JP2010198940A - Lens sheet for backlight - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens sheet for a backlight in which it can be prevented to form reflection layers 5 to portions except convex parts 21 in a process to form a reflection layer 5 and in which a form that opening parts 22 are contacted with an air layer is apt to be formed in the case other sheet is laminated to an incident face side of a lenticular lens sheet 2. <P>SOLUTION: In the lens sheet for the backlight constituted of the lenticular lens sheet 2, the lenticular lens sheet 2 has a plurality of cylindrical lens 23 groups arranged in parallel on an emitting face side, optical opening parts 22 on the incident face side in the vicinity of a light condensing part of respective cylindrical lenses 23, and a convex part 21 equipped with a reflection layer 5 in a region except the opening parts 22, and a height H (mm) of a part where the reflection layer 5 is installed out of the convex part 21 is expressed in formula (1): 0.06<H≤0.2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a backlight used for a liquid crystal display device, a signboard and the like.

  As backlights for illuminating a transmissive liquid crystal display, a lighting signboard, and the like from the back, there are an edge light method and a direct light method. The direct system is a system in which a plurality of light sources are arranged on the back surface of the apparatus, light is incident on the diffuser plate, the light is made uniform by the diffuser plate, and the light is extracted to the exit surface facing the incident surface (see, for example, Patent Document 1). ).

  There is an increasing demand for large-sized image display devices in monitors for televisions and personal computers. For backlights used in large-sized image display devices, the direct method, which is advantageous in terms of brightness improvement and uniformity, has become the mainstream. ing. The direct type backlight includes a reflection plate, a light source, a diffusion plate, a lens sheet, and the like from the back side. The reflection plate has a function of reflecting light emitted from the light source to the back side in the front direction. The diffusing plate has a function of diffusing light to reduce the appearance of the image of the light source and uniforming the in-plane luminance.

  The lens sheet has a function of converting diffused light into appropriate directivity. For example, in Patent Document 2, a lenticular lens is provided on the exit surface, a reflective layer is provided in addition to the condensing part of the lenticular lens on the entrance surface, and a portion other than the reflective layer is used as an opening, thereby allowing incident diffused light to be front-facing. A lens sheet that condenses light in a direction is disclosed (for example, Patent Document 2).

  In such a lens sheet, it is preferable to provide a convex portion at a position where the reflective layer on the incident surface is to be formed because a method such as applying the reflective layer to the top of the convex portion can be employed (for example, Patent Document 3). In patent document 3, the numerical value of 60 micrometers or less is shown as an upper limit of the height of the convex part which should form the reflective layer of an entrance plane. This is because the effect of light rays entering from the slope of the convex portion where the reflective layer is not formed and condensing in the front direction is reduced.

  However, when the light-reflective ink is provided on the top of the convex portion by roll printing or the like, the height of the convex portion is preferably higher than 60 μm from the viewpoint of preventing the ink from adhering to the opening. When the light reflective ink is made of a transparent binder mixed with a light diffusing material, for example, if the ink is thin, light is transmitted and cannot be sufficiently reflected. Therefore, the thickness of the ink needs to be 5 μm or more (for example, 10 μm), and it is preferable that the height of the convex portion is high.

Japanese Patent Laid-Open No. 2-17 JP 2005-221619 A JP 2007-086499 A JP 2003-149743 A

  The inventor paid attention to the height of the convex portion and found that a lens sheet having a higher convex portion than the conventional lens sheet can exhibit optical performance superior to that of the conventional art by setting the specification within a specific range.

The present invention is a backlight lens sheet comprising a lenticular lens sheet,
The lenticular lens sheet has a plurality of cylindrical lens groups arranged in parallel on the exit surface side,
On the incident surface side, there is an optical opening in the vicinity of the condensing part of the cylindrical lens, and in a region other than the opening, a convex part having a reflective layer is provided,
H (mm) is the height of the convex portion provided with the reflective layer.
0.06 <H ≦ 0.2 (1)
In particular, it is preferable that the lens sheet for backlight has a reflective layer on the side surface of the convex portion.

