JP2021060480A - Optical sheet and liquid crystal display device - Google Patents

Abstract

To provide an optical sheet and a liquid crystal display device that can suppress decrease in contrast while suppressing hue unevenness.SOLUTION: An optical sheet 30 provided between a liquid crystal panel 15 and a reflection type polarization film 28 of a liquid crystal display device 10 includes base material layers 31a and 31b, and an optical function layer 32 stacked on the base material layers 31a and 31b and including a plurality of light transmitting parts 33 disposed at predetermined intervals along the base material layers 31a and 31b and transmitting light, and a louver part 34 disposed between the adjacent light transmitting parts 33 and reflecting or absorbing light. The base material layers 31a and 31b have a retardation Re of 8000 nm or more.SELECTED DRAWING: Figure 3

Description

The present invention relates to an optical sheet provided between a reflective polarizing film of a liquid crystal display device and a liquid crystal panel, and a liquid crystal display device including the optical sheet.

A liquid crystal display device such as a car navigation device has a liquid crystal panel for displaying an image and a light source for irradiating the back surface of the liquid crystal panel with light. The light emitted from the light source passes through the liquid crystal panel, so that the observer can visually recognize the image. In order to suppress color unevenness in the screen of a liquid crystal display device and provide a high-quality image, it is important to appropriately control the directivity of light.

Patent Document 1 discloses an optical sheet provided between a light source and a liquid crystal panel. The optical sheet includes at least one base film layer, and the retardation Re of the base film layer is 15 nm or less. The optical sheet of Patent Document 1 suppresses the interference of light transmitted through the optical sheet by making the retardation Re of the base film layer relatively small in this way, and suppresses color unevenness.

Japanese Unexamined Patent Publication No. 2010-217871

The liquid crystal display device provided with the optical sheet described in Patent Document 1 is effective in suppressing color unevenness when an observer observes an image facing the screen of the liquid crystal display device. However, in a car navigation device, an observer seated in the driver's seat or passenger's seat of a vehicle is tilted with respect to the screen (for example, about 20 ° in the vertical direction and about 20 ° in the horizontal direction with respect to the normal of the screen). It is common to observe the image from a direction tilted by 40 °). The liquid crystal display device provided with the optical sheet described in Patent Document 1 has a problem that the contrast of an image is lowered when the observer observes the screen from such an inclined direction. Specifically, even when trying to display a black image, there is a problem that excessive light is emitted from the screen and a light black color is observed.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an optical sheet and a liquid crystal display device capable of suppressing a decrease in contrast while suppressing color unevenness.

In order to achieve the above-mentioned object, the present invention is an optical sheet provided between a reflective polarizing film of a liquid crystal display device and a liquid crystal panel, and is an optical sheet laminated on a base material layer and the base material layer. A functional layer, a plurality of light transmitting portions arranged along the base material layer at predetermined intervals to transmit light, and a louver portion arranged between adjacent light transmitting portions to reflect or absorb light. The retardation Re of the base material layer is 8000 nm or more.

Further, the retardation Re of the base material layer may be 8000 nm or more at a wavelength of 400 nm to 700 nm.

Further, the base material layers may be arranged so as to face each other with the optical functional layer interposed therebetween.

Another aspect of the present invention for achieving the above-mentioned object is a liquid crystal display device including an optical sheet, a reflective polarizing film and a liquid crystal panel arranged so as to face each other with the optical sheet interposed therebetween. is there.

According to the present invention, it is possible to provide an optical sheet and a liquid crystal display device capable of suppressing a decrease in contrast while suppressing color unevenness.

It is an exploded perspective view of the liquid crystal display device which concerns on embodiment. It is an exploded view of the liquid crystal display device of FIG. It is an exploded view of the liquid crystal display device of FIG. It is explanatory drawing of the manufacturing process of the optical sheet of FIG. It is explanatory drawing of the manufacturing process of the optical sheet of FIG. It is explanatory drawing of the manufacturing process of the optical sheet of FIG. It is an exploded perspective view of the liquid crystal display device which concerns on a modification.

Hereinafter, the optical sheet and the liquid crystal display device according to the embodiment will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same components are designated by the same reference numerals as much as possible in each drawing, and duplicate description is omitted.

<Embodiment>
The optical sheet 30 and the liquid crystal display device 10 including the optical sheet 30 according to the embodiment will be described with reference to FIGS. 1 to 6.

