Category and application of plastic additives for

2022-08-19
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Category and application of plastic additives for plastic film processing

plastic additives are chemicals added to improve the processability and serviceability of resins. There are usually more than ten kinds of plastic additives used. With the increase of plastic varieties, the expansion of applications and the continuous progress of processing technology, the types and varieties of additives are also increasing

plastic additives should be added in the processing and use of plastic films. Because the inherent properties of some resin or film products do not meet the requirements of the required processing technology, adding additives only needs to change their processability; However, some materials have better processing performance, but the product performance can not meet our requirements, so additives should be added to change the product performance. Of course, these two functions complement each other, sometimes to achieve these two purposes at the same time. Here we first introduce the additives that can change the performance of plastic packaging film

General requirements for additives

compatibility generally speaking, only when the additives have good compatibility with the resin, can the additives exist in the film for a long time, stably and uniformly, and play their functions effectively. If the original intention of "making copper alloy functional new materials is not compatible, it is prone to" migration ". It is "sweating" in liquid additives and "frost spraying" in solid additives. However, sometimes when the requirements for the film are not too strict, it can still be allowed to lack some compatibility. For example, the compatibility between the filler and the resin is not good, but as long as the particle size of the filler is small, it can still basically meet the performance requirements of the film. Of course, if it is treated with coupling agent or surfactant, it can give full play to its function. However, some additives that improve the surface properties of the film, such as opening agent and antistatic agent, require a little mobility to play a role on the surface of the film

durability durability requires that additives exist in the film for a long time with little or no loss, and the loss of additives 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. Adaptability to processing conditions some resins have harsh processing conditions, such as high processing temperature. At this time, whether the selected additives will decompose and whether the additives have corrosive effect on processing equipment should be considered

restrictions of film uses on additives. Films with different uses have certain requirements on the odor, toxicity, weather resistance, thermal performance, etc. of additives. For example, plastic bags for food are required to be non-toxic, so the additives used are different from those used in plastic bags for general packaging

synergism and phase antagonism in the coordination of additives in the same resin system, some two additives will produce "synergism", that is, they play a greater role than using a certain additive alone. However, if it is not properly matched, some additives may have "mutual resistance", which will weaken the function of each additive and even make some additives ineffective. This should be paid special attention to, for example, the combination of carbon black and amine or phenolic antioxidants will produce antagonism. Plasticizer and heat stabilizer plasticizer, which are commonly used in plastic packaging films, as the name suggests, are substances that increase the plasticity of materials, that is, substances added to the resin, on the one hand, increase the fluidity of the resin during molding, improve the processing performance, and on the other hand, increase the flexibility and elasticity of the film after making

heat stabilizer is an additive added for the purpose of improving the thermal stability of resin. It is mainly used for processing PVC and vinyl chloride copolymer. Under the irradiation of sunlight, light and high-energy rays, light stabilizer polymer materials will rapidly age, showing yellowing, embrittlement, cracking, surface loss of gloss, mechanical and electrical properties are also greatly reduced, and even eventually lose their use value. In this complex destruction process, ultraviolet light is the main reason for the aging of polymer materials. It is mainly the result of the combined action of ultraviolet rays in sunlight and oxygen in the atmosphere on polymer macromolecules

in order to protect the polymer material film from the damage of ultraviolet and oxygen and prolong their service life, light stabilizers are added to the plastic material, so this pair of parameter plastic materials should also be considered in the selection, so that they can absorb the ultraviolet energy in the resin and convert the absorbed energy in a harmless form. To inhibit or weaken the role of photodegradation and improve the light resistance of the material. Since most light stabilizers can absorb ultraviolet light, they are also called ultraviolet absorbers. To evaluate the quality of an ultraviolet absorber, we should consider the efficiency, processing, price, non-toxic, etc., and we cannot emphasize oneortwo effects alone. These conditions are summarized as follows:

can effectively absorb ultraviolet light with a wavelength of 290~410nm, and the absorption bandwidth; It can effectively eliminate or weaken the destructive effect of UV on the polymer, but has no effect on other physical and chemical properties of the polymer

n itself has good stability. After long-term UV exposure, it can improve the yield and yield without decreasing

n good thermal stability, no failure and discoloration due to heating during processing and use; It does not affect the processability of the polymer

n has good compatibility with polymers, does not separate and migrate during processing and use, is not easy to be extracted by water and solvent, and is not easy to volatilize

n non toxic or low toxic

n it is chemically stable and does not react with other components in the material to damage the performance of the material

n has low absorption of visible light, no coloring and discoloration

n it is cheap, easy to manufacture and rich in sources

according to the action mechanism of light stabilizers, they can be divided into four categories: ① light shielding agents (pigments); ② Ultraviolet absorbent; ③ UV quenching agent; ④ Free radical trapping agent. These four action modes constitute four levels that gradually deepen in light stabilization. Each level can inhibit the destructive effect of ultraviolet rays on polymer bodies. In the specific design coordination, it is a level or the protection of each level, which should depend on the requirements of the film and the use environment. After adding light stabilizer, although the amount is very small, its effect of preventing aging is very significant, generally only 0.1% to 0.5% of the weight of polymer needs to be added

