Note: Descriptions are shown in the official language in which they were submitted.
iZ44~33
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Imvrovements in and relating to Laminate Structures
This invention relates to laminate structures in which
one polymeric material is employed to provide a
different polymeric material with a su face or surface
layer of desired physical and/or chemical properties.
In particular it relates to providing a polyvinyl
chloride - coated substrate with a rubber surface
layer.
It is well-known that polyvinylchloride (PVC) is
incompatible with ~any rubbers such as styrene butadiene
rubber, or polychloroprene rubber. In fact it is
incompatible with most if not all of the rubbers which
might be used to provide the abrasion resistance and
good surface friction (traction) characteristics that
PVC lacks. It is certainly incompatible with such
rubbers which ars also capable of exhibiting high
fire/flame resistant properties. This is of particular
significance in the field of conveyor belting, where a
solid woven or plied PVC belt has excellent fire
properties, but poor abrasion resistance and relatively
poor ability to convey loose material at steep angles.
The expression "solid woven PVC belt" has its usual
meaning, namely a belt comprised of a solid woven
belting fabric impregnated with PVC. Likswise, a "plied
PVC belt" is one built up from a plurality of disc-ete
PVC-impregnated plies united by pressing/heating in the
usual manne-.
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It is also knownfrom DE-OS 2924757 that outer layers of
polychloroprene and polyvinyl chloride, respectively,
can be bonded together by means of a common interlayer
comprised of a mixture of a plastomer (thermoplastic)
~.d a;l elastomer which are -esistant to the material of
both the oute- layers and to the abso_ption of
compounding ingredients in the outer layers. According
to a preferred feature the adhesion can be further
improved if the polychloroprene of one outer layer
contains components of the interlayer and3Ol PVC from
the other oute~ layer. This is a very complex adhesive
system and in the case of the preferred embodiment just
referred to, the compounding of the polychloroprene with
ingredients of the adhesive layer can only detract from
the physical properties of the polychloroprene and hence
from the performance of the product.
According to the present invention a substrate comprised
of PVC is provided with a surface layer of a normally
PVC-incompatible rubber by a process which comprises
applying to said substrate a layer of an uncured nitrile
rubber adhesive compound, followed by applying a cover
layer of an uncured, normally PVC-incompatible rubber to
said layer and thereafter subjecting the resultant
laminate structure to a curing treatment.
Preferably the nitrile rubber adhesive is compounded to
be fire resistant. It has been found that superior
performance can be achieved by using the simple adhesive
system of this invention. No compounding of the
adhesive into either the substrate or the surface layer
is necessary to achieve improved pe-formance.
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It has been further found that the adhesion so achieved
is retained even after long-term dynamic flexing to
simulate protracted service.
The substrate may be a solid woven or plied PVC conveyor
belt and the layer of uncured fire resistant nitrile
rubber adhesive compound is preferably relatively thin,
for present purposes that is less than about 0.5mm
thick. A thickness of about 0.25 to 0.3mm has proved
satisfactory in the case of PVC conveyor belting. The
nitrile rubber layer may be applied in any of the ways
commonly used. Fo- example it may be sprayed as a
solvent dope, or spread, calendered or rolled into a
layer, in entirely conventional manner, following
compounding with fire retardants, etc in the usual way.
The expression "normally PVC-incompatible" means that
the material would not adhere satisfactorily if applied
directly to the PVC. The curing treatment would usually
be a vulcanising treatment under heat and pressure; it
is to be understood that both the nitrile rubber and the
other rubber should have incorporated into them such
curing or vulcanising agents as are necessary to ensure
that the cure rates of the two rubbers are compatible.
A particular prefe~red normally PVC-incompatible rubber
is a polychloroprene rubber such as that sold under the
Registered Tradema k NEOPRENE. A chlorosulphonated
poleythylene such as that sold under the registered
Trade Mar~ HYPALON may also be employed. Typically, the
cured cover layer will be in the range 1 to 4mm thick,
depending on the g.ade of belting involved. One or both
sides of the belt may be covered with the normally
PVC-incompatible rubber.
