Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to blends of conjugated
diene-containing butyl rubber with halobutyl rubber or butyl
rubber and to the covulcanization of such blends.
The expression "butyl rubber" is used in the rubber
industry to describe copolymers made from a polymerization reaction
mixture having therein from 70 to 99.5% by wt. of an isoolefin which
has about 4 to 7 carbon atoms, e.g., isobutylene and about 30 to
0.5~ by wt. of a conjugated multiolefin having from about 4 to 14
carbon atoms, e.g., isoprene. The resulting copolymers contain
85 to 99.5~ by wt. of combined isoolefin and about 0.5 to 15~ of
combined multiolefin. The preparation of butyl rubber is described
in U.S. Patent 2,356,128.
The polymer backbone o commercial butyl rubber is made up
primarily of isobutylene units, with just a few percent of isoprene
units. The isoprene units contribute the small amount of unsatura-
tion present in butyl rubber. The basic equation is represented by:
CH3 CH3
CH=C ~ CH =C-CH=CH2
CH3
isobutylene isoprene
which combine in the presence of Friedel-Crafts catalysts for form:
~ CH ~ ~ CH3 ~ ~ CH3 ~
( CH2, ) ~ CH2-C=CH-CH2 J ~CH2 , )
CH3 J x ~ ~ ~ CH3 ~ z
where x + z represent the number of isoolefin units incorporated in
the butyl rubber, while y represents the number of initial diolefin
units present, substan-
- 2 - 4
"'''' '
. . : : , ~ ,, , ;.- :
'::.. : : . : ~.,
,: . .
,,: ., . : . . :
- :. ~
~4 ~
''~ 1 tially as randomly inser~ecl units. The conjugated diole-2 fin, isoprene, loses one oleflnic linkage upon its essen-
3 tially random incorporation into the polymer backbone.
. .
': 4 Thus, butyl rubbler, as presently produced,
. . .
,; 5 contains only a small percentage of unsaturation, in the
~ 6 form of the single double bond associated with the iso-
- 7 prene residue which is incorporated more or less randomly
, 8 throughout the polymer chain.
9 It has been discovered that butyl rubber could
be produced con~aining conjug,ated unsaturation, which i~
11 essentially randomly distributed along the linear polymer
12 backbone. The general formula may be represented by:
,,, 13 ~ C~3~ ~ CH3 ~ ~ CH3
14 ~ H2 C ~ CH=C-CH=CH7 t CH2 C ~
~ CH ` ~ ~ CH ~ z
~,'' 16 where x, y and z have the values previously d~scribed,
,.
" 17 though at least one double bond may lay outside the
~,' 18 linear backbone.
19 ~his variation may be represented by the
formula:
` 21 ~ CH3 ~ ~ ~H2 ~ ~ CEI
~ 22 ~ H2-C ~ ~H2-C-CH=CH ~ 2 ,
Y' 23 ~ CH3 / x ~ Y ~ CH3 / z
~:,, 24 This new butyl rubber has been termed "high
,~ ~5 reactivity butyl" (HRB) and encompasses khe conjugated
,, 26 diene bu~yl rubber, regardless of where the unsatura-
'' 27 tion resides in the chain.
', 28 The HRB is more ~ompletely described in U.S.
29 Patent 3,816,371. One o~ the preferred methods of pre-
paring this butyl rubber is described in U.S. Patent
31 3~775,3~7.
32 One of the present inventors, Francis P. Baldwin,
.
.
- 3 -
~L~)48~L93
; has described the covulcanization of blends of from 10 to 90 wt.
conjugated diene butyl rubber with from 90 to 10 wt. % high un-
saturation rubber, such as natural rubber, styrene-butadiene rubber,
(SBR) and the like, in U.S. Patent 3,816,371.
