Note: Descriptions are shown in the official language in which they were submitted.
~;~3~9~i
METHOD AND APPARATUS FOR PRODUCING
PAPER AND OTHER NONWOVEN FIBROUS WEBS
TECHNICAL FIELD
This invention ;-elates to the manufacture of nonwoven fibrous
webs, such as paper, which are typically formed from an aqueous
slurry of fibers.
BAC KG ROU N D A RT
Paper and other nonwoven fibrous materials are typically
manufactured by depositing fibers suspended in a liquid onto a
foraminous support which allows the liquid to drain through while
retaining most of the fibers in the form of a web. The fibers lie
intertangled in the plane of the web and adhere to each other by
papermaking bonds or by binder added to the web. In the most
comrnon form of papermaking, the suspension of fibers in water,
commonly referred to as "the stock", is flowed onto a horizontal
upper run of a continuously moving endless belt of wire cloth
wrapped around a breast roll on one end and a couch roll on the
other. Water progressively drains from the stock through the wire
as the wire carries it from the breast roll towards the couch roll.
Supporting the upper run of the wire between the breast roll
and the couch rotl are a number of rotating rolls, known as "table
rolls", whose function is to accelerate the drainage of water from
the stock. Alternatively, the wire runs over "foils" which support
the wire and provide a more gentle drainage than the table roils.
Foils are more commonly used at higher machine speeds. Just
beyond the last table roll or foil in the direction of travel of the
wire, suction boxes are ernployed to further assist drainage of
water from the stock. The wire slides over the flat upper faces of
the suction boxes, which are provided with openings in communication
with vacuum pumps. The vacuum is necessary to draw additional water
from the web after all of the ''easy" water is removed by table rolls
or foils.
t
~ 3~19~
The wet web of fibers is removed from the wire af-ter passing
partially about a perforated "suction couch roll" provided wi-th an
internal suction box connected to a vacuum pump. The wet web is
then passed through a press section where additional water is
5 squeezed out of the web by press rolls and is absorbed by a felt
traveling along with the web. Final drying of the web takes place
in the dryer section or on a yankee dryer. A typical dryer section
consists of a series of small heated drums about which the web
pa s ses .
The stock is usually flowed onto the wire at a "consistency" of
one part of fibers to about two hundred parts of water, by weight.
This is described as ~0.5O consistency", meaning that the fiber
weight is 0.5O of the stock weight. The stock loses water progres-
sively as the wire passes from the breast roll to the couch roll,
15 and therefore, the consistency of the stock increases progress;vely
as it travels away from the breast roll. When the stock reaches 3
consistency of about 2.5% table rolls or foils are no longer effective
in accelerating the drainage of water from the web, and relatively
high vacuum (250mm. of Hg. for example) must be applied through
20 the suction boxes for further drainage. The web typically will
have a consistency of about 20% when it leaves the couch roll. The
consistency of the web is further increased to about 40% in the
press section, and the consistency of the web leaving the dryer
section is greater than 90O and considered completely dry for all
25 practical purposes.
A disadvantage of the conventional m0thod of forming a web is
the enormous volume of water which must be handled because of th0
low consistency of the stock, conventionally kept in the neighbor-
hood of 0.5% when flowed onto the wire in order to achieve accept-
30 ably uniform dispersion of the fibers in the water. Unless thisuniformity of dispersion is achieved, the "formation of the sheet"
is unacceptable. This is due to the phenomenon of "floccing" of
~23~
the fibers. That is, the fibers insist upon agglomerating unless
dispersed in a dilute suspension.
The amount of water removed from the web in this conventional
papermaking process is enormous. For exampler to make one Kg.
of paper requires about 200 Kg. of water to be deposited on the
wire at the breast roll. From this, about 175 Kg. are removed by
gravity or the slightly accelerated drainage at the table rolls or
foils. Another 20 Kg. are removed at the suction boxes and couch
roll and 2.5 Kg. in the press section. Final drying in the heatecl
dryer section only takes out about 1.5 Kg. of water.
By far the greatest amount, almost 9û%, of the water to be
removed is removed before the stock reaches the suction boxes.
