Note: Descriptions are shown in the official language in which they were submitted.
CA 02257707 1998-12-31
- 1 - '
Curing of Hutyl Rubber
Field of the Invention
This invention relates to curing of butyl rubber.
Background of the Invention
Butyl rubber is produced commercially by
copolymerizing isobutylene with small amounts of isoprene.
Butyl rubber in the uncured state is a weak material having
the typical properties of a plastic gum; it has no definite
elastic limit, that is, upon slow application of tensile
stress, it elongates almost indefinitely without breaking, and
exhibits virtually no elastic recovery after the stress is
removed. On the other hand, vulcanized or cured butyl rubber
is a strong, non-plastic material; it has an elastic limit,
as well as the ability to return substantially to its original
length after being stretched as much as several hundred per
cent.
Butyl rubber is typically cross-linked or vulcanized
by one of three basic methods. These are (1) accelerated
sulfur vulcanization, (2) cross-linking with dioxime and
related dinitroso compounds, and (3) a phenol-formaldehyde
Cresol) resin cure. This invention is concerned with the
latter curing method.
The curing agents generally used include phenols and
phenol-formaldehyde resins produced by condensation of a
phenol with formaldehyde in the presence of base. Typical
agents include 2,6-dihydroxymethyl-4-alkyl phenols and their
76533-9
CA 02257707 1998-12-31
- 2 -
polycyclic condensation polymers. Examples are given in U.S.
Patent No. 2,701,895 (February 15, 1955, which is hereby
incorporated by reference).
Curing occurs through the reaction of the methylol
groups of the phenols or resin with the uncured rubber to form
cross-linked structures. Mechanisms of such curing of butyl
rubber have been proposed (see for example R.P. Lattimer et
al, Rubber Chemistry 7 Technology, volume 62, pages 107-123,
1988 which is hereby incorporated by reference).
Cured butyl rubber has a number of uses, one of
which is in tire-curing bladders. Tire-curing bladders are
inflatable and have an annular toroidal form. The curing
bladder is disposed within a raw tire casing as an aid in
shaping a tire by applying internal heat and pressure to the
tire casing in a moulding press in which the tire is
vulcanized. For this purpose, the bladder is inflated with a
fluid heating medium, usually steam, under pressure, which
causes the bladder to expand and thereby forces the tire
casing into close conformity with the vulcanizing mould. Upon
completion of the vulcanization, the curing bladder is removed
from the tire, and inserted in another raw tire for a
repetition of the curing operation. The bladder is thus
repeatedly used for a number of cycles.
Subjecting phenol-formaldehyde resin cured butyl
rubber to elevated temperatures, such as those reached during
the process of curing tires, e.g., above 160°C, results in
hardening or ageing of the butyl rubber. As a result, the
76533-9
CA 02257707 1998-12-31
- 3 -
butyl rubber has a limited life in such applications.
Summary of the Invention
In one aspect, the invention provides a formulation
comprising uncured butyl rubber, a halogen-containing
compound, and a polycyclic phenol-formaldehyde resin having
dimethylene ether bridges and methylene bridges wherein the
molar ratio of dimethylene ether bridges to methylene bridges
is less than about 2.5:1 and the ratio of said polycyclic
phenol-formaldehyde resin to butyl rubber is less than 1:10.
Optionally, said formulation may also include a filler, a
process oil, a lubricant, and other desired ingredients known
to one skilled in the art.
In another aspect, the invention provides a process
for preparing the formulation described above comprising
admixing uncured butyl rubber, a halogen-containing compound,
and the polycyclic phenol-formaldehyde resin, wherein the
ratio of said polycyclic phenol-formaldehyde resin to butyl
rubber is less than 1:10.
In another aspect, the invention provides a flexible
vulcanizate made using the above formulation. Preferably, the
vulcanizate is in the form of a tire-curing bladder. The
vulcanizates of the invention display improved ageing
characteristics, compared with vulcanizates previously used
for this purpose. Formation of curing bladders is described,
for example, in the above-mentioned U.S. Patent No. 2,701,895.
A curing bladder is subjected to repeated applications of heat
and pressure, as pressurized steam at a temperature of about
76533-9
CA 02257707 1998-12-31
- 4 -
150°C or higher, often 160°C or higher, is injected into the
bladder during the tire-forming process. The vulcanizate of
the invention is suitable for this and similar applications,
as its improved to ageing properties enable it to withstand
these repeated applications better than other known
vulcanizates. Commercial curing bladders currently available
have a life of about 400 cycles, i.e., they can be used about
400 times before their properties have deteriorated such that
they are discarded. Vulcanizates of the formulation of the
present invention permit the life to be enhanced by at least
about 10% or more, i.e., to about 440 or more, and in some
instances the enhancement is about 30% or even 50% or more.
