JP2009210771A - Luminance-enhancing sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a luminance-enhancing sheet which is neither damaged nor colored even when arranged to be superposed on an optical sheet such as a diffusion sheet. <P>SOLUTION: The luminance-enhancing sheet 1 is superposed on the diffusion sheet 2, which is then used. Convex parts 11, in each of which light is made incident from the top thereof and the incident light is reflected on the inclined surface thereof, are formed on the light entrance surface of the luminance-enhancing sheet 1. On the same light entrance surface, a groove part 14 is arranged between the adjacent convex parts 11 and a light-reflective layer 15 is also formed between the adjacent convex parts. In particular, a concave part 12 is formed at the top of each convex part 11. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a brightness enhancement sheet used for a surface light source used for a transmissive liquid crystal display device or a signboard.

  A transmissive liquid crystal display device generally includes a liquid crystal panel in which pixels are arranged in a dot shape and a backlight, and realizes display of characters and images by controlling the light transmittance in each pixel. The backlight is composed of, for example, a combination of a cold cathode tube, a reflecting plate, a lens sheet, and the like, and the light emission amount distribution is controlled.

  Transmission type liquid crystal display devices are required to reduce power consumption and increase brightness. Achieving higher brightness is possible by increasing the number of light sources such as cold cathode fluorescent lamps, but this is not practical because it leads to an increase in power consumption. In view of this, a technique has been considered in which light emitted from the backlight in a direction greatly deviating from the normal direction is controlled to increase the luminance in the front direction (see, for example, Patent Document 1).

  Patent Document 1 discloses a brightness enhancement sheet having a convex portion on an incident surface. In this brightness enhancement sheet, the top of the convex part is a light incident part, the slope of the convex part is a light reflecting surface, and a light reflecting layer is provided between adjacent top parts (hereinafter sometimes referred to as a groove part). Of the light rays incident on the light incident portion, the light rays having a relatively small incident angle on the sheet surface (nearly perpendicular to the sheet surface) reach the emission side as they are and are emitted at a relatively small emission angle. In addition, among the light rays incident on the light incident portion, the light rays having a relatively large incident angle on the sheet surface (obliquely incident on the sheet surface) are refracted by the light incident portion, then reflected by the convex slope, and the front surface Bend in the direction. Further, the light beam incident on the light reflecting layer is reflected to the light source side, scattered and reflected by a light diffusing sheet or a reflecting member provided under the light source, and then reused by being incident on the brightness enhancement sheet again.

  For this reason, the brightness enhancement sheet disclosed in Patent Document 1 has an effect of condensing incident light, which is diffused light, in the front direction as a whole.

  Further, when the diffusion sheet is placed on the brightness enhancement sheet disclosed in Patent Document 1, the light incident portion of the brightness enhancement sheet comes into contact with the exit surface of the diffusion sheet. For this reason, the light incident portion may be damaged, resulting in uneven brightness. In addition, coloring, color unevenness, and brightness unevenness may occur due to the Newton ring phenomenon.

  These problems can be avoided by bonding the light incident portion of the brightness enhancement sheet and the exit surface of the diffusion sheet with a transparent adhesive or the like. However, in that case, another problem arises. Such a problem will be further described with reference to FIGS.

  As shown in FIG. 9, when the convex portion 11 of the brightness enhancement sheet 1 is not in contact with the exit surface of the diffusion sheet 2, the incident light beam is refracted at the top of the convex portion 11, so that it is incident at a relatively large incident angle. Even if it is a light ray, it proceeds at an angle within the critical angle inside the brightness enhancement sheet 1. Therefore, the light beam that has reached the slope 15 has a relatively large incident angle with respect to the slope 15 and is focused in the front direction.

  On the other hand, as shown in FIG. 2, when the top of the projection 11 of the brightness enhancement sheet 1 is bonded to the exit surface of the diffusion sheet 2, the incident light beam is not refracted at the top of the projection 11 and is relatively large incident. The light incident at the corner travels through the brightness enhancement sheet 1 at the same angle. Therefore, the light beam reaching the slope 15 has a relatively small incident angle with respect to the slope 15 and is not condensed in the front direction.

