CA1261518A - Adhesive for bonding cured epdm rubber - Google Patents

Abstract

ABSTRACT
An adhesive for bonding cured EPDM membranes is provided comprising A) a halogenated butyl rubber B) a pre-crosslinked butyl rubber C) a styrene/ethylene butylene/styrene block thermoplastic rubber D) a thermoplastic petroleum based hydrocar-bon feedstock derived aliphatic monomer resin and E) an aliphatic isocyanate

Description

A~)HESIVE FOR BONDING CURED EPDM RUBBER
_ _ _ This inventlon relates to an improved solvent based contact adhesive which is useful for providing a strong bond between sheets of cured ethylene-propylene-diene terpolymers (EPDM).
EPDM rubber is widely used in the tire industry.
However, the bonding techniques used in tires requires special surface preparation and high pressure and heat conditioning. When EPDM membranes are used as material other than for tires, such as for a roofing material, it is sometimes necessary tn prepare a lap seam bonding the EPDM menbranes to itself.
In the prior art, such as Skeist, I., Handbook of Adhesives, pp. B80, New York, Reinhold Publishing Corp., 1977, it is suggested that a neoprene-based adhesive mflY
be used for bonding EPD~S n1bber. Currently, the commonly used adhesive is one based on neoprene dissolved in a mixture of solvents and incorporating resins, fillers, curatives and stabilizers to a total solids content of about 23%. This compound develops a T-peel adhesion of approximately 2 lbs./inch width.
Adhesives based on neoprene generally have excellent resistance to creep and cold flow, but have the drawback of providing only low levels of bond strength to cured EPDM.

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Known contact adhesives based on butyl or polyiso-butylene polymers while developing good ultimate bond strengths to cured EPDM, have unsatisfactory creep, cold flow and heat strength characteristics. In addition, it is known that mixtures of neoprenes and butyls and/or polyisobutylenes do not overcome the short-comings of either component as set forth above.
EPDM itself is a poor adhesive polymer. When EPD~
is used as an adhesive the resulting compounds have little or no tack and when uncured are very thermoplas-tic.
It is therefore an object of the invention to provide an adhesive that will develop a good ultimate bond strength to the joining of cured EPDM membranes as well as maintaining satisfactory creep, cold flow and heat strength characteristics~ all without the addition of special surface preparations or the use of high pressure and/or heat.
In accordance with the invention, an adhesive formulation is provided comprising 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 rubbery poly tethylene-butylene) mid block, together with a petroleum hydrocarbon based aliphatic thermoplastic resin having a high soft~ning point and an aliphatic isocyanate.
The invention also provides an improved method for preparing said adhesive which method comprises the separate milling or mixing in a Banbury (tm) mixer of said halogenated and pre-crosslinked butyl rubbers and sequential additions when solubilizing the ingredients with the butyl rubbers first and the isocyanate modifier last lnto a cool churn which has baen purged of moisture.
In another aspect the present invention provides a process for making an adhesive for the bonding of cured EPDM membranes comprising:
(A) Milling or mixing separately, with carbon black, a halogenated butyl rubber of the formula:

CH~ CH2 IHl c~z CHJ
...-CI -CH2-CH2 I H-C-CH2- C-CH~ ~CH2~H-C-CHl I -CH2-where X is Cl or Br and n is about SO, and a pre-crosslinked butyl rubber of the formula:
CH, CH~ CH~ Cl~) ~CH~
_f--CH---CH2CH--C--CH2 -C--C112~ --CH~CH--~ :---CH2--C--CH2 CH~ l CH3 . CH~
î
- CH~ ~ CH
-CH~--C----CH2--f--CJI ~; CH--CHI--f-- . .
CH~ CH~ CH~ `CH
. . .--CH2--C--CH~CH CH~--C--__ Cll~ Cll~ I
where A = Crosslinking Agent and n is about 50, (B) Solubilizing the butyl rubbers of (A) with a styrene/ethylene butylene/styrene block thermoplastic rubber, a thermoplastic, petroleum hydrocarbon feedstock 9~1 ~9.~L~

derived aliphatic monomer resin derived from C5-C9 streams polymerized to varying molecular weights to gi~e a softening point range of 162~ -181C., an aliphatic isocyanate based on an adduct of 1,6-hexamethylene diisocy~nate, an alkali-metal alumino-silicate zeolite adsorben-t, and zinc oxide in an organic liquid having a solubility parameter of 8.5 - 8.9 and a hydrogen bonding index of 3.0 - 3.5.
In another embodimen-t, -the invention provides an adhesive made by -the ~bove-mentioned process.
The halogenated butyl rubber ingredient is pre-ferably Bromobutyl of 27-51 Mooney viscosity (ML 1~8 at 125C) and 2.0-2.5% bromine con~ent. The halogenated butyl rubber may be added at a concentration of 20.0-45.0 parts per hundred parts of rubber. Chlorobutyl rubber may be used in place of bromobutyl rubber. The Mooney viscosity of said chlorobutyl rubber is in ~he range 27-5l (ML 1+8 at 125C) and possesses a 1.1-1.3% chlorine content. Adhesives incorporating chlorobutyl rubber impart bond strengths between cured EPDM sheets higher than those given with neoprene adhesives currently used but lower than those given by the preferred bromobutyl rubber adhesives of this invention.
The molecular structure of regular butyl rubber by be schematically shown as represented by Skeist, I., Handbook of Adhesives, pp. 255, New York, Reinhold Publishing Corp. 9 1977, as follows:

_ _ ICH3 ICH3 jCH3ICH3 l H3 ... - C - CH2 - CH2 - CH = C - CH ~ C - CH~ CH2 - CH = C - CH2 - C - CH - .., CH3 1 CH3n at3 Where n is about 50 Halogenation of the above polymer is derived through a proprietary process with up to 90Z of the halogenation situated allylic to the double bond with retention of most of the unsaturation. This is schematically repre-sented as follows:

ICH3 IClH2 --CH3 1 CH2 CH3 - ~ C ~ CH2 - CH2 - CH - C - CH2 C - CH2- ~ CH2 - CH - C - CH2 - C - CH - . ., CH3 X _ CH3 ~ n X CH3 Where X is Cl or Br and n is about 5~

These halogenated butyl rubbers may be of the bromobutyl or chlorobutyl type made by Polysar Ltd., Sarnia, Ontario, Canada or by Exxon Chemical Company, Houston, Texas.
The pre-crosslinked butyl rubber is also derived from regular butyl rubber through a proprietary process by incorporating a crosslinking agerlt during the polymerization of the rubber. The finished product may be schematically represented as follows:

I H3 l H3 -CH3 1 CH3 CH3 ... -C-CH2-C11=CH C-CH2 C-CH2 1 - CH=CH-C-CH -C-CH --- --I \ _ CH3 ~ n A CH3 ... 2 CH2-C-C~CH-CH2-C-3 CH3 CH3 \ I-- CH31 n ---C~2-f-CH=CH ~ C~12-Ct...

CH3 _ 31 n Where n is about 50 and A is a crosslinking agent such as 1,4 divinyl benzene, methyl divinyl benzene, 1,3 butadiene, isoprene, 2-ethyl 1,3-butadiene, 1,6 hexa-diene, 1,6-hexanediol-diacrylate, 2 methyl-1,3-butadiene, butyleneglycol dimethylacrylate, 1,4 butanediol diacry-late, thiodiglycol dimethacrylate, diallyl maleate, decamethylene glycol diacrylate/ 2-chloro 1,3 butadiene, polyethylene glycol dimethyacrylate, 1 phenyl ethylene-1,2-dimethacrylate.
Not all of the unsaturation is reacted so that part of the butyl rubber is still soluble.
Such pre-crosslinked butyl rubber may be of the type made by Polysar Ltd., Sarnia, Ontario, Canada and m~y be of a weight percent solubility in cyclohexane of 15-50 percent and a concentration 40.0-65.0 par~s per hundred parts of rubber.
The styrene-(ethylene-butylene)-styrene block thermoplastic rubber ingredient may be of the type ~7~

produced by Shell Chemical Company, Houston, Texas with a styrene content of 28-29~ by weight, a midblock content of 71-72% by weight and tensile stxength of 4500-5000 lbs./in and said block copolymer used at a concentration of 15.0-20.0 parts per hundred of rubber.
A block copolymer also applicable in this invention is one where the butylene in the midblock is replaced by propylene to give a styrene-(ethylene propylene)-styrene block copolymer.
The general formula for these block copolymers is:

~H - CH~ ~ CH2 - CH2 - X t C~2 STYRENE POLYOLEFIN CO- STYRENE
UNIT POLYMER UNIT UNIT
Where X = propylene unit: - CH2 - CH2 -H3or butylene unit: CH3 - CH2 - CH - CH -and n is from 20 to 1200 and n' is from 70 to 700.
Refer to U.S. pa-tent 3,917,607 assigned to Ronald ~.
Crossland and James T. Harlan. "Alternately and prefer-ably the styrene/ethylene-butylene/styrene block copoly-mer may be oDitted and ethylene-propylene-non-conJugated diene terpolymer used instead at levels of from 0 to 20 parts, usually 5-15 parts per hundred parts by weight of total rubber. The absence of such block polymer makes it advisable to modify the concentration of the other ingredients in the adhesive compositions of this inven-tion, i.e. the halogenated butyl rubber ought to be present at 35-65, preferably 40-60 phr, the pre cross-linked butyl rubber is added at a 35~65, preferably 35-50 phr level, the thermoplastic, petroleum hydrocarbon feed stock derived aliphatic monomer derived from C5-Cg streams polymerized to certain molecular weights to give a softening range of 162 - 181C may be added to a 80-120, preferably 90-110 phr concentration, and the aliphatic polyisocyanate may be used at 10-40, preferably 10-30 phr level, it being understood that phr stands for parts per 100 parts of rubbery components present in the composition, all by weight.
These modified adhesive compositions allow the practitioner more time (ca. 2 hours~ for laying up the EPDM's to be adhered together rather than the 10-20 minutes usually available for that purpose."
The low molecular weight, high softenlng point, thermoplastic aliphatic type hydrocarbon based resin is made from petroleum monomers. The aliphatic resin is introduced to impart improved compatibility between the block copolymer and butyl rubbers, and to improve the high temperature heat strength of the butyl rubbers. The aliphatic resin is derived from hydrocarbon feedstock monomers possessing 5-9 carbon atoms polymerized to varying molecular weight ranges so as to give softening points of 162C to 181C. The preferred resin is one _9_ ~2 ~

possessing a higher softening point range from 175C-181C. The higher softening resin when incorporated into the formulations of this invention impart higher strengths to butyl and block copolymers mixtures at the test ~emperatures of about 70C. An example of high softening point resins applicable in the invention is the Piccovar (TM) series produced by Hercules, Inc. Wilming-ton, Delaware with a softening point of 175-181C, an acid number of less than 1 and a bromine number of 16.0-20.0 at a concentration of 120.0-160.0 parts per 100 rubber.
The organic isocyanate ingredient of the invention functions ~o provide a cure of the halogenated butyl rubber when exposed to moisture. Useful organic iso-cyanates include 1,6 hexamethylene diisocyanate; 2,4 and2,6-toluene diisocyanate; 4,4-diphenyl~ethane diiso-cyanate; polymethylene polyphenylisocyanate; 4,4-dicyclo-hexylmethane diisocyanate; xylylene diisocyanate; but, most of these tend to give either short gel times or reduced high temperature heat strength. A preferred type is Desmodur (TM) N-75 isocyanate available in a 75~
solution from Bovay Chemical Corporation, Pittsburgh, Penn. This material has an NCO content of 15.0 - 17.0~
and is an aliphatic compound which is an adduct based on 1,6 hexamethylene diisocyanate:

- 1 0 ~
-~ ~ H2~6 N C~ - N

Said isocyanate is used at concentrations in the range of 20.0-35.0 parts per 100 rubber.
To scavenge moisture inadvertently incorporated into the adhesive during manufacture and packaging, an adsorb-ent of the alkali-metal alumino-silicate zeolite family of compounds is added. Typical Molecular Sieves are SA
or 13X supplied by the Linde division of Union Carbide, New York, New York. Said Molecular Sieves are used at a concentration of 5.0-15.0 parts per 100 parts of rubber.
Optionally, where high temperature performance is re~uired, zinc oxide may be added at a concentra~ion of 0.5-2.0 parts per 100 parts of rubber. A typical zinc oxide is Protox*166 produced by New Jersey Zinc Co.
The zinc oxide is added to allow some modulus increase of the halogenated butyl rubber, but little enough s~ that the solution stability is not adversely affected.
The aforementioned ingredients are dispersed in an organic liquid having a solubility parameter of 8.5-8.9 and a hydrogen bonding index 3.0-3.5. Said solvent is used at a concentration of 500.0-640.0 parts per 100 parts rubber giving a total solids level of 31.0-37.0 percent. To improve eflse of application and drying of * trade mark.

the adhesive, the dispersing medium may be a blend of 2 or more solvents.
Carbon black may also be added for pigmenting purposes and/or to improve mill or Banbury (TM) process-ing of the butyl polymers. The carbon black may be ofmedium reinforcement character, having an ASTM number from N-285 thru N-330. Said carbon black is used at a concentration of 2.0-20.0 parts per 100 parts rubber.
In order to maximize solution stability, the ingred-ients are processed and mixed in a controlled sequence.The halogenated butyl and pre-crosslinked butyl are separately milled or mixed in Banbury (TM) mixer to homogenize them and work some of the nerve out. It has been found that carbon black improves the processing of the mill or the Banbury (TM) mixed batches. Solubiliza-tion of the adhesive is initiated by dispersing the mill/Banbury batches in 75% of the solvent. It is important that the heat build up be kept at a minimum throughout the solubilizing procedure. This is followed,

2~ after a period of 2-3 hours, by the addition of the thermoplastic resin, thermoplastic rubber and molecular sieves to begin scavenging moisture. At this point, the mixing vessel should be sealed and purged with nitrogen.
After another 2-3 hours, the zinc oxide should be added with the remaining solvent. The mixing vessel is then resealed and purged followed by mixing for l hour minimum or until smooth. This is followed by cooling of the churn to no more than 80~F. Any evaporated solvent is then replaced, along with blending in of the is~cyanate.
The above procedure results in a compound with a storage stability of greater than 5iX months. It has been found that a substantive deviation from the above procedure may result in a drop in stability to much less than six months.
The following examples, while not intending to be limiting of the invention, illustrate the invention in greater detail.
Example 1 This example illustrates the adhesion level gener-ated by the industry standard neoprene-based adhesive such as N-lO0 distributed by Carlisle Corp.
Test sa~ples were prepared by vigorously washing the surface of a particular .065" thick cured ~PDM membrane with a cloth soaked with heptane. l" x 6" strips were then cut. A thin coat of the N-100 adhesive was then brushed onto the strips and allowed to dry 15 min.
T-peel adhesion samples were prepared by bringing the whole adhesive coated side of one strip together with the adhesive coated side of another strip, followed by lamination with a hand roller. Lap shear adhesion samples were prepared by bringing strips together so a 1"
x 1" contact area was formed, followed by lamination with a hand roller. ~dhesion samples were then allowed to stand undisturbed for 7 days at 25C. This was followed by adhesion testing on an Instron (TM) tensile tester -13~ 5~ ~

with the jaw speed set for 2 in./min. and testing being performed at 25~C and 70C. The following results were obtained:
Table 1 5 Test @ 2 in./min.25C Results 70C Results T-Peel Adhesion 2.2 1/5 (lbs./in. width) Lap Shear Adhesion14.8 12.0 (lbs./in. ) All test samples showed adhesive failure at the adhe-sive/membrane interface.

Examp_e 2 This example illustrates the adhesion level gener ated by the adhesive and manufacturing procedure of the instant invention.
The following formulation was used to prepare the adhesive invention:
20 In~redient Parts By Weight Mill Batch A
Polysar Bromobutyl*X-2 45.0 Cabot Regal 300 Carbon Black2.0 47.0 Mill Batch B
. _ Polysar Butyl XL-20 40.0 40.0 * trade mark.

-14- ~2 ~

Churn Batch Parts By Wei~t Mill Batch A 47.0 Mill Batch B 40,0 Shell Kraton G1652 15.0 Hercules Piccovar AB180 150.0 Protox 166 ZnO 2.0 Molecular Sieves ~5A 10.0 Toluene 400.0 Hexane 100.0 Desmodur N-75 (75% solids solution) 25.0 789.0 Total Solids: 35.8%

The Bromobutyl with carbon black and pre-crosslinked butyl were mixed separately on a two roll mill for 20 minutes minimum. Above mill batches could also be processed in a Banbury (TM) for a minimum of 6 minu~es.
These mill batches were then cut-up and added to an adhesive churn loaded with 75% or 375 PPHR of the above 2n solvents, hexane and toluene. This was allowed to mix 2 hours minimum. This was followed by the addition of the Piccovar AB180, the Kraton G1652, the Molecular Sieves #5A. At this point, the churn was sealed and purged with dry nitrogen. This was allowed to mix an additional 2 hours minimum, followed by the addition of the zinc oxide and the remaining 25~ or 125 PPHR of solvent. The churn was again sealed, dry nitrogen purged and all.owed to mix 1 hour minimum or until smooth. The churn was then * trade mark.
.