In a further aspect, the invention provides a
process for making such vulcanizates comprising converting the
formulation to any desired shape and size, and vulcanizing at
elevated temperatures, preferably in the range of from 125 to
250°C, and more preferably at 150 to 200°C.
In a further aspect, the invention provides use of
the formulation described above as a tire-curing bladder
formulation.
Brief Description of the Figures
Figure 1 is a graph showing the stress (MPa) versus
hot air ageing time (hours) at 180°C of Formulations A in
accordance with the invention and comparative Formulations B,
with 1.5 molar % isoprene content, at various elongations.
Figure 2 is a graph showing the effect of hot air
76533-9
CA 02257707 1998-12-31
- 5 -
ageing on stress at 50% elongation for Formulation A at
varying isoprene contents.
Figure 3 is a graph showing the effect of hot air
ageing on stress at 50% elongation for Formulation B at
varying isoprene contents.
Figure 4 is a graph showing the stress (MPa) versus
strain (%) of Formulations A and B, with varying isoprene
content, after curing for 30 minutes.
Figure 5 is a graph of torque versus curing time at
180°C of Formulations A and B at varying isoprene content.
Detailed Description of the Invention
This invention is related to the unexpected
discovery that resin-cured butyl rubbers with improved
properties are obtained by curing the butyl rubbers with low
amounts of phenol-formaldehyde resins with low levels of ether
bridging. Such improved properties may include improved high-
temperature ageing characteristics, faster cure rates, and
better stress/strain properties. The invention provides a
formulation comprising such resin, an uncured butyl rubber, a
2o halogen-containing compound and, optionally, a filler, and a
process oil.
Base-catalysed phenol-formaldehyde resins are made
by condensing a phenol with formaldehyde in the presence of
base. The reaction results in the formation of phenol-
alcohols which may subsequently undergo condensation reactions
to form polycyclic phenols. An example of a polycyclic
phenol-formaldehyde resin is given below:
76533-9
CA 02257707 1998-12-31
- 6 -
OH OH OH
i H2 R 1 R 1 CH2w
HO O O O OH
R R n R
As shown, the phenol moieties are bridged by R'. These
bridging moieties, R', may be the same or different and may be
either methylene (-CH2-) or dimethylene ether (-CH2-O-CH2).
The integer n may have values from 0 to 10, preferably 0 to 5.
It is preferred that the integer n has a value sufficiently
high that the resin is a solid. The group R is an alkyl,
cycloalkyl, cycloalkylalkyl, aryl or aralkyl group. It may
contain up to about twelve carbon atoms. Preferred R groups
are alkyl groups containing up to 8 carbon atoms, especially
methyl, tert-butyl and tert-octyl groups; see U.S. Patent No.
2,701,895 for further examples.
The Applicant has noted that resin-cured butyl
rubbers with improved properties are obtained by curing with
phenol-formaldehyde resins with low levels of ether bridging.
According to this invention, the molar ratio of dimethylene
ether bridges to methylene bridges in the phenol-formaldehyde
resin is less than about 2.5:1, preferably less than about
1.7:1, most preferably less than about 1:1. Examples of
suitable phenol-formaldehyde resins which may be used in the
invention include the resin available under the trade-mark
HRJ-10518 (Schenectady International) which has a molar ratio
76533-9
CA 02257707 1998-12-31
_ 7 _
of dimethylene ether bridges to methylene bridges of about
0.65:1. The amount of phenol-formaldehyde resin in the butyl
rubber formulation should be about less than 9.5 parts,
preferably less than about 9 parts, more preferably less than
about 8 parts, to 95 parts by weight of uncured butyl rubber.
The amount of phenol-formaldehyde resin should not be less
than about 3 parts, preferably about 4 parts, more preferably
about 5 parts, to 95 parts by weight of uncured butyl rubber.
A preferred formulation uses 7 parts of phenol-formaldehyde
resin per 95 parts of uncured butyl rubber.
A butyl rubber composition requires a small amount
of a diene comonomer, usually isoprene, so that the
composition can undergo cross-linking, or curing. Grades of
butyl rubber can be distinguished by their isoprene content
and Mooney viscosity (related to the molecular weight).
