JPH0524109A - Manufacture of heat-shrinkable tube - Google Patents

Abstract

PURPOSE:To perform crosslinking by one process, to continuously perform molding, crosslinking and expanding processes and to reduce the restriction of an adaptable pipe diameter and wall thickness by molding a tubular molded product from a composition containing a crosslinking agent a photoreaction initiator and crosslinking the same at molding temp. or higher by the irradiation with UV rays. CONSTITUTION:A polyolefin composition is molded into a tubular molded object and, after polyolefin is crosslinked, the tubular molded object is expanded in its diameter at temp. equal to or higher than the molding temp. of the composition using pressure difference and cooled to the molding temp. or lower to manufacture a heat-shrinkable tube. Herein, the composition consisting of polyolefin, a crosslinking agent and a photoreaction initiator is molded into a tubular shape. When the molded object is irradiated with UV rays with a wavelength of 250-450mm for the sake of crosslinking, polyolefin is crosslinked in the presence of the photoreaction initiator, for example, diethoxyacetophenone and the crosslinking agent. Therefore, the diameter of the tube is expanded and the tube is cooled as it is to obtain a heat-shrinkable crosslinked polyolefin tube.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a heat-shrinkable tube, and more particularly to a method for producing a heat-shrinkable tube made of a crosslinked polyolefin with high production efficiency.

[0002]

2. Description of the Related Art Heat-shrinkable tubes utilize the so-called memory effect of polyolefins. To manufacture a polyolefin heat-shrinkable tube, uncrosslinked polyolefin is molded into a tube shape, crosslinked, and then heated to a temperature above the moldable temperature to melt and soften it into a rubber-like shape, which is then stretched and pressure difference, etc. To expand the diameter of the pipe (called expansion) and cool it as it is. When cooling, the strain due to tube expansion is preserved internally. In order to obtain a polyolefin heat-shrinkable tube, it is essential to crosslink the polyolefin to make the molecular structure three-dimensional.

For cross-linking polyolefins, a method using an organic peroxide such as dicumyl peroxide as a cross-linking agent, or a silane graft body of polyolefin is cross-linked by silanol condensation reaction in the presence of water and a catalyst. Known are silane grafting method (also known as silane water crosslinking method), γ-ray irradiation, electron beam irradiation and the like.

[0004]

However, the cross-linking of polyethylene using a known organic peroxide such as dicumyl peroxide (DCP) as a cross-linking agent is performed at about 120 ° C. (for example, when dicumyl peroxide is used as a polymerization initiator). (3) requires a high temperature, so that the tube is deformed or crushed during the cross-linking process, which is not suitable for manufacturing a heat-shrinkable tube.

In the silane grafting method, it is necessary to once graft the polyolefin, a large-scale facility is required for the grafting, and the reaction takes a long time.
Further, equipment such as a high temperature water tank or a steam bath is required for the cross-linking of the graft product by the silanol condensation reaction. Further, these steps cannot be continuous with the steps of forming the original tube and expanding the tube, resulting in poor production efficiency.

[0006] Crosslinking by γ-ray irradiation or electron beam irradiation not only requires equipment and labor for radiation protection, but also requires a long irradiation time for crosslinking, so it is separated from the steps of molding and tube expansion to separate steps. Therefore, the production efficiency is poor because these steps cannot be performed continuously. Further, since the electron beam has a low transparency, the applicable tube diameter and wall thickness are limited in the crosslinking by electron beam irradiation.

Therefore, an object of the present invention is to realize a method for producing a polyolefin heat-shrinkable tube, which is capable of producing a polyolefin heat-shrinkable tube in which crosslinking is carried out in one step and molding, crosslinking and tube expansion can be produced as continuous steps. Another object of the present invention is to realize a method for manufacturing a polyolefin heat-shrinkable tube, which has few restrictions on applicable tube diameter and wall thickness.

[0008]

In the present invention, crosslinking of polyolefin is performed in one step, and molding, crosslinking, and tube expansion can be manufactured as a continuous step, and applicable pipe diameter and wall thickness are less restricted, and polyolefin heat shrinkage is possible. In order to realize the tube manufacturing method, the polyolefin was cross-linked by ultraviolet irradiation after the original tube was molded and before the tube was expanded.

It is convenient to carry out the ultraviolet irradiation at the same temperature as the molding temperature of the original tube, but it may be carried out at a temperature higher than the molding temperature. In the latter case, a heating furnace or the like is provided downstream of the molding step, and ultraviolet irradiation is performed in the heating furnace or downstream of the heating furnace.

