CA1084317A

CA1084317A - Transfer and adherence of relatively dry paper web to a rotating cylindrical surface

Info

Publication number: CA1084317A
Application number: CA222,411A
Authority: CA
Inventors: Gregory A. Bates
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 1974-03-19
Filing date: 1975-03-18
Publication date: 1980-08-26
Also published as: NL7503183A; DE2511542A1; US3926716A; IE40834B1; SE7503046L; GB1442960A; IT1034406B; ES435763A1; BE826859A; LU72074A1; AU7873075A; JPS50160509A; IE40834L; FR2264917B1; FR2264917A1

Abstract

TRANSFER AND ADHERENCE OF
RELATIVELY DRY PAPER WEB TO
A ROTATING CYLINDRICAL SURFACE

Gregory A. Bates ABSTRACT OF THE DISCLOSURE

In manufacturing a soft and absorbent tissue paper, a moist web deposited from a fiber-water slurry, is contoured with the pattern from an open mesh conveying fabric and thermally dried to a relatively high fiber consistency.
Following these steps, the resulting relatively dry patterned web is imprinted as it is transferred and adhered to a rotating cylindrical surface in the form of a Yankee dryer utilizing an aqueous polyvinyl alcohol solution where the polyvinyl alcohol is characterized by a particular degree of hydrolysis and particular viscosity characteristics. By thermally drying to a high fiber consistency prior to the transfer step, the amount of drying load required to be carried by the Yankee dryer is reduced resulting in either (1) increased line speed as a result: of reduced Yankee drying load, which reduces the required residence time of the web on the dryer or (2) a reduction in the required diameter of the Yankee dryer, a significant reduction in capital equipment cost. By thermally drying the web to a relatively high consistency on the conveying fabric, a deeper more pronounced pattern in the Z direction is obtained due to an increase in web structure strength and resistance to compaction of the pattern. This results in increased bulk (lower density) and increased softness. As a result of utilizing the particular polyvinyl alcohol, transfer and adherence of the relatively dry web to the Yankee dryer is obtained so as to minimize the amount of skipped crepe whereby the problem of web breakage downstream of creping is eliminated.

