SILICONE-BASED PRODUCTS AND THEIR APPLICATIONS

Abstract

There is provided silicone based materials with enhanced tackiness upon cure. These may be used for cured self-adhering silicone-based products such as pressure sensitive adhesives, self-adhering materials and/or self-sealing materials, made from condensation curable silicone-based compositions, the compositions therefor and to applications for which said self-adhesive products may be used. In one particular application the cured silicone based material may be utilised as a self-sealing layer in an inflatable article such as a pneumatic tire.

Claims

1. A condensation curable silicone-based composition comprising: (i) an organopolysiloxane based polymer 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.; (ii) a cross-linker comprising a silyl functional polymer having at least two silyl groups, each silyl group containing at least two hydrolysable groups; and (iii) a condensation catalyst selected from the group consisting of titanates, zirconates, and combinations thereof; and optionally (iv) one or more reinforcing or non-reinforcing filler(s); 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+)].

2. The condensation curable silicone-based composition in accordance with claim 1, wherein filler(s) (iv) is present and selected from the group consisting of fumed silicas, precipitated silicas, calcium carbonate, carbon black, hollow glass beads, carbon nanotubes, and combinations thereof.

3. The condensation curable silicone-based composition in accordance with claim 2, wherein filler(s) (iv) comprises multiwall carbon nanotubes and/or carbon black.

4. The condensation curable silicone-based composition in accordance with claim 1, wherein the molar ratio of total silicon bonded hydroxyl groups to total hydrolysable groups is >2:1.

5. The condensation curable silicone-based composition in accordance with claim 1, wherein the composition is stored in two-parts, i) a base part comprising polymer (i) and fillers (iv), when present, and ii) a curing part comprising cross-linker (ii) and catalyst (iii).

6. The condensation curable silicone-based composition in accordance with claim 1, wherein polymer (i) additionally comprises polydiorganosiloxanes which have one silanol containing terminal group and one unreactive terminal group.

7. The condensation curable silicone-based composition in accordance with claim 1, wherein cross-linker (ii) additionally comprises silyl functional molecules having at least two silyl groups, where at least one silyl group contains one hydrolysable group.

8. A condensation cured self-adhering silicone-based product obtained from the condensation curable silicone-based composition in accordance with claim 1.

9. The condensation cured self-adhering silicone-based product in accordance with claim 8, wherein the product is a pressure sensitive adhesive, a self-adhering material, and/or a self-sealing material.

10. The condensation cured self-adhering silicone-based product in accordance with claim 8, as a puncture self-sealing layer in an inflatable article.

11. The condensation cured self-adhering silicone-based product in accordance with claim 10, wherein the inflatable article is a self-sealing pneumatic tire.

12. The condensation cured self-adhering silicone-based product in accordance with claim 11, wherein the self-sealing pneumatic tire comprises: a) a tire body having an outer tread surface and an inner surface; and b) a puncture self-sealing layer of the condensation cured self-adhering silicone-based product adhered to the inner surface.

13. The condensation cured self-adhering silicone-based product in accordance with claim 12, wherein the puncture self-sealing layer has a thickness of greater than 0.3 mm.

14. The condensation cured self-adhering silicone-based product in accordance with claim 12, wherein the puncture self-sealing layer has a thickness of between 0.5 mm and 10 mm.

15. An inflatable article comprising the condensation cured self-adhering silicone-based product in accordance with claim 8.

16. The inflatable article in accordance with claim 15, which is a self-sealing pneumatic tire.

17. An inflatable article comprising: an outer surface and an inner surface; and a self-sealing silicone layer applied on the inner surface; wherein the self-sealing silicone layer is cured from the silicone self-sealing composition in accordance with claim 1.

18. The inflatable article in accordance with claim 17, which is a pneumatic tire.

Description

EXAMPLES

Comparative Examples 1 and 2 Taken from WO2018024857

COMPARATIVE EXAMPLES

[0101] All viscosity measurements were made Brookfield cone plate viscometer RV DIII using the most appropriate cone plate at 23° C. unless otherwise indicated.

[0102] For the benefit of the examples the following commercially available tires were purchased and utilized for the comparative examples: [0103] Bridgestone® Turanza ER300 205/55/16 91H, [0104] Continental® Conti Premium Contact 5 205/55/16 91W, [0105] Goodyear® Efficient Grip 205/55/16 91H, [0106] Michelin® Energy Saver 205/55/16 91V, and [0107] Pirelli® Cinturato P7 205/55/16 91V.
Preparation of Comparative base A

[0108] 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 an 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

[0109] 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

[0110] 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

[0111] 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.

[0112] 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 (viscosity 100 100 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 Cross-linker content (mmol/100 g) 0.29 0.26

Evaluation of Hardness and Storage Modulus

[0113] 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

[0114] 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 Example 1, 2 and 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.

[0115] The products of Example 1, 2 and 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.

