JP2008209713A - Optical sheet, and backlight unit and display using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet wherein optical characteristics can be adjusted, without changing the shape of optical components, in improving the optical sheet used for an optical path control of an illumination for the backlight unit for a display device where liquid crystal display element is used. <P>SOLUTION: The optical sheet 88 has one surface 88A and the other surface 88B in the thickness direction, wherein the optical component for controlling at least any one of the outgoing direction, range, color, or the luminance distribution of a light incident from the one surface 88A is formed on the other surface 88B. On the one surface 88A, particles 93 that have reflectivity or light-shielding effects are provided on the one surface 88A. The maximum diameter of individual planes in contact with a base material 91 must be 300 um or smaller, irrespective of whether the particles 93 have regular shapes or not. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an improvement of an optical sheet used for illumination light path control in a display backlight unit mainly using a liquid crystal display element, and a backlight unit and a display (display device) on which the sheet is mounted. About.

A display typified by a liquid crystal display device (LCD) is remarkably widespread in a type including a light source necessary for recognizing provided information. 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.

  A brightness enhancement film (BEF) which is a registered trademark of 3M Corporation of the United States is widely used as an optical sheet for solving this problem.

BEF is a film in which unit prisms 72 having a triangular cross section are periodically arranged in one direction on a member 70 as shown in FIG.
The prism 72 has a size (pitch) larger than the wavelength of light.
BEF collects light from “off-axis” and redirects this light “on-axis” or “recycle” towards the viewer. To do.

  When using the display (when observing), the BEF increases the on-axis brightness by reducing the off-axis brightness. Here, “on-axis” is a direction that coincides with the visual direction of the viewer, and is generally the normal direction (direction F shown in FIG. 1) side with respect to the display screen.

  When the repetitive array structure of the prisms 72 is arranged in only one direction, only the direction change or recycling in the parallel direction is possible, and in order to control the luminance of the display light in the horizontal and vertical directions, the prism groups are arranged in parallel. Two sheets are stacked and combined so that the directions are substantially orthogonal to each other.

The adoption of BEF allows display designers to achieve the desired on-axis brightness while reducing power consumption.
As patent documents disclosing that a brightness control member having a repetitive array structure of prisms 72 typified by BEF is adopted for a display, many are known as exemplified in Patent Documents 1 to 3. ing.

In the optical sheet using the BEF as a brightness control member as described above, the light P from the light source 20 is finally emitted at a controlled angle φ by the refraction action x as shown in FIG. Thus, it is possible to control to increase the intensity of light in the visual direction F of the viewer.
However, at the same time, the light component due to the reflection / refraction action y is unnecessarily emitted in the lateral direction without proceeding in the visual direction F of the viewer.

Therefore, the light intensity distribution emitted from the optical sheet using the BEF as shown in FIGS. 1 and 2 corresponds to the visual direction F of the viewer, that is, the visual direction F as shown by the curve B indicated by the dotted line in FIG. Although the light intensity at the angle of 0 ° (corresponding to the on-axis direction) is the highest, as shown as a small light intensity peak around ± 90 ° shown on the horizontal axis in the figure, the light emitted from the horizontal direction is also wasted There is a problem that it increases.
A curve B in FIG. 3 is a light intensity distribution in the case of only one prism sheet, and a curve indicated by “vertical distribution” in the drawing corresponds to a direction in which the prisms 72 are arranged in parallel, and is indicated by “horizontal distribution”. The curved line corresponds to the longitudinal direction of the prism 72.
In general, a usage form in which two prism sheets are used in combination so that the directions in which the prisms 72 are arranged in parallel is substantially orthogonal.
A luminance distribution having such a light intensity peak is not desirable, and a smooth luminance distribution having no light intensity peak around ± 90 ° is more desirable.
In addition, if only the on-axis brightness is excessively increased, the width of the peaks in the graph (especially in the vertical distribution curve) becomes extremely narrow and the viewing area is extremely limited. Therefore, it is necessary to newly use a light diffusing film which is a separate member from the prism sheet, which is accompanied by an increase in the number of members.

