SELF-SEALING TIRES

Abstract

The present disclosure relates to self-sealing tires, a process for making said self-sealing tires and the use of a silicone composition cured via a condensation cure chemistry to form a self-sealing layer designed to function as both (i) a self-sealing tire puncture material, i.e., to seal puncture holes in the tread region of tires if/when punctured by a foreign body and (ii) as an adhesive for sound-absorbing foams adapted to reduce the noise generated by tires during travel.

Claims

1. A self-sealing pneumatic tire comprising: an inner surface and an outer surface having a profiled tread; a self-sealing silicone layer applied on the inner surface; and a sound-absorbing layer adhesively attached to the inner surface by way of the self-sealing silicone layer; wherein the self-sealing silicone layer is applied before the sound-absorbing layer is adhered thereto; wherein the self-sealing silicone layer is cured from a silicone self-sealing composition, the composition comprising: (i) at least one condensation curable silyl terminated polymer having at least two hydroxyl functional groups per molecule; (ii) a cross-linker selected from the group consisting of: silanes having at least two hydrolysable groups, optionally at least three hydrolysable groups per molecule group; silyl functional molecules having at least two silyl groups, each silyl group containing at least two hydrolysable groups, optionally at least three hydrolysable groups; and combinations thereof; (iii) a condensation catalyst selected from the group consisting of titanates, zirconates and combinations thereof; and (iv) reinforcing and/or non-reinforcing filler(s); wherein components (iii) and (iv) are not stored together prior to use; wherein the molar ratio of total silicon bonded-hydroxyl groups to total hydrolysable groups is between 0.5:1 and 2:1 using a silane cross-linker or 0.5:1 to 10:1, using a silyl functional molecule cross-linker; wherein the titanates and zirconates comprise M-OR functions, where M is titanium or zirconium and R is an alkyl group or chelate group; and wherein the molar ratio of M-OR functions of the catalyst (iii) to the sum of moisture present in the filler(s) (iv), as determined in accordance with ISO 787-2:1981, and total silicon bonded hydroxyl groups is between 0.01:1 and 0.6:1.

2. The self-sealing pneumatic tire in accordance with claim 1, wherein the sound absorbing layer is a sound-absorbing foam.

3. The self-sealing pneumatic tire in accordance with claim 1, wherein the sound-absorbing layer is a closed cell foam, an open cell foam, or a combination of both, and is optionally viscoelastic.

4. The self-sealing pneumatic tire in accordance with claim 1, wherein the sound-absorbing layer is selected from the group consisting of a polyurethane foam, a polyester foam, a polyolefin foam, a silicone foam, a polyether foam, and combinations thereof.

5. The self-sealing pneumatic tire in accordance with any preceding claim 1, wherein filler(s) (iv) is selected from the group consisting of fumed silicas, precipitated silicas, calcium carbonate, carbon black, hollow glass beads, carbon nanotubes, and combinations thereof.

6. The self-sealing pneumatic tire in accordance with claim 5, wherein filler(s) (iv) comprises multiwall carbon nanotubes and/or carbon black.

7. The self-sealing pneumatic tire in accordance with claim 1, wherein the molar ratio of total silicon bonded hydroxyl groups to total hydrolysable groups in the silicone self-sealing composition is between 1:1 and 2:1.

8. The A-self-sealing pneumatic tire in accordance with claim 1, wherein prior to application, the silicone self-sealing composition is stored in two-parts, i) a base part comprising polymer (i) and filler (iv), and ii) a curing part comprising cross-linker (ii) and catalyst (iii).

9. The self-sealing pneumatic tire in accordance with claim 1, wherein the silicone self-sealing composition comprises an organopolysiloxane based polymer (i) having not less than two silicon-bonded hydroxyl or hydrolysable groups per molecule and a viscosity of from 30,000 mPa.Math.s to 200,000 mPa.Math.s at 23° C.; and wherein upon cure, the composition provides a self-adhering silicone-based product having an absolute tackiness of >1.025, where absolute tackiness=−[tackiness strength (F−)]/[hardness strength (F+)].

10. The self-sealing pneumatic tire in accordance with claim 1, wherein the polymer (i) of the silicone self-sealing composition additionally comprises polydiorganosiloxanes which have one silanol containing terminal group and one unreactive terminal group.

11. The self-sealing pneumatic tire in accordance with claim 1, wherein cross-linker (ii) of the silicone self-sealing composition additionally comprises silyl functional molecules having at least two silyl groups, where at least one silyl group contains one hydrolysable group.

12. The self-sealing pneumatic tire in accordance with claim 1 wherein the self-sealing silicone layer has a thickness of greater than 0.3 mm.

13. The A-self-sealing pneumatic tire in accordance with claim 1, wherein the self-sealing silicone layer has a thickness of between 0.5 mm and 10 mm.

14. A process for preparing a self-sealing pneumatic tire, the method comprising: (a) providing a pneumatic tire comprising an outer surface having a profiled tread and an inner surface; (b) applying a self-sealing silicone layer on the inner surface; and (c) applying a sound-absorbing layer to the inner surface by adhesion to the self-sealing silicone layer; wherein the self-sealing silicone layer is cured from a silicone self-sealing composition, the composition comprising: (i) at least one condensation curable silyl terminated polymer having at least two hydroxyl functional groups per molecule; (ii) a cross-linker selected from the group consisting of: silanes having at least two hydrolysable groups, optionally at least three hydrolysable groups per molecule group; silyl functional molecules having at least two silyl groups, each silyl group containing at least two hydrolysable groups, optionally at least three hydrolysable groups; and combinations thereof; (iii) a condensation catalyst selected from the group consisting of titanates, zirconates and combinations thereof; and (iv) reinforcing and/or non-reinforcing filler(s); wherein components (iii) and (iv) are not stored together prior to use; wherein the molar ratio of total silicon bonded-hydroxyl groups to total hydrolysable groups is between 0.5:1 and 2:1 using a silane cross-linker or 0.5:1 to 10:1 using a silyl functional molecule cross-linker; wherein the titanates and zirconates comprise M-OR functions, where M is titanium or zirconium and R is an alkyl group or chelate group; and wherein the molar ratio of M-OR functions of the catalyst (iii) to the sum of moisture present in the filler(s) (iv), as determined in accordance with ISO 787-2:1981, and total silicon bonded hydroxyl groups is between 0.01:1 and 0.6:1.

15. The process for preparing a self-sealing pneumatic tire in accordance with claim 14, wherein the tire is vulcanized prior to application of the silicone self-sealing composition on to the inner surface.

16. The process for preparing a self-sealing pneumatic tire in accordance with claim 14, wherein the self-sealing silicone layer is cured prior to application of the sound-absorbing layer.

17. (canceled)

Description

EXAMPLES

[0137] Comparative Examples Taken from WO2018024857

All viscosity measurements were made Brookfield cone plate viscometer RV DIII using the most appropriate cone plate at 23° C. unless otherwise indicated.

[0138] For the benefit of the examples the following commercially available tires were purchased and utilized for the comparative examples: [0139] Bridgestone® Turanza ER300 205/55/16 91H, [0140] Continental® Conti Premium Contact 5 205/55/16 91W, [0141] Goodyear® Efficient Grip 205/55/16 91H, [0142] Michelin® Energy Saver 205/55/16 91V, and [0143] Pirelli® Cinturato P7 205/55/16 91V.

Preparation of Comparative Base A

[0144] 73.01 g of Nanocyl® NC 7000 carbon nanotubes, 3544.2 g of OH terminated polydimethylsiloxane exhibiting a viscosity of ca 50,000 mPa.Math.s and a number average molecular weight (Mn) of 63,000 g/mol and 382.8 g of Trimethoxysilyl terminated polydimethylsiloxane exhibiting a viscosity of ca 56,000 mPa.Math.s and an number average molecular weight (Mn) of 62,000 g/mol were added in a Neulinger 5 liter mixer. They were initially mixed for 2 minutes using a planetary mixer at 50 rpm, then for a further 15 minutes using the planetary mixer at 50 rpm and the disk at 700 rpm and finally for a further 30 minutes using the planetary mixer at 100 rpm and the disk at 700 rpm. The resulting base product was then unloaded into a pail.

Preparation of Base B

[0145] 1500 g of Evonik Printex A carbon black, 8825 g of OH terminated polydimethylsiloxane exhibiting a viscosity of ca 50,000 mPa.Math.s and an number average molecular weight (Mn) of 63,000 g/mol and 973 g of Trimethoxysilyl terminated polydimethylsiloxane exhibiting a viscosity of ca 56,000 mPa.Math.s and an number average molecular weight (Mn) of 62,000 g/mol were added in a 20 liter pail and was mixed 60 minutes with a Collomix Biax pail mixer.

