JP2009058658A - Optical sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture an optical sheet having a light transmission layer constituted by arranging prism lines of a high aspect ratio in parallel at minute pitches at a low cost so that it has stable optical characteristics. <P>SOLUTION: The optical sheet 1 has the light transmission layer 10 constituted by arranging prism lines 11, in each of which width becomes narrower toward a top end, in parallel. Roundness having radius curvature of R=3 μm to 30 μm is given to an intersection part between the upper surface 12 and the slope 13 of the prism line 11. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical sheet such as a display filter, a viewing angle control sheet, and a light diffusion sheet.

  A prism array with a substantially trapezoidal cross section is used as an optical sheet for display filters, viewing angle control sheets, light diffusion sheets, etc. that suppress external light reflection to improve image contrast or to expand or limit the viewing angle. Those having light transmission layers arranged in parallel are used (Patent Document 1, Patent Document 2, Patent Document 3).

  In such an optical sheet, it is preferable that the arrangement pitch of the prism rows is a fine pitch of 1 mm or less in response to higher definition of the image, and the width of the prism rows is increased in order to increase the viewing angle control effect. In some cases, it is desirable to increase the height (hereinafter referred to as aspect ratio) with respect to.

  On the other hand, as a method for producing a light transmission layer of such an optical sheet, a 2P molding method (Photo Polymerization) (Patent Document 3) using a molding die and an ultraviolet curable resin is known.

JP 2006-189867 A JP 2006-343711 A JP 2000-352068 A

  If the light transmission layer is manufactured by the 2P molding method, the cost becomes high because the ultraviolet curable resin is expensive.

  On the other hand, according to the extrusion molding method using a thermoplastic resin, a light transmission layer can be manufactured at a relatively low cost. However, when a prism array is manufactured with a fine pitch and a high aspect ratio, the shape from the mold is Low transfer performance is a problem.

  That is, the molten resin is not sufficiently filled to the back of the mold, and shape unevenness occurs in the shoulder portion of the prism row of the molded optical sheet.

  Further, since the molten resin does not adhere to the mold at the shoulder portion of the prism row, the surface roughness is different from that of the other portions that are in close contact. For this reason, when a light shielding material is laminated on the surface of the light transmission layer on the prism row side and then the excess light shielding material on the prism row is scraped off to fill the grooves between the prism rows with the light shielding material or the like, the surface roughness is reduced. Scraping unevenness occurs due to unevenness of the thickness.

  Then, due to the uneven shape of the shoulder and the unevenness of scraping off the light shielding material, the optical characteristics and the appearance are deteriorated, such as streaky unevenness being observed.

  In contrast, the present invention makes it possible to manufacture an optical sheet having a light transmission layer in which high-aspect-ratio prism rows are arranged in parallel at a fine pitch at low cost and with stable optical characteristics using a thermoplastic resin. For the purpose.

  When the present inventor manufactures an optical sheet having a light transmission layer in which prism rows are arranged in parallel, if the shoulder portion of the prism row is designed to be rounded within an allowable range, the die can be easily removed and transferred from the mold. It has been found that the unevenness of the shape of the shoulder and the roughness of the surface of the prism row obtained by improving the performance are reduced, and the optical performance and appearance are stabilized.

  That is, the present invention is an optical sheet having a light transmission layer in which prism rows narrowing toward the tip are arranged in parallel, and the intersection of the upper surface and the inclined surface of the prism row is rounded with a radius of curvature of 3 μm to 30 μm. An optical sheet is provided.

  Further, according to the present invention, as a mold for molding the light transmission layer of the optical sheet, a groove having a narrow width toward the groove bottom surface is juxtaposed on the mold surface, and an intersection of the groove bottom surface and the groove slope surface. Provides a mold having a roundness with a radius of curvature of 3 μm to 30 μm.

  Furthermore, the present invention provides a method for producing a light-transmitting layer by extrusion molding a thermoplastic resin using the above-mentioned mold as a method for producing this optical sheet.

