US3120172A

US3120172A - Method of compressing stacks of creped paper tissues

Info

Publication number: US3120172A
Application number: US239738A
Authority: US
Inventors: Kenneth M Enloe
Original assignee: Kimberly Clark Corp
Current assignee: Kimberly Clark Corp
Priority date: 1962-11-23
Filing date: 1962-11-23
Publication date: 1964-02-04
Anticipated expiration: 1981-02-04
Also published as: GB1071859A

Description

K. M. ENLOE Feb; 4, 1964 METHOD OF COMPRESSING STACKS OF CREPED PAPER TISSUES 4 Sheets-Sheet 1 Filed Nov. 23, 1962 w y 1 1| wwww on R w x AW O m mm 9C 0. m H .m A mm 0 mm K. M. ENLOE Feb. 4, 1964 METHOD OF COMPRESSING STACKS OF CREPED PAPER TISSUES 4 Sheets-Sheet 2 Filed Nov. 23, 1962 Feb. 4, 1964 K. M. ENLOE 3,120,172

METHOD OF COMPRESSING STACKS OF CREPED PAPER TISSUES Tiled Nov. 25, 1962 4 Sheets-Sheet 5 s; 1 R 3 J15}? w H Feb. 4, 1964 ENLQE 7 3,120,172

METHOD OF COMPRESSING STACKS OF CREPED PAPER TISSUES Filed Nov. 23, 1962 4 Sheets-Sheet 4 MINIMUM NIP SPACING m INCHES FOR 400 P -Y.

% MOKSTURE IN STACKS OF TISSUES United States Patent Kenneth l l. Enice, Neenah, Wis assignor to Kimberly- Qlarf; orperation, Neenah, Wis, a corporation of Eeiaware Filed Nov. 23, 1&2, Ser. No. 239,738 5 Claims. (Cl. liloil) h ly invention relates to paper tissues particularly suitable for facial usage and to methods for making and converting such tissues.

Creped facial tissues having a basis weight (uncreped) of about 7 or 8 pounds per ream of 2880 square feet have been in general usage. in one well known form, the tissues are interfolded and are packed in paperboard dispensing cartons having slots in panels thereof, so that each tissue when it is dispensed from its carton through the carton slot automatically brings the next successive tissue into accessible position.

Due to lack of sharpness of the folds of the tissues, air entrapment between the tissues, and other conditions, stacks of the tissues have in the past had an apparent thickness greater than the actual tissue thicknesses. Stacks of the tissues have thus been quite space consuming and have thus required higher cartons than should be necessary. in order to decrease the heights of the stacks of facial tissues and also to increase the quality of the tissues, particularly with respect to softness and linrpness, it has been previously proposed to compress the tissues prior to cartoning, so that the tissues retain a permanent reduced height. Such proposals were made in co-pending patent applications of Kennel. l. Harv/cod, Serial No. llQfilZ, filed May 9, 1961, and Lei-Roy L. Peterson et 2.1., Serial No. 111,417, filed lvlay 9, 1961.

In both the l-larwood and Peterson et a1. applications, it was suggested that the compression of facial tissue stacks might be accomplished by the use of a compressor having a plurality of platens carried by two endless chains.

.re chains were so disposed that a series of platens carried by one chain were disposed beneath a series of platens carried by the other chain, and the platens moved in generally parallel paths from positions with a relatively wide gap between them to positions in which a narrow gap existed between them. Cam mechanism was provided to be efiective to move the platens to their narrow positions, and the cam mechanism had a dwell holding the platens in their narrow gap positions for a brief period of travel o the platens. The stacks of tissues were compressed between opposite platens carried by the two chains as the platens approached their narrow gap positions, and the compression produced by this apparatus on individual stacks built up quite uniform internal pressure in each stack rising to a maximum as the minimum between the platens was reached. Due to the dwell in the cam mechanism, the minimum gap was maintained for a brief period; and, due to deformation of each stack during this brief period, the internal pressure within the stack declined from the peak pressure during this period, producing, however, a relatively permanent deformaiton of the SiZtCl".

t is an object of the present invention to utilize a different type of compression apparatus comprising one or more pairs of rotatable drums having a nip between eacr. pair through which the tissue stacks are passed. Such rotary compression apparatus may comprise, in addition, opposite endless belts backed by the drums for carrying he tissue stacks through the drum nips. Each of the tissue stacks as it passes through the nip between a pair of the drums is subjected to a maximum pressure of cornp ession; however, the maximum pressure does not exist throughout each tissue stack simultaneously but rather passes from one end of the stack to the other, since the drums exert a rolling action on each stack rather than providing a simple uniform compressive force. It is contemplated that the drums shall have a substantial speed, such as peripheral speeds of 20 to 208 feet per minute, and the maximum pressure thus is quite transitory as compared to the mar-:iinum pressures that exist in the tissue stacks with use of the l-larwood-Peterson et al. cornpressors.

Due to the different manner of compressing the tissue stacks with the two types of apparatus, l have found that different gaps are required by the rotary type of cornpressing apparatus as compared to the platen type. in particular, according to the nvention, in order to produce the same tissue steel; densities, the invent on proposes that the gaps in the rotary type of apparatus be smaller than the gaps utilized in the platen type of apparatus. adore specifically, ccording to the invention, it is proposed that the gaps of the rotary type of ap paratus be approximately ,6 oi the gaps utilized in the platen type of apparatus in order to produce tissue stacks having the same densities as produced by the platen type of compressor. The gaps will, or" course, with the rotary type of apparatus, vary with the number of pairs of drums etween which the tissue stacks are compressed; and, according to the invention, if more than one pair of such compressing drums are utili ed, the gaps may be thickened While still obtaining the desired results, as will be hereinafter set forth in more detail.

The invention consists of the novel methods, constructions, and devices to be hereinafter described and claimed for carrying out the above stated objects, and such other objects, as will be apparent from the following description ot a preferred form or the invention and method for practicing the in ention, illustrated with reference to the accompanying drawings, wherein:

FIG. 1 is a "e elevational View of compressing apparatus embod ing the principles of the invention and including a plurality of pairs of drums having nips between them between which articles cf yieldable material, such as stacks of facial tissues of creped paper, may be passed for compressing th articles;

FIG. 2 is a fragmentary side elevational View on an enlarged scale of one of the pairs of drums illustrating an article of yieldable material about to pass between the drums;

FlGS. 3, 4, and 5 are views similar to FIG. 2 with the article of yieldable material respectively in positions farther into the nip between the drums;

FlGS. 6, 7, and 8 are side elevational views of modified forms of the compressing apparatus;

FIG. 9 is a perspective View of a facial paper tissue stack which may be used in the compressing apparatus; and

FIG. 10 is a graph setting forth the gaps between drum pairs that may be used in connection with facial tissue stacks to provide commercially acceptable compressed product.

Like characters of reference designate like parts in the several views.

Referring now to the drawings and to FIG. 1, in particular, the illustrated compressing apparatus may be seen to comprise, "1 general, a framework 15,

rotatable drums

16, 17, is, 39, 2t and 21, on a lower level and rotatable drums 2.2, 23, 24, 12$, and Zr: on an upper level, all supported by means of the framework 15. The drums in to 26 each comprises a smooth cylindrical rim 2'7 and a central shaft 23 by means of which the drum is rotatably mounted. The drums it? and 21 have their shafts 2-? disposed in bearing blocks 2?" which rest on shelves 311 rormed by the framework 15. Adjusting

screws

31 and 32 are provided for holding the bearing blocks 29 in suitably adjusted positions on the shelves Bil.

Each of the drums 17 to 2% is mounted with respect to the framework 15 by means of a pair of levers 33 located on opposite sides of each drum and each pivotally connected to the framework at 34. A bearing block 35 is carried by each of the levers 33 for receiving one end of the shaft of the associated drum, and an adjusting mechanism 36, of my suitable type, is provided for adjustably fixing the end of each or the levers 33 with respect to the framework 15. An endless belt 37 is disposed about the drums 16 to 21. fie belt 37 may, for example, be stainless steel or saw steel about .049 inch thick and may, for example, be about seven inches wide. A series of support rollers 38 carried by the framework 15 are provided beneath the upper pass of the belt 37 between the

drums

16 and 17, and a series of additional support rollers 39 carried by the framework 15 are provided beneath the upper pass of the belt 37 between the

drums

2 and 21.

