CA1211971A - Extensible multi-ply tissue paper product - Google Patents

Abstract

EXTENSIBLE MULTI-PLY
TISSUE PAPER PRODUCT

Paul D. Trokhan ABSTRACT
An extensible multi-ply tissue paper product having high tensile energy absorption (TEA); high liquid absorbency; and, preferably, high tensile strength efficiency. The product comprises plies which are preferably embossed and discontinuously adhered together. The product has high tensile energy ab-sorption by virtue of having substantial extensibility in the machine direction which, preferably, results from its constituent plies having substantial MD ex-tensibility induced by having undergone wet and/or dry foreshortening during their manufacture. The product has synergistically high liquid absorbency by virtue of at least two plies of the product having sufficiently different stress/strain properties that one ply will sufficiently constrain unadhered portions of the other ply from being elongated in the plane of the paper when wetted that such unadhered portions of the constrained ply will pucker in the Z-direction as its foreshorten-ing-induced internal stresses are relieved. Prefer-ably, the constraining ply is high bulk, wet-micro-contracted tissue paper, and the other ply is dry-foreshortened tissue paper, e.g., dry-creped tissue paper. Also, the plies of preferred embodiments preferably have nominally equal MD extensibilities at rupture. Such preferred products have high tensile strength efficiency which is manifested by their having monomodal stress/strain characters. Embodiments of the invention such as two and three ply paper towels are especially useful for spill wipe-up applications.

Description

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EXTENSIBLE MULTI-PLY
TISSUE PAPER PRODUCT

Paul D. Trokhan ', DESCRIPTION
5 Technical Field This invention pertains to highly absorbent paper products: particularly sot, high bulk tissue paper products comprising two or more highly extensible plies of tissue paper having substantially different stress/strain p~operties:
. preerably at least through the lowest one-third of the range of MD extensibility of the product.

ross Rererenc~ 5~ Relate~ a~plicatlon Re~erence i5 made to a concurrently fil.ed Canadian patent application No~ 423,570 entitled "We~-Microcontracted Paper and Method of Making Such Papern.

Background ~rt U. S. Paten~ ~o. 3, 9~3, 638 which issued to Clifford B. Kemp on April 27, 1976 discloses a ~ Multi-Ply Absorbent Wiping Product Having Relatively Inextensible Center Ply Bonded To Highly Ex~ensible Outer Plies, and concomitant methods. Such a produ~t is stated to have supe~ior caliper and bulk impression when wet due to the fact that the unadhered area5 of the extensible oute~ plies ~ expand in t~e Z-direction (i.e., out of the plane ; ~ of the paper) when the stXucture beco~es wetted.
That is, in such a product ~herein the extensible outer plies are creped tissue papèr, wetting causes crepe induced stresses to be relieved.
Were the outer plies not constraîned by the rela-tively inextensible c nter ply they would become , ~' .

.
elongated in ~he plane of the paper when wetted.
However, being so constrained by a relatively inex-tensible center ply, the extensible outer plies expand outwardly (i.e., pucker in the Z-direction of the product) when the product is we~ted. Such paper has, however, low tensile energy absorption relative to embodiments of the present invention, all other things being equal, and does not have a monomodal stress/strain character as do preferred embodiments of ~he present invention as is discussed in grea~er detail herein-a~ter~

U.S. Patent 3,615,976 which issued to Dan D.
Endre.s et al:on October 26, 1971~discloses a Method of ; Pr~d~cing~ a~High B~lk~Macr~crepe:Product which, during ~ -15~ . its~ànufacture,. is~dampened~to effect puckering:of cr.eped wadding~to:preipitate:macrocrepe and~then dried~
to-preserve the~ma~rocrepe~ The creped wadding is~
secu~ed;by:adhesive in well spacéd zones to a drawn.
synthetic ~iber web which is substantially unaffected 2a: ~y the dampening.~

U.S. Patent 3,650~882 which issued to ~ordon D.
Thomas on March 21, 1972 discloses a Multi-Ply Paper Towel ~aving an elastically extensible inner ply of creped tissue disposed between less extensible, em-25 bossed outer plies. ~ ~ ~

U.S. Patent No. 4,10~,017 which issued to Thomas ::-Joseph Flautt, Jr. on July 11, 1978 discloses a Multi-Ply Tissue Product wherein, for example, plies of dissimilar creping characteristics are juxtaposed with less resultant caliper loss than normally precipitated by juxtaposing similarly creped plies.

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U.S. Patent No. 3,544,420 which issued to James A.
Murphy et al on December 1, 1970 discloses a Creped Tissue Product comprising bias oriented plies. The produc~ is s~ated to be extensible in both the longi-tudinal and transverse directions and is said to haveunusually good strength and resistan~e to bursting, particularly in the transverse direction albeit, preferably, the plies are identically creped.

U.SO Patent 4,072,557 which issued to Chrlstian Schiel on February 7, 1978 discloses a Method And ~pparatus For Shrinking A Traveling Web Of Fibrous Material which entails a differential velocity transfer of a paper web in:the wet~end of a papermaking machine -to effe~: shrinking (i.e:., wet--foreshortening of the:
15~ we~. Wet~-Loreshortened paper is. also disclosed in British Patent No. 1:,212:,473:which was published : :November 18~ lg70 and in Ganadia~ Patent-No.~79,436 ~:
which-issued-August 31, 1971; and both of whIch patents ; wPre~derived rrom Finnish Patent Application No~ 561/68 which has a priority date of March 1, 1968.
.. . . .. . . . .. . .. .. ... ....
As compared to the background art, the present invention provides a highly absorbent multi-ply tissue product wherein extensible plies having substantial individual tensile strengths but sufficiently different stress/strain p:roperties or stress/strain charaçters to synergistically interac~to effect high wet bulk and~liquid absorbency; and high tensile energy absorption. Preferably, the plies have sufficiently matched elongation properties that their tensile strengths are additive throughout the stress/strain domain of the product which product is accordingly -~L2~

i characterized by a monomodal stress/strain property.
A monomodal stress/strain property for such a multi-ply tissue paper product is hereby de~ined as a stress/strain curve having a single peak whereat all o~ the plies rupture vi~tually simul-taneously as co~pared to a bi~odal. or multi-modal stress!strain property for two-ply or multi-ply p~oducts, respectively, which results from i~
dividual plies ruptu~ing at di~ferent strai~
values.

