CA1262887A - Extrusion, deformation and irradiation of crosslinkable polymer and rubber composition laminate - Google Patents

Abstract

ABSTRACT MPo767 Abridgement A process for manufacturing a sealant coated heat recoverable polymeric article is disclosed. The process includes the steps of extruding at least two different poly-meric materials to form a unitary shaped article and thereafter exposing the shaped article to a source of radiation to thereby cross-link one of the polymeric materials and convert the other polymeric material into a tacky sealant. The article may be rendered dimensionally heat recoverable by either: a) deforming the article into a different shape at a temperature below the crystalline melt temperature of the cross-linkable material and then exposing the deformed article to a source of radiation or alter-natively, b) subsequent to an irradiation step, heating the article to about the crystalline melt temperature of the cross-linked material, distorting the article, and then cooling the article while maintaining it in the distorted shape to a temperature below the crystalline melt tem-perature; thereby by either method rendering the cross-linked portion of the article recoverable toward its original shape upon subsequent heating.

Description

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The present invention relates to a process for manufac-turing sealant coated articles. More partlcularly, the present invention relates to a process for manufacturing a heat recover-able polymeric article, a portion of which article possesses sealant properties.

Heat shrinkable tubing with a sealant coating on its interlor surface has been used for many years in a variety of commercial applications. For example, sealant line heat shrink-able tubing is used to insulate and seal electrical connectionsand to environmentally protect welded joints in pipe lines. Such sealant lined heat recoverable tubings are described in Wetmore, U.S. Patent Number 3,297,819. Similarly, sealant coated, longi-tudinally heat shrinkable tape has been applied to metallic pipes, pipe ~oints and the like to provide corrosion protection.

Because of their relatively low viscosities and gener-ally high tack, conventional sealant compositions do not readily lend themselves to processing in thermoplastic extrusion equip-ment. Heretofore, the best known process for manufacturing lengths of internally sealant coated heat shrlnkable tubing entailed a costly separate coating step, which frequently had to be manually carried out on a discrete piece basis. In this prior art process, flexible, heat shrinkabls tubing such as that described in Currie, U.S. Patent Number 2,027,962 and in Cook et al., U.S. Patent Number 3~Q86,242 is internally coated with a sealant applied with a brush or swab. Prior to application, the sealant composition is typically thinned with a solvent or heated to render it more fluid.
In contrast to the difficult problems encountered when coating a sealant material on the interior surface of a tubular article, a sealant layer can be applied to one surface of a lon-gitudinally heat recoverable backing tape with relative ease.
However, such a heat shrinkable tape fabrication process is not particularly efficient as it requires at least two relatively ~ Z~ ~8 ~7 slow speed s-teps, one to produce the backlng, and another sepa-rate step carried out subsequent to cross-linking the backing, to apply the coating thereto, again by swabbing or brushing.

The present invention provides novel and an efficient process for manu~acturing a sealant coated, dimensionally heat recoverable article.

The present invention also provides a unitary shaped article which is dimensionally heat recoverable and possesses a tacky, sealant material uniformly disposed along its extruded length.

The present invention again provides a melt processable polymeric composition which, when sub;ected to radiation, is readlly converted into an effective tacky sealant composition.

The present invention overcomes many of the disadvan-tages associated with sealant coated, dimensionally heat recover-able articles and the processes for their manufacture as known inthe prior art. It does so by providing a novel process for manu-facturing such articles which includes the steps of extruding a first radiation cross-linkable polymer composition and also extrudlng (preferably substantially slmultaneously) a second radiation convertible polymer composition to afford a unitary shaped article having a first configuration in which the article possesses portions formed respectively of the first and second compositions; and then exposing the shaped article to a source of radiation to initiate the formation of chemical bonds between adjacent polymer chains in the first composition, and to induce chemical change in the second composition, thereby transforming said second composition from a melt ~e.g. extrusion) processable composition to a tacky, sealant composition. The article in said first configuration may be rendered dimensionally heat recover-able by the step of distorting it at a temperature below thecrystalline melt temperature of the cross-linkable composition , ~ , ~ ~ 2~ ~7 into a second conEiguration either prior to the step of exposing the article to a source of radiatlon or alternatively~ subsequent to the irradiation step, by the steps of heating the artlcle to about the crystalline melt temperature of the first composltion;
distorting the article into a stretched second configuration; and then cooling the article while , . ..p .

