JP3339304B2 - Painted object and painting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention provides a solid coating having a topcoat layer formed on a basecoat layer having a metal substrate surface rendered hydrophilic. Further, the present invention provides a coating method capable of uniformly and robustly coating a top coat layer by making the surface of a metal substrate hydrophilic.

[0002]

2. Description of the Related Art In recent years, as environmental issues have been closed up, treaties, laws, laws,
Regulations are being tightened. In the field of paints used for various kinds of coatings, there is a tendency that solvent emission regulations (VOC regulations) such as the New Clean Air Act of the United States and the Federal Exhaust Gas Act (TA-Luft) of the United States are strengthened, especially overseas. As a countermeasure, the use of water-based paints has been spreading especially for metallic basecoats containing a large amount of organic solvents.
In Japan, restrictions according to these regulations are spreading, and automobile manufacturers are entering the stage of technology construction to develop water-based paints that are effective against these regulations and have a proven track record overseas. . (Technical Information Association, "Water-based paint and coating technology", pp. 239-57 (1992))

[0003]

However, since the water-based paint uses water as a solvent, it is extremely difficult to control the working width of the paint as compared with the conventional solvent paint. Factors that determine the width of the coating work include: I Finish appearance (skin, gloss, etc.) J Nure limit K Waki limit L Sagging limit. The control of these elements plays a role of a solvent having various properties, but there is a restriction that water-based paints cannot use this solvent much.

First, water has a poor surface wetting due to its higher surface tension than a solvent. Particularly, water-based paints, which are susceptible to the influence of humidity, have a noticeable poor wetting in a low humidity range. Phenomena) and armpits (bubbles). In order to suppress such a phenomenon, measures such as adding a small amount of a solvent having a high wetting effect, adding a useful auxiliary agent, and controlling the viscosity of the paint have been taken. A solution is required.

Secondly, since water is not lipophilic, cissing is liable to occur due to deposits such as oil. Particularly, melamine alkyd baking paint is used as a top coat immediately after surface treatment of iron material. There is much risk of cissing.

Third, since water has a high latent heat of vaporization, rapid heating causes bumping of the water, which tends to cause a fire. Therefore, it is necessary to provide a means for covering the problem of residual water content and bumping of water. In an automobile line, it is necessary to pass through a dry zone called a blow-off.
A more effective solution is needed.

[0007] Fourth, as in the preceding paragraph, due to the high latent heat of vaporization of water, the increase in viscosity at the time of coating is significantly lower than that of the solvent type, and sagging is likely to occur. In particular, the aqueous type is more susceptible to humidity than the solvent type, and causes extreme sagging at high humidity (80% or more), which is very difficult to control. To cope with this problem, measures such as using a high-thixotropic aqueous basecoat or adding a control agent or a solvent have been taken, but a more effective solution is required. .

Fifth, since water has a high dielectric constant, the electric resistance of the coating material becomes low, and a leak phenomenon occurs in the conventional internal electrode type electrostatic coating machine, so that the electrostatic coating becomes impossible. Various studies and countermeasures have been made on the combination of the electrostatic coating and the water-based coating for this problem, but a more effective solution is required.

As described above, various studies and countermeasures have been carried out on various coating problems arising from the characteristics of water, but the superiority of water-based paints in terms of VOC countermeasures, safety, coating environment, etc. Further technology construction is required to make full use of. (Technical Information Association, "Water-based paint and coating technology", pp. 239-57 (1992))

The present invention has been made in view of the above-mentioned problems in the prior art, and has as its object to make full use of the advantages of water-based paints, such as VOC countermeasures, safety, and coating environment. .

[0011]

Means for Solving the Problems The present invention has been studied in order to solve the above-mentioned problems, and by forming a top coat layer on a base coat layer having a hydrophilic surface of a metal substrate, The present inventors have found that a uniform and robust coated product of a metal substrate can be obtained, and have reached the present invention.

The present invention is based on the phenomenon of hydrophilization of the surface of a metal substrate by an optical semiconductor. That is, in order to achieve the above object, the coating method according to claim 1 uses a metal substrate surface.
A base made of or containing an optical semiconductor
In the process of forming a coating layer, light excitation caused by light irradiation
Therefore, the water wettability of the surface of the base coat layer is determined by contact with water.
Work to make hydrophilic so that it becomes 10 ° or less in terms of antenna
The water-based paint on the surface of the base coat layer.
Forming a top coat layer,
I do.

