JP2002014342A - Front light type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a front light with high efficiency, high contrast ratio and excellent flatness. SOLUTION: The liquid crystal display device has a pair of substrates (11, 12) and a liquid crystal layer 13 held between the pair of substrates. In the device, a light source 51 having a collimating means 52, a first light guide body 53 having a reflector which allows the light front the light source to enter through the side face and reflects the entering light to the display screen, and a second light guide body 58 having a reflector 62 which allows the light exiting form the lower part of the first light guide body to enter through the side face and reflects the entering light in the direction to above the other substrate are disposed above one substrate 11 of the pair of substrates. Moreover, a reflector 21 which reflects the light from the opposite substrate side is disposed on the other substrate 12 of the substrate pair.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION Interfaces have become increasingly important in order to facilitate the operation of multifunctional electronic devices. Since a liquid crystal display device characterized by its thinness, light weight, and low power consumption can be mounted without greatly changing the form of the electronic device, it is most suitable for these interfaces. The field of application to which the present invention pertains is a reflection type liquid crystal display device combined with an auxiliary light source, which can be used in various environments including from a dark room to outdoors in fine weather.

[0002]

2. Description of the Related Art A reflection type liquid crystal display device uses a reflector to perform display using light incident from the outside, so that a constant contrast ratio and a specified color range can be obtained regardless of the surrounding environment. In particular, in a bright environment such as outdoors, a display with better visibility than the transmissive liquid crystal display device can be obtained.

However, in a dark environment such as indoors where the lighting is weak, the amount of incident light is reduced, so that the display of the reflective liquid crystal display device becomes dark and the visibility is reduced. Even if a reflective liquid crystal display device having a reflectance equal to or higher than that of a printed matter is realized, it is inevitable that the display becomes darker in a darker environment, so that the decrease in brightness in a dark environment is compensated for. A supplementary light source is indispensable.

The auxiliary light source of the reflection type liquid crystal display device includes a front light. The front light includes a light guide distributed so as to cover the front surface of the display unit of the liquid crystal display device, and a light source disposed at an end thereof, and irradiates the display unit with auxiliary light source light from the front surface. A reflective liquid crystal display device having a front light is highly efficient because 100% of the pixel openings can be used for both reflective display and auxiliary light source lighting. Further, since the optical paths are the same during the reflective display and when the auxiliary light source is turned on, a certain color purity can be obtained during the reflective display and when the auxiliary light source is turned on.
In these two respects, a reflective liquid crystal display device having a front light is superior to a transflective liquid crystal display device using a backlight or the like.

A reflection type liquid crystal display device using a front light as an auxiliary light source is disclosed in, for example, JP-A-11-326903, JP-A-11-344707 and JP-A-2000-2000.
No. 75293.

[0006]

The conventional front light has a problem that the contrast ratio decreases due to light reflection at the interface between the light guide and the air layer. For example, if a layer of a matching oil or gel is formed between the light guide and the liquid crystal display, the interfacial reflection can be reduced, but the light from the light source will not be uniformly applied over the front surface of the display unit. This is because in the conventional front light, light from the light source is propagated to the end of the light guide by utilizing the interface reflection between the light guide and the air layer. In a conventional front light, a light source having a light-emitting portion, such as a cold-cathode tube, having approximately the same sectional area as a light guide is used. Since light spreads isotropically from the entire surface of the light emitting portion, the light source light travels in a wide angle range of about ± 42 degrees in the light guide, and the parallelism is extremely low. In order to propagate this to the end of the light guide while maintaining sufficient intensity, it is necessary to use interface reflection.

If the parallelism of the light from the light source is low, there is a component that travels at an angle that does not satisfy the condition of total reflection. Such light source light components are not completely reflected at the time of interface reflection, but pass through the interface between the light guide and the air layer to become leaked light. The leaked light goes to a direction other than the display unit and sometimes goes directly to the user, which is one of the causes of a decrease in the contrast ratio.

As described above, the conventional front light has the advantages of high efficiency and the like, but also causes interfacial reflection and leaked light, causing a low contrast ratio.

An object of the present invention is to reduce the interfacial reflection and leak light of a conventional front light, and to provide a front light having high efficiency, a high contrast ratio, and excellent flatness.

[0010]

One embodiment of the liquid crystal display device according to the present invention is a liquid crystal display device having a pair of substrates and a liquid crystal layer sandwiched between the pair of substrates. A first light guide having a light source provided with collimating means on the upper side of the light source, a reflector for entering light from the light source from a side surface and reflecting the incident light on the display surface, and a first light guide A second reflector having a reflector that reflects light emitted from the lower part of the body from the side and reflects the incident light toward the upper part of the one substrate;
And a reflector that reflects light from one of the pair of substrates is provided on another of the pair of substrates.