Preparation of the Mixtures

Comparative Example 1

[0146] 24.87 g of Trimethoxysilyl terminated polydimethylsiloxane having a viscosity of ca 56,000 mPa.Math.s and an number average molecular weight (Mn) of 62,000 g/mol and 0.133 g of tetra n-butyl titanate were mixed together with a dental mixer at 2300 rpm for 30 seconds. 250 g of base A was introduced into a plastic container. The pre-mixture of trimethoxysilyl terminated polydimethylsiloxane (viscosity, 56,000 mPa.Math.s) and tetra n-butyl titanate was added into the container and mixed for four periods of 30 seconds in a speed-mixer at 2300 rpm.

Comparative Example 2

[0147] 28.85 g of Trimethoxysilyl terminated polydimethylsiloxane having a viscosity of ca 56,000 mPa.Math.s and an number average molecular weight (Mn) of 62,000 g/mol and 0.155 g of tetra n-butyl titanate were mixed together with a dental mixer at 2300 rpm for 30 seconds. 290 g of base 2 was introduced into a plastic container. The pre-mixture of trimethoxysilyl terminated polydimethylsiloxane (viscosity, 56,000 mPa.Math.s) and tetra n-butyl titanate was added into the container and mixed for four periods of 30 seconds in a speed-mixer at 2300 rpm.

[0148] Tabulated details of the compositions of Comparative examples 1 and 2 tested are provided in Table 1. The results of the test on the tires as run below are depicted in Tables 2a-c.

TABLE-US-00001 TABLE 1 Compositions Comp. Comp. Weight parts Ex. 1 Ex. 2 Part 1-Base OH terminated polydimethylsiloxane 100 100 (viscosity ca 50,000 mPa .Math. s) Nanocyl ® NC 7000 carbon nanotubes 2.06 Printex ® A carbon black 17 Trimethoxysilyl terminated polydimethylsiloxane 10.8 10.8 (viscosity ca 56,000 mPa .Math. s) Part 2-Crosslinker and catalyst Trimethoxysilyl terminated polydimethylsiloxane 11.2 11.2 (viscosity ca 56,000 mPa .Math. s) tetra n-butyl titanate 0.06 0.06 SiOH/SiOR mol content 1.46 1.37 Xlinker content (mmol/100 g) 0.29 0.26

Evaluation of Hardness and Storage Modulus

[0149] A TA XT plus texture analyzer was used to monitor the hardness of the cured elastomer. The probe used is a polycarbonate cylinder terminated by a spherical end. The diameter of the probe and sphere is ½ inch (1.27 cm). A return to start program was used. The pre-test speed is 5 mm/s and the trigger force is 0.1 g. The test speed is 1 mm/s. the probe is inserted to a distance of 5 mm in the product and then removed to a distance where no significant force is measured. The maximum positive and negative force is measured and reported here. A higher positive force is representative of a harder elastomer. A higher negative force is representative of a tackier elastomer.

Evaluation of Sealing Efficiency

[0150] Holes of 3 mm diameter were cut on the rolling band of the tires with the help of a press and a cutting cylinder. The resulting product of Comparative examples 1 and 2 were respectively filled into 310 ml cartridges and applied onto the inside of the tires and smoothed with a ruler at the designed thickness.

[0151] The products of Comparative examples 1 and 2 were applied at the desired thickness to cover 3 holes in the tire without filling them. After 7 days of cure at 23° C. and 50% relative humidity the tires were mounted on wheels and pressurized at 1 bar (0.1 MPa). Nails of 5 mm diameter were pushed in the 3 mm holes to a distance of 40 mm inside the tire. The pressure was then increased to 2.7 bars (0.27 MPa) and the holes were removed from the tire.

[0152] In the following hours and days the leaking holes were filled with string repair plugs without cement, until no more leaks were observed, using optionally water to track leaks. The tires were kept for two weeks after repair. Results after 14 days without a loss of more than 0.1 bar (0.01 MPa) are reported in tables 2a and b. A 3/3 means that no leakage was observed on any of the 3 holes. 0/3 means that all three holes had to be repaired since they leaked.

