CA1331818C

CA1331818C - Polyethylene alkyl acrylate adhesive composition

Info

Publication number: CA1331818C
Application number: CA000592026A
Authority: CA
Inventors: Noel Marcel Michiel Overbergh
Original assignee: Raychem NV SA
Current assignee: Commscope Connectivity Belgium BVBA
Priority date: 1988-02-25
Filing date: 1989-02-24
Publication date: 1994-08-30
Anticipated expiration: 2011-08-30
Also published as: EP0330480B1; ATE88491T1; EP0330480A3; DE68906052D1; US4965320A; EP0330480A2; DE68906052T2; JPH026580A; GB8804408D0; JP2682864B2

Abstract

ABSTRACT
A hot-melt adhesive composition which comprises a mixture of:
(a) 25-40 parts by weight of a polyethylene alkyl acrylate terpolymer containing maleic anhydride and having a melt flow index as determined according to ASTM D1238-70 of at least 40; and (b) 25-70 parts by weight of a polyethylene alkyl acrylate copolymer having a melt flow index as determined according to ASTM D1238-70 of at least 40.

Description

1331~18 , POLYETHYLENE ALKYL ACRYLATE ~DHESIVE COMPOSITION
The present invention relates to an adhesive, par-ticularly a hot-melt, composition comprising a blend of polyethylene alkyl acrylates. The adhesive is especially useful in the cable accessories and pipeline industries for bonding to polyethylene and lead etc.
Environmental protection frequently has to be provided around substrates such as cables to protect them from con-taminants such as moisture. An excellent way to provide such protection is to surround the substrate with an adhe-sive composition, conveniently applied as a coating on a dimensionally-recoverable, preferably heat-shrinkable sleeve. Such a sleeve may be positioned around the substrate and heated, causing the adhesive composition to become molten or softened and causing the sleeve to shrink, driving the adhesive into bonding engagement with th~
substrate. The sleeve itself may, of course, provide environmental protection, and the quantity of adhesive required may be reduced by coating the sleeve only at its edges to provide a bond to the substrate.
A specific instance where environmental protection is required is around a cable splice, particularly in multi-core telecommunications cables, where missing cable sheath (removed in order to form the splice) has to be made good.
This may be done by installing a liner around the splice, -~
the liner preferably being shaped to provide a smooth tran-sition between the bulky splice and the smaller diameter cable or cables that enter and leave it. The liner is then surrounded by a heat-recoverable sleeve that extends past each end of the liner down onto intact cable jacket. The sleeve is internally coated with a hot-melt adhesive com-position and, when heated, it shrinks down and becomes ,'`~ ` , ;'` ' , bonded to each cable jacket and the liner between them. In this way leak paths from the outside environment into the now formed splice case are avoided, and the conductors of the cable protected from moisture etc.
Such splice cases may be expected to provide an environ-mental barrier for the lifetime of the cable, say at least twenty-five years. The cable, and splice case, may be sub-jected to temperature variations ranging from say -40C in winter to say +70C in the case of a cable exposed to direct sunlight, and the cable may be internally pressurized. As will be appreciated, these requirements of lifetime, tem-perature and pressure put severe demands on the performance of the adhesive. The problem is made more difficult because, for practical purposes, a given product may have to be suitable for many different environments, for example around buri~d cables in cold countries, and aerial cables in hot countries.

These performance requirements are themselves difficult to achieve at an acceptable price, but the difficulty can be seen to be particularly acute when one considers installa-tion conditions. Installation is at present carried out by heating the sleeve and consequently the adhesive with an open-flame torch, although electrical heating may be used.
It is clearly desirable that the amount of heat required to soften the adhesive be kept to a minimum. The weather may be cold, there may be little room in a man-hole for vigorous heating, an electrical heater may have limited power, and the cable or the sleeve may be damaged by high temperatures etc. Thus, there is a maximum acceptable installation tem-perature. ~lso, as noted above there is a wide temperature range over which the adhesive must retain its adhesive power. Unfortunately, the maximum allowable installation -, , , . . . ~ . . . - . -~ 133~ 81~