Most of this "white water" is recirculated through the system by
being combined with fresh fibers to be deposited on the wire. The
size and cost of equipment necessary to circulate this water is
enormous, as are the energy costs for driving the pumps that
recirculate it. For illustration, consider the amount of water
circulated in a typical paper machine proclucing 180 metric tons of
paper per day. Such a machine requires the circulation of 32
million Kg. of water per day ~420 I./sec.) just from the breast roll
and table roils or foils alone. In addition to the cost of the
equipment and energy needed to circulate this large amount of
water, the costs of chemically treating and retreating the water are
significant.
It has long been the dream of papermakers to eliminate the
need for such large quantities of water. However, obtaining
uniform paper formation and avoiding flocs or clumps has always
required that the fibers be dispersed in very large volumes of
water. Where fibers longer than conventional papermaking fibers
were desired to be added to the web, in part or totally, even
greater amounts of water have been necessary to maintain any
acceptable ~Jniformity.
9S
When the stock is first deposited on the wire at the breast
roll, the fibers are very mobile and the manner in which the water
is removed greatly affects the web formation. It is desirable to
remove the water in a controlled manner to assure good web
formation. This is conventionally accomplished by draining the
majority of the water by gravity or with the gentle assistance of
tabie rolls or foils and then subjecting it to vacuum boxes.
The point where fiber mobility has been sufficiently eliminated
to assure maintenance of fiber formation is commonly referred to as
the "dry line", because the appearance of the stock suddenly
changes from wet to dry. Typically, the dry line occurs at 3~% to
4~O consistency. Prior to reaching the dry line, great care must
be taken in dewatering the web. Fiber mobility in stock, on the
other hand, has always been believed necessary in the early steps
of dewatering to get the desired fiber orientation and uniformity of
formation. That is why prior art processes which employ so-called
"high consistency" stock use stock consistencies only up to 1% or
2%. These stocks are still well below the dry line consistency of
about 4%.
The nonwovens and papermaking art can be viewed as being
divided into two distinct types of processes. One is conventional
web forming starting with stock consistencies well below the dry
line as described above, and the other is dry forming, wherein no
water or other iiquid is employed. This latter process is typically
carried out on small, slow speed machines. Each of the processes
has its disadvantages. Until the present invention there have been
few if any commercially practicable alternative processes.
In addition to the other disadvantages of the prior art noted
above, uniform formation and basis weight in the cross-machine
direction has required complex flow spreaders to uniformly deposit
the stock upon the wire.
~2~
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DISCLOSURE OF THE INVENTION
In contrast to the p r ior art, the present invention permits the
formation of paper with much less water than in conventional paper-
making. The stock can be deposited on the wire at a fiber consistency
5 well beyond the dry line stage, and the web can be formed instanta-
neously with good fiber formation. The amount of water needed in
the process can be as little as from 8o down to 2o of that used
conventionally. The commercial impact of the savings is staggering.
In addition, the invention can provide products with improved proper-
10 ties over conventional paper. Examples of such improved propertiesare greater bulk and better formation, as well as others. These
sheets can be produced without loss of strength.
The present invention is a method and apparatus for producing
a nonwoven fibrous web in a very simple manner which provides
15 good formation and uniform basis weight across the width of the
papermaking machine.
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Various aspects of the invention are as follows:
Apparatus for producing a nonwoven fibrous web comprising:
A. means fox providing a reservoir of foamed fibers and
liquid dispersion;
B. a moving foraminous carrier member in contact with
the reservoir for carrying a layer of fibers from the
reservoir;
C. reduced pressure means adjacent the rsservoir for
providing on the side of the carrier member opposite the
reservoir a pressure which is lower than that of the foam
dispersion for breaking foam adjacent the carrier member and
for forming an unfoamed fibrous web on the carrier member
before it leaves the reservoir; and
D. means for removing the fibrous web from the carrier
member at a location remote from the reser~Toir.
