JPH09269487A - Light transmission plate, polarizing light source and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently emit light incident on the side surface of a light transmission plate from the upper surface thereof and to efficiently emit the light incident again through a circularly polarized light separating layer so as to improve light utilization efficiency by setting a phase difference by double refraction in a thickness direction to a specified value in the light transmission plate reflecting the light incident on the side surface by the lower surface and emitting it from the upper surface. SOLUTION: In this light transmission plate 1, the light incident on the side surface 14 is reflected by the lower surface 12 and emitted from the upper surface 11, and the phase difference by the double refraction in the thickness direction is set to 0-30nm, desirably, <=20nm. The smaller the phase difference by the double refraction in the thickness direction of the plate 1 is, such as 0-20mm, the more desirable result is obtained. In the case it is <=30nm, the circularly polarized light incident again through the circularly polarized light separating layer is guided to the lower surface 12 while keeping nearly equal circularly polarized light state without influence by the phase difference in substance. The return path light reflected by the lower surface 12 is also emitted while maintaining the circularly polarized state. Therefore, the brightness of the display of a liquid crystal display device is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide plate excellent in light utilization efficiency, a polarized light source device using the same, and a liquid crystal display device excellent in brightness utilizing the light guide plate.

[0002]

BACKGROUND ART Conventionally, as a side light type light guide plate in which light is incident from a side surface and emitted from an upper surface,
It is known that the lower surface is provided with a dot-like diffusion type or scattering type reflection layer. Since the reflection layer on the lower surface has a poor ability to emit incident light from the side surface to the upper surface due to total reflection on a flat surface, the incident light is diffusely reflected by multiple reflection or refraction and emitted to the upper surface. Further, with such a light guide plate, a large amount of light is emitted in an oblique direction, and light that can be effectively used is scarce. Therefore, a proposal has been made to superimpose a prism sheet or the like on the upper surface to make the emitted light vertical.

However, even when the emitted light is made vertical, when it is applied to a liquid crystal display or the like and is transmitted through a polarizing plate, about 55% of the emitted light is absorbed, so that light that can be effectively used is scarce and a bright display is difficult. There was a point. By the way, TN type and S
In a polarizing plate used for a liquid crystal display device such as a TN type, in the case of natural light, about 60% of the amount of light is absorbed and converted into heat or the like, and it is customary that the utilization efficiency of light is 35 to 45%. However, it does not exceed 50%.

Therefore, in order to improve the brightness of a liquid crystal display device or the like, it is necessary to improve the entire illumination system, and for that purpose, an illumination system that supplies light as polarized light to a polarizing plate to improve the light utilization efficiency is provided. Proposed (Japanese Patent Laid-Open No. 3-4
5906, JP-A-6-324333, JP-A-7-36032). In these devices, a reflective layer is closely attached to the lower surface of the light guide plate, and a circularly polarized light separating layer made of a cholesteric liquid crystal phase is provided on the upper surface, and incident light is reflected by the left and right circularly polarized light through the circularly polarized light separating layer. Split into light,
The reflected light is reflected through the reflective layer on the lower surface and re-emitted from the upper surface to improve the light utilization efficiency.

However, in any case, it was found that the ones which should show the light use efficiency of more than 50% do not show the expected values. In Japanese Unexamined Patent Publication No. 6-324333 and Japanese Unexamined Patent Publication No. 7-36032, since the lower surface is a reflective layer of a diffusion type or a scattering type, the amount of re-emitted light is reduced due to randomness of the emission direction or elimination of the polarization state. Although conceivable, even the metal reflective layer taught by JP-A-3-45906 has a problem that the re-emission efficiency is poor. This is because the bare metal reflection layer efficiently converts the circularly polarized light into the polarized light through reflection, and the emission direction is also regular.

[0006]

DISCLOSURE OF THE INVENTION The present invention is directed to the development of a light guide plate that efficiently emits incident light from the side surface from the upper surface and also efficiently emits re-incident light that has passed through the circularly polarized light separation layer. It is an issue.

[0007]

According to the present invention, incident light from a side surface is reflected on a lower surface and emitted from an upper surface, and a phase difference due to birefringence in a thickness direction is 0 to 30 nm. A light guide plate is provided.

[0008]

According to the present invention, the circularly polarized light reflected through the circularly polarized light separating layer and re-incident on the light guide plate is less susceptible to the change of its polarization state due to the phase difference, and is reflected at the lower surface portion through the metallic reflecting layer. Thus, when the polarization state is inverted, the light can be emitted as light that can pass through the circularly polarized light separation layer without changing the polarization state, and a light guide plate that can improve the display brightness of a liquid crystal display device or the like can be obtained.

In the above, if the light guide plate has a large phase difference, the circularly polarized light that is re-incident through the circularly polarized light separating layer is converted into elliptically polarized light, and the elliptically polarized light is further converted into elliptically polarized light by the return path reflected by the lower surface. . The elliptically polarized light is a composite of a linearly polarized light component and a circularly polarized light component. Since the linearly polarized light component does not pass through the circularly polarized light separating layer, that amount first reduces the utilization efficiency of the re-incident light. Further, in the wavelength range in which the light guide plate functions as a quarter-wave plate, the re-incident light is not subjected to polarization conversion, so that the amount of light in the polarization state that can pass through the circularly polarized light separation layer does not increase in that case either.

Further, the irregularity of the direction of the optical axis in the light guide plate, the change of the effected phase difference due to the incident / transmitted angle of light, the effect of the phase difference different for each wavelength, etc. are mediated by the circularly polarized light separating layer. The polarization conversion efficiency of circularly polarized light that has re-incident light and the long-axis direction of elliptically polarized light are greatly varied to significantly reduce the overall polarization conversion efficiency, which reduces the efficiency of re-incident light and reduces the light guide plate's use efficiency. Depending on the position, the amount of transmitted light and the spectrum of the emitted light are greatly changed to cause uneven brightness,
The quality as a light source and the display quality of a liquid crystal display device are degraded.

Incidentally, the light guide plate, especially the light guide plate having a fine prism structure on the lower surface is usually formed by injection molding of plastic such as polymethylmethacrylate, in which case it has an optical axis along the flow of the polymer. A birefringence pattern is generated, the average in-plane retardation is about 60 nm, reaches 100 nm near the gate portion, and the direction of the optical axis is not constant.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The light guide plate of the present invention is such that incident light from the side surface is reflected on the lower surface and emitted from the upper surface, and the phase difference due to birefringence in the thickness direction is 0 to 0.
The thickness is 30 nm, preferably 20 nm or less. Examples thereof are shown in FIGS. As shown in the figure, the light guide plate is usually formed of a plate having an upper surface, a lower surface facing the upper surface, and an incident surface including at least one side end surface between the upper surface and the lower surface. In the figure, 11 is an upper surface, 12, 16, 17, and 18 are lower surfaces, 13
Is the incident surface. In addition, 14 is a side surface and 15 is an incident surface 13.
Is a side end portion facing the side.

The phase difference due to birefringence in the thickness direction of the light guide plate is preferably as small as 0 to 20 nm, but if it is 30 nm or less, the circularly polarized light re-incident through the circularly polarized light separating layer has substantially no phase difference. It is possible to guide substantially the same circular polarization state to the lower surface without any influence, and it is also possible to emit the return light reflected on the lower surface while maintaining the circular polarization state.

The shape of the light guide plate is excellent in the emission efficiency from the upper surface, the emitted light is excellent in the perpendicularity to the upper surface, and can be effectively used, and the emission efficiency of the re-incident light through the circularly polarized light separating layer is also excellent. In view of the closeness of the outgoing direction to the initial outgoing direction, there is no limitation, but as shown in the figure, there is a structure that periodically has convex portions or concave portions having long side surfaces and short side surfaces on the lower surface. preferable. Furthermore, it is preferable that the thickness of the side end portion facing the incident surface is thinner than that of the incident surface, particularly, the thickness is 50% or less.

