JP2000147264A - Light control sheet and surface light source device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the high controllability of illuminating light by one sheet and to acquire high condensing ability to an illuminating light source having strong diffusivity by providing many prism-like incident elements having a light incident surface whose average tilt angle is specified degrees in parallel on either surface of a transparent thin plate-like sheet and providing a condensing element on the other surface thereof. SOLUTION: The prism-like incident (light incident) element 12 having a large vertex angle is formed on the lower side (light source side) of the light control sheet 10, and the condensing element 13 is formed on the upper side (light emitting side) thereof. By using the sheet 10 as a backlight light source, light source light extending over a wide angle range is condensed by the element 12 having the large vertex angle on the light source side first. The element 12 has the light incident surface whose average tilt angle is 5 to 35 deg.. A prism sheet is ordinarily used as the element 13 arranged on an opposite side to the light source side of the sheet 10. It is good to use a cylindrical lenticular lens array and a micro convex lens array and the like as the condensing element according to circumstances.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light control sheet for improving the optical characteristics of illumination light, and more particularly, to a light control sheet for improving the front luminance, the viewing angle, etc. of a surface light source used for a liquid crystal display and the like, and the light control sheet. The present invention relates to a surface light source device using a light control sheet.

[0002]

2. Description of the Related Art In recent years, a transmissive liquid crystal display device has been frequently used as a display device of a word processor or a personal computer.
A planar lighting device, that is, a backlight is provided on the back surface of the liquid crystal element. The backlight is a mechanism for converting a linear light source such as a cold cathode discharge tube into planar light.

[0003] Specifically, there are a method of disposing a light source directly below the back surface of a liquid crystal element, and a method of installing a light source on a side surface and obtaining a surface light source using a light guide element such as an acrylic plate (side light method). Typically, in the case of the sidelight system, an optical element such as a prism array is arranged on the light emitting surface to obtain desired optical characteristics. Here, this side light method is described in, for example, Japanese Patent Application Laid-Open No. 61-99.
187 and JP-A-63-62104.

[0004] In particular, in order to more effectively bring out the general characteristics of a liquid crystal display device that is lightweight and thin, it is preferable to use a sidelight system in which a backlight can be made thin. 2. Description of the Related Art Side-light type backlights are often used for display devices.

[0005]

The performance required of these backlights has been increasing in recent years. Particularly, in portable personal computers and TV monitors using a color liquid crystal display, there has been a demand for a backlight. Since the light transmittance of the color liquid crystal cell itself is extremely low, a light source having higher luminance is required as a backlight light source.

[0006] For this reason, it is inevitable to secure the front luminance by optical condensing action by using many sheets made of a prism array or the like, but using these sheets exclusively increases the interface loss of the emitted light rays, Furthermore, in order to cause a large increase in cost, the emergence of a technique for improving the illumination light characteristics by simpler optical means has been awaited.

[0007] In order to explain this situation in more detail, the viewing angle characteristics seen in the illumination light of a sidelight type backlight which has been printed with white ink on a conventionally used light guide and has a light extraction mechanism. By way of example, as shown at 41 in FIG. 4, it can be seen that it has a broad distribution over a wide angle range. FIG. 4 shows an example of viewing angle characteristics observed in illumination light of a direct type backlight in which a fluorescent tube is installed immediately below the back of a color liquid crystal cell.
It can be seen that this also has a broad distribution over a wide angle range, as shown in FIG.

When illuminating light having such a broad distribution is focused on the front surface, for example, the angle range of 45 degrees to 45 degrees shown in FIG.
It is important to direct outgoing light rays in a region deviating from the front as seen at 70 degrees (−45 degrees to −70 degrees). Therefore, the light source as shown in FIG. Install a prism with the apex angle on the side opposite to the side facing
Inclined light is collected in the front direction.

However, such a method has a very small light-collecting property with respect to a broad illumination light distribution in a direction perpendicular to the light (a direction perpendicular to the paper surface) shown in FIG. Prism sheets for directing light in this direction in the front direction are further provided in the cross direction, and a total of two prism sheets are arranged so that their generatrix is orthogonal to each other, and light is collected in the front direction.

