Note: Descriptions are shown in the official language in which they were submitted.
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RUBBER AND REBOND COMPOSITE SHEET
FIELD OF THE INVENTION
The present invention relates to a composite sheet and rolls comprising at
least one layer of rubber (which is ultimately cured) and at least one layer
of cured rebond material (rubber-crumb and urethane) and a method of
manufacturing same.
BACKGROUND OF THE INVENTION
113 It is known to combine layers of uncured rubber to form a dual/multi-
density rubber mat under heat and pressure. For example, it is known to
provide a composite sheet comprising a layer of uncured rubber faced on
one or each side with another layer of uncured rubber firmly bonded to
each other.
However, once cured, rubber is very difficult material to bond to other
material without some sort of adhesive/chemical bonding agent. Using
known techniques, the chemical bonding between a sheet of uncured
rubber to an already cured sheet of rubber would be very poor. Previous
dual layer rubber products include the vulcanization of uncured-to-uncured
rubber layers or utilize the gluing of cured/rebonded layers together.
Nothing in the prior art discloses the use of post industrial and/or post
consumer rubber (often referred to as "masticated rubber") combined in a
cured rubber-rebond composite sheet being utilizable in various
commercial products in an efficient and effective manner.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome, inter alia, the
shortcomings of the prior art described above by providing an improved
cured rubber-rebond composite sheet.
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In accordance with an aspect of the invention there is provided a rubber-
rebond composite sheet comprising a rebond layer having a first surface
and a layer of cured masticated rubber attached to said first surface.
In accordance with a further aspect of the invention there is provided a
method of
manufacturing a composite rebond and rubber sheet comprising the steps of:
(a) providing a layer of rebond having an outer surface;
(b) providing a layer of uncured masticated rubber upon said outer surface,
(c) heating and pressing said layers together so as to cure and bond said
rubber layer to said outer surface of rebond.
The invention contemplates the formulation of multiple layers such as rebond-
masticated rubber-rebond or further layers thereof in various combinations.
In accordance with an aspect of the invention, the layers may be mechanically
and /or chemically bonded together.
Various advantageous commercial applications exist for the product of the
invention which combine the benefits of both materials (masticated cured
rubber
being used as a lower unexposed layer having higher hardness, strength,
abrasion resistance and rebonded rubber being used as an exposed layer having
a lower hardness, being non staining, better visual appearance, lighter
weight).
This can be reverse if better abrasion needed.
Other advantages, features and characteristics of the present invention, as
well as methods of operation and functions and economies of manufacture,
will become more apparent upon consideration of the following detailed
description and the appended claims.
DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION
The product in accordance with an aspect of the invention comprises a
composite sheet having a layer of cured masticated rubber adhered to a
rebond layer (crumb-urethane product).
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A first layer of rubber in accordance with this invention is cured masticated
rubber. Prior to attachment to the rebond layer, the masticated rubber
layer comes in uncured form. Masticated rubber is a blend of uncured
friction cord (generally a natural rubber (NR)/ styrene butadiene rubber
(SBR) compound calendared onto tire belting) waste from tire
manufacturers, uncured NR/SBR compound waste from rubber processors
including tire manufacturers, ground up vulcanized tire rubber and fiber
from recycled scrap tires, various ground rubber and fiber materials from
internally generated waste and typical rubber processing and vulcanizing
ingredients. A preferred version of masticated rubber comprises a
thermoset rubber blend based on tire belt, tread and sidewall compounds
in both cured and uncured form that also contains fiber strands originating
from original tire manufacturing, homogeneously dispersed throughout the
blend. Additional fabric strands from other sources can also be
incorporated to further increase stiffness and tensile strength. The fiber,
blended into the masticated rubber mixtures increases stiffness adds
strength, increases the modulus and overall hardness of the final product
and reduces elongation or stretching of the rubber product. The fibers
utilized are typically a mixture of short and long fibers comprised of
polyester or nylon or other synthetic polymers. An example of masticated
rubber used in accordance with the invention to be cured and bonded to
the rebond layer is Symar rubber available from the applicant, National
Rubber Technologies Corp. Toronto, Canada.
No adhesive material is disposed between the masticated rubber layer and
the rebond layer
Crumb / Urethane product (Rebond) composition:
Rebond is made using discarded used tires. Tires are chopped up in small
granulate (Crumb) of different sizes (Mesh size) during this process steel
and fibers are removed. Then crumb is mixed with small amount of
urethane and compressed in a mold with or without heat to cure the mix.
Resulting product is a large cylinder (Log). Using special machine this log
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is cut in different thickness in a continuous roll. Colored cured granules
can be added to produce a different product appearance.
Advantageously, the heat and pressure conditions utilized to cure
masticated rubber sheets may be simultaneously used to bond the
masticated rubber layer to the rubber rebond layer. In a preferred process
in accordance with the invention, uncured masticated rubber is placed on
the outer surface of the rebond sheet. The rubber layer is then
simultaneously cured and bonded to the rebond layer. The rebond layer
may then be adhered to one side or both sides of the masticated rubber
using heat and pressure. Examples of how the rubber layer may be
adhered are: (i) by means of a compression molding process, and/or (ii) by
means of a continuous cure process.
(i) Compression Molding Process: In an example of a method of forming a
composite sheet in accordance with the invention, a standard compression
press machine may be utilized to form the composite sheet of masticated
rubber and rebond as follows. The rebond, preferably comprising of 85%
to 98% rubber crumb and/or buffings and 2% to 15% urethane. The whole
assembly of rebond layers and uncured masticated rubber layers are
heated and pressed together. Preferably the rubber-rebond composite is
pressed to a thickness of approximately 0.25 inches, although the
composite thickness could vary within the range of 0.08 inches to 2 inches
if desired. To achieve the best results of adherence of the masticated
rubber to rebond in an even manner, the preferred specific pressure
applied to the composite would be in the range of 100 psi to 500 psi and
the preferred temperature would be between 200 F to 350 F. The
preferred duration of application of this heat and pressure is between 2
minutes and 20 minutes. The composite product would be allowed to cool
and would have excess rubber trimmed as it exits the press. As desired, a
rubber-rebond product having a thickness outside of these ranges could be
utilized.
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(ii) Continuous cure process: The masticated rubber layer and the rebond
layer may be adhered together using a continuous curing process. The
continuous curing process involves an apparatus including conveyor
means which advances the rubber and rebond through the apparatus, a
heat source and a pressure source which are simultaneously applied to the
rubber and rebond as they are advanced through the apparatus, thereby
curing and bonding the masticated rubber layer to the rebond. The
preferred conveyor means comprises upper and lower stainless steel belts,
between which are carried the rebond and masticated rubber layers. In an
io example of the continuous curing process, a roll of rebond is positioned
horizontally at an entry position to the machine upon the upper and/or
lower belt. A roll of uncured masticated rubber is placed adjacent the entry
position. A sufficient amount of uncured rubber to cover the rebond layer
is dispensed from the roll, and is placed over the upper surface of the
rebond layer (or vice versa: rebond on top, masticated rubber on bottom).
The combined rubber and rebond layer are advanced by the moving belts
through the press machine. As the rubber and rebond layers are carried
between the upper and lower belts, through the continuous press, heat (in
the range of 200 F to 350 F) is applied to the rubber and rebond layers. In
combination with the heat applied, the lower belt moves the rubber and
rebond layers along the machine, and the layers are sandwiched between
the upper and lower belts, pressing the rubber to the desired thickness,
causing the rubber to be cured and bonded to the rebond layer. To achieve
the best results of adherence of rubber to rebond in an even manner, the
preferred specific pressure applied to the rubber and rebond layer
composite would be 100 psi to 500 psi. Once heated and pressed to the
desired thickness, the cured masticated rubber and rebond continues to an
exit position where it is allowed to cool and excess rubber is trimmed and
the cured masticated rubber-rebond composite material is cut and stacked
or rolled. As with the compression molding process, preferably the
composite material is pressed to a thickness of approximately 0.250
inches, although the rubber thickness could vary within the range of 0.080
inches to 2 inches if desired.
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Preferably, heat is applied by circulating steam or hot oil through the upper
and
lower platens of the press. Preferably, hydraulic pressure is applied by means
of a
hydraulic unit in combination with a plurality of hydraulic cylinders arranged
structurally to apply an even force distribution across the width of the
platens.
This force distribution acts to press the upper and lower platens of the press
together within a specific pressure range, as dictated by the product. The
pressing
time may vary anywhere from 2 to 20 minutes depending on the desired thickness
of the rubber, typically, the thicker the rubber layer, the longer the
pressing time.
io There may exist multiple layers of rebond and masticated rubber as part of
the product of this invention. It should be further understood that a layer of
rebond may be adhered to one or more layers of other types of rubber (eg.
All Natural Rubber).
The product produced in accordance with the invention, namely a cured
masticated rubber and rebond product has certain advantageous
commercial/industrial applications, as listed below. The cured masticated
rubber layer typically has a higher hardness, strength, higher weight, and
high abrasion resistance. Masticated rubber can stain (eg. If masticated
rubber comes in contact with metal for very long time, it will change the
color of metal to yellow). The rebond layer is softer, non-staining and has a
more appealing visual appearance. When attached together as a sheet, it
is often quite advantageous to have an upper rebond layer exposed to the
end user with a lower cured masticated layer below providing strength and
weight to the product. Such a configuration is especially desirable in the
following applications: athletic flooring, ice rink arena flooring adjacent
ice
surface, rooftop walkway mats, general floor matting. Other uses of the
product of the herein invention may be with truck flaps, truck bed mats. In
truck bed mat masticated rubber is exposed as higher abrasion resistance
is required.
The above description provides ample information for the person skilled in
the art to practice the invention. Furthermore, it will be evident that
modifications which are obvious to persons of ordinary skill in the art, may
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be made without departing from the spirit or scope of the invention, which
is accordingly limited only by the claims appended hereto, purposively
construed.
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