Method for debrass reinforcing elements of polymer articles

Abstract

The invention relates to a method for de-brass treatment of brass-coated steel fibres for reinforcing polymer articles, comprising at least one electrochemical treatment step in which the steel fibres are immersed in a treatment bath containing a sodium hydroxide solution at a concentration of between 10 and 1000 g / l and an anodic current is applied, wherein the mass current intensity is between 1 and 2500 A / kg steel fibres, the residence time of the steel fibres in the bath is at least equal to 7 minutes, and the treatment temperature is at least equal to 30 DEG C.

Description

Technical Field

[0001] The present invention relates to methods for treating metal components (particularly coated steel fibers for reinforcing polymer articles (particularly rubber articles)) and, in particular, methods for removing brass coatings present on these steel fibers to improve their recycling. Background Technology

[0002] Increased pressure on natural resources and the desire to minimize waste generation are prompting manufacturers to develop more and more recycling solutions.

[0003] Steel recycling is well-known. However, the proportion of steel recovered into castings faces the challenge of managing residues (i.e., all elements except iron). While some residues, such as carbon, silicon, or manganese, can be adjusted or eliminated during steel production, other impurities, such as copper or tin, are more difficult to extract and can cause problems, especially if an attempt is made to establish a “circular” system where used steel is recycled for reuse in the same purpose. Specifically, any closed-loop process leads to the accumulation of unrecoverable substances, which can ultimately limit the amount of steel recovered, particularly in the presence of copper (Environ. Sci. Technol. 2017, 51, 6599-6606).

[0004] Steel used to manufacture metal wires to reinforce polymer products (particularly rubber products, such as pneumatic or non-pneumatic tires, tracks, and conveyor belts) has very low tolerances in its chemical composition, primarily to allow for rigorous forming through wire drawing, and secondly to ensure sufficient mechanical strength to guarantee its reinforcing function. Therefore, the residue content in the steel composition must be as low as possible.

[0005] Therefore, establishing a recycling system for these metal wires requires very precise management of residue levels. Typically, these wires are coated with brass (a copper-zinc alloy) to improve rubber adhesion to their surfaces. Therefore, recycling them for reuse in the manufacture of tire-grade steel necessitates the development of solutions capable of effectively managing residue levels.

[0006] To achieve this goal, various solutions have been developed for de-brassing steel, that is, removing the brass coating present on the surface of steel components.

[0007] The document “Traitement des Matériaux Revêtus [Treatment of Coated Materials]”, M1458, Techniques de l'Ingénieur describes many chemical and electrolytic demetallization solutions, especially those based on alkaline solutions containing sodium cyanide.

[0008] Document DE2233157 describes the removal of copper from copper-plated steel sheets via electrolytic treatment using an ammonia bath with ammonium phosphate or ammonium borate. However, copper itself does not behave like brass (which is an alloy). Furthermore, this method requires specific management of the processed products (especially the ammonia solution), necessitating the implementation of specific protective measures.

[0009] Document CN103436899 describes the cleaning of the coating on tire steel cords. For this purpose, the cords are treated in a strongly alkaline bath of ammonia and sodium nitrate. The volatility of ammonia necessitates frequent refilling, and specific protective measures are also required.

[0010] Continuing their research, the applicant discovered that a de-brassification method under specific conditions can effectively remove the brass coating from steel fibers used to reinforce polymer products (particularly rubber products), regardless of whether these fibers are partially coated with rubber, thus paving the way for the recycling of these fibers into steelmaking processes for reuse in the manufacture of tire-grade steel. Summary of the Invention

[0011] This invention relates to a method for removing brass from brass-coated steel fibers used to reinforce polymer articles, comprising at least one electrochemical treatment step, wherein the steel fibers are immersed in a treatment bath containing a sodium hydroxide solution with a concentration between 10 and 1000 g / L and an anodic current is applied, wherein the current intensity per unit mass is between 1 and 2500 A / kg of steel fiber, the residence time of the steel fibers in the bath is at least 7 minutes, preferably at least 10 minutes, and the temperature of the treatment bath is at least 30°C.

