Note: Descriptions are shown in the official language in which they were submitted.
WO 91/16493 PCf/SE91/00275
2Q78877
Paper Machine for the Manufacture of High Bulk Soft Crepe Paper
Technical Field
The present invention relates to a paper machine for the manufacture of
soft crepe paper and including a wire section, which has at least one
forming fabric loop for forming a paper web, and a drying section in-
cluding a Yankee dryer, in which drying section the paper web is dried,
said paper machine having a first operative design for the manufacture
of soft crepe paper having certain measurements of bulk and softness, in
which first operative design a press section located between the wire
section and the drying section has a felt movable in an endless loop
and arranged to run from a pick-up device located at a tr~ansi-tiori be=-
tween the wire section and the press section to a press roll forming a
l5 nip with the Yankee dryer while carrying the paper web on its under side,
the carrying forming fabric being arranged to run up to said pick-up
device in the press section for the transfer of the formed paper web to
said felt.
Background Art ,
Conventional soft crepe paper machines of the above kind ire widely
known, see U.S. Patent No. 4,055,461, for example. The soft crepe paper
manufactured in such machines has certain limited values for bulk a.nd
softness. To achieve bulk and/or softness values above these limited
' values,. special methods have been utilized, such as mixing in expandable
microspheres of thermoplastics as disclosed in U.S. patent No. 4,619,734,
or utilizing machines operating with through-air drying by means of hot
air, see U.S. Patent Nos. 3;303,576, 3,812,000, 3,821,068 and 4,036,684,
for example, where the through-air drying is carried out on cylinders
having a perforated shell, which may be covered by a fabric, for exam-
ple, and where hot drying air is supplied internally and passes out
through the shell or the reverse.
However, the known conventional soft crepe paper machines of twin wire,
fourdrinier, or breast roll former type are designed in such a way that
they can not readily be converted into different operative designs for
WO 91/16493 PCT/SE91/00275
2U78~7"~
making it possible to manufacture soft crepe paper grades of consider-
ably different requirements for bulk and softness.
Disclosure of Invention
One object of the present invention is to eliminate the above problem
and provide a soft crepe paper machine, which in a simple manner can be
converted in order to be adapted to varying situations on the market,
such as actual competitive situation and wishes from the consumers.
,
This object is achieved in that the paper machine is designed to be simp-
le to rebuild between said first operative design and a second operative
design for the manufacture of-soft crepe-paper having higher measurements
of bulk and softness in relation to the first operative design, in which
second operative design a conveying and imprinting fabric loop is substi-
tuted for the felt of the press section, air current generating means
being provided along at least one of said fabrics for the removal of
water from the paper web by flow of air of ambient temperature through
the paper web carried by the fabric in question, cleaning means being
provided along the conveying and imprinting fabric for the cleaning
thereof so as to continuously maintain its permeability to water and
air, and means being provided for depleting the conveying and imprinting
fabric of water. before the arrival thereof at said pick-up device.
Another object of the invention is to eliminate the above problem and
provide a paper machine for the manufacture of a soft crepe paper grade,
which in respect of bulk and softness is comparable to the one manufac-
tured on a machine made for through-air drying by hot air:
This object is achieved in that the paper machine is provided with
(a) a wire section including at least one forming fabric for forming a
soft crepe paper web;
(b) a drying section including a Yankee dryer for drying the web;
(c) a press section located between the wire section and the drying sec-
tion and including a conveying and imprinting fabric for conveying the
web from the farming fabric to the Yankee dryer and a press roll for
pressing the web on to the Yankee dryer while imprinting the web;
WO 91/16493 PCT/SE91/00275
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(d) a pick-up device for picking up the web from the forming fabric and
transferring the web to the conveying and imprinting fabric without any
appreciable compaction of the web;
(e) means for cleaning the conveying and imprinting fabric;
(f) means for depleting the conveying and imprinting fabric of water
before the arrival thereof at said pick-up device; and
(g) air current generating means for removing water from the paper web
by running a flow of air of ambient temperature through the paper web,
said air current generating means having a capacity that is sufficient
for raising the dry solids content of the paper web to at least 25~o be-
fore the arrival of the paper web at the Yankee dryer.
