JPS61163832A - Manufacture of transparent, heat-resistant, heat-shrinkable tube - Google Patents

Abstract

PURPOSE:To obtain transparent, high heat-resistant, heat-shrinkable tubing with neither blooming nor bleeding by a method wherein resin composition consisting in containing specified amounts of thiolic antioxidant and of phenolic antioxidant to 100pts.wt. of copolymer resin is molded in a form of tube, irradiated with ionizing radiation, heated and inflated. CONSTITUTION:Resin composition consisting in containing 0.5-50pts.wt. of the trakis (methylene-dodecyl-thio-propionate) methane as thioloic antioxidant and 0.5-5.0pts.wt. of at least one kind out of tetrakis (methylene-3,5-di-tertiary butyl-4-hydroxy-hydrocinnamate) methane and 2,2'-(thio-di-ethyl-bis[3(3,5-di- tertiary butyl-4-hydroxy-phenyl)propionate] as phenolicantioxidant to 100pts.wt. of copolymer resin mainly composed of polyethylene resin or ethylene is molded in a form of tube, irradiated with ionizing radiation and, after that, heated up to a temperature exceeding the softening point of the resin and finally inflated. Less than 0.5pts.wt. of thiolic antioxidant and of phenolic antioxidant do not give enough heat resistance. More than 5.0pts.wt. of them produce blooming and bleeding, resulting in impairing the transparency of the tube.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a heat-shrinkable tube that has excellent heat resistance and is transparent.

[Prior Art] Recently, tubes used for covering N-wire terminals for electronic and electrical equipment, etc., have not only physical properties but also high heat resistance and transparency. Materials with or as required.

In order to impart heat resistance to polyethylene resins and copolymer resins mainly composed of ethylene, it is common to add an antioxidant that has the function of eliminating free radicals generated in the polymer.

However, in heat-shrinkable tubes manufactured by irradiating a resin composition with high-energy ionizing radiation to expand it, and then heating it above the softening temperature of the resin to expand it, oxidation inhibitors added by irradiation with radiation In order to provide a high degree of heat resistance, it is necessary to use a preliminary oxidation inhibitor to prevent the structure of the agent from being destroyed and losing its function, or the antioxidant to volatilize and disappear when the tube is heated. agent will have to be added.

If a large amount of antioxidant is contained in the resin, bloom or bleed will occur on the tube surface over time, causing the tube to lose its transparency.

Therefore, until now, a heat-shrinkable tube that has both high heat resistance and transparency has not been realized.

[Problems to be Solved by the Invention] The present invention has been made based on the above, and an object of the present invention is to provide a manufacturing method that can realize a transparent heat-shrinkable tube that has a high degree of heat resistance and is free from bloom and bleed. This is the purpose.

[Means for Solving the Problems] The method for producing a heat-shrinkable tube of the present invention includes adding tetrakis (methylene dodecyl thiopropyl), a thio-based antioxidant, to 100 parts by weight of a polyethylene resin or a copolymer resin mainly composed of ethylene. pionate) methane and 0.5 to 5.0 parts by weight of methane, and the phenolic antioxidant tetrakis(
At least one of methylene 3゜5 ditertiary butyl 4 hydroxyhydrocinnamate) methane or 2,2-(thiodiethyl bis[3(3,5 ditertiary butyl 4 hydroxyphenyl) propionate])
The resin composition is characterized in that a resin composition containing 5.0 parts by weight is formed into a tube shape, irradiated with ionizing radiation, and then heated to a temperature above the boiling point of the resin to expand it.

In the present invention, the polyethylene resin includes low, medium,
Any high density polyethylene may be used.

As a copolymer resin mainly composed of ethylene, ethylene-
Examples include propylene copolymer, ethylene-butene copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, and the like.

These resins can be used alone or in combination of two or more.

In the present invention, the thio-based antioxidant Tetrakis (methylene dodecyl thiopropionate methane) and the phenolic antioxidant Tetrakis (methylene 3.5 ditertiary butyl 4 hydroxyhydrocinnamate) are used.
Methane or 2,2-(thiodiethylbis[3(3,5
It has been found that it is important to use at least one of di-tert-butyl 4-hydroxyphenyl) propionate in combination, and that the synergistic effect of both can provide a high degree of heat resistance and provide a heat-shrinkable tube without bloom or bleed.

