EP2129755A1 - Method for the wet drawing of steel cables for reinforcing tyres - Google Patents

Abstract

The invention relates to a method for the wet drawing of a steel cable, also called "steelcord", for reinforcing a tyre, that uses, as a lubricant composition, an aqueous dispersion containing solid particles of a fatty acid ester including from 5 to 40 carbon atoms, in particular a diester of the formula R<SUP>1</SUP> - CO - O - A - O - CO - R<SUP>2</SUP>] in which R<SUP>1</SUP> and R<SUP>2</SUP> are hydrocarbon groups including from 5 to 23 carbon atoms, preferably from 13 to 21 carbon atoms. More particularly, the diester is a glycol distearate (EGDS). The use of such a diester, particularly in combination with a surfactant such as a block copolymer of ethylene oxide and C<SUB>3</SUB>-C<SUB>10</SUB> alkylene oxide, results in improved lubrication performance.

Description

 PROCESS FOR WET TREADING WIRE OF STEEL WIRES FOR REINFORCING PNEUMATIC BANDAGES

FIELD OF THE INVENTION

The present invention relates to metal wire drawing processes as well as to the use of water-based lubricants in such wire drawing processes.

It relates more particularly to lubricants in the form of aqueous dispersions and to their use for the wet drawing of steel wires intended to reinforce pneumatic tires (so-called "steelcord" type steel wires).

STATE OF THE ART

The drawing of Steelcord steel wire through dies is carried out under extremely severe conditions of temperature and pressure because of the important friction that develops then between wire and dies. This results in rapid wear of the surface of the die as that of the wire, the risk of breakage and occurrence of superficial defects of the wire.

A too rapid increase in the diameter of the die and therefore drawn wire is unacceptable from the industrial point of view.

To overcome the above problems, at least minimize them, it is known to use lubricants of the oily or aqueous type.

In the most extreme conditions, aqueous lubricants are generally preferred because of their superior cooling capacity of the metal. They have other benefits of being easy to use, low pollution and more economical.

The most commonly used commercial drawing lubricants are aqueous emulsions (see, for example, document FR 1 037 447) consisting of different fatty constituents in liquid form emulsified in the aqueous phase by a combination of surfactants. Different additives can be dissolved in the aqueous or fatty phase.

Lubricants in the form of an aqueous dispersion, based on a solid fatty phase (or "wax") dispersed in the aqueous phase, generally stabilized by a combination of surfactants, can also be used. Aqueous dispersions comprising in particular Solid particles of bis-amide waxes such as ethylene bis-stearamide (hereinafter abbreviated as "EBS") are quite common; they are known for the cold deformation of metals, in particular for rolling (see, for example, WO 02/062931 or US2004-072702, US 4,481,038).

Achieving a more efficient lubrication is a constant concern in Steelcord steel wire drawing, in order to achieve at least one of the following industrial objectives:

- higher productivity, for example a higher speed of drawing;

- a lower frequency of replacement of the dies;

less breakage of the wires during their stretching; the possibility of drawing harder, higher carbon steels under production conditions similar to those used for drawing less hard steels.

However, the applicants, during their research, discovered a new aqueous dispersion, simple formulation compared to those of the prior art, which provides a more effective lubrication meeting the above objectives.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to the use as a lubricating composition in a wet drawing process for obtaining steel wire for reinforcement of a tire (hereinafter also referred to as "steel wire"). Steelcord "), an aqueous dispersion comprising solid particles of a fatty acid ester having 5 to 40 carbon atoms.

Such a dispersion makes it possible not only, compared in particular with aqueous dispersions based on EBS, to improve lubrication performance under the extreme conditions of speed and temperature, in particular in terms of wear and friction, but also, compared with emulsions. to obtain a better consistency of the performance by limiting the possible interactions with the surface of the wire and its possible coating, and thus the evolution of the chemical composition of the drawing bath during its use (so-called "break-in" problem). bath ").

The invention also relates to a wet drawing method for obtaining Steelcord steel wire, said method comprising the following steps: - from a steel wire having a diameter greater than 0.6 mm;

stretching said wire through a series of dies of decreasing diameter, in the presence of a lubricating composition in the form of an aqueous dispersion, to a predetermined final diameter of less than 0.5 mm,

and being characterized in that said aqueous dispersion comprises solid particles of a fatty acid ester having 5 to 40 carbon atoms.

The invention also relates to a method of manufacturing a tire comprising rubber and at least one steel reinforcing element, said method comprising the following steps:

- from a steel wire having a diameter greater than 0.6 mm; stretching said steel wire through a series of dies of decreasing diameter, in the presence of a lubricating composition in the form of an aqueous dispersion comprising solid particles of a fatty acid ester having from 5 to

40 carbon atoms, until a fine wire less than 0.5 mm in diameter is obtained; optionally assembling a plurality of fine wires thus obtained to obtain a fine wire assembly; incorporating said fine wire and / or said assembly as a metal reinforcing element, as it is or previously incorporated in rubber in the green state, into the structure of a tire being manufactured; perform the cooking of the tire once its structure is complete.

The invention as well as its advantages will be readily understood in the light of the detailed description and the following exemplary embodiments.

I. DETAILED DESCRIPTION OF THE INVENTION

In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are% by weight.

I- 1. Lubricating composition

The lubricant composition used according to the invention therefore has the essential characteristic of being an aqueous dispersion and comprising solid particles of a fatty acid ester having from 5 to 40 carbon atoms. It may comprise various additives, in particular an amphiphilic compound such as a surfactant and / or an extreme-pressure additive. a) Fatty acid ester

By "fatty acid" it is recalled that it must be understood, by definition, an aliphatic carboxylic acid; this fatty acid therefore comprises from 5 to 40 carbon atoms (the carbon atom of the carboxylic group -COOH being included), preferably from 6 to 24 carbon atoms; it is more preferably a long chain fatty acid of 14 to 22, particularly 16 to 22 carbon atoms. By such definitions should be understood also mixtures of the corresponding fatty acids.

By "aqueous dispersion" is meant a liquid dispersion whose liquid is generally only water. However, it is conceivable to associate therein minimum quantities (preferably less than 10% by weight, or even less than 1% by weight) of solvents, the latter preferably being of low volatility.

"Solid particles" means particles which are solid at ambient temperature (23 ° C.), preferably over a temperature range of from 23 ° C. to at least 40 ° C., more preferably from 23 ° C. to at least 50 ° C; they may have a melting point of less than 200 ° C., especially less than 135 ° C., for example less than 70 ^° C. The melting point may be greater than or equal to 60 ° C. The fatty acid ester may be chosen in particular depending on the melting point, generally greater than the temperature at which the drawing process is carried out. It is not excluded, however, that the temperature exceeds this melting point very locally, such a phenomenon does not affect the invention.

The ester may be any type of ester, for example a diester or triester, especially an ester derived from a diol (or glycol), a polyol or a mixture of such alcohols. As examples of diols or polyols, there may be mentioned alkylenes glycol such as ethylene glycol or propylene glycol, or else glycerol.

According to a preferred embodiment of the invention, the ester corresponds to formula (I):

(I)

[R-COO-] _x -A - [- OH] _y in which:

- R is a hydrocarbon group, saturated or unsaturated, linear or branched (corresponding, of course, to that of the formula R-COOH of the corresponding fatty acid);

A is a hydrocarbon group, optionally interrupted by one or more heteroatoms, of valence x + y; x is an average number of 1 to 5; y is an average number of 0 to 5;

- x + y ranging from 1 to 10, preferably from 2 to 5.

In the present application, an average number can designate an integer or a decimal number.

If y is different from 0, it means that it is a partial ester. If y is 0, it means that it is a completely esterified compound. For example, if x + y = 2, y = 0 and x = 2, then it is a diester (totally esterified).

According to a preferred embodiment of the invention, A is a divalent group (x + y = 2; A - (- OH) _{x + y} is then a diol), and y is 0.

Preferably, the ester is a diester corresponding to formula (II):

(H) R ¹ - CO - O - A - O - CO - R ²

in which R ¹ and R ² , which are identical or different, are saturated or unsaturated hydrocarbon groups, preferably saturated (ie, alkyl groups), linear or branched, containing from 4 to 39, preferably from 5 to 23, in particular from 13 to 21, more particularly from 15 to 21 carbon atoms; A having the definition given above for the formula (I).

In the formula (II) above, the divalent group A may in particular meet the formula:

- (CH ₂ ) _z - [OE] _m - [OP] _m - (CH ₂ ) _z .-

in which :

z and z ', which may be identical or different, are integers from 1 to 10;

- OE is an optional ethylene oxide group;

OP is an optional propylene oxide group;

m and m ', which may be identical or different, are average numbers (integers or decimals) in a range from 0 to 100, preferably from 0 to 10.

If EO and / or OP groups are present, the diol compound of formula A - (- OH) _{2 from} which the ester is derived may be a product of (poly) ethoxylation and / or (poly) propoxylation, or condensation of ethylene and / or propylene glycol. Preferably the group A does not comprise groups EO and / or OP, and it is then preferentially an alkylene group; such a definition corresponds in particular to a specific diester of formula (III):

(III)

R ¹ - CO - O - (CH ₂ ) _Z - - O - CO - R ²

wherein A is an alkylene group [(CH ₂ ) _Z "] having (number z") from 1 to 15, preferably from 1 to 10 carbon atoms; A is especially selected from the group consisting of methylene, ethylene, propylene, butylene, and mixtures of these groups; R ¹ and R ² have the definitions given above for the formula (II).

The fatty acids and hydrocarbon groups (preferably alkyl) R, R ¹ and R ² previously described are well known. These are generally derived from vegetable oils. They can be present in mixtures. In the case of mixtures, the definition of all the groups, irrespective of the number of carbon atoms, if the group (or the corresponding acid) predominates in weight (relative majority, preferably absolute preferably at least 75%) corresponds to the definition. It is common to reduce the name to the group (or corresponding acid) group (or acid) majority.

According to a particular and advantageous embodiment of the invention, the diester of formula (III) above preferably corresponds to the more specific formula (IV):

(IV) H ₃ C - (CH ₂ ) _n - CO - O - (CU ₂ ) _Z "- O - CO - (CH ₂ ) _n - CH ₃

in which :

- z "is an integer of 1 to 10, preferably 1 to 4; - n and n ', identical or different, are integers from 12 to 20, preferably from 14 to 20.

According to a preferred embodiment, the invention is implemented with a saturated fatty acid, especially a saturated C ₆ -C ₂₄ fatty acid. Examples of saturated fatty acids are those selected from the group consisting of caproic acid (C ₆ ), caprylic (C g), capric (C ₀ ), lauric (Ci ₂ ), myristic (Ci ₄ ) palmitic (Cj ₆ ), stearic (C ₈ ), isostearic (C ₈ ), behenic (C ₂₂ ), lignoceric (C ₂₄ ) and mixtures of these acids.

Particularly used are saturated fatty acids selected from the group consisting of myristic (Ci ₄ ), palmitic (Ci ₆ ), stearic (Ci ₈ ), isostearic (Ci ₈ ), behenic (C ₂₂ ) and mixtures of these acids . In a particularly preferred manner, the ester used is a diester of stearic acid and a diol, in particular an alkylene glycol such as ethylene glycol.

The use of ethylene glycol distearate has proved particularly interesting. By "EGDS-based compound" is meant in the present application a compound or a composition comprising at least 75% by weight of ethylene glycol distearate, and optionally other compounds, for example ethylene glycol monostearate (" EGMS "). Unless otherwise specified or more precise with respect to the presence of other compounds, the term ethylene glycol distearate or the acronym EGDS will refer herein to an EGDS-based compound.

Ethylene glycol distearate is a well known compound, commercially available, corresponding to the particular formula (V) below:

(V) H ₃ C - (CH ₂ ) I ₆ - CO - O - (CH ₂ ) ₂ - O - CO - (CH ₂ ) ₆ - CH ₃

It is especially known for its use in crystallized form as a beading and / or viscosizing agent in cosmetic formulations, or as a bulk additive in thermoplastics as a lubricant for accelerating molding rates. It has also been described as engine oil lubricant in US 2,039,111.

In the drawing process according to the invention, the level of solid ester particles in the aqueous dispersion is preferably between 0.05 and 6%, more preferably in a range from 0.2 to 3%, by example within a range of 0.5 to 1.5%. The starting aqueous dispersion, if it is available in a more concentrated form (typically greater than 6%), is advantageously diluted according to the preferential percentages indicated above.

The ester particles preferably have a particle size distribution with at least 90% by weight of the particles whose size is between 0.1 and 50 microns. The particle size distribution may for example be determined using a light scattering or laser diffraction granulometer (for example Horiba LA-910 laser type).

The particle size may especially be fine (average size by weight between 0.5 and 10 microns) or coarser (average size by weight between 10 and 50 microns). It is not excluded that the particle size distribution is bi-populated, with a fine population, and a coarser population. The particles may in particular have a particle size distribution: with more than 50% by weight of particles of size between 0.5 and 10 μm, or

with more than 50% by weight of particles of size between 10 and 30 μm, preferably between 10 and 20 μm.

A very coarse particle size may in particular be difficult to stabilize. A very fine grain size can be binding.

The present invention is also applicable to cases where the previously described solid fatty acid ester particles are used in combination with other particles, whether solid or non-solid, capable of completing the lubricating base. In such a case, these solid particles of fatty acid ester are preferably more than 50%, more preferably more than 75%, for example more than 90% of the solid particles of wax forming the lubricating base of the lubricating composition used. in the drawing process of the invention. It is preferred, however, that these solid fatty acid ester particles constitute all the solid particles of wax forming the lubricating base.

b) Amphiphilic compound

According to a preferred embodiment, is associated with the previously described fatty acid ester an amphiphilic compound such as a surfactant for improving the dispersion in water of solid ester particles. Such a compound can contribute to stabilize the solid particles (preventing eg decantation that would affect the efficiency or require additional agitation means and may interfere with the shaping process). It can also help optimize lubrication efficiency.

The amphiphilic compound is preferably water-soluble. By water-soluble compound is meant a compound soluble in aqueous medium at 23 ° C at a concentration of 1% by weight.

Preferably, the amphiphilic compound is a surfactant, chosen in particular from the group consisting of anionic, cationic, amphoteric, zwitterionic, nonionic surfactants and mixtures of such surfactants. But it is not excluded to use more complex compounds such as polymers with different blocks of alkylene oxide block copolymers (the latter are classically classified as surfactants) or comb copolymers. The surfactants are generally amphiphilic compounds of relatively low molecular weight (for example less than 1000 g / mol) and / or polyalkoxylates.