  The optical sheet of the present invention has a light transmission layer in which prism rows are arranged in parallel, and the intersection between the upper surface and the inclined surface of the prism row has a roundness with a radius of curvature of 3 μm to 30 μm. When molding from a thermoplastic resin using the, the desired shape can be molded even if the aspect ratio is increased or the pitch is fine.

  Therefore, even if the light transmission layer is manufactured at low cost using a thermoplastic resin, it is possible to eliminate the deterioration of the optical characteristics and the appearance due to the uneven shape of the shoulder portion of the prism row.

  Hereinafter, the present invention will be described in detail with reference to the drawings. In each figure, the same numerals indicate the same or equivalent components.

  FIG. 1 is a perspective view of one embodiment of the optical sheet 1 of the present invention, and FIG. 2 is an xx sectional view of the light transmission layer 10.

  The optical sheet 1 is an optical sheet 1 that can be used as a display filter, a viewing angle control sheet, a light diffusion sheet, and the like, and includes a light transmission layer 10 and a light shielding portion 20.

  The light transmission layer 10 has a configuration in which prism rows 11 narrowing toward the tip end are arranged in parallel on one side.

  As shown in FIG. 2, the prism row 11 arranged in parallel on one side of the light transmission layer 10 has a substantially trapezoidal cross section in the parallel direction. And the shoulder part 14 which is the intersection of the upper surface 12 and the slope 13 of a prism row | line | column has the roundness of curvature-radius R = 3micrometer-30 micrometers. By rounding the shoulder 14 in this way, when the light transmission layer 10 is molded with a mold, the molten resin can be filled to the back of the mold, and the mold and the molten resin can be brought into close contact with each other, In addition, it can be easily removed from the mold. Therefore, it is possible to prevent the unevenness of the shape and the surface roughness from occurring in the shoulder portion 14 and to impart stable optical performance and appearance to the light transmission layer 10.

  On the other hand, if the curvature radius R is too small, the above-described effect due to the shoulder 14 being rounded cannot be obtained. On the other hand, if the radius of curvature R is too large, the ratio of the shoulder portion 14 to the pitch P is large, and the proportion of light that has passed through the shoulder portion 14 is increased. When used for, it causes problems such as blurred images. In addition, when the light shielding material is applied to the parallel surface side of the prism rows, the light shielding material on the upper surface of the prism rows is scraped, and the light shielding material in the groove between the prism rows is fixed to form the light shielding portion, scraping is performed. There arises a problem that unevenness of the width of the light shielding layer is likely to occur due to unevenness of the force pressing the tool.

The preferred size of the radius of curvature R depends on the pitch P of the prism row 11, and when the pitch P exceeds 300 μm,
Radius of curvature R = P × 0.01 (μm) to P × 0.2 (μm) Equation (1)
When the pitch P is 300 μm or less,
Radius of curvature R = P × 0.02 (μm) to P × 0.15 (μm) Equation (2)
It is preferable that
From the viewpoint of processing accuracy, a more preferable radius of curvature R is 5 μm to 20 μm.

  If the pitch P of the prism row 11 is larger than 500 μm, the ratio of the shoulder portion 14 to the pitch P becomes small, and it becomes difficult to obtain the above-described effect by rounding the shoulder portion 14. Therefore, it is preferable to make the pitch P less than 500 μm. In particular, 300 μm or less is preferable in order to cope with high definition of video. Further, the pitch P is preferably 30 μm or more from the viewpoint of mold manufacturing accuracy and molding processing accuracy.

  The ratio (aspect ratio = L5 / L1) between the height L5 and the bottom surface width L1 of the prism row 11 is set as appropriate from the viewpoint of the viewing angle to be controlled and the ease of molding. Since the effect of the present invention to make the surface round is remarkable, 0.8 or more is preferable, and 1 or more is more preferable. Moreover, 3 or less is preferable from the viewpoint of durability and moldability of a mold for molding the light transmission layer 10.

