Note: Descriptions are shown in the official language in which they were submitted.
~ ~7 ~ ~ ~
This invention relates to the treatment of
shaped structures and more part~cularly to a method for
treating shaped structures such as films and fibrous
textile materials to improve their adhesion to rubber.
Specifically, the invention pro~ides a new and useful com-
position of matter for treating shaped structures of organic
polymers to improve their ability to adhere to rubber under
severe flexing conditions.
Prior Art
-
Coatings of the type herein disclosed may be made
by use of a phenol-blocked isocyanate and a polyepoxide.
Such coatings are disclosed in U. S. Patent 3,307,966, issued
March 7, 1967 to Shoaf. Amine-blocked isocyanates are
known, for example, in U. S. Patent 3,692,719, issued
September 19, 1972 to Srail.
Statement of Invention
In accordance with the present invention, a novel
composition of matter, useful as a precoating for improving
adherence between rubbers and substrates of organic polymers,
is provided comprising a liquid carrier containing from
about 0.05% by weight to about 10.0% by weight of solids of
(A) a polyepoxide having an average of at least two epoxy
groups in each molecule, a melting point below about 150C.,
an average molecular weight below about 3000 and an epoxide
equivalent below about 2500 and (B) an amine-blocked diphenyl-
methane-4,47-diisocyanate; the weight ratio of SA)/5B)
being within the range of from about 0.01 to about 5.0, the
said liquid carrier being chemically inert to each of (A)
- 2 ~
~ 4~
and (B). The liquid carrier may be a solvent Eor one or
both of components (A) and (B) or either or both of (A)
or (B) may be suspended in the carrier as a dispersed or
emulsified phase. This composition, when applied and
processed as described below provides a final shaped struc-
ture bearing a coating of the reaction prod-uct of (A) with
(B) constituting from about 0.2 to about 5% by weight of
the coated structure. The composition of the present
invention is applied to the polymeric substrate by any
conventional means such as dipping, spraying, brushing,
padding or the like with the structure relaxed or under
tension. The wetted shaped structure is heated at a tem-
perature of from about 150C to about 235C. for a per-iod
of from 0.5 to about 15 minutes to remove the liquid carrier
and to cure the coating. Particularly where the shaped
structure is fibrous in nature, it is preferred that the
structure be subjected to at least sufficient tensioll to
prevent shrinkage during the wetting and subsequent curing
operations. Alternatively the reactants (A) and (B) can
be applied separately in either order from the same or
different liquid carriers to the shaped structure instead
of applying them simultaneously from the same carrier as
described above.
Following formation of the polyepoxide-polyiso-
cyanate reaction product on the shaped structure, rubber
coatings may thereafter be applied by conventional techniques,
preferably, but not necessarily, first coating with a
phenol-formaldehyde rubber latex, preferably an aqueous
resorcinol-formaldehyde solution and butadiene-vinyl
~7~38
pyridine latex as taught in U. S. Patent No. 2,990,313
to Knowles et al. (referred to hereinafter as an RFL
coating). Thereafter the rubber is applied. Optionally,
after at least partial curing of the polyepoxide and the
amine-blocked diphenylmethane-494'-diisocyanate and prior
to application of rubber, the organic polymeric structure is
given a second coating with a phenol-aldehyde rubber latex.
The product is a reinforced rubber shaped structure
In the examples illustrating the manner in which
the invention may be carried out and the advantages ob-
tained, two methods of determining the strength of the
adhesive bond are used:
(1) The "H-pull" test.
(2) The two-ply strip adhesion test.
The "H-pull" test is the well-known test described,
for example, in India Rubber World, 114, 213-219 (May 1946),
"Study of the 'H' Test for Evaluating the Adhesive
Properties of Tire Cord in Natural and GR-S Rubber."
Briefly, a dipped cord is cured across the center of two
small rectangles of rubber with a shor~ length of the cord
exposed between the rubber pieces forming the cross-bar
of the H. The pieces of rubber are gripped in an Instron
Tensile Testing machine and stress is applied so that the
cord is pulled out from one of the pieces of rubber. The
load required is regarded as a measure of the adhesion. In
the examples of the present specification, the width of
the rubber pieces are reduced to 1/4 inch since greater
width samples resulted in cord breaks rather than adhesive
failure due to the high level of adhesion experienced with
this new adhesive system.
