JP2002221613A - Light reflection sheet and surface light source device and liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively utilize light and to simplify structure by using a light reflection sheet which is a novel light controlling member and further to provide the light reflection sheet bringing about no leakage and no short circuit of a current used for the lighting of light source and a surface light source device and a liquid crystal display device using the same. SOLUTION: The light reflection sheet is characterized by having a number of nearly similar shaped basic units consisting of reflection faces aligned with <=5,000 μm pitch, further by making principal reflection directions of the nearly similar shaped basic units consisting of the reflection faces be almost constant, moreover by constructing the reflection faces with a metal substance with >=70% reflectance and, at the same time, by arranging a coating layer composed of a transparent insulating substance on the reflection faces.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light reflection sheet, a surface light source device and a liquid crystal display device using the same.
More specifically, the present invention relates to a light reflection sheet which is a novel light control member and is preferably used as, for example, a backlight of a transmission type liquid crystal display device, and a surface light source device and a liquid crystal display device using the light reflection sheet.

[0002]

2. Description of the Related Art In recent years, transmissive liquid crystal displays (displays) have been frequently used as monitors for personal computers and display devices such as thin TVs. A planar illumination device, that is, a backlight (surface light source device) is provided.
This surface light source device is a mechanism for converting a linear light source such as a cold cathode discharge tube into planar light.

[0003] Specifically, a method of arranging a light source immediately below the back surface of a liquid crystal element or a method of installing a light source on a side surface and converting the light into a planar shape using a translucent light guide such as an acrylic plate. A typical method is to obtain a surface light source (side light method), and a mechanism for obtaining desired optical characteristics by disposing an optical element such as a prism array on the light emitting surface.

[0004]

However, these conventional transmission type liquid crystal display devices have a problem that the structure is still complicated. The reason is that the illumination optical system having a simple structure capable of obtaining desired optical characteristics in the surface light source device has not been obtained, and the structure of the surface light source device has to be complicated. This type of liquid crystal display device (LC
D).

For example, in a surface light source device used as a backlight optical system of a transmission type liquid crystal display device, for example, optical sheets such as a prism sheet are frequently used in order to use illumination light from the surface light source device as effectively as possible. I was Therefore, the structure of the illumination optical system is complicated, and as a result, the assemblability is poor and the yield is low, resulting in an increase in cost.

Accordingly, the present inventor has developed a light reflecting sheet having a substantially similar basic unit having a reflecting surface with a concave cross section on the side opposite to the light emitting surface of a light guide, which is a component of the surface light source device. A simple structure in which most of the light emitted from the light guide is emitted to the light reflection sheet side, and the light reflection sheet changes the angle of illumination light in the front direction and condenses light by the basic unit. But it was found to be effective.

However, although it is effective to construct an optical system of an LCD backlight by a substantially similar basic unit (inclination surface array) composed of a reflecting surface, if it is desired to obtain preferable optical characteristics, the reflecting surface is not suitable. A reflection surface having specular reflection characteristics represented by silver and aluminum must be provided. In other words, in the case of a reflection surface of silver or aluminum, it is possible to efficiently change the angle of the light beam and collect light.

However, when the reflecting surface is formed of such silver or aluminum, the reflecting surface has high conductivity, which causes a problem of causing a leak or short circuit of a current used for lighting the light source. This is a particularly serious problem in a configuration using a high-voltage lighting power source that uses a discharge tube such as a cold-cathode tube generally used in a large LCD backlight as a light source. Therefore, if this problem cannot be solved, a practical surface light source device cannot be provided no matter how excellent a light reflecting sheet is developed to simplify the structure.

SUMMARY OF THE INVENTION An object of the present invention is to solve such a conventional problem. By using a light reflecting sheet, which is a novel light control member, effective use of light and simplification of the structure are achieved. Moreover, it is an object of the present invention to provide a light reflection sheet which does not cause leakage or short circuit of a current used for lighting a light source, and a surface light source device and a liquid crystal display device using the same.

[0010]

SUMMARY OF THE INVENTION The present invention is a light reflecting sheet, and is constituted as follows in order to solve the above-mentioned technical problem. That is, in the light reflecting sheet of the present invention, a large number of substantially similar basic units each having a reflective surface are arranged at a pitch of 5000 μm or less, and the main reflection direction of the basic units is substantially constant. % Of a metal material and a coating layer made of a transparent insulating material is provided on the reflection surface.

<Specific Configuration in the Present Invention> The light reflecting sheet of the present invention is composed of the above-mentioned essential components, but is established even when the specific components are as follows. The specific constituent element is characterized in that the metal substance is silver or aluminum, and the coat layer made of a transparent insulating substance is made of a transparent resin having a resistivity of 1.0 × 10 ⁶ Ω · cm or more.

Further, in the light reflecting sheet of the present invention, it is preferable that the substantially similar basic unit composed of the reflecting surface has a concave or convex cross section, and the substantially similar basic unit composed of the reflecting surface has a ridge line. It is preferable to form a large number in parallel. In the light reflecting sheet of the present invention, it is preferable that the substantially similar basic unit composed of the reflecting surface is configured by arranging a large number of concave mirrors or convex mirrors having a maximum diameter of 5000 μm or less.

Further, in the light reflection sheet of the present invention, it is preferable that the main reflection direction of the substantially similar basic unit having the reflection surface and the normal direction of the light reflection sheet form an angle of 15 degrees or more. Furthermore, it is preferable that the coat layer has a surface where Rz = 25 μm or less. In addition, a substantially similar basic unit consisting of a reflective surface is formed by coating a metal material on a thermoplastic resin film, and a stretched film is adhered to the back surface of the thermoplastic resin film to form the light reflection sheet of the present invention. Can be formed.

