JP3260688B2 - Surface light source device, polarizing surface light source device, and liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source device and a polarizing surface light source device which are excellent in light-collecting property of light emitted and effective use efficiency of light, and a liquid crystal display which is excellent in uniformity of brightness and which is bright and easy to see using the same. It relates to a display device.

[0002]

BACKGROUND OF THE INVENTION The light transmittance of liquid crystal cells and the like has been reduced due to colorization and high definition, etc. On the other hand, there has been a demand for a bright and easy-to-see liquid crystal display device, etc. While the provision of a small and lightweight backlight is an important issue, the group to which the present inventors belong first has, for the purpose of solving the problem, periodically having fine prismatic irregularities on at least one of the upper and lower surfaces, Side light type surface light source device that emits incident light from a light source disposed in one of the upper and lower surfaces with high directivity, and a polarizing surface having a selective reflection layer showing selective reflection of polarized light on the light emission side. A light source device has been proposed (Japanese Patent Application No. 7-321036).

In the above-mentioned polarization plane light source device, the light utilization efficiency is improved by causing the polarized light reflected through the selective reflection layer to travel backward through the reflection layer or the like on the back surface of the light guide plate and re-emitted from the light guide plate. In practical use, a prism-type light-condensing sheet (for example, manufactured by Three M Co., Ltd., B
EF or the like is disposed below or above the selective reflection layer on the light exit side of the light guide plate at an angle at which the diffused light is condensed, thereby improving the brightness in the front direction.

[0004] However, when the polarized light reflected through the selective reflection layer in the above re-enters the light guide plate via the light condensing sheet, it is bent obliquely on the prism surface of the light condensing sheet. The incident angle with respect to the reflective layer etc. on the back side deviates more than normal incidence, so the efficiency of inverting the polarization characteristics through the reflective layer etc. and converting it into a polarized state that can pass through the selective reflective layer decreases, and consequently the light use efficiency There has been a problem that the brightness as a polarization plane light source is reduced due to a decrease.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to a light guide plate (Japanese Patent Application No. 7-321036) in which emitted light exhibits a directivity close to the vertical direction due to the fine prismatic irregularities. The light diffused in the direction of the groove is also condensed and the brightness in the front direction is excellent, and the polarized light reflected through the selective reflection layer is incident on the reflection layer etc. on the back surface of the light guide plate with good perpendicularity and passes through the selective reflection layer The challenge is to develop a surface light source device that can efficiently reflect and invert to a polarization state that can be changed, has excellent light use efficiency based on its excellent conversion efficiency, and has excellent brightness in the front direction even when it is used as a polarized surface light source device. And

[0006]

According to the present invention, an incident light from the light incident side surface is provided on at least one of the upper and lower surfaces with continuous or discontinuous fine prismatic irregularities in a direction along the light incident side surface at a period of 50 to 500 μm. A light guide plate that emits light from one of the upper and lower surfaces, a light source disposed on the light incident side surface, and at least a prism sheet disposed between the light guide plate and the light source. The light guide plate side has a repeating structure of continuous isosceles formed of substantially isosceles triangles, the tops of the asperities are arranged in the vertical direction of the light guide plate, and the fine prism-shaped unevenness is diffused in the groove direction.
Focus the light from the light source in the direction perpendicular to the groove direction
An object of the present invention is to provide a surface light source device, wherein the light is incident from the light incident side surface.

According to the present invention, there is further provided a polarized light source device having a selective reflection layer exhibiting selective reflection of polarized light on the light exit side of the surface light source device, and the surface light source device or the polarized light source. An object of the present invention is to provide a liquid crystal display device having a liquid crystal cell on a light emission side of the device.

[0008]

According to the surface light source device of the present invention, the polarized light reflected via the selective reflection layer re-enters the light guide plate due to the structure in which the prism sheet is disposed between the light incident side surface of the light guide plate and the light source. In this case, it is possible to avoid passing through the prism sheet, and to suppress a change in the optical path of the re-incident light due to the prism surface or the like.

As described above, the polarized light reflected through the selective reflection layer is applied to the reflection layer on the back surface of the light guide plate while utilizing the advantage of the emitted light exhibiting the directivity close to the vertical direction by the light guide plate provided with the fine prismatic irregularities. On the other hand, the light can be incident with good perpendicularity, and the reflection can be efficiently inverted to a polarization state that can be transmitted through the selective reflection layer.

On the other hand, it is possible to condense the light diffused in the groove direction of the fine prismatic irregularities of the light guide plate through the prism sheet and make the light incident on the light incident side surface of the light guide plate with good perpendicularity to the groove direction. The light can also be emitted from the light guide plate emission surface with good directivity through the fine prismatic irregularities, and can be used effectively, and the light use efficiency and frontal brightness can be improved.

As a result, a surface light source device having excellent frontal luminance utilizing the advantage of a light guide plate in which emitted light exhibits a directivity close to the vertical direction is obtained, and the reflected polarized light passing through the selective reflection layer is selectively reflected by the selective reflection layer. A polarization plane light source device with excellent light use efficiency and frontal brightness by efficiently converting to a polarization state that can transmit light is obtained, and it is used as a backlight for excellent brightness uniformity for easy viewing and high display. A high-quality liquid crystal display device can be obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A surface light source device according to the present invention comprises: a light guide plate for emitting incident light from a light incident side surface from one of upper and lower surfaces; a light source disposed on the light incident side surface; It comprises at least a prism sheet disposed therebetween. Examples are shown in FIGS. 1 (a) and 1 (b). 1 is a light guide plate, 2 is a prism sheet, and 3 is a light source. 3
1 is a light source holder surrounding the light source 3, and 4 is a reflection layer.