The thinning of the end portion on the opposite side to the incident surface is achieved by the time when the light incident from the incident surface reaches the end portion on the opposite side as the transmission end, as shown by the thick arrows in FIGS. 5 and 6. This is advantageous in that the light can be efficiently incident on the short side surface of the lower surface, emitted from the upper surface via the reflection, and the incident light can be efficiently supplied to the target surface. Further, by adopting such a thin structure, the weight of the light guide plate can be reduced. For example, when the lower surface is a straight surface as shown in FIG. 2, the weight can be about 75% of the light guide plate having a uniform thickness.

The above-mentioned convex portion or concave portion on the lower surface is usually formed by an inclined surface consisting of a long side surface and a short side surface along the incident surface. By the way, examples of convex portions or concave portions on the lower surface are shown in FIGS. 5 (a) to 5 (d) and 6 (a) to 6 (d).
In FIGS. 5 and 6, 21, 22, 23 and 24 are convex portions, 25, 26, 27 and 28 are concave portions, and 31, 3
3, 35, 37, 42, 44, 46 and 48 are slopes forming long sides, 32, 34, 36, 38, 41, 43,
45 and 47 are slopes forming the short side surface.

The protrusions or recesses on the lower surface are formed periodically. That is, for example, when based on FIG. 1 and FIG. 5 (a) or FIG. 6 (a), the convex portion 21 or the concave portion formed of the inclined surfaces 31, 32 or 41, 42 in the direction along the incident surface 13 as shown by the arrow in FIG. The lower surface has 25 periodically.

The above-mentioned convex portion or concave portion is based on a straight line connecting the intersection points of the slope forming the convex portion or the concave portion with the lower surface, and whether the intersection point (vertex) of the slope surface protrudes from the straight line (convex), It depends on whether it is dented (concave). That is, FIG.
In the case based on the example shown in FIG. 6, the protrusions (21, 22, 2
3, 24) or slopes (31 and 32, 33 and 34, 35 and 36, 37) forming recesses (25, 26, 27, 28)
, 38, 41 and 42, 43 and 44, 45 and 46, 47 and 48), the intersection (vertex) of the slope protrudes beyond the straight line 20 indicated by an imaginary line connecting the intersection with the lower surface. It depends on whether it is convex (convex) or concave (concave).

Further, the long side surface and the short side surface of the slope forming the convex portion or the concave portion are judged based on the straight line connecting the intersection with the lower surface and the apex, but the point that the utilization efficiency of light is improved, etc. More preferably, the projected area of the long side surface on the upper surface is 3 times or more, and especially 5 times or more that of the short side surface. Further, the long side surface is arranged so as to be located on the incident surface side in the case of a convex portion, and to be located on the side end side opposite to the incident surface in the case of a concave portion. When the long side surface is a concave portion, it is preferable to arrange the short side surface.

That is, the slope, for example, FIGS. 1 and 5
In the case of FIG. 6A or FIG. 6A, the slopes 31 and 32 or 41 and 42 forming the convex portion 21 or the concave portion 25 are straight lines that connect the intersections with the lower surface (corresponding to the virtual line 20) and the vertices ( In the case of b, c, and d of FIGS. 5 and 6, it is assumed that the long side surfaces 31 and 42 and the short side surfaces 32 and 41 are based on the virtual line), and the long side surfaces 31 and 42 are The projection area on the upper surface 11 is three times or more that of the short side surfaces 32 and 41, and in the case of the convex portion 21, the long side surface 31 is on the incident surface 13 side and in the case of the concave portion 25. Is preferably arranged such that the long side surface 42 is located on the side end side 15 facing the incident surface.

As described above, in addition to the transmitted light which is directly incident on the short side face, the transmitted light which is incident on the long side face and is reflected by the short side face is reflected on the upper side face. Can be supplied to (output from), and the light utilization efficiency can be improved accordingly. Further, the long side surface is a portion that functions to re-emit the re-incident light reflected by the circularly polarized light separation layer in the case of a polarized light source device. It is 5 times or more, especially 10 to 100 times, that of the short side surface.

The shape of the lower surface of the light guide plate may be appropriately determined. Preferably, as described above, the inclined surface is made thinner at the end on the opposite side than the incident surface. In that case, the shape of the inclined surface may be arbitrarily determined, and may be an appropriate surface shape such as a linear surface illustrated in FIG. 2 or a curved surface illustrated in FIGS. 3 and 4. If the surface is not a straight surface, it is preferable that the angle is within 5 degrees of the average inclination angle at all positions on the lower surface, rather than the point of making the emission direction of the emitted light from the upper surface uniform.

The shape of the convex portion or the concave portion provided on the lower surface is also shown in FIG.
It is not necessary to be formed by a linear slope as illustrated in (a) to (d) and FIGS. 6 (a) to (d), and it may be formed by a slope including a refraction surface or a curved surface. Good. The projections or depressions do not need to have the same irregularities or the same shape on the entire lower surface, and a structure in which the shape or angle gradually changes from the incident side rather than the point at which emitted light with excellent perpendicularity is obtained is preferable. .

The projections or recesses on the lower surface are preferably as small as possible because the emitted light is emitted in stripes through the projections or recesses, and if the spacing is large, uneven brightness occurs and the brightness of the entire surface is uniform. It tends to decrease. The period of the convex portions or concave portions, which is preferable from the viewpoint of obtaining an upper surface excellent in brightness uniformity by preventing uneven brightness, is 500 μm or less,
In particular, it is 400 μm or less, especially 5 to 300 μm. If the period is less than 5 μm, the dispersion due to diffraction is large, making it unsuitable for a backlight for a liquid crystal display device.

The above-mentioned long side surface of the slope forming the convex portion or the concave portion is the upper surface 1 as illustrated in FIGS.
It is preferable that the inclination angle θ1 with respect to ₁ be 0 to 10 degrees, particularly 5 degrees or less, particularly 2 degrees or less. By setting the range of the tilt angle, as shown by the broken line arrows in FIGS. 5A and 6A, light transmitted at an angle larger than the tilt angle enters the long side surfaces 31, 42. In that case, the light is reflected by the upper surface 11 based on the inclination angle of the long side surface, is reflected at a more parallel angle, enters the short side surfaces 32, 41, and is reflected and emitted from the upper surface 11.

As a result, the incident angle of the light incident on the short side surface can be made constant, the variation in the reflection angle can be suppressed, and the emitted light can be made parallel. Therefore, by adjusting the angle of inclination of the long side surface and the short side surface of the slope forming the convex or concave portion, it is possible to give directivity to the emitted light, whereby the direction is perpendicular to or close to the upper surface. Light can be emitted at an angle.

By the way, in the light guide plate made of acrylic resin, the maximum angle of the transmitted light of the end face incident light is 41.8 degrees based on the refractive index (about 1.5), and the refractive index of the light guide plate increases. As a result, the maximum angle of the transmitted light becomes smaller. Therefore, when the inclination angle of the long side surface exceeds 10 degrees,
The ratio of the projected area to the upper surface of the long side surface is reduced, and the ratio of the transmission light that can control the emission direction through the long side surface is reduced, and the transmission light incident on the short side surface via the long side surface is also reduced. In addition, the dispersion of the reflection angle with the transmission light directly incident on the short side surface becomes large, and the controllability of making the outgoing light parallel is reduced, and the directivity of the outgoing light becomes poor. If the inclination angle of the long side surface is 0 degree, it is disadvantageous for the parallelization of the emitted light, but is allowed in the present invention.