temperature is not very much higher than the minimum accep-table upper limit to the range of service temperatures. We have therefore found that our adhesive should have a sharp melt transition.
In addition to a sharp melt transition, the adhes~ve should have a high peel strength to polyethylene, preferably non-flame-brushed as well as flame-brushed, and to lead, it should have good low temperature impact strength and low temperature flexibility, and it should have low viscosity at the installation temperature, say at 160C.
Attempts have been made to formulate adhesive com-positions that provide certain specific benefits, and the following prior art compositions based on polyethylene alkyl acrylates may be mentioned.
U.S. 4,252,858 (Chao, assigned to Raychem) discloses a hot-melt adhesive comprising an ethylene copolymer, a fluorocarbon elastomer and a tackifier. The copolymer may be the terpolymers of ethylene, ethylacrylate and methacrylic acid known by the trade marks DPD 6169 and DPD 6181. They have very low melt flow indices of about 6.
U.S. 3,983,070 (Penneck, assigned to Raychem) discloses an adhesive comprising a polar copolymer of an alpha-olefin (for example ethylene ethyl acrylate) or a mixture of such copolymers and a chemically treated silica filler.
Additives may be provided to achieve the desired flow pro-perties. An example of the ethylene ethylacrylate given is that known by the trade mark DPD 9169, which has a low melt flow index of about 20.
U.S. 4,374,231 (Doucet, assigned to Raychem) discloses a polyamide adhesive that includes an ethylene, acrylic acid, butyl acrylate terpolymer, with low melt flow indices.

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133~18 G.B. 2,111,065 (Raychem) discloses a hot-melt adhesive composition comprising a copolymer of ethylene, such as ethylene vinylacetate mixed with a copolymer such as ethy-lene butyl acrylate or ethylene, butyl acrylate, acrylic acid terpolymer, with low melt flow indices.

U.S. 3,485,783 (Kehe, assigned to Continental Can Co.) discloses a hot-melt adhesive comprising a mixture of an ethylene alkyl acrylate (which alkyl acrylate may be ethyl acrylate or butyl acrylate), an ethylene acrylic acid copo-lymer and a polymerized rosin ester.
U.S. 4,332,655 (Bereijka, assigned to Raychem) discloses a hot-melt adhesive comprising a blend of an adhesive ethy-lene copolymer, such as ethylene ethyl acrylate or ethylene butyl acrylate, and an elastomeric olefin havinq a saturated backbone. A wide range of melt indices for the adhesive ethylene copolymer is envisaged.
G.B. 1,581,559 (Raychem) discloses an adhesive com-position comprising an adhesive copolymer cross-linked by irradiation, and an aromatic tackifier. The copolymer may be that known by the trade mark DPD 6181, an ethylene ethyl acrylate copolymer of low melt flow index.
U.S. 4,146,521 (Godfrey, assigned to Eastman Kodak) discloses a hot-melt adhesive comprising polyethylene, an ethylene lower alkyl acrylate copolymer, a tackifier and a ~ -wax. The copolymer may be ethylene ethyl acrylate haviLng a low melt flow index (2-30) or ethylene butyl acrylate.
G.B. 1,041,065 (union Carbide) discloses an adhesive comprising an olefin high polymer having a melt index of less than 1000 (preferab]Ly less than 100) and an ethylene, acrylic acid terpolymer the third monomer of which may be . , , ethyl acrylate or butyl acrylate. The terpolymers have a melt flow index of less than 1000, preferably less than 100.
I have now formulated an inexpensive novel adhesive com-position based on polyethylene alkyl acrylate copolymers and terpolymers, particularly those including ethyl and/or butyl acrylates, that provides excellent low temperature flexibi-lity and good adhesion to cable substrates and having the appropriate flow characteristics to ensure good installabi-lity to heat-shrinkable articles. Unlike the prior art referred to above, the present invention combines polyethy-lene alkyl acrylate terpolymers and copolymers and optionally a tackifier. These ingredients will generally be extrusion mixable from pellet form, thus facilitating manu-facture.
Thus, the present invention provides a hot-melt adhesive composition comprising a mixture of:
(a) 25-40 parts by weight of a polyethylene alkyl acry-late terpolymer containing maleic anhydride and having a melt flow index as determined according to ASTM D1238-70 of at least 40 and preferably having an acid index of from 11-19 ~mg ROH per g by titration); and (b) 25-70 parts by weight of a polyethylene alkyl acry-late copolymer having a melt flow index as determined according to ASTM D1238-70 of at least 40.
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The terpolymer (a) is preferably a terpolymer of ethy-lene, ethyl and/or butyl (preferably ethyl) acrylate and maleic anhydride; and the copolymer (b) is preferably a copolymer of ethylene and ethyl and/or butyl (preferably butyl) acrylate. Other alkyl acrylates, particularly lower (espec~ally Cl-6, typically C2-5) acrylates may, however, be used .