Therefore, when a surface light source device that emits a broad diffused light, in which a light guide made of a thin transparent substrate is provided with a light scattering mechanism made of a printed pattern of white ink, is used as illumination light, the light source always crosses in the direction intersecting. Inevitably, two or more provided prisms must be used, so that the amount of illumination light decreases due to reflection loss at the interface. That is, the present invention has been made in view of such circumstances,
The present invention provides a light control sheet having a simple structure and easy production, which has high controllability of illuminating light despite being a single sheet, and exhibits high light condensing ability particularly for an illuminating light source having a high diffusivity. .

[0011]

According to the present invention, there are provided a plurality of prism-shaped incident elements which are formed of a transparent thin sheet, and which have a plurality of prism-shaped incident elements having a light incident surface having an average inclination angle of 5 to 35 degrees on one surface thereof. The present invention relates to a light control sheet provided with a light collecting element on a surface. Furthermore, the present invention relates to a surface light source device in which a light source is provided on a side of a thin transparent substrate, and the light control sheet is provided on a light emitting surface side of a surface light source member that emits light from the front side.

Further, the dimming sheet (illumination light characteristic improving sheet) and the surface light source device of the present invention are also realized when each component has the following characteristics, more specifically.
That is, the light-collecting element intersects the parallel direction of the prism-shaped incidence elements at an angle of 45 degrees or more, and a large number of prism-shaped emission elements having a light emission surface with an average inclination angle of 30 to 60 degrees are arranged in parallel. What is provided.

Further, the parallel direction of the prism-shaped incidence elements and the parallel direction of the prism-shaped emission elements intersect at an angle of about 90 degrees. In addition, the light extraction mechanism provided on the substantially plate-shaped light guide may be a print pattern using white ink, or a combination of white ink and a rough surface.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a light control sheet of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a light control sheet according to the present invention, FIG. 2 is a vertical cross-sectional view showing an example of the shape of a prismatic incident element of the light control sheet, and FIG. 4, FIG. 4 is a diagram illustrating a viewing angle distribution of illumination light emitted from a conventional surface light source, FIG. 5 is a longitudinal sectional view showing a locus of incident light rays on a conventional prism sheet, and FIG. 6 is an example of a surface light source element. FIG. 7 is a partially broken perspective view showing another example of the surface light source element, and FIG. 8 is a view showing a viewing angle distribution of illumination light obtained by the surface light source device of the present invention. .

In the figure, 10 is a light control sheet, 11 is a bus, 31
Is the inclination angle, 32 is the light exit surface, 33 is the normal to the light exit surface,
Reference numeral 34 denotes a sheet central plane of the light control sheet, 41 denotes a viewing angle distribution of a light guide printed with white ink, 42 denotes a viewing angle characteristic of a surface light source having a fluorescent tube disposed immediately below the back surface, and 61 denotes a light guide. , 6
2 is a reflector, 63 is a diffusion sheet, 64 is a reflector, 6
5 is a cold cathode tube, 66, 67, 68 and 69 are white inks,
Reference numerals 71, 72, 73, and 74 indicate rough surface dot patterns, respectively.

As shown in FIG. 1, the light control sheet 10 of the present invention comprises a prismatic incident (light incident) element 12 having a large vertex angle on the lower side (light source side) and an upper side (light exit side). The light-collecting element 13 is formed in (). When the light control sheet 10 is used as a backlight light source, the light source light over a wide angle range is first condensed by the prismatic incident element 12 having a large vertex angle on the light source side.

FIG. 3 shows this state. The light source beam 34 from a direction largely deviated from the front is converted in the front direction in order for the prism-shaped incident element 12 to function as a kind of convex lens. Further, a condensing element 13 described later is provided on a side of the light control sheet 10 opposite to the side on which the prismatic incident element 12 is provided.

In the dimming sheet 10 using such a condensing optical system, only one dimming sheet 10 can diffuse diffuse illumination light having a broad distribution when viewed from the normal direction to the light exit surface. It is possible to condense light in a three-dimensional manner, and despite the simple configuration, it is difficult for the intensity of illumination light to decrease due to reflection loss at the interface. In addition, in the conventional mode in which the prism apex angle faces the side opposite to the light source side (see FIG. 5), a ray component oriented in the normal direction of the light exit surface having relatively high intensity, that is, FIG. The light ray near 0 degree at 4 is shown in FIG.
As shown in (b), the prism inclined surface receives total internal reflection based on Snell's law and may not be effectively used, whereas the large vertex whose apex angle is directed toward the light source used in the present invention. In the prismatic incident element 12 having a corner,
Such a phenomenon does not occur, and there is an advantage that the light amount of the light source light can be used effectively.