  In order to overcome such drawbacks, there is a backlight unit 40 using an optical film 38 having a repetitive array structure of unit lenses instead of a prism as shown in FIGS. 4 and 5 (Patent Document 4). .

A lens 44 for guiding the light traveling in the optical film 38 to the liquid crystal panel is provided on the surface of the transparent film 39 of the optical film 38 on the liquid crystal panel side. As shown in the perspective view of FIG. 4, the lens 44 has a plurality of unit lenses repeatedly forming an array structure.
Further, on the other surface, a reflector 48 having a stripe pattern having an opening 46 in the vicinity of the focal plane of the lens 44 is provided.

The reflecting material 48 is obtained by mixing a mixture of white titanium dioxide (TiO ₂ ) powder in a solution such as a transparent adhesive with a predetermined pattern (when the unit lens is a semi-cylindrical convex cylindrical lens group, each unit lens Is formed in a stripe shape having an opening corresponding to 1: 1).
In FIG. 5, reference numeral 21 denotes a lamp house, reference numeral 23 denotes a cold cathode tube, and reference numeral 27 denotes a reflector.

A curve A shown in FIG. 3 shows the optical path control characteristics of the backlight when the optical sheet of FIGS. 4 and 5 is applied to the backlight unit.
Of the light emitted from the diffusion film 32, only the light that has passed through the opening 46 enters the lens 44 and is emitted after being condensed in a certain direction by the lens 44.
Then, the light is incident on the polarizing plate, and only light having a predetermined polarization component is guided to the liquid crystal panel.

  On the other hand, the light that could not pass through the opening 46 is reflected by the reflecting material 48, returned to the diffusion plate 26 side, and guided to the reflecting plate 27. Then, the light is incident on the diffusion plate 26 again by being reflected by the reflection plate 27 and is diffused again on the diffusion plate 26. As shown in FIG. 5, the light is squeezed into a predetermined angle φ and emitted by the lens 44.

In the backlight unit 40 using such an optical film 38, the size and the position of the opening 46 of the optical film 38 are adjusted, and the light is emitted from the lens 44 in the front direction while improving the light use efficiency. It can be controlled to increase the proportion of light.
Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500 JP 2000-284268 A

  In the case of a display having a large screen such as a monitor for a liquid crystal TV or a personal computer instead of a display having a relatively small screen such as a mobile phone or a mobile terminal, in order to make the luminance distribution in the screen uniform. It is preferable to adopt a direct backlight unit in which a light source is housed in a lamp house behind the screen, rather than a backlight unit using an edge light to a light guide plate.

As shown in FIG. 6, the backlight unit in the liquid crystal display device is in the form of a laminated structure of each element, and the diffusion film or DBEF80 / prism sheet or optical film 81 / diffusion film 82 / diffusion plate 83 is a light source. It is arranged on 84 lamp houses 85 accommodated. These laminated structures are designed so that uneven light from a light source is first converted into diffused light with a strong diffusion function, and then a desired luminance distribution is obtained with an optical element.
Hereinafter, the light control functions of the diffusion film or DBEF 80, the prism sheet or optical film 81, the diffusion film 82, etc. are collectively referred to as an optical member.

  Among optical members, prisms and lenses having a high light collecting function use the refraction function of unit prisms and unit lenses, and have an effect of increasing on-axis luminance by reducing off-axis luminance. These optical members are usually mass-produced using molds designed and produced in a shape that exhibits desired optical characteristics. Therefore, when a plurality of optical characteristics are required, a plurality of molds must be prepared, which takes time and cost. However, the customer's demand for optical properties is different, and a plurality of molds must be prepared because of slight differences.

  In order to solve the above problem, the present invention includes a second optical element that increases off-axis brightness of the optical sheet and does not impair the image on the display, and adjusts the second optical element. The object is to produce optical sheets with different optical performance from a single mold.

