JP3358890B2 - Birefringent optical plastic laminated sheet and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical plastic laminated sheet having birefringence, a method for producing the same, and a liquid crystal display device using the laminated sheet as a light-transmitting substrate.

[0002]

2. Description of the Related Art With the rapid progress of electronics technology, optoelectronics fields such as liquid crystal display devices and photoelectric conversion devices for solar cells are expanding. These optoelectronic devices are generally used for various applications by forming the devices on a glass substrate having a transparent conductive layer. However, glass has a problem in mechanical strength, particularly brittleness, and a substrate treated with a special treatment such as tempered glass is used to reduce the durability of the element. In particular, when incorporated in a portable device, the weight of the device is increased due to the large specific gravity of glass, and therefore, the glass substrate is made thinner, and a substrate of about 0.4 mm can be used. However, also in this case, there are problems that the yield is reduced due to cracks in the process and the impact resistance of the element is reduced due to the brittleness of the glass. As described above, toughness and light weight of the substrate are strongly desired, and from the viewpoint of light weight and impact resistance and compatibility with glass, the light transmittance is generally 80% or more, and the haze is generally high. Has an optical characteristic of 5% or less, and 0.2 to 0.2%.
There is a demand for an appropriately rigid plastic substrate having a thickness of about 5 mm. In addition, a process temperature required for forming an electronic element is 180 ° C. or higher, and the substrate is required to have high heat resistance.

Further, a super nematic liquid crystal display (S
In the case of TN-LCD), a polymer film (retardation film) in which retardation represented by the product of birefringence and thickness is controlled to a specific value in order to improve the display quality
Is generally attached to a glass substrate for use. When the substrate is made of plastic, it is expected to provide features that glass substrates do not have, such as adding a phase difference function to the plastic substrate itself to reduce costs.
Heat resistant and retardation is 100-700
There is a particular need for highly controlled plastic substrates in the nm range.

[0004] Therefore, an optically uniform film with low retardation is formed by solvent casting method from polyarylate, polysulfone, polyethersulfone, etc., which are known as heat-resistant polymers, and birefringence is given by thermal stretching. It has been proposed to use it in the form of a so-called plastic liquid crystal cell or the like (Japanese Patent Laid-Open No. 1-11881).
9, JP-A-4-156426). However, since the substrate is a film of about 0.1 mm and lacks rigidity compared to glass and is flexible, it cannot be shared with a process using a glass substrate, and because it is flexible, gap control over a large area Is difficult. Therefore, new process development is required, and it is not suitable for the purpose of obtaining a large-area plastic liquid crystal cell in which the defects of the glass substrate are eliminated by using the existing glass substrate process.

On the other hand, it is conceivable to increase the thickness of the film in order to impart rigidity and toughness. However, when the thickness is increased by the solvent casting method, defects such as foaming are liable to occur, and productivity is greatly reduced. Industrial implementation is difficult. On the other hand, a thickness of 200 to 100 having low birefringence by a melt extrusion process of polycarbonate, modified polyolefin or the like.
A polymer sheet of 0 μm has been proposed. However, in addition to insufficient heat resistance, when the film thickness is large, the controllability of thermal stretching is deteriorated, and it is difficult to maintain a specific retardation value uniformly. Therefore, it has rigidity and heat resistance that can maintain compatibility with the glass process, is excellent in impact resistance, and has a desired retardation that can be used for STN-LCDs and the like, and is an industrially usable substrate plastic. The fact is that no seat has been found yet.

[0006]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention is compatible with a glass process in an assembling process of a liquid crystal display device, and has a birefringence with controlled retardation which can satisfy mass productivity. An optical plastic laminated sheet is provided.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a rigid structure is obtained by forming a laminated structure of a layer having an optical function and a layer having a mechanical property. The present inventors have found that a birefringent optical plastic laminated sheet having optical characteristics can be obtained. That is, a first aspect of the present invention is to provide at least two first birefringent optically transparent polymers.
And a second layer made of an optically transparent polymer and having a lower birefringence than the first layer, wherein the at least two first layers are arranged on both sides of the second layer. The birefringent optical plastic laminate sheet, the second of the present invention is a film that comprises an optically transparent polymer and constitutes at least two first layers having birefringence,
A method for producing a birefringent optical plastic laminated sheet, comprising heat-sealing and laminating both surfaces of a film constituting an optically transparent polymer and constituting a second layer having a lower birefringence than the first layer. A third aspect of the present invention is to provide a liquid crystal display device using the birefringent optical plastic laminated sheet as a light-transmitting substrate.

