JPH11142646A - Reflective polarizer, liquid crystal device and electronic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflecting polarizer which obtains a high degree of polarization even for obliquely incident light. SOLUTION: This reflecting polarizer is constituted by stacking a 1st layer having refractive index anisotropy in a plane and a 2nd layer which does not have alternately in quantities and the ratio of the refractive index nz along the film thickness and refractive index ny perpendicular to the drawing direction in the plane among three main refractive indexes nx, ny, and nz of each layer is equal between both the layers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a reflective polarizer,
Further, the present invention relates to a liquid crystal device using the reflective polarizer, and further relates to an electronic device equipped with the liquid crystal device.

[0002]

2. Description of the Related Art Reflective liquid crystal devices and transflective liquid crystal devices with low power consumption are suitable for use in information tools such as PDAs and portable electronic devices such as mobile phones and watches. However, conventional reflective liquid crystal devices and transflective liquid crystal devices have a problem that the display is dark. Also, there is a problem that a transmission type liquid crystal device mainly used for a desktop consumes a large amount of power.

[0003] As one means for solving such a problem,
A method using a reflective polarizer using a birefringent dielectric multilayer film is disclosed in Japanese Patent Publication No. 9-506985.

The birefringent dielectric multilayer film has a function of reflecting a predetermined linearly polarized light component and transmitting other polarized light components. When such a reflective polarizer is used in a reflective liquid crystal device or a semi-transmissive reflective liquid crystal device, unlike a conventionally used metal reflector, it totally reflects light of a predetermined polarization component and also has an absorption polarizer. Because it does not absorb light, it has the feature of being very bright. Also, when such a reflective polarizer is used in a transmission type liquid crystal device, most of the light is converted into linearly polarized light, which has the effect of increasing the efficiency of the backlight.

[0005]

However, such a conventional reflective polarizer using a birefringent dielectric multilayer film also has a problem that the degree of polarization is low. In particular, the degree of polarization was low with respect to light incident from an oblique direction. Therefore, the conventional liquid crystal device using this has a problem that contrast cannot be obtained when viewed from an oblique direction.

Accordingly, an object of the present invention is to provide a reflective polarizer capable of obtaining a high degree of polarization even for light incident obliquely. Another object of the present invention is to provide a liquid crystal device having a wide viewing angle and a high brightness, and an electronic device with low power consumption.

[0007]

According to a first aspect of the present invention, there is provided a reflective polarizer comprising a first layer having in-plane refractive index anisotropy and a second layer having no in-plane refractive index anisotropy. A reflective polarizer comprising a large number of layers alternately stacked, wherein, among the three main refractive indices nx, ny, and nz of each of the layers, a refractive index nz in a film thickness direction and a stretching direction in a plane. Refractive index ny in the direction perpendicular to
Are equal to each other in the two layers. Although nx and ny exist in the in-plane principal refractive index, since this reflective polarizer is produced by stretching, the refractive index in the direction parallel to the principal stretching direction is nx, and the refractive index in the direction perpendicular to We will distinguish the rate from ny. Many substances are optically positive and therefore nx> ny, but optically negative substances such as polystyrene have nx <ny. Claim 1 indicates that nz / ny of the first layer is substantially equal to nz / ny of the second layer. With such a configuration, the reflective polarizer according to the first aspect can ensure a high degree of polarization even for light incident from an oblique direction.

According to a second aspect of the present invention, at least a liquid crystal device comprises:
A polarizing plate that absorbs a predetermined linearly polarized light component and transmits the remaining polarized light component, a liquid crystal cell having a liquid crystal composition sandwiched between a pair of substrates having a transparent electrode, and the reflective polarizer according to claim 1, A light absorbing plate, and these are arranged in the above order. With this configuration, the liquid crystal device according to the fourth aspect can provide a reflective or transflective display that is bright and has high contrast even when viewed from an oblique direction.

A liquid crystal device according to a third aspect of the present invention includes at least
A polarizing plate that absorbs a predetermined linearly polarized light component and transmits the remaining polarized light component, a liquid crystal cell having a liquid crystal composition sandwiched between a pair of substrates having a transparent electrode, and the reflective polarizer according to claim 1, A backlight is provided, and these are arranged in the order described above. With such a configuration, the liquid crystal device according to claim 3 can provide a bright transmissive display.

