JP5625261B2 - Optical sheet for brightness enhancement - Google Patents

Description

  The present invention relates to an optical sheet used for controlling a backlight illumination optical path for illuminating a transmissive liquid crystal display panel, which is mainly a liquid crystal display element, from the back surface, a backlight unit for a display equipped with the optical sheet, and The present invention relates to an image display.

  In recent years, liquid crystal display devices using TFT-type liquid crystal panels and STN-type liquid crystal panels have been commercialized mainly for color notebook PCs in the OA field.

  Such a liquid crystal display device employs a so-called backlight method in which a light source is disposed on the back side of the liquid crystal panel and the liquid crystal panel is illuminated with light from the light source.

  There are roughly two types of backlight units employed in this type of backlight system. “Light guide plate light guide method”, which is often referred to as the edge light style, and which makes multiple reflections of a light source lamp such as a cold cathode tube within a flat light guide plate made of acrylic resin or the like having excellent light transmittance, and does not use a light guide plate There is "direct type".

  As a liquid crystal display device on which a light guide plate light guide type backlight unit is mounted, for example, the one shown in FIG. 9 is generally known.

  In this, a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 is provided at the top, and a light guide plate 79 made of a transparent base material such as polymethyl methacrylate or acrylic having a substantially rectangular plate shape is provided on the lower surface side thereof. A diffusion film 78 is provided on the light exit side of the light guide plate.

  Further, a scattering reflection pattern portion for efficiently scattering and reflecting the light introduced into the light guide plate 79 in the direction of the liquid crystal panel 72 is provided on the lower surface of the light guide plate 79 by printing or the like. A reflection film 77 is provided below the scattering reflection pattern portion (not shown).

  Further, the light guide plate 79 is provided with a light source lamp 76 at the side end, and further covers the back side of the light source lamp 76 so that the light from the light source lamp 76 can be efficiently incident on the light guide plate 79. Thus, a high-reflectance lamp reflector 81 is provided. The scattering reflection pattern portion is formed by printing a mixture of white titanium dioxide 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 in the light guide plate 79. This is a device for imparting directivity to the incident light and guiding it to the light exit surface side to increase the luminance.

  Furthermore, recently, in order to increase the light use efficiency and increase the brightness, prism films 74 and 75 having a light condensing function between the diffusion film 78 and the liquid crystal panel 72 as shown in FIG. Has been proposed. The prism films 74 and 75 are configured to collect light emitted from the light exit surface of the light guide plate 79 and diffused by the diffusion film 78 on the effective display area of the liquid crystal panel 72 with high efficiency.

However, in the apparatus illustrated in FIG. 9, the control of the viewing angle is left only to the diffusibility of the diffusion film 78, which is difficult to control, and the center in the front direction of the display is bright and becomes darker toward the periphery. This characteristic is inevitable. For this reason, when the liquid crystal screen is viewed from the side, the luminance is greatly reduced, and the light utilization efficiency is reduced.
Furthermore, in the apparatus using the prism film illustrated in FIG. 10, two prism films are required, which not only greatly reduces the amount of light due to the absorption of the film but also increases the cost due to the increase in the number of members. It was also.

  On the other hand, in the direct type, a display device such as a large liquid crystal TV in which the light guide plate is difficult to use is used.

  As a direct liquid crystal display device, a device illustrated in FIG. 11 is generally known. In this, a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 is provided on the upper side, and is emitted from a light source 51 made of a fluorescent tube or the like on the lower surface side thereof and diffused by an optical sheet such as a diffusion film 82. The light is condensed on the effective display area of the liquid crystal panel 72 with high efficiency. In order to efficiently use the light from the light source 51 as illumination light, a reflector 52 is disposed on the back surface of the light source 51.

  However, even in the apparatus illustrated in FIG. 11, the control of the viewing angle is entrusted only to the diffusibility of the diffusion film 82, and it is difficult to control the viewing angle, the central portion in the front direction of the display is bright, and the darker toward the peripheral portion. This characteristic is inevitable. For this reason, when the liquid crystal screen is viewed from the side, the luminance is greatly reduced, and the light utilization efficiency is reduced. Furthermore, in the case of using a prism film, since the number of prism films is two, not only the light amount is greatly decreased due to absorption of the film but also the cost is increased due to an increase in the number of members.

  If the distance between the light sources 51 is too wide, uneven brightness tends to occur on the screen, and the number of light sources 51 cannot be reduced, leading to an increase in power consumption and an increase in cost.

