JPS636345B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a thermoplastic resin sheet or film.

Conventionally, chill roll methods, water cooling methods, and the like are known as methods for producing T-die quenched sheets or films of thermoplastic resins. However, with the chill roll method, during high-speed molding, air is introduced 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, and even thick sheets. 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, causing boiling spots due to boiling of the water surface, uneven cooling due to ripples and shaking of the water surface, uneven thickness and haze spots due to insufficient cooling, etc. It has the drawback that it causes unevenness and reduction in transparency and surface gloss, and 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, various proposals have been made regarding methods for improving the drawbacks of the water cooling method described above. For example, there is a method in which the molten resin film is cooled by a stream of cooling water flowing on both sides of the molten resin film, and a method in which the molten resin film is introduced into a space where cooling water flows down between rotating rolls having slits provided in a cooling tank. However, with these methods, there is a limit to the molding speed in order to obtain a sheet or film with excellent transparency, and it is also very difficult to control cooling.
It was not possible to form sheets etc. with a thickness of mm or more.

An object of the present invention is to provide a method for producing a thermoplastic resin sheet or film by a water cooling method that eliminates such problems.

The present invention involves introducing a film-like thermoplastic resin extruded in a molten state from a T-die into a viscous fluid having a viscosity of 2 to 3000 centipoise (cp) flowing down a slit to cool both sides of the resin. A method for producing a thermoplastic resin sheet or film, characterized by:

The thermoplastic resin used as a raw material for sheets and films in the present invention is not particularly limited, and includes, for example, polyolefins (polyethylene, polypropylene, etc.), polyester, polyamide, polyethylene terephthalate, polystyrene, polyvinyl chloride, polyvinylidene chloride, etc. In particular, crystalline thermoplastic resins, which have conventionally had problems with transparency and surface properties of sheets, etc., can be used without causing such problems. In addition, the sheets and films of the present invention include multilayer sheets and films, and further include silica,
Also included are those to which nucleating agents such as talc, para-tertiary butyl aluminum benzoate, and dibenzylidene sorbitol are added.

The viscous fluid used in the present invention has a viscosity of 2 to 3000 centipoise (cp), preferably 3 to 3000 centipoise (cp).
1000 cp, and a preferred example of the viscous fluid is an aqueous solution prepared by adding an organic or inorganic thickener to water. Here, various organic thickeners can be used, such as natural polymer substances, semi-synthetic products, and synthetic products. Natural polymer substances include starches such as Japanese starch, potato starch, and wheat starch; mannan such as konjac; seaweed such as agar and sodium alginate;
Plant mucilages such as gum tragacanth and gum arabic; Microbial mucilages such as dextran and levan;
These include proteins such as glue, gelatin, casein, and collagen. Semi-synthetic products include cellulosic substances such as viscose, methylcellulose, and cellboxymethylcellulose; soluble starch,
There are starch-based substances such as carboxymethyl starch and dialdehyde starch. In addition, synthetic products include polyvinyl alcohol, sodium polyacrylate, polyethylene oxide, and the like.

On the other hand, inorganic thickeners include silica sol, alumina sol, clay, water glass, and various metal salts.

In addition to aqueous solutions prepared by adding these thickeners to water, viscous substances such as polyethylene glycol, polypropylene glycol, and silicone oil can also be used alone. In the present invention, the viscous fluid is used to cool the thermoplastic resin film, and preferably has a liquid temperature in the range of -10 to +50°C. Particularly in the production of sheets with a thickness of 0.2 mm or more, it is effective to keep the liquid temperature below 20°C, particularly preferably below 10°C, to prevent the occurrence of haze spots.

To cool the thermoplastic resin film with a viscous fluid, the thermoplastic resin film extruded from a T-die in a molten state is introduced into the viscous fluid having a viscosity of 2 to 3000 cp flowing down the slit. FIGS. 1 and 2 are explanatory diagrams showing aspects of an apparatus for carrying out the method of the present invention.

To explain the method of the present invention with reference to FIG.
A thermoplastic resin film 2 extruded in a molten state from a die 1 is introduced into a slit 4 through which a viscous fluid 3 is flowing. This slit 4 is formed to be connected to a water tank 5 located below the T-die 1, and its length is not particularly limited, but is usually about 5 to 100 mm, and is preferably relatively short. Further, the slit interval is not particularly limited, and may be determined by taking into account the resin used, molding conditions such as molding speed, and the required properties of the product.

