Note: Descriptions are shown in the official language in which they were submitted.
1 1 6267~
~ his invention relates to the building or manufacturing of steel
cord reinforced belted ply rubber products and more specifically poly ply
pneumatic tire casings primarily used in automotive vehicles.
More particularly, according to one aspect this invention relates
to an improved ply skim stock formulation involving two additives which when
used together in minor quantities enhance the adhesion of the skim stock for
the brass plated steel reinforcing cords normally calendered in a sandwich
between layers of skim stock to make up the belted plies used in building
pneumatic tire casings.
Specifically, this invention provides a combination of additives
in the ply skim stock, when used as described, act synergistically to enhance
adhesion between rubber skim stock and the brass plated steel reinforcing
wires. ~he said combination consists essentially of not materially greater
than about 3.0 parts preferably not greater than 2.5 parts of a nickel or co-
balt soap of an oil soluble oreanic acid.
According to an aspect of the present invention there is provided
a composition of rubber having improved adhesion to metal which comprises
for each 100 parts by weight of rubber
a) a triazole in an amount not exceeding 0.5 parts by weight and
b) a substantially oil soluble metal compound of an organic acid
in an amount not exceeding 3.0 parts by weight, wherein the metal of the
metal compound is selected from the group consisting of nickel, cobalt and
combinations of nickel and cobalt.
A composition of rubber having improved adhesion to metal may com-
prise at least about 0.01 part by weight for each 100 parts by weight of
rubber of at least one triazole selected from the group consisting of benzo-
triazole and lower alkyl derivatives of benzotriazole and at least about 0.5
parts by weight for each 100 parts by weight of the rubber of at least one
-- 1 --
'~
i.
i 3 626~4
substantially oil soluble metal compound of an organic acid wherein the
metal is selected from the group consistin~ of nickel, cobalt and combina-
tions of nickel and cobalt.
The triazole may be an aromatic triazole such as, for example7
benzotriazole, tolyltriazole or mixtures thereof.
The present invention also provides a rubber ply skim stock an-
chored and reinforced by means of brass plated steel wire cords in said ply
useful in the manufacture of multiple ply tires, characterized in that the
skim stock comprises the synergistic combination of a triazole and a cobalt
or nickel soap of an oil soluble organic acid wherein in one hundred parts
by weight of the rubber in said skim stock said triazole is present in an
effective amount which does not exceed 0.5 parts by weight and said soap is
present in an effective amount which does not exceed about 3.0 parts by
weight. Preferably the soap is a cobalt salt of an oil soluble aliphatic
acid. Preferably the triazole is tolyltriazole.
According to the present invention triazole may be present in an
amount not exceeding 0.2 parts by weight and the soap may be present in an
amount not exceeding 2.5 parts by weight.
Also according to the present invention the soap may be present in
an amount of from about 1.0 part to less than 3 phr and the triazole may be
present in an amount of from about 0.05 parts to not more than 0.5 phr in
the said skim stock.
According to another aspect of the present invention there is pro-
vided the method of increasing adhesion of bra~s plated steel reinforcing
cords integrally within tire cord ply skim stock which comprises masticating
in the skim stock formula prior to incorporation of said steel cords and vul-
canization of said ply about a multiple ply tire, a quantity but not more
than about 0.2 phr of a triazole and a quantity but not more than 3 phr of a
-- 2 --
1 1 ~2674
metal salt of an oil soluble organic acid where the metal is selected from
cobalt and nickel ions. The triazole may be benzotriazole and/or the alkyl
(e.g. lower) derivatives thereof and the metal salt may be a cobalt salt of
an oil soluble aliphatic organic acid.
By oil soluble organic acid is intended those acids commonly used
to manufacture oil soluble metal soaps or salts as are illustratively used
as catalysts to promote oxidation and polymerization of drying oils, as
driers in the paint and varnish industry. ~hese acids range from the strai~Pt
aliphatic acids having about 8 carbon atoms to about 22 carbon atoms, both
saturated and unsaturated. Also included are acids containing aromatic
groups of complex nature including as illustrative, naphthenic acids. Some
of these acids have been selected for use in rubber formulations. So far as
has been determined, the structures of the acid co~ponent is not critical,
only that it be compatible (soluble~ in hydrocarbon acids, drying acids,
etc., so as to provide intimate contact of the metal cation of the product
metal soap or salt with the rubber formulation. ~he other essential compon-
ent as indicated above should not be in excess of about 0.5 parts by weight
comprising a triazole, e.g. benzotriazole or an alkyl derivative, per hundred
parts of rubber (hereinafter sometimes identified as phr) in the ply. His-
torically, aliphatic long chain fatty acids have been used of themselves inrubber compounding and are suitable for the ends of this invention as a
source of oil soluble organic anion.
In recent year~ in the United States brass plated steel cords have
come into prominence as replacement for earlier organic cord material used
in both bias ply and radial ply construction. Concern has developed over
; the dangers inherent in steel belted tires should water and corrosion agents
associated therewith reach the surfaces of the reinforcing steel cords em-
bedded in the ply skim stock. It is known that under such physical condi-
-- 3 --
1 1 8267~
tions the surfaces of the brass coated steel cords corrode or rust progressively
from a point of any break in adhesion between ply stock and wire band. With
entry of water borne contaminants, the bond between the metal cord and skim
stock progressively deteriorates and adhesion is destroyed, much as a zipper
opens serially from a point of beginning. The United States Department of
Transportation has been openly concerned with the obvious danger.
It is known, for example, that Shemenski of Goodyear in German
Offenlegensschrift 2,611,761 of October 28, 1976 disclosed a process for treat-
ment of brass coated steel tire cords to increase adhesion. In that disclosure
reference is made to prior art where a mineral oil solution of a salt of a long
chain fatty acid and a very small amount of triazole (benzotriazole) were used
in a treatment (immersion) of the plated brass coated steel cord.
The Shemenski disclosure appears to suggest treatment of a clean brass
coated steel tire cord with, among other things, selected triazoles. The
steel cord is apparently treated with a complex polymer film-former consisting
of benzotriazole and anions selected from the group consisting of chromates,
nitrites, tungstates, molybdates, dichromates, arsenites and sulfites and
cations of a salt which contains these anions including cyclohexylamine, iron,
cobalt, nickel, tin or zinc. As the reference is understood, a single aqueous
solution containing all the additives is most efficient and economical.
United States Patent 3,413,227*discloses broadly that triazoles
are useful in synthetic polymers and polishes to inhibit corrosion.
German Offenlegensschrift 2,227,013 of Decmeber 13, 1973 (based on
a Yokohama Rubber Co., application) also relates to improvement of adhesion of
variously plated steel tire cords. It is also understood to suggest surface
*Issued November 26, 1969 to Geigy Chemical Corp.
!~ - 4 -
1 1 62674
treatment of the plated steel cords with an aqueous medium. The treatment is
said to be effective after exposure to high humidity of liquid water.
Coconut amine acetate, tallow amine salicylate in mineral oil and
aqueous triazoles in water are listed. The rubbers in which the treated wires
are embedded are shown to contain in one instance (Table 2) 10 parts of cobalt
naphthenate and 0.5 parts of methylbenzotriazole per 100 parts of rubber. Most
rubber stocks disclosed contain no oil soluble metals soaps, but all contain
methylbenzotriazole.
The objective of the reference patent permits long periods of time
between embedment of the plate steel cord in the unvulcanized rubber stock in
humid atmospheres and vulcanized thereafter of the aged stock without loss of
adhesion of the steel cords to the rubber ply stock.
United States Patent 3,849,433(1) discloses use of specific tetra-
hydrobenzotriazole derivatives as corrosion inhibitors for copper and copper
alloys (brass) and anti-aging agents or antioxidants.
United States Patent 3,367,907(2) is directed to the stabilization
of polyethylene polymers due to contact with copper by use of benzotriazole
referred to as azimido benzene which new nomenclature more stickly calls l,H-
benzotriazole.
The latter references are relevant to show use of various traizoles
in polymeric stocks of elastomeric value as useful to inhibit copper plated
steel cord corrosion.
(1) Issued November 19, 1972 assigned to Rhein - Chemie Rheiman GmbH.
(2) Issued February 6, 1968 assigned to Bell Telephone Labs.
- 5 -
7 1 6~G7 4
The following discloses the best known practice of the invention:
A series of ply skim stocks were prepared in which the variations
were only in the presence or absence of a cobalt (soap), the presence or absence
of a triazole (tolyltriazole was chosen for the study) and as to the treatment
of the brass (65 - 25% copper, remainder zinc) plated steel reinforcing cord,
whether treated with triazole or untreated and whether the steel
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i J 62674
cord was sub~ected to aging at higll humidity environment (containing a des-
sicant or siccative agent such as silica gel).
The basic poly skim stock formula or recipe selected for the tests
is considered relatively standard in the manufacture of pneumatic tire ply
stock. Manufacture of the green, uncured or unvulcanized, rubber formulas
followed standard mixing procedure using a Banbury mixer. The term "phr" as
used herein indicates the parts by weight of the named ingredient per hundred
parts by weight of the selected volcanization elastomer or rubber. Rubber is
used herein in a generic sense and is intended to include both natural and
synthetic rubbers.
All of the test formulas were made over the following schedules:
The Banbury water temperature was 150F and the rotor speed held at 45 rpm.
One hundred parts of rubber were weighed into the mixer and after
4 minutes, 2 parts of an anti-ozonate (Santoflex 13* of Monsanto: N-(1,3,
dimethylbutyl)-N-phenyl-P-phenlenediamine); 0.4 parts P.V.I.* (Pre-vulcaniza-
tion inhibitor, a proprietary Monsanto product being a blend of a sulfenamide
accelerator and an organic inhibitor or retarder). P.V.I.* imparts scorch
safety in later processing; 27 1/2 parts of a black pigmented rubber master
batch (N 330 HAF)* a high abrasion furnace carbon black; 1 part stearic acid;
and when a part of the test formula, 2.5 parts of a 16% cobalt containing oil
soluble metal soap (cobalt naphthenate). Sometimes these soaps are called the
metal salts of oil soluble organic acids such as naphthenic and octoic acids.
Manobond* C-16**(Manche~,Ltd.) has been used in illustrating specific formulas
identified herein. Tolyltriazole is representative of the azoles.
After four minutes of heavy shear in the Banbury, another 27 1/2
** (Manobond C-16 is stated to contain a compound of the formula (R-CO2-Co-0)3B
where R is a branched hydrocarbon chain having an average of 21 carbon atoms,
5 of which were in methyl radicals; R may have a value of 18 to 22.)
* Trade Mark
-- 6 --
~. .,
1 1 62674
parts of the black pigment master batch and ~ parts of naphthenic oil were
incorporated. Into the rubber next was milled 5 parts Crystex* Sulfur (a
Stauffer Chemical product containing a minimum of 90% amorphoruks allotrope
of sulfur and the remainder principally rhombic sulfur in 2 to 3 micron size
state insoluble in oil); 0.75 parts of Vulkacit* DZ, (Bayer-Germany, under-
stood to be N,N-dicyclohexyl-2-benzothiazyl sulfenamide, and after ten minutes
the mill is cleaned and dumped. The temperature was recorded at the end of
the mixing time.
In all the examples produced for test the stocks handled well,
processed normally and the temperature before dumping was 275F. These ex-
amples are summarized in the following "Summary Table".
1 ~ 62674
SUMMARY TAB_
PLY SKIM STOCK FORMVLATIONS
TEST BLOCKS VULCANIZED
Material Blank ControlExp. 1 Exp. 2 Exp. 3
Natural Rubber 100.0 100.0 100.0 100.0 100.0
N330 (HAF) Black 55.O 55.0 55.0 55.0 55.0
Naphthenic Oil 4.0 4.0 4.0 4.0 4.0
Zinc Oxide 6.0 6.0 6.0 6.0 6.0
Stearic Acid l.O l.O 1.0 l.O l.O
(Metal Soap*) --- 2.5 --- ___ ___
Santoflex 13 2.0 2.0 2.0 2.0 2.0
COBRATEC TT-100$ ** --- --- 0.2 0.2 0.5
TT-100 Treated
Steel Cord --- --- No Yes No
Crystex Sulfur 5.0 5.0 5.0 5.0 5.0
Vulkacit DZ 0.75 0.75 0.75 0.75 0.75
P.V.I. 0.40 0-40 0.40 0 40-
174.15 176.65 174.35 174.35 174.65
SUMMARY TABLE CO~TINUED
MaterialExp. 4 Exp. 5 Exp. 6 Exp. 7 Exp. 8
Natural Rubber 100.0 100.0 lOO.0 100.0 100.0
N330 (HAF) Black 55.0 55.0 55.0 55.0 55.0
Naphthenic Oil 4.0 4.0 4.0 4.0 4.0
Zinc Oxide 6.0 6.0 6.0 6.0 6.0
Stearic Acid 1.0 l.O 1.0 1.0 l.O
Metal Soap*) --- 2.5 2.5 2.5 2.5
Santoflex 13 2.0 2.0 2.0 2.0 2.0
COBRATEC TT-100~ 0.5 0.05 0.5 0.2 0.2
TT-100 Treated
Steel Cord Yes No Yes No Yes
Crystex Sulfur 5.0 5.0 5.0 5.0 5.0
Vulkacit DZ 0.75 0.75 0.75 0.75 0.75
P.V.I. 0.40 0.40 0.40 0.40 0 40
174.65 176.60 176.60 176.85 176.85
* Manobond C-16 (Cobalt soap of long chain oil soluble organic acid.)
Refers to totyl triazole.
** Trade Mark
-- 8 --
~ 1 6~674
One aliquot portion of each batch was subJected to standard rhe-
ometer testing according to ASTM D-2084 standards at 290F, using 3 of arc
in the conical head, 100 cpm (cycles per minute), MPC Dyes (micro production
control dye) in the press, 20 seconds to preheat and a 60 minute test scan.
Time torque curves were automatically plotted as a data source on graph
paper.
A second aliquot portion was used on unaged brass plated steel
cord, 12 steel wire cords are used in each test block. The cords were in-
corporated into the unvulcanized test rubber stocks by calendqring the test
portions and forming a compressed sandwich of the steel cord strands in the
rubber matrix. Each set of cords in the test blocks were then vulcanized
in place at optimum cure as determined by rheometer (Monsanto) data at 290F.
Standard adhesion tests as in ASTM D-2229 were performed, and the data
recorded. Additionally, sets of wires vulcanized in skim stock test strips
were aged for seven (7) days at 70~ to 80% R.H. Comparative sets not so aged
were compared as reported in Table II.
In the tests herein identified as "Blank" or "B", there was no oil
~oluble organic cobalt soap or salt, nor tolyltriazole and the steel was not
treated with triazole. The "Control" of C skim stock contained a standard
amount of cobalt soap or salt of an oil soluble organic acid and the steel
cord was not triazole treated. Experiment 1 had no cobalt soap but 0.2 phr
of tolyltriazole. The steel cord was not treated. Experiment 2, no cobalt
soap, but the wire was tolyltriazole treated. Treatment consists of immers-
ing brass coat~d steel wire in a 0.2% by weight triazole in water solution at
140F for two minutes. Wire loops are withdrawn, rinsed with distilled
water, dried for 1 hour in an oven at 100F, and stored in a dessicated
atmosphere for test. Experiment 3 was identical with Experiment 1 except
the amount of triazole was increased to 0.5 parts, the wire was not treated.
_ g _
,:
1 1 62674
Experiment 4 was identical to Experiment 3, but the wire was triazole
treated. Experiment 5, the amount of the cobalt soap was 2.5 parts; the
triazole was reduced to only 0.05 parts and the steel wire cord was not
triazole treated. Experiment 6 was identical to Experiment 5 except the
wire cord was triazole treated. Experiment 7 had increased triazole in the
skim stock of 0.2 part or four times as ~uch as in Experiment 5, but was
otherwise identical to Experiment 5. Experiment 8 was identical to Exper-
iment 7, except the wire cord was treated with triazole ttolyltriazole).
All wire surface treatment, with tolyltriazole were the same. The above
data and test results are set out in the Tables which follow.
The wire adhesions were separately determined on each of the thir-
teen cords of brass plated steel wire (5 separate strands were in each cord
bundle) both aged and unaged and the average figure is reported, along with
the high and the low values in each of the foregoing adhesion experiments.
To facilitate the essential comparisons, the observed readings are
set out in the following Tables I and II. In order that concepts involved
in this disclosure may be fresh in mind, definitions below may be helpful.
