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Why is it necessary to add a humidifier next to the CHM sheeter machine

TIME : 2024-01-05 HITS : 16

The static electricity on paper has something to do with paper making. Under normal circumstances, the base paper is less charged when it leaves the factory, and the probability of coated paper being charged is also low. Since printing paper (whiteboard paper, cardboard, etc.) and coated paper are reprocessed on the basis of the original paper, even if the original paper is charged, it will be eliminated during the processing. 

Generally, paper with a basis weight of less than 80g/m2 has more static electricity. However, the static electricity on the paper is already there before printing on the machine or the static electricity is not obvious before printing. It is often caused by a sudden increase in static electricity after printing. Due to the presence of water in the offset printing process, it is rare for static electricity to appear after printing. For offset printing, static electricity mainly occurs before printing.

The main reason for static electricity on paper is frictional electricity. The charging of many objects is caused by friction. The friction between the paper and the calender during paper making, and the friction between the paper and the rubber cylinder and the impression cylinder during printing are all important factors in generating static electricity. The atomic nuclei of various materials have different binding forces on electrons, or have different affinity and alienation properties for electrons. When two different substances are in close contact, the electron-phobic side has a weak binding force on electrons, and some electrons will pass through the interface and attach to the surface of the electrophilic side. The result of this electron transfer is the formation of an electrical double layer at the interface. At this time, if the two substances separate quickly, the electron-phobic side becomes positively charged due to the loss of some electrons, and the electrophilic side becomes negatively charged due to the gain of some electrons. This is the essence of triboelectricity.

The paper, blanket, ink, printing plate, etc. in the printing materials have different affinity and alienation properties for electrons. During the printing process, the great pressure brings them into close contact, and the high speed makes them separate quickly. They are fully capable of friction generation. Electrical conditions. Therefore, it is understandable that tens of thousands of volts of static electricity appear during printing, especially since some papers have static electricity before printing. Static electricity has been generated in the paper during the manufacturing process. When it is packaged and sent to the printing factory before it can escape, some static electricity is still retained. This is also the reason why the paper is charged before printing. When using these papers, different methods should be adopted to eliminate static electricity based on the actual production conditions.

Static electricity is generated due to friction between paper and other substances or friction between paper. It changes greatly with the conductivity of the paper itself and the surrounding air. Static electricity appears on the dry sheet at the end of the dryer section of the paper machine and generally reaches its maximum during supercalender calendering. During the winding and rewinding, as well as printing processes, static charges can also be generated on dry paper due to friction.

Therefore, printing paper itself may contain a lot of static electricity, or static electricity may be generated during printing. Paper with static electricity will have a great impact on printing operations and printing quality. Due to the attraction of opposite charges, it is difficult to separate the papers. When printing on flat paper, multiple sheets of paper are fed into the printing press at the same time. When printing on web paper, it is difficult to rewind the paper. Also, because charges of the same sex repel each other, print drift often occurs. , resulting in inaccurate overprinting or uneven paper delivery.

Static-charged paper can also easily absorb dust and paper scraps in the air, causing them to adhere firmly to the printed matter and directly contaminate the printed matter; when the electrostatic charge accumulation field strength reaches the breakdown field strength of the surrounding medium, electrostatic spark discharge will also occur. , and even cause accidents such as fires. For the same paper, the drier it is, the greater its resistance is. Therefore, once the dry paper is rubbed and generates electricity, it will be difficult to circulate and stay.

If there is more moisture in the surrounding air at this time, the static electricity on the paper will be transmitted to the air without causing malfunction. Therefore, static faults are less likely to occur in rainy seasons than in dry seasons.

In the paper industry, humidification can be used to control paper moisture content and paper surface quality. Once paper is produced and rolled into a tube, it will be in contact with the surrounding environment for a long time at the end of the papermaking equipment. The moisture on the exposed paper surface will change with the surrounding humidity, thus affecting subsequent processing and packaging. Many questions come:

1.When the humidity is lower than 50%, the paper will shrink, curl, or become irregular in size, making it impossible to roll, resulting in a significant increase in production costs.

2.When the relative humidity is lower than 45%, static electricity will be generated, resulting in a decrease in product quality and an increase in the scrap rate. It is very easy for paper products to generate static electricity after being rubbed by machines.

3.Usually during the papermaking process, it is often necessary to cut the edge of the paper, and to break and rejoin the paper after each roll reaches a certain length, which will cause a large amount of paper in the production workshop. Paper scraps and paper powder, after the air humidity decreases, the dust is prone to dust problems due to the decrease in surface moisture content.

Spraying is usually used to prevent this kind of situation from happening, and the humidity in the workshop is usually controlled at about 55%. The nozzle is used to evenly humidify the roll paper plane during operation. Its functions are:

1. Maintain a certain humidity to make paper making more uniform; ensuring that moisture is retained in the paper can not only make the product more flexible, but also make the production and packaging stages more stable.

2. Prevent the adhesion of paper powder caused by static electricity; static electricity itself has a discharge charge, so it will not only cause paper adhesion and other consequences, but also cause damage to equipment, directly causing economic losses to the paper mill.

3. Prevent the paper from curling and deforming and causing ruffles during the paper making process;

4. Increase the moisture content of the paper, and the paper and the environment will reach a humidity balance. The paper will not be easily deformed and will not become brittle and break easily.

5. Humidification will effectively control the dust of paper powder and paper scraps and ensure the working environment of the workshop.