JP2009180970A - Optical member, backlight unit, and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical member, a backlight unit and a display device, capable of observing visually a defect observable visually through a liquid crystal panel when a backlight turned on, clearly by the optical member only, and capable of evading the defect from flowing into a following process, even when the defect affecting image quality is generated. <P>SOLUTION: In the optical member, a light emission face of a light diffusion sheet 9 is joined with a light incident face of an optical sheet 10 via an adhesive layer 16. The adhesive layer 16 has performance capable of observing visually the defect of 0.05 mm<SP>2</SP>clearly on a light emission face of the optical sheet 10, when irradiating a light incident face of the light diffusion sheet 9 with light, has the maximum value of a loss factor tanδ, that is a ratio of a storage shear modulus to a loss shear modulus, within a value of 1.2 or more to 1.7 or less in a range of -20°C or more to -10°C or less, and has a loss factor of 0.2 or more and less than 1.7 at an ambient temperature. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical member used for illumination light path control, a backlight unit using the same, and a display device, and more particularly to a direct backlight unit for a display using a liquid crystal display element and illumination light path control for the display device. The present invention relates to an improvement in the material of an optical member.

  In recent years, liquid crystal display devices (LCDs) using liquid crystal panels have been used for image display means for notebook personal computers and personal computer displays in the OA field, information terminal equipment, etc., information display means for information appliances such as large-screen TVs, and more. Has been used in various fields as an image display means of a mobile phone or a personal digital assistant (PDA).

In a display typified by a liquid crystal display device (LCD), a type having a built-in light source necessary for recognizing information to be provided has been widespread. Such a liquid crystal display device is a transmissive type, and a light source is provided on the back side of the liquid crystal panel, and 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 is provided. It has been adopted.
The backlight system is roughly divided by attaching a light source such as a cold cathode fluorescent tube (CCFT) along the side edge of a flat light guide plate made of acrylic resin or the like having excellent light transmittance. There are a light guide plate light guide method (edge light method) that multi-reflects light from the light guide plate and a direct type method in which a light source is arranged on the back surface of the liquid crystal panel without using the light guide plate.

Recently, for small liquid crystal display devices with a screen size of 20 inches or less used for notebook personal computers, personal digital assistants, etc., it has become mainstream to adopt an edge light system that can reduce power consumption and can be easily thinned. In medium to large liquid crystal display devices having a screen size of 20 inches or more, the direct type is the mainstream. In a battery-powered device such as a laptop computer, the power consumed by the light source occupies a substantial portion of the power consumed by the entire battery-powered device.
Thus, reducing the total power required to provide a given brightness increases battery life, which is particularly desirable for battery powered devices.
Liquid crystal display devices of 20 inches or more are required to be thinner, have a low viewing angle dependency, have high brightness, and have low power consumption. There is a need to deal with realization.

In direct-type backlights with multiple cold-cathode tubes in parallel, the shape of the emitted light source is directly visible through the diffuser plate that diffuses the emitted light, such as CCFT and LED (Light Emitting Diode) as the light source. Therefore, a resin plate having a very strong light scattering property is used as the diffusion plate. This diffuser plate usually requires a thickness of about 1 mm to 3 mm in order to give strong diffusibility, and because of the thickness, there is not a little light absorption, the light quantity from the light source is reduced, and the liquid crystal display is displayed. There is a problem of darkening.
In order to solve this problem, the optical sheet having the optical path control function and the light diffusing plate are integrated through an adhesive layer having a two-layer structure, thereby making the CCFT lamp image unclear and wide in the horizontal direction. Optical members that provide high front luminance at an angle have been developed (see Patent Documents 1 to 3).

