The basic concept of PVC lubricant
How to choose a good and suitable lubricant, first of all, the basic concept and theory of lubricant have a general and correct understanding and understanding. If you have a large understanding of basic concepts and theories, it may be difficult to choose a good or correct lubricant, or you may spend more time experimenting with validation and practice. Here, the basic concepts and theories of lubricant are briefly introduced:
1. External lubricant
After the lubricant is fused, a film is formed between the surface of the screw, the mould, the screw, and the surface of the PVC melt, which ACTS as a lubricating agent, which we call the external lubricant. The following performances and characteristics are shown in the PVC processing and production:
(1). Improve the gloss of the product surface and prevent the material from sticking to the hot metal surface.
(2). Adjust the material plasticizing point. The plasticizing point can be delayed by adding the external lubricant, and the plasticizing time can be delayed.
(3), the dosage is too high, can cause precipitate phenomenon. The addition of the external lubricant is too large, which can cause the precipitate of the die head, the qualitative slot and the product in the process.
(4). If the dose is too high, it will reduce the mechanical physical properties of the shock resistance. Because the lubricating agent content is too high (plastic sliding), will affect the material plasticizing effect, but also affect the mixing uniformity of material, so the production of the products will not be able to get good physical and mechanical properties such as resistance to impact.
(5). No effect or reduction of vica softening point. In general, the external slider does not affect the softening temperature of product vica, which is different from the internal lubricant.
(6). Excessive amount of addition has a negative effect on the welding strength of profiles, which can result in the peeling of pipe fitting oven and the transparency of products.
2. Internal lubricant
When the lubricant melts, it melts into the inside of the PVC melt, and the material that lubricates and reduces friction between the molecules in the melt is called an internal lubricant. The inner lubricant has the following characteristics in PVC processing and production:
(1). Reduce the friction in the molten resin. As defined above, the inner slider reduces friction and avoids the inner focus of the inner melt.
(2). Reduce melt viscosity and reduce die expansion. The melt viscosity is too high in the process, which will cause the melting pressure too large. The pressure is too high, the torque is increased, the shear force is larger, and the product is also easy to focus. At the same time, the pressure inside the spiral tube is too large, which is easy to cause the dilatation of the mold, and the mold expansion is too large, and it is easy to precipitate. Therefore, the addition of internal lubricant can avoid the coke and reduce the precipitation.
(3). Reduce vica softening point. The addition of 1PHR solid internal lubricant will reduce the temperature of the wika softening by 1~2 degrees, and the internal lubricant of the liquid will have a greater effect on the softening point of vica.
(4). Reduce melt fracture. Internal lubrication can help the material to be more uniform and better plasticized, improve the flow of logistics, and can reduce or eliminate the melt cracking phenomenon, especially in the case of high-speed extrusion.
(5). It is necessary to add a high amount of effect in the product.
(6). It is beneficial to increase the impact strength/favorable for the dichloromethane soaking experiment.
3. Internal/external lubricant.
We also call it internal/external slide agent. This is more in ester lubricants. Some of the performance is external and internal sliding is relatively balanced, some of the performance is stronger, less internal. And oxidized polyethylene wax is a kind of outer slip of the wax class, with a slight internal slip.
The understanding and clarity of the basic concept and the expression characteristics of the internal lubricating agent and the external lubricant are conducive to the adjustment of the correct direction of the formulation design.