U.S. patent number 3,860,369 [Application Number 05/447,253] was granted by the patent office on 1975-01-14 for apparatus for making non-woven fibrous sheet.
This patent grant is currently assigned to E. I. Du Pont de Nemours and Company. Invention is credited to Dale Merrill Brethauer, Jean Paul Prideaux.
United States Patent |
3,860,369 |
Brethauer , et al. |
January 14, 1975 |
APPARATUS FOR MAKING NON-WOVEN FIBROUS SHEET
Abstract
An improved apparatus for use in making nonwoven fibrous sheets
of organic synthetic polymers includes a spinneret orifice through
which a polymer solution is flash spun to form a plexifilamentary
strand directed in a generally horizontal direction toward a
rotating baffle whose axis of rotation is generally parallel to but
spaced from the axis of the extrusion orifice and whose surface is
contoured so as to simultaneously spread said strand into a planar
web, direct the web into a generally vertical plane downward toward
a collecting surface, and cause said web to oscillate in the plane
as the baffle rotates. The improvement consists of an aerodynamic
shield of specified configuration. The shield terminates at an edge
which lies substantially along an arc of a circle whose center lies
on the axis of rotation of the baffle. Since the plexifilamentary
strand impinges on the baffle at a point near its axis of rotation
and is deflected as a web which therefore oscillates through
various radial directions within the plane substantially
perpendicular to the rotation axis, only the specified shield
configuration will provide flow paths of approximately equal
impedance, independent of the instantaneous radial direction at
which the web leaves the baffle.
Inventors: |
Brethauer; Dale Merrill
(Wilmington, DE), Prideaux; Jean Paul (Richmond, VA) |
Assignee: |
E. I. Du Pont de Nemours and
Company (Wilmington, DE)
|
Family
ID: |
26973231 |
Appl.
No.: |
05/447,253 |
Filed: |
March 1, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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303044 |
Nov 2, 1972 |
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Current U.S.
Class: |
425/3; 264/DIG.8;
425/373; 425/224; 425/231; 425/456; 264/441; 264/469 |
Current CPC
Class: |
D01D
5/11 (20130101); D04H 3/16 (20130101); Y10S
264/08 (20130101) |
Current International
Class: |
D04H
3/16 (20060101); D01D 5/00 (20060101); D01D
5/11 (20060101); B29j 005/00 () |
Field of
Search: |
;264/5,22,176,24
;425/83,72,75,162,224,231,456,3,373 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Spicer, Jr.; Robert L.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This is a division of application Ser. No. 303,044 filed Nov. 2,
1972.
Claims
What is claimed is:
1. In an apparatus for forming a fibrous web that includes means
for flash spinning a polymer solution to form a plexifilamentary
strand entrained in a gaseous stream, means at one location for
spreading the strand to form a web and oscillating the web in a
generally vertical plane in a plurality of downward radial
directions toward a collecting surface and means positioned below
said spreading and oscillating means for charging said web, the
improvement comprising: an aerodynamic shield having front and rear
members disposed on each side of said plane below said spreading
and oscillating means, said members having surfaces facing said
plane, said surfaces terminating in edges equispaced from each
other and lying along arcs of equal radius extending from a
horizontal axis proximate to said one location, the surface of the
rear member facing said plane being substantially parallel to and
being a stepped surface stepped away from said plane in the
downward direction along one or more arcs concentric with the
terminating edge of the rear member, the surface of the front
member facing said plane being sea section of a surface of
revolution about said horizontal axis converging downwardly toward
said plane.
2. The apparatus as defined in claim 1, the surface of the front
member facing the vertical plane being a segment of a right
circular cone converging downwardly toward said plane at an angle
of about 5.degree..
3. The apparatus as defined in claim 1, said front and rear members
extending downward for a distance of from about 30 percent to about
60 percent of the distance from said one location to said
collecting surface.
4. The apparatus as defined in claim 3, said one location being a
rotating baffle, said front and rear members extending downward for
a distance of from about 30 percent to about 60 percent of the
distance from the edge of the baffle to said collecting
surface.
5. The apparatus as defined in claim 1, there being through ports
in said rear member at the location the surface of the rear member
facing the vertical plane is stepped away from said plane.
6. The apparatus of claim 5, said ports being equispaced from each
other along an arc concentric the terminating edge of the rear
member.
7. The apparatus as defined in claim 1, said means for charging the
web being incorporated in said shield.
