Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a method for the treatment of fibrous
material in the dry forming of a layer of fibres on a forming surface, and
to a product made by the method.
In a typical process for dry forming a fibrous web, dry fibrous -
raw material~ e.g. wood cellulose, which has been defibred in a hammer mill
into discrete fibres is conveyed in a stream of carrier air to a dispenser
from which it is laid by the stream of carrier air onto a foraminous forming
surface or band, suction being applied to the underside of the band immedi-
ately beneath the dispenser by a suction box to assist in the formation of
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the fibrous web. ;
If it is desired to producs a multi-ply paper or board by the
above process it is convenient to provide a series of dispensers, each with
its corresponding suction box, spaced in succession along the band. Conse- .
quently, successive plies will be laid one on top of the other. Each ~
dispenser is typically supplied with fibre from a hamme~ mill associated -
; with that dispenser.
The process and apparatus described above with reference to multi-
ply formation of dry-formed paper or board will hereinafter both be referred
'~ to as "of the type described".
.~ 20 Thus, in the first embodiment, this invention seeks to provide ;
a method of making a multi-ply web comprising providing a web of at least
three superimposed dry laid plies of fibrous cellulosic material, the outer
plies containing a stiffening agent and each inner ply containing a first
sizing agent different from the stiffening agent and which renders said
inner ply impervious to an aqueous solution of the stiffening agent of
the outer plies, moistening the web of superimposed plies and, consolidating
'; the moistened web by the application of heat and pressure.
In a second embodiment, this invention seeks to provide a multi-
~, ply web of consolidated dry-laid cellulosic fibre having at least three
plies characterized in that the outermost plies are provided with a
stiffening agent and at least the inner ply or plies next the outermost
plies are provided with a sizing agent rendering said inner ply or plies
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impervious to the stiffening agent of the outermost plies, whereby the
strength and stiffness of the web is concentrated in its outermost plies
and Q barrier is created between the outermost plies and said inner ply
or plies to facilitate delamination between the outermost plies and said
inner ply or plies on folding the web.
Preferably, the first sizing agent is added to the
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body of fibre constituting the intermediate plg at a hammer
mill associated with the formation o~ the intermediate ply.
The multi-ply web may be consolidated by hot moist
pressingO
When the web has been consolidated it may be further
treated by applying a second sizing agent to tha web when
dry or ~ubstantiallg dry to provide the web with a required
moisture content~ and hot moulding a surface o~ the sized
moist webO
When the method is used in the production o~ a multi-
ply folding box board, the stiffening agent mag be starch
and the first sizing agent may be a wax/rosin size.
The second sizing agent is prefera~ly selected from
the group including starch3 gelatine9 latex compounds, poly-
vinyl acetate or combinations thereof 9 with or without
mineral matter such as clayO
The second sizing agent may be applied to one or
both sides of the webO
According to a second aspect of the present inventlon
there is provided a multi-ply consolidated dry-formed ~ibrous
web comprising a pair of outer plies impregnated with a
stiffening agent, and an intermediate ply impregnated with an
agent rendering it relatively impervious to the stiffening
agent of the outer pliesO
The stiffening agent may be a starch, and the
impregnating agent of the intermediate ply may be a wax/rosin
size0
The difference in starch content of the plie8
together with other factors ensures that the degree o~ con-
solidation of the inner ply may be reduced relati~e to that
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o~ the outer pliesO This difference together with the
dif~erin~ starch contents and possible fibre ~urnish will
concentrate sti~fness at the surface and improve delamination
between outer and inner plies of the board to facilitate
creasing without crackingO
The invention is described merely by way o~ example
with re~erence to the accompanying drawings of which,
~igure 1 is a diagrammatic view of a machine
~or forming a multi-ply web of fibrous material
according to the invention,
Figure 2 is a cross-section $hrough a product
according to the invention9 at an intermediate
stage in its manufacture,
~igure 3 is a cross-section through the product
o~ tha invention, in its final ~orm, and
Figure 4 is an alternative form of the machine
shown in ~igure lo . -
Re~erring to Figure 1 o~ the drawings there is shown
a machine ~or making a multi-ply bvard from dry-laid fibres. -;
The machine comprises an endless plastics foraminous band 9
on which dry ~ibres are laid ~rom a succession o~ distributor
heads 10, 11, 12, 13 spaced along the bandO Vacuum9 or
suction boxes 14 are located underneath the band 9, beneath
each distributor head~ thus holding the fibres on the ~anda
Thus, each distributor head provides a ply o~ the ~inal
board9 heads 10, and 13 providing the outer plies~ and 11
and 12 the inner plies.
