JPH1027512A - Die for light guide plate, its manufacture, polarized light source device, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a die for light guide plate and a method for effectively manufacturing light guide plate whose phase difference due to complex refraction is less even in case of high volume production on the injection molding system is introduced, whereby a good transfer performance is ensured and wherefrom a polarized light source device or liquid crystal display device excellent in the light utilizing efficiency can be formed. SOLUTION: This die concerned is to make a light guide plate on the polymer injective filling system (K1), whereby the light incident to the side face of a plate-shaped object is emitted from either of the oversurface and undersurface, where a polymer injecting gate (K2) over the whole width substantially of the side face of the plate-shaped object is provided in a position (K13) mating with at least one side face of the plate-shaped object. Accordingly the light guide plate can be produced effectively and has a less phase difference due to complex refraction, wherein the separated light after transmission and/or reflection with a circular polarizing separation layer can be re-emitted efficiently without change in the polarized condition of the circular polarization to lead to enhancement of the lightness in displaying of a liquid crystal display device, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for molding a light guide plate suitable for forming a liquid crystal display device having excellent light utilization efficiency and excellent brightness and good visibility, a method for manufacturing the light guide plate, And a polarized light source device and a liquid crystal display device using the light guide plate.

[0002]

2. Description of the Related Art Conventionally, as a sidelight type light guide plate in which light is incident from the side surface of a plate-like object and emitted from the upper surface, a diffusion type or scattering type reflection layer such as a dot shape is provided on the lower surface. Things were known. 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 TN type liquid crystal display device or the like, in the case of natural light, about 60% of the light amount is absorbed, and the light use efficiency is usually 35 to 45%, and theoretically exceeds 50%. Nothing.

[0004] Therefore, to improve the brightness of a liquid crystal display device or the like, it is necessary to improve the entire illumination system. For this purpose, an illumination system that supplies light as polarized light to a polarizing plate to improve the light use efficiency has been proposed. (Japanese Unexamined Patent Application Publication No. 3-45
906, JP-A-6-324333, JP-A-7-36032. In these, a reflective layer is 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 the incident light is reflected and transmitted through the circularly polarized light separating layer by left and right circularly polarized light. The light is separated into light, and the reflected light is reflected through a lower reflective layer and re-emitted from the upper surface to improve light use efficiency. However, it was found that in any case, those which should show a light use efficiency of more than 50% do not show numerical values as expected.

[0005] In view of the above, the group to which the present inventors belong efficiently emits incident light from the side from the upper surface and efficiently re-emits the re-incident light through the circularly polarized light separating layer to improve the light use efficiency. As a result of diligent research aimed at obtaining an excellent light guide plate, we have found out that the low light utilization efficiency in the conventional technology is caused by the reflection structure on the lower surface of the light guide plate and the phase difference of the light guide plate. The overcoming light guide plate was proposed earlier (Japanese Patent Application No. 7-321036, Japanese Patent Application No. 8-104687).
issue)

That is, in the above, Japanese Patent Application No. 7-321
The light guide plate according to No. 036 is a light guide plate according to JP-A-6-324333 or JP-A-7-36032, in which the lower surface is a reflective layer of a diffusion type or a scattering type. Since the amount of re-emitted light is considered to be reduced due to the formation of light, the structure of the lower surface is optimized by forming an array of fine prisms to improve the directivity of emitted light and the maintainability of the polarization state.

In the light guide plate disclosed in Japanese Patent Application No. 8-104687, the metal reflection structure on the lower surface taught by Japanese Patent Application Laid-Open No. 3-45906 is designed to efficiently convert circularly polarized light through reflection and regularly emit light. In spite of this, the re-emission efficiency is poor, and it has been found that the cause is due to the phase difference of the light guide plate, and this was overcome. That is, if the light guide plate has a large phase difference due to birefringence, the circularly polarized light re-entered through the circularly polarized light separating layer is converted into elliptically polarized light, and the elliptically polarized light is further elliptically polarized on the return path reflected by the lower surface. Elliptical polarization is
It 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, this first reduces the efficiency of use of the re-incident light.

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. Therefore, even in this case, the amount of polarized light that can pass through the circularly polarized light separating layer is small. Does not increase. In addition, irregularities in the direction of the optical axis in the light guide plate, changes in the phase difference due to the incidence and transmission angles of light, and differences in the effect of the phase difference for each wavelength,
The polarization conversion efficiency of circularly polarized light re-entered through the circularly polarized light separation layer and the major axis direction of elliptically polarized light vary widely, greatly reducing overall polarization conversion efficiency and reducing the efficiency of use of re-incident light. At the same time, the amount of transmission and the spectrum of emitted light are greatly changed depending on the position of the light guide plate to cause uneven brightness, thereby deteriorating the quality as a light source and the display quality of a liquid crystal display device.

Incidentally, a light guide plate, particularly a light guide plate having a fine prism structure or the like on its lower surface, is usually formed by injection molding of a plastic such as polymethyl methacrylate. In this case, the light guide plate has an optical axis along the flow of the polymer. A birefringence pattern is generated, and the average in-plane phase difference is about 60 nm, which reaches 100 nm near the gate portion, and the direction of the optical axis is not constant. In addition, a weld line is generated at the interface where the branched polymers have joined, and this weld line does not cause any problem on the lower surface of the diffusion dot type, but causes light and darkness in the non-diffusion type using a fine prism structure or the like. Therefore, when the lower surface is a metal reflection structure, the polarization state is maintained at a high level, so that the phase difference of the light guide plate has a greater influence than the lower surface structure of a diffusion type or the like.

[0010]

In general, the light guide plate is manufactured by an injection molding method from the viewpoint of mass productivity. In that case, in terms of the reduction of the phase difference, it is advantageous to increase the melting temperature of the polymer to lower the viscosity, and to increase the molding temperature and pressure so as to lengthen the molding time such as the cooling temperature. Degradation of molding quality and transfer (molding) of the fine prism array on the lower surface due to
Since the light guide plate performance is reduced due to the shortage, and the heat resistance of the molded product is reduced, it is difficult to improve the molding of the light guide plate. Also, it is difficult to control the phase difference in the axial direction, and the variation of the phase difference axis occurs as in the related art. On the other hand, in the phase difference reduction measures other than those described above, the molding cycle is lengthened and the mass productivity by the injection molding method is reduced, and in the production method by a method other than the injection molding, the mass productivity becomes poorer.

