Note: Descriptions are shown in the official language in which they were submitted.
3~
;. ` .
Background o~ the Invention
The present i~vention concerns an improved me-
thod for adhering brass and brass~plated metal to rubber.
It also concerns a new class of rubber compou~ds having im-
pro~ed adhesion characteristics to brass plated metal.
The problem o~ securing adequate adhesion o~rubber to metal has been investigated extensively by those
skilled in the various aspects of ru~ber manu~acturing.
The best known reference on this subject, Buchan, Rubber
~ LI~a~3~ (Crosby~ Lockwood & Son, ~ondon, 1948~ des-
cribes the now widespread practice o~ vulcanization of rub~
ber onto a brass~plated metal substrate. The use of bonding
agents such as isocyanates, rubber halogens, a~d thermoplas-
tlcs, between the metal and the rubber is found in some ap-
plications.
l'he alteration of -the rubber compound i-tself to
; - : :
improve its adheslon to the metal substrate~has~been consi-
dered5 and~one such alteration is disclosed in Canadian Pa- `
tent 793,7940 An acidic compound and a free radical curing
system is incorporated into rubbers and rubbery copolymers
undèr the teachings o~ the Canadian patent.
.
Compounds of various rubbers, natural and syn-
thetic, with small amounts o~ certain polymeric polysul~ides,
are described in British Patent l,144,634. Advantages taught
in the Bri-tish patent are reduced sul~ur requirement, ease o~
compounding, and nonblooming vulcanlzates.
The adhesion of polysulfides to metals (aircraft
- ~uel tanks~) is mentioned in U. S Pa-tent 3,099,643, and
- their use as a cold setting adhesive for glass, wood and
metals is discussed in Jorczak and Fettes, "Pol~sulfide
, ~
:' ,
Liquid Polymers,"Industrial and En~ineering__Chemistr~ Vol.
~3, pp. 324, 327 (February, 1951).
Summary oE -the Invention
The objects of this invention are: tl) to provide
an improved method of adhering rubber compounds to brass-
plated metal substra-tes; and (2) to pro~ide a metal rein~or-
ced rubber compound wi-th improved adhesion. Other objects
will become apparent as the description proceeds.
The above stated objects are realized through the
use of rubber compounds containing small amoun-ts of polysul-
fide polymers.
In accordance with their invention, a
vulcanizable composite o~ a rubber composition and brass~
plated steel reinforcing material, the polymeric portion
of which is comprised of a polysulfide polymer and
ano-ther polymer selected ~rom the group consis-ting of
natural rubber and synthe-tic diene rubbers in which -the
amoun-t of polysulfide i5 from 0.1 to 10~ preferably
abou-t 0.5 -to about 7. 4, volume percent of the total
polymer content.
For the purposes of -this inven-tion, the polymeric
portion is comprised of a polysulfide polymer and a rubber
preferab~y selected from the group consisting of natural
rubber; blends of natural rubber and SBR rubber; blends of
natural rubber and solution polybu-tadiene rubber; SBR
rubber; emulsion polybutàdiene; e-thylene~ propylene~ dicyclo- ~;
pentadiene terpolymer, and polyisoprene. ~-~
For this invention the reinforcing material is
desirably selected from the group COi'lSiSting of brass- r
plated s-teel wire and fabric woven :Erom brass-plated
steel wire.
-Y ~" '--L_'--
For purposes of this application, the -te~Q r~
sulfide polymer" is defined to mean any organic elastomeric
polymer containing polysulfide linkages in the polymeric
chain. This class of polymers includes bu-t i5 not limi-ted
to Thiokols, sul~ur modified polychloroprenes, and sulfur
containing polymers oF diene monomers alone or copolymerized
with one or more other polymerizable unsaturated compounds
as described in U.S. Patent 2,234,204. A more detailed
description of these polymers follows.