As examples of anionic surfactants, mention may be made, without intending to be limited thereto: o alkylsulfonic acids, arylsulfonic acids, optionally substituted with one or more hydrocarbon groups, and the acid function is partially or completely salified, such as alkylsulfonic acids Cs-C _5O, particularly Cs-C _30, preferably _O Ci -C _22, and benzenesulfonic acids, naphthalenesulfonic acids substituted by one to three alkyl groups, Ci-C _30, preferably C ₄ -Cl _6, and / or alkenyl C ₂ -C _30, preferably C ₄ -C ₁₆ ; the mono- or diesters of alkylsulfosuccinic acids, of which the linear or branched alkyl part, optionally substituted by one or more hydroxylated and / or alkoxylated, linear or branched C ₂ -C ₄ (preferably ethoxylated, propoxylated, ethopropoxylated) groups; ); the phosphate esters chosen more particularly from those comprising at least one saturated, unsaturated or aromatic hydrocarbon group, linear or branched, comprising 8 to 40, preferably 10 to 30 carbon atoms, optionally substituted with at least one alkoxylated group (for example ethoxylated, propoxylated, ethopropoxylated). In addition, they comprise at least one phosphate ester group, mono- or diesterified so that one or two free acid groups or partially or totally salified. The preferred phosphate esters are of the mono- and diester type of phosphoric acid and alkoxylated (ethoxylated and / or propoxylated) mono-, di- or tristyrylphenol, or alkoxylated mono-, di- or trialkylphenol.

(ethoxylated and / or propoxylated) optionally substituted with one to four alkyl groups; phosphoric acid and an alcohol C ₈ -C _3O, preferably C _O -C ₂₂ alkoxylated (ethoxylated or ethopropoxylated); phosphoric acid and an alcohol in Cs-C _22, preferably C _O -C ₂₂ non-alkoxylated; o sulfate esters obtained from saturated or aromatic alcohols, optionally substituted with one or more alkoxylated groups (ethoxylated, propoxylated, ethopropoxylated), and for which the sulphate functional groups are in the free acid form, or partially or completely neutralized . By way of example, mention may be made of sulfate esters obtained more particularly from saturated or unsaturated C ₈ -C ₂₀ alcohols, which may comprise 1 to 8 alkoxylated units (ethoxylated, propoxylated, ethopropoxylated); sulphate esters obtained from polyalkoxylated phenol, substituted with 1 to 3 saturated or unsaturated C ₂ -C ₃ hydroxycarbon groups, and in which the number of alkoxylated units is between 2 and 40; sulfate esters obtained from polyalkoxylated mono-, di- or tristyrylphenol in which the number of alkoxylated units ranges from 2 to 40.

The anionic surfactants can be in acid form (they are potentially anionic), or in partially or totally salified form, with a counterion. The counterion may be an alkali metal, such as sodium or potassium, an alkaline earth metal, such as calcium, or an ammonium ion of the formula N (R) ₄ ⁺ in which R, which are identical or different, represent a hydrogen atom or a C ₁ -C ₄ alkyl radical optionally substituted by an oxygen atom.

As examples of cationic surfactants, mention may be made of quaternary fatty amines, optionally polyalkoxylated.

As examples of zwitterionic or amphoteric surfactants, mention may be made of betaines (in particular alkyldimethylbetaines and alkylamidoalkylbetaines such as alkylamidopropyldimethylbetaines), amine oxides (in particular alkyldimethylamine oxides and alkylamidoalkylamine oxides such as alkylamidopropyldimethylamine oxides), sultaines, derivatives of imidazoline, amphopropionates.

As examples of nonionic surfactants, mention may be made of:

o polyalkoxylated (ethoxylated, propoxylated, ethopropoxylated) substituted with at least one C ₄ -C _2O alkyl, preferably C ₄ -C _2, or substituted by at least one alkylaryl radical whose alkyl moiety is -C C ₆ . More particularly, the total number of alkoxylated units is between 2 and 100. By way of example, mention may be made of polyalkoxylated mono-, di- or tri (phenylethyl) phenols, or polyalkoxylated nonylphenols. Among the ethoxylated and / or propoxylated di- or tristyrylphenols, mention may be made of ethoxylated di- (phenyl-1-ethyl) phenol, containing 10 oxyethylenated units, ethoxylated di- (1-phenylethyl) phenol, containing 7 oxyethylenated units, sulfated ethoxylated di- (phenyl-ethyl) phenol, containing 7 oxyethylene units, ethoxylated tri- (phenyl-1-ethyl) phenol, containing 8 oxyethylene units, ethoxylated tri- (phenyl-1-ethyl) phenol containing 16 units oxyethylenes, sulfated ethoxylated tri- (phenyl-ethyl) phenol containing 16 oxyethylene units, ethoxylated tri- (phenyl-ethyl) phenol containing 20 oxyethylene units, ethoxylated tri- (phenylethyl) phenol phosphated, containing 16 oxyethylenated units; o alcohols or fatty acids C ₆ -C ₂₂ , optionally polyalkoxylated (ethoxylated, propoxylated, ethopropoxylated). In the case where they are present, the number of alkoxylated units is between 1 and 60; polyalkoxylated triglycerides (ethoxylated, propoxylated, ethopropoxylated) of vegetable or animal origin. Thus triglycerides from lard, tallow, peanut oil, butter oil, cottonseed oil, linseed oil, olive oil, are suitable. palm oil, grape seed oil, fish oil, soybean oil, castor oil, rapeseed oil, coconut oil coconut oil, and comprising a total number of alkoxylated units of from 1 to 60; the term ethoxylated triglyceride is intended both for the products obtained by ethoxylation of a triglyceride with ethylene oxide and for those obtained by transesterification of a triglyceride with a polyethylene glycol; polyalkoxylated sorbitan esters (for example ethoxylated, propoxylated, ethopropoxylated); o block copolymers of ethylene oxide and C ₃ -C ₁₀ alkylene oxide; fatty amines, especially C ₆ -C ₂₂ , optionally polyalkoxylated (for example ethoxylated, propoxylated, ethopropoxylated); in the case where they are present, the number of alkoxylated units may be between 1 and 60.

In particular, the following may be included in the composition, alone or in mixtures or combinations: nonionic surfactants of the fatty acid or polyalkoxylated fatty acid type (for example ethoxylated, propoxylated or ethopropoxylated) (Rhodia Alkamuls® family, by way of examples) ethoxylated castor oils: Alkamuls® OR36, Alkamuls® RC, Alkamuls® R81, Alkamuls® 696); o nonionic surfactants of alcohol type ethoxylated or ethoxy propoxylated, polyalkylene glycol, such as Rhodia's Rhodasurf® family of products, for example Rhodasurf® LA / 30, Rhodasurf® ID5, Rhodasurf® 860P; o ethoxylated aromatic or ethoxylated propoxylated nonionic surfactants, for example the Rhodia Igepal® family of products; surfactants of the ethoxy or propoxylated ethoxy block copolymer type, for example the family of Rhodia Antarox® products, such as Antarox® B848, Antarox® PLG 254, Antarox® PL 122, Antarox® SC 138; anionic surfactants, such as sulphonates, aliphatic sulphonates, sulphonates bearing ester or amide groups such as isothionates (sulphoester), taurates (sulphoamides), sulphosuccinates, sulphosuccinamates, or else sulphonates bearing no amide or ester groups, such as that alkyldiphenyoxide disulfonates, alkyl naphthalene sulfonates, naphthalene / formaldehyde sulfonates with for example dodecyl benzene sulfonates (Rhodacal® family of Rhodia, such as Rhodacal® 60BE for example; phosphate esters, for example the family Rhodafac® Rhodia such as Rhodafac® PA 17, Rhodafac® MB, styrylphenol compounds such as distyrylphenols, tristyrylphenols, which may be ethoxylated or ethoxylated propoxylated, phosphated, sulphated, for example the Soprophor® family of Rhodia such as Soprophor® DSS7, Soprophor® BSU, Soprophor 3D33, Soprophor 4D384, Soprophor® 796 Surfactants derived from terpenes, for example the Rhodoclean® family of Rhodia; o ethoxylated fatty amines, for example the Rhodameen® family of Rhodia products. According to a preferred embodiment, a surfactant of the nonionic type or a mixture of such nonionic surfactants is used, in particular to minimize the possible interactions with the water of the dispersion and its possible parasitic ions.

