JP6922220B2 - Optical sheet, image source unit, and liquid crystal display device - Google Patents

Description

The present invention relates to an optical sheet arranged on the observer side of a light source, an image source unit using the optical sheet, and a liquid crystal display device.

An image display device that emits an image to an observer, such as a liquid crystal display, is provided with an optical sheet provided with layers having various functions for emitting high-quality image light to the observer.

For example, in Patent Document 1, lens portions having a trapezoidal cross section are arranged at predetermined intervals, and a wedge-shaped portion between adjacent lens portions is filled with a material having light absorption, and the wedge-shaped portion is an observer. An optical sheet having a tip on the side and a bottom surface on the light source side is disclosed. Further, it is described in the same document that the relationship N2 <N1 is established when the refractive index of the main material constituting the lens portion is N1 and the refractive index of the main material constituting the wedge-shaped portion is N2. There is.

According to the optical sheet described in Patent Document 1, the light that has reached the interface between the lens portion and the wedge-shaped portion can be totally reflected and emitted to the observer side.

Japanese Unexamined Patent Publication No. 2006-171701

However, in the optical sheet described in Patent Document 1, there is a limit to the amount of light that can be totally reflected, and it has been desired to further improve the efficiency of light utilization.

Therefore, it is an object of the present invention to provide an optical sheet capable of increasing the efficiency of light utilization. Further, a video source unit using this optical sheet and a liquid crystal display device are provided.

Hereinafter, the present invention will be described.

One aspect of the present invention is an optical sheet arranged on the observer side of the light source (25), which has a predetermined cross section, extends in one direction, and has an interval in a direction different from the extending direction. A plurality of light transmitting portions (33) and a light absorbing portion (34) formed between the plurality of light transmitting portions are provided, and at least one of the interfaces between the light transmitting portion and the light absorbing portion is provided. It has a concave shape with respect to the light absorbing part, and at one end and the other end of the line (35, 135, 235) forming one interface in the cross section in the thickness direction, the line forming one interface is a broken line. In the case of a shape, the straight line extending from one end is the first straight line (35a, 135a), the straight line extending from the other end is the second straight line (35b, 135b), and the line forming one interface is curved. In some cases, when the tangent of the curve at one end is the first tangent (235a) and the tangent of the curve at the other end is the second tangent (235b), the concave shape is the first straight line and the second straight line. The optical sheet is formed so that the intersection of the first tangent line and the second tangent line is located at a position on the other end side of 50% of the thickness of the light absorbing portion.

In the above optical sheet, a concave shape may be formed only at one interface, or a concave shape may be formed at the other interface opposite to one interface.

Further, in the above optical sheet, in the concave type, the intersection of the first straight line and the second straight line, or the intersection of the first tangent line and the second tangent line is 75% or more of the thickness of the light absorbing portion. It can also be formed so that it exists at the position on the end side.

Another aspect of the present invention is a surface light source device (20) including a light source (25) and the above-mentioned optical sheet arranged on the observer side of the light source, and a liquid crystal display arranged on the observer side of the surface light source device. The image source unit (10) includes a panel (15), and one end of a line (35, 135, 235) forming one interface in the thickness direction cross section of the optical sheet is arranged on the light source side.

It is possible to provide a liquid crystal display device in which the image source unit (10) is housed in a housing.

Further, in this liquid crystal display device, when the light emitting surface of the optical sheet is arranged vertically, one interface is arranged so as to be on the lower side in the vertical direction of the light absorbing portion, and only one interface is concave. The shape may be formed.

According to the present invention, it is possible to efficiently totally reflect the incident light at the interface between the light transmitting portion and the light absorbing portion, and it is possible to increase the front transmittance.

It is an exploded perspective view explaining the image source unit 10. It is an exploded view which shows the cross section of the image source unit 10. It is an exploded view which shows the other cross section of the image source unit 10. FIG. 2 is an enlarged view focusing on the optical sheet 30 in FIG. FIG. 4 is a further enlarged view. FIG. 6A is a diagram for explaining the shape of the light absorbing unit 134, and FIG. 6B is a diagram for explaining the shape of the light absorbing unit 234. It is a figure explaining the optical sheet 330. It is a figure explaining an example of an optical path of light traveling on an optical sheet 30. It is a figure explaining the cross-sectional shape of the optical sheet which concerns on a reference example. It is a figure explaining the cross-sectional shape of the optical sheet which concerns on Comparative Example 11, Example 2, and Comparative Example 1. It is a figure explaining the cross-sectional shape of the optical sheet which concerns on Comparative Example 13, Example 4, and Comparative Example 2. It is a figure explaining the cross-sectional shape of the optical sheet which concerns on Comparative Example 15, Example 6, and Comparative Example 3.

Hereinafter, the present invention will be described based on the form shown in the drawings. However, the present invention is not limited to these forms. For ease of viewing in each figure, the repeated reference numerals may be omitted, and the shape may be deformed or emphasized.

FIG. 1 is a diagram illustrating one form, and is an exploded perspective view illustrating an image source unit 10 including an optical sheet 30. Further, FIG. 2 shows a part of an exploded cross-sectional view of the image source unit 10 along the line shown by II-II in FIG. 1, and FIG. 3 shows an exploded view of the image source unit 10 along the line shown by III-III. A part of the cross section is shown.
1 to 3 and the drawings described below also show the orientation in which the image source unit 10 is arranged when it is used as a liquid crystal display device, if necessary.

The video source unit 10 includes a power supply for operating the video source unit 10 in a housing (not shown), an electronic circuit for controlling the video source unit 10, and other ordinary equipment required for operating as the video source unit 10. It is stored and used as a display device. This embodiment is a liquid crystal image source unit and a liquid crystal display device including the same. The video source unit 10 will be described below.

The image source unit 10 includes a liquid crystal panel 15, a surface light source device 20, and a functional film 40.

The liquid crystal panel 15 is a liquid crystal display arranged between the upper polarizing plate 13 arranged on the observer side, the lower polarizing plate 14 arranged on the surface light source device 20 side, and the upper polarizing plate 13 and the lower polarizing plate 14. It has a layer 12. The upper polarizing plate 13 and the lower polarizing plate 14 decompose the incident light into two orthogonal polarizing components (P wave and S wave), and the polarizing component in one direction (direction parallel to the transmission axis) (for example, P). It has a function of transmitting a wave) and absorbing a polarizing component (for example, an S wave) in the other direction (direction parallel to the absorption axis) orthogonal to the one direction.

In the liquid crystal layer 12, a plurality of pixels are arranged vertically and horizontally in a direction along the layer surface, and an electric field can be applied to each region forming one pixel. Then, the orientation of the pixel to which the electric field is applied changes. As a result, the polarized light component (for example, P wave) parallel to the transmission axis transmitted through the lower polarizing plate 14 arranged on the surface light source device 20 side (that is, the light input side) is transmitted when passing through the pixel to which the electric field is applied. The polarization direction is rotated by 90 °, while maintaining the polarization direction as it passes through the pixels to which no electric field is applied. Therefore, depending on whether or not an electric field is applied to the pixels, the polarizing component (for example, P wave) transmitted through the lower polarizing plate 14 further transmits through the upper polarizing plate 13 arranged on the light emitting side, or the upper polarizing plate 13 is further transmitted. It is possible to control whether it is absorbed and blocked by.

In this way, the liquid crystal panel 15 has a structure in which the transmission or blocking of light from the surface light source device 20 is controlled for each pixel to express an image.

The liquid crystal panel is configured to be able to provide an image to the observer based on such a principle. Therefore, when illuminating from the back side of the liquid crystal panel, a large amount of light having a polarization component parallel to the transmission axis of the lower polarizing plate can be made to pass through the lower polarizing plate to improve the efficiency of light utilization. ..
Furthermore, due to the nature of the liquid crystal panel, the contrast and efficiency (transmittance) of the emitted light are excellent with respect to the incident light from the normal direction of the liquid crystal panel. However, when the incident light is oblique to the normal direction of the liquid crystal panel and the observer observes the light from an oblique direction, there are problems such as a decrease in contrast and low efficiency (transmittance). That is, in order to improve the light utilization efficiency, it is also effective to increase the incident light from the normal direction of the liquid crystal panel.

The type of the liquid crystal panel is not particularly limited, and a known type of liquid crystal panel can be mentioned. This includes, for example, TN, STN, VA, MVA, IPS, OCB and the like.

Next, the surface light source device 20 will be described.
The surface light source device 20 is a lighting device that is arranged on the side opposite to the observer side with respect to the liquid crystal panel 15 and emits planar light to the liquid crystal panel 15. As can be seen from FIGS. 1 to 3, the surface light source device 20 of this embodiment is configured as an edge light type surface light source device, and includes a light guide plate 21, a light source 25, a light diffusing plate 26, a prism layer 27, and a reflective polarizing plate. 28, it has an optical sheet 30 and a reflective sheet 39.

As can be seen from FIGS. 1 to 3, the light guide plate 21 has a base portion 22 and a back surface optical element 23. The light guide plate 21 is an overall plate-shaped member made of a translucent material. In this embodiment, one plate surface side that is the observer side of the light guide plate 21 is a smooth surface, the other plate surface side that is the opposite side is a back surface, and a plurality of back surface optical elements 23 are on the back surface. Are arranged.

Various materials can be used as the material forming the base portion 22 and the back surface optical element 23. However, a material that is widely used as a material for an optical sheet incorporated in a display device, has excellent mechanical properties, optical properties, stability, workability, and the like, and can be obtained at low cost can be used. This includes, for example, thermoplastic resins such as polymer resins having an alicyclic structure, methacrylic resins, polycarbonate resins, polystyrene resins, acrylonitrile-styrene copolymers, methyl methacrylate-styrene copolymers, ABS resins, and polyether sulfones. , Epoxy acrylate, urethane acrylate-based reactive resin (ionized radiation curable resin, etc.) and the like can be mentioned.

The base portion 22 is a portion to which light is guided through the inside thereof and is a base of the back surface optical element 23, and has a plate shape having a predetermined thickness.

The back surface optical element 23 is a protruding element formed on the back surface side of the base portion 22 (the side opposite to the side on which the reflective polarizing plate 28 is arranged), and is a triangular columnar shape in this embodiment. The back surface optical element 23 is a columnar shape in which a protruding top ridge line extends in the horizontal direction, and a plurality of back surface optical elements 23 are arranged side by side at a predetermined pitch in a direction orthogonal to the extending direction. The back surface optical element 23 of the present embodiment has a triangular cross section, but is not limited to this, and may have any shape such as a polygon, a hemisphere, a part of a sphere, and a lens shape.
The arrangement direction of the plurality of back surface optical elements 23 is preferably the light guide direction. That is, the ridges of the back surface optical elements 23 extend in the direction separated from the light source 25 and in the direction in which the light sources 25 are arranged, or in the direction in which the light source extends in the case of one long light source.

The "triangular shape" in the present specification includes not only a triangular shape in a strict sense but also a substantially triangular shape including limits in manufacturing technology and errors during molding. Similarly, other terms that specify shape and geometric conditions used herein, such as "parallel," "orthogonal," "ellipse," and "circle," are also bound in a strict sense. It shall be interpreted including an error to the extent that the same optical function can be expected.

The light guide plate 21 having such a configuration can be manufactured by extrusion molding or by molding the back surface optical element 23 on the base portion 22. In the light guide plate 21 manufactured by extrusion molding, the base portion 22 and the back surface optical element 23 can be integrally formed. Further, when the light guide plate 21 is manufactured by molding, the back surface optical element 23 may be the same resin material as the base 22 or a different material.

Returning to FIGS. 1 to 3, the light source 25 will be described. The light source 25 is arranged on one side surface (end surface) of the side surface (end surface) of the base portion 22 of the light guide plate 21 in the direction in which the plurality of back surface optical elements 23 are arranged. The type of the light source is not particularly limited, but it can be configured in various modes such as a fluorescent lamp such as a linear cold cathode tube, a point LED (light emitting diode), or an incandescent lamp. In this embodiment, the light source 25 is composed of a plurality of LEDs, and is configured so that the lighting and extinguishing of each LED and / or the brightness at the time of lighting of each LED can be individually and independently adjusted by a control device (not shown). There is.
In this embodiment, the light source 25 is arranged on one side surface as described above, but the light source may be arranged on the side surface opposite to this side surface. In this case, the shape of the back surface optical element is also formed according to a known example.

