CA1196133A - Adhesive composition - Google Patents

Abstract

ABSTRACT

An adhesive composition comprises (a) a thermoplastic polyamide having reactive amine groups;
(b) a thermoplastic copolymer of an alkene with an ethylenically unsaturated ester of an alkanol and a carboxylic acid, eg. vinyl acetate or ethyl acrylate, and optionally one or more acidic copolymers; and (c) a thermoplastic epoxy resin.

The components (a) and (b) are present in a ratio of from 35:65 to 75:25 by weight and component (c) is present in an amount of from about 8 to 79 parts per hundred parts of components (a) and (b) by weight, components (a), (b) and (c) existing separately in the form of particles that are mixed together.

Description

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- 2 - RK163 This invention relates to adhesives and to dimen-sionally reccverable articles containing such ad-hesives.

In many fields of application of adhesives it is desirable ~o provide an adhesive that will be activated by heat and will provide a strong bond between sub-strates both in the shear mode and in the peel mode.
In such applica~ions hot-melt adhesives have yained widespread use on account of their good bonding charac-telristics and ease of application. However hot-melt adhesives, by their nature, will not exhibit hign bond strengths at high temperatures, eg. in the region of their melting or softening points~ For high temper-ature applications therefore, curable adhesives such as epoxy adhesives have been used. However, whilst these adhesives exhi~it very high bond strengths in the shear moder their bond strength in the peel mode is extremely poor, often less .han 1 N(25mm) 1 due to their brittle-ness, and so are completely unsuitable for many uses.

According to one aspect of the present invention, there is provided an adhesive cornposition which com-prises:

(a) a thermoplastic polyamide havin~ reactive a~ine groups;

(b) a thermcplastic copolymer of an alkene with an ethylenically unsaturated ester of an alkanol and a carboxylic acid, the ester having up to 6 carbon atoms/ and optionally one or rnore acidic ccmonomers; and .,~

- 3 - RKl63 (c) a thermoplastic epoxy resin;

components (a) and (b) being present in a ratio of from 35:65 to 75:25 by weight and componen. (c) being present in an amount of from 8 to 79 parts per hundred parts of components (a) and (b) by weight, components (a), (b) and (cj existing separately from one another in the form of particles that are mixed together.

Preferably the components (a) and (b) are present in a ratio of from about 35:6S to 65:35, more pre~er-ably from about 4:6 to 6:4, especial~y from about 45:55 to 55:45 and most especially about 50:50 by weight.

The adhesive composition may be employed in thesame manner as a conventional hot-melt adhesive, e.g.
by applying it to one or both of ~he substrates to be bonded, bringing the substrates together and heating the adhesive, in this case to cause the particles to fuse. On heating the components (a), ~b) and ~c) react together to form a crosslinked network that is either infusible or has a melting or softening point that is significantly higher than the initial melting or so~tening point of the components, for example 30~
higher or even more. Often the softening points of the installed adhesive may be as high as 50C above the softening point of the initial components for example the softening point may be raised from a value of 90 to 95C up to 140C or higher. This increase in melting or softening point of the adhesive allows the adhesive to be used in conditions where it will be exposed to temperatures higher than its initial melting or soften-ing point and so combines low initial applicationtemperatures with high installed use temperatures~

~ ~43~

- 4 - ~K163 Another advantage of the compositions according to the invent,on is that, whilst they exhibit high bond st`rengths in the shear mode, they also exhibit surpris-ingly high bond strengths in the peel mode at elevated temperatures, for example in the order of 80 to 90 N(25 mm) 1 or more at 70C between polyethylene sub-strates. This is in contrast with conventional epoxy adhesives which exhi~it very low peel strengths~
Furthermore, the cured adhesives have low impact britt1eness points (e.g. -S to -10~C).