The present invention also provides the above-described backlight lens sheet that satisfies the following formulas (2) to (4).

0.35 × {(3 / C) / P} ≦ S ≦ 0.6 (2)
0.66 <t / P <1.16 × {(3 / C) / P} (3)
S ≧ 0.347 × t / P + 0.0511 × C × P (4)
here,
t (mm): sheet thickness from the exit side cylindrical lens trough to the opening P (mm): P (mm) the pitch of the lenticular lens comprising the cylindrical lens group
C (1 / mm): curvature near the top of the cylindrical lens S: ratio of the opening to the pitch when the pitch of the lenticular lens is 1

  Further, in the present invention, the above-described lens sheet for backlight and the transparent substrate are bonded at the top of the convex portion on the incident surface side of the lens sheet, and the opening on the incident surface side of the lens sheet is in contact with air. This is an optical member for backlight.

  In the lens sheet of the present invention, the height of the portion of the convex portion where the reflective layer is provided is larger than the conventional example. Therefore, in the step of forming the reflective layer, the reflective layer is formed on the portion other than the convex portion. Can be prevented. Further, when another sheet is bonded to the incident surface side of the lens sheet, it is easy to form a form in which the opening is in contact with the air layer. Moreover, since the thickness of the ink which forms a reflection layer can be enlarged, the reflection efficiency of a reflection layer can be improved.

It is a figure which shows the concept of this invention. It is a figure which shows an example of the diffusion sheet combined with the lenticular lens sheet of this invention. It is a figure which shows an example of the diffusion sheet combined with the lenticular lens sheet of this invention. It is a figure which shows an example of the diffusion sheet combined with the lenticular lens sheet of this invention. It is a figure which shows the cross section of the lenticular lens sheet used in the Example of this invention. It is a figure which shows the horizontal and vertical viewing angle characteristic of an example of the Example which concerns on this invention.

  The present invention will be described with reference to the drawings. FIG. 1 is a schematic view of a backlight according to the present invention, and a reflector 4, a light source 1, a light source side diffuser 3, and a lenticular lens sheet 2 are provided from the back side. The lenticular lens sheet 2 includes a cylindrical lens group in which a cylindrical lens 23 is arranged in parallel on the exit surface. The light emitted from the light source 1 and the light reflected by the reflecting plate 4 enter the light source side diffusion sheet 3. The light is diffused by the light source side diffusion sheet 3, and the in-plane luminance is made uniform.

A part of the light diffused by the light source side diffusion sheet 3 is in a region other than the vicinity of the light condensing part of the cylindrical lens 23 provided on the exit surface of the lenticular lens sheet 2 (hereinafter sometimes simply referred to as a lens sheet). The light enters the provided opening 22.
The light that has entered the opening 22 at an angle close to perpendicular to the lens sheet surface (small incident angle) travels straight through the lens sheet 3 as it is, and is nearly perpendicular to the main surface of the lens sheet 2 (small exit angle). Exit with Light that has entered the opening 22 at a large incident angle with respect to the main surface of the lens sheet 2 travels straight through the lens sheet 2 and is refracted at the exit interface of the cylindrical lens 23, and is an angle close to perpendicular to the sheet surface (small exit angle). ). Therefore, the light incident on the opening 22 of the lenticular lens sheet 2 is collected in the front direction.

On the other hand, part of the light diffused by the light source side diffusion sheet 3 is reflected by the reflective layer 5 provided on the convex portion 21 in a region other than the opening 22.
The light reflected by the reflective layer 5 travels to the light source side diffusion sheet 3 side, then is diffusely reflected within the light source side diffusion sheet 3, becomes diffused light, and enters the lenticular lens sheet 2 again, and condenses in the front direction. Is emitted. Hereinafter, in the present invention, the phenomenon in which light is reflected by the reflection layer 5 and emitted from the opening 22 of the lenticular lens sheet 2 in this way may be referred to as light reuse.
As described above, the backlight of the present invention diffuses the light from the light source 1 to make the in-plane luminance uniform, and further can condense in the front direction by the lenticular lens sheet 2 arranged on the exit surface side.
In the present invention, as the lens shape of the cylindrical lens 23, for example, an ellipse, a hyperbola, a parabola, and a shape approximated thereto can be adopted.

