JP2008203520A - Optical sheet, backlight unit using the same and display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet which has both of a lens part and a reflection layer and is advantageous since the yellowness degree of the optical sheet is suppressed and to provide a backlight unit for a display and the display apparatus. <P>SOLUTION: The lens part 45 obtained by forming a group of convex cylindrical lenses or hemispherical convex lenses in parallel is arranged on one surface of the optical sheet 38 in the thickness direction and the reflection layer 47 is arranged on the other surface of the optical sheet 38 in the thickness direction. The lens part 45 is made to face a liquid crystal panel 42 and the reflection layer 47 is made to face a light source (a cold cathode tube 23). The reflection layer 47 is composed of: a light reflecting part 48 arranged in an area including the surface of the optical sheet where light is not concentrated by the lens part 45; and a light transmissive part 46 arranged in the area other than that of the light reflecting part 48. The light reflecting part 48 contains an acrylic resin. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a display device including a backlight system that irradiates a display element whose display pattern is defined according to transmission / non-transmission or transparent / scattering states in pixel units, represented by a liquid crystal panel, from the back side. Regarding improvements.
As the display device in which a liquid crystal panel is used,
(1) A reflective liquid crystal display device of a type that does not have a built-in light source such as a backlight or an edge light but generates display light by ambient light such as sunlight or indoor illumination light.
(2) A reflective liquid crystal display device of a type that uses not only ambient light such as sunlight and indoor illumination light but also a front light arranged on the front side (observer side) of the liquid crystal panel as a built-in light source of the device.
(3) A transmissive liquid crystal display device of a type that uses illumination light from a built-in light source such as a backlight or an edge light mainly for generating display light regardless of ambient light such as sunlight or indoor illumination light.
(4) A transflective liquid crystal display device of a type that uses both illumination light from a built-in light source such as a backlight and edge light and ambient light such as sunlight and indoor illumination light to generate display light.
The present invention is applied to the types (3) and (4).

In recent years, liquid crystal display devices using a liquid crystal panel made of TFT or STN are being commercialized mainly in (color) notebook PCs (personal computers) in the OA field.
In such liquid crystal display devices, conventionally, a so-called backlight method has been adopted in which a light source is arranged on the back side (counter-viewer side) of the liquid crystal panel and the liquid crystal panel is irradiated with light from this light source. ing.
Such a backlight system is roughly divided by attaching a light source lamp such as a cold cathode fluorescent lamp (CCFT) along a side end portion 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 (so-called edge light method)” in which light from the light is multiply reflected within the light guide plate, and a “direct type method” in which the light guide plate is not used.

As a liquid crystal display device on which a light guide plate light guide type backlight system is mounted, for example, one having a configuration as shown in FIG. 1 is generally known.
In this, a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 is provided on the upper side, and a light guide plate made of a transparent base material such as PMMA (polymethyl methacrylate) or acrylic having a substantially rectangular plate shape on the lower surface side thereof. 79 is disposed, and a diffusion film (diffusion layer) 78 is provided on the upper surface (light emission surface) of the light guide plate.
Further, on the lower surface of the light guide plate 79, a scattering reflection pattern portion for efficiently scattering and reflecting the light introduced into the light guide plate 79 in the direction of the liquid crystal panel 72 is provided by printing or the like ( A reflection film (reflection layer) 77 is provided below the scattering reflection pattern portion.

  In addition, a light source lamp 76 is attached to the light guide plate 79 along the side end portion, and the back side of the light source lamp 76 is arranged so that the light from the light source lamp 76 is efficiently incident on the light guide plate 79. A lamp reflector 81 having a high reflectivity is provided so as to cover it. The scattering reflection pattern part is formed by printing, drying, and forming a mixture of white titanium dioxide (TiO2) powder in a solution such as a transparent adhesive in a predetermined pattern, for example, a dot pattern. This is one means for increasing the brightness by providing directivity to the light incident on the light plate 79 and guiding the light toward the light exit surface.

  Further, recently, in order to increase the light utilization efficiency and increase the brightness, as shown in FIG. 2, a prism film (prism layer) having a light condensing function between the diffusion film 78 and the liquid crystal panel 72 is used. ) 74 and 75 have been proposed. The prism films 74 and 75 are configured to collect the light emitted from the light exit surface of the light guide plate 79 and diffused by the diffusion film 78 on the effective display area of the liquid crystal panel 72 with high efficiency.