Thiokols are polymers obtained by -the reaction
between polysulfides of an alkali metal (e.gO sodium
polysulfide) and one or more organic dihalides (e.g.
ethylene dichloride). Other monomers such as
trichloropropane may he incorporated into the polysulfides
in minor amo~mts. They are available commercially in
several varieties o~ solid and liquid polymers.
The particular Thiokols utilized in the develop-
ment of -this inv~ntion are represen-tative of polysulfide poly-
- -2a-
mers commercially available. Their precise chemical compo-
sition is unknown to this applicant, and the molecular struc-
tures given may be subject to sligh-t variations having little,
if any, effect on their properties. They are as ~ollows:
m iokol A - a reaction product of sodium tetra-
sulfide and ethylene dichloride having the segmental molecu-
lar structure ~CH2CH2S4-)n. A more detailed description can
be ~ound in UO S0 Patents 1,890,191; ~,923,392 and Re. 19,
~07. U. S. Pate~t 19890,191 define~ the polymer as a product
comprising a compound composed of not less than 70 percent
sul~ur in chemical combination with CnH2n groups correspond
ing to olefins ha~ing less than four carbon atoms, the per-
cent being weight percent.
m iokol FA - a copolymer o~ ethylene dichloride 9
sodium polysul~ide and bis(2-chloroethyl) formal with hydroxyl
end groupsO Copolymers of organic dihalides (e.g. ethylene
dichloride and bis(2-chloroethyl) formal) are disclosed in
U. S. Patents 2,~63,614 ~Example 7 and page 10, column lj
lines 3 to 7 and 34) and 2, 363,615~ The fact that they con-
tain hydro~yl terminals is discussed in Fettes and Jorczak,
"Polysulfide Polymers," ~ ,
Vol. 42, pp. ~217, 2218, (Novem~er, 1950) and in U~ S. Pa- -
tent 2,606,173.
Except for the hydroxyl end groups, these copoly-
mers are defined in U. S~ Patent 2,363,6149 as a copolymer
which is ~ubstantially a chemical combination of a polymer of
the ~nit [RS1 to 6] and a polymer o~ the unit LR'S1 to 6]~ R
and R' being radical~ having structures selected from the
groups
.
~33~ 7
-- C ~ C --
(representing carbon atoms separated by intervening structure)
and
C - C - ~
(representing adjacent carbon atoms) where R and R' have dif-
feren-t specific structuresO In -the case of Thiokol FA, R is
-C2H~ and ~' is -C~I2CH20CH20CH2~H2-
m iokol ST - a copolymer of sodium polysulfide~
bis(2-chloroeth~1~ formal, and trichloropropane ~which pro-
duces branching in the polymer chains) with thiol end groups.
U0 S. Patent 2,363,614 (at page 8 to page 11, right column,
line 56) reveals the copolymeri2ation of 1,2,3-trisubstituted
propane with disu~stituted dlethyl formal in a solution of
sodium tetrasulfide. Such a polymerization is described in
detail in ~xamples I and XI of U. S. Patent 2,466,963. The
reductive cleavage reac-tion revealed in U S. Patent 2,466,
963 is~ according to Bertozzi, "Chemistry and Technology of
Elastomeric Polysulfide Polymers", ~L~Yl:~Y~ eb-L _~
, Vol. 41, pp. 114l 116 (February, 1968), used in the
synthesis of Thiokol ST elastomer.
Thiokol ST is comprised o~ the same generic type
of polymer units which Thiokol FA is comprised of with the
further limitations tha-t the sulfide linkages are disulfide -~
linkages9 R is the unit -CH2-CH-CH2- and R' i~ the unit
-cH2cH2ocH2ocH2cH2 -
Liquid Thiokols such as m iokol LP-31 - a liquid
copolymer of bis(ethylene oxy) methane groups and polysulfide
linkages with thiol end groups, having -the general structure~
.
