阅读说明：本技术 含有再生炭黑的充气轮胎用橡胶配混料 (Rubber compound for pneumatic tire containing regenerated carbon black ) 是由 A·卡尔泽塔 A·巴尔托洛尼 于 2018-06-28 设计创作，主要内容包括：一种充气轮胎用橡胶配混料，其包括可交联的不饱和链聚合物基料、炭黑、硅烷偶联剂和硫化体系。所述炭黑的一部分为具有表面官能团的来自裂解的炭黑，所述炭黑的一部分源自用包含至少一个硫醇基或二硫基的氨基酸化合物的处理。(A rubber compound for pneumatic tires comprising a cross-linkable, unsaturated-chain polymer base, carbon black, a silane coupling agent and a curing system. A portion of the carbon black is carbon black from cleavage having surface functional groups, the portion of the carbon black resulting from treatment with an amino acid compound comprising at least one thiol or disulfide group.)

1. A rubber compound for a pneumatic tire, the rubber compound comprising a cross-linkable, unsaturated-chain polymer base, carbon black, a silane coupling agent, and a vulcanization system, wherein a portion of the carbon black is carbon black from cracking having surface functional groups;

said compound being characterized in that a portion of said carbon black having surface functional groups resulting from cleavage originates from treatment with an amino acid compound comprising at least one thiol or disulfide group.

2. A rubber compound for pneumatic tires according to claim 1, characterized in that the amino acid compound is HSCH₂CHNH₂COOH or (SCH)₂CHNH₂COOH)₂。

3. A rubber compound according to claim 1 or 2, characterized in that said carbon from cracking has between 5 and 15% by weight of surface functional groups.

4. A compound according to any of the preceding claims, characterised in that said carbon black coming from cracking is present in said compound in an amount comprised between 2 and 25% of the total carbon black in phr.

5. A portion of a pneumatic tire made from a compound according to any one of the preceding claims.

6. A portion of a pneumatic tire as in claim 5, which is part of the carcass of a pneumatic tire.

7. Carbon black from cracking, wherein its surface has been activated by means of treatment with amino acid compounds having thiol or disulfide groups.

8. Carbon black from cracking according to claim 7, characterized in that the amino acid compound is HSCH₂CHNH₂COOH or (SCH)₂CHNH₂COOH)₂。

9. The carbon black from cracking of claim 7 or 8, wherein the carbon from cracking has between 5 and 15 wt.% surface functional groups.

10. Use of the carbon black from cracking according to claims 7 to 9 in rubber compounds for the manufacture of pneumatic tires.

Disclosure of Invention

The present invention relates to a rubber compound for pneumatic tires, comprising a regenerated carbon black, wherein the surface thereof has been activated by means of treatment with an amino acid compound comprising thiol or disulfide groups.

The invention also relates to a regenerated carbon black, the surface of which has been activated by means of treatment with an amino acid compound comprising thiol or disulfide groups, and to the use thereof in rubber compounds for the manufacture of pneumatic tires.

For ecological reasons, the need has long been noted for the correct disposal and recycling of used pneumatic tyres. For this reason, solutions have been sought which enable the recovery of at least part of their components. One of the components of a used pneumatic tire that is desired to be recycled for subsequent reuse is carbon black, which is considered a high end material.

The recovery of carbon black is carried out by means of a process for cracking scrap pneumatic tires. "carbon black from cracking" here and hereinafter refers to regenerated carbon black obtained by the technique of cracking used pneumatic tires. As known to those skilled in the art, the cracking process produces regenerated carbon blacks (carbon blacks from cracking) that do not have functional groups on their surface (A chemistry of surface morphology and chemistry of hydrolytic carbon black with synthetic carbon black, Powder Technology 160(2005) 190-. Such a characteristic of the carbon black from cracking inevitably has an influence on its surface activity.

Despite the fact that carbon black from cracking finds application in various fields, its use still presents many problems in the field of pneumatic tires. In fact, it has been found that, for the same surface area, the carbon black resulting from cracking has a lower reinforcing strength than the reinforcing strength of the first-used carbon black (the "first-used carbon black" here and in the following refers to non-regenerated carbon black). The lower reinforcing strength of the carbon black from cracking is due to its reduced surface activity towards the polymer base.

The low surface reactivity of carbon black from cracking is a serious limitation for its use as a replacement, even a partial replacement, for the first-used carbon black.

