Note: Descriptions are shown in the official language in which they were submitted.
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REINFORCEMENT FOR WALL SYSTEMS
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a fabric for reinforcing
stucco layers on walls, particularly on foam insulation
board on walls. The fabric has high strength, a soft
hand and alkali resistance. The fabric is resin-
bearing, made by weft insertion warp knitting, and
takes the form of a grid with openings between the
strands. The present invention also relates to a
method of making such reinforcement fabric, to a method
for reinforcing such wall systems, and to a wall
segment that utilizes the novel reinforcement disclosed
herein.
Description of the Related Art
A popular method of constructing walls comprises a wall
system in which a rigid plastic foam insulation board
is bonded to a concrete or other wall. The insulation
board is covered with a layer of reinforcement fabric
imbedded in a stucco or stucco-like material. The
fabric may be initially attached to the insulation
board mechanically with staples, nails, screws or the
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like. Alternatively, the fabric may be attached to the
insulation board by means of an adhesive spread onto
the insulation board. The stucco-like material, which
is often referred to as a base coat, is typically a
polymer modified cement containing for example Portland
cement and an acrylic or other polymer or copolymer.
During fabrication of the wall system, the fabric is
buried in the stucco-like material. The openings in
the fabric permit the stucco-like material to be pushed
through the fabric and contact the insulation board.
The stucco-like layer with reinforcement fabric buried
in it may range from about 1/16 inch to 1/4 inch thick.
Finally, a finishing coat is usually placed on top of
the base coat to provide, among other things, better
appearence and perhaps better weather resistance.
In such wall systems a wall segment may be prepared
either in situ on the outside of a building or in the
form of prefabricated panels.
A primary purpose of the reinforcement fabric in these
systems is to provide the wall with impact resistance
for durability. The reinforcement fabric must,
however, have several performance and application
requirements: (1) the reinforcement should be
5 economical; (2) the reinforcement should be as light in
weight as possible; (3) the reinforcement should
greatly increase the impact resistance of the wall
system; (4) the reinforcement should provide some
resistance to shrinkage cracking, which occasionally
10 occurs in, for example, polymer modified cement stucco
materials; (5) the fabric should confer vibration
resistance to the wall; (6) performance of the
reinforcement should not deteriorate significantly over
an extended period; (7) for purposes of installation,
15 the reinforcement should have applied thereto a resin
which gives the reinforcement a "hand" or "limpness" to
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conform to changes in the profile of the wall (for
example, at corners or bends), but the reinforcement
should not be so limp as to "bunch up" or fold during
trowelling of stucco thereon, nor should resin on the
reinforcement be so soft that the fabric sticks to
itself on the roll before installation (a phenomenon
known as "blocking"); and (8) the reinforcement must
have enough integrity to prevent distortion or
dislodging of the yarns during handling and covering
with stucco or stucco-like material.
Typically in the prior art, coated fabrics have been
used as the reinforcement in wall systems, but these
fabrics have been woven fabrics, manufactured using
standard weaving technology and a conventional weave,
such as a plain weave with looper yarns, hurl leno
weaves and leno weaves. Non-woven scrims of the kind
held together solely by adhesive resin have also been
used, but to a lesser extent. Leno weave is a weaving
process in which warp yarns are arranged in pairs and
fill yarn is shot straight across the fabric as in a
plain weave, but the warp threads are alternately
twisted in a left hand and right hand direction,
crossing before each pick is inserted. Examples of the
prior art fabrics are shown in Figs. 2 through 4. An
example of a leno weave is shown in Fig. 2. An example
of a hurl leno weave is shown in Fig. 3 and an example
of a plain weave with looper yarns is shown in Fig. 4.
These prior art reinforcement fabrics have typically
been composed of glass yarn or roving wherein the
individual warp yarns are generally lighter in weight
and weaker in strength than the weft yarn or roving.
In this way, the strength of each pair of warp yarns is
comparable to that of the individual weft yarns or
rovings.
