CA2565127C - Expanded foam products and method for making the same - Google Patents

Abstract

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. The method involves selectively forming a plurality of adjacent and generally parallel slits in the resilient material, expanding the slit material to form an expanded material, and fixedly attaching the expanded material to at least one substantially planar material.

Description

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

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.

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

3 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

4 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

5 characteristics of the processed resilient material and its performance in the finished product.

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.

6 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;

7 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;

8 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

9 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 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 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 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.

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 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 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-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 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 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 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 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.

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 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 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 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 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 .

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.

Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. 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.

2. The method of claim 1 wherein the slits extend from the first major surface toward the second major surface and the substantially planar material attached to the first major surface.

3. The method of claim 2 wherein the slits extend from the first major surface to the second major surface.

4. The method of claim 2 wherein the at least one substantially planar material is a first planar material and further comprising fixedly attaching a second substantially planar material to the second major surface, attaching the first and second planar materials together to form an envelope wholly surrounding the expanded material, and positioning a valve intermediate the environment and a void defined by the envelope to permit ingress and egress of air therein and therefrom.