Therefore, considering the principle of the optical system, the prism-shaped incident element 12 whose apex angle is directed to the light source side is determined such that the apex angle of the prism-shaped incident element 12 is appropriate to serve as a convex lens. Should be used for a backlight light source, and have a vertex angle of 50 degrees to 110 degrees.
It is essentially different in function from a prism having a vertex angle as small as degree. In order to clarify this condition, an output angle γ when a light beam emitted from the light source at an emission angle α based on FIG. And the solutions of the two types of inclined surfaces as γ1 and γ2, respectively.

[0020]

(Equation 1)

## EQU2 ## In addition, from the viewpoint that the prism-shaped incident element 12 functions as a so-called condensing lens as described above, the present invention is not limited to the triangular prism shape, and the average inclination angle may satisfy the above condition. As shown in FIG. 2, the above-described effect can be obtained even if the prismatic incident element 12 is a prism having a polygonal cross section, a prism having a curved top, a cylindrical lenticular lens, a group of pyramids having a polygonal cross section, or the like. It is quite possible to give

That is, the average inclination angle should satisfy 5 to 35 degrees. Here, the average inclination angle is an angle formed between the sheet central plane 34 of the light control sheet and the prism inclined plane as indicated by 31 in FIG. More specifically, it is defined as an average value when 100 points of the angle defined above are measured at a pitch of 10 μm.

As the inclination angle 31 of the prismatic incident element 12 whose apex angle is directed to the light source side, the range in which the light condensing action is exerted is 5 degrees to 35 degrees, preferably 7.5 degrees to 30 degrees.
Degrees, more preferably 10 degrees to 25 degrees. This is 110 to 170 degrees, preferably 120 to 165 degrees, more preferably 130 to 160 degrees as the apex angle of the triangular prism.
Corresponds to degrees. The broad diffused light from the light source is collected in the front direction by the prism having such a large vertex angle or the optical element group having the same average inclination angle.

Next, a prism sheet is usually used as the light-collecting element 13 disposed on the side opposite to the light source side of the light control sheet 10, but in some cases, a cylindrical lenticular lens array, a micro convex lens array, It may be a light-collecting element such as a group of minute polygonal pyramids (quadrangular pyramids, cones, etc.). In terms of condensing the light rays incident on the sheet, the present invention is not limited to the triangular prism sheet, and the average inclination angle is 30 to 60 degrees, preferably 40 degrees.
The light condensing element 13 having an average inclination angle of from 50 to 55 degrees, more preferably from 40 to 50 degrees, is provided.

These light-collecting elements 13 (prism sheets)
Are arranged such that the direction of the generatrix crosses the optical element group whose apex angle is directed toward the light source side at 45 degrees or more, preferably 60 degrees or more, and more preferably substantially 90 degrees. Since the light-collecting element 13 composed of a prism-shaped element or the like arranged so that the direction of the generatrix crosses the prism-shaped incident element 12 whose vertex angle is directed to the light source side, the vertex angle is directed to the light source side. Outgoing light rays that could not be condensed by the prismatic incident element 12, for example, light rays distributed in a direction perpendicular to the light shown in FIG. It is a mechanism to realize.

In a preferred embodiment of the present invention, the light control sheet 10 is formed of a resin material. Particularly, the base portion of the light control sheet 10 is made of an acrylic resin, a polycarbonate resin, or a polyester resin, and the base material surface is made of a known thermosetting or photocurable resin represented by an acrylic resin or the like. The optical element is formed.

Such a light control sheet has a light guide 61 (resin plate) having a light scattering mechanism (light scattering surface) formed of white inks 66 to 69 or the like, and a side light type backlight as a light extraction mechanism. A viewing angle distribution of illumination light, such as a direct-type backlight (not shown) in which a fluorescent tube is installed immediately below a display surface made of a liquid crystal display panel or the like and a luminance distribution is made uniform by a light diffusion plate or the like. This is particularly effective for improving the front luminance of a broad and broad surface light source.

