JPH11339528A - Transmission flat lighting system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmission flat lighting system suppressing deterioration of contrast that makes it hard to observe an image. SOLUTION: In a transmission flat lighting system 1, by forming a rugged light reflection pattern 7 on the side of a surface 6 of a transparent substrate 2, rays of light are uniformly emitted from the surface of the transparent substrate 2 irrespective of distances from a light source lamp 4 and radiated in a plane to a reflection liquid crystal display element L. Further, by disposing a transparent material 11 having a refractive index lower than, at least, the transparent substrate 2, between the reflection liquid crystal display element L and the transparent substrate 2 in a closely contacting manner with the two, interface reflection (Fresnel reflection) is suppressed and deterioration of contrast can be suppressed not to make it hard to observe an image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission type planar illumination device integrated with a display device used for a front illumination means such as a signboard or various reflection type display devices.
It is used as a front illumination means of a reflection type liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal display device that operates with low power consumption includes:
Due to its features such as thinness and light weight, demand for display devices mainly for computer applications is increasing. Since the liquid crystal, which is a component of the liquid crystal display device, does not emit light by itself, unlike a light emitting element such as a cathode ray tube, an illumination means for observing an image is required. Particularly, in recent demands for higher definition and color images, a configuration in which a high-luminance planar back light source is added as a liquid crystal display device is usually used. However, in order to turn on the planar rear light source, an excessive amount of electric power is required, which causes a problem that the characteristic of the liquid crystal, which is low power consumption, is reduced.

In particular, in portable liquid crystal devices which are widely used, taking advantage of a thin and lightweight liquid crystal display device, the consumption of an internal power source is increased by turning on a planar rear light source added to the liquid crystal display device. However, there has been a drawback that the usage time during carrying is extremely short.

In order to solve this problem, a reflection type liquid crystal element which functions without using a planar back light source by using ambient light as illumination means has been developed. In particular, high quality images in recent years have been developed. In response to the demand for the liquid crystal display, demand for a reflective liquid crystal element for color display is increasing. The most basic configuration of a reflective liquid crystal element for color display is to form a transparent electrode on one surface and two flat glass substrates provided with a polarizing plate on the other surface, and the transparent electrode side is spaced at a predetermined interval. Glass substrates are arranged so as to face each other, and a space between the glass substrates is filled with a liquid crystal material. Further, a color filter is provided on the glass substrate on the observation surface side, and a high-efficiency reflector is provided on the glass substrate on the back surface side. At this time, the transparent electrode plate of the glass substrate on the back side is patterned, and switching elements are connected to the transparent electrode plate to realize a desired image.

The reflection type liquid crystal element having such a configuration illuminates a screen brightly by reflecting ambient light incident on a reflection plate disposed on the back surface thereof, and allows an image to be observed.

However, since the reflection type liquid crystal element illuminates the screen with ambient light incident on the reflection plate as described above, the display quality depends on the surrounding brightness environment. In particular, a reflection type liquid crystal for color display must be provided with a color filter or the like, so that its reflectance is lower than that of a monochrome liquid crystal.
Therefore, the light beam irradiated on the screen is small (that is,
In a situation where the surroundings are relatively dark, the brightness of the screen is not sufficient, so that auxiliary lighting for observing the image is required.

As a preferred auxiliary illumination means for such a reflection type liquid crystal element, Japanese Patent Application No. Hei 9-347648 discloses a transmission type planar illumination device. The transmissive planar illumination device 1 ′ shown in FIG. 12 is arranged and used so as to cover the observation surface F of the reflective liquid crystal element L having the above-described configuration. As shown in FIG. 1, a linear light source lamp 4 is arranged near one end face 3 of a flat transparent substrate 2 formed of a material having high translucency and having a rectangular cross section. As the light source lamp 4, a cold cathode fluorescent tube (CCFL) or a hot cathode fluorescent tube (HCFL) or the like is used.

Here, in FIG. 13, the reflection type liquid crystal element L
One surface (the lower part of FIG. 13) of the transparent substrate
The observation surface (screen) side, which is the opposite surface (upper side in FIG. 13), is defined as the upper surface (front surface) 6.