Accordingly, the present invention provides a polarized light source device which is capable of efficiently obtaining a light guide plate having a small phase difference due to birefringence and good transferability even when mass-produced by an injection molding method, and which is excellent in light use efficiency. An object of the present invention is to develop a mold for molding a light guide plate capable of forming a liquid crystal display device and a method for manufacturing the light guide plate.

[0012]

According to the present invention, there is provided a mold for molding a light guide plate which emits light incident from one side surface of a plate-like object from one of upper and lower surfaces by a polymer injection and filling method. A mold for a light guide plate having an injection gate of a polymer over substantially the entire width of the side surface at a position corresponding to at least one side surface, and a light guide plate characterized by injection molding using the mold Is provided.

[0013]

According to the present invention, the light incident from the side surface of the plate-like object is efficiently emitted from one of the upper and lower surfaces, and the circularly polarized light reflected by the circularly polarized light separating layer and re-entered into the light guide plate is reflected by the light. It is hardly affected by the change in the polarization state due to the phase difference, and when it is reflected through the metal reflection layer on the lower surface and the polarization state is inverted, the light can efficiently pass through the circularly polarized light separation layer without change in the polarization state. The light is re-emitted, and the phase difference due to birefringence that can improve the brightness of the display of the liquid crystal display device etc. is small. It is possible to form a polarized light source device or a liquid crystal display device that can be molded with good quality, can obtain a high-quality product stably and efficiently, and is excellent in light use efficiency.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A mold according to the present invention is for molding a light guide plate for emitting light incident from a side surface of a plate-like object from one of upper and lower surfaces by a polymer injection filling method. An injection gate of polymer over substantially the entire width of the side at a position corresponding to at least one side of the object. Examples thereof are shown in FIGS. K1 is a light guide plate forming part, K2 is an injection gate, K13 is a side part forming an incident surface, and K3 is an opening gate.

As shown in the figure, a polymer injection gate K2
Is provided over a substantially entire width of the side surface at a position (K13) corresponding to at least one side surface of the plate-shaped object to be formed of the light guide plate forming portion K1. As a result, the polymer flows in one direction at a uniform flow rate in the injection direction inside the mold (light guide plate forming portion), so that birefringence does not easily appear, thereby reducing the phase difference. Further, the axial direction of the phase difference can be made uniform.

Further, as shown in FIG. 2, when an extraction gate K3 having substantially the entire width is provided on the opposing surface of the injection gate, the polymer injected from the injection gate collides with the opposing surface without the extraction gate. The polymer flow is prevented from being disturbed due to backflow, wraparound, stagnation, etc., and the unidirectional flow due to the uniform flow velocity of the injected polymer reaches more stably from the polymer injection side of the part to be the light guide plate to the other end,
The phase difference due to birefringence is further reduced in the entire portion serving as the light guide plate, and the axial direction of the phase difference is also aligned. Therefore, a portion having a large phase difference due to birefringence is generated at the end of the molded plate-like material, and it is possible to avoid the necessity of cutting the portion to obtain a target light guide plate.

In the above, substantially the entire width means a portion or a width used as a light guide plate in a formed plate-like material. In this case, in the conventional injection gate K4 formed on a part of the width portion used as the light guide plate as illustrated in FIG. 3, the polymer develops in a fan shape from the gate portion even under ideal molding conditions, The inside of the mold is filled through backflow, wraparound, stagnation, and the like, thereby increasing variations in optical distortion.

Therefore, in the injection gate K4 of the conventional specification, even if a portion having a small phase difference is formed at a corner or the like due to stagnation, there is a large birefringence in the flow trajectory when the injected polymer is filled in the mold. Optical distortion occurs, and the phase difference due to the birefringence generally ranges from about 100 to 200 nm near the injection gate based on the case where a light guide plate having a thickness of 3 mm is formed. In addition, the phase difference due to optical distortion due to the wraparound of the injected polymer is often about 50 to 100 nm, which overlaps with the 波長 wavelength region of the visible light region, and the direction of the optical axis also has large variations such as the wraparound form. This causes variations in polarization conversion efficiency, which causes uneven brightness of emitted light.

When the light guide plate is molded by the polymer injection and filling method such as the injection molding method as described above, the phase difference due to the birefringence and the direction of the phase difference axis due to the flow of the polymer injected and filled in the mold. Variations are likely to occur, and the fast axis is likely to appear in a direction parallel or perpendicular to the polymer flow.
Therefore, the injection and filling of the polymer into the mold is ideally a laminar flow filling with a uniform flow rate and a unidirectional flow when observed from the side of the light guide plate which is to be the emission surface. By providing a gate and an opening gate having a full width as necessary on its opposing surface, a substantially laminar flow similar to the ideal polymer filling flow is realized. as a result,
Even in the injection molding method which is a high-speed filling method of a polymer, a high-performance light guide plate having a small phase difference and having the same axial direction can be obtained. If the directions of the phase difference axes are not aligned,
It is difficult to compensate for the above-mentioned effect due to the phase difference, and it is also difficult to improve the light use efficiency.

In the mold of the present invention, the injection gate is provided at a position corresponding to the side surface of the light guide plate made of a plate-like material.
An injection gate may be provided on any of the surfaces. Rather than obtaining a light guide plate having a phase difference as small as possible, it is preferable to provide the light guide plate at a position corresponding to a side surface that becomes a light incident surface or a side surface facing the light incident surface. The injection gate is preferably provided only on one side to prevent turbulence due to collision of the polymer flow in the mold due to polymer injection from a plurality of sides.

When a rectangular light guide plate is formed on the basis of the light exit surface, the injection gate may be provided on either the long side surface or the short side surface. On the other hand, the light guide plate to be formed has a deformed shape such as a wedge shape as shown in the figure, and the thickness of the light guide plate on the side where the thickness is reduced is 1/10 or less, especially 1/5 or less, especially 1/5. In the case of / 2 or less, a portion corresponding to a side surface other than the side surface on which the thickness is reduced, particularly a side surface which is opposed to the side surface on which the thickness is reduced and which is usually used as an incident surface It is preferable to provide an injection gate at the portion where the injection is performed.

It is preferable that the inner surface of the mold in a portion used as a light guide plate is mirror-finished except for a portion where an injection gate or an extraction gate is provided. By such a mirror surface treatment, the above-described substantially laminar flow is achieved also on the inner wall surface of the mold, and the generation of a phase difference due to birefringence and the disturbance of the phase difference in the axial direction can be suppressed, and the molded product can be easily taken out. Also, the light transmission condition is improved. That is, according to a general pipe flow in which a vortex is generated near the wall surface due to the flow velocity being close to zero, disturbance of the polymer flow according to the vortex is predicted also in the vicinity of the inner wall surface of the mold, By making the inner wall surface mirror-like, a substantially laminar flow of the injected polymer is achieved also near the inner wall surface, and disturbance of the polymer flow is prevented, so that a high-quality light guide plate is formed. Therefore, it is more preferable that the wall surface on which the injection gate and the bleed gate are provided be mirror-finished.

The form of the injection gate and the bleed gate is not particularly limited, except that the form is provided at a position corresponding to the side surface of the plate-like material to be formed and over substantially the entire width of the side surface.
The opening may be at the same height as the height of the side surface, or may be at a small height. In the latter case, it is preferable that the opening line coincides with one of the upper and lower surfaces of the molded plate-like material from the viewpoint of obtaining a high-quality molded body. Unnecessary portions of the plate-like object formed through the mold are removed by cutting or the like as necessary, and a necessary surface is polished to a mirror surface or the like to obtain a target light guide plate.

The form of the light guide plate formed by using the mold according to the present invention may be any as long as the light incident from the side surface of the plate-like object is emitted from one of the upper and lower surfaces. Therefore, the form is not particularly limited, and is generally a plate-like form having an upper surface, a lower surface facing the upper surface, and an incident surface including at least one end surface between upper and lower surfaces. When a polarized light source device using a circularly polarized light separating layer is formed, as illustrated in FIGS. 4 to 7 in terms of light utilization efficiency, directivity of emitted light, and the like,
It is preferable that the thickness of the side end portion facing the incident surface is thinner than that of the incident surface, particularly, 50% or less.
In the light guide plate shown in the figure, the light exit surface formed by one of the upper and lower surfaces is represented by the upper surface, and the incident light from the side surface is reflected by the lower surface and emitted from the upper surface.
Reference numerals 6, 17, and 18 denote lower surfaces, 13 denotes an incident surface, 14 denotes a side surface, and 15 denotes a side end portion facing the incident surface 13.

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

A form of the light guide plate which can be preferably used for forming the polarized light source device is an emission surface (hereinafter, represented by an upper surface).
Outgoing light efficiency is excellent, and the outgoing light is excellent in perpendicularity to the upper surface and easy to use effectively, and the outgoing efficiency from the upper surface via reflection at the lower surface etc. of the re-incident light through the circularly polarized light separation layer etc. Also, the emission direction is similar to the initial emission direction. The realization is not limited to, for example, a method of providing an array of fine prismatic irregularities having a convex or concave portion in the direction of the incident surface consisting of a long side surface and a short side surface on the lower surface, or providing dots. It can be performed by a method or the like.

As described above, the protruding portion or the concave portion on the lower surface is formed by the slope formed by the long side surface and the short side surface along the incident surface, and an example of the convex portion or the concave portion is shown in FIG. ) ~
(D) and FIGS. 9 (a) to 9 (d). 8 and 9, 21, 22, 23 and 24 are convex portions, 25, 26,
27 and 28 are concave portions, and 31, 33, 35, 37,
Slopes 42, 44, 46 and 48 form long side surfaces;
2, 34, 36, 38, 41, 43, 45 and 47 are slopes forming short side surfaces.

The projections or depressions on the lower surface are formed periodically. That is, for example, FIG. 4 and FIG.
In the case based on (a), the incident surface 1 as shown by the arrow in FIG.
3 is a lower surface having periodically the convex portions 21 or the concave portions 25 formed of the inclined surfaces 31, 32 or 41, 42 in the direction along 3.

The above-mentioned convex or concave portion is determined based on a straight line connecting the intersection with the lower surface of the slope forming the convex or concave portion, whether the intersection (vertex) of the slope protrudes (convex) from the straight line or the concave. It depends on whether it is concave (concave). That is, when based on the example shown in FIGS. 8 and 9, the convex portions (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).

The long side and the short side of the slope forming the convex or concave portion are determined based on a straight line connecting the intersection and the vertex of the lower surface. More preferably, the projected area of the longer side surface with respect to the upper surface is three times or more, especially five 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. 4 and 8
9 (a) or FIG. 9 (a), the slopes 31 and 32 or 41 and 42 forming the convex portions 21 or the concave portions 25 are straight lines connecting the intersections of the lower surfaces (corresponding to the virtual lines 20) and the vertices. 8 and 9, the long sides 31, 42 and the short sides 32, 41 are based on the long sides 31, 42. The projection area with respect to the upper surface 11 is formed so as to be three times or more that of the short side surfaces 32 and 41. In the case of the convex portion 21, the long side surface 31 is on the side of the incident surface 13; Is preferably arranged such that the long side surface 42 is located on the side end 15 facing the incident surface.

As described above, in addition to the transmission light directly incident on the short side surface, the transmission light incident on the long side surface and incident on the short side surface via its reflection is also reflected on the short side surface by the reflection via the short side surface. Can be supplied (exited), and the light use 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, that is, the shape of one of the upper and lower surfaces other than the emission surface may be determined as appropriate. Preferably, as described above, the inclined surface is made thinner at the end on the opposite side than the incident surface. In this case, the shape of the inclined surface may be arbitrarily determined, and it is sufficient that the inclined surface is formed so that the end surface facing the incident surface becomes thinner than the incident surface based on a substantially continuous change. Therefore, an appropriate surface shape such as a linear surface as illustrated in FIG. 5 or a curved surface as illustrated in FIGS. 6 and 7 can be used. 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 or concave portion provided on the lower surface is also shown in FIG.
As shown in (a) to (d) and FIGS. 9 (a) to 9 (d), it is not necessary to form it with a linear slope, and even if it is formed with 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. .

