JP6078969B2 - Light diffusing film, polarizing plate, and liquid crystal display device - Google Patents

Description

  The present invention relates to a light diffusion film that can diffuse and transmit incident light, a polarizing plate using the light diffusion film, and a liquid crystal display device.

A liquid crystal display device such as a liquid crystal television includes a liquid crystal panel and a surface light source device that illuminates the liquid crystal panel from the back side. The liquid crystal layer of the liquid crystal panel contains information on the image to be displayed, but the liquid crystal layer itself does not emit light, so that the viewer can see it by transmitting the light from the surface light source device. Video can be provided.
Due to the nature of the liquid crystal layer, the contrast and efficiency (transmittance) of transmitted light are excellent with respect to incident light (light source light) from the normal direction of the liquid crystal layer. However, the incident light (light source light) obliquely with respect to the normal direction is out of phase and polarized light, so that it is necessary to block this, and the use efficiency of light from the surface light source device is correspondingly reduced. descend. In addition, a retardation film may be disposed in order to compensate for such a phase shift with respect to incident light from an oblique direction.

  In order to improve the light utilization efficiency and eliminate the need for a retardation film, the output light from the surface light source device can be collected as much as possible in the normal direction of the panel surface of the liquid crystal panel (parallel light flux). The optical system of the surface light source device has been devised. Thereby, the light from the surface light source device can be used efficiently, and a configuration that does not require a retardation film is also possible.

  However, when the light source light that is brought close to the normal direction of the panel surface of the liquid crystal panel is transmitted through the liquid crystal panel and emitted to the viewer side, a very bright image can be observed in front of the liquid crystal display device. When the liquid crystal display device is viewed at an angle deviated from the front, it becomes dark and the so-called viewing angle becomes very narrow.

  Therefore, a light diffusing member is used on the light exit surface side (image observer side) of the liquid crystal display panel in order to widen the viewing angle of light including video information transmitted through the liquid crystal display panel. Patent Documents 1 and 2 disclose a technique for diffusing light by forming a diffractive structure having a hologram shape between two stacked layers.

Japanese Patent Application No. 2011-13320 Japanese Patent Application No. 2011-132568

  According to the inventions described in Patent Document 1 and Patent Document 2, it is possible to widen the viewing angle by the diffraction phenomenon. However, when the diffractive structure having such a technique is specifically applied to a display device or the like, other problems may occur. For example, when a dark screen is viewed with the display device turned off, a rainbow-like color unevenness (hereinafter sometimes referred to as “rainbow unevenness caused by external light”) or video light is displayed on a part thereof. When video is provided, the contrast of the video may be reduced.

  Accordingly, in view of the above problems, the present invention is arranged on the viewer side with respect to the liquid crystal layer of the liquid crystal display device, thereby exhibiting a viewing angle expansion characteristic suitable for the characteristics as the liquid crystal display device and external light. It is an object of the present invention to provide a light diffusing film that can suppress the resulting rainbow unevenness and contrast reduction of image light. In addition, a polarizing plate and a liquid crystal display device using the light diffusion film are provided.

  The present invention will be described below. In addition, in order to make an understanding of this invention easy, the reference sign of an accompanying drawing is attached in parenthesis writing, However, This invention is not limited only to the form of illustration.

The invention according to claim 1 includes a diffractive structure (11) having a diffractive structure (11a) that diffuses and emits light incident substantially parallel to the normal direction of the incident surface, and expands the viewing angle; A light reflection suppressing layer (13) disposed on the side where light is diffused by the structure and suppressing surface reflection, and the diffractive structure has a light emitting surface in a posture in which a light emitting surface of the diffractive structure is vertically set. front with respect to the surface, that Yusuke horizontal plane direction, and a diffractive structure to produce a luminance distribution only in the vertical plane direction, a light diffusing film (10).

  Here, “substantially parallel” means light having a half-value angle in the range of 0 ° to 15 ° with respect to the normal direction of the light incident surface of the diffractive structure.

  The invention according to claim 2 is the light diffusion film (10) according to claim 1, wherein the light reflection suppressing layer (13) has a moth-eye structure.

The invention according to claim 3 is the light diffusing film (10) according to claim 1 or 2 , wherein the diffractive structure (11a) is a computer generated hologram.

The invention according to claim 4 is the light diffusion film (10) according to any one of claims 1 to 3 , wherein the diffractive structure (11) has a side on which light is diffused by the diffractive structure (11a). In addition, a translucent layer (12) having translucency is directly laminated, and a portion constituting the diffractive structure of the diffractive structure and the translucent layer have a refractive index difference.

In the invention according to claim 5 , in the light diffusion film (10) according to claim 4 , the refractive index of the portion having the diffractive structure (11a) is higher than the refractive index of the light transmitting layer (12).

The invention according to claim 6 is a polarizing plate having the light diffusion film (10) according to any one of claims 1 to 5 and a PVA layer (103) laminated on the light diffusion film ( 102).

The invention according to claim 7 includes a surface light source device (110) that generates substantially parallel light, and a liquid crystal panel (101) disposed on an observer side of the surface light source device. A liquid crystal layer (106), a lower polarizing plate (105) disposed on the surface light source device side of the liquid crystal layer, and an upper polarizing plate (102) disposed on the viewer side of the liquid crystal layer, A polarizing plate is a liquid crystal display device (100) which is a polarizing plate of Claim 6 .

According to an eighth aspect of the present invention, in the liquid crystal display device (100) according to the seventh aspect , the upper polarizing plate (102) has a PVA layer (103) on the liquid crystal layer (106) side, and an observer of the PVA layer. It is the order of the light diffusion film (10) on the side.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to exhibit a viewing angle expansion characteristic, generation | occurrence | production of the rainbow nonuniformity resulting from external light and the contrast fall of an image | video can be suppressed.

It is a figure explaining 1st embodiment and is sectional drawing which shows the structure of the light-diffusion film 10 typically. It is a figure explaining the light-diffusion characteristic of the diffraction structure in a 1st example. It is another figure explaining the light-diffusion characteristic of the diffraction structure in a 1st example. It is a figure explaining the light-diffusion characteristic of the diffraction structure in a 2nd example. It is a figure explaining the light-diffusion characteristic of the other diffraction structure in a 2nd example. It is a figure explaining the light-diffusion characteristic of the diffraction structure in a 3rd example. It is a figure explaining the light-diffusion characteristic of the diffraction structure in a 4th example. It is a figure explaining the flow for obtaining the shape of a computer generated hologram. 1 is a perspective view illustrating a liquid crystal display device 100 using a light diffusion film 10. FIG. FIG. 10 is an exploded view showing a cross section (cross section taken along line XX in FIG. 9) of the surface light source device. It is an exploded view which shows the other cross section (cross section along XI-XI of FIG. 9) of a surface light source device. It is the figure which expanded a part of FIG. It is the figure which expanded a part of FIG. It is a figure explaining the example of the optical path of external light.

  The above-described operation and gain of the present invention will be clarified from embodiments for carrying out the invention described below. Hereinafter, the present invention will be described based on embodiments shown in the drawings. However, the present invention is not limited to these embodiments.

  FIG. 1 is a diagram illustrating one embodiment, and is a cross-sectional view schematically showing a configuration of a light diffusion film 10. The light diffusion film 10 includes a diffractive structure 11, a light transmissive layer 12, and a light reflection suppression layer 13.

  The diffractive structure 11 is formed with a diffractive structure 11a with irregularities on one surface thereof. The diffractive structure 11a has a function of diffusing and transmitting incident light using a diffraction phenomenon. The diffractive structure 11a of this embodiment is a so-called relief hologram. Thus, in this embodiment, the diffraction structure 11a included in the diffraction structure 11 is a relief hologram. However, the present invention is not limited to this, and a diffractive structure having another diffractive structure may be used as long as it can exhibit a function of diffusing light using diffraction. Other diffractive structures include diffraction gratings (gratings), diffractive optical elements such as Fresnel lenses (DOEs, etc.), volume holograms, and structures in which an arbitrary pattern is continuously arranged to develop a diffraction phenomenon. be able to.

The diffractive structure 11 is formed by laminating a layer having a relief hologram shape 11a (diffractive structure 11a) on one surface of a base layer having translucency. The material for the base layer is preferably highly transparent and smooth, such as polyethylene terephthalate film, polyethylene film, polypropylene film, polyvinyl chloride film, acrylic film, triacetyl cellulose film, cellulose acetate butyrate film, etc. Can be mentioned. The thickness of the base material layer is preferably 1 μm to 1 mm, more preferably 10 μm to 100 μm.
Further, from the viewpoint of productivity, the layer having the diffractive structure 11a is preferably made of a material that can have a hologram shape before curing and can be fixed by curing it by some means. For example, (meth) acrylates such as polyester (meth) acrylate, urethane (meth) acrylate, epoxy (meth) acrylate, polyether (meth) acrylate, polyol (meth) acrylate, melamine (meth) acrylate, and triazine (meth) acrylate Radical-polymerizable prepolymers such as 1,6-hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, dipentaerythritol hexa Examples include ionizing radiation curable resins made of a composition comprising one or more selected from radically polymerizable unsaturated monomers such as (meth) acrylate. Here, “(meth) acrylate” means acrylate or methacrylate.
As the ionizing radiation used for curing, electromagnetic waves such as ultraviolet rays, X-rays and visible rays, or charged particle beams such as electron beams and ion beams are used. In particular, when ultraviolet rays are employed as the ionizing radiation, the ionizing radiation curable resin is referred to as an ultraviolet curable resin.
In addition, thermoplastic resins such as acrylic resins, polycarbonate resins, and styrene resins, epoxy resins, thermosetting urethane resins, and thermosetting polyester resins can also be used.
In this embodiment, the layer having the diffractive structure 11 a is made of a material having a higher refractive index than that of the light transmitting layer 12.

