The PVC compound granulation process is a process of making high-polymer resin and various additives and auxiliaries into granulated plastics after metering, sticking, plasticizing, and pelletizing. Plastic granules are semi-finished products of the plastic molding processing industry and are also extruded , Injection molding, hollow blow molding, foaming and other forming and processing raw materials.

There are two types of resin: powder and granular.

Extrusion granulation is the most basic and simple granulation method, which is widely used.

For various plastic molding and processing methods, compared with direct processing of powder, the advantages of using granulated pellets are as follows:

    (1) Convenient feeding, there is no need to install a forced feeder in the hopper.

    (2) The relative density of granular materials is greater than that of powder materials, and the strength of plastic products is better.

    (3) The resin is mixed with various solid powder materials or liquid additives more uniformly, and the physical properties of plastic products are more uniform.

    (4) The color of plastic products is uniform.

    (5) Granules contain less volatiles of air-containing agents, making it difficult for plastic products to generate air bubbles.

(6) The granules have no pollution to the extruder and production environment.

Production Process:

1. Preparations before ingredients

The preparation work before batching includes resin sieving, plasticizer filtration, powdered additive refining, color masterbatch powder preparation raw material drying, blocky additive heating and melting.

High polymer resins may be mixed with mechanical impurities or other impurities during the production, packaging and transportation. To prevent damage to the granulation equipment and reduce product quality, the resin must be used after sieving. Powder polyvinyl chloride generally uses a 40 mesh screen. Granular polyethylene or polypropylene can be sieved with a fine wire mesh slightly larger than the resin particle size.

The proportion of the slurry formula is the ratio of parts by weight, and the proportion is mainly determined by the apparent density of the powdery material. If the apparent density of the powdery material is large, a large amount of plasticizer needs to be added. Plasticizers generally use low-viscosity DOP. In the amount of plasticizer input, the amount added during refining should be deducted.

For rigid polyvinyl chloride products, because no plasticizer is added, generally a high-concentration polyvinyl chloride color masterbatch powder is produced first, and then added to the kneader and mixed. For example, this method is used for dyeing rigid PVC pipes. When using a kneader to manufacture the masterbatch, a stabilizer should be appropriately added to prevent the resin from decomposing.   

Some functional masterbatches, such as antistatic masterbatch, anti-blocking masterbatch, pearlescent masterbatch, filler masterbatch, etc., are easy to absorb moisture, and should be dried before adding to the extruder, otherwise it will affect production or reduce products quality.

2. Weighing formula

    Put into the kneader or mixer to mix, and the raw materials for plasticizing should first be estimated according to the equipment volume and the feeding coefficient.

3.Pinch

    Kneading can be divided into heating kneading and cooling kneading, using a high-speed kneader.

    Heating and kneading process conditions: soft PVC kneading time 10 ~ 15min, discharge temperature 95 ~ 100 ℃; hard PVC kneading time 5 ~ 10min, discharge temperature 100 ~ 110 ℃. In addition, the order of addition during kneading has an effect on the kneading quality.

    Cooling and kneading The temperature of the material coming out of the high-speed kneader is relatively high, exceeding 100 ° C. If it is placed in a storage barrel, it is prone to discoloration, agglomeration and even material decomposition. Therefore, it is necessary to immediately cool and mix to reduce the temperature of the material below 50 ° C before it can be stored for the extruder. The cooling and mixing process conditions are kneading time of 5 ~ 10min for both soft and hard polyvinyl chloride, and the temperature of the discharge material is below 50 ° C.

4.Extrusion granulation

    Extrusion granulation can use single screw and twin screw extruder. It mainly controls extrusion temperature, screw speed, cutter speed and pellet cooling. So that the pellets do not occur sticky particles, the particle size is uniform, and plasticization is better. The cutter speed is adjusted to 3 ~ 4mm of pellet length. The screw speed is adjusted so that the pellets do not stick.