Study on Dispersion Process of Water-based Plastic Gravure Printing Ink

This paper studied the preparation of water-based plastic gravure printing ink by changing different pigment dispersion technology parameters, and investigated the effect of ink dispersion technology on dispersion effect. The results show that using zirconia beads as grinding medium in sand mill has better grinding and dispersing effect of pigment than using glass beads. When using a sand mill to grind disperse pigments, a suitable diameter of grinding medium should be used. Grinding time has a great influence on pigment dispersion, so enough grinding time should be ensured. The effect of homogenizer on pigment dispersion is better than that of sand mill.

 

Waterborne ink is a new kind of green packaging printing material. Water-based inks do not contain volatile organic solvents, so it is a promising environmentally friendly printing ink. Water-based ink has developed from a single carton ink to a variety of substrates, multi-color overprinting, ink will be in paper, aluminum foil, vacuum aluminum film, gold and silver card, composite plastics, polymer plastics, metal and other substrates printing comprehensive development. Western developed countries have increasingly used water-based ink as packaging printing ink. Compared with solvent-based ink, water-based ink currently has low color density, poor gloss and other shortcomings, in addition to the national policy on solvent-based ink has not strict restrictions, so the development of water-based ink has not been popularized.

 

During the preparation of printing ink, pigment dispersion in the connection of material, but not the most energy and time-consuming process, grinding and dispersing directly affect the quality of the product, and the accuracy of the formula, the uniformity of ink and fineness control process, so the stand or fall of dispersion equipment, dispersion process control has a great impact on the quality of printing ink. Printing ink grinding equipment mainly includes sand mill, high-speed dispersing machine, roller mill, etc. Gravure printing ink belongs to liquid ink, usually using sand mill for grinding.

 

The water-based plastic gravure printing ink prepared in this experiment is a water-based ink system with acrylic resin as the connecting material. The abrasive dispersion of pigment in water-based ink system is a new topic in the field of ink. Foreign mature water-based plastic gravure printing ink production is also using sand mill for grinding and dispersing, and domestic water-based plastic gravure printing ink has not mature products, which is inseparable from the ink formula design and ink dispersion process is not perfect. At present, there are many researches on formula design of water-based plastic gravure printing ink in China, but few researches on dispersion process.

 

In the preparation process of water-based gravure printing ink, the dispersion effect of pigment in the resin directly affects the printing properties such as coloring power and adhesion of the ink. This study focuses on the dispersion effect of water-based gravure printing ink. Test in the first choice of the gravure ink preparation commonly used sand mill as dispersing equipment, in the process of preparing ink change of grinding media type, the diameter of the grinding media size and grinding process parameters such as time, use investigation prepared under different process parameters of laser granulometer ink dispersion effect, study the effect of different process parameters on the ink dispersion effect. In addition, the high pressure homogenizer with high performance dispersing equipment is used to disperse the ink, and the influence of different dispersing equipment on the dispersion effect is compared.

Ⅰ. The Experiment

1. The Raw Material

Pigment:

  • Carbon black (CABOT);
  • Brilliant blue.

Resin :

  • AZR acrylic resin;
  • S-2661b acrylic resin.

Additives:

  • dispersants 750 and 760(Digo additives);
  • Defoaming agent 810(Digao additives);
  • Wetting agent 245(Digco additive).

2. The Equipment

  • X-rite 530 densimeter;
  • 45 degree gloss tester;
  • Gj-2s type high speed stirring disperser;
  • Gravure prototyping.

3. The Method

Ink preparation:

The use of sand mill and high pressure homogenization mechanism to prepare ink, in the process of ink preparation to change the grinding medium type of sand mill, grinding medium particle size and grinding time and other process parameters.

Measurement:

Using laser particle size meter to measure ink particle size distribution.

Ⅱ. Results and Discussion

1.Influence of Different Kinds of Grinding Media on Dispersion Effect

In the experiment, two kinds of grinding media with the same diameter and a certain volume were selected. Under the same conditions of other grinding, the same amount of base ink was ground by using a sand mill, and then the particle size of pigment was measured by laser particle size meter, and the grinding effect of different grinding media was compared. The test results are shown in Figure 1.