In the present invention, the polyolefin includes polyethylene such as low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene and ultra low density polyethylene, as well as ethylene copolymers such as vinyl acetate and alkyl. Acrylate or alkylmethacrylate (eg methyl acrylate, ethyl acrylate, methyl methacrylate, glycidyl methacrylate), copolymer of propylene, butene, etc. with ethylene (may further contain other polymerizing components, eg butadiene), polypropylene, polybutene , Poly
(4-Methylpentene-1) and other α-olefin polymers other than ethylene, grafted modified polyethylene obtained by grafting polyethylene with maleic anhydride, fumaric acid, acrylic acid, methacrylic acid, etc. Substitution of chlorinated polyethylene, polystyrene, etc. Polyolefin is included, and these can be used individually or in combination of 2 or more types. However, the present invention is particularly useful when the polyolefin has a high melting temperature above 140 ° C., such as high density polyethylene, medium density polyethylene, linear low density polyethylene and the like. This is because the decomposition temperature of the cross-linking agent and the photoinitiator is relatively high (usually 140 ° C. or higher), so that even if a molding temperature of 140 ° C. or higher is used, they are not decomposed.

The resin composition capable of being crosslinked by ultraviolet rays is
It contains a polyfunctional monomer as a crosslinking aid and a photoreaction initiator.

Polyfunctional monomers include, for example, trimethylolpropane trimethacrylate, triethylene glycol dimethacrylate, triallyl cyanurate (triall).
ylcyanurate), triallyl isocyanurate (trially
l isocyanurate), diallyl phthalate
late), triallyl trimellitate (triallylyltrimell
Itate), divinylbenzene and the like. These may be used alone or in combination of two or more. The melting point of the polyfunctional compound is preferably lower than the temperature during molding of the resin composition or irradiation of ultraviolet rays, but it may be liquid or solid at room temperature. The suitable amount of the polyfunctional compound added is 0.1 to 10% by weight in the thermoplastic resin.

The photoreaction initiator has a wavelength of 250 to 450 mμ.
It is activated by absorbing the ultraviolet rays, and starts the cross-linking reaction between the polyolefin and the polyfunctional polymer. As the photoinitiator, for example, diethoxyacetophenone,
Acetophenone compounds such as 1-hydroxycyclohexyl phenyl ketone and 2-hydroxycyclohexyl phenyl ketone, benzoin, benzoin isobutyl ether, benzoin compounds such as benzyl dimethyl ketal, benzophenone, methyl benzoylbenzoate, benzophenone compounds such as acrylated benzophenone, Use of thioxanthone compounds such as thioxanthone and 2-isopropylthioxanthone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, benzyl-9,10-phenanthrenequinone, dibenzosuberone and 2-ethylanthraquinone You can You may use it in combination of 2 or more types of photoinitiator. The amount of the photoinitiator added to the resin composition is appropriately in the range of 0.1% by weight to 5% by weight in the resin composition.

The wavelength of the ultraviolet light irradiated for crosslinking is 25
0 to 450 nm is suitable. The irradiation dose is adjusted according to the degree of crosslinking required (the higher the degree of crosslinking, the greater the required irradiation dose). 200 mJ / cm ² or more is usually sufficient. The degree of crosslinking is evaluated by the gel fraction.

After the molding, when the composition is irradiated with ultraviolet rays for cross-linking, it is preferable to keep the temperature above the moldable temperature of the polyolefin composition. For that purpose, for example, a heating furnace or the like can be used. The temperature at the time of UV irradiation is preferably higher from the viewpoint of the crosslinking rate, but it is necessary to maintain the shape of the tubular molded body, and if the transparency of the polyolefin is impaired, the irradiation time will be extended. To determine the temperature.

To expand the pipe diameter, the inside of the softened pipe is usually pressurized with air or the like. In order to determine the outer diameter of the tube, tape, cloth, metal tube, etc. are used as a holding jig. Alternatively, the softened tube is housed in a metal tube,
A method of depressurizing the inside of the metal tube is also used. It is important to cool in a pressurized or depressurized state, and water cooling, air cooling or the like is used for cooling.