The light emitted from the prism or the lens is randomly blocked or reflected partially, and the area of the portion where the emitted light is blocked or reflected is changed, so that the entire first light element is not deformed. Distribution can be changed. However, if the portion where the emitted light is blocked or reflected has a certain size, it will be seen as a black spot from the observer and will be recognized as unevenness. As a result of trial and error, the present inventor has succeeded in providing an optical sheet that defines the area of the black spot and is not recognized as unevenness by increasing or decreasing the number and can change the luminance distribution.
In the present invention, the optical member that controls at least one of the light emission direction, range, color, and luminance distribution is referred to as a first optical element.
In the embodiment described later, the first optical element also has a light collecting function.
In the present invention, the portion where the emitted light is blocked or reflected is referred to as a second optical element.
That is, the invention according to claim 1 has one surface in the thickness direction and the other surface, and the light incident from the one surface is incident on the other surface in the emission direction, range, color, In the optical sheet provided with the first optical element for controlling at least one of the luminance distribution, the second optical element having a reflective property or a light shielding property is provided on the one surface. To do.
The invention according to claim 2 is characterized in that the second optical element is composed of a large number of particles having reflectivity or light shielding properties provided on the one surface.
According to a third aspect of the present invention, the first optical element is a lens unit including a convex cylindrical lens group or a hemispherical convex lens group, and a reflective layer is provided on the one surface, and the reflective layer is A light reflecting portion located in a non-condensing region of the lens portion, and a light transmitting portion located in the remaining region, and further composed of a material that reflects light and across the light transmitting portion. A bridging portion for connecting the light reflecting portions to each other is provided, and the second optical element is constituted by the bridging portion.
According to a fourth aspect of the present invention, the first optical element is a prism sheet in which a plurality of prisms are formed in parallel, a reflective layer is provided on the one surface, and the reflective layer is formed of the prism. The light reflecting portion arranged in parallel with the extending direction and a light transmitting portion located in a region other than the light reflecting portion, and further composed of a material that reflects light, the light reflecting across the light transmitting portion. A bridging part for connecting the parts is provided, and the second optical element is constituted by the bridging part.
The invention according to claim 5 is characterized in that a size of the second optical element bonded to the one surface is a maximum diameter of 300 μm or less.
The invention according to claim 6 is characterized in that the shape of the second optical element joined to the one surface is a circle having a maximum diameter of 300 μm or less.
The invention according to claim 7 is characterized in that the shape of the second optical element joined to the one surface is an ellipse having a major axis of 300 μm or less.
The invention according to claim 8 is characterized in that the shape in which the second optical element is bonded to the one surface is a polygon having a maximum diagonal dimension of 300 μm or less.

The invention according to claim 9 includes at least the direct light source on the back surface of the image display element that defines the display image, and the optical sheet according to any one of claims 1 to 8, wherein the optical sheet includes: A display backlight unit, wherein the first optical element is disposed toward the image display element.
According to a tenth aspect of the present invention, there is provided the surface light source comprising an edge light type light source and a light guide plate on the back surface of the image display element that defines a display image, and the optical sheet according to any one of the first to eighth aspects. At least, the optical sheet is a backlight unit for display, wherein the optical sheet is arranged with the first optical element facing the image display element.
According to the eleventh aspect of the present invention, there is provided an illumination light source disposed on the side opposite to the observer with respect to a display element in which a display pattern is defined in accordance with transmission / non-transmission or transparency / scattering in pixel units. In a display device configured to irradiate illumination light, pass through the display element to generate display light, and emit the display light to an observer side, an optical sheet is disposed immediately before the illumination light enters the display element, and the optical sheet Has one surface located on the illumination light source side and the other surface located on the display element side, and the light incident from the one surface is incident on the other surface in its emission direction and range. A first optical element for controlling at least one of color, luminance distribution is provided, and a second optical element having a reflective property or a light shielding property is provided on the one surface.

  According to the present invention, the first optical element that controls at least one of the direction, the range, the color, and the luminance distribution is formed on the opposite surface when the light incident from the substantially flat surface is emitted. In the optical sheet thus formed, it is possible to provide an optical sheet in which the distribution of emitted light is adjusted without changing the shape of the first optical element and without recognizing unevenness.

  Embodiments of the present invention will be described below. There are two main methods for carrying out the present invention.