The light guide plate has continuous or discontinuous fine prismatic irregularities in a direction along the light incident side surface on at least one of the upper and lower surfaces at a period of 50 to 500 μm, and receives incident light from the light incident side surface. One that emits light from one of the upper and lower surfaces is used. This makes it possible to obtain a bright surface light source with excellent light use efficiency.

FIGS. 2A to 2C show examples of the light guide plate. FIGS. 3A to 3C show examples of fine prismatic irregularities.
(C). In FIG. 2, 11 is the upper surface, 12, 1
6, 17 are lower surfaces, 13 is a light incident side surface, 14 is a lateral side surface, 1
Reference numeral 5 denotes a side end facing the light incident side surface 13. FIG.
, 18 and 19 are convex portions, 20 is a concave portion, and 2
2, 24 (25) and 28 are gentle slopes, and 23, 26 and 27 are adjacent faces or steep slopes.

The light guide plate is generally formed of a plate-like object having an upper surface, a lower surface opposite thereto, and a light incident side surface between upper and lower surfaces as shown in the figure. The plate-like object may be the same thick plate or the like, but preferably, as shown in the figure, the thickness of the side end portion 15 facing the light incident side surface 13 is smaller than that of the light incident side surface, particularly 50% or less. Of the thickness.

By reducing the thickness of the end on the opposite side as described above, FIG.
As shown by the thick arrow shown in FIG. 7A, the light incident from the light incident side surface efficiently enters the adjacent surface of the lower surface or the steep slope before reaching the opposite end portion as the transmission end, and reflects the upper surface through the reflection. More efficiently, and the incident light can be supplied to the target surface.
In addition, there is an advantage that the light guide plate can be reduced in weight.
Incidentally, when the lower surface is a straight surface as shown in FIG. 2A, the weight can be about 75% of the light guide plate having a uniform thickness.

As described above, the surface of the light guide plate on which the fine prismatic irregularities are formed is generally an inclined surface, but the inclined shape is arbitrary, and a linear surface as illustrated in FIG.
An appropriate surface shape such as a curved surface as illustrated in (b) and (c) can be used. When the surface is not a straight surface, the average inclination angle is 5 degrees at all positions on the surface on which the fine prismatic irregularities are provided, rather than at a point where the emission direction of the emitted light is made uniform (directivity).
It is preferably within the range of degrees.

The fine prismatic irregularities provided on at least one of the upper and lower surfaces of the plate-like object are periodically formed as projections or depressions on a continuous or discontinuous slope along the light incident side surface. The prism-shaped unevenness may have an appropriate uneven shape such as a groove or a step-like step, and is not particularly limited.

Further, the prism-shaped irregularities may be continuous or may be formed by intermittently arranging prism-shaped irregularities of a predetermined length. In addition, based on the straight line 21 connecting the intersection with the lower surface of the slope forming the projection or the recess in the illustrated example, whether the intersection (vertex) of the slope protrudes (convex) from the straight line or the depression It depends on whether it is concave (concave).

As shown in FIG. 3, the fine prismatic irregularities more preferable in terms of light emission efficiency and the like have a downward slope and an upward slope based on a straight line connecting the intersection with the lower surface and the vertex, as illustrated in FIG. Things. Thereby, in addition to the transmission light directly incident on the upward slope, the transmission light incident on the downward slope and incident on the upward slope through reflection thereof can be supplied to the output surface by reflection via the upward slope. The light use efficiency can be improved accordingly. The downward slope or the upward slope depends on whether the slope is a downward slope or an upward slope in a direction away from the light source.

In the above, the shape of the projections or depressions forming the fine prismatic irregularities does not need to be formed as a linear slope as illustrated in FIGS. 3 (a) to 3 (c). It may be formed by a slope including a surface or the like. Also, the projections or depressions need not have the same irregularities or the same shape over the entire surface, and the shape and angle gradually change from the light incident side surface side, rather than from the viewpoint of improving the perpendicularity of the emitted light. In particular, a structure in which the inclination angle of the upward slope with respect to the light guide plate reference plane sequentially increases from the light incident side surface side is preferable.

The above-described upward slope forming the convex portion or the concave portion corresponds to the reference plane (11) of the light guide plate as illustrated in FIG.
Is preferably a steep slope having an inclination angle θ ₁ of 35 to 45 degrees. By adopting such a steep slope, FIG.
As illustrated by the broken line arrow in (a), the incident transmission light from the light incident side that is incident directly or through the downward slope is received and reflected through the upward slope (steep slope) 23 and is almost perpendicular to the emission surface 11. The light can be efficiently emitted at an angle.

If the inclination angle of the upward slope is out of the above range, the deviation from the vertical direction becomes large, and it is difficult to give the emitted light directivity close to vertical, and the emission efficiency (utilization efficiency) of the transmitted light
May decrease. Note that, as described above, it is preferable that the angle of the steep slope is sequentially increased in the range of 35 to 45 degrees from the light incident side surface to the transmission end side of the incident light from the viewpoint of improving the perpendicularity of the emitted light. .

On the other hand, as shown in FIG. 3 (a), the downward slope forming the projections or depressions has an inclination angle θ ₂ of more than 0 ° to 10 °, particularly 5 °, with respect to the reference plane of the light guide plate. Hereafter, it is particularly preferable that the slope is a gentle slope of 2 degrees or less. By adopting such a gentle slope, light transmitted at an angle larger than the inclination angle is incident on and reflected by the downward slope 22 as illustrated by the broken line arrow in FIG. Based on the inclination angle, the light is reflected by the exit surface 11 at a parallel angle, enters the upward slope 23, is reflected, and exits from the exit surface.

