Polyvinyl chloride, polyurethane, polyamide, polyolefin. The most common are polyvinyl chloride (PVC) and polyurethane (PU).
Additives need to be selected according to different technological processes.
Take polyvinyl chloride (PVC) resin for example. There are ten possible additives.
1, plasticizer
The addition of plasticizer can reduce the force between PVC molecular chains, reduce the glass transition temperature, flow temperature and melting point of microcrystals contained in PVC plastics, improve the plasticity of resin, and make products soft and have good low temperature resistance.
The types of plasticizers are phthalate esters, linear esters, epoxy resins, phosphate esters, etc. As far as its comprehensive performance is concerned, DOP is a better variety and can be used in various PVC product formulations. Linear esters such as DOS are cold-resistant plasticizers, which have been used in agricultural films for a long time and have poor compatibility with PVC. Generally, it is appropriate to use less than 8 phr. In addition to good cold resistance, epoxy plasticizer also has heat resistance and light resistance, especially when used in combination with metal soap stabilizer. Wire and cable products should be flame retardant, and plasticizers with relatively good electrical properties should be selected. PVC itself is flame retardant, but most soft products after plasticization are flammable. In order to make soft PVC products flame retardant, flame retardant plasticizers such as phosphate ester and chlorinated paraffin should be added. The electrical properties of these two plasticizers are also better than other plasticizers, but with the increase of plasticizer dosage, the electrical properties generally show a downward trend. For non-toxic PVC products, non-toxic plasticizers such as epoxy soybean oil should be used. As for the total amount of plasticizer, it varies according to the requirements of product softness and the different uses, processes and use environments. The general calendering process produces PVC film, and the total amount of plasticizer is about 50 phr. Blowing film is slightly lower, generally 45~50 copies.
2. Heat stabilizer
The heat stabilizer must be able to capture the autocatalytic HCL released from PVC resin, or it can react with the unstable polyene structure produced by PVC resin in addition to preventing or reducing the decomposition of PVC resin. Generally, the characteristics, functions and product requirements of the heat stabilizer selected in the formula should be considered. For example:
Lead salt stabilizer is mainly used for hard products. Lead salt stabilizer has the characteristics of good thermal stability, excellent electrical properties and low price. However, it is toxic and easy to pollute products, and only opaque products can be produced. In recent years, a large number of composite stabilizers have appeared, and one-component stabilizers are in danger of being replaced. The composite stabilizer has the characteristics of strong specificity, little pollution and simple components for processing enterprises. However, because there is no uniform standard, there are great differences among composite stabilizers.
Barium cadmium stabilizer is a kind of heat stabilizer with excellent performance. Widely used in PVC agricultural film. Generally, barium, cadmium and zinc are used together with organic phosphites and antioxidants.
Calcium and zinc stabilizers can be used as non-toxic stabilizers in food packaging, medical devices and drug packaging, but their stability is relatively low. When the dosage of calcium stabilizer is large, the transparency is poor and it is easy to spray frost. Generally, polyols and antioxidants are used to improve the properties of calcium and zinc stabilizers. Recently, calcium and zinc composite stabilizers for hard pipes have appeared in China. Shenzhen sendeli plastic additives co., ltd has successfully developed CZX series nontoxic calcium and zinc stabilizers, which can meet the production of hard pipes and pipe fittings, and have been used in batches by pipe manufacturers such as liansu.
Organotin heat stabilizer has good performance and is an excellent variety of PVC hard products and transparent products. In particular, octyl tin has almost become an indispensable stabilizer for non-toxic packaging products, but its price is more expensive.
Epoxy stabilizers are usually used as auxiliary stabilizers. This stabilizer can be used in combination with barium, cadmium, calcium and zinc stabilizers, which can improve the stability to light and heat, but the disadvantage is that it is easy to seep out. There are also polyols and organic phosphites as auxiliary stabilizers.
In recent years, rare earth stabilizers and hydrotalcite stabilizers have also appeared one after another. The main feature of rare earth stabilizer is excellent processability, and hydrotalcite is a non-toxic stabilizer.
3. Antioxidants
In the process of processing and using, PVC products are oxidized by heat and ultraviolet rays, and their oxidative degradation is related to the generation of free radicals. The main antioxidants are chain break terminators or radical scavengers. Its main function is to combine with free radicals to form stable compounds and terminate the chain reaction. The main antioxidant of PVC is usually bisphenol A. There are also auxiliary antioxidants or hydrogen peroxide decomposers. The auxiliary antioxidants of PVC are triphenyl phosphite and diisooctyl phosphite. The combination of main and auxiliary antioxidants can play a synergistic role.
4. Ultraviolet absorber
When PVC products used outdoors are irradiated by ultraviolet rays within its sensitive wavelength range, PVC molecules become excited or their chemical bonds are destroyed, causing free radical chain reaction and promoting PVC degradation and aging. In order to improve the ability to resist ultraviolet rays, ultraviolet absorbers are often added. Commonly used ultraviolet absorbers for PVC include triazine -5, UV-9, UV-326, TBS, BAD and OBS. Triazine -5 has the best effect, but the film is slightly yellow because of its yellow color, which can be improved by adding a little phthalocyanine blue. UV-9 is commonly used in PVC agricultural film, and the general dosage is 0.2~0.5 phr. TBS, BAD and OBS, which belong to salicylic acid, have mild effects. When used together with antioxidants, they will get good anti-aging effect. For opaque products, the weather resistance is generally improved by adding light-shielding rutile titanium dioxide. At this time, if you add ultraviolet absorber, you need a lot of consumption, which is not cost-effective.
5. Chelating agent
Phosphite, which is often added in PVC plastic stabilization system, is not only an auxiliary antioxidant, but also a chelating agent. It can form metal complexes with harmful metal ions and promote the removal of HCL from PVC. Commonly used phosphites are triphenyl phosphite, diisooctyl phosphite and diphenyl phosphite. In PVC agricultural film, the general dosage is 0.5~ 1 phr. When used alone, it is easy to be colored at the initial stage and has poor thermal stability. Generally used with metal soap.
6. Lubricants
The function of lubricant is to reduce the friction between polymer and equipment and the internal friction between polymer molecular chains. The former is called external lubrication and the latter is called internal lubrication. Silicone oil, paraffin wax, etc. have external lubrication function, while monoglyceride, stearyl alcohol, ester, etc. have internal lubrication function. As for metal soap, there are both. In addition, it should be noted that "internal and external lubrication" is just a idiom, and there is no obvious boundary. Some lubricants play different roles under different conditions, such as stearic acid, which can play an internal lubrication role at low temperature or in a small amount, but when the temperature rises or the dosage increases, its external lubrication role gradually becomes dominant. Another special case is calcium stearate, which is used as an external lubricant when used alone, but can promote plasticization when used with hard lead and paraffin.
7. Inorganic filler
Adding some inorganic fillers into PVC as fillers can reduce the cost, improve some physical and mechanical properties (such as hardness, thermal deformation temperature, dimensional stability and shrinkage reduction), and increase electrical insulation and flame retardancy.
In the process of hard extrusion molding, the fillers of PVC products are generally calcium carbonate and barium sulfate. For injection-molded products, good fluidity and toughness are required, and titanium dioxide and calcium carbonate are generally suitable. The filler content of hard products within 10 has little effect on the properties of products. In recent years, in order to reduce the cost, people try their best to add fillers, which is unfavorable to the performance of products.
In soft products, adding a proper amount of filler will make the film have good elasticity, smooth and dry surface, high heat and pressure resistance and small permanent deformation. In soft products, talcum powder, barium sulfate, calcium carbonate, titanium dioxide and clay are usually used as fillers. Among them, talcum powder has little effect on transparency. In the production of film, the amount of filler can reach 3 parts, which affects the performance. At the same time, we should pay attention to the fineness of filler, otherwise it is easy to form lumps and break plastic. Calcium carbonate is mainly added to ordinary cables with attached layers; Adding calcined clay to the adhesion layer of insulated cable can improve the heat resistance and electrical insulation of plastics. In addition, antimony trioxide can also be added to soft products as filler to improve the fire resistance of products.
8. Colorants
Colorants used for PVC plastics are mainly organic pigments and inorganic pigments. PVC plastics have higher requirements for pigments, such as high temperature resistance during processing, no influence from HCL, no migration during processing, light resistance and so on. Commonly used are:
(1) Red is mainly soluble azo pigment, cadmium red inorganic pigment, iron oxide red pigment, phthalocyanine red and so on.
(2) Yellow mainly includes chrome yellow, cadmium yellow and fluorescent yellow; (3) Blue is mainly phthalocyanine blue.
(4) Green is mainly phthalocyanine green;
(5) White mainly uses titanium dioxide;
(6) Purple is mainly plastic purple RL;
(7) Black is mainly carbon black.
In addition, fluorescent whitening agent is used for whitening, gold powder and silver powder are used for color printing, and pearl powder makes plastics have pearly astigmatism.
9. Foaming agent
The foaming agents used for PVC mainly include ADC foaming agent, azodiisobutyronitrile and inorganic foaming agent. In addition, lead salt and cadmium salt also contribute to foaming, which can reduce the decomposition temperature of AC foaming agent to about 150~ 180℃. The amount of foaming agent depends on the foaming ratio.
10, flame retardant
Plastics used in building materials, electrical appliances, automobiles and airplanes all need flame retardancy. Generally, compounds containing halogen, antimony, boron, phosphorus and nitrogen have flame retardant effects and can be used as flame retardants.
The auxiliaries of polyurethane also include
Penetrant, emulsifier, softener, leveling agent, cell regulator, defoamer, antibacterial agent, surface treatment agent, finishing agent, PU modifier, waterborne polyurethane adhesive, etc.
The specific choice depends on the production process.
References:
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And various chemical dictionaries.