The material constituting the first layer can be obtained by orienting a polymer material having intrinsic birefringence. In general, it can be obtained by uniaxially or biaxially stretching a polymer film made of polyarylate, polycarbonate, polysulfone, polyethersulfone, polyvinyl alcohol, or the like having little optical anisotropy. These films can be obtained by a known film forming technique. However, from the viewpoint of surface properties and optical properties, films formed by a solvent casting method are most preferably used.

In the first layer, it is necessary to precisely control the retardation by stretching. On the other hand, the retardation is determined by the thickness of the film and the degree of molecular orientation,
The orientation of the molecules is greatly affected by the stretching conditions. Therefore, in order to precisely control the retardation, the first
It is preferable that the thickness of the layer is relatively thin and the control range of the stretching conditions is large. Therefore, the thickness of the first layer is 20 to 1
It is desirably selected from 50 μm, more preferably from 40 to 100 μm. In addition, Japanese Patent Laid-Open No.
No. 4, JP-A-3-85519, a special material in which the refractive index in the film thickness direction is adjusted so as to be different from any in-plane refractive index can also be suitably used.
The first layer may be not only a single layer but also two or more layers.

As the polymer material constituting the second layer, a material having a relatively low retardation and capable of imparting mechanical characteristics represented by rigidity when combined with the first layer is used. Widely selected. Since the retardation of the plastic laminated sheet of the present invention is expressed in the first layer which is optically highly controlled in advance, it is desirable that the second layer has a retardation as low as possible.
More preferably 50 nm or less, still more preferably 20 nm
It is as follows. However, like lamination by heat fusion,
When the second layer is laminated under the condition of undergoing thermal annealing in the laminating process, retardation substantially disappears in the annealing process, and thus the second layer material used may have retardation. Depending on the heat resistance required as a suitable material, other than polyarylate, polycarbonate, polysulfone, polyether sulfone,
Examples thereof include materials having a small intrinsic birefringence such as polymethacrylate and polyvinyl chloride, and materials obtained by molding a crosslinked polymer such as an epoxy resin into a film or sheet. Second
The layer may be not only a single layer but also two or more layers.

[0011] The optical plastic laminated sheet of the present invention comprises:
In order to enable compatibility with the glass process in assembling the liquid crystal display device, it is necessary to maintain appropriate rigidity. For this purpose, the sum of the thicknesses of the first layer and the second layer is 0.
It is preferably at least 2 mm, more preferably 0.1 mm.
3 to 0.7 mm. An excessively large thickness is not preferable because characteristics of using the polymer material are lost.

The plastic laminated sheet of the present invention has a first
It is characterized by having a layer and a second layer, and it is preferable to provide the first layer on both sides of the second layer. When the optical axes of the first-layer retardation films are kept parallel to each other, the retardations of the obtained sheets are sums of the respective sheets. In the case where the first layers are arranged in this manner, undesired deformation such as warpage of the obtained sheet can be prevented as compared with the case where the phase difference is developed in one first layer. Further, it is also preferable that the respective retardation films constituting the first layer are arranged such that their optical axes cross each other appropriately for the purpose of improving characteristics such as improving the contrast of the obtained liquid crystal display device. Normally, an STN liquid crystal display device requires a plurality of retardation films in addition to a substrate, but by adopting such a configuration, the substrate material has the function of a plurality of retardation films, so that the liquid crystal display This has the advantage that the configuration of the device can be simplified. The relative optical axis angles formed by the at least two first layers are variously determined in relation to various parameters for designing the liquid crystal display device. According to the present laminated sheet, a sheet having a required relative angle can be easily obtained. The laminated sheet is the first
-It does not restrict providing further layers other than a 2nd layer. The two or more first layers having birefringence may have the same or different retardation values. Further, if necessary, the kind of the material constituting the first layer may be changed.

The plastic laminated sheet of the present invention has a first
It can be obtained by laminating a film constituting the layer (retardation film) and a film constituting the second layer. Although it is possible to laminate using an adhesive, it is necessary to select an adhesive so as not to impair the heat resistance of the laminated sheet. From the viewpoint of property stability at high temperatures, it is particularly preferable to obtain the plastic laminated sheet of the present invention by heat lamination. In this case, it is necessary to select a material in consideration of the affinity between the first layer and the second layer. Furthermore, when the film constituting the first layer and the film constituting the second layer are formed into a molten sheet, they can be simultaneously heat-sealed.

