Modification method and curing method for curable resin, precuring device for curable resin, modification treatment system, and curing treatment system

Abstract

The present invention makes it possible to highly accurately control the degree of roughening during a matting treatment.　A modification method for a curable resin according to the present invention includes a precuring step for irradiating first light that has a principal wavelength of at least 200 nm on a light emission spectrum of a light source at the surface of a curable resin under an atmosphere that has an oxygen concentration of 0.3–21.0 vol%. A precuring device that executes the modification method: comprises a first light source that emits first light that has a principal wavelength of at least 200 nm on a light emission spectrum; and irradiates the first light at the surface of the curable resin.

Description

Method for modifying and curing hardening resin, and hardening resin pre-cure device, modification treatment system, and hardening treatment system

[0001] The present invention relates to a method for modifying and curing a curable resin, as well as a pre-cure device, a modification treatment system, and a curing treatment system for a curable resin.

[0002] Protective materials known as decorative materials and decorative sheets have been used to protect articles such as building interior materials (walls, ceilings, floors, etc.), housing equipment and furniture, and vehicle interior and exterior materials. Decorative materials and decorative sheets are required to have design properties in addition to surface properties such as scratch resistance, stain resistance, and weather resistance, as well as physical and mechanical properties required of protective materials, such as processability.

[0003] In order to improve the design of decorative materials and decorative sheets, treatments that reduce the gloss of the surface of the decorative material or decorative sheet and impart a matte effect are known. Treatments that reduce gloss and impart a matte effect are called matting treatments. Matting the surface of the decorative material or decorative sheet can improve the texture of the decorative material or decorative sheet. Matting treatment is carried out by forming irregularities on the surface of the resin. A specific example of a matting treatment is known in which ultraviolet light is irradiated onto a photocurable resin applied to the surface of the decorative material or decorative sheet, causing the applied resin to shrink and forming irregularities (wrinkles) on the surface that scatter visible light (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2021-137990

[0005] Matting treatments can produce a variety of roughening levels, from treatments that produce dense wrinkles, resulting in a large reduction in glossiness, to treatments that produce coarse wrinkles, resulting in a small reduction in glossiness. There is a need to control the degree of roughening produced by matting treatments. Therefore, the present invention aims to precisely control the degree of roughening produced by matting treatments of curable resins.

[0006] Initially, in order to control the degree of roughening in the matting treatment, we considered changing the irradiation amount of ultraviolet light used to form wrinkles. However, we found that changing the irradiation amount of ultraviolet light used to form wrinkles hardly changed the surface condition of the coating film. Next, we considered changing the type of paint used in the coating film or adjusting the formulation. However, changing the type of paint or adjusting the formulation took too much time and we were unable to control the degree of roughening with high precision. The inability to control the surface condition of the coating film means that we cannot control the desired gloss level. Therefore, the object of the present invention is to control the degree of roughening in the matting treatment with high precision.

[0007] The method for modifying a curable resin of the present invention includes a pre-cure step of irradiating the surface of the curable resin with first light having a dominant wavelength of 200 nm or more in the emission spectrum of a light source in an atmosphere having an oxygen concentration of 0.3 vol % or more and 21.0% or less.

[0008] Details will be explained in the "Embodiment of the Invention" section, but the pre-cure process will be briefly described below. The pre-cure process is a process performed prior to the matting process and the curing process following the matting process. In the pre-cure process, the surface of the curable resin is irradiated with a first light having a dominant wavelength of 200 nm or more in the emission spectrum of a light source in an atmosphere with an oxygen concentration of 0.3 vol% or more and 21.0% or less. As a result, curing progresses within the surface layer of the curable resin, while curing shrinkage does not progress significantly at the very surface, which is the outermost surface of the surface layer of the curable resin, preventing wrinkles from forming on the surface of the curable resin. By selectively curing only the interior of the surface layer of the curable resin, it is possible to limit the curing depth when wrinkles form in the subsequent matting process. In this specification, the curing process in the pre-cure process is sometimes referred to as "pre-curing." Control parameters for pre-curing include the dose of the first light, illuminance, irradiation time, oxygen concentration, etc. Controlling these control parameters allows the curing depth within the surface layer to be controlled. In other words, by controlling the control parameters of the pre-curing, such as the illuminance and irradiation time of the first light, the curing depth during the pre-curing can be controlled, and as a result, the curing depth during wrinkle formation in the matting process can be adjusted. The curing depth during wrinkle formation is related to the degree of wrinkle density, i.e., the degree of surface roughening in the matting process. Therefore, by controlling the control parameters of the pre-curing, the degree of surface roughening in the matting process can be controlled with high precision.

[0009] The dominant wavelength of the first light may be 300 nm or more and 450 nm or less.

[0010] The half width of the dominant wavelength of the first light may be 30 nm or less.

[0011] Prior to irradiating the first light, the method may include obtaining a relationship between the glossiness of the surface after surface modification and at least one parameter selected from the dominant wavelength, irradiation amount, illuminance, irradiation time, and oxygen concentration of the first light in the pre-cure process, and setting the at least one parameter based on the desired glossiness and the relationship.

[0012] When acquiring the relationship, the relationship may be acquired for each of the curable resins, and when setting the at least one parameter, the relationship may be set based on the relationship corresponding to the curable resin to be used.

[0013] After the pre-cure step, a matting step may be included in which the surface is roughened by irradiating the surface with a second light having a dominant wavelength of less than 200 nm in the emission spectrum of the light source.

[0014] The light source that emits the second light may be an excimer lamp.

[0015] The curable resin may be applied to a substrate, and at least one of the irradiation with the first light in the pre-cure step and the irradiation with the second light in the matting step may be performed on the substrate while it is moving.

[0016] The method for hardening the hardenable resin may include, after the modifying method, a curing step of irradiating the surface with ionizing radiation different from the first light and the second light to harden the hardenable resin.

[0017] The pre-cure device that performs the pre-cure process includes a first light source that emits first light having a dominant wavelength of 200 nm or more in an emission spectrum, and irradiates the first light toward the surface of the curable resin to pre-cure the inside of the surface layer of the curable resin.

[0018] The imaging device may include a chamber surrounding an optical path of the first light, and an oxygen concentration adjusting unit that adjusts the oxygen concentration of the gas supplied into the chamber to be between 0.3 vol % and 21.0 vol %.

[0019] The primary light source may be an LED light source that emits primary light having a dominant wavelength of 300 nm or more and 450 nm or less.

[0020] The curable resin modification processing system includes the pre-cure device and a matting device that roughens the surface after the pre-cure process by the pre-cure device, and the matting device may be equipped with a second light source that emits second light having a dominant wavelength of less than 200 nm in its emission spectrum.

[0021] At least one of the pre-cure device and the matting device includes a holding unit that holds the substrate on which the curable resin has been applied, and the holding unit may move the substrate when the curable resin is irradiated with light.

[0022] A curable resin curing treatment system may include the modification treatment system, and a curing device that uses ionizing radiation to cure the entire curable resin, including the curable resin modified by the modification system.

[0023] The degree of roughening of the matte treatment can be controlled with high precision.

[0024] 1 is a flow diagram illustrating a resin layer forming method; FIG. 2 is a diagram illustrating details of a pre-cure process; FIG. 3 is a diagram illustrating details of a mattifying process; FIG. 4 is a diagram illustrating details of a curing process; FIG. 5 is a graph showing the relationship between oxygen concentration and glossiness in a pre-cure process (dominant wavelength: 365 nm); FIG. 6 is a graph showing the relationship between oxygen concentration and glossiness in a pre-cure process (dominant wavelength: 395 nm); FIG. 7 is a graph showing the relationship between oxygen concentration and glossiness in a pre-cure process (dominant wavelength: 405 nm); FIG. 8 is a graph showing the relationship between irradiation dose and glossiness in a pre-cure process (dominant wavelength: 365 nm); FIG. 9 is a graph showing the relationship between irradiation dose and glossiness in a pre-cure process (dominant wavelength: 395 nm); FIG. 10 is a graph showing the relationship between irradiation dose and glossiness in a pre-cure process (dominant wavelength: 405 nm); FIG. 11 is a flow diagram illustrating a method for determining process parameters in a pre-cure process; FIG. 12 is a cross-sectional view of a pre-cure device; FIG. 13 is a modified example of a pre-cure device; FIG. 14 is a cross-sectional view of a mattifying device; FIG. 15 is a cross-sectional view of a curing device; FIG. 16 is a diagram illustrating a curing treatment system;

[0025] Embodiments of the present invention will be described with reference to the drawings. The drawings disclosed in this specification, except for graphs, are merely schematic illustrations. That is, the dimensional ratios in the drawings do not necessarily correspond to the actual dimensional ratios, and the dimensional ratios between the drawings do not necessarily correspond to the actual dimensional ratios or the number of each component shown in the drawings.

[0026] In the following, each drawing will be described with reference to the XYZ coordinate system as necessary. In this specification, when a direction is expressed and a distinction is made between positive and negative directions, it is described with a positive or negative sign, such as "+X direction" and "-X direction." When a direction is expressed without distinguishing between positive and negative directions, it is simply described as "X direction." In other words, in this specification, when simply referring to "X direction," it includes both "+X direction" and "-X direction." The same applies to the Y direction and the Z direction. In the embodiments described below, the direction of gravity is the -Z direction, the transport direction in which the workpiece is transported is the -Y direction, and the width direction of the workpiece is the X direction.

[0027] First Embodiment [Method of Forming Resin Layer] A method of forming a resin layer will be described with reference to Fig. 1 . The method of forming a resin layer includes, in this order, an application step S10 of applying a curable resin, a pre-cure step S20, a matting step S30, and a curing step S40. Of the methods of forming a resin layer, a method including the three steps of the pre-cure step S20, the matting step S30, and the curing step S40 constitutes a method of curing a curable resin. Of the methods of curing a curable resin, a method including the two steps of the pre-cure step S20 and the matting step S30 constitutes a method of modifying the surface layer of a curable resin.

[0028] [Coating Step] The coating step S10 is a step of coating the curable resin 5 onto the substrate 4. The coating method is not particularly limited. Examples of the coating method include die coating, in which the curable resin is extruded from a slit die arranged opposite the substrate 4 while the slit die and the substrate 4 are moved relative to each other to coat the curable resin onto the substrate 4; bar coating, in which the curable resin arranged on the substrate 4 is applied by scraping it off with a bar coater; spray coating, in which the curable resin is sprayed onto the substrate 4; dip coating, in which the substrate 4 is immersed in a bath of the curable resin; or curtain coating, in which the substrate 4 is immersed in a curtain (band) of curable resin flowing down.

[0029] The curable resin 5 of this embodiment is a photocurable resin. The photocurable resin of this embodiment is a bifunctional acrylate UV-curable resin, and includes a precursor of an acrylic resin, a photoinitiator for polymerizing the precursor, and a solvent. The precursor of the acrylic resin is composed of a monomer or oligomer having an acrylic group, or both a monomer and an oligomer having an acrylic group. A precursor of another resin (e.g., an epoxy resin) may be used instead of the precursor of the acrylic resin. A resin that is cured by ionizing radiation other than light (such as electromagnetic waves or charged particle beams not referred to as light) may be used instead of the photocurable resin.

[0030] [Pre-cure Step] The pre-cure step S20 is a step performed on the curable resin 5 applied to the substrate 4 prior to the matting step S30 and the curing step S40. The pre-cure step S20 will be described in detail with reference to Fig. 2. The pre-cure step S20 is performed in combination with the matting step S30 to modify the surface layers (5a, 5b) of the curable resin to a desired state.

[0031] A curable resin 5 is applied to a substrate 4. A first light L1 from a first light source 1 is irradiated toward the curable resin 5 to pre-cure the curable resin 5. The light irradiation atmosphere has an oxygen concentration of 0.3 vol% or more and 21.0% or less. A method for forming such a light irradiation atmosphere will be described. To the light irradiation area, (1) only air may be supplied, (2) a mixed gas of air and an inert gas may be supplied, (3) a mixed gas of CDA (Clean Dry Air) and an inert gas may be supplied, or (4) a mixed gas of oxygen gas and an inert gas may be supplied. A characteristic of pre-cure is that the curing reaction progresses in the inner part 5b of the surface layer of the curable resin 5, while the curing reaction does not progress much on the extreme surface 5a of the curable resin 5, and wrinkles are not formed. The reason for this characteristic will be described.

