JP2006106592A - Polarization conversion separating element and its manufacturing method, and surface light source device using the element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization conversion separating element and a surface light source device using the element in which one of the polarization components among two polarization components having mutually orthogonal polarization directions is efficiently converted to the polarization component that is same as the other polarization component and the polarized light beams are emitted to a prescribed direction with high transmissivity. <P>SOLUTION: A polarization conversion separating element 6 is provided with a film-like substrate 6a, a thin film laminated body 6b in which a low refractive index thin film 6b1 whose refractive index is equal to or greater than 0.05 and a high refractive index thin film 6b2 are alternatively laminated and an optically active layer 6c which is arranged adjacent to the thin film laminated body 6b. Thickness of each of the thin films 6b1 and 6b2 is in the range of (0.7 to 1.3)λ/4, wherein λ is the wavelength of the light beams within the thin films. The surface light source device is obtained by combining the polarization conversion separating element 6 with a primary light source 2, a plate shaped light guiding body 4 having a light emitting surface 42 consisting of a rough surface whose average inclined angle is 0.5 to 20 degrees and a prism sheet 8 in which a plurality of prism columns are arranged in a mutually parallel manner. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention converts one polarization component of two polarization components having polarization directions orthogonal to each other into the same polarization component as the other polarization component, and emits the other polarization component, thereby achieving high transmittance. The present invention relates to a thin polarization conversion / separation element that emits polarized light in a required direction, and further relates to a manufacturing method thereof and a surface light source device using the same. The surface light source device using the polarization conversion separation element of the present invention is suitable as a backlight unit for a large and thin liquid crystal display device.

  In recent years, color liquid crystal display devices have been widely used in various fields as monitors for portable notebook computers, personal computers, etc., or as display units for liquid crystal televisions, video-integrated liquid crystal televisions, mobile phones, personal digital assistants, and the like. Yes. In addition, with the increase in the amount of information processing, diversification of needs, compatibility with multimedia, and the like, liquid crystal display devices have been increased in screen size and definition.

  The liquid crystal display device basically includes a backlight unit and a liquid crystal display element unit. As the backlight unit, there are a direct type with a light source arranged directly under the liquid crystal display element unit and an edge light type with a light source arranged so as to face the side end face of the light guide. From the viewpoint of making it easier, an edge light type is widely used.

  By the way, since the light emitted from the conventional backlight unit is a set of light with non-uniform polarization directions (that is, non-polarized light), about half of the light is absorbed by the polarizing plate disposed on the incident side of the liquid crystal display element unit. Was wasted.

  As a solution to this problem, as disclosed in Japanese Patent Laid-Open No. 9-506984 (Patent Document 1), one of two polarization components of light orthogonal to each other is formed on the exit surface of the backlight unit. A method is used in which a polarization separation element having an action of transmitting a polarization component and reflecting the other polarization component is installed. By aligning the polarization transmission direction of the polarizing plate provided on the incident side of the liquid crystal display element unit with the polarization transmission direction of the polarization separation element, the polarization component that has been absorbed and wasted by the polarizing plate until now is polarized. The light is reflected by the separation element and returned to the backlight unit. The light returned to the backlight unit is reflected by the back surface of the light guide or the like, and enters the polarization separation element again. In addition, the polarization state of the light returned to the backlight unit changes while it is repeatedly reflected in the light guide, and a part of the light incident on the polarization separation element again passes through the polarization separation element. The light is reflected again. In this way, if there is no loss of light amount between the polarization separation element and the backlight unit, all the light will eventually pass through the polarization separation element, and the polarizing plate of the liquid crystal display element unit as before The light that is absorbed in should be gone.

  However, in actuality, the light is lost every time the light reflected by the polarization beam splitting element is reflected by the backlight unit, and thus the luminance is not improved as expected. Therefore, in order to increase the rate at which the light reflected by the backlight unit is incident again on the polarization separation element, it is possible to use a regular reflection sheet on the back surface of the light guide body. Has been proposed. In order to further increase the change in the polarization state due to reflection by the backlight unit, a prism array is provided on the back surface of the light guide, and the prism array extends in an oblique direction with respect to the polarization transmission surface of the polarization separation element. Such formation is disclosed in Japanese Patent Laid-Open No. 11-142849 (Patent Document 3).

On the other hand, as a surface light source device for a liquid crystal display device that increases the polarization component of emitted light, a groove having an angle inclination related to the Brewster angle is formed in a light guide unit body composed of a laminate of a plurality of light guide sheets Further, a light guide film formed by forming a plurality of light guide films on the light guide unit main body and further changing the polarization direction of light on the light guide film is disclosed in JP-A-11-15396. (Patent Document 4).
Japanese National Patent Publication No. 9-506984 JP-A-11-352479 Japanese Patent Laid-Open No. 11-142849 JP-A-11-153969

  However, in the method using the conventional polarization separation element, the loss due to the reflection between the polarization separation element and the backlight portion cannot be sufficiently reduced, and the brightness improvement effect by using the polarization separation element Was not enough.

  In addition, the conventional surface light source device for a liquid crystal display device that increases the polarization component of the emitted light described above requires a precise groove processing for the manufacture of the light guide, and has a drawback that it is not easy to manufacture.

  Accordingly, one of the objects of the present invention is to efficiently convert one polarization component of two polarization components having polarization directions orthogonal to each other into the same polarization component as the other polarization component, thereby achieving high transmittance. An object of the present invention is to provide a polarization converting / separating element capable of emitting polarized light in a required direction.

