1. Stabilizer

   Polyvinyl chloride (PVC) has good acid and alkali resistance, wear resistance, electrical insulation, flame retardant and low price advantages, is a very widely used thermoplastic. Although PVC has many of the above advantages, it has a fatal disadvantage, that is, poor thermal stability. PVC usually begins to degrade when heated to 140 ° C, and its processing and molding temperature is about 160-200 ° C, therefore, heat stabilizer must be added when processing and molding to inhibit the degradation of PVC. At present, the traditional heat stabilizers are mainly those containing metal ions such as lead salts, organotin and metal soaps.

The action of the heat stabilizer is.

   1）Metal soaps that neutralize HCl organic acids, basic salts of some inorganic acids, epoxy compounds, amines, metal alkols and phenols and metal mercaptans can react quickly with the HCl released by PVC decomposition to generate harmless compounds and play a stabilizing role.Obviously, such stabilizers act as inhibitors only by accepting and neutralizing HCl, and cannot prevent the decomposition of PVC.  

  2)Unstable chlorine atoms play an important role in the degradation of PVC. Therefore, the most effective stabilizer should be substituted with the weak link in the PVC molecule - the unstable chlorine atom before the PVC decomposition occurs, so as to replace the unstable chlorine atom that is easily degraded by the more heat-stable group. Heavy metal hydroxates and mercaptans can play this role. However, further studies have shown that these salts also react with HCl, thus reducing the effective amount of the substitution reaction; Moreover, the formed heavy metal chloride will promote the degradation of PVC. Therefore, the synergistic action of heavy metal hydroxates with alkali metals or alkaline earth metal hydroxates and epoxides can be used to improve the stabilization efficiency. 

   3)React with the unsaturated site   

The addition reaction of a stabilizing group with the unsaturated double bond on the PVC chain can inhibit the deHC1, and the achromatic effect is caused by the opening of the double bond of the conjugated polyenes, which is another effective stabilizing effect. For example, metallic mercaptans react with HCf to form mercaptans, which can be added to double bonds to form stable thioether bonds on the PVC chain.  

   4)Ton impurity   

Phosphite teresters and other stabilizers have the effect of neutralizing or passivating some resin impurities, trace metal pollutants, initiator residues, etc., so as to improve the thermal stability of PVC resin.  
A single stabilizer is often better than to meet a variety of requirements, a variety of stabilizer composite is often used means, the most ideal composite effect is to produce synergistic effect.

   PVC foam products on the most used stabilizer is lead salt stabilizer and calcium zinc stabilizer, with the environmental protection requirements more and more stringent and the cost of calcium zinc stabilizer more and more high, the application of calcium zinc stabilizer began to become more and more extensive. In the extrusion process of sheet metal, especially wide sheet metal, the molten material flows far away in the mold and has a long retention time, which has higher requirements for the thermal stability and fluidity of the formula, and must also have a high degree of weather resistance as an outdoor user. Therefore, in addition to the excellent long-term heat stabilizer, the calcium zinc stabilizer for the plate also needs to contain an effective auxiliary heat stabilizer that inhibits the initial coloring and a light stabilizer that provides weather resistance.     

Lack of stabilizer, yellow surface, paste, products brittleness, strength reduction, low foaming rate; If the stabilizer is too much, the blowing agent will decompose in advance, the gas will overflow from the feeding hole and the vacuum hole, and the cavity structure will crack or shrink marks.

2. Function of lubricant

2.1 Increase the melt index

  The melting index of polymer melt is an important parameter to characterize its processing fluidity.Generally, with the increase of temperature, the melt index increases, and the melt flow rate increases. Due to the limitation of factors such as the thermal stability of the material, the processing temperature cannot be increased indefinitely. And by increasing the processing temperature to reduce the melt viscosity will also increase energy consumption. At this time, adding appropriate amount of internal lubricant can change the rheological behavior of the resin melt, effectively increase the melt index, and achieve the purpose of reducing the melt viscosity and improving the flow of the melt.

2.2 Reduce endogenous heat

 Endogenous heat is the heat generated by internal friction during polymer flow. In the high-speed machining molding process, high shear converts a large amount of mechanical energy into heat energy, and the greater the viscosity of the melt, the stronger the shear force, so the more endogenous heat generated.

   The adverse consequence of endogenous heat can cause the polymer melt to overheat locally and reduce its thermal stability. The addition of internal lubricant can effectively reduce the viscosity of the melt and reduce the endogenous heat. The possible adverse consequence is that the low melt viscosity may make it difficult to carry out processes such as injection molding, in which case we should choose to give the internal structural units of the resin a high enough lubricity. A lubricant that also has a minimal effect on solvation of the polymer. In this way, the processing stability can be improved by reducing the friction heat generated by the internal interface of the resin or the generated endogenous heat can be dissipated as soon as possible, and the problems such as the reduction of melt viscosity and the decrease of the thermal deformation temperature of the product can be avoided.

2.3 Demoulding action

After the polymer processing, the product is formed. At this time, it needs to be relatively easy to fall off from the abrasive tool to improve processing efficiency and product quality. At this time, a lubricant with a demoulding effect can be added. The release lubricant is generally an external lubricant, mostly polar compounds, which have limited compatibility with the resin, can migrate from the melt to the surface, and the polar group has a certain affinity with the metal surface. In this way, a relatively stable and mutually isolated molecular layer is formed between the melt and the metal surface, thus inhibiting the adhesion between the polymer melt and the surface of the processing machine.

2.4 Delay plasticizing 

Delayed plasticization is another form of external lubricity in plastic processing. In PVC processing,PVC resin is melted under shear deformation and evenly mixed with various auxiliaries, and the requirements for resin melting are not consistent in specific circumstances. For example, in the initial stage of the molding process, it is often not desirable to prematurely melt the resin particles, and sometimes in order to obtain the best mechanical properties of the final product, the resin is not required to completely melt, which is especially obvious in the surface of high-impact polyvinyl chloride processing. By combining lubricants with low compatibility in the resin, it can migrate to the surface of the resin particles or melt at the processing temperature, so as to form a lubricating layer on the surface of the resin particles or melt and the metal surface of the processing machine, so as to produce a good slide, weaken the shear deformation effect, and delay the purpose of resin plasticization.

2.5 Prevent melt rupture

High viscosity at high shear rates leads to a surface phenomenon called melt cracking, which occurs because the precipitated material undergoes a regular adhesion/slip transition in the flow channel.

2.6 Improve the self-lubricity of the product 

Many plastic products require a good surface lubrication effect, such as gears, lubricants with external lubrication effects can often form a self-lubricating layer through migration or seepage to the surface of the product, resulting in permanent lubrication.
2.7 Smooth and anti-adhesion function

For plastic products with large specific surface area, surface adhesion often brings many difficulties to its production or application, many lubricants with external lubrication effect migrate to the surface of the product larger, and after cooling can form a evenly distributed thin coating, because the two interfaces are inserted into the isolation layer, so it gives the surface of the product sliding, and does not cause surface roughness. This functional additive is called a smoothing agent.

2.8 External Lubricant    
The most used external lubrication on foamed products are generally paraffin and PE wax, paraffin is easy to precipitate, so PE wax is generally used.     
External slip is insufficient, extruder 4, 5 zone temperature, not easy to control, easy to overtemperature, the board surface appears large bubble, bubble, yellow, plate surface rough; Friction shear heat increase, causing material decomposition, plate surface yellow, paste; 

Excessive external slip, poor plasticization, resulting in mold cavity scaling and product surface precipitation, prone to leucorrhea, uneven wall thickness and some symptoms on the surface of the irregular back and forth phenomenon.

2.9 Internal Lubricants   
Commonly used internal lubricants are stearic acid, 60, single glycine, 316 and so on.     
Internal lubrication is insufficient, material dispersion is not good, uneven plasticization, product thickness is difficult to control, the foam board is thick in the middle and thin on both sides, and there may be leucorrhea, adhesion to the mold cavity and local overheating.    

Excessive internal lubrication, foaming products brittle, heat resistance decline, and under a certain temperature and melting pressure into external lubrication, resulting in lubrication imbalance.  
The 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, and the mechanical properties of the product are reduced.     

The internal and external lubrication is excessive, the plasticizing torque is small, the melt plasticization is obviously insufficient, although the product has good smoothness, the pressure point bonding is poor, which seriously affects the mechanical properties of the product.     

The internal lubrication is less, the external lubrication is more, the plasticizing time is obviously extended, the plasticizing torque is reduced, the product is difficult to form and becomes brittle.    

The internal lubrication is more, the external lubrication is less, the plasticizing time is significantly shortened, there is a serious sticky wall phenomenon, the thermal stability time is shortened, and the surface of the product has a decomposition yellow line.

3. Calcium carbonate   

calcium carbonate molecular formula is CaCO3, molecular weight is 100, is a white powder, colorless, odorless, non-toxic, relative density of 2.71. The melting point is 1339℃. Slightly soluble in water, 10% suspension pH is 8 ~ 10. In case of dilute acid or heating to 825℃ decomposition, calcium oxide is generated, and carbon dioxide is released.

Calcium carbonate is the most commonly used filler, abundant resources, cheap. Calcium carbonate filler is divided into light calcium carbonate and heavy calcium carbonate, and the most commonly used filler is light calcium carbonate, and there are industrial precipitated calcium carbonate and ultra-fine active calcium carbonate series.

Light calcium carbonate is precipitated calcium carbonate, calcined from natural limestone into lime, and then put into water for digestion, carbon dioxide is inserted into the obtained lime milk (calcium hydroxide water emulsion) for carbonation, so that calcium carbonate precipitation, collection of precipitation, drying. The precipitation method has uniform particle size, large specific surface area, and good dispersion in the polymer base material.

Ultrafine calcium carbonate is a special crystalline calcium carbonate fine powder with an average particle size of less than 0.4um, all passed through the 325-mesh screen, oil absorption ≦40mL/100g, water ≦0.4%.

