Gravure ink composition, characteristics and preparation (1)

In the modern packaging and decorating printing process, gravure printing has been more and more widely used due to its thick ink layer, rich layers of prints, strong three-dimensional impression, stable color, high printing speed, and high print durability. Our factory is a professional cigarette label printing factory with several decades of history. In 1995, our factory introduced two gravure gravure printing production lines from French ATN company, which are specially used for printing soft and hard cigarette packaging. From printing, indentation, embossing, to die-cutting molding, 500,000 large boxes of various types of cigarettes are printed annually. However, in our work practice, we have found that gravure inks have a great influence on the quality of printed products. If the ink is not properly selected, or the ratio of the solvent is not appropriate, there will be a paste, a dirty path, a missing dot, and the printed product will not wear. In order to avoid this kind of phenomenon, it is necessary to understand the composition and characteristics of the gravure ink, and it is very easy to know when preparing the ink. Based on the work experience of the past few years, the composition, characteristics and preparation methods of the gravure ink are described below.

Gravure printing is a printing method that is relatively lithographic and letterpress printing. The image and text on the gravure are lower than the blank, and the shades of the original are expressed in terms of the size, depth, and shape of the image point. Due to the high printing speed of the gravure printing machine, the ink film is also required to dry fast. The gravure printing ink layer is very thick (gravure printing ink film thickness is generally 9-20μm, lithographic ink film thickness is only about 4μm), oxidized conjunctiva alone can not achieve the purpose of fast drying, so most of the gravure ink is used high Volatile quick-drying ink.

Its composition is roughly as follows: Pigment (dye)
10-15%
Solid resin (binder component)
25-35%
Adjuvant
0.5-4%

Filler
0-15%
Organic solvents (volatile components)
40-60%

Among the above-mentioned raw materials, pigments, solid resins and organic solvents are the three most important elements of gravure printing inks and are the key to determining ink performance.

First, the choice of pigment

Pigments are colored materials that are colorful, easy to color, and have a certain intensity. It colors the object with highly dispersed fine particles, or adheres to the body to be colored by means of a medium. In gravure printing inks, organic pigments are mainly used, and some inorganic pigments are also used to increase the hiding power of inks to meet the requirements of color varieties. In solvents, the degree of solvent resistance of a pigment (including chemical and physical stability) is the key to the success of a formulated ink.

The choice of gravure ink pigments depends on the print's requirements for color water resistance, solvent resistance, and lightfastness. In general, the selected pigment should meet the following conditions:

1. The texture is soft and vivid. It will not abrade the plate roller.
2. Good affinity with the resin binder, easy to disperse in the binder, no chemical reaction, no precipitation on the surface of the printed product.
3. Good dispersion, no condensation and sedimentation during storage.
4. Dispersed in the binder can exhibit good fluidity, and does not deteriorate due to storage.
5. Discoloration and discoloration do not occur in the corresponding solvent system, and there is good solvent release when the system is dry.
6. The free acid in the pigment does not corrode the rollers.
7. Strong coloring, low oil absorption, pigmentation should not occur sublimation phenomenon.

Second, the choice of resin

Resin is a general term for high molecular substances. In the gravure ink it is the binder of the pigment and at the same time it is a film-forming substance. It adheres the pigment to the substrate, and gives the ink with considerable strength and printability, so that the ink has sufficient leveling, ductility, gloss and the like on the substrate. Some properties of gravure inks, such as stickiness, gloss, dryness, abrasion resistance, and various corrosion resistance, are largely determined by the resins they contain. Whether the type of resin and its relationship with solvents and pigments meet the requirements for ink production, whether it can achieve the expected printing effect, depends heavily on the resin.

In the gravure printing ink, the selected resin should meet the following conditions:

1. It has strong adhesion on the substrate surface, high surface hardness after film formation, good acid and alkali resistance, chemical resistance and light resistance.
2. Higher softening point (usually above 140 degrees).
3. Can form a suitable glossy and flexible ink film.
4. It can form high concentration and low viscosity system with the selected solvent.
5. Good solvent release for quick drying.
6. Has good affinity and wettability with pigments.
7. Light color, odorless, transparent, reconstituted after drying.
8. Does not change color, does not damage the layout. It is stable in storage and does not react with pigments.

Third, the choice of solvent

In gravure inks, the solvent is also a binder. It is a true solvent for dissolving high-molecular substances such as resins, as well as a diluting diluent and a co-solvent for latent dissolution. However, its role is relative, that is, it is a true solvent for a certain kind of resin, but it is a kind of auxiliary solvent for other types of resin, and even two kinds of solvents are not real solvents for a certain kind of resin, but mixed together it is an excellent one. Solvents.

Solvents are used in gravure inks to dissolve resins, determine ink drying performance, and high speed ink viscosity. Whether the solvent and the resin adapt, the influence of the solvent on the pigment, the proper boiling point of the solvent, the flammability, toxicity of the solvent itself, etc. will also affect the quality of the ink.

In the case of gravure inks, liquid substances which can dissolve solids and semi-solid substances and form a transparent or light-colored solution can be used as a solvent, auxiliary solvent or latent solvent at room temperature or no higher than the boiling point. They must have the following conditions:

1. The boiling point is 80-150 degrees and it is inexpensive.
2. Can fully dissolve the selected resin.
3. Can dissolve the dried ink film remaining on the plate
4. Do not corrode printer rollers and doctor blades.
5. Non-toxic or micro-toxic, no abnormal irritant.
6. Have a suitable volatilization rate.

Solvents need to have good solubility, which means that the solute can be fully saturated at a certain temperature. The solvent is preferably one that can dissolve a large amount of the resin and has a relatively low viscosity of the binder.
The commonly used gravure ink solvents mainly have the following types:
1. Fats. Solubility is not so good, toxicity is low, and price is cheap. Such as gasoline, kerosene, n-hexane and so on.
2. Aromatic. Good solubility and toxicity. Such as: benzene, toluene, xylene and so on.
3. vinegar. Strong dissolving power, strong fruit smell, high price. Such as: ethyl acetate, butyl acetate and so on.
4. Alcohols. For some resins, the solubility is good, the odor is also good, the price is slightly higher, such as: ethanol, isopropanol, butanol, ethylene glycol and so on.
5. Ketones. Has a very strong dissolving power and bad smell. Such as: acetone, cyclohexanone.
6. Ether system. It has strong solubility in some resins, mild odor, and anti-freeze, but the price is high. Such as: ethylene glycol ether, ethylene glycol butyl ether and so on.