Light control filter and method for manufacturing the same

Abstract

The present invention provides a method for manufacturing a light-control filter that eliminates the need for a step of filling grooves with light-shielding material. [Solution] A method for manufacturing an optical control filter comprising a light-transmitting substrate layer, wherein a plurality of unpenetrating grooves are formed on one surface of the substrate layer, and a pair of opposing wall surfaces of the unpenetrating grooves form a rough surface due to minute irregularities, and the light transmittance of the rough surface is lower than the light transmittance of the substrate layer, the method for manufacturing an optical control filter comprising the step of irradiating one surface of a light-transmitting substrate film with a short-pulse laser to form the substrate layer having the plurality of unpenetrating grooves.

Description

Technical Field

[0001] The present invention relates to an optical control filter and a method for manufacturing the same.

Background Art

[0002] Conventionally, an optical control sheet installed in an information display body such as a display has been known (for example, Patent Document 1). By installing an optical control sheet on the display screen, it is possible to prevent the leakage of information due to peeking from the side.

[0003] In the method for manufacturing the optical control sheet disclosed in Patent Document 1, first, an optical transmission portion made of a transparent sheet having a plurality of groove portions arranged in parallel on the surface is formed, and then a light shielding band is formed by filling the groove portions with a light shielding material, thereby producing an optical control layer having a louver structure. When forming the light shielding band, ink containing an inorganic filler as the light shielding material is filled into the groove portions.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the method for manufacturing the optical control sheet described in Patent Document 1, as the groove portions become thinner, it becomes more difficult to fill the ink, and there is a problem that the light shielding performance is adversely affected due to filling defects and the mixing of air bubbles.

[0006] The present invention has been made in view of the above circumstances, and provides a method for manufacturing an optical control filter that does not require a step of filling a light shielding material into groove portions.

Means for Solving the Problems

[0007] [1] A light control filter comprising a light-transmitting substrate layer, wherein a plurality of non-penetrating grooves are formed on one surface of the substrate layer, the pair of opposing wall surfaces of the non-penetrating grooves forming a rough surface due to minute irregularities, and the light transmittance of the rough surface is lower than the light transmittance of the substrate layer. [2] The light control filter according to [1], wherein the groove width of the unpenetrated groove gradually narrows from the top to the bottom surface. [3] The light control filter according to [1] or [2], wherein the aspect ratio of the unpenetrated groove (depth / width of the uppermost groove) is 5 to 10. [4] The light control filter according to any one of [1] to [3], wherein the total light transmittance in the thickness direction of the substrate layer is 70% or more. [5] The light control filter according to any one of [1] to [4], wherein the material of the substrate layer is polycarbonate or silicone elastomer. A method for manufacturing an optical control filter as described in any one of [1] to [5], comprising the step of irradiating one surface of a light-transmitting substrate film with a short-pulse laser to form the substrate layer having the plurality of non-penetrating grooves. [7] The method for manufacturing an optical control filter according to [6], wherein the oscillation wavelength of the short-pulse laser is 343 nm, the pulse width is 500 femtoseconds or less, the repetition frequency is 1000 kHz or more, and the number of scan repetitions per unpenetrated groove is 10 or more. [Effects of the Invention]

[0008] In this invention, the process of filling the grooves with light-shielding material is unnecessary, allowing for greater design flexibility and the easy manufacture of light control filters exhibiting a desired viewing angle. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic top view showing an example of a light control filter according to the present invention. [Figure 2]This is a schematic cross-sectional view showing an example of a light control filter according to the present invention. [Figure 3] This is an example of the light control filter according to the present invention, fabricated in the example, and is a photograph of the cross-section in the thickness direction observed with a 200x magnification. [Figure 4] This is an example of the light control filter according to the present invention, fabricated in the example, and is a photograph of the cross-section in the thickness direction observed at 500x magnification. [Modes for carrying out the invention]

[0010] The present invention will be described below with reference to the figures. The dimensions and shapes of the figures exemplified in the following description are examples only, and the present invention is not necessarily limited to them. It can be implemented with appropriate modifications without changing the essence of the invention.

