Method for testing the in situ silanization of bright fillers

Abstract

The invention relates to a method of testing silanization, which permits inline control of the in situ silanization of light-colored fillers, especially precipitated silicas. This enables continuous in situ silanization in the production of rubber mixtures comprising silanized light-colored fillers, and representative control of the rubber mixture under production conditions. The process is additionally nondestructive and has a high tolerance for carbon black as an additional constituent of the rubber mixture.

Claims

1. A method of in-situ testing of the silanization of light-colored fillers in rubbers, the method comprising: extruding a mixture comprising at least one silanized light-colored filler and at least one rubber to form an extrudate, subjecting the extrudate to ultrasound waves within a frequency range from 4 to 10 MHz, and measuring the signal intensity of the ultrasound waves after transmission of the ultrasound waves through the extrudate, wherein the measured intensity relates directly to an amount of silanization.

2. The method as claimed in claim 1, further comprising determining the relative attenuation coefficient α.sub.rel of the extrudate in the frequency range of the ultrasound waves, wherein the relative attenuation coefficient relates inversely to an amount of silanization.

3. The method as claimed in claim 2, further comprising: determining the standard deviation of the relative attenuation coefficient α.sub.rel, and using the standard deviation to monitor the dispersion of the light-colored filler in the extrudate.

4. The method as claimed in claim 2, wherein: the light-colored filler is selected from mica, kaolins, chalks, calcium carbonates, talc, zinc oxides, aluminum oxides, titanium dioxides, silica and silicates; the ultrasound waves are produced by an emitter and detected at a receiver and the distance between the emitter and the receiver is more than 5 mm to 25 mm, and the rubber mixture comprises 50 to 250 phr of the light-colored filler.

5. The method as claimed in claim 4, wherein: the ultrasound waves have a frequency of 5 to 7 MHz; the distance between the emitter and the receiver is 10 mm to 25 mm, and the rubber mixture comprises 60 to 150 phr of the light-colored filler.

6. The method as claimed in claim 5, wherein: the distance between the emitter and the receiver is 15 to 20 nm; and the rubber mixture comprises 70 to 100 phr of the light-colored filler, the silanized filler is formed in the extruder from at least one light-colored filler and at least one silanizing agent at a silanization temperature of 140 to 160° C. the light-colored filler comprises silica; and the method further comprises monitoring the dispersion of the light-colored filler in the extrudate by at least one of: determining the coefficient of variation of the logarithm of the ultrasound wave intensity or of the ultrasound wave amplitude ln A, and using the coefficient of variation to monitor the dispersion of the light-colored filler in the extrudate; and determining the standard deviation of the relative attenuation coefficient α.sub.rel, and using the standard deviation to monitor the dispersion of the light-colored filler in the extrudate.

7. The method as claimed in claim 1, further comprising: determining the coefficient of variation of the logarithm of the ultrasound wave intensity or of the ultrasound wave amplitude ln A, and using the coefficient of variation to monitor the dispersion of the light-colored filler in the extrudate.

8. The method as claimed in claim 1, wherein the ultrasound waves are produced by an emitter and detected at a receiver and the distance between the emitter and the receiver is more than 5 mm to 25 mm.

9. The method as claimed in claim 1, wherein: the rubber mixture comprises 50 to 250 phr of the light-colored filler; and the light-colored filler comprises mineral natural and synthetic fillers that are not based on carbon black.

10. The method as claimed in claim 1, wherein the silanized filler is formed in the extruder from at least one light-colored filler and at least one silanizing agent.

11. A method of producing rubber mixtures comprising silanized light-colored fillers, the method comprising: mixing at least one light-colored filler with at least one rubber and at least one silanizing agent, and silanized the light-colored filler, and testing at least a portion of the rubber mixture by the method as claimed in claim 1.

12. The method as claimed in claim 11, wherein the silanization is effected at a temperature of 140 to 160° C.

13. The method as claimed in claim 11, wherein the process is conducted continuously or as a batchwise process, preferably continuously.

