JP2000056301A - Optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical device which has a wide field angle and good display quality and is made of a plastic substrate. SOLUTION: This optical device is constituted by arranging two phase difference films which have nearly equal phase differences and satisfy that R(0) is 30 to 90 nm and R(40)/R(0) is <=1.5, where R(0) is a phase difference measured from a perpendicular direction of a film surface and R(40) is a phase difference R(40) measured at 40 deg. in the direction perpendicular with respect to the phase delay axis in the film surface to make their phase delay axes substantially orthogonal to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device using a plastic film as a substrate and having a small viewing angle dependency.

[0002]

2. Description of the Related Art In recent years, electronic devices have become smaller and smaller, and liquid crystal display devices that take advantage of their light weight and compactness, such as notebook computers and word processors, have been increasingly used. Further, tools that are smaller and lighter, such as portable information terminals, have been developed. Various plastic films are used in such liquid crystal display devices of portable devices for the purpose of weight reduction. Further, an optical compensation film has been developed for the purpose of enhancing the function of a liquid crystal display device, but a plastic film may be used as a base for supporting such an optical functional layer.

[0003] Such a plastic film used in an optical device for handling polarized light is required to have optical isotropy in order to avoid undesired interaction with polarized light, and is expressed by the product of birefringence and thickness. It is required that the retardation is extremely small and the direction of the slow axis is uniform, and plastic films having optical characteristics satisfying the required characteristics are being developed.

[0004]

Such a plastic film is formed by a melt extrusion method or a solvent casting method using polycarbonate, polyarylate, polyether sulfone, or substituted norbornene resin. In the case of polycarbonate, as seen in JP-A-9-230316, the retardation (R (0)) measured from the vertical direction of the film is 10 nm or less, and the variation in the slow axis in the film plane is ± 5 °. The following transparent films have been proposed. However, it is unavoidable that molecules are slightly oriented in the plane of the film during molding, and the resulting film has some biaxiality. When such a film is used in an optical device, when viewed from the front of the film, it gives properties comparable to glass, but it is tilted by 40 ° in the direction perpendicular to the slow axis in the film plane to reduce the phase difference. When measured (R (40)), a phase difference of 2.5 to 3 times or more of R (0) occurs due to the biaxiality of the film (R (0)).
(40) / R (0) ≧ 2.5 to 3), and the liquid crystal display device has a practical problem of lowering the contrast and causing grayscale inversion as compared with the case where glass is used.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of such circumstances, and as a result, the viewing angle characteristics have been improved by arranging specific optical characteristics so that the retardation films compensate each other. It has been found that an improved optical device can be obtained, which has led to the present invention. That is, according to the present invention, the phase difference measured from the vertical direction of the film surface is represented by R
(0), 40 in the direction perpendicular to the slow axis in the film plane
When the phase difference measured by tilting is R (40), R
(0) is in the range of 30 nm or more and less than 90 nm, and R
(40) / R (0) is 1.5 or less and two retardation films having the same retardation are arranged such that their slow axes are substantially orthogonal to each other. The present invention relates to a characteristic optical device.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION

[0007]

[Embodiment] R (40) / R (0) is small, that is,
By using a retardation film with high uniaxiality, the viewing angle dependence of the retardation can be reduced, and although it depends on the refractive index of the film, R (40) / R (0) is approximately 1.1. Before and after, it becomes possible to greatly fall below a general value in a low retardation film. The uniaxiality of the film can be increased by stretching the film in one direction. However, the stretching causes a problem that R (0) increases and the phase difference when viewed from the front increases. However, by arranging another retardation film having the same retardation so that the slow axes in the film plane are substantially orthogonal, the combined retardation can be kept small. At this time, the phase difference when tilted is approximately twice as large as that measured with one sheet, but the viewing angle dependency can be kept small as compared with a known low phase difference film.