-- 4 --
~ ~)47~88
The two-ply strip adhesion test is carried out
on a laminated structure containing two plies o parallel
dipped tire cords (29 ends per inch) separaled by a thin
layer of rubber. The laminar structure is built up in
successive layers consisting of a cotton duck reinforcing
backing, a 25 mil sheet of un w lcanized rubber, a layer of
parallel cords, two layers of 25 mil rubber, another layer
of parallel cords, a 25 mil layer of rubber and a final
cotton duck backing. A small strip of Holland cloth or
other suitable material is inserted between the center two
layers of rubber at one end of the structure to prevent
bonding and allow a portion of each ply to remain free for
clamping when testing. The laminate is then molded, vul-
canized under pressure, and cut into l-inch wide strips.
The force required to separate the two fabric plies of
a l-inch wide strip is taken as a measure of the adhesion.
If desired, a woven fabric, such as used for conveyor belt
reinforcement, may be substituted for the parallel cords
when adhesion of fabric to rubber is being tested.
The rubber stock A referred to in the examples
is a blended natural rubbsr/styrene-butadiene rubber tire
skim stock of approximately 50/50 composition by weight.
In the following examples which illustrate the
invention, all parts and percentages are in parts by
weight unless otherwise specified.
EXAMPLE I
A solution of ~00 gm. diphenylmethane-4,4'-diiso-
cyanate in 1000 ml. dry trichloroethylene is slowly added
to a solution of 698 gm. dry dibutylamine in 500 mlO
dry trichloroethylene. The reaction is exothe~ic and
-- 5 --
is maintained at 70C by external cooling, Af-ter the
addition the mixture is heated to 80 90C for one hour.
After cooling to room temperature the precipitated
dibutylamine blocked diphenylmethyl~4~4'-diisocyanate is
filtered of~, dried at ~0C and micronized.
Polyepoxide A is prepared ~rom glycerol and
epichlorohydrin in accordance ~ith the disclosure o~ U.S.
Patent 2 902 398 (column 4~ lines 1-24: "Polyether A").
This material is a pale yellow liquid with an epoxide
equivalent o~ about 170, a corrected hydroxyl equivalent
of about 300, and a viscosity of about 1.2-2.0 poises at
25C. (This material is also available ~rom Shell Chemical
Co. a3 EPON~ Resin 812).
A homogeneous solution o~ 16.0 lbs. water and
0.24 lb, sodium dioctylsul~osuccinate (sold as AEROSOL OT*
by American Cyanamid) is prepared by stirring. Additional
water, 6.26 lb., at 90-lOO~F, and 7.5 lb. dibutylamine-
blocked diphenylmethane-4~4'-diisocyanate are added and the
mixture vigorously stirred until -the blocked isocyanate is
dispersed. m e dispersion is ball-milled ~or 72 hrs., pro-
ducing a white suspension conta-Lning 25 w-t. ~ blocked
isocyanate.
A coating composition (hereina~ter referred -to as
the Primary Coating Composition) (4.6~ solids) is prepared
by adding 1.29 lb. of the above slurry to 8.37 lbs. o~ wa-ter
containing 0.20 lb. 2~ aqueous gum tragacanth solution~ Then
0.14 lb~ polyepoxide A is added and the composition is
ready for use.
A resin master is prepared by adding 2024 pounds
o~ 1.7~ aqueous sodium hydrox-tde to 27~8 pound~ of water
* denotes trade mark
--6--
.~
at 75-78F~ stirring for one minute, adding l.38 pounds
o~ resorcinol flakes slowly to the resulting solution,
stirring for five minutes, adding 2.02 pounds of 37~0 aqueous
formaldehyde, stirring for two minutes, stopping the mixing
and aging the resin master at 75 to 78F ~or six hours,
The pH is 7.0 to 7.5.
A latex composition is prepared by adding 7.64
pounds of water at 75-78~ to 30.5 pounds of a ~l wt.
l,3-butadiene/styrene/2-vi~ylpyridine latex (sold as
GEN-TAC* by General Tire and Rubber Co.) adjusting the
temperature to 45~5OF~ adding l~42 pounds of 28~ aqueous
ammonium hydroxide, and stirring slowly for five minutes.
The resin master (33.41~ pound.s) is added to the
latex co~position wi-th slow mixing and after the addition
mixing is continued for three more minutes. This mixture
is aged for 12 hours at 45~50FO Its pH is then lO.0 to
10.4. The composition i8 kept at 45-50F and may be used
for 5 days. Thls composition is hereafter referred to as
the RFL coating composition.