[0013] The excitation wavelength of the optical semiconductor is less than 1 and the illuminance is 1 m.
The base coat is irradiated with light of W / cm ² or less.
It is preferred to make the layer surface hydrophilic.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a metal substrate whose surface is required to be hydrophilized is prepared, and a layer of an optical semiconductor or a layer containing an optical semiconductor is formed thereon. And the surface is made hydrophilic in response to the light excitation, and this is used as a base coat layer to form a top coat layer thereon.

When an optical semiconductor is directly contained in a general pigment, or when a thin film containing an optical semiconductor is applied to a surface coated with a general pigment, there is a risk of causing photo-oxidation degradation.
Therefore, when a layer of an optical semiconductor or a layer containing an optical semiconductor is used as a base coat layer, particularly when the base coat layer is colored, such photo-oxidative deterioration is prevented. Is required.

Furthermore, a member to form a coating film composed of a thin film containing an optical semiconductor, the coloring metal ions such as iron is used in a water environment that dissolved, possibly chromatic color metal impairing the appearance precipitated It is required to prevent such a phenomenon.

Accordingly, the present invention is to make the energy level of the conduction band of the optical semiconductor be a positive value when the hydrogen generation level is 0 eV. The conventional theory of the photo-oxidation-reduction reaction is that the conduction electrons-
A hole pair is generated, and then a reduction reaction by the generated conduction electrons and an oxidation reaction by the holes are simultaneously promoted and proceed. Accordingly, tin oxide or rutile, in which the energy level of the conduction band of the optical semiconductor is not sufficiently high on the negative side, has a structure in which the reduction reaction by conduction electrons does not easily proceed, and only the oxidation reaction by holes is easily promoted. In such a structure, conduction electrons become excessive, and electron-hole pairs generated by photoexcitation recombine without participating in the oxidation-reduction reaction. Therefore, practically neither oxidation reaction nor reduction reaction occurs. However, as described later, the hydrophilization phenomenon due to photoexcitation proceeds.

When a photooxidation-reduction reaction of an optical semiconductor is used to decompose an organic substance, the decomposition reaction is performed using water or oxygen in the environment. That is, conduction electrons generated by photoexcitation reduce oxygen to form superoxide ions (O
₂ ^-) to generate the hole is to oxidize the hydroxyl group to generate a hydroxyl radical (· OH), these highly reactive oxygen species (O ₂ ^- organics by oxidation-reduction reaction of and · OH) Is decomposed. Therefore, in order to effectively decompose organic substances by photooxidation and reduction, the energy level in the upper valence band for generating holes is determined by the oxygen generation level (+0.82) at which hydroxyl groups release electrons.
eV), and the energy level at the lower end of the conduction band where conduction electrons are generated is located more negative than the hydrogen generation level (0 eV) where hydrogen emits electrons and supplies to the oxygen side. It will be good. Therefore, conversely, in order to prevent organic substances from being effectively subjected to photooxidation-reduction decomposition, the energy level in the upper region of the ■ valence band must be positioned more negative than the oxygen generation level (+0.82 eV), or The energy level at the lower end of the band should be located on the positive side of the hydrogen generation level (0 eV).

When a photooxidation-reduction reaction of an optical semiconductor is used for precipitation of metal ions in water, metal ions are reduced and precipitated by conduction electrons generated by photoexcitation. (At the same time, holes oxidize hydroxyl groups in water to form hydroxyl radicals (.O
H). Therefore, for example, in order to effectively precipitate and remove iron ions from water, the energy level at the lower end of the conduction band where the conduction electrons are generated is the iron generation level (−
0.44 eV). Therefore,
Conversely, in order to prevent metal ions from being precipitated from water, the energy level at the bottom of the conduction band should be positioned more positive than the metal generation level. Excluding the noble metal, the metal generation level is on the negative side of the hydrogen generation level, so that the energy level at the bottom of the conduction band should be located on the positive side of the hydrogen generation level (0 eV). become.

