CA1155007A - Pattern densified fibrous web having spaced, binder impregnated high density zones, and method of making such a web - Google Patents

Abstract

PATTERN DENSIFIED FIBROUS WEB
HAVING SPACED, BINDER IMPREGNATED HIGH
DENSITY ZONES, AND METHOD OF MAKING SUCH A WEB

ABSTRACT

A soft, pattern densified fibrous web such as a paper sheet which web generally comprises a relatively low bond, high bulk, vaulted field and a patterned array of spaced zones of relatively high fiber density, at least a substantial proportion of which dense zones are at least partially impregnated with binder material; and method of making such a web. The method generally entails forming a low bond, pattern densified fibrous web; supporting dense zones of the web on a patterned array of spaced supports; displacing the unsupported portions of the web into the spaces intermediate the spaced supports; and applying a binder material to dense supported zones of the web. For instance, such a web may be made by: forming a pattern densified embryonic web from an aqueous slurry of low bond fibers; supporting dense zones of the embryonic web on outwardly facing knuckles of an impriiting carrier fabric and subjecting it to a differential pressure to effect displacing unsupported portions thereof out of the top-surface-plane of the knuckles and into the interfila-mentary spaces of the carrier fabric; predrying the embryonic web to a fiber consistency of from about 30 to about 95 percent or more,preferably from about 60 to about 90 percent;
gravure impregnating dense supported zones of the predried web with binder material; and finally drying the web. The degree of impregnating and bonding in the dense zones may be increased by applying mechanical compression to the impregnated zones subsequent to applying the binder material. The web may also be creped to increase its stretch and bulk, and to increase its softness by disrupting some of the interfilamentary bonds within the web.

Description

~^ ``
llSSO~)7 PATTERN DENSIFIED FIBROUS WEB
HAVING SPACED, BINDER IMPREGNATED HIGH
DENSITY ZONES, AND METHOD QF MAKING SUCH A WEB

. Peter Graves Ayers . John Michael Raley . " ~ - ' , , ~ Te`chni'c'al' Fi'e'ld - .
This invention relates to soft fibrous webs such'as '-, paper for,paper towels and tissue-paper, and a method of making such a web which'is reinforced at least in part by binder material. -~ .
B'a'ck~'roun't':~rt . ' In general, thé exemplary paten~s described below tisclose soft, re~atively hi'gh'bulk webs such'as paper, and .
concomltant processes, some'of which.inclute'pattern app}ied ~ 10 binder:materials such'as elastomers for the'purpose o -.~ s;trengthening the'fibrous webs without making them inordinately : .- inflexible'or hard or harsh to feeI.
:
: . U-.'S. Patent No. 2,.039,312 which issued May 5, 1936 to .~ . , J~.,H. Goldman discloses a Re~nforced Carded Web which may be . ~ }5~ reinforced by.a reticulated network of narrow lines of ~ impregnation with a suitable'binder which lines are preferabl~.~ spaced slightly less than the'average fiber length of the fibers constituting the web.

: ~ U.S'. Patents ~o. 2,880,111 and No. 3,009,822 which issued to A. H. Drelich et al. on March 31, 1959 and November 21, 1961, respectively, disclose fibrous Textile-.Like Nonwoven Fabrics. wherein the fibexs are held together by an adhesive or bonding material distributed amongst them in predetermined patterns of closely spaced discrete areas.
The latter patent also diæcloses lined patterns of binder as : well as a rotogravure method.of making such fabrics which . .
~r ~ ' 1~

, ~'~S50~)7

- 2 -includes the step of wetting a fibrous web prior to rotogravure printing a predetermined pattern of spaced binder segments.

U.S. Patent No. 3,301,746 which issued January 31, 1967 to Lawrence H. Sanford and James B. Sisson covers a Process For ~orming Absorbent Paper By Imprinting A Fabric Knuckle Pattern Thereon Prior To Drying And Process Thereof. Briefly, a high bulk fibrous web-is wet formet and predried to a fiber consistency of from about 30 to about 80 pçrcent by avoiding substantial mechanical compression until the web is '10 predried; then a knuckle pattern of an imprinting fabric is imprintet in the predried web while the remainder remains substantially uncompacted. The web may also be somewhat molded to the surface of the imprinting fabric by differential fluid forces prior to the predrying. Upon being imprinted, the imprinted ~ones become'compacted and relatively highly hydrogen bonded due to the'imprinting pressure'and the water remaining in the predried web prior to final drying. Thus, upon ~inal drying, the'resulting paper is pattexn compacted and bonded in the'image of the knuckle'pattern of the imprinting fabric.' It is be'Iieved that such paper i8 so~t and bulky because'of not befng com~acted overall and because the'fibers disposed in the uncompacted portion~ do not become highly hydrogen bonded a~ in theretofore conventional felt-pressing papermaking. U.S'. Patent No. 3,994,771 which issued November 30, 1976 to George Morgan, Jr., et al.
extended this technology to a Process For Forming A Layered Paper We~ Having Improved Bulk, Tactile Impression And Absorbency And Paper Thereof.

U.S'. Patent No. 4,158,594 which was filed June 24, 1971 and issued June 19, 1979 to Henry E. Becker et al. tiscloses Bonded, Differentially Creped, Fibrous Webs And Method of Making Same wherein creping bonding material such as latex is pattern graw re printed onto a dried, self-supporting fibrous web having relatively low intesfiber bonding strength.
The web is preferably creped prior to printing, and is printed while being ~orwarded onto a crep~ng cylinder from w&ich it is subsequentlY ~dlfferentially creped. This .

1~55007 patent recites that it is particularly desirable to apply the bonding material in a reticular pattern so that the bonding material forms a net-like web of strength over the fibrous web. Indeed, all of the disclosed examples were printed with a reticular pattern although both discrete spot bonding and reticular pattern bonding are shown in the figures. 'This technology was apparently bxoadened somewhat by the following commonly assigned patents although all commonly show gravure printing of bonding material onto dried, self-supporting fibrous webs: U.S'. Patents No.
' 3,.879,257 which issuet April 22, 1975; No. 3,903,342 which '' issued Sep'tember 2, 1975;' ant No. 4,000,237 w~ich issued December 28, 1976.

. .
U.S'. Patent No. 3,'812,000.which'is3ued ~ay 21, 1974 to J.L. 5al~ucci et al. discloses a Soft, Absorbent, ~ibrous, Sheet Material Formed By Avoiding Mechanical Compression Of' The Elastomer.Containing Fiber Furni~h Until The Sheet Is At Least 80X Dry. As tisclosed, an el'astomeric bonting material i8 i'ncluded in the fiber fuxnish ~o that it ~s distributed throughout the finished sheet. Attitionally, re such bonding material may be'applied to the sheet in a predetermined ~pattern by a patterned gravure'roll while the shee~ is being forwarded thro.ugh'a paper mach~ on a foraminous drying fabric. The pattern 18 stated to preferably be.a reticular hexagonal pattern. As compared to the Sanford-Sisson patent des'cr.ibed.above,' Sal w cci'et al. include.el'astomeric material in a low-bont ~urnish; predry to a greater extent; and may gravure'print a pattern of additional binder material on the web with a patterned gravure rolL. However, Salvucci et al.
expresslr teach away from pattern knuckle.compaction as taught by Sanford-Sisson because "the pres'sures generated by the knuckle pattern of the woven wire are'so high as to create hart portions of the web which glve a feeling of harshness.to the resulting protuct."

U.S. Patent No. 3,898,123 which issued August 5, 1975 to Charles H. PhillipY et al. di~closes a Method For Wet Print-Bonding Light-Weight Wet-Formed Fibrous Webs wherein a ~55007 self-supporting, wet-formed web has an aqueous resin binder applied by print-bonding rolls having etched or engraved printing surfaces, and which binder material is applied ~ intermediate two open draw free spans of the we~ prior to drying the web.

i U.. S. Patent No. 4,127,637 which issued November 28, 1978.to Eugene J. Pietreniak et al. discloses a Method Of I Manuaeturing A Dry-Formed, Embossed Adhesively Bonded, 1 Nonwaven Fibrous Sheet having spaced uncompacted fibrous zones on a compacted reticulated ibrous network wherein I binder m~terial is preferably.disposed in the ~ncompacted zones and through the compacted network.

. .
U.S. Patent No. 4,159,355 which issued June 26, 1979 to Kenneth Kaufman discloses Foam Bonding method and apparatus for applying a foamed binder in a uniorm and controlled metered flow t~ a.surface.of a.moving substrate such as a nonwoven web.

~dditi~nally, a paper titled Forming Of Lo~ Denæity Nonwoven Fabrics: Technology And Direction was presented by G.A.M. Butterworth on Nove~ber 13, 1979 at the International Air Laid And Low Density.Forming Seminar at the Hyatt Regency Hotel in Atlanta, Georgia. This paper provides a consolidated discussion of patents pertaining to low density webs including we~s which are at least part1ally impregnated with, for instance, binder materia~.

