JP3276062B2 - Coating surface modification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for modifying the surface of a baked cured coating applied to articles used outdoors such as automobiles. The bake-hardened coating film modified by the coating film surface modification method of the present invention has hydrophilicity, and lipophilic stains are less likely to adhere. Therefore, if the present invention is applied to an automobile outer panel coating film, the number of steps for car washing and waxing can be reduced.

[0002]

2. Description of the Related Art Dirt substances discharged from factories and automobiles, bird droppings, and various kinds of dirt substances such as sand and pollen adhere to coating films exposed to rain and wind, such as automotive exterior coating films. I do. This dirt is not something that is naturally removed, but needs to be removed by washing with water or waxing.

[0003] Particularly in recent years, dirt due to diesel particulates discharged from a diesel engine or the like has been conspicuous. This diesel particulate is mainly composed of unburned, partially or almost carbonized, carbon-like organic substances, but easily adheres to the surface of a lipophilic automobile outer panel coating film. Therefore, in recent years, stains on automobile coatings in urban areas are mainly composed of this carbonaceous substance.

[0004]

The washing and waxing for removing dirt is a complicated and troublesome operation. This work, especially outdoors in the winter, is troublesome due to the cold and cold, and tends to be left without removing dirt. However, if left for a long time without removing the dirt, the dirt is deposited by sunlight or acid rain, and the dirt becomes more and more difficult to remove.

The present invention has been made in view of such circumstances, and prevents the adhesion of lipophilic stain substances by modifying a baked cured coating film, and easily removes stains by washing with water. The purpose is to be.

[0006]

Means for Solving the Problems Claims for solving the above problems
The feature of the coating surface modification method according to Item 1 is that
On the surfaceApply photo-oxidation catalyst, then apply peak intensity 100 ~
1000mW / cm ^Two Irradiation of ultraviolet light under the conditions of
The purpose of the present invention is to modify the surface of a chemically coated film to be hydrophilic.

[0007] The feature of the coating film surface modification method according to claim 2 is that the coating film surface modification method according to claim 1 is characterized in that:
UV irradiation is performed under the condition of an integrated light amount of 5 to 30 J / cm < ² > .

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Acrylic / melamine-based paint is generally applied to the coating film of an automobile outer panel.
It is formed from a baked cured film baked at 0 ° C. In such a bake-cured coating film, since the hydroxyl group of the acrylic resin and the alkoxy group, methylol group, or imino group of the melamine resin react and cure, the hydrophilic group is crushed by the reaction and the surface becomes lipophilic. ing. Therefore, lipophilic dirt such as diesel particulates is likely to adhere.

[0009] Even if such contaminants adhere,
Since the surface of the bake-hardened coating film itself is lipophilic, it is easy to repel water, and it is difficult to remove dirt by rainfall or washing with water. The stains on the coating film include
There are two types of water stains. "Adhesive stain" means stains that have been attached without washing with water, and "water stain" means stains on the paint film after the stained paint film has been washed with water.

Therefore, in the present invention, the surface of the baked cured coating is modified to be hydrophilic by irradiating the surface of the baked cured coating with ultraviolet rays under predetermined conditions. This makes it difficult for lipophilic dirt substances to adhere, and reduces “adhesion dirt”. Even when lipophilic dirt is attached, water may enter between the dirt and the paint film during rainfall, causing the dirt material to float up from the paint film and removing the dirt material from the paint film. Therefore, the deposition of dirt substances is prevented, and can be easily removed by simple washing with water.

The irradiation conditions of the ultraviolet rays for modifying the bake-hardened coating film are as follows.
00 mW / cm ² , and the integrated amount of ultraviolet light is 30 to 150
J / cm ² . 100 mW / c peak intensity
If it is smaller than m ² , the effect cannot be obtained even if the integrated light amount value is satisfied due to insufficient intensity. In addition, the peak intensity is 100
If it is larger than 0 mW / cm ² , the intensity is too strong, and it becomes difficult to control the integrated light amount value.