Di'sc'losure O'f' The In~'en't'i'on In accordance with one aspect of the invention, an ex~enslble ~ult:i-ply product~i5 provi:ded which c omprises: two extensible plies~ha~ing at.least~ten 15 ~ perc.ent:extens.ibility:in:a~prlmary:~dlr:ection and~
sufficiently~di~fe~en~,~st,res~s~/strai~ prope~rties preferab:ly~throug~::the lowest one~third of' range:
of extensibility of the~;p~oduct in the prima~y direction -- that unadhered por~ions of one:ply will ~ pucker in ~he Z:-direction when t~e product is ' wetted; and which plies prefe~ably have subst2ntiaIly equal elon~ations at rupture. Such unadhered por~ions which are free to pucke~'~'are preferably provided by discontinuously bonding the plies ~
together. The pr~a~y direction is preferably the machine direction, and the ~D elongation at rup-ture of one ply~ is: preferably from abouc eighty to about one-hundred-twenty percent (80-120O of the other pIy; and, more preferably, ~ro~ about ninety to about one-hundred-ten percent (90-110%) of the other ply; ~ost pre~erably when wet. Each ply has substantial MD extensibility by virtue, preferably, of being ~D ~oreshortened after being wet laid.
Preferably, each ply is so ~oreshorte~ed rom 3.~ 7~

about ten to about forty percent; and more preferably from about fifteen to about thirty percent. Prefer-ably, at least one of the plies ~las its MD extensi-bility imparted by virtue of being MD foreshortened in the wet end of a papermaking machine without substan-tial compaction while the iber consistency immediately upstream from the point of foreshortening is in the range of from about ten to thirty percent, and more preferably from about ten to twenty percent, and most preferably from about ten to fifteen percent. Also, pre~erably 7 another ply has its MD extensibility and internal stresses imparted by virtue of being MD dry-foreshortened: for example, by being dry-creped.

Br~ie~;~Descriptions O;f_The Drawings While~the~specification~c~oncludes~with~ claims '~
particularl~-pointi~g~out an~distinctly c~laiming~
the;subject matter regarded as~ f~orming~the~pr~esent invention~ it is believed~ e lnvention will be better understood from the ~oLlowing description 20 ~taken in conjunction with the accompanying drawings in which:

Figure 1 is a somewha~ schema~ic, enlar~ed : scale, plan view of a partially peeled apart ;
fragmentary portion of an illustrative two-ply tissu~ pàper product embodiment of the present invention. ~ ~
:
Figure 2~is a somewhat schematic, fragmentary sectional view taken along line 2-2 of Figure 1.
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Figure 3 is a view of the illustrative product shown in Figure 2 after the product has been wetted.

Figure 4 is a somewhat schematic, enlarged scale, fragmentary sectional view of an illus-: trative three-pIy tissue paper product embodiment of the present invention.

Figure 5 is a view of the illustrative product shown~in Figure 4 after the product has been 10 :wetted.

Figures 6~ and,t are, some~hat~::schematic,~
enlarged~scale plane views~of`partia;lly~peeled~
ap:art~fragmen~:ta~:portions~:o~two-p;ly tissue-~paper' ` embo~diment;s~o~:the~ ~p~es~ent ~m venti;on.~:whi.c~ have 15~ ~ bimodal stress~/str:a~n.properties., : Figures 8 and 9 are graphs of wet and dry stress/strain:~data, respecti~ely, derived from a two-ply tissue paper product embodi~ent of the present invention as shcwn in Figure lr and from 20 ' sample~:of the tw~ types of paper f~om which the product was converted. ~ ~
:
Figures~10 and ll are graphs of wet stressl- :
:strain datà o~ the two two-ply tissue paper ; : products shown in Figures 6 and 7, respectively, : 25 and from samples of the two types of paper from which each of those bimodal products was con~
; verted.

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: Detailed Description Of The Invention Figure 1 is a plan view of a fragmentary portion of a two-ply tissue paper product 20 which is an exemplary embodiment of the present in-vention. Product 20 comprises a Eirst ply 2]. anda second ply 22 which plies are adhered together at only the spaced discrete areas designated adhered regions 23; and the remaining portions o~
each ply are not adhered to the other ply.

Basically, referring to the exemplary two~ply product 20, Figure 1, plies 21 and 22 are so made that they each have greater ~han ten percent (10%) ~ MD extensibility;.ply 22 is made to have a sub~
: ~ : stantially, higher; st~re'~slstra,in~pro~erty~;or 'curve~' , ".' '`
~ 15. than ply 21 through:~the Iowest.one-third~:o~ the: ~ :
: : : r~ange of MD elongation of product:20; and pl~les 21 and;i:22.are~preferably~made to:have~subst~antiaIly '~
equal strain val~es at:~upture. The differencas betw en their stress/strain properties precipitates : 20 puckering of unadhered portions of ply 21 when the : product is wetted; and the puckering precipitates high wet bulk and liquid absorbency for the product.
Indeed, such puckering is best pre~ipi~ated by saturating a flat sample of pro~uet 20 with water while it is lying on a flat surface and without applying any tensile stress to ~he sample or inducing any ~D strain in the sample. Accordingly, the pertinent portions of the stresslstrain curves o~ plies 21 and 22 are the initial, low stress/strain portions. In most s~ch two-ply products embodying the present invention, however, the stress/strain (i.e., the constrainer ply) curve o~ ply 22 will be substantially higher than the stress/strain ~2~

curve of ~ly 21 (i.e., the extender or puckering ply) through the lowes~ one-third of the principal portion of the s~ress/strain curve o the product which extends from the zero stress level (i~e,, the X-axis intercept) to the level of stress at which a first ply of the product ruptures. For this reason, such embodiments of the invention may be charac~erized by these elevational relationships among the stress/strain curves of the plies and the produc~ although it is not intended to thereby limit the present invention to products having such stress/strain relationships over the above de-scribed lowest one-third of the respective principal s~ress/strain ranges of-the products, Go~tin~ing ~lth;the brief7~d~scr.iption of,the 15~invention~,~product 20, Flgure L,~ has high~tensiLe ' ~ener~y absor~ption as a,res~lt of both~plies having~
greater than~en percent (10%)~extensibility; and the~
substantially equal strain values at rupture cause the prefer~ed product to be strength efficient as is mani-fest by a monomodal stress~/strain character. That is,the strengths of the plies 21 and 22 of the preferred product 20 are additive-throughout virtually their entire strain domains as opposed, for example, to ply strengths only being additive until one-ply breaks in a two-ply product comprising u~matched rupture-~strain plies having substantial indi~idual M~ tensile strengths~as is mani~est by such products having bimodal stress/strain characters. Thereore, all other things being equal, a monomodal stress/strain multi-ply 30 ~ tissue product~will have a higher breaking streng~h than a multi-modal stress/strain product comprising '71 substantially identical plies but for their elongation at rupture values. Indeed, i~ is believed that con-sumers perceive a product failure when they perceive the breaking o~ one ply so, all other things being equal, a bimodal stress/strain product is perceived to not be as good insofar as product strength is concerned as a monomodal stress/strain product comprising plies having substantial individual tensile strengths.
; Kowever, bimodal products having high tensile energy absorption derived from all of its constituent plies having substantial elongation are preceived by con-sumers to have better strength than similar products having lower tensile energy absorption. Parentheti-.~ , cal~ly, i~ a product wherei~ one pLy has~reIatively ~ -trivial MD tensile~streng~th9 the product could have a monomodal;~stress/strain character albeit comprising plies~hav~ing;~unma*ched r upture-straln~valueB~

By way of background, the str~ss/strain data~ and ; resulting stress/strain curves presented in Figures 8 through 11, inclusive, and as used h rein were obtained by testing samples havin~ gauge lengths of four inches (about 10 cm) and~which were one inch (2.54 cm.) wide by applying and recording tensile force in the machine-direction (MD) of t~e samples in an apparatus which stretched the samples at a rate o~
about ~our inches per minute (abou~ 10 cm. per minu~e~.
Thus, whereas stress per se is force per unit of ' .