While no~ intend~ng to limit the present invention to the following generalized distinctions, the present invention provides, as compared to the foregoing background art, a generally relati~ely low bond, high bulk, highly flexible pattern densiiet web such as a paper sheet ha~ing spaced discrete ~ones o relatively high fiber density which zones are suficiently impregnated with binder material to provide adequate sheet tens~le strength without compacting or impregnat-ing the surrounding low density portions o the web; ant the present invention provides a concomitant method of making .
- - .. .....

~55(~)7 such a web. That is, the background art does not disclose applying binder material to only relatively dense-zones of a fibrous web having a patterned array of spaced discrete high fiber density zones as provided by the present invention.
, , 5 Disclosure Of The'Invention In accordance with one broad aspect of the present invention there is provided a pattern densified fibrous web Iand concomitant method of making such a web which web has a ¦relatiuely high bulk field of relat:ively low fiber density, and a patterned array of spaced æones of relatively high fiber density at least a substantial proportion of which '~' zones are at least partially impregnated with'binder material, and in which web'the high bulk field is substantiall~
uncompacted and devoid of such binder material. The con-comitant method comprises the steps o~ forming a.pattern densified embryonic we~'having an arra~ of discrete high density ~ones disposed in a predetermined pattern; supporting the'embryonlc web on a eorresponding array of spaced supports 80 that at least each.'of a predet'ermined sub-array of t~e dense ~ones i~ ~uxtaposed one of a corresponding sub-array of the support's; and biasing the ~ub-array of supports towards a contacting type'impregnating means with the'sub-array of dense'zones disposed therebetween so that, through .~' coincidence of at least a substantial number of $he supports ~'25 of the sub-array and binder transfer portians of the ~mpregnatin~ means, at least a s~ubstantial proportion of the dense ones become at least partially impregnated. In the method, the array of spaced supports may be the knuckles of.
'' an endless imprinting carrier ~abric and the sub-array of such supports may be only the top-surface-plane knuckles of .. the fabric in fabrics ha~ing both top-surface-plane knuckles and sub-top-surface knuckles.. In fabrics having no sub-top-surface knuckles the sub-array of supports would in fact be the array of s~pports. For.maximum strength, all of the 135 high density zones are impregnated with binder material !whereas only some may only be partially impregnated in sheets wherein partial impregnation provid~s sufficient sheet strength for the intended use of the sheets.

' ~ .
-~55()()7 Impregnating means such as a full field gravure applicatormay be used to impregnate the dense zones of the web biased against it whereas less-than-full-field gravure applicators may be used to only partially impregnate all or some of the dense zones of the web, or wholly impregnate only some of the dense zones. Moreover, the method may further comprise the step of subjecting the impregnated zones to further mechanical pressure/compaction after they are impregnated to increase the binder penetration and interfiber bonding therein.
More particularly, the present invention, in its product aspect, resides in a pattern densified fibrous web comprising a relatively high bulk field having a relatively low fiber density, and a patterned array of spaced discrete zones of relatively high fiber density integrated with said rela-tively high bulk field, said high bulk field comprising a multiplicity of arched spans which corporately coact with said high density zones to provide said web with a vaulted, charac-ter, and at least a substantial proportion of said high density zones being at least partially impregnated with inter-fiber binder material through the full thickenss of said web, and said high bulk field being substantially devoid of said binder material.

Brief Description of the Drawings While the specification concludes with claims par-ticularly pointing out and distinctly claiming the subject matter regarded as forming the present invention, it is believed the invention will be better understood from the following description taken in conjunction with the accompanying drawings in which corresponding features are indentically designated, and in which:
Figure l is an enlarged photographic sectional view of a fragmentary sheet of paper embcdying the present invention.

~, .

- 6a - ~sso~7 Figure 2 is a fragmentary plan view drawing.of a sheet of paper embodying the present invention which sheet comprises a predetermined pattern of spaced high density zones disposed on a relatively high bulk field.

Figure 3 is a fragmentary ~ectional view drawing of a sheet of paper embodying the present invention which sectional view is taken along line 3-3 of Figure 2, and which sectional vie* generally corresponds to the photographic sectional view of Figure 1.

Figure 4 i9 a fragmentary sectional view drawing of a sheet of paRer~hich is substantially identical to that 64DWn in Figure 3 except the.1at, high tensity zones of the Figure 4 s;heet are not impregnated with binder material.

1155~(~7 Figure 5 is a side elevational, somewhat schematic view of a papermaking machine for manufacturing a wet laid fibrous web such as paper in accordance with the present invention.

Figure 6 is a fragmentary plan view of an exemplary imprinting carrier fabric such as may be used on the papermaking machine shown in Figure S and which imprints its top-surface-plane knuckle pattern into a web such as a sheet of paper to precipitate a pattern of co,mpacted zones.

,Figure 7 is a radially i~wardlY looking, fragmentary ''10 view of the surface of a rotogravure eylinder ha~ing a full fiel'd of truncated pyramidal reservoirs ~ormed therein, and having a partiall~ peeled b'ack opaque overlay disposed thereon which overlay is apertured ~n the knuckle pattern of the'imprinting carrier fabric shown in Figure 6.
.
Figures 8 through'l2 are partially masked fragmentary rotogravure cylinders which''are'substantially identical to that shown in Figure 7 except the'cylinders of Figures 8 th~ough'l2 are'less-than-full-fieId micropatter'ned to provide reservoirs over only about 75, 50, 50, 50, and 25 percent, respective}y, o their cylindrical surface areas.

Figure'13'is a somewhat schematic side elevational view of a handsheet impregnating apparatus~

Figure 14 i9 an enlarged scale,' fragmentary view of the roller-nip portion of the apparatus shown in Figure 13 and through which nip portion a handsheet disposed on an ~mprint-ing carrier fabric, and a flat gravure plate are being forwarded in ~uxtaposed relation.
.

Figure 15 is an enlarged scale, fragmentary view similar to Figure 14 except the handsheet of Figure 15 is not disposed on an imprinting carrier fabric as shown in Flgure 14.

J

-` l~SSO(~7 De`tailed De'scrip'tion'Of'The' Invention A fragmentary po~tion of a microtomed section of a paper sheet embodying the present invention is shown in the - photographic Figure 1 to comprise a fibrous web 20 comprising a multiplicity of fibers 21 which are disposed in relatively high density zones 22 and 23, and arcuate-shape relatively ~- low density span portions 24, and in which web the high density ~ones 22 and 23 are impregnated with a latex fiber . binder material 25.

'10 Briefly, as described more fully hereinafter in conjunction wi'th'diecusging web 20, Figures 2, 3 and 4, the present invention provides a soft, pattern densified fibrous web such as a.paper sheet whi'ch comprises a relatively low density fibrous fie~d.and a mNltiplicity of relatively high density fibrous zones disposed in a predetermined array, and in which'web ;each'of at least a substantial proportion of such'dehse zones are at least partially impregnated with a binder material of a type'which provides interfiber bonds which'are'preferably substantially more. flexible than.ordinary interfiber hydrogen bonds which occur between cellulosic fibers in ordinary papermaXing.. The web com~rises a principal . web'-strength fiber con'stituent comprising fibers of sufficient , average length with respect to the spacing of the impregnated high density zones that a substantial fraetion of the fibers wi'll have'spaced portions thereof disposed in adjacent ~mpregnated dense zones and in.overlapping bonded relation .. with portions of other fibers 80 that the bonded principal web-s~trength fiber~ constitute` a strength-skeletal-network : - of the web. Preferably, the low density field comprises arcuate-sha~e spans which are so disposed with respect to the dense zones that.the web has a ~aulted character. Also, preferably: the principal web-strength fibers have average lengths of about 2.0 mm or greater (e.g., softwood fibers);
but for the impregnated dense zones, the web is characterized by a relatively low degree of interfiber bonding which may be achieved by including debonders in the furnish, or through the use of low bond fibers; and the dense zonee preferably ~ .

. ~

~55~7 . _ 9 are qual in number to the number of imprinting knuckles of an imprinting fabric having a mesh count of from about 10-MD/10-CD to about 60-MD/60-CD filaments per inch ~from about 4 by 4 to about 24 by 24 machine direction filaments and cross machine direction filaments per centimeter, respectively) and more preferably from about 20-MD~20-CD to about 50-MD/50-CD filaments per inch (from about 8 by 8 to about 20 i by 20 machine dixection filaments and cross machine direc~ion j filaments per centimeter, respectiveIy).