On the upper surface 6 of the transparent substrate 2, a light reflection pattern 7 is formed. The light reflection pattern 7 includes a number of grooves 8 having a substantially triangular cross section and a flat portion 9 adjacent to the grooves 8.
It is composed of As shown in FIG. 13, the light reflection pattern 7 is formed with a groove 8 so that the brightness becomes almost uniform at any position of the transparent substrate 2 without being influenced by the distance from the light source lamp 4. Spacing varies by location. That is, the ratio of the width (occupied area) of the groove portion 8 to the width (occupied area) of the flat portion 9 is set to gradually increase as the distance from the one end surface 3 of the transparent substrate 2 increases.

When a transmission type planar illumination device 1 ′ as an auxiliary illumination having such a configuration is added, light emitted from the light source lamp 4 enters the inside of the transparent substrate 2 from one side end surface 3 of the transparent substrate 2. Then, while traveling toward the opposing surface 10 while repeating reflection and refraction inside thereof, the light is gradually emitted from the lower surface 5 of the transparent substrate 2 so that the reflection type liquid crystal arranged close to the transparent substrate 2 is formed. The element L is irradiated. Further, since the light reflection pattern 7 is formed on the transparent substrate 2, the amount of light emitted from the lower surface 5 can be made substantially uniform, so that the reflective liquid crystal element L is uniformly irradiated.

Although not shown in FIGS. 12 and 13, the peripheral surfaces of the light source lamp 4 and the one end face 3 are covered with a film-like reflecting member, so that the efficiency of light beam coupling can be improved. it can. Further, by covering the side surfaces of the transparent substrate 2 other than the one side end surface 3 with the reflection member, it is possible to prevent the light rays from being emitted from the side end surfaces, so that the amount of illumination from the lower surface 5 of the transparent substrate 2 can be increased. Can be. In particular, in the opposing surface 10 of the one side end surface 3, the other 2
Since the amount of emitted light is larger than that of the side surface, it is desirable to cover with a reflecting member.

Further, the light reflection angle changes according to the shape of the groove 8 of the light reflection pattern 7, so that the transparent substrate 2
The direction of light emission from the lower surface 5 of the lower surface 5 changes.
The shape of the groove 8 can be set as appropriate so that many light beams are emitted in a direction perpendicular to (i.e., the front direction).

When observing the observation surface F of the reflection type liquid crystal element L in a bright surrounding area, the power consumption is suppressed by turning off the light source lamp 4 of the transmission type planar illumination device 1 ′ to reduce the power consumption. It is possible to extend the use time by the power supply. At this time, although the transmission type planar illumination device 17 is provided on the observation surface F of the reflection type liquid crystal element L through the flat portion 9 of the light reflection pattern 7, the observation surface F is moved through the flat portion 9 of the light reflection pattern 7. Since it is possible to observe, it is possible to observe almost the same screen as when there is no transparent substrate 2.

[0014]

In order to secure the brightness of the screen of the reflection type liquid crystal element L, a transmission type planar illumination device 1 'as auxiliary illumination is added to the observation surface F side.
The screen can be observed without being affected by the surrounding brightness environment. However, when the observation surface F of the reflective liquid crystal element L is observed in a bright place due to the addition of the transmissive planar illumination device 1 ′, the contrast of the screen is significantly reduced (that is, the screen is whitened). It has been found.

The reason will be described below. That is, the image display of the reflection type liquid crystal element L is performed by ambient light reaching the reflection plate provided on the back surface of the reflection type liquid crystal element L and reflected by the light. This is because the incident ambient light is interface-reflected (Fresnel reflection) on the upper surface 6 and the lower surface 5 of the spread illuminating device 1 ′ or the observation surface F of the reflective liquid crystal display element L. As described above, when the ambient light is reflected at the interface, the contrast is reduced, and when the screen becomes white, there is a problem that it is difficult to observe an image.

Accordingly, the present invention has been made in order to solve the above-mentioned problems, and the results of various studies have been made. It is an object of the present invention to provide a transmissive planar illumination which suppresses a decrease in contrast that makes it difficult to observe an image. It is to provide a device.

