Water-based gravure ink formula design principles

In the formulation of aqueous inks, it is necessary to simplify as much as possible the most variables, as long as the four basic components of the ink are taken into consideration. This is the resin, pigments, volatiles (water, organic solvents) and additives (defoamers, Dispersants, etc.).

Gravure inks and flexographic inks are significantly different. One of the important differences is that the gravure printing is directly transferred to the substrate. The ink film is the one-time ink obtained from the ink fountain to the substrate. Compared to the flexographic printing, the ink is transferred several times. On the substrate. This is a typical water-based gravure ink applied to non-absorbent substrates using a 175-mesh, 45-degree tilt, 32-μm-deep cylindrical plate that enables 12-μm 15-μm ink particles to be printed on. Things.

If the water-based flexographic ink is applied to 200 mesh, and the blade and speed are adjusted, this plate will allow about 5 μm ink particles to be printed on the substrate. The result is that the gravure ink contains approximately 6% to 10% of the pigment, while the flexographic ink contains approximately 15% to 18% of the pigment. The difference in pigment content will affect the viscosity of the ink. In general, the pigment content is high and the viscosity of the ink is large. For ink designers, it is necessary to consider the shape of the pigment particle size distribution curve. The larger surface area of ​​the uniform particles will increase the viscosity of the ink. The data for an aqueous gravure standard ink is listed in the table below.

Water-based gravure standard ink system

Gravure Standard Ink Typical Formula

Component Name Category Quality %/% Solid %
1 Water Solvent 51.5 0
2 Pigment Blue 29 Pigment 12.0 100
Thickener 1—98 Additive 3.0 32
4 Defoamer 1020f Additive 0.4 100
5 Surfactant CT-136 Additive 0.6 89
6 Ink sol 6264,190 proofing solvent 5.0 0
7 Styrene-acrylic emulsion Zinpol 295 Resin 12.0 49
8 Propylene glycol methyl ether solvent solvent 0.6 0
9 26% ammonia additive 1.7 0
10 Acrylic Emulsion Joncryl 89, Resin 6.0 45
11 Acrylic resin Joncryl 678 resin 5.8 100
12 Wax Emulsion John26 Additive 1.2 25
13 Surfynol 104H Surfactant 0.2 100

Raw material selection and production of water-based gravure ink

1. Selection of waterborne ink raw materials The composition of waterborne gravure ink is: water-soluble resin, pigments, various additives and water. With water and alcohol as solvents, the key to the development and production of water-based gravure inks is water-soluble resins.

(1) Resin Selection The key technology for producing water-based gravure inks is water-soluble resins. There are many kinds of resins, such as alcohol-soluble phenol formaldehyde resin, water-based amino resin, water-based acrylic resin, water-based maleic acid rosin resin, polyvinyl alcohol, casein, hydroxy cellulose, latex, or latex.
The principle of its water-soluble is: polymer resin contains hydrophilic groups -COOH (carboxyl), -OH (hydroxyl), -NH2 (amino). After a certain process, the resin is made into organic amine salts and completely dissolved in water. Therefore, it is now possible to use a reaction of a carboxyl group and an amino group to form a viscous liquid that is soluble in water after salt.
RCOOH+NH2CH2CH2OH RCONH2CH2CH2OH+H2O
Water soluble.

A, acid value The size of the acid value reflects the amount of carboxyl (-COOH) in the resin. Small acid values ​​(below 95) are insoluble in water. A high acid value indicates a low degree of resin reaction and a small relative molecular weight. The prepared ink has a low dryness, good dilutability and water solubility. The acid value of the lost modified half ester resin is generally controlled at about 135-155.

B. Process problems
Salt formation of the resin should be performed at a strictly low temperature. This reaction is carried out in a solvent. Since the neutralization reaction is exothermic, if it is not carried out under 60 and stirring is carried out, ether, alcohols, amines are volatilized in a large amount and excessive amides are generated, affecting the organic amines. The content of complex salt will make the resulting ink less glossy.

C. Problems with pH At the same time, there is a problem with the pH of the amine salt. The pH is preferably between 8 and 9.5. PH value is too large, water solubility is good, but the dryness is obviously slow; PH value is too small, dry fast, but the water solubility is not good. Aminated resin solution viscosity (35 °C) is generally 0.3 - 0.5Pa.s.

(2) Selection of pigments In the selection of pigments, it has been experimentally shown that salt-based lake soluble azo pigments are not suitable. Due to the presence of sulfonic acid groups, carboxyl groups, etc., which react with amines and other ions in an alkaline medium, the non-alkali-resistant pigments are reactively coagulated, and others are applicable. If you can make a filter cake with active agent, you can improve efficiency.

(3) Solvent Selection Since the water's dissolving power and wetting ability are not large, the corresponding cosolvent should be selected. The required cosolvent must have the following conditions.
A. The selected resins, amines and their salts can be dissolved and miscible with water energy in any ratio.
B. To be non-toxic, non-irritating, non-flammable, and non-explosive.
C. To have a certain dilution capacity, the boiling range and latent heat should be appropriate.
D. In the ink contains a certain amount, otherwise the amount of water in the formula decreases.
Examples of such cosolvents include ethanol, n-(iso)propanol, ethylene glycol monomethyl ether acetate, ethyl cellosolve, and butyl cellosolve. The content of the cosolvent is about 11% in the ink.

(4) Neutralizing agent selection resin is neutralized into organic amine salts and dissolved in water. If the neutralizing agent is not properly selected, printing adaptability will completely fail. Therefore, the neutralizer must have the following conditions.
A, soluble in water, and no special smell.
B. Can form salt with the selected resin residue.
C, has a certain degree of volatility and release.
Ammonia hydroxide can be used as a neutralizer, but it is too tasteful. Amines, such as ethanolamine, are better, and the amount used is dependent on the pH and generally exceeds the theoretical amount.

2. Production of water-based gravure ink

Water-based gravure inks must be explored and tested during the formulation process from the formulation, process, physical and chemical properties and indicators.
In order to prevent the ink from foaming during use, antifoaming agents such as tributyl phosphate and silicone oil may be added to the formulation in an amount of about 0.5%. To prevent coalescence and mold during storage and transportation, stabilizers and dispersants may be used, such as light Body silica gel, sodium hexametaphosphate, etc. Antisepsis can be used benzoyl, sodium benzoyl sodium, etc., in an amount of 0.5% - 1.1%.
According to experience, the design of the water-based gravure ink is best controlled in the following range of viscosity, dryness.
Ink viscosity 50-105mPa·s (25°C rotation viscometer);a
Primary dry 10-20mm/15s (25°C);
The dryness is not more than 100m/160s (25°C).
The dry form of water-based inks cannot be ignored. Since the latent heat of evaporation of water is relatively large, the drying speed is slowed down, and at the same time, because the ammonium salt is decomposed due to heat instability, it is mainly volatile and dry, and it is reactively solidified and dried. Once the ink film is dried, it becomes water-insoluble. It's up.
Drying process is: a large amount of water and co-solvent volatilization; deamination; dehydration.
Because the ink is water-based, it is required that the printing unit has corresponding cooperation in printing production, color drying equipment, and operation and operation for different papers.
In the production and production technology of water-based gravure inks, the film properties (gloss and resistance), printing and storage stability (viscosity reactivity, mildew resistance), and drying speed (deformation of materials, printability) are still the key points to be solved. Further research and solution.

Source: cigarette packets ink information network