Brief Description of the Drawings
The invention will below be explained more in detail with reference to
the drawings, where
Fig. 1 schematically shows a preferred embodiment of a paper machine
according to the invention for the manufacture of soft crepe paper.
Fig.2 schematicaTTy shows a section of the paper machine according to
Fig.l equipped with a single-felted press co-operating with a press.roll
located at the Yankee dryer. ,
Fig.3 is a diagram illustrating the interrelation between density~and
basis weight of soft crepe paper manufactured in machines of two differ-
ent operative designs.
Modes for Carrying Out the Invention
With reference to figure 1 there is schematically shown parts of a con-
ventional paper machine suited for the manufacture of soft crepe paper,
such as tissue and other sanitary paper products. The shown paper ma-
chine is a twin-wire machine including a wire section 1, a press sec-
tion 3 and a drying section 5. Wire section 1 has a headbox 7, an end-
less carrying or inner forming fabric loop 9,~an endless covering or
outer.forming fabric loop 11, and a forming roll 13 that may have a per-
35forated surface and be equipped with internal suction apparatus or, al-
ternatively, have a plain surface. Headbox 7 discharges a single layer
or a mufti-layer stock jet into a gap between the two moving forming
fabrics 9, 11 for the forming of a paper web 15 by the drainage of water
WO 91/16493 PCT/SE91/00275
vU788'~7 4
from the stock. The two forming fabrics run together over the forming
roll 13 and then in individual loops over a plurality of rolls, which
are arranged to guide, align and tension the carrying or inner forming
fabric 9 and the covering or outer forming fabric, respectively. The
rolls for the covering forming fabric 11 include a breast roll 17 and a
guide roll 19, which is located a short distance downstream of the form-
ing roll 13 and may be called a turning roll. The covering forming fab-
ric 11 may leave the carrying forming fabric 9 and the paper web 15 ei-
ther immediately before fabric 9 and paper web 15 run off from forming
roll 13 or alternatively, when required or preferred, at.a transfer suc-
tion box 21 or some other transferring device, which preferably operates
by air flow, located between forming roll 13 and turning roll 19. The
carrying forming fabric 9 runs up to press section 3, where the paper
web 15 is transferred to press section 3 by means of a pick-up device 23
included in the press section.
Press section 3 has an endless looped movable fabric 25, which in a
first operative design of the paper machine is a felt, that is a fabric
provided with a fine fiber surface ("nap") of a natural or synthetic
material. The felt is arranged to convey paper web 15 from pick-up de-
vice 23 to a nip formed between a press roll 2.7 and a Yankee dryer 29
incorporated in the press section 5. Press ro11~27 presses paper web 15
on to the jacket surface of Yankee dryer 29 simultaneously as felt 25
and press roll 27, which in this operative design of the machine prefer-
ably is a roll having a perforated surface, remove moisture from the
paper web. After said nip felt 25 extends around a guide roll 31 and up
to and through a second nip formed between a second press roll 33 and
Yankee dryer 29, where felt 25 once more is pressed against paper web 15
to effect removal of any pattern caused by the perforated surface of the
first press roll 27. Downstream of second press roll 33 there are means
for cleaning and conditioning felt 25, which after the conditioning
thereof should have a moisture content suited for the picking up of
paper web 15 from carrying forming fabric 9.
Yankee dryer 29 is covered by a hood, not shown, in which hot air of
high velocity is ejected against paper web 15. The paper web is creped
off from Yankee dryer 29 by means of a creping doctor, not shown, in
WO 91/16493 , PCT/SE91/00275
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order to obtain a desired creping degree, whereupon the finished creped
paper web is wound in a reel-up (not shown).
