Left lead salt Right calcium zinc
one, Calcium zinc, Lead salt Stability advantages and disadvantages
1, lead salt stabilizer
Advantage:
Good thermal stability, especially long-term thermal stability;
Electrical insulation, good weather resistance;
Low price
Good processing performance suitable for various processes;
Disadvantages:
Chromatic aberration, cannot be used for transparent products!
Two words: toxic
2, calcium and zinc stabilizers
advantage:
Green products;
Thoroughly solve the pollution of sulfur and lead;
A small amount of lead in the material may combine with sulfur in the air, especially in hot and humid places.
Good switching adaptability; if lead stabilizers are used, replacing other stabilizers may cause cross-contamination, but calcium and zinc stabilizers can eliminate your concerns.
The proportion of light, can increase the inorganic filler, reduce costs.
two, The use of calcium zinc stabilizer notes:
Confirm the greenness of the stabilizer formulation; need to pay attention to whether the content of heavy metals (lead, cadmium, tin, antimony) can meet the requirements of the new national standards.
The calcium-zinc stabilizer has a strong internal lubricating effect. The external lubricant to be added is more. This is described below.
The thermal stability of calcium and zinc stabilizers is weaker than that of lead salts. The processing window is narrower and the control requirements are higher.
The operation process pays attention to the cycle of clear mold, the amount of calcium and zinc stabilizing agent lubricant is added, which will easily lead to increase of precipitation, which will affect the cycle of mold cleaning. The effect on large-scale production is greater, and the type of stabilizer should be selected strictly. If it is its own stability The agent needs to be accompanied by a PE wax (such as 108 Bonnie of Qingdao) or an oxidized wax with good lubricating effect in the later stage. It is also necessary to strictly control the degree of vacuum to reduce the precipitation and prolong the time for cleaning the mold.
Good stabilizer formulation and proper dosage have little effect on product appearance, material properties, aging resistance, etc.
Third, calcium and zinc stabilizer lubrication characteristics
In the process of replacing the lead salt stabilizer with a calcium-zinc stabilizing agent, the process parameters must be properly adjusted. Ultimately, it is necessary to achieve the material properties and plasticity that we need. Of course, it should be noted that the calcium zinc stabilizer used in the lubrication The amount of agent is more than lead salt. Please look down.
First, we need to understand the difference in the main components of the stabilizer:
Lead salt: 3PbO·PbSO4 (inorganic salt)
Calcium Zinc:
Stearic acid:
The reason why stearic acid is also brought in is to give us a better understanding of the effects of the ingredients in calcium and zinc stabilizers on lubricity.
As mentioned before, to maintain the uniform plasticity of PVC resin requires internal and external lubrication, the external energy is more evenly transmitted to the PVC resin, and stearic acid plays a role in internal lubrication. Look at the figure below, small circle represents hard The acid carboxylic acid with polar polarity, it is the role of this head can make stearic acid adsorbed on the PVC resin particles, can be in the process of the particle surface churning, play a role in internal lubrication.
Calcium stearate, zinc stearate, and stearic acid are structurally similar, with more charged calcium and zinc ions. How to understand charged ions, saying that the polarity is actually the attraction of the charge. Calcium The charge of zinc ion greatly enhances its polarity. It is known that the calcium stearate, zinc, etc. in the commonly used lubricants for PVC are the most polar. This gives it a stronger affinity with the PVC resin and thus weakens it. Eliminating the attraction of the ionic bonds in the layers inside the PVC resin particles, the PVC segments intertwined with each other are easy to diffuse, the formed sliding layer has high viscosity, large frictional heat, high mechanical transmission efficiency, and accelerated material heating. , Initiate the transitional plasticization of the resin. The lead salt itself does not have this effect.
In other words, calcium and zinc stabilizers not only have a stable effect, but also shorten the plasticizing time and can promote plasticization. If the original use of lead salt stabilizers, use calcium and zinc stabilizers, use the same lubricant (including Under the premise of stabilizing agent, using lead and salt can produce qualified products, and using calcium and zinc can promote the advance plasticization of materials, which may cause the phenomenon of no discharge.
The solution:
Pay attention to the amount of stearic acid, use less, use less, choose a reasonable choice of external lubricant, increase the amount of external lubricant, delay plasticization, use less lubricant if the heat-resistant condition permits. Strictly control the performance of other materials.