Ternary Adhesive Compositions

A class of adhesive compositions known as thermoplastic or hot melt adhesives have enjoyed continually increasing usage in many industrial applications. These adhesives, or hot melts, as they are commonly designated are solid or semi-solid combinations of film-forming resins, tackifying resins, rubbery polymers, plasticizers, waxes and similar materials which are added to the adhesive composition in order to impart various properties thereto.

Adhesive bonds derived from hot melts are particularly useful because (1) they are 100% solid materials and (2) they quickly form tough adhesive bonds simply by cooling -- i.e., no need for solvent evaporation, etc.

Adhesives derived from hot melts are particularly useful because of their very rapid set up or bonding time. Strong bonds are formed when the adhesive cools below its melt point and solidifies. There is no long wait for solvent or water evaporation or for chemical curing as with other types of adhesives. Depending on composition, hot melt adhesives can be prepared having good tack, high bond strength, good flexibility, low temperature properties, good environmental resistance, etc.

A typical class of hot melt adhesive composition utilizes polyolefin polymers as the base or carrier material. The polyolefin base is usually blended with other polymers and copolymers, resin tackifiers, and with modifiers and additives. Generally, the polyolefin carrier is polypropylene (either atatic or crystalline or both), EVA, or polyethylene.

In spite of the tremendous growth in the use of hot melts and the advantages to be realized by their use, the extent of their utilization has nevertheless been limited by several serious shortcomings. Polyolefin based hot melts, for example, usually suffer from the lack of strong adhesion to nonporous metallic surfaces, such as aluminum, steel and the like. They also tend to be quite brittle unless suitably modified. All hot melts generally suffer from low bond strengths at elevated temperatures. When heated, even well below their melt points, they tend to soften and lose strength.

The low temperature brittleness and high temperature softening difficulties of previous hot melts have been approached by changing to epoxy adhesives to which are added elastomers to make rubber toughened epoxies. However, it would be advantageous if the less expensive olefin polymers could be obtained having similar properties to the epoxies. This advantage has been achieved by the addition of a crosslinking agent to an adhesive comprising a thermoplastic elastomer and a tackifying resin.

Another type of useful adhesive system is the solution based adhesive including pressure sensitive adhesive formulations having multiple uses.

The present invention provides an adhesive composition having enhanced strength and high temperature resistance, which composition comprises

(a) thermoplastic elastomeric polymer preferably selected from ethylene propylene rubber (EPR), ethylene propylene diene monomer rubber (EPDM), polyisobutylene, butyl rubber, ethylene vinyl acetate and ethylene methacrylate copolymers grafted with C.sub.3 to C.sub.10 unsaturated mono- and polycarboxylic acids, anhydrides such as maleic anhydride, and derivatives thereof;

(b) a tackifying resin selected from petroleum hydrocarbon resins, polyterpene resins, and cyclopentadiene resins; and

(c) a cross-linking agent selected from di- or polyamine hydrocarbyl compounds having from 2 to 20 carbon atoms.

The term "adhesive" as used herein is in its classical sense a substance which holds materials together because of surface attraction. No one knows exactly what the theoretical base is regarding adhesiveness. However, all experts will concur that the overriding important characteristic of an adhesive is that the things which are bonded together, i.e., substrates, must be difficult to separate. This probably comes about as a result of intimate contacting.

Thus, when an adhesive is applied to a substance, it must be fluid enough and surface active enough to wet the substrate. Then it must be capable of hardening or setting so that it develops high cohesive strength. Preferably such cohesive strength is that comparable to what would be expected of a moldable, thermoplastic or thermoset material.

Conventional hot melt adhesives are well known and comprise a wide variety of described systems and systems which are actually used in commerce. Very generally, a major component will be a carrier polymer which can be a structurally strong polyolefin such as polyethylene or polypropylene to impart the high cohesive strength when the adhesive sets up after cooling. Other polymers used for their structural properties include nylons, vinyl acetate polymers, polyesters, polycarbonates, PVC, waxes, Saran, and the like. But other components are usually blended in.

