WO2007074936A1 - Prism sheet - Google Patents

Prism sheet Download PDF

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Publication number
WO2007074936A1
WO2007074936A1 PCT/JP2006/326362 JP2006326362W WO2007074936A1 WO 2007074936 A1 WO2007074936 A1 WO 2007074936A1 JP 2006326362 W JP2006326362 W JP 2006326362W WO 2007074936 A1 WO2007074936 A1 WO 2007074936A1
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WO
WIPO (PCT)
Prior art keywords
prisms
sides
prism sheet
axis
luminance
Prior art date
Application number
PCT/JP2006/326362
Other languages
French (fr)
Inventor
Kimitoshi Nagao
Original Assignee
Fujifilm Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to JP2005375761A priority Critical patent/JP2007178628A/en
Priority to JP2005-375761 priority
Priority to JP2005-375762 priority
Priority to JP2005375762 priority
Application filed by Fujifilm Corporation filed Critical Fujifilm Corporation
Publication of WO2007074936A1 publication Critical patent/WO2007074936A1/en

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Classifications

    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B5/00Optical elements other than lenses
    • G02B5/04Prisms
    • G02B5/045Prism arrays

Abstract

A prism sheet including a plurality of prisms arranged on a substrate, wherein each of the prisms has a shape of a cross-section, which is observed from a specific direction, being a polygon, the polygon includes a base of a bottom surface of each of the prisms and five or more sides, and is axisymmetrical with respect to a straight line serving as an axis that passes through a midpoint of the base and that is perpendicular to the base, and the five or more sides are designed so that in a case where a given one of the five or more sides is more distant from the base than another of the five or more sides, an angle formed by the axis and the given one of the five or more sides is larger than an angle formed by the axis and the another of the five or more sides.

Description

DESCRIPTION

PRISM SHEET

Technical Field

The present invention relates to a prism sheet for use in a flat display panel used in a flat-screen television, a portable telephone, a digital camera, a car navigation system, a computer, a PDA, a cash dispensing terminal, or the like, to enhance luminance .

Background Art

Generally, in a display apparatus, such as a liquid crystal display apparatus, using a backlight, a prism sheet is provided on a light guide plate, which guides light from the backlight to

5 a display screen, to enhance display luminance. Consider a member configured by arranging a large number of semicylindrical prisms on a transparent substrate as the prism sheet. Let θp denote an observation angle, at which the prism sheet is observed, with respect to a direction (0°) perpendicular to the transparent

1O substrate in the prism sheet of such a configuration. A curve a shown in FIG.4 represents a luminance characteristic that indicates the luminance detected at each observation angle θp when light is incident from a transparent substrate side, and that is obtained by simulation. A curve e_ shown in FIG. 4 represents a luminance

!5 characteristic in a case where the prism sheet is constituted only by the transparent substrate. In most cases, the screen of the display apparatus is observed from the front thereof. Thus, it is demanded to enhance luminance in a direction of the front thereof. As indicated by the curve a shown in FIG. 4, according to the prism sheet in which the semicylindrical prisms are arranged, the luminance in the direction of the front of the screen can be enhanced.

A prism sheet constituted by arranging a large number of triangular prisms, the apex angle of the transversal cross-section of each of which is 90°, on a transparent substrate 20, as shown in FIG. 7, is known as the prism sheet configured to further enhance the luminance in the direction of the front thereof (see, for example, JP-A-2003-270633 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") ) . Let θp denote an observation angle, at which the prism sheet 10 is observed, with respect to a direction (0°) perpendicular to the transparent substrate 20 in the prism sheet of such a configuration. A curve b shown in FIG. 4 represents a luminance characteristic that indicates the luminance detected at each observation angle θp when light is incident from the side of the transparent substrate 20, and that is obtained by simulation.

