Plastic additives, also known as plastic additives, are some compounds that must be added when the polymer (synthetic resin) is molded to improve its processing performance or to improve the performance of the resin itself. For example, in order to reduce the molding temperature of pvc resin, so that the product is soft and added plasticizer; such as in order to prepare lightweight, anti-vibration, heat insulation, sound insulation foam and to add a blowing agent; some plastics thermodegradation temperature and molding processing temperature is very close, without the addition of heat stabilizer can not be formed. Therefore, plastic additives occupy a particularly important position in plastic molding processing. A large class of additives for plastic molding products, including plasticizers, stabilizers, flame retardants, blowing agents, coupling agents, crosslinking agents, nucleating agents, fillers, lubricants, release agents, colorants, antistatic agents, antibacterial agents, etc.
plasticizer
Some plastics with high glass transition temperatures, in order to prepare soft products at room temperature and improve the melting fluidity during processing, it is necessary to add a certain amount of plasticizer. These small molecular weight oily plasticizers have good compatibility with polymers, they are distributed between the polymer chains, reducing the force between their molecules, so that it is easy to make the molecular chains move under a certain temperature and pressure, to achieve the purpose of processing and molding. Therefore, plasticizers have the effect of reducing the vitrification temperature and the minimum molding temperature of plastics. Usually the reduction value of the glass transition temperature is proportional to the volume component of the plasticizer.
Plasticizers can be divided into two categories: main plasticizers and secondary plasticizers: the main plasticizer is characterized by good compatibility with resin, high plasticization efficiency, migration resistance, low volatility, low oil (water) extraction, low flexibility. The compatibility of the secondary plasticizer is poor, mainly used with the main plasticizer to reduce costs, so it is also called an incremental agent.
Stabilizer
We all know that plastic products in the process of processing, storage and use, under the action of light, heat, oxygen, will occur fading, embrittlement, cracking aging phenomenon. To delay and prevent the occurrence of aging, stabilizers must be added. Mainly used to prevent heat aging, called heat stabilizers; mainly used to prevent oxidative aging, called antioxidants; mainly used to prevent photoaging, called light stabilizers, they are collectively referred to as stabilizers. The best plastic stabilizer today is methyl tin heat stabilizer (181 for short), which is very effective for calendering, extrusion, injection molding and blow molding of rigid polyethylene (PVC). Because of its high safety, it is especially used in food packaging and high-definition hard polyethylene products, at the same time, it is also widely used in plastic doors and windows, water pipes, decorative materials to replace other highly toxic plastic heat stabilizers. It has been widely used in the United States, Europe, and Japan. In recent years, 181 methyltin heat stabilizer has begun to be widely used in China.
Flame retardants
Additives that slow down the combustion properties of plastics are called flame retardants, which can be divided into four types according to different flame retardant mechanisms:
Combined with the decomposition products of plastics to produce a gas that can smoulder, such as antimony trioxide and PVC when it decomposes, hydrogen chloride is reacted, that is, antimony trichloride is generated with a extinguishing effect.
Absorb the heat generated during combustion to cool plastics to slow down the combustion rate such as aluminum hydroxide, aluminum hydroxide is the most common one used in flame retardants: it plays the role of fillers, smoke extinguishers, flame retardants, while the price is low, the impact on polymer properties is small, so it gets the growth rate of application is remarkable.
Provides a coating isolated from oxygen, such as phosphate esters, the main products are trimethylphenyl phosphate, etc., which are actually a plasticizer with flame retardant properties.
It can produce free radicals that prevent combustion reactions, and these free radicals can react with plastics to produce products with poor combustion performance.
Blowing agent
Blowing agents are a type of organic compound that releases gases when heated, and these gases remain in the plastic substrate to become foam with many fine foam structures.
As a good blowing agent should have the following conditions: a short period of time to release gas, the deflation rate can be adjusted, the gas released should be co₂, n₂ and other inert gases, easy to disperse and decompose in plastics, decomposition temperature is appropriate, decomposition when the heat is not large, decomposition reaction is irreversible, foaming agent non-toxic and so on. The most widely used blowing agent is azodicarboxamide.
Coupling agent
Coupling agent refers to a class of substances that can improve the interface characteristics between fillers and polymer materials. Usually, there are two functional groups in the molecular structure of the coupling agent: one can have a chemical reaction with the polymer matrix or has good compatibility; The other can form chemical bonds with inorganic fillers. For example, silane coupling agent, the general formula can be written as rsix3 (r is an active functional group with polymer molecules with affinity and reaction ability, such as vinyl, chloropropyl, epoxy, methacryloyl, amine group and mercapto, etc.; x is alkoxy group capable of hydrolysis, such as methoxy, ethoxy, etc.). After the enhancer or filler is treated with a coupling agent, a chemical modification can be obtained on its surface, and a bridge bond is formed between the dispersed inorganic phase and the continuous polymer, becoming a composite material, improving the role of the reinforcing agent or filler, organosilane is the most widely used coupling agent, and organotitanate is a more efficient coupling agent.