The present invention is a surface light source device which solves the conventional technical problem by using a light reflection sheet having the above-mentioned features in an illumination optical system. When the light reflecting sheet is used in the illumination optical system as a component of the surface illumination device, it is preferable to provide a printing pattern on the surface thereof.

Further, the surface light source device of the present invention further comprises a light guide disposed on the light reflection sheet on the reflection surface forming side, and a light source is provided at at least one end of the light guide. The light guide is provided with a mechanism that is provided and emits at least 65% or more of the emitted light toward the light reflecting sheet. The present invention is also a liquid crystal display device using such a surface light source device as backlight light source means.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a light reflecting sheet according to the present invention, a surface light source device and a liquid crystal display device using the same. FIG. 1 schematically shows a main part of a surface light source device 11 using a light reflection sheet 10 according to one embodiment of the present invention.

The surface light source device 11 of this embodiment includes a substrate, that is, a light guide 12 made of a translucent flat plate, and one end 13 of the light guide 12 extends along the end face of the side end. The linear light source 14 is disposed as described above. This linear light source 14
A fluorescent tube, an LED array, or the like can be used, but is not particularly limited thereto. As the linear light source 14, it is most preferable to use a cold-cathode tube which is excellent in luminous efficiency and easy to miniaturize.

The arrangement of the linear light source 14 is as follows.
The present invention is not limited to this embodiment. In addition, a single-lamp type in which a cold cathode tube is provided only at one end, two cold cathode tubes are provided at one end Two-lamp type, one or two cold-cathode tubes are provided at one end, and this is also provided at the opposite side end, for example, a two-lamp or four-lamp type. Representative.

In the present invention, the form of the light source is not limited to a linear light source. For example, in a small surface light source device, a point light source such as an LED can be used together with an optical rod. A reflector 15 is attached to one end of the light guide 11 so as to cover the linear light source 14 so that the direct light from the linear light source 14 and the light reflected by the reflector 15 can be efficiently used. The light is incident on the inside of the light source 12 from one side end which is a light incident end face.

The light guide 12 is, for example, a light-transmitting thin plate having a square shape with a thickness of about 4 mm, and one surface, which is the upper surface in FIG. The other surface (the lower surface in FIG. 1) on the opposite side is a surface 17 facing the light emitting surface.

The light reflecting sheet 10 is provided near the surface 17 of the light guide 12 opposite to the light exit surface 16.
The light reflection sheet 10 is configured such that a large number of basic units 18 each having an inclined reflection surface 18a are formed on the surface of a base material 19 at a fine pitch P. Here, the basic unit 18 means a basic shape unit of the light reflecting sheet 10 obtained as an aggregate of the inclined reflecting surfaces 18a having substantially similar shapes as shown in FIGS. 1 to 3 and FIGS. I do.

That is, the basic unit 18 is a minimum shape unit, which is a so-called unit cell, which loses the sameness or similarity when divided further. The pitch P is defined as the minimum length of the basic periods formed by the arrangement of the basic units 18 as shown in FIGS. 2, 3, and 13 to 18.

Since the light reflecting sheet of the present invention preferably has the function of changing the direction of light rays, as shown in FIG. 22, the parallel light flux 36a which is perpendicularly incident on the light reflecting sheet according to the present invention. However, it is preferable that the surface shape of the basic unit is set so that the direction of the basic unit is changed by the effect of the basic unit and the light is emitted in an oblique direction (the main reflection direction 36b). More specifically, the main reflection direction 3
The angle β between 6b and the normal direction of the light reflecting sheet is preferably 5 degrees or more, more preferably 20 degrees or more, and still more preferably 15 degrees or more.
It is preferable to determine the shape of the basic unit.

Further, the light guide 12 has a light extraction mechanism 20.
Is provided. The light extraction mechanism 20 is configured to selectively emit a light beam incident on the light guide 12 to the light reflection sheet 10 side.
It is necessary that the light beam emitted from the light guide 12 should emit 65% or more, more preferably 70% or more, and still more preferably 75% or more of the luminous flux on the 0 side, and this requirement is satisfied. The light extraction mechanism used is not particularly limited.

Here, a light extraction mechanism 2 provided in the light guide 12 to emit at least 65% or more of all the outgoing light rays emitted from the light guide 12 to the light reflection sheet 10 side.
Various modes can be considered as 0, and there is no particular limitation. However, as a most preferable mode, as shown in FIG. 4, a number of convex protrusions 21 are provided on a surface (surface on the light reflection sheet side) 17 of the light guide 12 opposite to the light emission surface 16. A light extraction mechanism 20 formed by a pattern can be used.

In addition, as shown in FIGS. 5 to 9, various surface shapes are designed so that most outgoing light rays emitted from the light guide 12 are directed to the light reflecting sheet 10. It is possible to do. That is, the embodiment shown in FIG. 5 is different from the embodiment shown in FIG.
Are formed in a predetermined pattern to form the light extraction mechanism 20.

The embodiment shown in FIG.
The concave 17 is formed on the surface 17 on the light reflection sheet 10 side
By forming 3a, a relatively protruding portion 23b is formed to form a light extraction mechanism. Further, in the mode shown in FIG. 7, a large number of grooves 24 having a V-shaped cross section are formed at predetermined intervals on the light emitting surface 16 of the light guide 12, thereby forming the light extraction mechanism 20.

