Coated filament and composite thereof with rubber

A filament, and optionally a cord of cabled filaments, as a composite of (A) a filament and/or cord of steel, (B) a brass and/or zinc coating thereon and (C) a undercoat comprised of selected compounds. The invention further relates to a composite of such filament and/or cord as a reinforcement with rubber.

FIELD OF THE INVENTION 
This invention relates to treatment of a filament or cord of 
metallic-plated steel, such as predominantly a brass and/or zinc-coated 
steel wire, and to the resulting treated article. It further relates to a 
composite of rubber and such treated article as reinforcement therefor. 
BACKGROUND OF THE INVENTION 
Vehicle tires, particularly pneumatic or semi-pneumatic tires, are often 
reinforced by means of cords consisting of twisted or cabled brass and/or 
zinc-coated steel filaments. Such tire cord is often composed of a high 
carbon-steel filament having a very thin layer of brass, such as alpha 
brass, sometimes with the brass coating itself also having a thin zinc 
layer thereon, or a ternary alloy addition, such as cobalt or nickel. The 
cord may be monofilament although it is more normally prepared by cabling 
or stranding several filaments together. Generally, the steel filament is 
prepared by coating with brass, such as by electroplating, then cold drawn 
and stranded and/or cabled to form the cord. 
Plated steel wire cords are generally subject to corrosion of the steel 
substrate and oxidation of the brass coating, particularly if improperly 
handled or stored prior to incorporation into a rubber composite which is 
ultimately shaped to a molded article such as a pneumatic tire. Corrosion 
and oxidation can also be caused from other external agents or elements in 
an environment where the cord is a reinforcement such as in a rubber 
composite. Such corrosion and oxidation can result in poor adhesion 
between the cords and rubber which, in turn, can result in a failure of 
the reinforcement in the rubber composite or can cause degradation of a 
good adhesive bond during service life of the composite. 
Clean, untreated brass coated steel wire will normally have a reasonably 
good initial adhesion to the adjacent rubber. However, the adhesion 
typically will drop with time, particularly with aging due to heat, stress 
and/or chemical degradation or corrosion effects. Various additives 
described in the literature have in certain instances shown improved 
initial and aged adhesion. Yet such additives have often not proved 
entirely satisfactory either due to required complexities in their 
preparation or the mixed results realized from their use. Indeed, some 
types of aging would show improved adhesion and others apparently no 
improvement. It is therefore desirable that an agent, or agents, be found 
which protect(s) the bare metallic surface and does not adversely affect 
initial adhesion to any great degree, while at the same time, improving 
aged adhesion of a vulcanized composite. Further, it it particularly 
desired that such adhesion enhancing process be relatively simple and 
economical. 
Various chemical reagents have been proposed and/or used to treat such 
coated wire for the purpose of protecting against corrosion and oxidation. 
For example, benzotriazole, tolyltriazole and naphthyltriazole, have been 
taught to be useful. Such reagents have sometimes been taught to be 
applied as a coating to the surface of a filament or cord by various 
methods, such as by immersing the wire in a water solution of the reagent, 
by treating the wire with the reagent in its molten form, or by exposing 
the wire to the reagent in its vapor phase. 
Although the mechanism is not clearly understood, apparently such reagents 
physcially or chemically combine with the wire or wire coating to offer 
protection against oxidation and/or corrosion while often maintaining 
adhesion to a rubber substrate. Perhaps the reagent coating on the wire 
affects the sulfur/copper bond which might be formed between the wire and 
the adjacent rubber in a rubber composite which is reinforced with the 
wire. 
It is important to appreciate, that reagents are continually being sought 
for the purpose of preventing or retarding oxidation and/or corrosion of 
the wire, particularly while the wire is in the form of reinforcement in a 
sulfur-cured rubber composite. In these regards, it is considered that it 
is not enough that reagents which are known or taught or thought to be 
corrosion inhibitors be arbitrarily chosen. This is because that such 
reagent, while it may be thought to be useful as a corrosion inhibitor, 
must also not degrade the adhesion between the cord and the rubber. 
Indeed, it is desired that such reagents actually enhance the cord to 
rubber bonding or adhesion. 
