TYRE AND ELASTOMERIC COMPOUND FOR TYRE, COMPRISING CROSS-LINKED PHENOLIC RESINS

Abstract

The present invention relates to elastomeric compositions for tyres and relative compounds, components and tyres comprising them, said compositions comprising an elastomeric polymer, a phenolic product, optionally already partially cross-linked, optionally an aldehyde and/or at least a methylene donor product and an oxidised carbon allotrope as a cross-linking catalyst. Advantageously, this catalyst is able to complete the cross-linking reactions of the phenolic resins in the conventional times and conditions of vulcanisation, or even more rapidly, providing mechanically stable compounds.

Claims

1. An elastomeric composition for tyres, comprising at least 100 phr of at least one diene elastomeric polymer (A), 0.5 to 50 phr of at least one phenolic product (B), optionally already partially cross-linked, 0.5 to 100 phr of at least one oxidised carbon allotrope (C) selected from oxidised carbon nanotubes, oxidised graphite, oxidised graphene and oxidised carbon black, 0 to 50 phr of at least one aldehyde and/or at least one methylene donor product (D), 0 to 120 phr of at least one reinforcing filler (E), and 0.1 to 15 phr of at least one vulcanising agent (F).

2. The composition as claimed in claim 1 wherein the at least one oxidised carbon allotrope (C) is oxidised carbon black.

3. The composition as claimed in any one of the preceding claims, wherein the at least one oxidised carbon allotrope (C) is characterised by one or more of the following parameters: an oxygen content higher than 20%, preferably higher than 30%, more preferably higher than 34% measured by elemental analysis; an oxygen/carbon 0/C ratio at least equal to 0.20, preferably higher than 0.30, more preferably higher than 0.50, even more preferably higher than 0.60 obtained from the elemental analysis data; a surface area (BET measured according to ISO 9277:2010) of at least 20 m.sup.2/g, preferably at least 40 m.sup.2/g.

4. The composition as claimed in any one of the preceding claims, wherein: the a least one diene elastomeric polymer (A) is selected from cis-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 at least one phenolic product (B) is selected from phenol, ethylphenols such as o-ethylphenol, m-ethylphenol, p-ethylphenol, and the like; isopropylphenols; butylphenols such as butylphenol, p-tert-butylphenol, and the like; alkylphenols such as p-tert-amylphenol, p-octylphenol, p-nonylphenol, p-cumylphenol, and the like; halogenophenols such as fluorophenol, chlorophenol, bromophenol, iodophenol, and the like; substituted monophenols such as p-phenylphenol, aminophenol, nitrophenol, dinitrophenol, trinitrophenol, and the like; cresols such as o-cresol, m-cresol, p-cresol, xylenols such as 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, 3,5-xylenol, and the like; bicyclic monophenols such as 1-naphthol, 2-naphthol, and the like; polyphenols such as resorcin, alkylresorcin—such as 2-methylresorcin, 5-methylresorcin, 2,5-dimethylresorcin, 4-ethylresorcin, 4-n-hexylresorcin and the like; 4-chlororesorcin, 2-nitroresorcin, 4-bromoresorcin and the like, pyrogallol, catechol, alkylcatechol, hydroquinone, alkylhydroquinone, fluoroglucine, bisphenol A, bisphenol F, bisphenol S, dihydroxynaphthalene and the like, novolacs and resoles, preferably from novolacs; at least one aldehyde (D), if present, is selected from formaldehyde, acetaldehyde, propionaldehyde, chloral, furfural, glyoxal, n-butylaldehyde, caproaldehyde, allylaldehyde, benzaldehyde, crotonaldehyde, acrolein, phenylacetaldehyde, o-tolylaldehyde, salicylaldehyde, preferably it is formaldehyde; at least one methylene donor product (D), if present, is selected from paraformaldehyde, trioxane, tetraoxymethylene, hexamethylenetetramine (EMTA), hexamethoxymethylmelamine (EMMM), preferably EMMM; at least one reinforcing filler (E), if present, is selected from carbon black, conventional silica, such as sand silica precipitated with strong acids, preferably amorphous, diatomaceous earth, calcium carbonate, titanium dioxide, talc, alumina, aluminosilicates, kaolin, silicate fibres and mixtures thereof; and the at least one vulcanising agent (F) is selected from sulphur, or alternatively, sulphur-containing molecules (sulphur donors), such as caprolactam disulphide (CLD), bis (trialcoxysilyl)propyl]polysulphides, dithiophosphates, phosphorylpolysulphide (SDT) and mixtures thereof, preferably it is sulphur.

5. The composition as claimed in any one of the preceding claims, which comprises: 1 to 30 phr, preferably 3 phr to 20 phr of at least one phenolic product (B); 1 to 50 phr, more preferably 2 to 20 phr, even more preferably 3 to 10 phr of oxidised carbon allotrope (C); preferably 1 to 8 phr, more preferably 2 to 6 phr of at least one aldehyde and/or at least one methylene donor product (D); optionally 3 to 90 phr of reinforcing filler (E); and 0.5 to 12 phr, preferably 1 to 10 phr of at least one vulcanising agent (F).

6. The composition as claimed in any one of the preceding claims, wherein the weight ratio between the at least one phenolic product (B), optionally already partially cross-linked and the aldehyde and/or the at least one methylene donor product (D) is comprised between 0.1:1 and 60:1, preferably between 0.5:1 and 20:1, more preferably between 1:1 and 8:1.

7. The composition as claimed in any one of the preceding claims, further comprising one or more additives selected from compatibilising agents, vulcanisation activators, vulcanisation accelerants, vulcanisation retardants, antioxidants, waxes and plasticisers.

8. The composition as claimed in any one of the preceding claims, comprising at least: 100 phr of at least one diene elastomeric polymer (A), 5 to 25 phr of a novolac (B), 2 to 6 phr of oxidised carbon black (C), 3 to 8 phr of a methylene donor product (D), 30 to 70 phr of carbon black (E), and 6 to 10 phr of sulphur (F).

9. A vulcanisable elastomeric compound for tyres obtained by mixing and optionally heating the components of the elastomeric composition for tyres according to any one of claims 1 to 8.

10. The vulcanisable elastomeric compound as claimed in claim 9, characterised by a maximum torque time t-MH, measured at 170° C. according to ISO 6502, lower than at least 20%, preferably at least 30%, more preferably at least 40% with respect to the maximum torque time t-MH of a vulcanisable elastomeric compound having the same composition but without the oxidised carbon allotrope (C).

11. A process for the preparation of the vulcanisable elastomeric compound as claimed in claims 9 and 10, which comprises I) working and optionally heating to a temperature not higher than 160° C. in at least one suitable mixer: at least one elastomeric polymer (A), optionally at least one phenolic product (B), optionally already partially cross-linked, optionally at least one oxidised carbon allotrope (C) selected from oxidised carbon nanotubes, oxidised graphite, oxidised graphene and oxidised carbon black and, optionally, at least one reinforcing filler (E), to yield a non-vulcanisable elastomeric compound (m1); II) incorporating into the non-vulcanisable elastomeric compound (m1): at least one vulcanisation agent (F) and, if present, at least one aldehyde and/or at least one methylene donor product (D), optionally, at least one vulcanisation accelerant and/or retardant agent, optionally at least one phenolic product (B), optionally already partially cross-linked, optionally at least one oxidised carbon allotrope (C) selected from oxidised carbon nanotubes, oxidised graphite, oxidised graphene and oxidised carbon black, provided that said at least one oxidised carbon allotrope (C) and said at least one phenolic product (B), possibly already partially cross-linked, are present in at least one of the steps I) or II), and working the compound, in the same or another suitable mixer, at a temperature not higher than 120° C., to yield a vulcanisable elastomeric compound (m2), and is Ill) discharging the vulcanisable elastomeric compound (m2).

12. The process as claimed in claim 11, which comprises: I) working and optionally heating to a temperature comprised between 130 and 160° C., in at least one suitable mixer: at least one elastomeric polymer (A), at least one phenolic product (B), optionally already partially cross-linked, at least one oxidised carbon allotrope (C) selected from oxidised carbon nanotubes, oxidised graphite, oxidised graphene and oxidised carbon black and, optionally, at least one reinforcing filler (E), to yield a non-vulcanisable elastomeric compound (m1); II) incorporating into the non-vulcanisable elastomeric compound (m1): at least one vulcanisation agent (F), if present, at least one aldehyde and/or at least one methylene donor product (D), optionally, at least one vulcanisation accelerant and/or retardant agent, and working the compound, in the same or another suitable mixer, at a temperature not higher than 105° C., preferably between 80 and 105° C., to yield a vulcanisable elastomeric compound (m2); and III) discharging the vulcanisable elastomeric compound (m2).

13. A tyre component comprising the vulcanisable compound as claimed in claim 9 or 10 or the vulcanised compound obtained by vulcanisation thereof.

14. The tyre component as claimed in claim 13, selected from tread band, base-layer, anti-abrasive layer, sidewall, sidewall insert, mini-sidewall, under-liner, rubber layers, bead filler, flipper, chafer and sheet, preferably selected from base-layer, anti-abrasive layer and bead filler.

15. A tyre for vehicle wheels comprising at least one tyre component as claimed in claim 13 or 14.

16. Use of at least one oxidised carbon allotrope (C) selected from oxidised carbon nanotubes, oxidised graphite, oxidised graphene and oxidised carbon black as cross-linking accelerant of at least one phenolic product (B), optionally already partially cross-linked, and preferably of at least an aldehyde and/or at least one methylene donor product (D), in a vulcanisable elastomeric compound for tyres.

Description

DESCRIPTION OF THE DRAWINGS AND FIGURES

[0175] The present invention will now be described hereinafter with reference to the accompanying drawings, provided only for illustrative and, therefore, non-limiting purposes, in which:

[0176] FIG. 1 shows a radial half-section of a tyre for vehicle wheels according to the invention.

[0177] FIG. 2 shows the DSC plot (heat flow W/g with respect to temp. ° C.) of the cross-linking temperatures of phenolic resins as the oxidised allotrope (C) varies, at 2% by weight, or in its absence.

[0178] FIG. 3 shows the DSC plot (heat flow W/g with respect to temp. ° C.) of the cross-linking temperatures of phenolic resins as the quantity of oxidised carbon black varies.

[0179] FIG. 4 shows the IR plot measured on oxidised (C) and non-oxidised carbon allotrope samples.

[0180] FIG. 5 is a rheogram showing the pattern over time of the pair S′ of reference elastomeric compounds (Ex. 6A) and of the invention (Ex. 6B and 6C) during and after vulcanisation.

[0181] FIG. 6 is a rheogram showing the pattern over time of the degree of vulcanisation X [X=(S′−ML)/(MH−ML)] of reference elastomeric compounds (Ex. 6A) and of the invention (Ex. 6B and 6C) during and after vulcanisation.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0182] FIG. 1 illustrates in a radial half-section a tyre for vehicle wheels, comprising in at least one of its components a vulcanised elastomeric compound prepared by vulcanising a vulcanisable elastomeric compound according to the invention, preferably in the bead filler, in the anti-abrasive layer and/or in the base-layer.

[0183] 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”.

[0184] 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, preferably made with the elastomeric compound of the invention.

[0185] The carcass layer 101 is optionally made with an elastomeric compound.

[0186] 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. 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.

[0187] 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.

[0188] An anti-abrasive layer 105 possibly made with the present elastomeric compound is arranged in an outer position of each bead structure 103.

[0189] 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.

[0190] 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.

[0191] 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.

[0192] A tread band 109 of vulcanised elastomeric compound is applied in a position radially outer to the belt structure 106.

[0193] 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.

[0194] 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. A base-layer 111, preferably of vulcanised elastomeric compound according to the invention, may be arranged between the belt structure 106 and the tread band 109.

[0195] 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.

[0196] 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.

[0197] 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.

[0198] Flipper 120 is a reinforcing layer which is wound around the respective bead core 102 and the bead structure 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.

[0199] Flipper 120 typically comprises a plurality of textile cords incorporated within a layer of vulcanised elastomeric compound.

[0200] 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.

[0201] 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).

[0202] 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.

[0203] Advantageously, the layer or sheet can extend on a surface substantially corresponding to the extension surface of said belt structure.

[0204] 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, base-layer, sidewall, mini-sidewall, sidewall insert, bead filler, flipper, chafer, sheet and anti-abrasive layer, preferably it is incorporated in the bead filler, in the anti-abrasive layer and/or in the base-layer.

[0205] 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.

[0206] 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.

EXPERIMENTAL PART

[0207] The description of some preparative examples according to the invention and comparative examples, given only for illustrative and non-limiting of the scope of the invention, is set out below. Hereinafter, the oxidised carbon allotrope (C) is also indicated by the term catalyst.

[0208] Analysis Methods

[0209] BET surface area: according to IS09277:2010

[0210] Elemental analysis: according to ASTM D5373 using the Thermo Flash EA 112 Series CHNS-O analyser.

[0211] DSC analysis: using the TA INSTRUMENTS Q20 instrument with a heating ramp of 10° C. a minute from 25° C. to 200° C. or preferably 220° C.

[0212] IR analysis: according to ASTM E1252-98 using the BRUKER Vertex70 spectrometer with DTGS detector, KBr beam splitter and a resolution of 2.0 cm.sup.−1. The powder samples were dispersed in KBr tablets.

[0213] 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 one and two rheometric units (ts1 and ts2) and the time necessary to achieve 30% (t30), 60% (t60) and 90% (t90), respectively, of the final torque value (Mf). The maximum torque value MH, the minimum torque value ML and the relative times t-MH and t-ML were also measured.

Example 1

[0214] Preparation of Oxidised Carbon Black

Example 1A (o-N110)

[0215] In a 2000 ml three-necked flask, thermostated with an ice bath, 120 ml of concentrated sulphuric acid, 2.5 g of sodium nitrate and 5 g of Cabot's N110 carbon black were added under magnetic stirring. After obtaining a uniform dispersion, 15 g of potassium permanganate were slowly added. The reaction mixture was kept at 35° C., under stirring, for 24 hours. Distilled water (700 ml) was introduced in small quantities, under stirring, and subsequently 5 ml of H.sub.2O.sub.2 (30% by weight aqueous solution) were added. The reaction crude was decanted into 7 l of distilled water, and centrifuged at 10000 rpm for 15 minutes with a Hermle Z323K centrifuge. After separation, the oxidised product was washed with 100 ml of a 5% aqueous solution of HCl and washed with 500 ml of distilled water. Finally, the product was dried in an oven at 60° C. for 12 hours. About 7 g of oxidised carbon black were obtained. The oxidised carbon black thus prepared (o-N110) was characterised by elemental analysis and IR analysis, as shown in Table 1 and FIG. 4.

[0216] The oxidised carbon black N110 examined under a microscope shows that it has substantially preserved the morphology of the starting N110 carbon black.

Example 1B (o-N234)

[0217] Starting from 5 g of Cabot's carbon black N234 and following the same procedure as in Example 1, 6.5 g of oxidised N234 carbon black were prepared.

[0218] The oxidised carbon black N234 thus prepared was characterised by elemental analysis and IR analysis, as shown in Table 1 and FIG. 4.

Example 2

Example 2A

[0219] Preparation of Oxidised Graphene (GO)

[0220] Starting from 5 g of graphite with high surface area of Asbury (HSAG TC 307, surface area 330 m.sup.2/g), and following the same procedure of Example 1, 6 g of oxidised graphene were prepared.

[0221] The oxidised graphene thus prepared was characterised by elemental analysis and IR analysis, as shown in Table 1 and FIG. 4.

Example 2B

[0222] Preparation of Oxidised Expanded Graphite (e-GO)

[0223] Starting from 5 g of expanded graphite and following the same procedure as in Example 1, 6 g of oxidised expanded graphite were prepared.

[0224] The oxidised expanded graphite thus prepared was characterised by elemental analysis and IR analysis, as shown in Table 1 and FIG. 4.

Example 3

[0225] Preparation of Oxidised Carbon Nanotubes (o-CNT)

[0226] 75 ml of concentrated nitric acid were poured into 225 ml of sulphuric acid concentrated at 0° C. in a reaction flask. 300 mg of Nanocyl NC 7000 multiwall carbon nanotubes (surface area 250-300 m.sup.2/g) were added, under nitrogen and magnetic stirring. The reaction mixture was heated to 60° C. and stirred for 24 hours. The dark suspension thus obtained was diluted in 2-3 I of deionised water and centrifuged at 10000 rpm for 15 minutes. The isolated powder was washed with 100 ml of 5% by weight aqueous HCl and then with deionised water, finally dried in an oven at 60° C. for 12 hours. About 300 mg of oxidised carbon nanotubes were obtained.

[0227] The oxidised carbon nanotubes thus prepared were characterised by elemental analysis as shown in Table 1.

