JPH08294986A - Transparent optical laminated sheet and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide a transparent optical laminated sheet which is optically transparent and has good visual characteristics and heat resistance and a method for making the laminated sheet. CONSTITUTION: A transparent optical laminated sheet is optically transparent and has retardation of 50nm or less and in which two heat resistant layers are formed in the outermost parts. A refractive index in the optical axis direction on the plane of the heat resistant layer is nx, a refractive index perpendicular to the optical axis on the plane is ny, and a refractive index vertical to the heat resistant layer is nz; Nz, which is a value of the optical property of the heat resistant layer and expressed by an equation of Nz=(nx-nz)/(nx-ny), is 4 or less, and the optical axis of the heat resistant layer are arranged not to be parallel with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent optical laminated sheet which has excellent viewing angle characteristics, is optically transparent, and has heat resistance, and a method for producing the same. More specifically, the present invention relates to a transparent optical laminated sheet compatible with glass as a substrate for optoelectronic devices such as liquid crystal display devices, and a method for manufacturing the same.

[0002]

2. Description of the Related Art With the rapid progress of electronics technology, attention has been paid to optoelectronic devices represented by liquid crystal display devices. Such an optoelectronic element is formed by disposing various functional materials on a glass substrate having a transparent conductive layer, and is used for various purposes. In particular, when an optoelectronic element using a glass substrate is used in a portable device, the specific gravity of glass is large, and therefore, in order to achieve the desired weight reduction as a portable device, it is extremely thin. Has become an important issue. At present, a glass substrate having a thickness of about 0.4 mm is available.

However, glass has insufficient mechanical strength. That is, glass is a material that is extremely brittle and is extremely fragile. Therefore, the element using the glass substrate is inferior in durability. In order to improve the durability of the element,
A glass substrate that has undergone a special treatment such as tempered glass, a metal frame for protecting the element from impact, and a plastic sheet for surface protection are used. However, these countermeasures do not essentially solve the problem of glass brittleness, so the problem of yield reduction due to glass breakage during the device manufacturing process cannot be solved.

In view of the above problems, there is a strong demand for a substrate material that is lightweight and does not exhibit brittleness (hard to break). From the viewpoint of lightness and impact resistance, expectations for optoelectronic devices using a plastic substrate are great, and some attempts have been made to put a plastic substrate having a thickness of about 0.4 mm, which is the same as a glass substrate, into practical use. There is.

A solvent casting method is known as a typical method for producing a plastic film having suitable properties as an optoelectronic device substrate (for example, high heat resistance and excellent surface smoothness).
However, this method can only produce a film having a thickness of about 200 μm. This is because when the film is thickened, defects such as foaming are likely to occur. Furthermore, when a film is made thick to give rigidity as a base material, it is difficult to industrially put it into practical use because the productivity is very low.
Therefore, a film having desired thickness and rigidity cannot be obtained. Alternatively, as a method for making a thick film, a melt extrusion method can be mentioned. In this method,
There are problems that the optical isotropy of the obtained film is impaired and the surface smoothness and appearance of the film obtained by a die line during molding are poor. Therefore, it is difficult to use the film obtained by the melt extrusion method as a substrate for optoelectronic devices.

In order to solve such problems, plastics having essentially low birefringence such as polymethylmethacrylate and modified olefins, and JP-A-6-19 are known.
It has been studied to use a curable plastic such as crosslinked acrylic or epoxy described in Japanese Patent No. 4501 in the form of a sheet. However, the former does not have heat resistance like glass, and the latter has problems such as low productivity and lack of industrial practicality.

Alternatively, it has been studied to laminate the films obtained by the above-mentioned solvent casting method to thicken the film, but at present, an adhesive excellent in heat resistance and reliability cannot be obtained. Further, in the case of heating and laminating, a high processing temperature is required, which causes unfavorable problems such as denaturation and coloring of the resin due to thermal deterioration.