Of the many unusual and interesting features of con~ugated
:
diene butyl rubber, it has recently been discovered that the rubber
develops its maximum tensile strength at higher carbon black concen-
trations, when compared with regular butyl or halogenated butyl rub-
`~ bers. This is particularly true with HAF-LS carbon black, where
maximum tensile strength of the conjugated diene butyl occurs with
75-80 parts black per 100 parts rubber (phr), as compared with 50-55
phr black with bo~h butyl and chlorinated butyl rubber. In addition
the conjugated diene butyl rubber cures in about one-fifth (1/5) the
time necessary to cure butyl or halobutyl rubber, even using relative
; "mild" cure packages.
It has now been discovered that the above-described tensile
strength and fast cure advantages of conjugated diene butyl rubber
can be synergistically achieved in butyl and halobutyl rubber, by
blending together from 5 to 95 wt. % (preferably 5 to 80 wt. ~)
20 conjugated diene-containing butyl rubber, with from 95 t~ 5 wt. %
(preferably 95 to 20 wt. %) of butyl or halobutyl rubber. The blend
is rein,forced with carbon black and cured with sulfur-type cure
systems or by use of a dienophilic compound, such as trimethylol-
propane trimethacrylate.
The resulting carbon black loaded, but uncured blends
have unusually high green strengths, and can be formed into inner
tubes. A particularly useful advantage of the blend is its
development of a complete cure in a
_ 4 _
. ~: .. .. .
~:. . . . ' ' . '
,, . ~ .
. .
; ~48~93
1 relatively short period of time, at commercially accept-
2 able temperatures.
3 It is well known that polymers prepared with
4 different monomers are rarely, if ever, compatible in
the physical sense. On the other hand, polymers pre-
6 pared from predominantly one monomer by a given mode of
7 enchainment and containing only minor structural per
8 turbations arising from copolymerization or chemical
; .
g modification can be expected to be compatible. Once
~- 10 the barrier of physical incompatibility i5 removed, one
`. 11 can anticipate full utilization of any possible chemical
~` 12 synergisms arising from the blending together of physi-
i,:
;3 cally compatible polymers containing minor chemical
.,
14 modifications,
We have found that the blending together of
16 isobutylene based polymers containing conjugated diene
17 groupings with other isobutylene based polymers con-
18 taining simple olefinic linkages and/or allylical-ly
19 substituted halogen atoms can lead to important conse-
quences, both of a technical and economic nature.
21 Thus, the blending ogether of minor ~uantities of con-
22 jugated diene-containing butyl rubber with major
23 quantities of regular butyl rubber can lead to faster
24 than anticipated (on an additive basis) cure rate,
higher than anticipated modulus and tensile strength,
26 much improved green strength after hot mixing and
27 better than anticipated interaction with carbon black.
28 The high reactivity butyl rubber, containing
29 the conjugated diene unsaturation, is prepared by dehy-
drohalogenation of halogenated butyl rubber.
31! Halogenated butyl rubber has been developed
32 in recent years and has contributed significantly to the
- 5 -
., .
1 elastomer business. A method of preparing halogenated
2 butyl rubber is described in U.S. Patent 3,099,644
3 Both chlorinated and brominated butyl rubber are typified
4 by:
~ CH3 ~ ~ CH3 ~ ~ CH3
1 6 ~ H2-C ~ CH-C-CH-CH ~ ~ ~2-C
7 \ C~ x ~ X H / y ~ CH3 ~ z
8 where x, y and z have ~he same values as for butyl rub-
9 ber, described above, though this structure is but one
of several which can be formed, depending on the condi-
11 tions of halogenation, the halogenating agent used, etc.