As shown in FIGS. 1 and 2, the integrated optical member described above includes a light diffusing plate 29 located on the light incident side and an optical sheet 30 located on the light emitting side. The optical sheet 30 is integrally bonded by a composite adhesive layer 31.
The optical sheet 30 includes a sheet-like or thin plate-like transparent base material 22, a semi-cylindrical lens 21 arranged in parallel on one surface of the base material 22, and an anti-lens surface of the base material 22 in parallel. A high-refractive index layer 24 and a low-refractive index layer 25 having light reflectivity formed in a stripe shape. Among these, the low refractive index layer 25 is provided on the condensing region of the semi-cylindrical lens 21 on the other surface of the base material 22, and the high refractive index layer 24 is formed on the other surface of the base material 22 on the semi-cylindrical lens 21. It is provided in the non-condensing region. The composite adhesive layer 31 includes a first adhesive or adhesive layer 26, a second adhesive or adhesive layer 8, and a transparent film 27.

When the display is used (observed), the optical member makes the lamp image of the light source unclear by making the light 33 emitted from the light source 32 uniform by the light diffusion plate 29, as shown in FIG. Only the light 34 traveling in the direction of being condensed in the front direction by the columnar lens 21 passes through the low refractive index layer 25 and contributes to the front luminance.
Further, the light 33 spreads when passing through the semi-cylindrical lens 21, and the light 35 diffused in a useless direction is a high refractive index layer having light reflectivity provided in parallel with the low refractive index layer 25. 24 is returned to the light source side, and again proceeds toward the light exit surface by the reflector in the lamp house.
By repeating such light reflection, the light 33 emitted from the light source 32 is involved in the front brightness without being wasted, so that a high front brightness is realized.
Further, by controlling the arrangement balance between the high refractive index layer 24 and the low refractive index layer 25 having a lens shape and light reflectivity, it is possible to maintain a gradual change in luminance distribution in a wide range in the horizontal direction. A more natural display can be realized.
Further, since it is not necessary to use a diffusion sheet and a brightness enhancement sheet that are conventionally used for improving the brightness of the liquid crystal display, the workability and convenience during the assembly of the display can be improved.
006/080530 in WO JP2007-213035 JP2007-228553

An optical member that integrates an optical sheet having a light path control function and a light diffusing plate as a brightness enhancement member for large and thin displays that have been actively developed in recent years is advantageous from the viewpoint of optical characteristics and handling properties. is there.
However, since the optical sheet has a structure in which the light reflecting layer and the air layer are arranged in parallel, or is integrated through an adhesive layer or an adhesive layer, light leaks in an unintended direction due to a minute missing of the reflecting layer. There is a possibility that light emission obstruction (dark spot defect) may occur due to (bright spot defect) or contamination with foreign matter.

When the size of the defect is small, there is a risk of being overlooked at the time of shipping inspection. In particular, the dark spot defect is often visible from the front through the liquid crystal panel when used as a display, and the defect outflow is the final product (display device ) Will have a fatal effect.
In addition, as the display device becomes thinner, the distance between the liquid crystal panel and the backlight unit tends to approach, so the lower limit of the defect size that can be seen through the panel is expected to decrease, and if a defect occurs Therefore, it is essential to prevent outflow to the subsequent process.

  The present invention has been made in view of the circumstances as described above, and defects that can be visually observed through the liquid crystal panel when the backlight is turned on can be clearly observed with an optical member alone, and defects that affect image quality occur. It is an object of the present invention to provide an optical member having an optical path control function capable of avoiding outflow to a subsequent process, a backlight unit using the same, and a display device.

The present invention has been made to achieve the above object, and the invention of claim 1 has an optical path control function for controlling at least one of a direction, a range, and a luminance distribution when emitting incident light. An optical member, comprising: a light diffusion sheet; an optical sheet having the optical path control function; and an adhesive layer that joins a light emitting surface of the light diffusion sheet and a light incident surface of the optical sheet. When the light incident surface of the joined light diffusion sheet is irradiated with light, a 0.05 mm ² defect can be clearly visually observed on the light emitting surface of the joined optical sheet. And the maximum value of the loss coefficient tanδ, which is the ratio between the storage shear modulus and the loss shear modulus, is 1.2 to 1.7 in the range of −20 ° C. to −10 ° C. Furthermore, the loss factor at room temperature is 0.2 or more and 1 And less than 7.

