Note: Descriptions are shown in the official language in which they were submitted.
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LINER STRUCTURES
Field of the Invention
This invention generally relates to structures suitable for use as non-
s adhesive, non-skid liners to cover and/or protect generally horizontal
planar
surfaces such as shelves, drawers, and the like and methods of making such
structures.
Backqround of the Invention
to Consumers use a wide variety of sheet materials in and around the home
as an underlayment and lining material. Decorative papers have been used for
many years to line shelves and drawers, for example. Some decorative papers
are provided with an adhesive on one side to provide a more permanent lining.
Plastic materials such as polyvinyl chloride have also been commonly provided
in
~s sheet form, often with an adhesive coating on one side, for use by
consumers as
liners.
An alternative type of liner structure is described in U.S. Patent No.
4,947,999. Such structures include a sheet of plastic material having a
substantially flat bottom side for lying on a subjacent surface of a shelf or
drawer.
2o An integral raised pattern of ridges project upwardly from a top side of
the sheet.
The tops of the ridges are generally coplanar and provide a reduced surface
area
for supporting articles such as glasses and tableware and for allowing air
flow
beneath the articles.
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While liner structures of this type offer certain advantages over liners
previously known in the field, still further improvements would be desirable.
For
example, a ribbed shelf liner product corresponding to the structures
described in
the aforementioned U.S. Pat. No. 4,947,999 is currently being marketed under
the trademark "PLAST-O-MAT". This product is constructed of a relatively stiff
and slippery plastic and has a tendency to curl when placed on a flat surface.
Thus, it is difficult to keep the liner in a desired position on a smooth
support
surface due to its tendency to slide along the support surface when subjected
to
a force parallel to the plane of the liner such as the force generated by
removing
to an article from the liner. This deficiency is acknowledged in U.S. Patent
No.
4,947,999, which describes the liner structure as having a "semi-rigid"
construction and suggests using double-faced tape to secure it in place.
Summary of the Invention
is This invention provides a liner structure suitable for covering or
protecting
horizontal support structures such as shelves, said liner structure comprising
a
flexible sheet having a top surface and a bottom surface. The flexible sheet
is
non-rigid and is constructed of a first polymeric resin which is sufficiently
soft to
render the flexible sheet non-curling and the bottom surface non-skid. A
plurality
20 of upwardly extending ridges constructed of a second polymeric resin which
is
harder than the first polymeric resin and which provides a low friction
surface on
the top edges of the upwardly extending ridges, are present on the top surface
of
the flexible sheet. In one embodiment of the invention, the bottom surface is
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non-flat and comprises downwardly extending ridges constructed of a soft
polymeric resin. The liner structures may be fabricated using a coextrusion
process.
Detailed Description of the Invention
The liner structures described in U.S. Patent No. 4,947,999 (incorporated
herein by reference in its entirety) may be improved by the use of two
different
polymeric resins in fabricating said structures. The bottom side of the liner
structure which facially engages the support surface is constructed of a
relatively
1o soft polymeric resin. This resin is selected so as to render the bottom
side of the
liner structure non-skid in character. The term "non-skid" means inhibiting or
hindering, but not preventing completely, slipping or sliding.
Thus, the bottom side should be non-adhesive, i.e., not fixed fastly to the
support surface. The area of the bottom side which is in contact with the
support
is surface should be effective to inhibit or hinder slipping or sliding of the
liner
structure tangentially, laterally, or in a plane parallel to the support
surface. The
use of tape or other adhesive to hold the liner structure in place on a smooth
support surface thus is unnecessary. Due to the lack of adhesive, the liner
structure may be readily picked up from the support surface for reuse or
2o replacement without damaging the support surface or leaving adhesive
residues,
which are often difficult to remove. The polymeric resin comprising the sheet
portion of the liner structure also is preferably selected to be sufficiently
flexible
that the liner structure conforms to the contours of the support surface when
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placed in contact with said support surface and remains in conformance for an
extended period of time (i.e., does not exhibit a significant degree of
curling).
The use of rigid or semi-rigid polymeric resins thus should be avoided when
fabricating the sheet portion of the liner structure.
s In a preferred embodiment of the invention, the polymeric resin used in the
sheet portion is comprised of polyvinyl chloride which contains an amount of
plasticizer effective to render the sheet portion flexible and non-skid.
Plasticized
polyvinyl chloride resins are well known and are described, for example, in
the
chapter entitled "Vinyl Chloride Polymers" in the Encyclopedia of Polymer
o Science and Engineering. Second Edition, Supplement Volume, pp. 822-889
(1989).
An example of a commercial resin suitable for use in the flexible sheet
portion of the present liner structure is APEX 3301-80NT resin (available from
the
Plastics Division of the Teknor Apex Company, Pawtucket, Rhode Island). This
is resin has a Shore A hardness (15 second reading) of 66/60, a specific
gravity of
1.16, a tensile strength of 1500 Ibs/sq. in., and an ultimate elongation of
450%.
