Organosilicon compounds, process for their production and their use

This application is a continuation of our copending application Ser. No. 10/443,167, May 22, 2003 now abandoned, which is relied on and incorporated herein by reference.

The present invention concerns organosilicon compounds, a process for their production and their use.

The use of silanes as coupling agents is known. Thus aminoalkyl trialkoxysilanes, methacryloxyalkyl trialkoxysilanes, polysulfanalkyl trialkoxysilanes and mercaptoalkyl trialkoxysilanes are used as coupling agents between inorganic materials and organic polymers, as crosslinking agents and surface modifiers (E. P. Plueddemann, “Silane Coupling Agents”, 2 nd Ed. Plenum Press 1982).

These coupling agents or bonding agents form bonds to both the filler and the elastomer, thus creating a good interaction between the filler surface and the elastomer.

It is also known that the use of commercial silane coupling agents (DE 22 55 577) with three alkoxy substituents at the silicon atom leads to the release of considerable amounts of alcohol during and after bonding to the filler. Since trimethoxy-and triethoxy-substituted silanes are generally used, the corresponding alcohols, methanol and ethanol, are released in considerable quantities.

It is also known from DE 10015309 that the use of a mercaptosilane in combination with a long-chain alkyl silane leads to rubber compounds with increased reinforcement and reduced hysteresis loss. The alkyl silane is needed to ensure reliable processability of the rubber compound.

A disadvantage of the known mercaptosilanes according to DE 10015309is the need to add alkyl silanes to rubber compounds in order to obtain particular properties.

It is also known that methoxy-and ethoxy-substituted silanes are more reactive than the corresponding long-chain alkoxy-substituted silanes and can therefore bond more quickly to the filler, such that from a technical and economic perspective the use of methoxy and ethoxy substituents cannot be avoided.

Organosilicon compounds having the general formula

are known from DE 10137809

wherein R is a methyl or ethyl group,

R′ is the same or different and a C 9 -C 30 branched or unbranched monovalent alkyl or alkenyl group, aryl group, aralkyl group, branched or unbranched C 2 -C 30 alkyl ether group, branched or unbranched C 2 -C 30 alkyl polyether group, R″ is a branched or unbranched, saturated or unsaturated, aliphatic, aromatic or mixed aliphatic/aromatic divalent C 1 -C 30 hydrocarbon group, X is NH (3-n) where n=1, 2, 3 and m=1, O(C═O)—R′″ where n=1 and m=1, SH where n=1 and m=1, S where n=2 and m=1-10 and mixtures thereof, S(C═O)—R′″ where n=1 and m=1 or H where n=1 and m=1, where R′″ equals C 1 -C 30 branched or unbranched alkyl or alkenyl group, aralkyl group or aryl group.

A disadvantage of the known organosilicon compounds according to DE 10137809 is the low hardness and dynamic rigidity in rubber compounds.

The object of the invention is to provide an organosilicon compound with which good hardness and dynamic rigidity values can be achieved in rubber compounds.

The object of the invention is also to provide an organosilicon compound with which comparable properties to those in DE 10015309 can be achieved in rubber compounds even without the addition of alkyl silanes.

The present invention provides organosilicon compounds having the formula I and/or II

wherein R is methyl or ethyl,

R 1 is the same or different and a C 9 -C 30 branched or unbranched monovalent alkyl, R 2 is a branched or unbranched, saturated or unsaturated, aliphatic, aromatic or mixed aliphatic/aromatic divalent C 1 -C 30 hydrocarbon, which are characterised in that R 1 is a mixture and the proportion of one component of the mixture is 10 to 50 mol %, preferably 10 to 40 mol %, particularly preferably 15 to 30 mol %.

R 1 can for example consist of 10 to 50 mol % C 14 H 29 and 90 to 50 mol % C 12 H 25 or of 10 to 50 mol % C 18 H 37 and 90 to 50 mol % C 16 H 33 . R 1 can also consist of more than two different R 1 compounds.

R 2 can denote CH 2 , CH 2 CH 2 , CH 2 CH 2 CH 2 , CH 2 CH 2 CH 2 CH 2 , CH(CH 3 ), CH 2 CH(CH 3 ), C(CH 3 ) 2 , CH(C 2 H 5 ), CH 2 CH 2 CH(CH 3 ), CH 2 CH(CH 3 )CH 2 or

The invention also provides a process for producing organosilicon compounds having the general formula I and/or II, which is characterised in that silanes having the general formula III

wherein R and R 2 have the meaning cited above, are reacted with mixtures of alcohols having the general formula R 1 —OH, wherein R 1 has the meaning cited above and is used as a mixture of at least two alcohols (R 1 is different), with elimination of R—OH, and R—OH is continuously separated off from the reaction mixture by distillation.

