Note: Descriptions are shown in the official language in which they were submitted.
This invention rela es to conveyor belts for tacky
substances, e.g. oil sand.
Such types of conveyor belts are required to pos-
sess suEficient strength and Elexibility under annual climatic
conditions for executing a long distance conveyance from
an oil sand excavation point to a bitumen separation treat-
ment plant, and because of this reason, steel cord conveyor
belts are normally used. How~ver, as conveyor belts using
general purpose rubbers which bond well with steel cords
do not possess non-adhesivenPss, oil sand will stick to
the belt su~Eaces and accumulate as thickly as one half
inch (12.7 mm) and over during operation. This adheriny
substance will generate unbalanced loading and overloading
of the belt and accelerate wear on pulleys and the like.
Heretofore, in conveyor belts for oil sand, the
non-adhesiYeness of the belts to oil sand has been main-
tained by sprinkling kerosene, gas oil, etc. over the belt
surfaces. However, since the sprinkling of oil is now forced
to be terminated for reasons of fire protection and safety~
other methods are now required to be adopted to prevent
the adhesion of oil sand. It may be one solution to give
the conveyor belt itself a non-adhesive property, but con-
veyor belts having the property of being non-adhesive to
oil sand are not hitherto known.
It is generally known that silicone and Teflon,
which have low solubility parameters (SP) and low critical
surface tensions (~c3, are effective in rendering a surface
non-adhesive. However, as silicone rubber does not bond
to steel cords and is expensive, it has a problem of mech-
anical strength and it is not economically feasible to di-
rectly form silicone rubber into steel cord conveyor belts,
and accordingly, no steel cord conveyor belts using sili-
cone rubber are hitherto known.
Accordingly, it is an object of the present inven-
tion to economically provide a conveyor belt which is non-
adhesive in itself to sticky substances including oil sand,
and ~hich does not require the use of sprinkled oil.
~r~5~i
-- 2 --
Vulcanization bonding of silicone rubber to gen-
eral purpose rubbers, inc~uding natural rubber (NR), poly-
styrene-butadiene copolymer rubber (SBR), polybutadiene
rubber (BR), polyacrylonitrile-butadiene copolymer rubber
(NBR), and polyethylene-propylene copolymer rubber (EPM
rubber), or to their blends is not ~nown yet. With regard
to this point, the present invention also has as an object
the provision of a conveyor belt which enables an inte-
grated combination oE a general purpose rubber steel cord
belt inner core layer and a silicone rubber surEace layer
through vulcanization bonding.
According to the present invention, there is pro-
vided a steel cord conveyor belt having a surface layer
comprising silicone rubber, an inner core layer comprising
steel cords and rubber bonded to the steel cords, and an
intermediate layer comprising a material which is bondable
to peroxide-vulcanized rubber and with sulfur-vulcanized
rubber and interposed between and bonded by vulcaniza-tion
to the surface layer and the inner layer.
Preferably, the sur~ace layer has a rubber content
of at least 30~ by weight. In one embodiment, the rubber of
the inner core layer comprises at least one rubber selected
from natural rubber ~NR), polystyrene-budadiene copolymer
rubber (ssR)~ polybutadiene rubber (sR) and a-blend of at
least two thereof and has a total polymer content of at
least 80~ by weight, and a rubber content oE at least 30%
by weight o ths total.
The intermediate layer materials is preferably
duc~, especially one treated with resorcinol formalin latex
(RFL treatment). Thus, the intermediate layer preferably
comprises duck which has been subjected to resorcinol Eorma-
lin latex treatment (RFL treatment) employing latex which
comprises at least 80% by weight vinylpridine latex (VP). A
variety of rubber elastomers are also useful as intermediate
layer materials, especialLy polyethylene-propylene-diene
ternary copolymer rubber (EPDM rubber) which can be vul-
canized with both peroxide and sulEur. Such intermediate
layer materials can be used together wi-th polyethylene-
-- 3 --
propylene copolymer rubber ~E~?M rubber), modified silicone
and ethylene-propylene copolymer rubber SSEP rubber) to
obtain better results.
More particularly, the invention includes embodi-
ments in which the intermediate layer comprises a poly-
ethylene-propylene~diene ternar~ copolymer rubber (EPDM
rubber) layer on the inner layer.