12 ~alogenated butyl rubber is commercially ~-
13 available and may be prepared by halogenating butyl
14 rubber in a solution containing 1 to 60% by weight
15 butyl rubber in a substantially inert C5-C8 hydrocarbon
16 solvent such as pentane, hexane, heptane, etc. and
17 contacting this butyl rubber cement with elemental halogen
18 for a period of about 2-25 minutes. There is then formed
19 the halogenated butyl rubber and a hydrogen halide, the
20 copolymer containing up to one or somewhat more,
21 especially in the case of bromine, halogen atom per
; 22 double bond initially present in the copol~mer, This
23 invention is not intended to be limited in any way by
24 the manner in which butyl rubber is halogenated or dehy-
25 drohalogenated and both chlorinated and brominated
26 butyl rubber are suitable for use in this invention.
27 Il~ustrative o halogenated butyl rubber is
28 Exxon Butyl HT 10~6B (a chlorinated butyl rubber which
29 before halogenation analyses ~l,B mole ~ unsaturation
30 and a viscosity-average molecular weight of about
31 450,000). ~owever, for the purposes of this invention,
32¦it is pre~erred that the butyl rubber starting material
;~ - 6 -
~ ~8193
1 have incorporated therein from about 0.5 ~o 6% of com-
2 bined diolefin, more preferably 0~5 to 3%, e.g., about
3 29~o
4 I Conventional high molecular weight butyl
- 5 rubber generally has a number average molecular weight
~ 6 of about 25,000 to about 500,000 preferably about 80,000
,...
7 to about 250,000, especially about 100,000 to about
8 200,000 and a Wijs Iodine No. of about 0.5 to 50, pre-
9 ferably 1 to 15. More recent low molecular weight
polymers are prepared to have number average molecular
11 weights of from 5,000 to ~5,000 and unsaturation
12 expressed as mole %, of 2-10.
13 A particularly advantageous method of pre-
14 paring conjugated diene-containing butyl polymers com- -
prises heating a solution of halogenated butyl rubber in
16 the presence of a soluble metal carboxylate. Suitable
17 metals are the polyvalent metals of Groups Ib, IIb, IVa,
18 and VIII, of the Periodic Table, having a relatively
19 high first ionization potential and whose halides are
20 soluble in the hydrocarbon reaction medium at the -
21 reaction temperature. Typical of these are zinc, iron,
22 mercury, nickel, copper, tin and cadmium carboxylates.
23 Especially useful are the soluble carboxylic
24 acid sal~s of zinc (e.g., zinc salts of naphthenic
acids). While useful in preparing the compositions of
26 the present invention, potential toxicity problems
27 which could be encountered in practicing the present in
28 vention m:ight limit the use of certain metals, such as
29 cadmium and mercury salts, fox example.
Zinc caxboxylate is the most preferred catalyst
31 in the present invention. However, in dehydrohaloge-
32 nating the halogenated butyl rubber, according to the
- 7 -
`: ~q)4~3193
: 1 present invention, zinc chloride is thought to be a
2 by-product in the reaction. Zinc chloride, being an
3 effective Friedel-Crafts t:ype catalyst, may lead to
4 molecular weight degradation or cxosslinking of the halo-
5 genated polymers, depending on the structure of the poly-
6 mer, the solvent employed or the reaction conditions.
7 This difficulty is overcome, in the present
8 invention by having present in ~he reaction zone a metal
- 9 oxide, hydroxide or carboxylate whose halogen salt is
: 10 insoluble in the reaction medium.
11 It has been found that the mole percent of
~: 12 conjugated diene unsaturation in the dehydrohalogenated
13 butyl, ranges from about O.S to about 2.5.
14 The conjugated diene-containing butyl rubber
may be cured b~ a variety of methods, such as sulfur
16 sulfur-containing curing agents, polyfunctional dieno-
17 philes such as acrylic and methacrylic acid esters, and
18 the like. .
19 It has been found that two disadvantages of
:. 20 butyl rubber in commercial applications, i.e., slow
` 21 cure rate and poor reinforcement capacity, can be over
22 come by blending ~utyl rubber with as little as 5-20
. .
23, wt, ~ of the conjugated diene-containing butyl rubber,
24 A synergistic effect permits the maintenance of a high
proportion of the reinforcement/curing advantages of
26 conjugated diene butyl in blends containing small
27 amounts of this high reactivity, conjugated diene butyl
:............. 28 rubber.
. 29 A preferred amount of HRB in the blend, with
.: 30 either butyl or halobutyl rubber, ranges from 5 to 80
31 wt. %, based on total rubber in the blend. Preferably,
32 the amount of HRB ranges from 10 to 60 wt. ~, when a
s~: 8
'
.~ . " . . ' , .. . .. .
~6~9L8193
1 sulfur-based cure system is used in vulcanizing the
2 carbon black loaded rubber blend. If a polyfunctional
- 3 dienophile is used to vulcanize the blend, the preferred
4 amount of HRB, in the blencl~ ranges from about 60 to 80
5 wt, ~, or if desired, somewhat higher.
6 Carbon black fillers are well known in the
7 art. However, a particularly useful reinforcing black
8 is HAF-LS Black. Other standard ingredients are also
9 normally added to the blended rubber compound prior to
10 vul~anization. These ingredients, as well as the carbon
11 black, are used in essentially commercially acceptable
12 ~mounts. In some applications, howeverJ advantage can
13 be taken of one of the ~eatures of the present invention,
14 by use of relatively high loadings of carbon black t~
15 achieve high tensile strength compounds. Loadings of up
16 to 70 to 85 phr o~ black, or higher, are particularly use
17 ful ~or this purpose.
18 Use of less "potent" accelerators, such as
19 the sulfenamides, are particularly useful in sulfur-type
20 vulcanization of the present blends. Xowever, for some
21 applications, the thiuram/thi azole type accelerators
< 22 might be useful. Typical of the sulfenamides is San-
23 tocure, which is N cyclohexyl-2-benzothiazole sulfen-
. 24 amide. The more mixed active accelerators may be repre- .
25 sented by Altax (benzothiazyl disul~ide) and Ethyl Tuads
26 (tetraethylthiuram disulfide) 7
27 When the polyfunctional dienophiles are used
'r' 28 to vulcanize the blend, cures may b~ obtained at tempera-
29 tures ranging from 200 up to 420F, When using the HRB/
30 halobutyl blends, zinc oxide may or may not be used.
-~ 31 Zinc oxide tends to cure halobutyl and use of ZnO would
~ 32 depend on whether the dienophile were needed, by itself,
_ g _
:
~(~4~ 3
1 as the vulcanization agent, or whether it would be used
. 2 as a cure enhancement agent.
3 The polyfunctio.nal dienophiles such as the
~ 4 acrylic and methacrylic acid esters are well known cross-
:.; 5 linking monomers, used in enhancing peroxide crosslinking
6 of ethylene~propylene rubber, and in preparing coatings
7 using free radical initiators, such as high energy radia-
.. 8 tion, UV, heat, etc, Typical of these are trimethylol-
9 propane trimethacrylate, 1.6-hexane diol diacrylate,
10 1.3-butylene glycol dimethacrylate, penfaerythritol tetra-
11 acrylate, trimethylolpropane triacrylate, polyethylen0
12 glycol diacrylate, triethylene glycol dimethacrylate,
13 and diethylene glycol diacrylate. These may be purchased
14 from the Sartomer Companyj West Chester, Pennsylvania.
. 15 The inventors have only listed a partial
16 sampling of the many polyfunctional dienophiles, and
.~ 17 are not thereby limiting their invention to those
- 18 listed.
` 19 The invention will be more completely under-
20 stood by reference to the following examples:
21 Exam~le 1
22 In order to demonstrate the preparation of
s 23 the high reactivity, conjugated diene-containing butyl
:- 24 rubber, the following experiment was aonducted.
A one liter glass, vapor jacke ed reactor,
26 fitted with stirrer and reflux condenser on reactor
27 and jacket, was charged.with 50 grams of a chlorinated
: . .
i~ 28 butyl rubber (Chlorobutyl HT-1068, manufactured by Exxon
29 Chemical Company, U.S.A.) in 500 cc of xylene, 4 g. ~inc
. 30 naphthenate, 0.5 g naphtenic acid, and 3 g. powdered
31 lime (Ca~). The zinc ~aphthenate,naphthenic acid and
; 32 CaO were added after the rubber was dissolved. The
.
~ - 10 -
.
~ 8~93
~ 1 reactor was then blanketed with nitrogen.
..
2 The vapor jacket, also charged with xylene,
3 was then brought to reflux, leading to a reactor tempera-
4 ture of about 135C. After 0.5, 1, 2 and 4 hours of
heating, 75 ml samples were withdrawn from the reactor,
-~ 6 placed in centrifuge tubes, diluted with approximately
- 7 30 ml of hexane and centrifuged.
8 The clear fluid in the tubes was then slowly
9 poured into rapidly agitated acetone to precipitate -
the polymer. The precipitate was then stored for 12
11 hours under 200 ml acetone containing 0.2 g, of an anti-
12 oxidant. The polymer was dried in a vacuum oven at
13 about 50~C for 16 hours.
14 Samples were submitted for chlorine analysis,
the results of which are in Table I.
16 TABLE I
;,.: ~
17 CHLORINE ANALYSIS
18 Reaction Time,
- 19 ~ ours % Cl _ % Cl Removed
A 0 1.14 0
~ . ~
21 B 0.5 0.24 78.8
; ` 22 C 1.0 ~.21 81.5
23 D 2.0 0.14 87.6
r'~ ' 24 E 4.0 ~0.06 >97
.,
~' 25 The material remaining in the reactor, which
'.! 26 was allowed to cool to ambient temperature after 4 hours
27 of heating at 135C was removed from the reactor and
28 diluted with about 600 ml hexane, the solids settled by
. .
~ 29 gravity and the polymer contained in the clear superna-
`~ 30 tant f luid precipitated in acetone. The precipitate
31 (designated Sample F) was treated in the same mannex as
32 the withdrawn sample~ in Table 1.
~ .
1~4~3~93
~, .
1 After drying, the Sample F was compounded as
2 follows:
3 Polymer Sample F 100 parts
4 m-phenylene-bis-maleimide 4.5
A sample of this material was placed in a mold in a
6 curing press for 60 minutes at 100C, On removal of the
7 crosslinked vulcanizate, a sample was immersed in cyclo-
8 hexane. At equilibrium the sample exhibited a swelling
9 ratio ~wt. of sample + wt. of solvent/wt. of sample) of
3.62, indicating a highly crosslinked network.
11 Drying and reweighing of the swollen sample
12 indicated insolubilization of greater than 96% of the
13 ~olymer.
14 ~
Using a conjugated diene-containing butyl
l~ rubber, prepared in the manner of Example 1, several
17 compounded blends were prepared with a chlorinated
18 butyl rubber. The halobutyl used was CHLOROBUTYh
l9 HT-1068 (as used in Example l). The con~ugated diene
butyl contained 0.21% of chlorine; had a dilute solution
~l viscosity ~DSV) ratio o~ .866/.747 ~.5/l) and a mole
22 of conjugated diene unsaturation of 1.45.
23 The blends were each heated in a cuxing mold
24 at 320F for times ran~ing from 20 minutes up to 160
minutes. Upon completion of the exposure to curing
26 temperatures, the specimens were placed in cyclohexane
27 and swell ratio determined, as in Example l.
28 The compound ingredients and the resulting
29 swell ratio are shown in Table II.
12 -
- , . . , ~ .
~:"
``:
:` ~
~L~4~3~
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. ~ ~ ~o~
. , ,
. I l I ~ . o
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~ ~ , , ,
o o I I I~1
O ~ ~ I ~ e
.~O ~ I I I~D ~ ~ ~ -:
I ~ 5
; , ~ ,
. ' , t
' I t
... , , ,
... , , , _ ,,~ ~ ~
' . CO U~ , ' , ~ ._ _ _ _
9 O O I I I 00 ~1
:................... O ~ II _ N ~ ~ C~
l Il~ . o
. . co ~1 1 ~ ~ ~D ~ ~ ~ N
` E~ t ' 5 ~
.~
,~ I I i _
, I ., , ~ ~
. ~ I , , ~ . o
", tn P: ~ o ~o u~
i ' ~ ~ O ~ U~ --O 1
., ~ ~, . . , , , o~ o ~ o~
. ~ o o j , , ` o . . o,, o
Cl~ A It~ ~~) N A
5 ~ 1 1 i ,~
H~ 1 1 i i I~: _ ~ .
. ~ I I I~-1 U) _ _ ,~
a E~ I ~ O O~ ~ oo 0
.
~i m ~ ,~
¢ D I I 1 3
., ' E~C~ ~ ~ I I I ~n
.~ I Z o I I I o a~ o o
.,. ~ ~ ~o I I ~ _l o ~ o~ u~
~. ~æ u~. t I I . . . ~ o
. . H H a~U~ I I I ~D ~tt~ t``J ~1
¢ ~ I I .. .~ . ,
.: O ~Z; l l l 11
:Z O ~ I I
I I ~ ~
~: Z
~1 I i I
~`J l l l ~
.,`' ~ O ~ I ~ ~ o
O I I I N ~ h ~ ~
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~ o o s~
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U
n
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: .
. . . .
.. . . .
9~
. 1 Examples 7-10
- 2 A sexies of experiments were conduc~ed to com-
:
3 pare the physical properties of several blends of butyl
4 'rubber (Exxon Butyl 268) wlth the conjugated diene
butyl used in Examples 2-6. The basic compound was:
6 Parts
. 7 Rubber 100
.. 8 Stearic Acid 1.0
.. 9 Carbon Black (GPF) 60.0
... .
:~. 10 FL~XON 840 0:1 20.0
11 ZnO 5.0
. 12 Sulfur 2,0
:.
13 Ethyl Tuads 1.0
14 Altax 1.0 :
; 15 The above compound represents an "inner tube"
16 formulation, and was prepared using a Midget Banbury
17 with the batch size adjusted to yield approximately 260
. 18 cc o~ product (upside down mixing technique with oil
- 19 added first to the black, 5 minute mixing time.) The
compounded blends were vulcanized for varying periods
21 of time at 307F. The above test samples were vulcanized
~ 22 and tested according to standard ASTM techniques.
.~ 23 The results of these comparlsons are found in
24 Table III.
: .
, ' ' .
~ , . .
.
; .
.
, . .
- 14 -
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.
: ~48~3
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., ~ D O o L~ ~ ~O ~ I cn ~7
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u~ a~
., ~ o
., oo ~1 noo~ n~ooo no~ o-n~
.,., a~ ~ ~ ,~ ~ o u~ o o ~;r co ~ l~ o
,., ,-",. ,,~ o U~ ~ ~ ,, ,, ~ ,
:~
~::
,.,, . ~:
.. ~ ~Dt` '
.. . .;: o o ~ ~ o o In u~ u~ o o 1` u~ O In o o o
~n CO ~ ~ ~1 _I ~.9 ~ N t~ 1 ~ O ~ ~ 1~ ~ U)
. ~ P
., li~
.'~........................................... .
