JP2011033643A - Optical path changing sheet, backlight unit and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical path changing sheet having high moldability and scratch resistance, and to provide a backlight unit and a display device each using the optical path changing sheet. <P>SOLUTION: The optical path changing sheet 40 has a fine uneven pattern 41 or 42 formed on at least one of a light incident surface 40a and a light exit surface 40b positioned on the opposite side of the light incident surface 40a. Film formation and formation of the fine uneven pattern 41 or 42 are simultaneously performed by extrusion-molding, and a transparent resin having a melt flow rate in the range of 8 to 25g/10min is used for molding the optical path changing sheet 40. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical path changing sheet that changes the optical path of light incident on a light incident surface and emits the light from the light exit surface, and a backlight unit and a display device that use the optical path changing sheet.

In recent years, liquid crystal display devices using TFT (Thin Film Transistor) type liquid crystal panels and STN (Super Twisted Nematic) type liquid crystal panels have been commercialized mainly for color notebook computers in the OA field.
Such a liquid crystal display device is a transmissive type, a light source is provided on the back side of the liquid crystal panel, a surface light source device that irradiates the liquid crystal panel by converting light from the light source into surface light emission, a so-called backlight unit Is adopted.

  The backlight unit is broadly classified as a “light guide plate light” in which a light source lamp such as a cold cathode fluorescent lamp (CCFL) is multiple-reflected in a flat light guide plate made of acrylic resin having excellent light transmission properties. Two types of methods are known: a “guide method” (so-called edge light method) and a “direct type” that directly illuminates with light from a light source lamp such as a CCFL without using a light guide plate.

As a liquid crystal display device equipped with an edge light type backlight unit, for example, the one shown in FIG. 9 is generally known.
In this type of liquid crystal display device, a liquid crystal panel 2 having both front and back surfaces sandwiched between polarizing plates 1 and 3 is disposed on the front side, and has a substantially rectangular plate shape on the back side of the liquid crystal panel 2. A light guide plate 7 made of a transparent base material such as polymethyl methacrylate (PMMA) or acrylic is disposed. Further, a diffusion film (diffusion layer) 4 is provided on the front surface side of the light guide plate 7, that is, the light emission surface side, and further, the light introduced into the light guide plate 7 is transmitted to the back surface side of the light guide plate 7. A scattering reflection pattern portion (not shown) for scattering and reflection so as to be uniform toward the liquid crystal panel 2 efficiently is provided by printing or the like, and a reflection film (reflection) is provided on the back side of the scattering reflection pattern portion. Layer) 8 is provided.

The light guide plate 7 is provided with a light source lamp 6 on the side thereof, and further covers the back side of the light source lamp 6 so that the light from the light source lamp 6 is efficiently incident on the light guide plate 7. Thus, the lamp reflector 5 having a high reflectance is provided.
The scattering reflection pattern portion was formed by printing a mixture of white titanium dioxide (titania) powder mixed with a transparent adhesive solution or the like in a predetermined pattern, for example, a dot pattern, and drying and forming the mixture. Therefore, directivity is imparted to the light incident on the light guide plate 7 and guided to the light exit surface, which is devised to increase the luminance.

  Recently, a prism film (prism layer) having a light condensing function is provided between the diffusion film 4 and the liquid crystal panel 2 as shown in FIG. ) 9 and 10 are proposed. The prism films 9 and 10 are emitted from the light exit surface of the light guide plate 7 and concentrate the light diffused by the diffusion film 4 on the effective display area of the liquid crystal panel 2 with high efficiency.

  On the other hand, direct type backlights are used in display devices such as large liquid crystal televisions where it is difficult to use a light guide plate. As the direct backlight type display, a liquid crystal display device shown in FIG. 10 is generally known. In this liquid crystal display device, a liquid crystal panel 2 having both front and back surfaces sandwiched between polarizing plates 1 and 3 is disposed on the front surface side, and a light source 12 made of CCFL or the like is disposed on the lower surface of the liquid crystal panel 2. Further, an optical sheet such as a light diffusing plate 11 is provided on the front side of the light source 12, and on the back side of the light source 12, light traveling from the light source 12 in the opposite direction to the liquid crystal panel 2 is directed to the liquid crystal panel 2 side. A reflector 13 for reflection is disposed. Therefore, the light emitted from the light source 12 is diffused by the light diffusing plate 11, and this diffused light can be condensed on the effective display area of the liquid crystal panel 2 with high efficiency.

  The light diffusing plate 11 used in the “direct type” display device is required to scatter the light from the linear light source and to be invisible through the light source because of the configuration of the liquid crystal display device. Scattered particles are blended, and various developments have been made in response to the recent rapid increase in direct type. Many of them are for the purpose of high transmittance and high diffusion, and control the kind, particle size, and blending amount of light scattering particles. As light scattering particles, those using true spherical particles have been reported. .

  However, when only spherical particles are used as the light scattering particles of the light diffusing plate, it has a diffusion characteristic that widens the viewing angle, and the lamp image is confirmed in a state where the bright part is spread, and the relatively bright part and the comparatively dark part. The portion can be visually recognized as striped luminance unevenness. Since it is necessary to reduce the light transmittance so that it is difficult to confirm the difference between the bright part and the dark part, there is a problem that the front luminance is lowered. Also in the liquid crystal display device shown in FIG. 10, since the viewing angle control is left only to the diffusibility of the light diffusing plate 11, the control is difficult, and the characteristic that the center of the liquid crystal display screen is bright and becomes darker as it is closer to the periphery. Inevitable. Therefore, when the liquid crystal display screen is viewed from the side, the luminance is greatly reduced, leading to a reduction in light utilization efficiency. Therefore, similar to the edge light method, various optical films are laminated on the light diffusion plate. The problem is being solved.

  In recent years, cases in which an optical sheet is formed by extrusion molding have been increasing for cost reduction, and in particular, an extruded sheet using polycarbonate has been attracting attention (see, for example, Patent Document 1).

JP 2004-53998 A

However, it is difficult to accurately form a lens shape such as a prism by extrusion molding. In order to solve this problem, when a resin having an extremely low melt flow rate (MFR) value is used, scratch resistance is obtained. There is a disadvantage that difficulty occurs in sex. That is, it has been difficult to produce an optical sheet having both high formability and scratch resistance.
On the other hand, in recent years, trial and error of thinning the display device has been actively carried out. However, as such thinning progresses, the heat during operation of the display device is likely to be trapped inside, so the internal temperature becomes higher than before. There is a concern that the image quality is degraded due to deformation of the optical sheet used.

The present invention has been made in view of such problems, and provides an optical path changing sheet having high moldability and scratch resistance, and a backlight unit and a display device using the optical path changing sheet. Objective.
Furthermore, an object of the present invention is to provide an optical path changing sheet that has high heat resistance and is not deformed by heat, and a backlight unit and a display device using the optical path changing sheet.

In order to solve the above problems, the present invention proposes the following means.
That is, the optical path changing sheet according to the present invention is an optical path changing sheet in which an optical path changing element is formed on at least one of a light incident surface and a light exit surface located on the opposite side of the light incident surface, and is formed by extrusion molding. Film formation and molding of the optical path changing element are performed at the same time, and the melt flow rate is made of a transparent resin in the range of 8 g / 10 min to 25 g / 10 min.

Here, when the melt flow rate is a value smaller than 8 g / 10 min, it is possible to obtain a stable surface state and thickness with high film forming properties, but on the occasion of shaping a fine uneven shape on the light emitting surface or light incident surface. The desired shape cannot be obtained. That is, there is a drawback that the formability is low because the resin is too hard.
On the other hand, when the melt flow rate is greater than 25 g / 10 min, the formability is high, and it is easy to form a desired fine uneven shape on the light exit surface or light entrance surface, but the resin is too soft, so the film formability is high. It has a drawback that the surface state and thickness are not stable, and the scratch resistance is low.
In this respect, in the optical path changing sheet of the present invention, since the melt flow rate value is set in the range of 8 g / 10 min to 25 g / 10 min, it is possible to achieve both formability and film formability. It is possible to obtain a scratch resistance level that can be used.
The melt flow rate is one of the most popular measures for indicating the fluidity of a polymer in a solution state, and it is an extrusion type plastometer that has a specified size under a constant pressure and a constant temperature. It is an index expressed in units of g / 10 min by measuring the amount flowing out from the nozzle (orifice).

  In the optical path changing sheet according to the present invention, the thickness is preferably set in a range of 0.5 mm or more and less than 2.0 mm.

When the thickness is less than 0.5 mm, the rigidity is insufficient. For example, when a display device is configured by incorporating an optical path changing sheet, there is a risk that the optical path changing sheet itself is deformed by the internal heat of the device when the display device is in operation. However, it is disadvantageous in that the handling property at the time of assembling the display device is deteriorated. On the other hand, when the thickness is increased to 2.0 mm or more, it is disadvantageous in that it is difficult to cope with the thinning of the display device.
In this respect, since the optical path changing sheet of the present invention has a thickness set in a range of 0.5 mm or more and less than 2.0 mm, it is possible to prevent deformation due to heat while corresponding to a reduction in thickness.

  In the optical path changing sheet according to the present invention, the thickness is preferably set in the range of 0.5 mm to 1.8 mm.

  Further, the optical path changing sheet according to the present invention is characterized in that the optical path changing element has a fine uneven shape for controlling at least one of a luminance distribution and a viewing angle.

  That is, since the optical path changing sheet of the present invention is molded from a resin having a melt flow rate of 8 g / 10 min to 25 g / 10 min, the moldability is high, and a fine uneven shape can be easily and reliably formed. . Therefore, by forming a fine uneven shape as intended, at least one of the luminance distribution and the viewing angle of light incident on the light incident surface can be controlled and emitted from the light emitting surface, and as an optical path changing sheet It becomes possible to demonstrate the function.

  Moreover, in the optical path changing sheet of the present invention, the contour of the fine concavo-convex shape in a sectional view along the thickness direction may have a shape including a straight line.

  Furthermore, in the optical path changing sheet of the present invention, the contour of the fine concavo-convex shape in a cross-sectional view along the thickness direction may have a shape including a curve.

  Moreover, in the optical path changing sheet of the present invention, the outline of the fine uneven shape in a sectional view along the thickness direction may have a shape including a straight line and a curve.

  Furthermore, in the optical path changing sheet of the present invention, the fine concavo-convex shape may be configured by arranging a plurality of unit concavo-convex shapes having the same shape.

  In the optical path changing sheet of the present invention, the fine uneven shape may be configured by arranging a plurality of unit uneven shapes having at least two different shapes.

  A backlight unit according to the present invention includes any one of the above optical path changing sheets, a light source that is disposed on the light incident surface side of the optical path changing sheet and that emits light, and the optical path changing sheet and the light source. And a light diffusion plate that diffuses light from the light source.

  According to the backlight unit having such a feature, since the melt flow rate is made of a transparent resin having a range of 8 g / 10 min to 25 g / 10 min, an optical path changing sheet having high moldability and scratch resistance is employed. By changing the optical path as intended, it is possible to emit light with high brightness and little luminance unevenness, and also prevent the optical path changing sheet from being damaged when the optical path changing sheet is incorporated into the backlight unit. be able to.

A display device according to the present invention includes the backlight unit and an image display element that displays an image by light irradiation from the backlight unit.
As a result, it is possible to display an image with high luminance and less luminance unevenness.

In the optical path changing sheet, the backlight unit and the display device of the present invention, since the melt flow rate of the transparent resin for molding the optical path changing sheet is set in the range of 8 g / 10 min to 25 g / 10 min, The scratch resistance can be improved.
Moreover, since the thickness of the optical path changing sheet is set in the range of 0.5 mm or more and less than 2.0 mm, it is possible to prevent deformation due to heat while corresponding to the reduction in thickness.

