Note: Descriptions are shown in the official language in which they were submitted.
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LOOSE-LAY FLOORING
The present invention relates to loose-lay
flooring and more ~articularly to loose-lay flooring
which will be suitable for use over stable or unstable
surfaces.
Background of the Invention
Decorative floor coverings comprising
resilient material have been in use for many years.
Usually these floor coverinas have been fastened to
subfloors with adhesives; however, the installation of
such coverings is time consuming and expensive.
Therefore, it is desirable to place the floor coverings
on subfloors without the use of adhesives; i.e., to
loosely lay the covering on the subfloor. In such
circumstances, the weight of the loose-lay floor
covering itself tends to-hold it in place, although it
may also be pinned to the subfloor by furniture,
appliances, and other objects which rest upon it.
Loose lay floor coverings should have the
following characteristics; namely, they should not curl
or dome; they should not shrink or grow with time or
under the influence of environmental change; they should
stay in place under the influence of a rolling load; and
they should withstand or accommodate the movement of
subfloors without buckling. The latter problem creates
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special difficulties because subfloors range from those
which are dimensionally stable (e.g. concrete) to those
which are dimensionally unstable (e.g. particleboard).
Other problems are also encountered depending on the
type of subfloor over which the loose-lay floor is
placed. Thus, the flooring industry has dedicated a
considerable amount of time and effort to develop a
loose-lay flooring which will have the aforement:ioned
characteristics.
Prior Art
Various references are found in the prior art
pertaining to loose lay flooring. U.S. Patent No.
3,821,059 ~iscloses segmentally accommodating loose-lay
flooring comprising a plurality of rigid elements that
lS distribute stresses within the flooring matrix such that
they appear as a series of small distortions. U.S.
Patent No. 3,364,05~ discloses a composite floor
comprising a base support, a release coat, a
waterproofing coat, a wear coat, and a to~ layer, said
composite floor being designed to avoid damage caused by
the movement of the subflooring. U.S. Patent No.
4,066,813 discloses a method for reducing growth
properties of resilient flooring having a fibrous
cellulosic backing by incorporating a small amount of a
growth inhibitor. In addition, a variety of patents
address the problem of stress relief by inclusion of a
series of deformable geometric configurations into
structural matrices. Examples of such are U.S. Patent
Nos. 4,146,666: 4,049,855; 4,035,536 and 4,020,205.
Nevertheless, none of the prior art references
adequately teach how to construct a flooring material
which may be loosely laid over the surface of a stable
or unstable subfloor.
Accordingly, one objective of the present
invention is to provide processes for designing and
constructing a loose-lay floor structure which will
accommodate the movement of an unstable subfloor without
buckling.
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~z~3~66 ~ LFM-7168
Another objective of th2 ~.es~nt invention is
to provide processes for desi~nin~ and constructing a
loose-lay floor structure which will accommodate the
movement of any type of subfloor without buckling,
doming and curling, and which will not move under a
rolling load.
Yet another objective of the present invention
is to provide a process by which a flooring material
having predictable subfloor accommodation
characteristics may be designed.
Still another objective of the present
invention is to provide ~loor structures which will have
the aforementioned attributes.
Still yet another objective of the present
invention is to provide methods by which products
comprising one or more reinforcing layer may be modified
in situ to provide suitable buckling characteristics.
These and other advantages of the present
invention will become apparent from the detailed
description of the preferred embodiments which follow.
Brief Description of the Drawings
FIGS. lA and lB illustrate a diagram of a
computer program which may be used to calculate the
contour curves of the present invention.
FIG. 2 illustrates the contour curve of
Example 1.
FIG. 3 illustrates the contour curve of
Example 2.
E~IG. 4 illustrates a structure as set forth in
30 Example 2.
FIG. S illustrates a structure as set forth in
Example 2.
FIG. 6 illustrates a structure as set forth in
Example 3.
FIG. 7 illustrates a structure as set forth in
Example 3.
FIG. 8 illustrates a structure as set forth in
Example 4.
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FIG. 9 illustrates the contour curve of
Exam~le 4.
FIG. 10 illustrates the contour curve of
Example 7
FIG. ll illustrates the contour curve of
r`xample 8.
FIG. 12 illustrates one example of a
continuous modification pattern.
FIG. 13 illustrates one example of a modified
contin~ous pattern.
FIG. 14 illustrates one example of a
discontinuous pattern.
FIG. 15 illustrates the contour curve
applicable to Examnles 9-13.
Summar~ of the Invention
The present invention concerns loose-lay floor
structures comprising at least two layers of reinforcing
material and processes to design and produce them.
Loose-lay floors may be designed which will be suitable
for use over stable subfloors, or which will accommodate
the movement of very unstable subfloors. Flooring
constructed according to this invention will have the
ability to resist buckling, curling and doming, and will
resist moving under a rolling load. A process is also
provided for modifying structures comprising a single
reinforcing layer in situ so as to convert structures
with unacceptable buckling characteristics into
structures with acceptable buckling characteristics.
Detailed Description of Preferred Embodiments
_
In one embodiment, the present invention
relates to a process for designing a resilient loose-lay
floor structure for use over subflooring having an
ascertainable subfloor dimensional change. Said process
comprises the steps of selecting a target critical
buckle strain for said floor structure, said critical
buckle strain being greater than the subfloor
dimensional change; selecting an approximate basis
weight for said floor structure, said basis weight being
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within the range of fro~ about 2 to about 10 pounds per
square yard; plotting a contour curve of the selected
critical buckle strain for said selected basis weight by
varying the bending stiffness values from about 0 to
about 9 inch-pounds and by varying the relaxed
compressive stiffness values from about O to about
lO,000 pounds per inch of width; determining from said
contour curve the range defined by the minimum and
maximum relaxed compressive stiffness values
corresponding to bending stiffness values of about 0.1
and about 9 inch-pounds, respectively; selecting a
matrix material and at l.east two layers of reinforcing
material such that the sum of the relaxed compressive
stiffness values for said materials falls within the
determined range, said ma~rix material and said
reinforcing materials being selected such that the sum
of the relaxed compressive stiffness values for said
reinforcing materials is not less than the sum of the
relaxed compressive stiffness values for said matrix
material; and determining from said contour curve the
bending stiffness value applicable to the sum of the
relaxed compressive stiffness values for said
reinforcing materials and said matrix material, whereby,
when sald layers of reinforcing material are disposed
within said matrix material such that the measured
bending stiffness of the resultant floor structure
corresponds to the determined bending stiffness, at
least one reinforcing layer being approximately above
the neutral bending plane of said resultant floor
structure and at least one reinforcing layer being
approxi~ately below said neutral bending plane, the
critical buckle strain for said resultant floor
structure will be approximately equivalent to the target
critical buckle strain and will be greater than the
strain expected to be caused by the subfloor dimensional
change.
In a second e~odiment, the present invention
relates to a process for making a resilient loose-lay
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floor structure for use over a s~bfloor having an
ascertainable subfloor dimensional change. Said process
comprises the steps of selecting a matrix material and
at least one reinforcing material, and disposing at
least two layers of reinforcing material within said
matrix material such that the bending stiffness of said
loose-lay floor structure is from about 0.1 to about 9
inch-pounds, at least one layer of reinforcing material
being approximately above the neutral bending plane of
said loose-lay floor structure and at least one layer of
reinforcing material being approximately below said
neutral bending plane, s~id matrix material and said
reinforcing materials being selected such that the sum
of the relaxed compressive stiffness values for said
reinforcing materials is not less than the relaxed
compressive stiffness value for said matrix material and
the basis weight of said floor structure is from about 2
to about 10 pounds per square yard, whereby the critical
buckle strain of said loose-lay floor structure is
greater than the strain expected to be caused by the
subfloor dimensional change.
In a third embodiment, the present invention
relates to a resilient loose-lay floor structure for use
over a subfloor having an ascertainable subfloor
dimensional change. Said floor structure has a basis
weight of from about 2 to about 10 pounds per square
yard and comprises a matrix material and at least two
layers of reinforcing material disposed within said
matrix material, at least one of said layers being
approximately above the neutral bending plane of said
loose-lay floor structure and at least one of said
layers being approximately below said neutral bending
plane. The sum of the relaxed compressive stiffness
values for said reinforcing materials is not less than
the sum of the relaxed compressive stiffness values for
said matrix materials. Said floor structure has a
bending stiffness of from about 0.1 to about 9
inch-pounds and a critical buckle strain greater than
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the strain expected to be caused by the subfloor
dimensional change.