Furthermore, none of these antioxidants impairs the transparency of the resin.

It is necessary to add each of the above-mentioned thio-based antioxidant and phenolic antioxidant in a range of 0.5 to 5.0 parts by weight per 100 parts by weight of polyethylene resin or copolymer resin mainly composed of ethylene. If it is less than 0.5 parts by weight, heat resistance will not be imparted sufficiently, and if it exceeds 5.0 parts by weight, bloom or bleed will occur and transparency will be impaired.

In the present invention, in addition to the above-mentioned components, a lubricant, a flame retardant, a filler, etc., which do not limit transparency, may be added as necessary.

The resin composition thus obtained is formed into a tube shape using an extruder or the like, crosslinked by irradiation with ionizing radiation such as an electron beam, and then expanded under heating at a temperature equal to or higher than the softening temperature of the resin.

When performing irradiation crosslinking, add a polyfunctional monomer in the range of 0.5 to 10 parts by weight to enable crosslinking at a low radiation dose and to prevent deterioration of the resin and antioxidant due to ionizing radiation. It is common to do so.

Examples of polyfunctional monomers include acrylates (diethylene glycol diacrylate, etc.), dimethacrylates (
diethylene glycol dimethacrylate, dipropylene glycol dimethacrylate, etc.), triacrylates (trimethylolethane triacrylate, trimethylolpropane triacrylate, etc.), trimethacrylates (trimethylolethane trimethacrylate, trimethalol propane, trimethacrylate, etc.) methacrylate, etc.), triallyl cyanurate, triallyl isocyanurate, diallyl maleate, etc.

[Examples] Examples of the present invention will be described below along with comparative examples, and cases will be explained separately for cases in which a polyfunctional monomer is contained and cases in which a polyfunctional monomer is not contained.

Table 1 is an example in which no polyfunctional monomer is contained,
A resin composition containing various components was extruded into a tube shape with an inner diameter of 0.6 mm and an outer diameter of 1.6 mm.
．． Crosslinking was performed by irradiating an IOMrad electron beam with a 5 MeV electron beam accelerator. The tube was then heated to 200° C. and expanded to have an outer diameter of 4.0 m.

The evaluation results for the heat-shrinkable tubes obtained in 8 cases are shown in the lower column of Table 1.

The aging characteristics were measured after aging at 158° C. for 7 days, and the transparency was evaluated visually after being left at room temperature for 120 days after manufacturing the heat-shrinkable tube.

Table 1 *2 Melt index 5.0, ethyl 7 acrylate content ff 19% Table 2 is an example of a case containing a polyfunctional upper knob, in which a resin composition containing various components was prepared with an inner diameter of 1.
0Iw+, was extruded into a tube shape with an outer diameter of 2.0 mm, and crosslinked by irradiating it with an electron beam of 10 Mrad using a 1.5 MeV electron beam accelerator. The tube was then heated to 180° C. and expanded to have an outer diameter of 5.0 mm.

The evaluation results for the heat shrinkable tubes obtained in 8 cases are shown in the lower column of Table 2.

The aging properties were measured after aging at 175° C. for 7 days, and the transparency was evaluated in the same manner as in the examples in Table 1.

Table 2 1 *2 Melt index: 5.0, ethyl acrylate content: 19% [Effects of the invention] As explained above, the present invention has a high degree of heat resistance, and also reduces the plume and bleed of antioxidants. Since it is possible to eliminate this, it is possible to realize a transparent heat-shrinkable tube.

Claims (1)

[Claims] (1) Add 0.5 to 5.0 parts by weight of tetrakis(methylenedodecylthiopropionate)methane, which is a thio-based antioxidant, to 100 parts by weight of a polyethylene resin or a copolymer resin mainly composed of ethylene, and a phenol-based antioxidant. The antioxidant tetrakis (methylene 3,5 ditertiary butyl 4 hydroxyhydrocinnamate) methane or 2
, 2' (thiodiethyl bis[3(3,5 ditertiarybutyl 4 hydroxyphenyl) propionate]) A resin composition containing 0.5 to 5.0 parts by weight of at least one of the following is molded into a tube shape and then ionized. 1. A method for producing a heat-resistant transparent heat-shrinkable tube, which comprises irradiating the resin with radiation and then heating the resin to a temperature above its softening point to expand the tube.