Therefore, for the purpose of improving the emission efficiency as in the conventional light guide plate, the slope (corresponding to the short side surface in the present invention) for reflecting the transmitted light and supplying it to the upper surface is enlarged and projected onto the upper surface. In the structure in which the area ratio is increased, and for that reason, the inclination angle of the other slope (corresponding to the long side surface in the present invention) is 20 degrees or more, the incidence probability of the transmitted light on this slope is extremely small and parallelization is achieved. It is difficult to give the emitted light a vertical directivity.

On the other hand, the above-mentioned short side surface of the inclined surface forming the convex portion or the concave portion has an inclination angle θ ₂ with respect to the upper surface 11 of 25 to 50 degrees, preferably 30 degrees or more, as illustrated in FIGS. Preferably there is. By setting such an inclination angle range, as shown in FIG. 5 (a) and FIG. 6 (a) by the broken line arrow, the transmitted light incident directly or through the long side surface is transmitted through the short side surface 32, 41. It is possible to efficiently emit light in a direction in which the light is reflected perpendicularly to the upper surface 11 or at an angle close thereto and effectively acts to improve the visibility of the liquid crystal display device or the like. If the inclination angle of the short side face is out of the range, the deviation from the vertical direction becomes large, and it is difficult to give the emitted light vertical directivity, and the emission efficiency (utilization efficiency) of the transmission light is reduced.

In the present invention, the shape of the incident surface of the light guide plate is not particularly limited and may be appropriately determined.
In general, the surface is perpendicular to the upper surface. However, for example, a shape corresponding to the outer periphery of the light source, such as a curved concave shape, can be used to improve the incident light rate. Further, an incident surface structure having an introduction portion interposed between the light source and the light source may be employed. The introduction portion can have an appropriate shape according to the light source and the like.

The shape of the upper surface is generally a flat surface or the like, but it may be a structure having a diffusion layer for the purpose of scattering on the surface if necessary. However, when forming a polarized light source device, a light guide plate that does not have a diffusing layer or a diffusing reflecting layer for scattering purposes on the lower surface or the upper surface, or a portion other than the incident surface including the intermediate layer of the light guiding plate is effective in terms of light utilization. Are more preferable. Therefore, it is preferable that the slope and the upper surface forming the convex portion or the concave portion on the lower surface are smooth.

The light guide plate can be formed of an appropriate material that is transparent according to the wavelength range of the light source. By the way, in the visible light region, for example, acrylic resin such as polymethyl methacrylate, polycarbonate resin such as polycarbonate and polycarbonate / polystyrene copolymer, about 400 to 700 nm like transparent resin and glass represented by epoxy resin and the like. Those exhibiting transparency in the wavelength range are exemplified.

A light guide plate having a phase difference of 0 to 30 nm due to birefringence can be formed, for example, by using a polycarbonate / polystyrene copolymer, Zeonex (trade name, manufactured by Zeon Corporation), or Optrez (trade name, manufactured by Hitachi Chemical Co., Ltd.). Such as injection molding using a material that does not easily generate birefringence, a method of lowering birefringence by annealing a light guide plate exhibiting birefringence at high temperature, epoxy resin, etc. Molding by casting method, injection molding method in which birefringence is less likely to occur by devising gate position, etc., large injection molded product is formed in advance and the phase difference of the central part etc. is small An appropriate method such as a method of cutting out a portion and a phase difference being a product of a refractive index difference of birefringence and a thickness to reduce the phase difference by thinning can be used.

Therefore, the light guide plate can be formed by an appropriate manufacturing method. As a preferable manufacturing method from the viewpoint of mass productivity and the like, for example, a method in which a liquid resin that can be polymerized by heat, ultraviolet rays, radiation, or the like is polymerized by filling or casting in a mold capable of forming a predetermined lower surface shape, A method of transferring a shape by pressing a thermoplastic resin to a mold capable of forming a predetermined lower surface shape under heating, a thermoplastic resin that is heated and melted or a resin fluidized through heat or a solvent to a predetermined shape. Examples include a method of filling a mold that can be molded. Although the thinning of the light guide plate described above is more advantageous in terms of weight reduction and reduction of necessary materials, the amount of incident light is reduced by the reduction of the incident surface, so that the required amount of incident light is secured. There is a limit, and there is a limit from this point because the influence of the mold becomes large in injection molding to increase birefringence and decrease moldability.

In the light guide plate of the present invention, the characteristics such as the angular distribution and the in-plane distribution of the emitted light are controlled based on the control of the area ratio of the short side surface and the long side surface, the inclination angle, the shape and the curvature of the lower surface, and the like. Can be adjusted. By the way, in the case of a light guide plate having a refractive index of 1.5 and a lower surface having no curvature, and a light guide plate from which the initial emission light is emitted vertically, the inclination angle of the long side surface with respect to the emission surface should be 6.6 degrees or less. Thus, the re-incident light passing through the circularly polarized light separating layer can be re-emitted with an angle change within 10 degrees. Further, in this case, when the lower surface has a curvature, the re-incident light is re-emitted with an angle change of 10 degrees or less by having a portion having the inclination angle of 6.6 degrees or less at a ratio of the predetermined area or more. be able to.

In the present invention, the light guide plate may be formed as a laminated body of different materials, such as a light guide portion for transmitting light and a sheet for forming a lower surface adhered thereto. It need not be formed as an integral monolayer of material. The thickness of the light guide plate can be appropriately determined depending on the size of the light guide plate and the size of the light source depending on the purpose of use.

When used in a liquid crystal display device or the like, the light guide plate generally has a thickness of 20 mm or less, preferably 0.1 to 10 mm, particularly 0.5 to 8 mm, based on the incident surface thereof. Also, the general area ratio between the incident surface and the upper surface is 1/5 based on the former / the latter.
１／1/100, especially 1/10 to 1/80, especially 1/15
~ 1/50. By the way, when the parallel light is incident from the incident surface, all of the incident light can be incident on the short side surface by making the short side surface of the integrated thickness corresponding to the thickness of the incident surface. When the inclination angle of the side surface is 45 degrees and the inclination angle of the long side surface is 0 degrees, the area ratio of the incident surface / upper surface is about 1/30.

In the above, the refractive index of the light guide plate is 1.5.
Then, as described above, the incident transmission light is within 41.8 degrees, and the smaller the angle, the greater the intensity. Therefore, the area ratio of the short side / long side is 1 based on the projected area of the upper surface. Even at about / 15, most of the incident light can be directly incident on the short side without passing through the long side, and high emission efficiency can be obtained.

In the above case, the light is emitted in the normal direction of the upper surface through the short side surface having an inclination angle of 45 degrees, but most of the re-incident light that has passed through the circularly polarized light separating layer is incident on the long side surface. To do. As a result, even if the area ratio of the short side / long side is set to 1/5 based on the projected area of the upper surface, ideally 83% of the re-incident light through the circularly polarized light separating layer is incident on the long side. The light is reflected and can be used as it is as re-emitted light.

On the lower surface of the light guide plate, if necessary, a reflective layer,
Preferably, a metal reflection layer can be provided. An example is shown in FIG. Reference numeral 2 denotes a reflective layer, which is a metal layer in the illustrated example. Such a reflective layer is effective in preventing the generation of light leakage from the lower surface and improving the emission efficiency. In the case of a polarized light source device, it also functions as polarized light conversion means. The reflection layer may be integrated on the lower surface, or may be laminated as a reflection sheet or the like, and in the present invention, an appropriate arrangement form can be adopted.