~ @
E~ ~ o o~ ~ o o o o u~ o u~ o ~ u~ o o o u~ u~ ~ o
r- o ~o In 1` Lr! ~ In ~ ~ ~ ~
o ~ o
:~ ~
¦ o Iv ~ ~ ~ a, a
~ :~ ~ l` ooooo~ ~` oooo-~ ~
.a~ ~ o ooooo~ oooo-- ~,1
.d 3~ ~ ~ ~ ~ ~
~ ~ ~ ~ V ~ ~ 5 ~ 3 ~ ~ 3 o ~ a~ ~ :
. . ta ~ ~ ~ ~ ~-- ~ u~
:- P~:~ ~ O ~ N ~11 111111 1~1 li] 1~1 1
:~ W r ~ C -1 N ~rJ D W 0~ lrJ D C ~1 0 5~
~1 ~1 ~1 _I ~i r-l ~I r--l ~I r-1 N ~`J N ~1 N N N N
: "
~'
~ 15 -
..:
.~ .
.
1 Green Strength Test
2 The green strength test, used in Examples
3 7-10, was developed by J~ ~. Rae, Esso ~esearch and
.:.
4 'Engineering Company, and is conducted on an Instron
-~ 5 testing machine. Using thls basic compound formulation
6 above, the rubber is compounded on the Midget Banbury,
7 using a load factor o 1.6. The mixing cycle comprises
8 adding black, ZnO, , oil and polymer in sequence. The
-~ 9 ram is then lowered, followed by mixing for 5 minutes.
Cooling water is used to control the dump temperature
11 to 270F (+10F).
-;` 12 The batch is then added to a cold mill and
13 worked for about 1-1/2 to 2 minutes. The rubber is mold-
14 ed in a DeMattia mold to form a notch which is 0.176
inches in diameter. Molding conditions are 10 minutes
16 at 212~F, The molded sample is water quenched and
17 stored overnight at 75F. The specimens are cut to a
18 1/4 inch by 4 inch size from a 3 x 6 inch pad. ~are is
- 19 taken to avoid air bubbles when cutting specimens.
` 20~ The Instron testing machine is used with a
21 "C" strain gauge cell which is standardized, immediately
.. . :
22 before using, with calibrated weights. The chart speed
23 is set at 5 inches per minute and the strain rate at 20
24 inches per minute. The distance (vertical) between the ~-
sampla jaws is adjusted to exactly 2 inches. The Instron ~
: , - .
26 movable jaw is adjusted so that after 2 inches of travel
27 (100% elongation) it stops automatically. The stress or
28 load is recorded automatically on the moving chart. The
29 time (seconds) for maximum imposed stress to decay 70%
is taken as the measure of green strength.
31 It is readily seen that the inner tube ~reen
32 strength was increased when the conjugated diene-con-
;
; - 16 -
~)48193
taining butyl rubber was blended with the regular butyl rubber~ The
increases are relatively small unless the masterbatch is heat trea-
ted. Although an exhaustive testing was not carried out on this
aspect, the inventors feel that the green strength of an actual
~s~
commercial tube compound comparable to Example 9 would be somewhere
between 16.5 and 52 lbs/in2 with at least a partial heat treatment
effect being created by the extrus:ion and factory mixing operations.
Using the Table III data for 300% modulus, and determining
the stress-strain curve, it was found that the blend (lO~ of Example
8) had a distinct cure rate advantage over the all-butyl compound
of Example 8. It was found that in order to achieve essentially
equivalent stress-strain values, it was necessary to cure the lO0
butyl 3 times longer than the 90% butyl (Example 8).
Moreover, the 90% blend (Example 8), in addition to having
- more "length" and strength than its all-butyl rubber counterpart, is
more rubbery, as determined by the method of A. M. Gessler, "Rubber
Age", 94, 602 (1964). Following the procedure outlined there, it
was found that the stress-strain curve of 90% blend was "sigmoidal"
in shape.
The use of more than 10% con~ugated diene-containing butyl
in the blend simply magnifies the differences which are shown in
Table III.
The words "Exxon sutyl"; "Altax"; "Ethyl Tuads"; 'IClorobutyl"
and l'Flexon", which appear throughout this document, are trade marks.
. "
.
.
- 17 -
.,