It is preferable that the projections or depressions on the lower surface are smaller because the emitted light is emitted in a stripe shape through the projections or depressions. If the spacing is large, uneven brightness occurs, and the uniformity of brightness over the entire surface is reduced. 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 has its 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 inclination angle, light transmitted at an angle larger than the inclination angle is incident on the long side surfaces 31 and 42 as illustrated by the broken arrows in FIGS. 8A and 9A. In this case, the light is reflected on the upper surface 11 at a more parallel angle based on the inclination angle of the long side surface, enters the short side surfaces 32 and 41, is reflected, and emerges 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 of 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.

Incidentally, 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.

Therefore, for the purpose of improving the emission efficiency as in the conventional light guide plate, the inclined surface (corresponding to the short side surface in the present invention) serving to reflect the transmission light and supply it to the upper surface is enlarged to project the light onto the upper surface. In a structure in which the area ratio is increased and the inclination angle of the other inclined surface (corresponding to the long side surface in the present invention) is set to 20 degrees or more, the probability of incidence of transmission light on this inclined surface is extremely small and parallel light is measured. It is difficult to make the emitted light have vertical directivity.

On the other hand, the above-mentioned short side surface of the slope forming the convex portion or the concave portion has an inclination angle θ ₂ with respect to the upper surface 11 of 25 to 45 degrees, particularly 30 to 4 as shown in FIGS.
Preferably it is 5 degrees. By setting the range of the inclination angle as described above, as illustrated by the broken arrows in FIGS. 8A and 9A, the transmission light incident directly or via the long side surface is transmitted to the short side surfaces 32 and 41. The light is reflected at an angle perpendicular to or close to the upper surface 11, and can efficiently emit light in a direction that effectively affects the visibility of a 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.

The shape of the incident surface of the light guide plate is not particularly limited, and may be determined as appropriate. 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 (emission surface) is generally a flat surface or the like, but if necessary, a structure having a diffusion layer on the surface for the purpose of scattering may be employed. However, when a polarized light source device is formed, a light guide plate having no diffusion layer or a diffuse reflection layer for scattering purposes that changes the polarization state on the lower surface, the upper surface, or a portion other than the incident surface including the intermediate layer of the light guide plate is used. It is more preferable from the viewpoint of the utilization efficiency of the product. Therefore, it is preferable that the slope or the upper surface forming the convex portion or the concave portion on the lower surface is smooth, and in particular, is a mirror-finished surface.

As a molding material for the light guide plate, an appropriate polymer exhibiting transparency according to the wavelength region of the light source can be used. Incidentally, in the visible light range, for example, an acrylic resin such as polymethyl methacrylate, a polycarbonate resin such as polycarbonate or polycarbonate / polystyrene copolymer, a wavelength range of about 400 to 700 nm such as a transparent resin represented by an epoxy resin or the like. And those showing transparency. Above all, a transparent resin that does not easily exhibit birefringence is preferably used, and examples thereof include a polycarbonate / polystyrene copolymer and Zeonex (trade names,
Zeon Corporation) and Optrez (trade name, manufactured by Hitachi Chemical Co., Ltd.).

The method for producing the light guide plate using the mold according to the present invention is not particularly limited. For example, an appropriate polymer injection and filling method such as a method of injecting a molding resin such as an epoxy resin into the mold is used. A manufacturing method can be adopted. The production method by the injection molding method is particularly preferable from the viewpoint of utilizing the mold according to the present invention. That is, according to the injection molding method using the mold of the present invention, optimal molding conditions in consideration of moldability, prevention of weld line generation, prevention of sink mark generation, suppression of phase difference, etc. according to the type of molding material, etc. It can be set widely, and the condition to balance them can be made higher, and the phase difference due to the birefringence in the thickness direction is small, and the dispersion of the axis of the phase difference is small. Can be manufactured.

The phase difference due to the birefringence in the thickness direction of the light guide plate can be obtained by maintaining substantially the same circularly polarized light state on the lower surface while maintaining substantially the same circularly polarized light state without substantially being affected by the phase difference. It is preferred that the return light guided and reflected on the lower surface be smaller while emitting the circularly polarized light while maintaining its circularly-polarized state, and is preferably 50 nm or less, particularly 40 nm or less, particularly 0 to 30 nm.
Is preferred. In order to achieve such a phase difference, for example, a light guide plate formed using the mold of the present invention, or a plate-like object is annealed at a high temperature to reduce the birefringence, or a large molded product is formed and the center thereof is formed. An appropriate system such as a system in which a portion having a small phase difference, such as a portion, is cut out to form a light guide plate can be adopted as necessary.

On the other hand, since the phase difference is the product of the thickness difference and the refractive index difference of birefringence, the phase difference can be reduced by the birefringence even by a method of thinning the light guide plate. In addition, thinning of the light guide plate is more advantageous than weight reduction and reduction of necessary materials.However, since the amount of incident light is reduced by reducing the incident surface, there is a limit from the point of securing the necessary amount of incident light. In the case of injection molding, the influence of the mold is increased to increase the birefringence and the moldability is reduced.

In the light guide plate using the mold of the present invention, the light output is controlled based on the above-described control of the area ratio between the short side surface and the long side surface, the inclination angle, the shape of the lower surface (the surface facing the emission surface), the curvature, and the like. Characteristics such as the angular distribution and in-plane distribution of the emitted light 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.

The array structure and the like of fine prismatic irregularities on the lower surface of the light guide plate can be formed, for example, by using the mold of the present invention.
It may be formed by laminating different kinds of materials such as a light guide plate main body that transmits light and a sheet for forming a lower surface adhered thereto. Therefore, the light guide plate does not need to be formed as an integrated single layer of one kind of material. 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.

