Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TEAR/PUNCTURE RESISTANT SEMI-LAMINATE MATERIAL
BACFCGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
The present invention relates to material which may
be used to wrap rolls or sheets of metal that is both
tear and puncture resistant, and particularly to
laminated thermoplastic materials.
2. DESCRIPTION OF THE RELATED ART
Various materials have been made with combined
layers of material so that the final product exhibits
the properties of both layers. No materials exist,
however,possessing the unique properties of the
present invention, including tear resistance, puncture
resistance and corrosion inhibitors.
U.S. Patent 2,742,388 issued April 17, 1956 to A.W.
Russell discloses a method of bonding and curing 2 or
more plastic sheets to provide enough rigidity for use
as structural members. The sheets are bonded at the
edges with a thermosetting resin and a cellophane
strip longitudinally between the edges to form a
pocket in which a shapine tool may be inserted with
the application of heat to soften and shape the
fibers.
U.S. Patent 3,130,647 issued April 28, 1964 to W.E.
Anderson, et al. describes a method of bonding a
resilient or fragile layer to a relatively
nonresilient layer, such as paper, by heat bonding
with the application of. pressure. U.S. Patent
3,715,251 issued February 6, 1973 to J.S. Prentice
teaches lamination of nonwoven mats of thermoplastic
fibers by adhesives or point welding to produce a
laminated nonwoven sheet of material.
U.S. Patent 4,668,566 issued May 26, 1987 to Ralph
V. Braun discloses a multilayer material comprising a
layer of polyethylene bonded to a layer of
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polypropylene to form a nonwoven fabric. U.S. Patent
4,748,070 issued May 31, 1988 to David C. Beehler
teaches a polypropylene web bonded to a polypropylene
film to increase the tear strength of the film. U.S.
Patent 4,749,423 issued June 7, 1988 to Vaalburg, et
al. describes a method of bonding a nonwoven web of
thermoplastic fibers.
U.S. Patent 5, 272, 023 issued December 21, 1993 to
Yamamoto, et al. describes a method of making a hot
melt adhesive fiber sheet. U.S. Patent 5,342,469
issued August 30, 1994 to Bodford, et al. discloses a
method of laminating a spunbond web of polyethylene
fiber to a film using adhesive in which the adhesive
layer is discontinuous. LJ.S. Patent 5,424,115 issued
June 13, 1995 t.o Ty J. Stokes teaches a method of
point bonding sheets of conjugate fibers such as
polyolefin and polyamide fibers.
Canadian Patent 639,751 published April 10, 1962
teaches a method of spot welding polyethylene film
sheets. French Patent 1,307,386 published September
17, 1962 describes methods of bonding sheets of
plastic mater=ials. German Patent 1,490,626 issued
August 13, 1963 describes an insulating paper for high
tension wires bonded by spot adhesives. Japanese
Patent 52-43594 describes bonding paper or cloth to a
polypropylene base by adhesives. Japanese Patent 60-
68934 describes a waterproof laminate composed of
three layers, the second being polyurethane.
None of the above inventions and patents, taken
either singularly or in combination, is seen to
describe the instant invention as claimed. None of
the above inventions and patents describe a material
combining tear and puncture resistance with corrosion
inhibition suitable for wrapping rolls or sheets of
metals such as steel and aluminum. Thus a
tear/puncture resistant semi-laminate material solving
the aforementioned problems is desired.
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SUMMARY OF THE INVENTION
The invention is a tear/puncture resistant
semi-laminate material. The material includes a first
layer of woven, high density polyethylene fibers. A
second layer is composed of low density polyethylene
film impregnated with a volatile corrosion inhibitor.
The layers are bonded together by bonding in narrow
strips at the edges of the respective layers and at
discrete, discontinuous intervals across the width of
the layers.
Also part of the invention is a tear/puncture
resistant semi-laminate material with a first layer of
woven polypropylene fibers. The second layer is
polypropylene film and is impregnated with a volatile
corrosion inhibitor. The layers are bonded together
as described above.
BRIEF DESCRIPTION OF THE DRAWINGS
The sole figure is an environmental, perspective
view of a t=ear/puncture resistant semi-laminate
material according to the present invention with the
layers separated to show the bonding of the layers.
Similar reference characters denote corresponding
features consistently throughout the attached drawing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In steel mills it is useful to wrap or separate
rolls or sheets of steel for protection during storage
or transport. Currently the material used is composed
of a layer of woven polyethylene bonded to a 1 mil
extrusion of film and a reinforcing ply of kraft
paper. When tears or punctures develop, the kraft
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paper tends to absorb water, and consequently the
steel can become corroded.
Further, the material currently used is prepared by
extruding the film over the layer of woven
polyethylene and heat bonding the layers by processing
the combined layers through the nip of rollers under
pressure to produce a material uniformly bonded
throughout its length and width. By uniformly bonding
the two layers of material together, the material
loses some of its elasticity.
The present invention relates to a material which is
tear and puncture resistant, having sufficient
strength and elasticity to prove useful in the metals
industry, where it may be used for wrapping rolls or
sheets of steel, aluminum, and other newly milled
metals to provide protection from the weather during
storage and transport. The material of the present
invention represents an improvement in the materials
currently available in the steel industry.
The materia7_ of the present invention is fabricated
from polymeric materials, specifically, thermoplastic
films and fibers. In the preferred embodiments, the
layers of the material are composed entirely of
polyethylene fibers and films, or entirely from
polypropylene fibers and films. Polyethylene and
polypropylene are considered desirable for this
application because among their many other properties,
they are recyclable, which is why layers of
polyethylene and polypropylene are not mixed.
In a preferred embodiment, the material has a layer
of woven high density polyethylene, bonded at points
or in strips around its edges or at discrete,
discontinuous intervals across its width to a layer of
low density polyethylene film to form sheets 60" to
120" wide. The layer of polyethylene film is
impregnated with a volati=Le corrosion inhibitor.
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In the preferred embodiment, as shown in the figure,
the invention comprises a material having two layers.
The top layer 10 is a layer of woven high density
polyethylene fibers having- a thickness between 3 mils
5 and 7 mils, preferably 5 mils. This layer provides
mufti-directional strength, i.e., tear resistance in
both the machine direction and the cross direction.
Fibers running in the machine and cross directions,
which may be in the ratio of about 8:4 lines per
square inch, provide this mufti-directional strength.
The woven polyethylene imparts ease of handling to the
material.
While the layer of woven polyethylene 10 imparts
significant benefits to th~~ material, nevertheless, it
is subject to breakage, viz., when great tensile
forces are applied to it. Therefore, the second layer
is a layer of extruded, nonwoven, low density
polyethylene film having a thickness between 1 mil and
6 mils, preferably 3 mils. The layer of polyethylene
20 film 20 gives the material puncture resistance. The
polyethylene film is water impermeable, providing
protection against water and moisture.
The layer of polyethylene film 20 is impregnated
with a volatile corrosion inhibitor, which may be
sodium nitrite, for example. Steel and other metals
are subject to corrosion from exposure to the weather,
undergoing oxidation in the presence of water. A
variety of methods are used to protect metals from
corrosion, such as electroplating, paint, etc. One of
the methods used to help prevent corrosion is the use
of volatile corrosion inhibitors, such as nitrites,
which form a gaseous layer coating the metal and
inhibit corrosion by reacting with water to form
nitrates.
In the preferred embodiment of the present
invention, sodium nitrite is used as the volatile
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corrosion inhibitor. The sodium nitrite is combined
with the polyethylene in the melt and extruded in the
polyethylene film. Other volatile corrosion
inhibitors are well known in the metals industry and
may be used in place of sc>dium nitrite.
The method of bonding used to laminate the two
layers is referred to as semi-lamination. Normally
materials to be laminated are coated uniformly
throughout their surface are with an adhesive or
thermosetting resin, or one layer is extruded over a
second layer and the layE=_rs are bonded by heat and
pressure. By contrast, the material of the present
invention is bonded by point welding, by heat bonding,
by ultrasonic bonding, by adhesive bonding, or other
appropriate conventional methods of bonding standard
in the industry, in na=rrow continuous strips 30
applied to the edges of t:he layer, and optionally at
discrete, discontinuous intervals across the width of
the layers, as shown in the=_ figure, defining spaces 40
or pockets.
The process of semi-lamination offers several
advantages. Since the layers are not uniformly bonded,
the vast majority of the surface area of the two
layers is in slidable contact so that the layers tend
to slide in relation to each other as the material is
wrapped around t:he metal, so that if a hole develops
in the woven layer, in all likelihood it will not have
a hole at the same position in the second layer.
Hence, any moisture entering through the hole in the
first layer tends to be trapped in the spaces 40 or
pockets between the layers. Since the polyethylene
film is impermeable to water, the metals are protected
from exposure to water, unlike materials currently
used which employ a reinforcing ply of kraft paper
which tends to absorb any water entering through a
hole in the trop layer. This method of lamination
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permits the finished material to retain the beneficial
properties of the material in each individual layer
while enjoying the advantages of combining the layers.
The basis weight of the finished material is
approx=imately 25 lbs . pE:r 1000 square feet . In
operation, the metal is wrapped in the material with
the third layer closest to the metal. In this manner
the metals derive the greatest degree of protection
from the layer containing the volatile corrosion
inhibitor.
The embodiment described above is composed entirely
from layers of polyethylene. It will be understood
that alternative embodiments may be made entirely from
polypropylene, comprising a layer of woven, tear
resistant polypropylene and a layer of polypropylene
film impregnated. with a volatile corrosion inhibitor,
within the specifications set forth above for
polyethylene. 'The advantage of using polyethylene,
particularly high density polyethylene, or
polypropylene, is that these materials are recyclable.
The preferred embodiments of the invention provide
a tear and puncture resistant material for wrapping
metals for storage or transport. The material has
improved moisture protection due to layering sheets,
so that a tear or puncture in one layer does not
necessarily extend to another layer. The material has
greater elasticity than materials currently used in
the industry. The material is produced using a method
of lamination in which the properties of one layer are
not affected by the properties of another layer or by
the process of :Lamination itself. The material also
inhibits corrosion by using a material having a layer
impregnated with a corrosion inhibitor.
It is to be understood that the present invention is
not limited to the embodiments described above, but
encompasses any and all embodiments within the scope
of the following claims.
