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Sunday, January 12, 2014

Thickness Measurement for Tissue

Thickness (or caliper) is a very important parameter in tissue production and converting.

One technique that can aid in the process is acquiring a thickness profile.  Getting a thickness profile across the machine enables the operator to pinpoint locations on the tissue machine where thickness varies.  This knowledge helps eliminate downstream issues in converting.



TAPPI Test Method T580, "Thickness (caliper) of towel, tissue, napkin and facial products", has a modified (reduced) lowering speed of the platen and a modified (lower) measuring force to give data that enables better characterization of key features of a tissue, napkin, or towel grade.  Both of these changes prevent the measuring head from 'dropping' on the tissue resulting in inadvertent lower thickness readings.  This method also describes the procedure for measuring bulking thickness and variations in tissue paper and tissue products.

TAPPI T580 uses a relatively low pressure 2 kPa (0.3 psi) because of the collapsible structure of tissue paper. TAPPI T 411 “Thickness (caliper) of paper, paperboard, and combined board” uses a relatively high pressure 50 kPa (7.3 psi).

An essentially identical method is described in ISO 12625-3 “Tissue paper and tissue products -- Part 3: Determination of thickness, bulking thickness and apparent bulk density.” 


The Technidyne PROFILE/Plus Thickness is capable of measuring according to any of these standards. It also provides automatic profiling capability to provide more thorough data providing greater information for converting processes.

Contact Rodger Segelstrom or look at the Technidyne website for more information.

TISSUE BACKGROUND

Tissue paper is produced on a paper machine that has a single large steam heated drying cylinder (yankee dryer) fitted with a hot air hood. The raw material is paper pulp. The yankee cylinder is sprayed with adhesives to make the paper stick. Creping is done by the yankee's doctor blade that is scraping the dry paper off the cylinder surface. The crinkle (crêping) is controlled by the strength of the adhesive, geometry of the doctor blade, speed difference between the yankee and final section of the paper machine and paper pulp characteristics.

The highest water absorbing applications are produced with a through air drying (TAD) process. These papers contain high amounts of NBSK and CTMP. This gives a bulky paper with high wet tensile strength and good water holding capacity. The TAD process uses about twice the energy compared with conventional drying of paper.

The properties are controlled by pulp quality, crêping and additives (both in base paper and as coating). The wet strength is often an important parameter for tissue paper.