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Many additives, lubricants, stabilizers, foaming agents and other additives are used in PVC foaming products, and these additives also restrict each other. In this article, Qingdao Sainuo pe wax manufacturer will take you to understand the characteristics of mutual checks and balances of various additives used in PVC foaming products.
1. External lubricant
The most commonly used external lubrication on foamed products generally includes paraffin wax and polyethylene wax. Paraffin wax is easy to precipitate, so polyethylene wax is generally used.
The external lubrication is insufficient, the temperature in zone 4 and 5 of the extruder is difficult to control, and it is easy to exceed the temperature. There are blisters, blisters, yellowing and rough plate surface on the plate surface; Friction shear heat increases, causing material decomposition, yellowing of plate surface and paste;
Excessive external lubrication and poor plasticization lead to scaling in the mold cavity and precipitation on the product surface, which is prone to leucorrhea, uneven wall thickness and irregular back and forth movement of some symptoms on the surface;
2. Internal lubricant
Common internal lubricants include stearic acid, 60, monoglyceride, 316, etc.
Insufficient internal lubrication, poor material dispersion, uneven plasticization, difficult to control product thickness, thick foam board in the middle and thin on both sides, leucorrhea, adhesion to mold cavity and local overheating may also occur;
Excessive internal lubrication, brittle foaming products, reduced heat resistance, and changed to external lubrication under a certain temperature and melt pressure, resulting in unbalanced lubrication; Insufficient internal and external lubrication, high melt viscosity, high plasticizing torque, serious melt wall adhesion, yellow decomposition line on the material surface, poor surface smoothness and reduced mechanical properties of the product; The internal and external lubrication are excessive, the plasticizing torque is small, and the melt plasticization is obviously insufficient. Although the product has good smoothness, the pressure point adhesion is poor, which seriously affects the mechanical properties of the product; There is less internal lubrication and more external lubrication, the plasticizing time is obviously prolonged, the plasticizing torque is reduced, the product is difficult to form and becomes brittle;
More internal lubrication, less external lubrication, significantly shorter plasticizing time, more serious wall sticking, shorter thermal stability time, and decomposition yellow lines on the product surface;
Lead salt stabilizer and calcium zinc stabilizer are the most widely used stabilizers in PVC foam products. With the more and more strict requirements of environmental protection and the higher cost performance of calcium zinc stabilizer, the application of calcium zinc stabilizer began to become more and more widely.
Insufficient stabilizer, yellowing of board surface, high brittleness of paste and products, reduced strength and low foaming rate;
If there are too many stabilizers, the foaming agent decomposes in advance, the gas will overflow from the feeding hole and vacuum hole, and the cavity structure will crack tendons or shrink marks;
4. Calcium powder
Light calcium with a particle size of about 1200 mesh is generally suitable for foaming products. Calcium powder is easy to absorb moisture and form bubbles and crazes on the surface of products, which will affect the appearance and physical properties. Therefore, pay attention to storage in rainy season.
When the particle size of calcium carbonate is too large, it is easy to mix unevenly, the plasticization time of mixture is delayed, and the screw torque is low;
When the particle size of calcium carbonate is too small, it is easy to agglomerate and change from small particles to large particles, which is similar to the consequence of too large particles;
When the dosage of calcium carbonate is too small, the cell lacks core, the number of cell decreases and the foaming rate decreases
When the dosage of calcium carbonate is too high, the relative content of resin in the components decreases, the melt strength decreases, and the plate section is easy to break bubbles;
5. Foaming regulator
Foaming regulator generally refers to acrylate processing additives with viscosity above 10. Wood plastic foaming products such as ecological wood and wall protection board generally use the type with fast plasticization. Foaming regulator with slow plasticization and high melt strength is generally used for foaming board, especially cabinet board.
The foam regulator is insufficient, the melt strength is poor, the cell is uneven, the cell will appear in the section and the density will increase;
There are too many foaming regulators, the melt strength is too large, the bubbles in the melt cannot expand, the product density is high, and the plate surface is prone to wavy lines, distortion and deformation;
6. Foaming agent
The largest amount of foaming agent is AC yellow foaming agent and NC white foaming agent. AC will release a lot of heat during decomposition, resulting in yellowing of products and a small amount of ammonia smell during decomposition; NC absorbs heat during decomposition, and decomposition is tasteless. Therefore, the two kinds of foam products are generally used in coordination.
The amount of foaming agent is insufficient, the foaming ratio is low, the product has few bubbles and high density;
If too much foaming agent is used, the melt strength will become low, the product is difficult to form, and the foam board section is easy to produce bubbles; Beyond a certain range, the product density becomes larger;
Yellow foaming agent is more, white foaming agent is less, and large and round bubbles are easy to appear in the section.
Therefore, the dosage of various additives has a degree and mutual restriction relationship. A small amount is not good, nor is a large amount bad. In production practice, we must go through repeated tests to give full play to the coordination effect of various raw materials, find the best balance point, fully improve the melt strength and foaming efficiency, and prolong the startup time.
Qingdao Sainuo Chemical Co., Ltd. We are manufacturer of PE wax, PP wax, OPE wax, EVA wax, PEMA, EBS, Zinc/Calcium Stearate…. Our products have passed the REACH, ROHS, PAHS, FDA testing.
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