Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
6;2~
This invention relates to manufacture of a bulky, soft
and absorbent paper web and is particularly applicable to the
manufacture of sanitary paper and similar products, such as
ti.ssue, toweling and similar papers wherein these characteristics
are particularly desirable.
Conventional papermaking techniques are generally un-
satisfactory for the manufacture of bulky, soft and absorbent
paper webs since they utilize prior to drying one or more press-
ing operations on substantially the entire surface of the paper ~ -
web to expel excess water, smooth the sheet and provide strength
thereto. While overall pressing operations are probably the most i~
efficient methods of dewatering and achieve requisite tensile
strength in a paper sheet by bringing the individual fibers of -
the web into close physical proximity, this operating efficiency
and increase in product strength are more than counter-balanced ,;
by destroying the desirable combination of softness, absorbency
and bulk desirable in sanitary and similar products.
A number of approaches have been developed in an `
at~empt to provide a soft, bulky and absorbent sheet which has
desirable strength characteristics. One approach is set forth in
.S. Patent No. 3,301,746 which discloses a process wherein a
paper web is formed with essentially no pressing, is thermally
pre-dried, and is then heavily compacted in a knuckle pattern
against a dryer drum while the web is still wet enough to allow
increase in bonding by compaction.
. . , ~
,., ~: .
. . .. :, :
.. . : . . ~ . .
6~
Pre-drying of the web shown in U.S. 3,301,7~6 is accom-
plished by means of a through-drying system in which hot gases
are passed through the web prior to imprinting of the knuckle
fabric at the dryer drum. Water removal using through-dryers of
the type utilized in the U.S. 3,301,746 process is very energy
intensive and such dryers are constructed and operated at con-
siderable expense.
Other systems have been developed for the manufacture
of an absorbent, soft, bulky web. One such arrangement is dis-
closed in U.S. Patent No. 3, 812 ~ 000 directed to a process wherein
an elastomeric bonding material is mixed with lignocellulosic
fibers and the web formed thereby is dried without mechanical
compression until it is at least 8~/o dry. The various techniques
taught for drying the web are radiant heat lamps, tunnel dryers,
or transpirati~n dryers (through-dryers) wherein air, preferably
heated, is used to pre-dry the web. Again, use of such pre-
drying techniques results in a considerable expenditure of
energy with consequent high expense.
Yet another technique is taught in U.S. Patent ~o,
3, 821~ 068~ According to the technique taught in this patent a
creped web i8 formed by deposition from an aqueous slurry of
principally lignocellulosic fibers and dried to at least 8~/o ..
fiber consistency or dryness without being subjected to mechani-
cal compression of the web to substantially reduce formation of
papermaking bonds which would form upon compression of the web
while wet. A creping adhesive is applied to one surface of the
web and the web is adhered to a creping surface with the web be-
ing dried on the creping surface to about 95% dryness level before ~-
removal with a creping blade. Pre-drying is again effected
, ' ~
- 2 - ~ ;
3L~)6~6Z~
thermally through the use of radiant heat lamps, tunnel dryers,
or preferably transpiration dryers. As stated above, such pre- ;~
drying arrangements are energy intensive and expensive.
All of the above-described methods operate on a common
assumption, that is, that pre-drying or dewatering without mecha-
nical compression is necessary to produce a product having ade-
quate strength and yet having the desirable characteristics ;~
associated with sanitary papers and the like of softness, bulk
- and absorbency. Since mechanical compression is avoided in the
pre-drying stage various expensive pre-drying substitutes must be
adopted to preliminarily dewater the sheet without compacting
same. It will be appreciated that such through-drying techniques
are wasteful in that they use up inordinate amounts of diminish-
ing natural resources such as natural gas.
It is therefore an object of the present invention to
provide a process for manufacturing a soft, bulky and absorbent
paper sheet having adequate strength and of a quality at least
comparable to the products produced by the above-described prior
art systems without the use of thermal pre-drying techniques. In
view of the teachings of the prior art, it is very surprising to
learn that a sheet of the type desired can be produced through
the use of a mechanical dewatering or pre-drying step. It is
perhaps even more surprising to learn that the process of this
invention may be used to produce a web whose bulk is actually ,
enhanced by passing it through a compression nip of a specific
nature.