Further, in the embodiment shown in FIG. 8, a large number of grooves 25 having a V-shaped cross section are formed at predetermined intervals on the surface 17 of the light guide 12 on the side of the light reflecting sheet 10 so that the light extraction mechanism 20 is formed. It was done. In the embodiment shown in FIG. 9, the light extraction mechanism 20 is formed by forming a large number of projections 26 having a mountain-shaped cross section at predetermined intervals on the light emission surface 16 of the light guide 12.

In addition to these various aspects, a mode in which a scatterer having forward scattering properties in a specific direction is provided in the light guide 12, and a diffractive optical element such as a hologram element and a surface relief element is provided in the light guide 12. There is no particular limitation on the light extraction mechanism, such as the mode provided on the surface, as long as it can emit at least 65% or more of the light emitted from the light guide 12 toward the light reflecting sheet 10 as described above. .

In the surface light source device of the present invention, such a shape restriction required for the light extraction mechanism 20 is limited to the light guide 1 on the light reflection sheet 10 side as described above.
It should be determined in view of emitting more than 65% of the outgoing rays from 2.

For example, this is shown in FIGS. 10 (a) and 10 (b).
When the projection 22 having a triangular cross section shown in FIG. 5 is formed on the surface 17 of the light guide 12, the apex angle β of the point is preferably 90 degrees or less, and Preferably it is 70 degrees or less, more preferably 50 degrees or less.

That is, as shown in FIG. 10 (b), as the apex angle β of the projection 22 formed on the surface 17 of the light guide 12 is increased and the cross-sectional shape thereof becomes mountain-shaped, The light exit surface 16 of the light guide 12 is totally reflected.
This is because an unnecessary light ray component 27 emitted in the direction increases, and by using a triangular cross-sectional shape having a small apex angle, as shown in FIG. It is possible to increase the light beam components 30 and 29 that draw the trajectory (the light beam component 29 emitted in the direction of the normal line 28 of the light guide 12 through the reflection process on the light reflection sheet 10).

Another example will be described. In the embodiment using the convex protrusions 21 shown in FIG. 4, FIG.
, The height h of the projection 21, in other words, the depth h of the projection 21 as viewed from inside the light guide 12.
And the value h / Wmin defined by the minimum opening width Wmin,
Preferably it is 0.5 or more, more preferably 0.6 or more, and still more preferably 0.7 or more.

The projection 21 shown in FIG.
As is clear from FIG. 11A, the cross section was elliptical, but when the cross section was rectangular as shown in FIG. The opening width becomes Wmin. If the convex protrusion 21 is designed so as to satisfy such a condition, a suitable shape is determined so that at least 65% or more of the light emitted from the light guide 12 is emitted toward the light reflection sheet 10. Can be.

As described above, the light extraction mechanism preferably used in the present invention and illustrated in FIGS. 4 to 9 has, to the last, a light beam emitted from the light guide 12 toward the light reflection sheet 10. Is determined from the viewpoint that 65% or more of the light is emitted. Although a detailed description of the design method in this regard is omitted, in short, for example, when the projections 23 having a triangular cross section are formed on the surface 17 of the light guide 12, those having a small apex angle are preferable.
For example, in a mode using the convex protrusions 22, it is necessary that the shape be sufficiently deep with respect to the opening width. The other light extraction mechanisms 20 shown in FIGS. 6 to 9 are similarly designed based on the above, taking into account the characteristics of light rays propagating in the light guide 12.

Here, in the light guide 12 used in the present invention, the ratio of the light flux selectively emitted to the light reflecting sheet side to the total light flux emitted from the light guide 12 is at least 65% or more. However, as described above, it is necessary for the effect of the optical design according to the present invention to function effectively. The measuring means for measuring the selectivity of the direction in which the light beam is emitted is as follows. .

That is, first, the black sheet 37 that absorbs light almost completely is provided at the position where the normal light reflection sheet is provided.
(Flocked paper or the like) is arranged, and as shown in FIG. 23, the light guide 12 is set in a normal direction and lit in the integrating sphere 38, and the light exit surface of the light guide 12 obtained at this time is set. The total luminous flux emitted from the side is defined as Σa.

Next, the direction of the light guide 12 is set upside down as usual (originally, the surface facing the light reflecting sheet is set to the light emitting surface side). And the total amount of luminous flux emitted from the surface opposite to the light exit surface of the light guide 12 obtained at this time is represented by Δb. At this time, the obtained numerical value, Σb / (Σa + Σb) × 100, is the ratio (%) of the luminous flux selectively emitted to the light reflecting sheet side.
This value is 65% or more, more preferably 70% or more, and still more preferably 75% or more.

In the surface light source device of the present invention, as described above, an optical system in which most of the light emitted from the light guide 12 is emitted toward the light reflecting sheet 10 is provided. As shown in FIG. 1, the light beam 30 having directivity that is obliquely incident on the light reflection sheet 10 is often used.

Therefore, in the surface light source device of the present invention, the light beam 30 selectively emitted from the light guide 12 toward the light reflecting sheet 10 is inclined as shown in FIG. Due to the effect of the substantially similar basic unit 18 composed of the reflecting surface 18a, the direction is deflected in the front direction of the light guide 12, and as a result, when the surface light source device 11 is viewed from the front, the illumination intensity is extremely high. Can be obtained.

This means that the configuration of the illumination optical system can be extremely simplified as compared with the conventional surface light source device. In the conventional surface light source device, the light is collected by a refractive optical system such as a prism array. In contrast to performing the light function and the bending function, in the present invention, the substantially similar basic unit 18 including the inclined reflecting surface 18a provided on the light reflecting sheet 10 is formed into a shape like a concave mirror, for example. By designing and the like, it becomes possible to provide the light reflecting sheet 10 with desired optical functions such as a condensing function and a bending function, and a surface whose structure is extremely simplified while maintaining the same optical performance. A light source device can be provided.

