JP2009069404A - Optical sheet, backlight unit using same, and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet of which the optical characteristics can be adjusted, without having to change the shape of an optical element or without the unevenness being recognized, in improving the optical sheet that has a function of converging or uniformizing light from a light source, and to provide a backlight unit for display, and a display device. <P>SOLUTION: The optical sheets 100, 102 are formed by arranging optical elements 80 on an emission surface side of a luminaire on a base material sheet 81. The optical element 80 controls at least either the direction, range, color, or the luminance distribution, when light is emitted from an incident surface, and a diffusion element for diffusing light in the optical element 80 is provided. The diffusion element is a light-transmissive member (a light-transmissive fine particle) 90 formed of resin and glass, or a fine bubble-like air layer 91. The maximum particle diameter per unit particle of the diffusion element is smaller than the formation pitch width of the optical element 80, and has 800-5000 particles/cm<SP>2</SP>per unit area on the base material sheet 81 of the diffusion element. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

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 has a viewer's visual direction F, that is, an angle with respect to the visual direction F is 0, as indicated by a dotted line B in FIG. Although the light intensity at ° (corresponding to the axial direction) is the highest, as shown as a small light intensity peak around ± 90 ° shown on the horizontal axis in the figure, the amount of light emitted from the horizontal direction is increased. There is a problem.
The graph of FIG. 3 shows the light intensity distribution when only one prism sheet is used, and the curve indicated by “vertical distribution” in the figure corresponds to the 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 view of the above circumstances, the present applicant has proposed an optical sheet exemplified in Patent Document 4 as an alternative product of a prism sheet represented by BEF.
The optical sheet according to the above publication is
Illumination light path control in a backlight unit for a display using a lens sheet having a lens unit composed of unit lens groups formed on the exit surface side, which is a non-incident surface side, on the incident surface side of light from the illumination light source In the optical sheet for
The lens sheet is configured to include a light reflecting layer having an opening corresponding to the lens portion on the exit surface side (see FIG. 4).

  In FIG. 4, the light from the light source 64 that could not pass through the opening formed on the incident surface side of the lens sheet 65 is reflected by the light reflection pattern 66 and returned to the light guide plate 79 side. Then, after repeated reflection at the interface with the light guide plate or within the light guide plate, any of the light enters the lens sheet 65 again through the opening, and is directed to the liquid crystal panel 68 after the exit angle is controlled within a predetermined angle. Are emitted.

In the backlight unit using such an optical sheet, by adjusting the size and position of the opening of the optical sheet, the efficiency of light utilization is improved, and the light emitted from the lens sheet 65 in the front direction S is increased. The ratio can be controlled to increase, and a light intensity distribution as shown by a solid line A in FIG. 3 is obtained.
Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500 JP 2000-284268 A

  Not a display with a relatively small screen such as a mobile phone or a mobile terminal, but a display with a large screen such as a monitor for a liquid crystal TV or a personal computer is used to make the luminance distribution in the screen uniform. It is preferable to adopt a direct type 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. 5, the backlight unit in the liquid crystal display device is in the form of a laminated structure of each element, and a diffusion film or DBEF 50 / prism sheet or optical sheet 51 / diffusion film 52 / diffusion plate 53 is used as a light source 54. It is arranged on the lamp house 55 in which is stored. Hereinafter, the light control functions of the diffusion film or DBEF 50, the prism sheet or optical sheet 51, the diffusion film 52, etc. are collectively referred to as an optical element. 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.

