Offset Printing 1000 Questions (100-106)

100. What is the transparency of the ink?

A: The transparency of an ink refers to the extent to which the ink film covers the printing material or is overprinted on the surface of another ink layer and is covered by the covering surface. It is an indicator of the ability of the ink film to cover the covered surface. , also known as the hiding power of ink. The transparency of the ink is generally transparent (non-hidden), translucent (half masking), and opaque (covered).

The transparency of the ink is of great significance for the color sequence design of three- or four-color printing and the color effect after printing. In three- or four-color printing, the transparency of the ink is the key to achieving the color reproduction effect of the printing subtractive method. In some multi-color printing, if the background color of the covered layer or the surface needs to be covered, the transparency should be low. The ink is printed to achieve the purpose of not exposing the background; otherwise, it is printed with a clear ink or a semi-transparent ink.

101. How to measure the transparency of ink?

A: The ink's transparency is generally expressed as the amount of ink required to cover 1cm2 of area. There are two methods for measuring the ink transparency at present.

1 scraping comparison method for qualitative determination of ink transparency. Generally, when determining the transparency of the ink, the degree of transparency of the ink can be determined by comparing the degree of appearance of the thick lines of the ink on the scratch paper.

2 Coverage force method: Quantitative measurement using a hiding power meter.

102. What is the ink coloring power? What is its effect on offset printing?
A: The coloring power of an ink refers to the ability of the ink layer to display the color intensity on the substrate. It is one of the quality indicators that characterize the ink concentration or saturation.

In the offset printing process, the coloring power of the ink is not only directly related to the printing effect and the quality of the printed product, but also related to the ink consumption per unit area. Strong coloring inks consume less ink than weak inks, and have good printing results. Offset printing ink coloring force of choice, usually according to the nature of the printed matter and graphics, such as the printing of a print based on the color mesh tone, the application of strong ink color printing, conducive to the reproduction of small outlets; printing When full-version prints are mainly printed in the field, they are printed using inks with weaker tinting strength. The determination of ink color strength in offset printing can usually be compared from the ink transfer amount on the surface of the ink roller to the ink density of the printed product. For example, if the ink transfer amount is large, the density of the ink is insufficient, indicating that the coloring power is weak. On the contrary, it is stronger.

103. What are the factors that affect the tinting strength of ink?

A: The strength of the ink color strength is related to the concentration, content and dispersion of the pigment in the ink, and the selective absorption and reflection of light waves by the ink ink film. In general, when the content of the ink pigment is large and the dispersion degree is large, the coloring power thereof is strong; otherwise, the coloring power of the ink is weak.

104. How to determine the tinting strength of ink?

A: The ink tinting strength is usually measured by a scraping contrast method. The specific operation is: Take standard white ink 2g, respectively, set the 0.2g standard ink and 0.2g sample ink diluted, and mix thoroughly. After scraping to make the sample ink reach the same concentration as the standard ink sample, it is calculated according to the following formula:

S=B/A×100%

Among them, S is the percentage of tinting power of the ink (100% of the standard ink sample), A is the weight (g) of the white ink consumed to dilute the standard ink sample, and B is the weight (g) of the white ink consumed to dilute the sample ink.

105. What is the fluidity of the ink?

A: The degree of ink flow refers to the degree of flow of ink after stress, expressed in millimeters. It is used to characterize the flow state and thinning phenomenon of the ink under certain viscosity. The fluidity of offset inks is related to the viscosity and consistency of the ink. It also depends on the inherent structure and yield value of the ink.

In offset printing, the control of ink flow is usually based on viscosity and consistency. The viscosity of the ink flow is small; on the contrary, the viscosity is small when the ink flow is large. The ink fluidity has a certain relationship with the dilute thickness of the ink, but there is no direct size relationship. For example, an ink with a large consistency and a small viscosity has a relatively large fluidity.

106. How to determine the flow of ink is good or bad?

A: The ink with the ideal fluidity has better ink leveling and ink receptivity in the ink fountain. The transfer and transferability between the ink roller or the printing plate and the blanket is also good. The ink layer on the printing plate and the blanket is good. Uniform, imprinted and ink film flat service, smooth, high gloss. When the degree of ink flow is too small, problems such as poor ink formation and uneven ink layer distribution may occur, and the surface of the ink film may also have ripples. When the ink flow is too large, the ink layer is thin, which tends to cause dot enlargement, the color of the print is not strong, and even when the ink is severe, it may cause turbidity.

(Author/Drilling)