JP4506572B2 - Optical sheet and backlight unit and display using the same - Google Patents

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 relates to a backlight unit and a display 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.

Brightness Enhancement Film (BE), a registered trademark of 3M, USA
F) 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 directs this light toward the viewer “on-axis (
on-axis) "redirect" or "recycle".

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. 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.
Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500

  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, control can be performed 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 is the light in the viewer's visual direction F, that is, the angle at 0 ° with respect to the visual direction F as shown in FIG. Although the intensity can be maximized, there is a problem that the amount of light emitted unnecessarily from the lateral direction increases as shown by a small light intensity peak around ± 90 ° shown on the horizontal axis in the figure.

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

On the surface of the transparent substrate 39 of the optical film 38 on the liquid crystal panel 42 side, the optical film 38 is provided.
A lens 44 that guides the light traveling in the interior to the liquid crystal panel 42 is provided. As shown in the perspective view of FIG. 5, 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 reflector 48 is formed by printing a mixture of white titanium dioxide (TiO ₂ ) powder in a transparent adhesive solution or the like in a predetermined pattern, for example, a dot pattern.

Thereby, only the light that has passed through the opening 46 out of the light emitted from the diffusion film 32 enters the lens 44 and is emitted after being condensed in a certain direction by the 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 reflector 48 and diffused by the diffusion plate 26.
Returned to the side and guided to the reflector 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. And by lens 44,
As shown in FIG. 6, the light is emitted within a predetermined angle φ.

In the backlight unit 40 using such an optical film 38, the optical film 3
By adjusting the size and position of the eight openings 46, while improving the light utilization efficiency,
Control can be performed so as to increase the proportion of light emitted from the lens 44 in the front direction S.
JP 2000-284268 A

As described above, an ink containing a white pigment typified by titanium dioxide (TiO ₂ ) powder is used as the reflective material 48 having a stripe pattern formed on the optical film 38.
For light that could not pass through the opening 46, increasing the reflectance by the reflector 48 leads to improvement in utilization efficiency when the light emitted from the light source (backlight) is used as display light. It is desired to increase the white pigment content, and for the purpose of improving the filling property, the white pigment particle size distribution and the white pigment having a volume ratio of 1 to 4 times the binder are mixed. Various ingenuity is given such as.

As described above, in an ink having a pigment content higher than that of a normal printing ink, the pigment is difficult to be fixed in the ink layer dried after pattern formation, and tends to peel off.
An object of the present invention is to propose the above optical sheet that can improve the above problems and can maintain a highly reflective stripe pattern in a stable state even after pattern formation.

In order to achieve the above object, the optical sheet according to the present invention comprises:
In an optical sheet used for illumination light path control in a backlight unit for display,
The flat surface on the side opposite to the lens portion of the lens sheet having a lens portion in which unit lenses made of semi-cylindrical convex cylindrical lenses are arranged on one side has a highly light-reflective surface facing the backlight light source side. A light reflection layer that reflects the light incident on the surface to the backlight source side;
The light reflecting layer has a stripe shape having an opening corresponding to each unit lens of the lens sheet in a ratio of 1: 1,
A surface thin film protective layer is formed on substantially the entire surface of the lens sheet on the side opposite to the lens portion so as to cover the light reflecting layer.

In the optical sheet according to the present invention, a pigment-rich ink layer containing, as a component, titanium dioxide (TiO ₂ ) powder, which is a light reflecting layer preferable for realizing white and high-luminance display light, is formed in a stripe pattern. Even after drying, it can be maintained in a stable state as a display device (or optical sheet), the use efficiency of backlight light can be improved, and high-intensity display light is visible A display device is obtained.

Embodiments of the present invention will be described below.
In forming the light reflecting layer, various methods such as printing (coating), transfer, and photolithography are generally selected as appropriate. When the parallel pitch of the unit lenses of the lens sheet is fine, each unit lens Therefore, a reflective layer (opening) is used as a method of the photolithography method by utilizing the condensing characteristic of the lens itself. It is effective to employ a so-called “self-alignment technique” that defines the formation location of the film.