In a fourth embodiment, the present invention
comprises a process for treating a potential resilient
loose-lay floor structure having a basis weight of from
about 2 to about 10 pounds per square yard and having at
least two layers of reinforcing material disposed within
a matrix material, at least one layer of reinforcing
material being approximately above the neutral bending
plane of said floor structure and at least one layer of
reinforcing material being approximately below said
neutral bending plane, said structure being unsuitable
for use as a loose-lay floor structure over a subfloor
having an ascertained subfloor dimensional change
because it has a bending stiffness which is in excess of
about 9 inch-pounds, ar a critical buckle strain which
is not greater than the asertained subfloor dimensional
change, or both, said process comprising the
modi~ication of at least one of said reinforcing layers
by external means such that the bending stiffness of the
resultant flooring structure is within the range of from
about 0.1 to about 9 inch-pounds and the critical buckle
strain of said resultant flooring structure is greater
than said ascertained subfloor dimensional change.
In a fifth embodiment, the present invention
comprises a process for preparing a flooring structure
comprising a single reinforcing layer, said structure
being suitable to accommodate the subfloor movement of a
subfloor having an ascertainable subfloor dimensional
change, said process comprising the steps of selecting a
flooring structure comprising a single encapsulated
glass reinforcing layer, the critical buckle strain of
said structure being less than the subfloor dimensional
change, and modifying said flooring structure in situ
such that the critical buckle strain becomes ~reater
than said s~bfloor dimensional change.
In a sixth embodiment, the present invention
comprises a flooring structure comprisinq a single
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reinforcing layer, said structure having been modified
ln situ such that its critical buckle ~train is greater
than the subfloor dimensional change of the subfloor
over which said structure will be used.
As used herein, "loose-lay floor structure~ is
a floor structure which will lie flat on a stable or
unstable subfloor, which will resist doming, curling,
buckling, or movement under a rolling load, which
preferably has a low structural stability value as
defined hereinbelow, and which need not be held in place
using adhesives.
As used herein, naccommodating floor
structure" is a loose-lay floor structure which will
accommodate or alter its size and shape to match that of
an unstable subfloor.
As used here~n, "subfloor dimensional chanae"
is a measure of the change in length of a subflooring
material under the conditions of its environment. This
change is expressed herein as change per unit length.
As used herein, "critical buckle strain~ is
the strain at which a loose-lay floor structure that is
compressed in a planar fashion will buckle.
As used herein, "relaxed compressive
stiffness~ is the approximate compressing force per inch
of width divided by the induced strain, the value of
said relaxed compressive stiffness being projected to a
1000-hour load relaxation and the compressive force
being applied in a planar fashion, the measurement being
taken in the linear portion of the stress-strain curve.
As used herein, "relaxed tensile stiffness" is
the approximate stretching force per inch of width
divided by the induced strain, the value of said relaxed
tensile stiffness being projected to a 1000-hour load
relaxation and the stretching force being applied in a
planar fashion, the measurement being taken in the
linear portion of the stress-strain curve.
As used herein, ~basis weight" is the weight
in pounds per square yard of a loose-lay flooring material.
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As used herein, "matrix material~ comprises
all components of a loose-lay flooring material,
excluding the reinforcing material.
As used herein, "bending stiffness~ is the
resistance to bending demonstrated by a loose-lay
flooring material as measured in inch-pounds using a
cantilever beam or eyuivalent method.
As used herein, "bending resistance" is a
' material parameter used in the theoretical deriYation of
the potential energy expression, and characterizes the
resistance of the flooring material to bending.
As used herei'n, "structural stability" is a
measure of the change in length in percent of a flooring
sample which has been heated at 180 F for six hours and
reconditioned at 73.4 F and 50% relative humidity for
one hour.
As used herein, the ~neutral bending plane" of
a strip of material, the ends.of which are being
subjected to a downward bending force, is an imaginary
line within said material above which the material is
under tension and below which it is under compression.
Loose-lay flooring should be expected to
maintain within acceptable limits the shape and
dimensions of the room in which it is placed, and it
should not shrink from the walls leaving unsightly gaps.
This requirement applies regardless of the nature of the
subfloor. Therefore, a desirable trait for such
flooriny is that it have a structural stability under
normal corlditions of not more than 0.5~ and preferably
not more than 0.1~.
If the subflooring on which the loose-lay
floor structure is to be placed is stable, the
characteristics which must be demonstrated by the
loose-lay floor are less stringent than for unstable
subfloors since minimal ~imensional changes of the
subflooring result in minimal planar compressions of the
floor structure. Nevertheless, problems can still be
encountered which relate to doming and curling, and to
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movement under a rolling load.
Conversely, unstable subfloors such as
particleboard dramatically increase the requirements for
a loose-lay flooring because such suhfloors tend to
expand and contract depending on the temperature and
relative humidity conditions within the structure in
which the subfloor resides. During winter months, dry
furnace-heated air tends to shrink unstable subfloors,
whereas during humid summer months such subfloors tend
to expand. A loose-lay floor structure that is laid
over such a subsurface at its maximum expanded position
and is pinned, attached or otherwise restricted by heavy
objects such as appliances experiences a variety of
stresses when the subfloor changes its dimensions. A
loose-lay flooring structure constructed according to
the prior art and having the required structural
stability is often unable to accommodate these stresses,
thus leading to doming, buckling or curling of the
flooring.
Surprisingly, we have discovered that
loose-lay floor structures comprising at least two
layers of reinforcing material may be constructed which
will meet all of the aformentioned criteria. As a
general rule, loose-lay floor structures with superior
accommodation characteristics result when the basis
weight and the bending stiffness are increased and the
compressive stiffness is lowered. Accordingly, by
following processes as set forth hereinbelow, loose~lay
flooring can be constructed which will have predictable
characteristics when applied over a subfloor having an
ascertainable subfloor dimensional change.
One factor which must be considered at the
outset is the amount of variation which can be expected
from a given subfloor. For example, subfloor shrinkage
can be expected to place a strain on the loose-lay floor
structure when it is compressed in a planar fashion by
the movement of the subfloor. If a flooring structure
is constructed with a critical buckle strain equi~alent
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to the expected subfloor dimensional change and the
flooring is compressed by the maximum expected shrinkage
of the subfloor, it will buckle. Thus, the critical
buckle strain of the floor structure must be greater
than the expected strain which will result from maximum
subfloor movement. A loose-lay floor structure will
experience the maximum compressive strain if it has been
installed on subflooring which is in its maximum
expanded condition; therefore, it should be designed to
withstand this strain without buckling.
Three significant parameters will affect the
tendency ~f the loose-lay floor structure to buckle.
These are the basis weight, bending stiffness and the
relaxed compressive stiffness, which were defined above.
The basis weight of ordinarily used resilient
flooring material usually varies from about 2 to about
10 pounds per square yard. As a general rule, the
greater the instability of the subfloor, the greater the
basis weight will have to be to prevent buckling because
the added weight of the flooring requires an increased
compressing force to induce buckling.
A second parameter is the bending stiffness of
the loose-lay flooring, the bending stiffness being a
measure of the ease with which the flooring will bend
and buckle~ Resilient sheet flooring material will
normally range in stiffness from very flexible (i.e.,
having a bending stiffness of ca 0.1 inch-po~lnds) to
fairly stiff (i.e., having a bending stiffness of ca 9
inch-pounds). Sheet flooring will rarely have a bending
stiffness exceeding the latter value because it must be
transported on rolls. Should the bending stiffness be
greater than 9, problems can be encountered with
cracking, bending, and folding when the flooring is
wound on small diameter rolls.
The third parameter is the relaxed compressive
stiffness which will be discussed in more detail below.
