Note: Descriptions are shown in the official language in which they were submitted.
CA 02488747 2004-10-18
SLIP RESISTANT FITTED COVER
FIELD OF THE INVENTION
This invention relates to fitted covers of textile and other fabrics used to
cover
various articles such as vehicles, equipment, household items, apparel items
and the like.
More specifically, the invention relates to fitted covers having a cross-
extensible strip
disposed peripherally on the cover to render the cover resistant to slipping
off the
covered article.
BACKGROUND OF THE INVENTION
Sheets of fabric are often used to cover an underlying article to protect the
article
from adverse effects of environmental exposure and/or wear during use. Tarps
protecting vehicles or equipment, such as barbecue grills, are examples of the
former and
upholstery seat covers, bed sheets and mattress pads are examples of the
latter. Often the
covers have an aesthetic as well as functional purpose. An age old problem
with such
covers has been preventing the cover from partially or completely coming off
the article
during use while attaching the cover such that it can be easily removed for
cleaning,
repair and/or to gain unrestricted access to the underlying article.
A traditional technique has been to utilize an elastic cord at the periphery
of the
sheet fabric such that when the cover is deployed on the article, the elastic
is stretched
peripherally and maintained under tension. With respect to bed sheets,
mattress pads and
furniture seat covers, it is known to use a peripherally elastic skirt at the
periphery of the
sheet or pad in place of or in combination with an elastic cord. Examples of
such skirt
technology is disclosed in US patents of Xymid, LLC, including nos. 5,287,574;
5,247,893; 5,187,952; 5,603,132; 5,636,393; 6,199,231 and 6,272,701. Another
conventional method of reducing the tendency of the cover to come off the
article has
been to use a high friction surface on the surface of the cover facing the
article. These
techniques function with a varying degree of success primarily when the
covered article
is not disturbed, e.g., for a tarp covering a car or boat not affected by
wind, or a dust
cover for furniture seldom or never used. However, when the cover is subject
to motion
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or disturbance during use, such as a mattress cover on a bed, none of the
established
techniques provide fully satisfying results.
A very common product for covering mattresses for beds is a "fitted" sheet.
Some styles use an elastic cord to gather the outer edge of the sheet, as
mentioned above.
Despite the use of very high modulus cords, i.e., strongly elastic, such
sheets tend to
"ride up" over the bottom edge of the mattress to expose the side of the
mattress to view
and also can come off enough to expose the top of the mattress during normal
use.
Another drawback is that the elasticity of the cords degrades with time under
tension and
due to thermal effects during laundering. Fitted sheets that use conventional
skirts of
typically up to about 6 inches in width with or without elastic cord borders
sometimes
have an unacceptable appearance and still are not completely successful at
maintaining
the sheet in place or retaining their anti-slipping performance after long
time in use.
There remains a need to have a cover for an article that better resists the
tendency
to ride up or come off the article. It is desirable to have an article cover
that retains its
ability to stay in place over long time in use. There is a great need for an
effective slip-
resistant cover, especially for covering mattresses, which is aesthetically
attractive.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a cover for an article comprising
(a) a sheet of substantially non-stretchable fabric, the sheet defining a
characteristic length, and
(b) a strip of cross-extensible fabric having an inner edge attached to the
sheet
in a peripheral direction and having a substantially uniform transverse
peripheral
unstretched width of about 1-30% of the characteristic length of the sheet,
in which the strip can stretch in a transverse peripheral direction by an
incremental
extension of at least about 150 % of the unstretched width under a tensile
force of less
than about 160 g/cm of unstretched width.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of a mattress covered with a fitted sheet in
accordance with an embodiment of this invention.
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Fig. 2 is an elevation cross section view of the covered mattress of Fig. 1
taken
along line 2-2.
Fig. 3 is a bottom view of the covered mattress of Fig. 1.
Fig. 4 is an elevation cross section view of a cover for a mattress according
to
another embodiment of this invention.
Fig. 5 is an elevation cross section view of a cover for a mattress according
to
another embodiment of this invention.
