JPH0313561B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a heat-resistant optical film, and more particularly to a heat-resistant polymer resin extrusion film used for optical applications requiring heat resistance. This invention relates to a multilayer extruded film that has significantly reduced uneven transmission of light rays in the longitudinal direction of the film, which is called a die line. Optical applications that require the heat resistance described here include transparent conductive films for flexible liquid crystal display elements, heat-resistant polarizing element protective films, optical recording medium substrate films, magneto-optical recording medium substrate films, and heat-resistant color filters. be.

(Prior Art) Conventionally, glass plates and polymer resin plates and films formed by a casting method or a solution drooling method have been used or considered as materials for these purposes. However, glass plates cannot be used for applications that require flexibility, and have the disadvantage that they are weak against impact and cannot be made thin. Therefore, polymer resins and films are being considered as flexible and impact-resistant materials, but in terms of optical homogeneity, casting methods and solution drooling methods, which are extremely unproductive methods, are being considered. However, satisfactory characteristics have not been obtained. Furthermore, polymer resins that can be processed into a film by such a method are limited to polymethyl methacrylate, cellulose triacetate, and the like.

Furthermore, when used as a transparent conductive film for a flexible liquid crystal display element, it is necessary to heat it at a temperature of 150° C. or higher for several hours in the liquid crystal display element assembly process. Furthermore, since polarizing plates are used in automobile meter displays, there is a need for a polarizing element protective film that does not undergo deformation or coloring even when exposed to temperatures of 120° C. or higher for long periods of time. Furthermore, when used as an optical recording medium substrate film, it is desirable that the film not be significantly deformed or colored by heating with laser light. The heat resistance of polymethyl methacrylate and cellulose triacetate is suitable for such applications.
Not enough. On the other hand, polyether sulfone resin has recently been developed as a polymer resin that has excellent transparency and heat resistance and can be formed into a film by extrusion film forming method with good productivity. This resin is produced by polycondensation reaction of dihydroxydiphenylsulfone or its derivatives, and for example, ICI Co., Ltd.
It is sold under the product name “VICTREX”.

The present inventor conducted research in order to develop a material for optical applications that require heat resistance as described above by forming a film from the above-mentioned polymer resin by extrusion film formation, and as a result, It was discovered that a polymer resin film is optically isotropic and has the optimum characteristics as a transparent conductive film for flexible liquid crystal display elements. As a result of research aimed at applying this method to optical applications, it was discovered that the uneven transmission of light rays that occurs in the longitudinal direction of the film, called a die line, is a serious drawback when using plane wave-like light rays. For example, in a transmissive liquid crystal display element that does not use a light scattering plate, the image may shift due to the die line of the film, and in the case of an optical disc that uses laser light, the laser light is refracted by the die line of the film, causing the recording track to be distorted. This may cause the inconvenience that the light may become detached from the light receiving head or may not advance to the light receiving head.

(Objective of the Invention) In view of the above circumstances, the present invention was developed with the aim of obtaining a heat-resistant optical film that significantly reduces die lines, which could not be obtained using conventional extrusion film forming technology. A layer made of a polyethersulfone resin with an intrinsic viscosity of 0.35 or less using dimethylacetamide as a solvent is laminated on at least one side of a layer made of a polyethersulfone resin with an intrinsic viscosity of 0.40 or more. It was discovered that a coextruded film was suitable for this purpose, and the present invention was completed.

(Structure of the Invention) The present invention is a coextruded film made of a polyethersulfone resin produced by a polycondensation reaction of dihydroxysulfone or a derivative thereof, which has an intrinsic viscosity of 0.40 or more when dimethylacetamide is used as a solvent. This is a heat-resistant optical film characterized in that a polyethersulfone resin layer having an intrinsic viscosity of 0.35 or less and using dimethylacetamide as a solvent is laminated on at least one side of the polyethersulfone resin layer.

Although it has not been completely clarified by what mechanism the die line is reduced by the present invention, it will be explained as follows.

