Active energy ray-curable coating composition

Abstract

In order to reduce light absorbed by a coated object and suppress an increase in temperature of the coated object, this active energy ray-curable coating composition contains an active energy ray-curable resin and a light-reflecting agent in an amount capable of suppressing an increase in temperature of the coated object. The light-reflecting agent is contained in an amount that causes the temperature increase level of the coated object to be 1945000°C·lx or less, or the light-reflecting agent is contained in an amount of 29-75 wt%.

Description

Active energy ray curable coating composition

[0001] The present invention relates to an active energy ray-curable coating composition.

[0002] A known photocurable coating composition contains a photocurable resin, a photopolymerization initiator, and an extender pigment such as precipitated barium sulfate (Patent Document 1). The extender pigment is used in an amount ranging from 1 to 30 parts by weight per 100 parts by weight of the photocurable resin.

[0003] Japanese Patent Application Laid-Open No. 2005-246299

[0004] When a car is left in the hot sun in midsummer, the temperature inside the car can reach around 50°C, so it is desirable that a coating film formed on the exterior panels of the car body reduce the amount of light absorbed by the exterior panels and suppress the temperature rise of the exterior panels. In this specification, this function of the coating film is referred to as a temperature-reducing effect, but when the above-mentioned conventional photocurable coating compositions were examined, it was confirmed that they had almost no temperature-reducing effect.

[0005] The problem to be solved by the present invention is to provide an active energy ray-curable coating composition that can reduce the amount of light absorbed by a substrate and suppress a temperature rise on the substrate.

[0006] The present invention solves the above problems by including an active energy ray-curable resin and a light reflecting agent in an amount sufficient to suppress a temperature rise in the coated object.

[0007] According to the present invention, it is possible to reduce the amount of light absorbed by the object to be coated, and to suppress a rise in the temperature of the object to be coated.

[0008] Fig. 1 is a cross-sectional view showing an example of a multilayer coating film using an active energy ray-curable coating composition according to the present invention. Fig. 2 is a side view showing a method for testing the temperature-reducing effect of a coating film using an active energy ray-curable coating composition according to the present invention. Fig. 3 is a plan view showing a method for testing the temperature-reducing effect of a coating film using an active energy ray-curable coating composition according to the present invention. Fig. 4 is a graph showing the relationship between the content of a light reflecting agent and the amount of temperature rise.

[0009] <<Active Energy Ray-Curable Coating Composition>> The active energy ray-curable coating composition of an embodiment according to the present invention comprises an active energy ray-curable resin, a light reflector in an amount sufficient to suppress a temperature rise in an object to be coated, a solvent, and, if necessary, a colorant as well as known coating additives (for example, an antifoaming agent such as silicone oil, a fluorine-based surfactant, a silicone-based surfactant, a leveling agent such as an acrylic copolymer, a thickener, a viscosity reducer, etc.).

[0010] In this specification, the term "active energy rays" encompasses light such as ultraviolet rays and electron beams, and the active energy ray-curable resin composition of this embodiment includes ultraviolet-curable resin compositions and electron beam-curable resin compositions. Ultraviolet-curable resin compositions include ultraviolet radical-curable resin compositions such as epoxy acrylate resins, urethane acrylate resins, thermosetting acrylic resins, and thermosetting polyester resins, and cation-curable resin compositions such as ultraviolet-curable epoxy resins. Because ultraviolet rays have a lower curing energy than electron beams, ultraviolet-curable resin compositions are used in conjunction with a photopolymerization initiator. In contrast, electron beam-curable resin compositions can use the same materials as the ultraviolet-curable resin compositions described above, and because electron beams have a higher curing energy, the polymerization initiator can be omitted.

[0011] The active energy ray curable resin of this embodiment may be either a crystalline resin or an amorphous resin. However, when the content of the light reflecting agent is increased, it is preferable to use an amorphous resin. This is because the light reflecting agent is considered to be mixed into the amorphous portion. Examples of amorphous active energy ray curable resins include acrylic resins, such as polymethyl methacrylate resin.

[0012] The light reflector of this embodiment has the property of reflecting sunlight including infrared rays, and preferably has a light reflectance of 99% or more, although this is not particularly limited. Examples of the light reflector of this embodiment include barium sulfate, titanium oxide, zirconium dioxide, aluminum oxide, magnesium oxide, aluminum nitride, boron nitride, silica, mica powder, and powdered glass. Among these, it is more preferable to use barium sulfate and / or titanium oxide as the light reflector of this embodiment.