  The translucent layer 12 is a layer having light transmissivity, which is laminated on the surface of the diffractive structure 11 on the side having the diffractive structure 11a. As a result, the translucent layer 12 follows the uneven shape of the diffractive structure 11a to form an interface with the diffractive structure 11a.

The translucent layer 12 can be composed of an adhesive having a refractive index lower than that of the layer having the diffractive structure 11a in the diffractive structure 11. As the adhesive, an acrylic resin type or silicon resin type can be applied. In order to lower the refractive index of the pressure-sensitive adhesive, a low-refractive index material such as a fluorine-based resin or magnesium fluoride fine particles may be added to the pressure-sensitive adhesive. As a means for realizing the refractive index difference between the layer having the diffractive structure 11a and the light-transmitting layer 12, a high refractive index material such as zirconium oxide, zinc oxide, tungsten oxide or the like in the material of the layer having the diffractive structure 11a. Fine particles consisting of can also be added. The average particle diameter of the fine particles of these low refractive index material and high refractive index material is not more than the shortest wavelength (380 nm) of visible light, preferably 10 nm, in order to ensure sufficient transparency in the visible light wavelength region. The range is ˜200 nm. When the difference in refractive index between the layer having the diffractive structure 11a and the light transmitting layer 12 is made sufficiently large, it is preferable to add a high refractive index material to one of the two layers and add a low refractive index material to the other.
Here, the difference in refractive index between the layer having the diffractive structure 11a and the light transmitting layer 12 is not particularly limited, but is preferably 0.1 or more.

Here, the material which comprises the translucent layer 12 can also be comprised with the other material which has translucency other than an adhesive agent. Other materials that are highly transparent and can follow the uneven shape of the diffractive structure 11a are preferably those that can be cured after being laminated by applying to the diffractive structure 11 before curing. For example, (meth) acrylates such as polyester (meth) acrylate, urethane (meth) acrylate, epoxy (meth) acrylate, polyether (meth) acrylate, polyol (meth) acrylate, melamine (meth) acrylate, and triazine (meth) acrylate Radical-polymerizable prepolymers such as 1,6-hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, dipentaerythritol hexa An ionizing radiation curable resin composed of one or two or more compositions selected from radically polymerizable unsaturated monomers such as (meth) acrylates can be mentioned.
As the ionizing radiation used for curing, electromagnetic waves such as ultraviolet rays, X-rays and visible rays, or charged particle beams such as electron beams and ion beams are used. In particular, when ultraviolet rays are employed as the ionizing radiation, the ionizing radiation curable resin is referred to as an ultraviolet curable resin.
In addition, thermoplastic resins such as acrylic resins, polycarbonate resins, and styrene resins, epoxy resins, thermosetting urethane resins, and thermosetting polyester resins can also be used.

  The light reflection suppressing layer 13 is a layer laminated on the surface of the light transmitting layer 12 opposite to the diffractive structure 11, and has a function of suppressing light reflection. The means for suppressing the reflection of light by the light reflection suppressing layer 13 is not limited, but in this embodiment, a so-called moth-eye structure is provided. That is, the light reflection suppressing layer 13 is formed by laminating a microprojection layer that has a large number of microprojections and forms a moth-eye structure on one surface of a base layer having translucency.

The base layer of the light reflection suppressing layer 13 can be made of the same material as the base layer of the diffractive structure 11 described above. Among these, it is preferable to use triacetyl cellulose (TAC) because of its good transmittance and excellent retardation characteristics.
In addition, the thickness of the base layer of the light reflection suppressing layer 13 is preferably as thin as possible in order to maintain high light transmittance. On the other hand, a certain amount of thickness is required from the viewpoint of supporting the microprojection layer. Necessary. From this viewpoint, the thickness of the base layer of the light reflection suppressing layer 13 is, for example, 20 μm to 200 μm.

The microprojection layer is formed as a layer made of a cured resin, and has a light reflection suppressing structure with a so-called moth-eye structure, which is composed of a large number of microprojections on the surface.
Each microprotrusion constituting the moth-eye structure has a size and an arrangement capable of exhibiting a light reflection suppressing structure.
With respect to the average value P _ave and the standard deviation σ for the interval P, the interval between the apexes of adjacent minute projections is P,
The maximum interval P _max is set to P _max = P _ave + 3σ,
When the maximum wavelength 780 nm of the visible light wavelength band is λ _max , P _max ≦ λ _max
By doing so, a light reflection suppressing structure is configured.

The visible light that needs the light reflection suppressing effect may not include the maximum wavelength 780 nm in the visible light wavelength band. However, in order to obtain a light reflection suppression effect for visible light of any wavelength, reflection suppression is performed for a minimum wavelength of 380 nm (hereinafter referred to as “λ _min ”), which is the smallest wavelength in the visible light wavelength band. If the structure can exhibit the effect, the light reflection suppressing effect can be exhibited even for light having a wavelength longer than λ _min . From such a viewpoint, more preferably, the maximum interval P _max is P _max ≦ λ _min . P _max is set in consideration of the above viewpoints and the like. Here, a specific example of P _max is 50 nm to 300 nm.

The height of the minute protrusion is about 150 nm to 450 nm. The height of the microprojection is the difference in height between the top of the microprojection and the valley bottom between adjacent microprojections, in other words, adjacent to the top of the microprojection in the direction perpendicular to the envelope surface of the microprojection layer surface. It is a distance with the valley bottom part between the microprotrusions. The heights of the plurality of microprotrusions may be aligned, uneven, or any. The height of the microprojections is preferably larger from the viewpoint of making the refractive index change smoother in the direction perpendicular to the envelope surface of the microprojection layer surface.
In terms of smoothing the change in refractive index, the cross-sectional area of the microprotrusion in the plane parallel to the envelope surface of the microprotrusion layer gradually increases from the top to the valley bottom of the adjacent microprotrusion. Shape is preferred. Further, it is more preferable that the cross-sectional area of the top is zero or close to zero.

  The arrangement of the microprojections in the horizontal plane may be either regular or irregular (random). Here, the horizontal plane is a plane parallel to the envelope surface of the surface of the microprojection layer.

  As the curable resin constituting the microprojection layer, a thermosetting resin such as urethane or epoxy, or an ionizing radiation curable resin such as acrylic or epoxy can be used. Among them, typically, for example, an ionizing radiation curable resin curable with ultraviolet rays or an electron beam is used. As the ionizing radiation curable resin, an acrylate resin that is typically one embodiment of an acrylic resin can be used. As the acrylate resin, a resin composition containing at least one of a prepolymer (or oligomer) and a monomer can be used.

As prepolymer (or oligomer), polyester (meth) acrylate, urethane (meth) acrylate, epoxy (meth) acrylate, triazine (meth) acrylate, silicone (meth) acrylate, acrylic (meth) acrylate Etc. can be used.
Monomers include polyfunctional monomers such as trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ethylene oxide modified dipentaerythritol hexa (meth) acrylate, (meth) Monofunctional monomers such as ethyl acrylate, 2-ethylhexyl (meth) acrylate, methoxyethyl (meth) acrylate, and butoxyethyl (meth) acrylate can be used.
In the present specification, (meth) acrylate means acrylate or methacrylate.

  Such an ionizing radiation curable resin may contain other additives as required. Such additives can include various known additives. For example, when the resin composition is cured by ultraviolet irradiation, a photopolymerization initiator such as acetophenone or benzophenone is added. In addition, release agents such as silicones and fluorines, leveling agents, various thermoplastic resins such as acrylics and polyesters, dilution solvents, plasticizers, stabilizers, UV absorbers, antistatic agents, etc. should be added. Can do.

  The light reflection suppressing layer 13 described above is produced by forming a microprojection layer on the base material layer, but the method is not particularly limited. For example, there are a hot press method, an injection molding method, a melt extrusion method and the like. Among them, in particular, the 2P method in which a resin liquid of ionizing radiation curable resin is brought into contact with a mold and shaped can accurately form fine surface irregularities on the order of submicrons such as a light reflection suppressing structure. Also, it is excellent in productivity and is a preferred method for forming a microprojection layer.