The essence of the present invention i5 that
if one skilled in the art knows the amount of subfloor
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dimensional change that will occur, that person can
design and construct a loose~lay floor structure which
will have a critical buckle strain that is greater than
the strain which will be exerted on the loose-lay
flooring by the subfloor. Preferably, the loose-lay
floor structure will also have a suitable structural
stability. Using mathemetical formulas derived from the
theory of buckling, one or more critical buckle strain
contour curves can be generated for selected basis
weights by varying the relaxed compressive stiffness
values and the bending stiffness values or,
alternatively, the bending resistance values. For
convenience, the curves displayed herein illustrate
plots of bending stiffness versus relaxed compressive
stiffness for constant basis weight and constan~
critical buckle strain values. By determining a range
of applicable compressive stiffness values from the
curve, appropriate matrix materials and reinforcing
materials can be selected. A bending stiffness value
for the floor structure can then be determined for these
materials and a suitable floor structure can be
constructed by appropriately disposing at least two
layers of reinforcing material within said matrix
material,
The relaxed compressive stiffness of the
loose-lay floor structure will approximate the sum of
the relaxed compressive stiffness values for the
components of said flooring. Thus, by obtaining the
relaxed compressive stiffness values for materials which
may comprise the matrix material and the reinforcing
layers, at least two of the latter to be disposed within
the matrix material, appropriate materials can be
selected such that the sum of the respective relaxed
compressive stiffness values falls approximately within
the range of relaxed compressive stiffness values
indicated by the curve. The actual relaxed compressive
stiffness value may then be determined by constructing a
test floor structure and, using this value, the target
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bending stiffness value may be ~et~rm;n?~l from the
curve. Alternatively, the sum of the relaxed
compressive (tensile) stiffness values may be used to
theoretically predict the required ben.ling stiffness.
It must be recognized that results which are
theoretically calculated for a flooring structure will
depend to a certain extent on experimentally measured
values as well as on other variables which are less
predictable; therefore, some variation fro~ the
theoretically predicted results can be expected. For
that reason, this latter approach is less satisfactory.
Once the desired bending stiffness has been
determined, the reinforcing layers may be disposed
within the matrix material such that a bending stiffness
essentially equivalent to the desired bending stiffness
is obtained. The loose-lay floor structure thus
obtained should have a critical buckle strain capable of
withstanding the strain which will be imposed on it by
the subfloor.
Stiffness is a well-known characteristic which
may be determined in a variety of ways. Standard tests
are well known in the art. For example, ANSI/ASTM D
747, also known as the Olsen Stiffness Test, describes a
standard method for determining the stiffness of
plastics using a cantilever beam. For purposes of the
present invention, satisfactory values may be obtained
using a l-inch span and measuring the bending moment
values at a bend angle of 20. As used herein, the
bending moment determined by the Olsen Stiffness Test is
equivalent to the bending stiffness.
More difficulty is encountered in obtaining
relaxed compressive stiffness data for materials which
may be used to construct the loose-lay floor struct~re.
Such measurements may readily be made by conventional
means for the matrix material, taking into account the
relaxation of the material under stress with time. The
resulting relaxed compressive stiffness values projected
to l000-hour relaxation by means well known in the art
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should be used to practice the present invention.
Conversely, reinforcing materials, which may
be of thin, light-weight construction, usually do not
lend themselves to such measurements. Therefore, the
information can be estimated by measuring the relaxed
tensile stiffness of the material, also taking into
account the relaxation of the material under stress with
time. For preferred materials, the relaxed tensile
stiffness, when properly measured, will be of
approximately the same magnitude as the relaxed
cgmpressive stiffness. Accordingly, relaxed tensile
stiffness values may be substituted for relaxed
compressive stiffness values.
The contour curves referred to above may be
derived by conventional mathematical means~ Theoretical
models for determining buckling characteristics are well
known in the art. For example, A. D. Rerr has
published, among others, a paper concerning vertical
track buckling in High Speed Ground Transportation
Journal, 7, 351 (1973). Loose-lay floor structures are
similarly amenable to such theoretical studies.
Accordingly, the potential energy, ~ , of a sheet
flooring structure after buckling may be calculated from
the following formula~
~ = 3C ~ 2 ~ QLO2(1-E)Tan ~ + KLOll-(l-E)Sec ~]2-KLoE2
Lo
where C = bending resistance
~ = angle of lift-off of the buckle
Q = basis weight
K = relaxed compressive (or tensile) stiffness
Lo = one half the length of the buckled area prior
to application of the strain that caused the
buckle
E = the compressive strain applied to create the
buckle
The bending resistance, C, may be calculated from the
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bending stiffness meas~red according to the Olsen
Stiffness Test, using the following equation
C = M S
_w
b~
where Mw = the measured bending stiffness
S = the span used in the test
b = the width of the test specimen
0 = the angle in radians at which the measurement
was taken
The critical buckle strain may be calculated mathemati-
cally by applying the principle of minimum potential
energy. Bending stiffness values, Mw, are sonverted to
bending resistance values, C~ Upon setting the
derivatives of ~ with respect to ~ , and of ~
with respect to Lo~ equal to zero, assigning values for
E and Q, and varying C and K within known limits,
solutions can be obtained where E becomes the critical
buckle strain. For example, this may be accomplished by
using the Newton-P~athson Method of solving non-linear
simultaneous e~uations. The solutions obtained ~y
varying these bending resistance and relaxed compressive
(tensile) stiffness values within known ranges yields
tables of points of critical buckle strain. From these,
one or more contour curves of constant critical buckle
strain can b,e plotted for use as hereinafter described.
As noted above, the contour curves illustrated herein
are plotted in terms of bendin~ stiffness, Mw, and
relaxed compressive stiffness, R, rather than in terms
of bending resistance, C, and K. The values of C used
for calculation ~re converted from Mw values. A flow
chart for a computer program which may be used to
generate this information is illustrated in FIGS. lA and
lB, which must be read together. Of course it will be
appreciated that parameters which are ascertainable by
reference to various curves may also be determined by
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purely mathematical means. The use of such nldthematical
means to derive the information required to practice the
present invention is a matter of choice to the artisan.
Accordingly, language in the specification and in the
claims which refers to the plo~ting of curves and the
like will also be deemed to include such mathematical
alternatives.
In practicing the present invention, loose-lay
flooring may be constructed for use over a particular
subfloor having an ascertained or ascertainable subfloor
dimensional change, or it can be constr~cted for use
over subflooring having an expected subfloor dimensional
change. As used herein, the expression "having an
ascertainable (or ascertained) subfloor dimensional
change'` will be considered to encompass all of these
alternatives. In any event, the objective will be to
construct a loose-lay floor structure which has a
critical buckle strain that is sufficient to accommodate
the expected subfloor dimensional change. At one
extreme are very stable subfloors, such as concrete, for
which the subfloor dimensional change (and hence the
critical buckle strain) would be minimal. At the other
extreme are very unstable subfloors, such as
particleboard, for which the maximum subfloor
dimensional change value (and hence the critical buckle
strain) should be about 0.003.
Once the desired critical buckle strain of the
flooring is known, an approximate basis weight for the
flooring material can be selected. Any suitable
resilient flooring material can be used, including
polyvinyl chloride resin, acrylic resin, vinyl acetate
resin, vinyl chloride-vinyl acetate copolymers, and the
like. Furthermore, the flooring material may also
comprise wear layers, decorative layers and the like.
Structures comprising these materials usually have a
basis weight of from about 2 to about 10 pounds per
square yard, although lighter or heavier weights may be
desired in certain circumstances. Since the basis
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weight is not critical when a loose-lay flooring is to
be placed over a stable subfloor, basis weights for such
usage will preferably vary from about 2 to about 5
pounds per square yard to conserve cost. Conversely,
for unstable subfloors, basis weights of from about 5 to
about 10 pounds per square yard will be preferred.
Nevertheless, these values are provided merely as
approximations and are not intended to limit the scope
of the invention.
r~ext, using the selected basis weight, a
contour curve of the desired critical buckle strain is
plotted from data points obtained by varyin~ the bending
stiffness values over a range of from about ~ to about 9
inch-pounds, and by varying the relaxed compressive
stiffness values over a range of from about 0 to about
10,000 pounds per inch of width.
As previously noted, the bending stiffness of
resilient flooring material is usually limited by
practical considerations to be within the range of from
about 0.1 to about 9 inch-pounds. However, as the
subfloor dimensional change increases, higher bending
stiffness values will be preferred. Thus, over an
unstable subfloor having a subfloor dimensional change
of 0.0015, where greater accommodation of subfloor
movement is required from the floor structure, higher
values such as from about 1 to about 9 inch-pounds are
preferred. For subfloors having a subfloor dimensional
change of 0.0025 or more, a bending stiffness of from
about ~ to about 9 inch-pounds is preferred, and, for
subfloors having a subfloor dimensional change of 0.0030
or more, a bending stiffness of about 3 to about 9
inch~pounds is preferred.
The actual relaxed compressive stiffness range
which will be applicable to the flo,or structure will be
discernible from the contour curve and, once this range
is known, matrix materials and at least two layers of
reinforcing materials can be selected such that the sum
of the relaxed compressive ~or tensile) stiffness values
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- 18 - LFM-7168
for these materials falls within the indicated range.
The sum of these values also gives, from the curve, the
target bending stiffness for the floor ~tructure. Thus,
the reinforcing material can be disposed within the
5 `matrix material such that the target bending stiffness
is achieved.