[0011]

FIG. 6 shows an example of the structure of a liquid crystal display device according to the present invention. It mainly consists of a front light and a liquid crystal display element. The front light mainly includes a point light source, collimating means, a first light guide, and a second light guide. The second light guide has an antireflection layer between the front surface and the liquid crystal display element.

As the light source, a point light source that emits light in a region sufficiently smaller than the cross section of the first light guide and the second light guide is used. As the point light source, for example, a light emitting diode or an electroluminescent element can be used. The light emitted from the point light source spreads isotropically around the point light source, but the light emitting portion is sufficiently smaller than the cross section of the light guide. Therefore, it is possible to convert the light into parallel light by a collimating unit having a size approximately equal to the thickness of the light guide. The collimating means is a transparent medium, and is distributed in a convex shape around the point light source. Due to refraction between the collimator and the air interface, the traveling direction of the light emitted from the point light source is concentrated within an angle range of about ± 15 degrees.
Further, due to refraction upon entering the first light guide, the traveling direction of the light is concentrated within an angle range of about ± 10 degrees.

Light with high parallelism propagates to the end of the light guide without using interface reflection. Therefore, in the present invention,
An anti-reflection layer is formed at the air interface of the light guide to thoroughly reduce interfacial reflection, which is a cause of a decrease in contrast.

Further, light having a high degree of parallelism can be converted into a uniform linear light source by metal reflection on metal surfaces arranged in a stripe. When a metal surface inclined at 45 degrees with respect to the traveling direction of the light is arranged on the light beam, the traveling direction of the light source light is converted by 90 degrees. Furthermore, when the metal surface is divided into stripes and arranged on the light beam while leaving a gap, the cross-sectional area of the light beam can be linearly expanded by the length of the space. If the parallelism of the light is high, all the light is reflected by the reflector, and no light leaks from the interval between the stripes. Further, since metal reflection is used for light reflection, no light leaks during reflection.

At the time when the light enters the first light guide, the cross-sectional area of the light beam of the light source light is substantially equal to the square of the thickness of the first light guide. The first light guide is arranged at an end of the display unit,
The light source light is reflected by the stripe-shaped reflecting surface disposed over the entire end of the display unit, so that the cross-sectional area of the light flux is linear (thickness of the first light guide × first light guide). ) And is incident on the second light guide.

The second light guide is located on the front surface of the display section and has a stripe-shaped reflecting surface disposed over the entire display section. By reflecting the light from the light source, the light flux of the light from the light source is made planar, the cross-sectional area of the light is expanded to the same extent as the area of the display unit, and the light enters the display unit of the liquid crystal display device.

The second reflector is located on the front surface of the display unit, but the second reflector has a light absorber on the side opposite to the side facing the display unit, that is, on the side facing the user. The light incident from the outside is absorbed by the light absorber before entering the second reflector. When viewed from the normal direction of the display unit, the area ratio of the second reflector to the display unit is 10% or less.
It is suppressed to 0% or less. The width of the second reflector is 1
Since it is sufficiently smaller than the width of a pixel, the second reflector does not completely block any one pixel. Therefore, the display is not impaired because the second reflector is located on the front surface of the display unit.

Further, the first reflector and the second reflector may be distributed in a mesh shape, a grid shape or a dot shape in addition to the stripe shape.

In the case where the air layer is close to the second light guide, to reduce the interfacial reflection between the air layer and the second light guide, a metal oxide film is formed directly on the second light guide. Etc. may be deposited. Alternatively, a film having an antireflection layer may be attached to the upper part of the light guide. When another transparent medium or an optical member approaches the second light guide, the two are laminated via an antireflection layer, and an air layer is removed from between the two. In this case, a photoreactive transparent resin, a thermosetting transparent resin, or silicone gel can be used for the antireflection layer. These materials have a characteristic that the fluidity is high at an early stage and the fluidity is reduced or solidified after light irradiation or heating. By utilizing this feature, for example, the antireflection layer may be formed by arranging the light guide and other components at a fixed gap using a spacer, and pouring the above-mentioned material into the gap to solidify.

