Expanded foam products and methods for producing the same

An expanded resilient product and methods for making the same are disclosed. The product is characterized as a geometric solid of resilient material that has a plurality of slits formed therein. Each slit is defined by a first surface having a protruding portion and second surface having a recess portion corresponding to the protruding portion of the first surface which together form an interlocking fit between the two. Forces are applied to the product sufficient to dislodge a protruding portion of the first surface from the complementary recess portion of the second surface, thereby forming a plurality of gaps. The product is then permitted to relax, whereupon the protruding portions compressively contact the complementary recess portions of the second surface. But because of the interlocking fit, the protruding portions are prevented from re-engaging the recess portions and thereby maintain the expanded nature of the product. A method for manufacturing the product involves the creation of the slits and subsequent physical expansion of the resilient product to produce the self-sustaining gaps or apertures.

FIELD OF THE INVENTION 
The present invention pertains to an expanded foam product and methods for 
making the same, and more particularly, to a foam product derived from a 
solid piece of foam having a plurality of slits formed therein and which 
is capable of sustaining 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 IFD value of a foam 
is derived by measuring the force required to reduce the thickness of a 
15".times.15".times.4 polyurethane foam sample by 25% when depressing an 8 
inch diameter disk having a surface area of approximately 50 in.sup.2 
thereinto. Thus, an IFD value of 40 means that 40 pounds of force on a 50 
square inch disc is required to decrease an established foam sample's 
thickness by 25%. See ASTM D3574-91. 
Current technologies and manufacturing restrictions prevent the reliable 
production of blown foam products having an IFD value of less than about 
12 pounds. 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 
oftentimes 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. 
SUMMARY OF THE INVENTION 
The present invention is broadly characterized as a reduced density 
resilient product resulting from the selective slitting of a geometric 
solid of resilient material wherein each slit is defined by a first 
surface having at least one protruding portion forming an interlocking or 
mating fit with an opposite and complementary recess formed by a second 
surface. The reduction in density occurs when the slit is expanded by, for 
example, the application of forces sufficient to overcome the interlocking 
fit between the two surfaces and to dislodge the protruding portion from 
the complementary recess. The aperture or gap formed as a consequence of 
this dislodgement is advantageously self-sustaining due to the resistance 
of the protruding portion of the first surface from re-engaging with the 
complementary recess of the second surface. 
A method for manufacturing the described 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 surface of 
the resilient material and interlocks with an opposite and complementary 
recess defined by a second 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 
uniformally 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 characteristics of the processed 
resilient material and its performance in the finished product. 
In preferred form, a slab of open cell foam is used and the slits are 
staggered so that a first row of slits is offset from a second and 
subsequent even rows of slits, but aligned with a third and subsequent odd 
rows. This alternating pattern permits sufficient extension of the foam to 
allow the protruding portion to dislodge from the complementary recess 
portion without causing undesirable distortion of the material. 
A feature of the invention 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 covering 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. 
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 does not 
significantly decrease 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.

