In-line ultrasonic check for detecting the partial vulcanization of a rubber mixture in the in situ silanization of bright fillers

Abstract

The invention relates to a method for checking the silanization of pale-colored fillers, where a mixture comprising at least one silanized pale-colored filler, preferably silanized silica, and comprising at least one rubber is irradiated with ultrasound waves in a frequency range of 4 to 10 MHz, preferably of 5 to 7 MHz, and the signal strength of the ultrasound waves is determined after transmission through the rubber mixture, where the relative attenuation coefficient α.sub.rel of the rubber mixture in the frequency range of the ultrasound waves is determined, the standard deviation σ of the relative attenuation coefficient α.sub.rel is determined, and α.sub.rel and σ are used for detection of incipient crosslinking of the rubber mixture.

Claims

1-17. (canceled)

18. A method for checking the silanization of pale-colored fillers, comprising: irradiating a rubber mixture comprising at least one silanized pale-colored filler and at least one rubber with ultrasound waves in a frequency range of 4 to 10 MHz and determining the signal strength of the ultrasound waves after transmission through the rubber mixture, where a relative attenuation coefficient α.sub.rel of the rubber mixture in the frequency range of the ultrasound waves is determined, a standard deviation σ of the relative attenuation coefficient α.sub.rel is determined, and ard and a are used for detection of incipient crosslinking of the rubber mixture.

19. The method as claimed in claim 18, wherein the rubber mixture is produced at a temperature of above 160° C.

20. The method as claimed in claim 18, wherein the incipient crosslinking of the rubber mixture is detected in that the standard deviation σ of the relative attenuation coefficient α.sub.rel of the incipiently crosslinked rubber mixture is above 0.5 (1/m) and the relative attenuation coefficient a.sub.res of the incipiently crosslinked rubber mixture is below 0 (1/m).

21. The method as claimed in claim 18, wherein the moving standard deviation σa.sub.g of the relative attenuation coefficient α.sub.rel of the incipiently crosslinked rubber mixture, produced at a temperature of above 160° C., is above 1 (1/m), based on a measurement time of 1 to 50 s and the relative attenuation coefficient α.sub.rel of the incipiently crosslinked rubber mixture, produced at a temperature of above 160° C., is below 0 (1/m).

22. The method as claimed in claim 18, wherein the at least one silanized pale-colored filler is produced from at least one pale-colored filler and at least one silanizing agent.

23. The method as claimed in claim 22, wherein the rubber mixture comprises less than 10 phr of crosslinking agent other than the at least one silanizing agent and the at least one silanized pale-colored filler.

24. The method as claimed in claim 18, wherein the standard deviation a is the moving standard deviation σ.sub.g.

25. The method as claimed in claim 18, wherein the mixture is extruded and the resultant extrudate is irradiated with sound.

26. The method for the production of a rubber mixture comprising at least one silanized pale-colored filler where, at a temperature of above 160° C., at least one pale-colored filler is mixed with at least one rubber and with at least one silanizing agent, and where at least a portion of the resultant rubber mixture is checked by the method as claimed in claim 18.

27. The method as claimed in claim 26, wherein the method for the production of a rubber mixture comprising at least one silanized pale-colored filler is implemented at a temperature of above 160° C. to 200° C.

28. The method as claimed in claim 26, where the moving standard deviation σ.sub.g of the relative attenuation coefficient α.sub.rel of the rubber mixture is below 0.5 (1/m) based on a measurement time of 1 to 100 s and the relative attenuation coefficient α.sub.rel of the rubber mixture is below 0 (1/m) and equal to or above -15 (1/m).

29. The method as claimed in claim 18, wherein the at least one pale-colored filler is selected from the group consisting of mica, kaolin, siliceous earth, calcium carbonates, zinc oxide, aluminum oxide, titanium dioxide, silicas, chalk and talc.

30. The method as claimed in claim 22, wherein the at least one silanizing agent is a silane selected from the group consisting of bis(3-triethoxysilypropyl) tetrasulfide, bis(triethoxysilylpropyl) disulfide, 3-thiocyanatopropyltriethoxysilane, 3-mercaptopropyl-di(tridecan-1-oxy-13-penta(ethyleneoxide))ethoxysilane, gamma-mercapto-propyltrimethoxysilane, and bis(3-triethoxysilypropyl) tetrasulfide.

