JPS60260319A - Manufacture of heat-shrinkable tube - Google Patents

Abstract

PURPOSE:To obtain a covering material that will not develop a crack even if a profiled core material is covered therewith, by covering a molded item with a tube whose composition is different in degree of crosslinking depending on positions that are covered. CONSTITUTION:A silan-crosslinked polyethylene tube consisting of a highly crosslinked section (A) extending an arc of 90 deg. and a lower crosslinked section (B). The section (A) has a gel fraction of 70% and the section (B) has a gel fraction of 52%. The tube is put over a core material 2, and is heated at 140 deg.C for 30min so that it is shrunk uniformly over the core material 2. This covering material will not develop a crack or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a heat-shrinkable tube suitable for forming a protective coating layer on a member having an irregular cross-section.

Conventionally, heat-shrinkable tubes are described in U.S. Patent No. 2027
No. 962 and No. 3,086,242, etc., and are widely used as various protective coating products.

These heat-shrinkable tubes do not cause any particular problems as long as they are cylindrical in shape after shrinking. However, when a protective coating is applied to a member having an irregular cross section, various problems arise. That is, if the contact surface between the inner surface of the heat-shrinkable tube 1 and the core material 2 has the same shape as shown in FIG. 1, there will be no particular problem, but as shown in FIGS. is cylindrical and the core material 2, 2'
When the heat-shrinkable tube has an irregular cross-sectional shape, the shrinkage rate of the heat-shrinkable tube accumulates at the periphery and is almost uniform.
After the tube is covered and heat-shrinked, only the protrusion 3 or the corner part 3' becomes thinner than the other parts, and this part is prevented from shrinking sufficiently, leaving no room for shrinkage. It will probably remain as it was.

Therefore, if used as is, warping would occur in the protrusions and some corners in a short period of time.

When used in such an unstable condition, the protrusions and corners often play an important role in the performance of the core material, so it is unlikely that these parts will become thin or crack. This was a serious problem in practical terms and significantly reduced the commercial value of Rashi.

In order to improve such defects, the present invention aims to improve crosslinking methods, materials,
The method of the present invention was developed as a result of intensive research into tube structures and the like.

That is, the method of the present invention involves forming a silane-crosslinked olefin tube with different degrees of crosslinking at predetermined positions depending on the periphery by coextrusion, and then heating and expanding the diameter of the tube to form a predetermined shape with a uniform wall thickness. After that, the 11 is fixed.

Silane crosslinking in the method of the present invention? As Liolefin,
A silane-grafted polyolefin is obtained by grafting an organic unsaturated silane onto a polyolefin in the presence of a free radical generating agent, and then the silane-grafted polyolefin is extruded into a predetermined shape, and then in the presence of a silanol condensation catalyst, It can be crosslinked by contacting with moisture, and is described in, for example, Japanese Patent Publication No. 48-1711, Japanese Patent Application Laid-Open No. 57-49101, and the like.

Conventionally, manufacturing tubes with different degrees of crosslinking only at predetermined positions in the circumferential direction by electron beam crosslinking or peroxide chemical crosslinking of polyolefins has been extremely complicated and difficult to operate. It was not possible to produce it industrially due to the high manufacturing cost. However, by applying the silane crosslinking method as described above, it is easy to obtain tubes with different degrees of crosslinking, such as making certain parts of the tube have a higher or lower degree of crosslinking than other parts. The present invention was achieved by discovering this.

Du1,/I as base I remer in the method of the present invention
J ethylene, polypropylene, ethylene-globylene di- or ternary copolymer, ethylene-vinyl acetate copolymer,
Ethylene ethyl acrylate copolymer or chlorinated polyethylene alone or in a blend is used.

In addition, as an organic unsaturated silane compound, vinyltrimethoxysilane (VTMO8,0H2=CH-8t(OCH
3),), 1 vinyl)'), i-toxin, F/(V
TE)O8,CT(2=CH,Sl(QC2H5),
) are typical examples.

The blending amount of both is 0.5 to 5 parts, preferably 1 to 3 parts, of the organic unsaturated silane compound per 10 parts by weight of the bispolymers (hereinafter referred to as "parts").

If the amount is less than 0.5 parts, sufficient grafting will not occur, and if it exceeds 5 parts, molding will become difficult and economical.

In addition, as a free radical generator, a compound that generates a free radical site in polyolefin at 100'C or higher,
For example, dicumirno, -oxide, 1,3-bis(t-
Typical examples include (butylperoxyisoglobil) benzene. The amount of the free radical generator to be blended is 0.01 to 1.0 parts, preferably 0.01 to 1.0 parts, per 100 parts of the pace polymer.
If the amount is less than 0.01 part, the graft reaction will be insufficient, and if it exceeds 1.0 part, extrusion processability will be difficult.

In addition, various silanol condensation catalysts are known, but dibutyltin silaurylate is a typical example, and its blending amount is o, oi to 0 per 100 parts of the pace polymer.
．． If the amount is less than 0.01 part, the crosslinking rate will be slow, and if it exceeds 0.5 part, the extrusion processability will decrease.

Next, we will explain the manufacturing method of silane-crosslinked polyolefin in which the degree of cross-linking is varied at predetermined positions by dipping in the peripheral area. First, a silane compound and a free radical generator are mixed in the pace polymer at the above ratio. Then, heat history is applied to this in a single-screw or twin-screw extruder to form a silane graft tomer. Make small molds. This method is a two-stage process method, which is divided into a silane graftomer manufacturing process and a molding process in which a catalyst is mixed with the silane graftomer and extruded, and a one-stage process method that integrates both processes. That is, the catalyst is mixed at the same time as the silane graftomer is produced, and the silane graftomer and extrusion molding are carried out in one step, but the latter method is economically advantageous.

In the method of the present invention, when it is desired to obtain a tube in which only a predetermined portion of the peripheral portion has a different degree of crosslinking,
When producing the above graftomer, silane graftomers with different degrees of crosslinking are prepared by adjusting the blending amount or thermal history of silane and free radical generator, and these are shared using multiple extruders. It can be extruded simultaneously using an extrusion method.

By exposing the extruded silane graft to a moisture environment, the crosslinking reaction is accelerated and a silane crosslinked polyolefin is obtained.

Next, this silane cross-linked polyolefin tube is heated,
The diameter is expanded by an appropriate means such as applying internal pressure to form a predetermined shape with a uniform wall thickness, and the expanded diameter is cooled and fixed to obtain the heat-shrinkable tube of the present invention.

This heating diameter expansion process is generally carried out after the silica/graft polyolefin tube is crosslinked in a moisture atmosphere, but the tube is heated and expanded before the crosslinking process. A crosslinking treatment may be performed after the stress remains.

Therefore, if the degree of crosslinking differs in the peripheral area of the tube, the diameter of the area with a lower degree of crosslinking will be larger than the area with a higher degree of crosslinking in a method in which air is pumped into the tube to apply internal pressure when expanding the tube by heating. Since the rate becomes large, heating diameter expansion using such an internal pressure method may result in poor workability or poor appearance of the product. Therefore, instead of using the internal pressure method, it is effective to use a suitable diameter expanding tool or to directly heat and expand the graft tube before crosslinking.

This heating and diameter expansion of the tube is generally done in a separate process from the extrusion molding of the tube.

- A method in which air is pumped into the tube during the cooling process to expand the diameter of the tube following extrusion molding is also extremely advantageous economically.

Next, examples of the present invention will be described. ) Example (1)
) As shown in Figure 4, a silane crosslinked polyethylene tube with an inner diameter of 10 wφ and a wall thickness of 2 cm, consisting of A1 and a low crosslinked part B forming a 90° angle with a highly crosslinked part, was made of the paste polymer shown in Table 1. Created.

