JP5066919B2 - Optical sheet - Google Patents

Description

  The present invention relates to an improvement in an optical sheet having a brightness enhancement function in a display represented by an image display device (liquid crystal display) incorporating a liquid crystal display element.

Since the liquid crystal display is not self-luminous type like other image display devices (plasma display panel, organic EL display, field emission display, etc.), a light source, that is, a backlight unit 40 (see FIG. 1) is required. Is almost. The backlight unit 40 includes, for example, a light source (cold cathode tube 23) housed in a lamp house (light reflecting sheet) 27 and an optical sheet 60 such as a light diffusion sheet.
Therefore, in the liquid crystal display, the power consumption of the backlight unit 40 is added to the power consumption necessary for driving the liquid crystal display element 42.
Therefore, in order to reduce the power consumption of the backlight unit 40 as much as possible, an attempt is made to reduce the total power consumption of the display by using an optical sheet having a brightness enhancement function.

As a brightness enhancement sheet for reducing the power consumption of the backlight unit, a brightness enhancement film (BEF) developed by 3M USA is known.
JP, 6-102506, A An optical sheet in which a prism shape is formed on one surface of a translucent film and transparent convex dots are formed on the other surface, and further combined with a light guide plate and a diffusion film. The liquid crystal display device is provided as a liquid crystal display device having high luminance and no moiré phenomenon.

  The 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 to the display screen (direction F shown in FIG. 2).

  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.
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, 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, although the light intensity distribution emitted from the optical sheet using BEF as shown in FIGS. 2 and 3 has the highest light intensity in the visual direction F of the viewer, the light emitted wastefully from the lateral direction is also present. There is a problem that it increases.

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

A lens 44 for guiding the light traveling in the optical sheet 38 to the liquid crystal display element 42 is provided on the surface of the transparent base material (transparent support) 39 of the optical sheet 38 on the liquid crystal display element 42 side. As shown in the perspective view of FIG. 5, the lens 44 has a plurality of unit lenses repeatedly forming an array structure.
Further, a light reflection layer 48 having a stripe pattern having an opening 46 in the vicinity of the focal plane of the lens 44 is provided on the other surface.
The light reflecting layer 48 is a stripe in which light reflecting portions 47 containing a white pigment and having a light reflecting function, and openings 46 provided at positions corresponding to unit lenses or unit prisms 1: 1 are alternately arranged. It is a structure of the shape.

  The light reflecting layer 48 is obtained by mixing a mixture of white titanium dioxide (TiO2) powder in a transparent adhesive solution or the like with a predetermined pattern (if the unit lens is a semi-cylindrical convex cylindrical lens group, each unit lens Is formed in a stripe shape having an opening 46 corresponding to the ratio 1: 1.) And printed (or transferred).

FIG. 6 is an explanatory diagram showing 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 enters the polarizing plate 49 and only light having a predetermined polarization component is guided to the liquid crystal display element 42.

  On the other hand, the light that could not pass through the opening 46 is reflected by the light reflection layer 48, returned to the diffusion plate 26 side, and guided to the reflection 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. 6 and is emitted by the lens 44 after being narrowed within a predetermined angle φ as shown in FIG.

In the backlight unit 40 using such an optical sheet 38, the size and the position of the opening 46 of the optical sheet 38 are adjusted to increase the light use efficiency, and the light is emitted from the lens 44 in the front direction F. Can be controlled to increase the proportion of light emitted.
JP 2000-284268 A

  However, the backlight unit disclosed in Patent Document 4 is advantageous in terms of the utilization efficiency of the backlight light source, but requires the formation of a light-reflective stripe pattern in addition to the production of the lens portion. There are problems such as variations in brightness due to variations in edge shape.

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide an optical sheet, a backlight unit, and a display that adjust the edge shape and do not cause variations in optical characteristics.

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 the optical sheet is formed on a thin plate-like transparent support and one surface of the transparent support. It has a structure in which unit lenses or unit prisms are arranged in parallel in a stripe shape, and has a light reflecting layer on the other surface of the transparent support, and the light reflecting layer has a light reflecting function containing a white pigment. The light reflecting portion has a stripe structure in which openings provided at positions corresponding to the unit lenses or unit prisms at a ratio of 1: 1 are alternately arranged, and the location of the light reflecting portion facing the opening The edge in contact with the transparent support has a periodic structure that periodically changes along the longitudinal direction of the reflecting portion, and the edge is formed by the edge of the opening sandwiched between the edges on both sides. Width When the P, where the variation width of the periodic structure of the edge and [Delta] P, Ri range der of ΔP <P / 3, the pattern pitch of the periodic structure of the edge when the T, T <at 58.2μm Oh, wherein the Rukoto.

  2. The optical sheet according to claim 1, wherein an arrangement pitch of the unit lenses is 0.3 mm or less.

  The optical sheet according to claim 1, wherein the transparent support has a thickness of 30 μm to 200 μm.