[0032] The first light L1 reaches the entire surface layer (5a, 5b) of the resin. The photochemical reaction in the surface layer (5a, 5b) of the resin will be described. First, the reaction in the interior 5b of the surface layer will be described. The photoinitiator in the curable resin 5 absorbs the first light L1, causing an initiation reaction in which highly active radicals are generated from the photoinitiator. These radicals cleave carbon-carbon double bonds contained in the acrylic resin precursor (monomer or oligomer, or both monomer and oligomer; hereinafter, these may be collectively referred to as "monomer, etc.") in the curable resin 5, generating highly active monomers, etc. The highly active monomers, etc., polymerize with other monomers, etc., extending the polymer chain, and a chain reaction in which new radicals are generated proceeds. This reaction is called a propagation reaction. During the propagation reaction, if a termination reaction occurs in which no new radicals are generated even when monomers, etc., combine, the series of polymerization reactions stops. In this way, the curable resin 5 hardens due to the polymerization reaction of the curable resin 5 in the interior 5b of the surface layer.

[0033] Next, an example of a reaction path on the electrode surface 5a will be described. On the electrode surface 5a of the curable resin 5, oxygen molecules contained in the gas in the environment where the substrate 4 is placed dissolve and diffuse into the uncured resin. The photoinitiator on the electrode surface 5a absorbs the first light L1, and highly active radicals are generated from the photoinitiator. At least a portion of the generated radicals do not act on the acrylic resin precursor, but instead radicalize the oxygen molecules present there. The radicalized oxygen molecules act on the polymer undergoing the growth reaction, terminating the polymerization reaction. In other words, on the electrode surface 5a where oxygen molecules can penetrate, the penetrated oxygen molecules inhibit the polymerization reaction. Hereinafter, the inhibitory effect of oxygen molecules on the polymerization reaction will be referred to as the "oxygen inhibition effect." Note that the reaction path through which the oxygen inhibition effect described here occurs is merely an example and is not limited to the above-mentioned reaction path. Furthermore, the first light L1 has a dominant wavelength of 200 nm or more in the emission spectrum, and the absorption efficiency of the first light L1 by the curable resin 5 (precursor or photoinitiator) is lower than the absorption efficiency of the second light (having a dominant wavelength of less than 200 nm) used in the matting step, so the first light L1 does not cause strong cure shrinkage on the extreme surface 5 a. Therefore, wrinkles are not formed on the extreme surface 5 a by the first light L1.

[0034] In the pre-curing, in order to dissolve oxygen molecules into the extreme surface 5a of the uncured resin, a first light is irradiated onto the surface of the curable resin in an atmosphere with an oxygen concentration of 0.3 vol% or more and 21.0% or less. By using light with a dominant wavelength of 200 nm or more, which intentionally generates an oxygen inhibition effect and makes it difficult for wrinkles to form, the polymerization (curing) reaction of the resin is promoted in the interior 5b, while the polymerization (curing) reaction of the curable resin is prevented from progressing on the surface 5a.

[0035] In this specification, the surface layer (5a, 5b) of the resin refers to the range in the depth direction of the resin that can receive enough light irradiation to activate the photoinitiator and polymerize the resin in the pre-cure step and matting step. The thickness of the surface layer (5a, 5b) of the resin varies depending on the conditions of the light irradiation.

[0036] In this specification, the term "polar surface 5a" is used to refer to the region where oxygen molecules dissolve in the resin and can cause an oxygen inhibition effect. Therefore, the polar surface 5a has a certain thickness. The thickness of the polar surface 5a varies depending on the parameters of the pre-cure process described below. The thickness of the polar surface 5a is preferably, for example, 50 μm or less, and more preferably 30 μm or less. The interior 5b of the surface layer refers to the entire region of the surface layer (5a, 5b) excluding the polar surface 5a.

[0037] The dominant wavelength of the first light L1 is preferably 200 nm or more and 450 nm or less, and more preferably 300 nm or more and 450 nm or less. In this specification, the term "dominant wavelength" is determined based on the emission spectrum. For example, a dominant wavelength of the first light L1 of 200 nm or more and 450 nm or less means that the first light L1 satisfies at least one of the following conditions: (1) light that exhibits intensity over a broad wavelength band in the emission spectrum, with the peak emission wavelength showing the maximum intensity being 200 nm or more and 450 nm or less; (2) light that exhibits an emission spectrum showing multiple maximum intensities (multiple peaks), with any of the multiple peaks falling within the wavelength range of 200 nm or more and 450 nm or less; or (3) light that exhibits an integrated intensity of at least 30% or more of the total integrated intensity in the emission spectrum. The dominant wavelength of the first light L1 may be selected based on the wavelength that promotes radicalization of the photoinitiator used. Furthermore, it is preferable that the first light L1 has a small half-width of the peak including the dominant wavelength in the emission spectrum (hereinafter referred to as the "half-width of the dominant wavelength"), and for example, light having a half-width of the dominant wavelength of 30 nm or less is used. A small half-width makes it easier to control the radicalization of the photoinitiator. Light having a half-width of the dominant wavelength of 30 nm or less can be obtained, for example, by using a semiconductor solid-state light source such as an LED, or a mercury lamp with an optical filter.

[0038] [Matte Forming Step] The matte forming step S30 will be described with reference to Figure 3. In the matte forming step S30, second light L2 from the second light source 2 is irradiated toward the surface. The second light L2 is light having a dominant wavelength of less than 200 nm in its emission spectrum. The second light source 2 is placed in a housing 8 that is purged with an inert gas G1. Thus, the second light L2 from the second light source 2 is irradiated onto the curable resin 5 in an environment that contains almost no oxygen molecules.

