JPS5835132B2 - Netsukaso Seiji Yugo Tai Film Seikeihou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for melt extrusion molding of thermoplastic polymers, and particularly to a method for producing a film with excellent surface smoothness.

The surface smoothness of a thermoplastic polymer film is an important property that affects the commercial value of the film.

In particular, a smooth surface is required for photographic and mold release applications that utilize the surface, but even for general products, the quality of the roll, which is the general packaging style, is influenced by the surface smoothness, which in turn affects quality. This is because it has a huge impact.

The thermoplastic polymer film is manufactured by extruding the sheet from an orifice of a die using a melt extrusion method, bringing it into contact with a cooling roll, and rapidly cooling and solidifying the film.

At this time, defects called die lines, which are marked over a long period in the extrusion direction, often appear on the surface of the film.

This die line is a micro thickness unevenness, but if it becomes extreme, it will leave traces on the biaxially stretched film button and sheet even after a few seconds, and the gauge band (
Thick areas overlap to form convex orbital bands) or chicken wire (diamond mesh pattern).

This becomes more of a problem for non-stretched or stretched products in the extrusion direction.

One way to improve the surface smoothness of a film or sheet is to cool the molten thin film (hereinafter referred to as molten film) by pressing smooth surfaces (in most cases using roll surfaces) on both sides of the molten film immediately after extrusion from a die. However, there is a limit to the adjustment of macroscopic thickness unevenness, so even though it is effective for thick objects with a thickness of several layers, it is difficult to make both sides of the molten film uniform in the width direction for thin objects with a thickness of several tens of microns below IWrn. It is difficult to bring the rolls into contact with each other, making it difficult to put it into practical use.

Japanese Patent Publication No. 42-11507 proposes a method for obtaining a smooth surface by floating a polymer film on molten metal.

Although this method provides a good smooth surface, it has the problem that it is difficult to rapidly cool the film from a high temperature state, and in the case of crystalline polymers, it is difficult to obtain an amorphous film.

In order to rapidly cool and solidify the film from a high-temperature amorphous state using this method, the molten metal bath must be kept at a high temperature up to the vicinity of the cooling guide roller, but this will cause unevenness when the film is pulled up from above the molten metal. This results in excessive elongation and loss of flatness.

The temperature is low enough to maintain the film form (
Japanese Patent Publication No. 42-11507 states that the temperature is below the melting point of the synthetic resin used) A molten metal tank must be used.

Therefore, crystalline polymers, especially polymers with a high crystallization rate, crystallize and become extremely difficult to stretch as a raw material for stretching.

As mentioned above, there is no suitable method for eliminating the die line by directing the molten thin film during casting.Therefore, when extruding from a die, it is necessary to extrude the film by shifting the film in a direction perpendicular to the extrusion direction, or to roll it up by vibrating it. This method can be avoided, but it has a major disadvantage in terms of product yield.

The inventors have arrived at this invention as a result of intensive research into eliminating die lines during melt extrusion film formation.

That is, in the process of melt extrusion film formation, the molten film is brought into contact with a casting roll having a surface with excellent peelability and heat resistance at a temperature below the adhesive temperature of the polymer to the cast roll, and then the roll is coated with the molten film. 11. In an inert gas atmosphere, the polymer coating is immersed in molten metal at a temperature higher than the melting point of the polymer, and after being pulled up, it is brought into contact with a roll at a temperature lower than the casting roll temperature and solidified by cooling. An improved method for forming polymeric films is provided.

The present invention will be explained below with reference to the drawings.

In FIG. 1, 1 is a T-die, and 2 is excellent in peelability and heat resistance.

For example, a casting roll made by coating polytetrafluoroethylene, its copolymer, other fluororesins, silicone resin, alumina, zirconia, or other ceramics, etc., 3 separates the film from the casting roll and cools it. Turning roll with nip roll for solidifying and transferring to the next process, 4 is a molten metal tank,
Reference numeral 5 denotes a baffle plate which divides the inside of the tank 4 and allows the heating conditions to be changed for each division.

As the heater 6 for heating the tank 4, a plate-type heater or a drop-in type heater attached to the bottom and side surfaces of the tank 4 is sufficient.

Then, an inert gas such as nitrogen is flowed into the space inside the tank 4 so that the molten metal 8 and the polymer film are not subjected to oxidation or other deterioration.

The molten metal 8 is a low melting point alloy having a melting point lower than the melting point of the polymer, such as a Wood's alloy, a Newton's alloy, or an alloy in which lead, bismuth, tin, etc. are mixed into an arbitrary composition.

The molten film T extruded into a sheet form from the die 1 is cast onto a casting roll 2 whose surface has excellent peelability and heat resistance.

Here, the surface of the casting roll 2 is transferred to the casting roll contacting surface 7' of the molten film 7, the die line is erased, and the molten film 7 is cooled and becomes solidified or semi-solidified.

The solidified or semi-solidified polymer film is immersed in the molten metal 8 as the casting roll 2 rotates.

