Several important technical indicators of offset printing ink

The technical indicators of ink have important guiding significance for printing. The technical indicators that are generally more closely related to offset printing mainly include the following aspects:

(I) Ink concentration

Ink concentration is an indicator of pigment content Pigments generally account for about 20% of the total ink. The ink concentration is large at the time of printing. With the same amount of ink, the color of the printed matter is strong, whereas the color of the printed matter is light. The ink has a large concentration, and the amount of ink used for printing is small, the ink layer is thin, and it is relatively dry. Especially when printing a large area on the ground, the concentration of ink has a significant effect on the print quality. Because when using high-concentration inks, the printing ink layer is thin and the fixing speed is fast. This can reduce the stickiness of the printed product, and the color balance of each color can be easily adjusted.

The ink industry judges the density of ink by measuring the coloring power. The tinting strength is determined by the ability of the pigment in the ink to absorb and reflect light. Shows the strength of ink display color. It is usually measured by diluting the ink with white ink, so it is also referred to as dilute intensity or dilute concentration.

(B) The viscosity of ink

The viscosity of the ink is an important indicator in printing, it is tested with the ink stickiness meter. The value of the viscosity of the ink refers to the amount of force separating the ink film between the two rolls of the viscometer. The viscosity of the ink is too large or too small to affect the quality of the printing. When the viscosity of the ink is too large, problems such as poor ink transfer, poor transferability, poor paper-drawing, and poor overprinting are easily caused. If the viscosity is too small, problems such as excessive ink transfer amount, dot gain, ink emulsification, and dingy tend to occur.

At a certain temperature, the viscosity of the selected ink is not too large when the printer is fast, and vice versa. In addition, the relative viscosity of each color ink is selected according to the printing sequence. Under normal conditions, there is no need to adjust the viscosity of the ink. For adjustment, additives can be selected according to their viscosity and consistency. Generally, the viscosity is large, and when the consistency is suitable, the viscosity can be adjusted without decreasing viscosity. If the viscosity is large and the consistency is also large, it can be used as an auxiliary agent that reduces both viscosity and viscosity.

(iii) Dryness of ink

The drying process of the offset ink on the paper is the process in which the ink changes from a non-polar colloidal fluid with a large fluidity to a fixed state. The general measure of offset ink is divided into two indicators:

1. Fixing speed It means that the ink changes from a natural flow state to a semi-solid state. In other words, the prints are not sticky when they are superimposed on a certain height, and they are called dry. The initial drying of the ink is determined by the resin structure chosen for the design. The initial drying time is short, but it is not completely dry.

2. Oxidative conjunctiva drying is what printing is talking about. The drying time is longer, generally more than 8 hours, and it is completely dry. The dryness of the ink is determined by the type and amount of the desiccant and can be adjusted within a certain range.

At present, the offset printing inks are all resin type, and the fixation speed is faster. In theory, the quicker the better the initial dry, but the early dryness will affect the gloss of printed materials. The operator of the offset printing press always hopes that the ink will be dried quickly on the paper and not dry in the ink fountain. This is impossible. Generally about 80% of the ink conjunctiva drying time is between 16-30 hours. If the conjunctiva drying time is too short, it will easily cause the skin to hold the roller on the machine, and it will print the copperplate paper or long-lived printing. You can choose the ink with longer conjunctiva drying time. For advanced coated paper, cardboard, or short-lived, you can choose a fast dry ink.

(d) gloss of ink

The gloss of the ink is the ratio of the amount of light that is positively reflected and the amount of light that is reflected by the standard plate when the ink sample is illuminated by a specific light source at a certain angle, expressed as a percentage. The brightness of prints gives a direct impression. In general, the higher the gloss feeling, the better the printing effect. Although the gloss of prints has a certain relationship with the wetting liquid used for printing and the absorptivity of paper, it is mainly determined by ink. This property of the ink is mainly dependent on the binder and the pigment therein. The binder and pigment in the ink should have good printability, and the resin itself has high gloss. The luster of the ink printed on the paper is high. Glossy inks tend to start a little slower. The ink with high gloss when overprinted on a monochrome machine must control the overprinting time, otherwise the phenomenon of crystallization of the ink is likely to occur.

(e) Fineness of the ink

The fineness of the ink indicates the pigment in the ink, the filler particle size, and the uniformity of the distribution in the binder. The fineness of the ink is directly related to the nature of the pigment and the particle size. The finer the fineness, the more stable the properties of the ink and the fullness and strength of the printed product outlets. On the other hand, in the printing, it is easy to suffer from the shortcomings of the printing plate, such as low ink-repelling rate, pile-up of ink, emptiness of outlets, expansion, and uncleanness of outlets.

Source: Ke Yin Network