The optical plastic laminated sheet of the present invention is
As described above, since the first layer and the second layer are laminated, it is possible to obtain a film by forming a film to be the first layer in which retardation is controlled in advance, and then laminating the film with the second layer. Thus, a birefringent optical sheet having an appropriate thickness with a highly controlled retardation can be obtained. The in-plane retardation distribution of the obtained sheet is not preferable because it causes display unevenness when assembled in a liquid crystal display device. However, according to the present invention, the retardation is highly controlled to 10 nm or less per cm. You can get a sheet.

When forming a sheet by heat lamination,
It is necessary to suppress undesired changes in retardation of the first layer due to heat during lamination. Specifically, for example, the first layer is formed of a material having a higher glass transition temperature than the second layer, and the undesired change in retardation is controlled by laminating the first layer at a temperature equal to or lower than the glass transition temperature of the first layer. be able to.

Due to the high glass transition temperature of the first layer, the second layer
It is not necessary that the layer have a glass transition temperature above the required heat resistance. That is, at the time of heating,
This is because the form can be maintained by the first layer having high heat resistance, and the mechanical strength at the time of handling near room temperature can be exhibited by the second layer. For this purpose, it is preferable that the first layer made of a highly heat-resistant material be present on both surfaces of the second layer.

A suitable material combination largely depends on the heat-resistant temperature required for the plastic laminated sheet. In particular, when heat resistance of 150 to 180 ° C. or more required for a liquid crystal process is required, a plastic mainly composed of polyarylate or polycarbonate having an aromatic group in a main chain is preferably used as the first layer. . Details are described in JP-A-57-73021 and JP-A-2-23372.
No. 0, JP-A-2-88634, etc., and its glass transition temperature is 160 ° C. or higher, preferably 180 ° C.
It is composed of a material having a temperature of at least 200C, more preferably at least 200C. In this case, the preferred second layer is a polyarylate or polycarbonate plastic having a relatively low glass transition temperature. Polycarbonate containing bisphenol A as a component is highly compatible with polyarylate and polycarbonate constituting the first layer, and is particularly preferable in terms of characteristics and cost.

According to the heat laminating method, in particular, by laminating the second layer by heating it to a temperature higher than the glass transition temperature, the second layer receives the effect of thermal annealing.
Therefore, since the retardation of the second layer, which had a single film, is reduced by the thermal annealing, the retardation of the obtained plastic laminated sheet is determined by the first layer. Therefore, it has the feature that the optical properties highly controlled by the retardation film can be inherited by the plastic laminated sheet as it is.

The required heating temperature depends on the material to be laminated, but is generally higher than the glass transition temperature of the material constituting the second layer and preferably lower than the glass transition temperature of the material constituting the first layer. It is. In particular, performing the heat lamination at a temperature lower than the glass transition temperature of the first layer by 10 ° C. or more can keep the retardation return during the heat lamination at 20 nm or less, and thus the birefringence of the obtained plastic laminated sheet. It is preferable for controlling the properties to a high degree. One suitable heating lamination method is a heating / pressing lamination method using a heating roll or a belt. In order to prevent undesired deformation during heating, it is effective to apply a tension to the sheet that does not affect the optical characteristics. The heating lamination may be performed in a plurality of stages, for example, after pre-compression bonding at a relatively low temperature, heating to the lamination temperature and fusing. Also,
A vacuum lamination method can also be used to prevent entrapment of bubbles during heating lamination.

The thickness of the plastic laminated sheet of the present invention having the above structure is preferably 0.2 to 1 mm, and 0.3 to 0 mm in order to maintain the compatibility or compatibility with glass in the process such as rigidity. 0.7 mm is particularly preferred. As for optical characteristics, the total light transmittance is preferably 70% or more. Since the optical plastic laminated sheet of the present invention has birefringence in advance when compared with a glass substrate,
It simultaneously has the function of a retardation film required for a TN liquid crystal display element, and can be used as a substrate for a new type of liquid crystal display element. As the surface property of the STN substrate, a surface roughness of 0.2 μm or less, more preferably 0.1 μm or less is desired, but this requires using a film obtained by a solvent casting method as the first layer film. Can be achieved more easily. Therefore, there is a feature that the pre-polishing of the surface required for the glass substrate is unnecessary or simplified.