However, in these methods illustrated in FIG. 1 and FIG. 2, the control of the visual field range is left only to the diffusibility of the diffusion film 78, which is difficult to control, and the central part in the diffusion direction goes brightly to the peripheral part. The characteristic which becomes so dark is inevitable.
For this reason, when the liquid crystal screen is viewed from the side, the luminance is greatly reduced, and the light utilization efficiency is reduced.
Furthermore, in the method using the prism film illustrated in FIG. 2, two prism films are required, which not only greatly reduces the amount of light due to the absorption of the film but also increases the cost due to the increase in the number of members. It was also.

On the other hand, the direct type is used for a display device such as a large liquid crystal TV in which it is difficult to use a light guide plate.
As a direct type liquid crystal display device, the configuration illustrated in FIG. 3 is generally known. In this, a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 is provided on the upper side, and a row of light sources 51 made of fluorescent tubes or the like is provided on the lower surface side thereof. A diffusion film (diffusion layer) 74 is provided on the surface.
Further, recently, a prism film (prism layer) having a light condensing function between the diffusion film 74 and the liquid crystal panel 72 as in the case of FIG. ) Is proposed.
This prism film collects the light emitted from the light source 51 and diffused by the diffusion film 74 on the effective display area of the liquid crystal panel 72 with high efficiency.

However, even in the configuration illustrated in FIG. 3, the control of the visual field range is left only to the diffusibility of the diffusion film 74, and it is difficult to control, and the characteristic that the central part in the diffusion direction becomes brighter and darker as it goes to the peripheral part is Inevitable.
For this reason, when the liquid crystal screen is viewed from the side, the luminance is greatly reduced, and the light utilization efficiency is reduced. Furthermore, in the method using a prism film, since the number of prism films is two, not only the light quantity is greatly reduced due to absorption of the film, but also the cost is increased due to an increase in the number of members.
Further, if the distance between the light sources is too wide, uneven brightness tends to occur on the screen, and the number of light sources cannot be reduced, leading to an increase in power consumption and an increase in cost.

By the way, in such a liquid crystal display device, light weight, low power consumption, and high brightness are strongly demanded as market needs, and accordingly, the backlight system mounted on the liquid crystal display device is also light weight, low consumption. Power and high brightness are required.
In particular, in a color liquid crystal display device that has recently made remarkable progress, the panel transmittance of the liquid crystal panel is significantly lower than that of a monochrome-compatible liquid crystal panel. It has become an indispensable issue for obtaining power consumption.
However, in the conventional configuration as described above, it is difficult to say that the demand for high luminance and low power consumption has been sufficiently met today, because the liquid crystal display device is further reduced in thickness. The development of a backlight system that can realize a liquid crystal display device with high brightness, high display quality, and low power consumption is awaited.

  In view of the above situation, the present applicant includes a liquid crystal panel and light source means for irradiating light from the back side to the liquid crystal panel, and the light source means has a lens layer for guiding light from the light source to the liquid crystal panel. A liquid crystal display device provided with a light shielding portion having an opening in the vicinity of the focal plane of the lens layer is proposed. (For example, see Patent Document 1)

Patent Document 1 discloses a configuration in which a lens sheet 15 having a light shielding portion 18 is disposed between a liquid crystal panel and a backlight unit, as shown in FIG.
The effect obtained by interposing the lens sheet 15 having the above-described structure is that the diffusibility of the light emitted from the light guide plate can be modulated (collimated) by the lens action, and can be emitted with the direction aligned on the liquid crystal panel side. It is in the point.
In addition, by forming the light-shielding portion 18 having an opening at a specific location, it is possible to selectively increase the amount of light incident on the pixels of the liquid crystal panel, improving the use efficiency of the backlight, and the opening. It can be mentioned that the viewing area of the display light can be controlled by controlling the shape.

In addition, when the lens sheet is used in a direct type backlight unit that does not employ a light guide plate constituting an edge light type surface light source, a light diffusion layer (light diffusion plate) is provided between the light source and the lens sheet. A configuration in which a single or a combination of light diffusion films is interposed is employed.
By interposing the light diffusing layer, the silhouette of the light source (lamp image) by the cold cathode ray tube (CCFL) or LED is strongly visualized, and a part in the screen called a hot spot or hot bar appears locally bright. This eliminates the phenomenon and makes the display luminance distribution in the screen uniform.