Method for producing a nonwoven fibrous web on the
papermaking machine comprising the steps of:
A. forming a foamed dispersion of fibers and liquid;
~: B. depositing the foamed dispersion into a reservoir
extending continuously across the width of the papermaking
machine;
C. continuously moving at least one foraminous carrier
member in contact with the reservoir;
D. providing a pressure adjacent the reservoir on the
2 5 side of the carrier member opposite the reservoir which is
lower than that of the foam dispersion and which breaks
the foam adjacent the carrier member and forms an unfoamed
fibrous web thereon before it leaves the reservoir;
E. preventing unbroken foam dispersion from leaving the
reservoir with the fibrous web on the carrier member; and
F. removing the fibrou~ web from the support member.
, ~;
-c, ~ ~
- 8- ~ ~3~995
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 of the drawings illustrates schematically the preferred
apparatus for carrying out the present invention. FIG. 2 is an
enlarged view of the section of the apparatus where the web is
formed adjacent to the reservoir.
BEST MODE FOR CARRYING OUT THE INVENTION
The paper machine shown in the drawings includes three main
sections: stock preparation section 1; web formation section 2; and
press section 3. A complete apparatus would also include a drying
section, but since this additional section is conventional, it is not
s how n .
The stock preparation section 1 is illustrated by foaming appa-
ratus 4 being fed stock at a high consistency through inlet 5 and
being supplied air through inlet 6. A suitable apparatus which
provides mechanical agitation of the stock in the presence of air is
used as the foaming apparatus 4. An example of a satisfactory
apparatus is a Micar Processor Reactor manufactured by Black
Ciawson, which consists of a shell and rotor fitt~d with vanes or
bars arranged in a variety of angles to impart micro and macro
mixing. The stock is fed into the foaming apparatus 4 in the form
olF a vsry high consistency slurry of papermaking fibers and water.
The consistency of the stock should be as high as possible while
still providing the desired product properties and will preferably
vary between about 6% and about 309~. Consistenci0s lower than
this range do not benefit from all of the advantages of the
invention. Consistencies higher may not have enough free water
to permit satisfactory haming.
~3~
A surfactant in water is added to the foaming apparatus
through inlet 7. The surfactant can be provided by any
conventional surface tension reducing material which will permit
foaming of water and which is compatible with the properties sought
5 in the paper being manufactured. Examples of satisfactory
surfactants are sodium lauryl sulfate, rosin size and an aqueous
blend of anionic surfactants and ethylene glycol monobutyl ether.
The amount of surfactant can be varied to provide the desired foam
stability, but will typicaily be on the order of 0.2% by weight of
10 the stock.
Air can be delivered along with the stock through inlet 5 or it
can be delivered in part or wholly through air inlet 6 under
sufficient pressure to enable it to enter the apparatus 4. Higher
pressure is unnecessary, since foaming is accomplished through the
15 mechanical agitation of the apparatus driven by motor 8. The
surfactant, liquid and fibers are subjected to mechanical shearing
action in the presence of the air to produçe a foamed liquid and to
uniformly disperse the fibers.
The stock is sufficiently foamed to provide a volumetric
20 increase wherein preferably at least 66% of the volume is air and
more preferably from about 75% to about 95% of the volume is air.
The minimum air volume ratio is generally needed to provide good
formation. The higher the ratio, the better separation of the fibers.
The air bubbles in the foam replace water in a conventional water
~5 dispersion and act to keep the fibers dispersed and separated from
each other. Accordingly, the most uniform dispersion requires
higher air volume ratios for higher consistency stock. Higher
ratios also provide higher volumes of material to be handled and
more air to be removed upon breaking the foam and forming the web,
30 all of which ;s, of course, vastly easier than handling the amount
of water used in a conventional process, and the foam provides a
much more stable dispersion than the water it replaces in a conven-
tional papermaking stock.
9S
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The bubble size of the foam is not critical in the sense of
having an exact size, but it must be small enough to provide a foam
which remains stable until the web is formed. That is to say, the
foam must hold the fibers in theis dispersed state until they are
5 about to take a permanent placement in the web. The smaller the
bubbles the more stable the foam will be. Typically, the bubble
size will be small enough to be barely visible to the naked eye.
Preferably, the foamed dispersion will be permanently stable.
That is to say, the dispersion will remain intact indefinitely unless
10 some special step is taken to destabilize and collapse the foam.
Examples of such steps are external mechanical pressure being
applied to the foam or the foam being subjected to a pressure which
is lower than the pressure in the foam. The latter is preferably
accomplished by exposing the foam to a partial vacuum, such as by
15 providing a suction through a screen which collects the fibers. It
would also be possible to produce and maintain the foam at a higher
than atmospheric pressure and then collapse the foam by exposing
it to atmospheric pressure.
The permanently stable foamed dispersion of the present
20 invention when left to dry, either to the air or in a heater, without
subjecting it to a destabilizing step will maintain the fiber
dispersion even after drying. Subject only to a small amount of
shrinkage from drying, the high volume, low density structure of
the foamed dispersion can be maintained even after drying. Thus,
25 if a significant volumetric increase is produced by foaming, a 3:1
ratio (66% air~ or higher for example, the majority of the volumetric
increase will remain in the dried product. That is, shrinkage will
be less than 50% and preferably less than 20%. Useful fibrous
products can be made with all or at least a majority of the fibers
30 being papermaking fibers or all or at least a majority of the fibers
being nonpapermaking fibers if an adhesive is added to the liquid
before foaming. Such products can be useful for insulation or
cushioning materials, among other things.
~2~3~9~5
The foamed stock is deiivered from the foaming appara-tus 4
through a conduit g to a stock reservoir 10 forrned by two continu-
ously moving foraminous or permeable wires 11 and 12 converging
towards each other to form a nip. The wires can be provided by
5 conventional fourdrinier wires. The wires are brought closely
together as they move past vacuum foam breakers 13 and 14 spaced
apart a short distance from each other. Each of the vacuum foam
breakers 13 and 14 are preferably provided by suction rolls having
a partial vacuum within. The vacuum is preferably greater than
10 75 mm . of H g .
The foamed stock emitted from conduit 9 piles up in the
reservoir 10 to form a pond 15 (a reservoir or accumulation of
material unenclosed or open to the atomosphere) of stock extending
continuously across the width of the papermaking machine and from
15 which a thin wide sheet-like flow of stock is continuously drawn
into the nip. The suction from vacuum foam breakers 13 and 14
assists the moving wires in drawing stock into the nip. At the
same time the suction creates a zone of lower pressure than in the
foam, which collapses the foam and forms the web. An exceptionally
20 valuable advantage obtained by this apparatus is that the web so
formed will have uniform basis weight and uniform formation across
its width even with wide variations of height across the width
of the pond or reservoir. There is no need for a cornplex flow
spreader to deliver the stock. In fact, the conduit 9 can be
25 provided by a series of circular pipes positioned across the width
of the machine, the number of which depends upon the width of the
wi res .
The suction from the foam breakers 13 and 14 simultaneously
accomplishes in a single step destabilizing and breaking or
30 coliapsing of the foam, removal of at least a portion of the foam
medium (air along with some water ancl surfactant) and formation of
the web on the wires 11 and 1~. Prior to collapsing the foam
essentially no water will drain from the foam.
A continuous web 20 is formed between the two wires 11 and
12, and it travels with the wires for a short distance until the two
wires separate. A vacuum box 16 placed behind wire 11 is used to
gently urge the web 20 to follow wire 11 when the wires separate.
5 Further along the path of wire 11, felt 17 is brought into contact
with the web and the web is transferred to the felt with the
assitance of vacuum box 18. The felt 17 and web 20 then travel
together through press rolls 1~ where water leaves the web. From
there the web 20 is removed from felt 17 and delivered to one or
10 more additional press rolls (not shown) and then to a conventional
drying section (not shown), if desired. In some processes, it
might be desirable to leave out the press section to maintain a
higher bulk in the web. In such cases, the web may be dried by
through-air driers. Where a press section is employed, the sheet
15 can enter it drier than a conventional sheet, thereby requiring less
pressing and resulting in higher bulk.