[0012] definition

[0013] In this invention, unless otherwise expressly stated, all percentages (%) shown are mass percentages (%).

[0014] Furthermore, any numerical interval expressed as "between a and b" represents a range of values ​​from greater than a to less than b (i.e., excluding the limits a and b), while any numerical interval expressed as "from a to b" represents a range of values ​​from a upward to b (i.e., including the strict limits a and b).

[0015] As is known to those skilled in the art, the term "de-brassification" refers to the removal of a brass layer coated on steel fibers.

[0016] The method according to the invention is a method for debresting steel fibers used to reinforce polymer articles. The term "polymer article" refers to an article comprising a metal reinforcing element and a polymer matrix (e.g., a resin or rubber composition). The term "rubber article" refers to any rubber article reinforced with steel fibers. These articles are particularly selected from pneumatic or non-pneumatic (i.e., vehicle weight supported by means other than pressurized gas, such as by struts) vehicle tires, conveyor belts, belts, or tracks, and the term "rubber" is understood herein to refer to any polymeric compound exhibiting elastic behavior.

[0017] The term "steel fiber for reinforcing polymer articles" refers to new steel fibers used to incorporate into polymer articles, or steel fibers extracted from polymer articles, whether these are in a "raw" or non-crosslinked state, or in a "cured" state, i.e., crosslinked or vulcanized. The steel fibers are reinforcing elements made of coated steel and cut in the manner described in the method according to the invention.

[0018] Preferably, the rubber product is selected from vehicle tires, tracks, and conveyor belts, and most preferably from vehicle tires.

[0019] Generally, a vehicle tire comprises a crown with two axial ends, each extending radially inward through the sidewalls and then radially inward through a bead that contacts the rim, collectively defining an internal annular cavity. More specifically, the crown radially from the outside in includes a tread (intended to contact the ground via a rolling surface), crown reinforcements, and carcass reinforcement portions designed to reinforce the tire. The carcass reinforcements connect the two sidewalls by extending within the radially inner portion of the crown and are anchored in each bead to a circumferential reinforcement element, typically of the bead line type.

[0020] Polymer articles, particularly rubber articles, are processed by cutting, sorting, and shredding in a manner known to those skilled in the art. The fragments containing metal reinforcing elements are then granulated in a granulator and washed to reduce their rubber content. At the end of this process, the individually obtained steel fibers preferably have a length of no more than 10 cm. Preferably, the diameter of the steel fibers is 0.1 mm to 2 mm, more preferably 0.1 mm to 0.8 mm, and very preferably 0.1 mm to 0.5 mm.

[0021] The rubber content of the steel fibers processed in the method according to the invention is preferably 0 to 15% by weight of the steel fibers, more preferably 0 to 10% by weight of the steel fibers, and more preferably 0 to 4% by weight of the steel fibers.

[0022] The steel fibers processed in the method according to the invention are steel fibers coated with a metallic brass coating, wherein the brass content is preferably from 0.01% to 0.50% by weight relative to the metal mass in the steel fibers. These fibers are preferably derived from the crown reinforcement or carcass reinforcement of vehicle tires, which are reinforced with metal wires.

[0023] Preferably, the copper content in the steel fiber is 0.1% to 0.3% by weight and the zinc content is 0.05% to 0.20% by weight, relative to the metal mass in the steel fiber.

[0024] According to the present invention, steel fibers are immersed in a treatment bath containing a sodium hydroxide solution with a concentration of 10 to 1000 g / L, preferably 50 to 500 g / L, and very preferably 75 to 300 g / L, and an anodic current is applied. At concentrations above 1000 g / L, there is a risk of sodium hydroxide precipitation, while at concentrations below 10 g / L, the concentration is too low to allow for effective current conduction.

