Gaseous diffusion resistant tube

[54] GASEOUS DIFFUSION RESISTANT TUBE

[75] Inventor: Jerker Skarelius, Virsbo, Sweden

[73] Assignee: Wirsbo Bruks Aktiebolag, Sweden

[21] Appl. No.: 579,552

[22] Filed: Feb. 13,1984

Related U.S. Application Data

[63] Continuation-in-part of Ser. No. 208,585, Nov. 20, 1980, abandoned.

[30] Foreign Application Priority Data

Nov. 28, 1979 [GB] United Kingdom 7941044

[51] Int. CM F16L 11/00

[52] U.S. CI 138/103; 138/137;

138/140; 138/178; 428/36

[58] Field of Search 138/128, 137, 140, 141,

138/172, 103; 428/35, 36

[56] References Cited

U.S. PATENT DOCUMENTS

2,800,145 7/1957 Peierls et al 138/137 X

2,971,538 2/.1961 Brumbach 138/137 X

3,184,358 5/1965 Utz 138/137 X

3,956,544 5/1976 Harrington 138/137 X

4,035,534 7/1977 Nyberg 138/137 X

4,044,187 8/1977 Kremkau 138/137 X

4,178,401 12/1979 Neinberg et al 138/137 X

4,244,914 1/1981 Ranalli et al 138/137 X

Primary Examiner—James E. Bryant, III

Attorney, Agent, or Firm—Ostrolenk, Faber, Gerb &

Soffen

[57] ABSTRACT

A gaseous resistant tube comprising an inner core of a heat resistant polymeric material, typically cross-linked polyethylene, protected outer layer of impact resistant material and an intermediate layer of non-metalliferous gaseous resistant material, wherein the intermediate layer is bonded to at least one of the inner core and the outer layer by bonding material compatible with each of the materials to be bonded and is sufficiently elastic that it will not delaminate or rupture either itself or the adjoining layer under heat cycling conditions. In a preferred embodiment of the invention, the bonding material is preferably a material different from the layer to which it bonds.

1 Claim, 3 Drawing Figures

GASEOUS DIFFUSION RESISTANT TUBE

DESCRIPTION

This application in a continuation in part of U.S. Ser. 5 No. 208,585 Jerker Skarelius, filed on Nov. 20th., 1980, now abandoned.

British Patent Specification No. 1,158,011 describes and claims a method of forming a cross-linked material which comprises subjecting a cross-linkable material to a plurality of instanteous compressions at a pressure greater than 2,000 atmospheres to raise the temperature of the material to a level just below the threshold which crosslinking of the material takes place, forming or J5 shaping of the material and thereafter causing or allowing crosslinking of the material to occur. Material produced in accordance with Patent No. 1,158,011 has been found to be an excellent material for use in the piping of hot water and materials generally having a temperature 20 not above 120° C. and not being a solvent for the particular crosslinked polyolefin. In particular, cross-linked polyethylenic material formed in accordance with Patent No. 1,158,011 has been found excellent in use for a large number of years. 25

With the advent of more rigorous operating conditions, a demand has risen for a gaseous diffusion resistant plastics tube otherwise having the properties of the crosslinked material produced in accordance with British Patent No. 1,158,011 referred to above. Many pro- 30 posals have been put forward and typical of them are proposals to include a layer of metal foil bonded to the crosslinked polyolefinic material either on a surface thereof or bonded as an intermediate layer therein. This solution suffers from the disadvantage that while the 35 initial construction works well, continued heat cycling produces eventual delamination of the foil layer from the adjacent layers within the tube and/or produces cracks or splits. The effect of delamination and/or cracks or splits is to allow once again the passage of gas 40 through the material via the breaks and/or the splits in the material itself. This has been a problem that has been long known in the construction of, for example, telephone cables and many attempts have been made to overcome it. The solutions for telephone cables are not, 45 however, compatible in this particular case, since the continual heat cycling of the tube used in a heating system whereby the temperature of the tube is continuously alternating between hot and cold, (e.g.: 5° C. to 95° C.) produces a more rigorous environment. The 50 basic problem is that the differential expansion between the core material of the tube and the material constituting the gaseous diffusion resistant layer has to be such that the integrity of each and the bonding of one to the other is maintained. 55

U.S. Pat. No. 3,561,493 describes a composite tube comprising two or more layers in which each discrete layer is conjoined with its neighbour by means of a jointing layer composed by mixtures of the two constituent plastics which separately form the discrete layers 60 to be conjoined. While such a construction may be acceptable in terms of mechanical strength and ageing resistance, it is not per se suitable in circumstances where repeated temperature cyeling occurs since shear forces are generated which lead to delamination of such 65 composite tubes.

U.S. Pat. No. 3,184,358 also relates to the production of laminated tubing; and proposes a method for increas

ing the bond between co-extruded thermoplastic layers, eg: polyethylene and nylon.

In one example of this method linear polyethylene and linear nylon are used. These polymeric linear materials are provided with a number of substitutable hydrogen atoms by way of available cross-links at their surface.

Polystyrene gas is interposed between the materials to provide a molecular cross-link via the styrene molecules. This provides a good bond under heat stable conditions. However, under heat cycling the differential coefficience of linear expansion of the materials leads to deformations and cracks over the longer term, and hence, oxygen penetration.

This process, in addition to failing to provide a product which is heat-cycling stable, is also chemically unsuited to use with fully cross linked materials, since such materials have no sites for styrene substitution.

Accordingly, a new approach to the provision of heat-cycling stable gaseous diffusion resistant tubes was required. Another possible approach to the manufacture of polymeric laminates lies in U.S. Pat. No. 4,044,187. This relates to the production of gaseous diffusion resistant tubes comprising a core of a material which is fully cross-linked, and a second and, optionally, a third material which is partially cross-linked. This process requires substrate irradiation, laminate formation, and reirradiation of the so formed laminate, and hence is not suitable to co-extruded products.

The irradiation provides a good cross-linking, but because cross-linking radically effects linear expansion in response to heat and because the material must be differentially cross-linked, the product is only suitable for its intended use as a food container. If subjected to heat cycling, some delamination must occur, particularly if placed under internal pressure at a temperature cycling hourly or longer between 5° to 95° C. Thus, the approach of this application is of no help in the production of heat-cycling stable thermoplastic tubes.

We have now found that an improved product of this type can be produced by using as a core, a fully cured or cross-linked material, and subsequent bonding layers which substantially eliminate discontinuities therein; such for example as may occur with the inclusion of small air bubbles trapped between the intermediate layer and the inner or outer layer.

According to the present invention, there is provided a dimensionally stable gaseous resistant tube comprising a liquid resistant inner core of a heat resistant fully cured or cross-linked polymeric material, a protective outer layer of an impact resistant polymeric material, both being formed of materials having substantially similar coefficients of linear expansion, and an intermediate layer of a non-metalliferous gaseous resistant material interposed therebetween and adhering thereto, wherein the intermediate layer adheres directly or indirectly to the inner core and to the outer layer and is sufficiently elastic such that it will not delaminate or rupture either itself or the adjoining layer under heat cycling conditions.

The intermediate layer may be any gaseous resistant plastics material bondable with both the inner core and the outer layer. The intermediate layer may be bonded by bonding means which may be a priming layer and/or adhesive layer to assist bonding. The bonding means is preferably a priming layer and/or adhesive layer dissimilar to the material to be bonded. Where both a priming layer and an adhesive is employed at least one