JPS5962106A - Thermally contractive substance - Google Patents

Abstract

PURPOSE:To provide the titled substance for covering steel pipe which is caused to positively adhere to the surface of a steel pipe without hardly causing cathode peeling even if the steel pipe is processed by electrical anticorrosion treatment by such an arrangement wherein a layer of thermosetting type adhesive is formed on the surface of polyolefine family thermal contractive substrate through a layer of hotmelt adhesive. CONSTITUTION:On the surface of a tubelike thermal contractive substrate made of polyolefine family material such as PE, PP, etc., a layer of hotmelt adhesive such as copolymer of ethylene-vinyl acetate, polyamide resin, etc. is provided. On the layer of this adhesive, a layer of thermosetting type adhesive such as epoxy resin, unsaturated polyester resin, etc. is formed and the titled substance is thus obtained. In this case, it is permissible to add, to said hotmelt adhesive, a kind of wax preferably at the ratio of lees than 80 part for 100 part (weight) of polymer, and adhesion giving resin at the ratio of less than 100 part.

Description

[Detailed description of the invention] The present invention relates to heat-shrinkable articles.

A heat-shrinkable product in which a hot-melt adhesive layer mainly composed of ethylene-vinyl acetate copolymer, polyamide resin, etc. is formed on the inner circumferential surface of a heat-shrinkable polyethylene chain to protect pipelines for fluid transportation. For example, it may be heat-shrinked on a welded part of a steel pipe to provide corrosion protection.

Incidentally, it is common practice to conduct cathodic protection by passing a weak current through pipelines. However, the anti-corrosion coating layer formed by heat shrinking of the heat-shrinkable article has a problem in that hydrogen gas generated by a weak electric current applied to the pipeline for cathodic protection is likely to separate (cathode peeling). . This tendency is further promoted when a through-hole reaching the surface of the steel pipe is formed in the anticorrosive coating layer, as the current is concentrated near the through-hole, and the cathode peeling region expands approximately concentrically with the through-hole.

Although various attempts have been made to prevent such cathode peeling, no practical means have yet been provided.

In order to solve the above-mentioned problems of the prior art, the present inventors have conducted various studies and found that thermosetting adhesives such as epoxy resins and polyester resins have excellent resistance to cathodic peeling. Although it does not have sufficient adhesion to a heat-shrinkable base material made of polyolefin material, it was discovered that by interposing a hot melt adhesive, the two could be firmly bonded, and this led to the completion of the present invention. 0 That is, the heat-shrinkable article according to the present invention is one in which a thermosetting adhesive layer is formed on the surface of a heat-shrinkable base material made of a polyolefin material via a hot melt adhesive layer. The heat-shrinkable base material in the present invention is made of a polyolefin material such as polyethylene or polypropylene, which is formed into a tube shape, a notebook shape, etc., and then crosslinked as necessary, and then hot stretched in a predetermined direction. Further, if desired, additives such as anti-aging agents, fillers, pigments, ultraviolet absorbers, flame retardants, antistatic agents, etc. may be added in appropriate amounts.

On the surface of this heat-shrinkable base material, hot-melt adhesives containing polymers such as ethylene-vinyl acetate copolymer, polyamide resin, ethylene-acrylic acid copolymer, and ethylene-ethyl acrylate copolymer are applied. layers are provided.

These hot melt adhesives include waxes such as rough-in wax, micro wax, and low molecular weight polyethylene wax, aliphatic petroleum resins, aromatic petroleum resins, copolymer petroleum resins, coumaron indene resins, and aliphatic petroleum resins. About 80 parts by weight of O waxes, which can be blended with tackifying resins such as cyclic saturated petroleum resins, are added to 100 parts by weight of the polymer.
The tackifying resin is usually used in an amount of about 100 parts by weight or less per 100 parts by weight of the polymer.

In the present invention, a thermosetting adhesive layer whose main component is a thermosetting resin having adhesive properties such as epoxy resin, unsaturated polyester resin, or phenol resin is further formed on the hot melt adhesive layer.

Although this thermosetting adhesive has excellent resistance to cathodic peeling, its adhesion to a heat-shrinkable base material made of a polyolefin material is not necessarily sufficient. By disposing the adhesive layer at a distance of λ between the two, a practical heat-shrinkable article in which the two are firmly bonded can be obtained.

The thermosetting adhesive is preferably formed on the hot melt adhesive layer in a B-stage state, but it can also be formed in other ways, for example, by encapsulating at least 1% of the base agent or curing agent.

The present invention is configured as described above, and since the thermosetting adhesive is brought into close contact with the steel pipe, it is difficult to cause cathode peeling even when cathodic protection is applied, and the corrosion protection function for the steel pipe can be maintained for a long period of time.

The present invention will be explained below using examples.

Example A hot-melt adhesive layer with a thickness of l myx was formed on the inner peripheral surface of a heat-shrinkable tube made of cross-linked polyethylene with an inner diameter of 80 mm, a wall thickness of 1.2 fi, a length of 450 mm, and a heat shrinkage rate of 50%. do. As a hot melt adhesive, an aliphatic cyclic saturated petroleum resin (softening point 10 (
1°C) 20 parts and low molecular weight polyethylene wax, wax (
Next, epoxy resin powder in a B-stage state (manufactured by Nitto Denko Corporation, trade name Nidotsu Kuuder NP2O0) was dissolved in Setone, and then applied onto the hot melt adhesive layer. An epoxy resin powder was applied in an amount of 809 fifr to form an epoxy resin thermosetting adhesive layer to obtain a heat-shrinkable tube.

In order to determine the resistance of this heat-shrinkable tube to cathode peeling, a test was conducted in the following manner.

Two steel pipes (50A) each having a length of 500H are prepared, and the heat-shrinkable tubes are heated with a burner to heat-shrink the tubes and bring them into close contact with the steel pipes.

Next, one through hole with a diameter of 10 mm reaching the surface of the steel pipe was made in the anticorrosive coating layer formed on the steel pipe using a heat-shrinkable cheapo, and a cathodic peel test was performed according to ASTM (2005)-42. The area of the scrotum was observed on the outer periphery of the through hole. In addition, the test conditions are the control gold electrode-i
, sv, temperature was 20° C., and period was 30 days.

For comparison, the heat-shrinkable tube with only the hot melt adhesive layer formed on the inner circumferential surface was subjected to the same test, and the results were as follows.
The cathode peeling area was large with a radius of about 30ag, and the resistance to cathode peeling was poor.

patent applicant Nitto Electric Industry Co., Ltd.

Claims (1)

[Claims] On the surface of a heat-shrinkable base material made of polyolefin material,
A heat-shrinkable article in which a thermosetting adhesive layer is formed through a hot melt adhesive layer.