WO2016055953A1

WO2016055953A1 - Rubber compound for tyre portions

Info

Publication number: WO2016055953A1
Application number: PCT/IB2015/057670
Authority: WO
Inventors: Valeria Grenci
Original assignee: Bridgestone Corporation
Priority date: 2014-10-07
Filing date: 2015-10-07
Publication date: 2016-04-14

Abstract

A rubber compound comprising at least one cross-linkable unsaturated chain polymer base, silica functionalized with amine groups, a silane bonding agent belonging to the class of polysulphide organosilanes and a vulcanization system. The silica functionalized with amine groups is obtained through reaction of the silica with alkanolamine compounds having the general formula HOR₁NR₂R₃ where : R₁ is a straight or branched aliphatic chain with a number of carbon atoms ranging from 4 to 12; and R₂ and R₃, which are equal to or different from one another, are H or (CH₂)nCH₃, where n is an integer ranging from 0 to 4.

Description

"RUBBER COMPOUND FOR TYRE PORTIONS "

TECHNICAL FIELD

The present invention relates to rubber compounds for portions of a tyre .

BACKGROUND ART

As is known, part of research in the tyre field is concentra^ted on obtaining tyre treads with ever- improving performance in terms of rolling resis ance and abrasion resistance .

In this respect , the use of silica as a reinforcement filler in tread compounds has long been known . The choice of silica is dictated by the advantages it gives in terms of rolling resistance and wet grip .

Silica is used in combination with silane bonding agents , which by bonding with the silanol groups prevents the formation of hydrogen bonds between particles of silica and, at the same time , chemically bonds the silica to the polymer base .

A very interesting class of silane bonding agents is that of the mercaptoalkyltrialkoxy silanes. In fact, this class of silane bonding agents ensures rubber compounds have a significant improvement in rolling resistance .

In particular, the compound indicated below is the one found to be most effective .

SH (CH₂ ) 3Si {OCH₂CH₃ ) (O (CH₂CH₂0) 5 (CH₂) ₁₃CH₃ ) ₂ However, it has been found that the use of this class of silane bonding agents causes an increase in the viscosity of the compound during processing, with obvious consequences on its processability . Generally, to remedy the aforementioned processability problems, the use plasticizing oils in the compound is resorted to, which, although being able to lower the viscosity of the compound, nevertheless entail deterioration in terms of abrasion resistance .

In addition, another of the drawbacks associated with the use of mercaptoalkyltrialkoxy silanes concerns their high cost .

The need was thus felt to be able to prepare rubber compounds for tyres devoid of mercaptoalkyltrialkoxy silanes , without this resulting in deterioration in terms of rolling resistance .

The applicant has surprisingly found that the use of silica functional!zed with amine groups in rubber compounds , in the presence of silane bonding agents of the polysulphide organosilanes class , is capable of giving lower viscosity and better abrasion resistance with respect to compounds comprising mercaptoalkyltrialkoxy silanes , but without worsening the rolling resistance .

DISCLOSURE OF INVENTION

The subject of the present invention is a rubber compound comprising at least one cross - linkable unsaturated chain polymer base , silica functional!zed with amine groups , a silane bonding agent belonging to the class of polysulphide organosilanes and a vulcanization system; said compound being characterized in that the silica functionalized with amine groups is obtained through a reaction of the silica with alkanolamine compounds having the general formula HOR_:NR₂R₃ where :

Ri is a straight or branched aliphatic chain with a number of carbon atoms ranging from 4 to 12 ; and

R₂ and R₃ , which are equal to or different from one another, are H or (CH₂) nCH₃ , where n is an integer ranging from 0 to 4.

Another subject of the present invention is a rubber compound comprising at least one cross -linkable unsaturated chain polymer base , silica functionalized with amine groups , a silane bonding agent belonging to the class of polysulphide organosilanes and a vulcanization system ; said compound being characterized, in that said amine groups have the general formula -ORiNR₂R₃

where :

R₂ and R₃, which are equal to or different from one another, are H or ( CH₂ ) nCH₃ , where n is an integer ranging from 0 to 4.

In this document, the term "vulcanization system" means a complex of ingredients comprising at least sulphur and accelerator compounds , which are added in a final mixing step of compound preparation for the purpose of facilitating the vulcanization of the polymer base once the compound is subj ected to a vulcanization temperature.

In this document , the term " cr c s s -linkable unsaturated chair- polymer base" means any natural or synthetic non cross-linked polymer capable of acquiring all the chemica1/physica1 and mechanical characteristics typically acquired by elastomers following cross - linkage (vulcanization) with sulphur-based systems .