Next, the light diffusing plate 26 will be described. The light diffusing plate 26 is a layer that is arranged on the light emitting side of the light guide plate 21 and has a function of diffusing and emitting light incident on the light diffusing plate 21. As a result, the uniformity of the light emitted from the light guide plate 21 can be further improved, and the scratches existing on the light guide plate 21 can be made inconspicuous.
As a specific embodiment of the light diffusing plate, a known light diffusing layer can be used, and examples thereof include a form in which a light diffusing agent is dispersed in a base material.
Further, the light diffusing plate 26 may be integrally arranged on the light emitting surface of the light guide plate 21 or may be a separate body when the light emitting surface of the light guide plate 21 is smooth. Further, in the present embodiment, the prism layer 27 is integrally formed on the surface of the light diffusing plate 26, and is configured to function as a support for the prism layer 27.

As can be seen from FIGS. 1 to 3, the prism layer 27 is a layer provided with a unit prism 27a that is provided on the liquid crystal panel 15 side of the light diffusing plate 26 and is convex toward the liquid crystal panel 15 side. The unit prism 27a has a predetermined cross section and has a form extending in a direction orthogonal to the light guide direction of the light guide plate 21. A plurality of unit prisms 27a are arranged in the light guide direction. Further, in the present embodiment, the direction in which the unit prism 27a extends is parallel to the direction in which the light transmitting portion 33 and the light absorbing portion 34, which will be described later, extend. As a result, the light traveling to the light transmitting unit 33 and the light absorbing unit 34 can be turned in a direction approaching the front direction, the light absorbed by the light absorbing unit 34 can be reduced, and the light utilization efficiency can be further improved. be able to. However, the present invention is not limited to this, and the direction in which the unit prism 27a extends may be a direction orthogonal to the direction in which the light transmitting portion 33 and the light absorbing portion 34 extend in a plan view.
As the cross-sectional shape of the unit prism of such a prism layer, a known shape can be applied according to a required function. In this embodiment, the light is formed so as to have a function of concentrating the light in the front direction, but conversely, the light can be further diffused by the shape.

Next, the reflective polarizing plate 28 will be described. The reflective polarizing plate 28 decomposes the incident light into two orthogonal polarization components (P wave and S wave), and transmits the polarization component (for example, P wave) in one direction (direction parallel to the transmission axis). It has a function of reflecting a polarizing component (for example, an S wave) in the other direction (direction parallel to the reflection axis) orthogonal to the one direction. A known structure of such a reflective polarizing plate can be applied.
As such a reflective polarizing plate, a known one can be applied.

Here, the direction in which the transmission axis of the reflective polarizing plate 28 extends is the same as the direction in which the transmission axis of the lower polarizing plate 14 extends, and the light transmission section 33 and the light absorption section 34 of the optical functional layer 32 described later. Is preferably 1 ° or more and 41.7 ° or less in the front view of the image source unit 10 with respect to the extending direction. More preferably, it is 1 ° or more and 20 ° or less.

Next, the optical sheet 30 will be described. FIG. 4 is an enlarged view of a part of the optical sheet 30 in FIG. 2, and FIG. 5 is a further enlarged view of FIG.

The optical sheet 30 includes a base material layer 31 and an optical functional layer 32 arranged on one surface of the base material layer 31 (the surface on the light guide plate 21 side in this embodiment). The optical functional layer 32 has a predetermined cross section and extends in one direction along the surface of the base material layer 31, and a plurality of light transmitting portions 33 are arranged at intervals in a direction different from the extending direction. And a light absorbing portion 34 formed between the plurality of light transmitting portions. In this embodiment, the direction in which the light transmitting portion 33 and the light absorbing portion 34 extend is the horizontal direction, and the direction in which the transmitting portion 33 and the light absorbing portion 34 are alternately arranged is the vertical direction.

Further, as will be described later, the optical sheet 30 has a function (collection) of changing the traveling direction of the light incident from the incoming light side and emitting the light from the outgoing light side to intensively improve the brightness in the front direction (normal direction). It has an optical function). Further, it has a function of absorbing light traveling at a large angle with respect to the front direction (light absorption function).

As shown in FIGS. 1 to 5, the base material layer 31 is a transparent flat sheet-like member that supports the optical functional layer 32.
Various materials can be used as the material forming the base material layer 31. However, a material that is widely used as a material for an optical sheet incorporated in a display device, has excellent mechanical properties, optical properties, stability, workability, and the like, and can be obtained at low cost can be used. Examples thereof include polyethylene terephthalate resin (PET), triacetyl cellulose resin (TAC), methacrylic resin, polycarbonate resin and the like. Among these, it is preferable to use a TAC, a methacrylic resin, or a polycarbonate resin having less birefringence in consideration of the combination of the surface light source device 20 and the lower polarizing plate 14. Further, in applications requiring high heat resistance such as in-vehicle applications, a polycarbonate resin having a high glass transition point is desirable. Specifically, the glass transition point of the polycarbonate resin is 143 ° C, and it is suitable for in-vehicle applications where durability at 105 ° C is generally required.

The optical functional layer 32 is a layer laminated on one surface of the base material layer 31 (the surface on the light guide plate 21 side in this embodiment), has a predetermined cross section, extends in one direction, and is different from the extending direction. A plurality of light transmitting portions 33 arranged at intervals in the direction and a light absorbing portion 34 formed between the plurality of light transmitting portions are provided.
As will be described later, at least one of the interfaces between the light transmitting portion 33 and the light absorbing portion 34 has a concave shape with respect to the light absorbing portion 34. In this embodiment, the light absorbing portion 34 has a concave shape on the upper side in the vertical direction.