[0013] The particle size of the light reflecting agent of this embodiment is not particularly limited, but is preferably more than 0 and 10 μm or less. By making the particle size of the light reflecting agent 10 μm or less, it is possible to prevent the light reflecting agent particles from being exposed on the surface of the coating film and falling off, which is particularly effective when the content of the light reflecting agent is high.

[0014] The light reflecting agent of this embodiment is preferably dispersed in the coating film and contained in an appropriate amount so that sunlight incident on the coating film does not pass through the coating film and is not absorbed by the steel plate to be coated. In other words, the light reflecting agent of this embodiment is preferably contained in an amount that can suppress the temperature rise of the steel plate to be coated. Specific examples of the amount that can suppress the temperature rise of the coated object include an amount that results in a temperature rise of the coated object of 1,945,000°C·lx or less, preferably an amount that results in a temperature rise of 1,920,000°C·lx or less, more preferably an amount that results in a temperature rise of 1,750,000°C·lx or less, even more preferably an amount that results in a temperature rise of 1,400,000°C·lx or less, and even more preferably an amount that results in a temperature rise of 1,280,000°C·lx or less. This is because if the temperature rise of the coated object exceeds 1,945,000°C·lx, the temperature rise of the coated object cannot be sufficiently suppressed. The lower limit of the temperature rise of the coated object is approximately 1,190,000°C·lx, due to the limit of the solids ratio of the paint, i.e., the relationship with coating workability.

[0015] Alternatively, specific examples of the amount that can suppress the temperature rise of the coated object include a reflector content of 29 to 75 wt%, preferably 37 to 75 wt%, more preferably 44 to 75 wt%, even more preferably 50 to 75 wt%, and even more preferably 54 to 75 wt% relative to the total paint. This is because a reflector content of less than 29 wt% cannot sufficiently suppress the temperature rise of the coated object. The upper limit of the reflector content is 75 wt%, due to the limit of the solids content of the paint, i.e., in relation to coating workability.

[0016] In the active energy ray-curable coating composition of this embodiment, the solid content ratio including the active energy ray-curable resin and the light reflecting agent is preferably 90% by weight or less, because if the solid content ratio including the active energy ray-curable resin and the light reflecting agent exceeds 90% by weight, the coating workability using a coating tool such as an applicator decreases.

[0017] <<Multilayer Coating Film>> Figure 1 is a cross-sectional view showing an example of a multilayer coating film 1 using an active energy ray-curable coating composition according to the present invention. The multilayer coating film 1 of the embodiment shown in the figure is composed of an electrodeposition coating film 12 formed on the surface of a steel plate 11, an intermediate coating film 13 formed on the surface of this electrodeposition coating film, a top coating film 14 formed on the surface of this intermediate coating film 13, and a clear coating film 15 formed on the surface of this top coating film. An aluminum plate may be used instead of the steel plate 11.

[0018] The electrodeposition coating film 12 is made of a thermosetting paint with an epoxy resin such as polyamine resin as the base resin, and is formed to a thickness of, but not limited to, 10 to 25 μm. The intermediate coating film 13 and the clear coating film 15 are made of a thermosetting paint with an acrylic resin, alkyd resin, polyester resin, or the like as the base resin, and the intermediate coating film 13 is made to a thickness of, but not limited to, 15 to 30 μm, and the clear coating film 15 is made to a thickness of, but not limited to, 15 to 30 μm.

[0019] In the multilayer coating film 1 of this embodiment, the active energy ray-curable coating material according to the embodiment of the present invention described above is used for the topcoat coating film 14, and is formed to a film thickness of, but not limited to, 15 to 30 μm. However, the active energy ray-curable coating material according to the embodiment of the present invention can also be used for the electrodeposition coating film 12, the intermediate coating film 13, or the clear coating film 15 other than the topcoat coating film 14.

[0020] <<Effects of the embodiment>> As described above, the active energy ray-curable coating composition of the present embodiment contains an active energy ray-curable resin and a light reflecting agent in an amount sufficient to suppress a temperature rise in the substrate, and therefore, when sunlight containing infrared rays is incident on the laminate coating film 1 as shown in Figure 1 , the sunlight is reflected by the light reflecting agent in the topcoat coating film 14 formed from the active energy ray-curable coating composition of the present embodiment, and as shown by the dotted line, can be prevented from being absorbed by the steel plate 11. This suppresses a temperature rise in the steel plate 11, leading to an effect of reducing the temperature inside the vehicle cabin.

[0021] Furthermore, according to the active energy ray-curable coating composition of the present embodiment, the light reflecting agent is contained in an amount such that the temperature rise of the coated object is 194,500°C·lx or less, and therefore, specifically, absorption of sunlight including infrared rays by the steel sheet 11 can be suppressed.