Preferably, the intermediate layer includes at
least one rubber selected from the group consisting of poly-
ethylene-propylene copolymer rubber (PEM rubber~ and modi-
fied silicone and ethylene-propylene copolymer blended rubber
l~EP rubber) between the polyethylene~propylene-diene ternary
copolymer rubber ~EPDM rubber) layer and the surface layer.
The intermediate layer may include EPM rubber
or EPM rubber and SEP rubber interposed between the duck
and the surface layerO
In the following, preferred embodiments of the
present invention will be d~scribed in detail and in con-
crete terms, together with numerical values.
Silicone rubber is vulcanized with peroxide, and
a rubber for steel cord bonding is vulcanized with sulfur.
These rubbers do not bond with each other. They do not
bond with each other even if a blend of both rubbers in
equal amounts is used as an intermediate substance. The
bonding strength between silicone rubber and this inter-
mediate layer is l to 3 kg, and the bonding strength betweenthis intermediate layer and the steel cord bonding rubber
is merely 3 to 5 kg. This is due to inhibition of vul-
canization of silicone rubber when sulfur is present in
peroxide-vulcanized rubber. The present invention at least
partly mitigates this incompatibility between said rubbers.
The conditions of preferred embodiments of the present inven-
tion were as follows:
~aterials Tested
_
(a) Duck
Ducks used in the present invention include single
and mixed fabrics of nylon~ po]yester, vinylon, cotton,
:~2~n8~ ss
etc. Ducks have 800 to 20000 deniers lengthwise, and
800 to 20000 deniers crosswise, and the counts are
10 to 100 per 5 cm lengthwise, and 10 to 100 per 5
cm crosswise. When duck is to be treated, the resor-
cinol formalin latex -treatment (RFL treatment) is ap-
propria-te, and it is advisable to use latex having
a vinylpyridine (VP) latex conten-t of 80% or over of
the total latex.
The test material (A) was of nylon in both the
warp and the weft, and the warp was a single twist
yarn of 1260 deniers and the weft was 10 yarns of 1260
deniers twisted together. The counts were 80 per
5 cm lengthwise, and 15 per 5 cm crosswise.
The composition of the RFL was 1.3~ resorcinol,
1.9% 37%-formaline, 0.05~ NaOH, 28% 40%-vinylpyridine
latex, and 68~75% water, and the treatment was effected
by baking at 150C for 5 minutes.
(b) Silicone rubber
It is appropriate to use silicone rubber having
a rubber content of at least 30~. The test material
(B) consisted of 100 parts of SH861U of Toray Silicone
Industries, and 3 parts of dicumylperoxide (40~) of
Nippon Oils & Fats Co., Ltd.
(c) Rubber Eor steel cord bonding
The following composition was used as the -test
material (C)~
Natural rubber (NR) 60
Polystyrene-bu-tadiene copolymer
rubber (SBR) 40
ZnO (zinc oxide) 10
Stearic acid (S.A.)
Resorcinol 4
Hexame-thylenete-tramine 2.3
Vulcanization accelerator CZ
(N-cyclohexyl2-benzothiazylsul~onamide) 1.2
Carbon black 35
Silica 30
12~8~S~
Softener 10
Colophony 5
Litharge 2
Sulfur 2
5 (d) Polyethylene-propylene-di.ene ternary copolymer rubber
(EPDM rubber)
The following composition was used as the test
material ID);
EP93 (Japan Syn~heti.c Rubber Co., Ltd.) 100
Carbon HAF 50
Oil Inaphthene base~ 20
ZnO (zinc oxide) 5
Stearic acid (S.A.)
