GB1603488A - Method of making laminated recoverable articles - Google Patents

Description

(54) METHOD OF MAKING LAMINATED RECOVERABLE ARTICLES (71) We, RAYCHEM CORPORATION, A Corporation organised according to the laws of the State of California, United States of America, of 300 Constitution Drive, Menlo Park, California 94025, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the preparation of recoverable hollow articles comprising an inner member which is composed of an elastomeric material and which is elastically deformed from its natural dimensions, and an outer member which maintains the inner member in its deformed state.

U.S. Patent No. 4,035,534 (Nyberg, assigned to Raychem Corporation) and the corresponding British Patent No. 1,440,254 describe heat-recoverable hollow articles which comprise a first member which is composed of an elastomeric material and is deformed from its natural dimensions and a second member which maintains the first member in its deformed state at ambient temperatures but is composed of a material which on heating is sufficiently weakened, without flowing, to allow recovery of the elastomeric member. The article may be for example in the form of a sleeve comprising a first tubular elastomeric member which is secured by an adhesive to a second tubular member, which second member is optionally heat-shrinkable. In the preferred method of making such articles the inner member and the restraining means are bonded together with the inner member unstretched, the laminar article is heated and radially expanded, and the article is cooled in the expanded condition. Alternatively the inner member can be expanded and then bonded to the restraining member, but it is stated that "such a process is often more difficult".

French Patent Application No. 7,618,236 and the corresponding U.S. Patent No.

4,070,746 (Evans et al to Raychem) and Canadian Patent No. 1078477 describe recoverable hollow articles comprising an inner member, preferably of an elastomeric material, which is held in a radially extended condition by an outer restraining means, the inner member and the restraining means being secured together by means of a bond which can be broken to allow the inner member to shrink radially. Preferably the restraining means is capable of being peeled away from the inner member; the peeling process can be assisted by applying a solvent to the bond line. The restraining means may be composed of a frangible material which can be broken by means of a sharp blow, for example a rigid thermoplastic such as polyvinyl chloride. Alternatively the restraining means can have weakened portion such as score lines which enable it to be peeled away from the inner member, as for example a metallic tube which is spirally scored or serrated. The preferred method of making such articles is to form a restraining means of the desired size; to coat the inner surface of the restraining means and the outer surface of the inner member with a suitable adhesive; to expand the inner member into contact with the restraining means; to hold the inner member in contact with the restraining means for a time sufficient for a bond to be formed; and finally to remove the expansion forces.

When making articles as described above, the bond formed between the inner member and the restraining means must be strong enough and uniform enough to prevent premature recovery of the inner member. On the other hand, when the restraining means is to be removed during use of the article, the stronger the bond, the more difficult it is to remove the restraining means.

We have now discovered an improved method of making a recoverable hollow article comprising (1) a hollow inner member which is composed of an elastomeric material and which is elastically radially extended from its natural dimensions and (2) a hollow outer restraining means whose inner surface is secured to the outer surface of said inner member through a layer of a hot-melt adhesive and which thus maintains said member in said radially extended condition, which method comprises (1) preparing an assembly comprising a hollow restraining means and, within said restraining means but not contacting said restraining means, a heated, hollow inner member composed of an elastomeric material and having a coating of a hot-melt adhesive on the outer surface thereof, said hot-melt adhesive being at a temperature above its bonding temperature; (2) subjecting said hollow member to radial expansion forces so that said hot-melt adhesive contacts the inner surface of said restraining means and under conditions such that the pressure between the hollow member and the restraining means is in the range of from P1 to P2, where P1 is the pressure which can be generated by increasing the radius of the restraining means by 5% by an expansion of the hollow member and P2 is the maximum pressure which can be generated by increasing the radius of the restraining means by an expansion of the hollow member within the elastic limit of the exterior of the restraining means; (3) cooling said assembly to reduce said hot-melt adhesive below its bonding temperature; and (4) removing said expansion forces.

In a preferred embodiment of the invention, the restraining means is freely expanded (ie.

without any external confinement, eg. in air) by an amount between 5% and an amount such that the exterior of the restraining means is not stretched beyond its elastic limit.

However, the invention includes processes in which an equivalent pressure is exerted on the bond line between the restraining means and the inner member by any means. For example the restraining means can be surrounded by a shell against which it is pressed by the expansion forces.

The restraining means used in the process of the invention is preferably composed of an organic polymeric material such that the restraining means is capable of a limited degree of elastic radial expansion, for example at last 5% at 210C. On the other hand, if it is too elastic, it will not serve its function of maintaining the inner sleeve in a radially extended condition. Preferably the material has an elastic limit at 21"C between 5 and 60%, particularly between 15 and 50%, especially between 15 and 40%. It is important that the elastic limit of the exterior of the restraining means should not be exceeded in the process.

Therefore, when the restraining means is expanded in the process, as is preferred, the expansion thereof is preferably not more than 80% of the expansion at the elastic limit at 21"C, and it is preferably 10 to 75% of the expansion at the elastic limit at 21"C. For preferred restraints the expansion ratio will be 1.05 to 1.4, particularly 1.05 to 1.20.

It will be noted that reference is made herein to the elastic limit of the exterior of the restraining means. Especially when the restraining means is composed of a thermoplastic material, as is preferred, the elastic limit of the material decreases rapidly with increasing temperature. It is, of course, inevitable that the interior of the restraining means will be heated by heat transfer from the inner member and the adhesive, and as a result the interior of the restraining means may well undergo plastic deformation. In order to prevent plastic deformation of the exterior of the restraining means, it is possible to take positive steps to cool the outside of the restraining means throughout the expansion step, but satisfactory temperature control can usually be achieved by expanding the assembly in air and quenching the assembly, eg. by putting it into a bath of water or other liquid, as soon as expansion is complete.

It is desirable that the inner surface of the restraining member should also carry a layer of the hot melt adhesive, since this improves bonding between the inner member and the restraining means.

The expansion forces which are used to expand the inner member can be generated in any convenient way, for example by means of an expansible mandrel or hydraulically.

For further details of suitable materials for the inner member, the hot-melt adhesive and the restraining means, and of the dimensions, configurations, uses and other details of the articles which can be prepared by the process of this invention, reference should be made to the patent specifications referred to herein.

The invention is illustrated by the following examples, in which parts, percentages and ratios are by weight.

EXAMPLE 1 Part A The ingredients shown in Table A were blended together in a Banbury mixer.

TABLE A Ingredient Parts Polychloroprene (Neoprene TRT) 100 Antioxidant (Agerite Stalite S) 2 Magnesium oxide (Maglite D) 2 Carbon black (Vulcan 3) 5 Alumina trihydrate (Hydral 705) 10 Silica (HiSil 233) 15 Antimony trioxide 15 Stearic Acid 0.5 Plasticiser (Flexol TOF) 4 ZnO (Kadox 15) 5 Curing Agent (Thiate E) 0.75 Curing Agent (Epon 828) 1 "Maglite", "Vulcan", "Thiate" and "HiSil" are trade marks.

The blend was molded at about 175"C for about 10 minutes into an elastomeric tube having a thickness of about 0.125 inch, an internal diameter of about 0.75 inch and a length of about 17 inch (Tube A).

Part B The ingredients shown in Table B were blended together in a Banbury mixer TABLE B Ingredient Parts Block copolymer of polytetramethylene ether an polytetramethylene terephthalate (Hytrel 4056) 70 Ethylene/vinyl acetate (18%) copolymer 30 (Alathon 3170) Antioxidant (Irganox 1010) 0.1 Chalk filler (Vicron 15-15) 125 Pigment (Wilson 50-OR-18) 2.5 "Irganox" is a trade mark The blend was extruded into a tube having a thickness of about 0.085 inch t 0.005 inch, an internal diameter of about 1.5 inch + .020 inch, and cut into lengths of about 18 inch (Tube B).

Part C The outer surface of Tube A was coated with a 1% solution of a 60/40 mixture of Hytrel 4056 and Dyvax 772 in methylene chloride; "Dyvax" is a trade mark. The inner surface of Tube B was abraded by passing the tube over a rotary abrasion wheel and then coated with a 10% solution of a 60/40 mixture of Hytrel 4056 and Dyvax 772 in methylene chloride.

(Dyvax 772 is a block copolymer which is substantially the same as Hytrel 4056 but of lower melting point). After evaporation of all the methylene chloride, Tube A was heated to about 165"C and immediately placed over an expansible mandrel. Without delay, Tube B, which was not preheated, was placed symmetrically over Tube A. The mandrel was then expanded until Tube A had first contacted Tube B and then expanded Tube B by 5-10%.

The whole assembly was then rapidly placed into water at about 20"C, where it was left for about 4 minutes. After the assembly had been removed from the water, the mandrel was contracted and withdrawn. Tube A and Tube B contracted until Tube B had returned to about its original configuration.

Part D Longitudinal parallel score lines about 0.008 inch deep and about 1/2 inch apart were then made with a razor blade on the outer surface of Tube B, the score lines running from end to end, as shown in Figure 1 of British Patent Specification No. 2018527A (corresponding to German Offenlegungsschrift 2914562).

Part E The article thus made was stored until it was required, end plugs being inserted to ensure that Tube A did not recover prematurely. When the time came to use the article, the end plugs were removed, and the article crushed, e.g. between the operator's hands or between his foot and the floor, to open up the score lines. The article was then placed over one of two mine cables which were to be spliced. The cables were spliced and the article positioned around the splice. A suitable solvent, i.e. a fluid which will substantially weaken the adhesive bond and which may be, but is not necessarily, a solvent for the adhesive, e.g.

1,1,1-trichloroethane, was applied to the bond line at one end of the article. Tube B was grasped by the operator in the region to which solvent had been applied and was pulled away from the splice. Tube B tore along the adjacent score lines, so that a longitudinal strip of Tube B could be peeled away; further solvent was applied to help in the peeling process.

Successive strips of Tube B were removed in the same way until Tube A had completely recovered and Tube B had been completely removed.

EXAMPLE 2 Parts A, B and C The procedure of Parts A, B and C of Example 1 was followed to prepare an article comprising expanded Tube A secured to Tube B.

Part D Two parallel, longitudinal score lines, about 0.5 inch apart and each about 1 inch long, were made with a razor blade on the outer surface of Tube B at one end of the article, as shown in Figure 7 of British Patent Specification No. 2018527A (corresponding to German Offenlegungsschrift 2914562). The score lines were about 0.050 inch deep.

Part E The article thus made was stored until it was required, end plugs being inserted to ensure that Tube A did not recover. When the time came to use the article, the end plugs were removed, and the end of the article bearing the score lines was crushed to open up the score lines. The article was then placed over one of two mine cables which were to be spliced. The cables were spliced and the article positioned around the splice. The spliced cables and the article were then placed so that the article was at an angle of 15-30 to the horizontal, with the score lines at the top. A solvent was applied to the bond line in the area of the score lines and the region of Tube B defined by the score lines was grasped by the operator and pulled away from the splice, thus creating a pocket into which further solvent was placed.

The solvent penetrated between Tube A and Tube B, and this process was accelerated by the operator kneading the article between his hands. After about 1.5 to 2.5 minutes, the penetration of the solvent had weakened the bond between Tubes A and B sufficiently to cause separation of Tube A from Tube B so that it recovered around the splice. Tube B was then scored from end to end with a razor blade or knife; the score line was opened up by crushing the tube along the score line; and the tube ripped open with a knife or by hand.

The articles prepared in Steps A to D of Examples 1 and 2 had the following properties.

Tensile stress at 100% elongation of Tube A 175-250 psi Peel Strength of Bond between Tubes A and B 7-12 pli 2% Secant Modulus of Tube B at 21"C 20,000 psi Ultimate Elongation of Tube B at 21"C 79-85% % Torn Depth of Tube B 50-60% EXAMPLE 3 The procedure of Example 1 was followed except that Tube A was made from the ingredients set out in Table C below.

TABLE C Ingredient Parts Polychloroprene (Neoprene GW) 100 Magnesium Oxide (Maglite D) 1.5 Silica (Hi Sil 233) 35 Silane Al89 0.5 Stearic acid 0.6 Antioxidant (Octamine) 0.7 Antioxidant (Agerite DPPD) 1.3 Carbon Black (Thermax) 5 Polyethylene oxide glycol (Carbowax 4000) 3 Tricresyl phosphate (plasticiser) 12.5 ZnO (Kadox 15) 5 "Thermax", "Octamine" and "Carbowax" are trade marks.

