WO1987000190A1

WO1987000190A1 - Thermosetting adhesives for use with heat-recoverable closures

Info

Publication number: WO1987000190A1
Application number: PCT/US1986/001302
Authority: WO
Inventors: Thomas J. Bonk
Original assignee: Minnesota Mining And Manufacturing Company
Priority date: 1985-07-08
Filing date: 1986-06-17
Publication date: 1987-01-15
Also published as: BR8606767A; JPS62503176A; EP0229114A1; ZA865034B; KR880700038A; AU5998286A

Abstract

A thermosettable adhesive composition which has excellent cohesive strength when activated and cured. The composition is comprised of a dimer acid based amine-terminated polyamide and an acidic ethylene copolymer comprised of repeating units derived from a major amount of ethylene and a minor amount of one or more alpha,beta-ethylenically unsaturated acids, the composition being adhesively crosslinked. These adhesives are especially useful in sealing a heat-recoverable closure to a substrate after the closure has been caused to recover about the substrate.

Description

THERMOSETTING ADHESIVES FOR USE WITH HEAT-RECOVERABLE CLOSURES

Technical Field of the Invention This invention relates to an adhesive having exceptional utility in conjunction with heat-recoverable closures. More specifically, the invention relates to a thermosetting adhesive composition containing an amine-terminated dimer-based polyamide and an acidic ethylene copolymer.

Background of the Invention

Hot-melt adhesives are typically 100 percent solids adhesive which are capable of melting or flowing under heat. Upon cooling, the adhesive forms a tenacious bond to various substrates. One area of utility for hot-melt adhesives is in conjunction with heat-recoverable closures. Such closures can be utilized around cable splices or repairs in the telecommunication field, for example, with the closure caused to recover around the desired cable portions to provide the requisite seal. In many instances, in order to prevent the ingress of water or humidity into the electrical wires contained within the cable, it is customary to use a sealant between the closure and the cable, one example of which is a hot-melt adhesive. As heat is applied to the heat-recoverable closure to cause same to recover around the substrate it is desiged to seal, the hot-melt adhesive softens within the closure to effect a satisfactory bond and seal. In such situations, the hot-melt adhesive must be capable of wetting the heat-recoverable substrate, it must be capable of developing good adhesion to polyethylene or other cable jacket materials conventionally used in the telecommunications field, it must be able to maintain good adhesion at 60°C, and it must also have a satisfactory viscosity to avoid excessive dripping of the adhesive during the recovery process. Conventionally available hot-melt adhesives have not been found which satisfy all the foregoing characteristics. One such hot-melt adhesive which is commercially available is based on polyamide chemistry. However, such materials do not possess sufficient cohesive strength at 60°C to provide satisfactory utility with a heat-recoverable closure.

U.S. Patent No. 4,018,733 to Lopez et al. discloses hot melt adhesives assertedly useful with heat shrinkable articles comprising a polyamide and either a terpolymer of ethylene, an ethylenically unsaturated carboxylic acid and a vinyl ester of an aliphatic acid, or a copolymer of ethylene and an aliphatic ester of an ethylenically unsaturated carboxylic acid, together with a tackifier. In Example 4 thereof, it appears that patentees provide a mixture of a polyamide with a copolymer of ethylene and an ethylenically unsaturated carboxylic acid, with commentary that same is "effective", although data presented therein would not lead to a conclusion that crosslinking can occur with such a system, nor is there any other indication in the specification that crosslinking occurs with the system disclosed. Furthermore, blends of polyamide with copoly- meric esters will not lead to a crosslinked adhesive, regardless of the temperature the system is heated to.

Summary of the Invention This invention relates to a thermosettable adhesive comprised of: a) an amine-terminated polyamide derived from dimer acid, and b) an acidic ethylene copolymer comprised of repeating units derived from a major amount of ethylene and a minor amount of one or more alpha,beta-ethylenically unsaturated acids, wherein said mixture is adhesively crosslinked.

Preferred adhesives are those having a major amount of polyamide and a minor amount of acidic ethylene copolymer, e.g., wherein the amount of the copolymer ranges from about 5 percent to about 40 percent by weight of the hot-melt adhesive mixture.

