Problem of Material Selection in High-Temperature Cooked Intaglio Compound Ink Formula (Part 2)

3.2 The choice of pigment

High temperature resistant cooking gravure plastic composite ink has a series of special requirements for pigments: 1 color should be bright; 2 gloss is better; 3 high coloring power, which is a measure of the use of pigment and the economic value of the conditions; 4 transparency and hiding power is better Depending on the application of the ink, the transparency and hiding power of the pigment have different requirements; 5 The amount of oil absorption should be small, so that the ink concentration can be easily increased, the ink property can be easily adjusted; 6 the wetting and dispersing property is better, and the pigment is connected in the ink The dispersion ability in the material directly affects the success or failure of the preparation of the ink; 7 other physical and chemical properties, such as light resistance, heat resistance, solvent resistance, acid and alkali resistance, resistance to migration, and other pigments with few properties, only according to the application The special requirements, choose the right variety.

The pigments used in high temperature resistant intaglio plastic composite inks must first be solvent-resistant, followed by high-temperature cooking, and can withstand temperatures above 160°C without discoloration. According to the standard, the black pigments used in the ink are all carbon black; most of the white pigments are rutile titanium dioxide; the pigment inks are tested conditionally, such as the pigmented condensed azo and benzimidazolone azos. Ingredients, indigo blue, and indigo green, etc., they can be 200 °C high temperature without discoloration.

3.3 Selection of Wetting and Dispersing Agents

The wetting and dispersing of pigments is an important part of the manufacturing technology of high temperature resistant intaglio plastic composite inks. The pigments are crushed into fine particles and evenly distributed in the ink binder to obtain a stable suspension mixed system. The dispersion of pigments in the ink is quite complex and is generally considered to be related to wetting, smashing, and stabilization. Wetting refers to replacing the adsorbent on the surface of the pigment such as air, moisture, etc. with a resin liquid, an organic solvent, or an additive, that is, a process of changing from a solid/gas interface to a solid/liquid interface; smashing refers to using a mechanical force to agglomerate The secondary particles disperse into fine particles close to the primary particles to form a suspension dispersion; the stability means that the suspension dispersion formed can still be in a dispersed suspension state without external force. Wetting and dispersing agent is a kind of special surfactant and it has both pigments

Wet and spread two functions. Its wetting and dispersing action is to reduce the surface tension of the substance, so that the molecules of the surfactant are adsorbed on the surface of the pigment, thereby generating charge repulsion or steric hindrance, preventing the pigment from producing harmful flocculation and leaving the dispersion system in a stable state of suspension. . The dispersant for high temperature resistant cooking gravure plastic compound inks is generally anionic surfactant. Its main component is carbonic acid ester or special metal aluminum chromium complex, light yellow or yellow brown liquid, it is an oil-soluble dispersant, improving Dispersion of pigments in the ink prevents flooding and discoloration of pigments in the ink, improves color concentration and color development, and enhances adhesion and composite fastness of the ink film to the plastic film.

3.4 The choice of wax powder

High temperature resistant cooking gravure plastic compound ink formula usually add some special wax powder, it can provide excellent anti-abrasion and scratch resistance for printing ink film, anti-adhesion and increase ink fluidity, improve printability and improve Processing performance. Since the wax particle diameter is about 5 μm, which is larger than the diameter of the pigment particle and the thickness of the ink film, the wax particle can protrude the ink film and make the ink film surface rough. When the plastic film is printed on the ink for a long period of time, the rough ink film is advantageous in preventing the back side from sticking, and it is also advantageous for the uniform coating of the post-processed glue to enhance the composite fastness. Adding wax powder to the ink can also eliminate the drawback that the ink can easily fall off the roller during high-speed printing.

Most high temperature resistant cooking gravure plastic compound ink formulas should use high molecular weight straight chain type synthetic polyethylene wax with high melting point and strong hardness. There are two methods before and after adding. The general added amount is 1%～2% of the total weight of ink. Under normal circumstances, it is added before the ink is grinded, which is favorable for dispersing and improving the fluidity. Note that the grinding temperature should not be too high, so as to avoid deformation and aggregation of the wax particles and affect the performance. There is also a paste made of resin and organic solvent, which is added during the tack-adjustment and color-matching stage of the ink. However, in order to do so, it is necessary to prevent some organic solvents with strong penetrating power from dissolving the wax particles, resulting in recrystallization and coarsening. Some performance.

