CA2150469A1

CA2150469A1 - Heat-recoverable composition and article

Info

Publication number: CA2150469A1
Application number: CA002150469A
Authority: CA
Inventors: George Pieslak; Walter J. Greuel, Jr.; Tony G. Alvernaz; Jozef Van Beersel; Noel Marcel Michel Overbergh
Original assignee: Individual
Current assignee: Raychem Corp
Priority date: 1992-12-03
Filing date: 1993-12-02
Publication date: 1994-06-09
Also published as: JPH08504226A; EP0672090A1; WO1994012581A1; RU95113348A

Abstract

An adhesive composition suitable for sealing to polypropylene. The composition comprises 10% to 90% by weight ethylene polymer, e.g. an ethylene homopolymer such as polethylene or an ethylene copolymer, 10 % to 90% by weight modified polypropylene, 0 % to 30 % by weight rubber, and 0 % to 25 % by weight tackifier. The composition is useful when it is part of a heat-recoverable article (2) which is used to provide a protective coating onto a polypropylene-coated steel pipeline (4), particularly at a joint or weld (12) in the pipe.

_

Description

~WO 94/12581 21 S O ~ 6 9 PCT/US93/11686 H~AT-RFCOVF~AP~ F COMPO~T~ON ANn A~TICI,F
BACKGROU~D OF THF. INVENTION

s Field of the Invention This invention relates to dimensionally recoverable articles, particularly heat-recoverable articles. and to an adhesive suitable for use with such articles.

Introduction to the lnvention Pipelines composed of steel pipe are commonly used to transport a variety of liquids and gases. Depending on the application and the envilu~ ent, the pipe mav be used above the ground or it may be buried. In order to protect the pipe from abrasion~
s corrosion, and degradation due to exposure to sun, soil, moisture, and other elements~
it is often necess~ry to coat the exterior of the pipe with a ,~-ut~live layer. The nature of this ~loL~;Iive layer depends on the environment to which the pipe is exposed. but, for many applications. the protective layer is polymeric. The ,ur~Lecli~/e layer may comprise a polymer tape which is coated with a mastic layer and is then applied to the 20 pipe, or it may comprise an epoxy which is sprayed or painted onto the pipe. Another type of effective coating is a fusion bonded epoxy coating in which the epoxy powder is sprayed onto the pipe and is then cured to form a pinhole-free layer which is suitable for use up to about 60C. Frequently the ~lulc~ e coating colll~lise,s a number of layers, for example an epoxy layer which is imm~iizlt~ly adjacent the pipe and an outer s polyrner layer such as polyethylene. Such coatings provide the advantages of the epoxy and the polymer and are useful up to a lell")el~ re of about 110C.

Recently a number of manufacturers have introduced coatcd steel pipe which is design~ to withstand exposure lem,u~ tLIres of up to 110C. Such pipe generally has a 3 () coating which comprises an inner layer of fusion bonded epoxy, an optional adhesive layer, and an outer layer of polypropylene. These layers provide excellent protection to the steel pipe because they combine the excellent a&esion and cathodic disbonding resict~nce of the epoxy with the low moisture absorption. Iow moisture transmission.
and abrasion resi~t~nce of polypropylene. The difficulty with such pipe is that there are 3 5 currently no easily insr~ ble coatings for the pipe joints or welds that are created when pipe is repaired or leLIofiLl~d, e.g. when two pieces of pipe are attached to one another.
Therefore, when a joint or a weld must be made to the polypropylene-coated pipe.~iffic~llt and time-con~ntning procedures must be followed to ensure that the pipe joint t .

21504~ -2-or weld is adequately ~lulGcled. For example, one technique requires preheating the weld region to about 240C by induction heating, then applying a layer of fusionbonded epoxy powder followed by a layer of polypropylene. To ensure adequate adhesion, the polypropylene sheet is heated with a torch and smoothed out with as spatula. The procedure, which l~Uil~S a skilled cr~ftcm~n, is especi~lly difficult to carry out in the field where the conditions are not easily controlled.

One technique for supplying a ~ute~ /e coating layer to a pipe joint or weld in the field is by the use of a heat-recoverable polymeric article, i.e. a heat-shrinkable polymeric article such as a sleeve, sheet, or tape, in combination with a heat-activatable sealant. The polymeric material of the article has been crocclink~qA during the production process so as to enh~nf~e the desired .1;", .~cio~ recovery. One method of producing a heat-recoverable article comprises shaping the polymeric material into the desired heat-stable form, subsequently crosslinking the polymeric m~ten~l, heating the ~rticle to a IGI11~1~1lU1G above the crystalline melting point of the polymer (or, for amorphous m~teri~lc~ the softening point of the polyrner), d~,rullliu-g the ar~icle, and cooling the article while in the dercllllled state so that the deformed state of the article is retained. In use, because the deformed state of the article is heat-unct~ble, application of heat, by means of a torch or other heat source. will cause the article to assume its 20 original heat-stable shape. For many applic~tionc~ the article is rltqsi~necl to shrink down onto the substrate.

To çnh~nce adhesion to the subst~t~, such heat-recoverable articles generally comprise a layer of a heat-activatable sealant which is positioned adjacent the substrate.
2s When the article is heated, the t,_lllp~.~ture of the heat-activatable sealant rises above its activation l~ I", G SO that a strong bond is forrned between the polymeric ~rticle and the substrate. Suitable se~ ntc include hotmelt adhesives and m~cti~s Good adhesion of the coating to the substrate is particularly important to avoid cathodic disbonding.
Cathodic disbonding occurs as a result of the ill")r,ssed electric current that is applied 3 o to the pipe to prevent corrosion of the iron in the steel pipe. Many adhesive c~,lnl)osiLions which are used to bond a l,l. Le-;Li~le coating onto a pipe are adversely affected by the hll,ulGssed electric current. As a result, the bond weakens and the adhesive pulls away from the pipe, leaving segments of the pipe surface exposed to the corrosive conditions of the environment.