As a result, the incident angle of the light incident on the upward slope can be made constant, the variation of the reflection angle can be suppressed, and the emitted light can be made parallel. Therefore, by adjusting the inclination angles of the downward slope and the upward slope that form the convex portion or the concave portion, it is possible to give directivity to the emitted light,
Thus, light can be emitted at an angle close to the vertical direction with respect to the emission surface.

The period of the fine prismatic irregularities, that is, the period of the convex portions or concave portions forming the same, is 50 to 500 μm as described above in view of averaging the brightness over the entire surface.
m. Particularly, a preferable period is 400 μm or less, particularly 300 μm or less.

The shape of the light incident side surface of the light guide plate is not particularly limited, and may be appropriately determined. Generally,
The plane is perpendicular to the exit plane. The thickness of the light guide plate can be appropriately determined depending on the size of the light guide plate, the size of the light source, and the like according to the purpose of use. A typical thickness when used for a liquid crystal display device is 20 mm based on the light incident side surface.
Hereinafter, it is particularly 0.1 to 10 mm, particularly 0.5 to 8 mm.

The light guide plate can be formed by an appropriate method using an appropriate material exhibiting transparency according to the wavelength range of the light source. Incidentally, in the visible light region, for example, a transparent resin or glass represented by an acrylic resin, a polycarbonate resin, an epoxy resin, or the like can be used.

Although the light guide plate can be formed by a cutting method or the like, a preferable manufacturing method from the viewpoint of mass productivity is to heat a mold or roll capable of forming predetermined fine prismatic irregularities to a thermoplastic resin. A method of transferring a shape by pressing to a mold, a method of filling or casting a liquid resin which can be polymerized by heat, ultraviolet rays or radiation, into a mold or a roll capable of forming a predetermined fine prism-like unevenness, or a method of performing a polymerizing treatment, or a transparent method. While applying on the substrate,
Alternatively, a method of polymerizing after coating, a method of filling a thermoplastic resin melted by heating or a resin fluidized through heat or a solvent into a mold capable of forming predetermined prismatic irregularities by an injection method, or the like. can give.

The light guide plate may be formed as a laminate of different kinds of materials, such as a light guide part for transmitting light, which is bonded to a sheet having fine prismatic irregularities. Need not be formed as an integral monolayer.

As illustrated in FIG. 1, a reflection layer 4, preferably a metal reflection layer, can be provided on the surface of the light guide plate 1 on which the fine prismatic irregularities are provided, if necessary. Such a reflection layer is effective for preventing the generation of light leaking from the fine prism-shaped uneven surface and improving the emission efficiency. In the case of a polarization plane light source device combined with a selective reflection layer, it also functions as polarization conversion means.

When functioning as the above-mentioned polarization conversion means, a reflection layer made of metal is particularly preferable. According to such a metal reflection layer, the polarization characteristics can be efficiently inverted at the time of reflection, and the polarization conversion efficiency is superior to that obtained by total reflection or diffuse reflection through an interface having a different refractive index.
Incidentally, when circularly polarized light or linearly polarized light is incident on the metal surface substantially vertically, the conversion efficiency of the left and right of circularly polarized light or the vibration plane of linearly polarized light becomes 9%.
The efficiency of 0 degree conversion is a value close to 100%.

The metal reflection layer, which is preferable from the viewpoint of polarization conversion efficiency, has a metal surface containing at least one kind of metal having a high reflectance such as aluminum, silver, gold, copper or chromium. The metal reflective layer having excellent adhesion to the light guide plate can be formed as a coating layer in which a metal powder is mixed with a binder resin, or a layer provided with a metal thin film by a vapor deposition method or the like. One or both surfaces of the metal reflective layer may be provided with an appropriate coat layer for the purpose of improving reflectance, preventing oxidation, and the like, if necessary.

As the light source 3 disposed on the side of the light guide plate,
An appropriate one can be used, but for example, a linear light source such as a (cold or hot) cathode tube, a point light source such as a light emitting diode, or a linear or planar array thereof can be preferably used. A cold cathode tube is particularly preferable from the viewpoint of low power consumption and durability.

As shown in FIG. 1 (b), the prism sheet 2 disposed between the light guide plate 1 and the light source 3 has a repetitive structure of a continuous isosceles triangle formed on the light guide plate side of one side of the sheet. Is used, and the tops of the irregularities are arranged in the vertical direction of the light guide plate. The prism sheet may be simply placed on the light incident side surface of the light guide plate, or may be fixed to the light incident side surface of the light guide plate via an adhesive layer or the like as necessary so that the space due to the unevenness is maintained. May be. FIG. 1B shows a state where the light source holder 31 in FIG. 1A is removed.

As described above, the light from the light source diffused in the groove direction of the fine prismatic irregularities of the light guide plate is condensed through the prism sheet and is incident on the light incident side surface of the light guide plate with good perpendicularity to the groove direction. The light can also be emitted from the light guide plate emission surface with good directivity through the fine prismatic irregularities, and the brightness in the front direction can be improved.

In the case of a polarization plane light source device provided with a selective reflection layer, since the prism sheet is on the light incident side of the light guide plate, the polarized light reflected through the selective reflection layer is guided without passing through the prism sheet. It is possible to suppress a change in the optical path of the re-incident light that re-enters the optical plate and passes through the prism surface or the like.

The prism sheet can be formed of an appropriate material exhibiting transparency according to the wavelength region of the light source, and its material and manufacturing method include those exemplified for the light guide plate described above. The irregularities are formed in a continuous state so as to perform a constant function in the thickness direction of the light guide plate.