Furthermore, and most importantly, plastic films inherently have retardation (ie optical anisotropy). Therefore, it is essentially inferior in optical characteristics as compared with glass. Specifically, when a film having a large retardation is used as a substrate in a display device, the contrast is lowered. Furthermore, even when the viewpoint is inclined from the normal direction of the display screen (viewing angle dependency), the contrast of the display screen varies depending on the viewpoint.

In order to solve these problems, the present inventors have found that at least one heat-resistant layer made of an optically transparent polymer such as polyarylate or polycarbonate, and a glass lower than the material constituting the heat-resistant layer. We have proposed a transparent optical laminated sheet having excellent heat resistance, which is formed by laminating a rigidity imparting layer made of an optically transparent material having a transition temperature. Then, by using a film formed by the solvent casting method for the heat-resistant layer, a transparent optical laminated sheet having a low retardation and surface smoothness, which can be practically used as a substrate for an optoelectronic element, was obtained. Furthermore, by using a resin having a high glass transition temperature, a transparent optical laminated sheet having heat resistance that can be practically used as a substrate for optoelectronic devices was obtained. This sheet could be practically used as a substrate for optoelectronic devices even in terms of rigidity.

However, the heat-resistant layer film has a lower retardation as compared with the conventional plastic film, but the retardation of at least about 10 to about 20 nm remains, and it has essentially optical anisotropy. . When such films are laminated for thickening, the retardation of each film may be added depending on the laminating direction of the films. As a result, the laminated sheet has a large optical anisotropy as compared with glass, resulting in insufficient optical characteristics.

On the other hand, although it is possible to reduce the retardation of the laminated sheet by arranging the optical axes of the respective films so as not to be parallel to each other, generally, the viewing angle dependence tends to increase, and the liquid crystal display tends to increase. It becomes an unsuitable substrate for the device.

As described above, a plastic laminated sheet having a low retardation and an excellent viewing angle characteristic (that is, a small viewing angle dependency) has not been obtained yet.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and its object is to provide excellent viewing angle characteristics and optical transparency.
Another object of the present invention is to provide a transparent optical laminated sheet having heat resistance, a method for producing the same, and a transparent optical laminated sheet for a liquid crystal display device.

[0014]

DISCLOSURE OF THE INVENTION As a result of intensive investigations, the present inventors have found that at least 2 having specific optical characteristics.
A transparent optical laminated sheet having excellent viewing angle characteristics, being optically transparent, and having heat resistance by arranging two layers such that the optical axes of the two layers are not parallel to each other and laminating the layers by a specific method. The present invention has been completed and the present invention has been completed.

In the present specification, an optically transparent polymer has a light transmittance of 80% or more and a haze value of 5.
% Or less means. The viewing angle dependency means the retardation change when the viewpoint is inclined from the normal direction of the film. Further, the visual angle characteristic value means a retardation value when observed from a direction inclined by 45 ° with respect to the optical axis direction. The viewing angle characteristic value and the retardation value in the normal direction of the film are useful as indices for easily evaluating the optical characteristics as a substrate for an optoelectronic element. The smaller the viewing angle characteristic value and the retardation value, the more excellent the optical characteristics.

In the present specification, the optical characteristic value Nz means that the refractive index in the optical axis direction on the film plane is nx, the refractive index in the plane and a direction perpendicular to the optical axis direction is ny, When the refractive index in the vertical direction is nz, it is a characteristic value represented by the following equation.

[0017]

(Equation 3)

This Nz is a value representing the state of orientation of the film (in particular, the biaxiality of the film). The larger the Nz, the greater the biaxial orientation, and the perfect uniaxially oriented film has an Nz of 1. . Nz is useful as an index that represents the influence of stacking, particularly on the viewing angle dependency.

The transparent optical laminated sheet of the present invention is optically transparent and has a retardation of 50 nm or less, and a transparent optical laminated sheet having heat-resistant layers in the uppermost layer and the lowermost layer, the heat-resistant layer being Optical characteristic values Nz of
Is 4 or less, and the heat-resistant layer is arranged so that the optical axes thereof are not parallel to each other.

In a preferred embodiment, the heat axes of the heat-resistant layer are arranged so as to be orthogonal to each other.

