Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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RUBBERY ADHESIVE CEMENTS
Technical Field
This invention relates to a rubbery adhesive
cement and its use in bondillg rubber surfaces to form
laminates.
Background Art
The uses of rubbery adhesive cements for the
bonding of rubber surfaces are well known, particularly
in the fields of tire manufacturing and tire
retreading. It is a common method in tire
manufacturing, to apply an unvulcanized tread to a tire
carcass by means of coating the bias cut tread ends
with a rubbery adhesive cement and mating those ends.
In tire retreading operation~s, either unvulcanized or
vulcanized treads or tread-forming strips are applied
to used tire carcasses which have been prepared by
buffing off the old tread and coating it with a rubbery
adhesive cement. Other areas of use are the
manufacturing of rubber goods including, but not
limited to, airsprings, conveyor belts, power
transmission belts, hose, fuel cells, shoe products,
rubberized roofing and dunnage bags.
When used in rubber bonding applications, rubbery
adhesive cements should provide: (1) good green tack,
(2) good green strength, and (3) compound
compatibility. Green tack is a measure of the ability
of the two mating surfaces to grab quickly and hold
together while the item is being built. Green strength
is a measure of the ability of the spliced surfaces to
remain bonded throughout the aging period prior to
vulcanization. Compatibility with the rubber compound
provides an adhesive layer interface which exhibits a
similar vulcanization rate as the rubber compound.
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This allows the interface to reach the same state of
vulcanization and to exhibit similar dyna~ic
properties, thus reducing the possibility of an opening
occurring at the splice. Compatibility is measured by
the hot vulcanized adhesion test, described infra.
As tread stock compositions change, there arises a
need for new and different adhesive cements.
Disclosure of the Invention
,
There is disclosed lamitlates containing an
adhesive blend, a rubbery adhesive cement as well as a
method of using said cement, and products which can be
prepared Erom the use of said cement.
The rubbery adhesive cement comprises:
(A) solvent and
(B) a vulcanizable rubbery polymer blend dissolved
in said solven-t wherein said blend is comprised of,
based on 100 parts thereof:
(a) 5 to 50, preferably 20 to 35, parts by weight,
of at least one rubbery conjugated diene polymer having
25% to 55%, preferably 30~ to 50%, side chain
unsaturation and having a Mooney viscosity of from 80
to 150 ML4 at 100C as measured according to ASTM
D1646, and correspondingly
(b) 50 to 95, preferably 65 to 80 parts by weight
of at least one other rubbery polymer, preferably a
diene polymer.
Solvents which may be used in the practice of this
invention include any organic solvents capable of
dissolving the vulcanizable rubbery polymer blend
(hereinafter referred to as rubber blend). The
solvents should not appreciably degrade the rubber
blend. Exemplary of such organic solvents are hexane,
mineral spirits, naphtha, octane, gasoline,
rubbermaker's solvent or blends thereof. Generally,
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the solvent portion of the rubbery adhesive cement
comprises 70% to 95% based on the total weight of the
cement. More specifically, the level of solvent, may
better be determined by considering such criteria as
ease of application and mode of application. The
viscosity of the cement .should be low enough to allow
smooth application and complete coverage by means of
manual or automated applicators. ~lowever, i~, should be
sufficiently viscous and concentrated to deposit an
effective amount without flowing off the surface to be
bonded.
The term "side chain unsaturation", as wsed
herein, means the side chain unsaturation expressed as
a percentage of the total polymer as determined by
infra-red spectroscopy. More specifically, it relates
to the microstructure of polymers wherein the monomer
units of the conjugated dienes polymerize by adding
across only one of the carbon to carbon double bonds,
thus leaving the other double bond pendantly branched
from the straight chain portion.
As used herein, polymers containing 25~ to S5~
; side chain unsaturation shall hereinafter be referred
to as branched polymers. This should no-t be construed
as excluding lesser amounts of side chain unsaturation
from being present in the other rubbery polymers which
comprise the rubber blend.
The rubber blend portion of the rubbery adhesive
cement is comprised of: the branched polymer; at least
one other rubbery polymer, preferably a diene polymer;
and other compounding ingredients as are commonly used
in the art of producing vulcanizable rubbery adhesive
cements.
