Pulp molded products have become a rapidly growing new type of packaging material in recent years, and they are an excellent alternative to wood. The production process of pulp molding can be summarized into five major steps: pulping, blending, forming, drying, shaping, and post-processing.
Pulping, Blending, and Forming Step: This is the first step in the production of pulp molded products, which is mainly borrowed from the papermaking process. Since waste paper comes from a wide range of sources, it needs to be carefully sorted and all kinds of impurities removed before pulping. Next, the sorted and purified waste paper is ground and pulped into uniform paper fibers. Then, the pulp is blended to meet the requirements of the product that will be produced, as the density, hardness, and color of the raw waste paper may differ. Finally, the pulp is coated with adhesives, such as rosin, paraffin emulsion, or rosin-paraffin adhesive. The concentration of the pulp during production should be relatively high, around 1%-2%. Equipment: pulper, blending pool, pulp pool, etc.
Forming Step: The forming process of pulp molded products mainly uses a series of methods such as vacuum molding and slurry molding to shape the original pulp fibers into the desired shape designed by the mold. Vacuum molding is the most commonly used and effective method. After forming, the mold is lifted with the help of hydraulic cylinders, and the upper and lower molds are closed to compress the product, which primarily squeezes out some of the moisture in the product. Typically, the moisture content of the product after compression ranges from 50%-75% due to different levels of extrusion. Equipment: molding machine.
Drying Step: The drying of pulp molded products is usually carried out in a periodic or continuous drying oven, with the main purpose of reducing the moisture content of the product to 10%-12%. Hot air is mainly used to dry the product in the drying oven or continuous drying conveyor. The initial temperature is 250℃-300℃ (the moisture content of the product decreases by 50% in 7-10 seconds), and then it drops to 100℃-105℃. In a continuous drying oven, the product is conveyed through different temperature zones until it is dried to a moisture content of approximately 10%-12%. Equipment: drying machine.
Shaping Step: The shaping of pulp molded products is typically carried out by hot extrusion on a hot molding machine, making the product denser, with uniform wall thickness, smooth and flat surface, and improved strength, which is essential for the product. Sometimes, some marks need to be pressed on the paper mold, which can be done in this step to avoid unclear or rough marks. Equipment: trimming and shaping machine.
Post-processing Step: After drying, pulp molded products can be used, but sometimes special post-processing is needed, such as polishing, coating baking, or printing patterns and text on the surface. Depending on the characteristics of different products, manual or automatic packaging machines can be used for counting and packaging. Equipment: automatic packaging machine.
