CA1043684A - Method of making corrugated paperboard - Google Patents

Abstract

Abstract of the Disclosure A method of manufacture of double-faced, multiwall, and paired single-faced corrugated boards in-cludes the step of applying a chemical gelatinization temperature depressant to the tips of the flutes of cor-rugated medium or substrate prior to application of a starch adhesive to the corrugated medium and before the last liner is bonded to the corrugated medium. The gelatinization temperature depressant enables use of lower temperatures in the hot plate section where the single-faced board plies and/or last liner are bonded to the corrugated substrate and facilitates use of a starch ad-hesive with a high total solids content which provides a good wet tack for subsequent handling of the board and minimizes board defects such as warping and washboarding caused by inefficient ant uneven moisture redistribution or removal in the hot plate section.

Description

METHOD OF MAKING CORRUGATED PAPERBOARD
Back~round of Invention The invention relates to a method of applying two component adhesives to unite liners to webs of corru-gated board. In the manufacture of double-faced corrugat-ed board, a first liner i8 glued to one side of a corru-gated substrate and 8 second liDer is subsequently lami-nated to the other side of the corrugated substrate. In the manufacture of multiwall corrugated board, a liner i9 glued to one side of each corrugated substrate and sub-sequently these single-faced boards and another liner are laminated together. In the manufacture of paired single-faced boards, two corrugating mediums which have been dampened are corrugated at the same time, a liner is glued to ooe side of the paired mediums at the corrugating machine, a second liner is sub~equently glued to the other side of the board, and the paired single-faced boards are separated during stacking.
The desired objectives in the process of assemb-ling the single-faced board or boards and another liner are to maintain a good production rate in which the assemb-led board has good wet tack strength to enable immediate cutting of t~e board from the web and stacking of the board Other ob~ectives are to minimize brittle board with cracked lines, shrinksge, warp and washboarding caused by excessive heat, and to eliminate poor drying with warp and structural weakness caused by insufficient heat. Conventional appara-tus and method for laminating the second liner to the sub-strate containing one liner and the corrugated intermediate ~-layer i8 ~hown in Fig. 1 of the Griffith U. S. Patent 3,434,901. The corrugated substrate i8 p-ssed sround pre-he~ter drum to rai~e the temperature of the corru-g~tion~ ~nd travels p~st ~n adhesive ~pplicator in which ~ su~pension of starch is transferred to the corrug~ted i ~ ;
medium. The second liner which is ~180 trained over ~ pre-he~ter roll i~ contacted to the botto~ of the corrugated ~. ;-sub~trJte with the ssse~bled la~ina subsequently passing-~
through a hot plate section he~ted by stes~. The he~t at the hot pl~te sections c~uses gelatiniz~tion of the starch to bond the corrug~ted oediuo to the ~econd liner ant also removes excess ~oisture and increase~ the solids cooteot of the starch at the glue line. The conventional process re-quires an expensive hot plate section which may be 40 feet or ~ore in length ~nd requires con~iderable space and ex-pense to operate. A nu~ber of she de~ects in the finl~hed board are csused by the uneven he-tiog and inefficient dry-ing in the hot pl~te section, causing warping and wash-bo~rdiDg io the fini~hed board which causes tifficulty in priDting on the liner.
Various efforts hsve been oade to i prove the con-ventional ~ethod and to eli~in~te washboarding ~nd warping of the fini~hed bo~rd by att-~pting to reduce the he~t re-quired at the hot plate section by loweriDg the gel point of the starch in adv~nce of the hot plate section or by ~odlfying th ~ethods and location of heat applic~tion.
Griffith U. S. Patent 3,434,901 discloses the ~ethod of ~ .
golatiDizing tke ~t~rch after it is applied to the substrate by a stea- spr-y prior to application of the second liner.

