Urea masterbatch for addition to elastomeric compositions

Abstract

The invention relates to a urea masterbatch comprising at least one elastomer, an organic or inorganic filler, water and a urea compound of the general formula (R1, R2) N-CO-[(NR5)-R6-(NR7)-CO] n-N (R3, R4), wherein the groups R1, R2, R3 and R4 are each independently selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 5 to 24 carbon atoms, an aryl group having 6 to 30 carbon atoms and an aralkyl group having 7 to 25 carbon atoms, the groups R2 and R3 may together form a ring, the groups R1, R2, R3 and R4 are each optionally interrupted and / or substituted by one or more heteroatoms, the group R6 is a divalent hydrocarbon group, and the groups R1, R2, R3 and R4 are each optionally interrupted and / or substituted by one or more heteroatoms. The present invention relates to a masterbatch, preferably divalent methyl phenyl, n being an integer equal to 0 or 1, the weight ratio of water to organic or inorganic filler in said masterbatch being less than or equal to 2, said masterbatch not comprising a system for crosslinking an elastomer.

Description

Technical Field

[0001] The present invention relates to the field of components for producing rubber compositions, more specifically to masterbatches comprising at least one urea compound. "Urea masterbatch" is understood to mean an uncrosslinked rubber composition having a high content of urea and intended for producing a rubber composition. Background Art

[0002] It is known to use in certain parts of pneumatic tires rubber compositions that exhibit high stiffness during small deformations of the pneumatic tire, as shown in patent application WO 02 / 10269. Resistance to small deformations is one of the properties that a pneumatic tire must exhibit in order to respond to the stresses to which it is subjected.

[0003] Such hardening can be achieved by increasing the content of reinforcing fillers or by incorporating certain reinforcing resins into the constituent rubber compositions of the components of the pneumatic tire.

[0004] Various solutions that have been developed include rubber compositions comprising a combination of epoxy resins and urea compounds, as shown, for example, in document WO 2021 / 181032.

[0005] Urea derivatives can also be used as vulcanization activators in vulcanizable rubber compositions. For example, document US 5096978 proposes the use of substituted ureas for this purpose.

[0006] However, urea obtained in granular form is a compound that is difficult to disperse uniformly in elastomeric compositions. It is certainly possible to increase the homogenization time or the mixing duration, but this generally reduces the rigidity of the final composition, in particular due to the scission of the elastomer chains.

[0007] In the course of their research, the Applicant discovered a urea masterbatch formulation that can be well incorporated into elastomeric compositions, thus improving the properties of these compositions compared to compositions in which urea is incorporated by methods known to those skilled in the art, namely in granular form. Summary of the invention

[0008] Therefore, the present invention relates to a urea masterbatch, which comprises at least one elastomer, an organic filler or an inorganic filler, water and a urea masterbatch of the general formula (R1, R2)N-CO-[(NR5)-R6-(NR7)-CO] n-N(R3, R4) urea compound, wherein the groups R1, R2, R3 and R4 are each independently selected from a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 5 to 24 carbon atoms, an aryl group having 6 to 30 carbon atoms and an aralkyl group having 7 to 25 carbon atoms, the groups R2 and R3 can form a ring together, the groups R1, R2, R3 and R4 are each optionally interrupted and / or substituted by one or more heteroatoms, the group R6 is a divalent hydrocarbon group, preferably a divalent methylphenyl group, n is an integer equal to 0 or 1, the weight ratio of water to organic filler or inorganic filler in the masterbatch is less than or equal to 2, and the masterbatch does not contain an elastomer crosslinking system. DETAILED DESCRIPTION

[0009] definition

[0010] The carbon-containing compounds mentioned in the specification can be compounds of fossil origin or bio-based origin. In the case of compounds of bio-based origin, they can be partially or completely derived from biomass, or can be obtained by renewable starting materials derived from biomass. This particularly relates to polymers, plasticizers, fillers, etc.

[0011] Elastomer

[0012] The urea masterbatch according to the present invention comprises at least one elastomer. As is known, elastomers are polymers that exhibit elastic properties after crosslinking.

[0013] Preferably, the urea masterbatch according to the invention comprises at least one diene elastomer.Thus, the urea masterbatch may comprise only one diene elastomer or a mixture of more than one diene elastomer.

