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Solid electrification, such as the electrostatics of printing materials, cylinders, ink rollers, and blankets, is called in the academic community as “electronics for wearâ€; gas discharges, such as the static electricity of inks, adhesives, etc. The academic community is called "carrier ion."
The appearance of static electricity has brought unexpected hazards and inconvenience to the packaging process. The theory is to use "grounding" or "ion neutralization", whether it is "ambient relative humidity" or "electrical elimination", or to add "antistatic agents" to printing materials and printing aids. The purpose is to The resistivity of the surface layer of the packaging material of the volume resistance polymer decreases below 1010 ?. In order to reduce the electrostatic accumulation in the packaging molding process, in order to promote innovation in packaging technology.
Flexible packaging manufacturers bear the brunt of this challenge. However, in the past, due to lack of people's attention enough, there has been a light or heavy accident. Such as product quality decline, casualties, scrapping of goods within the storage period. In response to this problem, the author focuses on the causes of static electricity, static electricity prevention, and elimination of static electricity. The following introduction is superficial, so that it can be discussed with packaging colleagues to achieve higher prices and better prices for packaging products.
â– Electrostatic phenomena We know that printing materials (the manufacturers of resins and pulps generally do not add auxiliaries) are the main carriers for commodity packaging; printed materials (including inks, adhesives) are the main means for decorating packaging and disseminating product information; Post-processing (glazing, laminating, heat sealing) is an effective measure to improve, make up, and improve the quality of commodity packaging. Static electricity is also brought about by the above three aspects.
Now analyze the consequences of the generation of electrostatic phenomena:
1 The static electricity caused by plastics affects the printing quality and affects the printing quality, and post-processing glazing, laminating, heat sealing and conveying woven bags, film overprinting is not allowed; 2 discharge often causes electric shock, fire, powder explosion, etc.; 3 paper electrostatic often causes Automatic feeding difficulties and paper delivery, affecting the normal printing process operations; 4 ink electrostatic and adhesive static often lead to ink film and film uneven and poor adhesion and poor printing quality; 5 commodity electrostatic adsorption dust often Affect the appearance and reduce the price; there are high-speed operation of packaging and printing machinery electrostatic mist (also known as fog) discharge resulting in electric shock, fire and wounding and so on.
â– Electrostatic failure 1. During the compounding, heat-sealing and printing of general polymer plastics, the processing consequences caused by static electricity have become commonplace. For example, static electricity adsorbs dust onto a record, causing noise and impairing sound effects.
Static electricity often makes electronic computers misaligned. For this reason, as early as the 1990s, people summarized the following static sequences of some materials: + nylon → wool → wood → glass fiber → cotton yarn → metal → paper → rubber → polyvinyl chloride → polytetrafluoroethylene → - (ie Any type of substrate has been charged. Generally, the charge on the substrate is negative. The surface of the electrostatic object in the electrostatic sequence rubs the surface of the substrate. The positive charge generated can be cancelled by the negative charge on the right side. This is called electrostatic sequence elimination.
2. To prevent plastic static electricity, it is necessary to reduce or prevent friction. While reducing the generation of electrostatic charges, the static electricity lines that have already been generated should be leaked as soon as possible to avoid the accumulation of static electricity, which can be conducive to the smooth production of seal welding of goods or composite production processes.
Therefore, in the plastic antistatic method, no matter whether it is conducted directly through the circuit, or to increase the environmental humidity or use the organic antistatic agent, it must have the following:
On the one hand, the surface type of the plastic system should be: 1 low price and easy to get; 2 low toxicity and no irritation; 3 no effect on the color of packaging printing ink; 4 while the effect is high, it is still effective in extremely low temperature and humidity. 5 compatible with the plastic glow after the surface is strong and washable, wear without dissipating; 6 may be dispersed or soluble with a suitable volatilization gradient (with solvent).
On the other hand refers to the internal type: 1 low price and easy to get; 2 non-toxic or non-irritating; 3 for sheet, film, woven bags (silk) and other packaging products do not produce adhesion; 4 easy with other plastic additives Synergy; 5 easy to melt and do not increase the difficulty of the production process; 6 is compatible with polymer plastics does not produce frost, can maintain the transparency of the packaging film; 7 can withstand 120 ~ 300 °C high temperature without change; 8 add plastic is not due to resistance Static agents cause deterioration of their properties. For example, a plastic cornea factory in Hubei because of the improper use of antistatic agents, the production of biaxially stretched PP plastic film when coated on the cigarette box after the cream, instead of affecting the decoration of the bright color quality.