The general thickness of the light guide plate for use in a liquid crystal display device or the like is 20 mm or less, preferably 0.1 to 10 mm, particularly 0.5 to 8 mm based on the incident surface. 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 set to 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 passing through the circularly polarized light separating layer is incident on the long side surface. I 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 with the lower surface of the light guide plate, or may be stacked as a reflection sheet or the like, and can take an appropriate arrangement form.

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 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.

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 reflection layer having excellent adhesion to the lower surface of the light guide plate can be formed as a coating layer in which metal powder is mixed with a binder resin, or as a thin metal attachment layer 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-described light guide plate, the light that has been collimated with high precision is emitted using the light guide plate in a direction that is advantageous in visual recognition and has excellent perpendicularity, and the light from the light source is efficiently used to increase the brightness. Various devices such as an excellent surface light source device and a polarized light source device, and a liquid crystal display device which is bright and easy to see and has excellent low power consumption can be formed.

FIGS. 11 and 12 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 the surface light source device is formed, as necessary, as shown in the figure, a light source surrounding the light source to guide the divergent light from the linear light source to the side surface of the light guide plate, as shown in the drawing. The holder 52, a diffusion layer 53 disposed on the upper surface of the light guide plate to obtain uniform surface light emission, and a combination body provided with appropriate auxiliary means such as a prism sheet for controlling the emission direction of light can also be used.

As for the reflection layer, as shown in FIG.
Instead of the reflective layer 2 or together with the reflective layer,
A reflecting plate 54 can be provided along the lower surface of the light guide plate 1. 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 one such as a resin sheet provided with a thin metal sheet, 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.

As a reflector, particularly when a polarized light source device or the like is formed, the reflection angle of the reflected light when parallel light is incident is considered because the spread of re-emitted light is suppressed. 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. Note that, as the light source holder, a resin sheet or a metal foil provided with a high-reflection 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 superior in brightness uniformity by preventing the occurrence of light and dark unevenness, and can be formed as an appropriate diffusion layer with a fine uneven surface or a diffusion plate. . When used for forming a polarized light source device as described above, the arrangement of the diffusion layer that changes the polarization state is not preferable, but the arrangement of the diffusion layer that does not easily change the polarization state is preferable in terms of equalizing brightness. Rather preferred.

The polarized light source device according to the present invention generally converts incident light having no polarization characteristics into right and left circularly polarized light as transmitted light or reflected light through a circularly polarized light separating layer, and converts it into polarized light with high efficiency. 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.

FIGS. 13 and 14 illustrate a polarized light source device according to the present invention. This is configured by disposing a circularly polarized light separating layer 61 above the upper surface 11 of the light guide plate 1 in the surface light source device 5 described above. 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. 14, reference numeral 62 provided on the upper surface of the circularly polarized light separating layer 61 is a retardation layer as linearly polarized light converting means.

According to the above-described device, the light emitted from the upper surface of the light guide plate 1 enters the circularly polarized light separating layer 61, and the predetermined (tentatively left) circularly polarized light on the left and right is transmitted and the predetermined (right) outside. 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 a reflection function portion formed of a reflection layer or the like on the lower surface, re-enters the circularly polarized light separating layer, 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, the light guide plate according to the present invention provides highly parallelized outgoing light having excellent perpendicularity, so that most of the re-incident light passing through the circularly polarized light separating layer is directed to the long side surface. The incident light is reflected without largely changing the angle based on the gentle inclination angle, and the light can be re-emitted in a direction similar to the initial outgoing light with a small change in the angle, and thus with good perpendicularity. 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 converted into a predetermined circularly polarized light with high efficiency by the reflection reversal thereby, so that the light can be extracted efficiently. In addition, since the emitted light has excellent perpendicularity, there is an advantage that the change in the traveling direction of light due to refraction at an interface having a different refractive index is small.

In the light guide plate according to the present invention, on the lower surface of the light guide plate, such as a scattering reflection means or a diffusion reflection means made of dots or the like,
Appropriate means for emitting the incident light from the side surface from the upper surface may be provided, but as the light guide plate in the case of forming the polarized light source device, the re-incident light through the circularly polarized light separating layer reflects the reflected light on the lower surface of the light guide plate. Since the light is re-entered into the circularly polarized light separating layer via the means and emitted, the emitted light has poor directivity, and the conversion efficiency of the re-incident light through the circularly polarized light separating layer is 50% or less, and the light is used. The effect of increasing the efficiency is poor, which is not preferable.

On the other hand, even with a total reflection means such as a prism, even if the light guide plate has a refractive index of 1.5, the conversion efficiency through the re-incident circularly polarized light separating layer is 45% or less. Does not re-emit at all depending on the angle of the re-incident light passing through the circularly polarized light separating layer because the conversion efficiency is further reduced, and the reflection hardly occurs when the incident angle exceeds the total reflection condition. Cannot be used as re-emitted light, so that the effect of increasing light use efficiency is unlikely to occur. In this case, too, it is not preferable as a light guide plate when a polarized light source device is formed.

Further, in order to prevent the re-incident light from being unable to be re-emitted, if the lower surface of the light guide plate has a prism structure which is advantageous for re-emission, the initial emitted light is reduced, and conversely, it is advantageous for the initial emission. In the case of a prism structure, the re-emission direction of the re-incident light is greatly changed from the initial emission light, and the efficiency of polarization conversion through the lower surface is low, so that the initial emission and the re-emission of the re-incident light are good. It is difficult to obtain a prism structure compatible with the above, and also in this case, it is difficult to produce the effect of increasing the light use efficiency, which is also unfavorable as a light guide plate when forming a polarized light source device.

In addition, the angle of deviation from the vertical direction, which is inconvenient for reflecting means that makes it difficult to give directivity to the light emitted through the circularly polarized light separating layer or for display such as liquid crystal display, which deteriorates visibility, is greatly reduced. Reflection means with poor verticality of the output angle, which includes a large amount of output light components in the direction of 45 degrees or more with respect to the vertical direction, can be guided even if a prism sheet is arranged on the upper surface of the light guide plate to correct the verticality. Since the light is incident on the reflection surface on the lower surface of the light plate at an angle greatly deviated from the vertical direction, the effect of enhancing the light recycling efficiency is poor, and it is also not preferable as a light guide plate when a polarized light source device is formed.

