Offset Printing 1000 Questions (142-151)

142. What is the fluidity of the ink? What does it mean for offset printing?

A: The fluidity of the ink includes viscosity, adhesiveness, viscoelasticity, and yield and thixotropy. It mainly depends on the properties of the pigment and the binder, and its manufacturing process, in which the content of the binder directly affects the fluidity of the ink. In the printing press, there are mainly the following three aspects of the phenomenon of flow: 1 when the container is poured into the ink fountain, easy to ink is called fluidity; otherwise, it is poor. 2 When the ink is output from the ink fountain, the ink that is easily inked is referred to as fluidity; if not, it is poor. 3 When it is used to distribute ink, transfer ink, and apply ink, it is easy to spread, transfer, and transfer. It is called fluidity; if not, it is poor.

In the offset printing process, the correct control of the ink flow has important process significance. Moderate fluidity not only ensures the normal flow of ink on the press, but also makes the print even and flat. If the fluidity is too large, the ink will slip on the ink roller, resulting in an increase in the geometric size of the print, which will damage the screen level and increase the penetration of the ink on the paper. If the fluidity is too small, the ink supply will be out of order and the ink will not be uniformly distributed. , can not guarantee the uniformity of ink color printing, or even caused by the lack of ink on the layout caused by the flower version. At present, the evaluation of ink flowability in China is generally within the range of 30 to 50 mm for the control of the ink flow of a four-color (or three-color) version of a sheet-fed offset printing press.

143. What is the ink under ink? What does it mean for offset printing?

A: The phenomenon of ink flow from the ink fountain is called ink under ink. When the ink is output by the ink fountain roller, it is only affected by the external force of the ink fountain roller. Its flow conditions are mainly the gravity and surface tension of the ink itself. In addition to the liquidity of the ink, the ink ink depends on its own leveling. The rheological properties such as sex, viscosity, yield value, thixotropy, and stringiness.

In the offset printing process, the ink under ink directly affects the amount of ink supplied per unit time, and the ink layer thickness during the transfer and transfer process. Therefore, in actual printing adjustment of the amount of ink under the ink, in addition to adjusting the ink fountain roller speed (or rotation angle), or the local adjustment of the ink blade blade clearance, it should pay more attention to the automatic or manual ink mixing, and change the ink's yield value and touch Denaturation, to ensure that it has a constant amount of ink in each moment, otherwise the ink can not be properly transferred to the ink fountain roller, the formation of ink stagnation phenomenon, resulting in poor ink supply or ink supply interruption failure.

144. What is the transitivity of ink? What does it mean for offset printing?

A: After the ink is output by the ink roller, the flow phenomenon presented is called ink transferability.

In the offset printing process, the thickness and uniformity of the ink layer on the surface of the printing plate are achieved through a series of ink rollers. The ink transferability is directly related to the distribution and distribution of the ink volume. And its smooth transfer throughout the process. In general, the process of ink from the ink fountain to the printing plate is mainly dependent on the ink's own viscosity, stringiness and thixotropy. Under normal circumstances, when the drawing property and viscosity are appropriate, the ink exhibits better transferability, and the ink amount distribution is also better; when the drawing property and the viscosity are too large, the transferability is deteriorated, and the ink amount distribution is also deteriorated; When ink is too long, it is easy to cause ink flying.

145. What is the transferability of ink? What does it mean for offset printing?

A: When the ink is transferred and dispensed (from the ink fountain, and after a complex transfer and distribution until it is successfully transferred to the surface of the printed sheet to form a print), the flow phenomenon presented is called the transferability of the ink, and it is suitable for ink operations. Sexual subject.

The transferability of the ink can be understood from two aspects: on the one hand, the transfer of ink between the ink transfer, the uniform ink and the ink roller; on the other hand, the ink between the printing plate and the blanket, the blanket and the printed sheet. Transfer. The former is mainly affected by the ink and transmission, while the latter is also affected by printing conditions (such as printing

Brush type, printing speed, printing pressure, etc.) and blanket, paper effect. That is, the transferability of the ink is shown during the entire transfer, distribution, and separation (or splitting) of the ink, which is of great significance for offset printing. The quality of ink transfer is mainly determined by the drawability and viscosity of the ink, and also related to its wettability, viscosity, yield value, thixotropy, and surface tension.

