WO2019201790A1

WO2019201790A1 - Rubber composition for tyres with good wet grip and rolling resistance properties

Info

Publication number: WO2019201790A1
Application number: PCT/EP2019/059496
Authority: WO
Inventors: Neven MARKOVIC; Louis Reuvekamp
Original assignee: Apollo Tyres Global R&D BV
Current assignee: Apollo Tyres Global R&D BV
Priority date: 2018-04-20
Filing date: 2019-04-12
Publication date: 2019-10-24
Anticipated expiration: 2020-10-20
Also published as: NL2020806B1

Abstract

Rubber composition for tyres with good wet grip and rolling resistance properties The present invention relates to a cross-linkable rubber composition comprising a rubber component and a resin component; wherein the resin component comprises a blend of at least two resins wherein - the first resin is a coumarone-indene resin, and - the second resin is a resin selected from the group of C5 resins, C9 resins, polyterpene resins, or a mixture thereof; wherein the ratio of the second resin to the coumarone-indene resin is in a range of ≥ 1:10 to ≤ 10:1, the ratio referring to the respective weight (w/w).

Description

Rubber composition for tyres with good wet grip and rolling resistance properties

The present invention relates to a cross-linkable rubber composition comprising a rubber component and a resin component, a method of preparing a cross-linkable rubber composition comprising a rubber component and a resin component, a cross-linked rubber composition obtained by cross-linking such a rubber composition, a method of preparing a tyre and a tyre.

Tyre performances are highly dependent on its construction parts. A tyre tread is one of the most important component of a pneumatic tyre. It is the only part of the pneumatic tyre which has to be in contact with a road. Therefore, variety of performances such as wet grip, abrasion resistance and low rolling resistance are dependent on the rubber composition of the tread for a pneumatic tyre.

It is well known in rubber compounding that there is a trade-off between wet grip and rolling resistance. The tread compound can be optimized to exhibit good wet grip by using high Tg polymers like SBR but it normally results in high rolling resistance. On the other hand, tuning the rubber compound by using low Tg polymers like BR to reduce rolling resistance possibly leads to impairment in wet grip. Several types of resins are therefore introduced to increase the wet grip properties but these often have a negative effect on the rolling resistance. In order to obtain high performance tyres, all properties need to be improved simultaneously.

The researchers are constantly in search for new solutions and materials for finding a way to enhance above mentioned properties at a same time. It has been described in the prior art to use resin to improve wet traction. The prior art shows that the higher the concentration of a resin used the better the wet grip evaluated by tan d at 0°C. Also, resins applied in higher concentration bring high shift of glass transition temperature (Tg) of the compound.

WO2015124681A1 describes a rubber composition based on at least one diene elastomer, a reinforcing filler, a vulcanisation system and a combination of plasticisers, said combination of plasticisers comprising more than 15 phr (parts by weight per hundred parts of elastomer) of hydrocarbonated resin having a glass transition temperature (Tg) of between -40°C and 20°C and a resin having a Tg higher than 20°C, the total amount of plasticiser being higher than, or equal to, 40 phr, and the amounts of reinforcing filler and plasticiser being such that the ratio of the total amount of filler and the total amount of plasticiser ranges between 1.3 and 2.

WO2015124684A1 describes a rubber composition based on at least one diene elastomer, 110 to 160 phr of reinforcing filler, a vulcanisation system and a plasticising system comprising at least one hydrocarbonated resin having a Tg of between -40°C and 20°C, the total amount of plasticiser being higher than, or equal to, 70 phr.

W02017001614A1 describes a rubber composition made up of: at least one diene elastomer; 50 to 160 phr of inorganic reinforcement filler; a vulcanisation system; a plasticising system including at least one hydrocarbon resin having a Tg of from -40 °C to 20 °C; as the coupling agent, a hydroxysilane polysulphide having the general formula (I): (HO)a R(3-a) Si— R'— Sx— R'— Si R(3-b) (OH)b where the groups R, which can be the same or different, are hydrocarbon groups preferably comprising 1 to 15 carbon atoms, the groups R', which can be the same or different, are divalent bonding groups preferably comprising 1 to 18 carbon atoms, a and b, which can be the same or different, are equal to 1 or 2, and x is a number no lower than 2; and a primary amine of formula (IV): R-NH2 where R is a straight or branched hydrocarbon group including 8 to 24 carbon atoms, said composition being free from or including less than 0.5 phr of guanidine derivative.