The optical functional layer 32 in this embodiment has a cross section shown in FIG. 4 and has a shape extending to the back / front side of the paper surface. That is, the optical functional layer 32 includes a light transmitting portion 33 having a pentagonal shape in the cross section shown in FIG. Further, a light absorbing portion 34 having a pentagonal cross section is provided between two adjacent light transmitting portions 33. One of the interfaces of the light transmitting portion 33 and the light absorbing portion 34 has a concave shape with respect to the light absorbing portion 34.

The light transmitting portion 33 is a portion whose main function is to transmit light, and in this embodiment, the light transmitting portion 33 is an element having a pentagonal cross-sectional shape in the cross sections shown in FIGS. 2 and 4. The light transmitting portions 33 extend in the horizontal direction while maintaining the cross section along the layer surface of the base material layer 31, and are arranged at predetermined intervals in a direction different from the extending direction (vertical direction in this embodiment). A groove having a pentagonal cross-sectional shape is formed between the adjacent light transmitting portions 33. The groove is filled with a necessary material described later to form a light absorbing portion 34. In this embodiment, the adjacent light transmitting portions 33 are connected by a sheet-shaped connecting portion 32a on the long lower bottom side.

The light transmitting portion 33 has a refractive index of Nt. Such a light transmitting portion 33 can be formed by curing the light transmitting portion constituent composition. Details will be described later. The value of the refractive index Nt is not particularly limited, but as will be described later, the refractive index is determined from the viewpoint of appropriately reflecting light (including total reflection) at the interface between the light transmitting portion 33 and the light absorbing portion 34. It is preferably 1.47 or more and 1.61 or less, more preferably 1.49 or more and 1.56 or less, and particularly preferably 1.56. If the refractive index Nt is less than 1.47, the difference in the refractive index from the light absorbing unit 34 must be small, and it is often difficult to properly reflect light at the interface. On the other hand, when the refractive index Nt exceeds 1.61, the material forming the light transmitting portion is often easily cracked, and the moldability may be inferior.

The light absorbing portion 34 is formed between the adjacent light transmitting portions 33, and has a cross-sectional shape corresponding to the cross-sectional shape of the interval formed between the light transmitting portions 33. Therefore, it has a pentagonal cross-sectional shape. The light absorbing unit 34 has a refractive index of Nr and is configured to be able to absorb light. Specifically, the light absorbing particles are dispersed in a light transmitting composition such as a light transmitting resin having a refractive index of Nr. The refractive index Nr is lower than the refractive index Nt of the light transmitting portion 33. By making the refractive index of the light absorbing unit 34 smaller than the refractive index of the light transmitting unit 33 in this way, the light incident on the light transmitting unit 33 under predetermined conditions is appropriately totally reflected at the interface with the light absorbing unit 34. Can be made to. Further, even if the total reflection condition is not satisfied, some light is reflected at the interface.
The value of the refractive index Nr is not particularly limited, but is preferably 1.47 or more and 1.61 or less, more preferably 1.49 or more and 1.56 or less, and particularly preferably 1,49. If the refractive index Nr is less than 1.47, it may be difficult to properly reflect light at the interface with the light transmitting portion 33. On the other hand, when the refractive index Nr exceeds 1.61, the material forming the light absorbing portion is often easily cracked, and the moldability may be inferior.

The difference in the refractive index between the refractive index Nt of the light transmitting portion 33 and the refractive index Nr of the light absorbing portion 34 is not particularly limited, but is preferably greater than 0 and 0.14 or less, and more preferably 0. It is 0.05 or more and 0.14 or less. By increasing the difference in refractive index, more light can be totally reflected.

Here, the shape of the cross section of the optical functional layer 32 in the thickness direction will be further described.
In the optical functional layer 32 of this embodiment, a light absorbing portion 34 is formed between adjacent light transmitting portions 33. Therefore, one light absorbing unit 34 has two interfaces with the light transmitting unit 33. At least one of these interfaces (in this embodiment, the interface on the upper side of the light absorbing portion 34 in the vertical direction) is concave with respect to the light absorbing portion 34.

FIG. 5 is an enlarged view of a part of FIG. 4, and is a diagram for explaining the shape of the interface between the light transmitting portion 33 and the light absorbing portion 34.
As shown in FIG. 5, the line 35 forming one interface having a concave shape in the cross section is formed from one end X of the line 35 opposite to the base material layer 31 to the base material 31. It has a first straight line 35a extending in the direction of the above, and a second straight line 35b extending in a direction away from the base material 31 from the other end Y of the line 35 on the base material layer 31 side. Since the first straight line 35a and the second straight line 35b have different angles with respect to the sheet surface normal, the line 35 has an intersection Z between the first straight line 35a and the second straight line 25b. It has a broken line at the inside corner.

The intersection Z of the first straight line 35a and the second straight line 35b exists on the other end Y side of the thickness direction position which is 50% _{of the thickness direction size D k of the light absorbing portion 34.} It is preferable that it is formed so as to. As a result, the front transmittance can be improved, and the light utilization efficiency can be improved.
That is, as shown in FIG. 5, the thickness direction distance D _i from one end X to the intersection Z is the thickness D _k of the light absorbing portion,
_Di / D _k > 0.5
Is. More preferably, it is 0.75 or more, that is, 75% or more. As a result, light can be collected in the front direction, so that the front transmittance can be further improved.

On the other hand, due to the improvement in the front transmittance in this way, the transmittance of the light emitted at an angle significantly deviating from the front direction is reduced. According to this, it can be said that it was possible to control the light emission angle by controlling the light to be concentrated in the front direction and suppressing the light in the other directions.

Further, as shown in FIG. 5, the angle formed by the first straight line 35a and the normal direction of the seat surface is θ _1, and the angle formed by the second straight line 35b and the normal direction of the seat surface is θ _2. Then, since one of the interfaces has a concave shape, θ ₁ and θ ₂ have a relationship of _{θ 1} > θ _2. The specific angles of θ ₁ and θ ₂ are not particularly limited, but it is preferable that θ ₁ is 5 ° or more and 20 ° or less, and θ ₂ is 0 ° or more and 10 ° or less. As a result, the front transmittance can be efficiently improved. Further, the angle formed by the interface between the light transmitting portion 33 and the light absorbing portion 34 shown by _{θ k} in FIG. 5 and the normal of the layer surface of the optical functional layer 32 is not particularly limited. , 0 ° or more and 10 ° or less, and more preferably 1 ° or more and 10 ° or less.