The die line phenomenon occurs when the molten polymer resin flowing through the die is extruded as a film from an opening called the die lip, and when it is extruded as a film, it partially sticks and pulls strings (called stringiness), resulting in film formation. This is thought to produce minute irregularities on the surface of the film, which are perceived as uneven transmission of light rays due to the lens effect. The mechanism of adhesiveness and stringiness of molten polymer resin is extremely complicated.
Furthermore, although it has not been fully elucidated, stickiness and stringiness are generally treated using the Maxwell model, and it is explained that they are strongly recognized when the relaxation time is comparable to the time during which the fluid is stretched. On the other hand, when forming polymer resin into a film by solvent extrusion, shape retention,
Processing will be carried out at a compromise between the contradictory properties of fluidity, but this condition is usually
This is an area with excellent stringability.

That is, what the present invention contemplates is a coextruded multilayer structure in which the intermediate layer is a component that functions to maintain shape, and the surface layer is a component that reduces stickiness and stringiness under the processing conditions of the intermediate layer. The aim is to achieve this goal by creating a film.

The significance of the structure according to the present invention is that polyether sulfone resin is suitable for heat-resistant optical films due to its heat resistance and optical properties. In addition, by coextruding components with the same molecular structure, they are completely integrated without an adhesive layer, and since they have the same refractive index, there is no loss of light transmittance due to interfacial reflection.

The most important thing is that at the extrusion processing temperature of polyethersulfone resin with an intrinsic viscosity of 0.40 or higher using dimethylacetamide as a solvent, polyethersulfone with an intrinsic viscosity of 0.35 or lower using dimethylacetamide as a solvent is The melt viscosity of the resin is extremely low, resulting in reduced stickiness and stringiness. There are two methods for coextrusion film formation: the feedblock method and the multi-manifold die method. However, when coextruding resin layers with different melt viscosities, the multi-manifold die method is suitable in terms of the uniformity of the thickness of each layer. There is.

Note that the polyether sulfone resin in the present invention may contain small amounts of stabilizers, lubricants, pigments, etc. as additives.

(Effect of the invention) According to the present invention, in the conventional extrusion film forming method,
Heat-resistant polymer resin films with little unevenness in light transmission due to die lines, which have been extremely difficult to obtain, can be easily obtained, making them suitable for flexible liquid crystal display elements, transparent conductive films, heat-resistant polarizing element protective films, and optical recording medium substrates. It is suitable for use as optical films that require heat resistance, such as films, magneto-optical recording medium substrate films, and heat-resistant color filters.

(Example) Sumitomo Chemical Co., Ltd.'s polyether sulfone resin "Victrex" PES200P (intrinsic viscosity in dimethylacetamide solvent: 0.40) was melted in the first extruder, and a multi-manifold die for three-layer coextrusion was used. connected to the intermediate layer feed pipe. on the other hand,
"Victrex" PES500P (intrinsic viscosity 0.32 in dimethylacetamide solvent) was melted by a second extruder, passed through a flow divider, and connected to surface layer feed pipes provided on both sides of the intermediate layer. The laminated film extruded from the die is casted onto a cooling drum whose surface temperature is adjusted to 210°C.
A 100μ thick three-layer coextruded film with the configuration shown in the figure was obtained. When this film was observed under sunlight and fluorescent light, a uniform image of the light source was seen, with no uneven transmission due to die lines.

(Comparative example) "Victrex" PES600P (intrinsic viscosity 0.48 in dimethylacetamide solvent) is used as the middle layer, "Victrex" PES200P (intrinsic viscosity 0.40 in dimethylacetamide solvent) is used as the surface layer, extrusion conditions are set to 20℃ high temperature for 600P. A three-layer coextruded film was created using the following settings, but the die line was not improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a three-layer coextruded composite film that is one embodiment of the present invention. 1 is the middle class,
Polyether sulfone resin with an intrinsic viscosity of 0.40 or more using dimethylacetamide as a solvent,
2 and 2' are the surface layers, which are polyether sulfone resins having an intrinsic viscosity of 0.35 or less when dimethylacetamide is used as a solvent.

Claims (1)

[Claims] 1. A coextruded film made of a polyethersulfone resin produced by a polycondensation reaction of dihydroxydiphenylsulfone or its derivatives, the polyethersulfone resin having an intrinsic viscosity of 0.40 or more using dimethylacetamide as a solvent. A heat-resistant optical film characterized in that a polyether sulfone resin layer having an intrinsic viscosity of 0.35 or less and using dimethylacetamide as a solvent is laminated on at least one side of the layer.