Note: Descriptions are shown in the official language in which they were submitted.
7~i753
se 1218
C~POSITE I~ERL~S
AND METffCD FCR T~E
PREPARA~N ~;~
'
~E3NIC~L F~D
This invention pertains to non-wcven, fibrous oomposite materials in
sheet form which are particularly useful as dimensionally stable backings and
interliners for surface oovering laminates. A method of producing these sheets
and laminates is also disclosed.
Background of the Invention
Laminated surface ooverings for walls, ceilings, floors and furniture,
such as counter, table and desk tops have been known for many years. These
ooverings are typically formed of polyvinylchloride as a homopolymer or
oopolymer, or scme other resinous material such as polyurethane. To supPlement
the mechanical strength of the resins during processing and in the final
product, such surface coverings generally incorporate a fibrous backing or
interliner. m e fibrous material employed for many years has been asbestos,
which has set a standard for stability, strength and other phy~ical and
chemical properties, including the ability to retain dimensional stability over
a wide range of temperature and isture conditions. However, as~estos has
~ ~ -2- 1Z7~753
been linked to serious health hazards and its use has been banned or severely
limited in many countries.
A long list of fibrous materials have been suggested to be used alone
or in combination in an effort to replace asbestos in backing and interliner
sheets employed for this plrpose. The various fibers have included
polyolefins, polyesters, polyamides, or the like alone or in combination with
glass fibers and wccd pulp as well as other cellulosic fibers. To date, no
composite employing any of these fibers, individually or in ocmbination, has
been able to provide a replacement material equivalent to a ccmposite employing
asbestos fibers.
The use of cellulosic fibers, such as wood pulp, as the sole fibrous
component in the laminates and backing sheets has been suggested. However,
sheets incorporating only cellulose fibers are subject to marked
hygroe xpansivity. The resulting product is often dimensionally unstable and
swelling will often cccur in the sheet and in any laminated surface covering in
which the sheet is incorporated. A marked curl about the borders of the
laminate and buckling between the lateral margins will also occur, sometimes
resulting in the delamination of the backing sheet from the surface coverings.
To illustrate the significance of dimensional stability, surface
coverings must be ca~able of use in a wide variety of climatio conditions,
particularly humidity and temperature. m ese surface ooverings are applied to
walls, floors, and other substrates, using adhesives. m e alignment and
abutment of contiguous segments of surface covering must remain in registry
after application. Any expansic~ or contraction of the backing sheet may
result in delamination fro~ the surface ooating which is ty~ically a stable
vinyl layer. In extreme cases, this may result in the separation of the
laminate from the surface of the floor or wall to which the laminate has been
applied.
~ _3_ l;Z 7~j 753
A method in which standard papermaking apparatus xuld be employed in
the manufacture of a material for use as a backing sheet or interliner that
w~uld be dimensionally stable and substantially resistant to delamination wDuld
be particularly useful. If, in addition, the material aLso exhibited a high
internal bond and did not beocme brittle and, further, exhibited the physical
properties of a material incorporating asbestos fibers, it w~ld also represent
a significant step forward in the art.
Objects of the Present Invention
It is a primary object of the present i~vention to prcvide non-woven,
fibrous ccmposite materials in sheet form which are useful as dimensionally
stable backings and interliners for surface covering laminates.
It is a further object of the present invention to provide a method
for the manufacture of non-woven, fibrous oomposite materials useful as
dimensionally stable backings and interliners for surface covering laminates
which method emDlovs standard papermaking apparatus.
m ese and other objects of the present invention will become obvious
to those skilled in the art when considered in view of the follcwing detailed
description and claims.
According to one embodiment of the present invention, there are
provided non-woven, fibrous composite materials in sheet form which are
prepared from:
i) a mixture of fibers oomprising
a) a cellulosic fiber oomponent comprising predominately
softwood pul~ brushed or refined to a degree of external and
~4~ lZ7~753"
internal fibrillation characterized in that the fibers, in
the form of a T~PPI Standard Ebndsheet, have a breaking
length of at least about eight kilometers (8 km) and a
: density of at least about sixty-seven one-hundredths of a
gram per cubic centimeter (0.67 g/cc), and
b) a non-cellulosic fiber ~.wu~ent cul~rising at least one
water-dispersible fiber chosen from the group consisting of
glass fibers, rock wool and other mineral fibers, and
preferably glass fibers;
ii) a mixture of acrylic resins ~.wrising
a) a soft resin ~"~nent ccmprising an anionic, water-
insoluble soft acrylic binder resin, which resin has a glass
transition temperature of from -30C to -10C, and
b) a hard resin component comprising an anionic, water-
insoluble hard acrylic binder resin, which resin has a glass
transition temperature of from 20 & to 40C;
iii) a filler component comprising at least one particulate, anionic,
water-insoluble, inorganic filler;
. iv) a first flocculant oomponent oomprising a water-soluble cationic
organic wet strength resin flocculant; and,
v) a second flocculant component ccmprising an anionic organic
~ _5- ~Z76753
. flocculant in a sufficient quantity to adjust the electrokinetic
potential of the oombined ~ul~unents to from about -10 millivolts
to about +10 millivolts;
,
all of which are precipitated into a bonded relationship.
According to another embodiment of the present invention, there is
provided a process for the preparation of a non-woven, fibrous ccmposite
material which process comprises the steps of:
a) seFarately mixing together with at least a sufficient quantity of
water to form a first aqueous dispersion,
.
i) a cellulose fiber oomPonent oomprising predominately
softwcod pulp fibers, which fibers in the form of a I~PPI
Standard ~andsheet have a breaking length of at least eight
kilometers (8 km) and a density of at least sixty-seven one-
hundredths of a gram per cubic centimeter(0.67 g/cc), and
ii) a filler ~.4~ent comprising at least one particulate
anionic, water-insoluble inorganic filler;
b) mixing together with at least a sufficient quantity of water to
form a second aqueous dispersion,
i) a soft resin component ocmprising an anionic, water-
insoluble soft acrylic binder resin, which resin has a glass
transition t~mperature of from -30C to -10C, and
' ~ -6- 127~i753
ii) a hard resin comFonent ~u~urising an anionic, water-
~nsoluble hard acrylic binder resin, which resin has a glass
transition temperature of frcm 20qC to 40C;
c) mixing with at least a sufficient quantity of water to form a
third aqueous dispersion,
i) a ncn-ccllulosic fiber oomponent comprisin~ at least one
water-dispersible fiber chosen frcm the group consisting of
glass fibers, rcck wcol, and other muneral fibers,
d) preparing a first combined aqueous dispersion by ~lbining the
first aqueous dispersion prepared in step (a) with the second
aqueous dispersion prepared in step (b)
e) adding to the first combined aqueous dispersion prepared in step
(d), an excess of a first flocculant ~ ent co~prising a water-
soluble cationic organic wet strength resin flocculant;
f) preparing a seccnd oombined aqueous dispersion by combining the
first combined aqueous dispersion prepared in step (d) with the
third aqueous dispersion prepared in step (c)s
g) adding to the second oonbined aqueous dispersion prepared in step
(f) a second flccculant component comprising an anionic organic
flccculant in a sufficient quantity to adjust the electrokinetic
potential of said second co~bined aqueous dispersion to from
~ _7_ 1Z7t;75~
,.
about -10 millivolts to about +10 millivolts; and
h) precipitating substantially a11 of said resin components and
filler oomponent into a bonded relationship with said cellulosic
- .
- and non-cellulosic fibrous components.
. .
Brief Description of the Drawin~
The figure is a diagrammatic view of an apparatus illustrating the
method of the present invention.
