Resin reflective film

Abstract

This film made of resin has at least two types of regions having different refractive indexes from each other, has a thickness of 20-5,000 μm, has, with respect to deep UV having a wavelength of 220-300 nm, a total reflectance of at least 60%, and has a diffuse-reflectance of at least 60%.

Description

[Technical Field]

[0001] The present invention relates to a resin reflective film. [Background technology]

[0002] The sterilizing effect of ultraviolet light has long been studied. Until now, low-pressure mercury lamps and xenon lamps were the mainstream sources of ultraviolet light. However, in recent years, LEDs capable of emitting wavelengths in this range have been developed, and sterilization devices equipped with LEDs or sterilization methods using LEDs have been developed. For example, Patent Document 1 describes a fluid sterilization module that irradiates a fluid flowing through a flow path with ultraviolet light to sterilize the fluid. To efficiently diffuse the ultraviolet light irradiated from the light source over a certain area, it is effective to use a reflective material that can efficiently and evenly reflect the ultraviolet light. In the fluid sterilization module described in Patent Document 1, an ultraviolet-reflecting material is used for the inner tube that forms the cylindrical treatment flow path.

[0003] Known examples of UV-reflecting materials include metal materials and resin materials. Examples of such metal materials include aluminum foil for UV-reflecting materials, which exhibits high UV reflectance by controlling aluminum particles (Patent Document 2), and aluminum reflective members having a reflective layer or a UV-transmitting resin layer on the surface of an aluminum material (Patent Document 3). Furthermore, known resin materials include multilayer laminates of fluorine-based resins and silicone-based resins. For example, multilayer optical films having two fluoropolymer materials with different refractive indices and UV-reflecting polymer films having two different polymer layers are known (Patent Documents 4 and 5). Sintered, compressed, or porous molded bodies made of polytetrafluoroethylene (PTFE) are also known as UV-reflecting materials. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-187657 [Patent Document 2] International Publication No. 2017 / 158989 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-042183 [Patent Document 4] Special Publication No. 7-507152 [Patent Document 5] Japanese Patent Application Laid-Open No. 2015-165298 Summary of the Invention [Problem to be solved by the invention]

[0005] Metallic materials usually specularly reflect ultraviolet light. Therefore, when irradiating water or air with ultraviolet light to sterilize it, if a metallic material is used as a reflective material, even if the apparent reflectivity is high, the reflected intensity (illuminance) of the ultraviolet light will be weak depending on the angle, and the ultraviolet light will not be able to be distributed evenly throughout the water or air, making it difficult to achieve sufficient sterilization efficiency. Furthermore, when a multilayer laminate of fluorine-based resins or silicone-based resins is used as a reflector, the refractive index of the resin itself is limited, making it difficult to increase the refractive index difference between layers to a level that achieves sufficient reflectance. For this reason, for example, the polymer films described in Patent Documents 4 and 5 currently do not provide sufficient reflected illuminance in the deep ultraviolet region.

[0006] Furthermore, PTFE sintered and compressed porous compacts have numerous crystal grain boundaries or pores inside, giving them excellent ultraviolet reflective properties. However, to ensure that these sintered and compressed porous compacts exhibit sufficient ultraviolet reflective properties, they must be thicker than a certain amount (e.g., about 10 mm). As a result, such thick sintered and compressed porous compacts are less flexible and less flexible to process, which places restrictions on where the ultraviolet reflective material can be applied.

[0007] In view of the above circumstances, an object of the present invention is to provide a resinous reflective film that has excellent diffuse reflection performance for ultraviolet light, particularly deep ultraviolet light, and that is also excellent in flexibility and has a high degree of freedom in processing. [Means for solving the problem]

[0008] The above-mentioned problems of the present invention have been solved by the following means. (1) A resin reflective film having two or more regions with different refractive indices, the thickness of the resin reflective film being 20 to 5000 μm, and having a total reflectance of 60% or more and a diffuse reflectance of 60% or more for deep ultraviolet light with a wavelength of 220 to 300 nm. (2) The reflective resin film according to (1) above, wherein the thickness of the reflective resin film is 50 to 1000 μm. (3) The resin reflective film according to (1) or (2) above, wherein the two or more types of regions constituting the resin reflective film each have a light transmittance of 30 to 100% for deep ultraviolet light having a wavelength of 220 to 300 nm. (4) The reflective resin film according to any one of (1) to (3) above, wherein at least one of the two or more types of regions constituting the reflective resin film is an air bubble. (5) The resin reflective film according to any one of (1) to (4) above, which has a repeating structure in which resin portions (resin regions) and void portions (gas regions) are repeated. (6) The resin reflective film according to (5) above, wherein the width of at least one resin part constituting the repeating structure part and / or the width of at least one void part is 0.1λ to 20λ where λ is the wavelength of the incident ultraviolet light. (7) The resin reflective film according to any one of (1) to (6), wherein the resin material constituting the resin reflective film is a fluorine-containing resin or a silicone resin, and the resin reflective film is produced by foaming an inert gas impregnated in the fluorine-containing resin or the silicone resin film. (8) The resin reflective film according to any one of (1) to (6), wherein the resin material constituting the resin reflective film is a fluorine-containing resin, and the fluorine-containing resin film is stretched to form bubbles and / or voids inside. (9) The resin reflective film according to any one of (7) or (8), wherein the density (Q) of the resin reflective film relative to the density (P) of the resin material constituting the resin reflective film satisfies Q / P=0.2 to 0.99. (10) A sterilization device comprising an ultraviolet light source and the resin reflective film according to any one of (1) to (9) above.

