The problem of ink sticking and back rubbing in the printing process

Because the ink is drying too slowly, the ink is too soft, too thin, and the amount of ink to be supplied is too large, the ink on a printed sheet is smeared on the back of the upper sheet. Most of this occurs in the larger solid (or dark) portion of the ink on the print. Sticking, sticking, and sticking (commonly referred to as sticking together) is the most serious phenomenon of sticky backs. This refers to the situation where printed piles of printed matter are stuck together. The second side of imprinting and sticking is that the first side is printed on the second side immediately after it is printed. As a result, stickiness appears in the printing. This is mainly caused by the following factors:

(1) Paper with a rough printing surface requires a large amount of ink.

(2) Printing double-sided glossy paper.

(3) The ink volume is large at the sites where the printing is in the field or where the density is high.

(4) When printed on an absorptive sheet with an oxidatively drying ink.

(5) The amount of the ink desiccant is too much, and it is easy to oxidize heat in the paper stack, resulting in the ink being sticky and making the paper stick together.

(6) Ink emulsification causes stickiness.

At present, the following measures are generally adopted to solve the problem of sticky back of prints:

(1) Use fast-drying inks. Use infrared dryers for web offset presses.

(2) Use dusting to prevent sticky back.

(3) Use a cool stand to reduce the stack height.

(4) Printing on rough paper by increasing the printing pressure and reducing the amount of ink.

(5) Control the pH and amount of dampening solution to prevent ink emulsification.

(6) Adjust the workshop temperature and humidity and rearrange the printing color sequence.

(7) The area of ​​the graphic text is too large and the ventilation is strengthened after printing.

(8) Adjust the amount of desiccant.

(9) Use a non-adhesive agent or a sticking liner.

In recent years, printing companies in many regions of the country have printed inks that have dried and filmed, and have not returned to the film or stuck in a short period of time. However, after the printing process or the finished product is delivered to the user for a period of time, the ink film feels. Non-smooth, refers to the severe phenomenon of sticking when sticking or sticking or packing. The reproduction of this phenomenon is actually due to the fact that the softening point of the ink binder of the packaging printing product is too low. Of course, when the ink is diluted, the ink is mistakenly added with too much slow-drying solvent or the appearance of dampness due to inhalation of moisture.

Approach

(1) Strictly choose the ink types produced by regular manufacturers and with technical parameters.

(2) Surface treatment should be performed on substrates that are stained with oils, waxes, etc. during printing.

(3) Select the ink with higher softening point in the ink system.

(4) In the dry printing, the ink of one color is printed after the ink of one color is about to dry.

(5) Strictly control the temperature and humidity of the printing shop.

Case number one

A certain factory in the south processed a batch of wine boxes, which had a relatively large area on the ground. The surface was sticky and stained on the back for several days after printing. After the investigation, it was found that this phenomenon occurred not only in a printing factory. Many printers have similar situations.

case analysis

This is related to the local temperature and humidity. Under normal circumstances, if the temperature is low and the humidity is high, the finished or semi-finished products after printing must be ventilated to avoid the above failures.

Case 2

A factory uses J2205 type machine, 157g/m2 paper to print off the portrait, when the yellow, magenta two-color printing and then printing sky blue, black, found that the first two color bonding is serious, the color of the edge of the stick is difficult to tear open.

case analysis

There are two possible reasons for this phenomenon. One is that the yellow and magenta inks are heavier and have a larger area. Second, the ink emulsification is more serious. This should not only pay attention to the amount of wetting fluid, but more importantly, the semi-finished products printed on the surface of the ink should be shaken after being formed into films, ie, the semi-finished products should be piled on another paper table after shaking.