  Furthermore, another object of the present invention is to provide a surface light source device that is thin and extremely high in luminance, using such a polarization conversion / separation element, having a simple light guide structure and easy to manufacture. is there.

According to the present invention, as a solution to the above technical problem,
A thin film stack comprising a plurality of thin films stacked and a difference in refractive index between adjacent thin films of 0.05 or more, and an optically active layer disposed adjacent to the thin film stack. A polarization conversion separation element,
Is provided.

  In one aspect of the present invention, the optically active layer is bonded to the thin film laminate. In one aspect of the present invention, the thickness of each of the thin films is in the range of (0.7 to 1.3) λ / 4, where λ is the wavelength of light used in the thin film. In one aspect of the present invention, the thickness of the thin film is in the range of 0.1 to 100 μm. In one aspect of the present invention, one of the thin films constituting the thin film stack is a low refractive index thin film having a refractive index of 1.48 or less, and the other of the thin films constituting the thin film stack is It is a high refractive index thin film having a refractive index of 1.5 or more. In one aspect of the present invention, the low refractive index thin film comprises a (co) polymer obtained using a monomer containing a fluorine atom. In one aspect of the present invention, the low refractive index film is made of a (co) polymer obtained by using an olefin, methacrylate, acrylate, ester or ether containing a fluorine atom as a monomer. In one aspect of the present invention, the high refractive index thin film comprises a (co) polymer obtained using a monomer containing a phenyl group. In one embodiment of the present invention, the high refractive index film is obtained using benzyl methacrylate, phenyl methacrylate, phenylethyl methacrylate, benzyl acrylate, vinyl benzoate, orthochlorostyrene, parafluorostyrene, or paraisopropylstyrene as a monomer. (Co) polymer, polystyrene or polycarbonate. In one aspect of the present invention, at least one of the thin films constituting the thin film laminate is made of an active energy ray curable resin. In one aspect of the present invention, the active energy ray-curable resin contains fluorine. In one aspect of the present invention, the active energy ray-curable resin contains at least one of a phenyl group and chlorine. In one aspect of the present invention, the optically active layer is a cholesteric liquid crystal layer. In one aspect of the present invention, the optically active layer comprises an amorphous polymer compound having optical isomerism. In one aspect of the present invention, the optically active layer is made of a substance synthesized by a living organism. In one aspect of the present invention, the optically active layer is polylactic acid or a polyester-based condensation polymer.

Further, according to the present invention, as a solution to the above technical problem,
A method of manufacturing the polarization conversion separation element, wherein the thin film stack is formed by sequentially stacking the thin film by a solvent casting method, a casting method, or a spin coating method. Manufacturing method of separation element,
as well as,
A method for manufacturing the polarization conversion separation element, wherein the thin film laminate is formed by stretching a composite extrusion of the thin film,
Is provided.

  In one embodiment of the present invention, after the thin film stack is formed, the thin film stack is subjected to heat treatment at a temperature of 80 ° C. or higher.

Further, according to the present invention, as a solution to the above technical problem,
A plate having a primary light source, a light incident end surface to which light emitted from the primary light source is incident and light emitted from the primary light source is incident, a light emitting surface from which the guided light is emitted, and a back surface on the opposite side The light output surface of the light guide is a rough surface with an average inclination angle of 0.5 to 20 degrees, and the polarization conversion separation element is provided on the light output surface. A surface light source device characterized by being disposed;
Is provided.

  In one aspect of the present invention, the distribution peak light of the emitted light from the light emitting surface of the light guide forms an angle of 50 to 75 degrees with respect to the direction of the normal line of the light emitting surface. In one aspect of the present invention, a light deflection element is disposed on the polarization conversion separation element, and the light deflection element connects a plurality of prism rows extending in a direction along the light incident end face of the light guide to each other. This is a prism sheet arranged in parallel.

  In the polarization conversion / separation device of the present invention as described above, a thin film laminate in which thin films having a refractive index difference of 0.05 or more are laminated adjacent to each other, and the thin film laminate are arranged adjacent to each other. In combination with the optically active layer, the thin film laminate reflects one polarization component of two polarization components having polarization directions orthogonal to each other and guides it to the light guide through the optically active layer, Reflecting here and re-entering the thin film stack through the optically active layer enables efficient conversion to the same polarization component as the other polarization component, and emits polarized light in the required direction with high transmittance. It becomes possible to make it.

  In addition, according to the present invention, by using such a polarization conversion separation element, it is possible to provide a thin and extremely high luminance surface light source device that has a simple light guide structure and can be easily manufactured.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic partial perspective view showing one embodiment of an edge light type surface light source device using a polarization conversion separation element according to the present invention.

  As shown in the drawing, in the surface light source device of the present embodiment, one side end surface is a light incident end surface 41, one of two main surfaces substantially orthogonal to this is a light emitting surface 42, and the other is a back surface 43. The light guide 4, the primary light source 2 disposed opposite to the light incident end surface 41 of the light guide 4, and the polarization conversion separation element 6 disposed on the light exit surface 42 of the light guide 4 And an optical deflecting element 8 disposed on the polarization converting / separating element 6 and having a light incident surface 81 and a light exit surface 82.