Fig. 6 is an elevation cross section view of a cover for a mattress according
to
another embodiment of this invention.
Fig. 7 is an elevation cross section view of a cover for a mattress according
to
another embodiment of this invention.
Fig. 8 is an elevation cross section view of a cover for a mattress according
to
another embodiment of this invention.
Fig. 9 is an elevation cross section view of a cover for a mattress according
to
another embodiment of this invention.
Fig. 10a is an elevation cross section view of a mattress covered with an
embodiment of the present invention as deployed prior to activity tending to
remove the
cover.
Fig. l Ob is an elevation cross section view of the mattress covered with an
embodiment of the present invention of Fig. 10a after activity on the mattress
tending to
remove the cover has occurred.
Fig. 11 is a perspective view of a mattress illustrating placement of a cover
slip
resistance testing apparatus.
DETAILED DESCRIPTION OF THE INVENTION
The invention can be understood generally with reference to the elements of a
fitted fabric cover illustrated in Figs. 1-3. In the figures, like parts have
the same
reference numbers. The article being covered is a mattress 2, although other
objects
could be exemplified. Mattress 2 has an approximately rectangular cross
section (Fig. 2)
which is characterized by a broad, largely flat, top, horizontal sleeping
surface 3 and
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vertical, typically smaller dimension sides 4. Corners 5 between the mattress
top and
sides, and between the mattress bottom 8 and sides are rounded in the
illustration.
Optionally, the corners can be sharp.
The mattress is covered with a fitted bedsheet 10 which has a main part,
occasionally referred to herein as the "sheet" 12 formed from a substantially
non-
stretchable fabric material. The sheet extends over the top, sides and some of
the bottom
of the mattress from 12a to 12b. Adjacent to the sheet is a strip 14 of a
cross-extensible
fabric. The strip has an inner edge which is attached to sheet 12
circumferentially at the
rim of the sheet seen in Fig. 1 as points 12a and 12b. At the outer edge of
the strip 14
which also is a continuous circumferential boundary 15, is attached an elastic
cord 16.
The term "substantially non-stretchable" with respect to the fabric of sheet
12
means that the sheet is largely, although not absolutely, not stretchable.
That is, it will
not strain to a great extension without breaking apart. This is not to
preclude the sheet
fabric from stretching a small amount such as would be expected from bed
covering
fabrics. The term "cross-extensible" is used herein to denote that fabric of
the strip can
stretch in a transverse peripheral direction. Cross-extensibility will be
discussed in
greater detail, below. The peripheral direction is parallel to the periphery
of the edge of
the sheet, that is, in the direction of arrows "P" in Fig. 3. The transverse
peripheral
direction is thus as shown by arrows "C" in this figure.
Another aspect that is useful in understanding this invention is the
"characteristic
length" of the sheet. The characteristic length is the longest linear
dimension of the
sheet. This dimension will depend somewhat on the shape of the sheet. For a
circular
sheet, the characteristic length is the diameter. For an oval or elliptical
sheet, it is the
diameter coincident with the major axis. For the rectangular sheet depicted in
Figs. 1-3,
the characteristic length is the length of the sheet measured from point 12a,
up one side 4
across the top 3 down the other side 4 to point 12b. The "width" of the strip
is the
transverse peripheral dimension W (Fig. 3). The width of the strip is
substantially
uniform. This is not readily apparent from the drawings which are not drawn to
scale.
By "substantially" uniform is meant that the actual width may deviate from
perfectly
uniform by a slight degree in view that the material being measured is a cross-
extensible
fabric. Such material is normally difficult to control to very precise
dimensions.
Preferably, the width of the strip may be characterized as narrow. That is,
the width is
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much less than the characteristic length of the sheet. While the upper bound
of the width
is not critical, it is contemplated that a minimum width of about 0.5 inch (13
mm) is
recommended to allow the strip to perform its slip-resistant function as will
be explained.
Subject to the minimum width dimension just mentioned, the preferable width
dimension
in a tension-free state, i.e., when relaxed, is about 1-10 % of the
characteristic length.
