Physical Testing of Paper

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Packing and Cylinder Pressure

PRESSMAN TIPS  Packing and cylinder pressure seem to be the number one culprit in printing related problems. It is absolutely necessary for the press operator to check and maintain proper printing pressure between plate, blanket, and impression cylinders. Press manufacturers should be able to supply this valuable infor mation. Most of the time the packing information is located on a plate on the press or in the operating manual. How much pressure is too much? Most operators feel that is .004" squeeze is good, then .008" must be better, and if that doesn't work then an extra .002" - .004" will certainly help. This will without a doubt effect quality and production. Most presses should operate with .004" - .006" squeeze between cylinders. Any more than this can cause problems like dot gain, emulsification, bearing shock marks (streaks), poor register and fit to name a few. It would take several paragraphs to explain how each one of these problems ...
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Pre-Press-Color halftone & Screen angles

In reproducing colour pictures that were originally continuous tone, printing requires us to overlay the CMYK images as halftones. If the halftones are AM (amplitude modulated), they will be formed from regular patterns of fixed frequency. The need to rotate the angles of the halftone patterns comes from the fact that printing cannot precisely plac e down one halftone dot on top of a previously printed other-coloured dot. Commercial-quality colour printing typically has 60 dots per cm in both the horizontal and vertical direction. Slight inaccuracy in placing four identical patterns on top of each other will result in an unpleasant moiré or screen clash. By rotating the screen patterns at 30° from each other it is possible to reduce the frequency of the moiré to a level which is below the visual threshold – it becomes too small to be obtrusive. That reduced moiré is the pattern which is commonly called the printing rosette. As the halftone patterns are crossed lines at 90°, we only hav...
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Ink Mileage

Ink mileage is usually defined as the number of copies produced with a kilogram of ink, or more commonly quoted in the newspaper industry as the kgs of ink required to print a thousand impressions on paper. . Estimating ink mileage has always been a difficult task. This is because there are several interest ing factors that control the amount of ink required to achieve the final ink density. The factors that most influence the ink requirements are as follows: 1) Strength of the ink 2) Substrate 3) Print Density Control 4) Ink and Water Balance 5) Print coverage Strength of the ink The key factor here is the level of pigment in the final ink formulation which determines how much ink is required to achieve density. The pigment is the ingredient in the ink that either absorbs or reflects light. When ink is printed on paper, what we are trying to do is to change the light reflection off of the paper so that the reader perceives color. The pigment type has certain characteristics to ...
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