It has been found that copolymers of ethylene and an acidic comonomer are preferred to copolymers of ethylene and alpha,beta-unsaturated esters because a mixture of the former adhesive can be cured to improve cohesive strength, while the latter adhesive does not cure. This invention also relates to a heat-recover¬ able article having the adhesive described above applied as a coating on at least a portion of one major surface thereof.

Detailed Description of the Invention In my initial work to improve existing hot melt adhesives, an improvement in the viscosity character¬ istics thereof was attempted by the addition of an ethylene/acrylic acid copolymer thereto. It was dis¬ covered that along with an increase in viscosity of the composition at 177 C, the mixture cured at that tempera¬ ture, after retention of from 2 to 3 hours, into a tough elastomeric mass. Because the reaction was rather slow, the result created a homogeneous mass with very little byproduct formation, which can typically cause bubbles from gas evolution, same being detrimental to the purposes for which the hot-melt is utilized in heat-recoverable articles. It was noted that the product lost its thermoplastic character and could not be remelted to a form suitable for reknifing into sheet form. Conversely, conventional hot-melt adhesives taught to be useful with heat recoverable articles, but without the acidic ethylene copolymer additive, have been noted to develop a thermally and oxidatively degraded surface layer when heated at 177°C for up to 12 hours. However, removal of this layer exposes unchanged hot melt, which, while being somewhat more viscous, is still thermo¬ plastic. Conversely, the addition of the ethylene/acrylic acid copolymer has been found to result in a homogeneous thermoset material with elastomeric characteristics at 177°C.

While the adhesives of this invention are "hot-melt" adhesives in the sense that they, at least initially, soften when subjected to heat to activate the adhesive, they are not conventional hot-melt adhesives because the adhesive crosslinking thereof introduces substantial thermoset characteristics thereto. While not wishing to be limited to a particular theory, the reaction mechanism is thought to be based on an acid/base interaction to crosslink the composition. Thus, by varying the amount of the copolymer and the curing time and temperature, the adhesive and cohesive strengths of the hot-melt can be altered as desired. The optimal degree of crosslinking is achieved when the forces needed to cause cohesive failure are substantially equalized with the forces needed to cause adhesive failure of the composition. The determination of the precise curing conditions needed to obtain this optimal degree of crosslinking is well within the skill of the artisan.

Accordingly, the adhesive compositions of this invention are adhesively crosslinked. By "adhesively crosslinked" is meant that the composition has been subjected to an elevated temperature during activation of the adhesive for a time sufficient to crosslink the adhesive to improve its cohesive strength without significantly detracting from the adhesive strength obtained by melt activation of the adhesive.

Many factors influence the crosslinkability of the composition, most notably the amine number of the polyamide and the acid number of the acidic ethylene copolymer, as well as the time and temperature of the cure of the composition. In general, higher amine numbers, higher acid numbers, longer cure times and higher cure temperatures will result in greater degrees of crosslinking. Accordingly, each of these factors should be considered in determining the precise composi- . tion and cure procedure for a given desired crosslinked adhesive of this invention.

The preferred use of my adhesive is to seal a 5 heat-recoverable sheet material to a substrate, e.g., a telecommunicational cable breach or splice, about which the sheet material has been securely wrapped and then caused to recover. Because this use will generally be in the field, using equipment for heating that is typically 0 associated with heat-recoverable sheet materials, there are practical limits on the curing time and temperature of the adhesive associated with this use. Accordingly, the remaining factors which affect the cure of the adhesive, ie., the amine number of the polyamide and the 5 acid number of the ethylene copolymer, should be adjusted to provide commercially useful cure times. In this regard, the amine number of the polyamide will range from about 70 to about 200, more preferably from about 90 to about 180, and the acid number of the acid ethylene 0 copolymer will range from about 40 to about 170, more preferably about 50 to about 155.

