JPS60208242A - Heat-resistant optical film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a heat-resistant optical film, and more specifically to a heat-resistant polymer resin extrusion film used for optical applications requiring heat resistance. This invention relates to a multilayer extruded film that significantly reduces the unevenness of light transmission that occurs in the longitudinal direction of the film, which is called a die line. Optical applications that require heat resistance mentioned 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 casting method have been used or considered as materials for these purposes. However, glass plates have the disadvantage that they cannot be used in applications that require flexibility, are susceptible to 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 pouring methods are extremely unproductive methods. However, satisfactory characteristics have not been obtained. Further, polymer resins that can be processed into a film by such a method are limited to polymethyl methacrylate, trivine vinegar, cellulose, and the like.

Furthermore, when used as a transparent conductive film for flexible liquid crystal display elements, 150% is used in the liquid crystal display element assembly process.
It is necessary to heat for several hours at a temperature above ℃. - Also, in order to use polarizing plates in automobile meter displays, 1
There is a desire for a polarizing element protective film that does not undergo deformation, coloring, etc. even when exposed to temperatures of 20° C. or higher for a long period of time. Also,
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 insufficient for such uses. On the other hand, polyethersulfone resin and polysulfone resin have recently been developed as polymeric resins that have excellent transparency and heat resistance, and can be made into films using extrusion film formation, which is highly productive. The former is produced by polycondensation reaction of dihydroxydiphenylsulfone or its derivatives,
For example, 1. It is sold by C.I. under the trade name 'VICTREX'. The latter is produced by a copolycondensation reaction of dihydroxydiphenylsulfone or its derivatives with bisphenol-A or its derivatives, and is sold, for example, under the trade name 'UDEL' by U.C.C. .

The present inventor conducted research in order to form a film using the above-mentioned polymer resin by extrusion film formation, and to develop a material that can be used for optical purposes requiring heat resistance as described above, and as a result, the polymer resin It was discovered that the 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 the die line, is a serious drawback when using plane wave 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 on optical discs that use laser light, the laser light is refracted by the die line of the film, causing images that are deviated from the recording trunk. A problem arises in that the light does not advance to the light receiving head.

(Purpose of the Invention) In view of the above-mentioned circumstances, we conducted research to create a heat-resistant optical film that significantly reduces die lines, which could not be obtained using conventional extrusion film forming technology. This led to the discovery that the film had fewer grain lines than a film that was extruded as a single product, and after conducting various studies, the present invention was completed.

(Structure of the Invention) The present invention comprises a polyethersulfone resin produced by polycondensation reaction of dihydroxydiphenylsulfone or its derivative as an intermediate layer, diphenylsulfone or its derivative on both sides, and bisphenol-A. A three-layer coextruded composite film having a surface layer made of a polysulfone resin produced by a copolycondensation reaction with a polysulfone resin or a derivative thereof, and a two-layer coextruded composite film having a polysulfone resin layer on one side of the layer made of a polyethersulfone resin. It is an extruded composite film.

The mechanism by which the die line is reduced according to the present invention has not been completely clarified, but it will be explained as follows.

The die line phenomenon is caused by the fact that when the molten polymer resin flowing through the die is extruded as a film from an opening called dicing, it partially sticks and draws strings (called stringiness). Since minute irregularities are produced on the surface of the deposited film, it is thought that the resulting lens effect causes uneven transmission of light, which is perceived as unevenness. The mechanisms of tackiness and stringiness of molten polymer resins are extremely complex and have not yet been elucidated, but tackiness and stringiness are generally treated using the Maxwell model, where the relaxation time is determined by the pull of the fluid. It is explained that it is strongly recognized in cases of the same extent as the length of time being extended. On the other hand, when melt-extruding polymeric resins into films, processing is carried out at a compromise between the conflicting properties of shape retention and fluidity, but this condition usually depends on the adhesion and stringiness. It will be a rich area.

That is, what the present invention intends is to use a resin that functions for shape retention as an intermediate layer, and under the drilling conditions of the intermediate layer,
The objective is to be achieved by forming a coextruded multilayer film with a surface layer of a resin that reduces stickiness and stringiness.

The significance of the structure according to the present invention is that polyethersulfone resin and polysulfone resin are suitable for heat-resistant optical films due to their heat resistance and optical properties, and that at the processing temperature of polyethersulfone resin, The adhesiveness and stringiness of polysulfone resin are reduced, and the affinity between polyethersulfone resin and polysulfone resin is high, so they can be completely integrated without an adhesive layer, and the refractive index of both is extremely high. Because of the approximation, there is almost no loss in light transmittance due to interface reflection. The present invention also specifies a two-layer coextruded composite film having a layer made of polysulfone resin on one side of the layer made of polynylene sulfone resin. This is because there are cases where this is required. In this case, the die line reduction effect will be halved, but polyether sulfone resin is slightly superior to polysulfone resin in terms of heat resistance and chemical resistance, and if the difference becomes significant, this The configuration is as follows. There are two methods for coextrusion film formation: the feed block 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. .

Note that the polyethersulfone resin and polysulfone resin in the present invention contain a small amount of stabilizer as an additive.
It does not matter if it contains lubricants, pigments, etc.

(Effects of the Invention) According to the present invention, it is possible to easily obtain a heat-resistant polymer resin film with less uneven transmission of light rays due to the die line, which was extremely difficult to obtain by conventional extrusion film-forming methods. Suitable for use as optical films that require heat resistance, such as transparent conductive films for 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. It is.

(Example) Sumitomo Chemical's Pictrex J PES resin was melted in the first extruder and connected to the middle layer of a multi-manifold die for three-layer coextrusion. "Needel" polysulfone resin, the second
The mixture was melted by an extruder, passed through a flow divider, and connected to surface layer feed pipes provided on both sides of the intermediate layer. The heating conditions of the first extruder and the second extruder and the shape of the screen are as shown in Table 1.

All feed pipes and multi-manifold dies in Table 1 were temperature controlled to 350°C. The discharge amount of the first and second extruders was adjusted to 4゛1 by the screw rotation speed, and the extruded film was cast on a cooling drum whose surface temperature was adjusted to 190°C to form the structure shown in Fig. 1. A three-layer coextruded film was obtained. The thickness of the intermediate layer (1) is 80μ,
The thickness of the surface layers (2) and (2) was 10 μm each, and the total thickness was 100 μm torn. When this film was observed under sunlight and fluorescent light, a uniform image of the light source was observed, with no uneven transmission due to die lines.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of three-layer and two-layer coextruded composite films of the present invention. 1 is an intermediate layer made of polyethersulfone resin, and 2.2' is a surface layer made of polysulfone resin.

Claims (1)

[Claims] 1) Copolycondensation of dihydroxydiphenylsulfone or a derivative thereof with bisphenol-A or a derivative thereof on at least one side of a polyethersulfone resin layer produced by a polycondensation reaction of dihydroxydiphenylsulfone or a derivative thereof. Heat-resistant optical coextrusion composite film 0 having a polysulfone resin layer produced by reaction