A Study of the Relative Effectivness of Four Insolubilizing Agents in Starch-Latex and Protein-Latex Coatings

The process of offset lithography requires several unique characteristics in paper. One of these is an ability in the sheet surface to accept water without deteriorating. Offset coatings commonly use starch and protein in their binder systems. These adhesives are inherently water sensitive. The characteristic of water resistance in coated grades can be obtained through the use of crosslinking agents. Among the more commonly used are unreaformaldehyde, melamine-formaldehyde, and glyoxal. A more recent development involves the use of ammonium zirconium carbonate. Through the years many studies have examined the effects of various insolubilizing agents in starch coatings. Most of these have analyzed only one agent and have all but excluded protein coatings. A need seemed to exist for a comparative analysis of the commonly used insolubilizing agents in both starch and protein coatings. The lack of literature concerning ammonium zirconium carbonate suggested that its analysis should be included. A series of starch and protein based coatings were prepared using 16 parts adhesive and 100 parts clay. Styrene-butadiene latex was included in both coatings. Urea-formaldehyde, melamine-formaldehyde, and glyoxal were added at levels of 5, 7, 9, 11, and 13 percent based on dry starch or protein. Ammonium zirconium carbonate, due to its purported superior insolubilizing efficiency was added at levels of 1, 3, 5, 7, and 9 percent. A four pound coat weight was applied by a hand-held blade drawdown technique to a 45 pound base sheet. Testing of water resistance was carried out via an on-press technique. The samples were allowed to cure two months before testing. The samples were allowed to cure two months before testing. Results showed that urea-formaldehyde produced the highest degree of water resistance. Ammonium zirconium carbonate was competitive with UF and MF resins when added at levels greater than 5%, even when those agents were added at higher levels. Glyoxal harmed starch-latex coating water resistance. Analysis of the protein-latex coatings proved inconclusive