JP2012053170A - Method for manufacturing film material, method for manufacturing lower polarizing plate, lower polarizing plate, liquid crystal display panel, and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for inexpensively manufacturing a protective film capable of changing a traveling direction of incident light.SOLUTION: The manufacturing method includes: an extrusion step for heating and extruding thermoplastic resin 56a along with a diffusion component 57 to form a film material 90; and a pressurizing step for passing the film material between a belt member 86b and a molding roll 84, while pressurizing the film material between the belt member 86b and the molding roll 84 disposed facing the belt member. In the pressurizing process, the film material is pressurized across a section NZ with a certain length L along the moving passage. Alternatively, in the pressurizing step, a surface 55a forming a side which is in contact with the belt member of a protective film 55 is cooled so as to become a flat face.

Description

  The present invention relates to a method of manufacturing a protective film for a lower polarizing plate that is bonded to a polarizer to form a lower polarizing plate for a liquid crystal display panel, and in particular, changes the traveling direction of light incident on the liquid crystal display panel. It is related with the manufacturing method of the protective film which can be made.

  The present invention also relates to a method for manufacturing a lower polarizing plate for a liquid crystal display panel, and more particularly to a method for manufacturing a lower polarizing plate that can change the traveling direction of light incident on the liquid crystal display panel.

  Furthermore, the present invention provides a lower polarizing plate, a liquid crystal display panel and a display device including a protective film produced by such a production method, a liquid crystal display panel comprising a lower polarizing plate produced by such a production method, and The present invention relates to a display device.

  Today, display devices including a liquid crystal display panel and a surface light source device that illuminates the liquid crystal display panel from the back side are widely used.

  The surface light source device includes a light source and a large number of optical sheets for changing the traveling direction of light from the light source. As in the example of the surface light source device 120 shown in FIG. 9, in many cases, in a large number of optical sheets, a light diffusing sheet that diffuses light from the light source to hide the image of the light source (make it inconspicuous). 29, a diffusion plate 28, and light collecting sheets 30 and 35 having a function (light condensing function) for narrowing the traveling direction of light in the front direction and improving the luminance in the front direction.

  On the other hand, the liquid crystal display panel includes a liquid crystal cell capable of controlling the orientation of the liquid crystal for each pixel, a lower polarizing plate disposed on the light incident side of the liquid crystal cell, an upper polarizing plate disposed on the light output side of the liquid crystal cell, have. Each polarizing plate includes a polarizer that transmits light of a specific polarization component and absorbs light of components other than the specific polarization component, and a protective film that is bonded to the polarizer and protects the polarizer. Yes.

  Of these, the protective film is usually composed of a simple translucent film due to cost constraints, and does not positively exert an optical effect on the transmitted light. In addition, a protective film with an optical function does not exist, but considering the adhesive function with the polarizer and the protective function to protect the polarizer, the protective film on the side that does not actually face the polarizer The surface is merely a mat surface (for example, Patent Document 1).

Japanese Patent Laid-Open No. 9-258013

  However, a sufficient diffusion function cannot be imparted to the protective film to the extent that one surface of the protective film is matted. On the other hand, if a protective film having a function of actively changing the traveling direction of light can be manufactured at a low cost, the degree of freedom in designing the luminance characteristics and viewing angle characteristics of an actual display device will be remarkably increased. Can be improved. Further, there is a possibility that the number of optical sheets incorporated in the surface light source device can be reduced. In this case, the manufacturing cost of the surface light source device and the display device can be directly reduced, and the surface light source device and the display device can be reduced. Can also be made thinner.

  The present invention has been made in consideration of such points, and a manufacturing method that can inexpensively manufacture a protective film for a lower polarizing plate that can change the traveling direction of light incident on a liquid crystal display panel. The purpose is to provide.

The method for producing a protective film according to the present invention is a method for producing a protective film for a lower polarizing plate,
Extruding step, in which a film material including a layer having the thermoplastic resin and the diffusion component dispersed in the thermoplastic resin is formed by heating and extruding the thermoplastic resin together with the diffusion component;
A pressure process in which the formed film material passes between the belt member and the molding roll while being pressed between the belt member and the molding roll disposed to face the belt member; With
In the pressurizing step, the film material is pressed by the molding roll and the belt member over a certain length of section along the movement path, and applied to the belt member of the protective film made of the film material. It cools so that the surface which makes the contact side may become a flat surface.

In the manufacturing method of the protective film according to the present invention, the certain length at which the film material is pressed by the molding roll and the belt member is L (mm), and the moving speed of the film material is F ( mm / sec), the temperature of the belt member may be T (° C.), and the following equation (a) may be satisfied.
0.16 ≦ L / (F × T) × 100 ≦ 0.96 Formula (a)

  In the pressurizing step of the method for producing a protective film according to the present invention, the film material is formed while the layer having the thermoplastic resin and the diffusion component dispersed in the thermoplastic resin is in contact with the belt member. You may make it pass between the said forming roll and the said belt member.

  In the method for producing a protective film according to the present invention, the layer having the thermoplastic resin and the diffusion component dispersed in the thermoplastic resin forms one surface of the protective film made of the film material, Roughness Ra measured according to JISB0601 (1982) on the one surface of the protective film may be 0.9 μm or less.

  In the method for producing a protective film according to the present invention, the roughness Ra measured according to JIS B0601 (1982) on the surface forming the side of the protective film made of the film material that is in contact with the belt member is 0. It may be 9 μm or less.

  In the method for producing a protective film according to the present invention, the roughness Ra measured according to JIS B0601 (1982) on the surface forming the side of the protective film made of the film material that is in contact with the molding roll is 0. It may be 4 μm or less.

  In the extrusion step of the method for producing a protective film according to the present invention, the second thermoplastic resin is also heated and extruded, and the layer having the thermoplastic resin and the diffusion component dispersed in the thermoplastic resin; A film material including a second layer made of the second thermoplastic resin and laminated on the layer may be formed.

  In the method for producing a protective film according to the present invention, a protective film including only the layer having the thermoplastic resin and the diffusion component dispersed in the thermoplastic resin may be produced.

  In the method for producing a protective film according to the present invention, after the pressurizing step, irregularities corresponding to the presence of the diffusing component may be formed on the surface of the film material that has been in contact with the molding roll. .

  In the pressurizing step of the method for producing a protective film according to the present invention, an uneven surface may be formed by the molding roll on the side of the film material that contacts the molding roll.

  In the pressurizing step of the method for producing a protective film according to the present invention, a prism surface constituted by unit prisms arranged side by side is formed by the molding roll on the side of the film material that contacts the molding roll. It may be. In such a method of manufacturing a protective film according to the present invention, a plurality of unit prisms are arranged along an arrangement direction parallel to the film surface of the film material, and each unit prism is parallel to the film surface and the arrangement. It may extend in a direction that intersects the direction.

  In the method for producing a protective film according to the present invention, the haze value of the protective film made of the film material may be 60% or more and 90% or less.

In the method for producing a protective film according to the present invention, the protective film made of the film material may have a moisture permeability of 10 g / m ² · 24 hr or more at a temperature of 40 ° C., a humidity of 90% RH, and 24 hours. Good.

  In the method for producing a protective film according to the present invention, the thermoplastic resin may be a polycarbonate resin.

The manufacturing method of the lower polarizing plate according to the present invention is as follows:
A step of adhering the protective film manufactured by any of the methods for manufacturing a protective film according to the present invention, and a polarizer;
The polarizer is bonded to the film material from the side of the protective film that is in contact with the belt member.

  In the manufacturing method of the lower polarizing plate according to the present invention, the protective film and the polarizer may be bonded together by water bonding.

  The method for producing a lower polarizing plate according to the present invention includes a step of cutting or punching a web-like material having the protective film and the polarizer adhered to each other, and sequentially obtaining the lower polarizing plate from the web-like material. , May be further provided.

  In the bonding step of the manufacturing method of the lower polarizing plate according to the present invention, the web-shaped or single-wafer polarizer and the web-shaped protective film may be bonded.

The lower polarizing plate according to the present invention is
A protective film produced by any of the methods for producing a protective film according to the present invention described above;
A polarizer adhered to the protective film,
The polarizer is bonded to the protective film from the side of the protective film that is in contact with the belt member.