The reinforcing material will comprise fibrous
materials, many of which are conventionally used in the
art. Examples of such materials are fibrous mats
comprising glass, polyester, rayon, nylon and the like,
or combinations thereof. Very lightweight materials on
the order of 0.S ounce per square yard are preferred.
Reinforcing materials used in loose-lay flooring should
have a relaxed compressive stiffn~ss which is as uniform
as possible in all directions. Woven materials tend to
have directional strength depending on whether the
material is compressed or stretched in a machine
direction or across machine direction. Such directional
strength variation is minimized with non-woven
materials; therefore, non-woven materials are preferred.
Specialized reinforcing materials having
unique characteristics may also be used. One such
non-woven material is a glass mat comprising a binder
which dissolves or softens in the presence of
plasticizers found in typical matrix materials.
Although the use of such material makes the prediction
of relaxed compressive stiffness values much more
difficult, there are also advantages. For example,
reinforcing materials containing soluble binders are
often heavier in nature and easier to handle in a
production environment than materials which do not
contain such binders. Thus, they may be used where
handleability is a problem, but where it is also
desirable to produce a floor structure having a reduced
relaxed compressive stiffness.
In the usual situation, the majority of the
relaxed compressive (tensile) stiffness of the total
flooring will be provided by the reinforcing material.
- 19 - LFM-71~8
The matrix material, being a resilient plastic, is
usually not dimensionally stable and in most situations
will stretch or compress quite easily. The reinforcing
material, however~ does not readily compress or stretch.
Preferably, the relaxed compressive stiffness of the
reinforcing material will be about 5 times that of the
matrix material and more preferably about 10 times that
of the matrix material. Suitable flooring can be made
with reinforcing material and matrix material having
similar relaxed compressive stiffness values. However,
the sum of the relaxed compressive stiffness values for
the reinforcing materials should not be less than the
sum of the relaxed compressive stiffness values for the
matrix materials.
The bending stiffness of a loose-lay floor
structure constructed according to the present invention
will vary depending on how the reinforcing layers are
disposed within the matrix material. In most instances
it will be desirable to have the reinforcing material
disposed within the matrix material in a substantially
planar fashion. However, as set forth below, it may be
preferable in certain circumstances to dispose the
reinforcing material in a non-planar fashion.
Preferably, two reinforcing layers will be used,
although suitable loose-lay flooring can be produced
using m~re than two reinforcing layers.
As a general rule, the greater the separation
of the two layers, the greater the bending stiffness.
Thus, if one reinforcing layer is disposed near the top
surface of the matrix material and one is disposed near
the bottom surface, the bending stiffness will be
greater than if both reinforcing layers are disposed
near the neutral bending plane of the composite
material.
Combinations of reinforcing materials may also
be used. Rather than using two layers of the same
reinforcin~ material in a matrix material, a lighter
reinforcing layer can be used in combination with a
- 20 - LFM-7168
heavier reinforcing layer. The heavier reinforcing can
be placed closer to the neutral bending plane, but it
will still produce a bending stiffness comparable to
that of a lighter weight reinforcing material dispo.sed
closer to the surface of the matrix material.
Nevertheless when using heavier material, care m~st be
taken not to exceed the desired relaxed compressive
stiffness of the final product.
The use of such combinations can have great
importance as, for example, where the surface of the
matrix material is embossed, or where a wear layer is
applied. If a lighter-weight reinforcment is placed
near the surface of a matrixr embossing will tend to
deform the reinforcement so that it is no longer planar,
thus reducing its contribution to the rela~ed
compressive stiffness of the flooring structure.
However, if a somewhat heavier reinforcment is used,
that reinforcment could be disposed further away from
the surface of the matrix, thereby diminishing the
effects of the embossing~ Similarly, if a wear layer
with high compressive stiffness is to be applied, the
neutral bending plane will be higher up in the composite
str~cture than it would be when such a layer was not a
component of the original matrix material. In such a
situation, it might be necessary to place a lighter
weight reinforcing material in the wear layer in order
to achieve an adequate bending stiffness and relaxed
compressive stiffness. Nevertheless, this problem may
likewise be avoided by disposing a heavier reinforcing
layer in the matrix material.
Other alternatives are also available to
modify the characteristics of a flooring structure. For
example, a reinforcing material has its greatest relaxed
compressive/tensile sti fness when it is in a planar
config~ration. If the reinforcing layer is disposed in
a matrix material in a non-planar fashion, or if it is
modif ied such that a s~bstantial portion of the
reinforcing layer does not lie in the same plane, the
L ~ ~
- 21 - LFM-7168
~elaxed compressive/tensile stiffness wi~l b~ reduced.
The former may be achieved by disposing tine r~inforcing
within the matrix in a wavy or ~rinkled manne~-; however,
modification may be achieved in a variety of ~.~ays. For
example, the reinforcing may be deformed ~rom a planar
configuration by embossing or other similar tr~atment.
Another means of reducing relaxed compressive/
tensile stiffness of a reinforcing material is by
modifying the material in a manner which does not affect
planarity. For example, such modifications would
include means such as perforating, cutting, punching
holes, and the like, or.by folding to break the fibers
and then again flattening the reinforcing material.
Accordingly, "modifications" as used herein in relation
to the changing of relaxed compressive stiffness
characteristics will be deemed to comprise all of the
aforementioned possibilities and combinations thereof,
as well as the use of reinforcing materials having
dissolvable or softenable binders.
These modifications may be achieved as a
matter of foresight or hindsight. Thus; a reinforcing
material having too high a relaxed compressive stiffness
value may be pretreated in such fashion that the relaxe~
compressive stiffness is reduced to a satisfactory
value, after which it may be disposed within the matrix
material. Alternatively, the flooring structure may ~e
constructed and the relaxed compressive stiffness and/or
the bending stiffness me~sured. Adjustments can then be
made by modifying one or more of the reinforcing layers
in situ. In this way, flooring structures which might
not otherwise be suitable for use over a given subfloor
may be treated so as to impart the necessary bending
stiffness and/or relaxed compressive stiffness values.
This technique is also applicable to flooring
structures comprising single reinforcing layers. A
number of such structures have been described in the
prior art. For example, U.K. Patent No. 1,525,018
discloses structures comprising glass reinforcing
.~
1~ ;6 ~
22 - LFM-7168
layers, the density of the glass being about 80 to about
160 grams per square meter. Similarly, U.K. Patent
Application Nos. 2,012,618A, 2,018,618A and 2,019,253A
refer to fibrous tissues having a density of about 10 to
about 60 grams per square meter. Related structures
comprising encaps~lated glass are also described in U.S.
Patent N~s. 4,242,380 and 3,980,511. Furthermore,
structures comprising nylon, polyester and other woven
and non-woven materials are likewise known in the art.
When heavy gauge reinforcing is used to
provide adequate dimensional stability, such structures
can fail when placed over unstable subfloors. Applicants
have discovered that in situ modification may be used to
advantage on these structures. For example, flooring
structures comprising a single layer of glass
reinforcing were physically cut in various patterns,
such as those illustrated in FIGS. 12-14. FIG. 12
illustrates a pattern of square cuts which were deep
enough to pierce t~e reinforcing layer, the structure
otherwise being left intact. This pattern is referred
to as a continuous modification pattern because there is
still a continuum of reinforcing available within the
flooring structure; e.~., longitudinally along l~nes A-A
and transversely along lines B-B Gf FIG. 12. A modified
continuous pattern is illustrated in FIG. 13, the linear
nature of the continuum of reinforcing being
substantially disrupted.
A different type of cutting pattern referred
to as a discontinuous pattern is illustrated in FIG. 14.
In this instance, the cutting is accomplished in both
longitudinal and transverse directions so that no
continuum of reinforcing remains. It is understood,
however, that the patterns disclosed herein are provided
merely by way of illustration, and that other geometric
designs and patterns will also provide suitable results.
The selection of a particular pattern may depend on
artistic preferences, as well as on structural
requirements. Accordingly, the design or pattern which
' .a ff~ c ~
- 23 - LFM-7168
is selected will be largely a matter of choice to the
artisan.
In situ modifications may also be accomplished
by embossing-type techniques in which the application of
external forces disrupts the integrity of the
reinforcing layer. All such techniques are included
within the definition of ~modifications" as hereinbefore
described.