[0009] Generally, "ultraviolet rays" refer to electromagnetic waves with wavelengths shorter than those of visible light. In the present invention, "deep ultraviolet rays" refer to electromagnetic waves with a wavelength in the range of 200 to 300 nm. In the present invention, "total reflectance" means the sum of "specular reflectance" and "diffuse reflectance." Furthermore, "specular reflectance" means the proportion of irradiated light that is specularly reflected, and "diffuse reflectance" means the proportion of irradiated light that is diffusely reflected. [Effects of the Invention]

[0010] The resin reflective film of the present invention has excellent diffuse reflection performance for ultraviolet light, particularly deep ultraviolet light, and is also excellent in flexibility and has a high degree of freedom in processing. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a photograph, shown as a substitute for a drawing, of the cross section of the reflective material produced in Example 1, which was freeze-fractured in a high vacuum and photographed with a scanning electron microscope. [Figure 2] FIG. 2 is a photograph, shown as a substitute for a drawing, of the cross section of the reflective material produced in Example 1, which was freeze-fractured in a high vacuum and photographed with a scanning electron microscope. [Figure 3] FIG. 3 is a photograph, shown as a substitute for a drawing, of the cross section of the reflective material produced in Example 6, which was freeze-fractured in a high vacuum and photographed with a scanning electron microscope. [Figure 4] FIG. 4 is a photograph, shown as a substitute for a drawing, of the cross section of the reflective material produced in Example 6, which was freeze-fractured in a high vacuum and photographed with a scanning electron microscope. [Figure 5]FIG. 5 is a schematic diagram for explaining a method for measuring ultraviolet irradiance in Test Example 2. [Figure 6] FIG. 6 is a schematic diagram for explaining a method for measuring ultraviolet irradiance in Test Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0012] A preferred embodiment of the resin reflective film of the present invention will be described. The resin reflective film of the present invention (hereinafter also referred to as "the reflective film of the present invention") has two or more types of regions with different refractive indices. With this structure, deep ultraviolet rays can be diffusely reflected efficiently and evenly in multiple directions. That is, the reflective film of the present invention has a total reflectance of 60% or more and a diffuse reflectance of 60% or more for deep ultraviolet rays with a wavelength of 220 to 300 nm. In addition, the thickness (film thickness) of the reflective film of the present invention is 20 to 5000 μm.

[0013] The reflective film of the present invention exhibits desired and sufficient reflective properties even in a thin film form. From the viewpoint of improving the diffuse reflection performance for deep ultraviolet light with a wavelength of 220 to 300 nm, the film thickness of the reflective film of the present invention is preferably 30 μm or more, more preferably 40 μm or more, even more preferably 50 μm or more, and also preferably 100 μm or more. Furthermore, from the viewpoint of improving the flexibility of the reflective film and increasing the degree of freedom in processing, the film thickness is preferably 3000 μm or less, more preferably 2000 μm or less, even more preferably 1000 μm or less. From the same viewpoint as above, the film thickness of the reflective film of the present invention is preferably 30 to 3000 μm, more preferably 40 to 2000 μm, even more preferably 50 to 1000 μm, and still more preferably 100 to 1000 μm.

[0014] From the viewpoint of increasing the total reflectance and diffuse reflectance for deep ultraviolet light with a wavelength of 220 to 300 nm to a desired level, the reflective film of the present invention is preferably configured to have regions with different refractive indices alternately laminated. Such a laminated configuration also includes a configuration in which one region is present in another region in a dotted or linear pattern when observed in cross section. Furthermore, the entire reflective film of the present invention may have the above-described laminated configuration, or only a portion of the reflective film of the present invention may have the above-described laminated configuration.

[0015] In the present invention, the regions having different refractive indices have different refractive indices with respect to deep ultraviolet light having a wavelength of 220 to 300 nm. If the refractive indices between the regions differ at wavelengths commonly measured, such as visible light, the refractive indices with respect to deep ultraviolet light having a wavelength of 220 to 300 nm will generally also differ. Since the refractive index generally increases as the wavelength of irradiation decreases, the phrase "different refractive indices with respect to deep ultraviolet light having a wavelength of 220 to 300 nm" means that the regions have different refractive indices with respect to the same wavelength. From the viewpoint of improving the diffuse reflectance of the reflective film, the refractive index difference between the regions having different refractive indices is preferably 0.005 or more, more preferably 0.01 or more, even more preferably 0.05 or more, even more preferably 0.1 or more, even more preferably 0.2 or more, and even more preferably 0.3 or more. Furthermore, the practical refractive index difference is 2.0 or less. By increasing the difference in refractive index between the regions with different refractive indexes, the reflection at the interface between the regions with different refractive indexes increases, resulting in an improvement in the diffuse reflectance of the reflective film.

[0016] The light transmittance of each region constituting the reflective film of the present invention for deep ultraviolet light having a wavelength of 220 to 300 nm is preferably 30% or more, more preferably 50% or more, and even more preferably 60% or more. Furthermore, the light transmittance is usually 100% or less, and may be 95% or less. In other words, the components constituting each region of the reflective film are preferably substances or gases with low absorption ability for deep ultraviolet light. Furthermore, in the present invention, "light transmittance" refers to the light transmittance of a single region. That is, even when one region is contained within another region, the light transmittance of each single region is preferably 30% or more, more preferably 50% or more, and even more preferably 60% or more. By using such components, the ultraviolet reflection efficiency of the resulting reflective film can be further improved. The light transmittance for deep ultraviolet light having a wavelength of 220 to 300 nm can be measured by the method described in the Examples below.