14. The method as claimed in claim 11, wherein the silanizing agent comprises a silane, preferably bis(3-triethoxysilypropyl) tetrasulfide.

15. The method of producing rubber mixtures according to claim 11, wherein more than 10% by volume of the rubber mixture is tested.

16. The method of producing rubber mixtures according to claim 11, wherein 100% by volume of the rubber mixture is tested.

17. A method of producing crosslinkable rubber mixtures comprising silanized light-colored filler, the method comprising producing the rubber mixtures according to the method as claimed in claim 11, and adding one or more crosslinking agents before, during, and/or after the production of the rubber mixture.

18. A method of producing vulcanizates comprising the crosslinkable rubber mixtures produced in accordance with the method as claimed in claim 17, the method comprising vulcanizing the crosslinkable rubber mixture at a temperature of 100° C. to 200° C.

19. The use of measurement devices for determining the sound wave amplitude and/or sound wave intensity at a frequency of the ultrasound waves within a range from 4 to 10 MHz, for a method as claimed in claim 1.

20. The use of measurement devices as claimed in claim 19, wherein the attenuation coefficient is determined in the region of the frequency of the ultrasound waves.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) FIG. 1 schematically illustrates, by way of example, the detection band consisting of the ultrasound sensor pairs (4), i.e. one transmitter and one receiver for each pair, and the flow channel (5) in top view.

(2) FIG. 2 schematically illustrates the arrangement in FIG. 1 in side view.

(3) FIG. 3 schematically illustrates an arrangement composed of an extruder (1), the detection band consisting of the ultrasound transducer pairs (4) and the flow channel (5) and the ultrasound sensor electronics (2), and a computer as evaluation unit (3).

(4) FIG. 4 plots an inline quality control for mixture batch R1M1 of the Examples.

(5) FIG. 5 plots an inline quality control for mixture batch R2M1 of the Examples.

(6) FIG. 6 plots an inline quality control for mixture batch R3M1 of the Examples.

(7) FIG. 7 plots an inline quality control for mixture batch R4M1 of the Examples.

(8) FIG. 8 plots an inline quality control for mixture batch R5M1 of the Examples.

(9) FIG. 9 plots the dependence of the relative sound attenuation coefficient on frequency for mixture batches R1M1 to R5M2 of table 4 of the Examples.

(10) FIG. 10 illustrates the correlation of the relative sound attenuation coefficients with Mooney viscosity.

(11) The invention additionally provides a method of producing rubber mixtures comprising silanized light-colored fillers, wherein at least one light-colored filler is mixed with at least one rubber and at least one silanizing agent and silanized, and wherein at least a portion of the rubber mixture obtained is tested by the method of the invention for testing of silanization. Preferably more than 1% by volume, more preferably more than 10% by volume, most preferably 100% by volume, of the rubber mixture obtained is tested by the method of the invention for testing of silanization. The method of the invention can be conducted continuously or as a batchwise method, preferably continuously.

(12) In a further preferred embodiment of the method of the invention, the extruder is used simultaneously as mixing unit for the production of the rubber mixture, as well as in situ silanization and for production of the extrudate by the testing method of the invention. In this case, at least one light-colored filler, one silanizing agent and one rubber each are fed to the extruder, and the silanized filler is formed therein from the silanizing agent and the light-colored filler.

(13) The silanizing agent used is preferably at least one silane. Silanes in the context of the invention are compounds containing silicon and hydrogen, and also further atoms of other chemical elements. Preference is given to silanes with trialkoxysilyl groups. Preference is further given to bifunctional silanes in which one functional group can react with the surface of a light-colored filler, for example trialkoxysilyl groups, and the other functional group can take part in the crosslinking reaction of the rubber, for example vinyl, thiol or polysulfane groups.