For example, if it were only desired to prevent the corrosion of the wire, 
then it could be treated with the material such as vasoline, mineral oil 
or lacquer. However, it is surely readily recognized that such materials 
would be expected to seriously inhibit adhesion of the cord to rubber. 
Therefore, it is desired to provide a treatment for steel filament or cord 
which has been previously metal or metal alloy plated such as with alloys 
containing predominantly brass and/or zinc, and to the resultant treated 
article. It is further desired to form a composite of rubber and such 
filament or cord as a reinforcement. It is also desired to provide 
articles containing such reinforcements such as pneumatic and 
semi-pneumatic tires, as well as industrial hose and industrial belts such 
as power transmission and conveyor belts. 
DISCLOSURE AND PRACTICE OF THE INVENTION 
In accordance with an aspect of this invention, a filament, optionally in 
the form of a multiple of filaments cabled together as a cord, is provided 
as a composite of (A) a filament and/or cord of steel, (B) a 
microscopically porous metallic coating thereon, comprised primarily of 
brass and/or zinc, and (C) an overcoat composed of (1) at least one 
compound selected from the grouping consisting of those of the following 
formulae: 
##STR1## 
(2) at least one diphenyl carbazide or 1,5-pentamethylene tetrazole, (3) a 
synergistic mixture comprised of 100 parts by weight benzotriazole and 
about 10 to about 150, preferably about 25 to about 100, parts by weight 
of a compound having the formula: 
##STR2## 
(4) a synergistic mixture of (i) 100 parts by weight benzotriazole or 
substituted benzotriazole of Formula (I) and, correspondingly, (ii) about 
20 to about 75, preferably about 25 to about 50 parts by weight of at 
least one of dithiooxamide, 1,2,4-triazole, 2,1,3-benzothiadiazole and/or 
about 0.5 to about 10, preferably about 1 to about 8 parts by weight of at 
least one compound having the formula: 
##STR3## 
where R is a radical selected from at least one of nitro-, and saturated 
alkyl radicals containing from 1 to 10, preferably 1 to 6 carbon atoms, 
where R' is selected from radicals of R and hydrogen, where R" is a 
radical selected from at least one of --NH--C.sub.6 H.sub.5 and 
--CS--NH--NH--C.sub.6 --H.sub.5, radicals, where X is a radical selected 
from at least one of sulfur, oxygen and ammonium, where X' is a radical 
selected from at least one of saturated alkyl radicals containing 1 to 10, 
preferably 1 to 6 carbon atoms, alkyl substituted or unsubstituted phenyl, 
benzyl or cyclohexyl; where M is a radical selected from at least one of 
alkali metal radical, preferably sodium or potassium, a polyvalent metal 
selected from at least one of copper and zinc, or an alkali earth metal, 
preferably calcium, or hydrogen; where Y is a radical selected from at 
least one of hydrogen and hydroxyl radicals, and where Q is a radical 
selected from at least one of hydrogen or --SM radicals. 
Preferably, the radicals of R, R' are selected from methyl, ethyl and nitro 
radicals. The alkyl substituted radical of X' is more preferably a hexyl 
radical. X is preferably selected from sulfur and oxygen radicals and M is 
preferably an alkali metal, particularly sodium or potassium. 
Preferably Y is a hydroxyl radical and Q is a hydrogen radical. 
In further accordance with this invention, a composite is provided composed 
of sulfur-cured rubber and containing therein, said treated filament or 
cord as reinforcement therefor. 
In additional accordance with this invention, such a rubber reinforcement 
composite is provided in which a portion of the treatment agent or 
material is contained in the rubber. 
In further accordance with this invention, a pneumatic rubber tire is 
provided having a generally toroidal shape and comprised of a tread, 
spaced inextensible beads and sidewalls connecting said beads and tread 
with a supporting carcass therefor, where said carcass is a composite of 
sulfur-cured rubber containing therein said treated filament or cord as 
reinforcement therefor. 
In the practice of this invention, representative of various compounds of 
Formula (I) are 5-nitrobenzotriazole and 5-methylbenzotriazole. 
Representative of the various compounds of Formula (II) are 
2-mercaptobenzothiazole, 2-mercaptobenzothiazole sodium salt, 
2-mercaptobenzooxazole, 2-mercapto-6-nitrobenzothiazole, 
2-mercapto-6-methylbenzothiazole, benzoxazole and benzothiazole. 
