17. Color flutters or inconsistent The colors of prints are different in the same position on the same paper or in the same position on different papers. The reason is due to the fact that the used inks are inconsistent in terms of color, pigment content, consistency, brightness, etc. In the same batch of inks, chemical reactions or flocculation of some of the pigments occurs during storage; light conditions in the printing shop are not uniform when the colors are deployed; The amount of ink given by the printer is inconsistent; the temperature and humidity have changed during the printing and drying process, which causes a change in the proportion of ink permeation, resulting in a difference in gloss and color between the printed products; due to inconsistent dryness; The release agent was added too much; the quality of the dot plate was inconsistent, resulting in an unbalanced color addition and subtraction.
The solution is: check the customer's color standard and the amount of ink applied to the print; the ink should be kept in good condition; the printer must operate under consistent and ideal conditions; the quality, surface properties and color of the paper should be strictly checked Comparing colors should be done under good daylight conditions. Do not perform in dark corners or under different artificial light. It is best to be judged by one person. Check if the drying speed of ink is consistent with the standard. Flocculated The ink should be redispersed and checked for proper fluidity; if the ink has deteriorated, it should be replaced with a new ink.
18, speckle spot is the color of the field prints of different shades and formation of stains. This drawback is more likely to occur when printing in the field using a flatbed press. The green and brown colors are the colors that easily cause this phenomenon. The reason is due to the fact that the ink film is too thick, the transfer is not proper, the print on the paper is uneven, and there is a squeezing; the ink film is too thin and does not completely cover the surface of the paper; the ink is too viscous, resulting in ink split during imprinting Bad; broken ink filaments do not flow well on the paper as beads (commonly referred to as scaly in China); inks are too oily, too long to equilibrate, or remove ink too softly; inks produce material The content is too little; the color is too weak (light); the cover (fold) printing is more prone to spotting than monochrome, especially when the bottom color is already crystallized, the overprint color is not easy to print plump or have a flat feeling on the first color .
The solution is: use a round flat or circular press to print; use a flexible pad for paperboard or harder paper; use more uniform ink roller; print pressure can not be too large; The design uses dot patterns. Paper and ink should be compatible with each other; harder paper should use thick and sticky ink, which can reduce the disadvantages of extrusion. If it is due to thick prints, thick and strong inks can be used, which can be printed thin. If it is due to too thin prints, you can mix in the amount of colorless ink remover, the ink printed thicker. If the coloring power of the ink is too high and the opaque white ink is used to remove it, the paper may not be covered properly. If the ink is too oily, some magnesium carbonate can be added and redispersed with a three-roller or the corresponding pigment. The ink should be made opaque with titanium dioxide instead of transparent fillers. For the ink used in the platform machine, pigments with relative density and oil absorption similar to each other should be selected so as to avoid the use of pigments with a large relative density. If plain ink is used, the spots are bright and light. This is because these parts of the ink are not permeated, and the final ink that does not form a continuous film can be used.
19, poor gloss due to the link material in the ink is too thin; ink dryness is too slow or too strong suction modified paper; caused by ink infiltrated the paper and make the prints uneven and dull.
The solution is: check the ink drying time, if the ink is drying too slowly, you can add some dry oil, and add a small amount of bright light material, varnish or resin type material; or use poor absorption of paper.
20. Drying too fast The ink dries too fast in the ink fountain and on the machine. On the blanket, the ink thickens on the machine and picks up and piles up. This is because the ink contains too much desiccant; the ink contains solvents that volatilize too quickly; the printing shop's temperature is too high, the air is too dry or the air circulation is too good.
The solution is: a small amount of petroleum jelly, castor oil or paraffin oil is mixed into the ink to reduce the drying rate; a small amount of anti-skinning agent or anti-oxidant is added; ventilation in the workshop is not so good.
21. Fading The color of the ink fades during the printing process, or the color of the ink fades when the printed matter is stacked (during drying). The reason is that heat is generated in the paper stack due to the oxidation of the ink, and this heat will fade some of the color; the amount of desiccant in the ink is too much; the pigment is not heat-resistant or the pigment or filler in the ink.
22, weak color due to the link material in the ink is too thin, after the printing ink binder material infiltrated the paper, making the print lack luster. Although the coloring power of this type of ink was satisfactory at the time of inspection and met the standard, the color of the printed product was still insufficient.
The solution is: in the ink should be used thicker link material; with quick-drying synthetic resin binder, it has light after drying, increase the color strength; use different pigments to make ink, cover with a layer of bright oil, make the color Brightly colored.
