1. Stabilizer
The most widely used stabilizer on PVC foamed products is lead salt stabilizer and calcium zinc stabilizer. With the increasingly strict requirements of environmental protection and the increasing cost performance of calcium zinc stabilizer, the application of calcium zinc stabilizer has become more and more extensive.
Insufficient stabilizer, yellow board, paste, products brittleness, strength, low foaming rate;
If the stabilizer is too much, the foaming agent decomposing in advance, the gas will overflow from the feeding hole and vacuum hole, and the cavity structure will crack or shrink;
2. External lubricant
Foamed products on the application of the most general external lubrication paraffin, PE wax, paraffin easy to precipitate, so generally use PE wax.
The extruder temperature in 4 and 5 zones is not easy to control, and it is easy to overheat.
The increase of frictional shear heat causes material decomposition, yellowing of the board surface and paste.
Excessive external sliding, poor plasticizing, resulting in mold cavity scaling and product surface precipitation, easy to appear leucorrhea, uneven wall thickness and some symptoms in the surface of irregular movement phenomenon;
3. Internal lubricant
Commonly used lubricants include stearic acid, 60, monoglyceride, 316, etc.
Insufficient internal lubrication, poor material dispersion, uneven plasticizing, product thickness is difficult to control, the middle of the thick foam plate on both sides of the thin, may also appear leucorrhea, mold cavity adhesion and local overheating phenomenon;
Excessive internal lubrication, foaming products brittle, heat resistance, and in a certain temperature and melting pressure under the action of external lubrication, resulting in lubrication imbalance;
Internal and external lubrication is insufficient, the melt viscosity is large, the plasticizing torque is large, the melt wall adhesion phenomenon is serious, the material surface has yellow decomposition line, the surface smoothness is poor, the mechanical properties of the products decreased;
Internal and external lubrication are excessive, plasticizing torque is small, melt plasticizing is obviously insufficient, although the smooth of the product is good, but the pressure point adhesion is poor, seriously affect the mechanical properties of the product;
Less internal lubrication, more external lubrication, plasticizing time significantly extended, plasticizing torque reduced, products molding difficulty, become brittle;
There is more internal lubrication, less external lubrication, the plasticizing time is obviously shortened, there is a serious phenomenon of wall adhesion, the thermal stability time is shortened, the surface of the product has decomposition yellow line;
4, the calcium powder
Generally, light calcium with particle size of around 1200 mesh is preferred for foaming products. Calcium powder tends to absorb moisture and forms bubbles and silver lines on the surface of products, affecting the appearance and physical properties. Therefore, attention should be paid to storage in the rainy season.
When the particle size of calcium carbonate is too large, it is easy to mix unevenly, the plasticizing time of the mixture is delayed, and the screw torque is low.
When the particle size of calcium carbonate is too small, it is easy to aggregate, from small particles to large particles, similar to the consequences of large particles;
When the dosage of calcium carbonate is too little, the number of bubbles decreases and the foaming rate decreases.
When the dosage of calcium carbonate is too much, the relative content of resin in the component decreases, the melt strength decreases, and the section of the plate is prone to bubble breaking.
5. Foaming regulator
Foaming regulator is to point to viscosity to be in 10 above commonly the acrylic ester kind processing assistant agent, among them the type such as wood of ecological wood, clapboard of wood model kind foaming product USES plastic to change fast commonly, foaming board especially ambry board chooses the foaming regulator with big strength of plasticizing slow melt commonly.
Foam regulator is insufficient, melt strength is poor, the bubble hole is not uniform, the section will appear bubble hole, the density increases;
Too much foam regulator, melt strength is too big, melt bubbles cannot expand, product density is high, the surface is prone to appear wavy, distortion, etc.
6. Foaming agent
The amount of foaming agent is AC yellow foaming agent and NC white foaming agent, AC in the decomposition process will release a lot of heat, resulting in yellow products, and decomposition will have a small amount of ammonia flavor;
NC in the decomposition process will absorb heat, and decomposition tasteless, so the two types of foaming products are generally used in coordination.
The foaming agent dosage is insufficient, the foaming ratio is low, the product bubble hole is few, the density is large;
Foaming agent dosage is too much, melt strength will become low, it is difficult to shape products, foaming plate section is easy to produce bubble hole;
Beyond a certain range, the product density becomes larger;
Yellow foaming agent is too much, white foaming agent is too little, the section is easy to appear large and round bubble hole.
Therefore, the dosage of all kinds of auxiliary agents have a degree and the relationship of mutual restriction, less is not good, is not too much is not good, in the production practice must go through repeated tests, give full play to the coordination effect of various raw materials, find the best balance point, fully improve melt strength and foaming efficiency, extend the starting time.