According to a second aspect of the present invention, in the optical member of the first aspect, the thickness of the adhesive layer is 10 μm or more and less than 30 μm.
According to a third aspect of the present invention, in the optical member according to the first aspect, the adhesive layer maintains adhesiveness in a range of −40 ° C. or higher and 90 ° C. or lower.

According to a fourth aspect of the present invention, in the optical member according to any one of the first to third aspects, the adhesive layer is made of a clear type adhesive having no light diffusibility.
According to a fifth aspect of the present invention, in the optical member according to any one of the first to third aspects, the adhesive layer is made of an adhesive having light diffusibility.
According to a sixth aspect of the present invention, in the optical member according to any one of the first to fifth aspects, the adhesive layer includes a light emitting surface of the bonded light diffusion sheet and a light incident surface of the optical sheet. The central portion is configured not to warp in a convex shape toward the light exit surface of the optical sheet when heated.

  The invention according to claim 7 is the optical member according to claim 1, wherein the optical sheet includes a sheet-like or thin plate-like transparent base material, and a semi-cylindrical convex lens group provided on one surface of the base material or A lens sheet having a lens portion composed of a convex cylindrical lens group, and a high refractive index layer and a low refractive index layer having light reflectivity provided on the other surface of the substrate, wherein the low refractive index layer is the other The high refractive index layer is provided in the non-condensing region of the lens portion on the other surface.

  The invention according to claim 8 is a backlight unit for display, and includes at least the light source and the optical member according to any one of claims 1 to 7.

  The invention according to claim 9 is a display device, wherein an image display element that defines a display image according to transmission / light shielding in pixel units, and the backlight unit according to claim 7 on the back surface of the image display element. It is characterized by providing.

In the optical member of the present invention, the backlight unit using the same, and the display device, the light incident on the light diffusion sheet bonded to the adhesive layer that bonds the light emitting surface of the light diffusing sheet and the light incident surface of the optical sheet. When the surface is irradiated with light, it has a performance that allows a defect of 0.05 mm ² to be clearly observed on the light exit surface of the bonded optical sheet, and has a storage shear modulus and a loss shear modulus. The loss factor tanδ, which is the ratio, is present in the range of -20 ° C to -10 ° C in the range of 1.2 to 1.7, and the loss factor at room temperature is 0.2 to less than 1.7 By using the pressure-sensitive adhesive, the defects that affect the image quality of the display device have been generated while maintaining the advantages of the optical properties and handling properties of the integrated brightness enhancement sheet. Avoid spill It is possible.
In the present invention, since a transparent support is not used for the pressure-sensitive adhesive layer, the amount of warping during heating is smaller than that of an integrated brightness enhancement sheet having a two-layer pressure-sensitive adhesive structure with a transparent support interposed therebetween. This makes it suitable for use in thin displays.

(Embodiment 1)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
3 is a schematic cross-sectional view showing an example of an optical member according to the present embodiment, FIG. 4 is a schematic cross-sectional view showing a configuration of a backlight unit using the optical member according to the present invention, and FIG. 5 is a backlight according to the present invention. It is a schematic sectional drawing which shows the structure of the display apparatus using a unit. In each figure, the scale of each part does not coincide with the actual scale.

The optical member shown in the present embodiment includes a light diffusion sheet 9 and an optical sheet 10 having an optical path control function, as shown in FIG. The light emitting surface of the light diffusion sheet 9 and the light incident surface of the optical sheet 10 are joined by an adhesive layer 16.
When the adhesive layer 16 irradiates light on the light incident surface of the bonded light diffusion sheet 9, a 0.05 mm ² defect can be clearly observed on the light emitting surface of the bonded optical sheet 10. It has a certain performance, and the maximum value of the loss coefficient tanδ, which is the ratio between the storage shear modulus and the loss shear modulus, is 1.2 to 1.7 in the range of −20 ° C. to −10 ° C. Furthermore, the loss factor at room temperature is 0.2 or more and less than 1.7. Moreover, this adhesion layer 16 consists of one layer of adhesives, and the thickness is 10 micrometers or more and less than 30 micrometers.