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Such conventional reinforcements are generally referred
to as "scrim" in U.S. Patent 4,522,004, "woven glass
fiber scrim" in U.S. Patent 4,525,970, or "open-weave
mesh" in U.S. Patent 4,578,915.
We have discovered, however, that it is possible to
achieve results comparable to those achieved by the
prior art but using significantly less weight of yarn
in the fabric, with consequent economies and reduced
weight in the final wall. Alternatively, with the
reinforcement of our invention, at comparable weight
and cost, one is able to achieve greater strength,
durability and impact resistance.
Accordingly, it is one object of the present invention
to produce an improved fabric for reinforcing wall
systems.
It is another object to reinforce a wall system and to
provide a wall segment that utilizes the improved
fabric of the present invention.
These and other objects that will become apparent may
be better understood by the detailed description
provided below.
SUMMARY OF THE PRESENT INVENTION
The present invention relates to a new reinforcement
fabric for wall systems, to a method of making that
reinforcement, to a method for reinforcing walls with
that reinforcement, and to wall segments made with that
reinforcement. In making the reinforcement, a first
set of substantially parallel yarns running in a first
direction, and a second set of substantially parallel
yarns running in a second direction, are arranged in an
overlying relation at a substantial angle to one
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another. The first and second sets of yarns are
affixed together by weft insertion warp knitting
loosely with affixing or tie yarn to form an open grid
fabric. A polymeric resin is applied to the yarns at a
level of 10 to 150 parts dry weight of resin to 100
parts by weight of the fabric. That is, resin is
applied at 10$ to 150$ DPU (dry-weight pick up). The
resulting reinforcement is a high strength, soft hand,
alkali resistant, resin-bearing open grid weft inserted
warp knit fabric including first and second sets of
substantially parallel yarns affixed together at a
substantial angle to one another by loosely tensioned
affixing yarns and the resin.
The present invention includes securing the
reinforcement to a wall and applying a coating of a
stucco-like mixture to fill openings in grid, and cover
the grid. The invention may be used in situ or in
prefabricated wall segments. In a wall segment the
invention may be imbedded in a stucco-like coating
mixture and combined with a rigid insulation board. In
this embodiment, the mixture and reinforcement are
affixed to the board. "Stucco" is used in this
specification to include any stucco-like material or
coating such as polymer modified cements currently used
in the reinforced wall systems referred to above.
The fabric of this invention exhibits superior
performance and ease of application at a lower cost as
compared to prior reinforcements for wall systems.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of fabric utilized in
the present invention.
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Figure 2 shows a perspective view of a leno woven
fabric according to the prior art.
Figure 3 is a perspective view showing a hurl leno
woven fabric according to the prior art.
Figure 4 is a perspective view showing a plain woven
fabric with looper yarns according to the prior art.
Throughout the Figures the same reference numerals
designate the same or corresponding parts.
DETAILED DESCRIPTION OF THE INVENTION
The fabric of the present invention is depicted in
Figure 1. The fabric 100 essentially occupies two
planes. The warp or machine direction yarns or rovings
10 occupy and define one plane, and the weft or cross
machine direction yarns or rovings 20 occupy and define
a second plane. These yarns are tied together in a
knitting process in which the knitting or tie yarn 30
is a lightweight flexible yarn wrapping the warp yarns
and capturing the weft yarns. Figure 1 is not intended
to show precisely the path of knitting yarn 30; the
exact paths possible, which will vary depending on the
machine and stitch used, are well known to those of
skill in the art. The fabric 100 is further locked
together by a polymeric resin 40. The particular resin
40 must be chosen for compatibility with the particular
yarns, and with the finishes on those yarns, and for
the best properties in the final wall system, but those
of skill in the art can determine which resin is best
for a given yarn and finish. The two-plane
construction of the reinforcement of this invention
minimizes the crimp or bending of the yarns or rovings,
which is an advantage over prior art reinforcements in
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which the yarns are kinked or crimped as they zig-zag
between the three planes involved in those prior art
constructions. In addition, minimal crimp allows
better penetration of the polymeric resin 40.
