DE19617039A1 - Precipitated silicas, process for their preparation and use of vulcanizable rubber mixtures - Google Patents

Description

Precipitated silicas are used as reinforcing fillers in Vulkanisierbaren rubber mixtures used.

(Wolff, E.H. Tan: Performance of Silicas with different Surface areas in NR. Lecture given on the occasion of the ACS Meetings, New York City, N.Y., April 1986;

S. Wolff, R. Panenka, E.H. Tan: Reduction of Heat Generation Truck Tire Tread and Subtread Compounds. lecture Held on the occasion of the International Conference on Rubber, Jamshedpur (India), Nov. 1986).

As an essential parameter for the characterization of a Precipitated silica serves the surface, which either by adsorption of nitrogen (ISO 5794/1, Annex D) or of rubber technology of greater relevance by adsorption of CTAB according to ASTM D 3765-92. In reference to to be obtained on the rubber technical data Precipitated silicas according to ISO 5794/1 in six Classified by surface classes.

In the tire application, however, almost exclusive Precipitated silicas with CTAB surface areas between 100 and 200 m² / g used. (U.S. Patent 5,227,425)

S. Wolff: The Influence of Fillers on Rolling Resistance presented at the 129 ^th Meeting of the American Chemical Society Rubber Division New York NY, April 8 to 11, 1986).

This is due to the fact that precipitated silicas in the Tire application high strength values and especially in the Tread area have a good abrasion resistance have to. This is only through the use of  Precipitated silicas with this above Surface area guaranteed. Precipitated silicas with On the other hand, CTAB surfaces <200 m² / g are almost becoming today not used. However, just these precipitated silicas should be characterized by a particularly good abrasion resistance characterized and therefore in the practical tire application be of particular interest. The essential reason for their non-employment is due to the fact that Precipitated silicas with increasing surface extremely poorly distributed in the rubber mixture (to disperse) to let. This poor distributability then leads to these products do not have the expected value image and thus no advantages, sometimes even disadvantages, compared with the tire precipitation silicas used today achieve.

The reason for this poor dispersion of higher surface area Precipitated silica is another important Property of the precipitated silica, namely its Structure (measured by DBP absorption according to ASTM D 2414). Especially important, however, is theirs Macro pore size distribution (measured by means of Hg- Porosimetry according to DIN 66 133) and their change with the Surface.

(U. Görl, R. Rausch, H. Esch, R. Kuhlmann:
Silica structure and its influence on the rubber technical value image. Lecture, held on the occasion of the German Kauchuk Conference in Stuttgart, June 1994).

In other words, the macropore size distribution increases usually with rising surface, if not succeeds by suitable precipitation measures in the Production of precipitated silica with the same surface in addition to produce larger pores.

In particular precipitated silicas with CTAB surfaces <220 m² / g requires special precipitation measures in order to  despite the high surface still sufficiently large macropores and thus to have good dispersion behavior.

It is known to precipitate with the physically chemical parameters:

BET surface area 35 to 350 m² / g Ratio BET / CTAB surface area 0.8 to 1.1 Pore volume PV 1.6 to 3.4 ml / g Silanol group density (V₂ = consumption of NaOH) 6 to 20 ml Mean aggregate size 250 to 1500 nm CTAB surface 30 to 350 m² / g DBP number 150 to 300 ml / 100 g V₂ / V₁ after Hg porosimetry 0.19 to 0.46 preferably 0.20 to 0.23 DBP / CTAB 1.2 to 2.4

to use in rubber mixtures (DE-A 44 27 137).

The object of the invention is thus the production and Characterization of precipitated silicas with CTAB Surfaces <200 m² / g, which are characterized by particularly high Macro pore size distribution and thus by very good Distinguish dispersion in the rubber compound.  

