Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-09-22
2001-11-06
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S493000, C523S216000
Reexamination Certificate
active
06313211
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the production of rubber mixtures containing 1 to 500 parts by weight of one or more water-repellent fillers with a methanol wettability of ≧5 wt. % to 100 parts by weight of rubber, characterized in that said water-repellent fillers are blended with one or more rubber latices and the mixture is then processed jointly, and also to rubber mixtures that can be produced with this process. The present invention relates furthermore to the use of the rubber mixtures produced by the process according to the invention for the production of tires, treads or molded articles of all kinds.
BACKGROUND OF THE INVENTION
The production of silica-filled rubber mixtures requires a clearly higher mixing effort in comparison with rubber mixtures filled with carbon black. On the other hand, the greater mixing effort could in principle be avoided if the silica could be coagulated with the rubber latex immediately after production of the latter. However, the precipitation silicas currently employed for the production of tires are not readily suitable for this process, since for the most part they remain in the aqueous phase in the course of coagulation.
U.S. Pat. No. 5,166,227 describes a process for the production of emulsion-rubber mixtures filled with silica, in which a dispersion of silica and a rubber latex are spray-dried jointly. This process has the disadvantage that the entire quantity of water has to be vaporized in energy-intensive manner.
U.S. Pat. No. 4,757,101 describes a process for the production of free-flowing powdered elastomers filled with silica, in which silica is precipitated with a rubber latex. In this case other silicas are employed with rubber latices for other fields of application without sulfurous silyl ethers.
U.S. Pat. No. 2,727,876 describes rubber mixtures consisting of a large number of rubber types and esterified silicas.
SUMMARY OF THE INVENTION
It has now been found that special water-repellent oxidic or siliceous fillers can be processed together with emulsion-rubber latex without appreciable portions of the fillers remaining in the aqueous phase and consequently being lost. In combination with sulfurous silyl ethers it is possible for rubber mixtures having excellent processing behaviour and vulcanisates having surprisingly good mechanical and dynamic properties to be produced which are suitable in particular for abrasion-resistant tire treads having low rolling resistance and high wet-skid resistance and which are clearly superior to the vulcanisates produced by the conventional mixing process from solid rubber and untreated or water-repellent silica.
DETAILED DESCRIPTION OF THE INVENTION
The invention provides a process for the production of rubber mixtures containing 1 to 500 parts by weight of one or more water-repellent fillers with a methanol wettability of ≧5 wt. % to 100 parts by weight of rubber, characterized in that said water-repellent fillers are blended with one or more rubber latices and the mixture is then processed jointly.
Water-repellent fillers are to be understood to mean oxidic or siliceous fillers such as precipitation silicas or precipitated silicates that are not wetted by water at room temperature. Preferred fillers have a content of physically bonded water amounting to <3 wt. %, in particular <1 wt. %, and a “methanol wettability” of >5 wt. %, in particular 10 to 60 wt. %. The “methanol wettability” in this connection specifies the minimum content (in percent by weight) of methanol in a methanol/water mixture that is capable of wetting the filler.
Determination of the methanol wettability is carried out as follows:
200 mg of the silica and 50 ml water are passed into a 250-ml round-bottomed flask having a magnetic stirrer. The (partly) water-repellent silica remains on the surface of the water. Then the tip of a measuring pipette filled with methanol is immersed in the liquid phase (in order to avoid direct contact with the silica) and the methanol is allowed to flow in slowly. At the same time stirring is effected with the magnetic stirrer, so that a vortex arises in the liquid. Methanol is added until such time as the solid substance is wetted. This is the case when the silica is no longer distributed over the entire surface of the liquid phase (which already contains methanol) and the relatively clear, film-free liquid becomes visible.
Evaluation: the methanol wettability is expressed as wt. % methanol of the methanol/water mixture, in accordance with the following formula
methanol wettability (in wt. %)=(0.79×number of ml MeOH/0.79×number of ml MeOH+50)×100
Numerous suitable methods for imparting water-repellency to oxidic and siliceous fillers are described in the literature, such as, for example, the treatment of precipitation silicas and precipitation silicates with inorganic and organic fluorides, as described in U.S. Pat. No. 2,477,695 and U.S. Pat. No. 2,625,492, or the production or aftertreatment of precipitation silicas by neutralization of silicate solutions with organohalosilanes such as dimethyldichlorosilane, for example, as described in DE 1 229 504.
Particularly well suited are water-repellent fillers having methanol wettability values from 10 to 60 wt. %, based on precipitation silicas or precipitated silicates that
(A) before, during or after a drying treatment were added to 0.5 to 200, preferably 1 to 50, parts by weight, relative to 100 parts by weight of filler, of a water-insoluble organic compound or
(B) before, during or after a drying treatment accompanied by partial or total conversion of the silanol groups were caused to react with 0.5 to 200, preferably 1 to 50, parts by weight, relative to 100 parts by weight of filler, of a compound containing hydroxyl groups or
(C) before, during or after a drying treatment accompanied by partial or total conversion of the silanol groups were caused to react with 0.1 to 20, preferably 0.1 to 10, parts by weight, relative to 100 parts by weight of filler, of a reactive silicon compound.
The water-repellent fillers to be used in accordance with the invention can be produced according to method (A) by, for example, a precipitation silica or a precipitated silicate being mixed before, during or after a drying process in which the water content is lowered to less than 3 wt. %, in particular <1 wt. %, with a water-insoluble organic compound. The water content is to be understood to mean that content of physically bonded water which at a drying temperature of 105° C. can be removed within 2 hours (DIN ISO 787/2).
Suitable water-insoluble compounds in the sense of method (A) are, for example, saturated and unsaturated fatty acids and waxes as described in DE 2 419 759, synthetic plasticizers such as dioctyl phthalate, adipate, modified fatty acids such as dimerized or oligomerized fatty acids, natural unsaturated oils such as olive oil, rapeseed oil, castor oil, sunflower oil, soybean oil, cottonseed oil, linseed oil, peanut oil and also the corresponding unsaturated or hydrated fatty acids and the transesterification products thereof with monovalent to hexavalent C
1
-C
20
alcohols, naphthenic, paraffinic or aromatic mineral oils, water-insoluble alcohols such as, for example, dodecanol, stearyl alcohol, undecylenic alcohol and oleyl alcohol, synthetic oils such as, for example, lubricating oils based on polyester or polyether, silicone oils such as, for example, polydimethyl siloxanes, dialkyl polysulfides such as, for example, dioctyl polysulfide, adducts of sulfur on unsaturated oils and on unsaturated fatty-acid esters such as, for example, reaction products of sulfur with olive oil, soybean oil or castor oil, reaction products of sulfur with unsaturated alcohols such as, for example, undecylenic alcohol and oleyl alcohol, furthermore low-molecular rubbers, in particular polybutadiene oil, liquid butadiene/acrylonitrile copolymers, liquid polyisobutylene, liquid natural rubber. Moreover use may also be made, by using solvents or in latex form, of high-
Scholl Thomas
Trimbach Jurgen
Wendling Peter
Bayer Aktiengesellschaft
Cain Edward J.
Cheung Noland J.
Gil Joseph C.
LandOfFree
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