In this respect, it has been experimentally demonstrated that even partial replacement of the first-used carbon black by carbon black from cracking leads to a significant deterioration of the mechanical properties of the compound, such as abrasion resistance, tensile strength, modulus value M%.

EP3173251 discloses rubber compounds for tires comprising a cross-linkable unsaturated-chain polymer base, carbon black, a silane coupling agent and a vulcanization system, wherein a portion of the carbon black is a regenerated carbon black obtained by cracking of the tire, containing hydroxyl and/or carboxyl groups on its surface.

As can be immediately shown, the possibility of using carbon black from cracking in the preparation of compounds for pneumatic tires would have great advantages in ecological and economic terms.

The applicant has implemented a solution whereby it is possible to prepare rubber compounds for pneumatic tires in which a portion of the carbon black used for the first time is replaced by carbon black originating from cracking without incurring the drawbacks of the prior art and therefore without reflecting any deterioration as regards the mechanical properties of the compound itself.

The object of the present invention is a rubber compound for pneumatic tires comprising a cross-linkable unsaturated-chain polymer base, carbon black, a silane coupling agent and a vulcanization system; said compound being characterized in that a portion of said carbon black is carbon black from cleavage having surface functional groups, said portion of carbon black resulting from a treatment with an amino acid compound comprising at least one thiol or disulfide group.

Here and hereinafter, the vulcanization system means a compound of ingredients comprising at least sulphur and a promoting compound, these ingredients being added in the last blending step when preparing the compound and being intended to promote the vulcanization of the polymer base when the compound is subjected to vulcanization temperatures.

Here and hereinafter, the term "crosslinkable unsaturated chain polymer base" refers to any natural or synthetic non-crosslinked polymer capable of exhibiting, after crosslinking (vulcanization) with a sulfur-based system, all the chemical, physical and mechanical characteristics normally exhibited by elastomers.

Preferably, the amino acid compound having a thiol group is HSCH₂CHNH₂COOH (cysteine) or an amino acid compound having a disulfide group is (SCH)₂CHNH₂COOH)₂(cystine).

Cystine is the oxidized form of cysteine.

When cysteine is added to the mixture, it is rapidly converted/reduced to other forms, such as cystine.

Preferably, the carbon from the cleavage has between 5-15 wt% surface functional groups.

The functional groups are determined by means of CHNS elemental analysis, while the composition of the material can be determined by means of TGA analysis.

Preferably, the carbon black from cracking is present in the compound in an amount of between 2 and 25% of the total carbon black in phr. By total carbon black is meant the sum of the first used carbon black and the carbon black from cracking.

Another object of the invention is a pneumatic tire part made from the compound of the invention. Preferably, the pneumatic tire portion is a portion of a casing of a pneumatic tire.

Another object of the invention is a carbon black from cracking, wherein its surface has been activated by a process of treatment with an amino acid compound comprising thiol or disulfide groups.

Another object of the invention is the use of carbon black from cracking in rubber compounds for the manufacture of pneumatic tires, wherein the surface thereof has been activated by a process of treatment with an amino acid compound comprising thiol or disulfide groups.

For a better understanding of the present invention, the following examples are given for the purpose of illustration and not of limitation.

Detailed Description

Two comparative compounds (a and B) and a compound according to the invention (C) were prepared. The three example compounds have a typical composition for the shoulder portion of a pneumatic tire. This characteristic is not limiting, as long as the invention can also be applied to compounds associated with other parts of pneumatic tires, preferably those associated with the carcass.

The first comparative compound (a) as filler comprises the first-used carbon black.

The second comparative compound (B) differs from the first comparative compound (a) in that a portion of the first-used carbon black has been replaced by carbon black from cracking, which, however, has not undergone any surface activation treatment.

Surface activation treatment refers to a process in which the carbon black from the cleavage is treated with an amino acid, allowing modification of the surface properties without changing the bulk properties.

The compound (C) according to the invention differs from the first comparative compound (a) in that a portion of the carbon black used for the first time is replaced by carbon black from cracking which has previously been subjected to a surface activation treatment according to the invention.

In the following description, "untreated carbon black derived from cracking" refers to regenerated carbon black obtained from a pneumatic tire cracking process but not subjected to an activation treatment according to the present invention; and "treated carbon black from cracking" refers to regenerated carbon black obtained from a pneumatic tire cracking process and subjected to treatment according to the present invention.

All example compounds included the same amount of all carbon black in phr (first used carbon black + carbon black from cracking).

Example compounds were obtained according to the following procedure.

