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
1999-10-20
2001-01-16
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
06174951
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to new surface-modified oxide or siliceous fillers and their use for the preparation of rubber mixtures and of rubber vulcanisates. The rubber mixtures obtained by using these modified fillers are suitable for the production of highly reinforced, abrasion-resistant mouldings, in particular for the production of tires having a low rolling resistance and a high abrasion resistance.
BACKGROUND OF THE INVENTION
The treatment of the surfaces of fillers in order to improve the filler/matrix coupling in thermoplastic and thermosetting composites and in filled rubber systems is known. Thus U.S. Pat. Nos. 4,514,231 and 4,704,414 describe the treatment of fillers with polysulfide silyl ethers having the structure (R
n
1
(RO)
3−n
Si—(Alk)
m
—Ar)
p
)
2
(S)
x
, in particular bis(triethoxysilylpropyl) tetrasulfide. According to DE 2 141 159 and 2 255 577, the addition of the same polysulfide silyl ethers to the mixture of rubber and untreated filler (“in situ surface modification”) is also appropriate for the production of highly reinforced and abrasion-resistant rubber articles. A disadvantage of the use of polysulfide silyl ethers for improving the filler/matrix coupling is its expensive production process and the high raw-material costs associated therewith.
U.S. Pat. Nos. 2,736,669 and 2,801,185 describe a process for hydrophobing silicas which is based on the treatment of silicas with alcohols at particular temperatures. But the silica treated in this way does not show an improved reinforcing effect in a rubber matrix.
SUMMARY OF THE INVENTION
It has now been found that the esterification of oxide and siliceous fillers with unsaturated compounds containing hydroxyl groups and treatment with sulfur and/or with a sulfur donor leads to effective new fillers, the advantages of which lie on the one hand in the considerably decreased raw-material costs compared with those of the silica/silane system and on the other hand in the distinctly improved rheological behaviour of the rubber mixture (low viscosity of the mixture, little swelling after extrusion), the distinctly more favourable dynamic hysteresis properties (low heat build-up, low rolling resistance) of the rubber vulcanisates prepared by this means as well as the improved ageing performance of the vulcanisates under thermal and dynamic stress (reversion resistance) associated with a high abrasion resistance.
DETAILED DESCRIPTION OF THE INVENTION
The present invention therefore provides surface-treated oxide or siliceous fillers, prepared by esterification of an oxide or siliceous filler with from 0.1 to 50 parts by weight of an unsaturated compound containing hydroxyl groups and treatment with from 0.1 to 50 parts by weight sulfur (each based on 100 parts by weight of filler used) or sulfur donor, the two procedures being carried out either in succession or together.
Here the reaction temperatures for the esterification of the unsaturated compounds containing hydroxyl groups with the oxide or siliceous filler are from room temperature (25° C.) up to the decomposition temperature of the compound containing hydroxyl groups, preferably from 50° C. to 250° C., and the temperature for the treatment of the sulfur is from room temperature up to 250° C., preferably from 120° C. to 200° C.
The reactions may be carried out without solvents or in a solvent, optionally with the application of a vacuum or of a pressure of 1 to 100 atm and also in the presence of additional vulcanising chemicals, such as accelerators, retarders, antioxidants, plasticisers and other cross-linking agents for rubber.
The surface-treated oxide and siliceous fillers according to the invention are powders which have been rendered partially or completely hydrophobic and whose values for wettability by methanol are 0 to 55%. In this connection, the wettability by methanol states the minimal proportion of methanol (in per cent by weight) in a methanol/water mixture which is capable of wetting the filler. The method for determining the wettability by methanol is described in the experimental section of the present patent application.
By oxide and siliceous fillers are meant all known naturally occurring or synthetic inorganic fillers which, by reason of containing hydroxyl groups or oxide groups, can undergo a surface reaction with the unsaturated compounds containing hydroxyl groups, with the elimination of water. Examples of these include precipitated or pyrogenic silica, aluminium hydroxide, aluminium silicate, calcium silicate, calcium sulfate, china clay or calcined clay.
The following are particularly preferred:
highly disperse silicas, prepared, for example, by precipitation of solutions of silicates or by flame hydrolysis of silicon halides having specific surfaces of 5 to 1000 m
2
/g, preferably 20 to 400 m
2
/g (BET surface area) and primary particle sizes of 10 to 400 nm. The silicas may optionally also be present as mixed oxides together with other metal oxides, such as the oxides of Al, Mg, Ca, Ba, Zn, Zr and Ti.
synthetic silicates, such as aluminium silicate, alkaline-earth silicates such as magnesium silicate or calcium silicate, having BET surface areas of 20 to 400 m
2
/g and primary particle diameters of 10 to 400 nm
natural silicates, such as kaolin and other naturally-occurring silicas
glass fibres and glass fibre products (mats, strands) or glass microbeads.
metal oxides, such as zinc oxide, calcium oxide, magnesium oxide, aluminium oxide
metal carbonates, such as magnesium carbonate, calcium carbonate, zinc carbonate
metal hydroxides such as, for example, aluminium hydroxide, magnesium hydroxide.
The molecular weight of the unsaturated compounds containing hydroxyl groups has an effect on the technical process of carrying out the reaction with the fillers. Thus in the case of volatile, low-molecular unsaturated compounds containing hydroxyl groups, precautionary measures have to be taken, for example, the application of a pressure of 1 to 100 atm, to ensure that they do not escape at the high reaction temperatures, whereas in the case of highly polymeric unsaturated compounds containing hydroxyl groups, the high viscosity necessitates the use of solvents or introduction in the form of aqueous latex. The unsaturated compounds containing hydroxyl groups may therefore be of low molecular weight or polymeric and have molecular weights of from 58 (alkyl alcohol) up to 500,000. Molecular weights of 150 to 10,000 are preferred. Unsaturated compounds containing hydroxyl groups and having molecular weights of 200 to 5000 are most particularly preferred.
The hydroxyl group content of the compounds is so calculated that there is at least one hydroxyl group in the molecule, preferably 0.1 to 15 hydroxyl groups per 1000 atomic mass units, and OH values of 4 to 800. Compounds having OH values of 4 to 400 are particularly preferred. The OH value, as defined in DIN 53 240, gives the number of mg of KOH equivalent to the quantity of acetic acid which is chemically bound by 1 g of substance on acetylation. Primary and secondary hydroxyl groups are preferred to tertiary bonded hydroxyl groups.
The number of double bonds in the compounds is so calculated that there is at least one double bond in the molecule, preferably 0.2 to 18 double bonds per 1000 molecular weight units, corresponding to iodine values of 5 to 470. Particularly preferred iodine values are within the range of 35 to 470. The iodine values are generally determined by the addition of iodine chloride in acetic acid according to Wijs, DIN 53 241, Part 1. The iodine value defines the quantity of iodine in grams which is chemically bound by 100 g of substance.
Besides the hydroxyl groups, the compounds may contain additional functional groups, for example, carboxylic acid and metal salts thereof, carboxylic esters, carboxylic acid amide, sulfonic acid and metal salts thereof, sulfonic esters and sulfo groups, amino groups, phosphoric acid groups and phosphorous acid and esters thereof, silyl ethers and halogen atoms. The effect of the surface-modifie
Bayer Aktiengesellschaft
Cain Edward J.
Cheung Noland J.
Gil Joseph C.
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