JP3361012B2 - Polarized light source device and liquid crystal display device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarized light source device which is excellent in light utilization efficiency and which prevents generation of moire between a light guide plate showing uneven brightness and a liquid crystal cell, and good visibility which is excellent in brightness utilizing the same. Liquid crystal display device.

[0002]

[Background Art] Conventionally, a reflective layer is closely attached to the lower surface of a sidelight type light guide plate that allows light to enter from the side surface and to exit from the upper surface, and a circularly polarized light separating layer made of a cholesteric liquid crystal phase is provided on the exit surface. Through the circularly polarized light separation layer, the incident light is separated into left and right circularly polarized transmitted light and reflected light,
There has been proposed an illumination system in which the reflected light is reflected through a reflection layer on the lower surface and re-emitted from the emission surface (Japanese Patent Laid-Open No. 3-45906 and Japanese Patent Laid-Open No. 32-3243).
3 and JP-A-7-36032).

In the above-mentioned illumination system, about 55% of the light emitted from the light guide plate is absorbed by the non-polarized ordinary light when it passes through the polarizing plate, and the light that can be effectively used is poor. The purpose of this is to prevent the absorption by the polarizing plate so that the light can be supplied, thereby improving the light utilization efficiency and improving the brightness of the liquid crystal display device and the like. However, none of these lighting systems
It was found that those that should have a light use efficiency of more than 0% do not show the expected value.

That is, in JP-A-6-324333 and JP-A-7-36032, since the lower surface is a diffusion type or scattering type reflection layer, re-emission is performed by eliminating the randomness of the emission direction or the polarization state. The amount of light decreases. on the other hand,
In the metal reflective layer taught by Japanese Patent Application Laid-Open No. 3-45906, the circularly polarized light that is re-incident through the circularly polarized light separating layer is reflected by the reflective layer and travels toward the light source side, thereby lowering the utilization efficiency of the re-incident light. .

[0005]

In view of the above, the group to which the present inventors belong is that the incident light from the side surface is efficiently emitted from the emission surface and the re-incident light via the circularly polarized light separating layer is also efficiently emitted. As a result of intensive research to obtain a light guide plate with excellent light utilization efficiency, the light guide plate that emits light through fine prismatic irregularities succeeded in that, and was previously proposed (Patent application 7 No. 321036).

However, bright and dark unevenness in the form of bright lines appears on the light guide plate due to the emission through the fine prismatic irregularities, and this causes moire with the pixels of the liquid crystal cell to visually confirm the liquid crystal display device. It has been found to reduce the sex.
Moire can be prevented by setting the pitch of the prismatic irregularities to about ⅕ of the pixel interval, but in that case, the pitch of the prismatic irregularities needs to be about several μm. In addition, it causes a problem that the display quality is greatly deteriorated due to the interference due to the fine pitch and the dispersion due to the diffraction.

Therefore, the present inventors have tried to level the above-mentioned bright and dark unevenness with a diffusion layer. However, with the conventional diffusion sheet, the polarization state is eliminated and the light utilization efficiency is reduced,
It was found that there is a problem that hinders a dramatic improvement in light reuse efficiency through fine prismatic irregularities. Therefore, according to the present invention, the incident light from the side surface is efficiently emitted from the emission surface, and the re-incident light via the circularly polarized light separating layer is also efficiently emitted to prevent uneven brightness of the emitted light by the light guide plate which is excellent in light utilization efficiency. To develop a polarized light source device capable of achieving a liquid crystal display device which is excellent in brightness and does not cause moire.

[0008]

Means for Solving the Problems According to the present invention, at least one of upper and lower surfaces has fine prismatic irregularities, and the incident light from a side surface is emitted from one of the upper and lower surfaces in a state with uneven brightness and darkness. Has a circularly polarized light separation layer and a diffusion layer, and the diffusion layer
Is the polarized light based on the light reflected or transmitted by the circularly polarized light separation layer.
Provided is a polarized light source device, which is arranged at a position where the light passes through, and whose diffusion layer has a phase difference of 30 nm or less based on vertically incident light having a wavelength of 633 nm.

[0009]

According to the present invention, the circularly polarized light which is reflected through the circularly polarized light separating layer and re-enters the light guide plate is reflected through the metal reflection layer or the like on the lower surface portion to invert the polarization state so that the circularly polarized light separating layer is obtained. Is efficiently emitted as light that can be transmitted through the liquid crystal, and the emitted light having uneven brightness is leveled through the diffusion layer with almost no change or cancellation of the polarization state due to phase difference or diffusion. It is possible to obtain a polarized light source device capable of improving the display brightness of a display device or the like. In the above, if there is a large phase difference in the diffusion layer, the circularly polarized light emitted or re-incident through the circularly polarized light separating layer is converted into elliptically polarized light, and the elliptically polarized light is a composite of the linearly polarized light component and the circularly polarized light component. Since the component does not pass through the circularly polarized light separating layer, the light utilization efficiency is reduced.

Further, in the wavelength range in which the diffusion layer functions as a quarter wave plate or a wave plate corresponding to an odd multiple thereof, circularly polarized light is linearly polarized, so that re-incident light through the circularly polarized light separating layer is re-incident. Since it cannot pass through the circularly polarized light separating layer, the light utilization efficiency does not increase. Furthermore, the irregularity of the direction of the optical axis in the diffusion layer, the change of the influence phase difference due to the incident and transmission angles of light, and the influence of the phase difference depending on the wavelength, etc. The polarization conversion efficiency of the circularly polarized light, the major axis direction of the elliptically polarized light, and the like are greatly varied, so that the overall polarization conversion efficiency is significantly reduced and the utilization efficiency of the re-incident light is reduced.

[0011]

The polarized light source device of the present invention has a light guide plate that has fine prismatic irregularities on at least one of the upper and lower surfaces and emits incident light from the side surface from one of the upper and lower surfaces in a state with uneven brightness. of having a circularly polarized light separation layer and a diffusion layer on the emitting surface side and the reflected diffusion layer according to the circularly polarized light separation layer or transmitted light
Is arranged at a position where polarized light based on
The phase difference of the diffusion layer is 30 nm or less based on vertically incident light having a wavelength of 633 nm. Examples thereof are shown in FIGS. 1, 2 and 3. Reference numeral 1 is a light guide plate, 3 is a diffusion layer, 4 is a circularly polarized light separating layer, 2 is a reflecting layer, and 5 is a retardation layer functioning as a linearly polarized light converting means.

The polarized light source device shown in the figure comprises a diffusion layer 3, a circularly polarized light separation layer 4 and, if necessary, a retardation layer 5 arranged above an emission surface (upper surface) 11 of the light guide plate 1. The diffusion layer is, as shown in the figure, between the light guide plate 1 and the circularly polarized light separation layer 4, between the circularly polarized light separation layer 4 and the phase difference layer 5, or the light emission side of the phase difference layer 5 such as the light emission side of the light guide plate. It can be arranged at an appropriate position on the side.

In the above, the light guide plate is intended to emit incident light from the side surface from one of the upper and lower surfaces and to re-emit the re-incident light that has passed through the circularly polarized light separating layer from the circularly polarized light separating layer. The circularly polarized light separating layer is intended to convert incident light having no polarization property into left and right circularly polarized light as transmitted light or reflected light to convert it into polarized light and take it out. The diffusion layer is
An object of the present invention is to equalize the brightness unevenness of the light emitted from the light guide plate and to make the brightness of the emitted light as uniform as possible over the entire surface. The retardation layer is intended to linearly polarize circularly polarized light emitted through the circularly polarized light separating layer into light that easily passes through the polarizing plate.

