Note: Descriptions are shown in the official language in which they were submitted.
5926 KON
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.
,~
--2--
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
--3--
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:
-- 5 --
_ _
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
-12-
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
-17-
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.
-18-
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.