[0014] As is known to all, a "diene" elastomer (or diene rubber, if no distinction is made), whether natural or synthetic, is understood to mean an elastomer composed at least partly (i.e. homopolymer or copolymer) of diene monomer units (monomers bearing two conjugated or non-conjugated carbon-carbon double bonds).

[0015] These diene elastomers can be divided into two categories: “essentially unsaturated” or “essentially saturated”. “Essentially unsaturated” is generally understood to mean a diene elastomer derived at least partly from conjugated diene monomers and having a content of units of diene origin (conjugated dienes) greater than 15% (mol %); thus, diene elastomers such as butyl rubber or EPDM-type copolymers of dienes with α-olefins do not fall within the aforementioned definition but may be more particularly referred to as “essentially saturated” diene elastomers (low or very low content of units of diene origin, always less than 15%). The diene elastomer comprised in the composition according to the invention is preferably essentially unsaturated.

[0016] Diene elastomers that can be used in the composition according to the invention are understood in particular to mean:

[0017] a) any homopolymer of a conjugated or non-conjugated diene monomer having 4 to 18 carbon atoms;

[0018] b) Any copolymer of a conjugated or non-conjugated diene having 4 to 18 carbon atoms and at least one other monomer.

[0019] The other monomers may be ethylene, olefins or conjugated or non-conjugated dienes.

[0020] Suitable conjugated dienes are conjugated dienes having 4 to 12 carbon atoms, in particular 1,3-dienes, such as in particular 1,3-butadiene and isoprene.

[0021] Suitable olefins are vinyl aromatic compounds having 8 to 20 carbon atoms and aliphatic alpha-monoolefins having 3 to 12 carbon atoms.

[0022] Suitable vinylaromatic compounds are, for example, styrene, (o-, m- or p-)methylstyrene, the commercial “vinyltoluene” mixtures and p-(tert-butyl)styrene.

[0023] Suitable aliphatic α-monoolefins are in particular acyclic aliphatic α-monoolefins having 3 to 18 carbon atoms.

[0024] The urea masterbatch according to the invention preferably comprises at least one essentially unsaturated diene elastomer.

[0025] Preferably, the urea masterbatch comprises as elastomer at least one elastomer selected from polybutadiene (BR), natural rubber (NR), synthetic polyisoprene (IR), butadiene copolymers, isoprene copolymers and mixtures of these elastomers. The butadiene copolymer is particularly selected from styrene-butadiene copolymers (SBR).

[0026] As is known, "isoprene elastomer" is understood to mean an isoprene homopolymer or copolymer, in other words a diene elastomer chosen from natural rubber (NR), synthetic polyisoprenes (IR), various isoprene copolymers and mixtures of these elastomers. Isoprene copolymers include in particular isobutylene-isoprene (butyl rubber-IIR) copolymers, isoprene-styrene (SIR) copolymers, isoprene-butadiene (BIR) copolymers or isoprene-butadiene / styrene (SBIR) copolymers. The isoprene elastomer is preferably chosen from natural rubber, synthetic cis-1,4-polyisoprenes and mixtures thereof; among these synthetic polyisoprenes, polyisoprenes having a content (mol %) of cis-1,4-linkages greater than 90%, more preferably greater than 98%, are preferably used. Preferably, according to any one of the arrangements of the present application, the diene elastomer is a natural rubber.

[0027] Very preferably, the urea masterbatch comprises as elastomer at least one elastomer selected from natural rubber, synthetic polyisoprene, butadiene-styrene copolymers and mixtures of these elastomers. The urea masterbatch very preferably comprises as elastomer a mixture of natural rubber or synthetic polyisoprene and butadiene-styrene copolymers. During the production of the urea masterbatch, it was observed that the presence of SBR improves the dissolution of urea in the urea masterbatch.

[0028] Preferably, the content of diene elastomer (preferably isoprene elastomer, preferably natural rubber) in the urea masterbatch is from 50 to 100 phr. Preferably, the content of SBR in the urea masterbatch is in the range of from 0 to 50 phr.

[0029] filler

[0030] The urea masterbatch according to the present invention comprises an organic filler or an inorganic filler. The filler present in the urea masterbatch according to the present invention can minimize or even prevent the presence of water in the masterbatch as inclusions; such inclusions may make the incorporation of the masterbatch into an elastomeric composition more difficult.

