Plastic formula design surface looks very simple, but in fact contains a lot of internal links, in order to design a high-performance, easy processing, low price formula, the selection of additives need to consider a lot of factors, is put forward the following factors for reference:
First, according to the purpose to achieve the selection of additives
According to the purpose to achieve the selection of suitable additives, additives should be able to give full play to its expected effect, and achieve the specified indicators. The prescribed indicators are generally the national standards, international standards, or customer performance requirements.
Second, auxiliaries have selectivity to resin
Red phosphorus flame retardant to PA, PBT, PET effective; Nitrogen flame retardants are effective on oxygen-containing classes, such as PA, PBT, PET, etc. Nucleating agent has good effect on copolymerized polypropylene. The heat-resistant modification of glass fiber has good effect on crystalline plastics but poor effect on amorphous plastics. Conductive plastics filled with carbon black work well in crystalline resins.
Three, the form of additives
The form of auxiliaries with the same composition has a great influence on the modification.
1, the shape of additives
The enhancement effect of fibrous auxiliaries is good. The degree of fibrosis of additives can be expressed by length-diameter ratio. The greater L/D, the better the enhancement effect, which is why we add glass fiber from the vent. Molten state than powder is beneficial to maintain length-diameter ratio, reduce the probability of broken fiber.
Spheroidal auxiliaries have good toughening effect and high brightness. Barium sulfate is a typical spherical additive, so the filling of high gloss PP is barium sulfate, and small amplitude rigid toughening can also be used by barium sulfate.
2, the size of additives
A. Influence of particle size of auxiliary agent on mechanical properties
The smaller the particle size, the more beneficial to the tensile strength and impact strength of the filling material.
B. Effect of particle size of auxiliary agent on flame retardant performance
The smaller the particle size of the flame retardant, the better the flame retardant effect. For example, the smaller the particle size of hydrated metal oxides and antimony trioxide, the smaller the amount needed to achieve the same flame retardant effect.
C. Influence of particle size of auxiliaries on color matching
The smaller the particle size of the colorant, the higher the coloring power, the stronger the covering power, the more uniform color. But the particle size of colorant is not the smaller the better, there is a limit value, and the limit value of different performance is different. For coloring power, the limit particle size of azo colorants is 0.1μm, and that of phthalic colorants is 0.05μm. For covering power, the limit particle size of colorant is about 0.05μm.
D. Influence of particle size of auxiliary agent on electrical conductivity
Taking carbon black as an example, the smaller its particle size is, the more likely it is to form a network conductive pathway to achieve the same conductive effect, and the amount of carbon black added is reduced. But like colorants, there is a limit to particle size, particle size is too small to gather and difficult to disperse, but the effect is not good.
3, the surface treatment of additives
The compatibility of additives and resins is better, so as to ensure that additives and resins disperse according to the expected structure, ensure the completion of the design indicators, ensure that the effect of lasting play in the service life, extraction resistance, migration resistance, precipitation resistance. If most formulations require additives and resins to be evenly dispersed, for barrier formulations, additives are expected to be distributed in the resin middle layer. In addition to a few additives such as surfactants, good compatibility with resin is the key to play its efficacy and increase the amount of additives. Therefore, it is necessary to improve or improve its compatibility, such as using compatibilizers or coupling agents for surface activation treatment.
After the surface treatment of all inorganic additives, the modification effect will be improved. In particular, filler is the most obvious, other glass fiber, inorganic flame retardant and so on.
Surface treatment is based on coupling agents and compatibilizers, such as silane, titanate ester and aluminate ester, and compatibilizers are maleic anhydride graft polymer corresponding to resin.