Detailed Description of the Present Invention
The present invention provides non-wcven, fibrous composite materials
in sheet form which are particularly useful as dimensionally stable bac~ings
and interliners for surface oovering laminates. Also as noted above, the
composites are prepared from:
i) cellulosic fibers; and refined softwood pulp is preferred;
ii) non-cellulosic fibers; and glass fibers are preferred;
iii) inorganic fillers; and calcium carLJ.~ate is preferred;
iv) soft binder resins; and a soft acrylic resin with a glass
transition temperature of from -30C to -10C is preferred;
v) hard binder resins; and a hard acrylic resin with a glass
transition temperature of from 20C to 40C is preferred;
vi) water-soluble cationic wet-strength resin flccculants; and
~ -8- 1.;~7fj'~S~
.
polycaprolactone-epichlorohydrin resins and epichlorohydrin-
polyamide resins prodùced with capralactam are preferred; and
vii) anionic organic flocculants, and a polyorganoFhosph2te is
preferred.
Attention to the refining of the softwcod ~ulp, as measured by
breaking length and density, may well be critical to secure the internal
strength necessary to a satisfactorv backing sheet or interliner. To an
aqueous dispersion of suitably refined softwood pulp are~added a blend of
anionic binder resins, and an anionic filler. This dispersion is treated with
an excess amount of a water-soluble cationic wet-strength resin flocculant and,
in turn, introduced and thoroughly mixed together with an aqueous dispersion of
non-cellulosic fiber which is preferably ccmminuted fiber glass. In this
regard it has been found that dispersal of the fiber glass mav be facilitated
by the use of a cationic surfactant anti-static agent. Such an anti-static
agent assists in releasing the sizing agent typically present in oommercially
available glass fiber. An anionic organic flocculant is finally added to the
oombined dispersion, as necessary, to adjust the d ectrokinetic potential of
this ~ ined system back within the ran~e of from about -10 millivolts to
about +10 millivolts, and finally, substantially all of the binder resins,
filler, pulp and glass fibers are precipated into a bonded relationship.
The electrokinetic or "zeta" potential of the system may vary more
widely in the earlier stages of the process, and potentials of +20 millivolts
have been reoorded without adverse effect on the final product. However, the
zeta potential should be adjusted to within the range from about -10 millivolts
to about +10 millivolts before the final product oomposite material is
precipated and dried.
It is possible that the final addition, the anionic organic
-9- 1 ~7~753`
flocculant, may be obviated if the zeta potential is already within the
required range. Addition of the flocculant should in fact be avoided if it
would carry the zeta potential outside this range.
In the preferred embcdiment ~he material is precipated in sheet form,
and the sheet is carried into a standard paper making machine on a forming wire
or other support, where the liquid, which is primarily water, is drained away
and the sheet is dried. An optional size, preferably of the same hard acrylic
resin, may then be deposited on one or both siaes of the resulting sheet in a
manner well known to the art.
After the non-woven fibrous oomposite material has been fosm~d into a
sheet in this manner it may be further processed into a surface oovering
material. This is typically done by depositing one or mDre layers of vinyl
chloride polymers or copolymers in liquid form, preferably as a plastisol, and
gelling and printing the Folymer, then ooating the printed surface with a
transparent resinous wear-layer and heating to fuse the resins.
The figure is intended to be a diagrammatic view of an apparatus
illustrating the method of the present invention. This apparatus, shown
generally as (10) includes a plurality of mixing and holding tanks,
collectively referred to herein as the "wet endn (12) coupled with relatively
stanaard paper-making and dryin~ machinery, oollectively referred to herein as
~dry end~ (14).
In the wet end (12), an aaueous dispersion of a particulate,
anionic, inorganic filler (16) is prepared in a mixing tank (18) such as a
standard hydropulper known to the art.
The anionic, water-insoluble inorganic filler employed in the
preferred embodiment of the present invention is calcium carbonate. This
filler is co~mercially available in a grade in which the particles are
oonminuted to a particle size such that 100 percent of the particles will pass
~1
- 1 o 127~75;~
through a 60 mesh screen (using U.S. Standard Mesh sizes) and 96 percent of the
particles will pass through a 100 mesh screen. Another commercial grade which
is useful in the practice of the present invention has a distribution of
particle sizes such that 100 percent of the particles will pass t~rough a 12
mesh screen and 96 percent of the particles will pass through a 325 mesh screen
(44 microns).
Particularly preferred in the practice of the present invention is a
ccmmercially available grade of crushed limestone oontaining from about 96% to
about 98% calcium carbonate, about 1 percent M2qnesium oxide, about 0.1 percent
ferric oxide, a out 0.25 percent to 0.75 silica, and 0.2 Percent to 0.3 percent
alumina as well as traces of sulfur and phosphorus pentoxide on the order of
about 0.003 percent and 0.004 percent, respectively.
m e amount of anionic filler employed in practice of the present
invention will vary from about 20 percent to about 35 oercent on a dry weight
basis.
With further reference to the figure, agitation of a suitable quantity
of water and the filler is a~uamplished by some means, illustrated as (20) in
the Figure, to prepare a suitable dis~ersion. m is is often facilitated by the
addition of a defoaming agent and many such agents are known to the art. The
resulting dispersion is pu~ped by some means such as a pumD (22) through feed
line (24) into a dro~ chest (26). With continued reference to the figure,
anionic softwocd pulp fibers are refined to a high degree of internal and
external fibrillation as an aqueous dispersion in one or re refiners, shown
in the figure as (30), which is specially equipced with agitation means (32)
adapted to brush and fibrillate the pulP fibers. When suitably treated, the
a~ueous dispersion in the refiner (30) is transferred bv some means such
as pump (34) through feed line (36) into drop chest (26). To assure effective
dispersion and fibrillation, the ooncentration of pulp fibers in the refiner
-11- 1~7~i7S3
.
(30) should not normally exceed about 5 percent. Although operable within a
range of from about 0.S per~ent to S percent or more, a concentration of about
4 percent pulp is reoommended for ocmmercial purposes.
The term "consistency" as used throughout this specification and in
the claims which follow shall be used to refer to the dry weight proportion of
dispersed or dissolved materi~ls in aqueous dispersions or solutions,
respectively.
m e refining step is believed to be critical to the present ~nvention
and the primary objective of the refining step is the roughening of the wood
fiber surface, severing of the fibers al~l~ their lengths, and swelling of the
treated fibers. This treatment is referred to as external and internal
fibrillation as opposed to predominantly external fibrillation which includes a
cross-sectional chopping action which abbreviates the length of the fibers.
When properly fibrillated in order to secure the advantages of the
present invention, the wood pulp fibers should have a tensile strength,
expressed as breaking length in a TAPPI Standard ~andsheet prepared according
to TAPPI Method T-205 om-81, of at least 8 to 12 kilometers (km) at room
temperature, and preferably within the range of 10 to 12 kilometers (km). The
fibers should also have a density in such a Handsheet of from about 0.67 to
about 0.72 grams per cubic centimeter (gm/cc), and preferably from about 0.68
to about 0.70 gm/cc.
The wood pulp fibers emploYed in the process as thus described and
incorporating the particular tensile strength and bonding properties expressed
as breaking length and density, while retaining generally maximum fiber length,
have been obtained using a ~ouble Disc refiner, manufactured by the Beloit
Corporation~Jones Division, for large volume mill production. Small laboratorv
- -12- 127~i~753
control s~l~les and handsheets, can be advantageouslv prepared with a
laboratory Valley beater. The cross-sectional cho~ping of the fibers can be
minimized in the foregoin~ ref ners. Another desirable beater for use in the
practlce of the present invention is the Jones Bertrams beater.