Here, the light reflecting sheet 10 used in the present invention is preferably a flexible base material 19 having a thickness of about 1000 μm or less, but the form such as the thickness is appropriately selected depending on the application object and is not necessarily limited to this. Not something. However, a preferred substrate 19 is a thermoplastic resin film. In addition, the reflectance is high from the viewpoint of high efficiency, that is, 70%.
It is desirable to use a metal material having the above high reflectivity.

Here, in the present invention, the reflectance of 70% or more means that the reflectance is achieved in the visible light spectrum region because the reflectance is used for display by human eyes. Nor. That is, J
As defined in IS-Z8120, the ratio of the reflected luminous flux energy to the incident luminous flux energy in the visible light spectrum region has the above value, and is preferably 7
It is 5% or more, more preferably 85% or more, particularly preferably 88% or more, and very preferably 91% or more.

In the present invention, it is necessary to avoid a change in color tone in the light reflection sheet portion, and it is preferable that the light reflection sheet portion has reflection characteristics as flat as possible in the visible light spectrum range. Therefore, the value of the spectral reflectance at 550 nm, which is located substantially at the center of the visible spectrum, is used as the reflectance, and a preferable value range can be defined.

In addition, the above-mentioned reflectance means the reflectance of the material located on the surface of the inclined surface that substantially causes reflection, and specifically, the surface of the inclined surface is represented by silver or aluminum. As described above, it is preferable to provide a material having a high reflectance and a small change in color tone. In some cases, the coat layer 31 or the like is provided on the reflective surface. The reflectivity referred to here is the reflectivity of the surface of the material itself, which does not have the coat layer 31 and the like and substantially contributes to reflection such as a metal material. It means.

In order to prevent the arrangement of the basic units 18 from being recognized on the screen, it is important that the arrangement pitch P of the substantially similar basic units 18 is as fine as possible. Is 5000 μm or less, preferably 1000 μm or less, more preferably 500 μm
It is as follows.

As a substantially similar basic unit 18 composed of an inclined reflecting surface 18a having a reflectance of 70% or more provided on the surface of the light reflecting sheet 10, as shown in FIG.
As shown in FIG. 3B, the basic unit 18 has a sawtooth cross section, or as shown in FIGS. 3A and 3B, the basic unit 18 has a mountain shape.
Is a structure that has periodicity only in one axial direction, and has a pitch of 3
000 μm or less, preferably 800 μm or less, more preferably 300 μm or less, a basic unit 18 comprising a parallel linear and flat inclined reflection surface 18 a in which the ridges 18 b are arranged in parallel when the light reflection sheet 10 is viewed from above. Is used.

This is shown in FIGS. 2A and 2B and FIG.
As shown in (a) and (b), in a mode in which the ridge lines 18b of the inclined flat reflecting surface 18a are arranged substantially in parallel, cutting using a diamond cutting tool or an end mill is easy to apply, so This is because molds are easy to manufacture, miniaturization is easy, and mass productivity is extremely high.

By using such a light reflecting sheet 10 in which a large number of parallel linear and flat inclined reflecting surfaces 18a are arranged, the pattern formed by the above-mentioned convex projections 21 is used as the light extraction mechanism 20 and the light guide 12 The light emitted from the light guide 12 designed so that most of the light flux emitted from the light guide sheet goes to the side where the light reflecting sheet 10 is disposed is converted into a light guide 12 by the effect of the parallel linear and flat inclined reflecting surface 18a. Normal 28
Since the light is reflected in the direction, it is possible to obtain an illumination light beam having extremely suitable characteristics as the surface light source device 11.

As shown in FIG. 12, the preferred range of the inclination angle α of the inclined reflecting surface 18a used for the substantially similar basic unit 18 depends on the light extraction mechanism 2 used.
0, and should be determined appropriately from the viewpoint of converting the direction of the light beam emitted from the light guide 12 to the direction of the normal line 28 of the light exit surface 16.

For example, as shown in FIG. 4, an embodiment in which the projection 21 is used as the light extraction mechanism 20, or FIG.
In the embodiment using the projections 22 having a triangular cross-section as shown in the above, the inclination angle α of the inclined reflecting surface 18a is preferably in the range of 50 to 7 degrees, more preferably in the range of 40 to 10 degrees, and still more preferably. A range of 34 degrees to 15 degrees is preferably used.

It is preferable that the cross section of the inclined reflecting surface 18a constituting each basic unit 18 be concave as shown in FIGS. This is not limited to the embodiment in which a large number of parallel linear and inclined reflecting surfaces suitably used in the present invention are arranged, as well as the embodiment in which concave mirror-shaped basic units 18 are arranged as shown in FIGS. Is also preferably used.

Also in this case, the range preferably used as the inclination angle α of the inclined reflecting surface 18 a is from the viewpoint of converting the direction of the light beam emitted from the light guide 12 into the direction of the normal line 28 of the light emitting surface 16. For example, in each of the embodiments using the convex protrusion 21 or the triangular protrusion 22 as the light extraction mechanism 20 as shown in FIGS. 4 and 5, the concave cross section as shown in FIG. Is preferably in the range of 50 ° to 7 °, more preferably in the range of 40 ° to 10 °, and still more preferably 3 °.
The range is 4 degrees to 15 degrees.

The light reflecting sheet 10 uses the basic unit 18 having the reflecting surface 18a having a concave cross section as a reflecting element.
, The light beam 30 having a broad spread emitted from the light extraction mechanism 20 provided in the light guide 12 is converted into a light beam 29 having a sharper angular characteristic (a light beam closer to a parallel light beam). In other words, the light can be emitted in the direction of the normal line 28 of the light guide 12. In other words, the light emitted from the light guide 12 is more collimated by the light-collecting effect of the concave mirror. This makes it possible to convert the emitted light into a light beam having extremely high brightness in the direction of the normal 28.

