Pulp Molded Packaging Product Manufacturing Process
Pulp Molded Packaging Product Manufacturing Process
1. Production Principle
Pulp molded packaging products are made using recycled paper materials such as old newspapers, cardboard, and paper scraps from printing or packaging factories. The production process utilizes electricity and steam as energy sources and water as a medium. It involves key stages such as pulping, fiber separation, forming, drying, and hot pressing.
The recycled paper is first disintegrated into pulp fibers using a hydrapulper. The pulp is then refined through a fiber separator, mixed with functional additives (e.g., waterproofing, anti-static agents), diluted to the required consistency, and pumped into the forming machine. The slurry forms a wet pulp mold on a specially designed metal screen mold using vacuum suction. After drying and hot pressing, the finished molded pulp product is ready for packaging or delivery.
This process is environmentally friendly, cost-effective, and energy-efficient, offering a sustainable alternative to plastic packaging.
2. Process Overview
Raw Materials → Pulping → Impurity Removal → Fiber Refining → Additives Mixing → Forming → Drying → Hot Pressing → Finished Product
3. Pulp Preparation
Raw materials include both market pulp and recycled paper. Market pulp is typically used for food-grade products, while recycled paper is used for industrial packaging items like egg trays and electronic cushioning.
Recycled paper often contains impurities such as tape, staples, and binding materials. These are removed during pulping and screening processes:
- Hydrapulper: Breaks down paper into fibers and removes long strip contaminants using a rope cleaner.
- Heavy Contaminant Collector: Periodically removes heavy debris.
- High-Concentration Cleaner & Fiber Separator: Further refines the pulp and separates usable fibers.
Depending on the product, the beating process may be skipped or performed using intermittent or continuous refiners. Chemical additives, such as sizing agents (rosin, wax emulsions), are added to improve water resistance and product strength. The recommended dosage is 2%–5% of the dry fiber weight. The finished pulp slurry is stored for the forming stage.
4. Forming Process
The forming stage uses the vacuum forming method, which is ideal for high-volume pulp molding production. A vacuum draws pulp fibers onto a mesh mold surface, creating a wet mold shape. This process is performed on fully automatic machines equipped with single or multiple molds, depending on product dimensions.
The molded products have high moisture content (up to 75%) and require further drying before final shaping. This method allows precise molding and consistent production quality.
5. Thermal Drying
Drying is a critical step, as each kilogram of molded product involves the evaporation of 3.5–4 kg of water. Hot air convection drying is commonly used, requiring consistent air temperature (110–120°C) to avoid fiber degradation and deformation.
Key drying factors:
- Uniform airflow distribution (recommended speed: ~5 m/s)
- Low humidity inside the drying chamber
- Proper insulation to reduce heat loss
- Partial reuse of exhaust heat to lower energy consumption
This process uses steam-based drying, where steam heats the air through a heat exchanger. Excess steam condenses and returns to the boiler, creating a cost-effective and eco-friendly drying cycle.
6. Hot Pressing and Final Shaping
After drying, hot pressing is used to improve product density, strength, and surface smoothness. This step ensures accurate dimensions and prevents deformation. Proper moisture content before pressing is crucial; overly dry products may lead to poor reshaping.
Before pressing, dried products are rested for 24 hours to ensure moisture balance. The hot pressing process is carried out using standalone hydraulic machines to guarantee consistent product quality.