It is a longitudinal cross-sectional view of the display apparatus which concerns on embodiment. It is a longitudinal cross-sectional view which shows the other structure of an optical path change sheet | seat. It is a longitudinal cross-sectional view which shows the other structure of an optical path change sheet | seat. It is a longitudinal cross-sectional view which shows the other structure of an optical path change sheet | seat. It is a longitudinal cross-sectional view which shows the other structure of an optical path change sheet | seat. It is a longitudinal cross-sectional view which shows the other structure of an optical path change sheet | seat. It is a longitudinal cross-sectional view which shows the other structure of an optical path change sheet | seat. It is a longitudinal cross-sectional view which shows an example of the display apparatus of an edge light system. It is a longitudinal cross-sectional view which shows an example of the display apparatus of an edge light system provided with the prism film. It is a longitudinal cross-sectional view which shows an example of a direct type backlight type display apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, about the optical path change sheet | seat which concerns on embodiment of this invention, it demonstrates with the backlight unit and display apparatus using the same.

As shown in FIG. 1, the display device 100 according to the embodiment is a liquid crystal display device configured by providing an image display element 90 on the light emission side of a backlight unit 80 that emits light upward. In addition, an image is displayed by emitting display light whose display is controlled by an image signal from the image display element 90 toward the observer side (upward side in FIG. 1).
Hereinafter, based on such an arrangement, the upper direction in FIG. 1 may be simply referred to as the front direction or the viewer side, and the lower direction may be simply referred to as the back side.

  The image display element 90 is preferably an element that displays an image by transmitting / blocking light in pixel units. An image with high image quality can be displayed as long as the image is displayed by transmitting / blocking light in pixel units.

  As the image display element 90, a liquid crystal display element is used in the present embodiment. A liquid crystal display element is a typical element that transmits / shields light in pixel units and displays an image, and can improve image quality and reduce manufacturing cost compared to other display elements. Can do.

  The liquid crystal panel as the image display element 90 includes, for example, a back side of a liquid crystal cell (display element or panel) that controls a light transmission state according to an image signal for each of a plurality of pixel regions formed in a rectangular lattice shape. A polarizing plate for controlling the polarization direction of light is laminated on the viewer side. The liquid crystal cell includes a pair of glass substrates and a liquid crystal layer sandwiched between them.

  The image display element 90 is a so-called transmissive display panel in the present embodiment, but may be a transflective display panel. Alternatively, instead of the image display element 90 as a liquid crystal panel including the liquid crystal cell 90, another display panel, for example, a display panel that displays a still image with a light-transmitting coloring pattern may be used.

  The backlight unit 80 is a light emitting device having a light emitting surface with substantially the same area as the display screen of the image display element 90, and the light diffusing plate 30, the optical path changing sheet 40, Are stacked in this order.

  In the light source unit 20, a plurality of linear light sources 21 having a cylindrical shape extending in the depth direction of the paper surface are arranged at a constant pitch so as to be parallel to each other, and the back surfaces of these linear light sources 21 A direct type system is adopted in which the side and the side are surrounded by the lamp house 21.

As the light source 21, a cathode tube (CCFL), a semiconductor laser, an EL, an LED arranged in a line shape, or the like can be used.
In addition, the lamp house 22 has a box shape with an opening on the viewer side, and is composed of a light-reflective film such as a white film or a white sheet, or a sheet. Note that. The lamp house 22 may be a reflector configured by attaching a general film, sheet or the like on a support such as a metal plate.

  The light source 21 may be a point-like point light source capable of emitting light radially instead of a linear one. In this case, the light sources 21 are arranged in a matrix in a two-dimensional direction along the light emission surface of the backlight unit 80, and the back side and the side of the light source 21 thus arranged are surrounded by the lamp house 22. It is configured as a direct type.

  For example, a light emitting diode (LED) can be used as the light source 21 as the point light source. When configuring this light emitting diode, for example, a system that emits white light by combining light emitting elements that emit light of a single color is generally used. Further, the light source 21 as a point light source may be, for example, a normal fluorescent lamp, a halogen lamp, a semiconductor laser, or the like. Furthermore, the point light source is not limited to the above-described one, and it may be a single monochromatic LED element covered with at least one kind of phosphor.