The polyamides that are most suitable for ~orming component (a) of the adhesive compositions are those polyamides that are conventionally used to form hot-melt adhesive~. These polyamides are characterized by the fact that their amide linkages are separated by an average of at least fi~teen carbon atoms and have amorphous structures in contrast with the more highly crystalline, fibre forming polyamides such as nylon 6 or nylon 6.6.

In general, any dicarboxylic acid in which the carboxylic acid groups are separated by a bivalent hydrocarbon group which may be saturated or unsatur-ated, aliphatic, aromatic or cycloallp~atic or ~hich may have two or more aliphatic, aromatic or cycloali-phatic moieties, can be used to form the polyamides.
Where long chain diamines are used, that is diamines having chains of at least fifteen carbon atoms separating the nitrogen atoms~ dicarboxylic acids such as adipic, sebacic, suberic, succinic, glutaric, isophthalic, terephthalic and phthalic acids may be, and preferably are, used. Of the dicarboxylic acids, dimeric fatty acids are preferred. The term ~dimeric fatty acid" is intended to include any acid obtained by dimerising saturated, ethylenically unsaturated or acetylenically unsaturated naturally occurring or synthetic monobasic aliphatic carboxylic acids containing from 8 to 24 carbon atoms. Such dimeric fatty acids are fully described in U.S.
Patent Specification No. 4,018,733.
In the diamines that may be used to form the polyamides, the nitrogen atoms are separated by a hydrocarbon group which may be aliphatic, cycloaliphatic or aromatic or may have a combination of any two or more aliphatic, cycloaliphatic or aromatic moieties and, in addition, it may contain ether linkages such as in the diamines prepared from diphenyl ether. Examples of such diamines include straight chain or branched alkylene diamines, having from 2 to 40 carbon atoms in the alkylene group, e.g. ethylene diamine, 1,3-diaminopropane, hexamethylene diamine, 9-aminomethyls-tearylamine alld 10-aminoethylstearylamine; 1,3-di-~-piperidyl propane, diaminodicyclo-hexylmethalle; methylene dianiline alld bis(aminoethyl)diphenyl oxide.
Dimeric fat di.amines and "ether d:iamines" may also be used. These diamines are also described in U.S. Patent No. 4,018,733 mentioned above, and U.S. Patent No. 3,010,782.

1 ' ~

S~l her~in by ~efe~erJce. Usually the amine number of the polyamide will be a~ least 2, preferably at least 5 and especially at least 7 and may be as high as 44 or even higher. For example, the amine number may be as high as 55 or higher provided that the polya~ide remains thermoplastic , the upper limit for the amine number usually being determined by the preferred melting or softening point of the polyamide.

As stated above, component (b) is a copolymer of an alkene with an ethylenically unsaturated alkanol/
carboxylic acid ester containing up to 6 carbon atoms, the term "copolymer" as used herein being defined as ir,c1uding terpolymers and polymers formed from four or more comonomers. Thus~ the copolymer may contain additional comonomers which are preferably acidic, e.g.
are ethylenically unsaturated carboxylic acids, such as acrylic acid, and especially such that the copolymer has an acid number of at least 0.5, more especially at least 1 and most especially at least 3. In addition or altern~tively the copolymer has an acld number of not more than 100. The alkene is preferably a C2 to C6 alkene, more preferably a C2 to C4 alkene, -alkenes being preferred e.g~ 1-butene. The most preferred alkene however is ethylene. The preferred ethylen-ically unsaturated esters are vinyl acetate and ethylacrylate. Examples of materials that may be used are described in the U.S. patent specification No.
4,018,733 to Lopez et al mentioned above.

Any of a number of thermoplastic epoxy resins may be used as component (c). The epoxy resin preferably has an epoxy number of at least 200, more preferably at least 500 and especially at least 800 mmol kg 1 The ~ , - RK163 upper l~mit for the epoxy number is determined by the melting or softening point or the resin, the higher the epoxy number the lower the melting or softening point thereof. The preferred resins will have an epoxy number of not ~ore than 4000, especially not more than 3000 mmol kg 1. Preferred epoxy resins are those based on bisphenol A or epoxy cresyl novolake resins and also multifunctional epoxy resins.

