GB1559383A - Molten reagent treatment of metal filaments in filament orcord form - Google Patents

Description

(54) MOLTEN REAGENT TREATMENT OF METAL FILAMENTS, IN FILAMENT OR CORD FORM (71) We, THE GOODYEAR TIRE & RUBBER COMPANY, a corporation organise under the laws of the State of Ohio, United States of America, with offices at 1144 East Market Street, Akron, Ohio, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement :- This invention relates to the treatment of' brass coated steel filament, in filament or cord form, to aid and/or retain cord/rubber adhesion and/or improve corrosion resistance.

Pneumatic vehicle tires are often reinforced by means of cords prepared from brass coated steel filaments. This tire cord is frequently high carbon steel or high carbon steel cord with a thin layer of alpha bráss.

Use may be made of a monofilament, but normally a cord is prepared from several filaments which are stranded together. The filament is coated with brass, cold drawn and then stranded to form the cord. In most instances, normally depending upon the type Of tire being reinforced, the strands of filaments are further cabled to form the final cord.

Brass plated st$el wire tire cords are sus. jet to corrosion of the steel structure and oxidation of the brass plating if improperly handled prior to incorporation into a tire. Corrosion and oxidation can be a cause of poor adhesion between the cord and rubber, and more importantly can result in a deterioration of the physical properties of the cord.

Various chemical reagents such as benzotriazole (BTA) have been propose to protect such vire against corrosion and oxidation. Such reagents are described in our C. K. Patent Specification No. I 536 727.

These re gents normally have been applied by immersing the wire in a water solution of the ragent. The wire is then dried to remove the water. The reagents react with wire to offer it protection against oxidation and/or corrosion. For example, BTA reacts with the copper to form a polymer layer.

This layer must be sufficiently thin to allow a sulfur/copper bond to be formed between the wire and the adjacent rubber within the tire, and yet the film must be of such a continuous uniformity as to facilitate resistance to corrosion.

Water application of reagents such as BTA require lengthy immersion and drying times which can be expensive in commercial operation. The poor wettability of metal cord contributes to the length of the immersion time. This porosity of the brass coating presents the possibility that water may be occluded and therefore difficult to remove by drying. ? herse is also the possibility that vit bill be difficult for the water to penetrate the porous openings because of surface tension effects. Where the tire filament is freshly drawn, the filament is cooled by the water immersion thereby requiring expensive reheating of the cord both to dry the cord and to promote the rection between the reagents and the cord. It is therefore necessary that a method be found which does not require the use of expensive equipment and which permits the rapid treatment of the cord.

It is an object of the present invention to provide an efficient, IONN, cost method of applying chemical reagents such as BT. A to brass coated steel filaments, said method being capable of rapidly treating the filaments and reaching even remote surfaces, e. g. those exposed by porosity of the brass or those within the interstices in the case of a cord. IL is also an ob. iect of the present invention to provide a method which will not require the use of drying equipment or other expensive and time consuming follow-up treatments. It is still another objet of the present invention to provide treated brass coated steel tire cord possessing effective corrosion resistance.

The objectes of the present invention can be accomplished, in a process of treating a brass coated steel filament, in filament or cord form, with a reagent which reacts chemically with the brass surface, or with the steel surface insofar as it is exposed by porosity of the brass, so as to aid and/or retain adhesion between a cord comprise of the filament and adjacent eventually vulcanized rubber, and/or which improves the resistance of the filament or cord to corrosion, by the improvement wherein the portion of the ragent, this reagent being an organic reagents, which is in direct contact with either surface is in molten form. The present organic reagents include compound capable of preventing the oxidation of the steel substrate and/or capable of preventing the corrosion of the brass. The only limitation regarding the use of the organic reagent in solid form, provided that is is chemically reactive as specified above, is that on coming in contact with the steel or brass surface concerned, that portion directly in contact with the said surface is or becomes molten.

The process of the present invention can be used to treat the filament after drawing but before standing, after standing to form the cord, in the form of woven fabric or as multiple ends such as may be used at a creel calendering operation. In fact, the method can be used at any point in the manufacture of the cord and even subsequent thereto, the only requirement being that the cord be treated at some point before it becomes a reinforcing element in the tire or other rubber product.

The organic reagents employed in the process of the present invention inclue, but are not limited to, reagents selected from the group consistng of precipitation compound as mentioned below, oxidizing compound, and compound having the following structural formula

wherein the adjacent carbon atoms are joined to form a benzene or naphthalene ring, said ring being substituted (for example, with a single methyl group) or unsubstituted, and wherein A and B are selected from the group consisting of-N-or-CH-, with the proviso that A and B are never both -CH-, said agent being capable of being employed in molten form. The abovementioned precipitation compound have been described in our U. K. Patent Specification No. 1536727 and include compound selected from the group consisting of organic borates, organic phosphates and organic metaphosphates.

The oxidation compound include organic nitrites.

The above-mentioned precipitation compound perform their function by aiding in the formation of a protective film through an indirect oxidizing (buffering) mechanism.

The oxidation compound offer protection by directly oxidizing metallic ions in the substrate surface.

Examples of organic compound which can be used in the practice of the present invention include organic alkyl, cycloalkyl and aryl derivatives of m-boric acid, o-boric acid and pyro-boric acid as well as m-, o-, pyro and hypo-phosphoric acid.

Preferably the organic reagent contains some moisture since water enhances the ability of the agents to prevent corrosion and to provide improved aged adhesion, that is, to retain to some measure the original adhesion. Said moisture can be introduced in any manner while the filament or cord is being exposed to the organic ragent. Another embodiment involves exposing the filament or cord to an atmosphere having a high moisture content prior to or subsequent to the molten organic reagent treatment.

Any manner of exposing the filament or cord to the organic reagent in molten form will result in some improvement in corrosion or oxidation resistance.

Optimum conditions can be routinely determined for each system and will depend upon such variables as filament or cord temperature, exposure time, and the nature of the organic reagent used.

The filament or cord can be used as treated, or subsequently heated to flash off excess reactants and/or to continue the rection between the organic reagent and the filament or cord to the desired state of completion, if the desired state has not already been reached.

In one embodiment the filament or cord is simply passed through the molten organic ragent. In another embodiment it is passed through the organic reagent in solid form, which may, for example, but need not be a powdered form, the Filament or cord being at a temperature above the melting point of the organic reagent so as to melt the solid organic reagent adjacent to the surface of the filament or cord. Excess reagent may attach itself to the surface of the workpiece whether it be a filament or a cord. This can be more significant where the workpiece has interstices. Since excess organic reagent on the surface of the filament or cord can be detrimental to adhesion, the excess material must be removed in some manner, for example by flashing it off with heat.

By passing the filament or cord through the molten or meltable solid organic ragent, the disadvantages of the aqueous solution treatment are avoided. In addition, the filament or cord is exposed to the organic reagent in its most concentrated form.

The agents can be used alone or in combination. Likewise a series of treatment units can be used, each containing a different agent. It is preferred that one stage of the treatment should involve the use of BTA or an analogous agent.

The brass coated steel filaments which can benefit by the practice of the present invention include filaments in the form of cords which have been treated by methods or with material other than described herein, but which are scull susceptible to (i. e. would still benefit from being protected against) oxidation and/or corrosion.

As mentioned earlier, if moisture is desired, it can be introduced, for example, by the introduction of steam into the rection area, the provision of water occluded in the molten agents, etc. te manner by which the water is introduced is not critical.

There is no reason why the present method can not be combine with other methods, provided that they are compatible with it. For example, the filaments or cords can be first treated in an aqueous solution of one reagent followed by treatment with BTA or an analogous reagent in molten form.

In selecting agents, order of treatment, etc., one should consider that film formation with compound such as BTA can possibly cover the exposed steel so as to minimize content thereof with other agents.

It is believed that a reduction of the porosity, for example by film formation on the filament or cord surface, may result in improved corrosion resistance and adhesion retention.

As a guideline, but not a limitation, one can measure the porosity of the filament or cord by immersing it in a potassium ferrocyanide solution. The darker the resulting cord, the greater its porosity. In this way the degree of porosity can be estimated before, during, and after treatment.

The brass coating of a typical brass coated steel filament or cord is microscopically porous, thereby exposing small areas of steel surface to any surrounding environment. It is believed that BTA interacts with copper in a brass coating to form a polymeric complex of BTA plus copper. This polymeric complex is insoluble in most solvents and serves as a protective barrier to any environment degradation of the underlying brass. On the other hand, anions from the precipitation and oxidation compound, it is theorized, interact with iron and iron oxide from steel surfaces exposed through microscopic pores to form an adherent oxide film which protects the steel. It is not necessary that the barrier lasers of polymeric complexes adsorbe be extremely thick. In fact, as mentioned earlier, such layers should not be so thick as to interfere with the sulfur rection required for bonding the filament or cord to the rubber, the adhesion of rubber to metal cord requiring the formation of copper-sulfur bonds.

The practice of the present invention results in increased surface protection of brass coated steel filaments or cords prior to rubber encapsulation and improved aged adhesion of vulcanized brass coated steel/rubber composites. It also prevents cord failure due to excessive corrosion during the use of the product, e. g. during the use of a tire reinforced with the cord.

The rubber surrounding the metal can be any rubber, preferably diene rubbers such as natural rubber, rubbery copolymers of butadiene with styrene or acrylonitrile, polybutadiene and polyisoprene.

The fact that the adhesion between the copper in the brass and the adjacent rubber is dependent upon the presence of sulfur requires the use in the adjacent rubber of either free sulfur or a compound capable of donating sulfur such as 2 (morpholinodithio) benzothiazole.

Aged metal to rubber adhesion is particularly poor when the rubber contains oxygen, moisture, and an amine resin capable of releasing ammonia. For example, rubbers containing hexamethylenetetramine (HMTA) such as in a resorcinol/HMTA in situ resin system, vhere oxygen and moisture levels are sufficiently high, can tend to have poor aged-adhesion to brass or brass coated steel.

The use of the present process is particularly beneficial in such systems.

Further, coatings on in-process filaments or cords protect the filaments or cords from deleterious effects of moisture (humidity) and oxidation, i. e., improve factory storage lift.

By the term"high-carbon"steel as used in the present specification, we mean what is known as carbon steel, also called ordinary steel, also called straight carbon steel or plain carbon steel, e. g., American Iron and Steel Institute Grade 1070 highcarbon steel (AISI 1070). Such steel owes its properties chiefly to the presence of carbon without substantial amounts of other alloying elements. In this respect see Metals Handbook, The American Society for Metals, Metals Park, Cleveland, Ohio.

The term"brass"includes, but is not limited to, alpha brass or compositions in which the major component is alpha brass, i. e., which contain from abour 65 to 75 percent copper and 35 to 25 percent zinc, respectively.

The following examples contain illustrations of, but do not limit the practice of the present invention. The adhesion values given in the examples relate to cable embedded in black loaded unvulcanized natural rubber which was then vulcanized, and were obtained by measuring the force necessary to separate the cable from the vulcanized composite ; they are given in kilograms.

Example I A drawn brass coated steel cable at room temperature was passed slowly (possibly at a speed of about 25 to 50 yards per minute) through a tube containin molten benzotriazole (BTA). The cable was then sub. lected to an ultra high temperature to flash off the excess BTA. The initial adhesion value (obtained as stated above) of the treated cable to vulcanized carbon black loaded natural rubber was 37 (kilograms).

The corrosion resistance of the cable in a high temperature, high humidity environment was rated excellent.