For pipe protection, conventional heat-recoverable articles are sleeves which comprise a backing layer, generally polyethylene or a copolymer comprising ethylene.
in contact with a hotmelt adhesive~ which is often a polyethylene-based adhesive. The 21~0469 hotmelt adhesive is selected to have adequate adhesion both to the backing layer and to the substrate. Most conventional polyethylene-based heat-recoverable sleeves do not adhere well to a polypropylene-coated pipe, and those sleeves which do have goodadhesion cannot be used for pipelines which are exposed to high Iclllpelatures, e.g.
s more than 110C, because they contain adhesives or mastics which soften and disbond from the pipe at high l~,l"~w~tures. Although there are a number of coln.-.~"-ial O polypropylenes and modified polypropylenes which can be used in adhesives which stick well to polypropylene-coated pipes, these materials do not have good adhesion to polyethylene b~t ~ing layers. FUILIIC~IIIUIt;~ because polypropylene degrades when o cro~link~ by means of electron beam irradiation, a heat-recoverable sleeve comprising a polypropylene backing layer is nol practical.

SUMMARY OF THE INVENT~ON

s We have now discovered that a heat-recoverable article which has good adhesion to steel, polyethylene, and polypropylene, has good c~th~ic disbonding recict~nce, and is suitable for use at L~ tures up to 110C can be made if the adhesive layer comprises both an ethylene polymer and polypropylene. ln a first aspect, this invention provides an adhesive composition suitable for sealing to a substrate which comprises polypropylene, said composition comprising (a) 10% to 90% by weight ethylene polymer which is an ethylene homopolymer, an ethylene copolymer, or a morlifierl ethylene polymer in which a cherni~l moiety has been grafted onto a polyethylene backbone;

(b) 10% to 90% by weight modified polypropylene which (i) comprises a chemic~l moiety which is an unsaturated carboxylic acid or acid derivative and which has been grafted onto a polypropylene backbone, and (ii) has a 2% secant modulus of less than 690 MPa ( 100,()00 psi ):
and (c) 0% to 30% by weight rubber; and (d) ()% to 25% bv weight tackifier.

WO 94/12581 PCT/US93/11686 ~
2150~

In a second aspect this invention provides a heat-recoverable article comprisinga heat-recoverable polymeric element said element having coated on at least a p~art ot` a surface thereof an adhesive composition according to the first aspect of the invention.
In a third aspect. this invention provides an assembly which comprises ( 1 ) a substrate which comprises polypropylene; and o (2) an adhesive according to the first aspect of the invention which is in contact with and seals to the substrate.

BRIEF DESCRIPTION OF THE DRAWING

s The invention is illustrated in the drawing in which Figure 1 shows a pc.~l,~;P,~e view of a heat-recoverable article of the invention positioned on a substrate:

Figure 2 shows a cross-section~l view of the article of the invention along line2-2 of Figure l; and Figure 3 shows a cross-section~l view of an article of the invention covering a weld between two pipes.

DETAILED DESCRIPTION OF THE INVENTTON
~5 The adhesive composition of the invention is particularly useful in adhering tO
polypropylene. Particularly ~l~[cll~d co"lpo~itions of the invention adhere to steel and/or to polyethylene in addition to polypropylene. In this specifi~sion a composition is said to have adhesive character if the peel strength of the composition to the substr~t~. as measured by ASTM D-1000 is greater than 0 N/mm at 23C.
Adhesives of the invention preferably have a peel strength to polypropylene of ~t least 0.9 N/mm (5 pli) particularly at least 1.2 N/mm (7 pli) especially at least l.X N/mm (10 pli) at 23C. In addition the a&esives of the invention exhibit adhesive character at elevated ~el,lp~ ulc e.g. 110C or 120C. When the peel strength of an adhesive of 3s the invention is measured at l 10C the adhesives preferably have a peel stren~th of at least 0.02 N/mm (0.1 pli) p~rticularly at least 0.05 N/mm (0.3 pli), especially at le~s 0.09 N/mm (0.5 pli). The disclosure of ASTM D-1000 is inco")o~ted herein by reference. It is ~"c~llcd that a&esives of the invention have similar peel strenSgIhs at ~WO 94/12581 2 1 5 0 ~ 6 9 PCT/US93/11686 ~3C and 110C as those described for polypropylene for substrates comprising steel and substrates comprising polyethylene. The polypropylene to which the adhesive composition adheres may be a film, sheet, or article of polypropylene which has sufficient thickness and integrity to stand alone, or it may be in the forrn of a coatin,~
s over a part or all of a substrate such as a pipe. The compositions of the invention are particularly useful in adhering to polypropylene-coated steel pipe.