- 2 -This Griffith patent also discloses the ~pplic~tion of a chemical gel point depressant to the starch adhesive on the corrugated substrate prior to application of the second liner. One of the difficulties with the application of the chemical to the starch at this stage i8 thst the early gelatinization of the exterior surface of the starch adhesive inhibits sufficient penetr~tion of the adhesive into the second liner and thus does not provide as fir~ a bond as de~ired.
Su~m~ry of Invention The pre8ent invention i8 concerned with the step of adhesively securing the second liner to the corrugated substrate to form either double-faced or paired single-faced bo~rds, or single-faced plies and a last liner to for~
multiwall board. More particularly the invention rel~te~ to the che~ical gel~tinizatioD of the adhesive (typically starch) used in the ~anuf~cture of corrugated board, thus to reduce the heat aDd ~oisture previous1y required in the conventional process to acco~plish the gelatinizstion of the starch.
The ~ethod of the invention overco~es the defici-encies of tbe prior rt ~ethods by application of the gel point depres8ant to the tips of the flutes of the corrugated substrate prior to the application of the starch adhesive to the flute tips. This causes gelatinization to proceed from the tips of the flutes through the inDer ~urface of the starcb adhesive which is in contact with the gel depres-sant agent towards the outer exposed surface of the starch adhesive. This technique initiates gelatinization of the ,:

iDnermost l~yer of ~dhesive ~t the e~rliest possible ~om-ent, substantially contemporaneously with the first contact of the adhesive with the flute tips. Yet gelatinization of the outermost lsyer of adhesive i8 delayed until after con- ~
tact is made with the second liner of double faced board, ;
thus insuring atequate penetration of the starch adhesive into the surface of the second liner at the liner i8 applied and before any Qaterial gelat~nization thereof has occured. ;
These adv~ntages also accompsny the use of the invention in the production of either ~ultiwsll or paired single-faced boards.
The use of the chemic~l gel poiot depressant as disclosed herein ensbles use of a stsrch suspension with a higher total solids content than in prior srt process.
The method of the inventioD provides a thin, well-defined glue line with good wet tsck strength for subsequent hand-liog of the double-faced bosrd sfter it leaves the hot pl~te ~nd minimizes the smount of water needed in the stsrch.
This technique reduces the need to evaporste water from the product, reduces the tempersture re4uirements for the hot plate, hence minimizing the problems sssociated with uDeven redistribution of moisture iD the hot plate section and the high heat thereof 8uch a8 wsrp, w~shbosrding, etc.
The gel point depressant is prevented from enter-ing the stsrch reservoir vis tbe s~srch or glue ~pplicator roller by controlling the thickness of the gel point depres-s~nt on the flute tips and the thickness of stsrch costing on the glue roller. The gel point depresssnt is spplied in a thin film to the tips of the flutes only, and prior to the ~~
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- $ V~684 application of the starch. The film has a thickoess sub-stantially less thao the coating of ~tarch adheYive carried by the glue roll. The thicker starch layer or coating on the glue roller splits, transferring some ~t~rch to the tips of the flutes with the remaining part of the coating oo the glue roller being recycled to the glue reservoir free of the depressant agent.
The cheoical gelatinization process of the in-vention provides the desired bonding of the last liner or multiwall plies with a decrease in board rejects. The process also enables higher machine speets and higher pro-duction because of the reduced length and temperature of the hot plate ~ection necessary to complete the gelatini-zation of the starch adhesive.
Further ob~ects, features and advantages of the present invention will become apparent from the ~llowing disclosure.
DescriPtion of Drawin~,s Fig. 1 is a scheQatic diagram of one form of ap-paratus employed to practice the method of the invention and illustrates ~he method.
Fig. 2 is an eolarged diagrammatic view showing the application of the gel point depressant to the tips of the flute~ at station A of Fig. 1.
Fig. 3 is an enlarged diagramQatic view sho~ing the application of the starch adhesive to the tips of the flutes and over the coating of gel point depres~ant at station B of Fig. 1.

J 0~3684 Fig. 4 is an enlarg~d diagramm~t-ic vie~r shoT,rin~ t'ne application of the second liner to the flute tips at station C
o~ Fig. 1., Description of Preferred E~lbodiment . .
Although the disclosure hereof is detailed and exact to enable those sk-illed in the art to practice the inventionf the physical embodiments herein disclosed merel~ exemplify the invention which may be embodied in other specific structure, ~he scope of the invention is de~ined in the claims appended hereto.
The method of the invention can utilize various two component adhesives. In the disclosed embodiment starch and a gel point depressant are illustrated as such a two component adhesive. As specifically illustrated, the pre~erred embodiment relates to a method of constructing a double-faced or double-linéd corrugated board 8 and in particular, the application o~
a second liner 10 to a lamina 13 which includes a corrugated medium or substrate 14 formed at the corrugation station and a first ~ace or liner 12 laminated thereto along the flute tips 11. The apparatus shown in Fig. 1 is downstream of the corruga-tion station (not shown) and includes a conventional pre-'neater drum 16 which raises the temperature o~ the web 13 prior to application of the adhesive at the glue station B. T'ne web lamin~ 13 is trained around idler rollers 20 and 22, and a drum 24 and moves ~rom the glue station B in wh~oh a glue roller l9 ' ....