  Here, when the convex portion 21 has a trapezoidal shape, the problem that light rays enter from the side surface of the convex portion 21 can be solved by forming a reflective layer on the side surface of the convex portion 21. At this time, in order to form the reflective layer 5 on the side surface of the trapezoidal convex portion 21, for example, a method for forming a light shielding layer on a lenticular lens sheet described in Patent Document 4 can be applied, but the present invention is not limited thereto. Is not to be done. It is also effective to provide the reflective layer 5 on almost the entire surface of the convex portion 21 by providing a roundness at the top of the convex portion 21.

  In the present invention, since the convex portion 21 is higher than the conventional one, the reflective layer 5 can be easily formed without part of the material of the reflective layer adhering to the opening 22. As a material for the reflective layer, a white ink mixed with a white pigment such as titanium oxide, zinc oxide or calcium carbonate, a reflective ink mixed with a metal powder, a metal thin film layer, or the like can be used. The reflective layer 5 needs to have a thickness sufficient to reflect light. For example, the thickness of white ink is preferably 5 μm or more. On the other hand, considering the ease of formation, the reflective layer is preferably 20 μm or less. As the base material of the white ink, a thermosetting resin, a solvent-type adhesive, an ultraviolet curable resin, or the like is preferable.

The aperture ratio S, which is the ratio of the apertures 22 to the pitch of the cylindrical lens group, is preferably 60% or less. If it is larger than this, since the proportion of light incident on the opening 22 is incident on the adjacent cylindrical lens 23, the effect of condensing in the front direction decreases.
On the other hand, the aperture ratio S is preferably 35 × {(3 / C) / P}% or more. For example, when C = 20 (1 / mm) and P = 0.15 (mm), the aperture ratio is 35% or more, and when C = 17.5 (1 / mm) and P = 0.15 (mm) Has an aperture ratio of 40% or more. If it is smaller than this, the ratio of repeating the reflection between the reflection layer 5 and the light source side diffusion sheet 3 or the reflection plate 4 on the back of the light source increases, and the light use efficiency decreases.
Here, the expression (2) means that the smaller the value of C × P, the larger the aperture ratio is preferable. That is, the smaller the C × P = P / R, that is, the larger the R / P, the larger the aperture ratio is preferred (where R is the radius of curvature (mm) and the reciprocal of the curvature C (1 / mm)). Is). This is because the aperture 22 is provided near the focal point of the cylindrical lens 23, but the aperture ratio may not be reduced when the radius of curvature near the top of the cylindrical lens per pitch is large.

Formula (3) shows a preferable range of the ratio t / P between the thickness t and the pitch P of the lens sheet 2. First, the value of t / P is preferably larger than 0.66. If it is less than this, the thickness becomes too thin, and there is a high possibility of causing problems such as tearing of the sheet during handling. Further, the value of t / P is preferably smaller than 1.16 × {(3 / C) / P}. For example, when C = 20 (1 / mm) and P = (mm), the value of t / P is preferably smaller than 1.16, C = 17.5 (1 / mm), P = (mm) In this case, the value of t / P is preferably smaller than 1.13. If it is more than this, the ratio of incident light to the adjacent lens among the light beams incident on the opening 22 will increase, and the effect of condensing in the front direction may be reduced.
Here, equation (3) means that the smaller the value of C × P, the greater the sheet thickness t. That is, when C × P = P / R is small, that is, when the radius of curvature R / P in the vicinity of the top of the lens per pitch is large, the effect of condensing in the front direction is unlikely to decrease even if the sheet thickness is increased. Means that.

