Technical Field

This invention relates to a new solvent-based contact adhesive suitable for bonding sheets of cured EPDM membranes to each other and to different roof deck substrates, such as concrete, plywood, isocyanurate foam, and fiberboard.

Background Art

The use of cured EPDM single ply membranes as a material for roofing has been in existence for about 20 years. When employed in this capacity, it is often necessary to bond the EPDM membrane to many different roof deck substrates, such as concrete, plywood, isocyanurate foam, and wood fiberboard. The current industry standard bonding adhesive is a neoprene based material consisting of neoprene dissolved in a mixture of solvents and incorporating resins, fillers, curatives and stabilizers to a total solids content of about 23%. This adhesive develops peel adhesion values in the range of 2 to 4.5 lbs./inch width when EPDM membrane is adhered to the substrates mentioned above.

Neoprene-based adhesives generally develop rapid initial strength and possess excellent resistance to creep and cold flow, however, they exhibit relatively poor resist¬ ance to moisture and high temperatures prevalent on roofs.

Known contact adhesives based on butyl or polyisobutylene polymers, while having moisture resistance and the ability to develop good ultimate bond strength to cured EPDM, exhibit creep, cold flow and heat strength characteristics which are unsatisfactory. It has also been found that mixtures of neoprenes with butyls and/or polyisobutylenes do not adequately overcome those shortcomings discussed hereinabove.

EPDM itself is a poor adhesive polymer. When EPDM

is employed as an adhesive, the resulting compounds have little or no tack and, when uncured, are very thermoplastic.

Accordingly, there is a need in the art for a bonding adhesive which would develop a good ultimate bond strength when joining cured EPDM membrane to various substrates, while maintaining satisfactory creep, cold flow and heat strength characteristics, as well as resistance to moisture and heat conditions generally found on a roof.

One adhesive having the aforementioned desirable characteristics is disclosed in U.S. Patent No. 4,501,842 and RE 32,634, which describe an adhesive for bonding cured EPDM membranes having a formulation of a blend of three rubbers - namely, (1) a halogenated butyl rubber; (2) a pre-crosslinked butyl rubber; and (3) a-three-block copolymer with polystyrene end blocks and a rubber poly(ethylene-butylene) mid block, together with a petroleum hydrocarbon based aliphatic thermoplastic resin having a high softening point and a curing agent of an aliphatic isocyanate.

Similarly, U. S. Patent No. 4,603,164 describes a butyl-based adhesive for bonding cured EPDM membranes. The adhesive of this patent includes (a) a halogenated butyl rubber; (b) a pre-crosslinked butyl rubber; (c) an ethylene- propylene-nonconjugated diene terpolymer; (d) a petroleum hydrocarbon based aliphatic thermoplastic resin having a high softening point; and (e) an aliphatic isocyanate.

These patents show that butyl adhesives provide superior ultimate bond strength to the joining of cured EPDM membranes, and are capable of maintaining satisfactory creep, cold flow and heat strength characteristics. Since isocyanates are suspected carcinogens, however, an adhesive that is devoid of any isocyanates or related compounds would be an advantageous contribution to the art.

A butyl-based adhesive which does not depend on isocyanates for bonding cured EPDM membranes is described in U.S. Patent 4,851,462. The adhesive of this patent includes:

(a) a pre-crosslinked halogenated butyl rubber; and (b) a petroleum hydrocarbon based aliphatic thermoplastic resin having a high softening point. However, the thixotropic characteristics of this adhesive do not make it suitable for use on substrates which are relatively porous. Consequently, there is a need for an adhesive which can bond EPDM to a variety of substrates, including those which are porous.