The upper drum 22 is supported with respect to the, framework 15 by means of bearing blocks 40 which re-' ceive the shaft 23 of the drum 22 and which are disposed on shelves 4?. provided by the framework 15. Adjusting screws *42 and 43 carried by the framework 15 are provided for adjustably holding the bearing locks 49 in suitable positions on the shelve-s 41.

Each of the drums 25 to 25 is supported by means of a pair of support levers 44 located on opposite sides of each drum. Each support lever 44 is pivotally mounted at 45 with respect to the framework 15 and each lever 44 carries a journal block 46 for receiving one end of the shaft 2-8 of the associated drum; A piston-cylinder assembly 47 connected to any suitable source of fluid pressure, such as compressed air, is provided for applying a force on each of the levers 44 tending to rotate the lever downwardly about its pivotal connection 45. A stop mechanism 48 of any suitable construction, comprising, for example, a selectively operable screw 49 having a nut t) on it in contact with a portion of a lever 44 may be provided for adiustably holding each lever in any selected position, the screw 49 and nut 54) holding the lever against the action of the associated piston-cylinder assembly '47.

Journals 46 are also provided for the drum 26 and are carried by means of levers 51 pivotally mounted at 52 with respect to the framework 15. A piston-cylinder assembly 47 acts on each lever 51, and stop mechanisms 53 similar in basic construction to the stop mechanisms 48 may be provided for the levers 51.

A belt 54 is provided about the drums 22 to 26, and this belt may be of the same width and construction as the belt 37. A relatively narrow belt 55, which may be of the same material as the

belts

37 and 54, but which may be, for example, about one inch wide, assuming that the belts 3'7 and 54 are seven inches wide, is provided about the belt 54. The narrow belt 55 is held spaced with respect to the surface of the belt 54 at one end of the apparatus by means of an auxiliary roller 56 which is fixed with respect to the framework 15. The narrow belt 55 is also held spaced with respect to the drum 26 at the other end of the apparatus by means of another auxiliary roller 57 positioned adjacent the drum 25 and carried by the framework 15. The roller 57 is so positioned that the

belts

55 and 37 have a relatively small angle b between them.

The apparatus above described is particularly suitable for compressing articles of yieldable material having the form of a rectangle parallelepiped, the cross sections of which are rectangles. Such an mticle may be a stack 53 of interfolded facial tissues 59 (see FIG. 9) of creped tissue paper. which stack is substantially compressible to reduced height. The apparatus above described is disclosed and claimed in the co-pending application of Charles T. Banks, Serial No. 235,645, filed November 6, 1962, for Papermaking Machine.

In the operation of the compressing device shown in FIG. 1, such an article 58 may be placed on the belt 37 at the intake end of the apparatus, which is its left end as seen in the figure, on the exposed part of the belt 37, approximately beneath the roll 56. The drums 16 to 26 are driven by any suitable driving mechanism so that the

belts

37 and 54 travel in the direction indicated by the arrows A. As will be observed, the

drums

23 and 17, the drums 24 and 13, the

drums

25 and 19, and the drums 26 and 28 form vertically disposed pairs which have nips between them; and these hips are successively of less thickness, so that the

upper belts

54 and 55 and the lower belt 37 approach each other in the nips between the respective upper and lower drums closer at the discharge end of the apparatus which is its right end as seen in FIG. 1. The product 58 moves along with the belts in the direction A between the upper and lower drums, and as it passes through the nips between the pairs of upper and lower rolls, it is progressively compressed to a greater and greater extent until it moves away from between the

rolls

26 and 26 onto the exposed portion of the lower belt 37 at the discharge end of the machine. The product 58 has thus been compressed substantially from its condition in which it is placed on the belt 37, and assuming that the product 58 is made up of folded creped facial tissues, it retains a permanent reduced height so that the facial tissues as a stack may be packed into substantially thinner cartons than would otherwise be necessary.