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.- . . .. ~ , "; .. ,; .. , 10~36~4 picks up ~,lue f'rom a rescrvoir 21 and applies it to th~ we~
Th~ web 1~ th~n moves to a hot plate section 26 which includes a series of steam h~ated chests 27, 28 where the second liner 10 is bond~d to the web 13. A pressure belt ~0 holds the web a~ainst the second liner 10 and the steam chests 28. The steam chests 28 provide the heat to remove excess moisture and complete gelatinization of the starch as presen-tly described. The belt 30 in cooperation with a belt ~2 serve to draw the liner 10 and web 13 through the stations A, B and C. A final cut-off section 34 severs individual sheets or boards 15 from the double-faced corrugated web 8.
The second liner 10 is also trained around a pre-heater drum 36 and various idler rollers 37 before application to the web 1~ of corrugated medium at the hot plate section 28.
As thus far described, the apparatus and sequential operation is typical of conventional double-faced corrugated board manufacture.
In accordance with the method of the invention, a gel point depressant or a gelatinizing agent 40 is applied to t'ne . 20 tips 42 of the flutes 44 of corrugated substrate 14 at station A, prior to application of the bonding adhesive thereto at the ~lue station B. When a typical starch adhesive is employed at the glue station B, the gel point depressant 40 desirably comprises a solution of a caustic hydroxide such as sodium hydroxide which is Lnexpensive and lowers the temperature ~ I
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10436~4 lev~l at whLch ~cl~tini~at-Lon of the s~arch occurs. O~her hydroxides can be employed. A~ t~1~ gelatinlzation temperature, the raw starch which is in the form Or small ~ranul~s, swell3 considerably, absorbs much of the available water> ~n~ is partially solubilized. The gelatinization process greatly increases the mixture's viscosity and its wet tack to hold t~le board 8 together un~il the glue line dries to give rigid non-plastic dry adhesion.
~he depressant 40 is applied only to the tips 42 of the flutes (Figs. l, 2) by an applicator roller 43 wnich is coated with a solution of sodium hydroxide by a suppl-y roller 45 which picks up the soIution from a reservoir 47. Inasmuch as the solution is applied only to the tips 42 of the flutes in the form Or caps 46, only a limited quantity is required as compared with the use of a spray as shown in the Gri~fi~h U.S.
patent 3,434,901 which applies a coating o~ gel point depressant t,o thc entlre corrugated substrate, and then only arter th~
starch adhesive is previously applied to the corrugated substrate.
Re~err~ng to Fig. l, as the web 13 moves through the 20 ~ glue station B, the glue or adhesive 50 which is typically a starch~suspension in water is applied to the tips 42 of the , M utes over the gel depressant caps 46, in the ~orm ol a coverin~
~ ~1 ;layer 52. (Fig. ~) ;1 ~; . Entry o~ ihe gel point depressant 40 into the glue ~ 25; reservoir 21 is prevented by controlling the thickness "D"
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1043~34 ) of ~he caps 46 Or dep~essant and the thicknes~ "E" of ~he glue coating 51 on the glue roller 19, thus to take advantage of a film splitting phenomenon. Film splitting results when a liquid is fed into the nip between two surfaces which separate and in which the liquid wets both surfaces. As the nip opens, a part of the liquid is carried away from the nip by each of the surfaces with the proportions of the film carried away by each surf'ace dependin~ on film thickness, pressure, speed of the surfaces, porosities, viscosity and ease of wetting of the surfaces.
With respect to the method of the invention, the film splitting occur~ in the starch layer 51 (Fig. 3) on the glue roller 19. The thin layer or cap 46 of sodium hydroxide solution is not carried into the glue reservoir 21 because the relatively thick layer 51 of starch solution spllts at 57 with the film layer 52 of starch adhering to the tips of the flutes and the f'ilm layer 61 adhering to the glue roller 19. The film splittlng of the starch at the glue station is because the starc'n film 51 is the thicker of the two liquid layers 46, 51, the corru~ated substrate 14 is more porous than the glue roller, and the viscosity of the starch at the starch-caustic interf'ace 49 is higher-than that of the layer yet to be gelatinized.
If film splitting did not occur, some of the gel point depressant would be carried into the glue pot 21 and cause progressive gelatinization of the glue supply. miS would _ g _ , .; , . . ' . .