~26~138~7 main-taining it in the second configuration thereby providing an ar-ticle recoverable to or towards its first configuration upon subsequen-t heating.

Thus, in one aspect thereof the present invention pro-vides a process for manufacturing a sealant coated dimensionally heat-recoverable laminated sheet comprising the steps of: select~
ing a first polymer composition comprising a radiation cross-linkable polymer; forming a second polymer composition by admix-ing a thermoplastic component and a rubber component in propor-tions such that the composition comprises 30 to 95% of the ther-moplastic component and 5 to 70% of the rubber component, said second composition being radiation convertible to a sealant com-position; extruding said first and second polymer compositions to form a unitary laminated sheet possessing two layers formed respectively of said first and second polymer compositions and being in a first configuration; deforming said sheet at a temper-ature below the crystalline melt temperature of said first compo-sition into a second configuration; and exposing said sheet to a source of radiation to initiate the formation of chemical bonds between ad;acent polymer chains in said first composition, and to induce chemical change in said second composition, thersby con-verting said second composition from a melt processable composi-tion to a sealant composition and rendering said first composi-tion recoverable towards said first configuration upon subsequentheating. Suitably the laminated sheet is stretched along its longitudinal axis.

In a further aspect thereof the present invention pro-30 ; vides a process for manufacturing a sealant coated, dimensionally heat-recoverable dual layer tubular article comprising the steps of: selecting a first polymer composition comprising a radiation cross-linkable polymer; forming a second polymer composition by I admixing a thermoplastic component and a rubber component in pro-portions such that the composition comprises 30 to 95% of the thermoplastic component and 5 to 70% of the rubber cornponent, ~Z62887 said second composition being radiation convertible to a sealant composition; extruding said first and second polymer compositions to form a unitary dual layer tubular article possessing an outer tubular layer formed from said first radiation cross-linkable polymer composition disposed concentrically around an inner tubu-lar layer formed from said second radiation convertible polymer composition and being in a first configuration; e~posing said article to a source of radiation to initiate the formation of chemical bonds between adjacent polymer chains in said first com-position, and to induce chemical change in said second composi-tion, thereby converting said second composition from a melt pro-cessable composition to a sealant composition; heating said art-icle to about the crystalline melt temperature of said first com-position; deforming said article into a second configuration; and cooling said article while maintaining it in said second conflgu-ration thereby rendering it recoverable towards said first con-figuration upon subsequent heating. Suitably said dual layer tubular article is deformed by uniform radial expansion.

In a stili further aspect thereof the present invention provides a process for manufacturing a sealant coated dimension~
ally heat-recoverable dual layer tubular article comprising the steps of: selecting a first polymer composition comprising a radiation cross-linkable polymer; forming a second polymer compo-sition by admixing a thermoplastic component and a rubber compo-nent in proportions such that the composition comprises 30 to 95%
of the thermoplastic component and 5 to 70% of the rubber compo-nent, said second composition being radiation convertible to a sealant composition; ~ e ~ ~ said first and second polymer com-positions to form a unitary dual layer tubular article possessingan outer tubular layer formed from said first radiation cross-linkable polymer composition disposed concentrically around an inner tubular layer formed from said second radiation convertible polymer composition and being in a first configuration; deforming 35 j said article at a temperature below the crystalline melt tempera-ture of said first composition into a second configuratlon; and - 5a -~ Z~2~387 exposing said article to a source of radiation to initlate the formation of chemical bonds between ad~acent polymer chains in said first composition, thereby converting said second composi-tion from a melt processable composition to a sealant composition and rendering said first composition recoverable towards said first configuration upon subsequent heating. Suitably the dual layer tubular article is deformed by uniform radial expansion.