The flexible sheet in preferred embodiments of the invention is
substantially continuous, i.e., it does not contain any holes, perforations or
other
openings. This feature renders the liner structure esthetically pleasing in
2o appearance and allows the liner structure to be easily cleaned using a
sponge or
the like. The liner structure thus completely protects the support structure
surface from dirt, dust, water, food particles and the like. Another advantage
of
the liner structures of the present invention is the "cushioned" effect
imparted by
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the rubbery and relatively soft polymeric resin. This reduces the tendency of
fragile items such as glasses and fine china to break, crack or chip when
placed
forcefully on a hard support surface such as a wood shelf.
In certain embodiments of the invention, the liner structure is substantially
s solid and substantially free of pockets and other voids of significant size.
However, in other embodiments, the flexible sheet is foamed (e.g.,
microcellular)
in character.
The bottom surface of the flexible sheet may be flat or substantially flat so
that when the liner structure is placed on a planar surface such as a shelf,
all or
io substantially all of said bottom surface is in direct contact with the
planar
surface. However, in a preferred embodiment of the invention, the bottom
surface has means such as ridges extending downwardly and defining an
integral raised pattern on the bottom side of the flexible sheet. The bottom
edges of the downwardly extending ridges preferably are coplanar to provide a
1s level supporting "surface" or means. This arrangement of downwardly
extending
ridges provides a reduced, substantially horizontal surface area in contact
with
the planar surface. Air may thus flow underneath the liner structure, thereby
discouraging moisture accumulation and the growth of mold and mildew.
The downwardly extending ridges may be incorporated as a plurality of
2o parallel ridges which are straight or non-linear (e.g., in a wave or zig
zag pattern).
In one embodiment of the invention, the downwardly extending ridges are
underneath and parallel to the upwardly extending ridges. The bottom surface
of
the liner structure thus may have an undulating or "rippled" appearance.
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In one embodiment of the invention, the flexible sheet is uniform in
thickness (typically, from about 0.005 inches to about 0.05 inches). In other
embodiments, however, the thickness of the flexible sheet is varied,
preferably in
a regular manner or pattern. For example, the thickness of the flexible sheet
s may be relatively thin (e.g., about 0.01 inches) inbetween the upwardly
extending
ridges and relatively thick (e.g., about 0.05 inches) underneath the upwardly
extending ridges. Varying the thickness of the flexible sheet may also be used
to
create the downwardly extending ridges.
The downwardly extending ridges should be constructed of one of the
o relatively soft polymeric resins previously described in connection with the
sheet
portion of the liner structure.
In one embodiment of the invention, the same relatively soft polymeric
resin is used in both the sheet and downwardly extending ridges since this
will
simplify the fabrication of the liner structure. It will generally be
desirable for the
1s downwardly extending ridges to be gently rounded or even flat to ensure
that
sufficient friction exists between the bottom edges of the ridges and the
surface
on which the liner structure is supported to render the liner structure non-
skid.
The means extending upwardly from the flexible sheet and defining an
integral raised pattern on the top side of the flexible sheet are, on the
other hand,
2o constructed (at least on their top edges) of a harder polymeric resin than
the
polymeric resin used to form the bottom side of the flexible sheet. Said means
may, for example, take the form of ridges. By using a harder polymeric resin,
articles placed on the raised pattern may be readily removed from the liner
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structure even in a direction generally parallel to the plane of the liner
structure
since the coefficient of friction will be relatively low. This feature is
particularly
advantageous where the ridges have relatively thick top edges and thus have a
relatively large surface area in contact with the bottom of an article placed
on the
s linear structure. However, the polymeric resin used to fabricate such ridges
should not be so rigid or inflexible that the ridges interfere with the
ability of the
liner structure to conform to the contour of the support surface. For the same
reason, the harder polymeric resin is preferably not present in the areas
between
the upwardly extending ridges. If a relatively stiff polymeric resin is used
to
o create the upwardly extending ridges, the cross-sectional area of the ridges
may
be reduced as needed in order to maintain the desired flexibility of the
overall
liner structure.
In a preferred embodiment of the invention, the polymeric resin used to
form the upwardly extending ridges is compatible or miscible with the
polymeric
is resin used to fabricate the sheet portion so that good adhesion is
developed
directly between the ridges and the sheet portion. The use of a separately
applied adhesive layer to join the ridges to the sheet portion therefore is
not
necessary. The resulting liner structure is nevertheless highly resistant to
delamination (separation of the ridges from the flexible sheet). The upwardly
2o extending ridges (or at least the top edges thereof) in one desirable
embodiment
are comprised of a polyvinyl chloride resin. While this resin may be
plasticized,
the plasticizer level typically will be lower than the plasticizer level in
the flexible
sheet polymeric resin and sufficiently low so as to impart a low coefficient
of
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friction to the exposed surfaces of the top edges of the upwardly extending
ridges.