  In the 2P method, as a method of bringing a resin liquid made of an uncured resin composition into contact with the mold surface of the mold, (a) a method of directly applying the resin liquid to the mold surface of the mold, and (b) a substrate A method in which a resin liquid is applied onto the surface of the base material to be a layer to form a resin liquid layer formed on the base material layer, and then the resin liquid layer is brought into contact with the mold surface of the mold, and (c) molding There is a method in which a resin liquid is dropped and supplied between the base material layer and the mold surface of the molding die with respect to the base material layer to be brought into contact with the mold surface of the mold.

When the light diffusing film 10 having the above-described configuration is arranged in a display device, the light from the light source is diffused and transmitted by the action of the diffractive structure 11, thereby allowing the viewing angle. Can be spread. Further, since reflection of external light is suppressed by the light reflection suppression layer 13 with respect to external light, there is no reflection in the so-called screen and the contrast of the video light can be improved.
On the other hand, when the light source of the display device is not turned on to make a dark screen, it is possible to suppress rainbow unevenness caused by external light.
Such an effect will be described in detail later.

  Moreover, since the diffractive structure 11 a is covered with the light transmitting layer 12 by providing the light transmitting layer 12, it does not appear on the surface of the light diffusion film 10. Accordingly, it is not necessary to consider that the diffractive structure 11a exists even when the light reflection suppressing layer 13 is laminated. Furthermore, one and the other of the diffractive structure 11a are necessarily the diffractive structure 11 and the light transmitting layer 12, and the material of the one and the other sandwiching the diffractive structure 11a changes regardless of the layer in which the light diffusion film 10 is laminated. There is nothing to do. Therefore, it is possible to obtain the same diffraction regardless of what layer the light diffusion film 10 is laminated.

Next, a preferable example of the diffractive structure 11a provided in the present embodiment will be described. The diffractive structure 11a has a shape capable of transmitting incident light from the diffractive structure 11 side so as to diffuse the incident light to the translucent layer 12 side within a predetermined range. Specifically, the diffractive structure 11 is arranged on the liquid crystal display device 100 (see FIG. 9), two of the four sides of the rectangular light diffusion film body 10 are set horizontally, and the other two sides are set. When it is set to a vertical posture (vertical posture), that is, when the light emitting surface of the diffractive structure 11 is arranged so as to stand in a vertical direction, the light diffusion film 10 is a front surface of the diffractive structure 11, a horizontal plane. The light is diffused so that a luminance distribution is generated only in the viewing angle in the inner direction and in the vertical plane.
Therefore, in the liquid crystal display device 100, when an observer views the screen, it is only necessary to be able to observe an image or an image at a viewing angle in the front, horizontal plane, or vertical plane. Transmission of image light can be suppressed with respect to the corners. Therefore, since unnecessary transmission of light can be suppressed, the light use efficiency from the light source can be improved. In addition, since light is diffused by using diffraction, contrast reduction caused by backscattering of external light, which has been a problem in the case of a viewing angle widening member using refraction of light scattering particles, etc., and image sharpness It is possible to prevent so-called image blur in which the degree decreases.

  Here, it can be assumed that the incident light on the light diffusion film 10 is substantially parallel to the light incident surface normal of the light diffusion film 10. Specifically, like the liquid crystal display device 100 described later, the surface light source device 110 strongly deflects the direction of light in the normal direction and converges and collimates the normal direction of the light diffusion film 10. In this case, light that is substantially parallel to the direction is incident on the light diffusion film 10. “Substantially parallel” at this time means light having a half-value angle in the range of 0 ° to 15 ° with respect to the normal direction of the light incident surface of the light diffusion film 10. Therefore, it is preferable that the desired light can be diffused even if the light incident on the light diffusion film 10 has a half-value angle of ± 1 ° to ± 15 °.

  Such a diffractive structure 11a is not particularly limited as long as it exhibits the above functions, but among them, a computer generated hologram is preferable. According to the computer generated hologram, a diffusion range and a diffusion mode of transmitted light can be arbitrarily set, and desired light diffusion characteristics can be obtained. Hereinafter, the diffraction structure 11a using a computer generated hologram will be described with a plurality of examples.

  First, the light diffusion characteristics of the diffractive structure 11a according to the first example will be described. FIG. 2 is a diagram for explaining the light diffusion characteristics of the diffractive structure 11a according to the first example. 2A to 2C are diagrams showing the relationship between the viewing angle of the light diffusion film 10 and the luminance. More specifically, the light diffusing film 10 is arranged on the liquid crystal display device 100 (see FIG. 9), two of the four sides of the rectangular light diffusing film 10 are horizontal, and the other two sides are vertical. It is the figure which showed the relationship between a viewing angle and a brightness | luminance when it stood as a certain attitude | position (attitude in which the light emission surface was stood | rightened vertically). 2A shows the relationship between the viewing angle and the luminance in the horizontal plane, FIG. 2B shows the relationship between the viewing angle and the luminance in the vertical plane, and FIG. 2C shows the viewing angle in the plane of 45 ° obliquely. It is the relationship between corners and brightness. According to the diffractive structure 11a of the first example, when diffracting and diffusing the light incident from the diffractive structure 11 side, it has high luminance near a viewing angle of 0 ° (that is, the front direction with respect to the light exit surface). It can be seen that light is transmitted. In addition, in the horizontal plane and the vertical plane, there is luminance at viewing angles of ± 30 ° to ± 40 °. On the other hand, in the plane of 45 °, it does not have such luminance except near the viewing angle of 0 °. Therefore, according to the first example, bright image light can be observed in the front direction with respect to the light exit surface, ± 30 ° to ± 40 ° in the horizontal plane, and ± 30 ° to ± 40 ° in the vertical plane.

  In order to obtain such light diffusion characteristics, the luminance near the viewing angle of 0 ° uses diffraction zero-order light, and ± 30 ° to ± 40 ° in the horizontal plane and ± 30 ° to ± 40 in the vertical plane. For the luminance of 40 °, the diffracted primary light can be used. Accordingly, when obtaining the shape of the computer generated hologram, it is sufficient to configure so that the primary light is diffracted to a desired angle. FIG. 3 shows an explanatory diagram. FIG. 3 is a graph showing the light diffusion characteristics related to the primary light. The horizontal axis is the horizontal in-plane viewing angle, and the vertical axis is the vertical in-plane viewing angle. A hatched portion in FIG. 3 is an angle range in which luminance should be obtained by primary light. Therefore, the light diffusion characteristics described above can also be expressed as shown in FIG. Then, based on the diagram shown in FIG. 3, an original diagram for finally obtaining a hologram shape by Fourier transform is obtained, and by applying Fourier transform or the like to this, the above-mentioned light diffusion characteristics are finally obtained. Can be obtained. How to obtain a specific diffraction structure 11a using FIG. 3 will be described later.

  Here, the ratio of the luminance magnitude of the primary light (luminance at a viewing angle of ± 30 ° to 40 °) to the luminance magnitude of the zero-order light (luminance at a viewing angle of 0 °) is not particularly limited. However, it is preferable that the brightness of the primary light is 0.1 times or more than the brightness of the 0th-order light.

  In the first example, the luminance in the horizontal plane viewing angle of ± 30 ° to ± 40 ° and the vertical in-plane viewing angle of ± 30 ° to ± 40 ° are configured to be the same. (Refer to FIG. 2 (a) and FIG. 2 (b)), the luminance in the horizontal plane viewing angle ± 30 ° to ± 40 ° may be larger than the luminance in the vertical plane viewing angle ± 30 ° to ± 40 °. . According to this, when the light diffusing film 10 is disposed in, for example, a stationary liquid crystal display device, the luminance distribution in the horizontal plane is particularly important, so that it is possible to obtain light diffusing characteristics commensurate with this.

Next, the light diffusion characteristics of the diffractive structure 11a according to the second example will be described. FIGS. 4 and 5 show diagrams corresponding to FIG. 3 among the diagrams illustrating the diffraction structure 11a according to the second example. 4 and 5, the example shown in FIG. 4 is an example in which the luminance is increased in a plurality of angle ranges in the horizontal plane viewing angle and the vertical plane viewing angle. More specifically, in addition to the high brightness in the front due to the 0th order light, the brightness in the range of ± 30 ° to ± 40 ° and ± 60 ° to ± 70 ° in the horizontal and vertical planes by the primary light. Get higher.
On the other hand, the example shown in FIG. 5 is an example in which the luminance increases in a wider angle range than the first example in the horizontal plane viewing angle and the vertical in-plane viewing angle. More specifically, in addition to the high brightness in the front due to the 0th-order light, the brightness is increased in the range of ± 30 ° to ± 70 ° in the horizontal plane and the vertical plane by the primary light.
Thus, in the second example, a hologram shape that diffuses light in a wider range in the horizontal plane and the vertical plane is formed, and when applied to a liquid crystal display device, a wide viewing angle corresponding to this can be obtained. It becomes possible.