In a further aspect thereof the present invention pro-vides a process for manufacturing a sealant coated, dimensionally heat-recoverable laminated sheet comprising the steps of: select-ing a first polymer composition comprising a radiation cross-linkable polymer; forming a second polymer composition by admix-ing a thermoplastic component and a rubber component in propor-tions such that the composition comprises 30 to 95% of the ther-moplastic component and 5 to 70% of the rubber component, said second composition being radiation convertible to a sealant com-position; extruding said first and second polymer compositions to form a unitary laminated sheet possessing two layers formed respectively of said first and second compositions and being in a first configuration; exposing said sheet to a source of radiation to initiate the formation of chemical bonds between ad~acent polymer chains in said first composition, and to induce chemical change in said second composition, thereby converting said second composition from a melt processable composition to a sealant com-position; heating said sheet to about the crystalline melt tem-perature of said first composition; deforming said sheet into a second configuration; and cooling said sheet while maintaining it in said second configuration thereby rendering it recoverable towards said first configuration upon subsequent heating. Suit-ably said laminated sheet is stretched along its longitudinal axis.

The advantages of the present invention will become apparent to those skilled in the art when the following descrip-tion of the best mode contemplated for practiclng the invention - 5b -

2~387 is read in conjunction with the accompanyi.ng drawing wherein llke reference charac-ters refer to the same or similar elements and in which:

Figure 1 is a perspectlve view of an extruded tubular article formed from two concentrically disposed polymer composi-tions;

Figure 2 is a perspective view of a sealant lined heat recoverable sleeve formed in accordance with the process of the invention;

Figure 3 is a perspective view of an extruded sheet article formed from two layers of polymer compositions;

Figure 4 is a perspective view of a sealant coated, longitudinally heat shrinkable polymeric tape produced in accor-dance with the process of the invention;

Figure 5 is a block flow diagram of a preferred sequence of process steps employed in the practice of the inven-tion;

- 5c -28iS7 and Figure 6 is a block flow diagram of another preferred sequence of process steps employecl in the practice of the invention.

DETAILED DESCRIPTIO~ OF A E'RBFER~ED EMBODIMENT
. . ~

Referring now generally to the several figures, and specifically to Figure 1, there is shown an extruded two layer tubular article 10. The outer layer 1 is formed from a radiation cross-linkable polymer composition. The inner layer 2 is formed from a radiation convertible polymer ~- composition. Both polymer compositions are ~ l-y easily processable in conventional thermoplastic extrusion equipment. It is to be understood that there are a variety of alternative manufacturing processes that can be 1~ employed to form the extruded tubular article 10 For example the radiation convertible polymer composition used to form the inner layer 2 can be extruded as a tube and wound onto a take up reel. Subsequently, the radiation cross-linkable polymer composition used to form the outer layer 1 can be extruded over the inner layer 2 to form the tubular article 10. Alternatively, if two extruders are available, the extrusion of each of the two polymer compositions can be performed "in line" thereby eliminating the need to handle the tubing twice. Typically, in such a process the radiation convertible polymer composition would be extruded into a tube, run through a water bath, dri~d, 2i3137 and fed into the back of a second extruder which would apply the outer layer of the radiation cross-linkable polymer composition.

Another, and preferable manufacturing process for fabri-cating the tubular article 10 employs a pair of extruders which simultaneously feed the two polymer compositions into a co-extrusion head where in the two polymer compositions meet and form the dual layer tubular article 10 substan-tially simultaneously. Co-extrusion is the preferred fabri-cation technique for tubular article 10 because it makes iteasier to control such product perameters as for example, wall thickness and concentricity.