Vulcanization accelerator TMTM
(tetramethylthiuram monosulfide) 1.5
Vulcanization accelerator MBT
(2-mercaptobenzothiazole) 0.5
Sulfur 1.5
(e) Polyethylene-propylene copolymer rubber (EPM rubber)
The following compo,ition was used as the test
20 material (E):
FPll (Japan Synthet:ic Rubber Co., Ltd.) 100
Carbon HAF 50
Oil (paraffin base) 10
Dicumylperoxide (40~) 3
Ethylenedimethacrylate (EP~A) 3.3
(f) Blended rubber of modifi,~d silicone and ethylene-
propylene copolymer (SEP rubber)
The following compo,ition was used as the test
material ~F):
SFP171U (The Shin-Etsu Chemical Co., Ltd.)].00
Dicumylperoxide 3
Age register MB (2-mercaptobenzimidazole)
In order to bond silicone rubber and steel cord
bonding rubber together, the above-mentioned test
materials were combined ~s follows:
~z~
Control case lI) B-C ISilST)
Present invention's
embodiment (II) B-A-C ISi/duck/ST)
Present invention's
embodiment ¦III) B-F-E-A-C ISi/SEP]EP~
duck/S~)
Present invention's
embodiment lIV) B-F-E-D-C (Si/SEP~EPM/
EPD~/ST)
Conditions of Execution (Test Co_ditions)
Rubber sheets of 40 mm wide by 180 mm long by
2 mm thick and duck pieces of 40 mm wide by 180 mm long
were prepared, and they were combined to form the afore-
mentioned complex structures. These complex structures
were press-vulcanized at 155C for 30 minutes. The pres-
sure for pressing was 50 kg/c:m2. The press-vulcanized
structures were cut into pieces of 1 inch (25.4 mm) wide
and used as the samples for bonding strength measurement.
The 1 inch wide samples of the test material com-
binations prepared in the manner described above were
separated at the separating velocity of 100 mm/min, and
the results of the separating force measurement between
respective consecutive layers were as follows:
Control case (I) 1 to 3 kg (between B and C).
~resent Invention's
embodiment III) 12 to 15 kg (between B and A)/
15 to 20 kg (between A and C).
Present invention's
embodiment (III) 12 to 16 kg (between B and F),
15 to 20 kg (between F and E),
25 to 30 kg (between E and A),
15 to 20 kg (between A and C~.
Present invention's
embodiment (IV) 12 to 16 kg (between B and F),
15 to 20 kg (between F and E),
20 to 25 kg (between E and D),
15 to 20 kg (between D and C).
As sho~n by the control case (I), mere combination
of silicone rubber ~Si~ and the rubber for steel cord bond-
ing lST) not in accordance with the present invention re-
suIted in a small bonding strength, and in fact, they did
not bond together. In contrast with this control test,
s~
the present invention's embodiment (II) wherein a duck piece
alone was interposed as an int:ermediate layer, the present
invention's embodiment ~ wherein a duck piece was pro-
vided on the rubber for steel cord bonding (ST), and peroxide-
vulcanized EPM rubber and SEP rubber were interposed be-tween
said duck piece and silicone rubber (Si~, and the present
invention's embodlment (IV) wherein EPDM rubber which can
be vulcanized with peroxide and with sulfur was provided
on the rubber for steel cord honding ~ST), and EPM rubber
and SEP rubber were interposecl between EPDM rubber and
silicone rubber lSi) all resu]ted in a large bonding strength,
and as a result, the present invention can provide a rela-
tively inexpensive conveyor belt which possesses a variety
of strength properties required of a conveyor belt as well
as non-adhesiveness to sticky materials including oil sand.
Furthermore, the present invention can be reduced
to practice with a variety of modifications within the scope
of the invention, and the combinations and orders of the
materials used are not limi-tecl to the aforementioned three
embodiments of the invention. In other words, when duck
is used, in addition to the combination of Si/duc~/ST of
the present invention's embodiment (II) wherein duck is
used by itself as the intermeçliate layer, when duck is used
together with EPM rubber, a combination of Si/EPM/duck/ST
is satisfactory, which differs from the present invention's
embodiment (III), Si/SEP/EPM/duck/ST, in omitting SEP. When
EPDM is used on the rubber of the surface layer, in addition
to the combination of Si/SEP/E:PM/EPDM/ST of the present
invention's embodiment (IV), c:ombinations of Si/EP~/EPDM/ST,
Si/EPDM/ST, and Si/SEP/EPDM/ST are satisfactory. Naturally,
modifications o~ configuration and/or composition of each
material, and modi~ications of the treating conditions within
the scope o~ known technology are included within the scope
of the present invention. Inclusion of duck serves to pre-
vent cracking due to i~pacts of the material to be conveyed(oil sand).