'7il cross-sectional area, the graphed stress data are ~ presented in grams force tensile strength per unit of ; sample width. Also these stress/strain graphs were derived from testing several replicate samples --generally four -- and averaging the data therefrom.

Foreshortening as used herein is defined as reducing the lPngth of a web in the macroscopic sense by proportionally reducing the length o~ each minute incremental length portion of the web. For example, a web is said to be wet-foreshortened in the machine direction in a papermaking machine when the web is trans~erred a~ a relatively low iber consistency from ! ~ ~ a carrler or fonming wire ~traveling~at velocity Vl to a slower mov~ing tran~sfer fabric traveling at~a velocity V2; and-the~degree of;wet-foreshortening is defined as (U~-V ~/V~ expressed as~a~percentage~. Similarly, a web l ~ 2 1 ~ ~ -is~said to;~e dr~y~-fores~ortened in the machine di-rection when it is dry-creped or crinkled or the like to~effect reducing lts length in the machine dlrection~.
For exampLe, a web may be dry-foreshor~ ned by dry-creping it from a creping cylinder having a peripheral velocity of V2 wiith a crepingldoctor blade, and reeling the paper at a velocity V4 which is slower than V2.
Nominally, dry-creping is ef~ected at a web ~iber consistency of about eighty-five percen~ or more; and generally is e~fected at web consistencies of ninety-i~e percent or more. The degree of dry-foreshortening/-dry-creping is then defined as (V2-V4)/V2 expressed as a percentage. Moreover, in papermaking machines having 30` suitable geometries and speed control equipment, a web can be both wet-foreshortened and dry-foreshortened (e.g., dry-creped) in which event the total degree of foreshortelling is defined using the above velocity relationships as (Vl-V4)/Vl expressed as a percentage.

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Referring again to Figure 1, ply 21 is extensible tissue paper which preferably has a relatively hig~
degree of extensibility by virtue of being dry-creped or otherwise being dry-foreshortened. The corrugated appearancP of the unadheredtunembossed portions of ply 21 in Figure 1 is, albeit greatly exaggera~ed, intended to represent a relatively uniformly creped.paper sheet such as disclosed in U.S. Pa~ent 3,301,746 which;issued January 31, 1967 to L. H. San~ord and J. B. Sisson.
Such paper is characterized by relatively uniform crepe, a relatively low stress/strain modulus through .
its low and intermediate one-third ranges of MD exten-: sibility, and a rela~ively high modulus through the ~highest.one-third of its range of MD extensibi~ity to 15: the level o~ strain at which:it ruptur~es. RelativeIy little stress~ is required to pul:l most:of`the~crepe out of~such paper;~and, a~ter mosit o the-crepe has been ~-pulled out, relatively~ ttle ad~itional strain results as the level of stress~ is increased sufficiently to break the paper:. The machine direction strain at which rupture of such dry-creped paper occurs is directly~
related to the degree of foreshortening o the paper which is effected by dry-creping, and the rupture stress vaIue (i.e., t~e level o~ machine-direction 25` stress at which rupture occurs~ is dependen~ on the strength property of the papermaking furnish (i.e., the fibers and additives, if any) as well as the degree and type of bonding within the paper. To some extent it is also dependent on the impact angle of the creping blade: greater impact angles causing less tensile strength reduction due to dry-creping than smaller impact angles.

Ply 22, Figure 1, is extensible tissue paper having a higher stress/strain modulus through the lowest one-third of its range of MD extensibility than ~2~ 7 Ply 21, and preferably has all or a substantial portion of its MD extensibility imparted by virtue of under-going substantial machine-direction foreshortening in the wet-end of a papermaking machine: i.e., wet foreshortening. Preferably, this is effected by transferring the web from a carrier ~abric to a sub-stantially slower moving open-weave transfer fabric wîthout substantial overall compaction while the web has a relatively low fiber consistency so that the paper has high bulk/low density. Such paper is here-inafter alternatively designated wet-microcontracted paper or I~C-paper.

~ile not intending to be bound by a theory of ~operation, it is~believed that~ the fibers o~ we~t-foreshortened~paper in general, and~Q WMC-paper In particular are somewhat~folded~and~bonded together in:
~such~a~way~that~applied ~MD-~stress preripitate`s u~
folding and/~or straightening of the fibers as inter--~ibe~ bonds are peeled apart. Thus, it is believed that the higher ;stress/strain modulus through the lowest one-third o~ the range o MD extensibility of such paper as compared to dry-creped paper is due to the stress required ~o peel the interfiber bonds apar~
in addition to unfolding and/or straigh~ening the fibers per se, whereas dry-foreshor~ening does not precipitate such additional interfiber bonds which must be peeled apart to pull dry-foreshortening induced stretch ou~ of the paper. Indeed, dry-creped paper acts somewhat like a multiplicity of freely hinged panels which ofer relatively little resis~ance ~o unfolding: at least in the low and inter~ediate ranges of its MD extensibility.

The oregoing description of an exemplary embodi-ment of the present invention comprising plies 21 and ~z~

22 which are, preferably, dry-foreshortened and wet-oreshortened, respectively, is not intended to pre-clude one or both plies from being hybrids thereof so long as they in fact have sufficiently different low-range stress/strain properties that one will constrain theother ply from elongating in the plane o~ the paper when wetted and thereby precipitate puckering of unadherPd portions of the other ply: and wh~ch plies, preferably, have substan~ialIy equal elongation at rup~ure values.

Figure 2 is a somewhat schematic sectional view of the exemplary product 20 taken along line 2-2 thereof;
and wherein the crepe induced undulations o~ ply 21 are greatly exaggerated, and the normal undulations of the wet-micro~ontracted papex ply-Z2 are:not shown in order to more clearIy depic~ the~-~source of the~extra length.
:of ply~2l~ between.~the;~adhered.areas which i~s~available : to induce the~puckering shown:in:~Figure 3.~ The: dry-:~
creped ply 21 and the WMC-paper ply 22 have been.
20~ juxtaposed, dry.-embossed, and adhesively adhered.
together as disclosed in U.S~ Patent 3,414,459 which issued December 3, 1968 to E. ~. Wells~. That is, plies 21 and 22 ar embossed and adhesively adhered together ~ in confronting regions 23, while their remaining `25 portion~ r~tain their original characters. Preferably, the embossments of plies 21 and 22 are so configured and disposed that the unadhered portions.of plies 21 and 22 are in Z-direction spaced relation ~o enhance the dry bulk impression of the~paper although it is not : -~ 30 intended to thereby limit the present invention to : paper products having such Z-direction spaced unbonded portions, or to paper products having embossed plies.
Moreover, although all of the confronting embossed : portions of the plies of product 20, Figure 2, are adhered together as with a bonding adhesive, it is not ~2~ 7~

:
~ 14 -intended to thereby limit the invention to ei~her such products having all of such confronting embossed portions adhered together or to such products wherein ; adherence is achieved by adhesive bonding ma~erial.