A 30φ single-screw extruder is used to form part A, and a 55φ single-screw extruder is used to form part B. The two extruders are connected with a Kumon head, each with a set cylinder temperature of 120 to 160°. It is extruded.

Table 1 (1) Pace polymer for low degree of crosslinking (part B) (M, I:
3.0g710min, density 0.92EIA) Vinyltrimethoxysilane 2 Perhexa 3 MO, 15 (manufactured by NOF Corporation) (2) Pace polymer for highly crosslinked parts (Part A) Po, Engineering fL
/7* 100 parts (M, I: 3.0V 10 minutes, density 0.92%) Vinyltrimethoxysila/2 Perhexa 3M O,3 (NOF Corporation g) The above tube was then heated at 50°C. After the crosslinking treatment was carried out by leaving it in an atmosphere of 8870% for 3 days, it was heated to a temperature above its melting point to expand the inner diameter to 50 mm and was then cooled and fixed at the expanded diameter. A heat-shrinkable tube of the present invention was obtained.

When the degree of crosslinking of the thus obtained heat-shrinkable tube of the present invention was measured, the r fraction of part A was 70.

When the uninvented tube was coated on a core material having a round surface shape as shown in No. 5@IK and heated at 140° C. for 30 minutes, the coating thickness was uniform over the entire circumference and the entire circumference was shrunk. Further, this coating material was heat-treated at 200° C. for 7 hours, but no cracks or the like were observed.

Example (2) As shown in FIG. 6, a highly crosslinked part A at an angle of 30°,
Inner diameter 10+I+++Iφ, wall thickness 2 consisting of low crosslinking part B
A silane-crosslinked I-lyolefin tube was prepared from the base polymer shown in Table 1 and heated at 50°C and RH70.
% atmosphere for 3 days to carry out crosslinking treatment. Next, this tube is heated to a temperature above its melting point, and the inner diameter is 5
When the core material was coated to a diameter of 0 theoretical φ and heated at 140° C. for 30 minutes, the entire circumferential surface was coated with approximately uniform shrinkage. This coating material was then heated to 200°C.

Comparative Example A silane crosslinked polyethylene tube having a uniform degree of crosslinking and having an inner diameter of 10 mm and a wall thickness of 2 mm was obtained using a 55 mm uniaxial extruder using the low crosslinking degree pace polymer in Example (1). In this case, a normal tube head was used without using a common head.

The tube thus obtained was coated with a core material as shown in Figure 2 and heated at 140°C for 30 minutes.The tube shrunk sufficiently and was able to pass through the coating without cracking, but the protrusions and The wall thickness at the corners was significantly thinner than at the pond. When this coating was further heated to 200° C. for 7 hours, cracks appeared at the protrusions and the tube detached from the core material.

As detailed above, according to the method of the present invention, heat-shrinkable chips for protective coating of irregularly shaped core materials can be obtained through a simple process, and the degree of crosslinking can be distinguished by coloring, among other remarkable effects. has @

[Brief explanation of the drawing]

Figures 1 to 3 are cross-sectional views of a conventional covering made of a heat-shrinkable tube as a core material. This shows the case. FIGS. 4 and 6 are cross-sectional views showing an example of a heat-shrinkable tube made by the method of the present invention, and FIGS. 5 and 7 are cross-sectional views of a covering body in which a core material is coated with the heat-shrinkable tube of the present invention. FIG. 1... Heat-shrinkable tube with uniform degree of crosslinking, 2...
Core material 3, 3/... protrusion, 4... heat-shrinkable tube with a different degree of crosslinking, A... highly crosslinked part, B... low crosslinked part. Applicant's agent Patent attorney Takehiko Suzue 9 Figure 1 Figure 2 Figure 3 Figure 4 A Figure 5

Claims (1)

[Claims] A silane crosslinked polyolefin tube having portions with different degrees of crosslinking at predetermined positions along the periphery is formed by coextrusion, and then the tube is heated to expand its diameter to form a predetermined shape, and then cooled and fixed as is. A method for manufacturing a heat-shrinkable tube, characterized by: