Light diffusion sheet, adherend with sheet, and method for producing same

Abstract

To provide a light diffusion sheet that can form a light diffusion layer easily by being attached to an adherend such as a light sensor and also can increase a yield, an adherend with a sheet using the light diffusion sheet, and a method for manufacturing the adherend.SOLUTION: In an optical diffusion sheet in which an optical diffusion material is mixed in silicon rubber, one surface in the thickness direction is used as a glare surface with a surface roughness Ra of not larger than 0.70 μm and another surface is used as an anti-glare surface with a surface roughness Ra in the range from 0.80-.3.0 μm. The glare surface of the optical diffusion sheet is brought into contact with a glass adherend and is heated, and the optical diffusion sheet is attached to the adherend.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a light diffusing sheet, an adherend with the sheet, and a method for producing the same. [Background technology]

[0002] For example, in order to reduce power consumption, mobile communication terminals such as smartphones are equipped with optical sensors such as illuminance sensors and ambient light sensors, and a mechanism is adopted to change the brightness of the screen according to the brightness of the surroundings. When detecting the brightness of the surroundings using an optical sensor in this way, it is important that the optical sensor is omnidirectional, so that the brightness of the entire surroundings can be detected regardless of the orientation of the optical sensor. Therefore, in order to increase the omnidirectionality of the optical sensor, a layer containing a light diffusing material is sometimes provided on the optical sensor. For example, Patent Document 1 discloses that an adhesive layer containing a light diffusing material is provided by printing on a semiconductor element having a light receiving section. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-29525 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional method of forming a light diffusing layer by printing, uneven printing can result in insufficient diffusion performance, leading to problems of low yield.

[0005] The present invention aims to provide a light diffusion sheet that can be attached to an adherend such as an optical sensor to easily form a light diffusion layer and increase yields, an adherend with the sheet using the light diffusion sheet, and a method for manufacturing the same. [Means for solving the problem]

[0006] The present invention has the following aspects. [1] A light diffusion sheet in which a light diffusing material is blended with silicone rubber, One surface in the thickness direction is a glare surface having a surface roughness Ra of 0.70 μm or less, The other surface of the light diffusing sheet is an anti-glare surface having a surface roughness Ra of 0.80 to 3.0 μm. [2] The light diffusing sheet according to [1], wherein a total light transmittance of light incident from the anti-glare surface is 40 to 70%. [3] The light diffusion sheet according to [1] or [2], having a haze of 90% or more. [4] A glass substrate and the light diffusion sheet according to any one of [1] to [3], The light diffusing sheet is attached to the adherend so that the glare surface is in contact with the adherend. [5] A method for producing an adherend with a sheet, comprising heating the light diffusion sheet while the glare side of the light diffusion sheet according to any one of [1] to [3] is in contact with a glass adherend, thereby attaching the light diffusion sheet to the adherend. Effect of the Invention

[0007] According to the present invention, it is possible to provide a light diffusion sheet that can be attached to an adherend such as an optical sensor to easily form a light diffusion layer and increase yields, an adherend with the sheet using the light diffusion sheet, and a method for manufacturing the same. [Brief description of the drawings]

[0008] [Figure 1] 1 is a graph showing the results of measuring the light transmittance of the light diffusion sheet of Example 1 at angles from −80° to 80°. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In the present invention, the "surface roughness Ra" is the center line average roughness defined by JIS B 0601-2013, and is a value measured by a measuring instrument in accordance with the same standard. "Total light transmittance" is a value measured in accordance with JIS K7136. "Haze" is a value measured in accordance with JIS K 7361. "Rubber hardness" is a value measured using a type A durometer in accordance with JIS K 6253-3: "Vulcanized rubber and thermoplastic rubber -- Determination of hardness -- Part 3: Durometer hardness."