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The copolymer (b) consists essentially of ethylene and one or more ~preferably one) alkyl acrylate, there pre-ferably being no third comonomer present. Any third como-nomer is preferably present as less than 5 mole ~, more preferably less than 2 mole %, especially less than 1 mole ~. Similarly, the terpolymer preferably consists essen-tially of the three specified monomers, any fourth pre-ferably beinq present as less than 5 mole %, more preferably less than 2 mole ~, especially less than 1 mole %.
The adhesive composition may usefully be used in con-junction with, preferably supplied as a coating on, a heat-recoverable article. The heat-recoverable article may comprise an extended continuum, or it may comprise a com-posite material for example one shrinkable by virtue of a shrinkable fibre component thereof. Preferred composite materials comprise shrinkable fibres and a polyethylene matrix material to which the adhesive composition is bonded.
The adhesive thus may be used to form a bond between the ~ -polyethylene matrix and a polyethylene cable jacket. In one embodiment, the composite material comprises a shrinkable fabric of shrinkable high density polyethylene ~preferably weft) and glass fibres (preferably warp) together with a low density polyethylene matrix, and optionally incorporating a strengthening or moisture barrier layer in the form of a thin aluminum or other metal foil.
Such a composite or other recoverable article is pre~
ferably in the form of a tubular or wrap-around sleeve, and ;~
may be used to provide environmental protection around a pipe or cable, for example, a cable splice. Where a branched cable splice is to be sealed, a branch-off clip such as that disclosed in G.B. 1,604,981 may be used to bring or maintain together circumferentially-separated portions of . ~ :
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The composition of the invention may additionally comprise a flow-temperature- or viscosity-modifying agent.
Examples include tackifiers, waxes, modified waxes, polyiso-butylene and that known by the Monsanto trade mark, Santicizer (e.g. N-ethyl o- and p-toluene sulphonamides) and equivalents. In general, ingredients that increase visco-sity are preferably avoided. Furthermore, I prefer that the composition is not subjected to cross-linking, particularly is not irradiated. The term "tackifier" is used in the adhesives art to mean a material which when added to an adhesive promotes its adhesion to a substrate, by increasing its ability to wet the substrate. Examples of tackifiers include low molecular weight polymers of monomers that con-tain ethylenic unsaturation and are free of polar groups.
Specific examples include Nevpene 9500 (trade mark) which is believed to be a copolymer of a mixture of aromatically- and aliphatically-substituted ethylene, and Piccotex 75 (trade ~ ~;;
mark of Industrial Chemical Corp.) which is believed to be a copolymer of vinyl toluene and alpha-methylstyrene.
Preferred tackifiers, however, comprise terpene phenolic resins such as SP 553 (trade mark, Schenectady Corp.) and Nevillac Hard (trade mark of Neville), particularly the former. The tackifier preferably has a Brookfield viscosity at 160C of 80-1500 centipoises; a ring-and-ball softening point as determined according to ~STM E-28 of 50-130C, more preferably 80-120C, or preferably 110-120C, particularly about 115C; and a molec~llar weight of less than 3000.
Given the basic components of the composition of the invention, the skilled man after reading this specification ..
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1331! 818 will be able to choose a tackifier or other flow-temperature-or viscosity-modifying agent to achieve the desired properties, namely one or more of:

(a) a ring-and-ball softening point as determined according to ASTM E-28 of from 90-110C, preferably 95-105C;
(b) a viscosity as determined according to ASTM D3236 at 160-C of from 40-110 Pa.s, preferably 60-90 Pa.s;
(c) a viscosity as determined according to ASTM D3236 at 200C of from 10-50, preferably 15-40 Pa.s, more preferably 20-35 Pa.s;
(d) an impact brittleness as determined according to IS0 974 of less than -30-C, preferably less than -35~C; and (e) a peel strength to non-flame-brushed and/or flame-brushed polyethylene as determined according to QAPK K027 of - greater than 150 N/25 mm, preferably greater than 200 N/25 mm, especially greater than 250 N/25 mm, the measurements being made at 21-C.

I have found that all of these properties can be achieved using the above defined mixture of polyethylene alkyl acrylates, each of high melt flow index, together with from 5-15, preferably 10-15, parts by weight of SP 553 or equivalent as tackifier. The use of alternative tackifiers -~
or alternative quantities will in general allow chosen ones of the above properties to be achieved.

