Cross-Reference to Related Application

This application is a continuation-in-part of U.S. Serial No. 07/575,990 filed August 31, 1990, which is a continuation- in-part of U.S. serial no. 07/571,459 filed August 21, 1990 both of which are incorporated herein by reference.

Field of the Invention

This invention is an improved adhesive elastomeric composition for bonding substrates together, having improved properties of flowability.

Background of the Invention

Uncured adhesive elastomeric compositions suitable for bondiriy diverse substrates such as other elastomers, metals, plastics, glass, fibers, paper and fabrics, have been disclosed by the inventors hereof in application serial numbers

07/575,990 and 07/571,459. It is often desirable to apply such compositions to the substrates in a flowable form. For example, in industrial operations such as automobile manufacturing, shoe manufacturing or rotomolding of rubber parts it is desirable to use such compositions to replace welding in an assembly-line-type process. Compositions having reduced viscosity so as to be pumpable through supply lines are desirably used.

As is taught in the above U.S. patent applications, adhesive rubber compositions can be prepared by the addition of certain polymeric adducts to elastomeric compositions. This invention involves the addition of low molecular weight elastomers to such elastomeric/polymeric compositions to produce flowable compositions.

The flowability of an adhesive elastomeric composition can be increased by using elastomers of low molecular weight and viscosity in the formulation, so as to increase the flowability of the mixture, however, in general, the flowability of such compositions cannot be increased without sacrificing tensile and bond strength.

Bond strength, as measured by lap shear tests, is a direct indication of adhesive strength. Theoretically bond strength cannot be greater than two times tensile strength. The present compositions achieve adhesiveness of up to about 1.4 times

tensile strength. However, as the present invention shows, adhesiveness is not directly proportional to tensile strength.

As is known to the art, the degree of crosslinking is also not a direct measure of the tensile strength or bond strength of a composition. Too high a degree of crosslinking can make a composition brittle and promote cracks.

While greater crosslinking may improve tensile strength up to an optimum point which varies from elastomer to elastomer, most elastomers are cured beyond this optimum point, and thus crosslink enhancing coagents would not enhance tensile strength, but rather would lower tensile strength. Such coagents are usually used to improve compression set, improve modulus and decrease elongation, or to enable the use of fillers in the composition. When elastomers having an average molecular weight low enough to flow freely at reasonably low temperatures (e.g., less than about 100%), are used to formulate the adhesive compositions, the cured product is less tough than would be desirable, i.e., elongation is greater than desirable at a given tensile or bond strength.

When nonliquid elastomers are cured in the presence of crosslink-enhancing agents, percent elongation decreases and modulus at 100% increases. For example, Colorado Chemical Specialties, Inc. Bulletin CCS-107, "High Vinyl 1-2 Liquid Polybutadiene Ricon EPDM/EPM Coagents" discloses that when a preferred crosslink enhancing agent of this invention, Ricon

153™ of Advanced Resins, Inc. (formerly Colorado Chemical Specialties, Inc., Grand Junction, CO) is added at 10 phr (parts per hundred) to EPDM rubber formulations, percent elongation decreases from 440 to 250 and 100% modulus increases from 210 to 380. However, elongation percent for cured flowable adhesive rubber compositions should be less than about 200%, and preferably less than about 180%.

It was surprising to find that flowable compositions could be made with acceptable tensile strengths and that the adhesiveness of such compositions could be improved by the addition of crosslink-enhancing coagents, while maintaining good tensile strength and improving elongation properties

(toughness) .

Crosslink-enhancing coagents known to the art include liquid polybutadienes having the properties of high 1,2 vinyl content, such as Ricon 153™ and Ricon 154™, polybutadiene products of Advanced Resins, Inc., Grand Junction, Colorado, di, tri and tetra functional acrylates and methacrylates, triallylcyanurate (TAC) , triallylisocyanurate (TAIC) , triallyltrimellitate (TATM) , and N,N-metaphenylenedimaleimide (HVA-2) . These coagents have been used as crosslink-enhancing coagents primarily with peroxide-cured elastomers. HVA-2 and the Advanced Resin products have also been used with sulfur- cured elastomers. These agents have been used to make the elastomers harder and more resistant to swell. However, such

coagents have not been known o increase the adhesiveness of an elastomer.

Summary of the Invention

An uncured adhesive elastomeric composition is provided having a Mooney viscosity at most about 20 at a temperature of 125°C, comprising:

(a) An elastomer having a raw Mooney viscosity ML 1 + 4 at 125°C between about 20 and about 85, and preferably between about 40 and about 70, and having the ability to be cured by peroxide, sulfur or resin systems. Preferably this elastomer is used in an amount between about 30 and about 70 phr, and more preferably in an amount between about 40 and about 60 phr. The upper limit of concentration used may vary depending on the particular compounds chosen as components of the elastomeric com' osition of this invention, and should not be so high as to renuer the final mixture too viscous to be pumpable. A preferred elastomer is EPDM 70A of Epsyn Copolymer Rubber and Chemical Company of Baton Rouge, La.

(b> A synthetic resin curable by the same cure system as co pone _ (a) above, having a molecular weight between about

30,000 and about 70,000. This resin is preferably Trilene 65, a product of Uniroyal Chemical Company, Middlebury, Conn. A suff- -dent amount of this resin should be used to lower the

Mooney viscosity of the mixture to at most about 20 and preferably at most about 5 at a temperature of about 125°C. Too high a proportion of this elastomer will lower tensile and bond strengths to unacceptable levels. Preferably this elastomer is used in an amount between about 30 and about 70 phr, and more preferably in an amount between about 40 and about 60 phr. Preferably this resin has an analogous structure to the elastomer of component (a) , e.g. , a polymer having identical or similar units but with a shorter chain length.

(c) An unsaturated polymeric adduct of a dicarboxylic acid or dicarboxylic acid derivative wherein the acid or derivative moiety comprises at least about three weight percent of said adduct. This adduct should be used in an amount sufficient to provide adhesive properties to the mixture, but not so high as to degrade physical properties such as speed of curing, tensile strength, and the like. Preferably the adduct is used in an amount between about 5 and about 40 phr, and more preferably in an amount between about 10 and about 20 phr. As will be understood by those skilled in the art, the components of the elastomeric compositions of this invention are expressed in parts per hundred (phr) whereby the total phr of component (a) plus component (b) equals 100. Additional components are expressed in phr based on their proportion to the sum of components (a) plus (b) , so that the total phr for all components in the composition will be greater than 100. Preferred adducts are the maleic adduct resins sold by Advanced Resins, Inc. of Grand Junction Colorado under the trademark

RICOBOND, as described in Advanced Resins, Inc. Bulletin dated June 6, 1991 based on a paper presented at the 138th Meeting of the Rubber Division, American Chemical Society, Washington, D.C. October 9-12, 1990.

(d) A curing agent such as peroxide, sulfur and sulfur donors and accelerators, or resin cure systems, such as bromophenol or SP1055 of Schenectady Chemical Company. Preferably peroxide curing agents are used, and more preferably, dicu yl peroxide. The amount of curing agent used, as is known to those skilled in the art, should be sufficient to bring about cure in a reasonable period of time without excessive scorch or detract,ng from the adhesive properties of the composition.

Compositions according to the foregoing, surprisingly, exhibit tensile strengths in the desired range, i.e., greater than about 8 MPa, preferably greater than about 10 MPa, and more preferably greater than about 12 MPa.

It is often desirable to produce an adhesive rubber elastomer having a lower percent elongation, and a higher 100% modulus than the compositions described above. In a further embodiment of this invention, it has been discovered that the addition of crosslink-enhancing coagents will bring about the desired properties to a much greater degree than predicted from a knowledge of the behavior of these coagents in non-flowable elastomeric systems. Moreover, the adhesiveness of the

elastomer is significantly increased by the addition of these coagents. Therefore the compositions of this invention advantageously also include:

(e) a crosslink-enhancing coagent having a viscosity from about 300 to about 5000 poise at a temperature of 45°C, and more preferably about 2,500 poise at 45°C. Preferred resins are those having at least fifty percent 1,2 vinyl content, such as the 1,2 polybutadiene resins, e.g. the Ricon 153™ compound described in Colorado Chemical Specialties, Inc. Bulletin CCS 1-7, supra. and the closely related product Ricon 154™ also described in said CCS Bulletin. Other useful coagents are di, tri and tetra functional acrylates and methacrylates, triallylcyanurate (TAC) , triallylisocyanurate (TAIC) , triallyltrimellitate (TATM) and N,N-meta-phenylenediamaleimide (HVA-2) . The coagent should be used in amounts sufficient to bring about enough crosslink density to provide tensile strength of the cured product within acceptable limits while lowering percent elongation and increasing adhesiveness and modulus. Preferably ultimate elongation percent of the cured composition should be less than about 200 and more preferably less than about 180, and modulus at 100% should be at least about 1.0 MPa and more preferably, at least about 3.0 MPa.

Equivalent compositions can be made using elastomers having a molecular weight equivalent to the resultant average molecular weight of components (a) and (b) , e.g., between about

40,000 and about 800,000, having a viscosity low enough to be

pumpa ^v in combination with components (c) and (d) , and optionally (e) .

A method of making flowable adhesive elastomeric compositions is also taught comprising the following steps: adding to a composition comprising an elastomer as described in paragraph (a) above and a curing agent as described in paragraph (d) above, a lower molecular weight resin as described in paragraph (b) above; and then mixing in an adducted resin as described in paragraph (c) above in an amount sufficient to provide adhesive properties to the mixture. As will be appreciated by those skilled in the art, additional components such as carbon black and fillers, as well as antioxidants, and tackifiers may be added to the mixture. It is preferred that the adduct (c) be added last, and it may be added simultaneously with the low molecular weight resin (b) . In a further embodiment, the method comprises the addition of a crosslink-enhancing coagent as described in paragraph (e) above. The coagent may be added with the resin (b) and adduct (c) , or prior to addition of the adduct (c) .

It is preferred that fillers, preferably carbon black be used in the mixtures. As is known to the art, such fillers are capable of increasing the tensile strength of the product. These materials should be mixed by shearing to break up the molecular structure and this requires that the mixture be more viscous than the pumpable formulation finally resulting from the process of making the compositions of this invention.

Therefore, the fillers should be mixed into the composition prior to adding the resin components (b) , (c) and (e) .

As is understood in the art, for best results the components should be homogeneously mixed.

The compositions of this invention are used in a method for adhesively bonding together substrates such as other elastomers, metals, plastics, glass, fibers, paper and fabrics, or for bonding the elastomer itself to a substrate. In use, the adhesive elastomers of this invention are flowed onto the substrates to be bonded, and cured in-situ whereby the substrates are bonded together, or the elastomer may be bonded to only one substrate.

Detailed Description of the Preferred Embodiments.

In a preferred embodiment of this invention, a flowable adhesive elastomeric composition is provided. Epsyn 70A EPDM rubber is preferred as the basic elastomer (component (a) ) . This elastomer may be used in amounts between about 30 and about 70 phr, and preferably in the amount of about 60 phr. It is preferred that reinforcing fillers, particularly carbon black, be added to the mixture in an amount between about 30 and about 75 phr. Carbon black helps increase the tensile strength of the cured elastomer. The curing agent is then added, preferably a peroxide such as dicumyl peroxide as DiCup 40 E, product of Hercules Co. of Wilmington, Delaware, in an

amount sufficient to cure the mixture, e.g., about 15 phr. Other components such as antioxidants, e.g., Agerite Resin D, product of R. T. Vanderbilt Company of Norwalk, Connecticut; antiozonates such as methyl niclate, also a product of R. T. ^* 5 Vanderbilt Company; and tackifiers such as Wingtack 95, product of Goodyear Company of Akron, Ohio, may also be added to the mixture as required. As is known in the art, antioxidants and antiozonates are added in small amounts, such as about 1 phr. Tackifiers may be added in amounts between about 5 and about 10 40 as required for building tack. In addition, cure accelerators known to the art such as TMTD and other materials known to the art may be added.

The lower molecular weight resin is then added. Trilene 65 is preferred when EPDM rubber is used as the high molecular

15 weight elastomer because of its structural similarity. This component may be added in amounts between about 30 and about 70 phr, preferably at about 40 phr. Concurrently, or following addition of this component, it is preferred that a crosslink enhancing coagent such as a 1,2 polybutadiene resin, e.g. Ricon

20 153 or 154, is added in an amount sufficient to lower the percent elongation of the cured product to less than about 180. This amount will generally be around 10 to 15 phr. Finally, or concurrently with the lower molecular weight resin and the coagent, it is preferred that a polymeric adduct of a

^* 25 dicarboxylic acid or anhydride, preferably a maleic acid anhydride of an unsaturated polybutadiene, such as Ricobond 1756, Ricobond 1731 or Ricobond 1031, is added in an amount

sufficient to provide adhesive properties to the mixture. This component may be added in amounts between about 5 and about 40 phr, and preferably is added at about 10 phr.

The foregoing components are milled into the mixture containing the high molecular weight elastomer and curing agents. It may be necessary to cool the mixture during mixing to facilitate mixing and removal from the mixing equipment.

The flowable mixture is then applied to a substrate, such as a plastic or metal automobile part, a further substrate whose bonding to the first substrate is desired is then placed in contact with the flowable mixture, and the mixture is cured in situ, resulting in a strong bond between the substrates. Preferably the bond is at least as strong under stress conditions such as tearing and pulling, as the substrates themselves.

The following Examples are provided by way of illustration, not by way of limitation of this invention, which is defined by the scope of the claims hereof.

EXAMPLES

Example .. Preparation c a Pumpable Adhesive EPDM

Pumpable. adhesive EPDM elastomer was mixed on a two roll lab mill. First, carbon black was mixed into Epsyn 70A EPDM rubber followed by DiCup 40KE. DiCup 40KE is a product of Hercules Company of Wilmington, Delaware, consisting of 40% dicumyl peroxide on clay. This was sheeted to ensure a homogenous mixture, then Trilene 65, Ricon 154 (a crosslink- enhancing coagent) , and Ricobond 1756 (a maleinized polymeric adduct) were simultaneously milled into the rubber along with otaer ingredients known in the art. The formulation was allowed to rest for 24 hours at room temperature and then sampled for testing.

Standard tests for rubber were used including: Vulcanization Characteristics Using Oscillating Disk Cure Meter, ASTM D2084-79; Measurement of Rubber Properties in Tension, ASTM D 412-80; Tear Resistance, ASTM D 624-73, Shore A hardness, and Impact Resilience of Rubber by vertical rebound, ASTM D-2632. Samples were also prepared for lap shear testing on aluminum, steel, and stainless steel. Standard metal strips were used. The aluminum and steel strips were gently sanded and washed with methanol. Stainless steel strips und" went no surface preparation. Test samples were cured urii,.. pressure at 160°C for 30 minutes.

The impact Resilience of Rubber by Vertical Rebound, ASTM D-2632, was performed on a Shore Resliometer. A Shore Durometer was used for hardness testing. Specimen thickness was determined with an Ames 202 thickness gauge. The tensile and tear tests were determined using a GCA/Precision CRE 500 Universal Tester at 508 mm/minute or 50.8 mm/minute as indicated by ASTM. Results are set forth in Table 1.

TABLE 1 EPDM Pumpable System

EPDM 70A 60.0

Trilene 65 40.0

HAF N762 Carbon Black 75.0

Dicumyl Peroxide (40%) 15.0

Ricon 154 10.0

Ricobond 1756 10.0

210.0

Rheometer Data. ASTM D-2084

Model: MP10 Range: 100 Clock: 24 min. Speed: 100 cps

Die: Micro Arc: 1 Temperature: 160°C

Initial Viscosity dNm 13.6 Minimum Viscosity dN 9.0 Scorch Time (Tsl) Min. 1.2 Cure to 90% (T90) Min. 13.4 Maximum Torque Mh dNm 70.0 Cure Rate Index 8.2

Tensile Strength MPa 14.5 Ult. Elongation % 70.0 Modulus @ 50% MPa 10.8 Rebound Resilience 39.0 Shore A Hardness 86.0 Die C Tear Strength kN/m 17.0

Lap Shear Strength ASTM D-816 MPa

On Aluminum (1) 18.2

On Steel (1) 15.4

On Stainless Steel (2) 13.6

(1) Sanded and wiped with methanol

(2) No Preparation

Example 2. Comparison of Tensile Strength of Cured

Elastomer Composition with and without Crosslink-enhancing Coagent and Maleinized Polymer

Formulas containing a crosslink-enhancing coagent, Ricon

154, and a maleinized polymeric adduct (Ricobond 1756) were compared to formulas without these additives. The formulas were mixed and tested as described in Example 1. Results are set forth in Table 2. These results show dramatic increase in both adhesiveness (lap shear strength) and tensile strength with the additives.

TABLE 2

COMPARISON OF TENSILE STRENGTH OF CURED ELASTOMER COMPOSITION WITH AND WITHOUT CROSSLINK-ENHANCING COAGENT AND

MALEINIZED POLYMER

WITHOUT WITH

Copolymer EPDM 70A Uniroyal Trilene 65 HAF N762 Carbon Black Agerite Resin D (Antioxidant) Methyl Niclate (Antiozonate) Ricon 154 Ricobond 1756 DiCUP 40KE Wingtack 95

208.0 242.0

Rheometer Data, ASTM D-2084 Model: MP10 Range: 100 Clock: 24 min. Speed: lOOcps Die: Micro Arc: 1 Temperature: 160°C

Unaged Physicals ASTM D-412. Press Cure @ 160°C. 30 min.

Die C Tear KNm 7.71 16.99

Lap Shear Strength, ASTM D-816 MPa

On Aluminum 0.02 19.13

Example 3. Comparison Effect of Crosslink-enhancing

Coagents on Physical Properties of EPDM Pumpable Elastomer Without Maleinized Polymers

Formulas containing crosslink-enhancing coagents (Ricon 154) and trimethylolpropanetrimethacrylate (TMPTM) , the latter at concentrations of 5 and 15 phr, were compared with formulas without these coagents. None of the formulas contained maleinized polymers. The formulas were mixed and tested as described in Example 1. Results are set forth in Table 3.

Useful elastomer compounds were obtained when Ricon 154 was added to EPDM/Trilene compounds. It is unusual to attempt using 15 phr TMPTM in such a system because it has poor compatibility at high concentrations in most elastomers. This appeared to be the case with this system, although a freshly mixed compound could be cured to give a product with quite reasonable physical properties. The main difficulty with this system was that it was very plasticized and tacky, and in general, did not handle well. It should be noted that none of the systems described in Table 3 had lap shear values in bonding to aluminum comparable to those obtained when Ricobond resins (maleinized polybutadiene resins) were added to the systems.

TABLE 3

COMPARISON OF EFFECT OF CROSSLINK-ENHANCING COAGENTS ON

PHYSICAL PROPERTIES OF EPDM PUMPABLE-ELASTOMER

WITHOUT MALEINIZED POLYMERS

Model: MP10 Range: 50 Clock: 24 min. Speed: lOOcps Die: Micro Arc: 1 Temperature: 160°C

Unaged Physicals ASTM D-412, Press Cure @ 160°C. min.

Die C Tear KN/ 42.4 28.3 39.2 37.3

Lap Shear Strength. ASTM D-816 MPa

On Aluminum (1) 1.9 4.3 2.8 5.8

(1) Sanded and methanol washed

Example 4. Comparison of Formulas With and Without

Maleinized Polymers, and Crosslink-enhancing Coagents

Formulas containing and not containing maleinized polymers (Ricobond) were compared in the presence and absence of crosslink-enhancing coagents (Ricon 154 and TMPTM) . A high shear internal mixer (Banbury) was used to mix a masterbatch containing EPDM 70A, Trilene 65, Carbon Black N762, Agerite Resin D, Methyl Niclate, Dicup 40KE, and Wingtack 95. The various compounds described in Table 4 including the standard were then mixed on a two roll mill. Most of the compounds were so plasticized that they had to be cooled during mixing in order to achieve good results and during removal from the mill. Some of the compounds would probably have been easier to mix in a sigma blade mixer or an extruder, or both. However, for laboratory compounding, the cooled roll mill was satisfactory. Results are shown in Table 4. These results show that maleinized polybutadiene alone produced adhesion on aluminum significantly greater than that observed when only Trilene or when Trilene and a coagent were used. However, it is evident from the data that the combination of Trilene, coagent and maleinized polybutadiene gives the best adhesive compound. It is also evident that this particular combination also results in very highly crosslinked rubber as can be seen from the values for elongation which are significantly lower than the values for the compositions lacking the crosslinking enhancing coagents. The adhesive strength in lap shear is related to the strength of the rubber, since the usual failure of the bond to

aluminum in this system is tearing of the rubber, not failure at the interface of rubber to aluminum. It should be noted that this is only part of the picture, since compound B resulting from coagei t Ricon 154 is highly crosslinked, but does not have high lap shear strength.

TABLE 4 EFFECTS OF RICON AND RICOBOND ON TRILENE MODIFIED EPDM FORMULAS

Formulation STD A B D E H

0

5

0

5

TABLE 4 (CONTINUED)

Formulation STD B D E H

Mooney Viscosity : 25.40 : 16.50 17.03 16.38

(250F) Unaged Physicals ASTM D-412 Press Cure @ 160°C. mm.

Lap Shear Strength, ASTM D-816 MPa

On Aluminum (1) 1.9 4.3 2.8 8.0 10.9 7.1 13.3 11.5 13.7

(1) Sanded and methanol washed