Crosslinking agent
Crosslinkers are mainly used in polymer materials (rubber and thermoset resins). Because the molecular structure of the polymer material is a linear structure, the strength is low when there is no crosslinking, easy to pull off, and there is no elasticity, the role of the crosslinker is to produce chemical bonds between the linear molecules, so that the linear molecules are connected to each other, forming a network structure, so as to improve the strength and elasticity of the rubber, the crosslinking agent used in the rubber is mainly sulfur, and the accelerator should be added. General crosslinking agents mostly refer to organic peroxides, such as polyethylene crosslinking agents can use dipropylene peroxide.
Nucleating agent
Nucleating agent is suitable for polyethylene, polypropylene and other incomplete crystalline plastics, by changing the crystallization behavior of the resin, accelerating the crystallization rate, increasing the crystallization density and promoting the fine refinement of the grain size, to shorten the molding cycle, improve the transparency of the product, surface gloss, tensile strength, rigidity, heat deformation temperature, impact resistance, creep resistance and other physical and mechanical properties of the new function additive.
Reinforcements and fillers
In many plastics, reinforcing materials and fillers occupy a considerable proportion, especially reinforced plastics and calcium-plastic materials. The main purpose is: in order to improve the strength and rigidity of plastic products, generally add a variety of fiber materials or inorganic substances. The most commonly used reinforcing materials are: glass fiber, asbestos, quartz, carbon black, silicate, calcium carbonate, metal oxides and so on.
lubricant
Polymers in the thermal processing process, often to add a small amount of lubricant to process, to achieve the purpose of convenient demolding. Lubricants can be divided into two types: external lubricants and internal lubricants. The main role of the external lubricant is to make the polymer melt body can smoothly leave the hot metal surface of the processing equipment and facilitate its flow, the external lubricant and the polymer compatibility is poor, but at the interface between the polymer and the metal to form a thin layer of lubricant. The internal lubricant has good compatibility with the polymer, which can reduce the cohesion between the polymer molecules, thereby contributing to the flow of the polymer and reducing the heating caused by the heat of internal friction. The most commonly used external lubricant is stearic acid and its metal salts, and the internal lubricant is low molecular weight polyethylene.
Release agent
A release agent is a functional substance that lies between the mold and the finished product. Mold release agents are chemically resistant and are not dissolved when in contact with the chemical composition of different resins, especially styrene and amines. The release agent also has heat resistance and stress properties, and is not easy to decompose or wear; the release agent is bonded to the mold without being transferred to the part being processed, and does not hinder painting or other secondary processing operations. Due to the rapid development of injection molding, extrusion, calendering, molding, lamination and other processes, the amount of mold release agent has also been greatly improved.
Colorants
Colorants are insoluble in ordinary solvent chemicals, so to obtain the ideal coloring properties, it is necessary to use mechanical methods to evenly disperse the pigments in plastics. Inorganic pigments have excellent thermal stability and light stability, low price, but the coloring force is relatively poor, the relative density is large; organic pigments have high coloring power, bright color, complete chromatography, and small relative density, and the disadvantages are that the properties of heat resistance, weather resistance and hiding power are inferior to inorganic pigments. Colorants mainly include masterbatches and fluorescent brighteners.
Masterbatches
A masterbatch is a aggregate made by uniformly loading an extraordinarily large amount of pigment or dye into a resin. Its basic composition includes: pigments or dyes, carriers, dispersants, additives; has the following advantages: conducive to maintaining the chemical stability and color stability of pigments, improve the dispersibility of pigments, simple operation, easy color change, clean environment, save time and raw materials.
Fluorescent brightener
Fluorescent brightener is a fluorescent dye, or white dye, is also a complex organic compound, its property is to excite the incident light to produce fluorescence, so that the dyeing substance to obtain a fluorite-like glittering effect, so that the naked eye to see the substance is very white. According to the parent classification of fluorescent brighteners, they can be roughly divided into nine categories: carbocyclic, triazinodistyrene, distyrene-triazole, benzoxazole, furan, benzofuran and benzimidazole, 1,3-diphenyl-pyrazole, coumarin, naphthaleimide and miscellaneous.
Antistatic agent
Antistatic agents play a role in eliminating or reducing static electricity generated on the surface of plastic products. Most antistatic agents are electrolytes, and their compatibility with synthetic resins is limited, which can migrate to the surface of the plastic to absorb moisture and eliminate static electricity.
Antibacterial agent
With the continuous enhancement of people's safety awareness, more and more people have begun to buy antibacterial plastic products. Antibacterial agents are used in antibacterial plastics. Antimicrobials are chemicals that can keep the growth or reproduction of certain microorganisms (bacteria, fungi, yeast, algae, viruses, etc.) below the necessary level for a certain period of time. Antibacterial agents are substances with bacteriostatic and bactericidal properties.