The liquid crystal display panel according to the present invention comprises:
The lower polarizing plate manufactured by any of the manufacturing methods of the lower polarizing plate according to the present invention described above, or the lower polarizing plate according to the present invention described above,
An upper polarizing plate;
A liquid crystal cell disposed between the lower polarizing plate and the upper polarizing plate.

A display device according to the present invention comprises:
A liquid crystal display panel according to the present invention as described above;
A surface light source device that illuminates the liquid crystal display panel from the back side.

  ADVANTAGE OF THE INVENTION According to this invention, the protective film for lower polarizing plates which can change the advancing direction of the light which injected into the liquid crystal display panel can be manufactured cheaply. For this reason, the freedom degree of design about the luminance characteristic and viewing angle characteristic of an actual display apparatus can be improved.

FIG. 1 is a perspective view showing a schematic configuration of a display device for explaining an embodiment according to the present invention. 2 is a cross-sectional view showing a lower polarizing plate incorporated in the liquid crystal display panel of the display device of FIG. FIG. 3 is a partially enlarged view of FIG. 2 and is a view for explaining the operation of the protective film of the lower polarizing plate. FIG. 4 is a diagram for explaining an example of a protective film manufacturing method and a protective film manufacturing apparatus. FIG. 5 is a diagram corresponding to FIG. 3 and is a diagram for explaining a modification of the protective film and the lower polarizing plate. FIG. 6 is a perspective view for explaining another modified example of the protective film and the lower polarizing plate. FIG. 7 is a cross-sectional view showing a schematic configuration of a display device in which the lower polarizing plate of FIG. 6 is incorporated. FIG. 8 is a graph showing the angular distribution of the luminance ratio with respect to the front direction measured for the display devices according to the example and the comparative example. FIG. 9 is a perspective view showing a conventional display device corresponding to FIG. FIG. 10 is a cross-sectional view corresponding to FIG. 7 and showing a conventional display device.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings attached to the present specification, for the sake of illustration and ease of understanding, the scale, the vertical / horizontal dimension ratio, and the like are appropriately changed and exaggerated from those of the actual ones.

  1 to 4 are diagrams for explaining an embodiment according to the present invention. Among these, FIG. 4 is a figure for demonstrating the manufacturing method of the protective film of a lower polarizing plate. Meanwhile, FIG. 1 to FIG. 3 are diagrams for explaining an example of a protective film that can be produced by the manufacturing method of FIG. 4, and a lower polarizing plate, a liquid crystal display panel, and a display device that can be produced using this protective film. It is. First, with reference to FIGS. 1-3, the protective film, lower polarizing plate, liquid crystal display panel, and surface light source device which can be produced by this Embodiment are demonstrated, and the manufacturing method of a protective film is demonstrated after that.

  The display device 10 shown in FIG. 1 is a liquid crystal display device, and includes a liquid crystal display panel 40, a surface light source device 20 disposed on the back side of the liquid crystal display panel 40 (the side opposite to the observer side), have. The surface light source device 20 is a device that illuminates the liquid crystal display panel 40 in a planar shape from the back side. On the other hand, the liquid crystal display panel 40 functions as a shutter that controls transmission or blocking of light from the surface light source device 20 for each pixel and forms an image.

  As the surface light source device 20, a conventionally known direct type or edge light type backlight can be used. The surface light source device 20 shown in FIG. 1 is configured as a direct-type backlight, and includes a light source 25, a reflecting plate 22 that covers the light source 25 from the back side, and a sheet disposed on the observer side of the light source 25. Shaped optical members 28, 30, and 35. As an example, the light source 25 includes linear cold cathode tubes 25a arranged in parallel. As the sheet-like optical member, a diffusion plate 28, a first light collecting sheet 30, and a second light collecting sheet 35 are provided from the light source side toward the observer side. As will be described later, the surface light source device 20 can be variously modified. For example, the light emitting unit of the light source 25 may be configured by two-dimensionally arranged LEDs.

  The diffusing plate 28 is a member for diffusing the light from the light source 25 to make the uneven brightness uniform according to the configuration of the light source 25. The diffusion plate 28 forms a so-called backlight unit together with the light source 25 and the reflection plate 22.

  The two light collecting sheets 30 and 35 are members for adjusting luminance characteristics, and typically function to improve the luminance in the front direction. More specifically, the light collecting sheets 30 and 35 have an angle formed by the traveling direction of the transmitted light and the front direction nd from the light collecting sheets 30 and 35 more than before the light incident on the light collecting sheets 30 and 35. The traveling direction of the transmitted light is changed so as to tend to decrease after emission.

  As a specific configuration, the two light-collecting sheets 30 and 35 shown in the figure are respectively sheet-like main body portions 32 and 37 and a plurality of unit optical elements 33 and 38 arranged on the main body portions 32 and 37. ,have. The unit optical elements 33 and 38 are arranged side by side along the arrangement direction, and extend linearly in a direction intersecting (more specifically, orthogonal) with the arrangement direction. Each unit optical element 33, 38 has a triangular shape protruding to the light exit side in a cross section orthogonal to the longitudinal direction. In this example, the first light collecting sheet 30 is configured in the same manner as the second light collecting sheet 35.

  The condensing sheets 30 and 35 having such a configuration mainly exhibit a condensing function with respect to light of a component along a direction parallel to the arrangement direction of the unit optical elements 33 and 38. In the example shown in FIG. 1, the arrangement direction of the unit optical elements 33 of the first light collecting sheet 30 located on the light incident side is the unit optical element of the second light collecting sheet 35 located on the light exit side. It is orthogonal to the 38 arrangement directions. Thereby, the light which permeate | transmits the two condensing sheets 30 and 35 comes to be condensed from two different directions. In the illustrated example, the arrangement direction of the unit optical elements 38 of the second light-collecting sheet 35 located on the light output side is parallel to the arrangement direction of the cold cathode tubes 25 a that constitute the light source 25.

  With the configuration of the sheet-like members 28, 30, and 35 as described above, the light emitted from the arc tube 25a of the light source 25 has a uniform in-plane brightness distribution and a luminance peak in the front direction. The direction of travel is deflected. Thereby, the surface light source device 20 emits light in a planar shape from the light emitting surface 20a, and illuminates the liquid crystal display panel 40 from the back side.

  In the present specification, the “light exit side” refers to the downstream side in the traveling direction of light from the light emitting unit 25a of the light source 25 to the viewer through the liquid crystal display panel 40 without wrapping the traveling direction (observer side, In FIG. 1, the “light-incident side” is the direction in which the light travels from the light emitting portion 25 a of the light source 25 through the liquid crystal display panel 40 to the viewer without being folded back. It is upstream.

  Further, in the present specification, the terms “sheet”, “film”, and “plate” are not distinguished from each other only based on the difference in names. Therefore, for example, a “sheet” is a concept including a member that can also be called a film or a plate. As a specific example, the “protective film” includes a member called a “protective sheet”.

  Further, in this specification, the “sheet surface (film surface, plate surface)” is the same as the planar direction of the target sheet-like member when the target sheet-like member is viewed as a whole and globally. It refers to the surface to be used. And in this Embodiment, the sheet surface of each condensing sheets 30 and 35, the panel surface of the liquid crystal display panel 40, the plate surface of the lower polarizing plate 50 mentioned later, the film surface of the protective film 55 mentioned later, the display apparatus 10 The display surface 10a and the light emitting surface 20a of the surface light source device are parallel to each other. In this specification, the “front direction” refers to a direction parallel to the normal direction nd to the display surface 10 a of the display device 10.

  Furthermore, terms used in the present specification for specifying shapes and geometric conditions, for example, terms such as “triangle”, “parallel”, “orthogonal”, “symmetric”, etc. are not bound to a strict meaning. Therefore, it should be interpreted including an error to the extent that a similar optical function can be expected.

  Furthermore, “unit optical element”, “unit shape element”, “unit prism”, and “unit lens” in this specification refer to the optical action such as refraction and reflection on the light, and change the traveling direction of the light. It refers to an element having a function to be changed, and is not distinguished from each other based only on a difference in designation. Similarly, “prism” and “lens” are not distinguished from each other based solely on the difference in designation.

  Next, the liquid crystal display panel 40 will be described. As described above, the liquid crystal display panel 40 includes the pair of polarizing plates 45 and 50 and the liquid crystal cell 41 disposed between the pair of deflecting plates 45 and 50. Among these, the polarizing plates 45 and 50 have a function (absorption type polarization separation function) of decomposing incident light into orthogonal polarization components, transmitting one polarization component, and absorbing the other polarization component. Yes.

