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The printability and failure analysis of UV offset printing ink

Time: 2018-03-21

The printability and failure analysis of UV offset printing ink

 

From the advantages and disadvantages of UV offset printing ink, Jiaxing Holywill’s technical engineers claim this version, blanket, roller, cleaning liquid, ink additives and environmental printability of the UV offset ink, analysis bad adhesive, ink emulsification, serious drop ink, ink blot rabbit curing and drying is not complete and wrong color arrangement inappropriate printing.

1.Printing failure in UV offset printing ink

The UV offset ink printability has a large gap compared with traditional ink. UV resin   selection and collocation is not appropriate, unreasonable additive, wrong storage environment is not suitable, improper operation in the printing process. and other reasons, there are often not enough ink adhesion, ink, ink droplets, Molamo serious emulsification curing and drying is not complete, the color sequence arrangement inappropriate, the following are some analysis and Discussion on these issues, to find out a set of process control parameters for UV offset.

1.1   Ink adhesion is not enough

Because of the poor permeability of film, synthetic paper, metal and plastic sheet, the adsorption capacity of ink is weak. Even after UV curing, the adhesion of ink is poor, and the printing quality is not high. In order to improve the adhesion of the ink: at the substrate, we usually do the surface corona treatment on the material. We need to keep the UV offset printing ink in the substrate with good bearing surface energy requirements in 40dyne or above must be inspected before printing on the surface energy of the substrate, when using corona out, to understand the corona treatment time, corona treatment after a week will automatically degenerate, we'll have to do it again if necessary corona treatment, otherwise it will affect the drying and curing ink adhesion fastness. Standing on the ink level, we need to select suitable ink for printing substrates, such as synthetic paper, and the UVP30 of Jiaxing Holywilll has good adhesion to the ink produced by the main resin. For example, plastic films and sheets, we need to match with Holywill’s UVP30 ink resin to improve the crosslinking density of the ink layer to improve the adhesion.

 

1.2   Serious emulsification of Ink

Aluminum foil cardboard printing with UV offset printing ink, when start printing, there is a little scared around printing dot, text is not clear, which is mainly caused by ink imbalance. Compared with UV ink and oily ink, the fountain supply slower in UV offset ink, and printing ink layer is thinner, caused the serious emulsification, emulsion ink will be stacked on the rollers and the residue in the layout and blanket, caused the graphic is not clear. The concentration of the fountain solution and the temperature of the environment will also have a great influence on the emulsification of the ink. Reduce printing speed, control printing speed in 5000-8000 printing / hourly, and reconfigure the fountain solution, control IPA concentration at 11-13%, conductive rate is 1800-1900uS/cm, pH value is 5.6-6, temperature is 5-10℃, it can control UV offset printing ink emulsification better.

 

1.3   Ink Misting and Tearing phenomenon

UV offset printing ink viscosity is large and flow is slow. But at room temperature is high or low humidity conditions, after a long time printing speed, ink viscosity will be substantially smaller, flow is enhancing, easy to produce scattered drops of ink, ink misting phenomenon appeared. When the ink emulsification is too severe, water in UV offset printing ink will affect the rate of ultraviolet radiation, thereby reducing conjunctiva strength, although sometimes the ink curing, curing ink film has water and a friction or adhesive tape sticky, you will find the ink layer is pulled off, tearing phenomenon appeared.

1.4   Ink curing and drying is not completely

In UV offset printing, sometimes in order to improve UV printing color saturation, printing pressure is bigger, ink thickness is thicker, dot gain is serious, it will exacerbate the difficulty of ink curing. In order to ensure the color reduction, it can only maintain a large printing pressure. At this time, still need to moderately reduce the speed of printing, printing ink drying and curing speed of UV matching; slow, UV irradiation time is relatively long, so that the ink completely cured, found that the actual use of printing speed control 6000~7000 /, the curing effect is good. Adjusting the distance between UV tube and substrate, increasing the intensity of UV light, can also accelerate the ink curing. In addition, we should consider the influence of ink emulsification on ink curing.