A commercially available polyethylene terephthal-
ate tire cord h~ving a lO00 (denier)/2 (ply-twist)/2 (ply-
twist) construction is dipped in Primary Coating Composition
and then heated in an oven for one minute at 232C ~450F)
~mder an applied stretch of ~. The percent pick-up (dry
solids) is about OD5~
The coated cord is then dipped in RFL Goating
Composition and heated in an oven for one minute at 2l8C
(425F) with a relaxation of ~. The percent pick-up of
this RFL coating is about 3~6.
A rubber Compound is prepared on a rubber roll
mill according to the ~ollowing recipe:
* denotes -trade mark
7 --
:,
~7~
~ Parts by Wel~
Natural Rubber (smoked sheet No~) 50
S~R-1500a 50
HAF carbon blackb 35
Stearic acid
Zinc oxide 3
Petroleum oilC 9.37
Antioxidantd
2,2'-Dithiobisbenzothiazole
Sulfure 3-13
A 15-mil 9 in. x 18 in. sheet of rubber stock is
placed, backing side up, on a building drumJ the backing is
removed, tire cord i5 wound onto the drum across the ~ull
width using the maxlmum end count available without over-
lapping the cord, the ~reshly exposed side of ~nother
15-mil 9 in. x 18 in. sheet o~ rubber stock is placed
against the cords on the drum, and the assembly is stitched
a _ Non-pigmented sulfur curable elastomer made b~
copolymerizing 1,3-butadiene and styrene at 6 C
continuously in a continuous water phase using emulsi-
fiers, vi~cosity regulators and a redox catalyst
system. It contains about 23.5~ ~tyrene by weight and
has a Mooney viscosity (ML-l ~ L~/100C) o~ 52.
b _ AS~I Designation N-330.
c _ Naphthenic petroleum oil ASTM D-2226 Type 103 ha~ing
Saybolt Universal Viscosity values of 2525 and 87.2
at 100F and 210F respectively, a molecular weight
of 395, and a viscosity~gravity constant of 0.889.
(Sun Oills tradename ~or thiæ oil is CIRCOSOL 1~240.)
d _ Polymerlzed 2,2,1~-trimethyl-1,2-dihydroquinoline,
m1p~ 74C (Monsanto's tradename ~or this materlal is
AGE RI~E RESIN D.)
e _ Amorphous, insoluble sulfur with 20~ oil. (St&u~er
Chemical~s registered trademark ~or this composition is
CRYSTEX.)
~ 8
and removed from the drum. Two warps are cut, each
8-7/8 in. long and 9-7/8 in. wide.
Six 8-7/8 in. x 9-7/8 in. pieces of 125-mil
rubber stock and two pieces of polyester fabric are cu~.
Two more pieces of 2 in. x lO in. polyester fabric are cut.
A laminated structure is built up in successive
layers. First, two of the 125-mil rubber sheets are jo:ined
(longer ends parallel). Then, successively, polyester
fabric and one more 125-mil rubber sheet are positioned.
One 8-7/8 in. x 9-7/8 in. warp is placed parallel to the
9 in. dimension; the side originally next to the buildlng
drum is down. Two 2 in. x 10 ~n. fabric strips are placed
at both ends of the mold perpendicular to the cord direction.
The other 8-7/8 in. x 9-7/8 in. warp are placed on top and
in line with the first set (the side originally next to
the building drum is up). The remaining layers are added
to duplicate the first ply, 2 125-mil sheets being the
last to be positioned. The 2 in. x 10 in. fabric strips
at the center of the pad allow a portion o each ply to
remain free for clamping when testing.
The laminate 1s then molded, cured under pressure,
and cut into one-inch wide strips. The force required to
separate the two fabric plies of a one-inch wide strip is
called the two-ply strip adhesion value.
In general the pad is cured at 6 tons to~al
pressure for 60 minutes at 150C.
Two-ply strip adhesion test pads are made using
the coated polye~ter tire cord and the black loaded natural
rubber/SBR~1500 s~ock described above. Some pads are tested
at once at 60C. [140F.]~ others are aged at 162.8C
~ 7~88
[325F.] for 8 hours. The unaged pad gave an adhesion
value o~ 54 lbs./in. and the aged pad gave an adhesion
value of 14 lbs./in.
"H-pull" specimens are made using the coated
polyester tire cord and the black loaded natural rubber/
SBR-1500 stock described above. An unaged specimen gave
a value of 35 lbs.
