Note: Descriptions are shown in the official language in which they were submitted.
-~ GT-1980
1 160~08
Heat and Humidity Resistant Steel Cord
Reinforced Rubber C~mposite
m e invention relates to vulcanized rubber reinforced with
bright steel cord.
The problem of corrosion of bright steel wire and the
consequent loss of adhesion between steel wire and rubber in
steel wire reinforced tires is well-known. A considerable
amount of effort has been devoted towards the understanding of
the mechanism(s) of corrosion and adhesion loss. Based on the
results of the above studies, some progress has been made in
solving this problem using the approach of modifying the rubber
stocks and/or brass plating. Gne approach to the solution to
the corcosion problem of steel reinforcement in tires is
described in ~.S. patent 4,052,524 Harakas lg77. Harakas found
that if one first cleaned the steel reinforcing wire~with acid
or base, followed by a water rinse, coated the reinforcing wire
with amino alkyl silane, then re~orcinol formaldehyde latex
(RFL) and then embedded the coated wire in rubber, the
hydrolytic stability of the composite was improved. Ihe
adhesion recited in the Harakas patent, however, may well have
been due to the resorcinol formaldehyde resin employed.
m e problem with the Harakas invention is that the steel~
reinforcing wire must first be cleaned then coated with an
amino silane and then coated with a resin latex before it is
incorporated into the rubber. Along the same lines, see U.S.
patent 4,236,564 Kalafus et al. 1980, which teaches that a
phenolformaldehyde coating on the bright steel cord provides
protection of the bond from heat and humidity degradation.
U.S. patent 3,0~8,847 (Pines 1963) broadly discloses treating
metal surfaces with specific amino functional organo silanes to
improve initial adhesion.
The present invention solves the problem of the multi-step
Harakas method and improves the humid aged adhesion of the
bright steel cord to rubber. The present invention is directed
to first coating uncleaned bright steel cord with an amino
functional organo silane then incorporating the cord directly
l 160408
without a resin coating into a speci~ically formulated phenolic
resin and silica containing rubber.
In the present invention, bright steel cord is bondea to an
unvulcanized vulcan~æable rubber, by coating the cord, which is
uncleaned, i.e., free of acid or base surface treatment prior to
coating, with an amino functional organo silane. The unvulcanized
vulcanizable rubber contains a resorcinol and hexamethylol melamine
bonding agent, a hydrated silica and other conventional rubber
compounding ~n~redients as required. The coated bright steel cord
and the unvulcan~zed vulcanizable rubber are combined to form a
composite which is then vulcanized. The resulting product has
good adhesion.
Thus, one aspect of the invention is a method of bonding
bright steel cord to an unvulcanized vulcanizable rubber, which
method comprises coat~ng sa~d cord, sai~d cord being free of acid or
base surface treatment prior to coating, with~ an amino functional
organo silane wherein said vulcanizable rubber contains a resorclnol
and hexamethylol melamine bond~ng agent, a hydrated s~ ca and
other conventional rubber compounding ~ngredients, combin~ng said
coated bright steel cord and said unvulcanized vulcanizable rubber
to orm a composite and vulcan;~zing said composite, and another
aspect of the invention is a vulcanized composite of bright steel
cord and a rubber compound, free of any resorc;nol formaldehyde
latex type organ~c adhes~ve~ said cord bein~ free of pr~or acid or
base surface treatment and being coated w~th an amino functional
organo s~lane, sa;~d rubber compound containing prior to
vulcanization a resorcinol and hexamethylol melamine bonding a~ent,
a hydrated silica, and other conventional rubbe~ compounding
1 160408
ingredients.
By an amino functional organo silane is meant a silane
having silicon bonded hydrolyzable groups such as lower alkoxy, and
in addition, an amino functional organic group. By amino
functionality organic group is meant an organic group which has at
least one amino functionality and is bonded to the silicon by a
silicon-carbon bond. The preferred amino functional organo silane
is N-~-(N-vinylbenzylamino) ethyl-y-aminopropyl-tri-methoxysilane
monohydrogen chloride.
In the following examples, the amino functional organo
~ilane coated cord was prepared by dipping bright steel cord in a
water or alcohol solution of the silane. All dips were prepared
by mixing together appropriate amounts of n-propanol and water and
then adding the required amount of silane coupling agents to give
a solution containing 1-5% (by weight) of silane. The most often
used concentration was 2% by weight. The dip pH adjustment (when
needed) was done w-ith 0.1 N NaOh or glacial acetic acid. All dips
were aged for at least one hour (at room temperaturel before use.