  Next, the light diffusion characteristics of the diffractive structure 11a according to the third example will be described. FIG. 6 shows a diagram corresponding to FIG. 3 among the diagrams for explaining the diffraction structure 11a according to the third example. In the example shown in FIG. 6, in addition to the viewing angle described in the first example, the luminance is also increased in the range of −10 ° to + 10 °. That is, the diffractive structure 11a is formed so as to continuously diffuse light from the front to ± 45 ° in the horizontal plane and from the front to ± 45 ° in the vertical plane. Accordingly, when applied to a liquid crystal display device, images can be continuously observed in the range of ± 45 ° in the horizontal plane from the front and ± 45 ° in the vertical plane from the front.

Next, the light diffusion characteristics of the diffractive structure 11a according to the fourth example will be described. FIG. 7 shows a diagram for explanation. The upper part of FIG. 7 shows the horizontal luminance distribution in this example. Here, the luminance distribution having the maximum luminance at the viewing angle of 0 ° is due to the 0th order light, and the luminance distribution having the maximum luminance at the angle other than the viewing angle of 0 ° is due to the primary light. The lower part of FIG. 7 is a diagram for obtaining a diffraction structure 11a for realizing such a luminance distribution, and corresponds to FIG. As can be seen from FIG. 7, in this example, the viewing angle at which the maximum luminance of the primary light is outside the half-value angle of the zero-order light (the viewing angle position at which the luminance is halved with respect to the maximum luminance). It is comprised so that it may become a corner.
According to the hologram shape (diffraction structure) having such light diffusion characteristics, the continuity between the zero-order light and the first-order light can be improved. Therefore, when this is applied to a liquid crystal display device, it is possible to observe images continuously from the front to the horizontal plane and from the front to the vertical plane.
In FIG. 7 and the above description, only the horizontal in-plane viewing angle has been described, but the same applies to the vertical in-plane viewing angle.

  In each example described above, it has been described that the light incident on the light diffusion film 10 has the same spread in the horizontal plane direction and the vertical plane direction. However, when the light diffusion film 10 is used in a liquid crystal display device, the light incident on the light diffusion film 10 does not necessarily have the same spread in the horizontal plane direction and the vertical plane direction. In this way, when the incident light has different spreads depending on the direction (for example, an elliptical shape), if the light diffusion film 10 is applied as it is, there is a range in which the light is diffused in the horizontal plane and the vertical plane. It may be different. For this, the diffraction structure 11a can be corrected in advance so that the same light diffusion range is possible in the horizontal plane and in the vertical plane in consideration of the characteristics of the incident light. Further, a hologram shape can be formed so that desired light diffusion characteristics can be obtained by utilizing the fact that the light diffusion range is different between the horizontal plane and the vertical plane.

  Moreover, each example demonstrated above is an illustration, and it is possible to form the hologram shape for obtaining a desired light-diffusion characteristic besides the above. In this embodiment, only the 0th-order light and the 1st-order light in diffraction are considered, but higher-order light higher than the 2nd-order light may be considered.

  The above-described computer generated holograms are obtained by arranging a plurality of minute unit computer holograms having the respective optical functions described above and combining them, or unit computer holograms arranged in a compound eye shape. For example, a unit computer hologram is formed in a square shape, and a plurality of the unit computer holograms having a square shape are densely arranged in a vertical / horizontal lattice pattern, or a so-called zigzag pattern in which vertical or horizontal lines are shifted by half a pitch every other row. Can be mentioned. In addition, it is also conceivable that the unit computer generated holograms are not densely arranged with no gap but are sparsely arranged with a predetermined gap or arranged based on a predetermined pattern. Of course, the shape of the unit computer hologram is not limited to a square, and may be formed in any shape including a rectangle and other polygons. Further, the shape and arrangement of unit computer holograms included in one computer hologram are not necessarily constant, and may be changed depending on the location.

  In the present embodiment, the example in which the light reflection suppressing function is exhibited by providing the light reflection suppressing layer 13 with the moth-eye structure is shown, but the present invention is not necessarily limited to this, and other means (so-called “AR”) ) Light reflection suppression may be performed. Examples thereof include a light reflection suppressing layer formed by laminating a large number of layers having different refractive indexes.

  Next, an example of the manufacturing method of the light diffusion film 10 will be described. The light diffusing film 10 includes a step of obtaining a specific shape of the diffractive structure, a step of producing a mold based on the obtained diffractive structure, a step of forming the diffractive structure on the diffractive structure using the die, and a translucent layer. It is manufactured including the step of forming and the step of laminating the light reflection suppressing layer. Each step will be described below.

  The step of obtaining a specific shape of the diffractive structure can use a known method as long as the shape having the optical function described above can be obtained. Here, a method for obtaining a hologram shape of a computer generated hologram as a diffraction structure described as a preferred embodiment of the light diffusion film 10 will be described. Since the computer generated hologram itself is known, a known method (for example, Japanese Patent No. 4620220) can be applied to a method for obtaining the computer generated hologram shape. Here, an example will be described.

  In general, a computer generated hologram is obtained as follows. In other words, assuming a certain hologram and the reproduction distance from it is sufficiently large compared to the size of the hologram, and illuminating light parallel to the normal of the hologram surface, the diffracted light obtained on the reproduction image surface is Expressed by Fourier transform of the amplitude distribution and phase distribution (Fraunhofer diffraction). Therefore, in order to give a predetermined diffracted light to the reproduction image plane, a computer generated hologram arranged on the hologram plane is repeatedly repeated with Fourier transform and inverse Fourier transform while applying a constraint condition between the hologram plane and the reproduction image plane. The method to obtain | require is known (Gerchberg-Saxton iterative calculation method).

Therefore, it is considered to obtain a computer generated hologram that diffracts light only to a predetermined observation area when light parallel to the normal line of the hologram surface is illuminated from behind by using the Gerchberg-Saxton iterative calculation method. Here, for easy understanding, the amplitude distribution on the hologram surface is _represented by A _HOLO , the phase distribution on the hologram surface is represented by φ _HOLO , the amplitude distribution on the reproduction image surface is represented by A _IMG , and the phase distribution on the reproduction image surface is represented by φ _IMG . . The flow is shown in FIG.
Here, when obtaining a specific shape of a computer generated hologram, it is calculated by creating and calculating an amplitude distribution based on the angular distribution as shown in FIGS. 3, 4, 5, 6, etc. described above. be able to.

In the surface region (x0 ≦ x ≦ x1, y0 ≦ y ≦ y1) in which the computer generated hologram is formed in step S1, 1 is given to A _HOLD as an initial value, and a random value is given to φ _HOLD .
In step S2, a predetermined Fourier transform is applied to the initialized value to obtain A _IMG and φ _IMG .
In step S3, if it is determined that A _IMG is substantially constant within a predetermined area and is substantially 0 outside the predetermined area, A _HOLD and φ _HOLD initialized in step S1 are the desired computer holograms. It becomes.

On the other hand, if it is determined in step S3 that such a condition is not satisfied, a constraint condition is assigned in step S4. Specifically, A _IMG is set to 1, for example, in the predetermined area, and is set to 0 in the other areas, and φ _IMG is maintained as it is.
Next, a predetermined inverse Fourier transform is performed under the condition after the binding condition is given in step S5.
The value on the hologram surface obtained by the inverse Fourier transform is given a constraining condition in step S6, A _HOLD is set to 1, and φ _HOLD is multivalued (approximate the original function to a digital step-like function (quantum )). However, in the case where φ _HOLD may have continuous values, this multi-value conversion is not necessarily required.

  And it returns to process S2 and Fourier-transform is given to the value. Thereafter, the same processing as described above is performed, and it is repeated until the condition of step S3 is satisfied (until convergence), thereby obtaining a final desired computer generated hologram.

  Next, a process for producing a mold based on the obtained diffraction structure will be described. In order to form the hologram shape 11a (diffraction structure 11a) in the diffraction structure 11, a mold having an uneven shape capable of transferring the obtained computer generated hologram shape to a material to be the diffraction structure 11 is required. Here, a process of manufacturing the mold will be described. Although a known method can be used for manufacturing such a mold, an example will be described below.

First, a resist layer having dry etching resistance is formed in a thin film shape on a chromium thin film of a photomask blank plate in which a surface low-reflection chromium thin film is laminated on a substrate such as synthetic quartz. As an example of the resist for dry etching, ZEP7000 manufactured by Nippon Zeon Co., Ltd. can be used. The resist is laminated by spin coating using a spinner or the like.
The resist layer is subjected to pattern exposure. The pattern exposure can be performed by a plate-like pattern, laser beam scanning with a laser drawing apparatus, or electron beam scanning with an electron beam drawing apparatus.
This exposure forms a readily soluble part in which the resist resin is cured and an unexposed part. Therefore, the resist pattern is formed by removing the easily soluble part by solvent development by spray development performed by spraying a developer. Form.

  Using the formed resist pattern, the portion of the chromium thin film not covered with the resist is removed by dry etching, and the underlying quartz substrate is exposed in the removed portion. Next, dry etching is similarly performed on the exposed quartz substrate, and the quartz substrate is etched. The quartz substrate in which the concave portion generated by the progress of etching, the chromium thin film, and the resist thin film are sequentially coated from the bottom. A convex portion made of the original portion is formed. Thereafter, the resist thin film is removed by dissolution or the like, and a quartz substrate having a concave portion formed by etching the quartz substrate and a convex portion composed of a portion where a chromium thin film is laminated on the top is obtained.

