How to eliminate static electricity in packaging printing?
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It is well known that the materials used in the packaging and printing industry, such as paper, plastics, inks, adhesives, guide rolls (the department is treated with anodized natural alumina) are all insulators; printing, compounding, rewinding, slitting and other processes are high-speed friction, Contact and separation of "surface" engineering. The generation of static electricity in packaging and printing factories is mainly related to the chemical composition, molecular structure, mechanical properties, smoothness, motor energy, ambient temperature and humidity, external mechanical action such as contact pressure and speed of friction separation. The type of the film, the type of contact, the contact time, the contact area, and the separation speed are different, and the generated electrostatic discharge time and voltage are different. How do you eliminate static electricity in packaging printing? Anmei Mall comes to analyze and analyze with you.
First, the harm of static electricity
Once the paper is electrostatically charged, it will cause a lot of trouble for printing. The first is that under the action of static electricity, the paper and the paper are tightly sucked and cannot be cleaned. In the printing process, because of the electrostatic attraction, the sheets are tightly pasted together, sometimes two, sometimes several, sometimes a piece of paper is difficult to separate, which causes the paper separation nozzle to absorb the paper, which seriously affects the printing efficiency. . When plastic materials are used for color printing, due to electrostatic discharge, it is often found that the burr-like ink overflows on the edge of the printed product, and the overprinting deviation increases. The static electricity generated by the ink may cause shallow mesh or missed printing; the plastic film and the ink adsorption environment Foreign matter such as dust and hair is prone to quality problems such as knife wire. In the process of rewinding, slitting, bag making, etc., electrostatic discharge will destroy the photoelectric correction system and electromagnetic control system of the equipment.
Second, the method of eliminating static electricity
In order to combine the actual production, the use of packaging materials (what products are packaged), the premise of the use of customers, etc., different antistatic technologies are used to eliminate static electricity. Common antistatic techniques are as follows:
1. Physical elimination method
The physical elimination method is a method of eliminating the inherent characteristics of static electricity without changing the function of the material. For example, the "grounding" elimination method is to install an antistatic brush on the process. Place the brush body on the winding or unwinding of the paper or plastic roll, and make the grounding end of the static eliminating brush reliably grounded, but not on the equipment or the guide roller. Due to the possibility of poor grounding of the equipment; the department guide rolls are treated by anodizing, the surface is naturally alumina, and the alumina is not electrically conductive.
2. Chemical elimination method
The chemical elimination antistatic method, that is, the antistatic agent treatment technology, mainly uses an antistatic agent (surfactant) to modify the resin or the substrate by means of adding (filling) technology or coating technology, and is more thorough and Complete antistatic technology. However, since the addition or coating of the antistatic agent causes a change in the chemical composition of the material, the technique is not suitable for the treatment of paper, and is only used for the modification of the plastic resin.
Especially in the packaging of food, medicine, cosmetics, chemical products, etc., pay attention to safety, hygiene and compatibility with the matrix resin, etc., so the technical content is high. The packaging material with antistatic function not only eliminates various quality accidents caused by static electricity, but also improves the packaging efficiency for the customer and ensures the sealing strength, thus obtaining the customer's approval.
2.1 Additive processing technology
The technology (ie, masterbatch technology) is to mix the additive antistatic agent with a certain concentration (a few to several tens of percent) with a thermoplastic resin, and add a variety of additives, after melting, mixing, granulation , made of antistatic masterbatch. The choice of antistatic agent should pay attention to the compatibility with the matrix resin. If the compatibility is too poor, the antistatic particles produced are inferior; but the compatibility is too good, the rate of migration of the antistatic agent to the surface is too slow, and it is difficult to form an antistatic water film. The same resin as the resin of the product is selected as the matrix resin, and in the process of melting, kneading, and granulating, the processing temperature is kept as low as possible, and the antistatic agent is prevented from decomposing or even deteriorating due to poor heat.
The antistatic plastic film is prepared by using antistatic particles, and a three-layer (ABC) co-extrusion blow molding process is often used. Pay attention to the proportion of antistatic masterbatch to be determined according to the concentration of the active substance, and adjust according to the test results, so that the surface resistivity ps is about 1011 Ω; the increase of the addition not only increases the cost of the product, but also the later The processing steps have an adverse effect.
2.2 Coating treatment technology
The coating type antistatic agent treatment technology is to form an ionic surfactant into an antistatic coating and apply it on the surface of the plastic film to prevent charge accumulation. The selection of the coating type antistatic agent is determined according to the work function of the coated substrate. Plastic materials have a large work function, which is easy to carry negative electricity; when the work function is small, it is positively charged. The order of work function of common plastic materials is as large as possible. PP and PE are easily negatively charged and should be coated with cationic surfactant. PET and PA are easily positively charged. Anionic surface should be used. The active agent is coated. The surface tension of the plastic film is required to be greater than 38 dyn/cm; the antistatic coating has good film forming property, abrasion resistance, chemical resistance and long-lasting effect.