Some resin or film products have inherent properties that do not meet the requirements of the processing technology, and need to add additives to change their processability. Others have better processability, but the product performance can not meet the requirements, and additives should be added to change the product performance.

  Requirements for Auxiliaries in Films

  Compatibility

  Poor compatibility will lead to "migration" phenomenon, which is manifested in "sweating" in liquid auxiliaries and "frosting" in solid auxiliaries.

Sometimes, when the film is not strictly required, it can be allowed to be incompatible, such as the incompatibility between filler and resin is not good. As long as the filling particle size is small, it can still meet the basic requirements of film performance. If treated with coupling agent or surfactant, it can better play its role. However, some additives, such as openers and antistatic agents, which can improve the surface properties of thin films, are required to have a slight mobility in order to make them play a role on the surface of thin films.

  Durability

  Auxiliaries are required to exist in thin films for a long time without or little loss, and the loss of auxiliaries is mainly through three ways: volatilization, extraction and migration. This is mainly related to the molecular weight of the additives, the solubility in the medium and the solubility in the resin.

Processing conditions

The processing conditions of some resins are harsh. If the processing temperature is high, we should consider whether the selected additives will decompose and whether the additives have corrosive effect on the processing equipment.

  Film usage

  Films for different purposes have different requirements on the odor, toxicity, weather resistance and thermal properties of additives. For example, plastic bags for food are different from those for general packaging because they are non-toxic.

Synergistic and antagonistic effects in the coordination of auxiliaries

In the same resin system, some two kinds of additives will produce "synergistic effect". If improperly matched, some additives may produce "antagonism", which will weaken the function of each additive, or even make it lose its function, such as carbon black and phenolic antioxidants combined will produce antagonism.

  Auxiliaries to Change Film Packaging Performance

  Plasticizers and heat stabilizers

  Plasticizers and thermal stabilizers can greatly improve the compatibility of film materials.

  Plasticizer, as its name implies, is to increase the plasticity of materials. On the one hand, it increases the fluidity of resin and improves the processing performance. On the other hand, it can make the film more flexible and elastic.

Thermal stabilizers are mainly used to improve the thermal stability of resins.

Light stabilizer

  Polymer materials will rapidly aging under the irradiation of sunlight, light and high-energy radiation, showing yellowing, brittleness, cracking, surface loss of luster, mechanical and electrical properties greatly reduced, and even lost the use value. In this complex process of damage, ultraviolet radiation is the main cause of aging of polymer materials. This is mainly due to the combined action of ultraviolet light in the sun and oxygen in the atmosphere on polymer macromolecules.

The role of light stabilizers:

It can effectively absorb ultraviolet radiation with wavelength of 290-410 nm, eliminate or weaken ultraviolet radiation, protect polymer film from ultraviolet radiation and oxygen damage, prolong service life and improve light resistance of materials. Since most of the light stabilizers can absorb ultraviolet light, they are also called ultraviolet absorbers.

  Addition of light stabilizer:

  According to the mechanism of light stabilizer, it can be divided into: light shielding agent (pigments), ultraviolet absorber, ultraviolet quenching agent, free radical trapping agent. These four modes of action constitute four levels in the process of light stabilization.

  The anti-aging effect of light stabilizer is remarkable even though the amount of light stabilizer is very small. Generally, only 0.1%~0.5% of the weight of polymer is needed.

  Antioxidants

  For most plastic varieties, in the process of manufacture, processing, storage and application, they are sensitive to oxidative degradation. Oxygen infiltration into plastic films can react with almost all polymers, leading to degradation or cross-linking, thus changing the properties of materials. A small amount of oxygen can dramatically change the strength, appearance and properties of these polymers. Under hot working and sunshine, the oxidation rate is faster. Therefore, the oxidation of polymers is usually divided into thermal oxidation and photooxidation. The final result of this reaction is performance aging. If these reactions are not stopped, the polymer can be oxidized quickly and lose its use value.

Different plastics have different stability to oxygen, so some plastics do not need antioxidants. Some must be added antioxidants. The function of antioxidants is to capture the active free radicals and interrupt the chain reaction. The purpose is to delay the oxidation process and speed of plastics.

Generally speaking, the protective effect of amine antioxidants is higher than that of phenols. However, due to the varying degrees of discoloration of amines under the action of light and oxygen, they are not suitable for light, bright and transparent films, so they are seldom used in plastic films.

According to the antioxidant effect, antioxidants are divided into main antioxidant and auxiliary antioxidant. Aniline has better antioxidant effect, but its pollution is bigger. It is mainly used in rubber products. Phenolic antioxidant effect is slightly worse, but its pollution is smaller and its comprehensive effect is better. It is mostly used in plastic film. Mercaptan or thioester and phosphite are usually classified as auxiliary antioxidants and used with main antioxidants to produce synergistic effects and prolong the effectiveness of antioxidants.

Lubricant

Polymers usually have a high viscosity after melting, when added