Description

~ 7 BACKGROUND OF THE INVENTION
This invention relates to the manufacture of a soft and absor~ent paper web especially suitable for use in tissue, towelling and sanita~y products.
More particularly, th:is invention relates to a manufacturing process where a moist web is carried on an open mesh conveying fabric and is thermally dried. he thermally dried web is imprinted with the conveying fabric pattern as it is transferred and adhered to a rotating cylindrical surface in the form of a Yankee dryer. rhis type of process is disclosed in Sanford et al U.S. Patent No. 3,301,746, commonly -owned by the assignee of the present invention~
It has been discovered that drying thè paper web to a relatively high consistency prior to imprinting is advantageous, and the more thorough that drying is, the more significant the advantages that are achieved. In the present ~ ~-context the term "imprinting" is intanded to mea~ the impression of the fabric imprinted into the web at the time of its transfer to the Yankee dryer. It is recognized that some fabric pattern impression is imparted to the moist paper web while being carried on the fabric but this is not to the same degree or extent which occurs in the imprinting step when the web is transferred to the Yankee dryer.
To particularize these advantages, it is noted that increasing the thermal drying of the web prior to its transfer to the rotating cylindrical surface allows a reduction in the Yankee drying load; and this allows an increase in line speed, since the amount of time required by the rotating cylindrical surface to provlde the final fiber consistency is line speed .~
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limiting. And if thermal drying is carried out to higher web consistencies prior to transfer to the rotating cylindrical surface, not only i; line speed increased, but a smaller diameter Yankee dryer can be used, resulting in significant savings in equipment costs.
Besides providing processing and eguipment advantages, drying to a relatively high degree prior to transfer to the rotating cylindrical surface provides product advantages. In particular, the drier the web is at the time of transfer, the more permanent is the fabric impression in the Z direction, that is in the direction perpendicular-to the web major surfaces, in other words, a more distinct and deeper ~ ' impression is obtained. This improved impression results in ~ greater bulk (lower denslty) and increased softness.
However, drying the web to relatively high fiber consistencies prior to transfer to the rotating cylindrical surface to obtaih the above advantages can result in a problem in transferring and adhering the relatively dry web to the cylindrical surfacè. In particular, when the conventional animal glue disclosed at column lQ, lines 23-25 of the Sanford ;
et al patent is utilized in an attempt to improve the bond between the imprints and a Yankee dryer surface, a problem of insufficient bonding is noted when the web to be transferred ;~
has an average fiber consistency exceeding about 68~. As a result of this insufficient bonding~ very few imprints are in contact with the Yankee dryer so that the web is not uniformly dried, and this non-uniformly dried state in conjunction with the insufficient bonding results in a very irregular crepe .:
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~that is, an excessive amount of skipped crepe). This very irregular crepe results in a significantly increased web bxeakage problem in the processing sequence downstream of creping, especially in the processing sequence between the 5 creping blade and the calender stack. This web breakage pxoblem becomes more severe as the fiber consistency of the web to be transferred is increased. When the fiber consistency of the web being transferred exceeds about 80~, the adherence with the animal glue is so poor that the resulting crepe has such irregularity that the web breaks in substantially every instance and the resulting product has poor softness characteristics. -The present invention is concerned with obtaining ` the advantages resulting from drying to a relatively high consistency during intermediate drying without the web breakagedisadvantage occurring, which results from insufficient bonding of imprints to the rotating cylindrical surface upon which the subsequent creping step takes place.
With this in mind, consideration was given to the use of adhering agents other than the composition specifically described in Sanford et al. Several classes o~ polymeric materials were considered of which~polyvinyl alcohols were preferred. It has been discovered that only particular polyvinyl alcohols are operative to obtain the advantages resulting from drying to a relatively high consistency prior to transfer to the rotating cylindrical surface while entirely eliminating the breakage problem which occurs upon the use f ¦;
the above described animal glue composition. The present invention is concerned with the sel~ction and definition of these particular advantageous polyvinyl alcohols.
This invention, then, resides in a process for manufacturing a soft and absor~ent tissue paper web having a uniform basis weight of about 5 to about 40 pounds per 3000 square feet, said process comprising the steps of:
(a) drying without compacting a moist paper web to provide a fiber consistency exceeding about 68% and ranging up to about 98% whiie said web is on a patterned imprinting -fabric;
(b) imprinting the resulting relatively dry web with the pattern of the imprinting fabric; and `~
(c) aplplying an aqueous polyvinyl alcohol solution to cause transfer and adherence of the imprinted web to the rotating surface of a dryer drum, said polyvinyl alcohol being characterized by a degree of hydrolysis ranging from about 80% to about 90~ and a viscosity as a 4% aqueous solution at 20C exceeding about 20 centipoises.
The objects a~d advantages of-the invention will ;~
be evident from the following detailed description.
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BRIE~ DESCRIPTION OF THE DRAWINGS
Figures L~ and lB schematically illustrate a papexmaking process where the instant invention is applicable. Figure lB follows ~igure lA in the processing sequence.
Figure 2 is a view taken at line 2-2 of Figure lA
and illustrates the portion of the process concerning the mak~-up and use of adhering agent solution.
Figure 3 is a view taken at line 3-3 o Figure 2 depicting details of apparatus for applying adhering agent solution to a Yankee surface.

DETAILED DESCRIPTION
With continuing reference to Figures lA and lB, a papermaking furnish is delivered from a closed headbox r 10 to a Fourdrinier wire 12.
The Fourdrinier wire 12 is supported by breast .
roll 14 adjacent to headbox 10 and couch roll 16 which is spaced from and horizontally ali~ned with breast roll 14.
It follows a travel path defined by breast roll 14, couch roll 16, and return roll 18 which is spaced downwardly and vertically offset from couch roll 16. The Fourdrinier wire 12 in following the travel path established by rolls 14, 16 and 18 passes over roll 14, then moves hori~ontally toward roll 16, then passes over roll 16 and moves downwardly~ ¦
then turns around and under roll 18, then moves toward roll 14 and pssses around and over roll 14.
.--- , The headbox 10 forms a paper web 20 on the Fourdrinier wire 12 having a dry basis weight ranging ~or example from about 5 to about 40 pounds per 3000 sguare feet and an initial fiber consistency ranging for example from about 0.1% to about 0~3%. The formed web travels along the Fourdrinier wire 12 between breast roll 14 and couch roll 1~ and continues along with Fourdrinier wire 12 during a portion of its path between couch roll 16 and return roll 18. .
Forming devices 22 and 24 are positioned near breast ~ .-....... .
. roll 14 and succes~ively bear on the underside . . - --of Fourdrinier wire 12 to remove water from the web 20. : ::
Trimming nozzles 26 may be positioned downstream of forming deYice 24 to trim the sides of the web. i A suction box 28 is positioned under the Fourdrinier wire 12 adjacent couch roll 16 so as to draw ;-~ater from the web 20 through wire 12.
As a result of the action of the forming devices 22 and 24 and the suction box 28, the web is dewatered to i~
provide a fiber consistency ranging for example from about .:
10% to about 25%.
As the Fourdrinier wire 12 is in the portion of its travel path between couch roll 16 and return roll 18, the partially dewatered web 20 is transferred to the conveying and imprinting fa~ric 30.

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. The fabric 30 follows a travel path defined by a guida roll 32, a guide roll 34, a guide roll 36, a pressure roll 38, a guide roll 40, a guide roll 42 and a guide roll 44. The fabric in following this travel path passes under guide roll 32, then moves in a direction diagonally downwardly away from wire 12, then passes under guide roll 34, then moves substantially horizontally, then passes under guide roll 36.
and turns upwardly therearoundt then moves upwardly and passes over and around pressure roll 38, then moves back in the direction of Fourdrinier wire 12, then passes under and around guide roll 40, then moves diagonally upwardly in a direction away from Fourdrinier wire 12, then passes over and around guide roll 42, then moves substantially horizontally in a ~ direction toward Fourdrinier wire 12, then passes over and , ', around guide roll 44 at a locatlon adjacent couch roll 1~, then passes diagonally downwardly so as to be aligned with and `~
adjacent the initial portion of the travel path of wixe 12 between couch roll 16 and,return roll 18, then passes under '`
roll 32.
The conveying and imprinting fabric 30 has a mesh ' structure and is formed of filament so that when a vacuum is .' exerted to pul:L the moist web against the fabric, the web partially assumes the contour of the supporting surface of the fabric including its knuckle pattern. The fabric may be a '~
woven polyester monofilament as described in U.S. Patent No.
3,473,576 issued to John S. Amneus on'~ctober 21, 1969.or it may have the characteristics of the fabric described in U.S.
Patent No. 3,905,863 o~ Peter G. Ayers, issued ~ 7 ,..... .. .... . . . .. .

September 16, 1975, both said p~ten~s being commonly owned by the assignee of the present invention.
Preferably the fabric has its knuckle surfaces abraded away in accordance with the teaFhings of U.S. Patent No . `~
3,573,164, lssued March 30, 1971 to Norman D. Friedberg et al, said patent being also c~mmonly owned by the assignee of the present invention. ;
The transfer of the moist web from the Fourdrinier wire 12 to the fabric 30 i5 accomplished utilizing a vacuum box 46 positioned opposite fabric 30 between rolLs 44 and 32.
In this transfer the partially dewatered web is separated-~
from the wire 12 and attaches to the fabric 30 and thereupon travels with ~abric 30 through a portion of its travel path as . .
described hereinafter.
A multi-stage vaauum box 48 is posltioned on the ~ : ., :, . .
siae of fabric 30 opposite that in contact with web 20 at a location between transfer vacuum box 46 and guide roll 32. As aepicted, the vacuum box 48 is a three-stage vacuum box containing compartments-with the vacuum in each being ;~
.
~ independently adjustable. It functions to pull web 20 against fabric 30 so a;s to form a web conforming to the mesh pattern of the fabrio. ; ;~
As the web 20 travels along with fabric 30 between guide rolls 32 and 44 it is thermally dried. This drying is carried out wlthout compacting the web. This is accomplished using a hot air drier 50 which is positioned on the same side of fabric 30 as is web 20 so as to direct hot air at the web 20~ The hot air dryer 50 is preferably in the form illustrated and described in U.S. Patent No. 3,303,576 issued February 14, :: :

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1967 to James B. Sisson, which patent is commonly owned by ~he assignee o~ the present invention. An exhaust fan 5~
is posltioned across from drier 50 on the opposite side of fabric 30 to remove moisture evaporati~g from the web.
This drying is carried out to ei-fect a fiber consistency in the web exceeding about 68% and ranging up to about 98%, that is to relatively high fiber consistencies. As previously explained, drying to these rel'atively high fiber consistencies ' ,prior to imprinting against the ro~ating c~lindrical surface results in the obtainment of process advantages (lower thermal load on the Yankee dryer which allows increased line speed) and product advantages (increased softness and absorbency) compared to drying to a lesser extent previous to imprinting.
` The limitation of exceeding about 68~ has been selected in this case because the adhering agent inveniion has unique advantage as explained previously with r~spect to webs dried previous to imprinting to that extent, namely the elimination of web breakage downstream of creping and more uniform cross direction moisture profiles. The upper limit of about 98~ has been selected because at fiber consistencies exceeding this, overdrying of the sheet occurs which will diminish subsequent sheet control.
The web 20 having been subjected to thermal drying by the drier 50 continues along with fabric 30 until both reach pressure roll 38 whereupon web'20 is transferred to the rotating cylindrical surface of Yankee dryer 54.
As web 20 is being transferred to the rotating cylindrical surface of the Yankee dryer 54 it is also being ~ .
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~ 7 imprinted with a knuckle patternO This i5 effected by pressure roll 38 pressing web 20 and ~abric 30 against the rotating cylîndrical surface.
After the web 20 is transferred from fabric 30 to the rotating cylindrical surface, the fabric 30 having been freed of the web is washed with water sprays 56 and dried by a vacuum box 58 and then follows its travel path to pick up uncompacted web to be imprinted in the manner previously described.
~he web 20 having been transferred to the rotating cylindrical surface is dried to final fiber consistency if not already at such consistency, whereupon it is creped from the surface by a doctor blade 60. While on a Yankee, the web is ~ generally exposed to a temperature of at least 212F. and usually not exceeding 350P. The creped dr ed web then passes under a guide roll 62 and over a Mt1 Hope roll (not depicted), ~hen through a calender stack 64 and then is wound on take-up reel 66 which is driven by driving roll 68. -Turning now to the transfer of web 20 ~rom fabric ~ 30 to the rotating cylindrical surace of the Yankeedryer, the web is transferred with the aid of an aqueous solution of adhering agent which is sprayed on the - rotating surface upstream o~ the point where ~he web is transferred to it. This adhering agent solution improves the bond between the imprints and the rotating cylindrical surface.
In other words, adhering agent solution is applied to cause txansfer and adherence of the imprinted web to a rotating cylindrical surface. The adhering agent solution application is generally denoted by numeral 70 on Figure lA.

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~,: ' , , ~ . ' . . " '' ' ' 3L~ 7 . Turning now with particularity to the adhering agent application and with continuing reference to Figures

2 and 3, the adhering agent application system comprises a make-up tank 72, a hold tank 74, an applicator described in 5 detail later, and means for recirculating adhering agent solution between the hold tank and the applicator~
The make-up tank 72 is equipped with an agitator 76. Provision is made for adding,water and steam into tank ' 72 as indicated by arrows in Figure 2. The agitation and steam are to effect solution o adhering agent solids in water. The particular make-up procedure will be described in detail later. After the adhering agent solids have been dissolved in the water to make up the adhering agent ~ solution, the made-up solution is passed by gravity flow via a pipe 78 equipped with a valve 80 to the hold tank 74.
, The hold tank 74 is in a recirculation loop with a trough 82 which is positione'd~adjacent the surface of ~ , Yankee dryer 54 upstream of the loca~ion where web 20 is to be transferred to that surface. The recirculation loop ,~
comprises a feed line 84 equipped with a pump 85 whlch communicates between the bottom of hold tank 74 and the bottom of trough 82 whereby adhering agent solution i5 fed from the bottom of hold tank 74 into trough 82. The recirculation loop is completed by a return line 86 which provldes communication `,~ -between an overflow outlet in trough 82 and the open top ofhold tank 74~ The overflow outlet in trough 82 coacts with the rest of the recirculation means and functions to establish a constant level of adhering agent solution in trough 82 as indicated in Figure 3.

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A device for applying ~dhering agent solution to the rotating cylindrical surfac~ is particularly disclosed in Figure 3 and it includes the trough 82. It also includes a rotating cylindrical foraminous member 88 axially aligned S with the long dimension of the trough and with the surface of the Yankee 54 and positioned so that a portion of it extends below the upper level of the adhering agent solution in trough 82. The foraminous member 88 is adapted to be rotated by means 89 (Figure 2) so that a poxtion of its surface moves into the liquid in trough 82 and lifts liquid ~rom the trough holding it in its interstlces as a result o sur~ace tension~
A pipe 90 is coaxial with and positioned inside of the cylindrical foraminous member 88, It contains a slot 92 ~ positioned to direct air through member 88 in the direction of the rotating cylindrical surfa~e of the Yankee ~4 whereby :.
adhering agent solution is carried -from the interstices of -~
member 88 and applied to the rotating cylindrical surface.
Having described a milieu for the invention, the instant invention lS now turned to with particularlty. As previously explained, the invention herein resides in the selection and definition of the particular adhering agent which is applied. The preferred adhering agent for use herein is used in aqueous solution and is a polyvinyl alcohol characterized by a degree of hydrolysis ranging from about 80% to about 90~ and a viscosity as a 4% aqueous solution at 20C. exceeding about 20 centipoises. Preferably the polyvinyl alcohol is characterized by a deg~ee of hydrolysis ranging from about 86~ to about 90% and a viscosity as a 4 . .... _ _: .. . .. .... . . .. . .. . .

343~L7 aqueous solution at 20~C. above about 35 centipoises.
Polyvinyl alcohols having these properties are commercially availahle and particular polyvinyl alcohols are disclosed in terms of degree of hydrolysis and viscosity as a 4%
aqueous solution at 20C. in a book entitled "Polyvinyl Alcohol" by C. Finch, published by John Wiley and Sons (New York 1973), a copy of which is in the U.S; Patent Office Scientific Library under number TP1180~V48.P$5.
The aqueous solution which is applied herein desirably contains a concentration of the above described particular polyvinyl alcohol ranging from about 0.1% to about l~ by weight. The lower limit is related to the applicator design and is selected so that the applicator -will be able to apply the correct amount of adhering agent ~ ;to the rotating surface of the Yankee in the time available.
The upper limit is selected so as to minimize the amount o ~ ., adhering agent building up on the rotating cylindrical surface which in turn minimizes wear on the stripping means used to control such build-up.
The aqueous solution is applied to the rotating -~
cylindrical surface to provide from about 0.05 pounds to about 2 pounds of polyvinyl alcohol (on a dry basis) per `~ ;ton of paper produced (on a dry basis), preferably from about 0.3 to about l pound of polyvinyl alcohol ~on a dry basis) per ton of paper produced ton a dry basis). If less ;~
than about 0.05 pounds per ton of paper (on a dry basis) is utilized, the adherence of the imprints to the rotating~
cylindrical surface may not be sufficient to obtain the . ~, ,~.~, . ' , ' ' . ' ' ', . . ' , ! ~

L,3~7 advantages of the invention. If more than about 2 pounds of polyvinyl alcohol solids per ton of paper on a dry basis is utilized, the adherence can be so great that the doctor blade will have difficulty removing the paper.
S Turning now with partlcularity to the method of adhering agent application depicted in Figures 2 and 3, water is added into tank 72 and polyvinyl alcohol solids are added thereto with agitator 76 belng run at high speed.
After the solids have been thoroughly dispersed in the water steam is injected into the water to bring its temperature to a level usually ranging from about 160F to about 190F.
- This temperature is maintained over a period of time ranging ~;
for example from about 30 minutes to about one hour by the - periodic injection thereinto of steam. During the steam ;~;;
injection the agitation is slowed so as to minimize the `
possibility of foam production. As a result of this procedure the polyvinyl alcohol solids are dissolved in the water. At this point valve 80 is opened and the adhesive solution is drained into hold tank 74. Pump 85 is then started to provide ~ -a level of adhering agent solution in trough 82 and a recirculatlon rate is provided between hold tank 74 and trough 82 ranging for example from about 0.5 gallons per minute to about 1.5 gallons per minuté. Foraminous member 88 is rotated an~ air flow into nozzle 90 is effected. Preferably the air flow is maintained constant and the rate of application of . .
ad~ering agent solution to the rotating surface is adjusted by ~

