / cm ³ or more, resulting in poor abrasion resistance. The finish of the film tends to be poor. Considering these points, a more preferred number average molecular weight of the resin is 2,
000 or more and 30,000 or less.

The above-mentioned polyfunctional acrylic resin and organosiloxane resin can be used alone. However, in order to further enhance the scratch resistance and weather resistance as the outermost coating film, these resins are used. Is preferably used in combination, and a preferable combination ratio is a polyfunctional acrylic resin /
10 to 90/9 in the ratio of the polyfunctional organosiloxane resin
It is in the range of 0 to 10, more preferably 20 to 80/80 to 20.

Examples of the curing agent that may be used together with the polyfunctional acrylic resin and the organosiloxane resin include the aminoplast resin described above again, and specifically, melamine resin and urea resin. Resins, benzoguanamine resins and the like. Among these, a melamine resin is particularly preferred. Specifically, an n-butylated melamine resin obtained by etherifying a condensation polymerization product of melamine and formaldehyde with a monohydric alcohol having about 1 to 4 carbon atoms, an isobutylated melamine Resins and the like are exemplified.
It is also possible to include a small amount of an isocyanate-based prepolymer for adjusting the crosslinking density.

The preferred mixing ratio of the polyfunctional acrylic resin and / or the organosiloxane resin and the aminoplast resin preferably mixed as a curing agent is 50 to 90 parts by mass to 10 to 50 parts of the latter in terms of mass ratio. Range.

In the clear coat layer forming agent used in the present invention, any solvent such as toluene, xylene, ethyl acetate and butyl acetate is used in addition to the above-mentioned vehicle components to ensure coatability. In addition, UV absorbers and light stabilizers to enhance the durability (physical properties and yellowing resistance, etc.) of the clear coat layer, surface modifiers and viscosity control agents to improve the paintability and the surface smoothness of the coating film, etc. It is also possible to contain an appropriate amount. It is also possible to add a small amount of a coloring agent as long as the transparency is not impaired.

The present invention is constituted as described above. In particular, the crosslink density and thickness of the clear coat layer constituting the skin layer (outermost layer) are specified, and preferably, the clear undercoat formed on the lower layer side is specified. By adjusting the cross-linking density and thickness of the layer and solid coat layer to the appropriate range, it is possible to improve both the abrasion resistance and the heat / heat repetition, which were conventionally difficult to achieve, and further improve the paint finish and weather resistance. It is possible to provide a decorative coating film having excellent properties. And according to the forming method of the present invention, it is possible to stably and surely provide an aesthetic coating film having such excellent characteristics.

[0071]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to experimental examples. However, the present invention is not limited to the following experimental examples, and the present invention is not limited thereto. Modifications can be made and all of them are included in the technical scope of the present invention.

Experimental Examples Using the paints (coat layer forming agents) shown in Tables 1 to 15 below, a laminated coat layer described later was formed. In each table, resin characteristics are described together with the raw material composition and the mixing ratio when each resin is manufactured.

The production of each paint type was carried out as follows. [Base coat layer forming agent] First, according to the resin composition, each raw material monomer is dissolved in a solvent at a predetermined ratio, and a catalyst dissolved in an appropriate amount of the solvent is dropped at 70 to 160 ° C. By heating for 10 hours, each resin is synthesized. Each obtained resin solution, melamine resin dissolved in a predetermined solvent according to the paint formulation, and aluminum flake, catalyst, light stabilizer, ultraviolet absorber,
A base coat layer forming agent is prepared by mixing with a light stabilizer, further adding an appropriate amount of a surface conditioner and a viscosity controlling agent, and mixing uniformly.

[Clear Undercoat Layer Forming Agent] First, according to the resin composition, each raw material monomer is dissolved in a solvent at a predetermined ratio, and the catalyst dissolved in an appropriate amount of the solvent is dropped in a nitrogen gas atmosphere at 70 to 70%. Each resin is synthesized by heating at 160 ° C. for 1 to 10 hours. Each obtained resin solution, melamine resin dissolved in a predetermined solvent according to the paint formulation, and aluminum flakes, catalyst, light stabilizer,
A clear undercoat layer forming agent is prepared by mixing with an ultraviolet absorber and a light stabilizer, further adding an appropriate amount of a surface conditioner and a viscosity controlling agent, and mixing uniformly.

[Solid coat layer forming agent] First, according to the resin composition, each raw material monomer is dissolved in a solvent at a predetermined ratio, and a catalyst dissolved in an appropriate amount of the solvent is dropped in a nitrogen gas atmosphere to 70-160. Each resin is synthesized by heating at 1 ° C. for 1 to 10 hours. Each obtained resin solution, melamine resin dissolved in a predetermined solvent according to the paint formulation, and aluminum flakes, titanium oxide, catalyst,
A clear base coat layer forming agent is prepared by mixing with a light stabilizer, an ultraviolet absorber, and a light stabilizer, further adding an appropriate amount of a surface conditioner and a viscosity control agent, and mixing uniformly.

[Clear coat layer forming agent] According to the resin composition of the acrylic resin, each raw material monomer is dissolved in a predetermined ratio in a solvent, and a catalyst dissolved in an appropriate amount of the solvent is added dropwise thereto under a nitrogen gas atmosphere. 1-1 at 70-160 ° C
By heating for 0 hour, each acrylic resin is synthesized. Also, regarding the organosiloxane resin,
According to each resin blend, each raw material monomer is dissolved in a solvent at a predetermined ratio, and a catalyst dissolved in an appropriate amount of water is heated dropwise at 0 to 50 ° C. for 1 to 10 hours under a nitrogen gas atmosphere. Then, synthesis of each organosiloxane resin is performed.

The acrylic resin and / or organosiloxane resin solution obtained above is mixed with a catalyst, an ultraviolet absorber, a light stabilizer and the like according to each coating composition, and further, an appropriate amount of a surface conditioner is added thereto and mixed uniformly. By doing so, a clear coat layer forming agent is prepared.

The amounts of the functional groups and the number average molecular weights shown in the respective tables refer to the values measured by the methods described above. The suppliers of the agents described as trade names in the table are also shown below. "Cymel 327": melamine resin manufactured by Mitsui Toatsu Chemicals, Inc. "Super Beckamine": melamine resin manufactured by Dainippon Ink and Chemicals, Inc. "Uban 120": melamine resin manufactured by Mitsui Toatsu Chemicals "FR-606C": Aluminum flake “Sandbar 3206” manufactured by Asahi Kasei Kogyo Co., Ltd .: UV absorber manufactured by Sando Co., Ltd. “Sandbar 3058”: Light stabilizer manufactured by Sando Co., Ltd. “KP321”: Surface conditioner manufactured by Shin-Etsu Chemical Co., Ltd. “CAB381-2”: EASTMAN CHEMICAL PRODUCTS,
Inc. viscosity control agent “MG100S”: Dainippon Ink and Chemicals, Inc. “CR-95”: Ishihara Sangyo Co., Ltd. titanium oxide powder “Cyclomer A200”: Reactivity from Daicel Chemical Industries, Ltd. monomer

[0079]

[Table 1]

[0080]

[Table 2]

[0081]

[Table 3]

[0082]

[Table 4]

[0083]

[Table 5]

[0084]

[Table 6]

[0085]

[Table 7]

[0086]

[Table 8]

[0087]

[Table 9]

[0088]

[Table 10]

[0089]

[Table 11]

[0090]

[Table 12]

[0091]

[Table 13]

[0092]

[Table 14]

[0093]

[Table 15]

Table 1 above relates to base coat layer forming agents, all of which satisfy the requirements of the present invention.

Table 2 relates to the clear base coat layer forming agent, and paint Nos. FCC1 to 3 satisfy the preferable requirements defined in the present invention. On the other hand, paint Nos. FCC 4 to 5 have a cross-linking reactive functional group content of the resin, and paint Nos. FCC 6 to 7 have a number average molecular weight of the resin which is outside the preferable requirements of the present invention.

Table 3 relates to the solid coat layer forming agent, and paint Nos. FS1 to FS3 satisfy the preferred requirements of the present invention. On the other hand, paint Nos. FS4 to FS5 have a cross-linking reactive functional group content of the resin, and paint Nos. FS6 to FS7 have a number-average molecular weight of the resin which is outside the preferable requirements of the present invention.

Tables 4 to 15 relate to the clear coat layer forming agent.
Table 9 shows an organosiloxane resin, Tables 10 to 14 show a combination of an acrylic resin and an organosiloxane resin, Table 15
Shows an example using an acrylic resin.

In these clear coat layer forming agents, paint No. SHC1-3, SMC1-3, SIC1-3, SBC1-3, SOC1-3,
SLC1-3, SSC1-3, SXC1-3, SPC1-3, SYC1-3, SZC1
-3 and SRC1-6 satisfy all the preferable requirements of the present invention. On the other hand, paint No.SHC4, SMC4, SIC4, SBC
4, SOC4, SLC4, SLC7, SSC4, SSC7, SXC4, SXC7, SPC
4, each resin of SPC7, SYC4, SYC7, SZC4, SZC7 has a crosslinking reactive functional group amount, and paint No.SHC5-6, SMC5-6, SIC5 ~
6, SBC5-6, SOC5-6, SLC5-6, SSC5-6, SXC5-6, SP
C5-6, SYC5-6, SZC5-6 each number average molecular weight,
Each departs from the preferred requirements of the invention.

Next, an experimental example using each of the above paints is shown in Table 16.
To 41. In each table, the type of the coating material applied on the zinc / nickel-plated steel sheet as the base material, the coating method, and the coating film performance are shown. The crosslink density of the coating film shown in each table was obtained as "E '/ 3RT" as described above, and the dry film thickness was obtained by an electromagnetic film thickness meter (manufactured by Kett Science Laboratory Co., Ltd.). In addition, W shown in the section of coating method
/ W indicates a wet and wet method, D / W indicates a dry and wet method, and W / D indicates a wet and dry method. The coating film performance was evaluated in four steps according to the following methods.

Scratch resistance: Using a friction tester type I, the active area with the coating film was set to 20 mm × 20 mm, and the load was 300 g.
The reciprocating speed is 0.5 times / s with the moving distance of 100 mm and the contact finger at f
The gloss retention after 10 reciprocations at ec is determined by the following formula and evaluated based on the following criteria: 20 ° gloss retention (%) = [gloss after test / gloss before test]
× 100 (%) ☆: 95% or more and 100% or less ：: 90% or more and less than 95% ○: 80% or more and less than 90% ：: Less than 80%.

Finishing property: PGD value was measured using a PGD meter manufactured by Nippon Shiken, Ltd., ☆: 1.5 or more ◎: 1.0 or more, less than 1.5 ：: 0.8 or more, less than 1.0 ▲: less than 0.8.

Cooling / heat repetition: 10 cycles of cooling / heating were performed with (-30 ° C × 1 hour → room temperature × 1 hour → 80 ° C. × 1 hour → room temperature × 1 hour) as one cycle, and evaluated according to the following criteria. : No cracks even in 10 cycles ◎: Cracks occur in 8 to 9 cycles ○: Cracks occur in 6 to 7 cycles: Cracks occur in 5 cycles or less.

Weather resistance: After exposure for 3600 hours using a sunshine carbon arc lamp type weather resistance tester, evaluation was made at a 60 ° gloss retention obtained by the following formula. 60 ° gloss retention (%) = [after test Gloss / gloss before test] ×
100 (%) ☆: 95% or more, 100% or less ：: 90% or more, less than 95% ○: 80% or more, less than 90% ：: Less than 80%.

[0104]

[Table 16]

[0105]

[Table 17]

[0106]

[Table 18]

[0107]

[Table 19]

[0108]

[Table 20]

[0109]

[Table 21]

[0110]

[Table 22]

[0111]

[Table 23]

[0112]

[Table 24]

[0113]

[Table 25]

[0114]

[Table 26]

[0115]

[Table 27]

[0116]

[Table 28]

[0117]

[Table 29]

[0118]

[Table 30]

[0119]

[Table 31]

[0120]

[Table 32]

[0121]

[Table 33]

[0122]

[Table 34]

[0123]

[Table 35]

[0124]

[Table 36]

[0125]

[Table 37]

[0126]

[Table 38]

[0127]

[Table 39]

[0128]

[Table 40]

[0129]

[Table 41]

From the above Tables 16 to 41, analysis can be made as follows.