Other suppliers of suitable production equipment in the United States
include: Bolton-Emerson; C-E Bauer, a subsidiary of Combusticn Engineering;
and the Sprout-Waldron Division of the Roppers Co., Inc.
Operative only with respect to some pul~ types, and therefore less
preferred refiners include the breaker beater of the hollander type, the
Hydropulper manufactured bv Black Clawson, Inc., Middletown, Ohio, the
Dynopulper and Vortex beater.
Typically, the pulp is initially received as a dry sheet that is
slushed, that is, dispersed and refined, in an aqueous medium. A refiner, such
as one of those named above, is em~loyed for this purpose, and the pulp is
treated for a sufficient period of time to obtain the desired properties. This
time will vary with the particular type of pulp ~mployed. The pulp is first
brought to a consistency of, from about 0.75 percent to about 5 percent,
preferably from about 2 percent to about 4 percent, at a temperature of about
70F to 80F, and preferably from about 74F to about 78F. Where a
consistency at the higher end of the foregoing range is employed, a sufficient
quantity of water may be added to the refined fibers to bring the dispersion
within the range of about 1 percent to about 3 percent consistency and most
desirablv about 2 percent before introduction into the drop chest (26).
To secure all of the advantages of the present invention, it is
believed to be most advantageous to emPloy, as the cellulosic fibrous
ccmponent, wcod pul~ derived from softwoods ~gymnosperms). Included within
, -l3- 127~j7~3
.
this term are the evergreens such as spruce, pine, and the like, having longer
fibers than those of the hardwGods. The softwoods preferred for use herein are
characterized by an average length to thickness (diameter) ratio, determined
microscopically, of about 60:l to 120:l and preferably about lOO:l
respe tively. The softwocd fi ers vary in length from about 0.05 inch to about
0.2 inch.
Commercially available pulps of this kind will typically oontain a
small percentage of hardwood, usually in the range of ten to twenty percent, or
more. Providing the necessary external and internal fibrillation can be
obtained, such pulps are entirely cperable for the purposes of the present
invention.
The operative softwood pulps include those characterized as mechanical
pulp or groundwcod and chemical pulp including, sulfite and sulfate, and
preferablv sulfate kraft, pulp as described in Kirk-Othmer, EncycloDedia of
Chemical Technology, pages 495 and 496, vol. 14 (1967) or, indeed, that
derived from the soda process.
In the practice of the sulfite process, the wood is digested in a
solution of calcium bisulfite and sulfurous acid. In the sulfate or kraft
process, a mixture of sodium hydroxide and sodium sulfide is used; the sulfide
being derived frcm the reduction of sodium sulfate introduced into the process
in the course of treatment.
m e unbleached variety of mechanical, semi-chemical or chemical pulp
is generally preferred over the bleached or semi-bleached pulP because of the
greater adsorbency of the unbleached pul~ in general. Unbleached chemical pulp
is preferred, too, because of its generally greater strength and durabilitv.
However, any of the foregoinq ~ulps may be used if they are capable of
~ 14- ~;~7~;753
attaining a density and breaking length as a result of internal and external
fibrillation necessary to the practice of the invention. Preferred pulps will
attain these characteristics more easily.
A preferred source of pulp fibers for use herein is Mac~enzie
unbleached softwood pulp manufactured by British Columbia Forest Products,
Inc., Vancouver, British Columbia, Canada. Slightly more preferred, although
bleached, is ~inton ~i-Brite bleached softwood pulp available oommercially from
the St. Regis Co.~vration. miS pulp has been refined to a breaking length
after refining of 10 to 11 kilometers. Also useful, alth3ugh less preferred,
is St. Croix bleached pulp manufactured by Georgia Pacific Corporation at
Wbcdland, Maine.
Particularly preferred in the practice of the present invention are
kraft sulfate softwood pul~ fibers having an average fiber length of 0.05 inch
to 0.2 inch and a length to width ratio of about 80:1 to 120:1 and more
particularly about 100:1.
All of these oommercially available wood pulp fibers are anionic.
Fibrillation, as the term is used throughout this specification, has
previously referred to only the external fibrillation of wood pulp fibers, a
property measurable by use of standard visual microscopic techniques and
determination of drainage prQperties or freeness. m e usual measure of this
latter property is the Canadian Standard Freeness Test (CSF~ wherein the
freeness value is determined acoording to T~PPI Standard T 227 m58 on a sample
of 3 gr~.~ of pulp fibers diluted with water to 1000 cubic centimeters (cc).
In terms then of the external fibrillation required in the Pulp fibers of the
present invention, a CSF of from at least about 260cc to 600cc is required, but
this measure of the requisite degree of external fibrillation is not adequate
`" -15- 1 2l7 6'7~ 3
.
to fully secure the objects of the present invention. Internal fibrillation
may be demonstrated by an increase in fiber swelling and flexibility and these
characteristics are not measured adequately b~ drainage or freeness
determinations. ~igh internal fibrillation, together with a significant degree
of external fibrillation are required for the develcpment of high internal bond
strength in accordance with the invention.
m e increase in fiber swelling and flexibility resulting from
ineernal fibrillation causes the density of the pulp handsheet to increase.
By requiring minimum strength properties of the wood fibers together with a
minimum density, the degree of internal bond strength of the pulp fibers can be
defined.
The internal bond properties obtained by the oombination of external
and internal fibrillation is believed to result in the promotion of sites for
latex and filler deposition and adhesion. In addition, these pro~erties aid in
the development of a suitable wet tensile strength, necessary when a wet web
formed of the proper materials is transferred from a standard Fourdrinier paper-
making machine to the drying rollers typically employed in papermaking.
Finally, these proPerties are believed to aid in obtaining a dry composite
sheet final product with a density appropriate for use as a backing sheet or
interliner in a surface o~vering laminate. It has been found, therefore, that
with the proper degree of internal fibrillation, an inexpensive inorganic
filler can be emplcyed to reduce the ooncentration of expensive polymeric
latices while still obtaining a composite sheet with a satisfactory internal
bond.
The degree of external and internal fibrillation may be accurately
determined by the oombination of density and the tensile strength, as measured
bv breaking lenqth, of the pulp fibers.
lZ'7~753
,~ -16-
Breaking length and density are each determined from a $~PPI Standard
Randsheet prepared from the pulp fibers by TAPPI T205 om 81, and measured by
I~PPI T494 om 81 and TAPPI T220 om 83, respectively. To determine breaking
length using hand sheets so prepared, TAPPI T494 om 81 is employed to yield a
value in kilometers by means of the equation:
. 3.658 x tensile strength in lb/in.
Break mg IRngth =
basis weight in lb./1000 sq. ft.
Density is detenmined using TAPPI T220 om 83 b~ yield a value in gr~,s
per cubic centimeter using the equation: -
. R (mass per unit area in g/~)
Denslty =
25.4 x thickness in mils.
0.1~22 x basis weight in lb/l,000 sa. ft.
thickness in mils.
Using these standards, a softwood pulp having a breaking length of
from 8km to 12km and a density of about 0.67 gm/cc to about 0.72 gm/cc is
oonsidered important in the attainment of a oomposite sheet material
incorporating all of the advantages of the invention. Also important is the
ionic stabilization and the zeta potential of the mixture formed into the
composite sheet. These materials include the anionic pulp fibers, essentially
neutral glass or other non-cellulosic fibers, anionic latices, and anionic
filler as well as both cationic and anionic flocculants.