The possibilities for manufacturing process variations in the extruding step can be seen by reference to Figure 3 wherein a two layered laminated sheet article 30 is shown with the first radiation cross-linkable polymer composition forming an outer layer 1 and the second radiation convertible polymer composition forming an inner layer 2. For example, either polymer composition could be extruded in a first pass and the other composition laminated to the first sheet in a subsequent e~trusion pass. Alternatively, the sheet article 30 can be formed in a single pass using in line extrusion techniques. Another process variation entails separately extruding layers of each composition and laminating them together in a separate bonding operation. Preferably, a substantially simultaneous co-extrusion process is used to form the laminated sheet article 30. Because of the ~2887 multiplicity of extrusion process variations that can be used to form shaped articles, as used herein the process step called "extruding" is intended to include multiple pass extrusions, in line extrusions, sl1bsequent laminations of previously extruded components, and simultaneous extrusions made with co-extrusion tooling.

Two pr-t~e~é process variations are available to impart the property of heat recoverability to those portiorls of a shaped article formed from the first, i.e. radiation cross-linkable, polymer composition. These process variations areshown diagrammatically in Figures 5 and 6. In general, although not invariably, higher recovery ratios can be obtained by using the process shown in Figure 5. This pro-cess is described in greater detail in the Cook et al. U.S.
Patent referenced above.

For selected applications, modest expansion and asso-ciated recovery are frequently adequate. For example, in the manufacture and use of sealant coated heat recoverable tape used to protectively wrap metallic pipelines, a longi-tudinal expansion and associated recovery of lO to 20% issufficient. The process shown diagrammatically in Figure 6 allows sealant coated heat shrinkable tape to be manufac-tured at lower cost than heretofore thought possible. The preferred manufacturing process employing the present inven-tion involves the co-extrusion of the first and second polymer compositions to form the laminated sheet article 30 shown in Figure 3. The sheet 30 passes over a chilled ~LZ~;2~

_g_ calendar roll (not shown) which is typically part of a three roll stack of the type well known to those skilled in the art of polymer sheet extrusion. rrhe sheet 30 is sub-sequently passed through a set of calendar rolls (also not S shown) which axe rotating at dif~erent surface velocities to impart the desired amount of longitudinal stretch (typisally 10 to 20%) to the sheet. Before the sheet is wound on to a ta~e up reel, the edges are trimmed to produce a tape of uniform width. At this point, the sheet is very easy to handle because the layer formed from the second radiation convertible polymer composition does not exhibit significant tack, self adhesion or other properties which would make handling awkward. Manufacture of the heat shrinkable, sealant coated tape 40 is completed by exposing the sheet to a source of radiation to thereby cross-link the first polymer composition and form cross-lin~ed outer layer 3 shown in Figure 4 and simultaneously convert the second polymer composition into a tacky sealant composition shown as sealant layer 4 in Figure 4.

The preferred source of radiation is ionizing radiation such as high energy electrons such as those produced by an electron beam generator~ However, it is to be understood that other sources of radiation can also be suitably employed, preferably other sources of ionizing rad.iationO A
sheet of release paper (not shown) can suitably be disposed between adjacent layers of the sealant coated tape as it leaves the electron beam and is wound onto a ta~e-up reel to facilitate subsequent handling of the product.

2~387 ~ s has been heretofore indicated, the present invention entails the discovery of a novel and superior process for the fabrication of heat recoverable sealant coated articles.
In addition, my invention entails the discovery that certain materials when subjected to irradi.ation at a dose level of from about 2 to about 50 megarads, preferably 5 to 20 meqarads, are transformed from extrusion processible thermoplastics into tacky sealants.

As used herein the term "sealant" connotes an adhesive material which is used for filling voids and interstices to provide a seal against moisture, dust, solvents and/or other fluids. Sealant compositions are viscid, water resistant macromolecular compositions resembling Newtonian fluids in exhibiting both viscous and elastic response to stress.
They usually, although not invariably, exhibit (in the sense of A~TM 1146) second order cohesive blocking (and preferably second order adhesive blocking to substrates such as metals as well) at a temperature between room temperature and the crystalline melt or glass transition temperature or range of the sealant composition. They will preferably have a cohesive strength qPnerally of the same order as their adhe-sive strength. Conventional sealant compositions usually comprise mixtures of elastomers, or mixtures of thermoplastic polymers, or both, and include both mastics and hot melt sealants as described in Bullman, Adhesives Age, November 1976, pages 25-28. Mastics generally consist of mixtures of substantially non-crystalline materials, for example, bituminous materials, elastomers, or ~Z62~3~37 thermoplastic polymers. Sealants, including those prepared according to the instant invention, frequently contain inert fibrous or powdered fillers, tackifiers, stabilizers and/or antirads.