  As an example of the self-alignment method, a photopolymer layer having a characteristic that adhesiveness disappears due to light exposure is formed on the entire surface on the anti-lens side flat surface. Of the condensing part (part where the photopolymer adhesive property disappears) / non-condensing part (the part where the photopolymer adhesive property remains) specified according to the action, white only at the part corresponding to the non-condensing part A technique for transferring and forming the transfer layer is effective.

<White transfer sheet (thermal transfer foil)>
FIG. 7 is a cross-sectional view showing an example of a (heat-sensitive) white transfer sheet used to form a striped light reflection layer.
The white transfer sheet 10 has a configuration in which a white transfer layer 14 is disposed on a base sheet 12.
As the material of the base sheet 12, PP (polypropylene), PET (polyethylene terephthalate), PE (polyester), or the like well known in the technical field is used.
The thickness of the base sheet 12 is selected in the range of 6 to 50 μm (preferably about 16 to 25 μm).

As the white transfer layer 14, a binder resin made of EVA (ethylene vinyl acetate) containing 30% or less vinyl acetate by weight and having a melt flow rate of 10 g / min or more, and a volume ratio more than this binder resin. Mix with 1 to 4 times white pigment.
As the white pigment, titanium dioxide, barium sulfate, magnesium oxide and the like well known in the art are used.

By mixing the binder resin and the white pigment at such a mixing ratio, the white transfer layer 14 having a thickness of 10 × 10 ⁻⁶ m or more can be formed. The binder resin is not limited to EVA, and another resin may be used. However, a binder resin that is not hard and has a small molecular weight is preferable.

In addition, a dispersing agent, wax, or the like may be added as appropriate to the white transfer layer 14 formed in this manner to stabilize the white transfer layer 14.
As well known in the art, surfactants and surface smoothing agents are also used for the dispersants and waxes used in such applications.

A binder resin made of EVA containing PP as a base sheet 12 and containing 28% vinyl acetate by weight and having a melt flow rate of 40 g per minute, and titanium dioxide having a volume ratio four times that of the binder resin. A white transfer layer 14 having a thickness of 13 × 10 ⁻⁶ m was formed.

  When such a white transfer sheet 10 was used to transfer and form a white layer, it was possible to realize an extremely high reflectance of 91% in total light reflectance at a wavelength of 545 nm.

Moreover, a fine stripe pattern with a pitch of 200 × 10 ⁻⁶ m (200 microns) and a width of 100 × 10 ⁻⁶ m (100 microns) can be accurately formed on the white layer. did it.

Although the white transfer layer 14 is very effective in terms of optical characteristics (hue and reflectance), as described above, the pigment is fixed in the ink layer dried after pattern formation because of the high pigment content. It tends to be difficult to peel off.
Therefore, in the present embodiment, a transfer sheet for providing the surface thin film protective layer 13 so as to cover the surface on which the (light-sensitive) white transfer sheet 10 forms the striped light reflection layer is employed.

<Surface thin film protective layer: transfer sheet>
FIG. 8 is an explanatory view showing the transfer sheet 100 according to the present embodiment, and has a configuration in which the adhesive layer 15 is formed on the base sheet 12 via the surface thin film protective layer 13.
As the material of the base sheet 12, PP (polypropylene), PET (polyethylene terephthalate), PE (polyester), or the like well known in the technical field is used.
The thickness of the base sheet 12 is selected in the range of 6 to 50 μm (preferably about 16 to 25 μm).

As the surface thin film protective layer 13, it is preferable to use a transparent resin containing PMMA (polymethyl methacrylate) as a main component.
In addition to the transparency (translucency) that does not impair the reflection characteristics of the lower white transfer layer 14 (light reflection layer) when applied to the form of an optical sheet, the surface thin film protection layer 13 includes the white transfer layer 14. A function to protect against peeling is required.
The thickness of the surface thin film protective layer 13 is preferably in the range of 1 to 10 μm.
In forming the surface thin film protective layer 15 having mechanical strength, it is also effective to perform a curing treatment by irradiation with heat or radiation, and for imparting hard coat properties, curing is performed by irradiation with ultraviolet rays or electron beams. Use of a photopolymer is preferable in terms of hardness.
Curing treatment of the surface thin film protective layer 13 by radiation irradiation is performed at any stage when the transfer sheet 100 is formed or after the transfer layer is transferred to the optical sheet.