[Constitution]
First, the configurations of the optical sheet 30 and the liquid crystal display device 10 according to the embodiment will be described with reference to FIGS. 1 to 3. FIG. 1 is an exploded perspective view of the liquid crystal display device 10 according to the embodiment. 2 and 3 are exploded views of the liquid crystal display device 10. For convenience of explanation, when the horizontal direction, the thickness direction, and the vertical direction are defined as shown in FIG. 1, FIG. 2 shows the liquid crystal display device 10 from the direction along the horizontal direction, and FIG. 3 shows the liquid crystal display device 10. , The liquid crystal display device 10 is shown from the direction along the vertical direction.

The liquid crystal display device 10 is housed in a housing (not shown) together with a power supply, an electronic circuit, and the like. The liquid crystal display device 10 is provided in the passenger compartment of an automobile (not shown) and functions as a part of the navigation device. The liquid crystal display device 10 includes a liquid crystal panel 15, a surface light source device 20, and a functional film 40.

The liquid crystal panel 15 has a liquid crystal layer 12, an upper polarizing plate 13, and a lower polarizing plate 14. The upper polarizing plate 13 is arranged on the observer side, and the lower polarizing plate 14 is arranged on the surface light source device 20 side. The liquid crystal layer 12 is arranged between the upper polarizing plate 13 and the lower polarizing plate 14.

The upper polarizing plate 13 and the lower polarizing plate 14 decompose the incident light into two orthogonal polarizing components (P wave and S wave), and the polarizing component in one direction (direction parallel to the transmission axis) (for example, P). It has a function of transmitting a (wave) and absorbing a polarizing component (for example, an S wave) in the other direction (direction parallel to the absorption axis) orthogonal to the one direction.

In the liquid crystal layer 12, a plurality of pixels are arranged vertically and horizontally in a direction along the layer surface. By applying an electric field to each region forming one pixel, the orientation of the pixels in the region changes. As a result, the polarized light component (for example, P wave) parallel to the transmission axis transmitted through the lower polarizing plate 14 arranged on the surface light source device 20 side (that is, the light input side) is transmitted when passing through the pixel to which the electric field is applied. The polarization direction is rotated by 90 °, while maintaining the polarization direction as it passes through the pixels to which no electric field is applied. Therefore, depending on whether or not an electric field is applied to the pixels, the polarizing component (for example, P wave) transmitted through the lower polarizing plate 14 further transmits through the upper polarizing plate 13 arranged on the light emitting side, or the upper polarizing plate 13 is further transmitted. It is possible to control whether it is absorbed and blocked by.

As described above, the liquid crystal panel 15 is configured to control the transmission or blocking of light from the surface light source device 20 for each pixel and provide an image to the observer. Therefore, when irradiating light from the back surface side of the liquid crystal panel 15, a large amount of light having a polarization component parallel to the transmission axis of the lower polarizing plate 14 is allowed to reach, so that the lower polarizing plate 14 is transmitted and the light is used. Efficiency can be increased.

Further, due to the nature of the liquid crystal panel 15, the contrast and efficiency (transmittance) of the emitted light are excellent with respect to the incident light from the normal direction of the liquid crystal panel 15. However, when the incident light is oblique to the normal direction of the liquid crystal panel 15 and the observer observes the light from an oblique direction, there are problems such as a decrease in contrast and low efficiency (transmittance). That is, in order to improve the light utilization efficiency, it is also effective to increase the incident light from the normal direction of the liquid crystal panel 15.

The type of the liquid crystal panel 15 is not particularly limited, and a known type of liquid crystal panel can be used. For example, as the liquid crystal panel 15, TN, STN, VA, MVA, IPS, OCB and the like can be used.

The surface light source device 20 is an illumination device that emits planar light to the liquid crystal panel 15. The surface light source device 20 is arranged on the side opposite to the observer side with respect to the liquid crystal panel 15. The surface light source device 20 is configured as an edge light type surface light source device, and includes a light guide plate 21, a light source 25, a light diffuser plate 26, a prism layer 27, a reflective polarizing film 28, and an optical sheet 30. ..

The light guide plate 21 has a base 22 and an optical element 23. The base 22 has a plate shape having a predetermined thickness. The base portion 22 guides light and is a base portion of the optical element 23. As the material forming the base 22 and the optical element 23, various materials can be used. However, a material that is widely used as a material for an optical sheet incorporated in a display device, has excellent mechanical properties, optical properties, stability, workability, and the like, and can be obtained at low cost can be used. This includes, for example, thermoplastic resins such as polymer resins having an alicyclic structure, methacrylic resins, polycarbonate resins, polystyrene resins, acrylonitrile-styrene copolymers, methyl methacrylate-styrene copolymers, ABS resins, and polyether sulfone. , Epoxy acrylate, styrene acrylate-based reactive resin (ionized radiation curable resin, etc.) and the like can be mentioned.