The UV-curable polyolefin composition includes an antioxidant, a photoinitiator aid, an adhesion promoter, a thixotropy promoter, a filler, a plasticizer, a lubricant, a processing aid, a non-reactive polymer and a flame retardant. , Flame retardant aids, anti-softening agents, drying agents, dispersants, wetting agents, anti-settling agents, thickeners, color separation preventing agents, antistatic agents, UV absorbers, mildew-proofing agents, rodent-proofing agents, Various additives such as ant agents, fireproofing agents, coloring agents, brightening agents, matting agents, antiblocking agents, and antiskinning agents may be included.

[0018]

In the method of manufacturing the heat shrinkable tube according to the present invention,
After molding a composition comprising a polyolefin, a crosslinking aid, and a photoinitiator into a tube, and then irradiating it with ultraviolet rays, the polyolefin is crosslinked in the presence of the photoinitiator and the crosslinking aid, so that the diameter of the tube can be increased. When cooled as it is, a heat-shrinkable crosslinked polyolefin tube is obtained. Since the ultraviolet irradiation is sufficient for a relatively short time, it can be performed continuously between the molding process and the pipe expanding process.

Examples will be shown below to further explain the present invention. [Example 1] 100 parts by weight of low-density polyethylene having a density of 0.92 and a melt index of 0.3, 1 part by weight of triallyl isocyanurate as a polyfunctional monomer, and 2,2-dimethoxy-2-phenyl as a photoinitiator A composition containing 1 part by weight of acetophenone was extruded from an extruder kept at a temperature of 150 ° C. into a tube having an inner diameter of 3 mm, an outer diameter of 5 mm and a wall thickness of 1 mm, and then a wavelength distribution of 250 to 450 nm at a temperature of 150 ° C. ( 2000mJ of ultraviolet rays with a maximum wavelength of 360nm)
/ Cm ² irradiation to crosslink polyethylene. Further, at a temperature of 150 ° C., air with a pressure of 0.5 kg / mm ² was press-fitted into the tube to expand it to an outer diameter of 10 mm, expand the tube (the outer diameter is regulated by wrapping tape), and cool in a pressurized state. , A heat shrinkable tube was manufactured.

The gel fraction of the resulting heat-shrinkable tube was measured at a temperature of 110 ° C. using xylene as a solvent.
It was 2%. When heated at 200 ° C. for 2 minutes, the heat shrinkability was 90%, and the shrinkage was almost to the original outer diameter.

Example 2 100 parts by weight of an ethylene-vinyl acetate copolymer containing 28 mol% of vinyl acetate component, 2 parts by weight of triallyl isocyanurate as a polyfunctional monomer, and 4-chlorobenzophenone as a photoinitiator. The composition containing 0.5 part by weight was extruded, cross-linked and expanded in the same manner as in Example 1 except that the temperature was 120 ° C. to produce a heat-shrinkable tube.

The gel fraction of the resulting heat-shrinkable tube was 43.
%Met. The heat shrinkability was 93% when heated to 200 ° C. for 2 minutes.

Comparative Example When triallyl isocyanurate was omitted in Example 1 or when 4-chlorobenzophenone was omitted in Example 1, in both cases, when the same temperature was maintained after extrusion molding, The molded product hangs down by its own weight, and the original tube of the desired shape cannot be obtained.

[0024]

In the present invention, since UV crosslinking is used,
Since the crosslinking can be performed in one step, and the molding, crosslinking, and tube expanding steps can be performed continuously, a crosslinked polyolefin heat-shrinkable tube can be efficiently produced.
Further, the method for producing a polyolefin heat-shrinkable tube of the present invention has few restrictions on applicable tube diameter and wall thickness.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location B29L 23:22 4F C08L 23:00 7107-4J (72) Inventor Tadashi Ikeda Hitachi City, Ibaraki Japan 5-1-1 Takamachi, Electric Cable Research Laboratory, Hitachi Cable Ltd.

Claims (1)

Claim: What is claimed is: 1. A composition comprising a polyolefin is molded into a tubular shape, the polyolefin is crosslinked, and the diameter of the tubular molded article is expanded by a pressure difference at a temperature not lower than the moldable temperature of the composition. While maintaining the diameter, cooling to a temperature lower than the moldable temperature to produce a heat-shrinkable tube, wherein the composition contains a crosslinking aid and a photoreaction initiator, and the crosslinking is A method for producing a heat-shrinkable tube, which is performed by irradiating the tubular molded product with ultraviolet light at a temperature not lower than a moldable temperature.