When functioning as the above-mentioned polarization converting means, a reflecting layer made of a metal is particularly preferable. With such a metal reflection layer, the polarization characteristics can be efficiently inverted at the time of reflection, and the polarization conversion efficiency thereof is superior to that obtained by total reflection or diffuse reflection via the interface having a different refractive index.
Incidentally, when circularly polarized light is incident on the metal surface substantially perpendicularly, the conversion efficiency of the left and right circularly polarized light becomes nearly 100%, and the incident angle is 3
A conversion efficiency of 90% or more is shown up to 0 degree.

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

According to the above-mentioned light guide plate of the present invention, the light parallelized with high precision is emitted in the direction excellent in verticality, which is advantageous for visual recognition, and the light from the light source is efficiently used. It is possible to form various devices such as a surface light source device and a polarized light source device which are excellent in brightness, and a liquid crystal display device which is bright and easy to see and is excellent in low power consumption.

8 and 9 illustrate a surface light source device having a light guide plate according to the present invention. 1 is a light guide plate and 5 is a surface light source device using it. In this, the light source 51 is arranged on the incident surface 13 of the light guide plate, and can be used as a sidelight type backlight or the like. As the light source, an appropriate one can be used. 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.

When forming the surface light source device, a light source that surrounds the light source, such as the reflection layer 2 on the lower surface of the light guide plate and the light source that guides the divergent light from the linear light source to the side surface of the light guide plate, as shown in the figure, if necessary. A holder 52, a diffusion layer 53 arranged on the upper surface of the light guide plate for obtaining uniform surface emission, and a suitable auxiliary means such as a prism sheet for controlling the emission direction of light may be used as a combination body.

As for the reflection layer, as shown in FIG. 9, a reflection plate 54 may be provided along the lower surface of the light guide plate 1 instead of the reflection layer 2 or together with the reflection layer 2. The method of providing the reflection plate on the lower surface of the light guide plate has an advantage that the re-emission angle of the re-incident light through the circularly polarized light separating layer can be reduced when the long side surfaces have the same inclination angle. The reflection plate can be in accordance with the reflection layer described for the light guide plate. In the polarized light source device, a reflection plate having a metal reflection surface can be preferably used. Therefore, as the reflection plate, an appropriate material such as a resin sheet provided with a metal thin film, a metal foil, or a metal plate can be used. The surface of the reflector does not necessarily have to be a mirror surface, and may be formed as a whole with a plurality of surfaces having a small angle or a continuous curved surface.

Further, as the reflection plate, particularly in the case of forming a polarized light source device or the like, the reflection angle of the reflection light when parallel light is made incident is suppressed from the point of suppressing the spread of the re-emitted light. Half-width of half-width of spread is within 10 degrees, especially 5
Those within a degree are preferred. Therefore, as the reflection plate, an appropriate reflection plate having a high reflectance, a small spread of the reflection angle, and no diffuse reflection can be used. It may be one having a rough surface such as unevenness or a rolling roll so that the reflection angle of reflected light is slightly widened. As the light source holder, a resin sheet or a metal foil provided with a high reflectance metal thin film is generally used. In the case where the light source holder is bonded to the end of the light guide plate via an adhesive or the like, the formation of a convex portion or a concave portion on the lower surface of the bonding portion may be omitted. Further, the light source holder can be extended to the lower surface of the light guide plate so as to serve also as a reflection plate.

The arrangement of the diffusion layer is advantageous for forming an upper surface which is excellent in uniformity of brightness by preventing the occurrence of uneven brightness and can be formed as an appropriate diffusion layer such as a fine uneven surface or a diffusion plate. . However, as described above, the arrangement of the diffusion layer is not preferable when used for forming the polarized light source device.

In the polarized light source device according to the present invention, incident light which generally does not exhibit polarization characteristics is separated into left and right circularly polarized light as transmitted light or reflected light through a circularly polarized light separating layer, and is efficiently converted into polarized light and taken out. The purpose is to In this case, the above-described light guide plate according to the present invention provides highly parallelized outgoing light with excellent perpendicularity, and allows the re-incident light via the circularly polarized light separating layer to be initially emitted with little angle change. It is possible to re-emit with good consistency with the direction of the emitted light.

A polarized light source device according to the present invention is illustrated in FIGS. This comprises a circularly polarized light separating layer 61 disposed above the upper surface 11 of the light guide plate 1 in the above-mentioned surface light source device 5. In the embodiment, the circularly polarized light separating layer is the light guide plate 1.
Are disposed immediately above the upper surface 11 having no diffusion layer. In FIG. 11, a circularly polarized light separating layer 61 provided on the upper surface 62 is a retardation layer as a linearly polarized light converting means.

According to the above apparatus, the light emitted from the upper surface of the light guide plate 1 is incident on the circularly polarized light separating layer 61, the predetermined (provisionally left) circularly polarized light in the left and right is transmitted, and the light outside the predetermined (right). The circularly polarized light of is reflected, and the reflected light re-enters the light guide plate as return light. The light that is re-incident on the light guide plate is reflected by the reflection function portion including the reflection layer on the lower surface, is incident on the circularly polarized light separating layer again, and is again separated into transmitted light and reflected light (re-incident light).
Therefore, the re-incident light as reflected light is confined between the circularly polarized light separation layer and the light guide plate and repeatedly reflected until the light becomes predetermined circularly polarized light that can pass through the circularly polarized light separation layer. In view of the above, it is preferable that the first re-incident light is emitted without repetition of reflection, especially with the repetition number as small as possible, in view of the utilization efficiency of the re-incident light.

In the above, since the above-mentioned light guide plate according to the present invention provides the emitted light which is highly accurately parallelized and has excellent verticality, most of the re-incident light that has passed through the circularly polarized light separating layer is incident on the long side surface. The incident light is reflected without changing the angle on the basis of the gentle inclination angle, and can be re-emitted in a direction similar to the initial emitted light by the reflection with a small angle change, and thus with good verticality. As a result, the direction of the initial emission light and the direction of the re-emission light are excellent, and the first re-incidence light is efficiently emitted without repetition of reflection to obtain light with excellent polarization characteristics in a state of low loss and excellent use efficiency. be able to.

When the light guide plate has a metal reflection layer, the re-incident light is highly efficiently converted into a predetermined circularly polarized light by the reflection inversion due to the re-incident light, so that the light can be efficiently extracted. Further, since the emitted light is excellent in verticality, it has an advantage that a change in the traveling direction of light due to refraction at an interface having a different refractive index is small.

In the above-mentioned conventional light guide plate, the re-incident light that has passed through the circularly polarized light separating layer is scattered or diffusely reflected (dots) or twice totally reflected (prisms) through the lower surface of the light guide plate. It will re-enter the circularly polarized light separation layer. However, in the case of the scattering reflection type or the diffuse reflection type, the emitted light has poor directivity, and since it re-enters as scattered light, the conversion efficiency through the circularly polarized light separation layer cannot exceed 50%, and the light utilization efficiency is high. The effect of increasing

On the other hand, in the case of the total reflection type, the conversion efficiency through the re-incident circularly polarized light separating layer is 45% even if the light guide plate has a refractive index of 1.5. Depending on the reflection angle, the conversion efficiency will be further reduced. Also, when the incident angle exceeds the total reflection condition, reflection hardly occurs. Therefore, depending on the angle of the re-incident light that passes through the circularly polarized light separating layer, it does not re-emit at all, and the re-incident light cannot be used as re-emitted light. In addition, the effect of improving the light use efficiency is unlikely to occur.