The optical element 23 is formed on the back surface side of the base portion 22 (the side opposite to the side on which the reflective polarizing film 28 is arranged). The optical element 23 protrudes from the base 22 and has a triangular prism shape. The optical element 23 is formed so that the ridgeline of the protruding top extends in the horizontal direction. On the back surface side of the base portion 22, a plurality of optical elements 23 are arranged side by side at a predetermined pitch in the vertical direction. The optical element 23 has a triangular cross section, but is not limited to this, and may have any shape such as a polygon, a hemisphere, a part of a sphere, and a lens shape. The arrangement direction of the plurality of optical elements 23 is preferably the light guide direction. That is, they are arranged in a direction away from the light source 25, and the ridgeline of each optical element 23 extends in the direction in which the light source 25 is arranged, or in the direction in which the light source extends in the case of one long light source.

The light guide plate 21 having such a configuration can be manufactured by extrusion molding or by molding the optical element 23 on the base 22. In the light guide plate 21 manufactured by extrusion molding, the base portion 22 and the optical element 23 can be integrally formed. Further, when the light guide plate 21 is manufactured by shaping, the optical element 23 may be the same resin material as the base 22 or a different material.

The light source 25 is arranged on one side surface of the side surface of the base portion 22 of the light guide plate 21 in the direction in which the plurality of optical elements 23 are arranged. The light source 25 is composed of a plurality of LEDs (light emitting diodes). The light source 25 is configured so that the lighting and extinguishing of each LED and / or the brightness at the time of lighting of each LED can be individually and independently adjusted by a control device (not shown).

The light diffusing plate 26 has a function of diffusing and emitting incident light. The light diffusing plate 26 is provided on the light emitting side of the light guide plate 21. As a result, the uniformity of the light emitted from the light guide plate 21 can be further enhanced, and the scratches existing on the light guide plate 21 can be made inconspicuous. Further, the light diffusing plate 26 functions as a support for the prism layer 27.

The prism layer 27 is provided on the liquid crystal panel 15 side of the light diffusing plate 26, and has a plurality of unit prisms 27a. The unit prism 27a projects toward the liquid crystal panel 15 side and extends in a direction orthogonal to the light guide direction of the light guide plate 21. As a result, the light can be focused in the direction in which the light is controlled by the optical function layer 32 (vertical direction in the present embodiment), and the light can be efficiently totally reflected by the optical function layer 32, so that the light utilization efficiency can be improved. ..

The reflective polarizing film 28 decomposes the incident light into two orthogonal polarizing components (P wave and S wave), and transmits the polarizing component (for example, P wave) in one direction (direction parallel to the transmission axis). It has a function of reflecting a polarizing component (for example, an S wave) in the other direction (direction parallel to the reflection axis) orthogonal to the one direction. A known structure of the reflective polarizing film 28 can be used.

The optical sheet 30 includes a base material layer 31a formed in a sheet shape and an optical functional layer 32 laminated on the base material layer 31a. Further, the second base material layer 31b is arranged so as to face the base material layer 31a with the optical functional layer 32 interposed therebetween.

The base material layers 31a and 31b are flat plate-shaped members that support the optical functional layer 32. Various materials can be used as the materials forming the base material layers 31a and 31b, but in the present embodiment, the base material layers 31a and 31b are all polyester films.

The optical functional layer 32 has a light transmitting portion 33 and a louver portion 34. The light transmitting portion 33 is a portion whose main function is to transmit light, and has a substantially trapezoidal cross-sectional shape in the cross sections shown in FIGS. 1 and 2. The light transmitting portions 33 maintain the cross section along the layer surfaces of the base material layers 31a and 31b and extend in the horizontal direction, and are arranged in the vertical direction at predetermined intervals. A groove 33a (see FIG. 5) having a substantially trapezoidal cross section is formed between the adjacent light transmitting portions 33. The louver portion 34 is formed by filling the groove 33a with a material described later.

The light transmitting portion 33 has a refractive index of Nt. Such a light transmitting portion 33 can be formed by curing a predetermined composition, as will be described later. The value of the refractive index Nt is not particularly limited, but a material having an excessively high refractive index is often fragile, and as will be described later, light is appropriately reflected at the interface with the louver portion 34 on the slope of the trapezoidal cross section. From the viewpoint of (including total reflection), the refractive index is preferably 1.47 to 1.65, more preferably 1.49 to 1.57.