WHAT WE CLAIM IS: 1. A method of making a recoverable hollow article comprising (1) a hollow inner member whch is composed of an elastomeric material and which is elastically radially extended from its natural dimensions and (2) a hollow outer restraining means whose inner surface is secured to the outer surface of said inner member through a layer of a hot-melt adhesive and which thus maintains said member in said radially extended condition, which method comprises (1) prepanng an assembly comprising a hollow restraining means and, within said restraining means but not contacting said restraining means, a heated, hollow inner member composed of an elastomeric material and having a coating of a hot-melt adhesive on the outer surface thereof, said hot-melt adhesive being at a temperature above its bonding temperature; (2) subjecting said hollow member to radial expansion forces so that said hot-melt adhesive contacts the inner surface of said restraining means and under conditions such that the pressure between the hollow member and the restraining means is in the range of from P1 to P2, where P1 is the pressure which can be generated by increasing the radius of the restraining means by 5% by an expansion of the hollow member and P2 is the maximum pressure which can be generated by increasing the radius of the restraining means by an

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. Tensile stress at 100% elongation of Tube A 175-250 psi Peel Strength of Bond between Tubes A and B 7-12 pli 2% Secant Modulus of Tube B at 21"C 20,000 psi Ultimate Elongation of Tube B at 21"C 79-85% % Torn Depth of Tube B 50-60% EXAMPLE 3 The procedure of Example 1 was followed except that Tube A was made from the ingredients set out in Table C below. TABLE C Ingredient Parts Polychloroprene (Neoprene GW) 100 Magnesium Oxide (Maglite D) 1.5 Silica (Hi Sil 233) 35 Silane Al89 0.5 Stearic acid 0.6 Antioxidant (Octamine) 0.7 Antioxidant (Agerite DPPD) 1.3 Carbon Black (Thermax) 5 Polyethylene oxide glycol (Carbowax 4000) 3 Tricresyl phosphate (plasticiser) 12.5 ZnO (Kadox 15) 5 "Thermax", "Octamine" and "Carbowax" are trade marks. WHAT WE CLAIM IS:

1. A method of making a recoverable hollow article comprising (1) a hollow inner member whch is composed of an elastomeric material and which is elastically radially extended from its natural dimensions and (2) a hollow outer restraining means whose inner surface is secured to the outer surface of said inner member through a layer of a hot-melt adhesive and which thus maintains said member in said radially extended condition, which method comprises (1) prepanng an assembly comprising a hollow restraining means and, within said restraining means but not contacting said restraining means, a heated, hollow inner member composed of an elastomeric material and having a coating of a hot-melt adhesive on the outer surface thereof, said hot-melt adhesive being at a temperature above its bonding temperature; (2) subjecting said hollow member to radial expansion forces so that said hot-melt adhesive contacts the inner surface of said restraining means and under conditions such that the pressure between the hollow member and the restraining means is in the range of from P1 to P2, where P1 is the pressure which can be generated by increasing the radius of the restraining means by 5% by an expansion of the hollow member and P2 is the maximum pressure which can be generated by increasing the radius of the restraining means by an

expansion of the hollow member within the elastic limit of the exterior of the restraining means; (3) cooling said assembly to reduce said hot-melt adhesive below its bonding temperature; and (4) removing said expansion forces.

2. A method according to Claim 1 wherein said restraining means is freely expanded by an amount between 5% and an amount such that the exterior of the restraining means is stretched within its elastic limit.

3. A method according to Claim 2 wherein said restraining means is expanded by 10 to 75% of the expansion at the elastic limit thereof at 21"C.

4. A method according to Claim 2 or Claim 3 wherein the expansion ratio of said restraining means is 1.05 to 1.20.

5. A method according to any one of Claims 1 to 4, wherein said restraining means is composed of a thermoplastic organic polymeric material having an elastic limit at 210C of 5 to 60%.

6. A method according to Claim 5 wherein said polymeric material has an elastic limit at 21"C of 15 to 50%.

7. A method according to any one of Claims 1 to 6, wherein said assembly is quenched by putting it into a bath of liquid as soon as expansion has been completed.

8. A method according to Claim 1 carried out substantially as described in any one of the Examples.

9. A recoverable hollow article made by a method according to any one of Claims 1 to 8.