If offset ink is not drying, first distinguish slow drying, set-off and weak rub resistance. Check the substrate, ink film and dampening conditions. Change one variable at a time and compare samples.
Determine whether the problem is with fixation, drying or resistance
In conventional sheetfed offset, fixation on an absorbent substrate involves the penetration of liquid ink components into the paper. The layer becomes less mobile, but does not have to reach its final resistance yet. Oxidative drying, on the other hand, involves the reaction of the binder with oxygen. Pre-setting does not mean complete drying. These processes may occur simultaneously.
Record when the problem occurred: laying out, turning, cutting or transporting. Check whether the ink smears, transfers to an adjacent sheet, or wipes off dry. A similar trace does not always mean the same cause.
Check the substrate and the compatibility of the ink with its surface
Compare the current order with the last valid print run. Have you changed the paper, its batch, coating or printing side? The grammage itself does not describe the surface behavior. Paper with low absorbency may prolong the initial curing of the ink.
In the case of plastics and other non-absorbent substrates, check the intended use of a specific series of inks. Don’t assume that a product used on paper will also work on foil.
Greater absorbency does not always solve the problem either. When the substrate absorbs the binder too intensely, the pigment may remain poorly bonded on the surface. The print then becomes dry – this is a possible symptom of chalking, and not just a waiting time that is too short.
Check the ink film and the ink-water balance
Check if the problem occurs on the entire sheet or mainly on the sheets. Compare your color measurement results to your production target. Don’t increase the ink feed just because the print visually appears too weak.
If you need an excessive coat to achieve the color, discuss the color strength of the ink with your supplier. A more highly pigmented series can achieve the required color with a smaller layer thickness. When selecting black offset ink also take into account the required intensity, abrasion resistance and further processing.
Excessive application of fountain solution may hinder fixation. Measure pH and conductivity, check the dosage of the concentrate and compare the results with the manufacturer’s recommendations. Work with the smallest amount of solution that still produces stable printing and clean non-printing areas. Do not adopt one parameter range for all concentrates.
If you suspect a problem with the ink system, also check the condition of the rollers. The selection of cleaning agents is described in the guide printing chemicals and roller care.
Take into account temperature, humidity and method of laying the layer
Record the conditions in the hall and where the prints are stored. Compare them to the conditions of successful production. Don’t judge drying solely by the number of hours after printing. Drying is influenced by temperature, humidity, layer thickness and the amount and properties of the solution emulsified in the ink. Check the recommendations for the ink series and substrate used.
For high coverage, check the stack height and the operation of the powdering device. Select the powder for the base and further processing. The powder limits contact between the sheets, but does not replace the drying of the ink.
Recognize the symptom before trying again
The table below helps you choose the direction of control. It does not replace the evaluation of samples and order parameters.
| Symptom | What to check | When to enable provider |
|---|---|---|
| The ink is reflected on adjacent sheets. | Ink layer, dampening, stack height and powder. | When process correction does not reduce bounce. |
| The dry print wipes off like powder. | Possible chalking and absorbency of the substrate. | Before changing the binder or adding auxiliaries. |
| The sheets stick together in a stack. | Burping, pressure and excessive heating of the stack. | When the problem returns with correct settings. |
| The problem occurs after changing the paper. | Absorption, coating and compatibility of the substrate with the ink series. | When you need to compare ink on both substrates. |
Check the additives before you reach for the dryer
Before adding the dryer, check the ink’s technical data sheet and the recommendations of its supplier. Write down all the additions that have already gone into the ink duct. Drying agents, antioxidants and anti-skinning agents alter the original drying properties. Adjust the dose only to the specific ink, additive and confirmed cause of the problem.
Record the name of the additive, its quantity and the mass of the ink into which you introduced it. Please provide this information to your supplier before your next correction. Do not add another preparation just because the previous attempt did not bring improvement.
Change ink based on sample and job requirements
A change makes sense when the current series does not suit the substrate or further processing requirements. It does not necessarily help if the cause is excessive dampening or improper production conditions.
Arrange a comparative test with the supplier. Keep the conditions the same and change one factor at a time. Compare readiness for planned processing, color quality, consumption and amount of waste paper. Only then should you assess the justification for changing the series and the cost of the accepted print run.
Before cutting, turning or laminating, inspect samples according to the procedure agreed for the given process. The lack of a touch mark alone does not constitute a full assessment of the readiness of the item.
Prepare ink, substrate and process data for diagnosis. Enter the batch number, machine model, symptom and time since printing. Include a list of additives and processing requirements. See ours process inks for sheet-fed offset printing to a specific substrate and order.