WO2013062030A1

WO2013062030A1 - Optical sheet, surface light source device, and transmissive image display device

Info

Publication number: WO2013062030A1
Application number: PCT/JP2012/077547
Authority: WO
Inventors: 尚規奥
Original assignee: 住友化学株式会社
Priority date: 2011-10-27
Filing date: 2012-10-25
Publication date: 2013-05-02
Also published as: JP2013110094A; CN103890482A; TW201323950A; KR20140091685A; TWI615642B

Abstract

An optical sheet (30) formed by a translucent resin is provided with: a side surface (33) which serves as an entry surface where light transmitted from point-like light sources (22) enters; and an exit surface (31), which is formed in a direction that intersects with the side surface (33), from which planar light exits. Convex sections (35), which extend in the thickness direction of the sheet, are positioned side-by-side on the side surface (33) in the longitudinal direction (Y) of the side surface (33). If the length, in the longitudinal direction of the side surface (33), of a light-emitting region of a point-like light source is denoted as W, the positioning interval (P), in the longitudinal direction of the side surface (33), of the convex sections (35) is set to 0.34W.

Description

Optical sheet, surface light source device, and transmissive image display device

The present invention includes an optical sheet capable of emitting light incident from a plurality of discretely arranged point light sources in a planar shape, a surface light source device including the optical sheet, and the surface light source device. The present invention relates to a transmissive image display device.

As a direct type image display device which is an example of a transmissive image display device, a device in which a light source is disposed on the back side of a transmissive image display unit is widely used. Examples of the transmissive image display unit include a liquid crystal display panel in which linear polarizing plates are arranged on both surfaces of a liquid crystal cell. As the light source, a plurality of linear light sources such as a straight tube type cold cathode ray tube are arranged and used in parallel with each other.

In such a direct-type image display device, it is desirable that the light from the light source can be uniformly dispersed to uniformly illuminate the transmissive image display unit. Therefore, a light control plate, which is a single light diffusion plate, is disposed between the light source and the transmissive image display unit. The light control plate has a function of changing the direction of light incident from the light source side and emitting the light from the opposite transmissive image display unit side. (For example, refer to Patent Document 1).

In recent years, transmissive image display devices have been made thinner, surface light source devices in which light sources are arranged on the end side have been developed, and a light guide plate for spreading light emitted from the end portions over the entire screen has been developed in the past. It is starting to be used in place of the light diffusing plate. In addition, as an environmental measure, light emitting diodes (LEDs) are increasingly used as light sources that do not contain mercury (Hg) and have low power consumption.

The light guide plate is mainly made of highly light transmissive resin. And it is calculated | required by the light-guide plate that the light of LED arrange | positioned at the edge part of a light-guide plate is spread uniformly on the whole screen by the reflection and scattering effect in a light-guide plate.

In addition, as an edge light type planar light source that effectively utilizes the light of the LED light source and has uniform brightness, it is a plate member made of a translucent member, and an irregular reflection portion is formed on the lower surface. A thing provided with the light guide plate whose upper surface is a light-emitting surface is known (for example, refer to patent documents 2). Further, as an edge light type light guide plate, one having an uneven shape that disperses light from an LED light source in a plate thickness direction is formed on an incident surface (see, for example, Patent Document 3).

JP-A-7-198913 JP 2001-342263 A JP 2008-10291 A

However, in the light control plate used in the conventional surface light source device, the light from the point light source cannot be made sufficiently uniform, especially between adjacent light sources near the end of the light control plate, There was a problem that an area with insufficient brightness occurred.

Therefore, the present invention provides an optical sheet that can sufficiently uniformly disperse light from a point light source, and can reduce an area where brightness is insufficient, and a surface provided with the optical sheet. An object of the present invention is to provide a light source device and a transmissive image display device.

Also, when the positional relationship between the point light source and the optical sheet is deviated, the area where the brightness is insufficient may be enlarged. For example, the translucent resin is heated and expanded by the heat generated by the point light source, and as a result, the positional relationship between the point light source and the optical sheet may be shifted, and the area where the brightness is insufficient may be enlarged. . Therefore, there is a demand to suppress the expansion of the area where the brightness is insufficient even when the positional deviation between the point light source and the optical sheet occurs. In addition, since the light incident on the optical sheet is spread by the lens effect, there is a possibility that the light cannot be spread when the focus of the incident light on the lens is deviated. There is also a need to improve this.

The present invention is an optical sheet formed of a translucent resin, and is formed in a side surface serving as an incident surface on which light emitted from a point light source is incident, and in a direction intersecting the side surface. A plurality of light emitting surfaces that extend in the thickness direction of the optical sheet and are arranged side by side in the longitudinal direction of the light incident surface. A convex portion is formed, and the arrangement interval P in the longitudinal direction of the convex portion satisfies the following expression (1).
P ≦ 0.34W (1)
(W is the length in the longitudinal direction of the incident surface of the light emitting region existing on the side of the point light source facing the incident surface of the sheet)

According to the above configuration, the light from the point light source arranged to face the side surface of the optical sheet is incident from the side surface of the optical sheet, and is formed into a planar shape from the emission surface formed in the direction intersecting the side surface. Light is emitted. Moreover, the light incident from the side surface serving as the incident surface of the optical sheet is spread to a wider range in the longitudinal direction of the incident surface of the optical sheet by the convex portion. Thereby, the area | region where the brightness of the edge part (side surface side vicinity) of the entrance plane side of an optical sheet is insufficient in front view can be reduced. In addition, the structure by which all the side surfaces of an optical sheet may become an incident surface may be sufficient, and the structure by which only one side surface among several side surfaces becomes an incident surface may be sufficient.

Further, since the convex portion is formed so that the arrangement interval P satisfies the formula (1), even if the optical sheet is displaced in the longitudinal direction of the incident surface, the optical sheet is The influence of the position shift can be suppressed, and the expansion of the area where the brightness is insufficient can be suppressed.

Here, it is preferable that the convex portion has a prism shape having an apex angle of 50 ° to 150 °. Thereby, the light incident from the incident surface is suitably diffused in the longitudinal direction of the incident surface.

The present invention also includes the optical sheet, and a plurality of point light sources that are opposed to the side surface that is the incident surface of the optical sheet and are discretely arranged in the longitudinal direction of the incident surface. It is the surface light source device characterized by the above.

According to the above configuration, since the optical sheet is provided, the light from the point light source arranged to face the side surface of the optical sheet enters from the side surface of the optical sheet and is formed in a direction intersecting with the side surface. Planar light is emitted from the exit surface. Moreover, the light incident from the side surface serving as the incident surface of the optical sheet is spread to a wider range in the longitudinal direction of the incident surface of the optical sheet by the convex portion. Thereby, the area | region where the brightness of the edge part (side surface side vicinity) of the entrance plane side of an optical sheet is insufficient in front view can be reduced. In addition, the structure by which all the side surfaces of an optical sheet may become an incident surface may be sufficient, and the structure by which only one side surface among several side surfaces becomes an incident surface may be sufficient.

Further, since the convex portion of the optical sheet is formed so that the arrangement interval P satisfies the formula (1), even if the optical sheet is misaligned in the longitudinal direction of the incident surface, the surface The light source device can suppress the expansion of the region where the brightness is insufficient by suppressing the influence of the positional deviation between the point light source and the optical sheet.

Further, as the point light source, an LED light source that exhibits the maximum luminous intensity in the normal direction of the point light source and has a half-value width of the luminous intensity distribution of 40 ° to 80 ° is preferable.

Further, the present invention provides the above-described surface light source device and a transmission type that is disposed to face the emission surface of the surface light source device, and that displays an image by receiving light emitted from the surface light source device. And a transmissive image display device comprising an image display unit.

According to the above configuration, since the surface light source device is provided, the light from the point light source arranged to face the side surface of the optical sheet enters from the side surface of the optical sheet and intersects with the side surface. Planar light is emitted from the formed emission surface. Moreover, the light incident from the side surface serving as the incident surface of the optical sheet is spread to a wider range in the longitudinal direction of the incident surface of the optical sheet by the convex portion. Thereby, the area | region where the brightness of the edge part (side surface side vicinity) of the entrance plane side of an optical sheet is insufficient in front view can be reduced. In addition, the structure by which all the side surfaces of an optical sheet may become an incident surface may be sufficient, and the structure by which only one side surface among several side surfaces becomes an incident surface may be sufficient. According to such a transmissive image display device, the light from the point light source can be sufficiently uniformly dispersed to form planar light, and transmission is performed by the uniformly dispersed planar light. The mold image display unit can be illuminated.

Further, since the convex portion of the optical sheet is formed so that the arrangement interval P satisfies the formula (1), even if the optical sheet is displaced in the longitudinal direction of the incident surface, the optical sheet is transmitted. The type image display device can suppress the influence of the positional deviation between the point light source and the optical sheet, and can suppress the expansion of the region where the brightness is insufficient.

According to the optical sheet of the present invention, the light from the point light source incident from the side surface serving as the incident surface can be sufficiently uniformly dispersed in the longitudinal direction of the side surface serving as the incident surface. The surface light source device and the transmissive image display device of the present invention can also exhibit the same effect.

In addition, the optical sheet, the surface light source device, and the transmissive image display device of the present invention can enlarge an area where the brightness is insufficient even when the positional deviation between the point light source and the optical sheet occurs. Can be suppressed.

It is sectional drawing which shows typically the structure of one Embodiment of the transmissive image display apparatus which concerns on this invention. It is an enlarged plan view which shows the edge part of the light-guide plate in FIG. It is an enlarged view which shows the edge part and LED light source of the light-guide plate in FIG. It is a graph which shows an example of the light emission distribution of a LED light source. It is a top view which shows the edge part and LED light source of the light-guide plate which concern on other embodiment. It is a top view which shows the positional relationship of a prism shape, LED light source, and a luminance value measurement point. It is a figure which shows a brightness | luminance profile when the optical sheet of Example 2 exists in a reference position. It is a figure which shows the brightness | luminance profile when the optical sheet of Example 2 has shifted | deviated 1.0 mm from the reference position. It is a figure which shows a luminance profile in case the optical sheet of the comparative example 2 exists in a reference position. It is a figure which shows the brightness | luminance profile in case the optical sheet of the comparative example 2 has shifted | deviated 1.0 mm from the reference position.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same element or an equivalent element, and the overlapping description is abbreviate | omitted. The dimensional ratios in the drawings do not necessarily match those described.

FIG. 1 is a cross-sectional view schematically showing a configuration of an embodiment of a transmissive image display device according to the present invention. FIG. 1 shows the transmissive image display device 1 in an exploded manner.

(Transparent image display device)
The transmissive image display device 1 includes a transmissive image display unit 10 and a surface light source device 20 disposed on the back side of the transmissive image display unit 10 in FIG. In the following description, as shown in FIG. 1, the arrangement direction of the surface light source device 20 and the transmissive image display unit 10 is referred to as a Z direction (plate thickness direction), which is two directions orthogonal to the Z direction and orthogonal to each other. These two directions are referred to as the X direction and the Y direction.

Examples of the transmissive image display unit 10 include a liquid crystal display panel in which linearly

polarizing plates

12 and 12 are arranged on both surfaces of a liquid crystal cell 11. In this case, the transmissive image display device 1 is a liquid crystal display device (for example, a liquid crystal television). As the liquid crystal cell 11 and the

polarizing plates

12 and 12, those used in the transmissive image display device 1 such as a conventional liquid crystal display device can be used. Examples of the liquid crystal cell 11 include known liquid crystal cells such as TFT type and STN type. The transmissive image display unit 10 is disposed so as to face the emission surface 31 of the surface light source device 20 and displays an image upon receiving irradiation of light emitted from the surface light source device 20.

(Surface light source device)
The surface light source device 20 includes a light guide plate (optical sheet) 30 and an LED light source (point light source) 22 disposed to face the side surface 33 of the light guide plate 30.

(light source)
The LED light source 22 functions as a point light source of the surface light source device 20 and is disposed so as to face the side surfaces 33, 33 extending in the X direction of the light guide plate 30, as shown in FIG. The plurality of LED light sources 22 are discretely arranged along the longitudinal direction (X direction) of the side surface 33. The arrangement interval L of the LED light sources 22 is normally 5 mm to 150 mm. For example, the length W in the X direction of the issue region of the LED light source 22 is about 3.5 mm.

In FIG. 2, the LED light source 22 package is indicated by a one-dot chain line, and the light emitting region 22L of the LED light source 22 is indicated by a solid line. The width W (length in the X direction) of the light emitting region 22L is smaller than the package width PW (length of the outer shape in the X direction) of the LED light source 22. The light emitting area refers to a light emitting area. In FIG. 2, the light emitting region 22 </ b> L of the LED light source 22 is arranged so that the center N in the width direction coincides with the bottom 36 of the recess between the

convex portions

35, 35 of the light guide plate 30. The center N in the width direction of the light guide plate 30 may not coincide with the bottom 36 of the recess between the

convex portions

35, 35.

