Methods and measures to eliminate static electricity during printing

Inevitably, static electricity is generated in the printing process, resulting in a reduction in print quality, and in serious cases, it can cause fires.
The general measures for eliminating static electricity are:
· All conductive surfaces are electrostatically grounded;
Increase the conductivity of the material;
Increase surface conductivity by increasing relative humidity or performing surface treatments;
Increase air conductivity;
· Reduce the working speed accordingly;
· Appropriate choice of contact materials;
• Control the surface contact temperature appropriately.
If the desired effect cannot be achieved with a single measure, several measures can be combined and used.
The printing materials in printing are mainly paper and plastic. They all live in non-conductor-insulating materials and need special methods and techniques to eliminate them. There are mainly two methods of eliminating static electricity during the Indian drama: chemical elimination and physical elimination.
1. Chemical Elimination Method Chemical Elimination is generally performed by placing a layer of antistatic agent on the surface of the substrate and making the substrate conductive to a slightly conductive insulating material.
(1) The antistatic agent used in the paper printing materials is a kind of tetravalent salt chemical. After being coated on the paper surface, the tetravalent salt absorbs moisture from the air under low humidity, so that the resistance through the material surface is reduced. Another is to add some chemicals to the material to increase the porosity of the material and loosen the surface of the material. Its role is to absorb moisture, thereby eliminating static electricity.
(2) The antistatic agents used in plastic printing materials are some surfactants. The molecules contain polar hydrophilic groups and non-oily lipophilic groups. The lipophilic groups have certain compatibility with plastics, hydrophilic groups can be Ionization or adsorption of moisture in the air, forming a thin layer of conductive layer, can leak the charge, thus playing an antistatic role.
In the printing process, the method of chemical elimination of static electricity is strictly speaking, it belongs to the printing material processing and processing.
In addition, the application of chemical anti-static methods is very limited. For example, when printing paper is added with chemical components, it may have an adverse effect on the quality of the paper, such as reducing paper strength, adhesion, tightness, etc. Not used.
2. The physical elimination method has many physical methods to eliminate static electricity, and the technology has also developed rapidly. At the same time, there are also some corresponding devices. The physical age elimination method and device are now analyzed as follows:
(1) "Earthing" elimination method. This is also the simplest method. It uses a conductor to connect static electricity to ground and “ground” to equal the potential of the earth. The original static charge will leak through the earth. Although this method is simple, it has no effect on general insulating objects.
The "Earthing" elimination method is useful for certain conditions in a printing factory. For example, two adjacent printers, although they all have wire grounding, there may still be a potential difference between them due to the different levels of static charge leakage. In order to avoid discharging each other, they need to be connected by wires to eliminate the electrostatic influence between each other.
(2) Humidity control elimination method. It is achieved by controlling the relative humidity of the printing environment. Figure 2 shows the relationship between paper surface resistance and air relative humidity.
Figure 2 shows that the surface resistance of the paper decreases as the relative humidity of the air increases. It can be seen that increasing the relative humidity of the air can increase the resistivity of the paper surface, thereby accelerating the leakage of electric charge. If the original paper before printing has been electrostatically charged, it can be fully humidified and then printed.
The suitable environmental conditions for the printing shop are that the temperature is about 20°C and the relative humidity is about 65%.
(3) Material friction static elimination method. Different materials ask each other for friction, and positive or negative charge due to loss of electrons (or ions). From Table 1, it can be seen that when the former material is rubbed against each other, the former always has a positive charge while the latter has a negative charge. Therefore, if the printed paper has been charged with static electricity, it is generally negative. Then the material in front of the paper in Table 1 can be used to rub the paper surface, and the generated positive charge can be offset with the original negative charge so as to achieve static elimination.
(4) Static elimination equipment. The static-eliminators commonly used in printing plants include inductive, high-pressure corona discharge, and radioisotope types. The principle of eliminating static electricity is the same. Chengdu ionized all molecules in the air into ions. Because ions have different electrical properties, the air becomes the ion layer and becomes the conductor of electricity. When the printing material passes through the ion space, part of the charged electrostatic charge is neutralized, and part of it is carried away by the air, so as to achieve the purpose of eliminating static electricity. This method of using the instant elimination of static electricity is mostly good for paper printing. Two types of static eliminators, the discharge type and the ionization type, are analyzed.
1 discharge static eliminator. The static eliminator is shown in FIG. When the static eliminator operates, the alternating current is converted into a direct current of 9000 to 10000 V. The electrode needle discharges at a distance of 100 to 200 mm from the paper, and the paper is neutral by the exchange of positive and negative charges.
The AC power is preferably 50Hz. When the paper is 100m/m2 or higher, it is recommended to spray 0.1MPa compressed air in the discharge area. The inner diameter of the air injection pipe is 6~13mm, the diameter of the injection hole is 1mm, and the hole pitch is 50~60mm. The wide air volume is 0.49 ~ 0.66L/min to continuously disperse the ionized air and improve the effect of eliminating static electricity. The electrode needle uses a stainless steel needle of 0.9~f1mm and extends 10mm from the tube surface. The working principle of the static eliminator is to eliminate static electricity by neutralizing positive and negative charges. The static eliminator has been applied in many printing factories.
2 away from the air static eliminator. It is the use of ionized air to neutralize the charge and eliminate static electricity.
Ionized air is an ordinary indoor air that is ionized into positive and negative ions, and plays a role in neutralizing static electricity on the substrate surface. Because the positive and negative charges attract each other, ionized air can exist for a very short time, only a fraction of a second. Therefore, ionized air must be continuously generated to supplement. The generation of ionized air requires energy. The device for generating ionized energy is an ionized air device, which has an electric induction type, a power type, or a nuclear energy type.
FIG. 4 shows one type of ionization air static eliminator, which is called a rod type ionization air device. The best position of the rod-shaped device is 2.5cm above and below the web printing material, and 15cm away from the roller, corrector, platform, and frame. On a printing press, several paper sticks or static power may be required.
This static eliminator is based on the combination of nuclear energy and electrical induction. It has unique advantages: The number of ions generated is not limited. The higher the surface voltage or the faster the conveying speed, the more ions it produces. Therefore, it has been widely used in various kinds of processing and printing requiring the elimination of static electricity, and is particularly suitable for static elimination of reel material processing.
Static elimination has a certain relationship with the surface of printing materials. In general, neutralization of a surface electrostatic charge can act as a static elimination and control of both surfaces. Usually, the electrostatic charge is generated from the surface and affects the other surface. Therefore, elimination of static electricity at one side can eliminate static electricity on both surfaces. However, static elimination is also required on both sides. For example, on paper coating machines, static elimination must be performed on both sides. As to whether or not to eliminate single-sided or double-sided, it is necessary to conduct on-site determination and analysis.