The second operative design of the paper machine is intended for the
manufacture of a soft crepe paper having higher values of bulk and soft-
ness than what is obtainable in the paper machine according to the first
operative design. To achieve this we substitute a conveying and imprint-
ing fabric for felt 25. The use of imprinting fabrics in the manufacture
of soft crepe paper, their functioning and the advantages achieved there-
by are well known, cf. Pulp & Paper, November 1977, Hanson, J.P..,
"What's going on in tissue?", pages 93-102, especially pages 98 - 100
(Never underestimate knuckle power), for example. Further, we provide
air current generating means 35, 37 and 39 along at least one of
carrying or inner forming fabric 9 and conveying and imprinting fabric ..
25 for removing water from paper web 15 by passing air of ambient
temperature through the paper web 15 carried by the fabric in question,
we provide cleaning means 41 ,43 and 45 along conveying and imprinting
fabric 25 for the cleaning thereof, so as to continuously maintain its
permeability to water and air, and we provide means 47 for depleting .
conveying and imprinting fabric 25 of water before the fabric arrives at
the pick-up device 23.
The conveying and imprinting fabric 25 can either run over the same
rolls as the felt ran over, or guide roll 31 may be bypassed, so that
the conveying and imprinting fabric runs from the first press roll 27,
which in the second operative design preferably is roll having a plain
surface, along the jacket surface of Yankee dryer 29 directly to the
second press roll 33. In both cases it is suitable that the second press
roll 33 be taken out of pressing engagement with Yankee dryer 29, so
that the paper web 15 will not be. exposed to a second imprinting opera-
tion. The first imprinting operation is effected where the first press ~ .
roll 27 presses paper web 15 on to Yankee dryer 29, and the pressing on
is carried out with a force that preferably is at least 50 kN/m web
width. If, however, in the secand operative design the first press roll
27 is a roll having a perforated surface, e.g: a suetion roll, it is
suitable to expose the paper web 15 to a second imprinting operation by
means of the second press roll 33 in order to remove the pattern that
may be caused by the perforations of the first press roll 27.
WO 91/164 ~ rl ~ ~ ~ .~ PCT/SE91/00275
6
For the paper machine in the second operative design to operate in the
intended manner and produce a marketable soft crepe paper grade it is of
utmost importance to maintain conveying and imprinting fabric 25 clean
and, in addition, depleted of water upon its arrival at pick-up device
23. Because thereof, the cleaning equipment 41, 43, 45 is more extensive
than what is required for cleaning and conditioning a felt in a conven-
tional soft crepe paper machine and comprises a plurality of oscillating
needle jet shower pipes 41, a plurality of fish-tail jet shower pipes 43
and a plurality of suction boxes 45. After installation of these shower
pipes and suction boxes, they may, of course, be used also for the clean-
ing and conditioning of a felt, but then you do not normally use all of
the shower pipes and the suction boxes. Two of the fish-tail jet shower
-pipes 43 are shown located and directed so as to produce a~fTooded nip
where fabric 25 starts wrapping a guide roll. A flooded nip is particu
larly suitable for the cleaning and conditioning of a felt but is useful
also for the cleaning of conveying and imprinting fabric.25.
A conditioned felt shall contain such an amount of water that the pick-
ing up of paper web 15 from forming fabric 9 is facilitated. In contrast
hereto the conveying and imprinting fabric 25 is to be depleted of water
by a water depleting means 47 upstream of the pick-up location. The wa-
ter depleting means 47 suitably operates by means of an air flow passing
through the conveying and imprinting fabric, and in the shown embodiment
it is a suction box 47 but it would, of course, be possible to use alter-
natively a blow nozzle solely or in combination with the suction box.
Suction box 47 and at least one of suction boxes 43 may suitably be moun-
ted so as to make them easily movable between an active position, in
which they engage fabric 25, and an inactive position, in which they do
not, since they do not have to be active when fabric 25 is a felt. A
plurality of shower water save-alls 49 are provided for collecting the
shower water passing through fabric 25 without being sucked into the
cleansing suction boxes 45.