As is seen from the curve b, the luminance in the direction of the front of the screen in the case of the prism sheet of FIG. 7 is higher than that represented by the curve a. However, in a case where the angle θp is in the vicinity of ±45°, whose absolute value is half the apex angle of the prism 30, the luminance is substantially 0. It is known that in the case of the triangular prism, almost no light is outputted in the direction corresponding to a half the apex angle thereof. Disclosure of the Invention

A prism sheet constituted by prisms, the shape of a cross-section of each of which is that of a part between troughs of a sine curve, is known as the prism sheet configured to further enhance the luminance in an oblique direction. The luminance characteristic of such a prism sheet is similar to that represented by the curve a shown in FIG. 4.

Thus, a prism sheet enabled to achieve both enhancement of luminance in a font direction thereof and that of luminance in an oblique direction has been demanded. In the case of the prism sheet having the luminance characteristic represented by the curve b shown in FIG. 4, the luminance in the oblique direction corresponding to an angle of 45° is almost 0. Thus, although the luminance in the front direction is sufficient, the angle of view is small.

Although a sufficient luminance in the oblique direction can be assured by using the prism sheet constituted by arranging a large number of semicylindrical prisms, the luminance in the front direction is considerably reduced in this case, as compared with the case of using the triangular prisms.

To increase an angle of view, a display apparatus is demanded to enhance the luminance in the case of viewing the screen from an oblique direction, in addition to the luminance in the case of viewing the screen from the front direction thereof. The invention is accomplished in view of the above circumstances. An object of the invention is to provide a prism sheet enabled to obtain effects in satisfactorily enhancing luminance .

(1) According to a first aspect of the present invention/ a prism sheet comprising a plurality of prisms arranged on a substrate, wherein each of the prisms has a shape of a cross-section, which is observed from a specific direction, being a polygon, the polygon includes a base of a bottom surface of each of the prisms and five or more sides, and is axisymmetrical with respect to a straight line serving as an axis that passes through a midpoint of the base and that is perpendicular to the base, and the five or more sides are designed so that in a case where a given one of the five or more sides is more distant from the base than another of the five or more sides, an angle formed by the axis and the given one of the five or more sides is larger than an angle formed by the axis and the another of the five or more sides. (2) The prism sheet according to the item (1), wherein the plurality of the prisms are arranged in a matrix on the substrate.

(3) The prism sheet according to the item (1), wherein each of the prisms is a' polygonal prism extending in the specific direction, and a plurality of the polygonal prisms are arranged in a direction perpendicular to the specific direction.

(4) The prism sheet according to any one of the items (1) to (3) , wherein the plurality of prisms have a pitch of arrangement being irregular.

(5) According to a second aspect of the present invention, a prism sheet comprising a plurality of prisms arranged on a substrate, wherein each of the prisms has a shape of a cross-section, which is observed from a specific direction, being a polygon, the polygon includes a base of a bottom surface of each of the prisms and five or more sides, and is axisymmetrical with respect to a straight line serving as an axis that passes through a midpoint of the base and that is perpendicular to the base, the six or more sides are designed so that one of the six or more sides satisfies both the conditions that the one side is in contact with other two of the six or more sides at both ends thereof, respectively, and that an angle formed between the axis and the one side is smaller than an angle formed between the axis and each of the other two of the six or more sides, and the six or more sides are also designed so that none of the six or more sides satisfies both conditions that the one side is in contact with other two of the six or more sides at both ends thereof, respectively, and that an angle formed between the axis and the side is larger than an angle formed between the axis and each of the other two of the six or more sides.

(6) The prism sheet according to the item (5), wherein the plurality of the prisms are arranged in a matrix on the substrate.

(7) The prism sheet according to the item (5), wherein each of the prisms is a polygonal prism extending in the specific direction, and a plurality of the polygonal prisms are arranged in a direction perpendicular to the specific direction.