  As the light source unit 20, in addition to the direct type as described above, a light source lamp such as a cold cathode fluorescent lamp (CCFL) is subjected to multiple reflection within a flat light guide plate made of acrylic resin or the like having excellent light transmittance. An edge light system may be used.

  The light diffusing plate 30 is a plate or sheet formed by dispersing a light diffusing region in a transparent resin. As the transparent resin, a thermoplastic resin, a thermosetting resin, or the like can be used. For example, a polycarbonate resin, an acrylic resin, a fluorine acrylic resin, a silicone acrylic resin, an epoxy acrylate resin, a polystyrene resin, a cycloolefin polymer, Methyl styrene resin, fluorene resin, polyethylene terephthalate (PET), polypropylene, acrylonitrile styrene copolymer, acrylonitrile polystyrene copolymer, and the like can be used.

The light diffusion region is preferably made of light diffusion particles. This is because suitable diffusion performance can be easily obtained. As the light diffusing particles, transparent particles made of an inorganic oxide or a resin can be used. As transparent particles made of an inorganic oxide, for example, silica, alumina or the like can be used. The transparent particles made of resin include acrylic particles, styrene particles, styrene acrylic particles and cross-linked products thereof, melamine / formalin condensate particles, PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy resin), FEP (tetrafluoroethylene). Fluoropolymer particles such as fluoroethylene / hexafluoropropylene copolymer), PVDF (polyfluorovinylidene), and ETFE (ethylene / tetrafluoroethylene copolymer), silicone resin particles, and the like can be used.
Moreover, you may use combining 2 or more types of transparent particles from the transparent particle mentioned above. The size and shape of the transparent particles are not particularly limited and can be set as appropriate.

  When light diffusing particles are used as the light diffusing region, the thickness of the light diffusing plate 30 is preferably 0.1 to 5 mm. When the thickness of the light diffusing plate 30 is 0.1 to 5 mm, optimum diffusion performance and brightness can be obtained. On the other hand, if the thickness is less than 0.1 mm, the diffusion performance is insufficient, and if it exceeds 5 mm, the amount of resin is large and the luminance is reduced due to absorption.

The optical path changing sheet 40 changes the optical path of the light emitted from the light source 21 and diffused by the light diffusing plate 30 and transmits it to the image display element 90 side, and has a substantially plate shape or a substantially sheet shape. The sheet surface facing the back side is a light incident surface 40a, and the sheet surface facing the front side located on the opposite side of the light incident surface 40a is a light emitting surface 40b.
Moreover, in this embodiment, the fine uneven | corrugated shape (optical path changing element) 41 is shape | molded by the light-incidence surface 40a side of the optical path change sheet | seat 40, and also the fine uneven | corrugated shape (optical path changing element) is also given to the light-projection surface 40b side. 42 is shaped.

  The optical path changing sheet 40 as described above is formed from a transparent resin. Examples of the transparent resin include an acrylic resin, a polystyrene (PS) resin, a methacryl styrene copolymer (MS) resin, and a polycarbonate (PC). Examples thereof include resins, acrylonitrile styrene copolymer (AS) resins, cycloolefin polymers (COP), copolymers containing these as components, and mixtures of these resins.

Moreover, in this embodiment, the melt flow rate (MFR) of the transparent resin which shape | molds the optical path changing sheet 40 is set to the range of 8g / 10min-25g / 10min. Furthermore, the thickness of the optical path changing sheet 40 is set in a range of 0.5 mm or more and less than 2.0 mm, and more preferably in a range of 0.5 mm or more and less than 1.8 mm.
The melt flow rate is one of the most popular measures showing the fluidity of a polymer in a solution state and is also referred to as a solution index. With an extrusion plastometer, under a constant pressure and a constant temperature, It is an index expressed in units of g / 10 min by measuring the amount flowing out from a nozzle (orifice) having a prescribed size.