  With only the above method, only a binary part of the convex part and the concave part (high and low two steps, and a depth of another level surface occurs in addition to the surface of the original quartz substrate) is obtained. However, by repeating the photo-etching process consisting of resist formation → pattern exposure → resist development → dry etching of chromium thin film → dry etching of quartz substrate → resist removal for those obtained above Photoetching can be further performed on the concave portions and the convex portions generated by the first photoetching. By repeating this a plurality of times, it is possible to accurately obtain a plurality of irregularities having a height difference. In this way, after obtaining the predetermined number of steps, the chromium thin film is removed by wet etching to obtain a computer generated hologram type in which irregularities with a predetermined number of steps are formed on the surface of the quartz substrate.

  Next, a process for forming the diffraction structure using the produced computer generated hologram will be described. As a method of replicating a computer generated hologram using the mold, for example, a method of pressing the mold against a resin layer that is softened by heating, an injection method, a casting method, or the like can be used. As the resin used in these methods, both thermoplastic and thermosetting can be used. Industrially, an uncured resin composition preferably containing an ultraviolet curable resin is brought into contact with the surface on which the unevenness of the mold is formed, and a film serving as a base material layer of the diffractive structure 11 is formed on the opposite side of the resin composition. Lamination is performed so that the resin composition is sandwiched between the mold and the plastic film. From such a state, the resin composition is cured by irradiating ultraviolet rays or the like, and then the film and the ultraviolet curable resin composition layer cured and formed into a hologram shape are released from the mold. A diffractive structure 11 is formed. That is, it is the diffractive structure 11 in which the layer having the diffractive structure 11a is laminated on one surface of the base layer having translucency.

  Next, the process of forming a light transmissive layer on the diffractive structure 11 will be described. The light transmissive layer 12 can be formed by a method in which the above-described material having a function as an adhesive is applied on the diffractive structure 11. When a thermoplastic resin, a thermosetting resin, or an ultraviolet curable resin is used as the light-transmitting layer 12, a squeegee is used for the thermoplastic resin, the thermosetting resin, or the ultraviolet curable resin before curing as exemplified above. It is possible to use a method in which the material is coated on the diffractive structure 11 and cured by a curing method corresponding to the material used.

  In the step of laminating the light reflection suppressing layer, the light reflection suppressing layer 13 is stacked on the formed light transmitting layer 12. If the light-transmitting layer is a layer that exhibits a function as an adhesive, the light reflection suppressing layer may be laminated using this. When the translucent layer 12 does not have a function as an adhesive, the light reflection suppressing layer 13 is laminated through the adhesive layer. The manufacturing method of the light reflection suppressing layer 13 itself is as described above.

  The light diffusion film 10 can be manufactured by the method as described above.

  Next, the liquid crystal display device 100 using the above-described light diffusion film 10 will be described. FIG. 9 is an exploded perspective view focusing on the liquid crystal panel 101 and the surface light source device 110 in the display device 100. The liquid crystal display device 100 will be described with reference to FIG.

The display device 100 includes a liquid crystal panel 101 and a surface light source device 110. Further, the display device 100 is provided with normal equipment that is necessary to operate as a display device, although the description is omitted.
In FIG. 9, the viewer is on the page.

  The liquid crystal panel 101 includes an upper polarizing plate 102 disposed on the viewer side, a lower polarizing plate 105 disposed on the surface light source device 110 side, and a liquid crystal layer disposed between the upper polarizing plate 102 and the lower polarizing plate 105. 106.

The upper polarizing plate 102 is configured by laminating a PVA layer 103 and a light diffusion film 10.
The PVA layer 103 is formed by impregnating a PVA (polyvinyl alcohol) layer with iodine, and is stretched. The PVA layer 103 is laminated on the liquid crystal layer 106 and has two polarized components (for example, P Wave, S wave, etc.), transmits a polarization component (for example, P wave) in one direction (direction parallel to the transmission axis), and transmits the other direction (parallel to the absorption axis) perpendicular to the one direction. Direction) and a polarizing plate body (so-called “polarizer”) that substantially exhibits a polarizing action. A known layer can be applied to the PVA layer 103.
The light diffusion film 10 is the above-described one laminated on the PVA layer 103 and has a function of diffusing and transmitting incident light.

  The lower polarizing plate 105 also includes a PVA layer, which decomposes incident light into two orthogonally polarized components (for example, P wave and S wave) in one direction (a direction parallel to the transmission axis). It has a function of transmitting a polarization component (for example, P wave) and absorbing a polarization component (for example, S wave) in the other direction (direction parallel to the absorption axis) orthogonal to the one direction.

  The liquid crystal layer 106 is formed by sealing a liquid crystal material between a pair of glass plates. A plurality of unit cells that form pixels are arranged so that an electric field can be applied to each unit cell, and the alignment direction of the liquid crystal molecules in the unit cell to which the electric field is applied changes. A polarized light component in a specific direction (in this embodiment, P wave) transmitted through the lower polarizing plate 105 disposed on the surface light source device 110 side (that is, the light incident side) passes through the unit cell to which an electric field is applied. The polarization direction is rotated by 90 °, while the polarization direction is maintained when passing through a unit cell to which no electric field is applied. For this reason, depending on whether or not an electric field is applied to the unit cell, the polarization component (P wave) in a specific direction transmitted through the lower polarizing plate 105 is disposed on the light output side of the lower polarizing plate 105 and the PVA layer 103 of the upper polarizing plate 102. It is possible to control whether the light is further transmitted through the (polarizer) or is absorbed and blocked by the PVA layer 103.

  In this way, the liquid crystal panel 101 is configured to display an image by controlling transmission or blocking of light from the surface light source device 110 for each unit cell (pixel).

Next, the surface light source device 110 will be described. FIG. 10 shows a cross-sectional view of the surface light source device 110 along the line XX in FIG. 9, and FIG. 11 shows a cross-sectional view along the line XI-XI.
The surface light source device 110 is an illuminating device that is disposed on the opposite side of the liquid crystal panel 101 from the viewer side and emits planar light to the liquid crystal panel 101. As can be seen from FIGS. 9 to 11, the surface light source device 110 is configured as an edge light type surface light source device, and includes a light guide plate 111, a light source 115, an optical sheet 120, and a reflection sheet 125. Yes.

  As can be seen from FIGS. 9 to 11, the light guide plate 111 has a base 112 and a unit optical element portion 113. The base 112 is a flat plate-like member, and is configured by dispersing light scattering particles 112b in a main portion 112a having translucency. The light scattering particles 112b act on the light traveling in the main portion 112a by changing the traveling direction of the light by reflection or refraction. Such a light diffusing function (light scattering function) of the light scattering particles 112b can be achieved, for example, by using the light scattering particles 112b having a refractive index different from that of the material forming the main portion 112a. In addition, the material which can have a reflective effect with respect to light may be sufficient.

  As can be seen from FIGS. 9 to 11, the unit optical element portion 113 is a portion formed on the surface of the base portion 112 on the optical sheet 120 side, and a plurality of unit optical elements 113 a are arranged in parallel. The unit optical element 113a is a columnar element that maintains the cross section appearing in FIG. 11 and extends in the direction toward the back of the drawing, and the extending direction is a direction orthogonal to the direction in which the unit optical elements 113a are arranged.

  FIG. 12 shows an enlarged view paying attention to the unit optical element 113a of FIG. As can be seen from FIG. 12, the unit optical element 113 a has a convex triangular prism shape having a base on one surface of the base 112 and protruding from the base 112. The main cut surface shape shown in the figure (the shape in a cross section perpendicular to the extending direction of the unit optical element) has a triangular shape. In the unit optical element 113a of the present embodiment, the apex that faces the base is curved as the main cut surface.

Moreover, it is preferable that the main cut surface shape of the unit optical element 113a satisfies at least one of the following condition A and condition B.
Condition A: Angles other than the apex angle of the main cut surface triangular shape, that is, the angles θ ₁ and θ _{2 of} the base angles located on the base 112 of the main cut surface triangular shape are 25 ° or more and 45 ° or less.
Condition B: The ratio (Ha / Wa) of the height Ha of the unit optical element 113a to the length Wa of the base of the unit optical element 113a is 0.2 or more and 0.5 or less.
When at least one of the condition A and the condition B is satisfied, as will be described later, of the light emitted from the light guide plate 111, the component along the direction in which the unit optical elements 113a are arranged (left and right direction in FIG. 11) The light collecting effect is very effectively exerted.

In this embodiment, the unit optical element 113a is a cross section appearing in FIGS. 11 and 12 (a cross section along the direction in which the unit optical elements 113a are arranged, but also matches the main cut surface of each unit optical element 113a. Isosceles triangle. According to this, it is possible to effectively increase the luminance in the front direction and to impart symmetry to the luminance angular distribution in the plane along the arrangement direction of the unit optical elements 113a. Therefore, it is preferable that the two base angles θ ₁ and θ ₂ of the triangular cross section in the cross section are equal.