[0010] [Light diffusion sheet] The light diffusion sheet of the present invention is a light diffusion sheet in which a light diffusion material is blended with silicone rubber. Since the light diffusion sheet of the present invention is a sheet using silicone rubber, it has excellent heat resistance and excellent adhesion to a glass substrate. Furthermore, since the light diffusion sheet of the present invention contains a light diffusion material, it has excellent light diffusion properties.

[0011] The silicone rubber is not particularly limited, and may be, for example, a silicone rubber generally called millable rubber, which is made of a diorganopolysiloxane whose molecular chain end is blocked with a hydroxysilyl group or a vinylsilyl group and an organic peroxide.Also, a so-called addition reaction type organosilicone rubber may be used, which is made by blending a diorganopolysiloxane having at least two vinyl groups bonded to silicon atoms in the molecule with an organohydrogenpolysiloxane having at least three hydrogen atoms bonded to silicon atoms in the molecule and a platinum catalyst.

[0012] The rubber hardness of the silicone rubber can be set according to the thickness of the light diffusion sheet. For example, when the thickness of the light diffusion sheet is 30 to 50 μm, the rubber hardness of the silicone rubber is preferably 50 to 80°. When the rubber hardness of the silicone rubber is equal to or higher than the lower limit of the above range, the flexibility and stretchability of the light diffusion sheet become appropriate, and handling becomes easy. When the rubber hardness of the silicone rubber is equal to or lower than the upper limit of the above range, the light diffusion sheet has excellent processability. The silicone rubber contained in the light diffusing sheet may be of one type or of two or more types.

[0013] The light diffusing material may be any material that scatters at least a part of the incident light, and examples thereof include known colorants for coloring resin materials, inorganic fine particles, and organic fine particles. Among them, white pigments such as titanium oxide are preferred because they have excellent light diffusing properties and can easily secure sufficient haze. The light diffusing material contained in the light diffusing sheet may be one type or two or more types.

[0014] The amount of the light diffusing material may be appropriately adjusted depending on the type of light diffusing material, the required haze, total light transmittance, thickness of the light diffusing sheet, etc. When the light diffusing sheet is thin, the amount of the light diffusing material is increased, and when the light diffusing sheet is thick, the amount of the light diffusing material is decreased, thereby adjusting the light diffusing effect obtained. For example, when a white pigment such as titanium oxide is blended into a light diffusing sheet having a thickness of 30 to 50 μm, the amount of the white pigment can be 1.0 to 3.0 parts by mass with respect to 100 parts by mass of silicone rubber.

[0015] The light diffusion sheet of the present invention has one surface in the thickness direction which is a glare surface having a surface roughness Ra of 0.7 μm or less, and the other surface which is an anti-glare surface having a surface roughness Ra of 0.8 to 1.5 μm. The light diffusion sheet of the present invention is used by being attached to an adherend with the glare surface facing the adherend.

[0016] The surface roughness Ra of the glare surface of the light diffusion sheet is 0.70 μm or less. If the surface roughness Ra of the glare surface is 0.70 μm or less, the adhesion between the glare surface of the light diffusion sheet and the adherend is excellent. In addition, from the viewpoint of handling of the light diffusion sheet, the surface roughness Ra of the glare surface can be set in the range of 0.01 to 0.70 μm, for example.

[0017] The surface roughness Ra of the anti-glare surface of the light diffusion sheet is 0.80 to 3.0 μm, preferably 0.90 to 2.0 μm, and more preferably 0.95 to 1.5 μm. If the surface roughness Ra of the anti-glare surface is equal to or greater than the lower limit of the above range, a sufficient light scattering effect is easily obtained and the handling properties are excellent. In addition, foreign matter is less likely to adhere to the anti-glare surface. If the surface roughness Ra of the anti-glare surface is equal to or less than the upper limit of the above range, the light diffusion sheet is easy to manufacture.