(14) Very particular preference is given to the following silanes:

(15) bis(3-triethoxysilylpropyl) tetrasulfide (Si69), bis(triethoxysilylpropyl) disulfide (Si75), bis(tri-ethoxysilylpropyl) disulfide (Si266), 3-thiocyanatopropyltriethoxysilane (Si264). VP Si 363® (from Evonik Industries), vinyltriethoxysilane, vinyltris(beta-methoxyethoxy)silane, gamma-mercaptopropyltrimethoxysilane, gamma-aminopropyltrimethoxysilane, gamma-glycidoxy-propyltrimethoxysilane, aminoethyl-gamma-aminopropyltrimethoxysilane, triamino-functional silanes, gamma-chloropropyltriethoxysilane, tris(1-methoxyethoxy-propyl-2-oxy)vinylsilane.

(16) Silanization is a chemical attachment of a silane to the surface of the light-colored filler. The attachment is effected by condensation reactions between hydrolyzable groups of the silanes used and chemical groups on the surface of the filler. The silanization of the light-colored filler is preferably conducted in a rubber mixture (in situ silanization) at temperatures in the range from 140° C. to 160° C. For this purpose, in each case, at least one rubber, silane and light-colored filler are mixed and subjected to a temperature within the above-specified range.

(17) The rubber mixture here typically contains 5% to 15% by weight of silanizing agent based on the total proportion of light-colored fillers.

(18) The rubber mixtures here may comprise further fillers, further additives such as aging stabilizers, plasticizers, etc., crosslinking agents, vulcanization accelerators and/or vulcanization retardants and/or further auxiliaries.

(19) Further fillers are, for example, carbon-based fillers, for example carbon black, graphite, carbon nanotubes, and magnetizable fillers such as carbonyl iron powder, iron oxides, ferrites and/or fibers, for example aramid fiber pulp and carbon fibers.

(20) Suitable aging stabilizers are coloring and noncoloring aging stabilizers, for example paraphenylendiamines, isopropylphenylparaphenylenediamine (IPPD), para-phenylene-diamine (6PPD), N,N-ditolyl-p-phenylenediamine (DTPD), etc., amines, for example trimethyl-1,2-dihydroquinoline (TMQ), (phenyl)amine]-1,4-naphthalenedione (PAN), bis(4-octylphenyl)amine (ODPA), styrenized diphenylamine (SDPA), mono- and bisphenols, for example 2,2′-methylenebis(4-methyl-6-tert-butylphenol) (BPH), 2,2′-isobutylidenebis(4,6-dimethylphenol) (NKF), 2,2′-dicyclopentadienylbis(4-methyl-6-tert-butylphenol) (SKF), 2,2′-methylenebis(4-methyl-6-cyclohexylphenol) (ZKF), 2,6-di-tert-butyl-p-cresol (BHT), substituted phenol (DS), styrenized phenols (SPH), mercaptobenzimidazoles, for example 2-mercaptobenzimidazole (MBI), 2-mercaptomethylbenzimidazoles (MMBI), zinc 4- and 5-methyl-2-mercaptobenzimidazoles (ZMMBI).

(21) Plasticizers are, for example, long-chain esters and/or ethers, such as thioesters, phthalic esters, alkylsulfonic esters, adipic esters, sebacic esters, dibenzyl ethers and/or mineral oils (paraffinic, aromatic, naphthenic or synthetic oils).

(22) Crosslinking agents in the context of the invention are network node formers. Network node formers are molecules that can connect two individual polymer chains to one another, for example sulfur (soluble or insoluble) and/or sulfur donors, for example dithlomorpholines (DTDM), tetramethylthiuram disulfides (TMTD), tetraethylthiuram disulfide (TETD), dipentamethylenethiuram tetrasulfides (DPTT), phosphoryl polysulfides, for example Rhenocure® SDT/S from Rhein Chemie Rheinau GmbH and/or peroxides, for example di-tert-butyl peroxides, di(tert-butylperoxy)trimethyl-cyclohexanes, di(tert-butylperoxyisopropyl)benzenes, dicumyl peroxides, dimethyl-di(tert-butylperoxy)hexyne, butyl di(tert-butylperoxy)valerate, resorcinol, aldehyde-amine condensation products, for example hexamethylenetetramine, resorcinol-formaldehyde precondensates and/or vulcanization resins, for example halomethylphenol resin, quinone dioximes, bisphenols.