As described above, the light guide plate which can be preferably used for forming the polarized light source device emits the incident light from the side surface from the upper surface with high efficiency, and the emitted light has high directivity, particularly, perpendicularity to the upper surface. It has excellent directivity and excellent re-emission efficiency of re-incident light through the circularly polarized light separation layer, and the directivity and emission angle of the re-emitted light are as small as possible with the directivity and emission angle of the initial emission light. The coincident and re-incident light that has passed through the circularly polarized light separating layer is emitted with a small number of reflection repetitions, especially without repetition of reflection.

In the above description, the coincidence of the emission angles of the re-emitted light and the initially-emitted light is poor, and if the emission directions are significantly different, their luminance cannot be added, and they cannot be effectively used for improving the visibility of a liquid crystal display device or the like. But rather in different directions at different angles.
One peak luminance is shown, and visibility is reduced. In this way, the highly parallelized outgoing light having excellent perpendicularity is formed through the light guide plate, and is separated into the initial outgoing light and the re-incident light through the circularly polarized light separating layer. A light guide plate in which it is difficult to re-emit with good consistency between the initially emitted light and the emission direction is not preferable when forming a polarized light source device.

In the present invention, as the circularly polarized light separating layer for forming the polarized light source device, an appropriate layer that separates 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, 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 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, in a single cholesteric liquid crystal layer, there is usually a limit to a wavelength region showing selective reflection (circular dichroism), and the limit may be a wide range up to a wavelength region of about 100 nm. However, since it does not cover the entire range of visible light desired when applied to liquid crystal display devices, etc., in such a case, a cholesteric liquid crystal layer with different selective reflection is superimposed to expand the wavelength range showing circular dichroism. Can be done.

In the case of a cholesteric liquid crystal layer, the central wavelength of selective reflection based on the liquid crystal phase is 300 to 900.
nm is a combination that reflects circularly polarized light in the same polarization direction,
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 light that can be reflected as circular polarized light outside the predetermined range matches the wavelength range of emitted light based on the light guide plate as much as possible 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, and there is no 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 cholesteric liquid crystal layer can be formed from a liquid crystal polymer by a method according to a 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 substrate, for example, an appropriate substrate such as a film made of a plastic such as triacetyl cellulose, polyvinyl alcohol, polyimide, polyarylate, polyester, polycarbonate, polysulfone, polyether sulfone, or epoxy resin, or a glass plate Can be used.

The solidified layer of the liquid crystal polymer formed on the substrate can be used as it is with the substrate as a circularly polarized light separating layer, or can be peeled off 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 can be developed by a heating and melting system or can be developed as a solution using 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 a suitable coating machine such as a bar coater, a spinner, a roll coater, and a gravure printing method. Upon development, a cholesteric liquid crystal layer superimposing method via an alignment film may be used as necessary.

The thickness of the cholesteric liquid crystal layer is 0.5 to 100 μm, preferably 1 to 100 μm, from the viewpoints of preventing the disorder of the alignment and the decrease of the transmittance and the selective reflection (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 in which a cholesteric liquid crystal layer composed of a low molecular weight substance is sandwiched between transparent substrates such as glass or film, and a cholesteric liquid crystal layer composed of a liquid crystal polymer is supported by a transparent substrate. , A cholesteric liquid crystal layer formed of a liquid crystal polymer film, or a form in which these forms are superimposed in an appropriate combination. In addition, the cholesteric liquid crystal layer can be adjusted according to its strength and operability.
It can also be supported by a layer or a support of two or more layers. 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.

It is preferable that the circularly polarized light separating layer is formed as a flat layer in order to make the above-mentioned separation performance uniform and to cope with the wavelength shift of the 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 shown in FIG. 14, when a linearly polarized light converting layer 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 becomes Receive 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 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 arranged on the circularly polarized light separating layer as necessary aims at converting the polarized light emitted from the circularly polarized light separating layer into a state having a large amount of linearly polarized light component. is there. 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 the display by directly entering the polarized light emitted from the circularly polarized light separating layer into the liquid crystal cell without using the polarizing plate, but it is possible to achieve the display by using the polarizing plate. A polarizing plate may be used as needed because it can improve the quality and the like.
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.

Incidentally, when natural light or circularly polarized light is made incident on a usual iodine-based polarizing plate, its transmittance is about 43%, but when linearly polarized light is made to coincide with the polarization axis, it becomes 80%. , The light use efficiency is greatly improved, and a liquid crystal display 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, 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 circularly polarized light separation 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. Preferably, it has a major axis direction in a parallel direction, and can convert it into flat elliptically polarized light 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 above-mentioned retardation layer,
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 can be formed of an appropriate material and preferably provides a transparent and uniform retardation. In general, a retardation plate is used.

The phase difference 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. 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 10
What gives a phase difference of 0 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.

In the case where two or more retardation plates are used in the visible light region, a layer having a phase difference of 100 to 200 nm as described above is often included as one or more odd layers, which has a large linear polarization component. 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 formed by stretching a film made of polycarbonate, polysulfone, polyester, polymethyl methacrylate, 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 phase difference and the direction of the optical axis to be set in the retardation layer can be appropriately determined according to the intended vibration 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, the polarized light source device according to the present invention prevents reflection loss and the like by reusing the reflected light (re-incident light) from the circularly-polarized light separating layer as the outgoing light by polarization conversion. If necessary, the light is converted to a light state containing a linearly polarized light component through a retardation layer or the like, so that the light can be easily transmitted through the polarizing plate to prevent absorption loss, thereby improving light use efficiency. . 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 having excellent light use efficiency and excellent brightness and excellent perpendicularity as described above, and are easy to increase the area and so on. It can be preferably used for various devices such as a backlight system in a device or the like. 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. 15 illustrates a liquid crystal display device 7 using the polarized light source device 6 according to the present invention in a backlight system. 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.