To practice the in situ modification invention
on an existing structure comprising a single reinforcing
layer, essentially the same sequence of events as
described earlier for more complex structures should
preferably be employed. First, the instability of an
actual or proposed subfloor should be considered and a
desired critical buckle strain should be selected for
the end product whereby this critical buckle strain is
greater than the subfloor dimensional change. The basis
weight of the existing structure can then be measured
and one or more curves of constant critical buckle
strain can be generated by setting E equal to the
desired critical buckle strain, Q equal to the basis
weight and varying the bending stiffness, Mw, and the
relaxed compressive stiffness, R, as hereinbefore
described. The bendin~ stiffness and the relaxed
compressive stiffness of the existing structure can then
be measured.
The measured relaxed compressive stiffness in
most instances, and especially where the existing
structure contains a very heavy reinforcing material,
will not be relatable to the curve~ However, the
measured bending stiffness can be used in conjunction
with the curve to determine the relaxed compressive
stiffness which should be demonstrated by the desired
end product. Thus, if the existing structure is
modified in situ so that the resulting structure has a
relaxed compressive stiffness which approximates that
determined from the curve, the critical buckle strain of
this resulting product should be such that the structure
12;~
- 24 - LFM-7168
can be used o~ !.a intended subfloor. It has been
found that, by applying such techniques to structures
which have unsuitable buckling characteristics,
structures are produced which have extremely good
performance characteristics.
Although in situ modification causes
substantial reductions of the relaxed compressive
stiffness values, the bending stiffness values are
relatively unaffected in most instances. Thus, the
initially determined bending stiffness may be used to
predict the required relaxed compressive stiffness from
the curve. In those uncommon instances where the
bending stiffness shows a significant change, the
necessary relaxed compressive stiffness value may be
determined from the curve using the bending stiffness
value for the modifie~ structure~
The present invention has the advantage of
providing a relatively reliable way to predict the
characteristics of loose-lay flooring structures, and it
also provides guidelines by which the various parameters
may be modified so as to predictably alter the
characteristics of such structures.
The following examples will be illustrative to
demonstrate, but not to limit, the advantages of the
present invention.
EXAMPLES
Structures Comprising At Least
Two Reinforcing Layers
Example 1
This example illustrates a process for
desi~ning a loose-lay flooring structure for use over a
subfloor having a subfloor dimensional change of 0.001.
The target critical buckle strain for the desired
flooring structure is selected to be 0.0016 and the
basis weight of the flooring structure is selected to be
4.6 pounds per square yard. Accordingly, for purposes
of calculation, E is assigned the value of the target
critical buckle strain (0.0016) and Q is assigned the
~2~6~`
- 25 - LFM-7168
basis weight (4.6 pounds square yards). By using the
assigned values in the equations set forth in the
specification, varyirlg the bending resistance, C, such
that the bending stiffness, Mw, is varied between 0 and
9 inch-pounds, varying the relaxed compressive
stiffness, K, from 0 to 10,000 pounds per inch of width,
and solving the resulting equations, a series of points
of constant critical buckle strain corresponding to the
varied values f ~w and K are obtained (FIG. 2). From
the curve, the relaxed compressive stiffness
corresponding to the bending stiffness value of 0.1
inch-pound is 200 pounds per inch of width (ppiow) and
that corresponding to 9 inch-pounds is 930 ppiow.
A reinforcing material from International
Paper Co., Identification No. IP042081-2, is selected
for evaluation. This material is a nonwoven mat
comprised of S0% glass and 50% polyester fiber and
having a weight of 0.524 ounce per square yard. The
relaxed tensile stiffness of this material is measured
as follows: A sample 2 inches wide and 12 inches in
length is c~t and clamped in the jaws of an Instron
Tensile Tester such that the jaws are separated by a
distance of $ inches. The jaws are then moved apart at
a rate of 0.02 inch per minute ~ntil the sample has
elongated by 0.3%; i.e., the strain on the sample is
0.003. Jiaw movement is stopped and the load on the
sample is monitored for 90 minutes. The load decay
curve is then extrapolated to 1,000 hours by means well
known in the art, giving a relaxed tensile stiffness of
227 ppiow.
A PVC plastisol matrix material is prepared
having the followiny formula:
Component Parts by ~lei~ht
PVC Homopolymer resin (MWt = 106,000~ 100
35 Primary plasticizer 45
Secondary plasticizer 15
Organotin stabilizer 2
Silica gel thickener
n
6~ -
- 26 - LFM-7168
The relaxed tensile stiffness value measllred using the
Instron Tensile Tester is 74 ppiow. Therefore, the
ratio of the ppiow values for the two reinforcing layers
to that of the matrix material is 454:74 or 601:1.
The s~m of the relaxed compressive stiffness
values for the two layers of reinforcing material and
the matrix material is 528 ppiow and, from the curve,
the bending stiffness corresponding to this ppiow value
is 1.65 inch-pounds. Accordingly, a flooring structure
having a basis weight of 4.6 pounds per square yard
sho~ld have a critical buckle strain greater than 0.001
when constructed from the above materials such that the
bending stiffness is 1.65 inch~pounds, one reinforcing
layer being disposed above the neutral bending plane of
the resulting floor structure and the other reinforcing
layer being disposed ~elow said neutral bending plane.
To verify this, a flooring structure is
~onstructed for testing using a high velocity air
impingement oven and a reverse roll coater. A layer of
vinyl matrix material 0.01 inch thick is applied to a
release carrier. A layer of the reinforcing material is
laid on the matrix material and allowed to saturate,
after which the composite material is gelled in an oven
at 275 F. for two minutes. After cooling, a second
layer of matrix material 0.07 inch thick is applied to
the surface of the gelled sample and this composite
structure is gelled in the oven at 275 F. for two
minutes. A third layer of matrix material D.01 inch
thick is applied to the gelled substrate and a second
layer of reinforcing material is placed in the wet
plastisol and allowed to saturate. After saturation of
the mat, the composite structure is gelled in an oven at
275 F. for two minutes and then fused at 380 ~. for
2.5 minutes. After cooling, the fused composite
structure is pressed between platens having a
temperature of 320 F. to consolidate the gauge to 0.08
inch. Pressure is maintained for 30 seconds to give a
material with a basis weight of 4.58 pounds per square
6~`~
- 27 - LFM-7168
yard and a bending stiffness, measured according to
ANSI/ASTM D 747, of 1.65 inch-pounds.
To verify its suitability, a sample is placed
in an environmental test chamber on a piece of par-
ticleboard having a subfloor dimensional change of
0.001. The particleboard is at its maximum expanded
position and the sample is affixed thereto such that,
when the sample-on-subfloor combination is subjected to
a simulated, l,000-hour summer-winter seasonal change,
the floor sample is subjected to the strain imposed by
the movement of the subfloor. The ability of the floor
structure to accommoda~e the imposed strain without
buckling demonstrates that it has a critical buckle
strain in excess of 0.001. Verification may also be
achieved by using the measured basis weight, bending
stiffness, and relaxed compressive stiffness values of
the resulting floor structure and then calculating the
critical buckle strain mathematically.
Example 2
This example illustrates the construction of a
flooring structure whereby an intermediate test struc-
ture is employed.
A foamable polyvinyl chloride plastisol matrix
material having the following composition and a
viscosity of 10,000 cps is prepared by means well known
in the art.
Parts by
Ingredient Weight
Dispers iOII Grade
PVC Homopolymer Resin, MWt 105,000 36.00
Dispersion Grade
PVC Homopolymer Resin, MWt 80,400 36.00
Blending Grade
PVC Homopolymer Resin MWt 81,100 28.00
35 Epoxy-type plasticizer 1.00
C36~ ~
- 28 - LFM-7168
Parts by
Inqredient Wei~ht
.
Dioctyl phthalate 50.00
Blowing agent activator 0.20
5 Stabilizer 0.15
Azodicarbonamide blowing agent 0.66
Feldspar filler 18.00
The following structure is prepared for use
over a subfloor having an expected subfloor dimensional
change of 0.0015. The target critical buckle strain for
this floor structure is selected to be 0.0018.
The expected subfloor dimensional change of
0.0015 indicates that the subfloor is of medium
stability. Therefore, a basis weight of 4.1 pounds per
square yard is selected for the sample. Using these
data, a contour plot is prepared as set forth in Example
1 wherein E is 0.0018, Q is 4.1 pounds per square yard,
and ~w and K are varied between 0 and 9 inch-pounds and
0 and 10,000 ppiow, respectively. From the plot
obtained (FIG. 3), the range of relaxed compressive
stiffness values corresponding to bending stiffness
values of 0.1 and 9 inch-pounds is determined to be 150
to 750 pounds per inch of width.