(23) Accelerators are, for example: carbamates or triazines, for example hexamethylenediamine carbamate (HMDC), organic triazines, thiazoles, for example 2-mercaptobenzothiazole (MBT), zinc mercaptobenzothiazole (ZnMBT), thiadiazoles (TDD), sulfenamides, such as cyclohexylbenzothiazolesulfenamides (CBS), dibenzothiazyl disulfide (MBTS), butylbenzothiazolesulfenamide (TBBS), dicyclohexyl-benzothiazolesulfenamide (DBS), 2-(4-morpholinylmercapto)benzothiazole (MBS), thiurams, such as tetramethylthiuram monosulfide (TMTM), tetraethylthiuram disulfide (TETD), tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBTD), dipentamethylenethiuram tetra(hexa)sulfide (DPTT), dithiocarbamates, such as Zn dimethyldithiocarbamates (ZDMC), Cu dimethyldithiocarbamates, Bi dimethyldithiocarbamates, Zn diethyldithiocarbamates (ZDEC), tellurium diethyldithiocarbamates (TDEC), Zn dibutyldithiocarbamates (ZDBC), Zn ethylphenyldithiocarbamates (ZEPC), Zn dibenzyldithiocarbamates (ZBEC), Ni dibutyldithiocarbamates (NBC), selenium diethyldithiocarbamates (SeEDC), selenium dimethyldithiocarbamates (SeDMC), tellurium diethyldithiocarbamates (TeEDC), thiophosphate and dithiophosphate, for example zinc O,O-di-n-butyldithiophosphate (ZBDP), zinc O-butyl-O-hexyldithiophosphate, zinc O,O-diisooctyldithiophosphate (ZOPD), dodecylammonium diisooctyldithlophosphate (AOPD), for example the Rhenogran® ZDT, ZAT, ZBOP products from Rhein Chemie Rheinsu GmbH, urea/thioureas, for example ethylenethiourea (ETU), N,N,N′N′-tetramethylthiourea (TMTU), diethylthiourea (DETU), dibutylthiourea (DBTU), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (Diuron) etc., and/or xanthogenate accelerators, for example zinc isopropylxanthogenate (ZIX), guanidines, for example diphenylguanidine (DPG) and/or N′,N-di-ortho-tolylguanidine (DOTG) and the guanidine-free substitute accelerators, such as Rhenogran® XLA 60,

(24) Vulcanization retardants, for example N-nitrosodiphenylamine, N-cyclohexylthiophthalimide (CPT), e.g. Vulkalent® G), sulfonamide derivatives (e.g. Vulkalent® E/C), phthalic anhydride (e.g. Vulkalent® B/C), or benzoic anhydride.

(25) Auxiliaries are, for example, dispersion auxiliaries, for example fatty acids, steric acid, oleic acid, activators, for example zinc oxide, lead oxide, bismuth oxide, lithium carbonate, sodium carbonate and/or calcium hydroxide, magnesium oxide, flame retardants such as antimony oxide, etc.

(26) The aforementioned fillers, additives, plasticizers, crosslinking agents, vulcanization accelerators and/or vulcanization retardants, auxiliaries etc. are familiar to the person skilled in the art and can also be used in granulated form, for example as polymer-bound additives or as the crosslinker masterbatches described in EP2314442A.

(27) The rubber mixtures can be processed further, for example to give masterbatches, base mixtures and crosslinkable rubber mixtures.