Alcohol mixtures comprising 10 to 50 mol % C 14 H 29 OH and 90 to 50 mol % C 12 H 25 OH or alcohol mixtures comprising 10 to 50 mol % C 18 H 37 OH and 90 to 50 mol % C 16 H 33 OH can be used, for example. Alcohol mixtures comprising several components (R 1 ) can also be used.

Lorol Spezial or Stenol 1618 (cetyl/stearyl alcohol) produced by Cognis or Ecorol 68/50 (cetyl stearyl alcohol) produced by Ecogreen Oleochemicals, for example, can be used as R 1 —OH alcohol mixtures.

In the process according to the invention a mixture can be formed in which none, one, two or three of the RO groups are replaced by R1O groups. The ratio of RO to R1O groups can be determined by the molar ratio of the silane having the general formula III to the alcohol having the formula R1-OH. For example, an organosilicon compound having an average analysis according to formula I can be obtained by reacting two molar equivalents of the alcohol mixture having the formula R1-OH with one molar equivalent of the silane having the general formula III. For example, an organosilicon compound having an average analysis according to formula II can be produced by reacting one molar equivalent of the alcohol mixture having the general formula R1-OH with one molar equivalent of the silane having the general formula III.

The reaction can be accelerated by means of neutral, acid or basic catalysts, such as e.g. hydrochloric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, toluene-para-sulfonic acid, sodium hydroxide solution, potassium hydroxide solution, sodium methylate, sodium ethylate, ion-exchange resins Amberlyst 15, Deloxan ASP I/9 or metal compounds, in particular titanates, known for example from U.S. Pat. No. 2,820,806.

The reaction can be performed at temperatures between 20 and 200° C., preferably between 20 and 150° C. In order to avoid condensation reactions it can be advantageous to perform the reaction in a moisture-free atmosphere, ideally in an inert gas atmosphere.

The organosilicon compounds according to the invention can be used as coupling agents between inorganic materials (for example glass fibres, metals, oxidic fillers, silicas) and organic polymers (for example thermosets, thermoplastics, elastomers), or as crosslinking agents and surface modifiers. The organosilicon compounds according to the invention can be used as coupling agents in tires made from rubber filled with silica and/or starch.

The invention also provides rubber compounds that are characterized in that they contain rubber, filler, such as e.g. precipitated silica, optionally other rubber auxiliary substances, and at least one organosilicon compound according to the invention.

The organosilicon compound according to the invention can be used in quantities of 0.1 to 20 wt. %, relative to the quantity of rubber used.

Addition of the organosilicon compounds according to the invention and addition of the fillers can preferably take place at material temperatures of 100 to 200° C. However, it can also take place later at lower temperatures (40 to 100° C.), for example together with other rubber auxiliary substances.

The organosilicon compound can be added to the mixing process both in pure form and attached to an inert organic or inorganic support. Preferred supporting materials are silicas, waxes, thermoplastics, natural or synthetic silicates, aluminum oxide or carbon blacks.

The following fillers can be used as fillers for the rubber compounds according to the invention:

Carbon blacks: The carbon blacks to be used here are produced by the lamp black, furnace or channel black process and have BET surface areas of 20 to 200 m 2 /g, such as e.g. SAF, ISAF, HSAF, HAF, FEF or GPF carbon blacks. The carbon blacks can optionally also contain heteroatoms such as Si for example. Highly disperse silicas, produced for example by precipitation of solutions of silicates or flame hydrolysis of silicon halides with specific surface areas of 5 to 1000, preferably 20 to 400 m 2 /g (BET surface area) and with primary particle sizes of 10 to 400 nm. The silicas can optionally also be present as mixed oxides with other metal oxides, such as Al, Mg, Ca, Ba, Zn and titanium oxides. Synthetic silicates, such as aluminum silicate, alkaline-earth silicates such as magnesium silicate or calcium silicate, with BET surface areas of 20 to 400 m 2 /g and primary particle diameters of 10 to 400 nm. Synthetic or natural aluminum oxides and hydroxides Natural silicates, such as kaolin and other naturally occurring silicas. Glass fibres and glass fibre products (mats, strands) or glass microbeads.

Highly disperse silicas, produced by precipitation of solutions of silicates, with BET surface areas of 20 to 400 m 2 /g, can preferably be used in quantities of 5 to 150 parts by weight, relative in each case to 100 parts of rubber.

The cited fillers can be used alone or in a mixture.

In a particularly preferred embodiment, 10 to 150 parts by weight of light-colored fillers, optionally together with 0 to 100 parts by weight of carbon black, and 1 to 10 parts by weight of the organosilicon compound according to the invention having formula I and/or II, relative in each case to 100 parts by weight of rubber, can be used to produce the compounds.