[0017] Of the two or more regions having different refractive indices in the reflective film of the present invention, one region is made of a resin. The resin may be a matrix. The resin used in the reflective film of the present invention is made of a resin material having low absorption ability for deep ultraviolet light with a wavelength of 220 to 300 nm. By using such a resin material, the ultraviolet light reflection efficiency of the resulting reflective film can be further improved. Furthermore, the two or more regions having different refractive indices may be made of resin materials having different refractive indices.

[0018] The resin material is preferably one or more resins selected from fluorine-containing resins and silicone resins. Among these, fluorine-containing resins are more preferred from the viewpoints of rigidity and reducing the influence on electronic components. The fluorine-containing resin is preferably one or more resins selected from polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene-ethylene copolymer (ETFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyvinylidene fluoride (PVDF), and tetrafluoroethylene / perfluoroalkyl vinyl ether / chlorotrifluoroethylene copolymer (CPT). From the viewpoints of relatively easy melt processing and good mechanical properties, one or more resins selected from PCTFE, ETFE, PFA, and CPT are more preferred. All of the fluorine-containing resins exemplified above have a light transmittance of 30% or more for deep ultraviolet light with a wavelength of 220 to 300 nm. In particular, it is preferable to use a resin having a light transmittance of preferably 50% or more, more preferably 60% or more, for deep ultraviolet light with a wavelength of 220 to 300 nm. These resin materials may contain various additives, such as heat stabilizers, organic lubricants, organic or inorganic fine particles, and antistatic agents, within the range that does not impair the effects of the present invention.

[0019] Furthermore, it is preferable that at least one of the two or more regions having different refractive indexes in the reflective film of the present invention is a region made of a gas, an inorganic material, or a liquid.From the viewpoint of increasing the refractive index difference between the regions having different refractive indexes, it is preferable that at least one of the regions having different refractive indexes in the reflective film of the present invention is a region made of a gas, that is, at least one of the regions is made of bubbles and / or pores. In the present invention, "gas" refers to a gas present in voids formed as bubbles or voids inside a resin or inorganic material or at the interface between them. Furthermore, in the present invention, the concept of "gas" includes not only the atmosphere but also gases such as inert gases that are not included in the atmospheric composition. That is, it is preferable for the reflective film of the present invention to have bubbles and / or voids inside, and by incorporating these bubbles or voids, deep ultraviolet light can be diffusely reflected efficiently and evenly in multiple directions. The shape of the bubbles and / or voids is not particularly limited and can be appropriately designed as long as it does not impair the effects of the present invention. For example, in a plan view of the cross section, the shape may be a circle, an ellipse, a nearly ellipse such as an elongated ellipse, or an elongated ellipse with acute angles at both ends formed by facing nearly circular arcs.

[0020] When the reflective film of the present invention has a region made of an inorganic material, examples of the inorganic material include alumina, boron nitride, silica, and alkaline earth metal fluorides. Furthermore, when the reflective film of the present invention has a region made of a liquid, examples of the liquid include water, organosiloxane, and fluorine-based inert liquid.

[0021] When the region of the reflective film of the present invention includes a region made of resin and a region made of gas, the reflective film of the present invention can be obtained by forming the film into a form having bubbles or voids inside the resin, from the viewpoint of increasing the total reflectance and diffuse reflectance of the obtained film to a desired level for deep ultraviolet light with a wavelength of 220 to 300 nm. That is, the reflective film of the present invention can be obtained by forming the film into a form having bubbles or voids inside the resin. That is, the reflective film of the present invention can be obtained in a form in which voids are scattered throughout the resin material. Furthermore, when the reflective film of the present invention has regions made of resins with different refractive indices, from the viewpoint of increasing the total reflectance and diffuse reflectance of the resulting film to the desired level for deep ultraviolet light with a wavelength of 220 to 300 nm, each region can be made of a resin material with a different refractive index, and resin materials with different refractive indices can be laminated, or a form can be used in which a region made of one resin material is dotted with a region made of the other resin material. Furthermore, voids such as air bubbles and pores can be formed in the regions made of these resins or at the interface between them. Furthermore, when the reflective film of the present invention has a region made of a resin and a region made of an inorganic material, from the viewpoint of increasing the total reflectance and diffuse reflectance of the resulting film to the desired level for deep ultraviolet light with a wavelength of 220 to 300 nm, a resin material and an inorganic material with a refractive index different from that of the resin material can be used, and the region made of the inorganic material can be interspersed in the region made of the resin material. Furthermore, the region made of this resin material can also be interspersed with regions made of a resin material with a refractive index different from that of the resin material. Furthermore, voids such as bubbles or pores can be further formed in or at the interface between the regions made of these resin materials or inorganic materials.

[0022] When the reflective film of the present invention includes a region made of resin and a region made of gas, in order for the reflective film of the present invention to exhibit the desired reflective performance against deep ultraviolet light, it is preferable that the reflective film has a repeating structure in which resin parts (resin regions) and void parts (gas regions) are repeated when observed in cross section (planar observation of the cross section).

