JP3394025B2 - Front light light guide plate - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a front light guide plate arranged for illumination on the display side of a reflective liquid crystal,
More specifically, the present invention relates to a front light guide plate having a diffraction grating on its surface in order to obtain a high-luminance display screen.

[0002]

2. Description of the Related Art Liquid crystal display devices are used not only for computer display units and control panel display units for home electric appliances, but also for mobile phone display units in a reduced size. As a result, power consumption and weight are reduced.・ The demand for thinner products is increasing. In order to meet this demand, it is becoming more and more probable that the liquid crystal display device is of a reflective type, the backlight is replaced with a front light, and natural light is used to illuminate the display section in the daytime.

Conventionally, as such a reflection type liquid crystal display device, for example, one shown in FIG. 7 is known (Japanese Patent Laid-Open No. 11-218757). The liquid crystal display device 31 is a transparent resin having a reflective liquid crystal 33 having a reflecting plate 32 on the back surface, a horizontal back surface 34a disposed on the display side of the liquid crystal, and a surface 34b inclined at an angle α with respect to the back surface. Made light guide plate 34, a lamp 35 arranged along the end face on the thick side of the light guide plate 34, and a lamp holder 36 for covering the lamp in a semicircular shape with an inner surface serving as a reflection mirror.
The light guide part 34 and the light source part 37 constitute a front light unit 38.

Illumination of the display screen of the liquid crystal 33 in the liquid crystal display device 31 is performed as follows. That is, the light emitted from the lamp 35 of the light source unit 37 is incident on the light guide plate 34 from the thick side end face as shown by the broken line arrow, and the light with a large incident angle φ at the end face is refracted at the surface 34b and goes upward. On the other hand, the light having a small incident angle φ is emitted toward the back surface 34a by total reflection, and the light traveling toward the back surface is refracted and is emitted downward from the back surface 34a to enter the liquid crystal 33 and penetrate the liquid crystal 33, and is reflected further downward. After being reflected by the plate 32, it penetrates the liquid crystal 33 upward, and then penetrates the light guide plate 34 upward to reach the eyes of the user located above the liquid crystal display device 31.

In this liquid crystal display device 31, the mutual relationship among the incident angle φ at the end surface of the light guide plate, the exit angle η at the front surface, the exit angle σ at the back surface and the inclination angle α of the light guide plate 34 is based on Snell's law. The tilt angle α of the light guide plate 34 that gives the maximum amount of light guided to the liquid crystal side and the minimum amount of leaked light on the surface is determined to be 20 °, and is displayed in the gradation display of the pixel array of the liquid crystal 33. The characters, figures, and images to be displayed from the lamp 35 to the light guide plate 3
The light guided through 4 illuminates it from above, and the reflected light allows the user to clearly recognize it.

[0006]

However, the conventional light guide plate 34 is inclined so that the amount of light guided to the back surface 34a is geometrically and optically maximized by using Snell's law, which is a pure optical refraction law. Since the front surface 34b and the back surface 34a are formed so as to have the angle α, and the front surface 34b and the back surface 34a are mirror surfaces that simply refract or totally reflect light in a geometrical optical manner, a large amount of light emitted from the lamp 35 is efficiently supplied to the liquid crystal 33. When the brightness of the lamp 35 is low or the surroundings are bright, the liquid crystal 33 is illuminated. There is a problem that the display characters are not clearly visible due to a shortage. Further, the amount of light reaching the lamp 35 naturally decreases as it approaches the thin-side end of the light guide plate 34,
Since no means for compensating for this decrease in the amount of light is provided, when the liquid crystal 33, and thus the light guide plate 34, becomes long, the illuminance on the display screen of the liquid crystal 33 becomes non-uniform, and the displayed characters and the like cannot be clearly seen. Occurs.

Therefore, an object of the present invention is to replace the conventional light guide plate, which is a mirror surface whose front and back surfaces form a predetermined angle with each other and which simply refracts and totally reflects light by geometrical optics, because of difficulty in fine processing. By utilizing the diffraction phenomenon based on the wave-like property of light by the diffraction grating, which has never happened, it is possible to obtain much higher and more uniform brightness over the entire display surface of the liquid crystal, and thus the power consumption of the light source. Another object of the present invention is to provide a front light light guide plate that can also extend the life of the battery by reducing

[0008]

In order to achieve the above object, the present invention provides a front light guide plate which can be arranged as a front light on the display side of a liquid crystal, wherein the front light guide plate is at least one end surface of the light source. a transparent plate-like member which light is incident on the surface of the plate-shaped body, a diffraction grating for diffracting the light incident from the light source to emit toward the liquid crystal from the back surface of the plate-like body, 200
To 20 μm width provided at a predetermined pitch of 300 μm
It is characterized in that a plurality of them are provided in the lattice part .

