WO2021060282A1 - Optical sheet, liquid crystal display device, and optical sheet testing method and manufacturing method - Google Patents

Abstract

The present invention provides an optical sheet with which light unevenness is suppressed, a liquid crystal display device, and an optical sheet testing method and manufacturing method. This optical sheet is provided with a base material layer, and an optical functional layer having a plurality of light transmitting parts arranged with a predetermined interval therebetween along the base material layer, and a louver part disposed between the light transmitting parts adjacent to each other. The optical sheet has a hanging amount of 10 mm or less when being disposed on a support base with one end thereof being protruded by 100 mm from an end part of the support base along a direction in which the plurality of light transmitting parts and the louver parts of the optical functional layer are alternately arranged, and the optical sheet is not cracked when being bent so as to be wound around a mandrel with a diameter of 150 mm along a direction orthogonal in the surface of the optical sheet to the direction in which the plurality of light transmitting parts and the louver parts of the optical functional layer are alternately arranged, and/or the optical sheet has a water absorption of 1.33% or less in a water absorption test based on JIS K 7209.

Description

Optical sheet, liquid crystal display device, and test method and manufacturing method of optical sheet

The present invention relates to an optical sheet arranged on the observer side of a light source, a liquid crystal display device using the optical sheet, and a test method and a manufacturing method of the optical sheet.

Liquid crystal display devices such as in-vehicle displays and liquid crystal televisions are equipped with optical sheets having various functions in order to control the light emitted from the light source and provide high-quality light to the observer.

In Patent Document 1, a layer in which a prism portion (referred to as a light transmitting portion in the present specification) and a light absorbing portion (referred to as a louver portion in the present specification) are alternately arranged on one surface of a base film layer. There is disclosed an optical sheet which has the above and can suppress bending even if it is made thin.

Japanese Unexamined Patent Publication No. 2017-198735

When an optical sheet as described in Patent Document 1 is used for a liquid crystal display device, each module of the liquid crystal display device and this optical sheet are combined and mounted on a housing of the liquid crystal display device. When mounting an optical sheet as described in Patent Document 1, fixing is performed by adhesion or tightening with a frame of a housing, but depending on the fixing method, bending may occur due to the weight of the optical sheet or the like. Therefore, there is a problem that unevenness of light transmitted through the optical sheet occurs due to this bending.

In order to suppress such unevenness of light, it is conceivable to increase the rigidity of the optical sheet so that the optical sheet does not easily bend. On the other hand, it is known that such an optical sheet is manufactured by a manufacturing method in which the manufacturing efficiency is improved by using a plurality of rolls. In the manufacturing process using a plurality of rolls, if the rigidity of the optical sheet is too high during the transfer of the optical sheet between the rolls, that is, the so-called roll-to-roll process, the optical sheet cannot follow the roll and cracks. It may end up. Therefore, it is desired to develop an optical sheet capable of suppressing a decrease in manufacturing efficiency while suppressing the occurrence of uneven light.

Further, the optical sheet described in Patent Document 1 suppresses bending by providing sufficient rigidity at the time of use, but further consideration may be required depending on the usage environment of the optical sheet. For example, when a car navigation system including a liquid crystal display device having an optical sheet is mounted on an automobile and used, changes in the vehicle interior environment may affect the optical sheet. In particular, when the inside of the vehicle is in a hot and humid environment, the optical sheet of the liquid crystal display device may be deformed (bent) as the temperature and humidity rise (particularly due to moisture absorption of the optical sheet). Due to such deformation (deflection) of the optical sheet, there is a problem that unevenness of light transmitted through the optical sheet occurs.

The present invention has been made to solve any or all of the above-mentioned problems, and the optical sheet selected to be particularly suitable for use in a liquid crystal display device, particularly an in-vehicle liquid crystal display device. , An object of the present invention is to provide a liquid crystal display device using this optical sheet, and a test method and a manufacturing method of the optical sheet.

In order to achieve the above-mentioned object, the present invention is an optical sheet provided between a reflective polarizing plate 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 optical sheet comprises, and the optical sheet comprises, along the direction in which the plurality of light transmitting portions and louver portions of the optical functional layer are alternately arranged. The amount of sagging when one end of the sheet is projected 100 mm from the end of the support base is 10 mm or less, and the optical sheet has a direction in which a plurality of light transmitting portions and louver portions of the optical functional layer are alternately arranged. When the optical sheet is bent so as to be wound around a mandrel having a diameter of 150 mm along the direction orthogonal to the surface of the optical sheet, no cracks occur, and / or the optical sheet absorbs water according to a water absorption rate test based on JIS K 7209. It has a configuration of an optical sheet having a water absorption rate of 1.33% or less.

Further, the optical sheet may further have a second base material layer arranged so as to face the base material layer with the optical functional layer interposed therebetween.

Further, the coefficient of linear thermal expansion of the material of the base material layer of the optical sheet may be 4.9 to 5.6 (× 10 ^-5 / ° C.).

In addition, another aspect of the present invention for achieving the above-mentioned object is a liquid crystal comprising the above-mentioned optical sheet, a liquid crystal display device arranged so as to face each other across the optical sheet, and a reflective polarizing plate. It is a display device.

In addition, another aspect of the present invention for achieving the above-mentioned object is a base material layer and an optical functional layer laminated on the base material layer, which are spaced apart from each other along the base material layer. It is a test method of an optical sheet including an optical functional layer having a plurality of light transmitting portions arranged in an array to transmit light and a louver portion arranged between adjacent light transmitting portions to reflect or absorb light. The optical sheet is arranged on the support base, and one end of the optical sheet is projected 100 mm from the end portion of the support base along the direction in which the plurality of light transmitting portions and the louver portions of the optical functional layer are alternately arranged. The sagging amount determination step for determining whether or not the sagging amount at the time is 10 mm or less, and the optical sheet are optical in the direction in which a plurality of light transmitting portions and louver portions of the optical functional layer are alternately arranged. The crack determination step of determining whether or not cracks occur by bending so as to wind around a mandrel having a diameter of 150 mm along the direction orthogonal to the sheet surface, and / or the water absorption rate of the optical sheet is based on JIS K 7209. If the water absorption rate measurement step measured by the water absorption rate test and the water absorption rate measured by the water absorption rate step are 1.33% or less, it is passed, and if the water absorption rate of the optical sheet is larger than 1.33%, it is rejected. The configuration of the optical sheet and / or the water absorption, which includes the water absorption rate determination step, and is determined in the sag amount determination step that the sag amount is 10 mm or less and that no crack is generated in the crack determination step. This is an optical sheet test method in which the configuration of an optical sheet determined to pass in the rate determination step is determined to be an appropriate configuration.