Representative of compounds (III) are diphenylthiacarbazone and 
1,3-diphenyltriazene. 
A representative compound of Formula (IV) is 1,2,3-benzothiazine-4(3H)one. 
Representative compounds of Formula (V) are 1-hydroxybenzotriazole, 
6-methylbenzotriazole and 5-nitrobenzotriazole. 
Representative of the various compounds of Formula (VI) are potassium 
hexylxanthate, potassium ethylxanthate. 
Preferred combinations are 1-hydrobenzotriazole with benzotriazole; 
potassium or sodium hexylxanthate with benzotriazole with or without a 
small amount of water vapor; 5-nitrobenzotriazole with benzotriazole; and 
benzotriazole with a small amount of water. 
In the practice of this invention, the coating can be applied by various 
methods such as by aqueous dip, non-aqueous dip, aqueous/non-aqueous dip, 
vapor deposition, vapor deposition plus a solvent which can be aqueous or 
non-aqueous, step-wise addition, such as by first solution deposition and 
then vapor deposition. 
The aqueous dip method can be accomplished by dissolving the coating 
material(s) in water and passing the wire filament or cord through it at 
about 30.degree.-80.degree. C. (liquid temperature) to provide the desired 
thickness of protective coating. The aqueous dip can be comprised of, for 
example, one part by weight of water and one to five parts by weight of 
the coating material(s). 
The invention can be accomplished by a non-aqueous dip by passing the wire 
or filament through an alcohol solution comprised of, for example, 100 
parts by weight methanol and/or isopropanol and about one to five parts by 
weight coating material(s). 
The material can be applied by an aqueous/non-aqueous dip which can be 
composed of, for example, 50 parts by weight water, 30-70 parts by weight 
ethanol and/or isopropanol and one to five parts by weight coating 
material. 
The material(s) can be deposited on the filament and/or cord by a vapor 
deposition by, for example, passing the wire filament or cord through a 
vapor of the coating material caused by heating the material above its 
boiling point. This can also include an additional, as a simultaneous or 
sequential, water vapor treatment. 
The material can be applied in a molten form to the filament and/or cord by 
heating the material above its melting point and passing the wire filament 
or cord through it. 
The material can be applied by a combination of vapor deposition and 
solvent deposition (aqueous and/or non-aqueous) by the following method: 
Heat 4.7 grams of benzotriazole with 0.3 grams of potassium hexylxanthate 
in 100 milliliters of water in a container and heat to 100.degree. C. 
using nitrogen as a vapor carrier gas. 
The material can be applied by a step-wise addition, such as first by vapor 
and then by solution by the following technique: 
Apply benzotriazole in the vapor state at about 160.degree. C. then dip 
into 60.degree. solution of 0.2 percent of potassium ethylxanthate. 
Alternately, at least a part of the material may be mixed directly with the 
rubber and applied to the filament or cord or applied to both the rubber 
and cord, although it must be recognized that some materials will act 
better than others as adhesion aids, since some materials have been 
observed to clearly provide better adhesion of cord to rubber when applied 
directly to the cord. 
The brass or zinc coating of a typical brass, zinc, or brass-zinc coated 
steel cord is microscopically porous, thereby exposing small areas of 
steel surface to any surrounding environment. It is believed that agents 
herein interact with copper in such a brass coating to form a polymeric 
complex of agent plus copper and/or zinc. This polymeric complex is 
insoluble in most solvents and serves as a protective barrier to any 
environmental degradation of the underlying brass. 
It is not reasonably practical to describe within rigid limits the weights 
of polymeric complex to be formed or the amounts of agent to be applied 
much less the thickness of the respective barrier layers. Optimum 
thicknesses and amounts are a function of variables such as nature of the 
brass, zinc, or brass-zinc surface, viz., mode of deposition, thickness of 
initial oxide layers, magnitude of residual stresses, copper content, 
brass thickness, as well as the reactivity of the rubber-vulcanization 
system. However, as very general guidelines, but not in any sense 
limitations, the total barrier layers should nominally be in the range of 
about 10 to about 100 angstroms. 