[0018] The total light transmittance of the light incident from the antiglare surface of the light diffusion sheet of the present invention is preferably 40 to 70%, more preferably 45 to 65%, and even more preferably 50 to 60%. If the total light transmittance of the light diffusion sheet is within the above range, when the light diffusion sheet is applied to an optical sensor, the non-directionality is improved, and it becomes easy to sense not only the external light from the direction in which the optical sensor is facing, but also the brightness of the entire surroundings.

[0019] The haze of the light diffusion sheet of the present invention is preferably 90% or more, more preferably 95% or more, and even more preferably 97% or more. If the haze of the light diffusion sheet is equal to or more than the lower limit, a sufficient light diffusion effect is easily obtained, and when the light diffusion sheet is applied to an optical sensor, the non-directionality is improved. The higher the haze of the light diffusion sheet, the better, and the theoretical upper limit is 100%.

[0020] When the light diffusion sheet of the present invention is irradiated with light from the anti-glare surface side in a direction parallel to the thickness direction of the sheet, the ratio T1 of the light transmittance in the 30° direction to the thickness direction to the light transmittance in the thickness direction (0° direction) is preferably 10 to 100%, more preferably 20 to 80%, and even more preferably 30 to 70%. If the ratio T1 is equal to or greater than the lower limit, the non-directionality is improved when the light diffusion sheet is applied to an optical sensor. If the ratio T1 is smaller within the above range, the amount of the light diffusing material blended is reduced and the total light transmittance is increased, so that the sensor sensitivity is less likely to be adversely affected.

[0021] When the light diffusion sheet of the present invention is irradiated with light from the anti-glare surface side in a direction parallel to the thickness direction of the sheet, the ratio T2 of the light transmittance in a 60° direction to the thickness direction to the light transmittance in the thickness direction (0° direction) is preferably 10 to 100%, more preferably 10 to 60%, and even more preferably 15 to 50%. If the ratio T2 is within the above range, the non-directionality is improved when the light diffusion sheet is applied to an optical sensor. If the ratio T2 is smaller within the above range, the amount of the light diffusing material blended is reduced and the total light transmittance is increased, so that the sensor sensitivity is less likely to be adversely affected. The light transmittance in the 0° direction, 30° direction, and 60° direction can be measured by a goniophotometer (for example, GC5000L manufactured by Nippon Denshoku Industries Co., Ltd.).

[0022] The thickness of the light diffusion sheet of the present invention is preferably 15 to 70 μm, more preferably 20 to 60 μm, and even more preferably 30 to 50 μm. If the thickness of the light diffusion sheet is equal to or greater than the lower limit of the above range, sufficient processability is easily ensured, and flexibility and stretchability become appropriate, making handling easy. In addition, since it is not necessary to blend a large amount of light diffusing material to achieve a sufficient light diffusion effect, deterioration of the physical properties of the silicone rubber can be suppressed. If the thickness of the light diffusion sheet is equal to or less than the upper limit of the above range, it is easy to make a product equipped with the light diffusion sheet thinner.

[0023] The use of the light diffusion sheet of the present invention is not particularly limited. For example, when the light diffusion sheet of the present invention is attached to the optical filter or cover glass of a light sensor such as an environmental light sensor or an exposure sensor, the light incident on the light diffusion sheet from the opposite side of the light receiving section is diffused, and the amount of light reaching the light receiving section of the light sensor is increased. This improves the sensitivity of the light sensor.

[0024] The method for producing the light diffusion sheet of the present invention is not particularly limited. For example, a liquid composition containing a liquid silicone rubber and a light diffusing material is coated on a release film, and a release film is further laminated on the coating film made of the liquid composition and sandwiched therebetween, and the release film is peeled off to obtain a single light diffusion sheet. The surface roughness Ra of the glare surface and the anti-glare surface of the light diffusion sheet can be adjusted by the surface condition of the release film in contact with them. For example, the anti-glare surface of the light diffusion sheet can be formed by using a release film having irregularities on the surface in contact with the anti-glare surface. The anti-glare surface of the light diffusion sheet may also be formed by a known roughening treatment such as sandblasting.

[0025] [Substrate with sheet] The sheet-attached adherend of the present invention comprises a glass adherend and the light diffusion sheet of the present invention. In the sheet-attached adherend of the present invention, the light diffusion sheet of the present invention is attached to the adherend so that the glare surface is in contact with the adherend.

[0026] The adherend is preferably an optical filter (infrared filter, ultraviolet filter, etc.) or a cover glass in an optical sensor such as an environmental light sensor or an exposure sensor. By attaching the light diffusion sheet of the present invention to these adherends, the amount of light reaching the light receiving portion of the optical sensor increases, thereby increasing the sensitivity of the optical sensor.

[0027] An example of a method for producing an adherend with the sheet of the present invention is to heat the light diffusion sheet of the present invention while the glare surface of the light diffusion sheet is in contact with a glass adherend, and then attach the light diffusion sheet to the adherend. Hydrogen bonds are formed between hydroxyl groups generated by thermal decomposition of the silicone rubber and hydroxyl groups of the glass, so that the light diffusion sheet can be attached to the adherend with high adhesive strength.

[0028] The heating temperature when attaching the light diffusion sheet to the adherend is preferably 150 to 250° C., more preferably 160 to 230° C., and even more preferably 180 to 220° C. If the heating temperature is equal to or higher than the lower limit of the above range, the time required to bring the light diffusion sheet into close contact with the adherend is shortened. If the heating temperature is equal to or lower than the upper limit of the above range, it is easy to prevent the silicone rubber from yellowing due to thermal degradation.

[0029] As described above, the light diffusion sheet of the present invention has a silicone rubber containing a light diffusing material, and has a glare surface and an anti-glare surface with a surface roughness Ra controlled within a specific range. By using silicone rubber and having a glare surface, the light diffusion sheet of the present invention has excellent adhesion to a glass adherend. By using the light diffusion sheet of the present invention, a light diffusion layer can be easily formed by attaching the sheet to an adherend such as an optical sensor, and the yield of the adherend with the sheet is increased, improving productivity.

[0030] In addition, in the sheet-attached adherend to which the light diffusion sheet of the present invention is attached, the glare surface comes into contact with the adherend, and the anti-glare surface is exposed. This anti-glare surface is an interface with a large difference in refractive index between air and silicone rubber, and has an uneven surface, so it has excellent light diffusion properties. In addition, the light diffusion sheet also has excellent internal light diffusion properties because it contains a light diffusing material. Therefore, when the sheet-attached adherend to which the light diffusion sheet of the present invention is attached is applied to an optical sensor, the light incident from the anti-glare surface is diffused both on the anti-glare surface and inside the light diffusion sheet, so that not only the external light in the direction in which the optical sensor is facing, but also the external light in the entire surroundings can be sensed, and the sensor has excellent non-directional properties. EXAMPLES

[0031] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following description.

[0032] [Example 1] A liquid composition was prepared by blending 1.2 parts by mass of titanium oxide as a light diffusing material with 100 parts by mass of liquid silicone rubber (product name "KE1950-70-A / B", rubber hardness: 68°, manufactured by Shin-Etsu Chemical Co., Ltd.). After the liquid composition was applied onto a release film, a release film having an uneven surface was sandwiched over the coating film made of the liquid composition, heated in this state at 140°C for 2 minutes, and the release film was peeled off to obtain a light diffusing sheet with a thickness of 50 μm. The surface roughness Ra of the glare surface of the obtained light diffusing sheet was 0.6 μm, and the surface roughness Ra of the anti-glare surface was 1.0 μm.

[0033] [Comparative Example 1] A light diffusion sheet was obtained in the same manner as in Example 1, except that the release film arranged on the glare side was changed to a release film having an uneven surface. The surface roughness Ra of both sides of the obtained light diffusion sheet was 1.0 μm and 1.0 μm, respectively.

[0034] [Surface roughness Ra] The surface roughness Ra of the glare surface and the anti-glare surface was measured using a measuring instrument (product name "LEXT OLS4100", manufactured by Olympus Corporation) conforming to JIS B 0601-2001.

[0035] [Total light transmittance] The total light transmittance of the light diffusion sheet was measured using a haze meter (NDH4000, manufactured by Nippon Denshoku Industries Co., Ltd.) conforming to JIS K7136.

[0036] [Hayes] The haze of the light diffusion sheet was measured using a haze meter (NDH4000, manufactured by Nippon Denshoku Industries Co., Ltd.) conforming to JIS K 7361.

[0037] [Ratio T1, Ratio T2] Using a goniophotometer (product name "GC5000L") manufactured by Nippon Denshoku Industries Co., Ltd., the light diffusion sheet was irradiated with light from the anti-glare side in a direction parallel to the thickness direction of the sheet, and the light transmittance was measured at angles of -80° to 80° with respect to the thickness direction (0° direction). The light source of the goniophotometer was a halogen lamp equipped with a color filter with a peak at 550 nm. Then, the ratio T1 of the light transmittance in the 30° direction with respect to the thickness direction to the light transmittance in the thickness direction (0° direction), and the ratio T2 of the light transmittance in the 60° direction with respect to the thickness direction to the light transmittance in the thickness direction (0° direction) were calculated. The light transmittance of the light diffusion sheet of Example 1 was measured at angles of -80° to 80°, and the results are shown in FIG.

[0038] [Adhesion strength] The glare surface of the light diffusion sheet obtained in each example (the surface with the smaller surface roughness Ra in the case of Comparative Example 1) was brought into contact with a glass plate and heated at 210°C for 1 hour to attach the light diffusion sheet to the glass plate. Next, a 90° peel test was performed using a universal material testing machine RTF-1250 manufactured by A&D Tensilon Co., Ltd. at a crosshead speed of 100 mm / min to measure the adhesion strength between the light diffusion sheet and the glass plate.

[0039] The measurement results for each example are shown in Table 1.

[0040] [Table 1]

[0041] As shown in Table 1, the light diffusion sheet of Example 1 having a glare surface and an anti-glare surface with a surface roughness Ra controlled within a specific range had high haze, ratio T1, and ratio T2, and was excellent in light diffusion. In addition, it had excellent adhesion to a glass plate, and could be easily attached to a glass plate to form a light diffusion layer. On the other hand, the light diffusing sheet of Comparative Example 1, which did not have a glare surface, had inferior adhesion to the glass plate compared to Example 1.

Claims

1. A light diffusion sheet made of a silicone rubber sheet containing a light diffusing material, which is attached to an adherend that is an optical filter or a cover glass of an optical sensor to form a light diffusion layer, the light diffusing material is titanium oxide, One surface in the thickness direction is a glare surface having a surface roughness Ra of 0.70 μm or less, the other surface is an anti-glare surface having a surface roughness Ra of 0.80 to 3.0 μm; The light diffusing sheet, wherein the glare surface is a surface to be attached to the adherend, the anti-glare surface is exposed when the glare surface is attached to the adherend, and an interface with air is formed at the anti-glare surface.

2. 2. The light diffusing sheet according to claim 1, wherein a total light transmittance of light incident from the antiglare surface is from 40 to 70%.

3. 3. The light diffusing sheet according to claim 1, which has a haze of 90% or more.

4. A glass substrate and the light diffusing sheet according to any one of claims 1 to 3, The light diffusing sheet is attached to the adherend so that the glare surface is in contact with the adherend.

5. A method for producing an adherend with a sheet, comprising heating the light diffusion sheet while the glare surface of the light diffusion sheet according to any one of claims 1 to 3 is in contact with a glass adherend, and attaching the light diffusion sheet to the adherend.

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