[0228] Elemental Analysis

[0229] The results of the elemental analysis carried out on samples of oxidised allotropes prepared according to Examples 1-3 are summarised in the following Table 1:

TABLE-US-00001 TABLE 1 (% by weight) Sample Example C H O S O/C o-N234 1B 60.3 1.7 35.0 2.8 0.58 o-N110 1A 50.3 2.3 41.7 5.4 0.83 GO 2A 56.1 1.2 39.8 2.7 0.71 e-GO 2B 59.4 0.6 37.1 2.6 0.62 o-CNT 3 79.9 0.3 19.5 — 0.24

[0230] As can be seen in Table 1, oxidised carbon black (examples 1A and 1B) is characterised by a higher sulphur content, compared to oxidised graphene (Examples 2A and 2B). Surprisingly, in contrast to what is taught in the literature, for example in the article Schonefield, Industrial and engineering chemistry 1934, page 571, vol. 27 no. 5. the oxidised carbon allotrope does not depress the vulcanisation reaction, as shown in Example 6.

[0231] IR Analysis

[0232] FIG. 4 shows the IR analysis plots of oxidised (o-N110, o-N234, e-GO, GO) and non-oxidised (N110, HSAG) carbon allotrope samples. As confirmation of the elemental analysis, the diagram shows the important presence of oxidised species in the oxidised carbon black samples (o-N110 and o-N234), which are instead of less intensity in the other oxidised allotropes and absent in the non-oxidised compounds (see in particular the signs in the area between 800 and 1700 cm.sup.−1).

Example 4

[0233] Cross-Linking Tests According to the Type of Oxidised Carbon Allotrope

[0234] To evaluate the effect on the cross-linking kinetics of the various catalysts, with the same content, mixtures were prepared comprising 0.5 g of resorcin, 0.5 g of hexamethoxymethylmelamine (EMMM) and 20 mg (equal to 2% by weight of the mixture) respectively of the selected catalyst, of non-oxidised carbon black N110, of graphite with high surface area HSAG not oxidised and without any catalyst, as summarised in the following Table 2:

TABLE-US-00002 TABLE 2 Different catalysts at 2% by weight Test Sample Abbreviation type Notes Ex. 4A o-N110 INV With oxidised carbon black Ex. 1A Ex. 4B No catal. COMP Without catalyst and without allotrope Ex. 4C e-GO INV With oxidised expanded graphite Ex. 2B Ex. 4D o-N234 INV With oxidised carbon black Ex. 1B Ex. 4E o-CNT INV With oxidised carbon black Ex. 3 Ex. 4F HSAG COMP Without catalyst, with graphite large surface area Ex. 4G N110 COMP Without catalyst, with carbon black INV according to the invention; COMP comparative

[0235] The mixtures were reacted in increasing temperature scan.

[0236] From the DSC plot, measured on the samples shown in Table 2, it was possible to observe the effect of the compound under examination on the kinetics of the cross-linking reaction, evaluating it in terms of variation of the peak temperature (delta T) of the catalysed reactions (Ex. 4A, 4C, 4D and 4E) with respect to the peak temperature of the non-catalysed reactions (Ex. 4B, 4F and 4G).

[0237] In particular, FIG. 2 shows the DSC plot of the reaction temperature of the samples of the mixtures of Examples 4A to 4G.

[0238] The graph shows that all oxidised allotropes exhibit catalytic activity on the cross-linking and that oxidised carbon black (0-N110 and o-N234) has a decidedly higher effect than oxidised expanded graphite (e-GO) and oxidised carbon nanotubes (o-CNT), in lowering the peak temperature value.

[0239] In fact, the peak temperature values are respectively about 150° C. for the oxidised carbon black (o-N110, Ex. 4A), 165° C. for oxidised expanded graphite (e-GO, Ex. 4C), for oxidised carbon nanotubes (o-CNT, Ex. 4E) and 170° C. for samples without catalyst (Ex. 4B, 4F and 4G).

[0240] From the trend of the curves it is also evident that the oxidised carbon black obtained from the carbon black having a higher surface area (sample o-N110, Ex. 4A, original surface area about 130 m.sup.2/g) is more effective in lowering the peak T compared to the sample o-N234 (Ex. 4D, original surface area about 110 m.sup.2/g), prepared with the same procedure but starting from a carbon black with a lower surface area.