Summary of the Invention

The invention relates to an adhesive formulation which incorporates a blend of two types of rubbers including a pre-crosslinked halogenated butyl and a polystyrene- ethylene/butylene-polyεtyrene (S-EB-S) block thermoplastic rubber. A variation to this formulation incorporates a blend of five types of rubbers including the two mentioned above with three additional rubbers: a halogenated butyl, a pre- crosslinked substantially non-halogenated butyl and an EPDM. A further variation to this formulation incorporates a blend of three types of rubbers including the two mentioned above with a low molecular weight, highly tacky polyisobutylene. Another variation of this formulation incorporates a blend of four types of rubber including the two mentioned above along with polyisobutylene rubber and a styrene-butadiene rubber (SBR) . All formulations may contain at least one high softening point thermoplastic resin to impart increased heat resistance to the adhesive and at least one lower temperature softening point thermoplastic resin to impart tack properties to the adhesive. Solvents may also be included, if desired.

The adhesives of this invention provide heat and weather resistance exceeding that provided by the neoprene- based adhesive that is currently the industry standard for bonding EPDM membranes to such roof deck substrates. The bond strengths of cured EPDM to these roof deck substrates through the use of the adhesive of this invention are equal

to or higher than those obtained when using the current neoprene bonding adhesive. In addition, higher levels of bond strengths of the adhesive of the invention are retained over time with aging.

It is therefore an object of the present invention to provide an adhesive that will develop a good ultimate bond strength when joining cured EPDM membrane to various substrates, while maintaining satisfactory creep, cold flow and heat strength characteristics.

It is a further object of the present invention to provide such an adhesive which is devoid of isocyanates or related compounds.

It is another object of the present invention to provide a sprayable adhesive that will bond cured EPDM membrane to various substrates equally to or better than conventional neoprene adhesives, but one which will have better resistance to moisture and high temperatures.

Description of the Preferred Embodiments

In accordance with the present invention, there is disclosed an adhesive composition for bonding cured EPDM membrane to various roof deck substrates which comprises a formulation of two rubbers: a pre-crosslinked halogenated butyl rubber and a three-block copolymer with polystyrene end blocks and a rubbery poly(ethylene/butylene) mid block. Another adhesive composition includes three additional rubbers: a halogenated butyl rubber; a pre-crosslinked butyl rubber; and an EPDM rubber. Another composition includes an additional rubber: a low molecular weight polyisobutylene. This latter formulation may preferably include a styrene- butadiene rubber.

Each formulation also contains at least one high temperature softening point thermoplastic resin to impart increased heat performance characteristics to the adhesive and at least one lower temperature softening point

thermoplastic resin to impart tack properties to the adhesive. Each formulation also utilizes at least one organic solvent in an amount sufficient to act as a dispersion medium for the rubbers and resins.

The present invention provides a composition and method for developing a bond strength of cured EPDM membrane to various roof deck substrates which are equal to or higher than those obtained with the current neoprene-based bonding adhesive compositions, while maintaining satisfactory creep, cold flow and heat strength characteristics, and providing an adhesive exhibiting better resistance to moisture and high temperatures and a longer useful service life.

The preferred- components and their concentration in the adhesive compositions of the invention are as follows:

The first rubber component is a pre-crosslinked halogenated butyl rubber component which may be comprised of a mixture of halogenated butyl rubbers possessing different degrees of crosslinking and which is present at a concentration of 30-95 parts per hundred parts rubber (PPHR) , preferably between 60-90 PPHR for a two or three rubber component formulation and between 35-65 PPHR for a five rubber component formulation. The molecular structure of the crosslinked halogenated butyl can be schematically represented as:

where X is Cl or Br, and M, N, Y and Z, may vary but

preferably equal 96, 2, 1 and 1, respectively.

The second rubber component is a styrene-ethylene/ butylene-styrene block thermoplastic rubber of the type produced by Shell Chemical Company, Houston, Texas, and having a styrene content of 12-14%, a mid block content of 86-88% and a tensile strength of 3,300-3,500 lbs./in. 2. This component is added at a concentration of 5-50 PPHR, and preferably 10-40 PPHR.

An optional third rubber component is a halogenated butyl rubber of the type produced by Polysar Limited, Sarnia, Ontario, Canada. This component is preferably a bromobutyl rubber having a 27-51 Mooney viscosity (ML 1+8 @ 125° C) and 2.0 - 2.5% Bromine content. When used, this halogenated butyl rubber is added at a concentration of 0-20 PPHR, and preferably at 5-15 PPHR.