The narrow belt 55 is utilized to prevent the adherence of the top sheet of each stack of tissues to the relatively wide upper belt 54. Stacks of facial tissues when compressed commonly collect a static electricity charge on them so that the top sheet of the stack tends to adhere to an upper belt, and the narrow belt 55 has the relatively small angle b with respect to the belt 37 at the discharge end of the apparatus so that the belt 55 draws off the top tissue with respect to the belt 54 but is sulficiently narrow so that in itself it does not cause adherence of the upper sheet to itself.

As will be hereinafter described more fully, the first pair of

drums

23 and 27 are sufiiciently spaced so that their principal function is to drive the air out of a stack of tissues 58, and the succeeding pairs of drums take the principal load in compressing the tissues. FIGS. 2, 3, 4, and 5 may be referred to for detailed showings of the. manner in which the last three pairs of drums function to compress a stack of tissues, these figures showing, for example, the

drums

19 and 25. As will be observed -from FIG. 2, the upper and

lower belts

54 and 37 are in contact with the peripheries of the

drums

19 and 25, and the illustrated tissue stack 58 is approaching the nip between the drums traveling in the direction A. The

belts

54 and 37 in their :free positions, before a tissue stack has been positioned on the lower belt 37 to move through the apparatus, are shown as 54' and 37, and it will be observed that the

belts

54 and 37 are moved substantially apart by the tissue stack 58.

FIG. 3 illustrates the tissue stack 5% entering the nip between the drums '19 and 25, and it will be observed from this figure that the upper belt 54 in contact with the trailing parts of the tissue stack 58 is bulged outwardly due to the outward force exerted by the stack 58. PEG. 4 shows the tissue stack 58 still farther into the nip between the

rolls

19 and 25, and FIG. 5 illustrates the tissue stack '58 approximately halfway through the nip between the rolls 19 and -25. ln the FIG. 5 condition, the tissue stack still bulges the upper and

lower belts

54 and 37 outwardly at the entrance end of the nip between the rolls, but the tissue stack has taken a relatively permanent set as it passes through the nip so that the

belts

37 and 54 at the discharge end of the nip are only slightly farther apart than the thickness of the nip.

The compressing apparatus illustrated in FIG. 6 is substantially the same as that illustrated in FIG. 1, except that one pair of the compressing rolls has been omitted. The FIG. 6 compressing apparatus includes the lower drums 17a, 13a, and 2942 corresponding to the

drums

17, 18, and 2% and

upper drums

23a, 24a, and 26a corresponding to the

drums

23, 22, and 25. The lower drums also include end drums 16a and 21a, and the belt 37a is disposed about the drums 16a, 1%, 13a, 29a and 21a. The upper drums also include an upper drum 22a, and the upper belt 54a is disposed about the

drums

22a, 23a, 24a, and 26a. The narrow belt 55a extends around these upper drums and also the small

sized rolls

56a and 57a. The FIG. 6 form of apparatus functions in substantially the same manner as the FIG. 1 form except that a fewer number of compressing nips are utilized.

The 7 form of compressing apparatus is basically the same as the forms above described except that only two pairs of compressing drums are utilized instead of the three pairs in the FIG. 6 form and the four pairs in the FIG. 1 form. The FIG. 7 form of apparatus iricludes lower compressing drums 17b and 2%, respectively, having nips with upper compressing drums 23b and 26b. Bottom end drums 16b and 21th are provided in addition to the drums 17b and 2%, and the lower belt 37!: extends around the lower drums. An upper drum 2!) is also provided, and the upper belt Sb extends around the three upper drums. An auxiliary belt 551) extends around the upper three drums and also the end rolls 56b and 571; corresponding to the rolls '55 and 57. An article 53 is compressed by the PEG. 7 form of apparatus in the same manner as by the forms of the compressing apparatus previously described except in this case only two compressing nips are effective on the product.

The FIG. 8 form of apparatus utilizes only one pair of compressing drums, namely the drums 2% and 25c corresponding to the drums 2t) and 2.6 in the first illustrated form of the compressing apparatus. End drums 16c and 210 are also utilized, and the bottom belt 370 extends around the three lower drums. An upper drum 220 is also provided, and the upper belt 540 extends around the two upper drums. The auxiliary belt 550 extends ar and the upper two drums and also about the two and rolls 56c and 57c. The FIG. 8 form of apparatus functions in substantially the same manner as those forms previously described except that only the single compressing nip is effective on the product 58.

