JPS6023979B2 - Tubular biaxial stretching method for polyhexamethylene adipamide film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to maintaining the shape of the tubular film being stretched within an appropriate range, thereby making it possible to produce polyhexamethylene adipamide that is uniform, in particular, substantially free from unevenness in transparency. The present invention relates to a method of manufacturing a polyamide tubular double-stretched film.

Generally, in the tubular two-way stretching of polyhexamethylene adipamide, necking-like stretching spots occur all around the film circumference at the beginning of the transverse stretching, and these spots do not disappear until the end of the stretching, resulting in increased thickness and transparency. However, only biaxially stretched films with non-uniform properties such as film properties can be obtained. The non-uniform stretching of polyhexamethylene adipamide has a characteristic not seen in other resins in that even if the thickness unevenness is small enough to pose no practical problem, transparency unevenness occurs significantly. As a method for uniform biaxial stretching of thermoplastic resin into a tubular shape, it is already known that it is necessary to maintain the shape of the tubular film being stretched under appropriate conditions.
Polyethylene terephthalate (Special Publication No. 51-48676)
No.).

However, in the case of polyhexamethylene adipamide, it was not possible to obtain a two-way stretched film that was uniform, particularly without unevenness in transparency, under these conditions. Therefore, as a result of intensive studies to obtain a polyhexamethylene adipamide biaxially stretched film that is uniform, particularly transparent, and free from unevenness, using the tubular biaxial stretching method, we found that The present invention was achieved by discovering that there is a difference in the shape and uniformity of the stretched film up to the point where 50% of the transverse stretching is completed.

That is, in a method in which a polyamide tubular unstretched film consisting essentially of polyhexamethylene adipamide is stretched twice by simultaneously applying tension in the film traveling direction and in the transverse direction, the shape of the film being stretched is determined by the parameter Q. It has been found that a uniform polyhexamethylene adipamide tubular two-malt stretched film can be obtained by a tubular two-malt stretching method characterized by stretching while maintaining 2.5SQ<8.0. In the present invention, polyamide consisting essentially of polyhexamethylene adipamide refers to polyhexamethylene adipamide alone or copolymerized with other polyamides such as nylon 6 to the extent that the properties are not substantially changed. It is a combination or a mixture.

Note that fillers and the like may be added to an extent that does not substantially change the properties. Here, Q is the length along the center axis of the stretching bubble from the lateral stretching start point to the 50% lateral stretching end point,
It is a value divided by 1/4 of the value obtained by subtracting the unstretched film diameter from the stretched film diameter at the end of lateral stretching.

Figure 1 is an explanatory diagram of q according to a cross section of the film including the central axis of the stretching bubble, and shows the lateral stretching start point, the lateral stretching end point, and the lateral stretching 5.
This diagram shows the 0% end point, etc. When Q<2.5, necking in the form of vertical cracks along the direction of film propagation occurs near the starting point of transverse stretching, and this non-uniformity is not resolved even after the completion of stretching, resulting in a non-uniform biaxially stretched film. and
In particular, intermittent streak-like transparency spots with a nearly constant angle to the direction of film travel occur. And Q≧8
．． At 0, the stretching bubbles vibrate violently, the stretching ratio also fluctuates, and only a non-uniform stretched film can be obtained. Q is freely adjusted by appropriately selecting the film temperature in the stretching zone, its temperature gradient along the direction of film travel, and the internal pressure of the stretching bubble, depending on conditions such as the stretching ratio and the speed at which the film is fed out after stretching. be able to. A common method for biaxially stretching a tubular shape is to introduce an unstretched tubular film between two pairs of nip rolls with different circumferential speeds, then inject air into the tube while heating it with hot air or an infrared heater, and stretch it twice. However, implementation of the present invention is not limited to this method.

The polyamide unstretched film substantially consisting of polyhexamethylene adipamide used in the present invention is preferably one with a low crystallinity that is melt extruded from a tar and then rapidly cooled by a method such as mandrel cooling.

In addition, in the present invention, the stretching ratio is 2.
5-4. Peep sound, stretching temperature is 70 to 180 in film temperature
qo is preferred. In the present invention, it is particularly important to emphasize that the uniformity of the polyamide tubular biaxially stretched film consisting essentially of polyhexamethylene adipamide is within the stretching region of the film being stretched, which has already been claimed for other resins. It was found that there is no correlation with the overall average shape, but there is a correlation with the shape from the lateral stretching start point to the 50% lateral stretching end point.

The present invention based on this discovery is completely new and cannot be deduced from existing knowledge. Examples and comparative examples will be shown below to explain the present invention in more detail.

Examples 1 to 3, Comparative Examples 1 to 4 Polyhexamethylene adipamide of 3.8 mm (25 mm, 96% sulfuric acid) was heated at 280 degrees through a circular die with a diameter of 16 mm.
Extruded at o, diameter 145mm, thickness 110mm, density 1.
1201/mi tubular wire stretched film 4.5/mi
The film was formed at a take-up speed of n.

However, since the density changes depending on the absorption rate of the sample, the sample was measured using a toluene-carbon tetrachloride density gradient tube using a sample whose moisture content was adjusted to 0.2% or less as measured by the Karl Fischer method. This stretched film is continuously guided at a speed of 4.5/min to a tubular two-ball stretching machine shown in Fig. 2, air is injected into the tube, and the film is advanced by two pairs of nip rolls with different circumferential speeds. Tubular biaxial stretching was performed by simultaneously applying tension in the direction and the transverse direction.

In FIG. 2, 1 is a tubular unstretched film, 2 is a low-speed nip roll, 3 and 4 are shielding plates made of a cold air ring and an elastic body for fixing the stretching start point, 5 is a heating ring, and 6 is a film in a stretching castle. Controls the film temperature gradient along the direction of travel.

- a heating hood with an inner diameter of 58 mm and a length L for heating, 7
8 is a deflator, 8 is a high-speed nip roll, and 9 is a tubular two-way stretched film. Table 1 shows the results of the stretching conditions, the Q of each condition, the fluctuation of the stretching bubbles, the fluctuation of the stretching ratio, and the unevenness of transparency of the obtained stretched film.

Here, Q is calculated by using a transparent polycarbonate sheet as a heating hood, taking a photograph of the stretched bubble shape during stretching from outside the heating hood, and correcting the distortion caused by the photograph.

It can be seen that a uniform polyhexamethylene adipamide tubular two-way stretched film can be obtained in the range of 2.5 miQ<8.0.

Table 1

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram regarding Q, which is a component of the present invention, and FIG. 2 is a side sectional view showing the main parts of a stretching device for carrying out the present invention. DESCRIPTION OF SYMBOLS 1... Tubular unstretched film, 2... Low speed nip roll, 3... Cold air ring, 4... Shielding plate, 5... Heating arming, 6... Heating hood, 7... Defrader, 8
... High-speed nip roll, 9... Tubular two-ball stretched film. Figure 1 Figure 2

Claims (1)

[Claims] 1 In a method of biaxially stretching a polyamide tubular unstretched film consisting essentially of polyhexamethylene adipamide by simultaneously applying tension in the film traveling direction and the transverse direction, the shape of the film being stretched is defined in the text. A tubular biaxial stretching method characterized by stretching while maintaining a parameter α of 2.5≦α<8.0.