  This is because when the loss coefficient tan δ exceeds the above range, the softness is insufficient and the adhesion is insufficient, and when the loss coefficient tan δ is below the above range, the hardness is insufficient and the air layer (corresponding to a low refractive index layer described later). This is disadvantageous in that it may fill up and cause bright spot defects. In addition, when the thickness of the adhesive layer 16 is less than 10 μm, not only the dark spot defect caused by the foreign matter but also the optical sheet rises when the foreign matter is caught between the light diffusion sheet 9 and the optical sheet 10. There are disadvantages in that there are two points: a point where a bright spot defect occurs and a point where the integrated holding force between the optical sheet 10 and the light diffusion sheet 9 is insufficient. In addition, when the thickness is 30 μm or more, when the optical member according to the present invention is handled alone, the lower limit of the defect size that can be clearly seen becomes large, and the defect that becomes visible through the liquid crystal panel when the display is in operation is later. This is because it is disadvantageous in that it has a risk of flowing into the process.

  On the other hand, when the loss factor is within the above range, the balance between adhesion and air layer retention is satisfied within the practical temperature range, and the thickness is 10 μm or more and less than 30 μm, so that it can be visually observed through the liquid crystal panel when the display is in operation. All size defects are clearly visible, and even if a defect that affects image quality occurs, it is possible to avoid outflow to the subsequent process, and to maintain integration This is advantageous in that the force is sufficient.

  Further, if the adhesive layer 16 is composed of a plurality of adhesive layers via a transparent support as in the prior art, it can be clearly seen due to loss of light or imbedding of defects at the interface between the adhesive layers. Since the lower limit of a certain defect size becomes large and the lamination of different materials, the amount of warpage during heating tends to increase due to the difference in linear expansion coefficient, which is unsuitable for use in thin displays. Since it becomes disadvantageous at a point, it is desirable that the pressure-sensitive adhesive layer 16 has a configuration not using a transparent support.

The adhesive layer 16 is a pressure-sensitive adhesive that maintains adhesiveness at −40 ° C. or higher and 90 ° C. or lower, including the expected operating temperature range of the display device, in consideration of environmental resistance when incorporated and used inside the display device. Was selected.
Further, the adhesive layer 16 may be a clear type adhesive having no light diffusibility, or a light diffusion type adhesive containing a filler or the like.

As shown in FIG. 3, an optical sheet 10 having an optical path control function shown in the present embodiment includes a sheet-like or thin plate-like transparent base material 2 made of polycarbonate (PC), acrylic, polyethylene terephthalate (PET), or the like. In addition, a lens sheet 1 having a lens portion 1a composed of a semi-cylindrical convex lens group or a convex cylindrical lens group formed of thermoplastic or UV curable resin is provided on one surface of the substrate 2.
A light-sensitive material 3 is bonded to the other surface of the substrate 2 opposite to the lens sheet 1, and a light-reflective high refractive index layer 4 and a low refractive index are formed on the surface of the light-sensitive material 3 opposite to the lens sheet 1. The rate layer 5 is arranged in a stripe shape so as to face the lens portion 1a. The high refractive index layer 4 and the low refractive index layer 5 are formed by a transfer method using the fact that the photosensitive material 3 is divided into a cured portion and an uncured portion by irradiating UV from the lens portion 1a side. The low refractive index layer 5 is provided in the condensing region of the lens portion 1a on the other surface of the base material 2, and the high refractive index layer 4 is provided in the non-condensing region of the lens portion 1a on the other surface of the base material 2. ing.
The low refractive index layer 5 consists of a space, and the front luminance can be improved most efficiently by filling the space with air. Further, the shape of the lens portion 1a is not limited to a semi-cylindrical shape.

