JP3249982B2 - Optical element - Google Patents

Description

The present invention relates to an optical element having an optical phase difference function,
In particular, the present invention relates to an optical element having a small dependence of an optical path difference on an incident angle.

[Prior Art] Conventionally, an anisotropic film or sheet of a transparent resin (hereinafter, “film or sheet” is abbreviated as a film) or a film having an optical retardation function (hereinafter, abbreviated as an optical retarder) or Liquid crystal cells have been used for special applications. Optical retarders have become increasingly important with recent developments in optical technology.For example, in black-and-white liquid crystal display panels, the anisotropic properties of polycarbonate resin are used to compensate for the birefringence inherent to liquid crystals, which causes coloring. Oriented oriented films and the like are employed. However, these conventional optical retarders have the disadvantage that the optical path difference greatly changes depending on the incident angle of light, and when used in a black and white liquid crystal display panel, oblique compensation is not performed properly and coloring occurs. There is a problem that the viewing angle becomes narrow.

[Problems to be solved by the invention]

An object of the present invention is to solve the above-mentioned problems of the prior art,
That is, the development of an optical element having a small dependence of the optical path difference on the incident angle.

[Means for solving the problem]

An object of the present invention is to provide: (A ′) a plate-like object having an optical phase difference function in which the maximum principal refractive index axis is in the thickness direction and the intrinsic birefringence is negative; A laminate of a positively-oriented anisotropic oriented film or sheet or a balance oriented stretched product, wherein the laminate is a pair of films whose optical path difference and incident angle dependence of the optical path difference are substantially equal. Alternatively, they are achieved by an optical element characterized in that they are made of sheets and are superposed such that directions having a large degree of orientation cross each other in an angle range of 90 ° ± 35 °.

The plate-like material (A ') having an optical retardation function is a material exhibiting birefringence with respect to incident light perpendicular to the surface, for example, anisotropic orientation obtained by uniaxial stretching or unbalanced biaxial stretching. Examples include a film or a liquid crystal cell.
In particular, an anisotropic oriented film is preferable because a film having a large area and an appropriate optical path difference can be easily obtained.

As the material having a positive intrinsic birefringence value of the film (B '), a polyester resin such as a polycarbonate resin, a cellulose diacetate resin, a polyvinyl alcohol resin, a polyphenylene oxide resin, and polyethylene terephthalate can be used.

Particularly, a polycarbonate resin, a cellulose diacetate resin, and a polyvinyl alcohol resin having excellent transparency are preferable.

If necessary, additives such as a lubricant and an ultraviolet absorber may be added to the resin for the film.

As the liquid crystal cell having an optical retardation function, a liquid crystal cell in which the liquid crystal is aligned in the cell by rubbing, for example, a homogeneous alignment or a twist alignment can be used.

The balanced orientation stretched product does not substantially exhibit birefringence with respect to incident light perpendicular to the plane, and can be produced, for example, by stretching a transparent resin in a balanced biaxial manner. As the transparent resin, the aforementioned resins can be used.

For a plate-like object having the maximum principal refractive index axis in the thickness direction, the intrinsic birefringence value needs to be positive. Not applicable. For example, when a film having a negative intrinsic birefringence value with respect to a plate-like object having the maximum principal refractive index axis in the thickness direction is used, the incident angle dependence is rather large, and the effect of the present invention cannot be realized.

When the plate-like material having an optical retardation function is a uniaxially stretched product or an unbalanced biaxially stretched product, the direction of the maximum principal refractive index value is a plane direction in a resin having a positive intrinsic birefringence value, and is negative. In the case of the resin (3), the thickness direction is applied. That is, the anisotropic oriented film and the balanced oriented film need to be made of resins having intrinsic birefringence values of opposite signs. In the case of a liquid crystal cell having a homogeneous orientation or a twist orientation, the orientation is in the plane direction.

In the film (B ') or a laminate thereof according to the present invention, a pair of anisotropic oriented films having substantially the same optical path difference and the incident angle dependence of the optical path difference have a large orientation degree of 90 ° ± 35 °. It is preferable that they are overlapped so as to cross each other in the angle range of ゜. With this structure, the laminate has substantially no birefringence with respect to vertically incident light.