The molecular structure of regular butyl rubber is schematically illustrated, as represented by Skeist, I. , HANDBOOK OF ADHESIVES, pp. 225, New York, Reinhold Publishing Corp., (1977), as follows:

. ..

where n can vary but is generally about 50.

For this optional third rubber component, halogenation of the butyl rubber polymer illustrated above can be performed in any known manner, but, is preferably derived through a process proprietary to Polysar which achieves up to 90% of the halogenation situated allylic to the double bond with retention of most of the unsaturation.

An optional fourth rubber component is a pre- crosslinked, non-halogenated butyl rubber of the type

produced by Polysar Limited, -Sarnia, Ontario, Canada, with a weight percent solubility in cyclohexane of 15-50%. This component is added at a concentration of 0-20 PPHR, and preferably at 3-15 PPHR.

An optional fifth rubber component is an EPDM rubber of 65-80 Mooney viscosity (ML4 at 125° C) produced by Uniroyal Chemical, Inc., Naugatuck, Connecticut. This component is added at a concentration of 0-5 PPHR, and preferably at 1-3 PPHR.

Representative of such pre-crosslinked halogenated butyl rubber components contemplated herein, which components are available from Polysar Limited, Sarnia, Ontario, Canada, are those designated as XL-40302, XL-60302 and XL-75302, each possessing different degrees of crosslinking. These components can be used individually or as mixtures to make up the pre-crosslinked halogenated butyl rubber component of the adhesive formulation.

An optional sixth rubber component is a low molecular weight polyisobutylene rubber produced by Exxon Chemical Co., Houston, Texas. This rubber is added at a concentration of 0-20 PPHR, and preferably at 2-15 PPHR.

An optional seventh rubber component is a styrene- butadiene rubber. This is a random mixture of styrene and butadiene, and is conventionally known as SBR. A typical SBR is produced by Ameripol Synpol, Port Neches, Texas and is known as Ameripol 4503. This rubber is added at a concentration of 0-20 PPHR, and preferably at 5-15 PPHR.

Preferably, the sixth rubber component, alone or in combination with the seventh rubber component, is utilized in combination with the first and second rubber components. Also, the third, fourth, fifth and sixth rubber components ma be utilized in combination with the first and second rubber components.

The resin component of the present invention includes at least one high softening point thermoplastic resi

to impart increased heat performance characteristics to the adhesive. Added to the formulation is at least one other resin which possesses a lower temperature softening point to impart tack properties to the adhesive.

Examples of high temperature softening point resins are thermoplastic aliphatic hydrocarbon types made from petroleum monomers. These aliphatic resins are derived from hydrocarbon feedstock monomers possessing from about 5 to 9 carbon atoms, which are polymerized to varying molecular weight ranges so as to achieve softening points in the range of about 150 and 200°C, preferably from about 160 to 185°C. The most preferred high temperature softening point thermoplastic resin is selected from the PICCOVAR™ series produced by Hercules, Inc., Wilmington, Delaware, and has a softening point of about 175 to 181°C, an acid number of less than about 1 and a bromine number of about 16 to about 20. This resin is used at a concentration of 15-50 PPHR, and preferably at 20-45 PPHR.

Other examples of high temperature softening point resins are thermoplastic aromatic hydrocarbon types made from copolymerization of pure aromatic monomers. The softening point range for these resins is between about 150 and 163°C. The most preferred resin is selected from the ENDEX™ series produced by Hercules, Inc., Wilmington, Delaware, and has a softening point of about 159°C and an acid number of less than about 1. This resin is used at a concentration of 0-6 PPHR, and preferably at 1-5 PPHR.

Examples of resins with lower temperature softening points are those derived from fully hydrogenating aliphatic hydrocarbon resins produced by polymerization of pure monomer hydrocarbon feedstocks. The softening point range is about 120 to 130 ^β C and an acid number of less than 1. The preferred resin is selected from the REGAL-REZ™ series produced by Hercules, Inc., Wilmington, Delaware. This resin is used at a concentration of 10-40 PPHR, and preferably at 15-35 PPHR.