Therefore, in the conventional surface light source device, the light-collecting effect realized by using an expensive member which is difficult to manufacture such as a prism array can be realized without using such a member. , While maintaining almost the same optical characteristics, the surface light source device can be made to have a very simplified configuration, reducing the number of assembly steps, improving the yield, reducing the probability of dust contamination, reducing cost, etc. It has a great many advantages as a practical surface light source device.

By the way, from the viewpoint of the light collecting property of the surface light source device of the present invention, the inclined reflecting surface 18a having a concave cross section is used.
Is preferably used for the basic unit 18 as described above, but as another embodiment of the substantially similar basic unit 18 including the inclined reflecting surface 18a,
As shown in FIGS. 15 to 18, the maximum diameter is 3000 μm or less, preferably 800 μm or less, and more preferably 30 μm or less.
An example in which a structure in which concave mirror-like reflecting surfaces 18a each having a size of 0 μm or less are arranged is used. In such an embodiment, light can be condensed not only in one direction but also in two orthogonal directions. Therefore, as compared with the above-described embodiment in which a large number of parallel linear and inclined reflecting surfaces 18a are arranged, the light is condensed further. It is possible to improve the light properties.

In the case where the linear light source 14 is provided only on one side 13 of the light guide 12 as in the surface light source device 11 of the embodiment shown in FIG. It is preferable to dispose the light reflection sheet 10 formed on the opposite surface 17 in the mode shown in FIG. 13, that is, the light reflection sheet 10 formed by arranging the base units 18 of the parallel linear and sawtooth concave reflection surfaces 18a. In the case where the linear light sources 14 are respectively disposed on the opposite side portions 13a and 13b of the light guide 12 as shown in FIG. 20, the light reflecting sheet 10 has a form shown in FIG. Light reflecting sheet 1 formed by arranging basic units 18 of corrugated concave reflecting surfaces 18a
It is preferred to use 0.

The reflective material used for the light reflecting sheet 10 in the present invention is not particularly limited, but it is most preferable to coat the surface with silver or aluminum to form the reflective surface 18a from the viewpoint of ease of manufacture. It is. In particular, a method of forming a thin silver reflective layer using a dry process such as vacuum evaporation, sputtering, or ion plating and coating the surface is most preferable.

Before the vacuum deposition of silver, for example, a matte treatment is performed by sandblasting the surface of the base material sheet on which the substantially similar basic unit 18 having the inclined reflecting surface 18a is formed. You can also.
By performing such processing, it becomes possible to impart a proper light diffusing property to the specular reflection surface, to increase the angular distribution characteristics of the emitted light, suppress the glare of the illumination light, or reduce the liquid crystal cell. It is possible to obtain effects such as prevention of generation of a moiré pattern due to interference with the gate array.

When the reflecting surface 18a is formed of such silver or aluminum, the reflecting surface 18a has a high conductivity, which causes a problem of causing a leak or a short circuit of a current used for lighting the light source. This is a particularly serious problem in a configuration using a high-voltage lighting power source that uses a discharge tube such as a cold cathode tube generally used in a large LCD backlight as a light source as described above.

For this reason, a coating layer 31 made of a transparent insulating material is provided on the reflecting surface 18a made of silver or aluminum. This coat layer 31 preferably has a smooth surface by completely filling the concave portion of the reflection surface as shown in FIGS. 1 to 3 and FIGS. The reason why the surface of the coating layer 31 is made smooth by disposing a transparent insulating material so as to fill the concave portion of the reflection surface is as follows.

In an LCD backlight, it is necessary to correct bright lines and dark areas near the light source and to adjust the overall color tone. Therefore, it is often necessary to print on the surface of the light reflecting sheet. That is, by printing a light-absorbing black dot pattern or a light-diffusing white dot pattern on a light-reflecting sheet, the bright lines and dark areas near the light source are corrected, and the practical effective light-emitting area is expanded. You can do it.

However, if a coat layer made of a transparent insulating material is provided along with the surface shape of the substantially similar basic unit, the surface shape of the basic unit remains on the surface of the light reflecting sheet, and the printing ink "Smearing" and "who" occur. Therefore, in order to prevent this, the surface of the light reflection sheet needs to be a smooth surface embedded with a transparent resin or the like.

More specifically, the surface of the coat layer made of a transparent resin has an Rz value specified by JIS B0605 of 25 μm or less, preferably 20 μm or less, and more preferably 15 μm or less. Such a coat layer 3
Examples of the insulating substance for forming 1 include a transparent resin represented by a thermoplastic resin such as an acrylic resin or a polyester resin, a photocurable resin, or a thermosetting resin, or a transparent ceramic (silica, titania, etc.). Is typical).

The coating layer 31 made of the insulating material further has a resistivity of 1.0 × 10 ⁶ Ω · cm or more, preferably 1.0 × 10 ⁷ Ω · cm or more, more preferably 1.0 × 10 ⁷ Ω · cm or more.
A transparent resin of 10 ⁸ Ω · cm or more is the most suitable in terms of high electrical insulation, ease of manufacture, low cost, and the like. Also,
"Transparent" in the term "transparent insulating material"
It means that the total light transmittance is 85% or more, preferably 87% or more, more preferably 90% or more.