The invention is particularly adaptable for use with facial tissues 59, the sheets of which have a. basis weight of about 6 to pounds per ream of 2880 square feet (drier basis weight uncreped). Still more particularly, it is contemplated that the basis weight of the sheets may be about 7.6 pounds per ream. Each individual tissue preferably comprises two plies of such sheets, and the tissues are folded, such as being interfolded. The furnish used for the paper is bleached by conventional processes so as to remove any color material as well as other impurities usuflly removed by such bleaching processes. in addition, no sizing is added to the furnish so that the tissues are quite absorbent, particularly in View of the light basis Weight of the sheets.

The paper sheeting of which the facial tissues are composed may be made on a conventional paper-making machine of the type particularly suitable for use in making lighhveight sheets. The paper web manufactured by the machine is doctored 05 a Yankee drier drum constituting the terminal end of the papermaking machine; and preferably the web under these conditions has a moisture content in the range of three to five percent. The moisture in the web may be determined by conventional measuring methods such as by weighing the web prior to complete voiding of moisture from the web as by heating and subsequent to such evacuation. The doctor blade which doctors the web oil the drier drum of the machine crepes the web to a certain extent, and this creping may be on the order of percent; that is, the web is decreased in length by the doctor blade to less than half its length when in posit-ion on the drier drum of the machine. For this degree of creping, the web has a crepe ratio of 2.2., the crepe ratio being the length on the drier divided by the final length. In this case, one foot of web on the drier has been longitudinally compressed to 5 /2 inches, so that the crepe ratio is 2.2. The doctor blade in its action crinkles the web in creping it, producing peaks and valleys in the web, with the peaks being relatively sharp and high compared to the thickness of the web.

Subsequent to being creped from the drier, the web is calendered and is stretched, and the total stretching is preferably such as to decrease the creping from the 2.2 ratio previously mentioned to about a 1.2 ratio. For the Web having a length on the drier of one foot and shortened by creping to a length of 5 /2 inches, the Web in being calendercd is stretched back to a length of 10 inches so that its crepe ratio is now 1.2 (one foot drier length divided by 10 inches final length), and this ratio may well vary in the range of 1.05 to 1.30. The estretching of the web by the calender and the calendering action by the rolls of the calender acting with pressure on the web as it passes between the rolls have the effect of rendering the tissue quite soft and limp, so that the tissue has these desirable qualities for use as a facial tissue.

Subsequent to calendering, the tissue may be cut and interfolded so as to form the tissue stacks 58. The cutting and interfolding may be by any suitable conventional apparatus (not shown). If desired, moisture may be added to the tissues prior to their being interfolded. For storage and usage at ordinary humidities and temperatures, it has been found that the tissues have approximately 5 /2 percent moisture content to be in equilibrium under these conditions; and, therefore, the tissues are preferably provided with a moisture content of 5 /2 percent :1 percent prior to interfolding.

Compressing of the tissue stacks 5% by any of the machines previously described has the efiect of providing tissues of improved quality. The compressed tissues are desirably soft and limp, and they are smoother than prior uncompressed tissues, due to the fact that the sharp peaks produced by the creping have been dulled or depressed by the compression. The tissue stacks me each packed within a carton prior to delivery to the consumer, and some clearance is provided between the top of the stack and the top of the carton. The tissues thus expand within their cartons, allowed by the difference in height between the tissue stacks and cartons, during the storage period of the stacks after cartoning; and this reexpansion results in softer tissues. Although the peaks due to the creping tend to again rise with the release of interfacial bonding that occurs during storage, the original condition of high peaks of crepe is never again reached, so that the tissues remain smoother.

The compression also produces stacks of tissue that have a substantial uniform height which is substantially 1 ss than hei hts of previous uncompressed tissue stacks. These reduced height compressed stacks thus allow the use of cartons or" substantially less height for packing the tissue stacks. For example, tissue stacks of 260 tissues or 460 sheets which have been interfolded so as to produce stacks having a cross section substantially half the size of each individual ply, when compressed according to the Lvention, have heights of approximately 2%, inches after storing and aging of two weeks or more so that the stacks may be packaged in cartons of 2 /2 inches height, while the same number of interfolded tissues without compressing required cartons of four inches i height.