More preferably, the nonionic surfactant is selected from the group consisting of polyalkoxylated phenols, optionally polyalkoxylated C ₆ -C ₂₂ alcohols or fatty acids, polyalkoxylated sorbitan esters, polyoxyalkylenated block polymers, and mixtures of such compounds. .

Advantageously, the surfactant is chosen from the group consisting of block copolymers of ethylene oxide and C ₃ -C ₁₀ alkylene oxide, ethoxylated and / or propoxylated di- or tristyrylphenols and optionally polyalkoxylated fatty amines. and mixtures of such compounds.

More particularly, the surfactant is a block copolymer of ethylene oxide and C ₃ -C ₁₀ alkylene oxide, in particular a polyoxyethylene and polyoxypropylene block copolymer.

Such a polyoxyethylene and polyoxypropylene block copolymer can in particular respond to the structure of the formula:

[OE] p- [OP] p .- [OE] _p .

in which :

- OE is an ethylene oxide group; p and p ', which are identical or different, are average numbers in a range from 2 to 1000, and

OP is an optional propylene oxide group; p "is an average number within a range of 2 to 1000.

The ratio by weight between the groups OE and OP may in particular be between 90/10 and 10/90, for example in a range from 70/30 to 40/60. The total number of units OE and OP can in particular be between 20 and 500, for example in a range from 50 to 200. By way of example, use may especially be made of the surfactant Antarox® SC 138 marketed by Rhodia.

According to a preferred embodiment, the mass ratio between the amphiphilic compound and the solid ester particles is between 1/100 and 10/100, preferably in a range of 2.5 / 97.5 to 7.5 / 92.5. Thus, typically the aqueous dispersion may comprise between 0.01% and 0.6%, more preferably from 0.02 to 0.3%, especially from 0.05% to 0.25% of amphiphilic compound (% by weight) .

c) Extreme pressure additive

According to a preferred embodiment, the aqueous dispersion comprises an additive type "extreme pressure", usually intended to further improve lubrication under the most severe temperature conditions and preserve a lubricant film between the wire and the die.

The extreme pressure additive is preferably water-soluble. By water-soluble compound is meant a compound soluble in aqueous medium at 23 ° C at a concentration of 1% by weight.

The latter may optionally be of an amphiphilic nature, in this case used for example in replacement or in addition to the amphiphilic compound or surfactant described in paragraph b) above.

Although an extreme-pressure additive has been unexpectedly found to be non-essential in the aqueous dispersion used in accordance with the invention, it is believed that such an additive, particularly a phosphate ester, may, however, be favorable, at least in in some cases, to the dispersion of the particles and therefore to the lubrication, without acting in accordance with a conventional extreme-pressure lubrication mechanism.

Preferably, the extreme-pressure additive is an extreme-pressure additive based on sulfur and / or phosphorus. For example, the aqueous dispersion may comprise a combination of an amphiphilic compound such as a surfactant, non-phosphorus and / or non-sulfur, with a phosphorus or sulfur-containing amphiphilic extreme-pressure additive.

The extreme-pressure additive is especially chosen from the group consisting of phosphate esters, optionally polyalkoxylated, phosphonates, sulphates, sulphides, polysulphides and mixtures of these compounds.

More preferably, the extreme pressure additive is a phosphate ester. The phosphate ester can in particular be a compound of formula:

(R ¹ O) _x -P (^ O) (OH) _x ..,

in which the group R 'represents an optionally polyalkoxylated hydrocarbon group, x ¹ and x "being equal to 1 or 2, with the proviso that the sum of x' and x" is equal to 3. The group

R 'can in particular be an alkyl, alkylaryl, polyalkylaryl, (polyarylalkyl) aryl group (the alkyl groups which may be linear or branched, saturated or unsaturated), C 1 -C ₃₅ , preferably C ₅ -C ₃₀ (not counting the number of carbon atoms of the possible polyalkoxylates); the polyalkoxylated compounds may be polyethoxylated compounds; the degree of alkoxylation may especially be in a range from 1 to 80, preferably from 1 to 15.

Preferably, the phosphate ester corresponds to the following formula:

[R "- (OA") y - O] _{x -} PC = O) (OH) _x .

formula in which the R "groups, which may be identical or different, represent a hydrocarbon radical comprising 1 to 30 carbon atoms; the" A "groups, which may be identical or different, represent a linear or branched alkylene having 2 to 4 carbon atoms; y 'which is a mean value is within a range of 0 to 100; x 'and x "are equal to 1 or 2, provided that x' + x 'is equal to 2.

More particularly, R 'and R "represent a hydrocarbon radical containing 1 to 30 carbon atoms, aliphatic, cycloaliphatic, saturated or unsaturated, or aromatic, preferably the radicals R' and R", which are identical or different, are alkyl radicals. or alkenyls bearing one or more linear or branched ethylenic unsaturations containing 8 to 26 carbon atoms. By way of examples of such radicals, mention may be made especially of stearyl, oleyl, linoleyl and linolenyl radicals. In addition, the radicals R and R ", which may be identical or different, may be aromatic radicals bearing alkyl, arylalkyl or alkylaryl substituents, these radicals comprising 6 to 30 carbon atoms. include, inter alia, nonylphenyl, mono-, di- and tri-styrylphenyl radicals.

More particularly, the groups OA ", which may be identical or different, correspond to an oxyethylenated, oxypropylenated, oxybutylenated radical, or mixtures thereof, Preferably said group corresponds to an oxyethylenated and / or oxypropylenated radical, whereas the value of y, average, it is preferably in a range from 0 to 80.

Useful extreme-pressure additives are marketed by Rhodia under the names Lubrhophos® and Rhodafac®.

It is mentioned that the extreme pressure additives are preferably present in the formulation in salt form, neutralized. The neutralization can be obtained using any organic or mineral base. It is possible in particular to use organic amines, for example optionally polyalkoxylated fatty amines. More details are given below. The level of extreme pressure additive in the aqueous dispersion is preferably between 0.01% and 5%, more preferably in a range of 0.1 to 2% (% by weight).

d) Other additives

As mentioned above, the aqueous dispersion may comprise at least one base. The base is preferably water soluble. By water-soluble is meant soluble compounds in aqueous medium, at 23 ° C, at a concentration of 1% by weight. By way of nonlimiting examples, mention may be made of hydroxides, hydroxycarbonates, carbonates, bicarbonates, alkali metal, ammonia.

Preferably, the bases employed are organic bases which are more particularly chosen from primary, secondary or tertiary amines or polyamines, comprising at least one hydrocarbon radical having 1 to 40 carbon atoms, linear, branched or cyclic, optionally substituted by a or more hydroxyl radicals, and / or one or more alkoxylated groups. Said alkoxylated groups are preferably ethoxylated units. In addition, the number of alkoxylated units, if present, is less than or equal to 100.

According to a preferred embodiment of the invention, when the amines have at least two amino functions, said functions are separated two by two by a number of carbon atoms from 2 to 5. As suitable amines, it is possible to mention monoethanolamine, diethanolamine, ethylenediamine, aminoethylethanolamine, aminomethylpropanolamine. The polyalkoxylated fatty amines can also be used as organic base, such as those marketed by Rhodia under the name Rhodameen ^® CS20.

The aqueous dispersion used according to the invention may comprise other compounds often commonly present in aqueous lubricating compositions. These may be, for example, anti-foam additives, anti-corrosion additives, anti-tartar additives, preservatives, pH modifiers, buffers, and the like.

1-2. Preparation of the aqueous dispersion

The aqueous dispersion can be prepared by any method known to those skilled in the art, for example by simple mixing of its various constituents.