The invention relates to precipitated silicas, which characterized in that they have a CTAB surface from 200 to 400 m² / g (according to ASTM D 3765-92), a DBP number (according to ASTM D 2414) between 230 and 380 ml / 100 g, one Silanol group density (V₂ consumption of NaOH) from 20 to 30 ml and one for the respective surface area typical, by Hg porosimetry (DIN 66 133) too determining macro pore size distribution for particular Pore size intervals (incremental application method) such as have:

Another object of the invention is a method for Production of precipitated silicas according to claim 1, which is characterized in that one in one on 30 to 90 ° C, preferably to 50 to 80 ° C, heated template from water, with the addition of small amounts of Sulfuric acid adjusted to a pH of 5 to 5.9 is, while keeping the pH of 5.0 to 5.9 constant by simultaneous feed of alkali metal silicate solution and Sulfuric acid, with continued shearing during the entire fall time, by 30 to 120-minute interruption the precipitation, the implementation up to one Solid concentration of 40 to 60 g / l performs the Precipitated silica suspension filtered, washed and the  Filter cake undergoes a brief drying, optionally ground or granulated.

Another object of the invention are vulcanizable Rubber mixtures or the use of the Silica according to the invention in vulcanizable Rubber compounds, which are characterized that these mixtures 5 to 100 parts, in particular 15 to 60 parts of the silicas, based on 100 parts of rubber, contain. The silicas of the invention can thereby the mixture as a powder or in low-dust form, for. B. as Granules or microbeads, in the rubber industry usual way on a kneader or on the roller be added to the rubber mixture. Can be used also polymer batches, bales or powders where the Silica according to the invention during the preparation of Rubber mixture are introduced.

Another object of the invention are inventive Precipitated silicas which are characterized that on their surfaces with organosilanes of the formulas I to III

[R _n ¹ (RO) _3-n Si- (Alk) _m - (Ar) _{p] q} [B] (I)

or

R _n 1 (RO) _3-n Si (alkyl) (II)

or

R _n 1 (RO) _3-n Si (alkenyl) (III)

be modified, where:

B: -SCN, -SH, -Cl, -NH₂ (if q = 1) or -S _x - (if q = 2),
R and R¹: an alkyl group having 1 to 4 carbon atoms, the phenyl radical, where all radicals R and R¹ may each have the same or a different meaning,
n: 0; 1 or 2,
Alk: a divalent straight or branched hydrocarbon radical having 1 to 6 carbon atoms,
m: 0 or 1,
Ar: an arylene radical having 6 to 12 C atoms, preferably 6 C atoms,
p: 0 or 1 with the proviso that p and n do not simultaneously denote 0,
x: a number from 2 to 8,
Alkyl: a monovalent straight or branched unsaturated hydrocarbon radical having 1 to 20 carbon atoms, preferably 2 to 8 carbon atoms,
Alkenyl: a monovalent straight or branched unsaturated hydrocarbon radical having 2 to 20 carbon atoms, preferably 2 to 8 carbon atoms.

The modified on the surface with organosilanes Precipitated silicas can be prepared by adding the precipitated silicas with the organosilanes in Mixtures of 0.5 to 50 parts, based on 100 parts Precipitated silica, treated.

In a preferred embodiment of the invention, as Organosilane bis (triethoxysilylpropyl) tetrasulfane or  a solid dosage form, for example in a mixture with carbon black.

The addition of one or more silanes can on the one hand simultaneously with the invention Silicas are made to the rubber mixture, wherein the Reaction between precipitated silica and silane during the Mixing process takes place at elevated temperatures. To the others may be adding the silanes to the Precipitated silica / rubber mixture in the manner take place that one the precipitated silica before the addition to the rubber mixture with one or more silanes treated and the pre-modified silica to Added rubber compound. Such a measure can carried out analogously to the procedure according to DE-A 40 04 781.