Preferably, at least one of R₂ and R₃ is H . Preferably, R₂ and R₃ are H .

Preferably, the silica functionalized with amine groups has a nitrogen content ranging from 2 to 30% by weight . Preferably, the silica functional!zed with amine groups is used in the compound in a quantity ranging from 20 to 90 phr .

Preferably, the silane bonding agent is used in the compound in a quantity ranging from 1 to 15 phr .

Another subj ect of the present invention is a tyre tread made with a compound of the present invention.

Yet another subject of the present invention is a tyre comprising a tread made with a compound of the present invention .

BEST MODE FOR CARRYING OUT THE INVENTION

Some embodiments are provided below, purely by way of non- limitative example .

Four rubber compounds were made , of which the first three ( Compounds A-C) constitute comparative examples, while the last (Compound D) was made according to the principles of the present invention.

In particular, comparative Compound A represents an example of the compounds currently in use and employs non- functionalized silica and a mercaptoalkyltrialkoxy silane as the silane bonding agent , comparative Compound B employs silica functional!zed with amine groups and a mercaptoalkyltrialkoxy silane as the silane bonding agent , and comparative Compound C employs non- functionalized silica and a silane bonding agent belonging to the class of polysulphide organosilanes .

Compound D, representing the invention, is the only one that employs silica functionalized with amine groups and a silane bonding agent belonging to the class of polysulphide organosilanes The compounds in the examples were prepared according to a standard procedure, which is not relevant for the purposes of the present invention .

- preparation of the compounds - (first mixing step)

Before starting the mixing, the polymer base, the silica and the silane bonding agent were loaded in a tangential -rotor mixer with an internal volume of between 230 and 270 litres , reaching a filling factor in the range 66-72%.

The mixer was operated at a speed of 40-60 rpm and the mixture that was formed was discharged once a temperature in the range 145-165°C was reached.

( second mixing step)

The mixture obtained in the previous step was again processed in the mixer, operated at a speed of 40-60 rpm and then discharged once a temperature in the range 130-150°C was reached .

( third mixing step)

Stearic acid and the vulcanization system composed of sulphur, accelerators and zinc oxide , were added to the mixture obtained in the previous step, reaching a filling factor in the range 63-67%.

The mixer was operated at a speed of 20-40 rpm and the mixture that was formed was discharged once a temperature in the range 100-110°C was reached.

Table I lists the compositions of Compounds A - D in phr.

TABLE I

A B C D

S-SBR 50.0

E-SBR 40.0 BR 10.0

Silica* 85.0 85.0

Silica* * 85.00 85.00

Silane bonding agent* 7.3 7.3

Silane bonding agent* * 7.3 7.3

Zn o ide 1.7

Sulphur 2.0

DPG 1.5

MBTS 1.0

TBBS 1.0

StS3.-1- 1C 3.C 1d 1.0

S-SBR is a polymer base obtained via a solution polymerization process with an average molecular weight in the 800-1500xl0³ and 500-900xl0³ ranges , respectively, with a styrene of between 10 and 45% and a vinyl content of between 20 and 70% .

E-SBR is a polymer base obtained via an emulsion polymerization process with an average molecular weight in the 500-900xl0³ range , respectively, with a styrene content of between 20 and 45% and used with an oil content of between 0 and 30% .

BR is a butadiene rubber with a cis 1 , 4 content of at least 40%.

Silica* is silica with a surface area of approximately 170 m²/g and marketed with the name Ultrasil VN3 by the company EVONIK.

Silica* * is silica functionalized with amine groups made using the method described below: 20 gr of 6 -amino- 2 -methyl -heptan- 2 -oi was dissolved in an aqueous solution; the solution was left in reflux for 20 minutes ; 100 gr of Silica* was added to the aqueous solution, under agitation and reflux; the aqueous solution was kept at a temperature of 100 °C for an hour, after which the silica was filtered and washed several times with distilled water and then dried . The silica functional!zed with amine groups so obtained has a nitrogen content of 2% by weight .

It has been verified that Silica* * comprises functional amine grou s with the formula -OC (CH₃) 2CH2CH2CH2CH (CH₃) NH₂.

Silane bonding agent* belongs to the mercaptoalkyltrialkoxy silanes class ( structural formula

SH (CH₂) ₃Si (OCH₂CH₃) (0 (CH₂CH₂0) ₅ {CH₂) ₁₂CH₃) ₂) and is marketed with the name SI363.

Silane bonding agent** belongs to the polysulphide organosilanes class ( structural formula

(CH₃CH₂0) ₃Si (CH₂) ₃SS (CH₂) ₃Si (OCH₂CH₃) ₃) and is marketed with the name SI75.