When a light diffusing layer is provided on the flat surface of the lens sheet on the side opposite to the lens portion, the flat surface without a step is not clear between the flat lens sheet and the light diffusing layer. When both are substances having a refractive index close to each other, incident light does not enter the unit lens at an intended angle, and it becomes difficult to exhibit optical characteristics as designed by the unit lens.
In particular, when adopting a configuration in which the lens sheet and the light diffusion layer are laminated and integrated via an adhesive layer or an adhesive layer, unexpected generation of incident light components (or deterioration of the function due to the light diffusion layer) is caused. It becomes easier to invite and it becomes more difficult to achieve optical characteristics as designed.

The present applicant has further proposed an optical sheet having the configuration shown in FIG. 5 in view of the above circumstances. (See Patent Document 2)
In the following description of the present application, “diffusion” and “scattering” of optical characteristics, “adhesive layer” and “adhesive layer”, and “optical sheet” and “optical film” according to the present application are synonymous. Will be used.

  In the optical sheet used for illumination light path control in the backlight unit for display, the optical sheet scatters at least the illumination light to the exit surface side which is the non-incident surface side in order from the incident light incident side. A light scattering layer, an adhesive layer or an adhesive layer, and adhered or adhered to the light scattering layer by the adhesive or adhesive material, and has a highly light reflective surface facing the emission surface side of the light scattering layer A light reflecting layer for reflecting light scattered by the light scattering layer to the light scattering layer side, and a flat back surface fixed to the other surface of the light reflecting layer, and a plurality of unit lenses disposed on the surface The light reflecting layer has an opening corresponding to 1: 1 for each of the unit lenses, and the thickness of the adhesive layer or the adhesive layer is larger than that of the light reflecting layer. Characterized by thinness .

The optical sheet 10 shown in FIG. 5 includes a light diffusion layer 13 that guides the light L from the light source 20 from the incident surface 11 and scatters the light L toward the emission surface 12 side.
A light reflecting layer 14 is fixed to the light emitting surface 12 of the light diffusion layer 13 by an adhesive layer 18. The light reflecting layer 14 is made of, for example, white ink, a metal foil, or a metal vapor deposition layer, and a plurality of openings 15 made of, for example, an air layer are regularly provided.
By making the adhesive layer 18 thinner than the light reflecting layer 14, it is preferable that a portion of the adhesive layer 18 that does not contact the light reflecting layer 14 enters the opening 15 and is buried.

The behavior of light in the backlight unit using the optical sheet 10 shown in FIG. 5 will be described.
Light L from the light source 20 is incident from the incident surface 11 of the light diffusion layer 13.
Here, the light L incident on the light diffusion layer 13 is randomly scattered.
Of the scattered light, only the light γ that has passed through the opening 15 is guided to the lens sheet 17.

Since each opening 15 is provided so as to face the apex of each unit lens 16 provided in the lens sheet 17, each unit lens 16 has only the light confined by each corresponding opening 15. Is guided.
That is, since each opening 15 functions like a slit, only light γ with a narrowed scattering angle is incident on each unit lens 16, so that light incident on the unit lens 16 from an oblique direction is incident. Therefore, it is possible to eliminate the light that is emitted in the lateral direction without traveling in the visual direction F of the viewer.

On the other hand, the light β that could not pass through the opening 15 is reflected by the light reflection layer 14 and returned to the light diffusion layer 13 side.
Then, after being similarly scattered in the light diffusion layer 13, eventually becomes light γ with a narrowed scattering angle, then enters the unit lens 16 through the opening 15, and enters the predetermined angle φ by the unit lens 16. It is emitted after being diffused.

As described above, the light L from the light source 20 is scattered, and only the light γ with a narrowed scattering angle can be incident on the unit lens 16, and the light that could not be incident on the unit lens 16 is wasted. Therefore, it is possible to emit light while controlling the diffusion range while improving the utilization efficiency of the light from the light source 20.
JP 2000-284268 A WO2006 / 080530

Incidentally, as described above, various optical sheets are used for the backlight member of the liquid crystal display in order to satisfy various optical performances such as desired light collection and diffusion.
Among them, in an optical sheet having both a lens portion and a reflective layer on both sides in the thickness direction of a single transparent substrate (single plate material or film), for example, a component called a reflective layer in addition to a prism Therefore, the degree of yellowing of the optical sheet may increase due to heat and humidity, which is disadvantageous in obtaining a clear display image.
The present invention has been devised in view of the above circumstances, and an object of the present invention is to provide an optical sheet and a display which are advantageous in suppressing the degree of yellowing of an optical sheet having both a lens portion and a reflective layer. It is to provide a backlight unit and a display device.