FIG. 3 is an enlarged view showing an end portion of the light guide plate and the LED light source in FIG. FIG. 3A shows a case viewed from the Z direction. FIG. 3A shows a gap G between the LED light source 22 and the convex portion 35 of the light guide plate 30 in the Z direction. The gap G between the LED light source 22 and the light guide plate 30 is a distance between the tip of the convex portion 35 and the surface of the LED light source 22 on the light guide plate 30 side of the light emitting region 22L.

FIG. 3B shows the LED light source 22 from the Y direction (light guide plate 30 side). In FIG. 3B, the height of the package of the LED light source 22 (the length of the outer shape in the Z direction) is PH, and the height of the light emitting region 22L (the length in the Z direction) is H.

The dimensions of an example of the LED light source 22 are shown in Table 1. Table 1 shows an example of the size of the width W of the light emitting region 22L, the height H of the light emitting region 22L, the width PW of the package, and the height PH of the package of the LED light source 22.

In Table 1, unit 1 is an LED light source manufactured by Nichia Corporation. The unit 2 is an LED light source mounted on a Panasonic television. The 7020 package, the 5030 package, and the 4215 package of the units 3, 4, and 5 are generic names based on the external size. Examples of manufacturers that manufacture LED light sources include SamsungLED, LGInnotek, SeolSemiconductor, Lumens, ToyotaGosei, ChiMei, Lighting, Everlight, Lite-on, and the like.

The width W of the light emitting region 22L of the LED light source 22 is 1.0 to 10.0 mm, preferably 2.0 to 7.0 mm. The height H of the light emitting region 22L of the LED light source 22 is 0.5 to 5.0 mm, preferably 1.0 to 3.0 mm. The height H of the light emitting region 22L is preferably equal to or less than the thickness t of the light guide plate 30. The position of the LED light source 22 in the Z direction is preferably arranged so that the center of the light guide plate 30 in the Z direction coincides with the center of the light emitting region 22L in the Z direction.

The gap G between the LED light source 22 and the light guide plate 30 is 0.0 to 7.0 mm, preferably 0.5 to 3.0 mm.

As the LED light source 22, those having various light emission distributions can be used. However, the light intensity in the normal direction (Y direction) of the LED light source 22 is maximum, and the half width of the light intensity distribution is 40 ° or more and 80 °. What has the light emission distribution which is below is suitable. Specific examples of the LED light source type include a Lambertian type, a shell type, and a side emission type.

FIG. 4 is a graph showing an example of the light emission distribution of the LED light source. FIG. 4 shows the relationship between the emission angle φ and the emission light intensity, assuming that the emission light intensity in the normal direction of the LED light source (emission angle φ = 0 °) is 1.0 (reference). In the LED light source having the light emission distribution shown in FIG. 4, the half width is about 60 °. In addition, you may use the LED light source which has another light emission distribution.

(Light guide plate)
The light guide plate 30 has a rectangular shape when viewed from the plate thickness direction Z. The size of the planar view shape of the light guide plate 30 is selected so as to match the target screen size of the transmissive image display device 10, but is usually 250 mm × 440 mm or more, preferably 1020 mm × 1800 mm or less. The planar view shape of the light guide plate 30 is not limited to a rectangle, but may be a square, but in the following, it will be described as a rectangle unless otherwise specified.

The light guide plate 30 has a plate shape made of a translucent resin that transmits light. The light guide plate 30 may be a sheet or a film.

The light guide plate 30 includes a pair of main surfaces (31, 32) facing in the Z direction (plate thickness direction), a pair of side surfaces 33, 33 facing in the Y direction, and a pair of side surfaces (not shown) facing in the X direction. ) And.

One main surface (31) of the pair of main surfaces facing in the Z direction functions as an emission surface 31 that emits planar light. The emission surface 31 is disposed on the transmissive image display unit 10 side, and the other main surface (back surface 32) is disposed on the opposite side to the transmissive image display unit 10. In addition, a reflection sheet (reflecting plate) that reflects light is applied at a position facing the back surface 32.

