JPS5843251B2 - Thermoplastic resin film manufacturing method - Google Patents

Description

Detailed Description of the Invention The present invention reduces the pressure in the space enclosed by the die, mandrel, and film to adjust the position where the film first contacts the mandrel, thereby improving crystallinity with good transparency and uniform stretchability. This invention relates to a method for producing a tubular film made of thermoplastic resin uniformly and stably for a long time.

Generally known methods for cooling and solidifying tubular molten films include air cooling, liquid cooling using a liquid such as water, and solid contact cooling in which the film is brought into contact with a solid having excellent thermal conductivity such as a metal. The solid contact cooling method is the best in this respect.

Therefore, the solid contact cooling method is particularly suitable for producing a tubular film with good transparency and excellent uniform stretchability using a resin with a fast crystallization rate, such as polyhexamethylene adipamide resin.

Solid contact cooling methods include a method in which the film is contacted from the outside and a method in which it is contacted from the inside, but since there is post-shrinkage when the tubular molten film is cooled and solidified, it is necessary to improve the cooling effect by making good contact between the film and the cooling body. In order to increase the film diameter and make the film diameter constant, a solid contact cooling method using a mandrel from inside the film (mandrel cooling method) is better.

In a film manufacturing method using a mandrel, the following two points are important and often cause problems in order to uniformly and stably manufacture a film with good transparency and excellent uniform stretchability over a long period of time.

■ Sufficient adhesion between the film and mandrel near the point where the film first contacts the mandrel.

If the degree of adhesion is too small, the heat exchange between the mandrel and the film will be insufficient, and the cooling rate of the molten film will be slow.
Crystallization progresses, making it impossible to obtain the desired film with good transparency and uniform stretchability.

■ Prevents air bubbles from being trapped between the film and the mandrel.

When bubble-like air is enclosed, the area does not come into close contact with the mandrel, so crystallization progresses, resulting in significant whitening, as well as uneven thickness and significantly poor flatness, resulting in a non-uniform film with no commercial value.

These two points are particularly problematic when manufacturing a large-diameter tubular film with a diameter of 50 mm or more.

That is, as the diameters of the die and mandrel are increased in order to produce a large-diameter tubular film, the degree of adhesion between the film and the mandrel decreases, and the occurrence of air bubbles increases significantly.

The following method is known as a conventional technique for solving these problems.

First, as a method for increasing the degree of adhesion between the mandrel and the film, a method is known in which the speed at which the film moves while touching the mandrel is increased relative to the outflow speed of the film at the exit of the die lip (% Kosho No. 44-15917). There is.

In this method, it is necessary to make the die lip gap sufficiently large relative to the product film thickness.

However, if the die lip gap is made too large, the resin pressure loss at the die lip portion becomes extremely small, which impedes uniform extrusion, so this method is not commonly used because the manufacturing conditions under which it works effectively are limited.

Particularly, almost no effect was observed in the production of large-diameter tubular films with a diameter of 507/L7IL or more, in which the degree of adhesion between the mandrel and the film was very small.

Next, as a measure to prevent the inclusion of air bubbles, a method has been proposed in which an annular air is blown at the position where the film first contacts the mandrel (Japanese Patent Publication No. 44-15917).

This method has a large possibility of causing disturbance to the film in a flowing state, and is not a preferable method for producing a uniform film. Also, since the prevention effect is small, it is especially Almost no effect was observed in the production of large-diameter tubular films of 501 m or more.

As described above, with the prior art, it has not been possible to uniformly and stably produce a tubular thermoplastic resin film with good transparency and uniform stretchability for a long time, regardless of the diameter of the tubular film.

Therefore, the present inventors conducted various studies to solve the above-mentioned problems, and as a result, they arrived at the present invention.

That is, the method of the present invention uses a film manufacturing apparatus consisting of an annular die and a mandrel arranged perpendicularly to the center of its circular slit, and by reducing the pressure in the space enclosed by the die, mandrel, and film, the film is attached to the mandrel. This is a thermoplastic resin film manufacturing method that consists of adjusting the position of initial contact.

As the degree of vacuum in the space enclosed by the die, mandrel, and film increases, the position where the film first contacts the mandrel moves toward the die, and the degree of adhesion between the film and the mandrel increases, resulting in a transparent product with low crystallinity. A film with good properties and uniform stretchability can be obtained, and furthermore, the inclusion of air bubbles between the film and the mandrel does not occur.

However, if the position is too close to the die side, the film will not slide smoothly on the mandrel, and horizontal stripes will appear on the film, or in severe cases, the film will break.

Therefore, it is important to adjust the degree of pressure reduction so that the position is at an appropriate position.

In addition, a precise pressure reducing device is required to maintain the position at an appropriate position at all times.

It is also possible to use a device that detects fluctuations in the internal and external pressures of the molten film and automatically controls the degree of pressure reduction.

It is preferable that the mandrel circulates a refrigerant inside the mandrel, and the length thereof is the length necessary to sufficiently cool the film.
In addition, a metal with good thermal conductivity is used, and its surface has a thermal conductivity of 0.2
It is desirable to have a roughness of p Rmax or more and 3.0 μRmax or less.

The present invention is preferably applied to an apparatus in which the inner diameter of the slit of the die is smaller than the outer diameter of the mandrel, which facilitates uniform and stable film formation, but is not necessarily limited to this.

FIG. 1 schematically shows an example of an apparatus for carrying out the invention.

