JPH0456730B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a polyurethane composite film used for display films, particularly printed cover films for flat switches, printed cover films for pen input, panels, etc. [Prior Art] In recent years, keyboards and switches whose surfaces are coated with multicolored printed plastic sheets have come into use for calculator keyboards, office automation equipment keyboards, home appliance switches, and the like. These flat switch keyboards are superior to conventional button switches in terms of dustproofness, waterproofness, design, and greatly reduced number of parts, so they are beginning to be widely used. The plastic sheets used in flat switch keyboards are mainly polyester films or polycarbonate films with a thickness of 100 to 200 microns and are printed in multiple colors on the back side. The reason these films are used is
This is because it has excellent heat-resistant dimensional stability and transparency.
However, since these films are hard, there is no click feeling when the switch is pressed, so there is a feeling of anxiety as the user cannot directly check the switch with their fingers. To this end, countermeasures have been taken, such as a method of confirming with a sound or a method of confirming with an indicator lamp, but these methods also require more time to confirm and are slower in operation than a button switch with a clicky feel. In addition, since force is required to input, it is tiring to operate for a long time, and furthermore, input errors are likely to occur if the center of operation is not pressed. Instead of these hard plastic films,
Although soft polyvinyl chloride film has been considered, it has not been put to practical use due to problems such as plasticizer migration and poor thermal dimensional stability. Thermoplastic polyurethane films have recently begun to be used as films that have excellent rubber elasticity, eliminate the above-mentioned drawbacks of hard films, and have excellent thermal dimensional stability. When thermoplastic polyurethane film is used, the drawbacks caused by the lack of clickiness seen with polyester films and polycarbonate films can almost be eliminated, and there is no problem of plasticizer migration seen with flexible polyvinyl chloride films. Thermal dimensional stability is also sufficiently satisfactory for office equipment and especially home appliances without a heat source. However, this polyurethane film also has two major drawbacks. It is lightfast and printable. Regarding light resistance, even if used indoors, sunlight or fluorescent light will cause yellowing after a few months, greatly reducing the initial printing effect, and if yellowing is severe, it may be difficult to check the displayed content. It becomes possible. Regarding printability, polyurethane film swells very easily in solvents, so advanced technology is required to select solvents during printing and control the accuracy of drying conditions. I won't be able to do it. Switch cover printing film requires a high degree of printing accuracy compared to normal display printing and packaging material printing because switch position accuracy is required due to the application. However, even with advanced printing technology and control precision, conventional polyurethane sheets have not been satisfactory in terms of production yield. [Object of the Invention] The present invention relates to a printing film used as a printed cover film for flat switches, and was completed through intensive research to solve the drawbacks of the above-mentioned polyester film, polycarbonate film, soft polyvinyl chloride film, and polyurethane film. This is what led to this. [Structure of the Invention] The present invention is a thermoplastic polyurethane which has a light transmittance of 0% in a wavelength range of 360 nm or less and a total light transmittance of 70% or more when the first layer has a thickness of 150 to 200 μm. The second layer is made of polyamide resin, and coextrusion is performed, and immediately after extrusion, the surface of the first layer is processed to have a matte or satin finish, and the center average roughness of the surface is 0.5 to 50 μm. This is a method for producing a polyurethane composite film characterized by the following. The details of the present invention will be explained with reference to the drawings. FIG. 1 is a cross-sectional view of a coextruded composite film of the present invention. 2 is a thermoplastic polyurethane, and 3 is a two-layer composite film of polyamide resin. The surface 1 of the thermoplastic polyurethane 2 is matte or satin-like, and the center line average roughness of the surface is
It is 0.5-50μm. The thermoplastic polyurethane used in the present invention is
Based on thermoplastic polyurethane such as polyester or polyether, 0.1 to 5 parts by weight of ultraviolet absorbers such as benzotriazole, benzophenone, and salicylate are added to smooth both sides of the sheet and form a 150 to 200 μm thick film. When the thickness is set, the total light transmittance is 70% or more, and
It has a light transmittance of 0% in the wavelength range of 360 nm or less. An antioxidant, a lubricant, etc. may be added to the thermoplastic polyurethane, if necessary. The thickness of the thermoplastic polyurethane layer is preferably in the range of 50 to 800 μm from the viewpoint of quality design. In addition, the polyamide resin used in the present invention should be selected according to the flow characteristics of the thermoplastic polyurethane to be coextruded, such as 6-nylon, 6.6-
Nylon, 6.10− nylon, 11− nylon, 12−
Although nylon or the like is used, polyamide resins having a low melting point are preferred for molding. Furthermore, the thickness of the polyamide resin layer is 1/2 or less of the thickness of the thermoplastic polyurethane. If it exceeds 1/2, the rubber elasticity of the thermoplastic polyurethane will be impaired, and the click feeling will decrease when a flat keyboard is used. It goes without saying that the polyamide resin is thermally fused to the thermoplastic polyurethane. Immediately after coextrusion, the surface of thermoplastic polyurethane is made matte or matte.
The thermoplastic polyurethane side of the layered composite film is brought into contact with a predetermined embossed cooling roll, or
Immediately after coextrusion, a process paper for forming a replica of the desired surface roughness is laminated by roll pressure bonding and then peeled off. [Effects of the Invention] The manufacturing method of the present invention makes it possible to minimize the dimensional changes that occur in conventional polyurethane films after printing, and makes it possible to produce printed films that meet the dimensional accuracy required for switch mechanisms with high productivity. I was able to get it. In addition, regarding light resistance, when using the polyurethane composite film of the present invention, the degree of discoloration in the conventional 40-hour discoloration test was determined by the FEDOMETER discoloration test.
It was confirmed that the light resistance was equivalent to 600 hours and about 15 times as long. [Example] (1) Thermoplastic polyurethane (Takeda Pharmaceutical Company Limited)
Immediately after co-extruding 250 μm of Takerakku After the process, the paper was peeled off to obtain a matte polyurethane composite film with a centerline average roughness of 20 μm on the thermoplastic polyurethane surface. As a comparative example, the same thermoplastic polyurethane was extruded using a single-layer die to a thickness of 300 μm, and matting was performed in the same manner as in the example. The shrinkage rates of each film after being left in an atmosphere of 100°C and 120°C for 10 minutes were measured, and the results were as shown in the table below. 【table】

[Brief explanation of drawings]

FIG. 1 is a sectional view of a two-layer composite film obtained according to the present invention.

Claims (1)

[Claims] 1 The first layer is 360nm when the thickness is 150-200μm.
It is a thermoplastic polyurethane that has a light transmittance of 0% in the following wavelength range and a total light transmittance of 70% or more, and the second layer is a polyamide resin. The surface of the layer is matte or satin-like, and the center average roughness of the surface is 0.5.
A method for producing a polyurethane composite film, which is characterized by processing it so that the film has a thickness of ~50 μm.