TYRE SEALANT LAYER

Abstract

A method to produce a compound for a tyre sealant layer, comprising a swelling step, during which a crumb rubber is immersed in a process oil chosen among the ones belonging to the families of paraffin process oils, naphthene process oils or natural process oils, so as to obtain a crumb rubber that swells due to the absorption of the process oil; and a following mixing step, during which said swollen crumb rubber is mixed with at least one polymer base consisting of an essentially saturated polymer.

Claims

1. A method to produce a compound for a tyre sealant layer; said method being characterized in that it comprises a swelling step, during which a crumb rubber is immersed in a process oil chosen among the ones belonging to the families of paraffin process oils, naphthene process oils or natural process oils, so as to obtain a crumb rubber that swells due to the absorption of said process oil; and a following mixing step, during which said swollen crumb rubber is mixed with at least one polymer base consisting of an essentially saturated polymer.

2. A method according to claim 1, characterized in that said process oil is chosen from TDAE and RAE.

3. A method according to claim 1, characterized in that said swollen crumb rubber makes up at least 5% by weight of the overall reinforcing filler of the compound for sealant layers; said overall reinforcing filler being available in the compound in a quantity ranging from 3 to 50 phr.

4. A method according to claim 3, characterized in that said swollen crumb rubber makes up at least 30% by weight of the overall reinforcing filler of the compound for sealant layers.

5. A method according to claim 1, characterized in that said swelling step is carried out at a temperature ranging from 50 to 200 C.

6. A method according to claim 1, characterized in that said crumb rubber has a size ranging from 40 to 200 mesh.

7. A method according to claim 1, characterized in that said polymer base consisting of an essentially saturated polymer is a halobutyl and/or butyl rubber.

8. A compound for tyre sealant layers obtained with the method according to claim 1.

9. A tyre sealant layer obtained with the compound according to claim 8.

10. A tyre comprising a sealant layer according to claim 9.

Description

BEST MODE FOR CARRYING OUT THE INVENTION

[0019] Some embodiment examples are given below for purely illustrative non-limiting purposes.

[0020] Three compounds for sealant layers were produced, the first two of which (A and B) are comparison examples while the third (C) is an example of the invention.

[0021] In particular, the comparison compound A represents a compound generally used to produce a sealant layer, while the compound of comparison B differs from compound A in that the carbon black has been completely replaced with crumb rubber not swollen with process oil.

[0022] The compound of the invention C differs from compound A in that the carbon black has been completely replaced with crumb rubber swollen with process oil according to the method of the present invention.

[0023] Table I shows the compositions in phr of the three compounds.

TABLE-US-00001 TABLE I A B C Br-IIR 100 Liquid p-butene 350 Carbon black 20 Non-swollen crumb rubber 20 Crumb rubber swollen with TDAE 20 Br-IIR stands for bromobutyl rubber.

[0024] The procedure both for the swelling step and the mixing step is described below.

[0025] Activation Step (Only for Compound C)

[0026] Non-swollen crumb rubber was kept immersed in TDAE oil at a temperature of 130 C. for 240 min. In this way swollen crumb rubber was obtained by absorption of the oil.

[0027] Mixing Step

[0028] The ingredients reported in Table I were mixed together and kept under stirring at a temperature of 100 C. for 10 min.

[0029] From each of the compounds produced as described above, a sealant layer was produced, which then underwent a pressure retention test following puncturing of the tyre on which it was applied. In particular, the pressure retention tests were performed both with the tyre at a standstill and with the tyre in rotation (20 Hz).

[0030] The test was performed on tyres on which a respective sealant layer produced with a respective compound A-C was applied, in the same conditions. Specifically, the sealant layer is extruded directly on the surface of the inner cavity of the tyre.

[0031] The tyres, after being inflated with the same internal pressure, were subjected to the same puncturing conditions with subsequent removal of the object used for the puncturing. For each of the tyres subjected to the test, pressure retention 24 h after puncturing (and subsequent removal of the object) was evaluated.

[0032] Table II shows the air retention evaluations expressed in a form indexed to the result obtained with the compound A both with the tyre at a standstill (static conditions) and with the tyre in rotation (20 Hz)(dynamic conditions). The higher the indexed value, the better the pressure retention.

TABLE-US-00002 TABLE II A B C Pressure retention in static conditions 100 105 120 Pressure retention in dynamic conditions 100 110 125

[0033] As can be seen from the results of Table II, the sealant layer produced with the compound subject of the present invention is able to guarantee a considerably higher pressure retention than that of the sealant layers produced with the comparison compounds in both static and dynamic conditions.

[0034] In particular, the comparison example B shows that it is not only the presence of crumb rubber that gives the sealant layer greater effectiveness, but that the crumb rubber must be used in its swollen form due to the absorption of process oil.

[0035] The inventors have ascertained that the swollen crumb rubber performs the function of releasing process oil at the point in which the sealant layer is subjected to a deformation, for example a puncturing action. In this way, the release of process oil locally improves the visco-elastic characteristics of the sealant layer allowing the same to improve the effectiveness of the sealing action.

[0036] In other words, the crumb rubber performs the function of support with localized release of a liquid adapted to improve the performance of the sealant layer in the event of puncturing of the tyre.

[0037] In said regard it is important to highlight the choice of the process oil as the liquid used to swell the crumb rubber and to be released by the latter as defined above. The process oil is an essential element of the present invention as it has characteristics such as to act as a plasticizer, to interact with the crumb rubber to be incorporated therein, not to react with the polymer base and to be stable at the tyre operating temperatures.

[0038] Lastly, it should be underlined that the present invention also offers an environmental advantage as it entails the use of a waste material (crumb rubber) which would otherwise constitute a source of pollution and would involve a cost for the disposal thereof.