Lubricants in PVC Additives

Polyvinyl chloride (PVC), a general-purpose plastic widely used in construction, packaging, electronics, automobiles, and many other fields, often has properties that are insufficient to meet complex processing and usage requirements. Therefore, the application of various lubricants, processing aids, impact modifiers, and other additives has become a key means to improve PVC performance and expand its application range.

External lubricants play the role of "lubricant messengers" in PVC processing. Their core function is to facilitate the smooth passage of PVC melt through processing equipment, reducing friction and adhesion between the melt and the metal surfaces of the equipment, ensuring stable and efficient processing.

From a mechanism of action perspective, external lubricants typically have low surface tension. Under the high-temperature environment of PVC processing, they can quickly migrate to the surface of the PVC melt and form a thin lubricating film at the contact interface between the melt and processing equipment (such as the barrel and screw of an extruder, and the mold of an injection molding machine).

This lubricating film acts like a "barrier," effectively reducing the coefficient of friction between the melt and the metal surface, thereby reducing energy consumption during processing and preventing localized overheating caused by excessive friction.

Simultaneously, it prevents PVC melt from sticking together within the processing equipment, allowing for smooth demolding or extrusion of the products, thus ensuring the appearance quality and dimensional accuracy of the finished products.

Common external lubricants include paraffin wax, polyethylene wax, stearic acid, and its salts. Different types of external lubricants have different performance characteristics.

For example, paraffin wax has good lubrication effects, but its thermal stability is relatively poor. Under high-temperature processing conditions, it is prone to volatilization or decomposition, thus affecting the durability of lubrication.

Polyethylene wax, on the other hand, has excellent thermal stability and lubrication durability, maintaining good lubrication effects over a wide temperature range. However, its compatibility is relatively poor, and excessive addition may affect the mechanical properties of PVC products.

In practical applications, it is necessary to rationally select the type and amount of external lubricant based on the specific processing technology (such as extrusion, injection molding, calendering, etc.), processing temperature, and product requirements.

Generally, the addition amount of external lubricant is between 0.1% and 1.0%. Insufficient addition will result in insignificant lubrication, potentially leading to processing difficulties and a rough surface. Excessive addition may cause precipitation, affecting the surface gloss and subsequent secondary processing performance (such as printing and coating).

In actual PVC processing, a single additive is rarely used alone; usually, multiple additives are used together to achieve synergistic effects and better performance improvements.

For example, using lubricants in combination with processing aids can not only improve the processing fluidity of PVC but also promote resin plasticization, further enhancing the surface and mechanical properties of the product. Using impact modifiers in combination with processing aids can enhance the impact resistance of the product while improving the processing process and ensuring the stability of product quality.

However, some issues need to be considered when selecting and using these additives. First, the compatibility between additives must be considered. Poor compatibility between different additives may lead to layering, precipitation, and other phenomena, affecting the effectiveness of the additives and the performance of the product.

Second, the total amount of additives added must be controlled. While the synergistic effect of multiple additives can improve PVC performance, excessive addition can not only increase production costs but also adversely affect the basic properties of PVC. Finally, the type and ratio of additives should be rationally selected based on the specific processing technology and product requirements to achieve the best cost-effectiveness and performance.

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