Briefly, a web embodiment of the present invention as described above is preferably made by forming a pattern densified web of flbers of appropriate lengths, flexibility, and bonding propensity; supporting high density zones of the web 'on an array of spaced supports which'are'preferabl~
! ~5 generally coplanar; deflecting the webs low density span po~tions out o the plane of the supports; and im~regnating at least a substantial proportion o~ the dense'~ones. The degree of ~mpregnation andlor bonding may be'increased by ' sub~'ect~ng the'high'density zones to mechanical compression after the'basic impregnation has been effected. For ins~ance, a wet formed ~mbryonic web may be'so pattern densified and defl'ected by a differential fluid pressure while the embryonic i, web is disposed on an appropriate imprinti~g carr*er fabric as described hereinafter in conjunction with discussing Figure'6; and the impregnating may be effected, for instance, by a pressure biaæed gravuxe apparatus a3 also des'cribed hereinater. Preferably, the web i9 also creped, calendered and reeled after being impregnated and dried to further increase'its stretch, bulk and softness, and to control its 3Q caliper.

Referring again to ~igure 1, web 20 and the preferred process for making it in accordance with the present invention 'are described hereinafter as paper sheet 20 and papermaking processes, respectively, although it is not intended to thereby limit the pre~ent invention.

` - 10 - `

Figure 3 is a fragmentary sectional view drawing of a paper sheet 20 embodying the present invention which view is taken along line 3-3 of Figure 2, and which sectional view drawing generally corresponds to the photographic sectional . 5 view of Figure 1. That is, paper sheet 20 is shown in Figure 3 to comprise arcuate-shape low density span portions i 24 which are alternately spaced by relatively long and short 1 high density zones 22 and 23, respectively, which dense zones j ' are generally planar and are impregnated with binder material

3 io 2~. As may be 3een in Figure 2, a mul.tiplicity of dense zones 22 and 23'are disposed in a predetermined pattern or ! arra~ on a generally low'density field o~ which portions 24, - Figure 3, are'representative.

j Figu~e 4 is a fragmentary sectional view drawing of.a 15' pattern densified paper sheet 20a which generally corresponds with'paper sheet 20, Figure'3, except paper sheet 20a i9 not impregnated with binder material'. That is, paper sheet 20a ~8 a pattern tensified web which'has not.had lts high ' density ~ones impregnated with binder material in accordance 20 with'the present invention. Also, the'reIative fiber density . of zones 22a and 23a of unimpregnated sheet 20a is shown to ¦ be somewhat less tha'n the fiber densi~y of zones 22 and 23 ~
' o æheet 20 because ~ones 22a and 23a have not been subjected ... ~- : to the'mechanical compaction experienced by zones 22 and ~3 through the practice'of the present invention.as hereinbefore - des'cribed, .
. - Figure 5 is a fragmentary, somewhat schematic side elevational view of an exemplary paperm2king machine 30 - through the use of which paper sheet embodiments of the present invention can be made and the proce~ of the present invention can be'practiced. Papermaking machlne 30 is a . fixed roof former type papermaking machine wherein a ~ibrous slurry is delivered from a headbox 32 onto a Fourdrinier wire 33 passing over a vacuum type breast roll 34. The Fourdrinier wire then passes,over a forming board 35 and suction box 36 and is further looped about turning roll~ 41 through 46. The slurry i~ partially dewatered by the vacuum _ ___ __ _,_ . . ., , .. . . .. . .... : . . .

1155(~7 and table roll action of the breast roll. Further dewatering is precipitated by forming board 35 and suction box 36 so that an embryonic fibrous web 20e is formed and forwarded on the Fourdrinier wire to a first transfer station generally designated 50 where it is transferred from Fourdrinier wire 33 to an endless intermediate carrier fabric 51 which ' paxtially wraps roll 42, passes over suctio'n boxes 52 and 53, then over vacuum transfer box 54, and thèn is looped about rolls 55, 56, 57 and 58. Dewatering is furthered as the'embryonic web' 20e'is forwarded in sandwiched relation - bet'ween Fourdrinier wire'33 and.fabric 51 past suction boxes 52 and 53, and then over a portion of vacuum transfer box 54 after which the'embryonic web 20e is disposed and forwarded on abric 51 to an endless imprinting carrier fabric 59 at a second transfer station des~gnated 60. At the second transfer station 60, embryonic web' 20e ~s trans~erred.by the action of vacuum transfer box'61 from the'intermediate.'carrler fabric 51 to the'imprinting carrier fabric 59 which'is looped.paat/about suction box 62,.turn~ng roll 63, blow ' through predryer 64, impregnating means 6~, turning roll 66, pressure roll 67, turning roll 68, showers 69, suction box 7~-, and turning rolls 71 and 72~ At this time,rformation of the web' continues due'to the'differential fluid pressure , applied to the web to effect the'second transfer and fiber mobility enabled by a sufficientlr high water content ~preferably a fiber consistency of 30 percent or less), the . embryonic web'becomea' pattern densified with'denae ~ones of fibers juxtaposed the knucklea of the imprinting carrier fabric 59. After being tranaferred to ~he ~mprin~ing carrier fabric 59, the embryonic web i9 further dewatered by suction - box 62 and blow-through'predryer 64; then partially impregnated with binder material. 25 by pressure biased impregnating means 65; and then transferred to Yankee dryer 75 by the action o pressure roll 67 which is biased towards the Yankee dryer by biasing means 76. Transfer of the web to the Yankee dryer and adherence thereto is enabled by creping adhesive applied through'applicator 77. Finally, upon being fully dried on the Yankee dryer~ the transformation of . ~ .
~ .

~s~

embryonic web 20e to paper sheet 20 is completed as the final drying thereof is effected and, preferably, it is creped from the Yankee dryer by the action of doctor blade 78. Preferably, the paper sheet 20 is then calendered and reeled to control its caliper and enable its subsequent conversion from reels into paper products such as paper towels, and toilet and facial tissue paper. Also, in the event the binder material requires curing, such curing may be effected at least in part after the paper sheet has been removed from the papermaking machine.
Figure 6 is a plan view of the top, outwardly facing surface of an exemplary imprinting carrier fabric 59 which may be used on a papermaking machine such as papermaking machine 30, Figure 5, to practice the present invention.
Fabric 59 is a five-shed satin weave of polyester monofila-ments which were woven using a 1, 4, 2, 5, 3 warp pick sequence and wherein the filaments 90-1 through 90-5 which extend in the machine direction, MD, alternately pass over four and under one of the filaments 91-1 through 91-5 which extend in the cross machine direction, CD; and wherein the CD filaments alternately pass over one and under four MD filaments.
Fabric 59 has been stressed, heat set, and sanded to provide coplanar sets of long MD imprinting knuckles 92, and rela-tively short l-over CD imprinting knuckles 93. The outwardly facing surfaces of coplanar sets of knuckles 92 and 93 corporately define a top-surface-plane of fabric 59. Fabric 59 also has adjacent pairs of sub-top-surface filament crossovers designated 94 which, by virtue of the weave, stressing, and heat setting are recessed below the top-surface-plane of the fabric. Such a fabric is described more fully in the commonly assigned U.S. Patent No.

4,239,065 of Paul Dennis Trokhan, granted December 16, 1980. Also, such a fabric is particularly useful for making soft and absorbent imprinted paper having uncompressed portions circumscribed by picket-like lineaments of alternatiely spaced areas of compacted fibers and non-compacted fibers which compacted fiber areas or zones are - 13 - 1~55~7 precipitated by imprinting the top-surface-plane knuckles of the fabric into a relatively uncompacted, low density, high bulk paper sheet. This is more fully described in the commonly assigned U.S. Patent No. 4,191,609 of Paul Dennis Trokhan, issued March 4, 1980. While the 5-shed fabric 59, Figure 5, has been described above as exemplary with respect to the present invention it is not intended to thereby limit the present invention to any particular fabric weave, or knuckle geometry or disposition.
Impregnating means 65, Figure 5, comprises roto-gravure cylinder 81, backing roll 82, biasing means 83, and reservoir 85 which is adapted by means not shown to maintain a relatively constant predetermined level of liquid impregnating material 25 therein. This level insures that a downwardly facing arcuate portion of rotogravure cylinder 81 is immersed in the impregnating material. Doctor means, not shown, are provided for removing the excess impregnating material from the rotogravure cylinder as it rotates upwardly towards the traveling embryonic web. Synchronous drive means, not shown, may also be provided as needed to obviate deleterious drag on the embryonic web as it passes through the nip between rotogravure cylinder 81 and backing roll 82. While, as described, impregnating means 65 of papermaking machine 30 is a gravure type applicator, it is not intended to thereby limit the present invention to gravure applicators or impregnators. Rather, it is believed that other contacting type applicators such as, for instance, foam applicators may be used to practice the present invention.
Figure 7 is an enlarged scale, radially inwardly looking view of a fragmentary portion of an exemplary rotogra-vure cylinder 81 which has its cylindrical surface covered by a partially peeled back, opaque mask 96 which is apertured in the top-surface-plane knuckle pattern of imprinting carrier fabric 59, Figure 6. That is, apertures 92a and 93a in mask .'i .~