Whilst it has been observed that the peel strength of the adhesive generally increases with the epoxy resin content within the range of 8 to 79 parts per hundred parts of components (a) and (b), this increase is not very ~reat and it is preferred that the compo-sition contains more than 70, more preferably not more than 60, especially not more than 50 and most especially not more than 40 parts of component (c) per hundred parts of .he total of components (a) and (b) by weight~ The components (a), (b) and (c) preferably each has a melting point in the range of from about 60 to about 120C, more preferably from about 70 to about 120C and especially from about 70 to 100C. Composi-tions based on such materials are found to cure when heated to the melting or softening point of the compo-nents but also to have good storage life, e.g. greaterthan 4 months, at storage temperatures as high as 40 to There is essentially no limit on the particle size of the reactive componen~s ih that the articles can still show a synergistic in rate and/or level of cure even with very large particles although the absolute value of the cure rate will decrease with large par-ticles. Preferably the reactive components will have a weight average particle slze of not more that 10Q0, especially not more than 500 and most especially not more than 300 micrometres. Preferably the reactive components have a weight average particle size of at least 1~ more preferably at least 5 and especially at least 10 micrometres. The particle size of the reac-tive components may conveniently be adjusted by sieving the particles through an appropriatel~ sized mesh in which case it is preferred that the particulate compon-ents are substantially free of particles greater than500 micrometres in size. The preferred particle size ranges are rom S to 300 and especially 10 to 200 micrometres.

A number of inert components may be incorporated in the compositions as long as they do not adversely affect the increase in rate or level of cure of the adhesive composition. Also it is preferred if ~hey do not adversely affect the storage life of the adhesive.

There is essentially no limit to the particle size of the components of the adhesive although in practice it is preferred for them to have a weight average particle size of not more than 1000, especially not more than 500 and most especially not more than 300 micrometres. Preferably they have a weight average particle size of at least 1, more preferably at least 5 and most preferably at least 10 micrometres.

According tG another aspect of the invention there is provided a method of bonding a pair of surfaces together, which comprises (i) interp~sing between the surfaces an an adhesive composition which comprises:

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- g - P~K163 (a) a thermoplastic polyamide having reacti~e amine groups;

(b) a thermoplastic copolymer of an alkene with an ethylenically unsaturated ester of an alkano~ and a carboxylic acid, the ester ha~ring up to 6 carbon atoms~ and optionally one or more acidic comonomers; and (c) a thermoplastic epoxy resin;

components (a) and (b) being present in a ratio of from 35.65 to 75:2S by weight and component (c) being present in an amount of from 8 to 79 parts per hundred parts of components (a) and (b) by weight, components (a), (b) and (c) existing ~eparately from one another in the form of particles that are mixed together.
(ii) bringing the surfaces together; and (iii) heating the adhesive composition to cause the articles to fuse.

Because of the advantageous properties of the adhesive compositions according to the invention, especially their high temperature peel strength, the compositions are particularly suitable for use with dimensionally recoverable articles.

Dimensionally recoverable articles are articles having a dimensional configuration that may be made substantially to change when subjected to the appro-priate treatment. Of particular interest are dimen-sionally heat-recoverable articles, the dimensional configuration of ~hich may be made substantially to change when subjected to heat-treatment ~ 10 - RK163 Usually these articles recover, on heating, towards an original shape trom which they have prev-iously been deformed, but the term "heat-recoverable", as used herein, also includes an article which, on heating, adopts a new configuration, even if it has not been previously deormed.

In their most common form, such articles comprise a heat-shrinkable sleeve made from a polymeric material exhibiting the property of elastic or plastic memory as described, for example, in U.S. Patents 2,027,962;
3,0~6,242 and 3,957,372. As is made clear in, for example, U.S. Patent 2,C27,962, the original dimension-ally heat-stable form may be a transient form in a continuous process in which, ror example, an extruded tube is expanded, whilst hotl to a dimensionally heat-unstable form but, in other applications, a preformed dimensionally heat stable article is deformed to a dimensionally heat-unstable form in a separate stage.