A 50% glass fiber/50% polyester fiber
reinforcing material having a basis weight of 0.524
ounce per square yard is selected, as is the matrix
material described above. The relaxed tensile stiffness
value for the foamed matrix is 42 pounds per inch of
width whereas the value for the reinforcing material is
227 pounds per inch of width. Accordingly, because two
reinforcing layers are used, the total of the relaxed
tensile stiffness values is ~alculated to be 496 pounds
per inch oE width, as follows:
36~;~
- 29 - LFM-7168
Relaxed Tensile Stiffnes.s
Component ~pounds per inch of width)
Matrix material 42
First reinforcing layer (Rl) 227
Second reinforcing layer (R2) 227
496
This value is within the range of 150 to 750 pounds per
inch of width determined from the curve. Furthermore;
the sum of 454 pounds per inch of width for the two
reinforcements is approximately 10 times greater than
the value of 42 measur~d for the matrix material, which
is a desirable relationship.
The actual relaxed compressive stiffness of
the composite struct~re is determined experimentally by
constructing a test structure according to the following
procedure. A layer of matrix material 0.027 inch thick
is coated on a release carrier and one layer of the
reinforcing material is placed in an approximately
planar fashion on top of the wet surface. The
reinforcing layer is allowed to saturate and the
material is gelled at 280 F for 1.5 minutes. After
cooling, a second layer of plastisol matrix material
essentially comprising the central portion of the
eventual composite structure is coated at a thickness of
0.029 inch on the gelled substrate. A second layer of
reinforcing material is placed in the wet plastisol and
allowed t:o saturate, after which the material is gelled
at 280 F for 1.5 minutes. After the composite has
cooled, a third coating of plastisol 0.02 inch thick is
placed on the gelled surface. This composite is gelled
at 280 F. for 1.5 minutes to give a structure having a
thickness of 0.076 inch. When fused at 420 F, the
blowing agent is activated and the structure is expanded
to a final thickness of 0.117 inch. This structure is
illustrated in FIG. 4 in which Rl and R2 are the
reinforcing layers and Sl and S2 are the lower and upper
surfaces, respectively. The relaxed compressive
- 30 - LFM-716&
stiffness value of this structure is measured to be 538
pounds per inch of width as compared to the predicted
relaxed tensile stiffness value of 496 pounds per inch
of width.
S Referring again to FIG~ 3~ the relaxed
compressive stiffness value of 538 pounds per inch of
width indicates that the hending stiffness of the
finally constructed sample should be 3.3 inch-pounds.
However, the bending stiffness of the test structure is
measured to be 0.81 inch-pounds. This value is substan-
tially below the desired value; therefore, a second com-
posite is constructed. In this sample, represented by
FIG. 5, the reinforcing layers are separated by a
greater distance in order to increase the bending
stiffness.
The procedu~e followed is essentially the same
as that set forth above. A layer of matrix material is
coated to a thickness of 0.01 inch on a release carrier
and one layer of reinforcing material, Rl, is placed in
an approximately planar fashion on top of the coated
surface. When saturation is complete, the material is
gelled at 280 F for 1 minute. Af~er cooling, a layer
of matrix material 0.050 inch thick is coated on the
gelled material and gelled by heating at 280 F for 2
minutes. A third coating of plastisol 0~015 inch thick
is then placed on the gelled surface and a second layer
of reinforcing material, R2, is placed in the wet
plastisol. After saturation is complete, the material
is gelled 1:o give a composite structure having a
thickness of 0.075 inch. The resulting structure is
then ~used at 420 F to activate the blowing agent and
expand the final structure to a thickness between Sl and
S2 f 0.117 inch. The bending stiffness of this
structure is measured to be 3.29 inch-pounds.
As noted above, this structure is intended
for use over the subfloor having an expected subfloor
dimensional change of 0.0015. To verify its suitability,
a ~ample is placed on such a subfloor at its maximum
~2~ f~
- 31 - LFM-7168
expanded position and affixed to it. When the floor
sample-on-subfloor combination is subjected to a
simulated, 1000-hour, summer-winter seasonal change as
set forth in Example 1, no buckling occurs, thus indi-
cating that it has a critical buckle strain of greaterthan 0,0015.
The structural stability of this floor
structure is determined by measurin~ the length of a
sample, heating it at 180 F for six hours,
reconditioning it at 73.4 F and 50% relative humidity
for one hour, and then remeasuring the length. The
percent change in length (the structure stability) is
found to be -0.02%. This is a desirable value which
indicates that the floor struct~re is dimensionally
stable.
Example 3
The following additional structures are
prepared to illustrate the variations in bending
stiffness caused by changing the position of the
reinforcing materials within the matrix. The structure
of FIG. 6 is prepared in a single step process
essentially as described in Example 2 except that a
single layer of plastisol 0.075 inch thick is placed on
the release carrier. Upon expansion, a thickness of
0.118 inch between surfaces S1 and S2 is obtained, and a
bending stiffness of 0.20 inch-pounds is measured for
this structure.
A structure similar to that of FIG. 5 is
prepared except that a Manville glass fiber mat having a
basis weight of 20 grams per square meter (ca. 0.6
ounce per square yard) is employed for Rl and R~. When
expanded to a thickness of 0.118t the structure has a
bending stiffness of 5.66 inch-pounds.
The structure of FIG. 7 is prepared in the
manner used to prepare the structure of FIG. 5 (Example
2), except that the material is not heated to expand the
plastisol. The resulting unfoamed matrix has a
thickness of 0.077 inch and the separation between
~LZ~0066~?
- 32 - LFM-7168
Rl and R2 is 0.054 inch. The bending stiffness of this
structure is 1.49 inch-pounds, which is substantially
less than the value of 3.29 inch-pounds obtained for the
structure of FIG. 5.
When the results obtained for these structures
are compared, several generalities can be madeO First,
extremely low bending stiffness values are obtained in
the absence of the two reinforcing layers. Secondly,
comparing FIGS. 4 and 5, bending stiffness is increased
when the distance between the reinforcing layers Rl and
R2 is increased. The same result is also obtained when
a relatively lighter weight reinforcing material is
replaced by a heavier material. Finally, referring to
FIGS. 5 and 7, bending stiffness may also be varied by
controlling the amount of expansion of the matrix
material.
Example 4
A structure similar to that of FIG. 5 of
Example 2 is prepared, the difference being that a clear
PVC plastisol wear layer, W, is added to the surface of
the structure. This structure is illustrated in FIG~ 8
and is also designed for use over a subfloor having a
subfloor dimensional change of 0.0015; therefore, a
target critical buckle strain of 0.0018 is also chosen
for this sample. The basis weight for the sample, due
to the increase in weight attributable to the wear
layer, is 4.7 pounds per square yard.
The contour curve generated for these
parameters; as set forth in Example l is illustrated in
FIG. 9. From this curve, it is seen that a ranqe of
relaxed compressive stiffness values of 160 to 790 is
possible over a bending stiffness ran~e of 0.1 to 9
inch-pounds. Using the relaxed tensile stiffness value
of 227 for the reinforcing layer~ 42 for the matrix
material and a measured value of lO for the 0.01-inch
thick wear ~ayer, the sum of the relaxed tensile
stiffness values for the proposed structure is predicted
to be 506 pounds per inch of width.
~L Z II D O C~
~, ,.
- 33 - LFM-7168
A test structure is constructed essentially as
set forth in Example 2, except that the wear layer is
included. The l,000-hour relaxed compressive stiffness
value for this structure is 572 pounds per inch of
width. The curve of FIG. 9 indicates that the bending
stiffness value corresponding to this relaxed
compressi~e stiffness value is 3.4 inch-pounds. This
value is comparable to that obtained for the structure
illustrated by FIG. 5: therefore, the structure of FIG.
8 is prepared in which reinforcing layer Rl is disposed
approximately 0.01 inch above surface Sl and reinforcing
layer R2 is disposed 0.01 below surface S2. The bending
stiffness for this structure is shown to be 3.40
inch-pounds. When this structure is tested as described
in Example 1, no buckling occurs, indicating that it is
suitable for use over a subfloor having a subfloor
dimensional change of O.OOlS. Furthermore, the
structural stability, meas~red as set forth in Example
2, is -0.06~, indicating that the structure is
dimensionally stable.
