Discussion on Quality Control of Plastic Gravure Printing Process (4)

4 solvent residue
National standard GB/T10005-1998 requirements for solvent residues for the total amount of <10mg/m2, benzene content <2mg/m2, and European and American countries have higher requirements for solvent residues, benzene content is generally not greater than 0  5<mg/m2. With the current level of printing in our country, the benzene content below 2mg/m 2 has been very difficult. The residual solvent mainly exists in the process of printing and dry recycling, while the benzene solvent is mainly caused by printing residue (if the drying path of the dryer is long, the drying capacity is sufficient, and sometimes the printed residual solvent is volatilized. ). Because, we are now mainly discussing printing solvent residues. 

Printed solvent residues mainly result from the following aspects:
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1Ink's own solvent release properties
Different inks have very different solvent release properties. In particular, some low-grade inks have relatively poor solvent release due to the use of relatively low-grade binder resins and pigments, and the residual amount of solvents in their prints is relatively large. The high-grade ink is better (such as Toyo's LA series ink, the residual solvent is very small). In addition, although the alcohol-soluble ink does not contain a benzene-based solvent, the solvent residue of the printed product is also affected by the solvent releasability of the ink itself. Therefore, before using the ink, it is best to understand the tendency of the residual solvent to the ink manufacturer in order to make corresponding treatment. 

2 The volatilization rate of the solvent
The solvents used in printing inks are basically mixed solvents. The volatilization rate has the greatest influence on the solvent residues. Excessive use of slow-drying solvents or high-boiling components in the mixed solvents can cause severe solvent residues. Therefore, the rational design of mixed solvent formulations is a very important technical problem. 
Impact of 3rd Edition Roll Design
If a plate has both a solid ground color and a very shallow layer, it is extremely difficult to control the residual solvent. When the volatilization rate of the solvent is increased, the plate will be blocked at the shallow mesh, and the volatilization rate of the solvent will decrease, and there will be a large amount of solvent residue in the field. Therefore, this design should be avoided as much as possible during plate making. 

4 Drying conditions
The drying conditions include the length of the drying oven, the air volume, and the air temperature, which determine the drying efficiency. Poor drying will increase the amount of residual solvent. However, it should be noted that increasing the air volume and air temperature will increase the drying efficiency. However, when the ink layer is thick, it may cause the surface to dry quickly, which will hinder the escape of the solvent in the inner layer and lead to an increase in the residual amount. 

5 printing speed 
The speed of printing determines the length of the drying time. It should be gradually increased to ensure that the printing ink layer is sufficiently dry. 

6Air humidity and concentration of organic solvents in the air
The increase in the air humidity and the concentration of organic solvents in the air can seriously impede the volatilization of the solvent in the ink layer, resulting in increased solvent residue. If conditions permit, sucking clean and dry fresh air into the drying oven will greatly benefit the reduction of solvent residues. 

7 printing film 
The solvent absorption of the printing film also has a great influence on the solvent residue. 8 Printed products can also reduce solvent residues if they can be treated with a certain amount of aging. Therefore, it is beneficial to put it in a ventilated place and recombine it after printing. 

In addition, I would like to say a digression here. In order to ensure the quality of the final product, the poorest barrier film should be used as a printing layer as far as possible when designing the product structure, and a barrier layer and a heat sealing layer with a higher barrier property should be composited underneath it to avoid possible internal packaging. Contamination of material. 

5 Imprinting is not allowed
Overprint quality is the most intuitive indicator of print, and it has many influencing factors. Due to the different equipment and overprint quality, we will only discuss the influencing factors under the same equipment conditions. Basically can be divided into: 1 printing substrate thickness uniformity. 2 embossing pressure roller deformation. 3 printing tension changes. The design of the 4th roller is irrational and the machining accuracy is poor. 5 The printing speed changes. 6 The drying temperature is too high. 7 roller sticky. 

If it is a computer, it will also be affected by the blocking of the scanning point, the dirt on the reflector, the ambient light, the dry hot air, the computer waveform, and the computer malfunction. 

In addition, problems such as scratches (fouling), blocking, ghosting, etc. may occur during the printing process. As long as everyone carefully observes and analyzes, the cause of the problem can be overcome. It is not discussed here.