Examples of uncured butyl rubber useful in this invention may
have from about 0.5 mol% to about 10 mol% isoprene, and
preferred butyl rubbers contain from about 0.5 to about 2.5
mol% isoprene, more preferably from about 0.9 to about 2.1
mol% of isoprene. Mention is made particularly of butyl
rubber having about 1.4 to about 1.6 mol% isoprene. Some
suitable butyl rubbers have a Mooney viscosity of about 25 to
70, preferably about 30 to about 63 (RPML 1 + 8 Q 125°C).
A halogen must be present in the formulation.
Examples of halogen-containing compounds include organic
compounds such as olefin-containing polymers having pendant
chlorine atoms, such as polychloroprene, available under such
76533-9
CA 02257707 1998-12-31
_ g _
trade-marks as Baypren (Bayer), Butachlor (Distagul) and
Neoprene (Du Pont). The amount present in the formulation is
preferably within the range of about 1 to about 10 parts, more
preferably about 4 to about 6 parts, most preferably about 5
parts by weight to about 95 parts of uncured butyl rubber.
Alternatively, chlorine-containing salts, for example stannous
chloride, can be used as the halogen-containing compound. It
is possible that the required halogen, e.g., chlorine or
bromine, atom is provided as a component of one of the other
l0 essential ingredients of the formulation, rather than being
provided by a separately added compound. For instance, it is
possible to use a chlorinated or brominated butyl rubber, or a
chlorinated or brominated polycyclic phenol-formaldehyde
resin, rather than a separately added compound such as
polychloroprene or stannous chloride. It is preferred,
however that unhalogenated butyl rubber and unhalogenated
phenol-formaldehyde resin are used and that the halogen is
added in, say, polychloroprene or stannous chloride. In
general, halogen-containing compounds are known to persons
20 skilled in the art, who will know what halogen-containing
activators can be used, and in what amounts, or can readily
determine this by routine experimentation that does not
involve the exercise of any inventive faculty.
Fillers may be added to the formulation. Examples
of fillers include talc, calcium carbonate, clay, silica,
titanium dioxide, and carbon black. Carbon black is
preferred; more preferably, the carbon black ranges from N-
76533-9
CA 02257707 1998-12-31
- 9 -
770 to N-110; most preferably the carbon black is N-351,
classified in accordance with ASTM D1765 (see Maurice Morton,
"Rubber Technology" 3rd Edition, Chapman & Hall, New York,
1995, pages 69-70, hereby incorporated by reference). The
amount of filler present in the formulation is preferably
within the range of about 40 to about 80 parts, more
preferably about 45 to about 60 parts, most preferably about
50 parts by weight to 95 parts of uncured butyl rubber.
The formulation of the invention may contain a
process oil, and many suitable process oils are known to those
skilled in the art. Examples of suitable process oils include
castor oil and paraffinic oils.
Zinc oxide may be added as an activator, suitably in
an amount of up to about 8 parts, preferably about 5 parts,
per hundred parts of rubber. Stearic acid may also be added,
to assist in solubilising the zinc oxide in the formulation.
The butyl rubber formulation described may be made
by mixing the components of the butyl rubber formulation
described above, and additionally any other desired optional
ingredients such as accelerator, extender, lubricant,
plasticizer, and the like, in any convenient manner used in
the rubber industry, e.g. on a mill or in an internal mixer.
Vulcanizates can be made from the formulation of the
invention by converting the formulation to any desired shape
and size, and vulcanizing at elevated temperatures, usually in
the range of from 125 to 250°C, and preferably at 150 to
200°C. The vulcanization may be carried out in any commonly
76533-9
CA 02257707 1998-12-31
- 10 -
known manner, as in a mould under pressure, or in an open
container in an oven, for a suitable period of time, usually
within the range of from 5 minutes to 24 hours, the higher
temperatures being employed with the shorter time within the
stated ranges. Examples of vulcanizates include tire-curing
bladders, conveyor belting for hot-materials handling, and
high-temperature service hoses.
In another aspect, the invention provides a
formulation comprising uncured butyl rubber, a halogen-
containing compound, and a polycyclic phenol-formaldehyde
resin having dimethylene ether bridges and methylene bridges,
wherein the molar ratio of dimethylene ether bridges to
methylene bridges is less than about 2.5:1 and the ratio of
uncured butyl rubber to said polycyclic phenol-formaldehyde
resin is greater than 10:1 and may be as much as 20:1.