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 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.

Accordingly, the liquid crystal cell to be used is not particularly limited, and an appropriate one can be used. When a polarized 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 a liquid crystal cell using a twisted nematic liquid crystal or a super twisted nematic liquid crystal, for example. 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. A liquid crystal display device 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 purpose of the above-mentioned compensating retardation plate 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 a retardation plate for compensation, an appropriate retardation plate can be used according to a wavelength range or the like, and it may be formed as one or two or more superposed layers.

The light guide plate used in the liquid crystal display device preferably emits light in a direction perpendicular to or close to the upper surface. If the emitted light is shifted from the vertical direction, the light is emitted 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 components forming the light guide plate, the surface light source device, or the polarized light source device or the liquid crystal display device may be integrally or partially laminated and fixed. However, they may be arranged in an easily separable state. Various diffusion plates and the like can be arranged on the upper surface of the surface light source device, but in the case of a polarized light source device, a diffusion plate or the like that can maintain polarization characteristics is appropriately formed on the upper surface of the light guide plate or the upper surface of the retardation layer. Position.

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

In 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.

[0107]

Reference Example 1 A side-chain cholesteric liquid crystal polymer having an acrylic main chain and having a glass transition temperature of 57 ° C. was formed on a polyimide rubbed surface of a triacetyl cellulose film by spin coating, and then formed at 130 ° C. One additional 30 seconds after heating
The mixture was heated at 10 ° C. for 2 minutes and rapidly cooled to obtain a circularly polarized light separating plate having a mirror-like 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 cholesteric liquid crystal polymer having an acrylic main chain and having a glass transition temperature of 64 ° C. was formed on a polyimide rubbed surface of a triacetyl cellulose film by a spin coating method. 1 second after heating for 2 seconds
The mixture was heated at 20 ° C. for 2 minutes and rapidly cooled to obtain a circularly polarized light separating plate exhibiting a mirror-like 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 having a glass transition temperature of 75 ° C. was formed on a polyimide rubbed surface of a triacetyl cellulose film by a spin coating method. 1 second after heating for 2 seconds
The mixture was heated at 25 ° C. for 2 minutes and rapidly cooled to obtain a circularly polarized light separating plate exhibiting a mirror-like selective reflection state. This is 585-695
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 superposed circularly polarized light separating plate. This is 420
Good selective reflectivity was exhibited in the wavelength range of ６695 nm, and 90% or more was selectively reflected in the specular direction in this region.

Example 1 A thickness 1 over the entire width was set at a position corresponding to the incident surface as shown in FIG.
mm injection gate, width 195 mm, depth 15
0 mm, thickness of incident surface 5 mm, thickness of opposite end 1 mm, upper surface is flat, lower surface is curved surface (FIG. 6) projecting downward from the incident surface toward the opposite end near the plane, and perpendicular to upper surface 4 sides, and effective width 185 of the concave portion (FIG. 9a) parallel to the entrance surface
mm, a mirror-finished metal mold having a light guide plate forming part for transferring and forming the concave form shown in Table 1 was formed, and then subjected to release treatment, followed by pressure bonding and heating to 80 ° C. ° C
Polymethyl methacrylate melted by heating was filled through an injection molding machine, and after 120 seconds, the mold was opened to obtain a light guide plate.

The above concave portions are 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.

Example 2 As shown in FIG. 2, a light guide plate was used in the same manner as in Example 1 except that a mold having a 1 mm-thick and 20 mm-depth punching gate was additionally formed at a position facing the injection gate. Obtained. Table 2 shows the shape of the recess.

Example 3 According to Example 1, injection molding was performed using a mold for forming a wedge-shaped plate having a smooth lower surface without a prism array, and a 5 mm-thick plate was formed on the lower surface of the obtained plate. A light guide plate was obtained by providing light diffusion dots in which titanium oxide was dispersed in a pattern in which the area gradually increased from the incident surface toward the opposite end having a thickness of 1 mm.

Comparative Example 1 The width 3 was set at a side position 45 mm away from the position corresponding to the incident surface.
A light guide plate was obtained in the same manner as in Example 1, except that a mold having an injection gate having a thickness of 0 mm and a thickness of 1.5 mm and having the form shown in FIG. 3 was used. Table 2 shows the shape of the recess.

Comparative Example 2 A width 3 was set at a side position 45 mm away from the position corresponding to the incident surface.
According to Example 3, except that a mold having an injection gate of 0 mm and a thickness of 1.5 mm and a wedge-shaped plate having a smooth lower surface and having no prism array was used, a mold according to FIG. 3 was used. A light guide plate was obtained.

[0117]

[Table 1]

[0118]

[Table 2]

Evaluation Test 1 Retardation Distribution The retardation of the light guide plates obtained in Examples and Comparative Examples was examined with a birefringence measuring apparatus (ADR-100XY, manufactured by Oak Co., Ltd.). 16 (Example 1) and FIG. 17 (Comparative Example 1) show the distribution of the phase difference and the optical axis of the light guide plate obtained in Example 1 and Comparative Example 1. The numerical value in the figure is the phase difference (nm), the line is the direction of the optical axis, and in Comparative Example 1, the injection gate was located on the left side surface in the figure.

Natural Light Luminance A cold-cathode tube having a diameter of 3 mm was arranged on the incident surface of the light guide plate obtained in each of the examples and comparative examples. The cold-cathode tube was surrounded by a light source holder made of a silver-evaporated polyester film. A reflective sheet made of a silver-evaporated polyester film is disposed on the lower surface of the light plate to obtain a sidelight type surface light source device, and a polarizing plate (G1220DUN) is disposed on the upper surface thereof to turn on the light source and the width of the light guide plate. The surface luminance in the vertical direction at each position at the center of the upper surface in the direction is measured using a colorimeter (Cinolta, C
S-100) in a dark room.