As illustrated in FIG. 1, a plurality of light guide plates 1 made of a transparent plate are provided on a surface 1a which is a mirror surface, and a plurality of grid parts 2 are provided at intervals of a pitch d in grid portions 2 provided at every pitch P, for example. When the diffraction grating 3 (engraved groove) is processed by, the light I incident from the one end surface 1c of the light guide plate 1 toward the front surface 1a is diffracted by the diffraction grating 3 toward the back surface 1b as shown by an arrow. However, between the incident light I and the diffracted light D, the incident angle is i, the diffraction angle is θ, the wavelength of the light is λ, and m is an integer.
Is established. (sini-sin θ) = ± m (λ / d) (1) D1, D2, and D3 in the figure are diffractions when m in the above formula (1) is ₁ , ₂ , and ₃ , respectively. It shows the direction of light. Since the incident angle of the incident light I on the grating portion 3 of the surface 1a is larger than the critical angle φ (for example, φ = 42 ° in the case of an acrylic light guide plate), 1
The next diffracted light D ₁ is a diffraction angle θ ₁ close to the incident angle i, the second diffracted light D ₂ is a diffraction angle θ ₂ narrower than θ ₁ , and the third diffracted light D _{3 is}
Has a diffraction angle θ ₃ narrower than θ _{2 and} each undergoes reflection-type diffraction on the front surface 1a toward the back surface 1b. Since the incident angle of the 1st and 2nd order diffracted light with respect to the back surface 1b is larger than the critical angle φ, the 1st and 2nd order diffracted lights D ₁ and D ₂ are totally reflected by the back surface 1b and further into the light guide plate 1 at a further distance. Although guided, the diffracted light D ₃ , ... Of the _third or higher order is refracted at an exit angle larger than its incident angle and goes out from the back surface 1b downward, and the reflection plate 32 at the lowermost part.
(Refer to FIG. 7), the liquid crystal 33 penetrates back and forth by being reflected,
The user's eyes are reached after penetrating the light guide plate 1 upward.

Therefore, in the front light guide plate of the first aspect, the wavelength λ of the light source is increased so that the proportion of the high-order diffracted light D ₃ , ... Contribution to the illumination of the reflective liquid crystal to the total diffracted light is increased. On the other hand, if the pitch P and the lattice spacing d are appropriately set, the display screen of the liquid crystal is illuminated very brightly by the reflected light of the reflector, and the displayed characters can be clearly recognized. The light distribution method using the diffraction grating of the present invention is essentially different from the conventional wedge-shaped light guide plate having front and back surfaces of mirror surfaces and the light guide plate having an optical prism array on the front and back surfaces. In comparison, the grating spacing d of the diffraction grating ranges from submicron to several tens of microns (0.1 to 10 μm) and is 1/10.
On the order of 0, adjacent smooth surfaces between a large number of fine groove lines cooperate and synergize to remarkably strongly diffract light as a wave and emit it downward, and a reflection-type surface light source with extremely high brightness. Is obtained. A light guide plate having such a diffraction grating is, for example, machined with an engraved groove on the inner surface or molded with a die having a hologram electroformed film of the diffraction grating lined therein, or an engraved groove is formed on the back surface of the light guide plate. It can be directly machined or printed, or can be made by printing or attaching a hologram film. In addition, the reflective liquid crystal has a diffraction grating.
The lattice part that is blocked does not allow light from below to pass through,
The pitch is too small because it does not contribute to the recognition.
With this, it is difficult to see the displayed characters even if the illumination brightness can be improved.
Become In the front light guide plate, the grid part
The pitch of the wiring lines that divide the pixel array whose pitch is liquid crystal
Since it is 200 to 300 μm, which is close to
It is possible to maintain good brightness while ensuring good visibility.
Can .

According to a second aspect of the present invention, there is provided a front light guide plate, wherein a plurality of the diffraction gratings are provided at predetermined grating intervals in a grating portion provided at a predetermined pitch on the mirror-finished surface of the plate-like body. At least one of the cross-sectional shape of the diffraction grating, the ratio of the diffraction grating portion occupying a predetermined pitch, and the predetermined grating interval increases the brightness on the surface of the front light guide plate and makes it uniform, and characters displayed on the liquid crystal, It is characterized in that it is set so that the visibility of a figure or an image is improved.