It is important that the strip has a cross-extensible stretch characteristic,.
This
means that the strip can extend to a large deformation with very little
tensile force
applied. The ability of the cover to retain its position on the article is
thought to be
largely attributable to this characteristic of the strip. Preferably the cross-
extensible strip
can stretch in a transverse peripheral direction by an incremental extension
of at least
about 150 % of the unstretched, (i.e., tension free) width when tensioned by a
force of
less than about 160 g/cm of the width. That is, the width under tension of 160
g/cm of
width is at least 2.5 times the unstretched width. More preferably, the strip
should
stretch to an incremental extension of at least 200 %.
Although the strip is able to stretch in the transverse peripheral direction
to great
extent under low tensile load, it is not necessarily elastic. That is, it is
not critical that the
strip can return substantially completely to the unstretched transverse
peripheral
dimension when a tensile load is removed. Elasticity in the transverse
peripheral
direction can adversely promote the tendency of the cover to pull off the
article unless
the strip exhibits a strong elasticity in the peripheral direction. Strong
elasticity occurs if
the strip can stretch to at least about 50% and exhibits a contraction force
of at least
about 0.3 N (300 g-force) at 50% extension. In a preferred embodiment, the
strip is
substantially inelastic in the peripheral direction.
The strip is preferably an open fabric. That is, open area between yarns or
other
structural components of the fabric, sometimes referred to as porosity, is a
large
percentage of the overall fabric area. The fabric can be woven, non-woven or
knitted
construction. Knitted fabric is much preferred because the knit-forming loops
usually
can easily separate to a large extent with little tension applied. Netting or
mesh is also
preferred. The open aria is generally at least about 20 %, and preferably at
least about
50%. Especially effective are net-like strips stitched, knit or woven with
bare elastic
yarns. A strip of perforated elastomeric film having intermittent parallel
slits is also
contemplated to be useful. It is not critical that the strip possesses a high
coefficient of
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friction between itself and the article being covered to resist slipping.
Nevertheless, it is
possible and beneficial to utilize a strip that does have a high coefficient
of friction.
To use the novel slip resistant cover, the cover is placed over the article
such that
the cross-extensible strip is positioned beyond an edge of the article. For
example, in
Fig. 10a, the strip 14 is located under the mattress and beyond bottom corners
5 of the
mattress 2. The sheet 15 thus extends along the sides, around the bottom
corners and
under the mattress. When the article or cover moves in a way tending to pull
the cover
off of the article due to an activity or external force, the cross-extensible
strip stretches in
the transverse peripheral direction. The deformation is large because the
strain-to-tensile
stress characteristic of the fabric is very high. Also, the open areas between
the strip
fabric structural elements expand. The motion tends to pull the substantially
non-
stretchable sheet to ride up from below the mattress and up the side. However,
the strip
is drawn around the bottom corner as seen in Fig. l Ob and the structural
elements snag
the edge of the article and thereby hold the attached sheet part of the cover
from riding
up farther. It should be further noted that a cover optionally can be
initially deployed
with the strip extended around corners of the article to be covered such that
the corner
snags the strip. Motion or applied force will not normally cause the snagged
strip to
release from the corner and the sheet will remain substantially in place. Thus
it is not
critical to deploy the cover with the strip completely positioned beyond the
corner of the
covered article.
To resist or prevent cover removal, the strip should be initially positioned
beyond
the bottom corner of the article, for example, as seen in Fig. 3. This
positioning of the
strip can be facilitated by placing the sheet in transverse peripheral
tension, especially in
the area near the edge which causes the cover to pull under the article. The
transverse
peripheral tension can be imparted by providing a peripherally elastic element
of such
length that the element is stretched when the cover is deployed. The elastic
element
should have a strong elasticity in the peripheral direction. The strip may
itself be
peripherally elastic or the peripherally elastic element can be extrinsic to
the strip. For
example as mentioned, the peripherally elastic element can be an elastic cord.
