Process for preparing compounds for tyres and tyres comprising them

Abstract

The present invention relates to a process for preparing a vulcanisable elastomeric compound for tyres, characterised by the use of a particular vulcanisation-activating filler and by the methods of adding additives, in particular the compatibilising agent (silane), which occurs only after completion of the reaction between the activating filler comprising zinc and the fatty acid (stearic acid). The present process, advantageous in itself due to the possible reduction of the times and of the energy required for vulcanisation, allows preparing compounds which, with the same performances compared to the traditional ones, can have a reduced zinc content, and consequently a lower release thereof from tyres during use at an environmental level.

Claims

1. A process for preparing a vulcanisable elastomeric compound for tyres, said process comprising at least: mixing (1) at least one elastomeric polymer (A) and at least one additive for elastomeric compounds, with the exception of vulcanising agents (B), to produce a non-vulcanisable elastomeric compound; mixing (2) the non-vulcanisable elastomeric compound and at least one vulcanising agent (B), to give a vulcanisable elastomeric compound; and unloading of the vulcanisable elastomeric compound, wherein in one or more of the mixing steps, adding at least one fatty acid (C), at least one product (D) comprising zinc directly bound to a white filler and at least one compatibilising agent (E), and wherein the at least one compatibilising agent (E) is added after the complete addition and processing of the at least one fatty acid (C) and at least one product (D) comprising zinc directly bound to a white filler.

2. The process as claimed in claim 1, wherein the at least one fatty acid (C), the at least one product (D) comprising zinc directly bound to a white filler, and the at least one compatibilising agent (E) are all added in the mixing step (1).

3. The process as claimed in claim 1, wherein the at least one fatty acid (C) and the at least one product (D) comprising zinc directly bound to a white filler are added in the mixing step (1) and the at least one compatibilising agent (E) is added in the mixing step (2).

4. The process as claimed in claim 1, wherein the processing of the at least one fatty acid (C) and the at least one product (D) comprising zinc directly bound to a white filler is carried out at a compound temperature at least equal to the melting temperature of the fatty acid (C) or higher.

5. The process as claimed in claim 1, wherein the mixing step (2) is carried out at a compound temperature lower than 160° C.

6. The process as claimed in claim 1, wherein: the at least one diene elastomeric polymer (A) is chosen from 1,4-polyisoprene, 3,4-polyisoprene, polybutadiene, optionally halogenated isoprene/isobutene copolymers, 1,3-butadiene/acrylonitrile copolymers, styrene/1,3-butadiene copolymers, styrene/isoprene/1,3-butadiene copolymers, styrene/1,3-butadiene/acrylonitrile copolymers, and mixtures thereof the vulcanising agent (B) is chosen from sulphur and sulphur donors and when sulphur donors, the sulphur donors are chosen from caprolactam disulfide (CLD), bis[(trialkoxysilyl)propyl]polysulphides, dithiophosphates, phosphorylpolysulphide (SDT), and mixtures thereof.

7. The process as claimed in claim 1, wherein the fatty acid (C) is chosen from saturated or unsaturated fatty acids ranging from 8 to 26 carbon atoms, esters thereof, salts thereof, and mixtures thereof.

8. The process as claimed in claim 1, wherein the zinc in the product (D) is present as zinc oxide.

9. The process as claimed in claim 1, wherein the white filler of the product (D) is chosen from silica and silicates and when silicates, the silicates are chosen from bentonite, nontronite, beidellite, volkonskoite, ectorite, saponite, sauconite, vermiculite, sericite, sepiolite, paligorskite or attapulgite, montmorillonite, halloysite, optionally modified by acid treatment and/or derivatised, and mixtures thereof.

10. The process as claimed in claim 1, wherein the product (D) comprising zinc directly bound to a white filler is zinc oxide on silica.

11. The process as claimed in claim 1, wherein the compatibilising agent (E) is a silane chosen from those having at least one hydrolysable group, of general formula (I):
(R).sub.3Si—C.sub.nH.sub.2n—X  (I) wherein the R groups, which may be the same or different, are chosen from alkyl, alkoxy or aryloxy groups or from halogen atoms, and provided that at least one of the R groups is an alkoxy or aryloxy group or a halogen; n is an integer ranging from 1 to 6; X is a group chosen from nitrous, mercapto, amino, epoxide, vinyl, imide, chlorine, —(S).sub.mC.sub.nH.sub.2n—Si—(R).sub.3 and —S—COR, wherein m and n are integers ranging from 1 to 6 and the R groups are as defined.

12. The process as claimed in claim 1, wherein: the fatty acid (C) is added in a total amount ranging from 0.05 to 20 phr; the product (D) comprising zinc directly bound to a white filler is added in a total amount ranging from 1 to 100 phr; and the compatibilising agent (E) is added in a total amount ranging from 0.1 phr to 20 phr.

13. The process as claimed in claim 1, further comprising adding one or more further additives, and the one or more further additivies are chosen from vulcanisation accelerants (F), vulcanisation retardants (G), reinforcing fillers (H), antioxidants (I), waxes (L) and plasticisers (M).

14. A vulcanisable elastomeric compound obtained according to the process as of claim 1.

15. The vulcanisable elastomeric compound as claimed in claim 14, wherein zinc is present in an amount of less than 4 phr.

16. A tyre component comprising the vulcanisable compound as claimed in claim 14 or the vulcanised compound obtained by vulcanisation thereof.

17. The tyre component as claimed in claim 16, wherein the tyre component is chosen from tread band, under-layer, anti-abrasive elongated element, sidewall, sidewall insert, mini-sidewall, under-liner, rubber layers, bead filler, and sheet.

18. A tyre for vehicle wheels comprising at least one tyre component as claimed in claim 17.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a radial half-section of a tyre for vehicle wheels, comprising at least one component formed by an elastomeric compound prepared according to the process of the invention.

(2) FIG. 1 shows a radial half-section of a tyre for vehicle wheels according to the invention.

(3) In FIG. 1, “a” indicates an axial direction and “X” indicates a radial direction, in particular X-X indicates the outline of the equatorial plane. For simplicity, FIG. 1 shows only a portion of the tyre, the remaining portion not shown being identical and arranged symmetrically with respect to the equatorial plane “X-X”.

(4) Tyre 100 for four-wheeled vehicles comprises at least one carcass structure, comprising at least one carcass layer 101 having respectively opposite end flaps engaged with respective annular anchoring structures 102, referred to as bead cores, possibly associated to a bead filler 104.

(5) The carcass layer 101 is optionally made with an elastomeric compound.

(6) The tyre area comprising the bead core 102 and the filler 104 forms a bead structure 103 intended for anchoring the tyre onto a corresponding mounting rim, not shown.

(7) The carcass structure is usually of radial type, i.e. the reinforcing elements of the at least one carcass layer 101 lie on planes comprising the rotational axis of the tyre and substantially perpendicular to the equatorial plane of the tyre. Said reinforcement elements generally consist of textile cords, such as rayon, nylon, polyester (for example polyethylene naphthalate, PEN). Each bead structure is associated to the carcass structure by folding back of the opposite lateral edges of the at least one carcass layer 101 around the annular anchoring structure 102 so as to form the so-called carcass flaps 101a as shown in FIG. 1.

(8) In one embodiment, the coupling between the carcass structure and the bead structure can be provided by a second carcass layer (not shown in FIG. 1) applied in an axially outer position with respect to the first carcass layer.

(9) An anti-abrasive strip 105 optionally made with an elastomeric compound is arranged in an outer position of each bead structure 103.

(10) The carcass structure is associated to a belt structure 106 comprising one or more belt layers 106a, 106b placed in radial superposition with respect to one another and with respect to the carcass layer, having typically textile and/or metallic reinforcement cords incorporated within a layer of vulcanised elastomeric compound.

(11) Such reinforcement cords may have crossed orientation with respect to a direction of circumferential development of tyre 100. By “circumferential” direction it is meant a direction generally facing in the direction of rotation of the tyre.

(12) At least one zero-degree reinforcement layer 106c, commonly known as a “0° belt”, may be applied in a radially outermost position to the belt layers 106a, 106b, which generally incorporates a plurality of elongated reinforcement elements, typically metallic or textile cords, oriented in a substantially circumferential direction, thus forming an angle of a few degrees (such as an angle of between about 0° and 6°) with respect to a direction parallel to the equatorial plane of the tyre, and coated with vulcanised elastomeric compound.

(13) A tread band 109 of vulcanised elastomeric compound is applied in a position radially outer to the belt structure 106.

(14) Moreover, respective sidewalls 108 of vulcanised elastomeric compound are applied in an axially outer position on the lateral surfaces of the carcass structure, each extending from one of the lateral edges of tread 109 at the respective bead structure 103.

(15) In a radially outer position, the tread band 109 has a rolling surface 109a intended to come in contact with the ground. Circumferential grooves, which are connected by transverse notches (not shown in FIG. 1) so as to define a plurality of blocks of various shapes and sizes distributed over the rolling surface 109a, are generally made on this surface 109a, which for simplicity is represented smooth in FIG. 1.

(16) An under-layer 111 of vulcanised elastomeric compound can be arranged between the belt structure 106 and the tread band 109.

(17) A strip consisting of elastomeric compound 110, commonly known as “mini-sidewall”, of vulcanised elastomeric compound can optionally be provided in the connecting zone between sidewalls 108 and the tread band 109, this mini-sidewall generally being obtained by co-extrusion with the tread band 109 and allowing an improvement of the mechanical interaction between the tread band 109 and sidewalls 108. Preferably, the end portion of sidewall 108 directly covers the lateral edge of the tread band 109.

(18) In the case of tubeless tyres, a rubber layer 112, generally known as “liner”, which provides the necessary impermeability to the inflation air of the tyre, can also be provided in a radially inner position with respect to the carcass layer 101.

(19) The rigidity of the tyre sidewall 108 can be improved by providing the bead structure 103 with a reinforcing layer 120 generally known as “flipper” or additional strip-like insert.

(20) Flipper 120 is a reinforcing layer which is wound around the respective bead core 102 and the bead filler 104 so as to at least partially surround them, said reinforcing layer being arranged between the at least one carcass layer 101 and the bead structure 103. Usually, the flipper is in contact with said at least one carcass layer 101 and said bead structure 103.

(21) Flipper 120 typically comprises a plurality of textile cords incorporated within a layer of vulcanised elastomeric compound.

(22) The bead structure 103 of the tyre may comprise a further protective layer which is generally known by the term of “chafer” 121 or protective strip and which has the function of increasing the rigidity and integrity of the bead structure 103.

(23) Chafer 121 usually comprises a plurality of cords incorporated within a rubber layer of vulcanised elastomeric compound. Such cords are generally made of textile materials (such as aramide or rayon) or metal materials (such as steel cords).

(24) A layer or sheet of elastomeric compound can be arranged between the belt structure and the carcass structure. The layer can have a uniform thickness. Alternatively, the layer may have a variable thickness in the axial direction. For example, the layer may have a greater thickness close to its axially outer edges with respect to the central (crown) zone.

(25) Advantageously, the layer or sheet can extend on a surface substantially corresponding to the extension surface of said belt structure.

(26) In a preferred embodiment, a layer of elastomeric compound as described above, referred to as under-layer, can be placed between said belt structure and said tread band, said under-layer preferably extending on a surface substantially corresponding to the extension surface of said belt structure.

(27) The elastomeric compound according to the present invention can be advantageously incorporated in one or more of the components of the tyre selected from the belt structure, carcass structure, tread band, under-layer, sidewall, mini-sidewall, sidewall insert, bead, flipper, chafer, sheet and anti-abrasive strip, preferably incorporated at least in the sidewalls and/or in the under-layer.

(28) According to an embodiment not shown, the tyre may be a tyre for motorcycle wheels which is typically a tyre that has a straight section featuring a high tread camber.

(29) According to an embodiment not shown, the tyre may be a tyre for bicycle wheels.

(30) According to an embodiment not shown, the tyre may be a tyre for heavy transport vehicle wheels, such as trucks, buses, trailers, vans, and in general for vehicles in which the tyre is subjected to a high load. Preferably, such a tyre is adapted to be mounted on wheel rims having a diameter equal to or greater than 17.5 inches for directional or trailer wheels.

(31) FIG. 2 is a microscopic image of a ZnO/SiO.sub.2 (D) activating filler measured with a high resolution transmission electron microscope (HRTEM), which shows the zinc oxide particles anchored to the silica surface.

(32) FIG. 3 schematically shows the possible structure of the complex which is formed by reaction between stearic acid and ZnO nanoparticles anchored on SiO.sub.2, wherein Y represents a counter-ion such as an OH group or an acetate.

(33) FIG. 4 is an ATR-FTIR spectroscopic image showing the formation of the complex shown in FIG. 2, by reaction between stearic acid and ZnO nanoparticles anchored on SiO.sub.2 (graph a) in comparison to the standard ZnO and stearic acid system (graph b), heated at 120° C. for 5 minutes in a simplified vulcanisation model. In this model, low molecular weight molecules are used which mimic the reactivity of the polymer, such as for example 2,3-dimethyl-2-butene used to simulate isoprenic rubbers.

(34) FIG. 5 shows the normalized curve of the torque values [(Sx−Smin)/(Smax−Smin)*100] measured over time (min) during the vulcanisation of a vulcanisable compound according to the invention and of a comparative compound (Ex. 7.2 and 7.1). FIG. 6 shows the normalized curve of the torque values [(Sx−Smin)/(Smax−Smin)*100] measured over time (min) during the vulcanisation of two comparative vulcanisable compounds (Ex. 8.1 and 8.2) and of a compound according to the invention (Ex. 8.3).

(35) The description of some preparative examples according to the invention and comparative examples, given only for illustrative and non-limiting of the scope if the invention, is set out below.

EXPERIMENTAL PART

(36) Analysis Methods

(37) The ATR-FTIR analysis was performed with a Perkin Elmer Spectrum 100 instrument (spectra with a resolution of 4 cm.sup.−1, region from 650 to 400 cm.sup.−1, 32 scans) (see FIG. 4).

(38) High Resolution Transmission Electron Microscopy (HRTEM) was performed with a 300 KV Jeol 3010 microscope with a high resolution polar pole (point-to-point resolution 0.17 nm) and equipped with a slow-scan Gatan CCD 792 camera. The powders were suspended in isopropanol and a drop of 5 μl of this suspension was deposited on a perforated carbon film supported on a 3 mm copper grid for the TEM assay (see FIG. 2)

(39) Determination of the Zinc Content in the Activating Filler (D)

(40) The zinc oxide content anchored on a white filler (D) can be measured by ICP-AES spectrometry (Inductively Coupled Plasma-Atomic Emission Spectroscopy) with ICP simultaneous plasma spectrometer (TJA IRIS II model; excitation source: radiofrequency generator with 27.12 MHz frequency and variable output power up to 1750 W).

(41) Determination of the Zinc Content in the Compound by X-Ray Fluorescence (XRF)

(42) The X-ray fluorescence analysis is based on the emission effect produced by a primary X-ray beam of high intensity and appropriate energy, incident on the sample.

(43) The sample was prepared by passing about 2 g of vulcanised compound between the cylinders of a cold laboratory mixer until a homogeneous and compact sheet with a thickness between 0.5 and 0.7 mm was obtained.

(44) A circular specimen of about 4 cm in diameter was then cut from the sheet and was introduced into the instrument sample holder (wavelength dispersion X-ray fluorescence spectrometer, model ARL—XRF 8420+).

(45) MDR rheometric analysis (according to ISO 6502): a rheometer Alpha Technologies type MDR2000 was used. The tests were carried out at 170° C. for 20 minutes at an oscillation frequency of 1.66 Hz (100 oscillations per minute) and an oscillation amplitude of 0.5°, measuring the time necessary to achieve an increase of two rheometric units (TS2) and the time necessary to achieve 30% (T30), 60% (T60), 90% (T90) and 100% (T-MH), respectively, of the maximum torque value (MH). The maximum torque value MH and the minimum torque value ML were measured and their difference was calculated (MH-ML).

(46) Properties of Vulcanised Materials

(47) The elastomeric materials prepared in the previous examples were vulcanised to give specimens on which analytical characterisations and the assessment of static and dynamic mechanical properties were conducted.

(48) Unless otherwise indicated, vulcanisation was carried out in a mould, in hydraulic press at 170° C. and at a pressure of 200 bar for about 10 minutes.

(49) The hardness in IRHD degrees (23° C.) was measured according to the ISO 48:2007 standard on samples of the elastomeric materials vulcanised under the conditions set out in the experimental part.

(50) Determination of the Total Cross-Linking Degree and of the Mono- and Disulphide Bonds (% by Weight)

(51) The measurement of the total quantity of bonds or degree of total cross-linking (total number of bonds expressed as moles per gram of compound, mol/g) was performed by exploiting the swelling effect of toluene on the compound. A highly cross-linked compound will have a lower tendency to absorb the solvent than a compound in which the cross-linking is lower. According to this principle, an inverse relationship was established between the amount of solvent absorbed and cross-linking. The quantity of absorbed solvent was determined gravimetrically by calculating the weight difference between the sample swollen at equilibrium with the solvent and the same sample after complete removal of the absorbed solvent, by vacuum drying. The technique of swelling in toluene was also used for the determination of the quantity of mono and disulphide bonds, however, preceded by a treatment with suitable reactants capable of selectively separating the polysulphide bonds. A mixture of piperidine and propan-2-thiol was used to cleave all the polysulphide bonds (containing 3 or more sulphur atoms). The subsequent swelling therefore measured only the contribution of the remaining mono and di-sulphur bonds.

(52) The measurement of the total amount of the bonds and the determination of the mono and disulphide bonds were carried out in parallel on two different portions of the same sample, in two different reaction containers, according to the following procedure.

(53) A sample of a vulcanised compound of 10×10×1 mm.sup.3 (0.10±0.05 g) was immersed in toluene at 25° C. in a laboratory flask and kept in the dark for seven days. The toluene was replaced with fresh toluene after three days. On the seventh day, the swollen solid mass was weighed, then vacuum-dried at 70° C. for 12 hours and reweighed.

(54) The volumetric fraction of the swollen rubber was calculated using this equation:

(55) $V_r=\frac{\left(m_d-{\mathrm{fm}}_0\right).Math.{\rho }_p^{-1}}{\left(m_d-{\mathrm{fm}}_0\right).Math.{\rho }_p^{-1}+m_{\mathrm{so}}.Math.{\rho }_s^{-1}}$
where m.sub.0 is the weight of the compound before swelling; m.sub.sw the weight of the swollen compound; m.sub.d is the weight of the compound dried after swelling; m.sub.so is the weight of solvent within the swollen mass given by m.sub.sw−m.sub.d; ρ.sub.p=0.94 g.Math.cm.sup.−3 is the density of the polymer; ρs=0.87 g.Math.cm.sup.−3 is the density of toluene; f is the filler fraction determined by TGA. The cross-link density (v), i.e. the number of chains bound by gram on two different polymer chains, was evaluated according to the Flory-Rehner equation [Thermodynamics of high polymer solutions, J. Chem. Phys. 10 (1942) 51-61].

(56) $v=\frac{\left[\ln \left(1-V_r\right)+V_r+\chi V_r^2\right]}{-2.Math.{\rho }_p.Math.{V_s\left(V_r\right)}^{1/3}}$
where Vs=105.91 is the molar volume of toluene and χ is the solvent-polymer interaction parameter of Flory which is 0.43 for toluene-isoprenic rubber (IR).

(57) The static mechanical properties were measured at 23° C. according to the ISO 37:2005 standard.

(58) In particular, the 100% elongation load, referred to as CA1, the load at break CR and the elongation at break AR % were measured on samples of the elastomeric materials mentioned above.

(59) Tensile tests were performed on dumbbell-type straight-line specimens (ISO37-2011, T=23° C.) or on ring specimens (ISO37-2011, T=23° C.).

(60) The dynamic mechanical properties were measured according to the following methods:

(61) Dynamic modules E (tensile/compression): they were measured using an Instron dynamic device in compression-traction mode according to the following procedure. A sample of the subject vulcanised elastomeric compounds having a cylindrical shape (length=25 mm; diameter=18 mm), subjected to pre-load compression up to 25% of the longitudinal deformation with respect to the initial length and maintained at the predetermined temperature (equal to +23° C. or 70° C.) for the whole duration of the test, was subjected to a dynamic sinusoidal strain having an amplitude of ±3.5% with respect to the length under pre-load, with a frequency of 100 Hz. The dynamic elastic properties were expressed in terms of elastic (E′), viscous (E″) and Tan delta (loss factor E″/E′) tensile/compression dynamic modulus. The Tan delta value was calculated as the ratio between the viscous dynamic module (E″) and the dynamic elastic modulus (E′), both being determined by the above dynamic measurements.

(62) G (shear) dynamic modules: they were measured using a Monsanto RPA rheometer 2000 according to the following method: cylindrical test specimens with weights in the range of 4.5 to 5.5 g were obtained by punching the vulcanisable elastomeric composition of the samples and their vulcanisation in the instrument “RPA” (at 170° C. for 10 minutes). The vulcanised samples were subjected to dynamic measurement of the elastic shear modulus (G′) at 70° C., 10 Hz frequency, 0.1% and 10% strain.

(63) The dynamic elastic properties were expressed in terms of elastic (G′), viscous (G″) and Tan delta (loss factor G″/G′) shear dynamic modulus.

Example 1

(64) Preparation of Activating Fillers (ZnO/SiO.sub.2) According to the Prior Art

(65) ZnO/SiO.sub.2 activating fillers were prepared by the following procedure described in Chemical Engineering Journal 275 (2015) 245-252.

(66) Powdered silica (0.426 moles, precipitated silica Rhodia Zeosil MP1165, specific surface area BET 160 m.sup.2/g), was dispersed in 0.90 L of anhydrous ethanol by sonication for 10 min (pulses: 1 s; 20 kHz). Subsequently, Zn(CH.sub.3COO).sub.2 was added to the silica suspension. 2H.sub.2O (quantity in Table 1) and NaOH (0.10 mol) under stirring, at 65° C.:

(67) TABLE-US-00001 TABLE 1 Zn acetate. ZnO content Sample 2H.sub.2O (mol) (% by weight) 1A 0.205 14.2 1B 0.081 7.7 1C 0.015 4.0

(68) The ZnO nanoparticles, originated by hydrolysis, condensed on the silica surface forming samples with different amounts of zinc. After 20 minutes, the solid ZnO/SiO.sub.2 particles were filtered, then washed four times with ethanol and air dried at room temperature.

Example 2

(69) Preparation of Fillers Activating the Vulcanisation (ZnO/SiO.sub.2)

(70) 1.2 litres of ethanol, 4.7 g of NaOH and 8.9 g of zinc acetate dihydrate under stirring were introduced into a 3-liter flask until completely dissolved. The solution thus obtained was heated up to 65° C., until it became milky due to the probable formation of zinc compounds of the [Zn(OH)n].sup.n+ type. 17.06 g of silica were then added (Rhodia Zeosil MP1165, BET specific surface area 160 m.sup.2/g), maintaining the temperature at 65° C. for 20 minutes under stirring. The suspension was then filtered through filter, washing the solid with 200 ml of ethanol three times, finally drying the product in air at room temperature.

(71) 19.4 g of solid consisting of silica nanoparticles were obtained, with a ZnO load of about 12.3% by weight.

Example 3

(72) Preparation of Fillers Activating the Vulcanisation (ZnO/Sepiolite)

(73) 1 g of sepiolite was dispersed in 50 ml of 0.01 M NaOH and left under stirring at room temperature for 24 h. The dispersion was centrifuged at 9000 rpm for 30 min. The precipitate was dispersed several times in deionized water to allow an optimal washing and recovered again by centrifugation up to neutral pH. The solid was dried by lyophilisation. In another flask, 140 ml of ethanol and 0.56 g of NaOH (conc. NaOH=0.1 M) were added and stirred at 65° C. for 10 min. After dissolving the soda, zinc acetate dihydrate (0.39 g) was added and left under stirring until the solution became cloudy. Finally, 1 g of previously treated sepiolite was added and left under stirring for 20 minutes.

(74) The product was filtered on Buchner, washed 3 times with fresh ethanol and dried in a stove overnight at 80° C.

(75) Characterisation of Vulcanisation Activating Fillers (D)

(76) Samples of the activating fillers prepared in Example 2 were subjected to the following assays:

(77) TABLE-US-00002 TABLE 2 Analytical method Result Property X-ray diffraction No signal Amorphous state of ZnO (XRD) UV-Visible 3.29-3.47 eV Energy absorption of absorption (UV-Vis) ZnO particles (micro vs nano) Total attenuated 963-965 cm.sup.−1 Absence of the signal reflectance (ATR- related to silanols FTIR) (Si—OH) Inductively coupled 9-13% by weight Amount of ZnO anchored plasma mass on silica spectroscopy (ICP)

Example 4

(78) Preparation of Synthetic Isoprene-Based Elastomeric Compounds for Under-Layer

(79) In this example, a comparison was made between a conventional compound for an under-layer comprising a traditional filler (silica) and an activating agent (ZnO microcrystalline) (Comparative 4.1), a compound comprising an activating filler (ZnO/SiO.sub.2) but prepared according to a standard process with simultaneous addition of the silane (Comparative 4.2), a compound comprising an activating filler (ZnO/SiO2) prepared by adding the silane together with said filler and only after the stearic acid (Comparative 4.3, as described in Chem. Eng, 2015, 245, page 247, par. 2.4) and a compound according to the invention (Example 4.4), in which the silane was added at a later step, when the stearic acid had completely reacted with the zinc of the activating filler.

(80) The elastomeric compounds of Examples 4.1-4.4 below were prepared according to the methods described herein. The quantities of the various components are indicated in phr and shown in the following Table 3:

(81) TABLE-US-00003 TABLE 3 Comp. Comp. Comp. Inv. ZnO Step Ingredients 4.1 4.2 4.3 4.4 content 1-0 IR 100 100 100 100 1-1 Silica 40 26.9 26.9 26.9 1-1 Stearic acid 2 2 — 2 1-1 6PPD 2 2 2 2 1-1 Silane — — 3.2 — 1-1 ZnO/SiO.sub.2 Ex. 2 — — 14.9 — 1.84 (12.3%) 1-2 ZnO/SiO.sub.2 Ex. 2 — 14.9 — 14.9 1.84 (12.3%) 1-2 Stearic acid — — 2 — 1-2 ZnO (80%) 2.3 — — 1.84 1-2 Silane — 3.2 — — 1-3 Silane 3.2 — — 3.2 2-0 CBS 1.6 1.6 1.6 1.6 2-0 Sulphur (67%) 3 3 3 3
wherein:
IR: high-cis synthetic polyisoprene (min. 96%), obtained by polymerisation in solution with Ziegler/Natta catalyst; Supplier NIZHNEKAMSKNEFTECHIM EXPORT;
Silica: ZEOSIL 1115 MP (specific surface area BET 95-120 m.sup.2/g, white microbeads obtained by precipitation from sodium silicate solutions with sulphuric acid. It does not contain crystalline silica. Supplier SOLVAY RHODIA OPERATIONS
Stearic acid: Supplier TEMIX OLEO SRL
6PPD: N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, Supplier: SOLUTIA/EASTMAN
ZnO (80): 80% zinc oxide, 20% polymeric binder and dispersing agent, Supplier LANXESS ADD
silane: TESPD Bis-(3-triethoxy-silyl-propyl)disulphide, Supplier JINGZHOU JIANGHAN FINE CHEM
CBS: N-cyclohexyl-2-benzothiazilsulphenamide, cyclohexylamine content<1%, DUSLO Supplier
sulphur: Crystex OT33 amorphous sulphur, insoluble in CS2 and in toluene. Treated with 33% hydrotreated heavy naphthenic distillate (petroleum), Supplier EASTMAN.

(82) The mixing was carried out in several steps using an internal Thermo Haake Reomix laboratory tangential rotor mixer (250 ml mixing chamber).

(83) In the first step (1-0) the elastomeric polymers were introduced and chewed for 30 seconds at 60° C. (set temperature).

(84) In the following step (1.1) the traditional filler, the antioxidant and possibly the stearic acid, the activating filler, the silane were added.

(85) The mixing continued for 2 minutes, until reaching 120° C.±5° C.

(86) After 12-24 hours, in the following step (1.2) carried out using the same mixer, the ZnO (Comparative 4.1) or the activating filler ZnO/SiO.sub.2 (Comparative 4.2, Comparative 4.3 and Invention 4.4) were introduced, for the Comparative 4.2 the silane and for the Comparative 4.3 the stearic acid. The mixing was continued for about 2 minutes, until the reaction between stearic acid and zinc was completed, reaching 125° C.±5° C. In the following step 1.3, for some examples the silane was added and the mixing was prolonged for another 2-3 minutes, after which the compounds were discharged.

(87) After 12-24 hours, in step (2), carried out using the same mixer, the vulcanising agent (Sulphur) and the accelerant were introduced, and the mixing continued for about 2 minutes, until reaching 95° C.±5° C., when the compounds were discharged. The elastomeric compounds 4.1-4.4 prepared above were evaluated for the behaviour in vulcanisation (170° C., 10 min) and subsequently, in terms of static and dynamic mechanical properties, according to the methods described above. The results of these tests, recalculated considering 100 the value obtained with Comparative 4.1, are summarised in the following Table 4:

(88) TABLE-US-00004 TABLE 4 Measured parameter Unit Comp. 4.1 Comp. 4.2 Comp. 4.3 Inv. 4.4 In vulcanisation MH dNm 100 93 (−7%) 93 (−7%) 97 (−3%) MH-ML dNm 100 84 (−16%) 102 (+2%) 99 (−1%) T-MH min. 100 65 (−35%) 77 (−23%) 100.6 (+0.6%) After vulcanisation Tan D at 70° C., — 100 69 (−31%) 113 (+13%) 54 (−46%) 10 Hz, 9% G′ at 70° C., KPa 100 88 (−12%) 95 (−5%) 86 (−14%) 10 Hz, 9% G″ at 70° C., KPa 100 61 (−39%) 107 (+7%) 47 (−53%) 10 Hz, 9% CR MPa 100 n.a. 82 (−18%) 110 (+10%) CA1 MPa 100 n.a. 65 (−35%) 107 (+7%)
wherein
MH (maximum torque): is the torque measured when cross-linking can be considered complete;
MH-ML: difference between maximum torque MH and minimum torque ML;
T-MH: it is the time necessary to reach the complete cross-linking of the sample;
Tan D (hysteresis) was calculated as the ratio of the G″/G′ modules (deformation of 9% at 70° C.);
G′ (9%) is the shear elastic modulus measured at 70° C. at a deformation amplitude of 9%;
G″ (9%) is the viscous shear modulus measured at 70° C. at a deformation amplitude of 9%;
CR indicates the stress at the elongation at break (MPa);
CA1 indicates the stress measured at 100% deformation (MPa);
n.a. not measured.

(89) From the values of MH, CR and CA1 reported in Table 4 it is shown that the activating filler ZnO/SiO.sub.2 guaranteed at least the same mechanical and kinetic vulcanisation properties of the standard microcrystalline ZnO system, with the same quantity of Zn and filler (Invention 4.4 vs Comparative 4.1).

(90) Moreover, due to the modification in the order of addition of the ingredients of the present process, i.e. with the early addition of stearic acid in step 1.1 and, in particular, the delayed introduction of silane in step 1.3, it was observed that the vulcanised compound of the invention (4.4) showed a significant decrease of the tan D and of the viscous shear modulus (G″) at 70° C. (10 Hz and 9%) of 46% and 53% respectively. These properties are predictive of a decrease in the rolling resistance during operation, which results in increased tyre travel and therefore greater environmental sustainability.

(91) If, on the other hand, the silane was added at the same time as the ZnO/SiO.sub.2 in step 1.2, as in the mixture of Comparative 4.2, the reduction of tan D and modulus G″ at 70° C. was only 31% and 39%.

(92) Comparative 4.3 shows the negative effects of adding ZnO/SiO.sub.2 together with silane, in particular on G″ values at 70° C., where we can even see a 7% increase compared to the significant reduction (−53%) of the sample according to the invention (4.4).

Example 5

(93) Preparation of Elastomeric Compounds Based on Synthetic Isoprene and Polybutadiene for Tyre Sidewall.

(94) In this example it was decided to evaluate, for the same process according to the invention, the effect of the incorporation of the Zn/SiO.sub.2 filler with respect to the traditional ZnO on the vulcanisation parameters and on the mechanical properties of a synthetic isoprene-based compound 40% and high cis polybutadiene 60%.

(95) The elastomeric compounds of Examples 5.1 and 5.2 below were prepared according to the methods described herein. The quantities of the various components are indicated in phr and shown in the following Table 5:

(96) TABLE-US-00005 TABLE 5 ZnO Step Ingredients Comp. 5.1 Inv. 5.2 content 1-0 IR 40 40 1-0 BR 60 60 1-1 Silica 40 26.9 1-1 Stearic acid 2 2 1-1 6PPD 2 2 1-2 ZnO/SiO.sub.2 Ex. 2 — 14.9 1.84 (12.3%) 1-2 ZnO (80): 2.3 — 1.84 1-3 Silane 3.2 3.2 2-0 CBS 1.6 1.6 2-0 Sulphur (67%) 3 3
wherein:
BR butadiene with high cis content (97.5%), neodymium polymerised, Supplier ARLANXEO; and the other ingredients are the same as in the previous example 4.

(97) The mixing was carried out in several steps as described in Example 4 by adding the ingredients in the quantities, in the step and in the order indicated in Table 5, in particular by adding the stearic acid (1.1) early and the silane (1.3) later.

(98) The elastomeric compounds 5.1-5.2 thus prepared above were evaluated for the behaviour in vulcanisation (170° C., 10 min) and subsequently, in terms of static and dynamic mechanical properties, according to the methods described above. The results, recalculated considering 100 the value obtained with Comparative 5.1, are summarised in the following Table 6:

(99) TABLE-US-00006 TABLE 6 Unit of Measured parameter measurement Comp. 5.1 Inv. 5.2 In vulcanisation ML 100 84.6 (−15.4%) MH dNm 100 110.7 (+10.7%) MH-ML dNm 100 116.5 (+16.5%) T-MH min. 100 87.8 (−12.2%) After vulcanisation Tan D at 70° C., 10 Hz, — 100 79 (−21%) 9% G′ at 70° C., 10 Hz, 9% KPa 100 95 (−5%) G″ at 70° C., 10 Hz, 9% KPa 100 75 (−25%) DG′ at 70° C., 10 Hz, KPa 100 94 (−6%) 9% and 3%
wherein
DG′ at 70° C., 10 Hz, 9% and 3% is the difference in shear modulus measured at 70° C. at a deformation amplitude of 9% or 3% respectively (predictive of rolling resistance) and the other parameters have the meaning shown above.

(100) From the values of MH, G′ and DG′ shown in Table 6 it is noted that, with the same the preparation process and elastomeric polymers, the activating filler ZnO/SiO.sub.2 guaranteed good mechanical properties and a significant decrease of the hot tan Delta, predictive of a decrease in the tyre rolling resistance during operation.

(101) In the process according to the invention (Inv. 5.2) a significant decrease in the T-MH cross-linking time was also observed.

Example 6

(102) Preparation of Elastomeric Compounds Based on Synthetic Isoprene and Polybutadiene for Tyre Sidewall

(103) In this example it was decided to evaluate, for the same process according to the invention, the effect of the incorporation of the Zn/SiO.sub.2 filler with respect to the traditional ZnO on the vulcanisation parameters and on the mechanical properties of a synthetic isoprene-based compound 40% and high cis polybutadiene 60%, in the presence of a vulcanization system different from the previous one.

(104) The elastomeric compounds of Examples 6.1 and 6.2 below were prepared according to the methods described herein. The quantities of the various components are indicated in phr and shown in the following Table 7:

(105) TABLE-US-00007 TABLE 7 ZnO Step Ingredients Comp. 6.1 Inv. 6.2 content 1-0 IR 40 40 1-0 BR 60 60 1-1 Carbon black CB 17 17 1-1 Wax 1 1 1-1 Silica 20 6.88 1-1 Stearic acid 2 2 1-1 6PPD 1.5 1.5 1-2 ZnO/SiO.sub.2 Ex. 2 — 14.95 1.84 (12.3%) 1-2 ZnO (80): 2.3 — 1.84 1-3 Silane 1 1 2-0 TBBS 1.87 1.87 2-0 Sulphur (67%) 2 2 2-0 50% TESPT on 2.4 2.4 CB 330
wherein:
Carbon black CB: produced with the furnace process, supplier ORION ENGINEERED CARBONS;
Wax: mixture of normal paraffins and iso, with bimodal distribution (can contain at most 1% of polyethylene PE), Supplier REPSOL LUBRICANTES Y ESPECIAL;

(106) TBBS: Nt-butyl-2-benzothiazilsulphenamide, supplier LANXESS; and the other ingredients are the same as the previous examples.

(107) The mixing was carried out in several steps as described in Example 4 by adding the ingredients in the quantities, in the step and in the order indicated in Table 7, in particular by adding the stearic acid (step 1.1) early and the silane (step 1.3) later.

(108) The elastomeric compounds 6.1-6.2 thus prepared above were evaluated as regards the type of cross-linking after vulcanisation (170° C., 10 min) and subsequently, in terms of static and dynamic mechanical properties, according to the methods described above. The results, recalculated considering 100 the value obtained with Comparative 6.1, are summarised in the following Table 8:

(109) TABLE-US-00008 TABLE 8 Unit of Measured parameter measurement Comp. 6.1 Inv. 6.2 In vulcanisation MH dNm 100 94.8 (−5.2%) MH-ML dNm 100 98.3 (−1.7%) After vulcanisation Mono- and disulphides % w/w 100 111 (+11%) Tan D at 70° C., — 100 91 (−9%) 10 Hz, 9% G′ at 70° C., 10 Hz, KPa 100 97 (−3%) 9% DG′ at 70° C., 10 Hz, KPa 100 75 (−25%) 9% and 3%

(110) From the values reported in Table 8 it is noted that, all the variables being equal, including the vulcanisation system, the ZnO/SiO.sub.2 activating filler and the addition methods of the process of the invention guaranteed a noticeable decrease of the hot tan D together to an increase in the mono- and disulphides, with a less hysteretic behaviour of the compound, predictive of a lower resistance to rolling of the tyre during operation.

Example 7

(111) Preparation of Elastomeric Compounds Based on Natural Rubber for Under-Layer

(112) In this example it was decided to evaluate the effect of the incorporation, according to the process of the invention, of the ZnO/SiO.sub.2 filler with respect to the traditional ZnO, with the same filler and zinc content, on the vulcanisation parameters and on the mechanical properties of a compound based on natural rubber.

(113) The elastomeric compounds of Examples 7.1 and 7.2 below were prepared according to the methods described herein. The quantities of the various components are indicated in phr and shown in the following Table 9:

(114) TABLE-US-00009 TABLE 9 ZnO Step Ingredients Comp. 7.1 Inv. 7.2 content 1-0 NR 100 100 1-0 Stearic acid 2.0 2.0 1-1 Carbon black CB 23.0 23.0 1-1 Silica 22.8 — 1-1 Stearic acid 2.0 2.0 1-1 ZnO 3.3 — 3.3 1-1 ZnO/SiO.sub.2 Ex. 2 — 26.0 3.2 (12.3%) 1-2 TMQ 1.3 1.3 1-2 6PPD 3.0 3.0 1-2 Wax 1.0 1.0 1-2 TESPD (silane) 2.2 2.2 2-0 TBBS 1.3 1.3 2-0 PVI 0.3 0.3 2-0 Sulphur (67%) 4.5 4.5
wherein:
NR: natural rubber (cis 1,4-polyisoprene), SIR 20, supplier PT. KIRAnA MUSI PERSADA, SFN;
ZnO: microcrystalline, white powder, supplier ZINCOL OSSIDI;
TMQ: polymerised 2,2,4-trimethyl-1,2-dihydroquinoline, supplier LANXESS;
PVI: N-cyclohexyl thiophthalimide, supplier SHANDONG YANGGU HUATAI CHEM, and the other ingredients are the same as the previous examples.

(115) The mixing was carried out in several steps as described in Example 4 by adding the ingredients in the quantities, in the step and in the order indicated in Table 9, in particular by adding the stearic acid (step-0) even earlier and the silane (step 1.2) later.

(116) The elastomeric compounds 7.1-7.2 thus prepared above were evaluated as regards the vulcanisation parameters and subsequently, in terms of static and dynamic mechanical properties, according to the methods described above. The results, recalculated considering 100 the value obtained with Comparative 7.1, are summarised in the following Table 10:

(117) TABLE-US-00010 TABLE 10 Unit of Measured parameter measurement Comp. 7.1 Inv. 7.2 In vulcanisation (170° C., 10 min) T30 min. 100 59 (−41%) T60 min. 100 57 (−43%) T90 min. 100 57 (−43%) T-MH min. 100 60 (−40%) After vulcanisation (30 min at 151° C.) E″ 10° C., 10 Hz, 7.5%-20% MPa 100 105 (+5%) Tan Delta 10° C., 10 Hz, — 100 111 (+11%) 7.5%-20% E″ 23° C., 10 Hz, 7.5%-20% MPa 100 105 (+5%) Tan Delta 23° C., 10 Hz, — 100 111 (+11%) 7.5%-20% E″ 100° C. 10 Hz 7.5%-20% MPa 100 95 (−5%) Tan Delta 100° C., 10 Hz — 100 100 (0%) 7.5%-20% (170° C., 10 min) traction on ring specimens CR MPa 100 114 (+14%) AR % 100 117 (+17%)
wherein:
T30, T60, T90 and T-MH are the time required to reach respectively 30% (T30), 60% (T60), 90% (T90) and 100% (T-MH) of the maximum torque value (MH);
E″ is the viscous tensile/compression dynamic modulus,
E′ is the elastic tensile/compression dynamic module,
Tan delta is the ratio between the viscous dynamic module (E″) and the dynamic elastic modulus (E′),
AR is elongation at break.

(118) From the values shown in Table 10 it is noted that, all other variables being equal, the activating filler ZnO/SiO.sub.2 gave the compound of the invention of Ex. 7.2 better static mechanical properties (CR and AR, respectively increased by 14% and 17%) and a faster vulcanisation kinetics with respect to the compound of Comparative 7.1, comprising conventional microcrystalline ZnO (compare the values of T30, T60, T90 and T-MH). The differences in vulcanisation kinetics can be appreciated from the pattern of the graph curves shown in FIG. 5.

(119) The ZnO/SiO.sub.2 activating filler and the preparation process according to the invention led to an increase in hysteresis at temperatures of 23° C. and 10° C. of the vulcanised compounds, with a corresponding increase in the module E″, predictive of better tire performance on the wet. Otherwise, at 100° C. a hysteresis similar to the reference was observed, predictive of a comparable resistance to rolling and abrasion of the tyre during operation.

Example 8

(120) Preparation of Elastomeric Compounds Based on Natural Rubber for Under-Layer

(121) In this example, a comparison was made between two traditional comparative under-layer compounds—including traditional (silica) and activating (microcrystalline ZnO) (Comparative 8.1 and 8.2) prepared the first according to the present process with early addition of ZnO and silica and subsequent silane (step 1.2) and the second with a different process, in which the silane and silica are introduced initially in step 1.1 and the ZnO and stearic acid subsequently in step 2.0—with a compound according to the invention, comprising instead the activating filler ZnO/SiO.sub.2 (D) and prepared with the late addition of silane (step 1.2) (Invention 8.3). The elastomeric compounds of Examples 8.1-8.3 below were prepared according to the methods described herein. The quantities of the various components are indicated in phr and shown in the following Table 11:

(122) TABLE-US-00011 TABLE 11 ZnO Step Ingredients Comp. 8.1 Comp. 8.2 Inv. 8.3 content 1-0 NR 100 100    100    1-0 Stearic acid 2.0 — 2.0 1-1 ZnO 2.6 — — 2.6 1-1 Carbon black CB 23.0 23.0  23.0  1-1 Silica 18.2 18.2  — 1-1 TESPD — 1.4 — 1-1 ZnO/SiO.sub.2 Ex. 2 — — 20.7  2.6 (12.3%) 1-2 TMQ 1.3 1.3 1.3 1-2 6PPD 3.0 3.0 3.0 1-2 Wax 1.0 1.0 1.0 1-2 TESPD 1.4 — 1.4 2-0 ZnO — 2.6 — 2.6 2-0 Stearic acid — 2.0 — 2-0 TBBS 1.3 1.3 1.3 2-0 PVI 0.3 0.3 0.3 2-0 Sulphur (67%) 4.5 4.5 4.5
where the ingredients are the same as in the previous examples.

(123) The mixing was carried out in several steps as described in Example 4 by adding the ingredients in the quantities, in the step and in the order indicated in Table 11.

(124) The elastomeric compounds 8.1-8.3 thus prepared above were evaluated as regards the vulcanisation parameters and subsequently, in terms of static and dynamic mechanical properties, according to the methods described above. The results, recalculated considering 100 the values obtained with Comparative 8.1, are summarised in the following Table 12:

(125) TABLE-US-00012 TABLE 12 Unit of Measured parameter measurement Comp. 8.1 Comp. 8.2 Inv. 8.3 In vulcanisation (170° C., 10 min) ML (23° C.) dN m 100 100 83 (−17%) T30 min. 100 89 (−11%) 67 (−33%) T60 min. 100 87 (−13%) 65 (−35%) T90 min. 100 86 (−14%) 67 (−33%) After vulcanisation (30 min at 151° C.) E″ 10° C., 10 Hz, 7.5%-20% MPa 100 100 (0%) 109 (+9%) Tan Delta 10° C., 10 Hz, 7.5%-20% — 100 98 (−2%) 112 (+12%) E″ 23° C., 10 Hz, 7.5%-20% MPa 100 99 (−1%) 109 (+9%) Tan Delta 23° C., 10 Hz, 7.5%-20% — 100 96 (−4%) 112 (+12%) E″ 100° C. 10 Hz 7.5%-20% MPa 100 95 (−5%) 87 (−13%) Tan Delta 100° C., 10 Hz 7.5%-20% — 100 91 (−9%) 91 (−9%) Traction on ring specimens CR MPa 100 98 (−2%) 99 (−1%) AR % 100 94 (−6%) 106 (+6%)

(126) From the values shown in Table 12 it is noted that, all other variables being equal, the compound of the invention (Ex. 8.3, process of the invention, activating filler ZnO/SiO.sub.2) with respect to the comparative compounds of Ex. 8.1 (process of the invention but standard microcrystalline ZnO) and of Ex. 8.2 (standard process and standard microcrystalline ZnO) showed an increase in hysteresis at 10° C. and 23° C., with an increase in module E″, predictive of a good tyre behaviour on the wet and a significant reduction at high temperatures (100° C.), mainly due to the decrease of the E′ module, predictive instead of improved rolling and abrasion resistance of the tyre in use.

(127) Furthermore the compound of the invention Ex. 8.3 showed a significant decrease in the vulcanisation time (see the values of T30-T90).

(128) Considering the vulcanisation times reported in Table 12 (T30-T90) an increase was observed switching from a standard compound (Comparative Ex. 8.2, standard zinc process and compound) with the compound of Ex. Comparative 8.1 (standard process of the invention and zinc compound) to indicate how the late addition of the compatibilising agent characterising the present process does not lead by itself to an increase in the cross-linking speed but, surprisingly, only in the specific case of the use of zinc in the form of an activating ZnO/SiO.sub.2 filler.

(129) The differences in vulcanisation kinetics can be appreciated also from the pattern of the graph curves shown in FIG. 6.

(130) FIG. 6 shows the normalized curve of the torque values [(Sx−Smin)/(Smax−Smin)*100] measured over time (min) during vulcanization at 170° C. for 10 min of the vulcanisable compound according to the invention of Ex. 8.3 with respect to the comparative compounds of Ex. 8.1 and 8.2. As can be seen, the sample of the invention 8.3 shows the faster vulcanisation kinetics compared to both the comparatives 8.2 and 8.1.

(131) Furthermore it is noted that the microcrystalline zinc introduced in step 1.1. of Ex. 8.1 results in slower kinetics.