CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Italian Patent Application No. 102017000103274 filed on 15/09/2017, the disclosure of which is incorporated by reference.

TECHNICAL FIELD

The present invention relates to a compound for the preparation of a tread with a porous surface.

BACKGROUND ART

Historically, in order to ensure the traction of the pneumatic tyre on snow or ice (in winter conditions) , the tread in question is equipped with gripping elements, such as studs.

This solution, notwithstanding whether it is capable of ensuring the traction of the pneumatic tyre in winter conditions, nevertheless turns out to be disadvantageous under conditions other than those of winter, thereby forcing the user to have to change the pneumatic tyres should the conditions no longer be those of winter.

In order to provide pneumatic tyres that would be usable under both winter conditions and other conditions (absence of snow or ice), treads with a porous surface were introduced. The presence of pores makes it possible to increase the contact surface area between the tread and the road and to create a path for the layer of water that forms between the tread and the road to flow away, thereby rendering it particularly suitable also in the event of rain.

Generally, the approach used in the rubber industry in order to obtain a tread with a porous surface is that of introducing specific chemical agents (blowing agents) to the compound being prepared, which are capable of creating chemical reactions during the vulcanization step that bring about the release of compounds in the gaseous state and that are responsible for the formation of pores . Today, such a solution suffers the disadvantage in relation both to the fact that the blowing agents used generally turn out to be hazardous to the health of the operators and to the environment and to the fact that the pores can represent mechanically weak points in the tread.

The need was therefore felt to be able to provide a solution that guarantees the manufacture of a tread with a porous surface but without, in so doing, incurring the disadvantages of the prior art .

DISCLOSURE OF INVENTION

The object of the present invention is a compound for manufacturing a tread for pneumatic tyres comprising at least one cross-linking unsaturated-chain polymeric base suitable for assuming the chemical/physical and mechanical characteristics of an elastomer following cross-linking, a filler, a vulcanization system and a reinforced porosity system; said compound being characterized in that said reinforced porosity system comprises a compound of the general the formula (I) and a reinforcement fiber made of a combination of polyethylene and a hydrophilic compound

wherein, Ri, R2 and R3 identical or different from each other are chosen from the group composed of: H, CH3, CH3CH2, CH3CH2CH2, CH3CH2CH2CH2, CH2CHCHCH, CH3CH3CH, C ₆ H ₅ , CeHii, C10H7, CH3C6H4CH3, CH3CH2C6H5, C ₆ H ₄ OH, C4H5O2, CH3C6H4OCH3, CH3OC6H4OCH3, NH ₂ , C ₆ H ₄ NH ₂ , C4H7NH, C ₆ HioNH ₂ , C (CH ₃ ) ₂ OH, C5H9NH, NH2CH2C7H12, CHCHOCH ₂ C ₆ H ₅ , CeHioOH, CH2C6H3C3H2NH, SO3C6H4CH3, C ₆ H ₄ N0 ₂ , CeHii, C10H7, C ₆ H ₄ OH, CH ₃ OC ₆ H ₄ , (CH ₃ ) 3CC ₆ H4, CH3C6H3NO2, (CH ₂ ) ₃ C1, CH ₃ X, CH3CH2X, CH3CH2CH2X, CH ₃ CH2CH2CH2X,C6H ₅ X, C ₆ H ₅ CH ₂ X, (CH ₃ ) 3CX, C4H3X, CH2CHCH2X, C6H4SO3CH3X, C6H4NO2X, CeHnX, C10H7X, OHCH2CH2X, OHC4H4X, CH ₃ OC ₆ H ₄ X, (CH ₃ ) 3CC ₆ H ₄ X, CH2C6H4CHX, NH ₂ C ₆ HioX, OHC (CH ₃ ) 2X, NHC5H9X, NHC5H9NC5H9X, NH2CH2C7H12X, OHCeHioX, NHCH2C6H3C3H2X, where X can be 0 or S. Here and hereinafter, the term "reinforced porosity system" means a combination of compounds suitable for manufacturing the formation within the tread of structurally reinforced pores during the vulcanization step of the pneumatic tyre.