The liquid crystal display element comprises a first substrate, a second substrate, and a liquid crystal layer. The liquid crystal layer is sandwiched between the first substrate and the second substrate, and the first substrate and the second substrate are formed by a liquid crystal layer. Means for applying a voltage to the One of the first substrate and the second substrate has a reflector. Either the first substrate or the second substrate has a color filter, and may perform color display. The voltage applying means may be a pair of matrix electrodes. Alternatively, it may be an active element such as a thin film transistor or a thin film diode.

Further, the embodiments of the present invention will be described in more detail using specific examples. (Embodiment 1) FIG. 1A shows the configuration of a line light source according to the present invention, and FIG. The line light source of the present invention can be used as a front light in combination with, for example, a reflection type liquid crystal display device. FIG. 1 corresponds to a state observed in the normal direction of the display unit in that case. Point light source 51,
A collimating means 52, a first light guide 53,
The first light guide has a first light incident part 54, a first light reflecting part 55, and a first light emitting part 56.

The point light source is a light emitting diode that emits white light. Since the light emitting diode is manufactured by a semiconductor process, the size of the light emitting portion can be set to 0.2 mm or less. Even if the thickness of the first light guide is sufficiently reduced to 2 mm, the size of the light emitting portion is one tenth of that. The point light source is provided with collimating means made of a transparent medium such as an acrylic resin on the upper surface thereof. The collimating means is convexly distributed above the point light source, has a diameter of 3 mm, and has a thickness of the first light guide. And substantially larger than the light emitting portion. Since the light emitting section mainly emits light isotropically in the forward direction, the light propagates almost isotropically even inside the collimating means. At this time, the propagation direction of the light source light is within an angle range of ± 70 degrees or more. However, when the light exits from the collimator, the light is refracted by the difference in the refractive index at the interface between the collimator and air, and the propagation direction is changed. Since the collimator has a convex shape centered on the point light source, after the light is emitted from the collimator, the propagation direction of the light from the light source is concentrated within an angle range of ± 15 degrees.

After the light source light has once passed through the air layer, it enters the first light guide from the first light incident portion. The first light guide is made of an optical plastic such as an acrylic resin, and is formed by injection molding using a mold. Also at this time, the light is refracted by the difference in the refractive index at the interface between the first light guide and the air, and the propagation direction of the light source light is concentrated within an angle range of ± 10 degrees. In this way, the light emitted from the point light source by the two refraction processes is converted into parallel light.

The light from the light source is incident on the first reflecting portion, is reflected there, changes its traveling direction by 90 degrees, and travels toward the first light emitting portion. The first light reflection portion has a surface parallel to the traveling direction of the light source light,
It consists of a plane which makes 45 degrees to the traveling direction of the light source light. 4
The surface forming 5 degrees is the first light reflector 57. Aluminum is deposited on the entire surface of the first light reflecting portion. When observing the first reflection portion from the first light incidence portion, only the first light reflector can be seen. When observing the first reflecting portion from the first light emitting portion, the light emitted from the point light source is emitted by the first light reflecting portion because the first light reflectors are distributed in a stripe shape at intervals. By being reflected, it is spread over the entire first light emitting portion.

For example, if the width of each first light reflector in the first reflecting portion is 20 μm and the gap is 80 μm,
Light beams having a width of 20 μm are emitted at intervals of 80 μm. Actually, since the propagation direction of the light source light has an angle range of ± 10 degrees, the interval between the light beams is narrowed, and light closer to a perfect line light source is obtained.

As described above, by using a point light source that is sufficiently smaller than the thickness of the first light guide, collimating the light using a point light source, and reflecting the light with a striped reflector spaced apart, A line light source was obtained. (Embodiment 2) The configuration of the surface light source of the present invention is shown in FIG. The surface light source of the present invention can be used as a front light in combination with, for example, a reflection-type liquid crystal display device. FIG. 2 corresponds to a state observed from the normal direction of the display unit in that case. The line light source according to the first embodiment and the second light guide 58 are formed, and the second light guide is formed of an acrylic resin. In this embodiment, two line light sources are provided at the end of the second light guide.

FIGS. 3A and 3B are views of FIG. 2 viewed from the side. FIG. 3A shows a configuration of a second light guide, and the second light guide is composed of a second light incident portion 59, a second light reflecting portion 60, and a second light emitting portion 61. Having. The first light emitting part and the second light incident part are close to each other, and the second light guide receives light from the second light incident part.