  Among optical elements, 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 elements are usually mass-produced by using a mold designed and produced in a shape exhibiting 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 achieve the above object, the present invention provides an optical sheet having a function of converging or uniformizing light from a light source, an incident surface on which light from the light source is incident, and a back surface thereof from the incident surface. An optical sheet in which an optical element that controls at least one of a direction, a range, a color, and a luminance distribution when emitting light is formed, and includes a diffusing element that diffuses light in the optical element. It is an optical sheet.
The present invention also provides the optical sheet according to claim 1, wherein the optical element is a prism or a lens.
The present invention also provides the optical sheet according to claim 1, wherein the diffusing element is a light-transmitting resin fine particle or a fine bubble-like air layer.
The present invention also provides the optical sheet according to any one of claims 1 to 3, wherein a maximum particle size per unit particle of the diffusing element is shorter than a formation pitch width of the optical element. .
The present invention also provides the optical sheet according to any one of claims 1 to 4, wherein the diffusing element has a circular shape.
Further, the present invention provides the optical sheet according to any one of claims 1 to 4, wherein the diffusing element has an elliptical shape.
The present invention also provides the optical sheet according to any one of claims 1 to 4, wherein the diffusing element has an indefinite shape.
The optical sheet according to any one of claims 1 to 7, wherein the optical sheet includes a base sheet, the optical element is provided on a surface of the base sheet, and the base sheet of the diffusing element is provided. The optical sheet is characterized in that the number per unit area is 800 / cm ² or more and 5000 / cm ² or less.
In the optical sheet according to any one of claims 1 to 8, the optical sheet includes a base sheet, the optical element is provided on a surface of the base sheet, and the optical element is thermoplastic or radiation. An optical sheet comprising a cured product of a curable resin and formed by polymerizing and bonding on the surface of the base sheet, or the optical element being integrally formed with the base sheet It is.
Moreover, this invention is a backlight unit for a display characterized by including at least a direct light source and the optical sheet according to any one of claims 1 to 9.
The present invention also provides a display backlight unit comprising at least an edge light source and a surface light source including a light guide plate and the optical sheet according to any one of claims 1 to 9. .
According to another aspect of the present invention, there is provided an image display element comprising a liquid crystal display element that defines a display image in accordance with transmission / shielding in pixel units, a light source using a cold cathode ray tube or laser, EL, and LED. A display device comprising the described backlight unit.
Further, the present invention provides an image display element comprising a liquid crystal display element that defines a display image in accordance with transmission / light-shielding in pixel units, a light source using a cold cathode ray tube or a laser, EL, and LED. A display device comprising the optical sheet described above.

  According to the present invention, an optical element in which one surface is an incident surface, and an optical element that controls at least one of a direction, a range, a color, and a luminance distribution when emitting light incident from the incident surface is formed on the opposite surface. It is possible to provide an optical sheet, a display backlight unit, and a display device that can adjust the optical characteristics of the sheet without changing the shape of the optical element and without recognizing unevenness.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 6 is a side view showing a display device including an optical sheet 100 using a prism or a lens as an optical element, and FIG. 7 is a side view showing a display device including an optical sheet 102 provided with a reflective layer on the back surface of the lens sheet. It is.

That is, the optical sheets 100 and 102 according to the same embodiment are configured by arranging the optical element 80 on the light exit surface side of the illumination on the base sheet 81.
As a material of the base material sheet 81, PET (polyethylene terephthalate), an acrylic sheet, a PC (polycarbonate) sheet or the like well known in the technical field is used.
Examples of the optical element 80 include thermoplastics such as polycarbonate resin, acrylic resin, fluorine acrylic resin, silicone acrylic resin, epoxy acrylate resin, polystyrene resin, cycloolefin polymer, methylstyrene resin, fluorene resin, PET, and polypropylene. Or using a radiation curable resin.

  Alternatively, there is a method of creating the optical element 80 and the base sheet 81 at a time by extrusion or injection molding.

  When a lens is used for the optical element 80, a light reflecting layer 86 may be provided on the incident surface side as shown in FIG. The presence or absence of the light reflecting layer 86 is determined depending on which of the necessary light collecting function and cost is taken.

  In the case of providing the light reflecting layer 86, it is preferable to use a white pigment and a metal vapor-deposited layer and to select one having high reflectivity and little 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 light reflecting layer 86 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 in advance, UV is irradiated from the lens side, and then a light reflecting layer is bonded to the uncured portion. With this method, the lens and the reflective layer can be easily arranged in a 1: 1 correspondence.

  The light reflecting layer 86 is formed by integrating and molding the optical element 80, the base material sheet 81, and a lens sheet with irregularities on the other surface by extrusion or injection molding, and then using the irregularities. It can also be created by applying a reflective ink in a pattern.

The optical element 80 controls at least one of the direction, the range, the color, and the luminance distribution when emitting light from the incident surface, and a diffusing element that diffuses the light is provided in the optical element 80. .
Here, two methods of creating the diffusing element will be described.
As the first method, as shown in FIG. 8, there is a method in which a light-transmitting member (light-transmitting fine particles) 90 of resin or glass is arranged inside the optical element 80. As an example, there is a method in which light-transmitting particles are mixed and taken into the optical element 80 at the same time when an optical element pattern is formed by pressure welding molding, extrusion molding, injection molding or the like using a mold.
Examples of the light transmissive member 90 include polycarbonate resin, acrylic resin, fluorine acrylic resin, silicone acrylic resin, epoxy acrylate resin, polystyrene resin, cycloolefin polymer, methylstyrene resin, and fluorene as described above. If the refractive index of the optical element 80 is M and the refractive index of the light transmissive member 90 is N, it is assumed that the refractive index difference between the two is | M−N | ≧ 0. It is desirable to satisfy the relationship of 01. This is because if the difference in refractive index between the two is less than 0.01, sufficient light diffusibility cannot be obtained.

  As the second method, as shown in FIG. 9, there is a method of providing a fine bubble-like air layer 91 inside the optical element 80. Specifically, a method of forming a pattern of the optical element 80 on the base sheet 81 using a radiation curable resin and providing a fine bubble-like air layer 91 inside the optical element 80 will be described below as an example. State. In this case, as shown in FIG. 10, the optical element 80 generally has a pattern forming method in which a resin 31 is applied on the surface of a base material sheet 32 (base material sheet 81), and the reverse shape of the concavo-convex shape is formed on the surface. While the resin coating side is in pressure contact with the roll-shaped mold 34 included in the substrate, radiation 33 is irradiated through the base sheet 32, and the resin 31 applied on the surface of the base sheet 32 is cured, thereby having a desired uneven shape. The optical element is manufactured by a method of forming on the surface of the substrate sheet 32. Here, after the bubbles are mixed into the resin 31 using the bubble generating device, the bubbles are applied onto the surface of the base sheet 32, and the pattern of the optical element 80 is formed. A fine bubble-like air layer 91 can be provided inside.

The shape of the light transmissive member 90 and the fine bubble-like air layer 91 may be a regular shape or an indefinite shape, but the maximum diameter is shorter than the formation pitch width of the optical element 80 and the formed base material sheet 81 The number per unit area must be 800 / cm ² or more and 5000 / cm ² or less. When providing a fine bubble-like air layer, it is necessary to control these by controlling the bubble generator. The density of the bubbles in the resin is adjusted by changing the pressure at the time of foam ejection in the generator and the shape of the foam ejection port.

When an optical sheet prepared as in the present invention is applied to a backlight unit for a display and a liquid crystal display device, the optical performance can be controlled by subsequent processing even in the shape of the same optical element, and the display screen has no unevenness. Can be provided.
Example 1

  As the optical element 80, a lenticular lens sheet in which semi-cylindrical convex cylindrical lens groups are arranged in parallel in one direction is formed by a UV curing molding method in which an acrylic UV curable resin is disposed on a PET base sheet 81. did. In addition, the lens was formed in the range in which formation pitch was settled in 100 micrometers-200 micrometers. The pattern formation mechanism is the same as that described in paragraph 0027.

Here, a UV resin mixed with light-transmitting resin beads having various diameters of 10 μm to 200 μm was applied on the PET base material sheet 81 and patterned to form a lens sheet (optical element 80). . In addition, a lens sheet sample with a difference in the amount of each bead was prepared. In the lenses with different pitches, the diameters of the mixed resin beads were shorter than the pitch widths. This is because if resin beads having a diameter larger than the pitch width of the lens are mixed in the UV resin, the beads do not enter the concave / convex mold of the mold during pattern formation, and the shape of the lens itself collapses.
In addition, the refractive index of the lens cured with UV resin is about 1.5, and the resin beads used this time are fluorine-based acrylic resin, and the refractive index is about 1.3. The difference in refractive index is about 0.2, and sufficient light diffusibility can be obtained.
(Example 2)

  As the optical element 80, a lenticular lens sheet 95 in which semi-cylindrical convex cylindrical lens groups are arranged in parallel in one direction by a UV curing molding method in which an acrylic UV curable resin is disposed on a PET base sheet 81. 11 and 12). In addition, the lens was formed in the range in which formation pitch was settled in 100 micrometers-200 micrometers. The pattern formation mechanism is the same as that described in paragraph 0027.