In a preferred embodiment of the present invention, the light reflecting sheet 10 is basically made of, for example, a polyester resin, an acrylic resin, a polycarbonate resin, a polyamide resin, a polyarylate resin, or a cyclic polyolefin as described above. The concave reflection surface array is formed by a base material 19 made of a thermoplastic resin film typified by a base resin or the like, and shaping by hot press molding or shaping by a photocurable resin is suitably used.

At this time, embossing of a thermoplastic resin film typified by polycarbonate, polyester, polyarylate or the like with a heating roll is suitable from the viewpoint of productivity. In addition, when only a thermoplastic resin film is used for an LCD backlight, the rigidity is insufficient, and the sheet may be bent. That is,
Deflection of the sheet deteriorates luminance unevenness and causes a problem of deterioration in appearance.

As a countermeasure against this problem, the surface of the thermoplastic resin film (the surface opposite to the surface on which the reflection surface is formed) is typified by an adhesive 32 such as biaxially stretched polyester or biaxially stretched polypropylene. It is preferable that the stretched films 33 are bonded to each other so as to have a required rigidity. The bonding of the base material 19, that is, the thermoplastic resin film and the stretched film 33 may be performed by fusion instead of the adhesive 32.

In the present invention, a liquid crystal display device uses an electro-optical effect of liquid crystal molecules, that is, optical anisotropy (refractive index anisotropy), orientation, and the like, and applies an electric field to or applies an electric current to an arbitrary display unit. It refers to a device that performs display by using a liquid crystal cell, which is an array of optical shutters, driven by changing the alignment state of liquid crystal and changing light transmittance and reflectance.

More specifically, transmission type simple matrix driving super twisted nematic mode, transmission type active matrix driving twisted nematic mode, transmission type active matrix driving in-plane switching mode, transmission type active matrix driving multi-domain vertical aligned mode, etc. Liquid crystal display device.

By configuring the surface light source device of the present invention as a backlight light source for these liquid crystal display elements in a liquid crystal display device, the surface light source device using the light reflecting sheet described above can be made thinner (less sheets). It is possible to obtain a liquid crystal display device with improved image quality, particularly with less bright lines, with a simple structure, improved assemblability, high yield, and reduced cost.

[0072]

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) A size of 210.0 × 190.0 mm, a thickness of 2 mm near the light source, and a position farthest from the light source, obtained by injection molding of an acrylic resin (Acrypet TF8 manufactured by Mitsubishi Rayon) as the light guide 12. Then 0.6m
It is assumed that a linear light source 14 composed of a cold-cathode tube is disposed on a thick portion using a wedge-shaped acrylic plate whose thickness changes in the short side direction of m. A fine convex protrusion (directionally selective light extraction mechanism) formed of a smooth surface having a rectangular opening shape patterned so as to be relatively large in a direction (a direction parallel to the linear light source) is formed in the light guide 12. Formed.

FIG. 11B is an enlarged view of the projection.
The depth h of the projection is 48.0 μm, the minimum opening of the projection when viewed in a sectional view in a direction perpendicular to the linear light source 14 is a field Wmin of 75.0 μm, and the maximum opening width, that is, The length of the opening in the direction parallel to the linear light source 14 is in the range of 80 μm to 240 μm, and is gradually increased as the distance from the light source increases, as described above.

Here, the mold used for forming the convex protrusions is as follows:
A dry film resist having a thickness of 50 μm (manufactured by DuPont) is laminated on a glass plate, a pattern is formed by photolithography, electrodes are deposited on the glass plate patterned with the dry film resist, and this is used as a master. It is obtained by using a nickel electroforming mold.

On the side of the light guide 12 where the light extraction mechanism 20 composed of the convex protrusions is not provided (on the light exit surface 16 side of the light guide 12), the light condensing property of the light guide 12 is further enhanced. As shown in FIG. 21, the apex angle is 90 degrees and the pitch is 50 degrees.
A light condensing element 34 composed of a prism array of μm is formed.
4 is arranged so as to be perpendicular to the side end portion 13 where it is disposed.

The convex protrusion serving as the light extraction mechanism 20 of the light guide 12 is provided on the side on which the light reflecting sheet 10 is provided.
The convex projections act as a direction-selective light extraction mechanism, and 69% of the light flux emitted from the light guide 12 is directed to the light reflection sheet 10 by the effect of selectively emitting light to the light reflection sheet 10 side. An emitted light guide suitable for use in the present invention was obtained.

The light reflecting sheet 10 has a sectional shape shown in FIG.
The light reflection sheet 10 having a parallel linear diametric slope in which the ridge lines shown in FIG. The pitch is set to 100 μm, and a silver sputtering layer is used for the reflection layer. On the surface of the silver sputtering layer, a photocurable acrylic resin having a resistivity of 1.74 × 1013 Ω · cm does not impair the printing surface. Coated smoothly. The value of Rz specified in JIS B0605 of the surface coated with the photocurable acrylic resin is 2.1.
μm.

The angle of inclination of the inclined surface was 25 degrees, and the sectional shape of the inclined surface was concave. By configuring such an optical system, a light beam emitted from a light guide obtained by a convex protrusion (a direction-selective light extraction mechanism) having a smooth surface provided on the light guide to the light reflection sheet side. Was converted in direction and condensed by the light reflection sheet 10 to obtain an illumination optical system in which light rays were emitted in the front direction of the light guide.

Further, a band-like bright portion (bright line) was generated near the linear light source in parallel with the linear light source.
As shown in FIG. 21, a black light-absorbing pattern 35 is provided over a width of 7.5 mm in the vicinity of the cold cathode tube 0,
The mechanism was designed to suppress bright lines generated near the linear light source.