In the front light guide plate of the second aspect, at least one of the sectional shape of the diffraction grating, the ratio of the diffraction grating portion to the predetermined pitch, and the predetermined grating interval increases the brightness on the surface of the front light guide plate, and It is set to be uniform and to improve the visibility of characters, figures or images displayed on the liquid crystal. That is, the diffraction grating of the light guide plate occupies the pitch Pi between the grating portions, for example, as the cross-sectional shape changes from a sine wave to a sawtooth shape as the distance from the one end surface 1c on the light source side, that is, the amount of light reaching from the light source decreases. The ratio of the diffraction grating portion is gradually increased or the grating interval d is gradually shortened. Therefore, the light from the light source is weakly diffracted on the one end face 1c side where the light amount is large, and is strongly diffracted toward the far side where the light amount is small, so that the illumination light having a very uniform brightness is formed on the liquid crystal from the back surface 1b of the light guide plate. It is emitted toward and the displayed characters and the like can be clearly seen over the entire screen.

The front light guide plate according to claim 3 is characterized in that a diffraction grating for diffracting the light diffracted by the diffraction grating on the front surface toward the liquid crystal is provided on the back surface of the plate-shaped body. .

In the front light guide plate of the third aspect, since the transmission type diffraction grating is also provided on the back surface of the plate-like member, not only the high order reflected by the reflection type diffraction grating on the surface but also the low order. In addition to the diffracted light from the back side being diffracted again by the back side diffraction grating and emitted toward the liquid crystal below, the back side diffraction grating also diffracts the light directly incident on the back side through one end face from the light source. And emits toward the liquid crystal below. Therefore, the light emitted from the light source is more effectively used for illuminating the liquid crystal, and the brighter front light allows the displayed characters and the like to be seen more clearly.

According to a fourth aspect of the present invention, there is provided a front light guide plate in which a prism array having a sawtooth cross section is formed on the back surface of the plate-like body.

According to another aspect of the present invention, in the front light guide plate, each vertical wall of the sawtooth prism array provided on the back surface of the plate-like body is diffracted by the diffraction grating on the front surface and has a large emission angle. Is emitted toward the liquid crystal, and each inclined wall of the prism array captures high-order diffracted light with a small emission angle diffracted by the diffraction grating on the surface and emits it toward the liquid crystal. Therefore, low-order diffracted light, which cannot be effectively used without the prism array, can also be used for illuminating the liquid crystal, and display characters and the like can be seen more clearly with a brighter front light.

A front light guide plate according to a fifth aspect of the present invention is characterized in that a concavo-convex array having a rectangular cross section is formed on the back surface of the plate member.

In the front light guide plate of the fifth aspect, each vertical wall of the concavo-convex array having a rectangular cross-section provided on the back surface of the plate-like body is diffracted by the diffraction grating on the surface, and the low-order diffraction is large. Light is captured and emitted toward the liquid crystal, and each horizontal wall of the concavo-convex array captures high-order diffracted light with a small emission angle diffracted by the diffraction grating on the surface and emits it toward the liquid crystal.
Therefore, low-order diffracted light that cannot be effectively used without the concavo-convex array can also be used for illuminating the liquid crystal, and display characters and the like can be seen more clearly with a brighter front light.

[0019]

[0020]

A front light guide plate according to a sixth aspect of the present invention is characterized in that the diffraction grating is inclined at an angle of 0 to 25 ° with respect to the end face on which the light from the light source is incident.

In the reflection type liquid crystal, when the pitch of the grating portion of the front light guide plate is close to the pitch of the wiring lines of the liquid crystal and the width of the grating portion is constant and the grating interval is constant, the regular arrangement of the diffraction grating is Moire fringes are generated by interfering with the regular arrangement of the wiring lines. In the front light guide plate according to claim 7, since the diffraction grating is inclined at an angle of 0 to 25 ° with respect to the end face on which the light of the light source is incident, interference between the regular arrays is mitigated. Generation of moire fringes is suppressed, and good visibility of displayed characters and the like can be secured.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 2 is a sectional view showing an embodiment of the front light guide plate of claims 2 and 5 used for illumination of liquid crystal. The front light guide plate 1 is made of a transparent resin plate, and is arranged parallel to the front surface of the liquid crystal 33 having the reflection plate 32 on the same back surface as that described with reference to FIG. . Light I from a light source (not shown) is incident on the front light guide plate 1 from the one end face 1c substantially in parallel, and diffracts the incident light I so as to be emitted from the back face 1b toward the liquid crystal 33 as shown by an arrow. The diffraction grating 3 is provided on the surface 1a.