Thus, hot melts can have an elastomeric component such as ethylene propylene rubber (EPR), ethylene propylene diene monomer terpolymer (EPDM), polyisobutylenes, (i.e., vistanex, butyl rubber), chlorinated polyethylenes, chlorinated butyl rubbers, and the like.

Generally, elastomers having a relatively low unsaturation or no unsaturation at all such as previously specified are used, since it is desirable to avoid oxidation which occurs with highly unsaturated elastomers.

Furthermore, other polymers which are non-elastomeric can be blended in. They can include block copolymers of ethylene and propylene, random copolymers of ethylene and propylene with each other; and with vinyl allylic monomers such as vinyl acetate, styrene, acrylic acid, acrylates and the like. Thus, a wide variety of olefinic polymers and copolymers will be chosen by the blender in order to achieve the particular goals he has in mind.

In the composition of the invention the graft polymers can be prepared by known methods in the art, e.g., those to be found in U.S. Pat. Nos. 3,177,269; 3,177,270; 3,270,090; British Pat. Nos. 1,217,231; 679,562 and the like.

The preferred modifying monomers which are grafted to the backbone of the thermoplastic elastomeric polymer are C.sub.3 to C.sub.10 unsaturated mono- and polycarboxylic acids with preferably at least one olefinic unsaturation, anhydrides, salts, esters, ethers, amides, nitriles, thio, glycidyl, cyano, hydroxy, glycol, and other substitute derivatives thereof.

Examples of such acids, anhydrides and derivatives thereof, include maleic acid, fumaric acid, itaconic acid, citronic acid, acrylic acid, glycidyl acrylate, C.sub.2 to C.sub.10 alkyls, cyano-acrylate, hydroxy C.sub.2 to C.sub.10 alkyl methacrylates, acrylic polyethers, acrylic anhydrides, methacrylic acid, crotonic acid, isocrotonic acid, mesaconic acid, angelic acid, maleic anhydride, itaconic anhydride, citraconic anhydride, acrylonitrile, and methacrylonitrile. Metal salts of the acids are useful.

Other monomers which can be used either by themselves or in combination with one or more of the carboxylic acids or derivatives thereof include C.sub.3 to C.sub.20 vinyl monomers such as propylene, butene, hexene and the like, and monovinyl aromatic compounds, i.e., styrene, chlorostyrenes, bromostyrenes, alpha methyl styrene and the like.

Other monomers which can be used are C.sub.6 to C.sub.20 vinyl esters and allyl esters, such as vinyl butyrate, vinyl laurate, vinyl strearate, vinyl adipate and the like. Monomers having two or more vinyl groups, such as divinyl benzene, ethylene dimethacrylate, triallyl phosphite, dialkylcyanurate and triallyl cyanurate can also be employed.

Nevertheless, the most outstanding results and the highly preferred embodiments of this invention are those in which the graft copolymer meets some highly specific criteria. Primary is the concept that the graft copolymer not only contain grafted active functionality, but that the backbone polymer itself be reduced considerably in melt viscosity, so that it is more compatible with other components of the total adhesive composition and also exerts a much more powerful adhesive influence on the overall composition.

Thus, grafted high melt flow polymers have a double adhesive action. One is obtainable through the wetting activity of the more easily flowable polymer and the other is the chemical attraction of the active groups on the graft copolymer, e.g., carboxylic acid groups, glycidyl groups, etc. This attraction is particularly useful on nonporous surfaces.

The tackifying resins useful in the adhesive compositions of this invention can be a hydrocarbon resin such as ADTAC-B hydrocarbon resin prepared according to the process disclosed in U.S. Pat. No. 3,701,760 as well as other hydrocarbon resins, synthetic polyterpenes, rosin esters and the like. One such suitable tackifying resin is a hydrocarbon resin having a softening point of 100.degree. C. and available commercially as Eastman Resin H-100 from Eastman Chemical Products, Inc. Other hydrocarbon tackifying resins can be prepared by the polymerization of monomers consisting primarily of olefins and diolefins and include, for example, the residual by-product monomers resulting from the manufacture of isoprene. These hydrocarbon tackifying resins typically exhibit a Ring and Ball Softening Point of from about 50.degree. to 135.degree. C.; an acid number of from about 0 to 2; a saponification value of less than about 1; and an iodine value of from about 75-100. Examples of such commercially available resins of this type are "Wingtack 95" as sold by the Goodyear Tire and Rubber Co. and the Sta-Tac and Betaprene H resins sold by the Reichhold Chemical Corp.

Also suitable resins are the terpene resins such as the polymeric, resinous materials including the dimers as well as higher polymers obtained by polymerization and/or copolymerization of terpene hydrocarbons such as the alicyclic, monocyclic, and bicyclic monoterpenes and their mixtures, including allo-ocimene, carene, isomerized pinene, pinene, dipentene, terpinene, terpinoline, limonene, terpentine, a terpene cut or fraction, and various other terpenes. Particularly useful starting materials are terpene mixtures containing at least 20% beta-pinene and/or limonene or dipentene (racemic limonene), and the "sulfate turpentine" obtained as a by-product in the sulfate pulping process.

The aromatic hydrocarbon resins are of intermediate molecular weight, e.g., from about 300 to about 6,000, preferably about 750 to 1,000, and which have a softening point of less than 50.degree. C. and are viscous liquids at room temperature. Suitable commercially available resins include "Piccolastic" A, D and E series. One such resin is Piccolastic A-25 which is a polystyrene resin having a softening point of 25.degree. C., a color of 3 (Gardner), an acid number <1 and a specific gravity of 1.05 and a melt viscosity of 100 poise at 47.degree. C.

A preferred group of tackifying resins include the Escorez brand tackifying resins produced by Exxon Chemical Company, Polymers Group. These resins have the advantages properties shown in Tables 1 and 2 below.

The third primary component of the present invention is an amine cross-linking or curing agent. The amine is preferably a diamine or polyamine which binds to the acid or anhydride groups of the graft copolymer adhesive base material. The amine is more preferably a hydrocarbyl polyamine having 2 to 20 carbon atoms in the hydrocarbyl group. Exemplary of such di-and polyamine cross-linking agents are ethylene diamine, diethylene triamine (DETA), triethylene tetramine (TETA), tetramethyl diamine, tetraethylene pentamine, hexamethylene diamine, octamethylene diamine, bis-(p-aminocyclohexyl) methane, dicamethylene diamine, dodecamethylene diamine, octadecamethylene diamine, eicosylene diamine, diethyl toluene diamine, phenylene diamine and the like. The amine curing or cross-linking agent can be employed at from about 0.01 to about 13% by weight of the EP rubber, and more preferably from about 0.1 to about 2% by weight.

The cross-linking agent may be encapsulated so as to break with heat, pressure, shear, sonication, or irradiation. Encapsulation of crosslinking agents is known in the art and is described in references such as the article entitled "Microencapsulation" in Kirk-Othmer Encyclopedia of Chemical Technology, 3rd edition, volume 15, John Wiley and Sons, 1981, pp 470-493.

We have found it useful to encapsulate the crosslinking agents such as, tetraethylene pentamine (TEPA) in a high melting shell material comprising maleated polypropylene. Other shell forming materials which are well known in the art of encapsulation can suitably be employed. Typically, encapsulation can be accomplished by suspending TEPA as fine insoluble droplets in a suitable diluent such as hot normal octane. The shell forming material such as maleated polypropylene is dissolved in hot octane and slowly added to the TEPA droplet suspension. The maleated polypropylene diffuses to the TEPA droplets and crosslinks around the surface of the droplets forming hard shells thereby providing encapsulated crosslinking agents.

In addition to the above listed components, it is desirable for the hot melt adhesive composition to contain about 0.1 to about 1.5 percent by weight, preferably about 0.25 percent to 1.0 percent by weight, of one or more stabilizers or antioxidants. Antioxidants that are effective for each of the various components can be used. Such antioxidants include, for example, Ionox 330 [tris(di-t-butyl-p-hydroxybenzyl) trimethylbenzene], Dalpac 4C2 [6-di(t-butyl)-p-cresol], Naugawhite (alkylated bis-phenol), Butyl Zimate (zinc dibutyl dithiocarbamate), Ethyl 702 [4,4'-methylene bis(2,6-di-tert-butylphenol)], Irganox 1010 tetrakis (methylene-3-(3',5'-di-t-butyl-4'-hydroxy-phenyl) propionate]methane, Cyanox 1212 (American Cyanimid) lauryl stearyl thiodipropionate, Irganox 1076 [octadecyl] 3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate], Cyanox LTDP (dilauryl 3,3'-thiodipropionate), and the like.

Some compositions of this invention include from about 35 to about 45 weight percent of tackifier resin, from about 15 to about 20 percent by weight of a microcrystalline wax, from about 25 to about 30 percent by weight of at least one normally solid maleic anhydride grafted-ethylene vinyl acetate copolymer and from about 5 to about 20 percent of the normally semi-liquid or liquid maleic anhydride grafted-ethylene vinyl acetate copolymer, preferably about 5 to about 10 percent by weight. The optional antioxidant or stabilizer can be added to the components at about 0.1 to about 1.5 percent and preferably from 0.1 to about 1 percent by weight and typically, 0.5 percent.

An additional and optional component of the present blend formulation is a microcrystalline wax. The microcrystalline waxes of choice are known. Such waxes are derived from refined fractions of crude oil and therefore consist essentially of paraffinic hydrocarbons which contain significant amounts of branched chain and cycloparaffins as well as aromatics. This composition of components is characterized by exhibiting the formation of only small crystalline regions in the solid wax so that these waxes, as compared to paraffin waxes with fewer branched and cyclic groups, are generally softer and more flexible than an otherwise comparable paraffin wax having a similar melting point or range.

Typically microcrystalline waxes that are suitable for use in formulating hot melt adhesives of the present invention are Shellwax 905 brand supplied by the Shell Chemical Company of 600 Summer Street, Stamford, Conn. 06904; Micro Hex R brand supplied by the Witco Chemical Corporation, Sonneborn Division, 277 Park Avenue, New York, N.Y. 10017; and Victory brand wax supplied by Petrolite Corporation, Bareco Division, 6910 E. 14th Street, Tulsa, Okla. 74112. Other microcrystalline waxes can be selected from other suppliers as long as the selected wax exhibits properties similar to those for Shellwax 905 which are summarized in the following Table 3:

Also especially suitable for the invention is Exxon Chemical Company's Escomer.RTM. H-101 which has the typical properties given in Table 4 below:

Moore and Munger's Paraflint H-1 (Sasol) wax has similar properties.

Although several brands of microcrystalline waxes are provided, it should be understood that such waxes are well known in the art and are readily available commercially.

Other optional but suitable components for the formulations of the invention are refined hydrocarbon oils such as are commonly used in adhesives including paraffinic, aromatic, and naphthenic oils such as Witco's Kaydol and Arco's Tufflo naphthenic oil.

Also usable as optional components are alcohols such as methanol, ethanol, etc. up to long chain waxy alcohols.

The refined oils serve to reduce viscosity and improve surface tack properties such as rolling ball tack. The alcohols prevent physical associations resulting in gels in solvent-based adhesive formulations. In hot melt adhesives the alcohols delay cross-linking thereby providing control such as increased pot-life.

The hot melt adhesive compositions of this invention are prepared by blending together the components in the melt at a temperature of about 325-375.degree. F. (160 to about 200.degree. C.) until a homogenous blend is obtained. The blending takes about 1 hour. Various methods of blending materials of this type are known to the art and any method that produces a homogenous blend is satisfactory. These components blend easily in the melt and a heated vessel equipped with a stirrer is all that is required. For example, a cowl's stirrer provides an effective mixing means for preparing these hot melt adhesive compositions. The components are added in no particular order. However, generally, the tackifying resin is added first and heated in the vessel until molten. Thereafter the maleated ethylene propylene rubber copolymer or, alternatively, the rubber and resin are placed in the vessel together (to keep a reduced viscosity) and the heating and mixing is begun. Then the microcrystalline wax is added. In general the curing or cross-linking agent which may be encapsulated is added to the mixture last and preferably just before use. e.g., by spraying the amine onto a pressed-out sheet of adhesive or onto the substrates to be bonded and the blend is cured at a suitable temperature for a sufficient time to provide good adhesion.

In a solvent based formulation, the tackifying resin, maleated ethylene-propylene rubber copolymer, oil and crosslinking agent can be dissolved in a suitable solvent such as toluene. Alcohols such as methanol are added to prevent gel formation.

The present invention can be more easily illustrated by reference to the following non-limiting examples.

Maleated ethylene propylene rubber was blended with a tackifying resin and wax in proportions typical of standard hot melt adhesives, as shown in Table 5. The blending was done in a laboratory blender at 190.degree. C. for 70 minutes. The viscosity of the resultant blend is also shown in Table 5. The blend was drawn down with an eight path applicator into thin sheets and diethylene triamine (DETA) was sprayed on the sheets. The sprayed sheets were then sandwiched between aluminum strips and cured by heating in an impulse sealer at 175.degree. C. and 20 psig for 15 seconds. The amount of DETA cross-linking agent employed and the adhesion test results are shown in Table 6 below.

The Shear Adhesion Fail Test (SAFT) uses the following equipment and procedures:

Equipment and Materials

Impulse heat sealer

1".times.4" strips of substrate

Razor blade knife

1" bar

Mechanical convection oven (80-250.degree. C.)

Gardner knife

Micrometer

Solvent removal oven

4.5 lb. rubber roller

Hole punch

Sample Preparation

1. Samples prepared as hot melt adhesives are melted and drawn down into a 5 mil film using an 8 path applicator.

2. Samples which have been solution blended are drawn down on the appropriate backing with a Gardner knife and dried in a solvent removal oven. Typically the dry coating thickness will be 1-5 mils. Coating thickness is measured with a micrometer.

Test Conditions

Sealing temperature range: 120-180.degree. C.

Sealing pressure range: 15-40 psig

Sealing time: 0.5-15 seconds

Oven temperature ramp rate: 10.degree. C./15 minutes

Procedure

1. Hot Melt Blended Samples

Place a 1".times.1" sample of adhesive between the ends of two 1".times.4" strips of substrate in a Lap Shear configuration. Place this sample between two pieces of release paper and heat seal at the appropriate conditions.

2. Solution Cast Samples

Cut 1".times.4"strips from the film coated on the backing. Overlap the ends of these strips 1" in a Lap Shear configuration. Either heat seal this sample in an impulse heat sealer at the appropriate conditions or laminate the bond with a 4.5 lb. rubber roller (2 passes).

3. Prepare 4 replicates of each sample to be tested. Hang each sample in the oven so that the samples hang vertically. Punch a hole in the lower end of each sample and attach a 500 gram or 1000 gram weight.

4. Begin testing with the oven temperature at 80.degree. C. and stairstep the temperature up 10.degree. C. every 15 minutes to a maximum temperature of 250.degree. C.

5. Record the temperature at which the bond fails and the weight falls.

Reporting Data

1. Report the average failure temperature of the 4 replicates of each sample.

2. Report the sealing conditions used to prepare each sample.

As indicated from Table 6 above, the peel strength and Shear Adhesion Failure Temperature (SAFT) were good to excellent. Normally, hot melt adhesives have SAFT values which are typically about 150.degree. F. (66.degree. C.). Therefore, the present SAFT results, all being above 150.degree. F. (66.degree. C.), exceed the typical values, and all the results with DETA are above the 206.degree. F. (96.6.degree. C.) SAFT value of the hot melt adhesive without DETA. The tensile strength results were run after curing at 175.degree. C. for 15 minutes and show a surprising increase in tensile strength over the adhesive formulation without DETA.

A typical pressure sensitive adhesive formulation according to Table 7 was prepared using maleated ethylene propylene rubber blended with a tackifying resin, an oil and diethylenetriamine cross-linking agent. The blends, 15 wt.% total solids concentration, were solution blended in xylene/methanol solvent. A film was drawn down on an aluminum sheet and the solvent flashed off at 100.degree. C. for 10 minutes to yield a dry coating thickness of 3 mils. The results of testing the pressure sensitive formulations are also given in Table 7.

The proportion of ethylene in the maleated ethylene propylene rubber was varied to determine the effect on adhesive properties. Formulations were prepared both without diethylene triamine (DETA) and with 2 parts by weight of DETA, the remaining components included 60 parts by weight E-5320 resin and 40 parts by weight maleated ethylene propylene rubber (in which the proportion of ethylene to propylene is varied from 43 to 77%). The adhesive was made by mixing the components in a xylene/methanol solution and casting the solution as a film onto aluminum sheets. Coating thickness after solvent evaporation was 5 mils. The sheet was cut into strips and heat sealed for 30 seconds at 175.degree. C. to cure and bond the adhesive. The strips were then subjected to SAFT and peel strength tests with the results shown in Table 8 below.

As seen in Table 8, one concludes that in the absence of DETA, the SAFT increases with increasing ethylene content about 30.degree. C., from 120.degree. to 150.degree. C. Surprisingly, with the DETA or other cross-linking system, SAFT values of greater than 250.degree. C. are achievable. However, as the ethylene content increases the peel strength decreases. Further, the failure mode is usually a cohesive failure for uncured systems, but a mixed cohesive/adhesive failure for cured systems. It should be noted that while peel strengths of the cured systems decrease compared to the uncured systems, except for the highest ethylene content (run 3--3); nevertheless, cured peel strengths are quite reasonable.

In the following example, a lower softening point resin and the effect of adding an oil to lower the blend viscosity was investigated.

A blend of maleated ethylene propylene rubber with a tackifying resin and either with or without a curing or cross-linking agent was prepared as indicated in Example 2 except that the tackifying resin had a lower softening point. For comparison examples of this invention with a tackifying resin of a higher softening point, e.g., such as in Example 2, are included. The formulation data parts by weight and test results from SAFT and peel strength test are summarized in Table 9 below. Also included in the adhesive formulations are added oils to reduce blend viscosity.

The foregoing data show that the lower softening point resin improved the SAFT values in the uncured system. The conditions of the SAFT test are not always sufficient to cure the adhesive containing the amine cross-linking agent completely. Thus, performance was not as satisfactory for the laminated samples as for the heat sealed samples. In addition to metal, the formulations adequately bond to polypropylene. The addition of a viscosity reducing oil (Runs 5 and 6 compared to Runs 3 and 4) decreased performance results.

In an effort to reduce viscosity and provide formulations having lower melt viscosity for better flow properties and still maintain good adhesion, a lower viscosity polymer was used in formulations for which the properties of the final adhesive were determined.

A maleated ethylene vinyl acetate copolymer was blended with a tackifying resin and an amine cross-linking agent which was triethylene tetramine (DETA) in the weight proportions shown in table 10. The melt viscosity at 160.degree. C. was checked before adding the amine cross-linking agent.

Several blend formulations containing a low and high molecular weight maleated ethylene propylene rubber were prepared, containing a low softening point tackifying resin and an amine cross-linking agent, such as triethylene tetraamine (TETA). The formulations were also tested without amine cross-linking agent. All formulations were measured for viscosity, without the amine. The results of the SAFT are given below with component parts by weight in the formulations. All formulations were heat cured at 175.degree. C. for 30 seconds. Results are in table 11.

All formulations without amine failed at SAFT conditions less than 85.degree. C.

The bonding of aluminum/nylon and aluminum/aluminum films using an adhesive of this invention is illustrated in the following example.

Several blend formulations were prepared and tested for peel strength in bonding films of aluminum/aluminum and aluminum/nylon to make laminated films. Two formulations of the present invention were prepared and compared with a known polyurethane/diisocyanate two-part adhesive, recommended for film applications. The blend formulations in parts by weight and results of the test are given in Table 12 below.

The data show that formulations of this invention give similar peel strengths to the currently used adhesive. Additionally, when placed in an autoclave at 260.degree. F. under water, test strips of Run 2 showed no delamination compared with test strips of the polyurethane/diisocyanate system which showed substantial delamination.

Several additional laminations were carried out using maleated EP copolymer with Escorez 5000 based adhesives. Two 25 gallon batches were prepared, the first contained 11 weight percent solids of Escorez E-5380 with maleated EP and the second contained Escorez E-5320 with maleated EP. The adhesives were laminated under varying conditions to bond nylon and aluminum films. Variable conditions during the several laminations included adhesive batch, presence or absence of amine cross-linking agents, lamination line speed and adhesive coating weight. Tests of laminated films immersed in pressurized water at 260.degree. F. for 1 hour in an autoclave revealed no delamination. However, some samples from the E-5380 resin batch formed channels between the layers where water apparently had permeated between the nylon and aluminum from the edge. The best performance on water immersion was obtained from use of the E-5320 resin, about 0.1 weight percent based on the polymer of triethylene tetramine and a high coating weight.

A maleated ethylene propylene rubber having a MFR of 20 was blended with tackifying resin and an amine cross-linking agent as shown for run 2 in Table 13 below. Run 1 without the amine is for comparison.

This formulation has a viscosity such that it would be pumpable in some hot melt adhesive equipment and has a measurable polyken tack at room temperature.

A. Reference: Modified ASTM D-2979

B. Equipment and Materials:

Polyken Probe Tack Tester (with brass rings)

Text specimens (approximately 1".times.1" dimensions)

Solvent (for cleaning probe and brass rings -- usually acetone)

C. Sample Preparation:

Test specimens are cut from standard films (see "Film Preparation") to roughly 1".times.1" dimension.

D. Test Conditions:

Tests are run at standard conditions (temperature of 23.degree. C..+-.2.degree. C. and relative humidity of approximately 50%). Before each test clean and dry the probe tip and the brass rings. Set the dwell time on the machine to "1" second and the speed to 1 cm/sec. Make sure instrument is level (check low gauge).

E. Procedure:

1. Turn the instrument on and let it warm up for approximately 5 minutes.

2. After warm up, zero the machine by placing the "Peak Track" button in the "Track" position. Now adJust to zero by turning the "zero" knob until "000" appears on the digital readout.

3. Place "Peak Track" button in the "Peak" position.

4. Place the test specimen (adhesive side down) onto the smooth surface of a clean brass ring (see FIG. 1). Make sure there is a good seal between the test specimen and the brass ring by rubbing the prepared ring on a smooth, hard surface.

5. Place the prepared ring on the probe spindle.

6. Press the "Reset" button.

7. Press the "Test" button.

8. Record the digital display reading.

F. Calculations:

Report the average of not less than five determinations (reported in grams) as the polyken tack value. Additional determinations may be necessary if the spread of the first five is wide.

G. Critical Factors:

Probe tip and brass rings must be clean and dry. There must be a good seal between the adhesive and the brass ring.

The following example demonstrates adhesive formulations with other tackifier resins including the superior-performing ECR-111 aliphatic tackifier resin and two liquid tackifier resins. The formulations in parts by weight and measured properties are shown below. Also shown are formulations without an amine of the invention.

This example demonstrates adhesive formulations with other tackifier resins including blends of tackifiers. Also shown is the effect of replacing some tackifiers with oil. Several levels of amine are shown. Notice, SAFT is increased in all cases where an amine of the invention is added. The formulations in part by weights and measured properties are shown in Tables 15 and 16 below.

This example demonstrates the effect of molar ratio of maleic anhydride to triethylene tetramine. It also shows the effect of different curing conditions and the results of other types of adhesive testing such as T-peel and lap shear. An interesting finding is that higher levels of amine improve shear strength for bonding galvanized metal but decrease shear strength for bonding aluminum. The example also illustrates that the maleic anhydride to TETA ratio should be below about 16 to 1 achieve high SAFT values. Formulations and measured properties are shown in Table 17.

This example demonstrates that maleated elastomers other than EP rubber, such as maleated chlorobutyl rubber, can be used in this invention. Formulation and measured properties are given in Table 18.

This example illustrates that the subject invention can be supplied in hot melt form by using high melting amines or other latent curatives. The maleated EP polymer and tackifier ECR-111 were hot melt blended in a Z-blade mixer at 100.degree. C. The temperature was reduced to 100.degree. C. and dicyandiamine (DICY) was added. The mixture was then blended another five minutes and used as a hot melt adhesive. Table 19 shows the formulation and some measured properties which are seen to depend on cure conditions. Of course, other high melting or latent curatives could be used in a similar fashion.

This example illustrates that the subject invention can be supplied in hot melt form by the use of encapsulated crosslinking agents.

Tetraethylene pentaamine (TEPA) was encapsulated by suspending TEPA as fine insoluble droplets in hot normal octane. Maleated polypropylene was dissolved in hot octane and was slowly added. The maleated polypropylene diffused to the TEPA droplets and cross-linked around the surface of the droplets forming hard shells. On cooling and washing, microcapsules containing TEPA were recovered.

Maleated EP rubber was blended with tackifier and oil. The mixture was equilibrated at 120.degree. C. and then the encapsulated TEPA was blended in over a five minute period and then the mixture was poured out onto release paper. A portion of this was pressed between two pieces of silicon release paper in a hydraulic press at 120.degree. C. to form a film six to eight mils thick. Test samples were then prepared from this film. During all this preparation, there was no indication of crosslinking, gelling or viscosity increase. Thus, the microcapsules were apparently staying intact.

The formulation and measured properties are shown in Table 20. Notice that both temperature and pressure had an effect on resulting SAFT. Of course, other types of encapsulated crosslinking agents and other methods for making them could be used. The capsules could be made susceptible to breakage by heat, shear, sonication, chemical reactions, radiation or other means.

From the foregoing description, the present invention contemplates as a preferred cross-linking agent triethylene tetramine, diethylene triamine, tetraethylene pentamines, and diethyl toluene diamine. Furthermore, the preferred amount of the cross-linking agent is from about 0.01 to about 15 percent by weight of the rubber, with from about 0.05 to about 2 percent by weight being preferred, and from about 0.1 to about 1 percent by weight being more preferred. As a result, a preferred composition of this invention is an adhesive composition in which the thermoplastic elastomer is present at about 20 to 60 percent by weight, the tackifying resin is present at about 30 to about 70 percent by weight and the cross-linking agent is present at about 0.05 to about 2 percent by weight.

For formulations with resins such as Escorez 5320 or Escorez 5380, some preferred compositions include: (a) 20-50 weight percent maleated EP rubber, 30-60 weight percent tackifier, and 1-15 weight percent ethylene diamine; and (b) 30-60 weight percent maleated EP rubber, 50-70 weight percent tackifier, and 0.5-5 weight percent ethylene diamine or other amine.

Having described the invention, skilled artisans can readily envision various alternatives and changes which are within the spirit and scope of the present invention. Therefore, it is desired that the present invention be limited only by the lawful scope of the following claims.