-15~

cooled down to 80F maximum, followed by volume adjust-ment to compensa~e for evaporated solvent and Desmodur N-75 isocyanate. Adhesion test samples were then pre-pared, treated and tested in the same ashion described in Example 1. Test resul~s were as follows:

Table 2 Test @ 2 in./min.25C Results 7_ Results T-Peel Adhesion 6.4 2.4 lo (lbs./in. width) Lap Shear Adhesion35.7 18.8 (lbs./in.2) All 25C tested samples showed a mixture of adhesive and cohesive failure within the adhesive; 70C tested samples showed all cohesive failure.

Example 3 This example illustrates the resulting loss of adhesion when the high softening point thermoplastic resin level falls below 120 PPHR. Resin concentration in this instance was 100 PPHR. T-peel adhesion samples only were prepared and aged in the same fashion discussed in Example 1. Test results were as follows:

-16~

Table 3 T-Peel Adhesion @ 2 in./min.
Test Temperature(lbs./in. width) 25C 4.5 70C 0.7 25C tested samples showed mixed adhesive and cohesive failure within the adhesive, 70C tested samples showed all cohesive failure.
lo E,xample 4 This example illustrates the resulting loss in adhesion when the isocyanate is eliminated from the compound. T-peel adhesion samples only were prepared and aged in the same fashion discussed in Example 1. Test results were as follows:
Table 4 T-Peel Adhesion @ 2 in./min.
Test Temperature(lbs./in. width) 25C 4.0 20 70C 0.9 All test samples showed cohesive failure within the adhesive.
Example 5 This example illustrates the resulting loss in adhesion when the zinc oxide i5 eliminated rom the compound. T-peel adhesion samples only were prepared and aged in the same fashion discussed ln Example 1. Test results were as follows:
Table 5 T-Peel Adhesion @ 2 in./min.
Test Temperature(lbs./in. width) 25C 6.3 70C 1.2 25C tested samples showed mixed adhesive and cohesive failure within the adhesive; 70C tested samples showed all cohesive failure.
Example 6 This example illustrates the resulting loss in stability when manufacturing procedure is varied from that procedure stated herein. 2.0 PPRH of zinc oxide was added to the Bromobutyl Banbury stock instead of to the mixing churn. The resulting adhesive was extremely rough and snotty in appearance and gelled in only 2.5 weeks.
Example 7 This example illustrates the resulting loss in stability when mixing vessel temperature at the point of isocyanate addition is significantly above 80F. The mixing sequence followed was that described in example 2, except, the solution temperature at the point of isocyan-ate addition was not reduced to lower than 140F. The resulting adhesive looked very good initially, but gelled in only 2 weeks.

Example 8 Following essentially the procedure of Example 2, an adhesive composition was prepared and evaluated using the recipe below:

In~redient Parts per ~eight Mill Batch A
Polysar Bromobutyl X-2 48 Mill Batch B
Polysar Butyl XL-50/l 42 Royalene [trademark] 539~1)10 Churn Batch Mill Batch A 48 Mill Batch B 54 15 Hercules Piccovar A-B 180 lOO
ZnO 2 Antioxidant(2) 2 Molecular Sieves #5A lO
Toluene 387 20 Xylene 43 Hexane lO7 Desmodur N-75 20 .
Total 773 Solids, % 29.9 The test results were as follows:

Test @ 2"/min. at 25C at 70C
T-Peel adhesion (lbs./in. width) 8.0 1.4 Lap sheer adhesion, psi 42.3 14.2 Remarks:
~1) EPDM; ML-4 at 125C = 70 (2) Irganox ~trademark] 1010 The data indicate the good adhesion obtained for cured EPDM using the composition of this invention.
In the absence of polyisocyanate, the T-Peel adhe-sion values at 25C and 70C were only 6.5 and 0.4 lbs./in. width, respectively.

Claims (2)

What is claimed is:

1. A process for making an adhesive for the bonding of cured EPDM membranes comprising:
(A) Milling or mixing separately, with carbon black, a halogenated butyl rubber of the formula:

where X is Cl or Br and n is about 50, and a pre-crosslinked butyl rubber of the formula:

2. The adhesive made by the process of claim 1.