PROCESS FOR MANUFACTURING AN ELONGATED STEEL ELEMENT TO REINFORCE RUBBER PRODUCTS

Abstract

A process for manufacturing an elongated steel element for reinforcing rubber products includes forming, on an elongated steel element, a coating of a ternary or quaternary alloy of copper-M-zinc, where M is one or two metals selected from cobalt, nickel, tin, indium, manganese, iron, bismuth and molybdenum; drawing the elongated steel element in an aqueous lubricant containing a phosphorus compound and nitrate; and twisting two or more of the elongated steel elements into a steel cord. A copper content inside the coating is 58 to 75 wt %. A content of the one or two metals inside the coating is 0.5 to 10 wt %. A final reduction in a diameter of the elongated steel element occurs during the drawing step. The phosphorus compound is present on and/or in the coating in an amount of 0.3 to 1 mg/m.sup.2 of the coating, as measured via an Inductively Coupled Plasma technique.

Claims

1. A process for manufacturing an elongated steel element configured to reinforce rubber products, the process comprising the following steps: a step of forming a coating on an elongated steel element, the coating comprising a ternary or quaternary alloy of copper-M-zinc, wherein M is one or two metals selected from the group consisting of cobalt, nickel, tin, indium, manganese, iron, bismuth and molybdenum, a copper content inside the coating ranges from 58 weight percent to 75 weight percent, a content of the one or two metals inside the coating ranges from 0.5 weight percent to 10 weight percent, a remainder is zinc and unavoidable impurities, and the one or two metals are present throughout the coating; a step of drawing the elongated steel element having the coating formed thereon in an aqueous lubricant containing a phosphorus compound, and a step of twisting two or more of the elongated steel elements into a steel cord performed after the step of drawing the elongated steel element having the coating formed thereon in the aqueous lubricant, wherein a final reduction in a diameter of the elongated steel element occurs during the step of drawing the elongated steel element having the coating formed thereon in the aqueous lubricant, the phosphorus compound being present on and/or in the coating in an amount ranging from 0.3 milligram per square meter to 1 milligram per square meter of the coating, as measured via an Inductively Coupled Plasma technique, the aqueous lubricant further comprising nitrate in an amount above a detection level of a ToF-SIMS technique.

2. The process of claim 1, wherein the copper content inside the coating ranges from 61 weight percent to 70 weight percent.

3. The process of claim 2, wherein the content of the one or two metals inside the coating ranges from 2 weight percent to 8 weight percent.

4. The process of claim 1, wherein the elongated steel element comprises a steel wire or a steel cord.

5. The process of claim 1, wherein a content of the remainder is lower than 0.1 weight percent.

6. The process of claim 1, wherein a thickness of the coating ranges from 0.05 m to 0.50 m.

7. The process of claim 1, wherein the coating does not include triazoles, imidazoles, or indazoles.

8. The process of claim 1, wherein a diameter of the elongated steel element ranges from 0.03 mm to 1.20 mm.

9. The process of claim 1, wherein a level of roughness of the elongated steel element ranges from 0.10 m to 2.0 m.

10. The process of claim 1, wherein a tensile strength of the elongated steel element ranges from 1500 MPa to 4500 MPa.

11. The process of claim 1, wherein the elongated steel element is not treated with triazoles, imidazoles, or indazoles.

12. The process of claim 1, wherein the aqueous lubricant comprises an aqueous emulsion containing more than 90% water, an oil, surfactant, soap, the phosphorous compound, and a pH buffer.

13. The process of claim 1, wherein the aqueous lubricant comprises phosphates, sulfates, nitrates, 0-containing hydrocarbons and fatty acid residues, and N-containing hydrocarbons.

14. The process of claim 1, wherein the step of forming the coating on the elongated steel element comprises: electroplating the elongated steel element with a copper solution; electroplating the elongated steel element with a cobalt solution; electroplating the elongated steel element with a zinc solution; and applying a thermal diffusion process to create the ternary alloy comprising CuCoZn.