A plurality of diffraction gratings 3 are provided at a grating interval 2 on a grating portion 2 provided at a pitch Pi on a surface 1a forming a mirror surface. The diffracted light by the diffraction grating 3 is expressed by the relational expression (1) of diffraction.
As already described above, the low-order ones are guided through the front light guide plate 1 toward the other end surface 1d by repeating the total reflection, and the high-order ones are emitted downward from the back surface 1b. Pi and the lattice spacing d are set so that the ratio of the high-order diffracted light that contributes to the illumination of the reflective liquid crystal 33 to the total diffracted light with respect to the wavelength λ of the light source is large, and the lattice spacing d is a constant value. The ratio of the diffraction grating portion to the pitch Pi is set to be gradually larger as the distance from the light source is increased, that is, the other end surface 1d is approached, and the decrease in the amount of light reaching from the light source is compensated by the increase in the density of the diffraction grating. By the light emitted from the back surface 1b, uniform illumination brightness for the liquid crystal 33 is obtained over the entire surface. Specifically, for example, the pitch Pi of the grating portion 2 is 200 to 300 μm, ten diffraction gratings 3 of each grating portion 2 are provided at a grating interval of d = 2 μm, and the width of each grating portion 2 is Is 20 μm.

Pitch of the above-mentioned lattice portion Pi = 200-300 μm
Is approximately equal to the pitch of the wiring lines that partition the pixel array of the liquid crystal 33. The reason why the pitch Pi is set in this way is that the grating portion 2 in which the diffraction grating 3 is present scatters the light from below reflected by the reflection plate 32 of the liquid crystal 33 and does not pass it upward, so that it is displayed on the liquid crystal 33. Since it is disadvantageous for the user to visually recognize the characters, figures, and images, if the pitch Pi is too small, the ratio of the non-visual contribution portion increases and the good visibility cannot be secured even if the surface brightness is improved. The pitch Pi is made substantially equal to the pitch of the wiring lines of the liquid crystal 33 that do not originally contribute to the display.

In the present embodiment, the pitch Pi between the grating portions 2 is
Was shortened toward the other end surface 1d, but the pitch was made constant, the cross-sectional shape of the diffraction grating was gradually changed from a sine wave to a sawtooth shape, the grating interval d was gradually shortened, and the width of the diffraction grating portion and the mirror surface portion were changed. It is also possible to increase the intensity of the diffracted light by changing the ratio of the width of the light from small to large and compensate for the decrease in the light amount from the light source. Further, when the size of the front light guide plate is smaller than that of the light source, even if the diffraction grating having a constant pitch and a constant grating interval is provided on the surface of the front light guide plate 1 as described in claim 1, the The liquid crystal can illuminate the liquid crystal brighter and more uniform than before, and the displayed characters can be clearly seen.

In the present embodiment, the diffraction grating 3 is formed at the same time as the light guide plate by using a mold having a grating interval d of several μm and a machined groove on its inner surface. ,
Created by in-mold molding with a hologram film of a diffraction grating inserted at intervals of 0.1 to 10 μm, machining of engraved grooves on the back surface of the light guide plate, or printing on the back surface of the light guide plate or pasting the diffraction grating film with a hologram. can do.

The front light guide plate 1 having the above structure illuminates the liquid crystal 33 as follows. Light I incident from the light source on the one end surface 1c of the front light guide plate 1 in a substantially horizontal upward direction
When hitting the diffraction grating 3 in the grating portion 2 provided with the pitch Pi on the surface, is diffracted by the cooperation of a large number of scribed grooves adjacent to each other at the grating interval d, and the low-order diffracted light is indicated by the arrow D in FIG.
_{As shown in FIG. 1,} the total reflection is repeated to guide the inside of the front light guide plate 1 toward the other end surface 1d, and high-order diffracted light is refracted from the back surface 1b as shown by an arrow in FIG.
It is emitted to 3. The emitted light penetrates the liquid crystal 33 obliquely downward and is reflected by the reflection plate 32 at the bottom, and then the liquid crystal 3
After penetrating 3 obliquely upward again, the front light guide plate 1
It enters and penetrates it upwards, exits the surface 1a and reaches the eyes of the user located above.

