There are many kinds of lubricants, each specific product has specific different characteristics, can be familiar with each specific lubricant product performance advantages and disadvantages, the use of methods, is conducive to our better design of excellent formula. This requires long-term practice and verification by field technicians, and continuous summing up of practical application experience.

On how to choose the right lubricant, we have explored certain methods and bases in practice:

1. Substructure of lubricant score
The understanding of the molecular structure of the lubricant, including functional group, chain length, single double bond, branch chain, isomerization, etc. is helpful to make a preliminary judgment of the lubricant properties.

But chemically, small differences in the structure of the same kind of substance can lead to huge differences in performance. For example, substances with the same molecular structure sometimes have very different properties and effects of cis-trans chemical structures. Therefore, when examining a lubricant, the molecular structure can only be a preliminary performance determination, and can not be too hasty and arbitrary.

2, the polarity of the lubricant
As previously introduced, according to the principle of similar dissolution, PVC is a polar material, and the lubricant is a polar or non-polar substance, which can be roughly used as the definition of internal lubrication and external lubrication.

The word "similar" or "similar" must be grasped in polarity. If it is the same polar material, but the polarity is very different from that of PVC, it will not be well dissolved.

3. Heat resistance of lubricant
The heat resistance of lubricant has always been an important indicator ignored by most production technicians! The heat resistance of a lubricant refers to the ability of a lubricant to resist thermal decomposition or changes in the properties of a heated material.

The use environment of lubricant is in high temperature materials, machine screws, screws, molds, if the lubricant has been thermal decomposition or material properties have changed at the temperature used, it will not be able to play a lubricating role. At the same time, the residual material decomposition by heat decomposition will also affect the performance and appearance of PVC products. We often see mold coke, product surface drawing and other defects, often with the lack of heat resistance of the lubricant decomposition has a great relationship.

So we often see that if we use lubricants with poor heat resistance, such as stearic acid, paraffin, PE wax with low melting point, etc., there is often insufficient lubrication in the later processing period, resulting in processing difficulties, or poor gloss on the surface of the product, which is because the decomposition failure is insufficient lubrication in the later period. If at this time we add good heat resistant PE wax, ester external slip agent or high quality heat resistant good oxygen PE wax, we can solve the problem.

Many technicians in the design of the formula, often with "early lubricant", "medium lubricant", "late lubricant". In terms of experience: in this way, there is a complete lubrication system before and after processing to ensure that the processing is smooth. In fact, this is because most of the "early lubricant" begins to decompose and fail in the middle of the processing, and most of the "middle lubricant" begins to decompose and fail in the late processing.

If there is a lubricant that has excellent heat resistance, plays an external lubrication role in the early stage, and does not decompose and fail in the middle and late stages, then this lubricant has the role of "early lubricant", "middle lubricant", and "late lubricant" at the same time.

As we introduced the ester lubricant know: the ester lubricant melting point is low, between 45 and 65 ° C, but the ester lubricant has good heat resistance, the general heat resistance temperature range from 200 to 320 ° C, in PVC processing basically will not fail and decompose. Therefore, extra-ester lubricants can have the effect of early, middle and late lubrication at the same time. This is also the reason why the overall amount of ester lubricants added in the PVC formula is nearly half less, because there is basically no consumption and decomposition.

How to test and know the heat resistance of a lubricant, the strict practice is to carry out thermogravimetric test (TGA test), but because the TGA test is relatively complex and the equipment is expensive, the general factory has the conditions to carry out a simple evaluation of the oven heat test

4. Volatility resistance of lubricant

In the same way, the volatility resistance of lubricants has always been ignored by most production technicians. Resistance to volatility refers to the ability of a material to resist changing from a solid or liquid to a gas at a certain temperature.

If a lubricant has good lubrication effect and good heat resistance, but most of it is vaporized and evaporated during processing, then this lubricant is not a good lubricant. Like hexadecadecyl alcohol, stearic acid, etc.