(8) The prism sheet according to any one of the items (5) to (7) , wherein the plurality of prisms have a pitch of arrangement being irregular . The invention can provide a prism sheet enabled to obtain effects in satisfactorily enhancing luminance. Brief Description of the Drawings

The invention disclosed herein will be understood better with reference to the following drawings of which:

FIG. 1 is a schematic cross-sectional view of a prism sheet, which illustrates a first embodiment of the invention;

FIGS. 2A and 2B are graphs respectively illustrating luminance characteristics of a conventional prism sheet and the prism sheet according to the first embodiment of the invention; FIG. 3 is a graph illustrating a luminance characteristic of the prism sheet according to first embodiment of the invention FIG. 4 is a schematic cross-sectional view of a prism sheet, which illustrates a second embodiment of the invention;

FIGS. 5A and 5B are graphs respectively illustrating luminance characteristics of a conventional prism sheet and the prism sheet according to the second embodiment of the invention;

FIG. 6 is a graph illustrating a luminance characteristic of the prism sheet according to the second embodiment of the invention; and

FIG. 7 is a schematic cross-sectional view of a conventional prism sheet.

Best Mode for Carrying Out the Invention

(First embodiment)

Hereinafter, a first embodiment of the invention is described with reference to the accompanying drawings.

FIG. 1 is a partial schematic cross-sectional view of a prism sheet, which illustrates an embodiment of the invention. The prism sheet for exemplifying the embodiment of the invention has a configuration represented by a locus of a cross-section shown in FIG. 1, which is obtained by moving the cross-section in a direction (hereunder referred to as a specific direction) perpendicular to paper on which FIG. 1 is drawn. The prism sheet shown in FIG. 1 has a substrate 2, such as a transparent substrate or a film substrate, which is made of a plastic material, and a large number of prisms 3 on one side of the substrate 2.

The prisms 3 are polygonal prisms extending in the specific direction. A large number of the prisms 3 are arrange in a direction perpendicular to the specific direction. The length in the specific direction of each of the prisms 3 is equal to, for example, the length from one end pixel to the other end pixel of display pixels arranged in the longitudinal direction of a screen of a liquid crystal display apparatus, on which the prism sheet 1 is mounted. The number, of prisms 3 is equal to, for example, to the number of display pixels arranged in a lateral direction of the screen of the liquid crystal display apparatus, on which the prism sheet 1 is mounted. The pitch of arrangement of the prisms 3 may be either regular or irregular. In a case where the pitch of arrangement of the prisms 3 is set to be irregular, the generation of moire due to the arrangement of color filters placed above the prism sheet 1 and to the arrangement of the prisms 3 can be inhibited.

Preferably, the length in the specific direction of each of the prisms 3 is equal to or less than a liquid crystal display device displaying one pixel or one color filter on the screen of the liquid crystal display apparatus, on which the prism sheet 1 is mounted. That is, preferably, the length in the specific direction of each of the prisms 3 ranges from 5 μm to 1000 μm.

The shape of a cross-section of each of the prisms 3, which is observed from the specific direction, is a polygon including a base 3a of the bottom surface thereof and six or more sides 3b to 3g. This polygon is axisymmetrical with respect to a straight line A serving as an axis that passes through the midpoint of the base 3a and that is perpendicular to the base 3a. An angle formed between the axis A and each of the sides 3b and 3e is 30°. An angle formed between the axis A and each of the sides 3c and 3f is 45°. An angle formed between the axis A and each of the sides 3d and

3g is 60°.

Thus, as indicated by dashed lines at the leftmost prism 3, as viewed in FIG. 1, the sides 3b and 3e constitute a part of a prism having a triangular cross-section whose apex angle is 60°. The sides 3c and 3f constitute a part of a prism having a triangular cross-section whose apex angle is 90°. The sides 3d and 3g constitute a part of a prism having a triangular cross-section whose apex angle is 120°. Consequently, the characteristics of the three prisms respectively having the triangular cross-section whose apex angle is 60°, the triangular cross-section whose apex angle is 90°, and the triangular cross-section whose apex angle is 120° can be imparted to each of the prisms 3.

The six sides 3b to 3g are designed so that in a case where a given one of the six or more sides is more distant from the base 3a than another of the six or more sides, an angle formed by the axis A and the given one of the six or more sides is larger than an angle formed by the axis A and the another of the six or more sides. This is with the purpose of approximating the shape of a cross-section of each of the prisms 3, which is observed from the specific direction, to a semicircle. A characteristic equivalent to the characteristic of the prism, the shape of a cross-section of which is a semicircle, can be imparted to each of the prisms 3 by approximating the shape of a cross-section of each of the prisms

3, which is observed from the specific direction, to a semicircle.

Preferably, an angle formed between the axis A and each of the sides 3b and 3e, which are closest to the base 3a among the six sides 3b to 3g, is equal to or more than 30°. Also, preferably, an angle formed between the axis A and each of the sides 3d and 3g, which are furthest from the base 3a among the six sides 3b to 3g, is equal to or less than 90°, more preferably, 85°.

Let θp denote an observation angle, at which the prism sheet 1 is observed, with respect to a direction (0°) perpendicular to the substrate 2. A curve c shown in FIG. 3 represents a luminance characteristic indicating the luminance detected at each observation angle θp, which is obtained by simulation, in a case where light is incident from the side of the substrate 2, and where the angle θp is set to a direction perpendicular to the specific direction.

The prism having the triangular cross-section, whose apex angle is 90°, has a luminance characteristic as indicated by the curve b shown in FIG. 3. The prism having the triangular cross-section, whose apex angle is 60°, and the prism having the triangular cross-section, whose apex angle is 120°, have characteristics obtained by shifting the angles θp, at which the luminance is substantially 0 according to the characteristic represented by the curve b, to angles close to +30° and ±60°, respectively. The characteristic of each of the prisms 3 is obtained by multiplying the characteristics of the three prism having the triangular cross-sections by certain weighting coefficients, respectively, and adding up the weighted characteristics. Thus, as indicated by the curve c, the luminance is not 0 at the angles θp other than ±90°. Consequently, in the case of using the prisms 3, the luminance in the oblique direction can be enhanced, as compared with the case of using the prisms having the characteristic represented by the curve b. Additionally, each of the prisms 3 has the characteristics of the three prisms having the triangular cross-sections. Thus, as illustrated in FIG. 3, in the case of using the prisms 3, the luminance in the front direction can be enhanced, as compared with the case of using the prisms having the characteristic represented by the curve a. FIG. 2A illustrates a luminance characteristic representing a luminance that is detected at each observation angle θp, at which the prism sheet 10 having a configuration shown in FIG.7 is observed, with respect to a direction (0°) perpendicular to the substrate 20 and that is obtained by simulation, in a case where light is incident from the side of the substrate 20, and where the angle θp is set to the specific direction. FIG. 2B illustrates a luminance characteristic representing a luminance that is detected at each observation angle θp, at which the prism sheet 1 is observed, with respect to a direction (0°) perpendicular to the substrate 2 and that is obtained by simulation, in a case where light is incident from the side of the substrate 2, and where the angle θp is set to the specific direction. As is seen from FIGS. 2A and 2B, even when the prism sheet is observed in the specific direction, in the case of using the prism sheet 1, the luminance in the oblique direction is high, as compared with the case of using the prism sheet 10.

Thus, the prism sheet 1 is designed so that each of the prisms

3 has the characteristics of a plurality of prisms respectively having cross-sections whose apex angles differ from one another, and that the shape of the cross-section of the entire prism sheet 1 is approximated to a semicircle. Consequently, the prism sheet 1 has advantages of both the prism having a triangular cross-section and the prism having a semicircular cross-section. Thus, the prism sheet 1 can achieve both the enhancement of the luminance in the front direction and that of the luminance in the oblique direction.