The optical functional layer 32 will be further described. The optical functional layer 32 is not particularly limited, but for example, the light transmitting portion 33 and the light absorbing portion 34 are formed as follows.
_{The pitch between the light transmitting portion 33 and the light absorbing portion 34 represented by Pk} in FIG. 4 is preferably 20 μm or more and 100 μm or less, and more preferably 30 μm or more and 100 μm or less. _{Further, the thickness of the light absorbing portion 34 shown by Dk} in FIG. 4 is preferably 50 μm or more and 150 μm or less, and more preferably 60 μm or more and 150 μm or less.
Then, in FIG. 4, the second straight 35b side of the light absorbing portion 34 the width of the side of the (right side, the base layer 31 side) _{W a} is 2μm or more 10μm or less, the first straight line 35a of the light absorbing portion 34 The width of the side (the left side of the paper surface, the side opposite to the base material layer 31) is preferably 5 μm or more and 30 μm or less _{for W b.}
Further, indicated at W _C in FIG. 4, it is preferable the size of the direction component along the sheet surface with the first straight line 35a is is 2μm or more 14μm or less. Further, the size of the component in the direction along the sheet surface at the interface on the other side represented by _{W d is preferably 2 μm or more and 14 μm or less.}
By setting it within these ranges, the efficiency of light utilization can be improved.

In this embodiment, one of the interfaces between the light transmitting portion 33 and the light absorbing portion 34 is a polygonal line composed of two straight lines in the cross section in the thickness direction, but the present invention is not limited to this form, and three or more interfaces are formed. It may be a polygonal line consisting of straight lines. FIG. 6A illustrates an optical sheet in which one interface is a polygonal line composed of three straight lines 135a, 135b, and 135c in a cross section in the thickness direction. FIG. 6A is an enlarged view of only the cross section of the light absorbing portion 134.
Also in this case, in the cross section in the thickness direction, a line extending the first straight line 135a extending from each of one end X and the other end Y of the line 135 forming the interface on one side of the light transmitting portion and the light absorbing portion 134. It suffices that the position of the intersection Z with the line extending the second straight line 135b satisfies the above condition.

Further, the interface on one side of the light transmitting portion and the light absorbing portion may be curved in the cross section in the thickness direction. FIG. 6B is an enlarged view of only the cross section of the light absorbing portion 234 of the optical sheet whose interface on one side is curved in the cross section in the thickness direction.
In this case, in the cross section in the thickness direction, the tangents at one end X and the other end Y of the curve 235 forming the interface on one side of the light transmitting portion and the light absorbing portion 234 are the first tangents 235a and the second tangents. When 235b is set, the intersection Z between the first tangent line 235a and the second tangent line 235b may exist so as to satisfy the above conditions.

Up to this point, only one of the interface between the light transmitting part and the light absorbing part has been concave, but the shape is not limited to this, and the other interface on the opposite side of one interface also has a concave shape with respect to the light absorbing part. May have. This further improves the front transmittance. In that case, as in the optical sheet 330 illustrated in FIG. 7, the interface on one side and the interface on the other side are line targets with respect to the dotted line A parallel to the thickness direction in the cross section in the thickness direction. It may be the light absorption unit 334. Thereby, unevenness of light can be suppressed.

Further, the plurality of light transmitting portions 33 and the light absorbing portions 34 may all have the same cross-sectional shape, or may have different cross-sectional shapes having predetermined regularity. The pitch interval may also be different for each pitch.

When the image source unit 10 is viewed from the front of the observer side, the angle formed by the direction in which the light transmitting portion 33 extends and the direction in which the transmission axis of the lower polarizing plate 14 extends is greater than 1 ° and greater than or equal to 41.7 °. It is preferable to have. As a result, it is possible to suppress the change in the polarizing component due to reflection at the interface between the light transmitting portion 33 and the light absorbing portion 34 and improve the transmittance. More preferably, this angle is greater than 1 ° and less than or equal to 20 °. According to this, the change in the transmittance due to the change in the formed angle becomes small, the variation given to the performance by the variation in the formed angle in manufacturing can be reduced, and it is possible to provide an optical functional layer with stable performance. can.

The optical sheet 30 can be manufactured, for example, as follows.
First, the light transmitting portion 33 is formed on the base material layer 31. In this method, a base material sheet to be a base material layer 31 is inserted between a mold roll having a shape on the surface capable of transferring the shape of the desired light transmitting portion 33 and a nip roll arranged so as to face the mold roll. do. At this time, the mold roll and the nip roll are rotated while supplying the composition constituting the light transmitting portion between the base sheet and the mold roll. As a result, the groove corresponding to the light transmitting portion (the shape obtained by reversing the shape of the light transmitting portion) formed on the surface of the mold roll is filled with the composition constituting the light transmitting portion, and the composition is formed on the surface of the mold roll. It follows the shape.

Here, examples of the composition constituting the light transmitting portion include ionizing radiation curable resins such as epoxy acrylate-based, urethane acrylate-based, polyether acrylate-based, polyester acrylate-based, and polythiol-based resins.

The composition sandwiched between the mold roll and the base sheet and forming the light transmitting portion filled therein is irradiated with light for curing by a light irradiation device from the base sheet side. Thereby, the composition can be cured and its shape can be fixed. Then, the base material layer 31 and the molded light transmitting portion 33 are released from the mold roll by the mold release roll.

Next, the light absorption unit 34 is formed. In order to form the light absorbing portion 34, first, the composition constituting the light absorbing portion is filled in the space between the formed light transmitting portions 33. Then, the excess composition is wiped off with a doctor blade or the like. Then, the remaining composition can be cured by irradiating the remaining composition with ultraviolet rays from the light transmitting portion 33 side to form the light absorbing portion 34.
Here, the pressure at which the doctor blade or the like is pressed against the surface on the open side of the groove formed between the light transmitting portions (the surface on the reflective polarizing plate 28 side in FIGS. 1 to 4) is adjusted. A non-filled portion, which is a portion where the material constituting the light absorbing portion is not filled, may be formed.