Polarization Luminance The circularly polarized light separating plate obtained in Reference Example 4, a phase difference plate having a phase difference of 130 nm, and a polarizing plate are sequentially arranged on the upper surface of the above-mentioned surface light source device to obtain a polarized light source device. The surface luminance was examined according to the method. The rotation of the polarizing plate was adjusted so as to exhibit the maximum luminance.

The results are shown in Tables 3, 4 and 5.

[Table 3]

[0123]

[Table 4]

[0124]

[Table 5]

From Tables 1 and 2, Examples 1 and 2 and Comparative Example 1 were obtained.
Table 3 shows that the lower surface structure of the light guide plate is almost the same.
It is considered that there is almost no difference in luminance between the natural light from the surface light source device and the influence of the lower surface structure of the light guide plate on the luminance. It can be seen from Tables 3, 4, 5 and FIGS. 16 and 17 that the phase difference and the change in the optical axis direction are larger in the comparative example. From these points, it can be evaluated that the mold according to the present invention is effective in suppressing the phase difference and the change in the optical axis direction.

In comparison with Tables 3, 4 and 5 between Examples 1 and 2 and Comparative Example 1 and between Example 3 and Comparative Example 2, the luminance ratio of the polarized light source / natural light source is small in the portion where the phase difference is large. In the comparative example, the degree of improvement in luminance based on the luminance ratio is poor and the change in luminance depending on the position is large, but in the example, the degree of improvement in luminance based on the luminance ratio is large and the change in luminance depending on the position is small. I understand. From these points, when the polarizing light source is used, the phase difference and the change in the optical axis direction have a large effect, and it can be evaluated that the polarizing plate by the mold of the present invention is effective for improving the brightness when the polarizing light source is used. .

Further, from Tables 3, 4 and 5, the effectiveness is as follows:
It can be seen that this is also true when the lower surface structure is the diffusion dot structure according to the third embodiment. However, as compared with the first and second embodiments and the third embodiment, the finer prism structure than the diffusion structure improves the brightness of the polarized light source. It can be evaluated as advantageous.

Evaluation Test 2 A twisted nematic liquid crystal cell was arranged on the polarizing plate of the above-mentioned polarized light source device using the light guide plate of Example 1 or Comparative Example 1, and a polarizing plate was arranged thereon to display a liquid crystal. When the device was obtained and its surface brightness was compared, in the example, almost the entire surface was able to realize a bright display with uniform brightness, but in the comparative example, the difference in brightness was large, and the overall brightness was lower than in the example. The display is dark, and the display is particularly dark at a position corresponding to the portion where the phase difference is large in FIG.

From the above results, a circularly polarized light separating layer is disposed on a light guide plate having a small phase difference and a small change in the optical axis by the mold of the present invention to provide a polarized light having excellent uniform luminance on the entire exit surface. It can be seen that a light source device can be obtained, and a bright and easy-to-see high-quality liquid crystal display device can be formed using the light source device.

[Brief description of the drawings]

FIG. 1 is an explanatory perspective view of an example of a mold.

FIG. 2 is an explanatory perspective view of another mold example.

FIG. 3 is an explanatory perspective view of a conventional mold.

FIG. 4 is an explanatory perspective view of an example of a light guide plate.

FIG. 5 is an explanatory side view of another example of the light guide plate.

FIG. 6 is an explanatory side view of still another example of the light guide plate.

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

FIG. 8 is an explanatory side view of an example of a convex portion;

FIG. 9 is an explanatory side view of an example of a concave portion.

FIG. 10 is an explanatory side view of still another light guide plate example.

FIG. 11 is a side sectional view illustrating an example of a surface light source device.

FIG. 12 is a side sectional view of another example of the surface light source device.

FIG. 13 is a cross-sectional side view illustrating an example of a polarized light source device.

FIG. 14 is a side sectional view illustrating another example of the polarized light source device.

FIG. 15 is a side sectional view illustrating an example of a liquid crystal display device.

FIG. 16 is an explanatory plan view of a phase difference distribution of the light guide plate according to the first embodiment.

FIG. 17 is an explanatory plan view of a phase difference distribution of the light guide plate of Comparative Example 1.

[Explanation of symbols]

K1: Light guide plate forming part K2: Injection gate K3: Open gate 1: Light guide plate 11: Upper surface 12, 16, 17, 18: Lower surface 21, 22, 23, 24: Projection on lower surface 25, 26, 27, 28: Depressions 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: Diffusion layer 54: Reflector 6: Polarized light source device 61: Polarization separation device 62: Phase difference layer (linear polarization conversion device) 7: Liquid crystal display device 71, 74: Polarized light Plate 72: Liquid crystal cell 73: Diffusion layer

Claims (11)

[Claims] 1. A mold for molding a light guide plate which emits light incident from one side surface of a plate-like object from one of upper and lower surfaces by a polymer injection and filling method, and corresponds to at least one side surface of the plate-like material. A light guide plate mold having a polymer injection gate over substantially the entire width of a side surface thereof. 2. The light guide plate mold according to claim 1, wherein an injection gate over the entire width is provided at a position corresponding to a light incident surface of the light guide plate or a side surface thereof. 3. The mold for a light guide plate according to claim 1, wherein a mold is provided at a position facing the injection gate over the entire width, and the gate is substantially free of polymer. 4. The light guide plate mold according to claim 1, wherein a side surface other than the surface having the injection gate or the extraction gate is mirror-finished. 5. The light guide plate mold according to claim 1, wherein the light guide plate has periodically formed fine prismatic irregularities in at least one of the upper and lower surfaces in the direction of the incident surface. 6. A light guide for forming a light guide plate having an end face which is thinner than an incident face, based on a substantially continuous change of one of the upper and lower faces which is not the exit face. Light plate mold. 7. A method for manufacturing a light guide plate, comprising injection molding using the mold according to claim 1. 8. A light guide plate formed by using the mold according to claim 1. Description: 9. A polarized light source device comprising a light guide plate according to claim 8, and a circularly polarized light separating layer disposed on the light exit surface side. 10. A liquid crystal display device comprising the light guide plate according to claim 8 on one side of a liquid crystal cell. 11. A liquid crystal display device comprising the polarized light source device according to claim 9 on one side of a liquid crystal cell.