In a preferred embodiment, the heat resistant layer is made of a resin selected from the group consisting of amorphous polyester, amorphous polycarbonate, and amorphous polyarylate.

In a preferred embodiment, the transparent optical laminated sheet has a rigidity-imparting layer between the heat-resistant layers, and the rigidity-imparting layer is optically transparent and constitutes the heat-resistant layer. The material has a glass transition temperature lower than that of the material.

In a preferred embodiment, the transparent optical laminated sheet further has a gas barrier layer on at least one outermost surface.

[0024] In a preferred embodiment, the transparent optical laminated sheet further has a transparent conductive layer on at least one outermost surface.

The transparent optical laminated sheet for a liquid crystal display device of the present invention is optically transparent and has a retardation of 50 nm or less and a transparent optical laminated sheet for a liquid crystal display device having heat-resistant layers as the uppermost layer and the lowermost layer. In the sheet, the heat-resistant layers each have an optical characteristic value Nz of 4 or less, and the heat-resistant layers are arranged so that their optical axes are not parallel to each other.

The method for producing a transparent optical laminated sheet of the present invention is optically transparent and has a retardation of 5
A method for producing a transparent optical laminated sheet having a heat-resistant layer as an uppermost layer and a lowermost layer having a thickness of 0 nm or less, the step of arranging a film forming the heat-resistant layer so that optical axes thereof are not parallel to each other, and bonding The process of laminating the film forming each layer by thermocompression bonding without using an agent.

In a preferred embodiment, the film for forming the heat resistant layer is formed by a solvent casting method.

In the liquid crystal display device of the present invention, the above transparent optical laminated sheet is used as a substrate.

The transparent optical laminated sheet of the present invention has heat resistant layers as the uppermost layer and the lowermost layer. The heat-resistant layer is a layer for imparting heat resistance to the laminated sheet and preventing thermal deformation during high temperature heating. Further, since the heat resistant layer is preferably optically transparent, the polymer used for the heat resistant layer is an optically transparent polymer. Examples of these polymers include polyarylate, polycarbonate, polysulfone, polyether sulfone, polyvinyl alcohol, cellulose acetate, polyester, polyimide, polyolefin, polystyrene, styrene-based copolymer, polymethylmethacrylate, and methacrylic-based copolymer. To be From the viewpoint of heat resistance, polyarylate, polycarbonate, polysulfone, polyethersulfone, and polyester are preferable, and amorphous polyarylate, amorphous polycarbonate, and amorphous polyester are particularly preferable.

These polymers may be used alone or
Two or more kinds may be used in combination. The form of combination may be either a blend or a copolymer.

Further, considering transparency, film or sheet moldability, industrial availability, and compatibility,
Amorphous polyarylates and amorphous polycarbonates having aromatic groups in the main chain are particularly preferred. Particularly preferred specific examples include substituted or unsubstituted hydroxyphenylpropane, substituted or unsubstituted hydroxyphenylmethane, and homopolymers and copolymers containing a substituted or unsubstituted hydroxyphenylcycloalkane as a monomer component, and blends or Alloy can be mentioned. Polyarylate is a polymer obtained from an aromatic dicarboxylic acid and a divalent phenol, and polycarbonate is a polymer composed of a carbonic acid ester of a divalent phenol. These polymers are described in, for example, JP-A-57-73021 and JP-A-1-13.
No. 583, No. 2-88634, No. 2
No. 23720.

The glass transition temperature of the polymer used for the heat-resistant layer is preferably 160 ° C. or higher, more preferably 18
The temperature is 0 ° C or higher, and most preferably 200 ° C or higher. When the glass transition temperature is less than 160 ° C, the heat resistance required in the liquid crystal cell manufacturing process is insufficient.

These polymers are formed into a film having a desired thickness by a solvent casting method, a melt extrusion method or the like to obtain a heat resistant layer film. From the viewpoint of optical characteristics and surface smoothness, the solvent casting method is preferable.

The optical characteristic value Nz value of the heat-resistant layer is 4 or less, preferably 3.5 or less, more preferably 3 or less. N
When the z value exceeds 4, the resulting laminated sheet has insufficient viewing angle characteristics as a base material.