[0008] The retardation film used in the present invention is R
(0) is in the range of 30 nm or more and less than 90 nm, and R
(40) / R (0) must be 1.5 or less and have the same phase difference. Such a retardation film is
The retardation of one retardation film can be canceled by the other retardation film by arranging the retardation axes in a direction substantially orthogonal to the retardation film, and the combined retardation can be kept extremely low. it can. It is desirable that the two retardation films have the same R (0), and the difference is 1
It is preferably 0 nm or less, more preferably 5 nm or less. The preferred range of R (40) / R (0) is 1.
05 to 1.5, and more preferably 1.1 to 1.2. Such a retardation film is disclosed in JP-A-2-424.
06, JP-A-6-194646, JP-A-9-187
The film can be easily obtained by performing film formation and stretching using a known method as shown in, for example, No. 828. In particular, in order to keep R (40) / R (0) small, that is, to make the uniaxiality of the retardation film as large as possible, free-end uniaxial stretching is the most preferable method. The stretching temperature and the stretching ratio are also important for the uniaxiality of the obtained retardation film, and it is necessary to determine the optimal conditions. Further, it is also possible to obtain a highly uniaxial retardation film by a method of performing thermal annealing while heating the film near the glass transition temperature without substantially stretching the film to reduce the biaxiality of the film.

Preferably, the range of R (0) is 30 nm or more and less than 90 nm, more preferably 40 nm to 70 nm.
nm. When the phase difference is smaller than 30 nm, it is difficult to control the phase difference value and the uniaxiality, and when two sheets are combined, it is difficult to cancel the phase difference. On the other hand, when the phase difference is 90 nm or more, the absolute value of the change in the phase difference when tilted increases, so that it is difficult to achieve the object of the present invention of improving the viewing angle characteristics. That is, the combined retardation of the two retardation films having the arrangement according to the present invention,
R (0) and R (40) / R within a range not exceeding 30 nm
It is preferable to select (0). Also, the dispersion of the slow axis in the plane of the retardation film is important, and is preferably within ± 10 °, more preferably within ± 5 °.

As the retardation film, a known plastic film can be used. That is, a plastic film of a polyvinyl chloride, acrylonitrile, styrene, polyolefin, substituted norbornene, or the like can be suitably used in addition to a polycarbonate, a polyarylate, a polysulfone, or a polyethersulfone.

When post-processing such as forming a transparent conductive layer or various coating layers on the retardation film, heat resistance may be required depending on the processing conditions. In the assembly process of touch panels and liquid crystal displays,
Generally, it has a heating process of 100 ° C. to 150 ° C. By optimizing the processing conditions, the heating temperature can be reduced, but the glass transition temperature of the plastic constituting the retardation film is preferably 80 ° C. or higher,
More preferably 120 ° C. or higher, further preferably 160 ° C.
That is all. To illustrate a preferred plastic,
A substituted or unsubstituted cycloalkylidene group having 5 carbon atoms
Polyarylates, polycarbonates and polyester carbonates containing the above bisphenol component having an alkylidene group or an aralkylene group as a part of the bisphenol component. More specifically,
1,1-bis (4-hydroxyphenyl) -cyclohexane, 1,1-bis (4-hydroxyphenyl) -3,
3,5-trimethylcyclohexane, 3,3-bis (4
-Hydroxyphenyl) -pentane, 4,4- (4-hydroxyphenyl) -heptane, 4,4- (4-hydroxyphenyl) -phenylmethane as a bisphenol component, such as polycarbonate, polyarylate and polyester carbonate. However, it is not limited to this.