  FIG. 7 is a side view showing a prism and a lens sheet used as the first optical element. FIG. 8 is a side view showing a lens sheet with a reflective layer used as the second optical element.

That is, in the optical sheet 88 according to the embodiment, the first optical element 90 is disposed on the light emission surface side on the base sheet 91 (in other words, the side on which the base sheet 91 faces the display element). Become. As the material of the base material sheet 91, PET (polyethylene terephthalate), acrylic sheet, PC (polycarbonate) sheet or the like well known in the technical field is used. The optical element is made using a thermoplastic or UV curable resin.
That is, in the present embodiment, the optical sheet 88 has one surface 88A in the thickness direction and the other surface 88B, and the light incident from the one surface 88A on the other surface 88B is emitted in the direction of emission. , A first optical element 90 for controlling at least one of range, color, and luminance distribution is formed.

  Alternatively, there is a method in which the first optical element 90 and the base material 91 are formed at a time by extrusion or injection molding.

  Further, when a lens is used for the first optical element 90, a reflective layer 92 may be provided on the incident surface side (light source side) as shown in FIG. The presence or absence of the reflective layer 92 is determined depending on which of the necessary light collecting function and cost is taken.

  In the case of providing the reflective layer 92, it is preferable to use a white pigment and a metal vapor deposition layer that have high reflectivity and low light absorption. As the white pigment, titanium dioxide, barium sulfate, and magnesium oxide well known in the art are used, and as the metal deposition layer, silver or the like is used.

  The reflective layer 92 can also be formed by a transfer method using a UV curable adhesive material. A UV curable adhesive material is bonded to the surface opposite to the lens (optical element 90) in advance, UV is irradiated from the lens side, and then a reflective layer is bonded to the uncured portion. With this method, the lens (optical element 90) and the reflective layer 92 can be easily arranged in a 1: 1 correspondence. More specifically, as shown in FIGS. 4, 5, and 12, the light reflecting portion 92 </ b> B (48) located in the non-condensing region of the lens unit and the remaining region (non-condensing region of the lens unit) The reflection layer 92 corresponding to the light transmission portion 92A (46) located can be easily formed.

  Further, the reflective layer 92 is formed by integrating and molding the first optical element 90, the base material 91, and the lens sheet with irregularities on the other surface by extrusion or injection molding, and then using the irregularities. It can also be made by a method of applying an ink showing light reflectivity in a pattern.

As one of the methods for creating the second optical element, as shown in FIGS. 9 and 10, the back surface (surface on the light source side) of the substrate 91 in FIG. 7 is light-shielding or reflective with resin or glass. There is a method of arranging a large number of particles 93.
That is, it has one surface 88A in the thickness direction and the other surface 88B, and the light incident from the one surface 88A on at least one of the emission direction, range, color, and luminance distribution on the other surface 88B. In the optical sheet 88 on which the first optical element 90 that controls the above is formed, a large number of particles 93 having reflectivity or light shielding properties are provided as the second optical element on one surface 88A.
The optical sheet 88 is disposed with the first optical element 90 facing the display element.
The shape of the particle 93 (member 93) having light-shielding properties and reflectivity may be either a regular shape or an irregular shape, but the maximum diameter of each contact surface with the substrate 91 must be within 300 μm.
If it demonstrates in detail, the magnitude | size with which the particle | grains 93 will be joined to the surface of the base material 91 is 300 micrometers or less in maximum diameter.
Specifically, the size of the particles 93 bonded to the surface of the base material 91 is a circle having a maximum diameter of 300 μm or less, or an ellipse having a major axis of 300 μm or less, or a maximum diagonal dimension. It is a polygon of 300um or less.
The first optical element 90 is a prism or a lens.
As a method for arranging the light-shielding and reflective particles 93, a method of attaching the light-shielding and reflective particles 93 to the substrate 91 can be mentioned.

  A configuration in which a hard coat layer, a diffusion layer, or a PET, PC, or acrylic sheet on which these layers are formed is disposed on the incident surface of the substrate 91 is also within the scope of the optical sheet of the present invention. In this case, the light-shielding and reflective particles 93 must be disposed on these coat layers.

