Chapter 2: Common Definitions in the Tissue Industry

Yankee Dryer CleanerAs mentioned in Chapter 1, jargon is used within just about any industry and is often confusing to newcomers. The tissue market is not excluded. The following is a continuation of the list of common terms and definitions published earlier this month used within the tissue industry by operators, management and vendors.

Strength related chemistry

These chemistries are used to add a functional property to the sheet that cannot be produced through the creping process. Wet strength is important to towels and napkins and is not developed without the addition strength chemistries.

CMC – Carboxymethylcellulose. A white, water-soluble polymer derived from cellulose, used as a coating and sizing for paper and textiles. Used for dry strength and as a charge scavenger in high dosage wet strength towel processes. Negatively charged product.

Dry strength – Tensile strength enhancement product. Glyoxyalated Polyacrylamide (GPAM) fed at a pH of 6 to 9. Starches and CMC are other dry strength products.

Temporary wet strength – A GPAM polymer. A low solids product with a short shelf life. Used in low pH (5 to 7) systems. Common in high-end bath tissue to reduce pilling.

Wet strength resin – A low pH (3 to 5) polymer that will crosslink as the pH rises and dries. The bonding with the fibers is permanent.

This next section of terms and definitions are functional properties or characteristics important for: softness or hand feel (see definition below) in bath or facial tissue; dry strength in all products; temporary wet strength for high end bath tissue; wet strength in bath, towel and napkin grades; getting the packaging to fit properly; brightness and dirt count for visual standards; and the end users.

Absorbency – The amount of water a sample will absorb in a given time or the time to absorb a given amount of liquid. Important for retail towel production.

Basis weight – Sometimes called the grammage or substance, this is the weight (mass) per unit. In Europe this is normally expressed as grams per square meter, gsm, or g/m2. The weight in pounds of a ream of paper of a basic size, usually 25 × 38 inches (63 × 96 cm) for book stock, 17 × 22 inches (43 × 55 cm) for writing stock, and 20 × 26 inches (50 × 66 cm) for cover stock.

Imperial basis weight ream size – The imperial measurement of ream size in tissue is pounds/3000 square feet. The metric measurement is grams per square meter (gsm). To convert imperial units to metric units, divide by 0.6.

Brightness – The measure of whiteness or lack of other colors in the sheet.

Bulk – The total thickness of eight sheets as measured and expressed in mils or microns.

CD tensile – Cross machine direction tensile strength.

Dirt count – The count or measurement of the total amount of dark materials imbedded in the tissue sheet.

Dispersability or flush test – Finished products are tested to see how quickly they break up when subjected to water and shear. Important for all bath tissues.

Dusting – The debris or dust that falls from converted tissue; a critical issue for bath and facial tissue.

MD tensile – Machine direction tensile strength.

MDS or stretch – Machine direction stretch is the length the sheet stretches before it breaks in the MD tensile test. Expressed as a percentage.

Hand feel – A panel of experts tests a sample and rates the tissue softness according to existing standards.

Pilling – A negative side effect to bath tissue when it is wetted and pieces stick to the   end user. This test is important to high-end bath tissue producers.

Tensile strength – The maximum stress a material can withstand while being stretched or pulled before failing or breaking. The resistance of a material to longitudinal stress, measured by the minimum amount of longitudinal stress required to rupture the material. The strength required to pull a test strip apart. The units vary but most will be ounces/3 inches, grams/3 inches, grams/1 inch or 25 mm.

Wet/dry strength ratio – The ratio of the wet tensile strength/dry tensile strength, typically expressed as a percentage. Important in retail towel production.

Wet tensile strength – Tensile strength after curing the sheet and wetting the strip. Cure at 105°C for five minutes. TAPPI STD T 456. Important to towel manufacturers.

Operational definitions

These terms are used by operations personnel to describe the equipment, processes, and products as used in tissue manufacturing.

Air side – The side of the sheet exposed to the hood air during the drying process.

Cases – Converting operations measure their production in cases produced. The case unit will vary in size by brand and grade.

Creping – Crinkling of paper during drying to produce a soft, elastic sheet – giving the tissue added thickness and absorbency. The collision the paper sheet on the Yankee has with the creping blade. This action on the sheet will produce more bulk and reduce the strength of the sheet. As the intensity of this collision increases, a sheet with higher softness and more bulk will be produced.

Creping doctor – The main doctoring unit on the machine where the tissue is creped.

Cut-off or skinner doctor – The doctor blade above the creping blade. It is loaded when the creping doctor blade is changed.

Cleaning doctor – This doctor is not installed on all machines and is used to clean the coating off the Yankee prior to the chemistry addition with the spray boom shower.

Chatter – To vibrate during cutting so as to produce surface flaws on the work. Damage in the Yankee surface from the doctor blade not riding smoothly in the Yankee coating.

eTAD – Technology developed by Georgia-Pacific. It is a hybrid dry crepe process that uses a TAD-type fabric to add structure to the sheet to make a more absorbent towel from recycled fibers.

Yankee side – The sheet side attached to the Yankee prior to creping and is typically the softest.

Through Air Drying (TAD) – A process for tissue drying with the paper web running over a perforated drum where hot air is blown through the web. Some TAD tissue papers are made without creping (un-creped through air drying- UCTAD). In addition, most machines incorporate a transfer from high-speed to low-speed rolls, which can have a similar affect as creping. Some TAD tissue papers are crepe finished using TAD machines which include a Yankee dryer. The bulk and functional properties are dependent on the type of TAD fabric and fibers used in the process. Yankee creping has little effect on the development of the sheet produced.

UCTAD – A TAD process without a Yankee.

Percent crepe   Yankee speed-reel speed divided by Yankee speed. A high quality bath can be 25%.

Crepe count or CBI – Crepe bars per inch. The counting of the surface bars on the Yankee side of the sheet.

Crepe ratio – Dryer speed/reel speed

Yankee basis weight – Actual sheet weight before creping occurs. Reel weight with the creping backed out or reel basis weight multiplied by the reel speed divided by the Yankee speed.

Sheet flying or loose – The sheet is poorly attached to the Yankee prior to blade and chemistry changes need to be made.

Sheet tight – The sheet is not releasing from the blade and release needs to be added or adhesive reduced to properly control the sheet.

To learn more about Kadant’s Yankee solutions, contact me at info@kadant.com.