FIG. 3B is a diagram showing an optical path in the second light guide. The light from the light source propagates through the second light guide and reaches the second reflector. The second reflecting portion has a large number of groove-shaped structures, and the inner wall thereof forms an angle of 45 degrees with the traveling direction of light. Aluminum is vapor-deposited on the inner wall of the groove-shaped structure, and this portion forms the second light reflector 62. A black pigment is laminated on the upper part of the second light reflector, and this part is the light absorber 63. The groove structure is formed by embossing an acrylic resin. The second light reflector is selectively formed only on the inner surface of the groove-like structure by mask vapor deposition of aluminum. The light absorber is selectively formed only in the portion where the second light reflector exists by patterning a resist containing a black dye. The width of the light absorber is about 20 μm, and the interval between the light absorbers is 180 μm
And transparent, the aperture ratio is 90%.

Returning to FIG. 2, when the second light guide is observed from the normal direction of the display section, only the light absorber is observed. The second light reflector is shielded by the light absorber by being formed below the groove structure. The light absorbers are distributed in a stripe shape, and the direction of the stripe forms 25 degrees with respect to the four sides of the display unit. When combined with a liquid crystal display device, the stripes of the light absorber and the grids of pixels form moiré. In this case, by setting the stripes of the light absorber to the above angle, the pitch of the moiré becomes so large that the moiré cannot be recognized. Can be smaller.

When viewed from the second light incident portion side, the second light reflection can be seen side by side without any gap. Since the parallelism of the light from the light source is high, light does not leak from the gap between the second reflectors. As shown in FIG. 3B, the course of the light source light is changed by 90 degrees by the second light reflector, and the light source light travels toward the second light emitting portion.

As described above, a thin surface light source which is transparent when viewed from the second reflecting portion side and emits light only to the second light emitting portion side is obtained. (Embodiment 3) FIG. 4 shows the structure of the surface light source of the present invention. FIG.
Is a state observed from the same direction as in FIG. In the present embodiment, the shape of the second light guide is different from that of the second embodiment, a step is formed on one side of the end, and the second light incident portion is divided into three portions. Two line light sources are provided at the center and one line light source is provided at the end of the line light source. A total of four line light sources are provided.

The linear light source according to the first embodiment has a structure in which a point light source and a collimating means protrude from the end of the first light guide, but a step is formed at the end of the second light guide. Four line light sources could be arranged without the point light source and the collimating means overlapping. (Embodiment 4) The structure of the surface light source of the present invention is shown in FIG. FIG.
Is a state observed from the same direction as in FIG. In the present embodiment, the line light source is different from that of the first embodiment, and a point light source and two collimating means are provided at the end. By mounting two line light sources, four point light sources are provided.

As in the third embodiment, a surface light source having the same brightness can be produced without forming a step at the end of the second light guide. Example 5 The surface light source of Example 2 was combined with a reflection type liquid crystal display device as a front light. FIG. 6 shows a cross section of the reflection type liquid crystal display device of this embodiment. The second light emitting section and the display section of the reflection type liquid crystal display device are stacked so as to be close to each other.

The first substrate is made of soda glass and has a thickness of 0.5 mm. The first substrate has a black matrix 19, a color filter 18, a planarizing layer 20, a scanning electrode 14, and a first alignment film 16 on the side close to the liquid crystal layer. The black matrix contains a black pigment, and its layer thickness is 1 μm. The color filter is composed of red, green and blue stripes, the stripe width is 80 μm, and the gap width is 5 μm. The direction of the stripe of the color filter is orthogonal to the direction of the stripe of the scanning electrode, and is parallel to the direction of the stripe of the signal electrode 15 on the second substrate, and its period is also equal to that of the signal electrode. The flattening layer is made of an acrylic resin and has a thickness of 1 μm. The scanning electrode is made of indium tin oxide (ITO) and has a layer thickness of 100 nm. Further, the scanning electrode has a stripe shape, the width is 240 μm, and the width of the gap is 15 μm. The first alignment film is Sun Ever manufactured by Nissan Chemical Industries, Ltd.
It is composed of a polyimide-based organic polymer and has a layer thickness of 0.2.
μm.

The second substrate is made of soda glass similarly to the first substrate, and has a thickness of 0.5 mm. The second substrate has a reflector 21, an insulating layer 22, a signal electrode 15, and a second alignment film 17 on the side close to the liquid crystal layer. The reflector is made of aluminum and has a layer thickness of 200 nm. The insulating layer is made of acrylic resin similarly to the flattening layer, and has a thickness of 2 μm.
m. The signal electrode is made of ITO, and its layer thickness is 10
0 nm. Also, the signal electrodes are striped,
Its width is 70 μm and the width of the gap is 15 μm.
The direction of the stripe of the signal electrode is orthogonal to the scanning electrode on the first substrate, and a matrix electrode is formed in a pair with the scanning electrode.
The second alignment film is Sun Ever manufactured by Nissan Chemical Industries, Ltd.

