Does the particle turn white as soon as it is placed? 3 reasons for PVC frost deposition

doPVCPeople have all encountered this: the surface of newly produced particles is fine, but after a period of time, a layer of white frost like substance appears, which can be easily rubbed off by hand.

This is what is often said in the industrySpray frost.

　　First distinguish between true and false: distinguish the type of frost spray

Don't be in a hurry when encountering frost spray. Rub the white surface with your hand:

Can be wiped off and feels smooth - mostlylubricantorplasticizerPrecipitation;

Cannot be wiped off, the surface turns black - it may be a reaction product of fillers or stabilizers;

It only appears in cold weather - most likely due to the low-temperature precipitation of cold resistant additives.

Industries are usually divided into'Pressure analysis'(precipitation on the mold during processing) andSpray frost/oilThere are two types of precipitation on the surface of the finished product.

Distinguish before taking action, avoid taking detours.

More than 90% of frost spraying problems are rooted inrecipe.

PVC is a polar material, and many additives are non-polar. There is thermodynamic incompatibility between the two, and if the dosage exceeds the "capacity" of the system, it will migrate to the surface.

　　Focus on investigating three categories:

　　1. Excessive lubricant

If too much lubricant such as stearic acid and paraffin is added, exceeding the capacity of PVC, it will migrate to the surface and form a waxy white frost. This is the most common reason. Suggest reducing the amount of external lubricant used or switching to a higher molecular weight and lower mobility external lubricant variety; If there is an excess of internal lubricant, the internal lubrication system needs to be adjusted accordingly.

　　2. Plasticizer migration

Soft PVC is more common. Some plasticizers have limited compatibility with PVC, and the precipitation rate increases exponentially when the dosage exceeds 50 phr. It is possible to switch to higher molecular weight plasticizers or add additives to help stabilize.

　　3. Cold resistant additive precipitation

In winter or low temperature environments, some cold resistant plasticizers are more prone to frost spraying. The lower the temperature, the lower the solubility of the additive, and the faster the precipitation.

If there is no problem with the formula, it may also spray frost. The problem lies inProcessingUp there.

Insufficient plasticization, uneven mixing, and high local concentration of additives can cause them to run towards the surface.

Excessive temperature or shear strength are also not acceptable - the hydrogen chloride produced by PVC thermal degradation reacts with metal stabilizers to form white salt precipitates, which is a "false spray frost".

Many particles are fine when they leave the factory, but when they reach the customer's hands, they spray frost. The problem isstorageLink

High temperature and humidity, sudden cooling and heating, and lack of ventilation in the material pile can all accelerate precipitation.

　　3-step quick troubleshooting method

Appearance: Hand rub to determine if it is the precipitation of additives or the migration of fillers

Check the formula: focus on lubricants, plasticizers, and cold resistant additives

Verification: Determine the type using oven or freezing methods, and perform infrared analysis if necessary

The problem of frost spraying may seem simple, but it actually involves multiple aspects such as formula, process, and storage. Only by finding the root cause can it be completely solved.

　Author/Zhang Ziyi