Further, in another aspect of the present invention for achieving the above-mentioned object, the optical sheet is manufactured by adopting the structure of the optical sheet determined to be an appropriate structure by the above-mentioned test method of the optical sheet. , A method for manufacturing an optical sheet.

According to the present invention, it is possible to provide an optical sheet and a liquid crystal display device that suppress light unevenness without lowering the manufacturing efficiency, and / or the optical sheet is less bent even in a high temperature and high humidity environment, and the optical sheet. It is possible to provide an optical sheet and a liquid crystal display device that suppress unevenness of light transmitted through the light. Further, it is possible to carry out a test for finding a configuration of an optical sheet that suppresses such light unevenness, and to manufacture an optical sheet that suppresses light unevenness based on the result of the test.

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 an enlarged view paying attention to the optical sheet of FIG. It is a figure which showed the optical sheet which concerns on other embodiment. 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 a figure which shows the outline of the sagging amount test.

Hereinafter, the optical sheet and the liquid crystal display device according to the embodiment will be described with reference to the attached 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.

[Constitution]
First, the configuration of 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 4. 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 the sake of simplicity, 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. FIG. 4 shows an enlarged view of the optical sheet 30 shown in FIG. 2 rotated 90 degrees counterclockwise when viewed from the cross-sectional direction in order to show the configuration of the optical sheet 30 shown in FIG. 2 and the like. FIG. 5 is a diagram corresponding to FIG. 4 with respect to the optical sheet according to another embodiment. Although description is omitted, such a liquid crystal display device 10 operates as a liquid crystal display device 10 in a housing (not shown), such as a power source for operating the liquid crystal display device 10 and an electronic circuit for controlling the liquid crystal display device 10. It is a liquid crystal display device that is housed together with the usual equipment required to do so. The liquid crystal display device 10 will be described below.

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 operates 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. The lower polarizing plate 14 is an example of a polarizing film.

In the liquid crystal layer 12, a plurality of pixels are arranged vertically and horizontally 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 diffusion plate 26, a prism layer 27, a reflective polarizing plate 28, an optical sheet 30, and a reflective sheet 39. are doing.

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, polymer resins having an alicyclic structure, methacrylic resins, polycarbonate resins, polystyrene resins, acrylonitrile-styrene copolymers, methyl methacrylate-styrene copolymers, ABS resins, polyether sulfone and other thermoplastic resins. , 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 plate 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.

Note that the "triangular shape" in the present specification includes not only a triangular shape in a strict sense but also a substantially triangular shape including limits in manufacturing technology and errors during molding. Similarly, other terms that specify shape and geometric conditions used herein, such as "parallel," "orthogonal," "ellipse," and "circle," are also bound in a strict sense. It shall be interpreted including an error to the extent that the same optical function can be expected.

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 molding, 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 of the side surface of the base 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 type of the light source is not particularly limited, and in addition to the LED, it can be configured in various modes such as a fluorescent lamp such as a linear cold cathode tube and an incandescent lamp. In this embodiment, the light source 25 is arranged on one side surface as described above, but the light source may be arranged on the side surface opposite to this side surface. In this case, the shape of the optical element is also formed according to a known example.

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. As a specific embodiment of the light diffusing plate, a known light diffusing plate can be used, and examples thereof include a form in which a light diffusing agent is dispersed in a base material.

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, has a predetermined cross section, and has a direction different from the light guide direction of the light guide plate 21 (in this embodiment, a direction orthogonal to the light guide direction in a plan view). It has an extending form. A plurality of unit prisms 27a are arranged in the light guide direction. As the cross-sectional shape of the unit prism of such a prism layer, a known shape can be applied according to a required function. Depending on the shape, light can be further diffused or condensed. As a result, the light can be collected 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, and the light utilization efficiency can be improved. ..

The reflective polarizing plate (film) 28 decomposes 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 wave). ), And 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 such a reflective polarizing plate 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 one surface of the base material layer 31a (the surface on the light guide plate 21 side in this embodiment). There is. The optical sheet 30 is basically formed by the combination of the base material layer 31a and the optical functional layer 32, but in addition to this, a second group is formed so as to face the base material layer 31a with the optical functional layer 32 interposed therebetween. The material layer 31b may be arranged. The embodiments shown in FIGS. 1 to 4 (particularly refer to FIG. 4) include both a base material layer 31a and a second base material layer 31b (hereinafter, referred to as “the present embodiment”). As a result, the rigidity of the optical sheet 30 is increased as compared with the case where the base material layer 31a is used alone, the occurrence of bending at the time of mounting on the liquid crystal display device 10 is suppressed, and unevenness of light is suppressed. Becomes possible. Further, the embodiment shown in FIG. 5 shows an optical sheet 30'composed of a combination of a base material layer 31a and an optical functional layer 32, and the optical sheet 30' includes a second base material layer 31b. Not. It is also possible to use such an optical sheet 30'if it has sufficient rigidity.

Further, in the present embodiment, a protective layer (not shown) that protects the optical functional layer 32 may be further laminated on the second base material layer 31b. By laminating the protective layer, it is possible to impart an effect of protecting the optical functional layer 32 from external damage and the like, and an effect of suppressing warpage when the optical sheet 30 is produced. As the material used for the protective layer, a known material such as an ultraviolet curable urethane acrylate can be used. Further, the protective layer may be subjected to antireflection treatment, antiglare treatment, antistatic treatment, hard coat treatment and the like. The thickness of the protective layer is preferably 5 μm or more and 30 μm or less. If the thickness of the protective layer is less than 5 μm, it becomes difficult to apply the coating stably, and if it is thicker than 30 μm, the cost of the material used increases. The haze of the protective layer is preferably 5% or more and 50% or less. If the haze of the protective layer is less than 5%, it may adhere to the film arranged on the surface of the protective layer (for example, the reflective polarizing plate 28 in FIGS. 1 to 3). On the other hand, when the haze of the protective layer exceeds 50%, the light transmitted through the protective layer is diffused too much, so that the front luminance tends to decrease.