Further, in order to prevent the re-incident light from being unable to be re-emitted, when the lower surface of the light guide plate has a prism structure advantageous for the re-emission, the initial emission light is lowered, and conversely it is advantageous for the initial emission. When the prism structure is used, the re-emission direction of the re-incident light changes significantly from the initial emission light, the conversion efficiency of the polarized light through the lower surface also decreases, and the initial emission and re-injection light re-emission are good. It is difficult to obtain a prism structure that can satisfy both requirements, and even in this case, the effect of increasing the light utilization efficiency is unlikely to occur.

In addition, in any of the scattering reflection type, the diffuse reflection type and the total reflection type, it is difficult to give directivity to the outgoing light through the circularly polarized light separating layer, and the outgoing angle thereof is poor in verticality. In this case, a large amount of emitted light components in the direction of 45 degrees or more with respect to the vertical direction, which is inconvenient for a display such as a liquid crystal display that reduces visibility, is largely deviated from the vertical direction. Even if a prism sheet is placed on the upper surface of the light guide plate to correct the verticality, the light is incident on the reflection surface of the lower surface of the light guide plate at an angle that is largely deviated from the vertical direction. Poor.

As described above, in the conventional light guide plate, as in the present invention, the outgoing light which is highly accurately parallelized and has excellent verticality is formed and is initially output through the circularly polarized light separating layer. It is difficult to separate the incident light and the re-incident light and re-emits the re-incident light with good matching in the emission direction with the initial emission light.

In the present invention, the light guide plate which can be preferably used for forming the polarized light source device allows incident light from the side surface to be emitted from the upper surface with high efficiency, and the emitted light has high directivity, and in particular, perpendicularity to the upper surface. In addition to exhibiting directivity, it has excellent re-emission efficiency of the re-incident light through the circularly polarized light separating layer, and the re-emission light has a directivity and an emission angle that match the directivity and the emission angle of the initial emission light as much as possible. In addition, the re-incident light that has passed through the circularly polarized light separating layer is emitted with a small number of reflection repetitions and, in particular, without repeated reflections.

In the above, the coincidence of the emission angles of the re-emitted light and the initial emitted light is poor, and if the emission directions are largely different, their brightness cannot be added, and it cannot be effectively used for improving the visibility of the liquid crystal display device or the like. But rather 2 in different directions
One peak luminance is shown, and visibility is reduced.

In the present invention, as the circularly polarized light separating layer for forming the polarized light source device, an appropriate layer for separating left and right circularly polarized light as transmitted light and reflected light can be used. As the circularly polarized light separating layer which can be preferably used, a layer having a cholesteric liquid crystal phase, a sheet having a layer composed of a liquid crystal polymer exhibiting a cholesteric phase, a sheet obtained by developing the layer on a glass plate or the like, or a cholesteric phase is exhibited. Examples include a film made of a liquid crystal polymer.

According to the cholesteric liquid crystal phase, the left and right circularly polarized light can be selectively separated into either one by transmission or reflection, and the uniformly aligned liquid crystal phase containing the cholesteric liquid crystal provides reflected light without scattering. The cholesteric liquid crystal phase has a small change in optical characteristics with respect to a change in viewing angle and is excellent in a wide viewing angle, and is particularly suitable for forming a direct-view liquid crystal display device which can be directly observed even in an oblique direction.

The circularly polarized light separating layer can be formed as a single layer or as a laminate 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. That is, a single-layer cholesteric liquid crystal layer usually has a limit in the wavelength range exhibiting selective reflection (circular dichroism), and the limit may be a wide range extending to a wavelength range of about 100 nm. However, when it is applied to liquid crystal display devices, etc., it does not reach the entire range of visible light, so in such a case a wavelength range showing circular dichroism is expanded by overlapping cholesteric liquid crystal layers with different selective reflection properties. Can be made.

By the way, in the case of the cholesteric liquid crystal layer, the central wavelength of selective reflection based on the liquid crystal phase is 300 to 900.
A combination that reflects circularly polarized light of the same polarization direction with the nm one,
And the central wavelength of selective reflection is different, especially 50nm each.
A circularly polarized light separating layer capable of covering a wide wavelength range such as a visible light range can be efficiently formed by using the above different combinations and superimposing two to six types. The point that the combination of those that reflect the circularly polarized light in the same polarization direction as the superimposed product is such that the phase state of the circularly polarized light reflected by each layer is aligned to prevent a different polarization state in each wavelength range, The aim is to increase the available polarization.

Therefore, as the circularly polarized light separating layer, a layer in which the wavelength range of the light which can be reflected as the circularly polarized light outside the predetermined range coincides with the wavelength range of the emitted light based on the light guide plate is preferably used. If the emitted light has a dominant wavelength such as a bright line spectrum, it is necessary to match the wavelength of the reflected light based on the cholesteric liquid crystal phase or the like to one or more dominant wavelengths such as efficiency of polarization separation. This is a sub-optimal measure from the point of view, and is also advantageous for reducing the thickness of the circularly polarized light separating layer by reducing the required number of superpositions. In this case, the degree of coincidence of the wavelengths of the reflected light is 20 times for one or more main wavelength lights of the light guide plate.
It is preferable to set the range within nm.

As the cholesteric liquid crystal, an appropriate one may be used without any particular limitation. A cholesteric liquid crystal molecule having a larger phase difference has a wider wavelength range of selective reflection, and can be preferably used in terms of reduction of the number of layers and a margin for a wavelength shift at a large viewing angle. Further, a liquid crystal polymer can be preferably used in terms of weight, self-sustainability, and the like. Incidentally, examples of the cholesteric liquid crystal polymer include a main chain type liquid crystal polymer such as polyester, a side chain type liquid crystal polymer including an acrylic main chain, a methacryl main chain, and a siloxane main chain, and a nematic liquid crystal polymer containing a low molecular weight chiral agent. And chiral component-introduced liquid crystal polymers, and nematic and cholesteric mixed liquid crystal polymers. From the viewpoint of handleability, the glass transition temperature is 30 to 150.
The liquid crystal polymer of ° C. can be preferably used.

The formation of the cholesteric liquid crystal layer from the liquid crystal polymer can be carried out by a method according to the conventional alignment treatment. Incidentally, as an example, a liquid crystal polymer is developed on a suitable alignment film composed of a film formed of polyimide or polyvinyl alcohol on a substrate and rubbed with a rayon cloth or an oblique vapor deposition layer of SiO. Is heated above the glass transition temperature, below the isotropic phase transition temperature, and cooled to below the glass transition temperature in a state in which the liquid crystal polymer molecules are in the state of the Grand Jean orientation, forming a solidified layer in which the orientation is fixed. Method.

As the above-mentioned substrate, for example, triacetyl cellulose, polyvinyl alcohol, polyimide, polyarylate, polyester, polycarbonate, polysulfone, polyether sulfone, a film made of a plastic such as an epoxy resin, or a suitable glass plate. Can be used.

The solidified layer of the liquid crystal polymer formed on the substrate can be used as a circularly polarized light separating layer as it is as an integrated body with the substrate, or can be peeled from the substrate and used as a circularly polarized light separating layer made of a film or the like. When it is formed as an integral body with a film substrate, it is preferable to use a film having a phase difference as small as possible from the viewpoint of prevention of a change in the state of polarization. Note that the circularly polarized light separating layer may be provided directly on the light emitting surface of the light guide plate.

The liquid crystal polymer may be developed by a heating and melting method or as a solution with a solvent. As the solvent, for example, an appropriate solvent such as methylene chloride, cyclohexanone, trichloroethylene, tetrachloroethane, N-methylpyrrolidone, tetrahydrofuran, or the like can be used. The development can be performed by an appropriate coating machine such as a bar coater, a spinner, a roll coater, or a gravure printing method. Upon development, a method of superposing a cholesteric liquid crystal layer with an alignment film interposed may be adopted if necessary.