In FIG. 1, 1 is an annular die, 2 is a mandrel with an internal cooling mechanism, 3 is a deflator, 14 is a take-up nip roll, 5 is a tubular film, 6 is a molten resin inlet, 7 is a mandrel cooling water supply port, and 8 is a Mandrel cooling water outlet, 9
, 10゜L12, 13 and 14 are devices for adjusting the degree of vacuum in the space A enclosed by the die, mandrel and film, 9, 10 and 11 are needle valves;
12 is an air chamber, 13 is a fan, 1
4 is a decompression degree measuring device.

By using such a device, it is possible to control the degree of vacuum in the space A enclosed by the die, mandrel, and film, thereby adjusting the position B where the film 5 first contacts the mandrel.

Note that the hanging device applicable to the present invention is not limited to the one shown in FIG.

The vine resin applicable to the present invention includes polyolefin resins such as polypropylene, polyester resins, polyhexamethylene adipamide, polyε-capramide, poly11-aminoundecanamide, polylaurinamide, and copolymers and blends thereof. and other polyamide resins.

However, it is particularly suitable for producing tubular films of polyamide resins which have a fast crystallization rate and are difficult to obtain into low-crystallized unstretched films that can be stretched uniformly, and also of polyhexamethylene adipamide, which has a particularly fast crystallization rate among polyamide resins.

Examples will be shown below to explain the present invention in more detail.

Example 1 ηr3.8 (25°C, 296% sulfuric acid solution) Polyhexamethylene adipamide with a diameter of 160 mm and a lip gap of 0 and 5
Extruded at 280°C from an annular die with a surface roughness of 1.
0μRmax diameter 145 trim1 length 2507n
Contact cooling was performed from the inside of the molten film using a mandrel made of hard chromium plated 7IL aluminum with a surface temperature of 50°C, and using the same equipment as shown in Figure 1, a die,
By reducing the pressure in the space A contained by the mandrel and the film, the position B where the film first contacts the mandrel is adjusted to a position 20 mm above the die lip surface, and a tubular film with a diameter of 145 mm and a wall thickness of 150 μm is heated to 4.0 m. /
The film was formed at a take-up speed of min.

As a result, a tubular film having a density of 1.1224 and a haze of 9.6%, low crystallinity, good transparency, and good uniformity without unevenness due to inclusion of air bubbles was obtained stably for more than 8 hours.

In addition, surface roughness is determined by JISB-0601, and cloudiness is determined by JIS.
K-6714, and the density was measured by placing the film into a carbon tetrachloride-toluene density gradient tube at 25° C. within 10 minutes, being careful not to flood the film after film formation.

Example 2 The film obtained in Example 1 was continuously introduced into a tubular biaxial stretching machine, and was stretched by 3.5 times in length and 3.5 times in width at a stretching temperature of 120°C.
When the film was biaxially stretched 5 times, a uniform stretched film was obtained that remained stable for 8 hours or more.

The physical properties of the obtained stretched film are shown in the table below.

The obtained film had high strength and good transparency.

In addition, the tensile test conditions are as follows.

Test piece size 1071X71! X 120mm, chuck distance 50mm, cross head speed 100mm 1min
Comparative Example 1 A film was formed under the same conditions as in Example 1 except that the space enclosed by the die, mandrel, and film was not depressurized.

The position where the film first contacted the mandrel was 38 degrees from the die lip surface.

The resulting film had a density of 1.1302 and a haze of 68.3.
Comparative Example 2 The film obtained in Comparative Example 1 was stretched under the same conditions as Example 2. Comparative Example 2 had no commercial value due to high crystallinity, poor transparency, and unevenness due to bubble-like air inclusions. Continuous stretching was completely impossible due to the breakage.

Example 3 ■ 0.65 (35°C, O-chlorophenol solution) polyethylene terephthalate was prepared using a device similar to that shown in Fig. 1, with a diameter of 160 mm and a lip gap of 0.5 m.
A tubular film with a diameter of 145 mm and a wall thickness of 330 μm was formed by extruding it at 280° C. from an annular die of 1.3 mm, cooling it with a mandrel, and reducing the pressure in the space enclosed by the die, mandrel, and film, and the density was 1.1338. Cloudiness 5.4%
A film with low crystallinity, good transparency, and good uniformity without unevenness due to inclusion of air bubbles was stably obtained.

The mandrel was made of aluminum plated with hard chrome and had a surface roughness of 2.5 μRmax, with a diameter of 145 mm and a length of 250 mm, and the temperature was controlled from the inside so that the surface temperature was 56° C.

The take-up speed is 4.0 m/min, and the position where the film first contacts the mandrel is 25 mm from the die lip surface.
It was kept in position.

This film was continuously guided into a tubular biaxial stretching machine and biaxially stretched 3.5 times in length and 3.8 times in width at a stretching temperature of 120°C, resulting in a stable and uniform stretched film with a thickness of 25μ. Obtained.

Note that the density was measured by putting the sample into a carbon tetrachloride-n-hebutane density gradient tube at 25°C.

Other measurements were performed using the same method as shown in Example 2.

[Brief explanation of drawings]

FIG. 1 is a schematic partial cross-sectional view showing an example of a device applied to the present invention.

Claims (1)

[Claims] 1. A die,
A method for manufacturing a thermoplastic resin film, which comprises adjusting the position where the film first contacts the mandrel by reducing the pressure in the space enclosed by the mantle and the film and controlling the degree of pressure reduction.