Incidentally, in the foregoing description, it has been described that the shape of the cross-section of each of the prisms

3 is a polygon including the base 3a and the six sides 3b to 3g. However, the shape of the cross-section of each of the prisms 3 is not limited thereto. To impart the characteristics of a plurality of prisms having cross-sections, whose apex angles differ from one another, to each of the prisms 3, it is sufficient that the shape of the cross-section of each of the prisms 3 is a polygon including the base 3a and five or more sides. For example, each of the prisms may be configured so that a side extending in parallel to the substrate 2 is provided between the sides 3d and 3g of each of the prisms 3 shown in FIG. 1. A curve d shown in FIG. 1 represents a luminance characteristic of the prism of such a configuration. As is seen from FIG. 4, according to the characteristic represented by the curve d, the luminance in the oblique direction is high, as compared with the case of the characteristic represented by the curve b. Also, according to the characteristic represented by the curve d, the luminance in the front direction is high, as compared with the case of the characteristic represented by the curve a. Also, in a case where the prism sheet is designed so that the shape of a cross-section of each of the prisms 3 is a polygon including the base 3a and thirteen or more sides, and that the angular conditions are satisfied, the shape of the cross-section of each of the prisms 3 is too close to a semicircle. Thus, the luminance in the front direction cannot be maintained. Consequently, preferably, the number of sides other than the base 3a is equal to or less than twelve.

Also, in the foregoing description, it has been described that the prism sheet 1 has the configuration represented by the locus of the cross-section shown in FIG. 1, which is obtained by moving the cross-section in the specific direction. However, the configuration of the prism sheet 1 is not limited thereto. For example, the prism sheet may be configured by setting the shape of the cross-section of each of the prisms 3 shown in FIG. 1 to be a polygon, which is represented by a locus obtained when rotating the cross-section thereof around the axis A, and by then arranging the prisms 3 like a matrix on one side of the substrate 2. In this case, the size in plan view of each of the prisms 3 is equal to or less than a liquid crystal display device displaying one pixel or one color filter on the screen of the liquid crystal display apparatus, on which the prism sheet 1 is mounted. That is, preferably, the size in plan view of each of the prisms 3 ranges from 5 μm to 1000 μm. Also, the pitch of arrangement of the prisms 3 may be either regular or irregular.

In a case where the prism sheet 1 having the aforementioned configuration is mounted on a liquid crystal display apparatus by placing the prisms 3 opposite to liquid crystals by being outwardly directed, light utilization efficiency can be further enhanced.

Incidentally, in the foregoing description, it has been

5 described that the polygon, which is the shape of the cross-section of each of the prisms 3, is axisymmetrical with respect to a straight line A serving as an axis that passes through the midpoint of the base 3a and that is perpendicular to the base 3a. However, the polygon may be asymmetrical. For example, in a peripheral portion

0 of the screen when the prism sheet is mounted in the display apparatus, each of the prisms 3 may be inclined toward the center of the screen.

(Second embodiment)

Hereinafter, a second embodiment of the invention is 5 described with reference to the accompanying drawings.

With reference to the second embodiment, in which parts similar to those previously described with reference to the first embodiment are denoted by the same reference numerals.

The shape of a cross-section of each of the prisms 3', which 1O is observed from the specific direction, is a polygon including a base 3a' of the bottom surface thereof and six or more sides 3b' to 3g' . This polygon is axisymmetrical with respect to a straight line A serving as an axis that passes through the midpoint of the base 3a' and that is perpendicular to the base 3a' . An angle formed '5 between the axis A and each of the sides 3b' and 3e' is 60°. An angle formed between the axis A and each of the sides 3c' and 3f' is 30°. An angle formed between the axis A and each of the sides 3d' and 3g' is 45°. Thus, as indicated by dashed lines at the leftmost prism 3' , as viewed in FIG. 3, the sides 3b' and 3e' constitute a part of a prism having a triangular cross-section whose apex angle is 120°. The sides 3c' and 3f' constitute a part of a prism having a triangular cross-section whose apex angle is 60°. The sides 3d' and 3g' constitute a part of a prism having a triangular cross-section whose apex angle is 90°. Consequently, the characteristics of the three prisms respectively having the triangular cross-section whose apex angle is 60°, the triangular cross-section whose apex angle is 90°, and the triangular cross-section whose apex angle is 120° can be imparted to each of the prisms 3' .

