Electrostatic Analysis in Printing (Part 2)

5 static electricity test

The purpose of electrostatic testing in packaging and printing plants is to analyze the degree of harm, study preventive measures, and determine the effectiveness of static elimination. Special personnel must be assigned to conduct regular electrostatic testing of anti-static shoes, conductive shoes, and anti-static overalls. The test results should be archived and submitted to the relevant departments at a higher level. Electrostatic testing includes the following items:

1 object with electrostatic performance prediction. The surface resistivity of the object is measured by a high resistance meter or an ultra high resistance meter, and the range is preferably 10-10 KΩ).

2 In the actual production process, the charged body is charged with static electricity. The measuring range of the electrostatic potential of the electrified body is 100 kV, the precision is 5.0, the measurement of ambient air temperature and relative humidity, the measurement of the operating speed of the charged body, the determination of the concentration of flammable gas, and the value of the conductive ground-to-ground resistance Determination. Among them, the ACL-350 introduced by Derek is the world's smallest compact non-contact digital electrostatic meter, which can measure the electrostatic voltage value and electrostatic polarity on the surface of an object. The meter is simple to operate, with a measurement and hold button and a set button, and is widely used.

3 safety measures use effect judgment test. Static potential measurement instrument range is suitable for 0-lOkV, precision is 5.0, the detection point must be selected behind the electrostatic safety device.

6 Measures to prevent electrostatic damage

Measures to prevent electrostatic hazards in packaging and printing workshops It is suggested that the following aspects should be taken into consideration: All electrostatic processes, equipment, and locations must be protected against static electricity; in areas where explosive gasses may be present in the surrounding environment, ventilation measures must be strengthened. The concentration is controlled below the explosion limit; after the electrostatic safety measures are taken, the static potential of the insulator should be controlled below 10 kV to prevent the electric insulator from causing the electric shock to the operator; when the electric shock is applied to the operator, it may cause a second accident. On occasions, with the exception that the electrostatic potential of the insulator should be controlled below 10kV, corresponding safety measures shall be taken for the equipment; and where there is an explosion and fire hazard, the operator must wear anti-static shoes or conductive shoes, anti-static overalls; the operating area shall be When laying conductive ground, the conductive ground-to-ground resistance should be less than 10Ω and must be constantly checked to maintain its conductive properties.

In short, workers in the packaging and printing industry must pay enough attention to the static electricity generated in the production process to ensure safe production.

Effective methods and techniques for controlling static electricity

In the printing process, static electricity brings many hazards. It not only hurts the operators, but also makes qualified prints completely messy. To prevent static electricity from time to time, it is best to start with it and destroy it before it harms production.

Static electricity generated area

In addition to the parts where paper and rollers come in contact with, such as the paper guide rollers, nip rollers, floating rollers, print heads, delivery stacks, reel-up devices, overprint rollers, etc., static electricity also appears in some other applications. Such as plastic film base, printing machinery and coating production line. Under these circumstances, if the static electricity is not controlled effectively, the accumulation of dust will reduce the number of qualified products and subject the operator to electric shock. In addition, if solvent-type inks are used, fire and explosion may also occur.

UV inks are particularly susceptible to electrostatic phenomena, causing some of the particles in the ink to adhere to blankets and other machine parts. It is likely to cause secondary contamination of the printed sheets, some white spots (deinking failures) or ring-shaped white spots. Static electricity makes the cleaning roller abnormally difficult, and if the roller is not cleaned cleanly, the quality of the product is also reduced, and the number of shutdowns and time are increased. Eliminating or reducing static electricity to less than 500 volts is very important for cleaning the drum, which can greatly improve work efficiency. Otherwise, the drum itself may absorb more dust than before cleaning, making production impossible.