[0025] The residence time of the steel fibers in the bath is at least 7 minutes, preferably at least 10 minutes. Preferably, the residence time is adjusted so that the content of the metal coating relative to the metal mass in the steel fibers is reduced by at least 90%. Preferably, at the end of the debridement process, the total mass content of copper and zinc in the steel fibers is less than 0.005% for copper and less than 0.005% for zinc, relative to the metal mass in the steel fibers.

[0026] Electrochemical treatment of steel fibers with sodium hydroxide solution can remove brass from the steel fibers even in the presence of residual rubber, offering reduced processing time and excellent selectivity compared to chemical treatment. Specifically, known chemical treatments in the prior art can remove some of the metal coating, but also extract some iron from the steel.

[0027] The method according to the invention is carried out at a temperature of at least 30°C, preferably at least 40°C, and more preferably below or equal to 80°C. These temperatures, combined with other operating parameters, allow for a reduction in the risk of emissions due to evaporation during operation, while maintaining excellent debridement performance.

[0028] The current intensity per unit mass is 1 to 2500 A / kg steel fiber. Preferably, the current intensity per unit mass is 1 to 500 A / kg steel fiber, more preferably 1 to 300 A / kg steel fiber, more preferably 2 to 300 A / kg steel fiber, and very preferably 5 to 20 A / kg steel fiber. These intensities, combined with other operating parameters, allow for a good trade-off between the debridement of the steel fibers and the duration of the debridement treatment.

[0029] The present invention also relates to the use of steel fibers obtained by the debridement method according to the present invention in the manufacture of reinforcing wires for reinforcing polymer articles.

[0030] The steel fibers treated in the method according to the invention have significantly reduced copper and zinc content, thus breaking the recycling limits associated with the presence of copper in recycled steel (copper is difficult to manage), and opening up the possibility of recycling them at higher contents to produce new steel for reinforcing reinforced polymer articles (especially for reinforcing vehicle tires). Detailed Implementation

[0031] Example

[0032] In the following examples, various types of steel fibers are processed. The first batch (hereinafter referred to as "bare fibers") consists of brass-coated metal wire scrap derived from the manufacture of reinforcing wires for pneumatic tires. Therefore, these fibers do not contain rubber and are not integrated into polymer products such as rubber products.

[0033] The second batch (hereinafter referred to as "rubber fibers") comes from the processing of scrap pneumatic tires. These tires are processed in a manner known to those skilled in the art by cutting, sorting, and shredding. The fragments, containing brass-coated cords, are then granulated in a granulator and washed in a manner appropriate to obtain aggregates containing approximately 4% by weight of rubber (E51 category scrap metal according to AFNOR standard AF 08-821).

[0034] For each batch, the steel fibers are each no longer than 10cm.

[0035] The "naked fiber" contains 160 mg of brass per 100 g of metal, which is 0.16% by weight relative to the metal mass in the steel fiber. Elemental analysis shows that the brass consists of 64.4% copper and 35.6% zinc by weight, while the steel consists of 0.7% carbon, 0.5% manganese, 0.2% silicon, and 98.6% iron by weight. Other elements such as chromium and molybdenum are present in negligible amounts.

[0036] Compared to the mass of metal in the steel fiber, the "rubber fiber" contains 0.15% by weight of a brass coating. Elemental analysis shows that the brass consists of 63.6% copper and 36.4% zinc by weight. The composition of the steel is the same as that of the "bare fiber".

[0037] De-brassization percentage

[0038] To determine the percentage of debridement, the procedure was performed as follows: The brass coating content (T1) on the steel fibers was measured prior to treatment, expressed as mg / 100g metal. The fiber sample was treated, and the coating content (T2) on the steel fibers was measured again.

[0039] Then calculate the extraction percentage as follows: Extraction% = (T1-T2) / T1×100.

[0040] To determine the coating content on the fiber, the method is carried out in a manner known to those skilled in the art, by etching the steel fiber and then determining the copper and zinc elements in the etching solution used.