  As the primary light source 2, a linear light source extending in the Y direction can be used. As the linear primary light source 2, for example, a fluorescent lamp or a cold cathode tube can be used. The primary light source 2 is not limited to a linear light source, and a point light source such as a light emitting diode (LED), a halogen lamp, a metahalo lamp, or the like can be used. It may be arranged in a shape. In addition, the primary light source 2 is installed not only when facing the one side end face (light incident end face) 41 of the light guide 4 as shown in FIG. 1, but also with the side end face 41 if necessary. Can also be disposed opposite to the opposite side end face. Although not shown, the primary light source 2 can be provided with a reflector so that light emitted therefrom can be efficiently incident on the light incident end face 41 of the light guide 4.

  The light guide 4 is disposed in parallel with the XY plane and has a rectangular plate shape as a whole. The light guide 4 has four side end faces, and at least one of the pair of side end faces substantially parallel to the YZ plane is a light incident end face 41. The light incident end face 41 is disposed to face the primary light source 2, and the light emitted from the primary light source 2 enters the light incident end face 41 and is introduced into the light guide 4.

  The two principal surfaces substantially orthogonal to the light incident end surface 41 of the light guide 4 are respectively positioned substantially parallel to the XY plane, and one of the surfaces (upper surface in the drawing) is the light emitting surface 42. At least one of the light exit surface 42 or the opposite back surface 43 has a rough directional light exit function unit, a plurality of lens arrays such as a prism array, a lenticular lens array, and a V-shaped groove. By providing a directional light emitting function unit composed of a lens surface formed substantially parallel to the light incident end surface 41, the light emitting surface while guiding the light introduced from the light incident end surface 41 through the light guide 4 42 emits light having directivity in the outgoing light distribution in a plane (XZ plane) orthogonal to both the light incident end face 41 and the light outgoing face 42. If the angle between the direction of the peak of the outgoing light distribution in the XZ plane and the light outgoing surface 42 is a, this angle a is preferably 15 to 40 degrees, and the full width at half maximum of the outgoing light distribution is 10 to 40 degrees. It is preferable that

  The rough surface and the lens array formed on the main surface of the light guide 4 should have an average inclination angle θa in the range of 0.5 to 20 degrees according to ISO 4287 / 1-1984. This is preferable from the viewpoint of improving the uniformity of luminance. The average inclination angle θa is more preferably in the range of 1 to 12 degrees, and more preferably in the range of 1.5 to 11 degrees. The average inclination angle θa is set to an optimum range by a ratio (L / t) between the thickness (t) of the light guide 4 and the length (L) in the direction (X direction) in which incident light propagates. Is preferred. That is, when the light guide 4 having a L / t of about 20 to 200 is used, the average inclination angle θa is preferably 0.5 to 7.5 degrees, more preferably 1 to 5 degrees. It is a range, More preferably, it is the range of 1.5-4 degree | times. Moreover, when using the thing with L / t of about 20 or less as the light guide 4, it is preferable that the average inclination | tilt angle (theta) a shall be 7-12 degree | times, More preferably, it is the range of 8-11 degree | times.

  The average inclination angle θa of the rough surface formed on the light guide 4 is obtained by measuring the rough surface shape using a stylus type surface roughness meter in accordance with ISO 4287 / 1-1984 and setting the coordinate in the measurement direction as x. From the obtained gradient function f (x), the following equation (1) and equation (2) can be used. Here, L is the measurement length, and Δa is the tangent of the average inclination angle θa.

Δa = (1 / L) ∫ ₀ ^L | (d / dx) f (x) | dx (1)
θa = tan ⁻¹ (Δa) (2)
Further, the light guide 4 preferably has a light emission rate in the range of 0.5 to 5%, more preferably in the range of 1 to 3%. This is because when the light output rate is less than 0.5%, the amount of light emitted from the light guide 4 tends to be small and sufficient luminance cannot be obtained. When the light output rate is greater than 5%, the vicinity of the primary light source 2 is present. This is because a large amount of light is emitted, the attenuation of light in the X direction within the light emitting surface 42 becomes significant, and the luminance uniformity on the light emitting surface 42 tends to decrease. Thus, by setting the light emission rate of the light guide 4 to 0.5 to 5%, the angle (peak angle) of the peak light in the light distribution (in the XZ plane) of the light emitted from the light emission surface is light. Light having a high directivity from the light guide 4 that is in the range of 50 to 75 degrees with respect to the normal of the exit surface and the full width at half maximum of the exit light distribution (in the XZ plane) is 10 to 40 degrees. Can be emitted.

In the present invention, the light emission rate from the light guide 4 is defined as follows. The relationship between the light intensity (I ₀ ) of the emitted light at the edge on the light incident end face 41 side of the light emitting face 42 and the emitted light intensity (I) at a distance L from the edge on the light incident end face 41 side is If the thickness (dimension in the Z direction) of the light guide 4 is t, the following relationship (3) is satisfied.

I = I ₀ · [α / 100] (1− [α / 100]) ^{L / t} (3)
Here, the constant α is the light emission rate (% unit), and per unit length (a length corresponding to the light guide thickness t) in the X direction orthogonal to the light incident end surface 41 on the light emission surface 42. This is the ratio at which light is emitted from the light guide 4. The light emission rate α is obtained from the gradient by plotting the relationship between the logarithm of the light intensity of the light emitted from the light exit surface 42 on the vertical axis and (L / t) on the horizontal axis. Can do.

