CA1098269A - Solid or molten reagent treatment of metal tire cord - Google Patents

Abstract

Abstract of the Disclosure Brass coated steel tire cord is treated with solid or molten benzotriazole and/or other treatment agents to promote corrosion resistance and cord to rubber adhesion retention.

Description

This invention relates to the treatment of brass coated s-teel cord -to prevent corrosion of the cord and to improve cord/rubber adhesion retention.
Pneumatic vehicle tires are often reinforced by 5 means of cords prepared from brass coated steel filaments.
m is -tire cord is frequently high carbon s^teel or high carbon steel cord with a thin layer of alpha brass. me cord may be a monofllament? but normally is prepared ~rom se~eral filaments which are stranded together. The fila~
ment is coated with brass, cold drawn and -then stranded to form the cord. In most instances7 normally depending upon the type of tire being reinforced, the strands of ~ilaments~
~ are ~urther cabled to ~orm the ~inal cord.
- Brass plated steel wlre tire cords are svhject -to corrosion o~ the steel structure and oxidation of the brass plating if improperly handled prior to incorporation into a tire. Corrosion and oxidation can result in poor adhesion between the cord and rubber and more importantly in a .. . .
deterioration of the physical properties o~ the cord.
Various chemical reagents such as benzotriazole (BTA) have been proposed to protec-t such wire against oorrosion and oxldation. m ese reagents normally have been applied by immersing the wire in a water solution~o~ the reagent. me wire is then drled to remove the w2ter. The reagents react with wire to o~fer it protection against oxidation and/or corrosion. For example, BTA reacts with the copper to ~orm a polymer layer. This layer mus-t be sufficiently thin to allow a sulfur/copper bond to be ~ormed between the wire and the adjacent rubber within the ' ~i ., tire, and yet the film must be of such a continuous uni-formity as to facilitate resis-tance to corrosion.
Water application of reagents such as BTA
re~uires lengthy îmmersion and drying times which can be expensive in commercial operations. me poor we-tability of metal cord contributes to the length o~ the immers-on time. The porosity of the brass coQ-ting presents the possibility that water may be occluded and therefore difficult to remove by drying. There is also the possi-bility that it will 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 expensi~e ~ ;
reheating of -the cord both to dry the cord and to promote the reaction between the reagents and the cord. It is there~ore 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 desired to provide an ef~icient, low cost zo method o~ applying protective agents to brass coated steel - !
wire, said method~belng capable o~ rapidly treating the wlre`and reaching even remote surfaGes o~ the wire. It is ~lso desired to provide a method which will not require the use of drying equipment or other expensive and time consuming follow-up treatments. It is further desired to provide treated brass co~ted steel tire cord possessing effective corrosion resistance.
The present invention can be accomplished by 7 treating the cord during the course of its preparation or thereafter with reagents capable of promoting and/or retaining adhesion between the metal cord and adjacen-t vulcanized rubber and/or capable of impro~ing the resis-tance of the cord to corrosion priorto incorporation into the tire, said reagent being in a solid or molten sta-te.
Said reagents include compounds capable of preventing the oxidation of the steel substrate and/or capable of preventing the corrosion of -the brass. me only limita-tion regarding the use of the reagent in solid form is that on coming in contact with the wire 7 the portion directly in contact wi-th the wire becomes molten.
me process of the present invention can ~e used to treat the filament after drawing but before stranding~ after stranding to form the cord, in the .orm 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 an~ point in the manufacture o~ the cord and even subsequent -thereto, the only requirement being ~hat the cvrd be treated at some point before it becomes a reinforci4g element in the tire or other rubber product.
Accordingly, the in~ention more specifically is a process of treating a brass coated steel filament - which comprises -treating said filament with molten benzo-triazole subsequent to a drawing step for said filament and where the temperature of the wire is abo~e the melting point o~ said benzotriazole.
The invention also includes such a process where the treated filament is subjected to a water vapor treatment.