The louver portion 34 is formed in the groove 33a of the adjacent light transmitting portions 33, and has a cross-sectional shape similar to the cross-sectional shape of the groove 33a. The louver portion 34 has a refractive index of Nr and is configured to be able to absorb light. Specifically, the light absorbing particles are dispersed in a transparent resin having a refractive index of Nr. The refractive index Nr is lower than the refractive index Nt of the light transmitting portion 33. In this way, by making the refractive index of the louver portion 34 smaller than the refractive index of the light transmitting portion 33, the light incident on the light transmitting portion 33 under predetermined conditions is appropriately totally reflected at the interface with the louver portion 34. Can be done. Further, even if the total reflection condition is not satisfied, some light is reflected at the interface. The value of the refractive index Nr is not particularly limited, but a material having an excessively high refractive index is often fragile, and 1.47 to 1.65 is preferable and more preferable from the viewpoint of appropriately performing the total reflection. Is 1.49 to 1.57.

The difference between the refractive index Nt of the light transmitting portion 33 and the refractive index Nr of the louver portion 34 is not particularly limited, but is preferably greater than 0 and 0.14 or less, and preferably 0.05 or more and 0.14 or less. Is even more preferable. By increasing the difference in refractive index, more light can be totally reflected.

The functional film 40 is provided on the light emitting side of the liquid crystal panel 15 and has a function of improving the quality of image light and protecting the liquid crystal display device 10. For example, as the functional film 40, an antireflection film, an antiglare film, a hard coat film, a color tone correction film, a light diffusion film and the like can be used. Further, the functional film 40 may be formed by using a plurality of these films in combination.

[Method of manufacturing optical sheet]
Next, a method of manufacturing the optical sheet 30 will be described with reference to FIGS. 4 to 6. 4 to 6 are explanatory views of a manufacturing process of the optical sheet 30.

As described above, the base material layers 31a and 31b of the optical sheet 30 are all polyester films. The polyester film can be obtained by condensing an arbitrary dicarboxylic acid with a diol. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and diphenylcarboxylic acid. Acid, diphenoxyetanedicarboxylic acid, diphenylsulfoncarboxylic acid, anthracendicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid Acids, malonic acids, dimethylmalonic acids, succinic acids, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, Dimeric acid, sebacic acid, suberic acid, dodecadicarboxylic acid and the like can be used.

Examples of the diol include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, and 1,4. -Butandiol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfone and the like can be used.

As the dicarboxylic acid component and the diol component constituting the polyester film, one type or two or more types may be used, respectively. As the polyester resin constituting the polyester film, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and the like can be used, preferably polyethylene terephthalate and polyethylene naphthalate, and preferably polyethylene terephthalate. it can. The polyester resin may contain other copolymerization components. From the viewpoint of mechanical strength, the proportion of the copolymerization component is preferably 3 mol% or less, preferably 2 mol% or less, and more preferably 1.5 mol% or less. These resins are excellent in transparency as well as thermal and mechanical properties. In addition, these resins can easily control the retardation Re by stretching.

The polyester film can be obtained according to a general manufacturing method. Specifically, the polyester resin is melted and extruded into a sheet, and the unoriented polyester is stretched in the vertical direction at a temperature equal to or higher than the glass transition temperature by utilizing the speed difference of the rolls, and then laterally stretched by a tenter. A stretched polyester film can be obtained by stretching, heat-treating, and if necessary, relaxing treatment. The stretched polyester film may be a uniaxially stretched film or a biaxially stretched film.

The production conditions for obtaining the polyester film can be appropriately set according to a known method. For example, the longitudinal stretching temperature and the transverse stretching temperature are usually 80 to 130 ° C., preferably 90 to 120 ° C. The longitudinal stretching ratio is usually 1.0 to 3.5 times, preferably 1.0 to 3.0 times. The lateral stretching ratio is usually 2.5 to 6.0 times, preferably 3.0 to 5.5 times.

The retardation Re can be controlled within a specific range by appropriately setting the stretching ratio, stretching temperature, and film thickness. For example, the higher the difference in stretching ratio between longitudinal stretching and transverse stretching, the lower the stretching temperature, and the thicker the film, the easier it is to obtain high retardation Re. On the contrary, the lower the difference in stretching ratio between the longitudinal stretching and the transverse stretching, the higher the stretching temperature, and the thinner the film, the easier it is to obtain a low retardation Re. Further, the higher the stretching temperature and the lower the total stretching ratio, the easier it is to obtain a film having a low ratio (Re / Rth) of retardation Re and retardation Rth in the thickness direction. On the contrary, the lower the stretching temperature and the higher the total stretching ratio, the higher the ratio (Re / Rth) of the retardation Re and the thickness direction retardation Rth can be obtained. Further, the heat treatment temperature is usually preferably 140 to 240 ° C, preferably 170 to 240 ° C.

The temperature of the relaxation treatment is usually 100 to 230 ° C., preferably 110 to 210 ° C., more preferably 120 to 180 ° C. The amount of relaxation is usually 0.1 to 20%, preferably 1 to 10%, and more preferably 2 to 5%. The temperature and the amount of relaxation of the relaxation treatment are preferably set so that the heat shrinkage rate of the polyester film after the relaxation treatment at 150 ° C. is 2% or less.

