Note: Descriptions are shown in the official language in which they were submitted.
CA 02565127 2006-11-08
EXPANDED FOAM PRODUCTS AND METHODS FOR PRODUCING THE SAME
This application is divided from Canadian Patent Application Serial Number
2,208,029 filed January 3, 1996.
Field of the Invention
The present invention pertains to expanded foam products and methods for
making the same, and more particularly, to foam products derived from a solid
slab
of foam having a plurality of slits formed therein and which are capable of
providing
an expanded state to thereby alter the effective IFD and density values
thereof.
Background of the Invention
It is well known in the field of cushioning that comfort and support are
determined in large part by the amount and characteristics of the supporting
material. Cushioning characteristics or the Indentation Force Deflection (IFD)
value
of a foam material is derived by measuring the force required to reduce the
thickness of a 15" (38.1 cm) x 15" (38.1 cm) x 4" (10.16cm) polyurethane foam
sample by 25% when depressing an 8 inch (20.32cm) diameter disk having a
surface area of approximately 50 in2 (322.58cm2) thereinto. Thus, an IFD value
of
40 means that 40 pounds (11.6 bar) of force on a 50 in2 (322.58cm2) disk is
required to decrease an established foam sample's thickness by 25%. See ASTM
D3574-91. The IFD value can be affected by inherent properties such as the
material's chemical composition, physical structure, and density or by post
manufacture structural manipulation such as the removal or addition of
adjuncts.
Current technologies and manufacturing restrictions prevent the reliable
production of blown foam products having an IFD value of less than about 12
pounds (3.48 bar). Regarding this limitation, a common solution has been to
"core"
the foam product to create collapsible voids therein. For example, a foam slab
is
cored to remove foam to thereby decrease its overall weight and decrease its
overall effective IFD value. A significant consequence of this weight and IFD
CA 02565127 2006-11-08
reducing methodology is the generation of unused and often times unwanted foam
material resulting from the coring process. It is therefore desirable to
reduce and
preferably eliminate the generation of this waste material. In addition, the
coring
process can be labor intensive compared to other processes such as slicing,
stamping, or molding.
It is therefore desirable to provide a resilient material for use, for
example, in
self-inflating mattresses, which is light, retains appropriate tensile
strength
properties, achieves acceptable self-inflation properties, and is generally
easy to
incorporate into such mattresses, and which does not generate any waste by-
product.
SUMMARY OF THE INVENTION
The present invention is directed to methods of manufacturing reduced
density resilient materials. A common feature of all method embodiments is
that a
resilient material is made lighter through mechanical alteration but involves
virtually
no generation of wasted resilient material. Methods to produce a reduced
density,
resilient structure are characterized by selectively forming a cut or slice in
a slab of
resilient material from one perimeter surface towards an opposing perimeter
surface (although is it not necessary to have the cut or slit extend
therethrough),
expanding the cut or sliced material by applying tensioning to the material,
and
retaining the expanded state either by fixedly attaching the expanded material
to at
least one sheet of flexible material or by utilizing a slit design that is
characterized
by a first inner surface having at least one protruding portion forming an
interlocking
or mating fit with an opposite and complementary recess formed by a second
inner
surface. Products resulting from execution of the aforementioned methods are
less
dense than would be accomplished using just the resilient material without
mechanical manipulation, retain most of the desirable qualities associated
with use
of a non-altered resilient material, and involve no generation of waste
material.
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CA 02565127 2006-11-08
Accordingly, the present invention provides a method for creating an
expanded resilient product from a solid resilient material having a first
major surface
in general opposition to a second major surface, and bounded by a perimeter
surface comprising: (a) selectively forming a plurality of adjacent and
generally
parallel slits in the resilient material; (b) expanding the slit material to
form an
expanded material; and (c) fixedly attaching the expanded material to at least
one
substantially planar material.
In one embodiment, cuts are made in a slab of resilient material having two
opposing and substantially planar major surfaces and a two major and two minor
perimeter surfaces. The cuts extend from one perimeter surface to the opposing
perimeter surface (preferably the minor perimeter surfaces) and depend from
one
of the two planar major surfaces but do not extend to the second major planar
surface thereby yielding a staggered siped pattern of slits. Upon tensioning
of the
major perimeter surfaces in opposite directions, the slab extends to create an
accordion or corrugated like structure. While the structure is in this
configuration, at
least one sheet of flexible material is bonded to the structure's major
surface which
assists in retaining the physical attributes of the expanded structure.
Preferably a
second sheet of flexible material is bonded to the opposing major surface and
the
perimeter of the sheets also bonded together, thereby enveloping the slab. If
it is
desired to envelope the resilient material in this manner, the flexible sheets
should
be, but not must be, impervious to fluid/air. By incorporating a valve
extending from
the chamber defined by the sheets to the environment, control over the fluid
pressure in the chamber can be regulated.
Variations of the basic invention include modifying the geometry, placement,
and number of the slits, and manipulating an unslit slab to create a
corrugated
geometry. For example, extending perimeter cuts can be made into a slab of
resilient material to yield two complimentary slabs characterized as having a
web
portion and a plurality of extending portions defining transverse or
longitudinal
channel of several geometries. The resulting complimentary slabs can be
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CA 02565127 2006-11-08
incorporated into a mattress as described above, or can be modified by
isolating
each channel segment, such as by slicing the material from the extending
portion
through the base portion, to produce a plurality of channel prisms. The
channel
prisms may then be aligned and bonded to a pair of fluid impervious sheets to
enclose the channels and thereby define a void. In this form, the slab
resembles
one that has been cored, yet again, no waste material has been generated.
In another embodiment, the physical properties of the resilient material are
not changed, however its geometry is modified by manipulating the slab into a
sinusoidal pattern wherein the slab peaks collectively define a first and
second
planar surface. Fluid impervious sheets may then be attached to the peaks and
their perimeters sealed to produce an enclosed structure. By using a valve
fluidly
coupling the chamber defined by the sheets and occupied by the resilient
corrugated slab with the environment, a self-inflating structure can be
obtained.
In yet another embodiment, a first and second slit convergently depend from
an arbitrary location on the major surface of a resilient slab. The slits
extend from
one perimeter surface to the opposing perimeter surface but do not in fact
converge
within the body of the slab. A second pair of slits, divergently depend from
the
opposing major surface and are spaced from and parallel to the first slits.
All slits
are linearly symmetrical. Similar cuts are made in the remaining material.
Force is then applied to the resulting structure to cause extension of the
material in a direction substantially perpendicular to the major planar
surfaces. At
this juncture, fluid impervious skins may be bonded to the major planar
surfaces, or
additional force can be applied whereupon the structure laterally contracts,
thereby
causing the major planar surfaces to become coextensive again. However,
plurality
a lateral or transverse voids are created, thereby approximating the
insulative
values of a cored slab, but without generating waste material in the process.
A method for manufacturing the described self-sustaining expanded
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CA 02565127 2006-11-08
product comprises the steps of creating a plurality of slits in a geometric
solid of
resilient material wherein each slit is defined by a protruding portion on a
first inner
surface of the resilient material and interlocks with an opposite and
complementary
recess defined by a second inner surface of the resilient material; applying
force to
the material so as to dislodge at least one protruding portion from its
complementary recess; and permitting the protruding portion to compressionally
contact the second surface to thereby define a self-sustaining gap.
The foregoing modification of a solid resilient material to create self-
sustaining apertures or gaps is possible in part because of the nature of
resilient
material. It is the ability of the protruding portion and complementary recess
of the
material to first, deform and dislodge or separate from each other when
sufficient
forces are presented, second, return to their original shape thereafter, and
third,
resist re-interlocking either because of friction forces or physical
interference that
permits the creation and maintenance of self-sustaining apertures or gaps in
the
resilient material without requiring coring or generating waste material in
order to
reduce density and IFD values. With proper selection of the slitting
configuration
and the initial dimensions of the slab of resilient material, a larger self-
sustaining
slab of the desired dimensions and density, or IFD, can be manufactured
repeatedly for use in uniformly sized final products. In addition, the types
of
interlocking patterns that can be used are virtually unlimited. However,
because
each pattern has its unique attributes, one pattern may not be suitable for
all
applications.
From the foregoing, it can be seen that the effective density and IFD values
for any given resilient material can be modified without incurring any
material
waste. The effective density and IFD values of a resilient material can be
decreased more by creating more slits, longer slits, or longer protruding
portions. In
this manner, the initial IFD value of a resilient material can be modified to
create
"softer" material. The shape of the slits, amount of distortion when:
expanded, and
aspect ratio of the open spaces are all significant to the
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CA 02565127 2006-11-08
characteristics of the processed resilient material and its performance in the
finished product.
10
A feature of this embodiment is the slit slab's ability to physically distort
in
response to compression forces, thereby causing the webs defining the
apertures
or gaps to collapse. When the slit slab is used for load support,
compressional
forces are usually applied in a direction parallel to the slit axis so as to
capitalize
on the column strength created by the webs. However, when the maximum load
supporting force is exceeded, the web advantageously buckles and causes the
aperture or gap to close when the column buckles in embodiments having
sufficient sectional thickness and web dimensions. By permitting such closure,
thermal convection that otherwise might be significant, is lessened by the
closure
of the apertures or gaps. In the field of mattresses and the like, where
thermal
transmission is an important factor, the ability to have a foam slab of very
low
IFD, yet to have high insulating values when in use, is of particular benefit.
Another feature of the invention concerns the manipulation of the slab
itself into differing configurations. For example, an expanded slab having a
proportionally small perimeter height can be circumvoluted to bring opposing
perimeter segments into contact with one another to thereby form a cylinder of
expanded material. Such a configuration can be used for insulating pipe,
conduits, and the like, either alone or in combination with covaring materials
that
surround the central bore and/or the outer perimeter of the cylinder.
Conversely,
a slab having a proportionally large perimeter can be put on end so as to
receive
compressional loading in a direction substantially aligned with the major
direction
of the slits to provide different IFD values.