Further, Japanese Patent Application Laid-Open Nos. 6-18879 and 7-16
For example, the present invention can be applied to a surface light source element that emits scattered light having directivity disclosed in U.S. Pat. The average tilt angle should be set so that it is directed in the front direction by the prism part which turned the corner. Even in such a light control sheet 10 according to the present invention in which an average inclination angle suitable for directional scattering is set, the characteristic of condensing a broad light source is still maintained. By using the light source, it is possible to collect a light source in which directional scattering and broad scattering are mixed.

That is, in the case of a backlight using a scattered light having directivity as a light source, provided with a reflecting mechanism (rough surface) 71-74 element comprising a rough surface or the like on the surface of the light guide plate 61, JP-A-6-18879, etc. In general, a prism sheet having a small apex angle of 50 to 90 degrees and having an apex facing the light source 65 is disposed such that the generatrix is parallel to the tubular light source. Was.

However, in the prism facing the light source 65 having such a small apex angle, the light scattering mechanism (white ink) 6 in which white ink is printed on the surface of the light guide plate 61 is used.
Broad scattered light scattered by 6 to 69 has no ability to condense, so that, for example, light emitted from a light guide having a mixture of rough surfaces 71 to 74 and white inks 66 to 69 is efficiently condensed. It is difficult.

On the other hand, in the light control sheet 10 of the present invention, the prism-shaped incident element 12 having a large apex angle and facing the light source side is not only capable of not extremely narrowing the directivity of the outgoing light beam but also having a very small angle. Even after setting the average inclination angle appropriate for the directional scattering by the rough surfaces 71 to 74 and the like, since the characteristics of condensing the broad light source are still maintained, the rough surfaces 71 to 74 and the white ink 66 to 74 are retained. By using 69 together, broad scattered light is also collected, and a viewing angle characteristic suitable for use as a backlight is realized.

That is, since the light control sheet 10 of the present invention also has the above-described features, the light control sheet 10 of the present invention can be used as a surface light source having high directivity, such as a light guide in which rough surfaces 71 to 74 and white inks 66 to 69 are mixed. The viewing angle characteristics in the direction 33 perpendicular to the tubular light source 65, which tends to be narrow only with the rough surfaces 71 to 74, can be suitably used.
It can be expanded by using together.

It is also preferable to provide a diffused sheet 63 such as a frosted glass between the light guide plate 61 and the light control sheet 10 in order to make the entire light amount uniform. Further, a reflector 64 is usually provided on the side opposite to the light exit surface side to increase the amount of light. Although the light supply means 65 of the surface light source in the present invention is not particularly limited, a fluorescent tube (cold cathode tube, hot cathode tube), a tungsten incandescent bulb, an optical rod, an LED array and the like are typical, and Is usually provided with a reflector 62.

In particular, it is most preferable to use a cold-cathode tube as a linear light source that can be easily reduced in size and increased in luminance. In the present invention, a liquid crystal display utilizes the electro-optic effect of liquid crystal molecules, that is, optical anisotropy (refractive index anisotropy), alignment, and the like, and applies an electric field or conducts electricity to an arbitrary display unit to align the liquid crystal. The display is performed by using a liquid crystal cell, which is an array of optical shutters, driven by changing the light transmittance and the reflectance.

Specific examples thereof include liquid crystal display elements of a transmission type simple matrix driving super twisted nematic mode, a transmission type active matrix driving twisted nematic mode, and the like. By configuring a liquid crystal display as the backlight light source means, it is possible to impart characteristics suitable for a liquid crystal display, such as high brightness, a wide viewing angle, and low price.

[0036]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist.

Example 1 The surface light source device shown in FIG. 6 was constructed. Size 100m made of polyethylene terephthalate as base film
Using a film having a size of mx 100 mm, a thickness of 200 μm, and a light transmittance of 92%, a triangular prism with a pitch width of 150 μm facing the light source and having an average inclination angle of 25 degrees and a top angle of 130 degrees is light-cured on the surface of the film. A triangular prism having an average inclination angle of 45 degrees and a vertex angle of 90 degrees on the side opposite to the side on which the prism is formed, and a triangular prism having a generatrix directed to the light source side. Is formed so as to form an angle of 90 degrees, thereby forming a light control sheet. An acrylic resin having a size of 100 mm × 100 mm and a thickness of 4 mm was used as a surface light source, and a TiO ₂ -containing white ink patterned so that the area became relatively larger as the distance from the light source was increased.

