Views: 3 Author: Site Editor Publish Time: 2024-10-14 Origin: Site
Calcium carbonate filler masterbatch is a particle with a volume similar to the base resin of plastic products made by mixing calcium carbonate with carrier resin and mixing and granulating. It has a wide range of application value in the plastics industry. Before masterbatch processing, the surface of calcium carbonate powder is modified to increase its dispersibility, which can greatly improve the crosslinking with the resin. However, there are still 5 issues that need to be paid attention to during the production of calcium carbonate filler masterbatch:
1. Surface modification of calcium carbonate
In order to evenly disperse the calcium carbonate particles in the filler masterbatch into the base plastic, the calcium carbonate particles must be completely coated first. If the calcium carbonate has been agglomerated during the production of the filler masterbatch, then the agglomerated particles cannot be opened in the blown film extruder, and many white spots will inevitably form on the film. Even white hard particles may form "clouds".
To solve the agglomeration problem of calcium carbonate particles, we need to pay attention to two aspects:
First, excessive friction should be prevented during surface treatment. Once static electricity is generated due to friction, agglomeration is very likely to occur.
Secondly, the amount of surface treatment agent should be sufficient. When the surface of the particles is changed to lipophilic by the coupling agent, its surface energy is greatly reduced, and it is not easy for them to agglomerate with each other.
2. Calcium carbonate filling ratio
The higher the proportion of calcium carbonate in the filler masterbatch, the lower the raw material cost of the product and the more competitive it is in the market. Since calcium carbonate particles are small in size, large in number, and have a large total surface area, more carrier resin is needed to coat them, which requires not only a low melt viscosity of the carrier resin, but also a sufficient amount.
In order to obtain a film-grade filler masterbatch with good performance, the weight percentage of calcium carbonate is generally not more than 80%, and the weight percentage of the carrier resin is generally not less than 13%.
3. Physical mixing state
There are different opinions on what form the materials in the high-speed mixer should be mixed into. Some people have tried mixing into a complete paste before discharging the materials and just mixing mechanically to make the materials uniform, and discharging the materials while the particles of the carrier resin remain in the original particle form. There is no obvious difference in the effect of the filling masterbatch made from the two extreme cases in the application of the film.
Our experience is that it is best to discharge the material immediately when the carrier resin has begun to melt and is in full contact with the surface-treated heavy calcium to form lumps but not to form a paste. If it forms a paste, discharging the material is very difficult, which wastes time and reduces production efficiency. If the material is still in the state of particles and powder, not only can the components not be uniform, but also when feeding the material into the twin-screw extruder, the particles and powder will separate again, resulting in some products with more heavy calcium and some with more resin, which will cause uneven materials when blowing the film, and it is very easy to cause "clouds" or white spots.
4. Selection of extruder
The extruder used for material mixing, kneading and granulation is also very important. The co-rotating parallel twin-screw extruder is far superior to the single-screw extruder with a mixing section, and the reciprocating single-screw extruder is better than the co-rotating parallel twin-screw extruder in the production of film-grade filling masterbatch with ultra-fine heavy calcium as the main raw material.
The advantages of compounding and granulating equipment can make up for the deficiencies in the surface treatment of calcium carbonate in high-speed mixers and the initial mixing with carrier resins. Therefore, the selection of artificial extrusion compounding and granulating equipment and the selection and arrangement of threaded sleeves are also crucial.
5. Cooling method
In the granulation part, the operation mode of strand water cooling should be avoided as much as possible, because of the problem of manual operation level and responsibility. Once the material is water-containing, it will bring great hidden dangers to the blown film.
If polyethylene resin is used as the carrier resin, it is appropriate to use the air-cooled die surface hot cutting process. The shape and size of the particles are very particular. Generally, a round piece with a diameter of 3 to 5 mm and a thickness of about 1 mm is appropriate. This is mainly to facilitate mixing with the particles of the matrix resin during film blowing, and to melt quickly in a short time to facilitate mixing with the matrix resin material.
When the extruder has a large diameter (such as a diameter above Φ72mm) and the output is higher than 300kg/h, it is difficult to make a hot die head with air-cooled die surface, the temperature is difficult to control, the particles cannot be cooled down, and they are easy to stick together. At this time, it is appropriate to use the conveyor belt cooling method, and this method is suitable for the production of various filling masterbatches or modified special materials, but it requires a longer cooling distance and requires a larger site.
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