  In addition, the back surface 43, which is another main surface to which the directional light emitting function unit of the light guide 4 is not provided, is a surface (YZ surface) parallel to the primary light source 2 of the light emitted from the light guide 4. In order to control the directivity, it is preferable to form a lens surface in which a large number of lens rows extending in a direction substantially perpendicular to the light incident end surface 41 (X direction) are arranged. In the embodiment shown in FIG. 1, a lens having a rough surface formed on the light emitting surface 42 and an array of a large number of lens rows 43 a extending on the back surface 43 in a direction substantially perpendicular to the light incident end surface 41 (X direction). A surface is formed. In the present invention, contrary to the embodiment shown in FIG. 1, a lens surface may be formed on the light emitting surface 42 and the back surface 43 may be a rough surface.

  As shown in FIG. 1, when a lens array is formed on the back surface 43 or the light emitting surface 42 of the light guide 4, the lens array includes a prism array, a lenticular lens array, and a V-shaped groove extending substantially in the X direction. However, it is preferable that the YZ section has a substantially triangular prism array.

  In the present invention, when a prism row is formed as a lens row formed on the light guide 4, the apex angle is preferably in the range of 70 to 150 degrees. This is because by setting the apex angle within this range, the light emitted from the light guide 4 can be sufficiently collected, and the luminance of the surface light source device can be sufficiently improved. That is, by setting the prism apex angle within this range, the full width at half maximum of the emitted light distribution is 35 to 65 degrees on the plane perpendicular to the XZ plane including the peak light in the emitted light distribution (in the XZ plane). The emitted light can be emitted, and the luminance of the surface light source device can be improved. When the prism row is formed on the light emitting surface 42, the apex angle is preferably in the range of 80 to 100 degrees. When the prism row is formed on the back surface 43, the apex angle is 70 to 80 degrees. Or it is preferable to set it as the range of 100-150 degree | times.

  In the present invention, light diffusing fine particles are mixed and dispersed in the light guide instead of or in combination with the light emitting surface 42 or the back surface 43 as described above. What provided the directional light emission function may be used. In addition, the light guide 4 is not limited to a wedge shape in which the thickness of the XZ section gradually decreases as the distance from the light incident end surface 41 increases as shown in FIG. It may be a shape. Further, the surface light source device as shown in FIG. 1 is combined with another surface light source device symmetrical with respect to the YZ plane so as to be integrated, so that 2 of the light guide 4 as described above on the opposite side. It can be set as the structure which has arrange | positioned the primary light source 2 facing the one side end surface 41. FIG. In that case, the shape of the integrated light guide is such that the center is thin and both ends are thick in the X direction.

  Although not shown, it is preferable to dispose a light reflector facing the back surface 43 of the light guide 4. Examples of such light reflectors include those in which a metal reflective film is formed on the surface of a synthetic resin sheet.

  The polarization conversion separation element 6 includes a film-like substrate 6a, a thin film laminate 6b, and an optically active layer 6c. The film-like substrate 6a supports the thin film laminate 6b and the optically active layer 6c bonded thereto, and may be any material having appropriate mechanical strength and translucency.

  The thin film laminate 6b is formed on the lower surface of the film-like substrate 6a, and includes a plurality of first type thin films 6b1 and a plurality of second type thin films 6b2. The first type thin film 6b1 and the second type thin film 6b2 are alternately stacked. The first type of thin film 6b1 is made of a first material having a first refractive index n1 and has a thickness t1. The second type thin film 6b2 is made of a second material having a second refractive index n2 (> n1) and has a thickness t2. For convenience, the first type of thin film is called a low refractive index thin film, and the second type of thin film is called a high refractive index thin film. The refractive index n2 is higher than the refractive index n1 by 0.05 or more, preferably 0.1 or more, more preferably 0.15 or more. If the difference between the refractive index n2 and the refractive index n1 is too small, the function of polarization conversion described later tends to decrease, and the number of thin films required to obtain the required light transmission performance tends to be excessive. The upper limit of the difference between the refractive index n1 and the refractive index n2 is naturally determined by the combination of the low-refractive index thin film 6a1 and the high-refractive index thin film 6b2 that can be actually laminated, but is, for example, 0.3 or 0.25. . The thickness t1 of the low refractive index thin film and the thickness t2 of the high refractive index thin film are in the range of (0.7 to 1.3) λ / 4, depending on the wavelength λ in each thin film of the used light. Preferably, the thicknesses t1 and t2 of the thin film are set in the range of (0.9 to 1.1) λ / 4. In the case of using white light, it is preferable to use three types of laminates corresponding to the three primary colors of RGB.

  The pair of the low-refractive index thin film 6b1 and the high-refractive index thin film 6b2 constituting the thin-film laminate 6b efficiently converts one of the two polarized components whose polarization directions are orthogonal to each other into the other polarized component. And is transmitted together with the original other polarized component incident thereon. Increasing the number of pairs of the low refractive index thin film 6b1 and the high refractive index thin film 6b2 makes it possible to transmit light arriving at the thin film stack 6b with higher efficiency. From this point, preferably, the number of pairs of the low refractive index thin film 6b1 and the high refractive index thin film 6b2 is 3 (that is, the number of thin films 6) or more, preferably 5 (that is, the number of thin films 10) or more. However, if the number of pairs of the low refractive index thin film 6b1 and the high refractive index thin film 6b2 is too large, the manufacturing cost increases. Therefore, it is preferable to set it to an appropriate upper limit, for example, 10 (that is, the number of thin films 20) or less. . The efficiency of the action of the thin film laminate 6b can be increased by setting the thin film thicknesses t1 and t2 to a value close to λ / 4 as described above.