In the present invention, as the light guide plate, one having fine prismatic irregularities on at least one of the upper and lower surfaces to emit incident light from the side surface from one of the upper and lower surfaces with uneven brightness is used. Examples of such a light guide plate are shown in FIGS. As shown in the drawing, the light guide plate is usually formed of a plate-like object having upper and lower surfaces, one of which is an emitting surface, and an incident surface having at least one side end surface between the upper and lower surfaces. In the example shown in the figure, the top surface serves as the exit surface, and 11 is the exit surface, 1
2, 16, 17, and 18 are lower surfaces, and 13 is an incident surface. Reference numeral 14 is a side surface, and 15 is a side end portion facing the incident surface 13.

The light guide plate guides the circularly polarized light re-incident through the circularly polarized light separating layer to the lower surface while maintaining its circularly polarized state in good condition without the influence of the phase difference, and returns the return light reflected by the lower surface to the circularly polarized light. From the viewpoint of emitting light while maintaining the state, it is preferable that the retardation due to birefringence in the thickness direction is as small as that of the diffusion layer, and is preferably 30 nm or less, particularly 0 to 20 nm.

The shape of the light guide plate is excellent in the emission efficiency from the emission surface, the emitted light is excellent in the perpendicularity to the emission surface, and is easily used effectively, and also the emission efficiency of the re-incident light through the circularly polarized light separating layer is improved. Although not particularly limited in terms of the closeness of the outgoing direction to the initial outgoing direction, as shown in the figure, fine prismatic irregularities are used to form convex or concave parts consisting of long and short sides. The structure having a specific structure is preferable. Further, it is preferable that the thickness of the side end portion facing the incident surface is thinner than that of the incident surface, and preferably 50% or less.

The reduction of the thickness of the end portion on the opposite side to the incident surface is as follows: The light incident from the incident surface reaches the end portion on the opposite side as the transmission end, as shown by the thick arrows in FIGS. 8 and 9. This is advantageous in that the light can be efficiently incident on the short side surface of the prismatic concave-convex surface, emitted from the emission surface via the 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 made lighter, and for example, when the prismatic uneven surface is linear as shown in FIG. 5, the weight can be about 75% of that of the light guide plate having a uniform thickness.

The convex portion or concave portion forming the prism-shaped irregularities is usually formed by an inclined surface composed of a long side surface and a short side surface in the direction along the incident surface. By the way, examples of the convex portion or the concave portion are shown in FIGS. 8A to 8D and FIGS. 9A to 9D. In FIG. 8 and FIG. 9, 21, 22, 23 and 24 are convex portions, 25, 26, 27 and 28 are concave portions, and 31,
Slopes 33, 35, 37, 42, 44, 46 and 48 forming long side surfaces, 32, 34, 36, 38, 41, 4
3, 45 and 47 are slopes forming the short side surface.

The protrusions or recesses are formed periodically. That is, for example, FIG. 4 and FIG. 8A or FIG. 9A
4 based on the above, the convex portion 2 composed of the slopes 31, 32 or 41, 42 in the direction along the incident surface 13 as shown by the arrow in FIG.
1 or concave portions 25 are periodically provided.

It should be noted that the above-mentioned convex portion or concave portion is based on a straight line connecting the intersection points of the slope forming the convex portion or the concave portion with the reference plane, and whether the intersection point (vertex) of the slope surface protrudes from the straight line (convex). , Depending on whether it is recessed (concave). That is, in FIG.
Based on the example illustrated in FIG. 9, the convex portions (21, 22, 2
3, 24) or bevels (31 and 32, 33 and 34, 35 and 36, 37) forming recesses (25, 26, 27, 28).
And 38, 41 and 42, 43 and 44, 45 and 46, 47 and 48), the straight line 20 shown by the imaginary line connecting the intersections with the reference plane.
On the basis of the above, it depends on whether the intersection (vertex) of the slope surface is projected (convex) or recessed (concave) from the straight line 20.

Further, the long side surface and the short side surface of the slope forming the convex portion or the concave portion are judged based on the straight line connecting the intersection and the apex with the reference surface, but the point that the utilization efficiency of light is improved. Therefore, it is preferable that the projected area of the long side surface with respect to the exit surface is 3 times or more, and especially 5 times or more that of the short side surface.
Furthermore, in the case of a convex portion, the long side surface is arranged on the incident surface side, and in the case of a concave portion, it is arranged so as to be located on the side end side facing the incident surface. The long side is
In the case of a concave portion, it is preferable to arrange so that the short side surface is located.

That is, the slope, for example, FIGS. 4 and 8
In the case of FIG. 9A or FIG. 9A, the slopes 31 and 32 or 41 and 42 forming the convex portion 21 or the concave portion 25 are straight lines connecting the intersections with the reference plane (corresponding to the virtual line 20) and the vertices. (Corresponding to a virtual line in the case of b, c and d in FIGS. 8 and 9)
It is assumed that the long side surfaces 31, 42 and the short side surfaces 32, 41 are formed on the basis of the above, and the projection area of the long side surfaces 31, 42 is three times or more of that of the short side surfaces 32, 41. And the long side surface 3 in the case of the convex portion 21.
1 is on the incident surface 13 side, and in the case of the concave portion 25, the long side surface 42
Is preferably arranged so as to be located on the side end side 15 facing the incident surface.

As described above, in addition to the transmitted light that is directly incident on the short side surface, the transmitted light that is incident on the long side surface and is reflected by the short side surface is also emitted by reflection through the short side surface. The light can be supplied (emitted) to the surface, and the light utilization efficiency can be improved. 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, and from this point, a preferable projection area for the emission surface of the long side surface is , More than 5 times that of the short side, especially 1
It is 0 to 100 times. The uneven brightness of the light emitted from the light guide plate is largely due to the area difference between the short and long side surfaces, and the light emitted through the short side surface is likely to be a bright line.

The shape of one or both of the upper and lower surfaces of the light guide plate on which the prismatic irregularities are provided may be appropriately determined. Preferably, as described above, as the inclined surface, the end portion on the opposite side of the incident surface is made thinner. In that case, the shape of the inclined surface may be arbitrarily determined, and may be an appropriate surface shape such as a linear surface illustrated in FIG. 5 or a curved surface illustrated in FIGS. 6 and 7. If it is not a straight surface, it is more than 5 from the average tilt angle at all positions of the surface where the prismatic unevenness is provided, rather than the point of making the outgoing direction of outgoing light from the outgoing surface uniform.
It is preferably within the range.

The shape of the prismatic irregularities provided is also shown in FIG.
As illustrated in FIGS. 9A to 9D, it does not need to be formed by a linear slope, and may be formed by a slope including a refraction surface and a curved surface. Good. In addition, the projections or recesses do not need to have the same projections and recesses or the same shape on the entire prism-shaped concavo-convex surface, and the shape and angle gradually change from the incident side rather than the point of obtaining emitted light with excellent verticality. The structure is preferred.