The thickness of the cholesteric liquid crystal layer is 0.5 to 100 μm, and preferably 1 to 100 μm, from the viewpoints of preventing alignment disorder and transmittance reduction, and selective reflectivity (wavelength range showing circular dichroism). 70 μm, particularly preferably 1 to 50 μm. In forming the cholesteric liquid crystal layer or the circularly polarized light separating layer, various additives such as stabilizers, plasticizers, and metals can be added as necessary.

The circularly polarized light separating layer used in the present invention is, for example, a cell form in which a cholesteric liquid crystal layer made of a low molecular weight material is sandwiched between transparent substrates such as glass and film, and a cholesteric liquid crystal layer made of a liquid crystal polymer is supported by a transparent substrate. It is possible to adopt an appropriate form such as the above-mentioned form, a form made of a film of a liquid crystal polymer of the cholesteric liquid crystal layer, or a form in which those forms are superposed in an appropriate combination.

In the above-mentioned case, the cholesteric liquid crystal layer can be held by one or two or more supports depending on its strength and operability. When a support having two or more layers is used, the retardation is as small as possible, for example, a non-oriented film or a triacetate film having a small birefringence even when oriented, in order to prevent a change in the state of polarization. Those can be preferably used.

The circularly polarized light separating layer is preferably formed as a flat layer from the viewpoint of making the separation performance uniform and coping with the wavelength shift of obliquely incident light. It is preferably flat. For the superposition of the cholesteric liquid crystal layer, the use of a liquid crystal polymer is particularly advantageous from the viewpoints of production efficiency and thinning.

In the present invention, as illustrated in FIG. 11, when the linearly polarized light converting means 62 is provided above the circularly polarized light separating layer 61, the circularly polarized light emitted from the circularly polarized light separating layer is incident on the linearly polarized light converting means and the phase thereof is changed. Undergo a change. In this case, light having a wavelength whose phase change corresponds to １ ／ wavelength is converted into linearly polarized light, and light of other wavelengths is converted into elliptically polarized light. The converted elliptically polarized light becomes flatter elliptically polarized light as it approaches the wavelength of the light converted to the linearly polarized light. As a result, light in a state containing a large amount of linearly polarized light components that can pass through the polarizing plate is emitted from the linearly polarized light conversion means.

As described above, the linearly polarized light converting means arranged on the circularly polarized light separating layer as needed is intended to convert the polarized light emitted from the circularly polarized light separating layer into a state having a large amount of linearly polarized light components. is there. By converting into a state in which there is a large amount of linearly polarized light component, it is possible to make the light easily transmitted through the polarizing plate. In the case of a liquid crystal display device, for example, this polarizing plate is an optical element that prevents deterioration of polarization characteristics caused by a change in viewing angle with respect to a liquid crystal cell and maintains display quality, and realizes a higher degree of polarization. It functions as an optical element that achieves display quality.

That is, in the above description, it is possible to achieve the display by directly entering the outgoing polarized light from the circularly polarized light separating layer into the liquid crystal cell without using the polarizing plate. A polarizing plate may be used as necessary because it can 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 circularly polarized light separating layer is converted into a predetermined linearly polarized light via the linearly polarized light converting means.

By the way, when natural light or circularly polarized light is made incident on a usual iodine type polarizing plate, its transmittance is about 43%, but when linearly polarized light is made incident with its polarization axes aligned, it is 80%. Therefore, it is possible to obtain a transmissivity of more than 100 .mu.m, so that the light utilization efficiency is significantly improved and a liquid crystal display or the like having excellent brightness can be realized. Also, in such a polarizing plate, 99.99%
Can be achieved. It is difficult to achieve such a high degree of polarization by using the circularly polarized light separation layer alone, and particularly the degree of polarization with respect to obliquely incident light tends to decrease.

As the linearly polarized light converting means, any suitable means can be used according to its polarization characteristics. In the case of circularly polarized light, a retardation layer capable of changing its phase can be preferably used. As the phase difference layer, the circularly polarized light emitted from the circularly polarized light separating layer can form a large amount of linearly polarized light corresponding to the phase difference of ¼ wavelength, and other wavelengths can be combined with the linearly polarized light as much as possible. It is preferable to use the one having a major axis direction in a parallel direction and capable of converting into a flat elliptically polarized light which is as close to linearly polarized light as possible.
The linearly polarized light converting means may be provided integrally with the circularly polarized light separating layer or the polarizing plate of the liquid crystal cell.

By using the retardation layer as described above,
Arrange such that the direction of the linear polarization of the emitted light and the major axis direction of the elliptically polarized light are 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 can be formed of an appropriate material and preferably provides a transparent and uniform retardation. In general, a retardation plate is used.

The retardation imparted by the retardation layer can be appropriately determined according to the wavelength range of the circularly polarized light emitted from the circularly polarized light separating layer. Incidentally, in view of the wavelength range and conversion efficiency in the visible light region, taking into consideration that most retardation plates exhibit positive birefringence wavelength dispersion than their material characteristics, the phase difference is small, Especially 100-200nm, especially 10
In many cases, a material that gives a phase difference of 0 to 160 nm can be preferably used.

The retardation plate can be formed as one layer or as a superposed layer of two or more 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 a retardation plate having two or more layers for the visible light region is used, it is often the case that a layer giving a retardation of 100 to 200 nm is included as one or more odd-numbered layers because of a large amount of linearly polarized light components. It is preferable in terms of obtaining 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 obtained by stretching a film made of polycarbonate, polysulfone, polyester, polymethylmethacrylate, polyamide, polyvinyl alcohol or the like. It is preferable that the error of the phase difference in the plane of the retardation layer is smaller than the point of maintaining the emission intensity and the emission color uniformly at a wide viewing angle, and in particular, the error is ± 10 nm.
The following is preferred.

The retardation set in the retardation layer and the direction of the optical axis can be appropriately determined according to the intended oscillation direction of the linearly polarized light. By the way, in the case of a retardation layer giving a phase difference of 135 nm, linearly polarized light (wavelength 5) whose vibration direction is +45 degrees or −45 degrees with respect to the optical axis according to the direction of circularly polarized light.
40 nm). When the retardation layer is composed of two or more layers, especially when the outer surface layer is occupied by a layer providing a retardation of 100 to 200 nm, it is preferable to set the arrangement angle based on the layer.

As described above, in the polarized light source device according to the present invention, the reflected light (re-incident light) by the circularly polarized light separating layer is reused as the emitted light by the polarization conversion to prevent the reflection loss and the like, and If necessary, it is possible to improve the light utilization efficiency by converting the linearly polarized light component into a rich optical state through a retardation layer or the like to easily transmit through a polarizing plate and prevent absorption loss. . By this method, the amount of light transmitted through the polarizing plate can be ideally increased about twice, but the linearly polarized light component that can be transmitted through the polarizing plate is more than 65%, particularly 70% It is preferable to include the above.

The light guide plate and the polarized light source device using the light guide plate according to the present invention provide light which is excellent in light utilization efficiency, is bright, and is excellent in verticality, and is easy to be enlarged in area. It can be preferably used in various devices such as a backlight system in the device. In that case, it is also possible to arrange a diffusion plate or the like capable of maintaining the polarization state as much as possible on the polarized light source device.

FIG. 12 illustrates a liquid crystal display device 7 using the polarized light source device 6 according to the present invention in a backlight system. Reference numeral 71 is a lower polarizing plate, 72 is a liquid crystal cell, 73 is an upper polarizing plate, and 74 is a diffusion plate. The lower polarizing plate 71 and the diffusion plate 74 are provided as needed.