The diffraction grating 3 is a light guide plate 34 having a mirror surface on the front and back sides and a wedge shape as described in the prior art example of FIG. 7, or a conventional prism array that individually totally reflects light with a side of about 0.16 mm by geometrical optics. In comparison, a large number of engraved grooves cooperate on the order of 1/100 in size,
Since light as a wave is synergistically diffracted in a specific direction in a synergistic manner, a diffracted light having a much higher intensity than that of the conventional example can be obtained. Moreover, the pitch Pi of the diffraction grating 3 and the grating interval d
Is set so that the ratio of the high-order diffracted light that contributes to the illumination to the total diffracted light is large, and the pitch Pi is the other end surface 1d.
The closer it is to, the shorter it is set. Therefore, the diffracted light can be effectively used for illuminating the liquid crystal 33, and the decrease in the light amount with the distance from the light source can be compensated by the increase in the density of the diffraction grating.
The liquid crystal 33 can be illuminated with high brightness and very uniformly over the entire surface by the light emitted from the back surface 1b. In addition, the pitch Pi between the grating portions 2 is set to the liquid crystal 3 that originally does not contribute to the display.
Since the pitch is set to 200 to 300 μm, which is approximately equal to the pitch of the wiring lines of No. 3, the ratio of the whole surface 1a of the lattice portion 2 that does not directly contribute to the visual recognition of the user can be suppressed, and the characters and figures displayed on the liquid crystal 33 can be suppressed. , The user can recognize the image well.

By the way, the light I from the light source is red (R) or green.
Since white light has a spectral distribution with peaks in (G) and blue (B), as can be seen from the fact that λ is present in the relational expression (1) of diffraction, white light is divided into R, G, and B by diffraction. Disperse.
Therefore, if the frontlight light guide plate 1 is used as a backlight of a transmissive liquid crystal, the illumination light remains dispersed and the color display of the liquid crystal cannot be properly viewed. However, the front light guide plate 1 of the present invention is
The light from the light source, which is arranged on the surface side of the reflective liquid crystal 33, reaches the eyes of the user after being reflected by the reflection plate 32 at the bottom, so that the separated R, G, and B are mixed in the optical path on the way. As a result, it returns to white light, so that a proper color display can always be seen.

Front light guide plate 1 according to the present embodiment
The same material, same size to confirm the improvement of the surface brightness of
A conventional light guide plate with a V-shaped groove at a pitch of 250 μm on the surface of a plate (length 40.8 mm x width 60 mm) was used as a comparison target. The light was made incident on one end face to measure the luminance distribution on the surface of the light guide plate. As a result, it was found that the front light light guide plate 1 of the present embodiment is 1.5 to 2 times brighter than that of the comparison target. Therefore, when the front light guide plate 1 is applied to a front light such as a home appliance or a reflection type liquid crystal display part of a mobile phone, which needs to be lighter and thinner, a much higher and more uniform brightness can be displayed. It can be obtained over the entire screen, and by extension, the life of the battery can be extended by saving power of the light source.

The diffraction grating 3 has a back surface 1b of the front light guide plate 1 (not shown) as described in claim 3.
Also, a transmission type diffraction grating can be provided. The relief shapes of reflective and transmissive diffraction gratings can be obtained by using a computer to perform calculations that cause desired diffraction, based on the theoretical equation of diffraction derived from Maxwell's equations. , The reflectance can be changed. The diffraction grating on the back surface is provided at the same position in the longitudinal direction as the diffraction grating 3 on the front surface and with the same grating portion width in view of visibility. With this configuration, low-order diffracted light (see D ₁ and D _{2 in} FIG. 1) that is not emitted from the back surface 1b only by being diffracted by the reflection type diffraction grating 3 on the front surface 1a is transmitted through the back surface 1b. And is diffracted, and most of the light is emitted to the liquid crystal 33 from the back surface 1b. Further, the light which directly enters the diffraction grating on the back surface through the one end face 1c of the frontlight light guide plate 1 is similarly diffracted and emitted from the back surface 1b. Therefore, the light emitted from the light source is more effectively used for illuminating the liquid crystal 33 without waste, and the displayed characters and the like can be visually recognized more clearly by the brighter front light.