Description
BACKGROUND OF THE INVENTION
This invention relates to a process and apparatus used in the
preparation of nonwoven fibrous sheets of synthetic organic
polymers. More particularly, it is directed to a process and
apparatus for spreading a plexifilamentary strand into a planar
web, directing the web toward a surface, charging the web and
collecting the web in the form of a nonwoven fibrous swath.
Steuber, U.S. Pat. No. 3,169,899 describes a process for making a
nonwoven sheet from flash-spun fibrous materials. In the flash
spinning technique, a solution of an organic polymer which is under
pressure and at a temperature far above the boiling point of the
solvent is extruded into an area of substantially atmospheric
pressure. As the material issues from the orifice, the solvent
flash evaporates and a plexifilamentary strand is formed. The
plexifilamentary strand is composed of very thin film fibril
elements which are interconnected in a three-dimensional network as
described in detail in Blades and White, U.S. Pat. No. 3,081,519.
The three-dimensional network is spread into a wide web by causing
it to be swept along a smooth path past a curved surface baffle
whereupon the expanding solvent gas spreads the material. By
oscillating the deflecting baffle, the web can be directed to
various areas across the width of a moving collecting belt where it
is deposited in the form of swaths. The web can be
electrostatically charged to both further increase its width
through mutual electrostatic repulsion between fibrils and also
attract the swath to the belt and immobilize the deposit. A fibrous
nonwoven sheet is thereby obtained.
In an alternative process described in Pollock and Smith, U.S. Pat.
No. 3,497,918, the oscillating baffle can be replaced by a rotating
baffle, having specially contoured surfaces, which simultaneously
spreads and oscillates the web as it is directed through an
electrostatic device to apply uniform electrostatic charge on the
web and promote uniform deposition of the web on a moving
collecting surface. A suitable charging apparatus is described in
Kilby and Smith, U.S. Pat. No. 3,456,156. The apparatus consists of
an annular disc target electrode which is concentric with the
rotating baffle and rotates independently of said baffle. A
multineedle ion gun is positioned opposite the target plate, the
needles being aimed at a portion of the target electrode to provide
a corona discharge zone. The fibrous material moving in a planar
path between the target electrode and the ion gun needles is
electrostatically charged before being deposited on the moving
collecting surface.
A number of requirements must be satisfied in order to obtain wide,
fibrous, nonwoven sheets having a uniform appearance and a uniform
basis weight. In general, wide nonwovens are obtained by blending
and overlapping the swaths from several spinning positions. Smith,
U.S. Pat. No. 3,549,453, describes a mechanism for making fine
adjustments and varying the weight distribution of the swaths
deposited on the collection surface. Tests have shown that optimum
basis weight uniformity in the cross machine direction (i.e., the
direction at right angles to the direction of movement of the
receiving surface) is obtained when the width of the swaths at this
surface is within certain limits which depend on the shape of the
cross machine direction basis weight profile of each swath. This
width is a function of the amplitude of the oscillation imparted to
the web by the baffle, the amount of electrostatic charge on the
web and the distance between the baffle and the receiving
surface.
Isakoff, U.S. Pat. No 3,593,074, describes a short diffuser device,
termed a "scoop", which "squeezes" the gaseous stream to increase
its width, thereby also increasing the width of the entrained web.
This scoop is situated between the baffle and the corona charging
station, and leads to improvements in sheet uniformity by
permitting shorter baffle-to-receiving surface distances for a
given swath width. However, as spinning throughputs are increased,
the larger volumes and velocities of gas produced in the flash
spinning operation create an undesirable increase in turbulence.
This increases the random oscillation of the web producing a
nonwoven sheet having less than the desired uniformity.
SUMMARY OF THE INVENTION
An apparatus is provided for forming a fibrous web that includes
means for flash spinning a polymer solution to form a
plexifilamentary strand entrained in a gaseous stream, means at one
location (e.g., a rotating baffle) for spreading the strand to form
a web and oscillating the web in a generally vertical plane in a
plurality of downward radial directions toward a collecting surface
and means positioned below said spreading and oscillating means for
charging said web. The improvement comprises an aerodynamic shield
having front and rear members disposed on each side of said plane
below said spreading and oscillating means. The members have
surfaces facing said plane, said surfaces terminate in edges
equispaced from each other that lie along arcs of equal radius
extending from a horizontal axis proximate to said one location.