The first substrate has 120 scanning electrodes, the second substrate has 160 × 3 signal electrodes, and the number of pixels is 120 ×
160 × 3, and the diagonal length of the display unit is 2 inches.

The spherical polymer beads having a diameter of 6 μm were dispersed at a rate of about 250 per mm ² , and the thickness of the liquid crystal layer was set to approximately 6 μm over the entire display portion. The liquid crystal layer exhibits a nematic liquid crystal layer at least in the range of 0 to 50 degrees Celsius. The first alignment film and the second alignment film were subjected to an alignment treatment by a rubbing method, and the pretilt angle of the liquid crystal layer was set to about 5 degrees. Further, the twist angle of the liquid crystal layer was set to 240 degrees, and about 1% by weight of the optically rotatory substance S811 manufactured by Merck Co., Ltd., enables 1/160 duty drive.

A first polarizing plate, a first phase plate, and a second phase plate were arranged above the first substrate. First phase plate 25
And the second phase plate 26 are NRF films manufactured by Nitto Denko Corporation, and the polarizing plates 27 are G12 films manufactured by Nitto Denko Corporation.
20 DU was used.

An azimuth that divides the orientation processing direction of the first alignment film and the second alignment film into two equal parts is defined as an azimuth of 0 degree, and an azimuth is defined in a counterclockwise direction. Azimuth is 13
The attachment was performed so that the azimuth angle of the absorption axis of the first polarizing plate was 120 degrees. The wavelength of the first phase plate is 550n.
The retardation at m was 180 nm.

In a liquid crystal display device having a configuration in which a reflection plate is disposed close to a liquid crystal layer and one polarizing plate is used, in order to perform dark display, light incident on the liquid crystal display device must be reflected when the light reaches the reflection plate. Must be circularly polarized. Since the wavelength of visible light is distributed in the range of about 400 nm to 700 nm, the incident light must be circularly polarized in a wide wavelength range mainly at 550 nm where human visibility is maximized. When the liquid crystal layer has a twisted structure as in this embodiment, the liquid crystal layer shows both optical rotation and birefringence, but the phase plate shows only birefringence. Therefore, if one phase plate is used, the optical rotation of the liquid crystal layer cannot be compensated, and the visible light cannot be circularly polarized. By using two phase plates and setting the retardation and the slow axis azimuth as described above, it becomes possible to convert visible light into circularly polarized light, and a high contrast ratio is obtained.

As the adhesive interposed between the polarizing plate and the first phase plate, an adhesive in which fine particles were mixed was used. Due to the difference in the refractive index between the fine particles and the pressure-sensitive adhesive, the pressure-sensitive adhesive in which the fine particles are mixed has light diffusivity. As a result, the light incident on the liquid crystal and the light reflected by the reflector are diffused to reduce the specular reflection component, thereby making the visibility at the time of reflection display closer to that of paper. In addition, the same effect can be obtained by using a diffuse reflector having minute irregularities on the reflective surface as the reflector.

A reflection type liquid crystal display device is connected to a driving device,
This was combined with the surface light source of Example 2. The reflection type liquid crystal display and the surface light source are made of an anti-reflection layer 35 made of epoxy resin.
, And an air layer was removed from between them to remove interfacial reflection. In addition, a silicon-based gel or a photopolymerizable polymer can be used for the antireflection layer. The anti-reflection layer is formed by applying a fluid epoxy resin in the vicinity of the center of the display portion of the liquid crystal display device in a convex shape, placing a surface light source on the resin, and applying pressure, thereby stretching the epoxy resin thinly and uniformly. And was formed. When the fluidity of the epoxy resin is sufficiently high, the reflection type liquid crystal display device and the surface light source may be stacked via a spacer, and the epoxy resin may be penetrated between the two by utilizing a capillary phenomenon.

The display characteristics of the liquid crystal display device prepared as described above were evaluated. First, display characteristics in the case where light is incident from the outside without turning on the surface light source and the light is reflected and displayed are evaluated. An integrating sphere light source was used as a light source, light was uniformly incident from all solid angles within a range of 45 ° from the substrate normal, and the component reflected in the normal direction of the substrate plane was measured. A normally closed type applied voltage characteristic in which the reflectance increases with the applied voltage is obtained. The contrast ratio was 16: 1 and the reflectance was 15.8%.