The polypropylene present in the substrate, i.e. the material to which the adhesive co.ll~)osi~ion adheres, may be either a crystalline isotactic polypropylene or an o amorphous polypropylene, depending on the specific application. The polypropylene may be conventional, unmo~ifieA polypropylene which col~ ises at least 75% by weight of the polypropylene homopolymer, i.e. at least 75% of the polymer has a polymer backbone -(CH-CH(CH3))-. Alternatively, the polymer may be modified polypropylene. ln this specification, the term "mollifie~ polypropylene" is used to 5 mean any polypropylene in which the backbone of the polymer has been chemir~lly changed or otherwise altered to enhance the physical or chrmir~l ~)lU~J.,. ~ies of the polymer. Such mn-lifir:ltion can be achieved during the polyrnerization process or in post-polymrri7~tion step, for exarnple by grafting a chemir~l moiety such as an unsaturated carboxylic acid or acid derivative onto the polymer backbone, by inserting a 20 monomrr to form a block copolymer, by incol~uoldtiIlg a specific chain-blocking agent, or by any other suitable means. In addition, the term "mo~ifi~A polypropylene"
inrlllrirs those polymer alloys and blends, either reacted or u~ a-;lGd, which comprise polypropylene and which have different chemir~l and/or physical ~lu~l~ies from conventior-~l unmodified polypropylene. Alloys and blends include those materials in 2s which polypropylene is mixed with rubber such as ethylene propylene diene rubber (EPDM).

The polypropylene of the adhesive is a modified polypropylene as described above. Particularly p.G~ d are polypropylenes in which a r,hemir~l moiety such as an 3 0 unsaturated carboxylic acid or acid derivative has been grafted onto the polymer backbone. Among suitable chrmir~l moirties are acrylic acid, meth~crylic acid, and maleic acid. Polymers in which the chemical moiety is an anhydride, especially maleic anhydride, are particularly ,v.er~l~Gd. When an anhydride is present, it is preferred th~t there be at least ().1% bv weight of the polymer of anhydride grafted onto the 35 polypropylene backbone. It is ~-tfcll~d that the modified polymer contain less than 1(~%, preferably less than ~%, particularly less than 6% by weight of acid (present a~
an acid moiety), as determined by titration. Cc,-l-ll-~l-;ially available modified polypropylenes which can be used in this invention include anhydride-modified WO 94112581 j PCT/US93/11686 215~9 -6- --polypropylenes such as OrevacTM PP-M. Orevac~ PP-CA100. and Orevac'~ PP-C
(also known as Orevac M, Orevac CA100. and Orevac C, respectively), available ~rom Atochem; AdmerTM QFSOOE and AdmerlM QB540E, available from Mitsui;
FusabondTM 108, FusabondTM 109, and FusabondTM '~03, available from DuPont:
s PlexarTM 420, available from Qll~nh~m; QestronTM EP 2070G, available from Himont:
and PolybondTM 3002, available fTom BP Performance Polymers. Other modified polypropylenes which may be suitable for applications in which good cathodic disbol1dlllel.L ~;~ru--l,ance is not required include acrylic acid-grafted polypropylenes such as Polybond~M 1001, PolybondTM 2005, PolybondTM 2015, available from BP
o l'elr~ lance Polymers.

We have found that in order for the adhesive of the invention to have good c~thoAi~ disbondment pc.ro----ance, it is nec~ $~ry that the mo~ ~ polyp~.~pylene of the adhesive have a 2% secant modulus. as measured in accordance with ASTM D-~82-s 91, Test Method A, described hereinafter, of less than 690 MPa (100,000 psi), preferably less than 620 MPa (90,000 psi), particularly less than 552 MPa (80,0(0 psi), especially less than 483 MPa (70,000 psi).

Adhesive compositions of the invention comprise 10 to 90% by weight moAifieA polypropylene, preferably 15 to 85% by weight motlifie~3 polypropylene,particularly 20 to 80% by weight mo iifi~A polypropylene, espeçi~lly 20 to 75% by weight moriifiP,d polypropylene, the weight percent being Ille~ul~d in terms of the total cc,.l",osition. In addition, conven~ion~l, unmodified polypropylene may be present.

2s The adhesive composition also comprises 10 to 90% by weight of an ethylene polymer, preferably 15 to 85% by weight of an ethylene polymer, particularly 2() to 80% by weight of an ethylene polymer, especially 20 to 75% by weight of an ethylene polymer, the weight percent being measured in terms of the total composition. The ethylene polymer may be an ethylene homopolymer, e.g. very low density polyethylene, low density polyethylene, linear low density polyethylene, medium density polyethylene, or high density polyethylene; an ethylene copolymer, e.g.
copolymers of ethylene and vinyl acetate, ethyl acrylate. methyl acrylate, or acrylic acid:
an ethylene terpolymer: or blends thereof. The ethylene polymer may be any conventional ethylene polymer in which the chemic~l properties are not changed. The 3s exact type and formulation of the conventional ethylene polymer is selected based on the identity of the material to which the adhesive is to be adhered and the required OSU-G ~..~ u-~ of the final product during normal O~la~iOI1. Alternativelv~ the ethylene polymer may be a modified ethylene polymer, i.e. any ethylene polymer which ~ WO 94/12581 215 0 4 6 9 PCT/US93/11686 has been chçmir .lly changed or otherwise altered to enhance its physical or chemical l~lu~llies. As with polypropylene, such modification can be achieved by graftin~ a ch~mic~l moiety such as an unsaturated carboxylic acid or acid derivative, e.~. acrvlic acid, maleic acid, or maleic anhydride, onto the polymer backbone, by insertin~ ~
., s monomer to form a block copolymer. or by any other suitable means. Co~,nmerciallv available m~ifieA polyethylenes which can be used in this invention include polyethylenes sold by Quantum under the traden ~me Plexar, e.g. PlexarT~' 013 orPlexarTM 206; those sold by DuPont under the tr~den~me Fusabond, e.g. FusabondrMD110, FusabondTM D158, and FusabondTM D185; those sold by BP P~.ro~ ance o Polymers under the tr~Aen~me Polybond, e.g. PolybondTM 1009 and Polybond''''' 2021; and those sold by Mitsui under the tr~Aer ~me Admer, e.g. Admerr~' L100(). and AdmerTM L2000.