  On the other hand, the liquid crystal cell 41 has a pair of transparent substrates and a liquid crystal layer provided between the transparent substrates. An electric field can be applied to the liquid crystal layer for each region where one pixel is formed. Then, the alignment of the liquid crystal layer applied with an electric field changes. As an example, the polarization component in a specific direction (direction parallel to the transmission axis) transmitted through the lower polarizing plate 50 disposed on the light incident side passes through a region of the liquid crystal layer to which an electric field is applied in the liquid crystal cell 40. At that time, the polarization direction is rotated by 90 °, and the polarization direction is maintained when passing through the liquid crystal layer to which no electric field is applied. For this reason, depending on whether or not an electric field is applied to each region of the liquid crystal layer, whether the polarization component in a specific direction transmitted through the lower polarizing plate 50 further transmits through the upper polarizing plate 45 disposed on the light output side of the lower polarizing plate 50. Alternatively, it is possible to control whether the light is absorbed and blocked by the upper polarizing plate 45. In the present specification, “upper and lower” in the “upper polarizing plate 45” and the “lower polarizing plate 50” means “upper” on the light emission side, that is, the image observer side with respect to the liquid crystal cell 41, and incident light. The side is called “bottom”.

  Here, the lower polarizing plate 50 will be described in more detail with reference to FIGS. The lower polarizing plate 50 includes a polarizer 51 that can exhibit an absorption polarization separation function, and a protective film 55 bonded to the polarizer 51. As shown in FIG. 3, the protective film 55 is laminated on the polarizer 51 from the side that does not face the liquid crystal cell 41, in other words, from the light incident side, and protects the polarizer 51 from the outside.

  Further, an adhesive layer (not shown) is provided between the polarizer 51 and the protective film 55 so as to be adjacent to the polarizer 51 and the protective film 55 and adheres the polarizer 51 and the protective film 55 to each other. It may be. The adhesive layer for enhancing the adhesion between the polarizer 51 and the protective film 55 can be formed using various conventionally known adhesives. As one specific example, for example, an adhesive layer can be formed using an aqueous adhesive mainly composed of a polyvinyl alcohol-based resin. In addition, the adhesion in this specification is a concept including adhesion and gluing, and similarly, the adhesive in this specification is a concept including pressure-sensitive adhesive and glue.

  Various polarizers have been developed to date, and any of these polarizers can be used as the polarizer 51. As a specific example, a polarizer 51 based on a polyvinyl alcohol film can be used. A polarizer 51 based on a polyvinyl alcohol-based film absorbs or dyes a dichroic dye such as iodine or a dye on a polyvinyl alcohol-based film, and then uniaxially stretches and aligns to absorb light. Properties can be imparted to the polyvinyl alcohol film.

  Next, the protective film 55 will be described. As well shown in FIG. 3, the protective film 55 includes a main portion 56 made of a thermoplastic resin 56 a and a diffusion component 57 dispersed in the main portion 56. As the thermoplastic resin 56a forming the main portion 56, various resin materials having excellent optical characteristics, for example, polycarbonate resins can be used. The polycarbonate resin is also suitable as a material used for the polarizing plate 50 in that it has a low retardation.

  On the other hand, the diffusing component 57 can be composed of a granular material having a refractive index different from that of the main portion 56, or a granular material that itself has reflectivity. The granular material forming the diffusion component 57 may be a metal compound, a porous material containing a gas, or may be a simple bubble. Further, the shape of the diffusion component 57 made of a granular material is not particularly limited. Therefore, the diffusion component 57 does not need to be spherical (particulate) as in the illustrated example, and can have various shapes such as a spheroid shape and a linear shape.

  The protective film 55 can exhibit a diffusion function of diffusing light due to the diffusion component 57 dispersed in the main portion 56. The degree of the diffusion function of the protective film 55 caused by the internally added diffusion component 57 is set as appropriate by setting the thermoplastic resin constituting the main portion 56, the thickness of the main portion 56, the configuration of the diffusion component 57, the concentration of the diffusion component 57, and the like. By doing so, it is possible to adjust within a very wide range. Specifically, it is also possible to set the haze value of the protective film 55 within a range that is not normally reached by simply matting the surface layer portion, for example, within a range of 60% to 90%. is there.

  As shown in FIGS. 2 and 3, the light exit side surface 55 a that faces the polarizer 51 of the protective film 55 is formed as a flat surface. Thereby, it becomes possible to laminate | stack and adhere | attach the protective film 55 and the polarizer 51 stably, preventing mixing of air etc. On the other hand, in the illustrated example, the light incident side surface 55b opposite to the side facing the polarizer 51 of the protective film 55 is formed as an uneven surface. The unevenness provided on the light incident side surface 55b is caused by the diffusion component 57 dispersed in the main portion 56. More specifically, the diffusion component 57 is exposed or the outline of the diffusion component 57 is raised. Is formed.

  The light incident side surface 55 b of the protective film 55 forms not only the light incident side surface of the lower polarizing plate 50 but also the light incident surface 40 b of the liquid crystal display panel 40. For this reason, the illustrated protective film 55 exhibits a diffusion function due to not only the diffusion component 57 dispersed in the main portion 56 but also the unevenness of the light incident side surface 55b.

  In this specification, “flat (surface)” used for the surface 55 a of the protective film 55 facing the polarizer 51 ensures stable lamination and adhesion between the protective film 55 and the polarizer 51. It refers to the flatness (surface) to the extent possible. For example, when the surface roughness of the surface 55a facing the polarizer 51 of the protective film 55 is measured as the center line average roughness Ra in accordance with JIS B0601 (1982), it may be 0.9 μm or less. It can be said that it is flat.

  Even though the protective film 55 is internally added with the diffusing component 57, the light exit side surface 50a of the protective film 55 is flat, so that the protective film 55 and the polarizer 51 are attached by so-called “water sticking”. Can be laminated and glued. Specifically, the protective film 55 and the polarizer 51 are overlapped with each other with an aqueous solution (or suspension) mixed with water or a suitable additive such as a surfactant interposed therebetween. To go. Thereby, the protective film 55 and the polarizer 51 can be laminated | stacked, preventing mixing of foreign materials, such as air. At this time, an adhesive (for example, glue) is mixed with water or an aqueous solution (or suspension), or an adhesive layer is provided in advance on at least one of the protective film 55 and the polarizer 51, You may make it adhere | attach the protective film 55 and the polarizer 51 positively.

In addition, in order to promote the removal of moisture from the protective film 55 and the polarizer 51 after “water sticking”, the moisture permeability of the protective film 55 is 10 g / m under the condition of a temperature of 40 ° C. and a humidity of 90% RH. It is preferably ² · 24 hours or more. However, if the moisture permeability is too high, warping or bending due to moisture absorption may occur. Therefore, the moisture permeability is preferably 400 g / m ² · 24 hr or less as measured at a temperature of 40 ° C. and a humidity of 90% RH. . In addition, the moisture permeability in this specification refers to the numerical value measured using the cup method based on JISZ0208.

  Next, mainly with reference to FIG. 4, the manufacturing method of the protective film 55 which consists of the above structures is demonstrated. In the following description, the protective film 55 is formed as a film material 90 made of an extruded material obtained by an extrusion process.

  First, the extrusion apparatus 80 that can be used for manufacturing the protective film 55 will be described. As shown in FIG. 4, the extruding device 80 includes an extruding machine 82 including a die 82 a, a forming roll 84, a backup unit 86 disposed so as to face the forming roll 84, and downstream of the forming roll 84 and the backup unit 86. Guiding means 88 arranged on the side. The guiding means 88 is configured as a pair of guide rolls 88a.

  The molding roll 84 has a cylindrical outer shape, and in this example, the cylindrical outer peripheral surface of the molding roll 84 is a smooth surface. However, when it is desired to positively mold the surface of the extruded material 90, a groove corresponding to the shape to be molded may be formed on the cylindrical outer peripheral surface of the molding roll 84. The columnar molding roll 84 is rotatable about a rotation axis passing through the center of the column.