When the UV peak intensity is in the above range, if the integrated light amount is less than 30 J / cm ² , no effect is obtained due to insufficient light amount, and if it exceeds 150 J / cm ² , the effect of preventing contamination is obtained. However, there is a case where trouble such as yellowing occurs in the coating film due to deterioration due to ultraviolet rays. As the ultraviolet rays used, those having a wavelength longer than 290 nm are desirable. Irradiation with ultraviolet light having a wavelength shorter than 290 nm may cause deterioration of the coating film and cause other obstacles such as yellowing. An ultraviolet lamp, a germicidal lamp, or the like can be used as such an ultraviolet light source.

In the modification method of the present invention, the surface of the baked and cured coating film is oxidized by irradiation of ultraviolet rays under predetermined conditions, and
It is considered that the formation of a polar group such as COOH and -C = O renders the compound hydrophilic. Therefore, adhesion of lipophilic dirt is prevented, and even if it adheres, it is often removed by rainfall. As a result, the deposition of dirt on the coating film can be prevented, and the dirt can be easily removed by washing with water or the like.

In the modification method of the present invention, a photo-oxidation catalyst is first applied to the surface of the baked and cured coating film, and the surface is irradiated with ultraviolet light having a peak intensity of 100 to 1000 mW / cm ² . According to this method, photooxidation catalyst is activated by irradiation of ultraviolet rays, and more oxidizing the bake hardening coating surface with the oxidizing power of the UV itself, be modified baking cured coating film surface hydrophilic it can.

Here, the activity of oxidizing the coating film by the photo-oxidation catalyst is stronger than the activity of oxidizing the coating film by the ultraviolet light itself. Therefore, according to the method of the present invention , the irradiation amount of ultraviolet rays can be reduced. Specifically, although in the ultraviolet peak intensity is required in the range of 100 ~1000mW / cm ^2, it is preferable ultraviolet integral light quantity is 5 J / cm ² or more. If the integrated amount of ultraviolet light is less than 5 J / cm ² , when the irradiation time is short, the oxidizing power of the photo-oxidation catalyst is not sufficiently exerted, and the oxidation of the coating film by the ultraviolet light and the photo-oxidation catalyst is insufficient. In some cases, it may be difficult to develop

[0016] Note that in the invention of claim 1 can be expressed the same hydrophilic by reducing the ultraviolet ray integral light amount.
Therefore, the ultraviolet irradiation time can be shortened, and the deterioration of the inside of the coating film can be suppressed by the small amount of integrated ultraviolet light. That is, according to the method of claim 1, since the oxidation of the coating film by oxidizing power and ultraviolet itself activated photooxidation catalyst by ultraviolet proceed simultaneously, it is possible to shorten the ultraviolet ray irradiation time Can be modified to hydrophilicity in a short time.

[0017] As the baking cured coating film is modified by the invention of placing serial to claim 1, acrylic / melamine baking and curing the coating film, polyester / melamine baking and curing the coating film, acrylic / benzoguanamine bake hardening coating film, polyester / benzoguanamine Examples include bake-hardened coatings, acrylic / acid-epoxy bake-hardened coatings, and polyester / acid-epoxy bake-hardened coatings. The composition of the bake-cured coating film may be a solid coating film containing various pigments, or a metallic coating film or a clear coating film containing no pigment.

[0018] The photooxidation catalyst according to claim 1, zinc oxide (ZnO), tin oxide (SnO _2), titanium oxide (TiO _2), an oxide semiconductor such as gallium oxide (Ga ₂ O ₃₎ Can be used. Among them, oxidizing power,
In consideration of safety, cost and the like, it is particularly recommended to use titanium oxide. The amount of this photo-oxidation catalyst applied to the surface of the bake-hardened coating film is 0.0
The range is preferably from 1 to 0.1 g / cm ² . If the coating amount of the photo-oxidation catalyst is less than 0.01 g / cm ^{2, the} effect of oxidizing the coating film is weak, and almost no effect is obtained, and 0.1 g / cm ²
Even if it is applied more, the effect is saturated and the ultraviolet rays hardly reach the coating film because it is shielded by the oxidation catalyst layer, so that it may be difficult to hydrophilize.

In order to apply the photo-oxidation catalyst to the surface of the bake-hardened coating film, the powder of the photo-oxidation catalyst can be applied by spraying on the surface of the coating film. It is preferably applied as a liquid in the form of a solution or a dispersion. When applying as a liquid, known application means such as a brush coating method, a dip coating method, a spray coating method, a shower coating method, and a roll coating method can be used.