[0022] Furthermore, according to the active energy ray-curable coating composition of the present embodiment, the light reflecting agent is contained in an amount of 29 to 75% by weight, and therefore, specifically, absorption of sunlight containing infrared rays by the steel sheet 11 can be suppressed.

[0023] Furthermore, according to the active energy ray-curable coating composition of the present embodiment, the active energy ray-curable resin is an amorphous resin, and therefore can contain a large amount of light reflecting agent, which can further suppress absorption of sunlight containing infrared rays by the steel sheet 11.

[0024] Furthermore, according to the active energy ray-curable coating composition of the present embodiment, the light reflecting agent is barium sulfate and / or titanium oxide, and therefore, more specifically, it is possible to suppress absorption of sunlight containing infrared rays by the steel sheet 11.

[0025] Furthermore, according to the active energy ray-curable coating composition of the present embodiment, the light reflectance of the light reflecting agent is 99% or more, and therefore, more specifically, it is possible to suppress the absorption of sunlight containing infrared rays by the steel sheet 11.

[0026] Furthermore, according to the active energy ray-curable coating composition of this embodiment, the particle size of the light reflector is more than 0 and 10 μm or less, so that the light reflector particles can be prevented from being exposed on the surface of the coating film and falling off, which is particularly effective when the content of the light reflector is large.

[0027] Furthermore, according to the active energy ray-curable coating composition of the present embodiment, the solid content ratio including the active energy ray-curable resin and the light reflecting agent is 90% by weight or less, so that deterioration of coating workability using a coating tool such as an applicator can be suppressed.

[0028] Furthermore, since the active energy ray-curable coating composition of this embodiment is applied to the outer panels of an automobile body, it is possible to suppress temperature rise inside the automobile even when the automobile is left under the scorching sun of midsummer.

[0029] The present invention will be explained below by way of examples that further embody the active energy ray-curable coating composition according to the present invention and comparative examples. However, the specific values ​​below are examples and comparative examples for understanding the present invention and are not intended to limit the present invention.

[0030] Example 1 50 g of ultraviolet-curable paint (DIC Corporation, solids content 60%) was mixed with 21 g of barium sulfate (Sakai Chemical Industry Co., Ltd., average particle size 0.2 μm) as a light-reflecting agent, and the resulting paint was applied to the surface of a 0.15 m × 0.07 m steel plate using an applicator. The plate was then irradiated with ultraviolet light to produce a coating film with a cured film thickness of 10 to 15 μm. The content of the light-reflecting agent in the ultraviolet-curable paint used was 21 / (50 + 21) × 100 = 29.6 wt %.

[0031] Figure 2A is a side view showing a test method for the temperature reduction effect of a steel sheet sample 2 on which a coating film was formed, and Figure 2B is a plan view of the same. Light from a 40 W incandescent lamp 3 was irradiated onto the surface of the coating film of steel sheet sample 2 on which a coating film had been formed as described above, from a position with a center-to-center distance R of 0.2 m. Thermocouples 4 and 5, which serve as temperature sensors, were fixed to the center and one end of the back surface of steel sheet sample 2. The temperature of steel sheet sample 2 before irradiation with light from the incandescent lamp 3 was 25°C. 30 minutes after the start of irradiation with light from the incandescent lamp 3, when the temperatures detected by thermocouples 4 and 5 had stabilized, was measured, and the temperature was 46.2°C at the center, as shown in Table 1.

[0032] The 40W incandescent lamp 3 is equivalent to a luminous flux of 485 lumens (lm). The relationship between the luminous flux Φ (lm) and the illuminance E (lx) is expressed as follows: ２ ), then E = Φ / area, so the illuminance per unit area E = 485 / (4πR ２ ・M)=485lm÷(4×π×(0.2m) ２ × 0.15 m × 0.07 m) = 91,893 lux (lx). As mentioned above, when light from a 40 W incandescent lamp 3 was irradiated onto a steel plate sample 2 at 25°C with a coating film formed on its surface, the temperature at the center measured by the thermocouple 4 rose to 46.2°C, and therefore the amount of temperature rise of the steel plate sample 2 was (46.2°C - 25°C) × 91,893 lx = 1,948,132°C·lx. The results are shown in Table 1 and Figure 3.

[0033] Examples 2 to 14 Steel plate sample 2 was prepared under the same conditions as in Example 1, except that the weight of barium sulfate as a light reflector mixed into 50 g of the ultraviolet-curable coating material in Example 1 was set to the weight shown in Table 1, and the temperature rise of steel plate sample 2 was measured using the test method shown in Figures 2A and 2B. The results are shown in Table 1 and Figure 3.

[0034] Comparative Example 1 A steel plate sample 2 was prepared under the same conditions as in Example 1, except that the weight of barium sulfate as a light reflector mixed into 50 g of the ultraviolet-curable coating material in Example 1 was changed to 0.5 g, and the temperature rise of the steel plate sample 2 was measured using the test method shown in Figures 2A and 2B. The results are shown in Table 1 and Figure 3.

[0035] Comparative Example 2: A coating was prepared by mixing 160 g of barium sulfate as a light reflector with 50 g of the UV-curable coating material of Example 1. An attempt was made to apply this coating material to the surface of a steel plate of the same size as Example 1 using an applicator, but the coating material got caught on the applicator and a uniform film could not be formed. Therefore, measurement of the temperature rise of steel plate sample 2 using the test method shown in Figures 2A and 2B was abandoned.

[0036]

[0037] Examples 15 to 28 and Comparative Examples 3 and 4 Steel plate sample 2 was prepared under the same conditions as in Examples 1 to 14 and Comparative Examples 1 and 2, except that the reflecting agent in Examples 1 to 14 and Comparative Examples 1 and 2 was titanium oxide (manufactured by Sakai Chemical Industry Co., Ltd., average particle size 0.2 to 0.3 μm), and the temperature rise of steel plate sample 2 was measured using the test method shown in Figures 2A and 2B. The results are shown in Table 2.

[0038]

[0039] <<Discussion>> In all of Examples 1 to 14, which used barium sulfate as the light reflecting agent, and Examples 15 to 17, which used titanium oxide, it was confirmed that the effect of suppressing a temperature rise in the steel plate sample 2 was greater when the content of the reflecting agent relative to the total paint was 29 to 75 wt %, compared to Comparative Example 1 or 3. It was confirmed that the effect of suppressing a temperature rise in the steel plate sample 2 was particularly enhanced when the content was 37 to 75 wt %, more preferably 44 to 75 wt %, even more preferably 50 to 75 wt %, and even more preferably 54 to 75 wt %.

[0040] Similarly, for Examples 1 to 14 in which barium sulfate was used as the light reflector, the effect of suppressing the temperature rise of the steel plate sample 2 was confirmed when the amount of temperature rise of the steel plate sample 2 was 1,945,000°C·lx or less, compared to Comparative Example 1. In particular, it was confirmed that the effect of suppressing the temperature rise of the steel plate sample 2 was further enhanced when the amount was 1,920,000°C·lx or less, more preferably 1,750,000°C·lx or less, even more preferably 1,400,000°C·lx or less, and even more preferably 1,280,000°C·lx or less.

[0041] Furthermore, from the results of Example 14 and Comparative Example 2, and Example 17 and Comparative Example 4, it was confirmed that when the solid content ratio including the ultraviolet curable resin and the light reflecting agent was 90% by weight or less, there was no problem with the coating workability, but when it exceeded 90% by weight, it was not possible to apply the coating in a uniform film form.

[0042] REFERENCE SIGNS LIST 1... multilayer coating film 11... steel plate 12... electrodeposition coating film 13... intermediate coating film 14... top coating film 15... clear coating film 2... steel plate sample 3... incandescent lamp 4, 5... thermocouple

Claims

1. an active energy ray-curable resin; and a light reflecting agent in an amount sufficient to suppress a temperature rise of an object to be coated.

2. 2. The active energy ray-curable coating composition according to claim 1, wherein the light reflecting agent is contained in an amount such that the temperature rise of the coated object is 1,945,000° C.·lx or less.

3. 3. The active energy ray-curable coating composition according to claim 1, wherein the light reflecting agent is contained in an amount of 29 to 75% by weight.

4. 4. The active energy ray-curable coating composition according to claim 3, wherein the active energy ray-curable resin is an amorphous resin.

5. 3. The active energy ray-curable coating composition according to claim 1, wherein the light reflecting agent is barium sulfate and / or titanium oxide.

6. 3. The active energy ray-curable coating composition according to claim 1, wherein the light reflecting agent has a light reflectance of 99% or more.

7. 3. The active energy ray-curable coating composition according to claim 1, wherein the particle size of the light reflecting agent is greater than 0 and not greater than 10 μm.

8. 3. The active energy ray-curable coating composition according to claim 1, wherein a solid content ratio of the active energy ray-curable resin and the light reflecting agent is 90% by weight or less.

9. 3. A method for coating an automobile body, comprising coating the active energy ray-curable coating composition according to claim 1 or 2 on the outer panel of the automobile body.

10. 10. The method for painting an automobile body according to claim 9, wherein the active energy ray-curable paint composition is applied to a film thickness of 10 to 500 μm, and then cured by irradiating with active energy rays.