A useful measure of the degree of crosslinking of the adhesive, apart from, but indicative of, the adhesive and cohesive failure of the adhesive, is the gel 5 extraction value of the crosslinked adhesive as deter¬ mined by the procedure disclosed hereinafter. In this procedure, substantially all of the uncrosslinked poly¬ amide and acidic ethylene copolymer are extracted into solution, the remaining gel being comprised of that ^*0 portion of the adhesive composition which is insoluble due to crosslinking. When this procedure is used, the amount of uncrosslinked material extracted from the adhesive should generally range from about 98% to about 50% of the thermosettable adhesive. In the heat-recover- ^*5 able sheet material applications of this adhesive, the amount of uncrosslinked material will range from about 95% to about 80% by weight of the thermoset adhesive because cohesive strengths of 30-40 pli are sufficient in most of these applications. Higher cohesive strengths can be obtained with greater crosslinking, i.e., more unextracted material. Of course, if any of the components of the adhesive composition are unextracted by the procedure before crosslinking, an allowance must be made for this initial insolubility, i.e., the % extracted targets should be lowered accordingly.

As a result of this invention, it was found that a lower viscosity polyamide based adhesive, which is better able to wet the surface of the heat recoverable substrate, can be utilized. With the addition of the acidic ethylene copolymer, the heat of application, i.e., the heat used to cause the heat-recoverable article to recover and to soften the hot-melt adhesive, causes the adhesive to cure to the point where higher cohesive strength is obtained. In contrast, present commercial hot-melt adhesives designated for use with heat recover¬ able articles typically are taught to be high strength hot melts but exhibit poor wetting by the hot-melt adhesive because- of heat and pressure limitations, or exhibit poor adhesion to a low energy surface because of the higher polarity polyamide molecule.

The two essential components of the hot-melt adhesive of this invention, as noted above, are an amine-terminated polyamide derived from dimer acid and acidic ethylene copolymer.

The amine-terminated polyamides useful in this invention are known in the art and are ordinarily prepared by mixing an equivalent excess of a polyamine with a polycarboxylic acid at least a portion of which is a dimer acid. The amount of polyamine utilized should be sufficient to provide a polyamide having an amine number greater than the acid number, preferably an amine number ranging from about 70 to about 400. Suitable diamines include primary diamines which may be ideally represented by the formula

H-N-R-NH- where R is an aliphatic, cycloaliphatic or aromatic radical, preferably having from 2 to about 40 carbon atoms. While R is preferably a hydrocarbon radical, R may optionally either contain ether linkages such as the diamines prepared from diphenyl ether. If R is aliphatic, it can a saturated straight or branched chain radical. Representatives of such diamines are the alkylene diamines having from 2 to 20 carbon atoms (preferably 2 to 6) such as ethylene diamine, 1,2-diamino propane, 1,3-diamino propane, 1,3-diamino butane, tetramethylene diamine, pentamethylene diamine, hexamethylene diamine, decamethylene diamine, and octadecamethylene diamine. In addition, aliphatic diamines carrying 1 to 3 lower alkyl substituents or a higher alkyl substituent are useful, for example, 2,5-dimethyl hexamethylenediamine, 2-methyl-4-ethylhexamethylenediamine, 2-methyl-4-ethyl- hexamethylenediamine, 2-ethyl-4-methylhexamethylene- diamine, a mixture of 2,4,4-trimethylhexamethyldiamine and 2,2,4-trimethylhexamethylenediamine or a mixture of 9-aminomethylstearylamine and 10-aminoethylstearylamine. in addition, aromatic diamines such as metaxylylene diamine, piperazine, isophorone diamine, and l,3-di-4-piperidyl propane can also be utilized.

Dimeric fat diamines, sometimes referred to as dimer diamines, can also be used. These diamines are prepared by amination of dimeric fatty acids as described in U.S. Patent No. 3,010,782. As indicated therein, these diamines are prepared by reacting polymeric fatty acids with ammonia to produce the corresponding nitriles and subsequently hydrogenating the nitriles to the corresponding amines. Upon distillation, the dimeric fat diamine is provided which has essentially the same structure as a dimeric fat except that the carboxyl groups are replaced by -CH-NH- groups. Diamines which are interrupted by oxygen atoms in the chain (also called ether diamines) and which are also suitable can be represented by the general formula

H-N-(CH 2-.)n-0-R-O)x-(CH2-.)n-NH-2 wherein n can be a number from 3 to 5, wherein x can have a value of 1, 2, or 3, and where R is an alkyl group with a chain length of 1 to 12 carbon atoms, which also may carry alkyl substituen^s of 1 to 4 carbon atoms.

