Seven notes on adding anti-crust agent to offset printing ink

The oxidation of printing ink, the oil of modified resin, the amount of pigments, fillers, driers used, the environmental temperature and humidity during the storage of the finished ink have a certain effect on the crust of the ink, so they are used in When anti-crusting agents are used, the above factors must be taken into consideration. At the same time, the basic knowledge of the following seven aspects such as the amount of addition should also be noted:

1. Amount added

Generally calculated according to the ink material (because the main component of the skin is the main raw material of the ink) or calculated according to the total amount of printing ink, while also considering the influence of other components.

Usually the amount of addition is between 0.1-0.3%. Because of the difference in temperature and humidity throughout the year, there is a certain difference in the speed of skin formation. Therefore, it is 0.1% in winter, 0.3% in summer, and 0.2% in spring and autumn, depending on the ingredients of the formula.

2. Ink film drying rate

We have proved in practice: in offset inks made by alkyd resin, the amount of methyl ethyl oxime is generally 1%. Although the drying speed is slightly longer, it is still within the standard range of printing regulations. This is because the complex formed by the adjuvant and the drier causes the drier to temporarily lose its activity, so it is different from the traditional principle of using a phenolic compound to capture the activity and freely terminate the polymerization reaction. Therefore, the influence of such compounds on the drying rate is not great. If the amount is too large, the volatilization time is prolonged. After the complex is disintegrated too slowly, the film printing speed of packaging printing ink is often affected.

3. Yellowing

Once the anti-skin agent exceeds 0.3%, it will often cause yellowing of the printed graphic ink film. Especially when used in white ink, yellowing will occur after long-term storage, so strictly controlling the amount of addition or changing to butyraldehyde oxime can avoid the occurrence of yellowing.

4. Color

After adding anti-crust agent to the ink, it often directly affects the color of the ink. Usually, the adjustment ink affects more than the color ink, and the white or yellow ink affects the dark ink. Generally, this phenomenon is difficult to observe by visual inspection and has nothing to do with the amount of addition. Although we already know that the printed image and text film drying has no effect on the hue of the ink film application, but in the presence of certain pigments (such as amphoteric pigments) and driers, the color tone of the color graphic ink film for packaging printing There will be a significant difference between them, which has disturbed the hue. When we encounter this kind of situation, we should make continuous proofs during the ink making process and make the color difference test first. Its purpose is to avoid affecting the appearance quality of the ink film due to color change after printing.

5. Printing ink film status

Although the anti-skin agent will not have any effect on the state of the printed ink film, when the ink is stored for a long time, crystals will be precipitated, resulting in turbidity of the ink after film formation and affecting the gloss of the ink. If the material and the binder, pigment, filler and drier in the ink system are not properly designed and matched, larger particles will appear. This should be tested before printing.

6. Gloss and weather resistance

After adding the anti-skin agent, the gloss of the printing ink will not only be affected, but also the gloss retention. Second, after adding the auxiliary agent, the weather resistance of the printed graphic ink film has been significantly improved and improved.

7. How to use

Anti-crusting agents are generally added during ink adjustment and are added with stirring at room temperature. For volatile inks, in order to control the ink, the coloring material will form a skin during the grinding, dispersion and storage, especially during the printing process. It is advisable to add a part of the ink during printing, and add a part before printing.

Above we have made some discussions on the causes and treatment of ink skinning. In actual work, we may encounter various problems of one kind or another. After the principle of drying), it should not be difficult to analyze and judge.