[0020]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Reference Examples, Examples, and Comparative Examples. ( Reference Example 1) A steel plate having an electrodeposition coating film was subjected to a polyester / melamine-based undercoating and intermediate coating, and after water polishing, a white coating plate having an acrylic / melamine-based white coating film formed thereon was prepared. / 140 after spray coating with clear melamine paint
A test piece was prepared by baking at 30 ° C. for 30 minutes. The thickness of the clear coating film is 30 to 50 μm.

Using this test piece, ultraviolet light having a wavelength of 290 to 450 nm was applied to the surface of the clear coating film, and the peak intensity was 10
Irradiation was performed so that 0 mW / cm ² and the integrated light amount value became 30 J / cm ² . Specifically, the surface of the test piece was irradiated for 10 minutes from a distance of 25 cm using an ultraviolet lamp having an output of 80 W / cm. The peak intensity was obtained from a UV intensity meter, and the integrated light intensity value was obtained by setting the UV intensity meter to an integration mode.

In addition to measuring the contact angle of water with the coating film irradiated with the ultraviolet light, the XPS (ESCA)
The surface oxygen concentration was measured by analysis, and the results are shown in Table 1.
Next, the test piece treated as described above was exposed outdoors for 3 months so that the coated surface was inclined at 60 degrees with respect to the horizontal plane, and the coated film after the exposure and the initial coated film before the exposure were measured by a color difference meter. The color difference (ΔE ₁ ) from the film was measured. The exposed coating film was washed with a sponge, and the color difference (ΔE ₂ ) between the washed coating film and the initial coating film before exposure was also measured. Table 1 shows the results.

( Reference Examples 2 to 19 and Comparative Examples 1 to 10) The types of clear coating films were acrylic / melamine-based and acrylic /
Reference Example 1 except that it was selected from two levels of acid-epoxy
A test piece was prepared in the same manner as described above, and was irradiated with ultraviolet rays in the same manner as in Reference Example 1 except that the peak intensity of the ultraviolet rays and the integrated light amount were variously changed. After exposure in the same manner as in Reference Example 1, two kinds of color differences were measured in the same manner, and the results are shown in Table 1. Further, the contact angle and the surface oxygen concentration of the representative test pieces of Reference Examples and Comparative Examples after UV irradiation (before exposure) were measured in the same manner as in Reference Example 1, and the results are shown in Table 1. Note that Comparative Examples 1 and 2 are blanks that are not irradiated with ultraviolet light.

(Evaluation)

[0025]

[Table 1]

From Table 1, it can be seen that the test piece of each reference example is comparative example 1
And it is clear that (ΔE ₁ ) is smaller than that of Comparative Example 2, and that the dirt is hardly adhered by the irradiation of the ultraviolet rays. Further, it is clear that the test pieces of each reference example have a smaller (ΔE ₂ ) than that of the comparative examples 1 and 2, and that the ultraviolet light irradiation reduces the scale stain after washing with water.

When the reference examples are compared with the comparative examples 1 and 2, the contact angle of water is remarkably reduced by the irradiation of ultraviolet rays, and the surface oxygen concentration is more than doubled to 20 at%.
The above high concentration is obtained. This means that the surface of the bake-hardened coating film was oxidized by the irradiation of the ultraviolet rays, which indicates that the hydrophilicity was increased. That is, the dirt is hard to adhere to the coating film of each reference example,
It is presumed that the reason is as follows.

Since the baking-cured coating film irradiated with ultraviolet rays of a predetermined condition is hydrophilic as described above, the lipophilic stain substance hardly adheres. Also, even if the dirt substance adheres to the coating film, as shown in FIG. 1, when it rains, the raindrop 1 adheres to the surface of the coating film 3 so as to envelop the dirt substance particles 2, and the coating film 3 is hydrophilic. The raindrop 1 gradually penetrates between the hydrophilic coating 3 and the dirt particles 2, and finally the dirt particles 2
Floating from. As a result, the dirt substance particles 2 flow down together with the raindrops 1 and are removed from the coating film 3, so that dirt hardly adheres.