31. A method for the production of crosslinkable rubber mixtures comprising at least one silanized pale-colored filler, where one or more further crosslinking agents are added after the production of the rubber mixture as claimed in claim 26.

32. A method for the production of vulcanizates comprising the production of crosslinkable rubber mixtures comprising silanized pale-colored fillers as claimed in claim 31 and subsequent vulcanization at a temperature in the range of 100° C. to 200° C.

Description

[0083] Preferred embodiments of the device of the invention are depicted in FIG. 1 to FIG. 3. FIG. 1 describes in plan view by way of example the detection band, consisting of the ultrasound sensor pairs (4), i.e. one sender and one receiver for each pair, and of the flow channel (5). FIG. 2 depicts a side view of the arrangement in FIG. 1. FIG. 3 shows an arrangement of an extruder (1), the detection band, consisting of the ultrasound transducer pairs (4) and the flow channel (5), and the ultrasound-check electronics (2), and a computer as evaluation unit (3).

METHOD FOR THE PRODUCTION OF A RUBBER MIXTURE COMPRISING AT LEAST ONE SILANIZED PALE-COLORED FILLER

[0084] The invention further provides a method for the production of a rubber mixture comprising at least one silanized pale-colored filler where, at a temperature of above 160° C., at least one pale-colored filler is mixed with at least one rubber and with at least one silanizing agent, and where at least a portion of the resultant rubber mixture is checked by the method of the invention for checking the silanization.

[0085] It is preferable that more than 1% by volume, particularly preferably more than 10% by volume, very particularly preferably more than 25% by volume, very very particularly preferably more than 50% by volume, most preferably more than 80% by volume, of the resultant rubber mixture is checked by the method of the invention for checking the silanization.

[0086] The production method is preferably implemented at a temperature of above 160° C. to 200° C., particularly preferably of above 160° C. to 180° C.

[0087] The above method is preferably a method for the production of a rubber mixture comprising at least one silanized pale-colored filler, where at least one pale-colored filler is mixed with at least one rubber and at least one silanizing agent at a temperature of above 160° C., and where at least a portion of the resultant rubber mixture is checked by the method of the invention for checking the silanization, and where the moving standard deviation σ.sub.g of the relative attenuation coefficient α.sub.rel of the rubber mixture is below 0.5 [1/m], preferably below 0.3 [1/m], based on a measurement time of 1 to 100 s, preferably of 1 to 50 s, particularly preferably 1 to 15 s, and the relative attenuation coefficient α.sub.rel of the rubber mixture is below 0 [1/m], preferably below −5 [1/m], particularly preferably below −5 [1/m] and equal to or above −15 [1/m].

[0088] It is preferable that the rubber mixture obtained by the abovementioned preferred method has not yet been incipiently crosslinked.

[0089] The method of the invention can be operated here continuously or as batch method.

[0090] In a preferred embodiment, the method for the production of a rubber mixture comprising at least one silanized pale-colored filler is implemented before the extrusion of the resultant rubber mixture, and the method for checking the silanization is implemented by irradiation with sound, in an extruder, of the extrudate obtained by the extrusion.

[0091] In another preferred embodiment, the method for the production of a rubber mixture comprising at least one silanized pale-colored filler and the method of the invention for checking the silanization are implemented in the same extruder. In this case, at least one pale-colored filler, at least one silanizing agent and at least one rubber are introduced into the extruder and the silanized pale-colored filler is formed therein from the silanizing agent and the pale-colored filler.

[0092] In the last-mentioned embodiment it is optionally possible that at least one pale-colored filler, at least one rubber and at least one silanizing agent are premixed at a temperature of below or equal to 160° C. within or outside of the extruder, and that this mixture is then irradiated with sound in the extruder.

[0093] The descriptions and preferred ranges mentioned at an earlier stage above in relation to the method of the invention for checking the silanization apply analogously to the components used in the method for the production of a rubber mixture comprising at least one silanized pale-colored filler, where said components include, but are not restricted to, the at least one pale-colored filler, the at least one rubber and the at least one silanizing agent.