In many adhesive co..,,uo~7iLions of the invention, it iS desirable that rubber be 15 present to inc;ease the flexibility of the cc,-lJ~siLion and to enh~nre the adhesive nature of the composition. Among those rubbers which may be used are natural and synthetic rubbers, particularly ethylene propylene rubbers. ethylene-propylene-diene rubbers (EPDM), butyl rubbers, polyisobutylene rubbers. and thermoplastic elastomers such as those based on styrene-but~Aiene-styrene or styrene-isoprene-styrne linear or radical 20 block copolymers. The rubber is optional in the adhesive composition. Rubber may comprise 0 to 30% by weight of the total colllpo~iLion, preferably 5 to 30% by weight, particularly 10 to 30% by weight, especially 15 to 25% by weight. A single rubber or two or more dir~lGnt types of rubber may be present in order to achieve dirrt,~ t physical and adhesive pl~ .ies. When more than one rubber is present, the rubber' 5 culll~ reflects the total weight percent of all the rubbers.

Also present in many compositions of the invention is a tackifier. The term "t~r~ifier" is used in adhesive art to denote a ma~erial which, when added to anadhesive co~ ,o~ilion, promotes its adhesion to a substrate by increasing its abilitv to 30 wet the substrate. It is often ~ d that the t~r~ifi~-,r be a low molecular wei~ht polymer of lllono''lG'~. which contain ethylenic unsaturation and are free of polar groups. Suitable tackifiers include NevpeneTM 9500, available from Neville Chemical.
which is believed to be a copolymer of a mixture of arom~tir~lly and aliphaticallv substituted ethylenes, PiccotexTM 75, available from Hercules, which is believed to be 3 5 copolymer of vinyl toluene and c~-methylstyrene, and EscorezlM 5320, available from Exxon. The t~ifier is optional in the adhesive composition. Therefore, the tackifier comprises 0 to 25% by weight of the total cc-ll~ .iLion, preferably S to 20~o by weight.
particularly 10 to l 8% by weight.

Wo 94/12581 PCT/US93/11686 21~0~6~ -8-The adhesive composition can also contain additional additives such as stabilizers, pigm~ntc, flame retardants, fillers, waxes, and crocclinking agents. If present, these components generally comprise at most about 20% by weight of the total s composition, preferably at most about 15% by weight, particularly at most about 1()~
by weight.

The cu,l",o"ents of the composition can be mixed in any convenient manner~
for example by using convenrion~l mixing e~ui~ nL such as BrabenderTM or BanburylM mixers, extruders, or mills. Following mixing, the co~llposiLion can be shaped ~p~lu~liately for the desired use. For example, the composition can be formed into a sheet, e.g. by extrusion, which can be wrapped or arranged around a subst rate.
or the com~,o~ ion can be coated onto a backing layer, e.g. by extrusion, spraying, p~inting, or other type of coating application.

The adhesive co,llpo~.iLions of the invention can be used for any application. In one particular appliration~ the adhesive is used as part of a heat-recoverable article which is used to provide a covering on a pipe. A heat-recoverable article is an article, the ~lim~oncion~l configuration of which may be changed by subjecting the article to heat t~ ent In their most collllllon form, such articles comp;ise a heat-shrinkable sleeve made from a polymeric material exhibiting the ~lu~lly of elastic or plastic memory.
Alternatively, heat-recoverable articles can be molded into shapes int.on~iecl for specific applir~tionc. Articles comprising such elastic or plastic Ill~ ,ly are described, for example, in U.S. Patents Nos. 2,027,962 (Currie); 3,086,242 (Cook et al); and '' 5 3,597,372 (Cook), the disclosures of which are incorporated herein by reference.

Conver-tion~l heat-recoverable sleeves used to provide a ~lu~ e coating to pipes have either a tubular elongate configuration or a flat configuration. Where the m~ter of the pipe or other substrate is very large, thus making extrusion of a 3 o sufficiently large tubular sleeve difficult, or where no free end of the substrate is available, thus preventing positioning of a tubular sleeve, it is cûllllllon to use a wrap-around article. A wrap-around article is an article, typically in the form of a sheet, that is inct~ by wrapping it around the object to be covered so that opposed longitn~in ll edges overlap. A closure means is applied to secure together the opposed longitll~in,ll 3s edges. Such articles are described in U.S. Patent Nos. 4,200,676 (Caponigro et al) and 4,803,104 (Peigneur et al), the disclosures of which are incorporated herein by reference.

~ Wo 94/12581 2 1 5 0 4 6 ~ PCTf~S93/11686 The adhesive of the invention is particularly suitable for use in makin~ a bond between a polypropylene-coated steel pipe and a polyethylene-based heat-recoverable sleeve. The adhesive can be applied to the sleeve prior to in~t~ tion on the pipe or other substrate~ it can be applied directly to the pipe or other substrate prior to s in~t~ tion of the sleeve, e.g. as a coating applied in the factory, or it can be used in the form of a sheet which is inserted between the pipe or other substrate and the heat-recoverable sleeve. In any case, the heat-recoverable sleeve may have one or more coatirlg layers which are applied before the adhesive of the invention. For example, many conventional heat-recoverable sleeves are coated with a layer of polyarnide which u lies between the backing layer of the sleeve and the adhesive of the composition. When the adhesive composition is applied to the heat-recoverable sleeve, it generally has a thickness of 0.025 to l.0 mm (0.001 to 0.040 inch). It is not necessary that theadhesive composition cover an entire surface of the heat-recoverable sleeve; often strips of adhesive at the edges of the sleeve or wraparound article are s--ffi~içnt to make adequate connection to the substrate. When adhesives of the invention are used with heat-recoverable articles, if there is an adhesive failure, the pr~f~ d failure mechanism is between the adhesive and the backing, i.e. the heat-recoverable article, rather than between the adhesive and the substrate, e.g. the polypropylene-coated pipe. lt is particularly important that the adhesive failure be uniform, i.e. that all of the adhesive stick to the pipe. A "mixed" failure, in which there is partial adhesion to both the backing and the pipe, in~ic~t~s that the strength of the bond to the substrate is less than desirable.