In rheometer cure and adhesion tests (see ASTM D-2084 and D-2229,
respectively) and from data inherent therein the following factors are to be
found:
Minimum torque or ~ is the lowest point on the curve and is be-
fore vulcanization begins. The maximum torque or ~ is the maxi~um torque
developed during the sixty minutes of the test run. The scorch time is de-
noted by tS2. As vulcanized or crosslinking begins, the foot pounds of
torque increase. The time in minutes from ~ to a two number point rise in
torque defines the "scorch time". This time is representative of the safety
period available in commercial ~llcanization operations and it is important
that it not be materially shortened. It is desirable to have a relatively
-- 10 --
1 3 6267~
long time period to onset of the defined two point rise in torque. Ti~le to
90% of maximum torque tc (90) is recorded. While the selection of 90% is
arbitrary, optimum physical properties are developed in the test specimen
by this time. It is also desirable that the curve flatten out substantially
parallel with the time axis, as this flat characteristic of the curve demon-
strates control over the final cure quality that it can be held uniform from
batch to batch. This control data where collected of record then allows
knowledge of a predictable state of cure. It is useful in a study of addi-
tives, as additives to ply skim stock studies determine influence of use of
the additives on the final rubber tire quality.
In t}le wire cord pullout tests used in measuring adhesion of the
ply wire cord, the pullout forces essentially change with time after vulcan-
ization. It is desirable, therefore, to keep this time uniform in compar-
ative testing. Wire adhesion is reported in the pounds of force required to
pull each one of the thirteen steel wire cords individually from the vulcan-
ized rubber test block.
The following tables present the various test data and identify
briefly the foregoing skim stock formulation identity.
-- 11 --
i ~ 6267
o
~ O O u~ u~ t- a
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E~ ~ r~ ~ ~ r~
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o ~o a .~ ~o '
E'l r-i O C~ CU N N g.
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c~ ~ ~ ~ ~ o 8 o o ~ o h ~ .
I ~ ~ h ~ ~ cq ~ ~ ~o h ~ h ~ ~ h
R ~ r~ r~
h ~ ~ q *
m æ ~ ~ æ d æ ~ ,,q Z; h ~ æ ~ ~
æ
~ c~ r1 ~
æ
-- 12 --
i 1 ~2674
'~
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h cO r-ltr~ co C'J
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X~ ~lo ou~XO Xo XO
cq m u~
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~ tD ,!~ ~I bD b~ rl O ~ h
rl ~ El C) O
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0 0 ~ h 0 0 0 0 rl ~ O O P
h
a~ o o O,!~t O O O O O O,q o o
E~ m æ ~ æ ~,I z ~ c~J z ~J ~ ~ z ~ o
i ~ 62674
,_
,~ ~ ~ o ~ ~
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rl ~ 0~ N 0
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1~ I 11~
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H I Fl ~I b O ~0 0 C~
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t~ ~ O ~O
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~;ZS U~ 1- CJ U~ N ~D N r--N CO N
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bq ~ H
u~ a~ I~ Ir~ t~
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~ ~ O U~ O O O ~ O
E-l ~ u~ * c~ ~ o ~ * tq o c~
-- 14 --
i 1 62~7~
As Table II is ~irected specifical~y to the adhesion tests, an
analysis of the data there presented is of specific i~portance.
Example 6 is ~irst noted as the adhesion i5 the poorest ~alue on
the unaged sample. It will be found that the skim stock here i6 identical
to that in Example 5, except that the unaged sample was pretreated with tri-
azole. Example 5, on the other hand, is outstanding in that the unaged
sample required 126.2 lbs. of pull to break the rubber-wire adhesion in the
unaged sample and 114.6 lbs. with the aged sample, a loss of 12 or 9.52%.
Example 6, ~arying only in the pre-treatment of the sa~ple witb triazole,
lost 90 lbs. of adhesion force or 71.4% of its unaged adhesive strength
throuBh pre-coating the wire with the triazole, when the skim stock con-
tained the synergistic combination of metal soap and triazole alone, as in
Example 5.
It is also obser~ed that the aged sample in number 6 is practically
identical in value to the unaged sample, no apparent effect, for better or
worse. Howe~er, the adhesion in both cases is very poor.
Returning to Example 5, we find not only the highest adhesion of
wire to skim value in the unaged sample, but also in the aged sample, with a
1088 upon aging o~ 9.52%. Example 7, identical in composition to Example 5~
except it has 0.20 parts triazole, about 4 times the quantity, has about 11%
less adhesion resulting in the unaged sample, but 7 1/4Z less adhesion after
aging. This suggests that the amount o~ triazole used in the skim stock is
critical and while 0.2 part (phr) in the synergistic combination is not max-
imum, further attention should be given to other cited factors in the skim
stock, as may be shown and more clearly apparent from the rheometer tests
(~able I).