Suitable polymeric resins for use in the upwardly extending ridges include
POLYFLEX 118514 (available from Flex Technologies, Inc.) and APEX 3189
s (available from the Plastics Division of the Teknor Apex Company). These PVC
resins have the following characteristics:
POLYFLEX 118514 APEX 3189
Shore A Hardness (15 sec. reading) 85 78/65
Specific Gravity 1.34 1.37
io Tensile Strength (Ibs./sq. in.) 3700 2950
Ultimate Elongation (%) 330 320
In one embodiment of the invention, the raised pattern is defined by a
plurality of generally parallel ridges. The ridges may be straight or in the
form of
a wavy or zig-zag pattern or the like. The top edges of the ridges may be
is pointed, rounded or flat. Generally, a flat top edge is not preferred as
air
circulation will be restricted and articles placed on the liner structure may
be
somewhat more difficult to remove, particularly if the ridge is relatively
wide, due
to the increase in the surface area of the ridge in contact with the bottom
surface
of the article. The top edges of the ridges should be coplanar to provide a
level
2o supporting "surface" or means. In a preferred embodiment of the invention,
the
ridges are rounded with a width at their base in the range of from about 0.05
to
about 0.15 inches and a height in the range from about 0.03 to about 0.10
inches
(as measured from where the ridge is joined to the bottom web). It is not
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necessary for the upwardly extending ridges to be fabricated entirely from the
relatively hard polymeric resin. The lower portion of each ridge, for example,
may be comprised of the relatively soft polymeric resin with the relatively
hard
polymeric resin being used only as a thin cap on the top edge of the ridge.
The
s spacing of the ridges may be adjusted as desired to provide effective
support to
articles placed on the liner structure. For example, the ridges should be
sufficiently close together to prevent tall, relatively narrow articles such
as
glasses from tilting and falling over. Spacings in the range of from about 0.3
inches to about 0.5 inches are effective for this purpose, for example.
to The upwardly extending ridges not only impart a pleasing design texture to
the liner structure, but also create channels into which excess water from
glasses
and dishes may readily drain and then evaporate. The liner structures of the
present invention thus have a reduced tendency, as compared to previously
known flat top liners, to develop water rings and the like.
is A coextrusion process may be used to fabricate the liner structures of the
present invention. In such a process, the relatively soft polymeric resin used
to
form the flexible sheet component is extruded simultaneously with multiple
extrusions of the relatively hard polymeric resin used to form the plurality
of
upwardly extending ridges. The extruded melts are brought together in a
2o common co-extrusion die having the desired cross-section of the liner
structure
at elevated temperatures and pressures effective to form bonds at the
interfaces
between the two polymeric resins. The relatively hard polymeric resin thus is
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extruded through the die only at isolated points corresponding to the intended
positions of the individual upwardly extending ridges.
While the polymeric resins used to construct the flexible sheet and the
ridges may both be clear or similarly pigmented to provide a liner structure
s having a unitary appearance, the decorative appearance of the liner
structure
may also be easily varied as desired. For example, the web material and the
ridge material may be pigmented in complementary or contrasting colors.
Alternatively, the web material may be unpigmented or clear and the ridge
material colored.
o The liner structures of the present invention may be fabricated to any
suitable length and width. For example, where the liner is designed to be used
on a household shelf of conventional width, the liner width may be adjusted
accordingly (e.g., from about 10 to about 15 inches) by selection of a
coextrusion
die of the appropriate dimension. Alternatively, a wider coextrusion die may
be
used and the coextruded liner structure cut to the desired width by slitting
or the
like. Coextrusion permits a liner structure of essentially infinite length to
be
manufactured. To facilitate packaging and handling, however, the liner
structure
will generally be cut to a shorter suitable length (e.g., from about 3 feet to
about
12 feet). The end user may readily cut the liner structure to fit the support
2o structure using scissors, a razor knife or the like.
Figures 1-3 illustrate in cross-section different embodiments of the present
invention. Flexible sheets 1, 3 and 6 are constructed of a first polymeric
resin
which is sufficiently soft to render the flexible sheets non-curling and the
bottom
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surfaces of the flexible sheets (which contact the support surface on which
the
liner structure is placed) non-skid. In Figure 1, the bottom surface of the
flexible
sheet is flat. In Figures 2 and 3, downwardly extending ridges 5 and 8 project
from the flexible sheet to provide the desired non-skid contact with the
support
s surface.
A second polymeric resin which is harder than the first polymeric resin is
utilized to form upwardly extending ridges 2, 4 and 7. The upwardly extending
ridges in Figures 1 and 3 are rounded at their top edges, whereas the upwardly
extending ridges in Figure 2 are pointed.
io Figure 4 is a perspective view of three liner structures A, B, and C in
accordance with the present invention. In liner structure A, the upwardly
extending ridges (which appear as dark stripes on the top surface of the
flexible
sheet) are straight and parallel to each other and are spaced at regular
relatively
wide intervals. In liner structure C, the upwardly extending ridges are spaced
is more closely together. Liner structure B illustrates an intermediate ridge
spacing.
In each of these liner structures, the flexible sheet is of variable thickness
and
contains downwardly extending ridges on its bottom surface, with each
downwardly extending ridge being underneath and parallel to a corresponding
upwardly extending ridge.