Another object of the invention are rubber mixtures and / or vulcanizates containing the precipitated silicas according to the invention, which are optionally modified with organosilanes. The precipitated silicas according to the invention can be used in all rubbers which are listed with accelerator / sulfur but also peroxidically crosslinkable rubbers, as listed in DIN / ISO 1629. Mention may be made, for example, of elastomers, natural and synthetic, oil-extended or not, as a single polymer or blend with other rubbers, for example natural rubbers, butadiene rubbers, isoprene rubbers, butadiene-styrene rubbers, in particular SBR, prepared by the solution polymerization process, Butadiene-acrylonitrile rubbers, butyl rubbers, terpolymers of ethylene, propylene and non-conjugated dienes. Furthermore, the following additional rubbers are suitable for rubber mixtures with the rubbers mentioned:
Carboxylic rubbers, epoxy rubbers, trans-polypentenamer, halogenated butyl rubbers, rubbers of 2-chlorobutadiene, ethylene-vinyl acetate copolymers, ethylene-propylene copolymers, optionally also chemical derivatives of natural rubber and modified natural rubbers.

Also known are the usual other ingredients such as Rubber, natural fillers, plasticizers, Stabilizers, activators, pigments, Anti-aging agents and processing aids in the usual dosages.

The precipitated silicas according to the invention, with and without Silane, find use in all rubber applications, such as Example tires, conveyor belts, seals, V-belts, Hoses, soles etc.

Examples

Test methods used in the examples are:

Roughness factor F²H ASTM D 2663-89 ML (1 + 4) DIN 53 523/524 tensile strenght DIN 53 504 Module 300% DIN 53 504 elongation DIN 53 504 Shore A hardness DIN 53 505 DIN abrasion DIN 53 516 MTS data DIN 53 513 Tear strength DIN 53 507

Feedstocks used in the application examples are:

trade name Description / Company Buna VSL 1954 / S 25 Styrene-butadiene rubber produced by the solution polymerization method (Bayer AG) Buna CB 11 S Butadiene rubber (Bayer AG) Protector G 35 Ozone protection wax (Fuller)   X50-S Bis (triethoxysilylpropyl) tetrasulfane / N 330 50:50 blend (Degussa AG)

The silanol group density is determined according to G.W. Sears, Analytical Chemistry, 12, 1982-83 (1956).

Determination of the macropore size distribution by means of Hg porosimetry:

Method: DIN 66 133
Device: Autopore II 9220 (Micromeritics GmbH)
Sample preparation:

• - Pre-drying of the sample 15 h / 100 ° C.
• Cool to room temperature desiccator
• Transfer the sample (0.05-0.1 g) into penetrometer

Device:

• - Pressure range 4 kPa-200 MPa (53 measuring points)
• - Contact angle 140 °
• Hg surface tension 0.48 N / m.

Determination of the dispersion by means of roughness measurement of vulcanizate:

Method: ASTM D 2663-89
Device: Surfanalyzer
Procedure: The surface roughness is determined by means of a diamond needle moving over a freshly cut vulcanizate surface and the values are calculated after electronic processing in the form of a roughness factor. This factor is composed of the number of signals (F) and their intensity (H) as follows:

Surface roughness factor = F²H

The interpretation of this factor says from that the dispersion of Fillers in the polymer matrix all the more cheaper, the lower this factor is.

example 1 Production and Characterization of Inventive Precipitated silicas in the CTAB surface area of 200-250 m² / g

In a tub with an Ekato disc stirrer and equipped with a MIG stirrer from Ekato, are stirring 50 m³ of hot water and so much commercial sulfuric acid (96%) submitted to pH 5.5 is reached. While maintaining a precipitation temperature of 78 ° C and pH 5.5 are simultaneously 7.6 m³ / h commercial sodium silicate solution (weight modulus 3.42, Density 1.348) and 0.7 m³ / h sulfuric acid (96%) in 70 Minutes added. During the entire precipitation is the Ekato disc stirrer SR (diameter 320 mm, 6 blades, 740 rpm) in operation. After 12 minutes, the addition of the Educts sodium silicate solution and sulfuric acid for 80 Minutes interrupted. Also during this Interruption time, the two agitators in operation held. The precipitated silica is on a Filter press separated, washed and the filter cake subjected to spray drying or spin flash drying and optionally granulated dry between two rollers.  