115S~7 96 are sized and dis?osed in the image of the top-surface-plane knuckle pattern of fabric 59, Figure 6. The entire gravure surface of rotogravure cylinder 81 is defined by a ~ full field pattern of truncated pyramidal cavities or reservoirs 100. In use, as an em~ryonic web 20e is carried through the nip of impregnating means 65 of papermaking machine 30, Figure 4, only the dense zones-of the web which are Juxtaposed top-suxface-plane knuckles 92 and 93 of fabric 59 are biased against the rotogra~ure cylinder 81.
This substantially limits the pattern of impregnation to the pattern of the high density zones ~uxtaposed the top-surface-plane knuckles 92 and 93 of fabric 59. Thus, the pattern of impregnation is determined by the patterned array of top-surface-plane knuckles of the imprinting carrier fabric rather than a pattern on the. rotogravure cylinder. Also, the p~ttern of impregnation of the web' is in registration with the pattern of dense ~ones; of the web.as illustrated in web''20, Figures 1 and 3. However, the area of the web'which . becomes impregnated may in fact be substantially larger than 20 the'sanded areas of knuc~Ies.92 and 93 because the filament~
of the woven fabric 59 gradually slope away from the sanded areas of the knuckle~ and thus cause web.portions contiguous thereto to be'impregnated along with the web port~ons ~mmediately ~uxtaposet the sanded areas of the knuckles.
- 25 Furthermore, it i8 believed that the absence of biasing of .' . the'unsupported span portions of the embryonic web substantially obviates transfer of binding material thereto from rotogravure cylinder 81. Moreover,' displacement of the unsupported span portions into the ~nterilamentary spaces of the imprinting fabric may be effected to virtually totally obviate their being impregnated by rotogravure cylinder Bl-Figures 8 through 12 are simllar to Figure 7 except thealternate embodiment rotograVure cylinders 81a through 81e of Figures 8 through 12, respectively, are provided with less-than-full-field-checkerboard type patterns of reservoirs 100 which reservoirs cover 75, 50, 50, 50, and 25 percent, respectively, of the working surfaces of cylinders 81a, 81b, 81c, 81d, and 81e. Thu~, s~ch les~-than-full-field patterned ~ : .

.. _ . . . ..

c. ! ~

115i5~7 rotogravure cyiinders will coact with a patterned imprinting fabric to apply impregnating material to only the surface portions of an embryonic web which are in registered relation with top-surface-plane knuckles and adjacent reservoir

5 portions of the rotograVure cylinder pattern. Such patterned cylinders are useful with respect to providing various degrees of web strength through binder impregnation while preserving various complementary- degrees of binter free surface areas. Thus, strength may be increased by ~mpregnating 10 larger percentages of web surface area. Furthermore, whereas the alternate embodiment, less-than-full-field, rotogravure cylinders 81a through'81e have relativel~ small checkerboard-type patterns with'respect to the knuckle pattern of fabric 59, Figure'6, less-than-full-field patterns (not shown) having 15 larger open (non-printing~non-~mpregnating) areas may be used to assure not impregnating a substantial proportion of the dense zonei as weIl as concurrently assuring that a substantial proportion of the dense'zones will be.impregnated.. This is useful w~en, for instance,' creping of the'finished web is 20 desired and the binder substantially vitiates the'intended function of a creping athesi~e'(e.g.: polyvinyl alcohol applied by spray applicators 77, Figure 5), the proportion of binder impregnated zones is maintained great enough to provide adequate web strength'while the proportion of 25 non-binder-~mpregnated zones is.made great enough to enable the'creping adhesive to securely affix those zones to the Yankee'tryer (creping cylinder) to control the web ant the .creping thereof in substantlally the manner disclosed.in the hereinbefore referenced Sanford-Sisson patent (u~s. Patent No.
3,3~1,746).
Figure 13 is a somewhat schematic side elevational view of a handsheet impregnating apparatus 106 which comprise~
rotatably mounted', rubber covered rolls 107 ant 108, a slanted feed plate 109, a horizontal feed plate 110, and a ~eceiving plate 111. Means not shown are provided to pressure 35 bias rolls 107 and 108 together, and to synchronously rotate rolls 107.and 108 in the directlons indicated by the arrows drawn thereon.

~ `

~550~7 Figure 14 is a fragmentary enlarged scale view of the nip portion of apparatus 106, Figure 13, which view shows fragmentary sections of rolls 107 and 108, a gravure plate 115, and a paper handsheet 116 disposed on the under side of an imprinting carrier fabric 117. Figure 15 is substantially identical to Figure 14 except the handsheet 116 in Figure 15 is self-supported; i.e., not disposed on an`imprinting carrier fabric.
!
In use, referring to handsheet impregnating apparatus ~, '10 106, Figures 13'~hrough 15, a gravure'plate 115 is placed on j 'plate 110 with its pattern side'up and with its cells filled wi'th binder material. Then, a handsheet 116 is placed on plate 109. Handsheet 116 may be associated with an imprinting carrier fabric 117 as indicated in Figure'14, or not so associated as indicated by the'absence of such'a fabric 117 from Figure 1~. Then, rolls 107 and 108 are biased together wi'th'a predetermined force'and rotated s~nchronously while t~e ~andsheet 116 and the gravure'plate 115 are simNltaneously moved 90 that their leading edges enter the nip between the' rolls. Thus, as the'handsheet and gravure'plate pass through ~he'nip, the'handsheet becomes impregnated. When the web is associated with'a fabric durinz impregnation as shown in ,~ Figure14, the pattern of web impregnation is the knuckle :! -pattern of the fabric when a full f~eld gravure plate is used. Therefore, when the handsheet has been pattern den~ified by formation on an imprinting carrier fabric so that the dense zones of the handsheet are ~uxtaposed the knuckles of the imprinting~carrier fabric, only the dense zones of the handsheet become impregnated by a full ield graw re pLate through the use of handsheet impregnating apparatus 106.

Briefly, referring back to Figure 5, an embryonic web 20e is preferabLy formed and forwarded without sub~ecting it to substantial mechanical'compaction until it reaches the impregnating means 65. By including a principal web-strength fiber constituent in the'furn~sh which constituent cQnsists of fibers having a predetermined average length relation with respect . - , . ...
.. _ ___ __. . ... . _ _ . _., _ ... _ .~ .. ., , _ , .. . . ..... . . .

' ' 1 ~5 5 0n7 to the knuckle pattern of the imprinting carrier fabric 59, ` and by controlling dewatering, a pattern densified embryonic web may be formed in which web relatively high fiber density zones are juxtaposed the outwardly facing knuckles of imprinting carrier fabric 59, and in which web the remaining portions which are unsupported and span the spaces between the knuckles have relatively low fiber density. Preferably, the unsupported spans.are also acted on by sufficient differential fluid pressure while the web'i~ at a sufficiently l~w fiber consistency to sufficiently displace the unsupported spans intc the'interfilamentary spaces between ~he knuckles ¦ of the imprinting carrier fabric.to obviate their being impregnated by impregnating means 65 although'it is not intended to thereby limit the present invention. The embryonic web''is pxeerabI~ predried to from about 30 to about 95 . percent fiber consistency ant more'preferably to from about 60 to about 90 percent fiber consistenc~ prior to being im~regnated. ~Lso, preferably the drying is suficiently asymmetrical to try the'unsupported portions of the web substantially more than the'dense portions. This may be effected, for instance,' by blow through predrying of the web . while'it i8 disposed on the'imprinting carrier fabric of -~
papermaking machine'30. Thi8 enhances the'Z-direction penetration of the binder material through the thicknes's of - 2S the web and lessens the propensity o~ the binder material to migrate laterally in the X-Y direc~ions into the low density porti.on~ of the web. Such X-Y migration into the low density por~ions of the web from the high density zones i8 further inhibited tue to their relative capillary st~uctures:
' 30 i.e.', normal~iy capillary flow is greater from low density to . . hi'gh density ~nes than from high density to low density zones. Moreo~er, with respect to latex type binder emulsions in particular, i~ is beii~ved that the.commencement.of X-Y
migration from relatively wet zones into dry areas acts to ¦ 35 dewater such emulsions and cause them to coagulate rather than migrate very far into the dry areas.
, - , , :, .

. ~
.

... . , . , . , ... _ _._ __._....... _, _ .. _ __ _ _ . . . .. .. ... ... .... .. . . .... .

~SSC~7 .,.-`
In addition to the impregnation of the high density zones which is effected as the web is carried on the imprinting carrier fabric 59 through the pressure biased impregnating means 65, Figure 5, the biasing also precipitates some compaction of and bonding within the high density zones of the web. Subsequently, as the high density zones of the web are again sub~ected to knuckle pressure~between pressure roll 67 and Yankee'dryer 75, the'penetration.of the binder is enhanced, and the degree of compaction and bonding within the high density ~ones i~ 'increased.

A number of handsheet examples as we~l as papermaking machine examples are described be~ow. Brie1y, the'handsheet examples evidence the benefits of impregnating only dense zones of a pattern densified paper sheet in accordance with the present invention; and the'papermaking machine examples evide'nce'the-benefit of sub~-ecting impregnated high density - zones to further mechanical pressur.e.after the impregnating, and the'benefits which may be derived from the'present in~ention through-'the use'of different impregnating materials.
. .
'HANDSHEE~ ~XAMPLE' I
A pattern densifi'ed, one'foot square'(about 30 cm square) handsheet having a basis weight of about 16.5 pounds per 3000 square feet (about 27 grams per. square meter) was ormed from a fibrous furnish on a fo.raminous polye~ter 25- fabric of the 5-shed satin weave'shown in Figure 6 and . having a 36-MDl32-CD filaments per inch (about 14-MD by 12~6-CD fiIaments per centimeter) mesh count. The'urnish comprised about 60 percent by fiber weight of Tongacel ~registered t~ademark of'Lo~isiana Pacific Corporat~-on) . 30 K 324N, a relatively low bond, long fiber, post bleach cold caustic extracted dissolving grade Worthern Softwood Sulfite which is available from Louisiana Pac~fic Corporation, and about 40 percent by fiber weight of relati~ely long softwood fibers which were obtained from The Buckeye Cellulose : 35 Corporation under the designation Grand Prairie Prime, a Northern Softwood Kraft. After formation and draining., the .... . . .. . ~ ... . . . , __ . ... _ _ ... .

sson7. ' handsheet was further dewatered by pulling the fabric with -the handsheet disposed thereon over a vacuum slot having 10 inches (about 25.4 centimeters) of mercury vacuum applied ~ thereto. The handsheet was then dried on a can type dryer while still disposed on the fabric and in its original relation thereto. The dried handsheet was then ~mpregnated in its zones ~uxtaposed the top-surface-plane knuckles of the fabric by passing the fabric/sheet c~mbination and a full-field gravuxe plate through'the handsheet impregnating apparatus 106 as indicated in the enlarged scale'Figure 14 - and as hereinbefore described. The latex binder comprised a 25 percent solids, self-crosslink~ng acrylic latex emulsion whi'ch was obtained from R~hm and Haas Company, Philatelphia, Pennsylvania, and which was designated TR-520. The'latex binder further comprised ammonium nitrate (NH4N03), a latent acid catalyst, in the amount of about 0.5 percent by weight of latex solids;"Pluronic L-92"of about 1.0 percent by weight of latex solids, which is a nonionic surfactant sold by BASF Wyandotte Corporation, Parsippany, New Jersey, and which was added to serve as a finishéd product wetting agent; ammonium hydroxide (NH40H) in sufficient ~mount to raise the pH of the binder solution to about 5.0; Lithium 'Acetate (CH3C021i) in the a~ount of 200 ppm Lithium based on the weight of latex solids to serve as a tracer to facilitate analysis of samples to ascertain their latex content; and an anio~ic ~ater soluble dye was added to allow visual lnspection of the impregnation patter~. The grawre'plate was etched to provide a full field o~ reservoirs which numbered abou~
2~,500 reservoirs per square lnch (about 3500 reservoirs per sqUare centimeter) and the corporate volume of the reservoirs Wa8 ~bout 1.2 microliters per square centimeter of etched area.

'HANDSHEET'E~AMPLE'2 Hantsheet Example 2 was a replicate of Handsheet Example 1 insofar a3 variables in ~he making thereof permitted.

* Trademark 0 .. . . _ . ..

1155(~-)7 'HAND'SHEE~ EXAMPLE' 3 Handsheet Example 3 was prepared like Handsheet Examples 1 and 2 except for Number 3 the etched, full field gravure pattern comprised about 40,000 reservoirs per square inch (about 6200 reservoirs per square centimeter), and the corporate volume of the reservoirs was about 2.2 microliters per square centimeter.

. 'HAND'SHEE~ EXAMPEE 4 . -:
Handsheet Example 4 was prepared like Handshe~t Example 1 except that after-it was dried on.its forming fabric it was removed therefrom, rotated 90 degrees with'respect ; thereto, and reassociated.therewith with'adhesive tape.
Thus, the pattern of the ~one'densified handsheet was pIaced out of registration with the'knuckle patte~n of the fabric `15 prior to impregnation 90 that comparative'data could be obtained with respect to out-of-registration impregnation-~Handsheet Example 4) versu~ in-registration im~regnation (Hand~heet Examples 1, 2 and 3) of pattern densified fibrous webs .
' ........................ '.. ' . ' ~NDSHEE~ EXAMPLE 5 I Handsheet Example'5 was prepared like Handsheet Example j 4 except, prior to impregnation, the densified structure of i the handshee~ was placed out of registration with the ' knuckle pattexn of the fabric by removlng the handsheet rom the'fabric and t~rning thè handsheet over prior to reassociating it with the fabric with adhesive tape.' Thls hantsheet provided fuxther out-of-reg~stxation-impregnation data which is tabulated along with the corresponding data from Handsheet Examples 1 through 4 in Table I.

' HAND'SHEET'EXAMPLE' 6 Whereas Handsheet Examples ~ through 5 were'pattern densified during their formation on relatively coarse 36 X 32 mesh fabrics o the 5-shed satin weave shown in Figure 6, Handsheet Example 6 was ~ormed with relatively uniform density on a relat~vely fine mesh fabric having llO'X 95, ~' :' ~
.

` 13L55~)7 . - 21 -.
MD X CD filaments per inch (about 43 X 37, MD X CD filaments per centimeter), and woven with a 4-shed satin weave using a 1, 2, 3, 4 warp pick sequence. But fox the different forming fabrics, Handsheet Example 6 was made and dried in the same manner and of the same furnish as Handsheet Example 1.
However, because the relatively fine mesh 4-shed satin weave j fabric described above is much smoother than the relatively coarse 5-shed fabric shown in Figure 6, and because the fibers of the furnish were very long with'respect to the knuckle-to-knuckIe span of the 110 X 95, 4-shed as compared . to the coarser 36 X 32, 5-shed fabric, the handsheet formed I . on the'4-shed was reIatively uniformly dense as compared to 1 ' the'pattern densified Handsheet Examples 1 through 5, inclusive.
But, it is not intended to thereby imply th~t pattern densified sheets cannot be formed on fine mesh fabrics such as the 4-shed satin weave des'cribed above. After being dried, Handfiheet Example 6 was removed from the 110 X 95 forming . fabric and taped onto a 36 X 32 mesh,' 5-shed fabric identical to thoQe.used for Handsheet Examples 1 through 5 prior to bein~ ~mpregnated by passing it through handsheet impregnating apparatus 106 in the manner indicated in Figure 14. The gravure plate and the latex binder composition were also the same'for Handsheet Example 6 as for Handsheet Examples 1, 2, 4 and 5. Thus, Handsheet Example 6 was a pattern impregnated sheet of relatively uniform density which yielded data which is also tabulated in Table 1 or conveniently comparing the pattern densified/pattern impregnated Handsheet Examples 1 through 3 embodying the pres~nt invention with the unio~m densitylp~ttern impregnated Handsheet Example 6.

. 30 Referring now to Table I, the Handsheet Examples 1 through 3 embodying the present invention clearly ~a~e superior (lower) bending modulus ti.e., greater flexibility) as compared to.the out-of-registration impregnated/pattern . 'densified Handsheet Examples 4 and 5, and as compared to the pattern impregnated/uniform density Handsheet Example 6.
..'.' ...

~155(~7 TABLE I
Binder Wet Total on Product, Total DryTotal Wetrenslle, Handsheet Percent of Area Tensile Tensile Percent of Bending 5ExampleWeight of Covered, Strength,Strength, Dry Total Modulus, Number Fibers_ Percentg/inch g/inch Tensile Kg/cm2 7 . 82 39 . 1 986 414 42. 0 31 . 9 ' 2 8.32 38.2 sos 355 39.2 21.3 3 10.56 51. 61379 598 43.4 31.9 .
¦ 10 4 9.17 65.41093 415 38.0 45.9 8.48 6~.3 948 399 42.1 43.6

6 9.68 58.41089 416 38.2 67.4 HAND~HEE~ EXAMPLE~''7'AND' 8 ~ Two additional Handsheet Examples embodying the present ¦ 15 invention were'prepared in the'same'manner and with the same furnish as Handsheet Examples 1 through 3 except the gra w re plates were engraved to provide'different levels of binder -addition. Pert~nent data from.these two examples are tabulated in Tabt'e II; in particulax, comparative dry strength and we~ strength'data which'evidences that embodiments of the present invention have'greater strength'derived from a . given amount of binder than the'non-pattern densified Handsheet Example 9 described next.

. HAND'SHEET EX~MPLE 9 . 25 This handsheet was of relatively uniform density and . ' was formed~ dewatered and dried substantially identlcally to .Handsheet Example 6 uqing the same furnish as for Handsheet Examples 1 through 8. Howe~er, whereas Handsheet Example 6.
was impregnated by a full-field gra w re plate while backed by a 36 X 32 5-shed fabric in the manner shown in Figure 14, Handsheet Example 9 was impregnated in the manner shown in Figure 15; that is, not backed'by a fabric. In this instance, the gravure plate 115 was prepared with a pattern identical in size and geometry to the top-surface-plane knuckles of a 36 X 32 5-shed fabric, Figure 6. The gravure pattern comprised abou~ 22,500 reservoirs per s~uare inch of reservoirs , .
_.. _. . _ ...... . . . __._ ._ _ . .

