At the end of this module, you will be able to:
- History of Corrugating Adhesives
- Gelling of Starch
- Adhesive Application on a Corrugator
- Starch Adhesive Formulations
- Viscosity and Shear Force
- Controlling Viscosity
- Single Face vs. Double Face Adhesives
- Critical Bonding Variables
- Water-resistant Adhesives
The following key questions are answered in this module:
What are the main ingredients in a typical corrugating adhesive?
Contemporary corrugating adhesives typically contain a mixture of uncooked starch, caustic, borax, and water, suspended in a cooked starch paste.
Why are both cooked and uncooked starch used in corrugating adhesives?
The cooked starch acts as a thickener in the adhesive mixture supplied to a corrugator, while the uncooked starch acts as the actual adhesive in the corrugated board.
What is the definition of "gel temperature"?
"Gel temperature""is the temperature at which uncooked starch will hydrate and swell, or "gel," in water. It is this gelling of starch in water which allows it to act as a thickener and an adhesive.
Why is "high-shear" mixing used in the preparation of starch-based adhesives?
The viscosity (or resistance to flow) of a starch-based adhesive is greatly affected by shear, and viscosity affects how the adhesive transfers to and penetrates into medium and liner. High-shear mixing subjects the adhesive to shear early on to ensure a relatively stable viscosity. It also reduces prep time.
How are water-resistant corrugating adhesives made?
Water-resistant corrugating adhesives are made by adding a resin to the starch-based adhesive mixture. When this mixture is heated on the corrugator, the resin helps form bonds that are water resistant.
Below is a transcript of the video sample provided for this module:
The term "viscosity" refers to the ability of a liquid to flow. A thin, fast flowing liquid has a low viscosity, while a thick, slow flowing liquid has a high viscosity. Viscosity is important in corrugating adhesives because it effects how the adhesive transfers to the medium, and how it penetrates into the medium and liner. If the adhesive paste is too thin, or has low viscosity, the water in the adhesive will quickly wick into the medium, and there may not be enough water present for the uncooked starch to gelatinise. The board exiting the corrugater may be dry and brittle, with poor bonding. If the past is too thick, or has high viscosity, it won't transfer well to or from the glue roll, and once it transfers, it will tend to sit on top of the flute tips. Because it penetrates very slowly into the medium, this can lead to soft, wet board exiting the corrugater. Also, the thick paste can stagnate in areas of the glue pans, leading to jelling problems at the single facer and double facer glue units.
Use the additional resources and links below to learn more about this topic: