[China Packaging Network News] It is well known that materials used in the packaging and printing industry, such as paper, plastics, inks, adhesives, and guide rollers (the department is anodized by natural alumina) are insulators; printing, compounding, rewinding, slitting, etc. It is also a "surface" project for high-speed friction, contact, and separation. The production of static electricity in packaging and printing plants is mainly related to the chemical composition, molecular structure, mechanical properties, degree of smoothness of the insulation material, the motor energy and the ambient temperature and humidity, the external mechanical action conditions such as the contact pressure, the speed of friction separation, and other factors. The type of the film, the contact type, the contact time, the contact area, and the separation speed are different, and the generated electrostatic discharge time and voltage are different.
First, the harm of static electricity
Once the paper is charged with static electricity, 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 sucked tightly and cannot be neat. In the printing process, due to electrostatic attraction, the sheets are glued together tightly, sometimes two, sometimes several, sometimes a stack of paper is difficult to separate, resulting in the paper suction nozzle unable to suck the paper, severely affecting the printing efficiency . When the plastic material is used for color printing, due to the electrostatic discharge, it is often found that the edge of the printed product overflows with burr-like ink, and the overprint deviation increases; the static electricity generated by the ink will produce a shallow net or missing printing; the plastic film and the ink absorb the environment. Dust, hair and other foreign objects prone to knife and other quality problems. When rewinding, slitting, bag making and other processes, electrostatic discharge will destroy the device's photoelectric correction system, electromagnetic control system.
Second, the method to eliminate static electricity
To combine the actual production, the use of packaging materials (packaged products), customer preconditions, etc., to take different anti-static technology 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. Such as "grounding" elimination method is to install anti-static brush on the process. Put the brush body in the winding or unwinding position of the paper or plastic coil, and make the grounding end of the antistatic brush reliably grounded, and it cannot be connected to the equipment or the guide roller. Due to the possibility of poor grounding of the equipment; the department's guide rollers are anodized, the surface of which is alumina, and the alumina is non-conductive.
2. Chemical elimination method
The method of chemical antistatic treatment, ie, antistatic agent treatment, is mainly a method of applying an antistatic agent (surfactant) to a resin or a substrate by means of an additive (filling) technique or a coating technique to modify the motor energy. Perfect antistatic technology. However, since the addition or coating of an antistatic agent causes a change in the chemical composition of the material, the technique is not applicable to the treatment of paper and is only used for the modification of plastic resins.
Especially in the packaging of food, medicine, cosmetics, chemical products, etc., to pay attention to safety, hygiene and compatibility with the matrix resin, etc., and therefore higher technical content. The packaging material with anti-static function not only eliminates all kinds of quality accidents caused by static electricity, but also improves the packaging efficiency for the customer and ensures the strength of the seal, which is recognized by the customer.
3, add type processing technology
This technology (ie masterbatch technology) is to add additive antistatic agent at a certain concentration (a few percent to a few tens percent) with a thermoplastic resin, and add a variety of additives, through melting, mixing, granulation The antistatic masterbatch was prepared. The selection of antistatic agents should pay attention to the compatibility with the matrix resin. If the compatibility is too poor, the prepared antistatic particles have poor performance; however, when the compatibility is too good, the antistatic agent migrates to the surface at a too slow rate 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. In the process of melting, mixing and granulating, the processing temperature should be kept as low as possible to prevent the antistatic agent from decomposing or even deteriorating due to poor thermal stability.
The use of antistatic particles to prepare antistatic plastic films often uses a three-layer (ABC) co-extrusion blow molding process. Pay attention to the proportion of antistatic masterbatch to be added according to the concentration of its effective substance, and make appropriate adjustments based on the test results so that the surface resistivity ps can be about 1011 Ω; the increase in the amount of addition will not only increase the cost of the product, but also the later period. The manufacturing process has an adverse effect.
4, coating type processing technology
The coating type antistatic agent treatment technology is to make an ionic surfactant into an antistatic coating and apply it on the surface of a plastic film to prevent charge accumulation. The choice of coating type antistatic agent should be determined according to the work function of the coated substrate. If the work function of a plastic material is large, it is easily negatively charged; if its work function is small, it is positively charged. The order of the work function of the common plastic materials from large to small has been previously discussed, PP, PE is extremely easy to negatively charged, it should be coated with cationic surfactant; PET, PA is easy to positively charged, should use anionic surface Active agent coating. The surface tension of the plastic film is required to be greater than 38 dyn/cm; the antistatic coating has good film-forming properties, abrasion resistance, chemical resistance, and durability.