One should consider the fact that "over protection" of the cord with the 
treatment agents can possibly result in a cord, which, while resistant to 
corrosion, may not have desired adhesion pooperties. Therefore, care 
should be taken that excessively high levels of the agent or material in 
the rubber or on the cord not be used. For example, a relatively thick 
coating of a 50/50 mixture of benzotriazole and potassium hexylxanthate 
has been observed to give good oxidation protection to bare brass coated 
steel tire cord. However, although it was observed that initial adhesion 
to rubber was very good observed aged adhesion was very poor unless rubber 
compounding recipe changes were instituted to account for the higher agent 
levels on the cord. 
Therefore, in view of such observations and the fact that compounds 
naturally vary in activity, statements herein relating to levels and 
amounts of treatment materials are to be considered as guidelines and not 
strict limitations in most cases. 
The practice of the present invention has been observed to result in 
increased surface protection of brass-coated steel prior to rubber 
encapsulation and improved aged-adhesion, in many cases with improved 
initial, i.e., original adhesion of vulcanized brass-coated steel/rubber 
composites. 
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 and can be 
compounded with conventional ingredients such as carbon black, zinc oxide, 
stearate or stearic acid, anti-degradant, sulfur, etc. However, as recited 
earlier, the effect of the agents used in this invention on vulcanization 
systems should be considered and the vulcanization system adjusted 
accordingly. The steel wire described in this invention relates generally 
to 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 high-carbon 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. 
Brass relates to compositions in which the major component is alpha brass, 
i.e., which contains from about 62 to 75 percent copper and 38 to 25 
percent zinc, respectively. 
The practice of this invention is further illustrated by reference to the 
following example which is intended to be representative rather than 
restrictive of the scope of the invention. Unless otherwise indicated, all 
parts and percentages are by weight.

EXAMPLE 1 
Rubber compounds, identified herein as compounds A and B, were prepared for 
the purpose of testing brass-coated steel wire which have been treated 
with the reagents used in this invention. The rubber compounds were mixed 
by conventional techniques according to the following recipe shown in 
Table 1. 
TABLE 1 
______________________________________ 
Parts by Weight 
Compound A B 
______________________________________ 
Natural rubber 100 100 
Stearic acid 2 2 
Zinc oxide 10 10 
Amine antioxidant 1 1 
Sulfur 3 5 
Sulfonamide-type accelerator 
1 1 
Cobalt Compound 3 1 
Carbon black 55 55 
______________________________________ 
The treated cord samples according to this invention were evaluated by 
potentiostat, by hydrogen embrittlement testing and by a rubber adhesion 
test. 
The potentiostat can be described as electrochemical technique that can 
yield comparative information on corrosion rates. 
The hydrogen embrittlement test can be described as applying a DC (direct 
current) current to a sustained loaded wire in a one normal sulfuric acid 
solution and measuring the time to failure due to absorption of hydrogen. 
The rubber adhesion test can be described by embedding wire between two 
layers of compounded rubber, curing the rubber, and then measuring the 
force required to pull out the wire from the rubber. 
Static adhesion was measured in the standard manner (ASTM Designation D 
2229-73 "Standard Method of Testing for Adhesion of Vulcanized Rubber to 
Steel Cord"). 
Adhesion tests were applied to composites of the treated cord and rubber, 
(1) after a 35-minute cure at 311.degree. F., (2) after immersing the 
cured composite for 96 hours in salt water at 194.degree. F., (3) after a 
20-day aging uncured green block at 90 percent humidity at 98.degree. F., 
and (4) after 6 hours steam aging at 248.degree. F. of the cured 
composite. 
TABLE 2 
______________________________________ 
Hydrogen Embrittlement Test Applied 
Rubber Method of Result of 
Reagent Component Application 
Test Applied.sup.1 
______________________________________ 
No treatment A -- 55 sec 
(Control) 
BTA.sup.2 A aqueous dip 
72 sec 
BTA + hexylxanthate 
A aqueous dip 
176 sec 
______________________________________ 
.sup.1 In the hydrogen embrittlement test, the longer the time to failure 
the better the effect of the treatment. 
.sup.2 Benzotriazole. 