  The “triangular shape” in the present specification is not limited to a triangular shape in a strict sense, but may include a substantially triangular shape including limitations in manufacturing technology, errors in molding, and the like. If it is within a range where a function equivalent to the optical function to be performed can be secured, it is included in the “triangular shape”. Similarly, terms used in the present specification to specify other shapes and geometric conditions, for example, terms such as “parallel”, “orthogonal”, “ellipse”, “circle”, etc. are bound to the strict meaning. Therefore, it should be interpreted including an error to the extent that a similar optical function can be expected.

The dimensions of the light guide plate 111 having the above-described configuration can be set as follows as an example. First, as a specific example of the unit optical element 113a, the width Wa (see FIG. 12) along the plate surface of the light guide plate 111 can be set to 20 μm or more and 500 μm or less, and the normal direction nd to the plate surface of the light guide plate 111 is nd. The height Ha (see FIG. 12) of the unit optical element 113a along the line can be 4 μm or more and 250 μm or less. Further, when the cross-sectional shape of the unit optical element 113a is a triangular shape, the angle of the apex angle θ ₃ (see FIG. 12) can be 90 ° or more and 125 ° or less.
On the other hand, the thickness of the base 112 can be 0.5 mm to 6 mm.

  The light guide plate 111 having the above-described configuration can be manufactured by extrusion molding or by molding the unit optical element 113a on a base material. Various materials can be used as the material forming the main portion 112a of the base 112 of the light guide plate 111 and the unit optical element 113a. However, it is widely used as a material for an optical sheet incorporated in a display device, and has excellent mechanical properties, optical properties, stability, workability, and the like, and can be obtained at low cost, such as acrylic, styrene, polycarbonate, Transparent resins mainly composed of one or more of polyethylene terephthalate, acrylonitrile and the like, and epoxy (meth) acrylate and urethane (meth) acrylate-based reactive resins (ionizing radiation curable resins and the like) can be suitably used. On the other hand, the light scattering particles 112b are, for example, particles made of a transparent material such as silica (silicon dioxide), alumina (aluminum oxide), acrylic resin, polycarbonate resin, or silicone resin having an average particle diameter of about 0.5 μm to 100 μm. Can be used.

  In the light guide plate 111 manufactured by extrusion molding, the base portion 112 and the unit optical element portion 113 can be integrally formed. Further, when the light guide plate 111 is manufactured by extrusion molding, the unit optical element portion 113 may be the same resin material as the material forming the main portion 112 a of the base portion 112.

  Returning to FIGS. 9 to 11, the light source 115 will be described. The light source 115 is disposed on each of a pair of side surfaces that are both ends in the longitudinal direction (extending direction) in which the unit optical element 113a extends, among two opposing plate-like side surfaces of the base 112 of the light guide plate 111. The The type of the light source is not particularly limited, but may be configured in various forms such as a fluorescent lamp such as a linear cold cathode tube, a point LED (light emitting diode), or an incandescent lamp. In the present embodiment, the light source 115 is composed of a plurality of LEDs, and the output of each LED, that is, the lighting and extinguishing of each LED and / or the brightness when each LED is lit, is controlled by a control device (not shown). It is configured so that it can be adjusted independently from the output of the LED.

  Next, the optical sheet 120 will be described. As can be seen from FIGS. 9 to 11, the optical sheet 120 is provided on the surface facing the light guide plate 111, that is, on the light incident side surface, out of the surface of the main body 121 and the main body 121. Unit prism portion 122.

  As will be described later, the optical sheet 120 changes the traveling direction of light incident from the light incident side and emits the light from the light outgoing side, thereby intensively improving the luminance in the front direction (normal direction of the light emitting surface). (Condensing function). This light condensing function is mainly exhibited by the unit prism portion 122 of the optical sheet 120.

  As shown in FIGS. 9 to 11, the main body 121 functions as a flat sheet-like member that supports the unit prism portion 122. Of the surfaces of the main body 121, the surface opposite to the side facing the light guide plate 111 is the light exit side surface. In the present embodiment, the light outgoing side surface of the main body 121 is formed as a flat (flat) and smooth surface. However, the light emission side surface is not limited to being a smooth surface, and may be a surface with a minute unevenness (so-called mat surface), and it is possible to apply a surface form as required. is there.

  The unit prism part 122 is arranged so that a plurality of unit prisms 122 a are arranged along the light incident side surface of the main body part 121 as shown in FIGS. 9 to 11. More specifically, the unit prism 122a is a columnar member formed so as to extend while maintaining the predetermined main cutting surface shape shown in FIG. The extending direction is a direction perpendicular to the direction in which the unit prisms 122a are arranged, and is a direction shifted by 90 degrees with respect to the direction in which the unit optical element 113a of the light guide plate 111 extends. Therefore, the extending direction of the unit prism 122a and the extending direction of the unit optical element 113a are orthogonal to each other when the display device is viewed from the front.

  The longitudinal direction of the unit prism 122a intersects the transmission axis of the lower polarizing plate 105 of the liquid crystal panel 101 when observed from the front. Preferably, the longitudinal direction of the unit prism 122a of the optical sheet 120 is a surface parallel to the display surface of the display device with respect to the transmission axis of the lower polarizing plate 105 of the liquid crystal panel 101 (the sheet surface of the main body 121 of the optical sheet 120). Intersecting at an angle greater than 45 ° and less than 135 °. The angle here means the smaller one of the angles formed by the longitudinal direction of the unit prism 122a and the transmission axis of the lower polarizing plate 105, that is, an angle of 180 ° or less. . In particular, in the present embodiment, the longitudinal direction of the unit prisms 122a of the optical sheet 120 is orthogonal to the transmission axis of the lower polarizing plate 105 of the liquid crystal panel 101, and the direction in which the unit prisms 122a of the optical sheet 120 are arranged is The liquid crystal panel 101 is preferably parallel to the transmission axis of the lower polarizing plate 105.

  Next, the sectional shape of the unit prisms 122a in the arrangement direction will be described. FIG. 13 is an enlarged view of a part of the optical sheet 120 in FIG. Here, nd represents the normal direction of the sheet surface of the main body 121.

  As can be seen from FIG. 13, in this embodiment, the unit prism 122 a has an isosceles triangular cross section in which the surface of the main body 121 on the light guide plate 111 side protrudes. That is, the width of the unit prism 122a in the direction parallel to the sheet surface of the main body 121 decreases as the distance from the main body 121 increases along the normal direction nd of the main body 121.

  In the present embodiment, the outer contour of the unit prism 122a is axisymmetric with respect to an axis parallel to the normal direction nd of the main body 121, and the cross section is an isosceles triangle. As a result, the luminance on the light exit surface of the optical sheet 120 has a symmetrical angular distribution of luminance about the front direction on the surface parallel to the arrangement direction of the unit prisms 122a.

Here, although not particularly limited dimensions of the unit prisms 122a, apex angle theta ₄ is 60 ° to 70 ° (see FIG. 13), base width W is suitably by about 50 [mu] m (see FIG. 13) In many cases, it is possible to obtain a light condensing characteristic.

  The optical sheet 120 having the above-described configuration can be manufactured by extrusion molding or by forming the unit prism 122a on a base material. Various materials can be used as the material forming the optical sheet 120. However, it is widely used as a material for an optical sheet incorporated in a display device, and has excellent mechanical properties, optical properties, stability, workability, and the like, and can be obtained at low cost, such as acrylic, styrene, polycarbonate, Transparent resins mainly composed of one or more of polyethylene terephthalate, acrylonitrile and the like, and epoxy (meth) acrylate and urethane (meth) acrylate-based reactive resins (ionizing radiation curable resins and the like) can be suitably used.

  In the present embodiment, the unit prism having a triangular cross-section as described above has been described. However, the present invention is not limited to this, and the light guide plate 111 is not limited to this. It may be a pentagon facing the side. Further, the shape of the slope may be a polygonal line or a curve.

  Returning to FIGS. 9 to 11, the reflection sheet 125 of the surface light source device 110 will be described. The reflection sheet 125 is a member that reflects light emitted from the back surface of the light guide plate 111 and makes the light enter the light guide plate 111 again. The reflection sheet 125 is a sheet that is capable of so-called specular reflection, such as a sheet made of a material having a high reflectivity, such as a metal, or a sheet containing a thin film (for example, a metal thin film) made of a material having a high reflectivity as a surface layer. It can be preferably applied. Thereby, it becomes possible to improve the convergence property of light, and the energy use efficiency can be improved.

  Next, the operation of the display device 100 having the above configuration will be described with an example of an optical path. However, this optical path example conceptually shows the optical path, and does not strictly represent the degree of refraction or reflection.

  First, as shown in FIG. 10, the light emitted from the light source 115 enters the light guide plate 111 through the light incident surface on the side surface of the light guide plate 111. FIG. 10 shows an example of an optical path of light L21 and L22 incident on the light guide plate 111 from the light source 115 as an example.