[0011] ≪Light Control Filter≫ A first aspect of the present invention is a light control filter comprising a light-transmitting substrate layer, wherein a plurality of non-penetrating grooves are formed on one surface of the substrate layer. Figure 1 is a top view of a light control filter 10 in which a plurality of unpenetrating grooves 2 are arranged in parallel on one surface 1a of a base film 1 which serves as the base layer. Figure 2 is a cross-sectional view taken in the direction of arrow XX in Figure 1.

[0012] Each unpenetrated groove 2 is a V-shaped or U-shaped groove opening into one surface 1a, with approximately the same shape and length, and has a groove bottom. The width of each unpenetrated groove 2 gradually narrows from the top to the bottom surface. In other words, the pair of opposing wall surfaces (inner wall surfaces) inside each unpenetrated groove 2 have a slope.

[0013] The virtual top surface facing the bottom surface of the non-penetrating groove 2 is at the same height as one of the surfaces 1a. The groove width of the non-penetrating groove 2 is maximum at the top surface and gradually narrows towards the lower bottom surface. As the groove width at the top surface (i.e., the uppermost groove width), it can be appropriately selected within the range of, for example, 5 to 100 μm, 10 to 50 μm, or 20 to 40 μm. As the groove width of the bottom surface, it can be appropriately selected within the range of, for example, 0.1 to 10 μm. The groove width at the top surface and the groove width of the bottom surface are each taken as the average value of groove widths at five or more randomly selected points along the longitudinal direction of the groove.

[0014] As the depth of the non-penetrating groove 2, it can be appropriately selected within the range of less than the thickness of the base material film 1, for example, 50 to 500 μm, 80 to 250 μm, or 100 to 180 μm. The depth of the non-penetrating groove 2 is measured along the thickness direction of the base material film 1 and is taken as the average value of depths at five or more randomly selected points along the longitudinal direction of the groove.

[0015] The aspect ratio represented by (depth / uppermost (top surface) groove width) of the non-penetrating groove 2 can be appropriately selected within the range of, for example, 3 to 20, 5 to 15, or 8 to 12.

[0016] As the pitch of the non-penetrating grooves 2 arranged parallel to each other at approximately regular intervals, it can be appropriately selected within the range of, for example, 50 to 500 μm, 80 to 250 μm, or 100 to 180 μm. The pitch of the non-penetrating groove 2 is taken as the average value of pitches at five or more randomly selected points.

[0017] A pair of opposing wall surfaces (inner wall surfaces) constituting each non-penetrating groove 2 form a rough surface with minute irregularities, and the light transmittance of the rough surface is lower than that of the base material layer 1. Here, as will be described later, the minute irregularities are formed by irradiating the material of the base material layer 1 with a short-pulse laser during the formation of the non-penetrating groove 2. Due to the rough surface, the light incident on the wall surface is scattered, and inevitably the light transmittance is lower than the state before laser irradiation.

[0018] In the light control filter 10 having the non-through groove 2 with the inner wall surface roughened in this way, a plurality of non-through grooves 2 arranged in parallel function as light shielding bands of a louver structure, and control the traveling direction of light transmitted through the light control filter 10 in the thickness direction. For example, as shown in FIG. 2, the light rays L1 to L3 incident from the other surface (lower surface) 1b of the light control filter 10 exit from the one surface (upper surface) 1a, but other light rays (not shown) incident at an angle shallower than the light rays L2 and L3 are blocked by the non-through groove 2 and scattered. As a result, only specific light rays L1 to L3 can be transmitted.