The anisotropically oriented film constituting the laminate is manufactured by the same method as that of the same resin as the film mentioned as the plate-like material having the optical retardation function, but the maximum principal refractive index axis is in the thickness direction. Is required to be a resin film having a negative intrinsic birefringence value. In addition, a plate-like object having a maximum principal refractive index value in the thickness direction needs to have a positive intrinsic birefringence value. Not applicable,
For example, when an anisotropic oriented film having a positive intrinsic birefringence value with respect to a plate-like object having a maximum principal refractive index axis in the plane direction is used for a laminate, the incident angle dependence becomes rather large, and the present invention Effect cannot be realized.

The difference between the optical path difference and the incident angle dependence of the optical path difference of the pair of anisotropically oriented films constituting the laminate must be within 15%, and particularly preferably within 5%. These anisotropically oriented films are desirably superimposed such that the directions having a large degree of orientation cross each other in an angle range of 90 ° ± 35 °. When the angle becomes more than 35 ° from right angle,
The laminate has birefringence with respect to perpendicular incident light. The birefringence of the laminate generally needs to be within 30 nm in terms of optical path difference, and particularly preferably within 10 nm. If the birefringence is present, the optical characteristics of the optical phase difference element produced therefrom, that is, the optical path difference and the incident angle dependency are different depending on the direction of superposition with (A), and the optical characteristics are not constant. In addition, the reduction of the incident angle dependency becomes insufficient.

As an anisotropic oriented film, the ratio of the vertical and horizontal stretch ratio is
When an unbalanced biaxially stretched product of 0.5 to 2 is used, a good laminate having little birefringence can be easily obtained, and the optical phase difference element obtained therefrom has excellent incident angle dependence, which is preferable.

 The optical element of the present invention can be realized in various forms.

Preferred embodiments will be described below with reference to FIGS. Here, (A) is a plate-like object having an optical retardation function, and (B) is an anisotropic oriented film or a laminate thereof. When it is composed of a plurality of (A) or (B), these are represented by (A1), (A2) ..., (B1), (B2) ...
Indicated by

FIG. 1 shows the simplest form comprising a pair of (A) and (B), and FIG. 2 shows a protective film or sheet (C) having a hard coat film or the like on both sides.

FIG. 3 shows an embodiment in which (B2) is further provided in addition to (B1). For example, a film or a laminate thereof made of a resin having a large absolute value of intrinsic birefringence (B1) has a coarse incident angle dependence. (B2), which is a film made of a resin having a small absolute value or a laminate thereof, and is further finely adjusted.

FIG. 4 shows a form in which (B1) and (B2) are arranged on both sides of (A). For example, when (A) is a polyvinyl alcohol resin film, (B1) and (B2) have light resistance and This is a mode in which an acrylic resin film or a laminate thereof having good moisture resistance is used and can be prevented from being deformed by moisture absorption.

FIGS. 5 and 6 show (A1) and (A2) arranged so that their long axes are parallel to each other, so that the optical path difference of the optical element becomes the sum of the two. By preparing a plate-like object having an optical phase difference function having different optical path differences, optical elements having various optical path differences can be obtained by combining these. FIG. 5 shows the improvement of the entire incident angle dependence with one sheet (B), and FIG. 6 shows the incident angle dependence of (A1) and (A2) with (B1) and (B2), respectively. It is an improvement.
The arrangement order may be changed such that (A1), (A2) or (B1), (B2) are at both ends.

FIGS. 7 and 8 show a configuration in which the long axes of (A1) and (A2) are arranged at an angle of, for example, 30 °, which is known to improve the contrast ratio in a monochrome liquid crystal display panel. FIG. 7 shows a combination of (B) and FIG. 7, in which the overall incident angle dependency is improved with one sheet (B), and FIG. 8 shows incident angles of (A1) and (A2). The dependency was improved by (B1) and (B2), respectively. Again, (A
The arrangement order may be changed such as 1), (A2) or (B1), (B2) at both ends.

FIG. 9 shows the case where the protective film of the polarizing plate is used as (B), and there is an advantage that the whole constituent material is reduced.

In the optical element of the present invention, (A) and (B) are arranged so that their faces are parallel to each other, and they may be separated from each other, may simply be stacked, or may be adhered, Further, a plate-like object that does not hinder the effects of the present invention may be interposed. In addition to the preferred examples shown in FIGS. 1 to 9, the number of (A) and (B) is three or more, and a protective film (C) is disposed at both ends or one end in addition to the example of FIG. Is possible.

Further, in the optical element of the present invention, when the anisotropic film, which is a component of the laminate, is a biaxially stretched film having close vertical and horizontal draw ratios, the components are separated as shown in FIG. Can also be taken.