A preferred embodiment of the optical device according to the present invention is a transparent touch panel. In particular, JP-A-61-1
74587, JP-A-3-121523 and JP-A-10-102
In a resistive touch panel disposed between a polarizing plate and a liquid crystal cell as shown in JP-A-48625, one of the films according to the present invention is used as an electrode substrate having optical isotropy on the input surface side. Used, the second retardation film, the first retardation film and the slow axis in the plane of the film are arranged in a direction substantially orthogonal to, or used as an opposing electrode substrate, or at an appropriate position. By inserting the touch panel, a touch panel with little viewing angle dependence can be obtained. The touch panel can be used in combination with a liquid crystal display device. At this time, the relative arrangement between the polarization axis of the light emitted from the liquid crystal cell and the slow axes of the two retardation films is not particularly limited, but it is preferable to determine the optimal arrangement in consideration of the display image quality.

Another preferred embodiment of the optical device according to the present invention is a liquid crystal display device. In the liquid crystal display device, the retardation film according to the present invention is used as a base film for at least one electrode substrate, and the second retardation film is substantially perpendicular to the first retardation film and the slow axis. A liquid crystal display device having little viewing angle dependence can be obtained by arranging them in different directions and using them as opposing electrode substrates, or by inserting them in appropriate positions in the same axial direction.

Further, a liquid crystal display device with a touch panel, in which the touch panel and the liquid crystal display device are combined, is also provided.
It is a preferred optical device according to the present invention.

[0015]

EXAMPLES The methods for measuring the physical properties shown in Examples and Comparative Examples are described below. <Phase difference> Using a micro polarization spectrophotometer manufactured by Oak Works,
Place the sample horizontally on the stage and measure at 515n
The phase difference was measured using light of m (R (0)). afterwards,
The sample was placed in a direction perpendicular to the slow axis in the plane of the film.
And the phase difference was measured in the same manner (R (40)).

Hereinafter, the present invention will be described in detail with reference to examples. (Example 1) 1,1-bis (4-hydroxyphenyl)
Polycarbonate composed of -3,3,5-trimethylcyclohexane, bisphenol A (molar ratio 7: 3), and phosgene [molecular weight: ηSP / C = 0.85 (32 ° C., 0.32 g / dl in chloroform), glass transition Temperature is 206
C. (DSC)], R (0) = 5 at a thickness of 60 μm.
A retardation film having a thickness of 5 nm, R (40) = 62 nm, R = 1.12 and a variation of the slow axis of ± 1.5 ° was defined as a first retardation film. On the surface of this retardation film, an epoxy acrylic ultraviolet curable coating liquid in which divinylbenzene filler having an average particle diameter of 2 μm was dispersed was applied and cured to form a hard coat layer having a thickness of about 2 μm. Furthermore,
On this surface, ITO was formed by a sputtering method to prepare a retardation film having a transparent conductive layer having a surface resistance of 400Ω / □. This film was used as the first transparent conductive substrate in FIG. As a second transparent conductive substrate, a glass substrate having a transparent conductive layer having a surface resistance of 200Ω / □ was used,
I assembled a transparent touch panel. Further, as a second retardation film, R (0) = 50 nm, R (0) = 50 nm, made of polycarbonate made of bisphenol A,
(40) = The first retardation film and the slow axis are provided on the opposite side of the transparent conductive layer of the second transparent conductive substrate constituting the touch panel using the retardation film of 56 nm and R = 1.12. Were arranged so as to be orthogonal to each other and bonded via an adhesive.

On the other hand, a polarizing plate having a surface anti-reflection coating was used and bonded to a first retardation film constituting a touch panel using an adhesive. Further, a backlit T with the display surface side polarizing plate removed via a spacer
A liquid crystal display device with a touch panel was assembled by overlapping the transparent electrode substrate surface made of glass of the FT type liquid crystal display device. At this time, the polarization axis of the polarizing plate bonded to the touch panel was arranged in the same direction as the polarization axis of the display-side polarizing plate removed from the liquid crystal display device.

In this liquid crystal display device, when a display image was observed while being tilted in the horizontal direction of the display surface, no gradation inversion was observed even when the display image was tilted by 50 ° or more. Comparative Example 1 As in Example 1, R (0) = 12 nm,
Using a low retardation film with R (40) = 38 nm and R = 3.2, a liquid crystal display device with a touch panel was assembled without using a second retardation film. When the liquid crystal display device was observed in the display image while being inclined in the horizontal direction of the display surface, the contrast was reduced from around 40 °, and tone inversion was recognized at a smaller angle than in Example 1.