Examples of ether diamines of this general formula are: l,7-diamino-4-oxoheptane,

1,ll-diamino-6-oxoundecane, l,7-diamino-3,5-dioxoheptane, 1,10-diamino-4,7-dioxoundecane, 1,10-diamino-4,7-di- oxo-5-methyldecane, 1,ll-diamino-4,8-dioxoundecane, l,ll-diamino-4,8-dioxo-5-ethylundecane, and the like. The diamine may be employed alone or mixtures of two or more may be employed. The most preferred diamines are the alkylene diamines in which the alkylene has from 2 to 6 carbon atoms and mixtures thereof with dimeric fat diamine. The polybasic acid used to form the newly terminated polyamide preferably consists predominantly of dimer acid. By predominantly it is meant that at least about 60 percent of the carboxylic acid groups of a dibasic acid mixture used to form the polyamide are the dimer acid component. Dimer acid is known in the art to be a mixture of many isomers with various degrees of unsaturation prepared from the polymerization of saturated and/or unsaturated fatty acids.

Other dicarboxylic acids include dicarboxylic acids or esters which can be defined by the formula

R-_^OOC-COOR-_^ and R-^OC-R-COOR_j^ where R is an aliphatic, cycloaliphatic, or aromatic hydrocarbon radical preferably having from 1 to 20 carbon atoms (the most preferred being where R is an alkylene radical having 6 to 12 carbon atoms) and R, is hydrogen or an alkyl group (preferably having from 1 to 8 carbon atoms). Illustrative of such acids are oxalic, malonic, adipic, sebacic, suberic, pimelic, azalaic, succinic, glutaric, isophthalic, terephthalic, phthalic acids, benzenediacetic acid, p-phenylene dipropionic acid, naphthalene dicarboxylic acids, and 1,4- or 1,3-cyclo- hexane dicarboxylic acid. The polyamides used in the practice of this invention will preferably have a number average molecular weight ranging from about 2000 to about 10,000 and can be prepared by conventional amidification techniques. In general, this amidification is preferably conducted at a temperature ranging from about 180°C to about 280°C after simple admixture of the desired quantities of polyamide and polycarboxylic acid reactives. The reaction results in the formation of the desired polyamide and the evolution of water or alcohol having the formula

R-_^OH wherein R is as described above. Illustrative polyamides suitable for incorporation into the composition of the present invention are those disclosed in U.S. Patent Nos. 3,249,629, 3,449,273 and 4,018,733, the disclosures for which are incorporated herein by reference.

Acidic ethylene copolymers useful in the present invention are prepared from a major amount of ethylene and a minor amount of an alpha,beta-ethy- lenically unsaturated carboxylic acid having from 3 to 8 carbon atoms. Examples of suitable ethylenically unsaturated carboxylic acids include the alpha,- beta-unsaturated acids such as acrylic and methacrylic acid. The amount of acid in the acidic ethylene copolymer should be sufficient to yield a copolymer having an acid number between about 40 to about 170, more preferably between about 51 (6.5% acrylic acid) and 156 (20% acrylic acid) . The copolymers of this invention can be readily prepared by copolymerizing a mixture of the appropriate comonomers in the presence of a free radical polymeri¬ zation initiator such as a peroxygen compounds, e.g., lauryl peroxide or t-butyl peracetate, or an azobis nitrile compound, e.g., azobisisobutyronitrile, at a somewhat elevated temperature and pressure, 80°C to 100° c, at a pressure of about 1000-1700 atmospheres. The resulting polymer is separated from the unpolymerized materials, e.g., by evaporation of the latter. By varying the monomers employed, the concentrations of the monomers and mixtures and the reaction mixture and polymerization conditions such as reaction time, pressure and tempera¬ ture, polymers of desired kind and degree of polymeri¬ zation in an acid number can be readily obtained. These two polymers can also be made by batch polymerization methods, but nonhomogeneous polymers frequently result. Continuous methods in which a suitable mixture of the comonomers and initiator is continuously passed through a reaction zone maintained at the desired temperature and pressure conditions are therefore preferred because they yield substantially homogeneous copolymeric products. Reaction zone and rate of flow of reaction mixture therethrough should be such as to provide a residence time that is appropriate in accordance with the desired degree of polymerization.