The irregularities on the prism sheet are formed in a substantially isosceles triangle shape, preferably an isosceles triangle shape, so that they work equally in the width direction of the light guide plate.
The angle of inclination of the slope can be appropriately determined according to the degree of spread of the incident light from the light source in the width direction. Generally, the slope angle is 10 to 80 degrees (vertical angle 160 to 20 degrees), especially 20 to 70 degrees (vertical angle 140 to 40 degrees), particularly 30 to 6 degrees.
It is a substantially isosceles triangle with 0 degrees (vertical angle 120 to 60 degrees).

Further, the pitch of the repetitive structure of the irregularities on the prism sheet can be determined as appropriate, but generally, the pitch is 20 times.
~ 500 μm, especially 25-300 μm, especially 30-100
μm. The thickness of the prism sheet can be appropriately determined depending on the light guide plate or the like to be arranged, but is generally 1 mm or less, particularly 5 to 500 μm, particularly 10 to
It is 200 μm.

When forming the surface light source device, FIG.
4, a light source holder 31 surrounding the light source for guiding the divergent light from the light source 3 to the side surface of the light guide plate 1 as needed, a diffusion layer 5 for obtaining uniform surface light emission, leak light It is also possible to provide a combination body in which appropriate auxiliary means such as a reflection layer 4 for prevention and an optical path deflecting sheet 6 are arranged at appropriate positions.

As the light source holder, a resin sheet or a metal foil provided with a high-reflectance metal thin film is generally used.
The disposition of the diffusion layer is advantageous for forming a surface light source device that is superior in brightness uniformity by preventing the occurrence of brightness unevenness, and can be formed as an appropriate diffusion layer using a diffusion plate, a fine uneven surface, or the like. When a polarization plane light source device is formed, a diffusion layer having a small diffusion angle is preferable from the viewpoint of maintaining the polarization state.

As for the reflection layer, the reflection layer 4 described above is used.
Alternatively, or together with the reflection layer, a reflection sheet can be provided along the surface of the light guide plate on which the fine prismatic irregularities are formed. The reflection sheet can conform to the reflection layer described for the light guide plate. Therefore, in the case of the polarization plane light source device, a reflection sheet having a metal reflection surface can be preferably used.

The optical path deflecting sheet is disposed for the purpose of controlling the optical path of the light emitted from the light guide plate. Therefore, as shown in FIG. 4, the optical path deflecting sheet 6 is disposed on the light emitting side on the upper and lower surfaces of the light guide plate 1. The optical path deflecting sheet exhibits the characteristics of optical path control based on the repetitive structure of the concavities and convexities imparted thereto according to the above-described prism sheet, but in the present invention, the optical path deflecting sheet is used when the polarizing surface light source device is used as described above. May change the course of the polarized light reflected by the selective reflection layer and cause inconvenience.

In the present invention, from the viewpoint of preventing the occurrence of the above-mentioned inconveniences, an optical path deflecting sheet preferably having a repetitive structure of continuous irregularities formed of scalene triangles arranged in one direction on one surface can be preferably used. In the case of a surface light source device having no selective reflection layer, an optical path deflecting sheet having an appropriate repetition structure of irregularities can be used because the inconvenience problem unlike the above-mentioned polarizing surface light source device does not occur.

As an optical path deflecting sheet having a repetitive structure of continuous irregularities formed of a scalene triangle arranged in one direction on one side, a streak-shaped groove composed of a gentle slope 62 and a steep slope 63 as shown in FIG. Those having 61 periodically are preferable. In particular, as shown by the broken line arrow in FIG. 5, as much as possible, ideally 100% light is applied to the gentle slope which is the main part of the optical path change (α, α ₁ , α ₂ ) by the wedge plate function. , The inclination angle θ ₃ with respect to the reference plane is 5 to 3
It is preferable that the grooves 61 have a streak-like groove 61 composed of a gentle slope 62 of 5 degrees and a steep slope 63 having an inclination angle θ ₄ of 60 degrees or more. Note that the steep slope is a loss light in which light incident on the steep slope cannot be used effectively, so that the light incident thereon is suppressed as much as possible by 75 to 110 degrees, especially 85 to 90 degrees.
More preferably, the angle of inclination is in degrees.

The period of the streak grooves formed by the gentle slope and the steep slope can be appropriately determined according to the characteristics of the light emitted from the light guide plate for controlling the optical path. From the viewpoint of prevention and the like, the thickness is preferably 80 μm or less, particularly preferably 65 μm or less, and particularly preferably 10 to 50 μm.

The optical path deflecting sheet can be formed of an appropriate material exhibiting transparency according to the wavelength range of the light source, and its material and manufacturing method can be in accordance with the above-described light guide plate and prism sheet. Therefore, the optical path deflecting sheet can be formed in an appropriate form such as an independent sheet made of a sheet or the like, or an auxiliary layer directly formed on an optical component such as a light guide plate.

As shown in FIG. 6, an optical path deflecting sheet can be obtained, for example, by forming a predetermined groove on a transparent substrate 64 by coating. In addition, 5 in FIG.
It is a diffusion layer as described above. The thickness of the optical path deflection sheet is
Although it can be appropriately determined according to the size of the light guide plate emission surface,
Generally less than 1mm, especially 5 to 500
μm, especially 10 to 200 μm.

As illustrated by the broken line arrow in FIG.
Since the light path change by 2 is in the thickness direction, if the light emitted from the light guide plate shows directivity in the direction away from the light source (left side in the figure), the gentle slope becomes thin in the direction away from the light source. It is preferable to dispose the optical path deflecting sheet in the state from the viewpoint of verticalizing the emitted light. On the other hand, when the directivity of the light emitted from the light guide plate is opposite, it is preferable to arrange the light path deflecting sheet in a state where the light path deflecting sheet becomes thinner in a direction approaching the light source.