127~753
, -17-
It should be noted in this oontext, that density and breaking length
may be determined conveniently for a particular refined pulp by preparation of
hand sheet samples using the Valley 8eater. m ese results should be fairly
well-matched by the pulp handsheet compared to high volume mill prcduction of
,
refined pulp sheet of an equivalent density and breakinq 1~ ~th and, therefore,
a similar degree of internal fibrillation~ using a Beloit Double-Disc refiner,
for example. It should also be noted that multipass refining of the pulp m2y
be employed in both the laboratory and mill to secure the desired density and
breaking length, if necessary.
m e concentration of wcod pulp fibers in the final product oomDosite
sheet by dry weight is within the range by weight of from akout 15 percent by
weight to akout 45 percent. A ooncentration of 20 percent to 40 percent, and
more particularly about 25 percent to 30 percent, by dry weight of the
ccm¢osite sheet, is preferred.
With continued reference to the figure, an aqueous dispersion of a
mixture of acrylic latexes (38) is next prepared. For the purpose of
illustration, this aqueous dispersion is prepared in mixing tank (40),
although the materials could be added directly to drop chest (26). In the
mixer this dispersion is agitated by agitation means (42) and then transferred
by some means such as pump (44) through feed line (46) into drop chest (26)
where the aqueous dispersions of filler (16) and fibrillated wood pulp (28)
have been kept agitated by some means represented as (48).
The hard or stiff acrylic resin polymer and the soft and flexible
acrylic polymer forming the blend of latices are incorporated into the aqueous
dispersion in drop chest (26) with the mixture of the filler and anionic wood
pulp fibers. This aqueous dispersion is anionic and a cationic wet stren~th
resin is added to ~erform as a flocculant.
~ 18- 1 27tj753
.
The acrylic polymers employed in the preferred embodiment of the
invention are those water-insoluble resins prepared from acrylic and
methacrylic mcncmers of the formula, C~2-CtR)COORl, wherein R is hydrogen
or methyl, and Rl is an alkyl radical of from l to 8 carbon atoms, and
preferably from 1 to 4 carbon atcms.
Illustrative of the preferred oomonomers within the foregoing formula
are, methyl methacrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate,
ethyl methacrylate, i~obutyl methacrylate, propyl methacrylate and ~sopropyl
methacrylate. ~ess preferred oomonomers are, for example, n-pentyl acrylate,
iscctyl methacrylate and the like.
The hard or stiff acrylic polymers emPlcyed in the present invention
are characterized in that at least 50 percent and uP to 100 percent of the
acrylic monomer present is methyl methacrylate, i.e., where in the foregoing
structural formula each of R and Rl is methyl. The oomponents of the soft
acrylic polymer are the same as those described above, provided, however, that
the oontent by weight of methyl methacrylate does not exceed about 35 percent
of the total of the comonomers present.
The glass transition temperature (Tg) of the soft acrylic resins of
the invention is within the range of -30 & to -10C; and m~st desirably,
about or precisely, -23C. The Tg of the hard oomponent acrylic resin
binder is within the range of about 20C to 40 & , and preferably, about
or precisely, 30C.
The glass transition temperature (Tg), as emploved throughout this
specification and in the claims is defined as the temperature at which the
torsional mcdulus of an air dried film is 300 kilograms per sauare centimeter
(Kg/sq. cm.~. The T~ is usuallv about 8C to 10C above the film-forming
~ 19- 127~j75~ ~
.,
temperature of the latex. m e concentration of the acrylic polymers in their
initial aqueous dispersion (38) in mixer (40) is normally within the range of
about 40 percent to SO percent, and preferably about 45 percent to 48 percent
by weight.
The p~ of these initial aqueous dispersions of these acrylic polymers
is typic~lly less than 7, and generally within the range of 3.0 to 4.0,
although this will vary with the particular latex and manufacturer.
In the practice of the present invention, the p~ of this dispersion
should be preferably within the range of about 7.5 to about 10, and still mDre
preferably from about 8.5 to about 9.5. It is contemplated that the aqueous
dispersion of these latex polymers can be brought to a suitable pH by the
addition of a c~ base, and ammonium hydroxide has been employed
advantageously in this regard.
When the aqueous dispersions of these acrylic polymers are brought to
a pH of at least 7, the latices lose their particulate form and become viscous
and even gel-like at high concentration. When dried in accord x e with the
present invention, these acrylic polymers will form a binding film.
The soft latex typically incorporates as a dispersant or emulsifier,
an alkylaryl polyether alcohol, and more particularly, an ethoxylated
alkyl phenol wherein the alkyl mDiety contains from six to eight carbu.. at~.
and is preferably an octyl phenol in which there are present 2 to 4 ethylene
oxide substituents.
The hard latex also includes an alkylaryl polyether aloohol, and m~re
particularly, an ethoxylated alkyl ~henol wherein the alkyl moiety contains
from nine to twelve carbon atoms, e.g., nonylphenol, and includes S to 8
ethylene oxide substituents. In addition to the alkyl phenol, a second
~ -20- ~2~tj753 `
;
emulsifier may be present such as a sodium al~yl laurate, wherein the alkyl
substituent oontains from eight to eighteen, and preferably fifteen carbon
atoms.
The amounts and combinations of these dispersants or wetting agents
will vary with the specific acrylic latex employed and the ooncentration of
latex in the pretreatment dispersion.
An illustrative emulsion or dispersion of a hard acrylic latex
preferred for use herein is that oommercially available under the trademark
R~OFLEXR TR-407 from RDhm and Raas Cbmpany, Philadelphia, Pennsylvania. An
illustrative and preferred soft acrylic resin for employment herein is that
commerci~lly available from the Union Chemicals Division of Union Oil Co.,
under the trademark AMSCO-RESR 6922.
The predominance of ærylate and methacrylate m~nomers and comcnomers
in the latices em~loyed has been foun~ to be important in achieving both
satisfæ tory adhesion of the fibrous csmFosite sheet to polymeric vinyl
coatings, and satisfactory resistance to internal delamination of the composite
sheet. m e ærylate resins also assure better adhesion of the cellulosic
fibers and retention of the filler in the non-woven ~ usite sheet as well.
The avoidance of the styrene, butadiene, or vinyl moncmers or comonomers helps
to obviate the need for antioxidants and avoid the tendency to e~brittlement
and discoloration of the final product oomDosite sheet.
The soft acrylic polymers, which dry at room temperature, permit the
quick drying and cure during the draining and drying of the comçosite sheet in
standard paper-making equiDment. This avoids most of the energy costs required
where extensive evaporative drying and cure are required. m e use of a soft
latex also provides a more flexible com~osite sheet, one which is more readily
r~~ -21- 1 27tj753
subject to molding about particular surfaces to which the sheet, or a surface
covering laminate incorporating the sheet, is applied.
It should be specifically noted that the processing temperatures in
the fonmation or u x of the composite sheet of the present invention should not
exceed the melting point of the soft acrylic resin oomponent emDloyed. This is
particularly true with respect to the temperatures encountered in the
evaporative drying of the fibrous web, any curing required subsequent to the
a~ylication of a sizing agent, as well as the gelling, curing or other heat
treatment of a plastisol or other material incident to producing a surface
wvering laminate employing the composite sheet.
The hard acrylic polymer is present in the latex blend in the
proportion of about 1:1 by weight of hard to soft resin. As such, total
concentration of latex will be maintained which will obtain the desired
properties in the final cc~Fvsite product sheet without unwanted tackiness that
would foul the papermaking equipment used to prepare the oomDosite sheet, or
the calendering or other apparatus used to prepare a surface covering laminate
emDloying the composite sheet.
