METHODS, APPARATUS, AND CHEMICAL COMPOSITIONS FOR SELECTIVELY COATING FIBER-BASED FOOD CONTAINERS
Methods and apparatus for vacuum forming and subsequently applying topical coatings fiber-based food containers. The slurry includes one or more of an embedded moisture barrier, vapor barrier, and oil barrier, and the topical coating comprises one or more of a vapor barrier, a moisture barrier, an oil barrier, and an oxygen barrier, for example polyvinyl alcohol, sugar alcohol, citric acid, and cellulose nanofibrils.
1 . A method of manufacturing a microwave container of the type characterized by a bottom region bounded by a circumferential sidewall, comprising the steps of:
providing a wire mesh mold approximating the shape of the container;
preparing an aqueous fiber based slurry comprising at least one of hardwood virgin fiber and softwood virgin fiber;
adding an embedded moisture barrier to the slurry;
immersing the mold in the slurry;
drawing a vacuum across the mold within the slurry until a desired thickness of fiber particles accumulates at a surface of the mold;
removing the accumulated particles from the mold;
drying and pressing the accumulated particles in a press to thereby form the container;
transferring the container from the press to a coating station; and
applying a topical barrier layer to the inside surfaces of the container at the coating station.
2 . The method of claim 1 , wherein the embedded moisture barrier comprises 2%-5% alkyl ketene dimer (AKD).
3 . The method of claim 1 , further comprising:
adding a dry strength additive to the slurry, wherein the dry strength additive comprises 0.5%-4.5% starch.
4 . The method of claim 1 , wherein the topical barrier layer comprises about 6.5%-8.5% solids in a water solution.
5 . The method of claim 4 , wherein the topical barrier comprises polyvinyl alcohol, sugar alcohol, citric acid, and cellulose nanofibrils (CNF).
6 . The method of claim 4 , wherein the topical barrier comprises 30%-40% polyvinyl alcohol, about 30%-50% sugar alcohol, 9%-18% citric acid, and 4.5%-6.5% CNF.
7 . The method of claim 4 , wherein the topical barrier comprises about 36% polyvinyl alcohol, about 45% sugar alcohol, about 13.5% citric acid, and about 5.5% CNF.
8 . The method of claim 1 , wherein the topical barrier layer comprises about 6%-8% solids in a water solution.
9 . The method of claim 8 , wherein the topical barrier comprises 30%-40% polyvinyl alcohol, about 30%-50% sugar alcohol, 9%-18% citric acid, and 3%-12% CNF.
10 . The method of claim 8 , wherein the topical barrier comprises about 38% polyvinyl alcohol, about 38% sugar alcohol, about 14% citric acid, and about 10% CNF.