- 1~55(~)7 (about 3,500 reservoirs per square centimeter of reservoirs) and was derived from a 150 X 150 lines per inch (about 59 X
59 lines per centimeter) screen which was superimposed on a knuckle-pattern print made from the 36 X 32 5-shed fabric 59, Figure 6, to make a negative which was then used in producing an acid etched gravure plate. Therefore, the uniform density Handsheet Example 9 was pattern impregnated in the sa~e pattern as Handsheet Examples 7 and 8 embodying the present invention. However, whereas Handshe~t Examples

7 and 8 were pattern densified prior to their being impregnated in their dense ~onesj Handsheet ~xample 9 was of uniform density; i.e., having no dense zones.

'TAB~E'II
. W~t Total - Tensile, .Blnder' Total Dry Total ~et Percent , Percent o~ Tensile Tensile of Dry ~andsheet - Basis Weight Weight Strength~ Strength, Total Example lbs/3000 sq.ft. of Fibers g/ibch '~/inch Tens~le 7 16.2 . '4.64 . 703 ,258 '36.7 20 8~ ' 16.0 5.40 ' .834'317 38.0 9 15.4 5.02 540 175 31.6 . ,.
; Another benefit which ma~ be derived from the present invention is precipitated by the application of pressure to the.binder impregnated de~se zones as, referring to F~gure 25 5, the pattern densified embryonic web 20e ~backed by fabr~c . 59) passes through the pressure biased nip intermediate pressure roll 67 and Yankee dryer 75 prior to the inal . drying and creping of the web. The following example, . Example I0, illustrates this.
..........

Basically, a papermaking machine of the general configuration as papermaking machine 30, Figure 5, was run to produce two families of samples. during which run: the percent of latex solids in the binder emulsion in reservoir 35 85 was incremented fxom 10 to 25 and then to 40 pereent; the after predryer (APD) iber consistency was varied from about .. .. . _ . , . . _ ~ ._.. ... __ . ... _ _ . _ .... _ _ . .. ._ _ . ._ _. . . _ .. _ . : .. .

l~sson7 68 percent to about 91 percent; and samples were taken from adjacent the- doctor blade 7~ which samples had about zero crepe, and from intermediate roll 66 and pressure roll 67.
~ In the data tabulated in ~able IIIa and IIIb, the former samples are designated Pressed Samples, and the latter `
samples are designated Unpressed Samples; and pairs of samples are designated by pair numbers which pairs each comprise a Pressed Sample and an Unpressed Sample.
, . ......................... - .
TABEE Illa POST INPREGNATION PRESSING OF DENS~ ZONES
PRESSED S~MPLES VS. UNPRESSED SAMPLES
. Total Wet Ratio, T~sile Strength, Pressed To j 15Perce~t APDX OP Total Dry Unpressed Sample Sollds Piber. Tensile Strength (Ratlo of Pair In Latex Conaistency, - - Column 4 toNo. Binder Percent `PresSed UnPressed Column 5) 1 10 76.0~8.~ 28.3 .99 2 10 88.927.6 26.1 - 1.06 3 25 67.639.7 32~4 1.23 4 25- 88.740.2 27.9 1.44 67-.639.0 31`.4 1.24 6 40 90.931.4 21.5 1.46 .., -~ 25 - ~ABLE IIIb :~ EXAMPLE 10 POST IMPREaN~TION PRESSING OF DENSE ZONES
_ PRESSED.SAMPLES VS. UNPRESSED SAMPLES
Wet Tensile Strength, g/inch Pair Pressed - Unpressed - No. MD CD Total MD CD Total 3 115 80 195 99 63.162 . 6 - 43 54 97 56 41 97 _ _ ,,, _, ., . . , _ _, . . _ . . . _ , . . . . ... . . . ...... . ~ . . .

~s50n7 The s~amples of Example 10 were made on a papermaking machine of the general geome~ry of machine 30, Figure 5, using the 60 percent Tongacel/40 percent Grand Prairie Prime (low bond/kraft softwood fibers, respectively), long fiber furnish as used to make Handsheet ~xamples 1 through 9 descxibed above. This furnish was chosen to produce, if not impregnated in accordance with the present invention, a weak web with less than 150 grams per inch total tensile strength (the sum of t~e machine direction tensile strength plus the cross machine direction strength). A 0.12 percent fiber consistency pulp slurry of this furnish was distributed on a Fourdrinier wire 33 of a 4-shed satin weave having a 78 X
60, MD X CD filament mesh count per inch (about 31 by 24 filaments per centimeter). Dewatering was progressiveIy effected while the web was being forwaxded on the 78 X 60 Fourdrinier wire, and then on intermediate carrier wire 51 of the same mesh, weave, and material as the Fourdrinier wire to increase the fiber consistency of the web to about 22 percent prior to being transferred to the ~mpr~nt~ng carrier fabric 59 which was a 5-shed satin weave of the type shown in Figure 6 and having 31 X 25, MD ~ CD filaments per inch (about 12 X 10 filaments per centimeter). Further dewatering was precipitatet by vacuum transfer box 61 and the triple vacuum box 62 to provide a fiber consistency of about 32 percent. `The resu~t of vacuum transferring from the 78 X 60 intermediate carrier fabric 51 to the 31 X 25 imprinting carrier fabric 59 and the vacuum dewatering thereon caused the web to become pattern densified thereby completing the formation of the pattern densified web:
discrete spaced dense zones ~uxtaposed top-surface-plane knuckles of imprinting carrier fabric 59. and relatively low de~sity spans or portions between those knuckles. These conditions also caused the unsupported portions of the web to be displaced by the vacuum induced differential fluid (air) pressure into the interfilamentary voids of fabric 59.
The web was then predried by blow through predryer 64 to an APD fiber consistency in the range stated sbove: about 68 percent to about 91 percent. The web, still disposed on abric 59 then was forwarded thereon through a full-field ... ... . .

;55 pattern, pressure biased gravure impregnating means of the type described hereinbefore which caused the dense zones of the web to be pressed against the gra wre cylinder 81 and - thereby become impregnated; however, the low density span portions were not so impregnated by virtue of having been sufficiently displaced into the interfilamentary spaces of fabric 59 to substantially obviate their being impregnated by the impregnating means. Additionall~, binder impregnation of the low density ~pan portions was substantiaIly;obviated by not press~ng them against the rotogravure cylinder'81.
' Rotogravure cylinder 81 was engraved with a full-field pattern of'reservoirs (cells) number~ng about 3500 per ~quare'centimeter ant ha~ing a total volume of about 1.4 microliters per square centimeter.

The binder material used to impregnate the sample~ of Example'10 was the same'latex emu'lsion as for the hereinbefore described handsheets except: the'percent solids was incremented from 10 to 25 and then to 40 percent; and very law'levels of commercial deoamers"(Foammastes 160L"~and 20~Colloid 694~were'added to suppress foaming of the latex emulsion 25 in reservoir 85 as cylinder 81 rotated therethrough and the'excess latex was doctored therefrom. "Fozmmaster 160L'was obtained from Diamond Shamrock Co~poration, Cleveland, Ohi'o; and Colloid 694 was obtained from Colloids, Inc., Newark, New Jersey.
.
' Further with'respect'to Example 10, backing roll'82, Figure 5, was an 80 Shore A Durometer rubber covered roll;
'' and pressure roll 67 was an 85 Shore A ~urometer rubber -coveret roll. Roll 82 was biased`towards cylinder 81 with a .
orce of about 20 pounds per lineal inch (about 3.5 Xilograms per lineal centimeter); and pressure roll 67 was'biased towards Yankee cylinder 75 at about 440 pounds per lineal inch (about 78 kilograms per lineal cent~meter). The creping adhesive which was applie~ to Yankee dryer 75 via spray applicators 77 to enable creping wa~"Gel~atol 20-90"*~a*
polyvinyl alcohoilacetate manufactured by Monsanto Co., St.
- Louis, Mi~souri. After being creped from the Yankee dryer * Trademark ** Trademark ; *** Trademark 1~55~7 _ 27 -75 by doctor blade 78, the paper web from which the pressed samples were taken was reeled at the same speed as the Yankee; thus the samples exhi~ited virtually zero residual ~ crepe so that residual crepe would not be a substantial difference between the pressed samples and the unpressed ~samples which were obtained as follows. The unpressed ' samples of Example 10 were obtained by pressing a sheet width, adhesive coated, rotatabl~ mounted spool against the web' on fabric 59 running from roll 66 towards pressure roll 1~ 67 to accumulate sufficient web on the'spool to run samples i - thereof which were not adulterated by.the adhesive on the ¦ spool. The'samples were tested to obtain the TabIes IIIa.and IIIb data after being cured for about 5 minutes at about 300F.. (about 150C.~'). . ' '15 Generally, the data in Tables IIIa and IlIb indicate that post-impregnation pressing as described hereinbefore precipitates improved wet tensile strength;' and greater wet tensile'strength'for a 25 percent level of solids in a latex ' binder emulsion thaff for either a 10 percent-or 40 percent level of solids. Furthermore,' post-~mpregnation pressing aIso generally improves the ratio of total wet stxength to total dry strength of-the paper which is generally regarded as a performance parameter for paper towels and the like.
. _ . , . Three more papermaking experiments which'are designated 25~ and described below a~ Examples 11, 12, and 13 were conducted . to produce papers embodying the present invention: that is, pattern dens.ified papers having discrete, spaced, binder impregnated zones of h~gh fiber tenslty and otherwise being .
s~bstantially low bond, high bulk, unimpregnated structures.
Data from these examples are'tabulated in Table IV~
. ' ' ' ' .