[0031] Suitable organic or inorganic fillers may include any type of filler that can be incorporated into an elastomeric composition, provided that the filler is capable of at least partially trapping water.

[0032] Preferably, the organic filler or inorganic filler is selected from carbon black, silica, alumina, chalk, clay, bentonite, talc, kaolin and mixtures thereof.

[0033] All carbon blacks, in particular carbon blacks of the HAF, ISAF or SAF type conventionally used in tires ("tire-grade" carbon blacks), are suitable for use as carbon black. "Tire-grade" carbon blacks more particularly include reinforcing carbon blacks (ASTM grades) of the 100, 200 or 300 series (for example N115, N134, N234, N326, N330, N339, N347 or N375 carbon blacks), or higher series carbon blacks (for example N660, N683 or N772), depending on the application sought. These carbon blacks can be used in commercially available individual form, or in any other form, for example as carrier for some of the rubber additives used. The carbon black may, for example, have been incorporated into an isoprene elastomer in the form of a masterbatch (see, for example, patent applications WO 97 / 36724 or WO 99 / 16600).

[0034] Carbon black is characterized by various properties, in particular the specific surface area and the compression oil absorption number (COAN).The COAN of carbon black is measured according to standard ASTM D3493-16.

[0035] The BET specific surface area of ​​carbon black is measured according to standard ASTM D6556-10 (multipoint method (at least 5 points) - gas: nitrogen - relative pressure p / p0 range: 0.1 to 0.3).

[0036] The physical state in which the inorganic filler is provided is not critical, whether it is in the form of a powder, granules, beads or any other suitable densified form.

[0037] The inorganic filler is preferably selected from mineral fillers of the siliceous type, in particular silicon dioxide (SiO2) or aluminous type, in particular aluminum oxide (Al2O3), chalk, clay, bentonite, talc, kaolin and mixtures thereof, preferably from silica, chalk, talc, kaolin and mixtures thereof, more preferably from silica, talc, kaolin and mixtures thereof. Very preferably, the inorganic filler is selected from silica, kaolin and mixtures thereof.

[0038] The silicon dioxide used may be any silicon dioxide known to those skilled in the art, in particular one having a BET surface area and a CTAB specific surface area of ​​less than 450 m 2 / g, preferably 30m 2 / g to 400m 2 / g of any precipitated or fumed reinforced silica. Examples of highly dispersible precipitated silicas ("HDS") include Ultrasil 7000 and Ultrasil 7005 silicas from Degussa, Zeosil 1165MP, 1135MP and 1115MP silicas from Rhodia, Hi-Sil EZ150G silica from PPG, Zeopol 8715, 8745 and 8755 silicas from Huber or high specific surface area silicas such as those described in patent application WO 03 / 16837.

[0039] The BET specific surface area of ​​the silica is determined in a known manner by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" (Vol. 60, p. 309, February 1938), more specifically in accordance with the French standard NF ISO 9277 of December 1996 (multipoint volumetric method (5 points) - gas: nitrogen - degassing: 160° C. for 1 hour - relative pressure p / p0 range: 0.05 to 0.17).

[0040] The CTAB specific surface area of ​​silica is determined according to French Standard NF T 45-007 of November 1987 (method B).

[0041] In the preferred case where the inorganic filler comprises silica, the BET surface area of ​​the silica is preferably between 45 m 2 / g to 400m 2 / g, more preferably between 60m 2 / g to 300m 2 / g.

[0042] The composition according to the invention preferably contains no inorganic filler-elastomer coupling agent or contains less than 5% by weight of inorganic filler-elastomer coupling agent relative to the weight of the inorganic filler, preferably less than 2% by weight, more preferably less than 1% by weight of inorganic filler-elastomer coupling agent relative to the weight of the inorganic filler.

[0043] As is known, a "coupling agent" (or "linking agent") is understood to mean an agent capable of coupling an inorganic filler to an elastomer. In particular, it is not the reinforcing effect on the urea masterbatch that is sought in an organic or inorganic filler, but its hydrophilic effect. The use of fillers similar to those used in the elastomeric composition into which the urea masterbatch is to be incorporated, only ensures improved compatibility when mixing these elements.

