What is the main basis for printing? ——Ink [Buke Printing ]

2. Types of Ink

According to different methods, ink can also be classified into different types. Commonly used inks include relief printing ink, planographic printing ink, gravure printing ink, screen hole printing ink, special functional ink, etc.

The ink used for letterpress printing can be divided into lead printing ink for books and periodicals, lead printing color ink (copperplate ink), lead printing plastic ink, rubber letterpress plastic ink (flexographic plastic ink), letterpress water-based ink, letterpress rotary printing ink, etc. according to different characteristics. These types of inks are basically infiltration drying inks. During the printing process, attention should be paid to the occurrence of problems such as poor adhesion, powdering, and dirtiness.

Offset printing inks include various offset printing inks, offset printing iron inks, offset photosensitive inks, offset thermosetting inks, etc. Ink used in lithography requires high coloring power and water resistance, as well as good fluidity and drying speed.

The ink used for gravure printing includes various gravure inks, engraved gravure inks, gravure plastic film inks, etc.

The ink used for screen printing includes screen printing ink, screen plastic ink, oil-based transcription ink, water-based transcription ink, etc.

In addition to the commonly used inks mentioned above, there is also an ink that can achieve a certain special effect, such as microplastic ink, gold silver ink, fluorescent ink, magnetic ink, security anti-counterfeiting ink, conductive ink, replication ink, monitoring ink, temperature indicator ink, color rendering ink, edible ink, etc.

3. Characteristics of Ink

Ink is a paste like adhesive with certain fluidity, and its properties are determined by factors such as viscosity, yield value, thixotropy, fluidity, and dryness.

Viscosity: It is a property that prevents the flow of fluid substances. It is a measure of the ability of fluid molecules to interact with each other and hinder their relative motion, that is, the resistance to fluid flow. The viscosity of ink is related to the transfer of ink during the printing process, as well as the properties and structure of the paper. If the viscosity of ink is too high, the transfer of ink is not easy to be uniform during the printing process, and it may cause the paper to become rough, resulting in the layout becoming blurred; Low viscosity can cause ink to emulsify and become dirty, affecting the quality of printed materials. The requirements for ink viscosity during the printing process depend on factors such as the printing speed of the printing machine, the degree of flexibility in the paper structure, and changes in temperature and humidity in the surrounding environment.

Yield value: refers to the minimum moving stress required to initiate the flow of a liquid. If the yield value of ink is too high, its fluidity will deteriorate and it will not be easy to open. If the yield value is too low, the dots during printing are prone to smudging, resulting in unclear printed products. The yield value is related to the structure of the ink and has a direct impact on the flowability of the ink. It is an important indicator for detecting the quality of offset and gravure ink.

Thixotropy: refers to the phenomenon where ink changes from thick to thin with the stirring action when subjected to external force, and then returns to its original consistency when the stirring action stops. Due to the thixotropy of ink, the ink on the ink roller is subjected to the rotational action of the printing machine, which increases its fluidity and extensibility, making it easier for the ink to transfer; After the ink is transferred to the paper through printing, it loses the effect of external force, and the ink changes from thin to thick without overflowing to the surrounding area, forming a good imprint. If the thixotropy of the ink is too high, it will make it difficult for the ink in the ink hopper to rotate, which will affect the ink transfer function of the ink roller.

Liquidity: refers to the ink flowing like a liquid under its own gravity, determined by the viscosity, yield value, and thixotropy of the ink, and closely related to temperature. The fluidity of ink is related to whether the ink can be poured out of the container, transported from the ink storage tank to the ink hopper of the printing machine, smoothly transferred from the ink hopper, well distributed on the printing machine, transferred to the layout, and transferred to the substrate, and also affects the printing effect.

4. Drying of Ink: Drying of ink refers to the process in which ink adheres to printed materials to form imprints, and then transforms from a liquid or paste to a solid film. This process is completed by the transition of the edge material in the ink from a liquid or paste to a solid. Because the connecting materials and their formula ratios used in various inks are different, the drying process of the ink is also different. After the ink is transferred from the printing plate to the surface of the printed product, a part of the connecting material in the ink penetrates, and the solvent in the connecting material also begins to evaporate. Some connecting materials begin to undergo chemical or physical reactions, gradually increasing the viscosity and hardness of the imprinting ink layer on the surface of the substrate, ultimately forming a solid film layer. Lithographic offset printing ink is mainly dried with oxidized film.