A generally suitable method for determining the viscosity of sealant materials is set forth in ASTM D-3570 (Procedure A or B).

Conventional sealants, as previously indicated, are generally not suitable for extrusion processing because of their high degree of tackiness and low melt strength. My invention overcomes this problem and permits rapid and facile extrusion in that a thermoplastic organic polymeric material (the sealant precursor) is available in the form of relatively free flowing pellets which do not adhexe to each s~ 15 other and which do not slump or otherwise ~ fie their pellet configuration prior to entrance into the extruder barrel. As previously indicated, a particularly advan-tageous process of the instant invention for fabricating the sealant coated, heat recoverable articles involves coextru-sion of the polymer which is to be rendered heat recoverable and the polymer which is convertible into a sealant. To be suitable for coextrusion with a thermoplastic of the type suitable for radiation cross-linking (to enable the ther-moplastic to be made heat recoverable), the co-extrudate (i.e. the precursor polymer which is radiation convertible to a sealant) should have a viscosity ranging from about O.l to about 106 poise, preferably 102 to 104 poise, at its extrusion temperature. The extrusion temperature of the co-extrudate will conventionally be approximately equal to the melting point of the thermoplastic.

Conventional sealants are tac~y, exhibit severe slump and generally have unsuitable viscosities for extrusion, much less coextrusion with thermoplastics. It is for this reason that as heretofore indicated, conventional sealants ordinarily require separate, relatively expensive procedures to apply them as a coating ~frequently solvent diluted) onto thermoplastic articles.

I have discovered certain polymeric compositions (i.e.
sealant precursors), which prior to irradiation have low tackiness, exhibit little slump and have viscosities which permit facile extrusion or coe~trusion. The sealant precursor compositions useful in the practice of the instant invention can be processed on high speed compounding equip-ment for thermoplastics to produce free flowing pellets.
These pellets can be extruded or, alternatively, coextruded with another polymeric material (i.e. a radiation cross-linkable thermoplastic) to form a unitary article which is heat recoverable. Exposing the formed article to irradiation crosslinks the thermoplastic and transforms the sealant precursor into a tacky sealant material. The visco-sity of the sealant precursor will suitably be greater before irradiation than after. This is desirable since a relatively high viscosity for the sealant precursor simplifies coextrusion, and low viscosity after irradiation improves the wettability of the sealant.

~L262~313~7 Another advantageous property of the compositions of the Co r~, f~, o~ C n t ~ r o~o o ~ f ~
instant invention lS that by ad]usting their ~mp~ ~ion I
can ensure that they exhibit cohesive and adhesive blocking of either the first or t:he second degree after irradiation. Second degree blocking connotes that if opposing surfaces are pressed together and then separated there will be a transfer of sealant material. First degree blocking connotes the situation where no transfer of material occurs. Blocking is defined in greater detail in ASTM Method D-1146. First degree adhesive blocking is advantageous in that it allows tubular articles with an interior sealant coating to slide freely along a pipe or cable, and tape articles to be applied as a pressure sen-sitive tape. Unwinding of the sealant coated tape to adjust position is also possible prior to heat recovery. Second degree adhesive bloc~ing is characteristic of mastic type materials which manifest self sealing and reduced craft sensitivity. Another benefit of my sealants is that they have good load bearing characteristics and~not creep at high ambient temperatures.

The sealant precursors of ~he instant invention contain as essential components a thermoplastic (Component A) and a rubber ~Component B). Other conventional constituents of sealants such as stabilizers, antirads, inorganic and/or organic fillers and tackifiers may also be present if desired.

Based on the combination of Components A and B only Component A will comprise 30 to 95% of the combination .

(preferably 50 to 90%) and Component B correspondingly 5 to 70% (preferably 10 to 50%).