The material used as the light absorbing portion is not particularly limited, but for example, a photocurable resin such as urethane (meth) acrylate-based, polyester (meth) acrylate-based, epoxy (meth) acrylate-based, and butadiene (meth) acrylate-based resin. Examples thereof include a composition in which colored light-absorbing particles are dispersed.
Here, "(meth) acrylate" means "acrylate or methacrylate".

Further, instead of dispersing the light absorbing particles, the entire light absorbing portion can be colored with a pigment or a dye.
When light absorbing particles are used, light absorbing colored particles such as carbon black are preferably used, but the present invention is not limited to these, and specific wavelengths are selectively absorbed according to the characteristics of image light. Colored particles may be used. Specific examples thereof include organic fine particles colored with metal salts such as carbon black, graphite and black iron oxide, dyes and pigments, and colored glass beads. In particular, colored organic fine particles are preferably used from the viewpoints of cost, quality, availability, and the like.
The average particle size of the colored particles is preferably 1.0 μm or more and 20 μm or less, more preferably 1.0 μm or more and 10 μm or less, and further preferably 1.0 μm or more and 4.0 μm or less.
Here, the "average particle size" means an arithmetically averaged diameter obtained by observing 100 light absorbing particles with an electron microscope and measuring their diameters.

As a result, the optical sheet 30 in which the optical functional layer 32 is laminated on one surface of the base material layer 31 is produced.

Returning to FIGS. 1 to 3, the reflection sheet 39 of the surface light source device 20 will be described. The reflective sheet 39 is a member for reflecting the light emitted from the back surface of the light guide plate 21 and causing the light to enter the light guide plate 21 again. The reflective sheet 39 is a sheet that enables so-called specular reflection, such as a sheet made of a material having a high reflectance such as metal and a sheet containing a thin film (for example, a metal thin film) made of a material having a high reflectance as a surface layer. It can be preferably applied.

The functional film 40 is a layer that is arranged on the light emitting side of the liquid crystal panel 15 and has a function of improving the quality of image light and protecting the image source unit 10. Examples thereof include an antireflection film, an antiglare film, a hard coat film, a color tone correction film, a light diffusing film, and the like, and these are configured alone or in combination of two or more.

Next, the operation of the image source unit 10 having the above configuration will be described with reference to an optical path example. However, the optical path example is conceptual for explanation, and does not strictly represent the degree of reflection or refraction.

First, as shown in FIG. 2, the light emitted from the light source 25 enters the light guide plate 21 via the light entering surface on the side surface of the light guide plate 21. FIG. 2 shows, as an example, an optical path example of the light L21 and L22 incident on the light guide plate 21 from the light source 25.

As shown in FIG. 2, the lights L21 and L22 incident on the light guide plate 21 are repeatedly totally reflected by the difference in refractive index with air on the light emitting side surface of the light guide plate 21 and the back surface on the opposite side thereof, and are in the light guide direction (FIG. 2). Proceed to the right side of the page of 2.

However, the back surface optical element 23 is arranged on the back surface of the light guide plate 21. Therefore, as shown in FIG. 2, the light L21 and L22 traveling in the light guide plate 21 change their traveling directions depending on the back surface optical element 23, and are incident on the light emitting surface and the back surface at an incident angle less than the total reflection critical angle. There is also. In this case, the light can be emitted from the light emitting surface of the light guide plate 21 and the back surface on the opposite side thereof.

The lights L21 and L22 emitted from the light emitting surface head toward the light diffusing plate 26 arranged on the light emitting side of the light guide plate 21. On the other hand, the light emitted from the back surface is reflected by the reflective sheet 39 arranged on the back surface of the light guide plate 21, enters the light guide plate 21 again, and travels in the light guide plate 21.

The light traveling in the light guide plate 21 and the light that is turned by the back surface optical element 23 and reaches the light emitting surface at an incident angle less than the total reflection critical angle are in each area in the light guide plate 21 along the light guide direction. Occurs. Therefore, the light traveling in the light guide plate 21 is gradually emitted from the light emitting surface. As a result, the light amount distribution of the light emitted from the light emitting surface of the light guide plate 21 along the light guide direction can be made uniform.

The light emitted from the light guide plate 21 then reaches the light diffusing plate 26 to improve the uniformity. Then, the light is diffused or condensed by the prism layer 27 as necessary (condensed in this embodiment), and the light emitted from the prism layer 27 then reaches the reflective polarizing plate 28. Here, the light in the polarization direction along the transmission axis of the reflective polarizing plate 28 passes through the reflective polarizing plate 28 and heads toward the optical sheet 30.
On the other hand, the light in the polarization direction along the reflection axis of the reflective polarizing plate 28 is reflected as shown by the dotted arrows L21'and L22' in FIG. 2 and returned to the light guide plate 21 side. The returned light is reflected by the light guide plate 21, the back surface optical element 23, or the reflective sheet 39, and travels to the side of the reflective polarizing plate 28 again. At the time of this reflection, the polarization direction of a part of the light is changed, and a part of the light is transmitted through the reflective polarizing plate 28. The other light is returned to the light guide plate side again. The light reflected by the reflective polarizing plate 28 can be transmitted through the reflective polarizing plate 28 by repeating the reflection. As a result, the utilization rate of the light from the light source 25 is increased.
Here, the light emitted from the reflective polarizing plate 28 has its polarization direction along the transmission axis of the lower polarizing plate 14, and is polarized light transmitted through the lower polarizing plate 14.

The light emitted from the reflective polarizing plate 28 is incident on the optical functional layer 32. The light incident on the optical functional layer 32 is polarized light that passes through the lower polarizing plate 14, and travels with the following optical paths.