[0094] In the process for the production of a rubber mixture comprising at least one silanized pale-colored filler it is preferable to use 5 to 15% by weight of at least one silanizing agent, based on the total content of pale-colored fillers in the rubber mixture.

OTHER ADDITIONAL SUBSTANCES

[0095] The rubber mixtures comprising at least one silanized pale-colored filler can comprise other additional substances, for example other fillers, other additives such as aging inhibitors, plasticizers, other crosslinking agents, vulcanization accelerators and/or vulcanization retarders and/or other auxiliaries.

[0096] For the purposes of the present invention, the phrase “other fillers” means fillers other than the at least one pale-colored filler described in more detail at an earlier stage above and the at least one silanized pale-colored filler.

[0097] Examples of other fillers are carbon-based fillers, e.g. carbon black, graphite, carbon nanotubes, and also magnetizable fillers such as carbonyl iron powder, iron oxides, ferrites and/or fibers, e.g. aramid fiber pulp and carbon fibers.

[0098] The following are suitable as aging retarders: coloring and noncoloring aging retarders, e.g. paraphenylenediamines, isopropylphenylparaphenylenediamine (IPPD), para-phenylenediamine (6PPD), N,N-ditolyl-p-phenylenediamine (DTPD), amines, e.g. trimethyl-1,2-dihydroquinoline (TMQ), [(phenyl)amine]-1,4-naphthalenedione (PAN), bis(4-octylphenyl)amine (ODPA), styrenated diphenylamine (SDPA), mono- and bisphenols, e.g. 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), styrenated phenols (SPH), mercaptobenzimidazoles, e.g. 2-mercaptobenzimidazole (MBI), 2-mercaptomethylbenzimidazoles (MMBI), zinc 4- and 5-methyl-2-mercaptobenzimidazoles (ZMMBI).

[0099] Examples of plasticizers are long-chain esters and/or ethers, for example thioesters, phthalic esters, alkylsulfonic esters, adipic esters, sebacic esters, dibenzyl ethers, and/or mineral oils (paraffinic, aromatic naphthenic or synthetic oils).

[0100] For the purposes of the present invention, the phrase “other crosslinking agents” means crosslinking agents other than the at least one silanized pale-colored filler described in more detail at an earlier stage above and the at least one silanizing agent.

[0101] Other crosslinking agents can be:

[0102] network node-formers: network node-formers are molecules which are capable of bonding two individual polymer chains to one another, e.g. [0103] sulfur (soluble or insoluble) and/or sulfur donors, e.g. dithiodimorpholines (DTDM), tetramethylthiu ram disulfides (TMTD), tetraethylthiuram disulfide (TETD), dipentamethylenethiuram tetrasulfides (DPTT), phosphoryl polysulfides, e.g. Rhenocure® SDT/S from Lanxess Deutschland GmbH and/or [0104] peroxides, e.g. di-tert.-butyl peroxide, di(tert.-butylperoxy)trimethylcyclohexane, di(tert.-butylperoxyisopropyl)benzene, dicumylperoxides, dimethyldi(tert.-butylperoxy)hexyne, di(tert.-butylperoxy) butylvalerate, [0105] resorcinol, aldehyde-amine condensates, e.g. hexamethylenetetramine, resorcinol-formaldehyde precondensates and/or vulcanization resins, for example halomethylphenolic resin, [0106] quinone dioximes [0107] bisphenols.