  The backup means 86 has two or more support rolls 86a and an edgeless belt member (belt) 86b spanned between the two or more support rolls 86a. In the illustrated example, the backup means 86 has two support rolls 86a. Each support roll 86a is formed in a columnar shape, and is rotatable around a rotation axis passing through the center of the column. The rotation axes of the support rolls 86a are parallel to each other, and are also parallel to the rotation axis of the forming roll 84. And the two or more support rolls 86a can drive the belt member 86b spanned over the said support roll 86a by rotating centering around a rotating shaft line.

  In the illustrated example, one of the two support rolls 86a is configured as a nip roll 86a1 that is disposed to face the forming roll 84. The other of the two support rolls 86a is configured as an adjustment roll 86a2 that determines the moving path of the belt member 86b with the nip roll 86a1.

  As shown in FIG. 4, the belt member 86 b between the nip roll 86 a 1 and the adjustment roll 86 a 2 is deformed corresponding to the outer contour of the molding roll 84 by pressing from the molding roll 84. . For this reason, as will be described later, the film material 90 passing between the belt member 86b and the molding roll 84 passes over the nip section NZ of a certain length L along the movement path, and the belt member 86b and the molding roll 84 Will continue to be pressurized. In the configuration shown in FIG. 4, for example, the length L of the nip section NZ can be adjusted as appropriate by adjusting the position of the support roll 86a, particularly the adjustment roll 86a2.

  The forming roll 84, the nip roll 86a1, the adjustment roll 86a2, and the belt member 86b are configured using various materials. For example, as the forming roll 84, the nip roll 86a1, and the adjustment roll 86a2, a metal roll, a roll whose center portion is made of metal and whose surface layer portion is made of an elastic body (for example, rubber) can be used. Further, as the belt member 86b, a durable metal-free belt, for example, a belt-shaped member made of a metal alloy such as a chromium alloy or a nickel alloy can be used.

  Next, a method for manufacturing the above-described protective film 55 using such an extrusion device 80 will be described. First, a thermoplastic resin (for example, a pellet-shaped thermoplastic resin material) 56 a that forms the main portion 56 is put into the extruder 82 together with the granular material 57 a that forms the diffusion component 57. The thermoplastic resin 56 a that forms the main portion 56 is heated to the glass transition temperature or higher in the extruder 82, and the heated and softened resin material is extruded by the extruder 82.

  As an example, when a polycarbonate resin having a glass transition temperature around 140 ° C. is used as the thermoplastic resin 56a that forms the main portion 56 of the protective film 55, the thermoplastic resin 56a immediately after passing through the die 82a. The thermoplastic resin 56a may be heated in the extruder 82 so that the temperature of the resin becomes about 300 ° C. Moreover, when producing the protective film 55 by extrusion processing, the average particle diameter (arithmetic average of the particle diameter calculated by the volume equivalent method, the same shall apply hereinafter) of the granular material 57a that forms the diffusion component 57 is 1 μm to 12 μm. The content of the granular material 57a that forms the diffusing component 57 can be more than 0% by weight and 40% by weight or less.

  In this way, the film material 90 having the thermoplastic resin 56a and the diffusion component 57 dispersed in the thermoplastic resin 56a is formed as an extruded material. At this time, in the die 82a of the extruder 82, the thickness of the film material 90 can be controlled to a desired thickness.

  As will be described later, a film material 90 is formed by so-called coextrusion, and the film material 90 includes a layer having a thermoplastic resin 56a and a diffusion component 57a dispersed in the thermoplastic resin 56a, and the layer. And a second layer stacked on each other. However, here, for the sake of better understanding of one embodiment of the present invention, in order to produce the protective film 55 shown in FIG. 2, the thermoplastic resin 56a and the diffusion component 57a dispersed in the thermoplastic resin 56a. A description will be given of an example in which a film material 90 composed only of a layer having a layer (in this example, a layer to be called a diffusion layer) is formed as an extrusion material.

  The film material 90 extruded from the extruder 82 proceeds between the forming roll 84 and the backup means 86. At this time, the molding roll 84 rotates at a peripheral speed synchronized with the moving speed F (mm / second) of the film material 90, and the belt member 86b of the backup means 86 also rotates at a speed synchronized with the moving speed of the film material 90. It is driven by. In addition, the forming roll 84 is disposed so as to face the nip roll 86a1 of the backup means 86, and is positioned so as to pressurize (clamp) the film material 90 with the nip roll 86a1 via the belt member 86b. Yes. Further, the adjustment roll 86 a 2 of the backup means 86 is positioned so that the belt member 86 b supported between the adjustment roll 86 a 2 and the nip roll 86 a 1 is deformed along the outer contour of the molding roll 84. As a result, the film member 90 passes between the belt member 86b and the molding roll 84 while being supported by the belt member 86b and the molding roll 84, and is positioned between the molding roll 84 and the nip roll 86a1. While traveling through the section NZ having a predetermined length L as the starting point, the belt member 86b and the molding roll 84 are in a pressurized state.

  The film member 90 is adjusted in thickness by being pressed between the belt member 86 b and the molding roll 84. Further, since the film member 90 is pressurized while proceeding through the section NZ of the predetermined length L, the granular material 57a constituting the diffusion component 57 is stably pushed into the thermoplastic resin material 56a.

  Further, the temperature of the molding roll 84 and the temperature T of the belt member 86 b are usually lower than the temperature of the film material 90 extruded from the extruder 82. Therefore, the film member 90 is deprived of heat by the belt member 86b and the molding roll 84 that are in contact with each other while being pressed between the belt member 86b and the molding roll 84. That is, the film member 90 is positively cooled while being pressed between the belt member 86b and the molding roll 84.

  Among these, the belt member 86 b has a smaller heat capacity than the molding roll 84. Therefore, even if the belt member 86b absorbs heat from the film material 90, the belt member 86b performs sufficient heat dissipation while not in contact with the film material 90. For this reason, when the belt member 86b comes into contact with the film material 90 again, the temperature of the belt member 86b is sufficiently lowered, and the belt member 86b promotes cooling of the film material 90. As a result, when the film material 90 is separated from the belt member 86b of the backup means 86, not only the surface layer portion of the film material 90 on the belt member 86b side but also the inside of the film material 90, the glass transition point for the thermoplastic resin 56a. The film material 90 can be sufficiently cooled by the belt member 86b from the side in contact with the belt member 86 so as to reach a temperature equal to or lower than the temperature.

  As a result, on the side of the surface 90a that has been in contact with the belt member 86b of the film material 90, no significant temperature drop occurs thereafter. Further, when the temperature is lowered to a temperature not higher than the glass transition temperature of the thermoplastic resin 56a that forms the main portion 56, the thermoplastic resin 56a has a certain degree of deformation resistance. For this reason, it becomes difficult to produce the thermal deformation etc. resulting from the difference of the thermal expansion coefficient of the thermoplastic resin 56a which makes the main part 56, and the granular material 57a which makes the diffusion component 57. That is, after being released from pressurization between the belt member 86b and the molding roll 84, the thermoplastic resin 56a (main portion 56 of the protective film 55) of the film material 90 is retracted, and the granular material 57a (diffusing component 57). ) Is suppressed from rising, and the surface 90a of the film material 90 in contact with the belt member 86b can be maintained as a flat surface.

With regard to this point, as a result of the earnest studies by the inventors, when the following formula (b) is satisfied, the film material 90 made of the thermoplastic resin 57a including the diffusion component 56 (the granular material 56a) It was confirmed that the surface 90a on the side that was in contact with the belt member 86b could be flat even after the film material 90 was cooled to room temperature. In the formula (b), “L” is a length (mm) along the movement path of the film material 90 in the section NZ where the film material 90 is pressed by the molding roll 84 and the belt member 86a. is there. Further, “F” in the formula (b) is the moving speed (mm / second) of the film material 90, and “T” in the formula (b) is the temperature (° C.) of the belt member 86b.
0.16 ≦ L / (F × T) × 100 ≦ 0.96 Expression (b)

  The value of “L / (F × T) × 100” in the formula (b) is large in the cooling capacity from the belt member 86b to the film material 90 made of the thermoplastic resin 57a including the diffusion component 56 (the granular material 56a). As it becomes, it grows. When the value of “L / (F × T) × 100” is less than 0.16, the temperature of the film material 90 on the side in contact with the belt member cannot be sufficiently lowered, and finally the film material 90 is formed. Concavities and convexities corresponding to the presence of the diffusion component 57 are formed on the surface of the protective film 55 that is in contact with the belt member. Further, even the temperature of the surface 90a in contact with the belt member of the film material 90 is not sufficiently lowered, and as a result, the film material 90 cannot be smoothly separated from the belt member 86b and contacts the belt member of the film material 90. In some cases, a streak pattern (horizontal step) generally along the width direction orthogonal to the traveling direction of the film material 90 may be formed on the surface 90a. On the other hand, when the value of “L / (F × T) × 100” exceeds 0.96, the cooling capacity of the film material 90 from the belt member 86 and the cooling capacity of the molding roll 84 are greatly different. As a result, deformations such as large warp and bending that could not be removed were generated.