If the amount of dirt attached is small, dirt deposited on the coating film due to sunlight or acid rain is reduced, and water stain is also reduced. Further, when comparing each reference example and each comparative example, the peak intensity of the ultraviolet light to be irradiated is 100 to 1000 m.
W / cm ² and the integrated light amount is 30 to 150
It can be seen that when it is in the range of J / cm ² , hydrophilicity is high and stain resistance performance is good.

It should be noted that ultraviolet rays are naturally contained in the sun rays, but the ultraviolet ray peak intensity in the sun rays is 6.4 mW.
/ Cm ² , so that the integrated UV light value is 30 to 1
Even at 50 J / cm ² , oxidation of the surface of the baked cured coating film is not sufficient, and it is difficult to make it hydrophilic. (Example 20) A test piece having an acrylic / melamine-based clear coating film similar to that of Reference Example 1 was prepared, and an aqueous dispersion of titanium oxide (titanium oxide concentration: 5% by weight) was applied by brush coating. The applied amount is 0.01 g / cm ² in terms of titanium oxide solid content.

Here, the concentration of titanium oxide in the aqueous dispersion is:
Experiments have shown that a range of 5 to 50% by weight is preferred. When the concentration of titanium oxide is lower than 5% by weight, a single application step does not reach the predetermined application amount, and it is necessary to perform the application step a plurality of times until the predetermined application amount is reached. On the other hand, if the titanium oxide concentration exceeds 50% by weight, the viscosity becomes high and brush coating becomes difficult, and the formed titanium oxide layer becomes thick and shields ultraviolet rays, so that it is difficult for the ultraviolet rays to reach the coating film. .

Next, with the applied aqueous dispersion coating still wet, an ultraviolet lamp similar to that used in Reference Example 1 was used to apply a wavelength of 290 to 450 nm to the surface of the clear coating.
Was irradiated such that the peak intensity was 100 mW / cm ² and the integrated light amount was 5 J / cm ² . The ultraviolet ray may be applied after the applied aqueous dispersion is dried. However, by irradiating the ultraviolet ray in a wet state, a cooling effect by the latent heat of evaporation of water is obtained, and thus the deterioration of the coating film due to heat is obtained. Can be suppressed.

The obtained test piece was washed with water and dried, and then Reference Example 1 was obtained.
The water contact angle after ultraviolet irradiation (before exposure) was measured in the same manner as described above. Further, the coated surface was exposed outdoors for 3 months so that the coated surface was inclined at 60 degrees with respect to the horizontal plane, and the color difference (ΔE ₁ ) between the coated film after exposure and the initial coated film before exposure was measured by a color difference meter.
Table 2 shows the results. (Examples 21 to 23) As shown in Table 2, the test pieces coated with the aqueous dispersion of titanium oxide in the same manner as in Example 20 exhibited peak ultraviolet intensities of 100 mW / cm ² and 500 mW / cm ² . 2 levels,
Irradiation with ultraviolet rays was performed in the same manner as in Example 20, except that the integrated light amount was changed variously at two levels of 5 J / cm 2 and 10 J / cm ² . Then, the water contact angle was measured in the same manner as in Reference Example 1, and after exposure, ΔE ₁ was measured. The results are shown in Table 2.

Examples 24 to 26 As shown in Table 2, titanium oxide was prepared in the same manner as in Example 20 except that the amount of application was variously changed by changing the concentration of the aqueous dispersion of titanium oxide. For the coated test piece, the peak intensity of ultraviolet light was 100 mW / cm ² and 500
2 levels of mW / cm ² , integrated light intensity values of 5 J / cm ² and 1
Irradiation with ultraviolet light was performed in the same manner as in Example 20, except that various changes were made at two levels of 0 J / cm ² . Then, the water contact angle was measured in the same manner as in Reference Example 1, and after the same exposure, ΔE ₁
And the results are shown in Table 2.

(Comparative Example 11) The amount of integrated light was 10 J /
Example 20 is the same as Example 20 except that ultraviolet rays were irradiated so as to be cm ² . About the obtained test piece, Reference Example 1
The water contact angle was measured in the same manner as in
₁ was measured and the results are shown in Table 2.

(Comparative Example 12) The amount of integrated light was 20 J /
Example 20 is the same as Example 20 except that ultraviolet rays were irradiated so as to be cm ² . About the obtained test piece, Reference Example 1
The water contact angle was measured in the same manner as in
₁ was measured and the results are shown in Table 2.