Example S
A sample identical to that prepared in Example
4 is constructed except that the side containing the
wear layer is mechanically embossed to a depth of 0.005
inch. The relaxed compressive stiffness measured for
this struct:ure is 546 pounds per inch of width as
compared to 572 pounds per inch of width for the
unembossed structure. No buckling occurs when this
structure is tested in the usual manner, thus indicating
that it is also suitable for use over a subfloor having
an expected subfloor dimensional change of 0.0015. The
structural stability, determined as previously
described, is -0.04%.
Example 6
This example illustrates the use of
reinforcing materials having a dissolvable binder
whereby the character of the reinforcing material
changes in situ.
- ( lZ~
- 34 LFM-7168
A 100ring structure for use over a subfloor
having a subfloor dimensional change of 0.002 is
desired. Accordingly, a target critical buckle strain
of O.OD26 is selected, as is a basis weight for the
flooring str~cture of 6.0 pounds per square yard. Using
these values for E and Q, respectively, and varying the
relaxed compressive stiffness K between O and 10,000
ppiow and the bending stiffness Mw between O and 9
i~ch-pounds, a contour curve is constructed as
previously set forth. From the curve (not shown), the
range of applicable relaxed compressive stiffness values
is seen to be 135 to 600~ppiow. The matrix material
used in Example 2, but containing in addition 34 parts
by weight of butyl benzyl phthalate plastisizer, and
having a relaxed tensile stiffness of 30 p~unds per inch
of width is selected ~or use with reinforcing material
SAF 50/2 obtained from Manville Corporation. The
reinforcing material has a meas~red relaxed tensile
stiffness of 352 ppiow; thus, the expected relaxed
compressive stiffness of a structure comprising two such
reinforcing layers and the indicated matrix material
should be 734 ppiow. It is known, however, that the
reinforcing material will lose a portion of its
stiffness contribution when placed in a vinyl matrix,
apparently due to softening of the reinforcing
material's binder in the presence of the plastisizer
present in the plastisol.
- A test structure comprising two layer~ of
reinforcing material in the matrix material is
constructed as follows: A layer of the plastisol
described above, containing butyl ~enzyl phthalate to
fac~litate softening of the binder, is coated on a
chrome steel plate at a thickness of 0.015 inch and one
layer of SAF 50/2 reinforcing material is placed in the
wet plastisol. When the reinforcement is saturated, the
material is gelled at 400 F for one minute and cooled.
Thereafter, a layer of plastisol approximately 0.045
inch thick is placed on the gelled material and gelled
12~,3~b`1
- - 35 - LFM-7168
by heating at 400 F for 1.5 minutes. A third layer of
plastisol 0.015 inch thick is applied to the gelled
surface and a second layer of SAF 50/2 reinforcement is
placed in the wet plastisol and allowed to saturate.
The sample is then heated at 420 F for 3.5 minutes to
fuse the product. The resulting structure has a
thickness of 0.130 inch and a measured basis weight of
6.0 pounds per square yard. The relaxed compressive
stiffness value for this structure is measured to be
567 pounds per inch of width, which is significantly
lower than the sum estimated above for this structure.
From the curve, the bending stiffness corresponding to
the relaxed compressive stiffness value of 567 pounds
per inch of width is 7.5 inch-pounds. The measured
bending stiffness f~r the struc~ure is determined to be
7.47 inch-pounds.
The above values are within the expected range
of values. Accordingly, a sample is subjected to a
l,000-hour summer-winter heating séason test, as
previously illustrated, in order to deter~ine its
suitability. No buckling is observed; therefore, the
sample is suitable for use over a subfloor having a
subfloor dimensional change of 0.002. The structural
stability is determined to be +0.06~.
Exa~le 7
This example illustrates that reinforcing
material disposed within a flooring structure may be
modified by external means such that the relaxed
compressive stiffness of the reinforcing material and
hence the relaxed compressive stiffness and the bending
stiffness of the flooring structure are reduced.
A flooring structure is desired for use over a
subfloor having a subfloor dimensional change of 0.001;
therefore, a target critical buckle strain of 0.0015 is
selected, as is a basis weight of 3.0 pounds per square
yard. A contour curve is plotted in the usual manner
and, from the curve (FIG. 10), the range of applicable
relaxed compressive stiffness values is found to be 155
z`~o~.~
- 36 - LFM-7168
to 770 ppiow.
The following materials are selected to
construct the flooring structure.
Relaxed Tensile 8asis
Stiffness Weight
Component (ppiow) (lbs/sq. yd.)
Manville Reinforcement
SH-20/1 512 0.04
Manville Reinforcement
S~1-50/10 761 0.11
PVC Plastisol 30 2.85
Using these materials, a flooring structure is
constructed with the heavier reinforcement near the
backing. A coating of plastisol 0.015 inch thick is
placed on a suitable release carrier and a layer of
SH-50/10 reinforcement is placed in the plastisol and
allowed to saturate. After saturation of this
reinforcement, the material is gelled for one minute at
280 F. On the gelled substrate is placed a second
coating of the same plastisol composition at a thickness
of 0.032 inch. A layer of SH-20/1 reinforcement is
placed on the top surface of the plastisol, allowed to
~aturate, and then fused at 425 F to expand the struc-
ture to a final thickness of 0~115 inch. Upon cooling
and sepiaratin~ the structure from the release carrier, a
; basis weight of 3.0 pounds per square yard is obtained.
The structure demonstrates a relaxed compressive
stiffness of 1303 pounds per inch of width and a bending
stiffness of 5.50 inch-pounds. From the above cited
range; it is obvious that the relaxed compressive
stiffness of 1303 ppiow is too high, and that Shis
structure will not exhibit the target critical buckle
strain.
To reduce the relaxed compressive stiffness of
this flooring structure, a sample is inverted and placed
in a press such that the surface adjacent the SH-50/10
reinforcement is on top. Over this structure is placed
:
P
`~ ( 12~066-~ ~
- 37 - LFM-7168
a section of plasti~ ~t~ria~ having a prismatic
textured face with a pattern depth of approximately 0.05
inch. Press~re is applied to the flooring structure and
the plastic such tha~ ~he prismatic surface is pressed
into the flooring structure to the depth of the prism
pattern, thereby disrupting the character of the
SH-50/10 reinforcing layer. The relaxed compressive
stiffness of the modified sample of flooring structure
is 547 pounds per inch of width and the bending
stiffness is 3.21 inch-pounds. The critical buckle
strain for this structure is seen to be 0.0015 from the
curve, thus indicating that it is suitable for use over
a subfloor having a subfloor dimensional change of
0.001. Furthermore, the structural stability is
determined to be -0.06%, indicating that the structure
is dimensionally stable.
Example 8
Thi~ example illustrates the construction of a
Plooring structure comprising a wear layer, a decorative
layer, a foamed plastisol, and reinforcing materials.
A particleboard subflooring haviny a subfloor
dimensional chan~e of 0.0025 is ~elected for use.
Therefore, a target critical buckle strain of 0.0036 is
selected for the flooring structure, as is a basis
weight of 6.9 pounds per square yard. A contour curve
is constructed in the usual manner and, from the curve
(FIG. 11), the applicable compressive stiffness range is
seen to Ibe 90 to 420 ppiow.
The following components are used to
30 construct this flooring structure.
Relaxed Tensile Basis Component
Stiffness Weight Thickness
Component (ppiow) (lbs/æq. yd.) (inch)
PVC wear layer 10 0.56 0.01
35 Decorative layer 36 3.27 0.052
PVC foam layer 35 3.00 0.10
International Paper
Reinforcement
IP042081-2 227 0003275 0.007
.,
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- 38 - LFM-7168
The foamable plastisol composition of Example
2 is coated on a release carrier at a thickness of 0.01
inch and the non-woven reinforcing layer from Example 1
is placed on the surface of the plastisol and allowed to
saturate. The material is then gelled at 280 F for one
minute and cooled to room temperature. A second layer
of plastisol 0.035 inch thick is applied to the surface
of the gelled layer, heated at 425 F to expand the
foamable plastisol to a thickness of 0.10 inch and
cooled to room temperature. The basis weight of this
composite material is 3.0 pounds per square yard.
Onto the cool structure is placed a coating of
a urethane adhesive composition 0.002 inch thick and the
coating is then heated at 250 F to evaporate the
solvent. The urethane adhesive comprises 10% by w~ight
urethane block copolymer, 88% by weight methyl ethyl
ketone and 2 ~ by weight silica gel thickener.