[0108] Examples of vulcanization accelerators are: [0109] carbamates and triazines, e.g. hexamethylenediamine carbamate (HMDC), organic triazines, [0110] thiazoles, e.g. 2-mercaptobenzothiazole (MBT), zinc mercaptobenzothiazole (ZnMBT), thiadiazoles (TDD), [0111] sulfenamides, for example cyclohexylbenzothiazolesulfenamide (CBS), dibenzothiazyl disulfide (MBTS), butylbenzothiazolesulfenamides (TBBS), dicyclohexyl-benzothiazolesulfenamide (DCBS), 2-(4-morpholinylmercapto)benzothiazole (MBS), [0112] thiurams, for example tetramethylthiuram monosulfide (TMTM), tetraethylthiuram disulfide (TETD), tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBTD), dipentamethylenethiuram tetra(hexa)sulfide (DPTT), [0113] dithiocarbamates, for example 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), [0114] thiophosphate and dithiophosphate, e.g. zinc O,O-di-n-butyl dithiophosphate (ZBDP), zinc O-butyl-O-hexyl dithiophosphate, zinc O,O-diisooctyl dithiophosphate (ZOPD), dodecylammonium diisooctyl dithiophosphate (AOPD), e.g. the Rhenogran® grades ZDT, ZAT, ZBOP from Rhein Chemie Rheinau GmbH, [0115] urea/thioureas, e.g. ethylenethiourea (ETU), N,N,N′N′-tetramethylthiourea (TMTU), diethylthiourea (DETU), dibutylthiourea (DBTU), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) etc., and/or [0116] xanthate accelerators, e.g. zinc isopropyl xanthate (ZIX), [0117] guanidines, e.g. diphenylguanidine (DPG) and/or N′,N-di-orthotolylguanidine (DOTG) and the guanidine-free replacement accelerators, for example Rhenogran® XLA 60, examples of vulcanization retarders are N-nitrosodiphenylamine, N-cyclohexylthiophthalimide (CPT), e.g. Vulkalent® G), sulfonamide derivates (e.g. Vulkalent® E/C), phthalic anhydride (e.g. Vulkalent® B/C), or benzoic anhydride.

[0118] Examples of auxiliaries are dispersion aids, e.g. fatty acids, stearic acid, oleic acid, activators, for example zinc oxide, lead oxide, bismuth oxide, lithium carbonate, sodium carbonate and/or calcium hydroxide, magnesium oxide, and flame retardants, for example antimony oxide, etc.

[0119] The abovementioned other fillers, additives, plasticizers, other crosslinking agents, vulcanization accelerators and/or vulcanization retarders, auxiliaries, etc. are familiar to the person skilled in the art and can also be used in granulated form, e.g. in the form of polymer-bound additives or in the form of the crosslinker masterbatches described in EP2314442A.

[0120] The rubber mixtures can be further processed, for example to give masterbatches, base mixtures and crosslinkable rubber mixtures.

[0121] Masterbatches typically have a high proportion of additives, based on rubber, and comprise by way of example:

2.5 to 90% by weight of rubber
0 to 50% by weight of plasticizers
2 to 80% by weight of silanized pale-colored fillers
0 to 20% by weight of dispersing agents
0 to 10% by weight of silane.

[0122] Base mixtures are rubber mixtures which, before they are used for practical purposes, require further addition of crosslinking agents and optionally of vulcanization accelerators, for example:

100 phr of rubber
0 to 100 phr of plasticizers
0 to 200 phr of fillers, at least 10% of these being silanized pale-colored fillers
0 to 30 phr of auxiliaries and
0 to 10 phr of aging retarders.

[0123] Crosslinkable rubber mixtures are rubber mixtures which additionally comprise 0.01 to 20 phr of one or more other crosslinking agents and optionally vulcanization accelerators and optionally vulcanization retarders.

[0124] Particular preference is given to crosslinkable rubber mixtures which comprise 30 to 110 phr of carbon black and precipitated silica, 3 to 9 phr of silane, 2 to 7 phr of zinc oxide, and also 0.5 phr to 4 phr of sulfur and 1 to 5 phr of accelerator.

[0125] The invention also comprises a method for the production of crosslinkable rubber mixtures comprising at least one silanized pale-colored filler, where one or more further crosslinking agents are added after the production of the rubber mixture comprising at least one silanized pale-colored filler.

[0126] The production of the masterbatches, of the base mixture and of the crosslinkable rubber mixture preferably takes place by the methods well known to the person skilled in the art, for example those described in PCT/EP2009/058041. Fillers, auxiliaries, other crosslinking agents and/or aging retarders are mixed here together with the rubber in a mixing assembly. Examples of suitable mixing assemblies are internal mixers, roll units and extruders. Internal mixers with discharge extruder are particularly suitable.

[0127] In one embodiment of the invention, the rubber mixture comprising at least one silanized pale-colored filler is produced in a first step by the method of the invention. In a following step, the mixture is homogenized.