For some purposes it may be desirable to add small quantities of one more polyamides to the mixture. A suitable polyamide is one having an amine number below 5, preferably below 4. For example up to 15 parts by weight of a polyamide -~
may be added, although I have found that satis- ;

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I prefer that the polyethylene alkyl acrylate terpolymer has a melt flow index as defined of at least 70, more pre-ferably from 100-300. This terpolymer may, for example, comprise: a terpolymer of ethylene; ethyl acrylate and/or butyl acrylate (preferably ethyl acrylate); and maleic anhydride. It preferably has a ring-and-ball softening point as determined according to ASTM E-28 of 80-125C, more preferably 95-120C. Its viscosity as determined according to ASTM D3236 at 160C is preferably from 120-140 Pa.s.
Preferred terpol~mers include that known by the trade mark Lotader 8200 (Companie de France), and equivalents.
The polyethylene alkyl acrylate copolymer preferably has a melt flow index as defined of at least 70, more preferably 100-300. It preferably has a ring-and-ball softeninq point as determined according to ASTM E28 of 80-125C, more pre-ferably 90-115C. Its viscosity as determined according to ASTM D3236 at 160C is preferably from 70-150 Pa.s.
Preferred copolymers include polyethylene butyl acrylates such as that known by the trade mark Lotader HX-8280 (Companie de France), and equivalents, and polyethylene ethyl acrylates such as those known by the trade marks Alathon 704 ~DuPont) and EA 89821 (USI), and equivalents.
The composition preferably has:
(a) 28-38 parts by weight of the polyethylene alkyl acrylate terpolymer; and (b) 55-70 parts by weight of said polyethylene alkyl acrylate copolymer.

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0?.' ~ - . ~ - ' ` '' ' '~ ' ~3~:~18 I prefer that the composition consist essentially of the polyethylene alkyl (preferably ethyl) acrylate terpolymer, the polyethylene alkyl (preferably butyl) acrylate copo-lymer, the tackifier and optionally, the polyamide.
Preferably any other component is present as less than 10 parts by weight, more preferably less than 5 parts by weight, especially less than 2 parts by weight. Examples of permissible minor components include stabilizers such as antioxidants, a preferred amount of which is about 1 part by weight. In particular I prefer that the composition con-tains substantially no vinyl acetate nor copolymer thereof.
The invention is further illustrated by the following examples.
Example 1 The following ingredients, the first two at least ini-tially in pellet form, were mixed for 45 minutes in a mixer at 210C~
30 parts by weight of Lotader 8200 59 parts by weight of Lotader HX 8280 10 parts by weight of Tackifier SP553 -~
1 part by weight of antioxidant.
The resulting composition had a viscosity as determined ~- -according to ASTM D3236 at 160C of 74 Pa.s, and at 200C of 25 Pa.s. Its ring-and-ball softening point as determined ~ -according to ASTM E28 was 102C, and its impact brittleness (ISO 974) was -38C.
The composition was coated onto a heat-shrinkable sleeve having a polyethylene surface, and the coated sleeve was bonded, using the composition of the invention, to the following substrates, the following peel strengths (QAPK
R027) being recorded:

1331~`8 flame-brushed polyethylene (21C) 258 N/25 mm non-flame-brushed polyethylene (21C) 260 N/25 mm Lead (21C) 350 N/25 mm Aluminum (21C) 258 N/25 mm flame-brushed polyethylene t50C) 31 N/25 mm flame-brushed polyethylene (60C) 14 N/25 mm Example 2 Example 1 was repeated, but using the following ingre-dients:
Lotader 820035 parts by weight Lotader HX 8280 59 parts by weight Tackifier SP553 15 parts by weight Antioxidant1 part by weight.
T~e composition had a viscosity (ASTM D3236) at 160C of 68 Pa.s., and at 200C of 25 Pa.s. Its ring-and-ball sof-tening point (~STM E28) was 102C, and its low temperature impact brittleness (ISO 924) was -30C.
The composition when applied to a shrinkable sleeve having a polyethylene surface was tested for peel strength (QAPR R027), and the results were 282 N/25 mm to flame-~-brushed polyethylene at 21C, and 251 N/25 mm to non-flame-brushed polyethylene at 21C.
; Example 3 Example 1 was repeated, but using the following ingre-dients:
Polyamide with 5 parts by weight amine number below 4 Lotader 8200 30 parts by weight ;.: .
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1~318~8 Lotader HX8280 64 parts by weight Tackifier SP553 15 parts by weight Antioxidant 1 part by weight The composition had a viscosity (ASTM D3236) at 160C of 87 Pa.s., and at 200C of 30 Pa.s. Its ring-and-ball sof-tening point (ASTM E28) was 105C, and its low temperature impact strength (ISO 974) was -30C.
The composition when applied to a shrinkable sleeve having a polyethylene surface was tested for peel strength (QAPR R027) and the results were 233 N/25 mm to flame-brushed polyethylene at 21C, and 229 N/25 mm to non-flame-brushed polyethylene at 21C. -, ~ -','~,- ~':

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Claims

1. A hot-melt adhesive composition which comprises a mixture of:

(a) 25-40 parts by weight of a polyethylene alkyl acrylate terpolymer containing maleic anhydride and having a melt flow index as determined according to ASTM D1238-70 of at least 40; and (b) 25-70 parts by weight of a polyethylene alkyl acrylate copolymer having a melt flow index as determined according to ASTM D1238-70 of at least 40.