DPG is the acronym for diphenyl-guanidine .

MBTS is the acronym for mercaptobenzothiazole disulfide .

TBBS is the acronym for N- tert-butyl-2 -benzothiazole - sulphenamide .

The compounds listed in Table I were subjected to a viscosity measurement and, once vulcanized, to rolling resistance , silica dispersion index and abrasion resistance measurements . In particular, the rolling resistance and silica dispersion derive from the dynamic properties of the compounds . The rolling resistance parameter is correlated to values of tan δ at 60°C; the smaller the value of tan5 at 60°C_f the better the rolling resistance . The dispersion index is given by the ratio 100 x ΔΕ' /E' o . nstrain _/ where ΔΕ' is given by the difference E ' c . i%strain-E ' ₄ . ₀ strain · The smaller the dispersion inde , the better the dispersion of the silica in the polymer matri . The viscosity was measured in accordance with ASTM Standard D1646, the dynamic properties were measured in accordance with ASTM Standard D5992 and the abrasion resistance was measured in accordance with DIN Standard 53516.

Table II lists the values of the above measurements indexed to values of comparison Compound A .

TABLE II

For a more ra id assessment of the values shown in Table II , it should be specified that for the viscosity parameter, the lower the values , the more they are preferred; while for the dispersion, rolling resistance and abrasion resistance parameters , the higher the values , the more they are preferred .

From the values shown in Table II , it can be deduced that the use of silica functional!zed with amine groups in the presence of a silane bonding agent of the polysulphide organosilanes class , succeeds in ensuring that the compound has lower viscosity values and, above all , an important as well as unexpected improvement in terms of abrasion resistance , while at the same time maintaining the dispersion and rolling resistance values unchanged .

Such a result derives from an unexpected synergetic effect between the silica functional!zed with amine groups and the silane bonding agent of the polysulphide organosilanes class .

The synergetic effect is demonstrated by the fact that the separate use of silica functionalized with amine groups and the silane bonding agent of the polysulphide organosilanes class does not produce comparable improvements in terms of abrasion resistance . In fact , Compound B shows how the use of silica functionalized with amine groups together with a mercaptoalkyltrialkoxy silane can only slightly improve silica dispersion, which consequently reflects in a slight improvement in abrasion resistance , without however reducing the viscosity; whereas , Compound C shows how the use of nonf nctional!zed silica in combination with a silane bonding agent of the polysulphide organosilanes class , notwi hstanding it being able to improve the viscosity, maintains the abrasion resistance values unchanged, while at the same time causing deterioration in dispersion and rolling resistance , as was easily expected .

In other words , analysis of the comparative examples clearly shows that such a marked improvement in abrasion resistance for Compound D of the invention derives from an unexpected synergetic effect between silica functionalized with amine groups and a silane bonding agent of the polysulphide organosilanes class.

Claims

1. A rubber compound comprising at least one cross -linkable unsaturated chain polymer base , silica functional!zed with amine groups , a silane bonding agent belonging to the class of polysulphide organosilanes and a vulcanization system; said compound being characterized in that the silica functionalized with amine groups is obtained through reaction of the silica with alkanolamine compounds ha ing the general formula HOR₁NR₂R₃

where :

R₂ and R₃ , which are equal to or different from one another, are H or (CH₂)nCH₃, where n is an integer ranging from 0 to 4.

2. A rubber compound comprising at least one cross - linkable unsaturated chain polymer base , silica functionalized with amine groups , a silane bonding agent belonging to the class of polysulphide organosilanes and a vulcanization system; said compound being characterized in that said amine groups have the general formula -OR₁NR₂R₃

where :

R₂ and R₃ , which are equal to or different from one another, are H or { CH₂ ) nCH₃ , where n is an integer ranging from 0 to 4.

3. A rubber compound according to claim 1 or 2 , characterized in that at least one of R₂ and R₃ is H .

4. A rubber compound according to claim 3 , characterized in that R₂ and R₃ are H .

5. A rubber compound according to one of the preceding claims , characterized in that the silica functionalized with amine groups has a nitrogen content ranging from 1 to 30% by- weight .

6. A rubber compound according to one of the preceding claims , characterized in that the silica functional!zed with amine groups is used in the compound in a quantity ranging from 20 to 90 phr .

7. A rubber compound according to one of the preceding claims, characterized in that the silane bonding agent is used in the compound in a quantity ranging from 1 to 15 phr .

8. A tread manufactured with a compound according to one of the preceding claims .

9. A tyre comprising a tread according to claim 8.