According to the present invention a method is provided
for the manufacture of a soft, bulky and absorbent paper web ;
-- 3 --
, . .
.
`
~L06~L62(:~
having adequate strength for use as s~nitary paper and the like.
In the method of the invention an uncompacted wet web
is supported on an imprinting fabric having compaction elements
formed for example by knuckles at the warp and weft crossover
points of the filaments of an open mesh fabric. The imprinting
fabric is characterized by having a surface void volume of
from about 15 cubic centimeters per meter squared (cc/m ) to
about 250 cc/m2, preferably from about 40 cc/m to about 150
cc/m , and a knuckle contact area of from about 5% to about
5~/O, and preferably from about 2~/o to about 3,5%, The paper
web is selectively mechanically dewatered by passing the wet
web through a first compression nip formed between the imprint-
ing fabric and a conventional papermaker's dewatering wet felt
so that significant compacting of the web occurs only in the
vicinity of the compaction elements comprised of the knuckles,
whereafter the selectively mechanically pre~dried web is
finally dried.
In a preferred embodiment the selectively mechanically
dewatered pre-dried web is retained on the imprinting
fabric after it passes the first compression nip and is
thereafter applied to a heated creping surface at a second
compression nip formed between the creping surface and the
imprinting fabric. The web remains essentially undisturbed
on the imprinting fabric as it is transported between the com- ,
pression nips so that the fabric compaction elements contact
essentially the same portions of the web at the second com- ~-
pression nip that were contacted at the first compression nip. -~
The web i5 then thermally dried, creped and removed from the
creping surface,
In another aspect of the invention there i9 provided
apparatus for selectively mechanically pre-drying a paper web
formed on a papermaking machine comprising in combination:
- 4 -
, ,
. . .
z~ ::
an imprinting fabric having a web supporting surface including
spaced compaction elements comprising from about 5% to about
5~/O of the area of the web supporting surface, said imprinting
fabric having a surface void volume of from about 15 cc/m `~
to about 250 cc/m ; and a papermaker's dewatering felt
positioned adjacent to said imprinting fabric and forming a
compression nip therewith through which said web is adapted
to pass and be selectively mechanically pre-dried and signi-
ficantly compacted between the fabric and felt only in the
vicinity of said spaced compaction elements. ~
In yet another aspect of the invention there is pro- ~ -
vided an apparatus for manufacturing a bulky, soft and
absorbent paper web comprising in combination: means for
forming an uncompacted web, the apparatus defined
above for the selective mechanical pre-;drying, wherein the
imprinting fabric is movably mounted, and means for finally ~;
drying the mechanically pre-dried web. .~ :
Fig. l is a schematic side view of a preferred form of
apparatus for carrying out the method of the invention' ~ ,
`,' ,~
'''''
$.~ _ 5 -
~L0616'~
Fig. 2 is a view showing details of the first compres-
sion nip;
Fig. 3 is a schematic side view of another form of
apparatus for carrying out the method of the invention' i
Fig. 4 is a schematic side view of yet another form of
apparatus for carrying out the method of the invention: and
Fig. 5 is a schematic illustration of the technique
employed to establish the surface void volume of an impxinting
fabric. (Figure 5 appears on the same sheet as Figure 2).
Referring now to Fig. 1 a papermaking machine is illus-
trated which may be utilized to manufacture a strong, soft, bulky
and absorbent sheet according to the process of the present
invention. The machine includes an imprinting fabric 10 supported
by support rolls 12 in the form of a continuous loop. Fabric 10
is adapted to pick up an essentially uncompacted paper web from
any sheet-forming device such as headbox 13 and fourdrinier wire
14. The precise mechanism for delivering the slurry to the im-
printing fabric 10 is a matter of choice. It is important, how-
ever, that the web be essentially uncompacted prior to placement
on the fabric.
The imprinting fabric 10 continuously moves in the `
direction of the arrows. The fabric has certain characteristics -~
that must be employed when practicing the process of the present i~
invention. The imprinting fabric must incorporate means defining ~ -
compaction elements which compact tha paper web supported by the `
imprinting fabric during the selective mechanically pre-drying
or dewatering ~tep that will be desaribed in detail below. 5he
,''
'''.
.,
-- 6 --
62~ ~-
compaction elements may for example be defined by the knuckles
formed at the warp and weft crossover points of the filaments of
an open mesh fabric. The imprinting fabric has a surface void
volume of from about 15 cc/m2 to about 250 cc/m2, and preferably
from about 40 cc/m2 to about 150 cc/m2, with the compaction ele-
ment area of the imprinting fabric constituting between about 5%
and about 50/0, and preferably from about 20% to about 35%~ of the
total web supporting surface area of the fabric.
The surface void volume of an imprinting fabric is
defined as the fabric void space occupied by a plastic sheet of
specified composition when pressed into the imprinting fabric from
the normal web contacting side thereof at a temperature of 212 F
for 5 minutes at a uniform pressure of 50 psi. The plastic sheet
is a random copolymer of vinyl chloride and vinyl acetate wherein
the vinyl chloride content is 83.2% and the vinyl acetate content
is 16 ~ and contains 0 . 92% plasticizer. The copolymer has a -;~
Dilute Solution Viscosity logarithmic viscosity nu~ber of
0 639 (ASTM D 1243-66) ~
The first step is to determine the total void space
defined by an imprinting fabric between the outer surfaces thereof.
To determine this figure, six 1 X 3-inch specimens of fabric are
cut with a 3-inch dimension corresponding to the warp direction
of the fabric. Individual specimens are weighed and recorded to
the nearest 0.1 milligram. Three of the specimens are separately
sandwiched between pairs of glass slides with a plastic sheet of
the aforedescribed composition, said sheet being positioned on the
normal paper web contacting surface of the fabric. The sandwiched '~
plastic sheet is three inches long and 1 inch wide to correspond
to the fabric dimensions and has a caliper of 21.6 mils. The
,.
... , . ; . . ; :
, , ,, , . .
. ~. . - .. ,-. . .
~61~;~
sandwiches are then pressed for 5 minutes at 212 F and 50 psi,
After pressing, the glass slide in contact with the fabric is
removed and the three remaining sandwiches (glass slide - plastic
sheet - fabric) are separately clamped by means of binder clips
for subsequent processing.
The three sandwiches are now immersed in molten paraffin
wax maintained in a suitable container at 160F. The three pieces
of separate fabric are also so immersed. With the six specimens
(three sandwiches and three pieces of fabric) still immersed, the
wax container is transferred to a vacuum oven and held under
vacuum to remove entrapped air from the specimens. The specimens
are individually removed from the hot wax and placed on separate
glass 1 X 3-inch slides. Additional molten wax is added to over-
flow the top surface of each specimen and a second glass slide
pressed on the surface to force out excess wax. The binder clips
are of course removed from the sandwich specimens prior to this '
step. The wax-filled specimens are then chilled to allow the
glass slides to be removed from the specimens without disturbing -
the wax. One suitable approach for effecting chilling is to chill
the specimens on an aluminum block in a dry-ice-acetone bath,
Fig. 5 shows a fabric A (partially broken away for illustration) ;~ ;
having impressed therein from the normal web contacting side there-
o a plastic sheet B of ~he specified type. On the other side
wax C fills the rest of the void volume of the fabric. It will be
appreciated that the volume of the fabric occupied by the plastic '
sheet is the surface void volume.
The next step is to remove excess wax from the specimens
by scraping same with a suitable tool. In the case of the fabric
specimens, the wax is scraped down to the knuckle level of both
:
-- 8 -- -
, ~ ,.-.. .
620
surfaces of the fabric and from the edges. In the case of the
sandwich specimens, the wax is scraped from the specimen edges and
down to the knuckle level of the side of the fabric not in engage-
ment with the plastic sheet.
To determine the surface void volume, the total volume
of wax remaining in the three separate fabric specimens is first
determined. This is done by weighing the three waxed fabric
specimens to the nearest 0.1 milligram. The total volume (Total
Void Volume) occupied by the wax in the fabric specimens (expressed
in cubic centimeters per square meter) is calculated according to
the following formula:
(Weight of waxed (Initial fabric
specimen, g) - weight, g)
Total Void Volume =
(3 in2) (0.767 g/cc) (6.452 X 10 4 m2/in2).