[0128] In another embodiment of the invention, the rubber mixture comprising at least one silanized pale-colored filler is produced in a first step by the method of the invention. In a following step, the mixture is homogenized. In a following step, one or more further crosslinking agents are added to a further mixing assembly after cooling of the rubber mixture to a temperature below or equal to 130° C. This embodiment is preferably used in the large-scale industrial production of the rubber mixture comprising at least one silanized pale-colored filler, particularly preferably in the production of more than 100 kg.

[0129] The phrase “following step” means in this context that the corresponding step must follow the previously mentioned step, but not directly. It is possible that there are also one or more other steps present between the previously mentioned step and the following step.

[0130] Particular preference is given here to continuous methods in which the masterbatches or base mixtures, or else the crosslinkable rubber mixtures, are produced in one or more process steps using one or more extruders.

[0131] Very particular preference is given to the production method described in DE-A-102008040138 for crosslinkable rubber mixtures, where the base mixture is produced in at least one noncontinuous kneader process, and further crosslinking agents in the form of the crosslinker masterbatches described in EP-A-2314442 are added to the base mixture, and the crosslinker masterbatches are mixed with the base mixture in a continuous process by use of an extruder.

[0132] The invention moreover provides a method for the production of vulcanizates comprising the inventive production of crosslinkable rubber mixtures comprising silanized pale-colored fillers and subsequent vulcanization at a temperature in the range of 100° C. to 200° C.

[0133] The invention likewise also comprises the use of measurement devices for the determination of the ultrasound wave amplitude a, integrated ultrasound wave amplitude A and/or ultrasound wave intensity i, integrated ultrasound wave intensity I at one or more frequencies in a range of 4 to 10 MHz, preferably of 5 to 7 MHz, for the test method of the invention, for the method of the invention for production of rubber mixtures in general and specifically of crosslinkable rubber mixtures. This also preferably comprises the use of the measurement devices mentioned for the determination of the relative attenuation coefficient α.sub.rel in the abovementioned method.

[0134] The present invention therefore provides a silanization-checking method which allows in-line monitoring of the in-situ silanization of pale-colored fillers, in particular of precipitated silicas. The method of the invention permits low-cost production of rubber mixtures comprising silanized pale-colored fillers, because production can take place at high temperatures, in particular of above 160° C. The relative attenuation coefficient α.sub.rel of the rubber mixture, and also the standard deviation σ of the relative attenuation coefficient α.sub.rel, preferably the moving standard deviation σ.sub.g, serve for the detection of incipient crosslinking of the rubber mixture.

[0135] The method moreover is nondestructive and has high tolerance for carbon black as additional constituent of the rubber mixture.

[0136] The headings used in the description are intended merely to serve for subdivision, without any concomitant limiting effect.

[0137] The examples, images and figures below serve for illustration of the invention, without any concomitant limiting effect.

EXAMPLES

[0138] The components of a typical rubber mixture for tire treads were provided as in table 1:

TABLE-US-00001 TABLE 1 Formulation of a typical rubber mixture for tire treads Density Quantity Trade name Ingredients [g/cm.sup.3] [phr] Buna ® CB 24 Butadiene rubber Lanxess 0.91 15 Deutschland GmbH Buna ® VSL Solution styrene-butadiene Lanxess 0.95 116.9 5025-2 HM rubber Deutschland GmbH Corax ® N-234 Carbon black Orion Engineered 1.8 35 Carbons GmbH Ultrasil ® VN3 Silica Evonik Industries 2 55 AG ASM-TMQ Aging retarder Lanxess 1.1 3.0 2,2,4-trimethyl-1,2- Deutschland GmbH dihydroquinoline ASM-6PPD Aging retarder Lanxess 1 2.5 N-1,3-dimethylbutyl-N′- Deutschland GmbH phenyl-p-phenylenediamine Antilux ® 654 Aging retarder: Lanxess 0.9 2.0 mixture of selected paraffins Deutschland GmbH and microwaxes with moderate molecular-weight distribution Aflux ® 37 Mixture of surface-active Lanxess 0.98 2.0 substances with fatty acids Deutschland GmbH Stearic acid Peter Greven 0.89 1 GmbH & Co. KG Weiβsiegel Zinc oxide Norzinco GmbH 5.6 2 Si69 Bis(triethoxysilylpropyl) Evonik Industries 0.866 4.8 tetrasulfide AG

[0139] These components were mixed in various batches in accordance with the mixing specification in table 2.