[0039] In this embodiment, an excimer lamp is used as the second light source 2, but other lamps (e.g., a low-pressure mercury lamp emitting light at 185 nm) may also be used. Because the second light L2 is irradiated in an environment with almost no oxygen molecules, the oxygen inhibition effect does not occur in the matting step S30. Therefore, curing also proceeds at the extreme surface 5a. Because light with a dominant wavelength of less than 200 nm is used, curing of the resin at the extreme surface 5a is accompanied by shrinkage of the resin. This roughens the extreme surface 5a of the resin. The unevenness of the roughened extreme surface 5a diffuses visible light, resulting in a matte effect that reduces the gloss of the extreme surface. Since the interior 5b of the surface layer has already been cured in the pre-cure step S20, even if the second light L2 reaches the interior 5b in the matting step, polymerization accompanied by shrinkage does not occur in the interior 5b.

[0040] The degree of roughening of the resin is related to the thickness of the extreme surface 5a. If the thickness of the extreme surface 5a is thick, the degree of roughening of the extreme surface 5a of the resin will be greater, and the glossiness will be lower. If the thickness of the extreme surface 5a is thin, the degree of roughening of the extreme surface 5a of the resin will be smaller, and the glossiness will be less likely to decrease. As will be described in detail later, the thickness of the extreme surface 5a is determined by the control parameters of the pre-curing in the pre-cure process. Therefore, the glossiness (degree of matting) can be determined by the control parameters of the pre-curing. In other words, the desired glossiness can be set by controlling the parameters of the pre-curing.

[0041] [Curing Step] The curing step S40 will be described with reference to FIG. 4. In the curing step S40, the third light source 3 irradiates the curable resin 5 with third light L3. In this embodiment, the third light source 3 is a high-pressure mercury lamp, and the third light L3 is light with a dominant wavelength of 250 to 500 nm in its emission spectrum. The third light L3 penetrates deep into the curable resin 5, beyond the surface layers (5a, 5b). It cures the uncured layer 5c, which is closer to the substrate 4 than the surface layers (5a, 5b). Furthermore, if uncured regions remain partially in the surface layers (5a, 5b) in the pre-curing step, these uncured portions are also cured in the curing step. As a result, the entire curable resin 5 is cured after the curing step S40 is completed.

[0042] In this embodiment, since a high-pressure mercury lamp is used as the third light source 3, light irradiation in an inert gas environment is not necessarily required. However, a different light source type may be used as the third light source 3. For example, the third light source 3 may be a charged particle beam source (e.g., an electron beam source) or an LED. When a charged particle beam source (e.g., an electron beam source) is used as the third light source 3, it is necessary to purge the housing 8 surrounding the light source 3 with an inert gas G1 to create an environment with a reduced oxygen concentration, or to create a vacuum environment. The third light L3 does not necessarily have to be light with a dominant wavelength of 250 to 500 nm. An emission spectrum with a dominant wavelength outside the 250 to 500 nm range may be used for the third light L3.

[0043] [Oxygen Concentration and Glossiness] As mentioned above, the desired glossiness can be achieved by controlling the control parameters of the pre-cure process. Here, the relationship between the oxygen concentration and glossiness, which is closely related to the oxygen inhibition effect, will be described.

[0044] FIG. 5 shows the oxygen concentration (O ２ 1 is a graph showing the relationship between the concentration of oxygen and gloss. This graph was obtained from the results of the following experiment. In the experiment, samples were subjected to a pre-cure process in environments with seven oxygen concentrations: 0.2 vol%, 0.3 vol%, 0.5 vol%, 1 vol%, 5 vol%, 10 vol%, and 21 vol%, followed by a matting process and a curing process. The surface gloss was then measured. The primary light source 1 was an LED light source (Ushio Inc.: UniJet E110Sd-HC, Model: U365A-F95-PY) with a dominant wavelength of 365 nm. The gloss was measured at 85° using a BYK micro-tri-gloss gloss meter (Model: 4563).

[0045] The 85° gloss value will now be explained. The 85° gloss value is a value based on the measurement method adopted in the specular gloss measurement method specified in JIS Z 8741-1997. Specifically, the measured value is the standard value when the reflectance of 10% of light incident on a glass surface with a refractive index of 1.567 at an incident angle of 85° is set to 100. For example, an "85° gloss value of 30" means that the reflectance of light incident on a glass surface with a refractive index of 1.567 at an incident angle of 85° is 3%.

[0046] In the graph of FIG. 5, all samples were exposed to a radiation dose of 1.6 mJ / cm 2 in the pre-cure process. ２ The irradiation amount is set so that the irradiation amount is the integrated light amount, i.e., the product of the illuminance on the irradiated surface and the irradiation time. The irradiation amount is set using an illuminance meter suitable for the wavelength of the light used. For example, when the dominant wavelength of the first light L1 is 365 nm, a UVD-S365 manufactured by Ushio Inc. was used as the illuminance meter. The same substrate and the same resin were used for all samples, and the process conditions in the pre-cure step, except for the oxygen concentration, were the same. The matting step used the same excimer lamp (dominant wavelength 172 nm) for all samples, and was performed at 150 mJ / cm in an environment with an oxygen concentration of 50 ppm or less. ２ The curing process was carried out in air using the same high-pressure mercury lamp (dominant wavelength: 250 to 500 nm) for all samples, with an irradiation dose of 600 mJ / cm. ２ was treated with an irradiation dose of .

[0047] As shown in Figure 5, gloss decreased with increasing oxygen concentration. It is believed that high oxygen concentrations strongly inhibit oxygen during the pre-cure process, resulting in a thicker uncured surface and the formation of large wrinkles during the matting process, resulting in a decrease in gloss. By obtaining the relationship shown in Figure 5 in advance, it is possible to control the oxygen concentration to obtain the desired gloss. In particular, since slight changes in oxygen concentration between 0.3 vol% and 5 vol% significantly change the gloss value, controlling the oxygen concentration between 0.3 vol% and 5 vol% is preferable to obtain the desired gloss value. Although the gloss value at an oxygen concentration of 0.2 vol% is less than 100, it is close to 100 and the change in appearance is small, making this undesirable.