15. The process of claim 14, wherein the step of forming the coating on the elongated steel element comprises: electroplating the elongated steel element with a Cu.sub.2P.sub.2O.sub.7 solution; electroplating the elongated steel element with a CoSO.sub.4 solution; electroplating the elongated steel element with a ZnSO.sub.4 solution; and applying a thermal diffusion process to create the ternary alloy comprising CuCoZn.

16. The process of claim 14, wherein electroplating the elongated steel element with the copper solution comprises using a current density of 8.6 A/dm.sup.2 or higher; and electroplating the elongated steel element with the zinc solution comprises using a current density of 8.8 A/dm.sup.2 or lower.

17. The process of claim 14, wherein the step of forming the coating on the elongated steel element further comprises cleaning a surface of the elongated steel element with a sulfuric acid solution prior to performing electroplating.

18. The process of claim 14, wherein the step of forming the coating on the elongated steel element further comprises removing excess ZnO formed during the thermal diffusion process by dipping the elongated steel element having the ternary alloy in an acid.

19. The process of claim 1, wherein drawing the elongated steel element having the coating formed thereon in the aqueous lubricant occurs in a single step.

20. A process for manufacturing an elongated steel element configured to reinforce rubber products, the process comprising the following steps: a step of forming a coating on an elongated steel element, the coating comprising a ternary or quaternary alloy of copper-M-zinc, wherein M is one or two metals selected from the group consisting of cobalt, nickel, tin, indium, manganese, iron, bismuth and molybdenum, a copper content inside the coating ranges from 58 weight percent to 75 weight percent, a content of the one or two metals inside the coating ranges from 0.5 weight percent to 10 weight percent, a remainder is zinc and unavoidable impurities, and the one or two metals are present throughout the coating; a step of adding phosphorous on and/or in the coating in an amount ranging from 0.3 milligram per square meter to 1 milligram per square meter of the coating, as measured via an Inductively Coupled Plasma technique, the step of adding phosphorous consisting of drawing the elongated steel element having the coating formed thereon in an aqueous lubricant containing a phosphorus compound and nitrate in an amount above a detection level of a ToF-SIMS technique; and a step of twisting two or more of the elongated steel elements into a steel cord performed after the step of adding phosphorous on and/or in the coating.

Description

MODE(S) FOR CARRYING OUT THE INVENTION

[0063] Two sample steel wires with a diameter of 1.98 mm are provided with a ternary alloy coating as follows:

i) pickling in a H.sub.2SO.sub.4 solution to clean the surface of the steel wire;
ii) electroplating with copper from a Cu.sub.2P.sub.2O.sub.7 solution; solution contains 25 g/l copper and 180 g/l pyrophosphate; current density is 8.6 A/dm.sup.2 or higher for a higher copper content;
iii) electroplating cobalt from a CoSO.sub.4 solution; solution contains 40 g/l cobalt and current density is 22 A/dm.sup.2;
iv) electroplating with zinc from a ZnSO.sub.4 solution; solution contains 50 g/l zinc and current density is 8.8 A/dm.sup.2 or lower for a lower zinc content;
v) applying a thermal diffusion process to create the ternary alloy CuCoZn;
vi) removing excess of ZnO formed during diffusion process via a dip in an acid;
vii) rinsing and drying.

[0064] Steel wire 1 has following coating composition: 63.5 wt % Cu, 4.0 wt % Co, the remainder being Zn.

[0065] Steel wire 2 has following coating composition: 67.0 wt % Cu, 4.0 wt % Co, the remainder being Zn.

[0066] The steel wires are subjected to a final reduction in diameter during a wet wire drawing operation.

[0067] Three different lubricants are used: I-X-Y.

[0068] Lubricant I is the lubricant to be used in the context of the present invention. Lubricant I is an aqueous emulsion containing more than 90% water, an oil, surfactant, soap, phosphorus compound and a pH buffering system. The pH is also partially buffered by working of amines.

