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Precautions for using calcium and zinc stabilizers

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Precautions for using calcium and zinc stabilizers

January 22
18:35 2021

Advantages and disadvantages of calcium zinc stabilizers and lead salt stabilizers

1. Lead salt stabilizer

Advantage:

Good thermal stability, especially long-term thermal stability;

Good electrical insulation and weather resistance;

Low price

Good processing performance is suitable for various processes;

Disadvantages:

Chromatic aberration cannot be used for transparent products!

Two words: poisonous

2. Calcium and zinc stabilizer

advantage:

Green environmental protection products;

Thoroughly solve the phenomenon of sulfur and lead pollution;

A small amount of lead in the material may be combined with sulfur in the air, especially in places with high temperature and humidity.

Good switching adaptability; if the original lead salt stabilizer is used, replacing other stabilizers may cause cross contamination, but calcium and zinc stabilizers can dispel your worries.

The specific gravity is light, and inorganic fillers can be appropriately added to reduce costs.

2. Precautions for using calcium and zinc stabilizers:

Confirm the green and environmental protection of the stabilizer formula; pay attention to whether the content of heavy metals (lead, cadmium, tin, barium) can meet the product and meet the requirements of the new national standard.

The calcium-zinc stabilizer has a strong internal lubricating effect, and more external lubricants need to be added. This is introduced 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.

Pay attention to the mold cleaning cycle during the operation. The addition of calcium and zinc stabilizer lubricants is likely to increase the precipitation, which will affect the mold cleaning cycle. It has a greater impact on large-scale production, and it is necessary to strictly select stabilizers. If it is its own stabilizer, it needs to be combined with PE wax with good lubricating effect in the middle and late stages (such as Qingdao Bonny 108) or oxidized wax. Strictly control the degree of vacuum, which can reduce precipitation and prolong the cleaning time of the mold.

The formulation of a good stabilizer and the appropriate dosage have little effect on the appearance, material properties, and aging resistance of the product.

Calcium zinc stabilizer lubrication characteristics

In the process of replacing the lead salt stabilizer with calcium and zinc stabilizers, the process parameters must be adjusted appropriately, in the final analysis, to achieve the material properties and plasticization we need. Of course, it should be noted that calcium and zinc stabilizers use more lubricants than lead salts. Please look down.

First of all, we need to understand the difference in the main components of stabilizers:

Lead salt: 3PbO・PbSO4 (inorganic salt)

Calcium zinc:

Stearic acid:

The reason why stearic acid is also brought over is to give us a better understanding of the influence of the ingredients in calcium and zinc stabilizers on lubricity.

As mentioned before, to maintain the uniformity of the plasticization of PVC resin, the internal and external lubrication needs to be combined to transfer external energy to the PVC resin more uniformly, and stearic acid plays the role of internal lubrication. Look at the picture below. The small circle represents the polar carboxylic acid end of stearic acid. It is the function of this head that allows stearic acid to be adsorbed on the PVC resin particles, which can churn on the surface of the particles during processing. The role of internal lubrication.

Calcium stearate, zinc stearate and stearic acid have similar structures, with more charged calcium ions and zinc ions. How to understand charged ions? To put it bluntly, the polarity is actually the attraction of electric charges. The charge of calcium and zinc ions greatly enhances its polarity. It is necessary to know that calcium stearate, zinc, etc., have the strongest polarity among the lubricants commonly used in PVC. This gives it a stronger affinity with the PVC resin, thereby weakening or eliminating the attraction of the ionic bonds of the inner layers of the PVC resin particles, and promoting the intertwined chain segments of the PVC to easily diffuse, and the formed sliding layer has high viscosity and generates heat by friction. Large, high transmission efficiency of mechanical force, accelerates the temperature of the material, and initiates the resin over-plasticization. The lead salt itself has no such effect.

That is to say, in addition to its stabilizing effect, calcium and zinc stabilizers also shorten the plasticization time and promote plasticization. If the original lead salt stabilizer is used, use calcium and zinc stabilizer. Under the premise of using the same lubricant (including the stabilizer), the lead salt can produce qualified products, and the use of calcium and zinc will promote the advancement of materials Plasticization may cause no discharge.

Solution: Pay attention to the amount of stearic acid, use less if possible, choose a reasonable external lubricant, increase the amount of external lubricant, delay plasticization, and use less lubricant when heat-resistant conditions allow. Strictly control the performance indicators of other materials.

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