[0048] Fig. 6, like Fig. 5, is a graph showing the relationship between oxygen concentration and gloss in the pre-cure process. The only difference from Fig. 5 is that an LED light source (UniJet E110Sd-HC, model: U395A-F49-PY, manufactured by Ushio Inc.) with a dominant wavelength of 395 nm was used as the first light source 1. The pre-cure process was carried out on the samples under seven oxygen concentrations: 0.2 vol%, 0.3 vol%, 0.5 vol%, 1 vol%, 5 vol%, 10 vol%, and 21 vol%. For all samples, the irradiation dose in the pre-cure process was 6.6 mJ / cm. ２ The illuminance meter used to set the irradiation amount of light having a dominant wavelength of 395 nm was UVD-S405 manufactured by Ushio Inc.

[0049] In the case of Figure 6, as in the case of Figure 5, it was found that the glossiness decreased as the oxygen concentration increased. This makes it possible to obtain a desired glossiness by controlling the oxygen concentration. In particular, since the glossiness value changes significantly with even a slight change in the oxygen concentration in the atmosphere between 0.3 vol% and 5 vol%, it is preferable to control the oxygen concentration between 0.3 vol% and 5 vol% in order to obtain a desired glossiness. Although the glossiness value is smaller than 100 at an oxygen concentration of 0.2 vol%, it is not preferable because the glossiness value is close to 100 and the change in appearance is small.

[0050] Fig. 7 is a graph showing the relationship between oxygen concentration and glossiness during the pre-cure process, similar to Fig. 5. The only difference from Fig. 5 is that an LED light source with a dominant wavelength of 405 nm (UniJet E110II-HD, model SSLS-U405A-436, manufactured by Ushio Inc.) was used as the first light source 1. The pre-cure process was carried out on the samples under seven oxygen concentrations: 0.2 vol%, 0.3 vol%, 0.5 vol%, 1 vol%, 5 vol%, 10 vol%, and 21 vol%. For all samples, the irradiation dose during the pre-cure process was 20.3 mJ / cm. ２ The illuminance meter used to set the irradiation amount of light having a dominant wavelength of 405 nm was UVD-S405 manufactured by Ushio Inc.

[0051] In the case of Figure 7, as in the case of Figure 5, it was found that the glossiness decreased as the oxygen concentration increased. This makes it possible to obtain a desired glossiness by controlling the oxygen concentration. In particular, since the glossiness changes significantly with even a slight change in the oxygen concentration in the atmosphere between 0.3 vol% and 1 vol%, it is preferable to control the oxygen concentration between 0.3 vol% and 1 vol% in order to obtain a desired glossiness. Although the glossiness is smaller than 100 at an oxygen concentration of 0.2 vol%, it is not preferable because the glossiness is close to 100 and the change in appearance is small.

[0052] [Irradiation Dose and Glossiness] Next, the relationship between irradiation dose and glossiness in the pre-cure process will be described. Figure 8 illustrates the glossiness (85° gloss value) when the irradiation dose of an LED light source (Ushio Inc.: UniJet E110Sd-HC, Model: U365A-F95-PY) with a primary light L1 having a dominant wavelength of 365 nm is changed. As mentioned above, the glossiness is the 85° gloss value measured using a BYK micro-tri-gloss glossmeter (Model: 4563). Analysis of the experimental results revealed that the glossiness increases with increasing irradiation dose. This is because increasing the irradiation dose accelerates curing in the pre-cure process, which in turn reduces the degree of curing in the matting process, making it less likely for wrinkles to form. This is thought to be the result of the increased glossiness.

[0053] This relationship between the irradiation amount and the gloss level does not change even when the wavelength of the first light L1 is changed. Figure 9 shows the gloss level (85-degree gloss value) when the irradiation amount of an LED light source (UniJet E110Sd-HC, model: U395A-F49-PY, manufactured by Ushio Inc.) whose dominant wavelength of the first light L1 is 395 nm is changed. Figure 10 shows the gloss level (85-degree gloss value) when the irradiation amount of an LED light source (UniJet E110II-HD, model: SSLS-U405A-436, manufactured by Ushio Inc.) whose dominant wavelength of the first light L1 is 405 nm is changed. It was found that even when the dominant wavelength is 395 nm or 405 nm, the gloss level increases as the irradiation amount increases, as in the case of a dominant wavelength of 365 nm.

[0054] In this specification, it has been explained that the dose of irradiation represents the cumulative amount of light, i.e., the product of the illuminance on the irradiated surface and the irradiation time. Therefore, the existence of a relationship between the dose of irradiation and the glossiness indicates that there is a relationship between the illuminance and the glossiness, and that there is a relationship between the irradiation time and the glossiness.

[0055] [Curable Resin Components and Glossiness] The reason why differences in dominant wavelength affect glossiness is because the radicalization of photoinitiators is wavelength-dependent. Wavelength dependence differs depending on the type of photoinitiator. Therefore, even if the irradiation conditions and oxygen concentration in the pre-cure process are the same, glossiness varies depending on the type of photoinitiator. A curable resin always contains a resin to be polymerized and a photoinitiator. Furthermore, a curable resin may contain a solvent, if necessary. Changes in the components of the curable resin, such as the concentration of the photoinitiator or the type of resin, affect curability and ultimately glossiness. Therefore, if at least one of the type and amount of resin, the type and amount of photoinitiator, and the type and amount of solvent is different, it is preferable to treat the curable resin as a different curable resin and then consider the relationship between the curable resin and glossiness.

[0056] [Pre-cure process parameters and glossiness] To summarize the above, the parameters of the pre-cure process include the oxygen concentration in the light irradiation atmosphere in the pre-cure process, the irradiation amount of the first light L1, the illuminance of the first light L1, the irradiation time of the first light L1, the wavelength of the first light L1, and the components of the curable resin (type and concentration of the photoinitiator, components of the curable resin). These parameters affect the glossiness.

[0057] FIG. 11 shows a method for obtaining a desired gloss level by acquiring and using the relationship between pre-curing process parameters and gloss level in advance. First, the information to be acquired is acquired. The first information is the specified conditions for the pre-curing process. The specified conditions, which are conditions that do not change during the pre-curing process, are acquired in advance (S1). The specified conditions may be, for example, the components of the curable resin or the photoinitiator contained in the curable resin, or the wavelength of the first light L1. The specified conditions are not always the same but vary depending on the situation. The second information is the relationship between the pre-curing process parameters and gloss level. This relationship is acquired in advance through experiments or simulations (S2). Specifically, the relationship may be provided in the form of a table showing the relationship between the pre-curing process parameters and gloss level, in the form of a function describing the relationship, or in the form of a program such as an algorithm for calculating the relationship. The third information is the target gloss level. The target gloss level is acquired in advance (S3).