Example 2 Polyarylate film (glass transition temperature: 215 ° C .; manufactured by Kanegabuchi Chemical Industry Co., Ltd.)
-1100) with a thickness of 60 μm obtained by uniaxially stretching
(0) = 53 nm, R (40) = 60 nm, R = 1.1
4 is the first retardation film, thickness 60μ
m (R) = 50 nm, R (40) = 56 nm, R =
A liquid crystal display device with a touch panel was assembled in the same manner as in Example 1, except that a polycarbonate retardation film made of bisphenol A of 1.12 was used as the second retardation film. In the liquid crystal display device, when a display image was observed while being tilted in the horizontal direction of the display surface, no grayscale inversion was recognized even when the display image was tilted by 50 ° or more.

Example 3 Polyarylate film (glass transition temperature: 215 ° C .; F, manufactured by Kanegafuchi Chemical Industry Co., Ltd.)
-1100) with a thickness of 60 μm obtained by uniaxially stretching
(0) = 53 nm, R (40) = 60 nm, R = 1.1
Gas barrier coating is performed on the film which is 4, and further, an ITO electrode is formed by a DC sputtering method,
A transparent electrode substrate was created. A divinylbenzene-based bead is sandwiched between two upper and lower transparent electrode substrates provided with a polyimide film oriented so as to cover the ITO electrode, and a liquid crystal injection port is formed while the periphery is sealed with an epoxy-based sealant. Stuck together. At this time, n of the two substrates
It was arranged so that x was orthogonal. Next, after injecting liquid crystal from the injection port, the injection port was sealed with a sealant to form a liquid crystal cell. A polarizing plate and a polarizing plate with a reflecting plate were stuck on this liquid crystal cell, respectively, to obtain a monochrome type reflective liquid crystal display device. The liquid crystal display device was compared with the liquid crystal display device assembled using the low retardation film of Comparative Example 1 by 4%.
When the display surface was observed at an angle of 0 °, the coloring of the panel was small.

[0021]

According to the present invention, it is possible to obtain an optical device made of a plastic substrate and exhibiting good display quality at a wide viewing angle.

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[Procedure amendment]

[Submission date] October 12, 1998 (1998.10.
12)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Added

[Correction contents]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of a liquid crystal display device equipped with a transparent touch panel, which is one example of an optical device according to the present invention. The arrow indicates the slow axis direction of the retardation film.

[Description of Signs] 1 Polarizer 2 First transparent conductive substrate (first retardation film) 3 Second transparent conductive substrate 4 Second retardation film 5 Liquid crystal cell 6 Transparent conductive layer A Touch panel

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 BA02 BA06 BB03 BB42 BB46 BC22 2H089 HA18 JA07 QA16 TA01 TA14 2H091 FA11X FA11Z FD07 FD10 GA01 GA03 KA10 LA13 LA17 LA19 5B087 AB04 AE09 CC02 CC13 CC14 CC37

Claims (3)

[Claims] 1. The phase difference measured from the direction perpendicular to the film surface is R (0), and the phase difference measured by inclining 40 ° in the direction perpendicular to the slow axis in the film surface is R (40). At this time, R (0) is in the range of 30 nm or more and less than 90 nm, R (40) / R (0) is 1.5 or less, and two retardation films having the same retardation are compared with each other. An optical device characterized in that the slow axes are arranged to be substantially orthogonal. 2. The optical device according to claim 1, wherein the optical device is a liquid crystal display device, and at least one of the retardation films is used as a transparent electrode substrate constituting the liquid crystal display device. 3. The optical device according to claim 1, wherein the optical device is a resistive touch panel, and at least one of the retardation films is used as a transparent electrode substrate constituting the touch panel.