Here, the detailed shape of the fine irregularities 41 and 42 in the optical path changing sheet 40 will be described.
In the present embodiment, the fine concavo-convex shape 41 formed on the light incident surface 40a side has a plurality of cylindrical lenses arranged in parallel with a cylindrical lens extending in a semicircular cross section or a semi-elliptical cross section as a unit concavo-convex shape. It has a lenticular lens array shape, that is, the contour of the fine concavo-convex shape 41 is a shape including a curve.
Further, the fine concavo-convex shape 42 formed on the light emitting surface 40b side has a prism array shape in which a plurality of triangular prisms are arranged in parallel with a triangular prism extending in a cross-sectional view as a unit concavo-convex shape. The outline of the fine concavo-convex shape 41 is a shape including a straight line.

  In this embodiment, the fine irregularities 41 and 42 of the optical path changing sheet 40 are formed on both the light incident surface 40a side and the light emitting surface 40b side of the optical path changing sheet 40, but at least the light incident surface 40a side. And the light emission surface 40b side. Further, the shapes of the fine irregularities 41 and 42 are not limited to the above-described shapes, and can be appropriately changed according to the configuration of the light source unit 20.

  For example, as shown in FIG. 2, the light incident surface 40a is not formed with the fine concavo-convex shape 41, and the triangular prism array-like fine concavo-convex shape 42 is formed only on the light exit surface 40b side. May be.

  As shown in FIG. 3, the light incident surface 40a is not formed with the fine concavo-convex shape 41, and the lenticular lens array-like fine concavo-convex shape 42 is formed only on the light exit surface 40b side. May be.

  Further, as shown in FIG. 4, the fine uneven shape 42 is not formed on the light exit surface 40b side, and the fine uneven shape 41 having a triangular prism array shape is formed only on the light incident surface 40a side. May be.

  Furthermore, as shown in FIG. 5, the fine uneven shape 41 may not be formed on the light incident surface 40a, and the fine uneven shape 42 may be formed only on the light exit surface 40b side. In this fine concavo-convex shape 42, each unit concavo-convex shape forming the fine concavo-convex shape 42 is a shape in which one side has a cylindrical lens shape and the other side has a prism lens shape with the apex as a boundary. That is, the outline of the fine uneven shape 42 is a shape including a straight line and a curved line.

  Note that, in the fine uneven shapes 41 and 42 in the optical path changing sheet 40, the unit uneven structures 41 and 42 all have the same shape on the light incident surface 40a and the light exit surface 40b, but the present invention is not limited to this. In other words, the fine uneven shapes 41 and 42 may have a shape in which a plurality of unit uneven shapes forming at least two different shapes are arranged.

  That is, for example, as shown in FIG. 6, the light incident surface 40a is formed with a fine concavo-convex shape 41 having a lenticular lens array shape, and the light emitting surface 40b is a unit having a triangular prism shape and a cylindrical lens shape. The fine uneven | corrugated shape 41 which consists of uneven | corrugated shape may be formed.

  For example, as shown in FIG. 7, the light incident surface 40a is formed with a fine uneven shape 41 in which cylindrical lenses are arranged at regular intervals, and the light exit surface 40b has a triangular prism shape and a cylindrical lens. The fine uneven | corrugated shape 41 which consists of the unit uneven | corrugated shape which makes a shape may be formed.

In such an optical path changing sheet 40, the concave and convex shapes 41 and 42 are integrally formed by extruding the transparent resin, that is, the film forming and the optical path changing element are simultaneously formed. The
Here, for example, when the fine uneven shape is formed in multiple stages by a method such as forming the fine uneven shape on the base film with an electron beam curable resin or the like, the number of steps and cost increase, which is not preferable. In addition, in the method of applying an optical path changing element using a stamper after forming a sheet to a desired thickness, if the film formation and shape application are performed in multiple stages, the line length becomes long, so a large apparatus installation space is required. Or the number of parameters that need to be managed increases.
In this regard, the number of steps and cost can be reduced by integrally forming the optical path changing sheet 40 by extrusion molding. In addition, the line length can be shortened, and the conditions necessary for providing the shape can be incorporated into the film forming conditions, thereby reducing the management parameters.