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CA 02565127 2006-11-08
The present invention is especially suited for use in the construction of
self-inflating foam mattresses wherein light weight, low density, reasonable
tensile strength, and compactibility are highly desirable. By bonding a fluid
impervious skin to and about a slab of expanded resilient material, a lighter
weight inflatable mattress can be created that still exhibits sufficient
compressional resiliency to provide self-inflating characteristics. Moreover,
use of
the present invention in its various embodiments does not significantly
dec~~ease
the foam's ability to act as a tensile member as required in order to maintain
the
load distribution and volume characteristics necessary for such self-inflating
foam
filled mattresses.
These and other features of the invention will become apparent upon
reading the description of the invention and inspection of the accompanying
drawings as well as the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a partial elevation view of a foam slab through which narrow
straight slits have been cut;
Fig. 2 is similar to the slab in Fig. 1, but wherein the foam has been
expanded by extending the slab in a direction perpendicular to the slit
or:en;ation;
Fig. 3 is cut-away perspective view of the slab shown in Fig. 2 whey ein
two fluid impervious sheets have been bonded to the slab;
Fig. 4 is a partial elevation view of a thin foam stab that has been formed
into a corrugated shape with sheets bonded to portions of both major surfaces;
Fig. 5 is a cross section elevation view of an apparatus used to form the
article illustrated in Fig. 4;
Fig. 6 is a cross section elevation of the thin foam slab of Fig. ~~ shcv,~n
formed in a mandrel rack and bonding to a first of two fluid impervious
sheets;
Fig. 7 is similar to Fig. 6 but wherein the mandrel rack has been removed
and the second fluid impervious sheet bonded to the slab;
Fig. 8 is a partial elevation view similar to that shown in Fig. 4, but
wherein the foam slab has been formed into a pattern to enclose triangular
shaped voids;
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CA 02565127 2006-11-08
Fig. 9 is an elevation view of a foam slab showing regular channels formed
therein;
Fig. 10 is an elevation view of a thick foam slab from which two slabs
similar to the type shown in Fig. 9 can be created;
Fig. 1 1 is an elevation view of a foam slab showing "T" shaped channels
formed therein;
Fig. 12 is an elevation view of a segmented core embodiment wherein a
plurality of "U" shaped segments are adjacently located and two flexible sheet
are bonded thereto;
Fig. 13 is an elevation view of the a slit pattern used to produce two,
complimentary slabs from ~ single slab;
Fig. 14, an elevation view, shows the segmentation of one of the slabs of
Fig. 13 into a plurality of "U" shaped segments;
Fig. 15 illustrates the slit pattern, in elevation, in a slab of foam to
produce
a vertically expanded foam core;
Figs. 16, 17, and 18 show the resulting configuration when the slab of Fig.
15 is partially and fully extended vertically by selective application of
forces
perpendicular to the major surfaces;
Fig. 19 is a plan view of a slab of foam material having an alternating
stagger pattern of unexpanded self-sustaining slits;
Fig. 19A is an enlarged perspective view of several self-sustaining slits of
Fig. 19 and details the various portions of the same in phantom;
Fig. 20 shows the slab of Fig. 19 after having been laterally expanded to
dislodge substantially all protrusions from their corresponding recesses and
then
released to allow the protrusions to interfere with the edges of the recesses
to
hold the gaps open;
Fig. 20A is an enlarged perspective view of several self-sustaining
apertures or gaps of Fig. 20 and details the various portions of the same in
phantom;
Fig. 21 is a side elevation of the slab illustrated in Fig. 20;
Fig. 21 A is similar to Fig. 21 but shows the slab beins subject to a
distributed compressive force so that the webs defining the apertures or gaps
collapse the same;
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CA 02565127 2006-11-08
Fig. 22 is a plan view of a stamping die that may be used in creating the
self-sustaining g~.p embodiment of the present invention;
Fig: 23 shows a partial perspective view of an embodiment of the invention
wherein a modified slab is oriented so as to accept compressive forces in a
direction substantially aligned with the major axis of the slits;
Fig. 24 shows the foam slab of Fig. 20 in a circumvoluted state so as to
create a cylinder;
Figs. 25A - G illustrate several examples of die elements which create
physical interlock between the protruding portion of the first inner surface
and the
complementary recess portion of the second inner surface upon compressive
application to an unslit foam slab;
Figs. 26A - B illustrate several embodiments of the invention that utilize a
tether to connect the protruding portion with the receiving portion to thereby
limit
expansion, improve uniformity of the gaps, and increase the expanded slabs
stability;
Fig. 27A is a side elevation similar to Fig. 21, except that the gaps do not
extend from one surface to an opposing surface, but instead, terminate in the
body;
Fig. 27B is an embodiment similar to that shown in Fig. 27A, but wherein
the gaps are formed only on one side;
Fig. 27C illustrates a resulting product similar to that of Fig. 27B, but
which is formed by combining a fully slit and a non-slit slab;
Fig. 27D illustrates a plan view and partial cut-away of an embodiment
combining aspects of the embodiment shown in Fig. 27C but wherein two
primary slit slabs are bonded together in an orthogonal relationship; and
Fig. 28 is a plan view with a partial cut-away showing an expanded foam
slab used in a self-inflating, air mattress or pad wherein an air-impermeable
skin is
bonded to the upper and lower surfaces of the expanded slab and the perimeter
is
sealed except for an inflation/deflation valve.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following discussion relates to several embodiments of the present
invention. Unless specifically described otherwise, all foam slabs have two
major
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CA 02565127 2006-11-08
planar surfaces and a pair of major and a pair of minor perimeter surface. The
slabs are preferably constructed from blown polyurethane having an initial IFD
value of 15 pounds (4.35 bar). All flexible sheets are preferably woven and
constructed from nylon, although any natural or synthetic polymer or material
will
provide adequate results, and have been treated on one side thereof with a
thermoplastic coating to facilitate the bonding of a foam slab when the two
components subjected to heat and pressure.