[0017]

As a means for solving the above-mentioned problems, according to the first aspect of the present invention, there is provided a transmission type planar lighting device in which a transparent substrate is disposed so as to cover the surface of a reflection type liquid crystal display element. Arranging a light source lamp close to at least one or more side surfaces of the transparent substrate, forming a light reflection pattern made of irregularities on the front surface side of the transparent substrate, and further between the reflective liquid crystal display element and the transparent substrate. Is characterized in that at least a transparent material having a refractive index lower than that of the transparent substrate is closely attached to both surfaces.

According to the second aspect of the present invention, assuming that the refractive index of the transparent material is N1 and the refractive index of the resin substrate is N2,
The ratio of N1 is in the range of 1.05 ≦ N2 / N1 ≦ 1.15.

According to a third aspect of the present invention, the transparent material is a liquid, a gel, or an elastic body.

According to a fourth aspect of the present invention, the light reflection pattern is formed by the groove and the flat portion.

According to a fifth aspect of the present invention, the light reflection pattern is formed by connecting inclined surfaces having a triangular cross section.

With the above-described configuration, the transmission type planar illumination device of the present invention forms a light reflection pattern composed of irregularities on the surface side of the transparent substrate, and emits the emitted light regardless of the distance from the light source lamp. Uniform light emission on the surface of the transparent substrate, and between the reflective liquid crystal display element and the transparent substrate,
By interposing a transparent material having a refractive index lower than that of the transparent substrate at least on both sides, interfacial reflection (Fresnel reflection) is suppressed.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In describing the structure of a transmission type planar illumination device 1 according to the present invention, the same as the transmission type surface illumination device 1 'described in the section of the prior art with reference to FIGS. Members are given the same reference numerals, and detailed description thereof is omitted. As shown in FIGS. 1 and 2, the configuration of the transmissive planar illumination device 1 is almost the same as that of the conventional device, and mainly includes a transparent substrate 2 and a light source lamp 4, and is different from the conventional device 1 ′. Is that a transparent material 11 having a refractive index smaller than that of at least the transparent substrate 2 is closely disposed between the observation surface F of the reflective liquid crystal element L and the lower surface 5 of the transparent substrate 2. Other configurations are the same as the conventional one.

As described above, the transmission type planar illumination device 1 of the present invention is used.
The reason why the transparent material 11 having a smaller refractive index than the transparent substrate 2 is provided will be described below in comparison with the conventional transmissive planar illumination device 1 '. It has been found that it is sufficient to suppress Fresnel reflection as described above in order to prevent the screen from becoming white due to a decrease in the contrast of the observation surface F of the reflective liquid crystal element L. Here, assuming that ambient light is incident from the front of the transmission type planar illumination device 1, 1 ′,
The Fresnel reflectivity on the lower surface 5 of the transparent substrate 2 is represented by the following equation (1).

{(N2-N1) / (N2 + N1)} ² × 100 (%) (1)

Here, N1 is the refractive index of a substance in contact with the lower surface 5 of the transparent substrate 2, and N2 is the refractive index of the transparent substrate 2. In the case of the conventional transmissive planar illumination device 1 ′, since the substance in contact with the lower surface 5 of the transparent substrate 2 is air, the refractive index N1 is approximately 1
It is. On the other hand, in the configuration of the transmission type planar illumination device 1 of the present invention, since the transparent material 11 is closely arranged on the lower surface 5 of the transparent substrate 2, the refractive index N1 is the refractive index of the transparent material 11. Since the Fresnel reflectivity can be expressed by the above equation 1, the refractive index of the transparent material 11 (that is, the refractive index N1)
Becomes smaller than 1 and becomes the minimum 0 when it becomes equal to N2. Therefore, it is desirable that the refractive index of the transparent material 11 is equal to the refractive index of the resin substrate 2.

Further, in order to function as the transmission type planar illumination device 1, the entire observation surface F of the reflection type liquid crystal element L must be uniformly irradiated regardless of the position of the light source lamp 4. For this reason, the traveling state of the light emitted from the light source lamp 4 when entering the transparent substrate 2 from the one end face 3 will be described first with reference to FIG. In FIG. 3, the light source lamp 4, not shown, is located on the left side, so that the light rays basically travel from left to right. Here, in order to explain the traveling state of the light beam, typical traveling states are roughly divided into three, and each traveling example a, b, and c will be described.