Active calcium carbonate (colloidal calcium carbonate) refers to calcium carbonate filler obtained by treating with chemical substances such as advanced fatty acids. The surface treatment of calcium carbonate with fatty acid (such as stearic acid, lauric acid, capric acid, etc.) or fatty acid salt solution, organosilane coupling agent, etc., can make the surface of the filler particles coated with a layer of hydrophobic organic matter. Through modification, can improve the compatibility and binding force of the filler and polymer, reduce the water absorption of the filler itself, used in polyurethane sealant and other systems, can improve storage stability, and can increase the amount of filler without reducing the performance of the product.

The average particle size of micro-active calcium carbonate is ≦1.0um, the oil absorption value is 85 ~ 110mL/100g, the calcium carbonate (on dry basis) ≧96.0%, the activation rate ≧96%, the water content ≦0.50%, the whiteness ≧90. The fatty acid content was (1.0±0.5) %. The bulk density is 0.40 ~ 0.60g/mL, and the specific surface area (BET) is generally 25 ~ 50m2/g.

Heavy calcium carbonate, also known as stone powder, is made from natural limestone by dressing, dry grinding and grading.  There are heavy active calcium carbonate, heavy ultra-fine calcium carbonate, heavy micro-fine calcium carbonate and various whiteness (85 ~ 95) of various fineness (120 ~ 600 mesh) of heavy calcium carbonate. The heavy calcium carbonate is subdivided into single powder, double powder, three powder and four powder according to the fineness. Sanfei powder is commonly used, its calcium carbonate content ≧95%, water ≤ 0.5%, 45um sieve residue ≤ 0.5%.

  Foamed products generally use light calcium with a particle size of about 1200 mesh, calcium powder is easy to absorb moisture and form bubbles and silver lines on the surface of the product, affecting the appearance and physical properties, so pay attention to rainy season storage.   

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 torque of the screw is low. When the particle size of calcium carbonate is too small, it is easy to agglomerate, from small particles to large particles, similar to the consequences of too large particles.

When the dosage of calcium carbonate is too low, the number of pores 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 plate section is prone to bubble breaking.

4, foaming regulator    
PVC foam regulator belongs to acrylic processing AIDS, has all the properties of ordinary processing AIDS, with PVC has unparalleled compatibility with other materials, can achieve melt plasticization of PVC at a lower temperature, and can speed up plasticization, forming a gel network, and then improve melt fluidity and surface gloss. We know that PVC is an amorphous material, and the melt strength decreases with the increase of melt temperature, and the melt strength increases with the decrease of melt temperature.      

It can greatly improve the melt strength of PVC materials. Industrial production of PVC molecular weight is generally 50,000-110,000, the molecular weight of the foam regulator is much more than the molecular weight of PVC, can be very good PVC molecules wrapped together, through the amount of adjustment, can make the foam core in a controllable range of expansion, prevent the occurrence of bubbles and gas overflow, and can solidify the bubble body, prevent the collapse of the bubble body, the formation of a large number of uniform small bubbles. We know that when a large bubble is broken down into numerous small bubbles, the comparative area of the bubble will be greatly increased, and the volume of the product will not change, so the density will be greatly reduced.     

Of course, foaming regulators are divided into many varieties, only for more product design. For example, foam board, free foam board, relatively thin, need better fluidity and lower melt strength, in the selection of the need to choose plasticizing faster, slightly smaller melt strength of the foam regulator, and the crust foam cabinet board, for the melt strength requirements are relatively high, should choose the melt strength of the foam regulator. For foaming regulators, plasticizing fast and melt strength is a contradiction, plasticizing fast and melt strength is large, it is bound to have better results on foaming products    

Foaming regulator generally refers to the viscosity of more than 10 acrylic processing AIDS, of which ecological wood, wallboard and other wood plastic foam products generally use the type of plasticizing fast, foaming board, especially the cabinet board, generally use plasticizing slow melt strength of foaming regulator.     
The foaming regulator is insufficient, the melt strength is poor, the bubble hole is not uniform, the section will appear the bubble hole, the density increases.    
Foaming regulator too much, melt strength is too large, the bubble in the melt can not expand, the product density is high, the plate surface is easy to appear wavy, distorted deformation;

5. Foaming agent  
The largest amount of blowing agent is AC yellow blowing agent and NC white blowing 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 smell; NC will absorb heat during the decomposition process, and the decomposition is tasteless, so the two kinds of foam products are generally coordinated.    

The amount of foaming agent is insufficient, the foaming ratio is low, the product has fewer bubble holes and larger density.     
If the amount of foaming agent is too much, the melt strength will be low, the product is difficult to form, and the section of foaming board is easy to produce bubble holes; Beyond a certain range, the product density becomes larger.     

Yellow blowing agent is more, white blowing agent is less, and the cross section is easy to appear large and round bubble holes.     
Therefore, the amount of various auxiliaries have a degree and mutual constraints, the amount is not small, not much is not good, in the production practice must go through repeated trials, give full play to the coordination effect of various raw materials, find the best balance point, fully improve the melt strength and foaming efficiency, extend the boot time.