As heretofore indicated, the sealants of the instant invention can be "tailored" so as to manifest, after irra-diation, either first or second order blocking dependingupon the requirements of the application. Although the pre-cise ratio of Component A/Componerlt B required to afford a sealant manifesting first order blocking will vary depending upon the chemical nature and molecular weight of Components A and ~, I have found that if the ratio of A : B is > 2.5 :
1 the sealant will ordinarily manifest first order blocking.
If the ratio A : B is < 2.5 : 1 the sealant will obviously manifest second order blocking.

Chemically Componen~ A may be defined as a thermoplastic polymer. Thermoplastics are materials which differ from thermosets or elastomers in that when subjected to heat they do not cure or set but rather soften to a flowable state in which they can be forced from a heated cavity such as an extruder head. Suitable polymers include copolymers of ethylene, propylene, vinyl chloride and vinylidene fluoride and copolymers thereof with each other and/or with one or more other copolymerizable olefinic co-monomers such as vinyl acetate, methyl and ethyl acrylate, halogenated ethylenes and halogenated propylenes; styrene-diene block copolymers, polyamides, and polyesters.

Component B of the sealant has been described as a "rubber". As used herein the term "rubber" is intended to ~l2~ 37 encompass not merely natural and synthetic rubber but also those synthetic rubber like materials exhibiting elastomeric or rubber like properties. Suitable rubbers for Component B
include polyisobutylene, butyl rubber, brominated or chlorinated butyl rubber and epichlorohydrin rubber. A cri-tical requirement of Component B is that it undergo chain scission when subjected to irradiation since this chain scission is believed to be the mechanism whereby the melt processable sealant precursor is transformed into a tacky sealant. Radiation generally has the effect of causing cross-linking of rubbers so it is essential that the rubbers of the instant invention have a scission/cross-linking ratio at 20C of > ~

The practice of the invention is illustrated by the following example in which all parts are by weight.

Example I

The properties of an irradiated sealant prepared according to the teaching of the present invention (Formulation B) compared to those of a typical conventional mastic type sealant (Formulation ~) in Ta~le 1. TMA flow temperature and T-peel data show the superior load bearing capability of Composition B. Finally, blocking and tack data of Composition B show first degree blocking with the sealant manifesting good tack. Irradiation was at a dose level of ~ and 1~ megarads. Irradiation at 8 megarads of Formulation A results in a fall off in T-peel values.

~26Z1~387 TABLE I
Weight %
Composition _ A_ B
Butyl Rubber 50.0 ----Atactic Polypropylene 50.0 ----Butyl Rubber ---- 15.0 Ethylene/Vinylacetate Thermoplastic ---- 18.5 Ethylene/Vinylacetate/
Methacrylic Acid Thermoplastic Terpolymer 50.0 Tackifier (Hydrogenated hydrocarbon) 15.0 Antirad 1.0 Antioxidant 0.5 PROPERTIES

Composition _ A B B B
Radiation Dose (Mrads) _ 0 0 816 IMA 50% Flow Temperature (C) 23 >60>60 65 T-Peel (PLI) Polyethylene to Polyethylene 1 1010 10 Polyethylene/Ethylene vinyl acetate to Polyethylene/Ethylene2 >15>15 >15 vinyl acetate Dynamic Viscosity ~t 90C, 400 radian/ sec. (10 poise) 1.8 2.2 2.0 1.9 ~628~37 Melt Flow at 150~C, 2160gm (gm/lOmin.~* >200 54 67 82 Falling Ball Tack (cm of roll) 0 12 9 7 *Note that material having melt flow values in excess of 200 and high tack makes coextrusion inconvenient or impossible.
However, within such outer limit the greater the melt flow the less the craft sensitivity.
EXAMPLE II

The properties of adhesive compositions with elastomer content varying from lO to 25 wt.~ are shown in Table 2. T-peel and melt flow data show the load bearing capabilities of these adhesives and the improvements in flow after irradiation.

