CA1048193A - Convulcanization of conjugated diene-containing butyl with halobutyl and butyl rubber - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Blends of 5 to 95 wt. % conjugated diene-containing butyl rubber with 95 to 25 wt. % halobutyl or butyl rubber are capable of higher carbon black loading and have faster cure times, unusually high tensile strength and improved green strength. The blends may be cured with dienophilic compounds or sulfur-based cure packages.

Description

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:

CH=C ~ CH =C-CH=CH2 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, .
.

~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 `: ~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.

;,.: ~

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.

- , . . , ~ .

~:"
``:

:` ~
~L~4~3~

... , , , _ .
. ~ ~ ~o~
. , , . I l I ~ . o ., . l l l ~
~ ~ , , , 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 ~ ~
. ~ ~i ~ ~
, ~ ~ ~
." O . o U~ ,.
U h ~
:` o .', ~ , 0 1::

~ o o s~
.1 o ~ ~ ctt ~D h U
n ;.
..
~ -- 13 --: .
. . . .
.. . . .

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.
: .
, ' ' .

~ , . .
.

; .
.
, . .

,:

: ~ .

.
: ~48~3 . ~,~
~, ' o o o a co Ln o In o o ~ ~n 1~ o o L~ O O
., ~ D O o L~ ~ ~O ~ I cn ~7 ,..
:.:
.,.
,, 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.

. "

.
.

.,

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A composition of matter comprising a curable blend of from 5 to 95 weight percent (wt.%) conjugated diene-containing butyl rubber consisting essentially of a copolymer consisting of from 85 to 99.5% by weight of an isoolefin having from 4 to 7 carbon atoms, combined with 15 to 0.5% by weight of a conjugated diolefin having from 4 to 14 carbon atoms, containing in the linear backbone conjugated diene unsaturation, the co-polymer having a number average molecular weight of from about 5,000 to 500,000 and from 95 to 5 wt.% of a rubber selected from the group consisting of butyl or halogenated butyl rubber.

2. The composition of claim 1, wherein there is also present in the curable blend from 50 to 85 parts, per hundred parts rubber, of a carbon black.

3. The composition of claim 2, wherein the carbon black is HAF-LS carbon black.

4. The composition of claim 1, wherein the curable blend contains a sulfur-type vulcanization system.

5. The composition of claim 1, wherein the curable blend contains a polyfunctional dienophilic vulcanization system.

6. The vulcanized composition of claim 1.

7. The composition of claim 5, wherein the polyfunctional dienophile is selected from a di- or higher acrylic or methacrylic acid ester.

8. The composition of claim 1, wherein there is from 10 to 60 wt. % conjugated diene-containing butyl rubber.

9. The composition of claim 5, wherein there is from 60 to 95 wt. % conjugated diene-containing butyl rubber and from 40 to 5 wt. %
halogenated butyl rubber.

10. The composition of claim 9, wherein the halogenated butyl rubber is chlorinated butyl rubber.

11. An inner tube which comprises a curable blend of from S
to 95 weight percent (wt.%) conjugated diene-containing butyl rubber con-sisting essentially of a copolymer consisting of from 85 to 99.5% by weight of anisoodefin having from 4 to 7 carbon atoms, combined with 15 to 0.5%
by weight of a conjugated diolefin having from 4 to 14 carbon atoms, con-taining in the linear backbone conjugated diene unsaturation, the copolymer having a number average molecular weight of from about 5,000 to 500,000 and from 95 to 5 wt. % of a rubber selected from the group consisting of butyl or halogenated butyl rubber, carbon black, oil, and a vulcanization system.

12. A method of manufacturing an inner tube which comprises blending a curable blend of from 5 to about 95 weight percent (wt. %) conjugated diene-containing butyl rubber consisting essentially of a copolymer consisting of from 85 to 99.5% by weight of an issolefin having from 4 to 7 carbon atoms, combined with 15 to 0.5% by weight of a con-jugated diolefin having from 4 to 14 carbon atoms, containing in the linear backbone conjugated diene unsaturation, the copolymer having a number average molecular weight of from about 5,000 to 500,000 and from about 95 to about 5 wt. % of a rubber selected from the group consisting of butyl or halobutyl rubber with carbon black, oil, and a vulcanization system, shaping the resulting rubber compound into the inner tube and subsequently vulcanizing said inner tube.

13. A tire inner liner which comprises a curable blend of from 5 to 95 weight percent (wt.%) conjugated diene-containing butyl rubber consisting essentially of a copolymer consisting of from 85 to 99.5% by weight of anisoolefin having from 4 to 7 carbon atoms, combined with 15 to 0.5% by weight of a conjugated diolefin having from 4 to 14 carbon atoms, containing in the linear backbone conjugated diene unsaturation, the co-polymer having a number average molecular weight of from about 5,000 to 500,000 and from 95 to 5 wt. % of a rubber selected from the group consist-ing of butyl or halogenated butyl rubber, carbon black, oil, and a vul-canization system.

14. A method of manufacturing a tire inner liner which comprises blending a curable blend of from 5 to about 95 weight percent (wt.%) conjugated diene-containing butyl rubber consisting essentially of a co-polymer consisting of from 85 to 99.5% by weight of an isoolefin having from 4 to 7 carbon atoms, combined with 15 to 0.5% by weight of a conjugated diolefin having from 4 to 14 carbon atoms, containing in the linear back bone conjugated diene unsaturation, the copolymer having a number average molecular weight of from about 5,000 to 500,000 and from about 95 to about 5 wt.% of a rubber selected from the group consisting of butyl or halobutyl rubber with carbon black, oil, and a vulcanization system, shaping the resulting rubber compound into the inner liner and subsequently vul-canizing said inner liner.