Here, when the UV curable resin is applied onto the PET base sheet 81, a bubble generating device is used, the shape of the bubble outlet of the device is increased, and bubbles having a diameter of about 10 μm to 100 μm are generated inside the resin. Then, a pattern was formed and a lens sheet 95 was created. As shown in FIGS. 11 and 12, as a result of observing the shape and measuring the diameter of the fine bubble-like air layers 96 and 97 from the lens surface side using a scale loupe, the formed air layer has a maximum diameter. It was either an oval shape long in the lens array direction exceeding the lens pitch width or a circular shape having a maximum diameter within the lens pitch width. FIG. 11 shows the state of the elliptical air layer 96 observed from above the lens surface, and FIG. 12 shows the state of the circular air layer 97.
(Example 3)

  As the optical element 80, a semi-cylindrical convex cylindrical lens group is formed by a UV curing molding method in which a UV curable resin such as epoxy, urethane, polyester, polyether, and epoxy acrylate is disposed on a PET base sheet 81. A lenticular lens sheet formed in parallel in the direction was formed. In addition, the lens was formed in the range in which formation pitch was settled in 100 micrometers-200 micrometers. The pattern formation mechanism is the same as that described in paragraph 0027.

  Here, when the UV curable resin is applied on the PET base sheet 81, a bubble generating device is used, the shape of the bubble outlet of the device is reduced, and fine bubbles having a diameter of about 10 μm to 100 μm are formed inside the resin. A lens sheet was formed by generating a pattern. As a result of observing the shape of a fine bubble-shaped air layer and measuring the diameter from the lens surface side using a scale loupe, all the formed air layers were contained in a circular shape having a maximum diameter within the lens pitch width.

In addition, the amount of the diffusing element made of resin beads or a fine bubble-like air layer should be multiplied by four by counting the number in the range of 0.5 cm × 0.5 cm on the base sheet 81 using a scale loupe. FIG. 14 shows the number per 1 cm ² .
(Measurement example)

The optical sheet 100 prepared by providing resin beads or fine air bubbles in the lens as diffusion elements in the lens as in Examples 1 to 3 above was actually used in the liquid crystal display device as shown in FIG. Incorporated into the backlight, the brightness and the display state of the image were confirmed. In FIG. 13, reference numeral 99 denotes a luminance measuring machine.
The luminance was measured by incorporating the prepared optical sheet 100, and the luminance of the lens sheet in a normal state in which no element that diffuses light was provided was measured. FIG. 14 shows the result of the 140 μm pitch lens optical sheet.
Regardless of the size of the light diffusing element, the sample with an application rate of less than 800 pieces / cm ² had almost no change in the luminance ratio and half-value angle, and no adjustment of the optical characteristics was observed. On the other hand, if the amount of the light diffusing element exceeds 5000 / cm ² , it is recognized as luminance unevenness in the image state.
Also, in samples containing an elliptical air layer whose maximum diameter exceeds the lens pitch width and is long in the lens array direction, even if the amount of application is within 5000 / cm ² , it is recognized as uneven brightness in the image state Some were done.
Therefore, when the maximum diameter of the light diffusing element is shorter than the pitch width of the lens and the scattering rate is 800 / cm ² or more and 5000 / cm ² , the luminance ratio is 0.94 to 0.99. The half-value angle varied depending on conditions within the range of 45.4 ° to 46.9 °, and the overall optical characteristics could be adjusted without recognizing unevenness. Changes in brightness and half-value angle within this range can greatly contribute to fine adjustment of optical characteristics in response to customer requests.

  In addition, in the optical sheet of the lens having other pitch widths, the luminance ratio and the half-value angle range are different due to the difference in condensing property of the lens, but the change in the optical characteristics with respect to the size of the light diffusing element and the scattering amount, Regarding the unevenness of the display state, the same tendency as the 140 μm pitch lens described above was shown. Therefore, it was found that the overall optical characteristics can be adjusted within the above-described condition range regardless of the width of the lens pitch.