[0058] Based on these three pieces of information acquired in advance, undetermined parameters for the pre-cure step are determined (S5). Based on the determined parameters, irradiation with the first light L1, i.e., the pre-cure step S20, is carried out.

[0059] [Pre-cure Apparatus] One embodiment of a pre-cure apparatus for performing the pre-cure process is described below. FIG. 12A is a cross-sectional view of the pre-cure apparatus. The pre-cure apparatus 100 includes a first light source 10 that emits ultraviolet light, a first housing 14 in which the first light source 10 is disposed, and a control unit 15. The first housing 14 has a ceiling surface along the XY plane and side surfaces along the XZ or YZ plane, and is hollow inside. In this embodiment, the emission direction of the first light L1 from the first light source 10 is the -Z direction, and the first housing 14 is not located in a direction close to the curable resin 5, but has an opening in the same direction for extracting the ultraviolet light. The pre-cure apparatus 100 is positioned so that the opening faces the transport path for the substrate 4 coated with the curable resin 5. Then, as the substrate 4 is transported along the transport path in the +Y direction, the curable resin 5 on the substrate 4 is exposed to the first light L1.

[0060] The interior of the first housing 14 is filled with atmosphere adjustment gas G2. The oxygen concentration of the atmosphere adjustment gas G2 is adjusted, and the gas is produced by a two-gas mixing valve 7. The two-gas mixing valve is connected to an inert gas supply source 12 and an outside air suction port 13, and by changing the mixing ratio of outside air, i.e., air, and the inert gas from the inert gas supply source 12, the atmosphere adjustment gas G2 is obtained, adjusted to a desired oxygen concentration. The inert gas is preferably nitrogen. The two-gas mixing valve 7 is electrically connected to a control unit 15. The control unit 15 controls the two-gas mixing valve 7 to adjust the oxygen concentration to the desired level. Here, the inert gas and air are mixed, but oxygen gas or CDA (Clean Dry Air) may be mixed with the inert gas instead of air.

[0061] An oxygen concentration meter (not shown) that measures the oxygen concentration may be disposed inside the first housing 14. The two-gas mixing valve 7 is adjusted according to the oxygen concentration measured by the oxygen concentration meter. The oxygen concentration meter may be electrically connected to the control unit 15, and a measurement signal from the oxygen concentration meter may be transmitted to the control unit 15, which may then control the two-gas mixing valve 7 based on the transmitted signal.

[0062] In this embodiment, the primary light source 10 is an LED light source that emits ultraviolet light. The primary light source 10 includes only one type of LED light source and obtains the first light L1 fixed to one emission spectrum. In this embodiment, the dominant wavelength of the first light L1 is 300 nm or more and 450 nm or less. The primary light source 10 is electrically connected to a control unit 15. The control unit 15 controls the primary light source 10 to turn the primary light source 10 on and off and adjust the emission intensity. The control unit 15 adjusts the emission intensity of the primary light source 10 to achieve a desired illuminance. Alternatively, the primary light source 10 may include only multiple types of LED light sources, and the control unit 15 may obtain the first light L1 that can be switched to multiple emission spectra. This allows the dominant wavelength of the first light L1 to be changed. Alternatively, the primary light source 10 may be a light source that emits light with a wide wavelength band, such as a high-pressure mercury lamp. A light source that can switch to multiple dominant wavelengths may be realized by combining a high-pressure mercury lamp with a filter that limits specific wavelengths.

[0063] In this embodiment, the substrate 4 coated with the curable resin 5 is placed on a conveyor belt 51. Therefore, the conveyor belt 51 determines the conveyance path. Rollers 52 that drive the conveyor belt 51 are rotated by a motor M1. The motor M1 is electrically connected to a control unit 15. The control unit 15 controls the motor M1 to vary the conveyance speed of the conveyor belt 51. The control unit 15 controls the illuminance, which is set based on the light emission intensity of the first light source 10, and the irradiation time, which is set based on the conveyance speed of the conveyor belt 51, thereby setting the irradiation amount (accumulated light amount) of the first light source 10 to a desired value.

[0064] In this embodiment, the conveyor belt 51 and the motor M1 that drives the conveyor belt 51 are not components of the pre-cure device 100. The transport means is not limited to a type that includes the conveyor belt 51. For example, the transport means may be a type in which the substrate 4 is transported by guide rollers, or a type in which the substrate 4 is transported by a robot arm. Details of the transport means that transports by guide rollers will be described later.

[0065] 12A , the first light source 10 is disposed inside the first housing 14. However, as shown in FIG. 12B , the first light source 10 may be disposed outside the first housing 14. In FIG. 12B , the light extraction portion of the first light source 10 is located on the ceiling surface of the first housing 14. By disposing the first light source 10 outside the first housing 14, it is possible to easily install a cooling mechanism as a countermeasure against heat generation associated with the lighting of the first light source 10. Furthermore, the heat-generating portion of the first light source 10 may be located outside the first housing 14, and the light extraction portion of the first light source 10 may be located inside the first housing 14. Alternatively, the first light source 10 may be disposed away from the first housing 14, and the first light L1 may be incident on the inside of the first housing 14 using a combination of an optical system and a light-transmitting member that guides the first light L1.

[0066] In the pre-cure device 100, the first housing 14 is not an essential component. The first housing 14 is merely one example for irradiating the first light L1 in an atmosphere with a desired oxygen concentration. A configuration in which gas adjusted to a desired oxygen concentration is sprayed along the emission direction of the first light L1 is also acceptable. In that case, the first housing 14 is not required. Furthermore, the first housing 14 is not required when irradiating the first light L1 in an atmosphere with an oxygen concentration fixed at 21 vol%, i.e., in the air.

[0067] The control unit 15 receives the above-mentioned first information (specified conditions for the pre-cure process), second information (relationship between pre-cure process parameters and glossiness), and third information (target glossiness). The control unit 15 determines the parameters for the pre-cure process and controls the first light source 10, the two-gas mixing valve 7, and the motor M1 based on the determined parameters. The first information, second information, and third information may be input to the control unit 15 from an input device, or may be input to the control unit 15 from a computer connected to the control unit 15 via a telecommunications line.