The pitch of the convex portions or concave portions on the prismatic concave and convex surface is such that the emitted light is emitted in stripes through the convex portions or concave portions, so that uneven brightness is suppressed and moire with the liquid crystal cell is prevented. The smaller the better. The preferable cycle of the convex portion or the concave portion in consideration of manufacturing accuracy is 500
It is less than or equal to μm, preferably less than or equal to 300 μm, and particularly 20 to 250 μm. If the period is less than 20 μm, the production efficiency is poor in terms of manufacturing accuracy, and if it is less than several μm, dispersion due to interference or diffraction increases and it becomes unsuitable for a backlight for a liquid crystal display device.

The long side surface of the inclined surface forming the convex portion or the concave portion has an inclination angle θ ₁ with respect to the emission surface 11 of 0 to 10 degrees, preferably 5 degrees or less, as shown in FIGS. 8 and 9.
Particularly, it is preferably twice or less. By setting such an inclination angle range, light transmitted at an angle larger than the inclination angle is incident on the long side surfaces 31, 42 as illustrated by the broken line arrows in FIGS. 8A and 9A. In that case, the light is reflected by the emission surface 11 based on the inclination angle of the long side surface, reflected at a more parallel angle, enters the short side surfaces 32, 41, and is reflected and emitted from the emission surface 11.

As a result, the incident angle of the light incident on the short side surface can be made constant, the variation in the reflection angle can be suppressed, and the emitted light can be made parallel. Therefore, by adjusting the inclination angle of the long side surface and the short side surface of the slope forming the convex portion or the concave portion, it is possible to give the emitted light directivity, and thereby, the direction perpendicular to the emission surface or It becomes possible to emit light at a close 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, if the inclination angle of the long side surface exceeds 10 degrees,
The ratio of the projected area of the long side surface to the emission surface is reduced, and the ratio of transmitted light whose emission direction can be controlled via the long side surface is reduced.
In addition, the variation in the reflection angle between the transmitted light that has entered the short side surface via the long side surface and the transmitted light that has directly entered the short side surface becomes large, and the controllability of making the emitted light parallel light decreases. The directivity of emitted light becomes poor. When the inclination angle of the long side surface is 0 degree, it is disadvantageous in collimating the emitted light, but it is allowed in the present invention.

On the other hand, the above-mentioned short side surface of the inclined surface forming the convex portion or the concave portion has an inclination angle θ ₂ with respect to the emission surface 11 of 25 to 50 degrees, preferably 30 degrees or more, as illustrated in FIGS. 8 and 9. Is preferred. By setting the range of such an inclination angle, as shown by broken line arrows in FIGS. 8A and 9A, the transmitted light incident directly or through the long side surfaces can be transmitted through the short side surfaces 32 and 41. It is possible to efficiently emit light in a direction in which the light is reflected perpendicularly to the emission surface 11 or at an angle close thereto and effectively acts to improve the visibility of the liquid crystal display device or the like. If the inclination angle of the short side surface is outside the above range, the deviation from the vertical direction becomes large, it is difficult to give the emitted light vertical directivity, and the emission efficiency (utilization efficiency) of the transmitted light also decreases.

Regarding the shape of the incident surface of the light guide plate,
There is no particular limitation and it may be appropriately determined. Generally, it is a surface perpendicular to the emission surface, but it is also possible to improve the incident light rate by forming a shape such as a curved concave shape according to the outer circumference of the light source or the like. Further, it is also possible to adopt an incident surface structure having an introduction portion interposed between the light source and the light source. The introduction part may have an appropriate shape depending on the light source and the like.
The shape of the emission surface is generally a flat surface, but if necessary, fine prismatic irregularities as described above can be provided, or a diffusion layer can be provided.

The light guide plate can be formed of an appropriate material that is transparent according to the wavelength range of the light source. By the way, in the visible light region, for example, an acrylic resin such as polymethylmethacrylate, a polycarbonate resin such as polycarbonate or a polycarbonate / polystyrene copolymer, a transparent resin typified by an epoxy resin, or a glass of about 400 to 700 nm is used. Those that exhibit transparency in the wavelength range are mentioned.

The light guide plate can be formed by an appropriate manufacturing method.
As a preferable manufacturing method from the viewpoint of mass productivity and the like, for example, a liquid resin that can be polymerized by heat, ultraviolet rays or radiation,
A method of polymerizing by filling or casting into a mold capable of forming a predetermined prismatic unevenness, or a method of transferring a shape by pressing a thermoplastic resin under heating to a mold capable of forming a predetermined prismatic unevenness, Examples include a method of filling a heat-melted thermoplastic resin or a resin fluidized through heat or a solvent into a mold that can be molded into a predetermined shape.

The light guide plate may be formed as a laminated body of different materials, such as a sheet in which a prism-shaped uneven surface forming sheet is adhered to a light guide portion for transmitting light, and may be formed of one kind of material. It need not be formed as an integral monolayer. The thinning of the light guide plate described above is more advantageous in terms of weight saving and reduction of required materials, but from the point of securing the necessary incident light amount because the incident light amount is reduced by reducing the incident surface. There is a limit.

In the above-mentioned light guide plate, the characteristics such as the angular distribution and the in-plane distribution of the outgoing light are controlled based on the control of the area ratio and the inclination angle of the short side surface and the long side surface, the shape and the curvature of the prismatic uneven surface. Can be adjusted. By the way, in the case of a light guide plate in which the refractive index is 1.5 and the prismatic concave-convex surface has no curvature, and the initial emission light is emitted vertically, the inclination angle of the long side surface with respect to the emission surface is 6.6 degrees or less. Thus, the re-incident light that has passed through the circularly polarized light separating layer can be re-emitted with an angle change within 10 degrees. Further, in that case, when the prismatic concave-convex surface has a curvature, the re-incident light can be changed within an angle of 10 degrees by having a portion in which the inclination angle is 6.6 degrees or less in a ratio of the predetermined area or more. It can be re-emitted.

The thickness of the light guide plate can be appropriately determined depending on the size of the light guide plate and the size of the light source depending on the purpose of use. When used in a liquid crystal display device, the light guide plate generally has a thickness of 20 mm or less, preferably 0.1
-10 mm, especially 0.5-8 mm. In addition, the general area ratio of the entrance surface and the exit surface is 1/5 to 1 based on the former / the latter.
/ 100, especially 1/10 to 1/80, especially 1/15 to 1
/ 50. By the way, when parallel light is incident from the incident surface, it is possible to make all of the incident light incident on the short side surface by making the short side surface of the integrated thickness corresponding to the thickness of the incident surface,
In that case, assuming that the inclination angle of the short side surface is 45 degrees and the inclination angle of the long side surface is 0 degrees, the area ratio of the incident surface / the emission surface is about 1/30.

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

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

1 and 2 are provided on the opposite surface of the light emitting surface of the light guide plate.
If desired, a reflective layer 2, preferably a metal reflective layer, may be arranged as illustrated in FIG. The reflective layer is effective in preventing the generation of leaked light from the facing surface and improving the emission efficiency, and functions as a polarization conversion unit of the polarized light source device. The reflection layer may be integrated with the facing surface, or may be laminated as a reflection sheet or the like, and in the present invention, an appropriate arrangement form can be adopted.

In the above case, the reflection layer made of metal can efficiently invert the polarization characteristic at the time of reflection, and the polarization conversion efficiency thereof is higher than that of the case of total reflection or diffuse reflection through an interface having a different refractive index. Are better. By the way, when circularly polarized light is incident substantially perpendicularly to the metal surface, the conversion efficiency of the left and right of the circularly polarized light is close to 100%, and the conversion efficiency of 90% or more is shown up to an incident angle of about 30 degrees.

A metal reflecting layer which is preferable from the viewpoint of polarization conversion efficiency has a metal surface containing at least one metal having a high reflectance, such as aluminum, silver, gold, copper or chromium. The metal reflection layer, which has excellent adhesion to the facing surface of the light exit surface of the light guide plate, can be formed as a coating layer in which metal powder is mixed with a binder resin, an additional layer of a metal thin film by a vapor deposition method, or the like. The metal reflection layer may be formed as a multi-layer 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 or preventing oxidation, if necessary.

As for the reflective layer, instead of the reflective layer 2 or together with the reflective layer, a reflective plate 6 may be provided along the facing surface of the emission surface of the light guide plate as illustrated in FIG. The method of providing the reflection plate on the facing surface of the light guide plate has an advantage that the re-emission angle of the re-incident light through the circularly polarized light separation layer can be reduced when the inclination angles of the long side surfaces are the same. For the reflector, it can be based on the above-mentioned reflective layer,
A reflector having a metal reflecting surface can be preferably used. Therefore, as the reflection plate, a resin sheet provided with a metal thin film, a metal foil, a metal plate, or the like can be used. The surface of the reflection plate does not necessarily need to be a mirror surface, and may be formed uniformly as a plurality of surfaces with a small angle or a continuous curved surface.

As the reflection plate, the half angle of the half-value width of the spread of the reflection angle of the reflected light when parallel light is incident is within 10 degrees, especially 5 because of the fact that the spread of the re-emitted light is suppressed.
Those within the degree are preferable. Therefore, as the reflection plate, an appropriate one having a high reflectance and a small spread of the reflection angle and which does not cause diffuse reflection can be used. It may have irregularities or a rough surface such as a rolling roll so that the reflection angle of the reflected light is slightly widened.

According to the above-mentioned light guide plate, it is used to emit highly collimated light in a direction having excellent verticality, which is advantageous for visual recognition, and makes efficient use of the light from the light source to increase the brightness. An excellent polarized light source device can be obtained, and various devices such as a liquid crystal display device which is bright and easy to see and excellent in low power consumption can be formed.

The sidelight type backlight is usually formed by disposing the light source 7 on the incident surface of the light guide plate as shown in the figure. Any appropriate light source can be used as the light source, but for example, a linear light source such as a (cold or heat) cathode tube, a point light source such as a light emitting diode, or an array body having a linear or planar shape thereof can be preferably used. A cold cathode tube is particularly preferable in terms of low power consumption and durability. When forming the backlight, a light source holder 71 that surrounds the light source for guiding the divergent light from the linear light source to the side surface of the light guide plate, and a prism for controlling the emission direction of the light, as necessary, as shown in the figure. It is also possible to make a combination body in which an appropriate auxiliary means such as a sheet is arranged.

As the light source holder, a resin sheet or a metal foil provided with a high reflectance metal thin film is generally used. When the light source holder is adhered to the end portion of the light guide plate via an adhesive or the like, the prismatic unevenness can be omitted in the adhered portion. Further, the light source holder may be extended to a predetermined surface of the light guide plate so that it also serves as a reflection plate.

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

That is, most of the light re-incident through the circularly polarized light separating layer is emitted to the long side surface by emitting highly parallelized light excellent in verticality, and the angle is determined based on the gentle inclination angle. It is preferable to use a light guide plate that reflects light without significantly changing the angle, and re-emits light in a direction close to the initial outgoing light by reflection with little change in angle, and thus with good verticality. According to such a light guide plate, the initial emission light and the re-emission light have excellent coincidence in direction, and the first re-incident light is efficiently emitted without repeated reflection, and light having excellent polarization characteristics is utilized with less loss. It can be obtained in excellent condition.

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

In the above, the coincidence of the emission angles of the re-emitted light and the initial emitted light is poor, and if the emission directions are largely different, their brightness cannot be added, and they cannot be effectively used for improving the visibility of a liquid crystal display device or the like. But rather 2 in different directions
It shows two peak luminances and reduces visibility.

In the scattering reflection type or diffuse reflection type light guide plate described above, the re-incident light that has passed through the circularly polarized light separation layer passes through the scattering reflection or diffuse reflection (dots) that has passed through the lower surface of the light guide plate, and the circularly polarized light separation layer. In this case, since the emitted light has poor directivity and is re-incident as scattered light, the conversion efficiency through the circularly polarized light separation layer cannot exceed 50%, and the light utilization efficiency is reduced. Poor in enhancing effect. In addition, the emission angle of the emitted light is also poor in verticality, which is inconvenient for a display such as a liquid crystal display that deteriorates visibility. Many are included.

Even if a prism sheet is arranged on the exit surface of the light guide plate to correct the verticality, the light is reused because it is incident on the reflection surface on the lower surface of the light guide plate at an angle largely deviated from the vertical direction. Poor effect of increasing efficiency. Therefore, as in the present invention, the outgoing light that is highly accurately parallelized through the light guide plate and has excellent verticality is formed, and is separated into the initial outgoing light and the re-injected light through the circularly polarized light separating layer, and the re-incident light is re-injected. It is difficult to re-emit the light with good matching in the emission direction with the initial emission light.

It is preferable that the diffusion layer has a larger divergence angle of the light in order to level the uneven brightness of the light emitted from the light guide plate. That is, as the light emitted from the light guide plate is diffused and spread, the more the light is incident on many pixels of the liquid crystal cell, the more the glare due to the moire due to the interference with the pixels is suppressed. On the other hand, as described above, the smaller the divergence angle of the light is, the more preferable from the viewpoint of the polarization conversion efficiency of the re-incident light that has passed through the reflection layer of the light guide plate.

Therefore, the spread angle based on the full width at half maximum of light is 30 based on the spread angle when the parallel light is incident (half width at half maximum, the same hereinafter) from the viewpoint of the above-mentioned leveling and polarization conversion efficiency.
An angle that is less than or equal to a degree and can enter two or more pixels is preferable. The angles that can enter the two or more pixels are determined by the size and pitch of the pixels, the distance between the diffusion layer and the pixels of the liquid crystal cell, and the like.

By the way, when the pixel pitch is 330 μm, the substrate thickness of the liquid crystal cell is 700 μm, and the diffusion layer is arranged immediately in front of the liquid crystal cell substrate, the divergence angle by diffusion is set to 13 ° or more so that the light is incident on a plurality of pixels. Can be 2
At 5 degrees, the light can always be incident on 3 pixels or more. Therefore, when a retardation layer or the like is interposed between the diffusion layer and the liquid crystal cell substrate or when the pixel pitch is small, the light can be made incident on a plurality of pixels with a narrower spread angle.

On the other hand, the leveling of the uneven brightness of the light emitted from the light guide plate can also be performed by mixing a plurality of bright lights (short side surfaces), preferably adjacent bright lights. By the way, when the pitch of the prismatic irregularities in the wedge-shaped light guide plate is 200 μm and the refractive index is 1.5, the divergence angle at which the light emitted from the adjacent short side faces can be mixed is 17 degrees in the portion with a thickness of 1 mm. . Considering the width of the short side surface, adjacent bright lights can be mixed even if the angle is smaller. The same applies when the thickness of the light guide plate is thicker than 1 mm.

The divergence angle due to the diffusion layer is 30.
When the angle exceeds the angle, the angle of the light emitted from the polarized light source device becomes wider, the amount of light emitted in an unnecessary direction increases, and the light re-incident at a large angle becomes stray light, which reduces the effective use of light. FIGS. 10A and 10B show the difference in brightness unevenness depending on the presence or absence of the diffusion layer. (A) is the one without the diffusion layer 81, and (b) is the one 8 with the diffusion layer.

The diffusion layer in the present invention has a phase difference of 30 nm or less based on vertically incident light having a wavelength of 633 nm,
It is preferably 0 to 20 nm. Angle of incidence 30
It is more preferable that the phase difference is 30 nm or less based on the light having a wavelength of 633 nm which is incident within the range of 0 to 20 nm.

As described above, if the diffusion layer has a large phase difference, the circularly polarized light passing through the circularly polarized light separating layer is converted into elliptically polarized light, and the linearly polarized light component of the elliptically polarized light cannot be transmitted through the circularly polarized light separating layer. It reduces the efficiency of light utilization. Further, in the wavelength range in which the light guide plate functions as a quarter-wave plate or a phase difference plate of an odd multiple thereof, circularly polarized light passing through the circularly polarized light separating layer is converted into linearly polarized light and becomes light that cannot be transmitted through the circularly polarized light separating layer. It is conceivable that not only the utilization efficiency of the light will not increase, but also it will become darker due to reflection loss and absorption loss due to other optical elements.

Therefore, it is preferable that the diffusion layer does not exhibit the birefringence as exemplified in the above-mentioned light guide plate or is made of a material having a small birefringence. Further, the retardation is a product of the refractive index difference of the birefringence and the thickness, and therefore it is preferable that the retardation be as thin as possible.

Further, the diffusion layer is a tristimulus of light based on the measurement of the transmitted light from the other surface of the linearly polarized light of an arbitrary polarization plane incident from one surface by the rotation analyzer method in view of the conservation of polarization state. It is preferable that the major axis strength indicated by Y in the values is 5 times or more, and especially 8 times or more the minor axis strength. When the intensity ratio is 5 times or more, the light loss due to the phase difference of the diffusion layer can be suppressed to 20% or less, which is advantageous for improving the brightness.

The diffusion layer is, for example, a method of forming a particle-dispersed resin layer, a method of surface roughening treatment such as sandblasting or chemical etching, a method of craze generation by mechanical stress or solvent treatment, a mold provided with a predetermined diffusion structure. Can be appropriately formed as a coating layer for a light guide plate, a circularly polarized light separating layer, a retardation layer, a diffusion sheet, or the like by an appropriate method such as a transfer forming method. The diffusion sheet can be formed by a method in which a transparent substrate made of glass, plastic or the like is provided with a diffusion structure according to the above. As the plastic, those exemplified as the light guide plate as described above can be used.

A diffusion sheet that can be preferably used is one in which a resin layer containing a fine powder such as silica fine particles is provided on a plastic substrate having a small retardation such as a triacetyl cellulose substrate. In that case, it is preferable that the fine powder and the resin layer in which the fine powder is dispersed and contained have the same refractive index as possible from the viewpoint of the diffusion effect, and it is preferable that the resin layer is free from bubbles and the like.

The unevenness on the surface of the resin layer is 7 μm or less in average height based on the valley portion, preferably 0.01 to 5 μm, especially 0.5 to 4 μm, so that diffusion effect and moire can be prevented. Is more preferable. As described above, the diffusion layer is
It can be arranged between the light guide plate and the circularly polarized light separating layer, between the circularly polarized light separating layer and the retardation layer, or on the outgoing light side of the retardation layer, and two or more layers can be arranged at those positions.

As the circularly polarized light separating layer, an appropriate layer for separating left and right circularly polarized light as transmitted light and reflected light can be used.
The circularly polarized light separating layer which can be preferably used is a layer having a cholesteric liquid crystal phase, a sheet having a layer made of a liquid crystal polymer exhibiting a cholesteric phase, a sheet obtained by developing the layer on a glass plate or the like, or exhibiting a cholesteric phase. Examples include films made of liquid crystal polymers.

According to the cholesteric liquid crystal phase, the left and right circularly polarized light can be selectively separated into either one by transmission or reflection, and the uniformly aligned liquid crystal phase containing the cholesteric liquid crystal provides reflected light without scattering. The cholesteric liquid crystal phase has a small change in optical characteristics with respect to a change in viewing angle and has a wide viewing angle, and is particularly suitable for forming a direct-viewing type liquid crystal display device or the like which is 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. The superposition is advantageous in that the separation function has a wider wavelength range and the wavelength shift of obliquely incident light is dealt with, and in that case, superimposition is performed with a combination of different central wavelengths of light reflected as circularly polarized light outside the predetermined range. It is preferable.

That is, a single-layer cholesteric liquid crystal layer usually has a limit in the wavelength range exhibiting selective reflection (circular dichroism), and the limit may be a wide range extending to a wavelength range of about 100 nm. , Even in that wavelength range does not reach the whole range of visible light desired when applied to a liquid crystal display device or the like, and in such a case, a cholesteric liquid crystal layer having different selective reflectivity is superimposed to exhibit circular dichroism. The wavelength range can be expanded.

By the way, in the case of the cholesteric liquid crystal layer, the central wavelength of selective reflection based on the liquid crystal phase is 300 to 900.
A combination that reflects circularly polarized light of the same polarization direction with the nm one,
And the central wavelength of selective reflection is different, especially 50nm each.
The 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 superposing 2 to 6 kinds thereof.

The point that the circularly polarized light of the same polarization direction is reflected in each layer and is made into a superimposition is that the circularly polarized light reflected by each layer has the same phase state and has different polarized states in each wavelength range. The purpose is to prevent and increase the amount of polarized light in a usable state. Therefore, as the circularly polarized light separating layer, a layer in which the wavelength range of the light that can be reflected as the circularly polarized light outside the predetermined range matches the wavelength range of the outgoing light based on the light guide plate as much as possible can be preferably used.

When the emitted light has a dominant wavelength such as an emission line spectrum, it is necessary to match the wavelength of the reflected light based on the cholesteric liquid crystal phase with one or more dominant wavelengths of the polarized light separation efficiency. It becomes the next best measure from the viewpoint of sex,
It is also advantageous for thinning the circularly polarized light separation layer by reducing the required number of superpositions. In that case, the degree of matching of the wavelengths of the reflected light is
It is preferable to set the range within 20 nm for each of one or more main wavelengths of the light guide plate.

As the cholesteric liquid crystal, an appropriate one may be used without any particular limitation. A cholesteric liquid crystal molecule having a larger phase difference has a wider selective reflection wavelength range, and can be preferably used from the viewpoints of a reduction in the number of layers and a margin for wavelength shift at a large viewing angle. A liquid crystal polymer can be preferably used in terms of weight and self-supporting property.

Incidentally, as the cholesteric liquid crystal type liquid crystal polymer, for example, a main chain type liquid crystal polymer such as polyester, a side chain type liquid crystal polymer having an acrylic main chain, a methacrylic main chain, a siloxane main chain or the like, and a low molecular weight chiral agent are contained. Examples thereof include nematic liquid crystal polymers, chiral component-introduced liquid crystal polymers, and mixed nematic and cholesteric liquid crystal polymers. From the viewpoint of handleability, a liquid crystal polymer having a glass transition temperature of 30 to 150 ° C. can be preferably used.