[0044] The urea masterbatch according to the present invention preferably contains 5 to 80 phr of organic or inorganic filler, preferably 10 to 75 phr of organic or inorganic filler, which can capture the water present in the urea masterbatch, thereby minimizing or even preventing the presence of water inclusions.

[0045] water

[0046] The urea masterbatch according to the present invention contains water, and the weight ratio of water to organic filler or inorganic filler in the masterbatch is less than or equal to 2. The presence of water can ensure a more uniform distribution of urea in the urea masterbatch, in particular by promoting the dissolution of urea.

[0047] Preferably, the weight ratio of water to organic or inorganic filler is less than or equal to 1. A weight ratio of water to organic or inorganic filler of less than or equal to 2, preferably less than or equal to 1, unexpectedly enables better performance when the urea masterbatch is incorporated into the elastomeric composition.

[0048] Preferably, the water content in the urea masterbatch according to the present invention is in the range of 3 to 50 phr, preferably 5 to 30 phr. Lower contents cannot sufficiently improve the dispersion of urea in the masterbatch, while too high a content increases the risk of water inclusions.

[0049] Urea

[0050] The urea masterbatch according to the present invention comprises a urea masterbatch having the general formula (R1, R2)N-CO-[(NR5)-R6-(NR7)-CO] n -N(R3,R4) urea compounds, wherein the groups R1, R2, R3, R4, R5 and R7 are each independently selected from:

[0051] Hydrogen atoms,

[0052] an alkyl group having 1 to 20 carbon atoms,

[0053] cycloalkyl groups having 5 to 24 carbon atoms,

[0054] an aryl group having 6 to 30 carbon atoms, and

[0055] · an aralkyl group having 7 to 25 carbon atoms,

[0056] wherein the groups R2 and R3 may together form a ring, the groups R1, R2, R3 and R4 are each optionally interrupted and / or substituted by one or more heteroatoms, the group R6 is a divalent hydrocarbon group, preferably a divalent methylphenyl group, and n is an integer equal to 0 or 1.

[0057] A divalent hydrocarbon radical is understood to mean a divalent group consisting of carbon and hydrogen, preferably containing 1 to 20 carbon atoms, more preferably 1 to 10 carbon atoms.

[0058] When n is equal to 0, the general formula is (R1, R2)N-CO-[(NR5)-R6-(NR7)-CO] n -N(R3,R4) becomes (R1,R2)N-CO-N(R3,R4). When n is equal to 1, the general formula is (R1,R2)N-CO-[(NR5)-R6-(NR7)-CO] n -N(R3,R4) becomes (R1,R2)N-CO-(NR5)-R6-(NR7)-CO-N(R3,R4).

[0059] In the general formula, it is understood that the divalent group CO represents a carbon atom connected to an oxygen atom via a double bond, the group (R1, R2)N (or N(R3, R4)) represents a nitrogen atom connected to the group R1 and the group R2 (or R3 and R4) via a covalent bond, and the group NR5 (or NR7) represents a nitrogen atom connected to the group R5 (or R7).

[0060] Examples of urea compounds in which the radicals R2 and R3 together form a ring are 2-imidazolidinone or ethylene urea.

[0061] Preferably, the groups do not together form a ring.

[0062] Preferably, the urea compound is a monourea (thus n=0), and the groups R1, R2, R3 and R4 are each independently selected from hydrogen and a hydrocarbon compound selected from:

[0063] an alkyl group having 1 to 20 carbon atoms,

[0064] cycloalkyl groups having 5 to 24 carbon atoms,

[0065] an aryl group having 6 to 30 carbon atoms, and

[0066] · an aralkyl group having 7 to 25 carbon atoms,

[0067] Therein, the radicals R1, R2, R3 and R4 are each optionally substituted.

[0068] Preferably, the groups R1 and R3 are both hydrogen atoms. The urea is then a compound of the formula R2-HN-CO-NH-R4.

[0069] In a preferred arrangement, at least one group R2 or R4 is an aromatic group having 6 to 8 carbon atoms, preferably a phenyl group.Preferably, in this preferred arrangement, the urea compound may be N-phenylurea or 1,3-diphenylurea.

[0070] In a preferred arrangement, the urea compound is a diurea (ie n=1) in which the groups R1, R2, R3 and R4 are methyl groups, R5 and R7 are hydrogen atoms and R6 is a divalent methylphenyl group. An example of such a diurea compound is the compound Amicure UR2T from Evonik of the formula 1,1'-(4-methyl-m-phenylene)bis(3,3-dimethylurea).

