Views: 2 Author: Site Editor Publish Time: 2024-07-22 Origin: Site
Plastic additives, also known as plastic auxiliaries, are compounds that must be added to polymers (synthetic resins) during molding to improve their processing properties or to improve the performance of the resin itself.
Choose different additives according to different purposes
Toughening - choose elastomers, thermoplastic elastomers and rigid toughening materials.
Reinforcement - choose glass fiber, carbon fiber, whisker and organic fiber.
Flame retardant - bromine (ordinary bromine series and environmentally friendly bromine series), phosphorus, nitrogen, nitrogen/phosphorus composite intumescent flame retardants, antimony trioxide, hydrated metal hydroxide.
Antistatic - various antistatic agents.
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), samarium iron nitrogen (SmFeN), aluminum nickel cobalt magnetic powder three categories.
Thermal conductivity - metal fiber and metal powder, metal oxide, nitride and carbide; carbon materials such as carbon black, carbon fiber, graphite and carbon nanotubes; semiconductor materials such as silicon and boron.
Heat resistance - glass fiber, inorganic filler, heat resistant agent such as substituted maleimide and β-crystal nucleating agent.
Transparency - nucleating agent. For PP, the sorbitol series Millad 3988 of α-crystal nucleating agent has the best effect.
Wear resistance - graphite, molybdenum disulfide, copper powder, etc.
Insulation - calcined kaolin.
Barrier - mica, montmorillonite, quartz, etc.
Surface treatment of additives
Good compatibility between additives and resins can ensure that the additives and resins are dispersed according to the expected structure, ensure the completion of design indicators, ensure that their effects are lasting during the service life, and are resistant to extraction, migration, and precipitation. For example, most formulas require that the additives and resins are evenly dispersed, while for barrier formulas, it is hoped that the additives are layered in the resin.
Except for a few additives such as surfactants, good compatibility with resins is the key to exerting their efficacy and increasing the amount of additives. Therefore, it is necessary to try to improve or improve their compatibility, such as using compatibilizers or coupling agents for surface activation treatment.
After the surface of all inorganic additives is treated, the modification effect will be improved. This is especially obvious for fillers, and others include glass fibers, inorganic flame retardants, etc.
There are also coupling agents and compatibilizers as the main ones, such as silanes, titanates, and aluminates, and compatibilizers are maleic anhydride grafted polymers corresponding to resins.
Amount of additives
Some additives have an optimal amount
For example, conductive additives can be added after the electric path is formed, and adding more will have no effect; coupling agents can be used for surface coating, and adding more will have no effect; antistatic agents can be used to form a charge leakage layer on the surface of the product.
Relationship between additives and other components
Synergistic effect
It means that the effect of two or more additives added together in the plastic formula is higher than the average value of their individual additions.
In anti-aging formulas, specific synergistic effects include: two phenolic antioxidants with different steric hindrances of hydroxyl ortho-substituents have a synergistic effect.
In flame retardant formulas, examples of synergistic effects mainly include: in halogen/antimony composite flame retardant systems, halogen flame retardants can react with Sb2O3 to generate SbX3, and SbX3 can isolate oxygen, thereby achieving the purpose of increasing the flame retardant effect.
Anti-effect
It means that the effect of two or more additives added together in the plastic formula is lower than the average value of their individual additions.
In the anti-aging plastic formula, the specific antagonistic effects are: HALS light stabilizers are not used together with thioether auxiliary antioxidants, because the acidic components generated by thioethers inhibit the light stabilization effect of HALS.
In the flame retardant plastic formula, the main examples of antagonistic effects are: the use of halogen flame retardants and silicone flame retardants will reduce the flame retardant effect; the use of red phosphorus flame retardants and silicone flame retardants also has antagonistic effects.
The components of the formula should be mixed evenly
Some components should be added in batches
For formulas with too much filler, it is best to add the filler twice. The first time is in the feeding hopper, and the second time is in the middle side feeding port. For example, if PE is added with 150 parts of aluminum hydroxide in a halogen-free flame retardant formula, it must be added twice, otherwise it cannot be granulated.
For the coupling agent treatment of fillers, it is generally necessary to spray it in three times to achieve uniform dispersion and good coupling effect.
Reasonable arrangement of the order of addition
In the formula of PVC or filler masterbatch, the order of adding various materials is very important. In the formula of the filling masterbatch, the filler should be added first. After mixing and heating, the water in it can be removed, which is conducive to the subsequent coupling treatment. In the PVC formula, the external lubricant should be added later to avoid affecting the uniform mixing of other materials.
Negative impact of the formula on other properties
The designed formula should not deteriorate or affect the basic physical and mechanical properties of the resin to the minimum extent. At least the original performance should be retained, and it is best to improve some properties of the original resin by the way.