The thickness of the light reflecting layer is an optical sheet according to claim 1 or 2, wherein it is 5 m to 30 m.

Transmittance of the light reflecting layer is an optical sheet of claim 1, 2 or 5, wherein a 15% or less.

A light source by the cold cathode fluorescent tube or LED, is disposed on the light emission side of the light source, the display backlight unit, characterized in that it comprises at least an optical sheet according to any one of claims 1 to 5 is there.

An image display device comprising a liquid crystal display device which defines a display image in accordance with the transmission / light shielding for each pixel, a display characterized by comprising a backlight unit 請 Motomeko 6 wherein.

As shown in FIGS. 5 and 8, the optical sheet 38 used for the illumination optical path control in the display backlight unit of the present invention has a thin plate-like transparent support 39 and one surface of the transparent support 39. The unit lens 44 or the unit prism has a structure in which stripes are arranged in parallel.
A light reflecting layer 48 is provided on the other surface of the transparent support 39.
In the light reflection layer 48, a light reflection portion 47 containing a white pigment and having a light reflection function, and an opening portion 46 provided at a position corresponding to the unit lens 44 or the unit prism 1: 1 are alternately arranged. This is a striped structure.
As shown in FIG. 7, the edge 50 where the portion of the light reflecting portion 47 facing the opening 46 contacts the transparent support 39 has a periodic structure that periodically changes along the longitudinal direction of the light reflecting portion 47. ing.
The edge 50 is in the range of ΔP <P / 3, where P is the line width of the opening 46 sandwiched between the edges 50 on both sides, and ΔP is the variation width of the periodic structure of the edge 50.
By making the edge-shaped periodic structure (see FIG. 7) of the light reflecting layer 48 within a range satisfying ΔP <P / 3, it is possible to prevent the occurrence of luminance variations.
The luminance variation due to the variation in the shape of the edge portion 50 of the light reflecting layer 48 of the optical sheet is proportional to the area of the opening 46. When the length in the stripe direction is a minute unit, the area ratio of the opening 46 can be regarded as the ratio of the opening line width.
The maximum line width of the opening 46 is P + ΔP, the minimum line width of the opening 46 is P−ΔP, and the maximum ratio due to the variation in the opening line width is (P−ΔP) / (P + ΔP) Equation 1
Thus, the luminance ratio can also be expressed by this equation.
The recognizable brightness ratio of the human eye is generally less than 0.5 in dark / bright, so if the brightness ratio expressed by Equation 1 is greater than 0.5, the observer will recognize the brightness variation. I can't do it.
Therefore, if the relationship of ΔP <P / 3 is satisfied from (P−ΔP) / (P + ΔP)> 0.5, luminance variation due to variation in shape of the edge portion 50 of the stripe does not occur.

By satisfying T <58.2 μm as the pattern pitch T of the periodic structure of the shape of the edge portion 50 of the light reflecting layer 48, it becomes possible to prevent luminance variation and visualization of the shape of the edge portion 50.
Since the resolution of the human eye is generally a viewing angle of 1 minute, when observed at a position 20 cm from the display, the pattern pitch that can be identified from the following equation is 58.2 μm.
C / L = tan θ
C: Identifiable pattern pitch [m]
L: Observation distance [m]
θ: Viewing angle [degree]
Here, calculation was performed by substituting the observation distance of 20 cm for L and 1 minute (1/60 degrees), which is the resolution of the human eye, for θ.
That is, if the pattern pitch is less than 58.2 μm, it cannot be recognized by human eyes. Therefore, when the pattern pitch T satisfies T <58.2 μm, the shape of the edge portion 50 is not visible, and the change in luminance generated in the shape of the edge portion 50 cannot be identified by the human eye.

Further, by setting the arrangement pitch of the unit lenses 44 to 0.3 mm or less, it is possible to cope with high resolution of the display, and when the thickness of the transparent support 39 is 30 μm to 200 μm, the transparent support It is possible to maintain the strength of 39.
If the thickness of the light reflecting layer 48 (light reflecting portion 47) is 5 μm to 30 μm, it is possible to obtain light reflectance.
If the transmittance of the light reflecting layer 48 (light reflecting portion 47) is 15% or less, it is possible to solve the problem of penetrating transmitted light due to light transmitted through the light reflecting layer 48 (light reflecting portion 47). .

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 5 is a cross-sectional view of the optical sheet of the present invention.

Example 1
For the transparent support 39, a PET film (Toyobo: A4300) was used.
A transparent support 39 having a thickness of 75 μm was used.

  The lens portion 44 has a shape of a plurality of cylindrical lenticular lenses having a substantially semi-cylindrical shape. An ultraviolet curable resin was applied to the transparent support, passed through a lens molding roll, and the shape of the lens molding roll was transferred. At the same time, the resin layer was cured by ultraviolet irradiation to perform lens molding.

