Foreword

Plastic additives, also known as plastic additives, are compounds added to improve the processing properties of polymers (synthetic resins) during molding or to improve the properties of the resin itself. The main role is to improve the process performance of the polymer, optimize the processing conditions, improve the processing efficiency and improve the performance of the product, and improve the use value and life of the product. For example, in order to reduce the molding temperature of the polyvinyl chloride resin, the plasticizer added to make the product soft; and the foaming agent added for the purpose of preparing a lightweight, shock-resistant, heat-insulating, sound-insulating foam; thermal decomposition of some plastics The temperature is very close to the molding temperature and cannot be formed without the addition of a heat stabilizer. Therefore, plastic auxiliaries play a particularly important role in plastic molding processing. Auxiliaries for plastic molding processing include heat stabilizers, plasticizers, antioxidants, light stabilizers, flame retardants, foaming agents, antistatic agents, colorants and brighteners, fillers, coupling agents , lubricants, mold release agents, etc.

First, the stabilizer

Heat stabilizer

The heat stabilizer is mainly used for polyvinyl chloride and its copolymer. In the process of hot processing, there is a small amount of molecular chain cleavage to release hydrogen chloride before the melt flow is reached, and hydrogen chloride is an accelerated chain reaction of molecular chain rupture. The catalyst, so the hydrogen chloride which has just been decomposed is not removed in time, and the polymer chain is continuously cracked into a low molecular compound, so that the plastic such as polyvinyl chloride cannot be processed. By adding an appropriate basic substance to the polyvinyl chloride, the decomposed hydrogen chloride can be neutralized immediately to achieve the purpose of stabilizing the polyvinyl chloride.

Commonly used heat stabilizers are classified as main stabilizers and auxiliary stabilizers:

Main stabilizer: mainly salts and soaps containing heavy metal cations such as lead, calcium, cadmium, zinc, antimony, aluminum, lithium and strontium.

Among them, lead sulfate and lead stearate are the most widely used.

Auxiliary stabilization: mainly refers to epoxidized oils and esters, and they also have a certain plasticizer function.

2. Antioxidants

Antioxidants are a class of chemicals that, when present in small amounts in a polymer system, retard or inhibit the progress of the polymer oxidation process, thereby increasing polymer life. Commonly used plastic antioxidants are generally classified into five categories according to their molecular structure and mechanism of action: hindered phenols, phosphites, thio compounds, complexes, and hindered amines (HALS).

3. UV absorber

The polymer is photodegraded by exposure to ultraviolet light. Ultraviolet absorbers are chemicals that absorb ultraviolet light or reduce the transmission of ultraviolet light. They convert energy and convert high-energy ultraviolet light into energy in the form of heat or non-destructive long light waves. The polymer is protected from UV damage.

The ultraviolet absorbers can be classified into the following categories according to their chemical structures: salicylates, benzophenones, benzotriazoles, substituted acrylonitriles, triazines, and hindered amines.

4. Light shielding agent

A light-shielding agent is a substance which can absorb light waves which are harmful to a high-polymer, and then convert the light energy into heat energy to scatter or reflect the light wave, thereby shielding the high-polymer. The light shielding agent mainly has black or white substances such as carbon black, zinc oxide, titanium white powder, zinc antimony white, which can absorb or reflect light waves.

Second, processing aids

Processing aids are additives used to improve the rheology and forming properties of plastics, usually additives with low viscosity or surface energy and certain lubricating properties; mainly including plasticizers and lubricants.

Plasticizer

Plasticizers can increase the mobility of polymer molecular chains and reduce the crystallinity of polymer molecular chains by increasing the van der Waals force between polymer molecules, thereby increasing the flexibility, extensibility, plasticity, and plastic flow of plastics. Temperature and hardness are conducive to the molding of plastic products. Commonly used plasticizers are phthalates, sebacates, chlorinated paraffins, and the like.

Plasticizers can be divided into two main categories: primary plasticizers and secondary plasticizers:

The main plasticizer is characterized by good compatibility with resin, high plasticizing efficiency, migration resistance, low volatility, low oil (water) extraction, low temperature flexibility; poor compatibility of secondary plasticizer with resin, mainly It is used in conjunction with the main plasticizer to reduce costs.

2. Lubricant

It can improve the friction and adhesion between the particles of plastic layers and the metal surface of the melt and processing equipment, increase the fluidity of the resin, achieve the plasticizing time of the resin, and maintain the continuous production of additives. Lubricant.

Lubricants can be divided into external lubricants and internal lubricants.

The primary function of the external lubricant is to allow the polymer melt to smoothly exit the hot metal surface of the processing equipment. The external lubricant is less compatible with the polymer, but forms a thin layer of lubricant at the interface between the polymer and the metal. The most common 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 contributing to the flow of the polymer and reducing the temperature rise caused by the internal friction heat. The most common 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 is not dissolved when it comes into 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 easily decomposed or worn; the release agent is bonded to the mold without being transferred to the workpiece to be processed, and does not hinder painting or other secondary processing operations. Due to the rapid development of processes such as injection molding, extrusion, calendering, molding, lamination, etc., the amount of release agent is also greatly increased.

Third, reinforcing materials and fillers

In many plastics, reinforcing materials and fillers occupy a considerable proportion. The main purpose is to add various fiber materials or inorganic materials in order to increase the strength and rigidity of plastic products or to reduce production costs. The most commonly used reinforcing materials are: glass fiber, asbestos, quartz, carbon black, silicate, calcium carbonate, metal oxide and the like.