To complete the description of the apparatus, wires 11 and 12
continue around a continuous loop driven by nip^forming drive rolls
21 and about carrying rolls 2~ and guide rolls 23. Likewise, felt 17
20 continues around carrying rolls 22 and tension roll 24. Located
adjacent the path of the felt 17 is a shower 25 for washing the
felt 17 and a suction box 26 for dewatering.
Referring to FIG. 2, reservoir 10 formed by pond 15 of foamed
dispersion extends downwardly to the point of closest convergence
25 between carrier wire 11 and carrier wire 12. (A reservoir is
defined herein as an accumulation of materiai in a stream of flow
wherein the quantity of the material being removed from the
reservoir can differ widely from the quantity entering the reservoir
from moment to moment.) The two wires converge together at this
30 point to form a nip, the spacing of which is establishecl by the
spacing between vacuum foam breakers 13 and 14. Onè wire is
needed to form the web against, and the other wire serves to
prevent unbroken foam from leaving the reservoir. In practice,
~3~9~
both wires provide both functions to some extent. However, it
would be possible to employ oniy one wire and some other device,
such as a doctor blade, to prevent the unbroken foam from leaving
the reservoir.
Each foam breaker, shown here schematically in cross-section
consists of outer rotatable cylinders 27 and 28 drilled or otherwise
perforated to provide openings to vacuum chambers 29 and 30. The
foam breakers may be provided by conventional rotatable suction
rolls commonly used in papermaking. The vacuum chambers are
provided by adjustable radially extending baffles which define the
suction zone in each foam breaker. The lower baffle of each is
preferably positioned at the nip or the point of rlosest convergence
of the wires, which is also the boundary of the reservoir. From
the point of the lowermost baffle downstream the foam in the
dispersion has been collapsed and the fibrous web 20 formed
between the wires 11 and 12.
Each lower baffle could be positioned above (upstream of) the
nip in some circumstances, but generally it would not be desirable,
since there would be no means of escape for air and/or water
squeezed out as the web proceeded into the nip. Also, it generally
would not be desirable to place it below (downstream of) the nip
because it would tend to draw the wire from its natural stra;ght
path after leaving the nip. Each upper baffle forming the vacuum
chamber is positioned at another point adjacent the reservoir to
plare the entire vacuum chamber in vacuum communication with the
reservoir. Its preferred position will depend upon machine speed
and vacuum level. An example of a satisfactory position is between
about 2 and 15 circumferentially from the center point of the nip.
It may be desirable for the positions of the upper and lower baffles
in the two foam breakers to be different in some circumstances.
The vacuum levels in the two foam breakers 13 and 14 do not
have to be the same. In fact, it is preferable that the vacuum be
slightly higher in foam breaker 13 to encourage the forraed web to
~23~9~S
-14-
stay with wire 11 when the wires separate. Too great a vacuum
level can cause the web to stick too tightly to the w;re. It should
also be noted that the vacuum level can affect the thickness of the
web formed.
The spacing between the foam breakers will be related to the
desired web thickness and vacuum level. As an illustration, the
spacing between wires 11 and 12 will typically be between about 0.3
mm. and about 1.5 mm. for 100 9 /m 2 basis weight paper. The
foam breakers may have their positions fixed rigidly or, preferably,
mounted for slight movement towards and away from each other and
being resiliently urged towards each other by springs or fluid
driven pistons.
Although the fibers employed in the present invention are
preferably papermaking fibers in the majority, and more preferably
in total, which form papermaking bonds upon drying, nonpapermaking
fibers, such as synthetic fibers, can also be employed, in which case
it may be desirable for adhesives to be added for additionat bonding.
The following examples further illustrate the invention.
EXAMPLES 1-9
Z0 In the following examples, foamed fiber papermaking stocks of
softwood and hardwood fibers were prepared at 8%, 15% and 20%
consistency (fiber weight to stock weight). The surfactant was a
mixture of the following with about 180 Kg. of water added.
Parts by Dry Weight
PEXOL ~a pale fortified rosin size .36 Kg.
manufactured by Hercules, Inc. ~
Mearlcel 3û05 (an aqueous blend of anionic .19 Kg.
surfactants and ethylene glycol
monobutyl ether, The Mearl Corp.