Referring to Table I, it is observed that Example 5 and Example 7
provide no unusual data, except it is noted that the scorch time is somewhat
- 15 -
~ 3 ~2674
reduced over the Blank. This sugeests that one or both the additives are
adversely affecting the safe or scorch period. The Control, which contains
the oil soluble, organometallic soap only has an extremely shortened scorch
time of the order of about 39% decrease over the Blank Ex. 1 contains no
metal soap but some T~ (tolyltriazole) and has lost only about 5% of scorch
time t9.0 to 8.5). However, Ex. 1 (Table II) is over 48% poorer in adhesion
(unaged) and over 22% poorer in adhesion that the (aged) wire tests. Atten-
tion having been called to the rheometer data of Table I as to Ex. 1, it is
also startling to find the time to 90% cure for the Blank. Ex. 1 containing
no (metallic soap), and also Ex. 3 which contains no metallic soap as having
90% cure-times over 125% greater than when the metallic soap is in the syn-
ergistic combination (with the triazole) as in Examples 5 and 7. One also
observes in Table I that the Examples 5 and 7 have gained back most of the
safety period scorch time lost between the Blank (no metal soap) and the Con-
trol (metal salt alone) was used. Note Examples 5 and 7 both contain the
combination and demonstrate a desirable recovery in scorch time and a min-
imal effect on cure time.
There are several other observations and conclusion~ of consider-
able intere~t that can be formed upon study of the data presented in the
Tables which suggest other areas of exploration which may be of value. We
leave these for further study and consideration.
One should preferably avoid use of brass plated reinforcing wire
treated with triazole, for in all observed instances where brass plated
steel cord was exposed to the triazole prior to incorporation in the green
or unvulcanized skim stock, the skim stock adhesion to the plated wire after
vulcanization was not above 44 pounds (See Ex. 4, aged wire). Such wire
treatment in the practice of this invention does not appear to be advan-
tageous ~
- 16 -
i 1 62674
In summary, one finds that less than 3 parts by weight of an oil
soluble me~al compound of an oreanic acid wherein the metal is selected from
cobalt, nickel and mixtures thereof per 100 parts of rubber stock and from
trace amounts to not ~ore than 0.5 parts of a triazole and preferably less
than 0.2 parts of triazole in combination with selected metal soaps or salts
of oil soluble fatty acids in an amount but not greater than about 2.5 phr
produces an unexpected increase in adhesion of the brass plated steel tire
cord when part of the original skim stock recipe (after vulcanization).
Amounts within the preferred synergistic combination of triazole (e.g. benzo-
triazole and the lower alkyl derivatives thereof) ana metal soaps are also
found not to interfere with the scorch time and the cure time. Xowever, when
larger amounts of the named additives are used, the latter values, critical
to practical application and adhesion increase may be materially altered.
An example is where the metal soap component is from about one part
to less than about 3.0 phr and the triazole is from 0.05 parts to not m~re
than 0.5 phr in the said skim stock.
Specifically, the quantity of triazole is not more than about 0.2
phr and the quantity of metal salt of an oil soluble organic acid where the
metal is selected from cobalt and nickel ions is not more than 3.0 phr.
~he present invention also relates to a pneumatic vehicle tire con-
taining rubber, filler, curing agent, brass-to-rubber bonding agent other
than cobalt, cure accelerator, carbon black and zinc oxide, the tire being
reinforced at least in part with brass plated steel cord, and characterized
by the presence of an effective amount of an aromatic triazole in the rubber
surrounding the steel cord.
The present invention further relates to a pneumatic vehicle tire
containing rubber, filler, curing agent, brass-to-rubber bonding agent other
than cobalt, cure accelerator, carbon black and zinc oxide, the tire being
- 17 -
1 3 62674
reinforced at least in part with brass plated steel cord, whereln the im-
provement comprises the presence of up to 0.5 phr of an aromatic triazole
in the rubber surrounding the steel cord.
The triazole may be selected from the group consisting of benzo-
triazole and totyltriazole.
The tire may include the presence of effective amounts of a rub-
ber-to-brass adhesion promoter containing cobalt in the rubber surrounding
the steel cord, preferably including the presence of up to 2.5 phr of the
adhesion promoter containing cobalt. An antioxidant may be present in the
rubber surroundine the steel cord.
- 18 -
