Discussion on Quality Control of Plastic Gravure Printing Process (III)

Third, the common cause of failure in the gravure printing process

1 squeegee blade (knife wire, knife wire) 

Scratch marks are the faults that have the greatest impact on the quality of the printing process. The reasons for its occurrence and handling methods have been discussed in the "Guangdong Packaging". 

2  color deviation 

The color of the printed product is consistent with two aspects: on the one hand, it means that the same batch of colors is the same; on the other hand, it means that the colors of different batches are the same. For a printed matter, it is very difficult to ensure that it is consistent with the same batch, and the consistency of different batches is even more difficult. How to ensure that the colors of printed products are the same, we can refer to the article "How to Solve the Color Difference of Plastic Gravure" in Ma Pingdong's article in the third issue of Printing Technology magazine in 2001. 
I will simply outline and supplement this question below.
1 Effect of ink: This is the main factor that determines the consistency of the print color, the hue of the used printing ink should be stable, the color difference between the same batch and different batch should be kept as small as possible, and new ink should be added frequently during printing; for the spot color ink ( In particular, some spot colors formulated with white ink should be agitated frequently to prevent the separation of these composite colors; the ink should preferably remain sticky during printing; the solvent added during printing should not be contaminated by other colors. In addition, the ink used for printing should be the same as that used for proofing (same manufacturer, same series, same model) so as to ensure uniform color. 
2 The effect of the blade: The material of the blade, the size of the assembly, the position of the contact plate, the angle and the pressure have a great influence on the color of the print, especially the light color of the light screen. The softer the squeegee (or when the assembly is long), the darker the print. The larger the distance between the contact point of the doctor blade and the printing plate and the printing point, the lighter the color of the printed product. The greater the pressure of the blade, the lighter the color of the print.
Effect of the 3rd version of the roller: The plate roller becomes light after use for a period of time and the amount of ink is reduced resulting in color deviation. Therefore, after a certain number of prints, consider replating rolls. In addition, the color will become lighter if blocking occurs. 
Influence of other printing conditions: The temperature and humidity of the printing shop, the printing speed and the solvent drying speed, the printing pressure, and the hardness of the imprinting roller all affect the color of the printed product. 
5 Influence of the light source: It is best to use a standard light source (D65) or daylight as the light source, and the light source should be located directly above the light source.
Because of the difference in the spectral band of the light source, the hue of some colors will change. The difference in light source angle also affects the hue of the color. 
In the final analysis, when the color of a printed product deviates, it is necessary to consider several factors, such as the amount of ink applied to the ink, the amount of transfer, the color of the ink itself, and the condition of the light source during observation. 

3Incomplete (blocked and missed) 

During gravure printing, the ink will adhere to the recessed cells of the plate roller, and it will be transferred to the printing plastic film by the role of the platen roller. The transfer rate is different due to the difference between the printing material and the printing process. The general transfer rate is about 50% to 70%. When the transfer rate declines or does not transfer due to its species, it will cause the loss of network points or incomplete network points, because the loss of network points caused by the blockage of network points is called blockage, because the network points caused by the imprinting roller or substrate are lost. For missing prints. 

Blocking is mainly caused by ink drying, impurities, plate quality, ink quality or solvent quality:
Ink drying is basically caused by the following:
1 The old printing was not cleaned. 
2 The solvent drying speed is too fast (the printing speed does not match the solvent evaporation rate). 
3 Dry hot air is blown onto the plate. 
4 The distance between the contact point of the doctor blade and the platen and the embossing point is too large.  When dust, moisture, air bubbles, and other impurities are present in the ink, the ink transfer rate will decrease due to the decrease in the actual amount of ink in the cells, and some of the coarser particles may even be embedded in the cells. 

The precision and angle of electric engraving at the cell site during plate making will also affect the transfer of ink, resulting in insufficient or missing network sites.

The quality of inks and solvents is also one of the causes of blockage. If the fluidity of the ink is not good, the printing viscosity is too high, the ink has deteriorated or mixed with different series of inks, an inappropriate solvent or solvent ratio is used, even Inappropriate handling when adding solvent inks will affect the transferability of the ink and cause blocking. 

The influence of the active particles: When printing for a certain period of time, the ink will produce many active groups, these groups will be combined with the chromium ion of the plate roller, when these binders are in the shallow part of the gradient version, their binding force Impede the transfer of ink to the substrate, resulting in blockage, its basic performance is: shallow screen version of the flower. To solve these problems, you can add an active slowing agent (such as CHY-1 printing aid) to the ink. 

Leakage is mainly caused by pressure roller, film, improper operation, etc.:
1 uneven roller or air bubbles will cause serious leakage phenomenon. 
2 The film is corona or contaminated during use, causing partial corona insufficiency. 
3 The amount of ink in the ink tank is insufficient, and the printing roller is partially lack of ink. 
4 There is a hard object stuck under the printing blade, and the ink scrapes off to cause the ink mark scraper. 
6 Print missing due to blocking or ink peeling. There are many reasons for the adhesion and detachment of the ink. Everyone generally considers the ink, film, and solvent residues, but often neglects the mismatch between the temperature and the air volume during drying, the false drying phenomenon caused by the low temperature and high air volume, and the printing film after drying. Cooling is not enough. 