Generally, a liquid crystal display device includes a liquid crystal cell functioning as a liquid crystal shutter, a driving device associated with the liquid crystal cell, a polarizing plate,
It is formed by appropriately assembling components such as a backlight and a compensating retardation plate if necessary.
In the present invention, there is no particular limitation except that the above-described light guide plate, or a surface light source device or a polarized light source device using the light guide plate is used, and the light guide plate can be formed according to a conventional method. Especially,
A direct-view liquid crystal display device can be preferably formed.

Therefore, the liquid crystal cell to be used is not particularly limited, and any suitable one can be used. When a polarized light source device is used, it is advantageously used for displaying by making light in a polarized state incident on a liquid crystal cell, and for example, it can be preferably used for a liquid crystal cell using a twisted nematic liquid crystal or a super twisted nematic liquid crystal. It can also be used for a non-twist liquid crystal, a guest-host liquid crystal in which a dichroic dye is dispersed in a liquid crystal, or a liquid crystal cell using a ferroelectric liquid crystal. The liquid crystal driving method is not particularly limited.

From the viewpoint of obtaining a display of a good contrast ratio by the incidence of a high degree of linearly polarized light, as a polarizing plate, especially as a polarizing plate on the backlight side, for example, an iodine type or dye type absorption type linear polarizer, etc. A liquid crystal display device using one having a high degree of polarization is preferable. When forming a liquid crystal display device, for example, a diffusion plate or an antiglare layer, an antireflection film, a protective layer or a protective plate provided on a polarizing plate on the viewing side, or a compensating retardation plate provided between a liquid crystal cell and a polarizing plate. The appropriate optical element can be appropriately arranged.

The above-mentioned retardation plate for compensation is intended to compensate for the wavelength dependence of birefringence and improve the visibility. 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 plate for compensation, an appropriate one may be used depending on the wavelength range and the like, and may be formed as one layer or a superposed layer of two or more layers.

The light guide plate used in the liquid crystal display device can preferably use one that emits light in a direction perpendicular to or closer to the upper surface. However, if the emitted light deviates from the vertical direction, the direction of emergence through a prism sheet or the like. Can be modified. In that case, those that do not change the polarization state as much as possible can be preferably used.

In the present invention, the optical elements or parts forming the above-mentioned light guide plate, surface light source device, polarized light source device or liquid crystal display device may be wholly or partially laminated and fixed integrally. However, it may be arranged in a state of being easily separated. It should be noted that various diffusing plates and the like can be arranged on the upper surface of the surface light source device, but in the case of the polarized light source device, a diffusing plate and the like that can maintain the polarization characteristics can be arranged on the upper surface.

As described above, incident transmission light from the side surface is emitted at a vertical angle or an angle close to it by controlling the emission direction through the short side surface, and the incident light is efficiently transmitted, which is excellent in verticality and parallelism. By using the light guide plate of low phase difference according to the present invention that efficiently forms emitted light, it is possible to form a bright polarized light source device having excellent light utilization efficiency, and further to form a bright, easy-to-see liquid crystal display device with low power consumption. it can.

When forming a liquid crystal display device or the like, especially when a polarized light source device combined with a circularly polarized light separating layer is used,
It supplies outgoing light with excellent perpendicularity and parallel light, and re-emits the re-incident light through the circularly polarized light separation layer with little loss and angle change due to scattering, etc., and with good consistency with the direction of the initial outgoing light. A light guide plate that efficiently supplies emitted light in a direction effective for improving visibility can be preferably used. Further, a light guide plate which is thin, has excellent in-plane uniformity of emitted light, and has little unevenness in brightness can be preferably used.

[0097]

【Example】

Reference Example 1 After forming a side chain type cholesteric liquid crystal polymer having an acrylic main chain and a glass transition temperature of 57 ° C. on a polyimide rubbing-treated surface of a triacetyl cellulose film by spin coating, heating at 130 ° C. for 30 seconds 1 more
It was heated at 10 ° C. for 2 minutes and then rapidly cooled to obtain a circularly polarized light separating plate exhibiting a specular selective reflection state. This is 420-505
It shows good selective reflectivity in the wavelength range of nm, and 9
0% or more was selectively reflected in the regular reflection direction.

Reference Example 2 A side chain type cholesteric liquid crystal polymer having an acrylic main chain and a glass transition temperature of 64 ° C. was spin-coated on the polyimide rubbing-treated surface of a triacetyl cellulose film, and then at 30 ° C. at 30 ° C. 1 second after heating for 1 second
It was heated at 30 ° C. for 2 minutes and rapidly cooled to obtain a circularly polarized light separating plate exhibiting a specular selective reflection state. This is 500-590
It shows good selective reflectivity in the wavelength range of nm, and 9
0% or more was selectively reflected in the regular reflection direction.

Reference Example 3 A side chain type cholesteric liquid crystal polymer having an acrylic main chain and a glass transition temperature of 75 ° C. was formed on the surface of a triacetylcellulose film treated with polyimide by a spin coating method, and then at 30 ° C. at 30 ° C. 1 second after heating for 1 second
It was heated at 45 ° C. for 2 minutes and cooled rapidly to obtain a circularly polarized light separating plate exhibiting a specular selective reflection state. This is 595-705
It shows good selective reflectivity in the wavelength range of nm, and 9
0% or more was selectively reflected in the regular reflection direction.

Reference Example 4 The circularly polarized light separating plates obtained in Reference Example 1, Reference Example 2 and Reference Example 3 were laminated to obtain a superimposed circularly polarized light separating plate. This is 420
Good selective reflectivity was exhibited in the wavelength range of ˜705 nm, and 90% or more of this region was selectively reflected in the specular reflection direction.

Example 1 A transparent epoxy resin was poured into a mold-treated metal mold, heated at 100 ° C. for 2 hours, further heated at 150 ° C. for 3 hours to be cured, and then slowly cooled to form a light guide plate. Obtained. This light guide plate has a width of 195 mm, a depth of 150 mm, a thickness of the entrance surface of 5 mm, a thickness of 1 mm at its opposite end, a top surface is flat, and a bottom surface is a curve protruding from the entrance surface toward the opposite end to a lower surface close to a plane. The surface (Fig. 3) is provided with a recess (Fig. 6a) parallel to the incident surface with an effective width
It had a size of 85 mm and the recess had the form shown in Table 1.

The concave portion is measured by a surface shape measuring device. With the virtual lower side in the cross section of the recess as the reference side, the short side and the long side are determined based on the length of the left and right sides divided by the normal to the reference side from the vertex (the intersection of the short side and the long side). The projection width of the surface on the upper surface was determined, and the height was determined by the normal length between the vertex and the reference side. The reversal of the sign of ± between the short side surface (θ ₂ ) and the long side surface (θ ₁ ) with respect to the upper surface means that the measurement direction is reversed when the upper surface is used as a reference. This is because the measurement direction of the surface is the positive direction.

Example 2 A mold set was heated, and from its side surface, a flowable polymethylmethacrylate that had been heated and melted was charged under pressure and left under pressure at 170 ° C. for 2 hours to obtain a light guide plate. This light guide plate has a width of 195 mm, a depth of 150 mm, a thickness of the entrance surface of 5 mm, a thickness of 1 mm at the opposite end, a top surface is flat, and a bottom surface projects from the entrance surface toward the opposite end to a lower side close to a plane and is the thickest. As shown in Table 1, the concave part (Fig. 6a) parallel to the incident surface has an effective width of 185mm on the curved surface (Fig. 3) located 25mm from the incident surface. The angle of the short side surface increases, the angle of the long side surface decreases, and the area ratio thereof decreases.

Comparative Example 1 A light guide plate was obtained in the same manner as in Example 2 except that the mold was rapidly cooled after pressure filling. The form of the recess is shown in Table 1.