Therefore, the light path deflecting sheet can be arranged by appropriately adjusting the groove direction of the unevenness on the basis of the directivity of the light emitted from the light guide plate. Can be arranged so as to intersect with the groove direction. Such an intersecting arrangement is also effective in preventing the occurrence of moire due to interference with pixels of the liquid crystal cell and the like.

As described above, according to the surface light source device of the present invention, the highly collimated light is emitted in a direction having excellent perpendicularity, which is advantageous for visual recognition, and the light from the light source is efficiently used to increase the brightness. Various devices can be formed, such as a polarization plane light source device excellent in brightness and a liquid crystal display device which is bright and easy to see and has low power consumption, and can be preferably used as a sidelight type backlight or the like.

The above-mentioned polarization plane light source device aims to convert incident light having no polarization characteristics into polarized light with high efficiency by using a selective reflection layer that selectively reflects polarized light through transmission and reflection. In that case, the surface light source device according to the present invention,
Providing highly accurate parallelized outgoing light with excellent perpendicularity, and re-emit reflected light (return light) through the selective reflection layer with good consistency of the direction with the initial outgoing light with little angle change To make things possible.

FIG. 7 illustrates a polarization plane light source device 7 according to the present invention. This is configured by disposing a selective reflection layer 71 exhibiting selective reflection of polarized light on the light emission side of the above-mentioned surface light source device. In the embodiment, a material that transmits predetermined circularly polarized light and reflects circularly polarized light other than predetermined light is used as the selective reflection layer. In FIG. 7, a layer 72 provided on the upper surface of the selective reflection layer 71 is a linearly polarized light converting means for converting circularly polarized light into linearly polarized light.

According to the polarization plane light source device 7, light emitted from the light guide plate 1 of the surface light source device enters the selective reflection layer 71, and predetermined (tentatively left) circularly polarized light on the left and right is transmitted. The circularly polarized light outside the predetermined (right) direction is reflected, and the reflected light returns to the light guide plate as return light. The light that has re-entered the light guide plate is reflected by the reflection function portion including the reflection layer 4 on the lower surface, re-enters the selective reflection layer, and is again separated into transmitted light and reflected light (return light). Therefore, the return light as reflected light is confined between the selective reflection layer and the light guide plate and is repeatedly reflected until it becomes a predetermined circularly polarized light that can pass through the selective reflection layer.

In the above, the surface light source device according to the present invention provides a highly parallelized outgoing light having excellent perpendicularity,
Most of the return light through the selective reflection layer is incident on the downward slope of the fine prismatic irregularities in the light guide plate, and is reflected without greatly changing the angle based on the gentle inclination angle. A state in which light can be re-emitted in a direction similar to that of the emitted light, and therefore with good verticality, the coincidence of the directions of the initial emitted light and the re-emitted light is excellent, and the light having excellent polarization characteristics is highly efficient with little loss. Can be obtained at

As in the case of the surface light source device illustrated in FIG. 4, even when the optical path deflecting sheet 6 is provided on the light guide plate 1 and the selective reflection layer is disposed through the sheet, the above-described optical path deflecting sheet can be used. Most of the return light passing through the selective reflection layer 71 has a gentle slope 62.
Since the gentle slope is excellent in reversibility and does not significantly change the optical path of the return light, the return light can be re-emitted from the selective reflection layer with good verticality as described above, Light with excellent coincidence of the directions of the initially emitted light and the re-emitted light and excellent polarization characteristics can be obtained in a state with little loss and excellent utilization efficiency.

As described above, the return light through the selective reflection layer is:
Since light is re-emitted through reflection by the downward slope or gentle slope of the light guide plate, the light guide plate used for forming the polarization plane light source device has a projected area of the downward slope or gentle slope with respect to the reference plane of the light guide plate adjacent thereto. Surface, especially, more than 5 times that of uphill or steep slopes, especially more than 7 times, especially 10
It is preferably from 100 to 100 times from the viewpoint of light use efficiency and the like. This relationship of the projection area ratio can be said to be the same even when the optical path deflecting sheet is arranged, for the gentle slope 62 which is the substantial transmission surface of the return light and the steep slope 63 corresponding thereto.

The light guide plate used for forming the polarization plane light source device is provided on the side of the light guide plate other than the light exit surface so as to efficiently reflect the return light through the selective reflection layer through the downward slope. And / or a reflection sheet. When the reflection layer or the like has a metal reflection surface, the return light is highly efficiently converted into a polarized state that can be transmitted through the selective reflection layer by reflection reversal, whereby light can be efficiently extracted.

As the selective reflection layer, an appropriate means capable of separating light having different polarization characteristics through transmission and reflection, such as the above-described separation into left and right circularly polarized light, can be used. In the present invention, it is not necessary to have a complete separation function, but it is preferable that the other state of polarized light included in polarized light separated by transmission or reflection is as small as possible.

Incidentally, examples of the selective reflection layer include those which selectively separate circularly polarized light or linearly polarized light. Specific examples of those that selectively separate circularly polarized light include a cholesteric liquid crystal phase and the like. Specific examples of those that selectively separate linearly polarized light include a multilayer film exhibiting anisotropy of reflectance by birefringence. And so on.

The selective reflection layer may be composed of a single layer of the above-mentioned cholesteric liquid crystal phase or multilayer film, or may be a laminate or a cell in which they are supported or sandwiched by a transparent substrate such as a plastic film or a glass plate. It may have an appropriate form. As the cholesteric liquid crystal phase, those composed of a cholesteric liquid crystal polymer are particularly preferable from the viewpoint of handleability and the like.