Figure 3 depicts the exemplary two-ply paper product 20 as shown in Figure 2 after the product has been wetted. Wet~ing causes the crepe ridges 24 o ply 21 to unfold. However, because of the higher stress/-strain modulus of ply 22 thr~ugh its low range of extensibility as compared to ply 21, ply 22 constrains ply 21 from being elongated substantially in the plane of the paper. Thus, as the crepe ridges unfold due to ~ I ~ ^th,e relief of crep,e~ i~duc~d str.ess~s, ~he unadhered~
~ ~1 D ''~ '~ ' ' por~i~s ~f ply 2~ p~ck~èr~ up in the Z-direction. IT~is lS ~puckering ph;enomenon enhances the wet bulk of the paper as~wel~l as;~its liquld~absorbRncy.

Figure 4 is a fra~gmentary sectional view which is similar to Figure 2 and which shows an exemplary three-ply embodiment of the present invention: i.e., paper product 50 comprising an extensible c~nter ply 51 (e.g., a wet-~oreshortened web) disposed bPtween two extensible dry-creped plies 52 and 53, and adhered together in the regions designated 54. Pl~ 51 is made to have a suficiently highe~ stress/strain~modulus in .its low range of extensibility as compared to plies 52 and~S3 that, upon wetting the product, plies 52 and 53 are constrained by ply 51 from elongating in the plane of the paper as the crepe ridges 24 of plies 52 and 53 unfold. Thus, the unadhered 30 creped portions of plies 52 and 53 pucker in the Z-direction as is shown in Figure 5. As stated hereinabove with respect to the puckering of product 20, such puckering enhances the wet bulk of the paper produc~, and increases its liquid absorbency.

Figures 6 and 7 arP plan views which are S similar to Figure 1 but in which the back plies 31 and 32 of products 30 and 40, respectively, are dry-creped two percent (2%) and ten percent (10%), respectively, whereas the back ply 22 of product 20, Figure 1, is wet-foreshortened paper as de-scribed hereinbefore. The front ply 21 of pro-ducts 20, 30, and 40, Figures 1, 6, and 7 are substantially identical; and all of the products were converted~in the manner-~previously described with resp~ec~ to~product`2'0~'That is:, in'a'cco'rdance r . .
~S~ ~wIth the previously referenced WeIls patent..

: Figur~es &~and 9'are~, a's:stated hereinbefore, graphs o wet:and. dry stress/s~rain data, respeetively~
derived from samples~o a two-ply tissue paper product ; embodiment of t:he pres:ent invention as shown in Figure 1, and from ~samples of the two types of paper from which the product was:converted; and which samples were made and tested as described herein.

Figures lO and ll are, as stated hereinbefore, graphs of wet stress/strain da~a of samples of~
the two two-ply tissue paper products shown in:
Figures Ç and 7, respectively, and~from sampl~s of the two types of paper ~rom which each of those bimodal products was converted; and which sampIes were made and tested as described herein.

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INTRODUCTION TO SAMPLES
Two groups of samples were made and tested to obtain comparative data with respect to embodi-ments of the present invention and other multi-ply ' 5 tissue paper products.

Briefly, Sample Group I consisted of three two-pLy tissue paper pro~ucts 20, 30, and 40, Figure 1, 6, and 7, respectively, which are of the same general configuration but which were dif-ferent in the degree and type of machine-direction foreshortening of their back plies 22, 3I, and 32, respectively. Al~ had identical front plies as in-dicated by the front~ply of each product being~
,de~signated ply 21'. ~The papers- from~which the~se`
products were;~converted are identified in Tables I
"~,and~ by the~ir~respec~tive-~ply designators~with a ',suffix~BG~('l.e.,~be~'ore cQnverting)~. P~rtinent~data~
~rom products~20-,`30, and 40 are tabulated in Tables ~'III and~IV.

''~ -TABLE I
; , Type and Degree of Dry Pa ~r 'MD Foresh'ort'ening 'Ba's'i's' W~'.* ''Cali~e'r~*
21BC Dry-Creped, 25% 19.0(3I.0)15.3(0.39) -22BC WMC, 20% ' ' 18.4(30.0)14.2(0.36) 31BC Dry-Creped,~ 2~/o 18.9(30.8) 9.0~0.23~
32BC ~ Dry-~reped, 10~/o 19;.0(31.0) 12.0(0~30) *~ Pounds/3000 sq. ft. (grams/sq. me~er) Mils (mm) :

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: ~ABLE II

~enRS~tu~rength~ MD Stretch 7 %
Pa~er D_y We~t_ Dry Wet : 31BC 955 335 8 15 32~C 680 255 16 25 :
* gms.~i~ch (2.54 cm.) Width.

T~LE III
Density***, Product : Caliper** ~ms/cc (Plies) ~ Basis Wt.* ~ ~ D~y ~ Wet Dry Wet 20.(21,22?~ 35.2 (57.~) 25.0(0.635) ~6.6~c.42~ o.oso 0.~136 30;(21,31~ 36~.3 ~(59.. 2)~ 21.2(0.538) 16.2:(0.411) :0.110. :0~143 ::
15~ 40~2l,.32.).~ 35.0 (57.~ 2.0(0.559). 35:.0:(0.38~ 0.102~ 4 *~ Po~nds/3000 sq.:~t. (gramslsq. mete~
** Mils tmm~
*** C~mputed ~ro~ Basis Wei~h~ ~d Calipe~ Data TABLE IV
.
~et MD
Te~sile Strength Reid Product Conversion Absorption :H.~.C.*
(P`lies) E`~ficie~ ~lme, econds G/S~* _G/G~.~**
25~ 2~(21,22): ~7~% 23.2 64.0 14.4 3Q~21931) ~ 57% :2~.6 63.7 13.9 40(21,32) 59% 32.:9 57.8 13.0 * Horizontal Absorpti~e Capacity ** grams per sample sheet `~** grams per gram of fiber of sample sheet 7~

All three of the Group I samples comprised a twenty-five percent (25%~ dry-creped ply 21 and a second ply which plies were embossed and dis-continuously adhesively laminated to~ether in accordance ~ith U.S. Patent 3,414,459-Wells. In product 20, Figure 1, an exe~plaxy embodiment o the present inventio~J the second ply was a twenty percent (20V/o~ wet-microcontracted ply 22; in product 30, Figure 6, the second ply was a two-percent ~2V/o) dry-creped ply 31; and in product 40, Figure 7, the second ply was a ten-percent (10%) dry-creped ply 32.~ Thus~, the~plies of product 20 were diifferent: in the degree~an,d type of ~ore-short~ening-~i.e~., 20Z-wet ~. 25%,-dry) whereas- the 15~ plies~o~p,roducts 30~ and~40- dl~'fered,only~i~ the degree~of,`~dry-oreshRrteniNg~(dry-cxep~ By~way~
of~comp~arison; product Z~ has~ s~trength èficient str~cture'which~is manifes~ed by a~monomodal j stresslstr:ain property as opposed to products 30 and 40 being~substantial~y less strength efficient as manifested'by bi~odal wet ~stress/strain properties as described hereinbefore. Howe~er, all ~anifest high tensile ener~y absorption relative to similax products wherein one ~ly is ~elatively inextensi-; 25 ble: e.g~ such products as disclosed in U.S.
Patent 3,953,638-Kemp albeit the Kemp s~ructures ~comprise three-plies o~ which the middle ply is~
said to have less than about ten percent (10%) stretch.

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.

3'7~

More specifically) still referring to Sample Group I, four (4) ~ypes (i.e., different degrees and types of machine-direction foreshortening) of tissue paper were made and are hereby identified in Tables I and II by designators 21BC, 22BC, 31BC
and 32BC. Upon conversion to make products 20, 38 and 40, papers 21BC, 22BC, 31BC and 32BC became pIies 21, 22, 31 and 32, respectively. That is, for example, the paper which became ply 21 of products 20, 30, and 40 is designated 21BC in Tables I~and II. rn the same vein, the desig-nators for wet a d~dry sampIes of these papers ~have~suffixes~W~and~D, respectively,~ in the graphs ~ ~shown in~Figures~8 through~ inclusive: or 1~ instanc:e, the~curve~designated~21B-W in Figure^&
was derived from wet sample3 of thei pre-conversion paper 21BC which, upon conversion, became ply 21 of product 20, Figure 1. ;To avoid unduly re-dundant descrip~ions, these distinguishing suf-fixes are us d throughout the remainder of the sam~le descriptions.

Papers 21BC~, 22BC, 31BC and 32BC were~made and reeled in accordance with U.S~ Patent 4,191,609 which is~sued to P. D. Trokhan on~March 4, 1980;
25 ` and all were made from the same furnish (northern :

:

softwood kraft), in the same papermaking ~achine, and under the same conditions albeit for the type and degree o machine-direction foreshortening.
Additionally, these papers had their high density zones impregnated with a latex binder mat~rial which was applied by a rotogra w re apparatus prior to~ disassociating them from the imprinting/carrier fabric o~ the papermaking machine.

Reels of papers 21BC and 22BC, Table I, were converted into product 20, Figure 1, consisting of plies 21 and 22, respectively, by embossing them and laminating them together as shown in Figures 1 ,, ~ ; and 2,, and as, disclosed~'in~ U.S~. Patent,3,,4~14,~459 Wells. Four wet an'd dry~s'amFles, OI e'~ac-h of'the , 15~ ~ papers~21BG and 22BC, and of product 20 were stre~ss,/s~r~ain~te-sted~and~averaged (i.e,.~ data from~
each set of four samples was averaged) to~generate~
the~ data~which are plotted in Figures 8~ and 99 respectively.

~ StiIl referring to Figures 8 and 9, papers 21BC and 22BC (i.e., curves 21BC-W and 21BC-D, and 22BC-W and 22BC-D~ were sufficiently matched wi~h respect to their elongation at rupture values that t~e stress~strain curves 20W and 20D for the wet and dry~product 20, respecti~ely,,were monomodal.
However, curves~20W and 20D are not the arithmetic sums of curves 21~BC-W and 22BC-W; and of 21BG-D
and 22BC-D, respectively. The dif~erences in their elongation at rupture values are primarily ; 30 due to some potential elongation of the papers being pulled out incident to their being converted into product 20; and the peak tensile strengths are not the arithmetic sums of the component pIy papers due to complex factors such as the strengthen-: ing imparted by adhesive used to laminate the plies together with a pattern of discrete adhered regions, and due to ~he fact that some intra-ply paper bonds are broken by embossing as an incident to converting. The portions of curves 20W and 20D to the right o the peaks reflect the decay of ~he tensile force after rupture of the product has occured and before the test apparatus was turned off.

Continuing to refer to Figures 8 and 9, the characters of curve 21BC-W with respect to curve 22BC-W, and of curve 21BC D wi~h respect ~o curve 22BC-D arej resp ctively, differen~: curve 21BC-W
being~substan~ia,l'ly~more~,upwardly-concave:tllan :
lS ~ curve'22~:-W~:especiall'y~be~o~or~y~perc Q t:~wet stretch; and~curve:22BC-D being~substan~ially~:
linea~ whereas~:curve::21BG-D has a high degree~o~
:, upward concavity.,~Also~, curves 2~Be-w and 2,2BC-D
are substantia~lly higher than curves 21BC-W and~
21BC-D, respec~ively, through the low and inter-mediate thirds of the range o~ the MD stretch/~
extensibility o~ product 20 (curves 20W and 20D, Figures~ 8 and 9, respectively). This relationshlp -- especially when wet --~infers the relationship 25~ between plies 21 and 22 per se of produc~ 20 whirh precipitates high liqu;d absorption in products 20 derived therefrom as has been describ~d he~ein-beore. ~ :

Parenthetically, one would expect the stress/
strain curves of plies 21 and 22 (not shown) to be : shifted somewhat leftward from the stress/strain ` : curves of their respective parent pre-conversion tissue papers due to some MD extensibility normally being pulled out incident to being converted from .

~ `

reeled papers into a multi-ply tissue paper product.
Thus, as stated just above, the relationships among the stresslstrain curves of the plies and the product may be inferred from the rela-tionships among the pre-conversion papers and the product which are shown ln Figures 8 through 11, in~lusive.

Continuing still further to refer to Figures 8 and 9, although the papers from which plies 21 and 22 of the described exemplary embodiment were made were sufficiently matched to precipita~e monomodal stress/strain curves for bo~h wet and dry samples of product 20 (i.e., curves 20W and,

2~D~ respectively)~ is::not inten~ed~ to~thereby ' .15~ imlt~th~present~inven~lon Rather, matching the.
plies~to provide:~products- having~either a~wet,or : : : dr~monomoda,l stress.fstrain :property is deemed,to.
; ~ be wi~thin:the s;cope o~the~present invention.
Indeed.,:as exemplified by products 30: and 40 20 ~ having bimodal wet stress/s~rain moduli, Figures 10 and ll:respe tively, monomodality is not : essential:for either wet or dry samples so long as ` they have high tensile energy absorption and liquid absorbency as described hereinbefore.
: :
; 25 Referring now to products 30 and:40, Figures ' : 6 and 7, respectively, reels o papers 21BG and - 31BC, Table I, were~converted into product 30, Figure 6, and r:eels of paper 21BC and 32BC, Table : I~, were converted into product 40, Figure 7, by embossing them and laminating them together as described hereinbefore with respect to product 20, Figure 1: i.e., in accordance with U.S. Patent '7~

3,414,459-WellsO Four wet samples of each of the papers 21BC, 31BC, and 32BC, and of products 30 and 40 were stress/strain tested and averaged (i.e., data from each set of four samples was averaged) to generate the data which are plotted in Figures 10 and 11.