3.5 Selection of Antistatic Agents

When the gravure plastic ink is printed at a high speed, due to accumulation of static electricity, it may cause problems such as offset, blur, spots, beards, and edge repulsion. In serious cases, fire or explosion may occur. Therefore, adding an antistatic agent to the ink is to reduce the surface resistance of the plastic film during the printing process and eliminate the static electricity to solve the above-mentioned problems in printing. Anionic antistatic agents are generally used in plastics and inks, including higher fatty acid salts, alkyl phosphate salts, alkyl sulfate salts, and sulfonate salts, which are soluble in water, ketones, and alcohols. Organic solvents such as benzenes and benzenes are sold as aqueous solutions of organic solvents containing 30% to 60% of actives. High temperature resistant cooking gravure plastic composite ink is mainly used as the antistatic agent of ethyl phosphonate isopropanol solution, the added amount accounts for 0.1% ~ 0.3% of the total ink, without any adverse effects on the ink.

3.6 Adhesion Promoting Resin and Fumed Silica Powder Selection

In the ink system of polyurethane and chloroacetic resin, since the flexibility of the chloroacetic resin itself is not enough, it is necessary to use an adhesion promoting resin to improve its flexibility. High temperature resistant cooking gravure plastic composite ink formula will add some modified chlorinated polypropylene resin solution, the solid content is generally about 20%, increase the adhesion of polyurethane ink on the plastic film, enhance the dispersion effect and fluidity. Fumed silica powder, also called matt powder, is generally easy to disperse after it is organically surface-treated. Its role in high-temperature cooking-retarding plastic composite inks is:

1 Prevent pigment from settling and maintain the long-term rheological properties and fineness of the ink;

2 Improve the sag of the ink film when the ink is printed on the machine to prevent the generation of water marks;

3 It can also be used like wax powder to facilitate uniform coating of adhesives and improve composite fastness.

3.7 Selection of Organic Solvents

The plastic gravure ink is mainly formed by the solvent evaporation and drying. When the ink is printed on the surface of the substrate, the ink film thickness decreases and shrinks due to the volatilization of the solvent. The solvent evaporation of the ink solvent film is mainly divided into two stages: the first is the "wet stage" controlled by the surface layer; the second is the "dry stage", and the solvent volatilization rate is controlled by the diffusion of the solvent inside the integral ink film.

When there is a true solvent, it ensures that the resin and other polymers fully stretch and interact with each other, and the leveling property is good. If the true solvent volatilizes too quickly and only the co-solvent remains in the residual solvent, the polymer molecules tend to form a tight curl or even precipitate out. It is particularly important that solvent evaporation causes endothermic cooling and a rise in polymer concentration, which increases the surface tension of the ink film and causes the solution to flow from a low surface tension zone to a high surface tension zone. This is a peak-wool flow, which easily produces “orange peel”. And floating color phenomenon, so to maintain the necessary amount of true solvent is an important condition to ensure the ink film leveling.

For polyurethane and vinyl acetate resin ink systems, toluene, xylene, ethyl acetate, butanone, isopropyl alcohol are commonly used solvents, but also methyl isobutyl ketone, ethylene glycol monobutyl ether, propylene glycol Ether and other special organic solvents. Among them, benzenes and alcohols are only auxiliary solvents for polyurethane and chloroacetic resins. Ketones and esters are true solvents, but the evaporation rate is too fast. Therefore, special solvents such as methyl isobutyl ketone, ethylene glycol monobutyl ether, and propylene glycol methyl ether are also used to adjust the volatilization rate and solubility, enhance the dispersive power of the mixed solvent, and increase the dissolution parameters so that the ink always presents a good fluid. State, to ensure the smooth progress of the printing work.

Source: Network of thermosetting resins: Yu Durkin