Paint plate Nos. 1 to 7, 22 to 28, 43 to 49, 64 to 7
0, 85-91, 106-112, 128-134, 150-156, 172-17
8, 194 to 200, 216 to 222, 238 to 244 are examples that satisfy all the preferable requirements of the present invention, and are excellent in all of abrasion resistance, finish of coating film, repetition of cooling and heating, and weather resistance. Is shown.

On the other hand, paint plates No. 8, 29, 50, 71,
92, 113, 114, 135, 136, 157, 158, 179, 180, 201, 2
02, 223, 224, 245, and 246, the crosslink density of the clear coat layer formed as the skin layer and the amount of the crosslinkable reactive functional group of the resin are out of the requirements of the present invention, and the crosslink density is small and the scratch resistance is low. Possibility is poor, or the crosslink density is too large, and the cooling / heating repeatability is poor.

Paint plates No. 9, 30, 51, 72, 93, 115, 137,
159, 181, 203, 225, and 247, the number average molecular weight of the resin constituting the clear coat layer is too small outside the preferred range, and the crosslinking density of the layer is insufficient, and sufficient scratch resistance is not obtained. .

Paint plates No. 11, 12, 32, 33, 53, 54, 74, 7
5, 95, 96, 117, 118, 139, 140, 161, 162, 183, 18
4, 205, 206, 227, 228, 249, and 250 are comparative examples in which the dry film thickness of the clear coat layer deviates from the requirements of the present invention. Satisfactory scratch resistance is obtained with a thin film having a dry film thickness of less than 1 μm. On the contrary, if the thickness exceeds 20 μm and the thickness becomes excessively large, the repetition of cooling and heating deteriorates.

Paint plates No. 19-21, 40-42, 61-63, 82-8
4, 103-105, 125-127, 147-149, 169-171, 191-19
3, 213 to 215, 235 to 237, and 257 are comparative examples in which the coating method deviates from the requirements of the present invention, and the adhesion between the layers becomes insufficient when dry and wet coating is employed,
The paint finish has deteriorated and the weather resistance has also deteriorated.

In the case of the paint plate Nos. Other than the above, the clear coat layer constituting the skin layer satisfies the requirements of the present invention, and is tentatively included in the scope of the present invention. It is positioned as a reference example lacking any of the above, and one of the above-mentioned four kinds of coating film properties is becoming insufficient in accordance with the following preferred missing requirements.

That is, paint plate No. 10, 31, 52, 73, 94, 11
6, 138, 160, 182, 204, 226, 248, the finish properties of the coating film is somewhat poor because the number average molecular weight of the resin constituting the clear coat layer forming agent is too large, paint plate No. 13, 14, 34 , 3
5, 55, 56, 76, 77, 97, 98, 119, 120, 141, 142, 16
3, 164, 185, 186, 207, 208, 229, 230, the crosslink density of the clear undercoat layer and the amount of the crosslinkable reactive functional groups of the resin are outside the preferred requirements of the present invention, so that the thermal repeatability or weather resistance She is short of sex.

Paint plates No. 15, 36, 57, 78, 99, 121, 14
3, 165, 187, 209, 231 has a poor weather resistance because the number average molecular weight of the resin constituting the clear undercoat layer is smaller than the preferred range of the present invention, paint plate No. 1
6, 37, 58, 79, 100, 122, 144, 166, 188, 210, 232
Is because the number average molecular weight of the resin constituting the clear base coat forming agent is too large, and the paint finish is slightly poor.
No. 17, 18, 38, 39, 59, 60, 80, 81, 101, 102, 123,
124, 145, 146, 167, 168, 189, 190, 211, 212, 233,
234 has poor dry finish or slightly lacks heat / heat repeatability because the dry film thickness of the clear undercoat layer deviates from the preferred requirements of the present invention.

In the coated plates Nos. 251 and 252, the crosslink density of the solid coat layer and the amount of the crosslinkable reactive functional group of the resin were out of the requirements of the present invention. On the other hand, the coated plate No. 253 has a somewhat poor weather resistance because the crosslink density of the solid coat layer and the number average molecular weight of the resin are out of the preferable requirements of the present invention.