The light reflecting layer 48 was made of white ink mainly composed of TiO ₂ , had a thickness of 12 μm, and had a transmittance of 6%.

The stripe shape of the light reflection layer 48 (a stripe structure in which the light reflection portions 47 and the openings 46 are alternately arranged) was formed by a photolithography method using the following photosensitive photopolymer.
A photopolymer layer having a characteristic that the adhesiveness disappears due to light exposure is formed on the entire surface on the side opposite to the lens portion, and is defined according to the light condensing action of each unit lens by exposure from the lens portion side. A method of transferring and forming a white transfer layer only at a portion corresponding to the non-light-collecting portion of the light-collecting portion (the portion where the photopolymer adhesive property disappears) / the non-light-condensing portion (the portion where the photo-polymer adhesive property remains) But I made it.
In this case, the stripe shape of the light reflecting layer 48 is that the opening line width P is 52 μm, the fluctuation width of the periodic structure with the edge portion 50 shape: ΔP is 3 μm, and the pattern pitch of the periodic structure with the edge portion 50 shape is T = 10. .1 μm.
As a result of observing with a liquid crystal display in which the backlight unit 40 provided with the optical sheet 38 was incorporated, there was no luminance variation and no visible edge shape.

(Example 2)
The stripe shape of the light reflection layer 48 is such that the light reflection layer 48 is applied to the non-lens surface of the transparent support 39 after the lens is molded, and laser light is incident from the lens surface side, and the light reflection layer of the lens condensing part It could also be created by a method of removing 48.
In this method, the stripe shape of the light reflecting layer 48 is such that the opening line width: P is 65 μm, the fluctuation width of the periodic structure of the edge portion 50 shape: ΔP is 15 μm, and the pattern pitch of the periodic structure of the edge portion 50 shape is T. It was 30.0 μm.
As a result of observing with a liquid crystal display in which the backlight unit 40 provided with the optical sheet 38 was incorporated, there was no luminance variation and no visible edge shape.

  From Examples 1 and 2, if the value characterizing the stripe shape of the opening line width: P, edge shape periodic structure variation width: ΔP, edge shape periodic structure pattern pitch: T is within the scope of the claims, It was experimentally confirmed that luminance variation and edge shape visualization did not occur.

  The example given here is only an example, and does not limit these configurations.

Schematic which shows the structure of a general display. 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. Explanatory drawing which shows an example of the display by this invention. The perspective view which shows the optical sheet by this invention. Explanatory drawing which shows the optical path control characteristic of the backlight by the optical sheet of this invention. The top view which looked at the optical sheet by this invention from the light reflection layer side. The expanded sectional view of the stripe part of the light reflection layer of the optical sheet by this invention.

Explanation of symbols

21 Lamp House 23 Backlight Light Source 23a Backlight Light 26 Diffuser 27 Reflector 32 Diffuser Film 38 Optical Sheet 39 Transparent Base 40 Backlight Unit 42 Liquid Crystal Display Element 44 Lens 46 Opening 47 Light Reflector 48 Light Reflective Layer 49 Polarizing plate 50 Edge portion 60 of light reflection layer Optical material laminate 70 Member 72 Unit prism

Claims (7)

In an optical sheet used for illumination light path control in a backlight unit for display,
The optical sheet is
A thin transparent support,
Having a structure in which unit lenses or unit prisms are arranged in parallel on one surface of the transparent support;
A light reflecting layer on the other surface of the transparent support;
The light reflection layer has a stripe shape in which a light reflection portion containing a white pigment and having a light reflection function and openings provided at positions corresponding to the unit lenses or unit prisms in a 1: 1 ratio are alternately arranged. Is the structure of
The edge where the portion of the light reflecting portion facing the opening contacts the transparent support has a periodic structure that periodically changes along the longitudinal direction of the reflecting portion,
The edges of the line width of the opening sandwiched on both sides of the edge When the P, where the [Delta] P the variation width of the periodic structure of the edge, Ri range der of [Delta] P <P / 3,
If the pattern pitch of the periodic structure of the edge is T, Ru T <58.2μm der,
An optical sheet characterized by that.   2. The optical sheet according to claim 1, wherein the arrangement pitch of the unit lenses is 0.3 mm or less.   The optical sheet according to claim 1, wherein the transparent support has a thickness of 30 μm to 200 μm. The thickness of the light reflecting layer is, according to claim 1 or 2 optical sheet, wherein it is 5 m to 30 m. Claim 1, 2 or 5 optical sheet, wherein a transmittance of the light reflecting layer is 15% or less. A light source by the cold cathode fluorescent tube or LED, the light source of the disposed on the light exit side, display backlight unit, wherein at least comprising an optical sheet according to any one of claims 1-5. Comprising an image display device comprising a liquid crystal display device which defines a display image in accordance with the transmission / light shielding for each pixel, the backlight unit 請 Motomeko 6,
A display characterized by that.

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