The formation of the cholesteric liquid crystal layer from the liquid crystal polymer can be carried out by a method according to the conventional alignment treatment. By the way, as an example, a liquid crystal polymer is spread on an appropriate alignment film formed by forming a film of polyimide, polyvinyl alcohol or the like on a substrate and rubbing it with rayon cloth, or an oblique vapor deposition layer of SiO. To a glass state by heating to a glass transition temperature or higher and lower than the isotropic phase transition temperature, and cooling to below the glass transition temperature in a state in which the liquid crystal polymer molecules are Grandjean aligned to form a solidified layer in which the orientation is fixed. The method etc. are given.

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

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

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

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

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

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

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

As shown in FIGS. 1 to 3, by disposing the circularly polarized light separating layer 4 on the exit surface side of the light guide plate 1, the light emitted from the light guide plate is incident on the circularly polarized light separating layer, and the left and right portions are separated. The predetermined (provisionally left) circularly polarized light is transmitted, and the non-predetermined (right) circularly polarized light is reflected, and the reflected light re-enters the light guide plate as return light. The light that has re-entered the light guide plate is reflected by the reflective function portion including the reflective layer on the lower surface and re-enters the circularly polarized light separating layer,
It is again separated into transmitted light and reflected light (re-incident light).

Therefore, the re-incident light as the reflected light is confined between the circularly polarized light separating layer and the light guide plate and is repeatedly reflected until it becomes a predetermined circularly polarized light which can be transmitted through the circularly polarized light separating layer. In the present invention, from the viewpoint of the efficiency of use of the re-incident light, etc., it is preferable that the first re-incident light is emitted without repetition of reflection, with the number of repetitions being as small as possible as described above. .

As illustrated in FIGS. 2 and 3, the circularly polarized light separating layer 4
On the light emission side (upper side) of the above, a retardation layer 5 as a linear polarization conversion means can be provided. In that case, the circularly polarized light emitted from the circularly polarized light separating layer is incident on the phase difference layer and undergoes a phase change, and the light having a wavelength corresponding to the quarter phase change is converted into linearly polarized light. Wavelength light is converted to elliptically polarized light. The converted elliptically polarized light becomes flatter elliptically polarized light as it becomes closer to the wavelength of the light converted to the linearly polarized light. As a result, light having a large amount of linearly polarized light components that can pass through the polarizing plate is emitted from the retardation layer.

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

That is, in the above, it is possible to achieve the display by directly entering the outgoing polarized light from the circularly polarized light separating layer into the liquid crystal cell without using the polarizing plate, but by using the polarizing plate, the above-mentioned display is achieved. A polarizing plate may be used as necessary because it can improve the quality.
In that case, the higher the transmittance to the polarizing plate is, the more advantageous it is in terms of display brightness, and the higher the transmittance is, the more the linear polarization component in the polarization direction that matches the polarization axis (transmission axis) of the polarizing plate is included. Therefore, for that purpose, the outgoing polarized light from the circularly polarized light separating layer is converted into a predetermined linear polarized light through the linear polarized light converting means.

By the way, when natural light or circularly polarized light is made incident on a usual iodine type polarizing plate, its transmittance is about 43%, but when linearly polarized light is made incident with the polarization axes aligned, it becomes 80%. It is possible to obtain a transmissivity in excess of%, so that the utilization efficiency of light is significantly improved and a liquid crystal display or the like having excellent brightness can be realized. Moreover, in such a polarizing plate, 99.99
A degree of polarization of up to% can also be achieved. It is difficult to achieve such a high degree of polarization by using the circularly polarized light separating layer alone, and the degree of polarization with respect to obliquely incident light is likely to decrease.

As the retardation layer, the circularly polarized light emitted from the circularly polarized light separating layer can form a large amount of linearly polarized light corresponding to the phase difference of 1/4 wavelength, and light of other wavelengths can be converted to the linearly polarized light. Those having a major axis in parallel directions as much as possible and capable of converting into flat elliptically polarized light as close to linearly polarized light as possible are preferable. The retardation layer may be provided integrally with the circularly polarized light separation layer, the diffusion layer, or the polarizing plate of the liquid crystal cell.

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

The retardation imparted by the retardation layer can be appropriately determined according to the wavelength range of circularly polarized light emitted from the circularly polarized light separating layer. Incidentally, in view of the wavelength range and conversion efficiency in the visible light region, taking into consideration that most retardation plates exhibit positive birefringence wavelength dispersion than their material characteristics, the phase difference is small, Especially 100-180nm, especially 11
A material that gives a phase difference of 0 to 150 nm or less can be preferably used.

The retardation plate can be formed as one layer or as a superposed layer of two or more layers. In the case of a retardation plate consisting of one layer, it is preferable that the birefringence has a smaller wavelength dispersion because the polarization state can be made uniform for each wavelength. On the other hand, the superposition of retardation plates is effective for improving the wavelength characteristics in the wavelength range, and the combination thereof may be appropriately determined according to the wavelength range and the like.

When a retardation plate having two or more layers for the visible light region is used, it is often the case that a layer giving a retardation of 100 to 180 nm is included as one or more odd-numbered layers as a linear polarization component. It is preferable in terms of obtaining light. 100-180
The layers other than the layer that gives the phase difference of nm are usually 200 to 400.
It is preferable to form a layer that gives a phase difference of nm from the viewpoint of improving wavelength characteristics and the like, but it is not limited to this.

The retardation plate can be obtained, for example, as a birefringent sheet obtained by stretching a film made of polycarbonate, polysulfone, polyester, polymethylmethacrylate, polyamide, polyvinyl alcohol or the like. From the viewpoint of maintaining uniform emission intensity and emission color over a wide viewing angle, it is preferable that the in-plane retardation error of the retardation layer is small, and in particular, the error is ± 10 nm.
The following is preferable.

The retardation and the direction of the optical axis 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 that gives a retardation of 135 nm, depending on the direction of circularly polarized light, the vibration direction is +45 degrees or -45 degrees linearly polarized light (wavelength 5
40 nm) is obtained. When the retardation layer is composed of two or more layers, particularly when the outer surface layer is occupied by a layer giving a retardation of 100 to 180 nm, it is preferable to set the arrangement angle based on the layer.

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

As described above, the polarized light source device according to the present invention provides light that is excellent in light utilization efficiency, bright, and excellent in verticality and has little unevenness in brightness and darkness. It can be preferably used for various devices such as a backlight system in the above.

FIG. 11 illustrates a liquid crystal display device 9 using the polarized light source device 8 according to the present invention in a backlight system. Reference numeral 91 is a lower polarizing plate, 92 is a liquid crystal cell, 93 is an upper polarizing plate, and 94 is a compensating diffusion plate. Lower polarizing plate 9
1 and the compensation diffusion plate 94 are provided as needed.

Generally, 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, if necessary, a retardation plate for compensation.
The present invention is not particularly limited except that the above-mentioned polarized light source device is used, and it can be formed according to the conventional method. In particular, a direct-viewing type liquid crystal display device can be preferably formed.