The following silanes were employed.
Silanes
A-1100 y-Am~nopropyltriethoxysilane (Un~on Carbide)
A-1120 N-~-(Aminoethyl)-y-Aminopropyltrimethoxysilane (Union
Carb~de)
Z-6020 N-~-(aminoethyl)-y-aminopropyltrimethoxysilane (Dow Corn~ng)
Z-6026 Aminoalkyltrimethoxysilane + polyol (Dow Corn~ng)
Z-6032 N-~-(N-vinylbenzylamino)ethyl~y-aminopropyltrimethoxy-
s~lane monohydrogen chloride (Dow Corning]
- 2a
l 160408
-- 3
The following rubber compound was used in the first set of
examples.
Ingredients Parts
Natural Rubber. 46.S0
SBR-15511 38.50
Polybutadiene15.00
Endor Peptizer2 0.14
FEF Black 45.00
Hi-Sil 2153 15.00
~LE4~ 2.00
Aromatie Oil 5.00
Zine Oxide 3.00
Stearie Acid 1.50
Arofene 831851.50
Cohedur RL6 4,70
Santoeure NS7I.20
~ c, :
Crystex Sulfur3.00 :
Emulsion copolymerlzed styrene-butadiene rubber
2Activated æinc salt of pentachlorothiopnenol :
3Precipitated hydrated amorphous silica ~ :
4High-temperature reaction product of diphenylamine:and:
acetone ;
50ctylphenol formaldehyde, non-heat reaetive
6E~ual parts of resoreinol and hexamethylol melamine
pentamethyl ether with a small amount of dibutyl~phthalate for
viseosity control
7N-t-butyl-2-benzothiazolesulfenamide
820~ oil-treated crystex, polymerized sulfur :~
~ Ir~Je~ k.
1 ~fiO408
-- 4 --
A lx5x0.25 mm construction bright steel cord obtained from
Bekaert Steel Wire Corporation was used in these studies. As
controls, brass-plated steel cords of lx5x0.2S mm construction
obtained from Bekaert Steel Wire Corporation and from National
Standard Company were used.
~ 11 cord processing was done on a dipping unit consisting
of a dip tank and a curing oven. The oven temperature ranged
between 90-225C. The temperature was monitored at three
points along the oven (two ends and the middle) and is reported
as such. Processing times varied between 60~180 seconds,
giving cord processing rates of 1-3 metres/minute.
Cord pullout adhesion test (similar to ASTM D-2~29) was
used exclusively in these studies. In this test, cord is
embedded in 12.7 mm (V2 in.) rubber block and the force
required to pull the cord out of rubber is recorded. Eight or
sixteen pulls were generally averaged to give the adhesion
values reported. ~he test (crosshead) speed was 12.7 cm (5
in.) per minute.
The cord-rubber adhesion samples were cured at 153C for 35
minutes and stored at room temperatures for at least 1~6 hours
before testing.
Tb evaluate the effect of humid aging on adhesion, the
adhesion samples were placed in a cylinder containing 100 ml of
deionized water and sealed. Humid aging was carried out by
placing the cylinder in an oven maintained at 121C. After the
desired aging period, the samples were removed from the
cylinder, allowed to equilibrate to room temperature
(approximately one hour) and tested for adhesion as mentioned
above.
m e adhesion data for bright steel cords treated with
silanes of various amine functionalities are given in Table I.
The data show that the unaged adhesions for the various silane
treated cords are essentially equivalent to that of the Bekaert
brass-plated cord and some even approach that of the National
Standard brass-plated cord. The humid aged adhesions for the
1 ~604~
silane treated cords are considerably higher than that of the
brass-plated (Bekaert or National Standard) control cords. Of
particular significance are the adhesion values obtained for
the bright steel cords treated with D~w Corning's Z-6032 silane
at dip pH of 7.4.
m e data in Table I also show that no significant advantage
(if any at all) is seen in adjusting the FH of the silane dip
to 4.5 as recommended by Dow Corning. All the aminofunctional
silanes, therefore, can be used by simply diluting thè
as-received materials in appropriate water + n-propanol
mixtures.