Examples
Butyl Rubber Formulations
Two different types of butyl rubber formulations
were prepared. Formulations A are in accordance with the
invention, and contain a phenol-formaldehyde resin with a
molar ratio of dimethylene ether bridges to methylene bridges
of 0.65:1. Formulations B are comparative and contain a
different phenol-formaldehyde resin with a molar ratio of
dimethylene ether bridges to methylene bridges of 2.9:1. The
isoprene content in the uncured butyl rubber component was
varied to make up a series of five examples of each of
Formulations A and B. The isoprene content was one of the
76533-9
CA 02257707 1998-12-31
- 11 -
following: 0.88, 1.18, 1.49, 1.79, and 2.09 mol % of
isoprene. Amounts are given in parts by weight:
A B
Uncured Butyl Rubberl 95 95
Polychloroprene2 5 5
Carbon Black N-351 50 50
Castor Oil 7.5 7.5
Stearic Acid 1.5 1.5
Zinc Oxide 5 5
Phenol-Formaldehyde Resin3 7
Phenol-Formaldehyde Resin4 7
lThe uncured butyl rubber contains 0.88, 1.18, 1.49, 1.79 or
2.09 mol % isoprene unit. 0.88 mol % corresponds to exclusive
use of PB100; whereas 2.09 mol % corresponds to exclusive use
of PB402. Mixtures of PB402 and PB100 were used to make the
other mol %'s. PB100 and PB402 are commercially available
from Bayer Inc., and have Mooney's of 32.7 and 33.4,
respectively (RPML 1 + 8Q125°C).
2Baypren 210 is commercially available from Bayer Inc. It is
a polychloroprene with medium crystallinity.
3Used was HRJ-10518, commercially available from Schenectady
International and containing a molar ratio of dimethylene
ether bridges to methylene bridges of 0.65:1.
4Used was SP-1045, commercially available from Schenectady
International and containing a molar ratio of dimethylene
ether bridges to methylene bridges of 2.9:1.
Tests were performed on Formulations A, the
formulations of the invention, and compared with similar tests
performed on Formulations B, formulations not of the
invention. Subjecting the butyl rubber formulations to
temperatures of 180°C first results in vulcanization or curing
of the rubber. Longer times, such as 6 hours or more, result
76533-9
CA 02257707 1998-12-31
- 12 -
in ageing or hardening of the rubber. This may be the result
of cross-linking, or some form of unwanted chemical alteration
of the polymer network.
The effect of elevated temperature (180°C) on the
stress at various strains for Formulations A and B with 1.5
molar % of isoprene is shown in Figure 1 and Table I. In
every case, the aged (6 hours or more) modulus is much lower
for Formulation A, the formulation of the invention.
The effect of varying isoprene content of
Formulations A and B on the stress as a function of ageing
time is shown in Figures 2 (Formulations A) and 3
(Formulations B) and Tables II (Formulations A) and III
(Formulations B). Comparison of the two Figures shows that in
all cases Formulations A give lower stress after ageing (i.e.
ageing being 6 hours or more at elevated temperature).
The stress after curing, but no ageing, was also
examined. Stress-strain tests were performed on both types of
Formulations, varying the isoprene content, after a 30 minute
cure at 180°C. The results are given in Table IV and in
Figure 4. In this case, the unaged stress is higher for
Formulations A.
The initial cure rate of Formulations A and B is
shown in Figure 5. As shown, especially over the first 20
minutes the initial cure rate is faster for Formulations A.
76533-9
CA 02257707 1998-12-31
- 13 -
oD lf1 N ~O lD M N t0 N
d~ rl Ln In M d~ O Lf1 O
M d~ N M N M N M
a
0
4" 1 M d~ N d~QO N N Lf1N N o0
O N N M L(1d~ l~ 00 rid~
O
O ~ ~ ~ t~d~ lf1M M N M N
M
4 1 ~ O
x
f'a
d~ N ~O Ino0 I~ l0N d~ d~M
L~
e-i O rl 41 l~N L~M
N Lfl
l~d~ d' N M N N
u1 N
O
O 1l1 ri O
11 N W
a
O O 1D 01 L~rl rl M M d~ M Lfl
01 01 Lf1M 00 01 Lll
I~
O
~ H ~ ~ . ~p. . . . . N
tll M d~ N N rl rl
N
a O
3
'~ ' N H
b
ri
4) ~ 111 N N d~ N ~DL~ 01 O~lD
O ~ l0
r l ~ w~lO~Lf1tl1Lf1Lf1N N O
O O
d~ M N N r-Ir-1ri r-1r-1
r-1
a
o b m ..