  As shown in FIG. 10, the light L21 and L22 incident on the light guide plate 111 repeatedly undergoes total reflection due to a difference in refractive index with air on the surface of the unit optical element portion 113 of the light guide plate 111 and the back surface on the opposite side. It proceeds in the extending direction of the unit optical element 113a.

  However, the light scattering particles 112b are dispersed in the main portion 112a of the base 112 of the light guide plate 111. For this reason, as shown in FIG. 10, the light L21 and L22 traveling in the light guide plate 111 has their traveling directions irregularly changed by the light scattering particles 112b, and the unit optical element unit 113 at an incident angle less than the total reflection critical angle. And may enter the opposite surface. In this case, the light can be emitted from the unit optical element portion 113 of the light guide plate 111 and the surface on the opposite side.

  Lights L21 and L22 emitted from the unit optical element unit 113 travel toward the optical sheet 120 disposed on the light output side of the light guide plate 111. On the other hand, the light emitted from the back surface opposite to the unit optical element portion 113 is reflected by the reflection sheet 125 disposed on the back surface of the light guide plate 111, enters the light guide plate 111 again, and passes through the light guide plate 111. Proceed (not shown).

  The collision between the light traveling in the light guide plate 111 and the light scattering particles 112b dispersed in the light guide plate 111 occurs in each section along the light guide direction in the light guide plate 111. For this reason, the light traveling in the light guide plate 111 is gradually emitted from the light exit surface. Thereby, the light quantity distribution along the light guide direction of the light emitted from the unit optical element portion 113 of the light guide plate 111 can be made uniform.

  In particular, the unit optical element portion 113 of the illustrated light guide plate 111 is constituted by a plurality of unit optical elements 113a, and the cross-sectional shape of each unit optical element 113a is a shape formed by chamfering a triangle or a vertex angle of a triangle. . That is, the unit optical element 113a has inclined surfaces 113aa and 113ab with respect to the back surface of the light guide plate 111 (see FIG. 12). Therefore, the lights L21 and L22 emitted from the light guide plate 111 via the unit optical element 113a are refracted when emitted from the light guide plate 111, for example, as indicated by the light L41 in FIG. This refraction is a refraction that approaches the sheet surface normal line nd in the arrangement direction of the unit optical elements 113a (the angle formed with the normal line nd becomes small). By such an action, the unit optical element unit 113 can narrow the traveling direction of the transmitted light to the front direction side with respect to the light component along the direction orthogonal to the light guide direction. That is, the unit optical element portion 113 exerts a light condensing action on the light component along the direction orthogonal to the light guide direction.

As described above, when at least one of the following condition A and condition B is satisfied, the unit optical element portion 113 exerts the above-described light condensing function extremely effectively on the light emitted from the light guide plate 111. (See FIG. 12).
Condition A: Angles other than the apex angle of the main cut surface triangular shape, that is, the angles θ ₁ and θ _{2 of} the base angles located on the base 112 of the main cut surface triangular shape are 25 ° or more and 45 ° or less.
Condition B: The ratio (Ha / Wa) of the base height Ha of the unit optical element 113a to the width Wa of the unit optical element 113a is 0.2 or more and 0.5 or less.

  As described above, the emission angle of the light emitted from the light guide plate 111 is narrowed down to a narrow angle range centering on the front direction on a plane parallel to the arrangement direction of the unit optical elements 113a of the light guide plate 111.

The light emitted from the light guide plate 111 is then incident on the optical sheet 120. Similar to the unit optical element 113a of the light guide plate 111, the unit prism 122a of the optical sheet 120 exerts a condensing action on the transmitted light by refraction at the light incident surface of the unit prism 122a. However, the light whose traveling direction is changed by the optical sheet 120 is a component in a plane parallel to the arrangement direction of the unit prisms 122a in the optical sheet 120. What is the component condensed by the light guide plate 111? Different. That is, as indicated by L51 in FIG. 13, the light incident on the unit prism 122a is totally reflected at the interface based on the refractive index difference between the unit prism 122a and air. Then, the hypotenuse of the unit prisms 122a so that theta _4/2 inclined with respect to the seat surface normal nd, light reflection at the interface at an angle which is close to the normal nd than the incident light.

  That is, the light guide plate 111 narrows the light traveling direction within a narrow angle range centering on the front direction on the surface parallel to the arrangement direction of the unit optical elements 113a of the light guide plate 111. On the other hand, in the optical sheet 120, on the surface parallel to the arrangement direction of the unit prisms 122a of the optical sheet 120, the light traveling direction is narrowed down to a narrow angle range centering on the front direction. Therefore, the front direction luminance can be further increased by the optical action of the optical sheet 120 without impairing the front direction luminance increased by the light guide plate 111.

  Here, the lower polarizing plate 105 of the liquid crystal panel 101 selectively transmits, for example, only the P wave, which is one polarization component, and absorbs, for example, the S wave, which is the other polarization component. Therefore, when it is assumed that components along the arrangement direction of the unit optical elements 113a intersecting with the arrangement direction of the unit prisms 122a are sufficiently condensed in the front direction by the light guide plate 111, in observation from the front direction, The longitudinal direction of the unit prism 122a of the optical sheet 120 preferably intersects the transmission axis of the lower polarizing plate 105 of the liquid crystal panel 101 at an angle larger than 45 ° and smaller than 135 °. The arrangement direction of 122a is preferably parallel to the transmission axis of the lower polarizing plate 105. According to such a configuration, the utilization efficiency of the light source light in the liquid crystal panel 101 can be further increased.

  The unit prism 122a of the optical sheet 120 and the unit optical element 113a of the light guide plate 111 may have a cross-sectional shape that is strongly specialized in condensing light components orthogonal to the light guide direction. According to the surface light source device 110 designed in this way, the light utilization efficiency can be greatly improved.

  Further, the optical path will be described. The light emitted from the surface light source device 110 as described above enters the lower polarizing plate 105 of the liquid crystal panel 101. The lower polarizing plate 105 transmits one polarization component of incident light and absorbs the other polarization component. The light transmitted through the lower polarizing plate 105 is selectively transmitted through the PVA layer 103 of the upper polarizing plate 102 in accordance with the state of electric field application to each pixel. In this way, the light from the surface light source device 110 is selectively transmitted for each pixel by the PVA layer 103 of the lower polarizing plate 105, the liquid crystal layer 106, and the upper polarizing plate 102, so that the observer of the liquid crystal display device 100 can perform. You will be able to observe the video.

  As described above, the front luminance on the light exit surface of the surface light source device 110 is enhanced by the light condensing action by the light guide plate 111 and the light condensing action by the optical sheet 120. That is, in the liquid crystal display device 100 according to the present embodiment, the function of changing the light traveling direction within a narrow angle range centering on the front direction by the unit optical element 113a of the light guide plate 111 and the unit prism 122a of the optical sheet 120 ( By improving the utilization efficiency of the light source light by the light condensing function, it is possible to increase the luminance in the front direction very effectively. This eliminates the need for a retardation film.

  Further, the light transmitted through the PVA layer 103 enters the light diffusion film 10 as image light. As described above, the light diffusing film 10 can spread light substantially parallel to the normal direction of the light diffusing film 10 to a desired angle range. Therefore, the image light incident on the light diffusion film 10 is transmitted to the viewer side so that the viewing angle is widened (see L61 in FIG. 9).

On the other hand, external light is as follows. FIG. 14 is an explanatory diagram showing L71 which is an example of an optical path of external light. An optical path example indicated by a solid arrow L71 in FIG. 14 is an optical path example in the present embodiment. That is, reflection of the external light L71 irradiated to the light diffusion film 10 is suppressed by the light reflection suppression layer 13 of the light diffusion film 10. Thereby, so-called reflection of external light is suppressed, and as a result, the contrast of the image light can be improved.
Further, the light reflection suppression layer 13 can suppress rainbow-like color unevenness caused by external light. More details are as follows. An optical path indicated by a broken line arrow L71 ′ in FIG. 14 will be described as an example. If the light reflection suppressing layer 13 is not provided, external light passes through the light diffusion film as in L71 ′. Then, the transmitted external light is reflected at the interface between the light diffusion sheet 10 and the PVA layer 103 and travels toward the viewer, for example, as in an optical path L71 ′. The external light L71 ′ directed toward the observer side passes through the diffractive structure 11a along the way. At this time, the light is dispersed by the diffractive structure 11a based on the wavelength of the light, and a rainbow-like color unevenness occurs due to a phenomenon in which the angle of the transmitted light varies greatly depending on the color. As a result, the observer sees rainbow-like color unevenness due to external light and the diffraction structure. On the other hand, according to the light diffusing film 10, since it can suppress that external light L71 'generate | occur | produces, it becomes possible to suppress the rainbow nonuniformity resulting from the said external light.