The selective reflection layer, particularly the selective reflection layer composed of a cholesteric liquid crystal phase, may be composed of two or more layers. Superimposition is advantageous from the viewpoint of widening the wavelength range of the separating function and addressing the wavelength shift of obliquely incident light. In this case, superimposition is performed in a combination in which the center wavelengths of light reflected as circular polarized light other than predetermined light are different. Is preferred.

By the way, the central wavelength of the selective reflection is 300 to 9
A cholesteric liquid crystal layer of 00 nm is used to reflect circularly polarized light in the same polarization direction, and the center wavelength of selective reflection is different. It is possible to efficiently form a selective reflection layer that can cover a wide wavelength range such as a wavelength range.

In the above, the point that the circularly polarized light having the same polarization direction is superimposed by a combination of those that reflect the same polarized light is that the phase state of the circularly polarized light reflected by each layer is made uniform so that different polarization states are obtained in each wavelength region. And to increase the amount of polarized light that can be used. For the superposition of the cholesteric liquid crystal layer, the use of a liquid crystal polymer is particularly advantageous from the viewpoint of production efficiency and thinning.

In the present invention, as shown in FIG. 7, when the linearly polarized light converting means 72 is provided above the selective reflection layer 71 for selectively separating circularly polarized light, the phase of the circularly polarized light emitted from the selective reflection layer is changed. Can be changed. Therefore, light having a wavelength whose phase change corresponds to 変 化 wavelength is converted to linearly polarized light, and light of other wavelengths is converted to elliptically polarized light. The converted elliptically polarized light becomes flatter elliptically polarized light as it approaches the wavelength of the light converted into the linearly polarized light. As a result, light in a state containing a large amount of linearly polarized light component that can be transmitted through the polarizing plate is emitted from the linearly polarized light converting means.

As described above, the linearly polarized light converting means disposed on the selective reflection layer as necessary aims at converting the circularly polarized light emitted from the selective reflection layer into a state having a large amount of linearly polarized light component. . By converting the light into a state having a large amount of linearly polarized light components, the light can be easily transmitted through the polarizing plate. This polarizing plate is, for example, in the case of a liquid crystal display device, an optical element that maintains the display quality by preventing a decrease in polarization characteristics caused by a change in the viewing angle with respect to the liquid crystal cell, or a higher degree of polarization is better realized. It functions as an optical element that achieves display quality.

That is, in the above, it is possible to achieve display by directly entering the circularly polarized light emitted from the selective reflection layer into the liquid crystal cell without using a polarizing plate, but it is possible to achieve the display quality described above by using a polarizing plate. A polarizing plate is used as necessary, because it is possible to improve the quality. In this case, the higher the transmittance of the polarizing plate, the more advantageous in terms of display brightness, and the higher the transmittance, the more the linear polarization component in the polarization direction coinciding with the polarization axis (transmission axis) of the polarizing plate. Therefore, for that purpose, the polarized light emitted from the selective reflection layer is converted into predetermined linearly polarized light via the linearly polarized light converting means.

Incidentally, when natural light or circularly polarized light is incident on a usual iodine-based polarizing plate, its transmittance is about 43%. However, when linearly polarized light is incident on the same polarization axis, 80%. , The light use efficiency is greatly improved, and a liquid crystal display having excellent brightness can be realized.

As the linearly polarized light converting means, an appropriate means can be used according to its polarization characteristics. In the case of circularly polarized light, a retardation layer whose phase can be changed can be preferably used. As the retardation layer, circularly polarized light emitted from the selective reflection layer can form a large amount of linearly polarized light corresponding to a phase difference of 波長 wavelength, and light of other wavelengths can be combined with the linearly polarized light as much as possible. It is preferable to use a material that has a major axis direction parallel to the axis and can be converted into flat elliptically polarized light as close to linearly polarized light as possible.

By using the retardation layer as described above,
Arrange such that the direction of the linear polarization of the emitted light or the major axis direction of the elliptically polarized light is as parallel as possible to the transmission axis of the polarizing plate to obtain light with a large amount of linearly polarized components that can pass through the polarizing plate. Can be. The retardation layer is preferably formed of an appropriate material and gives a transparent and uniform retardation. In general, a retardation plate is used.

The retardation applied by the retardation layer can be appropriately determined according to the wavelength range of the circularly polarized light emitted from the selective reflection layer. By the way, in the visible light region, from the viewpoint of the wavelength range and conversion efficiency, etc., taking into account that most retardation plates show wavelength dispersion of positive birefringence from their material properties, those with a small phase difference, Especially 100-200nm, especially 100
What gives a phase difference of up to 160 nm can be preferably used in many cases.

The retardation plate can be formed as one layer or as two or more superposed layers. In the case of a retardation plate composed of one layer, the smaller the wavelength dispersion of birefringence, the better the polarization state can be uniformed for each wavelength. On the other hand, the superposition of the retardation plates is effective for improving the wavelength characteristics in the wavelength range, and the combination may be determined as appropriate according to the wavelength range.

When two or more retardation plates are used in the visible light region, it is often the case that a layer giving a phase difference of 100 to 200 nm is included as one or more odd-numbered layers as described above, so that the linear polarization component is large. It is more preferable to obtain light. 100-200
Layers other than the layer giving a retardation of nm are usually 200 to 400
It is preferable to form the layer with a layer giving a phase difference of nm from the viewpoint of improvement of wavelength characteristics and the like, but it is not limited to this.