Next, operations of the backlight unit 80 and the display device 100 including the optical path changing sheet 40 having the above-described configuration will be described.
The light emitted from the light source 21 of the light source unit 20 directly enters the light diffusing plate 30 or enters the light diffusing plate 30 through reflection by the lamp house 22. Then, the light diffusing plate 30 gives a light scattering effect and is sufficiently diffused, and then is emitted to the front side. This reduces the lamp image.
The light that has passed through the light diffusing plate 30 reaches the optical path changing sheet 40, and the optical path is changed by the fine uneven shapes 41 and 42 of the optical path changing sheet 40. That is, at least one of the luminance distribution and the viewing angle is controlled by the fine concavo-convex shapes 41 and 42 and is emitted to the front side.
Thus, the light that has passed through the optical path changing sheet 40 passes through the image display element 90 and is visually recognized by the observer as an image display.

Here, when the melt flow rate of the transparent resin for forming the optical path changing sheet 40 is a value smaller than 8 g / 10 min, a stable surface state and thickness with high film formability can be obtained, while the light incident surface 40 a and the light emission are obtained. When forming the fine irregularities 41 and 42 on the surface 40b, a desired shape cannot be obtained. That is, there is a drawback that the formability is low because the resin is too hard.
On the other hand, when the melt flow rate of the transparent resin is larger than 25 g / 10 min, the shapeability is high, and the desired fine irregularities 41 and 42 can be easily formed on the light incident surface 40a and the light emitting surface 40b, but the resin is soft. Therefore, the film forming property is low, the surface state and thickness are not stable, and the scratch resistance is low.

  In this regard, in the optical path changing sheet 40 of the present embodiment, the value of the melt flow rate of the transparent resin is set in the range of 8 g / 10 min to 25 g / 10 min, so that both formability and film formability are achieved. be able to. Furthermore, it is possible to obtain a scratch resistance level that can be used.

Further, for example, when the thickness of the optical path changing sheet 40 is less than 0.5 mm, the rigidity is insufficient, and when the display apparatus 100 is configured by incorporating the optical path changing sheet 40, the display apparatus 100 is in operation. There is a disadvantage in that the risk of the optical path changing sheet 40 itself being deformed by the internal heat increases, and the handling property at the time of assembling the display device 100 is deteriorated. On the other hand, when the thickness is increased to 2.0 mm or more, it is disadvantageous in that it is difficult to cope with the thinning of the display device 100.
In this respect, the optical path changing sheet 40 of the present embodiment has a thickness set in the range of 0.5 mm or more and less than 2.0 mm, preferably in the range of 0.5 mm or more and 1.8 mm or less, and therefore corresponds to thinning. However, it is possible to prevent deformation due to heat.

  Further, according to the backlight unit 80 of the present embodiment, the optical path changing sheet 40 having high moldability and scratch resistance is adopted by being made of a transparent resin having a melt flow rate in the range of 8 g / 10 min to 25 g / 10 min. Therefore, by changing the optical path as intended, it is possible to emit light with high luminance and little luminance unevenness, and when the optical path changing sheet 40 is incorporated into the backlight unit 80, the optical path changing sheet is damaged. It can be prevented from occurring.

  Furthermore, according to the display device 100 of the present embodiment, since the backlight unit 80 is mounted, it is possible to display an image with high luminance and little luminance unevenness.

  As mentioned above, although embodiment in this invention was described in detail, unless it deviates from the technical idea of this invention, it is not limited to these, A some design change etc. are possible.

In order to confirm the effect of the optical path changing sheet according to the embodiment, polycarbonate is selected as the transparent resin, and the melt flow rates are 5 g / 10 min, 8 g / 10 min, 15 g / 10 min, 25 g / 10 min, 30 g / 10 min, respectively. However, a total of 20 types of optical path changing sheets of 0.2 mm, 0.5 mm, 1.8 mm, and 2.0 mm were produced.
As the optical path changing element, a fine concavo-convex shape forming a triangular prism array shape with an apex angle of 90 ° was formed on the light exit surface.