To determine the volume of wax remaining in the three
sandwich specimens (Partial Void Volume) the plastic sheet is
first removed. The remaining fabric and wax are then weighed.
Partial Void Volume is calculated according to the following
formula: ~
Weight of Initial fabric ~ -
waxed specimen, g - weight, g
Partial Void Volume =
(3 in ) (0.767 g/cc) (6.452 X 10-4 m2/in2)
Surface Void Volume (cc/m2) = Total Void Volume - Partial Void
Volume ;~ '
The imprinting fabric transports the uncompacted web
into a nip defined by the impringing fabric 10 and a dewatering `~
felt 20. Here the selective mechanical dewatering or pre-
drying ~tep of the present invention takes place. The dewatering
felt 20 is of a closed loop construction being looped about a
g _
... :, .. ,
~106~Z0
plurality of spaced support rolls 22 and a vacuum roll 24. Posi-
tioned in opposed relationship to the vacuum roll 24 is a compres-
sion roll 26, formed of hard rubber or any other suitable material,
which together with the vacuum roll 24 serves to form a compression
nip between the imprinting fabric 10 and the dewatering felt 20.
Rolls 24 and 26 are loaded to a pressure in a range from about
20 pli to about 600 pli and preferably from about 50 pli to about
250 pli. The dewatering felt 20 may be of any conventional paper-
maker's dewatering wet felt construction. An e~ample of a felt
which has been found suitable for practicing the present invention
is an Albany medium Durasorb felt manufactured by the Albany Felt
Company and comprised of 51% wool and 49% synthetic material. The
referenced felt is a medium class needled felt with a satin weave
finish on the sheet surface and having a pe~meability (expressed
in CFM/Ft /1/2" H20) of 45.
Fig. 2 shows the cooperative relationship between the
imprinting fabric 10 and the dewatering felt 20 at the compression
nip formed between rolls 24 and 26. The paper web passing between
the nip is designated by reference numeral 30~ As the imprinting
fabric 10 and the web 30 progress along in the direction of the
arrow, the paper web comes into contact with the felt 20 and is
progressively compressed as the nip distance decreases. In addi-
tion to absorbing water from the web, the felt 20 serves to force
fibers of the web into the void spaces formed between the warp and
weft strands of the relatively open mesh imprinting fabric 10, with
the portions of the paper web not lying in the immediate vicinity
of the compaction elements formed hy the knuckles at the warp and
weft crossover points of the imprinting fabric remaining relatively
uncompacted. Although a plain press roll or a grooved press roll
~.' .
-- 10 _
, . . .. .. . . . . .. . .. . .. ..
6Z~ ~
may be satisfactory for some applications, it is preferred that
the roll 2~ be a vacuum roll that applies a vacuum to the under-
side of the dewatering felt 20 to assist in removal of water from ;
the paper web in the well known manner. It is believed that
because of the vacuum thus created, ambient air tends to flow
through the imprinting fabric 10, through the paper web and thence
into the dewatering felt, thus minimizing rewetting of the paper
web as it is passing out of the nip.
Referring once again to Fig. 1, the felt 20, which moves
at the same lineal speed as the imprinting fabric 10, moves in the
direction of the arrows along the path defined by the support rolls
22. The felt passes adjacent to one or more dewatering devices
such as vacuum box 34 to remove from the felt the water that has
been absorbed from the paper web 30. Before entering the nip
defined by rolls 24 and 26, the paper web has a fiber consistency ~ -
in the range from about ~/0 to aboui 25% and after leaving the
compression nip the paper web has a consistency of from about 2~/o
to about 3~/O. ,
It should be noted that the paper web 30 remains on the
imprinting fabric 10 after leaving the aforedescribed nip which
is utilized to selectively mechanically dewater or pre-dry the
web. According to conventional papermaking theory, the web should
follow the wet felt at the nip exit. This unexpected result is
believed to be caused by two factors; first, adhesion or coadhesion
by water from the wet paper web to the non-absorbent monofilament
fabric and, to a secondary degree, mechanical entanglement of the
web fibers in the monofilament fabric. In the nip the water
exposed to the needled side of the felt is wicked away by capillary ``
action in the vertical needled fibers assisted by the vacuum in the
,-, -- 11 --
'
'~6~;Z(~ -
suction press, whereas the water on the monofilament fabric side
forms a tight adhesive or cohesive bond with the web and the non-
absorbent monofilament fabric. The web and the direction it
travels are dictated by the water balance at its surface and the
surface it contacts and due to the fact that the web has been
impressed into the voids defined by the fabric filaments, there is
actually more surface contact area between the web and the mono-
filament fabric than there is between the web and the felt.