As will be described later, the optical sheet 30 and the optical sheet 30'(hereinafter collectively referred to as "optical sheet 30") change the traveling direction of the light incident from the incoming light side and emit the light from the outgoing light side in the front direction. It has a function (condensing function) to intensively improve the brightness (in the normal direction). In that case, changes in the polarizing component are suppressed, and these functions can improve the efficiency of light utilization. Further, it has a function of absorbing light traveling at a large angle with respect to the front direction (light absorption function).

The base material layer 31a and the second base material layer 31b are flat plate-shaped members that support the optical functional layer 32. Various materials can be used as the material forming the base material layer 31a and the second base material layer 31b, but in the present embodiment, the base material layer 31a and the second base material layer 31b are both polyesters. Although it is said to be a film, for example, a polycarbonate resin can also be used. The thickness of the base material layer is not particularly limited as long as the value of the water absorption rate of the optical sheet is 0.00% or more and 1.33% or less as described later, but it is preferable depending on the material. Is 60 μm or more and 250 μm or less.

As described above, since the optical sheet 30 is prevented from bending by having a predetermined base material layer, in this embodiment, at least a part of the optical sheet 30 and the liquid crystal panel 15 are not adhered to each other. It may have a portion, and the entire surface may not be adhered. Further, since the intensity of the light transmitted through the optical sheet 30 is greatly affected by the incident angle and the exit angle with respect to the optical sheet 30, the bending of the optical sheet 30 is suppressed, so that the light transmitted through the optical sheet 30 is uneven. In particular, uneven brightness can be suppressed.

As described above, various materials can be used as the material forming the base material layer 31a and the second base material layer 31b. However, it is preferable to use 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. Examples thereof include polyethylene terephthalate resin (PET), methacrylic resin, polycarbonate resin and the like. Among these, it is preferable to use a methacrylic resin or a polycarbonate resin having less birefringence in consideration of the combination of the surface light source device 20 and the lower polarizing plate 14. Further, in applications requiring high heat resistance such as in-vehicle applications, a polycarbonate resin having a high glass transition point is desirable. Specifically, the glass transition point of the polycarbonate resin is 143 ° C, and it is suitable for in-vehicle applications where durability at 105 ° C is generally required.

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, 2 and 4. As shown enlarged in FIG. 4, the light transmitting portion 33 extends in the horizontal direction while maintaining the cross section along the layer surfaces of the base material layer 31a and the second base material layer 31b, and is predetermined in the vertical direction. Are arranged at intervals of. A groove 33a (see FIG. 7) having a substantially trapezoidal cross section is initially formed between the adjacent light transmitting portions 33, and the groove 33a is filled with a material described later to form the louver portion 34. Will be done. The structure shown in FIG. 4 is a schematic structure and does not necessarily match the dimensions of the actual product. In various embodiments, as described below, the thickness of each layer may differ from the dimensional relationships shown. The method of forming the louver portion 34 will be described later with reference to FIG. 7.

The light transmitting portion 33 maintains the cross section along the layer surface of the base material layer 31 and extends in the front-back direction of the paper surface of FIG. 4, and at a predetermined interval in a direction perpendicular to the front-back direction (horizontal direction of FIG. 4). Arranged at (pitch: Pk). A groove having a substantially trapezoidal cross section is initially formed between the adjacent light transmitting portions 33, and the groove has a long lower bottom on the upper bottom side (light guide plate 21 side) of the light transmitting portion 33 and emits light. The transmission portion 33 has a trapezoidal cross section having a short upper bottom on the lower bottom side (liquid crystal panel side), and the louver portion 34 is formed by filling the transmission portion 33 with a necessary material described later. In this embodiment, the adjacent light transmitting portions 33 are connected by a long lower bottom side. In order to specify the structure of the optical functional layer 32, the following parameters are mainly used for the louver portion 34. Regarding the substantially trapezoidal shape of the louver portion 34 having a substantially trapezoidal cross section, the width of the short upper base is We, and the width of the long lower base is Wb. Let Dk be the thickness of the louver portion 34 (corresponding to the height of a substantially trapezoid).

The pitch of the light transmitting portion 33 described above (that is, the pitch of the louver portion 34) Pk is preferably 30 μm or more and 100 μm or less. Further, the angle formed by the interface between the louver portion 34 and the light transmitting portion 33 shown by θk in FIG. 4 and the normal of the layer surface of the optical functional layer 32 is preferably 1 ° or more and 10 ° or less. .. However, the angle may be outside this range, and may be, for example, 0 ° (that is, the hypotenuse coincides with the normal of the layer surface of the optical functional layer 32). The louver portion 34 shown in FIG. 4 has a substantially isosceles trapezoidal shape, but the length of one leg and the length of the other leg may be different. The thickness Dk of the louver portion 34 is preferably 50 μm or more and 150 μm or less, and more preferably 60 μm or more and 150 μm or less. The width We of the upper base and the width Wb of the lower base of the substantially trapezoidal portion of the louver portion 34 are appropriately selected so as to satisfy the relationship between the thickness Dk, the pitch Pk, and the angle θk of the louver portion 34 described above. By setting these parameters within a preferable range, the balance between light transmission and light absorption is often appropriate.

In this embodiment, an example is shown in which the interface between the light transmitting portion 33 and the louver portion 34 is a straight line in the cross section, but the present invention is not limited to this, and the interface may be a polygonal line, a convex curved surface, a concave curved surface, or the like. Good. Further, the plurality of light transmitting portions 33 and the louver portion 34 may have the same cross-sectional shape, or may have different cross-sectional shapes with predetermined regularity.

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 light is appropriately reflected at the interface with the louver portion 34 on the slope of the trapezoidal cross section (total reflection). From the viewpoint of including), the refractive index is preferably 1.47 to 1.65, more preferably 1.49 to 1.57.

The louver portion 34 is formed by filling a groove 33a initially provided between adjacent light transmitting portions 33 with a material described later, and finally has a cross-sectional shape similar to the cross-sectional shape of the groove 33a before filling. It becomes. 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 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 configuration of the liquid crystal display device 10 will be further described with reference to FIGS. 1 to 3. The reflective sheet 39 is a member for reflecting the light emitted from the back surface of the light guide plate 21 and causing the light to enter the light guide plate 21 again. The reflective sheet 39 is a sheet that enables so-called specular reflection, such as a sheet made of a material having a high reflectance such as metal and a sheet containing a thin film (for example, a metal thin film) made of a material having a high reflectance as a surface layer. It can be preferably applied.