[0071] Preferably, the urea compound does not contain aromatic rings.

[0072] Preferably, the radicals R1, R2, R3 and R4 are each a hydrogen atom. Urea compounds are then compounds of the formula H2N-CO-NH2, which are known as "ureas" or "carbonamides".

[0073] Therefore, the urea compound is very preferably selected from the following compounds: urea, N,N'-dimethylurea, ethylene urea, N-phenyl urea and 1,3-diphenyl urea, preferably selected from the following compounds: urea, N,N'-dimethylurea, N-phenyl urea and 1,3-diphenyl urea, very preferably selected from the following compounds: urea and N,N'-dimethylurea. Very preferably, the urea compound is a urea of ​​the formula H2N-CO-NH2.

[0074] The urea content in the urea masterbatch ranges from 20 to 150 phr, preferably from 30 to 140 phr, very preferably from 80 to 120 phr. Below said minimum values, the other materials constituting the urea masterbatch will be introduced in too high an amount into the elastomeric composition. Above these contents, it is more difficult to obtain a homogeneous masterbatch that allows a good dispersion of the urea in the elastomeric composition in which said masterbatch is intended to be used.

[0075] Cross-linking system

[0076] The elastomeric composition comprises a crosslinking system intended in particular to impart elastomeric properties thereto.The urea masterbatch to be incorporated into the elastomeric composition according to the invention does not comprise an elastomeric crosslinking system (ie a system capable of crosslinking the elastomer present in the urea masterbatch).

[0077] In particular, the urea masterbatch does not contain the crosslinking systems known to the person skilled in the art, such as, for example, sulfur-based and / or peroxide-based and / or bismaleimide-based crosslinking systems.

[0078] Preferably, the urea masterbatch according to the present invention contains no sulfur or less than 0.5 phr, preferably less than 0.4 phr, more preferably less than 0.2 phr of sulfur.

[0079] Various additives

[0080] The rubber composition according to the invention may also contain some or all of the conventional additives or processing aids known to those skilled in the art and commonly used in rubber compositions (in particular for pneumatic tires), such as plasticizers (e.g. plasticizing oils and / or plasticizing resins), pigments, protective agents (e.g. anti-ozone waxes, chemical anti-ozonants or antioxidants) or anti-fatigue agents.

[0081] In particular, the urea masterbatch according to the present invention preferably comprises a plasticizer, which is preferably selected from C5-based resins, C9-based resins, process oils, stearic acid, rosin and mixtures of these compounds, preferably selected from stearic acid, rosin and mixtures of these compounds.

[0082] “C5-based resin” and “C9-based resin” are understood to mean resins based on compounds comprising 5 carbon atoms and 9 carbon atoms, respectively.

[0083] Preferably, the composition according to the invention comprises no nitrile compounds or comprises less than 10 phr, preferably less than 5 phr, more preferably less than 2 phr, very preferably less than 1 phr and still more preferably less than 0.5 phr of nitrile compounds.

[0084] Preferably, the urea masterbatch is composed of at least one elastomer, an organic filler or an inorganic filler, water, a urea compound of the general formula (R1, R2)N-CO-N(R3, R4), and an optional plasticizer, wherein the groups R1, R2, R3 and R4 are each independently selected from a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 5 to 24 carbon atoms, an aryl group having 6 to 30 carbon atoms, and an aralkyl group having 7 to 25 carbon atoms, the groups R2 and R3 can form a ring together, the groups R1, R2, R3 and R4 are each optionally interrupted and / or substituted by one or more heteroatoms, the weight ratio of water to the organic filler or inorganic filler in the masterbatch is less than or equal to 2, and all these compounds are as described above.

[0085] Rubber composition

[0086] The invention also relates to a rubber composition based on an elastomer, preferably a diene elastomer, a reinforcing filler, a crosslinking system, 1 to 30 parts by weight of epoxy resin per hundred parts by weight of elastomer (phr) and 1 to 15 phr of a urea compound introduced in the form of a urea masterbatch according to the invention.