The traveling example a of the light beam is a light beam which is totally reflected by the groove 8 of the light reflection pattern 7 of the transparent substrate 2, transmitted through the lower surface 5 of the transparent substrate 2, and travels to the reflective liquid crystal element L. Specifically, the light reaches the observation surface F of the reflective liquid crystal element L. Next, in the traveling example b of the light beam, the light passes through the groove portion 8 and once advances to the outside of the transparent substrate 2, but refracts at the time of transmission through the groove portion 8 and advances again into the transparent substrate 2. The light is totally reflected by the inclined surface 8 and reaches the observation surface F of the reflective liquid crystal element L. Here, as described in the traveling example b of the light beam, the groove 8
The angle of the inclined surface of the groove 8 is set so as to refract the light transmitted through the light into the transparent substrate 2 again, so that the light emitted from the light source lamp 4 enters the resin substrate 2. Most of the light rays irradiate the reflective liquid crystal element L.

Further, in the traveling example c of the light beam, the light is totally reflected by the flat portion 9 of the light reflection pattern 7 of the transparent substrate 2 and reaches the lower surface 5. In the case of the conventional transmissive planar illumination device 1 ′, since the air below the lower surface 5 of the resin substrate 2 is air (refractive index: approximately 1), the light rays totally reflected on the upper surface 6 and traveling toward the lower surface 5 Example c
, The light is totally reflected on the lower surface 5. As described above, the light beam of the traveling example c1 ′ gradually travels in the transparent substrate 2 to the side far from the light source lamp 4, and does not exit to the outside of the resin substrate 2 in the schematic diagram shown in FIG. Therefore, the width of the flat portion 9 (that is, the groove portion 8)
Is appropriately adjusted, it is possible to separate a light beam traveling in the resin substrate 2 into outgoing light and advance light. Thereby, the light reflection pattern 7 is formed such that the ratio of forming the groove 8 increases and the width of the flat portion 9 gradually decreases as the distance from the light source lamp 4 increases (toward the right side in FIG. 13). Also, the desired emission light can be obtained on the opposite surface 10 opposite to the light source lamp 4, and the entire observation surface F of the reflective liquid crystal element L can be uniformly illuminated.

On the other hand, the transmission type planar illumination device 1 of the present invention
The transparent material 11 is closely arranged on the lower surface 5 of the resin substrate 2. At this time, if N1a is the refractive index of the transparent material 11, N2 is the refractive index of the transparent substrate 2, and the incident angle of the light beam shown in the progress example c on the lower surface 5 is θ, the condition for the total reflection of the light beam is as follows: Indicated by 2.

Sin θ ≧ N1a / N2 (2)

If Formula 2 is not satisfied, proceeding example c
As shown at 2 ', the light is refracted from the lower surface 5 to the outside of the resin substrate 2 by a predetermined angle and emitted, and reaches the observation surface F of the rear reflective liquid crystal element L. As described above, when the light beam is emitted out of the resin substrate 2 without being totally reflected by the lower surface 5, there is no advance light, and the total light beam represented by the advancing examples a, b, and c is a reflection type liquid crystal. Since the light beam irradiates the element L, only the side close to the light source lamp 4 is illuminated brightly, and the uniformity of illumination is significantly impaired. In order to maintain the uniformity of illumination, as is apparent from Equation 2, Equation 2 does not hold unless at least N2 is larger than N1a. Therefore, the refractive index of the transparent material 11 is larger than that of the transparent substrate 2. You also need to choose a lower one.

As described above, the refractive index of the transparent material 11 is set lower than the refractive index (N2) of the transparent substrate 2 in order to secure the uniformity of the illumination in consideration of Equations 1 and 2. In addition, from the viewpoint of suppressing Fresnel reflection and preventing a decrease in screen contrast, it is necessary to make the refractive index substantially equal to the refractive index of the transparent substrate 2. Therefore, the refractive index must be at least smaller than that of the transparent substrate 2. , And choose to balance the two.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS By changing the refractive index of the transparent material 11, it is determined whether or not the observation surface F of the reflection type liquid crystal element L provided with the transmission type planar illumination device 1 of the present invention becomes white, and illumination light. Observe the uniformity of

Example 1 The configuration of a transmission type planar illumination device 1 is the same as that described with reference to FIGS. 1 and 2, and a transparent acrylic resin flat plate (size: : 240 mm x 160 mm, plate thickness 3 mm, refractive index N
2 = 1.49), and the upper surface 6 of the transparent substrate 2 has a triangular groove portion 8 and a flat portion 9 having a triangular cross section parallel to its long side.
Is formed.