In the optical element of the present invention, (A) and (B) having various characteristics can be used, but in the form of one pair, the optical path difference at an incident angle of 45 ° in (B) is (A) A combination having a value close to the difference between the optical path difference perpendicular to the plane and the optical path difference when the optical path difference is inclined by 45 ° in the long axis direction is preferable because the incidence angle dependency is small.

Anisotropically oriented film used in the present invention, for example, by extruding the raw material resin, after forming into a film, uniaxially stretched at a temperature higher than the glass transition temperature of the resin by 10 to 40 ℃, or has anisotropy It is obtained by biaxial stretching under such conditions.

Similarly to the anisotropic oriented film, the balanced oriented film can be obtained by simply biaxially stretching the film at the same stretching ratio. The balanced orientation film has substantially no birefringence with respect to incident light perpendicular to the surface, but generally has an optical path difference of 30 nm or less, preferably 10 nm or less. If the balance is inferior, the optical characteristics of the optical element, that is, the optical path difference and the incident angle dependency are different depending on the direction of superposition with (A), so that a constant optical characteristic cannot be obtained.

In the present invention, 254 μm or more was distinguished from a sheet, and 254 μm or less was distinguished from a film.

Hereinafter, the method of measuring physical properties used in the description of the invention will be described.

-Optical path difference measurement method: polarizing microscope (manufactured by Nippon Kogaku Kogyo Co., Ltd.
LABOPHOT-POL) was used and measured according to a standard method. The dependence on the incident angle was measured by fixing the sample on the sample table at a predetermined angle.

・ Evaluation method of incident angle dependence: Based on the case where a light beam enters the optical element at right angles, the absolute amount of change in optical path difference when the incident light beam is inclined in the major axis and minor axis directions is calculated as a percentage. And the average value of the two was evaluated. The incident angle indicates an inclined angle.

〔Example〕

 The present invention will be specifically described with reference to examples.

Example 1 MS resin having a negative intrinsic birefringence (Nippon Steel Chemical Co., Ltd.)
Unstretched sheet of Estyrene MS-300) is uniaxially stretched at a stretching temperature of 130 ° C at a stretching ratio of 2.5 times with a constant width, and anisotropically oriented film with a thickness of 75μ with the maximum principal refractive index axis in the thickness direction I got 185 ° C from polycarbonate resin with positive intrinsic birefringence (A-2500, manufactured by Idemitsu Petrochemical Co., Ltd.)
And a thickness of 107 μm, which was produced by simultaneous biaxial stretching at a stretching ratio of 2 times in the vertical and horizontal directions at a stretching temperature of, and a balanced oriented film having no optical path difference observed from a direction perpendicular to the film surface.
An optically isotropic acrylic resin sheet with no orientation (paragrass, manufactured by Kuraray Co., Ltd.)
To produce an optical element. As shown in Table 1, the optical path difference of this optical element was -149 nm, and the incident angle dependence was as small as 6% at 45 °. Incidentally, the optical path difference of the anisotropic oriented film of MS resin was -147 nm, and the incident angle dependence of the optical path difference was large, being 27%.

Comparative Example 1 An anisotropic oriented film prepared by stretching a non-stretched sheet of the polycarbonate resin used in Example 1 at a stretching temperature of 180 ° C. and a draw ratio of 2.5 times at a fixed width and uniaxially, and a polycarbonate resin used in Example 1 An optical element was produced in the same manner as in Example 1 from the balanced oriented film. The incident angle dependence of the optical element was larger than that of the anisotropic oriented film alone, and was inferior to 34% at an incident angle of 45 °.

Comparative Example 2 An anisotropic oriented film of MS resin used in Example 1 and an acrylic resin having a negative intrinsic birefringence value (manufactured by Kuraray Co., Ltd.)
Unstretched sheet of parapet SH) is stretched at a stretching temperature of 140 ° C.
From a balanced oriented film prepared by simultaneous biaxial stretching at a draw ratio of 2.2 times and 2.2 times the width and having a thickness of 132 μm and no optical path difference observed from the direction perpendicular to the film surface, in the same manner as in Example 1. An optical element was manufactured. The incident angle dependence of the optical element was larger than that of the anisotropic oriented film alone, and was inferior to 69% at an incident angle of 45 °.