[0019] The number of the non-through grooves 2 provided in the light control filter 10 shown in FIGS. 1 to 2 is nine, but this is only an example, and the number is not particularly limited. The number is appropriately set according to the size of the light control filter 10, the purpose of use, and the pitch of the non-through grooves 2. Also, the length of the non-through groove 2 in the longitudinal direction is not particularly limited and is appropriately set according to the size of the light control filter 10 and the like. Further, in FIG. 1, the non-through grooves 2 are provided in the entire region excluding the frame portion of the base material layer 1, but the region where the non-through grooves 2 are provided may be a part of the surface of the base material layer 1 or the whole, and is appropriately set according to the use of the light control filter 10 and the like. Also, the non-through grooves 2 are arranged parallel to each other. Here, the term "parallel" includes not only the case of geometrically perfect parallelism but also the case where they are arranged in a degree that can be regarded as parallel in practice.

[0020] The bottom surface of each non-through groove 2 provided in the light control filter 10 of FIG. 2 is close to the lower surface 1b of the base material layer 1, but may be at a position farther from the lower surface 1b than in the illustrated example. For example, each non-through groove 2 may be provided on the surface of a thick light transmissive sheet, and the base material layer 1 may exist thicker further below from the bottom surface of each non-through groove 2.

[0021] Each open groove 2 in the light control filter 10 has a virtual top surface that opens to the outside, and the space inside the groove is exposed to the atmosphere. However, other transparent layers (not shown) may be laminated on the upper surface 1a of the base layer 1. Even in this case, from the viewpoint of improving the light shielding (light scattering) of each open groove 2, it is preferable that the inside of each open groove 2 is hollow and not filled with adhesive or the like. In addition, other transparent layers (not shown) may be laminated on the lower surface 1b of the base layer 1. These other transparent layers may be installed to protect, decorate, or reinforce the upper or lower surface of the light control filter 10.

[0022] From the viewpoint of improving the light transmittance of the light control filter 10, the total light transmittance in the thickness direction of the substrate layer 1 is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more. The total light transmittance of the substrate layer 1 is the value measured in accordance with JIS K7375:2008 for the portion of the substrate layer where the non-penetrating groove 2 is not formed or before the non-penetrating groove 2 is formed.

[0023] From the viewpoint of obtaining the above-mentioned desirable light transmittance, the material of the base layer 1 is preferably a transparent resin, and more preferably polycarbonate or silicone elastomer (silicone rubber).

[0024] ≪Manufacturing method for light control filters≫ A second aspect of the present invention is a method for manufacturing the optical control filter according to the first aspect, comprising the step of irradiating one surface of a light-transmitting substrate film (substrate layer) with a short-pulse laser to form the substrate layer having the plurality of non-penetrating grooves.

[0025] Ablation can be induced by scanning irradiation with a short-pulse laser, thereby roughening the inner wall surface of the unpenetrated groove. Specific laser irradiation conditions include, for example, a short-pulse laser with an oscillation wavelength of 343 nm, a pulse width of 500 femtoseconds or less, a repetition frequency of 1000 kHz or more, and a scan repetition count of 10 or more times per location of the unpenetrated groove.

[0026] While there are no particular restrictions on the angle at which the short-pulse laser is incident on the substrate film, an angle of 0 to 30 degrees relative to the perpendicular to the irradiated surface is preferred from the viewpoint of efficiently causing ablation. [Examples]

[0027] <Fabrication of light-controlled filters> A pulsed laser was irradiated onto one surface of a transparent polycarbonate film (160 mm long, 270 mm wide, 200 μm thick) from vertically above, forming multiple parallel grooves (150 mm long) along the longitudinal direction of the film, thereby creating an optical control filter (Figures 3 and 4). An Edgewave OPTEC MM-200 laser system manufactured by OPTEC Corporation was used as the laser device. The laser irradiation conditions were as follows: [Pulse width: 400 femtoseconds, Wavelength: 343 nm, Repetition frequency: 3000 kHz, Scan speed: 85 mm / second, Output: 8.555 W, Number of scans: 17] Cross-sections perpendicular to the longitudinal direction of multiple grooves of roughly the same shape arranged on the surface of the light control filter were cut out, the shape of each groove was measured, and the average value was calculated. The results were as follows: [Groove width (top): 20 μm, Groove width (bottom): 7 μm, Groove depth: 110 μm, Groove pitch: 100 μm, Aspect ratio (groove depth / groove width (top)): 5.5] When the light transmittance of the fabricated light-controlled filter was visually inspected, it was found that the inner walls of each groove were roughened by ablation, causing light to scatter and appear cloudy.