  The above 20 types of optical path changing sheets were evaluated, and (1) film forming / shaping properties, (2) handling properties when assembling the display device, (3) resistance to deformation due to heat, and scratch resistance were compared. did. In addition, the tolerance to the deformation | transformation by a heat | fever evaluated by putting in the direct light source liquid crystal television with the thickness of a backlight unit 40mm, and implementing a lighting test.

The evaluation results are shown in Table 1. Each evaluation was performed according to the following criteria.
Film forming property: “O” if there was no problem in the appearance of the molded sheet, and “X” if there was a problem in the appearance such as distortion and rough surface.
Shapeability: “O” if the desired shape was imparted to the sheet surface, and “X” if not. Handling property when assembling the display device: When the formed sheet is assembled into the display device, it is indicated as “O” if no wrinkles or creases occur, and “X” if it occurs.
Resistance to deformation due to heat: “O” if no large distortion or warping or the like leading to degradation of image quality occurs in the display device when the light source is lit, and “X” if it occurs.
Scratch resistance: ◯ when there is no scratch on handling or delivery, and × when it is attached.

As shown in Table 1, only when a transparent resin having an MFR (melt flow rate) in the range of 8 to 25 g / 10 min is used and extrusion is performed to a thickness in the range of 0.5 mm to 1.8 mm. It has been confirmed that it is possible to provide an optical path changing sheet having both good film formability and formability, and good heat deformation resistance, scratch resistance, and handling properties.
Further, from this result, even when the thickness is in the range of 0.5 mm or more and less than 2 mm, the film forming property and the shapeability are compatible, and the optical path changing sheet has good thermal deformation resistance, scratch resistance, and handling properties. It is inferred that it will be possible to provide

DESCRIPTION OF SYMBOLS 20 Light source part 21 Light source 22 Lamp house 30 Light diffusing plate 40 Optical path change sheet 40a Light incident surface 40b Light emission surface 41 Fine uneven | corrugated shape 42 Fine uneven | corrugated shape 90 Image display element 100 Display apparatus

Claims (11)

An optical path changing sheet in which an optical path changing element is formed on at least one of a light incident surface and a light exit surface located on the opposite side of the light incident surface,
Film formation and molding of the optical path changing element are simultaneously performed by extrusion molding,
An optical path changing sheet comprising a transparent resin having a melt flow rate in a range of 8 g / 10 min to 25 g / 10 min.   The optical path changing sheet according to claim 1, wherein the thickness is set in a range of 0.5 mm or more and less than 2.0 mm.   The optical path changing sheet according to claim 1 or 2, wherein the thickness is set in a range of 0.5 mm or more and 1.8 mm or less.   The optical path changing sheet according to any one of claims 1 to 3, wherein the optical path changing element has a fine uneven shape for controlling at least one of a luminance distribution and a viewing angle.   The optical path changing sheet according to claim 4, wherein an outline of the fine unevenness in a cross-sectional view along the thickness direction has a shape including a straight line.   The optical path changing sheet according to claim 4, wherein an outline of the fine uneven shape in a cross-sectional view along the thickness direction has a shape including a curve.   The optical path changing sheet according to claim 4, wherein a contour of the fine uneven shape in a cross-sectional view along the thickness direction has a shape including a straight line and a curved line.   The optical path changing sheet according to any one of claims 4 to 7, wherein the fine uneven shape is configured by arranging a plurality of unit uneven shapes having the same shape.   The optical path changing sheet according to any one of claims 4 to 7, wherein the fine uneven shape is configured by arranging a plurality of unit uneven shapes having at least two different shapes. The optical path changing sheet according to any one of claims 1 to 9,
A light source disposed on the light incident surface side of the optical path changing sheet and irradiating light; and
A backlight unit comprising a light diffusing plate disposed between the light path changing sheet and the light source and diffusing light from the light source. A backlight unit according to claim 10;
A display device comprising: an image display element that displays an image by light irradiation from the backlight unit.

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