The light incident on the optical functional layer 32 travels as follows, for example.
The light shown by L81 in FIG. 8 passes through the light transmitting portion 33 without reaching the interface between the light transmitting portion 33 and the light absorbing portion 34.
As shown by L82 in FIG. 8, the light traveling at a certain angle with respect to the sheet surface normal is the second straight line 35b in the thickness direction cross section of the interface on one side of the light absorbing portion 34 (FIG. 8). It reaches the interface forming (see 5), is totally reflected, and is transmitted through the light transmitting portion 33. At this time, in the present embodiment, _{due to the action of the inclination angle (θ 2} ) of the interface, the light reflected at the interface is brought closer to the direction parallel to the normal line of the liquid crystal panel 15 (that is, the front direction of the display device).

As shown by L83 in FIG. 8, the light incident on the optical functional layer 32 at a large angle with respect to the sheet surface normal is the first of the interfaces on one side of the light transmitting portion 33 and the light absorbing portion 34. It reaches the interface forming the straight line 35a (see FIG. 5), and _{due to the action of the inclination angle (θ 1} ) of the interface, the light is totally reflected and brought closer to the direction parallel to the normal of the liquid crystal panel 15.
The light shown by L84 in FIG. 8 reaches the interface forming the first straight line 35a (see FIG. 5) among the interfaces on one side of the light transmitting portion 33 and the light absorbing portion 34, and the inclination angle of the interface is reached. By the action of (θ ₁ ), the light is totally reflected and brought closer to the direction parallel to the normal line of the liquid crystal panel 15, and further travels toward the interface forming the second straight line 35b in the thickness direction cross section. Then, the light totally reflected at the interface forming the first straight line 35a is totally reflected at the interface forming the second straight line 35b in the thickness direction cross section, and is transmitted through the light transmitting portion 33.
As a result, the light incident on the optical functional layer 32 from the upper side of the paper surface at a large angle with respect to the sheet surface normal can be brought closer to the direction parallel to the normal of the liquid crystal panel 15.

As shown by L85 in FIG. 8, the light traveling from the lower side of the paper surface at a certain angle with respect to the sheet surface normal reaches the interface on the other side of the light absorbing portion 34, is totally reflected, and is a light transmitting portion. It passes through 33. At this time, in the present embodiment, _{due to the action of the inclination angle (θ k} ) of the interface, the light reflected at the interface is brought closer to the direction parallel to the normal of the liquid crystal panel 15.

In this way, the light shown in L82 to L85 is brought closer to the direction parallel to the normal line of the liquid crystal panel 15. As a result, it is possible to effectively provide the liquid crystal panel 15 with light that does not cause problems such as a decrease in contrast and color inversion when the light is transmitted through the liquid crystal panel 15.
When the light shown in L82 to L85 is reflected at the interface, even if the light is not totally reflected because the angle is smaller than the total reflection critical angle, some of the light is reflected at the interface. Such light also passes through the light transmitting portion 33 in the same manner.

On the other hand, as shown by L86 in FIG. 8, the light incident on the optical functional layer 32 at an even larger angle with respect to the sheet surface normal is absorbed by the light absorption unit 34 and is not provided to the liquid crystal panel 15. As a result, it is possible to absorb light that causes problems such as a decrease in contrast and color inversion.

As described above, the optical sheet 30 is provided with an interface having the above-mentioned predetermined concave shape at least one of the interfaces of the light transmitting portion 33 and the light absorbing portion 34, so that the optical sheet 30 has a single inclination angle. Even light that is not reflected and is absorbed by the light absorbing unit 34 can be reflected. That is, it is possible to improve the light utilization efficiency by particularly increasing the front transmittance.
On the other hand, by improving the front transmittance in this way, it is possible to reduce the transmittance of light emitted at an angle significantly deviating from the front direction. According to this, it can be said that it was possible to control the light emission angle by controlling the light to be concentrated in the front direction and suppressing the light in the other directions.

As described above, according to the optical sheet 30, the light from the light guide plate 21 can be efficiently collected in the front direction, and the light that has not been collected is absorbed by the light absorption unit, so that appropriate light can be efficiently collected by the liquid crystal. It can be provided to the panel, and it is possible to greatly improve the efficiency of light utilization. Further, since light that could not be used in the past can be provided to the liquid crystal panel by utilizing one-step or multi-step reflection, it is possible to further improve the light utilization efficiency.

Further, the optical path will be described. The light emitted from the surface light source device 20 as described above is incident on the lower polarizing plate 14 of the liquid crystal panel 15. The lower polarizing plate 14 transmits one of the polarized light components of the incident light and absorbs the other polarized light component. The light transmitted through the lower polarizing plate 14 selectively transmits through the upper polarizing plate 13 according to the state in which the electric field is applied to each pixel. In this way, the liquid crystal panel 15 selectively transmits the light from the surface light source device 20 for each pixel, so that the observer of the liquid crystal display device can observe the image. At that time, the image light is provided to the observer via the functional film 40, and the quality of the image is improved.

In the example, the optical sheet was evaluated by changing the shape of the light absorbing portion and using a ray tracing simulation.

[Ray analysis simulation]
In the example, a ray tracing simulation was performed using Light tools (manufactured by Synopsys).

[Optical sheet]
Tables 1 to 4 summarize the cross-sectional shapes of the optical sheets according to the reference example, each example , and each comparative example in which the ray tracing simulation was performed.
Here, assuming that the optical sheet according to the reference example, each example , and each comparative example is composed of the following materials, the conditions are set and the simulation is performed.

<Base layer>
-Material: Polycarbonate resin-Refractive index: Refractive index 1.59
・ Thickness: 130 μm
<Optical functional layer>
-Material and refractive index of the light transmitting part: UV-curable urethane acrylate having a refractive index of 1.56-Material and refractive index of the light absorbing part: UV-curable urethane acrylate having a refractive index of 1.49 contained carbon black. The concentration of carbon black was such that a layer having a thickness of 60 μm containing carbon black was formed in an ultraviolet curable urethane acrylate having a refractive index of 1.49, and the OD value (Optical Density value) was 2.9. ..
<Light source>
-A light source was used so that the brightness at a viewing angle of 45 ° up and down in the vertical direction was 30% when the front brightness was 100%.

