Under the influence of various factors, it is inevitable that various faults will occur in the printing process, which will affect the quality of the printed matter. Therefore, the printing operators must have the ability to distinguish the faults of the printed matter, and can adjust the corresponding printing parameters according to the faults. Today, printers will learn our common printing faults and adjustment methods with you.

Analysis and solution of the printing product breakage

The damage of the printed product mainly refers to the breakage of the paper mouth, and the reasons and adjustment methods for the damage are as follows:

1）The paper delivery teeth and the roller teeth are inaccurate.

Adjustment method: adjust the paper feeder correctly or adjust the height of the front gauge.

2）Offset machine paper part of the teeth row of each teeth adjustment is not appropriate.

Adjustment method: adjust each tooth pad of paper receiving tooth row again to make it straight and high consistent, and carefully adjust the teeth 'holding force to make it balanced.

Analysis and solution of printing fold fault

The paper appears "Lotus edge" or "tight edge" and other phenomena, so that the paper can not be printed in flat state.

1） The temperature and humidity of printing workshop are unstable, and the difference is too big.

Adjustment method: the printing workshop is treated with humidity control, which keeps the temperature and humidity constant, and the general temperature is 23 ℃ ± 3 ℃, humidity 50% ± 5%； The paper bank with the same or little difference with the printing environment temperature and humidity is established to keep the moisture content of the paper stable.

2）The cylinder pressure is inconsistent. When paper teeth are held in the paper to enter the drum, there will be air flow on the paper surface. If the paper can not be evenly rolled and pressed at the moment of rolling, it will produce folds.

Adjustment method: calibrate the cylinder pressure. Adjust the lining and pressure according to the standard package specified by the equipment, and measure and calculate it for many times to make the pressure of the drum uniform; Replace the rubber cloth in time to prevent the printing products from folding due to the aging and losing elasticity.

3) The paper teeth have different teeth or different paper teeth, which causes the overall displacement or deformation of the paper is inconsistent.

Adjustment method: check the paper teeth. The paper teeth in the paper are mainly checked in terms of the flatness, the chip integrity, the uniformity of the force, the fit gap of the tooth sleeve, the elasticity of the paper supporting spring, etc., and also the relevant screws and pin shafts are loose and broken to ensure the smooth handover of the paper.

4） The dirt on the surface of the drum is accumulated, which makes the surface of the drum uneven, and the paper is not evenly pressed, resulting in folds.

Adjustment method: clean the dirt on the roller surface and pillow in time and keep it clean.

Analysis and solution of printing spot fault

1） The paper surface is irregular, that is, the paper smoothness is low, resulting in the uneven ink on the paper surface and spots.

Adjustment method: change paper, increase printing pressure, etc.

2） Ink emulsification is serious. For the ink with good transparency, ink emulsification is too fast, which will reduce ink viscosity. When applying large printing pressure, the ink on the protruding part of the paper surface is easy to be squeezed out, and ink will be spotted when it falls on the printing plate field and other parts.

Adjustment method: reduce the amount of moistening solution, select ink with high viscosity, and adjust printing pressure properly.

Analysis and solution of the smudge on the back of the printed product

1）The pH value of the solution is too high. The pH value of the solution which is favorable for printing should be between 4.3 and 5.5. When the pH value is higher than 5.5, the drying speed of the ink will be reduced, causing the back surface to rub dirty.

Adjustment method: a certain amount of acid can be added to the solution to reduce the pH value of the solution.

2）The viscosity of ink is too low, which causes the fluidity to be too large. When printing, the ink absorption and paste of the layout will cause the layout to get dirty, and at the same time, it will affect the drying speed of the ink, and cause the back surface to rub dirty.

Adjustment method: adjust the amount of ink adjusting oil or choose ink with high viscosity.

3） The ink layer of the printing plate is too thick, or the amount of additives is not appropriate when inking, which slows down the drying speed of the ink, causing the back to rub dirty.

Adjustment method: add appropriate desiccant and anti viscosity agent to the ink to speed up drying.

4）Ink drying is not good or ink quantity is too large.

Adjustment method: add appropriate desiccant and anti glue agent in ink, or reduce ink quantity properly if it does not affect ink color of printing ink.

Analysis and solution of print through and back through faults

1. The reason and adjustment method of print through printing：

1）Ink contains too much non drying oil.

Adjustment method: should speed up the ink drying speed.

2）The ink viscosity is low.

Adjustment method: can be mixed with high viscosity ink, but before use to ensure that the ink mixed evenly.

2.The reasons and adjustment methods for the back penetration of printing products:

1）The ink layer is too thick.

Adjustment method: the ink with thin quality and high color concentration can be used instead.

2）The paper is too thin and transparent.

Adjustment method: should reduce the pressure, choose thick and low transparency paper.

The possible causes and adjustment methods of common faults in offset printing are introduced. The reasons for the failure are various, including the machine reasons, the human operation errors, which cannot be generalized or fixed. Therefore, the printing operators should try their best to master the relevant knowledge of printing technology and mechanical properties of various machines, and earnestly summarize the production practice experience, and better prevent and eliminate various printing faults, Then reduce the production of defects and improve the quality of the printed products.