But the objective fact is that everything has two sides. When improving a certain performance, other performance may be reduced, which can be said to be a loss for one thing. Therefore, when designing the formula, it is necessary to consider it comprehensively and try not to affect other properties. For example, the high filling formula has a great impact on the mechanical properties and processing properties of the composite material, the impact strength and tensile strength are greatly reduced, and the processing fluidity is deteriorated.
If the product has specific requirements for the mechanical properties of the composite material, specific compensation should be made in the formula, such as adding elastomeric materials to compensate for the impact performance and adding lubricants to improve the processing performance.
Which properties are often affected in the formula?
Impact
Most inorganic materials and some organic materials reduce the impact performance of the formula.
In order to compensate for the impact strength, elastomers need to be added when designing the formula. For example, in the PP/talc/POE formula of the filling system, and in the ABS/decabromo/antimony trioxide/toughener formula of the flame retardant system.
Transparency
Most inorganic materials have an effect on transparency. Choosing inorganic materials with a refractive index similar to that of the resin will have a smaller effect on transparency.
Recently, transparent filler masterbatches are more popular, mainly for HDPE plastic bags. Adding special varieties of talc has little effect on transparency, but it is not absolutely no effect.
Organic materials also have an effect on transparency. For example, in PVC toughening, only MBS does not affect transparency, while CPE, EVA, and ACR all affect its transparency.
Among inorganic flame retardant materials, colloidal antimony pentoxide does not affect transparency.
Color
When designing the formula, you must pay attention to the color and color change of the additive itself. Some additives themselves are very dark in color, which will affect the color of the product and make it difficult to process light-colored products. For example, carbon black is black, and only dark-colored products can be processed.
Others such as graphite, red phosphorus, molybdenum disulfide, metal powder and industrial slag are colored in themselves, so be careful when choosing. Some additives are white in themselves, but they change color due to high temperature reaction during processing. For example, wollastonite is white in itself, but it becomes light gray after being filled into resin.
Other properties
The thermal conductivity of plastics is generally modified by adding metal and carbon thermal conductors, but this type of thermal conductor is also a conductive agent. While improving thermal conductivity, it will also improve electrical conductivity, thereby affecting insulation.
And thermal conductivity is often used for materials that require insulation, such as circuit boards, connectors, packaging materials, etc. For this reason, thermal conductivity cannot be added to insulate thermal conductivity, only insulating thermal conductors can be added, such as ceramic metal oxides.
What other properties should the formula have?
The formula must ensure appropriate processability to ensure the molding of the product and have no adverse effects on the processing equipment and the use environment.
The heat resistance of the additives in the composite material should be good, and no evaporation or decomposition will occur at the processing temperature (except for cross-linking agents, initiators and foaming agents); the addition of additives should have little effect on the original processing performance of the resin; the wear and corrosion of the equipment by the added additives should be as small as possible, and no toxic gas should be released during processing to avoid harming the health of employees.
Fluidity
Most inorganic fillers affect the processability. If the amount added is large, it is necessary to add processing modifiers to compensate for the lost fluidity, such as adding lubricants.
Organic additives generally promote processability, such as decabromodiphenyl ether and tetrabromobisphenol A flame retardants can promote processing fluidity, especially tetrabromobisphenol A.
General modified formulas require the addition of an appropriate amount of lubricant.
Heat resistance
Ensure that the additives do not decompose during the processing, except for foaming agents, initiators, and cross-linking agents that must be decomposed due to functional requirements.
Precautions
Aluminum hydroxide is not suitable for use in PP due to its low decomposition temperature and can only be used in PE.
Tetrabromobisphenol A is not suitable for flame retardancy of ABS due to its low decomposition temperature.
Most organic dyes have low decomposition temperatures and are not suitable for high-temperature processing of engineering plastics.
The decomposition temperature of spices is low, generally below 150°C, and can only use EVA and other resins with low processing temperatures as carriers.
Modified plastic formulas require the addition of antioxidants due to strong shearing during processing to prevent thermal decomposition and yellowing of raw materials.
Environmental protection of plastic formula components
Requirements: All kinds of additives in the formula are harmless to operators, equipment, users, and the contact environment.
In the past, the scope of environmental protection requirements was small, and it was only necessary for food, medicines, etc. to be non-toxic when in contact with the human body.
Now the requirements are higher, and indirect contact with the human body is not allowed, and it must not pollute the environment, such as soil, water, and atmosphere.
Price and source of additives
On the basis of meeting the above requirements of the formula, the lower the price of the formula, the better. When selecting additives, you must choose low-priced types for the same type of additives.
Choose low-priced raw materials as much as possible - reduce product costs
Choose stock raw materials as much as possible - no need to buy
Choose local raw materials as much as possible - low transportation costs, can reduce inventory and save working capital
Choose domestic raw materials as much as possible - imported raw materials are greatly affected by factors such as foreign exchange, trade policies, and transportation time
Choose universal raw materials as much as possible - new raw materials have few distributors, are not easy to buy, and have unstable performance
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