The following table sets forth concisely the thicknesses per inch and the densities that have been found to 7 after this re-expansion are indicated.

occur in tissue stacks compressed according to the teachlngs of'the present invention:

Tissues Plies Thiclzl fi i Thickuesses Density (2-p1y) messes per inch (gm/cu. inch) 1n0 200 400 1 /3 1 to 1%. 400 to 275 3.95 to 2. 75 2c0 400 200 2% z to 2% 400 m 355 3.95 m 3.51 300 600 1,200 3% 3 to 3% 400 to 243 3.95 to 3.39

Referring to the above table, in explanation, the

thicknesses lists the total number of thicknesses in 9 each stack which is twice the number of sheets or plies due to the fact that each tissue is folded over on itself in the stack. In the column entitled thicknesses per inch, the number of thicknesses per inch of stack height It will be observed that the number of thicknesses of paper per inch of stack height varies from 400 to 278. The density of the re-expanded stacks is in the Density column of the table and is in grams per cubic inch. It is to be noted from the table that the densities vary from 2.75 grams per cubic inch to 3.95 grams per cubic inch. The tissue stacks, according to the table, have heights (the stacks being unrestrained and exerting substantially no pressure on theircartons), from 1 inch to 1 inches, 2 inches to 2% inches and 3 inches to 3 /2 inches, respectively. The densities are given for the paper in bone. dry condition and if measurements of these tissues are made at various moisture contents, the densities measured, of course, will be greater. densities between 2.75 and 3.95 grams per cubic inch, the densities will range between 2.91 grams per cubic inch to 4.19 grams per cubic inch at 6 percent moisture content. The moisture contents are on the basis of weights, the weight of a stack including the weight of the moisture being used as the basis. 6 percent moisture content, for example, indicates that the moisture by weight amounts to 6 percent of the Weight of the stack prior to removal of moisture therefrom. Although the figures given in this table are considered important regardless of variations in basis weight and crepe ratio, they are considered particularly important for a final crepe ratio of about 1.2 and a drier basis weight of about 7.6 pounds per ream of 2880 square feet.

In order to. produce the tissue stacks having the various number of thicknesses per inch and densities listed in the abovetable, it has been found that the compressing apparatus illustrated in FIG. 8 should have the predeter- For example, in lieu of the 4 mined nip thicknesses between the drums 26c and 26 and, more particularly, between the belts 37c and 540 in a vertical plane passing through the centers of the two drums 2th: and 260, which are illustrated by curves A and B in FIG. 10. If gaps between the

belts

37c and 54c within; the nips between the drums Ztlc and 26c as set forth in curve B are utilized, the relatively small densities of tissue in the vicinity of 3.95 grams per cubic inch will be obtained, while if the gaps denoted by the curve A in FIG. 10 are utilized, densities of tissue stacks of about 2.75 grams per cubic inch will be obtained. If gaps as illustrated by curve C in FIG. 10 are utilized, curve C denoting a satisfactory average operating gap level, densities of the resulting tissue stacks between 2.75 and 3.95 grams per cubic inch will be obtained.

It will be observed from a study of curves A, B, and C in FIG. 10 that the gaps in the nips between the rolls 'Ztic and 260 increase for obtaining these timue densities as the moisture in the stacks of tissues increases. In other words, less pressure and a larger gap are successful in obtaining the same tissue densities if the moisture content of the tissue stack is higher than if the moisture content is lower. For example, at 4.0 moisture content, according to curve B, a gap of about .44 inch for a 400-ply tissue stack would be required to obtain the same results that a gap of .70 inch will produce if the moisture content of the tissue stack is 10 percent.

With the other illustrated machines, having a plurality of compressing nips through which the tissue stacks are passed, being utilized, gaps between the opposed drum pmrs may be greater to obtain the desired increased density product. If a plurality of equal gaps are used with the machine illustrated in FIG. 1, for example, the gaps to obtain the densities of 2.75 grams per cubic inch in the tissue stacks are illustrated by the curve D in FIG. 10. Obviously as the gaps are reduced in thickness toward the curvcs A, B, and C, the stack densities will increase.

