JP4815930B2 - Light transmissive film, backlight device, and liquid crystal display device - Google Patents

Description

  The present invention relates to a light transmissive film, a backlight device, and a liquid crystal display device suitable for use as, for example, a brightness enhancement film for an edge light type backlight unit.

  A liquid crystal display (LCD) is lower in power consumption, smaller and thinner than a cathode ray tube (CRT), and is now available in mobile phones, digital cameras, and PDAs (Personal Digital Display). Various sizes are widely used, from small devices such as Assistants) to large-sized LCD TVs.

  Liquid crystal display devices are classified into a transmission type, a reflection type, and the like. In particular, a transmission type liquid crystal display device includes a backlight unit as an illumination light source in addition to a liquid crystal display panel in which a liquid crystal layer is sandwiched between a pair of transparent substrates. The backlight unit includes an edge light type as well as a direct type in which a light source is arranged directly under a liquid crystal display panel.

  The edge light type backlight unit has a light guide plate disposed on the back surface of the liquid crystal display panel, a light source disposed at one end of the light guide plate, and a surface opposite to the light emitting surface of the light guide plate. It is composed of a reflective plate and the like for covering. Conventionally, a cold cathode fluorescent lamp (CCFL) that emits white light has been widely used as a light source.

  On the other hand, a configuration is known in which a light transmission film called a brightness enhancement film is disposed between a light guide plate and a liquid crystal display panel for the purpose of distributing light source light in the front direction. The brightness enhancement film is composed of a prism sheet in which prisms having a substantially triangular cross section are periodically arranged at a fine pitch on one surface. In addition to a configuration in which the prism structure surface is disposed toward the liquid crystal display panel, this prism sheet has a configuration in which the prism structure surface is disposed toward the light guide plate. Hereinafter, in the present specification, the arrangement of the latter prism sheet is also referred to as “reverse prism” for convenience.

  FIG. 6 shows a configuration example of an inverted prism-shaped prism sheet. In FIG. 6, reference numeral 1 denotes a prism sheet, and prisms 1P are arranged at a constant pitch on the lower surface side. A light guide plate 2 has a linear light source (CCFL) (not shown) arranged on the left side in the drawing.

  Normally, when the prism sheet is arranged in an inverted prism shape, the light guide plate 2 is designed so that the angle of light extracted from the light exit surface 2a is shallow (α is small). Each prism 1P of the prism sheet 1 has a certain apex angle θ. Then, light L emitted from the light emitting surface 2a of the light guide plate 2 at a shallow angle is incident from one inclined surface 1a of the prism 1P and totally reflected by the other inclined surface 1b, so that the vertical direction (liquid crystal display Start up to the front of the panel. Thereby, the light source light is condensed in the front direction, and the front luminance is improved.

  Various prism apex angles θ are known depending on the specifications, and a typical angle is 63 °. In this case, when the refractive index of the prism sheet is about 1.59, the emission angle α from the light guide plate 2 for the light L to rise in the vertical direction is about 25 °.

  However, in the liquid crystal display device using the prism sheet having the above-described configuration, moire (striped pattern) occurs due to the effect of overlapping the pixels of the liquid crystal display panel having a periodicity and the prism sheet, and the image quality is improved. This causes a problem of seriously damaging.

  Therefore, as a method for reducing the occurrence of moire, conventionally, the prism sheet and the periodic structure of the pixels are arranged at an angle (for example, refer to Patent Document 1 below), or the prism ridge line is not a straight line but a curved line. Or the like (see Patent Document 2 below), or the pitch and height of the prism are changed non-constantly (Patent Document 3 below), and the optical interference is suppressed by destroying the periodicity in the relationship between the prism sheet and the pixels. The method is common.

  FIG. 7 shows a configuration of a backlight unit described in Patent Document 3 below. In FIG. 7, 3 is a light guide plate, 4 is a reflection plate, 5 is a prism sheet having an inverted prism shape, and 6 is a linear light source. As shown in the figure, the prism sheet 5 is irregularly changed in prism arrangement pitch by varying the height while keeping the apex angle of each prism 5P constant. As a result, the periodicity of the prism arrangement is broken to suppress the generation of moire interference fringes.