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.

Next, the operation of the liquid crystal display device 10 having the above configuration will be described with an example of an optical path. However, the optical path example is conceptual for explanation, and does not strictly represent the degree of reflection or refraction.

First, as shown in FIG. 2, the light emitted from the light source 25 enters the light guide plate 21 via the light entering surface on the side surface of the light guide plate 21. FIG. 2 shows, as an example, an optical path example of the light L21 and L22 incident on the light guide plate 21 from the light source 25.

As shown in FIG. 2, the lights L21 and L22 incident on the light guide plate 21 are repeatedly totally reflected by the difference in refractive index with air on the light emitting side surface of the light guide plate 21 and the back surface on the opposite side thereof, and are in the light guide direction (FIG. Proceed to (2) downward on the page).

However, the optical element 23 is arranged on the back surface of the light guide plate 21. Therefore, as shown in FIG. 2, the light L21 and L22 traveling in the light guide plate 21 change their traveling directions depending on the optical element 23, and may be incident on the light emitting surface and the back surface at an incident angle less than the total reflection critical angle. is there. In this case, the light can be emitted from the light emitting surface of the light guide plate 21 and the back surface on the opposite side thereof.

The lights L21 and L22 emitted from the light emitting surface head toward the reflective polarizing plate 28 arranged on the light emitting side of the light guide plate 21. On the other hand, the light emitted from the back surface is reflected by the reflective sheet 39 arranged on the back surface of the light guide plate 21, enters the light guide plate 21 again, and travels in the light guide plate 21.

The light traveling in the light guide plate 21 and the light that is turned by the optical element 23 and reaches the light emitting surface at an incident angle less than the total reflection critical angle are generated in each area in the light guide plate 21 along the light guide direction. .. Therefore, the light traveling in the light guide plate 21 is gradually emitted from the light emitting surface. As a result, the light amount distribution of the light emitted from the light emitting surface of the light guide plate 21 along the light guide direction can be made uniform.

The light emitted from the light guide plate 21 then reaches the light diffusing plate 26 to improve the uniformity. Then, the light diffused or condensed by the prism layer 27 as needed and emitted from the prism layer 27 reaches the reflective polarizing plate 28. Here, the light in the polarization direction along the transmission axis of the reflective polarizing plate 28 passes through the reflective polarizing plate 28 and heads toward the optical sheet 30. On the other hand, the light in the polarization direction along the reflection axis of the reflective polarizing plate 28 is reflected as shown by the dotted arrows L21'and L22' in FIG. 2 and returned to the light guide plate 21 side. The returned light is reflected by the light guide plate 21, the optical element 23, or the reflective sheet 39, and travels to the side of the reflective polarizing plate 28 again. At the time of this reflection, the polarization direction of a part of the light is changed, and a part of the light is transmitted through the reflective polarizing plate 28. The other light is returned to the light guide plate side again. The light reflected by the reflective polarizing plate 28 can be transmitted through the reflective polarizing plate 28 by repeating the reflection. As a result, the utilization rate of the light from the light source 25 is increased. Here, the light emitted from the reflective polarizing plate 28 has its polarization direction along the transmission axis of the lower polarizing plate 14, and is polarized light transmitted through the lower polarizing plate 14.

The light emitted from the reflective polarizing plate 28 is incident on the optical functional layer 32. The light incident on the optical functional layer 32 is polarized light that passes through the lower polarizing plate 14, and travels with the following optical paths. That is, for example, as shown by L41 in FIG. 5, the light transmitting portion 33 is transmitted without reaching the interface with the louver portion 34. Alternatively, as shown by L42 in FIG. 5, it reaches the interface with the louver portion 34 and is totally reflected to pass through the light transmitting portion 33. At this time, in the present embodiment, due to the action of the inclination angle (θk) of the interface, the light reflected at the interface is brought closer to the direction parallel to the normal line of the liquid crystal panel 15. Further, even if the light is not totally reflected because the angle is smaller than the total reflection critical angle, some of the light is reflected at the interface. Such light also passes through the light transmitting portion 33 in the same manner. As a result, it is possible to effectively provide the liquid crystal panel 15 with light that does not cause problems such as a decrease in contrast and color inversion when the light is transmitted through the liquid crystal panel 15.

On the other hand, as shown by L43 in FIG. 5, the light incident on the optical functional layer 32 at a large angle with respect to the sheet surface normal is absorbed by the louver portion 34 and is not provided to the liquid crystal panel 15. Therefore, it is possible to absorb light that causes problems such as a decrease in contrast and color inversion.

With such an optical sheet 30, the light from the light guide plate 21 is efficiently collected, and the light that is not collected is absorbed by the louver portion, so that appropriate light can be efficiently provided to the liquid crystal panel. It is possible to greatly improve the efficiency of light utilization.

Further explain the optical path. The light emitted from the surface light source device 20 as described above is incident on the lower polarizing plate 14 of the liquid crystal panel 15. The lower polarizing plate 14 transmits one of the polarized light components of the incident light and absorbs the other polarized light component. The light transmitted through the lower polarizing plate 14 selectively transmits through the upper polarizing plate 13 according to the state in which the electric field is applied to each pixel. In this way, the liquid crystal panel 15 selectively transmits the light from the surface light source device 20 for each pixel, so that the observer of the liquid crystal display device can observe the image. At that time, the image light is provided to the observer via the functional film 40, and the quality of the image is improved.

In the above-described form, the optical functional layer 32 has the short upper bottom of the light transmitting portion 33 facing the light guide plate 21 side and the long lower bottom facing the liquid crystal panel 15 side, but this may be inverted. That is, the short upper bottom of the light transmitting portion may be oriented toward the liquid crystal panel side, and the long lower bottom may be oriented toward the light guide plate side. In this case, it does not have a light condensing action, but it can maintain the polarization direction transmitted through the lower polarizing plate and provide light to the lower polarizing plate, so that the light absorbed by the lower polarizing plate can be suppressed to a small extent. It is possible to improve the light utilization efficiency (transmittance).