Further, the plastic laminate sheet of the present invention may be provided with a gas barrier layer or a transparent conductive layer on the surface. Unlike the glass substrate, the plastic laminated sheet of the present invention has low barrier performance against oxygen and water vapor and low resistance to organic solvents. Therefore, if necessary, an organic gas such as ethylene-vinyl alcohol (EVAL: registered trademark) or vinylidene chloride is used. Barrier processing, silicon oxide,
It is also possible to perform an inorganic gas barrier process made of silicon nitride, alumina, or the like. If necessary, an anchor coat layer for the purpose of improving the adhesion of the barrier layer can be present between the barrier layer and the plastic laminated sheet of the present invention. Further, a hard coat treatment represented by a siloxane-based or acrylic-based material can be easily performed. In addition, using the first layer that has been subjected to various processes on the surface,
It is also possible to directly obtain a secondary processed laminated sheet. For example, by using a retardation film having a transparent conductive layer on the surface as the first layer, a transparent conductive plastic laminated sheet having birefringence can be directly obtained.

The plastic laminated sheet having birefringence of the present invention is interchangeable with glass in terms of heat resistance and optical properties, but is different from glass in that it has excellent impact resistance and is lightweight, so that it has a large area. Is useful as a substrate material for a liquid crystal display element, which is required. Furthermore, since it has a birefringence controlled in advance, when it is used as a substrate for an STN liquid crystal display device, it does not require a separate retardation film and can be simplified in configuration. Moreover, since the birefringence can be controlled in advance with a thin film, the birefringence of the laminated sheet does not fluctuate much in the plane, and is particularly useful as a substrate for a large STN liquid crystal having good display characteristics. .

[0023]

EXAMPLES Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples. Example 1 A film formed by a solvent casting method, having a glass transition temperature of 215 ° C. and a retardation of 10 nm was 58 μm.
An m-thick polyarylate transparent film (trade name: Elmec F-1100: manufactured by Kaneka Corporation) was uniaxially stretched to obtain a retardation film having a retardation of 380 ± 3 nm. This retardation film is used as a first layer, and as a material of a second layer, a polycarbonate film having a glass transition temperature of 150 ° C., a retardation of 30 nm and a thickness of 400 μm, which is formed by a melt extrusion method, is used. The two polyarylate phase difference films are sandwiched between the two polyarylate phase difference films so that their optical axes indicate 70 ° with each other, and are heated and fused to obtain a 550 μm thick, 300 mm × 400 mm laminated sheet which is firmly fused. Was. In the obtained laminated sheet, the two first layers had retardations of 388 ± 5 nm and 390 ± 4 nm, respectively. The light transmittance was 89% and the haze value was 1.5%.

Example 2 The polyarylate transparent film used in Example 1 was uniaxially stretched to obtain a retardation film having a retardation of 200 ± 3 nm. This retardation film is used as a first layer,
As the material of the second layer, the polycarbonate film used in Example 1 was used, and the polycarbonate film was sandwiched between two polyarylate retardation films so that their optical axes were parallel to each other, and heated. Fused, firmly fused 550 μm thick and 300 mm × 40
A laminated sheet of 0 mm was obtained. The obtained laminated sheet is 3
It had a retardation of 88 ± 5 nm. The in-plane retardation distribution showed a good value of 3 nm or less per cm. The light transmittance was 88% and the haze value was 1.2%.

Example 3 A polycarbonate film having a glass transition temperature of 150 ° C. and a retardation of 130 nm and a thickness of 400 μm and having a retardation of 130 nm was formed in the same manner as in Example 1 as a material for the second layer. The two polyarylate films described in 1 were heat-fused to obtain a 550 μm-thick laminated sheet. 2 that constitutes the obtained laminated sheet
The retardation of the first layer is 390 ± 4
nm and 385 ± 3 nm, and the initial retardation of the second layer did not significantly affect the retardation of the obtained laminated sheet, and had the same optical performance as in Example 1. The light transmittance is 89%, and the haze is
e) The value was 1.5%.

Example 4 A film was formed by a solvent casting method and had a glass transition temperature of 215 ° C. and a retardation of 420 nm.
The polyarylate retardation film having a thickness of μm was used as the first layer, and the polycarbonate film used in Example 1 was used as the second layer.
Used as a layer. The optical axes of the two first layers are relatively 45 °.
The second layer is interposed in the direction of
An m-thick laminated sheet was obtained. The retardations of the two first layers after lamination were 403 nm and 409 nm, respectively. The light transmittance was 88%, and the haze value was 1.6%.