[0041] Steel corrosion

[0042] To evaluate the extent of corrosion of the steel by the treatment, the iron present in the chemical bath at the end of the treatment was measured. The more iron in the chemical bath, the more steel in the steel fibers will be corroded by the treatment, which is detrimental. The amount of iron present in the treatment bath is equal to the amount of iron present in the steel fibers before the treatment.

[0043] Analysis showed that, apart from treatment with sodium hydroxide and ammonia, the evaluated non-electrochemical treatments resulted in a significant amount of iron in the treatment bath, with dissolved iron accounting for more than 20% of the iron weight present in the steel fibers before treatment. Chemical treatment with ammonia diluted in a 30% wt% aqueous hydrogen peroxide solution could yield good performance, but this approach could not be used due to the high ammonia-related limitations.

[0044] The evaluated electrochemical and non-electrochemical sodium hydroxide treatments resulted in very little iron extraction from the steel fibers, with the amount of dissolved iron less than 0.05% by weight of the iron present in the steel fibers before treatment.

[0045] result

[0046] The conditions and results of the various treatments are shown in Table 1. It can be seen that the method carried out under the conditions of the present invention can obtain excellent debridement of steel fibers, while limiting the extraction of iron from steel, especially compared with known chemical treatments.

[0047] [Table 1]

[0048]

Claims

1. A method for removing brass from brass-coated steel fibers used to reinforce polymer articles, comprising at least one electrochemical treatment step, wherein, The steel fibers are immersed in a treatment bath containing a sodium hydroxide solution with a concentration between 10 and 1000 g / L and an anodic current is applied. The current intensity per unit mass is 1 to 2500 A / kg of steel fiber. The residence time of the steel fibers in the bath is at least 7 minutes and the temperature of the treatment bath is at least 30°C.

2. The method for removing brass according to the preceding claim, wherein, The temperature of the treatment bath is at least 40°C.

3. The method for removing brass according to any one of the preceding claims, wherein, The current intensity per unit mass is 1 to 500 A / kg steel fiber, preferably 1 to 300 A / kg steel fiber, more preferably 2 to 300 A / kg steel fiber, and very preferably 5 to 20 A / kg steel fiber.

4. The method for removing brass according to any one of the preceding claims, wherein, The temperature of the treatment bath is below or equal to 80°C.

5. The method for removing brass according to any one of the preceding claims, wherein, The concentration of sodium hydroxide in the treatment bath is 50 to 500 g / L, and very preferably 75 to 300 g / L.

6. The method for removing brass according to any one of the preceding claims, wherein, The rubber content of the steel fiber is 0 to 15% by weight of the steel fiber, preferably 0 to 10% by weight of the steel fiber, and more preferably 0 to 4% by weight of the steel fiber.

7. The method for removing brass according to any one of the preceding claims, wherein, The brass coating content of the steel fiber is from 0.01% to 0.50% by weight relative to the mass of metal in the steel fiber.

8. The method for removing brass according to the preceding claims, wherein, The copper content in the steel fiber is 0.1% to 0.3% by weight, and the zinc content is 0.05% to 0.20% by weight, relative to the metal content in the steel fiber.

9. The method for removing brass according to any one of the preceding claims, wherein, The steel fibers have a diameter of 0.1 mm to 2 mm.

10. The method for removing brass according to any one of the preceding claims, wherein, Each of the steel fibers has a length of no more than 10 cm.

11. The method for removing brass according to any one of the preceding claims, wherein, The dwell time is adjusted to reduce the metal coating content relative to the metal mass in the steel fiber by at least 90%.

12. The method for removing brass according to any one of the preceding claims, wherein, The polymer article is a rubber article selected from vehicle tires, tracks and conveyor belts, and is very preferably composed of vehicle tires.

13. The method for removing brass according to any one of the preceding claims, wherein, Steel fibers are derived from the crown reinforcement or carcass reinforcement of vehicle tires, which are reinforced with metal wires.

14. Use of steel fibers derived from the debridement method according to any one of the preceding claims in the manufacture of reinforcing wires for reinforcing polymer articles.

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