Further, in the liquid crystal display device 100, if the diffraction structure having the above-exemplified light diffusion characteristics of the light diffusion film 10 is applied, an image is viewed at a viewing angle in the front, horizontal plane, and vertical plane when the observer views the screen. The transmission of the image light can be suppressed with respect to a viewing angle in an oblique plane that is not important for the observer. Therefore, since unnecessary transmission of light can be suppressed, the light use efficiency from the light source can be improved.
Furthermore, if the hologram shape 11a (diffractive structure 11a) of the light diffusion film 10 is a computer generated hologram, the light diffusion range and the like can be adjusted to a desired one.

  Note that the configuration of the liquid crystal display device 100 described here is an exemplification, and the configuration can be changed as long as it is not contrary to the gist of the present invention. For example, although the liquid crystal display device 100 to which the light diffusion film 10 is applied has been described here, the light diffusion film 20 may be applied instead of the light diffusion film 10. Further, in the upper polarizing plate 102, the PVA layer 103 is disposed on the liquid crystal layer 106 side, and the light diffusion film 10 is disposed on the observer side. On the contrary, the light diffusion film 10 is disposed on the liquid crystal layer side, and the observer. A PVA layer may be provided on the side.

  Further, the surface light source device is not limited to the surface light source device 110 described above, and may be in other forms as long as it can efficiently transmit light substantially parallel to the normal direction of the liquid crystal panel. For example, in the surface light source device 110 of the present embodiment, the example in which the unit optical element portion 113 is disposed on the optical sheet 120 side of the base 112 in the light guide plate 111 has been described. However, the present invention is not limited to this, and the unit optical element part is provided on the reflection sheet side of the base part, provided on both sides of the optical sheet side and the reflection sheet side of the base part, or the unit optical element part is not disposed. The form formed only from a base may be sufficient. Moreover, the form which permeate | transmits directly to an optical sheet so that the light from a light source may incline diagonally without arrange | positioning a light-guide plate can also be employ | adopted.

  Examples will be described below.

(Liquid Crystal Display Device of Example 1)
In Example 1, a liquid crystal display device to which the light diffusion film 10 described in the first embodiment was applied was produced. More specifically, in Example 1, an edge light type liquid crystal display device having the layer configuration shown in FIG. 9 was produced.
The light diffusion film 10 was produced as follows. That is, a layer having a diffractive structure by shaping a hologram mold using an ultraviolet curable resin (DSCP563, refractive index 1.58) manufactured by Fujifilm Corporation on Fujitac TD-80UL. A silicon-based adhesive (SD4570 manufactured by Toray Dow Corning Co., Ltd., refractive index: 1.41) was formed on the molding surface so as to be embedded in the concavo-convex shape of the hologram without any gap. Further, a light diffusing film was produced by laminating a triacetyl cellulose film (TAC film, thickness 80 μm, 5 ° reflectance 0.05%) having a moth-eye structure on the adhesive.

(Liquid Crystal Display Device of Example 2)
In Example 2, in place of the light reflection suppressing layer having the moth-eye structure used in Example 1, a liquid crystal display device using a light diffusion film in which a layer having a light reflection suppressing function other than the moth-eye structure was applied was manufactured. Except for the light diffusion film, the same liquid crystal display device as in Example 1 was used. The light diffusion film according to Example 2 was produced as follows. That is, a layer having a diffractive structure is formed on a TAC base material by molding a hologram mold using an ultraviolet curable resin (DAN563 refractive index 1.58 manufactured by SSCP), and a silicon-based layer is formed on the molding surface. An adhesive (SD4570 manufactured by Toray Dow Corning Co., Ltd., refractive index 1.41) was formed so as to be embedded in the concavo-convex shape of the hologram without any gap. Further, an antireflection (so-called “AR”) treated triacetylcellulose film (TAC film, manufactured by Dai Nippon Printing Co., Ltd., DSG03, thickness 80 μm, 5 ° reflectance 0.05%) is laminated on the adhesive. Thus, a light diffusion film was produced.

(Liquid Crystal Display Device of Comparative Example 1)
In Comparative Example 1, in place of the light reflection suppressing layer provided in the light diffusing film shown in Example 1, a liquid crystal display device to which a light diffusing film formed with a layer of triacetyl cellulose (TAC, thickness 80 μm) is applied. Was made.

(Liquid Crystal Display Device of Comparative Example 2)
In Comparative Example 2, only the antireflection (AR) -treated TAC film (80 μm, 5 degree reflectivity 1.2%) provided in the light diffusion film of Example 2 was used, and the diffraction structure and the translucent layer were formed. A liquid crystal display device to which a film not provided was applied was produced.

(Liquid Crystal Display Device of Comparative Example 3)
In Comparative Example 3, a liquid crystal display device to which a film composed only of a layer made of triacetyl cellulose (TAC, thickness of 80 μm) used in Comparative Example 1 was applied.

(Evaluation items and evaluation methods)
For the liquid crystal display devices of Example 1, Example 2, and Comparative Examples 1 to 3, the total light transmittance, rainbow unevenness due to external light, viewing angle, contrast, and thickness were evaluated, These were comprehensively evaluated.
Each was evaluated as follows.
The total light transmittance was measured with a haze / transmittance meter (Murakami Color Research Laboratory, HM-150).
Rainbow unevenness caused by external light is a relative evaluation of color unevenness in the screen when the liquid crystal display device is displayed in black and visually observed from the light exit surface side (observer side). The case where it is not visually recognized is “◎”, and the case where it is recognized slightly is “◯”. The case where it was clearly recognized was designated as “x”.
The viewing angle is a relative evaluation of the brightness when the liquid crystal display device is displayed in white and visually observed from an angle of 45 degrees with respect to the normal line of the light emitting surface from the light emitting surface side. The liquid crystal display device of Example 1 was defined as “◯” as a reference, and “X” was defined as a case where it was clearly felt darker than that.
Contrast ratio is measured with a luminance meter (Konica Minolta, CS2000), and the relative contrast is evaluated as “◎”, “○”, “△”, “×” from the highest contrast value. did.
The thickness was measured with a film thickness meter (manufactured by Tester Sangyo Co., Ltd.).

(result)
The results are shown in Table 1.

As can be seen from Table 1, in Examples 1 and 2, the thickness is slightly increased, but it is understood that the rainbow unevenness and contrast caused by the external light and the viewing angle are compatible and good. Among them, the moth-eye structure of Example 1 is more effective than the others.
On the other hand, Comparative Example 1 has a diffractive structure, so the viewing angle is good, but there are problems with rainbow unevenness and contrast caused by external light as described in the problem.
Since Comparative Examples 2 and 3 do not have a diffractive structure, the viewing angle is narrow. On the other hand, since rainbow unevenness caused by external light does not occur, it can be understood that the rainbow unevenness caused by external light is caused by the diffractive structure.

DESCRIPTION OF SYMBOLS 10 Light diffusion film 11 Diffraction structure 11a Diffraction structure 12 Light transmission layer 13 Light reflection suppression layer 100 Liquid crystal display device 101 Liquid crystal panel 102 Upper polarizing plate 103 PVA layer (polarizer)
DESCRIPTION OF SYMBOLS 105 Lower polarizing plate 106 Liquid crystal layer 110 Surface light source device 111 Light guide plate 112 Base part 112a Main part 112b Light scattering particle 113 Unit optical element part 113a Unit optical element 115 Light source 120 Optical sheet 121 Main body part 122 Unit prism part 122a Unit prism 125 Reflective sheet

Claims (8)

A diffractive structure having a diffractive structure that diffuses and emits light incident substantially parallel to the normal direction of the incident surface and expands the viewing angle;
A light reflection suppressing layer disposed on the side where light is diffused by the diffraction structure and suppressing surface reflection ;
The diffractive structure is in a posture in which the light exit surface of the diffraction structure is erected vertically, the front with respect to the light exit plane, the horizontal plane direction, and the light that having a diffractive structure to produce a luminance distribution only in the vertical plane direction Diffusion film.   The light diffusion film according to claim 1, wherein the light reflection suppressing layer has a moth-eye structure. The diffractive structure is a computer generated hologram, the light diffusion film according to claim 1 or 2. The diffractive structure is directly laminated with a translucent layer having translucency on the side where light is diffused by the diffractive structure,
The light-diffusion film as described in any one of Claims 1-3 in which the site | part which comprises the said diffraction structure of the said diffraction structure, and the said translucent layer have a refractive index difference. The light-diffusion film of Claim 4 whose refractive index of the site | part which has the said diffraction structure is higher than the refractive index of the said translucent layer. A polarizing plate comprising the light diffusing film according to any one of claims 1 to 5 and a PVA layer laminated on the light diffusing film. A surface light source device that generates substantially parallel light, and a liquid crystal panel disposed on an observer side of the surface light source device,
The liquid crystal panel includes a liquid crystal layer, a lower polarizing plate disposed on the surface light source device side of the liquid crystal layer,
An upper polarizing plate disposed on the viewer side of the liquid crystal layer,
The upper polarizing plate is a polarizing plate according to claim 6 .
Liquid crystal display device. The liquid crystal display device according to claim 7 , wherein the upper polarizing plate is in the order of the PVA layer on the liquid crystal layer side and the light diffusion film on the viewer side of the PVA layer.

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