JPH04118214A - Manufacture of transparent film, sheet or tube - Google Patents

Abstract

PURPOSE:To make it possible to obtain film, sheet or tube remarkably excellent in transparency by a method wherein polyethylene-based resin is extruded in the form of molten film and, immediately after being heated so as to have the surface temperature, which is higher than the temperature of a die by 30 deg.C or more and, at the same time, not higher by 250 deg.C or more then the meeting point of resin, quenched. CONSTITUTION:As the polyethylene-based resin 4, low-density polyethylene is used so as to produce film having the thickness of 120mum with a 75mm diameter extruder (L/D=28) and a T-die having the width of 500mm in order to form at the take-off speed of 30m/sec with an air knife and a chill roll. In addition, an air gap was 300mm. In that case, the temperature of the T-die was 160 deg.C. The measured surface temperature of which were radiant-heated with a far infrared heater provided at the intermediate part between the T-die and the chill roll, was 250 deg.C. The above-mentioned molten film was quenched with the chill roll having the temperature of 20 deg.C so as to obtain film having the thickness of 120mum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a film, sheet or tube having extremely high transparency.

[Prior art 1] In general, thermoplastic resins are easily plasticized by heat using an extruder, rolls, etc., extruded from a flat or circular die with slits, cooled by a medium such as air or water, and drawn off to form a thin film. It solidifies as it grows. Generally used polyethylene resins (for example, low-density polyethylene resins) are extruded from a T-die using the T-die process, cooled with air using an air knife, etc., and then taken off at a speed of 50 to 60 m/min. Meanwhile, it is cooled and solidified by coming into close contact with a rotating water-cooled chill roll. At this time, the polyethylene resin is crystallized due to its crystallinity. In this process, generally, when the molding temperature, that is, the temperature at which the polyethylene resin is extruded from the die, is increased, the transparency of the obtained film, sheet, or tube is improved due to the quenching effect.

[Problem to be solved by the invention]

However, if the extrusion temperature is too high, the resin will thermally decompose, causing oxidative deterioration, and if the extruder is operated continuously day and night, deteriorated substances will adhere to the inside of the extruder, causing accidental extrusion. This causes gels and black spots to appear on the product (film, sheet, or tube), significantly reducing the quality of the product.

On the other hand, if the molding temperature is set to a low temperature so that the resin does not deteriorate in order to solve these defects of the product (prevent deterioration), a sufficient cooling effect cannot be obtained because the rapid cooling effect is insufficient. There is a problem. In particular, this effect was significant when processing materials with relatively poor thermal stability.

For these reasons, the present invention is a film that does not have these drawbacks (intervening spots), that is, uses polyethylene resin and has extremely excellent transparency.

The purpose is to obtain sheets or tubes.

[Means for Solving the Problems 1] In order to solve the above-mentioned problems, the present inventors have conducted extensive research, and based on a concept completely different from conventional methods, they have developed a method of melt-extruding thermoplastic resins at low temperatures and then molding them by extrusion at high temperatures. A film with high transparency and high gloss that was previously unobtainable by producing a rapid cooling effect that exceeds that of the previous film.

Heading that sheets or tubes are obtained.

The present invention has now been completed.

That is, according to the present invention, the above problem is solved in a method of manufacturing a film, sheet or tube by melt extruding a polyethylene resin, extruding the molten film from a die, and cooling it while taking it. In the period between cooling and solidification, the molten film is heated again from the outside or inside so that the surface temperature of the molten film is 30°C or more higher than the die temperature and 250°C or more higher than the melting point of the resin. This problem can be solved by a method for manufacturing transparent films, sheets, or tubes, which is characterized by raising the temperature to a high temperature and then immediately quenching it.

The present invention will be specifically explained below.

+11 Polyethylene Resin Polyethylene resins to which the present invention can be applied include so-called high-pressure polyethylene R or lower [referred to as polyethylene resin (A)], which is produced using only ethylene and a free radical catalyst, and which has ethylene as its main component. copolymer with α-olefin [hereinafter referred to as [polyethylene resin (B)]
and copolymers E with other monomers containing ethylene as a main component (hereinafter referred to as polyethylene resin (C)).

The present invention can be applied to any of these polyethylene resins, but in order to obtain special characteristics in terms of transparency, resins that have a density of less than 0.935 g/c rd and are of poor quality are required. desirable.

Further, as resins to which the present invention can be applied, the polyethylene resin (A), polyethylene resin (B), and polyethylene resin fcl may each be used alone,
They may be used in a mixed manner or in a layered manner.

In the case of mixing and laminating, the polyethylene resin fAl
, fB) , (C+ may be a mutual combination, or may be a mixture or lamination of other compatible or adhesive thermoplastic resins.The thermoplastic resin used for these mixtures or laminations may be 0. Although it may have a density of 935 g/c rn' or more, it is desirable that the overall density as a mixture or laminate is 0.935 g/c rn' or less.