  By the way, in such a liquid crystal display device, light weight, low power consumption, high luminance, and thinning are strongly demanded as market needs, and accordingly, a backlight unit mounted on the liquid crystal display device is also included. Light weight, low power consumption, and high brightness are required.

  In particular, in color liquid crystal display devices that have recently made remarkable progress, the panel transmittance of the liquid crystal panel is much lower than that of a monochrome-compatible liquid crystal panel. It is essential to obtain low power consumption.

  However, as described above, it is difficult to say that the conventional device sufficiently satisfies the demand for high luminance and low power consumption, and the user has low price, high luminance, high display quality, and low power consumption. The development of a backlight unit capable of realizing a power liquid crystal display device is awaited.

JP 2007-256575 A Japanese Patent Application No. 2008-125670 Special table 2008-515026 gazette

In recent years, attempts have been made to realize the functions of a plurality of optical sheets used in a backlight unit with a smaller number of optical sheets. For this reason, development of optical sheets having both light collecting and diffusing functions has been actively conducted. However, many of the optical sheets with such functions have a precise and fine microstructure on the surface, and since they are placed on top of each other, the optical sheet surface is caused by friction caused by vibration or impact. There is a problem that the scratches (hereinafter referred to as wear marks) are likely to occur, and the display quality deteriorates accordingly.
In order to prevent the occurrence of such wear marks, it is possible to use a method of coating the surface with a highly scratch-resistant material, but there are problems of light loss, cost increase, warpage, etc. due to the coating layer. As a result, a complete solution has not been reached.

  An object of the present invention is to provide an optical sheet for improving brightness which is advantageous in improving scratch resistance without coating the surface of the optical sheet.

As a means for solving the above-mentioned problems, the invention according to claim 1 is such that a large number of fine first convex lenses extending in one direction are arranged in parallel on one side of a translucent substrate. A second lens comprising a first lens array, wherein a plurality of fine second convex lenses extending in a direction intersecting the extending direction of the first convex lens are arranged in parallel on the top of each first convex lens. An optical sheet in which an array is formed, each first convex lens of the first lens array has a trapezoidal prism shape, and a lens cross section of the second convex lens perpendicular to the extending direction of each second convex lens, The two corners on the lens surface of each second convex lens in the lens cross section perpendicular to the extending direction of each second convex lens , and the corners located at both ends of the upper base are rounded trapezoidal The acute angles formed with the substrate are θ1 and 2 and the positions of the lens surface portion where θ1 and θ2 are 40 ° are A and B, respectively, the entire region on the lens tip side including A and B is referred to as the lens top portion, and A and B Is the width of the lens top, the length of the width of the lens top is 5 % or more and 30% or less of the linear distance connecting both ends of the lens in the lens cross section. An optical sheet characterized by the above.
However, when there are a plurality of lens surface portions where θ ₁ and θ ₂ are 40 °, positions A and B are closest to the lens apex portion among them.
Moreover, the example of a shape of each 2nd convex lens in the lens cross section perpendicular | vertical to the extending direction of a 2nd convex lens is shown in FIG.

The invention according to claim 2 is the optical sheet according to claim 1 , wherein the other surface of the substrate is configured by a substantially flat portion and a plurality of protrusions protruding from the flat portion. An optical sheet characterized by the above.

The invention described in claim 3 is a backlight unit for display and an image display display on which the optical sheet according to claim 1 is mounted.

  The surface of the optical sheet is scratched when the lens tip is scraped or crushed by friction. Therefore, in the present invention, the occurrence of scratches is prevented by providing a substantially flat portion of a certain level or more at the tip of the lens, and deterioration of display quality due to wear marks is suppressed.

It is explanatory drawing by the cross-sectional shape example of the optical sheet which is embodiment of this invention. (a), (b) is sectional drawing which shows the example of a shape of the optical sheet which is embodiment of this invention. (a), (b) is sectional drawing which shows the example of a shape of the optical sheet which is embodiment of this invention. (a), (b), (c) is sectional drawing which shows the example of a shape of the optical sheet which is embodiment of this invention. (a), (b), (c) is sectional drawing which shows the example of a shape of the optical sheet which is embodiment of this invention. (a), (b), (c) is sectional drawing which shows the example of a shape of the optical sheet which is embodiment of this invention. (a) It is a perspective view which shows the example of a shape of the optical sheet which is embodiment of this invention. (b) It is sectional drawing which shows the example of a shape of the optical sheet which is embodiment of this invention. It is explanatory drawing of the type | mold of the optical sheet which is embodiment of this invention. It is explanatory drawing which shows the structural example of the liquid crystal display device by a prior art. It is explanatory drawing which shows the structural example of the liquid crystal display device by a prior art. It is explanatory drawing which shows the structural example of the liquid crystal display device by a prior art. It is explanatory drawing which shows the cross section of the backlight structural example using the optical sheet of this invention.