Further, a diffusion plate is provided on the light exit surface of the light guide, and a reflection sheet made of foamed polyethylene terephthalate is provided on a surface facing the light exit surface, and the illumination light characteristic is improved thereon. A sheet was provided to form a surface light source element. A cold cathode tube having a tube diameter of 3 mm was used as a light source, the periphery of the cold cathode tube was covered with a reflector, and a voltage was applied via an inverter to light the lamp. The luminance distribution with respect to each emission angle from the center of the planar light guide element was measured using a luminance meter (BM-7 manufactured by Topcom). The result is shown as 81 in FIG.

Example 2 The surface light source device shown in FIG. 7 was constructed. A dot pattern composed of a rough surface using a mold formed on a plate similar to the acrylic resin plate used as the light guide so that the area of the dot pattern composed of the rough surfaces 71 to 74 increases as the distance from the light source 65 increases. Is transferred to the white ink 6.
A dot pattern consisting of 6 to 69 was printed to form a light guide, and the other conditions were the same as in Example 1 and the luminance distribution was measured. The result is shown as 82 in FIG.

Comparative Examples 1 and 2 Dimming was performed using a light guide printed with the same white ink as in Example 1 and a light guide mixed with the same rough surface pattern and white ink as in Example 2. The luminance value was measured in the same manner as in Examples 1 and 2, except that the sheet was not used.
The results are shown in FIG. 8 as 83 and 84, respectively.

[0041]

The light control sheet of the present invention has a high illuminating light controllability even though it is a single sheet, and exhibits a high light condensing ability especially for an illuminating light source having a strong diffusive property. A simple, easy-to-production and low-cost light control sheet can be provided. In addition, in order to have a feature to collect both high-intensity scattered light with directivity and scattered light with diffusivity,
It is possible to achieve both high front luminance and a wide viewing angle. These characteristics can respond to the demand for the optical characteristics of the illumination light for the diversified liquid crystal display backlight with high controllability in recent years.

[Brief description of the drawings]

FIG. 1 is a perspective view of a light control sheet according to the present invention.

FIG. 2 is a longitudinal sectional view showing an example of the shape of a prismatic incident element of the light control sheet according to the present invention.

FIG. 3 is a longitudinal sectional view showing a trajectory of an incident light beam on a light control sheet according to the present invention.

FIG. 4 is a view exemplifying a viewing angle distribution of illumination light emitted from a conventional surface light source.

FIG. 5 is a longitudinal sectional view showing a locus of an incident light beam on a conventional prism sheet.

FIG. 6 is a partially broken perspective view showing an example of a surface light source element.

FIG. 7 is a partially broken perspective view showing another example of the surface light source element.

FIG. 8 is a view showing a viewing angle distribution of illumination light obtained by the surface light source device of the present invention.

[Description of Signs] 10 Light control sheet 11 Bus bar 31 Inclination angle 32 Light emission surface 33 Normal line of light emission surface 34 Sheet central surface of illumination light characteristic improvement sheet 41 Viewing angle characteristic of light guide printed with white ink 42 Viewing angle characteristics of a surface light source provided with a fluorescent tube immediately below the back surface 61 Light guide 62 Reflector 63 Diffusion sheet 64 Reflector 65 Cold cathode tube 66, 67, 68, 69 White ink 71, 72, 73, 74 Rough surface Dot pattern

Claims (6)

[Claims] 1. A prismatic light-receiving element comprising a transparent thin sheet having a light incident surface having an average inclination angle of 5 to 35 degrees on one surface thereof, and a light-condensing element provided on another surface. Light control sheet. 2. A large number of prismatic light emitting elements having a light emitting surface with an average inclination angle of 30 to 60 degrees, in which the light condensing element intersects the parallel direction of the prismatic light incident elements at an angle of 45 degrees or more. The light control sheet according to claim 1, wherein the light control sheet is provided. 3. The light control sheet according to claim 2, wherein the parallel direction of the prism-shaped incidence elements and the parallel direction of the prism-shaped emission elements intersect at an angle of substantially 90 degrees. 4. A light source is provided on a side of a thin transparent substrate,
A surface light source device comprising: a surface light source member that emits light from the front side; 5. The surface light source device according to claim 4, wherein a light scattering mechanism composed of a print pattern made of white ink is provided on the opposite side of the light emitting surface of the thin transparent substrate. 6. The surface light source device according to claim 4, wherein a reflection mechanism having a rough surface is provided on the thin plate-shaped transparent substrate.