Another example of a resin with a lower temperature softening point is SP-553, produced by Schenectady Chemicals, Inc., Schnectady, New York, which is an oil-soluble, thermoplastic, terpene phenolic resin having a softening poin of about 115 ^β C. This resin is used at a concentration of 0-2 PPHR, and preferably at 10-20 PPHR.

A solvent blend of slow and fast evaporating solvents is used for dispersing the components in the adhesive. Such solvent blend generally includes a mixture of liquid aliphatic and aromatic organic compounds. A concentration of between about 350 and 650 PPHR, and preferably between about 390-610 PPHR, is generally used.

One skilled in the art could select the preferred combinations of components for the adhesives of the invention by routine testing.

Examples:

The following examples illustrate the invention in more detail with regard to the most advantageous components for the adhesive compositions.

Example 1 (Comparative) : This example illustrates the adhesion level obtained using an industry standard neoprene- based adhesive such as Carlisle Corp. 90-8-30A.

Test samples were prepared from 1" x 12" EPDM stri and 6" x 8" pieces of various substrates. A thin coat of a conventional neoprene adhesive was applied by brushing on 5" of the EPDM strip leaving 1" x 7" of the EPDM uncoated. A strip of adhesive 2" x 5" was applied to the short length of the substrate. The brushed adhesive was allowed to dry for minutes, after which the coated EPDM strip was placed into contact with the dried adhesive on the substrate. The sampl were allowed to condition. for 7 days at 23°C + 2 ^β C before testing. The conditioned samples were tested in an Instron

Tester by inserting the substrate into the lower jaw of the tester and the uncoated portion of the EPDM strip into the top jaw, the configuration being such that the sample is peeled at an angle of 180° at 2 in./ in. The following results were obtained for peel tests performed at 25 ^β C:

Table 1

Substrate Peel Adhesion (lbs./in. width)

Isocyanurate foam 2.2 (fiberglass faced)

1/2" wood fiberboard 1.8

CDX plywood 2.3

Example 2: This example illustrates the adhesion level obtained by a preferred adhesive composition according to the invention. The amount of each component is based upon 100 parts of the rubber components.

Polysar bromobutyl X-2 (10 parts) , Uniroyal Chemical EPDM 539 (2 parts) and Polysar crosslinked butyl XL-30102 (9 parts) were mixed in a Banbury to produce a rubber masterbatch. Polysar crosslinked bromobutyl XL-75302 (49 parts) and Kraton block copolymer G-1657 (30 parts) were added to the masterbatch and solubilization was initiated by adding a solvent blend of 261 parts toluene and 261 parts hexane into the mixing vessel. Then 35 parts of Piccovar AB-180, 4 parts of Endex 160 and 26 parts of Regal-Rez 1126 (all resins produced by Hercules) were added to the mixer. The components were mixed for 24 hours and the resulting admixture was cooled.

The resulting adhesive formulation was applied to the EPDM membrane strips and substrates in the manner described above in Example 1 and, in addition, the EPDM-to- substrate assembly was conditioned and tested also in the manner of Example 1. The test results appear in Table 2.

Table 2

Substrate Peel Adhesion (lbs./in width)

Isocyanurate foam 2.7 (fiberglass faced) 1/2" wood fiberboard 3.1

CDX plywood 2.3

The adhesive composition of the invention provides equal or improved performance to that of the conventional adhesive.

Example 3 (Comparative) : This example illustrates the adhesion level retained by bonded samples using the neoprene standard when subjected to elevated temperatures such as thos which can occur on a roof having a black EPDM membrane which is exposed to direct sunlight on a hot sunny day. Samples were prepared the same way as in Example 1. The EPDM-to- substrate assemblies were allowed to condition at 23°C + 2° C for 24 hours rather than 7 days prior to beginning aging. Th EPDM-to-substrate assemblies were then aged at 100 ^C C + 2 ^β C fo a period of 7 days then allowed to cool to 23°C + 2°C. The results of peel tests performed at 23 ^β C + 2°C appear below in Table 3.