In order to achieve the above object, the present invention provides an optical sheet used for illumination light path control in a display backlight unit, wherein a convex cylindrical lens group or a hemispherical convex lens group is formed on one surface in the thickness direction of the optical sheet. Are provided in parallel, a reflective layer is provided on the other surface in the thickness direction of the optical sheet, and the reflective layer is provided in a region including a non-light-collecting surface by the lens unit. It is comprised by the light reflection part and the light transmission part provided in the area | regions other than the said light reflection part, The said light reflection part is comprised including the acrylic resin, It is characterized by the above-mentioned.
According to another aspect of the present invention, there is provided a display backlight unit comprising at least a direct light source and the optical sheet according to claim 1 on a back surface of an image display element defining a display image.
According to another aspect of the present invention, there is provided a display backlight comprising at least a surface light source including an edge light type light source and a light guide plate and an optical sheet according to claim 1 on the back surface of an image display element that defines a display image.・ It is a unit.
In addition, the present invention irradiates illumination light from an illumination light source disposed on the side opposite to the observer with respect to a display element whose display pattern is defined according to transmission / non-transmission or transparency / scattering in pixel units. In the display device configured to generate display light through the display element and emit the display light to an observer side, an optical sheet is disposed immediately before the illumination light is incident on the display element, and the optical facing the display element A thickness of the optical sheet facing the illumination light source is provided on one surface in the thickness direction of the sheet by providing a lens portion in which a convex cylindrical lens group or a hemispherical convex lens group for guiding illumination light to the display element is formed in parallel. A reflective layer is provided on the other surface in the vertical direction, and the reflective layer includes a light reflecting portion provided in a region including a non-light condensing surface by the lens portion and light provided in a region other than the light reflecting portion. Consists of transmission part Is, the light reflecting portion is characterized in that it is configured to include an acrylic resin.

  According to this invention, since the light reflection part is comprised including an acrylic resin, the yellowing degree of the optical sheet which has both a lens part and a reflection layer is suppressed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 6 is an explanatory diagram showing an embodiment in which the present invention is applied to a liquid crystal display device including a direct type backlight unit 40.
An optical sheet 38 is provided facing the liquid crystal panel 42.
A lens portion 45 in which a convex cylindrical lens group or a hemispherical convex lens group is formed in parallel is provided on one surface in the thickness direction of the optical sheet 38, and the reflective layer 47 is provided on the other surface in the thickness direction of the optical sheet 38. Is provided.
The lens unit 45 faces the liquid crystal panel 42, and the reflection layer 47 faces the light source (cold cathode tube 23).
The reflection layer 47 includes a light reflection portion 48 provided in a region including a non-light-collecting surface by the lens portion 45 and a light transmission portion 46 provided in a region other than the light reflection portion 48.
In the present embodiment, a cylindrical lens 44 (unit optical element) for guiding the light traveling in the optical sheet 38 to the liquid crystal panel 42 is arranged in parallel on the surface of the transparent base 39 of the optical sheet 38 on the liquid crystal panel 42 side. Is provided. In place of the semi-cylindrical convex cylindrical lens 44, there may be a substantially hemispherical convex lens or a prism.

Furthermore, a reflective layer 47 having a stripe pattern is provided on the other surface.
The reflection layer 47 includes a light reflection part 48 and a light transmission part (opening part) 46 provided in a region other than the light reflection part 48, in other words, near the focal plane of the lens 44.
The light reflecting portion 48 is formed by printing a mixture of white titanium dioxide (TiO ₂ ) powder mixed with a transparent adhesive solution in a predetermined pattern, for example, a dot pattern. The reflective layer 47 including the light reflecting portion 48 can also be formed by transfer (UV bonding or thermocompression bonding).
As a result, only the light that has passed through the opening 46 out of the light emitted from the diffusion film 32 enters the cylindrical lens 44 and is emitted after being condensed in a certain direction by the cylindrical lens 44.
Then, the light enters the polarizing plate 49 and only light having a predetermined polarization component is guided to the liquid crystal panel 42.