Adhesives of the invention have good ~rol~llance for c~tho-lic disbondment at elevated tc~ aLule, e.g. 80 to 95C or hotter, when tested according to ASTM G-42 described below. The cathodic disbonding radius at 95C after 30 days is less than 35 mm, preferably less than 30 mm, particularly less than 25 mm, especially less than 20 mm. In addition to the good cathodic disbondment performance, the adhesive retains its adhesive character at the elevated tt;lll~l~tul~.
The adhesive of the composition is also useful for making a seal over a component, around one or more components, or between two components which are design.o~ to survive exposure to relatively high ~ llpeldlllres. For example, the adhesive composition can be used to seal a fiber optic splice case outlet or to make a 3 5 seal between the base plate and the dome-shaped cover of a fiber optic splice case such as that disclosed in U.S. Patent No. 4,913,522 (Nolf et al), the disclosure of which is inc~l~,ul~ted herein by reference. Fiber optic splice closure systems in which the WO 94/12581 PCT/US93/11686 ~
21504~9 ~ -IO-adhesive of the invention can be used are sold by Raychem Corporation of Menlo Park.
California under the tr~drn:~me FOSCTM.

The adhesive of the invention is also useful as part of an assembly in which a .~ sllbst~t-: which comprises polypropylene is in contact with the adhesive. Thepolypropylene of the substrate may comprise all or part of a surface coating of the substrate, e.g. a pipe, or the entire substrate may be made of polypropylene, e.g. ;l molded part or component. For many applications it is ,ul~f~ d that the polypropylene of the substrate be in the form of a layer which surrounds the substrate.

The adhesive of the invention may also be used as part of a method for making a connection between a layer or an article which comprises polypropylene, e.g. apolypropylene-coated pipe, and a layer or an article which comprises polyethylene, e.g.
a polyethylene-cont~ining backing layer of a heat-recoverable article. In such a method.
s the adhesive layer is positioned in contact with the substrate which comprisespolypropylene, heat is applied to allow the adhesive to melt and flow while in contact with the substr~te, and the adhesive is then allowed to cool, producing a bond between the adhesive (and any b~r~ing or carrier to which it is ~tt~rhrd) and the substrate.

The invention is illustrated by the drawing in which Figure 1 shows a heat-recoverable ar~ticle 2 in the form of a polymeric tube recovered onto ~.lb~lldte 4 which is a pipe. Not shown in Figure I is the polypropylene layer 6 which coats pipe 4.
Adhesive layer 8 which is part of the heat-recoverable article 2 lies between the pipe 4 and the b~rking layer 10 of heat-recoverable article 2.
2s Shown in Figure 2 is a cross-sectional view along line 2-2 of Figure l. Visible in this view is the polypropylene coating layer 6 and the adhesive layer 8.

Figure 3 shows a cross-sectional view of a weld 12 between two pipes, 4,14.
Adhesive layer 8 bonds to the backing layer 10 of the polyrneric heat-recoverable sleeve 2, the polypropylene coating 6,16 of the two pipes, and to the weld 12 itself.

The invention is illustrated by the following exarnples.

3s Example 1 (Comparative Example) The ingredients of Adhesive A, listed in Table 1, were mixed and applied by ex~rusion to a 0.75 mm (0.030 inch) thick high density polyethylene backing laver ~WO 94/12581 21~ 0 4 6 9 PCTi~Js93/11686 which had been crosclinkç~l and expanded about 28% prior to the application of the adhesive. The adhesion of the adhesive to various substrates was then measured at room ~ ulc (approximately 23C) and at 120C following the peel strength test procedure of ASTM D- 1000, the disclosure of which is incorporated herein by s reference. In that test, the adhesive-coated backing was recovered onto a pipe and was cut on the pipe into test specimens with a width of 25 mm ( 1 inch). Each specimen W.Ui cut parallel to the direction of the pipe to create a free end which was clamped in the jaw of an lnstronTM tester. After allowing the sample to equilibrate to the desired ~e,~ dture (either 23C or 120C) in the thermal cha,llbel of the tester, the jaw o separation speed of the Instron tester was set at 51 mm/minute (2 inches/minute ~. The amount of force required to peel the layer from the pipe was recorded as pounds/linear inch. To determine the adhesion to steel, the adhesive-coated backing was recovered onto a steel pipe with an outer rli:~m~ot~ r (OD) of 60 mm (2.36 inch) which had been preheated to 170-180C. To d~telllline the adhesion to polypropylene, the adhesive-5 coated backing was recovered onto a polypropylene-coated steel pipe which had been preheated to a lc~llycld~ure of 170-180C. Three different polypropylene-coated pipes were tested, pipe with an OD of 0.10 m (4 inch) from Atochem, pipe with an OD of0.25 m (10 inch) from Himont, and pipe with an OD of 0.41 m (16 inch) from Duval.
The coating on the Duval pipe was mo~lifiscl polypropylene. There was no significant 20 dirr~l~nce in the results depending on the specific pipe used. The adhesion of the a&esive to the polyethylene backing was also monitored during the test.