The surface of the rear member facing said plane is substantially
parallel thereto and is a stepped surface, stepped away from said
plane in the downward direction along one or more arcs concentric
with the terminating edge of the rear member. The surface of the
front member facing said plane is a section of a surface of
revolution about said horizontal axis that converges downwardly
toward said plane.
The surface of the front member facing the vertical plane
preferably is a segment of a right circular cone converging
downwardly toward said plane at an angle of about 5.degree..
The front and rear members extend downward for a distance of from
about 30 percent to about 60 percent of the distance from said one
location to said collecting surface.
There are ports in said rear member at the location the surface of
the rear member facing the vertical plane is stepped away from said
plane.
The invention concerns an improved process that includes the steps
of entraining a web in a gaseous stream flowing in a generally
horizontal path toward one location, directing and oscillating said
web and said stream from said one location in a plurality of
downward radial directions in a substantially vertical plane
through ambient gas toward a collecting means, and collecting said
web on said collecting means as a fibrous sheet, the improvement
comprising: converging said stream in said downward radial
directions within a shield presenting substantially equal flow
impedances in said radial directions. The process may include the
step of aspirating said ambient gas into said shield generally in
said downward radial directions.
Although some web deceleration can be tolerated within the
aerodynamic shield of this invention, the primary function of the
shield is not to diffuse the gas stream but rather to protect it
and the entrained web as shaped by the rotating baffle and prevent
premature mixing with the ambient gas. Accordingly, the exit gap
width between front and rear shield members is selected such that
there is neutral gas pressure on the members, i.e., the average
internal and external gas pressures are equal. The actual gap width
required is, of course, a function of the rate of gas generation by
flash vaporization, the quantity of gas entrained and aspirated
into the shield, the dimensions of the shield, etc. However, under
any given set of spinning conditions the required gap width is
readily determined by the neutral pressure condition.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional elevation indicating schematically the
arrangement of various elements of an apparatus which can be used
in the practice of the invention.
FIG. 2 is a more detailed cross-sectional view of a portion of a
preferred embodiment of the aerodynamic shield of the present
invention.
FIG. 3 is a view of the web facing surface of the front shield
member of FIG. 2.
FIG. 4 is a graph presentation of data showing the improved machine
direction sheet uniformity provided by the apparatus and process of
the present invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
Referring to FIG. 1, a spinneret device 1 is shown connected to a
polymer solution supply source. Polymer solution 2 under pressure
is fed through an orifice 3 into intermediate pressure or letdown
pressure zone 4 and then through spinning orifice 5 into web
forming chamber 6. The extrudate from spinning orifice 5 is a
plexifilamentary strand 7. Due to the pressure drop at spinning
orifice 5 and the high temperature of the spinning solution,
vaporization of solvent creates a vapor blast which, by passage
along the surface of baffle 8 concomitantly with plexifilament 7,
generally follows the path of advance from spinning orifice 5 to
collecting surface 9, thereby creating a flow pattern within
chamber 6 as indicated by the arrows in FIG. 1. Baffle 8 is mounted
on shaft 10 which is mounted in bearing 11 and is rotated by means
not shown. The surface of baffle 8 is so contoured that the
plexifilamentary strand 7 issuing from orifice 5 is deflected into
a generally vertical plane and simultaneously spread laterally to
form a plexifilamentary web 21 which oscillates from side-to-side
as baffle 8 is rotated.
The plexifilamentary web 21 passes from baffle 8 directly into the
aerodynamic shield of this invention. The shield is comprised of
front member 18 and a rear member comprising elements 13 and 17.
Multineedle ion gun 14 is mounted on the interior surface of front
member 18, and is connected to constant current power source 35
which supplies a potential of approximately 50-60 kilovolts. A
corona discharge occurs between needles 14 and target plate 13
which is disposed so that the vapor blast originating at 5 and
deflected by baffle 8 series the plexifilament web along its
charging surface. Target plate 13 is connected via commutating ring
and brushes to ground by wire 15 and microammeter 16 which
indicates target plate current.
Target plate 13 is an annular metal disc electrode, and is
preferably covered with a dielectric insulating surface as
disclosed in U.S. Pat. No. 3,578,739. Target plate 13 together with
concentric annular segment 17 comprise the rear member of the
aerodynamic shield, and are adapted to be rotated concentrically
with, but independent of, baffle 8 by means not shown. During
rotation of the rear member, its interior surface passes by
rotating brush 20, driven by means not shown, so that the surface
of target plate 13 and adjacent parts may be cleared of any debris,
thereby furnishing a continuously cleaned surface for optimum
operation of the corona discharge. At intervals, in a circular
pattern, the rear shield member is pierced by ports 19 through
which ambient gas may be aspirated into the step region between
concentric disc segments 13 and 17.
