Pigment is the main component of ink, is a fine powder-like solid colored substance, can show ball, flake and other irregular shape. Generally, the diameter of pigment particles is in the range of several hundred nanometers to tens of microns (10-7~10-5m). The pigment can be evenly dispersed in the medium, but it is insoluble in the medium and does not react with the medium. Pigment is a colored body, it gives the ink color, at the same time, its dispersion, aggregation and directly affect the fluidity of the ink, chemical stability and dryness. Ink factory pigment selection error or improper use of ink, will cause a lot of quality problems, pigment caused by quality problems, do the following analysis, for the reference of peers.

First, classification of pigments

Pigments can be divided into inorganic pigments and organic pigments according to the characteristics of compounds. In organic pigments, they can be divided into lake pigments, color pigments and pigment dyes according to different molecular aggregation states. According to the different molecular structure, it can be divided into azo pigments and phthalocyanine pigments. According to the color characteristics, it can be divided into color pigments (such as yellow, magenta, green, etc.) and achromatic pigments (such as black, white, gray).

Quality problems caused by pigment problems

1. Knife line problems caused by pigments

1)The pigment of the ink itself is badly ground, resulting in hard particles. (General ink fineness requirements ≤15μm).

2)When the ink is used for a long time, the resin wrapped in the pigment is missing, and the coarse particles produced by the pigment particles are clumped, condensed, and returned. In addition, the ink factory uses a carrier of color lake pigments, such pigments are soluble dyes precipitated with a precipitant, and then dyed on the high dispersion of aluminum hydroxide, barium sulfate, aluminum barium white and other carriers. This kind of ink will be used for a long time will wash away the dye, carrier separation, carrier clumping.

Solution

1)Turn upside down and shake the new ink before opening the bucket.

2)The new and old ink is filtered with more than 100 mesh filters before entering the ink plate.

3)The ink that has been used for a long time is found to have floating pigments on the surface of the ink plate, indicating that the resin is not enough, and the ink mixing oil should be added for sufficient mixing and dispersion. It is best to mix the old ink with a dispersion mixer, and the printing plant can prepare a simple dispersion mixer.

2.Pigment caused by poor ink temperature resistance, high temperature cooking or bag hot press after discoloration

Cause analysis

The ink factory used the wrong pigment, the use of non-temperature resistant pigment. The printing factory used the wrong ink, and the ink that did not withstand temperature was used on the products of high temperature cooking bags.

Solution

When purchasing ink, we should check the ink information provided by the ink factory, and scientifically choose good ink according to the temperature resistance of the product. Some companies have a lot of products, the use of ink types, such as surface printing ordinary ink, PVC ink, etc., different types of ink must be stored in different areas, it is best to place in the warehouse, to avoid employees to take the wrong ink, resulting in accidents. For example, the ink factory uses the pigment that is not resistant to temperature for high temperature cooking ink, so the ink factory should be isolated according to the type of pigment.

3.After high temperature cooking, different colors of bags, bags brittle, tensile strength becomes worse

Reason analysis

When the ink factory produces ink, the pigment is used incorrectly, some azo pigments are permeable, and the pigments penetrate into the film at high temperature, the film performance changes, the packaging bag becomes brittle, and the tensile strength deteriorates.

Solution: Replace the ink, or use the ink of other brand ink factory, and then cook at high temperature under the same conditions, and then compare the tensile strength after cooking. The most common yellow and red inks are prone to such problems.

4.Bag or label is not fast

Reason analysis

The pigment is not fast to sunlight and will change color for a long time, especially yellow and red.

Solution: When the packaging factory buys ink, first check the operating instructions provided by the ink factory, and choose the ink with a fast grade of 8 or more. The printing factory can do the fast light test first, and use it after passing the test to avoid causing greater losses to suppliers and themselves.

5.The envelope (CPP, PE single film) in a high temperature and high humidity environment, placed for a period of time after the red

Cause analysis:

After the surface printing ink containing cellulose nitrate printing PE or CPP film, under the condition of high temperature, high humidity and no ventilation, the color of the unprinted space will turn red. This is because under certain circumstances, cellulose nitrate decomposes into gaseous nitrogen oxide NOx at high temperatures, which REDOX reaction occurs with phenolic antioxidants in the film to produce colored quinone red substances.

Solution:

Place the product in a well-ventilated place after production. Use inks that do not contain nitrocellulose. This phenomenon is reversible, and the discolored film roll is placed in a sunny place until the color is restored.

Conclusion

Correct selection of ink, understanding of ink pigments and other basic knowledge is very important, help us to systematically solve the quality problems caused by improper use of ink in daily work.

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