The foam was formed in a Mica~'Processor apparatus and had an air
content of about 87% by volume. Each of the stocks were further
'~
~'
subdivided into three parts One part was not subject to further
treatment, a second part included a starch binder and a third part
included starch binder and clay pigment. Each of the slurry
samples were deposited onto a wire cloth and formed into webs in a
5 web forming section similar to that disclosed in the drawings. The
webs were subjected to the following conventional paper tests to
determine their usefulness as conventional products:
Opacity: This test measures the ability of paper to
prevent light from passing through it.
For a plain uncoated paper a unitless value
of 70 is acceptable. Coated papers for
printing, would be expected to have
opacity values in the nineties.
Gurley Density: This porosity test measures in seconds
the amount of time it takes for 100 cc. of
air to pass through 6.45 cm.2 of paper.
Without any addition of filler or coating, a
plain uncoated paper should exhibit a
minimum porosity of about 1 or 2 secs. A
minimum for coated printing base papers
should be about 20 secs.
- Mullen: This test measures in Kg./cm. 2 the amount
of pressure paper will withstand before it
ruptures. A range of about 0.35
Kg./cm.2 for uncoated printing paper to
9. 8 Kg . /cm . 2 for coated paper is normal .
Scott Bond: This test measures in cm.^Kg.,the amount
of work necessary to split a sheet in the
Z-direction. For uncoated printing papers
a minimum of 11.5-23 can be expected.
Coated papers may be as high as 460-580 .
Ash Retention: This test measures the amount of filler
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~L~3~
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(e.g., clay) in the sheet as a weight
percentage of the total sheet.
Table I displays the results of testing Examples 1-3, Table ll for
Examples 4-6, and Table lll for Examples 7-9. For comparison
5 purposes an uncoated paper web made by conventional means from
stock of hardwood and softwood fibers at 0.5~ consistency and
including clay filler was also tested and included in Table 1.
Table I
8~ Foamed Fiber Samples
Conventional Ex.1 Ex.2 Ex.3
Sample with w/Starch
Starch ~ Clay
Basis Weight(g./m. 2) 81 91 88 86
Caliper(mm./sheet) 0.11 0.17 0.16 0.18
Opacity 88.8 86.2 85.7 88.6
Gurley Density(sec. ) 12.1 2.37 2.0 2.4
Mullen(Kg./cm. 2) 1.18 0.41 0.45 0.41
Scott Bond(cm.-Kg.) 57.27 42.49 67.77 68.47
Ash Retention 6% -- -- 8.5%
It can be seen from Table I that 8% consistency foamed fiber
samples compare favorably with conventionally formed paper.
Moreover, the bulk can be seen to be significantly greater than in
the conventionally formed paper.
The conventional sample and Example 1 were further subjected
to a calendering operation by passing the samples twice through a
nip created by steel rolls at a nip pressure of 36 Kg.per linear cm.
On visual inspection of the samples after calendering, it was
apparent that the formation of the foamed fiber sheet was very good
and the surface appearance was good, and both were as good as or
better than for the conventional sample.
23~35
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_able l I
15~6 Foamed Fiber Samples
Ex.4 Ex.5 Ex.6
W/StarchW/Starch ~ Clay
Basis Weight~g./m. 2) 108 145 185
Caliper(mm./sheet) 0.20 0.28 0 33
Opacity 88.6 93.2 96.4
G u rley Density ( sec . ) t .47 1.62 1.6
Mullen(Kg./cm. 2) 0 40 0.39 0.32
Scott Bond(cm.-Kg.) 96.98 128.16 92.36
The results of Table ll show that Examples 4,5 and 6 satisfy the
basic requirements for plain paper and in some instances exceed
them .
Table l l l
20% Foamed Fiber Samples
Ex.7 _x.8 Ex.9
W/StarchW/Starch ~ Clay
Basis Weight(g./m.2) 166.5 183 183
Caliper(mm./sheet) 0.29 0.30 0.36
Opacity 95.15 94.6 96.4
Gurley Density(sec.l 1.3 3.6 0.8
Mullen(Kg.tcm.2) 0.48 0.64 0.32
Scott Bond(cm. -Kg. ) 92.36 103.9 ---
The results of Table lll show that Examples 7, 8 and 9 satisfy the
basic requirements for plain paper and in some instances exceed
th em .
