Common ink failures and solutions

Flying ink

Flying ink is an ink failure that often occurs in newspaper printing. The so-called “flying ink” means that very fine ink particles are drawn into filaments at the working ink roller, and two or more breaks occur. In addition to partially retracting the ink roller, the remaining parts are formed due to the large surface tension. Drops are thrown by high-speed printing presses and diffuse into the air.

1. Cause

There are many reasons for the formation of ink droplets. Incorrect ink transfer roller adjustment, poor quality of the roller surface, rapid printing speed, characteristics of the ink itself, and uncomfortable temperature and humidity in the workshop and environmental conditions can cause ink flying. The following specifically introduces the solution of flying ink.

2. Solution

1) Adjust the ink transfer roller

Operators to adjust the ink roller (flat roller) method is not uniform, such as, some with kraft lamination, some with the ink roller stamping width of the plastic pull law, resulting in the pressure between the roller is not standardized. Too tight adjustment between the ink roller, easy to damage the roller; over-tuned, it will lead to flying ink.

The ink transfer system of a typical printer includes an ink core roller, an anilox roller, two ink transfer rollers, two ink rollers, and two printing rollers. A more specific ink roller adjustment procedure should be:

In the first step, the thickness of the initial ink layer on the ink fountain roller is adjusted uniformly. For machines using a fine anilox roller, the thickness of the ink layer is preferably set to 0.12 to 0.18 mm. With a coarse anilox roller, the initial ink layer thickness is preferably 0.23 to 0.30 mm. The second step is to adjust the anilox roller and ink. The gap of the core roller keeps it balanced. Machines using fine anilox rollers are suitable for gaps of 0.09 to 0.1 mm. For rough textured models, gaps of 0.15 to 0.18 mm are appropriate. The third step is to use an anilox roller and the first transfer roller. The embossing is adjusted to 8mm. In the fourth step, the embossing width between the two transfer rollers and the two interlinking rollers, the second interlinking roller and the inside and outside printing roller is maintained at 6 to 7mm.

In the process of adjusting the ink roller, it is best to adjust the ink roller spacing with yellow ink; the ink of the ink roller must be uniform when adjusting, the smaller the ink volume, the smaller the adjustment error; and the spacing between the rubber rollers should be checked regularly. The spacing is not The specification should be adjusted in time, and the deformed rubber roller should be replaced in time to prevent flying ink.

The adjustment and detection of the rubber roller in the usual production can not only prolong the service life of the rubber roller, but also effectively prevent the occurrence of flying ink.

2) Adjust ink and ink

News ink is mainly composed of non-polar mineral oil. It has low electricity, high solid content, and is not easy to disperse. If the design is unreasonable, it often appears that the silk head is too long and causes flying ink. The ink itself is a pseudo-plastic fluid with poor dispersion (uniform distribution of the pigment in the binder), causing irregular breakage of the ink and the generation of flying ink. The viscoelasticity of the ink is good, the ink is short, and the ink is light, whereas the ink is more heavy.
The solution is to add a thick binder to the ink to increase the viscosity of the ink and increase its cohesion to increase the dielectric constant. Try to use good wettability pigments and mineral oil to make ink, or add anti-rheological additives (such as bentonite, wax, etc.), black ink should be properly increased carbon black content, increase color intensity, but also pay attention to reduce the amount of ink .

In addition to control the temperature and humidity of the workshop, ventilation should not be too strong. The temperature of the printing shop is 20～25°C and the humidity is 50%～60%. If the temperature is too high, the ink's fluidity will increase, the viscosity will decrease, and the flying ink phenomenon will obviously increase.

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Ink emulsification

In the offset printing process, the emulsification of the ink is an inevitable phenomenon, and offset printing relies on moderate ink emulsification to achieve ink transfer. However, if the ink is over-emulsified, a thick layer of meshed, burr-like floc-like ink can accumulate on the surface of the roller when it is stopped.

Over-emulsification of ink (sometimes the surface of the ink core roller is not inked, and some of the water is collected at the contact of the ink groove and the ink core roller) will cause the newspaper image to have a light color, a dull appearance, and a serious distortion of the dot. The drying speed of the ink is slow, and the back of the print is seriously dirty.

Factors that lead to severe emulsification of the ink are the characteristics of the ink, the properties of the printing paper, the concentration of the fountain solution, the temperature and humidity of the workshop, and the printing speed.

1. Ink characteristics

Inverse relationship between ink viscosity and emulsification, flowability and emulsification are proportional to each other. The ink has high viscosity, strong water resistance, and low emulsification value. On the contrary, the ink has small viscosity, strong fluidity, reduced cohesion between molecules, and is easy to emulsify. The acid value of the ink should not be too large. The free fatty acid in the ink is a typical surfactant. The higher the content, the stronger the polarity of the ink and the more serious the emulsification. At the same time, the high ink acid value requires a thicker fountain solution. Will exacerbate ink emulsification. In addition, the amount of auxiliary materials having emulsification factors such as resins, diluting agents, and driers are controlled in ink manufacturing.

2. Paper properties

The surface of the newsprint contains certain surface active substances and fillers. During the printing process, due to dampening of the fountain solution and peeling of the blanket, these substances are transferred to the ink roller through the printing plate, and then transferred back to the ink fountain by the ink roller. Mixing with the ink reduces the viscosity of the ink and destroys the ink's water resistance, resulting in increased emulsification of the ink. Therefore, it is necessary to select newsprint with tight paper, good water resistance, less powder on the surface, and less hair loss.