The precipitated silica according to the invention has a CTAB Surface area of 206 m² / g, a DBP number of 298 ml / 100 g and a Silanolgruppendichte (V₂) of 20.5 ml. The Macro pore size distribution is as follows:

Example 2

In a tub with an Ekato disc stirrer and equipped with a MIG stirrer from Ekato, are stirring 50 m³ of hot water and so much commercial sulfuric acid (96%) submitted to pH 5.5 is reached. While maintaining a precipitation temperature of 78 ° C and pH 5.5 are simultaneously 7.6 m³ / h commercial sodium silicate solution (weight modulus 3, 42, Density 1.348) and 0.7 m3 / h sulfuric acid (96%) in 56 Minutes added. During the entire precipitation is the Ekato disc stirrer SR (diameter 320 mm, 6 blades, 740 rpm) in operation. After 12 minutes, the addition of the Educts sodium silicate solution and sulfuric acid for 80 Minutes interrupted. Also during this Interruption time, the two agitators in operation held. The precipitated silica is on a Filter press separated, washed and the filter cake subjected to spray drying or spin flash drying and optionally granulated dry between two rollers.  

The precipitated silica according to the invention has a CTAB Surface area of 240 m² / g, a DBP number of 314 ml / 100 g and a Silanolgruppendichte (V₂) of 21.0 ml. The Macro pore size distribution is as follows:

Example 3 Production and Characterization of a Invention Precipitated silica in the CTAB surface area of 250-300 m² / g

In a tub with an Ekato disc stirrer and equipped with a MIG stirrer from Ekato, while stirring 57 m³ of hot water and so much commercial sulfuric acid (96%) submitted to pH 5.5 is reached. While maintaining a precipitation temperature from 55 ° C and pH 5.5 are simultaneously 8.2 m³ / h commercial sodium silicate solution (weight modulus 3.42, Density 1.348) and 0.75 m3 / h sulfuric acid (96%) in 56 Minutes added. During the entire precipitation is the Ekato disc stirrer SR (diameter 320 mm, 6 blades, 740 rpm) in operation. After 13 minutes, the addition of the Educts sodium silicate solution and sulfuric acid for 90 Minutes interrupted. Also during this Interruption time, the two agitators in operation held. The precipitated silica is on a Filter press separated, washed and the filter cake  subjected to spray drying or spin flash drying and optionally granulated dry between two rollers.

The precipitated silica according to the invention has a CTAB Surface area of 283 m² / g, a DBP number of 349 ml / 100 g and a Silanolgruppendichte (V₂) of 24.0 ml. The Macro pore size distribution is as follows:

Example 4 Production and Characterization of a Invention Precipitated silica in the CTAB surface area of 300-400 m² / g

In a tub with an Ekato disc stirrer and equipped with a MIG stirrer from Ekato, while stirring 57 m³ of hot water and so much commercial sulfuric acid (96%) submitted to pH 5.5 is reached. While maintaining a precipitation temperature from 50 ° C and pH 5.5 are simultaneously 8.2 m³ / h commercial sodium silicate solution (weight modulus 3.42, Density 1.348) and 0.75 m3 / h sulfuric acid (96%) in 56 Minutes added. During the entire precipitation is the Ekato disc stirrer SR (diameter 320 mm, 6 blades, 740 rpm) in operation. After 13 minutes, the addition of the Educts sodium silicate solution and sulfuric acid for 90 Minutes interrupted. Also during this Interruption time, the two agitators in operation  held. The precipitated silica is on a Filter press separated, washed and the filter cake subjected to spray drying or spin flash drying and optionally granulated dry between two rollers.