Table 3

Substrate Peel Adhesion (lbs./in. width)

Isocyanurate foam 1.7 (fiberglass faced)

1/2" wood fiberboard 1.5

CDX plywood 1.2

Cinder block 1.1

Example 4: This example illustrates the increased heat resistance obtained by the adhesive of the invention describe in Example 2. Test samples were prepared the same way as in

Example 1. The EPDM-to-substrate assemblies were then conditioned, aged and tested as in Example 3. The test results appear below in Table 4.

Table 4

Substrate Peel Adhesion (lbs./in. width)

Isocyanurate foam 2.6

(fiberglass faced)

1/2" wood fiberboard 1.8

CDX plywood 3.7

Cinder block 1.4

The results indicate an increase in peel adhesion ranging from about 20 to 208 percent compared to the conventional neoprene adhesive.

Example 5 (Comparative) : This example illustrates the adhesion level retained by bonded samples using the neoprene standard when exposed to water, elevated temperatures, and freezing temperatures, such as those weather conditions a roof would experience during the course of a year. The samples were prepared the same way as in Example 1. The EPDM-to- substrate assemblies were allowed to age at 23° + C 2 ^β C for 24 hours prior to beginning aging. The substrate assemblies were then conditioned 7 days in water at 70" C and 1 day at -40* C. The samples were then peeled immediately at -40° C. The test results appear below in Table 5.

Table 5

Substrates Peel Adhesion (lbs./in. width)

CDX plywood 1.9

Cinder block 1.4

Example 6: This example illustrates the increased weather resistance of the adhesive of the invention described in

Example 2 when exposed to heat, water, and freezing temperatures. Test samples were prepared the same way as in

Example 1. The EPDM-to-substrate assemblies were then aged e and tested the same way as in Example 5. The test results appear below in Table 6.

Table 6

Substrate Peel Adhesion (lbs./in. width) 0 CDX plywood 3.2

Cinder block 3.4

The results for the adhesive composition of the invention illustrate an increase in peel adhesion ranging from 68 to 5 143% compared to the conventional neoprene adhesive.

Example 7 (Comparison) : This example illustrates the adhesio performance of the industry standard neoprene based adhesive when larger widths of EPDM membrane are separated from the 0 substrate.

Test samples were prepared from 6" x 18" pieces of EPDM membrane and 6" x 9" pieces of 1" thick "Marrero" wood fiberboard. A thin coat of the neoprene adhesive was applied by brushing onto a 6" x 8" area of the EPDM membrane leaving 5 6" x 10" of the EPDM uncoated. A thin coat of the neoprene adhesive was applied to a 6" x 8" area of the 1" thick wood fiberboard leaving 6" x 1" of the wood fiberboard uncoated. The adhesive is allowed to dry for 30 minutes, after which th coated EPDM area was placed into contact with the dried 0 adhesive on the substrate area. The samples were allowed to condition for 7 days at 23' C + 2" C before testing.

The conditioned samples were tested in an Instron Tester by inserting the substrate into the lower jaw of the J. tester and the uncoated portion of the EPDM into the top jaw.

the configuration being such that the sample is peeled at an angle of 180" at 2"/min. The test results appear below in Table 7.

Table 7

Substrate Peel Adhesion (lbs.)

1" wood fiberboard 13.8

Example 8: This example illustrates the adhesion level obtained by another adhesive composition of the invention in which the solvent system is adjusted to decrease the swelling of the EPDM membrane. The amount of each of the solvent components employed in the adhesive formulation is based upon 100 parts of the rubber components. The solvent blend consisted of 221 parts of toluene,

6 parts of xylene, 73 parts of acetone, and 222 parts of textile spirits. The remaining solid components are the same as in Example 2.

The resulting adhesive formulation was applied to the EPDM membrane piece and 1" thick wood fiberboard substrate in the manner discussed in Example 7 and, in addition, the EPDM-to-substrate assembly was aged and tested in the same manner as in Example 7. The test results appear in Table 8.