EXAMPLE 10
--. 30 Dry lap pulp having a mixture of about 60% softwood fibers
and 40% hardwood fibers was cut up and added to a Micar processor
apparatus with simultaneous addition of watf~r to provide a fiber
consistency of about 25%. In the fiber processor, sodium lauryl
3~
sulfate (a surfactant manufactured by du Pon-t as Duponal C)~was
metered in as a 0.5,, solution in water and mixed with the pulp.
Generation of foam in this mixture was almost immediate as it
progressed to the first mixing/processing disc. The processor
5 dispersed the fibers in the foam and also broke up lumps.
Followin~3 this, the mixture was passed through a second treating
unit consisting of a 15 cm. diameter t~lbe about 1.3 m.long with a
motor driven shaft extending through the center and having
a~3itating fingers to further insure dispersion of the fibers in the
10 foam and to increase the foam ratio. The foamed slurry had a fiber
consistency of about 15o by weight and an air content of about 93%
by volume.
The foamed fiber slurry was delivered to a downwardly
converging nip formed by two air permeable wires traveling at a
15 speed of about 16 m./min. in an arrangement similar to the web
formation section described in the drawings, except that the foam
breakers were provided by nonrotating slotted pipes. The slot for
one pipe was 6 mm. high and the slot for the other was 3 mm.
high. Both extended across the full width of the web to be
20 formed. The vacuum applied was about 100 mm. of Hg. for one
foam breaker and about 40 mm. of Hg. for the other foam breaker.
The gap between the wires at the nip was 0.38 mm. The angle of
the center point of the 6 mm. vacuum slot at the higher vacuum
foam breaker was about 5 upwards from the nip. The angle of the
25 center point of the 3 mm. wide vacuum slot at the other foam
breaker was about 0.75 upwards from the nip.
The vacuum collapsed the foam and formed a web on the wires.
After formation, the web followed one wire and was transferred to a
felt using a suction pick-up device. It was then passed through a
30 double felted first press, transferred to the second felt by suction
pick-up, removed from the second felt and then dried.
The web prepared by this process had a basis weight of 118
g./m. 2 and when examined had better appearance and feel than
lE~
~236~ 5
,9
most sheets formed by conventional means. In general the
formation was excellent, the look-through appearance having much
more uniform translucency than conventional papers. The formation
approached the parchment-like softness of good cellulose drafting
paper normally made by heavily refining the fibers. Specifically,
the floc size distribution was greatly reduced compared to
conventionally made paper, from a characteristic range of 1 to 20
mm. down to a range of about 1 to 3 mm. The floc clouds larger
than 10 mm. or so common in many conventional papers were
completely absent. Furthermore the densest flocs in the paper of
the example had less than half the density of flocs in conventional
paper .
EXAMPLE 1 1
A foam was created by mixing in a Waring blender under high
speed 20 ml. of water and 45 cc. of sodium lauryl sulfate surfactant
(290 solution in water). With continuous high speed mixing, 47.~ g.
of a 25% consistency slurry of papermaking fibers and 14 g. of
titanium dioxide pigment were added. A uniform foam fiber
dispersion of about 26o solids was obtained.
The mixture was applied to a forming apparatus having a web
formation section similar to that used for Example 10, except that
one of the wires was covered with an impermeable plastic film to
block any drainage or vacuum effects from that side. This film was
also intentionally wrinkled slightly. The vacuum applied by the
uncovered foam breaker was about 125 mm. of Hg., and it ~ollapsed
the foam and formed a web.
The paper sheets thus formed exhibited conventional wire
pattern on the side formed on the llnblocked wire, but the side
formed against the film covered wire was smooth overall with ridges
replicating the wrinkles of the plastic film. This exampie illustrates
the ability to form a two-sided sheet with significant variations in
the surface effects.
