Note: Descriptions are shown in the official language in which they were submitted.
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Background of the Invention
Field of the Invention
The invention relates to a method for producing a
smooth dimensionally stable, low-porosity fiber sneet material
particularly suitable as a backing for thermoplastic vinyl resin
composition surface coverings.
Description of the Prior Art
Glass fiber webs having good dimensional stability as
well as superior strength characteristics are described in U.S.
Patent 3,622,445. Also, porous, self-supporting, mica-containing
sheet materials are disclosed in U.S. Patent 3,523,061, and the
production of sheet-like products from siliceous stock material,
such as glass fibers, ceramic flakes, glass flakes, mica, and
the like, are disclosed in U.S. Patent 3,005,745.
Summary of the Invention.
One of the conventional films utilized as a backing for
thermoplastic vinyl resin composition decorative surface
coverings, such as floor coverings, commonly in use is a beater-
saturated asbestos fiber felt, such as that described in U.S.
Patent 2,759,813. The use of such felts has proven quite
successful in that the backings are essentially moisture
impervious, and products formed on such backings may be utilized
both on or below grade where moisture conditions might prove
deleterious to felt backings based on cellulose or wood fibers
or other organic materials which might be adversely affected by
moisture.
In recent years, the utilization of asbestos in
various products has become suspect. Considerable effort has
gone into the design of products which would be equivalent in
structural and physical properties but in which the use of the
asbestos fibers ~ould be eliminated. Glass fiber webs, being
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strong yet flexible, rot resistant and dimensionally stable,
would appear to be suitable and, for example, the glass fiber
webs described in U.S. Patent 3,622,445 would appear to possess
the desired properties for use as replacements for the beater-
saturated asbestos fiber felts such as that described in U.S.
Patent 2,759,813. Typically, however, glass, organic fiber
felts, are of an open, porous nature due to the manner in which
the "toothpick"-like fibers orient and pack themselves.
I have discovered that a backing sheet may be formed which
is of a low porosity and which is smoother than conventional
glass fiber-containing felt. This sheet is formed by incorpora-
ting a significant amount of mica flakes in the slurry composi-
tion utilized for forming the sheet. Generally, I prepare a glass
fiber containing slurry of low consistency wherein the solids
consist essentially of, based on 100 parts by weight glass fibers,
3 to 15 parts by weight organic fibers, 30 to lOQ parts by weight
mica flakes, and 5 to 20 parts by weight organic binder, preferably
in the form of heat reactable fibrous material. This slurry is
sheeted out on conventional paper-forming equipment such as a
Rotoformer (Sandy Hill Corporation) or an inclined Fourdrinier,
excess water is drained and the resultant sheet material is dried
and the binder set. As a last step, the sheet thus formed is
saturated with melamine, styrene-butadiene rubber latex which may
be filled with conventional fillers such as limestone and which
may be pigmented with conventional pigments such as titanium
dioxide.
Thus, in accordance with the present teachings, a method is
provided for making a smooth, dimensionally stable mica-filled
glass fiber sheet which has a low porosity which comprises pre-
paring an aqueous slurry having a pH below about 4.0 and consist-
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ing essentially of glass fibers and, based on 100 parts by
weight of glass fibers, from 3 to 15 parts by weight organic
fibers, 30 to 100 parts by weight mica flakes and 5 to 20 parts
by weight binder. The slurry is deposited onto a moving screen
and excess water removed to form a water laid sheet and the sheet
is dried to set the binder.
In accordance with a further embodiment, a mica filled glass
fiber web of low porosity is provided which consists essentially
of 100 parts by weight of low alkali content glass fibers which
have diameters in the range of 3 to 15 microns and an average
length of ~ to ~ inch, from 3 to 15 parts by weight synthetic
organic fibers of an average length of ~ to ~ inch and deniers
between about 1 and 6, 30 to 100 parts by weight mica flakes of
a size range between about 10 and 100 mesh, and 5 to 20 parts
by weight binder.