JP 2003-295181 A JP 2005-123046 A Japanese Patent Laid-Open No. 6-82635

  However, although the configurations of Patent Documents 1 to 3 have a certain effect in reducing moire, particularly in an edge-light type backlight unit, the front luminance is lowered and the viewing angle changes depending on the location. There are many cases where harmful effects occur.

  In particular, in the method described in Patent Document 3 described with reference to FIG. 7, in the case of an edge light type backlight unit, most of the light source light is emitted from the light guide plate 3 at a substantially constant emission angle. The difference in the height of the prisms 5P causes variations in the amount of light incident on the individual prisms 5P, and this causes the in-plane luminance uniformity to deteriorate. As a result, it is necessary to dispose a sheet having a corresponding diffusion effect between the prism sheet and the liquid crystal display panel, but the light transmittance is reduced and the luminance cannot be improved.

  It is possible to reduce moire by changing the arrangement pitch of the prisms at a constant height. However, in this case, the prism apex angle cannot be made constant, so that the light condensing property varies from region to region. As a result, the front luminance decreases and the in-plane luminance varies.

  The present invention has been made in view of the above-described problems, and has an object to provide a light transmission film, a backlight device, and a liquid crystal display device that can effectively suppress moire while achieving uniform in-plane luminance distribution. To do.

  In solving the above problems, the light transmissive film of the present invention is a light transmissive film in which a plurality of prisms having a constant apex angle are continuously arranged in one direction on a light incident side surface. At least a part or all of the prism includes an inclined surface portion that serves as a light incident portion and a continuous surface portion that extends from the inclined surface portion toward a base portion of another adjacent prism.

  With this configuration, by forming the prism surfaces so that the formation heights of the continuous surface portions are different between the prisms, the prism array pitch can be irregularly changed with the apex angle being constant. Brightness can be improved and moire can be reduced.

  Also, with the above configuration, it is possible to make the formation height of each prism constant in a state where the arrangement pitch is irregularly changed, so that the in-plane luminance distribution can be made uniform.

  The continuous surface portion is a surface that communicates between the inclined surface portion and the base portion of another adjacent prism, and the shape thereof is not particularly limited, and may be a flat surface or a curved surface, and may be perpendicular to the film surface. It may be non-vertical. If this continuous surface portion is formed as a surface perpendicular to the film surface, the adjustment range of the pitch of the prism can be expanded.

  When the backlight device or the liquid crystal display device is configured using the light transmitting film having such a configuration, the prism surface of the light transmitting film is directed to the light emitting surface of the light guide plate. And the said inclined surface part of each prism is orient | assigned to the one side edge part side of the light-guide plate in which a light source is arrange | positioned. As a result, the in-plane luminance distribution can be made uniform, and at the same time, image quality deterioration due to the occurrence of moire can be suppressed.

  As described above, according to the light transmission film of the present invention, the prism arrangement pitch can be irregularly changed in a state where the apex angle and the prism height are constant. As a result, the in-plane luminance distribution can be made uniform while effectively reducing moire.

  Further, according to the backlight device and the liquid crystal display device of the present invention, the in-plane luminance distribution can be made uniform, and at the same time, the degradation of image quality due to moire can be suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following structures, A various deformation | transformation is possible based on the technical idea of this invention.

  FIG. 1 is an exploded side view showing a schematic configuration of a liquid crystal display device 10 according to an embodiment of the present invention. The liquid crystal display device 10 includes a backlight device 12 and a liquid crystal display panel 16. The backlight device 12 includes a backlight unit 13 and a prism sheet 11 as a light transmission film according to the present invention. Note that another optical element such as a diffusion sheet or a polarization separation sheet may be further disposed between the prism sheet 11 and the liquid crystal display panel 16.