Example 5

[0241] Cross-Linking Tests as the Quantity of Oxidised Carbon Black Varies (o-N110)

[0242] To evaluate the effect on the cross-linking kinetics of increasing quantities of catalyst, precisely from 0.2% to 2% by weight with respect to the weight of the mixture, mixtures containing 0.5 g of resorcin, 0.5 g of hexamethoxymethylmelamine (EMMM) and 2 mg, 10 mg or 20 mg respectively of oxidised carbon black of Ex. 1A (o-N110) were prepared. For comparison, similar mixtures comprising 2% of oxidised carbon black N110 or not comprising any catalyst were prepared, as shown in the following Table 3:

TABLE-US-00003 TABLE 3 Increasing catalyst o-N110 content Mixture Abbreviation Test sample in FIG. 3 type Notes Ex. 5A o-N110 0.2% COMP 0.2% catalyst Ex. 1A Ex. 5B o-N110 1% INV 1% catalyst Ex. 1A Ex. 5C o-N110 2% INV 2% catalyst Ex. 1A Ex. 5D No catal. COMP Without catalyst Ex. 5E N110 2% COMP Without catalyst, with 2% carbon black INV according to the invention; COMP comparative

[0243] The mixtures were heated and reacted analogously to Example 4.

[0244] From the DSC plot shown in FIG. 3, the effect of increasing quantities of catalyst can be observed (Ex. 5A-5C), in terms of variation of the peak temperature (delta T), on the kinetics of the cross-linking reaction with respect to the samples without catalyst of Examples 5D and 5E.

[0245] The graph shows a marked effect on the cross-linking kinetics of the catalyst already at the concentration of 1% (sample of Ex. 5B) while for a concentration of 0.2% there is no macroscopic effect (Ex. 5A, delta T not evident). Furthermore, the absence of catalytic activity of carbon black per se (non-oxidized, N110, Ex. 5E) was confirmed.

Example 6

[0246] Preparation of Elastomeric Compounds for Tyres (for Bead Filler)

[0247] Elastomeric compounds for tyre bead filler were prepared as described herein.

[0248] The ingredients listed in Table 4 below were processed in three steps (Steps 1 to 3) using a Haake Rheolab mixer: in the first step, isoprenic rubber, non-oxidised carbon black, 6-PPD antioxidant, stearic acid and zinc oxide were introduced and the processing was continued for 6-7 minutes, until reaching 155° C.±5° C., when the composition was discharged. After 12-24 hours, in the second step, carried out using the same mixer, the novolac phenolic resin, the EMMM formaldehyde precursor were introduced and, respectively, no catalyst (Ex. 6A), oxidised graphene (Ex. 6B), oxidised carbon black (Ex. 60). The processing continued for about 3 minutes, until reaching 95° C.±5° C., when the compound was discharged. After 12-24 hours, in the third step, carried out using the same mixer, the TBBS accelerant, the sulphur vulcanising agent and the PVI retardant were introduced. The processing continued for about 2 minutes, until reaching 95° C.±5° C., when the compound was discharged.

TABLE-US-00004 TABLE 4 Ex. 6B Ex. 6C Ex. 6A INV INV COMP oxidised oxidised without graphene carbon black catalyst GO o-N110 1st step IR 100 100 100 Black N326 50 50 50 6PPD 2 2 2 Stearic acid 2 2 2 Zinc oxide 3 3 3 2nd step EMMM 5.1 5.1 5.1 GO Ex. 2A 4 o-N110 Ex. 1A — — 4 Novolacca resin 10 10 10 3rd step TBBS 1.5 1.5 1.5 Vulcanising agent 8 8 8 PVI 0.3 0.3 0.3
wherein
INV according to the invention; COMP comparative
IR is a high cis-1,4-polyisoprene rubber (SKI-3 from Nižnekamsk),
N326 is carbon black produced by Cabot,
6-PPD is N-1,3-dimethylbutyl-N-phenyl-p-phenylenediamine Santoflex produced by

Flexsys,

[0249] Stearic acid is produced by Sogis,
Zinc oxide is produced by Zincol oxides,
EMMM is hexamethoxymethylmelamine at 65% by weight on an inert support, Cyrez 964 PC, by Cytec,
TBBS is N-terbutyl 2-benzothiazil sulphenamide, Vulkacit NZIEGC produced by Lanxess,
PVI is cyclohexyl thiophthalimide Santogard PVI, Flexsys,
Vulcanising agent is Sulphur Redball Superfine, International Sulphur Inc.,
Novolacca resin is ALNOVOL PN 320 from Allnex,
o-N110 and GO are respectively oxidised carbon black and oxidised graphene, prepared as described in Examples 1A and 2A respectively.