The paint plate No. 254 has a slightly poor finish due to the too large number average molecular weight of the resin constituting the solid coat forming agent, and the paint plates No. 255 and 256 have a dry film of the solid coat layer. Since the thickness deviates from the preferable requirements of the present invention, the weather resistance or the heat / heat cyclability is slightly poor.

Since the paint Nos. 258 to 269 do not contain a hydrolyzable silyl group and / or silanol group as a functional group, the amount of the crosslinking reactive functional group satisfies the prescribed requirement, but the crosslinking density is out of the preferred requirement. And abrasion resistance tends to be insufficient.

[0142]

According to the present invention, the crosslink density and the thickness of the clear coat layer constituting the skin layer are specified, and the thin clear coat layer having a high crosslink density is used as the skin layer. By forming a relatively thick clear undercoat layer or solid coat layer with a slightly lower crosslink density, preferably on the lower layer side, it has both excellent scratch resistance and repetition of cooling and heating, and It is possible to provide a beautiful coating film which is excellent in properties and finish of coating.

[Brief description of the drawings]

FIG. 1 is a graph showing the influence of the crosslink density in a conventional clear coat layer on scratch resistance and thermal repetition.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (reference) // C09D 5/00 C09D 5/00 Z F term (reference) 4D075 AE10 CA02 CA04 DA06 DB01 DC12 EA43 EB22 EB43 EB52 4J038 CG141 DA142 DA162 DA172 DL031 EA011 GA03 MA14 NA11 PA07

Claims (10)

[Claims] The crosslink density of the skin layer is 5 × 10 ⁻³ or more.
Thickness 1-20 containing 5 × 10 ^-2 mol / cm ³ cross-linked resin
An abrasion-resistant coating film having a μm clear coat layer formed thereon. 2. A clear undercoat layer having a thickness of 20 to 80 μm containing a crosslinked resin having a crosslink density of 5 × 10 ^{−4 to} 5 × 10 ⁻³ mol / cm ³ is formed below the clear coat layer. The scratch-resistant coating film according to claim 1, wherein 3. The scratch-resistant coating film according to claim 2, wherein a base coat layer is formed further below the clear base coat layer. 4. A solid coat layer having a thickness of 20 to 80 μm containing a crosslinked resin having a crosslink density of 5 × 10 ^{−4 to} 5 × 10 ⁻³ mol / cm ³ is formed below the clear coat layer. The abrasion-resistant coating film according to claim 1. 5. The scratch-resistant coating film according to claim 1, wherein the clear coat layer contains a polyfunctional acrylic resin and / or an organosiloxane resin. 6. A dry base coat layer forming agent having a dry film thickness of 20 to 80 on a base coat layer formed on a substrate surface.
After wet-on-wet painting to make μm,
Forming a scratch-resistant coating film on the clear base coat layer by applying a clear coat layer forming agent wet-on-wet so as to have a dry film thickness of 1 to 20 μm, and then baking and drying. Law. 7. A solid coat layer forming agent is wet-on-coated on the surface of the base material so that the dry film thickness is 20 to 80 μm.
After the wet coating, a clear coat layer forming agent is wet-on-wet coated on the solid coat layer so as to have a dry film thickness of 1 to 20 μm, and then baked and dried. A method for forming a coating film. 8. The method according to claim 8, wherein the clear coat layer forming agent is 5 to 20.
Acrylic resin having a cross-linking reactive functional group of mol / kg resin and a number average molecular weight of 1,000 to 50,000 and / or
The method for forming a scratch-resistant coating film according to claim 6 or 7, wherein the method comprises an organosiloxane resin. 9. The clear base coat layer forming agent or the solid coat layer forming agent has a crosslinking reactive functional group of 0.5 to 5 mol / kg resin and has a number average molecular weight of 1,000 to 1,000.
The method for forming a scratch-resistant coating film according to any one of claims 6 to 8, comprising 50,000 reactive oligomers and / or reactive polymers. 10. The base coat layer forming agent is 0.5 to 3
It has hydroxyl groups of mol / kg resin and has a number average molecular weight of 1,0.
10. An acrylic resin containing from 0.00 to 50,000 and an aminoplast resin as a curing agent.
The method for forming a scratch-resistant coating film according to any one of the above.