Analysis of common faults in ink during printing
1. Ink gelation problem
Oily inks used in the packaging and printing industry are prone to gelation problems, and occasionally such problems occur in solvent-based (volatile dry-type) and water-based inks. The molecular weight of the resin in the ink system is too large, so that the viscosity of the ink is too high; the content of the resin binder in the ink is too high; the acid value of the ink system is too high; the pigment or filler in the ink has a certain alkalinity; The desiccant content is too much or the order of addition is improper; the solvent system, especially the fast-drying solvent content, is caused by six reasons. The first two are in the field of physics. It is easy for experienced ink manufacturers or packaging and printing operators to take these two points into consideration and take measures to prevent gelation; the latter four are due to the ink manufacturing process. The application of auxiliary additives is improper, the temperature of the dispersion process is too high, and the solvent volatilizes too quickly.
For the problem of ink gelation, the industry has proposed many solutions, summed up: adding a metal salt of naphthoic acid to the ink; adding aliphatic hydrocarbons and esters when the ink is too thick or gelatinized due to excessive polymerization of the binder. Diluting with a solvent such as a ketone; adding a rosin to the gelled ink which is reacted into a soap, dissolving it in a linoleum, and using a high acid value substance to remove the gelation of the ink; for the gelation problem of the aqueous ink, an inorganic salt is required. To control it. In addition, a small amount of anti-expansion breaker (1.5% to 2.5% of the pigment content) is added to the ink formulation to prevent gelation of the ink during the ink production stage.
2. Ink deinking failure
In the printing process, sometimes the ink roller and the ink roller are not inked, which is the ink deinking, mainly due to the lack of oiliness of the ink. This is most common in black inks. Black ink with carbon powder as a raw material is inferior. Although the necessary oily auxiliary materials have been added in the manufacture of inks, deinking occurs. For this kind of black ink, it is effective to dilute some with dilute ink. If the contrast of the product image is large and the ink cannot be diluted, it can be solved by dropping some oleic acid in the ink.
3. The ink is peeling off
Ink stripping refers to the fact that the ink on the printed matter is wiped off like a dry powder after drying. The main reason is that the binder in the ink penetrates into the paper in a large amount, causing the ink to lose its viscosity, and the pigment particles are too coarse; The binder is too dilute or uses too much non-volatile, immiscible solvent; the paper absorbs too much and the binder penetrates too quickly. The treatment methods and preventive measures mainly include: adding adhesive varnish to the ink (ie, viscous oil with higher viscosity); appropriately increasing the amount of desiccant; controlling the pH of the dampening solution to 5-6, reducing the dampening solution Dosage; the best method for printing on already pulverized paper is to use a clear adhesive or a varnish to print it once to make it better bonded.
4. The ink is drying too slowly or too fast
The ink drying is too slow mainly because the water supply is too large (layout), the pH of the dampening solution is too small, the printing shop temperature is too low or the humidity is too high, too much varnish is added to the ink, the paper absorbability is poor, and the dry oil is too much. Caused by small reasons. For this problem, it is necessary to strictly control the moisture of the layout is too small, master the pH value of the fountain solution, pay attention to the amount of ink adjuvant and desiccant to solve the problem. If the print does not dry, the print should be aired in time to ventilate the air to allow the air to enter the paper to speed up the conjunctiva.
If the ink dries too fast, it will form a "crystallization", so that the latter color will not be printed, mainly due to excessive drying oil or excessive stacking time of semi-finished products, which is often in the yellow version or Occurs when the light background is full. If this problem occurs, if the number of products that cannot be overprinted is small, use a clean soft cloth 蘸 magnesium carbonate powder, gently rub the surface of each print to make the surface rough; use infrared rays to illuminate the ink layer. If the amount is large, the humidity adjustment treatment can be performed to make the ink layer absorb moisture and expand, and the surface is roughened. After the surface of the ink layer becomes thick, the latter color ink is easily attached.