23, after the use of alcohol-soluble varnishes, the dots of the printed products are unclear, there are bleeds around the imprints, and sometimes the color of the bleed is different from that of the original prints. The reason is that the ink is not completely dry; the ink is not resistant to alcohol solvents; and the pigment in the ink is not resistant to alcohol solvents.
The solution is: use an oil-based varnish; print a layer of diluting agent on the printed product, and then cover it.
24. Adhesive sheets are pasted together into a single piece, especially after heating. The reason is that the ink dries too slowly; the solvent remains in the ink film; or there is a plasticizer in the ink film; the softening point of the adhesive used in the ink is too low.
The solution is: to add more volatile solvents in the ink; change with a new ink; reduce the amount of plasticizer in the ink; use a higher softening point of the binder.
25, phantom (image)
When there is a phantom, there is a situation in which a pattern of another part is seen in a large area of ​​the real region, that is, the pattern is repeated in other places. This situation is also called a phantom; or a blank embossed form appears on the ground. Called negative illusion. The cause of the phantom is due to poor ink distribution.
The solution is: increase the amount of ink; replace the ink transfer roller roller.
26, imprinting cylinder stacking ink In letterpress printing, under the paper and on the impression cylinder can collect the ink. The reason is that the dryness of the ink is too slow; the amount of ink given is too large; it may also be due to pinholes in the paper.
The solution is: use slightly sticky and fast dry ink to reduce the amount of ink; and the use of pinhole-free paper.
27. There are many non-printing areas (blank areas) that are small in size like pinholes around the field of the pinhole prints. The printed products show many tiny round holes. The pinhole is the ink "cellular eye" or "blister."
Mechanical pinholes are the same size of trachoma and evenly spread throughout the print. The distribution of chemical pinholes is relatively messy and often varies in size.
The mechanical pinhole is caused by the contact of the ink on the plate with a portion of the recessed area of ​​the paper surface. The ink dries too quickly in the ink roller; the ink is too thin, especially ink using a fast-drying solvent; the ink film is too thin; and mechanical impurities adhere to the plate.
Chemical pinholes are due to the fact that the ink does not properly wet the surface of the substrate, resulting in a film that does not form a flat and continuous film. The surface energy of water-resistant cellulose films and foils is too high, resulting in bead-like holes. The surfaces of water-resistant cellulose films and foils are generally coated with a layer containing paraffin wax, barrel grease, and plasticizer. These materials have relatively high surface tension for the solvents used in flexible inks. The material, which results in poor surface wetting, shrinks the ink into pits or blisters, and chemical pinholes appear. The temperature of the printing shop is too low and the humidity is too high; the solvent power of the solvent in the ink is lowered; and the chemical pinholes are also caused by the ink having too little viscosity or being too dry.
The solution is:
(1) Mechanical pinholes increase the viscosity of the ink; reduce the dryness of the ink; printed thicker.
(2) Chemical pinholes Anti-pinhole agents are added to the ink to improve the wettability of the ink. The temperature of the printing room is lowered to reduce the humidity in the printing room. The ink fountain is covered; the ink is dried quickly; printing is used. The substrate (coil) can be preheated first, which can also improve the printing performance on the surface; adding a small amount of plasticizer to the ink can improve the wettability and the flexibility of the film; adding appropriate solvent can also improve the wettability; or change the use of New structure of ink.
Dirt accumulation: Since the ink is too sticky or the dry oil in the ink is not suitable, the ink is caused to thicken and dry on the machine. At this time should check whether there is skin in the ink, the thickness is appropriate; the ink on the machine and the dryness of the paper is appropriate; if the ink is too thick and dry too fast, you can use thick and dry too fast, you can use thin Ink oil, wax additive or slurry dissolving agent is mixed and diluted.
28, ink filling (poor filling)
Due to the poor rheological properties of the ink, the ink is too thick. Although the ink roller gives a lot of ink, it cannot be sufficiently filled into the intaglio ink hole.
The solution is: use dilute ink or high boiling point solvent to properly dilute and remove the ink; change the ink with good rheology.
29, thin line break due to improper ink viscosity, too thick or too thin too thick, resulting in printed parts of the thin line is not continuous, disconnected.
The solution is: if the ink is too thick and sticky, you can dilute the ink with dilute ink or high-boiling solvent; if it is too thin, you can add some thick ink. (Zhou Zhen) (To be continued) ("Packaging Printing")