The cross-sectional shape of the groove 8 of the light reflection pattern 7 is triangular. In order to set the inclination angle of the triangular groove 8, an angle α, an angle β and an angle γ are determined as shown in FIG. . The angle α is the base angle on the side closer to the light source lamp 4 among the base angles of the triangle formed assuming the virtual base S. Further, the angle β is a base angle different from the angle α, and the angle γ is the vertex angle of the virtual triangle (that is, the groove 8
Valley). The groove portion 8 makes the angle γ constant at 60 °, and the angle α extends from the one end surface 3 toward the facing surface 10.
The angle β is continuously changed so as to be 48 ° to 52 ° and further 46 °, and the angle β is also changed accordingly.

The depth of the groove 8 is fixed at 10 μm, and the width of the flat 9 is gradually reduced as the distance from the light source lamp 4 increases in order to change the relative ratio between the groove 8 and the flat 9. I have. Specifically, the ratio of the width of the groove portion 8 to the flat portion 9 is changed from one end face 3 to the width of the resin substrate 2.
The area up to one-half is fixed at 0.1, and the ratio of the groove 8 is gradually increased toward the facing surface 10,
The ratio is set to be 1.2 in the vicinity of the facing surface 10.

The light source lamp 4 has an outer diameter φ2.
A 3 mm cold-cathode fluorescent tube is used and abuts against one end surface 3. Then, the light source lamp 4 is controlled by an inverter to produce a tube current of 3.
Lighting is performed with a sine wave of 5 mA and a lighting frequency of 60 KHz.

Further, although not shown in FIGS. 1 and 2, a reflection film or a mirror-finished aluminum plate on which a metal such as white or silver is deposited so as to cover the light source lamp 4 and the one end surface 3 A lamp reflector formed of any one of a reflection plate obtained by bending a metal plate such as the one described above is provided, and a light beam emitted from the light source lamp 4 travels into the transparent substrate 2 with high efficiency. In addition, on the side end surface of the transparent substrate 2 other than the one end surface 3 where the light source lamps 4 are arranged, the light emitted from the side end surface is reflected again to increase the amount of illumination by making the light incident on the resin substrate 2 again. It is covered with members. In particular, the arrangement of the reflection member is more effective on the facing surface 10 because the amount of emitted light is greater than the other two surfaces. As described above, the lamp reflector and the reflecting member that increase the irradiation light amount are the transmission type planar illumination device 1 of the present invention.
It is desirable to use as much as possible.

Further, as the transparent material 11, a refractive index N1a is used.
Of five different materials (polycarbonate resin, acrylic resin, fluorinated acrylic resin, transparent silicon rubber and amorphous fluororesin) and one without the transparent material 11 (ie air). Thus, a sample of the transmission type planar illumination device 1 was prepared.

A reflection type liquid crystal element L having a size almost equal to that of the transparent substrate 2 was arranged on the back surface of the transmission type planar illumination device 1 having such a configuration, and an image thereof was observed. At this time, the transparent material 11 and the reflection type liquid crystal element L are closely arranged.

The result of observing the image is shown in FIG.
Regarding the uniformity of the illuminating light and the degree of whitening of the screen, a sample that cannot be used as a product is marked with x, and a good sample is marked with ○. As is clear from FIG. 4, both the uniformity of the illuminating light and the degree of whiteness of the screen are good because the transparentness of the refractive index N1a where N2 / N1a is in the range of 1.05 to 1.15 is obtained. It turned out that the material 11 should be used.