Formula (4) shows the relationship between the value of the lens sheet thickness t / P per pitch and the value of C × P (that is, the reciprocal of the radius of curvature per pitch) and the preferable range of the aperture ratio S. . This is based on the calculation result obtained by changing t, C, and S in various ways.
In the present invention, the thickness t of the lenticular lens sheet 2 is the distance from the valley portion of the lens 23 to the opening 22, and the thickness of the lens 23 and the thickness of the convex portion 21 provided on the side opposite to the lens are the thickness of the sheet. Not included in t.

  Moreover, it is preferable that the lens pitch of the lenticular lens sheet 2 in this invention shall be 40 micrometers or more and 300 micrometers or less. If it is smaller than this, manufacturing and handling become difficult. If the lens pitch is larger than this, a moire pattern in which the pixel pitch of the liquid crystal screen and the lens pitch appear to interfere may be conspicuous. 40 μm or more and 200 μm or less is preferable.

  Further, the lenticular lens sheet 2 of the present invention is preferably bonded to the light source side diffusion sheet 3 on the reflective layer 5 side. This is because the sheet can be handled as an integrated optical member, and the assembly process of the backlight is simplified. When pasting together, it is preferable to provide an air layer between the opening 22 and the light source side diffusion sheet 3. This is because the light beam is refracted at the opening 22 and the component incident on the adjacent lens among the diffused light incident from the opening 22 can be reduced and can be effectively condensed in the front direction.

  In the present invention, since the reflective layer 5 is provided on the convex portion 21, an air layer can be easily provided between the opening 22 and the light source side diffusion sheet 3.

  The lenticular lens sheet 2 of the present invention can be manufactured by a known manufacturing method. For example, an extrusion method or a molding method using an ultraviolet curable resin. The extrusion method is particularly preferable from the viewpoint of productivity.

  The lenticular lens sheet 2 can be provided with a diffusion layer that does not adversely affect the brightness improvement in the front direction in order to prevent scratches and moire. Further, in order to further adjust the viewing angle characteristics, fine surface irregularities can be provided.

  The width of the opening 22 may be different between the center portion and the end portion of the sheet. When the width of the opening at the end is made larger than that at the center, the viewing angle at the end increases, so that it is possible to prevent the end from becoming dark when the screen is viewed from the front.

The preferable light diffusibility in the vicinity of the emission surface of the light source side diffusion sheet 3 combined with the present invention will be described with reference to FIGS.
FIG. 2 shows a schematic diagram of the path of light reflected by the reflective layer in the vicinity of the interface between the reflective layer 5 and the light source side diffusion sheet 3. As described above, the light incident on the reflection layer 5 once travels toward the light source side diffusion sheet 3, then is diffusely reflected to the emission side in the light source side diffusion sheet 3, and becomes diffused light and again enters the lenticular lens sheet 2. . However, not all of the reflected light necessarily enters the opening 22, and a part of the light is repeatedly reflected between the reflective layer 5 and the light source side diffusion sheet 3. Here, since the reflection efficiency in the reflection layer 5 and the light source side diffusion sheet 3 and on the reflection plate 4 is not actually 100%, a light loss occurs.

On the other hand, FIG. 3 shows a schematic view of a light path reflected by the light source side diffusion sheet 3 according to the first embodiment and the reflective layer 5 of the present invention. In the first embodiment, the light source side diffusion sheet 3 includes a diffusion layer 32 containing a diffusing agent on the incident surface side, and a transparent layer 31 that does not contain a diffusing agent on the emission surface side. The light incident on the reflective layer 5 once travels toward the light source side diffusion sheet 3, then passes through the transparent layer 31, and is diffusely reflected to the emission side in the light source side diffusion sheet 3. The possibility of reflection at a distant position increases. Accordingly, since the component that is repeatedly reflected between the reflection layer 5 and the light source side diffusion sheet 3 can be reduced, the light utilization efficiency is increased. The transparent layer 31 may contain a small amount of a diffusing agent so as to have a diffusing power smaller than that of the diffusing layer 32.
The thickness of the transparent layer 31 or the layer having a small diffusion power is preferably 0.5 times or more and 10 times or less the lenticular lens pitch. If it is less than this, the effects of the present invention may not be fully exhibited. Even if it is more than this, the effect of the present invention will not be exhibited remarkably, but rather it will hinder the reduction in thickness and weight of the backlight.

