How to make pvc compound formula for pvc pipes
Pipe is one of the main products processed by extrusion molding.
The outstanding advantages of PVC plastic pipe: the relative density is small, equivalent to 1/4-1/7 of metal; the electrical insulation performance and chemical stability are excellent; the installation and construction are convenient, the maintenance is easy; the unit energy consumption is low. However, compared with metal, its mechanical properties are lower, the operating temperature range is narrower, and the expansion and contraction deformation is larger.
Plastic pipes are used to transport liquids, solids, gases, and as wire and cable jackets and structural materials. The main application areas are: building water supply pipes, building drainage pipes, buried drainage pipes, gas pipes, sheath pipes, agricultural pipes, industrial pipes. Housing construction, environmental protection and governance, agricultural water-saving irrigation, transportation, communications, water conservancy, energy and other infrastructure projects make plastic pipes have a very broad market.
Pvc pipe formula design
The principle of design formula is based on the requirements of use, according to China has developed various types of pipe standards, pipe formulations include: PVC resin, impact modifiers, stabilizers, processing modifiers, fillers, pigments and external lubricants And other ingredients.
1. PVC resin
In order to obtain rapid and uniform plasticization, a suspension-type loose resin should be used.
——Resin for double-wall corrugated pipe, especially with good molecular weight distribution and impurity quality, to reduce the “fish eye” in the pipe, avoid the collapse of the pipe corrugation and the crack of the pipe wall.
——The resin used for the water supply pipe should be “hygienic”, and the residual vinyl chloride in the resin should be within 1mg/kg. In order to ensure the quality of the pipe and reduce the defective rate, the source of the resin should be stable.
At present, the main heat stabilizers used in China are: metal soaps, composite lead salt stabilizers, rare earth composite stabilizers, and organotin stabilizers.
Heavy metal-containing stabilizers (such as Pb, Ba, and Cd) are harmful to human health, and these stabilizers have a limited amount of use in water supply pipe formulations. In the single-screw extrusion process, the heat history of the material is longer than that of the twin-screw extrusion process, and the former uses more than 25% of the stabilizer. The double-wall corrugated pipe has a higher head temperature and a longer residence time of the material in the handpiece, and the amount of stabilizer in the formulation is more than that of the ordinary pipe formulation.
The role of the filler is to reduce costs. Try to use ultra-fine active fillers (higher price). The amount of pipe is larger than that of profiles. If the amount of filler is too large, the impact resistance will decrease and the pressure resistance of the pipe will decrease.
Therefore, in chemical pipes and water pipes, the amount of filler is Within 10 copies. Drainage pipe, cold bend threading sleeve can use more filler, and increase the amount of CPE to change the impact performance.
For pipes with lower performance requirements for pipes and rain pipes, the amount of filler can be large, but the wear on twin-screw extruders is more serious.
(1) Processing modifier: ordinary pipe can be used less or not; bellows and thin-walled pipe are used more.
(2) Impact modifier: less than the amount of profile, two reasons: 1. performance, low temperature resistance, tensile strength 2. Cost
(3) Other additives, colors, etc.: As the anti-aging agent, the profile must be added with titanium dioxide. The formulation of the hard
PVC pipe is mainly pigment, mainly titanium dioxide or carbon black, which can be selected according to the appearance requirements of the pipe.
5. external lubricant and stabilizer matching
(1) Select an external lubricant that matches the stabilizer
a. Organotin stabilizer. The organotin stabilizer has good compatibility with PVC resin and has a strong tendency to adhere to the metal wall. The cheapest external lubricant matched with it is a paraffin-based paraffin-calcium stearate system.
b. Lead salt stabilizer. The lead salt stabilizer has poor compatibility with the PVC resin and is only attached to the surface of the PVC particles, which hinders the fusion between the PVC particles, and is usually matched with a lead stearate-calcium stearate external lubricant.
(2) The amount of external lubricant. If the amount of external lubricant is still not enough to meet the material processing requirements, consider adding a small amount of internal lubricant. When an impact-resistant toughening modifier is used, since the viscosity of the melt is large, the possibility of adhering to the metal surface is large, and it is often necessary to increase the amount of the external lubricant; the thin-walled tube extruded by the same equipment is more than the same specification. Thick wall tubes require more external lubricant. When the processing temperature is high, the tendency of the melt to adhere to the metal surface is large, and more external lubricant is added.