In the paper forming process, especially in the printing process, there are many aspects of static electricity. For example, Danmingkou Guangming Printing Factory used the glue of the Liuliping paper mill in the city and caused mutual adhesion due to mutual attraction. They also caused difficulties in paper feeding and paper delivery, which greatly hindered the normal rapid offset printing operations. At this point, the factory no longer purchased paper from Liuliping. Another example is Nanyang City, Henan Province, a printing factory in the 60,000 high-speed offset printing process, a large number of adsorption of paper dust and other impurities, shift operations only open and stop.
In recent years, the author has learned from the interactions with the operators of packaging and printing companies that: When the static electricity generated by the paper is severe, the air discharge may be caused by an extremely high potential (such as the volatilization of the solvent also causes this failure), resulting in electric shock or fire. Commonly known as "magnetic fog." It is not surprising that there are casualties.
In charged inks, “static ink spots†can often appear on packaged prints, which may be caused by the discharge of the printing machinery during the high speed operation.
For more than a decade, people have not only discovered the “darkness†caused by ink discharge. It also concludes that the discharge of printed graphic lines will lead to the appearance of “black whiskers†and that in the printing process, some of the graphics and texts adsorb dust and cause “printing†of printed products (usually the introduction of silicone oil). eliminate). Recently, we introduced the antistatic agent A into the ink system and the electrostatic phenomenon disappeared.
In addition to the static electricity of printing inks, the electrification of adhesives in paper, plastic pastes, and plastics, papers, and aluminum foils is indispensable in many occasions. The adhesive is misted due to charging, causing serious contamination of the paste and the complex adhesive molding operation environment; employees are also subject to electric shocks by the solvent of the adhesive system. For example, a color printing factory in Xiangfan City was damaged due to inadequate protective measures and was almost destroyed by fire on December 20, 1998. In view of the above phenomenon, zinc oxide is usually introduced into the system so that the generated static charge is leaked as soon as possible.
The static electricity of printing machinery is often due to the static electricity accumulation caused by the strong frictional force of many parts in high-speed operation. The old-fashioned or non-standard ink production with insufficient electricity elimination device, the flexographic flexographic printing, rotogravure and vertical printing of printing processing are not perfect. Sanding or high-speed dispersion of ink, etc., relying on the vulgarity of production and marketing companies has been far from 200 to 300 meters of a multi-color soft, convex, concave high-speed rotary printing and lamination. And 300,000 sheets per hour (60,000 rpm) offset newspapers were printed. This is because when the machine is running at a high speed, the voltage in some places sometimes reaches 20,000 volts, and when the current exceeds 100 μA, the influence of this powerful voltage and current on the process of packaging printing and film heat sealing is intricate and intangible. The production cost will be greatly increased, and in particular, the mechanical discharge will cause harm to the operators. Static electricity directly affects the development of China's flexible packaging industry. This is not an alarmist. It will be one of the serious issues that must be seriously faced before and after the WTO accession.
â– elimination measures 1, "grounding method." The metal conductor is electrically connected to the ground, making it equipotential with the earth, and the charge leaks through the earth. This is just the easiest way to eliminate static electricity. 2, "ion neutralization method." The air is ionized to generate both positive and negative ions to neutralize static elimination on plastics, paper, inks, adhesives, and the like. 3, "environmental relative humidity method." For example, the static electricity of the paper, spraying a certain amount of water onto the paper or the floor, after the moisture absorption and moisture absorption overnight can eliminate static electricity and boot printing. 4, "Electrical Law." A corona discharge or discharge device is installed on a packaging printing or laminating machine, or a device equipped with a radioisotope smashing device is used to eliminate static electricity. 5, "antistatic agent method." In the plastic, paper, ink, varnishes, adhesives and other systems to introduce the right amount of light machine or organic antistatic agent.
In addition to structural modification, conductive pathways are formed to achieve antifouling effects. 1 Such as inorganic metals, carbon fibers, carbon black, etc.; 2 organic such as cationic alkyl phosphates, anionic quaternary salts, nonionic polyethylene glycol vinegar or acid, zwitterionic imidazole derivatives and many more.
The mechanism of action of inorganic and organic antistatic agents varies widely. However, most manufacturers tend to absorb moisture, lubrication, and electrically conductive materials. (Liu Jiaju He Lizheng)
Due to the mechanical action of high-speed operation, the phenomena of solid charging and gas discharge that occur during packaging, printing, and post-processing are called "electrostatic theory."