Here and hereinafter, the term "cross-linkable unsaturated- chain polymer base" refers to any natural or synthetic non-cross- linked polymer capable of assuming all of the chemical-physical and mechanical characteristics typically assumed by elastomers after cross-linking (vulcanization) with sulfur-based systems.

Here and hereinafter, vulcanization system refers to a complex of ingredients comprising at least sulfur and accelerating compounds, that in the preparation of the compound are added in a final mixing stage and have the purpose of promoting the vulcanization of the polymer base once the compound is subjected to a vulcanization temperature.

Preferably, Ri and R2 are H and R3 is NH2.

Preferably, in said reinforcement fiber the hydrophilic compound is covered with polyethylene.

Preferably, said fiber is made with polyethylene functionalized with ethylene vinyl alcohol (EVOH) .

Preferably, said compound of the general formula (I) and said reinforcement fiber are present in the compound in a phr ratio between 0.5 and 2.0.

Preferably, both said compound of the general formula (I) and said reinforcement fiber are present within the compound in a quantity of between 2 and 10 phr.

Preferably, said reinforced porosity system is added to the compound being prepared during the productive mixing step.

A further object of the present invention is a tread portion being manufactured with the compound of the present invention.

A still further object of the present invention is a pneumatic tyre comprising a tread portion manufactured with the compound, object of the present invention. A further object of the present invention is a method for the preparation of a compound for the manufacture of a tread with a porous surface for pneumatic tyres; said method comprising (i) a non-productive mixing step wherein are mixed together a cross linking unsaturated chain polymer base suitable for assuming the chemical- physical and mechanical characteristics of an elastomer following cross-linking and at least one filler and (ii) a productive mixing step wherein a vulcanization system is added to and mixed with the compound being prepared; said method being characterized in that during said productive mixing step a reinforced porosity system is added comprising a compound of the general formula (I) and a reinforcing fiber made of a combination of polyethylene with a hydrophilic compound

wherein, Ri, R2 and R3 identical or different from each other are chosen from the group composed of: H, CH3, CH3CH2, CH3CH2CH2, CH3CH2CH2CH2, CH2CHCHCH, CH3CH3CH, C ₆ H ₅ , CeHii, C10H7, CH3C6H4CH3, CH3CH2C6H5, C ₆ H ₄ OH, C4H5O2, CH3C6H4OCH3, CH3OC6H4OCH3, NH ₂ , C ₆ H ₄ NH ₂ , C4H7NH, C ₆ HioNH ₂ , C(CH ₃ ) ₂ OH, C5H9NH, NH2CH2C7H12, CHCHOCH ₂ C ₆ H ₅ , CeHioOH, CH2C6H3C3H2NH, SO3C6H4CH3, C ₆ H ₄ N0 ₂ , CeHii, C10H7, C ₆ H ₄ OH, CH ₃ OC ₆ H ₄ , (CH ₃ )3CC ₆ H4, CH3C6H3NO2, (CH ₂ ) ₃ C1, CH ₃ X, CH3CH2X, CH3CH2CH2X, CH ₃ CH2CH2CH2X,C6H ₅ X, C ₆ H ₅ CH ₂ X, (CH ₃ ) 3CX, C4H3X, CH2CHCH2X, C6H4SO3CH3X, C6H4NO2X, CeHnX, C10H7X, OHCH2CH2X, OHC4H4X, CH ₃ OC ₆ H ₄ X, (CH ₃ ) 3CC ₆ H ₄ X, CH2C6H4CHX, NH ₂ C ₆ HioX, OHC (CH ₃ ) 2X, NHC5H9X, NHC5H9NC5H9X, NH2CH2C7H12X, OHCeHioX, NHCH2C6H3C3H2X, where X can be 0 or S.

