Thursday, June 11, 2009

Printing Ink Problems – FULL BRIEFS

Sometime you have to meet some of printing ink problems in your printing business works. You should know about printing problems related with inks to solve your problems and continuing your printing jobs smoothly.

The transfer of ink from one sheet to the next sheet is known as setoff and is usually caused by too much ink being applied to the substrate and/or ink that is slow drying. The ink can be transferred from the front of one sheet to the back of the next and vice versa.

Slow Drying
One of the most common printing related problems is ink that dries too slowly. When ink dries slowly it may smudge and smear on the printed surface. The ink may also transfer from the front of one sheet to the back of the next one (setoff) and vice versa. Setoff is usually the result of too much ink being applied to the printing paper because of improper press settings. Both high humidity in the production area and high moisture content in the printing paper affect the ability of the ink to dry properly.

Poor Binding and Rub
This condition is sometimes confused with slow drying. With poor binding and rub, the ink is actually dry but the pigment can be easily rubbed off the surface. This can be caused by ink that does not have adequate bonding properties for the type of printing paper on which it is being printed. An excessive amount of the vehicle soaks into the paper leaving all of the pigment on the surface with nothing to hold it there. It is possible to salvage a print application with this problem by applying a coat of varnish to seal the pigment.

Ink Adhesion
Ink adhesion is actually the result of setoff and slow drying ink, which in turn are usually the result of poorly adjusted press settings. The quantity of ink applied to the sheet or web can be so excessive that the ink acts as an adhesive, causing the sheets stick together. A printed document with any of the printing from the front showing up on the back and/or the printing from the back showing up on the front, is a definite sign that the press settings were not adjusted correctly for the type of printing surface, the type of ink used, or the coverage area.

Mottling is a condition referring to an uneven appearance in the solid portions of a printed document, which can be caused by uneven absorption of ink, nonabsorbent printing papers, the wrong ink for the particular printing paper used, or faulty press adjustments.

Fill-in can cause a muddy look in printed screens and halftones and a speckled appearance in highlight areas. Areas of detail may disappear entirely. The causes of fill-in are contamination of the ink with paper fibers, lint, dirt and dust; substandard ink; the wrong choice of ink for the job; and/or improper press settings.

Misting occurs when an ink with too much length is used on high-speed presses. Poorly adjusted ink rollers also contributes to the problem. The ink actually turns into a fine mist and if the problem is significant, the mist may create a fog in the press area. The mist makes contact with everything in the area, including the surface of the printed application. Misting can give the finished product a speckled and dirty appearance and create health hazards for press operators.

If a printed document has blotchy areas that are outlined by a non-printed line, it can be the result of piling. Piling is usually caused by faulty paper or ink. The printing paper may contain excessive paper dust or a poor coating. The coating may be partially removed as it passes through the press, adhering to the printing blanket and plate, causing the blotchy appearance. The vehicle in the ink may not carry the pigment properly, which allows the pigment to pile on the plate and blanket of the press.

Color Matching
Occasionally, a color that is printed does not match the color that was intended. As with many printing related problems, improper press settings can be the cause, but other variables may also contribute to the problem. The color and texture of the paper changes the printed colors, so the choice of printing paper must considered early in the planning stage of the project. Some of the ink colors can change slightly as they age, which may cause large color shifts, especially when older inks are mixed together to produce other colors. Lighting conditions influence the appearance of color, which is why it is very important for the customer and printer to have a good proof to work from.

Trapping refers to the alignment of colors on a printed document, such as a document printed with four-color process printing. Trapping may be required to correct the registration of colors on a print project. Successful trapping depends a great deal on the tack of the ink. The first color printed on the sheet should have a higher tack than the second color printed, and so on. This will greatly improve the trapping abilities.

Show Through
Show through is a term used to describe when the printed area of a document shows through to the other side of the sheet. Show through is especially annoying when there is printing on both sides of the document. This is usually caused by the use of printing paper that is too thin or transparent or ink that is applied too heavily on the printing surface.


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