Printing, pre-press, publishing and photography services – yesterday, today and tomorrow

Contents:

1. DELIVERING HIGH-QUALITY GRAPHICS REQUIRES PROPER EQUIPMENT
2. WAYS TO IMPROVE
3. CONVERTING MANAGEMENT PRINCIPLES

WAYS TO IMPROVE One of the major contributors to poor graphics is the amount of pressure being applied from either the anilox roll to the printing plate or from the impression cylinder to the board. This problem may be caused by improper mounting, interchanging plates between various items, or because the operator does not have gauges or dials on the machine to determine the proper settings. They may be missing or covered with ink making them unreadable. In many cases, the gauges are improperly calibrated. The increased pressure will normally lead to "haloing" or beading of ink on the plates on most printed work or distortion and dot gain with process printing.

In addition, some plants are still mounting printing plates in the flat, which leads to problems when mounting them on the printing cylinder. The plates will stretch when mounting in the round on the cylinder and cause the bond or sealing of the plates to break loose. This practice allows the printing plates to rise up off the mounting and can cause quality problems such as stray printing marks.

The caliper of both the plates and the mounting material is extremely important in order to attain the graphics desired. If the machine cylinders are designed for a combined height of plate and backing of .28O inches, then the plates and mounting material must come to the operators at .28O inches plus or minus .0025 inches. It is extremely important that the person buying the printing plates and mounting materials specify those requirements to his supplier. Then check with a plate micrometer to ensure they meet those specifications.

Do not send plates and mounting to the machine expecting the operator to compensate for variances greater than those specified. operators will usually compensate by applying additional pressure, leading to the problems mentioned above.

Printing plates are quite expensive and therefore require delicate handling and proper storage to ensure that the plates are not damaged or the life of the plates shortened. Never store printing plates where they are exposed to sunlight or extreme heat or near electrical motors. Sunlight and electrical motors emit ozone, which will quickly harden printing plates leading to printing and ink transfer problems as well as plate life reduction.

In order to produce good graphics, a printing environment must be free of all contaminates. In the box plant there is paper fibre dust, ink contaminates and oil mists, for example. Machines have to be maintained and kept very clean. Plants have to stop the practice of using air hoses to blow off paper dust, which accumulates rapidly in the manufacturing of a box. Use vacuum systems to keep the printing machines clean and ink filters to keep ink contaminates out of the printing process. In addition, clean the anilox rolls with the proper brushes to ensure the anilox cells are not dirty or plugged, which affects print quality.

Durometer plays an important role in the transfer of ink and can impact graphics. Therefore, durometer should be specified and checked using a Shore A durometer gauge. Plates will harden over time, and at an accelerated rate if exposed to extreme heat. The lower the durometer the more ink carrying capacity.

As the plate raises in durometer it will begin to carry less ink to the printed surface. It is important to monitor this characteristic on a regular basis to ensure that when plates or rolls get hard they are replaced accordingly.

The lack of ink viscosity controls in a plant can lead to problems with the quality of graphics. Too many plants check the ink viscosity only when they begin the job and do not check it throughout the run. Nor do they follow recommended practices when adding fresh ink, which often leads to problems with color variations. Plants producing higher quality graphics will have to start using extenders or overprint varnishes and not water in order to maintain proper pH and color control.

The process of fingerprinting printing units allows for plants to evaluate their equipment capabilities. The process requires a properly designed printing test plate, which can provide a plant with a great deal of information on its press and crew capabilities. Many plate suppliers can assist in designing and providing the test plate as well as assist the plant in conducting the fingerprinting or press audit. The length of the audit will depend on the number of color stations to be analyzed and the condition of the existing equipment. A plant should invite its equipment, substrate, ink, anilox roll, and plate suppliers to participate in conducting the audit and interpreting the findings or establishing the limits of the press.

Test plates should include solid coverage areas, half tone areas, positive and reverse type areas, grey scales, register marks, variations of line art, impression gauges, and wet trap areas for at least two colors or multicolor process work.

A fingerprint audit will establish:

• Printing or graphic limitations of each unit;
• Ink transfer capabilities;
• Ink metering capabilities;
• Machine parallelism;
• Sheet transfer capabilities and/or sheet length variation;
• Registration accuracy in the machine direction.

Before conducting the fingerprinting exercise, go over the machine to determine the conditions of levelness, parallelism, plugged or dirty anilox cells, backlash of gears or gear train, and the diameters and wear of the rolls and cylinders.

The fingerprinting process allows a plant to evaluate its capabilities against requests from sales but more importantly, allows the plant to use the test plates on an ongoing basis for monitoring the machine wear and capabilities over time.