JP2007178628A - Prism sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a prism sheet capable of obtaining satisfactory luminance improving effects. <P>SOLUTION: In the prism sheet 1 having a large number of prisms 3 arranged on a base plate 2, the shape of cross-section, when each of the prisms 3 is viewed from a specified direction, is a polygon which consists of a bottom edge 3a constituting a bottom surface of the prism 3 and six edges 3b to 3e, the polygon is symmetrical with respect to a straight line A, which passes through the midpoint of the bottom edge 3a and is vertical to the bottom edge 3a, and the six edges 3b to 3e are brought into contact with two edges on both ends, wherein there is formed an edge of an angle with respect to the axis A, which is smaller than the angle formed by each of the two edges with respect to the axis A; and so that there is not an edge formed of an angle with respect to the axis A, which is larger than the angle formed by each of the two edges on both ends, with respect to the axis A. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a prism sheet for improving luminance used in flat panel displays used in flat-screen televisions, mobile phones, digital cameras, car navigation devices, computers, PDAs, cash dispenser terminals, and the like.

  Generally, in a display device using a backlight such as a liquid crystal display device, a prism sheet is provided on a light guide plate that guides light from the backlight to the display surface side in order to improve display luminance.

  As this prism sheet, a structure in which a large number of semicylindrical prisms are arranged on a transparent substrate is considered. In the prism sheet having such a configuration, the observation angle of the prism sheet when the direction perpendicular to the transparent substrate is set as a reference (0 °) is θp, and detection is performed at each observation angle when light is incident from the transparent substrate side. The luminous intensity characteristic obtained by simulation of the intensity of the light to be obtained is a curve a shown in FIG. A curve e shown in FIG. 3 is a curve showing luminous intensity characteristics when the prism sheet is only a transparent substrate. Since display devices are mostly viewed from the front, it is required to improve the luminance in the front direction. As shown by the curve a in FIG. 3, according to the prism sheet in which the semi-cylindrical prisms are arranged, the luminance in the front direction can be increased.

  As shown in FIG. 4, a prism sheet 10 in which a large number of triangular prisms 30 having an apex angle of 90 ° are arranged on a transparent substrate 20 is known as a prism sheet configured to further improve the luminance in the front direction ( For example, see Patent Document 1). The observation angle of the prism sheet 10 when the direction perpendicular to the transparent substrate 20 is a reference (0 °) is θp, and when light is incident from the transparent substrate 20 side, the intensity of light detected at each observation angle is The luminous intensity characteristic obtained by the simulation is a curve b shown in FIG.

  As can be seen from the curve b, the luminous intensity in the front direction is larger than that of the curve a, but the luminous intensity is almost zero in the vicinity of ± 45 ° where the angle θp is ½ of the apex angle 90 ° of the prism 30. You can see that As described above, it is known that almost no light is emitted in the direction of half the apex angle of a triangular prism.

  As a structure for improving luminance in an oblique direction, a prism sheet is also known in which the cross-sectional shape of the prism is a shape from a trough to a trough of a sine curve. The luminous intensity characteristic of such a prism sheet is close to the curve a in FIG.

JP 2003-270633 A

  In order to widen the viewing angle, a display device is required to improve luminance when viewed from an oblique direction in addition to luminance when viewed from the front direction. In the prism sheet having the characteristics shown by the curve b in FIG. 3, since there is almost no luminance in the oblique 45 ° direction, the luminance in the front direction is sufficient, but the viewing angle is narrow. If a prism sheet with a large number of sinusoidal prisms is used, the luminance in the oblique direction can be ensured. However, in this configuration, the luminance in the front direction is lower than when a triangular prism is used. End up.

  From the above, there has been a demand for a prism sheet that can achieve both improvement in luminance in the front direction and improvement in luminance in an oblique direction.

  This invention is made | formed in view of the said situation, and it aims at providing the prism sheet which can acquire a favorable brightness improvement effect.

  The prism sheet of the present invention is a prism sheet having a large number of prisms arranged on a substrate, and the cross-sectional shape when the prism is viewed from a specific direction has a bottom side constituting the bottom surface of the prism, and six prism sheets. It is a polygonal shape consisting of the above sides, the polygonal shape is a line-symmetrical shape with a straight line passing through the midpoint of the base and perpendicular to the base, and the six or more sides are There are two sides that are in contact with each other at both ends, and there are sides that are smaller than the angle between each of the two sides and the axis. It is designed so that there is no side where two sides are in contact with each other, and the angle formed between the two axes is larger than the angle formed between each of the two sides and the axis.

  In the prism sheet of the present invention, the plurality of prisms are arranged in a matrix on the substrate.

  In the prism sheet of the present invention, the prism has a polygonal column shape extending in the specific direction, and a large number of the prisms in the polygonal column are arranged in a direction orthogonal to the specific direction.