(Embodiment 2) Subsequently, a resin substrate 2 processed with a polycarbonate resin (refractive index N2a = 1.59) was used, and the other structure was the same as that of the embodiment 1 in the transmission type surface condition. The lighting device 1 was prepared, and the uniformity of the illuminating light and the degree of whitening of the screen were evaluated in the same manner as in Example-1.

The results are shown in the chart of FIG. In FIG. 5, the whiteness of the screen is indicated in the column of the amorphous fluororesin, and the whiteness of the screen indicates that the screen is not whitened and is not good but is relatively small. From FIG. 5, it can be seen that good results are obtained for both the uniformity of the illumination light and the degree of whitening of the screen because the transparent material 1 having the refractive index N1a in which N2 / N1a is in the range of 1.05 to 1.15.
It turns out that one should be used.

The transparent material 11 in the transmission type planar illumination device of the present invention is closely arranged on the lower surface 5 of the resin substrate 2 as described above. Here, the close arrangement refers to a position between the transparent material 11 and the resin substrate 2 (the same applies to the reflection type liquid crystal element L).
If there is a gap of 1 μm or more, the gap is equivalent to the existence of an air layer, and the effect of the present invention described above is eliminated. Therefore, it is necessary to arrange the transparent material 11 in a range where the gap is at least smaller than 1 μm. Say. further,
When the transparent material 11 is a solid, even if the transparent material 11 is closely arranged in the initial state, the transparent material 11 may be changed due to an environmental change or the like.
May be peeled off. For this reason, it is desirable that the transparent material 11 be made of a liquid, a gel-like body, and an elastic body, and be always in close contact with each other even due to environmental changes.

In the transmission type planar illumination device 1 of the present invention described in detail above, the light reflection pattern 7 realizes uniform illumination light by changing the width of the flat portion 9 while keeping the depth of the groove 8 constant. However, instead of this, as in the case of the transmissive planar illumination device 1 shown in FIGS. 6 and 7, the interval at which the grooves 8 are formed is fixed, and the depth gradually increases as the distance from the light source lamp 4 increases. Even if the light reflection pattern 7 is formed so as to be deep, uniformity of the illumination light can be realized. Further, a light reflection pattern combining both may be formed.

Further, the cross-sectional shape of the groove 8 is not limited to a triangle as in this embodiment, but can be appropriately set so that the amount of emitted light is substantially uniform on the lower surface 5 side of the resin substrate 2. For example, it may be a quadrangle as shown in FIG. Further, as shown in FIG. 9, a curved surface similar to an inclined surface composed of a plurality of planes may be used.

Although the light reflection pattern 7 is constituted by the groove 8 and the flat portion 9, in the present invention, the light reflection pattern 7 is formed in order to obtain uniformity of irradiation light. However, as shown in FIGS. 10 and 11, the groove 8 'may be formed by continuously forming the groove 8' in parallel with the light source lamp 4 (that is, without providing the flat portion 9).

The processing for forming the groove 8 of the light reflection pattern 7 can be performed by cutting with a diamond cutting tool. In that case, in order to fix the machining tool, the angle γ of the valley corresponding to the apex angle of the groove 8 having a substantially triangular cross section must be set constant. For this reason,
The sum of the inclination angle α and the inclination angle β is always constant,
As described when actually forming the light reflection pattern 7 in the embodiment, the inclination angle α and the inclination angle β are appropriately changed within a changeable range to form the light reflection pattern 7.
More efficient planar illumination can be realized.

In manufacturing the transmissive planar illumination device 1 of the present invention, the material of the transparent substrate 2 may be any material that can efficiently transmit light, and acrylic resin is used because of its transparency and workability. Most suitable. However, the present invention is not particularly limited to this, and various thermoplastic transparent resins such as a vinyl chloride resin, a polycarbonate resin, an olefin resin, and a styrene resin can be used. In some cases, an inorganic transparent material such as a thermosetting transparent resin such as an epoxy resin or an allyl diglycol carbonate resin or various glass materials can be used.

The resin substrate 2 can be formed by direct machining such as cutting and grinding. In the case of a resin material, various moldings such as cast molding, extrusion molding, hot press molding, and injection molding are used. Although the method can be applied, the injection molding method using a resin material is the most excellent in terms of productivity.

