In the packaging and printing industry, various inks are often used, but different inks have different functions. Today, I will take you to the viscosity of the ink and distinguish the difference in the use of different inks from the viscosity.
1) The "sticky" ink with relatively high viscosity and poor fluidity has good adhesion, high intramolecular friction or cohesion, strong adhesion, and fast fixation. It can be printed with "sticky" ink to get clear Round dots, and "sticky" ink has good water resistance, is not easy to emulsify, has good "ink receiving", easy to dry, smooth dots, bright ink color, saturated color, and thick ink layer. Therefore, this ink is more suitable for the following situations:
(1) For printing paper with good gloss and high surface strength, such as coated paper, glass cardboard, white cardboard and other papers, and gold and silver cardboard and other papers with good smoothness and non-absorptive paper, it is also suitable for "sticky" Sexual ink;
(2) It is suitable for fine products with higher printing network lines, and it is easy to obtain strong, clear, and full-color images;
(3) When printing gold and silver inks, and printing fluorescent inks, it is also necessary to adjust the viscosity of the ink to make it strong and not dirty;
(4) For the pearlescent ink in the form of phosphor flakes, it is also necessary to adjust the viscosity of the ink for printing.
Since the viscosity of the ink is an important factor in the transfer of dots, in practice, the viscosity of the ink should be adapted to the printing process according to changes in different conditions, and appropriate adjustments should be made to increase or decrease the viscosity of the ink. It is to make certain adjustments to the cohesion of the ink to adapt the viscosity of the ink to the requirements of the actual printing conditions. The specific adjustment methods for increasing the "viscosity" mainly include:
(1) Add an appropriate amount of tackifier to increase the viscosity, such as No. 0 varnish;
(2) Add high-viscosity resin oil to increase viscosity;
(3) Add an appropriate amount of high-viscosity ink to increase the viscosity.
Due to the high cohesive force and strong adhesion of the "sticky" ink with high viscosity, it is not suitable for use in some cases, such as printing on offset paper, white paper and other paper with low paper strength, the printing speed is faster, and the ambient temperature is higher. If the layout is based on a large solid area, a lower viscosity ink must be used. If the viscosity of the ink is too high, a viscosity reduction treatment is required. The usual ways to reduce "stickiness" are as follows:
(1) Add a certain amount of silicone oil;
(2) Adding less than 2% and no more than 5% of viscosity reducing agent to reduce viscosity;
(3) Add high-boiling kerosene to reduce viscosity, and the dosage should not exceed 10-20ml per kilogram;
(4) Add a certain amount of corn starch, petrolatum and other viscosity-reducing substances.
2) "Thick" ink with a large consistency, but with a certain viscosity and adhesion, due to poor fluidity and poor ductility, the ink is paste-like, not easy to level, and the imprinted ink film is not easy to spread during printing. Graphic transfer It is more accurate, not easy to be deformed, and the ink color is more vivid and full. Therefore, the "thick" ink is more suitable for the following situations:
(1) It is suitable for printing large solid fields, products with hollow characters or small characters, because they are not easy to level and spread, hollow characters or small characters are not easy to produce smearing;
(2) It is suitable for printing products with shallow dots in the large solid area, and a thick solid field can be obtained, while the dots are relatively clear and not easy to expand:
a. When the ambient temperature is high, the vehicle speed is slow, and the dot graphics are the mainstay, the ink is generally adjusted appropriately for printing;
b. When the paper has high surface strength and poor ink absorption, the ink should also be appropriately thickened for printing.
In actual production, if there is no ink with the corresponding consistency, or the consistency of the ink becomes smaller and cannot meet the requirements of use, then the "thickening" treatment must be carried out to reduce the fluidity of the ink. The specific "thickening" treatment methods are mainly:
(1) Add NaOH, the addition amount is about 1%-3%, this method has a faster effect, and it is a simple and effective way to adjust the ink thickness;
(2) Adding tackifier, such as No. 0 varnish, if added with China Hydrocarbon Petroleum Resin, it can have the effect of color development, quick drying, brightening, and improving printing performance. But pay attention to the amount to be appropriate, not too much;
(3) If the ink is not viscous enough under the influence of temperature, the original ink of the same hue can also be added to the ink.
3) The ink with smaller consistency and lower viscosity, due to its good flow, can be stretched well under the mutual squeeze of the ink rollers, has good transfer performance, is easy to ink, and the ink is in the ink layer between each printing transfer surface It can be leveled and spread quickly, and the imprinted ink film is smooth and clean. Therefore, in some cases, it is also necessary to reduce the consistency of the ink, such as:
(1) The paper is of poor quality, relatively rough, large ink absorption, or low surface strength, easy to pull hair and powder, such as the use of poorly printed offset paper, book paper, white board paper, etc.;
(2) When the layout is dominated by solid and large color blocks;
(3) When the workshop temperature is high and the printing speed is fast;
(4) The paper is damaged. If the ink is too thick, the damage may be aggravated. Therefore, the ink with higher fluidity should be used for printing.
The main methods to reduce ink consistency are:
(1) Adding a certain amount of diluent, such as adding low viscosity, high fluidity No. 6 varnish, this method is better, but the dosage should be controlled, generally not exceeding 10% of the ink dosage;
(2) Stir the ink fountain frequently, because the ink has thixotropy, its flow characteristics will be improved as the degree of agitation increases, thereby reducing the viscosity of the ink;
(3) Add less than 2% viscosity reducer.