  In order to avoid this problem, when the angle θ of the slope 15 in the convex portion 11 of the brightness enhancement sheet 1 is increased as shown in FIG. 3, the height of the convex portion 11 is decreased. Therefore, even a light beam incident at a relatively large incident angle is not reflected by the inclined surface 15, reaches the exit surface as it is, is refracted at the interface, and is not condensed in the front direction.

  As shown in FIG. 4, reducing the angle θ of the slope 15 of the brightness enhancement sheet can improve the performance of condensing light in the front direction, but there are problems in terms of mold manufacturing, shape transferability, releasability, and the like. .

JP-A-10-106327

  As described above, when the brightness enhancement sheet and the diffusion sheet disclosed in Patent Document 1 are arranged to overlap, problems such as scratches and coloring may occur, but on the other hand, there is a problem that light is not collected in the front direction when bonded. is there.

  The present invention has been made to solve such a problem, and provides a brightness enhancement sheet that does not cause problems such as scratches and coloring even when it is placed over an optical sheet such as a diffusion sheet. Objective.

  The brightness enhancement sheet according to the present invention is provided on the incident surface side, and includes a convex portion that receives light from the top and reflects light on the inclined surface, and a light reflecting portion provided between the convex portions. It is the brightness improvement sheet | seat provided, Comprising: The recessed part was formed in the top part of the said convex part.

  Here, it is preferable that the concave portion is a part of an arc in a cross section.

  Moreover, it is desirable that the concave portion is formed by providing a depression in the entire region of the top portion.

  The recess may be formed by providing a recess only in the central region of the top.

  In a preferred embodiment, the maximum depth of the concave portion is 0.5 μm or more, and the maximum depth of the concave portion is 20% or less of the width of the top portion.

  The brightness enhancement sheet according to another aspect of the present invention is provided on the incident surface side, and the light provided between the convex portion and the convex portion that receives light from the top and reflects the light on the inclined surface. It is a brightness improvement sheet | seat provided with the reflection part, Comprising: At least one part of the top part of the said convex part is a thing lower than the top part of the said light reflection part.

  In the above-described brightness enhancement sheet, a diffusion sheet is disposed on the incident surface side.

  According to the present invention, it is possible to provide a brightness enhancement sheet that does not cause problems such as scratches and coloring even when it is placed over an optical sheet such as a diffusion sheet.

  First, a schematic configuration of the brightness enhancement sheet according to the embodiment of the invention will be described. FIG. 1 shows a cross-sectional view of the brightness enhancement sheet. FIG. 2 is a cross-sectional view showing symbols for explaining the size of each part of the brightness enhancement sheet. The brightness enhancement sheet 1 according to the present embodiment is used together with an optical sheet such as a diffusion sheet 2. The diffusion sheet 2 is provided on the incident surface side of the brightness enhancement sheet 1, enters the light emitted from the light source, diffuses it, and emits it to the brightness enhancement sheet 1. The brightness enhancement sheet 1 and the diffusion sheet 2 may be adhered to each other in the light reflecting layer 14 with a transparent adhesive, but may be used simply by being overlapped.

  A plurality of convex portions 11 are formed on the incident surface side of the brightness enhancement sheet 1. The convex portion 11 is formed so as to protrude from the base portion toward the light source side, and is formed in a conical shape such that its cross section becomes smaller as it approaches the tip portion. For example, the convex portions 11 have a conical shape, a quadrangular pyramid shape, or the like, and are arranged at equal intervals. The top part of the convex part 11 functions as a light incident part that receives light from a light source or the like.