W02017001616A1 describes a rubber composition based on at least one diene elastomer, a reinforcing filler, a vulcanisation system and a plasticising system, said reinforcing filler comprising predominantly by weight a very high specific surface area silica, having a CTAB specific surface area greater than 170 m2/g and said plasticising system comprising at least more than 15 phr of a hydrocarbon resin having a Tg between -40°C and 20°C.

Although the wet grip is increased by the use of the resins in the rubber composition for tyres as disclosed by the state of the art, it also increases the rolling resistance which makes its not compatible to be used as a compound for the tread of a summer tyre. Therefore, the object to be achieved by this invention is to provide improvement in wet grip and at the same time in the rolling resistance.

The object is achieved by a cross-linkable rubber composition according to claim 1, a method of preparing a cross-linkable rubber composition according to claim 11, a cross- linked rubber composition according to claim 12, a method for preparing a tyre according to claim 14 and a tyre according to claim 15. Advantageous embodiments are the subject of the dependent claims. They may be combined freely unless the context clearly indicates otherwise.

Accordingly, a cross-linkable rubber composition is provided, the cross-linkable rubber composition comprising a rubber component and a resin component. The resin component comprises a blend of at least two resins wherein

o the first resin is a coumarone-indene resin, and

o the second resin is a resin selected from the group of C5 resins, C9 resins, polyterpene resins, or a mixture thereof,

wherein the ratio of the second resin to the coumarone-indene resin is in a range of > 1:10 to < 10:1, the ratio referring to the respective weight (w/w).

It has surprisingly been found that improved performance of a tyre regarding wet grip and rolling resistance can be provided by such blends of resins. A combination of the second resin and the coumarone-indene resin in a tyre tread compound showed a balanced improvement in the wet grip and the rolling resistance. The amount of resins may be applied instead of oil in the composition.

According to one embodiment of the invention, the rubber component is selected from the group of solution styrene butadiene rubber (SSBR), butadiene rubber (BR) or a mixture thereof. The SSBR rubber component may contain one type of styrene butadiene rubber (SBR) rubber or several different types. Preferably, at least one type of SBR rubber is manufactured according to the solution process (SSBR or solution SBR). Likewise, the BR rubber component may contain one type of BR rubber or several different types.

According to one embodiment of the invention, the amount of the rubber component is, per hundred parts by weight of rubber (phr), in a range of > 1 to < 100 phr.

It is further understood that in formulations discussed in connection with the present invention the phr amount of all rubber components adds up to 100.

The cross-linkable rubber composition according to the invention comprises cross- linkable groups in the individual rubber components. They may be cross-linked (cured, vulcanised) by methods known to a skilled person in the rubber technology field. The cross-linkable rubber compositions may be sulphur-vulcanizable and/or peroxide - vulcanizable. Other vulcanization systems may also be used. If desired, additional additives besides TPE can be added. Examples of usual additives are resins, stabilizers, antioxidants, lubricants, fillers, dyes, pigments, flame retardants, conductive fibres and reinforcing fibres.

According to one embodiment of the invention, the second resin has an average molecular weight Mw in a range of > 880 g/mol to < 4500 g/mol, preferably between > 1000 g/mol to < 2500 g/mol, more preferably between > 1200 g/mol to < 2000 g/mol and most preferably it is ³l500 g/mol.

In embodiments, the Coumarone-Indene (Cl) resin may have a low or very low softening point, for example of 30°C, and/or the second resin may have a high softening point. A use of resin dual blends comprising low Tg and high Tg may further support a balanced improvement in the wet grip and the rolling resistance.

According to one embodiment of the invention, the second resin is selected from the group of C5 resins with a softening point in a range of > 100 °C to < H0°C, C9 resins with a softening point in a range of > 85 °C to < l40°C or polyterpene (PT) resins with a softening point in a range of > 105 °C to < l25°C (ring and ball method according to ASTM D3461), or a mixture thereof.

Commercially available C5 resins are, for example, Piccotac 1098, Piccotac 1115, Impera R1507, Impera R1508, Impera R1607, Impera R1608 from Eastman Chemical Company, Quintone A100, Quintone K100, Quintone C200H, Quintone C210 from Zeon etc.

a Methyl styrene (AMS) resins with a softening point in a range of > 85 °C to < 140 °C are a preferred group of C9 resins.

Commercially available C9 resins are, for example Sylvatraxx 4401 from Kraton Corporation, Impera P1505, Picco A100, Picco A120, Picco A140 from Eastman Chemical Company, Kristalex 3070, Kristalex 3085, Kristalex 3100, Kristalex F115, Piccotex 75, Piccotex 100 from Eastman Chemical Company etc.

Commercially available Terpene resins are, for example, Sylvagum TR90 and Sylvatraxx 4125 from Kraton Corporation; Dercolyte A 115, Dercolyte A 125, Dercolyte S 115 from DRT (les Derives Resiniques et Terpeniques). According to one embodiment of the invention, the coumarone-indene resin has a softening point in a range of > 10 °C to < 30 °C (ring and ball method according to ASTM D3461).

Representative of coumarone-indene resins are, for example, Novares C10 and Novares C30 from R1JTGERS Resins BV.

According to one embodiment of the invention, the amount of coumarone-indene resin is in a range of > 1 phr to < 29 phr, preferably in a range of > 5 to < 25 phr, more preferably in a range of > 10 phr to < 20 phr, and most preferably it is 15 phr.

According to one embodiment of the invention, the amount of the second resin is in a range of > 1 phr to < 29 phr, preferably in a range of > 5 to < 25 phr, more preferably in a range of > 10 phr to < 20 phr, and most preferably it is 15 phr.

According to one embodiment of the invention, the total amount of coumarone-indene resin and second resin is in a range of > 20 to < 40 phr, and most preferably it is 30 phr. In embodiments, the amount of coumarone-indene resin is at least 10 phr of a total amount of 30 phr to 40 phr of a dual blend with the second resin. Advantageously, 10 phr of Cl resin in the blend leveled the rolling resistance performance. In the dual blends a concentration of 15 phr Cl improved the tyre performance prediction. In embodiments, the amount of each of the Cl resin and the second resin are 15 phr. With 15 phr of each of these resins the recipes achieved optimized results.

According to one embodiment of the invention, the ratio of the second resin to the coumarone-indene resin is in a range of > 1:10 to < 10:1, preferably in a range of > 1:5 to < 5:1, more preferably in a range of > 1:1 to < 2:1 the ratio referring to the respective weight.

According to one embodiment of the invention, the second resin is a polyterpene resin, and the ratio of the polyterpene resin to the coumarone-indene resin is in a range of > 1:1 to < 2:1.

The invention also relates to a method of preparing a cross-linkable rubber composition comprising the steps of:

- providing a rubber component; - adding a blend of at least two resins wherein the first resin is a coumarone-indene resin, and the second resin is is a resin selected from the group of C5 resins, C9 resins, polyterpene resins, or a mixture thereof, and wherein the ratio of the second resin to the coumarone-indene resin is in a range of > 10:1 to < 1:10, the ratio referring to the respective weight (w/w);

- adding curing agents.

Another aspect of the present invention is a cross-linked rubber composition obtained by cross-linking a rubber composition according to the invention.

In an embodiment, the cross-linked rubber composition has a tan delta at 0°C of > 0.5 to < 0.7 (determined from dynamic mechanical analysis (DMA) measurements according to ISO 4664-1, frequency 10 Hz, 0.1% dynamic strain) and a tan delta at 60 °C of > 0.1 to < 0.16 (determined from dynamic mechanical analysis (DMA) measurements according to ISO 4664-1, frequency 10 Hz, 6 % dynamic strain).

The present invention also relates to a method of preparing a tyre, comprising the steps of:

- providing a tyre assembly comprising a rubber composition according to the invention;

- cross-linking at least the rubber composition according to the invention in the tyre assembly.

Another aspect of the invention is a tyre tread obtained by cross-linked rubber composition according to the invention.

The present invention also encompasses a tyre comprising a tyre tread, wherein the tyre tread comprises a cross-linked rubber composition according to the invention.

Examples of the invention

The invention will be further described with reference to the following examples, tables and figures without wishing to be limited by them.

In the figures show:

Figure 1 : A graph of the tan6 as a function of temperature (-80 to 25°C) for various dual blend resin compositions of the present invention as compared to a reference composition. Figure 2: A graph of the tand as a function of temperature (30 to 80°C) for various dual blend resin compositions of the present invention as compared to a reference composition.

Figure 3: A graph of the tand as a function of temperature (-80 to 25°C) for PT/CI resin blend composition (1:1) of the present invention as compared to a reference composition.

Figure 4: A graph of the tand as a function of temperature (30 to 80°C) for PT/CI resin blend composition (1:1) of the present invention as compared to a reference composition.

Figure 5: A graph of the tand as a function of temperature (-80 to 25°C) for PT/CI resin blend composition (2:1) of the present invention as compared to a reference composition.

Figure 6: A graph of the tand as a function of temperature (30 to 80°C) for PT/CI resin blend composition (2:1) of the present invention as compared to a reference composition.

In accordance with the preceding, cross-linkable rubber compositions were prepared. For the preparation of the composition according to the present invention two resins were used in the blend. One of the two resins was a coumarone-indene resin having a low softening point in all formulations and the other resins were high softening point resins.

Example 1:

One of the two resins was Cl resin in all formulations and the other resins were high softening point resins. The recipes of dual resin blends which were compared for dynamic mechanical analysis included blends of Cl and C9 resins, Cl and polyterpene (PT) resins and Cl and C5 resins. The total amount of resin was kept the same at 30 phr and equal concentration of two resins was used (ratio of 1:1 w/w).

The table below shows the compositions of the reference dual blend (Ref-DB), C9/CI dual blend resin, PT/CI dual blend resin, and C5/CI dual blend resin.

Table 1: Reference Compound and The Dual Resin Blends Compounds Formulation

SSBR had a styrene content of 21% and 62.2% vinyl groups and a Tg of -25°C and Mooney Viscosity of 49.1MU.

BR was neodymium catalyzed polybutadiene with high amount of linear chains and mostly cis-l,4 butadiene conformation with a viscosity of 44MU.

The C9 resin was Impera 1505 from Eastman Chemical Company which had an average molecular weight Mw of 4285 g/mol, and a softening point of H9°C (ring and ball method according to ASTM D3461).

The polyterpene resin was Sylvatraxx 4125 from Kraton Corporation which had an average molecular weight Mw of 1090 g/mol, and a softening point of l25°C (ring and ball method according to ASTM D3461).

The C5 resin was Piccotac 1115 from Eastman Chemical Company had an average molecular weight Mw of 3800 g/mol, and a softening point of H0°C (ring and ball method according to ASTM D3461).

The coumarone-indene resin was C30 from Rutgers which had an average molecular weight Mw of 281 g/mol, had a softening point of 20 to 30°C (ring and ball method according to ASTM D3461). Silica contained 7% bound water and had a surface area of l65m²/g.

TESPT silane had a sulfur content of 22% and average 3.75 sulfur atoms in the sulphur chain.

TDAE oil had a viscosity of 4l0m²/s at 40°C and a Tg of -42°C.

Zinc Oxide had a density of 5.61 kg/l and Stearic Acid with melting point between 68- 70°C.

6PPD (N-phenyl-N'-l,3-dimethylbutyl-p-phenylenediamine) had a melting point of 56°C.

Paraffin wax with 2% polyethylene and congealing point of 62-72°C was used.

Two accelerators were used; TBBS (N-tert-butylbenzothiazole-2-sulphenamide) with melting point of l09°C and DPG (diphenyl guanidine) with melting point between 144 and l5l°C and alkalinity of 10.2 on pH scale.

Sulfur containing 1% of a mineral oil with melting point of 1 l5°C and pH of 6.8.

Abbreviations used are: TESPT (tetrasulphide silane); TDAE (treated distillate aromatic extract; processing oil); TBBS (N-tert-butyl-2 benzothiazole sulfenamide); DPG (diphenyl guanidine); TBzTD (tetrabenzyl thiuram disulfide); 6PPD (N-l,3- dimethylbutyl)-N-phenyl-p-phenylenediamine).

Measurement of Dynamic Mechanical Propertiesof Ref-DB blend in comparison to C9/CI, PT/CI and C5/CI resin blends

A dynamical spectrum of the compounds was collected by the instrument Metravib DMA +450 dynamic spectrometer in double shear mode. Measurements of the material dynamic behavior were run in two different settings. In the first set-up the temperature was varied, and in the second, a different strain was applied.

In the temperature variation method there were two sub steps. In the first sub step, the temperature was in the range of -80°C to 25°C and the dynamic strain was 0,1%. In the second sub step, the temperature was in the range of 25°C to 80°C but the dynamic strain was higher and it was set at 6%. The reason of the increased dynamic strain at higher temperatures was the effort to simulate the real tyre conditions for the rolling resistance prediction. In both sub test the frequency was constant at lOHz. The results of the dual blends dynamical mechanical analysis were very close to each other. The results depicted that in temperature sweep measurements from -80 to 25°C (Figure 1) only C5-CI resins formulation created 5°C less Tg shift. The exception was not peculiar because the C5 and the Cl resins individually are not known to highly shift the Tg. Surprisingly, the inventors found out that the results were equivalent to the other 30phr resin recipes and tan d peaks were narrow and the peak heights were same. This indicated the domination of the Cl resin in the blends since the tan d maximum values of the single C9 and C5 resin compounds are known to be much lower. Additionally, the Cl resin combined with the C5 did not increase incompatibility which inventors have presumed with C5 resin but it was completely opposite and the compatibility was enhanced. Moreover, it was not likely that the l5phr of a high softening point resins will efficiently phase separate and the PT-CI resin blend behaves as the PT formulation.

The most important anticipated outcome of DMA results in temperature range from 30 to 80°C (Figure 2) is lowering of the resin blends tan d graphs compared to the Ref-DB. This means that going from lOphr in ternary blend to l5phr of the Cl in dual resin blend brings not equal but improved rolling resistance prediction performance when compared to the results of single Cl resin compounds. Also, there is no preference in the high softening point resin when it is mixed with the Cl resin in this concentration. Furthermore even on this level of similarity there were insignificant but explainable variations. In tan d results the C5/CI is the closest to the reference and at the same time with C5 resin alone in the recipes the worst rolling resistance is obtained. Negative energy dissipation influenced also the C9 resin where its tan d curve is higher than the reference in whole temperature range. The lowest fuel consumption prediction parameter among dual rubber- resin blends has PTCI recipe since its constituent the PT resin tan d matched the reference value around 70°C. The most interesting observation anyhow was the crossing of the C5high resin based blend with two other blends at around 35°C. Nevertheless moduli of dual resin blends are significantly lower in comparison to the reference and marginal rise from other blends is observed with C9 based blend recipe.

Example 2: The table below shows the compositions of the reference compounds Cl and C2 and the resin blends II and 12.

Table 2: Reference Compound and The Dual Resin Blends Compounds Formulation

*phr - Parts per hundred rubber

Measurement of Dynamic Mechanical Properties

In a first test the dynamic mechanical properties of the reference compound Cl was compared with the compound II. A dynamical spectrum of the compounds was collected by the instrument Metravib DMA +450 dynamic spectrometer in double shear mode.

Measurements of the material dynamic behavior were run in two different settings. In the first set-up the temperature was varied, and in the second, a different strain was applied.

In the temperature variation method there were two sub steps. In the first sub step, the temperature was in the range of -80°C to 25°C and the dynamic strain was 0,1%. In the second sub step, the temperature was in the range of 25°C to 80°C but the dynamic strain was higher and it was set at 6%. The reason of the increased dynamic strain at higher temperatures was the effort to simulate the real tyre conditions for the rolling resistance prediction. In both sub test the frequency was constant at lOHz.

Table 3: Mechanical and Physical properties of Cl and II

In a second test the dynamic mechanical properties of the reference compound C2 was compared with the compound 12. The tests as described above provided the following results.

Table 4: Mechanical and Physical properties of C2 and 12

DMA results of compounds with resin blends in different ratios of PT:CI=l:l (w/w) and PT:CI=2:l (w/w) are depicted in Figures 3-6 respectively. The total amount of resins was 30phr. The tan d graph at low temperatures (Figures 3 and 5) depicts that the Tg shift of the compound with increased concentration of PT resin is higher. Therefore this compound will have a better wet grip. However, tan d at 0°C looks similar and by assessment based on this parameter both compounds will have similar improvement in wet grip. DMA results at high temperatures (Figures 4 and 6) show that the higher the concentration of the Cl resin the lower the tan d at 60°C and consequently the better the rolling resistance. Furthermore with even smaller amount of Cl resin it can be designed that the PT resin compound has no increased rolling resistance. Therefore, the application of PT and Cl resin blend wet grip and rolling resistance performances can be tailored by the concentration of Cl resin.

Claims

Claims:

1. A cross-linkable rubber composition comprising a rubber component and a resin component; characterised in that

the resin component comprises a blend of at least two resins wherein

- the first resin is a coumarone-indene resin, and

- the second resin is a resin selected from the group of C5 resins, C9 resins, polyterpene resins, or a mixture thereof;

2. The cross-linkable rubber composition of claim 1, wherein the rubber component is selected from the group of solution styrene butadiene rubber (SSBR), butadiene rubber (BR) or a mixture thereof.

3. The cross-linkable rubber composition of claim 1 or 2, wherein the amount of the rubber component is, per hundred parts by weight of rubber (phr), in a range of > 1 to < 100 phr.

4. The cross-linkable rubber composition according to one of claims 1 to 3, wherein the second resin has an average molecular weight Mw in a range of > 880 g/mol to < 4500 g/mol.

5. The cross-linkable rubber composition according to one of claims 1 to 4, wherein the second resin is selected from the group of C5 resins with a softening point in a range of > 100 °C to < H0°C, C9 resins with a softening point in a range of > 85 °C to < l40°C or polyterpene resins with a softening point in a range of > 105 °C to < l25°C (ring and ball method according to ASTM D3461), or a mixture thereof.

6. The cross-linkable rubber composition according to one of claims 1 to 5, wherein the coumarone-indene resin has a softening point in a range of > 10 °C to < 30 °C (ring and ball method according to ASTM D3461).

7. The cross-linkable rubber composition according to one of claims 1 to 6, wherein the amount of coumarone-indene resin is in a range of > 1 phr to < 29 phr.

8. The cross-linkable rubber composition according to one of claims 1 to 7, wherein the amount of the second resin is in a range of > 1 phr to < 29 phr.

9. The cross-linkable rubber composition according to one of claims 1 to 8, wherein the ratio of the second resin to the coumarone-indene resin is in a range of > 1:5 to < 5:1, the ratio referring to the respective weight.

10. The cross-linkable rubber composition according to one of claims 1 to 9, wherein the second resin is a polyterpene resin, and the ratio of the polyterpene resin to the coumarone-indene resin is in a range of > 1:1 to < 2: 1.

11. A method of preparing a cross-linkable rubber composition according to one of claims 1 to 10, comprising the steps of:

- providing a rubber component;

- adding a blend of at least two resins wherein the first resin is a coumarone- indene resin, and the second resin is is a resin selected from the group of C5 resins, C9 resins, polyterpene resins, or a mixture thereof, and wherein the ratio of the second resin to the coumarone-indene resin is in a range of > 10:1 to < 1:10, the ratio referring to the respective weight (w/w);

- adding curing agents.

12. A cross-linked rubber composition, characterised in that it is obtained by cross- linking a rubber composition according to one of claims 1 to 10.

13. The cross-linked rubber composition according to claim 12 with a tan delta at 0 °C of > 0.5 to < 0.7 (determined from dynamic mechanical analysis (DMA) measurements according to ISO 4664-1, frequency 10 Hz, 0.1% dynamic strain) and a tan delta at 60 °C of > 0.1 to < 0.16 (determined from dynamic mechanical analysis (DMA) measurements according to ISO 4664-1, frequency 10 Hz, 6 % dynamic strain).

14. A method of preparing a tyre, comprising the steps of: - providing a tyre assembly comprising a rubber composition according to one of claims 1 to 10;

- cross-linking at least the rubber composition according to one of claims 1 to 10 in the tyre assembly.

15. A tyre comprising a tyre tread, characterised in that the tyre tread comprises a cross-linked rubber composition according to one of claim 12 or 13.