Example 2 An anisotropic oriented sheet having a maximum principal refractive index axis in the thickness direction obtained from an acrylic resin having a negative intrinsic birefringence value (parapet SH, manufactured by Kuraray Co., Ltd.) at a magnification of 1.1 × 2.2. An optical element was prepared by sticking both from the polycarbonate resin balanced orientation film used in Example 1. First
As shown in the table, the optical path difference of this optical element was -144 nm, and the incident angle dependence was as small as 6% at an incident angle of 45 °. Incidentally, the optical path difference of the acrylic resin anisotropic alignment sheet is -150 nm, and the incident angle dependence of the optical path difference is large, 32%
Met.

Example 3 A film prepared from the polycarbonate resin used in Example 1 by sequential biaxial stretching at a stretching temperature of 185 ° C. and a stretching ratio of 1.8 times in length and 2.2 times in width was applied so that the directions of large orientation were orthogonal to each other. The sheets were stacked to produce a laminate in which no optical path difference was observed from the vertical direction.

An optical element was produced in the same manner as in Example 1 except that the laminate and the anisotropic oriented film of MS resin in Example 1 were superposed. As shown in Table 2, the optical path difference of this optical element is -14.
At 5 nm, the incident angle dependence was as small as 7% at an incident angle of 45 °. Incidentally, the optical path difference of the anisotropic alignment film of MS resin is -147 nm, the incident angle dependence of the optical path difference is large, 27
%Met.

Comparative Example 3 An optical element was produced in the same manner as in Example 3 from a laminate of the anisotropic oriented film of the polycarbonate resin used in Example 1 and the polycarbonate resin used in Example 3. The incident angle dependence of the optical element was larger than that of the anisotropic oriented film alone, and was inferior to 33% at an incident angle of 45 °.

Comparative Example 4 An anisotropic oriented film of MS resin used in Example 1 and an acrylic resin having a negative intrinsic birefringence value (manufactured by Kuraray Co., Ltd.)
Unstretched sheet of parapet SH) is stretched at a stretching temperature of 140 ° C.
Two layers of films made by sequential biaxial stretching with a stretching ratio of 1.8 times and 2.2 times horizontal so that the directions of high orientation are orthogonal to each other. "Laminate with no optical path difference from the vertical direction Thus, an optical element was manufactured in the same manner as in Example 1. The incident angle dependence of the optical element was larger than that of the anisotropic oriented film alone, and was inferior to 78% at an incident angle of 45 °.

Example 4 Lamination of an anisotropic oriented sheet having a maximum principal refractive index axis obtained in a thickness direction of 1.1 × 2.2 from the acrylic resin used in Comparative Example 4 and a polycarbonate resin used in Example 1 From the body, both were adhered to produce an optical element. Second
As shown in the table, the optical path difference of this optical element was as small as 6% at an incident angle of -45 nm at an incident angle of -152 nm.
Incidentally, the optical path difference of the anisotropic oriented sheet of acrylic resin is -15
It was 0 nm, and the incident angle dependence of the optical path difference was large, being 32%.

[Effects of the Invention] The optical element of the present invention has made it possible to provide an optical element having a birefringence characteristic in which the incident angle dependence of the optical path difference is small, which has been impossible in the past. The present invention is suitably used, for example, as an optical element for compensating a phase difference in a black and white liquid crystal display.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 10 show preferred embodiments of the optical element of the present invention.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-239421 (JP, A) JP-A-3-233407 (JP, A) JP-A-2-256023 (JP, A) JP-A-3-3 85519 (JP, A) JP-A-3-24502 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 5/30

Claims (6)

(57) [Claims] (A ') a plate-like object having an optical retardation function having a negative intrinsic refractive index having a maximum principal refractive index axis in a thickness direction thereof; and (B') having a positive intrinsic birefringence value. An optical element comprising: a film or a sheet having no optical phase difference function with respect to vertical incident light. 2. The optical element according to claim 1, wherein the plate-like material (A ′) is an anisotropically oriented film or sheet which is a uniaxially stretched product or an unbalanced biaxially stretched product. 3. The optical element according to claim 1, wherein the film or sheet of (B ′) is a stretched product with balanced orientation. 4. The optical element according to claim 1, wherein the film or sheet of (B ′) is a laminate of an anisotropic oriented film or sheet having a positive intrinsic birefringence value. 5. A laminate comprising a pair of films or sheets whose optical path difference and incident angle dependence of the optical path difference are substantially equal to each other, wherein the directions of the large degree of orientation are mutually 90 ° ± 35 °. The optical element according to claim 4, wherein the optical element is overlapped so as to intersect. 6. The optical element according to claim 4, wherein the anisotropically oriented film or sheet constituting (B ′) is an unbalanced biaxially stretched product.