The results of the testing are shown in Table II. Adhesive A showed no adhesion to the polypropylene-coated pipe, but had good adhesion to the polyethvlene 25 backing and to m~co~ted steel.

Also tested was the pe,ro"l~ance of Adhesive A under c~th~lic disbonding.
The resict~nce of the adhesive to cathodic disbonding was measured following theprocedure of ASTM G-42. the disclosure of which is incorporated herein by reference.
30 In the c~tho lic disbonding test, a slab of the adhesive was attached to a polyethylene backing layer and was then recovered onto a shot-blasted steel pipe with an outer mett-r of 51 mm (2 inches). I'he end of the pipe which was to be hlllllel ~ed was sealed with a watertight end cap. A hole (holiday) was drilled through the backing and the adhesive (but not through the pipe) in the center of the pipe to expose the metal 3 5 surface of the pipe at that point. The pipe was then immersed in an electrolvte solution comprising water and 1% by weight of each of sodium chloride, sodium sulfate. and sodium carbonate. A potential of 1.5 volts was applied to the pipe, thus making the pipe a cathode in the electrolyte solution which also contained a sacrificial anode. The 21~0~6~ -12-sample and electrolyte solution were m~inmin~ at 95C for 30 days. The pipe w,l~i then removed and the area around the holiday was inspected to determine the extent o~`
disbon-l n .f nt The approximate radius of the disbondment area surrounding the holiday was measured in millimçters (mm) and recorded. Adhesive A had a c~thc-iir s disbonding radius of 10 to 15 mm.

Example 2 (Comparative Example) Following the procedure of Example l, Adhesive B was piGp~-_d and tested.
o This adhesive showed good adhesion to polyethylene and steel but low adhesion to polypropylene-coated steel. Adhesive B had a c~tho lic disbonding radius of 22 mm.

Example 3 Following the procedure of Example 1, Adhesive C was ~ Lc;d and tested.
This adhesive showed good adhesion to polyethylene, steel, and polypropylene-coated steel. Tests of peel strength for this adhesive were con~ncte~l on Atoc hem polypropylene-coated pipe (2.59 N/mm ( 14.8 pli) at 23C, 0.16 N/mm (0.9 pli) at110C), Himont polypropylene-coated pipe (2.24 N/mm (12.8 pli) at 23C, 0.12 N/mm (0.7 pli) at 110C), and Duval polypropylene-coated pipe (3.85 N/mm (22.0 pli) at 23C). The c~tho lir disbond-llg radius, when tested following the procedure of Example 1, was 14 mm.

Example 4 Using Adhesive C, a film with a thickness of 0.25 mm (0.010 inch) was p-~ d and inct~lleA on both the steel pipe and the polypropylene-coated steel pipe which had been preheated to a l~l."~.dture of 230C. On top of Adhesive C. a backing layer coated with Adhesive A (as described in Example 1) was inct~lle~l The composite device was then tested as in Example 1. It exhibited good adhesion to polyethylene, steel, and polypropylene-coated steel.

~wO 94/12581 2 1 5 0 ~ 6 ~ PCT/US93!11686 TABLE I
Adhesive Compositions (Weight %) Cc"l~onent A (Co""u~ti~e) B (Co~ e) C
~loAifieA HDPE 55.6 27.8 Modified PP 55.6 27.8 PIB 13.9 13.9 13.9 EPDM 10.0 10.0 1().() Tackifier 15.0 15.0 15.0 Pigment 3.0 3.0 3.0 St-bili7.ors 2.5 2.5 2.5 s Notes to Table I:

MoAifi~ HDPE is PlexarTM 013, a monified high density polyethylene available from Qll~ntllm-l~oAifi~ PP is OrevacTM C a polypropylene moAified by the addition of more than o 0.1% by weight anhydride, and having a 2% secant moAIl~ of about 426 MPa (61,800 psi), available from Atochlom.
PIB is VistanexTM L-80, solid polyisobutylene rubber available from Exxon.
EPDM is Dut~alTM 044, ethylene propylene diene rubber available from MonteAi~on.
Tackifier is NevpeneTM 9500, a t~nkifi~-r available from Neville ~hemic~l~
Pigment is a color concentrate ct --l .;..;--g carbon black and ethylene/ethyl acrvlate copolymer.
St~hili7ç,~ include antioxidant and a metal deactivator such as that described in U.S.
Patent No. 4 997 685.

WO 94/12581 PCT/US93/11686 ~
21~ ~ 4~ -14-TABLE II
Adhesion tO Various Substrates (Peel Strength in Newtons/mm (Pounds/linear inch)) Substrate Tem~erature PP-coated Exarnple Adhesive (C) Polyethylene Steel Steel*
A 23 7.88 (45! >7.88 (>45) () A 120 0.88 (5) >0.88 (>5) NT
2 B 23 1.66 (9.5) >1.66 (>9.5~Low B 120 0.18 (1.0) >0.18 (>1.0)NT
3 C 23 3.40 (19.4) >3.40 (>19.4)Good C 120 0.21 (1.2) >0.21 (>1.2) NT

4 C 23 3.71 (21.2) >3.71 (>21.2)Good C 120 0.40 (2.3) >0.40 (>2.3) NT

* PP-coated Steel was a polypropylene-coated steel pipe available from ~toçhem (convention~l polypropylene) or Duval (morlifi~A polypropylene).
"NT" in~ tes that no test was con~ A for that condition. "Low" int~ t~s that the adhesion was 0.35 to 0.52 N/mm (2 to 3 pli) at 23C and that there o was adhesive failure to the polypropylene co~ting, i.e. between the adhesive and the polypropylene coating. "Good" in~ at~s that the adhesion was in the range of 3.68 N/mm (20 pli) or greater at 23C and that any failure occurred between the adhesive and the backing.

