The single biggest cost of printing is paper, followed by ink, and then by consumables such as printing plates, blankets, blanket wash, fountain solution, etc. The other important factors affecting the cost of printing are press down time due to make ready, wash ups, press maintenance and also importantly, the skill of the printers.
The paper is by far the biggest cost factor, so naturally the more paper is converted to sellable copies (newspapers), the lower the cost of printing. Paper waste reduction is influenced by all the factors listed above as follows.
Quality of the Paper Used
Good quality paper will reduce the number of web breaks; reduce piling, linting, plate wear. Therefore, buying cheaper, lower quality paper can be a false economy, because what the printer saves on the cost of the paper can be greatly offset by increase in paper waste due to more web breaks, more wash up cycles, and longer make ready times.
Some papers can contain additives in them, such as minerals, which can cause plate wear due to the abrasive nature of the minerals used, as well as fountain solution contamination, due to the chemical additives present in the paper dissolving in the fountain solution.
Ink is also a very significant contributor to the cost of printing as well as to the print quality. Again, cheaper ink does not always result in cost savings, but can actually increase the cost of printing. The properties of the inks, which will have a direct influence on the cost of printing and on the quality of the print include :-
(1) Pigment Strength
Many cheaper inks will have a lower pigment strength, which will result in more ink usage and can also cause ink balance problems, trapping problems and, poor ink-water balance. This will result in piling, ink feedbackm emulsification and dot gain.
(2) Binder in the Ink
Poor or insufficient binder (resin system) will influence rub resistance, strike through, and can have a negative effect on ink-water balance.
(3) Tack of the Ink
This determines the trapping properties of the process set, ink transfer from roller to the blanket and to the stock. Poor transfer properties will result in longer make ready, a need for continuous adjustment of the press settings during the run, ink build up on the rollers, and on the blankets, more wash ups, and more press down time. Excessively high tack inks can also cause web breaks.
Good quality plates which are properly exposed and developed will have a longer production life. It will also contribute positively to the print, quality giving a high quality reproduction of the text and the images printed, and less plate wear.
Needless to say, the actual quality and suitability of the printing plate for the printing process and for the press they are used on is very important. And is cutting the plates square, and are correctly under pack. This will result in better print quality, longer plate life, and reduced plate cracking.
A good blanket will increase productivity, give better print quality, and reduce paper waste and press down time. Conversely a poor quality or unsuitable blanket for the job will increase the cost by increasing paper waste, increased press down time, and poorer print quality.
Here are seven properties that directly affect how well a blanket will run on an offset printing press :-
(1) Tensile Strength
Blankets should only be tightened around the cylinder with enough force to prevent movement on the run, nothing more. This is because the tensile strength, or the ability of the woven fabric to withstand the pull around the cylinder, is only so strong. The basic idea is to have the blanket stretch as little as possible because the blanket can rip. And also the blanket height is lost as more torque is applied to the mounted blanket.
(2) Solvent Resistance
Each press room has its own arsenal of chemicals. An important property of a blanket is that it must resist the tendency to swell, crack or distort when coming in contact with these chemicals. They can creep easily into the sides of the blanket and cause distortion to the image. Additionally, some inks or fountain solutions can actually affect the face of the blanket, and cause it to swell. Selecting the right wash up solvents and the right fountain solution will avoid these problems.
Every time a shipment arrives into the press room, you must check the calliper of the blanket. Have a proper spring loaded blanket gauge for doing this. Check all four corners of the blanket, and accept no more than plus or minus one thousandth of an inch. Any more is unacceptable, as it will affect dot gain, and possibly even cause tension or web breaks.
(4) Surface Release
Typically, the smoother a blanket is, the better the image it will reproduce on the paper. The problem is that smoother blankets will not release the ink as easily as one with a rough surface.
There must be a balance. If you observe that you get too many wraps on the start-up, or you notice that the paper rides up the blanket before releasing to the next printing unit, you could have more than a tension problem. Additionally, the problem could also be a chemical one as the ink may physically bond more readily to the rubber surface. Work with your manufacturer in getting the right product.
Most offset printing presses uses compressible blankets as they give more flexibility and produce sharper images. A compressible layer is built into the blanket which literally acts like a sponge, allowing up to 7% compressibility. This property though, is slowly lost during the life of the blanket. Most printers nowadays get from 10 to 15 million impressions from these blankets until they must be replaced.
There is usually at least one layer inside the blanket that consists of a sewn fabric. It is this fabric’s strength that holds the blanket together. It is sewn in such a way that the most strength is given to the circumferential property. When tightening the blanket, a certain amount of stretch will occur as these threads pull on one another. However overdoing it will cause your blanket height to go down, and possibly rip the blanket.
Nobody is perfect. Even blanket manufacturers will sometimes send blankets that are not completely square. Or possibly, they were not square to how the fabric was sewn. If the blanket is crooked in this respect, this will cause major tension and slur problems. There should be a quality check before mounting a blanket. A good rule of thumb is this: If it’s not fitting on the cylinder properly, there is likely a good reason for it. Check!
There are of course more properties of a blanket that the makers will take into account, but these seven characteristics are the ones that will matter the most in the press room.