An example of the fabric construction of the present
invention is a weft inserted warp knit product having
approximately six ends per inch in both the warp and
weft directions, but possibly as few as 1.5 ends in
each direction and as many as 12 ends in each
direction. Preferably, the ends of the first and the
second sets are arranged in each set at an average of 3
to 10 ends per inch.
As used herein, the term "yarn" refers to light weight
bundles of filaments, usually having some twist, as
well as to rovings, which are heavier, sometimes
approximately ten times heavier per unit length than
yarn, and have substantially no twist. The term "ends"
refers to a single yarn or a group of yarns combined
together to make a single strand in the final grid.
The warp and weft yarns of fabric 100 may have a linear
density of 33 to 2000 Tex (grams per thousand meters).
Preferably, the yarns of the first and the second set
have a linear density between 100 and 2000 Tex and most
preferably, 130 to 400 Tex. The weight and strength of
the yarns selected depends on the performance range
desired. The features of the particular yarn,
including filament diameter and the type and level of
chemical sizing on the yarn before knitting, may be
selected by those of skill in the art in accordance
with the desired properties for the particular end use.
Although fiberglass yarns are preferred, others such as
nylon, aramid, polyolefin and polyester may be used in
various combinations.
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The ends 10 of the first set and the ends 20 of the
second set are arranged in an overlying relation and at
a substantial angle to one another. This angle may be
on the order of ninety degrees. However, it is not
necessary to orient the ends of the first and second
sets orthogonally. Rather, this angle may vary between
sixty and one hundred twenty degrees or more.
The knitting yarn 30, which is typically a low weight
polyester tie yarn in the linear density range of 40 to
200 dTex, may preferably be knit in a chain stitch.
Other suitable tie yarns may be nylon, olefin, acrylic,
modacrylic, rayon, acetate, polyvinyl chloride,
polyvinyl dichloride, or polyvinyl difluoride.
Preferably, knitting is done with a chain stitch and a
loose tension on the knitting yarn. A preferable loose
tension for fabrics with a preferable number of ends
per inch (4 to 8 ends in cross-machine direction) and
with a preferable weight of structural yarns (130 to
400 Tex), is at least about 3.1 yards of knitting yarn
for every one yard of ends 10 in the warp direction. A
standard tension with this kind of fabric is about 3
yards of knitting yarn for every one yard of ends 10 in
the warp direction. If one increases this ratio to 3.1
to 1 the result is essentially no tension, or as little
tension as possible without creating open loops in the
knitting yarns, which may occur at a ratio of 3.3 to 1.
This loose knitting is believed to be important because
it permits the polymer resin when applied in later
processing to penetrate the warp yarn more uniformly
and deeply. Breakage of warp yarns is frequently a
source of failure in these wall systems.
The fabric 100 typically has applied to it a polymer or
polymer blend resin 40 to confer properties to the
fabric such as stability, alkali resistance, and
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strength improvement to the reinforcement. The glass
transition temperature of the resin is important to the
present invention for providing the desirable soft hand
of the fabric. A soft hand is preferred. However, an
overly soft fabric has the tendency to stick to itself
on a roll. This is known as blocking. In the present
invention, for any given weight of yarn "hand" is
primarily determined by the glass transition
temperature characteristics of resin applied to the
reinforcement. The glass transition temperature of the
resin of the present invention is typically in the
range of -30°C to +20°C, but may extend from -40°C to
+40°C. The resin selected is preferably flame
retardant. It is also preferable to use alkali and
water resistant resins, such as those consisting of
polyvinyl chloride, styrene butadiene rubber, acrylic
and styrene acrylate polymers and copolymers.