Here and hereinafter the term "non-productive mixing step" refers to a mixing step wherein, to the cross-linkable unsaturated chain polymer base are added and mixed the ingredients of the compound with the exception of the vulcanization system; while the term "productive mixing step" refers to a mixing step wherein the vulcanization system is added to and blended in the compound being prepared .

BEST MODE FOR CARRYING OUT THE INVENTION

For a better understanding of the invention, the following examples are for illustrative and non-limiting purposes.

EXAMPLES

There were two comparison compounds (A and B) and a compound of the invention (C) . The first comparison compound (A) is a tread compound without the reinforced porosity system, while the second comparison compound (B) is a tread compound whose reinforced porosity system comprises the lone general formula compound (I) as defined in the claims, therefore, without the presence of the reinforcement fiber made of the funct ionalized polyethylene with hydrophilic groups.

The example compounds were obtained according to the procedure below:

- preparation of the compounds -

(1 ^st mixing step)

Before the start of the mixing, a mixer with tangential rotors and an internal volume of between 230 and 270 liters was loaded with the cross-linkable polymer base, the recycled rubber, the silica, a silane bonding agent, the carbon black, the resin and the process oil reaching a fill factor of 66-72%.

The mixer was operated at a speed of between 40-60 revolutions/minute, and the mixture thus formed was discharged once a temperature of between 140-160 °C had been reached.

(final mixing step)

Sulfur and the vulcanization agents, and just for compounds B and C, the reinforced porosity system and antioxidants were added to the mixture obtained from the previous step, reaching a fill factor of between 63-67%.

The mixer was operated at a speed of between 20-40 revolutions/minute, and the mixture thus formed was discharged once a temperature of between 90-110 °C had been reached.

Table I shows the compositions in phr of the three compounds.

TABLE I

CB is carbon black identified by the letters N134.

The silica used is ULtrasil 5500 GR marketed by Evonik.

The silane binding agent used is Si75.

The resin used is marketed under the name HIKOTACK P90 by the company Kolon Chemical CO LTD

The process oil used is marketed under the name Nytex 832 by the company Nynas

The compound of the general formula (I) used is urea (NH2CONH2) .

The reinforced fiber used is polyethylene combined with ethylene vinyl alcohol (EVOH) and marketed under the commercial code name S833 10T3 by the company KURARAY CO., LTD

The vulcanization agents consist of MBTS and CBS.

The antioxidant agents consist of TMQ and 6PPD

It was experimentally verified that compound B and C produce tread strips exhibiting a porosity with pores having an average surface area equal to 5 mm ² .

Respective samples were drawn from compounds A - C that, once vulcanized, were subjected to tests in order to be able to assess the wet traction (wet grip in IR) , winter performance (winter in the IR) , dry traction (dry grip in the IR) , the rolling resistance and the resistance to wear.

Compounds A - E prepared above were subjected to the

dynamicity test according to the ASTM D5992 and the wear test based on DIN abrader according to the ASTM 5963 standard.

As is known in the art, the values of TanD at 0°C, of E' at -20°C and of E' at 30°C are respectively indicative of the wet grip index, of the ice and of the snow conditions grip index and of the dry grip index. Furthermore, the values of TanD at 60°C are strictly correlated to the rolling resistance (the less the value of TanD at 60°C, the greater the rolling resistance) .

Recorded in Table II are the values of the characteristics indexed to compound A.

TABLE II

As is evident from the data of Table II, compared to the first comparison compound (compound A) , the compound obtained with the compound that is the object of the present invention (compound c) shows an overall improvement in those characteristics in relation to the road traction in different situations. Furthermore, from a comparison of the data in relation to comparison compound B and to the compound of the invention, C, it appears clear how the presence of the reinforcing compound turns out to be fundamental in obtaining the further advantage in relation to the rolling resistance .

In conclusion, the compound that is the object of the present invention, by virtue of the attainment of a porosity obtained via the participation of a reinforcing fibre, is able to ensure improved road traction under different conditions (dry, wet and winter) together with improved resistance to abrasion.