Next, the integrating sphere light source was turned off and the surface light source was turned on, and the display characteristics at this time were evaluated. As in the case of the reflective display, a normally closed type applied voltage characteristic was obtained, and the contrast ratio was 14: 1. Further, 25 cd / m ² brightness of the display is at the end of the light source side, 22 cd / m ² at the display section center,
It was 18 cd / m ² at the end on the side where no light source was present.

As described above, by using the surface light source of Example 2 as a front light in a reflection type liquid crystal display device, a contrast ratio of 10: 1 or more was obtained in both reflective display and surface light source lighting. When the front light was turned on, a bright display was obtained.

Further, when the surface light source of the present invention is disposed behind a transmission type liquid crystal display device, it can be used as a highly efficient backlight light source. Similarly, it can be used as a backlight light source of a transflective liquid crystal display device using a transflective reflector or a transflective liquid crystal display device in which one pixel is divided into a transmissive portion and a reflective portion. (Embodiment 6) In the liquid crystal display device of Embodiment 1, a touch panel 38 was laminated above a surface light source. FIG. 7 shows the configuration of the liquid crystal display device of this embodiment. An epoxy resin was inserted between the second light guide and the touch panel and cured to form an antireflection layer 35. Thereby, interface reflection at the interface between the second light guide and the touch panel was removed.

When the display characteristics without the point light source turned on were evaluated, the contrast ratio was 11: 1 and the reflectivity was 14.6%. When the display characteristics when the point light source was turned on were evaluated, the contrast ratio was 10: 1 and the brightness at the center of the display portion was 20 cd / m ² .

Since the surface light source of the present invention does not require interfacial reflection to guide the light of the light source, it is possible to remove interfacial reflection using an epoxy resin or the like. Even in the case of this embodiment in which the touch panel is mounted, the reflection at the interface between the light guide and the touch panel can be removed by using an epoxy resin or the like. Therefore, a contrast ratio of 10: 1 or more was obtained. (Embodiment 7) The method of forming the surface light source of Embodiment 2 was changed. FIG. 7 shows a method of forming a surface light source in this embodiment. An anti-reflection layer 35 is formed on one side of a plastic substrate 39 (FIG. 8).
(a)), a resist containing a black pigment was formed on the back surface, and this was patterned and left in a stripe shape.
Further, at the time of patterning, taper etching was performed so that the cross section became trapezoidal, and the light absorber 63 was obtained (FIG. 8B). Next, aluminum was formed on one side of the trapezoidal cross section of the light absorber by mask evaporation to form a second light reflector 62 (FIG. 8C). This substrate forms a second reflecting portion. Further, a transparent medium, such as a transparent epoxy resin, in a fluid state was applied thereon, solidified and then formed into a wedge shape to obtain a second light guide 58 (FIG. 8D).

The anti-reflection layer of the plastic substrate can be formed not only by directly forming it on the plastic substrate but also by attaching a transparent film having an anti-reflection layer.

Since the method of forming a front light according to the present embodiment does not require mold processing, the second light reflector can be uniformly formed over the entire surface without being affected by the mold processing accuracy as in the fifth embodiment. There is an advantage. (Eighth Embodiment) In the surface light source of the seventh embodiment, the shape of the reflection surface of the second light reflector is changed from a flat shape to a convex shape. Specifically, after the light absorber was patterned, it was heated and softened, and the cross-sectional shape was made convex. Aluminum was formed thereon by mask evaporation to form a second light reflector.

In this case, as shown in FIG. 10, each of the second light reflectors reflects the source light at various angles. Therefore, even when the surface light source of this embodiment is used as a front light in a reflection type liquid crystal display device having a low light diffusion property, light is reflected in a wide viewing angle range, and a high-quality texture like paper is obtained. There is an advantage. (Embodiment 9) When the surface light source of Embodiment 7 was combined with a reflection type liquid crystal display device, the manufacturing method was changed. The substrate on which the light absorber and the second light reflector were formed was disposed on the upper surface of the display section of the reflective liquid crystal display device 80 via two types of spacers as shown in FIG. The first spacer 81 is arranged at the end of the display unit on the side where the line light source is arranged, and the second spacer 82 is arranged at the end of the display unit on the opposite side. The height of the first spacer is 3 mm, and the height of the second spacer is 0.3 mm.
2 mm, thereby fixing the glass substrate with the light irradiation body in a state of being inclined with respect to the plane of the substrate (FIG. 9A). Next, the silicon gel is poured into the gap formed by the substrate on which the light absorber and the second light reflector are formed, and the reflective liquid crystal display device,
The space between them was completely filled. This was heated to be solidified to form a structure that also serves as the second light guide 58 and the antireflection layer 35 (FIG. 9B).