The precipitated silica according to the invention has a CTAB Surface area of 360 m² / g, a DBP number of 350 ml / 100 g and a Silanolgruppendichte (V₂) of 29.0 ml. The Macro pore size distribution is as follows:

The physicochemical characteristics of the according to the Examples 1 to 4 obtained precipitated silica granules are as follows:

Example 5 Precipitated silicas in a NR truck tread compound

step 1

Level 2

level 3

Vulcanizate data: 150 ° C / t _95%

The use of the precipitated silicas according to the invention results in almost hardness and abrasion equality to a significantly lower tan δ (60 ° C), causing the Target resistance and thus the gasoline consumption compared significantly reduce a standard truck tread compound leaves.  

The dispersion, measured by means of roughness measurement, is despite the high surface area of the precipitated silicas in the Range of soot standard.

Example 6

Precipitated silicas in a NR / BR truck tread compound

Mixing instructions: see example 5
Vulcanizate data: 150 ° C / t _95%

The mixtures of the precipitated silicas according to the invention show almost identical values for hardness and modulus excellent dispersion, good abrasion resistance and a very low tan δ (60 ° C) value (≅ rolling resistance).  

Example 7

Precipitated silicas in a NR / S SBR tread compound

Mixing instructions: see example 5
Vulcanizate data: 150 ° C / t _95%

By use of the precipitated silicas according to the invention can be with excellent dispersion and comparable Abrasion compared to the standard mixture of both the tan δ (0 ° C) (≅ wet skid resistance) improve as well as Reduce rolling resistance [tan δ (60 ° C)].

Claims (5)

1. Precipitated silicic acids, characterized in that they have a CTAB surface (according to ASTM D 3765-92) of 200 to 400 m² / g, a DBP number (according to ASTM D 2414) between 230 and 380 ml / 100 g, a silanol group density (V₂ consumption of NaOH) from 20 to 30 ml and a typical for the respective surface area, to be determined by Hg porosimetry (DIN 66 133) to be determined macro pore size distribution for certain pore size intervals (incremental application method) as follows: 2. Process for the preparation of precipitated silicas according to claim 1, characterized in that in one at 30 to 90 ° C, preferably at 50 to 80 ° C, heated template from water, with the addition of small amounts of sulfuric acid to a pH of 5 to 5.9, while keeping the pH constant. Value from 5.0 to 5.9 by simultaneous feed of Alkali silicate solution and sulfuric acid, under sustained shearing throughout the fall, by 30 to 120 minutes interruption of the precipitation, the reaction up to a solids concentration of 40 to 60 g / l, the Precipitated silica suspension filtered, washed and the  Filter cake undergoes a brief drying, optionally ground or granulated. 3. Vulcanizable rubber mixtures, characterized characterized in that these mixtures contain 5 to 100 parts, in particular 15 to 60 parts of the precipitated silicas according to claim 1, based on 100 parts of rubber, contain. 4. precipitated silicas according to claim 1, characterized in that on their surfaces with organosilanes of the formulas I to III [R _n ¹ (RO) _3-n Si- (Alk) _m - (Ar) _{p] q} [B] (I ) or R _n 1 (RO) _3-n Si (alkyl) (II) or R _n 1 (RO) _3-n Si (alkenyl) (III), wherein
B: -SCN, -SH, -Cl, -NH₂ (if g = 1) or -S _x - (if q = 2),
R and R¹: an alkyl group having 1 to 4 carbon atoms, the phenyl radical, where all radicals R and R¹ may each have the same or a different meaning,
n: 0; 1 or 2,
Alk: a divalent straight or branched hydrocarbon radical having 1 to 6 carbon atoms,
m: 0 or 1,
Ar: an arylene radical having 6 to 12 C atoms, preferably 6 C atoms,
p: 0 or 1 with the proviso that p and n do not simultaneously denote 0,
x: a number from 2 to 8,
Alkyl: a monovalent straight or branched unsaturated hydrocarbon radical having 1 to 20 carbon atoms, preferably 2 to 8 carbon atoms,
Alkenyl: a monovalent straight or branched unsaturated hydrocarbon radical having 2 to 20 carbon atoms, preferably 2 to 8 carbon atoms. 5. Rubber compounds and / or vulcanizates containing the Precipitated silicas according to claim 1, which optionally modified with organosilanes, contain.