In addition to the above, the embodiment of the light source side diffusion sheet of the present invention can adopt the following forms, for example.
Embodiment 2: A diffusion layer containing a high concentration diffusing agent is provided on the incident surface side, and a diffusion layer containing a low concentration diffusing agent is provided on the exit surface side.
Embodiment 3: A diffusion layer containing a diffusing agent having a large refractive index difference from the substrate is provided on the incident surface side, and a diffusing layer containing a diffusing agent having a small refractive index difference from the substrate is provided on the exit surface side. thing.
Embodiment 4: A diffusion layer in which the concentration of the diffusing agent is changed stepwise or continuously from the vicinity of the entrance surface to the vicinity of the exit surface.

  In the present invention, it is preferable to provide a reflector 4 on the back surface of the light source 1 as shown in FIG. The light from the light source 1 can be used effectively, and the light reaching the light source side without being diffusely reflected to the emission side in the light source side diffusion sheet 3 can be used effectively in the reuse of light.

  The light emission side of the light source side diffusion sheet 3 in the present invention is preferably flat considering the form to be bonded. In order to prevent scratches due to handling, etc., fine irregularities of Ra = 0.1 to 10 μm may be provided on the exit surface side.

  The incident surface side of the light source side diffusion sheet 3 may be flat, or may be formed with a prism row, a lens row 33, or a fine concavo-convex shape of about Ra = 0.1 to 10 μm. When the back light source 1 is a linear light source or a light source in which point light sources are arranged in a line, the incident surface side of the light source side diffusion sheet 3 is parallel to the arrangement longitudinal direction of the linear light sources or the point light sources. It is particularly preferable to provide a lens array or a prism array (see FIG. 4). This is because the in-plane luminance is made uniform.

においてＣ＝１７．５〜２０（１／ｍｍ）、Ｋ＝−１。ただしレンズ頂点をｘ＝ｙ＝０とし、ｘ＝−Ｐ／２〜Ｐ／２とする。
正面輝度比＝拡散板１枚に対する輝度比（％） In the present invention, when the lens shape, the sheet thickness t, and the ratio S of the openings are within a predetermined range, it is shown by calculation that a suitable viewing angle and high front luminance can be exhibited. FIG. 5 shows a cross section of the lens sheet in this embodiment.
The viewing angle characteristics were calculated by changing several levels of the following items of the lenticular lens sheet.
Lens pitch P: 0.15 (mm)
Convex height H: 0.05 to 0.0725 mm
Sheet thickness t: 0.1 to 0.2 (mm)
Ratio of opening S: 30 to 60 (%)
(S is the area ratio of the opening to the pitch when observed from the front of the sheet)
Convex shape: Symmetrical substantially trapezoid Reflective layer forming surface: trapezoid top and slope Convex slope angle: 85 degrees Convex corner shape: roundness of R = 0.02 mm

C = 17.5-20 (1 / mm), K = -1. However, the lens apex is set to x = y = 0, and x = −P / 2 to P / 2.
Front brightness ratio = Brightness ratio (%) for one diffuser

The calculation was performed under the following conditions.
・ Program name: Optical Tools Ver6.0.0, Optical Research Associates
-Characteristics of incident light: Lambert distribution-Refractive index of sheet: 1.549
-Reflection layer light transmittance: 13% (Lambert distribution)
-Reflection layer light reflectance: 87% (Lambert distribution)
-Reuse efficiency of light reflected by the reflective layer: 100%
-Reuse efficiency of light reflected by diffuser: 100%
-Reuse efficiency of light reflected by reflector: 95%
・ Integration calculation method: piecewise quadrature method in 5 ° increments

  The calculation results are shown in Table 1. Here, H = 0.05 mm is a comparative example. Examples with H = 0.0625 mm and 0.0725 mm are examples. In addition, when the convex portion height H is less than 0.06 mm as in the comparative example, there is a problem that when the reflective layer is formed, the reflective material easily adheres to the opening.