The amount of acidic ethylene copolymer in relation to the amount of amine-terminated polyamide is not critical in obtaining an adhesive in accordance with this invention. However, it has been found that the various properties of the adhesive are optimized when the concentration of acidic ethylene copolymer ranges from about 5 percent to about 40 percent by weight of the hot-melt adhesive.

The adhesives of this invention may also contain other functional additives such as fillers, treatments, dyes, thermo stabilizers, antioxants, anti- slip agents, plasticizers, nucleating agents and the like. In particular, additives such as tackifying resins and waxes, such as Piccofyn A-135, available from Hercules, and Epolene C-15, available from Eastman Chemical Products, respectively, can be added to increase the tack of the adhesive without detracting from the cohesive strength of the hot-melt adhesive of this invention. The adhesives of this invention are prepared by blending the amine-terminated polyamide and the acidic ethylene copolymer to form a mixture which can then be applied to a substrate that is to be adhesively bonded. The mixture can be made by simply melt blending the desired amounts of the components in conventional equipment, such as a Banbury mill, extruder or the like. The process of manufacture is not critical, so long as the mixtures are not substantially crosslinked prior to application to the substrates to be adhered; the blends are preferably made at the lowest temperature compatible with efficient mixing of the individual components to ensure avoidance of excessive crosslinking prior to use of the premix as discussed above.

The polymeric components of the blends can be dry mixed and the blending accomplihsed during a melt fabrication operation such as extrusion or injection melt fabrication, e.g., extrusion or injection molding. In the case of injection molding of these dry mixtures, screw plastication or other techniques capable of giving good mixing should be employed; alternatively, it is desirable to employ a rotating spreader or like device to ensure mixing of the components in the cylinder of the injection molding machine.

The mixture of this invention is preferably coated onto a surface of a heat-recoverable sheet material; i.e., that surface which will contact the substrate about which the heat-recoverable material is to be wrapped. The coating of the adhesive should generally be continuous on the interior face of the sheet material and is preferably of a thickness equal to or slightly greater than the thickness of the sheet material when freely recovered, i.e., a sheet that is allowed to recover under no significant tension. For example, with a sheet material that will freely recover to a thickness of about 20 mm, the coating will preferably range from about 20 mm to about 25 mm in thickness. Coating thicknesses ranging from about one-half to about twice the thickness of the freely recovered sheet material will also be useful.

Suitable heat-recoverable sheet materials are comprised of se icrystalline crosslinkable polymeric materials (e.g., polyethylene), and have been crosslinked and oriented by cooling in a stretched state to obtain shrink ratios of greater than 1 to about 8 times the unstretched length. Particularly preferred heat-recover- able sheet materials are disclosed in U.S. application Serial No. 752,946, filed concurrently herewith, the disclosure of which is incorporated herein by reference thereto.

These heat-recoverable closures are used to enclose substrates, generally cylindrical substrates, e.g., jacketed cables, conduits, etc., which have openings therein to seal those openings. The enclosure is accomplished by securely wrapping the heat-recoverable sheet material around a substrate and heating the material to cause it to recover about the substrate.

Examples Preparation of Adhesives

Samples of a thermosettable adhesive mixture were compounded by melt blending the ingredients at 350 F (177 C). The compounded adhesive was then knife coated onto a Teflon sheet at 20 mil thickness for further use. The same methology was also used to obtain the pure polyamide adhesive in sheet form.