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~8~7 adjusting the speed of rotation of the.for~minous member 88.
As a result of the selection of the adhesive constituent in accordance wi~h the present invention ~he we~
~0 can be thermally dried previous to imprinting to a fiber S consistency exceeding about 68% and ranging up to about 98 without web breakage occurring downstream of creping~
Conventional animal glues and other poly~inyl alcohols are disadvantageous with respect to web breakage at the~e f1ber consistencies.
Inasmuch as this inven~ion allows drying pxevious to imprinting to provide a relatively dry web, the process ,~ ;
advantage described hereinbefore of reducing the drying load on the Yankee thereby allowing increase in line speed and -- .
the product advantage described hereinbefore-of greater bulk ~;~

and increased softness compared to where there is thermal ~ ..... ..
drying to a lesser extent prior to impri~ting are obtained.
This i~vention also allows the reduction in the diameter of the Yankee required thereby ~roviding a significant reduction in equipme~t cost. ~.
The product obtained herein from the above described process is a soft and absorbent tissue paper web. It can be characterized, :Eor example, by having a uniform basis weiyht .
of about S to about ~ pounds per 3000 square feet. It has impressed in its surface the knuckle pattern and surface ~, :
contour of the imprinting fabric. The obtained paper web has :: ~
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a relatively low bulk density compared to paper manufactured in a conven~ional tissue manufacturing process.
The inventive concepts herein are illustrated in the following specific example. In this example the system S depicted in Figures lA, lB, 2 and 3 is utilized except that when the uncompacted web is dried to between 85% and 98%
while on fabric 30, a creping drum may be ut~lizad in place of a Yankee dryer 54.
EXAMPLE
A pulp slurry having 0.3% fiber consistency an~
containing 35~ bleached northern softwood kraft and 65%
bleached poplar sulfite, prerefined at 3.5% consistency in a conventional conical pulp refiner at 100 kw.-hr./ton is distributed by the headbox which is of conventional hydraulic design. The Fourdrinier wire 12 is of polyester woven with 78 warp and 62 weft strands per inch moving continuously at 1000 f.p.m. Flow and Fourdrinier wire movement are regulated 80 that a uniform moist paper~web, having a dry basis of 11.4 pounds per 3000 square feet, i5 formed on the Fourdrinier wire. The forming devices 22 and 24 and the suction box 2 remove water from the web to provide a fiber consistency of 25%. The suction box 28 contacts the underside of the Fourdrinier wire with a vacuum equivalent to 3 inches of Hg.
The vacuum box 46 effects a vacuum of 8 psig to effect transfer of the uncompacted web from the Fourdrinier to the fabric 30, The fabric 30 is woven with 36 warp strands per inch made of 0.016 inch diameter crimped polyester monofilament and 30 weft strands per inch similar to the warp strands, particularly in that they are crimped to the same degree, with a diclmeter of 0.016 inch. The three-stage box 48 is adjusted so that the first compartment which affects the S web exposes it to a vacuum of 12 psig, the second comparkment exposes the web to a vacuum of 12 psig and the third compartment exposes the web to aL vacuum of 10 psig. The thermal dryer 50 supplies air at a temperature required to effec~ a fiber consist~ncy prior to imprinting a~ indicated in the table below. The particular tempexature utilized depends upon the fiber consistency desired to be achieved.
A temperature of 380F. is utilized to achieve the fiber consistency of 50~ in the table below while a temperature of -;~
- ` 520P. is utilized to~achieve the iber consistency of 98% -noted in the table below with the temperature regula~ed ~o ` -le~els between 380F. and 520F. to achieve fiber consistencies between 50~ and 98~. The Yankee~dryer has a dlameter of 8 feet and a width~of 31 inches. The drled uncompacted web is imprinted with a nip pressure~at pressure roll 38 of 300 pounds per lineal inch to imprint the web with~
~- the pattern of the imprinting fabric. Adhering agent solution ~ ;
is applied by~applicator 70 at a point 12 inches upstream of ..
the nip between roll 38 and the drum of Yankee 54 and it is applied in a pattern which extends circumferentially on the surface of Yankee 54 about 3 to 4 inches. Various polyvinyl alcohols are utilized as indicated in the table. All of the ~:
poIyvinyl alcohols utilized are readily commercially obtainable ~.