The thickness of the heat-resistant layer varies depending on the heat-resistant shape stability required depending on the application, but is preferably 20% or more, more preferably 25% or more of the thickness of the obtained laminated sheet. . When the thickness is less than 20% of the laminated sheet, the heat resistance of the laminated sheet is insufficient. The thickness of the heat-resistant layer depends on the thickness of the laminated sheet, but specifically, it is preferably 50 to 150 μm.

The viewing angle characteristic value of the heat-resistant layer is preferably 50 n.
m or less, more preferably 30 nm or less, most preferably 20 nm or less.

The surface roughness (Ra) of the heat resistant layer is preferably 30 nm or less, more preferably 20 nm or less.

The transparent optical laminated sheet of the present invention preferably has a rigidity imparting layer between the heat resistant layers. The rigidity imparting layer is
It is a layer for imparting rigidity to the laminated sheet. The polymer used for the rigidity imparting layer is preferably a polymer having excellent affinity with the polymer used for the heat resistant layer. Therefore, the optimum polymer can be selected depending on the heat-resistant layer, but in consideration of versatility, cost, glass transition point, etc., polycarbonate obtained using bisphenol A is particularly preferable.

The glass transition temperature of the polymer used for the rigidity imparting layer is preferably 100 ° C. or higher, more preferably 140 ° C. or higher, most preferably 180 ° C. or higher. When the glass transition temperature is less than 100 ° C, the sheet rigidity is insufficiently maintained in the liquid crystal cell manufacturing process. Furthermore, it is 20 ° C higher than the glass transition temperature of the polymer used for the heat-resistant layer.
It is preferably lower than that, and more preferably 40 ° C. or higher.

These polymers are formed into a film having a desired thickness by a solvent casting method, a melt extrusion method or the like to obtain a film for a rigidity imparting layer. From the viewpoint of productivity and cost reduction of the laminated sheet, the melt extrusion method is preferable.

The thickness of the rigidity-imparting layer varies depending on the thickness of the heat-resistant layer and the characteristics of the laminated sheet required depending on the use, but is preferably 80% or less of the thickness of the obtained laminated sheet, It is preferably 75% or less. When the thickness exceeds 80% of the laminated sheet, the heat resistance of the obtained laminated sheet is insufficient. The thickness of the rigidity imparting layer depends on the thickness of the laminated sheet, but specifically, it is preferably 200.
Is about 500 μm.

The transparent optical laminated sheet of the present invention preferably has a gas barrier layer on at least either the uppermost surface or the lowermost surface (that is, the surface which is in contact with liquid crystal when used as a substrate). . As the gas barrier layer, a well-known organic gas barrier layer such as ethylene-vinyl alcohol copolymer (for example, manufactured by Kuraray Co., Ltd., Eval: registered trademark), polyvinyl alcohol, polyvinylidene chloride; silicon oxide, aluminum oxide, etc. Known metal oxide-based gas barrier layers; known metal nitride-based gas barrier layers such as silicon nitride and aluminum nitride. An optimum thickness of the gas barrier layer can be selected depending on the required gas barrier property.

The transparent optical laminated sheet of the present invention preferably further has a transparent conductive layer. The transparent conductive layer may be provided on the heat resistant layer or the gas barrier layer.
A typical example of the transparent conductive layer is a composite oxide of indium and tin (ITO). The thickness of the transparent conductive layer is optimally selected depending on the liquid crystal cell, but is preferably 30 to 200 nm.

The transparent optical laminated sheet of the present invention obtained by laminating each of the above layers has a thickness of preferably 0.2 to 1
mm, more preferably 0.3 to 0.7 m. If the thickness is less than 0.2 mm, the rigidity of the base material is insufficient. Therefore, sharing and compatibility with glass is difficult.

The viewing angle characteristic value of the laminated sheet is 50 nm or less, preferably 30 nm or less, more preferably 20 nm.
It is the following. When the viewing angle characteristic value exceeds 50 nm, the optical characteristics as a substrate for an optoelectronic element are insufficient. Furthermore, it is preferable that the ratio between the viewing angle characteristic value and the vertical characteristic value of the laminated sheet is small.