DESCRIPTION OF THE PREFERRED EMBODIME~TS
In accordance with this invention, a water slurry is
first formed by adding glass fibers, synthetic resin fibers,
small amounts of binder such as poly(vinyl alcohol) fibers
and mica flakes, together with a conventional dispersant such
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as sodium lauryl sulfate. Generally speaking, the percent by
weight of solids in the slurry is maintained at about 0.75~,
preferably between 0.5% and 1.0%. This slurry is maintained
at a pH of from about 2.5 to 3.0 by the addition of sulfuric
acid. Prior to flowing the slurry out onto the wire of the
paper-forming machine, it is diluted to a consistency between
about 0.01% and 0.05%, or usually about 0.02%. A distinct
advantage of the furnishes of my invention is that they pro-
vide for rapid drainage of water on the forming machine, allow-
ing for relative rapid forming rates. As water is drawn from
the furnish on the wire of the Rotoformer or inclined
Fourdrinier, a web forms which, on further draining, is then
dried under sufficient heat to activate the binder and form a
self-sustained sheet of about 3 to 7 ounces per square yard.
The dried sheet is thereafter saturated with a resin such as
a latex formed from a styrene-butadiene rubber latex to which
filler may have been added, together with small amounts of
pigment, if desired, and the saturated sheet is thereafter
cured to form the desired backing material.
In forming the slurry, we have found the glass fibers
of high strength formulations low in alkali and having a
diameter of 3 to 15 microns and generally an average diameter
of about 6 microns and an average length of approximately
1/4 - 1/2 inch may be utilized. Typically, the fibers are
produced from alkali-free E glass. Such fibers generally
have tensile strengths of about 500,000 p.s.i. at 75F. and
moduli of elasticity of about 10.5 x 106 p.s.i.
Synthetic organic fibers, such as polyester fibers,
poly-propylene fibers, acrylic fibers, acetate fibers, and
other commercially available fibers such as poly(vinyl chloride)
and polyamides such as nylon are suitable for the organic
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fiber portion of the furnish. The synthetic organic fibers
utilized in forming the slurry preferably have an average
length of from about 1/4 - 1/2 inch and deniers between about
1 and 6.
Although it will be readily evident that any typical
organic binder commonly used in paper making may be used, we
prefer the use of poly(vinyl alcohol) fibers since they seem to
assist in good sheet formation.
The mica flakes suitable for use in the present
product are of 20 to 100 mesh (U.S. Standard Sieve). Preferably,
the mica flakes are of 60 to 100 mesh.
All of the above ingredients are dispersed in water
to form a slurry or furnish by adding up to 2% by weight, based
on the weight of the solids, of a surface active dispersant,
such as sodium lauryl sulfate or trimethylene diamine.
Preferably, the slurry is maintained at a pH below about 4.0
and preferably from about 2.5 to 3.0, and-the pH is controlled
by metering into the slurry sufficient sulfuric acid to maintain
it at the desired pH.
Preferably an aqueous melamine-synthetic rubber latex
is utilized for saturating the paper and contains a styrene-
butadiene rubber latex, a water emulsion containing about 50%
by weight solids, and melamine in a weight ratio of styrene-
butadiene rubber to melamine of from about 6:1 to 10:1 dry
solids. This latex is preferably unfilled, although convention-
al inorganic fillers such as limestone may be added together
with, if desired, small amounts of conventional inorganic
pigments, for instance, titanium dioxide. Other latexes such
as the acrylics and acrylonitrile and even water solutions of
thermosetting resins such as phenolics and urea or melamine
formaldehydes might also be used although the melamine-styrene-
butadiene rubber latex is preferable for resilient flooring
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applications.