For comparison purposes, a solid foam, self-inflating mattress will be
referred to as the reference mattress. The normalized attributes of the
reference
mattress are as follows: weight of a 12" x 12" x 1 " (30.48cm x 30.48cm x
2.54cm) sample is 0.170 Ibs. (77.1 1 g); R value at 1 " (2.54cm) is 3.871; R
value
of 1 Ib. (0.4536kg) is 22.727.
Staggered Siped Embodiment
Turning now to the several figures wherein like parts have like reference
numerals, a first embodiment of the invention is shown in Figures 1, 2, and 3.
Figure 1 shows a uniformly thick slab of foam material 20 having upper major
surface 22, lower major surface 24, perimeter major surface 26a, and perimeter
minor surface 28a. Surfaces 26b and 28b are hidden from view and omitted for
clarity. A plurality of straight, staggered slits 30 depend therein at regular
intervals, alternately from major surface 22 and major surface 24. Slits 37
extend from perimeter surface 28a to 28b (not shown).
Figure 2 illustrates the physical structure resulting from application ~.
force
in the directions of the arrows, i.e., perpendicular to direction of slits 30.
As a
result, slits 30 are now expanded to form grooves 32. As a consequence of this
expansion, slab 20 becomes wider and has less sectional thickness than before
expansion. The degree of change in dimensions depends on the amount of force
applied, and the frequency and depth of slits 30.
After expansion, slab 20 is then bonded or fastened to fluid impervious
sheets 40a and 40b as is best shown in Fig. 3. Bonding surfaces 50 are
CA 02565127 2006-11-08
beneficially all part of major surfaces 22 and 24. Consequently, any treatment
of
these surfaces to facilitate bonding of sheets 40a and 40b thereto will be
retained. 'The attachment of sheets.40a and 40b to slab 20 ultimately limits
and
controls the stretch of slab 20.
In a preferred self-inflating mattress embodiment, slab 20 is expanded to
approximately one and a half times its original width whereafter its density
will
have been reduced by approximately thirty-five percent (35%). A significant
limitation concerning density reduction imposed on slab 20 is that tensile
portions
54 of expanded slab 20 contribute less compressive resistance and tensile
strength to the structure as the angle of tensile portion 54 relative to
sheets 40a
and 40b deviates from 90°. Thus, greater expansion will yield greater
reductions
in density, but wilt also decrease the desirable structural properties of the
slab,
such as tensile and compressionat strength.
The article resulting from the 50% increase in width dimensions has been
found to be an optimal balance between density reduction and burst
strength/peal
resistance. The embodiment shown has a weight reduction compared to the
reference mattress of about 34%; a decrease in the R value for a 1 " (2.54cm)
core of about 36%; and a decrease in the R value for a 1 Ib. (0.4536kg) core
of
about 3%.
A feature of this embodiment is that the amount of resilient material that
exists between sheets 40a and 40b throughout the structure tends to be fairly
constant, thus enhancing thermal insulation properties of the mattress.
Several
other embodiments discussed herein do not have this property.
Corrugated E ~nbodiment
Figure 4 illustrates a different embodiment of the invention wherein foam
slab 20', having a cross sectional thickness less than that of slab 20, is
formed
into a sinusoidal or corrugated shape and bonded to sheets 40a and 40b. The
corrugated slab has a plurality of bonding surfaces 50 that define two outer
coplanar surfaces at the exterior apexes thereof. The apex to apex distance is
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CA 02565127 2006-11-08
uniform throughout. Flexible sheets 40a and 40b 'are attached or bonded to
bonding surfaces 50 of corrugated slab 20' as described earlier. After
bonding,
sheets 40a and 40b prevent slab 20' from returning to its initial planar
configuration.
The strength of an inflatable mattress having corrugated slab 20' therein is
largely dependent upon the density of apexes, the angle of tensile portions 54
relative to sheets 40a and 40b, the tensile strength of the slab material
comprising the slab, and the thickness of slab 20'. In the illustrated
embodiment,
tensile portions 54 are roughly perpendicular to sheets 40a and 40b. This
geometry inherently provides a stronger structure than one with non-
perpendicular
tensile portions because the perpendicular portions experience minimal shear
force
when caused to tension.
In addition to good structural aspects, this type of mattress core compares
well to the reference mattress: a weight savings of about 2496 is realized;
the R
value for a 1 " (2.54cm) section is decreased about 4296; and the R value for
a 1
Ib. (0.4536kg) core is decreased by approximately 2596.