(28) Masterbatches typically have a high proportion of additives based on rubber and contain, for example:

(29) 2.5% to 90% by weight of rubber

(30) 0% to 50% by weight of plasticizers

(31) 2% to 80% by weight of silanized light-colored fillers

(32) 0% to 20% by weight of dispersion auxiliaries

(33) 0% to 10% by weight of silane

(34) Base mixtures are rubber mixtures to which crosslinking agents and optionally vulcanization accelerators still have to be added before practical use, for example:

(35) 100 phr rubber

(36) 0 to 100 phr plasticizers

(37) 0 to 200 phr fillers, of which at least 10% are silanized light-colored fillers,

(38) 0 to 30 phr auxiliaries and

(39) 0 to 10 phr aging stabilizers.

(40) Crosslinkable rubber mixtures are rubber mixtures which additionally contain 0.01 to 20 phr crosslinking agents and optionally vulcanization accelerators and vulcanization retardants.

(41) Particular preference is given to crosslinkable rubber mixtures containing, inter alia, 30 to 110 phr carbon black and precipitated silica, 3 to 9 phr silane, 2 to 7 phr zinc oxide and 0.5 phr to 4 phr sulfur and 1 to 5 phr accelerators.

(42) The invention also encompasses a method of producing crosslinkable rubber mixtures comprising silanized light-colored filler, in which one or more crosslinking agents are added before, during and/or after the production of the rubber mixture of the invention. The crosslinking agents can thus be added before, during and/or after the mixing of the light-colored filler with silanizing agent and rubber.

(43) The masterbatches, the base mixture and the crosslinkable rubber mixture are preferably produced by the processes familiar to the person skilled in the art as described, for example, in PCT/EP2009/058041. Fillers, auxiliaries, crosslinking agents and/or aging stabilizers are mixed here together with the rubber in a mixing unit. Suitable mixing units are, for example, internal mixers, roll systems, extruders. Internal mixers with an exit extruder are particularly suitable.

(44) In a further embodiment of the invention, in a first step, the base mixture is produced in a mixing unit. Temperatures of more than 140° C. to 160° C. can be achieved here. In a second production step, after the base mixture has cooled down to temperatures less then 130° C., crosslinking agents are added to the base mixture in a further mixing unit. Some of the crosslinking agents, vulcanization accelerators and/or vulcanization retardants may already have been added to the base mixture in the first production step.

(45) In a further preferred embodiment, the base mixture is produced in a mixing unit in the first step. Temperatures of more than 140° C. to 160° C. can be achieved here. In a second step, the mixture is homogenized. It is likewise possible here to reach temperatures of more than 140° C. to 160° C. In a third production step, after the base mixture has cooled down to temperatures less than 130° C., crosslinking agents are added to the base mixture in a further mixing unit. Some of the crosslinking agents, vulcanization accelerators and/or vulcanization retardants may already have been added to the base mixture in the first or second production step.

(46) Particular preference is given to continuous processes in which the masterbatches, base mixtures or else the crosslinkable rubber mixtures are produced in one or more process steps with one or more extruders.

(47) Very particular preference is given to the production process described in DE-A-102008040138 for crosslinkable rubber mixtures, in which the base mixture is produced in at least one batchwise kneader process, and crosslinking agents in the form of the crosslinker masterbatches described in described EP-A-2314442 are added to the base mixture and the crosslinker masterbatches are mixed with the base mixture in a continuous process with an extruder.

(48) The invention further relates to a process for producing vulcanizates comprising the inventive production of crosslinkable rubber mixtures comprising silanized light-colored fillers and subsequent vulcanization at a temperature in the range from 100° C. to 200° C.

(49) The invention likewise encompasses the use of measurement apparatuses for determination of the ultrasound wave amplitude a, integrated ultrasound wave amplitude A and/or ultrasound wave intensity i, the integrated ultrasound wave amplitude I of one or more frequencies in a range from 4 to 10 MHz, preferably from 5 to 7 MHz, for the test method of the invention, for the production methods of the invention for rubber mixtures in general and crosslinkable rubber mixtures in particular. This preferably also, encompasses the use of the measurement apparatuses mentioned for determining the relative attenuation coefficient α.sub.rel in the abovementioned processes.