  The thickness of the thin film laminate 6b is preferably in the range of 0.1 to 100 μm, for example. If the thickness is too thin, it may be difficult to obtain the required light transmission performance, or the stability of thin film formation may be impaired. On the other hand, if the thickness is too thick, light is easily guided in the direction along the surface of the thin film inside the thin film, and the loss of light increases.

  The low refractive index thin film 6b1 is a dielectric film having a refractive index of, for example, 1.48 or less. Examples of such a low refractive index thin film include those composed of (co) polymers obtained by (co) polymerization using monomers containing fluorine atoms.

  Examples of the fluorine atom-containing monomer used here include the following olefins, methacrylates, acrylates, esters and ethers.

Olefin:
(Perfluorobutyl) ethylene (perfluorohexyl) ethylene (perfluorooctyl) ethylene (perfluorodecyl) ethylene 1-methoxy- (perfluoro-2-methyl-1-propene)
1,4-divinyloctafluorobutane 1,6-divinyldodecafluorohexane 1,8-divinylhexadecafluorooctane methacrylate:
2,2,2-trifluoroethyl methacrylate 2,2,3,3,3-pentafluoropropyl methacrylate 2- (perfluorobutyl) ethyl methacrylate 2- (perfluorohexyl) ethyl methacrylate 2- (perfluorooctyl) ethyl Methacrylate 2- (perfluorodecyl) ethyl methacrylate 2- (perfluoro-3-methylbutyl) ethyl methacrylate 3- (perfluoro-3-methylbutyl) -2-hydroxypropyl methacrylate 2- (perfluoro-5-methylhexyl) ethyl Methacrylate 3- (perfluoro-5-methylhexyl) -2-hydroxypropyl methacrylate 2- (perfluoro-7-methyloctyl) ethyl methacrylate 3- (perfluoro-7-methyloctyl) 2-hydroxypropyl methacrylate 2- (perfluoro-9-methyldecyl) ethyl methacrylate 3- (perfluoro-8-methyldecyl) -2-hydroxypropyl methacrylate 2,2,3,3-tetrafluoropropyl methacrylate 1H, 1H, 5H-octafluoropentyl methacrylate 1H, 1H, 7H-dodecafluoroheptyl methacrylate 1H, 1H, 9H-hexadecafluorononyl methacrylate 1H, 1H, 11H-icosafluoroundecyl methacrylate 2,2,2-trifluoro-1- Trifluoromethyl ethyl methacrylate 2,2,3,4,4,4-hexafluorobutyl methacrylate acrylate:
2,2,2-trifluoroethyl acrylate 2,2,3,3,3-pentafluoropropyl acrylate 2- (perfluorobutyl) ethyl acrylate 3-perfluorobutyl-2-hydroxypropyl acrylate 2- (perfluorohexyl) ) Ethyl acrylate 3-perfluorohexyl-2-hydroxypropyl acrylate 2- (perfluorooctyl) ethyl acrylate 3-perfluorooctyl-2-hydroxypropyl acrylate 2- (perfluorodecyl) ethyl acrylate 2- (perfluoro-3 -Methylbutyl) ethyl acrylate 3- (perfluoro-3-methylbutyl) -2-hydroxypropyl acrylate 2- (perfluoro-5-methylhexyl) ethyl acrylate 2- (perfluoro -9-methyloctyl) ethyl acrylate 2- (perfluoro-9-methyldecyl) ethyl acrylate 2,2,3,3-tetrafluoropropyl acrylate 1H, 1H, 5H-octafluoropentyl acrylate 1H, 1H, 7H-dodecafluoro Heptyl acrylate 1H, 1H, 9H-hexadecafluorononyl acrylate 1H, 1H, 11H-icosafluoroundecyl acrylate 2,2,2-trifluoro-1-trifluoromethylethyl acrylate 2,2,3,4,4 , 4-Hexafluorobutyl acrylate ester:
Methyl perfluoropropionate Ethyl perfluoropropionate Methyl perfluorobutyrate Ethyl perfluorobutyrate Methyl perfluorooctanoate Ethyl perfluorooctanoate Methyl perfluoroacetate Ethyl perfluoroacetate Ethyl 5H-octafluoropentanoate Ethyl 7H-dodecafluoroheptanoate Ethyl 9H-hexadecafluorononanoate Ethyl 11H-icosafluoroundecanoate Ether:
2,2,2-trifluoroethyl methyl ether 2,2,2-trifluoroethyl difluoromethyl ether 2,2,3,3,3-pentafluoropropyl methyl ether 2,2,3,3,3-pentafluoro Propyl difluoromethyl ether 2,2,3,3,3-pentafluoropropyl 1,1,2,2-tetrafluoroethyl ether The high refractive index thin film 6b2 is a dielectric film having a refractive index of, for example, 1.5 or more. is there. Examples of such a high refractive index thin film include those composed of (co) polymers obtained by (co) polymerization using a monomer containing a phenyl group. Examples of the monomer containing a phenyl group used herein include benzyl methacrylate, phenyl methacrylate, phenylethyl methacrylate, benzyl acrylate, vinyl benzoate, orthochlorostyrene, parafluorostyrene, and paraisopropylstyrene. Further, as the high refractive index thin film, polystyrene or polycarbonate can be used.