[0023] The reflective film of the present invention may have thin resin columns, thin-walled resin columns, or thin protrusions of resin portions within the bubbles and / or pores. When a large number of resin portions consisting of resin columns, wall-shaped resin columns, or protrusions of resin portions are formed in the same direction, the resin portions constituting the repeating structure portion refer to the resin columns, and the voids constituting the repeating structure portion refer to the spaces between the resin columns. That is, the reflective film may have a repeating structure in which multiple resin columns are formed in the same direction within the bubbles and / or pores, resulting in a repeating structure in which resin portions and voids are repeated. In the present invention, "same direction" means approximately the same direction and is not limited to a form in which the resin portions face exactly the same direction, as long as the effects of the present invention are not impaired. In the repeating structure portion, the width (nm) of at least one type of resin portion or at least one type of void constituting the repeating structure portion in the direction in which the resin columns are repeated is preferably 0.1λ to 20λ, more preferably 0.2λ to 10λ, and even more preferably 0.5λ to 2λ, relative to the wavelength λ (nm) of incident ultraviolet light. By setting the width (nm) within the above range relative to the wavelength λ (nm) of ultraviolet light, the reflective performance of the reflective film can be improved. Furthermore, the reflective film of the present invention may have a plurality of bubbles and / or voids having the repeating structure portion. Preferably, two or more bubbles and / or voids are present in the thickness direction of the reflective film in the cross section, and more preferably three or more bubbles and / or voids are present.

[0024] FIG. 1 is a scanning electron microscope photograph of a cross section of one embodiment of the reflective film of the present invention cut in the thickness direction, and FIG. 2 is a further enlarged view of the repeating structure portion of FIG. 1. The reflective film (10) shown in FIG. 1 is made of a resin (1) and contains thin, approximately elliptical bubbles (2) in a plan view. Inside the bubbles (2), a large number of thin resin columns (4) are formed in the minor axis direction, as shown in FIG. 2. In the reflective film shown in FIG. 2, the entire interior of the approximately elliptical bubbles (2) in a plan view is a repeating structure portion (3) in which the resin portions (3-2) and void portions (3-1) are repeated. In the thickness direction of the reflective film (10) (the vertical direction in the drawing), multiple bubbles (2) having these repeating structures are present in an overlapping manner. The configuration of the reflective film of the present invention is not limited to that shown in FIG. 1. The desired reflective film can also be obtained by other methods, as demonstrated by the examples described below.

[0025] The reflective film of the present invention shown in Figures 1 and 2 can also be obtained by, for example, impregnating a resin film with an inert gas and then heating it to form fine voids or bubbles inside, thereby obtaining the desired reflective film.

[0026] The reflective film of the present invention may have, in a planar view of the cross section, bubbles that are approximately circular or approximately elliptical, and these bubbles and / or voids may be stacked in the thickness direction, thereby forming a repeating structure in which resin portions and voids are repeated. This stacking may be random or regular. In this case, the width (nm) of at least one resin portion and / or at least one void portion constituting the repeating structure, preferably the width (nm) of at least one void portion constituting the repeating structure, relative to the wavelength λ (nm) of the incident ultraviolet light, is preferably 0.1λ to 20λ, more preferably 0.2λ to 10λ, and even more preferably 0.5λ to 2λ. In this case, the width of the void portion refers to the size of the bubbles and / or voids, i.e., the diameter of the bubbles and / or voids, and the width of the resin portion refers to the spacing between the bubbles and / or voids. Here, in the present invention, the "diameter of the bubbles and / or voids" refers to the longest width perpendicular to the longest width within the bubbles and / or voids in a planar view of the cross section of the film. By setting the width (nm) within the above range relative to the wavelength λ (nm) of ultraviolet light, the reflective performance of the reflective film of the present invention can be improved. Furthermore, in planar observation of the cross section, the diameter of the bubbles and / or pores is preferably controlled to 20 nm to 6000 nm, can be controlled to 40 nm to 3000 nm, or can be controlled to 100 nm to 1000 nm. By controlling the diameter of the bubbles and / or pores to be within the above range, the reflective performance can be improved. Furthermore, particles of a material different from the matrix resin may be present inside the bubbles and / or pores. The particles are preferably made of a material that absorbs deep ultraviolet light less. Furthermore, the particles may be made less susceptible to mechanical and thermal deformation than the matrix resin. Examples of such particles include fluorine-based resins such as PTFE, boron nitride, alumina, glass frit, and silica (quartz). The particles may be derived from the fine particles added when forming pores (bubbles) by stretching, as described above and below. The reflective film of the present invention may also have a repeating structure in which elongated, approximately elliptical bubbles are stacked, resulting in a repeat of resin portions and void portions. The width (nm) of at least one of the resin portions or void portions constituting the repeating structure may be within the above-mentioned preferred range.

[0027] FIG. 3 is a scanning electron microscope photograph of a cross section of one embodiment of the reflective film of the present invention cut in the thickness direction, and FIG. 4 shows a further enlarged view of the repeating structure portion of FIG. 3. The reflective film (10) shown in FIG. 3 is made of a resin (1) and contains bubbles (2) that are approximately elliptical in plan view. In the reflective film shown in FIG. 4, a repeating structure portion (3) is formed by repeating void portions (3-1) formed by the bubbles (2) that are approximately elliptical in plan view and resin portions (3-2) formed by the resin (1). In addition, a plurality of these repeating structures are present overlapping each other in the thickness direction of the reflective film (10) (the vertical direction in the drawing). In FIG. 4, the lead line of reference numeral 3-1 is shown drawn from a different bubble from the lead line of reference numeral 2, but this is to make it easier to understand the repeating structure. The form of the reflective film of the present invention is not limited to that shown in FIG. 3, and the desired reflective film can be obtained with other forms, as will be demonstrated by the examples described later.