When the non-contact surface T of the casting roll comes into contact with molten metal 11 with a die line marked on its surface, the molten metal contact surface of this polymer film softens or melts, reducing the difference in surface tension and density between the polymer and molten metal 8. smoother than the relationship,
After being pulled up from the molten metal 8 and peeled off from the casting roll 2, it is immediately cooled naturally or rapidly cooled by the turning roll 3 and solidified to form a film that is smooth on both sides.

Although the smoothness of the casting roll non-contacting surface γ' of the polymer film is improved simply by immersion in the molten metal 8 as described above, contact with the turning roll 3 forms a more satisfactory surface.

Particularly, one of the advantages of this invention is that the results of macroscopic thickness adjustment in the lateral direction made by adjusting the opening degree of the die orifice remain unchanged.

The appropriate temperature for the casting roll 2 and the molten metal 8 varies depending on the type of polymer and the surface material of the casting roll 2, but the temperature of the casting roll 2 is below the sticking temperature of the polymer to this roll, preferably 45 to 120℃
As a result, if the temperature is low, the molten film extruded from the die 1 will not contact the casting roll 2 uniformly, causing spots; It becomes sticky easily.

The temperature of the molten metal 8 needs to be equal to or higher than the melting point of the polymer; at temperatures lower than this, there is little effect of eliminating die lines.

The upper limit is determined by the temperature at which the film sticks to the casting roll 2 after being immersed in the molten metal 8 and the heat resistance temperature of the surface material of the casting roll 2.

For example, when the polymer is polyethylene terephthalate and the surface material of the casting roll 2 is tetrafluoroethylene, the molten metal temperature is preferably 260 to 300°C.

Although the temperature gradient of the molten metal layer 4 can be appropriately applied, at least one portion thereof is set to the above-mentioned appropriate temperature.

The amount of immersion of the film into the molten metal 8 and the immersion time are related to the adhesion of the film to the casting roll 2.
In the appropriate temperature range of the casting roll 2z and the molten metal 8 described above, unless the immersion amount is particularly large or the immersion time is lengthened, thin films with a thickness of several tens of microns to about tmm will not stick to the casting roll 2. It can be carried out without causing any problems.

The amount of immersion and the immersion time are variable depending on the peripheral speed of the casting roll 2.

Example 1 Reduced viscosity measured at 35°C with 0-chlorophenol 1 solution is 0.73 dL/L? The polyethylene terephthalate was extruded into a sheet at 290°C through a T-die with an orifice length of 350 mm, and was brought into close contact with a 55φ casting roll coated with polytetrafluoroethylene rotating at 85°C, and the film was brought into close contact with this roll. An alloy of equal amounts of lead and bismuth (melting point 145
The film was immersed in a bath at 270°C containing 200°C for 2 seconds with nitrogen gas flowing through the upper space, and after being lifted from the molten alloy, the film was released from the casting roll and brought into contact with a hard chrome-plated turning roll at 70°C equipped with a chive roll. , and a film of 190μ was obtained.

Figure 2 shows a comparison of the surface smoothness of the molten metal contact surface with the conventional method in terms of surface roughness.

Surface roughness all-purpose surface shaping machine Sercom 3B (Tokyo Seimitsu ■
(manufactured by).

This unstretched film was substantially amorphous, transparent, and could be easily stretched.

Example 2 Nylon 110φ extruded from a T-die at 250°C and coated with polytetrafluoroethylene at 65°C
A cast film was placed on a casting roll, and the residue was heated at 280°C, 250°C, and 200°C from the entry side of the film using a jammer plate filled with Newtonian alloy (melting point 95°C) in a nitrogen gas atmosphere. The roll is immersed to a depth of 40°C in a bath whose temperature is controlled in three blocks.
After pulling the film out of the dipping bath for 4 seconds during FRI, the film was released from the roll, brought into contact with a mirror roll cooled to 25°C, and stretched in the extrusion direction. The film had very few streaks in the extrusion direction, had a good appearance, and had thickness irregularities in the lateral direction of ±5.0%, compared to ±12% in the conventional film forming method.

By using the method of the invention as described above, a thin thermoplastic polymer film with excellent surface smoothness can be easily produced.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, and FIG. 2 is a diagram showing the surface smoothing effect of the present invention, where a is the surface roughness curve of the film surface according to the conventional method, and b is the surface roughness curve according to the present invention. The surface roughness curve of the film surface is shown. 1...T-die, 2...Casting roll, 3...Turning roll, 4...
Tank, 5...Block plate, 6...Heater, 7...Melted film, 7'...Casting roll contact surface 7u,... Casting roll non-contact surface, 8... Molten metal.

Claims (1)

[Claims] 1. When forming a film by melt extrusion of a thermoplastic polymer, the molten film is brought into contact with a casting roll having a surface with excellent peelability and heat resistance at a temperature below the adhesive temperature of the polymer to the casting roll, and then the polymer film is formed. The casing 1 is brought into contact with a casting roll, is pressed in an inert gas atmosphere, immersed in molten metal at a temperature above the melting point of the polymer, and after being pulled up is brought into contact with a roll at a temperature below the casting roll temperature to cool and solidify. A method for forming thermoplastic polymer films.