b'As Crepe Frequency increases, the dimensions of the sheet also need to be incorporated on a microscopic level. Figure 5 shows the relationship between the Crepe Frequency and the ratio of Crepe Length (1/CF) to sheet thickness (80 microns).At low crepe counts, the crepe length is much larger than the sheet thickness and the sheet can bend or buckle as shown. However, as the crepe count approaches 30 crepes/cm, the ratio of crepe length to sheet thickness approaches 5:1. At this point the sheet cannot easily buckle.Instead, the sheet must expand or explode in the z-direction leadingFigure 5. Crepe frequency vs crepe length.to de-densification of the sheet.De-densification is accompanied byoccurs. Although measured tensilesmoothness, higher reel bulk, increased bulk, tensile breakdown,will drop, the stiffness, sheet densityhigher base sheet density, increased stretch/crepe, softness andand surface smoothness will movegreater loss of bulk through void volume. In stratified sheets wein softness-reducing directions. Thiswinding and converting.can often see sheet delamination 7. is attributed to a combination of theMore open pocket angle larger macrofold production due to thehigher crepe counts, higher This change in the way the crepebuildup of the sheet within the crepingtensile, lower stiffness, higher structure is created changes the basepocket. smoothness, lower reel bulk, sheet characteristics as follows: lower base sheet density, lower Crepe structure: as mentioned above,loss of bulk through winding and Tensile breakdown: Generally, closingopening the pocket promotes a finerconverting.the pocket angle increases tensilecrepe structure by allowing the sheet breakdown. This can be easilyto clear the shelf more quickly. TheIn order to maximize bulk generation, rationalized with the understandingcaveat with promoting a more openthe papermaker must maximize sheet that a more open pocket presentspocket for the benefits associated withexplosion via adhesion uniformity. a blade shelf to the incoming sheetthe finer crepe are that the impactLack of adhesion uniformity between which is angled away, allowing theon tensile breakdown, sheet handlingthe sheet and the Yankee will sheet to exit the creping pocketopening theand bulk targets must be dealt with. result in coarser crepe, forcing more quickly and efficiently. In this[creping]Creping with a more open pocketan opening of the pocket to meet manner, less of the kinetic energypocketnecessitates a greater level and asurface smoothness requirements is transferred into the fiber web. Itpromotes ahigher uniformity of adhesion of theand a potential step change loss is here that two competing theoriesfiner crepesheet to the Yankee coating. in bulk. A good explanation of the collide: higher energy creping instructure bymechanism and importance of the closed pocket should produceallowing theIn general, it can be assumed that: uniform adhesion can be obtained a more exploded sheet structuresheet to clearMore closed pocket anglevia Better Bond, Softer Tissue. Tissue which has higher bulk and greaterthe shelflower crepe counts, lowerWorld Magazine, Feb.-Mar. 2003. clothlike softness, but this is not whatmore quickly.tensile, higher stiffness, lowerJohn Stitt.TISSUE TECHNOLOGY INTERNATIONAL25'