In the practice o~ this i~vention, -the ~ilament ~ : :
can be in the form of a cord.
; The reagents o~ the present invention include, but are not limited to, reagents selected ~rom the group consisting o~ precipitation compounds, oxidizing compounds, and compounds having -the following structural ~ormula \ ~ A
1~ 3 , ~C~
H

. , ~ ~ , , . -3a- .
, :, ~

$~ .

wherein the adjacent carbon atoms are joined to form a benzene or naphthylene ring, said ring being suhstituted (for example, with a single methyl group) or unsubstitu-ted and wherein A and B are selected from the group consisting of -N- or -CH-~ with the proviso that A and B are ne~er both -CH-, said agent being in the form of a solid or a liquid. The precipitation compounds include compounds selected from the group consisting of organic borates organic phospha-te and organic metaphosphates. The oxida-tion compounds include organic nitrites~
The precipitation compounds offer their protec-tion through an indirect o~idizing (bu~fexing) mechanism.
The oxidation compounds offer protection by directly oxidizing metallic ions in the substrate surface.
Examples of organic compounds 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.
Pre~erably the 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 mois-ture can be introduced in any manner while the wire is being exposed to the reagent. Another embodiment in~olves exposing the cord to an atmosphere having a high moisture content prior to or subsequent to the liquid or solid treatment Any manner of exposing the cord to the solid or liquid form of the reagent will result in some improvement in corroslon or oxidation resistance.
Optimum conditions can be routinely determined for each system and will depend upon such variables as wire ~-tempera-ture, exposure time~ the reagent used, etc.
The wire can be used as treated or subsequently heated to flash off excess reactants and/or to continue the reaction between the reagent and the wire to the desired state of completion, if the desired state has not already ~ ;
been reached.
In one embodiment the wire is simply passed ~ ~ ;
through the molten reagent In another embodiment it is `~
passed through a solid~ for example~ but not limited to7 in powdered form~ the wire being at a temperature above the melting point of the reagent so as to melt the solid adja~
cent to the surface of the wire. Excess reagent may attach itself to the surface of the wire whether it be a filament or a cord. This can be more prevalent w:ere the wire has interstices. Since excess reagent on the surface ~;
o~ the wire can be detrimental to adhesion9 the excess material must be removed in some manner, for example by flashing it off with heat.
By passing the wire through the molten or melt-able solid reagent~ the disadvantages of the aqueous solution treatment are avoided. In addition, the wire is exposed to the reagent in its most concentrated form The agents can be used alone or in combination.
Likewise a series of units can be used~ each containing a different agent. It is preferred that one stage o~ the treatment involve the use of a BTA-type chemical agent.
The brass coated steel cord which can benefit by -5~

32,r~9 the practice of the present invention includes cord treated by methods or ~ith material other than described herein, bu-t which are still susceptible to oxidation and/or corro~
sion.
As mentioned earlier, if moisture is desired, it can be introduced, for example, by the introduction of steam into the reaction area, the addition of water to the molten agents~ etc. The manner by which the water is introduced is not critical.
There is no reason why the preseIlt method can not be combined with other methods. For example, the wire can be first treated in an a~ueous solution of one reagent followed by treatment with the BTA type material in molten or solid form.
In selecting agents, order of-treatment, etc., one should consider that film formatlon with compounds such as BTA can possible cover the exposed steel so as to min-imize contact thereof with other agents.
It is believed that a reduction of the porosity, ~or example by ~ilm formation on the cord surface~ may result in improved corrosion resistance and adhesion re-tention. ;~ ;
As a guideline~ but not a limitation~ one can measure the porosity of the wire by immerslng it in a potassium ferrocyanide solution. The darker the resultingcord, the greater its porosity. In this way the degree of porosity can be estimated before~ during, and after treat-ment The brass coating of a typical brass coated steel cord is microscopically porous~ thereby exposing small areas of steel surface to any surrounding environment~ It is believed that BTA interacts wlth 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 pro-tective barrier to any environmental degra-dation of the underlying brass. On the other hand~ anians from the precipitation and oxidation compounds~ 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 layers of polymeric complexes adsorbed be extremely thick. In fact~ as mentioned ear-lier, such layers should not be so thick as to interfere ~ i~
. ~
with the sulfur reactlon required for bonding the wire to ;~
the rubber, the adhesion of rubber to me~al cord requiring the formation of copper-sulfur bonds. ~ ;~
The practice of the pre~ent invèntion results in increased surface protection of brass coated steel prior to rubber encapsulation and improved aged adhesion of vulcan-ized brass coated steel/rubber composites. It also pre-vents cord failure due to excessive corroslon during the use of the product, e~g.a a tire being 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 acrylo~
nitrile, polybutadiene and polyisopreneO
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~ where 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 wire protect the wire from deleterious effects of moisture (humidity) and o~idation~ i.e.~ improve factory storage life.
By the term "high-carbon" steel as used in the present specification and claims~ applicant is referring to what is known as carbon steel~ also called ordlnary steel~ also called straight carbon steel or plain carbon steel? e.g., American Iron and Steel Institute Grade 1070 high-carbon steel (AISI 1070). Such steel owes its proper- -ties chiePly to -the presence o~ 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 about 65 to 75 percent copper and 35 to 25 percent zinc, respectively.
The follo~ing examples contain illustrations of~
but do not limit the practice of the present in~ention.
The adhesion data was obtained on cable embedded in black loaded unvulcanized natural rubber which was then vulcan-ized~
Example 1 A drawn brass coated steel cable at room temper-~
5 ature was passed slowly (possibly at a speed of about 25 ~ , to 50 yards per minute) through a tube containing molten~ ;
benzotriazole (BTA). The cable was then subjected to an ultra high temperature to flash off the excess BTA. The,~, , initiaI adhesion of the treated cable to vulcanized carbon black loaded natural rubber was 37 kilograms.~ The corro~
sion resistance of the cable in a high temperature~ high humidit~ environment~ was rated excellent.