To efficiently manufacture the corrugated embodiment illustrated in Fig. 4, .
translatable mandrel rack 64 is used in conjunction' with rotatable pinion
drum 66
as is shown in Figs. 5, 6, and 7. Here, rods 68 of drum 68 are in a meshing,
non-contacting relationship with mandrel members 62 of rack 64. Slab 20' is
fed
into the combination whereupon pinion rods 68 engage slab 20' and urge each
foam segment between the gaps in mandrel rack 64 defined by members 62.
Friction existing between each member 62 and non-bonding portion 52 prevents
slab 20' from restoring to its original planar shape.
Once slab 20' is wholly engaged with rack 64, sheets 40a and 40b may
then be bonded at bonding surfaces 50 which is best shown in Figs. 6 and 7.
Briefly described, sheet 40b is bonded to lower bonding surface 50 while slab
20'
is still present in rack 64. The rack is then removed and sheet 40a is
subsequently bonded to slab 20'. The resulting product, shown in Fig. 7, can
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CA 02565127 2006-11-08
then have a valve (not shown) placed at a convenient location on the perimeter
of
the sheets whereafter the perimeter can then be sealed to create a self-
inflating
air mattress.
A modified corrugated embodiment is shown in Fig. 8 wherein foam slab
20' is bent to form a plurality of tubular voids 34 having a triangular cross
section
that extend through the slab. In this embodiment, the surface area of bonding
surfaces 50 is increased to the extent that what were channels in the
embodiment shown in Fig. 4 now become cylinders, thereby further decreasing
thermal convection and approximating the thermal insulating values of a cored
slab, yet without generating any waste by-product.
Because they are not perpendicular to sheets 40a and 40b, tensile portions
54 do not transmit loads efficiently between sheets 40a and 40b. While this
configuration is not desirous, the advantage of this structure over many
others
described herein is that foam slab 20' is bonded or attached to sheets 40a and
40b over the entire structure surface. This bonding over the entire structure
surface minimizes peal/shearing forces occurring at the interface of bonding
surfaces 50 and sheets 40a and 40b.
Two Slab Channel Embodiment Derived From Single Slab
Figure 9 shows another embodiment of the invention in which a uniformly
thick resilient material slab 20 has a plurality of uniform rectangular cross
section
channels 36 formed therein. Because channels 36 have dimensions
complimentary to extending portions 56, it is possible to generate two such
slabs
from a single slab without generating waste material. One machine that is
often
used for this purpose is a contour cutter. A contour cutter is typically a
computer
controlled band saw that is used to cut material in a variety of patterns. As
illustrated in Fig. 10, two identical complementary slabs 20a and 20b are
produced with one pass of the contour cutter blade. Channels 36 ~n slab 20a
compliment extending portions 56 of slab 20b thereby reducing material loss
and
saving on fabrication cost.
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CA 02565127 2006-11-08
Returning to Fig. 9, the depth of the channel 36 in relation to the total
thickness of slab 20 determines the weight reduction. Satisfactory results hwe
been obtained when the deFth of channel 36 was equal to seven tenths of the
overall thickness of slab 20. There are, however, strength limitations of such
structures. When generally wider channels 36 are used, the maximum width of
any channel 36 is determined by the peal strength of the bond between sheets
40a and 40b, and bonding surfaces 50. For narrower channels, the minimum
width Limitation is determined by the sizes of anomalies or voids that may
naturally exist in the foam material. As the width of extending portions 56
approaches the size of possible anomalies, the resulting weakness of extending
portion 56 limits the lower end of useful channel thicknesses.
Figure 1 1 shoves a variation of the embodiment shown in Fig. 9. In this
embodiment, slab 20 has a plurality of uniform channels 38 having a "T" cross
section formed therein. Channels 38 are evenly spaced apart such that
extending
portions 56 have identical dimensions to complementary channels 38. As with
the structure shown in Fig. 9, the material and process savings occur in the
cutting of two stabs from a single larger slab and separating the cut slabs
from
each other.
The advantages of the T-shaped configuration in comparison to the simpler
approach in Figs. 9 and 10 is that the T-shape ;gas a greater bonding surface
50
to contact sheet 40a. This larger area of contact may serve to more firmly
bond
sheet 40a to slab 20, thereby reducing the potential for mattress failure due
to
pealing. Additionally, the greater bonding surface area decreases the area of
channel exposure to the sheet, thereby increasing the insulative value
associated
with a mattress constructed in this fashion.
Use of "T" shape channels and extending portions also provides increased
compression qualities. Many resilient materials when used in supporting
cushions, pads, or mattresses, exhibit useful insulation properties in their
uncompressed state. When used as a mattress, the insulation properties of the
part of the structure undergoing compression where the user is resting is of
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CA 02565127 2006-11-08
interest. Often, the greater the compression of a mattress, the greater the
loss of
insulation properties. When a full width, unaltered slab of resilient material
is
used as a core for a mattress, the compression deforms the resilient material
uniformly throughout the thickness of the mattress. Comparing such a mattress
with one in which the resilient material is configured as slab 20 in Fig. 1 1,
an
interesting and useful benefit occurs. In Fig. 1 1, extending portions 56
include
stem 58. As compressive loading of the cross section of slab 20 commences,
the compression occurs first in stem 58 until it is nearly fully compressed. -
I he
remainder of the cross section remains unaffected. Further loading of the
cross
section results in compression of the material surrounding bonding surfaces 50
until it is fully compressed. This suggests that this structure, when used as
a
mattress, should have better thermal insulation properties than the
conventional
channel embodiment shown in Fig. 9. Testing has shown as much as a twenty
percent improvement in insulation value of mattresses with T-shaped channels
over mattresses with conventional, exposed channels.
Segmented "U" Component Embodiment
Yet another embodiment of the invention is shown in Fig. 12. This
embodiment utilizes a slab created in much the same way as shown in Fig. 10
and segments each channel 36 at extending portions 56 to produce a plurality
of
identical U-shaped segments 42, as is shown in Figs. 12 and 14.
The segments 42 are then aligned so that extending portions 56 are
congruent and in contact with web portion 59 of each adjacent segment 42. In
this manner, each extending portion 56 defines bonding surfaces 50, and each
web portion 59 becomes a tensile portior: 54. U-shaped segments 42 may be
bonded together, or may simply be removable contact with one another. As is
shown best in Fig. 12, sheets 40a and 40b are bonded to bonding surfaces 50 of
extending portions 56 and hold the assembly of U-shaped segments 42 together.
In an inflatable or self-inflatable mattress using this slab configuration,
one
advantage in comparison to the others mentioned is that the assembly of U-
CA 02565127 2006-11-08
shaped segments 42 provides for complete foam to sheet bonding, with no
exposed voids to facilitate peal failure. Another advantage of this embodiment
is
that web portions 59 are perpendicular to sheets 40a and 40b and thus, acting
as
tensile portions 54, will efficiently transmit forces from one side of the
structure
to the other.
"Z" Siped Embodiment
Figures 15, 16, 17, and 18 show yet another embodiment of the invention
in which a plurality of slits 30 are made into .resilient slab 20. The
configuration
of the slits can be described in several different ways. Referring to Fig. 15,
a
first and second slit 30a and 30b convergently depend from an arbitrary
location
44 on major surface 22 of-slab 20. The slits extend from one perimeter surface
to the opposing perimeter surface but do not in fact converge within the body
of
slab 20. A second pair of slits 30c and 30d, divergently depend from major
surface 24 and are spaced from and parallel to slits 30a and 30b. ,All slits
are
linearly symmetrical about location 44. It has been found through
experimentation that for a 1 " (2.54cm) thick slab, slits 30a-d depend about
0.688 inches (1.7475cm) into slab 20 and slit pairs 30a and 30b, and 30c and
30d terminate their convergence at a minimum distance of about 0.500 inches
(1.27cm) from one another. The parallel spacing between opposite slit pairs,
i.e.,
30a and 30c, and 30b and. 30d is about 0.500 inches (1.27cm).
When selective forces are applied to slab 20 as best shown by the arrows
in Fig. 16, slab 20 extends to assume the illustrated configuration. If slab
20 is
then bonded to sheets 40a and 40b as shown in Fig. 17, only the vertical
dimensions change significantly. However, if additional selective force is
applied,
the resulting configuration will resemble that shown in Fig. 18. In the
expansion
process, the original dimensions of slab 20 are changed. Not only does the
thickness of slab 20 increase dramaticGlly in the direction of extension, the
dimensions in the axis perpendicular to extension noticeably lessens.
Self-Sustaining Gap Embodiment
16
CA 02565127 2006-11-08
Turning now to Fig. 19, the self-sustaining embodiment is shown in its
unexpended state. The invention is preferably derived from a single slab of
open
cell urethane foam 130 or other suitable lightweight and resilient material.
To
facilitate the creation of self-sustaining apertures or gaps, a plurality of
'slits 140
are formed in slab 130. As will be discussed later, the particular registry of
slits
140 is not as important as the fact that each slit forms two surfaces
generally
normal to the major surfaces of slab 130. To aid in the discussion of the
invention, the term longitudinal shall mean the direction which is
substantially
parallel to the predominant direction of the slits 140; the term lateral shall
mean
the direction which is substantially perpendicular to the predominant
direction of
the slits 140. Thus, in Fig. 19, longitudinal corresponds to the minor axis of
the
page while lateral corresponds to the major axis of the page. -
A detailed; fragmentary perspective view of several slits 140 is shown in
Fig. 19A. Slit 140 is defined by first inner surface 170, .which in part
includes
protruding portion 160, and by second inner surface 172, which in part
includes
complementary receiving or recess portion 168. 1n order for the invention to
function properly, it is important that an interlocking or interfering fit be
created
between protruding portion 160 and complementary receiving portion 168. This
interlocking fit is preferably physical (disengagement or engagement is
accomplished by physical deformation of the foam); however, it may rely solely
on friction. Protruding portion 160 has in ,its general form .head portion
164, and
stem or return portion 166 connecting head portion 164 and . base portion 162.
To achieve the previously mentioned physical interlocking fit, it is desirous
to
make head portion 164 dimensionally larger than stem or return portion 166.
Upon the application of generally opposing lateral force to slab 130,
protruding portions 160 disengage from receiving portions 168 because of the
resilient nature of slab 130, as shown in Fig. 20, While lateral forces are
the
most efficient, any force applied to slab 130 which results in the
dislodgement of
protruding portion 160 from complementary receiving portion 168 is suitable.
After the lateral force has been removed, head portion 164 of each protruding
portion 160 is brought to bear against base portion 162 of corrrplementary
17
CA 02565127 2006-11-08
receiving portion 168 as is also shown in greater detail in Fig. 20A. Because
the
resilient restoring force of the foam material used to create slab 130 is less
than
the force required to refit protruding portion 160 into complementary
receiving
portion 168, aperture or gap 174 is self-sustaining. Using the type and
dimensions of slits 140 shown in Fig. 19, an approximately 30°ib
increase in area
and 30% decrease in density is achieved. In addition, the IFD is similarly
reduced
by approximately 30°r6.
It is, of course, possible to vary the degree of slab expansion, by increasing
or decreasing the lateral length of each stem or return portion 166, the
characteristics of head portion 164, or the longitudinal length of slit 140.
In
addition, variation of the location and spacing of slits 140 also will affect
the
degree and nature of apertures or gaps formed after application of lateral
displacing forces. These aspects of the invention will be discussed in greater
detail below.
The elevation view of slab 130, which is shown in Fig. 21, illustrates that
the apertures or gaps 174 transverse the section of slab 130 to create
passages
extending from one major surface to the other. However, because these
passages represent only approximately 30°r6 of the total surface area,
the load
bearing capacity of slab 1 ~0 remains high. Nevertheless, if sufficient
loading is
presented to a major surface (assuming that the opposite major surface is
supported in a planar manner), the column strength associated with the slab
webs is exceeded and the passages will collapse as shown in Fig. 21 A. This
feature of the invention is of considerable importance when the expanded slab
is
used in applications wherein heat transmission or convection is a design
factor.
In o,~der to manufacture the reduced density resilient product, one need
only choose an appropriate slit design and pattern (slit design and pattern
choice
will be discussed in detail below). After making these choices, an appropriate
means for forming the slits in the slab must be chosen. A preferred method for
creating slits in a slab of resilient material is to subject an unslitted slab
of
resilient material to compressive cutting elements. Either a stamping die such
as
18
CA 02565127 2006-11-08
shown in Fig. 22 or a rotary die cutting drum can be used. The stamping die of
Fig. 22 has a plurality of cutting elements 134 arranged in the same pattern
as
desired to appear on a processed slab. For cuts in 1.5 inch ~3.~81 cm) thick
foam
having a low initial IFD, each cutting element 134 has a height of
approximately
0.125 to 0.5 inches (0.3175 to 1.27cm). Other means for creating the slit
pattern in a slab include melting, water cutting, laser cutting, and knife
cutting.
The orientation of a slit slab 130 depends largely on the application
chosen. For example, it is possible to orient slab 130 on its edge so as to
receive
compressive loads edge-wise or in the longitudinal direction. Due to the
direction
of the slit cut, longitudinal compressive loads will cause significant
longitudinal
collapse of slab 130 by permitting lateral bulging. In this configuration, a
significant reduction in IFD can be achieved without resorting to material
removal
processes. As best shown in Fig. 23, resilient foam material 130' having the
aforementioned properties can be created using on'e or more of the previously
described slitting or cutting processes.
An alternative use for the present invention is shown in Fig. 24, wherein
the slab of Fig. 19 is circumvoluted and the proximate perimeter ends are
secured
so as to form a cylindrical body having an open core. This embodiment of the
invention can be used as insulation for pipes and the like either alone or in
combination with an inner and/or outer covering. The embodiment can also be
used as lightweight packing or sound insulation material.
As discussed previously, a critical concept of the invention is the
interlocking fit between the protruding portion and the complementary
receiving
portion of the slab after formation of the slit in order to create the self-
sustaining
gaps or apertures that result upon the application and cessation of generally
oaposing lateral forces. To illustrate the diversity of possib?e shapes of
such
protruding portions, attention is drawn to Figs. 25A - ~5G.
In Fig. 25A, an inverted triangular frustum protruding portion 142 is
shown. Head portion 164 is linear, and stem or return portion 166 linearly
tapers
19
CA 02565127 2006-11-08
to base portion 162. Goblet shaped protruding portion 144 in Fig. 25B also has
a
linear head portion 164, but utilizes a curved stem or return portion 166. Tee
shaped protruding portion 146, whicl-. is shown in Fig. 25C, emphasizes an
extreme interlock configuration. Scallop shaped protruding portion 148 in Fig.
25D illustrates that head portion 164 may assume a convex or dome shape.
Similarly, head portion 164 of capstan shaped protruding portion 150 of Fig.