there are many commonly used light stabilizers, which mainly include: ① o-hydroxybenzophenones (such as UV-9, UV-531, etc.); ② Benzotriazoles (such as UV-P, UV-327, UV-326, etc.), ② salicylates (bad, TBS, etc.); ④ Triazines; ⑤ Substituted acrylonitrile ⑥ organic nickel complex; ⑦ Hindered amines. Among these absorbers, benzotriazole and triazine are the best

antioxidants have certain sensitivity to oxidative degradation in the process of manufacturing, processing, storage and application of most plastic varieties. Oxygen can penetrate into the plastic film and react with most polymers to cause 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 polymer materials. Under thermal processing and sunlight, the oxidation rate is faster. Therefore, the oxidation of polymers is usually divided into thermal oxidation and photooxidation. Finally, the result of this reaction is performance aging. If this kind of reaction is not prevented, it can quickly oxidize the polymer and lose its use value. Different plastics have different stability to oxygen, so some plastics do not need to add antioxidants. Some must be added with antioxidants. The role of antioxidants is to capture active free radicals and interrupt the chain reaction, in order to delay the oxidation process and speed of plastics. According to the action mechanism of antioxidant, it is effective for all plastics

the chemical structure of antioxidants can be divided into: 1. Phenols, including: mono phenol, bisphenol, triphenol, polyphenol, hydroquinone, thiobisphenol; 2. Amines, including naphthylamine, diphenylamine, p-phenylenediamine, quinoline derivatives, as well as phosphite esters, thioesters and other kinds

among the above categories, phenols and amines are the main antioxidants, accounting for more than 90% of the total. Generally speaking, amine antioxidants have higher protective efficacy than phenols. However, amines change color to varying degrees under the action of light and oxygen, and are not suitable for light, bright and transparent films, so they are less used in plastic films

according to the antioxidant effect, antioxidants are divided into main antioxidants and auxiliary antioxidants. Aniline has good anti oxygen effect, but it is highly polluting, and is mainly used in rubber products; Phenols have poor antioxidant effect, but less pollution and better comprehensive effect. They are mostly used in plastic films. Usually, mercaptans or thioesters and phosphites are classified as auxiliary antioxidants and used together with main antioxidants to produce synergistic effects and prolong the effectiveness of antioxidants

at present, the production and research of antioxidants are developing towards the direction of high efficiency, low toxicity and low price. Therefore, phenolic antioxidants will gradually surpass amine antioxidants. The compatibility between antioxidant and polyolefin plastics can be improved by substituting alkyl for some phenyl. Increasing the molecular weight of antioxidant is also an important way to improve the durability of antioxidant. Most antioxidants are easy to migrate, making the polymer unprotected. If the molecular weight of antioxidants is large enough and the possibility of migration is reduced, the effective life of antioxidants can be improved

lubricant polymers usually have high viscosity after melting. In the process of processing, when the molten polymer passes through narrow slots, gates and other channels, the polymer melt must have friction with the surface of processing machinery. Some friction is very detrimental to the processing of polymers. These friction reduce the melt fluidity, and serious friction will make the surface of the film rough, lack of gloss or appear flow lines. Therefore, it is necessary to add additives for the purpose of improving lubricity, reducing friction and reducing interfacial adhesion. This is the lubricant. In addition to improving the fluidity, lubricants can also act as melting accelerators, anti adhesion and anti-static agents, smooth agents and so on

lubricants can be divided into external lubricants and internal lubricants. The role of external lubricants is mainly to improve the friction between polymer melt and the hot metal surface of processing equipment. It has poor compatibility with polymers and is easy to migrate from the melt to the outside, so it can form a lubricating thin layer at the interface between plastic melt and metal. Internal lubricant has good compatibility with polymer. It plays a role in reducing the cohesion between polymer molecules in the polymer, so as to improve the internal friction heat generation and melt fluidity of plastic melt. The commonly used external lubricant is stearic acid and its salts; The internal lubricant is a low molecular weight polymer. Some lubricants have other functions. In fact, every lubricant has the function of realizing a certain requirement. Internal and external lubrication always work together, but it is more prominent in one aspect. The same lubricant will show different lubrication effects in different polymers or under different processing conditions. For example, under high temperature and high pressure, the inner lubricant will be extruded out and become the outer lubricant

in the production of plastic film, we will also encounter some adhesion phenomena. For example, in the production of plastic film, the two layers of film are not easy to separate, which brings difficulties to automatic high-speed packaging. In order to overcome it, a small amount of additives that increase the surface lubricity can be added to the resin to increase the external lubricity, which is generally called anti adhesion agent or smooth agent

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