  The width L2 of the bottom surface 16 of the groove 15 having a substantially wedge-shaped cross section between the prism rows 11 is preferably 2 μm or more from the viewpoint of the durability of the mold of the light transmission layer 10, and from the viewpoint of the shape transfer stability of the thermoplastic resin. The thickness is preferably 20 μm or less. Further, from the viewpoint of durability of the mold, the intersection between the bottom surface 16 and the slope 13 of the prism row 11 may be rounded.

  The upper surface width L3 of the prism array 11 is preferably 30 to 90% of the pitch P of the prism array 11 in terms of light utilization efficiency and viewing angle control ability. Here, the upper surface width L3 is a width obtained from the intersection of the extrapolation line of the upper surface 12 and the extrapolation line of the inclined surface 13 in the cross section of the prism row 11 as shown in FIG.

  The angle θ formed by the inclined surface 13 of the prism array 11 and the normal line of the light transmission layer 10 is appropriately determined depending on the purpose of use of the optical sheet 1, ease of mold manufacture and removal from the mold, etc. When used as a display filter, a viewing angle control sheet, or a light diffusion sheet that is disposed on the front surface of the display with the unit 20 facing the viewer, the angle is preferably 3 ° to 30 °. If this angle θ is too small, there may be a problem with the durability of the molding die for the light transmission layer 10 or a problem with the mold releasability between the mold and the molded product. On the other hand, if the angle θ is too large, a preferred viewing angle may not be obtained. When the slope 13 of the prism row 11 is bent or rounded, the portion having the smallest angle θ of the slope 13 may be set to the above-described angle range.

  As for the cross-sectional shape of the light transmission layer 10, as shown in FIG. 3A, the prism rows 11 may be continuous so that a wedge-shaped groove is formed between the prism rows 11. As described above, the prism rows 11 may be arranged in parallel at a predetermined interval so that a groove having a trapezoidal cross section is formed between the prism rows 11.

  Moreover, the upper surface 12 of the prism row 11 may be bent as shown in FIG. 3C, or the slope 13 may be bent as shown in FIG. As shown in 3E, the slope 13 may be curved. When the upper surface 12 of the prism row 11 is bent, the bent surface is preferably within 45 ° with respect to the sheet surface. This is because if this angle is too large, the same problem as when the ratio of the shoulder 14 to the pitch P increases may occur.

  The layer thickness L6 of the light transmission layer 10 is an important factor that affects the transfer performance of the prism array 11 when the prism array 11 is formed with a high aspect ratio by extrusion. Therefore, the layer thickness L6 is preferably about 1.5 to 3.5 times the height L5 of the prism row 11.

  The constituent material of the light transmission layer 10 can be a thermoplastic resin, an ultraviolet curable resin, or the like made of an acrylic resin, a styrene resin, a polycarbonate resin, or the like, but is preferably a thermoplastic resin from the viewpoint of cost.

  As a mold for forming the light transmission layer 10, a mold in which irregularities are arranged in a shape opposite to the arrangement of the prism rows 11 described above is used. FIG. 4 is a cross-sectional view of the mold 30. Therefore, a groove 31 that is narrower toward the groove bottom surface 32 is formed on the surface of the mold 30, and the intersection between the groove bottom surface 32 and the groove slope 33 has a roundness, and its radius of curvature R Is 3 μm to 30 μm.

  The molding die 30 of the light transmission layer 10 may be a flat plate shape, but as shown in FIG. 5, it is preferable to use a roll molding die 30b for extrusion molding in which the grooves 31 are formed in the circumferential direction of the roll. . Thereby, the light transmission layer 10 can be efficiently molded using the thermoplastic resin.

  In addition, the manufacturing method of metal mold | die 30 itself can cut and manufacture the metal mold | die material which consists of copper, brass, etc. with a cutting tool etc. by a conventional method.

  On the other hand, the light-shielding part 20 is formed by filling a light-shielding material in a substantially wedge-shaped groove between the prism rows 11 of the light transmission layer 10 and fixing it.

  As a light shielding material, white ink mixed with light diffusing agents such as resin fine particles, glass fine particles, metal oxide fine particles and various pigments, black ink such as carbon particles and black ink mixed with light absorbing agents such as black pigments, etc. Can be used. In addition, when not aiming at the improvement of external light contrast, the light shielding material may be white.