From the rollers 24 and 26 paper web 30 is conve~ed to a
movable creping surface such as the surface of Yankee dryer 40.
The paper web is pressed into engagement with Yankee dryer 40 by -
means of a compression roll 42 about which imprinting ~abric 10
is looped. The paper web remains essentially undisturbed on the
imprinting fabric as it is transported between the first compres-
sion nip formed between rollers 24 and 26 and the second compres-
sion nip formed between roll 42 and Yankee dryer 40 so that the
fabric compaction elements contact essentially the same portions ;
of the web at the second compression nip that were contacted at the
first compression nip. The pressure at the second compression nip
is in a range of from about 20 pli to about 600 pli, and preferably
from about 50 pli to about 250 pli.
It has been found that an adhesive will assist in the
transfer of the paper web to the creping surface of the Yankee and
in Fig. 1, a spray nozzle 44 is illustrated schematically as one -
means by which adhesive application may take place. In this
embodiment the adhesive is sprayed onto the surface of the paper
web just prior to the web and imprinting fabric passing between
roll 42 and Yankee dryer 40. In a configuration of this type a
suitable adhesive spray was found to be a 0.25% solution of E
- 12 _
.
6~
carboxymethyl cellulose (CMC). After the web 30 is dried on the
surface of the Yankee dryer, preferably to a dryness range of from
about 92% to about 9~/O solids, it is creped off the Yankee dryer
by a creping blade 50. The web is then converted in the usual
fashion. After the paper web leaves the imprinting fabric the
fabric is preferably cleaned as by means of a water spray nozzle
or steam jet 54, a vacuum box 58 disposed in association therewith,
or by any suitable conventional -fabric cleaning equipment.
Referring now to Fig. 3, another paper machine configu-
ration for practicing the method of the present invention is illus-
trated, this embodiment being particularly adapted to the manu-
facture of semicrepe tissue, toweling, filter papers and similar
products. This configuration utilizes many elements and structural
interrelationships in common with the configuration o~ Fig. l and
such common elements have been designated by the same reference
numerals. Specifically, the configuration of Fig. 3 includes a
headbox 13 whicn delivers a slurry to a fourdrinier wire 14. The
wet web formed on the wire 14 is transferred without significant
mechanical compression to a knuckled imprinting fabric 10. Imprint-
ing fabric lO delivers the web to a nip defined by the imprintingfabric lO and a dewatering felt 20, said web being selectively
mechanically compressed between imprinting fabric lO and felt 20
by vacuum roll 24 and compression roll 26 as was the case with
respect to the Fig. l embodiment. After passing through the nip
the web is retained on the imprinting fabric and transported
thereby to a Yankee dryer 40. The paper web remains essentially
undisturbed on the imprinting fabric as it is transported between
the first compression nip formed between roller 24 and 26 and the
second compression nip formed by compression roll 42 and the
- 13 -
: . , .
.
: :
6ZI~ ~
Yankee dryer. A spray nozzle 44 is utilized to spray adhesive
onto the paper web to assist in transfer of the web to the Yankee
dryer. The Yankee dryer then dries the web to a dryness in a
range of from about 4~/O to about 7~/O solids whereupon the web is
creped by means of a creping blade 50. The partially dried web
then proceeds along a path in engagement with a plurality of
rotating dryer drums 80 which serve to finally dry the web. Alter-
natively, final drying could be affected by a transpiration dryer.