Effectively control static electricity

It is always the printing industry's controversy to eliminate static electricity or to control it effectively. Although some products that control static electricity use the name “static electricity,” these products do not actually remove static electricity. It is almost impossible to completely eliminate static electricity, because static electricity will be present wherever there is contact, and the contact between various parts and materials inevitably occurs in the printing process, and static electricity cannot be avoided. produce.

We can reduce static electricity to a certain extent so that it is completely unaffected by the process of production. Although this is not realistic and necessary, we can effectively control the charge on the contact surface at a particular stage. For example, when the charged material passes through the ionizer, the static electricity decreases, and when the friction occurs again, the static electricity reappears.

Static control method

In packaging and printing companies, tinsel (gold paper) is the most commonly used method for controlling static electricity, in addition to carbon brushes for controlling static electricity. It is also the most attractive method. The key is that the cost of this method is relatively low. Although these static removal methods work well, it is difficult to say that they are the most appropriate method. For example, tinsel products often scratch the film base. Tinsel controls the speed of static electricity very quickly, but if it is more than 3,000 volts of static electricity, other methods have to be chosen. Most static-related transfer and printing problems can be solved by the tried and tested method of eliminating static electricity. In the fast-rotating web production line, the AC ion rod is a relatively common method of controlling static electricity, and the effect is very good, but the control range is extremely limited. It is recommended to install a few inches more on the surface of the drum in order to optimize the control performance.

According to the different charges generated corresponding to the corresponding positive ions or negative ions, the electrostatic neutralization, which is also a more popular method of controlling static electricity. The DC stick neutralizes the electrostatic energy in a wide range and is suitable for the winder, which can be used as an alternative to the expensive AC ion blower. In the packaging and printing market, the next step in controlling static electricity may have to focus on monitoring technology. The recently introduced Model 177 fieldmeter/monitoring system (developed by Monroe Electronics) is very useful for solvent-based inks and other explosive environments where the system can monitor and control four areas of the press cylinder at the same time. After controlling the electrostatic device, monitor the working efficiency of the ionizer.

Ion System also developed AC intelligent electrostatic neutralization equipment with built-in diagnostics and performance monitor. It consists of a solid, high-voltage energy supply, built-in monitoring circuit, computer interface module, and electrostatic neutralization rod. To manage each neutralizer and alert the operator of possible problems through a computer. With this trend, Simco recently introduced Blue Bar/M167, a supervised energy supply that monitors operations and warns operators of any problems with the control rods, such as bending or misconduct.

Positioning

Many of the design structures of the printing press have become sites for the accumulation of static electricity. If you want to control static electricity everywhere, you will need to add a lot of equipment. This kind of excessive control will cause unnecessary burden on the enterprise, and usually choose appropriate The device can control static electricity within an acceptable threshold. Where to place the static control device is just as important as choosing which method to control static electricity. Usually, a method called “minimum requirement” is adopted. The device that controls static electricity is directly positioned in the process and often causes problems due to static electricity. local. And those static electricity between 50 volts and 100 volts will not have any impact on production at all, so there is no need to consider it.

Some tips for controlling static electricity

Checking the ground – If the operator is often hit by static electricity, the first thing that should come to mind is checking if the ground connection is appropriate.

Increased humidity - After increasing the relative humidity (RH), static electricity is reduced a lot, because humidity can increase the electrical conductivity of some insulating materials. The relative humidity in the workshop should be at least between 55% and 60%. One negative effect of increasing the humidity is that the surface of the material is too moist and the working environment is not comfortable.

Consider many factors - the causes of static electricity are many, such as speed, tension, pressure and relative humidity. Checking the ground may help, but keep in mind that some materials may not have the ability to ground; reducing the speed at which the machine operates reduces the friction between materials may help, but it reduces production. Therefore, we must consider the issue in many aspects and try to balance the different factors as much as possible.

The accuracy of the control is measured—Measurement of control statics can increase the operational capacity of the control equipment and help determine whether new equipment needs to be replaced or whether it is necessary to change the location of the installed equipment.