The light transmittance of the laminated sheet is 80% or more,
Preferably 90% or more, the haze value of the laminated sheet is 5%
The following is preferably 1% or less.

The transparent optical laminated sheet of the present invention is preferably used as a substrate of a liquid crystal display device. Further, a transparent conductive layer for forming a pen input device is sequentially formed on one surface of the laminated sheet, and a gas barrier layer and a transparent conductive layer for driving a liquid crystal display device are sequentially formed on the other surface of the laminated sheet so that the pen input device is integrated. It is also possible to use it as a substrate for a liquid crystal display device that has become defective.

A preferred example of the method for producing a transparent optical laminated sheet of the present invention will be described below for the case of producing a laminated sheet having a rigidity-imparting layer and a heat-resistant layer as the uppermost layer in this order on the heat-resistant layer as the lowermost layer. explain.

In order to produce a transparent optical laminated sheet according to the present invention, the above-mentioned film for a heat-resistant layer and another film for a heat-resistant layer are thermocompression-bonded on the above-mentioned film for a heat-resistant layer without using an adhesive. Stack. By thermocompression bonding without using an adhesive, it is possible to prevent unfavorable phenomena such as a decrease in heat resistance of the laminated sheet due to the adhesive and discoloration of the adhesive at high temperatures.

As a typical example of a preferable thermocompression bonding method,
A heating and pressure laminating method using a heating roll or a heating belt can be mentioned. The heating temperature during lamination may vary depending on the polymer to be laminated, but is preferably higher than the glass transition temperature of the polymer used for the rigidity imparting layer and lower than the glass transition temperature of the polymer used for the heat resistant layer. The heating temperature employed in the present invention largely depends on the combination of polymers to be laminated, but specifically, it is preferably 100 to 200 ° C. Further, a vacuum laminating method can also be preferably used in order to more sufficiently eliminate air bubbles during lamination.

The thermocompression bonding may be carried out in one step or in a plurality of two or more steps. For example, a two-step thermocompression bonding method may be employed in which precompression bonding is performed at a relatively low temperature, followed by heating to a heating temperature and main compression bonding.

Regarding the laminating direction of each layer during thermocompression bonding, the relative positional relationship of the optical axes of the uppermost layer and the lowermost heat-resistant layer is important. That is, it is necessary to arrange the heat-resistant layer films so that the optical axes thereof are not parallel to each other. This makes it possible to reduce the retardation of the laminated sheet.

The method for producing the transparent optical laminated sheet of the present invention is not limited to the laminated sheet having the above three-layer structure,
It can also be applied to a laminated sheet having a two-layer structure or a multilayer structure of four or more layers.

[0054]

The transparent optical laminated sheet of the present invention has a heat-resistant layer having an optical characteristic value Nz of 4 or less, which is arranged so that the optical axes thereof are not parallel to each other. Also has a small viewing angle characteristic value and retardation. Since the retardation of the laminated sheet is substantially determined by the optical characteristics of the two heat resistant layers, it is possible to reduce the retardation of the laminated sheet by preventing the optical axes of the heat resistant layers from being parallel to each other. Is.
For example, when the optical axes are made orthogonal to each other, the retardation of the laminated sheet is the difference in retardation of the film forming the heat resistant layer. Furthermore, by using a heat-resistant layer having a specific optical characteristic of having an optical characteristic value Nz of 4 or less, the viewing angle dependency of the laminated sheet is also improved as compared with the case of each heat-resistant layer alone. That is, by stacking heat-resistant layers having specific optical properties in a specific relative positional relationship, it is possible to cancel the optical anisotropy inherent in each heat-resistant layer.