[0028] 3 and 4 , examples of methods for forming the reflective film of the present invention include adding organic or inorganic fine particles to a resin material, or adding organic or inorganic particles to a resin material together with a resin incompatible with the resin material, melt-extruding the material, and then stretching the material in at least one direction to form fine voids inside. Alternatively, the resin material may be molded into a film, and then physical force may be applied to the film to generate fine cracks, thereby achieving the desired reflective properties. Alternatively, the desired reflective film may be obtained by adding expandable particles to the resin material and melt-extruding the resulting material, or by injecting an inert gas such as carbon dioxide or nitrogen into the resin material or a film-shaped molded product thereof and extruding and foaming it.

[0029] In the reflective film of the present invention, the thickness (width) of the resin portions (resin walls) between the bubbles may be uniform or nonuniform, and may differ between the planar direction and the thickness direction of the film. Furthermore, the thickness of the resin walls in the planar direction of the film may be thicker than the thickness of the resin walls in the thickness direction of the film. By making the resin walls in the planar direction of the film thicker than the thickness of the resin walls in the thickness direction of the film, it is possible to achieve a particularly high reflectivity, ease of bending, and mechanical strength (tensile strength) of the film. That is, by making the resin walls in the thickness direction of the film thin, it is possible to impart a large number of repeating structures of resin portions and voids, thereby increasing the ultraviolet reflectivity. Furthermore, when the film is bent, the thin resin walls in the thickness direction of the film deform, making it easier to bend, and thus imparting further flexibility to the film. Meanwhile, by making the resin walls in the planar direction of the film thick, it is possible to achieve high mechanical strength (tensile strength). For example, it is also preferable that the thickness of the resin walls in the planar direction of the film is 1 μm or more and the thickness of the resin walls in the thickness direction of the film is less than 1 μm. The above cross-sectional observation can be carried out using a scanning electron microscope.

[0030] The reflective film of the present invention has a total reflectance of 60% or more for deep ultraviolet light in the wavelength range of 220 to 300 nm, as described above, preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more. In the present invention, "total reflectance for deep ultraviolet light in the wavelength range of 220 to 300 nm" means the average value of total reflectance for each wavelength (in 1 nm units, i.e., every 1 nm) in the wavelength range of deep ultraviolet light in the wavelength range of 220 to 300 nm. The total reflectance for deep ultraviolet light can be measured by the method described in the examples below.

[0031] Furthermore, the diffuse reflectance of the reflective film of the present invention for deep ultraviolet light in the wavelength range of 220 to 300 nm is 60% or more, as described above. This diffuse reflectance is preferably 70% or more, more preferably 80% or more, and even more preferably 89% or more. In the present invention, "diffuse reflectance for deep ultraviolet light in the wavelength range of 220 to 300 nm" means the average value of diffuse reflectance at each wavelength (in 1 nm units, i.e., every 1 nm) in the wavelength range of deep ultraviolet light in the wavelength range of 220 to 300 nm. The diffuse reflectance in the deep ultraviolet light wavelength range of 220 to 300 nm can be measured by the method described in the examples below.

[0032] In the reflective film of the present invention, the density (bulk density, Q) of the film (film having bubbles or pores) relative to the density (P) of the resin material itself constituting the film is preferably Q / P = 0.1 to 0.99, more preferably Q / P = 0.3 to 0.99, and even more preferably Q / P = 0.5 to 0.99. Note that the density P and density Q have the same unit. The density (bulk density) of the reflective film of the present invention can be measured by the underwater displacement method (JIS K 7112).

[0033] The method for producing the reflective film of the present invention will be described below.

[0034] <Production of reflective film by foaming fluorine-containing resin film> The structure shown in Figure 1 is a film obtained by impregnating a PCTFE film with carbon dioxide gas and then heating it to foam. By using a fluorine-containing resin as the resin material that constitutes the reflective film, it is possible to obtain a reflective film in which many fine pillar structures are formed inside the bubbles, as shown in Figure 1. An example of a method for obtaining a reflective film with such a unique bubble structure will be described below.

[0035] The production method exemplified here includes a gas filling step in which an inert gas (carbon dioxide, nitrogen, etc.) is impregnated into a fluorine-containing resin film under high pressure, and a heat foaming step in which heating is performed after the pressure is released to generate bubbles inside the resin. In the gas charging step, the fluororesin film is exposed to an inert gas under a pressure of preferably 1 to 20 MPa, more preferably 5 to 10 MPa, for preferably 1 to 100 hours, more preferably 2 to 24 hours, to charge the inert gas into the resin film. For this gas charging step, an autoclave or a pressure cooker, for example, can be suitably used. In the heat-foaming step, the fluorine-containing resin film after the gas-filling step is heated preferably at a temperature of 120 to 200° C., more preferably at 130 to 170° C., for preferably 0.5 to 3 minutes, more preferably 0.5 to 1 minute. By undergoing this step, a reflective film having bubbles or voids inside the resin film can be obtained. Furthermore, it is preferable to subject the fluorine-containing resin film to a heat treatment (annealing treatment) before the gas filling step. By subjecting the film to the annealing step and then proceeding to the gas filling step, the interior of the bubbles generated in the subsequent heat foaming step can be made to have a finer columnar structure as shown in Figure 1, and a repeating structure in which resin portions and air portions are densely repeated can be introduced into the film. This effectively increases the reflection efficiency of deep ultraviolet light, making it possible to more reliably achieve a total reflectance of 60% or more and a diffuse reflectance of 60% or more for deep ultraviolet light with a wavelength of 220 to 300 nm.