In a conventional paper machine the pick-up device may be a roll or shoe
having a plain surface. Far ensuring a picking up without any appreci-
able compaction of the paper web in the seeond operative design the pick-
up device preferably should operate with air flow through forming fabric
9, paper web l5 and conveying and imprinting fabric 25 and it may com-
WO 91/16493 PCT/SE91/00275
20'~8~'~~
prise a suction device, e.g. a suction roll or, as shown in the preferred
embodiment, a suction shoe 51. A still more improved effect is obtained
if a blow nozzle 53 is provided inside the loop of the carrying forming
fabric 9 and aligned with the suction zone of the shoe 51 or roll. The
pick-up device 23 operating with air flow will work excellently also in
the first operative design where fabric 25 is a felt. Then, blow nozzle
53 is not required for securing the picking up of paper web 15 from form-
ing fabric 9.
In order to remove in the second operative design at least so much water
from the newly formed moist paper web 15 without any appreciable compac-
tion thereof that when the paper web is pressed on to the hot jacket
surface of Yankee dryer 29 no-steam bubble formation occurs, which would
cause web 15 to come off the jacket surface in places, and also in order
to reduce the drying capacity needed, air current generating means are
provided for effecting a flow of air of ambient temperature through paper
web 15. In the embodiment shown in figure 1 the air current generating
means comprise two suction boxes 35, 37 located inside the loop of the
carrying forming fabric 9 between transfer suction box 2I and pick-up
device 23, and a suction box 39 located inside the loop of conveying and
imprinting fabric 25 between pick-up device 23 and first presg roll 27.
The number of suction boxes 35 , 37 and 39 and the location thereof be-
tween transfer suction box 21 and first press roll 27 may be varied with-
in the scope of the present invention. However, it is necessary to pay
attention to the moist and comparatively fragile soft crepe paper web
' ~ not adhering to strongly to carrying forming fabric 9 or conveying and
imprinting fabric 25. Means 55 may be provided, if desired, for applying
a suitable release agent to conveying and imprinting fabric 25 for the
purpose of reducing the adherence of web 15 to the fabric. Such means
illustratively is a spraying device 55 located on the web facing side of
fabric 25 immediately downstream of suction box 47. Conventional means,
not shown, are also provided for forming and maintaining at an optimum
and stable level a web adherence controlling coating on the jacket sur-
face of the yankee dryer 29. A natural coating substantially consists of
hemicellulose.and fiber fragments, but to improve control of the adhesive
properties of the coating an adhesive agent and/or a release agent may
b.e added. The amount of hemieellulose is controlled by controlling the
pH of the stock, while the chemicals may be added to the stock or applied
WO 91/16493 PCT/SE91/00275
8
to the formed paper web or, preferably, directly onto the jacket surface
of the yankee dryer. The adhesion of the web to the coating affects all
properties of the paper web, and the coating also affects the wear of
the yankee dryer surface and of the doctor blade.
Some dewatering of paper web 15 also ensues due to the flow of air into
transfer suction box 21 and suction shoe 51. In order to improve the
dewatering still more a steam box 61 for heating paper web l5 by means
of direct steam may be provided immediately upstream of suction box 35
and on the web carrying side of forming fabric 9. The heating reduces
the viscosity of the water, so that it will be easier to suck it out. In
addition, the dewatering rate will be increased by the sucking through
of air: If desired it is, of course, possible to provide in a correspond-
ing manner a second steam box, not shown, for heating web 15 by direct
steam immediately upstream of suction box 39 located inside the loop of
the conveying and imprinting fabric 39. In order to shield paper web 15
from condensate drippings and possible splashes of water when carried
hanging on the underside of conveying and imprinting fabric 25, a web-
covering heatable roof or shield element 63 is placed above the lower
run or flight of the conveying and imprinting fabric. Roof element 63
may be provided with conduits, not shown, for conducting hot v~ater or
steam therethrough but may also be heated in some other way, e.g. by
electricity.