As a linear light source, a cold cathode tube having a tube diameter of 2.0 mm was used, and high-frequency lighting was performed via an inverter to obtain a surface light source device. With a tube current of 6 mA, the average brightness in the plane was evaluated using a brightness measurement device (BM-7, manufactured by Topcom). As a result, an average brightness of 1740 nit was obtained. It was confirmed that the optical characteristics were sufficient for practical use.

Further, the leakage current from the cold cathode tube to the light reflecting sheet 10 was also extremely small, and the luminous efficiency of the cold cathode tube was kept sufficiently high, so that there was obtained a practically satisfactory electric characteristic. Furthermore, since no bright line is generated in the vicinity of the linear light source, the effective light emitting area can be made extremely wide (2.4 mm from the light incident side end of the light guide).

Comparative Example In the surface light source device described in the example, the surface of the light reflecting sheet was not coated with a photocurable acrylic resin, and a black light absorbing pattern was printed near the linear light source of the light reflecting sheet. A surface light source device was obtained in the same manner as in the example, except that it was not performed.

Since the leakage current from the cold-cathode tube to the light reflection sheet was large, the luminance at the same power consumption was greatly reduced to 229 nits as compared with the embodiment, and the performance in power consumption was low. In particular, application to battery-powered devices such as portable notebook computers has been difficult. Also,
Since bright lines are generated extremely strongly near the linear light source, the area near the light source cannot be an effective light emitting area (it cannot be used at all up to about 7 mm from the light incident side end of the light guide). It was difficult to narrow the frame of the light source device.

[0084]

As described above, according to the light reflecting sheet of the present invention and the surface light source device and the liquid crystal display device using the same, a large number of basic units each having a concave reflecting surface are formed on the surface of the base material at a fine pitch. When the incident light is deflected to a specific direction by making the main reflection direction by the concave reflection surface of each basic unit to be almost constant and making its reflectivity highly efficient It is possible to provide an inexpensive light control member that has a simple structure and can collect light so as to give a strong light intensity at the same time.

Further, according to the surface light source device of the present invention using the above-mentioned light reflecting sheet, the leak current from the light source to the light reflecting sheet is extremely small, and the light emitting efficiency of the light source is kept sufficiently high. It is possible to obtain electrical characteristics with no problem.

Further, according to the present invention, by using this surface light source device as, for example, an illumination optical system of a transmission type liquid crystal display device, a liquid crystal display device having a simpler configuration and excellent quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view schematically showing a main part of a surface light source device according to an embodiment of the present invention.

FIG. 2 is a light reflection sheet used in the surface light source device of the present invention, which is a light reflection sheet having a large number of basic units formed of parallel, straight and flat inclined reflection surfaces having ridges arranged in parallel. It is the partial top view of a sheet | seat, and sectional drawing cut | disconnected and shown by 2b-2b line.

FIG. 3 is a light reflection sheet used in the surface light source device of the present invention, in which a plurality of basic units each having a parallel straight and flat inclined reflection surface with ridges arranged in parallel are formed on the surface. Partial plan view of the light reflecting sheet of the embodiment and FIG.
It is sectional drawing cut | disconnected and shown by the b-3b line.

FIG. 4 shows an embodiment of a light extraction mechanism including a large number of convex protrusions formed on a surface of the surface light source device of the present invention opposite to the light exit surface of the light guide. It is sectional drawing which expands and shows schematically.

FIG. 5 shows another embodiment of the light extraction mechanism including a large number of triangular cross-section projections formed on the surface of the light guide opposite to the light exit surface in the surface light source device of the present invention. It is sectional drawing which expands a part and shows roughly.

FIG. 6 is a view showing a light extraction mechanism according to still another embodiment of a light extraction mechanism including a large number of concave dents formed on a surface of the surface light source device opposite to the light exit surface of the light guide. It is sectional drawing which expands and is shown roughly.

FIG. 7 is an enlarged view of a part of the light guide of the surface light source device according to another embodiment of the light extraction mechanism including a large number of V-shaped cross-sectional grooves formed on the light exit surface of the light guide in the surface light source device of the present invention. FIG.

FIG. 8 shows another aspect of the light extraction mechanism including a large number of V-shaped cross-section grooves formed on the surface of the surface light source device of the present invention opposite to the light exit surface of the light guide. It is sectional drawing which expands a part and shows roughly.

FIG. 9 is a view showing still another aspect of the light extraction mechanism including a large number of mountain-shaped projections formed on the light exit surface of the light guide in the surface light source device of the present invention, by enlarging a part of the light guide. It is sectional drawing which shows schematically.

10 is a configuration explanatory view schematically showing a state in which a light beam incident on a light guide becomes a surface light source and a state in which a light beam does not become a surface light source depending on a light extraction mechanism in the surface light source device of the embodiment shown in FIG. 1; It is.

FIG. 11 shows a depth h and a minimum opening width Wm of two examples of convex protrusions constituting a light extraction mechanism provided on a light guide.
It is a schematic structure explanatory view which shows the definition of "in".

FIG. 12 is a cross-sectional view showing a parallel linear and flat inclined reflecting surface of a basic unit formed on the light reflecting sheet shown in FIG. 2 in a partially enlarged manner, and showing an inclination angle of the inclined reflecting surface;

FIG. 13 is a light reflection sheet used in the surface light source device of the present invention, in which a plurality of basic units each having a parallel linear ridge and a concave inclined reflection surface are formed on the surface, and the ridge lines are arranged in parallel. 13A and 13B are a partial plan view and a cross-sectional view taken along line 13b-13b of the light reflecting sheet according to the embodiment.