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 diffuser plate 26 again by being reflected by the reflector 27 and is diffused again on the diffuser plate 26, and eventually becomes light with a narrowed incident angle, and then passes through the opening 46 to form a cylindrical lens. 44, and is emitted within a predetermined angle by the cylindrical lens 44.
In FIG. 6, reference numerals 21 and 27 denote reflectors, and reference numeral 23 denotes a cold cathode tube.

And in this Embodiment, the light reflection part 48 is comprised including the acrylic resin.
Since the light reflecting portion 48 requires patterning corresponding to the cylindrical lens 44, a relatively soft resin is desirable, and an acrylic resin is preferable.
The light reflecting portion 48 is made of a binder containing an acrylic resin and a pigment, and the pigment volume with respect to the total volume is desirably 50% or more from the viewpoint of suppressing the yellowing degree.

In the present embodiment, a cylindrical lens is molded with a UV curable resin on PET.
A UV curable adhesive was bonded to the surface opposite to the lens in advance, UV was irradiated from the lens side, and then a reflective layer was bonded to the uncured part.
With this method, the lens and the light reflecting layer can be easily arranged in a 1: 1 correspondence.

The reflective layer 47 (light reflecting portion 48) was made of titanium dioxide and acrylic resin or urethane resin at a volume ratio of 40:60.
Thereafter, the prepared sheet was stored in an environment of a temperature of 85 ° C. and a humidity of 85% for 1000 hours, and yellowing relative to the initial value was measured by the following method.
A diffusion plate, a diffusion sheet, a sample sheet, and a diffusion sheet were stacked in this order on the light source, the light source was turned on, and x and y of the emitted light on the normal line of the sample sheet were measured.
The measurement results are shown in FIG.

As can be seen from FIG. 7, the sample sheet having the light reflecting portion 48 configured to contain acrylic resin has a lower degree of yellowing than the sample sheet having the light reflecting portion 48 configured to include urethane resin. It is remarkable that
Therefore, according to the present embodiment, there is provided an optical sheet, a display backlight unit, and a display device that are advantageous in suppressing the degree of yellowing of the optical sheet 38 that has both the lens portion 45 and the reflective layer 47. This is advantageous in obtaining a clear image.

It is explanatory drawing of a display apparatus provided with the conventional backlight unit. It is explanatory drawing of a display apparatus provided with the conventional backlight unit. It is explanatory drawing of a display apparatus provided with the conventional backlight unit. It is explanatory drawing of a display apparatus provided with the conventional backlight unit. It is explanatory drawing of a display apparatus provided with the conventional backlight unit. It is explanatory drawing of a display apparatus provided with the backlight unit of this invention. It is a figure which shows the test result of this invention.

Explanation of symbols

  21, 27 ... Reflector, 23 ... Cold cathode tube, 32 ... Diffusing film, 38 ... Optical sheet, 40 ... Backlight unit, 42 ... Liquid crystal panel, 44 ... Cylindrical lens, 45 ... Lens Part, 47... Reflective layer, 49.

Claims (4)

In an optical sheet used for illumination light path control in a backlight unit for display,
On one surface in the thickness direction of the optical sheet, a lens portion is provided in which convex cylindrical lens groups or hemispherical convex lens groups are formed in parallel,
A reflective layer is provided on the other surface in the thickness direction of the optical sheet;
The reflection layer is composed of a light reflection portion provided in a region including a non-light-collecting surface by the lens portion, and a light transmission portion provided in a region other than the light reflection portion,
The light reflecting portion includes an acrylic resin.
An optical sheet characterized by that. On the back of the image display element that defines the display image,
A display backlight unit comprising at least a direct light source and the optical sheet according to claim 1. On the back of the image display element that defines the display image,
A display backlight unit comprising at least an edge light source and a surface light source comprising a light guide plate and the optical sheet according to claim 1. 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,
On one surface in the thickness direction of the optical sheet facing the display element, a lens unit is provided in which a convex cylindrical lens group or a hemispherical convex lens group that guides illumination light to the display element is formed in parallel,
A reflective layer is provided on the other surface in the thickness direction of the optical sheet facing the illumination light source;
The reflection layer is composed of a light reflection portion provided in a region including a non-light-collecting surface by the lens portion, and a light transmission portion provided in a region other than the light reflection portion,
The light reflecting portion includes an acrylic resin.
A display device characterized by that.

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