The six sides 3b' to 3g' are designed so that in the cross-section shown in FIG. 4, one of the six sides satisfies both the conditions that the one side is in contact with other two of the six sides at both ends thereof, respectively, and that an angle formed between the axis A and the one side (in the case shown in FIG. 4, the side 3c' or 3f' ) is smaller than an angle formed between the axis A and each of the other two of the six sides. The six sides 3b' to 3g' are also designed so that none of the six or more sides satisfies both the conditions that a side is in contact with other two of the six sides at both ends thereof, respectively, and that an angle formed between the axis A and the side is larger than an angle formed between the axis A and each of the other two of the six sides. This is with the purpose of approximating the shape of a cross-section of each of the prisms 3' , which is observed from the specific direction, to the shape of a part between troughs of a sine curve. A characteristic equivalent to the characteristic of the prism, the shape of a cross-section of which is a semicircle, can be imparted to each of the prisms 3' by approximating the shape of a cross-section of each of the prisms 3' , which is observed from the specific direction, to the shape of the part between the troughs of a sine curve. Preferably, an angle formed between the axis A and each of the sides 3b' and 3e' , among the six sides 3b' to 3g' , ranges from 50° to 85°. Also, preferably, an angle formed between the axis A and each of the sides 3c' and 3f ranges from 20° to 40°. Also, preferably, an angle formed between the axis A and each of the sides 3d' and 3g' ranges from 41° to 85°.

Let θp denote an observation angle, at which the prism sheet 1 is observed, with respect to a direction (0°) perpendicular to the substrate 2. A curve c/_ shown in FIG. 6 represents a luminance characteristic indicating the luminance detected at each observation angle θp, which is obtained by simulation, in a case where light is incident from the side of the substrate 2, and where the angle θp is set to a direction perpendicular to the specific direction.

The prism having the triangular cross-section, whose apex angle is 90°, has a luminance characteristic as indicated by the curve k/_ shown in FIG. 6. The prism having the triangular cross-section, whose apex angle is 60°, and the prism having the triangular cross-section, whose apex angle is 120°, have characteristics obtained by shifting the angles θp, at which the luminance is substantially 0 according to the characteristic represented by the curve k/_, to angles close to ±30° and ±60°, respectively. The characteristic of each of the prisms 3' is obtained by multiplying the characteristics of the three prisms having the triangular cross-sections by certain weighting coefficients, respectively, and adding up the weighted characteristics. Thus, as indicated by the curve cj_, the luminance is not 0 at the angles θp other than ±90°. Consequently, in the case of using the prisms 3' , the luminance in the oblique direction can be enhanced, as compared with the case of using the prisms having the characteristic represented by the curve fc/_. Additionally, each of the prisms 3' has the characteristics of the prisms having the triangular cross-section. Thus, in the case of using the prisms 3' , the luminance in the front direction can be enhanced, as compared with the case of using the prisms having the characteristic represented by the curve a/_, which is close to the luminance characteristic of the prism having the cross-section shaped like a sinusoidal wave. FIG. 5A illustrates a luminance characteristic representing a luminance that is detected at each observation angle θp, at which the prism sheet 10 having a configuration shown in FIG. 7 is observed, with respect to a direction (0°) perpendicular to the substrate 20 and that is obtained by simulation, in a case where light is incident from the side of the substrate 20, and where the angle θp is set to the specific direction. FIG. 5B illustrates a luminance characteristic representing a luminance that is detected at each observation angle θp, at which the prism sheet 1' is observed, with respect to a direction (0°) perpendicular to the substrate 2 and that is obtained by simulation, in a case where light is incident from the side of the substrate 2, and where the angle θp is set to the specific direction. As is seen from FIGS. 5A and 5B, even when the prism sheet is observed in the specific direction, in the case of using the prism sheet 1' , the luminance in the oblique direction is high, as compared with the case of using the prism sheet 10. Thus, the prism sheet 1' is designed so that each of the prisms 3' has the characteristics of a plurality of prisms respectively having cross-sections whose apex angles differ from one another, and that the shape of the cross-section of the entire prism sheet 1' is approximated to a shape like sinusoidal wave. Consequently, the prism sheet 1' has advantages of both the prism having a triangular cross-section and the prism having a cross-section shaped like a sinusoidal wave. Thus, the prism sheet 1' can achieve both the enhancement of the luminance in the front direction and that of the luminance in the oblique direction.