[0069] More particularly, lubricant I comprises phosphates, sulphates, nitrates, 0-containing hydrocarbons and fatty acid residues, N-containing hydrocarbons. The phosphates may be present as PO.sub.2.sup. or as PO.sub.3.sup. ions.

[0070] Reference lubricant X is an aqueous emulsion containing more than 90% water, mineral oil, surfactant, soap, phosphorus compound, extreme pressure additive, corrosion inhibitor of the triazole type, e.g. benzotriazole, and a pH buffering system. The pH is also partially buffered by working of amines.

[0071] More particularly, lubricant X contains phosphates, CN/CNO, benzotriazole, hydrocarbons, fatty acids and octylphosphate acid.

[0072] Reference lubricant Y is an aqueous emulsion containing more than 90% water, vegetable oil, surfactant, soap, phosphorus compound, extreme pressure additive, corrosion inhibitor of the triazole type, e.g. benzotriazole, and a pH buffering system. The pH is also partially buffered by working of amines.

[0073] More particularly, lubricant Y contains phosphates, CN/CNO, benzotriazole, hydrocarbons, fatty acids and octylphosphate acid.

[0074] Final steel wire diameter is 0.30 mm. After wet wire drawing the steel wires have been twisted into a 20.30 steel cord construction.

[0075] Combining the two steel wires 1 and 2 with the three lubricants I, X and Y, gives six different steel cord samples 1-I, 1-X, 1-Y, 2-I, 2-X and 2-Y. These six different steel samples have been vulcanized in a rubber compound. The pull-out force (POF) and the appearance ratio (APR) or rubber coverage have been measured on these samples.

[0076] Table 1 lists, amongst others, the amount of phosphorus on the surface of the ternary alloy coating.

TABLE-US-00001 TABLE 1 Cu Co Thickness P.sub.s Sample Lube (wt %) (wt %) coating (m) (mg/m.sup.2) 1-I inv I 64.00 3.7 0.26 0.85 1-X ref X 64.50 3.6 0.25 1.15 1-Y ref Y 64.20 3.7 0.25 1.31 2-I inv I 67.60 3.5 0.26 0.75 2-X ref X 68.00 3.5 0.25 1.07 3-Y ref Y 68.13 3.5 0.25 1.24 Inv = invention ref = reference P.sub.s = amount of phosphorus

[0077] Table 2 mentions the results of the pull-out test and of the appearance ratio test in under cure.

TABLE-US-00002 TABLE 2 Pull-out Force Appearence Sample (N) Ratio (%) 1-I inv 334 60 1-X ref 263 48 1-Y ref 223 33 2-I inv 338 68 2-X ref 279 60 3-Y ref 255 50

[0078] The invention samples 1-I inv and 2-I-inv clearly perform better both in the pull-out test as in the appearance ratio test.

[0079] The adhesion behaviour of invention samples 1-I-inv and 2-I-inv at regular cure (RC) and after steam aging (SA) are at an acceptable high level, see Table 3 hereafter.

[0080] RC is the TC90 time plus 5 minutes and TC90 is the time when the rubber reaches 90% of its maximum torque on a rheometer curve taken at vulcanisation temperature.

[0081] SA is steam cooking RC samples at 120 C. for 1 or 2 days.

TABLE-US-00003 TABLE 3 Sample POF (RC) POF (SA) APR (RC) APR (SA) 1-I-inv 421 359 85 83 2-I-inv 379 256 80 58 3-I-ref 377 142 80 28 3-X-ref 387 197 78 43 3-Y-ref 403 227 83 45

[0082] 3 refers to an elongated steel element with a more common brass coating copper-zinc.

[0083] 3-I-ref was drawn in lubricant I and has 63.95 wt % Cu in its coating and 0.81 mg/m.sup.2 phosphorus on or in its coating.

[0084] 3-X-ref was drawn in lubricant X and has 64.30 wt % Cu in its coating and 1.09 mg/m.sup.2 phosphorus on or in its coating.

[0085] 3-Y-ref was drawn in lubricant Y and has 64.20 wt % Cu in its coating and 1.28 mg/m.sup.2 phosphorus on or in its coating.