The aqueous dispersion can also be obtained by diluting a concentrated formulation in water. The dilution may for example be from 0.5 to 18 parts, preferably from 1 to 6 or 10 parts of concentrated formulation per 100 parts of water. The proportion by weight of Solid particles in the concentrated formulation may be greater than 6%, preferably greater than 10%, for example 20 to 35%.

If an extreme pressure additive is present, the concentrated formulation may comprise between 0.1% and 50% by weight of extreme pressure additive, preferably from 1% to 20%. Typically, the concentrated formulation may comprise from 0.1% to 6%, preferably from 0.2% to 3%, for example from 0.5% to 2.5% of the amphiphilic compound.

Some of the constituents or other additives may be optionally added after dilution or on dilution.

The concentrated formulation may be prepared for example from the fatty acid ester in solid form, in the form of flakes, coarse powder, granules, or flakes, commonly available commercially.

In order to obtain the dispersion of the particles, it is possible in particular to proceed either by grinding followed by dispersion in water, or by hot emulsification in water and then cooling.

The process for preparing the concentrated formulation may comprise in particular a step in which at least a portion of the amphiphilic compound is mixed with solid or liquid particles of the fatty acid ester, the particles and / or the amphiphilic compound being the case previously diluted in water.

The grinding can be carried out by any known technique. Cold grinding is preferred, in particular for limiting the heating and melting of the fatty acid ester. Chilling by cooled air jet makes it possible to obtain powders, for example with a particle size distribution centered on 15 to

20 μm. In particular grinding can be carried out using grinders available from Micro-Macinazione. The powder obtained can then be slowly incorporated with stirring (for example pale inclined faces, 200-400 rev / min) in an aqueous solution of the amphiphilic compound.

Hot emulsification is particularly suitable for obtaining a fine particle size. It is thus possible to mix water (for example about 70%) and the fatty acid ester in solid form (for example about 30%) and to bring the mixture beyond the melting point of the ester. This can for example be carried out in an emulsification tool having a rotor / stator type mixing system, for example the tool "Koruma Disho 100/45". The speed of the rotor makes it possible to control the energy engaged in the system, and to control the size of the formed ester droplets. Once the emulsion is obtained, it is diluted in cold water until the desired ester concentration is reached. The solidification of the droplets then occurs, and the dispersion of solid particles is obtained. Preferably, the cooling is brutal, uncontrolled, without a crystallization ramp. By this method, for example, it is possible to obtain particles having a size of approximately 0.3 μm, 1 μm or even 10 μm. The addition of the amphiphilic compound, if any, may be useful to ensure the stability of the dispersion once cooled; it can be added during the emulsification step, or after.

It should be noted that a hot emulsification process is not suitable for the preparation of formulations based on a wax having a melting point which is too high, much higher than the boiling point of water, atmospheric pressure. This is the case, for example, aqueous dispersions based on EBS (used according to the prior art).

According to particular embodiments, the dispersion and / or the concentrated formulation is substantially free of paraffin particles having a straight chain, preferably paraffins in general, with a melting point of greater than or equal to 71 ° C. or of their halogenated derivatives, associated with sulfonated castor oil and / or a mixture of C ₄ -C ₈ alkenyl succinic acid. According to more particular embodiments, the dispersion and / or the concentrated formulation is substantially free of paraffin particles having a straight chain, with a melting point greater than or equal to 71 ° C. or of their halogenated derivatives, associated with an anionic surfactant. By "substantially free" is meant less than 3%, preferably less than 1%, preferably less than 0.1%, preferably less than 0.01%, by weight of paraffin, preferably not at all.

1-3. Use of lubricating compositions in a wet drawing process

As already indicated, the invention also relates to a wet drawing method for obtaining a steel wire intended to reinforce a tire, said method comprising the following steps:

from a steel wire having a diameter greater than 0.6 mm; stretching said wire through a series of dies of decreasing diameter, in the presence of a lubricating composition in the form of an aqueous dispersion, to a predetermined final diameter of less than 0.5 mm,

and being characterized in that said aqueous dispersion meets the main definition as well as the preferred characteristics stated above.

Preferably, the starting steel wire has a diameter greater than 0.8 mm, for example between 0.8 and 2.0 mm. The predetermined final diameter is preferably less than 0.45 mm, for example in a range of 0.1 to 0.4 mm. The number of dies is preferably between 10 and 40, for example in a range from 15 to 30. The section reduction ratio per die is typically between 3% and 25%.

In a known manner, all the dies and therefore the wire itself being drawn are immersed in a so-called drawing bath, with the exception of the last die which may be immersed or in the open air, depending on the case. The wire is lubricated and cooled by the drawing bath, itself cooled by a circulation of water coupled to a heat exchanger. The operating temperature of the bath is preferably less than 40 ^° C.

The drawing speed, that is to say the output speed of the last die (equal to the winding speed of the drawn wire), is preferably between 5 and 25 m / s (meters per second), example in a range of 10 to 20 m / s.

The invention is implemented on steel wires, more preferably in pearlitic (or ferrito-pearlitic) carbon steel hereinafter referred to as "carbon steel", or else in stainless steel (by definition, steel comprising at least 11% chromium and at least 50% iron). But it is of course possible to use other steels.

When carbon steel is used, its carbon content is preferably between 0.4% and 1.2%, especially between 0.5% and 1.1%. It is more preferably between 0.6% and 1.0% (% by weight of steel), in particular between 0.68% and 0.95%; such a content representing a good compromise between the mechanical properties required and the feasibility of the son.

It should be noted that in applications where the highest mechanical strengths are not necessary, it is advantageous to use carbon steels whose carbon content is between 0.50% and 0.68%, especially 0, 55% to 0.60%, such steels being ultimately less expensive because easier to draw. Another embodiment of the invention may also consist, depending on the end applications concerned, of using steels with a low carbon content, for example between 0.2% and 0.4%, especially because of a cost lower and easier to draw.

The invention applies to a wet drawing process for obtaining any type of steelcord thin wire, whether it is of standard resistance (called NT for "Normal Tensile"), high resistance (called HT for "High Tensile"), very high resistance (called SHT for "Super High Tensile") as ultra-high resistance (UHT for "Ultra High Tensile").

The fine yarns obtained by the drawing process of the invention have a tensile strength (denoted Rm) which is preferably greater than 2000 MPa, for example between 2000 and 4000 MPa, more preferably greater than 2800 MPa, for example between 2800 MPa and 4500 MPa. Those skilled in the art know how to manufacture steel son having such resistance, in particular by adjusting the carbon content of the steel and / or the work hardening rates of these son.

The steel used, whether it is for example a carbon steel or a stainless steel, can be a so-called "clear" steel (that is to say uncoated) or be coated with a metal layer improving, for example, the properties of implementation of the steel wire, its properties of use or even those of any cable or tire for which it is intended, such as, for example, the adhesion properties, corrosion resistance properties; or resistance to aging.

According to a preferred embodiment, the steel used is covered with zinc or with a zinc alloy, in particular brass (Zn-Cu alloy); it is recalled that during the wire drawing process, the brass or zinc coating is well known to facilitate the drawing of the wire, as well as the bonding of the wire with the rubber. But the son could be covered with a thin metal layer other than a layer of brass or zinc, or a second layer used in addition to the first, having for example the function of improving the corrosion resistance of these yarns and / or their adhesion to the rubber, for example a thin layer of Co, Ni, Al, an alloy of two or more compounds Cu, Zn, Al, Ni, Co, Sn.

1-4. Use of drawn wire for the manufacture of a pneumatic tire

Steelcord steel wires obtained by the drawing process of the invention can then be assembled, for example cabled or twisted together, or even used as such to form reinforcing elements (or "reinforcements") of metal which are intended for the manufacture and reinforcement of pneumatic tires for motor vehicles.

