The present invention relates to a polymer coating for tyres. More specifically, the present invention relates to a polymer coating that can be used as a tyre repair mix, to which the following description refers purely by way of example.

BACKGROUND ART

Tyre repair mixes are normally produced in Banbury mixers, which involves at least two mixing steps : a longer, high-temperature first mixing step to produce the main mix, and in which ingredients such as carbon black, silica, a silane bonding agent, zinc oxide, stearic acid, wax, antioxidants, etc. are added and mixed with the polymer base; and a cooler second mixing step to complete the main mix, and in which curing agents, such as sulphur and accelerating agents are added to the mix from the first step. This is necessary to ensure dispersion of the curing agents at a temperature that does not cause premature curing of the mix. The resulting mix is then extruded into the required shape.

Though effective, repair mixes of the type described have the drawbacks of being energy-intensive to produce, and having to be stored prior to use.

That is, because of the way they are prepared, these mixes must be stored for more or less long periods of time before they are actually used, which therefore calls for storage management and facilities, and may also impair the characteristics and jeopardize use of the mix.

The Applicant has surprisingly discovered a polymer coating made from a water emulsion, and which may also be used as a repair mix.

DISCLOSURE OF INVENTION

According to the present invention, there is provided a polymer coating for tyres, made from a water emulsion comprising at least a cross-linkable polymer base, curing agents, and a surface-active agent of molecular formula (I)

(R₁CONR₂CHR₃COO^âˆ’)n Xⁿ⁺â€ƒâ€ƒ(I)

where:

R₁is an aliphatic group C₆-C₂₃,

R₂is H or an aliphatic group C₁-C₈,

R₃is H or an aliphatic or aromatic group C₁-C₈,

X is a metal cation, preferably an alkaline cation, and

n is an integer of 1 to 3.

The aliphatic group R₁preferably comprises a double bond.

The surface-active agent preferably has a molecular formula in the group comprising:

CH₃(CH₂)₇CHCH(CH₂)₇CONHCH₂COO^âˆ’X⁺, and

CH₂CH(CH₂)₈CONHCH₂COO^âˆ’ X^+.

Preferably, X⁺ is Na⁺.

The following are purely non-limiting examples for a clear understanding of the invention.

EXAMPLES

In the following examples, two surface-active agents (a, b) in the class according to the present invention were used:

- a surface-active agent (a) of molecular formula CH₃(CH₂)₇CHCH (CH₂)₇CONHCH₂COO^âˆ’ Na⁺;
- a surface-active agent (b) of molecular formula CH₂CH(CH₂)₈CONHCH₂COO^âˆ’ Na⁺.

Emulsions A and B

Two water emulsions (A and B), using respective surface-active agents (a) and (b) of molecular formula (I), were prepared.

Table I shows the compositions in phr of the water emulsion ingredients.

TABLE IABPOLYMER BASE100CARBON BLACK40ZnO2S2ACCELERATING AGENT2SURFACE-ACTIVE AGENT (a)2â€”SURFACE-ACTIVE AGENT (b)â€”2

The polymer base was S-SBR; the carbon black was N660; and the accelerating agent was TBBS.

The emulsions were produced by dispersing all the ingredients in Table I simultaneously in 1 litre of water. The resulting aqueous solution was stirred mechanically for 30 minutes, and then sonicated for 15 minutes to obtain a water emulsion.

The above method of producing the water emulsions is in no way to be inferred as a limiting aspect of the present invention.

Laboratory Testing

The water emulsions produced as described above were sprayed or brushed onto a surface, and the mixes obtained following evaporation of the water were test cured at different temperatures. More specifically, the rheometric properties of each mix were tested as per ISO Standard 6502.

Table II shows the rheometric property results. Quantities MH and ML are expressed in dNm, and T10 and T90 in minutes. The curing tests were performed at temperatures of 145Â° C., 160Â° C., 175Â° C. and 195Â° C.

TABLE IIA₁B₁145Â° C.ML2.021.95MH21.0620.96T1013.2814.6T9024.2125.45160Â° C.ML1.761.72MH21.3520.83T104.524.96T9011.1211.27175Â° C.ML1.511.52MH21.3820.73T101.541.8T905.445.69195Â° C.ML1.41.37MH20.6120.13T100.540.6T902.142.25

As anyone skilled in the art can see from the results in Table II, the rheometric and physical characteristics of the mixes made from the water emulsions according to the present invention in no way differ from those of conventional repair mixes, thus ensuring an effective repair coat. Moreover, the mixes made from the water emulsions according to the present invention can be cured rapidly, which is a major advantage when using the mixes on an already cured substrate.

Another important point to note is that, using the water emulsions according to the present invention, very thin coats can be formed, by spraying or brushing on the water emulsion and allowing the water to evaporate, to repair tyres with no increase in tyre weight.

Emulsions C, D and E

Another three emulsions were produced, all containing the ingredients of emulsion A, but differing from the latter as regards the content of carbon black. Testing the mixes with different carbon black concentrations is necessary to determine performance of the polymer coatings according to the present invention when applied to different tyre parts with different mechanical characteristics.

Table III shows the compositions in phr of the water emulsion ingredients.

TABLE IIICDEPOLYMER BASE100CARBON BLACK102030ZnO2S2ACCELERATING AGENT2SURFACE-ACTIVE AGENT (a)2

The characteristics of the ingredients are as shown in Table I.

Laboratory Testing

The water emulsions so formed were sprayed or brushed onto a surface, the rheometric properties of the mixes obtained following evaporation of the water were tested as per ISO Standard 6502 at a temperature of 160Â° C., and the physical properties (extensibility EB, ultimate tensile stress TB, modulus M %) were tested as per ISO Standard 37.

The results are shown in Table IV.

TABLE IVCDETB (MPa)5.88.318.1M25% (MPa)0.310.480.64M50% (MPa)0.490.660.95M100% (MPa)0.770.891.49M200% (MPa)1.151.212.72M300% (MPa)1.541.584.43M400% (MPa)2.062.096.53M500% (MPa)2.882.948.84EB (%)660760880ML (dN)1.761.882.17MH (dN)6.323.417.6T10 (min)0.150.140.13T50 (min)0.740.660.86T90 (min)1.91.952.98

The results in Table IV confirm those in Table II. In this case, too, the rheometric and physical characteristics of the mixes made from water emulsions C, D and E correspond with those of conventional mixes.

The major advantage of the present invention lies in enabling unscheduled, low-energy production of polymer coatings for tyre repair or embellishment. The polymer coatings according to the present invention therefore eliminate mix storage problems, and greatly reduce energy consumption as a whole, thus also reducing CO₂emissions.

The coatings according to the present invention also enable very thin coats of polymer material to be applied, with no impairment in effectiveness, unlike the extrusion process to which known mixes are subjected, which is unable to form overly thin layers for the technical reasons known to anyone skilled in the art.

Finally, using water emulsions, polymer layers can be applied (sprayed or brushed on) much more easily and effectively than known polymer layers.