According to a fourth aspect of the invention, there is provided an electronic apparatus including the liquid crystal device according to the second or third aspect as a display unit. With such a configuration, the electronic device according to the fourth aspect consumes less power and can obtain high-quality display.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a view showing a main part of the structure of a reflective polarizer according to the first embodiment of the present invention. The reflective polarizer is basically a birefringent dielectric multilayer film, and is formed by alternately stacking two types of polymer layers 101 and 102. The two types of polymers are selected from a material with a high photoelastic modulus and a material with a low photoelastic modulus, while taking care that the refractive indices of the ordinary rays of both are approximately equal. . For example, as a material having a large photoelastic modulus, P
EN (2,6-polyethylene naphthalate) is used as a small material for coPEN (70-naphthalate / 30-
(Terephthalate copolyester). When both films were alternately laminated and stretched about 5 times in the x-axis direction of the orthogonal coordinate system 103 in FIG. 1, the refractive index in the x-axis direction was about 1.88 in the PEN layer and about 1.64 in the coPEN layer. became. In addition, the refractive index in the y-axis direction is
The value for the N layer was about 1.64. When light is incident on the laminated film from the normal direction, the light component vibrating in the y-axis direction passes through the film as it is. This is the transmission axis.
On the other hand, the light component oscillating in the x-axis direction is composed of the PEN layer and the coP
Reflection occurs only when the EN layer satisfies certain conditions. This is the reflection axis. The condition is that the sum of the optical path length of the PEN layer (the product of the refractive index and the film thickness) and the optical path length of the coPEN layer (the product of the refractive index and the film thickness) is equal to one half of the light wavelength. is there. Such a PEN layer and a coPEN layer are each composed of several tens or more layers, preferably 100 layers or more, and 30 μm in thickness.
By stacking about m components, almost all of the components of light that vibrate in the x-axis direction can be reflected.

[0013] The ideal reflection polarizer produced in this way produces a polarization capability only with light of a single designed wavelength. Of course, in practice, the thicknesses of the PEN layer and the coPEN layer vary, so that the polarization ability is generated with a certain wavelength width, but the width is still several tens of nm. Therefore, in order to provide a polarizing capability over a wide wavelength range of visible light, a plurality of reflective polarizers having different polarization reflection wavelength ranges are stacked with their axes aligned. The reflective polarizer thus configured is
It exhibited a high degree of polarization of 90% or more over almost the entire visible light range.

The above is a description of the behavior of light incident on the reflective polarizer from the normal direction. The main focus of the present application lies in the behavior of light entering obliquely. FIG. 2 is a diagram showing the refractive index characteristics of two types of layers 101 and 102 constituting the reflective polarizer of the present invention. Reference numeral 201 denotes a refractive index ellipsoid of the polymer layer 101 formed by stretching a material having a large photoelastic coefficient, and reference numeral 202 denotes a refractive index ellipsoid of the polymer layer 102 formed by stretching a material having a small photoelastic coefficient. The three main refractive indices of each ellipsoid are nx, ny,
nz. However, the refractive indices 211 and 221 in the direction parallel to the main stretching direction in the plane of the layer (xy plane 231) are set to n.
x, refractive index 2 in the direction perpendicular to the main stretching direction in the plane of the layer
12 and 222 are ny, refractive indices 213 and 223 in the film thickness direction
Is nz. However, the main stretching direction corresponds to the x-axis direction in FIG. 1 in the above description, and indicates a direction in which the stretching ratio is larger when biaxial stretching is performed.

Now, as a result of precisely measuring the refractive index of each layer of the reflective polarizer of Example 1, as for the layer 101, nx =
1.874, ny = 1.644, nz = 1.621. For the layer 102, nx = 1.642,
ny = 1.640 and nz = 1.616, which were almost isotropic. However, this measurement is a value obtained by measuring a film prepared by separately forming the layer 101 and the layer 102 and stretching the same.

As described above, the layer 101 has in-plane refractive index anisotropy (nx-ny = 0.230), and the layer 102 has in-plane refractive index anisotropy (nx-ny = 0.002). ). Moreover, the ratio nz between nz and ny in the layer 101
/Ny=0.9860 means that nz and ny in layer 102
Nz / ny = 0.9854.

With this configuration, xz
The light 241 obliquely incident on the plane is also yz
The refractive index of light vibrating in parallel to the y direction, which is the transmission axis, or of light vibrating in the yz plane varies between the layers 101 and 102 with respect to the light 242 obliquely incident on the plane. Absent. That is, light vibrating in this direction is always transmitted and does not change the degree of polarization. Conversely, if the values of nz / ny are different, a part of the light 242 that is obliquely incident particularly on the yz plane will be reflected, and the degree of polarization will be degraded.