When the optical sheet 30 including the optical functional layer 32 having the above-described configuration is bent, unevenness of light when viewed from the user (observer) may occur. Specifically, in the optical sheet 30 shown in FIGS. 2 and 3, the deflection in the direction perpendicular to the surface of the optical sheet 30, that is, the direction shown as the thickness direction in FIGS. 2 and 3 is , Affects the occurrence of light unevenness when viewed from the user (observer). Among such bending directions of the optical sheet 30, in particular, bending in the thickness direction of the optical sheet 30 shown in FIG. 2, that is, a plurality of light transmitting portions 33 and louver portions 34 of the optical functional layer 32 are alternately arranged. The deflection in the direction orthogonal to the direction (the direction designated as the "vertical direction" in FIG. 2) in the paper surface of FIG. 2 causes unevenness of light when viewed from the user (observer). It has a big influence.

[Method of manufacturing optical sheet]
Next, a method of manufacturing the optical sheet 30 will be described with reference to FIGS. 6 to 8. 6 to 8 are explanatory views of a manufacturing process of the optical sheet 30.

As described above, the base material layer 31a of the optical sheet 30 and the optional second base material layer 31b are both made of polyester film. 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 Acid, malonic acid, dimethylmalonic acid, succinic acid, 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.

The dicarboxylic acid component and the diol component constituting the polyester film may be used alone or in combination of two or more. 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, a non-oriented polyester obtained by melting a polyester resin and extruding it into a sheet is stretched in the vertical direction at a temperature equal to or higher than the glass transition temperature by utilizing the speed difference of 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. For example, the polyester film used in Example 1 described later is stretched in the vertical direction and then in the horizontal direction at a temperature of 90 to 120 ° C., and the stretching ratio in the vertical direction is 2.0 times and the horizontal direction. The draw ratio in the direction is 4.5 times. Further, it is known that as the draw ratio increases, the breaking strength in that direction increases.

The thickness of the polyester film is arbitrary, and can be appropriately set in the range of, for example, 15 to 300 μm, preferably 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. 6, a base material layer is formed between a mold roll R1 having a shape (groove) on which the shape of the light transmitting portion 33 can be transferred and a 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 FIGS. 1, 4, etc.) between the polyester film 310 and the mold roll R1, the mold roll R1 and the nip roll R2 are shown in FIG. Rotate in the direction indicated by the arrow in 6. 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 type, a urethane acrylate type, a polyether acrylate type, a polyester acrylate type, or a polythiol type 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, etc.) 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. 7, 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 a 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 30 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.

As the composition 340 constituting the louver portion 34, for example, a photocurable resin such as urethane (meth) acrylate, polyester (meth) acrylate, epoxy (meth) acrylate, and butadiene (meth) acrylate can be used. Further, those resins in which colored light absorbing particles are dispersed can also be used.

Also, instead of dispersing the light absorbing particles, the entire louver part can be colored with a pigment or 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. Here, the "average particle size" means an arithmetically averaged diameter obtained by observing 100 light absorbing particles with an electron microscope and measuring their diameters.

When manufacturing 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. 8, 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 of the intermediate sheet 36b and the second base material layer 31b (polyester film 310) and sticking them together, the disturbance of polarization based on the phase difference and the accompanying color unevenness are caused. It is possible to prevent the occurrence and decrease in transmittance. The intermediate sheet 36b and the polyester film 310 are guided by rollers 380 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 around the roll R6. When the optical sheet 30 is wound by a predetermined length, the optical sheet 30 is cut, and the wound roll R6 is replaced with a new roll R6 to start the next winding.

When a protective layer (not shown) is provided in place of the second base material layer 31b in the optical functional layer 32, a sheet serving as a protective layer instead of the polyester film 310 described above is bonded to each other using a roll, a UV adhesive, or the like. It is possible. Further, when an additional protective layer is provided, it is possible to bond them together using a roll, a UV adhesive, or the like to further laminate them.

In this way, in manufacturing the optical sheet, there is a transfer of the optical sheet between a plurality of rolls, that is, a roll-to-roll process, and the optical sheet is finally wound up on the roll again.

Regarding the optical sheet manufactured in this way, two test methods will be described. The first test method is a test by a combination of a sagging amount test and a flexibility test. The second test method is a water absorption test. Each will be described as follows.

[First test method (hanging amount test and flexibility test)]
The test is performed using the optical sheet described below.

(Example 1)
The specific shape of the optical sheet according to the first embodiment is as follows.

<Base layer>
-Material: Polyester film-Thickness: 80 μm
<Optical functional layer>
-Pitch (see FIG. 4): Pk = 39 μm
・ Louver upper bottom width: 4 μm (Wa in Fig. 4)
・ Lower bottom width of louver: 10 μm (Wb in FIG. 4)
-Slope angle: 0 ° on one side and 3 ° on the other (θk in Fig. 4)
-Thickness of the louver (see FIG. 4): Dk = 102 μm
-Thickness of optical functional layer: 127 μm
-Material and refractive index of the light transmitting part: UV-curable urethane acrylate with a refractive index of 1.57-Material and refractive index of the louver part: UV-curable urethane acrylate with a refractive index of 1.49 and acrylic beads with an average particle size of 4 μm 20% by mass of black beads containing carbon black on the surface layer <second base material layer>
The following second base material layer was further bonded to the surface of the optical functional layer opposite to the base material layer with an acrylic pressure-sensitive adhesive.
-Material: Polyester film-Thickness: 80 μm

(Example 2)
In the optical sheet according to Example 1, the materials of the base material layer and the second base material layer are changed to cellulose triacetate (TAC) resin, respectively, and the thickness of the base material layer and the second base material layer is 60 μm, respectively. The optical sheet according to Example 2 was prepared by changing and laminating.

(Example 3)
In the optical sheet according to Example 1, the materials of the base material layer and the second base material layer are changed to polycarbonate (PC) resin, respectively, and the thicknesses of the base material layer and the second base material layer are changed to 130 μm, respectively. And bonded together to prepare an optical sheet according to Example 3.

(Comparative Example 1)
In the optical sheet according to Example 1, the material of the base material layer was changed to polycarbonate resin, the thickness of the base material layer was changed to 130 μm, and the second base material layer was not bonded to the optical sheet. Such an optical sheet was produced.