In general, it is contemplated that in a multinip compressor, the thicknesses of the nips between the opposed compressing drums shall preferably decrease from the intake end of the machine to the discharge end. The curves A, B, C, and D, in this case, are applicable particularly to the thinnest nip between the pairs of compressing drums. If the thickest compressing nips are relatively great compared to the thinnest gap between the pairs of the compressing drums, the compressing apparatus will approach in action that of the single gap machine iilustrated in FIG. 8. On the other hand, if the gaps of the pairs of compressing drums are more uniform, then the gaps required between all of the pairs of compressing drums may be thicker and closer to those denoted by the curve D.

Thus, in order to obtain the results set forth in the table given above, FIG. 10 should be followed to determine the thickness of the thinnest nip between the pairs of compressing drums or, more particularly, between the belts within the nips; however, the exact curve between the limiting curves B and D that should be used will depend on the number of compressing nips and the thicknesses of the compressing nips effective on the tissue stacks prior to the last compressing nip which is preferably the thinnest.

As will be observed from FIG. 10, the curves A, B, C, and D are straight lines. The curve B extends from about .44 inch at 4 percent moisture to .75 inch at 11 percent moisture; the curve C extends from about .49 inch at 4 percent moisture to .81 inch at 11 percent moisture; the curve A extends from about .58 inch at 4 percent moisture to .97 inch at 11 percent moisture; and, the curve D extends from about .70 inch at 4 percent moisture to 1.17 inch at 11 percent moisture. The nip spacings illustrated in FIG. 10 are for 400 plies or 800 thicknesses of the tissues.

As examples of the gaps that may be provided between the

belts

37 and 54 within the nips between the pairs of compressing rolls in the FIG. 1 form of compressing apparatus and the corresponding belts in the other forms of apparatus, the following gaps may be menioned, which provide substantially the same stack densities: In the single nip machine illustrated in FIG. 8, the gap may be .55 inch; in the two-nip machine illustrated in FIG. 7, the gaps may be .65 inch and .58 inch; in the 3-nip machine illustrated in PEG. 7, the gaps may be .65 inch, .62 inch and .60 inch; and in the 4-nip machine illustrated in FIG. 1, the gaps may be 1.37 inch, .65 inch, .62 inch, and .60 inch. The tissues used with these gaps should preferably have a moisture content of 5 /2 percent, which is a moisture content of the tissues that corresponds with ordinary humidities and temperatures. As will be noted from PEG. l0, curves B and D indicate that compressing of 400 ply (800 thicknesses) tissue stacks may be accomplished by using gaps between .50 inch and .80 inch. it will be noted that in the 4-nip machine the first gap is decidedly thicker than the other gaps and thus the cfoon/2 feet of the first pair of compressing drums is negligible in that there are no changes in thickness in the last three nips of the machine as compared to the nips in the FIG. 6 form of the machine. In the FIG. 1 form, the first nip thus is utilized for squeezing air out of the stacks between the adjacent tissue plies.

The speeds of the machines illustrated in FEGS. 1, 6, 7, and 8 are not critical; it has been found that the machines may be run at belt speeds of 20 or 200 feet per minute or speeds therebetween, for example, without substantial change of the gap thicknesses while still obtaining the same stack densities. In one particular form of machine, compressing drums of 48 inches in diameter have been utilized, and it is contemplated that the drum diameters may be changed within quite wide limits while still utilizing the gaps previously mentioned in order to obtain the stack densities listed in the above table.

The illustrated compressing apparatus including one or more compressing nips has advantageously been found to provide facial tissue stacks of an enhanced quality and smaller permanent height so that the stacks may be packaged in cartons of reduced height. It is contemplated that the tissues shall preferably be interfolded, and, therefore, the cartons utilized may be of a conventional type having slots in upper panels through which the tissues dispense one at a time. The permanent stack heights are such as to provide a clearance between the tops of the stacks and the slotted panels of the car-tons even after prolonged periods of storage and tissue stack height regrowth, so that the tissues may be dispensed without binding within the cartons.

I wish it to be understood that the invention is not to be limited to the specific methods and arrangements shown and described, except only insofar as the claims may be so limited, as it will be apparent to those skilled in the art that changes may be made without depart-ing from the principles of the invention.

