JPS635256B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a heat-shrinkable tube with a small longitudinal shrinkage rate. 2. Description of the Related Art A so-called heat-shrinkable tube made by tubular drawing of a synthetic resin extrusion-molded material tube is widely used for applications such as closely covering the outer surface of articles. When a heat-shrinkable tube is fitted onto an article and heated to cover it with shrinkage, the contraction of the tube in the radial direction is useful for adhering closely to the outer surface of the article, but if the contraction in the longitudinal direction is large, the tube before and after shrinkage will shrink. Since the longitudinal dimension of the material changes, which causes inconveniences such as inaccurate coating positions, it is practically desirable to have a longitudinal shrinkage rate of about 10% or less. However, in the conventional tubular stretching method, in order to prevent the tube from becoming unstable due to meandering during stretching, nip rolls are placed before and after the stretching process, and the roll speed on the downstream side of the tube is set higher than that on the upstream side. It is necessary to apply tension to the tube during stretching, and as a result, the tube is stretched not only in the radial direction but also in the longitudinal direction, resulting in a large longitudinal shrinkage ratio of the final heat-shrinkable tube.10
There were cases where it exceeded %. In addition, attempts have been made to reduce only the longitudinal shrinkage rate by applying relaxation heat treatment in the longitudinal direction while maintaining the radial dimensions of shrink tubes that have already been stretched in the longitudinal and radial directions. There were problems such as the need for complicated means for suppressing shrinkage. In view of the above-mentioned problems, the present inventors are currently considering a method for manufacturing a heat-shrinkable tube with a small vertical shrinkage rate. The present invention was achieved by discovering that when heating a heat-shrinkable tube, a shrinkage stress is generated so that no external tension is required, and that when the tube is subsequently stretched in the radial direction, the vertical shrinkage ratio of the resulting heat-shrinkable tube becomes smaller than that of the conventional heat-shrinkable tube. The gist of this is that when a material tube formed by melt extrusion molding of a synthetic resin through an annular die is tubularly stretched by internal fluid pressure, the synthetic resin extrusion speed and take-up speed are adjusted and the material tube is Ten%
The vertical shrinkage ratio of the material tube is then set to the speed ratio of the downstream roll to the upstream roll
A heat-shrinkable tube characterized in that it is heated between two sets of Nippro rolls with a ratio of 1.0 to 1.1, and then stretched in the radial direction between a supply roll and a take-off roll having the same speed as the supply roll. It depends on the manufacturing method. The present invention will be explained in more detail below based on the drawings. FIG. 1 is a schematic process diagram showing an example of carrying out the method of the present invention. In the figure, a material tube 1 is nipped by an upstream roll 2, passed through a heating tunnel 3 in the direction of arrow A, and then nipped by a downstream roll 4. Subsequently, compressed air B is introduced into the material tube 1 from the downstream side to regulate the outer diameter of the former 5.
Stretch it while regulating the dimensions and take it up with roll 6
It will be picked up. The material tube 1 is made by melt-extruding a synthetic resin such as polyvinyl chloride, crosslinked polyethylene, polyethylene terephthalate, or polypropylene through a circular die. It is necessary to give 1 a longitudinal shrinkage rate of 4 to 10%. In the present invention, the shrinkage rate refers to the shrinkage rate when a sample is heated for 5 minutes at a temperature of 10° C. above the stretching temperature. In other words, if it is less than 4%, in order to stably advance the tube, the speed ratio of the downstream roll 4 to the upstream roll 2 must be greater than 1.1 to apply tension to the tube 1, and the resulting final product The vertical shrinkage rate of the heat shrink tube is 10
%, the article cannot be coated accurately. On the other hand, if the longitudinal shrinkage rate of the material tube exceeds 10%, the shrinkage rate in the radial direction of the heat-shrinkable tube of the obtained final product tends to be small, causing practical problems such as the inability to tightly cover the article. The raw material tube thus obtained is supplied to the upstream roll 2 directly from an extruder (not shown) or once wound onto a reel and fed from the reel (not shown). In addition, in order to make the longitudinal shrinkage rate of the heat shrinkable tube of the final product 10% or less, it is necessary to increase the speed of the downstream roll 4 (speed r ₁ ) relative to the upstream roll 2 (speed r 1 ).
The speed ratio r ₂ /r ₁ of r ₂ ) may be made as small as possible within the range of 1.0 to 1.1 without making the progression of the tube unstable, and the tube may be heated within the heating tunnel 3.
In order to heat the material tube here, infrared rays, hot air, hot water, etc. can be used, and the temperature can be approximately equal to or higher than the stretching temperature. In short, it is sufficient to preheat the material tube to such an extent that it can be easily stretched in the subsequent stretching step, and the shrinkage stress generated in the tube at this time allows stable film feeding even if the ratio r ₂ /r ₁ is small. Subsequently, stretching is carried out in a continuous process using compressed air or the like at a temperature above the softening point and below the melting point of the material tube. In the example in Figure 1, the heating tunnel 3
