Analysis of various reasons for the expansion of outlets
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The relationship between ink and dot enlargement
Many factors in the ink such as pigment, viscosity, viscosity, and resin are all related to dot gain. The strength of the ink - its tinting strength - plays an important role in dot gain. The ink is squeezed through the printing plate and the blanket, and then squeezed between the blanket and the paper. The ink layer formed after two extrusions is usually very thin. The color strength of the ink is partly determined by the pigment in the ink. Pigments are often the most costly part of the ink. However, reducing the pigment also reduces the tinting power of the ink. When the ink layer is thick during printing, the problem of dot enlargement occurs. The ink has a high coloring power and the printed ink layer is thin, so that a desired desired color can be obtained.
In controlling the dot gain, the adhesion of the ink is also very important. The higher the viscosity of the ink, the smaller the dot gain. However, if the viscosity of the ink is too high and the degree exceeds the strength of the paper, the paper will "hair" and severely tear the paper.
Viscosity, also known as the flow properties of inks, depends primarily on varnish and pigments. Of course, temperature and water also affect viscosity. The temperature is low, the viscosity of the ink is high, and the degree of dot enlargement is also low; when the temperature is high, the viscosity of the ink is low, and the degree of dot enlargement is high. As we all know, the viscosity of the ink changes with temperature during the printing process.
In lithography, the feed rate of water has an effect on ink stickiness and dot gain. When the ink absorbs moisture during the printing process, the viscosity is reduced and the viscosity is lowered, which affects the dot enlargement. If there is too much water, the viscosity of the ink will decrease, and the degree of dot enlargement will increase, so that the problem of overprinting will occur. On the contrary, if the water is lacking, the viscosity of the ink increases, and the problem of paper fluffing will occur.
According to another study, soy-based inks affect outlets to a smaller extent than petroleum-based inks. As the degree of dot enlargement is reduced, the contrast of the printed product is also improved.
The relationship between paper and dot enlargement
Before printing, you must select the appropriate paper for the printed product. Especially considering the factor of dot enlargement, the choice of paper should be more cautious.
The printability of the paper depends on its surface characteristics, such as the fast acceptance of the transfer ink, and the greater the degree of dot enlargement of the print. Absorbency is a property that determines the rate and amount of ink penetration into the paper. The better the paper's absorption performance, the higher the percentage of dot gain. When the ink is fixed on the absorbent paper, penetration and diffusion occur. The rate at which paper absorbs ink plays a key role in the extent of dot gain. If you print 300 lines/inch of print, it is not wise to use highly absorbent paper.
The flatness of the paper is the degree of deviation between the actual surface of the paper and the ideal plane. The relationship with the expansion of outlets is that the higher the flatness of the paper, the smaller the dot enlargement, the lower the flatness, and the larger the dot gain.
There are many types of coated paper on the market, such as glossy coated paper and matt coated paper. Coated paper helps to improve the fidelity and color clarity of dot printing because it is less absorbent than non-coated paper. It is well known that low-absorbency paper has a small dot spread.
Non-coated paper has a high absorption, high-absorbency non-coated paper to print high-line images, resulting in a high percentage of dot gain.
Recycled paper, in theory, the dot enlargement is the same as the base paper, but in fact it is larger than the original paper.
The relationship between printing presses and outlets
There are many factors that cause the dot to expand in the printing press, such as printing machine speed, dampening fluid, blanket, ink roller, and the like. Printers generally believe that the dot size of web printing is larger than that of sheetfed printing.
The blanket is wrapped around the blanket cylinder, receives the image from the plate, and transfers it to the paper. There are two types of blankets, traditional blankets and compressible blankets, which produce clearer dots. Under pressure, the embossed line of the blanket will bulge on one side or both sides, and the nip line is the contact line between the blanket cylinder and the impression cylinder. Traditional blankets do not have compressible properties. Under pressure, try to restore the original shape and cause friction on the printing plate. This friction not only shortens the service life of the printing plate, but also causes such dot gain in so-called ghosting. Like traditional leather goods, the compressible blanket has a synthetic rubber surface layer and several layers of fiber backing. In addition to several layers of fibrous layers, the backing also includes one or more layers, such as foam, cork or nonwoven fibers, which will produce compression on the embossing line. This design accommodates greater squeezing forces and improves ink transfer performance.
Since the compressible blanket has a large lining range, the lining allows for a large tolerance, which is important because improper pressure can cause excessive dot enlargement. Selecting the thinnest lining thickness required will control the dot gain. Although the sizing of the compressible blanket is very versatile, we recommend not to exceed the 0.004-0.006 inch range.
The relationship between water and ink volume and dot gain
On an offset press, the inking device not only applies ink to the printed image, but can also perform other functions, such as leveling, to improve activity, and receive dampening fluid to emulsify the ink. All of the above factors will affect the expansion of outlets. The thicker the ink layer provided by the ink roller system, the more the non-directional dots are enlarged.
The wetting system applies a water-based wetting fluid to the plate to quickly and completely separate the image and non-image portions of the plate. The operator must maintain a balance between the water supply and the ink supply. Too much water supply may cause a decrease in the viscosity of the ink, thereby increasing the degree of dot enlargement.
Although electronic prepress technology, laser graphic output technology and optical density measurement technology provide some means for controlling dot enlargement, the complexity of lithographic process and the ever-changing technological changes will still bring troubles for dot enlargement to printers. Understanding how outlets expand, where they occur, and how they are controlled must help printers get high-quality prints.