[0087] Epoxy resins useful in the present invention include all polyepoxide compounds. These may include, for example, aromatic epoxy resins, alicyclic epoxy resins and aliphatic epoxy resins. For example, the aromatic epoxy resin may be an aromatic amine epoxy resin. These resins are preferably novolac epoxy resins, i.e. epoxy resins obtained by acid catalysts, which are different from resols obtained by base catalysts.

[0088] Particularly among the aromatic epoxy compounds, preferred epoxy resins are selected from the following types of resins: 2,2-bis[4-(glycidyloxy)phenyl]propane, poly[(o-cresyl glycidyl ether)-co-formaldehyde], poly[(o-phenyl glycidyl ether)-co-formaldehyde], poly[(phenyl glycidyl ether)-co-(hydroxybenzaldehyde glycidyl ether)], tris(glycidyloxyphenyl)methane, tetra(glycidyloxyphenyl)ethane and mixtures of these resins.

[0089] An “epoxy resin of the following type” is understood to mean a resin based on units of the components, ie comprising the components or oligomers of the components.

[0090] Epoxy resins are curing resins. "Curing resin" is understood to mean a resin that, when incorporated into a rubber composition with a curing agent, is able to increase the stiffness of the crosslinked rubber composition. However, the increase in stiffness of the rubber composition is usually accompanied by an increase in hysteresis loss.

[0091] More preferably, the epoxy resin is selected from the following types of resins: poly[(o-cresyl glycidyl ether)-co-formaldehyde], poly[(o-phenyl glycidyl ether)-co-formaldehyde], tris(glycidyloxyphenyl)methane, tetra(glycidylphenyl)methane and mixtures of these resins.

[0092] Very preferably, the epoxy resin used in the context of the present invention is chosen from epoxy resins having the following general formulae (I) and (II) and their derivatives, ie oligomers of compounds of the general formulae (I) and (II):

[0093] a.

[0094] b.

[0095] n is an integer representing the degree of polymerization, and n ranges from 1 to 15, preferably from 1 to 10, more preferably from 1 to 5, and very preferably from 1 to 3.

[0096] Examples of commercially available epoxy resins that can be used in the context of the present invention include, for example, DEN 439 epoxy resin from Uniqema, tris(4-hydroxyphenyl)methane triglycidyl ether epoxy resin from Sigma-Aldrich, Araldite ECN 1299 epoxy cresol novolac resin from Huntsman, Araldite EPN1138 epoxy phenol novolac resin from Huntsman, EPPN-502H, EPPN-501H and EPPN-501HY resins from Nippon Kayaku or EPON 1031 resin from Hexion.

[0097] Preferably, the rubber composition according to the invention comprises no curing resin other than epoxy resin, and in particular no resin of the phenol / aldehyde type.

[0098] The composition according to the invention contains between 1 and 30 phr of epoxy resin. If the content of amine-containing curing agent used in the context of the invention is below the minimum resin content, the technical effect sought will not be sufficient, while above the maximum values ​​indicated, there is a risk of excessively increasing the stiffness and of producing a disproportionately adverse effect on the hysteresis and elongation properties of the material. For all these reasons, the content of epoxy resin is preferably between 10 and 25 phr. More preferably, the content of epoxy resin in the composition according to the invention is between 10 and 20 phr.

[0099] The invention also relates to a process for producing a rubber composition as described above, said process comprising the step of incorporating a urea compound within the meaning of the present invention into the rubber composition via a urea masterbatch according to the invention.

[0100] Example

[0101] Measurement method

[0102] Tensile test

[0103] The tests were performed according to French standard NF T 46-002 of September 1988. All tensile measurements were performed under standard conditions of temperature (23±2° C.) and humidity (50%±5% relative humidity) according to French standard NF T 40-101 (December 1979).

[0104] In the second stretch (i.e. after conditioning), at 10% stretch (expressed as MA 10 The nominal secant modulus (or apparent stress in MPa) (calculated based on the initial cross-section of the specimen) was measured for samples cured at 150°C for 60 minutes.

[0105] The results are expressed on a base of 100, with composition C-1 being assigned a value of 100. A result greater than 100 means that the composition of the example in question exhibits a stiffness greater than that of the control.

[0106] Furthermore, the stress at break (in MPa) at 23°C ± 2°C is measured according to standard NF T 46-002 on original samples or on samples cured at 150°C for 25 minutes or at 160°C for 90 minutes. The energy at break is equal to the product of the elongation at break and the stress at break.