TABLE-US-00002 TABLE 2 Mixing specification Time Mixture constituent Note   .sup. 0-0.75′ Polymers Ram down .sup. 0.75′-1′20″ Carbon black, silica + Ram up Si69 + ZnO 1′20″ -   .sup.  Ram off 2′ Aging retarder, stearic acid, Aflux ® 37 3.5′-4  Turn Ram up 4′-5′ Ram down 5′ Discharge

[0140] The mixing parameter rotation rate was varied in accordance with table 3 for the various batches R1M1 to R5M1. R1-R5 here are the various formulations, and M1 is mixing stage 1.

TABLE-US-00003 TABLE 3 Process parameters of the internal mixer for the in-situ silanization of a typical rubber mixture from table 1 Batch Mixing parameter R1M1 R2M1 R3M1 R4M1 R5M1 Fill level [%] 70 70 70 70 70 Rotation rate [rpm] 40 50 70 100 135 Initial temperature [° C.] 70 70 70 70 70 Mixing time [min.] 5 5 5 5 5 Discharge temperature T.sub.A [° C.] 120 135 150 165 180

[0141] The mixtures R1M1-R5M1 are mixed for 5 min in a 1.5 I (Intermesh) internal mixer from Gumix S.A.

[0142] Different values of the mixing temperature are achieved via the differences in rotation rate of the internal mixer. The discharge temperature T.sub.A, measured by a method known to the person skilled in the art with use of a needle thermometer directly after discharge of the rubber mixture from the internal mixer, is a measure of the mixing temperature in the internal mixer and therefore of the temperature at which the rubber mixture is produced.

[0143] Table 3 shows the discharge temperature T.sub.A of the rubber mixtures with identical composition as a function of the process parameters for the in-situ silanization. The discharge temperature T.sub.A of the mixtures R1M1 and R2M1 are significantly below 160° C. The discharge temperature of R3M1 is 150° C., and this is the reference rubber mixture. The mixtures R4M1 and R5M1 were produced at above 160° C.

[0144] The method corresponds to a typical method for in-situ silanization processes in the tire industry for the first mixing stage.

[0145] After the mixing process in the internal mixer, the mixture batches were roll-milled on a two-roll mill from Rubicon Gummitechnik und Maschinentechnik GmbH, with temperature-control to 50° C. (cut three times toward the left and three times toward the right), and drawn off to give a milled sheet of the mixture. Strips were cut from the milled sheet. These strips were fed to an EEK32.12L single-screw extruder from Rubicon Gummitechnik und Maschinentechnik GmbH with a low level of mixing action. At the outgoing end of the extruder there is a sensor head equipped with two opposite ultrasound transducers separated by 10 mm, and there is also a temperature sensor T1 with a probe projecting into the flowing mixture, and a pressure/temperature sensor. This temperature sensor measures the pressure p and the temperature T2 at the rubber-metal interface. The width of the flow channel in the sensor head is 20 mm, and its height is 10 mm. The diameter of the ultrasound transducers is 8 mm. Sensor head and extruder were controlled to a temperature of 100° C. The screw rotation rate was 20 rpm. This corresponds to a throughput of about 1 kg of rubber mixture for every 10 min.

[0146] The in-line silanization check was implemented by using a pair of K6V1 ultrasound transducers from GE Sensing & Inspection Technologies GmbH in transmission. The ultrasound transducers were controlled by PCM 100LAN test electronics from Inoson GmbH. The piezoelectric effect was used to generate the ultrasound pulses every 150 ms in the ultrasound transducer. 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: 6 MHz. The ultrasound pulse from the transmitter passes through the rubber mixture that is being extruded, and is attenuated here by the rubber mixture. The oscillation amplitude a of the ultrasound signal is reduced. The receiver receives the acoustic signal and converts it to a voltage signal. The voltage signal is amplified (35 to 40 dB) by the hardware of the PCM100LAN, and passed to a computer. The computer uses what is known as Fast Fourier Transformation (FFT) to evaluate the first acoustic pulse of the “A scan”. The amplitude spectrum a(f) thus obtained as a function of the ultrasound frequency f was integrated between 5.8 and 6.2 MHz (cf. table 4), and the logarithm was calculated. The values thus obtained, In A(f.sub.min.,f.sub.max.) for the logarithmic integral were plotted for the various mixture batches R1 M1 to R5M1 as a function of the time t for 7.5 min together with the values from the temperature sensors T1 and T2, and also the pressure values. The time t.sub.oF required by the acoustic signal for transmission from the piezo crystal of the emitter to the piezo crystal of the receiver was additionally determined. This is achieved before discharge of the mixture from the sensor head at the outgoing end of the extruder. The residence time of the mixture in the sensor head was less than 1 minute.

