JPS5923532B2 - heat shrink tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-shrinkable tube that shrinks when heated.

Generally, plastics, which are filamentous polymer compounds, have so-called thermoplasticity, which means that they deform when external force is applied to them under heating, and when they are cooled, they solidify while remaining deformed.

However, if this plastic is allowed to undergo a cross-linking reaction, then when an external force is applied to the plastic while it is heated and the plastic is allowed to deform, it will remain deformed at room temperature. It is allowed to return to its shape. The speed of returning to the original shape is particularly remarkable for crystalline polymers.
The fact that this occurs rapidly near the melting point of the crystal can be well understood from a logical perspective. The heat-shrinkable tube is made of polyethylene or a copolymer of ethylene and other monomers, which is capable of cross-linking reactions between molecules.

That is, low-density polyethylene, medium-density polyethylene, high-density polyethylene, or copolymers of ethylene with vinyl acetate, ethyl acrylate, propylene, butene, etc. are used.

After forming these polymers into a pipe or tube shape, a crosslinking reaction is caused.

As a means for causing this cross-linking reaction, it is usually possible to use a method of irradiating with electron beams, gamma rays, ultraviolet rays, etc., or a method of adding an organic peroxide in advance and heating it after molding to cause cross-linking. can. It is also possible to add a silane coupling agent in advance, and after molding, immerse it in water to cause a bridge reaction. By applying an external force while heating the polymer that has caused a cross-linking reaction after molding in this way, it expands into the shape of a tube with a large inner diameter, and then is cooled while applying an external force. A tube is manufactured by being stretched circumferentially from the original pipe 30. The stretching ratio at this time can be increased from several tens of percent to 500% or more of the original inner diameter if necessary.

35 The heat-shrinkable tube thus manufactured maintains its expanded shape at room temperature, but when heated, it almost completely returns to its pre-expanded shape.

Heat-shrinkable tubes utilizing this phenomenon have been commercially available for over 15 years.

However, one of the drawbacks of these retractable tubes is that when the retractable tube is stopped in the process of deflation, non-uniform wall thickness often occurs. There is no problem at all if the shrinked tube is completely restored to its original shape by heating, but in general use, such cases are rare and the expanded tube is not used to make steel pipes, electric wires, cables, wires, etc. Its main purpose is to shrink it after it is covered and stop it while retaining the shrinkage force during the contraction, and is used for the purpose of protecting objects inserted inside or for heat insulation. In this way, when stopping mid-shrinkage, it is almost impossible to ideally and uniformly heat the product, and even when left in a uniform air temperature such as a high-temperature bath, partial shrinkage may occur. There is a time lag, and in most cases, uneven thickness occurs when the material is in close contact with an internal object after shrinking.

The present invention aims to eliminate such drawbacks and provide a method that makes the wall thickness of a shrunken tube as uniform as possible, and that does not cause non-uniform wall thickness even if there is some variation in heating.

That is, as a result of examining the temperature-shrinkage curve of such a shrinkage tube, it was found that the shrinkage curve against temperature has a very steep slope near the melting point of the crystal, as shown in FIG. Therefore, as a result of examining the temperature-shrinkage curve of a mixture of two or more types of polymers with different melting points and deformed in the same process as shrinkable tubes, it was found that the speed of shrinkage was clearly slower, and the shrinkage completely ended. It was recognized that a wider temperature difference than before was required for this purpose.

However, in a blend of polymers with different melting points, if the blending ratio of the polymer with the one melting point is less than 10% of the total, almost no effect appears to be observed.

The reason for this is considered to be that when the shrinkage force of a polymer with a low melting point is suppressed by the resistance of the crystalline parts of a polymer with a high melting point, it cannot be stopped by mixing the total amount of 10" or less. Regarding the types of polyethylene, the melting point increases in the order of low density, medium density, and high density, but in general, low density polyethylene is a polymer polymerized by the so-called high pressure method, and medium density polyethylene is a polymer polymerized by the Ziegler method. High-density polyethylene shall mean polyethylene polymerized by the Phillips method or the standard method.To put it simply, the Polyethylene The overlapping characteristics are as shown in Table 1 below.Detailed explanation will be given below based on the examples.
Inner diameter 30fm1 wall thickness 4mf1 using ordinary extrusion method using polyethylene of 2, black 3, 4, black 5, 6, and 7 black
A pipe with an outer diameter of 38 Iwn was produced, and a cross-linking reaction was carried out by irradiating the pipe with a vibrator using an electron beam accelerator, resulting in a gel fraction of approximately 60%.

The pipe that has undergone this cross-linking reaction is heated to a temperature above the melting point of each polyethylene, or above the melting point of the high-melting point material in the case of a mixture, specifically 140 to 150°C, and then expanded with pressurized air from the inside to have an inner diameter of approx. I expanded it until it became a 130tr1n tube, then cooled it down, then returned the internal pressure to normal pressure, and the inner diameter was about 120mm. of tubes were obtained. The actual measured value of wall thickness is approximately 0
．． 8? It was hot. When this tube is heated above the melting point of the X crystal, the inner diameter of the original pipe is almost 30frr1n.
returned to. Metal pipes with an outer diameter of 80 mm were inserted into these tubes, and the outer surface of the polyethylene tube was heated with a torch lamp to shrink the entire tube. After cooling, it was cut. The thickness of the cross section was measured. As a result, the wall thickness and thickness unevenness shown in Table 1 were obtained. The rate was obtained.

Polyethylene, which is the same material as these tubes, was subjected to the same cross-linking reaction, then stretched 4 times in one direction, cooled, and then heated to measure the temperature-shrinkage curve. Shown in Figure 1.