Thus, the present invention also relates to a tire manufacturing method comprising rubber and at least one steel reinforcing element, said method comprising the following steps:

- from a steel wire having a diameter greater than 0.6 mm;

stretching said steel wire through a series of dies of decreasing diameter, in the presence of a lubricating composition in the form of an aqueous dispersion as defined above, until a fine wire is obtained of diameter less than 0.5 mm;

optionally assembling a plurality of fine wires thus obtained to obtain an assembly of fine wires; incorporating said fine wire and / or said assembly as a metal reinforcing element, as it is or previously incorporated in rubber in the green state, into the structure of a tire being manufactured;

- Perform the cooking of the tire once its structure is complete.

Preferably, a carbon steel is used, its carbon content preferably being between 0.4% and 1.2%, especially between 0.5% and 1.1%. Preferably, the starting steel wire has a diameter greater than 0.8 mm, for example in a range of 0.8 to 2.0 mm. The predetermined final diameter is preferably less than 0.45 mm, for example in a range of 0.1 to 0.4 mm. The number of dies is preferably between 10 and 40, for example in a range from 15 to 30. The section reduction ratio per die is typically between 3% and 25%. The drawing speed is preferably between 5 and 25 m / s, for example in a range of 10 to 20 m / s. The fine wires obtained by drawing, before assembly, have a tensile strength Rm which is preferably greater than 2000 MPa, for example between 2000 and 4000 MPa, more preferably greater than 2800 MPa, for example between 2800 MPa and 4500 MPa.

The optional step of assembling the unitary fine wires leaving the drawing operation, in line or not with the latter, is typically a wiring operation (that is to say without significant torsion of the unitary wires) or of twisting (that is to say with torsion on the unit son) to obtain what is known to call a steel cord (or "steel cord").

During the assembly operation, the gum (rubber composition) in the green state may optionally be incorporated into the internal structure of the fine wire assembly, during the very operation of assembling the wires ( by the so-called "in situ scrubbing" technique) or just after said operation.

Fine drawn wires or cables (eg layered or stranded cables) can be individually "gummed" (ie, sheathed with a rubber composition) or "calendered", that is, ie pressed between two cylinders between two thin sheets of rubber composition; the cables then become calendered sheets. These gummed yarns or calendered plies (for the latter, generally cut into strips of suitable dimensions) are intended for all or part of the tire, for example at its top (in particular its belt) and / or its carcass reinforcement and / or its area beads.

The rubber used is preferably a diene elastomer chosen more preferably from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), different copolymers of butadiene, different copolymers of isoprene , and mixtures of these elastomers. A more preferred embodiment is to use an "isoprene" elastomer, i.e. a homopolymer or an isoprene copolymer, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), the various isoprene copolymers and mixtures of these elastomers.

The rubber composition is preferably of the vulcanizable type, that is to say that it comprises a so-called vulcanization system, that is to say based on sulfur (or a sulfur-donor agent) and various accelerators or vulcanization activators. It may also comprise all or part of the additives normally used in rubber matrices intended for the manufacture of tires, such as, for example, reinforcing fillers, anti-aging agents, antioxidants, plasticizing agents or extension oils. processing agents, anti-eversion agents, reinforcing resins, known adhesion promoter systems such as metal salts, for example, in particular cobalt or nickel salts.

Once the structure (or construction) of the tire is completed, the latter in the green state (that is to say still comprising the rubber in the green state), is subjected in known manner to a final cooking operation ( cross-linking or vulcanization), generally in a mold under high pressure and at high temperature (for example at 150 ° C. for about ten minutes).

II. EXAMPLES OF CARRYING OUT THE INVENTION

II- 1. Preparation of aqueous dispersions (concentrated formulations)

a) Raw materials used:

- EGDS: Rhodia Alkamuls® EGDS; scales of EGDS greater than 98% by weight;

EBS: grade WAXSO MK, micronized with a median diameter of 15 μm from SOGIS Industria Chimica Spa;

Paraffin: Sigma Aldrich product under No. 327204; linear saturated hydrocarbons, with a melting point of approximately 55 ^° C.

- SC138: Antarox® SC138 from Rhodia; polyoxyethylene and polyoxypropylene block copolymer (solid); - S40: Soprophor® S40 from Rhodia; ethoxylated tristyrylphenol (solid);

- DSS7: Soprophor® DSS7 Rhodia; sulphated ethoxylated distyrylphenol (viscous paste);

- CS20: Rhodameen® CS20 from Rhodia; ethoxylated fatty amine (liquid);

- EP: ethoxylated C ₁₂ -C ₁₈ phosphate ester of the Rhodafac® Rhodia product range. The experimental concentrated formulations, corresponding to the aqueous dispersions in diluted form C-2 to C-13 used in the following drawing tests, are given in Table 1 below (concentrations in% by weight of dry matter):

b) Preparation procedures:

All formulations are at pH 8-9. At the end of the procedure, the pH is adjusted if necessary using diethanolamine or phosphoric acid.

The indicated particle sizes are measured on a Horiba LA-910 (light scattering) apparatus, with a relative optical index of dispersed particles: 1.07-0.0Oi. The measurement is a volume average (that is, by weight) on the particle size distribution.

The concentrated formulations prepared are 60 kg (total weight) of which:

10% by weight of dispersed solid particles;

5% by weight of surfactant relative to the solid particles, ie 0.5% of surfactant relative to the total concentrated formulation; when a phosphate ester is added (C-5, C-6 and C-7): 5% by weight of EP relative to the dispersed particles, ie 0.5% of EP relative to the total concentrated formulation.

Procedure 1 An aqueous solution of the surfactant is prepared, and then the EBS is introduced into the aqueous solution, with moderate stirring (Rayneri type stirring motor, 200 rpm). If an extreme-pressure additive is used, it is added last in the form of a concentrated aqueous solution, whose pH is adjusted between 8 and 9 by adding diethanolamine, with moderate stirring (Rayneri engine, 200 turns / min). All operations are performed at room temperature (23 ° C).

Procedure 2

An aqueous solution of the surfactant is prepared which is heated to a temperature of 10 ° C. higher than the melting temperature of the wax used. The melted wax (at a temperature of 10 ° C. higher than the melting temperature of the wax used) is then introduced with stirring / grinding into the surfactant solution. This operation is conducted in a Koruma Disho 100/45 type apparatus. The size of the emulsion formed depends on the surfactant concentration, the speed (1000 to 3000 rpm) and the milling time. The wax composition of this emulsion is 30%. The size of the melted wax droplets can be adjusted between approximately 0.2 μm and 10 μm.

The emulsion is then diluted by a factor of three in cold water (5 ° C), simultaneously ensuring the quenching of the emulsion (and the solidification of the wax droplets) and the dilution at a concentration of 10%. wax. Depending on the amount of surfactant used to make the emulsion, surfactant is added to the dilution water to have a proper total surfactant composition. This operation is carried out in a tank cooled by water, with moderate agitation (Rayneri engine, 200 revolutions / min).

If an extreme pressure additive is used, it is added last in the form of a concentrated aqueous solution, the pH of which is adjusted between 8 and 9 by addition of diethanolamine, with moderate stirring (Rayneri engine, 200 rpm). min).

Procedure 3

The scales of EGDS are crushed using an air jet mill at 0 ° C. from Micro-Macinazione. The grinding energy (pressure and air flow) and the flow of EGDS are adjusted to obtain the indicated grain size. EGDS particles having a size of between 10 and 15 μm are obtained.