Each distributor head 10, 11~ 129 13 is supplied
with comminuted ~ibre, or a mixture of comminuted ~ibre and
other substances, from hammer mills 15, 169 17, 18 reæpect-
- ively.
Hammer mills 15 and 18 are ~ed with dry ~oQd pulp from
reels 19, 2a respectiyely. About 8~ by ~eight of dry Viscosol*, ~ -
a dry starch, is added to the pulp in hammer mill 18 from a
starch source 21.
Pre-broken dry groundwood pulp is fed into hammer mills
16, and 17 from receptacles 22, 23 respectively, and, before it
enters the hammer mills, is sprayed ~ith a ~ater-resistant wax~-
rosin size from sprays 26, 27 respectively. 10% by weight of
Viscosol dry starch is also added to the pulp in hammer mills 16
and 17 from starch sources 24, 25 respectively. Consequently,
the inner plies laid down by distributor heads 11 and 12 will be
water-resistant by virtue of the water-resistant rosin/wax size
they contain.
The resulting dry-laid multiply weh 8 is then moistened
by a water spray 28 on its uppermost ply (i.e. the one laid down
by distri~utor 13~ to provide a mositure content of about 35% by ;
weight. The moist web is consolidated by the passage around the
surface of a steam heated cylinder 29 at a temperature of 110C,
being pressed into contact therewith o~er one quarter of its
periphery by press rolls 30 at nip pressures of between 100 - 250
lb per linear inch (p.l.i.).
On leaving the cylinder 2~ the web 8 is moistened on
its underside (i.e. the ply laid down by distributor 10) by a
water spray 31 of 5-10% solution of VISCOSOL starch. The
moistened we~ h~s a mositure content of 15-20~ by weight. The
web passes through a nip 32 defined by a steam heated roll at
110C and a pressure roll applied at a pressure of 20-100 p.l.i.
to consolidate the underside or back ply. The web then passes
round a drying cylinder 33 at 110C. The dried web, containing
3Q typically 6-8~ by weight moisture then
* Trade Mark
passes through size press rollers 34 at a pressure o~ 50-250
pol~io A solution9 eOgO o~ 80% Viscosol starch and 20%
polyvinyl acetate is added at the press through nozzles 380
The size pressed web is subjected to a hot moist pressing~
action by passing around a steam heated cylinder 35 at a
temperature of 110C9 being pressed into contact therewith
by a rubber press roll 36 at a nip pressure o~ 20-5Q p~loio
This action smooths and consolidates the top sur~ace of the
boardO A similar hot moist pressing action may be e~fected
on the opposite sur~ace by another or ~urther heated cylinder
and press rollO The web passes onto coating and ~inishing
units depicted generally at 370
The sizing agent added to the web 8 by nozzles 38 `:
contains water and the quantity of agent used is controlled -:~
to ensure that the sized web which leaves the size press
rollers 34 has a total moisture content by weight of between
15 and 30%9 pre~erably about 25%o .
An alternative method of treating the moist sized
web after it leaves the rollers 34 is now described with :
reference to ~igure 4
The ~ized moist web a~ter leaving size press rollers
34 travels around a ~urther gulde roller 46 and is hot . :
mouldedlby passing through the pressure nip of a large heated .;.
roll 45 which cooperates with a press roll 47 around which
runs a ~elt 70 The moulded web then passes through the ~ ;
remainder of the ~inishing section which may involve a
coater and calender rolls be~ore being reeled up as ~inished
board on a supply drumO
Alternative sizing agents in liquid form include
gelatineg latex compoundsg polyvinylacetate or combination~ ;
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thereof~ with or without minera:L matter such as clayD
The sizing agent may be applied in any suitable
mannerO Instead of applying it to both surfaces of the we~
it may be applied to one surface only~
In this example the web grade is between 50 and 500
grams per square metre and is passed through the size pres~
and hot moulding rolls at therate of 200 feet per minute~
The roll 45 is steam heated to produce a surface temperature
of between 200 and 400~O The nip pressure between the
moulding rolls 45, 47 is between 50 and 250 lbs per linear
inchO ."