(50) The present invention thus provides a method of verifying silanization, which allows inline monitoring of the in situ silanization of light-colored fillers, especially precipitated silicas. This enables continuous in situ silanization in the production of rubber mixtures containing silanized light-colored fillers, and representative monitoring of the rubber mixture under production conditions. The process is additionally nondestructive and has a high tolerance for carbon black as an additional constituent of the rubber mixture.

(51) The examples, illustrations and figures which follow serve to illustrate the invention, without having any limiting effect.

EXAMPLES

(52) The components of a typical rubber mixture for tire treads according to table 1 were provided.

(53) TABLE-US-00001 TABLE 1 Formulation of a typical rubber mixture for tire treads Density Amount Trade name [g/cm.sup.3] [phr] Buna CB 24 Butyl rubber Lanxess Deutschland 0.91 30 GmbH Buna VSL 5025-2 Solution styrene- Lanxess Deutschland 0.95 70 HM butadiene rubber GmbH CB N-330 Carbon black 1.8 5 Ultrasil GR 7000 Silica Evonik industries AG 2 90 ASM-TMQ 2,2,4-Trimethyl-1,2- 1.1 1.5 dihydroquinoline ASM-6PPD N-1,3-Dimethylbutyl-N′- 1 2 phenyl-b-phenylene- diamine Stearic acid 0.89 1 WS zinc oxide Norzinco GmbH 5.6 2 Si-69 Bis(triethoxysilylpropyl) Evonik Industries AG 0.866 10 tetrasulfide

(54) These components were mixed according to the mixing method in table 2 in various batches.

(55) TABLE-US-00002 TABLE 2 Mixing method Time Mixture constituent Comment .sup.   0-0.75′ Polymers 0.75′-1′20″ Silica + Si69 + ZnO Ram up 1′20″ Ram down 2′ Aging stabilizers + stearic acid 3.5′ invert 5′ Ejection

(56) In the case of batches R1M1 to R5M2, the mixing parameters of speed and feed temperature were varied according to table 3.

(57) TABLE-US-00003 TABLE 3 Mixed batches of a typical rubber mixture from table 1 1st mixing stage 2nd mixing stage Batch Mixing parameters R1M1 R2M1 R3M1 R4M1 R5M2 Fill level [%] 70 70 70 70 70 Speed [rpm] 70 40 40 40 70 Feed temperature [° C.] 70 70 50 40 70 Mixing time [min.] 5 5 5 5 3 Energy input [W] 135 134 149 146 110 Ejection temperature T.sub.A [° C.] 147 126 117 112 142

(58) The mixture is, as specified in table 3, mixed in a 1.5 I internal mixer (Intermesh) from Gurnix S.A. for 5 min. The rubber mixture here contains silica and silane inter alia, and a little carbon black.

(59) The silane reacts above 140° C. with the silica surface. Below 140° C., no reaction takes place. As a result of the different mixing parameters, different values for the ejection temperature T.sub.A are achieved below (batch R2M1 to R4M1) and above (batch R1M1 and R5M2) 140′C. Batch R5M2 was additionally mixed for a second time in the internal mixer in order to complete the reaction (R5M2). This corresponds to a typical process for in situ silanizations in the tire industry. After the mixing process in the internal mixer, the mixture batches were homogenized on a twin roller system from Rubicon Gummitechnik und Maschinentechnik GmbH at a temperature of 50° C. (incised three times on the left and three times on the right) and drawn off to give a mixed sheet. Strips were cut out of the sheet. The strips were fed to an EEK32.12L single-shaft extruder from Rubicon Gummitechnik und Maschinentechnik GmbH with low mixing action. At the extruder outlet is a sensor head equipped with two opposite ultrasound transducers separated by 10 mm, and additionally a temperature sensor T1 with a probe that projects into the mixture flow and a pressure/temperature sensor. This temperature sensor measures the pressure p and the temperature T2 at the rubber/metal interface. The flow channel in the sensor head has a width of 20 mm and a height of 10 mm. The diameter of the ultrasound transducers is 8 mm. The sensor head and extruder were kept at a controlled temperature of 120° C. The screw speed was 20 rpm. This corresponds to a throughput of about 1 kg of rubber mixture per 10 min.