Although the tube is heated to the drawing temperature by heating therein, it may be further heated again in the drawing section. Further, in the example shown in FIG. 1, compressed air is supplied from the winding side of the tube and is blocked by the downstream roll 4, so that the tube does not swell in the heating tunnel 3. In the stretching process, there is no need to create a large speed difference between the supply roll 4 and the take-up roll 6 as in the conventional case, and it is sufficient to set both rolls at the same speed, for example, and stretch only in the radial direction. The reason for this is that the heating process prior to stretching is separated by the roll 4, so the distance of the stretching process is shortened, and the shrinkage and contraction of the material tube is not relaxed in the heating process prior to stretching, but is caused by radial contraction. It is thought that stable stretching can be performed because the shrinkage force in the longitudinal direction acts as tension during the stretching process. As described in detail above, the present invention is characterized in that a material tube, which has been given a vertical shrinkage rate of 4 to 10% in advance, is placed between two sets of nip rolls in which the speed ratio of the downstream roll to the upstream roll is as small as possible. It is characterized by being heated at and then stretched only in the radial direction,
It is possible to extremely easily and stably obtain a heat-shrinkable tube whose final product has a longitudinal shrinkage of 10% or less and a large radial shrinkage. Hereinafter, the present invention will be explained based on examples. Example 1 Low density polyethylene (melt index = 4)
Mix 100 parts by weight with 0.2 parts by weight of dicumyl peroxide and 2 parts by weight of vinyltriethoxysilane.
Silicon-grafted polyethylene was produced by heating at 200°C for 5 minutes, and then a masterbatch was prepared by mixing 2 parts by weight of dibutyltin dilaurate with 100 parts by weight of the same low-density polyethylene as described above, and 5 parts by weight of this masterbatch and the silicon grafted polyethylene were mixed. A material tube was obtained by extruding a mixture of 100 parts by weight of chemically modified polyethylene through an annular die at an extrusion temperature of 190°C. In order to obtain material tubes with constant inner diameter and wall thickness but different longitudinal shrinkage rates, the size of the annular die,
Molding was carried out by adjusting the take-up speed. The longitudinal shrinkage of this tube was measured by crosslinking the tube at 90° C., 40% RH for 5 days to reach a gel fraction of 73%, and then heating it at 120° C. for 5 minutes. Next, a cross-linked polyethylene material tube with a vertical shrinkage rate of 4.1 to 10.0% shown in Table 1 was heated using the apparatus shown in Figure 1 so that the temperature of the tube immediately after coming out of the heating tunnel was 110°C. Subsequently, the film was stretched twice in the radial direction using compressed air. At this time, the downstream roll 4 and take-up roll 6 of the heating tunnel have a feeding speed of 20 m/
With min constant, the upstream roll 2 was adjusted to the maximum speed within a range where the tube did not become unstable due to meandering or the like. The final product heat shrink tube obtained in this way is
Table 1 shows the results of measuring the shrinkage percentage in the longitudinal and radial directions when heated at 120°C for 5 minutes. The gel fraction of the cross-linked tube is determined by extracting ₁ g (2 g) of the sample with 150 g of xylene using a Soxhlet extractor (140°C, 24 hours), drying the undissolved matter, and taking the weight as ₂ g of gel. It was expressed as fraction=w ₂ /w ₁ ×100 (%). Comparative Example 1 A heat-shrinkable tube of the same material as in Example 1 was stretched in the same manner as in Example 1, except that the longitudinal shrinkage percentage was 1.2 to 3.8% and 10.4 to 20.5%. Table 1 shows the results of measuring the shrinkage rate in the radial direction.

[Table] As shown in Table 1, if the longitudinal shrinkage of the material tube is less than 4%, the longitudinal shrinkage of the resulting heat-shrinkable tube will exceed 10%. In addition, if the longitudinal shrinkage of the material tube exceeds 10%, the radial shrinkage of the heat-shrinkable tube of the final product will tend to decrease.
10% is required.

[Brief explanation of the drawing]

FIG. 1 is a schematic process diagram showing an example of an apparatus for carrying out the method of the present invention. 1...Material tube, 2...Upstream roll, 3
... Heating tunnel, 4 ... Downstream roll, 5 ...
Outer diameter regulation homer, 6... take-up roll.

Claims (1)

[Claims] 1. When tubularly stretching a material tube formed by melt-extruding a synthetic resin using an annular die using internal fluid pressure, the synthetic resin extrusion speed and take-up speed are adjusted to give the material tube a longitudinal shrinkage rate of 4 to 10%. The material tube is then rolled at a speed ratio of 1.0 to the downstream roll relative to the upstream roll.
After heating between two sets of Nitpro rolls set to 1.1,
A method for manufacturing a heat-shrinkable tube, which comprises subsequently stretching the tube in the radial direction between a supply roll and a take-off roll having the same speed as the supply roll.