[0250] The compounds thus prepared were subjected to measurement of the rheological properties (vulcanisation at 170° C. for 20 minutes) as shown in the following Table 5:

TABLE-US-00005 TABLE 5 Ex. 6A Ex. 6B Ex. 6C u.m. COMP INV INV ML dNm 2.54 2.68 2.96 MH dNm 33.39 29.46 33.14 ts1 min 0.58 0.62 0.55 ts2 min 0.69 0.73 0.67 t30 min 1.16 1.11 1.20 t60 min 2.80 2.36 2.32 t90 min 10.54 7.89 5.06 S′ at t60 dNm 21.04 18.73 21.06 S′ at t90 dNm 30.32 26.79 30.13 S″ at t90 dNm 3.83 2.58 3.39 t-ML min 0.31 0.32 0.28 t-MH min 19.87 19.27 10.52
wherein
u.m. unit of measurement;
ML and MH are minimum and maximum values of the compound torque measured in the MDR rheometric analysis;
ts1 and ts2 are the times, expressed in minutes from the beginning of the test, that the compound takes to reach the torque value ML+1 or ML+2, respectively;
t60 and t90 are the times at which the vulcanisation degree of the compound is equal to 60% and 90%, setting 0 the torque value ML and 100 the torque value MH;
S′ at t60 and t90 expresses the value of the component in phase with respect to the deformation imposed by the torque at 60 and 90 minutes of vulcanisation;
S″ at t90 expresses the value of the quadrature component with respect to the deformation imposed by the torque at 90 minutes of vulcanisation;
t-ML and t-MH are the minimum and maximum torque times, that is, the times required for the green compound to reach the minimum and maximum Mooney viscosity values at a given vulcanisation temperature.

[0251] As can be seen from the values of the rheological properties shown in Table 5 and from the pattern of the curves of the S′/time rheogram of FIG. 5, the oxidised carbon black (Ex. 6C) was found to be very active in the cross-linking reaction of the resins in the compound. In fact, in the samples according to the invention (Ex. 6C) S′ quickly reached the plateau value without further growth while the reference (Ex. 6A, without catalyst) showed the characteristic pattern of the marching modulus, which is observed when the cross-linking speed of the resin is not high enough to allow the reaction to be completed within normal vulcanisation times. In particular, it was noted that for the reference (Ex. 6A, without catalyst) the completion time of the cross-linking reactions at 170° C. was even greater than 20 minutes.

[0252] The sample of Ex. 6B (oxidised graphene catalyst), although reaching the maximum torque value in a time that is only slightly less than the reference (Ex. 6A), however, had a much flattened curve (FIG. 5) i.e. a less pronounced marching modulus. This preliminary data indicated that oxidised graphene could also be effective but that it probably needed higher quantities to provide better results.

[0253] Instead in the sample of Ex. 6C with oxidised carbon black according to the invention, the completion time of the cross-linking reactions at 170° C. was decidedly shorter and stood around 10 minutes, i.e. about half the time required for the reference sample (Ex. 6A), Particularly interesting was the effect on the terminal part of the curve, with a decreasing trend, indicative of exceeding the optimal time of completion of the vulcanisation.

[0254] From the rheogram of FIG. 6 it was clearly seen that the time required to reach 100% of the cross-linking of the compound according to the invention (Ex. 6C), comprising the oxidised carbon black (C), was much lower than that of the reference compound (Ex. 6A), without catalyst, while the reduction effect was less marked for the compound comprising oxidised graphene (Ex. 6B), in line with the DSC study of FIG. 2.

[0255] Finally, it could be seen in the initial part of the curve of the diagrams in FIGS. 5 and 6 and from the values of ts2 and t30 in Table 5 that, in the case of samples comprising oxidised carbon black (Ex. 6C) or oxidised graphene (Ex. 6B) according to the invention, the sulphur vulcanisation was not excessively accelerated, thus preventing possible scalding problems.