CA1061237A - Treatment of fibrous material - Google Patents

Abstract

Abstract In a process for making a multi-ply consolidated dry-formed fibrous web having at least three plies, the outer plies are impregnated with a stiffening agent (e.g. starch) and the intermediate plies are impregnated with a sizing agent (e.g. wax/rosin size) to render them impervious to the stiffening agent. After the web has been consolidated by hot moist pressing, its outer surfaces may be further sized and hot moulded.

Description

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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 . .
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 ~ - 2 --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 - 2a - -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 ~ . . .
' "' ' . ' ' ~ ' ~l Z3'î' 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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23'7 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 .
.

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 _ g _ ' ~ : ' . `

'7 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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Claims (12)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of making a multiply 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.

2. A method as claimed in claim 1 wherein the moistening and consolidating comprises spraying the web with water, passing the moistened web around the surface of a heated cylinder, and pressing the web into contact with the cylinder by press rolls at nip pressures of 100 - 250 pounds per linear inch.

3. A method as claimed in claim 2 comprising spraying the web with Water to provide an overall moisture content in the web of about 35% by weight, and heating the surface of the cylinder to about 110°C.

4. A method as claimed in claim 1 comprising incorporat-ing the stiffening agent in the fibrous cellulosic material prior to its formation into an outer ply.

5. A method as claimed in claim 1 comprising applying the stiffening agent in aqueous solution to the outer plies after the formation of the multiply web and subsequently passing the web through a size press.

6. A method as claimed in claim 1 comprising further treating the consolidated web by applying a second sizing agent in aqueous medium to the web when dry to provide the web with a required moisture. content, and hot pressing a surface of the moist sized web.

7. A method as claimed in claim 6 wherein the hot press-ing is performed by passing the web through a pressure nip between a heated roll and a press roll.

8. A method as claimed in claim 6 comprising providing the web with an overall moisture content of 15-30% by weight and carrying out the pressing at a temperature of about 110°C
and at a pressure of 20-50 pounds per linear inch.

9. A method as claimed in claim 1 when used in the production of a multiply folding boxboard, wherein the stiffen-ing agent is starch and the first sizing agent is a wax or rosin size.

10. A method as claimed in claim 6 wherein the second sizing agent is selected from the group comprising starch, gelatine, latex compounds, polyvinyl acetate, or combinations thereof.

11. A method as claimed in claim 1 comprising processing the cellulosic fibrous material in a hammer mill prior to its formation into a ply.

12. A multiply 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 impervious to the stiffening agent of the outermost plies, whereby the strength and stiffness of the web is concentrated in its outermost plies and a barrier is created between the outermost plies and said inner ply or plies to facilitate delamination between the outermost plies an said inner ply or plies on folding the web.