  In the brightness enhancement sheet 1 according to the present embodiment, a concave portion 12 that is recessed in a spherical shape is formed at the top portion (that is, the light incident portion) at the tip of the convex portion 11. As described above, the concave portion 12 is provided at the top of the convex portion 11, and thus has a concave portion. Since the air layer is formed, the top of the convex portion 11 is not damaged. Moreover, since the top part of the convex part 11 does not contact the exit surface of the optical sheet such as the diffusion sheet 2, coloring, color unevenness, and brightness unevenness due to Newton ring phenomenon do not occur. Further, since air exists in the concave portion 12, light is refracted at the concave portion interface at the top, and even a light ray incident at a relatively large incident angle with respect to the sheet surface is condensed in the front direction.

  The shape of the slope 13 formed on the side surface of the convex portion 11 can be a straight line or a part of a parabola in the cross section (see FIG. 3). In the case of a straight line, there is an advantage that the mold can be easily designed and manufactured.

  When the shape of the slope 13 is a part of a parabola, the light beam that passes through the focal point and is reflected by the parabola becomes parallel light perpendicular to the sheet. Therefore, as shown in FIG. 3, it is preferable to arrange the top of the convex portion 11 in the vicinity of the focal point F of a virtual parabola approximated from the shape of the slope. For example, the distance A from the vertex O to the top of the convex portion may be about 0.5 to 2 times the distance f from the vertex O to the focal point F of the virtual parabola approximated from the shape of the slope. preferable. Further, the shape of the slope 13 may be a polygonal line similar to a parabola, an ellipse, a hyperbola, or the like.

  The angle θ of the slope 13 shown in FIG. 5 is preferably 5 degrees or greater and 30 degrees or less. If it is smaller than this, there may be a problem in the durability, mold transferability and releasability of the mold. Further, even when the shape of the slope 13 is a polygonal line or a curve, the angle θ of the slope 13 is preferably 30 degrees or more and 5 degrees or less from the viewpoint of mold durability, molding transferability, and mold releasability. .

  The shape of the recess 12 can be a part of an arc in the cross section, as shown in FIG. It is also possible to use a “he” shape or a trapezoid. Moreover, in order to form an air layer between other optical sheets and to fully exhibit the above-mentioned effect, it is preferable to provide a dent on the entire top as shown in FIG. On the other hand, as shown in FIG. 5B, in consideration of scratch resistance and the like, a recess may be provided only in a part of the top, for example, only in the central region.

  The maximum depth C of the recess 12 is preferably 0.5 μm or more. If it is smaller than this, the problem caused by the Newton ring phenomenon may not be sufficiently solved. The maximum depth C of the concave portion 12 is preferably 20% or less with respect to the width H of the top portion of the convex portion 11. The maximum value φ of the angle formed by the inclined portion of the recess 12 and the sheet surface is preferably 30 degrees or less. When larger than this, formation of the light reflection layer 15 may become difficult.

  A light reflecting layer (light reflecting portion) 15 is provided in the groove portion 14 formed between the adjacent convex portions 11. Therefore, the light ray incident on the brightness enhancement sheet 1 other than the top of the convex portion 11 is reflected to the light source side, that is, the diffusion sheet 2 side, and scattered by the diffusion sheet 2 or a reflection member provided below the light source. After being reflected, it is reused by entering the brightness enhancement sheet 1 again. At least a part of the top of the convex portion 11 is lower than the top (re-external surface) of the light reflecting layer 15.

  As a method for forming the light reflecting layer 15, for example, light diffusing ink is applied to the entire surface on which the convex portion 11 is formed so as to sufficiently fill the groove portion 14, and ink other than the top portion is removed with a scraper. Then, there is a method of curing the ink. In addition, the ink can be filled only in the groove portion 14 by forming an ink reservoir at the end of the surface on which the convex portion 11 is formed and scraping off the ink reservoir with a scraper. Hereinafter, such a method of forming the light reflecting layer 15 may be referred to as a scraping method or a scraping printing method. For example, a rubber squeegee can be used as the scraper. The rubber hardness (according to JIS K6253) is preferably about 60 to 90.