In the manufacturing method of this embodiment, since the second light guide and the antireflection layer are formed at the same time, the manufacturing process can be simplified. (Embodiment 10) The surface light source and the reflection type liquid crystal display device shown in Embodiment 5 were used for a display device of a mobile phone. In a mobile phone, a protective glass is arranged on the front surface of the display device to prevent the display device from being damaged. In the present embodiment, the second refractive index matching layer was disposed between the light guide and the protective glass, and the interface reflection between the protective glass and the air layer interposed between the light guide and the protective layer was eliminated.

When the display characteristics were measured, almost the same display characteristics as in Example 1 were obtained. Since the front light of the present invention does not utilize the reflection at the air interface for light guide, even when the protective glass is present on the front surface of the light guide as in this embodiment, the refractive index between the light guide and the protective glass is low. A matching layer can be arranged. Thereby, interface reflection can be reduced and a high contrast ratio can be obtained. (Embodiment 11) The surface light source and the reflection type liquid crystal display device shown in Embodiment 5 were used for a display device of a mobile phone. In a mobile phone, a protective glass is disposed on the front surface of the display device to prevent the display device from being damaged. In this embodiment, the light guide is used also as the protective glass, and a hard coat is applied to the surface.

Since the front light of the present invention does not use the reflection at the air interface for light guide, even if the light guide is also used as a protective glass as in this embodiment, a hard coat is applied to the surface to cause damage. Can be difficult. Also, by using the light guide also as a protective glass, for example, compared to the case of using a transflective liquid crystal display device with a backlight,
The thickness and weight can be reduced by the amount of the light guide. (Comparative Example 1) In Example 5, a halogen lamp was used instead of the point light source and the collimating means.

When the display characteristics without the surface light source turned on were evaluated, the contrast ratio was 16: 1 and the reflectance was 15.
5%, which was the same property as that of Example 5. When the display characteristics when the surface light source was turned on were evaluated, the contrast ratio was remarkably reduced to 3: 1. Further, brightness 8.2cd / m ² at the end of the light source side, 4.9 cd / m ² on the display unit center is 3.3 cd / m ² at the end of the non-existent side of the light source, the brightness The homogeneity also decreased with the decrease.

Although the surface light source of the present invention requires light with high parallelism, the halogen lamp has a light emitting portion having a size larger than the thickness of the first light guide, and any light emitting portion of the light emitting portion. Emit light isotropically from a point. Therefore, the light of the halogen lamp has extremely poor parallelism. When the degree of parallelism is low, leakage light occurs, the contrast ratio decreases, and the brightness also decreases. Also,
Due to the large amount of leaked light, the light intensity at the end of the light guide is remarkably reduced, and the brightness of the display unit becomes uneven. (Comparative Example 2) In Example 5, a halogen lamp was used instead of the point light source.

When the display characteristics without the surface light source turned on were evaluated, the contrast ratio was 16: 1 and the reflectance was 15.
9%, which is a characteristic equivalent to that of Example 5. When the display characteristics when the surface light source was turned on were evaluated, the contrast ratio was remarkably reduced to 3: 1. Further, brightness 7.2 cd / m ² at the end of the light source side, 5.2 cd / m ² on the display unit center is 3.0 cd / m ² at the end of the non-existent side of the light source, the brightness The homogeneity also decreased with the decrease.

Although the surface light source of the present invention requires light with high parallelism, the halogen lamp has a light emitting portion having a size larger than the thickness of the first light guide, and any light emitting portion of the light emitting portion. Emit light isotropically from a point. Even if the collimator having the same size as the thickness of the first light guide is used, the parallelism is not improved. Therefore, for the same reason as in Comparative Example 1, the display characteristics when the flat light source is turned on are significantly reduced.

It is necessary to use a point light source whose light emitting portion is sufficiently smaller than the thickness of the first light guide. (Comparative Example 3) In Example 5, except for the surface light source of the present invention, a conventional front light utilizing interface reflection at an air interface was combined instead.

When the display characteristics without the front light turned on were evaluated, the contrast ratio was 7: 1.
The reflectance was 17.3%. When the display characteristics when the front light was turned on were evaluated, the contrast ratio was 5: 1,
The brightness is 25 cd / m ² at the end on the light source side and 2 at the center of the display.
2cd / m ^2, was 19 cd / m ² at the end of the non-existent side of the light source.