The branched polymers include homopolymers of
conjugated dienes, copolymers of two or more conjugated
dienes, and copolymers of one or more conjugated dienes
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with one or more monomers, e~g. vinyl monomers sucll as
styrene and acrylonitrile, the vinyl monomers usually
being present in amounts of 50% or less.by weight of
the copolymer. In the case of polybutadiene
homopolymers or copolymers, the side chain unsaturation
is of the 1,2-vinyl structure. In the case of
polyisoprene homopolymers or copolymers, the side chain
unsaturation is of the 1,2 vinyl structure and/or the
3,4 isopropenyl structure.
The branched polymers which may be used in the
practice of the present inventlon are generally
produced by polymerizing conjugated diene monomers or
blends thereof using an organolithium catalyst and
polymerization techniques as are more fully described
in U.S. Patent li,230,841, U.S. Patent 3,937,681 and
U.S. Patent 3,830,880. Preferred is branched polymer,
preferably medium-vinyl polybu-tadiene, containing 25%
to 55% side chain unsaturation. More preferred is
branched polymer, preferably medium-vinyl
polybutadiene, containing 30% to 50% side chain
unsaturation, and most preferred is branched polymer,
preferably medium vinyl polybutadiene, containing 40%
to 50% side chain unsaturation.
Particularly useful are those polymers polymerized
to a Mooney viscosity of from 80 to 150 ML4, preferably
90 to 130, more pre~erably 95 to 125, at 100C as
measured according to ASTM D1646. As a practical
matter, these high Mooney polymers are usually extended
with aromatic or naphthenic processing oils to reduce
the ~ooney viscosity to facilitate processing,
particularly where the polymer is reinforced with
carbon black. However, the polymers can be used
without any oil present. The oil levels used include
those typically used in oil extended polymers, These
levels vary with the Mooney by the base polymer, i.e.,
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non-extended polymers. The resultant Mooney of the oil
extended polymer is preferably, but not limited to 40
to 55 ML at 100C as measured according to ASTM D1646.
Preferred are the branched polymers, preferably
medium-vinyl polybutadienes, extended with 20 to 50,
more preferably 30 to 45, parts by weight of processing
oil per 100 parts by weight of branched polymer.
IJhen a Mooney value is given herein, unless
otherwise indicated, it is the Mooney of the polymer
with no oil present, e.g., before being extended with
an oil. Unless otherwise indicated, where parts by
weight of a polymer are referred to herein, it is the
parts by weight of the polymer without any extending
oil present. For example if a blend requires 25 parts
of medium vinyl polybutadiene and the medium vinyl
polybutadiene used contains 37.5 parts of oil,
approximately 34 parts of the oil extended medium vinyl
polybutadiene would be used.
The other rubbery polymers which are used in
combination with the branched polymers include, but are
not limited to, natural rubber; homopolymers of
conjugated dienes such as cis-1,4-polyisoprene and
cis-1,4-polybutadiene; copolymers of conjugated dienes
such as butadiene and isoprene; rubbery copolymers of a
conjugated 1,3-diene such as isoprene and/or butadiene
with up to 50 percent by weight of at least one
copolymerizable monomer such as monoolefins, including
vinyl monomers, such as styrene and acrylonitrile;
polychloroprene; butyl rubber; halobutyl rubber; and
rubbery copolymers of monoolefins containing
unsaturation, i.e., carbon to carbon double bonds, such
as terpolymers of ethylene7 propylene and a
non-conjugated dieneO In a preferred embodiment, the
other rubbery polymer is comprised of a blend of
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natural rubber and/or cis-1,4-polyisoprene, and a
rubbery styrene-butadiene copolymer (SBR).
It is preferred that the rubber blend is comprised
of 5 to 50, more preferably 20 to 35, parts by weight
of medium vinyl polybutadiene; 10 to 35 parts by weight
of natural rubber or cis-1,4-polyisoprene; and
correspondingly 40 to 60 parts by weight of SBR, all
parts being per 100 parts by weight of the rubber
blend. ~ost preferred is a rubber blend comprised of
ln 25 parts by weight of mediurn-vinyl polybutadiene, 20
parts by weight of natural rubber or
cis-1,4-polyisopre~e and 55 parts by weight SBR, all
parts being per 100 parts by weight of rubber blend.