In the present embodiment, the light diffusing and self-supporting sheet for constituting the optical member, that is, the light diffusing sheet 9 is composed of PC, cycloolefin polymer, acrylic, polystyrene (PS), or these materials in an arbitrary ratio. Examples thereof include a light diffusing plate, a light diffusing plate, and a transparent plate made of the above copolymer.
Moreover, the combination of the materials of the optical sheet 10 and the light diffusion sheet 9 is not limited as long as the optical member is a combination that does not cause a warp that protrudes toward the light emission side (liquid crystal panel side) during heating.
This is because if the optical member exhibits a warping behavior in which the optical member is convex toward the panel side, the liquid crystal panel is pressed, and there is a risk of degrading the image quality and causing damage to the liquid crystal panel.

Next, the configuration of the backlight unit will be described with reference to FIG.
The backlight unit shown in FIG. 4 includes an optical member 100 and a direct light source 110 arranged on the light incident side of the optical member 100.
The optical member 100 is configured in the same manner as the optical member shown in FIG. 3, and the same components as those of the optical member in FIG.
The light source 110 includes a plurality of lamps 17 including cold cathode ray tubes arranged at equal intervals along the light incident surface on the light incident surface side of the light diffusion sheet 9 of the optical member 100, and light from the lamps 17. The lamp house 18 that reflects the light to the light diffusion sheet 9 of the optical member 100 is provided.

In the backlight unit configured as described above, the light emitted from the lamp 17 is made uniform by the light diffusion sheet 9, thereby making the lamp image unclear. Only the light that has traveled in the direction of being condensed in the front direction by the lens unit 1 a passes through the low refractive index layer 5 and contributes to the front luminance.
The light emitted from the lamp 17 spreads when passing through the lens portion 1 a of the optical sheet 10, and the light diffused in a useless direction is a light reflection provided in parallel with the low refractive index layer 5. The light is returned to the light source side by the high refractive index layer 4 having the property, and proceeds again toward the light exit surface of the light diffusion sheet 9 by the reflection surface in the lamp house 18.
By repeating such light reflection, the light emitted from the lamp 17 is involved in the front brightness without being wasted, so that a high front brightness can be realized.
Since such a backlight unit includes the adhesive layer 16 similar to that of the embodiment shown in FIG. 3, the same effect as that shown in FIG. 3 can be exhibited.

Next, the configuration will be described with reference to FIG.
The display device shown in FIG. 5 is disposed so as to face the optical member 100, a backlight unit 120 including a direct light source 110 disposed on the light incident side of the optical member 100, and a light emitting surface of the optical member 100. And a liquid crystal panel 19 (corresponding to the image display element recited in the claims).
Since such a display device includes the adhesive layer 16 similar to that of the embodiment shown in FIG. 3, the same effect as that shown in FIG. 3 can be exhibited.

Next, examples of the present invention will be described.
Example 1
In order to show the effect of the present invention, an optical member having the structure shown in FIG. 3 and a display device having the structure shown in FIG. 5 are prepared, and the lower limit size of the visible defect by the optical member alone and the liquid crystal panel of the display device are passed. We compared the possibility of defect confirmation.
The comparison here is a typical configuration of the optical member according to the present invention, in which an optical sheet 10 formed by lens molding using a photocurable resin and a light diffusing sheet 9 made of PS are combined with an adhesive layer 16. This refers to a comparison of inspection suitability with respect to a defect size depending on the number of layers, thickness, and presence / absence of light diffusibility when an integrated structure is adopted.
In this case, regardless of the type of defect, the defect that is visible through the liquid crystal panel 19 when the backlight is turned on is indicated by a circle when the optical member alone can be accurately screened, and the optical member alone has no defect. In the judged sample, the panel judgment when a defect was confirmed through the liquid crystal panel was represented by x. The determination result at this time is shown in FIG.
In this example, the optical member and the display device were 37 inch size.

  As shown in FIG. 5, the maximum value of the loss factor is 1.2 to 1.7 in the range of −20 ° C. to −10 ° C., and the loss factor at room temperature is 0.2 or more. The adhesive layer 16 made of an adhesive that is less than 1.7 is a configuration that does not use a transparent support, and only when the thickness is 10 μm or more and less than 30 μm, defects that are visible through the liquid crystal panel 19 when the backlight is turned on, It becomes possible to accurately screen the optical member alone. That is, even if a defect that affects the image quality occurs, it is possible to avoid the outflow to the subsequent process, and the holding force necessary for the integration of the optical sheet 19 and the light diffusing sheet 9 is achieved. It was shown that it has enough.

  In addition, the adhesive layer 16 is a structure which does not use a conventional transparent support, and in a sample having a thickness of less than 10 μm, not only the reduction of the integrated holding force but also the optical sheet 10 and the light diffusing sheet 9 When a foreign object is caught between the optical sheets, the optical sheet around the foreign object may be lifted, and the defect size may be increased to make it unusable for use in a display device. For this reason, it was also confirmed that it is not desirable to make the thickness of the adhesive layer 16 less than 10 μm.

It is a schematic sectional drawing for demonstrating the structure of the integrated optical member which enabled the conventional brightness improvement. It is a schematic sectional drawing for demonstrating the optical path of the conventional integrated optical member. It is a schematic sectional drawing which shows an example of the optical member by this Embodiment. It is a schematic sectional drawing which shows the structure of the backlight unit using the optical member concerning this invention. It is a schematic sectional drawing which shows the structure of the display apparatus using the backlight unit concerning this invention. It is a figure which shows the test result in the Example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Lens sheet, 1a ... Lens part, 2 ... Base material, 3 ... Sensitive material, 4 ... High refractive index layer, 5 ... Low refractive index layer, 9 ... Light diffusion sheet, 10 ... Optical sheet, 16 ... adhesive layer, 17 ... lamp, 18 ... lamp house, 19 ... liquid crystal panel, 100 ... optical member, 110 ... light source, 120 ... backlight unit.

Claims (9)

An optical member having an optical path control function for controlling at least one of a direction, a range, and a luminance distribution when emitting incident light,
A light diffusion sheet;
An optical sheet having the optical path control function;
An adhesive layer that joins the light exit surface of the light diffusion sheet and the light incident surface of the optical sheet;
In the adhesive layer, when the light incident surface of the joined light diffusion sheet is irradiated with light, a defect of 0.05 mm ² can be clearly visually observed on the light emitting surface of the joined optical sheet. A value of 1.2 or more and 1.7 or less in a range where the maximum value of the loss coefficient tanδ, which is a ratio between the storage shear modulus and the loss shear modulus, is -20 ° C to -10 ° C. And the loss factor at room temperature is 0.2 or more and less than 1.7,
An optical member.   The optical member according to claim 1, wherein the pressure-sensitive adhesive layer has a thickness of 10 μm or more and less than 30 μm.   The optical member according to claim 1, wherein the adhesive layer retains adhesiveness in a range of −40 ° C. or higher and 90 ° C. or lower.   The optical member according to any one of claims 1 to 3, wherein the adhesive layer is made of a clear type adhesive having no light diffusibility.   The optical member according to any one of claims 1 to 3, wherein the adhesive layer is made of an adhesive having light diffusibility.   In the adhesive layer, the light exit surface of the joined light diffusion sheet and the central portion of the light entrance surface of the optical sheet do not warp convexly toward the light exit surface of the optical sheet when heated. The optical member according to any one of claims 1 to 5, wherein the optical member is configured.   The optical sheet includes a sheet-like or thin-plate-like transparent base material, a lens sheet having a lens portion including a semi-cylindrical convex lens group or a convex cylindrical lens group provided on one surface of the base material, and the base A light-reflective high-refractive index layer and a low-refractive index layer provided on the other surface of the material, wherein the low-refractive index layer is provided in the condensing region of the lens portion on the other surface, The optical member according to claim 1, wherein the refractive index layer is provided in a non-condensing region of the lens portion on the other surface. A light source and at least an optical member according to any one of claims 1 to 7,
A backlight unit for displays. An image display element that defines a display image according to transmission / shading in pixel units;
The backlight unit according to claim 7 is provided on the back of the image display element.
A display device.

Images