(2) Production of films, sheets, or tubes In order to produce films, sheets, or tubes using the above-mentioned polyethylene resin, a commonly used molding method (
For example, T-die method, inflation method, coextrusion method, etc.)
is used. In either case, the molding temperature cannot be determined unconditionally depending on the type of polyethylene resin or other thermoplastic resin used, but it is between 20°C and 130°C above the melting point of the resin used (preferably above the melting point). A high temperature (30°C to 120°C) is sufficient.

In the present invention, in the section until the molten film extruded from a die etc. at the above molding temperature is cooled and solidified,
It is important to heat the molten film again from the outside or inside to make the surface temperature of the molten film higher than the temperature of the die, and then immediately cool it rapidly. The surface temperature of the molten film resulting from this reheating is desirably at least 30° C. higher than the temperature of the die, and desirably no higher than 250° C. above the melting point of the resin used. If this temperature is not 30°C or more higher than the die temperature, the effect of the present invention will be insufficient. On the other hand, if the temperature is 250°C or more higher than the melting point of the resin being used, the resin will thermally decompose or deteriorate due to oxidation. Undesirable.

As a reheating method, a radiation heating method such as a nichrome heater or a ceramic heater-1 far infrared heater is preferable.

In addition, the reheated molten film must be immediately quenched, and quenching methods include air cooling and water cooling.
Water cooling method is more preferable.

The reason why the method of the present invention is effective is because the resin in the film state is instantaneously heated using a radiation heating method, so it can be heated to a much higher temperature compared to conductive heating in a mold such as a die. , the resulting film, sheet or tube has good gloss, as thermal deterioration of the resin does not occur and the rapid cooling effect increases.
Transparency will be dramatically improved. This effect will be specifically explained in the following examples, but it goes without saying that the present invention is not limited to the examples.

[Example 1 Table 1 shows the physical properties of the polyethylene resin used in the Examples and Comparative Examples. In addition, as an evaluation of transparency, the haze value is AST
M 01003-61, gross value is JIS 2874
11962, respectively.

Example 1 Using low density polyethylene (LDPE) shown in Table 1 as a polyethylene resin (Al), a 120μ thick film was cut using an air knife using a 75III extruder (L/D=281, a T-die with a width of 500mm). The molding process was carried out using a chill roll at a take-up speed of 30 m/sec.The air gap was 300+ am.The T die temperature was 160°C, and a far infrared heater was installed between the T die and the chill roll to form the molten film. The surface temperature of the molten film (bubble temperature when 1 OclI comes out from the die at the center of the externally heated part) was measured to be 250°C.

This molten film was rapidly cooled with a chill roll at a temperature of 20°C.
A film of LL was obtained.

Haze (%) and cross (%) were measured to evaluate the transparency of the film thus obtained. The results are shown in Table 2.

Comparative Example 1 A film was obtained by carrying out the same treatment as in Example 1 except that heating with a far-infrared heater was not performed in Example 1. The results are shown in Table 2.

Example 2, Comparative Example 2 Polyethylene resin (8) shown in Table 1 was used, and the thickness was 25 mm.
The same treatments as in Example 1 and Comparative Example 1 were carried out, except that the die temperature and molten film surface temperature were changed in order to form a 0μ sheet. Table 2 shows the respective conditions and results.

Examples 3 to 5 Table 2 shows the conditions and results of tubes formed using the inflation method instead of T-dies. Note that Example 4 is an example of a laminated sheet produced by three-layer coextrusion, and Example 5 is an example of a blend of resins fA] and (8+).

Comparative Examples 3 to 5 Examples 3 to 5 are the same as Examples 3 to 5, respectively, except that heating with a far-infrared heater was not performed. The results are shown in Table 2.

Comparative Example 6.7 Comparative Example 6.7 corresponds to Comparative Example 1 in which the T die temperature was increased.

From Table 2, in the comparison of Comparative Example 1.6, the haze value was 1015
%, 6.5%, and it can be seen that high-temperature molding clearly has superior transparency. However, when the T-die temperature is 270° C. as in Comparative Example 7, the resin undergoes thermal decomposition and stable molding becomes impossible.

On the other hand, it is clear that in the Examples, even though the die temperature was relatively low, by increasing the temperature of the fused film, the transparency was much better than in the Comparative Examples. Furthermore, even when the temperature of the molten film was 300''C, stable molding was possible without causing thermal decomposition.

(Hereinafter in the margin) [Effects of the Invention] The method of the present invention has made it possible to produce films, sheets, or tubes with extremely superior transparency compared to conventional methods.

Claims (1)

[Claims] In a method of manufacturing a film, sheet or tube by melt extruding polyethylene resin, extruding the molten film from a die, and cooling it while taking it, in the section where the molten film extruded from the die is cooled from the die and solidified. , This molten film is heated again from the outside or inside to a temperature where the surface temperature of the molten film is at least 30°C higher than the temperature of the die and no higher than 250°C higher than the melting point of the resin, and then immediately quenched. A method for producing a transparent film, sheet or tube, characterized by: