Electrical Failure Analysis of Paper and Printing

First, the paper caused by printing failure

(a) Quality factors of the system

1. Paper coating, uneven application

Paper is composed of fibers and the paper surface cannot be completely uniform. Therefore, it is necessary to coat the surface of the paper with a layer of inorganic mineral pigments and a binder to improve the surface quality of the paper. The finer the particles, the smoother and finer the coated surface, and the rougher the surface.

In addition, in order to reduce the phenomenon of de-powdering and hair loss of paper, a surface sizing process is adopted in papermaking, that is, a layer of adhesive is applied on the surface of the paper to improve the surface strength and gloss of the paper. Due to the high printing speed of modern printing presses, the ink and the paper surface are instantly disengaged, and the ink has a large pulling force on the surface of the paper, and it is required that the coating sizing on the paper surface be uniform.

2. Poor paper flatness

The flatness of the paper is poor, and the specific performance is as follows:

1 Bubble formation on the surface of the bubbling paper is due to the fact that when the paper passes through the heat dryer, the water escaping speed on the surface of the paper is lower than the speed produced by the internal vapor of the paper, and the internal vapor is formed under pressure in the paper.

2 paper with holes and pulp

This was formed during the screening and purification process of paper. The hole is formed after the paper is formed, and impurities are peeled off from the paper surface. Large holes can produce shutdowns or produce waste at the time of printing; large, hard blocks of paste can damage the plates and erasers during printing, which can affect the printing job.

To avoid the above phenomenon, the main measures taken are:

The 1 paper dryer has good ventilation equipment so that water vapor evaporated from the paper can be quickly discharged outside the house.
2 Perform secondary drying to accelerate moisture removal.
3 Carefully screen and purify the pulp.

(b) Water content of paper

1、Cause analysis

1. Paper from the paper mill to the printing plant until the printing process, due to transportation and storage, use and other aspects of the ambient temperature and humidity changes, combined with the paper structure of the fiber containing hydroxyl groups can form hydrogen bonds, when wet hydrophilic Swelling occurs; syneresis shrinks when dry. The paper around the water, dehydration speed faster than the center of the paper, so that the center of the paper and the surrounding water content is uneven, resulting in the paper's pressing and lotus leaf phenomenon, if used for printing, one is to lead to overprint printing products are not allowed; Second, Finished product wrinkles, causing waste products. The specific performance is:

1 tight edge phenomenon Paper is in a dry environment, the phenomenon of dewetting occurs, that is, the center of the wet speed paper is less than the paper around, so that the paper around the tension, the formation of a tight edge phenomenon.

2 lotus leaf phenomenon, the paper is in the air and humid environment, hygroscopic phenomenon occurs, that is, the speed of moisture absorption is faster than the center of the paper, and the paper forms a lotus leaf.

2, elimination method

1 When the paper has a tight edge phenomenon, sprinkle water around the paper stack or machine to re-absorb moisture around the paper, balance the moisture content of the paper, and restore the paper to a smooth level.
Paper is dried in an environment where the relative humidity is 6 to 8% higher than in the press room.

2 When the paper appears flounces, the paper can be knocked manually by hand to knock out the creases with a width of about 1cm and a length of about 10cm, so as to increase the stiffness of the paper so as to facilitate the paper feeding;
In severe cases, it is necessary to re-hang the paper.

(3) Static factors of paper

1. Causes and hazards

During the printing process, the paper on the stack is separated and transported forward by friction between the transfer belt and the platen. Between paper and paper, paper and machine are always in friction. Friction produces charge. When the charge is gathered, the paper is charged. When the paper has the same kind of polar charge, the papers are mutually exclusive, resulting in inaccurate overprinting during printing and a misfeeding of the paper; when the paper has a heterogeneous charge, it causes empty sheets, double sheets, and multiple sheets when the paper is fed. Improper overprinting and other problems; paper surface with static electricity is also easy to absorb some paper hair and dust, resulting in prints appear flowers or spots and other defects, so the elimination of paper static electricity is very important.

2. Exclusion method

1 Eliminating static electricity eliminators used in printing machines include induction static eliminators, high-frequency high-voltage static eliminators, and high-frequency static electricity eliminators, which should be placed close to the drum during installation.

2Improve the relative humidity of the printing shop. The generation of static electricity is related to the relative humidity of the operating environment. When the relative humidity of the workshop is lower than 40%, electrostatic problems are likely to occur. Therefore, when printing, sprinkle some water around the paper stack and the machine, or use air to humidify. Adjusts the relative humidity in the printing shop to avoid static electricity.

3 Humidifying the paper When the moisture content of the paper is low, the paper is susceptible to static electricity. When the paper is charged with static electricity, it is necessary to hang the paper or place the paper stack in a relatively humid environment for a period of time. However, care must be taken to prevent the occurrence of paper ruffles.

4 Reduce the speed of the printing press When the static electricity is severe, reduce the friction between the paper and the paper, the paper and the machine by reducing the speed of the printing press, thereby reducing the generation of electrostatic charge.

Second, the printer caused by improper adjustment of paper failure

During the printing, the paper passes through the feeder and the paper feed table, passes through the front gauge and the specified position, and is finally printed by the rolling of the blanket cylinder and the impression cylinder. In these links, improper adjustment of one part of the machine will affect the operation of the paper and cause printing failures. Therefore, the following machine parts must be adjusted.

1. Nozzle, mouthpiece, platen

Due to the uneven size of the paper blowing mouth, or the improper suction position of the suction nozzle, the paper cannot be separated to form double sheets or multiple sheets; the suction of the suction nozzle is too large, resulting in double sheets or multiple sheets, and the sheets are too short to form an empty sheet. Zhang.
Remedy: Adjust the amount of air and inspiratory volume through the two air valves on the air pump until it is suitable; adjust the position of the nozzle to the right.

　 2. Paper and paper rollers

Inconsistent transfer belts result in inconsistent rotation of each transport belt, which skews the paper. When the pressure roller is placed in an improper position or the rotation is inflexible, it causes the feed to skew, or the paper cannot be stretched naturally on the transfer table. The paper arches unevenly, and after the rolling, the printed products appear wrinkled.

Remedy: Adjust the axis of the conveyor belt under the control of the feeding table so that all the feeder belts are loosely connected. Check whether the axles are worn and the pressure is uniform. Fill the oil regularly.

　 3. Lateral pull

The paper is pulled by the front gauge and gauge to the side fence to complete positioning. When the tensile force of the side gauge is too large, the paper arches under the resistance of the side gimbal baffle. After the embossing, the printed product forms an inverted arc-shaped fold.
Remedy: Adjust the side gauge to normal.

　 4. Impression roller bite row

During printing, when the impression force of the impression cylinder is inconsistent, arching occurs at the mouth of the paper. After imprinting, the printed product forms a circular fold in the mouthpiece; or the paper corner is just half bitten by the impression cylinder and causes the paper edge to be subjected to excessive force. After the printing, a fold is formed at the edge of the paper.

Remedy: Check the teeth and the toothpaste, if there is wear, need to be replaced; adjust the teeth force to make it uniform; check the bite bite paper position is appropriate.

The relationship between printing quality and paper is very large. As a printing job, we must fully understand this point, continuously accumulate experience, and take corresponding measures so as to improve the quality of printed matter and reduce the scrap rate caused by paper factors.

Source: China Automation Network