FIG. 7A shows a shape example of the present invention when the first lens array 2 has a trapezoidal prism shape and the second lens array 3 has a triangular prism shape.
The optical sheet includes a translucent substrate 4, a first lens array 2, and a second lens array 3.
The first lens array 2 is configured by arranging a large number of fine first convex lenses 2 </ b> A extending in one direction in parallel on one side of a translucent substrate 4.
The second lens array 3 includes a large number of fine second convex lenses 3A extending in the direction intersecting the extending direction of the first convex lens 2A (the direction orthogonal to the present embodiment) at the top of each first convex lens 2A. Are arranged in parallel.
The first convex lens 2A is a trapezoidal prism, and the second convex lens 3A is a triangular prism. Therefore, a triangular prism is formed on the top of the trapezoidal prism. When the lens formed on the optical sheet is unidirectional, a light collecting effect can be obtained only on the lens arrangement direction side. Therefore, there are a narrow direction and a wide direction of the visual field.
FIG. 7B is a diagram illustrating a planar view of a cross-sectional shape of the optical sheet illustrated in FIG. That is, FIG. 7B shows the shape of the second convex lens 3A in the lens cross section perpendicular to the extending direction of the second convex lens 3A.

As an example, when the first convex lens 2A constituting the second lens array 3 has a semi-elliptical prism shape, a plan view of the cross-sectional shape in the plane P is as shown in FIG. In Figure 1, the length of the width of the lens top portions at w _1, the linear distance connecting the lens opposite ends (width of the second convex lens 3A) wrote in w _2.
That is, the invention according to claim 1 can be rephrased as an optical sheet characterized in that w ₁ is 3% or more of w ₂ and 30% or less.

An optical sheet wherein w ₁ is 30% of said w _2, compared with the optical sheet wherein w ₁ is 3% of said w _2, is observed decrease in 5% or more of brightness. Therefore, although the optical sheet of the present invention is advantageous for scratch resistance larger the value of basically the w _1, it is preferable that the w ₁ from the viewpoint of the luminance does not exceed 30% of the w ₂ .

The optical sheet of the present invention can achieve the same effect even when the second convex lens 3A constituting the second lens array has various other shapes.
FIGS. 2 to 6 show a plan view of the cross-sectional shape of the second convex lens 3A on the plane P. FIG.

  The direction in which the first convex lens 2A extends and the direction in which the second convex lens 3A extends are preferably approximately 90 °.

The optical sheet may have fine unevenness on the surface, and the surface may have light diffusibility. Here, examples of the fine unevenness include a convex cylindrical shape, a lens shape, and a triangular prism shape, but are not limited thereto, and the light diffusion function is compared before the fine unevenness is given. However, the shape is not limited to the above as long as the shape is improved.
In addition, fine irregularities can improve appearance characteristics such as optical adhesion, unevenness, and Newton rings.

  The optical sheet may have a multilayer structure or may include a transparent layer.

  The optical sheet of the present invention depends on the surface shape, and the thickness of the optical sheet is not particularly limited.

The optical sheet of the present invention includes polycarbonate resin, polystyrene resin, acrylic resin, fluorine-based acrylic resin, epoxy acrylate resin, methylstyrene resin, fluorene resin, cycloolefin polymer, polyethylene terephthalate, polypropylene, acrylic-styrene copolymer, styrene. -It is effective in various commonly used materials such as a butadiene-acrylonitrile copolymer.
It is also possible to have transparent particles dispersed in the main material.

As an example of the production method of the optical sheet of the present invention, a mold for producing the optical sheet 6 as shown in FIG. 8 is prepared, and the mold is produced by inverting the mold so that the optical sheet 1 of the present invention is produced. There is a technique for producing (the shape shown in FIG. 7). The first lens array mold part 7 in FIG. 8 forms the first lens array 2, and the second lens array mold part 8 forms the second lens array 3.
If an optical sheet having the same surface shape can be finally produced, the production means is not particularly limited.