The preferred acrylates also crosslink ucon heat curing without the
necessity for additional cross-linking CQmponentS. In addition, the preferred
ærylates are film forming in the absence of plasticizers. Plasticizers and
cross-linking agents known to the art may be employed, particularly where they
are desired for a specific end use. m eir use, however, is generally less
preferred.
m e average particle size of the latices emDloyed is generally within
a range, when measured microscopically, of from about 800 to 3000 angstroms,
and preferably from about 1000 to 1800 angstroms. Smaller or larger particle
~ -22-
753
sizes are believed to be operable in the practice of the present invention.
The percentage by drv weight of the latex blend present in the final
prcduct composite sheet may vary from about 20 percent to about 40 percent. In
the preferred embodiment, this percentage will vary from about 32 percent to
about 38 percent.
The latex blend and the filler are present in prooortions in which the
acidity of latex is substantially neutralized by the alkalinity of the filler.
A cationic flocculant (50) is introduced frc~ reservoir (52) into the
anionically stable aqueous dispersion of filler, paper pulp fibers and latex
blend ncw assembled in the drc~ chest (26). The amount emplcyed is scmewhat in
excess of that required to effectively destabilize the colloidal suspension
and cause oomDlete coagualtion and adsorption of the latices and filler by the
cellulosic fibers. The purpose of using an excess of this cationic flocculant
(50) is to ~rovide the maximum wet stren~th properties to the non-woven
ccnposite sheet consistent with securing the other objects of the invention.
The imbalance is indeed permitted to extend to an electrokinetic (zeta)
potential of +20 millivolts, or more, at this stage of the process. As
explained more fully belc~, the zeta potential is later adjusted to a point
within the range of +10 to -10 millivolts prior to the final coagulation and
draining of the product com~osite sheet. At that point a substantially clear
supernatant liquid is recover æ.
The water-soluble cationic flccculants emplc~ed herein are mDst
desirably polycaprolactonc cpichlorohydrin resins or epichlorohydrin-
polycaprolactone polvols. Illustrative of the former are those available
ccmmercially from the E.F. ~oughtc~ ~ Co., Valley Forge, Pennsylvania, under
the trade mark and grade designation REZ060L 388-15. Illustrative polvols are
,~ 23 1~7~753
those available ooTmercially from the Union Carbide Corp. under the trade mark
N~X.
Less desirable, but fully cperable as càtionic flocculants herein are
the epichlorohydrinpolyamide resins such as thDse ~ammercially available frcm
~ercules Incorporated undes the trade mark and grade designation RYMENE S57 and
POLYCUP 361.
In general, these cationic flocculants provide for a gradual, uniform
coagulation of latex and adsorption thereof and of the filler onto the
cellulosic fibers. In addition, these flocculants assist in providing a
product composite sheet with the required strength, wetability and resistance
to shrinkage. It is believed that these flocculants facilitate curing of the
latices at ambient temperature and confer toughness, adhesion and resiliency,
as well.
In terms of standard test procedures for assessing qualities such as
these, the inclusion of an excess of one of these cationic flocculants helps to
provide a composite material with excellent drainage procerties, mullen,
tensile and tear strength.
Even though the cationic flocculant is added in excess, the ionic
environment in which the flocculant effects a charge reversal is such that the
coagulation of latex and adsorption of filler is uniform and progressive and
secured without agglomeration that would render the product sheet inap~ropriate
for use. It should be noted that this is partially by virtue of the blend of
hard and soft latices of the present invention. The emulsifiers or dispersants
.~loved with the latices are believed to assist in this slow even build-up on
the fiber surface.
The amount of cationic flccculant added to the droP chest (26) is in
-24- 1~7~
excess of the amount required to secure oomplete coagulation of the latexes and
filler on and within the cellulosic ~ulp fibers. For general purposes, the
appearance of the coagulated material and the suPernatant liquid will dictate
to those skilled in the art the precise measure of excess flocculant to be
included. As noted above, the purpose of the excess is to impart superior wet
strength qualities to the composite sheet product both during processing and as
a finished product. C~l~lete destabilization of the dispersion and
precipitation of the filler and latices onto and adsorption by the cellulosic
fibers leaves a clear supernatant liquid. With the addition of a greater
excess of cationic flocculant, the ~dsorptic activity of the ionic components
of the mixture is reversed and the supernatant liquid will again become
clouded.
With continued reference to the figure, the mixture prepared in this
manner is then passed fr x the bottom of the drop chest (26) bv any means such
as the pump (54) through the feed line (56) and then through a holding or
slurry tank (58) and a second feed line (60) to a first precipitation tank
(62~. The mixture introduced into the precipitation tank (62) has a
consistency of about 1 percent to about 5 percent, and mcst desirably of about
4 percent, and oonstitutes approximately 85 percent of the dry weight
components e~ployed in forming the product composite sheet. This mixture is
next oonveyed through the conduit (64) by means of gravity.
Another aqueous dispersion is prepared in second precipation tank
(68). Water is introduced into the tank (68) into which a base, such
as ammonium hydroxide, is introduced to secure a pH of about 8 to about 12,
preferably frcm 8.5 to 10, and most desirably at or about 9. A water-soluble
cationic surfactant, serving in this instance as an antistatic agent, is
~ -25- 1 Z7~i7S3
introduced if necessary. In this regard it has been found that dispersal of
the non-cellulosic fibrous component, typi~lly glass fibers, may be
facilitated by the use of a cationic surfactant anti-static agent which assists
in releasing the sizing agent typically present in commerci~lly a~-ailable glass
fiber. The preferred cationic surfactant introduced into the second
precipitation tank (68) is x st desirably a pol~voxyethylated alkylamine in
which the alkyl moiety is within the range of from nine to eighteen carbon
atoms and preferably within a range of nine to ten carbon atoms. Nonylamine
and decylamine are particularly preferred. Each molecule of polyoxyethylated
alkylamine contains from S to 10 ethylene oxide m~ieties, and the amune has a
average molecular weight of from about 400 to 700.
The cationic surfactant is generally incorporated in the aqueous
dispersion in a concentration by weight of about 200 to 700 parts per million
(p~m), and preferably at or about 500 pDm.
To this solution is added a non-cellulosic fibrous oomponent chosen
from the group consisting of glass fibers, rock wool and other suitable mineral
fibers. Of these fibers, the presently preferred material is chopped glass
fibers such as one-eighth inch E Fiberglass of Owens-Corning, Illinois. Glass
fibers do not absorb any moisture, have high tensile strengths, very high
densities and excellent dimensional stability. The glass fibers have average
lengths of from about 0.1 inch to 0.7 inch and have an average di~l~ter in the
range of thirty-five one hundred-thousandths of an inch (35 hts) to about
fortv one hundred-tbousandths of an inch (40 hts). These oommercially
available fibers are characteristically sized with casein which causes the
otherwise ionically neutral glass fibers to form and remain in bundles. Sizes
such as this are ccnmonly employed by manufacturers of glass fibers and the
release of the sizing composition bv a cationic antistatic agent eliminates
fiber agglomeration and permits a uniform dispersion of the glass fibers upon
-26- lZ767S3
agitation of the dispersion in the precipitation tank. The consistancy of
glass fibers for effective dispersion is within the range of 0.5 percent to
about 3.0 percent, and most desirably about 1 percent, by weight of the
dispersion. The prccortion of glass flbers in the final com¢osite product
sheet is within the range of about 6 percent to about 23 percent by dry weight,
with preferred results generally secured at from about 9 percent to 20 percent
and most desirably at or abcut 15 percent by dry weiqht.
With oontinued reference to the figure, the aqueous disPersion
containing dispersed glass fibers is next transmitted from the bottom of the
precipitation tank (68) through the oonduit (70) and fan pump ~66! into the
common feed line (72) for delivery together with the mixture of the first
precipitation tank (62) into the machine chest (74). The dispersion from the
second precipitation tank (68) constitutes about 15 percent of the total volume
of the constituents of the final ocmPosite material.