3. Fountain solution concentration

Common dampening fluids include common fountain solutions, non-ionic surfactant fountain solutions, and alcohol fountain solutions. Alcohol fountain solution is an electrolyte-free solution, alcohol volatilizes quickly, greatly reducing the emulsification value of the ink. The ordinary fountain solution in the use of the process must control the concentration, the conductivity of the dampening solution in the tank should be controlled between 900 ~ 1400μs, the pH value is controlled between 4.8 ~ 5.5, if the fountain solution concentration is too high Will increase ink emulsification.

4. Workshop temperature and humidity and printing speed

The temperature and humidity of the workshop and the printing speed can also cause ink emulsification. The higher the workshop temperature, the greater the ink flowability, the smaller the viscosity, the weakened water resistance, combined with the high printing speed, the increase of the peeling force, the increase of the surface temperature of the ink roller, and the extreme emulsification of the ink. In addition, when the humidity in the workshop is high, especially in the rainy season in the south, the phenomenon of “cold sweat” often occurs on the surface of the machine. The dripping of condensed water along the surface of the machine into the fountain will inevitably result in ink emulsification. Therefore, the temperature and humidity of the workshop and the printing speed must be controlled during the production process.

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Pulling paper

During the printing process, the graphic part of the newspaper, especially the high density dark tone area, often appears that some of the paper fibers are pulled up.

Paper-drawing phenomenon and printing paper when the powder off, hair loss phenomenon in the formation of the reasons for the mechanism and solution are fundamentally different. The paper's powder and hair loss are the fibers or filler particles that fall off from the surface of the paper during printing. They are piled up on the blanket's graphic and cause the printed image and headline to appear "snowflake" under the magnifying glass. "Snow" is flat and there is no obvious phenomenon that the fiber is pulled up. The result of pulling the paper is that the fibers on the surface of the paper are pulled up. Its formation is mainly related to the viscosity of the ink and the tightness of the paper.

1. The viscosity of the ink

The viscosity of ink refers to the force that prevents the thin layer of ink from separating when the ink film is separated. The viscosity of the ink is very important to ensure the smoothness of the printing process and the stability of the printing quality. The ink is transferred from the ink roller to the other ink roller on the printing machine, from the ink roller to the printing plate, from the printing plate to the blanket, from the blanket to the paper, and the ink layer needs to peel once during each transfer to strip the ink. The force required for the layer is related to the viscosity of the ink. The greater the viscosity of the ink, the greater the force required to peel the ink layer. Due to the inhomogeneity of the ink transfer, if the ink is too viscous, the surface of the paper is easily peeled off by the ink film at the time of printing, that is, the paper is pulled. Ink mills are generally adjusted by the addition of a diluting solvent or mineral oil; printing plants can be adjusted by adding a suitable amount of viscosifier or No. 6 varnish. In addition, gelation of the ink occurs during the printing process will appear to pull the hair, the ink must be re-dispersed processing can be resolved.

2. The tightness of the paper

Pulling paper is also related to the tightness of the paper itself. In the production of paper, the tightness of the paper and ink absorption are a contradiction. If the tightness of the paper is too large, the ink absorbency will be reduced; if the paper has a loose texture, paper pull-out may occur easily.

In addition, in the printing process, if the temperature of the shop is too low, the viscosity of the ink becomes large, which may cause the paper pulling phenomenon to increase at the time of printing.

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Sticky

In the printing process, due to the slow drying of the ink, the ink is too soft, too thin, or the amount of ink to be given is too large, which can cause dirty or dirty images on newspapers. Most of this phenomenon occurs in the field or shaded part where the amount of printed ink is large.

1. Causes 1) The image is darker in the field and darker. Newspaper printing is not like commercial rotary printing. Although the printing speed is very fast, it does not include a drying device. The ink has just been printed in the field and the dark part of the newspaper. Impervious to dry, through the flap part of the bite and the transmission belt, easy to contact with the blank part, resulting in sticky.
2) Ink Emulsification Caused by Water and Large Ink In the printing process, large ink and large ink results in ink emulsification, which slows down the drying of the ink and causes the newspaper to become dirty.
3) Slow fixation of the ink If the fixing speed of the ink is slow, the penetrative dryness and coagulability of the ink are poor, and the newspaper can easily become dirty.
4) Surface properties of the paper The surface of the paper is smooth, dense, and poor in ink absorption. After printing, the ink floats on the paper, which cannot be penetrated and dried in a short time, and can also cause stickiness.
2. Solution

In the printing process, if the above problems occur, it is generally necessary to solve from the following aspects.
1) Viscous dirt caused by the machine structure can usually be solved by reducing the force of the carious teeth in the transmission system.

2) Adjust the machine's water transfer mechanism and ink transfer mechanism to ensure that the printing water has good quality, smooth water transfer, uniform ink supply, and moderate ink volume. In the printing process to control the ink balance, reduce the possibility of ink emulsification.

3) Adjust the internal structure of the ink, improve the cohesion of the ink, control the viscosity, use the ink with fast fixing speed and small residual viscosity, and at the same time improve the ink's penetration, drying and fixing properties.