Furthermore, since this laminated sheet has a smaller dependence of the retardation value on the observation direction, the substrate has no optical directivity when used as a substrate for an optoelectronic element. Therefore, when cutting the substrate into a desired size according to the application of the element, it is not necessary to consider the cutting direction. Therefore, the cutting efficiency is improved, and
Since the number of elements taken from the substrate of a predetermined size is increased, the production efficiency is remarkably improved, which greatly contributes to cost reduction. Regarding the angles of the optical axes of the heat-resistant layers, a desired angle is set depending on the alignment direction of the liquid crystal and the relative positional relationship with the polarizing film when the laminated sheet is actually used in a liquid crystal display device or the like. Can be done.

Since the transparent optical laminated sheet of the present invention preferably has a rigidity imparting layer, it has sufficient rigidity as a substrate. Furthermore, since the rigidity-imparting layer is protected on both sides by the heat-resistant layers, deformation does not occur even when the laminated sheet is used at high temperature. Furthermore, by stacking the heat resistant layer and the rigidity imparting layer, a thick film sheet having heat resistance can be obtained at low cost. This is because the heat-resistant layer film and the rigidity-imparting layer film can each be formed by a simple method, and furthermore, the films can be laminated while maintaining the excellent properties of the respective films to obtain a laminated sheet.

According to the method for producing a transparent optical laminated sheet of the present invention, since the rigidity imparting layer is heated to the glass transition temperature or higher during laminating, the effect of thermal annealing is obtained. Therefore, the optical anisotropy which the rigidity-imparting layer film alone has is reduced and improved by thermal annealing.
As a result, in the obtained laminated sheet, the contribution of the optical anisotropy of the rigidity imparting layer becomes extremely small. This means that a material having high optical anisotropy can be used as the material used for the rigidity imparting layer. That is, since it is not necessary to consider the optical anisotropy when molding the rigidity-imparting layer film, the productivity is remarkably improved. Therefore, the manufacturing method of the present invention has high industrial utility value.

On the other hand, since the heat-resistant layer is not affected by the thermal annealing, the retardation may increase when it is laminated. However, as in the present invention, a specific film having Nz of 4 or less has a specific relative thickness. By stacking layers in a positional relationship, it is possible to reduce retardation and improve viewing angle characteristics. When using a film with Nz of 4 or more,
The retardations cancel each other and decrease, but the viewing angle characteristic value increases due to the biaxiality of each film.

As described above, the transparent optical laminated sheet of the present invention is excellent in both optical characteristics and heat resistance, so that it can be shared with or compatible with glass, and is useful in a wide range as a substrate for optoelectronic devices. Furthermore, compared to glass, it is significantly superior in impact resistance and lightweight, so
It is particularly useful as a substrate material for a liquid crystal display device that requires a large area.

[0060]

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited thereto.

Example 1 As one heat-resistant layer film (Film A), the glass transition temperature was 215 ° C. and the thickness was 7
An optically transparent polyarylate film (Ermec F-1100: registered trademark, manufactured by Kanegafuchi Chemical Industry Co., Ltd.) having a thickness of 5 μm and an optical characteristic value Nz of 2.1 was used as the other heat-resistant layer film (film B). As an optically transparent polyarylate film having a glass transition temperature of 215 ° C., a thickness of 75 μm, and an optical characteristic value Nz of 2.2 (Kanefuchi Chemical Co., Ltd., Ermec F-1100: registered trademark) And a polycarbonate film obtained from bisphenol A having a glass transition temperature of 150 ° C., a thickness of 300 μm, and a retardation of 130 nm, which was molded by a melt extrusion method.

On each surface of the rigidity imparting layer film, the optical axis of the film A and the optical axis of the film B are orthogonal to each other.
Film A and film B were arranged respectively. The stacked films were thermocompression bonded at 200 ° C. for 50 minutes to obtain a laminated sheet having a thickness of 270 μm. The retardation and viewing angle characteristic values of the obtained laminated sheet were measured by TFM-120AFT manufactured by Oak Manufacturing Co., Ltd. The results are shown in Table 1.

Example 2 A laminated sheet was obtained in the same manner as in Example 1 except that the film A and the film B having the characteristics shown in Table 1 were used. This sheet was subjected to the same evaluations as in Example 1. Table 1 shows the evaluation results.