The mixture of the contents of the two precipitation tanks is
ap~roximately equal in volume and creates a dispersion havinq a consistancy
within the range of 0.75 percent to about 4.0 percent, and preferably about 2.7
percent. This mixture undergoes oontinued agitation in the m2chine chest (74)
before conveyance by some means such as the in-line pump (76) through the feed
line (78) to the headbox (80) of a substantially standard Fourdrinier
paPeLll~king machine. Between the pump (76) and the headbox (80), a
supplemental feed line (82) oonnects into the feed line (78). An anionic
flocculant illustrated as (86), such as a polyorganophosphate, is introduced
through this feed line (82) from the reservoir (84). The ooncentration of the
anionic flocculant added is sufficient to assure that the electrokinetic or
' ~ -27- 12~67S~
zeta potential of the viscous dispersion passing to the headbox ~80) is within
the range of about +10 millivolts and about -10 millivolts: and preferably from
+5 to -5 millivolts.
~ The achievement of a zeta potential within at least the broader range
is important to securing maximum adherence of the filler and latices to the
pulp fibers with the beneficial qualities they impart to the resulting sheet.
An undesired consequence of the failure to achieve a zeta potential within the
border range is the tendency to embrittlement of the product oomposite sheet.
The electrokinetic or zeta potential, as this term has been employed
throughout this specification and in the claims, refers to the drop in
potential expressed in millivolts occurring across the layer of ions at the
solid-liquid interface of the dispersions described herein.
m e zeta potential (Z), is measured as follcws:
4 " ed
Z =
Wherein:
e=electrical charge of the layer
d=thickness of the layer
D=dielectric constant of the particle
The zeta potential is influenced in the present instance by the amcunt
of refining which increases the negative charge of the pulp fiber and
decreases, as a consequence, the concentration of latex required.
The present invention seeks to effect a neutralization of this zeta
potential, that is, to brin~ the zeta potential, which has been allowed to vary
' -28~ 5;~--
up to a level as high as +20 millivolts, back within a lower range of +lO to -
10 millivolts and in fact as close to zero as is oommercially feasible in the
laboratory or mill. A wide va-ietv of anionic flocculants, stabilizers or
surfactants may be employed for this pur~ose. A polyorganophosphate, such as
the partially esterified phos~hate esters of polyvinyl alcohol including that
commercially available from E.F. Houghton & Co. under the trade mark and
grade designation ST~BILEX 8628 has been emDloYed for this purpose. Shown to
be even more preferred is the surfactant commercially available from Hercules
Incorporated under the trade mark RETSN 521.
With further reference to the figure, the increasingly viscous and
rapidly ooagulating dispersed oom~onents are conveved through feed line (78) to
the head box (80) of a substantially standard Fourdrinier paper machine shown
generally as (90) in the figure of the ap~aratus (10).
Employing relatively standard paper makina techniques, the coagulating
mass is taken up on a forming wire (92) and drained, with the draining water
conveyed through drainage box (94).The resulting ~ usite sheet (96) is
advantageously oonsolidated by passing through felted pressure rollers (98) and
then conveyed through a series of heated rollers (100) to effect evaporative
drying of the ~ usite sheet to a final mDisture level of approximately 6
percent.
A size, preferably of a particulate hard acrylic resin, dispered in an
aaiueous medium may be applied to one or both surfaces of the formed oomDosite
sheet (96) following the evaporative drying step. In the preferred embodiment
of the invention, such a sizing is employed to assure a smooth uninterrupted
surface free from errant fibers, or the like. This size serves as well to
assure adherence of any minor residues of impurities, filler or fibers that may
remain loose or akove the surface of the formed sheet.
In the figure, the application of the size is represented by a size
., ~
~ 29- lZ7tj75~.
press (102). ~cwever, such a sizinq agent may be applied by any conventional
system kncwn to the art, such as a reservoir with a knife coater, knife-over-
roll, reverse roll, roll ooaters or the like. The sizin~ applied sh~uld be
permitted to cure, and additional heated rollers may be provided for this
purpose.
Finally the cured oom¢osite sheet with or without the a~plication of a
size, may be used immediately for some purpose such as a backing or interliner
for surface covering laminates. Alternatively, the oomposite sheet ~96) may be
taken up and rolled upon itself for storage, transportation or the like, and
storage roll (104) illustrates such a su~Dly.
To further illustrate the oomposite sheets prepared in accordance with
the present invention, the following illustrative examples were carried out.
EXAMoeL~ I
Employing an apparatus similar to the one illustrated in the figure
and described in the specification, tw~ thousand one hundred seventy-seven
gallons (2,177 gal.) of water were added to a mixing tank. To this was added
one thousand two hundred twenty-nine pounds (1,229 lbs.) of ocmmercial grade
No. 4 calcium carbonate (CaC03) particles having a particle size such that 96
percent of the particles will pass through a U.S. Standard 60 mesh screen. One-
half gallon (0.5 gal.) of NXZ defoamer, weighing about four pounds (4 lbs.) and
~,.,~rcially available from the Diamond Shamrock Corporation was also added to
control foaming. m is mixture was agitated in the mixing tank at an initial
rate of two hundred twelve revolutions per minute (212 r~m). The mixture was
then transferred to a droD chest and chased with an additional five hwndred
gallons (500 gal.) of water. Agitation of the mixture oontinued at an initial
~ -30- 7~
rate of three hundred ninety-five revolutions ~er minute (395 rpm!.
The agitation of the mixture in the dro~ chest was increased to four
hundred ninety-four revolutions per minute (494 L~ll) and seven hurdred ninety-
three and two-tenths pounds (793.2 lbs.~ of resinous material were added. This
resinous material consisted of a blend of two resin comDonents. The first
resin consisted of an anionic, hard, water-insoluble acrylic latex suspension
with a 45.5 percent solids content, a glass transition t~.~erature (Tg) of
30C and a minimum film formation temperature of 22C. m is resin was
obtained commercially from the Rohm and Haas Co. under the trademark Rhcplex TR
407.
The second resin ccmponent oonsisted of an anionic, soft, water-
insoluble acrylic latex suspension with a 45 percent solids content and a glass
transition temperature ~Tq) of -23C. This resin was obtained oommercially
from Union Chemicals under the trademark Amres 6922.
The two resins were blended in pro~ortions which represented a 1:1
ratio on both a wet and dry weight basis.
A second aqueous dispersion was se~arately prepared by oombininq
eleven hundred seventy pounds (1,170 lbs.) of refined wocd pulp solids with
make-up water to total thirty-nine thousand pounds (39,000 lbs.). m e refined
pulp employed was softwood kraft obtained oommercially from the St. Regis
Corporation under the tradename Hilton ~i-Brite. In the aqueous dispersion,
the pulp w~s beaten and refined to a high degree of internal and external
fibrillation in a double disc refiner available oommerciallY frcm the 8eloit
Corporation. At the aonclusion of such refining, the pulp exhibited a breaking
lenqth of eight kilometers (8 km) and a density of sixty-eight one-hundredths
of a gram per cubic centimeter (0.68 g/cc) when prepared in the form of a T~PPI
~ -31- ~ 7~j753
Standard ~andsheet. The fiber length varied frcm about five one-hundredths of
an inch (0.05 in.) to about two-tenths of an inch (0.2 in.) and t~e length to
diameter thickness ratio varied from about sixty-to-one (60:1) to about one
hundred-to-one (100:1).
This second aqueous dispersion was transferred to drop chest and
chased with an additional five hundred gallons (500 gal.) of water. In the
drop chest, this second dispersion oombined with the other materials to yield a
dispersion with a consistancy of 2.86 percent and a Canadian Standard Freeness
of two hundred seventy milliliters (270 ml.).