[0028] <Evaluation of light control filters> The viewing angle of the fabricated optical control filter was evaluated as follows. A digital camera was placed in front of the display screen of a notebook computer with the optical control filter attached in close contact. The center of the lens of the digital camera was aligned directly with the center of the display, and the distance between the two centers was set to 350 mm. Two Chinese characters "Shin-Etsu" were displayed in a region of 10 mm vertically and 15 mm horizontally centered on the display, and an image was taken with the digital camera to check whether the two Chinese characters could be visually recognized through the optical control filter. Here, the viewing angle when the digital camera was at the position directly facing the display screen (true front) was set to 0 degrees. Hereinafter, the line connecting the center of the display screen and the center of the lens is called the line of sight, and the line of sight at a viewing angle of 0 degrees is particularly called the reference line of sight. Next, the digital camera was horizontally moved horizontally with respect to the display screen, and it was installed so that the angle (viewing angle) formed by the reference line of sight and the line of sight after movement was 15 degrees, and the readability of the Chinese characters was confirmed. Similarly, the readability of the Chinese characters was confirmed at positions with viewing angles of 30 degrees, 45 degrees, and 60 degrees. As a result, it was readable when the viewing angle was 0 to 15 degrees, barely readable when the viewing angle was 30 degrees, and unreadable when the viewing angle was 45 to 60 degrees.

[0029] <Geometric Consideration> Based on the premise that light does not pass through because the inner wall surface of each unpenetrated groove of the optical control filter is roughened, the direction of the light beam transmitted in the thickness direction of the optical control filter was geometrically calculated based on the shape and pitch of each unpenetrated groove provided in the optical control filter, and the same result as the above actual measurement evaluation was obtained. That is, it was confirmed that non-penetrating grooves that are difficult to transmit light can be formed by scanning irradiation with a pulsed laser. Also, it was found that an optical control filter having a desired viewing angle can be freely designed and manufactured based on geometric calculations.

Claims

1. A light control filter comprising a light-transmitting substrate layer, wherein a plurality of non-penetrating grooves are formed on one surface of the substrate layer, The pair of opposing wall surfaces of the aforementioned unpenetrated grooves form a rough surface due to minute irregularities. A light control filter wherein the light transmittance of the rough surface is lower than the light transmittance of the substrate layer.

2. The light control filter according to claim 1, wherein the groove width of the unpenetrated groove gradually narrows from the top towards the bottom surface.

3. The light control filter according to claim 1, wherein the aspect ratio of the unpenetrated groove (depth / width of the uppermost groove) is 5 to 10.

4. The light control filter according to claim 1, wherein the total light transmittance in the thickness direction of the substrate layer is 70% or more.

5. The light control filter according to claim 4, wherein the material of the substrate layer is polycarbonate or silicone elastomer.

6. A method for manufacturing an optical control filter according to any one of claims 1 to 5, A method for manufacturing an optical control filter, comprising the step of irradiating one surface of a light-transmitting substrate film with a short-pulse laser to form the substrate layer having the plurality of non-penetrating grooves.

7. The method for manufacturing an optical control filter according to claim 6, wherein the oscillation wavelength of the short-pulse laser is 343 nm, the pulse width is 500 femtoseconds or less, the repetition frequency is 1000 kHz or more, and the number of scan repetitions per location of the unpenetrated groove is 10 or more.

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