[0105]

[Table 1]

The phase difference and the optical axis of the light guide plates obtained in Examples 1 and 2 and Comparative Example 1 were measured by a birefringence measuring device (Oak Co., A
DR-100XY). The results are shown in FIG. 13 (Example 1), FIG. 14 (Example 2), and FIG. 15 (Comparative Example 1). As shown in the drawing, the retardation of 30 nm or less is maintained over the entire surface in the embodiment, but the average retardation is about 70 nm in the comparative example. The numerical value in the figure is the phase difference, and the line is the direction of the optical axis.

Example 3 A cold cathode tube having a diameter of 3 mm was arranged on the incident surface of the light guide plate obtained in Example 1, and the cold cathode tube was surrounded by a light source holder made of a silver-deposited polyester film. A side-light type surface light source device is obtained by arranging a reflection sheet made of a polyester film on which silver is vapor-deposited on the lower surface of the above, and the phase difference of 135 nm with the circularly polarized light separating plate obtained in Reference Example 4 on the upper surface thereof. A plate and a polarizing plate (G1220DUN) were sequentially arranged to obtain a polarized light source device. The rotation of the polarizing plate was adjusted so as to exhibit the maximum luminance.

Example 4 A polarized light source device was obtained in the same manner as in Example 3 except that the light guide plate obtained in Example 2 was used.

Comparative Example 2 A polarized light source device was obtained according to Example 3 except that the light guide plate obtained in Comparative Example 1 was used.

Evaluation Test 1 The light sources of the polarized light source devices obtained in Examples 3 and 4 and Comparative Example 2 were turned on, and the light was passed through the incident surface along the center of the light guide plate in the width direction.
The maximum luminance angle on the upper surface and the surface luminance at each position of mm, 70 mm, and 110 mm are measured by a color difference meter (manufactured by Minolta Co.,
CS-100) was used and examined in a dark room. Regarding the angle, the light source side was the negative direction and the opposite side was the positive direction with reference to the normal direction of the upper surface. The results are shown in Table 2. In the table, the ratio of the luminance in the case of Examples 3, 4 and Comparative Example 2 is shown as the light amount ratio, based on the luminance in the case where the circularly polarized light separating plate is not arranged.

[0111]

[Table 2]

It can be seen from Table 2 that the polarized light source device of the example has a higher surface brightness in the maximum emission direction than that of the comparative example. In addition, in the light amount ratio in the case where the circularly polarized light separating plate is not provided, it is found that the value is large in the example, and the improvement of the light utilization efficiency by the use of the circularly polarized light separating plate is large, and the uniformity of the brightness is even visible to the naked eye. Excellently, there was almost no change in luminance even in the portion corresponding to the vicinity of the gate of the mold. On the other hand, in the comparative example, it was found that the value of the light quantity ratio was small and the degree of improvement in light utilization efficiency by using the circularly polarized light separating plate was poor. Then, the change in the brightness was drastic. Further, the brightness change was notable for non-uniformity accompanied by color change.

The above-mentioned characteristics show that the re-incident light that has passed through the circularly polarized light separating plate is circularly polarized light that can be efficiently polarized and emitted on the entire surface of the light guide plate in the examples, and in the comparative example. It shows that the effect is small and non-uniform in the plane. From the above results, when the circularly polarized light separating plate is used, the phase difference of the light guide plate greatly affects the light use efficiency, and by reducing the phase difference, uniform and good polarization conversion is achieved, and in the conventional product. It can be seen that an unrealizable high light utilization efficiency can be achieved.

Evaluation Test 2 On the upper surfaces of the polarized light source devices obtained in Examples 3 and 4 and Comparative Example 2,
A liquid crystal display was obtained by disposing a super twisted nematic liquid crystal cell. This liquid crystal cell is provided with retardation plates on both sides thereof and is adjusted to a normally white monochrome mode. As a result of comparing the surface luminances in the non-selected state of this liquid crystal display device, it was found that the example has a higher luminance than the comparative example and is excellent in uniformity.

From the above results, comprehensively, the light guide plate according to the present invention efficiently converts the incident light from the side surface into the vertical type emitted light, and converts the light excellent in verticality and parallelism into incident light. It is possible to obtain a surface light source device that can be efficiently used, and to obtain a polarized light source device that efficiently polarizes the light through a circularly polarized light separating layer, and to form a bright and easy-to-view high-quality liquid crystal display device. I understand.

[Brief description of drawings]

FIG. 1 is an explanatory perspective view of an example of a light guide plate.

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

FIG. 3 is an explanatory side view of still another example of the light guide plate.

FIG. 4 is an explanatory side view of still another example of the light guide plate.

FIG. 5 is an explanatory side view of an example of a convex portion.

FIG. 6 is an explanatory side view of an example of a concave portion.

FIG. 7 is an explanatory side view of still another light guide plate example.

FIG. 8 is a side sectional view illustrating an example of a surface light source device.

FIG. 9 is a side sectional view illustrating another example of the surface light source device.

FIG. 10 is a cross-sectional side view illustrating an example of a polarized light source device.

FIG. 11 is a side view sectional view of another example of the polarized light source device.

FIG. 12 is a side sectional view illustrating an example of a liquid crystal display device.

13 is an explanatory plan view of the phase difference of the light guide plate of Example 1. FIG.

FIG. 14 is an explanatory plan view of the phase difference of the light guide plate according to the second embodiment.

15 is an explanatory plan view of the phase difference of the light guide plate of Comparative Example 1. FIG.

[Explanation of symbols]

1: light guide plate 11: upper surface 12, 16, 17, 18: lower surface 21, 22, 23, 24: convex portion on lower surface 25, 26, 27, 28: concave portion on lower surface 31, 33, 35, 37, 42, 44 , 46, 48: Long side surface 32, 34, 36, 38, 41, 43, 45, 47: Short side surface 13: Incident surface 2: Reflective layer 5: Surface light source device 51: Light source 52: Light source holder 53: Diffuse Layer 54: Reflection plate 6: Polarization light source device 61: Polarization separation means 62: Phase difference layer (linear polarization conversion means) 7: Liquid crystal display device 71, 74: Polarizing plate 72: Liquid crystal cell 73: Diffusion layer

Claims (9)

[Claims] 1. A light guide plate, characterized in that incident light from a side surface is reflected on a lower surface and emitted from an upper surface, and a phase difference due to birefringence in a thickness direction is 0 to 30 nm. 2. The retardation according to claim 1, wherein the phase difference is 20 nm or less, the lower surface periodically has convex portions or concave portions composed of long side surfaces and short side surfaces, and the inclination angle of the long side surface with respect to the upper surface. 0 to
In the case of 10 degrees, that of the short side surface is 25 to 50 degrees, the projected area of the long side surface with respect to the upper surface is three times or more of that of the short side surface, and there is a convex portion on the light incident surface side. A light guide plate in which the long side surface is the concave side surface when it is a recess. 3. The light guide plate according to claim 1, which does not include a diffuse reflection layer, and has a thickness of a light incident surface that is at least twice that of the end portion on the opposite side. 4. The light guide plate according to claim 1, which has a metal reflection layer on the lower surface or along the lower surface. 5. The upper surface of the light guide plate according to claim 1,
A polarized light source device having a circularly polarized light separating layer made of a cholesteric liquid crystal phase. 6. The polarized light source device according to claim 5, wherein the circularly polarized light separating layer is made of a liquid crystal polymer. 7. The polarized light source device according to claim 5, having a retardation layer above the circularly polarized light separating layer. 8. A liquid crystal display device comprising the light guide plate according to claim 1. 9. A liquid crystal display device comprising the polarized light source device according to claim 5.