EXAMPLE 2
Example 1 was repeated, only this time 471 grams
of morpholine was used in place of the dibutylamine.
Test samples fabricated using this amine-blocked isocyanate
gave an unaged two ply adhesion value of 52 lbs./in., and
an aged two ply adhesion value of 18 lbs./in.
Definitions of Components
The term "polyepoxide" is used to describe
uncured chemical compounds having an average of at least
two epoxy groups, i.e., at least two
--C~\C--
in each molecule, a melting point below 150C., an average
molecular weight below 3,000, and an epoxide equivalent
below 2,500. The preferred epoxy compounds are those
having a melting point below 100C., an average molecular
weight below 1,500, and an epoxide squivalent below 850.
They may be saturated or unsaturated, aliphatic, cyclo-
aliphatic, aromatic or heterocyclic and may con~ain sub-
stituents for hydrogen such as alkyl, halogen, hydroxyl
and alkoxy. Such compounds are commonly prepared by the
reaction of halohydrins with polyhydric alcohols or with
- 10 -
~ ~ 7 ~ ~ ~
polyhydric phenols; as for example, the reaction of epi-
chlorohydrin with glycerol or with bis-phenol Such com-
pounds are described in "Epoxy Resins" by ;Lee and Neville,
McGraw-Hill Book Company Inc., New York, 1957, pages l 21.
The term "epoxide equivalent" is the weight of resin in
grams which contain l gram chemical equivalent of epoxy
groups. The value is determined by the method described
in Lee and Neville, page 21. Many suitable specific poly-
epoxides, all of which are suitable in the present invention
are listed in U. S. Patent No. 2,902,398 to Schroeder, dated
September l, 1959.
The second essential component of the precoating
composition of the present adhesive system is a secondary
amine adduct of diphenylmethane-4,4'-diisocyanate. Compounds
of this type are relatively inert, being stable in the pres-
ence of water at room temperature. However, when heated to
temperatures above about 100C., these compounds dissociate,
yielding free isocyanate compounds capable of undergoing
all the reactions characteristic of polyisocyanate compounds.
Suitable secondary amines for blocking the diphenyl-
methane-4,4'-diisocyanate include those having the formula
HNRlR2 wherein Rl and R2 are monovalent hydrocarbon radicals,
either the same or different containing from l to 30 carbon
atoms and optionally also containing here~o atoms such as
O, N, and S in functional groups that do not react with
isocyana~es or Rl and R2 may also form a bivalent hydrocarbon
radical with the same limi~ations as above. Specific examples
of sui~able amines are:
~¢~47~8
morpholine
~N
H
2,6-dimethyl morpholine
the dibutylamines
the dipropylamines
the dipentylamines
the dihexylamines
the diheptylamines
diethylamine
diphenylamine
N-ethylaniline
3-anilinopropionitrile C6H5NH(CH2)2C_ N
anilinoacetonitrile C6H5NHCH2C~ N
4-anilino-2-butanone C6H5NH(CH2)2cOcH3
N-sec-octylaniline
N-butenylaniline
N-cyclohexylaniline
N-phenylbenzylamine
N,N'-diphenyl~ormamidine C6H5NHC = NC6H5
tetrahydrocarbazole
anilinoacetate
2-phenylindole ~
N ~6H5
H
benzpyrrole (indole)
skatole ~ CH3
- 12 -
~ ~ 7 ~ ~ 8
The polyepoxide-polyisocyanate reactants are
applied in a liquid carrier to the shaped structure. The
nature of the carrier is not critical. Water is generally
the most convenient carrier. Since the carrier acts solely
as a vehicle for the reactants, the reactants need not be
in solution in the carrier but may be dispe:rsed or emul-
sified in it. The concentration of reactants in the carrier
may vary widely but generally the use o~ compositions COII-
taining from about 0.05% to about 10% by weight of reac-
tants wherein the ratio of polyepoxide to amine-blocked
polyisocyanate is between about 0.01 to about 5.0 is satis-
factory. Pre~erably the ratio o~ reactants is between
about 0.05 to about 2 3.