(Convex part)
Here, a plurality of convex portions 35 that are convex outward in the Y direction are formed on the side surface 33. The convex portions 35 extend in the thickness direction (Z direction) of the sheet, and a plurality of the convex portions 35 are arranged side by side in the longitudinal direction (X direction) of the side surface 33. The plurality of convex portions 35 are arranged in parallel. The cross-sectional shape along the XY plane of the plurality of convex portions 35 is substantially uniform. The arrangement interval P in the X direction (longitudinal direction of the incident surface) of the convex portions 35 satisfies the following expression (1).
P ≦ 0.3W (1)
(W is the length of the light emitting area of the point light source 22 in the X direction.)

It is preferable that the plurality of convex portions 35 are arranged at intervals P of 0.07 mm or more and 1.0 mm or less in the X direction. In the present embodiment, the arrangement interval P of the convex portions 35 (interval between the bottoms of the concave portions) is, for example, 0.4 mm.

Further, it is preferable that the convex portion 35 has a prism shape as shown in FIG. The angle (vertical angle) θ of the apex of the prism shape is preferably 50 ° or more and 150 ° or less, and more preferably 110 ° or more and 140 ° or less. In the present embodiment, the apex angle θ of the prism shape is 90 °, for example. The plurality of prism shapes have a function of diffusing light from the LED light source 22 in the longitudinal direction (X direction) of the side surface 33.

The light guide plate 30 in which a flat surface is formed between the

convex portions

35 and 35 may be used. FIG. 5 shows a side surface 33 of the light guide plate 30 in which a flat surface 37 is formed between the

convex portions

35 and 35. When such a flat surface 37 is provided, the arrangement interval P of the convex portions 35 is such that the width w _{a in} the X direction of the convex portions 35 and the width w in the X direction of the flat surface 37 are shown in FIG. _It is the sum with _b .

(Construction material of light guide plate)
The light guide plate 30 is made of a translucent resin. The translucent resin is a resin that transmits light. The refractive index of the translucent resin is usually 1.49 to 1.59. As the translucent resin used for the light guide plate 30, methacrylic resin is mainly exemplified.

Examples of the methacrylic resin include monomers having methyl methacrylate as a main component. Specifically, a polymer obtained by polymerizing a monomer containing 50% by mass or more of methyl methacrylate may be used, or Polymethyl metal methyl obtained by polymerizing methyl methacrylate alone may be used, or a copolymer of 50% by mass or more of methyl methacrylate and 50% by mass or less of a monomer copolymerizable therewith may be used.

Examples of monomers copolymerizable with methyl methacrylate include, for example, ethyl methacrylate, propyl methacrylate, butyl methacrylate, benzyl methacrylate, 2-ethylhexyl acrylate, cyclohexyl methacrylate, bornyl methacrylate, adamantyl methacrylate, Methacrylic acid esters such as cyclopentanedienyl methacrylate; methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, bornyl acrylate, adamantyl acrylate Acrylates such as cyclopentadienyl acrylate; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, maleic anhydride, itaconic anhydride And its anhydride: 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl acrylate, acrylic acid, monoglycerol acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, methacryl Hydroxyl group-containing monomers such as acid monoglycerol; nitrogen-containing monomers such as acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, diacetone acrylamide, dimethylaminoethyl methacrylate; allyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate And epoxy group-containing monomers; and styrene monomers such as styrene and α-methylstyrene.

In addition, translucent resin is not limited to the said thing. As the translucent resin, resins other than those described above may be used, and examples thereof include styrene resins, polyethylene resins, polypropylene resins, cyclic olefin polymer resins, acrylonitrile-butadiene-styrene resins, polyethylene terephthalate resins, and polycarbonate resins. .

In applying the light guide plate to a liquid crystal display device, additives such as a light diffusing agent, an ultraviolet absorber, a heat stabilizer, and a photopolymerization stabilizer may be added to the light guide plate.

(Light guide plate forming method)
Examples of the method for forming the light guide plate 30 include extrusion molding, cast molding, and injection molding. The thickness t of the light guide plate is not particularly limited, but is preferably 0.3 mm to 10.0 mm, more preferably 1.5 mm to 8.0 mm, and particularly preferably 2.0 mm to 4.0 mm.

(Formation method of convex part)
As a method for forming the convex portion 35 (uneven shape), a hot press molding method can be applied. The convex part 35 can be formed on the side surface 33 of the light guide plate 30 by performing hot press molding using the opposite mold having a shape paired with the convex part 35 as a plate.