[0086] Table 4 hereunder summarizes the results of a ToF-SIMS analysis carried on steel cord sample 1-I-inv of the invention.

TABLE-US-00004 TABLE 4 Ion Mass (u) Position 1 Position 2 Elements F 19 3.32 3.57 S 32 45.97 47.44 Cl 35 239.10 361.63 Cu 63 100.00 100.00 CuH.sub.2O.sub.2 97 441.02 470.14 Phosphates, PO.sub.2 63 158.69 643.35 sulfates and PO.sub.3 79 502.96 1551.88 nitrates SO.sub.2 64 105.64 118.68 SO.sub.3 80 219.20 222.74 NO.sub.3 46 111.52 263.07 NO.sub.2 62 79.42 164.11 O-containing C.sub.2H.sub.2O.sub.2 58 120.42 183.53 hydrocarbons C.sub.3H.sub.3O.sub.2 71 176.96 275.66 and fatty acid C.sub.16H.sub.310.sub.2 255 13.25 33.91 residues C.sub.18H.sub.33O.sub.2 281 4.75 9.70 C.sub.18H.sub.35O.sub.2 283 12.23 42.70 N-containing CN 26 576.57 732.98 hydrocarbons CNO 42 311.18 426.13 Triazole C.sub.6H.sub.4N 90 2.58 3.81 C.sub.6H.sub.4N.sub.3 118 1.75 2.66

[0087] According to the present invention, the elongated steel elements lack triazoles on the coating, so they also lack benzotriazoles. Table 4, however, mentions some values for triazoles. However, these values are to be considered as noise level. Values higher than 5, e.g. higher than 10 are to be considered as above noise level.

[0088] The same is valid for imidazoles and for indazoles: explicit measuring these compounds by means of the ToF-SIMS technique would deliver noise values.

[0089] Table 5 hereunder mentions two possible tire rubber compound formulations together with its properties where an effective improvement on UC adhesion has been noticed.

TABLE-US-00005 TABLE 5 Ingredient Compound 1 Compound 2 Natural rubber TSR10 100 parts 100 parts ZnO - Zinc oxide 9 phr 9 phr Stearic acid 0.7 phr Carbon black HAFLS N326 65 phr 65 phr Anti-degradation compound 1.8 phr 1.8 phr 6PPD (*) Sulphur source Crystex 6.4 phr 6.4 phr HSOT20 Accelerator DCBS 0.8 phr Cobalt salt Manobond 680C 0.27 phr Accelerator TBBS 0.7 phr Retarder PVI 0.25 phr Properties Rheometer Cure at 150 C. Tc2 (min) 1.8 3.5 Tc90 (min) 12.0 13.0 M.sub.H (dNm) 31.5 30.6 Mooney at 100 C. Viscosity (MU) 66 70 Shore A Hardness 70 66 Breaking load (N) 336 337 Tensile strength (MPa) 22.5 23.0 Modulus 100% (N/cm.sup.2) 4.7 4.7 Modulus 200% (N/cm.sup.2) 10.3 11.1 Modulus 300% (N/cm.sup.2) 16.3 17.9 Elongation at break (%) 421 396 DMTA at 60 C. 10 Hz dynamic strain E (MPa) 12.61 8.58 E (MPa) 1.98 0.94 Tan () 0.157 0.109 DMTA = dynamic mechanical thermal analysis the Tan at 60 C. is an indication of the rolling resistance, the higher the value, the higher the rolling resistance.

[0090] Next to the ternary alloy compositions mentioned in Table 1, following compositions have also been tested:

TABLE-US-00006 % Cu % Co 67 4 67 2 63 4 70 2 70 4 67 6 63.5 8 63.5 1

[0091] Due to an improved adhesion performance and better rubber compound an increased tire endurance may be noticed.

[0092] In addition, the absence of cobalt in the rubber compound reduces the rubber heat ageing.

[0093] Finally a lower rolling resistance of about 2.5% to 4.0% or even more may be noticed.