(60) The inline quality control was conducted with a pair of K6V1 ultrasound transducers from GE Sensing & Inspection Technologies GmbH in transmission. The ultrasound transducers were actuated with the PCM 100LAN test electronics from Inoson GmbH. 10 to 40 ultrasound pulses per second were generated in the ultrasound transducer with the aid of the piezoelectric effect. The ultrasound transducer converts the voltage pulses to ultrasound signals. The ultrasound transducers were excited here with 7 bursts at the intrinsic frequency of the ultrasound transducer of 6 MHz. The ultrasound pulse of the transmitter moves through the extruded rubber mixture and is attenuated by the rubber mixture. The oscillation amplitude a of the ultrasound signal is lowered. The receiver receives the sound signal and converts it to a voltage signal. The voltage signal is amplified by the hardware of the PCM100LAN at 32.45 dB and passed to a computer. With the aid of the computer, the first sound pulse of the A scan is evaluated by what is called fast Fourier transformation (FFT). The amplitude spectrum a(f) thus obtained as a function of the ultrasound frequency f was integrated in five different frequency ranges (cf. table 4) and the logarithm was formed. The ln A(f.sub.min.,f.sub.max.) values thus obtained for the integral converted to a logarithm are plotted for the various mixture batches R1M1 to R4M1 and R5M2 as a function of time t. This is done before the mixture exits from the sensor head at the outlet of the extruder. The dwell time of the mixture in the sensor head was less than 1 minute. The result of the frequency range f.sub.min.=5.2 MHz to f.sub.max.=6.9 MHz is shown for each mixture batch in FIGS. 4 to 8. In addition, the coefficient of variation CV is shown for the values ln A(f.sub.min.,f.sub.max.) for 50 measurement points. The coefficient of variation CV is a measure of the mixing quality.

(61) The values for ln A(f.sub.min.,f.sub.max.) are used to calculate the relative attenuation coefficient α.sub.rel (f.sub.max.,f.sub.min.) by the Beer-Lambert law.
α.sub.rel.(f.sub.min.,f.sub.max.)=(ln A.sub.rel.(f.sub.min.,f.sub.max.)−ln A(f.sub.min.,f.sub.max.)/x  (1d)

(62) In this formula, x is the distance between the ultrasound transducers. In eq. (1d) is the mean value of ln A(f.sub.min.,f.sub.max.) of the reference mixture R5M2 (standard mixing method) for a duration for the extrusion of Δt=5 min. Table 4 shows the mean values for the relative attenuation coefficient α.sub.rel.(f.sub.min.,f.sub.max.) for a period of time from Δt=4 min to Δt=8 min, for the extrusion for each mixture batch. In addition, the standard deviation σ of the relative attenuation coefficients α.sub.rel.(f.sub.min.,f.sub.max.) was determined according to eq. (1d). In addition, the mean value of the pressure sensor p and the mean values for the temperature sensor T1 with probe and T2 without probe are reported. The speed of sound V.sub.S is determined from the distance x and the time t.sub.oF before the first voltage amplitude. It is necessary here to take account of the time t.sub.US=4 μs is of the ultrasound signal within the inlet of the ultrasound transducer according to eq. (2).
V.sub.S=x/(t.sub.oF−t.sub.US)  (2)

(63) In addition to the ultrasound indices, the Mooney viscosity ML1+4 (100° C.) was determined as a nonrepresentative offline standard quality control.