 

1.5   Color ordering is not appropriate

Usually UV offset ink is in printing, the ink layer on the substrate is thinner, when need to compare thick ink layer, it is difficult to achieve the desired reproduction effect. When the four-color overprint, using conventional printing color sequence of black, green, yellow, red, when black ink printing accounted for most of the area, green, red, yellow with ink is very low, the total amount of ink is not enough, resulting in color saturation. Considering the ink trapping rate, usually the first printing ink quantity smaller color ink, finally a large amount of black, so you can let the inking reach the highest, more full of color. Special attention should be paid to the printing concentration of black ink, sometimes in order to improve the printing solid sense and excessive increase of black ink, UV general easily through the magenta ink and the yellow ink, but it is difficult to through the cyan ink and black ink, resulting four-color ink whole curing is not good, not good adhesion, even cause rubbed against dirty.

 

  1. UV offset in printability

2.1 Pate requirements

UV printing ink printing is best to use special PS Version (e.g. Konica SUP plate) can be used directly; if you are using a general positive version of PS requires baking treatment. Because UV offset printing ink contains active monomer diluents and photoinitiator, they can decompose the dots on the common offset PS plate, and make the printing plate resistance rate decrease obviously. Therefore, UV offset printing is the best choice for the UV offset printing PS version.

 

2.2 rubber roll and rubber cloth requirements

UV offset must choose special UV glue stick (oily ink and /UV ink rollers) and UV special blanket. Because the activity of monomers in the printing UV in offset ink, will penetrate to the common offset rubber roller and blanket, especially the new rubber roller and blanket, on stage, because of a large number of absorption of this active monomer diluents, the ink in the active monomer diluents significantly decreased; in UV light curing that will cause the ink film does not completely cured, causing the printing is not resistant to friction; in addition, the activity of monomers will lead to ordinary rubber roller and blanket to swell, the printing is not normal.

 

2.3 Wetting requirements

The general use of UV offset fountain solution of alcohol or isopropyl alcohol fountain solution, concentration from 10% to 12% is appropriate, the alcohol evaporates quickly, can effectively transfer printing operation and roller frictional heat and keep the ink stability. The pH value of the moistening plate has a great influence on the printing quality of UV. The pH value of the moisturizing solution should be controlled in 5.6-6, and the pH value can be increased as much as possible under the premise that the plate is not dirty. The pH value is too small and the acid is too strong, which makes the ink and ink of the layout lose balance. The performance of the non graphic part of the water repellent oil is weakened, and the layout is dirty. This is mainly because the pH value is too small, easy to be emulsified ink, ink roller easy deinking phenomenon, so that the printing ink of grey and dull, so the control of fountain solution pH stability has an important influence on the quality of offset printing UV.2.4 cleaning fluid and auxiliary material requirements.

2.4 Requirements for cleaning fluid and auxiliary materials

Cleaning UV offset ink requires special cleaning liquid. Because solvent in ordinary solvent ink cleaning agent will damage UV offset rubber blanket, it will damage the photosensitive layer on the special UV offset printing plate, and also cannot clean the common PS version with UV special cleaning liquid. When the UV offset ink is used, a special auxiliary material is used to match the UV ink.

2.5 Environmental temperature and humidity requirements

When UV is printing, the ambient temperature and humidity of the workshop must be controlled. The temperature is about 18 -25 C, the relative humidity is about 50%-65%, the temperature in summer is 20-22, and the winter temperature is the best at 22-25. Temperature has an important influence on the surface tension of the fountain solution. Inappropriate temperature will seriously affect the ink balance of UV offset printing ink. In addition, if the environmental humidity is high, the curing reaction of UV ink is slow, and the binding ability of ink and substrate will be reduced. Therefore, when UV is printed, the ambient temperature and humidity of the workshop must be well controlled.

2.6 Preservation and requirements for use

UV offset printing ink to avoid direct sunlight or high temperature, the UV ink storage time is not long; the indoor validity is 6 months. This is mainly because the UV ink system memory in dark reaction, easily causing gel deterioration. The effective wavelength range of UV offset printing ink curing is 200-400nm, and the wavelength of some light sources in printing workshop is also in this range, which will cause the ink surface to slightly solidify. So we should