FIG. 3 is a diagram showing the dependence of the degree of polarization on the angle of incident light. (A) is the incident light angle dependence in the xz plane, and (b) is the incident light angle dependence in the yz plane. Reference numerals 301 and 311 show the characteristics of the reflective polarizer of Example 1, and it can be seen that a high degree of polarization is maintained regardless of the incident light angle.

For comparison, two conventional reflective polarizers A,
The characteristics of B are also shown.

The reflective polarizer A has a nx =
1.877, ny = 1.641, nz = 1.533, and nx = 1.642, ny = 1.6 for the layer 102
40, nz = 1.616. Nz in layer 101
Ny / ny = 0.9242 in the layer 102 is considerably smaller than the nz / ny ratio nz / ny = 0.9854 in the layer 102. In FIG. 3, reference numerals 302 and 312 show the characteristics of the reflective polarizer A. It can be seen that the degree of polarization is particularly poor with respect to light inclined to the yz plane.

The reflective polarizer B has a nx =
1.805, ny = 1.638, nz = 1.785, and nx = 1.642, ny = 1.6 for layer 102
40, nz = 1.616. Nz in layer 101
Ny / ny = 1.0897 is much larger than the nz / ny ratio nz / ny = 0.9854 in the layer 102. In FIG. 3, reference numerals 303 and 313 show the characteristics of the reflective polarizer B. It can be seen that the degree of polarization is particularly poor with respect to light inclined to the yz plane. When such a reflective polarizer having a poor degree of polarization in an oblique direction is used in a liquid crystal device, sufficient contrast cannot be obtained when viewed in an oblique direction.

(Embodiment 2) FIG. 4 is a view showing a main part of the structure of a liquid crystal device according to a second embodiment of the present invention. First, the configuration will be described. 4, reference numeral 401 denotes a polarizing plate;
02 is a retardation film, 403 is an upper glass substrate, 40
4 is a liquid crystal layer, 405 is a lower glass substrate, 406 is a light scatterer, 407 is a reflective polarizer, 408 is a light absorber, 409 is a scanning electrode made of ITO, and 410 is a signal electrode made of ITO. 401 and 402, 402 and 403, 405
And 406, 406 and 407, and 407 and 408 are adhered to each other with glue. Although the upper and lower substrates are drawn widely apart, this is for the sake of clarity of the drawing, and they are actually opposed to each other with a narrow gap of several μm to tens of μm. In addition to the components shown in the figure, a liquid crystal alignment film, an insulating film, spacer balls, a driver I
Although elements such as C and a drive circuit are also indispensable, they are not particularly necessary for describing the present invention, and are omitted because they may rather complicate the drawing and make it difficult to understand.

Next, each component will be described in order. The polarizing plate 401 has a function of absorbing a predetermined linearly polarized light component and transmitting other polarized light components. This is the most commonly used type of polarizing plate at present, and is produced by adsorbing a halogen substance such as iodine or a dichroic dye onto a polymer film such as polyvinyl butyral.

The retardation film 402 is, for example, a uniaxially stretched film of a polycarbonate resin, and is used for compensating the coloring of the display of the STN type liquid crystal device. T
In the case of an N-type liquid crystal device, it is often omitted.

The liquid crystal layer 404 is composed of a STN nematic liquid crystal composition twisted from 180 degrees to 270 degrees. When the display capacity is small, a TN liquid crystal composition twisted by 90 ° may be used. The twist angle is determined by the direction of the alignment treatment on the upper and lower glass substrates and the amount of the chiral agent added to the liquid crystal.

As the light scatterer 406, a plastic film in which transparent beads are dispersed can be used. Beads may be mixed in the adhesive and directly adhered to a liquid crystal device or the like. Alternatively, a light control plate that scatters only light incident from a specific angle may be used. Such a light control plate is sold by Sumitomo Chemical Co., Ltd. as Lumisty (trade name).
Note that the light scattering here refers to weak scattering that does not disturb the polarization. The light scattering plate is arranged for appropriately diffusing the reflected light of the reflective polarizer close to the mirror surface.

As the reflective polarizer 407, the one described in the first embodiment was used.

The light absorbing plate 408 is used by adhering a black vinyl sheet or black paper or by directly applying a black paint. In addition, if it is a relatively dark color other than black, it can be used depending on preference, such as blue, brown, and gray. This light absorbing plate is arranged for the purpose of absorbing unnecessary polarized light, but when this polarized light is used in a transflective liquid crystal device or the like,
What is necessary is just to use a translucent light absorption plate.