From the above, as one method of photohydrophilizing while suppressing the decomposition of resin and the precipitation of dissolved metal ions in water, the energy level of the conduction band of the optical semiconductor is set to 0 eV and the hydrogen generation level is set to 0 eV. In this case, it can be seen that there is a method that is positioned at a positive value.

Further, the present invention is to prepare a metal substrate whose surface is required to be hydrophilic, and form a transparent or colored thin film containing optical semiconductor particles and a hydrophilic substance which is not an optical semiconductor on the metal substrate. At this time, the optical semiconductor is kept almost in contact with the outside air. In such a state, most of the conduction electrons and holes generated by photoexcitation of the optical semiconductor do not diffuse to the surface, and the probability of contact with surface reactive species such as water, oxygen, and metal ions is greatly reduced. The oxidation-reduction reaction is suppressed. Then, the film thickness is thin enough so that the illuminance of the excitation light is 1 mW / cm ² or less and sufficient abrasion resistance can be exhibited.
Alternatively, it can be suppressed to such an extent that a photooxidation-reduction reaction hardly occurs under the amount of conduction electrons and holes generated in a coating film having a low content of optical semiconductor particles. Nevertheless, the photohydrophilization reaction proceeds as described later.

Further, the present invention provides a metal base material whose surface is required to be hydrophilic, and forms a transparent or colored thin film containing a substance which inhibits the photooxidation-reduction reaction of the optical semiconductor particles and the optical semiconductor on the metal substrate. Is what you do.

According to the present invention, a top coat layer of an aqueous paint is formed on the base coat layer obtained by the above method on the surface of a metal substrate.

According to the present invention, an optical semiconductor layer or a top coat layer containing an optical semiconductor is further formed on the base coat layer obtained by the above method on the surface of the metal substrate, and the optical semiconductor is excited. Irradiation with light of a wavelength equal to or less than the wavelength renders the surface hydrophilic in response to light excitation.

Here, the term "hydrophilization" refers to a phenomenon in which the surface wettability increases due to external factors and the contact angle with water decreases. The photohydrophilization is a case where the external factor is light in the above. Highly hydrophilizing and superhydrophilizing means hydrophilizing to a degree of contact angle with water of 10 ° or less, preferably 5 ° or less.

Optical semiconductors that can be suitably used in the present invention include anatase type titanium oxide, rutile type titanium oxide, zinc oxide, tin oxide, strontium titanate, tungsten trioxide, bismuth trioxide, and secondary oxide. Metal oxides such as iron are exemplified.

Optical semiconductors that can be suitably used in the present invention and have a positive energy level in the conduction band when the hydrogen generation level is 0 eV include tin oxide, tungsten trioxide, and dioxide trioxide. Metal oxides such as bismuth, ferric oxide, and rutile-type titanium oxide are exemplified.

The hydrophilic substance which is not an optical semiconductor and can be suitably used in the present invention includes at least one of inorganic oxides such as silica, amorphous titanium oxide and alumina, silanol, polysilanol, and an organo group bonded to a silicon atom. Examples thereof include silicone resins partially substituted with hydroxyl groups.

As substances that inhibit the photooxidation-reduction reaction of the optical semiconductor, there are known alkali metals, alkaline earth metals, alumina, zirconia, silica, antimony oxide, amorphous titanium oxide, aluminum, manganese and the like.

In the present invention, the thinner the film, the better. Preferably it is 1 μm or less, more preferably 0.2 μm or less. Then, the absolute amount of the optical semiconductor fixed to the base material can be reduced, and the photooxidation-reduction property can be further reduced. Also, the wear resistance is improved. More particularly 0.2
When the thickness is less than μm, it is easy to secure the transparency of the thin film containing the optical semiconductor, and the design and transparency of the underlayer can be maintained.

In the present invention, the content of the optical semiconductor is preferably 5 to 80% by weight, more preferably about 10 to 50% by weight, based on the optical semiconductor-containing layer. This is because the smaller the content of the optical semiconductor, the lower the photooxidation-reduction property. However, since the photohydrophilization phenomenon is also a phenomenon based on the photoexcitation phenomenon of the optical semiconductor, it is necessary to contain about 5% or more.