In the production of heat recoverable articles, tne polymeric material may be cross-linked at any stage in the production of the article that will enhance the desired dimensional recoverability. One manner of producing a heat-recoverable article comprises shaping the polymeri.c material into the desired heat-stable form, subse~uently cross-linking the polymeric mat-erial, heating the article to a temperature above a transition temperature thereof, for e~ample, the crystalline meltins~ point or, for amorphous materials the softening point, as the case may be, of the poly-mer~ deforming the article and cooling the article ~ R~163 whilst in the deformed state so that the deformed state oS the article is retained. In use, since the deformed state of the article is heat unstable, application of heat to raise the tempera~ure above the transition temperature will cause the article to assume its original heat-stable shape.

In other articles, a5 described, for example, in British Patent l,440,524, an elastomeric member such as an outer tubular member is held in a stretched state by a second member, such as in inner tubular member, which, upon heating weakens and thus allows the elasto-meric member tc recover.

Articles of thls type have, in recent years~
become widely used in a number of applications, for example for protecting objects such as electrical cables and cable splices or metal pipes from corrosion or other damage, for example damage caused by pene-tration of moisture.

The articles may be formed in a number of confi-gurations depending on the particular use. ~hey ma~v bein the for~ of a tube that has been extruded and expanded radially to render it heat-recoverable, the tube being either in continuous lengths or discrete pieces and being coated on its internal surface with the adhesive compositions. Alternativelyr the articles may be in the form of a sheet or tape that can be wrapped or wound around an object. ~ore complex shapes, commonly referred to as boots, transitions, udders or caps, may be formed by moulding the articles in the desired configuration and then expanding them or 9i~ t.3 -~ 12 -by the methods described in our copending U.K. Applications Nos.
8123069 and 8123072 (Serial Nos. ~083403A and 2083859A). The present invention is also suitable for the production of wrap-around devices.
So called wrap-around devices are employed for sealing, insulating or otherwise protecting a substrate where the use of a preformed tubular article such as a sleeve, is not possible or convenien-t e.g. in the case where the end of an elongate substrate is not accessible. In general, such wrap-around articles comprise at least a portion there-of which is adapted to be wrapped around a substrate to be covered and secured in tubular form by closure means. Thereafter, -the wrap-around closure may be heat-recovered tightly onto the substrate by application of heat. Examples of wrap-around devices are described in U.S. Patents Nos. 3,379,218, 3,455,326, 3,530,898, 3,542,079 and 3,574,318~ Another form of wrap-around device in which the curable adhesive may be used is -that described in U.K. Patent Application No.
8113486 (Serial No. 2076694A) in which the curable adhesive is used to orm a layer oE sealant that may be peeled away at any desired point to expose a closure adhesive.
The adhesive composition may be coated on the heat-recoverable article in a number of ways depending on the -type of article and adhesive composition. ~or example, where the a-rticle has an open, generally uniform con-figuration, it may be provided with a layer of tacky material for example pressure sensitive adhesive layer e.g. by spraying or in the form of a tape, and the adhesive composi~
tion may be applied as a powder to the pressure sensitive adhesive ~earing portions of the article and compressed thereon by applica,ion of pressure. ~lt-ernatively, the powder may be compressed into a coheren~ layer and then bonded to the article by means of a tacky materialO For either of these methods~ pressures in the order of 0.8 MPa (120 p~s.i.) and temperatures of about 15 to 30~C have been found to be most suitable. These methods of applying the adhesive composition are suitable for applications in which the adhesive contains no compo nents other than the particulate reactive components in addltion to those in which the adhesive does contain other components. In another method of applying the adhesive composition, the particula~e reactive compo~
nents are mixed with the other components which prefer-ably comprise or include a pressure-sensitive adhesive or a mastic and the whole composition is pressed onto the heat-recoverable article or pressed into a coherent film which is then adhered to the heat-recoverable article, the temperatures and pressures used preferably being the same as those mentioned above.