To determine or test the volatility of the lubricant, you can generally refer to an indicator: flash point. The higher the flash point, the better the volatility resistance.

In particular, it is also mentioned that ester lubricants have relatively good volatility resistance, and the flash point is roughly 210 to 240 degrees, or even higher. Generally, there is very little volatilization at the PVC processing temperature.

In actual production, if the vacuum port precipitation is serious, it is generally caused by the volatilization of lubricant.

5, the melting point of the lubricant
The melting point of the lubricant is often used by many technicians as the only criterion for judging the lubricant, in fact, this is a misunderstanding. Melting point, as an index in the evaluation of lubricant, has certain limitations and inaccuracies.

The melting point can only be used as a criterion to determine the effectiveness of the lubricant, but not as a criterion to determine the temperature range of the lubrication effect. As mentioned in the above two sections, the more important indicator of the lubrication effect of the processing temperature range is the heat resistance and volatility of the lubricant.

Many technicians have formed a vague and inaccurate concept: low melting point lubricants correspond to "early lubrication", medium melting point lubricants correspond to "medium lubrication", and high melting point lubricants correspond to "late lubrication". In fact, the accurate statement should be: low heat resistance and low volatile resistance of the lubricant corresponding to "early lubrication", high heat resistance and volatile resistance of the lubricant corresponding to "late lubrication".

We know from chemical substances that the melting point of a substance has no corresponding relationship with the heat resistance and volatility resistance of a substance.  Only in a certain class of substances can such a correspondence be possible.  For example, PE wax with pyrolysis method has a higher melting point, higher molecular weight and better heat resistance.  However, if it is the same PE wax, the poly PE wax with low melting point may have better heat resistance and better lubrication than the PE wax with high melting point
Collaborative application of lubricants

he lubricant has different melting point, different internal and external lubrication effect, and different compatibility with PVC. Therefore, a perfect PVC formula often requires a variety of lubricants to be used together to achieve the ideal effect.

Lubricants with low melting point have better initial effect, such lubricants include paraffin wax, butyl stearate, stearyl alcohol, polyol ester, stearic acid, etc.

Lubricants with high melting point are generally used as late lubrication, such lubricants are calcium stearate, barium stearate, 316 and so on.
The use of calcium stearate alone in the formula can accelerate plasticization, improve melt viscosity, increase torque, and have a certain demoulding effect, while the use of paraffin alone shows delayed plasticization, reduce torque, and no demoulding effect. When calcium stearate and paraffin wax (polyethylene wax) are mixed according to a certain proportion, good results are shown, and the material torque value can be reduced a lot, which is because the paraffin penetrates into the calcium stearate molecules, strengthening the lubrication effect, showing a strong synergistic effect. The same effect is also stearic acid and paraffin.

The use of a variety of lubricants in the PVC formula, penetrate each other, make up for the temperature difference, not only can reduce the total amount of lubricants used, but also make the processing range of PVC formula wider, improve the uniformity of PVC melt structure, improve the mechanical properties and appearance quality of the material, and ensure the lubrication balance of the material extrusion process. 

Comparison of the influence of various lubricants on PVC plasticizing speed

Calcium stearate plasticized the fastest, followed by monoglyceride, 60 again, and again lead stearate, oxidized polyethylene wax, stearic acid, PE wax, paraffin wax plasticized the slowest. Epoxy soybean oil, a plasticizer, has obvious effect on improving melt fluidity.

Lubricants generally have the characteristics of internal lubrication and external lubrication at the same time, and cannot absolutely have a single performance. In terms of the use effect, the greater the polarity, the better the compatibility with PVC, the more obvious the effect of increasing the inter-molecular mobility of PVC, the internal lubrication is dominant, on the contrary, the more prominent the non-polarity, the external lubrication is dominant.

In practical application, calcium stearate, monoglyceride, PETS, 60 and other internal lubrication is more prominent; PE wax, paraffin, 74 and other external lubricity is more prominent. Stearic acid, 316 series oxidized polyethylene wax, both inside and outside lubricity, 316 series release property is better.