In the present invention, the illuminance of the following wavelength excitation wavelength, preferably 0.0001~1mW / cm ^2, more preferably from about 0.001~1mW / cm ^2. This is because the lower the illuminance of light having a wavelength equal to or shorter than the excitation wavelength, the more the amount of generated electron-hole pairs decreases, so that the photooxidation-reduction property can be reduced. However, since the photohydrophilization phenomenon is also a phenomenon based on the photoexcitation phenomenon of the optical semiconductor, it is about 0.0001 mW / cm ^2.
The above excitation light illuminance is required.

In the present invention, the light source for exciting the optical semiconductor may be any light source capable of emitting illuminance of light having a wavelength equal to or less than the above-mentioned excitation wavelength, such as sunlight, a fluorescent lamp, an incandescent lamp, a metal hydride lamp, and mercury. Interior lighting such as lamps can be used.

In the present invention, an intermediate layer may be provided between the substrate and the optical semiconductor-containing layer. Thereby, the adhesion to the base material is increased, and the wear resistance is improved.

A base coat layer of a thin film containing optical semiconductor particles located at a positive value when the energy level is 0 eV and the energy level is 0 eV on the metal base material whose surface needs to be made hydrophilic. For example, there is the following method as a method for forming. (1) The above-mentioned optical semiconductor particles are applied to the surface of a metal base material and fired. (2) An organic salt compound containing an elemental metal species of the above-mentioned photosemiconductor metal oxide (alkoxide,
, Acetate, etc.) or non-oxide inorganic compounds (chlorides, sulfates, etc.) are hydrolyzed, applied to a substrate, and dehydrated by heating or the like. If the metal oxide is not crystallized like titanium oxide by this process, the metal oxide is further crystallized by heating. (3) The constituent metal of the semiconductor metal oxide is fixed on the surface of the metal base by sputtering or the like, and then oxidized by a method such as heating or electrode reaction. If the metal oxide is not crystallized like titanium oxide by this process, the metal oxide is further crystallized by heating.

The method of forming a thin film containing optical semiconductor particles and a hydrophilic substance that is not an optical semiconductor on a metal substrate that requires hydrophilization of the surface according to the present invention differs depending on the type of the hydrophilic substance that is not an optical semiconductor. (I) When the hydrophilic substance that is not an optical semiconductor is an inorganic oxide such as silica or alumina. (1) The optical semiconductor particles and the inorganic oxide particles are applied to the surface of a metal substrate and fired. (2) On the surface of the metal substrate, the optical semiconductor particles and an organic compound (alkoxide, alkoxide,
A hydrolyzate of a non-oxide inorganic compound (e.g., a chelate or an acetate) or a hydrolyzate of a non-oxide inorganic compound is applied to a metal substrate and subjected to a dehydration reaction by heating or the like. (3) On the surface of a metal substrate, the inorganic oxide particles and an organic compound (alkoxide, chelate, acetate, or the like) containing a metal element constituting the optical semiconductor particles or an inorganic compound that is not an oxide (chloride, A hydrolyzate of a sulfated oxide or the like is applied to a metal substrate and subjected to a dehydration reaction by a method such as heating. If the metal oxide is not crystallized like titanium oxide by this process, the metal oxide is further crystallized by heating. (II) In the case of a silicone resin in which at least a part of an organo group in which a hydrophilic substance which is not an optical semiconductor is bonded to a silicon atom is substituted with a hydroxyl group, the optical semiconductor particles and the silicone resin and / or a precursor thereof (organoalkoxy) Orchid and its hydrolyzate) is applied to a metal substrate and heated. Thereby, it is hydrolyzed as required, and then dehydrated and polymerized and hardened to fix the optical semiconductor particles and the silicone resin on the metal substrate. Thereafter, the optical semiconductor is irradiated with light having a wavelength equal to or shorter than the excitation wavelength to replace at least a part of the organo groups bonded to the silicon atoms in the silicone resin with hydroxyl groups.