In accordance with my process, the paper sheet as it
comes from the forming machine is transferred to can driers
where drying takes place simultaneous with the conversion of
the poly(vinyl alcohol) fibers to a binder. This action takes
place since the poly(vinyl alcohol) fiber dissolves in the hot
water, formed on contact with the drier, at approximately 80C.
and thus coats the glass fibers so as to yield a sheet
weighing between 3 to 7 ounces per square yard~ which is of
sufficient strength to pass through a sizing press. At the size
press, the latex saturant is added to a glass sheet with
saturation being carried out to the extent of from about 30%
to up to 100% pick-up dry weight of latex solids based on the
weight of the glass paper. After the size press, the
saturated sheet is then dried, wound up on a core, and removed
to a slitting operation to trim to the desired width.
The following example will illustrate a specific
embodiment of this invention.
An aqueous slurry is prepared by mixing fibers and
mica flakes with water at a consistency of about 0.75% by
weight solids. ~f the solids: 100 parts hy weight are glass
fibers having an average diameter of about 6 microns and an
average length of about 1/4 inch manufactured of a high strength,
alkali-free glass (E~glass); 4.0% by weight are synthetic
polyester fibers having a denier of about 1.5 and a length of
about 1/4 inch; 15.8 percent are poly(vinyl alcohol) fibers
having a denier of about 1.0 and a length of about 1/4 inch
and the balance of the solids are 70.3 parts by weight mica
flakes (60 mesh, U.S. Standard Sieve). About 1.0 part by
weight sodium lauryl sulfate is added to aid in dispersing the
solids in the slurry. Sulfuric acid is metered in to maintain
the pH of the dispersion at about 2.5. A conventional
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dispersion tank is used for slurrying and to contain the pre-
pared slurry. The slurry is pumped to a machlne chest just
prior to sheet formation and is further diluted to a solids
level of about 0.02~ by weight just prior to flowing the slurry
onto the paper making wire of a rotary paper making machine.
In forming the glass fiber mica filled sheet, the
sheet is transferred from the forming wire to can driers where
drying takes place simultaneously with conversion of the
poly(vinyl alcohol)fibers to a binder. Completion of the drying
on the first set of can driers yields a sheet which is of
sufficient strength to pass through a sizing press.
At the size press, the sheet is saturated with a
melamine modified synthetic rubber latex having 5n% by weight
solids of a styrene-butadiene rubber of approximately 50% by
weight styrene. Sufficient melamine is added to give a weight
ratio of styrene-butadiene rubber tomelamine of approximately
6:1. At the size press, the latex is added to the mica filled
glass fiber sheet with saturation being carried out to the
extent of about 66% pick-up dry weight of latex based on the
weight of the mica filled glass fiber paper. The saturated
sheet is then dried at 300 to 320F., wound up on a core, and
removed to a slitting operation to trim to the desired width,
in this case a width of 76 inches. The breaking strength of
the saturated sheet is about 96 pounds per inch of width at
74 F. and about 61.5 pounds per inch of width at 350F. It has
an air flow resistance of 35 cubic feet per minute per square
foot under a differential pressure of 1/2 inch of water when
measured in accordance with ASTM D-726-58.
To show the effect of varying mica content to glass
fiber content, a series of post saturated mica modified glass
fiber hand sheets were prepared and tested in accordance with
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ASTM D-726-58. The glass, polyester, and poly(vinyl alcohol)
fibers and mica flakes used were the same as in the example set
out above, with the exception that 20 mesh mica flakes were
employed. Each handsheet was saturated to about a 66~ pick-up
dry weight o~ latex based on the weight of the mica filled
glass fiber handsheet using the above described melamine/SBR
latex. As clearly indicated by the results set out in the table
below, the level of mica is critical to porosity.
Table I
Air Flow Resistance
Parts by Weight Mica (Cubic feet per minute
Based on 100 Parts per square foot -
By Weight Glass Fibers1/2 inch water column)
0 83.2
54-3
45.8
31.1
29.9
67 20.9
100 6.76
Sheets having satisfactory porosity lie at mica
levels between 30 parts by weight mica flakes and 100 parts
by weight mica flakes per 100 parts by weight glass fibers.
Such sheets prevent liquids such as plastisols and organosols
from being absorbed during plastic sheet processing typically
utilized in resilient flooring manufacture. The sheets also
minimize adhesive wicking during installation.
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