If the strip
is intrinsically peripherally elastic then a supplemental elastic cord is
optional and may
be excluded from the structure. If the strip is not suitably peripherally
elastic, a
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supplemental elastic element should be provided. Preferably, either the strip
should be
peripherally elastic or at least one elastic cord should be utilized in the
novel cover.
In a preferred embodiment, the inner edge of the strip is attached to the
sheet part
of the cover at a distance from the periphery of the sheet. This allows the
strip to be
partially or entirely concealed from view outside the cover by the sheet. Thus
the
superior slip resistant performance of the cover can be obtained with
excellent aesthetic
appearance of the cover when deployed.
A wide variety of configurations that utilize many combinations of elastic
cord
and strip attachment are thus contemplated. These configurations are
illustrated
schematically in Figs. 4-9 and are explained as follows. These figures
illustrate a cross
section of a cover for a mattress deployed similar to the cover in Fig. 2,
however, the
mattress is not shown for clarity.
Fig. 4 shows an embodiment in which cross-extensible strip 14 is attached at
its
inner edge 18 by a seam 19 to the periphery of sheet 15. The outer edge 17 of
the strip
is finished 20 in a conventional matter, for example, by a hem. No added
elastic cord is
present in this embodiment.
Fig 5 shows an embodiment in which the strip 14 is attached at its inner edge
18
to the periphery of sheet 15 and in which an added elastic cord 21 is attached
along the
junction between the sheet and the strip. A second elastic cord 22 is attached
at the outer
edge 17 of the strip. The presence of two added elastic cords can provide
greater
peripheral direction elasticity which can increase the resistance of the cover
to ride up or
come off of the covered article. While the illustrated examples depict
embodiments in
which elastic cords are positioned at the edges of the strip, it should be
understood that
one or more elastic cords, if present, can be positioned in the strip
intermediate the inner
and outer edges.
Fig. 6 shows an embodiment in which the strip 14 has a finished outer edge 17
and there is a single elastic cord 21 position along the junction between the
strip inner
edge and the sheet 15.
Figs. 7-9 show embodiments in which the inner edge 18 of the strip 14 is
attached
to the sheet 15 at a distance offset from the periphery 25 of'the sheet. These
embodiments are useful in applications where improved aesthetic appearance of
the
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cover is desired. The strip is hidden from view from outside the cover by the
tail 23 of
the sheet. The tail extends around the perimeter of the sheet and in a
transverse
peripheral direction from the point of attachment of the strip to the sheet
periphery 25.
In the embodiment shown in Fig. 7, the outer edge 17 of the strip has an
elastic cord 24
and the sheet periphery 25 has a finished end 28. The tai123 is seen to be
horizontally
oriented in Fig. 7 which is meant to suggest that it can be tucked between the
mattress
above and the bed foundation, e.g., spring unit or bed frame, below (not
shown). This
permits a bed sheet to be made up in a conventional manner. Optionally, the
tail can be
left to hang vertically downward along and below the sides of the mattress.
The strip
serves to retain the sheet in place despite the appearance that the sheet is
not tucked
under the mattress. This feature advantageously provides an aesthetic
appearance that
has not heretofore been available as for example in slip resistant bed
spreads.
Fig 8. shows a "hidden strip" embodiment similar to that of Fig. 7 in which
the
periphery of the sheet is equipped with an added elastic cord 30. The
embodiment
shown in Fig. 9 is similar except that the strip also has an added elastic
cord 32 that is
positioned at the outer edge. These and other variations of the invention are
contemplated to provide the designer with the ability to tailor the gripping
power of the
cover to meet the needs of a diverse range of article-covering utilities in
addition to
mattress sheet and pads, such as, cars, boats, barbecue grills, items of
apparel, e.g., hats,
decorative seat covers, toilet tank and toilet seat covers, cushion covers,
outdoor
mechanical equipment, e.g., generators, air conditioners, outboard motors,
lawn and
patio furniture, and the like.
EXAMPLES
This invention is now illustrated by examples of certain representative
embodiments thereof, wherein all parts, proportions and percentages are by
weight
unless otherwise indicated. All units of weight and measure not originally
obtained in SI
units have been converted to SI units.
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Example 1
A conventional "queen-size" woven cotton bed sheet having an integra138 cm
(15 inch) wide woven cotton skirt sewn to its perimeter was used as the sheet
for the
following tests.
A cross-extensible strip was made of a two-bar stitchbonded nonwoven of a
carded web consolidated with a spray of soft adhesive. The web was stitched
with 77
dtex /34 filament textured polyester in the backbar and 77 dtex Lycra elastic
filament
air/wrapped with a 44 dtex textured nylon filament in the front bar. Both bars
were
stitched at 14 gauge, 3.54 counts per cm (9 CPI). The bac:kbar had a stitch
pattern of
(1-0,1-2). The front bar pattern was an extensible (1-0, 1-0, 1-2,1-2) ripple
stitch adapted
to allow the fabric to stretch by a factor of 3-4 times in the transverse
peripheral
direction. An elastic cord was formed by tripling the number of single-end
yarn in the
front bar for 12 rows. The total dtex of elastic yarn in each row was 231.
This created a
10 cm wide strip with a 1.9 cm wide elastic cord on the edge. The cross-
extensible strip
was sewn to the side of the skirt to form a structure as seen in Fig. 2. The
strip was
found to stretch in the transverse peripheral direction by 150% with an
applied force of
about 90 g/cm of strip width.
The modified sheet was placed on a queen size mattress M (Fig. 11) of 30.5 cm
(12 inches) side height and the sheet was pulled under the inattress to fit
snuggly. A
spring-operable, so-called "fish scale" meter was attached to the top of the
mattress with
a hook H at a point 30.5 cm (12 inches) from a corner in a direction toward
the center of
the sheet and was oriented in direction of arrow F at an angle of 20 degrees
from vertical
toward the sheet center. The fish scale meter was pulled with an increasing
force starting
from zero. The force necessary to pull the strip and cord from under the
mattress and
around the lower mattress corner was observed as the "pull-off' force. Pulling
was
continued and the force necessary to cause the edge of the cover to slide up
along the
vertical side of the mattress was also observed as the "slide-up" force. The
experiment
was repeated several times and the average of pull-off and slide-up forces for
the trials
was calculated.
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Example 2
The procedure of Example 1 was repeated except that the inner edge of the
strip
was sewn inside the sheet 13.3 cm (5.25 inches) from the periphery of the
sheet, i.e., the
tail was 13.3 cm. The structure was as shown in Fig. 7.
Comparative Example 3
The queen size sheet used in the preceding examples was modified by extending
the skirt width to a total of 48 cm (19 inches) to equal the dimension of the
skirt plus
strip of the operative examples. The elastic cord from Exs. 1 and 2 without
the cross-
extensible strip was attached on the peripheral edge of the skirt under
tension. The
procedure of the prior examples was repeated.
Results of the average and ranges of pull-off and slide-up forces of the
examples
described above are shown in Table I, below.
Table I
Pull-Off Force Slide-Up Force
Average (N) Range (N) Average (N) Range (N)
Ex. 1 75.6 (17 lb) 71.2-80.1 (16-18 lb) 35.6 (8 lb) 35.6-40.0 (8-9 lb)
Ex. 2 80.1 (18 lb) 71.2-89.0 (16-20 lb) 35.6 (8 lb) 35.6-40.0 (8-9 lb)
Comp. Ex. 3 40.0 (91b) 35.6-44.8 (8-10 lb) 13.3 (3 lb) 13.3-17.8 (3-4 lb)
These results show that the addition of a cross-extensible strip dramatically
improved the slip resistance of the bed sheet.
Although specific forms of the invention have been selected in the preceding
disclosure for illustration in specific terms for the purpose of describing
these forms of
the invention fully and amply for one of average skill in the pertinent art,
it should be
understood that various substitutions and modifications which bring about
substantially
equivalent or superior results and/or performance are deemed to be within the
scope and
spirit of the following claims.
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