Table 8

Substrate Peel Adhesion (lbs)

1" wood fiberboard 15.0

Example 9: This example illustrates the adhesion level obtained by another adhesive composition of the invention in which the rubber masterbatch described in Example 2 has been replaced by the crosslinked bromobutyl XL-40302. This adjustment has been made to simplify production of the adhesive. The amount of each of the components employed in the adhesive formulation is based upon 100 parts of the rubber

components.

The solubilization of Polysar crosslinked bromobutyl XL-75302 (47 parts) , Polysar crosslinked bromobutyl XL-40302 (35 parts) , and Kraton block copolymer G-1657 (18 parts) was initiated by adding the solvent blend described in Example 8 into the mixing vessel. 2.3 parts of Endex 160, 38 parts of Piccovar AB-180, and 25 parts of Regal Rez 1126 were then added to the mixer.

The resulting adhesive formulation was applied to the EPDM membrane piece and 1" thick wood fiberboard substrate in the same manner discussed in Example 7 and, in addition, the EPDM-to-substrate assembly was aged and tested in the same manner as in Example 7.. The test results appear below in Table 9.

Table 9 Substrate Peel Adhesion (lbs.)

1" wood fiberboard 18.6

By comparing the results of Examples 7-9, it is seen that improved peel adhesion values are obtained by the use of the adhesive compositions of the invention.

Example 10 (Comparative) : This example illustrates the level of adhesion developed using the industry standard neoprene based adhesive when the time of conditioning before testing i reduced from 7 days to 3 days.

The test sample was prepared the same as in Example 7 except using "Sunbury" wood fiberboard as a substrate in placeof "Marrero". After the sample was conditioned for 3 days at 23"C + 2 ^β C, it was tested in the same manner as in Example 7. The test results appear in Table 10.

Table 10 Substrate Peel Adhesion (lbs.)

1" wood fiberboard 15.5

Example 11: This example illustrates the adhesion level obtained by another variation of the invention in which a low temperature softening point resin (SP-553) and a low molecular weight polyisobutylene rubber (Vistanex MML-80) are used to increase tack and initial green strength. The amount of each of the components employed in the adhesive formulation is based upon 100 parts of the rubber components. ___

The solubilization of Polysar crosslinked bromobutyl XL-75302 (43 parts) , XL-40302 (33 parts) , Kraton block copolymer G-1657 (14 parts) , and Vistanex MML-80 (10 parts) was initiated by adding a solvent blend of 180 parts toluene, 180 parts of textile spirits and 40 parts of acetone. Then, 25 parts of Piccovar AB-180, 23 parts of Regal Rez 1126, and 15 parts of SP-553 were added to the mixer.

The resulting adhesive formulation was applied to the EPDM membrane sheet and 1" "Sunbury" wood fiberboard in the same manner discussed in Example 7 and, in addition, the EPDM-to-substrate assembly was aged and tested in the same manner as in Example 10. The test results appear in Table 11.

Table 11 Substrate Peel Adhesion (lbs.)

1" wood fiberboard 18.0

By comparing the results of Examples 10 and 11, it is seen that improved peel adhesion values are obtained by the use of the adhesive compositions of the invention.

Example 12: This example illustrates the formulation of a sprayable high viscosity (6000 to 8000 cps) adhesive for bonding cured EPDM membrane to various roof deck substrates.

The solubilization of Polysar crosslinked bromobutyl XL-75302 (40.8 parts), XL-40302 (30.6 parts), Kraton block copolymer G-1657 (13.6 parts), Ameripol 4503 (10 parts) and Vistanex MML-80 (5 parts) was initiated by adding a solvent blend of 122.25 parts toluene and 366.75 parts of textile

spirits. Then, 25 parts of Piccovar AB-180, 23 parts of Regal Rez 1126 and 15 parts of SP-553 were then added to the mixer.

This formulation provides peel adhesion values which are comparable to those of Example 11, but in a sprayable formulation due to its favorable rheology.

While it is apparent that the invention herein disclosed is well calculated to fulfill the objects above stated, it will be appreciated that numerous modifications and embodiments may be devised by those skilled in the art, and it is intended that the appended claims cover all such modifications and embodiments ^'1 as fall within the true spirit and scope of the present invention.