The web is then passed through a calender stack 82 and wound unto
a parent roll for subsequent conversion.
Fig. 4 illustrates yet another paper machine configuration `~-
suitable for practicing the present invention. Following the same
reference numeral conventions employed with respect to the embodi-
ments of Figs. 1 and 3, the Fig. 4 configuration includes a head- '
box 13 which delivers a wet paper web 30 to a fourdrinier wire 14.
The web 30 is transferred in an essentially uncompacted state to
a knuckled imprinting fabric 10. The web is then passed through
a compression nip defined by imprinting fabric 10 and dewatering
felt 20, said imprinting fabric and felt being acted upon by vacuum
roll 24 and compression roll 26 in the manner previously described
with respect to other embodiments of ~his invention. After the
web 30 is selectively mechanically compressed between the knuckled
imprinting fabric and the felt it is separated from both the felt
and the imprinting fabric and is transported independently to a
plurality of dryer drum~ 80 and thence to a calender 86. Again,
final drying could be affected by a transpiration dryer rather than
dryer drums. The web is then rolled into a jumbo or parent roll
for subsequent conversion. After passing through the selective
mechanical compression nip the web 30 would stay with the imprinting
' .
- 14 -
`" '
~06~6Z~
fabric lO in the manner previously described with respect to the
Fig. l and Fig. 3 embodiments unless some means is employed to
separate the web and fabric from one another. In the present
embodiment this separation is facilitated by employing an air
or steam jet 88 which impinges against the non-web-supporting side
of imprinting fabric 10 along the full width thereof and serves
to lift the paper web therefrom. It has been found that the con-
~istency of the paper web 30 must be at least about 2~/o for the
web to maintain its integrity after removal from the imprinting
fabric.
As noted above, the paper web manufactured in accordance
with the teachings of the present invention has desirable physical
characteristics that one would normally associate in the prior art
only with thermally pre-dryed webs, as exemplified in U.S. Patent
No. 3,301,746, for example. The following examples illustrate the
sheet materials produced by the process of the present invention
and prior art thermall~ predryed materials. It is understood
that the examples are intended to be illustrative and not limiting,
and the scope of the invention is only to be construed by the
scope of the appended claims.
In the following examples the basis weight of a given
sheet is determined by TAPPI test No. T-410 and is expressed in
pounds per 3,000 square feet. Sheet bulk softness is expressed
as HOM/(caliper) X 10 . The HOM (Handle-O-Meter) test is des-
cribed in TAPPI T-498. The bulk softness (reciprocal of stiff-
ness) of a given sheet is calculated by dividing the HOM value
; by the square of the caliper of a single sheet being tested and
multiplying the quotient thereof by 10 .
.
,' ' ' , ~
~L06~620
Sheet bulk is a function of sheet density. In the
following examples the density of a given sheet is calculated by
determining the lobb caliper of the sheet and dividing same by the
basis weight of the sheet. Lobb caliper is dgtermined by placing
24 sheets between a jaw of opposed matching cylinders four inches
in diameter, under a load of 1.35 pounds per square inch, and
measuring the thickness of the stacked sheets to 0.001 of an inch.
The caliper of a single sheet is then determined by dividing the
lobb caliper reading by 24.
Example 1
As an illustration of the prior art, a commercial bath-
room tissue made using the thermal pre-dry process described in
the U.S. Patent No. 3,301,746, was tested and possessed the :
following general properties: `
Basis Weight, pounds/3,000 sq. ft. -------------- 18.1
Lobb Caliper, mils/24 sheets -------------------- 177
Lobb Density, g/cc ------------------------------ 0.156
Tensile, oz/in(MD) -------------------- 7 6
Tensile, oz/in(CD) ------------------------------ 5 0
Rate Water Absorbengy~ sJec/0.1 cc --------------- 1 9
HOM/(Caliper)2 X 10 ---------------------------- 0 75
Example 2
As an illustration of the present invention, the web was
initially formed from an aqueous paper fiber slurry on a vacuum
cylinder former. The wet web was transferred to a knuckled mono- -
filament imprinting fabric having 36 X 29 meshes per inch and
formed from filaments having a diameter of 0.0016 in. The web
supporting surface of the fabric had a knuckle pattern defined
by the warp and weft crossover points of the filaments. The
knuckle imprint area of the imprinting fabric constituted 2~/o of
' '~
- 16 -
., .