Yet another method of application, which is suitable for coating the internal surfaces of tubes or moulded articles, comprises spraying the adhesive onto the appropriate parts of the article. The adhesive may be sprayed in the form of the dry powder onto a sur~ace that is coated with a tacky material, e.g. a pressure sensitive adhesive1 or the particulate reactive compo nents may be dispersed in a non~solvent that contains a binder andr after the dispersion is sprayed onto the article, the non-solvent is allowed to evaporate.

- 1 4 ~ RX163 The following Examples illustrate the invention:
Examples 1 to 10 Samples of adhesive compositions according to the .0 invention were prepared by cryogenically grinding polyamide hot-melt adhesive or blend of adhesives, an ethylene copolymer and an epoxy resin, sieving the components to exclude particles of greater than 300 micrometres and mixing the particles to~ether. The ro~ling drum peel strength of the adhesive was measured at 70C in accordance with the procedure described in U~S. Patent No. 4,018,733 column 12.

The compositions and results are shown in Table I.

~AB~E I

EXAMPLE

parison Invention Comparison ~ ponents Trade name Parts by ~eight Polyamide Ma~cmelt 6301+
20 blend Eurelon 100 (9:1) 50 50 50 50 50 50 50 50 50 50 E.V.A. CXA 2002 50 50 50 50 50 50 50 50 50 50 Epoxy resin Epi~ote 1004 0 1 6 10 43-75 80 10C 200 400 Peel strength at 70 C/N(25mm) 1 50 20 29 83 88 99 30 Brittle ~ailure Examples 11 to 26 The procedure of Examples 1 to 10 was repeated with a numbr of compositions to demonstrate the limits for the propor~ions of polyamide and ethylene copoly~
mer. In addition to the peel strength~ the lap shear strength of the adhesive was measured at 70C in accordance with AST~-D638 between aluminium substrates.
The results are shown in Table II.

TABLE I I

Components Trade name 11 12 13 14 1S 16 17 18 19 20 21 22 23 24 25 26 INVENTION COMPARISON

PARTs BY WEIGHT

Polyamide blendMacromelt 6301+ 70 60 50 50 40 100 80 80 70 60 50 40 30 30 20 20 Eurelon 100 F,poxy resin Epikote 100410 10 10 10 10 10 Epoxy resin Epikote 100110 1n d~ Pont Peel stret1gth at 70~C/N(25 mm) 31 81 83 147 82 45 31 40 20 48 50 S5 24 15 43 30 Shear strength at 70C/N~25mm) 2 5~3 515 840 690 358 620 550 431 425 497 283 35Q

Examples 27 to 32 The procedure of Examples 10 to 19 was repeated usin~ a number of~ different ethylene copolymer compo-nents. The peel and shear strengths were measured at 70C and in each case the composition was compared with a corresponding composition containing no epoxy. The results are shown in Table III.