After exiting the aerodynamic shield, plexifilament web 21 is
deposited upon a collecting surface 9. The surface illustrated is a
continuous electrically conductive belt forwarded by drive roll 36.
The belt may either be grounded or charged to a positive or
negative potential by power source 37. Due to differences in their
electrostatic charge, the plexifilament web 21 is attracted to
surface 9 and clings to it in its arranged condition as a swath 38
with sufficient force to overcome the disruptive influences of
whatever vapor blast may reach this area. Since high rates of
production can generate high turbulence at chamber 6, auxiliary
corona devices 43 stationed just above the surface of belt 9 may be
employed to place even higher electrostatic charge on swath 38,
thereby pinning it even more tightly to belt 9. Wide sheets are
produced by blending and overlapping the output from several
spinning positions placed in an appropriate manner across the width
of a receiving surface such as the belt 9. The degree of uniformity
of the web deposits tends to increase as the aerodynamic shield is
extended to protect a greater fraction of the vertical distance
from the baffle to the receiving surface. However, unless some
free-fall is permitted, the web fibril orientation is biased too
heavily in the cross machine direction. Furthermore, too extensive
a shield can lead to nonuniform deposits and 37 hang-up" due to
electrostatic attraction and erratic clinging of the charged web to
the internal shield surfaces. Applicants have discovered that a
preferred balance in sheet uniformity and fibril directionality is
attained when the aerodynamic shield extends over about 30-60
percent of the vertical distance from the edge of the baffle to the
collecting surface. The sheet is then lightly compacted by roll 41
and is collected on windup roll 42 after passing through port 39
and flexible elements (or rolls) 40 which assist in retention of
vapor within chamber 6. A conventional solvent recovery unit 44 may
be beneficially employed to improve economic operation.
FIG. 2 is an enlarged cross-sectional view of a portion of the
aerodynamic shield depicted in FIG. 1. Front member 18 is
constructed of Lucite (trademark for Du Pont acrylic resin), its
exit lip 22 lies along a semicircle centered on rotating baffle
axis 23 and the angle of convergence 24 is 5.degree.. Multineedle
corona charging electrode 14 consists of 17 needles smoothly
graduated in length, spaced at intervals along conductor 25 to
provide a varying needle-to-needle target spacing. The needle
electrode is recessed in channel 31 cut into the web facing surface
of front member 18. The needles lie along an arc of a circle
centered on axis 23, and the angle subtended by the end needles as
viewed from the center of the circle is 140.degree., which is
sufficient to overlap the plexifilamentary web envelope throughout
its period of oscillation. (The angle subtended by channel 31,
viewed from the center of the circle is 166.degree..) The 17
needles pass through a curved strip of "Lexan" 26 whose width is
tapered to allow each needle point to protrude the same distance.
This strip thus bridges the gap between adjacent needles and
prevents plexifilamentary debris from building up from the base of
the individual needles during spinning, which debris could alter
the shape and intensity of the electrical field and thereby lead to
nonuniform corona generation and consequent erratic web charging
and sheet nonuniformities.
The rear shield member is comprised of metallic annular target
plate 13, coeered by a dielectric surface 27 having a volume
resistivity between 5 .times. 10.sup.9 and 1 .times. 10.sup.10 ohm
centimeters, and annular target plate extension 28 constructed of
Lucite plus concentric annular segment 17, also constructed of
Lucite. These rear shield member's elements are assembled by means
of annular "Lexan" (General Electric's polycarbonate resin) support
member 30 and thereby adapted to be rotated as a unit about axis
23. i.e., concentrically with baffle 8. (Baffle 8 is rotated at
much higher speeds than the rear shield unit). The step height
between elements 28 and 17 is designated 19a, and support member 30
is perforated at intervals by aspiration ports 19. The provision of
access ports in the rear member near the step permits a suitable
quantity of ambient gas to be aspirated into the aerodynamic shield
to form a protective cushion of gas which flows toward the exit lip
along the internal surface of the rear member.
