How to successfully apply alcohol-free printing in production? (two)

Mechanical adjustment

In particular, when printing with alcohol-free fountain solutions, the requirements for various types of parameter tolerances are more stringent, and any problems that may arise from the use of IPA may appear. Therefore, if you want to use alcohol-free printing, it is recommended to reduce the amount of alcohol consumption by about 8% first. If this adjustment will cause problems, then once you switch to alcohol-free printing, the problem is likely to be fully exposed.

(1) The key to the success of alcohol-free printing is the relationship between the hardness of the test roller and the nip line.

The main consideration should be the measuring roll, which requires a slightly lower hardness than when using alcohol dampening. The measuring roll usually has a hardness of 25 to 30 and sometimes hardens after printing. When using an alcohol substitute, the hardness of the measuring roller is reduced to 18-22. Because softer rolls tend to accept more water more easily, their softness increases the width of the nip between the measuring roll and the chrome alloy roll without increasing the pressure, which makes it easier for the print operator to adjust the width.

(2) Reduce the width of the nip between the chrome alloy roller and the wetting roller by adjusting

When using alcohol dampening, the nip width of the nip is usually 5/16 to 3/8 inch (8 to 10 mm) depending on the diameter of the roller. By increasing the width of the nip between the chrome roll and the plate cylinder, a thin film of water can be created and cause slippage between them, and the width of the nip may be reduced to 1 when using an alcohol substitute. 8 to 3/16 inches (3 to 5 mm). If there is not enough slip, the plate cylinder will drive the chrome roll.

In a typical alcohol wetting system, the metering roller and chrome roller are driven by the wetting system and the plate cylinder is driven by the printing press. If the plate cylinder starts to drive the chrome roll, the speed of the roll increases and the control of the wetting system suffers. If wetting abnormality occurs in the ink roller, the amount of ink at the ink roller end increases, which may cause splashing or spraying. Excessively high ink roller speeds can also place excessive pressure on the wetting device, possibly resulting in circuit disconnection and motor damage. Ideally, when using an alcohol-free fountain solution, the wetting system should be able to operate at the same speed (or slightly greater speed).

(3) Adjustment of measuring roller speed

Measurements of alcohol-free fountain solutions often need to be performed on damper rollers with higher rotational speeds (which can cause slip and tolerance control to be inadequate at high speeds).

(4) Consider water roller skew or bulge

Water roll bulge often occurs in some printing equipment where the measurement roll center diameter is larger than the edge diameter.

Some alcohol-free fountain solutions work well on skewed measuring rollers, while other machines require measuring rollers similar to chrome alloy rollers to reduce the pressure in the center of the drum.

When the plate is running to the middle of the wet or dry edge, the measuring roller must be skewed. If the plate does not receive enough water in the middle, a measuring roll similar to the chrome alloy roll should be used. The optimum skew angle should be determined experimentally because it may vary depending on the alcohol substitute used.

The formation of a curved foam line at the edge of the printing plate is a good expression of ink and water balance. After the printer stabilizes, shut down the foam line. The ideal ink balance produces a very shallow, uniform foam line in the width of the plate. If the plate is too dry, the width of the foam line increases; if too wet, the foam line disappears.

Maintain proper concentration

Over time, most alcohol substitutes will slowly evaporate from the wetting system, which, to a certain degree, may increase the concentration of substitutes and cause problems such as ink balance, ink layer and even coating adhesion. . Since there is no simple way to determine the concentration of substitutes, the system should be updated at least once a week.

The key to successful implementation of alcohol-free printing

(1) Give the fountain solution manufacturer a sample of the fountain solution for analysis to properly select the fountain solution and alcohol substitute according to the characteristics of the wetting system and the fountain solution used.

(2) Discuss with the fountain solution, ink and other suppliers and determine the problems of printing production, including the printing pressure pattern, wetting system, inking system, cylinder cleaning, blanket cleaning and paper type, etc., to ensure that they are completely compatible.

(3) Check the dampening roller pressure setting and hardness tester readings, including the ink roller and dampening roller, to ensure that the pressure between the plate cylinder and the blanket cylinder is properly set.

(4) Follow the manufacturer's comprehensive instructions. If it is stated that the recommended mixing of 3 to 8 ounces/gallon of water requires starting with the lowest 3 ounces, pH, conductivity readings, and recorded information serve as a starting point for reference.

(5) Run this mixed wetting system and supervise its printability and operating conditions, including how to roll up the plate, how to start the printing after the roller of the feeder unit is disengaged, and without excessive dampening fluid supply, Whether the printing plate can be cleaned automatically, feedback the relevant information to the fountain solution manufacturer.

(6) Regularly check the fountain solution. Paper coating, ink overflow, blankets, and roller cleaners may contaminate the fountain solution. Temperature, pH and conductivity readings are recorded every 3 hours during the printing process. From these print logs, find the solution mix that maintains the best working conditions.

(7) Observe changes in pH and conductivity during the printing process. When they reach a certain point, printing problems begin to appear, such as stencils and dirt. At this time, the fountain solution may be contaminated. At this time, these problems should be recorded in the print log.

(8) Drain and clean the wetting system once a week.

(9) Regularly have professional technicians with qualified technology inspect the water circulation system with the wetting system.