Other ingredients which are used in compounding
the rubber blend of the present invention are those
commonly used in formulating vulcanizable compounds.
Exemplary of these ingredients are: fillers and
reinforcing agents such as clays, silicas, and carbon
black; antidegradants which may consist of an
antioxidant and an antiozonant; vulcanizing agents such
as sulfur, zinc oxide, and accelerators; processing
oils; and unreactive tackifying resins.
The rubbery adhesive cement may be prepared by any
conventional means such as Banbury mixing and open mill
mixing of the rubbery polymer blend portion followed by
dissolution of the rubber blend in the solvent in an
agitated vessel. The method of combining the
ingredients is not normally critical. However, to
prevent premature vulcanization, it is preferred that a
multiple-stage mixing system be used wherein the
vulcanizing agents are added in the final stage.
The rubbery adhesive cements of the present
invention may be applied by any conventional means
including the use of brushes, spreaders, rollers and
spraying equipment. The cements may be applied to
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either vulcanized or un w lcanized compounds. Ihe
cements may be applied to either one or both of the
surfaces to be bonded.
The laminates which are formed by the practice of
this invention are comprised of two rubbery surfaces,
each surface being either vulcanized or unvulcanized,
wherein the surfaces have been adhered together by a
film of rubber between the surfaces, the film of rubher
being comprised of a rubber blend, based on lO0 parts
thereof:
(a) 5 to 50 parts by weight of at least one
rubbery conjugated diene polymer having 25% to 55~ side
chain unsaturation, and correspondingly
(b) 50 to 95 parts by weight of at least one other
rubbery polymer.
The laminates may be prepared by coating at least
one surface of the rubber with the rubbery adhesive
cement, allowing the cement to dry by evaporation of
the solvent, mating the two rubber surfaces and
vulcanizing the laminate/rubber fiim combination.
Alternatively, the two rubbery surfaces may be cemented
and mated prior to drying the cement, allowing the heat
of vulcanization to evaporate the solvent during the
vulcanization step. Still another method would be to
form an adhesive strip of rubber film by applying a
coat of the cement to a non-sticking surface, removing
the rubbery film after the sol-vent has evaporated, then
forming the laminate by inserting the adhesive strip
between the two rubber surfaces and vulcanizing the
combination.
The following examples are intended to illustrate,
but not to limit the practice of this invention. All
parts shown are parts by weight.
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Example 1
Rubbery adhesive cements were prepared by mixing
the cement formulations shown in Table I. Cements B
and D illustrate cements of this invention utilizing a
medium-vinyl polybutadiene.
TAELE I
CEMENT FORMUL~TIONS
PARTS
Cement Cement Cement Cement
Components A B C D
. 1 -76 -~7~-- S5--5S
O112extended SBR
SBR -- -- 1515
Cis 1,4-PBD3 25 - 25__
Cis 1,4-polyisoprene4 20 20 20 20
Oil-extended
medium-vinyl PBD5 -- 34 -- 34
Carbon black 62 62 6262
Processing oil 16 7 2213
Antidegradants
Unreactive Phenol Resin 78 78 78 78
Vulcanizing agents 10 10 1010
Gasoline 20572057 20572057
1. Emulsion styrene-butadiene extended with 37.5
parts aromatic oil.
2. Emulsion styrene-butadiene copolymer.
3. 1207 type polybutadiene.
4. Natural rubber
5. Medium-vinyl polybutadiene containing 45% vinyl
and extended with 37.5 parts aromatic oil.
Each of the cement formulations above were
evaluated on each of four different tire tread
compounds containing the polymer blends shown in Table
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II, all of which were compounded with conventional
compounding ingredients:
TABLE II
TIRE TREAD FO~ULATIO~IS
PARTS
Pol~mer Compound ~ X Y Z
Cis 1,4-polyisoprene 25 -~
Oil Extended SBR 55 70 70
Oil Extended Cis 1,4-PBD 20 30 -- --
Cis 1,4-PBD -- -- 30 30
Oil-extended medium-
vinyl PBD -- __ __ 70
Test strips of each tire tread compound were
cemented together by means of each cement and were
tested for green tack, green adhesion and hot
vulcanized adhesion.