Preparation and Testing of Closures The adhesive test results were obtained by means of a ring peel test on a polyethylene-jacketed air insulated telephone cable such as those manufactured by General Cable. For the ring peel test the cable was prepared using the standard telephone procedure of abrading the jacket with sandpaper and flame treating the abraded surface. The flame treatment step involves brushing the surface of the polyethylene cable material with the flame from a gas torch which has been adjusted to provide a bushy flame. Propane, natural or MAPP gas can be used. Generally, the cable surface attains a temperature of about 180°F (82°C) during this operation. The adhesive samples were applied to the surface of the cable by means of a heat reactive sleeve or tube. The cable samples were left to cool for 24 hours. Samples of the adhesives were prepared for testing by cutting the cable into one inch wide rings. A release liner previously placed, allowed formation of a tab. The samples were aged at the appropriate temperature for one hour prior to the adhesion test. The ring sample was placed onto a rotating mandrel fixture held in the upper jaw of an Instron. By gripping the tab with the lower jaw a ring peel test can be effected. The rate of crossarm travel in all tests was 1 mm/sec. The adhesive results were are reported in units of pounds per lineal inch width of the ring sample (pli). The reported adhesive strength values all reflect cohesive failure of the adhesive and thus are a reflection of the internal strength of^* that adhesive. All amounts of ingredients are reported in parts by weight (pbw) . The polyamides used in the following examples- were themoplastic polyamides based on dimerized fatty acids. The polyamides are available from Union Camp Corp. under the tradename Uni-Rez. PA-1, available as Uni-Rez 2655 is an amine-terminated polyamide having the following characteristics:

Ring & Ball Softening Point 100°C

Acid Number 0.9

Amine Number 90

PA-2, available as Uni-Rez 2641 is an acid-terminated polyamide having the following character¬ istics:

Ring & Ball Softening Point 138°C

Acid Number 10.0

Amine Number 18 PA-3, available commercially as Macromelt 6301 from Henkel Corporation is an amine terminated polyamide having the following characteristics:

Ring & Ball Softening Point 95°C Amine Number 130

The acidic ethylene copolymer (EAA) used was Primacor 5980 ethylene-acrylic acid copolymer available from Dow Chemical Co., having the following character¬ istics:

Melt Index: 300 g/10 min.

Acrylic Acid Content: 20% by weight Specific Gravity: 0.96

Examples 1-17 The set of adhesive results 1 to 9, in which the EAA is varied from 9 to 100%, show the unexpected increase in internal strength as measured by cohesive forces.

Table I

PA-1 EAA

Example (pbw) (pbw) 60°C 82°C % EAA

1 50 0 43 4.7 0

2 45 5 46 9.2 10

3 40 10 46 8.5 20

4 30 20 49 11.9 40

5 25 25 53 14.6 50

6 20 30 56 14.1 60

7 10 40 41 10.1 80

8 5 45 46 5.6 90

9 0 50 41 3.3 100

The 82 C cohesive strength values clearly show the results of mixing two low strength polymers together to result in a synergistic enhancement of high internal strength. When these results are contrasted with the addition of EAA to an acid-terminated polyamide polymer, the increase in internal strength is not present.

Table II

Comparative PA-2 EAA

Example (pbw) (pbw) 60°C H°£

10 50 0 22 4.4

11 45 5 22 3.2

12 40 10 29 3.8

13 30 20 34 4.4

14 25 25 40 4.2

15 20 30 40 4.4

16 10 40 41 4.4

17 5 45 43 5.6

Examples 18—2- \

Addition of proper tackifying resins and wax to the adhesive likewise shows the greater internal strength irregardless of the plasticizing effects of the additives. Each of the adhesives contained 4 pbw of a terpene resin available from Hercules as Piccofyn A135 and 4 pbw of .a polyolefin wax available from Eastman Chemical Products as Epolene C15 having a melt index of 4200, a ring and ball softening point of 94°C and a specific gravity of 0.90 g/cm .

Table III

PA-1 EAA

Example (pbw) (pbw) 60°C ϋ°£

18 50 0 47 3.1

19 45 5 58 4.5

20 40 10 50 4.5

21 25 25 56 8.8

22 20 40 41 7.4

23 5 45 39 5.6

24 0 50 32 3.1 Examples 25-30

The above series can be compared to the following in which the EAA was replaced by a comparable ethylene vinyl acetate (EVA) copolymer (Elvax 420 available from DuPont having a melt index of 150 g/10

3 min., % VA of 18 and specific gravity of 0.937 g/cm ).

The results show the enhancement of internal strength is absent due to the acid functionalities being neutralized by the acetyl group.

Table IV

PA-1 EVA 60°C 82°C

Example (pbw) (pbw) Pli pli

25 45 5 56 4.7

26 40 10 53 4.5

27 25 25 1 1.8

28 40 40 2 1.1

29 5 45 2 1.1

30 0 50 1 0.9

Examples 31 -36 Again to show the unique combination of amine-terminated polyamide and EAA copolymer the following table illustrates the effect of the use of an acid-terminated polyamide. The synergistic effect is not seen as in the above examples.