Example 2 A tube of molten BTA was mounted on a draw machine. A hot drawn brass coated steel filament as it exited the draw machine was passed through a 3/4 inch thickness of molten BTA at a speed of 900 meters per minute. A cable prepared therefrom had in initial adhesion value of 40. 4 and a wet adhesion value (as explained below) of 40. 0.

Its corrosion resistance was excellent. An untreated control had an initial adhesion value of 59 and a wet adhesion value (relating to the use of unvulcanized rubber soaked in water before the cable was embedded therein) of 34. The corrosion resistance was rated poor.

Example 3 A brass coated steel filament was passed through a 12 inch tube of powdered BTA at a rate of 900 meters Der minute after exitine from a draw machine. The Filament was at a temperature of about 200 C. The powder temperature was varied from room temperature to 120 F. to 180 F. (48. 9 C. to 82. 2 C). A cable was prepared from the nt filament and checked for adhesion.

Adhesion Powder Temperature (kilograms) Corrosion ( F) Initial Wet Resistance Room Temperature 49 43 Excellent 120 F. 41 31 Excellent 180 F. 45 38. 5 Excellent The untreated control for room temperature and 180 F. had initial and wet adhesion values of 57 and 29 respectively.

The untreated control for 120 F. had initial and wet adhesion values of 44 and 24.

Therefore the treatment resulted in wet adhesion improvements at each temperature.

Once the filaments are coated with the brass, treatment can begin. Treatment can occur with the reagents between the plating (coating) and drawing steps or between the drawing and standing steps and even on the final cord prior to calendering. Where the treatment results in film formation, it is preferably accomplished after drawing since drawing will naturally destroy the film continuity.

Any fusible (i. e. meltable) compound could be substituted for 8TA type compound if it reacts chemically with the brass, e. g. complexes with the copper in the brass to form an insoluble film, i. e. a film which is insoluble in any of the environments to which the material is to be expose. These compound include triazoles, imidazoles and indazoles. Such compound include those compound conforming to the structural formula recited earlier herein. The only requirement is that the agent be meltable.

Any of the previous working examples could have involved a subsequent heat treatment and/or exposure of the cable to water vapor.

Other materials which can be used, for example, to treat cable using the present method are triethyl phosphate and amyl nitrite.

Claims (1)

1. WHAT WE CLAIM IS :-

   1. In a process of treating a brass coated steel filament, in filament or cord form, with a reagent which reacts chemically with the brass surface, or with the steel surface insofar as it is exposed by porosity of the brass, so as to aid and/or retain adhesion between a cord comprise of the filament and adjacent eventually vulcanized rubber, and/or which improves the resictance of the filament or cord to corrosion, the improvement wherein the portion of the ragent, this reagent being an organic ragent, which is in direct contact with either surface is in molten form.

   2. The process of claim I wherein the filament is treated subsequent to a drawing step.

   3. The process of claim 2 wherein the organic reagent is benzotriazole.

   4. The process of claim I wherein the filament is in the form of a cord.

   5. The process of claim 1 wherein the filament is subjected to heat treatment and/or water vapeur treatment subsequent to the molten organic reagent treatment.

   6. The process of claim 4 where the cord is subsequently subjected to heat treatment and/or water vapor treatment.

   7. The process of claim I wherein the total organic reagent is in molten form.

   8. The process of claim I wherein the filament is passed through a solid organic ragent, the temperature of the filament being above the melting point of the organic ragent.

   9. The treated brass coated steel filament of claim 1.

   10. The treated cord of claim 4.

   11. The treated brass coated steel filament of claim I as part of a composite with vulcanizable rubber.

   12. The treated brass coated steel cord of claim I as part of a composite with vulcanized rubber.

   13. The treated brass coated steel cord of claim I as part of a reinforcement element in a pneumatic vehicle tire. f4. An improved process as claimed in claim 1, substantially as described in any of the foregoing Examples.

   15. A composite product comprising rubber and brass coated steel components, obtained by an improved process as claimed in claim 2, 3, 5, 6, 7, 8 or 14.