- A decorative binder/chip layer is prepared by
dicing a filled PVC composition into fine particles and
mixing the resulting chips with a binder composition to
form a particulate material suitable for deposition
using a stencil. The chip composition is as follows:
C~ponent Parts by Weight
Extrusion grade PVC homopolymer 100
25 Primary phthalate plasticizer 32.5
Epoxy-type plasticizer 7.5
Zinc stearate 0.7
~ Limestone filler 328
; The binder/chip composition is prepared by
blending 1,225 parts by weight of the chip composition
with 250 parts of solution-polymerized PVC resin, 123
parts primary plasticizer, 79.5 parts epoxy-type plasti-
cizer and 4.5 parts of stabilizer. Mixing is
accomplished using a Hobart Mixer with a wire whip
attachment, the mixing time being approximate~y five
minutes.
The previously prepared 0.10-inch thicX foam
,
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~2~06~
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- 39 - LFM-7168
sample on release carrier is perforated with a pin roll
which punches holes through the entire s~ructure at a
spacing o~ approximately 1/8 inch. The decorative
bi~der/chip composition is stenciled onto the perforated
foam surface forming a layer of approximately 0.085 inch
thick, the basis weight of this layer being 3.27 pounds
per square yard. A second reinforcing layer identical
to that used above is placed on the surface of the sten-
ciled layer and the,preformed PVC wear layer on a
release carrier comprising an adhesive is placed on the
chip layer such that the adhesive layer is in contact
with the upper reinforcing layer. The entire structure
is placed in a flat press with the upper platen heated
to 295 F and the lower platen being water cooled. ~he
press is closed, exerting a minimum pressure for eight
seconds in order to consolidate the decorative stenciled
layer from a thickness of 0.085 inch ~o a thickness of
0.052 inch. The press is then opened and an embossing
plate preheated to 275 F is inserted into the press.
The press is closed for eight seconds, applying
sufficient pressure to cause embossing of the structure
to a depth of 0.016 inch. The composite sample is then
removed from the press and cooled to room tempera~ure,
after which the top and bottom carrier layers are
removed.
The relaxed compressive stiffness of this com-
posite structure is measured to be 358 pounds per inch
of width. For this measured value a bending stiffness
of 5.5 is seen to be necessary by reference to the
contour curve. The value measure or this structure is
found to be 5.50 inch pounds; thus, no modification of
the structure is required.
To evaluate the sample it is placed in an
environmental test chamber for 1,000 hours where it is
subjected to a summer-winter environmental change as
described above. No buckling is observed; therefore,
the test result indicates that the structure is suitable
for use over a subfloor having a ~ubfloor dime,nsional
lZ~o~
- 40 - LFM-7168
change of 0.0025.
Structures Comprising a Single Reinforcing Layer
~ he following examples illustrate modification
technigues by which singly reinforced flooring
structures may be m~dified in situ.
A foam struc~ure comprising a singl~e
reinforcing layer and having a total thickness of 0.096
inch is prepared using the foamable plastisol described
in Example 2. A layer of plastisol approximately 15
mils thick is applied to a release carrier and a
non-woven glass fiber mat having a basis weight of 35
grams per square meter (Identification No. SH 35/6 from
Manville Corporation) is embedded in the wet plastisol.
The plastisol containing the embedded glass mat is then
gelled at 280 F for one minute. Upon cooling, a layer
of plastisol 32 mils ~hick is placed on the gelled sur-
face and the composite structure is fused a~ 430 ~ for
2.5 minutes. The resulting structure has a basis weight
of 2.8 pounds per square yard. The bending stiffness is
measured to be 0.330 inch-pounds and the relaxed
compressive stiffness is measured to be 1074 ppiow, both
measurements being made as hereinbefore described.
To illustrate the appli~ability of this
process, a curve is generated by arbitrarily selecting a
subfloor dimensional change of 0.0013 and then selecting
a targe~ critical buckle strain of 0.0015. By assigning
E the value 0.0015 and Q the value of 2.8 pounds per
square yard, and then varying the bending stiffness, Mw,
between 0 and 9 inch-pounds while varying the relaxed
compressive stiffness, K, between 0 and 10,000 ppiow, a
curve of constant critical buckle ~train i5 generated
tFIG. 15). From the curve, it is seen tha~ for a
structure having a bending stiffness of 0~330
inch-pounds, a relaxed compressive stiffness of 245
5 ppiow would be required. Thus, if the measured relaxed
compressive stiffness values are greater than 245 ppiow
the modified structures would not meet the target
~ritical buckle strains whereas, if the measured relaxed
,:
n
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- 41 - ~FM-7168
compressive stiffness values are equal to or less than
this figure, acceptable critical buckle strain values
would be obtained.
The utility of this approach may be seen from
Examples 9-13 in which the above control sample is
modified in various ways. A comparison of the modified
ppiow values indicates whether the modification would be
sufficient to give a product with a suitable critical
buckle strain.
Example 9
This example illustrates a series of in situ
modifications performed in a continuous pattern
according to the design illustrated in FIG. 12. In all
instances, the squares are cut in the indicated
dimensions and the mortar line (the distance between the
cut squares) is forme~ in the indicated dimension. The
column entitled Square Area indicates the percentage of
the total area which has been isolated from the
continuum of reinforcing by cutting. ~he measured
bending stiffness values and relaxed compressive
stiffness values are indicated for each modification.
The acceptability of each modification to provide a
suitable critical buckle strain is also indicated.
It is noted that regardless of the severity of
the modification, the bending stiffness values tend to
vary only slightly from the originally measured value.
~his is true in virtually all instances and indicates
that the target relaxed compressive stiffness value
which is originally estimated from the curve using the
measured bending stiffness value will also remain
e3sentially the same~
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Example 10
This example illustrates a series of
discontinuous pattern examples cut as illustrated in
FIG. 14.
Measured
Distance Relaxed
Separating Compressive Acceptable
Lines of Stiffness Modification Bending
Sample Cutting (Lbs/in of y ~ yes Stiffness
No.(inch) width) n = no(In.-Lbs.)
A 1/4 ~64 y .298
1~2 153 y .3?6
C 3/4 202 y .31~
D 1 202 y .330
.
Example 11
This example illustrates the mechanical
punching of a sample to internally disrupt the
reinforcing layer. A wire grid consisting of wire
having a diameter of 0.025 inch, the wires being
disposed 1/2 inch apart, is pressed into the sample
using a flat press and sufficient pressure to cause
disruption of the reinforcing layer. Disruption is
verified by taking a portion of the sample and
dissolving the plastic material in tetrahydrofuran.
Although the reinforcing layer is not completely
separated into square elements, onl~ a few fibers remain
to connect the elements together. The relaxed
~ompressive stiffness is 214 pounds per inch of width.
These results indicate that the sample ~ not as
30 significantly modified as a hand cut example (such as
Example 10), but it is modified sufficiently to be
acceptable.
~xample 12
This example illustrates external mechanical
modification using the prismatic surface described in
,~
12~0066
- 44 - L~M-7168
Example 7. This surface is pressed into the sample to a
depth of about 0.030" and a piece of the san*le i8
dissolved in tetrahydrofuran to remove the polymeric
material. Examination of the remaining glass fabric
shows that it has been deformed or dented, but not cut,
by the external modification. The relaxed compressive
stiffness is found to be 524 ppiow which indicates that
the samp~e will not have a suitable critical buckle
strain. When compared to the unmodified control
structure, a drop in the relaxed compressive stiffness
of the sample of about 50% is noted. This illustrates
how samples may be internally modified by compression
without causing actual separation of the reinforcing
layers. This observation has significance because it
indicates that encapsulated glass structures may be
physically modified in situ without adversely affecting
the structural inte~rity of a product.
Example 13
This example illustrates a modified continuous
pattern prepared according to the design illustrated in
FIG~ 13. The pattern is symmetrical and distances C-C,
D-D and E-E are all 1/4 inch~ The relaxed co~pressive
stiffness ~easured for this structure is 287 ppiow,
indicating that its critical buckle strain has been
dramatically improved, although it has not been improved
enough for this structure to meet the target critical
: : buckle strain of 0.0015. ~evertheless9 this result is
: quite favorable, especially when compared to the results
~ obtained for structures which have been modified by
; ~ 30 ~ther means.
As an example, the isol~ted sguare area of
: : ~ this sample is 41%. The isolated square area of a
sample cut according to example 9~ iQ 45%, yet the
relaxed compressive stiffness values are 401 ppiow for
that sample and 287 ppiow for the present sample. Thus,
in this instance, the modified continuous pattern is
superior.
our invention is not restricted solely to the
` ~LZ~6~'
-- 45 - LFM-7168
~escriptions and illustrations provided above, but
encompasses all modif ications envisaged by the following
claims .
~ '
: ' .