Incidentally, in the foregoing description, it has been described that the shape of the cross-section of each of the prisms 3' is a polygon including the base 3a' and the six sides 3b' to 3g' . However, the shape of the cross-section of each of the prisms 3' is not limited thereto. To satisfy the design conditions, it is sufficient that the shape of the cross-section of each of the prisms 3' is a polygon including the base 3a' and six or more sides . For example, each of the prisms may be configured so that a side extending in parallel to the substrate 2 is provided between the sides 3d' and 3g' of each of the prisms 3' shown in FIG. 4. A curve d' shown in FIG. 4 represents a luminance characteristic of the prism of such a configuration. According to the characteristic represented by the curve d/_, the luminance in the oblique direction is high, as compared with the case of the characteristic represented by the curve h/_. Also, according to the characteristic represented by the curve d/_, the luminance in the front direction is high, as compared with the case of the characteristic represented by the curve a/_. Also, as long as the design conditions are met, any number equal to or more than six can be employed as the number of sides other than the base 3a' . However, in a case where the number of

5 sides other than the base 3a' exceeds fourteen, the shape of the cross-section of each of the prisms 3' is too close to the shape of the part between troughs of a sine curve. Thus, the luminance in the front direction cannot be maintained. Consequently, preferably, the number of sides other than the base 3a' is equal

0 to or less than fourteen.

Also, in the foregoing description, it has been described that the prism sheet 1' has the configuration represented by the locus of the cross-section shown in FIG. 4, which is obtained by moving the cross-section in the specific direction. However, the

5 configuration of the prism sheet 1' is not limited thereto. For example, the prism sheet may be configured by setting the shape of the cross-section of each of the prisms 3' shown in FIG. 4 to be a polygon, which is represented by a locus obtained when rotating the cross-section thereof around the axis A, and by then arranging

!0 the prisms 3' like a matrix on one side of the substrate 2. In this case, the size in plan view of each of the prisms 3' is equal to or less than a liquid crystal display device displaying one pixel or one color filter on the screen of the liquid crystal display apparatus, on which the prism sheet 1' is mounted. That is,

'5 preferably, the size in plan view of each of the prisms 3' ranges from 5 μm to 1000 μm. Also, the pitch of arrangement of the prisms 3' may be either regular or irregular.

In a case where the prism sheet 1' having the aforementioned configuration is mounted on a liquid crystal display apparatus by placing the prisms 3' opposite to liquid crystals by being outwardly directed, light utilization efficiency can be further enhanced.

Incidentally, in the foregoing description, it has been described that the polygon, which is the shape of the cross-section of each of the prisms 3' , is axisymmetrical with respect to a straight line A serving as an axis that passes through the midpoint of the base 3a' and that is perpendicular to the base 3a' . However, the polygon may be asymmetrical. For example, in a peripheral portion of the screen when the prism sheet is mounted in the display apparatus, each of the prisms 3' may be inclined toward the center of the screen.

The present application claims foreign priority based on Japanese Patent Application (JP 2005-375761) filed December 27 of 2005, Japanese Patent Application ( JP 2005-375762) filed December 27 of 2005, the contents of which is incorporated herein by reference .