The liquid crystal device thus manufactured has a feature that it is 30% or more brighter than a liquid crystal device using a normal polarizing plate. There are two reasons. One is that the reflectance of metallic aluminum is only slightly less than 90%, whereas the reflective polarizer of the present invention has almost one of the light parallel to the reflection axis.
This is because 00% is reflected. Another reason is that ordinary absorption-type polarizers use dichroic substances such as halogen substances such as iodine and dyes, and the dichroic ratio is not necessarily high, so that about 20% of light is wasted. That is what we do.

Further, this liquid crystal device is capable of displaying a high contrast even when viewed from an oblique direction, and is characterized by an extremely wide viewing angle.

(Embodiment 3) FIG. 5 is a view showing a main part of a structure of a liquid crystal device according to a third embodiment of the present invention. First, the configuration will be described. In FIG. 5, reference numeral 501 denotes a polarizing plate;
02 is a counter substrate, 503 is a liquid crystal composition, 504 is an element substrate, 505 is a polarizing plate, 506 is a reflective polarizer, 507 is a light scattering plate, 508 is a light guide plate of a backlight, 509 is a light reflecting plate, and 510 is a back light. Light source of light, counter substrate 5
02, a color filter 511 and a counter electrode (scanning line) 512 are provided.
3, the pixel electrode 514, and the MIM element 515 are provided. Here, 501 and 502 and 504 and 505 are drawn apart from each other, but this is for the sake of clarity of the drawing, and they are actually glued together. Further, the space between the opposing substrate 502 and the element substrate 504 is drawn widely apart, but for the same reason, there is only a gap of about several μm to about several tens μm in practice. Although FIG. 5 shows a part of the liquid crystal device, only a 3 × 3 matrix formed by three scanning lines 511 and three signal lines 512 intersecting, that is, nine dots is illustrated. Actually have more dots.

The counter electrode 512 and the pixel electrode 514 were formed of transparent ITO. The signal line 513 was formed of metal Ta. In the MIM element, the insulating film Ta2O5 is made of metal Ta and metal C.
r. The liquid crystal composition 503 is a nematic liquid crystal twisted by 90 degrees, and the polarizing axes of the upper and lower polarizing plates are orthogonal to each other. This is a configuration of a general normally white TN mode.

The color filter 511 has three primary colors of additive color mixture: red (indicated by “R” in the figure), green (indicated by “G” in the figure), and blue (indicated by “B” in the figure). It consisted of three colors and was arranged in a mosaic. As the polarizing plate 501 and the reflective polarizer 506, the same ones as in Example 1 were used.

Although the MIM active matrix type liquid crystal device has been described as an example, the effect of the present invention is not changed even if a simple matrix type liquid crystal device is adopted. In such a case, connect the signal line to a rectangular IT
O is formed, and the MIM element and the pixel electrode are not provided. Further, instead of the TN mode, an STN mode using liquid crystal twisted from 180 degrees to 270 degrees is employed. A phase difference plate may be provided for the purpose of compensating the coloring of the display in the STN mode.

As the light guide 508 of the backlight, a flat plate of acrylic resin having good transparency was used, and a white paint was printed on its surface. A white light reflecting plate 509 was arranged on the back of the light guide to return light leaking backward, and an embossed light scattering plate 507 was arranged on the front to enhance the uniformity of illumination.

In the liquid crystal device manufactured as described above, the light emitted from the backlight, the light reflected by the reflective polarizer 506 is scattered by the light scattering plate 507, and returns again upward, so that the efficiency of the backlight increases. I do. In addition, thanks to the use of the reflective polarizer of the present invention, light incident from an oblique direction is reflected backward without being escaped and is reused, so that a brighter display can be achieved.

(Embodiment 4) Three examples of the electronic device according to the fourth aspect of the present invention will be described.

The liquid crystal device of the present invention is suitable for portable equipment used in various environments and requiring low power consumption.

FIG. 6A shows a mobile phone, and a main body 601 is shown.
A display unit 602 is provided in an upper part of the front surface of the display. Mobile phones are used in all environments, both indoors and outdoors. Especially, it is often used in cars, but the inside of cars at night is very dark. Therefore, it is desirable that the display device used in the mobile phone is a transflective liquid crystal device capable of performing transmissive display using auxiliary light as needed, mainly reflective display with low power consumption. The liquid crystal device of the present invention is brighter and has higher contrast than the conventional liquid crystal device in both the reflective display and the transmissive display.

