The most commonly used stabilizers on PVC foam products are lead salt stabilizers and calcium zinc stabilizers. With increasingly stringent environmental requirements and higher cost-effectiveness of calcium zinc stabilizers, their application has become more and more widespread.
Insufficient stabilizer, yellowing of the board surface, paste, high brittleness of the product, reduced strength, and low foaming rate;
Excessive stabilizers can cause premature decomposition of the foaming agent, leading to gas overflow from the feeding and vacuum holes, and cracks or shrinkage marks in the cavity structure;
2. External lubricant
The most commonly used external lubricants on foam products are generally
Paraffin Wax and
PE WAX. Paraffin wax is prone to precipitation, so PE wax is generally used.
Insufficient external sliding, difficult to control temperature in zones 4 and 5 of the extruder, prone to overheating, resulting in large bubbles, series of bubbles, yellowing, and rough surface of the board; Friction shear heat increases, causing material decomposition, yellowing of the board surface, and paste;
Excessive sliding and poor plasticization can cause scaling in the mold cavity and precipitation on the surface of the product, leading to white discharge, uneven wall thickness, and irregular back and forth movement of certain symptoms on the surface;
3. 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, and possible phenomena such as white discharge, adhesion to the mold cavity, and local overheating;
Excessive internal lubrication can cause the foam product to become brittle, resulting in a decrease in heat resistance. Under certain temperature and melt pressure conditions, it transforms into external lubrication, leading to an imbalance in lubrication;
Insufficient internal and external lubrication, high melt viscosity, high plasticizing torque, severe melt wall sticking phenomenon, yellow decomposition lines on the material surface, poor surface smoothness, and reduced mechanical properties of the product;
Both internal and external lubrication are excessive, the plasticizing torque is small, and the melt plasticization is significantly insufficient. Although the smoothness of the product is good, the adhesion of the pressure point is poor, which seriously affects the mechanical properties of the product;
Less internal lubrication, more external lubrication, significantly prolonged plasticizing time, reduced plasticizing torque, difficult product molding, and brittleness;
There is more internal lubrication and less external lubrication, the plasticizing time is significantly shortened, there is a more serious wall sticking phenomenon, the thermal stability time is shortened, and there are decomposition yellow lines on the surface of the product;
4. Calcium powder
Foam products are generally recommended to use light calcium with a particle size of around 1200 mesh. Calcium powder is prone to absorbing moisture and forming bubbles, silver lines, etc. on the surface of the product, which affects its appearance and physical properties. Therefore, it is important to store during the rainy season.
When the particle size of
Calcium Carbonate is too large, it is prone to uneven mixing, delayed plasticization time of the mixture, and low screw torque;
When the particle size of calcium carbonate is too small, it is easy to agglomerate and change from small particles to large particles, similar to the consequences of oversized particles;
When the dosage of calcium carbonate is too low, the foam lacks a core, the number of foam cells 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 cross-section of the board is prone to bubble breakage;
5. Foaming regulator
Foam conditioner generally refers to acrylic processing aids with a viscosity of 10 or above. Among them, wood plastic foam products such as ecological wood and wall panels generally use fast plasticizing types, while foam boards, especially cabinet boards, generally use foam conditioners with slow plasticization and high melt strength.
Insufficient foaming regulator, poor melt strength, uneven foam pores, and increased density in the cross-section;
Excessive foaming regulator, high melt strength, inability to expand bubbles in the melt, high product density, and easy occurrence of wave patterns, distortion and deformation on the surface of the board;
6. Foaming agent
The most commonly used foaming agents are AC yellow foaming agent and NC white foaming agent. AC releases a large amount of heat during the decomposition process, resulting in yellowing of the product and a small amount of ammonia odor during decomposition; NC absorbs heat during the decomposition process, and the decomposition is odorless, so two types are generally used in a coordinated manner in foam products.
Insufficient dosage of foaming agent, low foaming ratio, few foam holes in the product, and high density;
Excessive use of foaming agent can lead to a decrease in melt strength, making it difficult to shape the product and causing foam holes to form on the cross-section of the foam board; Beyond a certain range, the density of the product actually increases;
There are too many yellow foaming agents and too few white foaming agents, and the cross-section is prone to large and round bubbles.
Therefore, the dosage of various additives has a degree and mutual constraint relationship. A small quantity is not good, and a large quantity is not bad. In production practice, it is necessary to go through repeated experiments, fully utilize the coordination effect of various raw materials, find the optimal balance point, fully improve the melt strength and foaming efficiency, and extend the start-up time.
