Gravure ink composition, characteristics and preparation

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 ink composition Gravure printing is a printing method that is relatively lithographic and letterpress. 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% Auxiliary 0.5-4%
Filler 0-15% Organic solvent (volatile component) 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 Pigment is a colorful, easy to color, and have a certain intensity of colored matter. 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. Soft texture with vivid color, 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. Dispersion is good, coagulation and sedimentation will not occur during storage.
4. Dispersion in the binder can exhibit good flowability 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 will not corrode the roller.
7. Strong coloring, low oil absorption, pigmentation should not occur sublimation phenomenon.
Second, the choice of resin Resin is a generic term for macromolecules. 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 of the 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. Strong adhesion on the surface of the substrate, high surface hardness after film formation, good resistance to acids, alkalis, chemicals, and light.
2. Higher softening point (usually above 140 degrees).
3. Can form a suitable glossy and flexible ink film.
4. 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 printing ink, the solvent is also a kind of connection material. 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. Dissolves the dried ink film remaining on the plate. 4. Does not corrode printer rollers, doctor blades, etc.
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.
7. Mixed solvent. Refers to a solvent that combines two or more of the above solvents. The mixed solvent not only dissolves the resin well, but also adjusts the drying speed of the ink by changing the mixing ratio. Our factory uses a mixed solvent of toluene, ethyl acetate and ethanol. In gravure inks, both resin and solvent are binders. The main role of the binder is to bind the pigment on the surface of the substrate to form an ink film and achieve the purpose of displaying images and text. The pigments are transferred to the prints by the blocking effect of the binder. Secondly, on the printed products, the binder also plays a role of protecting color, showing luster and protecting the substrate. If the connection material is not prepared properly, it will not only fail to obtain bright and glossy prints, but also will produce a series of defects such as stencil, stickiness, scratches, and difficulty in drying. Even the connecting material is a gravure ink. The important component.
Characteristics of Gravure Ink 1. Flowability The fluidity is a comprehensive reflection of the relative density, viscosity, coagulation, yield value, thixotropy, and filament length of the gravure ink. Gravure inks are required to have better fluidity during the printing process. If the fluidity is not good, the viscosity of the ink is not easily controlled during the printing process. In the ink supply device, the ink is not smoothly conveyed, which may cause stencil printing, uneven coating, and the ink film may cause “orange peel”. Gloss is not good looking. However, the ink should have a certain color concentration and the pigment content should not be too low. However, when the pigment content in the ink reaches a certain level, it becomes a plastic fluid and the fluidity is very poor. In order to maintain good fluidity, the pigment and the binder should have good affinity. The binder should have an appropriate viscosity, proper wetting of the pigment, and minimum thixotropy and yield values ​​of the ink. Therefore, when preparing a gravure ink, the ink should be free and smooth, fine and uniform, and have a certain cohesion.
2. Viscosity Viscosity is the measure of the internal resistance of a fluid flow by the mutual attraction between fluid molecules and the ability to hinder their relative motion. The gravure ink viscosity is the right, is to ensure that it has a good transfer performance, get the key to good prints. And the viscosity can also determine the ink transfer rate, the viscosity is large, and the transfer rate is reduced.
The factors that affect the gravure ink viscosity are as follows:
1. The viscosity of the resin solution. The resin solution is a solution in which a certain amount of resin is dissolved in a solvent. If the viscosity of this solution is small, the viscosity of the ink is also small; otherwise it is large.
2. The matching of pigments and binders. If the condensation reaction does not occur between the pigment and the binder, the viscosity of the system is relatively small, and vice versa.
3. Miscibility and miscibility of solvents and resins. If the solvent can dilute the dispersion resin in any ratio, the viscosity decreases regularly as the solvent content increases.
When formulating a gravure ink, the ink's "usage viscosity" (the actual viscosity of the ink during the printing process) should be controlled within the range of 18-30 seconds/25 degrees.
Third, dry gravure ink is a volatile ink. The so-called volatilization refers to the process in which the energy of a liquid molecule reaches out of attraction between liquid molecules. Drying is the use of this property of the liquid, so that the solvent in the wet ink film escapes from the liquid to the solid volatilization process.
After the gravure ink is printed, it is required that the solvent in the ink layer escapes from the system instantaneously, so that the pattern speed of the print product is dry, so that the next process can be entered. The drying speed has a decisive influence on the tone, accumulation, and odor of printed products. When the drying is too fast, the ink remaining in the intaglio pit after wiping and wiping will reach the substrate immediately. The solvent will volatilize too quickly, the viscosity will increase and affect the ink transfer, and the high-light part will be under-inked. Paste version. At the same time, peeling occurs in the multi-color printing; when the drying is too slow, although the problem of transferability does not occur, the subsequent process cannot be performed, and overprinting is also difficult.
How fast the gravure ink dries depends on the volatilization rate of the ink solvent. The boiling point and volatilization rate ratios of various common solvents are listed below.