  The backlight unit 13 includes a light guide plate 2 made of a translucent material, a light source 15 disposed at one end of the light guide plate 2, and a reflection disposed on the back side (lower surface side in the drawing) of the light guide plate 2. It is composed of an edge light type provided with a plate 14. In the present embodiment, a linear light source such as CCFL is used as the light source 15, but in addition to this, one or a plurality of point light sources such as an LED (Light Emitting Diode) can be used.

  The light guide plate 2 is formed of an injection-molded body such as a colorless and transparent resin having translucency in the wavelength band of light used for the light source, such as acrylic resin, methacrylic resin, styrene resin, and polycarbonate resin. The reflecting plate 14 is provided with a metal foil (in some cases, a white coating film) such as silver or aluminum on the inner surface facing the light guide plate 2, and the light leaked from the light guide plate 2 is reflected from the prism sheet 11. It has a function of reflecting the reflected light in the front direction (upward in the figure).

  Next, details of the prism sheet 11 according to the present invention will be described.

  The prism sheet 11 has a function of making the in-plane luminance distribution of the light emitted from the backlight unit 13 uniform and improving the front luminance. The prism sheet 11 is formed in an inverted prism shape, and is disposed so as to face the prism structure surface toward the light emitting surface 2 a side of the light guide plate 2.

  FIG. 2 is an enlarged cross-sectional view of the prism sheet 11. The prism sheet 11 is made of a light transmission film in which a plurality of prisms 11P having a constant apex angle θ are continuously arranged in one direction on the lower surface side serving as a light incident surface. When applied to the edge-light type backlight unit 13 as in the present embodiment, the prisms 11P are set in a direction in which the arrangement direction intersects with the axial direction of the linear light sources 15 (orthogonal in this example). The

  One inclined surface portion 11a located on the light source side of the pair of prism inclined surfaces constituting the prism 11P is formed as an incident portion of light emitted from the light emitting surface 2a of the light guide plate 2. The other inclined surface portion 11b is formed as a total reflection surface that raises the light incident on one inclined surface portion 11a in the vertical direction.

  The inclined surface portion 11b is formed in a common size (inclined length) in each lens element 11P, but the inclined surface portion 11a is formed in a different size (inclined length) in each portion. Each inclined surface portion 11a is formed with a vertical surface portion 11c extending toward the base portion 11d of another adjacent prism (left prism in the drawing).

  The vertical surface portion 11c corresponds to the “continuous portion” of the present invention, and in the present embodiment, the vertical surface portion 11c is formed in a direction perpendicular to the sheet surface of the prism sheet. It may be.

  Each prism 11P is formed at the same height, and the arrangement pitch (distance between the prism tops) is different at each part as indicated by P1 to P5 in FIG. The sizes of P1 to P5 are greatly related to the formation height of the vertical wall portion 11c (or the inclined surface portion 11a) of each prism 11P. The higher the vertical wall portion 11c is, the wider the arrangement pitch is. The lower the pitch, the narrower the array pitch. Therefore, the arrangement pitch is irregularly changed by making the formation heights of the vertical surface portions 11c different between the prisms 11P.

  In this way, by forming one prism side surface of each prism 11P with two different surfaces, the inclined surface portion 11a and the vertical surface portion 11b, for example, the distance between the prisms can be arbitrarily changed simply by changing the formation height of the vertical surface portion 11c. It becomes possible. As a result, the prism structure surface can be formed at an arbitrary arrangement pitch and the periodicity can be destroyed simply by adjusting the formation height of the vertical surface portion 11c in each portion, so that the occurrence of moire can be effectively suppressed. Become.

  The prism 11P provided with the vertical surface portion 11c is not limited to being applied to all the prisms constituting the prism structure surface, and may be applied to some prisms. Note that the arrangement pitch of the prisms 11P may be changed between adjacent prisms individually, or a certain area including a plurality of prisms 11P is used as a unit so that a moire suppressing effect can be obtained, and the arrangement pitch for each unit. May be changed.