The resin 40, when applied in or above the preferred
range of 25 to 40$ dry weight pick-up, increases
integrity of the fabric by preventing yarn-to-yarn
slippage and assists the fabric in resisting alkali
damage. The resin may be applied to the fabric by
coating or dipping techniques. In standard, woven
reinforcement fabrics of the prior art, resin is
applied at the rate of about 15 to 20% dry weight pick-
up ("DPU"). In standard, non-woven reinforcements
DPU's of 100 to 120% are typically used because the
resin is required to hold the fabric together. In the
reinforcement of the present invention, the most
preferred resin amount to use is 25 to 40 DPU, and 10
to 80 DPU is less preferred. We have found that
resins, when used in the preferred range (i.e., about
double the amount used on standard woven
reinforcements), improve impact resistance by spreading
the force of the impact out among adjoining structural
fabrics. Weights of resin from 80 to 150 DPU are also
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possible, though economics may become a factor when
such large amounts are used.
As will be appreciated by those of skill in the art,
one may adjust the various process variables, both in
knitting and in applying resin, to alter the
performance and processability of the final fabric.
For example, using a loose tie yarn tension in the
knitting process and using contact drying following the
resin application process, will render the fabric
thinner than otherwise and improve the "hand" or
suppleness of the fabric.
The present invention has several advantages over
current reinforcement fabrics, as shown by the
following table:
Property ; Present Invention ;Leno ;Hurl Leno ;Nonwoven
Ex. #1 Ex. #2 ;Woven ;Woven ;Scrim
Relative ; 0.85 1.0 ; 1.0-1.4 ; 1.2-1.6 ; 1.2-1.8
Cost ' ' ' '
Impact ; 12-16 32-36 ; 12-16 ; 28-32 ; 28-36
(in-lbs.) ' ' ' '
Ends/In, ; 6 6 ; 6 ; 6 ; 5.5
MD
CD ; 5.5 5.5 ; 6 ; 5 ; 5.5
Area Wt. ; ; ; ;
(g/mz) ; 170 180 ; 160 ; 200 ; 240
Tensile MD ; 200 275 ; 170-200 ; 280-300 ; 250-290
(lbs/in) ; 230 315 ; 230-260 ; 300-320 ; 280-320
CD
Hand ; SOFT SOFT ; SOFT ; SL. FIRM ; SL. FIRM
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Block ; GOOD GOOD ; GOOD ; GOOD ;FAIR-GOOD
Resistance ' ' ' '
"MD" refers to machine direction, i.e., warp. "CD"
refers to cross-machine direction, i.e., weft.
"Impact" refers to the pounds of impact the wall system
will resist without significant denting in a standard
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test. "Area weight" is the weight of reinforcement
yarns per unit area. "Ends/In" refers to the number of
ends per inch; in leno, hurl leno and some non-woven
fabrics, a single end and may consist of two or more
yarns.
As shown by an analysis of the above results, the
reinforcement fabrics of the prior art are inferior in
at least one of the attributes noted above. Their
designs may be slightly altered to improve one
property, but it occurs at the expense of another. For
example, the hand of the nonwoven scrim may be improved
from slightly firm to soft (by using a softer coating),
but only at the expense of block resistance. Also, by
comparison, the fabric labelled "hurl leno woven" is
stronger than "leno woven". However, the cost and the
stiffness (hand) of the fabric must be increased as a
compromise to so increase strength.
The principal factor affecting both strength and cost
is the weight of the yarn and the number of yarns per
inch, which together result in an "area weight." The
difference between the fabric labelled as present
invention Example #1 and Example #2 is in the weight of
the yarns used. The heavier the yarn, the stronger the
fabric, albeit at increased cost. Within any one
construction type, those skilled in the art will find
that additional processing variables may be altered to
improve performance, but these additional variables do
not have as much influence as the particular
construction used. These additional variables include
the filament diameter, the sizing present on the yarn
before weaving or knitting, and the type, amount, and
degree of penetration of the resin applied to the
fabric after it is formed. We have found that these
factors vary among the various construction types in
the magnitude of their influence on impact resistance.
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The processes and products described herein are
representative and illustrative of ones which could be
used to create various reinforcement fabrics and wall
segments in accordance with the instant invention. The
foregoing detailed description is therefore not
intended to limit the scope of the present invention.
Modifications and variations are contemplated, and the
scope of the present invention is intended to be
limited only by the accompanying claims.
