Plastic additives, also called plastic additives, are compounds added to improve the processing performance of polymers (synthetic resins) or to improve the performance of the resin itself when it is molded. The main function is to improve the process performance of the polymer, optimize the processing conditions, increase the processing efficiency and improve the performance of the product, and increase the use value and life of the product. For example, plasticizers added to reduce the molding temperature of polyvinyl chloride resins to make products soft; and foaming agents added to prepare foams with light weight, shock resistance, thermal insulation, and sound insulation; thermal decomposition of some plastics The temperature is very close to the molding processing temperature, and molding cannot be performed without adding a heat stabilizer. Therefore, plastic additives occupy a particularly important position in the plastic molding process. Additives used in plastic molding processing include heat stabilizers, plasticizers, antioxidants, light stabilizers, flame retardants, foaming agents, antistatic agents, colorants and whitening agents, fillers, coupling agents , Lubricants, mold release agents, etc.
1. Heat stabilizer
Thermal stabilizers are mainly used for polyvinyl chloride and its copolymers. During the thermal processing of polyvinyl chloride, a small amount of molecular chain breaks and hydrogen chloride is released before reaching melt flow, and hydrogen chloride is an accelerated molecular chain break chain reaction Catalyst, so if you don’t rule out the newly decomposed hydrogen chloride in time, the polymer chain will continue to be cracked into low molecular compounds, so that plastics such as polyvinyl chloride cannot be processed. Adding appropriate alkaline substances to polyvinyl chloride can immediately neutralize the decomposed hydrogen chloride to achieve the purpose of stabilizing polyvinyl chloride.
Commonly used heat stabilizers are divided into main stabilizers and auxiliary stabilizers:
Main stabilizers: mainly salts and soaps containing heavy metal cations such as lead, calcium, cadmium, zinc, barium, aluminum, lithium, strontium, etc.
Lead sulfate and lead stearate are the most widely used.
Auxiliary stability: mainly refers to epoxidized oils and esters, at the same time they also have a certain function as a plasticizer.
Antioxidants are a class of chemical substances that, when present in small amounts in polymer systems, can delay or inhibit the progress of the polymer oxidation process, thereby increasing the service life of the polymer. Commonly used plastic antioxidants are generally divided into five categories based on molecular structure and mechanism of action: hindered phenols, phosphites, thios, composites, and hindered amines (HALS).
3. UV absorber
The polymer will undergo photodegradation when exposed to ultraviolet rays. Ultraviolet absorbers are a type of chemical substances that can absorb ultraviolet light or reduce the transmission of ultraviolet light. It can perform energy conversion and convert high-energy ultraviolet light into heat energy or non-destructive longer light waves to release energy to protect it. The polymer is protected from ultraviolet rays.
UV absorbers can be divided into the following categories according to their chemical structure: salicylates, benzophenones, benzotriazoles, substituted acrylonitriles, triazines, and hindered amines.
4. Light shielding agent
Light shielding agent is a kind of substance that can absorb light waves harmful to polymers, and then convert light energy into heat energy to scatter or reflect off the light waves, so as to shield the polymers. Light shielding agents mainly include carbon black, zinc oxide, titanium dioxide, zinc barium white and other black or white substances that can absorb or reflect light waves.
Processing aids refer to additives used to improve the rheology and molding properties of plastics processing. They are usually additives with low viscosity or surface energy and a certain lubricating effect; they mainly include plasticizers and lubricants.
Plasticizers have the effect of weakening the van der Waals force between polymer molecules to increase the mobility of polymer molecular chains, reduce the crystallinity of polymer molecular chains and increase the flexibility, extensibility, plasticity of plastics, and reduce the flow of plastics Temperature and hardness are beneficial to the molding of plastic products. Commonly used plasticizers are phthalates, sebacates, chlorinated paraffins, etc.
Plasticizers can be divided into two major categories: primary 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 temperature flexibility; secondary plasticizer has poor compatibility with resin, mainly It is used together with the main plasticizer to reduce costs.
It can improve the friction and adhesion between the particles of each layer of the plastic and the metal surface of the melt and the processing equipment, increase the fluidity of the resin, achieve the control of the plasticizing time of the resin, and maintain continuous production. Lubricant.
Lubricants can be divided into external lubricants and internal lubricants.
The main function of the external lubricant is to enable the polymer melt to smoothly leave the hot metal surface of the processing equipment. The compatibility of the external lubricant with the polymer is poor, but a thin lubricant layer is formed at the interface between the polymer and the metal. The most commonly used external lubricant is stearic acid and its metal salts.
The internal lubricant has good compatibility with the polymer, which can reduce the cohesion between the polymer molecules, thereby helping the flow of the polymer and reducing the temperature rise caused by the internal friction heat. The most commonly used internal lubricant is low molecular weight Polyethylene, etc.
3. Release agent
The release agent is a functional substance between the mold and the finished product. The release agent is chemically resistant and does not dissolve when in contact with the chemical components 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 adheres to the mold without being transferred to the processed part, 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 release agent has also been greatly increased.
Reinforcement materials and fillers
In many plastics, reinforcing materials and fillers occupy a considerable proportion, the main purpose is: in order to improve the strength and rigidity of plastic products or reduce production costs, generally add a variety of fiber materials or inorganic substances. The most commonly used reinforcement materials are: glass fiber, asbestos, quartz, carbon black, silicate, calcium carbonate, metal oxide, etc.