A tube of molten BTA was mounted on-a draw machine, ~A ho-t drawn brass coated steel filament as it e~ited the draw machine was passed through~a 3/4~inch'-`' ~' thickness of molten BTA at a speed of 900 meters per minute. `~ ; ' A ca~le prepared therefrom had an lnitial adhesion of ~0.4 and a wet adhesion of 40Ø Its corrosion~resistance was excellent., An untreated control had an initial adhesion of 59 and a wet adhesion (unvulcanized rubber soaked ln water before the cable was embedded therein) of 3~. The corrosion resistance was rated poor. ~ ' 3~ ; ~ ' A brass coated steel filament was~passed through a 12 inch tub~ of powdered BTA at a rate of 900 meters per minute after exiting from a draw machine. The filament was at a temperature of about 200 C. The powder temperature ' was varied from room temperature to 120 C. to 180 C. A
cable was prepared from the resultant filament and checked _9_ r~ ~

for adhesion.

Powder Tempera-ture Adhesion Corrosion toC ) Initial WetResistance Room Temperature 49 43 Excellent 5120 C. 41 31 Excellent 180 C. ~5 38~5 Excellent The untreated control for room temperature and 180 C. had initial and wet adhesion values of 57 and 29 respectively, The untreated control for 120 C. had ini-tial and wet adhesion values of 44 and 24. Therefore the treatment resulted in wet adhesion improvements at each temperature~
Once the cord is plated with the brass, treatment can begin. Treatment can occur with the reagents between the plating and drawing steps or between the drawing and stranding steps and even on the final cord prior to calen-dering, Where the treatment results in film formation~ lt is preferably accomplished ~er drawing slnce drawing will naturally destroy the film continuity.
An compound could have been substituted ~or BTA
type compounds, which complexes with the copper in the brass to ~orm an insolub~e film, i,e., insoluble in any of the envîronments to ~hich the material is to be exposed, These compounds include triazoles~ imidazoles and indazoles~
Such compounds include those compounds conforming to the structural formula recited earlier herein. The only re-quirement is that the agent be meltable.
Any of the previous working examples could have involved a subsequent heat treatment and/or exposure of the wire to water vapor.

Other materials which can be used, for example, to treat wire using -the present method are triethyl phos-phate and amyl nitriteO
While certain representative embodiments and details have been shown for the purpose of illus-trating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

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Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process of treating a brass coated steel filament which comprises treating said filament with molten benzotriazole subsequent to a drawing step for said filament and where the temperature of the wire is above the melting point of said benzotriazole.

2. The process of claim 1 where the treated filament is subjected to a water vapor treatment.

3. The process of claim 1 or 2 where the filament is in the form of a cord.