Further, in the uniaxial stretching and biaxial stretching treatments, after the lateral stretching, heat treatment or stretching treatment can be performed again in order to alleviate the distortion of the orientation spindle as represented by Boeing. .. The maximum value of the strain of the orientation spindle in the stretching direction due to Boeing is preferably within 30 °, more preferably within 15 °, and even more preferably within 8 °. If the maximum value of the distortion of the orientation spindle exceeds 30 °, non-uniformity of optical characteristics may occur between the single-wafers when the polarizing plate is formed in a later step and the single-wafer is formed. Here, the orientation main axis refers to the direction of molecular orientation at an arbitrary point on the polyester film. Further, the strain of the alignment spindle with respect to the stretching direction means the angle difference between the alignment spindle and the stretching direction. Further, the maximum value means the maximum value of the value in the direction perpendicular to the long direction. The orientation spindle can be measured using, for example, a retardation film / optical material inspection device RETS (manufactured by Otsuka Electronics Co., Ltd.) or a molecular orientation meter MOA (manufactured by Oji Measuring Instruments Co., Ltd.).

In order to suppress fluctuations in retardation Re in the polyester film, it is preferable that the thickness unevenness of the film is small. If the longitudinal stretching ratio is lowered in order to make a difference in retardation, the value of the longitudinal thickness spot may increase. Since there is a region where the value of the vertical thickness spot becomes very high in a specific range of the draw ratio, it is desirable to set the film forming conditions so as to exclude such a range.

The thickness unevenness of the polyester film is preferably 5.0% or less, more preferably 4.5% or less, still more preferably 4.0% or less, and more preferably 3.0% or less. Is particularly preferable. The thickness unevenness of the film can be measured by any means. For example, a tape-shaped sample (length 3 m) continuous in the flow direction of the film is taken, and a commercially available measuring instrument (for example, an electronic micrometer Millitron 1240 manufactured by Seiko EM Co., Ltd.) is used to measure 100 at a pitch of 1 cm. The thickness of the points is measured, the maximum value (dmax), the minimum value (dmin), and the average value (d) of the thickness are obtained, and the thickness unevenness (%) can be calculated by the following formula.
Thickness spot (%) = ((dmax-dmin) / d) x 100

The thickness of the polyester film is arbitrary and can be appropriately set, for example, in the range of 15 to 300 μm, preferably in the range of 30 to 200 μm.

The light transmitting portion 33 is formed on one surface of the base material layer 31a which is the polyester film formed as described above. As shown in FIG. 4, this is a base material layer between the mold roll R1 having a shape on the surface that allows the shape of the light transmitting portion 33 to be transferred and the nip roll R2 arranged so as to face the mold roll R1. The polyester film 310 to be 31a is inserted. At this time, while supplying the composition 330 constituting the light transmitting portion 33 (see FIG. 1 and the like) between the polyester film 310 and the mold roll R1, the mold roll R1 and the nip roll R2 are shown by arrows in FIG. Rotate in the direction indicated by. As a result, the groove formed on the surface of the mold roll R1 (the shape obtained by reversing the shape of the light transmitting portion 33) is filled with the composition 330, and the composition 330 conforms to the surface shape of the mold roll R1. Become.

As the composition 330 constituting the light transmitting portion 33, for example, an ionizing radiation curable resin such as an epoxy acrylate-based resin, a urethane acrylate-based resin, a polyether acrylate-based resin, a polyester acrylate-based resin, or a polythiol-based resin can be used.

The composition 330 sandwiched between the mold roll R1 and the polyester film 310 and filled therein is irradiated with light rays (ultraviolet rays or the like) from the polyester film 310 side by the light irradiating device 61. As a result, the composition 330 is cured. Then, the mold roll R3 is used to release the pre-filling sheet 36a composed of the polyester film 310 and the molded light transmitting portion 33 from the mold roll R1.

Next, the louver portion 34 is formed. In order to form the louver portion 34, as shown in FIG. 5, the composition 340 constituting the louver portion 34 is excessively supplied to the groove 33a between the adjacent light transmitting portions 33 of the pre-filling sheet 36a. Then, the excess composition 340 is scraped off by a blade 62 or the like. Then, the composition 340 remaining so as to fill the groove 33a is irradiated with light rays (ultraviolet rays or the like) from a light source (not shown). As a result, the composition 340 is cured, the louver portion 34 is formed, and the intermediate sheet 36b is obtained. For an optical sheet of the type in which the second base material layer 31b, which will be described later, is not bonded, the intermediate sheet 36b becomes the optical sheet as it is. The optical sheet 30 is wound on a roll (not shown). When the optical sheet 30 is wound by a predetermined length, the optical sheet 30 is cut, and the wound roll is replaced with a new roll to start the next winding.