FIG. 3 is a view of the web facing surface of front shield member
18 showing the needle electrode unit 14, channel 31, "Lexan" strip
26, and also indicating support members 29a and 29b. Front shield
member 18 is suspended from pivot points (not shown) inside members
29a and 29b, both located on a common horizontal axis, which thus
permits front shield member 18 to swing farther away from the rear
shield member momentarily whenever a mass of plexifilamentary
material may begin to plug the shield passageway. Also mounted
within members 29a and 29b are metal spring elements (not shown)
urging front member 18 back into normal operating position as soon
as the plug mass is expelled. Adjustable stops (not shown) are
provided such that the normal exit gap width 22a is set in the
range of from 1/8 to 3/8 inch, or the value at which no net gas
pressure difference exists on front element 18 in a direction
parallel to axis 23. The specific neutral pressure gap with width
may be established during spinning, for example, by temporarily
releasing the front member from the spring biasing means and
allowing it to swing free on its pivots and seek a position such
that pressure on the web side (or "inside") is in balance with the
ambient gas pressure on the opposite side ("outside"). Of course,
appropriate allowance or correction may need to be made should the
center of gravity of the front shield member not lie directly
beneath the pivot points. As may be noted from FIGS. 2 and 3, the
entrance edge of front member 18 has a configuration approximating
a section of a toroid, thus "surrounding" a portion of baffle 8 and
extending backward to a point close to the spinneret housing in
order to restrict entrainment of ambient gas while still providing
sufficient clearance of the occasional swinging motion required to
relieve adventitious plugs.
The web facing surface of the front member of the aerodynamic
shield must satisfy two requirements: (1) it should present
approximately equal gas flow impedance at all radial directions at
which the web may leave the rotary baffle in the vertical plane,
and (2) the spacing between confronting surfaces of front and rear
members should decrease on the average as the web moves radially
through the shield from entrance to exit. This decreasing
separation between shield members partially compensates for the
increase in width of the gas stream as it flows along diverging
radial directions within the vertical plane as directed by the
contoured surface of the rotating baffle, and thereby keeps the
cross-sectional area of the gas stream taken at right angles to its
direction of flow from increasing so rapidly that excessive
deceleration and sticking of the web to the shield can occur. The
equal impedance criterion is met by a front shield member whose web
facing surface is a section of a surface of revolution about the
rotation axis of the baffle; and since the rear member's surface is
approximately flat (apart from the annular steps), the convergence
criterion can simultaneously be satisfied most simply by choosing
the surface of the front member to be a segment of a right circular
cone. The optimum angle of convergence, (i.e., the angle between
the vertical and a straight line tangent to the web-facing surface
of the front member at two points proximate its entrance and exit
edges, respectively, measured on a vertical cross section
perpendicular to the web oscillation plane) is a function of the
detailed contour of the baffle surface, the number and size of the
steps in the rear shield member, etc. Fortunately, this convergence
angle appears to be not too sensitive to variations in these
parameters and a convergence angle of 5.degree. has been found to
be generally satisfactory. Various materials, e.g., Lucite, nylon,
Teflon (trademark for Du Pont fluorocarbon resin), various filled
nylons and Teflons, Nema G (laminated glass/epoxy insulating
materials), "Lexan", etc., can be used for members 17, 18, 26, 28
and 30, if desired.
In order to illustrate the improved uniformity of nonwoven sheets
made possible by the present invention, particularly at higher
productivities, a series of samples is prepared employing prior art
apparatus and compared with a series of samples prepared with the
present apparatus, using perecent coefficient of variation of basis
weight uniformity as the criterion.
PERCENT CV OF BASIS WEIGHT UNIFORMITY
A sheet of material about 500 inches long and at least 8 inches
wide is used. Eighty 1-inch diameter circles are cut from the sheet
along each of three rows, the center-center distances of these
circles being about 3 inches in the width direction of the sheet
and 6 inches in the length direction. The coefficient of variation
(percent CV) of the weights of these 1-inch circles in each row is
calculated and the average percent CV for the three rows is used as
a measure of the sheet uniformity.
EXAMPLE
Linear polyethylene having a density of 0.95 g./cc. and a melt flow
rate of 0.9 gram/10 minutes as determined by ASTM method
D-1238-57T, condition E, is flash spun from a hot
trichlorofluoromethane solution. The solution is continuously
pumped to the spinneret assembly under high pressure. The solution
then passes into a small chamber through a first orifice to reduce
the pressure to the desired value for flash spinning, and is then
immediately extruded into a region at substantially atmospheric
pressure through a second (spin) orifice. Initial flash
vaporization occurs inside a short cylindrical "tunnel" immediately
downstream and coaxial with the spin orifice, which serves to shape
the resulting high velocity gas and entrained strand. The resulting
plexifilamentary strand passes along the surface of a rotating
baffle which simultaneously spreads it, imparts lateral oscillation
and directs it vertically downwards through a corona charging zone
between a multineedle corona discharge electrode and a grounded
target plate toward a moving belt, where it is collected in
overlapping layers. The sheet is then lightly consolidated by
passage between a pair of rolls under a pressure of about 45
lb./lineal inch. The speed of the laydown receiver is adjusted
incrementally to obtain a set of nonwoven sheet samples of
graduated basis weights.
Two sets of plexifilamentary sheet samples are prepared. Set A is
prepared employing the aerodynamic shield of the present invention,
using the preferred embodiment detailed in FIGS. 2 and 3, and
having exit and entrance radii of 91/2 and 21/4 inches,
respectively, with a step height of 5/32 inch. For comparison, set
B is prepared employing the best available prior art apparatus,
namely, the "scoop" diffuser disclosed in U.S. Pat. No. 3,593,074
and in particular the embodiment described in Example 4 of the
patent. For each set of samples the optimum available baffle
designs are employed, together with the appropriate baffle-to-belt
distance required to obtain a 25 .+-. 21/2 inch swath width for the
plexifilamentary deposits on the belt. In addition, maximum
possible sheet uniformity is sought by applying the highest
electrostatic charge level to the web which can be tolerated
without causing web "hangups", disruptive lightening discharges,
etc. The specific parameters employed for each sample are listed in
Table I. All samples in set A are prepared employing a spin orifice
sized to yield a nominal polymer throughput of 100 lbs./hr., while
all samples in set B are prepared with a smaller orifice providing
a nominal 75 lbs./hr. of polymer.
The percent coefficient of variation of basis weight uniformity is
determined for the sheet samples within each set, as listed in
Table I, and the data are presented graphically in FIG. 4. Low
values of percent CV, corresponding to the greatest degree of
uniformity are, of course, preferred. It is apparent on comparing
the curves for sample sets A and B, that substantially superior
sheet uniformity is provided by the apparatus and process of the
present invention, than can be achieved by the best prior art
technology. This has been accomplished even at higher rates of
productivity (100 versus 75 lbs./hr.) which, except for the
benefits provided by the present invention, otherwise inherently
lead to degradation in sheet uniformity. It has also been observed
that the apparatus of the present invention provides the further
advantages of less variable swath width from run-to-run and
day-to-day, and substantially decreases sensitivity to other
process variables such as equipment alignment, web charge, etc.
TABLE 1
__________________________________________________________________________
Set A: -Aerodynamic Shield, Baffle Edge to Belt = 131/4 inches,
Spin Orifice = 52 .+-. 1/2 mils. Solution Tunnel Flow Rate Swath
Width Web Charge Basis %CV Samp. Conc. Temp. Pres. L/D (pph
polymer) (inches) (microcoulombs/ (oz./yd.sup.2) .degree. C. psig
gm.)
__________________________________________________________________________
1 12.6% 184 980 0.300"/0.300" 100.7 23.5 10 2.02 6.45 2 do. do. do.
do. do. do. 11 2.04 6.29 3 do. do. do. do. do. do. 12 1.97 6.91 4
do. do. do. do. do. 24 13 1.92 6.95 5 do. 185 1000 do. 105.0 23.5
11 1.98 7.15 6 do. do. do. do. 104.6 23.5 11 0.98 9.52 7 do. 186
do. do. 102.6 26 11 0.91 9.77 8 do. do. do. do. do. 26.5 11 2.07
6.71 9 do. do. do. do. do. -- 12 0.91 9.56 10 do. do. do. do. do.
27 13 0.86 9.70 Set B: scoop, Baffle Edge to Belt = 111/4 inches,
Spin Orifice = 44 .+-. 2 mils. 11 12.6% 185 1060 0.266"/0.266" 70.6
27.5 11.8 2.01 7.50 12 do. 186 do. 0.234"/0.234" 68.6 26 11.5 2.15
8.17 13 12.2% do. 1000 do. 72.6 22.5 11.7 0.91 12.44 14 do. do. do.
do. do. 23.5 11.1 0.95 12.01 15 12.6% 187 1100 0.234"/0.266" 85.3
24.5 10.1 1.15 10.94 16 do. 186 1060 do. 76.6 26 11.9 2.14 8.24 17
do. do. do. do. do. 26 11.9 2.14 7.60
__________________________________________________________________________
* * * * *