  Table 2 compares the results of the above calculation with Examples and Comparative Examples, and determines each item of the front luminance ratio and viewing angle. The front luminance ratio is based on a comparison with a comparative example that is the same in items other than the height of the convex portion being 0.0625 mm or 0.0725 mm. Further, the viewing angle is determined not by comparison with the comparative example but by the magnitude of the viewing half-value angle. Here, the meaning of each mark in the table is shown in Table 3.

The vertical half-value angle and horizontal half-value angle are both good (☆, ◎, ○), and the front luminance ratio is equal to or greater than that of the comparative example (any one of ☆, ◎, ○), and It is preferable that all of the expressions (2) to (4) are satisfied.

  Of the above-mentioned preferred embodiments of the present invention, those including items marked with asterisks or asterisks are more preferred, and Table 4 shows these as good. Among them, it is even more preferable that two or more items are evaluated as “☆” or “☆”, and Table 4 shows them as excellent. Among the remaining examples, those within the range satisfying all of the expressions (2) to (4) are shown as acceptable in Table 4. Table 5 shows the numerical values on the right side of the equation (4), and the area not shaded is a range that satisfies all the equations (2) to (4).

  FIG. 6 shows horizontal and vertical viewing angle characteristics when H = 0.0725 mm, t = 0.15 mm, S = 60%, and C = 17.5 (1 / mm).

  As described above, in the embodiment of the present invention, it is easy to form the reflective layer by providing the reflective layer on the convex part higher than the conventional one, and even when the reflective layer side and the diffusion plate are bonded together, the air layer is formed in the opening. Easy to secure. In addition, the viewing angle is excellent in a particularly preferable range of the embodiment, and the front luminance equivalent to or superior to that of the sheet provided on the convex portion where the conventional reflective layer is low can be exhibited.

1: Light source 2: Lenticular lens sheet, 21: Convex part, 22: Opening part, 23: Cylindrical lens 3: Light source side diffusion sheet, 31: Transparent layer, 32: Diffusion layer, 33: Lens array 4: Reflecting plate, 5 : Reflective layer

Claims (4)

A lens sheet for backlight composed of a lenticular lens sheet,
The lenticular lens sheet has a plurality of cylindrical lens groups arranged in parallel on the exit surface side,
On the incident surface side, it has an optical opening in the vicinity of the condensing part of each cylindrical lens, and has a convex part provided with a reflective layer in a region other than the opening,
H (mm) is the height of the convex portion provided with the reflective layer.
0.06 <H ≦ 0.2 (1)
A lens sheet for backlight.   The lens sheet for a backlight according to claim 1, wherein the shape of the convex portion is a trapezoid and has a reflective layer on the top and side surfaces of the convex portion. The backlight lens sheet according to claim 1 or 2, wherein the backlight lens sheet satisfies the following expressions (2) to (4).
0.35 × {(3 / C) / P} ≦ S ≦ 0.6 (2)
0.66 <t / P <1.16 × {(3 / C) / P} (3)
S ≧ 0.347 × t / P + 0.0511 × C × P (4)
here,
t (mm): sheet thickness from the cylindrical lens trough on the exit side to the opening P (mm): pitch of the lenticular lens comprising the cylindrical lens group C (1 / mm): curvature near the top of the cylindrical lens S : Ratio of the opening to the pitch when the pitch of the lenticular lens is 1.   The lens sheet for backlight according to any one of claims 1 to 3 and a transparent substrate are bonded to each other at the top of the convex portion on the incident surface side of the lens sheet, and the opening on the incident surface side of the lens sheet is air. An optical member for backlight, which is in contact with the optical member.

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