Further, instead of dispersing the light absorbing particles, the entire light absorbing portion can be colored with a pigment or a dye. When light absorbing particles are used, light absorbing colored particles such as carbon black are preferably used, but the present invention is not limited to these, and specific wavelengths are selectively absorbed according to the characteristics of image light. Colored particles may be used. Specific examples thereof include organic fine particles colored with metal salts such as carbon black, graphite and black iron oxide, dyes and pigments, and colored glass beads. In particular, colored organic fine particles are preferably used from the viewpoints of cost, quality, availability, and the like. The average particle size of the colored particles is preferably 1.0 μm or more and 20 μm or less.

When producing an optical sheet of a type including both the base material layer 31a and the second base material layer 31b, the second base material layer 31b is further attached to the intermediate sheet 36b. Specifically, as shown in FIG. 6, the intermediate sheet 36b is sent out from the roll R4, and the polyester film 310 serving as the second base material layer 31b is sent out from the roll R5 in the same direction. At this time, by matching the flow directions of the base material layer 31a and the base material layer 31b (polyester film 310) of the intermediate sheet 36b and sticking them together, the polarization is disturbed based on the phase difference, and the color unevenness and transmission associated therewith occur It is possible to prevent a decrease in the rate. The intermediate sheet 36b and the polyester film 310 are guided by rollers R6 and R7 so as to approach each other and are integrated. At this time, the polyester film 310 is arranged so as to face the base material layer 31a with the light transmitting portion 33 and the louver portion 34 interposed therebetween. By arranging an adhesive layer (not shown) made of an adhesive such as an acrylic adhesive between the intermediate sheet 36b and the polyester film 310, both can be bonded together. Then, the optical sheet 30 completed by bonding is wound on a roll (not shown). When the optical sheet 30 is wound by a predetermined length, the optical sheet 30 is cut, and the wound roll is replaced with a new roll to start the next winding.

Here, it is assumed that the retardation Re of the base material layers 31a and 31b in the plane direction is 8000 nm or more at a wavelength of 400 nm to 700 nm. Here, the retardation Re is
Re = (Nx-Ny) x d
It is represented by. Nx is the maximum in-plane refractive index of the base material layers 31a and 31b, and Ny is the minimum in-plane refractive index of the base material layers 31a and 31b. Further, d (nm) is the thickness of the base material layers 31a and 31b.

When the value of the retardation Re is close to the wavelength of visible light, color unevenness is likely to occur in the image in combination with the polarizing plate and the polarizing film of the liquid crystal panel 15 and the reflective polarizing film for the purpose of improving the brightness. Therefore, by setting the retardation Re to 8000 nm or more and making it significantly different from the wavelength of visible light, it is possible to suppress color unevenness and prevent a decrease in contrast.

The details are as follows. When birefringence occurs in the layer, different phase differences occur depending on the traveling direction of the light, and the spectral distribution of the light emitted outside the layer randomly fluctuates depending on the traveling direction of the light, so that it is observed as color unevenness. .. In particular, when the retardation Re has a value close to the wavelength of visible light (400 nm to 700 nm), the phase difference in the wavelength range of 400 to 700 nm of light becomes large and color unevenness becomes remarkable.

On the other hand, in the optical sheet 30 according to the present embodiment, the retardation Re of the base material layers 31a and 31b is set to 8000 nm or more, which greatly exceeds the wavelength of visible light. Therefore, it is possible to suppress light interference and suppress color unevenness.

Further, the base material layers 31a and 31b are arranged so as to face each other with the optical functional layer 32 interposed therebetween. This makes it possible to suppress light interference and suppress color unevenness while increasing the rigidity of the optical sheet 30 as compared with the case where the base material layers 31a and 31b are used alone.

[Measurement of brightness]
Here, an automatic variable luminance meter is used for the optical sheet according to the above embodiment (hereinafter, simply referred to as "execution") and the optical sheet according to the comparative example (hereinafter, simply referred to as "comparative example"). The brightness of the transmitted light was measured. In the embodiment, the retardation Re of the base material layer is set to 8000 nm or more as described above. Specifically, the retardation Re at a wavelength of 400 nm to 700 nm of the embodiment used for the measurement here is 8200 nm. On the other hand, in the comparative example, as described in Patent Document 1 described above, the retardation Re in the plane direction of the base material layer is set to 15 nm or less. Specifically, the retardation Re at a wavelength of 400 nm to 700 nm of the comparative example used in the measurement here is 10 nm.