Still referring to Figures 10 and 11, papers 21BC, 31BC and 32BC (i.e., curves 21BC-W, 31BC-W, and 32BC-W) were suf~iciently different with respec~ to their elongation at rup~ure values that the stress/strain curves 30W and 40W of~the wet samp~les~of products 30 and~40,~ Figures lQ and ll, respectively~, a~re bimoda;l~ ., have two peaks~

5~ No~twLthstanding the~fact that product;s ~3a~ and~
40 have~bimodal stre~ss/s-itrain~c~rve~s, they none~
theless have relativel~high tensile energy absorption;values - at least up- to their ~irst ; ~ peaks~ .e.,~the~rupture poin~ of their least extenslble plies~ -- than ~ere their least ex-tensible plies substantially less extensible:
e.g., havin~ wet MD extensibili~ies of less than ten percent.~ For example, reerring to Figure 10, ; t~e partial, pre-first-ply-rupture TE~ value for wet sampl4s~ of product 3~ is the shaded area 100 under curve 30W and to the left o~ peak 101; and~
was measured~to be about eighteen-hundred grams/inch.
I~t is believed to be obvious~that the corresponding partial Wet-TEA value~would be substantially less if the paper ~rom which ply 31 were made had equal strength buk substantially less wet MD extensibility ; ~ than the graphed sample. That is the area o~ the nearly triangular TEA area 100 would be directly reduced as the slope of the hypotenuse of the triangle was incre~sed (e.g., for samples having lower values of MD extensibility but equal rupture strength)O
~5 SAMPLE GROUP II
Brie1y, Sample Group II comprised three two-ply products. These were made and tested to illustrate that synergistic absorbency is derived from combining plies having substantially identical stretch but which were made sufficiently different that unadhered portions of one ply willjpucker in the Z-direction when the produc~ is wetted, as comp~aredSto combining two o~each of the dis-~similar^plies ~together.~ ;For example~,~consider afirst ply~to be~twenty per~c~ent (`20~io) wet-micro~
eontracte~d~and~a~sécon~ply to be~twenty-five~
~percent (25%)~dry-creped~ A product comprising ~
such a~firs~ ply and~such a dissimilar second ply which are discontinuously zdhered toge:ther has substantially greater absorbency thaN either a two-ply product consisting of two such first plies or a two-ply product consisting of two such second plies. `~ertinent data from these two-ply products and the papers ~from which they were converted are tabulated in Tables V and VI`, respectively.

- TABL~ V
Type &
30 ~ Paper Degree o~ Reeled Reeled , Sample MD Fore- Basis Caliper No. shortenin~, Weight* mils (mm) KK 31-BC 25% Dry-Creped 18.4(30.0~ 17.1(0.434) KK 33-BC 20% WMC 16.~3(27.4) 14.8(0.376) ` ~ ~
; 35 ;~ Pou~ds per 3000 sq. feet (grams per sq. meter) ' ~ .

~2~

T~BI,E VI
Wet MD Tensile ~eid Strength Con- Absorption H.A.C.
Product version Efficiency Time, Seconds G/S G/G
KX 31/31 77% 19.0 44.6 13.1 KK 31/33 69% 16~0 57.0 15.2 KK 33/33 73% 17.0 49.9 13.5 TEST DESCRIPTIONS
~enerally speaking, the ~roup I and II samples were tested as briefly described in the ~ollowing test procedures.

Dry Cali~er ~15 This test was run on a motorized micrometer such as~Model 549~whieh is available- ~rom Testing Machines,~Inc~: of~Amity~ille, Long~lsland, New ~ork.~ Product~samples~were subjected~to a loading~
of 80 ~m. per sqO in.~ under a two inch (5.08 cm.) diameter anvil. The micrometer was zeroed to assure tha~no foreign matter was present beneath the anvil prior to inserting the samples for measurement, and calibrated to assure proper readings. Measurements were read directly from the dial on the micrometer and are expressed in mils (mm.)~in Tables I, III, and V.
:
Wet Caliper This test was run utilizing the same in-3~ ~ strument and the same basic procedures utllized to measure dry caliper except th~t the produc~
samples were first satura~ed with water by immersing them and then gravity draining them for about three seconds while holding them in a slightly inclined attitude to remove excess water prior to making the measurement.

~Z~ 7~
I

Dry'MD Tensile S'trength ~ These data were obtained on an electronic tensile tester such as a Thwing-Albert Model QC
tensile tester such as is available from the Thwing-Albert Instrument Company of Philadelphia, Pennsylvania. Product samples were cut which were one inch wide by at least six inches long in the machine : direction. :Each sample strip was placed in the jaws of the tester, set at four inches (lO cm.) gauge length.
The crosshead speed during the ~est was four (43 inches (about lO cm.) per minute. Readings were taken di-rectly from the scale on the tester at the point of rupture and are~:expressed in grams/inch (gms./2:.54 :~: cm.) in-Table:XI:, and on Figure 9.

15~ Jet~MD' ~ensi'le St en&~h T.he~se.~datæ'were~obtained~on~the~same in~
strument~use~:'to~obtain dry tens:ile~strength-.
Ho~ever:,~ each sample was saturated:with water after it :was clamped 1n the te~ster but before movement of the crosshead ~aws of -the tes~er began. Such wetting : ~loated out some of the extensibility of:the samples ~efore the crosshead movement started which, for example, accounts for curve 21BC-W having i~ts ~-axis intercep~ at about twenty percent (:20%) wet stretch, Figures 8, 10, and ll.

Wet MD T'ens'ile Str'en'~ h_C'onv'e~sion~E'f~'ic'iency The:se data,. ~ables IV and VI`, were generated by calculations rather than direct tests per se.
: For e~ample, the 79% value ~or product 20, Table .

'7~

IV, was calculated by first summing the MD wet tensile strengths of the papers 21BC and 22BC from Table II
(i.e , 220 and 210, respectively). Then, that sum (i.e., 430) was divided into the MD wet tensile strength at rupture of product 20 (abou~ 340 as read from curve 20W, Figure 8), and expressed as a percent. The ` conversion efficiency data ~abulated in Table IV
evidences the strength efficiency of the exemplary monomodal embodiment of the present invention (i.e., product 20) as compared to the exemplary bimodal embodiments of the present invention (i.e., products 30 and 40).