FIG. 3 is a perspective view showing an example of the front light guide plate according to the fourth aspect. The front light guide plate 11 is a surface 1 which is a mirror surface of a transparent resin plate.
As in FIG. 2, a grating portion 2 having a diffraction grating having a grating distance d (see 3 in FIG. 4) is provided at 1a at a pitch Pi, and a prism array 12 having a sawtooth cross section is formed at a back surface 11b. ing. For the sake of visibility, each saw tooth has a vertical wall 12a provided at the same longitudinal position as the lattice portion 2 on the surface and an inclined wall 1 connecting the base of this vertical wall to the top of the vertical wall adjacent to the vertical wall 12a.
2b, and the top of each vertical wall 12a is the back surface 11 of the plate-like body.
Within a, the base of each vertical wall 12a is in the same plane parallel to the back surface 11a. Since the prism array 12 has the same pitch Pi = 200 to 300 μm as the grating portion 2 on the surface,
It has the same shape as an optical prism conventionally used for light distribution in this field.

The light I from the light source is incident on the one end face 11c of the front light guide plate 11 substantially horizontally as shown in FIG. Of the incident light, the upward light is diffracted by the diffraction grating 3 of the grating portion 2 provided on the surface 11a at the pitch Pi,
For example, the 0th to 3rd low-order diffracted light Dl is gently diffracted as shown by the arrow, is captured by the vertical wall 12a of the prism array 12 on the back surface, and is emitted toward the liquid crystal 33 while being refracted. The high-order diffracted light Dh is sharply diffracted as shown by the arrow, is captured by the inclined wall 12b of the prism array 12 on the back surface, and is emitted toward the liquid crystal 33 while being refracted. On the other hand, of the incident light, downward light goes directly to the back surface and is captured by the vertical wall 12a, as indicated by the arrow Dd.
The light is emitted toward the liquid crystal 33 while being refracted. In addition, the illumination of the liquid crystal 33 by these emitted lights is actually displayed by the light reflected by the reflection plate 32 at the bottom of the liquid crystal 33 penetrating the front light guide plate 11 upward as shown in FIG. Although the displayed characters and the like are to be visually recognized by the user, this illumination optical path is omitted in FIG. 4 so as to be immediately reflected on the surface of the liquid crystal 33.

According to the front light guide plate 11 of the present embodiment, if the rear surface 11b is a mirror surface, the low-order diffracted light Dl and the direct incident light Dd by the diffraction grating 3 on the front surface that cannot be emitted are directly incident on the rear surface. , Can be captured by the vertical walls 12a of the prism array 12 and emitted toward the liquid crystal 33. Therefore, the characters, figures, and images displayed on the liquid crystal 33 can be seen more clearly by the brighter front light.

FIG. 5 is a sectional view showing an example of the front light guide plate according to the fifth aspect. The front light guide plate 21 is a mirror-like surface 2 of a transparent resin plate.
As in FIG. 3, the grating portions 2 in which the diffraction gratings 3 are present at the grating intervals d are provided on the la 1a at the pitch Pi, and the concave-convex array 22 having a rectangular cross section is formed on the back surface 21b. In view of visibility, each rectangular groove includes a vertical wall 22a provided at the same longitudinal position as the lattice portion 2 on the surface, and a horizontal wall 22b connecting the base of this vertical wall and the base of the adjacent vertical wall, The top of each vertical wall 22a is in the back surface 21a of the plate, and each horizontal wall 22b is in the same plane parallel to the back surface 11a. The concavo-convex array 22 has the same pitch Pi = 200 as the lattice portion 2 on the surface.
~ 300 μm.

As shown in FIG. 5, the light I from the light source that is incident from one end face of the front light guide plate 11 in a substantially horizontal upward direction is diffracted by the diffraction grating 3 of the grating portion 2 provided on the surface 21a at the pitch Pi. The diffracted light D of the 0th to 3rd order
l is gently diffracted as shown by the arrow and is captured by the vertical wall 22a of the prism array 22 on the back surface, and while refracting, the liquid crystal 33
Diffracted light Dh that is emitted toward
Is sharply diffracted as shown by the arrow and the prism array 1 on the back surface
The light is captured by the second horizontal wall 22b and refracted and emitted toward the liquid crystal 33. On the other hand, of the incident light, which is directed downward, although not shown, it is directly captured by the vertical wall 22a toward the back surface and emitted toward the liquid crystal 33 while being refracted.
In FIG. 5, as in FIG. 4, the illumination optical paths by these emitted lights are omitted so that they are immediately reflected on the surface of the liquid crystal 33.