Weight %
Composition C D E F
Butyl Rubber lQ lS 20 25 Ethylene/Vinyl Acetate Thermoplastic Copolymer 23 18 13 8 Ethylene/Vinyl Acetate Methacrylic Acid Thermoplastic Terpolymer 50 50 50 50 Hydrogenated Hydrocarbon Tackifier 15 lS 15 15 Antirad Antioxidant 0.5 0.5 0.5Q.5 Proeerties T-Peel (PLl) PolyethyIene/Ethylene vinyl acetate to Polyethylene/Ethylene vinyl acetate, 10 Mrads 13 14 9 7 Melt Flow at 150C, 2160gm (gm/10 min.) 0 Mrads 59 4949 32 10 Mrads S9 6462 63 20 Mrads 48 5867 83

Claims (20)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for manufacturing a sealant coated dimen-sionally heat-recoverable laminated sheet comprising the steps of:

selecting a first polymer composition comprising a radiation cross-linkable polymer;
forming a second polymer composition by admixing a ther-moplastic component and a rubber component in propor-tions such that the composition comprises 30 to 95% of the thermoplastic component and 5 to 70% of the rubber component, said second composition being radiation con-vertible to a sealant composition;

extruding said first and second polymer compositions to form a unitary laminated sheet possessing two layers formed respectively of said first and second polymer compositions and being in a first configuration;

deforming said sheet at a temperature below the crystalline melt temperature of said first composition in to a second configuration; and exposing said sheet to a source of radiation to initiate the formation of chemical bonds between adjacent polymer chains in said first composition, and to induce chemical change in said second composition, thereby converting said second composition from a melt processable com-position to a sealant composition and rendering said first composition recoverable towards said first con-figuration upon subsequent heating.

2. The process of Claim 1 wherein the laminated sheet is stretched along its longitudinal axis.

3. The process of Claim 1 wherein the radiation crosslinkable polymer composition comprises a polymer selected from the group consisting of polyethylene, polyethy-lene vinyl acetate, polyethylene ethyl acrylate, polypropy-lene, polyamides and styrene-diene copolymers.

4. The process of Claim 1 wherein the rubber component is selected from the group consisting of polyisobutylene, butyl rubber, brominated butyl rubber, chlorinated butyl rubber, epichlorohydrin rubber and mixtures thereof.

5. A process of Claim 1 wherein said radiation conver-tible polymer composition from the group consisting of ethylene-vinyl acetate copolymer and ethylene-vinyl acetate copolymer and ethylene-vinyl acetate-methacrylic acid ter-polymer and a rubber component comprising butyl rubber.

6. A process for manufacturing a sealant coated, dimen-sionally heat-recoverable dual layer tubular article comprising the steps of:

selecting a first polymer composition comprising a radiation cross-linkable polymer;
forming a second polymer composition by admixing a ther-moplastic component and a rubber component in propor-tions such that the composition comprises 30 to 95% of the thermoplastic component and 5 to 70% of the rubber component, said second composition being radiation con-vertible to a sealant composition;

extruding said first and second polymer compositions to form a unitary dual layer tubular article possessing an outer tubular layer formed from said first radiation cross-linkable polymer composition disposed con-centrically around an inner tubular layer formed from said second radiation convertible polymer composition and being in a first configuration;

exposing said article to a source of radiation to initiate the formation of chemical bonds between adjacent polymer chains in said first composition, and to induce chemical change in said second composition, thereby converting said second composition from a melt processable composition to a sealant composition;

heating said article to about the crystalline melt tem-perature of said first composition;
deforming said article into a second configuration; and .

cooling said article while maintaining it in said second configuration thereby rendering it recoverable towards said first configuration upon subsequent heating.

7. The process of Claim 6 wherein said dual layer tubular article is deformed by uniform radial expansion.

8. The process of Claim 6 wherein said first radiation cross-linkable polymer composition comprises a polymer selected from the group consisting of polyethylene, polyethy-lene vinyl acetate, polyethylene ethyl acrylate, polypropy-lene, polyamides and styrene-diene copolymers.