The roll 45 has a smooth sur~ace or~a patterned
surrace depending on the required surface finish of the webO :
The roll 45 acts on the upper sur~ace of the web, iOe. the : :
surface not bearing the forming wire mark cr the likeO
In a modification of the invention, the w~b leaving
the moulding rolls 459 47 is hot mouldèd again but this~time
the other or wire-marked surface of the web is acted on by
the large heated roll of a further set of moulding rollsO
I~ the web leaving the moulding rolls 45, 47 lacks suf~icient
moisture for the further hot moulding9 it is re-sized to
provide the required moisture content before being passed to
the ~urther moulding rollsO With re-sizing~ both web
surfaces may be re-sized or; i~ only one sur~ace is sized
Where the roll 45 has a smooth surface, it has been
~ound that the invention provides the web with an excellent
smooth sur~ace or surfaces for subsequent printingO
Thus this example shown by Figure 4 provides a method
of treating a web o~ fibrous material made by a dry-forming
~echnique wherein after the web has been formed9 consolidated
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and dried it is sized to produce a moisture content o~ about
25% by weigllt and then the sized moist web i8 hot moulded by
passing it through a pressure nip-formed by a heated roll
co-operating with a pressure rol].0
The e~fect of the size pressing and hot pressing o~
the starch-containing outer plies o~ the web shown in Figures ,,
1 and 4 is to sti~fen and strengthen these outer pliesO
Penetration into the middle plies is limited by virture o~ the f.
amount o~ ~ater-repellent size in the middle pliesa The sti~
ening agents (eOgO starch) are thus concentrated in the.outer
plies, which are the ideal regions for improving the stif~ness ;,
''' o~ the webO
Sizing o~ the middle plies thus inhibits the take-up
~o~ eti~ening.chemicals such as starch which are applied to
15 ,the outer plies~ .
In ~igure..2 ~here..is.shown a section through t~-web `'
immediately after it has passed o~er drying-roll 33~ The :
'''-- inner plies 41.7 42 contain w~.ter-repellent size and the ~uter -.,
plies 40, 43 contain starchO Both ~aces have been consolidated.
The-w~b typically has a sti~ness, of 8 Kenley UnitsO A~ter
passing through the size press 34 the sti~ness of the web
typically becomes 12 Kenleg UnitsO ,
In ~igure 3 there is shown a section through the web
after it has passed through the size press 34 and hot moist
pressing tconsolidating) cylinder 350 Considerable additional
sti~fness and strength has been gi~en to the outer plies 40,
~3 but not transmitted to the middle plies 41, 420 Typically
the web has developed a stiffness of 15 Kenley UnitsO The
rinished web comprises in a,typical example9 top and back
liner plies of chemical pulp with 18% Viscosol starch and 1
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3'~7
p.vOaO and middle ply or plies v~ mechanical pulp with 8%
Viscosol starch and 3% sizeO ~ach ply is normally not homo-
geneous but increases in concentration o~ additives towards
the sur~ace~
The use of certain sizes (eOg~ wax-based) in the
middle plies can by themselves and by their action in
resisting penetration of stiffening agents9 bring about a
reduction in the degree o~ consolidation in the middle plies
relative to the outer pliesO Changes in the degree of con-
solidation can also be effected by other ~actors eOgO
moisture content and heatO These di~ferences together with
the di~ering content o~ sti~ening agents in the plies will
provide a barrier between the inner and outer plies~ ~his
barrier will af~ect the degree o~ delamination between the
inner and outer plies on creasing and can thus improve the
foldability o~ the web
The strength and sti~ness o~ the final web i 8 there-
~ore concentrated in its outer layersj and a barrier is
created between the middle plies and outer plies to ~acilitate
delamination between these plies on ~olding the board9
Variationæ may be made in the example o~ the method
described above. ~ess9 or no starch may be applied to the
pulp for the middle plies. The æizing agent ~or the middle
plies may contain a bonding or cross-linking agent such as
gums or hemicellulosesO Starch may be added to the pulp ~o~
the ~irst dispenser (10), or variations made in the amount
o~ starch added to dispenser 13 or spray unit 31 or at 280
In place o~ starch9 other materials such as hemicelluloses
or carboxy-methyl cellulose may be used to modi~y the basic
web to give the required stif~ness~strengt~ ~old character-
istics. Nip pressure and cylinder temperatures may be varied
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to suit individual web requirementsO Dif~erent types o~
pulp may be used ~or the various pliesO
The invention may be applied to ~eb for ~olding box-
board moulding boards9 fluting medium or container board~ .
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