Jargon is used within just about any industry and is often confusing to newcomers. The tissue market is not excluded. The following is a list of common terms and definitions used within the tissue industry by operators, management and vendors.
What is a Yankee dryer?
A Yankee dryer is a large, steam-heated, pressure vessel used in the production of tissue grades. Two critical operations occur at the Yankee dryer: (1) the sheet of the tissue is dried to its final moisture target and (2) it is creped by the creping doctor.
Yankee chemistry, adhesives, and related chemicals
Yankee chemistry refers to a particular material sprayed directly onto a Yankee dryer. The Yankee chemistry is used to achieve functional properties of the tissue and towel, and have a large impact on the production process. Yankee chemistry including adhesives, modifiers, releases, phosphates, and extenders are all typically sprayed directly onto a Yankee dryer by a spray boom shower.
Crosslinking adhesive – A low pH adhesive that reacts quickly and forms a thin, hard film and will not rewet. Wet strength resin is an example of a crosslinking polymer.
Dead cat adhesive – A neutral pH adhesive that will not crosslink and is rewettable.
Extender – A substance added to another substance to increase its volume or bulk. Polyvinyl alcohol (PVOH), Polyvinylpyrrolidone (PVP) or other low cost molecules that add some nature of adhesion or film forming to the spray on chemistry. Extenders are always used when Through-Air Drying (TAD) technology is used.
Hard coating – A thin, quick-setting coating that uses a crosslinking adhesive.
MAP – Monoammonium Phosphate. A white, crystalline, moderately water-soluble compound. A low pH source of phosphate for creping chemistry typically fed as a 20% active product.
Rewettable adhesive – A soft adhesive that will not crosslink and can be removed from the Yankee dryer with excess water or moisture streaks.
Soft coating – A thick coating film that is soft and rewettable.
Yankee adhesive – The glue or stick added in the spray boom shower to make the tissue develop a desired characteristic.
Yankee coating – The material attached to the Yankee shell which is usually a haze or white build up that makes a fine dust when removed.
Yankee modifiers and releases
Yankee chemistry has three major functions for tissue production: protection of the Yankee from wear, proper adhesion at the blade to provide the required crepe structure, and allowing the sheet to be removed from the Yankee in the desired form. Without the proper mix of chemistries sprayed on the Yankee, the sheet at the creping blade would be nothing but debris.
Modifiers – Non-oil products added to the spray boom shower to change or modify the nature of the film developed by the adhesive. The modifier film will react faster and be thicker than films created by an oil release.
Phosphates – A salt or ester of phosphoric acid, such as Monoammonium Phosphate (MAP) or Tetrapotassium Pyrophosphate (TKPP), used to prevent corrosion and promote adhesion when added to the spray boom shower. Typically used on metallized Yankee surfaces.
Plasticizer – A group of substances used in materials to impart viscosity, flexibility, softness, or other properties to the finished product. Additives that increase the plasticity or fluidity or a material. A glycerin based product used to soften harder adhesive films.
Release – The lube that helps the sheet release at the blade and provides lubrication for the creping process. These products are usually mineral oil based and are key in preventing fires after blade changes.
Spray Boom Shower – The shower used to spray the chemistry on the Yankee. Typically a 2 to 3% strength solution preheated to 110°F to 130°F is used. This shower typically uses a double or triple over lap and can add up to 10% of the drying load with the water added.
This is the first post in a two part series about common definitions in the tissue industry. Watch later this month for Chapter 2 and specifics for strength related chemistry and operational definitions.