Rotational plastic gravure in the dirty version of the solution to the problem

In plastic printing, high-speed gravure gravure printing often causes dirty-printing problems. The phenomenon is that the non-printing surface of the cylinder is also stained with a layer of resin (entrained pigment in the resin) and is transferred to the substrate to make printing. The object is flaky or appears as a serious thread stain.

The reasons are as follows:

1. The resin has an affinity for the chrome surface of the drum.

2. The system composed of the resin and the organic solvent is in an oversaturated state. A large amount of resin precipitates and is not dissolved by the solvent.

3. The ink has strong wettability on the surface of chromium, or the solvent used in the ink is a slow-drying solvent.

4. Scraper wear or poor grinding.

5. Scraper angle is wrong.

6. The surface of the roller is in poor condition (such as stencil, chrome plated, etc.).

Because a large amount of resin precipitates and coalesces together and the affinity of the resin to the roller, under the pressure of the blade, the resin will be tightly cut on the roller, which is the most important reason for the dirty plate. We know that solvents have the ability to dissolve resins or additives and auxiliaries, making pigments and resins easy to disperse, reducing the degree of linkage, and helping to attach the drum. Therefore, as long as the colloidal system composed of resin, pigment and organic solvent is not in the state of supersaturation, the resin does not separate out and does not coalesce, but a uniform and dispersed colloidal system, so that the pigment and resin in the ink have Better dispersion and fluidity. The affinity of the resin to the roller will not be clearly manifested, and the dirty printing phenomenon can be substantially avoided. Therefore, in addition to considering the strength of solvent dissolution, we must also pay attention to the ink's ripeness.

For the first three reasons, we can use the following measures to solve the dirty version.

1. Use solvent with strong dissolving power and volatile solvent. For example, the following solvent formulas can be used:

Toluene: Ethyl acetate = 1:1 or

Toluene: Ethyl acetate: Butanone = 4:3:3

The ratio is volume ratio, which can be appropriately changed according to production conditions and other quality requirements. Sometimes it is necessary to add appropriate amount of isopropanol to increase gloss and give better leveling.

2. Control the viscosity of the ink, according to our practical experience, such as using the Zahn No. 3 cup to measure, generally between 12s and 16s, the resin dissolves more completely and evenly dispersed, which can make the ink in a more ideal state. In the production process, we need to use a lean controller or artificially replenish the solvent according to the loss of various solvents to maintain the stability of the viscosity so as to ensure the ideal state of the ink.

3. We can choose to use a slightly rigid blade, soft blade scraping ink is not ideal, hard blade is easy to damage the drum, or to reduce the distance between the scraper blade and the hard piece (usually between 3mm ~ 5mm) . And use whetstone to grind, smoothen the edge, and then use metallographic 2# sand paper to polish.

4. The squeegee angle must be at an ideal angle (contact angle between 50° and 70°).

5. The drum needs to be polished with metallographic 2 # sandpaper before printing. If the drum is seriously damaged, it should be chromed again.

In short, doing the above 5 points, the dirty version phenomenon can be solved.