TABLE-US-00002 TABLE 2a Tire (5 mm thick coating)-Tightness of punctures after 2 weeks at 2.7 bars (0.27 MPa) Comp. Comp. Ex. 1 Ex. 2 Bridgestone ® Turanza ER300 205/55/16 91H 3/3 3/3 Continental ® Conti Premium Contact 5 3/3 3/3 205/55/16 91W Goodyear ® Efficient Grip 205/55/16 91H 3/3 3/3 Michelin ® Energy Saver 205/55/16 91V 3/3 3/3 Pirelli ® Cinturato P7 205/55/16 91V 3/3 3/3

TABLE-US-00003 TABLE 2b Tire (3 mm thick coating)-Tightness of punctures after 2 weeks at 2.7 bars (0.27 MPa) Comp. Comp. Ex. 1 Ex. 2 Bridgestone ® Turanza ER300 205/55/16 91H 2/3 3/3 Continental ® Conti Premium Contact 3/3 3/3 5 205/55/16 91W Goodyear ® Efficient Grip 205/55/16 91H 3/3 3/3 Michelin ® Energy Saver 205/55/16 91V 3/3 0/3 Pirelli ® Cinturato P7 205/55/16 91V 2/3 3/3

[0153] Comp. Examples 1 and 2 is showing excellent results for tightness, this shows that an appropriate crosslink density is required to obtain a product that will seal tires.

TABLE-US-00004 TABLE 2c Texture Analyser results and Absolute Tackiness Comp. Ex. 1 Comp. Ex. 2 F+ (g) 210 217 F− (g) 100 93 Absolute Tackiness 0.48 0.45

[0154] Texture analyzer results of the examples indicate that a compromise in hardness and tackiness must be achieved for an appropriate performance in the tire. Comp. Example 1 and 2 exhibit an appropriate balance of hardness and tackiness to close the gap caused by the nail without exhibiting creep, however they have a low absolute tackiness and as such may suffer from tackiness issues with some foreign bodies and self-sealing punctures. However, it will be seen that each of the compositions used above had an absolute tackiness of less than (<) 0.5 which is significantly less than those used herein.

Process for making Example 1

Part A

[0155] 80 kg of the following mixture was prepared. About 100 parts by weight of a silanol terminated polydimethylsiloxane having a number average molecular weight of about 60,000 g/mol and a viscosity of about 50,000 mPa.Math.s at 23° C. was mixed with about 3 parts by weight of trimethoxysilyl terminated polydimethylsiloxane having a number average molecular weight of about 63,000 g/mol with a viscosity of 56,000 mPa.Math.s at 23° C. and 17 part by weight of carbon black (Printex A) in a Drais mixer for about 15 minutes. The material was packaged in pails and then mixed 2×60 min in a collomix mixer.

Part B

[0156] 18 kg of the following mixture was prepared. About 100 parts by weight of trimethoxysilyl terminated polydimethylsiloxane having an average molecular weight in number of about 63,000 and a viscosity of 56,000 mPa.Math.s at 23° C. was mixed with 0.53 parts by weight of tetra n-butoxy titanium in a collomix.

[0157] Part A and Part B were mixed at a ratio of 10:1 in weight using a Rheinhardt dispensing equipment and applied on tires.

[0158] A Bridgestone® Ecopia 205/55 R16 91V was pre-cut with 10 holes of about 3 mm diameter in the rim of the rolling band of the tire. It was coated inside with a silicone sealant on the rolling band at a thickness of about 5 mm in average without filling the precut holes. On about half of the circumference of the tire a closed cell polyurethane foam was applied on the uncured silicone sealant.

[0159] After 28 days of cure, the foam cannot be removed from the tire. There is excellent adhesion of the foam on the tire. The only way to remove the foam is to crack the silicone layer.

[0160] After mounting the tire on a wheel, 20 nails of about 5 mm diameter were inserted in the tire inflated at about 2.7 bars. 10 nails in the sealant layer only and 10 nails in the sealant layer where the foam was applied. Half of each series of nail have been inserted in the precut holes and half of the series in the tire at various other locations in the rolling band.

[0161] No leakage has been observed at that point. Then all 20 nails have been removed for the tire. It was inspected for gas leakage over a period of 2 weeks. When leakage was observed for a period of more than a few minutes, the hole was repaired and then inspected again and left for 2 weeks after the last repair. The following results have been obtained:

TABLE-US-00005 Number of holes not repaired/number of nails inserted Precut holes of 3 mm Other locations Silicone sealant 4/5 5/5 Silicone sealant + foam 3/5 4/5

[0162] The results from the above table are showing that the self-sealing silicone layer is closing most of the punctures with the nails whether or not the foam is present. Hence, using the self-sealing silicone layer as an adhesive for the sound-absorbing layer does surprisingly not negatively affect the function of said layer to self-seal the tire.