PVC granulation processing production process and related requirementsPVC granulation processing production process and related requirements
The granulation process is the production process of high polymer resin and various additives and auxiliary agents into granulated plastic through metering, laminating, plasticizing, and pelletizing. Plastic granules are semi-finished products of plastic molding and processing industry, and are also extruded. , Injection molding, hollow blow molding, foaming and other raw materials for processing.
There are two types of resin: powder and granular.
Granulation by extrusion is the most basic and simple granulation method, and it is widely used.
For various plastic molding processing methods, the advantages of using granulated materials compared to powder processing are as follows:
(1) The feeding is convenient, and there is no need to install a forced feeder in the feeding 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 mixing of resin and various solid powder materials or liquid additives is more uniform, and the physical properties of plastic products are more uniform.
(4) Uniform color of plastic products.
(5) The particulate material contains less volatile matter of air agent, making plastic products less prone to air bubbles.
(6) The pellets have no pollution to the extruder and the production environment.
1. Preparation before ingredients
The preparation work before batching includes resin sieving, plasticizer filtering, powdered additive grinding, drying of raw materials for the preparation of masterbatch powder, and heating and melting of block additives.
During the production, packaging and transportation of polymer resin, mechanical impurities or other impurities may be mixed. To prevent damage to the granulation equipment and reduce product quality, the resin must be used after sieving. Powdered polyvinyl chloride generally uses a 40-mesh screen. Granular polyethylene or polypropylene can be sieved, and can be sieved with a fine wire mesh that is slightly larger than the resin particle size.
In order to prevent the mechanical impurities or black garbage in the plasticizer from being mixed into the product and affecting the performance of the product, when producing cable materials, the plasticizer is generally filtered with a 60~120 mesh filter screen (60 mesh for high viscosity and 120 mesh for low viscosity).
For powdery additives with coarse particles or easy to agglomerate, it is better to grind with plasticizer first, add the slurry, and mix and disperse in the resin more uniformly. The refining equipment is a three-roll grinder, the ratio of general additives and plasticizers in refining formula is about 1:1, and the slurry fineness index is 60~80μm.
The proportion of slurry formula is the ratio of parts by weight. The proportion is mainly determined by the apparent density of the powder material. If the powder material has a large apparent density, a large amount of plasticizer needs to be added. Plasticizers generally use DOP with low viscosity. In the plasticizer feeding amount, the amount added during refining should be deducted.
For rigid PVC products, because no plasticizer is added, generally high-concentration polyvinyl chloride masterbatch powder is first manufactured, and then added to the kneader to mix. For example, this method is used for dyeing rigid PVC pipes. When manufacturing masterbatch powder with a kneader, stabilizers should be added appropriately to prevent the resin from decomposing.
The resins and additives that are easy to absorb moisture must be dried to remove water before kneading or extruding. For example, nylon resin and ABS resin are easy to absorb water, and must be dried to a moisture content of less than 0.1%. Drying equipment includes: boiling dryer, vacuum dryer or vacuum drying hopper.
Some functional masterbatch, such as antistatic masterbatch, anti-blocking masterbatch, pearlescent masterbatch, filler masterbatch, etc., are easy to absorb moisture, should be dried before adding to the extruder, otherwise it will affect the production or reduce the product quality.
Both stearic acid and paraffin wax are used as lubricants in plastic processing. If it is directly added into the kneader, it will hit the baffle due to the high-speed rotation in the high-speed kneader and damage the baffle, so it must be heated and melted before being added to the kneader. The melting point of stearic acid is 69.60°C, and the melting point of paraffin wax is 60°C.
2. Weighing formula
Put into the kneader or mixer to mix, and the raw materials for plastic smelting should first estimate the feeding amount according to the equipment volume and feeding coefficient.
Accurately weigh according to the amount of feed, the weighing must be accurate, otherwise the quality of the product will be unstable. Weighing scales and automatic metering devices should be regularly checked and corrected to prevent quality fluctuations due to metering errors.
Kneading can be divided into heating kneading and cooling kneading, using high-speed kneading machine.
Process conditions for heating and kneading: kneading time of soft PVC 10-15min, discharge temperature 95~100℃; kneading time of hard PVC 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 higher than 100°C. If it is put into the storage barrel, it will easily change color, agglomerate or even decompose the material. Therefore, it is necessary to immediately perform cooling and mixing to reduce the temperature of the material to below 50°C before it can be stored for the extruder. The cooling and mixing process conditions for both soft and hard polyvinyl chloride are kneading time 5~10min, and the discharge temperature is below 50℃.
The 50L mixer is used for the internal mixing. The process conditions for the internal color masterbatch of soft polyvinyl chloride and polyethylene are as follows. 100~110℃; polyethylene mixing time 8~10min, mixing temperature 80~100℃, discharge temperature 140~145℃. The condensed materials are agglomerates, and no unplasticized powder or granules can be released.
4. Extrusion granulation
Single screw and twin screw extruders can be used for extrusion granulation. Mainly control the extrusion temperature, screw speed, cutter speed and pellet cooling. Make the granules not sticky particles, uniform particle size, better plasticization. The speed of the cutting knife is adjusted to the length of the granular material 3~4mm. The screw speed is adjusted so that the pellets do not block.
The temperature of single screw extruder with 65mm diameter is 140~150℃, 160~170℃, 150~160℃, 150~160℃, the speed is 20~30r/min; diameter 51 The temperature of the ~150mm twin screw extruder is 130~140℃, 140~145℃, 150~155℃, 145~150℃, and the screw speed is 15~20r/min. Granulated polyethylene with parallel twin-screw extruder with a diameter of 6mm, the temperature is 200~220℃, 230~240℃, 240~250℃, 250~260℃If you want to know more about it please do not hesitate to contact me. WhatsApp:+86-15966835076.