As a thin film which comprises the thin film laminated body 6b, what consists of active energy ray hardening resin can also be used. Examples of the active energy ray curable resin include an ultraviolet curable resin and an electron beam curable resin. When the low refractive index thin film constituting the thin film laminate 6b is composed of an active energy ray curable resin, a material containing fluorine as the active energy ray curable resin is used to make the refractive index 1.48 or less. It is preferable to do this. Such an active energy ray-curable resin includes an acid represented by the formula R ₁ —C (CH ₂ ) COOH [where R ₁ is H, CH ₃ , F, CF ₃ ], and a formula R _2. 3-perfluorobutyl-2-propen-1-ol, 3-perfluorohexyl-2-propen-1-ol, and 3-perfluorooctyl-2-propen-1-ol, which are alcohols represented by —OH And a polymer obtained by polymerizing using a bifunctional monomer represented by the formula R ₁ —C (CH ₂ ) COO—R ₂ obtained by esterification reaction. When the high refractive index thin film constituting the thin film laminate 6b is made of an active energy ray curable resin, in order to make the refractive index 1.5 or more, as an active energy ray curable resin, of the phenyl group and chlorine It is preferable to use one containing at least one. As such an active energy ray curable resin, those having a phenyl group include di (meth) acrylates of alkylene oxide adducts such as (CH ₂ CH ₂ O) adduct dimethacrylate of bisphenol A, bisphenol A (CH ₃ CH ₂ CH ₂ O) adduct dimethacrylate, trimethylolpropane acrylate benzoate, urethane acrylate such as phenyl glycidyl ether acrylate / tolylene diisocyanate urethane prepolymer, phenyl glycidyl ether acrylate / isophorone diisocyanate urethane prepolymer A polymer and a polymer obtained by polymerization using a bifunctional monomer such as phenylglycidyl ether acrylate / hexamethylene diisocyanate urethane prepolymer It can be given to. Examples of the active energy ray-curable resin include those made of a polymer obtained by polymerization using 1,3-butanedioldi (methyl-α-chloroacrylate) in the case of containing chlorine. .

  The plurality of thin films constituting the thin film laminate 6b may be composed of three or more types as long as the difference in refractive index between adjacent ones is 0.05 or more.

  The optically active layer 6c functions to rotate the polarization direction (polarization plane) with respect to the transmitted light. When the polarized component (s-polarized component) reflected by each thin film of the thin film laminate 6b enters the optically active layer 6c, the polarization direction (direction of the polarization plane) is rotated. Thus, the light subjected to the rotation of the polarization plane re-enters the light guide 4 and is reflected to reach the optically active layer 6c again. When passing through the light, the light undergoes the rotation of the polarization plane again to the thin film stack 6b. Re-enter. At the time of this re-incidence, it also includes a polarized component to be transmitted (p-polarized component). By repeating the reflection and transmission as described above, the thin film laminate 6b is emitted to form a film-like substrate. The amount of polarized light that passes through 6a can be increased.

  The function of polarization conversion by the polarization conversion separation element 6 will be described below with reference to FIG. FIG. 2 shows the progress of light (peak light) in the direction of the distribution peak of the emitted light from the light emitting surface 42 of the light guide 4 in the XZ plane. The angle formed by the peak light emitted from the light emitting surface 42 with the light emitting surface 42 is a, and this light is incident on the optically active layer 6c with an incident angle θ1 and travels through the optically active layer 6c to form a thin film. The light enters the high refractive index thin film 6b2 of the laminate 6b with an incident angle θ2, travels through the high refractive index thin film 6b2, and part of the light enters the low refractive index thin film 6b1 of the thin film laminate 6b with an incident angle θ3. Then, the film travels through the low refractive index thin film 6b1, and a part thereof is further incident on the high refractive index thin film 6b2 at an incident angle θ4, and the same goes through the high refractive index thin film 6b2 and the low refractive index thin film 6b1. To do. A part of this light is incident on the lower surface of the film-like substrate 6a from the uppermost low refractive index thin film 6b1, travels through the film-like substrate 6a, and exits from the upper surface at an emission angle θ1. To do.

  As described above, the angle a is 15 to 40 degrees, that is, the incident angle θ1 is 50 to 75 degrees. Here, for example, when the incident angle θ1 is 70 degrees, the incident angle θ3 to the low refractive index thin film 6b1 and the incident angle θ4 to the high refractive index thin film 6b2 are about 35 to 45 degrees. On the other hand, when the difference between the refractive index n1 of the low-refractive index thin film 6b1 and the refractive index n2 of the high-refractive index thin film 6b2 is 0.1 to 0.3, the polarization angle at the time of incidence on these film interfaces ( Brewster angle) is about 40 to 49 degrees. Thus, the incident angle to the low refractive index thin film 6b1 and the high refractive index thin film 6b2 is close to the polarization angle, and the separation efficiency between p-polarized light and s-polarized light at this interface is good.

  The s-polarized component reflected at the interface between the low-refractive index thin film 6b1 and the high-refractive index thin film 6b2 eventually reaches the optically active layer 6c. Is returned. The light re-incident on the light guide 4 that has undergone this rotation of the polarization plane is reflected by various portions of the light guide, reaches the optically active layer 6c again, and rotates again when passing through the optically active layer 6c. Receive. Therefore, the light that re-enters the thin film stack 6b also includes a p-polarized component that is a transmitted polarized component. This p-polarized light component is transmitted through the polarization conversion separation element 6 as described above.