The retardation plate can be obtained, for example, as a birefringent sheet or a liquid crystal polymer film obtained by stretching a film made of polycarbonate, polysulfone, polyester, polymethyl methacrylate, polyamide, polyvinyl alcohol or the like. From the viewpoint of maintaining the emission intensity and emission color uniformly at a wide viewing angle, it is preferable that the error of the retardation in the plane of the retardation layer is as small as possible, and it is particularly preferable that the error is ± 10 nm or less.

As described above, the polarization plane light source device according to the present invention prevents reflection loss and the like by reusing the reflected light (return light) by the selective reflection layer as the outgoing light by polarization conversion.
By converting the emitted light to a light state containing a linearly polarized light component through a retardation layer or the like as necessary, the light can be easily transmitted through the polarizing plate, absorption loss can be prevented, and light use efficiency can be improved. It is like that.

Therefore, as described above, the surface light source device and the polarized surface light source device according to the present invention provide light which is excellent in light use efficiency, is bright and has excellent verticality, and is easy to increase in area and so on. The present invention can be preferably applied to various devices as a backlight system in a device or the like, and a liquid crystal display device or the like that is bright, easy to see, and consumes low power can be obtained.

FIG. 8 illustrates a liquid crystal display device 8 using the polarization plane light source device 7 according to the present invention in a backlight system. 81 is a lower polarizing plate, 82 is a liquid crystal cell, 83 is an upper polarizing plate, and 84 is a diffusion plate. The lower polarizing plate 81 and the diffusion plate 84 are provided as needed.

In general, a liquid crystal display device includes a liquid crystal cell functioning as a liquid crystal shutter and a driving device, a polarizing plate,
It is formed by appropriately assembling components such as a backlight and a phase difference compensating plate as necessary. In the present invention, there is no particular limitation except that a liquid crystal cell is disposed on the light emission side using the above-described surface light source device or polarizing surface light source device, and the device can be formed according to a conventional method. In particular, a direct-view type liquid crystal display device can be preferably formed.

Accordingly, the liquid crystal cell used is not particularly limited, and an appropriate one can be used. When a polarization plane light source device is used, it is advantageously used for a display in which polarized light is incident on a liquid crystal cell, and can be preferably used, for example, for a liquid crystal cell using a twisted nematic liquid crystal or a super twisted nematic liquid crystal. However, it can also be used for a non-twist type liquid crystal, a guest-host type liquid crystal in which a dichroic dye is dispersed in a liquid crystal, or a liquid crystal cell using a ferroelectric liquid crystal. There is no particular limitation on the driving method of the liquid crystal.

It should be noted that a polarizing plate, particularly a backlight-side polarizing plate, such as an iodine-based or dye-based absorption-type linear polarizer, may be used instead of obtaining a display with a good contrast ratio due to the incidence of highly linearly polarized light. It is preferable to use one having a high degree of polarization. In forming the liquid crystal display device, for example, a diffusion plate or an anti-glare layer, an antireflection film, a protective layer or a protective plate provided on the viewing-side polarizing plate, or a phase difference compensating plate provided between the liquid crystal cell and the polarizing plate may be appropriately used. Optical elements can be appropriately arranged.

The purpose of the retardation compensator is to improve the visibility by compensating the wavelength dependence of birefringence and the like. In the present invention, it is arranged as needed between the polarizing plate on the viewing side and / or the backlight side and the liquid crystal cell. As the retardation compensating plate, an appropriate one can be used according to the wavelength range or the like, and it may be formed as one layer or two or more layers.

In the present invention, the optical elements and components such as the light guide plate, the optical path deflecting sheet, the selective reflection layer, the liquid crystal cell, and the polarizing plate which form the above-mentioned surface light source device, polarizing surface light source device and liquid crystal display device are generally formed. Alternatively, they may be partially laminated and integrated and fixed, or may be arranged in an easily separable state. Various diffusing plates and the like can be arranged on the upper surface of the surface light source device. In the case of a polarizing surface light source device, a diffusing plate or the like that can maintain polarization characteristics can be arranged on the upper surface.

[0084]

Example 1 Polymethyl methacrylate was heated and melted, poured into a metal mold at 100 ° C. in which a predetermined prism structure was formed, left standing for 1 minute, and gradually cooled to obtain a light guide plate. This light guide plate has a width of 19
5 mm, depth 150 mm, thickness of the light incident side surface 3 mm, thickness of the opposite end 1 mm, the upper surface (outgoing surface) is flat, and the lower surface protrudes downward from the light incident side toward the opposite end near the plane. A convex portion (FIG. 3a) parallel to the light incident side surface is formed at a period of 225 μm on the entire surface of the curved surface (FIG. 2b), and its downward slope is about 5 degrees and upward slope is about 40 degrees. And the projected area ratio of the down slope / up slope to the emission surface is 8/1.

Next, a cold cathode tube having a diameter of 3 mm is arranged on the light incident side surface of the light guide plate via a prism sheet, and is surrounded by a light source holder made of a polyester film on which silver is deposited, and a light source holder is provided on the lower surface of the light guide plate. A surface light source device was obtained by disposing a reflection sheet of the same material as above with the silver deposition layer side interposed therebetween. The prism sheet is formed by arranging a continuous groove of an isosceles triangle having an apex angle of 90 degrees on one surface at a period of 50 μm, and the groove is directed to the upper and lower surfaces of the light guide plate. It was arranged so that the formed side was the light incident side surface side.