As described above, the front light utilizing the interface reflection has much light reflection and leak light at the air interface, so that the contrast ratio is significantly reduced as compared with the fifth embodiment.

Since the line light source and the surface light source of the present invention are used by converting a point light source into parallel light, light is guided without using interface reflection. Therefore, interface reflection between adjacent structures can be reduced by using the antireflection layer. Further, since metal reflection is used, no light leaks at the time of reflection. Therefore, it is possible to remarkably increase the contrast ratio when the light source is turned on, as compared with the case where the conventional front light using interface reflection is used.

When the reflection type liquid crystal display device provided with the surface light source of the present invention is applied to a portable telephone or a portable information terminal, there is an effect that a display having a high contrast ratio can be obtained both in the reflection display and when the front light is turned on. . Further, when the front light is turned on, the display unit can be brightly illuminated with a smaller amount of light from the light source.

[0064]

According to the present invention, a liquid crystal display device having good contrast can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration and an optical path of a line light source according to a first embodiment.

FIG. 2 is a diagram illustrating a configuration and an optical path of a surface light source according to a second embodiment.

FIG. 3 is a diagram illustrating a configuration and an optical path of a surface light source according to a second embodiment.

FIG. 4 is a diagram illustrating a configuration and an optical path of a surface light source according to a third embodiment.

FIG. 5 is a diagram illustrating a configuration and an optical path of a surface light source according to a fourth embodiment.

FIG. 6 is a diagram showing a state in which the surface light source of the present invention is applied to a reflection type liquid crystal display device.

FIG. 7 is a diagram showing a state in which the surface light source of the present invention is applied to a reflective liquid crystal display device with a touch panel.

FIG. 8 is a view showing one of the methods of forming a surface light source according to the present invention.

FIG. 9 is a view illustrating one method of forming a surface light source according to the present invention.

FIG. 10 is a diagram illustrating a configuration and an optical path of a reflective liquid crystal display device according to an eighth embodiment.

[Description of Signs] 11: first substrate, 12: second substrate, 13: liquid crystal layer,
14 scanning electrode, 15 signal electrode, 16 first alignment film, 17 second alignment film, 18 color filter, 19
... black matrix, 20 ... flattening layer, 21 ... reflector, 22 ... insulating layer, 25 ... first phase plate, 26 ... second phase plate, 27 ... polarizing plate, 35 ... anti-reflection layer, 38 ... touch panel , 39: plastic substrate, 51: point light source, 5
2 ... Collimator means, 53 ... First light guide, 54 ... First light incident part, 55 ... First light reflecting part, 56 ... First light emitting part, 57 ... First light reflecting body, 58 second light guide, 5
9: second light incident portion, 60: second light reflecting portion, 61: second light emitting portion, 62: second light reflecting member, 63: light absorbing member, 80: reflective liquid crystal display device, 81 ... first spacer, 82 ... second spacer.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) G09F 9/00 336 F21Y 101: 02 // F21Y 101: 02 G02F 1/1335 530 (72) Inventor Kazuhiro Kuwahara Hitachi, Ibaraki 7-1-1, Omika-cho, Hitachi F-term in Hitachi Research Laboratory, Hitachi, Ltd. F-term (reference) 2H038 AA52 AA55 2H091 FA02Y FA08X FA08Z FA11X FA14Y FA23X FA35Y FA37X FA45X GA01 LA16 LA17 5G435 AA03 BB12 BB15 EE23 EE27 FF03

Claims (4)

[Claims] 1. A liquid crystal display device having a pair of substrates and a liquid crystal layer sandwiched between the pair of substrates, a light source having a collimating means on one of the pair of substrates, and a light source. From a side surface, and a first light guide having a reflector for reflecting the incident light on a display surface; and a light emitted from a side surface of the first light guide is incident from a side surface; A second light guide having a reflector that reflects incident light in a direction above the one substrate; and a second substrate on the other substrate of the pair of substrates, the one of the pair of substrates being closer to one of the substrates. Liquid crystal display device equipped with a reflector that reflects light from the light source. 2. The liquid crystal display device according to claim 1, wherein a plurality of reflectors of said first light guide are arranged at an angle of about 45 ° with respect to a side surface. 3. The liquid crystal display device according to claim 1, wherein a plurality of reflectors of said second light guide are arranged at an angle of about 45 ° with respect to a side surface. 4. The liquid crystal display device according to claim 1, wherein said light source is a point light source, and said collimating means is a transparent medium distributed convexly above said point light source.