(Comparative Example 2)
In the optical sheet according to Example 1, the material of the base material layer was changed to polycarbonate resin, the thickness of the base material layer was changed to 250 μm, and the second base material layer was not bonded to Comparative Example 2. Such an optical sheet was produced.

(Comparative Example 3)
In the optical sheet according to Example 1, the material of the base material layer was changed to polycarbonate resin, the thickness of the base material layer was changed to 500 μm, and the second base material layer was not bonded to the optical sheet in Comparative Example 3. Such an optical sheet was produced.

As described above, there are various combinations of the materials of the base material layer 31a and the second base material layer 31b of the optical sheet 30, the configuration of the optical functional layer 32, and the adhesive, and the completed optical sheet 30 varies. Can have various physical properties. Among such various optical sheets 30, those that are suitable for use in liquid crystal display devices and in-vehicle liquid crystal display devices and that do not reduce the manufacturing efficiency are determined by the tests described below.

[Dripping amount test]
FIG. 9 shows an outline of the sagging amount test of the optical sheet 30. FIG. 9 is a side view of the state of performing this sagging amount test. First, in an environment of a temperature of 25 ° C. and a humidity of 30%, a support base 50 having a flat upper surface is prepared, and an optical sheet 30 to be tested is placed flat on the upper surface of the support base 50. Next, from the end of the support base 50, along the direction in which the plurality of light transmitting portions 33 and the louver portions 34 of the optical functional layer 32 of the optical sheet 30 are alternately arranged (not shown in FIG. 9). One end of the optical sheet 30 is projected by 100 mm. (A temporary support portion (not shown) may be used to place one end of the optical sheet 30 on the temporary support portion and project it by 100 mm, and then remove the temporary support portion.) In the projected state, before hanging down. The optical sheet 30 of the above is shown by a broken line. As described in paragraph 0039 above, bending in a direction that has a large effect on the occurrence of light unevenness, that is, a direction in which a plurality of light transmitting portions 33 and louver portions 34 of the optical functional layer 32 are alternately arranged (in FIG. 2). Regarding the bending in the direction orthogonal to the "vertical direction") in the paper surface, the easiness of bending can be measured by the sagging amount test. The direction in which the plurality of light transmitting portions 33 and the louver portions 34 of the optical functional layer 32 of the optical sheet 30 are alternately arranged is the width direction orthogonal to the flow direction of the optical sheet 30 in the manufacturing process shown in FIG. Correspond.

The length of the protruding portion of the optical sheet 30 is 100 mm, whereas the length of the portion of the optical sheet 30 arranged on the upper surface of the support base 50 (that is, the portion not protruding from the support base 50) is , 100 mm or more is preferable. Then, the plate-shaped sheet retainer 51 is placed on the optical sheet 30 so as to press the portion of the optical sheet 30 arranged on the upper surface of the support base 50 from above, and the optical sheet 30 is placed on the support base 50. Hold on. The weight of the sheet retainer 51 is appropriately selected so that the optical sheet 30 does not rise from the upper surface of the support base 50 during the test, as will be described later. This weight depends on the size of the optical sheet 30, but can be selected from the range of several hundred grams to several kilograms. The optical sheet 30 projecting 100 mm from the end of the support base 50 hangs downward due to its own weight. The hanging optical sheet 30 is shown by a solid line. At this time, since the sheet retainer 51 presses the portion of the optical sheet 30 that is arranged on the upper surface of the support base 50 from above, the portion of the optical sheet 30 that is particularly near the end of the support base 50 is optical. It prevents the seat 30 from rising from the upper surface of the support base 50 as the protruding portion hangs down. By doing so, the amount of sagging can be measured accurately. The difference between the height of the optical sheet 30 arranged on the upper surface of the support base 50 and the height of the end portion of the hanging optical sheet 30 is taken, and this value is defined as the hanging amount F. If the rigidity of the optical sheet 30 is high, the amount of sagging F is small, and if the rigidity is low, the amount of sagging F is large.

[Flexibility test]
Since a roll-to-roll step is present in the manufacture of the optical sheet 30, if the rigidity of the optical sheet 30 is too high, the manufacturing method involving the roll-to-roll step may not be applicable. A flexibility test is performed to determine whether or not the target optical sheet 30 can be manufactured by a manufacturing method involving a roll-to-roll step. The flexibility test is a test for confirming the flexibility of the optical sheet 30, and is performed based on JIS K 5600-5-1. JIS K 5600-5 is a standard relating to a general coating test method, and in particular, a standard relating to a test method relating to the mechanical properties of a coating film. JIS K 5600-5-1 relates to bending resistance (cylindrical mandrel method) among the mechanical properties of the coating film, but in the present invention, this is used for the bending test of the optical sheet. It is an application.

The flexibility test in the present invention uses a type 2 test device out of the two types of test devices specified in JIS K 5600-5-1. The standard stipulates that the type 2 test equipment is used in combination with one of the mandrel diameters of 6, 10, and 13 mm, but the type 2 test equipment uses a mandrel of another diameter. It is noted in the standard that it is also good. In the flexibility test of the present invention, the flexibility of the optical sheet was tested using a cylindrical mandrel having a diameter of 150 mm with a type 2 test apparatus.

The flexibility test was performed by bending the optical sheet 30 so as to be wound around the mandrel of the test device and visually confirming whether or not the optical sheet 30 was cracked. The plurality of light transmitting portions 33 and louver portions 34 of the optical functional layer 32 of the optical sheet 30 are alternately arranged along the flow direction at the time of manufacturing the optical sheet 30 shown in FIG. 8 (shown in FIG. 8). The optical sheet 30 was bent so as to be wound around the mandrel along a direction orthogonal to the direction (not shown) in the plane of the optical sheet 30. This is for making the state of the optical sheet 30 at the time of the flexibility test correspond to the roll-to-roll process at the time of manufacturing the optical sheet 30. If there was no crack, it was judged as "pass", and if it was cracked, it was judged as "cracked".

[Confirmation of uneven light]
Regarding the occurrence of light unevenness, the optical sheets of each example and comparative example were mounted on a 12.3 inch IPS liquid crystal display, and the reliability was 1000 hours in an environment of 95 ° C. and 1000 hours in an environment of −45 ° C. It was visually confirmed whether or not there was unevenness in light when the liquid crystal display subjected to the sex test was operated.

Table 1 shows the measurement results of the sagging amount test, the judgment result of the flexibility test, and the confirmation result of light unevenness for each Example and Comparative Example.

From these results, it was found that light unevenness did not occur in any of the optical sheets with a sagging amount of 10.0 mm or less. On the other hand, even if the amount of sagging is 10.0 mm or less, in the case where cracks occur in the flexibility test (Comparative Example 3), light unevenness does not occur in the product, but a manufacturing method involving a roll-to-roll step is used. It is not appropriate because it affects the manufacturing efficiency of. Therefore, when the optical sheet is arranged on the support base and one end thereof is projected 100 mm from the end portion of the support base, the amount of sagging is 10 mm or less, and the optical sheet is bent so as to be wound around a mandrel having a diameter of 150 mm. It has been found that optical sheets (Examples 1 to 3) that do not occasionally crack are suitable.

That is, as compared with the comparative example, it is possible to suppress the occurrence of unevenness of light even when it is mounted on a liquid crystal display device, and it is also possible to prevent a decrease in manufacturing efficiency.

Further, based on this result, it is easy to determine whether or not the optical sheet having a predetermined configuration is suitable for use in a liquid crystal display device, particularly an in-vehicle liquid crystal display device, and can secure a predetermined manufacturing efficiency. It can be determined. That is, first, an optical sheet as a candidate for use is prepared, and the amount of sagging of this optical sheet is measured by the above-mentioned method to determine whether or not the amount of sagging is 10 mm or less. Further, as described above, the optical sheet is bent so as to be wound around a mandrel having a diameter of 150 mm, and it is determined whether or not cracks occur. Then, it was determined that the amount of sagging was 10 mm or less, and the optical sheet was determined to have not cracked when bent so as to be wound around the mandrel, and the optical sheet was determined to be acceptable for manufacturing. An optical sheet that adopts the optical sheet configuration (material, structure, etc.) and is suitable for use in liquid crystal display devices, especially in-vehicle liquid crystal display devices, and does not reduce manufacturing efficiency, according to the optical sheet manufacturing method as described above. Can be manufactured.

[Second test method (water absorption rate test)]
A second test method different from the above-mentioned first test method (hanging amount test and flexibility test), that is, a water absorption rate test will be described as follows. First, the samples used in the water absorption test are as follows.

(Example 1')
The same optical sheet as in Example 1 in the first test method described above was used as the optical sheet according to Example 1'.

(Example 2')
In the optical sheet according to Example 1', the material of the base material layer is changed to polycarbonate (PC) resin, the thickness of the base material layer is changed to 130 μm, and the second base material layer is not bonded. An optical sheet according to Example 2'was produced.

(Example 3')
In the optical sheet according to Example 1', the material of the base material layer was changed to polycarbonate resin, the thickness of the base material layer was changed to 130 μm, and the material of the second base material layer was changed to polycarbonate resin. The thickness of the second base material layer was changed to 100 μm and bonded to prepare an optical sheet according to Example 3'.

(Example 4')
In the optical sheet according to Example 1', the material of the base material layer is changed to polycarbonate resin, the thickness of the base material layer is changed to 250 μm, and the second base material layer is not bonded. An optical sheet according to ‘’ was produced.

(Comparative Example 1')
In the optical sheet according to Example 1', the materials of the base material layer and the second base material layer are changed to cellulose triacetate (TAC) resin, respectively, so that the thickness of the base material layer and the second base material layer is 60 μm. An optical sheet according to a comparative example having the same conditions as the others was prepared.

[Measurement of water absorption rate]
The water absorption rate of the optical sheet having the above-described configuration and which can be used in the liquid crystal display device is measured as follows. This measurement is made based on JIS K 7209. The outline of the two measurements performed on the samples of each example and comparative example is shown below.
(1) Water absorption rate when submerged at 23 ° C for 24 hours After measuring the weight of a sufficiently dried sample as a reference value, completely immerse it in distilled water at 23.0 ° C and leave it for 24 hours. After that, the sample is taken out from water, the weight thereof is measured, and the water absorption rate is determined based on the weight difference between the sample before and after immersion in water and the reference value.
(2) Water absorption rate when dried at 50 ° C for 24 hours After measuring the weight of a sufficiently dried sample as a reference value, the sample is completely immersed in distilled water at 23.0 ° C and left for 24 hours. Then, the sample is taken out of water, weighed, and then dried in an oven maintained at 50 ° C. for 24 hours. After that, the weight is measured, and the water absorption rate is determined based on the weight difference between the sample before and after drying and the reference value. Since the weight of the sample decreases in the process of the test, the water absorption rate as the rate of change becomes a negative value, but the actual water absorption rate takes the absolute value.

[Confirmation of uneven light]
Regarding the occurrence of light unevenness, the optical sheets of each example and comparative example were mounted on a 12.3 inch IPS liquid crystal display, and after 1000 hours had passed in an environment of a temperature of 65 ° C. and a humidity of 95%, the light unevenness was generated. The presence or absence was visually confirmed.

Table 2 shows the measurement results of the water absorption rate and the confirmation results of light unevenness for each Example and Comparative Example. The linear expansion coefficients of polyethylene terephthalate resin, polycarbonate resin, and cellulose triacetate resin, which are the materials of the base material, are also shown for each of the Examples and Comparative Examples in Table 2.

As shown in Table 2, light unevenness did not occur in all the examples having a water absorption rate of 1.33% or less, whereas the water absorption rate was larger than 1.33%, 2.60%. In Comparative Example 1 having the water absorption rate of No. 1, uneven light occurred.

By repeating the experiment, it was found that the deformation of the optical sheet due to water absorption of the optical sheet contributes to the occurrence of light unevenness. According to the experimental results, if the optical sheet has a water absorption rate of 1.33% or less, light unevenness does not occur. However, assuming the use of the product in a high temperature environment, the thermal expansion of the optical sheet (the contribution of the base material layer is considered to be dominant) can also be taken into consideration, and the base material layer of the optical sheet can be considered. It was found that it is more preferable that the coefficient of linear thermal expansion of the above is in ^{the range of 4.9 to 5.6 (× 10 -5 / ° C.).}

That is, according to Examples 1'to 4', the occurrence of light unevenness can be suppressed as compared with Comparative Example 1'.

Further, based on the result of the second test method, it can be easily determined whether or not the optical sheet having a predetermined configuration is suitable for use in a liquid crystal display device, particularly an in-vehicle liquid crystal display device. That is, first, an optical sheet as a candidate for use is prepared, and the water absorption rate of this optical sheet is measured by a water absorption rate test based on JIS K7209. Next, it is compared whether or not the measured water absorption rate is 1.33% or less, which is the threshold value. As a result of this comparison, if the water absorption rate of the optical sheet is 1.33% or less, it is judged as acceptable, and if the water absorption rate of the optical sheet is larger than 1.33%, it is judged as rejected. Then, by adopting the structure (material, structure, etc.) of the optical sheet judged to be acceptable, it is suitable for use in a liquid crystal display device, particularly an in-vehicle liquid crystal display device, according to the above-mentioned manufacturing method of the optical sheet. Optical sheets can be manufactured.

Based on the first test method (hanging amount test and flexibility test) or the second test method (water absorption rate test) described above, it is suitable for use in a liquid crystal display device, particularly an in-vehicle liquid crystal display device. Although each optical sheet can be easily discriminated, it is possible to further discriminate a more suitable optical sheet by combining these tests.

Specifically, Example 1 of the above-mentioned first test method (hanging amount test and flexibility test) and Example 1'of the second test method (water absorption rate test) are optical sheets having the same configuration. When confirming the unevenness of light accompanying any of the tests, the unevenness does not occur, and it can be determined that the optical sheet is suitable. Further, Comparative Example 1'of Example 2 of the first test method (hanging amount test and flexibility test) and the second test method (water absorption rate test) are optical sheets having the same configuration, and the hanging amount test and the hanging amount test and No unevenness occurred when confirming the light unevenness accompanying the flexibility test, but unevenness occurred when confirming the light unevenness accompanying the water absorption test. Further, Comparative Example 1 of the first test method (hanging amount test and flexibility test) is an optical sheet corresponding to Example 2'of the second test method (water absorption rate test). In this optical sheet, unevenness did not occur when confirming the unevenness of light accompanying the water absorption test, but unevenness occurred when confirming the unevenness of light accompanying the sagging amount test and the flexibility test. It is probable that these were caused by the difference between the environmental conditions for confirming the light unevenness associated with the sagging amount test and the flexibility test and the environmental conditions for confirming the light unevenness associated with the water absorption rate test. It is suggested that the suitability of adopting these optical sheets should be examined according to the humidity conditions of the environment.

In this way, by combining the first test method (hanging amount test and flexibility test) and the second test method (water absorption rate test), the configuration of the optical sheet of Example 1 (Example 1') is configured. However, it can be determined that the configuration is particularly suitable for use in an in-vehicle liquid crystal display device and does not reduce the manufacturing efficiency.

By the test method described above, it is possible to find an appropriate configuration of an optical sheet that suppresses unevenness of light. Then, the optical sheet can be manufactured by the above-mentioned manufacturing method by adopting the structure of the optical sheet found by this test method.

According to such a test method and a manufacturing method, it is possible to easily discriminate and manufacture an optical sheet suitable for use in a liquid crystal display device, particularly an in-vehicle liquid crystal display device, and the manufacturing efficiency does not decrease.

10 Liquid crystal display device 14 Lower polarizing plate (polarizing film)
30 Optical sheet 31a Base material layer 31b Second base material layer 32 Optical functional layer 33 Light transmitting part 34 Louver part

Claims (6)

1. An optical sheet provided between a reflective polarizing plate 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.
   In the optical sheet, the optical sheet is arranged on a support base, and one end of the optical sheet is supported on the support base along a direction in which the plurality of light transmitting portions and louver portions of the optical functional layer are alternately arranged. The amount of sagging when projected 100 mm from the end of the optical sheet is 10 mm or less, and the optical sheet has the optical in the direction in which the plurality of light transmitting portions and the louver portions of the optical functional layer are alternately arranged. No cracks occur when the optical sheet is bent to wrap around a 150 mm diameter mandrel along orthogonal directions in the sheet surface, and / or the optical sheet absorbs water according to a water absorption test based on JIS K 7209. It has a water absorption rate of 1.33% or less.
   Optical sheet.
2. The optical sheet according to claim 1, further comprising a second base material layer arranged so as to face the base material layer with the optical functional layer interposed therebetween.
3. The optical sheet according to claim 1 or 2, wherein the material of the base material of the optical sheet has a coefficient of linear thermal expansion of 4.9 to 5.6 (× 10 ^{-5 / ° C.).}
4. The optical sheet according to any one of claims 1 to 3 and
   A liquid crystal display device including a reflective polarizing plate and a liquid crystal panel arranged so as to face each other with the optical sheet interposed therebetween.
5. 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 a test method of an optical sheet including an optical functional layer having a louver portion which is arranged in and reflects or absorbs light.
   The optical sheet is arranged on a support base, and one end of the optical sheet is 100 mm from the end portion of the support base along the direction in which the plurality of light transmitting portions and louver portions of the optical functional layer are alternately arranged. The sagging amount determination step for determining whether or not the sagging amount when projected is 10 mm or less, and the optical sheet are alternately arranged with the plurality of light transmitting portions and louver portions of the optical functional layer. A crack determination step of bending the mandrel having a diameter of 150 mm so as to wind it around a mandrel having a diameter of 150 mm along a direction orthogonal to the direction in the plane of the optical sheet to determine whether or not cracks occur, and / or water absorption of the optical sheet. If the water absorption rate measuring step in which the rate is measured by the water absorption rate test based on JIS K 7209 and the water absorption rate measured by the water absorption rate measurement step is 1.33% or less, the result is passed, and the water absorption rate of the optical sheet is 1. Includes a water absorption rate determination step, which is rejected if it is greater than .33%.
   The configuration of the optical sheet determined in the sagging amount determination step to be 10 mm or less and no cracking in the crack determination step, and / or a pass in the water absorption rate determination step. A method for testing an optical sheet, which determines that the structure of the optical sheet is an appropriate structure.
6. A method for manufacturing an optical sheet, which manufactures the optical sheet by adopting the configuration of the optical sheet determined to be an appropriate configuration by the test method according to claim 5.

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