An aqueous solution of the surfactant is prepared, and then the EGDS particles are introduced into the aqueous solution, with moderate stirring (Rayneri engine, 200 rpm). If an extreme-pressure additive is used, it is added last as a solution concentrated aqueous, whose pH is adjusted between 8 and 9 by adding diethanolamine, with moderate stirring (Rayneri engine, 200 rev / min). The mixing operations are carried out at ambient temperature (23 ° C.).

H-2. Drawing tests

The following exemplary embodiments demonstrate that, in comparison with known solutions also using aqueous dispersions as a lubricating composition, the use in accordance with the invention unexpectedly leads to a compromise of superior properties, this even in the presence of a lubricating composition of particularly simple formulation.

In these examples, Steelcord thin carbon steel (NT type) fine wires coated with brass are made by wet drawing.

Apart from the formulation of the drawing lubricant, these yarns are prepared in a known manner, for example starting from machine wires (diameter 5 to 6 mm) of carbon steel (carbon content of about 0.7%), which the it is first drawn by drawing (dry) to an intermediate diameter of about 1.5 mm and a resistance of about 1100 MPa.

After heat treatment and then deposition of a coating of brass (for example 64% copper) on these intermediate son, is carried out on each wire a so-called "final" work hardening by cold drawing in a humid medium, through a series of dies (about twenty in total) whose diameter decreases gradually (section reduction ratio by die between 3% and 25%), to obtain a final diameter of 0.28 mm.

The lubricating wire drawing composition, in which the dies and the wire in formation are in a known manner immersed, is in all the examples in the form of an aqueous dispersion, one of them called "commercial" and several other experimental , the latter being in conformity or not with the invention.

The so-called commercial lubricant composition is made from a concentrated aqueous formulation "Supersol® 4419T" available from Rhodia, comprising particles based on EBS. It is used as a witness. For the sake of simplicity it is called "commercial formulation" or "commercial lubricant". In addition to the EBS particles, this concentrated commercial formulation includes various customary additives, including a surfactant and an ester-phosphate extreme pressure additive.

The other experimental dispersions tested comprise, at a concentration of 1% by weight, solid particles of the compounds (waxes) which follow: EGDS (ethylene glycol distearate);

- EBS (ethylene bis-stearamide); paraffin.

As explained in detail below, these aqueous dispersions are stabilized by various known commercial surfactants, they may contain in some cases an extreme pressure additive of the ester-phosphate type.

Experimental dispersions are prepared by dilution (up to a concentration of solid particles by weight of 1%) in water of experimental concentrated formulations, details of compositions and preparation of which have been given in the preceding paragraph.

For comparison, the formulas of EGDS and EBS are summarized below:

(EGDS) H ₃ C - (CH _{2) I6} - CO - O - CH ₂ - CH ₂ - O - CO - (CH ₂₎ i6 - CH ₃

(EBS) H ₃ C - (CH _{2) I6} - CO - HN - CH ₂ - CH ₂ - NH - CO - (CH _{2) 16} - CH ₃

The lubrication performance in the wet wire drawing machine is characterized by two parameters:

the loss of brass (expressed as a percentage of the initially deposited mass of brass) is measured by the difference between the mass deposited on the wire of intermediate diameter and the mass measured on the final fine wire (at the output of the last die); it is estimated that a brass loss of less than 10% is indicative of a good quality of lubrication; the die wear is characterized indirectly by measuring the increase in the diameter of the wire after 30 kg of drawn wire to the theoretical diameter initially targeted.

Effective lubrication can also be characterized by a low coefficient of friction, for example by a low coefficient of friction determined by tribology techniques, especially in a type of contact EHD ("Dynamic Elasto Hydro"). Effective lubrication can also be characterized by low wear, for example determined by material balances carried out in tribology studies, especially in a contact type EHD, or Falex type. The fine yarn obtained is also characterized in tension in order to measure its maximum mechanical strength, denoted Rm (measured according to the ISO 6892 standard of 1984, from the Force-Elongation curve of the yarn tested).

a) Trial 1

In this first test, the commercial lubricant "Supersol® 4419T" referred to above based on EBS (composition noted as CI) is compared with three experimental waxes (EBS, paraffin and EGDS), all three stabilized with the same known surfactant ( "Antarox® SC 138" marketed by Rhodia) (compositions respectively denoted C-2 to C-4).

Only the use of the composition C-4 is therefore in accordance with the invention.

Table 2 below summarizes the drawing results obtained with these four lubricating compositions.

Table 2

Firstly, a comparison of the experimental compositions C-2, C-3 and C-4 clearly demonstrates the superiority of the EGDS wax compared to the two other waxes, since in these highly simplified formulations, only the C-4 composition is reveals capable of drawing a significant length of steel wire; with the other two compositions C-2 and C-3, it is simply impossible to draw (breakage of the wire even before reaching the nominal speed of wire drawing).

Unexpectedly, the composition C-4 reveals an excellent lubricating power since, despite a formulation that could not be simpler (combination of a wax and a surfactant), results equivalent in terms of wear to those of commercial lubricant (CI control) which is itself fully formulated, and even improved with regard to the loss of brass.

In particular, it can be deduced that, contrary to what was commonly accepted by those skilled in the art so far, the use of an extreme pressure type additive is not necessarily essential for the drawing of Steelcord steel wire; this is the case for the aqueous dispersion used according to the invention.

b) Test 2 In this assay is reproduced Test 1 above by adding this time, in addition to the surfactant (Antarox® SC138), an extreme pressure _I2 C in phosphate ester-additive _I -C ₈ ethoxylated range of products Rhodafac® marketed by Rhodia. Since the commercial lubricant (Composition CI) is already formulated with an ester-phosphate additive, no other additive is added thereto.

Only the use of the composition C-7 is in accordance with the invention.

Table 3 below summarizes the drawing results obtained with these four lubricating compositions.

Compared to Table 2 above, Table 3 demonstrates that while the extreme pressure additive certainly makes the experimental formulations (C-5 and C-6) based on paraffin and especially EBS able to draw, this additive does not against no visible improvement in the composition used according to the invention (compare composition C-7 composition C-4 of the previous test 1).

In other words, the composition C-7 according to the invention, based on EGDS, is insensitive to the presence or absence of the extreme-pressure additive for good lubrication of the die. This is another remarkable and unexpected result for the skilled person.

c) Trial 3

In this test, the former EGDS and EBS waxes are compared again, this time in the presence of four different surfactants (all sold by Rhodia), all of them comprising at least one polyoxyethylene block as a hydrophilic unit and various hydrophobic units:

a surfactant ("Antarox® SC 138", solid), nonionic, of the polyoxyethylene and polyoxypropylene block copolymer type;

a surfactant ("Soprophor® S40", solid), nonionic, of the ethoxylated tristyrylphenol type, comprising tristyrylphenol as a hydrophobic unit; an anionic surfactant ("Soprophor® DSS7", viscous paste), of the sulphated ethoxylated distyrylphenol type having distyrylphenol as a hydrophobic unit;

a surfactant ("Rhodameen® CS20", liquid) of the fatty amine ethoxylated type comprising an aliphatic chain as a hydrophobic unit.

No other additive, in particular extreme pressure additive, is used in the experimental compositions tested. Only compositions C-4 and C-8 to C-10 are in accordance with the invention. The compositions C-2 and C-4 have already been tested in the preceding test 1.

Table 4 below summarizes the wire drawing results obtained with these eight lubricating compositions.

Table 4

* not measured (wire obtained outside tolerances)

The results in Table 4 clearly confirm the best performance of EGDS wax compared to EBS wax, regardless of the surfactant associated with it.

It is furthermore noted that the compositions C-4, C-9 and C-10 (in accordance with the invention) give an excellent performance from the industrial point of view, with a die wear rate of less than 2 μm combined with a loss of brass less than 10%. The best lubricant composition (C-4) is that based on EGDS and polyoxyethylene and polyoxypropylene block copolymer.