Embodiment 2 A selective reflection sheet for selectively separating circularly polarized light is disposed on the light emitting side of the surface light source device according to Embodiment 1 to obtain a polarizing surface light source device, and the TN type is provided on the light emitting side. A liquid crystal cell was arranged to obtain a liquid crystal display device. The selective reflection sheet is formed by spin-coating a side chain type cholesteric liquid crystal polymer on a polyimide rubbed surface of a triacetyl cellulose film, and then performing a heat alignment treatment to obtain a mirror-like selective reflection state (left circularly polarized light). The wavelength range of selective reflection comprising a side chain type cholesteric liquid crystal polymer having a different glass transition temperature in a method of forming a circularly polarized light separation layer is 420 to 505 nm,
Three types of circularly polarized light separating layers of 500 to 590 nm or 595 to 705 nm are formed and laminated in the order of the wavelength of selective reflection, which is a superposition type showing good selective reflectivity in the wavelength range of 420 to 705 nm. .

Comparative Example 1 A diffusing plate was arranged on the light emitting side of a light guide plate according to Example 1, and two prism-type condensing sheets (BEF, manufactured by Three M Co., Ltd.) were arranged thereon. A light source device was obtained. The condensing sheets were arranged so that the groove directions of the prisms at the top and bottom had a crossing angle of 90 degrees.

Comparative Example 2 A surface light source device according to Comparative Example 1 was used.
A polarizing plane light source device and a liquid crystal display device were obtained according to Example 2.

Evaluation Test Luminance and Half-Value Angle The luminance and half-value angle of the surface light source device obtained in Example 1 and Comparative Example 1 were examined. As a result, in Example 1, the luminance was 150
0 cd / m ² , the half-value angle in the vertical direction ± 40 degrees, and the half-value angle in the horizontal direction ± 30 degrees. In Comparative Example 1, the luminance was 1700 cd / m ² ,
The half value angle in the vertical direction was ± 25 degrees, and the half value angle in the horizontal direction was ± 25 degrees.

Front Brightness The front brightness of the liquid crystal display devices obtained in Example 2 and Comparative Example 2 was examined. As a result, in Example 2, 110 cd / m ² and Comparative Example 2
Was 95 cd / m ² .

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a side surface (a) and a plane surface (b) of an example of a surface light source device.

FIG. 2 is an explanatory view of an example of a light guide plate.

FIG. 3 is an explanatory side view of an example of fine prismatic irregularities.

FIG. 4 is an explanatory side view of another example of the surface light source device.

FIG. 5 is an explanatory side view of an example of an optical path deflection sheet.

FIG. 6 is an explanatory side view of another example of the optical path deflecting sheet.

FIG. 7 is an explanatory side view of an example of a polarization plane light source device.

FIG. 8 is a side view illustrating an example of a liquid crystal display device.

[Explanation of symbols]

 1: light guide plate 11: upper surface 12, 16, 17: lower surface 18, 19: convex portion 20: concave portion 22, 24 (25), 28: downward slope (slow slope) 23, 26, 27: upward slope (steep slope) 13 : Light incident side surface 2: prism sheet 3: light source 4: reflective layer 5: diffusion plate 6: optical path deflection sheet 61: groove 62: gentle slope 63: steep slope 7: polarization plane light source device 71: selective reflection layer 72: linear polarization conversion Means 8: Liquid crystal display 81, 83: Polarizing plate 82: Liquid crystal cell 84: Diffusion plate

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ identification code FI G02F 1/1335 510 G02F 1/1335 530 (58) Investigated field (Int.Cl. ⁷ , DB name) G02F 1/13357 F21V 8 / 00

Claims (8)

(57) [Claims] 1. At least one of upper and lower surfaces is provided with continuous or discontinuous fine prism-shaped irregularities in the direction along the light incident side surface.
A light guide plate having a period of 500 μm and emitting incident light from the light incident side surface from one of the upper and lower surfaces, a light source disposed on the light incident side surface, and disposed between the light guide plate and the light source; The prism sheet has at least a prism sheet, and the prism sheet is arranged on the light guide plate side of one side of the sheet with a repeating structure of continuous irregularities formed of substantially isosceles triangles in a state where the tops of the irregularities are in the vertical direction of the light guide plate. , The fine pre
The light from the light source that diffuses in the
Focus light in the direction perpendicular to the groove direction and from the light incident side
A surface light source device, which is incident . 2. The light guide plate according to claim 1, wherein the fine prism-shaped irregularities in the light guide plate receive and reflect the incident transmission light from the light incident side surface and emit the light to one of the upper and lower surfaces. A surface light source device having a steep slope of 45 degrees. 3. The surface light source device according to claim 2, wherein the angle of the steep surface is gradually increased in the range of 35 to 45 degrees from the light incident side surface to the transmission end side of the incident light. 4. The light guide plate according to claim 1, wherein the fine prismatic irregularities in the light guide plate have a gentle slope having an inclination angle of more than 0 ° to 10 ° with respect to a reference plane of the light guide plate, and The projected area ratio of the slope and the surface adjacent thereto to the reference plane of the light guide plate is 5 based on the gentle slope / adjacent surface.
Surface light source device that is more than double. 5. The light guide according to claim 1, further comprising an optical path deflecting sheet on upper and lower surfaces of the light guide plate on the light emitting side, wherein the optical path deflecting sheet is formed of a scalene triangle arranged in one direction on one side. A surface light source device having a structure. 6. A polarized surface light source device comprising a surface light source device according to claim 1, further comprising a selective reflection layer exhibiting selective reflectivity of polarized light on the light emission side. 7. The polarization plane light source device according to claim 6, wherein the selective reflection layer selectively reflects circularly polarized light or linearly polarized light. 8. A liquid crystal display device comprising a surface light source device according to claim 1 or a liquid crystal cell on the light emission side of the polarization surface light source device according to claim 6.