JPH0419012B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a thermoplastic resin sheet or film. [Prior Art and Problems to be Solved by the Invention] Conventionally, chill roll methods, water cooling methods, and the like are known as methods for producing T-die quenched films or sheets of thermoplastic resins. However, when using the chill roll method, during high-speed molding, air can be drawn in between the roll and the molten resin film, and the adhesion between the roll and the molten resin film is poor, resulting in uneven thickness and wrinkles. In such cases, there are drawbacks such as occurrence of curling due to the difference in cooling between the front and back surfaces of the molten resin film, and a decrease in transparency and surface gloss due to insufficient rapid cooling.
In addition, in the water cooling method, heat dissipation from the molten resin film occurs locally on the cooling water surface, resulting in uneven cooling due to ripples and shaking of the water surface, and insufficient cooling resulting in uneven thickness, uneven transparency, and uneven surface gloss. This has the disadvantage that high-speed molding cannot be performed. By the way, the water cooling method has the advantage of being able to cool sheets etc. more efficiently than the roll method. Therefore, as a method to improve the drawbacks of the water cooling method described above, it has been proposed to cool the molten resin film with a stream of cooling water flowing on both sides (Japanese Patent Publication No.
No. 17817). However, even with this improved method, it is difficult to efficiently produce sheets with excellent transparency and surface properties from crystalline resins such as polypropylene due to the low cooling efficiency and turbulent flow of cooling water. be. In other words, if the water level is high at the slit entrance from the point where the film-like thermoplastic resin first comes into contact with the cooling water,
Cooling water accumulates near the top surface, reducing the initial cooling effect and reducing transparency. Furthermore, in order to raise the water level and eliminate stagnation, the flow velocity must be increased, and in this case, turbulence cannot be prevented. The same applies to the case where the cooling water flows upward. Therefore, unless stagnation and turbulence of cooling water are prevented, it is impossible to uniformly cool the thermoplastic resin film, and as a result, sheets and films with excellent transparency and surface gloss cannot be obtained. [Means for Solving the Problems] The present invention provides a method for rapidly cooling a film-like thermoplastic resin extruded from a T-die in a molten state by introducing it into a slit through which cooling water of 30° C. or lower flows. The slit is connected to the water tank located below the T-die, projects vertically from the water tank, has an open bottom, has a length of 5 to 100 mm, and a width of 1 to 100 mm. Using a 5 mm single-stage slit, and using a water tank with a flat bottom and a water level of 7 mm or less as the water tank,
The present invention provides a method for producing a thermoplastic resin sheet or film, characterized in that cooling water is allowed to fall naturally into the slit while maintaining the water level at the slit entrance to 7 mm or less. The thermoplastic resin used as a raw material for sheets and films in the present invention is not particularly limited, and examples thereof include polyolefins (polyethylene, polypropylene, etc.), polystyrene, polyvinyl chloride, etc. Crystalline thermoplastic resins that have problems with surface properties can also be used without causing such problems. In addition, the sheets and films of the present invention include multilayer sheets and films,
Further, it also includes those to which nucleating agents such as silica, talc, paratertiary butylbenzoic acid, aluminum, and dibenzylidene sorbitol are added. The present invention basically relates to a method for producing thermoplastic resin sheets or films by water cooling. When a molten thermoplastic resin film extruded from a T-die is introduced into a slit through which cooling water flows, the water level at the entrance of the slit must be kept as low as possible, otherwise the thermoplastic resin film will not be cooled uniformly. Therefore, sheets and films with excellent transparency and surface gloss cannot be obtained. The manufacturing method of the present invention will be explained based on the drawings. In FIG. 1, a thermoplastic resin film 2 extruded in a molten state from a T-die 1 is introduced into a slit 3 into which cooling water is falling. This slit is formed to be connected to a water tank 4 located below the T-die 1, and usually has a length of 5 to 100 mm, but preferably 30 to 50 mm. The lower part of the slit 3 is open, ie, exposed to the atmosphere as shown in FIG. Here, the slit is special
If the lower part is submerged in water as shown in Figure 3 of Publication No. 30388, the flow rate of the cooling water flowing down through the slits cannot be made sufficiently high. Furthermore, it is virtually impossible to keep the water level at the entrance of the slit low. In the case of the water tank 4, it is preferable that the cooling water that comes into contact with the introduced film-like thermoplastic resin is fluidized while flowing in a laminar flow state. Therefore, the water level of the water layer should be as low as possible as described above, thereby preventing partial boiling and making the cooling point uniform. In the present invention, 7 mm
Maintain the water level at the slit entrance to 7 mm or less using a water tank with the following water level. By controlling the water level to such a low level, the cooling water can be smoothly flowed at the slit entrance without causing any stagnation. In the present invention, the water level at the slit entrance is set to 7 mm or less, and a water tank with a water level of 7 mm or less is used. In other words, the cooling water that has flowed into the water tank flows into the slit while forming a laminar flow with a water layer of 7 mm or less. No retention occurs. Further, as a natural effect, the cooling water contacts the molten film-like thermoplastic resin in a laminar flow state. By satisfying this configuration, a sheet with excellent transparency and surface condition can be obtained for the first time. If only the structure shown in FIG. 3 of Japanese Patent Publication No. 44-30388 mentioned above is used, the flow of cooling water at the slit entrance becomes turbulent, and the object of the present invention cannot be achieved. When the water level reaches 10 mm, boiling spots, haze spots, and curls occur on the obtained sheet, and the total haze becomes 25 to 28%, which is not preferable. Since the cooling water is flowing down from the water tank 4 to the slit 3, both surfaces of the thermoplastic resin film are uniformly cooled by the cooling water when passing through the slit 3. In other words, the traveling direction of the resin film and the cooling water are the same, and the cooling water flows in parallel on both sides of the resin film.
