Carbon blacks modified with organosilicon compounds, method of their production and their use in rubber mixtures

Carbon black is reacted with at least one organosilicon compound of the General Formula EQU [R.sup.1.sub.n (RO).sub.3-n Si-(Alk).sub.m -(Ar).sub.p ]q [B](I) EQU R.sup.1.sub.n (RO).sub.3-n Si-(Alkyl) (II) or EQU R.sup.1.sub.n (RO).sub.3-n Si-(Alkenyl) (III), and any excess of said organosilicon compound is extracted with a solvent. The products are useful as active fillers in rubber mixtures, carbon black suspensions and plastic mixtures which can be cross-linked with sulfur or peroxide.

The present invention relates to the production of (carbon) blacks 
chemically modified on the surface with organosilicon compounds, to these 
modified fillers themselves and to their use in vulcanizable rubber 
mixtures, plastic mixtures and suspensions of blacks. 
SUMMARY OF THE INVENTION 
The treatment of an oxide surface with organosilicon compounds containing 
alkoxy groups has long been known (see U.S. Pat. No. 3,227,675 and 
European Patent EP 177,674 and EP 0,126,871). The goal of all these 
efforts was and is to generate a bond between the inorganic component, the 
oxide filler, whether it be e.g. glass or also silicate fillers such as 
those used e.g. in the rubber industry (precipitated and pyrogenic 
silicas, clays, aluminum silicates, etc.), and an organic polymer of very 
different chemical composition. As a rule, this results in an improvement 
of the properties of the vulcanizate. Carbon blacks, e.g. furnace blacks, 
lampblacks and gas blacks, are not included among the oxide fillers. The 
reaction which occurs in the case of these substances between the 
alkoxysilyl groups and the OH groups on the surface can not take place on 
carbon black and therefore seems to make the building up of a chemical 
bond between carbon blacks and organosilicon compounds impossible. 
German patent DE 27 47 277 (.apprxeq.U.S. Pat. No. 4,128,438) discloses 
granulated mixtures of carbon black and organosilicon compounds; however, 
they are only used to work the organosilicon compound into 
silica-containing rubber mixtures in a more effective manner. In this 
case, the carbon black is only a carrier for liquid organosilanes in order 
to convert them into the solid state. The silane can be removed from such 
mixtures by means of extraction with organic solvents and therefore are 
not chemically bonded to the carbon black. 
After repeated attempts to adjust the properties of black-filled rubber 
vulcanizates via the use of blacks of differing structure and differing 
size of the specific surface, the problem of improving the properties of 
the vulcanizate via the addition of silane-modified blacks remains. 
SUMMARY OF THE INVENTION 
It has now been found that, if a suitable procedure is used, not 
inconsiderable amounts of organosilicon compounds can be bonded to the 
carbon black, depending on the surface and the structure of the carbon 
black and also on the selection of the organosilicon compounds. 
Therefore, in accordance with the present invention, carbon blacks are 
chemically modified with one or more organosilicon compound(s) of the 
General Formulas 
EQU [R.sup.1.sub.n (RO).sub.3-n Si-(Alk).sub.m -(Ar).sub.p ]q [B](I) 
EQU R.sup.1.sub.n (RO).sub.3-n Si-(Alkyl) (II) 
or 
EQU R.sup.1.sub.n (RO).sub.3-n Si-(Alkenyl) (III) 
in which 
B represents --SCN, --SH, --Cl, --NH.sub.2 (if q=1) or --Sx-- (if q =2), 
R and R.sup.1, which may be the same or different, represent an alkyl group 
containing 1 to 4 carbon atoms, the phenyl group, 
q represents 1 or 2 
n represents 0 1 or 2, 
Alk represents a bivalent straight or branched hydrocarbon group containing 
1 to 6 carbon atoms, 
m represents 0 or 1, 
Ar represents an arylene group containing 6 to 12 carbon atoms, preferably 
6 to 8 carbon atoms, 
p represents 0 or 1 provided that p and n do not simultaneously signify 0, 
x represents a number from 2 to 8, 
Alkyl represents a monovalent straight or branched unsaturated hydrocarbon 
group containing 1 to 20 carbon atoms, preferably 1 to 6 carbon atoms, 
Alkenyl represents a monovalent straight or branched unsaturated 
hydrocarbon group with 2 to 20 carbon atoms, preferably 2 to 6 carbon 
atoms, 
and on the surface of which blacks 0.1 to 15 % by weight of one or more of 
the named organosilicon compounds are bonded in such a manner that they 
cannot be extracted with an organic solvent, especially diethyl ether. The 
indication of % by weight refers to the total weight of the modified 
black. 