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from the Monsanto Chemical Company and others. In this example, of the polyvinyl alcohols utilized, Gelvato ~ 20-90 ~nd Gelvatol 20-60 are within t,he scope of the invention.
The other polyvinyl alcohols utilized, namely Gelvatol 1-90, Gelvatol 3-60, Gelvatol 20-30 and Gelva~ol 1-30 are outside the scope of the invention. In relation ~o the Gelvatols ;the first stated number indicates the percentage residual polyvinyl acetate and the next series of digits when multiplied by 1,000 gives the number corresponding *o the-ave~a~e molecular weight.
As indicated in Figure 2.1 of the book entitled "Polyvinyl Alcohol" by C. Finch described earlier, Gelvatol 20-90 has a degree of hydrolysis of about 88% and a viscosity as a 4%
aqueous solution at 20C. of about 40 centipoises, Gelvatol ` 20-60 has a degree of hydrolysis of 86 to 87% and a viscosity as a 4% aqueous solution at 20C. of slightly over 20;
Gelvatol 1-90 has a degree of hydrolysis from 99 to 100% and a viscosity of about 60 centipoises as a 4% aqueous solution i~
at~20C.; Gelvatol 3-60 has a degree of hydrolysis ranging from about 99 to 100% and a viscosity as a 4% aqueous ~
solution at 20C. of about 28-29 centipoises; Gelvatol 20-30 has a degree of hydrolysis of about 88% and a viscosity as a 4% aqueous solution at 20C. of approximately 6 centipoises;
, Gelvatol 1-30 has a degree~of hydrolysis ranging from about 99 to 100% and a viscosity as a 4% aqueous solution at 20C.
25~ of approximately 4 to 5 centipoises. The animal glue referred to below is formulated from a 100% liquid animal glue. The Gelvatols and animal glue are applied as 1% by .' .

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weight aqueous solutions. The Gelvatol solutions are made up by introducing 100 liters of cold tap water into make-up tank 72 with the agitator 76 operated at high speed, 1100 \~ J
grams Gelvatol solids are then added. The high speed agitation is continued for 20 minutes~ At this point steam is injected to bring the temperature of water to 180~.
The 180V~. temp~rature is main~ained by the periodic in~ection of steam during a 45-minute period. During the steam injection the agitation is slowed to minimize foam formation. At this point sufficient water is added to obtain a 1~ w~ight concentration of adhering agent solids. The above procedure-is sufficient to ~orm an aqueous solution of the adhering agent solids. In the make-up of the animal glue ` solution, the liquid animal glue is added into cold water in tank 72 under slow agitation and steam is injected to heat -the water to 140F. whereupon the combination is held for 20 minutes under slow agitation. In each case the aqueous solution is pumped from hold tank 74 at a rate of 1 gallon per minute.
.
~ Reticulated memher 88 has a mesh of 30 x 28 and is constructed of stainless steel wire; it is 21 inches wide and 12 inches in diameter. Pipe 90 is 2 inches in diameter and the slot 92 has ~ ?
a width of 0.025 inch; 3 psig air is utilized. The rate of adhering agent application is at about 1 pound adhering agent (on a dry basis) per ton of paper (on a dry basis). The paper produced in all cases is very absorbent (Reid test of 7-9 seconds) and soft (at least equivalen* to~commercially available p/oducts), and the higher the fiber consistency prior :' to imprintin~ the better the absorbency and the soter the paper is. The following table presents a comparison of v rious adhering agent solutions used in conjunction with webs having various fiber consilstencies as noted in the table prior to imprinting and indicates the advantage of the selected adhering agents o~ the instant invention over other adhering agents in respect to web breakage downstream ..
of creping. In the following table, ~0" denotes no breaks in a 24 hour period; "Few"-denotes a ew breaks in a 24 hour period; "Several" denotes several breaks in a 24 hour period; and "Continual" denotes breakage every time the web was attempted to be reeled up.