[0036] In the above-mentioned production method, the production of a reflective film by foaming a fluorine-containing resin film has been described. However, even when other resins with low deep ultraviolet absorption ability, such as silicone resins, are used, the reflective film of the present invention exhibiting the desired reflective performance can be obtained by foaming in the same manner.

[0037] In the reflective film obtained by the above foaming, the size of the bubbles formed inside the film (approximately elliptical bubbles in Figure 1) can be 0.1 to 50 μm, more preferably 0.5 to 30 μm, and also preferably 1 to 20 μm, in terms of the size in the thickness direction in the above cross-sectional observation.

[0038] <Production of reflective film by stretching fluorine-containing resin> The structure shown in Figure 3 is a film made by adding PTFE microparticles to a PCTFE film and then stretching it to create voids. By using a fluorine-containing resin as the resin material constituting the reflective film and adding microparticles of a material that absorbs little deep ultraviolet light and stretching it, it is possible to obtain a reflective film with a large number of fine pore structures (porous structure) as shown in Figure 3. An example of a method for obtaining a reflective film with such a porous structure will be described below.

[0039] The production method exemplified here includes a stretching step of stretching the fluorine-containing resin film. In the stretching step, the resin film is stretched in a heated atmosphere (e.g., 50 to 120°C) at a slow speed of, for example, 0.05 to 1.5 m / min until the stress reaches the yield point of the resin film, and once necking occurs after the yield point, the stretching speed is increased to, for example, 2.0 to 4.0 m / min. This stretching may be uniaxial or biaxial, and biaxial stretching is preferred from the viewpoint of increasing the number of bubbles or voids obtained. Furthermore, when stretching a resin film, it is preferable to add in advance fine particles or the like that are components different from the resin and knead them by a melt-kneading method, etc. When the resin contains fine particles or the like, an interface is formed between the resin film as a base material and the fine particles, and fine bubbles or voids can be generated from the interface during stretching. Examples of the fine particles to be added include polytetrafluoroethylene (PTFE), boron nitride, alumina, glass frit, etc. The amount of the fine particles to be added is preferably 1 to 50 mass %, more preferably 1 to 30 mass %, and even more preferably 5 to 20 mass %.

[0040] In the reflective film obtained by the above stretching, the size of the bubbles formed inside the film (approximately elliptical bubbles in FIG. 3) is preferably 0.1λ to 20λ, more preferably 0.2λ to 10λ, and even more preferably 0.5λ to 2λ, relative to the wavelength λ (nm) of the incident ultraviolet light, as the size in the thickness direction in the above cross-sectional observation. For example, the size of the bubbles in the thickness direction in the above cross-sectional observation can be 20nm to 6000nm, preferably 40 to 3000nm, and also preferably 100 to 2000nm.

[0041] It is practically difficult to accurately and unambiguously describe the minute and complex structure of the resin reflective film of the present invention. Therefore, in this invention, the structural features are specified as the invention-specifying matters, and the characteristics and, if necessary, the manufacturing method are also specified as the invention-specifying matters, and the invention is clarified by clearly indicating the differences from products of the prior art.

[0042] The reflective film of the present invention, which has excellent total reflectance and diffuse reflectance, can efficiently reflect deep ultraviolet light emitted from a light source, for example, by using it as a reflective film for a deep ultraviolet light source. Therefore, for deep ultraviolet light emitted from, for example, a mercury lamp, a metal halide lamp, a barrier discharge lamp, or a deep ultraviolet LED, light that has missed the target of irradiation can be reflected, making it possible to use all of the deep ultraviolet light. A unit combining such a light source and a reflective film can be suitably used in water sterilization equipment, space sterilization equipment, equipment (sterilization devices) for sterilizing the surfaces of materials such as medical supplies, household goods, various processed products, and foods.

[0043] Furthermore, the reflective film of the present invention highly reflects deep ultraviolet rays and prevents their transmission, and therefore can also be used as a shielding film for protecting items exposed to deep ultraviolet rays, for example. [Example]

[0044] The present invention will be described in more detail based on the following examples and comparative examples, but the present invention is not limited to these.

[0045] [Preparation of reflective film] The reflective films of Examples 1 to 6 and Comparative Examples 1 to 3 were produced by the following method. The reflective films of Examples 1 to 6 and Comparative Examples 1 to 3 all had a length of 100 mm and a width of 33 mm, and the thicknesses were as shown in the table below.

[0046] Example 1 Polychlorotrifluoroethylene (PCTFE) resin film (product name: Neoflon PCTFE, manufactured by Daikin Industries, Ltd.) was heat-treated for 10 minutes in an atmosphere at 180°C. The heat-treated resin film was placed in an autoclave and treated at 17°C and a pressure of 5.2 MPa for 24 hours to seal carbon dioxide gas into the resin film. The resin film was then removed from the autoclave and heated at 150°C for 1 minute to foam the carbon dioxide gas in the resin film, producing a reflective film with a thickness of 0.2 mm.

[0047] Example 2 A reflective film was produced in the same manner as in Example 1, except that the thickness of the resulting reflective film was 0.4 mm.

[0048] Example 3 A reflective film was produced in the same manner as in Example 1, except that the thickness of the resulting reflective film was 0.8 mm.

[0049] Example 4 A reflective film was produced in the same manner as in Example 1, except that the resin film used to produce the reflective film was replaced with a film of tetrafluoroethylene-ethylene (ETFE) copolymer (trade name: Neoflon ETFE, manufactured by Daikin Industries, Ltd.).