  As the ink binder, an ultraviolet curable resin, an adhesive composition in which the resin is dissolved in a solvent, a thermosetting resin, or the like can be used, and the ink binder is appropriately selected according to the refractive index applied to the light-shielding portion 20.

  That is, by making the refractive index of the light shielding part 20 lower than the refractive index of the light transmission layer 10, as shown in FIG. 6A, the total reflection at the interface between the light shielding part 10 and the prism row 11 is utilized, and the light utilization efficiency. In addition, as shown in FIG. 6B, the light diffusion effect can be improved.

  On the other hand, when a defect such as a so-called double image is caused by the light reflected at the interface between the light shielding unit 20 and the prism row 11, the refractive index of the light shielding unit 20 is approximately equal to or higher than the refractive index of the light transmission layer 10. It is preferable that

  Therefore, the refractive index of the light shielding part 20 with respect to the light transmission layer 10 is appropriately determined according to the use of the optical sheet 1 and the like.

  As a method for forming the light shielding portion 20, after forming the light transmission layer 10, a light shielding material is applied to the parallel surface side of the prism rows 11 so that the light shielding material remains in the grooves 15 between the prism rows 11. It is preferable to scrape off the excess light shielding material on the upper surface 12 of the row 11 using a rubber spatula, a metal blade, a metal roller, or the like. Thereby, the width | variety and depth of the light-shielding part 20 can be formed in the uniformly stable magnitude | size.

  In addition, as a method of forming the light shielding portion 20, a light shielding material that also serves as an adhesive is applied to the parallel surface side of the prism row 11, and then a light-transmitting sheet is superimposed on the coated surface so that the top portion of the prism row 11 is light. You may affix and affix on the state which touches a permeable sheet substantially.

  A light diffusing sheet, a colored sheet, an antiglare sheet, or the like in which light diffusing particles are dispersed may be arranged on the light shielding portion 20 side, the opposite side, or both of the light transmitting layer 10 as necessary.

  As shown in FIG. 7, the optical sheet 1 of the present invention can be mounted on the front surface of a display panel 40 such as a plasma display or a liquid crystal display, or used as a rear projection screen. In this case, the optical sheet may be mounted in the direction of the prism array toward the observer or the image light source in accordance with purposes such as external light contrast improvement, image light diffusion, and viewing angle control.

Example 1 (Production of light diffusion sheet)
A roll molding die 30 having a surface made of copper and having a groove 31 having the cross-sectional shape of FIG. 4 was manufactured. In this case, the dimensions of the groove 31 were as follows.

Bottom width L3: 74μm
Opening width L1: 101 μm
Depth L5: 128μm
Angle θ between normal line of groove bottom surface 32 and groove slope 33: 6 °
Curvature radius R: 13μm
Pitch P: 106 μm

  Using this roll molding die, a methacryl / styrene copolymer resin was extruded to form the light transmission layer 10 having the cross-sectional shape of FIG.

  Next, a black ink made of an acrylic ultraviolet curable resin containing 5% by weight of carbon particles having an average particle diameter of 5 μm is applied to the entire surface of the light transmission layer 10 on the prism array side, and then the prism array 11 using a metal roll. Black ink other than those filled in the substantially wedge-shaped grooves between them was scraped off, and the black ink was cured by irradiating with ultraviolet rays to form the light-shielding portion 20 to obtain a light diffusion sheet.

  The thickness of this light diffusion sheet was 230 μm. As a result of measuring the cross-sectional shape, the radius of curvature R of the shoulder portion 14 of the prism row was 13 to 15 μm, and the depth of the black ink was 105 to 110 μm.

Comparative Example 1
A light diffusing sheet was produced in the same manner as in Example 1 except that a roll forming mold having no roundness at the intersection between the groove bottom and the groove slope was used.

  The curvature radius R of the shoulder portion of the prism row of the light transmission layer of the obtained light diffusion sheet was 6 to 15 μm, and the depth of the black ink was 105 to 115 μm.

