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 food containers having deep sidewalls, a spray coating system includes a first nozzle for applying a full cone spray pattern to the bottom surface of the container, and a second nozzle for applying a hollow cone spray pattern to the inside surfaces of the side walls.
1. A method of manufacturing a microwave bowl of the type characterized by a substantially flat, circular, bottom region bounded by a circumferential sidewall, comprising the steps of:
providing a wire mesh mold approximating the shape of the bowl;
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 bowl;
transferring the bowl from the press to a coating station; and
applying a topical oil barrier layer to at least a portion of the bowl at the coating station;
wherein the coating station comprises a spray system and a conveyor configured to move the bowl along a direction of travel underneath the spray system, and the spray system comprises: a first nozzle configured to discharge a full cone spray pattern onto the bottom region of the bowl; and a second nozzle configured to discharge a hollow cone spray pattern onto the inside surface of the circumferential sidewall.
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 oil barrier layer comprises about 27.5% solids in a water solution.
5. The method of claim 4 , wherein the solids comprise a tackiness component and an emulsifier.
6. The method of claim 1 , further comprising the step of:
moving the spray system along the direction of travel such that: i) the first nozzle is disposed above and remains stationary with respect to the bowl for a first predetermined period of time; and ii) the second nozzle is disposed above and remains stationary with respect to the bowl for a second predetermined period of time.
7. The method of claim 6 , wherein the first period of time is one of: i) greater than; ii) equal to; and iii) less than the second period of time.