JPH04190877A - Curing method for photocurable coating material - Google Patents

Abstract

PURPOSE:To obtain a flat cured coating film by a method wherein the surface to be coated is irradiated with light from a plurality of oblique directions at the time of curing the photocurable coating material applied to the base material having different light reflectances at different places of its coating surface. CONSTITUTION:The base material having the part of a high reflectance and the part of a low reflectance is used in the surface 30 to be coated. This base material 3 is coated with a photocurable coating material 2 and, when this coat 2 is irradiated with light to be cured, the surface 30 is irradiated with light from a plurality of oblique directions until the photocurable coating material 2 reaches at least a hardening stage at which its fluidity is lost. In this way the entering light and the reflecting light are made uniform and a flat cured coating film is produced independently of the coating composition or film thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of curing a photocurable paint.

(Prior Art) Photocurable paints are widely used because they cure quickly by receiving light. Generally, after this photocurable paint is applied to the coated surface of a base material, it begins to harden by irradiating the photocurable paint with light from a lamp or the like. At this time, the curing speed of the photocurable paint depends on the illuminance of the light.

Therefore, in the past, the object to be irradiated was placed at a position where the illuminance was maximum, that is, vertically below the light source, so that all or most of the curing reaction proceeded.

(Problem to be Solved by the Invention) However, as shown in FIG. 6, the curing reaction occurs not only with the direct light 1 from the light source, but also through the coating film 2 and the coating surface 30 on the base material 3. It is also caused by the reflected light 1o. Particularly when the photocurable paint contains components that absorb light, such as dyes and pigments, fillers, and ultraviolet absorbers, or when the thickness of the coating film 2 of the photocurable paint is 0. 5
If it is thicker than mm, less direct light 1 reaches the bottom of the coating 2, so the curing reaction near the bottom depends more on the reflected light 1o from the coated surface 3o. In addition, if the surface to be coated 3o is printed in multiple colors, the reflectance of the direct light 1 passing through the coating film 2 may vary greatly depending on the printed area, making it difficult to obtain stable reflected light 10. I can't get it. That is, in the case described above, a high reflectance portion 31 and a low reflectance portion 32 are formed on the coated surface 30, resulting in a large difference in curing speed. As a result, the hardening and shrinkage of the high-reflectance portion 31 proceeds first, and the surrounding paint of the low-reflectance portion 32 that still remains fluid is attracted, causing the high-reflectance portion 31 to become convex. This results in unevenness corresponding to the printed pattern, such as a concave portion 32 of low reflectance, resulting in the inconvenience that a smooth coating film 2 cannot be obtained.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for curing a photocurable paint that can provide a smooth coating film.

(Means for Solving the Problems) The method for curing the photocurable paint of the present invention is to apply the photocurable paint to a base material whose light reflectance differs depending on the part of the surface to be coated, and to A method of curing a photocurable paint by irradiating it with light, in which light is applied from multiple diagonal directions to two surfaces to be coated, at least until the curing stage where the photocurable paint loses its fluidity. It is something that irradiates.

As the photocurable coating material, one containing a curable resin component and a photopolymerization initiator as essential components is used.

The curable resin component is a resin component that polymerizes and hardens when activated by a photopolymerization initiator.

This curable resin component includes unsaturated polyester type,
Various types such as acrylic type, thiol/ene type, and epoxy type can be used.

The photopolymerization initiator absorbs light in a specific range of wavelengths to generate active species and initiates the curing reaction of the curable resin component. As this photopolymerization initiator, radical polymerization type,
Various types such as cationic polymerization type can be used.

In addition, ingredients other than these include stabilizers such as ultraviolet absorbers and antioxidants, leveling agents, thickeners, fillers,
Various components such as a non-curable resin component, a solvent, and a coloring agent may be added as necessary.

The light source for curing the photocurable paint may be any light source that emits light with a wavelength of approximately 250 to 450 nm. For example, high-pressure or ultra-high-pressure mercury lamps, metal halide lamps, fluorescent lamps, xenon lamps, etc. can all be used.

The curing stage at which the photocurable paint loses at least its fluidity is:
Expressed as a reaction rate of the resin component, it is approximately 10% or more.

Irradiating the surface of the base material with light from multiple diagonal directions means that when the surface to be coated is a horizontal surface, the surface to be coated is not perpendicular to the irradiated light, and that the surface to be coated is not perpendicular to the irradiated light, and that the surface to be coated is irradiated simultaneously, continuously, or intermittently in multiple directions. This means that light is emitted from the direction of.

As shown in FIG.
The smaller the elevation angle θ, the smaller the angle of reflection of the irradiated light 1 transmitted through the coating film 2 on the coated surface 30. That is, since it is reflected more widely, the curing by the reflected light 10 progresses over a wider area, which is preferable. However, if this elevation angle θ is too small, the irradiation efficiency will deteriorate. For this reason, the preferable range of the elevation angle θ is 10 to 75 degrees, more preferably 20 to 60 degrees.

As a method of irradiating from a plurality of oblique directions, as shown in FIG. 2, the object 5 to be irradiated is arranged and irradiated so that a plurality of lamps 4 are positioned not vertically below the surface 30 to be coated. There are several methods. Furthermore, as shown in FIG. 3, even when there is only one lamp 4, a method can be considered in which one or more reflecting mirrors 6 are arranged and the reflected light is adjusted and irradiated using a shielding plate 7. In this case, the shape of the reflecting mirror 6 may be a flat surface or a curved surface.