9. The process of Claim 6 wherein the rubber component is selected from the group consisting of polyisobutylene, butyl rubber, brominated butyl rubber, chloronated butyl rubber, epichlorohydrin rubber and mixtures thereof.

10. A process of Claim 6 wherein said radiation conver-tible polymer composition from the group consisting of ethylene-vinyl acetate copolymer and ethylene-vinyl acetate-methacrylic acid terpolymer and a rubber component comprising butyl rubber.

11. A process for manufacturing a sealant coated dimen-sionally heat-recoverable dual layer tubular article comprising the steps of:

selecting a first polymer composition comprising a radiation cross-linkable polymer;

forming a second polymer composition by admixing a ther-moplastic component and a rubber component in propor-tions such that the composition comprises 30 to 95% of the thermoplastic component and 5 to 70% of the rubber component, said second composition being radiation con vertible to a sealant composition;

extending said first and second polymer compositions to form a unitary dual layer tubular article possessing an outer tubular layer formed from said first radiation crosslinkable polymer composition disposed con-centrically around an inner tubular layer formed from said second radiation convertible polymer composition and being in a first configuration;

deforming said article at a temperature below the crystalline melt temperature of said first composition into a second configuration; and exposing said article to a source of radiation to ini-tiate the formation of chemical bonds between adjacent polymer chains in said first composition, and to induce chemical change in said second composition, thereby con-verting said second composition from a melt processable composition to a sealant composition and rendering said first composition recoverable towards said first con-figuration upon subsequent heating.

12. The process of Claim 11 wherein the dual layer tubular article is deformed by uniform radial expansion.

13. The process of Claim 11 wherein the radiation cross-linkable polymer composition comprises a polymer selected from the group consisting of polyethylene, polyethylene vinyl acetate, polyethylene ethyl acrylate, polypropylene, polyamides and styrene-diene copolymers.

14. The process of Claim 11 wherein the rubber component is selected from the group consisting of polyisobutylene, butyl rubber, brominated butyl rubber, chlorinated butyl rubber, epichlorohydrin rubber and mixtures thereof.

15. A process of Claim 11 wherein said radiation conver-tible polymer composition from the group consisting of ethylene-vinyl acetate copolymer and ethylene-vinyl acetate-methacrylic acid terpolymer and a rubber component comprising butyl rubber.

16. A process for manufacturing a sealant coated, dimen-sionally heat-recoverable laminated sheet comprising the steps of:

selecting a first polymer composition comprising a radiation cross-linkable polymer; forming a second polymer composition by admixing a thermoplastic com-ponent and a rubber component in pr@portions such that the composition comprises 30 to 95% of the thermoplastic component and 5 to 70% of the rubber component, said second composition being radiation convertible to a sealant composition;

extruding said first and second polymer compositions to form a unitary laminated sheet possessing two layers formed respectively of said first and second com-positions and being in a first configuration;

exposing said sheet to a source of radiation to initiate the formation of chemical bonds between adjacent polymer chains in said first composition, and to induce chemical change in said second composition, thereby converting said second composition from a melt processable com-position to a sealant composition;

heating said sheet to about the crystalline melt tem-perature of said first composition;

deforming said sheet into a second configuration; and cooling said sheet while maintaining it in said second configuration thereby rendering it recoverable towards said first configuration upon subsequent heating.

17. The process of Claim 16 wherein said laminated sheet is stretched along its longitudinal axis.

18. The process of Claim 16 wherein said first radiation cross-linkable polymer composition comprises a polymer selected from the group consisting of polyethylene, polyethylene vinyl acetate, polyethylene ethyl acrylate, polypropylene, polyamides and styrene-diene copolymers.

19. The process of Claim 16 wherein the rubber component is selected from the group consisting of polyisobutylene, butyl rubber, brominated butyl rubber, chloronated butyl rubber, epichlorohydrin rubber and mixtures thereof.

20. A process of Claim 16 wherein said radiation conver-tible polymer composition from the group consisting of ethylene-vinyl acetate copolymer and ethylene-vinyl acetate-methacrylic acid terpolymer and a rubber component comprising butyl rubber.