  Next, the optimum range of the prism arrangement pitch will be described with reference to FIG. FIG. 3 shows the relationship between a conventional prism sheet 1 having an inverted prism shape and a light guide plate 2. The role of the prism 1P varies depending on the region, and is divided into three regions, a light incident region R1, a total reflection region R2, and a light non-incident region R3. The light incident region R1 is a region where light L emitted from the light emitting surface 2a of the light guide plate 2 at an angle α is incident. The incident light is totally reflected by the total reflection region R2 and raised in the vertical direction. Contributes to improved brightness. The light non-incident region R3 is a region where the light L emitted at an angle α cannot reach to enter the shadow of another adjacent prism 1P.

  Therefore, even if the shape of the other light non-incident region R3 is changed to a vertical plane, the light collecting action in the front direction can be maintained. In addition, with the change in the shape of the light non-incident region R3, the inter-prism distance can be adjusted while the apex angle θ is constant. The adjustment range of the arrangement pitch P at this time is represented by the following formula.

  In the above equation, H is the prism formation height, θ is the prism apex angle, and αmax is the maximum light output angle with respect to the light output surface of the light guide plate. For example, when H = 48 μm, θ = 63 °, and αmax = 35 °, the optimum range of the arrangement pitch P is 42 μm or more and 59 μm or less. The arrangement pitches P1 to P5 of each part of the prism 11P shown in FIG. 2 are formed so as to satisfy the above range.

  Here, the maximum value of the arrangement pitch P indicates when the formation length of the vertical surface portion 11c is zero in FIG. Further, the minimum value of the arrangement pitch indicates the maximum height of the vertical surface portion 11c at which light emitted at an angle of αmax does not enter the vertical surface portion 11c. When the arrangement pitch P becomes narrower than this, as in the example of formation with the under-pitch P ′ schematically shown in FIG. 4, as a result of a part of the incident light entering the vertical surface portion 11c, one light rises in the vertical direction. It is not preferable because it cannot be increased and the front luminance decreases.

  The prism sheet 11 is formed of a transparent film or sheet made of, for example, polycarbonate, polyvinyl, acrylic resin, polyamide, polyethylene terephthalate, poly α-olefin, fiber base resin, glass or the like having optical transparency. Each prism 11P is integrally formed on the surface of these transparent films. Or you may integrate the layer in which the prism 11P was formed on these transparent films at a post process. The method for forming the prism sheet 11 is not particularly limited, and for example, mold forming by hot pressing, mold forming using an ultraviolet curable resin, or the like can be performed.

  As described above, in the prism sheet 11 of the present embodiment, the prism surface is formed so that the vertical surface portions 11c are formed at different heights between the adjacent prisms 11P. Can be changed irregularly. Accordingly, it is possible to effectively suppress the occurrence of moire due to optical periodicity between the prism sheet and the liquid crystal display panel 16 while maintaining the light condensing property and suppressing the decrease in front luminance.

  Further, according to the present embodiment, since the formation height of each prism 11P can be made constant in a state where the arrangement pitch is irregularly changed, the in-plane luminance distribution can be made uniform at the same time. .

  5 shows a prism sheet 1 (A) having a conventional structure shown in FIG. 6, a prism sheet 5 (B) having a conventional structure shown in FIG. 7, and a prism sheet 11 (C) of the present embodiment shown in FIG. It is the experimental result which measured the luminance distribution characteristic about each of these.

  Like the prism sheet 1 having a prism structure having a constant pitch and a constant height shown in FIG. 5A, light is basically reflected on the upper surface of the total reflection region (R2 in FIG. 3) by the total reflection action at the prism portion. The intensity is the strongest, and the luminance is weak at the upper surfaces of the light non-incident region and the light incident region (R1, R3 in FIG. 3). However, since the prism sheet having the structure has periodicity in luminance distribution, moire occurs when the liquid crystal display panels are stacked.

  On the other hand, in the prism sheet 5 having the prism structure with the indefinite pitch and the indefinite height shown in FIG. 5B, the periodicity of the luminance distribution is broken, so that moire is hardly generated, but the light intensity in each place is uneven. It is not preferable.