. .

1~5501)7 TABLE IV

2-Ply Paper 2-Ply Paper 3-Layer Towel TowelToilet Tissue Basis Weight: pounds per 3000 34.2 39.2 16.8 sq.ft. (grams per square meter) (55-8) (63~9) (27.4) Caliper: mils t.~. ) 33.1 30.0 10.7 (0.83) tO.76) tO.27) Dry MD Tensile Strength: 465 924 196 . 10 grams~inch (græms/cent~meter~ (183) (364) (77) Dry CD Tensile Strength: 346 559 144 grams/inch (gra~s/centimeter) (136) (220) (57) Wet CD Tensile Strength: 157 176 Not græms~inch (grams/centimeter) (62) (69) Measured Wet/Dry CD T~n5ile S~rength 47X 31Z
I .. : , . .
Wet Tear Strength: grams 56.0 53.0Not Measured Stretch KD l9X 35X 23 Stretch CD llZ 9% 7X
Softness: .Sub~ective Panel Score Unit~, Example Versu~
-Contemporary Paper Product Of Comparable Ba~is Weight ~1.7 +1.0 +1.7 . Spill Wipe-Up:
3 Sub~ective Panel Score Units, :~ 25 Example ~ersus a Contemporary Paper Product of Ccmparable -Basi~ Weigbt -0.4 ~0.9Not Mea~uret Binder Content, Estimated As . Percent Of Fiber We~ght 62 n 2.4X
30 Binder: Type Latex Emulsion Polymeric Latex Emulsion Solution . Concentration 40Z Solids lOX Solu~ion 5Z Solids .. . ., .. .. ... , ,,, , _,,, , . ,, ,, _ _ ...... .. . _ .,, _ ._ ._. . . .. -- --.. _ _ . . . . .

55~f)7 Briefly, Exa~ples 11 and 12 were made using low bond Tongacel, described hereinbefore, in the furnishes to provide low bond webs, and the process conditions were so çontrolled that the webs were pattern densified when fully formed, and then impregnated with binder material in their dense ~ones to enhance both their wet and dry strengths: a latex emulsion binder for Example 11 and a polymeric solution type binder I for Example 12.

¦ ~Iore specifically, Example 11 was ma~e from the same 60% Tongacel/40% Northern Softwood Kraft and in thè same`
I manner as Example 10 except for a reIatively constant APD
'i fiber consistency of 78 percent; and except for the'latex binder having 40 percent solids and containing no lithium tracer or dye.' After the'paper web was creped and doctored rom the'Yankee dryer, Example-'ll was calendered by a rubberlsteel calender roll pair at about 58 pounds per square'inch (about 400 kPa) and reeled at a speed of 75 percent of the Yankee to provide a relatively high degree of ' residual crepe. The'reels of pap'er were then combined into 2-ply paper towels with the non-~ankee-contactin~ sides of both plies in face-to-face reIation, and embossed and athesively secured together as taught by U.S. Patent ~o.
3 3,414,4S9 which issued December 3, 1968 to E. R. Wells, and shown in sectional-view Figure 6 thereof. The combined 25 product was cured at 350F. for about 3'seco~ds, reeled, and then tested. The data are tabulated on Table IV. These paper towels exhibited ~igh strength and an extràordinary ratio of wet/dry CD tensile strength as compared to a variety of contemporary paper towels yet scored substantially higher 30 in subJectively percei~ed softness. Also, the data evidences thst the converting process removed a substantial portion of the residual crepe'in the paper.
. .. .
Example 12 was also made on a papermaking machine of the same'general geometry as machine 30, Figure 5, except, a three'chamber divided headbox (not shown) was used to deliver two types of flber slurries onto the Fourdrinier wire 33 in superposed relation. The first-down slurry ~uxtaposed the . , ., __ _ . , . ~ _ .. ,, .. . _ _. _ . _ . . . _ . . . . ..... ., _ . . ..

~5S0~7 Fourdrinier wire was identical to the low bonding pulp slurry o~'Tongace~'/Northern Softwood Kraft which was used to make Examples 10 and 11, and was issued from the bottom chamber of the headbox at a fiber consistency of about 0.20 percent. Northern Softwood Kraft slurries were simultaneously issued from both the center and top headbox chambers at a fiber consistency of about 0.12 percent. The Fourdrinier wire 33, and intermediate carrier fabric 51 were the same 78 X 60 mesh and wea~e,' respectlvely, as used for Examples 10 and 11. However, the imprinting carrier fabric 59 was the same 36 X 32, 5-shed mesh'and weave as used for Handsheet Example 1. Fiber consistency was 13 percent prior to transfer to fabric 59; 29 percent before p~edryer (BPD); and about 96 percent APD.

The binder used for Example 12 was a 10 percent solution of'Parez 63I NC'*a papermaking wet strength resin sold by Amer'ica~ Cyanamid Company, Wayne, ~ew Jersey. Thls is beIieved to be a reaction product of glyoxal wi'th a copolymer of dialkyl dimethyl ammonium chloride and acrylamide.

The rotograVure cylinder used for Example'12 was the same as for Examples 10 and 11; and the web was finished, creped, calendered, reeled, converted to 2-ply paper towels, and tested to the'same degree and in the same manner as Example ll except both plies were oriented to place their low bond layers on the outside of the structure. The re~ulting data are tabulated in Table I~.

Example 13 was formed as a 3-layer structure'using the 3-compartment headbox described above and in the same general manner in the same papermaking machine as Example 12. The three'layers consisted o Champion Eucalyptus on the top and bottom and Grsnd Prairie Prime .~orthern Softwood Kraft in the middle. The Champion ~ucalyptus was obtained rom Champ~on International Corporation, Stamford, Connecticut.
All pulps were at 0.13 percent consistency when distributed at three equal basis weight3 to produce a web on the machine of 17 7 pounds per 3000 square feet ~about 28.9 grams per 8quare meter) bagis weight. The kraft layer was made from * Trademark .

.. . . .. . .. ~ .,, ~ . . . .

low bonding pulp furnish whic~ had Quaker 200~*(a stearyl imidazoline made by Quaker Chemical Company, Consh~hocken, Pennsylvania) added at a level of about 0.25 weight percent of the kraft. The web was initially formed on the same 78 X
60 Fourdrinier wire used for Exam~les 10, 11, and 12, and subsequently transferred and dewatered as generally described with respect to those Examples. The imprinting carrier fabric wa~ a 3-shed semi-twill having a mesh c~unt of 31 X
25, MD X CD filaments/inch, and was treated to provide 10. ~mprinting knuckles as described in U.S. Patent No. 3,905,863 which issued September 16, 1975 to P. G. Ayers. The net result of vacuum transferring from a 78 X 60 intermediate fabric to a 31 X 25 imprinting carrier fabric and subsequent dewatering was to produce a web'on the 31 X 25 mesh imprinting carrier fabric of non-uniform density having l~w density portions ~uxtaposed the voids in the fabric, and high density zones iuxtaposed the fabric knuck$es.

The latex binder used was"Airflex 402'which was obtained from Air Products And Chemicals Inc., Allentown, Pennsylvania;
a dry strength vinyl-acetate ethylene emulsion. This was ad~usted to have'a 5Z leveI of sol~ds, and applied by the same rotogravure'cylinder of Example 10. The impregnated we~,' still tisposed on and in register with the 31 X 25 imprinting carrier fabric, was then pressed at about 440 pli ~about 78 kilogramæ per lineal centimeter) against the' Yankee'dryer, using'a rubber covered pressure roll with a Shore A Durometer hardness of 85 loaded against the dryer to impr~nt the ~nuckle pattern of the fabric into the web and thereby compaet the dense zones thereof. Gelvatol 20-90 polyvinyl alcohol/acetate manufactured by ~onsanto was applied to the Yankee dryer upstream from the pressure roll to adhere the web to the Yankee and allow creping at the doctor blade after the web was dried. The web was then run through a rubber roll/steel roll papermaking calendering nip at a light load and wound up on a reel at 82% of the Yankee speed. The reels of paper thus obtained were rewound and slit into standard toilet tissue rolls and tested. The test da.a are tabulated in Table IV.

