LU100944B1

LU100944B1 - Rubber composition for tyres

Info

Publication number: LU100944B1
Application number: LU100944A
Authority: LU
Inventors: Sebastiana Piras; Paola Nicolella
Original assignee: Apollo Tyres Global R & D Bv
Priority date: 2018-09-28
Filing date: 2018-09-28
Publication date: 2020-03-30
Also published as: EP3856834A1; WO2020064952A1

Abstract

The present invention relates to a cross-linkable rubber composition, the cross-linkable rubber composition comprising, per hundred parts by weight of rubber (phr): > 1 phr to < 150 phr of a rubber component; wherein the rubber component comprises a blend of three solution styrene-butadiene rubbers (SSBRs), wherein a first SSBR has a glass transition temperature (Tg, measured by DSC, according to ISO 22768) in a range of > -13°C to < - 10°C, a second SSBR has a Tg in a range of > -35 °C to < -20°C, and a third SSBR has a Tg in a range of > -70°C to < -50°C.

Description

| AD 41698 (P.064) . _1- LU100944 Rubber composition for tyres The present invention relates to a cross-linkable rubber composition comprising a rubber component, a method of preparing a cross-linkable rubber composition, a cross-linked rubber composition obtained by cross-linking such a rubber composition, a method of preparing a tyre tread and a tyre.

Tread rubber is one of the important portions of a pneumatic tyre which contributes enormously to the overall performance of a tyre. A tyre has to perform well in severe weather conditions and it has to exhibit variety of performances such as wet grip, dry grip, abrasion resistance and low rolling resistance.

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 glass transition temperature (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 lately used to increase the wet grip properties but this often have a negative effect on the rolling resistance (J Appl Polym Sci 65: 1429-1439, 1997).

To have a good balance between wet grip and rolling resistance, new materials and/or new compounding principles are always sought-after. Optimizing the tread compound for wet grip normally results in high rolling resistance. The main purpose of this invention is to provide a tyre tread which can improve wet grip without increasing rolling resistance. ; US 2015/0343843 A1 discloses a tread for a tire comprising a rubber composition that is based upon a cross-linkable elastomer composition, the cross-linkable elastomer composition comprising a high-Tg rubber being a highly unsaturated diene elastomer having a glass transition temperature of between —30°C and 0°C and a low-Tg rubber being a highly unsaturated diene elastomer having a glass transition temperature of between —110°C and —60°C. The tire tread manufactured from a rubber composition that includes both a high-Tg rubber component and a low-Tg rubber component that are incompatible with each other when mixed together provides a tire tread having improved snow traction over tire treads having a lower Tg.

US 4748168 A discloses a rubber composition for use in tire treads comprising a first

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AD 41698 (P.064) . 2. styrene-butadiene copolymer rubber having a glass-transition temperature between 20°C 00066 and -45°C, and one or more of a second styrene-butadiene copolymer rubber having a glass-transition temperature lower than -45°C; 80-130 parts by weight of a carbon black having a specific surface area greater than 120 m”/g, the amount being based on 100 parts by weight of the starting rubber; and 20-90 parts by weight of a softener having a viscosity-gravity constant between 0.90 and 0.98, the amount being based on 100 parts by weight of the starting rubber. The resulting composition has a storage shear modulus smaller than 500 MPa at -30°C which is excellent in friction performance, abrasion resistance and low-temperature resistance.

US 9040613 B2 discloses a rubber composition comprising at least one diene elastomer, one reinforcing filler and one plasticizing system, characterized in that the said plasticizing system comprises, in combination a plasticizing hydrocarbon resin which has a Tg greater than 0°C; and a tri- or pyromellitate ester. The rubber composition exhibits an improved wear resistance.

Optimizing the tread compound for wet grip normally results in trade-off in rolling resistance performance. The present invention has the object to provide a cross linkable rubber composition to be used in a tyre tread to serve well in very wide range of temperatures for both wet and 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 10, a cross- linked rubber composition according to claim 11, a method for preparing a tyre according to claim 13 and a tyre according to claim 14. 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, per hundred parts by weight of rubber (phr), > 1 phr to < 150 phr of a rubber component, wherein the rubber component comprises a blend of three solution styrene-butadiene rubbers (SSBRs), wherein a first SSBR has a glass transition temperature (Tg) in a range of > -13°C to <-10°C, a second SSBR has a Tg in a range of > -35°C to <-20°C, and a third SSBR has a Tg in a range of > -70°C to < -50°C. The glass transition temperatures Tg are measured by differential scanning calorimetry (DSC) 7 EE

’ AD 41698 (P.064) . -3- LU100944 according to ISO 22768. This norm specifies a heating rate of 20 °C/min. As used herein, “phr” is “parts per hundred parts of rubber by weight” and is a common measurement in the art wherein components of a rubber composition are measured relative to the total weight of rubber in the composition, i.e., parts by weight of the component per 100 parts by weight of the total rubber(s) in the composition. It was surprisingly found that a rubber composition that includes a blend of three SSBRs of different glass transition temperatures, one having a very high Tg, one having a high Tg and one having a low Tg when mixed together provides a tyre tread having better wet grip and lower rolling resistance. Without wishing to be bound by theory, it is believed that the very high Tg SSBR rubber and the high Tg SSBR rubber are incompatible with each other. Particularly, it is provided a blend of two high Tg SSBRs and one low Tg SSBR wherein one of the high Tg SSBRs has a very high Tg, preferably a Tg in a range of > -12 °C to < -10°C, most preferred a Tg of -12°C. Such very high Tg may be provided by a SSBR with high styrene and high vinyl content. It is assumed that the blend of the two high Tg SSBRs creates an immiscibility, thereby leading to a very broad tan delta curve in the cured rubber. The broad delta curve offers an increase in the wet grip (tan delta at 0°C) and shows a very steep decay of the curve at higher temperatures which implies a low rolling resistance index (tan delta at 70°). According to a preferred embodiment, the first SSBR has a styrene content in a range of > 30 weight-% to < 45 weight-% and a vinyl content in a range of > 45 weight-% to < 75 weight-%. Preferably the first SSBR has a styrene content of 40 weight-% and vinyl content of 65 weight-%. According to one embodiment, the second SSBR has a styrene content in a range of > 30 weight-% to < 40 weight-% and a vinyl content in a range of > 40 weight-% to < 50 weight-%. Preferably the second SSBR has a styrene content of 35 weight-% and a vinyl content of 40 weight-%. According to one embodiment, the amount of first SSBR is in a range of > 25 phr to < 45 phr. According to one embodiment, the amount of second SSBR is in a range of > 20 phr to < 40 phr.

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; AD 41698 (P.064) > - 4 - . . . 2. LU100944 According to one embodiment embodiment, the amount of third SSBR is in a range of > 10 phr to <40 phr. According to a further embodiment embodiment, the rubber component further comprises a polybutadiene rubber (BR), a natural rubber (NR) or a mixture thereof. Preferably, the rubber component further comprises a polybutadiene rubber. The amount of BR may be in a range of > 30 phr to < 70 phr. Preferably, the amount of BR is in a range of > 40 phr to < 50 ph. According to one embodiment, the composition comprises: Rubber component Polybutadiene Rubber 50.00 First SSBR 41.25 Second SSBR 20.00 — 30.00 Third SSBR 20.00 — 30.00 According to one embodiment, the composition comprises: Rubber component Polybutadiene Rubber | 50.00 First SSBR 41.25 Second SSBR 31.25 Third SSBR 25.00 The Butadiene Rubber may be a Nickel catalysed polybutadiene with high cis content. The first SSBR may be SE-6233 rubber, which is an oil extended functionalized high styrene and high vinyl SSBR and has a typical glass transition temperature of -12 °C. The second SSBR may be a SSBR functionalized NON oil extended SSBR selected from SSBR SLR-4602 having medium styrene and medium vinyl content, or XC-3737 having high styrene and medium vinyl content, or Tufdene S202 having high styrene and medium vinyl content and a typical glass transition temperature of -23 to -30°C. The third SSBR may be Sprintan SLR 3402 rubber having a low styrene/medium vinyl micro structure and a typical glass transition temperature of -60 °C. The invention also relates to a method of preparing a cross-linkable rubber composition comprising the steps of:

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; AD 41698 (P.064) . _-5- . LU100944 — providing > 1 phr to < 150 phr of a rubber component, wherein the rubber component comprises a blend of three different solution styrene-butadiene rubbers (SSBRs), wherein a first SSBR has a Tg in a range of > -13°C to <-10°C, a second SSBR has a Tg in a range of > -35 °C to < -20°C, and a third SSBR has a Tg in a range of > -70°C to < -50°C; — masticating the polymers in a Banbury mixer for 30-90 seconds; — adding the other ingredients and mixing at 80 to 100 rpm. 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 > 0.14 to < 0.25 (determined from DMA measurements according to ISO 4664-1, frequency 10 Hz,

0.1% dynamic strain) and a tan delta at 70 °C of > 0.12 to < 0.15 (determined from 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.

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 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 tand as a function of temperature (-80 to 25°C) for the reference compositions Bl and B2 and a cross-linkable rubber composition according to an embodiment of the present invention B3.

Figure 2: A graph of the tanô as a function of temperature (-80 to 25°C) for the reference compositions Al and A2 and a cross-linkable rubber composition according to an

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" AD 41698 (P.064) * Û 6 _ LU100944 embodiment of the present invention A3. Figure 3: A graph of the tand as a function of temperature (-80 to 25°C) for the reference composition Bl and the cross-linkable rubber compositions according to the present invention C2 and C3.

Figure 4: A graph of the tand as a function of temperature (30 to 80°C) for the reference compositions Bl and B2 and the cross-linkable rubber composition according to the present invention B3.

Figure 5: A graph of the tand as a function of temperature (30 to 80°C) for the reference compositions Al and A2 and the cross-linkable rubber composition according to the present invention A3. Figure 6: A graph of the tand as a function of temperature (30 to 80°C) for the reference composition BI and the cross-linkable rubber compositions according to the present invention C2 and C3. In accordance with the preceding, cross-linkable rubber compositions were prepared. For the preparation of the composition according to the present invention the method as disclosed in the description was used. The cross-linked composition was then tested for the rebound at 70°C. The cross linked composition was further tested by using DMA test. Example 1: The Table 1 below shows the reference compositions Bl and B2 and the cross-linkable rubber composition according to the present invention B3. Table 1: ponents Bi (PHR) | B2(PHR) | B3 (PHR) Butadiene Rubber, 40.00 38.46 38.46 high cis (Ni catalyst) First SSBR 7) 31.88 31.74 Second SSBR 30.00 EN 15.38 Third SSBR 30.00 19.23 23.08 Silica (HDS, MP) 83.00 83.00 83.00 TESPD (disulphide 6.65 6.65 6.65 silane)

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’ AD 41698 (P.064) . 7. LU100944 TDAE (processing 26.00 1.29 17.20 oil) Sulphur (soluble, 1% 1.90 1.90 1.90 oil) TBBS (N-Tert-Butyl- 1.90 1.90 1.90 2 benzo-thiazole sulfenamide) DPG (Diphenyl 2.21 2.21 2.21 guanidine) ZnO (Zinc oxyde 2.00 2.00 2.00 direct) sPPD TMQ (Polymerized 2.00 2.00 2.00 2,2,4 tri methyl 1,2 di hydro quinoline) Zinc salt of fatty 4.00 4.00 4.00 acids The Table 2 below shows the reference compositions Al and A2 and the cross-linkable rubber composition according to the present invention A3. Table 2: components Al A2 A3 (PHR) (PHR) (PHR) Butadiene Rubber, high 40.00 50.00 50.00 cis (Ni catalyst) First SSBR 75.65 41.25 Second SSBR 71.25 LL - | 31.25 Third SSBR 30.00 25.00 25.00 N 339 Carbon Black Silica (HDS, MP) 83.00 83.00 83.00 TESPD (disulphide 6.65 6.65 6.65 silane) TDAE (processing oil) 14.75 | 850 | Sulphur (soluble, 1% où TBBS (N-Tert-Butyl-2 1.90 2.30 2.30 benzo-thiazole EE.

AD 41698 (P.064) . 8. LU100944 es EPP guanidine) tri methyl 1,2 di hydro quinoline) The Table 3 below shows the reference composition Bl and the cross-linkable rubber compositions according to the present invention C2 and C3. Table 3: components B1 C2 C3 | em sw PR a TBBS (N-Tert-Butyl-2 benzo-thiazole 1.90 1.90 1.90 am TT Ba Ba

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’ AD 41698 (P.064) s ; - 9 - 100944 TMQ (Polymerized 2,2,4 tri methyl 1,2 di hydro 2.00 2.00 2.00 quinoline) Butadiene Rubber was Nickel catalysed polybutadiene with high cis content. The first SSBR was SE-6233 rubber, which is an oil extended functionalized high styrene and high vinyl SSBR and has a typical glass transition temperature of -12 °C.

The second SSBR was a SSBR functionalized NON oil extended SSBR selected from SSBR SLR-4602 having medium styrene and medium vinyl content, or XC-3737 having high styrene and medium vinyl content, or Tufdene S202 having high styrene and medium vinyl content and a typical glass transition temperature of -23 to -30°C.

The third SSBR was Sprintan SLR 3402 rubber having a low styrene/medium vinyl micro structure and a typical glass transition temperature of -60 °C.

Silica contained 7% bound water and surface area of 165m2/g.

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

TDAE (treated distillate aromatic extracted) denotes oil with viscosity of 410m2/s at 40°C and the Tg of -42°C.

Sulfur containing 1% of a mineral oil with melting point of 115°C and pH of 6.8.

Two accelerators were used; TBBS (N-tert-butylbenzothiazole-2-sulphenamide) with melting point of 109°C and DPG (diphenyl guanidine) with melting point between 144 and 151°C and an alkalinity of 10.2 on pH scale. Zinc Oxide with density of 5.61 kg/l and Stearic Acid with melting point between 68-70°C was used.

6PPD (N-phenyl-N'-1,3-dimethylbutyl-p-phenylenediamine) with melting point of 56°C.

Anti-ozone wax was Paraffin wax with 2% polyethylene and congealing point of 62-72°C. Analysis of the cross-linkable rubber composition according to the present invention: EE —————

° AD 41698 (P.064) * -10- The above mentioned compositions were analyzed by using the following test methods. The results of the tests are provided in the Tables 4 to 6 below and Figures 1 to 6. Rebound measurements were done on the Zwick/Roell 5109 Rebound Resilience Tester by the standardised ISO4662 method at 23°C and 70°C. Cylindrical samples of 53 mm in diameter and 12.5 mm in thickness were cured at 170°C for 12 minutes.

The dynamic measurements of the cured compounds were performed using a Metravib DMA +450 dynamic spectrometer in double shear mode according to ISO 4664-1. Samples were prepared as cylinders of 8 mm diameter and thickness of 2 mm cured at 170°C for 10 minutes. Samples were conditioned after vulcanisation for 24 hours at room temperature.

The dynamic measurements were conducted by a temperature sweep at constant frequency 10 Hz. A dynamic strain of 0.1% is applied for the temperature rage -80°C to 25°C followed by a 6% strain for the temperature rage 25°C to 80°C. An increased dynamic strain at higher temperatures is more reliable for the rolling resistance prediction. The full width at half maximum (FWHM) values can be determined by recording a DMA according to ISO 4664-1, frequency 10 Hz, 0.1% dynamic strain, and calculating the full width at half maximum of the tan delta curve. FWHM range >65 is considered to be good as it shows a better balance between the different properties of the cross linked rubber composition. The above mentioned analysis of different parameters provided the following results for the compositions of Table 1 which are shown below in Table 4.

Table 4 (FWHM) (°C) As can be seen in the figues 1 and 4, by using a blend of low Tg SSBR and two high Tg SSBRs (one of them having a very high Tg) a broad tan delta curve could be obtained. Immiscibility could be seen in the blend and as a result of this immiscibility the wet grip

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’ AD 41698 (P.064) ’ -11- an . . . an LU100944 indicator (tan delta 0°C) increased and the rolling resistance indicator (tan delta 70) remained the same or increases.

Table 5 depicts the analysis of different parameters for the compositions of Table 2. Table 5

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Full width half maximum | -52 to -9 | -56 to 40 | -52 to 15

(FWHM) (°C)

As can be seen in the figues 2 and 5, using another type of SSBR in the blend did not show the broader curve as was shown by the first example.

It was therefore considered necessary to have at least one SSBR with a very high Tg.

Table 6 depicts the analysis of different parameters for the compositions of Table 3. Table 6 Full width half maximum (FWHM) (°C) -63 to -12 -58 to 21 -54 to 12

As can be seen in the figues 3 and 6, using an immiscible blend shows a higher tan delta, 0°C (better wet grip) and lower tan delta, 70°C (lower rolling resistance). “HH ——

Claims

” AD 41698 (P.064 : -12- LU100944 Patent claims

1. A cross-linkable rubber composition, the cross-linkable rubber composition comprising, per hundred parts by weight of rubber (phr): > 1 phr to < 150 phr of a rubber component; characterised in that the rubber component comprises a blend of three solution styrene-butadiene rubbers (SSBRs), wherein a first SSBR has a glass transition temperature (Tg, measured by DSC, according to ISO 22768) in a range of > -13°C to < -10°C, a second SSBR has a Tg in a range of > -35 °C to < -20°C, and a third SSBR has a Tg in a range of > -70°C to <-50°C.

2. The rubber composition according to claim 1, wherein the first SSBR has a styrene content of 30-45 weight-% and a vinyl content of 45-75 weight-%.

3. The rubber composition according to claim 2, wherein the first SSBR has a styrene content of 40 weight-% and a vinyl content of 65 weight-%.

4. The rubber composition according to claim 1 to 3, wherein the second SSBR has a styrene content of 35 weight-% and a vinyl content of 40 weight-%.

5. The rubber composition according to claims 1 to 4, wherein the amount of first SSBR is in a range of > 25 phr to < 45 phr.

6. The rubber composition according to claims 1 to 5, wherein the amount of second SSBR is in a range of > 20 phr to < 40 phr.

7. The rubber composition according to claims 1 to 6, wherein the amount of third SSBR is in a range of > 10 phr to < 40 phr.

8. The rubber composition according to claims 1 to 7, wherein the rubber component further comprises a polybutadiene rubber (BR), a natural rubber (NR) or a mixture thereof. A ——

° AD 41698 (P.064) . -13- LU100944

9. The rubber composition according to one of claims 1 to 8, wherein the composition comprises: Rubber component Polybutadiene Rubber 50.00 First SSBR 41.25 Second SSBR 20.00 — 30.00 Third SSBR 20.00 — 30.00

10. The rubber composition according to one of claims 1 to 8, wherein the composition comprises: Rubber component Polybutadiene Rubber 50.00 First SSBR 41.25 Second SSBR 31.25 Third SSBR 25.00

11. A method of preparing a cross-linkable rubber composition according to one of claims 1 to 10, comprising the steps of: a. providing > 1 phr to < 150 phr of a rubber component, wherein the rubber component comprises a blend of three solution styrene-butadiene rubbers (SSBRs), wherein a first SSBR has a Tg in a range of > -13°C to < -10°C, a second SSBR has a Tg in a range of > -35 °C to < -20°C, and a third SSBR has a Tg in a range of > -70°C to < -50°C; b. masticating the polymers in a Banbury mixer for 30-90 seconds; c. adding the other ingredients and mixing at 80 to 100 rpm.

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

13. The cross-linked rubber composition according to claim 12 with a tan delta at 0 °C of > 0.14 to < 0.25 (determined from DMA measurements according to ISO 4664- 1, frequency 10 Hz, 0.1% dynamic strain) and a tan delta at 70 °C of > 0.12 to <

0.15 (determined from DMA measurements according to ISO 4664-1, frequency 10 Hz, 6 % dynamic strain).

" AD 41698 (P.064) ’ -14 - LU100944

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 claim 12 or 13.

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