TABLE 3 
______________________________________ 
Polarazation Test Applied 
Rubber Result of 
Reagent for Com- Method of Test Applied.sup.1 
Treating wire 
ponent Application .mu.A/cm.sup.2 
______________________________________ 
No treatment A -- 83 
BTA A aqueous dip 13 
BTA + diphenylthio- 
A non-aqueous dip 
6 
carbazone 
No treatment A -- 88 
BTA A vapor (solid) 
39 
BTA + ethylxanthate 
A vapor (aqueous 
30 
soln) 
2-mercaptobenzo- 
A vapor (solid) 
19 
thiazole 
______________________________________ 
.sup.1 .mu.A/cm.sup.2 means micro amperes per square centimeter. 
TABLE 4 
______________________________________ 
Humidity Aging Test Applied.sup.1 
Rubber 
Reagent for Com- Method of Adhesion 
Treating Wire ponent Application 
Retention % 
______________________________________ 
No treatment A -- 57% 
(Control) 
5-nitrobenzotriazole 
A aqueous/non- 
61% 
aqueous dip 
hydroxybenzotriazole 
A aqueous dip 
48% 
BTA + hydroxybenzo- 
A aqueous dip 
66% 
triazole 
2-mercaptobenzo- 
A aqueous/non- 
62% 
xazole aqueous dip 
______________________________________ 
.sup.1 Humidity aging is 20 days. 
TABLE 5 
______________________________________ 
Salt Water aging Water Test Applied.sup.1 
Reagent for Rubber Method of Adhesion 
Treating Wire 
Component Application 
Retention % 
______________________________________ 
No treatment A -- 66% 
(Control) 
BTA A vapor (from 
68% 
aqueous soln) 
BTA + hexylxanthate 
A vapor (from 
92% 
aqueous soln) 
______________________________________ 
.sup.1 Emersion in Salt Water is 96 hours at 90.degree. C. 
TABLE 6 
______________________________________ 
Humidity Aging Test Applied 
Reagent for Rubber Method of Adhesion 
Treating Wire 
Component Application 
Retention % 
______________________________________ 
No treatment B -- 71% 
(Control) 
BTA B vapor (from 
84% 
aqueous soln) 
BTA + hexylxanthate 
B vapor (from 
90% 
aqueous soln) 
2-mercaptobenzo- 
B vapor (from 
58% 
thiazole solid) 
______________________________________ 
TABLE 7 
______________________________________ 
Salt Water Aging Test Applied.sup.1 
Reagent for 
Rubber Method of Adhesion 
Treating Wire 
Component Application Retention % 
______________________________________ 
No treatment 
B -- 58% 
(Control) 
diphenylthio- 
B non-aqueous dip 
67% 
carbazone 
______________________________________ 
.sup.1 Emersion in Salt Water is 96 hours at 90.degree. C. 
TABLE 8 
______________________________________ 
Salt Water Aging Test Applied.sup.1 
Reagent for 
Rubber Method of Adhesion 
Treating Wire 
Component Application Retention % 
______________________________________ 
No treatment 
A -- 59% 
(Control) 
BTA A aqueous dip 62% 
diphenylthio- 
A non-aqueous dip 
82% 
carbazone 
BTA + dithio- 
A non-aqueous dip 
68% 
oxamide 
______________________________________ 
.sup.1 Emersion in salt water is 96 hours at 90.degree. C. 
TABLE 9 
______________________________________ 
Salt Water Aging Test Applied 
Reagent for Rubber Method of Adhesion 
Treating Wire 
Component Application Retention % 
______________________________________ 
No treatment 
B non-aqueous dip 
36% 
(Control) 
BTA B non-aqueous dip 
41% 
BTA + 1,2,4-tri- 
B non-aqueous dip 
67% 
azole 
BTA + 1-hydroxy- 
B aqueous dip 49% 
benzotriazole 
______________________________________ 
.sup.1 Emersion in salt water is 96 hours at 90.degree. C. 
TABLE 10 
______________________________________ 
Salt Water Aging Test Applied.sup.1 
Reagent for Rubber Method of Adhesion 
Treating Wire 
Component Application Retention % 
______________________________________ 
No treatment 
B -- 53% 
(Control) 
diphenylcarbazide 
B non-aqueous dip 
68% 
1,5-pentamethylene- 
B non-aqueous dip 
69% 
tetrazole 
______________________________________ 
.sup.1 Emersion in salt water is 96 hours at 90.degree. C.