The invention also provides a method of producing these modified blacks in 
which a homogeneous mixture of one or more organosilicon compounds 
according to General Formula I, General Formula II or General Formula III 
is produced with the carbon black in a vessel, the components of the 
mixture are subsequently reacted with each other for 1 to 60 minutes at 
50.degree. to 160.degree. C. in the mixing vessel itself or in another 
suitable tempering unit, e.g. a tempering bed, and then the organosilicon 
compound(s) which is (are), if applicable, not reacted is (are) extracted 
with an organic solvent. 
Suitable carbon blacks are the types of the various classes known in the 
rubber art, e.g. furnace blacks, (division according to ASTM D 1765), 
lampblacks and gas blacks as well as non-rubber blacks. 
Depending on the reaction, they can be used in powder form (fluffy), pellet 
form or as a granulate, depending on the purpose. 
It has been found that the amount of organosilicon compound(s) which can be 
maximally bound to the particular black and can thus no longer be 
extracted by means of organic solvents, especially diethylether, also 
provides the optimum rubber-technology performance which can be achieved 
for the particular carbon black and organosilicon compound. Extractable 
amounts of this compound (these compounds) which exceed this amount not 
only do not result in any further improvement of the properties of the 
vulcanizate but on the contrary result in a worsening of the 
rubber-technology properties. 
In order to be able to avoid the extraction of the excess amounts of 
organosilane, which is otherwise logical for the reasons cited, the amount 
of the organosilicon compound(s) which can be bound in alternating amounts 
as a function of the particular substances used is determined. 
Then, when the method of the invention is carried out on an industrial 
scale, only the amounts determined to be required for the reaction with 
the carbon black in this manner are used. 
The indication in % by weight refers to the compound(s) to be used in 
accordance with General Formulas I to III. The reaction product produced 
in powder form can subsequently be pelletized or granulated according to 
known methods if this appears to be advantageous for the intended use. 
The invention also provides vulcanizable rubber mixtures containing carbon 
blacks modified with organosilane compounds in accordance of the 
invention. For this purpose, the term "vulcanizable rubber" refers to 
rubber which can be cross-linked with sulfur or also with peroxide. 
The reaction products of the invention are added to the rubber mixture in 
an amount of 5 to 400 parts, relative to 100 parts rubber, especially 20 
to 200 parts, relative to 100 parts rubber. 
In comparison to mixtures with untreated carbon blacks, use of the modified 
carbon blacks of the invention results among other things in a distinct 
improvement of the moduli, the elasticity, the dynamic properties and the 
loss angle tan .delta.. The rubber properties also are improved in 
comparison with the use of carbon black/organosilicon compound mixtures. 
As noted above, suitable types of rubber include rubbers which can be 
cross-linked with sulfur and vulcanization accelerator(s) but also with 
peroxide to produce elastomers as well as mixtures of these rubbers. This 
includes the so-called diene elastomers, e.g. oil-extended natural and 
synthetic rubbers such as natural rubbers, terpolymers of ethylene, 
propylene and non-conjugated dienes. Also useful are copolymers of 
ethylene and propylene as well as carboxyl rubbers, epoxy rubbers, 
transpolypentamer, halogenated butyl rubbers, rubbers of 2-chlorobutane 
diene, ethylvinyl acetate copolymers, optionally also chemical derivatives 
of natural rubber as well as modified natural rubbers. 
Rubber mixtures containing the silane-modified carbon blacks of the 
invention can contain other components which are customary in the rubber 
industry such as e.g.: 
Additional reinforcing systems, that is, furnace blacks, channel blacks, 
lampblacks, thermal blacks, acetylene blacks, arc blacks, CK blacks, etc. 
as well as synthetic fillers such as silicas, silicates, aluminum oxide 
hydrates, calcium carbonates, natural fillers such as clays, siliceous 
chalks, chalks, talcums, etc. as well as silane-modified white fillers. 