4. Coupling agent
Coupling agent refers to a class of substances that can improve the interface properties between fillers and polymer materials. Generally, there are two functional groups in the molecular structure of the coupling agent: one can chemically react with the polymer matrix or have good compatibility; the other can form a chemical bond with the inorganic filler. Such as; silane coupling agent, the general formula can be written as RSiX3 (R is an active functional group with affinity and reactivity with polymer molecules, such as vinyl, chloropropyl, epoxy, methacryloyl, amine and mercapto Etc.; X is a hydrolyzable alkoxy group, such as methoxy, ethoxy, etc.). After the reinforcing agent or filler is treated with the coupling agent, its surface can be chemically modified, and a bridge between the dispersed inorganic phase and the continuous polymer is formed to become a composite material and enhance the reinforcing agent. Or the role of filler, organosilane is the most widely used coupling agent, and organic titanate is a more efficient coupling agent.
5. Crosslinking agent
The cross-linking agent is mainly used in polymer materials (rubber and thermosetting resin). Because the molecular structure of the polymer material is a linear structure, when it is not cross-linked, the strength is low, it is easy to break, and there is no elasticity. The role of the cross-linking agent is to generate chemical bonds between the linear molecules, so that the linear molecules are connected together. A network structure is formed to improve the strength and elasticity of the rubber. The cross-linking agent used in the rubber is mainly sulfur, and an accelerator is added. The general cross-linking agent mostly refers to organic peroxide, such as polyethylene cross-linking agent can use dicumyl peroxide.
Foaming agent is a kind of substance that can make the liquid or plastic state in a certain viscosity range, the plastic forms a microporous structure. According to the mechanism of action, the blowing agent can be divided into physical blowing agent and chemical blowing agent. Physical foaming agent: a type of compound that depends on the change of its physical state during the foaming process to achieve the purpose of foaming; chemical foaming agent: it will thermally decompose at a certain temperature to produce one or more gases to foam the polymer .
7. Nucleating agent
The nucleating agent is suitable for incompletely crystalline plastics such as polyethylene and polypropylene. By changing the crystallization behavior of the resin, it accelerates the crystallization rate, increases the crystal density and promotes the refinement of the grain size, so as to shorten the molding cycle, improve the transparency and surface New functional additives for physical and mechanical properties such as gloss, tensile strength, rigidity, heat distortion temperature, impact resistance, creep resistance, etc.
Colorants are chemical substances that are insoluble in common solvents, so to obtain the desired coloring performance, the pigment needs to be uniformly dispersed in the plastic by mechanical methods. Inorganic pigments have excellent thermal stability and light stability and low price, but the coloring power is relatively poor and the relative density is high; organic pigments have high coloring power, bright color, complete chromatogram and small relative density. The disadvantages are heat resistance, weather resistance and covering Properties such as force are not as good as inorganic pigments. Colorants mainly include masterbatch and optical brightener.
The color masterbatch is an aggregate made by uniformly loading super constant pigments or dyes in resin. Its basic composition includes: pigments or dyes, carriers, dispersants, additives; it has the following advantages: it is beneficial to maintain the chemical stability and color stability of pigments, improve the dispersion of pigments, simple operation, easy color transfer, clean environment, save time And raw materials.
2. Fluorescent brightener
Fluorescent whitening agent is a kind of fluorescent dye, or white dye, is also a complex organic compound, its characteristic is to stimulate the incident light to produce fluorescence, so that the dyed substance obtains a shining effect similar to fluorite, so that the naked eye The material seen is very white. According to the parent classification of optical brighteners, they can be roughly divided into carbocyclics, triazinylaminostilbenes, stilbene-triazoles, benzoxazoles, furan, benzofuran and benzene Nine types of imidazoles, 1,3-diphenyl-pyrazolines, coumarins, naphthalimides, and heterotypes.
As people's safety awareness continues to increase, more and more people begin to buy antibacterial plastic products. Antibacterial agents are used in antibacterial plastics. Antibacterial agent refers to a chemical substance that can keep the growth or reproduction of certain microorganisms (bacteria, fungi, yeast, algae, viruses, etc.) below the necessary level within a certain period of time. Antibacterial agents are substances with antibacterial and bactericidal properties.
10. flame retardant
The additives that slow down the burning performance of plastics are called flame retardants. Most plastics containing flame retardants are self-extinguishing or have a burning rate slowing effect.
11. Antistatic Agent
Any object has its own static charge, which can be negative or positive. The accumulation of static charges affects or even harms life or industrial production. The chemical substances that guide/eliminate the accumulated harmful charges so as not to cause inconvenience or harm to production or life are called antistatic agents. Antistatic agents generally have the characteristics of surfactants, with both polar and non-polar groups in structure. Commonly used polar groups (ie hydrophilic groups) are: anions of carboxylic acid, sulfonic acid, sulfuric acid, phosphoric acid, cations of amine salts, quaternary ammonium salts, and groups such as -OH, -O-; Polar groups (ie, lipophilic groups or hydrophobic groups) include alkyl groups, alkylaryl groups, and the like. There are five basic types of antistatic agents: amine derivatives, quaternary ammonium salts, sulfates, phosphates, and polyethylene glycol derivatives.