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 at least one rubber to form en 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 .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 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.

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

5. 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 more than 5 mm, preferably in the range from 10 mm to 25 mm, more preferably from 15 to 20 nm.

6. The method as claimed in claim 1, wherein: the rubber mixture comprises 50 to 250 phr of the light-colored filler, preferably 60 to 150 and more preferably 70 to 100 phr; and the light-colored filler comprises mineral natural and synthetic fillers that are not based on carbon black.

7. 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.

8. 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.

9. The method as claimed in claim 8, wherein the silanization is effected at a temperature of 140 to 160 C.

10. The method as claimed in claim 8, wherein the process is conducted continuously or as a batchwise process, preferably continuously.

11. The method as claimed in claim 8, wherein the silanizing agent comprises a silane, preferably bis(3-triethoxysilypropyl) tetrasulfide.

12. 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 8, and adding one or more crosslinking agents before, during, and/or after the production of the rubber mixture.

13. A method of producing vulcanizates comprising the crosslinkable rubber mixtures produced in accordance with the method as claimed in claim 12, the method comprising vulcanizing the crosslinkable rubber mixture at a temperature of 100 C. to 200 C.

14. 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, preferably from 5 to 7 MHz, for a method as claimed in claim 1.

15. The use of measurement devices as claimed in claim 14, wherein the attenuation coefficient is determined in the region of the frequency of the ultrasound waves.

16. 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, and the rubber mixture comprises 50 to 250 phr of the light-colored filler.

17. The method as claimed in claim 16, 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.

18. The method as claimed in claim 17, 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 agonizing 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 In 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 .sub.rel and using the standard deviation to monitor the dispersion of the light-colored filler in the extrudate.

19. The method of producing rubber mixtures according to claim 8, wherein more than 10% by volume of the rubber mixture is tested.

20. The method of producing rubber mixtures according to claim 8, wherein 100% by volume of the rubber mixture is tested.

Description

EXAMPLES

[0103] The components of a typical rubber mixture for tire treads according to table 1 were provided.

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

[0104] These components were mixed according to the mixing method in table 2 in various batches.

TABLE-US-00002 TABLE 2 Mixing method Time Mixture constituent Comment .sup.0-0.75 Polymers 0.75-120 Silica + Si69 + ZnO Ram up 120 Ram down 2 Aging stabilizers + stearic acid 3.5 invert 5 Ejection

[0105] In the case of batches R1M1 to R5M2, the mixing parameters of speed and feed temperature were varied according to table 3.

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

[0106] 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.

[0107] 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) 140C. 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.

[0108] 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. 3 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.

[0109] The values for ln A(f.sub.min,f.sub.max) are used to calculate the relative attenuation coefficient .sub.rel (f.sub.max,f.sub.min) by the Beer-Lambert law.

.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)

[0110] 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 t=5 min. Table 4 shows the mean values for the relative attenuation coefficient .sub.rel(f.sub.min,f.sub.max) for a period of time from t=4 min to t=8 min, for the extrusion for each mixture batch. In addition, the standard deviation of the relative attenuation coefficients .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 s is of the ultrasound signal within the inlet of the ultrasound transducer according to eq. (2).

V.sub.S=x/(t.sub.oFt.sub.US) (2)

[0111] In addition to the ultrasound indices, the Mooney viscosity ML1+4 (100 C.) was determined as a nonrepresentative offline standard quality control.

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 [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. .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

[0112] It can be seen in table 4 that the values for the relative sound attenuation rel, over and above 4 MHz for the batch R1M1 are significantly less than the values for batches R2D1, R3M1 and R4M1 (FIG. 6). The ejection temperature TA of the batch R1M1 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 of the values for the relative sound attenuation coefficient .sub.rel(f.sub.min,f.sub.max) is comparatively low, and so no clear conclusion is possible.

[0113] The low values for R1M1 and for R5M2 compared to R3M1 and R4M1 cannot be attributed to improved dispersion of the filler (here: the silica), as described in A. Schrder, L. Grff, 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 R1 M1 and R5M2 (in FIG. 1 and FIG. 5) 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 R1M1 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 .sub.rel(f.sub.min,f.sub.max) can only be explained by a chemical reaction of the silica surface with the silane.

[0114] Moreover, there is a further drop in the relative sound attenuation coefficient .sub.rel(f.sub.min,f.sub.max) when the silanization is completed in accordance with the standard method a in a second mixing step (comparison of R1M1 and R5M2). The values for the relative sound attenuation coefficient .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. 7). 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 coefficient .sub.rel(f.sub.min,f.sub.max).