  When the formula (b) is satisfied, only bending and warping that can be removed by correction by the guiding means 88 occurred as described later. In addition, when the film material 90 (protective film 55) is produced in such a manner that the formula (b) is satisfied after adopting normal conditions and materials for producing a transparent optical film by extrusion molding, While 90 passes between the belt member 86b and the molding roll 86, at least the temperature of the surface 90a of the film material 90 on the side in contact with the belt member 86b is lower than the glass transition temperature Tg of the thermoplastic resin 56b. And a temperature of 90% or less of the glass transition temperature Tg of the thermoplastic resin 56b (that is, a temperature of (Tg × 0.9) or less).

  Finally, the surface 90a on the side that is in contact with the belt member 86b of the protective film 55 made of the film material 90 can be made a flat surface, and as described above, by so-called "water pasting" The protective film 55 and the polarizer 51 can be laminated and bonded. Specifically, when the film material 90 (protective film 55) is produced within the range of normal conditions and materials when producing a transparent optical film by extrusion molding, as described also in Examples described later, The roughness Ra measured in accordance with JISB0601 (1982) on the surface of the film material 90 (protective film 55) that is in contact with the belt member 86b is 0.05 μm or more and 0.9 μm or less. became.

  On the other hand, the molding roll 84 has a significantly larger heat capacity than the belt member 86b, and is heated in many cases. That is, the cooling amount that the film material 90 receives from the molding roll 84 may be smaller than the cooling effect that the film material 90 receives from the edgeless roll 86 b of the backup means 86.

  In this case, when the film material 90 is separated from the molding roll 84, the temperature of the film material 90 is decreased only to the glass transition temperature of the thermoplastic resin 56 a only at the surface layer portion on the molding roll 84 side. The internal temperature is maintained above the glass transition temperature. As a result, on the side of the surface 90b that has been in contact with the molding roll 84 of the film material 90, a large temperature drop occurs across the glass transition point temperature of the thermoplastic resin 56a that becomes the main portion 56 after that, In connection with this, the thermal deformation etc. resulting from the difference of the thermal expansion coefficient of the thermoplastic resin 56a which makes the main part 56, and the granular material 57a which makes the diffusion component 57 arise. Typically, on the surface 90 b of the film material 90 that has been in contact with the molding roll 84, the portion of the thermoplastic resin 56 a that forms the main portion 56 recedes, and the granular material 57 a that forms the diffusion component 57. Will come to the surface. That is, as shown in FIGS. 2 and 3, irregularities corresponding to the presence of the diffusion component 57 are formed on the surface 90 b of the obtained protective film 55 that has been in contact with the molding roll 84.

  The film material 90 separated from the molding roll 84 is then cooled by the guiding means 88 and guided while being moderately warped and corrected for warping and bending. As described above, the protective film 55 made of the film material 90 formed by extruding the thermoplastic resin 56a as the diffusion component 57 together with the granular material 57a is produced. The flat light exit side surface 55a of the protective film 55 is formed by the surface 90a that is in contact with the belt member 86b of the backup means 86 of the film material 90, and the light incident side surface 55b provided with the unevenness of the protective film 55 is: It is formed by the surface 90b that has been in contact with the forming roll 84 of the film material 90.

  According to the manufacturing method described above, the web-like protective film 55 (web-like film material 90) can be produced. For this reason, the sheet-like polarizer 41 having a size corresponding to the lower polarizing plate 50 to be produced (one or a plurality of sheets) is sequentially bonded to the web-shaped protective film 55. Or by adhering the polarizer 41 formed in a web shape, a web-like material is obtained, and this web-like material includes a large number of lower polarizing plates 50 connected to each other. . Then, the lower polarizing plate is sequentially obtained by cutting (or appropriately taking out such as punching) the web-like material.

  That is, according to the manufacturing method described above, the web-like protective film 55 can be produced, and the lower polarizing plate 550 is efficiently produced while handling the protective film 55 on a roll-to-roll basis. be able to. Thereby, according to the method described above, not only can the protective film 55 be produced at low cost, but also the production of the lower polarizing plate 50 is facilitated by using the produced protective film 55, and as a result, It may be possible to manufacture the lower polarizing plate 50 at a very low cost.

  In the example described here, as shown in FIGS. 2 and 3, one surface (light-emitting side surface) 55a facing the polarizer 51 is formed as a flat surface, while the other surface is formed. The example in which the protective film 55 in which the (light incident side surface) 55b is formed as an uneven surface is manufactured is shown. Specifically, an example is shown in which the surface of the film material 90 that is in contact with the belt member 86b is a flat surface, and the surface of the film material 90 that is in contact with the molding roll 84 is an uneven surface. However, by increasing the cooling capacity from the molding roll 84 to the film material 90 as the extrusion material, not only the surface of the film material 90 that is in contact with the belt member 86b but also the molding roll 84 of the film material 90. The contacted surface can also be formed as a flat surface.

  In the first place, as in the embodiment described above, when the forming material is not actively applied to the film material 90 by the forming roll 84, the forming roll 86 is heated to a high temperature for the purpose of increasing the forming rate. There is no need to keep it. In particular, in this case, the cooling capacity of the film material 90 from the molding roll 84 can be greatly increased. As a result, the surface of the protective film 55 made of the film material 90 on the side that has been in contact with the molding roll 84 can be reduced. It can be a flat surface. Specifically, when the film material 90 (protective film 55) is produced within the range of normal conditions and materials when producing a transparent optical film by extrusion molding, the produced film material 90 (protective film 55) The roughness Ra measured according to JISB0601 (1982) on the surface which was in contact with the molding roll 84 of the present invention was able to be 0.01 μm or more and 0.4 μm or less.

  Next, the operation of the display device 10 mainly resulting from the protective film 55 manufactured by the above-described manufacturing method will be described with reference mainly to FIG.

  In FIG. 1, the light emitted from the light source 25 travels to the viewer side directly or after being reflected by the reflection plate 22, enters the diffusion plate 28, and isotropically diffuses. The in-plane distribution of brightness is made uniform by isotropic diffusion in the diffusion plate 28. The light diffused by the diffusion plate 28 then enters the first light collecting sheet 30.

  The light incident on the first light collecting sheet 30 is refracted on the light output side surface (prism surface) of the unit optical element 33 when exiting from the light collecting sheet 30. Due to this refraction, the traveling direction (outgoing direction) of the light traveling in the direction inclined with respect to the front direction nd is mainly the front direction compared with the traveling direction of the light just before entering the first light collecting sheet 30. It is bent so that the angle with respect to nd is small. Thus, the 1st condensing sheet 30 exhibits a condensing function with respect to the light from the light source 25. The light condensed by the first light collecting sheet 30 is a component mainly along the arrangement direction of the unit optical elements 33 of the first light collecting sheet 30.

  The light emitted from the first light collecting sheet 30 then enters the second light collecting sheet 35. Similar to the first light collecting sheet 30, the second light collecting sheet 35 exhibits a light collecting function with respect to light transmitted through the second light collecting sheet 35. However, the light condensed by the second light collecting sheet 35 is a component mainly along the arrangement direction of the unit optical elements 38 of the second light collecting sheet 35, and the component condensed by the first light collecting sheet 30. Is an orthogonal component. Therefore, by transmitting the two condensing sheets 30 and 35, the angular distribution of the brightness in the plane along two different directions can be adjusted.

  As described above, the light from the light source 25 is emitted from the light emitting surface 20 a of the surface light source device 20 formed by the light emitting surface of the second light collecting sheet 35. As a result, the surface light source device 20 illuminates the liquid crystal display panel 40 in a planar shape. The liquid crystal display panel 40 selectively transmits light from the surface light source device 20 for each pixel. Thereby, the observer of the transmissive display apparatus 10 can observe an image.