DESCRIPTION OF THE INVENTION 
Turning now to the several drawings wherein like numerals indicate like 
parts and more specifically to FIG. 1, the invention is shown in its 
unexpanded state. The invention is preferably derived from a single slab 
of open cell urethane foam 30 or other suitable lightweight and resilient 
material. To facilitate the creation of self-sustaining apertures or gaps, 
a plurality of slits 40 are formed in slab 30. As will be discussed later, 
the particular registry of slits 40 is not as important as the fact that 
each slit forms two surfaces generally normal to the major surfaces of 
slab 30. 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 40; the term lateral shall mean the 
direction which is substantially perpendicular to the predominant 
direction of the slits 40. Thus, in FIG. 1, 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 40 is shown in 
FIG. 1A. Slit 40 is defined by first surface 70, which in part includes 
protruding portion 60, and by second surface 72, which in part includes 
complementary receiving portion 68. In order for the invention to function 
properly, it is important that an interlocking or interfering fit be 
created between protruding portion 60 and complementary receiving portion 
68. 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 60 has in its general 
form head portion 64, and stem or return portion 66 connecting head 
portion 64 and base portion 62. To achieve the previously mentioned 
physical interlocking fit, it is desirous to make head portion 64 
dimensionally larger than stem or return portion 66. 
Upon the application of generally opposing lateral force to slab 30, 
protruding portions 60 disengage from receiving portions 68 because of the 
resilient nature of slab 30, as shown in FIG. 2. While lateral forces are 
the most efficient, any force applied to slab 30 which results in the 
dislodgement of protruding portion 60 from complementary receiving portion 
68 is suitable. After the lateral force has been removed, head portion 64 
of each protruding portion 60 is brought to bear against base portion 62 
of complementary receiving portion 68 as is also shown in greater detail 
in FIG. 2A. Because the resilient restoring force of the foam material 
used to create slab 30 is less than the force required to refit protruding 
portion 60 into complementary receiving portion 68, aperture or gap 74 is 
self-sustaining. Using the type and dimensions of slits 40 shown in FIG. 
1, an approximately 30% increase in area and 30% decrease in density is 
achieved. In addition, the IFD is similarly reduced by approximately 30%. 
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 
66, the characteristics of head portion 64, or the longitudinal length of 
slit 40. In addition, variation of the location and spacing of slits 40 
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 30, which is shown in FIG. 3, illustrates that 
the apertures or gaps 74 transverse the section of slab 30 to create 
passages extending from one major surface to the other. However, because 
these passages represent only approximately 30% of the total surface area, 
the load bearing capacity of slab 30 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. 3A. 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 order 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. 
4 or a rotary die cutting drum can be used. The stamping die of FIG. 4 has 
a plurality of cutting elements 34 arranged in the same pattern as desired 
to appear on a processed slab. For cuts in 1.5 inch thick foam having a 
low initial IFD, each cutting element 34 has a height of approximately 
0.125 to 0.5 inches. 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 30 depends largely on the application 
chosen. For example, it is possible to orient slab 30 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 30 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. 5, resilient foam material 30' having the aforementioned properties 
can be created using one or more of the previously described slitting or 
cutting processes. 
An alternative use for the present invention is shown in FIG. 6, wherein 
the slab of FIG. 1 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 opposing lateral forces. To 
illustrate the diversity of possible shapes of such protruding portions, 
attention is drawn to FIGS. 7A-7G. 
In FIG. 7A, an inverted triangular frustum protruding portion 42 is shown. 
Head portion 64 is linear, and stem or return portion 66 linearly tapers 
to base portion 62. Goblet shaped protruding portion 44 in FIG. 7B also 
has a linear head portion 64, but utilizes a curved stem or return portion 
66. Tee shaped protruding portion 46, which is shown in FIG. 7C, 
emphasizes an extreme interlock configuration. Scallop shaped protruding 
portion 48 in FIG. 7D illustrates that head portion 64 may assume a convex 
or dome shape. Similarly, head portion 64 of capstan shaped protruding 
portion 50 of FIG. 7E shows that a convex or dome shaped head portion 64 
may be used with a curved stem or return portion 66. Base portion 62' need 
not be linear as shown in FIG. 7F. Finally, FIG. 7G illustrates that head 
portion 52 may be concave and used in conjunction with base portion 62'. 
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 be different due to inherencies in the design. For example, 
tee shaped protruding portion 46 of FIG. 7C 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 
64 from receiving portion 68 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 each gap 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. 8A and 8B wherein head portion 64 is attached to receiving portion 
68 via tether portion 76. As illustrated in FIG. 8A, tether portion 76 can 
be characterized as an essentially linear portion of foam or a buckled 
portion of foam as shown in FIG. 8B. In either embodiment, tether portion 
76 connecting head portion 64 to receiving portion 68 prevents foam slab 
30 from over-expanding when forces are applied thereto in order to 
dislodge the head portions from the receiving portions. Moreover, the 
additional lateral tensile forces imparted by tether portion 76 further 
urge head portion into interfering contact with second surface 72 to 
thereby assure a uniformly expanded slab 30, 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 30 is 
the arrangement of slits 40. As is shown in FIG. 1, the columnar stagger 
of slits 40 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. 1 advantageously permits lateral 
displacement of protruding portions 60 from their complementary receiving 
portions 68 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 40 depend entirely through slab 30. FIG. 
9A illustrates an embodiment wherein apertures or gaps 74' depend into, 
but not through, slab 30; FIG. 9B illustrates a similar embodiment wherein 
apertures or gaps 74' are formed in only one side of slab 30. 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 30 having apertures or gaps 74 can 
be bonded to solid slab 30' as is shown best in FIG. 9C to achieve a 
structure similar to that shown in FIG. 9B. Finally, two slit slabs can be 
stacked in an offset manner to produce a product similar to that shown in 
FIG. 9C in that apertures or gaps 74 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. 9D. 
Lastly, the invention is exceptionally suited for applications that require 
compressional resiliency and adequate tensile strength, as well as light 
weight. FIG. 10 shows the invention being incorporated into a 
self-inflating, sealable mattress 80 commonly sold as the 
Therm-a-Rest.RTM. camping mattress (TAR). A detailed explanation of the 
technology behind the TAR can be found in U.S. Pat. No. 4,624,877, which 
is incorporated herein by reference. 
Substitution of slabs 30 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 wide slab can be expanded 
to 20 inches for use in 20 inch 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. 2 when used in the embodiment of FIG. 10. This reduction in 
tensile strength, however, does not prevent slab 30 from being used in a 
TAR mattress since the reduction is within the TAR tolerance limits. 
The slit orientation relative to mattress 80 in FIG. 10 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 80 is within 
the range for a conventional TAR mattress. Moreover, the inherent collapse 
of the apertures or gaps in mattress 80 when subject to sufficient 
compressional forces as described during the discussion of FIG. 3A will 
permit mattress 80 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 gaps), 
these areas of foam material retain adequate tensile element aspects 
required in the TAR technology.