[0068] [Mat Forming Apparatus] One embodiment of a mat forming apparatus for performing the mat forming process is described below. FIG. 13 is a cross-sectional view of the mat forming apparatus. The mat forming apparatus 200 includes a second light source 20 that emits a second light source 20, a second housing 24 in which the second light source 20 is disposed, a table 21 that transports the substrate 4, a gas outlet 22 that blows an inert gas G1, and a control unit (not shown). The second light L2 is irradiated while the table 21 is transported in the +Y direction. In this embodiment, the second housing 24 creates a closed environment isolated from the atmosphere so that the second light L2 is irradiated in an environment containing almost no oxygen molecules. The gas outlet 22 is positioned so that an inert gas G1 (e.g., nitrogen gas) can be sprayed onto the curable resin 5 immediately before irradiation with the second light L2. By spraying the inert gas G1 onto the curable resin 5, oxygen molecules remaining on the surface of the curable resin 5 are removed. The second housing 24 has an exhaust port 23. A constant air pressure is maintained within the second housing 24.

[0069] The second light source 20 may be a light source that emits second light L2 having a dominant wavelength of less than 200 nm in its emission spectrum. In this embodiment, the second light source 20 is an excimer lamp that emits light having a dominant wavelength of 172 nm. However, the second light source 20 may also be a low-pressure mercury lamp (e.g., one having a dominant wavelength of 185 nm), or may be the same as the first light source 10. The same pre-cure device 100 may also be used as the matting device 200.

[0070] The gas G3 is introduced into the second housing 24 from the side opposite the light emission surface of the second light source 20 (the +Z side relative to the second light source 20 in FIG. 13 ), passing through the second light source 20. The gas G3 is an atmosphere-adjusting gas. In this embodiment, the gas G3 is an inert gas for creating an inert gas atmosphere inside the second housing 24. However, when a paint that is not susceptible to oxygen inhibition is used in the matting process, a mixed gas of an inert gas and an oxygen-containing gas (air, CDA, or oxygen gas) may be used as the gas G3. Nitrogen gas may be used as the inert gas. However, instead of a high-purity inert gas, a mixed gas of an inert gas and an oxygen-containing gas (air, CDA, or oxygen gas) may be used. Even if the dominant wavelength of the second light L2 is less than 200 nm, a gas containing oxygen may be supplied into the second housing 24 if the oxygen concentration is low. Furthermore, when the dominant wavelength of the second light L2 is 200 nm or greater, a gas containing a high concentration of oxygen, such as air, may be supplied into the second housing 24. 12B, the second light source 20 may be disposed outside the second housing 24. In addition, if the matting device is configured to inject gas while irradiating the second light L2, the second housing 24 may be omitted.

[0071] [Curing Apparatus] One embodiment of a curing apparatus for performing a curing process will be described. FIG. 14 is a cross-sectional view of the curing apparatus. The curing apparatus 300 includes a third light source 30 that emits a third light L3, a third housing 34 located outside the third light source 30, a table 21 on which the substrate 4 is placed within the third housing 34, and a control unit (not shown). The third light source 30 is a high-pressure mercury lamp. In this embodiment, the curing apparatus 300 irradiates the third light L3 onto the curable resin 5 on the substrate 4 while the substrate 4 is stationary. The third housing 34 has a gas inlet 32 ​​and a gas outlet 33 for supplying an atmosphere-adjusting gas G5. The gas G5 supplied into the third housing 34 may be air, a mixture of air and an inert gas, CDA, a mixture of CDA and an inert gas, or a mixture of oxygen gas and an inert gas.

[0072] The third light source 30 of this embodiment includes a high-pressure mercury lamp 31. A cooling gas G4 passes around the high-pressure mercury lamp 31 to cool the high-pressure mercury lamp 31. A light-transmitting member 35 (e.g., a quartz material) that transmits the third light L3 is disposed between the third light source 30 and the third housing 34.

[0073] The third light source 30 in this embodiment may be a light source having a dominant wavelength of 250 to 500 nm in its emission spectrum. The energy rays emitted in the curing process to cure the curable resin 5 are not limited to ultraviolet light. Electromagnetic waves other than ultraviolet light, such as X-rays, visible light, and infrared rays, may also be used in the curing process. Furthermore, particle beams, particularly charged particle beams such as electron beams and ion beams, may also be used in the curing process. When using charged particle beams, it is preferable to purge the inside of the third housing 34 with an inert gas G1 to create an environment containing almost no oxygen molecules. A cooling gas G3 composed of an inert gas may be introduced into the third housing 34.

[0074] 12A, the third light source 30 may be disposed inside the third housing 34. In addition, if the curing device is configured to inject gas while irradiating the third light L3, the third housing 34 may be omitted.

[0075] <Second Embodiment> A second embodiment will be described. The following description will focus on features that are different from the first embodiment. Points not described in the second embodiment can be implemented in the same way as the first embodiment. The pre-cure device of the second embodiment is incorporated into the hardening treatment system together with the matting device and the curing device.

[0076] Fig. 15A shows a curing treatment system 500 including a pre-cure device 100, a mattifying device 200, and a curing device 300. In Fig. 15, the details of some of the devices among the pre-cure device 100, the mattifying device 200, and the curing device 300 are shown in a simplified manner. Details of each device not mentioned below are as described above and in the figures shown so far.

[0077] The pre-curing device 100 shown in FIG. 15A is a type in which the first light source 10 is disposed on the ceiling surface of the first housing 14 (see FIG. 12B ). The matting device 200 has a first sub-chamber 26 disposed upstream of the second housing 24, which houses the second light source 20, and a second sub-chamber 27 disposed downstream of the second housing 24. The first sub-chamber 26 and the second sub-chamber 27 each have an exhaust port, through which gas inside each sub-chamber (26, 27) is exhausted. The first sub-chamber 26 is primarily intended to prevent air from being brought into the second housing 24 in order to maintain a low-oxygen concentration atmosphere inside the second housing 24. The second sub-chamber 27 is primarily intended to exhaust ozone generated when oxygen is present inside the second housing 24, preventing it from leaking out.