2. An adhesive composition according to claim 1, in which the terpolymer (a) comprises a polyethylene ethyl acrylate terpolymer, a polyethylene butyl acrylate terpolymer or a mixture thereof.

3. An adhesive composition according to claim 1, in which the copolymer (b) comprises a polyethylene ethyl acrylate copolymer, a polyethylene butyl acrylate copolymer or a mixture thereof.

4. An adhesive composition according to claim 1, in which the terpolymer (a) comprises a polyethylene ethyl acrylate terpolymer and copolymer (b) comprises a polyethylene butyl acrylate copolymer.

5. An adhesive composition according to claim 1, which additionally comprises:

(c) from 5 to 15 parts by weight of a flow-temperature-or viscosity-modifying agent.

6. An adhesive composition according to claim 4 having:

(a) 28-38 parts by weight of said polyethylene ethyl acrylate terpolymer; and (b) 55-70 parts by weight of said polyethylene butyl acrylate.

7. An adhesive composition according to any one of claims 1 to 6 in which the melt flow index of terpolymer (a) or of copolymer (b) is at least 70.

8. An adhesive composition according to any one of claims 1 to 6, which additionally comprises:

(d) up to 15 parts by weight of a polyamide.

9. An adhesive composition according to any one of claims 1 to 6, in which the terpolymer (a) has a ring-and-ball softening point as determined according to ASTM E28 of 80-125°C.

10. An adhesive composition according to any one of claims 1 to 6, in which the copolymer (b) has a ring-and-ball softening point as determined according to ASTM E28 of 80-125°C.

11. An adhesive composition according to claim 5, in which the modifying agent has a ring-and-ball softening point as determined according to ASTM E-28 of 80-120°C.

12. An adhesive composition according to claim 5, in which the modifying agent comprises a tackifier.

13. An adhesive composition according to claim 12, in which the tackifier comprises a terpene phenolic resin.

14. An adhesive composition according to any one of claims 1 to 6 or 11 to 13, having a ring-and-ball softening point as determined according to ASTM E-28 of from 90-110°C.

15. An adhesive composition according to any one of claims 1 to 6 or 11 to 13, having a viscosity as determined according to ASTM D3236 at 160°C of from 40-110 Pa.s.

16. An adhesive composition according to any one of claims 1 to 6 or 11 to 13, having a viscosity as determined according to ASTM D3236 at 200°C of 15-40 Pa.s.

17. An adhesive composition according to any one of claims 1 to 6 or 11 to 13, having an impact brittleness as determined according to ISO 974 of less than -30°C.

18. An adhesive composition according to any one of claims 1 to 6 or 11 to 13, exhibiting a peel strength to non-flame-brushed polyethylene and/or flame-brushed as determined according to QAPK K027 of greater than 150 N/25 mm at 21°C.

19. An adhesive composition according to any one of claims 1 to 6 or 11 to 13, that contains substantially no vinyl acetate nor copolymer thereof.

20. An adhesive composition according to claim 1 that consists essentially of said terpolymer (a), said copolymer (b), a tackifier and optionally a polyamide.

21. An adhesive composition according to claim 20, containing substantially no polyamide.

22. A heat-recoverable article having thereon an adhesive composition, said composition being a composition according to claim 1.

23. An article according to claim 22, which comprises a composite material that is shrinkable by virtue of a shrinkable fibre component thereof.

24. An article according to claim 23, in which the composite material comprises shrinkable fibres and a polyethylene matrix to which the adhesive composition is bonded.

25. An article according to any one of claims 22-24, in which the article comprises a tubular or wrap-around sleeve.

26. A method of environmentally sealing a cable or a pipe which comprises:

(a) providing an adhesive composition according to claim 1;
(b) heating the composition;
(c) allowing or causing the composition to flow around a surface of the cable or pipe;
(d) allowing or causing the composition to cool.

27. A method according to claim 26, in which the composition is provided as part of a heat-recoverable article.