The changes that occur in the brightness of the embodiments and comparative examples were measured when the liquid crystal panel was provided (“with liquid crystal panel”) and when the liquid crystal panel was not provided (“without liquid crystal panel”). Luminance measurements were taken in two directions. First, the brightness was measured in the direction facing the liquid crystal panel or the optical sheet (that is, the direction in which the liquid crystal panel or the optical sheet is viewed along the normal: 0 ° in the vertical direction and 0 ° in the horizontal direction). Further, the brightness is measured in a direction in which the liquid crystal panel or the optical sheet is tilted upward by 20 ° (see FIG. 2) in the vertical direction and 40 ° (see FIG. 3) in the horizontal direction. It was.

Table 1 shows the luminance measured in this way. The measurement was performed when the liquid crystal panel was provided (“with liquid crystal panel”) and when the liquid crystal panel was not provided (“without liquid crystal panel”) and when the optical sheet was not arranged (“without optical sheet”). Using the brightness as a reference (100%), the brightness measured in each of the embodiment and the comparative example is shown as a percentage.

As shown in Table 1, when the liquid crystal panel was provided (“with liquid crystal panel”), no significant difference in brightness was observed between the embodiment and the comparative example.

On the other hand, when the liquid crystal panel is not provided (“without the liquid crystal panel”), the brightness measured in the direction inclined by 20 ° vertically upward and 40 ° horizontally from the normal of the optical sheet is the embodiment. The result was that the comparative example was higher than the comparative example. In the case where the liquid crystal panel is provided (“with liquid crystal panel”), in view of the fact that no significant difference in brightness was observed between the embodiment and the comparative example, from this result, the case where the liquid crystal panel is not provided (“with liquid crystal panel”). No liquid crystal panel "), in the comparative example, it can be considered that the component with disordered polarization is transmitted through the optical sheet. Such a component causes a decrease in the contrast of the image when the observer observes the screen from a direction inclined from the normal line of the liquid crystal panel.

That is, according to the embodiment, as compared with the comparative example, it is possible to suppress the transmission of components having disordered polarized light and suppress the decrease in contrast of the image.

Further, instead of the above embodiment, an optical sheet having a substrate layer retardation Re at a wavelength of 400 nm to 700 nm of 8400 nm or 10500 nm is used, and instead of the comparative example, a substrate layer retardation Re at a wavelength of 400 nm to 700 nm is used. Luminance was measured in the same manner as in the above method using an optical sheet of 2 nm or 7 nm. Here, too, a tendency similar to that in Table 1 was observed.

Further, when an optical sheet having a retardation Re of 3300 nm at a wavelength of 400 nm to 700 nm and a PET film having a thickness of 100 μm as a base material layer was prepared and the brightness was measured in the same manner as in the above method, a liquid crystal panel was provided. In that case, color unevenness occurred.

<Modification example>
Next, the optical sheet 30A and the liquid crystal display device 10A including the optical sheet 30A according to the modified example will be described with reference to FIG. 7. The modified example is different from the above embodiment in that a functional layer is added to the surfaces of the base material layers 31a and 31b of the optical sheet 30A. Among the components of the modified example, those having the same function as the components of the above-described embodiment are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

The liquid crystal display device 10A is provided in the passenger compartment of an automobile (not shown) and functions as a part of the navigation device. The liquid crystal display device 10A includes a liquid crystal panel 15, a surface light source device 20A, and a functional film 40. The surface light source device 20A is configured as an edge light type surface light source device, and includes a light guide plate 21, a light source 25, a light diffuser plate 26, a prism layer 27, a reflective polarizing film 28, and an optical sheet 30A. ..

The optical sheet 30A includes a base material layer 31a formed in a sheet shape and an optical functional layer 32 laminated on the base material layer 31a. Further, the second base material layer 31b is arranged so as to face the base material layer 31a with the optical functional layer 32 interposed therebetween.

Further, the anti-glare layer 37a is laminated on the surface of the base material layer 31a, and the anti-glare layer 37b is laminated on the surface of the base material layer 31b. Further, the antireflection layer 38a is laminated on the surface of the antiglare layer 37a, and the antireflection layer 38b is laminated on the surface of the antiglare layer 37b.