  When the groove 14 is filled with the light diffusive material to form the light reflecting layer 15, the refractive index of the light diffusive material after curing is preferably smaller than the refractive index of the convex portion 11. As a result, a part of the light beam incident on the inclined surface 13 is totally reflected and efficiently collected in the front direction.

When using total reflection, the form of leaving an air layer in the groove 14 is the most efficient. Therefore, the shape of the slope 13 may be a polygonal line as shown in FIG. 6A, and the narrow portion 131 and the wide portion 132 may be formed with the constriction 133 as a boundary.
By filling the groove portion 14 having such a shape with a relatively high viscosity ink, the light reflecting layer 142 is formed only in the wide portion 132 where the width of the groove portion 14 is relatively wide, and the air layer 141 is formed in the groove portion 14. The form to leave becomes possible. The viscosity of the ink is preferably 1000 mPa · s or more (25 ° C., E-type viscometer, 0.5 rpm), for example.

  As shown in FIG. 6A, the maximum width of the narrow portion 131 where the air layer 141 on the slope is left is 20 μm or less, preferably 15 μm or less. In addition to the shape shown in FIG. 6A, the shape of the slope 14 can be a stepped shape shown in FIG. 6B.

  Alternatively, the light reflecting layer 15 may be formed by forming a reflective layer on the slope 13 in advance by metal vapor deposition or the like and then filling the groove 14 with a light diffusing material. As described above, when the reflective layer is formed on the slope 13 of the convex portion 11, the refractive index of the light diffusing material filling the groove portion 14 is not particularly limited.

  Prior to the step of forming the light reflecting layer 15 by metal vapor deposition or the like, a release layer may be formed on the top of the convex portion 11. As the release layer, for example, polysiloxane can be applied by several μm. By applying polysiloxane to only the top of the convex portion 11 by roll printing or the like, applying metal vapor deposition to the entire surface on which the convex portion 11 is formed, and then removing the metal vapor deposition on the top portion with an adhesive member A light reflection layer can be formed only in the groove 14.

  When the brightness enhancement sheet 1 according to the present embodiment is used as a backlight for a liquid crystal display device, the pitch P (see FIG. 2) of the projections 11 may interfere with the pixels of the liquid crystal display device, and a moire failure may occur. is there. In order to avoid this, the pitch P of the convex portions 11 is preferably 1 mm or less, more preferably 0.5 mm or less, and particularly preferably 0.2 mm or less.

  The width H (see FIG. 4) of the top of the protrusion 11 is preferably 0.2 to 0.8 times the pitch P. If it is larger than this, the angle θ of the inclined surface 13 becomes too small, and it may be difficult to efficiently collect light in the front direction. If it is larger than this, the area ratio of the light reflecting layer 15 becomes too large, and the light use efficiency may be lowered. The light incident on the light reflecting layer 15 is reflected to the diffusion sheet 2 side, scattered and reflected by the diffusion sheet 2 or a reflecting member provided under the light source, and then reused by being incident on the brightness enhancement sheet again. However, since the actual reflectance is not 100%, if the proportion of light that is reused is too large, the light utilization efficiency decreases.

  The thickness T of the brightness enhancement sheet 1 according to the present embodiment has no particular influence on the optical performance, but is, for example, 0.1 to 2 mm. If it is smaller than this, there may be a problem in handling property in the backlight assembly process due to insufficient rigidity of the sheet. Even if it is larger than this, there is no particular advantage in handling, but it may hinder the reduction in thickness and weight of the backlight. The height D of the convex portion is preferably 5% to 70% with respect to the thickness T of the sheet. If it is larger than this, there may be a problem in handling such as easy tearing of the sheet. Even if it is smaller than this, there is no particular advantage in handling, but there are cases where the backlight is made thinner and lighter.

  In order to manufacture a sheet having convex portions, for example, an extrusion manufacturing method, a press molding method, a so-called 2P molding method using a photocurable resin, or the like can be used.

  In the case of an extrusion manufacturing method or a press molding method, for example, an acrylic resin, a styrene resin, or a polycarbonate resin can be used. In the case of the 2P molding method, in addition to the above resin, a polyethylene terephthalate resin can be used as the base sheet, and a urethane acrylate ultraviolet curable resin can be used as the photocurable resin.

  In consideration of the durability of the mold and the releasability of the molded product in such a molding method, chamfering, flat parts, and curved parts should be provided at the valleys (convex parts as molds) that connect adjacent tops. Is preferred (see FIG. 4). The width R of the chamfered portion is preferably about 1 to 5% with respect to the width H of the top portion of the convex portion 11.

  In the above example, the concave portion 12 is provided at the top of the convex portion 11, but not limited to this, as shown in FIG. 7, the light reflecting layer 15 formed in the groove portion 14 is made to be more than the top portion of the convex portion 11. The air layer 16 may be formed between the adjacent light reflecting layers 15 by projecting outward. At this time, as the light reflecting layer 15, an expansive ink having expansibility may be used.

Example.
FIG. 8 shows a configuration of the brightness enhancement sheet according to the example. The brightness enhancement sheet 1 has a thickness T of 400 μm, a pitch P of 50 μm, a width R of the top of the projection 11 of 3 μm, a radius of curvature R of the recess 12 of 10 μm, a width of the recess 12 of 23 μm, and a maximum depth C of the recess 12. Was 1 μm, and the depth D of the groove 14 was 77 μm.

It is sectional drawing which shows the structure of the brightness improvement sheet | seat concerning this invention. It is sectional drawing which shows the structure of the brightness improvement sheet | seat concerning this invention. It is a schematic diagram which shows the front-end | tip part vicinity of the convex part of the brightness improvement sheet concerning this invention. It is sectional drawing which shows a partial structure of the brightness improvement sheet | seat concerning this invention. It is a schematic diagram which shows the front-end | tip part vicinity of the convex part of the brightness improvement sheet concerning this invention. It is sectional drawing which shows the structure of the groove part of the brightness enhancement sheet concerning this invention. It is sectional drawing which shows the structure of the brightness improvement sheet | seat concerning this invention. It is sectional drawing which shows the structure of the brightness improvement sheet | seat concerning an Example. It is explanatory drawing for demonstrating the conventional problem. It is explanatory drawing for demonstrating the conventional problem. It is explanatory drawing for demonstrating the conventional problem. It is explanatory drawing for demonstrating the conventional problem.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Brightness improving sheet 2 Diffusion sheet 11 Convex part 12 Concave part 13 Slope 14 Groove part 15 Light reflection layer 16 Air layer

Claims (8)

A brightness enhancement sheet that is provided on the incident surface side, includes a convex portion that receives light from the top and reflects light on the inclined surface, and a light reflecting portion that is provided between the convex portions,
The brightness improvement sheet | seat in which the recessed part was formed in the top part of the said convex part.   The brightness enhancement sheet according to claim 1, wherein the recess is a part of a circular arc in a cross section.   The brightness enhancement sheet according to claim 1, wherein the recess is formed by providing a recess in the entire area of the top.   The brightness enhancement sheet according to claim 1, wherein the recess is formed by providing a recess only in a central region of the top.   The brightness enhancement sheet according to claim 1, wherein the maximum depth of the recess is 0.5 μm or more.   The brightness enhancement sheet according to claim 1, wherein the maximum depth of the concave portion is 20% or less of the width of the top portion. A brightness enhancement sheet that is provided on the incident surface side, includes a convex portion that receives light from the top and reflects light on the inclined surface, and a light reflecting portion that is provided between the convex portions,
At least a part of the top portion of the convex portion is a brightness enhancement sheet lower than the top portion of the light reflecting portion.   The brightness enhancement sheet according to any one of claims 1 to 7, wherein a diffusion sheet is disposed on the incident surface side of the brightness enhancement sheet.

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