As seen in FIG. 1, it was observed that the shrinkage curves of single polymers of FL1 and O2 were relatively steep with respect to temperature, and the temperature range of shrinkage was narrow. On the other hand, Ya4, Ya5,
For FL6, the speed of shrinkage is slow, and together with the results in Table 1, this shows that shrinkage progresses very smoothly despite variations in heating temperature, thus preventing uneven thickness. It has been shown. However, when looking at the temperature-shrinkage curves and thickness unevenness ratios from O3 and Ya7, it was found that if the mixing ratio was less than 10%, not much effect could be expected.

Furthermore, in addition to blending polymers with different melting points, we investigated the effect of using polyethylene alone with an intermediate density or melting point, but for example, polyethylene alone with a melting point of about 128°C, which has the same density as the mixed polyethylene of 6, has no effect. No effect could be recognized at all.

Example 2 The results of using a copolymer of ethylene and ethyl acrylate in place of the low melting point polyethylene of Example 1 are shown in Table 3, and the temperature-shrinkage curve is shown in FIG.

Furthermore, as in Example 1, the thickness unevenness rate of the shrink tube was
Shown in the table.

The temperature-shrinkage curve was investigated in the same manner as in Example 1, and the results are shown in FIG.

As a result, it was found that when two types of polymers with different melting points are used, a copolymer also exhibits similar effects. Example 3 Similarly to Example 2, an ethylene-ethyl acrylate copolymer was used as the low melting point ethylene copolymer, and the results are shown in Table 4 and FIG.

The shrinkage curve of the mixture had a gentle slope.

As shown in Examples 1 to 4, by mixing two types of polyethylene with different melting points or a copolymer of ethylene and other monomers, a shrink tube that shrinks very slowly was obtained. As a result, it was found that, regardless of the method of crosslinking reaction, clearly good results can be obtained in a mixed system of polyethylenes having different slopes of temperature-shrinkage curves with different melting points. In order to appropriately select the shrinkage curve of a shrink tube using polyethylene or a copolymer of ethylene and other monomers that has undergone the cross-linking reaction as described above, it is necessary to It is effective to mix polymers, and Example 4 shows the possibility of obtaining a more suitable temperature-shrinkage curve.
When we tried mixing different types of materials with different melting points, we obtained a curve with a similar gentle slope as shown in Table 5 and Figure 4.

Shrinkable tubes were manufactured using this material and the thickness unevenness after shrinkage was measured in the same manner as in Example 1. As a result, the thickness unevenness was 30% or less in all cases, giving good results.

Example 5 Next, the same thing happened when the crosslinking method was not ionizing radiation but an organic oxide, i.e., di-α- A sheet prepared by adding 0.6% of sulfur peroxide and then heated (160° C.) for cross-linking had a gel fraction of about 65%.

This polyethylene is heated to a temperature higher than the melting point of each polyethylene, or in the case of a mixture, higher than the melting point of the high melting point material.
A sample was prepared by stretching it 4 times at 0 to 150°C and cooling it to room temperature in the X state, and the temperature-shrinkage curve was determined in the same manner, and the results are shown in Table 6 and Figure 5. As can be seen from the above explanation and examples, a shrink tube is manufactured by causing a cross-linking reaction using polyethylene or a copolymer of ethylene and other monomers, and then deforming the tube under heating to increase the inner diameter. It is very effective to use a mixture of polyethylenes or copolymers with different melting points as the tube material in order to slow down the rate of shrinkage and make the wall thickness uniform after shrinkage during the process of increasing the temperature and shrinking. It turned out that.

There are currently various methods for producing shrink tubes, but basically a pipe or tube is made by molding polyethylene and then a cross-linking reaction is caused.

3. Expand the inner diameter while heating and cool under tension to fix the deformation strain as it is.

In the above process, the cross-linking reaction can be caused by electron beam irradiation, gamma ray irradiation, ultraviolet irradiation, or by adding an organic peroxide before molding and causing a heating reaction after molding to cause cross-linking. methods etc. will be adopted.

In addition, as a means of applying deformation strain while heating, it is possible to adopt methods such as blowing pressurized air into the interior, vacuum suction from the outside, and mechanical expansion from the inside. In the present invention, heat-shrinkable tubes can also be manufactured using these methods.

In addition, as a method for manufacturing a heat-shrinkable tube, a polyethylene sheet or film is manufactured in advance, the cross-linking reaction is reversed on this sheet or film by the method described above, and then the sheet or film is stretched in one direction (in most cases, in the direction of the roll). After causing deformation strain in one direction, if it is possible to wind the material in more than one layer on a rolling die that maintains this deformation strain, it can be wound several times, then heated to form a single piece, and after cooling, the mold is removed. It is known that shrink tubes can also be manufactured using different shaping methods. In any of these methods, it is possible to use polyethylenes or copolymers having different melting points, and it is possible to make the temperature-shrinkage curve gentler.

[Brief explanation of drawings]

Figures 1, 2, 3, 4, and 5 are graphs 7 showing the relationship between temperature and shrinkage rate (%) when a heat-shrinkable tube is heated at a rate of 2°C/min to cause it to shrink. be.

Claims (1)

[Claims] 1 After molding polyethylene or ethylene copolymer into pipes and tubes, the molded product that has caused intermolecular cross-linking reaction is deformed to increase the inner diameter while being heated, and then cooled to remove deformation strain. In heat-shrinkable tubes manufactured by fixation, two or more types of polyethylene or ethylene copolymers with different melting points are used at a mixing ratio of 10% (weight%) of the total.
) Mix so that there are two or more types of things contained above,
A heat-shrinkable tube, characterized in that the temperature at which the molded product is deformed is higher than the melting point of a high melting point polymer of the polymer mixture having different melting points.