33~ ~
Hs(c2H4-o-cH2-o-c2~4ss)xc2H4-o-c~2 0 C2 L~
LP-31 has a molecular weight of approximately 8000. Other
LP-type polymers have molecular weights ranging from approxi~
mately 500 to 4000. Molecular weights ~or a liquid polysul-
fide can be as high as 50,000 (as opposed to 100,000 to
200,000 for most solid polysulfides such as Thiokol A and FA)
according to U~ S. Patent 2,875,182. The preparation of
liquid LP-type polymers is described in Example XVII of U.S~
Patent 2,466,g63 and in U. S. Patent 2,875,182, Example 60
In U~ SO Patent 2t466,963, LP-type polymers are
described as polythiopolymercaptans in a liquid form at
ordinary temperatures (e.g. 25C.) comprising a series of
segmeric units having the general formula -SRS- linked to- ;
gether to form a polymer wherein R is a radical having a
structure selected from the group consisting of -C- desig-
nating a single carbon atom, - C - C ~ designating two
adjacent carbon atoms, and
~- -- C ... C --
;~ "'
designating two carbon atoms joined to and separated by in-
tervening ætructure. In the case of Thiokol LP-31, R is one
of the last type of radical9 in particular
-CH2CHz-O-CH2-0-CH2CH2~
The words "~hiokol LP", "Thiokol ~A", "Thiokol A"
and "Thiokol ST" are trademarks of Thiokol Chemical Corpora-
tion.
Sulfur modified polychloroprenes are described
in UO SO Pa-tent 1,950,439. That patent describes sulfur and
certain thiuram disulfides as catalysts for controlling -the
--5--
:
type of polychloroprene produced, maximizing yields, and :
controlling reaction rate. However, i-t was la-ter discovered :
that the sulfur actually becomes part o~ the polymer itself
~see Mochel, ~. E.~ "Structure of Neoprene" ? ournal of
r.~ Dg~ Vol. VIII, pp. 583-592 (1952 and Klebanskii
et al, J. Pol~m. Sci, Vol. 30, pp. 363-373 (1958)]. 1.
From a reading of the above references, sul~ur
modified polychloroprenes can be defined as the class of
polymers obtalned by polymerization of 2-chloro-1,3~butadiene
in -the presence of sulfur or thiuram disulfides as lis-ted
in U.S. Paten-t 1,950,4~9, page 2, column 2, lines 2 through
U.S. Patent 2,234,204 describes sulEur containing
polymers of "butadiene hydrocarbons" (defined at page 3,
column 2~ lines 1 through 8). The "bu-tadiene hydroca~bons"
may be used alone, in admixture wi-th each other, or with l~
.
one or more other polymerizable unsa-turated organic com-
. pounds, examples of which.are given at page 3, column 2,
lines.].7 through 35. Su~icient examples are included in
U.S. Patent 2?23h,204 to illustrate ~his class of polymer.
Typical of the class is -the polymer containing 100 par-ts
by weigh-t of 1,3~bu-tadiene, 50 parts by weigh-t of acryloni-
trile5 and 0.6 parts by weight of sulfur (Example No. 7
in the patent referred to).
The term "polysulfide polymer" also includes
: those polymers of UGS. Pa-tent 3,373,146 having polysul~ide ~
linkages in the polymer chain. This patent discloses
low mo~~.ecular weight (usually 500 to 10,000~ mercaptan :~
terminated copoly- :
~ -6~
mers of sul~ur and at least one diene monomer. The defini-
tion of these polymers is ~ound at column 2, lines 17 through
31 of the reference patent.
The preceding descriptions of polysulfide polymers
are not intended to be all-inclusive or limiting but are
merely illustrative.
Also9 the term "compound" as used herein means the
composition o~ matter formed by combining one or more rubbery
polymers selected ~rom the group consisting of natural rub-
ber, synthetic diene rubber, and polysulfide polymer with
conventional compounding ingredients, which ingredients typi-
cally include plasticizer, fatty acid, vulcanizing agent,
accelerator, age resistors, lubricant, and reinforcing filler.
In the practice of this invention, the rubber is
mixed in the conventional manner, for example, on a mill or
in a Banbury, with the usual compounding ingredients (e.g. ~ -
carbon black, processing oil, zinc oxide, fatty acid, sulfur,
accelerator, antioxidant, antiozonant, plasticizer, and wax).
j From 0.1 to 10.0 volume percent of the polymeric content (i.e.