  As the optically active layer 6c having optical rotation as described above, a layer made of cholesteric liquid crystal or a non-crystalline polymer compound having optical isomerism such as a layer made of polylactic acid or a polyester condensation polymer can be used. . The optically active layer 6c can be made of a material synthesized by a living organism. Examples of such a substance include poly (3-hydroxybutyrate-co-hydroxyhexanoate) known as a biodegradable plastic [weight average molecular weight: about 300,000 to about 900,000, melting point: 100 to 160 ° C.] can be used. Substances synthesized in this way are preferred because optical isomers having high purity and excellent optical activity can be obtained at low cost.

  FIG. 3 is an explanatory diagram of the shape and action of the XZ cross section of the prism row of the light deflection element 8. The light deflection element 8 has one of the main surfaces as a light incident surface 81 and the other surface as a light output surface 82. A large number of prism rows are arranged in parallel on the light incident surface 81, and each prism row is arranged on the primary light source side. It is composed of two prism surfaces, a first prism surface 84 positioned and a second prism surface 85 positioned far from the primary light source. In the embodiment shown in FIG. 3, the first prism surface 84 and the second prism surface 85 are both flat. The apex angle (α + β) of the prism row is preferably 35 ° to 80 °, more preferably 35 ° to 75 °, and still more preferably 40 ° to 70 °. Within this range, the direction in which the intensity of the light emitted from the light deflection element 8 is the strongest (the direction of the peak light) can be made to substantially coincide with the normal direction of the polarization conversion separation element 6 and concentrated in this direction. The polarized light can be emitted. The arrangement pitch P of the prism rows is, for example, 10 to 60 μm. In the present invention, it is particularly preferable that the light deflection element 8 has a large number of prism rows formed on the light incident surface 81 as described above. However, the light deflection element 8 has a large number of prism rows formed substantially in parallel on the light exit surface 82. May be.

  The light guide 4 and the light deflection element 8 of the present invention can be made of a synthetic resin having a high light transmittance. Examples of such synthetic resins include methacrylic resins, acrylic resins, polycarbonate resins, polyester resins, and vinyl chloride resins. In particular, methacrylic resins are optimal because of their high light transmittance, heat resistance, mechanical properties, and molding processability. Such a methacrylic resin is a resin mainly composed of methyl methacrylate, and preferably has a methyl methacrylate content of 80% by weight or more. When forming the rough surface of the light guide 4 and the light deflection element 8 or the surface structure such as the prism array or the lenticular lens array, the transparent synthetic resin plate is hot-pressed using a mold member having a desired surface structure. It may be formed, or may be formed simultaneously with molding by screen printing, extrusion molding, injection molding or the like. The structural surface can also be formed using heat or a photocurable resin. Furthermore, the surface of a transparent substrate such as a polyester resin, acrylic resin, polycarbonate resin, vinyl chloride resin, polymethacrylamide resin, or the like, or a rough surface made of an active energy ray curable resin is used. A structure or a lens array arrangement structure may be formed, or such a sheet may be bonded and integrated on a separate transparent substrate by a method such as adhesion or fusion. As the active energy ray-curable resin, polyfunctional (meth) acrylic compounds, vinyl compounds, (meth) acrylic acid esters, allyl compounds, (meth) acrylic acid metal salts, and the like can be used.

  A liquid crystal display device using the surface light source device of the present invention as a backlight by disposing a liquid crystal display element on the light emitting surface of the surface light source device having the above-described configuration (the light exit surface 82 of the light deflection element 8). Composed. The liquid crystal display device is observed by an observer through a liquid crystal display element.

  In the liquid crystal display element, only a specific polarization component is used. For this reason, a polarizing plate is disposed on the side where illumination light from the backlight is incident. That is, of the light incident on the liquid crystal display element from the surface light source device, only a specific polarization component that passes through the polarizing plate is effectively used for display. The polarization component in the direction orthogonal to the specific polarization component is absorbed by the polarizing plate and is not effectively used for display.

  In the surface light source device of the present invention as described above, the light emitted from the primary light source 2 and emitted through the light guide 4 is efficiently converted into a specific polarization component by the polarization conversion separation element 6, and then the liquid crystal display. Since the polarization direction of the outgoing polarization component matches the polarization direction of the polarization component transmitted through the incident-side polarizing plate of the liquid crystal display element, the light of the liquid crystal display device can be incident on the element. The utilization efficiency can be remarkably improved. Thus, the brightness of the liquid crystal display device is improved and the image display performance is improved.

  Hereinafter, the present invention will be described by way of examples.

  The polarization conversion separation element 6 described with reference to FIGS. Here, the low refractive index thin film 6b1 was formed by polymerizing 2,2,2-trifluoroethyl methacrylate. This polymer had a refractive index of 1.41 and a glass transition point of 80 ° C. The high refractive index thin film 6b2 was formed by polymerizing benzyl methacrylate. This polymer had a refractive index of 1.57 and a glass transition point of 70 ° C. These thin films were laminated on the sheet-like substrate 6a by using a spin coater so that a total of 10 layers (the thickness of each layer was 0.8 μm) were alternately formed. An optically active layer 6c was formed on the thin film laminate 6b thus obtained by applying polylactic acid to a thickness of about 20 μm using a spin coater.

  The polarization conversion separation element 6 obtained as described above is used for the primary light source 2 and the light guide 4 described with reference to FIGS. 1 to 2 (the emission angle 70 of the peak emission light from the light emission surface 42 in the XZ plane). In addition, a surface light source device was manufactured in combination with the light deflection element 8 and a liquid crystal display element was disposed thereon to manufacture a liquid crystal display device.