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~ ~ ~ g ~ ~ ~ :~ .~) ~, , ;-~1 -1: ~ 1 -1 ~1 r~r-J :: ~ O ;:,. ::
_5~ a) ~c) a) c o ~
: ~ ~ Z ~ ~ ~; ~ ~,".~ . ~ _~ ~,~ ,* ~* , ~
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As indicated by the above table web breakage downstream of creping is entirely eliminated even at fiber consistencies prior to imprinting as high as 98% when polyvinyl alcohols within the scope of the invention are utilized. On the other hand when other polyvinyl alcohols or animal glues re utilized there is at least some web breakage at fiber consistencies prior to imprinting greater than about 68%.
The above table clearly indicates the advantage of the present invention over the use of other adhering agents when fiber consistencies prior to imprinting greater than about 68~ are utilized.
While not wishing to be bound to any theory, it is speculated that the better adherence obtained by ` utillzing polyvinyl alcohols in accordance with the lS invention is obtained due to surface tension adhesion and hydrogen bonding supplied by the water solution of polyvinyl alcohol which is held as a film against the rotating drying cylinder and the polyvinyl alcohols of the invention act as a means for retaining the water at the ~
rotating drum surface. This would explain why the polyvinyl aIcohols that are operative have relatively low degrees of hydrolysis. It would also explain why higher fiber consistencies prior to imprinting are more difficult to transfer; this would probably be because there would not be enough surface water ln the web so $hat the surface tension adhesion and hydrogen bonding mechanism could come into play.
It is speculated that polyvinyl alcohols of medium high and high viscosity are required because these have a stable viscosity at the temperatures at the surface of the Yankee.

-22~

'. ~ .' : ' ' . ' '' . : ' ` ) ~34~L7 The ~iber consistencies herein are average fiber consistencies.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. For example, the particular polyvinyl alcohols selected and defined above have use in providing adherence between a web and a rotating cylindrical surface without web breakage occurring downstream of creping-in papermaking processes other than the one particularly 10 depicted in the Figures of the drawing as long as the process involves thermally drying without compacting a moist web to a fiber consistency exceeding about 68~ and ranging up to about 98~, imprinting the resulting relatively dry web with a pattern and transferring and adhering the imprinted web to a rotating cylindrical suxface in the form of a Yankee dryer where the web is dried to final fiber consisten~y (if not ~.
already at that consistency) and creped. For example, the papermaking process can be one in which the web forming carrier and the conveying and imprinting fabric are~one and :~
the same. Moreover, the adhering agent solution can be applied in ways other than that specifically describe.d, for ~ .:
example utilizing spray nozzles, separate water and glue sprays, etc. In view of the variations that are~readily understood to come within the limits of the invention, such limits are defined by the scope of the claims.

, ' ' , "
~ -23~

Claims

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

1. A process for manufacturing a soft and absorbent tissue paper web having a uniform basis weight of about 5 to about 40 pounds per 3000 square feet, said process comprising the steps of (a) drying without compacting a moist paper web to provide a fiber consistency exceeding about 68% and ranging up to about 98% while said web is on a patterned imprinting fabric;
(b) imprinting the resulting relatively dry web with the pattern of the imprinting fabric; and (c) applying an aqueous polyvinyl alcohol solution to cause transfer and adherence of the imprinted web to a rotating dryer drum, said polyvinyl alcohol being characterized by a degree of hydrolysis ranging from about 80% to about 90%
and a viscosity as a 4% aqueous solution at 20°C. exceeding about 20 centipoises.

2. A process as recited in claim 1, in which said polyvinyl alcohol is characterized by a viscosity as a 4%
aqueous solution at 20°C above about 35 centipoises.

3. A process as recited in claim 2, in which said polyvinyl alcohol is characterized by a degree of hydrolysis ranging from about 86% to about 90%.

4. A process as recited in claim 3, in which the rotating dryer drum is a Yankee dryer.

5. A process as recited in claim 1, in which the rotating dryer drum is a Yankee dryer.

6. A process as recited in claim 5, in which said polyvinyl alcohol is characterized by a viscosity as a 4%
aqueous solution at 20°C. above about 35 centipoises.

7. A process as recited in claim 1, in which said polyvinyl alcohol solution is applied to provide an amount of polyvinyl alcohol on a dry basis ranging from about 0.05 pounds to about 2 pounds per ton of paper on a dry basis.

8. A process as recited in claim 7, in which said polyvinyl alcohol solution is applied to provide an amount of polyvinyl alcohol on a dry basis ranging from about 0.3 pounds to about 1 pound per ton of paper on a dry basis.