In addition to the main component PMMA resin, the surface thin film protective layer 13 includes a slip agent (to provide slipperiness in film and sheet molding) and light diffusing fine particles (to impart light diffusibility as an optical sheet). At least one of them may be added.
In the present embodiment relating to the form of the thermal transfer sheet, an adhesive layer (heat seal agent) of the type activated by heating is used as the adhesive layer 15.
The thickness of the adhesive layer 15 is preferably in the range of 1 to 20 μm.

<Surface thin film protective layer: Pressure-sensitive transfer label>
The present invention can be applied in a form other than the form of a heat-sensitive transfer sheet, and a form of a pressure-sensitive transfer label can also be adopted.
The basic layer structure of the label is the same as that described above for the heat-sensitive transfer sheet, except that a pressure-sensitive adhesive is used in place of the adhesive layer 15 made of a heat sealant, and the label is used (to an optical sheet). The adhesive layer is covered with a release sheet so that the pressure-sensitive adhesive layer is exposed to the object to be adhered, which is different from the case of the heat-sensitive transfer sheet. (Not shown)

  FIG. 9 is an explanatory diagram showing a state in which a surface thin film protective layer is formed on the flat surface on the side opposite to the lens portion of the lens sheet by the above-described heat-sensitive transfer sheet (or pressure-sensitive transfer label).

  The optical sheet produced as described above is applied to the display device in the same manner as in FIG.

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. The perspective view which shows the optical sheet | seat of FIG. Explanatory drawing which shows the optical path control characteristic of the backlight by the optical sheet of FIG. Sectional drawing which shows an example of the (heat-sensitive) white transfer sheet used in order to form a stripe-shaped light reflection layer. Explanatory drawing which shows an example of the (heat-sensitive) transfer sheet used in order to form a surface thin film protective layer. FIG. 9 is an explanatory diagram showing a state in which a surface thin film protective layer is formed on the flat surface on the side opposite to the lens of the lens sheet by the heat-sensitive transfer sheet (or pressure-sensitive transfer label) of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 White transfer sheet 12 Base material sheet 13 Surface thin film protective layer 14 White transfer layer 15 Adhesive layer 20 Light source 26 Diffusion plate 27 Reflection plate 38 Optical film 40 Backlight unit 42 Liquid crystal panel 44 Lens 46 Opening 48 From striped pattern Reflective material 70 member 72 unit prism 100 transfer sheet

Claims (8)

In an optical sheet used for illumination light path control in a backlight unit for display,
The flat surface on the side opposite to the lens portion of the lens sheet having a lens portion in which unit lenses made of semi-cylindrical convex cylindrical lenses are arranged on one side has a highly light-reflective surface facing the backlight light source side. A light reflection layer that reflects the light incident on the surface to the backlight source side;
The light reflecting layer has a stripe shape having an opening corresponding to each unit lens of the lens sheet in a ratio of 1: 1,
The light reflecting layer contains a vinyl acetate having a weight ratio of 30% or less, a binder resin made of EVA with a mentholate of 10 g / min or more, and a volume ratio of 1 to 4 times the binder resin. It is formed by mixing with white pigment less than double,
It is formed on the light reflecting layer through a layer made of a heat sensitive adhesive or a pressure sensitive adhesive, and a surface thin film protective layer is formed on substantially the entire surface of the lens sheet on the side opposite to the lens. An optical sheet characterized by The light reflecting layer uses a transfer foil having a highly reflective material as a transfer layer,
By the exposure from the lens part side of the lens sheet, in the place corresponding to the non-condensing part defined on the flat surface on the opposite lens part side according to the condensing action of each unit lens,
The optical sheet according to claim 1, wherein the transfer layer is formed by transfer. The optical sheet according to claim 1, wherein the surface thin film protective layer is used in the form of a heat-sensitive transfer foil or a pressure-sensitive transfer label, and is formed on the light reflecting layer. The optical sheet according to any one of claims 1 to 3, wherein the surface thin film protective layer is made of a transparent resin mainly composed of PMMA (polymethyl methacrylate). The optical sheet according to claim 1, wherein the surface thin film protective layer includes at least one of a slip agent and light diffusing fine particles. 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. An image display element composed of a liquid crystal display element that defines a display image according to transmission / shading in pixel units;
A light source using a cold cathode ray tube or LED;
A display comprising the backlight unit according to claim 6.

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