In the case of the water tank 5, it is necessary that the viscous fluid in the membrane-like thermoplastic resin introduction part flow, and the liquid level (depth to the water surface) should be as low as possible. It is preferably 7 mm or less. When the liquid level reaches 10 mm, boiling spots, haze spots, and curls will occur on the resulting sheet or film, and the total haze will be as high as 20 to 30%, which is undesirable. Since a cooling viscous fluid flows from the water tank 5, the film-like thermoplastic resin is cooled by the fluid when passing through the slit 4. That is, both sides of the film-like thermoplastic resin are efficiently cooled by the fluid flowing in parallel. In this case, it is desirable that the flow rate of the viscous fluid be close to the traveling speed of the film-like thermoplastic resin. moreover,
The slit connected to the aquarium is 1 as shown in Figure 1.
It is not limited to the case of stages, but the film-shaped thermoplastic resin can also be cooled in multiple stages of two or more stages. Further, FIG. 2 shows another embodiment of the slit. That is, a pair of rotating endless belts 1
3 and 13' facing each other with an interval, the slit 14 is configured to allow the viscous fluid to flow down into the interval and to move the facing surface of the endless belt in the same direction as the flow direction of the viscous fluid. It's a slit. Here, the endless belt is preferably made of metal such as stainless steel, rubber, or materials coated with or impregnated with a resin having excellent heat resistance and smoothness such as fluororesin. The endless belts 13, 13' are driven by known means, for example drive rolls 15, 1 connected to a drive source such as a motor.
5'.

The reason why a viscous fluid with a viscosity of 2 to 3000 cp is used in the present invention is that because of the high viscosity of the fluid, even if the fluid falls at a high speed, it will not become a turbulent flow, and that it will flow uniformly, especially in the part where it first contacts the molten resin film. This is because uniform cooling becomes possible.

This makes it possible to obtain sheets with excellent surface conditions free of boiling spots and haze spots and with excellent transparency.

The cooled thermoplastic resin film is then sent to the water receiving tank 6. The water receiving tank 6 is provided with a guide roll 7 as shown in the figure, and the thermoplastic resin further cooled in the water receiving tank is transferred to the guide roll 7.
The film is then taken up by a take-up roll 8 and guided to a take-up roll. Note that the guide roll can also be used as a transfer roll for transferring the mirror surface of the roll onto a thermoplastic resin. Drawing, 9 is a water level adjustment board, 10 is an overflow board, 11 is a cooler, 12 is a pump, 16, 16' is a backup roll, 17,
17' is a tension roll.

According to the improved viscous fluid cooling method of the present invention, even when manufacturing sheets or films using crystalline thermoplastic resin as a raw material, it is possible to obtain non-oriented sheets with excellent transparency and surface gloss. can. Furthermore, the resulting sheet etc. has no uneven thickness or wrinkles, and has excellent homogeneity. Another feature of the present invention is that it is possible to efficiently produce relatively thick sheets and the like with high quality and high speed molding. In addition, the method of the present invention has the advantage that the equipment cost is low and cooling control is easy, so that the overall product cost can be reduced.

The sheets and the like obtained by the present invention are suitable for packaging foods, medicines, etc., and can also be used as raw materials for solid phase forming, such as air pressure forming, roll rolling, and stretch forming.

Next, the present invention will be explained in detail with reference to examples.

Example: Polypropylene (density 0.91 g/cm ³ , melt index 2.0 g/10 minutes) was produced using a T-die extrusion device (extruder 60 mm, L/D = 28, die width 500 mm, die lip opening 1.5 mm). Extruded.

The extruded molten resin was introduced into the cooling device shown in FIG. 1 to obtain a polypropylene sheet with a thickness of 0.2 mm. Note that the manufacturing conditions of the sheet are as follows.

Manufacturing conditions Resin temperature 240℃ Die temperature 280℃ Molding speed 25m/min Air gap 120mm Cooling water Sodium carboxymethyl cellulose
Tap water with 0.001% by weight added (viscosity: 20
Centipoise/20°C) Coolant temperature: 4°C Slit spacing: 1.5mm Slit length: 50mm Water tank liquid level: 3mm No boiling spots, haze spots, or curls were observed on the sheet thus obtained, and the total haze was 8 %
(internal haze 6%, external haze 2%), and had excellent transparency.

Comparative Example A polypropylene sheet was obtained in the same manner as in the example except that tap water was used as the cooling liquid. The resulting sheet showed haze spots, with a total haze of 28-32% (internal haze 20-24%).
%, external haze 8-12%).

[Brief explanation of the drawing]

FIGS. 1 and 2 are explanatory diagrams showing aspects of an apparatus used to carry out the method of the present invention. 1...T-die, 2...Membrane thermoplastic resin, 3
...Viscous fluid, 4...Slit, 13,13'...
...Endless belt.

Claims (1)

[Claims] 1. A film-like thermoplastic resin extruded from a T-die in a molten state has a viscosity of 2 to 2 when flowing through a slit.
A method for producing a thermoplastic resin sheet or film, which comprises introducing the resin into a 3000 centipoise viscous fluid to cool both sides of the resin. 2. The method according to claim 1, wherein the viscous fluid is water to which a thickener has been added.