[0116] 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 table 2. A 3/3 means that no leakage were 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. Ex. 1 Comp. Ex. 2 Bridgestone 3/3 3/3 Continental 3/3 3/3 Goodyear 3/3 3/3 Michelin 3/3 3/3 Pirelli 3/3 3/3

[0117] 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-00003 TABLE 2b Tire (3 mm thick coating)- Tightness of punctures after 2 weeks at 2.7 bars (0.27 MPa) Comp. Ex. 1 Comp. Ex. 2 Bridgestone 2/3 3/3 Continental 3/3 3/3 Goodyear 3/3 3/3 Michelin 3/3 0/3 Pirelli 2/3 3/3

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

[0118] 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 <0.5 which is significantly less than those used herein.

Examples and Comparative Example 3 and 4

Preparation of the Bases

[0119] The base compositions for the five compositions assessed were prepared using 260.87 g of OH terminated polydimethyl siloxane exhibiting a viscosity at room temperature as indicated in Table 3 below was mixed with 39.13 g of Printex A type carbon black from Orion using a speedmixer for 4 times 30 seconds at a speed of 2300 rpm. During each mixing a spatula was used to homogenize the mixture.

TABLE-US-00005 TABLE 3 Viscosities of polymers used in Mixtures A to E Viscosity of polymer (mPa .Math. s) Mixtures at 23° C. Method of determination of Viscosity A 13,500 Brookfield cone plate viscometer RV DIII using a cone plate CP-52 at 5 rpm B 50,000 Brookfield cone plate viscometer RV DIII using a cone plate CP-51 at 0.5 rpm C 80,000 Brookfield cone plate viscometer HBDVIII, Spindle CP-52 @ 5 RPM D 150,000 Brookfield cone plate viscometer HB DVIII, Spindle CP-52 @ 1 RPM E 330,000 Brookfield cone plate viscometer HB DVIII, Spindle CP-52 @ 1 RPM

Preparation of the Curing Agent

[0120] 313.04 g of Trimethoxysilyl terminated polydimethylsiloxane having a viscosity of ca 56,000 mPa at 23° C. (Brookfield cone plate viscometer RV DIII using a cone plate CP-52 at 3 rpm) was mixed with 1.25 g tetra n butoxy titanium using a speedmixer for 4 times 30 seconds at a speed of 2300 rpm.

Preparation of the Mixtures

[0121] 300 g of the base prepared as described here above were mixed with 26.09 g of curing agent mixed for 4 times 30 seconds at a speed of 2300 rpm. During each mixing a spatula was used to homogenize the mixture. The mixed compound was then mixed for 4 times 30 seconds at a speed of 2300 rpm. During each mixing a spatula was used to homogenize the mixture. The mixture was introduced in a 310 ml cartridge and dispensed in excess in an aluminum cup of 50 mm diameter and 15 mm height. The product was tooled with a metallic plate to make a flat surface and then allowed to cure at room temperature for 28 days.

Results

[0122] A Stable Micro Systems 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 Stable Micro Systems TA XT+ with a ½ inch (1.27 cm) hemisphere probe made of polycarbonate set to penetrate a sample 5 mm at a speed of 0.1 mm/s. in the product and then removed to a distance where no significant force is measured. The maximum positive [F+] and negative [F−] 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. However, as the probe must penetrate 5 mm inside the product a harder material is also inducing a harder pressure on the probe and generally increase the negative force measured. In order to determine the absolute tackiness, the ratio of both values was calculated as follows:

Absolute tackiness=−[F-]/[F+]

TABLE-US-00006 TABLE 4 Results A E Comparative B C D Comparative Unit Example Example Example Example Example Polymer mPa .Math. s 13,500 50,000 80,000 150,000 330,000 viscosity [F+] g 50 81 96 110 169 [F−] g −39 −96 −141 −124 −172 Absolute none 0.78 1.19 1.47 1.13 1.017 tackiness

[0123] A ratio above 1 is characteristic of a material that exhibit a higher tackiness strength [F−] than the hardness strength [F+]. Mixture B, C and D are showing a ratio above 1, which means their absolute tackiness is higher than mixture A and E. In order to maximize absolute tackiness, it is preferable to use a polymer that exhibits a viscosity comprised in between 13,500 and 330,000 mPa.Math.s in viscosity and more preferably in between 50,000 and 150,000 mPa.Math.s.

[0124] A ratio above 1:1, alternatively above 1.025:1 is characteristic of a material that exhibit a higher tackiness strength [F−] than the hardness strength [F+]. Mixture B, C and D are showing absolute tackiness values above 1.025, which means their absolute tackiness is higher than mixture A and E. In order to maximize the absolute tackiness, it is therefore preferable to use a polymer that exhibits a viscosity comprised in between 13,500 and 330,000 mPa.Math.s in viscosity and more preferably in between 50,000 and 150,000 mPa.Math.s.