[0147] The relative attenuation coefficient α.sub.rel(f.sub.min.,f.sub.max.) is calculated from the values for In A(f.sub.min.,f.sub.max.) by the Lambert Beer law.

α.sub.rel(f.sub.min.,f.sub.max.)=(In A.sub.ref.(f.sub.min.,f.sub.max.)−In A(f.sub.min.,f.sub.max.)/x   (1d)

x here is the distance between the ultrasound transducers. In formula (1d), the average value of In A.sub.ref.(f.sub.min.,f.sub.max.) is 4.06 a.u. for the reference extrudate R3M1 (with a mixing temperature between 140° C. and 160° C.) for an extrusion time of Δt=7.5 min. The distance between the acoustic transducers was 10 mm.

[0148] The result for the frequency range f.sub.min.=5.8 MHz to f.sub.max.=6.2 MHz for each extrudate is depicted in images 1 to 5.

[0149] Table 4 presents the average values for the relative attenuation coefficient α.sub.rel(f.sub.min.,f.sub.max.) for a period of Δt=7.5 min for the extrusion of each mixture batch, corresponding to images 1 to 5. These average values were calculated in accordance with formula (1e). In each case, the average value of the standard deviation a of the relative attenuation coefficient α.sub.rel(f.sub.min.,f.sub.max.) for Δt=7.5 min was moreover determined in accordance with formula (1f).

[0150] Table 4 also states the moving standard deviation σ.sub.g over a period of 8 s. The moving standard deviation σ.sub.g is calculated in accordance with formula (1h) from the moving average of α.sub.rel, calculated in accordance with formula (1g).

[0151] Images 1 to 5 depict the moving value of the standard deviation σ.sub.g for each measurement point n at the juncture t(n) for a time interval comprising 51 measurement points (x=y=25) from t(n−25) to t(n+25). The letter n here indicates the number of the measurement point. The standard deviation σ.sub.g is determined by using 25 measured values before the juncture t(n), the measured value at the juncture t(n) and the 25 measured values after the juncture t(n). The phrase “moving value” means that the standard deviation σ.sub.g is determined for the following measurement point n+1 at the juncture t(n+1) in the time interval t(n−24) to t(n+26). The time interval composed of 51 measurement points for the determination of σ.sub.g is therefore shifted by one measurement point. The moving standard deviation σ.sub.g of α.sub.rel(f.sub.min.,f.sub.max.) in images 1 to 5 was determined within a time interval of 8 s.

[0152] The average value for the pressure sensor p and the average values for the temperature sensor T1 with probe and T2 without probe are additionally stated. The velocity of sound V.sub.S is determined from the distance x and the time t.sub.oF to the first voltage amplitude. It is necessary here to take into account the lead time t.sub.US=4.6 μs of the ultrasound signal in both ultrasound transducers in accordance with formula (2).

V.sub.S=x/(t.sub.oF−t.sub.US)   (2)

[0153] In addition to the characteristic ultrasound values, the Mooney ML1+4 (100° C.) viscosity was determined.