* Trademark ** Trademark . . _ . . . _ , . . .

r 1~5SO~)7 While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, it is intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

~ .................. - __ . ., . __ __ ... _ . ..... . .

Claims (28)

Claims

1. A pattern densified fibrous web comprising a relatively high bulk field having a relatively low fiber density, and a patterned array of spaced discrete zones of relatively high fiber density integrated with said relatively high bulkfield, said high bulk field comprising a multiplicity of arched spans which corporately coact with said high density zones to provide said web with a vaulted character, and at least a substantial proportion of said high density zones being at least partially impregnated with inter-fiber binder material through the full thickness of said web, and said high bulk field being sub-stantially devoid of said binder material.

2. The pattern densified fibrous web of Claim 1 wherein said high density zones have a corporate surface area which constitutes from about 10 to about 50 percent of the total surface area of said web, and wherein the portions of said zones which are impregnated with said binder material underlie from about 25 to about 75 percent of the corporate surface area of said zones.

3. The pattern densified fibrous web of Claim 1 wherein said high density zones have a corporate surface area which constitutes from about 20 to about 40 percent of the total surface area of said web, and wherein the portions of said zones which are impregnated with said binder material underlie from about 25 to about 75 percent of the corporate surface area of said zones.

4. The e pattern densified fibrous web of Claim 2 or 3 wherein the portions of said zones which are impregnated with said binding material underlie about 50 percent of the corporate surface area of said zones.

5. The pattern densified fibrous web of Claim 1, 2, or 3 comprising a prin-cipal web-strength fiber constituent comprising fibers of sufficient average length with respect to the spacing of impregnated high density zones that a substantial fraction of said fibers will have spaced portions thereof disposed in adjacent impregnated high density zones and in overlapping bonded relation with portions of other fibers so that said fibers constitute a strength-skeletal-network of said web.

6. The pattern densified fibrous web of Claim 1, 2, or 3 comprising a prin-cipal web-strength fiber constituent wherein the fibers constituting said principal fiber constituent are relatively long papermaking fibers having average lengths of about 2.0 mm or more.

7. The pattern densified fibrous web of Claim 1, 2, or 3 com-prising a principal web-strength fiber constituent wherein the fibers consituting said principal fiber constituent are papermaking fibers and said web further comprises means for providing a relatively low degree of interfiber hydrogen bonding.

8. The pattern densified fibrous web of Claim 1, 2, or 3 com-prising a principal web-strength fiber constituent wherein the fibers constituting said principal fiber constituent are papermaking fibers and said web further comprises sufficient fiber-debonding material which is so disposed to obviate a high degree of interfiber hydrogen bonding intermediate paper-making fibers.

9. The pattern densified fibrous web of Claim 1, 2, or 3 com-prising a principal web-strength fiber constituent wherein the fibers consituting said principal fiber constituent are paper-making fibers and comprise papermaking fibers having a relatively low inherent interfiber hydrogen bonding propensity.

10. A method of making a pattern densified, partially impregnated fibrous web comprising a multiplicity of discrete zones of relatively high fiber density in which web at least a substantial proportion of said zones are at least partially impregnated with a non-fibrous impregnating material, said method comprising the steps of forming a fibours, pattern densified embryonic web having a multiplicity of discrete zones of relatively high fiber density which zones are disposed in a predetermined patterned array, supporting said embryonic web on an array of spaced supports so that each of a predetermined sub-array of said zones is juxtaposed one of a predetermined sub-array of said supports, and at least partially impregnating at least a substantial porportion of the supported predetermined sub-array of said zones with an impregnating material by biasing said predetermined sub-array of said supports towards a contacting type impregnating means with said sub-array of said zones disposed between said sub-array of said supports and said impregnating means.

11. The method of Claim 10 wherein said forming step comprises depositing an aqueous fibrous slurry onto a forming member and removing sufficient water therefrom to effect formation of an embryonic fibrous web, and said method further comprises the step of completing the drying of said embryonic web after said impregnating.

12. The method of Claim 10 or 11 wherein said supports are integrated into a loop of an imprinting carrier fabric having outwardly facing knuckles which knucles are designated said supports, said fabrics having meshes of from about 4-MD/4-CD to about 24-MD/24-CD filaments per centimeter.

13. The method of Claim 10 or 11 wherein said supports are integrated into a loop of an imprinting carrier fabric having outwardly facing knuckles which knuckles are designated said supports, said fabrics having meshes of from about 8-MD/8-CD
to about 20-MD/20-CD filaments per centimeter.

14. The method of Claim 10 or 11 wherein said web comprises a principal web-strength fiber constituent of fibers of sufficient average length with respect to the spacing of said supports constituting said predetermined sub-array of said supports that after said web is formed a substantial fraction of said fibers will have spaced portions thereof disposed on adjacent supports of said sub-array of said supports and in overlapping relation with portions of other fibers whereby said fibers constitute a strength-skeletal-network of said web with said overlapping portions of said fibers bonded together.

15. The method of Claim 10 or 11 wherein said impregnating material comprises a binder material.

16. The method of Claim 11 wherein said impregnating material comprises binder material and said aqueous fibrous slurry comprises a fibrous furnish of sufficiently low inherent interfiber bonding propensity that said embryonic fibrous web would have insufficient integral structural integrity to be self supporting while being impregnated with said binder material.

17. The method of Claim 11 further comprising the step of drying of said embryonic web in the absence of substantial mechanical compression to an average fiber consistency of from about 30 to about 95 percent prior to said impregnating.

18. The method of Claim 17 wherein said drying is conducted until said embryonic web has an average fiber consistency of from about 60 to about 90 percent prior to said impregnating.

19. The method of Claim 17 wherein said drying is effected in such a manner that the unsupported spans of said embryonic web are dried substantially more than the supported zones of said embryonic web.

20. The method of Claim 19 wherein said drying is effected by blow through drying means while said web is supported on said supports.

21. The method of Claim 10, 11 or 17, further comprising the step of sufficiently deflecting the spans of said embryonic web disposed intermediate said spaced supports into the spaces disposed intermediate said supports to substantially obviate impregnating said spans when said sub-array of said supports is biased towards said impregnating means.

22. The method of Claim 10, 11 or 17 further comprising the step of sufficiently deflecting the spans of said embryonic web disposed intermediate said supports into the spaces dis-posed intermediate said supports to substantially obviate impregnating said spans when said sub-array of said supports is biased towards said impregnating means wherein said de-flecting is effected by applying a differential fluid pressure across said supported web.

23. The method of Claim 10, 11 or 17 further comprising the step of subjecting said supported zones to substantial mechanical compression after said impregnating has been effected.

24. The method of Claim 10, 11 or 17 further comprising the step of subjecting said supported zones substantial mechanical compression after said impregnating has been effected and further comprising the step of sufficiently deflecting the spans of said embryonic web disposed intermediate said spaced supports into the spaces disposed intermediate said supports to substantially obviate impregnating said spans when said sub-array of said supports is biased towards said impregnating means.

25. The method of Claim 10, 11 or 17 wherein said pre-determined sub-array of said supports coacts with an impreg-nation pattern of said impregnating means so that said impregnating material is applied to only the portions of said zones disposed intermediate registered areas of said predetermined sub-array of said supports and said impregnating pattern during said impregnating.

26. The method of Claim 10, 11 or 17 wherein said predetermined sub-array of said supports coacts with an impregnation pattern of said impregnating means so that said impregnating material is applied to only the portions of said zones disposed inter-mediate registered areas of said predetermined sub-array of said supports and said impregnating pattern during said impregnating which further comprises the step of sufficiently deflecting the spans of said embryonic web disposed inter-mediate said spaced supports into the spaces disposed intermediate said supports to substantially obviate impregnating said spans when said sub-array of said supports is biased towards said impregnating means.

27. The method of Claim 10, 11 or 17 wherein said predeter-mined sub-array of said supports coacts with an impregnation pattern of said impregnating means so that said impregnating material is applied to only the portions of said zones disposed intermediate registered areas of said predetermined sub-array of said supports and said impregnating pattern during said impregnating which comprises the step of subjecting said supported zones to substantial mechanical compression after said impregnating has been effected.

28. The method of Claim 10 ,11 or 17 wherein said predetermined sub-array of said supports coacts with an impregnation pattern of said impregnating means so that said impregnating material is applied to only the portions of saidzones disposed intermediate registered areas of said predetermined sub-array of said supports and said impregnating pattern during said impregnating which comprises the step of subjecting said supported zones to substantial mechanical compression after said impregnating has been effected which further comprises the step of sufficiently deflecting the spans of said embryonic web disposed intermediate said spaced supports into the spaces disposed intermediate said supports to substantially obviates impregnating said spans when said sub-array of said supports is biased towards said impregnating means.