Therefore, the liquid crystal cell to be used is not particularly limited, and an appropriate one can be used. In particular, it is advantageously used for displaying by making light in a polarized state incident on a liquid crystal cell, and can be preferably used, for example, in a liquid crystal cell using a twisted nematic liquid crystal or a super twisted nematic liquid crystal, but a non-twisted liquid crystal. Also, it can be used for guest-host liquid crystal in which a dichroic dye is dispersed in liquid crystal, or a liquid crystal cell using ferroelectric liquid crystal. The liquid crystal driving method is not particularly limited.

From the point of view of obtaining a good contrast ratio by the incidence of a high degree of linearly polarized light, as a polarizing plate, particularly as a polarizing plate on the backlight side, for example, an iodine type or dye type absorption type linear polarizer, etc. A liquid crystal display device using one having a high degree of polarization is preferable. In addition, a polarizing plate on the backlight side, that is, a state in which the polarizing plate on the light emitting side of the diffusion layer and the optical axis of the diffusion layer are aligned or approximate to each other is preferable from the viewpoint of light utilization efficiency.

When forming a liquid crystal display device, for example, a diffusion plate or an antiglare layer provided on the polarizing plate on the viewing side, an antireflection film, a protective layer or a protective plate, or a compensating retardation plate provided between the liquid crystal cell and the polarizing plate. Appropriate optical elements such as the above can be appropriately arranged.

The above-mentioned compensating retardation plate is intended to improve the visibility by compensating for the wavelength dependency of birefringence and the like. In the present invention, it is arranged between the polarizing plate on the viewing side and / or the backlight side and the liquid crystal cell as necessary. As the retardation plate for compensation, an appropriate one may be used depending on the wavelength range and the like, and may be formed as one layer or a superposed layer of two or more layers. The retardation plate for compensation can be obtained as a stretched film or the like exemplified as the retardation plate for linearly polarized light conversion described above.

In the present invention, the optical elements or parts forming the above-mentioned polarized light source device or liquid crystal display device may be wholly or partially laminated and integrally fixed, or may be arranged in an easily separable state. It may be one. When forming a liquid crystal display device, etc., the emitted light with excellent verticality and parallelism is supplied, and the re-incident light that has passed through the circularly polarized light separation layer is in a state with little loss or angular change due to scattering etc. It is preferable to use a polarized light source device that re-emites light with a good coincidence with the direction and efficiently supplies the emitted light in the direction effective for improving the visibility.

[0104]

【Example】

Reference Example 1 After forming a side chain type cholesteric liquid crystal polymer having an acrylic main chain and a glass transition temperature of 57 ° C. on a polyimide rubbing-treated surface of a triacetyl cellulose film by spin coating, heating at 140 ° C. for 30 seconds 1 more
It was heated at 20 ° C. for 2 minutes and rapidly cooled to obtain a circularly polarized light separating plate exhibiting a specular selective reflection state. This is 420-505
Shows good selective reflectivity in the wavelength range of nm,
0% or more was selectively reflected in the regular reflection direction.

Reference Example 2 After forming a side chain type cholesteric liquid crystal polymer having an acrylic main chain and a glass transition temperature of 64 ° C. on a polyimide rubbing-treated surface of a triacetyl cellulose film by a spin coating method, the film was formed at 150 ° C. at 30 ° C. 1 second after heating for 1 second
It was heated at 30 ° C. for 2 minutes and rapidly cooled to obtain a circularly polarized light separating plate exhibiting a specular selective reflection state. This is 500-590
Shows good selective reflectivity in the wavelength range of nm,
0% or more was selectively reflected in the regular reflection direction.

Reference Example 3 A side-chain cholesteric liquid crystal polymer having an acrylic main chain and a glass transition temperature of 75 ° C. was spin-coated on the polyimide rubbing-treated surface of a triacetyl cellulose film, and then at 170 ° C. for 30 minutes. 1 second after heating for 1 second
It was heated at 45 ° C. for 2 minutes and cooled rapidly to obtain a circularly polarized light separating plate exhibiting a specular selective reflection state. This is 595-705
Shows good selective reflectivity in the wavelength range of nm,
0% or more was selectively reflected in the regular reflection direction.

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

Example 1 Polymethylmethacrylate was melted by heating, poured into a metal mold at 180 ° C., held for 1 hour, and then gradually cooled to obtain a light guide plate having an in-plane retardation of 10 nm or less. This light guide plate has a width of 1
95 mm, depth 150 mm, incident surface thickness 5 mm, opposite end thickness 1 mm, upper surface is flat, lower surface is a curved surface projecting from the incident surface toward the opposite end to a lower surface close to a plane (FIG. 6)
In addition, there was a recess (FIG. 8a) parallel to the incident surface with an effective width of 185 mm, and the recess had the form shown in Table 1.

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

[0110]

[Table 1]

A cold cathode tube having a diameter of 3 mm is arranged on the incident surface of the light guide plate obtained as described above, and the cold cathode tube is surrounded by a light source holder made of a polyethylene terephthalate film on which silver is vapor-deposited. A side sheet type surface light source device was obtained by arranging a reflection sheet made of a vapor-deposited polyethylene terephthalate film with the silver vapor deposition surface side interposed between the circularly polarized light separating plate obtained in Reference Example 4 and the phase difference of 135 nm. The retardation plate of 1 was arranged in that order, and the diffusion sheet was arranged to obtain a polarized light source device. The positions of the diffusing sheets were set between the light guide plate and the circularly polarized light separating plate, between the circularly polarized light separating plate and the retardation plate, or on the upper surface of the retardation plate.

In the above diffusion sheet, 10 parts (parts by weight, the same applies hereinafter) of silica fine particles having an average particle size of 1 μm and a standard deviation of 0.1 μm are dispersed in 100 parts of a commercially available ultraviolet curable resin, and the dispersion liquid is thickened. It was obtained by applying it to the surface of a 50 μm thick triacetyl cellulose film and curing it with ultraviolet rays.

Example 2 A diffusion sheet was obtained in the same manner as in Example 1 except that the amount of silica fine particles used was 20 parts, and a polarizing light source device was obtained using the diffusion sheet.

Example 3 A diffusion sheet was obtained in the same manner as in Example 1 except that silica fine particles having an average particle size of 2 μm were used, and a polarizing light source device was obtained using the diffusion sheet.

Comparative Example 1 A diffusion sheet was obtained in the same manner as in Example 1 except that a biaxially stretched polyethylene terephthalate film was used instead of the triacetyl cellulose film, and a polarizing light source device was obtained by using the diffusion sheet.

Comparative Example 2 A diffusion sheet was obtained in the same manner as in Example 1 except that titanium oxide powder having an average particle diameter of 1.5 μm was used instead of the silica fine particles, and a polarizing light source device was obtained using the diffusion sheet.

Comparative Example 3 A diffusion sheet was obtained in the same manner as in Example 1 except that 30 parts of silica fine particles having an average particle diameter of 8 μm were used, and a polarized light source device was obtained using the diffusion sheet.

Comparative Example 4 A diffusion sheet obtained by adhering the same triacetylcellulose film to the substrate side of the diffusion sheet obtained according to Example 1 with the optical axes aligned, was used, and according to Example 1 A polarized light source device was obtained.

Comparative Example 5 A polarized light source device was obtained in the same manner as in Example 1 except that the diffusion sheet was not used.

Evaluation Test 1 The thickness of the coating layers of the diffusion sheets obtained in Examples and Comparative Examples was examined with a film thickness measuring device (MCPD-1000 manufactured by Otsuka Electronics Co., Ltd.), and the surface was measured with a surface roughness meter. The average height of the irregularities was examined. In addition, the phase difference between the front direction of the diffusion sheet and the angle of 30 degrees vertically and horizontally is measured by a birefringence measuring device (ADR, ADR
-100XY, TFM-120CFT). Further, the long-axis intensity and the short-axis intensity when linearly polarized light was made incident were examined by a rotation analyzer method using a phase difference measuring device (manufactured by Otsuka Electronics Co., Ltd.). The long / short axis intensity ratio indicates the storage performance of the polarization state as described above. In addition, the transmittance when parallel rays were vertically incident on the diffusion sheet was also examined.

The above results are shown in Table 2.

[Table 2]

In the above description, there is a substantial difference in characteristics due to the arrangement position of the diffusion sheet, that is, between the light guide plate and the circular polarization separation plate, between the circular polarization separation plate and the phase difference plate, or the arrangement position of the upper surface of the phase difference plate. I was not able to admit.

Evaluation Test 2 A liquid crystal display device was obtained by disposing a super twist nematic liquid crystal cell on the upper surface of the polarized light source device obtained in each of Examples and Comparative Examples. This liquid crystal cell has retarders on both sides and is adjusted to a normally white monochrome mode.
The liquid crystal display device was adjusted so that the transmittance in the white state was maximized by changing the angle of the retardation plate directly above the circularly polarized light separating plate. The display state of the liquid crystal display device in the non-selected state was observed, and the change in front luminance due to the presence or absence of the diffusion sheet and the presence or absence of moire were examined.

The above results are shown in Table 3.

[Table 3]

From Table 2, it is found that the retardation of the diffusion sheet in Examples and Comparative Examples 2 and 3 is less than 30 nm, the retardation in Comparative Example 1 is very large, and the retardation in Comparative Example 4 is 57 nm. I understand. The diffusion sheets of Examples and Comparative Examples 1 and 4 were almost transparent, but milky white in Comparative Examples 2 and 3. Further, in terms of surface roughness, Examples and Comparative Examples 1, 2,
It can be seen that in Example 4, the average height is 5 μm or less, and in Comparative Example 3, it is as large as 9 μm. In addition, the long / short axis strength ratio is 8/1 or more in the examples, but is 4/1 or less in the comparative examples,
In particular, in Comparative Examples 2 and 3, not only the long / short axis intensity ratio, but also the observed intensity without the analyzer was 20% or more lower than that of the example.

On the other hand, from Table 3, in the liquid crystal display device, the moire was generated in Comparative Example 5 in which the diffusion sheet was not used, and the display was glaring. On the other hand, in Examples and Comparative Examples 1 to 4 in which the diffusion sheet was used, moiré could be prevented, but the decrease in front luminance was 20% or less in the case of not using the diffusion sheet in the Example. However, in the comparative example, the decrease was large and the screen display was dark. Even in the case of a liquid crystal display device, no substantial difference in characteristics was observed due to the difference in the arrangement position of the diffusion sheet.

From the above results, comprehensively, in the case of the embodiment, it is possible to achieve a bright display while suppressing a decrease in brightness by the diffusion sheet, and to realize high light utilization efficiency when combined with a circularly polarized light separating layer. Thus, it is possible to form a bright and easy-to-view high-quality liquid crystal display device that prevents moire.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an example of a polarized light source device.

FIG. 2 is a side explanatory cross-sectional view of another example of the polarized light source device.

FIG. 3 is a side explanatory cross-sectional view of still another example of the polarized light source device.

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

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

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

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

FIG. 10 is an explanatory diagram of bright and dark unevenness due to presence (a) or absence (b) of a diffusion layer.

FIG. 11 is a side explanatory cross-sectional view of an example of a liquid crystal display device.

[Explanation of symbols]

8: polarized light source device 1: light guide plate 11: upper surface 12, 16, 17, 18: lower surface 21, 22, 23, 24: convex portion 25, 26, 27, 28 on lower surface: concave portion 31, 33, 35, on lower surface 37, 42, 44, 46, 48: Long side surfaces 32, 34, 36, 38, 41, 43, 45, 47: Short side surface 13: Incident surface 2, 6: Reflective layer 3: Diffusing layer 4: Circularly polarized light Separation layer 5: Retardation layer 7: Light source 9: Liquid crystal display device

─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-6-265892 (JP, A) JP-A-7-20466 (JP, A) JP-A-6-324333 (JP, A) JP-A-7- 36032 (JP, A) JP-A-9-73083 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 6/00 F21V 8/00 G02F 1/13357

Claims (12)

(57) [Claims] 1. A circularly polarized light separating layer on the exit surface side of a light guide plate which has fine prismatic irregularities on at least one of the upper and lower surfaces, and which allows incident light from the side surface to exit from one of the upper and lower surfaces in a state with uneven brightness. And a diffusion layer, and the diffusion layer becomes a circularly polarized light separation layer.
Is placed at a position where polarized light based on reflected light or transmitted light
And the phase difference of the diffusion layer is at a wavelength of 633.
A polarized light source device having a wavelength of 30 nm or less based on vertically incident light of nm. 2. The wavelength according to claim 1, wherein the pitch of the prismatic irregularities in the light guide plate is 20 to 500 μm, the circularly polarized light separating layer is made of a sheet, and the phase difference of the diffusing layer is an incident angle within 30 degrees. 3 based on 633 nm light
A polarized light source device having a wavelength of 0 nm or less. 3. The tristimulus value of light according to claim 1 or 2, wherein the diffusion layer has a value obtained by measuring the transmitted light from the other side of the linearly polarized light of an arbitrary polarization plane which is incident from one side by the rotation analyzer method. A polarized light source device in which the major axis strength indicated by Y in the figure is 5 times or more the minor axis strength. 4. The diffusion layer according to any one of claims 1 to 3, wherein the diffusion layer is a diffusion sheet having a resin layer containing silica fine particles on a plastic substrate, and the resin layer has an average height of 5 μm or less with respect to a valley portion. A polarized light source device having an uneven surface. 5. The polarized light source device according to claim 1, wherein the light guide plate has fine prismatic irregularities parallel to the light incident surface on the lower surface. 6. The micro prism-shaped unevenness of the light guide plate according to claim 5, wherein the long side surface and the short side surface are formed, and the inclination angle of the long side surface with respect to the emission surface is 0 to 10 degrees. It is 2
A polarized light source device of 0 to 50 degrees. 7. The polarized light source device according to claim 1, having a retardation layer on the light exit side of the circularly polarized light separating layer. 8. The retardation layer according to claim 7, wherein
A polarized light source device comprising a retardation plate showing a retardation of 180 nm or a laminated retardation plate including the retardation plate. 9. The polarized light source device according to claim 7, wherein the diffusion layer is located between the circularly polarized light separation layer and the retardation layer. 10. The polarized light source device according to claim 7, wherein the diffusion layer is located on the light emission side of the retardation layer. 11. The polarized light source device according to claim 10, wherein a polarizing plate is provided on the light emitting side of the diffusion layer, and the optical axes of the polarizing plate and the diffusion layer are the same or approximate to each other. 12. A liquid crystal display device comprising the polarized light source device according to claim 1 arranged on one side of a liquid crystal cell having a polarizing plate on at least one side.