In addition to natural rubber, synthetic rubbers are also suitable to produce the rubber compounds according to the invention. Preferred synthetic rubbers are described for example in W. Hofmann, Kautschuktechnologie, Genter Verlag, Stuttgart 1980. They include inter alia

Polybutadiene (BR) Polyisoprene (IR) Styrene/butadiene copolymers with styrene contents of 1 to 60, preferably 2 to 50 wt. % (SBR) Isobutylene/isoprene copolymers (IIR) Butadiene/acrylonitrile copolymers with acrylonitrile contents of 5 to 60, preferably 10 to 50 wt. % (NBR) Partially hydrogenated or wholly hydrogenated NBR rubber (HNBR) Ethylene/propylene/diene copolymers (EPDM)

and mixtures of these rubbers. For the production of motor vehicle tires, anionically polymerized S-SBR rubbers (solution SBR) with a glass transition temperature above −50° C. and mixtures thereof with diene rubbers are of particular interest.

The rubber vulcanizates according to the invention can contain additional rubber auxiliary substances, such as reaction accelerators, antioxidants, heat stabilizers, light stabilizers, antiozonants, processing aids, plasticizers, tackifiers, blowing agents, dyes, pigments, waxes, extenders, organic acids, retarders, metal oxides and activators, such as triethanolamine, polyethylene glycol, hexanetriol, which are known to the rubber industry.

The rubber auxiliary substances can be used in known quantities, which are governed inter alia by the intended use. Conventional quantities are for example quantities of 0.1 to 50 wt. %, relative to rubber. Sulfur or sulfur-doning substances can be used as crosslinking agents. The rubber compounds according to the invention can moreover contain vulcanization accelerators. Examples of suitable principal accelerators are mercaptobenzothiazoles, sulfenamides, thiurams, dithiocarbamates, particularly preferably sulfenamides, in quantities of 0.5 to 3 wt. %. Examples of co-accelerators are guanidines, thioureas and thiocarbonates in quantities of 0.5 to 5 wt. %. Sulfur can conventionally be used in quantities of 0.1 to 10 wt. %, preferably 1 to 3 wt. %, relative to rubber.

Vulcanization of the rubber compounds according to the invention can take place at temperatures from 100 to 200° C., preferably 130 to 180° C., optionally under pressure of 10 to 200 bar. The rubbers can be mixed with the filler, optionally rubber auxiliary substances and the organosilicon compound according to the invention in known mixing units, such as rolls, internal mixers and compounding extruders.

The rubber compounds according to the invention are suitable for the production of moulded parts, for example for the production of pneumatic tires, tire treads, cable sheaths, hoses, drive belts, conveyor belts, roll coverings, tires, shoe soles, sealing rings and damping elements.

The organosilicon compounds according to the invention can be used together with large-surface-area silicas with CTAB 180-220 m2/g in rubber compounds, in particular in truck tire treads.

The rubber compound according to the invention can be used for the production of tire treads with improved, lower rolling resistance, improved wet skid resistance and equally good dry performance as compared with a similar rubber compound in which the organosilicon compound according to the invention is exchanged for bis-(3-triethoxysilylpropyl) tetrasulfide in a molar ratio relative to the silicon units of 1:1.8 to 1:2.7.

The rubber compound according to the invention can be used for the production of tire treads with improved, lower rolling resistance and improved wet skid resistance with equally good abrasion resistance as compared with a similar rubber compound in which the organosilicon compound according to the invention is exchanged for bis-(3-triethoxysilylpropyl) tetrasulfide in a molar ratio relative to the silicon units of 1:1.8 to 1:2.7.

The organosilicon compounds according to the invention have the advantage compared with organosilicon compounds according to DE 10137809 that hardness and dynamic rigidity E* are increased while tan δ 60° C. (correlated with rolling resistance) remains the same.

The organosilicon compounds according to the invention have the advantage that less methanol or ethanol is released than is the case with the known silanes while the reactivity remains the same. Due to their inactivity the non-volatile alcohols are not separated from the organosilicon compound or because of their non-volatility they remain in the polymer matrix. In both cases they are not released into the environment.

In addition, the organosilicon compounds according to the invention have the advantage that there is no need to add alkyl silane as described in DE 10015309, since in the organosilicon compounds according to the invention having formula I and/or II no deterioration in processability, as in the case of e.g. 3-mercaptopropyl trimethoxysilane or 3-mercaptopropyl triethoxysilane, has been found.

The rubber compounds according to the invention have the advantage as compared with rubber compounds containing bis-(3-triethoxysilylpropyl) tetrasulfide that dynamic rigidity is reduced and they are therefore especially suitable for winter tires (soft formulation).

FIG. 1 is a representation of a driving test track. The dots in FIG. 1 are measuring points on x,y-coordinates of the test track. The measuring points are linked with straight lines.