Tensile Energy Absorption TEA
~15 ' TE~ s dçfined;as- th~ e~ergy o~ wpr~ àb~sorb~dOpe~ 9 un~it of surface~area of~a sample as~the sample`is tensile~ strength tested until lt ruptures. A partial TEA is the energy;or~work~ab~sorbed as~he~tensiIe~force is increased ~rom one level to another: e.g., from zero to the level o~ stress required to break the first ply of a multi-pl~ product. The TEA of a product can be obtained by clamping a one-inch (2.54 cm.~ wide dry speeimen in two spaced sets of jaws when they are four inches (about 10 cm.) apart, and with any noticeable slack being pulled out of the strip beforP it is clamped. Strain is then applied to the specimen by mo~ing the jaws furt~er apart at a constant rate-o four inches/minute (10 cm./min.) while recording the elon~ation in inches and the load in grams until break-age of the specimen. To obtain wet TEA's, the samplesare saturated with water after being clamped, dry, between the jaws with all of the dry slack pulled out of them. The area under the load-elongation curve is then measured, for example, by an electronic inte~
grator. The TEA is then calculated using the equation:

;;' '~ TEA=lOOA/LW

~ ThP units of TEA are gram-inches per square inch `~ (or grams/inch) where:
: ;
; A = area under load-elongation curve in gram-inches;
L = initial span between clamp lines in : inches; and - : W = initlal:width of specimen in inches.

However, when the data are plotted as stress/-strain curves (e:.g., Figures 8-11), each TEA is simpLy the relevant area under i~s respective curve. For , ~ example, the, a~erage WET-TEA for the samples of product 20 from.::w~ich curve .Z~OW~:Figur~8~.,was- deriv~d can,be. .-~obtained: b:y~ln~ègr~ating~the area~under'the:p'ortion of ~;' ~' ';
15~ the~curve~:which, extends~from its X-axis:int~ercept 90~to~
it:s pea~ 9~ T~his~was-done~and~:-the:.re~sulting:computed.
WET-T~A 'i:s~àbout:~forty-fi~e:hundred;grams/lnch. ~
In the same~vein, the,par~ia~WET-TEA for product.
20 for the range~:o~ s~ress rom zero to point 92 was computed to~be about seven-hundred-seventy-five grams/inch by measuring the shaded area 93 in Figure 8.
; Point 92 is at the stress level equal to one-third the stress:level of point 91.: As is evident from Figure: 8, the ~WET-TEA contribution of ply 22 is in-~25 ferentially substantially greater than or ply 21 by ~ :
virtue of the~portion of area 93 under curve.22BC-W
: : being~much greaeer than the; corresponding~portion of ~ ;
: area 93 under curve~21BC-W. Parenthetically, the sum ,, of thos~e partial WET-TEA areas under curves 21BC-W and 22BC-W do not equal the partial WET-TEA area under curve 20W due to converting factors as described '~ ~ hereinbefore. Moreoverl it is apparent that products : having substantial MD elongation would have higher TEA
values than relativel~J inextensible products having the :35 same MD rupture stress value, Such higher TEA values Z~'7i~

- 29 _ correlate wi~h consumer perceived product strength properties.

MD Stretch MD stretch is the percent machine direction elongation of a structure prior to rupture and is read directly from a secondary scale on the Thwing-Albert tensile tester. Wet and dry MD stretch readings were ~aken coneurrently with wet and dry tensile strength readings.

10Rate Of Absorption: Reid Test This test comprises measuring the time in seconds required for O.lO ml. of distilled water ; to~be absorbed~ by a slngle~4 ln. by 4 in.,product , samples~using a,Reid~s,tyle~tester such as.is ~15~described in~detail in an~artLcle by;S.~G.~Reid entitled~"A~M:ethod~for~easuring the~Rat~e~o~
bsorption o~Wa;ter b~Creped~Tissue~ Paper,"~which~
appears~at pages~ T~115;~to T-117 o~ Pulp and Paper ~ ~:
Magazine~of Cana~a, Volume 68, No. 3, Convention Issue~, 196-7o Tests were~conducted by simultan-eously-opening a-~stopcoc~ o~-ated between a cali-brated pipette and a capillary tip contacting the product sample and starting a timer; observing the water level in the pipette as the water was being absorbed~by the product sample; and stopping the timer when exactly 0.10 ml. of water~ had~been dispensed f~om the calibrated pipette. Readings were taken direct~ly from~the timer and are expressed in seconds. Lower times are indicative of a higher rate of water ab-sorption.

Horizontal Absorptive Capacity Test_Q~
The test determines the amount of distilledwater absorbed and retained by an absorbent product while in the horizontal position. All samples 1 97~

were sheets having an MD length of about nine-and-eight-tenths inches (about 24.9 cm.) and a width of about eleven inches (abou~ 27.9 cm.), and we e conditioned for a minimum of two hours at 72C +
2F and 50% ~ 2~/RH prior to testing. The fol-lowing procedure was used. The DRY WEIGHT of afirst conditioned sample (A) was determined to the nearest .01 grams. A special holder comprised of an aluminum frame strung in a predetermined grid-like fashion with nylon monofilament of .012 in.
(0.3 mm.) diameter was tared. The sample was placed on the grid of the holder, covered with a like holder to prevent movement while in the bath, and submerged in distilled water at 72F (about :~: 23C): ror 30*~seconds. The 5ample was the~ gently ~ withdrawn`from the b~ath and allowed to drain in the horizont~al- position~ for 120+-5 se;conds~ While~
the sample was drainIng, the cover device was removed and alI excess water was wiped from the frame of the~sample holder. The weigh~ of the wet sample plus the~hoIder was then determined to the nearest 0.01 gm. while the wet sample was main-tained horizon~al in the hoIder. The sample holder tare weight was then substracted to yield ;
the wèight of the wetted sample (WET WEIGHT). The 25~ procedure was repeated with a second sample (B).
Sample B was oriented in the sample holder in a direc~ion orthogonal to that of sample A. The absorbency, both the weight of water per sheet and the weight o~ water per unit weight of fiber is 3~ the arithmetic average of ~he two samples. These values were calculated in the following manner and tabulated in T:bles IV and VI.
.

` ~2~37~1L

WET WEIGHT~ - DRY WEIGHTA ~ W~T WEIGHTB - DRY ~EIGHT~
____ _ ___ :
WEIGHT OF H20lUNIT WEIGHT OF FIBER
5 ~ 1 ~WET WEIGHTA ~ET WEIGNT
2 ~ DRY WEIGHTA DRY WEIGHT~

' While particular embodiments of the present invention~ha~e been illustrated and described, 10~ t would:be~ob~ious to-those skilled in the art :~:
th~t v-arious~other changes and modiications can-be;made~w~hout~dep~ar~ing~from~the spLri~and scope~
o~ the~ inven~ion~ s inten~de~; to cover~:in:~:the : appended ci~aims~all such~chan~es and modifications ~ ~ ~
15~ that are:withi~the sc~pe of~this~ invention. : : :

:~ What is claimed is:

:

`: : ~ :

,

Claims (33)

Claims:

1. An extensible multi-ply tissue paper product comprising a first ply and a second ply of tissue paper in associated relation with substantial juxtaposed portions thereof not adhered together, said plies comprising tissue papers having greater than ten percent extensibility in the primary direction of said product and having elongation at rupture values in said primary direction that are sufficiently close in value that said product has a monomodal stress/strain character in said primary direction, said first ply having a sufficiently higher stress/strain property than said second ply that unadhered portions of said second ply will pucker in the Z-direction of the product when the product is wetted.