FIG. 6B shows a watch, which is a main body 603.
The display unit 604 is provided at the center of the display. An important aspect in watch applications is luxury. The liquid crystal device of the present invention is not only bright, but also has little coloring due to a small characteristic change due to the wavelength of light. Also, there is little change in the background color due to the viewing angle. Therefore, a very high-quality display can be obtained as compared with the conventional liquid crystal device.

FIG. 6C shows a portable information device.
The display unit 606 is provided on the upper side of the display unit 05 and the input unit 607 is provided on the lower side. In addition, touch keys are often provided on the front of the display unit. Normal touch keys have many surface reflections,
The display is hard to see. Therefore, conventionally, a transmissive liquid crystal device has often been used even though it is portable. However, the transmissive liquid crystal device has a large power consumption that always uses a light source, and has a short battery life. Even in such a case, the liquid crystal device of the present invention can be used for portable information equipment because the display is bright and vivid not only in the transmission type but also in the reflection type and the transflective type.

[0042]

As described above, according to the present invention, it is possible to provide a reflective polarizer capable of obtaining a high degree of polarization even for light incident from an oblique direction. Further, the present invention can provide a liquid crystal device with a wide viewing angle and a high brightness, and an electronic device with low power consumption.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a main part of a structure of a reflective polarizer according to a first embodiment of the present invention.

FIG. 2 is a diagram showing refractive index characteristics of two types of layers constituting a reflective polarizer in Example 1 of the present invention.

FIG. 3 is a diagram showing the incident angle dependence of the degree of polarization of the reflective polarizer in Example 1 of the present invention.

FIG. 4 is a diagram illustrating a main part of a structure of a liquid crystal device according to a second embodiment of the present invention.

FIG. 5 is a diagram illustrating a main part of a structure of a liquid crystal device according to a third embodiment of the present invention.

FIG. 6 is a diagram illustrating an appearance of an electronic device according to a fourth embodiment of the present invention. (A) mobile phone, (b) watch,
(C) portable information devices.

[Explanation of symbols]

Reference Signs List 101 Layer with stretched material having high photoelastic modulus 102 Layer with stretched material having low photoelasticity 103 Orthogonal coordinate system, x-axis direction is stretching direction 201 Index ellipsoid of layer 101 202 Index ellipsoid of layer 102 211 The refractive index nx 212 in the direction parallel to the main stretching direction in the plane of the layer 101 The refractive index ny 213 in the direction perpendicular to the main stretching direction in the plane of the layer 101 The refractive index nz 221 of the layer 102 in the thickness direction of the layer 101 Refractive index nx 222 in the direction parallel to the main stretching direction in the plane Refractive index ny 223 in the direction perpendicular to the main stretching direction in the plane of the layer 102 Refractive index nz 231 xy plane in the film thickness direction of the layer 102 (reflection 232 xz plane (surface including both the stretching direction and the film thickness direction of the reflective polarizer) 233 yz plane (the direction perpendicular to the stretching direction of the reflective polarizer and the film thickness direction) Light incident from obliquely towards containing surface) 241 x-z light 242 in the y-z plane that is obliquely incident in a plane

Claims (4)

[Claims] The present invention is characterized in that a plurality of first layers having in-plane refractive index anisotropy and a plurality of second layers having no in-plane refractive index anisotropy are alternately laminated. A reflective polarizer,
Among the three main refractive indices nx, ny, and nz of each of the layers, the ratio between the refractive index nz in the film thickness direction and the refractive index ny in the direction perpendicular to the stretching direction in the plane is equal to each other in the two layers. And a reflective polarizer. 2. A liquid crystal cell comprising a polarizing plate that absorbs at least a predetermined linearly polarized light component and transmits the remaining polarized light component, and a liquid crystal composition sandwiched between a pair of substrates having transparent electrodes. A liquid crystal device comprising: the reflective polarizer according to any one of claims 1 to 4; and a light absorbing plate, and these are arranged in the above order. 3. A liquid crystal cell comprising a polarizing plate absorbing at least a predetermined linearly polarized light component and transmitting the remaining polarized light component, and a liquid crystal composition sandwiched between a pair of substrates provided with transparent electrodes. A liquid crystal device comprising: the reflective polarizer according to any one of claims 1 to 4; and a backlight, and these are arranged in the above order. 4. An electronic apparatus comprising the liquid crystal device according to claim 2 as a display unit.