However, the total amount of the fillers, including the modified carbon 
blacks, should not exceed the previously indicated upper limits of 400 and 
200 parts per 100 parts rubber. 
Conventional vulcanization accelerators used in the rubber industry (e.g. 
sulfenamides, 2-mercaptobenzothiazol (MBT), di-2-benzothiazyl disulfide 
(MBTS, triazine accelerator, thiurames) alone or in a mixture in amounts 
of 0.1 to 10 parts by weight relative to 100 parts by weight rubber. 
Vulcanization retarders such as e.g. Vulkalent E, di-(phenylthio)acetamide 
(PVI), likewise in amounts of 0.1 to 10 parts by weight relative to 100 
parts by weight rubber. 
Zinc oxide and stearic acid as vulcanization promoters in amounts of 0.5 to 
10 parts by weight relative to 100 parts by weight rubber. 
Antioxidant agents, antiozonants and anti-flexcracking antioxidants used in 
the rubber industry such as e.g. N-isopropyl-N,-phenyl-p-phenylene diamine 
(IPPD), poly-2,2,4-trimethyl-1,2-dehydroquinoline (TMQ) as well as waxes 
as light stabilizers and their blends. 
Softeners such as e.g. aromatic, naphthenic, paraffinic, synthetic 
softeners and their blends. 
Optional silanes such as e.g. bis(3-triethoxysilylpropyl) tetrasulfane, 
.gamma.-chloropropyltriethoxysilane, 
.gamma.-mercaptopropyltrimethoxysilane, vinyltrialkoxysilanes and their 
blends in an amount of 0.1 to 20 parts by weight, preferably 1 to 10 parts 
by weight per 100 parts by weight filler. 
Optional sulfur in an amount of 0.1 to 10 parts by weight per 100 parts by 
weight rubber. 
Optional dyes and auxiliary processing agents in the customary amounts. 
The mixture may be made in a manner known in the rubber industry in a 
closed mixer or on an open roll mill. 
The silane-modified carbon blacks of the invention may be used in mixtures 
such as those customarily used in tire construction, e.g. in the belt, 
carcass and bead area, in sidewall mixtures and adhesive mixtures as well 
as to industrial articles such as e.g. conveyor belts, V-belts, hoses, 
seals, engine mounts, suspension and damping elements and rubber-coated 
fabrics. 
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Test methods for use: 
Test method 
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Rheometer DIN 53 529 
Mooney test DIN 53 524 
Tensile strength DIN 53 504 
Breaking elongation 
DIN 53 507 
Modulus 100%, 200%, 300% 
DIN 53 507 
Tear resistance DIN 53 507 
Firestone Ball Rebound 
AD 20 245 
Shore A hardness DIN 53 505 
Abrasive wear DIN 53 516 
Goodrich flexometer 
ASTM D 623-62 
Heat buildup DIN 53 513 
MTS DIN 53 5/3 
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Initial and raw materials used: 
Buna .RTM. AP 451 EPDM 
RSS 1 ribbed smoked sheet 
(natural rubber) 
SMR CV standard Malaysian rubber 
(constant viscosity) 
Naftolen ZD aromatic softener 
Sunpar 2280 paraffinic softener 
Protector .RTM. G35 
antiozone wax 
Structol .RTM. 60 NS 
homogenizing resin 
Vulkanox .RTM. HS 2,2,4-trimethyl-1,2- 
dihydroquinoline 
Vulkanox .RTM. 4010 
N-isopropyl-N'-phenyl-p- 
phenylene diamine 
Vulkacit .RTM. MOZ benzothiazyl-2- 
sulfenmorpholide 
Vulkacit .RTM. L zinc-N-dimethyl- 
dithiocarbamate 
Vulkacit .RTM. CZ benzothiazyl-2- 
cyclohexylsulfenamide 
Vulkacit .RTM. DM dibenzothiazyl disulfide 
Si 69 bis(3-triethoxy- 
silylpropyl)-tetrasulfane 
Si 264 3-thiocyanatopropyl- 
triethoxysilane 
Si 230 3-chloropropyl- 
triethoxysilane 
Si 221 3-butenyltriethoxysilane 
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