The green tack test is a measurement of the force
required to separate two unvulcanized rubber compounds
after they have been cemented and pressed together A
sheet of the rubber compound is applied to a
non-elastic backing material. A cement is applied to
the rubber compound and allowed to dry. Two test
strips are placed in the tackmeter, one on each side of
a polyester band to which silicone has been applied.
The polyester band has a slit in it 3.175 mm wide,
through which the two test strips are contacted. A
pressure of 200 kPa is applied to two 15 cm pressure
blocks behind each test strip for 30 seconds. The
pressure is released and after 5 seconds, the
instrument peels the two strips apart at a rate of 25.4
cm per minute. The force required to separate the
`~ strips is read from a pen tracing on a chart. The
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chart is calibrated in dN from 0 to 20. Values beyond
the chart limit are shown as 20+.
The green tack was measured on the day the samples
were originally made and on samples which had been aged
at room temperature for 1, 3 and 6 days. The results
are shown in Table III.
TABLE III
GREEN TACK, dN
10 Compound WOrigin _ ~ 3 Day~s 6 Days
Cement A 17.0 19.0 17.0 18.5
Cement B 20~ 20-~ 20+ 20+
Cement C 13.0 17.0 18.0 15.0
Cement D 20.0 20+ 20+ 20+
Compound X~ 1 Da" 3 Days 6 D~ s
Cement A 17.0 20+ 18.5 18.5
Cement B 16.0 20.0 20+ 19.0
Cement C 13.5 17.0 17.0 15.5
Cement D 15.5 20+ 20+ 20+
Compound Y Original ~ y~ 6 Days
Cement A 16.5 18.0 17.5 16.5
Cement B 17.0 20+ 20+ 20~
Cement C 12.0 15.0 15.5 15.0
Cement D 17.0 20+ 20~ 20-~
Compound Z Original 1 Day ~ 6 Days
Cement A 17.5 20+ 16.5 19.0
Cement B 17.5 20.0 20+ 20+
Cement C 12.5 20.0 16.0 18.0
Cement D 16.0 20+ 20+ 20+
The green adhesion test is used to evaluate
adhesive strength. A rubber compound is milled to a
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thickness of 2.54 mm and a fabric backing is applied.
A cement is applied and allowed to dr~J. Two 100 mm x
100 mm pieces are cut from the sheet and a 25 mm strip
of a non-elastic material is applied to one end of each
piece. The cemented surfaces of the two pieces are
placed in contact with each other and rolled with a
rubber roller. The sample is allowed to set for 24
hours under a pressure of 3.5 kPa. Strips, 25 mm wide,
are cut Erom the samples and pulled apart on a
conventional tensile tester at 5 cm/min. Two strips
are pulled at room temperature and two at 50C. The
force is read in Newtons.
The green adhesion was measured a-t room
temperature and at 50C. The results are shown in
Table IV.
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TABLR IV
GREEN ADHESLON, NEWTONS
Compound ~J Room Temperature 50C
Cement A 13.5 7.5
5 Cement B 23.0 5.0
Cement C 11.0 2.5
Cement D 20.5 3.5
Compound X Room Temperature 50C
Cement A 14.0 7.5
Cement B 22.5 8.5
Cement C 11.5 5.5
Cement D 19.5 8.0
15 Compound Y Room Te~ 50C
Cement A 12.5 6.0
Cement B 20.5 6.0
Cement C 10.5 6.0
Cement D 18.5 6.5
Compound Z Room Temperature 50C
Cement A 19.5 9.0
Cement B 22.0 8.5
Cement C 17.5 7.5
Cement D 23.5 7.5
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~ lot vulcanized adhesion is a test of adhesion
where two unvulcanized rubber compound surfaces are
cemented and placed in contact through a 5 mm x 50 mm
sli-t in a strip of polyester film. The assembly is
then vulcanized. The test strip ends are at~ached to
the jaws of a conventional tensile tester, the jaws
being enclosed in an oven which has been preheated to
the test temperature. The strips are pulled at a rate
of 51 mm per minutes. The force is read in Newtons.
The hot vulcanized adhesion was measured on the
day the samples were originally made and on samples
which had been aged for 6 days at 70C. The results
are shown in Table V.