  In the prism sheet of the present invention, the arrangement pitch of the plurality of prisms is irregular.

  ADVANTAGE OF THE INVENTION According to this invention, the prism sheet which can acquire the favorable brightness improvement effect can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partial schematic cross-sectional view of a prism sheet for explaining an embodiment of the present invention.
The prism sheet for describing the embodiment of the present invention has a configuration indicated by a trajectory when the cross section shown in FIG. 1 is moved in a direction perpendicular to the paper surface of FIG. 1 (hereinafter referred to as a specific direction). A prism sheet 1 shown in FIG. 1 includes a transparent substrate such as plastic or a substrate 2 such as a film substrate, and a large number of prisms 3 arranged on one surface of the substrate 2.

  The prisms 3 have a polygonal column shape extending in a specific direction, and many prisms 3 are arranged in a direction orthogonal to the specific direction. The length in the specific direction of the prism 3 is, for example, the same as the length from the end to the end of the display pixels arranged in the vertical direction of the liquid crystal display device on which the prism sheet 1 is mounted. This is the same as the number of display pixels on the side of the liquid crystal display device on which the sheet 1 is mounted. The arrangement pitch of the prisms 3 may be regular or irregular. In the case of irregularity, it is possible to suppress the occurrence of moiré due to the arrangement of the color filter and the prism 3 arranged above the prism sheet 1.

  The length of the prism 3 in the direction orthogonal to the specific direction is equal to or smaller than the liquid crystal display element or one color filter for displaying one pixel of the liquid crystal display device on which the prism sheet 1 is mounted, that is, 5 μm. About -1000 micrometers is preferable.

  The cross-sectional shape of the prism 3 when viewed from a specific direction is a polygonal shape including a bottom side 3a constituting the bottom surface of the prism and six sides 3b to 3g. This polygonal shape is line-symmetric with respect to a straight line A passing through the midpoint of the base 3a and perpendicular to the base 3a. The angle formed between the sides 3b and 3e and the axis A is 60 °, the angle formed between the sides 3c and 3f and the axis A is 30 °, and the angle formed between the sides 3d and 3g and the axis A is 45 °. ing.

  Therefore, as shown by a broken line in the leftmost prism 3 in FIG. 1, the sides 3b and 3e constitute a part of a prism having a triangular apex angle of 120 °, and the sides 3c and 3f have a cross-sectional shape. It can be seen that a part of the prism having a triangular apex angle of 60 ° is formed, and the sides 3d and 3g form a part of the prism having a triangular apex angle of 90 °. As a result, the prism 3 can have the characteristics of three prisms having a triangular cross section and apex angles of 60 °, 90 °, and 120 °.

  In the cross-sectional shape shown in FIG. 1, the six sides 3b to 3g are sides where two sides, one at each end, are in contact with each other, and the angle formed with the axis A is different from each of the two sides and the axis A. There are sides (sides 3c and 3f in FIG. 1) that are smaller than the angle between the two sides, and two sides that are in contact with each other at both ends, and the angle with the axis A is 2 It is designed so that there is no side larger than the angle formed by each of the two sides and the axis A. This is because the cross-sectional shape when the prism 3 is viewed from a specific direction approaches the shape from the valley to the valley of the sine curve. By making the cross-sectional shape of the prism 3 close to the shape from the trough portion to the trough portion of the sinusoidal curve, the prism 3 can have a characteristic close to that of a prism having a semicircular cross-sectional shape.

  Of the six sides 3b to 3g, the angle between the sides 3b and 3e and the axis A is preferably in the range of 50 ° to 85 °, and the angle between the sides 3c and 3f and the axis A is in the range of 20 ° to 40 °. The angle formed between the sides 3d and 3g and the axis A is preferably in the range of 41 ° to 85 °.

  The angle of observation of the prism sheet 1 when the direction perpendicular to the substrate 2 is set as a reference (0 °) is θp, and when the light is incident from the substrate 2 side, the angle θp is swept in a direction perpendicular to the specific direction. The luminous intensity characteristic obtained by simulating the intensity of light detected at each observation angle is a curve c shown in FIG.

  A prism having a triangular cross section and an apex angle of 90 ° has characteristics as shown by a curve b in FIG. In addition, in the prism having a triangular cross section and apex angles of 60 ° and 120 °, the angle θp (except θp = ± 90 °) at which the luminous intensity of the curve b is almost 0 is around ± 30 ° or ± 60 °. Has moved properties. The characteristic of the prism 3 is obtained by weighting and adding these three characteristics with a certain coefficient. For this reason, as shown by the curve c, the luminous intensity in the portion where the angle θp is not ± 90 ° does not become 0, and the luminance in the oblique direction can be increased as compared with the prism having the characteristic of the curve b. . Further, since the prism 3 also has the characteristics of a prism having a triangular cross-sectional shape, the luminance in the front direction can be improved over the curve a which is close to the luminous intensity characteristic of a prism having a cross-sectional shape of a sine wave. .