[0050] Example 5 A reflective film was produced in the same manner as in Example 1, except that the resin film used to produce the reflective film was replaced with a film of tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA) copolymer (product name: Neoflon PFA, manufactured by Daikin Industries, Ltd.).

[0051] Example 6 10% by mass of PTFE particles (trade name: Polyflon PTFE, model number: M-12, particle size 0.1 μm, manufactured by Daikin Industries, Ltd.) was added to PCTFE resin, and the composite material was molded into a 0.5 mm thick film, which was then attached to a stretching machine (trade name: Tensilon universal testing machine, model number: RTA-2.5T, manufactured by Orientec Co., Ltd.) and stretched in an atmosphere at 120°C. The stretching speed was 0.5 m / min until the yield point of the resin film was exceeded, and after necking began, the stretching was increased to 3.0 m / min without interruption and stretching was continued to obtain a reflective material with a thickness of 0.25 mm.

[0052] The reflective films of Examples 1 to 6 all had a repeating structure consisting of a repeating sequence of resin portions and void portions, and the width (nm) of at least one resin portion and / or the width (nm) of at least one void portion constituting the repeating structure was 0.1λ to 20λ relative to the wavelength λ (256 nm) of the incident ultraviolet light. The widths of the resin and void portions were confirmed by freeze-fracturing each film in a high vacuum, observing the cross section with a scanning electron microscope (model number: JSM-6390LV, manufactured by JEOL Ltd.), and measuring the widths from the obtained data.

[0053] [Comparative Example] (Comparative Example 1) Polyethylene terephthalate (PET) resin film (raw material trade name: UNIPET RT553C, manufactured by Nippon Unipet Co., Ltd.) was heat-treated in an atmosphere of 180°C for 10 minutes. The heat-treated resin film was placed in an autoclave and treated at 17°C and a pressure of 5.2 MPa for 24 hours, thereby sealing carbon dioxide gas into the resin film. The resin film was then removed from the autoclave and heated at 220°C for 1 minute to foam the carbon dioxide gas in the resin film, producing a reflective film with a thickness of 0.5 mm.

[0054] (Comparative Example 2) As the reflective film, a 0.5 mm thick ultraviolet reflective aluminum foil (product name: MIRO-UV, manufactured by Material House Co., Ltd.) was used.

[0055] (Comparative Example 3) A polytetrafluoroethylene plate (trade name: Polyflon PTFE, model number: M-18, manufactured by Daikin Industries, Ltd., sintered compression molded body) having a thickness of 9.8 mm was used as the reflective film.

[0056] <Measurement of deep ultraviolet light transmittance of resin materials> Using a spectrophotometer (product name: U-4100, manufactured by Hitachi High-Technologies Corporation), light of each wavelength was irradiated from the front of each film before heat treatment (before foaming) or stretching (before pore formation). The amount of light captured by the detector when the amount of irradiated light was taken as 100% was taken as the transmittance, and measurements were made across the deep ultraviolet wavelength range of 220 to 300 nm. Each transmittance was read at 1 nm wavelength intervals from the resulting chart (measurement results), and the arithmetic average of the transmittances (81% measured values) for all wavelengths in the deep ultraviolet range was calculated, which was taken as the deep ultraviolet transmittance. All films measured were 100 μm thick.

[0057] <Test Example 1> The thickness of each of the obtained reflective films (Examples 1 to 6, Comparative Examples 1 to 3) was measured using a micrometer (product name: Coolantproof Micrometer, model number: MDC-25MX, manufactured by Mitutoyo Corporation). A Φ60 standard integrating sphere was attached to a spectrophotometer (product name: U-4100, manufactured by Hitachi High-Technologies Corporation), and the total reflectance of each reflective film was measured over the deep ultraviolet wavelength range of 220 to 300 nm, assuming that the total reflectance value of a Spectralon standard reflector (manufactured by Labsphere, white, model number: USRS-99-010) was 100%, and the diffuse reflectance of each reflective film was measured over the deep ultraviolet wavelength range of 220 to 300 nm, assuming that the diffuse reflectance of the Spectralon standard reflector was 100%. The reflectance was read for each 1 nm wavelength from the obtained chart (measurement results), and the arithmetic mean of the total reflectance (measured value (%) of 81) and the arithmetic mean of the diffuse reflectance (measured value (%) of 81) in the deep ultraviolet region were calculated, and these were designated as "deep ultraviolet total reflectance" and "deep ultraviolet diffuse reflectance," respectively. The results are shown in Table 1 below.

[0058] <Test Example 2> For the obtained reflective films (Examples 1 to 6, Comparative Examples 1 to 3), the ultraviolet illuminance at each reflection angle was measured as follows using an ultraviolet LED (emission wavelength 256 nm, model number: 265-FL-02-G01, manufactured by DOWA Electronics Co., Ltd.) and an ultraviolet illuminance meter (product name: ultraviolet illuminance meter UVR-300, model number: UD-250, manufactured by Topcon Technohouse Corporation). As shown in Figure 5, the UV LED light source was positioned at a 30° angle with respect to the center (center of gravity) of the film surface of each reflective film (the angle between the straight line connecting the UV LED light source and the center of the film surface and the perpendicular line extending from the center of the film surface was 30°). The UV illuminance meter was also installed at a position symmetrical to the UV LED light source, with the perpendicular line extending from the center of the film surface as the axis. In other words, the plane connecting the center of the film surface, the UV LED light source, and the UV illuminance meter intersected perpendicularly with the film surface, and the angle between the straight line connecting the UV illuminance meter and the center of the film surface and the perpendicular line was 30°. The distance from both the UV LED and the UV illuminance meter to the center of the film surface was 40 mm. With the UV LED fixed, the UV illuminance meter was moved from the 0° position to 30° and 60° positions as shown in Figure 6. Note that Figure 6 is a schematic diagram of the reflective film, UV LED light source, and UV illuminance meter shown in Figure 5 when viewed from X to Y, showing the state when the UV illuminance meter was moved to the 60° position. The UV illuminance detected by the UV illuminance meter at these 0°, 30°, and 60° positions was measured. The measurement results are shown in Table 1 below.