[0037] The method of forming an optical semiconductor particles on a metal substrate requiring hydrophilicity of the surface of the present invention, a thin film containing a substance that inhibits the photo-oxidation-reduction reaction of the optical semiconductor, for example the following methods . (1) A compound containing the optical semiconductor particles and the constituent metal species in the above-mentioned inhibitory substance is applied to the surface of the metal substrate, and baked. _
(2) On the surface of a metal substrate, a compound containing a constituent metal species in an inhibitory substance and an organic compound (alkoxide, chelate, acetate, etc.) or an oxide containing a constituent metal species of an optical semiconductor particle A hydrolyzate of an inorganic compound (chloride, sulfate, etc.) is applied to a metal substrate and subjected to a dehydration reaction by a method such as heating. If the metal oxide is not crystallized like titanium oxide by this process, the metal oxide is further crystallized by heating. An organic compound (alkoxide, chelate, acetate, etc.) or a non-oxide inorganic compound (chloride, sulfate, etc.) containing an optical semiconductor particle and a metal element constituting the above inorganic oxide on the surface of a metal substrate. Is applied to a metal substrate and subjected to a dehydration reaction by a method such as heating.

[0038]

EXAMPLES (Example 1) First, a 10 cm square iron substrate was washed and coated with a silicon layer in advance in order to smooth the substrate surface. For this purpose, the liquid A (silica sol) and the liquid B (trimethoxymethylsilane) of the coating composition “Glaska” made of Japan Synthetic Rubber are mixed at a weight ratio of 3, and this mixed liquid is applied to an iron substrate. At a temperature of 150 ° C. to obtain a 3 μm-thick silicon-coated iron plate. next,
On the surface of the iron plate, a thin base coat layer composed of an optical semiconductor (1 part by weight) and a silicone resin (1 part by weight) was formed. More specifically, anatase-type titania sol (TA-15, manufactured by Nissan Chemical Industries, Ltd.) and the above-mentioned “Glaska” solution A are mixed, diluted with ethanol, and further added with “Glaska” B solution, and titanium oxide is added. A silicone coating composition was prepared. Here, the liquid A and the liquid B of “Glaska” were adjusted to have a weight ratio of 3. This coating composition was applied to the surface of the iron plate and cured at a temperature of 150 ° C. to form a base coat layer comprising anatase-type titania particles and a silicone resin. 1 was obtained. This sample has 20W BLB
After irradiating with a fluorescent lamp (manufactured by Sankyo Electric Co., Ltd.) at an ultraviolet illuminance of 0.5 mW / cm ² , a contact angle measuring device (ERM) was used.
The contact angle between the sample and water was measured using a model GI-1000 manufactured by Company A). The contact angle was measured 30 seconds after a water drop was dropped on the sample surface from the micro syringe. The measurement result at this time was 2 °, and the surface of the base coat layer showed a high degree of hydrophilicity. Next, a colorable acrylic resin was coated on the surface of the base coat layer, and the appearance of the coating film was visually observed to examine pinholes, irregularities, and the like. As a result, the appearance of the coating film was excellent in smoothness and was in a good state. Further, according to Japanese Industrial Standards (JIS) H8602, the surface of the sample was scratched with a pencil lead, and the hardest pencil lead from which the top coat layer was peeled was detected (pencil hardness test). The result was 4H.

Example 2 A 10 cm square iron substrate was washed, and a 3 μm-thick silicon-coated iron plate was obtained in the same manner as in Example 1. Next, a colored thin glass basecoat layer composed of an optical semiconductor and a silicone resin was formed using colored "Glaska", and the sample No. 1 was formed. 2 was obtained. After irradiating with ultraviolet light under the same conditions as in Example 1, the contact angle of the surface of the base coat layer was measured. As a result, the contact angle was 3 °.
The surface of the layer showed a high degree of hydrophilicity. Next, a top coat of a thin film containing an optical semiconductor, a silicone resin, and a substance that inhibits a photooxidation-reduction reaction is formed on the surface of the base coat layer.
Layer was formed. More specifically, a new coating product obtained by adding silica, which is a substance that inhibits a photooxidation-reduction reaction, to the coating product prepared in Example 1, is applied to the surface of the base coat layer, and then cured. Irradiated with ultraviolet light. As a result of observing the surface of this sample, it was found to be excellent in smoothness and in a good state. In addition, the result of the pencil hardness test was 5H,
It was even more excellent in abrasion resistance.