(Comparative Example 13) The peak intensity was 500 m without applying titanium oxide.
Example 20 is the same as Example 20 except that ultraviolet rays were irradiated so as to be W / cm ² . With respect to the obtained test pieces, the water contact angle was measured in the same manner as in Reference Example 1, and after exposure, ΔE ₁ was measured. The results are shown in Table 2.

(Reference Examples 20 to 23 ) As shown in Table 2, a test was conducted in which titanium oxide was applied so that the application amount was 0.008 g / cm ² by changing the concentration of the aqueous dispersion of titanium oxide. The peak intensity of the ultraviolet light was set to two levels of 100 mW / cm ² and 500 mW / cm ² , and the integrated light amount was set to 10 J / cm ² and 30 J / cm ^2.
Irradiation with ultraviolet light was carried out in the same manner as in Example 20, except that the two levels were changed variously. Then, the water contact angle was measured in the same manner as in Reference Example 1, and after exposure, ΔE ₁ was measured. The results are shown in Table 2.

Table 2 shows Reference Example 1 and Table 1 shown in Table 1.
The results of Reference Example 9 are also shown. (Evaluation)

[0040]

[Table 2] From Table 2, the test piece of Example 20 to 26 was irradiated with ultraviolet light by coating a titanium oxide, despite the integral light amount as compared with Reference Example 1 and Reference Example 9 is low and about 1/6 a reference examples 1 and less hydrophilic water contact angle of 60 degrees or less in the same manner as in reference example 9, and it can be seen that the dirt becomes unlikely to adhere.

However, in Comparative Examples 11 to 13, Example 20 was used.
Even in Comparative Example 13 in which the intensity of ultraviolet light was increased, the water contact angle was as large as 80 or more, and the amount of dirt adhered was large even though the integrated light amount was equivalent to that of ~ 26. Examples 20 to 26 and Comparative Example 11
A significant difference in the modification methods of Nos. To 13 is the presence or absence of the application of titanium oxide, and it is clear that this greatly affects the hydrophilicity of the coating film. That is, according to the modification method of Example 20 to 26 is irradiated with ultraviolet rays in a state coated with titanium oxide, the integral light amount of Reference Example 1 and Reference Example 9, such as an equivalent UV peak intensity and about 1/6 ultraviolet By irradiation,
It can be realized the same hydrophilization and the like Reference Example 1 and Reference Example 9, it is possible to increase shorten the irradiation time.

In Reference Examples 20 and 22 , the degree of hydrophilization was lower than in Examples 21 and 23 because the amount of titanium oxide applied was small. Therefore, if the integrated light amount is set to this level, the amount of titanium oxide applied is 0.01 g / cm ^{2 with} respect to the area of the coating film.
It is desirable to make the above. However, Reference Example 21 and Reference Example
As shown in FIG. 23 , even if the amount of titanium oxide applied is small, high hydrophilicity can be obtained by increasing the integrated light amount.

[0043]

According to the method for modifying the surface of a coating film according to the first aspect, the surface of the baked and cured coating film is made hydrophilic, so that dirt substances are hardly adhered to the coating film and dirt stain is reduced.
Therefore, by applying the present invention to an automobile coating film, a beautiful state can be maintained for a long period of time even if the number of times of complicated and troublesome car washing and waxing is reduced, and maintenance costs can be reduced.

According to the method for modifying the surface of a coating film according to the second aspect, it is possible to shorten the ultraviolet irradiation time while maintaining the above-mentioned effects, thereby reducing the number of steps and suppressing the deterioration of the coating film. can do.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing how a stain is removed from a coating film modified by the present invention.

[Explanation of symbols]

 1: raindrop 2: dirt particles 3: coating film

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B05D 3/06 102 B05D 5/00

Claims (2)

(57) [Claims] 1. A photo-oxidation catalyst is applied to the surface of a bake-hardened coating film.
And then a peak intensity of 100-1000 mW / cm ² A method for modifying the surface of a coating film, which comprises irradiating an ultraviolet ray under the conditions described above to modify the surface of the baked cured coating film to be hydrophilic. 2. The method of claim 1] purple under the conditions of the integral light 5~30J / cm ²
The coating film according to claim 1, wherein the coating film is irradiated with an outside line.
Surface modification method.