2. The extensible multi-ply tissue paper product of Claim 1 wherein said plies have greater than said ten percent extensibility in said primary direction before said product is wetted.

3. The extensible multi-ply tissue paper product of Claim 1 wherein said plies have greater than said ten percent extensibility in said primary direction when said product is wet.

4. The extensible multi-ply tissue paper product of Claim 2 wherein said first ply has a sufficiently higher stress/strain curve than said second ply through the lowest one-third of a princi-pal range of stress of said product that unadhered portions of said second ply will pucker in the Z-direction of the product when the product is wetted, said principal range of stress extending from zero to the level of stress at which said first ply ruptures, and said higher stress/strain curve of said first ply relative to said second ply being manifested by the partial TEA contribution of said first ply to the partial TEA of the product being substantially greater than the corresponding partial TEA contribution of said second ply over said lowest one-third of said principal range of stress of said product.

5. The extensible multi-ply tissue paper product of Claim 4 comprising a third ply substantially identical to said second ply and juxtaposed the op-posite side of said first ply from said second ply.

6. The extensible multi-ply tissue paper product of Claim 1 wherein each said ply has from about fifteen to about thirty percent extensibility in said primary direction.

7. The extensible multi-ply tissue paper product;
of Claim 1 wherein the partial TEA contribution derived from said first ply is about two times as great or greater than the partial TEA contribution derived from said second ply when said product is elongated about ten percent in said primary direction.

8. The extensible multi-ply tissue paper product of Claim 1 wherein the stress/strain modulus of said first ply in said primary direction is about twice as great or more than the corresponding modulus of said second ply in the range of elonga-tion of said product of from about five to about ten percent in said primary direction.

9. The extensible multi-ply tissue paper product of Claim 1 wherein the stress/strain character of said first ply is substantially different from the stress/strain character of said second ply.

10. The extensible multi-ply tissue paper product of Claim 9 wherein said primary direction is the machine direction of each said ply as laid, said second ply comprising tissue paper having a sub-stantially non-linear stress/strain character which manifests a relatively low MD stress/strain modulus through the lowest one-third of the range of MD extensibility of said product and a substantially greater MD stress/strain modulus through the highest one-third of the range of MD
extensibility of said product.

11. The extensible multi-ply tissue paper product of Claim 10 wherein said first ply comprises extensible tissue paper having a substantially more linear MD stress/strain character than the MD
stress/strain character of said second ply.

12. The extensible multi-ply tissue paper product of Claim 10 wherein said first ply comprises extensible tissue paper having a reversely curved MD stress/strain character relative to the MD
stress/strain character of said second ply.

13. The extensible multi-ply tissue paper product of Claim 1 wherein said first ply has a MD elonga-tion at rupture value of from about eighty percent to about one-hundred-twenty percent of the MD
elongation at rupture value of said second ply.

14. The extensible multi-ply tissue paper product of Claim 13 wherein said first ply has a MD elonga-tion at rupture value of from about ninety percent to about one-hundred-ten percent of the MD elonga-tion at rupture value of said second ply.

15. The extensible multi-ply tissue paper product of Claim 1 wherein the tissue papers comprising said first ply and said second ply have each undergone MD fore-shortening in the range of from about 10 percent to about forty percent during their manufacture.

16. The extensible multi-ply tissue paper product of Claim 15 wherein said MD foreshortening of each of said ply is in the range of from about fifteen to about thirty percent.

17. The extensible multi-ply tissue paper product of Claim 1 wherein said product has said monomodal MD
stress/strain character when wet.

18. The extensible multi-ply tissue paper product of Claim 1 wherein said first ply is wet-micro-contracted tissue paper.

19. The extensible multi-ply tissue paper product of Claim 18 wherein the MD elongation at rupture values of said plies are so related that said product has a monomodal MD stress/strain character.

20. The extensible multi-ply tissue paper product of Claim 19 wherein said product has said monomodal MD
stress/strain character when wet.

21. The extensible multi-ply tissue paper product of Claim 1 wherein said plies are discontinuously bonded together.

22. The extensible multi-ply tissue paper product of Claim 1 wherein said plies are sufficiently em-bossed that at least about fifty (50) percent of their confronting surfaces are disposed in spaced apart relation.

23. The extensible multi-ply tissue paper product of Claim 22 wherein said plies are discontinuously bonded together.

24. The extensible multi-ply tissue paper product of Claim 1, comprising a third ply substantially identical to said second ply and juxtaposed the opposite side of said first ply from said second ply.

25. The extensible multi-ply tissue paper product of Claim 24 wherein the MD elongation at rupture values of said second ply and said third ply are so related to the MD elongation at rupture value of said first ply that said product has a monomodal MD stress/strain character.

26. The extensible multi-ply tissue paper product of Claim 25 wherein said product has said mono-modal MD stress/strain character when wet.

27. An extensible multi-ply tissue paper product comprising a first ply and a second ply of tissue paper in associated relation with substantial juxtaposed portions thereof not adhered together, said plies comprising tissue papers having greater than ten percent extensibility in the machine direction of said product, said first ply having a sufficiently higher stress/strain property than said second ply that unadhered portions of said second ply will pucker in the Z-direction of the product when the product is wetted, said plies having stress/strain properties which are so related that the partial TEA contribution derived from said first ply is about two times as great or greater than the partial TEA contribution derived from said second ply when said product is elongated about ten percent in said machine direction, said second ply comprising tissue paper having a substantially non-linear stress/strain character which manifests a relatively low MD stress/strain modulus through the lowest one-third of its range of MD extensi-bility and a substantially greater MD stress/strain modulus through the highest one-third of its range of MD extensibility, said plies having MD elonga-tion at rupture values which are so related that said product has a monomodal stress/strain character, and said plies comprise tissue papers which were each MD foreshortened from about fifteen to about thirty percent during their manufacture.

28. The extensible multi-ply tissue paper products of Claim 27 wherein said product has said mono-modal MD stress/strain character when wet.

29. The extensible multi-ply tissue paper product of Claim 27 wherein each said ply has from about fifteen to about thirty percent MD extensibility.

30. The extensible multi-ply tissue paper product of Claim 27 wherein said first ply has an MD elongation at rupture value which is from about ninety to about one-hundred-ten percent the MD elongation at rupture value of said second ply.

31. The extensible multi-ply tissue paper product of Claim 27 wherein said plies are sufficiently embossed that at least fifty (50) percent of their confronting surfaces are disposed in spaced apart relation.

32. The extensible multi-ply tissue paper product of Claim 27, comprising a third ply substantially identical to said second ply and disposed adjacent the opposite side of said first ply from said second ply.

33. The extensible multi-ply tissue paper product of Claim 32 wherein said product has said monomodal MD
stress/strain character when wet.