25E
shows that a convex or dome shaped head portion 164 may be used with a
curved stem or return portion 166. Base portion 162' need not be linear as
shown in Fig. 25F. Finally, Fig. 25G illustrates that head portion 152 may be'
concave and used in conjunction with base portion 162'.
Each of the foregoing embodiments of the protruding portion achieve the
desired interlocking fit with its complementary receiving portion. Each
embodiment achieves the desired aperture or gap formation by the same means,
although the quality and characteristics of the formed gap or aperture will ~e
different due to inherencies in the design. For example, tee shaped protruding
portion 146 of Fig. 25C is much less likely to collapse back into its
complementary receiving portion. However, the size of the resulting gap or
aperture created by dislodgement of head portion 164 from receiving portion
168
is more likely to be collapsed by the exertion of external forces due to the
nature
and structural qualities of the foam forming the gap. Hence, while e:.c~ g-p
formed will be self-sustaining, the structural properties of the surrounding
material defining each gap will depend largely upon the type of interlock
formed.
An additional embodiment worth noting is shown in an expanded state in
Figs. 26A and 26B wherein head portion 164 is attached to receiving portion
168
via tether portion 176. As illustrated in Fig. 26A, tether portion 176 can be
characterized as an essentially linear portion of foam or a buckled portion of
foam
as shown in Fig. 26B. In either embodiment, tether portion 176 connecting head
portion 164 to receiving portion 168 prevents foam slab 130 from over-
expanding when forces are applied thereto in order to dislodge the head
F~~rtions
from the receiving portions. Moreover, the additional lateral tensile forces
imparted by tether portion 176 further urge head portion into interfering
contact
CA 02565127 2006-11-08
with second surface 172 to thereby assure a uniformly expanded slab 130,
especially when large dimension slits are utilized or the slab undergoes
further
modifications which are dimensionally sensitive such as during manufacture of
self-inflating air mattresses.
Another factor that influences the overall performance of foam slab 130 is
the arrangement o'slits 140. As is shown in Fig. 19, the columnar stagger of
slits 140 can be a two row offset. Depending upon design considerations, a
three row offset can be used, or an irregular offset pattern can be chosen.
The
two row offset in Fig. 19 advantageously permits lateral displacement of
protruding portions 160 from their complementary receiving portions 168
because
the foam is not linearly continuous in the direction of lateral displacement,
as
would be the case if there was no offset at all.
It is not necessary to have slits 140 depend'entirely through slab 130.
Figure 27A illustrates an embodiment wherein apertures or gaps 174' depend
into, but not through, slab 130; Fig. 27B illustrates a similar embodiment
v~herein
apertures or gaps 174' are formed in only one side of slab 130. Such
embodiments may be useful in situations where thermal transmission is a
significant concern or the slab must be bent easily and stay in the bent
position.
Alternatively, expanded slab 130 having apertures or gaps 174 can be bonded to
solid slab 130' as is shown best in Fig. 27C to achieve a structure similar to
that
shown in Fig. 27B. Finally, two slit slabs can be stacked in an offset manner
to
produce a product similar to that shown in Fig. 27C in that apertures or gaps
174
do not generally depend entirely through the combined slab, but wherein both
slabs are expanded. This embodiment is best shown in the plan view of Fig.
27D.
Lastly, the invention is exceptionally suited for applications that require
compressional resiliency and adequate tensile strength, as well as light
weight.
Fig. 28 shows the invention being incorporated into a self-inflating, sealable
mattress 180 commonly sold as the Therm-a-Rest' camping mattress (TAR). A .
21
CA 02565127 2006-11-08
detailed explanation of the technology behind the TAR can be found in United
States Patent number 4,624,877.
Substitution of slabs 130 for a solid, non-slit foam slab beneficially reduces
compressional stiffness, weight, and density, while enhancing its
compactibility
and only slightly decreasing its tensile strength. For example, by
substituting slit
slabs, a 13 inch (33.02cm) wide slab can be expanded to 20 inches (50.8cm) for
use in 20 inch (50.8cm) wide mattress applications. Consequently, the amount
of foam material necessary to produce the mattress is decreased which
advantageously results in a lighter mattress. It should be noted that the
slab's
tensile strength is reduced by about 30% in the embodiment shown in Fig. 20
when used in the embodiment of Fig. 28. This reduction in tensile strength,
however, does not prevent slab 130 from being used in a TAR mattress since the
reduction is within the TAR tolerance limits.
The slit orientation relative to mattress 180 in Fig. 28 is in the
longitudinal
direction, as opposed to the lateral direction, to provide self-inflation
performance
comparable to non-slit pad mattresses. Initial tests have shown that when the
slits are laterally oriented, the self-inflation times are increased by
approximately
350%. Initial tests also indicate that the overall insulative value for
mattress 180
is within the range for a conventional TAR mattress. Moreover, the inherent
collapse of the apertures or gaps in mattress 180 when subject to sufficient
compressional forces as described during the discussion of Fig. 21 A will
permit
mattress 180 to maintain a satisfactory insulative rating when in use. And,
because foam material extends from one major surface to the other (except of
course in the areas occupied by the apertures or gapsl, these areas of foam
material retain adequate tensile element aspects required in the TAR
technology.
22