; 20 the natural rubber, polyisoprene, etc.) is a polysulfide
polymer, and the concentration of sulfur normally in the mix-
ture can be decreased. The resulting vulcanizable compound
is pressed onto the metal substrate (e.g. brass-plated steel
wire) which operation can be done on a rubber calender.
Various other operations (which depend upon the
desired end product) follow. For example, tire carcass
stock is cut and combined with other rubber components (e.g.
bead, tread stock~ and sidewalls) on a tire building machine.
These operations are followed by molding and cur-
-7-
ing under controlled pressure and temperature.
The principal benefit derived from the incorpora
tion of polysulfide polymer into the rubber compound is an
increase in the adhesion of the brass-plated metal su~strate
to the rubber in aged samples. In experiments, the adhesion
between the metal and the rubber in the modif'ied samples is
1.4 to 3.9 times that of unmodified stock.
There are other benefits incidental to the substi-
tution of polysulfide polymers for other rubber. ~en they
are used in natural rubber stocks they reduce the tendency
to reversion as shown in Rheometer tests. Experîments with
natural rubber have shown that the amount of sulfur can be
reduced, and heat build-up in the rubber on flexing is re-
duced.
~ Description of the Preferred Embodiments
The technique and materials of this invention are
useful in any application wherein the bonding of rubber to
: .
~ brass-plated metal or brass is important. They are particu-
. .
~ larly ad~antageous in the manufacture of tire carcass stock. ~
, ~
The term ~'carcass" refers to the fabric-reinforced parts o~
the tire also called body plies and belt. A typical applica-
tion of wire reinforced rubber is the belt ply which is bet-
ween -the radial plies and tread in a steel-belted radial tire.
Because tires are subject to many varying stresses
under a wide range of temperatures, adhesion of the carcass
rubber to its reinforcement is critical. Tires which are
retreaded many times such as truck and earthmover tires require
a durable carcass to outlas-t several tread applications. -~
Any sul~ur vulcanizable natural or synthetic rubber
33~ 7
may be utilized with polysulfide polymers in manufacturing
compounds o~ this invention. The rubbers typically used
include natural rubber ~e.g. smoked sheet) and diene rl1bbers
such as SBR, solution polybutadiene, emulsion polybutadiene,
synthetic polyisoprene, ethylene propylene dicyclopentadiene
terpolymer, and blends of the above.
The preferred amount of polysulfide is dependent
; upon the type of polymer to be utilized in the compound, the
type of polysul~ide and the condition for which the end pro-
duct is designed. However, it has been found that ~olume
percents ranging from 0.5 to 7.4 percent polysulfide are pre-
ferred.
Processing of the stock is the same as is normally
done without the polysulfide polymer with certain exceptions.
Before adding polysulfide to the compound mixture when using
Thiokol A, Thiokol FA or Thiokol ST, some rubber should be
incorporated into the polysulfide (e.g~ on a mill). It has
been found that a preliminary milling of natural rubber with
polysulfide in a weight ratio of 18 parts natural rubber to
10 parts polysulfide facilitates dispersion of the polysulfide
into the compound and improves tensile strength and tear
strength over stocks made without this prior mixing.
Also, as an aid in mixing of the polysulfide with
the other ingredients of the compound, a masterbatch of carbon
black and polysulfide polymer can be made using approximately
30 volumes of carbon black per 100 volumes of polysulfide.
m e carbon black and polysulfide masterbatch is easier to add
to an internal mixer such a~ a Banbury, and it helps to insure
an even distribution of carbon black throughout the compound.
3~`7
In the case of Thiokol LP, prior mixing with carbon
black or other rubb0r is unnecessary beca~se the liquid
Thiokols are easily incorporated into the composition.
The polysulfide or a masterbatch o~ polysulfide poly-
mer with rubber or carbon black preferably should be added to
the other compounding ingredients last, along with the sulfur.