The anti-glare layers 37a and 37b are formed of a composition obtained by mixing the following materials in a mass ratio of the numerical values shown on the right side of each.
-Acrylic-styrene copolymer particles (organic fine particles, average primary particle size 3.0 μm, refractive index 1.52, manufactured by Sekisui Plastics Co., Ltd.): 7
-Amorphous silica particles (inorganic fine particles, hydrophobic treatment, average particle size (laser diffraction / scattering method) 2.7 μm, manufactured by Fuji Silysia Chemical Ltd.): 2
-Pentaerythritol triacrylate (PETA) (product name "PETIA", manufactured by Daicel Cytec): 100
-Polymerization initiator (product name "Irgacure 184", manufactured by BASF Japan Ltd.): 5
-Polyether-modified silicone (product name "TSF4460", manufactured by Momentive Performance Materials): 0.025
-Toluene: 120
・ Cyclohexanone: 30
The amorphous silica particles are produced by a gel method.

In the step of forming the anti-glare layers 37a and 37b, first, the composition obtained by mixing the above-mentioned materials is applied to the surfaces of the base material layers 31a and 31b to form a thin film. Next, dry air at 70 ° C. is circulated through the thin film at a flow rate of 0.2 m / s for 15 seconds, and then dry air at 70 ° C. is further circulated at a flow rate of 10 m / s for 30 seconds to dry. This causes the solvent in the thin film to evaporate. Further, the thin film is cured by irradiating it with ultraviolet rays in a nitrogen atmosphere (oxygen concentration of 200 ppm or less) ^{so that the integrated light amount becomes 100 mJ / cm 2.} As a result, anti-glare layers 37a and 37b having a thickness of 4 μm at the time of curing are formed.

The antireflection layers 38a and 38b are formed by applying a predetermined composition. In the step of obtaining the composition, first, 0.2 parts by mass of a photopolymerization initiator (BASF, Inc., Irgacure 127) and 91.1 parts by mass of a diluting solvent (MIBK / AN = 7/3) are mixed. And stir until there is no undissolved residue. Here, 2.0 parts by mass of a photo-curing resin (manufactured by Nippon Kayaku Co., Ltd., KAYARAD-PET-30), 6.6 parts by mass of hollow silica particles (solid content 20% by mass, average primary particle diameter 60 nm), and 0. By mixing and stirring 1 part by mass of a leveling agent (Seika Beam 10-28 (MB) manufactured by Dainichiseika Kogyo Co., Ltd.), a composition for forming the antireflection layers 38a and 38b can be obtained. ..

By applying such a composition to the surfaces of the antiglare layers 37a and 37b, drying and irradiating with ultraviolet rays, antireflection layers 38a and 38b having a thickness of 100 nm and a refractive index of 1.36 can be formed.

For example, anti-glare layers 37a and 37b having a haze value of 7.9 are arranged on the surfaces of the base material layers 31a and 31b, and further, anti-reflection layers 38a having a reflectance of 0.8% are placed on the surfaces of the anti-glare layers 37a and 37b. When the optical sheet 30A on which, 38b was arranged and the brightness was measured in the same manner as in the above embodiment, further improvement in color unevenness and improvement in transmittance by 4% were confirmed.

The embodiments described above are for facilitating the understanding of the present invention, and are not for limiting and interpreting the present invention. Each element included in the embodiment and its arrangement, material, condition, shape, size, and the like are not limited to those exemplified, and can be changed as appropriate. In addition, the configurations shown in different embodiments can be partially replaced or combined.

For example, in the above-described modification, the optical sheet 30A has anti-glare layers 37a and 37b arranged on the surfaces of the base material layers 31a and 31b. However, the present invention is not limited to this form. The present invention also includes a configuration in which an antireflection layer is arranged on the surface of the base material layer.

10 Liquid crystal display device 14 Lower polarizing plate 28 Reflective polarizing film 30 Optical sheet 31a, 31b Base material layer 32 Optical functional layer 33 Light transmission part 34 Luber part 37a, 37b Anti-glare layer 38a, 38b Anti-reflection layer

Claims (5)

An optical sheet provided between a reflective polarizing film of a liquid crystal display device and a liquid crystal panel.
Base layer and
An optical functional layer laminated on the base material layer, between a plurality of light transmitting portions arranged along the base material layer at predetermined intervals and transmitting light, and adjacent light transmitting portions. It is provided with an optical functional layer having a louver portion, which is arranged in and reflects or absorbs light.
An optical sheet having a retardation Re of the base material layer of 8000 nm or more. The optical sheet according to claim 1, wherein the retardation Re of the base material layer is 8000 nm or more at a wavelength of 400 nm to 700 nm. The optical sheet according to claim 1 or 2, wherein the base material layers are arranged so as to face each other with the optical functional layer interposed therebetween. The optical sheet according to any one of claims 1 to 3, wherein at least one of an antiglare layer and an antireflection layer is arranged on the surface of the base material layer. The optical sheet according to any one of claims 1 to 4,
A liquid crystal display device including a reflective polarizing film and a liquid crystal panel arranged so as to face each other with the optical sheet interposed therebetween.

Images