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It has been found that the use of polychloroprene rubber
as a facing layer for a solid woven or plied PVC
impregnated belting ca-case results in conveyor belting
having outstanding propertie~ of abrasion resisrance,
traction and fire esistance. The use of a nitrile
rubber adhesive layer between the PVC and the
polychloroprene completely overcomes the problem of
incompatibility; the finished belt is essentially
integral and exhibits excellent interlaminar adhesion,
typically well in excess of that demanded by B.S. 3289,
for example. By contrast with the prior art referred to
earlier (DE-05 2924757) no plastomer component is
necessary in the adhesive layer. Furthermore only a
relatively thin layer is needed as opposed to the
lS relatively thick interlayers previously thought
necessary to, in effect, isolate the carcase and
facing.
It should be noted that whilst nitrile rubber alone may
be used as a facing, its flammability renders it
unacceptable in many applications. The use of additive
ingredients may almost completely alleviate this problem
of flammability, but only at the expense of other,
important properties. Additives of the kind needed to
significantly reduce flammability also considerably
detract from the normal characteristics of nitrile
rubber. It will be appreciated that fire retardants are
also normally compounded into polychloroprene rubbers
for belting applications. However, the level of
addition of such ingredients is very significantly less
than that needed for nitrile rubber, thereby enabling
full advantage to be taken of the properties of the
polychloroprene rubbe~ In order that the invention be
better understood three embodiments of it will now be
desc ibed by way of example.
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Example 1
A cotton-nylon solid woven belting fabric carcase about
6r,1m thick and 1 metre wide was impregnated with a ~C
plastisol using the process and apparatus of UK Patent
No. 2036818. An uncured, fire resistant nitrile rubber
adhesive compound was then calendered onto each face of
the impregnated carcase as a thin layer, about 0.3mm
thick. A 2mm thick facing layer of an uncured
polychloroprene rubber tNEOPRENE GRT) in the form of a
calendered sheet was then applied to each face of the
assembly. The polychloroprene rubber was a conventional
carbon-black -einforced abrasion resistant compound and
included materials for conferring fire resistance. The
conventional calendering could equally well have been
used. The assembled laminate was consolidated/cured by
heating in the p-ess to 160C for 15 minutes, followed
by cooling, still in the press.
The product was tested for its "cover adhesion"
properties using the method of B.S. 3289. The result
was a value of about 7KN/metre width. For all practical
purposes this meant that the layers were inseparable.
The belt was also fire resistant to B.S. 3289.
Example 2
A 6mm thick cotton-polyester solid woven carcase was
processed as in Example 1, but using a
chlorosulphonated polyethylene (~YPALON 40) instead of
NEOPREN~ rubber. The product exhlbited very good cover
adhesion of about 6KN/metre ~idth. On testing its
elongation properties under a load of 10~ of its
breaking strength, a result of less than 2~ was
achieved; this met French Specification NF
~81-651/1971.
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Example 3
In this case a plied belt was made using four 2mm plies
of cotton-polyester wover ca-case materi?l. The plies
were separately impreynated by dippiny in a PVC
plastisol. One face of each of two of the dipped plies
was then coated with an uncured fire resistant nitrile
rubber adhesive compound laye- (as per the previous
Examples) by calendering. A four-ply belt was then
built up with the nitrile layers on the two outer faces,
using a consolidating roller. A 2mm calendered sheet of
uncured polychloroprene rubber was also put onto the
outer faces by the same method. The polychloroprene
rubber was compounded as in Example l. The assembly,
comprising the four separate plies and facing laye s,
was then consolidated and cured in a belting p-ess, as
in the prevous Examples. After cooling, the belt was
slit to the required final width and tested as in
Examples 1 and 2. The cover adhesion was 7KN/metre
width and the belt was fire resistant, both to B~S.
3289. The elongation under 10~ of breaking load was
less than 2~.