As you can see, the grinding effect of zirconia beads is better than the grinding effect of silica beads. The size of the diameter of zirconium beads is nearly 1 cent of the size of zirconium beads after the diameter of the zirconium oxide beads. The minimum size of the two kinds of grinding media is the same.

This is because the density of the two grinding media is not the same, the density of glass beads is 2.4 ~ 2.6g/cm3, the density of zirconia beads is 6.0g/cm3.

Generally speaking, under the same diameter and speed of motion, the greater the density of the sphere, the greater the energy it has, and the greater the shear force generated by collision and friction. So the grinding effect of zirconia beads is better. The minimum particle size that can be achieved after grinding is closely related to the diameter of the grinding medium. There must be a certain gap between the grinding medium spherical body, the size of these gaps determines the size of the minimum particle size can be ground, two kinds of grinding beads with the same diameter, so the minimum particle size after grinding is the same.

2. Influence of Grinding Media with Different Diameters on Dispersion Effect

In the experiment, three kinds of zirconia beads with different diameters and a certain volume were selected. Under the same other grinding conditions, the same amount of base ink was grinded with a sand mill, and then the particle size of pigment was measured with a laser particle size meter, and the grinding effect of zirconia beads with different diameters was compared. The test results are shown in Figure 2.

It can be seen that the grinding effect of zirconia beads with particle size of 1.6 ~ 1.8mm is better. In general, the finer the dispersion of the product is required, the smaller the diameter of the grinding medium is used, because from the principle of grinding dispersion, the smaller the diameter of the grinding medium, the greater the probability of shear action in the sand mill barrel body collision. Therefore, the grinding dispersion efficiency is also improved.

However, this does not mean that the spheres can be reduced indefinitely, because the shear force generated when the spheres collide with each other is directly proportional to the diameter of the spheres. When the diameter of the spheres decreases to a certain value, the shear force will drop to insufficient to disperse the pigment aggregates, which makes the pigment dispersion rate drop sharply.

3. Influence of Different Grinding Time on Dispersion Effect

In the experiment, a certain amount of ink samples were taken from the sand mill at regular intervals, and then the laser particle size meter was used to measure the grinding effect. The test results are shown in Figure 3.

 

It can be seen that with the increase of grinding time, the pigment particle size has a trend of decline. With the increase of grinding time, the particle size of the part with small particle size decreases relatively little, and the particle size of the part with small particle size basically does not decrease again after 1 hour of grinding. With the increase of grinding time, the particle size of the part with high particle size decreased relatively larger, but after 1h, the particle size decreased significantly.

At the time of grinding, the base ink is dispersed under the collision and grinding of the medium, and the particle size is gradually reduced. But due to the problems of the equipment itself and there are certain gaps between the grinding medium, so the pigment particle size can not always be reduced, when a certain value is reached, the pigment particle size will reach the minimum value, will not decrease with the growth of grinding time.

4. Influence of Different Grinding Equipment on Dispersion Effect

Abrasive mill and high pressure homogenizer were selected for grinding test, and then the particle size of pigment was tested by laser particle size tester, and the grinding effect of the two grinding equipment was compared. The test results are shown in Figure 4.

It can be seen that the grinding effect of homogenizer is better, the pigment particle size has an overall decrease, the decrease of the pigment particle size of small particle size is larger, and the decrease of the pigment particle size of large particle size is smaller.

High pressure homogenizer with high pressure reciprocating pump as the power transmission and material conveying mechanism, the material conveying to the working valve (one level of homogenization valve and two emulsification valve) part. To deal with the material in the process of working through the valve, under high pressure to produce strong shear, impact and cavitation, so that the liquid material or liquid as the carrier of solid particles get ultrafine refinement.

The grinding and dispersing effect of homogenizer is better than that of sand mill. But the homogenizer is not suitable for industrial production because of the cost and grinding time problems.

Ⅲ. Conclusion

The results show that using zirconia beads as grinding medium in sand mill has better grinding and dispersing effect on pigment than using glass beads as grinding medium. When using a sand mill to grind disperse pigments, a suitable diameter grinding medium should be used. The grinding time has great influence on the dispersion of pigment, so enough grinding time should be ensured. The effect of homogenizer on pigment grinding and dispersing is better than that of sand mill.

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