This practice helps to prevent scorch.
The following examples are presented not to limit but
to illustrate the compounds and methods of this invention.
Unless otherwise stated parts are parts by weight per 100
parts by weight o~ total polymer and percentages are volume
percent of total polymer content. ~
Various vulcanized compounds have been manufactured ~-
experimentally and tested for original and aged adhesion and
- 15 heat build-up. The method o~ measurlng adhesion of brass
plated metal to the compound was as follows: test specimens
;~ were prepared by curing in a mold a rectangular block of~ polymer compound with dimensions o~ 12 mm. x 12 mm. x 75 mm.
,',! ~ into which had been embedded two brass plated steel cords 5
one at either end of the block. The mold was so designed
that the wires were embedded axially and symmetrically, and
insertion length of the wire in-to the block was always 19
mm. The wires did not go completcly through the block nor
did they touch each o-ther.
.1 ~
Su~ficient wire was left protruding from the ends of
the block to allow placement of a sample in the jaws of a
tensile tester such as a Scott tester or an Instron tester.
The two jaws or clamps of the testing apparatus held the two
wire ends. The rubber itsel~ was not held~. Force required
.
to pull one of the wires out of the block was measured with
a ~ixed jaw separation rate (5 cm. per minute was used).
Heat build-up in a compound was measured by the Goodrich
Flex Test, QSTM ~623.
The compo~ds used in evaluating the effectiveness
of the polysulfide polymers were natural r~bber compounds
designed for use in tire carcass stock. Where applicable, ::
reduction in sulfur or to-tal parts of sulfur used is shown
in the data tables which follow. ; ;~
EX.AMPLE I
A standard natural rubber compound, which shall be
referred to as Standard Compound A, was modified by replac-
ing part of the natural rubber in the compound with vary-
: ing amounts of Thiokol A and by varying the amount of sul-
fur used. Test results are shown in Table I. Adhesion test
specimens were cured 85 minutes a-t 13~ C.
Table 1
: : Modi~ications of Standard Compound A
Natural Rubber Vol.%100 95.6 94.4 92.6 92.6
20 : miokol A ~ Vol.% 0 4 4 5.6 7.4 7.4
~:: Sul~ur (parts) 6.5 5 5 5.5 5.5 4.0
Adhesion (Original)
in Newtons 483 562 403 492 501
Adhesion (Aged 10 days in
H20 at 90C) in Newtons 203 697 763 783 698
Temperature Rise, C. in
Goodrich Flex Test36.4 34.2 32.8 33.1 34.2
: All aged adhesions of the Thiokol stocks were ap-
,
proximately three times that of the control with~ut Thiokol~
EXAMPLE II
me procedure ~ollowed in this example is similar
to the previous example except that a different Standard
Compound, Standard Compound B, was used, and lower concen-
,
, .
. . .
trations of sulfur were tried. Thiokol A was again used as
a substitute for a portion of the natural rubber content.
Results appear in Table 2. r'
Table 2
Modifica-tions of Standard Compound B
Natural Rub~er Vol.~ 100 95.6 94.4 92.6 92.6
Thiokol A Vol.% 0 4.4 5.6 7.4 7.4
Sulfur (parts) 5.0 L~, 0 4 o 0 3 . 52 . 25
Adhesion (original) in
Newtons 622 934 867 907 836
Adhesion (aged 10 days in
H 0 at 90C.) in Newton~ 448 687 690 710 647
~-Tempe2rature Rise, ~C.) in
Goodrlch Flex Test 38.9 34.7 32,8 32. 234 . 7
All original and aged a &esions of the Thiokol con-
taining stocks exceeded that of the control. As in the pre- ;~
vious example, the Thiokol containing stocks demonstrated a
~, lower heat rise than the control.