  When the primary light source 2 was turned on and the front luminance of the liquid crystal display element was measured, the front luminance was improved by about 20% compared to the case where the polarization conversion separation element 6 was not used.

  In the thin film laminate 6b of the polarization conversion separation element, the peak light incident angle to the low refractive index thin film 6b1 is 40.4 degrees, the peak light incident angle to the high refractive index thin film 6b2 is 37 degrees, The angle was 41.9 degrees.

It is a typical fragmentary perspective view which shows one Embodiment of the surface light source device using the polarization conversion separation element by this invention. It is explanatory drawing of the function of the polarization conversion by a polarization conversion separation element. It is explanatory drawing of the shape and effect | action of a XZ cross section of the prism row | line | column of an optical deflection | deviation element.

Explanation of symbols

2 invention primary light source 4 light guide 41 light incident end face 42 light exit surface 43 back surface 6 polarization conversion separation element 6a film-like substrate 6b thin film laminate 6b1 low refractive index thin film 6b2 high refractive index thin film 6c optically active layer 8 light deflecting element 81 Light entrance surface 82 Light exit surface 84 First prism surface 85 Second prism surface

Claims (22)

A thin film stack comprising a plurality of thin films stacked and a difference in refractive index between adjacent thin films of 0.05 or more, and an optically active layer disposed adjacent to the thin film stack. A polarization conversion separation element characterized by that. The polarization conversion separation element according to claim 1, wherein the optically active layer is bonded to the thin film laminate. The thickness of each of the thin films is in the range of (0.7 to 1.3) λ / 4, where λ is the wavelength of light used in the thin film. The polarization conversion separation element according to any one of the above. The polarization conversion separation element according to claim 1, wherein a thickness of the thin film is in a range of 0.1 to 100 μm. One of the thin films constituting the thin film laminate is a low refractive index thin film having a refractive index of 1.48 or less, and the other of the thin films constituting the thin film laminate is a high refractive index of 1.5 or more. The polarization conversion separation element according to claim 1, wherein the polarization conversion separation element is a refractive index thin film. The polarization conversion separation element according to claim 5, wherein the low refractive index thin film is made of a (co) polymer obtained using a monomer containing a fluorine atom. The polarized light according to claim 6, wherein the low refractive index film is made of a (co) polymer obtained by using an olefin, methacrylate, acrylate, ester or ether containing a fluorine atom as a monomer. Conversion separation element. The polarization conversion separation element according to claim 5, wherein the high refractive index thin film is made of a (co) polymer obtained using a monomer containing a phenyl group. The high refractive index film is obtained by using benzyl methacrylate, phenyl methacrylate, phenylethyl methacrylate, benzyl acrylate, vinyl benzoate, orthochlorostyrene, parafluorostyrene or paraisopropylstyrene as a monomer, and polystyrene. The polarization conversion separation element according to claim 8, wherein the polarization conversion separation element is made of polycarbonate. The polarization conversion separation element according to claim 1, wherein at least one of the thin films constituting the thin film laminate is made of an active energy ray curable resin. The polarization conversion separation element according to claim 10, wherein the active energy ray-curable resin contains fluorine. The polarization conversion separation element according to claim 10, wherein the active energy ray-curable resin contains at least one of a phenyl group and chlorine. The polarization conversion separation element according to claim 1, wherein the optically active layer is a cholesteric liquid crystal layer. The polarization conversion separation element according to claim 1, wherein the optically active layer is made of an amorphous polymer compound having optical isomerism. The polarization conversion separation element according to claim 1, wherein the optically active layer is made of a substance synthesized by a living organism. The polarization conversion separation element according to claim 1, wherein the optically active layer is polylactic acid or a polyester-based condensation polymer. It is a method of manufacturing the polarization conversion separation element according to any one of claims 1 to 16, wherein the thin film laminate is formed by sequentially laminating the thin film by a solvent casting method, a casting method or a spin coating method. A method for manufacturing a polarization conversion separation element. It is a method of manufacturing the polarization converting / separating element according to any one of claims 1 to 16, wherein the thin film laminate is formed by stretching a composite extrusion of the thin film. A method for manufacturing a conversion separation element. The method for manufacturing a polarization conversion separation element according to any one of claims 17 to 18, wherein after the thin film laminate is formed, the thin film laminate is subjected to a heat treatment at a temperature of 80 ° C or higher. A plate having a primary light source, a light incident end surface to which light emitted from the primary light source is incident and light emitted from the primary light source is incident, a light emitting surface from which the guided light is emitted, and a back surface on the opposite side The light-emitting surface of the light-guide is a rough surface with an average inclination angle of 0.5 to 20 degrees, and any one of claims 1 to 16 is provided on the light-emitting surface. A surface light source device, wherein the polarization conversion separation element according to claim 1 is disposed. 21. The surface according to claim 20, wherein the distribution peak light of the emitted light from the light emitting surface of the light guide body forms an angle of 50 to 75 degrees with respect to the normal direction of the light emitting surface. Light source device. A light deflecting element is disposed on the polarization converting / separating element, and the light deflecting element includes a plurality of prism rows extending in a direction along the light incident end face of the light guide and arranged in parallel with each other. The surface light source device according to claim 20, wherein the surface light source device is a surface light source device.

Images