Remoistenable adhesives

Remoistenable adhesives are applied as water-borne adhesives and then dried. When dry, they have little or no tack. To apply the tape or label to the box, bottle, or other package structure, water must be applied to reactivate the adhesive. Then the full strength of the bond will develop as the water is removed. Such adhesives are commonly used for adhering paper to paper or to other materials. 

Remoistenable adhesives are water-based compositions that dry to a non-tacky film that may have its adhesive power regenerated by the absorption of water. Envelope gums are a familiar example. 

Discrete particle, flat gumming, solvent-based adhesives are another method of making remoistenable adhesives. The cold-water-soluble material (usually a dextrin) is suspended in a solvent and applied to the paper and dried. Since the dextrin is not soluble in the solvent, it is deposited in discrete particles. On contact with water, the dextrin swells and will glue two pieces of paper together. The dextrin is usually used at 40% solids and a viscosity of 1000... 

The early polyvinyl acetate emulsions were homopolymers protected with partially hydrolyzed polyvinyl alcohol. These high molecular weight polymers had great strength and set rapidly to hard, homy films. Today, these homopolymers are the workhorses of the industry due to their excellent adhesion to uncoated paper, wood, concrete, ceramics, and glass. In addition, they exhibit a fair degree of water sensitivity. This allows them to be easily cleaned from equipment and permits their use in remoistenable adhesives. 

Uses Binder, carrier, compounding agent, dispersant, stabilizer, protective colloid in polymerizations for textiles, paper, cement/plaster additive, films, ceramics, molded prods., mold release useful for remoistenable adhesives, wood adhesives, envelope, label, bookbinding, padding, carton sealing applies. 

The main use for these adhesives is the paper industry where they are used in multiwall bags, corrugated paper, etc. Dextrin, which is dry roasted starch, is used in remoistenable adhesives. 

Natural resins have been used as adhesives. Shellac is used in bonding mica splittings to form micaboard and used in abrasives. Gum arable is used in remoistenable adhesives. Copal gums are used in spirit-soluble lino cements. 

---