Plastic modification is to improve or increase the function of general resin by physical, chemical and mechanical methods, and to achieve the function of special environmental conditions in electricity, magnetism, light, heat, aging resistance, flame retardant, mechanical properties and so on. In order to reduce the cost of plastic products and improve their functionality, there will be plastic modification technology from the production of raw resin to the modification of plastic masterbatches of various specifications and varieties.
The purpose of surface modification of plastics can be divided into two main categories: one is direct application modification, the other is indirect application modification.
(1) Direct application modification of plastics surface refers to some modifications that can be directly applied, such as surface gloss, surface hardness, surface wear resistance and friction, surface aging resistance, surface flame retardant, surface conductivity and surface barrier. The surface modification of plastics has been developed and applied rapidly in recent years. For example, the surface barrier modification plays an important role in the barrier modification of plastics.
(2) The indirect application of surface modification of plastics refers to some modifications that lay the foundation for direct application, such as the modification of surface tension of plastics to improve the adhesion, printing and lamination of plastics. For example, in the case of plastics electroplating, only ABS coating fastness can meet the requirements for plastics without surface treatment; especially for polyolefin plastics, the coating fastness is very low, so surface modification must be carried out to improve the binding fastness with the coating before electroplating treatment can be carried out.
Why modification?
Plastic modification has its purpose, and the modification methods used for each purpose are different. Here are some modified requirements that are often encountered and their modification methods.
Changing the density of plastics
(1) reduce plastic density
You may be clear about reducing density, but in other words, you can see: let the plastic become lighter. There are three ways to reduce the density of plastics, namely, foaming modification, adding light filler and blending light resin. The foaming molding of plastic products is the most effective way to reduce its density. The density can only be reduced slightly by adding lightweight additives and blending lightweight resins. The decrease is only about 50%, and the lowest relative density can only reach about 0.5. The density of plastic foam products varies widely, with a minimum relative density of 10-3.
(2) increasing plastic density
Improving the density of plastics is a way to increase the relative density of original resins, mainly by adding heavy fillers and blending heavy resins. The main fillers are metal powder and heavy mineral fillers. Blending heavy resin can improve the density of plastics. This method improves the density of plastics by a relatively small margin, usually up to about 50%. It is mainly suitable for some light resins such as PE, PP, PS, EVA, PA1010 and PPO. The heavy resins often added are: PTFE, FEP, PPS and POM.
Improvement of the transparency of plastics
The transparency of plastics is introduced in the previous articles. Here is a brief introduction. The principle of improving the transparency of plastics is to make use of the relationship between crystal and transparency. The transparency of plastics is related to the crystallinity and crystal structure of plastics. The transparency of plastics can be improved by controlling the different morphological structure of plastics.
To measure the transparency of a material, many performance indicators need to be considered. Commonly used indicators are: transmittance, haze, refraction index, birefringence and dispersion. Among the above indexes, transmittance and mist are two main indicators to characterize the transmittance of materials, while refractive index, birefringence and dispersion are three main indicators to characterize the transmittance quality of materials. A good transparent material requires excellent and balanced performance.
The commonly used methods of changing crystal form are:
Control of crystal quality, such as crystal shape, spherulite content, crystal size and crystal regularity.
(2) Improving refractive index is mainly achieved by adding organic or inorganic substances with high refractive index which do not affect transparency.
(3) Reducing birefringence can achieve the goal of reducing birefringence by controlling the orientation in processing, that is, reducing the orientation degree.
(4) Adding and improving the transparency of plastics means adding small molecular substances into transparent resins to improve their transparency. Using this method, the transmittance, refractive index and birefringence can be improved.
5. Adding nucleating agent is the most effective way to increase the transmittance of transparent resin. Nucleating agent is a small molecule which can promote crystallization. It can play the role of crystal nucleation in the resin, making the original homogeneous nucleation into heterogeneous nucleation, increasing the number of crystalline nuclei in the crystalline system, increasing the number of microcrystals and reducing the number of spherulites, thus making the crystal size finer and improving the transparency of the resin.
Addition of high refractive index inorganic substances
Adding substances that can reduce birefringence.
Add anti fogging agent.
Improvement of hardness and flexibility of plastics
(1) the hardness of added plastics is a modification method of adding hard additives in plastics. The commonly used hardness additives are rigid inorganic fillers and fibers.
(2) The method of improving the surface hardness of plastics is to improve only the surface hardness of plastics products, while the internal hardness of products remains unchanged. This is a low cost method to improve hardness. This modification method is mainly used for shell, decorative materials, optical materials and daily necessities. This modification mainly includes three methods: coating, plating and surface treatment.
(3) The hardness of plastics is improved by blending and compounding: 1) The method of improving the hardness of plastics is to mix the low hardness resin with the high hardness resin to improve its overall hardness. The common blend resins are PS and PMMA.