According to the front light guide plate 21 of the present embodiment, if the rear surface 21b is a mirror surface, the low-order diffracted light Dl and the direct incident light on the rear surface, which cannot be emitted by total reflection, are generated. It can be captured by the vertical wall 22a of the concave-convex array 22 and emitted toward the liquid crystal 33. Therefore, the characters, figures, and images displayed on the liquid crystal 33 can be seen more clearly by the brighter front light.

FIG. 6 is a plan view showing an example of the front light guide plate according to the seventh aspect. In this frontlight light guide plate 1, only the point that the grating portion 4 provided on the surface 1a at a constant pitch P is inclined at an angle of β ° with respect to the one end surface 1c on which the light from the light source is incident is shown in FIG. Different from the embodiment. Therefore, the grating portion width and the grating interval d of the diffraction grating (not shown) are the same as those of the front light guide plate described in FIG. The reason that the grating portion 4 is inclined by β ° in this embodiment is to prevent the generation of moire fringes. That is, the liquid crystal 33
Since a large number of pixels are arranged in a matrix in the vertical and horizontal directions and these pixels are divided into a grid pattern by a source bus and a gate bus at a constant interval, a front light guide in which a grid portion is arranged on the liquid crystal at a constant pitch P. When the light plates 1 are overlapped with each other by a specific angle, the regular arrangement of the wiring lines interferes with the regular arrangement of the lattice portions, and moire fringes are observed when the front light guide plate 1 is viewed from above. The inventors have found that when the deviation angle β between the wiring line and the lattice portion is 0 to 25 °, the generation of moire fringes is suppressed, and particularly when β = 22.5 °, the moire fringes almost disappear. Note that if the pitch of the grating portions 4 is changed like Pi in the embodiment of FIG. 2, the regularity of the arrangement is weakened and moire fringes do not occur.

In this embodiment, the front light guide plate 1
Since the grid portion 4 is arranged so as to be inclined by the angle β with respect to the wiring line of the liquid crystal, even if the grid portion 4 is provided at the constant pitch P, the generation of moire fringes is suppressed and the liquid crystal is displayed on the liquid crystal. It is possible to clearly recognize displayed characters, figures, and images.

[0041]

As is apparent from the above description, the front light guide plate according to claim 1 of the present invention is characterized in that at least the surface of the transparent plate-like body on which the light from the light source is incident from one end face thereof,
A diffraction grating that diffracts the incident light and emits it from the back surface to the reflective liquid crystal below is formed at a predetermined pitch of 200 to 300 μm.
Since a plurality of 20 μm wide gratings are provided, the liquid crystal is illuminated extremely brightly from below by high-intensity diffracted light, making the liquid crystal lighter and thinner, saving the power of the light source, and extending the battery life. As a result, it is possible to obtain a display screen that is much more uniform and brighter than in the past. In addition, the grid
Is the pitch of the wiring lines that divide the liquid crystal pixel array
200 to 300 μm, which is close to
The lattice part that scatters the light from the liquid crystal originally contributes to the display.
Lighting brightness because it matches the pitch of the wiring line
It is possible to maintain good visibility while maintaining high
It

In the front light guide plate according to claim 2 of the present invention, a plurality of diffraction gratings are provided at predetermined grating intervals in a grating portion provided at a predetermined pitch on the surface forming a mirror surface, and the cross-sectional shape of the diffraction grating is At least one of the ratio of the diffraction grating portion to the predetermined pitch and the predetermined grating interval increases the brightness on the surface of the front light guide plate and makes it uniform, and the visibility of the characters, figures or images displayed on the liquid crystal. Is set so that even the part far from the light source of the front light guide plate is illuminated by the diffracted light in the same way as the part near the front light guide plate, and the characters displayed on the entire screen are illuminated by the very uniform and high brightness illumination. It is clearly visible.

In the front light guide plate according to claim 3 of the present invention, since the back surface of the plate-like body is provided with the diffraction grating for diffracting the light diffracted by the diffraction grating on the surface toward the liquid crystal, Not only the high-order and low-order diffracted light diffracted by the front diffraction grating, but also the light source light that is directly incident are also diffracted by the back diffraction grating and emitted toward the liquid crystal, so that the light from the light source is further It can be effectively used for illuminating liquid crystal, and display characters and the like can be visually recognized more clearly by a brighter front light, and power consumption of a light source can be saved.