EXAMPLE III
An experiment was done at 2~1 volume percent poly-
.~
sulfide polymer in Standard Compound A with a portion of ;
~t the carbon black ln the compound replaced by Hi-Sil 233
(a hydrated silicate filler marketed by PPG Industries, Inc.)
and at a reduced sulfur leve]. Tests were performed as in
the previous two examples with the addition of an adhesion
test on a sample aged 10 days in a nitrogen atmosphere at
121C. and 551. Kilopascals gauge pressure. Resul-ts are
reported in Table 3.
: :
-12-
~ 3~$`7 ~:
U~ ~ .
.
~ o o o C~i 0 0 U' ~ 2 ~ ~
~ U~ ~ ~
~o ..
. ~ ..
~ o U~
~1 O~ ~ C\l C-
.
E~ ~ O O C~l O 00 0
O Lri 15`\ ~ r
; ;-
O rl , ,
V ~: U~
C~ ~ ''.
~ O ~ O 00~ 0~ ~ O O ~ 0
0 ,!!~ C~ l
.~ ~ t,) J~
O : ~ '
:: ~I) ~
,~ C~ r-l C~l ~ ~ ,
~ i ~
, ~ O ~ ~ O O O 0
.-. ~ o
'' ~
: ~ O ~
0 O O O O O00 ~ ~ a~ ~ ~ o
O Ll'\ 1~ Cl~ ~ ~ ~
E-~ ~ h :~
, ~ i O ~ L~
~ _ O O O O OU~ I ~D O ~ Ll~
CH - O ~ I ~ ~C)~
O ~ ~ ~ ~ ~ :
~ ~ = = = = Ul :.
,Q 0
~ O
5 ~ ~ ~a) ul
, o o ~ :,
h t' ~ tq
~ S~ ~~ ~; ~ X '~'
h 'C 1~ ~ ~ nl ~--bD 'd ~ O-~l ~1~1
a) ~ h ~Do
m
o o o o ~ 'I o
o o o o ,~ u~ ~ a) a) ~ a~
;;
,
.
~3i33~7
Original adhesion in three o~ the four Thiokol-con-
-taining s-tocks was improved o~er the controls, and aged ad-
hesion of all the Thiokol-containing stocks was superior to
the controls. Comparison of the two controls reveals that
the use of Hi-Sil 233 filler produced greater hea-t rise in
the Goodrich Flex Test~ All of the Thiokol-containing stocks
show0d less heat rise than the control containing Hi-Sil.
Adhesion testing has also been done on compounds con-
taining blends of natural rubber wi-th solution polybutadiene
and blends of natural rubber with SBR rubber. The original
and aged adhesion test results for these blends demonstrated
improved adhesion for compounds containing polysulfide poly-
mer comparable to the data given above for natural rubber ~;
compounds.
m e curing characteristics of several compounds of
this invention were measured on an oscillating disk cure
meter (ASTM D2084). Tests were run at 149C. with a stock
containing 3.7 volume percent Thiokol ST in Standard Com-
pound A and at 135C. with stocks containing 7 volume per-
cent m iokol A in Standard Compound A and var~ing concen-
trations o~ sulfur in the compound. In the tests at 7 vo-
lume percent Thiokol A sulfur con-tent in the control was 6.5
parts while that in -the polysulfide containing stocks varied
from 4.0 to 5.5 parts~ Although the natural rubber control
stocks without polysulfide polymers exhibited a tendency to
reversion, the stocks containing polysulfide polymers mixed
with natural rubber did not.
Reversion is a decrease in measured -torgue or modulus
after maximum torque has been reached. It is measured as the -;
-14-
33~'7
time required to fall to 98 percent of maximum torque after
maximum tor~ue has been reached.
Polysulfide con-taining s-tocks also exhibited a con- ;
tinuing vulcanization effect resul-ting in higher maximum
tor~ue than the controls and longer times to reach maximum
torque. This phenomenon was true at all sul~ur levels test-
ed~
While certain representative embodiments and details
; have been shown for the purpose of illustrating the inven-tion, it wlll be apparent to those skilled in this art that
various changes and modifications may be made -therein with-
out departing from the splrit or scope o~ th- invention.
'
,