eventually prevcnt proper bonding o~ the second liner 10 to the su~strate 14.
A numb~r o~ advantages result from the application of - gel point depressant in advance o~ the application of the starch adhesive. Only a limited quantity of the gelatinizlng agent is required because it is applied only to the tips 42 of the M utes, this being the same limited area of the corrugating medium which is subsequently coated with the starch component 50.
Only a slight moisture penetration of gel depressing agent 40 occ~rs in the zone 55 (Fig.'2) of the tips 42, inasmuch as the 5 ~ sodium hydroxide solution which i9 typically used does not wet the corrugated medium as easi~y as water. Accordingly, the quantity of moisture in the corrugated substrate 14 and which must u'ltimately be eliminated in the hot plate section is initially reduced. Moreover, any rosin or other acid size in the second liner 10 is protected from adverse reaction with excess gelatinizing agent by the intervening starch component layer 52 (Pig. 4). The unsized corrugated medium 14 is not adversely e~fected by the gel point depressant. ' ~
20~ Inasmuch as the gelatinizing process starts at the ' interface 49 of the caustic and starch layers adjacent the flute tips, the appIication o~ gel point depressant to t'ne ~lute tips - ~ -42 in advance o~ the adhesive reduces the quantity o~ adhesive required by limiting the penetration'of the combined adhesive '' ~' ' and gel poln' depressant into the porous rorrugating medium 14, ~: .
' - 10 1 ' :... . . , . . .. - - . . . ~ . . ~., .

1C~3Uj~ 4 wllile ~rlrlittir~ suf'~ici~nt p~n~tration o~ the le~s porous s~cond liner a~ 61 because the outermost layer 63 Or the combined adllesive'and gel point depressant adjacent the second l-iner remains in a liquid state longer as it is the last'to be ~elatiniæed.
' ' ~tarti~g the gelatinizing process o~ the starch chemically before the application o~ the heat of the hot plate insures that the starch granules will have enough water to fully swell to form a good bond even if the adhesive's total solids are signi~icantly higher than that typically used in prior processes. The starch gelatinization process competes for the water at the glue line with the processes of liquid migration and water evaporation from the glue line upon the application of heat in the hot plate section 26. Thus a starch adhesive can be employed with a significantly higher total solids content.
In the prior art processj without the aid of a chemical gel point depressant, the hot plate heat was the -' primary means of gelatinizing the starch granules and driving off excess moisture from the glue l'ines. Competition between these two processes limited the useful range of the adhesive's total solids from about 15% to about 30%. In the prior art process, when the adhesive's total solids were belo~J this range, excessive heat was required to drive off the surplus moisture, thus limiting machine speed, promoting warpage, an~

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~0436~94 increasing steam costs for the steam chests. When th~
adhesive's total solids were above this range, weak board adhesion resulted because not enough moisture was present at the glue lines to fully gelatinize the starch before the heat drove the moisture away.
Tlle separate application Or a chemical gelatinizin$
agent in advance Or the application Or the starch aids the -~
starch granule gelatinizing process in its competition for water with the liquid migration and evaporation processes so that an adhesive with total'solids greater than this range may be used without interfering with good board adhesion, and with higher machine speeds, less warpage, and lower steam costs.
With the method of the invention, a total solids content in the starch of up to ~ ~ or more can be employed, and a substantially shorter hot plate section can be utilized because a gelatinized starch adhesive of this composition has enough ' wet tack strength to retain the board components assembled during processing of the completed web into individual finis'ned boards ' 15. Reduction of the length o~ the hot plate section is ' advantageous because a massive hot plate section acts æs æ heat '' sink and the temperatures cannot be rapidly changed for varia-tions in production requirements without substantial delays. ' ~' In the fabrication of some types of corrugated board, the hot plate section can be eliminated completely because of the efficient gelatlnization provi'ed by the method of the ' : .
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XX~K ,,1 10436~34 invention. Howcver, the draw section of the apparatus is still desirable to hold or press the a~sembled lamina togethe~ for a period of time sufficient to obtain a good wet bond.
The good immediate wet tac~ of the second liner 10 to t'ne corrugated substrate 14 enables use of maximum machine speeds of 650 feet per minute or more with lower hot plate section s~eam pressure and steam chest surface temperatures.
The corrugated board produced by the method of the invention provides an attractive board free Or defects with better surface for printing than board produced by prior art ~ethods. In addition, it has a stronger bond and higher tensile strength with a thin, well-defined glue line. Also, the finished boards arc flat and do not have to be cross-stacked to obtain a pallet'load of uniform height along the stack margins, thus automatic stacking can be employed as compared with manual stacking'used in prior art processes.
Although the method of th~ invention has been specifl-cally described for the construction of double-faced board, the met'nod can also advantageously be employed to unite two single-faced boards and a third liner to form a multiwall corrugatedboard, to unite a liner to a web composed of two corrugated mediums and~a liner to form paired single-faced boards. For example, the board layer 10 can comprise a corrugated medium with a single liner face, with the liner face being applied to the tips 42 of the flutes a~d at the hot plate sec~ion wit'n a third liner also applied at the same point in the sequence.

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Claims (8)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method of manufacture of double-faced corrugated paperboard, the improvement comprising the steps of applying a coating of gel point depressant of caustic hydroxide to the exposed flute tips of the cor-rugated medium faced with a single liner opposite the exposed flute tips by contact of an applicator carrying the depressant with the flute tips, applying an ad-hesive comprising a starch suspension in water over the coated flute tips with an adhesive roller and wherein the coating of adhesive on said roller is substantially thicker than the coating of gel point depressant on the flute tips to cause a splitting of the adhesive coating on the roller into an adhesive layer on the flute tips and an adhesive layer on the adhesive roller which iso-lates the depressant coating from the adhesive roller and the coating of adhesive film on the adhesive roller, initiating gelatinization of the adhesive starting from the interface of the adhesive and gel point depressant outwardly through the adhesive coating, and applying an additional board layer to the coated flute tips prior to material gelatinization of the outer exposed surface of the adhesive.

2. The improvement of claim 1 wherein said roller is operatively associated with an adhesive reser-voir and wherein the coating of adhesive on said roller is substantially thicker than the coating of gel point depressant on the flute tips to cause a splitting of the adhesive coating on the roller into an adhesive layer on the flute tips and an adhesive layer on the adhesive roller which isolates the depressant coating from the adhesive roller and the coating of adhesive film on the adhesive roller which adhesive coating is recycled back to the reservoir free of depressant.

3. The improvement of claim 1 wherein the ad-ditional board layer is a second liner.

4. The improvement of claim 1 wherein the ad-ditional board layer is a corrugated board with a single liner and a third liner.

5. The improvement of claim 1 wherein the ad-hesive comprises a starch suspension with a total solids content in excess of 40%.

6. In the method of making corrugated paper-board with a double liner, including the step of corru-gating a continuous web of corrugated medium to provide a series of flutes therein and applying a first liner to the corrugated medium, the improvement comprising the steps of applying a coating of gel point depressant of caustic hydroxide to the exposed flute tips of the corrugated medium faced with a single liner opposite the exposed flute tips by contact of an applicator carrying the depressant with the flute tips, applying an adhesive comprising a starch suspension in water over the coated flute tips with an adhesive roller and wherein the coating of adhesive on said roller is substantially thicker than the coating of gel point depressant on the flute tips to cause a splitting of the adhesive coating on the roller into an adhesive layer on the flute tips and an adhesive layer on the adhesive roller which isolates the depressant coating from the ad-hesive roller and the coating of adhesive film on the ad-hesive roller, initiating gelatinization of the adhesive starting from the interface of the adhesive and gel point depressant outwardly through the adhesive coating, and applying an additional board layer to the coated flute tips prior to material gelatinization of the outer exposed surface of the adhesive.

7. The improvement of claim 3 including the step of applying heat to the combined web after the second liner is applied to the corrugated medium.

8. The improvement of claim 7 including the step of applying pressure to the web after the second liner is applied to the corrugated medium.