  By the way, in the present embodiment, the protective film 55 of the lower polarizing plate 50 of the liquid crystal display panel 40 exhibits a diffusing function. In particular, the protective film 55 includes a main portion 56 and a diffusion component 57 dispersed in the main portion 56. Diffusion in the protective film 55 due to the internally added diffusion component 57 makes the surface matte by shaping, or the surface is matted by fixing granular materials to the surface layer portion with a doubler resin. Compared with the diffusion caused by this, the degree (diffusion intensity) and quality (diffusion uniformity) are remarkably superior. More specifically, when the surface is merely matted, light L33 that passes through is generated as shown by a two-dot chain line in FIG. On the other hand, in the protective film 55 according to the present embodiment, the diffusion component 57 is dispersed not only in the plane direction but also in the thickness direction. For this reason, when the light L31 and L32 that are not sufficiently diffused due to the uneven shape on the light incident side surface 55b of the protective film 55 also reaches the diffusion component 57 after that, at the interface between the diffusion component 57 and the main portion 56. The direction of travel can be changed by the refraction or the reflection at the surface of the diffusing component 57.

  As described above, the light from the surface light source device 20 can be diffused to some extent by the protective film 55. Thereby, the angle distribution of the brightness after the light is collected by the two light collecting sheets 30 and 35 can be changed gently.

  In addition, as described above, when the light collecting sheets 30 and 35 are used, the luminance angle is set so that the luminance in the front direction is intensively increased due to the refraction of the light collecting sheets 30 and 35 by the unit optical elements 33 and 38. Changes can be made to the distribution. However, on the other hand, when the condensing sheets 30 and 35 are used, the brightness of the image observed from a certain observation angle when the cutoff (observation angle (angle of the observation direction with respect to the front direction nd)) is increased. ) And side lobes (a phenomenon in which the second peak occurs in an angular region greatly inclined from the front direction in the luminance angle distribution). The occurrence of such inconvenience occurs particularly when the unit optical elements 33 and 38 of the light collecting sheets 30 and 35 have a triangular shape in a cross section along the longitudinal direction, as in the illustrated example. It was remarkable. For the purpose of improving such a problem, the conventional surface light source device 120 configured using the liquid crystal display panel 150 including the lower polarizing plate 150 in which the diffusion component 57 is not internally added is shown in FIG. As shown, a diffusion sheet 29 having a diffusion function is often provided on the light output side of the second light-collecting sheet 35 on the light output side.

  On the other hand, in the present embodiment, the lower polarizing plate 50 of the liquid crystal display panel 40 includes the protective film 55 that can exhibit an excellent diffusion function and can adjust the degree (strength) of the diffusion function in a wide range. It is out. For this reason, by adjusting the diffusion function of the protective film 55 so that the diffusion function equivalent to that of the diffusion sheet 29 included in the conventional surface light source device 120 can be exhibited, the optical characteristics of the entire display device can be improved. The diffusion sheet 29 can be omitted from the surface light source device 120 while maintaining. As a result, the number of sheet-like members included in the display device 10 (surface light source device 20) can be reduced. In this case, the manufacturing cost of the display device 10 (surface light source device 20) can be directly reduced. In addition, the display device 10 (surface light source device 20) can be thinned.

  The conventional display device 110 shown in FIG. 9 can be configured similarly to the above-described display device 10 shown in FIG. 1 except for the presence or absence of the diffusion sheet 29 and the configuration of the lower polarizing plate 150. For this reason, for the conventional display device 120 shown in FIG. 9, the same reference numerals as those used for the corresponding parts in the above-described embodiment are used, and redundant description is omitted.

  According to the present embodiment as described above, while the film material 90 made of the extrusion material containing the diffusion component 57 passes through the section NZ having a certain length L, the film material 90 is transferred to the molding roll 84 and the belt. While pressing with the member 86b, the film material 90 is cooled so that the surface 90a of the film material 90 contacting the belt member 86b finally becomes a flat surface. According to such a manufacturing method, the film material 90 (protective film 55) containing the diffusion component 57 and having at least one flat surface can be manufactured at low cost by so-called extrusion processing. The film material 90 is suitable for use as the protective film 55 for the lower polarizing plate in that it can be suitably bonded to the polarizer 51 by water bonding. At the same time, the film material 90 is suitable for use as the protective film 55 for the lower polarizing plate in that the traveling direction of light can be changed. Specifically, when this film material 90 is used as the protective film 55 for the lower polarizing plate, the degree of freedom in designing the luminance characteristics and viewing angle characteristics of the display device 10 can be significantly improved. There is a possibility that the number of sheet-like members (optical sheets) incorporated in the surface light source device 20 can be reduced. In this case, the manufacturing cost of the surface light source device 20 and the display device 10 can be directly reduced, and the surface light source device 20 and the display device 10 can be thinned.

  Note that various modifications can be made to the above-described embodiment. Hereinafter, an example of modification will be described with reference to the drawings as appropriate. In the drawings used in the following description, the same reference numerals as those used for the corresponding parts in the above-described embodiment are used, and redundant descriptions are omitted.

  In the above-described embodiment, the example in which the protective film 55 having the unevenness corresponding to the internally added diffusion component 57 formed on the light incident side surface 55b is shown, but the present invention is not limited thereto. As already described, both surfaces of the protective film 55 may be flat surfaces by adjusting the cooling capacity from the molding roll 84 side.

  In the above-described embodiment, the light incident side surface 55b of the protective film 55 is provided with irregularities formed due to the presence of the diffusion component 57, that is, the outline of the diffusion component 57 is raised. Although the example in which the unevenness is formed has been shown, it is not limited to this. For example, as shown in FIG. 5, unevenness may be formed on the light incident side surface 55b of the protective film 55 by shaping. In the manufacturing method of the protective film described above, when the molding roll 84 having the concavo-convex pattern formed on the outer peripheral surface is used, the concavo-convex pattern of the molding roll 84 is transferred to the surface 90b of the film material 90 on the side in contact with the molding roll 84. Thus, irregularities can be formed on the surface 90b of the film material 90 that contacts the molding roll 84 (that is, the light incident side surface 55b of the protective film 55). In addition, when unevenness is formed on the light incident side surface 55b of the protective film 55 by shaping, the unevenness due to the presence of the diffusing component 57 may not be formed on the light incident side surface 55b of the protective film 55 (see FIG. 5), or unevenness due to the presence of the diffusion component 57 may be formed in addition to the unevenness due to shaping.

  Further, the light incident side surface 55b of the protective film 55 may be configured as a prism surface formed by unit prisms 60 arranged side by side as shown in FIGS. Such a protective film 55 can be manufactured by using the molding roll 84 in which the groove | channel which has the cross-sectional shape corresponding to a unit prism was formed in the outer peripheral surface in the manufacturing method of the protective film 55 mentioned above. In the example shown in FIGS. 6 and 7, the protective film has a sheet-like main body portion 59 and unit prisms 60 arranged in parallel on the light incident side surface 59 b of the main body portion 59. Each unit prism 60 extends linearly in a direction orthogonal to the arrangement direction. 6 and 7, each unit prism 60 has a triangular shape or a shape formed by chamfering the apex angle of the triangular shape in a cross section orthogonal to the longitudinal direction. Such a protective film 55 can exhibit a light collecting function.

  FIG. 7 shows an example of how the protective film 55 is expected to have a light collecting function. In the example shown in FIG. 7, the surface light source device 20 includes a light guide plate 21, a light source 25 disposed on the side of the light guide plate 21, and a reflection sheet 22 a disposed on the back surface of the light guide plate 21. However, it is configured as a so-called edge light type backlight. Light from the light source 25 enters the light guide plate 21 from the side surface (incident surface) of the light guide plate 21, and repeats reflection between the pair of main surfaces of the light guide plate 21 along the light guide direction. move on. The light guide plate 21 is provided with a light extraction element (not shown), for example, white dots provided on the back surface of the light guide plate 21 facing the reflection sheet 22a, a diffusing component dispersed in the light guide plate 21, and the like. Light traveling through the light guide plate 21 is emitted from the light guide plate 21 toward the viewer so that the amount of emitted light is substantially uniform along the light guide direction. At this time, as shown in FIG. 7, a lot of light L71 emitted from the light guide plate 21 is emitted in a direction greatly inclined from the front direction nd.

  With respect to the light guide plate 21, the unit prisms 60 of the protective film 55 are arranged so that the arrangement direction thereof is parallel to the light guide direction of the light guide plate 21. Further, the unit prism 60 protrudes from the protective film 55 toward the light guide plate 21 side. The light L71 traveling toward the liquid crystal display panel along a direction greatly inclined from the front direction nd is incident on the protective film 55 via one surface of the unit prism 60, and then reflected by the other surface of the unit prism 60. (In particular, total reflection) and the traveling direction is deflected to the front direction nd side. In this way, the protective film 55 can exhibit a light collecting function.

  On the other hand, as shown in FIG. 10, the conventional edge light type surface light source device 220 used in combination with the liquid crystal display panel 140 including the conventional lower polarizing plate 150 often includes the light guide plate 21. A prism sheet (reflective prism sheet, inverted prism sheet) 129 was provided on the light output side. For this reason, the condensing function of the protective film 55 is made the same as the condensing function of the prism sheet (reflective prism sheet, reverse prism sheet) 129 included in the conventional surface light source device 220 shown in FIG. Thus, the prism sheet 129 can be omitted from the surface light source device 220 while maintaining the optical characteristics of the entire display device. Similarly, in the conventional surface light source device 220 shown in FIG. 10, the diffusion sheet 29 is further provided on the light output side of the prism sheet 129, but when the protective film 55 contains the diffusion component 57. It is possible to omit the diffusion sheet 29 by appropriately adjusting the degree of the diffusion function caused by the diffusion component 57. Thereby, by using the protective film 55 of FIG. 6 and FIG. 7, the manufacturing cost of the display device 10 can be significantly reduced, and the display device 10 can be significantly thinned.

  The configuration of the unit prism 60 described in the present modification is merely an example, and various modifications can be made according to the desired optical characteristics. Further, in the conventional display device 210 shown in FIG. 10, the same reference numerals as those used for the already described configuration are used for portions that can be configured the same as the already described configuration. Therefore, duplicate explanation is omitted.

  Furthermore, in the manufacturing method of a protective film mentioned above, the film material 90 which consists only of the layer which has the thermoplastic resin 56a and the diffusion component 57 (granular material 57a) disperse | distributed to the thermoplastic resin 56a is used as an extrusion material. However, the present invention is not limited to this. In the extruding step, the second thermoplastic resin is also heated to be extruded simultaneously with the thermoplastic resin 56a, and has a layer (diffusion layer) having the thermoplastic resin 56a and the diffusion component 57 dispersed in the thermoplastic resin 56a; A film material including the second layer made of the second thermoplastic resin laminated on this layer (diffusion layer) may be formed.

  Furthermore, in the above-described embodiment, the example in which the lower polarizing plate 50 includes the polarizer 51 and the protective film 55 bonded to the polarizer 51 from the light incident side has been shown. A protective film may also be provided on the light output side of the child 51. In addition, a retardation plate for compensating for the phase difference of light may be provided between the lower polarizing plate 50 and the liquid crystal cell 41. In this case, the protective film on the light output side of the lower polarizing plate 50 is You may make it also serve as the protective film of the light-incidence side of a phase difference plate.

  Further, in the above-described embodiment, the light emitting unit 25a of the light source 25 of the surface light source device 20 is formed of a cold cathode tube extending linearly, but is not limited thereto. As the light source 25, a light emitting unit composed of a dot-like LED (light emitting diode), a planar EL (electroluminescent body), or the like may be provided. Further, in the above-described embodiment, the example in which the protective film 55, the lower polarizing plate 50, and the liquid crystal display panel 40 are applied to the combination with the direct type surface light source device 20 has been shown. However, the present invention is not limited to this as described with reference to FIG. The above-described protective film 55, the lower polarizing plate 50, and the liquid crystal display panel 40 can be used together with the edge light type (also called side light type) surface light source device.

  Furthermore, in the above-described embodiment, an example of the overall configuration of the surface light source device 20 and the transmissive display device 10 has been described, but the present invention is not limited to this. For example, a further optical sheet such as a reflective polarization separation film may be additionally incorporated in the surface light source device 20 and the transmissive display device 10 or a sheet such as the light collecting sheets 30 and 35. Any one or more of the member may be deleted or replaced with another sheet member.

  In addition, although the some modification with respect to embodiment mentioned above has been demonstrated above, it is also possible to apply combining several modifications suitably.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited to this Example.

<< Survey 1 >>
Under various conditions, the thermoplastic resin is heated and extruded together with the granular portion by the method described with reference to FIG. 4 using the apparatus described with reference to FIG. A protective film having a diffusing component made of a product and dispersed in the main part was prepared. Under the present circumstances, the manufacturing conditions were variously changed and the some protective film was produced. For each protective film produced, the surface roughness Ra on the side that was in contact with the belt member, the surface roughness Ra on the side that was in contact with the molding roll, presence or absence of deformation such as warping or bending, polarization The adhesiveness by water sticking with the child was investigated.

[Configuration and production method of protective film]
The protective film was composed only of a layer having a main part made of a thermoplastic resin and a diffusing component made of a granular material and dispersed in the main part. In each protective film, a polycarbonate resin was used as the thermoplastic resin, and styrene fine particles were used as the granular material. The average particle size (primary particle size) of the styrene-based fine particles was set to 5 μm so that only 15% by weight was contained in the protective film. The thickness of the protective film was 80 μm.

For each protective film, the length L [unit: mm] along the movement path of the film material in the section NZ in which the film material forming the protective film is pressed by the molding roll and the belt member (section NZ in FIG. 4). Length L), the moving speed F [unit: m / min] (corresponding to the extrusion speed) of the film material that forms the protective film, and the temperature T [unit: ° C.] of the belt member were variously changed. Table 1 shows the conditions adopted for the production of each protective film. Further, Table 1 shows whether the conditions for producing each protective film (the length L of the pressing section, the moving speed F of the film material, and the temperature T of the belt member) satisfy the above-described formula (b). It also shows.
0.16 ≦ L / (F × T) × 100 ≦ 0.96 Expression (b)

On the other hand, among the protective films, other conditions were the same as each other under the following conditions.
-Heating temperature in the extruder: 300 ° C
-Mold roll temperature: 135 ° C
・ Pressing force (linear pressure) between the forming roll and the nip roll of the backup means: 16 kgf / mm

[Evaluation]
For each of the produced protective films, the roughness of the surface that was in contact with the belt member ("belt side surface") and the roughness of the surface that was in contact with the molding roller (roll side surface) were measured. . Roughness was evaluated as centerline average roughness Ra measured according to JISB0601 (1982). Table 1 shows the measurement results of the roughness Ra.

  In addition, the presence or absence of deformation such as warping or bending of the protective film was evaluated. In the use as a protective film for the lower polarizing plate, a sample that has been deformed to such a degree as to cause a problem is evaluated as “x”, and a sample that has not been deformed to the extent that a problem has occurred is evaluated as “good”. . The evaluation results are shown in Table 1.

  Furthermore, the adhesiveness by water sticking with a polarizer was evaluated. Under the present circumstances, the polarizer formed by making a polyvinyl alcohol film adsorb | suck an optical absorption anisotropy by making a polyvinyl alcohol film adsorb | suck iodine and then uniaxially stretching and orienting was used. Samples that were able to be applied with water while preventing the entry of air and foreign matter by the general procedure (conditions) when applying the polarizer and protective film to water were evaluated as “○” and applied to the polarizer. Samples in which air or foreign matters were mixed when water was applied in the general procedure (conditions) when water was applied to the protective film were evaluated as “×”.

<< Survey 2 >>
Display devices according to examples and display devices according to comparative examples were manufactured, and optical characteristics were compared. The display device according to the example and the display device according to the comparative example were manufactured as follows.

[Display device]
(Example)
A display device having the configuration shown in FIG. 1 was produced as a display device according to the example. As the light source and reflector of the surface light source device, those incorporated in a commercially available liquid crystal television (“Aquos” 32 inch manufactured by Sharp Corporation) were used. A diffusion plate manufactured by Sumitomo Chemical Co., Ltd. (haze value: 88%, total light transmittance: 55%) was used as the diffusion plate. The first condensing sheet and the second condensing sheet use the same optical sheet ("UPVII" manufactured by Dai Nippon Printing Co., Ltd.), and the arrangement directions of the unit optical elements are orthogonal to each other as in the above-described embodiment. Arranged to do so.

  Moreover, the liquid crystal cell of the liquid crystal display panel used what was built in the commercially available liquid crystal television (Sharp Corporation "Aquos" 32 inches). The upper polarizing plate utilized the polarizing plate which has a polarizer and a pair of protective film each water-pasted on the both sides of the polarizer. As a polarizer of the upper polarizing plate, a polarizer obtained by adsorbing iodine to a polyvinyl alcohol film and then imparting light absorption anisotropy to the polyvinyl alcohol film by uniaxial stretching and orientation was used. . A triacetyl cellulose film (TAC film) was used as a pair of protective films for the upper polarizing plate.

  On the other hand, the lower polarizing plate utilized the polarizing plate which has a polarizer, the protective film arrange | positioned at the light-incidence side of a polarizer, and the protective film arrange | positioned at the light emission side of a polarizer. The same polarizer as that of the upper polarizer was used as the polarizer of the lower polarizer. As the light exit side protective film of the lower polarizing plate, an extruded film made of polycarbonate in which no diffusing component is dispersed was laminated on the polarizer by water bonding.

On the other hand, the protective film laminated | stacked on the light-incidence side of the polarizer of a lower polarizing plate used the sample 5 produced by the above-mentioned investigation 1. FIG. The haze value of the light incident side protective film (Sample 4) of the lower polarizing plate was 86.2%. In addition, the moisture permeability of the light incident side protective film for the lower polarizing plate having a thickness of 80 μm obtained by the extrusion process is 60 g / m ² · 24 hr at a temperature of 40 ° C. and a humidity of 90% RH for 24 hours. became.

(Comparative example)
A display device having the configuration shown in FIG. 9 was manufactured as a display device according to a comparative example. In the display device according to the comparative example, in the surface light source device, a diffusion sheet (manufactured by Keiwa) having a haze value of 87% is further provided on the light output side of the light collecting sheet on the light output side, and the lower polarizing plate is inserted in the liquid crystal display panel. Except having made the light side protective film into the film made from a triacetyl cellulose (TAC film), it comprised identically using the member same as the display apparatus which concerns on an Example.

〔Evaluation methods〕
The angle distribution of luminance was measured in a state where the entire display was white on each display device. The measurement results are shown in FIG. BM-8 made by Topcon was used for measurement of the angular distribution of luminance. Further, regarding the angular distribution of luminance, the luminance in the horizontal direction H is measured by measuring the luminance from various directions within a plane parallel to both the arrangement direction of the unit optical elements of the light collecting side light collecting sheet and the front direction. By creating the distribution and measuring the luminance from various directions in a plane parallel to both the arrangement direction of the unit optical elements (cold cathode tube arrangement direction) and the front direction of the light-collecting sheet on the light emitting side. A luminance distribution in direction V was also created.

  The measurement result of the front direction luminance for the display device according to the example was 107% of the measurement result of the front direction luminance for the display device according to the comparative example. In addition, the half-value angle in the angular distribution of luminance was investigated and the following result was obtained. Note that the half-value angle is an inclination angle with respect to the front direction of the measurement direction in which half the peak front direction luminance is obtained. For the display device according to the example, the half-value angle in the horizontal luminance distribution H was 29 °, and the half-value angle in the vertical luminance distribution V was 26 °. On the other hand, for the display device according to the comparative example, the half-value angle in the horizontal luminance distribution H was 34 °, and the half-value angle in the vertical direction luminance distribution V was 24 °.

DESCRIPTION OF SYMBOLS 10 Display apparatus 20 Surface light source device 29 Diffusion sheet 40 Liquid crystal display panel 50 Lower polarizing plate 51 Polarizer 55 Protective film 55a Light emission side surface (one side surface)
55b Incident side (other side)
56 Main part 56a Thermoplastic resin 57 Diffusion component 57a Granules 59 Main body part 60 Unit prism 80 Extruder 82 Extruder 82a Die 84 Molding roll 86 Backup means 86a Support roll 86a1 Nip roll 86a2 Adjustment roll 86b Belt member 88 Guiding means 88a Guide roll 90 Film material 120 Surface light source device 140 Liquid crystal display panel 220 Surface light source device

Claims (18)

A method for producing a protective film for a lower polarizing plate,
Extruding step, in which a film material including a layer having the thermoplastic resin and the diffusion component dispersed in the thermoplastic resin is formed by heating and extruding the thermoplastic resin together with the diffusion component;
A pressure process in which the formed film material passes between the belt member and the molding roll while being pressed between the belt member and the molding roll disposed to face the belt member; With
In the pressurizing step, the film material is pressed by the molding roll and the belt member over a certain length of section along the movement path, and applied to the belt member of the protective film made of the film material. The manufacturing method of the protective film cooled so that the surface which made the side which was contacting may become a flat surface. The certain length at which the film material is pressed by the molding roll and the belt member is L (mm), the moving speed of the film material is F (mm / second), and the belt member The manufacturing method of the protective film of Claim 1 with which following Formula (1) is satisfy | filled by making temperature into T (degreeC).
0.16 ≦ L / (F × T) × 100 ≦ 0.96 Expression (1)   In the pressurizing step, the film material is placed between the molding roll and the belt member while the layer having the thermoplastic resin and the diffusion component dispersed in the thermoplastic resin is in contact with the belt member. The manufacturing method of the protective film of Claim 1 or 2 which passes.   Roughness Ra measured according to JISB0601 (1982) on the surface forming the side of the protective film made of the film material that is in contact with the belt member is 0.9 μm or less. The manufacturing method of the protective film as described in any one of 3.   Roughness Ra measured based on JISB0601 (1982) about the surface which made the side which was contacting the said forming roll of the said protective film consisting of the said film material will be 0.4 micrometer or less. The manufacturing method of the protective film as described in any one of 4.   In the extruding step, the second thermoplastic resin is also heated and extruded, the layer having the thermoplastic resin and the diffusion component dispersed in the thermoplastic resin, and the layer laminated on the layer and the first The manufacturing method of the protective film as described in any one of Claims 1-5 in which the film material containing the 2nd layer which consists of 2 thermoplastic resins is formed.   The manufacturing method of the protective film as described in any one of Claims 1-5 by which the protective film which consists only of the said layer which has the said thermoplastic resin and the said diffusion component disperse | distributed in the said thermoplastic resin is manufactured. .   The protection according to any one of claims 1 to 7, wherein an unevenness corresponding to the presence of the diffusion component is formed on a surface of the film material that has been in contact with the forming roll after the pressing step. A method for producing a film.   In the said pressurization process, the uneven | corrugated surface is shape | molded by the said forming roll on the side which contacts the said forming roll of the said film material, The manufacturing method of the protective film as described in any one of Claims 1-8. .   The said pressurization process WHEREIN: The prism surface comprised by the unit prism arrange | positioned side by side with the said molding roll is formed in the side which contacts the said molding roll of the said film material. The manufacturing method of the protective film as described in a term.   The plurality of unit prisms are arranged along an arrangement direction parallel to the film surface of the film material, and each unit prism is parallel to the film surface and extends in a direction crossing the arrangement direction. The manufacturing method of the protective film as described in any one of these.   The said thermoplastic resin is a manufacturing method of the protective film as described in any one of Claims 1-11 which is a polycarbonate-type resin. A step of bonding the protective film manufactured by the manufacturing method according to any one of claims 1 to 12 and a polarizer,
The manufacturing method of the lower polarizing plate by which the said polarizer is adhere | attached on the said film material from the side which was contacting the said belt member of the said protective film.   The method for producing a lower polarizing plate according to claim 13, wherein the protective film and the polarizer are bonded together by water bonding.   The method further comprising: cutting or punching the web-shaped material having the protective film and the polarizer adhered to each other to sequentially obtain a lower polarizing plate from the web-shaped material. Manufacturing method of lower polarizing plate. A protective film manufactured by the manufacturing method according to any one of claims 1 to 12,
A polarizer adhered to the protective film,
The polarizer is a lower polarizing plate bonded to the protective film from the side of the protective film that is in contact with the belt member. The lower polarizing plate manufactured by the manufacturing method according to any one of claims 13 to 15, or the lower polarizing plate according to claim 16,
An upper polarizing plate;
A liquid crystal display panel, comprising: a liquid crystal cell disposed between the lower polarizing plate and the upper polarizing plate. A liquid crystal display panel according to claim 17,
A surface light source device that illuminates the liquid crystal display panel from the back side.

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