Preparation of the Compounds

(first blending step)

Before the start of blending, the crosslinkable polymer base, the first-used carbon black, the carbon black from cracking (if desired) are charged into a mixer with tangential rotors and an internal volume of 2 liters, giving a filling factor of between 66 and 72%.

The mixer was operated at a speed of between 40-60 revolutions per minute and the mixture thus formed was discharged as soon as a temperature of between 140 and 160 ℃.

(second blending step)

The mixture obtained from the previous step is refilled in a mixer operating at a speed between 40-60 revolutions per minute and thereafter discharged once a temperature between 130-150 ℃ is reached.

(Final blending step)

Sulphur, vulcanising agents and antioxidants were added to the mixture obtained in the previous step to give a filling factor between 63 and 67%.

The mixer was operated at a speed of between 20-40 rpm and the mixture thus formed was discharged once a temperature of between 100 ℃ and 110 ℃ had been reached.

Table I shows the composition of the three compounds in phr.

TABLE I

	A	B	C
				NR	50	50	50
BR	50	50	50
				First used carbon black	70	55	55
Untreated carbon black from cracking	--	15	--
				Treated carbon black from cracking	--	--	15
Sulfur	1.4	1.4	1.4
				Vulcanization accelerator	10	10	10
Antioxidant agent	5.1	5.1	5.1

NR is a natural 1, 4-cis-polyisoprene rubber.

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

The first used carbon blacks are classified by the abbreviation N330.

Untreated carbon black from cracking originates from carbon black obtained by a process of cracking scrap pneumatic tires and has a carbon black content of between 30 and 80m²Specific surface area in the range of/g.

The treated carbon black from cracking is derived from untreated carbon black from cracking that has been subjected to an oxidation process as described below.

The antioxidant is Trimethylquinoline (TMQ).

The accelerator is N-tertiary butyl-2-benzothiazole sulfonamide (TBBS).

The procedure for the surface activation of carbon black from cracking is given below as an example.

An aqueous solution of 10% w/w cysteine was stirred at 200rpm for 4 hours at room temperature.

After keeping the carbon black from cracking in an oven at 120 ℃ for 24 hours, the carbon black from cracking was added to the above aqueous solution. The weight ratio of cysteine to carbon black from cleavage was 4/1. The resulting solution was stirred at room temperature for 72 hours. Once 72 hours have elapsed, the solution is filtered on a filter paper and subsequently washed with water until the water used for washing has been analysed by means of spectroscopic and chromatographic techniques to contain the amount of free cysteine.

The filtrate was then recovered and placed in an oven at 120 ℃ for 72 hours, and its composition was then characterized.

It was determined that the carbon black from cleavage functionalized as shown above had 8.5% functional groups.

From the compounds listed in table I, respective samples were obtained, which were subjected to mechanical property tests to verify the advantages obtained from the use of the carbon blacks from cracking treated according to the invention.

In particular, properties related to tensile strength, 300% modulus and crack propagation resistance were evaluated.

Mechanical properties were measured according to ASTM D412C.

Furthermore, a parameter called "bound rubber" was measured as an indicator of chemical-physical polymer-filler interaction; the non-vulcanized samples were tested to determine the fraction of insoluble compound after 24 hours of treatment in THF at room temperature.

The results obtained from the above tests are given in indexed form in table II with respect to the results obtained from compound a.

TABLE II

	A	B	C
				Tensile strength	100	85	100
Modulus of 300%	100	80	100
				Resistance to crack propagation	100	90	100
Bonding rubber	100	85	100

From the results reported in table II it is clear that the compound obtained according to the description of the invention (use of treated carbon black from cracking) is able to remedy the drawbacks due to the partial substitution of the carbon black from cracking for the carbon black first used.

In fact, the comparison between the data relating to compound B and the data relating to compound C demonstrates how the functionalization from the cleaved carbon black according to the invention can activate the surface of the carbon black from cleavage with respect to the polymer base in such a way as to restore the reinforcing strength of the first-used carbon black.

The object of the present invention is to provide the opportunity of using carbon black from cracking without compromising the mechanical properties of the compound.

As just disclosed, the possibilities offered by the invention relate to major advantages in terms of ecology. In fact, thanks to the present invention, it will be possible to make new pneumatic tires using carbon black derived from scrapped pneumatic tires.

Finally, despite the fact that the surface activation treatment of the carbon black from cracking necessarily implies additional costs, the possibility of using the carbon black from cracking, even if suitably treated, as a substitute for a part of the carbon black for the first use still represents an economic advantage.