Further, as a method of manufacturing the light guide plate 30 having the convex portion 35, an injection molding method may be applied. In the case of the injection molding method, it is preferable that the inner wall of the injection mold is provided with an opposite mold having a shape paired with the convex portion 35. Further, as a method of forming the convex portion 35, a lens film having the convex portion 35 provided on the surface thereof is prepared, and the surface opposite to the convex portion 35 is bonded to the side surface of the light guide plate 30. It is also suitable to do.

Examples of the convex portion 35 (concave / convex shape) include a lenticular lens shape, a trapezoidal shape, and a rectangular shape in addition to the prism shape described above.

According to such a light guide plate 30 according to this embodiment, light from the plurality of LED light sources 22 arranged to face the side surface 33 of the light guide plate 30 enters from the side surface 33 and is orthogonal to the side surface 33 ( Planar light is emitted from the exit surface 31 that intersects. The light incident from the side surface 33 of the light guide plate 30 is refracted by the convex portion 35 and spread in the X direction. Thereby, the area | region where brightness is insufficient in the edge part (side surface 33 vicinity) of the light-guide plate 30 can be reduced.

Further, according to the surface light source device 20 and the transmissive image display device 1 including the same according to the present embodiment, light from the plurality of LED light sources 22 is incident from the side surface 33, and the emission surface 31 is orthogonal to the side surface 33. From this, planar light is emitted. The light incident from the side surface 33 of the light guide plate 30 is refracted by the convex portion 35 and spread in the X direction. Thereby, the area | region where brightness is insufficient in the edge part (side surface 33 vicinity) of the light-guide plate 30 can be reduced. Therefore, the frame part for concealing the region where the brightness is insufficient at the end of the light guide plate 30 so as not to be seen from the display screen can be reduced. Therefore, the degree of freedom in designing the frame portion that is the peripheral portion of the display screen of the transmissive image display device 1 can be increased.

In the light guide plate 30 of the present embodiment, the convex portion 35 is formed so that the arrangement interval P satisfies the formula (1), P ≦ 0.34W (1), and thus the longitudinal direction of the side surface 33 In this case, even if the light guide plate 30 is misaligned, the influence of the misalignment can be suppressed and the enlargement of the region where the brightness is insufficient can be suppressed.

According to the surface light source device 20 according to the present embodiment, the plurality of convex portions 35 are arranged between the LED light sources 22 adjacent to each other in the longitudinal direction of the side surface 33, so that the space between the LED light source 22 and the light guide plate 30. Even when the positional relationship changes, it is possible to suppress the influence of the positional deviation and to suppress the expansion of the area where the brightness is insufficient. According to the surface light source device 20, it is possible to stably realize an effect of reducing an area where brightness is insufficient.

Hereinafter, an example of the optical sheet of the present invention will be described.

The optical sheet according to the example of the present invention and the optical sheet according to the comparative example were prepared, and an evaluation test was performed on these. In Examples 1 to 7 and Comparative Examples 1 to 3, an optical sheet 30 (optical sheet A) was prepared using Sumipec E011 (trade name, manufactured by Sumitomo Chemical Co., Ltd., PMMA) as a translucent resin. The optical sheet 30 has a thickness of 2 mm, and has a rectangular shape in plan view with a length (short side) of 40 mm and a width (long side) of 100 mm.

A plurality of convex portions 35 extending in the thickness direction (Z direction) are arranged on the side surface 33 on the long side of the optical sheet 30. The plurality of convex portions 35 were arranged side by side in the longitudinal direction (X direction) of the side surface (incident surface) 33. In Examples 1 to 7, the apex angle θ of the convex portion 35 (prism shape) was set to 55 ° and 90 °, respectively. In Examples 1 to 7, the arrangement interval P of the convex portions 35 (prism shape) was 0.2 mm, 0.4 mm, 0.7 mm, and 1.0 mm, respectively. In Comparative Examples 1 to 3, the arrangement interval P of the convex portions 35 was 2.0 mm and 8.5 mm, respectively. The convex portion 35 was formed by cutting the incident surface 33 (end surface on the long side) of the optical sheet using a diamond tool for forming the convex portion 35.