Examples 5 to 13 Following the procedure of Example 1. a number of formulations were prepared using the co~ onents listed for Adhesive C, but using different grades of mo~iifiPri polypropylene at 27.8% by weight of the composition. The peel strength at 23C and 120C was measured as in Example 1 after the adhesives were recovered onto a polypropylene-coated steel pipe. Also measured was the melt index of each adhesive?
following the ~lucedu~ in ASTM D-1238, Condition E, and the 2% secant modulus at23C of each polypropylene, following the procedure of ASTM D-882-91, Test Method A. In that test, a 250 mm (10 inch) strip of the polymer was clamped between the jaws 2s of a mechine with a constant rate of jaw separation. Using an initial strain rate of O. l mm~mm-min (0.1 in/in-min~ and a rate of grip separation of 25 mm/min (1.0 in/min ).

~WO 94/12581 215 0 ~ S 9 PCTIUS93/11686 the test was con~l-cte~ and the load versus extension was recorded. The test wasstopped when the sepcified extension of 2% was reached. The secant modulus was c~lc~ teA by dividing the stress at 2% strain by the 2% strain value. The reported secant modulus was the average of five sarnples. The results are shown in Table III.
s For all adhesives, the adhesion of the adhesive to the polypropylene-coated steel w~s greater than that to the polyethylene backing. In addition to these tests, a cathodic disbonding test was con~ cte~l for samples 7, 8, and 13. Following the proceduredescribed in Exarnple 1, test sarnples were tested at 110C for 30 days. The adhesive of Example 13 had a cathodic disbonding radius of 27 mrn; the adhesives of Exarnples 10 7 and 8 showed complete disbondment ~om the substrate.

TABLE III
Peel Strength and Melt Index for Various Adhesives Peel Stren~th 25to Secant N/rr~m Modulus (Pounds/linear inch~
pp ~elt F.x~mRle Po~ro~ylene Supplier 23C 120C Index MPa (psi)OrevacPP-M ,~t~hem 1.24 (7.1) 0.14 (0.8)11.1 512 (74,200) 6 Orevac CA100 ~to~htom 0.81 (4.6) 0.09 (0.5)26.5 99 (14,300) 7 Polybond2005 BP 2.64 (15.1) 0.11 (0.6)6.8 721 (104.700) 8 Polybond2015 BP 4.52 (25.8) 0.23 (1.3)5.8 452 (65,500) 9 Fusabond 108 DuPont 0.51 (2.9) NT* NT* 904 (131.100) 10 Fusabond 109 DuPont 0.30 (1.7) NT* NT~ 947 (137.4()0) 11 Fusabond 203 DuPont 0.53 (3.0) NT* Nr 714 (103,500) 12 Plexar420 Quantum 2.03 (11.6) 0.44 (2.5)3.3 356 (51.700) 13 Orevac PP-C ~tochem 4.10 (23.4) 0.14 (0.8)2.1 426 (61.800) NT* in~lirat~s that this p,~ y was not tested. Melt index numbers are in grams/10 minutes.

Examvles 14 to 23 Following the procedure of Example 1, a number of formulations were prepared and tested. Each formulation c- nt~ineA 13.9% by weight Vistanex~'`' L-8(1.
solid polyisobutylene rubber available from Exxon. 10.0% by weight Dutral1M ()44.

WO 94/12581 ; PCT/US93/11686 ~
21~0~ 16-ethylene propylene diene rubber (EPDM) available from Montedison. 15.0% by weight NevpeneTM 9500, a tackifier available from Neville Che~nic~lc, 3.0% by weight ofpigm~-nt which co~ ised a color concentrate cont~ining carbon black and ethylene/ethyl acrylate copolymer. and 2.5% by weight st~bili7~rs which includeds antioxidant and a metal deactivator such as that described in U.S. Patent No.4,997,6~5, the disclosure of which is inco~ dt~d herein by lc~.~nce. The remaining ingredients are shown in Table IV. For each adhesive colll~sition, an adhesive-coated polyethylene backing was recovered onto a steel pipe with an outer rii~m~ter of 51 mrn (2 inches) which had been ~ hea~ed to 230C. Peel strength of the adhesive o colll~o~ilion to the steel was then llR~ul~d at 23C, 110C, and 120C as in Example 1, using an Instron tester with a pull rate of 51 mm (2 inches)/minute.

Adhesion to polypropylene-coated steel was measured using pipe with an outer t~ - of 0.4 m (16 inches) which had been coated with an u~.~..orl;l~eA

5 polypropylene from Atoch~rn The polypropylene coating was ro~lghton~d and the pipe interior was pl~healcd to achieve a tclll~ldture of about 110C on the pipe surface prior to rccovering the adhesive-coated backing onto the pipe. To ensure that the adhesive flowed adequately, a~ ;nn~l heat was applied to the b~ing following recovery. The assembly was cooled and the adhesion was lllea~ul~ at 23C.
The melt index of the adhesive CC~ uosiL~OnS was ~ ul~ d as in Example 5.
Snf~ning points were Ill~,a~Ul~ d using a thermal ".~ ~h~";r~l analyær (TMA) with a 50 gram load. ('~tho lir disbonding at 95C for 30 days was also measured. The results of these tests are shown in Table V.
2s Wo 94/12581 215 0 4 ~ 3 PCTtUS93/11686 TABLE IV
Adhesive Compositions (Weight %) 14 15 16 17 1~ 19 20 21 22 ~3 PE127.8 41.6 14.027.8 27.827.8 27.8 PE2 27.8 27.8 PE3 27.8 27.8 PP113.9 14.0 41.6 27.8 27.8 27.8 PP213.9 27.8 55.6 5 Notes to Table IV:

PE1 is PlexarTM 013, a modified high density polyethylene available from Q~
PE2 is LotaderTM 8200, a polyethylene terpolymer available from Atochem o PE3 is LotaderlM 6600, a polyethylene terpolymer available from Attlch~m PP1 is OrevacrM C, a polypropylene m~ifi~ by the ~iition of more than 1% by weight anhydride and having a 2% secant mo~ llc of about 426 MPa (61.800 psi), available from Atochtom PP2 is QestronTM EP2070G, a polypropylene mo~ifiell by the addition of more thanS 1% by weight anhydride and having a 2% secant modulus of about 555 MPa (80,500 psi),available from IIill.ont.

WO 94/12581 PCT/US93111686 ~2~50~6~ ~ _ TABLE V
Test Results for Adhesives 14 to 23 14 1 15 ~ 7 1 ~ 19 1 20 ~ 23 PF./Steel N/mm 1.22 5.06 2.71 6.6211.21 1.79 0.353.41 5.48 3.80 pli 7.0 28.9 15.5 37.864.0 10.2 2.0 19.5 30.3 21.7 N/mm 0.25 0.23 0.32 0.190.05 0.14 0.070.16 0.19 0.14 pli 1.4 1.3 1.8 1.1 0.3 0.8 0.4 0.9 1.1 0.

N/mm 0.19 0.33 0.23 0.16NT 0.14 NT NT NT ().14 pli 1.1 1.9 1.3 0.9 0.8 0.8 PE/PP

N/mm 0.53 3.33 0.88 2.452.10 1.05 0.181.75 2.10 3.85 pli 3 19 5 14 12 6 1 10 12 22 Type AFPE AFPE AFPE AFPPAFPP AFPE AFPE AFPE AFPP AFPE

Soft.Pt. 122 122 140 120 118 122 141 94, 132 122 (C) 132 CDradius 26 22 22 34 total 20 13 total total 14 (mm) s Notes to Table V:
PE/Steel in~icates the peel strength in Newtons/mm (N/mm) and pounds/linear inch(pli) when the adhesive-coated polyethylene b~rking was ~tt~rherl to a bare steel pipe. "M" in~lir~tes that the failure was "mixed", i.e. that there was o some adhesive failure to the polyethylene b~rl~ing and some adhesive failure to the steel. In non-mixed failure, the adhesive failure is to the backing.
PE/PP inrlir~es the peel strength in N/mm (pli) when the adhesive-coated polyethylene backing was ~tt~rhrd to a polypropylene-coated steel pipe.
Type in-lic~tçs the type of failure observed during the peel test. AFPE inrlir~tes that s there is adhesive failure to the polyethylene. AFPP in~is~tçs that there is adhesive failure to the polypropylene.

'~ ' t . ' = ~ ,~
~Wo 94/12581 2 1 5C) ~ (99 PCT/US93/11686 Ml is melt index in grams/10 minutes as measured according to ASTM D-1238 Condition E.
Soft Pt. is the softening point in C of the adhesive coll~yosiLion as measured using a TMA with a 50 g weight. For adhesive 21, two softening points were smeasured.
CD radius is the cathodic disbonding radius in mm nlea~ul._d after 30 days at 95C.
"Total" inr~ica-~s that the polymer completely disbonded from the substrate.

Claims

What is claimed is:

1. An adhesive composition suitable for sealing to a substrate which comprises polypropylene, said composition comprising (a) 10% to 90% by weight ethylene polymer which is an ethylene homopolymer. an ethylene copolymer, or a modified ethylene polymer in which a chemical moiety has been grafted onto a polyethylene backbone;

(b) 10% to 90% by weight modified polypropylene which (i) comprises a chemical moiety which is an unsaturated carboxylic acid or acid derivative and which has been grafted onto a polypropylene backbone, and (ii) has a 2% secant modulus of less than 690 MPa (100,000 psi);
and (c) 0% to 30% by weight rubber, and (d) 0% to 25% by weight tackifier.

2. A composition according to claim 1 wherein the chemical moiety grafted to thepolypropylene backbone is an anhydride which is present at at least 0.1% by weight.

3. A composition according to claim 2 wherein the chemical moiety is maleic anhydride.

4. A composition according to claim l wherein the ethylene polymer is polyethylene.

5. A composition according to any one of claims 1 to 4 which comprises 15% to 85% by weight ethylene polymer and 15% to 85% by weight modified polypropylene.

6. A composition according to any one of the preceding claims which, when testedin accordance with ASTM Test G-42, has a cathodic disbonding radius at 95°C after 30 days of less than 35 mm.

7. A heat-recoverable article comprising a heat-recoverable polymeric element, said element having coated on at least a part of a surface thereof an adhesive composition according to any one of the preceding claims. said composition being suitable for sealing to a substrate comprising polypropylene.

8. An assembly which comprises (1) a substance which comprises polypropylene;and (2) an adhesive acccording to any one of claims 1 to 6 which is in contact with and seals to the substrate.

9. An assembly according to claim 8 wherein the substrate comprises a pipe.

10. An assembly according to claim 9 wherein the polypropylene of the substrate is in the form of a layer which surrounds the pipe.