I lB0408
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~ 160408
The performance of the aminosilane treated bright steel
cord was further compared with the brass-plated cord in
long-term in-rubber humid aged adhesion test. m e
corresponding data are given in TabIe II. m e unaged adhesions
for these silane treated cords are 5%-10~ lower than the
values obtained earlier for the corresponding cords (see Table
I) and are only 75~-90% of those for the brass-plated control
cord. In the humid aging test, however, the brass-plated cord
loses adhesion rapidly but the silane treated cords show much
higher adhesions. Once again the steel cords treated with Dow
Corning's Z-6032 silane stand out in humid aged adhesion
retention--showing essentially no loss of adhesion after humid
aging for 72 hours (the brass-plated cord loses 87~ of its
adhesion during this time). The silane treated cords
~espe.cially those treated with Z-6032 silane), therefore, may
perform bettee than the brass-plated cords in steel cord-rubber
composites.
1 160408
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~ 160408
g
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m e rubber compound used in the studies reported so far
contains bonding agents Hi-Sil and Cohedur RL. It was,
therefore, of interest to see what role, if any, these bonding
agents played in the bonding of aminosilane treated wires to
rubber. The recipes for the rubber compounds with and without
bonding-agents are as follows.
l 1~0~08
- 10 -
FORMULATIONS
for
TABLE III DATA
In~redients 1 2 4 3
Natural Rubber46.50 46.50 46.50 46.50
SBR-1551 38.50 38.50 38.50 38.50
Polybutadiene 15.00 15.00 15.00 15.00
Endor Peptizerl0.14 0.14 0.14 0.14
FEF Black 45.00 45.00 60.00 45.00
10 HAF Black - 15.00 - 15.00
Hi-Sil 2152 15.00 - - 15.00
BL ~ 2.00 2.00 2.00 `2.00
Aromatic Oil 5.00 10.00 5.00 10.00
zinc Oxide 3.00 3.00 3.00 3.00
15 Steari~c Acid 1.50 1.50 1.50 1.50
Arofene 8318 1.50 1.50 1.50 1.50
Cohedur RL5 4.70 4.70
Retarder W - - 1.00 1.00
Santocure NS 1.20 1.20 1.20 1.20
20 Crystex Sulfur3.00 2.50 2.0 2.50
Activated zinc salt of pentachlorothlophenol
2Precipitated hydrated amorphous silica
3High-temperature reaction product of diphenylamine and
acetone
Octylphenol formaldehyde, non-heat reactive
E~ual parts of resorcinol and hexamethylol melamine
pentamethyl ether with a small amount of dibutyl phthalate ~or
viscosity control
6Salicylic acid
7N-t-butyl-2-benzothiazolesulfenamide
820~ oil-treated crystex, polymerized sulEur
1 160408
11 -
While the curing characteristics and the properties of the
cured compounds are not identical, they are close enough to
enable a meaningful evaluation of the effect of bonding agents
on the adhesion of silane treated wires to rubber.
The adhesion data for the rubber compounds with and without
bonding agents are given in Table III.
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l 160~08
~ 13 -
The data show that the compound containing both Hi Sil and
Cohedur RL gave the highest adhesions. The compound containing
Cbhedur RL only also gave adequate adhesions. However, the
adhesions for the compound containing only Hi-Sil as the
bonding agent were essentially the same as those for the
compound containing no bonding agents. There is thus an
indication that perhaps the interactions between Cohedur RL in
the rubber c~mpound and the aminosilanes on the wire are
responsible for the bonding of aminosilane treated wires to
rubber. The differences in the adhesion values for the
compounds containing Cohedur RL + Hi-Sil and that containing
only Cbhedur RL may, at least partly, be due to differences in
the curing characteristics and/or the properties (e.g. tear
strength) of the two compounds.
It has been demonstrated that the bright steel cords
treated with the various aminosilane coupling agents adhere
very well to the rubber compounds containing Cohedur RL and
Hi-Sil. ~-e unaged adhesions of the aminosilane treated wire
were fowld to be equivalent to that of the Bekaert brass-plated
wire a~d swnewhat lower than that of the ~ational Standard
brass-plated wire. m e humid aged adhesions for the silane
treated wires were, however, found to be considerably better
than that of the brass-plated wires.
Dip pickup of the silane onto the cords was very small
indicating a molecular thickness of the silane on the cord was
sufficient. m e amount of dip pickup is small but effective.