[0059] The retention rate of ultraviolet irradiance when the angle of the illuminometer was changed from 0° to 30° and then to 60° is shown in Table 1 below as "Illuminance retention rate (%)." The illuminance retention rate (%) was calculated using the following formula 2. When the illuminance retention rate was 50% or more at both the 30° and 60° angles, the "reflection" was judged as "Good," and otherwise (less than 50%) the "reflection" was judged as "Poor." Illuminance retention rate (%) = [UV illuminance at 30° or 60°] / [UV illuminance at 0°] (Equation 2) In Test Examples 1 and 2, the thickness, deep UV total reflectance, deep UV diffuse reflectance, UV illuminance, and illuminance retention were measured at three random points on the surface of each reflective film (excluding points within 5 mm from the edge). The values ​​shown in Table 1 below are the average values ​​of these three points.

[0060] <Test Example 3> The bending workability of the resulting reflective materials (Examples 1 to 6 and Comparative Examples 1 to 3) was evaluated by the following evaluation method. We verified whether each reflective material could be bent and installed inside a resin pipe with an inner diameter of 40 mm. If it could be installed manually, the "bending workability" was judged as "Good", and if it could not be bent manually and installed, it was judged as "Poor". The results are shown in Table 1 below.

[0061] TIFF0007763179000001.tif22992

[0062] As can be seen from Table 1, the reflective film of Comparative Example 1, which is a PET foam film, absorbs deep UV light, resulting in significantly low deep UV total reflectance and deep UV diffuse reflectance. The reflective film of Comparative Example 2, which is an aluminum foil, also had low deep UV total reflectance and deep UV diffuse reflectance, and also had poor illuminance retention. The reflective film of Comparative Example 3, which is a sintered compression molded body of PTFE, had good deep UV total reflectance and deep UV diffuse reflectance. However, the diffuse reflection was angle-dependent, resulting in a somewhat poor performance in diffusing and reflecting incident deep UV light evenly in multiple directions. The reflective film of Comparative Example 3 was also thick at 9.8 mm and had poor bending processability. In contrast, the reflective films of Examples 1 to 6 are thin films that achieve a deep UV total reflectance and a deep UV diffuse reflectance of 80% or more by creating bubbles or voids inside the resin film. The resin reflective films that exhibit such reflective properties also have low angular dependency of the diffuse reflection of deep UV rays, and are excellent in the ability to diffusely reflect incident deep UV rays evenly in multiple directions. It was also found that the films can be made thin and have sufficient bending processability.

[0063] While the present invention has been described in connection with embodiments thereof, we do not intend to limit our invention to any of the details of the description unless otherwise specified, and believe that the claims should be construed broadly without departing from the spirit and scope of the invention as set forth in the appended claims.

[0064] This application claims priority based on Japanese Patent Application No. 2020-158811, filed on September 23, 2020, the contents of which are incorporated herein by reference as part of the present specification. [Explanation of symbols]

[0065] 1 resin 2. Bubbles 3 Repeating structure 3-1 Cavity 3-2 Resin part 4 pillars 10 Reflective film 11. Ultraviolet LED light source 12. Ultraviolet light meter

Claims

1. A resin reflective film having two or more types of regions with different refractive indices, wherein the resin material constituting the resin reflective film is a fluorine-containing resin, the thickness of the resin reflective film is 20 to 5000 μm, the total reflectance and diffuse reflectance for deep ultraviolet light with a wavelength of 220 to 300 nm are 60% or more and 60% or more, respectively, and at least one of the two or more types of regions constituting the resin reflective film is an air bubble and / or a void, The resin reflective film is formed by foaming an inert gas impregnated in the fluorine-containing resin film, or by stretching the fluorine-containing resin film to form bubbles and / or voids therein. Resin reflective film (excluding those in which the resin reflective film is woven fabric, knitted fabric, or nonwoven fabric).

2. 2. The resin reflective film according to claim 1, wherein the thickness of the resin reflective film is 50 to 1000 μm.

3. The resin reflective film according to claim 1 or 2, wherein the two or more types of regions constituting the resin reflective film all have a light transmittance of 30 to 100% for deep ultraviolet light having a wavelength of 220 to 300 nm.

4. The resin reflective film according to any one of claims 1 to 3, wherein the resin reflective film has a repeating structure in which resin portions (resin regions) and void portions (gas regions) are repeated.

5. The resin reflective film according to claim 4, wherein the width of at least one resin portion constituting the repeating structure and / or the width of at least one void portion is 0.1λ to 20λ relative to the wavelength λ of the incident ultraviolet light.

6. The density (Q) of the resin reflective film relative to the density (P) of the resin material constituting the resin reflective film satisfies Q / P = 0.2 to 0.

99. The resin reflective film according to any one of claims 1 to 5.

7. A sterilization device comprising an ultraviolet light source and the resin reflective film according to any one of claims 1 to 6.

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