What is claimed is:

1. A method of compressing stacks of creped paper tissues comprising, passing the stacks of tissues through the nip of a pair of rotatable cylindrical drums while the drums are rotating, said nip having a thickness depending on the moisture content of the tissues with the thickness varying between lower limits of .44 and .75 inch per 800 tissue thicknesses respectively at 4 percent and 11 percent moisture content of the tissues and proportional lower limits at moisture contents between 4 per cent and 11 percent and upper limits of .58 and .96 inch per 800 tissue thicknesses respectively at 4 percent and 11 percent moisture content of the tissues and proportional upper limits at moisture contents between 4 percent and 11 percent.

2. A method of compressing stacks of creped paper tissues comprising passing the stacks successively through a plurality of nips of pairs or" rotatable cylindrical drums while the drums are rotating, said nips having thicknesses depending on the moisture content of the tissues with the thicknesses varying between lower limits of .44 and .75 inch per 800 tissue thicknesses respectively at 4 percent and 11 percent moisture content of the tissues and proportional lower limits at moisture contents between 4 per cent and 11 percent and upper limits of .70 and 1.17 inch per 800 tissue thicknesses respectively at 4 percent and 11 percent moisture content of the tissues and proportional upper limits at moisture contents between 4 percent and 11 percent.

3. A method of compressing stacks of creped paper tissues comprising passing the stacks of tissues through succcessive nips formed by a plurality of pairs of rotatable cylindrical drums while the drums are rotating, said successive nips decreasing in thickness and having thicknesses depending on the moisture content of the tissues with the thicknesses varying between lower limits of .44 and .75 inch per 800 tissue thicknesses respectively at 4 percent and 11 percent moisture content of the tissues and proportional lower limits at moisture contents between 4 percent and 11 percent and upper limits of .70 and 1.17 inch per 800 tissue thicknesses respectively at 4 percent and 11 percent moisture content of the tissues and proportional upper limits at moisture contents between 4 percent and 11 percent.

4. A method of compressing stacks of creped paper tissues comprising passing the stacks of tissues through a plurality of successive nips formed by pairs of rotatable cylindrical drums while the drums are rotating, said tissues having approximately 5 /2 percent moisture content and the thicknesses of said nips being between .50 inch and .80 inch.

5. A method of compressing stacks of creped paper tissues having a basis weight (uncreped) of 7 to 8 pounds per ream of 2880 square feet comprising passing the stacks of tissues through a plurality of nips formed by pairs of rotatable cylindrical drums While the drums are rotating, said nips having thicknesses depending on the moisture content of the tissues with the thicknesses varying between lower limits of .44 and .75 inch per 800 tissue thicknesses respectively at 4 percent and 11 percent moisture content of the tissues and proportional lower limits at moisture contents between 4 percent and 11 percent and upper limits of .70 and 1.17 inch per 800 tissue thicknesses respectively at 4 percent and 11 percent moisture content of the tissues and proportional upper limits at moisture contents between 4 percent and 11 percent.

References Cited in the file of this patent UNITED STATES PATENTS 1,432,426 Taggart Oct. 17, 1922 1,989,048 Winter et a1 Jan. 22, 1935 2,960,023 Greiner et al Nov. 15, 1960 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N00 3 l20 l72 February 4 1964 Kenneth Mo Enloe It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 7 line 64 strike out the relatively small"; column 8, line 59, for "menioned" read --menti0ned --Q Signed and sealed this 10th day of November 1964,

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Aitesting Officer Commissioner of Patents

Claims

4. A METHOD OF COMPRESSING STACKS OF CREPED PAPER TISSUES COMPRISING PASSING THE STACKS OF TISSUES THROUGH A PLURALITY OF SUCCESSIVE NIPS FORMED BY PAIRS OF ROTATABLE CYLINDRICAL DRUMS WHILE THE DRUMS ARE ROTATING, SAID TISSUES HAVING APPROXIMATELY 51/2 PERCENT MOISTURE CONTENT AND THE THICKNESSES OF SAID NIPS BEING BETWEEN .50 INC AND .80 INCH.