Comparative Example 2
A light diffusing sheet was produced in the same manner as in Example 1 except that a roll forming mold having a curvature radius R of 35 μm at the intersection between the groove bottom and the groove slope was used.

  The curvature radius R of the shoulder portion of the prism row of the light transmission layer of the obtained light diffusion sheet was 35 to 37 μm, and the depth of the black ink was 90 to 110 μm.

Evaluation The light diffusion sheets of Example 1 and Comparative Examples 1 and 2 were mounted on the front surface of a 50-inch plasma display, and images were observed under room light illumination. In this case, the mounting direction of the optical sheet was set so that the prism row extends in the horizontal direction, and the side on which the black ink was applied was directed to the observer side.
The results are shown in Table 1.

  As shown in Table 1, when the light diffusion sheet of Example 1 was mounted on a plasma display, both the appearance and the external light contrast were good. On the other hand, in Comparative Example 1, the external light contrast was good, but in particular, when observed from an oblique direction, black and white random streaks were conspicuous and there was a problem in appearance. In Comparative Example 2, the external light contrast was slightly poor, and white streaky unevenness was conspicuous when observed from the top and bottom diagonal directions, and there was a problem in appearance.

  INDUSTRIAL APPLICABILITY The present invention is useful as an optical sheet such as a display filter, a viewing angle control sheet, a light diffusion sheet, and a manufacturing technique thereof.

It is a perspective view of an optical sheet. It is sectional drawing of a light transmissive layer. It is sectional drawing of a light transmissive layer. It is sectional drawing of a light transmissive layer. It is sectional drawing of a light transmissive layer. It is sectional drawing of a light transmissive layer. It is sectional drawing of a light transmissive layer. It is sectional drawing of a metal mold | die. It is a perspective view of the metal mold | die for extrusion molding. It is a light ray figure in the case of using as a viewing angle control sheet. It is a light ray figure in the case of using as a light-diffusion sheet. It is explanatory drawing of the usage method of an optical sheet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical sheet 10 Light transmissive layer 11 Prism row | line | column 12 Upper surface 13 Slope 14 Shoulder part 15 Groove | groove 16 Bottom surface 20 Light-shielding part 30 Mold 31 Groove 32 Groove bottom face 33 Groove slope 40 Display panel P Pitch of prism row R Prism row shoulder curvature radius

Claims (11)

  An optical sheet having a light transmission layer in which prism rows narrowing toward the tip are arranged in parallel, wherein the intersection of the upper surface and the inclined surface of the prism row has a roundness with a radius of curvature of 3 μm to 30 μm.   The optical sheet according to claim 1, wherein a cross section of the prism rows in the parallel direction is substantially trapezoidal.   The optical sheet according to claim 1, further comprising a light shielding portion between the prism rows.   The optical sheet according to any one of claims 1 to 3, wherein a ratio of a height to a bottom surface width of the prism row is 0.8 or more.   5. The optical sheet according to claim 1, wherein an angle θ formed by the slope of the prism row and the normal line of the light transmission layer is 3 ° to 30 °.   The optical sheet according to claim 1, wherein the pitch of the prism rows is 500 μm or less.   The optical sheet according to claim 1, wherein the light transmission layer is made of a thermoplastic resin.   A mold for forming a light transmission layer in which prism rows that are narrowed toward the tip are arranged in parallel, and a groove that is narrowed toward the bottom of the groove is arranged in parallel on the mold surface. A mold in which the intersection with the slope has a roundness with a radius of curvature of 3 μm to 30 μm.   The mold according to claim 8, wherein the groove is formed in a circumferential direction of the roll.   The method for producing an optical sheet according to any one of claims 1 to 7, wherein the light transmission layer is produced by extrusion molding of a thermoplastic resin using the mold according to claim 9. .   After the light transmission layer is manufactured, a light shielding material is applied to the parallel surface side of the prism rows, the light shielding material on the upper surface of the prism rows is scraped off, and the light shielding material in the grooves between the prism rows is fixed to fix the light shielding portion. The manufacturing method of the optical sheet of Claim 10 formed.