Approximately three percent (3%) of a cationic epichlorohydrin-
polycaprolactone resin, commercially available from E. F. Houghton & Co. under
the trademark RESZO6CL 388-15, was added to the combined aqueous dispersion to
induce coagulation and absorption of the latex blend and filler onto the
refined cellulosic wocd pulp. The contents of the drop chest were then
transferred to a first precipitation tank, and constituted 85 percent of the
total concentration by volume to be employed in forming the final product
ccm~u6ite sheet.
A third aqueous dispersion was separately prepared in a second
precipitation tank by oombining fifteen hundred gallons (1,500 gal.) of water
and one hundred pounds of chopped E fiber glass having an average len~th of
about one-eighth inch (1/8 in.) and an average diameter of about seven microns
(7 um). These fibers are available commercially from Owens-Corning
Corporation, and bear a casein coating which can be re~oved by a cationic
antistatic agent. For this reason, fifty-two pounds of a ~olyoxvethylated
alkylamine commercially available frcm the GAF Corporation under the trademark
RAT~PCL VP-532 was added to the aqueous dis~ersion. In addition, about one
pint of ammonium h~droxide ~NH4OH) was added to ad~ust the pH of this
`~ -32- 1Z7tj~5~
dispersion to 9Ø This aqueous dispersion oonstituted 15 percent of the t
concentration by volume to be employed in forming the final product composite
sheet.
Fol~owing agitaticn of this third aqueous disPersion for about one
minute, the oontents of both precipitation tanks were transferred to a machine
chest where agitation oontinued and the oombined dispersion was brought to a
consistancy of about 2.7 percent. The zeta potential of this combined
dispersion was about +20 millivolts and exhibited a milky white ~u~earance.
The dispersion was transferred through a line blender which introduced a
quantity of anionic surfactant, in this case a partially esterified phosphate
ester of polyvinyl alcohol available commerciatty from E. F. Houghton ~ Co.
under the trademark ST~BILEX 8628. The quantity of this additive was
sufficient to restore the zeta potential of the fibrous dispersion to within
the range of +10 to -10 millivolts. The dispersion was finally transferred
through the line blender to the head box of a Fourdrinier paper machine at a
flow rate of approximately four hundred eight gallons Per minute (408
gal/min). This anionic surfactant was added at a rate of approximately three
gallons per minute (3 gal/min) to yield an effective addition in continuous
operation of about 1.25 pounds per ton.
The aqueous dispersion, now in the form of a rapidlv coagulating
fibrous slurry, was passed from the head box and slice onto the forming wire of
a Fourdrinier papermaking machine. Drainage of the slurry began on the forminq
wire and was continued as the slurry was passed through rotary presses which
helped to consolidate the fibrous mass and form the oomposite sheet. Finally,
the composite sheet was dried to a moisture content of 6 percent by passing the
composite through a plurality of heated rollers. The comsosite sheet obtained
in this manner had a thickness which varied from fourteen mils to twenty mils.
~ . ~
1~:76~753
~ -33-
Undetermined quantities of unabsorbed impurities remained, mostly
representing the residue of the commercial calcium carbonate source
(limestone), but these were not a material concern.
A sizing ~ rising a ten percent solids aqueous dispersion of a hard
cationic acrylic latex commercially available frcm the Rohm and ~aas Co. under
the trademark ~HOPLEX T~-407, was applied to the composite sheet. The rate of
pick up varied frcm about three one-hundredths of a pound per square yard (0.03
lb./yd2) to about three tenths of a pound per square yard (0.3 lb./yd.2),
yielding a nominal thickness of from about one tenth of one percent (0.1%) to
about one percent (1%) of the sheet. The latex was applied to both sides of
the composite sheet by a kiss roll and the sheet was redryed.
The sized oomposite sheet was then skin coated in the following
manner. A 10 mil skin coat of vinvl resin plastisol was applied to a first
side of the composite sheet and cured for 30 seconds at 390F. The first-
coated side was placed on a non-woven felted release sheet commercially
available from Congoleum Corporation as CONGOLEUM Release Felt WS-86*and a
similar 10 mil coating of the same plastisol was then applied to the op~osite
side of the com¢osite sheet. This assembly was then heated to 390F for 3
minutes to cure the vinyl resin. Physical characteristics for the composite
sheet prepared in this manner are reported under S~,~le 1 in Table 3 which
appears below.
As noted previously, the processing temperatures encountered in the
evaporative drying of the com¢osite sheet, the curing of the sizing agent and
the curing of the plastisol skin coatings should not exceed the melting point
of the soft acrylic latex ~ vnent. m e formation of the ~,4usite sheet
prior to drying, and the after-treatment steps other than curing, e.g.,
sizing and apPlication of the plastisol skin coatings, were carried out at
ambient tem~erature.
* trade mark
,~ ~34~ lZ7ti7S3
EXAMPIE II
The softwood pulp of Table 1 was refined in a l~h~ratory Vallev Beater
at a consistency of 1 percent. The fibers were slushed with a 2250 gram
oounterweight on the bedplate lever arm of the beater for 15 minutes. -
Additional weight totalling 5,500 grams was then added and the pulp refined
to a breaking length of 8 to 10 km and a Canadian Standard Freeness (CSF) of
350 cubic centimeters. The refined woad pulp at a 1 percent consistency was
introduced into a mixture of the remaining ~ u..ents of Table 1 in sequence
following the manner described generallv in the previous ExamDle.
Table 1
Component Dry (grs.) W~t (cc.
Sequence of Addition
1. Water - 529.6
2. Cao~3 (ocmmercial grade) 32.0 32.0
3. RhoplextmTR-407 (Rohm and Haas Co.)10.0 21.7
and Amsco-Restm 6922 (Union Chemical) 10.0 21.7
4. St. Croixtm Bleached
Softwood pulp (Georgia Pacific) 30.0 1500.0
5. Rezosoltm 388-15 (E. F. ~oughton 3.0 20.0
& Co.)
85.0 2125.0
An aqueous disDersion of glass fibers was separately prepared
according to the am~unts listed in Table 2. This beqan by the introduction of
water, adjustment of the p~ to 8.0 to 8.5 with NH4OH and addition of the
~ ~35~ 127~j'75~
water-soluble cationic antistatic agent KATAPOLtm VP-532 (G~F Corporation~.
This antistatic agent is 20 percent solids, and was added at a concentration of
500 parts per million (ppm) drv weiqht, to the total batch weight. The fiber
glass was then added in a concentration of 1 percent and the mixture agitated
to remove the sizing fro~ the fibers and effect substantially oomplete
dispersion of the fibers.
Table 2
Co~Donent Dry (lbs.~ Wet (gal.
Sequence of Addition
1. Water - 1500.0
2. NH4Cff pH 8.5
3. Katapoltm VP-532 (G~F Cor~oration) 1.6 8.0
4. Sized 1/8" E Glass, S-114-1 15.0 17.6
(Owens-Corning Fiberglass)
16.6 1525.6
The formulations of Table 1 and Table 2 were mixed to obtain a consistencv of
2.7 percent. The formulations were then formed into sample sheets on a wire
screen and drained. Physical characteristics for the oomposite sheet prepared
in this manner are reported under Sample 2 in Table 3, which appears below.
~ 36- lZ7~7~
TABLE 3
Pro~erty Unit Sam¢le
1 2
Ream Weight Pounds per 480 Square Feet 26.7 25.2
Weight per square yardPounds per square yard 0.51 0.47
Caliper Inches .018 .0155
Gage per weight RatioCaliber per Ream Weight 0.677 0.62
Cold Tensile - 74F Pounds 93 94
Elongation Percent 2.7 2.6
Bent Tensile Pounds 70 7n
Mullen Pounds 83 90
Stiffness T/2 Units 59 3~
~ot Tensile - 350F Pounds 28 25
Water Absorpsion Percent 68.7 67.0
Plasticizer Immersion
Tensile Pounds 51 53
Elongation Percent 1.8 1.8
Stiffness T/2 Units 35 22
Internal Bond
Mcdified Keil Grams 180n 1500
IGT (Feet per minute, number
7 Ink 580 630+
~ ~3~ '7~j7S3
Terms appearing in Table 3 are defined as follows:
Cold Tensile: the tensile strength of the oom$osite material at
74 Fahrenheit. Portions of the sheets are cut into 1 inch by 8 inch strips
and the minimum thickness over the test area is determined. The tested strip
is pla~ed in an Instron testing machine having a 6 inch s~an and the elongation
and pounds at break are measured as the machine is operated at a head speed of
1 inch per minute. ,Results are reported on an average of 3 samples.
El~l~ation: The Elongation of the coT¢osite material that is
determined at room temperature over a 6 inch span at the time the cold tensile
is made.
Mullen: The lateral burst of the composite material as determined by
T~PPI test method T 403-os-76.
Stiffness (T/2): Regular stiffness of the cGm~osite material is
-
determined according to T~PPI test method T 489-os-76. The value obtained in
gram centimeters is ~orrected to a value for 30 mils thickness by multiplying
by the factor:
Thickness of the test sample in mils
Hot Tensile: The Tensile strength of the oomposite material at
350F. This physical property is tested in the same manner as Cold Tensile
except that the test sFe~imen is heated to 350oF while clamped in the jaws of
the Instron testing machine.
water Absorption: The w2ter absorption of the ccmposite
material is determined ~y soaking a samDle (2 inches by 4 inches) in water for
24 hours and recording the weight increase and calculating the percentage
~ -38- 1 Z~ 6 7 5
increase by weight.
Plasticizer ~mmersion: Plasticizer immersion re~uires that the test
samples be soaked in dioctyl phthalate (DOP) for 24 hours before testing.
Tensile, elongation and Stiffness T/2 are determined for treated samples in the
manner as they are in the absence of plasticizer.
Mcdified ~iel Test: The mcdified Riel Test is a measure of internal
bonding wherein 10 mils of a skin coat plastisol are applied to the bottom side
of a felted sheet of the invention and cured for 30 seconds at 290F. Ten
mils of the identical skin coat are then applied to the top side of the sheet.
(In the standard Riel Test, a layer of tape is ap~lied to both sides of the
sheet.~ The bottom side is then placed on a coated release paper, such as
Congoleum Release Fe]t WS-86*a oommerciallY available product of the Congoleum
Corporation, Kearny, New Jersey. The coated sheet is cured at 390F for an
additional period of 2 minutes. A one inch wide sample is then cut from the
sheet. The ends of the sample are delaminated sufficiently to enable the
separated ends to be placed within the the clamps of the Reil tester. The
drive motor for the upper jaw of the testing device is activated and the
undelaminated portion of the sample is then held at a right angle to the
direction of pull. The pull necessary to effect further delamination is
measured in grams.
When failure occurs, the samDle is inspected. The lccation of the
failure is observed to determine if the failure cccured in the surface coating
of plastisol or in the structure of the interliner sheet. Where the failure
first cccurs within the interliner itself, the results measured in grams per
inch, are aiven.
IGT Test: This test is emploved as a means for determining the
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_39- ~ ~z7~j~75~ `
internal bond of a felted sheet such as the composite sheet of the present
invention. The test measures the failure of internal bond caused by fatigue
which has been induced by the stress of sheer. The test also measures the
tendency of a specimen to blister or peel. In the test pr x edure, a viscous
black No. 7 letter press ink is applied to a wheel load against a strip
specimen under test. The IGT Tester subjects the specimen to an increasing
acceleration (ft./min.) which causes an internal rupture to occur. The test is
nonmally performed using the IGT printability tester type AlC2 of the Research
Institute for the Printing and Allied Industries according to TAPPI Method T499
SU-64. In the present testing however, Al or A2 instruments were ~l~loyed and
the No. 7 ink was chilled to increase its tackiness.
ExamDle III
The followinq oom wnents were mixed in sequence in a single reaction
vessel with moderate agitation.
-40- 1 Z~753
Table 4
CcmDonent nrv (lbs.~ Wet (cal.)
,
1. Water 8531.0
2. N~40H to PH 8.5
3. Ratapoltm VP5-32 1.6 8.0
4. 1/8~ E Glass, S-114-1 15.0 17.6
5. CaC~3 commercial grade No. 4 32.0 32.0
6. Rhoplextm TR-4Q7 latex 10.0 21.7
Amrestm 6922 latex 10.0 21.7
7. St. Croix Bleached Pulp 30.0 1500.0
8. Re~osoltm 388-15 3.0 20.0
9. Stabilextm 8628 as needed
101.6 10,160.0
Glass fibers were agitated for a period of about 1 minute before
introduction of the calcium carbonate. Then a blend of hard and soft latex
polymers, R~DPLEXtm TR-407 and AMREStm 6922, resPectively, and the refin æ
wood pulp were added. The pulp employed was St. Croix bleached softwood pulp
manufæ tured bv Georgia Pacific Corporation at Wbodland, Maine. The pulD was
separatelY refined to a high state of internal and external fibrillation. The
refined pul~ had a density of 0.6 gms/cc., a breaking length of 6 km, and a
Canadian Standard Freeness of 350 cc. A cationic epichlorohydrin poly~capro-
lactone, REZOSOLtm 388-15, was introduced to cause precipitation of the latex
and filler. The supernatant solution passed through a clear staqe to a milky
state, whereupon the anionic polyorgancphosphate, ST~BILEXtm 8628 of E.~.
Houghton & Co., was added to return the supernatant solution to a clear state.
At this ~oint the latex and filler ~ere substantially ~ letely Drecipitated.
.
.. ~ ,~,, . .. ,. . ~
` ^ -41- lZ7~75~
me resulting mixture received mil2, continued agitation after precipitation
and was then drained on a wire screen to form a product sheet which exhibited
physical proPerties similar to those reported above, exceDt that the internal
bond was weaker and might be considered unsuitable for the intended use.
Exam~le rv
(a) The prccess of Example I was repeated. Hkwever, the pro~Dortion of
calcium carbonate was reduced and the percentage of the latex blend was
increased to 35 percent by dry weight of the final composite. me other
oomponents were a2ded in the concentrations ~loyed in Example I, exceDt for
the amount of epichlorohydrin-Dolycaprolactone and organopolyFhosDhate
flocculants employed. The concentrations of these flo~culants were increased
from three pounds per ton (3 lbs./ton) to six pounds per ton (6 lbs./ton) to
secure the required coagulation an2 impart the desired wet strength to the
product sheet. The ambient temperature was 7~F. The product sheet was
treated with vinyl plastisol in the manner of Example I and tested. The
product showed an IGT in eYcess of 630 ft/min.
(b) The process of Exomple rv (a) was repeated, except that the
product sheet was not sized before a~plication of the vinyl plastisol. The
product sheet showed an IGT in excess of 630 ft/min.
It will be evident that the terms and exDressions that have been
employed herein are used as terms of description and not of limitation. There
is no intention in the use of such terms and expressions of excluding
equivalents of the features shown and described or portions thereof, and it is
recognized that various m~difications are possible within the soope of the
invention claimed.