  On the other hand, in the prism sheet 11 of the present embodiment having the prism structure with an indefinite pitch and a constant height shown in FIG. 5C, the periodicity of the luminance distribution is broken and the light intensity at each location is also reduced. Unevenness is suppressed. That is, according to the present embodiment, it is possible to make it difficult for moire to occur, and at the same time, it is possible to suppress a reduction in uniformity of in-plane luminance.

  Therefore, according to the present embodiment, for example, it is not necessary to provide a diffusion layer such as a light diffusion sheet on the light exit surface side of the prism sheet 11, and even if necessary, the thickness of the diffusion layer can be reduced. . As a result, the intensity of light incident on the liquid crystal display panel 16 can be increased, so that the luminance characteristics can be further improved.

1 is an exploded side view showing a schematic configuration of a liquid crystal display device 10 according to an embodiment of the present invention. It is principal part sectional drawing of the prism sheet 11 by embodiment of this invention. It is a figure explaining the condensing principle of the prism sheet 1 of the conventional structure. It is a figure explaining the example in which the prism arrangement pitch is inappropriate in the prism sheet. It is a figure which shows the luminance distribution characteristic of the prism sheets 1 and 5 of conventional structure, and the prism sheet 11 of embodiment of this invention. It is a schematic side view which shows the example of 1 structure of the conventional prism sheet. It is a schematic side view which shows the structure of the backlight unit provided with the other conventional prism sheet.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Light guide plate, 2a ... Light emission surface, 10 ... Liquid crystal display device, 11 ... Prism sheet (light transmission film), 11a ... Inclined surface part, 11c ... Vertical surface part (continuous surface part), 11d ... Base part, 11P ... Prism, DESCRIPTION OF SYMBOLS 12 ... Backlight apparatus, 13 ... Backlight unit, 14 ... Reflector, 15 ... Linear light source, 16 ... Liquid crystal display panel, L ... Light, P ... Prism arrangement pitch, R1 ... Light incident area, R2 ... Total reflection Region, R3 ... light non-incident region, α ... light emission angle from the light guide plate, θ ... apex angle of the prism

Claims (3)

A light incident surface in which a plurality of prisms having a constant apex angle are continuously arranged in one direction ;
A light exit surface opposite to the light incident surface,
At least a portion or all of a first inclined surface which is a light incident portion, a second inclined surface to totally reflect the light incident on the first inclined surface on the light emitting surface side of the plurality of prisms And a vertical surface portion formed in a light non-incident region extending from the first inclined surface portion toward the base of another adjacent prism ,
The plurality of prisms are formed at the same height, and have a different arrangement pitch according to the formation height of the vertical surface portion . A light guide plate made of a translucent material;
A light source arranged at one end of the light guide plate,
A plurality of prisms having a constant apex angle are arranged continuously in one direction, have a light incident surface on which light emitted from the light guide plate is incident, and a light output surface opposite to the light incident surface. A light transmissive film disposed on the light exit surface side of the light plate ,
At least a portion or all of a first inclined surface which is a light incident portion, a second inclined surface to totally reflect the light incident on the first inclined surface on the light emitting surface side of the plurality of prisms And a vertical surface portion formed in a light non-incident region extending from the first inclined surface portion toward the base of another adjacent prism ,
The plurality of prisms are each formed at the same height, and have a different arrangement pitch according to the formation height of the vertical surface portion . A liquid crystal display panel ;
A light guide plate made of a translucent material;
A light source arranged at one end of the light guide plate,
A plurality of prisms having a constant apex angle are arranged continuously in one direction, have a light incident surface on which light emitted from the light guide plate is incident, and a light output surface opposite to the light incident surface. A light transmissive film disposed on the light exit surface side of the light plate,

At least a portion or all of a first inclined surface which is a light incident portion, a second inclined surface to totally reflect the light incident on the first inclined surface on the light emitting surface side of the plurality of prisms And a vertical surface portion formed in a light non-incident region extending from the first inclined surface portion toward the base of another adjacent prism ,
The plurality of prisms are each formed at the same height, and have a different arrangement pitch depending on the formation height of the vertical surface portion .

Images