FIG. 12 shows a cross section of a backlight configuration example using the optical sheet of the present invention.
Light K from the light source 15 enters the diffusion plate 5 directly or after being reflected by the reflection plate 17. Thereafter, the light reaches the entrance surface of the optical sheet 1 from the exit surface of the diffusion plate 5. Finally, the light is emitted as L from the emission surface of the optical sheet 1. L reaches the liquid crystal layer 19 sandwiched between the polarizing plates 21. The light transmitted through here is emitted to S and is visually recognized by an observer. Note that the number of optical sheets to be used may be increased as appropriate.
In the drawing, the diffusion plate 5, the optical sheet 1, and the polarizing plate 21 are drawn apart for convenience in order to make the configuration easy to understand, but actually, the diffusion plate 5, the optical sheet 1, and the polarizing plate are drawn. 21 is arranged so as to overlap.

  The backlight unit using the optical sheet of the present invention may be a direct type or a light guide plate light guide type.

  As the light source of the backlight unit, various light sources such as CCFL, LED, organic or inorganic EL can be used.

  The optical sheet produced as described above has high scratch resistance compared to conventional optical sheets, and even when used on the panel-side outermost surface, generation of wear marks can be suppressed. When used in a backlight unit, a display having a desired display performance can be provided by using the optical sheet of the present invention in combination with various optical members such as commercially available diffusion plates.

[Example 1]
(Evaluation method of wear marks)
A 46-inch flat-screen LCD TV with a diffuser plate and optical sheet cut into a size of 1045 mm x 596 mm installed in a housing is stored in a packing box, and the packing box is set up so that the TV stands upright at room temperature. Vibrating for 60 minutes each in three directions, up and down, left and right, and front and back. As vibration conditions at that time, the frequency is 5 to 50 Hz and the amplitude is 0.2 to 19.8 mm.
Immediately after the end of vibration, the optical sheet was taken out from the television case, and the presence or absence of wear marks on the lens surface of the optical sheet 1 due to friction with the polarizing plate 21 was confirmed visually and with a laser microscope.

[Example 2]
(Verification of lens head length)
Using the lens top portion length w ₁ is different from a number of optical sheet width, was examined scratch resistance differences of the lens surface due to the difference w _1.
When the investigation of wear scar using the above evaluation method, the lens with respect to the straight line distance w ₂ connecting lens both ends in cross-section, wherein w ₁ is intense wear scar when 2% or less is checked, at least 3% Occasionally, the generation of wear marks was suppressed, and when it was 5% or more, no wear marks were generated.
Thus, is judge that improves the scratch resistance when w ₁ is at least w ₂ of 3% or more, and further remarkably improved scratch resistance when w ₁ is at least w ₂ of less than 5% I found out that

DESCRIPTION OF SYMBOLS 1 ... Optical sheet of this invention 2 ... 1st lens array 3 ... 2nd lens array 4 ... Base material 5 ... Diffusing plate 6 ... Optical sheet 7 ... 1st lens Array mold part 8 ... Second lens array mold part 15 ... Light source 17 ... Reflector 19 ... Liquid crystal layer 21 ... Polarizing plate 51 ... Light source 52 ... Reflector 71 ... -Polarizing plate 72 ... Liquid crystal panel 73 ... Polarizing plate 74 ... Prism 75 ... Prism 76 ... Light source 77 ... Reflective film 78 ... Diffusing film 79 ... Light guide plate 81 ..Reflector plate K: Light from light source L: Light emitted from optical member S: Visual direction of display

Claims (3)

Provided on one side of the translucent substrate is a first lens array in which a large number of fine first convex lenses extending in one direction are arranged in parallel, on the top of each first convex lens, An optical sheet formed with a second lens array in which a plurality of fine second convex lenses extending in a direction intersecting the extending direction of the convex lenses are arranged in parallel,
Each first convex lens of the first lens array has a trapezoidal prism shape,
The lens cross section of the second convex lens perpendicular to the extending direction of each second convex lens has a substantially trapezoidal shape with rounded corners located at both ends of the upper base,
The acute angles formed by two tangents on the lens surface of each second convex lens and the base material in the lens cross section perpendicular to the extending direction of each second convex lens are θ1 and θ2, respectively, and θ1 and θ2 are 40 °. Where A and B are the positions of the lens surface portion, and the entire region on the lens tip side including A and B is called the lens top portion, and the linear distance connecting A and B is the width of the lens top portion. If we call it
An optical sheet, wherein a width of the lens top is 5 % or more and 30% or less of a linear distance connecting both ends of the lens in the lens cross section. 2. The optical sheet according to claim 1 , wherein the other surface of the base member includes a substantially flat portion and a plurality of protrusions protruding from the flat portion. Backlight unit and an image display displaying for display equipped with the optical sheet according to claim 1 or 2.

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