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TABLE V
HOT VULCANIZED ADHESION, NEWTONS
After 6 Days
Compound_W Original at 70C
-
5 Cement A 20 30
Cement B 23 33
Cement C 18 25
Cement D 23 30
After 6 Days
~pound X Original at 70C
Cement A 35 20
Cement B 115 45
Cement C 25 20
15 Cement D 95 45
After 6 Daqs
Compound Y Original at 70C
Cement A 50 18
20 Cement B 95 25
Cement C 25 18
Cement D 80 40
After 6 Days
25 Compound Z Original at 70C
Cement A 50 25
Cement B 80 55
Cement C 30 15
Cement D - 75 60
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As is seen from the foregoing data, Cements B and
D, which are representative of the best mode of the
present invention, provided improved green tack, green
adhesion and hot vulcanized adhesion. Although still
useful as adhesive cements, two areas in tread splice
cementing where the rubbery adhesive cements of the
present invention have sho~m little or no improvement
were on tread stocks containing greater than 40 parts
natural rubber per 100 parts of total polymer and those
containing 70 parts or more carbon black per 100 parts
of total polymer.
Example 2
Following the procedure as shown in Example 1, a
rubbery adhesive cement is produced by substituting a
copolymer of styrene and butadiene containing 43% side
chain unsaturation for the medium vinyl polybutadiene.
The cement is applied to the various tread compounds of
Example 1 and adequate green tack, green adhesion and
hot vulcanized adhesion are obtained.
Example 3
; Following the procedures as shown in Example 1, a
rubbery adhesive cement is produced by suhstituting a
polyisoprene containing side chain unsaturation for the
medium-vinyl polybutadiene. The cement is applied to
the various tread compounds of Example 1 and adequate
green tack, green adhesion a-nd hot vu]canized adhesion
are obtained.
Industrial Applicab_lity
The following illustrate, but do not limit the
industrial application of the cements of the present
invention. A wide variety of rubber to rubber
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laminates can profit by the use of the adheslve
composition of the present invention.
The rubber surfaces which are laminated to~ether
can both be vulcanized, or both unvulcanized, or one
vulcanized and the other unvulcanized. The rubber
surfaces can be comprised of any conventional rubbers
which can be compounded in any conventionfll manner with
conventional compounds.
Rubbery adhe~sive cements ot the present invention
may be usecl in tire building applic~tions for cementing
the mating ends of extruded treads or any other areas
requiring a rubber to rubber bond. ~Iore advantageously
in tread splicing applications, it has been found that
the use of the cement of the present invention permits
its applicfltion to only one end of smaller tire treads
such as are used for passenger size tires. This
precludes the need for an operator to lift the extruded
tread in order to apply the cement to the bias cut end
which faces downward.
~hile one-end cementing is normally successful for
passenger tire treads, it is often necessary to apply
the cement to both ends of the heavier treads such as
are used in truck tires. This is because the weight of
those treads has a tendency to pull the splice apart.
Use of the disclosed cement 9 however, has heen found to
eliminate the need to use a restraining band around
truck tire treads to prevent splice opening as can
occur with some prior art cements.
Any tire tread stock will benefit by the use of
the adhesive cement of the present invention. Polymers
which may be used in the treads include, but are not
limited to, natural rubber and rubbery homopolvmers and
copolymers of dienes, particularly, conjugated dienes
such as butadiene-1,3 and isoprene as well as
copolymers of dienes with vinyl monomers such as
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acrylonitrile and styrene. Particular polymers
include, but are not limited to medium vinyl
polybutadiene cis-1,4 polybutadiene, polyisoprene,
rubbery butadiene/styrene copolymers and rubbery
butadiene/acrylonitrile copolymers. Blends of polymers
can also be used.
Other areas of applicability include those where
two or more layers of rubber are bonded to form a
laminate. Such uses include the bonding oE lap splices
in conveyor belts, the bonding o successive layers of
fabric or polymers in hose manufacture, the bonding of
].ap splices in rubber roofing applications and the
application of either unvulcaniæed or vulcanized treads
or tread strips in tire retreading operations. Again
any conventional rubbers will benefit by the use of
this adhesive.
~ 1hile certain representative embodiments and
details have been sho~m for the purpose of illustrating
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 scope of the
invention.
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