Example 3 A laminated sheet was obtained in the same manner as in Example 1 except that the films A and B having the properties shown in Table 1 were used. This sheet was subjected to the same evaluations as in Example 1. Table 1 shows the evaluation results.

Comparative Example 1 A laminated sheet was obtained in the same manner as in Example 1 except that the film A and the film B having the properties shown in Table 1 were used. This sheet was subjected to the same evaluations as in Example 1. Table 1 shows the evaluation results.

[0066]

[Table 1]

As is clear from Table 1, the optical characteristic value N
When a film having z of 4 or less is orthogonalized, the viewing angle characteristic value of the laminated sheet becomes 30 nm or less, which is lower than the viewing angle characteristic value of the film alone before lamination. Therefore, it is understood that the lamination improves the optical characteristics as compared with the film alone.

[0068]

According to the present invention, there are provided a transparent optical laminated sheet which has excellent viewing angle characteristics, is optically transparent, and has heat resistance, a method for producing the same, and a transparent optical laminated sheet for liquid crystal display devices. . This laminated sheet can be shared with or compatible with glass, and is widely useful as a substrate for optoelectronic devices. Furthermore, since it is remarkably excellent in impact resistance and light in weight as compared with glass, it is particularly useful as a substrate material for a liquid crystal display device that requires a large area.

Claims (10)

[Claims] 1. A transparent optical laminated sheet having heat-resistant layers as the uppermost layer and the lowermost layer, wherein the sheet is optically transparent and has a retardation of 50 nm or less, and a flat surface of the heat-resistant layer. When the refractive index in the optical axis direction above is nx, the refractive index in the plane and in the direction perpendicular to the optical axis direction is ny, and the refractive index in the direction perpendicular to the heat-resistant layer is nz, The optical characteristic value Nz of each of the heat-resistant layers represented is 4 or less. A transparent optical laminated sheet in which the heat-resistant layers are arranged so that their optical axes are not parallel to each other. 2. The transparent optical laminated sheet according to claim 1, wherein the heat-resistant layers are arranged so that their optical axes are orthogonal to each other. 3. The transparent optical laminate sheet according to claim 1, wherein the heat-resistant layer is made of a resin selected from the group consisting of amorphous polyester, amorphous polycarbonate, and amorphous polyarylate. 4. A material that has a rigidity-imparting layer between the heat-resistant layers, wherein the rigidity-imparting layer is optically transparent and has a glass transition temperature lower than that of the material forming the heat-resistant layer. The transparent optical laminated sheet according to any one of claims 1 to 3, wherein 5. The transparent optical laminated sheet according to claim 1, further comprising a gas barrier layer on at least one outermost surface. 6. The transparent optical laminated sheet according to claim 1, further comprising a transparent conductive layer on at least one outermost surface. 7. A transparent optical laminated sheet for a liquid crystal display device, which has heat-resistant layers as the uppermost layer and the lowermost layer, wherein the sheet is optically transparent and has a retardation of 50 nm or less, When the refractive index in the optical axis direction on the plane of the heat resistant layer is nx, the refractive index in the plane and in the direction perpendicular to the optical axis direction is ny, and the refractive index in the direction perpendicular to the heat resistant layer is nz. , The optical characteristic value Nz of each of the heat-resistant layers represented by the following formula is 4 or less: A transparent optical laminated sheet for a liquid crystal display device, wherein the heat-resistant layer is arranged such that the optical axes of the layers are not parallel to each other. 8. A method for producing a transparent optical laminated sheet having heat-resistant layers as the uppermost layer and the lowermost layer, wherein the sheet is optically transparent and has a retardation of 50 nm or less, Includes the following steps: a step of arranging the film forming the heat-resistant layer so that the optical axes of the films are not parallel to each other, and a step of laminating the films forming each layer by thermocompression bonding without using an adhesive. . 9. The method for producing a transparent optical laminated sheet according to claim 8, wherein the film forming the heat resistant layer is formed by a solvent casting method. 10. A liquid crystal display device using the transparent optical laminated sheet according to claim 1 as a substrate.