[0078] In this embodiment, the substrate 4 is a sheet-like decorative sheet. The substrate 4 is transported by a roll-to-roll method. That is, the sheet-like substrate is unwound from a roll (not shown) of the substrate 4 in an unwinding device, transported in the +Y direction along a transport path, and then wound up in a winding device. In the transport path, the substrate 4 is supported by a plurality of guide rollers 55. A coating means (not shown) for performing the coating step S10 is disposed along the transport path, and a curing treatment system 500 is disposed after the coating means. The housings of the pre-cure device 100, the matting device 200, and the curing device 300 are optimized for the sheet-like substrate 4 transported by the roll-to-roll method. The substrate 4 is transported in sequence to pass near a pre-cure device 100 for performing the pre-cure process S20, a matting device 200 for performing the matting process S30, and a curing device 300 for performing the curing process S40, and is irradiated with a first light L1, a second light L2, and a third light L3, respectively.

[0079] 15A may be modified to have no curing device 300. A system that does not include the curing device 300 and is composed of the pre-curing device 100 and the matte forming device 200 is called a modification treatment system.

[0080] 15B shows a configuration in which the curing treatment system 500 is combined with a type of transport means that transports the substrate 4 coated with the curable resin 5 by a conveyor belt 51. The conveyor belt 51 moves on guide rollers 55 together with the substrate 4 coated with the curable resin 5. The curing treatment system 500 can be applied to such a transport means, and can also be applied to a transport means that transports the substrate 4 by a robot arm.

[0081] The pre-cure device, the hardening treatment system 500, and the modification treatment system have been described above. The present invention is not limited to the above-described embodiments and modifications, and various changes and modifications can be made to the above-described embodiments and modifications without departing from the spirit and scope of the present invention.

[0082] The substrate 4 to be treated by the optical treatment device of this embodiment may be something other than a decorative material or a decorative sheet.

[0083] 1, 10: First light source 2, 20: Second light source 3, 30: Third light source 4: Substrate 5: Curable resin 5a: Extreme surface (of the surface layer of the curable resin) 5b: Inside (of the surface layer of the curable resin) 5c: Uncured layer (of the curable resin) 7: Two-gas mixing valve 8: Housing 12: Inert gas supply source 13: Outside air suction port 14: First housing 15: Control unit 21: Table 22: Gas outlet 23: Exhaust port 24: Second housing 26: First sub-chamber 27: Second sub-chamber 31: High-pressure mercury lamp 32: Gas inlet 33: Gas exhaust port 34: Third housing 35: Light-transmitting member 51: Conveyor belt 52: Roller 55: Guide roller 100: Pre-cure device 200 : Matting device 300: Curing device 500: Hardening treatment system G1: Inert gas G2: Atmosphere adjusting gas G3: Atmosphere adjusting gas G4: Cooling gas G5: Atmosphere adjusting gas L1: First light L2: Second light L3: Third light M1: Motor S10: Coating process S20: Pre-cure process S30: Matting process S40: Cure process

Claims

1. A method for modifying a curable resin, comprising a pre-cure step of irradiating the surface of the curable resin with first light having a dominant wavelength of 200 nm or more in the emission spectrum of a light source in an atmosphere having an oxygen concentration of 0.3 vol% or more and 21.0% or less.

2. The modification method according to claim 1, wherein the dominant wavelength of the first light is 300 nm or more and 450 nm or less.

3. The modification method according to claim 1, wherein the half width of the dominant wavelength of the first light is 30 nm or less.

4. The modification method according to claim 1, characterized in that it includes, prior to irradiating the first light, obtaining a relationship between the glossiness of the surface after surface modification and at least one parameter selected from the dominant wavelength, irradiation amount, illuminance, and irradiation time of the first light in the pre-cure process, and oxygen concentration, and setting the at least one parameter based on the desired glossiness and the relationship.

5. The modification method according to claim 4, characterized in that when acquiring the relationship, the relationship is acquired for each of the curable resins, and when setting the at least one parameter, the setting is based on the relationship corresponding to the curable resin used.

6. The modification method according to any one of claims 1 to 5, further comprising, after the pre-cure step, a matting step of irradiating the surface with a second light having a dominant wavelength of less than 200 nm in the emission spectrum of the light source to roughen the surface.

7. The method for modifying a substrate according to claim 6, wherein the light source for emitting the second light is an excimer lamp.

8. The modification method according to claim 6, characterized in that the curable resin is applied to a substrate, and at least one of the irradiation with the first light in the pre-cure process and the irradiation with the second light in the matting process is performed on the substrate while it is moving.

9. A method for curing a curable resin, comprising, after the modification method according to claim 6, a curing step of irradiating the surface with ionizing radiation different from the first light and the second light to cure the curable resin.

10. A pre-cure device comprising a first light source that emits first light having a dominant wavelength of 200 nm or more in the emission spectrum, and irradiating the first light toward the surface of the curable resin to pre-cure the inside of the surface layer of the curable resin.

11. A pre-cure device as described in claim 10, characterized in that it comprises: a chamber surrounding the optical path of the first light; and an oxygen concentration adjusting unit that adjusts the oxygen concentration of the gas supplied into the chamber to between 0.3 vol% and 21.0%.

12. The pre-cure device according to claim 10, wherein the first light source is an LED light source that emits first light having a dominant wavelength of 300 nm or more and 450 nm or less.

13. A system for modifying a curable resin, comprising: a pre-cure device according to any one of claims 10 to 12; and a matting device that roughens the surface after the pre-cure process by the pre-cure device, wherein the matting device is equipped with a second light source that emits second light having a dominant wavelength of less than 200 nm in its emission spectrum.

14. The modification processing system described in claim 13, wherein at least one of the pre-cure device and the matting device is provided with a holding unit that holds the substrate coated with the curable resin, and the holding unit moves the substrate when the curable resin is irradiated with light.

15. A curing treatment system for a curable resin, comprising: the modification treatment system according to claim 13; and a curing device that uses ionizing radiation to cure the entire curable resin, including the curable resin modified by the modification system.

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