Example 3 The following samples were prepared as comparative materials with those of Examples 1 and 2. First, a rust-preventive paint was applied to the surface of a 10 cm square iron plate to form a base coat layer. 3 was obtained. The contact angle of the surface of the base coat layer was measured, and a colorable acrylic resin was applied on the surface of the base coat layer to form a top coat layer.
Further, a pencil hardness test was performed. Further, after coating the surface of a 10 cm iron plate with phosphate, a rust preventive paint is applied,
Sample No. as a coat layer 4 was obtained. This bassco
The contact angle of the surface of the base coat layer was measured, and a colorable acrylic resin was applied on the surface of the base coat layer to form a top coat layer. Thereafter, the appearance of the coating film was observed, and a pencil hardness test was further performed. The results are shown in Table 1 together with the results of Example 1 and Example 2.

[0041]

[Table 1]

As is clear from the results of the comparative examples, the contact angle was large on the surface of the ordinary rust preventive paint. In No. 4, the surface condition after coating the top coat layer was remarkably inferior. In addition, No. 3, No.
In all cases, the results of the pencil hardness test are H to 3H,
No. 1, No. It is apparent that the sample No. 2 is inferior to 4H to 5H. Therefore, it can be said that the high degree of hydrophilization of the surface of the base coat layer by photoexcitation using an optical semiconductor greatly contributes to improving the coating properties of the water-based paint. In addition, it can be said that the hardened and dense coating film surface of the water-based paint contributes to the improvement of abrasion resistance and corrosion resistance. Further, if the base coat layer is colored, the color can be freely added (No. 2), which is considered to contribute to diversification of design. Furthermore, by forming the top coat layer as a highly hydrophilic thin film using an optical semiconductor, in addition to the above-mentioned effects, it is also possible to prevent dust, sludge, tar, pitch, hand grease and other oily stains. Also, the effect of self-cleaning or easy cleaning can be expected.

[0043]

According to the present invention, an optical semiconductor or a basecoat layer containing an optical semiconductor is formed on a metal substrate, and the optical semiconductor is rendered hydrophilic in response to photoexcitation by irradiation with light having a wavelength shorter than the excitation wavelength. It is intended to provide a coated article having a coated surface coated with a top coat layer and a coating method thereof. The basecoat surface which has been highly hydrophilized by light excitation is suitable for application of a water-based paint, and the surface of the paint film is smooth and excellent in abrasion resistance. Further, (1) When the hydrogen generation level is set to 0 eV as an optical semiconductor, the lower end of the energy level of the conduction band is located at a positive value so that photohydrophilization occurs while suppressing the photooxidation-reduction reaction. Or (2) the surface further contains a hydrophilic substance that is not an optical semiconductor, so that the optical semiconductor hardly comes into contact with the outside air; or (3) the photooxidation-reduction reaction of the optical semiconductor on the surface A thin film prepared by incorporating a substance that inhibits the formation of a varnish is particularly effective as a colored base coat layer, and also contributes to the thinning of the top coat layer by preventing the deposition and deposition of colored metals. I do. Further, the top coat layer is also made of a highly hydrophilic thin film using an optical semiconductor, thereby preventing dust, sludge, tar, pitch, hand grit and other oily stains, or self-cleaning, Alternatively, an effect that cleaning becomes easy can be expected.

Continuation of front page (56) References JP-A-5-139067 (JP, A) JP-A-7-28248 (JP, A) JP-A-5-155726 (JP, A) JP-A-62-246984 (JP) JP-A-7-171408 (JP, A) JP-A-61-133125 (JP, A) JP-A-2-273514 (JP, A) JP-A-6-198196 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B05D 1/00-7/26

Claims (2)

(57) [Claims] 1. An optical semiconductor comprising:
Step of forming a base coat layer containing an optical semiconductor, light
The base coat layer by photoexcitation caused by irradiation of
Convert the water wettability of the surface to a contact angle with water of 10 ° or less.
Hydrophilizing the base coat layer
Work to form a top coat layer composed of water-based paint on the surface
A coating method characterized by comprising: 2. The method according to claim 1, wherein the illuminance is equal to or less than an excitation wavelength of the optical semiconductor.
mW / cm ² By the following light irradiation, the base code
2. The surface of the coating layer is made hydrophilic.
Painting method.