For EBS, regardless of the surfactant used, the performance is either unacceptable or poor (composition C-13).

Other wire drawing tests, which comply with and are not in accordance with the invention, were carried out starting from an intermediate wire made of steel with a higher carbon content (0.9%), with a diameter of around 1.3 mm. (Resistance Rm equal to about 1200 MPa), for obtaining son type SHT of final diameter 0.23 mm. The results obtained fully confirmed the results of tests 1 to 3 described above.

Claims

1. Use as a lubricant composition in a wet drawing process, for obtaining a steel wire for reinforcement of a tire, an aqueous dispersion comprising solid particles of an ester of fatty acid having 5 to 40 carbon atoms.

2. Use according to claim 1, wherein the fatty acid has from 6 to 24 carbon atoms.

3. Use according to claim 2, wherein the fatty acid comprises from 14 to 22, preferably from 16 to 22 carbon atoms.

4. Use according to any one of claims 1 to 3, wherein the fatty acid ester is derived from a diol or polyol.

The use according to any one of claims 1 to 4, wherein the fatty acid ester has the formula:

(I)

[R-COO-] _x -A - [- OH] _y in which:

R is a hydrocarbon group, saturated or unsaturated, linear or branched; A is a hydrocarbon group, optionally interrupted by one or more heteroatoms, of valence x + y; x is an average number of 1 to 5; y is an average number of 0 to 5;

- x + y ranging from 1 to 10, preferably from 2 to 5.

Use according to claim 5, wherein the ester is a diester having the formula:

(H) R ¹ - CO - O - A - O - CO - R ² in which R ¹ and R, which are identical or different, are linear or branched, saturated or unsaturated hydrocarbon groups containing from 4 to 39, preferably from 5 to 23, carbon atoms.

7. Use according to claim 5 or 6, wherein R, or R ¹ and R ² respectively, comprise from 13 to 21, preferably from 15 to 21 carbon atoms.

Use according to any of claims 5 to 7, wherein the divalent group A has the formula:

- (CH ₂ ) _z - [OE] _m - [OP] _m .- (CH ₂ ) _z -

in which :

z and z ', which may be identical or different, are integers from 1 to 10;

OE is an optional ethylene oxide group;

OP is an optional propylene oxide group; m and m ¹ , identical or different, are average numbers in a range from 0 to 100, preferably from 0 to 10.

Use according to claim 6, wherein the diester has the formula:

(III)

R ¹ - CO - O - (CH ₂ ) _Z - - O - CO - R ²

wherein z "is an integer of 1 to 15, preferably 1 to 10.

The use according to claim 9, wherein the diester has the formula:

(IV)

H ₃ C - (CH ₂ ) _n - CO - O - (CH ₂ ) _Z - - O - CO - (CH ₂ ) _n - - CH ₃

in which :

z "is an integer of 1 to 10, preferably 1 to 4;

n and n ', identical or different, are integers from 12 to 20, preferably from 14 to 20.

Use according to any one of claims 5 to 10, wherein A is an alkylene selected from the group consisting of methylene, ethylene, propylene, butylene and mixtures thereof.

12. Use according to claim 10, wherein the diester is ethylene glycol distearate of formula:

(V)

H ₃ C - (CH ₂ ) I ₆ - CO - O - (CH ₂ ) ₂ - O - CO - (CH ₂ ) i ₆ - CH ₃

13. Use according to any one of claims 1 to 12, wherein the aqueous dispersion comprises between 0.05 and 6%, preferably from 0.2 to 3% of ester particles (% by weight).

14. Use according to any one of claims 1 to 13, wherein the ester particles have a particle size distribution with at least 90% by weight of the particles whose size is between 0.1 and 50 microns.

15. Use according to any one of claims 1 to 14, wherein the aqueous dispersion further comprises at least one amphiphilic compound.

The use of claim 15, wherein the amphiphilic compound is a surfactant.

The use of claim 16, wherein the surfactant is selected from the group consisting of anionic, cationic, amphoteric, zwitterionic, nonionic surfactants and mixtures of such surfactants.

The use of claim 17, wherein the surfactant is a nonionic surfactant.

Use according to claim 18, wherein the nonionic surfactant is selected from the group consisting of polyalkoxylated phenols, optionally polyalkoxylated C ₆ -C ₂₂ alcohols or fatty acids, polyalkoxylated sorbitan esters, polyoxyalkylenated block polymers and mixtures of such compounds.

The use according to claim 19, wherein the surfactant is selected from the group consisting of C ₃ -C ₁₀ alkylene oxide and alkylene oxide block copolymers, ethoxylated di- or tristyrylphenols, and or propoxylated, optionally polyalkoxylated fatty amines and mixtures of such compounds.

21. Use according to claim 20, wherein the surfactant is a block copolymer of ethylene oxide and C ₃ -C ₁₀ alkylene oxide, preferably a polyoxyethylene and polyoxypropylene block copolymer.

22. Use according to claim 21, wherein the block copolymer is a copolymer of structure [OE] _p - [OP] _{P "} - [OE] _{p '} , where:

EO is an ethylene oxide group; p and p ', which are identical or different, are average numbers in a range from 2 to 1000, and

OP is an optional propylene oxide group; p "is an average number within a range of 2 to 1000.

23. Use according to any one of claims 15 to 22, wherein the mass ratio between the amphiphilic compound and the ester particles is between 1/100 and

10/100, preferably in a range of 2.5 / 97.5 to 7.5 / 92.5.

24. Use according to any one of claims 1 to 23, wherein the aqueous dispersion comprises an extreme pressure additive.

25. Use according to claim 24, wherein the extreme-pressure additive is selected from sulfur-based and / or phosphorus-based extreme pressure additives.

26. Use according to claim 25, wherein the extreme pressure additive is selected from the group consisting of phosphate esters, phosphonates, sulfates, (poly) sulfides and mixtures thereof.

27. Use according to claim 26, wherein the extreme pressure additive is a phosphate ester.

28. Use according to any one of claims 24 to 27, wherein the aqueous dispersion comprises between 0.01% and 5%, preferably from 0.1 to 2% of extreme pressure additive (% by weight).

29. A method for wet drawing a steel wire for reinforcing a tire, comprising the steps of:

- from a steel wire having a diameter greater than 0.6 mm; stretching said wire through a series of dies of decreasing diameter, in the presence of a lubricating composition in the form of an aqueous dispersion, to a predetermined final diameter of less than 0.5 mm,

said method being characterized in that said aqueous dispersion meets the definition given in any one of the preceding claims 1 to 28.

The wire drawing method of claim 29, wherein the starting steel wire has a diameter greater than 0.8 mm.

The method of claims 29 or 30, wherein the predetermined final diameter is less than 0.45 mm.

32. The method according to any one of claims 29 to 31, wherein the number of dies is between 10 and 40.

33. A method according to any one of claims 29 to 32, wherein the section reduction ratio per die is between 3% and 25%.

34. The method of any one of claims 29 to 33, wherein the drawing speed is between 5 and 25 meters per second.

35. A method of manufacturing a tire comprising rubber and at least one reinforcing element made of steel, said method comprising the following steps:

- from a steel wire having a diameter greater than 0.6 mm;

stretching said steel wire through a series of dies of decreasing diameter, in the presence of a lubricating composition in the form of an aqueous dispersion as defined in any one of the preceding claims 1 to 28; , until a fine wire of diameter less than 0.5 mm is obtained;

optionally assembling a plurality of fine wires thus obtained to obtain an assembly of fine wires; incorporating said fine wire and / or said assembly as a metal reinforcing element, as it is or previously incorporated in rubber in the green state, into the structure of a tire being manufactured;

- Perform the cooking of the tire once its structure is complete.