In order to avoid the above mentioned formation of steam bubbles between
~, paper web 15 and Yankee dryer 29, the paper web should have a dry solids
content of at least about 25 % when the first press roll 27 presses web
15 on to Yankee dryer 29. The number of paper web dewatering suction
boxes 35, 37 and 39; the flow of air through web 15, and the possible
heating by direct steam are adjusted so as to achieve the aforesaid dry
solids content. As a supplement to or a substitute for the heating by
direct steam, heating by infrared (IR) radiation may be used, e.g. from
one or more hood-type IR heaters, not shown, or other equipment able to
emit IR-radiation..Hood-type IR heaters may also be used for facilitating
the drying of paper web 15 on Yankee dryer 29, and in figure 1 there is
shown one such~IR hood 65 placed somewhat downstream of second press
roll 33. A compact standard hood having a single row of IR elements can
emit about 125 kW/m web width. .
WO 91/16493 ~ ~ ~ ~ PCT/SE91/002'75
9
Usually, paper web 15 reaches a dry solids content of about 25-30% al-
ready on forming fabric 9, and the dry solids content is increased by
one or several more percent along conveying and imprinting fabric 25. If
it is desired to raise the dry solids content of web 15 still more~be-
fore the web is pressed on to Yankee dryer 29, it is possible to supple-
ment the paper machine with a conventional single-felted press, as shown
schematically in figure 2.
In figure 2 the conveying and imprinting fabric 25, which on its under
side carries paper web 15, runs from the bottom side of first press roll
27 up to and around a turning roll 67, from where it runs to the press
nip formed between first press roll 27 and Yankee dryer 29. Press roll
27 constitutes a counter roll of a~conventional single-felted press,
generally indicated by 69, having a press roll 71 and an endless felt 73
running over a plurality of rolls 75. A suction box 77 is provided in-
side the loop of conveying and imprinting fabric 25 upstream of turning
roll 67 for securing that paper web 15 will not be transferred to press
felt 73 but will remain adhered to conveying and imprinting fabric 25.
Such a conventional single-felted press will raise the dry solids con-
tent of paper web 15 by up to an additional five percent.
In a modification (not shown) of the singlefelted press of Fig. 2, the
lower press roll 71 is moved from its illustrated 6 o'clock position in
,relation to press roll 27 to a 7 o'clock position. This makes it possi-
ble to leave out turning roll 67 and suction box 77. After passing from
the nip formed between press roll 27, 71, the conveying and imprinting
fabric 25, carrying the paper web 15, will then follow the surface of
press roll 27 up to the nip formed by roll 27 with Yankee dryer 29. From
the press nip formed by rolls 27, 71 at the 7 o'clock position the press
felt 73 will be run to the 6 o'clock position, and then will pass tangen
tially and horizontally from roll 27. Consequently, paper web 15 will
not be transferred to the press felt 73, but will instead remain adhered
to the bottom side of conveying and imprinting fabric 25 when the latter
passes upwardly on press roll 27.
In order not to unnecessarily crowd the drawing with details, which mere-
ly show conventional equipment in paper machines and do not constitute
WO 9l/16493 PCT/SE91/00275
any part of the present invention, such details are omitted. Examples of
such non-shown details are cleaning devices for forming fabrics 9 and 11
and for press felt 73, and further, white water save-ails and devices
for stretching, aligning and driving the various endless fabrics.
5
Figure 3 is a diagram showing density as a function of basis weight for
soft crepe paper manufactured on one hand in a conventional paper ma-
chine according to the first operative design and on the other hand in
the same machine after a rebuilding thereof to the second operative de-
10 sign. A single-felted press in accordance with the variant shown in fig-
ure 2 was not used. Consequently, the upper line 79 relates to a soft
crepe paper manufactured in the conventional manner, and the lower line
81 relates to~soft crepe paper manufactured in the rebuilt machine, ~ ------ -
--
where the conveying and imprinting fabric was substituted for the pick-
up felt, and where water was removed from the paper web by passing air
of ambient temperature through the web in an amount sufficient for rais-
ing the dry solids content of the paper web to at least about 25% before
the paper web arrived at the Yankee dryer. As is apparent from the dia-
gram, the latter soft crepe paper 81 has a density, which at low basis
weights is about half the density of the conventional soft crepe paper,
and the percentage difference increases with increasing basis, weight.
