In the production process of plastics, polymers, additives and processing equipment are the three main material conditions.
Thermoplastics use a large variety of additives and quantities. In addition to the additives required for curing, the processing of thermosetting plastics requires relatively little other additives.
The amount of the auxiliary agent is small, generally a few percent or even a few thousandths of the weight of the polymer. However, plasticizers, reinforcing agents, fillers, softeners, and flame retardants are used in large amounts, ranging from 10 parts to dozens of parts. Although the amount of the auxiliary agent is small, the effect is remarkable, and even some polymers which have a large performance defect or are difficult to process and which have almost no practical value can be turned into a valuable material. Due to the use of auxiliaries, many fine chemical products are used more effectively. Therefore, the additive is also referred to as "industrial MSG".
Select additives according to purpose
Toughening - selection of elastomers, thermoplastic elastomers and rigid toughened materials;
Enhancement - selection of glass fiber, carbon fiber, whisker and organic fiber;
Conductive - carbon (carbon black, graphite, carbon fiber, carbon nanotubes), metal fiber and metal powder, metal oxide;
Magnetic - ferrite magnetic powder, rare earth magnetic powder including samarium cobalt (SmCo5 or Sm2Co17), neodymium iron boron (NdFeB), strontium iron nitrogen (SmFeN), aluminum nickel cobalt magnetic powder;
Thermal conductivity - metal fibers and metal powders, metal oxides, nitrides and carbides; carbon materials such as carbon black, carbon fibers, graphite and carbon nanotubes; semiconductor materials such as silicon, boron;
Heat resistant - glass fiber, inorganic filler, heat resistant agent such as substituted maleimide and beta crystal nucleating agent;
Transparent - nucleating agent, the sorbitol series Millad 3988, which has an alpha crystal nucleating agent for PP, works best;
Select additives according to product characteristics
First, the additives to improve stability
That is, stabilizers prevent or delay the deterioration of the polymer during processing, storage and use. Since the mechanism of aging varies, the stabilizing auxiliaries are divided into the following four categories:
(1) Free radical inhibitors: primary antioxidants, including amines and phenols;
(2) Peroxide decomposers: auxiliary antioxidants, mainly thiodicarboxylates and phosphites, usually used in combination with primary antioxidants.
2, light stabilizer
Ultraviolet light stabilizer
(1) Light shielding agent: carbon black, zinc oxide and some inorganic pigments;
(3) Quencher: mainly an organic chelate of nickel.
3, heat stabilizer
Generally refers to the stabilizer used in polyvinyl chloride and vinyl chloride copolymers.
(1) Main stabilizers: salt-based lead salts, metal soaps and salts, organotin compounds, and the like.
(2) Auxiliary stabilizers: epoxy compounds, phosphites, polyols, and the like.
(3) Composite stabilizer: consists of main stabilizers (mainly metal soaps and salts and organotin compounds) with auxiliary stabilizers and other stabilizers.
4, anti-fungal agent
Most of the polymers are insensitive to mold, but molds are susceptible to mold by adding plasticizers, lubricants, fatty acid soap heat stabilizers, etc., which can be used to mold molds. Mold inhibitors have many chemical types, including elemental organic compounds, nitrogen-containing organic compounds, dithiocarbamates, trihalomethyl sulfides, organic halides, and phenolic derivatives.
Second, additives to improve mechanical properties
Improvements such as tensile strength, hardness, rigidity, impact strength, thermal deformation, and the like. It mainly includes the following three categories:
1, resin cross-linking - divided into radiation cross-linking and chemical cross-linking
Chemical crosslinking is carried out by using a crosslinking agent, and a common organic peroxide is used in combination with some crosslinking agents and a crosslinking accelerator to increase the degree of crosslinking and the crosslinking speed. The crosslinking agent of the epoxy resin is a curing agent, and an amine and an organic acid anhydride are often used. Ultraviolet cross-linking photosensitizers are also crosslinkers.
2. Reinforcing agent, filler and coupling agent
Fiber-type fillers with reinforcing effect such as glass fiber, carbon fiber, metal whisker, etc.; fillers mainly include calcium carbonate, clay, talc, mica, silica, calcium sulfate, calcium sulfite, wood powder and fiber; The binder is an inorganic reinforcing material and a bridge between the filler and the organic polymer, which can significantly improve the mechanical strength of the plastic, mainly silane and titanate compounds containing functional groups.
3, anti-impact agent - used to improve the impact resistance of hard plastic products
Commonly used are: MBS (methacrylate-butadiene-styrene copolymer), ABS (acrylonitrile-butadiene-styrene copolymer), and CPE (chlorinated polyethylene).
Third, improve the processing performance of additives
Including lubricants, mold release agents, softeners, and the like. Plasticizers also have the effect of improving the processing properties of the polymer. Lubricants can improve the fluidity and mold release properties of polymers during thermoforming, including hydrocarbons, fatty acids and their amides, esters, metal soaps and other derivatives. The release agent is applied to the surface of the mold to make the molded article easy to release, and the surface is smooth, and silicone oil is often used.
Fourth, softening and lightweight additives
The vast majority of plasticizers are used in PVC and are the most consumed additives. The plasticizer is mainly composed of phthalic acid esters, and other aliphatic dibasic acid esters, trimellitic acid esters, phosphate esters, epoxy esters, polyesters, phenyl sulfonates and chlorinated paraffins. And so on.
2, foaming agent
Mainly used in foam plastics. Commonly used blowing agents are azo compounds, nitroso compounds, sulfonyl hydrazides and the like. The foaming aid for adjusting the decomposition temperature of the foaming agent includes ureas, organic acids and fatty acid soaps.
5. Inflammable additives
"Flammable" includes two concepts of non-combustible and flame retardant. The flame retardant auxiliaries currently used mainly refer to flame retardants. Plastics containing flame retardants burn slowly when exposed to a source of ignition and extinguish immediately after leaving the source of ignition.