146. What is the printing quality applicability of printing ink?

A: At a certain printing speed, under a certain printing pressure, after the blanket is transferred to the surface of the printed sheet, the ink film shows the fixation and drying speed, and the color, gloss, and fastness after film formation. The properties such as resistance to various printing effects are collectively referred to as the printing quality of the ink. Mainly include color, permeability, dryness, gloss, rubbing resistance and so on.

147. What is the color printability of the ink? What does it mean for offset printing?

Answer: In the printing, the color of the ink in color or non-colored printing is not based on the color appearance of the ink, but is based on the ink film that is cured on the surface of the printed sheet. The color of the ink is mainly determined by the color of the pigment used and the nature of the binder. The color displayed by the ink film is closely related to the intensity and wavelength of the illumination light, the photochemical properties of the surface of the substrate, the surface properties, and the thickness of the ink layer. .

The color of ink used for four-color (or three-color) edition color offset printing should theoretically be the complementary color of the color filter used when the original color is decomposed, but the three primary color inks actually used have the coloring phase impure, the brightness is dim, and the saturation is low. The defect, but also under different paper type and nature conditions, the gray balance of the field density value is different; in the printing process ink in the wet and dry state of the ink film shows the color is not the same. Therefore, it is particularly important to select an appropriate printing ink to satisfy the printing adaptability of the ink. This not only has practical technical significance for reproducing the tonality and color of the original document, but also is particularly important for displaying the artistic effect of the printed matter. In the current technical standards for ink products, numerical indicators have not been listed for color, only based on the "standard sample".

148. How to determine the color of the ink?

A: According to the specific conditions and conditions, there are currently 3 methods for determining the ink color:

1 scraping method. Take a small amount of standard sample ink and sample ink, respectively, and mix thoroughly, each will be placed on the top of the standard sample paper (offset printing paper or offset printing coating paper) side by side, with a scraper from top to bottom scraped into 3 ~ 5mm strip Thin ink film, thick black ink film that is harvested. Then, visually examine the difference between the base color, face color and ink color of the standard and the sample ink layer above the black band, and compare the color difference between them to make an assessment.

2 Densitometry. The solid density samples of the three primary color inks were placed under the red, green, and blue-violet filters of the color reflection densitometer, and their optical density values ​​of high, medium, and low were measured, and then they were calculated according to a prescribed formula. Hue error, grayscale, and actual efficiency.

3 The color of the ink can also be measured by a roller coating method, a printability tester, or a colorimetric spectrophotometer.

149. What is the permeability of ink? What are the factors that affect ink permeability?

A: Ink penetrability refers to the penetrating ability of ink ink layer transferred on the surface of the printed sheet, which is to characterize the penetrative phenomenon and properties of the ink in the early stage of the drying process. In the offset printing process, the infiltration process of the ink (linking material) includes two processes, namely an instant rapid infiltration process immediately after the printing pressure acts and a slow free infiltration process after the printing pressure disappears.

In the offset printing process, the permeability of the printing ink depends mainly on the nature of the linking material itself, but also on the printing pressure, the printing speed and the type of paper used, the surface properties (such as ink absorption, smoothness, etc.). In general, the ink ink layer penetrates through the paper. Because of the different types of inks and different viscosities, they exhibit different permeation properties and permeation rates. Generally, the permeability of the oxidized polymeric conjunctival ink is lower than that of the penetrating gel conjunctiva type ink.

150. What is the significance of ink permeability for offset printing?

A: The permeability of the ink is of great significance to the fixation of the imprinted ink layer, the drying and the tone reproduction after the conjunctiva of the ink layer, the glossiness, and the abrasion resistance. When the penetrability of the ink and the ink absorption of the paper are too strong, the phenomena of chalking, strike-through and the like are easily caused, and the color, gloss, and rubbing resistance of the ink film of the ink are markedly decreased; when the permeability of the ink is too small, It will cause the back of the printed sheet to become dirty (or dirty). In severe cases, the printed sheets that are stacked will become sticky.

151. How to determine the ink permeability?

A: The permeability of the ink is usually measured using a permeability tester. The specific method is to print (or squeegee) the test ink on a standard paper sample, then cover the same standard paper sample on the surface of the test paper, and install it on the permeability tester. After 5 seconds of printing (scratch printing), the paper is rolled. To the full length of the sample 1/3; at 30 seconds, rolling to 2/3; at 60 seconds, rolling the entire sample. Remove the sample and examine its penetration at different times to determine its permeability.

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"Printing Technology"