Since bulk is inverted density, a density of 200 kg/m3, for example,
corresponds to a bulk of 5 dm3/kg, and a density of 80 kg/m3 corresponds
to a bulk of 12.5 dm3/kg, the soft crepe paper in accordance with line
81 has at low basis weights twice as high a bulk as conventional soft
crepe paper and the percentage difference in bulk increases with in-
creasing basis weight.
The density of soft crepe paper manufactured in a conventional through-
air drying machine using hot air is essentially of the same order as
that indicated by the lower line 81. The bulk of a soft crepe paper grade
in accordance with the lower line 81 consequently is fully comparable to
the one manufactured in a through-air drying machine utilizing hot air.
While the softness has not been measured, it is well known that the soft-
ness increases with increasing bulk of the soft crepe paper. The in-
creased softness is appreciated by consumers but in some cases can result
in adaptation problems during conversion of the soft crepe paper web to
the desired end products.
._.. WO 91/16493 ~ ~ ~ ~ ~ PCT/SE91/00275
11
The rebuilding required for converting the paper machine according to
the invention from one operative design into the other essentially con-
sists of a change from pickup felt into conveying and imprinting fabric
or the reverse. What is additionally required is that certain components,
e.g. second press roll 33, water depleting suction box 47 and possibly
one of the suction boxes 45 of the cleaning means for conveying and im-
printing fabric 25, are changed from an inactive to an active position,
and that other components, such as one or more of shower pipes 41, 43
and the possible device 55 for applying a release agent on to the convey-
ing and imprinting fabric, are activated or inactivated. In addition it
is preferred, but not absolutely required, in cases where the first press
roll has a perforated surface, to substitute for said roll a roll having
-- ~a plain surface. The time required for the~rebuilding will' as a conse-
quence, be short. The rebuilding should be finished in only a slightly
longer time (about 12 hours or less) as is needed for changing the pick-
up felt in a conventional soft crepe paper machine.
The cost of converting an existing old soft crepe paper machine into
paper machine according to the present invention is estimated to be
10-20% of the price of a new through-air drying machine. Thius, for a
comparatively low machine cost a soft crepe paper manufacturer, can
produce a soft crepe paper grade, which with regard to bulk and softness
is fully comparable to the one manufactured in a machine using through-
' air drying by hot air. Roughly, the production will be halved, since a
lat~9e part of the dewatering is carried out by through-flow of air of
ambient temperature followed by drying on the Yankee dryer, which re-
quires a considerably lower machine speed, about half of that of a con-
ventional soft crepe paper machine, but production costs for the pro-
dueed high bulk soft crepe paper will be of the same order as with pro-
.duction in a through-air drying machine. A look at the costs of the end-
product sold to the consumer, e.g. a package of paper handkerchiefs,
shows that the change-over from conventional handkerchief paper to high
bulk handkerchief paper produced in the paper machine according to the
invention gives the possibility of such savings in the amount of paper
fibres used, that the cost for the finished product can be reduced. In
addition, the consumer will get a softer and more attractive product.
WO 91/16493 PCT/SE91/00275
12
The fact that it is possible to produce in a conventional soft crepe
paper machine a soft crepe paper without having to use a pick-up felt
must be characterized as unexpected. In addition it was unexpected that
the soft crepe paper grade produced in the machine according to the in-
s vention should be fully comparable, in respect of bulk and softness, to
the one produeed in a paper machine made for through-air drying by hot
air.
The invention has been described above with reference to a twin~wire
former of C-wrap type but, of course, it can be applied also in other
formers, e.g. twin-wire formers of S-wrap type, fourdrinier formers and
suction breast roll formers.
20
30 ,
