Paper bag printing has the following conditions:

1. Dot white dots.

The specific reasons are generally caused by static electricity of printing ink or static electricity of bearing objects. Or caused by the static electricity formed by diluting the solvent (because different solvents have different resistance). Generally speaking, it will appear when the temperature is high or the printing speed is fast. In addition, the front and back of the film are tight and loose, and the cause of static electricity is often seen in weather with high humidity.

The specific solution: the appropriate amount of antistatic agent can be added to the printing ink (excessive will directly affect the composite fastness), choose a solvent with small resistance to dilute the printing ink, and adjust the discharge and reception ground wire (generally speaking, the depth is 700 ~ 1500mm). Or control the humidity of the workshop.

2. Dot bleaching.

The specific reasons are caused by the poor mutual solubility of wax surfactants in the printing ink system. The second is mainly because the printing ink has not been redissolved in the printing process after the skin is transferred to the graphic.

Solution: Aromatic or ester true solvent should be added to promote it to dissolve again. Or install a blender in the ink hopper (such as the use of plastic pipes, on the outside of the unprinted plastic film, and then tie the two sides tightly in the ink head to rotate the printing ink), or add antioxidants to the printing ink manufacturing solution.

3. Crack-type bleaching.

One of the specific reasons is that the printing ink transfer performance is too poor, and the second is that the printing plate pattern is too shallow and the solvent in the printing ink system is most easily volatilized too fast.

In general, rough imprinting results in poor film formation, especially the bleaching caused by the inhalation of water in the printing ink system or the addition of ink diluent, most of which are generated in the summer workshop humidity is too high.

To solve the specific practice: replace the transferable printing ink or replace the deeper printing plate, or add a slow drying solvent to do the treatment. It is also possible to dehumidify the humidity of the workshop.

4. Whitening of the entire blot.

One of the specific reasons is that in the continuous printing time is too long, when the staff finds that the viscosity of the printing ink becomes sticky or thicker, a single solvent is repeatedly added, which breaks the balance of volatilivity of the mixed solvent in the original printing ink system, resulting in the rough and white ink layer when the printing ink film is formed. The second is that even if the operator adds the mixed solvent, the excessive addition usually reduces the content of synthetic resin in the printing ink, and the above-mentioned whitening phenomenon will also occur.

Specific solutions: one is to add 3% to 7% slow drying solvent, especially the true solvent that can plasticize the printing ink and resist the intrusion of water molecules; The second is the use of special thinner containing resin; The third is to add 5% to 15% of the ink mixing oil in the printing ink to overcome the bleaching caused by insufficient resin content, and the fourth is to install a central air conditioner that can regulate temperature and humidity in the workshop or eliminate it with a moisture absorber.

On the whole, most of the causes of bleaching are too high humidity in the workshop or working environment, and priority dehumidification can be more convenient and quick to find the cause of whitening phenomenon of Paper bag printing.

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