' ~
.. ,: : ,, ' , '' ~ , :
,1~
~(~6~6;~Q
.
1 the total fabric surface area and the fabric had a surface void
2 volume of 59 cc/m2.
3 The web was transported from the former to a first com-
4 pression nip formed between the imprinting fabric and a dewatering
felt. The papermakers felt was an Albany medium Durasorb, style
6 XY8253 felt. The dewatering felt was entrained around a vacuum
7 roll and a ~acuum of 10 in Hg was applied to the dewatering felt
8 at the surrace thereof opposing the surface in engagement with the ;~
paper web, The pressure at the compression nip was 130 pli. The
]0 fiber consistency of the web prior to entering the compression .
11 nip was 25% an~ after leaving same was 31%~ From the first com-
12 pression nip the selectiyely dewatered paper web was transported
13 to a Yankee dryer, the web remaining essentially undisturbed on
14 the imprinting fabric so that the fabric knuckles contacted essen-
tially the same portions of the web when the web was applied to
16 the Yankee dryer as those contacted at the first compression nip.
17 The imprinting fabric was entrained about a roll which compressed
18¦ the web against the Yankee surface by means of the imprinting
lg¦ fabric. The pressure at the second compression nip located at
20¦ the Yankee dryer was 140 pli. To assist in the transfer of the
21 selectively.mechanically dewatered web to the Yankee surface an
22 adhesive solution of 0.5% CMC and 0.0025 calcium stearate W2S
23 Isprayed onto the ~eb just prior to ~ransfer at a rate of
241 6.77 Kg/1000 m2. The sheet was ther~ally dried and then creped
25 1¦ from the Yankee dryer. ~he creped paper had the following gelleral
26j properties: i
27l Basis l~leight, pounds/3,000 sa. ft. ~ -- 18.1
l Lobb Caliper, mils/24 sheets ----~ -------- 178 i
28¦ Lobb Density, g/cc -------------------------- 0.156
Tensile, o/in(]~"D) --------------------- ---- 5.8l~ ,
291 Tensile, oz/in(CD) --------------------------- 5. o6
I Rate ~1ater Absorbency, sec/0.1 cc------------ 1.91
30; HOM/~caliper~2 x 105 -----------~ --------- o.76
31 ! I ~ .
32 ~
- 17 -
".: ~ ., . , , ~ :
.
.~: .
~)6~6;~0 '
. . . `:~
1 It may be seen from the above that a paper sheet having
2 desirable characteristics of strength3 softness, bulk and absorben Y
may, contrary to prior expectation~ be manufactured through utili-
4 ~ation of a selectively mechanically pre-drying technique which is
5 much cheaper in both cost of construction and operation than con-
6 ventional thermal pre-drying techniaues~ It wiil be appreciated
that the fabric to felt pre-drying arrangement disclosed may be
8 utilized in con~unction with other dewatering techniques which
avoid significant compression of the paper web in other than ~he
10 knuckle imprint areas. For example, referring to Fig. l, air or ;~
11 steam jets such as those indicated schematically and identified
12 by reference numerals 62 and 64 may be employed to assist in the
13 reliminary dewatering of the paper web. Vacuum boxes 68 and 70
14 may be used to ~move excess water dislodged from the paper web by
the jets 62 and 64. Similar arrangements could be employed in
16 association with the imprinting fabric lO downstream from the first
17 compression nip, In addition to assisting in the preliminary
l8 dewatering cf the web~ 3uCh j ets, wheil employed upstream from the
19¦ first compression nip~ serve to partially entangle web fibers in
20l the void spaces of the imprinting fabric. As previously noted3:
211 such entanglement is desirable to assist in the retention of the
22 ~eb on the imprinting ~abric as it passes through the first com~
23 pression nip. ¦
24
25 1
26
28!
30 ~
~11 , :,
`~, 321 . 1 ~
1~ - 18 I ;
. ~
