Pulp molding is a three-dimensional papermaking technology that uses waste paper as raw material and forms paper products of a certain shape on a molding machine using a special mold. In addition to making lunch boxes and tableware, pulp molding is also used for industrial cushioning packaging and is developing rapidly.
1. Environmental Protection
Pulp molding products are green and environmentally friendly products strongly recommended by the World Environmental Protection Agency. During the entire processing process, it is mainly physical reaction, and only a small amount of chemical substances are added as waterproof coating; pulping, adsorption molding, drying and shaping processes are also harmless to the environment. From the use of key raw materials to the end of the entire processing, its environmental protection awareness is very strong, and no discharge causes environmental pollution.
2. Recyclable
The raw material of pulp molding is waste paper, including board paper, waste carton paper, waste white edge paper, etc., which can be recycled and biodegraded; the tap water used in the production line is a closed circulation system, which only causes water vapor to evaporate into the air when the product is air-dried. There is no need to add tap water during the processing, so the water demand is not large.
3. Good cushioning and protection performance
Pulp molded products have their own special structure, which can extend the corresponding time by changing properties when loaded, absorb external energy, and thus reduce the impact and vibration of the packaged objects, which is the basic guarantee for improving the shock absorption capacity during transportation and handling.
4. Convenient transportation and low cost
The volume is smaller than that of foamed plastics, can be overlapped, and convenient transportation. At present, the product cost of paper tray products in China is basically the same as that of plastic foam products, and the cost of some paper tray products is already lower than that of plastic foam products.
Pulp molding products are a new type of packaging material that has grown rapidly in recent years and are an excellent substitute for wood. The production process of pulp molding can be summarized into five major steps: pulping - pulping - pulping, molding, drying, shaping, and post-processing.
1. Pulping-mixing-pulping process:
This is the first process of pulp molding products, which mainly draws on the papermaking process. Since the source of waste paper is relatively wide, it must be carefully classified and various impurities must be removed before pulping.
The second is shredding pulping, which grinds and pulps the sorted and purified several types of raw waste paper to transform them into uniform paper.
The third is to mix the pulp. Because the specific gravity, hardness and color of the raw waste paper are different, the pulp must be mixed according to the requirements of the products to be produced to meet the product requirements required by customers.
The fourth is pulp sizing. Generally speaking, the glue applied to the paper mold is rosin, paraffin latex or rosin paraffin glue. The sizing concentration of the pulp should be high during production, about 1%-2%.
Equipment: pulper, pulp mixing tank, pulping tank, etc.
2. Molding process:
The molding process of pulp molded products is mainly to form the original pulp fibers into the shape designed by the mold through a series of methods such as vacuum molding and grouting molding. Vacuum molding is the most commonly used and most effective one.
After the molding is completed, the model is raised with the help of a hydraulic cylinder, and the upper and lower models are closed to compact the product and then taken out. The main function of this compaction process is to squeeze out some of the water in the product; generally, due to different degrees of extrusion, the moisture content of the product after extrusion is about 50%-75%.
Equipment: molding machine.
3. Drying process:
Pulp molded products are usually dried in a cyclic or continuous drying furnace, mainly to reduce the moisture content of the product to 10%-12%. In the drying furnace or continuous drying conveyor, hot air is mainly used to dry the product. The initial temperature is 250℃-300℃ (the moisture content of the product is reduced by 50% within 7-10 seconds), and then the temperature is reduced to 100℃-105℃. There is a conveyor in the continuous drying furnace, and the product passes through different temperature zones in the furnace, and finally dried to a moisture content of about 10%-12%.
Equipment: dryer.
4. Shaping process:
Usually, the shaping of pulp molded products is done by hot extrusion on a thermoforming machine, which makes the products denser, with uniform wall thickness, smooth and flat outer surface, and improved wall strength, which is very necessary for the products. Sometimes some marks need to be pressed on the paper mold, which can be done in this process, so it is easier to avoid problems such as unclear marks and roughness.
Equipment: Shaping trimming machine.
5. Post-processing:
Molded pulp products can be used after drying, but sometimes they need special post-processing, such as calendering, coating baking or printing patterns and texts on the surface. Depending on the characteristics of different products, manual packaging or automatic packaging machine can be used for counting packaging.
Equipment: Automatic packaging machine.
At present, there are two types of equipment for overseas pulp molding production lines: vacuum filtration molding process and grouting molding method.
Vacuum filtration molding method is a more popular method for paper and plastic products. According to its different structures, there are three methods: rotary drum type, flip type, and reciprocating lifting type.
(1) Drum type
Continuous rotary production, high production efficiency, large mold investment, high mold processing precision, high equipment processing precision technical requirements, one set of concave mold with eight sets of convex molds. The mold needs to be processed by a CNC center, with a long processing cycle and large investment. Because it is continuous production, it is suitable for large-scale production of stereotyped products, such as plates, dinner plates, and egg trays; it is not suitable for industrial molding production.
(2) Flip type
The production efficiency is lower than that of the rotary drum type, and it is suitable for medium-volume and non-standard production of industrial molding. However, since it is a set of concave molds with two sets of convex molds, the molds need to be processed by a CNC center, which requires large mold investment and a long cycle.
(3) Reciprocating lifting type
The production efficiency is the same as the flip type, which is a very common production method at present. Since this equipment only needs a set of four-mold matching punches and does not require CNC center processing, it is particularly suitable for non-standard, small-batch, and fast-cycle industrial packaging products.
The grouting molding method is to calculate the required amount of slurry (raw material) based on different paper pulp packaging products and quantitatively introduce it into the forming mold core to absorb the molding. The suitable changes for this type of forming method are not big. Standard shaped products are commonly used in kitchenware formed products. Since the shaping calculation cannot be grasped, this forming method is not used in non-standard paper and plastic packaging (industrial packaging).
Applications of pulp molding include egg boxes, egg trays, fruit trays, flower pots, disposable medical bedpans, etc. It can also be used as packaging pads for eggs, fruits, precision devices, fragile glass, ceramic products, handicrafts, etc.
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