Pulp-molded egg trays, due to their loose texture and unique egg-shaped curved surface structure, exhibit superior breathability, freshness preservation, excellent cushioning, and positioning effects. They are particularly suitable for the bulk transportation and packaging of various poultry eggs such as chicken eggs, duck eggs, and goose eggs. When using pulp-molded egg trays to package fresh eggs, the breakage rate of the eggs during long-distance transportation can be reduced from the traditional packaging’s 8%-10% to below 2%. Currently, relevant national authorities have organized enterprises to formulate the BB/T 0015-2020 “Pulp-molded Egg Trays” (draft for solicitation of opinions) for trial use by production enterprises and consumers. Poultry egg trays are divided into egg trays and egg cartons. Egg trays are mainly available in specifications such as 20-pack, 24-pack, 30-pack, 36-pack, etc. Egg cartons are available in specifications such as 4-pack, 6-pack, 8-pack, 10-pack, 12-pack, 15-pack, 18-pack, 20-pack, etc. The external surface of some egg cartons can be directly printed or labeled with waistbands according to user requirements to enhance countertop display and sales effectiveness.
Paper Pulp Molded Dry-Press Production Process
Raw Materials for Production: The raw material for the production of pulp-molded products is waste paper. For the production of disposable tableware and high-end paper packaging products for food, grass commodity pulp boards are generally used, and their processing technology is relatively simple. The majority of raw materials for producing paper-molded industrial packaging products, however, are waste paper. The domestically recycled waste paper collected through various channels has a very complex composition. It includes printing waste paper mainly composed of grass pulp and waste newspapers primarily made from mechanical pulp. Additionally, there are discarded old paper boxes with a mixture of grass and wood pulp. The quality of various types of waste paper varies significantly, resulting in considerable differences in the performance and appearance of the produced pulp-molded products. Different varieties of waste paper can also have a certain impact on the forming and drying processes of the paper-molded products.
Pulping and Beating: Waste paper or grass commodity pulp boards are fed into a hydraulic pulper to be re-pulped. Hydraulic pulpers are divided into vertical and horizontal types, with vertical hydraulic pulpers being more commonly used in current pulp molding enterprises. For the production of paper-molded industrial packaging products, horizontal hydraulic pulpers can also be used, with a pulp consistency of 5% to 8% during the pulping process. The advantage of horizontal hydraulic pulpers is that they only disperse paper fibers without cutting them, resulting in high pulping efficiency, short processing time, low power consumption, simple structure, and a small footprint. Moreover, they can handle waste paper with a high content of impurities and metal contaminants. After pulping, the pulp falls into a pulp storage tank. Adjusting to the appropriate consistency, it is pumped into batch pulpers or continuous refiners, beaters, or refining machines for beating. Alternatively, depending on production needs, the pulped material can be processed through a high-consistency reject separator, fiber dissolver, and twin-disc refiner for reject removal, fiber dissolving, and beating. The well-beaten pulp is then discharged into a pulp storage tank or a stock chest for further use.
Pulp Formulation: During the beating process, various raw materials can be quantitatively added to the pulping tank according to the designed pulp ratio. The pulp mixture is then treated with sizing agents and small amounts of functional additives. For instance, adding sizing agents improves the liquid permeability performance of paper-molded products. The commonly used sizing agents include rosin, paraffin emulsion, or rosin-paraffin emulsion. For pulp prepared from non-bonded waste paper, it is necessary to add rosin sizing equivalent to 3% of the bone-dry fiber mass of the pulp. For pulp prepared from bonded waste paper, rosin sizing should be added at a rate of 1.5% to 2%. Talc powder can also be added to the pulp as a filler to achieve a higher pulp retention rate. A water suspension containing 20% to 30% talc powder filler can be rapidly stirred for 6 minutes, diluted with water, and then treated with chemical additives for 5 minutes to create a filler suspension. This suspension is then added to the pulp. During the pulp formulation process, an appropriate amount of white water or clear water should be added to adjust the pulp consistency for producing paper-molded products to a concentration of 1% to 2%.
Molding: The vacuum molding method utilizes vacuum filtration technology for shaping. The molding mold is placed in a pulp solution with a concentration of about 1%, creating a vacuum inside the mold cavity to form negative pressure. Fibers in the pulp uniformly deposit onto the mold surface, forming a wet paper mold on the mold screen. A significant amount of water is removed during vacuum suction. When the wet paper mold reaches the required thickness, it is removed from the molding slurry with the wet paper mold and transferred to a compression mold for pressurized dewatering. This process continues until the moisture content of the wet paper mold reaches 75% to 80%. Subsequently, compressed air is introduced into the mold cavity to release the wet paper mold. This method boasts high production efficiency, uniform product thickness, and is suitable for producing shallow items such as egg trays, fruit trays, dish bowls, and plate boxes.