In addition, as a method of creating the second optical element, a method of randomly arranging the bridging portions 94 on the reflective layer 92 as shown in FIGS.
11 is a cross-sectional plan view of the reflective layer, and FIGS. 12A, 12B, and 12C are cross-sectional views taken along line XX of FIG.
The reflection layer 92 is randomly provided with a bridge portion 94 made of a material that reflects light and connecting the light reflection portions 92 </ b> B across the light transmission portion 92.
The maximum diameter of the bridging portion 94 must be within 300 μm when viewed from the exit side of the optical sheet. At this time, the size of the randomly arranged bridge portions 94 is considered as a portion excluding the patterned light reflection portion 92B, and the maximum diameter must be within 300 μm.
As a method for randomly arranging the bridging portions 94, in the case of the transfer method, as shown in FIG. 12 (A), a transfer foil in which a pattern that is partially transferred at the time of transfer is previously attached to the substrate. And a method of changing part of the adhesion between the transfer material and the substrate, or conversely changing part of the adhesive strength of the UV curable adhesive. Alternatively, as shown in FIGS. 12B and 12C, a method of attaching a light-shielding or reflective member after forming a patterned reflective layer can be used.

  In the case of extrusion or injection molding, a surface treatment that is compatible with ink is randomly applied in advance, or an irregular shape that is randomly applied with ink is applied, or patterned light reflection is performed. A method of attaching a light-shielding or reflective member after forming the portion 92B can be mentioned.

When an optical sheet prepared as in the present invention is applied to a liquid crystal display device, a display in which the optical performance can be controlled by subsequent processing even in the same shape of the first optical element and the display screen is not uneven is provided. be able to.
(Example)

  FIG. 13 shows an embodiment of the present invention and its performance.

  As a first optical element, a cylindrical lens was made of UV curable acrylic resin on a PET substrate. Alternatively, prisms were formed on a PET substrate with UV curable acrylic resin.

  A UV curable adhesive was applied to the back surface of the prism sheet, and glass beads or resin beads colored with white ink having a diameter of 1 mm were sprayed as particles 93 and then cured with UV. The maximum diameter of the surface of the contact portion between the beads and the prism sheet was adjusted by the time from spreading to curing, and adjusted to include those adjusted to 300 um or less and those larger than 300 um. The application amount was also varied, and the number of beads per area was counted after the sample was prepared.

  As described in JP-A-2005-37694, the cylindrical lens sheet is formed with a reflection layer 92 including a white light reflection portion 92B and a light transmission portion 92A. A crosslinking agent 94 was created by spraying a release agent on the substrate of the transfer foil in advance and transferring the release agent irrespective of patterning. By adjusting the amount of droplets at the time of spraying, the one adjusted to 300 um or less and the one adjusted to include more than 300 um were prepared. The distribution amount was also varied, and the distribution was counted after the creation of the sample and the bridge portions 94 outside the patterning per area.

The sample prepared as described above was incorporated into a liquid crystal display, and the brightness and image display state were confirmed.
The luminance is expressed as a ratio by comparing the state in which the prepared optical sheet is incorporated with the state in which only the optical sheet is removed as a reference.
FIG. 13 shows the determination result.
When the size of the surface of the contact portion between the particle 93 or the bridge portion 94 and the prism sheet exceeds 300 μm, it is recognized as unevenness in the image. Those within 300um were not recognized as unevenness.
Further, when the number of the particles 93 or the bridge portions 94 is increased, the half-value angle is narrowed and the luminance is increased, and the overall optical characteristics can be adjusted. Moreover, the difference by the kind of used particle | grains 93 or bridge | crosslinking part 94 was not seen.

  The combination used this time is an example of an optical sheet, and the present invention is not limited to such a configuration.

  As described above, according to the present invention, the emitted light is partially shielded or reflected by the optical sheet, so that the optical characteristics can be adjusted without changing the shape of the first optical element. An optical sheet can be provided.

Explanatory drawing which shows "BEF" which is an optical sheet concerning a prior art Explanatory drawing which shows the optical path control characteristic of the backlight by BEF The graph which shows the optical path control characteristic of the backlight by BEF Explanatory drawing which shows the optical sheet which concerns on another type of prior art from BEF Explanatory drawing which shows the optical path control characteristic of the backlight by the optical sheet of FIG. Explanatory drawing showing an example of backlight Side view of optical sheet Side view of optical sheet with reflective layer Side view showing an example of the embodiment Side view showing an example of the embodiment Cross-sectional plan view of a reflective layer having a bridge XX sectional view of FIG. The figure which shows the result of an Example and a comparative example

Explanation of symbols

26 Diffusing plate 27 Reflecting plate 38 Optical sheet 40 Backlight unit 44 Lens portion 46 Opening portion 48 Reflecting material 70 having a stripe pattern 70 Member 72 Unit prism 80 Diffusion film or DBEF
81 Prism sheet or optical film 82 Diffusion film 83 Diffusion plate 84 Light source 85 Lamp house 90 First optical element 91 Base material 92 Reflective layer 93 Particle 94 Bridge portion

Claims (11)

Having one surface in the thickness direction and the other surface;
In the optical sheet provided with the first optical element that controls at least one of the emission direction, range, color, and luminance distribution of the light incident from the one surface on the other surface,
A second optical element having a reflective property or a light shielding property is provided on the one surface.
An optical sheet characterized by that. The second optical element is composed of a large number of particles having reflectivity or light shielding properties provided on the one surface.
The optical sheet according to claim 1. The first optical element is a lens unit composed of a convex cylindrical lens group or a hemispherical convex lens group,
A reflective layer is provided on the one surface;
The reflective layer includes a light reflecting portion located in a non-condensing region of the lens portion and a light transmitting portion located in the remaining region,
Furthermore, a bridge portion is provided that is made of a material that reflects light and connects the light reflecting portions to each other across the light transmitting portion,
The second optical element is composed of the bridge portion.
The optical sheet according to claim 1. The first optical element is a prism sheet in which a plurality of prisms are formed in parallel.
A reflective layer is provided on the one surface;
The reflective layer is configured to include a light reflecting part in parallel with the extending direction of the prism, and a light transmitting part located in a region other than the light reflecting part,
Furthermore, a bridge portion is provided that is made of a material that reflects light and connects the light reflecting portions to each other across the light transmitting portion,
The second optical element is composed of the bridge portion.
The optical sheet according to claim 1.   The optical sheet according to claim 1, wherein the second optical element is bonded to the one surface with a maximum diameter of 300 μm or less.   The optical sheet according to claim 1, wherein the second optical element is joined to the one surface in a circular shape having a maximum diameter of 300 μm or less.   The optical sheet according to claim 1, wherein the second optical element is joined to the one surface in an elliptical shape having a major axis of 300 μm or less.   2. The optical sheet according to claim 1, wherein the shape of the second optical element joined to the one surface is a polygon having a maximum diagonal dimension of 300 μm or less. On the back of the image display element that defines the display image,
A direct light source, and at least an optical sheet according to any one of claims 1 to 8,
The optical sheet is disposed with the first optical element facing the image display element,
A backlight unit for displays. On the back of the image display element that defines the display image,
A surface light source comprising an edge light type light source and a light guide plate, and at least an optical sheet according to any one of claims 1 to 8,
The optical sheet is disposed with the first optical element facing the image display element,
A backlight unit for displays. Illumination light is emitted from an illumination light source disposed on the opposite side of the observer to a display element whose display pattern is defined according to transmission / non-transmission or transparency / scattering state in pixel units, In a display device configured to pass through to generate display light and emit it to the viewer side,
An optical sheet is arranged immediately before the illumination light enters the display element,
The optical sheet has one surface located on the illumination light source side and the other surface located on the display element side,
A first optical element that controls at least one of the emission direction, range, color, and luminance distribution of light incident from the one surface is provided on the other surface,
A second optical element having a reflective property or a light shielding property is provided on the one surface.
A display device characterized by that.

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