Example 5 1,1-bis- (4-hydroxyphenyl) -3,3
Using a heat-resistant polycarbonate (glass transition temperature: 206 ° C.) containing 5-trimethylcyclohexane and bisphenol A as phenol components, a 75 μm thick A4-size heat-resistant polycarbonate film having a retardation of 8 nm was obtained by a solvent casting method. . Furthermore, the film is stretched in the vertical direction by uniaxial stretching at the free end.
Axial stretching was performed to obtain a retardation film having a retardation of 410 nm. This retardation film was used as a first layer, and as a material of a second layer, a polycarbonate film having a thickness of 200 μm and having a retardation of 20 nm formed by a melt extrusion method was used. And the retardation film was integrated 3
A laminated sheet having a thickness of 40 μm was obtained. The retardations of the two first layers after lamination are 392 nm and 390 nm, respectively.
nm. The in-plane retardation distribution is 1
It had a good uniformity of 2 nm. The light transmittance was 88%, and the haze value was 1.5%.

Example 6 The uniaxially stretched polyarylate retardation film used in Example 1 was used, and one surface sputtering method was used to form Si.
A 500 ° gas barrier layer of O _x was present. As the material of the second layer, the polycarbonate film used in Example 5 was used.
Two polyarylate films were overlapped and sandwiched on the surface where no gas barrier layer was present, and heat-fused in the same manner as in Example 1 to obtain a birefringent plastic laminated sheet having a barrier layer on the surface. This sheet had a thickness of 350 μm, an oxygen permeability of 0.7 cc / m ² / day or less, and the surface on which the barrier layer was present exhibited good chemical resistance.

Example 7 Using the laminated sheet obtained in Example 1, two upper and lower first sheets were used.
On the surface of one of the layers, a SiO _x layer was formed in a thickness of 500 ° and an ITO layer was formed in an order of 1500 ° by a vacuum sputtering method, to prepare a heat-resistant transparent substrate having a barrier layer and a transparent conductive layer. This laminated sheet has a surface resistance of 30Ω /
□, oxygen permeability was 0.8 cc / m ² / day or less. The retardation of the laminated sheet did not change before and after sputtering, and a transparent conductive laminated sheet having a good optical performance and a retardation was obtained.

[0030]

As described above, according to the present invention, impact resistance and
A heat-resistant transparent plastic laminated sheet having rigidity and excellent optical characteristics is provided. The plastic laminated sheet of the present invention is useful as an optical substrate in the field of optoelectronics.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ identification code FI G02F 1/133 510 G02F 1/133 510 (58) Field surveyed (Int.Cl. ⁷ , DB name) B32B 1/00-35 / 00

Claims (13)

(57) [Claims] A first layer comprising an optically transparent polymer and having a birefringence; and a second layer comprising an optically transparent polymer and having a birefringence smaller than the first layer. A birefringent optical plastic laminated sheet, wherein the at least two first layers are arranged on both surfaces of the second layer. 2. The optical plastic laminated sheet according to claim 1, wherein the optical axes of the at least two first layers are not parallel to each other. 3. The optical plastic laminated sheet according to claim 1, wherein the first layer has a retardation of 100 nm or more, and the second layer has a retardation of 50 nm or less. 4. The optical plastic laminated sheet according to claim 1, wherein the first layer and the second layer are directly laminated. 5. The optical plastic laminated sheet according to claim 1, wherein the glass transition temperature of the first layer is higher than the glass transition temperature of the second layer. 6. The optical plastic laminated sheet according to claim 1, wherein the first layer is made of an optically transparent heat-resistant polyarylate or polycarbonate having an aromatic group in a main chain. 7. The optical plastic laminated sheet according to claim 6, wherein the second layer is made of polycarbonate. 8. The optical plastic laminated sheet according to claim 1, which has a gas barrier layer on the surface of the first layer. 9. The optical plastic laminated sheet according to claim 1, having a transparent conductive layer on the surface of the first layer. 10. A film comprising at least two birefringent first layers made of an optically transparent polymer and a second birefringent film made of an optically transparent polymer and having a lower birefringence than the first layer. A method for producing a birefringent optical plastic laminated sheet, which comprises laminating and laminating a film constituting a layer on both sides by heating. 11. The method according to claim 10, wherein the glass transition temperature of the film constituting the first layer is higher than the glass transition temperature of the film constituting the second layer. 12. The film constituting the first layer is a film obtained by a solvent casting method.
Or the production method according to 11. 13. A liquid crystal display device using the optical plastic laminated sheet according to claim 1 as a light transmitting substrate.