. ''[fd~ N L~ Lf1l~t~ N ~ t~
~ 01
N L O M Q1 d~N e-iO
v1 bi 01
p ~ ~ M M N rl rlrl r1r-I
O
Id ~ H
N
I
U H
FC P4r.~G4 ~CP4
~ P4FC
P4
s~ s~~ >~ ~ ~ >~ s~~
O O O O O O s~
-r-I-r-I-rl-~ .-i-r-IO O O
.N O
rd tort td tdrd t~
r-Ir-Ir-Ir-I.-I.- Wd cd~d
cd
dP 6
N ~ ~ S~S~
O O O O O O i-aS-af-i
S-~
v~ w w w w w w o 0 0
~n w w 0
w
w
w o~ o~o~ o~ oMo~
(Y~ O O O O O O oV~oWo~
o~
EI O O O O O O O O Il1
t!1 M M N N rirl to L(1I~
N
N
76533-9
CA 02257707 1998-12-31
- 14
TABLE II
EFFECT OF HOT AIR AGEING ON STRESS AT 100% STRAIN FOR
FORMULATION A. WITH VARYING ISOPRENE CONTENT
Formulation A: Stress C~ 50% (MPa)
ISOPRENE
CONTENT 2.09 1.79 1.49 1.18 0.88
AGEING hrs Unaged 1.16 1.11 1.2 1.18 1.09
0.5 1.28 1.33 1.29 1.34 1.22
6 2.03 1.97 1.94 2.03 2
12 2.58 2.91 2.4 2.57 2.47
24 2.91 2.84 2.82 2.5 2.44
48 2.62 2.49 2.43 3 2.93
76533-9
CA 02257707 1998-12-31
- 15
TABLE III
EFFECT OF HOT AIR AGEING ON STRESS AT 100% STRAIN FOR
FORMULATION B~ WITH VARYING ISOPRENE CONTENT
Formulation B: Stress C~ 50% (MPa)
ISOPRENE
CONTENT 2.09 1.79 1.49 1.18 0.88
AGEING hrs Unaged 1.1 1.11 1.11 1.07 1.05
0.5 1.33 1.31 1.29 1.3 1.26
6 2.23 2.35 2.3 2.36 2.1
12 2.83 2.86 2.74 2.73 2.63
24 3.35 3.24 3.12 2.85 2.69
48 3.19 3.1 3.02 3.32 3.14
76533-9
CA 02257707 1998-12-31
- 16 -
i
OD r1 01OJ 01 d~ O M rl M 10 rl LI7O1 O M
M
OD d~ lf1rl O 01 r Lf110 01 M rl O tf1rl
1D
pp . . . . . O p~
O N r1r'Irl O O ri rl rl ~-1 01
H
U
0
0
0
H
H OD rl r1M OD d~ Lf1N d~ OD M r-1r ml ll1N
d~
rl O 01 rl O~ M ~D d~ ~O N O 01 rl N
~D
,~ . . pp ,-.~ . . . p~
H M rl rl O '-i N n-Iml rl O O
r1
O
M
01 d~ r r N r O V~rl N ll1r f-i01 In d~
O
d~ r M d~ O l0 O 01 N rl 01 ~ tf1
~O
W H ~ O
H M N rl r1 ri M v-Iri rl O Q1
U
P~
P4
W
ov ~ a~ov .~ M m r ~ r-ir w H d~ o o~
~
r o~ M M .-iow u vo m ~ M ~ o~ o o
w
r ,1 . . . . . ~
H M N rl rl O rl M N rl v-1O rl
ri
H
N
U
av ~" ~ M W o d~ o r-a~ p" H dm n W o m ~
o
o vo r m ~ o~ ao dwn r N M m N
r . . . . ,1 . o
N d~ N H rl O N M N rl O rl
N H r~
x
H
N
pq as awas as aP aP dP as dP aP
0 0 0 o m o 0 0 o m
H O O O Lf1N O O O 1f1N
M N rl M N r1
N
t71U1N 01 U7
O O
N .~ N
dP
W ~ W
E ~ ~ ~
O '-'N O '''
m b rtb -~ ~ b ro ro
rl 1J W PrW td rt11~ v H W W W td t0 1~ v
~ ~ ~ ~ ~ ~ ~ ~
v ~ ZJl-riN ,~ al -ri
., ~. _. --
p m ~ v v ~ m
p o 0 o O ~ 0 0 o O p
O o 0 0 o m rl v o 0 0 o w rl v
U M N H tf1N W EnI-I M N rl tl1N W N
O
N CplC~JCJ U C~ v v .t.' U CplCJ C~J~J v v
L'a 1~ 1.~ l~ l~
v W W W N UI b c0 N N W U7 W t0 c0
S-1 W W W N ~A E E W V! W U1 W E E
w v v v v v -~ -~ v v v v v
o s~ s~s~ s~ s~ a ~ ~ s~ N s~ s~ s~
H cn cncn cn cn p p x cn u w w n p p
76533-9