Table V

PA-2 EAA 60°C 82°C

Example (pbw) (pbw) pli pli

31 50 0 16 4.7

32 45 5 29 6.5

33 40 10 26 6.7

34 25 25 33 5.6

35 10 40 34 4.7

36 5 45 42 4.7 Examples 37-60 A series of adhesives were prepared and tested as in Examples 18-24. The amount of PA-3 used was 30 grams less the amount of EAA used as shown in the following Table. The resins were mixed, and applied as described above held at 177°C for the time indicated. Ring peel specimens were cut and tested as described above. The adhesives exhibited the peel strengths shown below. Examples 37-42 are comparative examples of PA-3, alone.

Table VI

Time Cured at 177°C

EAA 0. .5 hr. 1.0 hr. 2.0 hr.

Examples (pbw) Test Temperature (°C)

21° 60° 21° 60° 21° 60°

37 - 42 0 70 21 80 23 90 21

43 - 48 2 78 23 90 29 90 39

49 - 54 5 10C ) 27 100 34 * *

55 - 60 10 90 20 100 31 * * *Sample cured to highly crosslinked thermoset form that was unusable as an adhesive.

Extraction Data

Materials mixed at 177°C. Sheets were placed in a platen press with nominal pressure and heated for the indicated times at 177°C. Samples of the adhesive were placed in a Soxhlet Extractor apparatus and refluxed for 24 hours. A mixture of 50:50 toluene and n-propanol was used as an extractant. At the end of the extraction, the thimbles containing the samples were air dried and then dried in a vacuum oven at 100°C to a constant weight. Table VII

Example Composition Time % Extracted

61 PA-1 1 hr 94.4

3 hr 91.0

5 hr 79.6

62 EAA 1 hr 98.3

3 hr 98.5

5 hr 98.4

63 PA-1 1 hr 99.8 plus 3 hr 62.0

EAA 5 hr 35.0

Claims

What is claimed is:

1. A thermosettable adhesive mixture comprised of: a) an amine-terminated polyamide derived from a dimer acid, and b) an acidic ethylene copolymer comprised of repeating units derived from a major amount of ethylene and a minor amount of one or more alpha,beta-ethylenically unsaturated acids, wherein said mixture is adhesively crosslinked.

2. The adhesive mixture of claim 1 wherein the amount of uncrosslinked polymer ranges from about 95% to about 80% therein.

3. The adhesive mixture of claim 1 comprising a major amount of said polyamide and a minor amount of said acidic ethylene copolymer.

4. The adhesive mixture of claim 3 wherein the amount of said acidic ethylene copolymer ranges from about 5% to about 40% by weight of said mixture.

5. The adhesive mixture of claim 1 wherein the amount of said alpha,beta-ethylenically unsaturated acids in said acidic ethylene copolymer ranges from about 5 to about 25% by weight of said copolymer.

6. The adhesive mixture of claim 1 wherein said alpha,beta-ethylenically unsaturated acid is acrylic acid.

7. The adhesive mixture of claim 1 wherein said acidic ethylene copolymer consists essentially of a major amount of ethylene and a minor amount of one or more alpha,beta-ethylenically unsaturated acids.

8. The adhesive mixture of claim 1 wherein said amine-terminated polyamide has an amine number above about 70.

9. A method of sealing a heat-recoverable closure comprising: a) applying a coating of an adhesive mixture comprised of: i) an amine-terminated polyamide derived from a dimer acid, and ii) an acidic ethylene copolymer comprised of repeating units derived from a major amount of ethylene and a minor amount of one or more alpha,beta-ethylenically unsaturated acids, to a heat-recoverable sheet material; b) securely wrapping said heat-recoverable sheet material about a substrate to be enclosed with said coating of said adhesive mixture in contact with said substrate; c) heating the substrate to a temperature and for a length that is sufficient to cause said adhesive to become thermoset.

10. A method in accordance with claim 9 wherein said heating is in excess of that sufficient to cause said adhesive to soften and said heat-recoverable sheet material to recover.

11. A sealed article produced by the method of claim 9.