Next, an evaluation unit 1 and an evaluation unit 2 were prepared for the optical sheets 10 of Examples 1 to 7 and Comparative Examples 1 to 3. A white tape (TRUSCO TRT-50 double-sided tape) was adhered to the entire back surface 32 of the optical sheet 10.

In the evaluation unit 1, five LED light sources 22 (120 ° Lambertian type; NSSW 123B) were arranged in the long side direction of the optical sheet 30 at an interval of 7.5 mm (L). In the evaluation unit 1, the LED light source 22 is arranged at the center in the thickness direction (Z direction) of the optical sheet 30. And after arrange | positioning the LED light source 22 in a predetermined position, it wired to the base | substrate.

Next, after preparing a liquid crystal television (TH-19D2, manufactured by Panasonic) and removing the liquid crystal panel and various optical sheets, the evaluation unit 1 was installed on the reflector. At this time, the central LED light source 22 (22 </ b> A) of the five LED light sources 22 has

convex portions

35, 35 whose normal N is adjacent to the optical sheet 10 in the longitudinal direction of the incident surface 33. It arrange | positioned so that it might respond | correspond to the bottom 36 of an indentation in between. And the voltage 18V and the electric current 60mA were applied to the LED light source 22, and the LED light source 22 was turned on.

In the evaluation unit 2, among the LED light sources 22 preliminarily installed in the liquid crystal television (TH-19D2, manufactured by Panasonic), black tape is attached to the LED light sources 22 other than the central five light sources, and the light from the LED light source 22 is obtained. Was prevented from leaking outside.

Next, after removing the liquid crystal panel and various optical sheets mounted on the liquid crystal television (TH-19D2, manufactured by Panasonic), the optical sheet 30 was installed on the reflector. At this time, the central LED light source 22 (22A) of the five LED light sources 22 has

convex portions

35, 35 whose normal line N is adjacent to the optical sheet A in the longitudinal direction of the incident surface 33. It arrange | positioned so that it might respond | correspond to the bottom 36 of an indentation in between. Then, the power cable originally provided in the liquid crystal television was connected to a 100V outlet, and the LED light source was turned on.

Then, a luminance meter was installed so that the entire exit surface 31 of the optical sheet 30 was reflected. The luminance meter was arranged to face the emission surface 31, and the distance from the emission surface 31 to the tip of the luminance meter camera was 460 mm.

FIG. 6 is a plan view showing the positional relationship among the prism shape (convex portion 35), the LED light source 22, and the luminance value measurement point Q. FIG. As shown in FIG. 6, measurement points Q for measuring luminance were provided at equal intervals, and measurement positions were set using XY coordinates. The long side direction of the optical sheet A was the X direction, and the short side direction was the Y direction. For the evaluation unit 1, 50 measurement points Q are provided in the range of 30 mm in the X direction near the light source, and 50 measurement points Q are provided in the range of 20 mm in the Y direction. As a result, a total of 2500 measurement points Q are provided. Provided. For the evaluation unit 2, 50 measurement points Q are provided in the range of 34 mm in the X direction near the light source, and 50 measurement points Q are provided in the range of 20 mm in the Y direction. As a result, a total of 2500 measurement points Q are provided. Provided. And the luminance value in each measurement point Q was measured. The evaluation units 1 and 2 were installed, and the luminance value was collected immediately after the LED light source 22 was turned on.

At this time, when the LED light source 22 (22A) located at the center of the five LED light sources 22 is arranged so that the normal line N thereof corresponds to the concave-convex recess 36 (reference position, deviation amount). 0.0 mm), and when the optical sheet 30 was moved 0.5 mm and 1.0 mm in the X direction from the reference position, luminance values were collected immediately after the LED light sources 22 were turned on.

The average value of 2500 luminance values in total was calculated for the collected luminance values, and the results are shown in Table 2.

With respect to the collected luminance values, for

evaluation unit

1, 30 points in the 18 mm range in the vicinity of the light source, 20 points in the 8 mm range in the Y direction, about 600 points in total, and for evaluation unit 2, in the vicinity of the light source Contour graphs are created for a total of 640 points, 32 points in the range of 22 mm in the X direction and 20 points in the range of 8 mm in the Y direction, and whether the luminance profiles in the vicinity of each LED light source 22 are equal, Judgment of the quality of the luminance profile was evaluated by a sensory test. Evaluation of pass / fail judgment is shown in Table 2. Evaluation by a sensory test is evaluation by visual observation.