TABLE IIL
Components Trade name EXAMPLE
27 28 29 3~ 31 32 PARTS BY WEIGHT

Polyamide blend Macromelt 6301~ 50 50 50 50 50 50 50 50 50 50 50 50 50 Eure1On lQ0 ~9:1) Epoxy resin Epi~ote 1001 10 Epoxy resin Epikote 1004 10 10 10 10 10 10 EVA (acid No=1) Elvax 460 50 50 50 (du Pont) EVA (acid No=6) Elvax 4320 50 50 F~rA (acid No=36) CXA 2002 50 50 ~thylene ethyl DPD6169 acrylate (Union Carbide) 50 50 Ethylene butyl Lupolene A2910 acrylate acrylic (BASF) 50 50 acid Ethylene acrylic AC540A S0 50 acid \Allied Chem) Peel streng~h at 70 C/N(25 mm) 40 56 9 70 9 49 46 56 6 29 29 31 35 Shear strength at 70C/N(25mm) 2 505 404 374 323 353 ~15 404 358 ~6~33 - l9 - RKl63 ` 150 Parts of Versalon 1300 polyamide that had been modlfied by milling in 5% by weight of a reactive liquid polyamide sold under the trade name Vers.~.id 100 and had been cryog~enically ground to form a powder were mixed with lO0 parts of a powdered ethylene-vinyl acetate acid terpolymer sold under the trade name Elvax 4~60, 80 parts of a bisphenol P epoxy resin sold by Shell Chemicals under the type ~oO Epikote 1004, and 6 parts of a dimethylaminopyridine accelerator. The powder was then seived to remove all particles greater than 300 micrometres in size.

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as fol-lows:

1. An adhesive composition which comprises:

(a) a thermoplastic polyamide having reactive amine groups;

(b) a thermoplastic copolymer of an alkene with an ethylenically unsaturated ester of an alkanol and a carboxylic acid, the ester having up to 6 carbon atoms, and optionally one or more acidic comonomers; and (c) a thermoplastic epoxy resin;

components (a) and (b) being present in a ratio of from 35:65 to 75:25 by weight and component (c) being present in an amount of from 8 to 79 parts per hundred parts of components (a) and (b) by weight, components (a), (b) and (c) existing separately from one another in the form of particles that are mixed together.

2. A composition as claimed in claim 1 wherein component (b) has an acid number of less than about 100.

3. A composition as claimed in claim 1, wherein the ethylenically unsaturated ester of component (b) is vinyl acetate or ethyl acrylate.

4. A composition as claimed in claim 1, wherein the alkene of component (b) is a C2 to C4 alkene.

5. A composition as claimed in claim 4, wherein the alkene of component (b) is ethylene.

6. A composition as claimed in claim 1, wherein components (a) and (b) are present in a ratio of from about 35:65 to 65:35 by weight.

7. A composition as claimed in claim 6, wherein components (a) and (b) are present in a ratio of from about 4:6 to 6:4 by weight.

8. A composition as claimed in claim 7, wherein components (a) and (b) are present in a ratio of from about 45:55 to 55:45 by weight.

9. A composition as claimed in claim 1, wherein each of components (a), (b) and (c) has a melting or soften-ing point in the range of from 60 to 120°C.

10. A dimensionally-recoverable article having on at least part of a surface thereof an an adhesive composi-tion which comprises:

(a) a thermoplastic polyamide having reactive amine groups;

(b) a thermoplastic copolymer of an alkene with an ethylenically unsaturated ester of an alkanol and a carboxylic acid, the ester having up to 6 carbon atoms, and optionally one or more acidic comonomers; and (c) a thermoplastic epoxy resin;

components (a) and (b) being present in a ratio of from 35:65 to 75:25 by weight and component (c) being present in an amount of from 8 to 79 parts per hundred parts of components (a) and (b) by weight, components (a), (b) and (c) existing separately from one another in the form of particles that are mixed together.

11. A method of bonding a pair of surfaces together, which comprises (i) interposing between the surfaces an an adhesive composition which comprises (a) a thermoplastic polyamide having reactive amine groups;

(b) a thermoplastic copolymer of an alkene with an ethylenically unsaturated ester of an alkanol and a carboxylic acid, the ester having up to 6 carbon atoms, and optionally one or more acidic comonomers; and (c) a thermoplastic epoxy resin;

components (a) and (b) being present in a ratio of from 35:65 to 75:25 by weight and component (c) being present in an amount of from 8 to 79 parts per hundred parts of components (a) and (b) by weight, components (a), (b) and (c) existing separately from one another in the form of particles that are mixed together.
(ii) bringing the surfaces together; and (iii) heating the adhesive composition to cause the articles to fuse.