Unbalanced characterization of various additives in PVC foams application
The most widely used stabilizers in PVC foamed products are lead salt stabilizers and calcium zinc stabilizers. With the more strict requirement of environmental protection and the higher performance-price ratio of calcium zinc stabilizers, the application of calcium zinc stabilizers becomes more and more extensive.
The stabilizer is insufficient, the board surface yellows, the product brittleness is big, the strength reduces, the foaming rate is low;
Too Much stabilizer, foaming agent decomposition ahead of time, gas will be from the feed hole and vacuum hole overflow, a cavity structure will crack tendons or contraction mark.
2. External Lubricant
Foaming products on the application of the most external lubrication general paraffin wax, Pe wax, paraffin wax is easy precipitation, so the general use PE wax.
Lack of external slip, extruder 4,5 zone temperature, not easy to control, easy to over-temperature, plate surface appears big bubble, string bubble, yellowing, plate surface roughness;
Too much external sliding, bad plasticizing, resulting in mold cavity scale and product surface precipitation, easy to appear white band, wall thickness and some symptoms in the surface moving back and forth;
3. INTERNAL LUBRICANT
Common internal lubricants are stearic acid, 60, monoglyceride, 316 and so on
Lack of internal lubrication, poor dispersion of materials, uneven plasticization, product thickness is difficult to control, foam plate on both sides of the thick thin, there may be white belt, adhesion to the cavity and local overheating;
Too much internal lubrication: the foaming products become brittle, the heat resistance decreases, and in a certain temperature and melting pressure changes to external lubrication, resulting in lubrication imbalance;
The internal and external lubrication are insufficient, the melt viscosity is bigger, the plasticizing torque is bigger, the melt adhesion wall phenomenon is serious, the material surface has the yellow decomposition line, the surface smoothness is bad, the Product Mechanical Property Reduces;
Internal and external lubrication are excessive, plasticizing Torque is small, melt plasticizing is obviously insufficient, although the product smoothness is good but the pressure point adhesion is poor, seriously affect the mechanical properties of products;
The internal lubrication is less, the external lubrication is more, the plasticizing time is obviously prolonged, the plasticizing torque is reduced, the products are difficult to form, Brittle;/n/nThe internal lubrication is more, the external lubrication is less, the plasticizing time is shortened obviously, the wall sticking phenomenon is more serious, the heat stable time is shortened, the product surface has the decomposition yellow line;
Foamed products generally choose the particle size of about 1200 Mesh of light calcium is appropriate, calcium powder easy to moisture and formed on the surface of products, such as bubbles, silver, affect the appearance and physical properties, so pay attention to the 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 screw Torque is low.
When the size of calcium carbonate particles is too small, it is easy to agglomerate, from small particles into large particles, similar to the consequences of particles too large;
When the dosage of calcium carbonate is too small, the number of foam cells and the foaming rate decrease.
When the dosage of calcium carbonate is too much, the relative content of Resin in the component is reduced, the melt strength is reduced, and the plate section is easy to be broken.
5. Foam regulator.
Foam regulator generally refers to the acrylic processing AIDS with viscosity of more than 10, including eco-wood, wainscot and other wood-plastic foaming products generally use the type of rapid plasticization, foaming board especially Cabinet Board general selection of plasticizing slow melt strength of foaming regulator.
The foaming regulator is insufficient, the melt strength is poor, the foam hole is uneven, the cross-section will appear the foam hole, the density increases;
The foaming regulator is too much, the melt strength is too big, the bubble in the melt can not expand, the product density is high, the plate surface is easy to appear the ripple, the distortion and so on;
6. Blowing agent
The most used foaming agent is AC yellow foaming agent and NC white foaming agent, AC will give off a lot of heat during the decomposition process, resulting in products yellowing, and decomposition will have a small amount of ammonia; NC will absorb heat during the decomposition process, and decomposition tasteless Therefore, two kinds of foam products in general coordination.
The dosage of foaming agent is insufficient, the foaming rate is low, the product has few foam holes and the density is large/n/nIf the amount of foaming agent is too much, the melt strength will become low, the products will be difficult to form, and the cross-section of foaming board will be easy to form bubbles.
Yellow foaming agent more, less white foaming agent, section prone to large and round foam.
Therefore, the dosage of various auxiliaries has a relationship of degree and mutual restriction.In production practice, it is necessary to go through repeated tests to give full play to the coordination effect of various raw materials and find the best balance point Fully improve melt strength and foaming efficiency, extend the start-up time.