  The optical sheet and display device used this time are examples, and are not limited to the configuration according to the present invention.

  As described above, according to the present invention, the optical sheet is characterized in that the emitted light is partially diffused and emitted in the optical element, so that there is no unevenness without changing the shape of the optical element. An optical sheet, a backlight unit for display, and a display device that can adjust optical characteristics without being recognized can be provided.

Explanatory drawing which shows "BEF" which is an optical sheet which concerns on 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 an example of the backlight provided with the optical sheet. Explanatory drawing which shows an example of a display apparatus provided with the optical sheet which concerns on this invention. Explanatory drawing which shows an example of a display apparatus provided with the optical sheet with a reflection layer which concerns on this invention. Explanatory drawing which shows an example of the optical element sheet | seat which arranged the light transmissive member. Explanatory drawing which shows an example of the optical element sheet | seat which provided the air layer inside. The side view which shows the manufacturing process of an optical element sheet | seat. Explanatory drawing of the optical sheet which provided the elliptical air layer inside the optical element. Explanatory drawing of the optical sheet which provided the circular air layer inside the optical element. The figure which showed the mode of the brightness | luminance measurement. The figure which shows an Example and its result.

Explanation of symbols

20 Light source 65 Lens sheet 66 Light reflection pattern 70 Member 72 Unit prism 79 Light guide plate 50 Diffusion film or DBEF
51 Prism sheet or optical sheet 52 Diffusion film 53 Diffusion plate 54 Light source 55 Lamp house 79 Diffusion film or DBEF
80: Optical element 81 such as prism or lens ... Base sheet 82 ... Diffusion film 83 ... Diffusion plate 84 ... Light source 85 ... Lamp house 86 ... Light reflection layer 90 ..Light transmissive member 91... Air layer 30... Sheet unwinding portion 31... Radiation curable resin 32... Base material sheet 33. ... Sheet winding part 95 ... Lens 96 ... Elliptical air layer 97 ... Circular air layer 98 ... Liquid crystal panel 99 ... Brightness measuring machine

Claims (13)

In an optical sheet having a function of converging or uniformizing light from a light source,
An optical sheet in which an incident surface on which light from the light source is incident and an optical element that controls at least one of a direction, a range, a color, and a luminance distribution when emitting light from the incident surface on the back surface thereof are formed And
Including a diffusing element that diffuses light into the optical element;
An optical sheet characterized by that.   The optical sheet according to claim 1, wherein the optical element is a prism or a lens.   3. The optical sheet according to claim 1, wherein the diffusing element is a light-transmitting resin fine particle or a fine bubble-like air layer.   4. The optical sheet according to claim 1, wherein a maximum particle size per unit particle of the diffusing element is shorter than a formation pitch width of the optical element.   5. The optical sheet according to claim 1, wherein the diffusing element has a circular shape.   5. The optical sheet according to claim 1, wherein the diffusing element has an elliptical shape.   5. The optical sheet according to claim 1, wherein the diffusing element has an indefinite shape. 8. The optical sheet according to claim 1, wherein the optical sheet includes a base sheet, the optical element is provided on a surface of the base sheet, and the unit area of the diffusion element per unit area on the base sheet. An optical sheet having a number of 800 / cm ² or more and 5000 / cm ² or less.   9. The optical sheet according to claim 1, wherein the optical sheet includes a base sheet, the optical element is provided on a surface of the base sheet, and the optical element is cured by a thermoplastic or radiation curable resin. An optical sheet comprising a substrate and formed by polymerizing and bonding on a surface of the base sheet, or the optical element is integrally formed with the base sheet.   A backlight unit for display, comprising at least a direct light source and the optical sheet according to any one of claims 1 to 9.   A display backlight unit comprising at least an edge light source and a surface light source including a light guide plate and the optical sheet according to any one of claims 1 to 9. An image display element comprising a liquid crystal display element that defines a display image according to transmission / shading in pixel units;
A display device comprising the backlight unit according to claim 10. An image display element comprising a liquid crystal display element that defines a display image according to transmission / shading in pixel units;
Cold cathode ray tube or laser, EL, LED light source,
A display device comprising the optical sheet according to claim 1.

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