[0107] The results are expressed on the basis of 100, with composition C-1 being assigned a value of 100. A result greater than 100 means that the composition of the example in question exhibits a stress at break greater than that of the control.

[0108] Impact loss

[0109] The energy loss is measured to estimate the rolling resistance caused by the test composition by measuring the energy recovered at the eighth rebound of the sample to which the initial energy is applied at a temperature of 60° C., as described in standard DIN 53-512 of April 2000. This measured value is expressed as P60 and is calculated as follows: P60 (%) = 100 × (E0-E1) / E0, where E0 represents the initial energy and E1 represents the recovered energy. The lower this value, the less hysteresis loss the sample exhibits.

[0110] The values ​​are expressed on the basis of 100, with reference to P60 of composition C-1. Values ​​greater than 100 indicate that the impact loss is smaller and therefore the composition exhibits better rolling resistance properties.

[0111] The cure is expressed as the measured t90 value in minutes. The t90 value is determined according to ISO 6502, 2018.

[0112] Production of urea masterbatch

[0113] A masterbatch having the components shown in Table 1 was produced as follows:

[0114] The diene elastomer, urea, organic or inorganic filler and water are introduced continuously into an internal mixer (final fill level: about 75% by volume) at an initial container temperature of about 80° C. The thermomechanical processing (non-productive phase) is then carried out in one step lasting about 4 to 5 minutes in total, with processing above 80° C. for at least 1.5 min, until a maximum drip temperature of 95° C. is reached.

[0115] The compositions in Table 1 are expressed in phr (percent elastomer).

[0116] [Table 1]

[0117]

[0118] (1) Natural rubber

[0119] (2) SBR: styrene-butadiene rubber with 27% styrene units, 24% vinyl units and 46% 1,4-trans units, Tg: -48°C

[0120] (3) Silica 165G from Evonik, with a BET surface area of ​​about 180 m 2 / g

[0121] (4) Carbon black N326 (named according to standard ASTM D-1765)

[0122] (5) Urea from Univar Solutions

[0123] (6) Rosin from Diamantino

[0124] Preparation of composition

[0125] The following test was carried out in the following manner: the diene elastomer, reinforcing filler, epoxy resin and the various other ingredients, apart from the vulcanization system and the curing agent, were introduced continuously into an internal mixer (final fill level: about 70% by volume) at an initial container temperature of about 50° C. The thermomechanical processing was then carried out in one step (non-productive phase) lasting a total of about 3 to 4 min until a maximum drip temperature of 165° C. was reached.

[0126] The mixture thus obtained is recovered and cooled, and then sulfur, sulfenamide type accelerator and urea in dispersed form (composition C-1) or one of urea masterbatches produced according to the above steps are introduced into a mixer (homogeneous finisher) at 30° C., and the whole (production stage) is mixed for a suitable time (for example, between 5 min and 12 min). When urea is introduced in the form of urea masterbatch, the amount of masterbatch added is adjusted to obtain the amount of urea compound in the composition.

[0127] The composition thus obtained is then calendered in the form of rubber sheets (thickness ranging from 2 to 3 mm) or rubber sheets for measuring their physical or mechanical properties, or extruded in the form of shaped elements.

[0128] Crosslinking of the composition was carried out at a temperature of 160° C. under pressure for 15 min.

[0129] The reference composition is the rubber composition C-1 used as a reference in document WO 2021 / 181032:

[0130] [Table 2]

[0131] NR(1) 100 Carbon Black(2) 70 ZnO(3) 3 6PPD(4) 2.5 Stearic acid(5) 2 sulfur 3 CBS(6) 2 Epoxy resin(9) 12

[0132] Content in phr

[0133] (1) Natural rubber

[0134] (2) Carbon black N326 (named according to standard ASTM D-1765)

[0135] (3) Zinc oxide (industrial grade-Umicore)

[0136] (4) N-(1,3-dimethylbutyl)-N-phenyl-p-phenylenediamine (Santoflex 6-PPD from Flexsys)

[0137] (5) Stearin (Pristerene 4931 from Uniqema)

[0138] (6) N-cyclohexylbenzothiazolesulfenamide (Santocure CBS from Flexsys)

[0139] (7) Epoxy phenol novolac resin (EPN 1138 from Huntsman)

[0140] The various compositions C-1 to C-13 were obtained by adding urea in dispersed form (composition C-1) or in the form of a urea masterbatch to the formulations shown in Table 2, so as to obtain a urea content of 2 phr in each composition. For each composition, the percentage by weight of the urea masterbatch added relative to the weight of the mixture without urea shown in Table 2 is shown, so as to obtain 2 phr of urea in the composition produced.