Cooled efficiently. It is desirable that the cooling water flow speed be equal to or higher than the traveling speed of the film-like resin. Of course, it is preferable to round the entrance of the slit so that the cooling water can flow smoothly. The width of the slit is 1mm.
~5mm. The film-like resin introduced into the slit through which the cooling water flows and cooled as described above is transferred to the guide roll 5,
It passes through a drainer roll 6 and is taken up by a take-up roll 7. The guide roll 5 is effective in preventing curling by placing the resin film in the center of the slit, and can also serve as a set of pressure rolls to transfer the mirror surface of the roll. The temperature of the cooling water used in the present invention is 30°C.
The temperature below is preferably 2 to 30℃, and if necessary, add an appropriate surfactant to improve wetting with the film resin, or add a freezing point depressant to the cooling water for low-temperature cooling. You can also do this. In the figure, 8 is a water level adjustment plate, 9 is an overflow plate, 10 is a cooler, and 11 is a pump. [Effects of the Invention] According to the improved water cooling method of the present invention, even when manufacturing sheets or films using crystalline thermoplastic resin as a raw material, it is possible to produce sheets that are unoriented and have excellent transparency and surface gloss. Obtainable. Moreover,
The resulting sheets have excellent uniformity, with no uneven thickness, wrinkles, or curls. Further, the method of the present invention has features such as being able to obtain sheets etc. by high-speed molding at 10 m/min or more and having low cooling costs. Since the sheets and films obtained by the method of the present invention have excellent properties as described above, they are suitable for packaging foods, medicines, and the like. Moreover, it can also be used as a raw material for solid phase forming such as air pressure forming, roll rolling, and stretch forming. [Example] Next, the present invention will be explained with reference to an example. Example 1 Polypropylene (density 0.91 g/cm ³ , melt index 2.0 g/10 minutes) was extruded at a resin temperature of 280°C using a T-die extrusion device (extruder 60 mmφ, L/D = 28, die width
It was extruded into a film using a die lip opening of 550 mm and a die lip opening of 1 mm. Cool the extruded molten resin film with water (water temperature 16
℃), the water level was set to 7 mm or less and introduced into a fluidized slit (width 2 mm, length 45 mm), cooled, and after draining, taken off with a take-up roll at a forming speed of 20 m/min.
A polypropylene sheet with a thickness of 0.2 mm was manufactured.
Although the obtained sheet had slight haze spots, it was a sheet with good transparency and no boiling spots or curls. The total haze was 18% (internal haze: 8%, external haze: 10%).
Further, the thickness unevenness was less than ±3%. These results are shown in Table 1. Comparative Example 1 A polypropylene sheet was obtained according to Example 1 except that the water level was 10 mm. This sheet has boiling spots, haze spots, and curls.
The total haze was 25 to 28%, and the transparency, gloss, and surface properties were poor. Further, the thickness unevenness was ±12%. The results are shown in Table 1. Comparative Example 2 A molten resin film was extruded using the same raw materials and extrusion conditions as in Example 1, and was cooled by blowing air onto a mirror roll (40°C) using an air knife to obtain a polypropylene sheet. This sheet had very poor transparency with a haze of 42%, and air marks were observed. The results are shown in Table 1. Example 2 Molding was carried out in accordance with Example 1, except that polypropylene was used, the melt index was 8 g/10 minutes, the water tank water level was 4 mm, the slit width was 4 mm, the cooling water temperature was 4°C, and the molding speed was 10 m/min. A polypropylene sheet was obtained. The appearance of the sheet is good, and the total haze is 11% (internal haze: 5%, external haze:
6%). Further, the thickness unevenness was less than ±3%. The results are shown in Table 1. Comparative Example 3 A polypropylene sheet was obtained in the same manner as in Example 2, except that the water level in the water tank was 10 mm, but boiling spots and haze spots occurred and the appearance was poor. Further, the thickness unevenness was ±10%. The results are shown in Table 1. Examples 3 to 7 and Comparative Examples 4 to 15 Polypropylene sheets were obtained in the same manner as in Example 1, except that the conditions shown in Table 1 were used. Table 1 shows the measurement results of the physical properties of this sheet.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of an apparatus for carrying out the method of the present invention. 1...T-die, 2...Membrane thermoplastic resin, 3
...Slit, 4...Aquarium, 7...Take-up roll.

Claims (1)

[Claims] 1. When introducing a thermoplastic resin film extruded in a molten state from a T-die into a slit through which cooling water of 30°C or lower flows to rapidly cool it, the slit is located below the T-die. It is connected to the water tank, projects vertically from the water tank, and has an open bottom and has a length of 5 to 50 cm.
A single-stage slit with a diameter of 100 mm and a width of 1 to 5 mm is used, and the water tank has a flat bottom and a water level of 7 mm or less, and the water level at the entrance of the slit is maintained at 7 mm or less. A method for producing a thermoplastic resin sheet or film, characterized in that the cooling water is allowed to fall naturally into the slit.