Claims

1. A prism sheet comprising a plurality of prisms arranged on a substrate,
wherein each of the prisms has a shape of a cross-section, which is observed from a specific direction, being a polygon, the polygon includes a base of a bottom surface of each of the prisms and five or more sides, and is axisymmetrical with respect to a straight line serving as an axis that passes through a midpoint of the base and that is perpendicular to the base, and the five or more sides are designed so that in a case where a given one of the five or more sides is more distant from the base than another of the five or more sides, an angle formed by the axis and the given one of the five or more sides is larger than an angle formed by the axis and the another of the five or more sides.
2. The prism sheet according to claim 1, wherein the plurality of the prisms are arranged in a matrix on the substrate.
3. The prism sheet according to claim 1, wherein each of the prisms is a polygonal prism extending in the specific direction, and a plurality of the polygonal prisms are arranged in a direction perpendicular to the specific direction.
4. The prism sheet according to claim 1, wherein the plurality of prisms have a pitch of arrangement being irregular.
5. A prism sheet comprising a plurality of prisms arranged on a substrate, wherein each of the prisms has a shape of a cross-section, which is observed from a specific direction, being a polygon, the polygon includes a base of a bottom surface of each of "the prisms and five or more sides, and is axisymmetrical with respect to a straight line serving as an axis that passes through a midpoint of the base and that is perpendicular to the base, the six or more sides are designed so that one of the six or more sides satisfies both the conditions that the one side is in contact with other two of the six or more sides at both ends thereof, respectively, and that an angle formed between the axis and the one side is smaller than an angle formed between the axis and each of the other two of the six or more sides, and the six or more sides are also designed so that none of the six or more sides satisfies both conditions that the one side is in contact with other two of the six or more sides at both ends thereof, respectively, and that an angle formed between the axis and the side is larger than an angle formed between the axis and each of the other two of the six or more sides.
6. The prism sheet according to claim 5, wherein the plurality of the prisms are arranged in a matrix on the substrate.
7. The prism sheet according to claim 5, wherein each of the prisms is a polygonal prism extending in the specific direction, and a plurality of the polygonal prisms are arranged in a direction perpendicular to the specific direction.
8. The prism sheet according to claim 5, wherein the plurality of prisms have a pitch of arrangement being irregular.
PCT/JP2006/326362 2005-12-27 2006-12-27 Prism sheet WO2007074936A1 (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
JP2005375761A JP2007178628A (en) 2005-12-27 2005-12-27 Prism sheet
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EP2045517A3 (en) * 2007-10-03 2011-10-26 Rohm and Haas Denmark Finance A/S Turning film having multiple slopes

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JPH07230002A (en) * 1994-02-17 1995-08-29 Mitsubishi Rayon Co Ltd Luminance improved transparent sheet
JP2000231103A (en) * 1999-02-09 2000-08-22 Mitsubishi Rayon Co Ltd Lens sheet and back light and liquid crystal display device using the same
JP2002287256A (en) * 2001-03-27 2002-10-03 Mitsubishi Rayon Co Ltd Both-side lenticular lens sheet
JP2003140126A (en) * 2001-10-31 2003-05-14 Hitachi Ltd Liquid crystal display device
JP2004070309A (en) * 2002-06-12 2004-03-04 Samsung Electronics Co Ltd Prism sheet and liquid crystal display unit with same
WO2004019082A1 (en) * 2002-06-24 2004-03-04 Mitsubishi Rayon Co., Ltd. Light source device and light polarizing element
JP2004094051A (en) * 2002-09-02 2004-03-25 Keiwa Inc Optical sheet and back light unit using the sheet

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JPH07230002A (en) * 1994-02-17 1995-08-29 Mitsubishi Rayon Co Ltd Luminance improved transparent sheet
JP2000231103A (en) * 1999-02-09 2000-08-22 Mitsubishi Rayon Co Ltd Lens sheet and back light and liquid crystal display device using the same
JP2002287256A (en) * 2001-03-27 2002-10-03 Mitsubishi Rayon Co Ltd Both-side lenticular lens sheet
JP2003140126A (en) * 2001-10-31 2003-05-14 Hitachi Ltd Liquid crystal display device
JP2004070309A (en) * 2002-06-12 2004-03-04 Samsung Electronics Co Ltd Prism sheet and liquid crystal display unit with same
WO2004019082A1 (en) * 2002-06-24 2004-03-04 Mitsubishi Rayon Co., Ltd. Light source device and light polarizing element
JP2004094051A (en) * 2002-09-02 2004-03-25 Keiwa Inc Optical sheet and back light unit using the sheet

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2045517A3 (en) * 2007-10-03 2011-10-26 Rohm and Haas Denmark Finance A/S Turning film having multiple slopes

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