Fourth, the coupling agent

A coupling agent refers to a substance that improves the interfacial properties between a filler and a polymer material. Generally, two functional groups exist 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. For example; a silane coupling agent, the general formula can be written as RSiX3 (R is a reactive functional group having affinity and reaction ability with a polymer molecule, such as a vinyl group, a chloropropyl group, an epoxy group, a methacryl group, an amine group, and a fluorenyl group. Etc.; X is a hydrolyzable alkoxy group such as methoxy, ethoxy, etc.). After the reinforcing agent or filler is treated with a coupling agent, a chemical modification can be obtained on the surface, and a bridge bond is formed between the dispersed inorganic phase and the continuous polymer to become a composite material and enhance the reinforcing agent. Or the role of fillers, organosilanes are the most widely used coupling agents, and organic titanates are a more efficient coupling agent.

V. Crosslinker

The crosslinking agent is mainly used in a polymer material (rubber and thermosetting resin). Because the molecular structure of the polymer material is a linear structure, the strength is low, easy to break, and has no elasticity when not cross-linked. The role of the cross-linking agent is to generate chemical bonds between the linear molecules, so that the linear molecules are connected to each other. A network structure is formed, which increases the strength and elasticity of the rubber. The crosslinking agent used in the rubber is mainly sulfur, and an accelerator is added. A general crosslinking agent refers to an organic peroxide, and a crosslinking agent such as polyethylene can use dicumyl peroxide.

6. Foaming agent

A blowing agent is a type of rubber that can be in a liquid or plastic state within a certain viscosity range, and the plastic forms a microporous structure. The foaming agent can be classified into a physical foaming agent and a chemical foaming agent according to the action mechanism. Physical foaming agent: a type of compound that relies on changes in its physical state during foaming to achieve foaming purposes; chemical foaming agent: thermally decomposes at a certain temperature to produce one or more gases to foam the polymer. .

Seven, nucleating agent

The nucleating agent is suitable for incompletely crystallized plastics such as polyethylene and polypropylene. By changing the crystallization behavior of the resin, accelerating the crystallization rate, increasing the crystal density and promoting the grain size, the molding cycle is shortened, the transparency of the product is improved, and the surface is improved. New functional additives for physical and mechanical properties such as gloss, tensile strength, rigidity, heat distortion temperature, impact resistance, and creep resistance.

Eight, coloring agent

Colorants are insoluble in common solvent chemistries, so to achieve the desired coloring properties, mechanically dispersed pigments are uniformly dispersed in the plastic. Inorganic pigments have excellent thermal stability and light stability, low price, but relatively poor coloring power and high relative density; organic pigments have high tinting strength, bright color, complete chromatogram, and low relative density. The disadvantages are heat resistance, weather resistance and hiding. The properties such as force are not as good as inorganic pigments. Colorants mainly include masterbatches and optical brighteners.

Masterbatch

A masterbatch is an aggregate obtained by uniformly loading a super-constant pigment or dye into a resin. The basic composition includes: pigment or dye, carrier, dispersant, additive; has the following advantages: it is beneficial to maintain the chemical stability and color stability of the pigment, improve the dispersibility of the pigment, simple operation, easy color change, clean environment and time saving And raw materials.

2. Fluorescent whitening agent

Fluorescent whitening agent is a kind of fluorescent dye, or white dye, which is also a complex organic compound. Its characteristic is to excite the incident light to produce fluorescence, so that the dyed substance can obtain the effect of sparkling like fluorite, making the naked eye The material seen is very white. According to the parent classification of fluorescent whitening agents, they can be roughly classified into carbocyclic, triazinylaminostilbene, stilbene-triazole, benzoxazole, furan, benzofuran and benzene. Nine classes of imidazoles, 1,3-diphenyl-pyrazolines, coumarins, naphthalimides and miscellaneous substances.

Nine, antibacterial agents

As people's safety awareness continues to increase, more and more people are buying antibacterial plastic products. Antibacterial agents are used in antibacterial plastics. An antibacterial agent refers to a chemical substance that can keep the growth or reproduction of certain microorganisms (bacteria, fungi, yeasts, algae, viruses, etc.) below a necessary level within a certain period of time. Antibacterial agents are substances that have bacteriostatic and bactericidal properties.

Ten, flame retardant

The auxiliaries that slow down the burning properties of plastics are called flame retardants, and most of the plastics containing flame retardants are self-extinguishing or have a slowing rate of combustion.

XI, antistatic agent

Any object has its own static charge, which can be either negative or positive. The accumulation of static charge causes life or industrial production to be affected or even harmed, and the chemical substance that guides/eliminates the accumulated harmful charge so as not to cause inconvenience or harm to production or life is called an antistatic agent. Antistatic agents generally have the characteristics of a surfactant, both structurally polar and non-polar. Commonly used polar groups (ie, hydrophilic groups) are: anions of carboxylic acids, sulfonic acids, sulfuric acid, phosphoric acid, amine salts, cations of quaternary ammonium salts, and groups such as -OH, -O-; commonly used non- The polar group (i.e., the lipophilic group or the hydrophobic group) has an alkyl group, an alkylaryl group and the like. There are five basic types of antistatic agents: derivatives of amines, quaternary ammonium salts, sulfates, phosphates, and derivatives of polyethylene glycol.

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