(1). Concentration: Ink with high concentration uses less ink in offset machine, and the ink color is better; ink with small concentration uses more ink in printing, and the ink color is light;
(2). Fineness: that is, the size of the ink particles. If the ink fineness is high and the ink concentration is large, the dots of the printed matter are clear, full and forceful; if the ink fineness is low, the dots of the printed matter are easy to get hairy, and the printing plate will have a low print durability;
(3) If the viscosity is high, it is easy to cause uneven ink transfer, dot picks and printing mess and so on; if the viscosity is low, it is easy to cause ink emulsification and layout fouling;
(4) Fluidity: If the fluidity is large, the level of the image and text will be unclear, and the ink color will not be full; if the fluidity is small, the spread of the ink will not be smooth and even, and it will easily cause inconsistent ink color in the front and back of the printing surface of the same plate printing press;
(5) Lightfastness: inks with good lightfastness can print products with brilliant color, and the dots are full, solid, full of three-dimensional effect, and can be stored for a long time; if the ink is with poor lightfastness, the color of printed products such as the tinplate printing is easy to get lightened and darkened;
(6) Water, acid and alkali resistance: For offset printing inks, special attention should be paid to its resistance to water, acid, alkali resistance. Ink with strong water, acid and alkali resistance can printe products with bright colors, distinct layers and clear dots; ink with poor water, acid, alkali resistance can only print products with dark and weak color, unclear layers and unclean dots.
The pH value of the dampening water is generally between 3.8 and 4.6. In actual production, it should be adjusted according to the specific conditions of the printing conditions. If the acidity of the dampening water is too strong, the corrosion on the air bells in the blank part of the layout and the lipophilic foundation of the pictures and texts will be increased, which will cause messy printing, reduce the printing durability of the printing plate; at the same time, the ink is easy to emulsify, the ink roller will deink, and the printed matter will be dark and dull.
If the acidity of the dampening water is too weak, the hydrophilic and oil-repellent properties of the blank part of the printing plate will be weakened, the layout will easily get dirty and the plate will be smeared due to the expansion of the dots of the printed matter (During UV ink printing, if the dampening water acidity is too acidic, the layout will easily get dirty)
Color sequence refers to the sequential overprinting sequence of printing plates with different colors in multi-color printing, and different color sequences will produce various printing effects; it is very important to arrange the color sequence reasonably. But the color sequence is not absolute. The color sequence of the multi colour offset printing machine is generally arranged as follows: single color machine: yellow→magenta→cyan→black; two color machine: black→yellow, magenta→cyan (landscape printing) or cyan→red (character printing); when there are gold, silver, and full-page field printing, generally gold, silver, and full-page field printing are first, and then four color ink will be applied after the ink is dry.
As one of the professional offset printing machine manufacturers in china, Ruiyuan will show you some tips for identifying the size of moisture on a metal printing press. To identify the difference of moisture, we should first look at the moisture of the layout. This depends on the operator's experience. Generally speaking, if the moisture content is large, the amount of reflected light on the layout will be strong, and the side view will be brighter; on the contrary, the amount of reflected light on the layout will be weak, and the side view will be darker; if the moisture content is too large, it can also be observed from the following points:
(1). Use paper jam to shovel ink on the ink roller, and there will be small water droplets on the paper jam;
(2). There are small water droplets on the dampening vibrator, and deinking or water droplets will appear in the ink roller group;
(3). The water on the layout has not dried up after turning off the water or shutting down for a long time;
(4). The blotting dots are empty, and the ink color is dull;
(5). There are water shadows or water droplets at the tail end of the rubber cylinder of the metal printing machine.