FIG. 14 is a light reflection sheet used in the surface light source device of the present invention, which is another light reflection sheet in which a plurality of basic units each having a parallel linear ridge and a concave inclined reflection surface are formed on the surface. It is the partial top view of the light reflection sheet | seat of an aspect, and sectional drawing cut | disconnected and shown by 14b-14b line.

FIG. 15 is a light reflection sheet used in the surface light source device of the present invention, in which a plurality of basic units each having parallel ridges arranged in parallel and formed of parallel straight and concave inclined reflection surfaces are formed on the surface. FIG. 2 is a partial plan view of a light reflecting sheet according to an embodiment, and a cross-sectional view cut along line 15b-15b.

FIG. 16 is a partial plan view of a light reflection sheet used in the surface light source device of the present invention, which is a light reflection sheet of still another embodiment in which a plurality of basic units formed in a concave mirror shape are formed on the surface; It is sectional drawing cut | disconnected and shown by 16b-16b line.

FIG. 17 is a light reflection sheet used in the surface light source device according to the present invention, in which a plurality of basic units each having parallel ridges and arranged in parallel and concave and having inclined reflection surfaces are formed on the surface. FIG. 17 is a partial plan view of the light reflecting sheet according to the embodiment and a cross-sectional view cut along line 17b-17b.

FIG. 18 is a partial plan view of a light reflection sheet used in the surface light source device of the present invention, which is a light reflection sheet of still another embodiment in which a large number of basic units formed in a concave mirror shape are formed on the surface; It is sectional drawing cut | disconnected and shown by 18b-18b line.

19 is a cross-sectional view showing a part of the concave inclined reflecting surface of the basic unit formed on the light reflecting sheet shown in FIG. 13 and showing the inclination angle of the concave inclined reflecting surface;

FIG. 20 is a configuration explanatory view schematically showing a main part of a surface light source device according to another embodiment of the present invention.

FIG. 21 is a partial perspective view showing a main part of a surface light source device according to a preferred embodiment of the present invention.

FIG. 22 is an explanatory diagram illustrating a light beam direction changing function of the light reflecting sheet of the present invention.

FIG. 23 is an explanatory view illustrating a method for measuring the direction selectivity of a light beam of the light guide according to the present invention.

[Explanation of symbols]

Reference Signs List 10 light reflection sheet of one embodiment 11 surface light source device 12 light guide 13 one end of light guide on which light source is disposed 14 linear light source 15 reflector 16 light emission surface 17 on the side opposite to light emission surface Surface 18 Basic unit 18a Reflecting surface 18b Ridge line 19 Base material 20 Light extraction mechanism (pattern) 21 Convex projection 22 Triangular projection 23a Concave dent 23b Projection 24 V-shaped groove 25 V-shaped groove 26 Mountain-shaped protrusion 27 Unnecessary light ray component emitted in the direction of the light emitting surface 28 Normal line to the light emitting surface of the light guide 29 Light ray (light flux) deflected by the light reflecting sheet 30 From the light guide to the light reflecting sheet side Light beam component (light flux) 31 Coating layer made of transparent insulating material 32 Adhesive 33 Stretched film 34 Light-collecting element 35 Black light-absorbing pattern

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H042 DA02 DA04 DA11 DA17 DD04 DD08 DE04 2H091 FA16Y FA41Z FB08 FC02 FC12 FC25 FC29 FD07 FD15 FD23 LA11 LA17 LA18 5G435 AA00 AA03 AA16 BB12 BB15 GG24 KK05 KK07

Claims (12)

[Claims] 1. A large number of substantially similar basic units each having a reflection surface are arranged at a pitch of 5000 μm or less, and the main reflection direction of the basic unit is substantially constant, and the reflection surface has a reflectance of 70% or more. A light reflection sheet comprising a material, and a coating layer made of a transparent insulating material provided on the reflection surface. 2. The method according to claim 1, wherein the metal substance is silver or aluminum, and the coating layer made of the transparent insulating substance is made of a transparent resin having a resistivity of 1.0 × 10 ⁶ Ω · cm or more. The light reflecting sheet according to the above. 3. The light reflecting sheet according to claim 1, wherein the substantially similar basic unit including the reflecting surface has a concave or convex cross section. 4. The light-reflecting sheet according to claim 1, wherein the substantially similar basic unit composed of the reflecting surface has a plurality of ridges arranged in parallel. 5. The substantially similar basic unit composed of the reflecting surface is formed by arranging a large number of concave mirrors or convex mirrors having a maximum diameter of 5000 μm or less.
The light reflection sheet according to 1. 6. A main reflection direction of a substantially similar basic unit composed of the reflection surface and a normal direction of the light reflection sheet are 1.
2. An angle of at least 5 degrees.
6. The light reflecting sheet according to any one of items 1 to 5. 7. The surface of the coating layer has a surface roughness Rz = 25 μm.
7. The surface as described below.
The light reflecting sheet according to any one of the above. 8. The substantially similar basic unit comprising the reflection surface is obtained by coating the metallic substance on a thermoplastic resin film, and a stretched film is adhered to a back surface of the thermoplastic resin film. The light reflection sheet according to any one of claims 1 to 7, wherein 9. A surface light source device using the light reflecting sheet according to claim 1 in an illumination optical system. 10. The surface light source device according to claim 9, wherein a print pattern is provided on a surface of the light reflecting sheet. 11. The surface light source device according to claim 9, further comprising a light guide disposed on the light reflection sheet on the reflection surface forming side, and at least one side of the light guide. A surface light source device, wherein a light source is provided at an end and a mechanism for emitting at least 65% or more of emitted light toward the light reflecting sheet is provided in the light guide. 12. A liquid crystal display device using the surface light source device according to claim 9 as backlight light source means.