[0141] Table 3 shows compositions C-1 to C-13 and the results obtained.

[0142] [Table 3]

[0143]

[0144] Compared to non-inventive compositions (in particular reference composition C-1), it is observed that the compositions according to the invention exhibit better stiffness and hysteresis properties.

[0145] The compositions according to the invention also show better curing and excellent stress at break properties.

Claims

1. A urea masterbatch comprising at least one elastomer, an organic filler or an inorganic filler, water and a urea masterbatch of the general formula (R1, R2)N-CO-[(NR5)-R6-(NR7)-CO] n -N(R3, R4), wherein the groups R1, R2, R3 and R4 are each independently selected from a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 5 to 24 carbon atoms, an aryl group having 6 to 30 carbon atoms and an aralkyl group having 7 to 25 carbon atoms, the groups R2 and R3 may together form a ring, the groups R1, R2, R3, R4, R5 and R7 are each optionally interrupted and / or substituted by one or more heteroatoms, the group R6 is a divalent hydrocarbon group, preferably a divalent methylphenyl group, and n is an integer equal to 0 or 1, The weight ratio of water to organic filler or inorganic filler in the masterbatch is less than or equal to 2, the masterbatch does not contain an elastomer crosslinking system, and the content of urea compound in the mixture is in the range of 20 phr to 150 phr.

2. The urea masterbatch according to claim 1, wherein The weight ratio of water to filler is less than or equal to 1.

3. The urea masterbatch according to any one of the preceding claims, further comprising a plasticizer, preferably selected from C5-based resins, C9-based resins, process oils, stearic acid, rosin and mixtures of these compounds, preferably selected from stearic acid, rosin and mixtures of these compounds.

4. The urea masterbatch according to any one of the preceding claims, wherein At least one of the radicals R2 or R4 is an aryl radical having 6 to 8 carbon atoms, preferably a phenyl radical.

5. The urea masterbatch according to any one of claims 1 to 3, wherein The urea compound does not contain an aromatic ring.

6. The urea masterbatch according to any one of claims 1 to 3, wherein The urea compound is selected from the group consisting of urea, N,N'-dimethylurea, ethylene urea, N-phenyl urea and 1,3-diphenyl urea, preferably selected from the group consisting of urea, N,N'-dimethylurea, N-phenyl urea and 1,3-diphenyl urea, very preferably selected from the group consisting of urea and N,N'-dimethylurea.

7. The urea masterbatch according to any one of the preceding claims, wherein The content of the urea compound ranges from 30 phr to 140 phr, very preferably from 80 phr to 120 phr.

8. The urea masterbatch according to any one of the preceding claims, wherein The water content ranges from 3 to 50 phr, preferably from 5 to 30 phr.

9. The urea masterbatch according to any one of the preceding claims, wherein The content of the organic filler or the inorganic filler is in the range of 5 to 80 phr, preferably 10 to 75 phr.

10. The urea masterbatch according to any one of the preceding claims, wherein The organic filler or inorganic filler is selected from carbon black, silica, alumina, chalk, clay, bentonite, talc, kaolin and mixtures thereof.

11. The urea masterbatch according to any one of the preceding claims, wherein The elastomer is a diene elastomer, preferably an essentially unsaturated diene elastomer, preferably chosen from polybutadiene, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers and mixtures of these elastomers, very preferably chosen from natural rubber, synthetic polyisoprenes, butadiene-styrene copolymers and mixtures of these elastomers.

12. Rubber composition based on at least one elastomer, a reinforcing filler, a crosslinking system, 1 to 30 parts by weight of epoxy resin per hundred parts by weight of elastomer (phr) and 1 to 15 phr of a urea compound introduced in the form of a urea masterbatch according to any one of the preceding claims.

13. Process for producing a rubber composition according to the preceding claim, comprising a step of incorporating a urea compound into the rubber composition via a masterbatch according to any one of claims 1 to 11.

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