Coating knowledge: the role of plastic lubricants

Core tip: what are the functions of plastic lubricants? Polymers usually have high viscosity after melting In the process of processing, when the molten polymers pass through narrow slots, gates and other channels, the polymer melt must have friction with the surface of processing machinery Some of the friction is very harmful to the processing of polymers These friction will reduce the melt fluidity, and at the same time, it is strict Heavy friction can roughen, tarnish, or streaks the surface of the film Therefore, it is necessary to add additives to improve lubricity, reduce friction, and reduce interfacial adhesion This is the lubricant In addition to improving the fluidity of lubricant, it can also start melting accelerator and prevent Paint knowledge | precautions for wall paint color selection Recommended introduction: when painting the wall, the owner sometimes has difficulty in choosing what color of the wall paint to paint In fact, there is no ugly color in the wall paint, only the disharmonious color matching The use of wall color contains the knowledge of health Too strong color will stimulate people's perception, make people have a sense of fidgety, affect people's mental health Grasp the basic principles of wall color and paint a colorful space 1、 Wall paint color selection notice 1 Light color is generally used for the top surface Light colors make people feel light, dark colors make people feel heavy Usually, the treatment of rooms is from top to bottom, from shallow to deep For example, the ceiling and walls of rooms are white and Paint Home News: what are the functions of plastic lubricants? Polymers usually have high viscosity after melting In the process of processing, when the molten polymers pass through narrow slots, gates and other channels, the polymer melt must be connected with the processing machinery There are friction on the surface, some of which are very harmful to the processing of polymer These friction make the melt fluidity decrease At the same time, serious friction will make the film surface become rough, lack of luster or flow pattern Therefore, it is necessary to add additives to improve lubricity, reduce friction, and reduce interfacial adhesion This is the lubricant In addition to improving the fluidity, the lubricant can also play the role of melting accelerator, anti adhesion and anti-static agent, smooth agent and so on Lubricants can be divided into external lubricants and internal lubricants The main function of external lubricants is to improve the friction between polymer melt and hot metal surface of processing equipment It has poor compatibility with polymer and is easy to migrate from the melt to the outside, so it can form a lubricating thin layer at the interface between plastic melt and metal The internal lubricant has good compatibility with the polymer, which can reduce the cohesion between the polymer molecules in the polymer, so as to improve the internal friction heat generation and melt fluidity of the plastic melt The common external lubricant is stearic acid and its salts; the internal lubricant is a low molecular weight polymer Some lubricants have other functions In fact, each kind of lubricant has the function of realizing a certain requirement It always works together with internal and external lubrication, but it is more prominent in a certain aspect The same lubricant in different polymer or different processing conditions will show different lubrication, such as high temperature, high pressure, internal lubricant will be squeezed out and become external lubricant In the production of plastic film, we will encounter some adhesion phenomenon For example, in the production of plastic film, the two-layer film is not easy to separate, which brings difficulties to automatic high-speed packaging In order to overcome it, a small amount of additives can be added to the resin to increase the surface lubricity, so as to increase the external lubricity, generally known as anti adhesion agent or smooth agent In the molecular structure of general lubricants, there are two parts of long-chain nonpolar group and polar group Their compatibility in different polymers is different, which shows the effect of different internal and external lubrication According to the chemical composition, the commonly used lubricants can be divided into the following categories: fatty acids and their esters, fatty acid amides, metal soaps, hydrocarbons, organosilicon compounds, etc Lubricants have many functions in the actual processing of plastics For example, in the mixing and rolling process, they can prevent the polymer from sticking to the barrel, inhibit the friction heat generation, reduce the mixing torque and load, and thus prevent the thermal degradation of polymer materials During extrusion molding, it can improve the fluidity, improve the adhesion of polymer material to barrel and mould, prevent and reduce the retention In addition, it can improve the appearance and luster of the film From the perspective of processing machinery, external lubricants play an important role in mixing, calendering, plastic lining and other molding processes, while internal lubricants are more effective in extrusion and injection molding The amount of lubricant is generally 0.5% ~ 1% Attention should be paid to: 1 When the flow performance of polymer meets the needs of molding process, the effect of external lubrication should be mainly considered to ensure the internal and external balance; 2 The effectiveness of external lubrication should be based on whether it can form a complete liquid film on the plastic surface at the molding temperature, so the melting point of external lubricant should be close to the molding temperature, but the difference between 10 ℃ ~ 30 ℃ can form a complete film; 3 Do not reduce the mechanical strength and other physical properties of the polymer When selecting lubricant in production, it should meet the following requirements: 4 High and lasting lubrication efficiency; 5 Moderate compatibility with resin, balance of internal and external lubrication; no frost spraying and scaling; 6 Small surface gravity, low viscosity, good expansion at interface, easy to form interface layer; 7 Try not to reduce all kinds of excellent properties of the polymer, and do not affect the secondary processing performance of the plastic; 8 Excellent heat resistance and chemical stability, no decomposition and volatilization in the processing; 9 No corrosion of equipment, no pollution of film, no toxicity However, it is often difficult to achieve the purpose of using only one lubricant, which requires several lubricants to be used together In recent years, the development of composite lubrication is very fast When selecting, the role of lubricants can be viewed from multiple perspectives Commonly used lubricants are stearic acid, butyl stearate, oleamide, ethylene distearamide, etc Many paraffin materials can be used as lubricants, such as natural paraffin, liquid paraffin (white oil), microcrystalline paraffin and so on, but their functions are different Natural paraffin is mostly used for external lubrication and can be used as a lubricant and release agent for a variety of plastics Generally, the dosage is 0.2-1phr, but its compatibility, thermal stability and dispersion are not very good The dosage should not be too large It is better to use it together with the internal lubricant; while white oil is mostly used as the internal lubricant for PVC and PS, with good lubrication performance and thermal stability Generally, the dosage is 0.5phr They are non-toxic and can be used for food packaging Another kind of microcrystalline paraffin: it is also used as a lubricant in plastic processing, with a dosage of 1-2 phr Its thermal stability and lubricity are better than ordinary paraffin Low molecular weight polymers are also widely used as lubricants, such as polyethylene wax and low molecular weight polypropylene, which have good internal and external lubricity and are non-toxic Polyethylene wax is suitable for extrusion and calendering of PVC and other materials, and the dosage is generally 0.1-1phr, which can improve the processing efficiency, prevent film adhesion, improve the dispersion of filler or pigment, and the compatibility and transparency are not very good; irregular structure low molecular weight polypropylene can be used as the lubricant of rigid PVC and PE, with excellent performance, which can improve the dispersion of other additives, and the dosage is 0.05-0.5phr [focus on WeChat official account "paint net"; 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