  FIG. 2A shows the prism sheet 10 having the configuration shown in FIG. 4 where θp is the observation angle of the prism sheet 10 when the direction perpendicular to the substrate 20 is the reference (0 °), and light is transmitted from the substrate 20 side. It is a figure which shows the luminous intensity characteristic which calculated | required with the intensity | strength of the light detected by each observation angle when the angle (theta) p was passed in the specific direction when it injected. In FIG. 2B, the observation angle of the prism sheet 1 when the direction perpendicular to the substrate 2 is set as a reference (0 °) is θp, and when the light is incident from the substrate 2 side, the angle θp is set to a specific direction. It is a figure which shows the luminous intensity characteristic which calculated | required the intensity | strength of the light detected by each observation angle when it touched by simulation. As can be seen from FIG. 2, it can be seen that the prism sheet 1 has higher luminance in the oblique direction even when observed in a specific direction.

  Thus, according to the prism sheet 1, the prism 3 has the characteristics of each of the plurality of prisms having different apex angles, and the overall cross-sectional shape is designed to approach a sine wave shape. However, both the triangular prism and the sinusoidal cross-sectional prism can have the advantages, and both the improvement in luminance in the front direction and the improvement in luminance in the oblique direction can be achieved.

  In the above description, the cross-sectional shape of the prism 3 is a polygonal shape composed of the base 3a and the six sides 3b to 3g, but is not limited thereto. In order to satisfy the above design conditions, the cross-sectional shape of the prism 3 may be a polygonal shape including a base 3a and six or more sides. For example, a configuration in which a side parallel to the substrate 2 is provided between the sides 3d and 3g of the prism 3 shown in FIG. A curve d in FIG. 3 is a luminous intensity characteristic of the prism sheet having such a configuration, and it can be seen that the luminance in the oblique direction is higher than that of the curve b and the luminance in the front direction is higher than that of the curve a. Further, as long as the above design condition is satisfied, the number of sides other than the base 3a may be any number as long as it is six or more. However, if this number exceeds 14, the cross-sectional shape of the prism 3 becomes too close to the shape from the valley to the valley of the sinusoidal curve, and the luminance in the front direction cannot be maintained. For this reason, the number of sides other than the base 3a is preferably 14 or less.

  In the above description, the prism sheet 1 has a configuration indicated by a locus when the cross section shown in FIG. 1 is moved in a specific direction. However, the configuration is not limited thereto. For example, the prism 3 shown in FIG. 1 may be a polyhedron indicated by a locus when the section is rotated about the axis A, and the prism 3 may be arranged in a matrix on one side of the substrate 2. In this case, the size of the prism 3 in plan view is the same as or smaller than a liquid crystal display element or one color filter for displaying one pixel of the liquid crystal display device on which the prism sheet 1 is mounted, that is, 5 μm to About 1000 μm is preferable. The arrangement pitch of the prisms 3 may be regular or irregular.

  When the prism sheet 1 having the above-described configuration is mounted on the liquid crystal display device with the prism 3 facing the outside and mounted on the liquid crystal display device, the light utilization efficiency can be further improved.

  In the above description, the polygonal shape of the prism 3 is a line-symmetric shape with the straight line A passing through the midpoint of the base 3a and perpendicular to the base 3a as an axis, but it may be asymmetric. For example, the prism 3 may be inclined toward the center of the screen around the screen when the prism sheet is mounted on the display device.

The schematic sectional drawing of the prism sheet for demonstrating embodiment of this invention The figure which shows the luminous intensity characteristic of the prism sheet The figure which shows the luminous intensity characteristic of the prism sheet Schematic sectional view of a conventional prism sheet

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Prism sheet 2 Transparent substrate 3 Prism 3a Base 3b-3e Side A Axis

Claims (4)

A prism sheet having a large number of prisms arranged on a substrate,
The cross-sectional shape when the prism is viewed from a specific direction is a polygonal shape including a bottom side constituting the bottom surface of the prism and six or more sides,
The polygonal shape is a line-symmetric shape with a straight line passing through the midpoint of the base and perpendicular to the base as an axis,
The six or more sides are sides where two sides, one at each end, are in contact with each other, and an angle formed by the axis is smaller than an angle formed by each of the two sides and the axis. There is no side that is present and has two sides in contact with each other at both ends, and the angle between the two axes is greater than the angle between each of the two sides and the axis. Prism sheet designed for. The prism sheet according to claim 1,
A prism sheet in which the plurality of prisms are arranged in a matrix on the substrate. The prism sheet according to claim 1,
The prism is a polygonal column extending in the specific direction,
A prism sheet in which a large number of the prisms in a polygonal column are arranged in a direction orthogonal to the specific direction. The prism sheet according to any one of claims 1 to 3,
A prism sheet in which an array pitch of the plurality of prisms is irregular.

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