Further, FIGS. 9 to 12 show diagrams for explaining the cross-sectional shape of the optical sheet according to the reference example, each example , and each comparative example.
FIG. 9 is a diagram illustrating a cross section in the thickness direction of the optical sheet according to a reference example having no concave shape at any interface, and FIG. 10 shows a recess only at the upper interface in the vertical direction of the light absorbing portion. Comparative example 11 having, example 2 a diagram for explaining a cross section in the thickness direction of the optical sheet according to Comparative example 1, in FIG. 11, Comparative example 13 having a recess on either side of the interface in the vertical direction above and below, example 4, The figure for explaining the thickness direction cross section of the optical sheet according to Comparative Example 2, FIG. 12, shows Comparative Example 15 , Example 6, and Comparative Example 3 having a concave shape only at the lower interface in the vertical direction of the light absorbing portion. The figure explaining the cross section in the thickness direction of the optical sheet is shown.

Here, in FIGS. 9 to 12, the top and bottom of the paper surface are in the vertical direction, the left and right sides of the paper surface are in the thickness direction (the right side of the paper surface is the observer side, the left side of the paper surface is the light source side), and the back / front direction of the paper surface is the horizontal direction.
The angle of the straight line forming the interface is the angle formed by the straight line and the normal direction of the sheet surface, and is an angle following θ ₁ , θ ₂ , and θ _k in FIG.
The intersection is the intersection of the first straight line and the second straight line, and is a portion following Z in FIG.
Further, the distance to the intersection, a thickness direction of the size from the intersection to the light source side of the edge of the light absorbing portion is sized to following the D _i of FIG.

The light absorbing portion of the optical sheet according to Example 13 , Example 4, and Comparative Example 2 is formed line-symmetrically with respect to a line parallel to the thickness direction of the optical sheet according to the example of FIG. ..

[evaluation]
The following items were evaluated in the optical sheets according to the above-mentioned reference example, each example , and each comparative example, and the results are summarized in Table 5.
(1) Front transmittance (transmittance in the direction normal to the sheet surface of the optical sheet).
(2) Transmittance at a position of 40 ° in the horizontal direction and 20 ° in the upper direction in the vertical direction (transmittance from the driver's viewpoint). In Table 5, it is described as "20 ° transmittance".
(3) Transmittance in the range of 40 ° or more and 80 ° or less on the upper side in the vertical direction. In Table 5, it is described as "40 ° to 80 ° transmittance".
The results in Table 5 show the values of each example as a percentage, with the results of the reference examples as 100%.

[result]
The front transmittance of Example 2, Example 4, Example 6, Comparative Example 11, Comparative Example 13, and Comparative Example 15 was higher than that of Reference Example, and the front transmittance of Comparative Examples 1 to 3 was lower than that of Reference Example. .. Therefore, it was found that the intersection of the first straight line and the second straight line exists at a position closer to the observer than 50% of the thickness of the light absorbing portion, so that the light is focused on the front surface.

Moreover, the actual施例2 has a high front transmittance than Comparative Example 11, Example 4 has a high front transmittance than Comparative Example 13, Example 6 had the result that high front transmittance than Comparative Example 15 rice field. On the other hand, the transmittance in the range of 40 ° or more and 80 ° or less in the vertical direction is lower in Example 2 than in Comparative Example 11 , Example 4 is lower than Comparative Example 13 , and Example 6 is higher than Comparative Example 15. Was also a low result. As a result, it is considered that the intersection of the first straight line and the second straight line exists at a position on the observer side of 75% or more of the thickness of the light absorbing portion, so that the light is further focused on the front surface. Be done.

Comparative Example 15 and Example 6 had better 20 ° transmittance than the other examples. The position of 40 ° in the horizontal direction and 20 ° in the vertical direction is the so-called "driver's viewpoint". That is, when the light emitting surface of the optical sheet is arranged vertically, one interface is arranged so as to be on the lower side in the vertical direction of the light absorbing portion, and a concave shape is formed only on one interface. It was found that the transmittance from the driver's point of view can be improved. Further, as described above, Example 6 has a lower transmittance in the range of 40 ° or more and 80 ° or less in the vertical direction upper side than Comparative Example 15. Therefore, the optical sheet according to the sixth embodiment can prevent reflection on the windshield and the like.

10 Image source unit 15 Liquid crystal panel 20 Surface light source device 21 Light guide plate 25 Light source 26 Light diffusion layer 27 Prism layer 28 Reflective polarizing plate 30, 330 Optical sheet 32 Optical functional layer 33 Light transmission part 34, 134, 234, 334 Light absorption Part 35a, 135a First straight line 35b, 135b Second straight line 235a First tangent line 235b Second tangent line

Claims (5)

An image source unit including a light source, a surface light source device including an optical sheet arranged on the observer side of the light source, and a liquid crystal panel arranged on the observer side of the surface light source device.
The optical sheet is
A light transmitting portion having a predetermined cross section and extending in one direction, and a plurality of light transmitting portions arranged at intervals in a direction different from the extending direction.
A light absorbing portion formed between the plurality of light transmitting portions is provided.
At least one of the interfaces between the light transmitting portion and the light absorbing portion has a concave shape with respect to the light absorbing portion.
When the line forming the one interface is a broken line at one end of the line forming the one interface in the thickness direction and the other end of the line forming the one interface on the liquid crystal panel side. Is a straight line extending from one end as a first straight line, a straight line extending from the other end as a second straight line, and when the line forming the one interface is curved, is a tangent to the curve at the one end. Is the first tangent, and the tangent of the curve at the other end is the second tangent.
The concave shape is
The intersection of the first straight line and the second straight line, or the intersection of the first tangent line and the second tangent line, is located on the other end side of the thickness of the light absorbing portion of 75%. Formed to be present in
Video source unit . Wherein the said concave is formed on only one of the interface, said and one interface other interface opposite Ru one linear der, image source unit according to claim 1. The video source unit according to claim 1, wherein the other interface opposite to the one interface also has the concave shape with respect to the light absorbing portion. A liquid crystal display device in which the video source unit according to any one of claims 1 to 3 is housed in a housing. The video source unit according to claim 2 is a liquid crystal display device housed in a housing.
When the light emitting surface of the optical sheet is arranged vertically,
A liquid crystal display device arranged so that the interface on which the concave shape is formed is on the lower side in the vertical direction of the light absorbing portion.

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