Examples of methods for irradiating light from a plurality of directions simultaneously, continuously, or intermittently include methods in which the light source or the object to be irradiated is rotated, horizontally or vertically linked.

Incidentally, such irradiation from multiple oblique directions may be performed at least until the photocurable paint reaches the curing stage where it loses its fluidity.After that, irradiation from oblique directions may be continued. , irradiation may be performed from the vertical direction.

In the present invention, the curing stage in which fluidity is lost refers to a curing stage in which the reaction rate of the resin component is approximately in the range of 10 to 90%. This reaction rate can be directly measured by the gel fraction measured by immersing the resin component in a solvent that dissolves it.

(Function) According to the method of the present invention, by irradiating the surface to be coated with light from a plurality of oblique directions, light is incident and reflected in all directions on the surface to be coated, so that light rays are reflected on the surface to be coated. Even if the base material has different ratios depending on the part, when the incident light and reflected light are made uniform,
The photocurable paint applied to the surface to be coated will be cured.

(Example) Hereinafter, Examples according to the present invention and Comparative Examples to be compared with these will be given to specifically clarify the differences in the present invention.

In addition, as a photocurable paint, urethane acrylate (manufactured by Negami Kogyo Co., Ltd., Art Resin UUV-1255) 60, tetrahydrofurfuryl acrylate 40g, methylphenylglyoxylate (photopolymerization initiation side) Ig,
0.2 g of 2.6-di-t-butyl-P-cresol (antioxidant) and 0.2 g of 2-(2″-hydroxy-5′-methylphenyl)henzotriazole (ultraviolet absorption side)
g was mixed and used.

As a base material, a 1 mm thick, 50 mm square soft vinyl chloride sheet with a 1 rM square black and white checkered pattern printed thereon was used.

An object to be irradiated was one in which the photocurable paint was cast onto the substrate to a thickness of 1/3 inch.

A metal halide lamp with an input of 80 W/am was used as a light source.

[First Example] As shown in FIG. 4, an object to be irradiated 5 is placed in the center of a turntable 8 with a diameter of 10 cm, and while rotating at a speed of 10 revolutions per minute, a distance of 50 cm from the object to be irradiated 5 is set. Elevation angle 30
The above-mentioned light source 4 was arranged so as to have a positional relationship of .degree., and irradiated for 3 minutes to cure the photocurable paint on the substrate.

As a result, the obtained irradiated object had a flat and hardened coating film, and when visually inspected by reflecting a fluorescent lamp, the coating film was free from distortion.

[Second Embodiment] As shown in FIG. 5, an irradiated object 5 placed on a turntable 8 is conveyed by a held-con hair 9, and the irradiated object 5 conveyed on this held-con hair 9 is exposed to the light r1.
．． The apparatus was configured to irradiate according to 4.

Note that the distance between the irradiated object 5 and the light source 4 was 40 cm, and the elevation angle was 30°. In addition, the irradiated object 5 and the light source 4 at the start of irradiation
The horizontal distance L1 between the
Rotated at 0 rotations. Then, the object 5 to be irradiated is passed under the light #4, and moving irradiation is performed until the horizontal distance L2 between the object 5 and the light source 4 is 40 cm again, and the photocurable paint on the substrate is hardened.

As a result, the obtained irradiated object had a flat and hardened coating film, and when visually inspected by reflecting a fluorescent lamp, the coating film was free from distortion.

[Comparative example]

Place the object to be irradiated vertically under the above light source, irradiate for 3 minutes,
The photocurable paint on the substrate was cured.

As a result, the irradiated object obtained had irregularities formed on the coating film corresponding to the checkered pattern of the base material, and when visually observed by reflecting a fluorescent lamp, it was found that fine wavy shapes were formed in response to the irregularities. A distortion had occurred.

(Effects of the Invention) As described above, according to the present invention, the photocurable paint applied to the surface to be coated is cured while the incident light and reflected light are made uniform. A flat cured coating can be obtained regardless of the coating composition or coating thickness.

[Brief explanation of the drawing]

1 to 5 are drawings according to the present invention, in which the first
The figure is a schematic diagram explaining the light irradiation state according to the curing method of the present invention, FIG. 2 is a schematic diagram explaining the light irradiation method according to the curing method of the present invention, and FIG. A schematic diagram explaining another method of irradiation, FIG. 4 is a schematic diagram explaining a light irradiation method according to the first embodiment, and FIG. 5 is a schematic diagram explaining a light irradiation method according to the second embodiment. 6 are schematic diagrams illustrating the state of light irradiation according to the conventional curing method. 1...Direct light (light) 10...Reflected light (light) 2...Coating film (photocurable paint) 3...Base material 30...Coated surface Patent applicant Sekisui Chemical Co., Ltd. Company Representative Hiroshi 1) Kaoru Figure 1 Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1) A photocurable paint is applied to a base material whose light reflectance varies depending on the part of the coated surface, and the photocurable paint is irradiated with light to produce a photocurable paint. A method for curing a photocurable paint, the method comprising: irradiating the surface to be coated with light from a plurality of oblique directions, at least until the curing stage where the photocurable paint loses fluidity. .