In addition to the polyepoxide and the amine
blocked polyisocyanate adduct, the preferred aqueous pre
coating composition of this invention may also contain, i~
desired, optional materials such as wetting agents, dis-
persing agents, viscosity builders~ and epoxide curing
agents and promoters such as a tertiary amine. For example,
a dispersing agent, such as an alkyl aryl polyether alco-
hol or sodium dioctylsul~osuccinate may be used to disperse
a finely-divided solid isocyanate adduct in water ~or the
preparation of the precoating composition. The viscosity of
the coating composition may be adjusted by the addition of
well-known thickening agents such as gum tragacanth, or by
a compound such as the acetate salt of polydiethylamino-
ethylmethacrylate which ser~es both as a viscosity builder
and as an ami~e catalyst non-reactive to epoxides at room
temperature but reactive at elevated temperatures.
~g)4~88
As pointed out previously, after applying the
liquid carrier containing the polyepoxide-polyisocyanate
reactants to the shaped structure it is necessary that
reaction be made to occur between the reactants. A
temperature at least about 135C. and preferably at least
about 150C. is required to promote reaction. Higher tem-
peratures may be employed to hasten the reaction but usually
a temperature within the range of from about 150C~ to
about 235C. is preferred in the treatment of fibrous
structures. The period necessary for this operation
wi.ll vary widely depending upon factors such as the nature
of the carrier and the temperature employed. The shorter
periods are favored by higher temperatures and more volatile
solvents. When treating fibrous structwres it is generally
preferable to perform this "curing" operation with the
structure under at least sufficient tension to prevent
shrinkage. At times it is advantageous to apply su~f,icient
tension to stretch the structure during this operation.
When the composition is applied as taught herein the shaped
structure will pick up a coating of reactants constituting
from about 0.2 to about 5% by weight of the coated structure.
Generally it is preferred to adjust concentrations and con-
ditions of application to provide a coated structure con-
taining reactants constituting about 0.5 to about 2.5V/~ by
weight of the coated structure.
The polymeric structures bearing the cured poly-
epoxide-polyisocyanate coating may be bonded to rubber in
the customary manner by use of heat and pressure ~o o:rm
reinforced articles in which both the dry and wet adhesion
of the synthetic polymer to rubber is outstanding, and in
- 14 -
1U147~8
which both cold and ~ot adhesion is superior to that
hitherto known. The adhesion afforded by the composition
of this invention is about e~uivalent on polyester struc-
tures over a broader range of application and testing
conditions and in a wider variety of rubber stocks, to
that obtained with other adhesive systems known. While
the composition i9 particularly valuable for polyester
structures~ it is to be understood that it is also suitable
for other polymeric structures, such as polyamide fibers;
as well as cellulosic structures and the natural ~ibers.
The combination of polyepoxide and amine-blocked
diphenylmethane-4,4'-diisocyanate is preferable to the
conventional combination of a polyepoxide and a phenol
or a beta-naphthol blocked diisoc~anate, in that during
the c~ring cycle the amine vaporizes to a lesser extent
than the phenol and beta-naphthol do; furthermore, the
amines are inherently less toxic and polluting than are
these other compounds.
Prior to applying the rubber coating, it is pre-
ferred (but not essential) to overlay the cured polyepoxide-
polyisocyanate coating with at least about 0.5/O by weight
(and preferably from about 2 to about 25% by weight) of
adhesive coating of a phenol-aldehyde condensate (~or
example as taught in United States Patent 2,330,217 to ~Iunn
dated September 28, 1943) and a butadiene-vinyl pyridine
latex. Such compositions and their methods of application
are well known in the art and taught in detail in United
States Patent 2,990,313 to Knowles et al. dated June 27,
1961.
- 15 -
~4718~
The nature of the "rubber" in the final shaped
structure is not critical and may be either a natural or
a synthetic ~ubber. Furthermore, the technLique of apply-
ing the rubber to the reinforcing structure prepared in
accordance with the present invention (e.g., filmS fiber
or the like~ is accomplished by conventional and well
known techniques. It will be apparent to those skilled in
the art that thq rubber stock applied may contain additives
such as w lcanizers, fillers, pigments, antioxidants and
the like.
Compositions produced according to the presen~
invention may be utilized for a wide variety of important
industrial applications. They may be used, for example, in
the preparation of pneumatic tires for automobiles, buses,
tractors and aircraft, in transmission belts, conveyor
belts, floor tiles, hoses, raincoats, luggage, and the like.
Especially valuable results are obtained when
the coating composition of this invention is applied to
polyester fibers and other shaped structures such as those
prepared from polyethylene terephthalate. Illustrative of
the polyesters useful in preparing shaped structures which
may be bonded to rubber by the process of this invantion
are those disclosed in United States Patents 2,465,319,
2,965,613 and 2,901,466.
- 16 -