As the evaluation by the sensory test, when the distribution of the luminance profile in the vicinity region of each LED light source 22 is the same, the determination of “◯: good” is performed, and one of the five LEDs used for the evaluation is When there was any difference in the luminance profile, “x: no” was determined.

7 and 8 are diagrams showing luminance profiles of the optical sheet of Example 2. FIG. FIG. 7 shows a case where the optical sheet is arranged at the reference position, and FIG. 8 shows a case where the optical sheet is shifted by 1.0 mm from the reference position. 7 and 8, it can be seen that the luminance change is small even when a deviation occurs.

9 and 10 are diagrams showing luminance profiles of the optical sheet of Comparative Example 2. FIG. 9 shows the case where the optical sheet is arranged at the reference position, and FIG. 10 shows the optical sheet from the reference position. The case where 1.0 mm has shifted | deviated is shown. 9 and 10, it can be seen that the luminance change is large before and after the shift.

Although the present invention has been specifically described above based on the embodiment, the present invention is not limited to the embodiment. For example, the point light sources may be arranged along one side surface extending in the long side direction of the optical sheet, or may be arranged along one side surface extending in the short side direction. Further, the point light sources may be arranged along two side surfaces extending in the long side direction of the optical sheet, or may be arranged along two side surfaces extending in the short side direction. In addition, it is preferable that the point light source is arrange | positioned in the position corresponding to the recessed part formed between adjacent convex-shaped parts.

In addition, the longitudinal direction of the side surface serving as the incident surface is the Y direction in the side surface 35 facing the X direction, and the X direction in the side surface facing the Y direction.

Further, the convex portions are preferably arranged at equal intervals with a pitch P of 0.03 mm to 10.0 mm in the longitudinal direction of the incident surface, but may be arranged with other pitches P. That is, the convex part should just be arrange | positioned so that Formula (1) may be satisfy | filled.

Further, the apex angle of the prism shape which is the convex portion is preferably 50 ° to 150 °, but may be other angles. Further, the convex portion may have a shape other than the prism shape.

The LED light source 22 may be a white LED. Further, a plurality of LEDs may be arranged at one place to constitute one light source unit. For example, as one light source unit, LEDs of three different colors of red, green, and blue may be arranged close to each other and arranged side by side. And the light source unit which has several LED is arrange | positioned discretely according to the arrangement | positioning direction mentioned above. In such a case, it is preferable that different LEDs are arranged as close to each other as possible. When a plurality of LED light sources are provided in this way, the plurality of LED light sources are considered as one unit, and the end to end of the light emission region of this one unit corresponds to W.

DESCRIPTION OF SYMBOLS 1 ... Transmission type image display apparatus, 10 ... Transmission type image display part, 20 ... Surface light source device, 22 ... LED light source (point light source), 30 ... Light guide plate (optical sheet), 31 ... Output surface, 32 ... Back surface, 33: side surface (incident surface), 35: convex portion (prism shape).

Claims

An optical sheet formed of a translucent resin,
A side surface serving as an incident surface on which light emitted from the point light source is incident;
It is formed in a direction intersecting with the side surface, and emits planar light.
A plurality of convex portions extending in the thickness direction of the optical sheet and arranged in the longitudinal direction of the incident surface are formed on the side surface serving as the incident surface,
The optical sheet, wherein an arrangement interval P in the longitudinal direction of the convex portions satisfies the following formula (1).
P ≦ 0.34W (1)
(W is the length in the longitudinal direction of the incident surface of the light emitting region existing on the side of the point light source facing the incident surface of the sheet)
The optical sheet according to claim 1, wherein the convex portion has a prism shape having an apex angle of 50 ° or more and 150 ° or less.
The optical sheet according to claim 1 or 2,
A surface light source device comprising: a plurality of point light sources that are opposed to a side surface serving as an incident surface of the optical sheet and are discretely arranged in a longitudinal direction of the incident surface.
The surface light source device according to claim 3, wherein the point light source is an LED light source that exhibits a maximum luminous intensity in the normal direction and has a half-value width of a luminous intensity distribution of 40 ° or more and 80 ° or less.
A surface light source device according to claim 3 or 4,
A transmission-type image display unit that is disposed to face the emission surface of the surface light source device, and that displays an image upon irradiation with light emitted from the surface light source device. A transmissive image display device.