In the front light guide plate according to claim 4 of the present invention, since the prism array having a sawtooth-shaped cross section is formed on the back surface of the plate-shaped body, each vertical wall of the sawtooth-shaped prism array and Since each slanted wall captures low-order and high-order diffracted light diffracted by the diffraction grating on the surface and emits it toward the liquid crystal, use low-order diffracted light that cannot be used without a prism array for illumination. With the brighter front light, the displayed characters can be seen more clearly, and the power consumption of the light source can be reduced.

In the front light guide plate according to claim 5 of the present invention, since the concave-convex array having a rectangular cross section is formed on the back surface of the plate-shaped body, each vertical wall and each horizontal surface of the concave-convex array having a rectangular cross section. Since the wall captures low-order and high-order diffracted light diffracted by the surface diffraction grating and emits it toward the liquid crystal, low-order diffracted light that cannot be used without an uneven array can also be used for illumination. The display characters and the like can be visually recognized more clearly by the brighter front light, and the power of the light source can be saved.

[0046]

In the front light guide plate according to claim 6 of the present invention, since the diffraction grating is inclined at an angle of 0 to 25 ° with respect to the end face on which the light of the light source is incident, the grating portion is formed. Interference between this regular array and the regular array of liquid crystal wiring lines is mitigated even if the pitch or lattice spacing is constant, and moire fringes are suppressed, ensuring good visibility of displayed characters. can do.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing in principle the diffraction of light by a diffraction grating provided on the surface of a front light guide plate.

FIG. 2 is a cross-sectional view showing an example of a front light guide plate according to the present invention used for illuminating a reflective liquid crystal.

FIG. 3 is a perspective view showing another embodiment of the front light guide plate of the present invention.

FIG. 4 is a cross-sectional view showing an illumination optical path by the front light guide plate of FIG.

FIG. 5 is a cross-sectional view showing another embodiment of the front light guide plate of the present invention.

FIG. 6 is a plan view showing another embodiment of the front light guide plate of the present invention.

FIG. 7 is a cross-sectional view showing a reflective liquid crystal using a conventional front light guide plate.

[Explanation of symbols]

1,11,21 Front light guide plate 1a, 11a, 21a surface 1b, 11b, 21b back side 1c, 11c, 21c One end surface 1d, 11d, 21d other end surface 2,4 lattice part 3 diffraction grating 12 Prism array 12a, 22a Vertical wall 12b inclined wall 22b horizontal wall P, Pi lattice pitch Dl Low-order diffracted light Dh Higher-order diffracted light Light from the I light source

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI G02F 1/13357 G02F 1/1335 530 (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 6/00 331 F21V 8 / 00 601 G02B 5/18 G02F 1/1335 G02F 1/13357

Claims (6)

(57) [Claims] 1. A front light guide plate which can be arranged as a front light on the display side of a liquid crystal, wherein the front light guide plate comprises a transparent plate-like body on which light from a light source is incident at least from one end face. A diffraction grating that diffracts light incident from the light source so as to be emitted from the back surface of the plate-shaped body toward the liquid crystal is provided on the front surface of the body at a predetermined pitch of 200 to 300 μm.
A front light guide plate, wherein a plurality of the light guide plates are provided in a 0 μm-wide lattice portion . 2. A front light light guide plate according to claim 1, the diffraction grating of the diffraction grating cross-sectional shape,
At least one of the ratio of the diffraction grating portion to the predetermined pitch and the grating interval increases the brightness on the surface of the front light guide plate and makes it uniform, and the visibility of the characters, figures or images displayed on the liquid crystal. The front light guide plate is characterized in that it is set to improve. 3. The frontlight light guide plate according to claim 1, wherein a diffraction grating that diffracts light diffracted by the diffraction grating on the front surface toward the liquid crystal is provided on the back surface of the plate-shaped body. The front light guide plate is characterized by being. 4. The front light guide plate according to claim 1 or 2, wherein a prism array having a sawtooth-shaped cross section is formed on the back surface of the plate body. 5. The frontlight light guide plate according to claim 1 or 2, wherein a concavo-convex array having a rectangular cross section is formed on the back surface of the plate-shaped body. 6. The front light the light guide plate according to any one of claims 2 to 5, the diffraction grating is tilted at an angle of 0 to 25 ° to the end face on which light is incident of the light source The front light guide plate is characterized by being.