TABLE-US-00004 TABLE 4 Results of the measurements on the rubber mixtures during extrusion (measurement conditions and characteristic ultrasound values), and also on the extruded rubber mixtures (Mooney viscosity and RPA 2000) from table 3. The standard deviation from the average value is stated with “±” after the average value. Batch Unit R1M1 R2M1 R3M1 R4M1 R5M1 Standard process monitoring Mooney [MU] 106 101 99 97 112 ML1 + 4 (100° C.) viscosity RPA 2000 [kPa] 1145  1070  1032  941  876 G′(1%, 1 Hz, 60° C.) Measurement conditions Pressure p [bar] 72 ± 1 69 ± 1 68 ± 1 68 ± 1 74 ± 2 T1 [° C.] 95 ± 1 95 ± 1 95 ± 1 95 ± 1 95 ± 1 T2 [° C.] 104 ± 1  103 ± 1  103 ± 1  103 ± 1  103 ± 1  Characteristic ultrasound values V.sub.S [m/s] 1331 ± 1  1329 ± 1  1328 ± 1  1326 ± 2  1331 ± 2  Relative [1/m]  4 ± 1  1 ± 1  0 ± 1 −8 ± 1 −22 ± 3  attenuation coefficient α.sub.rel (5.8 MHz to 6.2 MHz) Moving [1/m]    0.2    0.1   0.2   0.1    1.3 standard deviation σ.sub.g of α.sub.rel for 8 s

[0154] Table 4 shows that for rubber mixtures the value of the dynamic storage modulus G′ (1%, 1 Hz, 60° C.) decreases with increasing discharge temperature T.sub.A (cf. table 3).

[0155] The Mooney ML1+4 (100° C.) viscosity values initially likewise decrease with increasing discharge temperature T.sub.A in accordance with progressive silanization of the silica surface. However, R5M1 exhibits a large increase of Mooney ML1+4 (100° C.) viscosity in comparison with R4M1 and R3M1. R4M1 and R3M1 have not yet undergone incipient crosslinking, whereas R5M1 has.

[0156] It is apparent in table 4, and also in images 1 to 5, that the acoustic attenuation coefficient α.sub.rel correspondingly decreases with increasing discharge temperature of the rubber mixtures. The values of the relative acoustic attenuation coefficient α.sub.rel correlate here with the storage modulus G′(1%, 1 Hz, 60° C.). The attenuation coefficient α.sub.rel resembles the storage modulus G′(1%, 1 Hz, 60° C.) in being a measure of the efficiency of silanization of the silica surface if the rubber mixtures R1M1 to R5M1 are established at comparable values for pressure and temperature during ultrasound measurement. As table 3 shows, this is the case.

[0157] The relative attenuation coefficient α.sub.rel of the extrudate R5M1 is significantly below 0 [1/m], with a value of −22 [1/m].

[0158] Another very significant difference of the extrudate R5M1, in comparison with R1M1 to R4M1, is the moving standard deviation σ.sub.g of the values for α.sub.rel in small time intervals of <15 s. The line relating to the values for ard of the extrudate R5M1 (image 5) fluctuates to a significantly greater extent than the lines relating to R1M1 to R4M1 (images 1 to 4). Accordingly, the average value of the moving standard deviation σ.sub.g of α.sub.rel for 8 s in table 4 for the extrudates R1M1 to R4M1 is small: 0.1 m.sup.−1 and, respectively, 0.2 m.sup.−1. The moving standard deviation σ.sub.g of α.sub.rel for 8 s for R5M1 with a discharge temperature T.sub.A of 180° C. is very large: 1.3 m.sup.−1. R5M1 has undergone incipient crosslinking; this correlates with the high Mooney ML1+4 (100° C.) viscosity of R5M1.

[0159] The standard deviation σ.sub.g of the relative attenuation coefficient α.sub.rel over the entire extrusion time of 7.5 min is 1 m.sup.−1 for the extrudates R1M1 to R4M1 and 3 m.sup.−1 for R5M1. However, with the long time interval of 7.5 min, the relative difference of the standard deviations σ between the extrudates R1M1 to R4M1 and R5M1 is significantly smaller than that of the moving standard deviations σ.sub.g. The reason for this is that over a prolonged time interval even small fluctuations in the measurement conditions and/or extrusion parameters make a contribution to the standard deviation, and the total standard deviation value therefore increases.

[0160] Detection of incipient crosslinking of a rubber mixture can accordingly preferably be defined by way of the moving standard deviation σ.sub.g of α.sub.rel over a period of 1 to 100 s, particularly preferably of 1 to 50 s, very particularly preferably of 1 to 15 s, in the present case 8 s.

[0161] The comparable values for the velocity of sound V.sub.S in all batches R1M1 to R5M1 proves that mixing temperature, pressure and composition of the mixture batches are uniform.