In this embodiment, a linear fluorescent tube is used as a light source. However, the present invention is not limited to this. For example, a light source having a structure in which a plurality of LED elements are arranged, or a plurality of minute incandescent bulbs are arranged. A light source having such a configuration can also be used.

[0053]

As described in detail above, the transmission type planar illumination device of the present invention according to the first aspect of the present invention forms a light reflection pattern composed of irregularities on the surface side of a transparent substrate, thereby emitting luminous rays. Irrespective of the distance from the light source lamp, it is possible to uniformly emit light on the surface of the transparent substrate and irradiate the reflective liquid crystal display element in a planar manner, and further, at least between the reflective liquid crystal display element and the transparent substrate. By placing a transparent material with a lower refractive index than the transparent substrate in close contact on both sides,
Since interfacial reflection (Fresnel reflection) is suppressed, it is possible to prevent a decrease in contrast that makes it difficult to observe an image.

According to a second aspect of the present invention, when the refractive index of the transparent material is N1, and the refractive index of the resin substrate is N2, the ratio of N2 / N
By setting the ratio of 1 to be in the range of 1.05 ≦ N2 / N1 ≦ 1.15, it is possible to surely realize uniform planar light emission and to suppress interfacial reflection.

According to the third aspect of the present invention, when the transparent material is formed of a liquid, a gel, or an elastic body, it can be securely arranged in close contact with the resin substrate and the reflective liquid crystal display element.

According to the fourth and fifth aspects of the present invention, since the light reflection pattern is formed by a groove and a flat portion, or is formed by an inclined surface having a triangular cross section, the light emitted from the light source lamp is transparent in a plane. The light is emitted from the substrate, and its production is easy.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a structure of a transmission type planar illumination device of the present invention.

FIG. 2 is a cross-sectional view showing a structure of the transmission type planar illumination device shown in FIG.

FIG. 3 is a cross-sectional view for explaining the shape of the light reflection pattern of FIG.

FIG. 4 is a table showing observation results of the transmission type planar illumination device according to Example-1.

FIG. 5 is a table showing observation results of the transmission type planar illumination device according to Example-2.

FIG. 6 is a perspective view showing a structure of a transmission type planar illumination device different from FIG. 1;

FIG. 7 is a cross-sectional view showing the structure of the transmission type planar illumination device of FIG.

FIG. 8 is a cross-sectional view for explaining a shape of a light reflection pattern different from FIG.

FIG. 9 is a cross-sectional view for explaining a shape of a light reflection pattern different from FIG.

FIG. 10 is a perspective view showing a structure of a transmission type planar illumination device different from FIG. 6;

11 is a cross-sectional view showing the structure of the transmission type planar illumination device of FIG.

FIG. 12 is a perspective view showing the structure of a conventional transmission type planar illumination device.

13 is a cross-sectional view illustrating the structure of the transmission type planar illumination device of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmissive planar illumination device 2 Transparent substrate 4 Light source lamp 5 Lower surface 6 Upper surface 7 Light reflection pattern 8 Groove 9 Flat part 11 Transparent material L Reflective liquid crystal element

Claims (5)

[Claims] 1. A transmissive planar illumination device in which a transparent substrate is disposed so as to cover a surface of a reflective liquid crystal display element, wherein a light source lamp is disposed in proximity to at least one or more side surfaces of the transparent substrate, and light having irregularities is provided. A reflection pattern was formed on the surface side of the transparent substrate, and a transparent material having a lower refractive index than at least the transparent substrate was disposed between both surfaces of the reflective liquid crystal display element and the transparent substrate. A transmission type planar illumination device, characterized in that: 2. When the refractive index of the transparent material is N1 and the refractive index of the resin substrate is N2, the ratio of N2 / N1 is 1.05 ≦ N.
The transmission type planar illumination device according to claim 1, wherein the ratio is in a range of 2 / N1 ≤ 1.15. 3. The transmissive planar illumination device according to claim 1, wherein the transparent material is a liquid, a gel, or an elastic body. 4. The transmissive planar illumination device according to claim 1, wherein the light reflection pattern is formed by a groove and a flat portion. 5. The transmission type planar illumination device according to claim 1, wherein the light reflection pattern is formed by connecting inclined surfaces having a triangular cross section.