(64) TABLE-US-00004 TABLE 4 Analysis of the extruded batches from table 3 Extruded batch after 1st mixing stage 2nd mixing stage Batch R1M1 R2M1 R3M1 R4M1 R5M2 Standard process control Mooney viscosity [MU] 143 150 151 not 122 ML1 + 4 (100° C.) measurable Measurement conditions Pressure ρ [bar] 31 ± 3  34 ± 1  35 ± 1  38 ± 1  34 ± 2  T1 [° C.] 124 ± 1  125 ± 1  125 ± 1  124 ± 1  124 ± 1  T2 [° C.] 122 ± 1  122 ± 1  122 ± 1  121 ± 1  121 ± 1  Ultrasound indices V.sub.S [m/s] 1214 ± 3   1218 ± 2   1220 ± 3   1222 ± 2   1218 ± 3   Rel. attn. coeff. α.sub.rel. (1.1 MHz to 1.7 MHz) [1/m] 1 ± 2 3 ± 2 3 ± 2 2 ± 2 0 ± 1 (1.7 MHz to 2.8 MHz) [1/m] 3 ± 2 4 ± 2 3 ± 2 2 ± 2 0 ± 2 (2.8 MHz to 4.0 MHz) [1/m] 4 ± 2 6 ± 2 6 ± 3 4 ± 2 0 ± 2 (4.0 MHZ to 5.2 MHz) [1/m] 5 ± 2 9 ± 3 9 ± 3 9 ± 2 0 ± 2 (5.2 MHz to 6.9 MHz) [1/m] 7 ± 3 14 ± 3  15 ± 4  14 ± 2  0 ± 2

(65) It can be seen in table 4 that the values for the relative sound attenuation αrel. over and above 4 MHz for the batch R1 M1 are significantly less than the values for batches R2D1, R3M1 and R4M1 (FIG. 9). The ejection temperature TA of the batch R1 M1 is above 140° C., and so the silanization reaction was able to take place. The ejection temperature TA of the batches R2M1, R3M1 and R4M1 was below 140° C., and so no silanization reaction was able to take place. Below 4 MHz, the difference relative to the standard deviation 6 of the values for the relative sound

(66) The low values for R1 M1 and for R5M2 compared to R3M1 and R4M1 cannot be attributed to improved dispersion of the filler (here: the silica), as described in A. Schroder, L. Graff. L. Wawrzinski, Kautschuk Gummi Kunststoffe, 67 (2015), 11. The ultrasound amplitude increases therein with increasing filler dispersion; at the same time, the coefficient of variation CV decreases. By contrast, the coefficient of variation CV of the mixtures R1M1 and R5M2 (in FIG. 4 and FIG. 8) assumes values above 0.2%. The values for the coefficient of variation of the mixtures R3M1 and R4M1, by contrast, are all less than 0.2%. It appears that the higher energy input during the kneading process for batches R3M1 and R4M1, owing to the lower temperature, leads to improved filler dispersion. Nevertheless, the values for ln A (f.sub.min., f.sub.max.) of the batches R3M1 and R4M1 are lower than for R1 M1 and R5M2. Since batches with the same composition were used and no significant changes in the measurement conditions (identical values for p, T1, and T2) were observed in the inline quality control, the different relative sound attenuation coefficients αrel(f.sub.min., f.sub.max.) can only be explained by a chemical reaction of the silica surface with the silane.

(67) Moreover, there is a further drop in the relative sound attenuation coefficient α.sub.rel. (f.sub.min., f.sub.max.) when the silanization is completed in accordance with the standard method σ in a second mixing step (comparison of R1M1 and R5M2). The values for the relative sound attenuation coefficient α.sub.rel.(f.sub.min.,f.sub.max.) at a frequency of >4 MHz correlate with the values for the Mooney viscosity ML1+4 (100° C.) as the offline standard method for quality control for uncrosslinked rubber mixtures (FIG. 10). This clearly shows that the quality of the in situ silanization can be determined with the aid of the determination of the relative sound attenuation coefficent α.sub.rel.(f.sub.min.,f.sub.max.).