Metal ink introduction

Metallic inks are inks with a unique metal shiny effect that are made by substituting fine metal foils for pigments or dyes in traditional inks. The commonly used metallic ink is mainly silver ink and gold ink. The silver ink is made of aluminum pigments; gold inks are generally prepared from copper pigments and zinc pigments in different proportions. By controlling and changing their proportions, they can produce green gold, blue gold, and red gold inks or Required Pantone metallic ink.

Metal ink production process

The following are the basic production processes for metallic inks: Copper, Aluminum, and Zinc Raw Materials ➝ Melting, Atomization, Screening, Grinding, Screening, Filtering, Filtering, Mixing, Mixing, Finishing Compared to the production of common inks, the biggest difference is the production process of metallic inks. It is the preparation process of metallic pigments, especially the grinding process. Since the aluminum pigments tend to explode during the grinding process, a wet grinding process must be used. In addition, the metal ink uses the reflection effect of the metal foil particles to achieve a metallic luster. To ensure a good mirror reflection effect, the metal pigment grinding process is gentler than ordinary pigments to avoid breaking the shape of the metal sheet. During the grinding process, attention should also be paid to the selection of additives. Different types of additives can produce floating or non-floating metal inks. The former has good metallic gloss, but poor adhesion and wear resistance. It cannot be colored. Although the latter has a little metallic gloss, it has good adhesion and wear resistance, especially good coloring. Users should choose floating or non-floating products according to actual needs, which is very important, otherwise it will affect the performance of post-processing and final products.

Metal ink characteristics

The following describes the characteristics of the metallic ink from three aspects of optical properties, mechanical properties, and chemical properties.

1. Optical properties

(1) Differences from general ink optical characteristics

Because the optical properties of metallic pigments are different from those of common pigments, the optical properties of metallic inks produced are also very different from ordinary inks. The color of ordinary inks does not change with the observation angle, while for metallic inks, the change of viewing angle changes the hue and brightness of the metallic ink.

(2) Factors that affect the optical properties of metallic inks

The shiny effect of metal inks is the result of the combination of specular and diffuse reflections of metallic pigments. In order to achieve a better metallic effect, the specular reflection of the metallic pigment should be increased to reduce diffuse reflection. The main factors that affect the optical properties of ink are the following.

1 The larger the size of the metal pigment particle size, the better the specular reflection effect of a single pigment particle, and the higher the metallic gloss of the metal ink, the worsening of its hiding power and dot reproducibility. The smaller the size of the metal pigment particle size, the better the covering power and dot reproducibility of the metal ink, but due to excessive diffuse reflection of the edge, the metal gloss of the metal ink may be reduced. Users can choose the suitable particle size according to their own requirements, but choose a specific printing method. Different printing methods require the use of metal inks of different metal pigment particle sizes, otherwise there will be cases where the particle size is too large, the ink cannot be transferred smoothly during the printing process, or the particle size is too small to print well.

2 The particle size distribution of metallic pigments is also a factor that affects the optical properties of metallic inks. The particle size of the metal ink we usually refer to refers to the average particle size D50 of the metal pigment in the ink. For example, a metal ink of 10 μm means that 50% of the pigment particle size is less than 10 μm. This indicator is not very accurate. The description of the performance of metal inks is good or bad.

Many users will find that when you use different manufacturers of metal inks, although their technical data shows the same size of the particle size, but the metal ink hiding power and metal gloss after printing may sometimes be very different, this is because The metal pigments in different manufacturers' metallic inks have narrow and narrow particle size distributions. The same average particle size, the narrower the particle size distribution, the more uniform the overall arrangement of the pigment, the better the gloss and hiding power of the produced metallic ink, so the analysis of particle size distribution on the characterization and quality control of metallic pigments is Very important, it is also an important embodiment of the technical level of different metal pigment manufacturers.

3 The shape of metal pigment particles in traditional metallic inks is irregular and is called cornflakes (corn grain, see Fig. 1). Since the shape of each metallic pigment particle is irregular and the edges are not smooth, the specular reflection effect of particles is poor. The diffuse reflection on the edge is serious, so the metallic luster and hiding power of the metal ink are also poor. Aika used the latest condensation and grinding technology to produce a new type of silver dollars (silver dollar type, see Figure 2). Each particle of this metallic pigment has a nearly circular structure, a uniform size, a good mirror reflection effect, and an excellent ink metal effect and hiding power produced by it. Therefore, this new type of metallic pigment has been widely used as soon as it is introduced.

2. Mechanical properties

Since the metal raw materials used to produce metallic inks are relatively soft and thin metal sheets, they are sensitive to shear forces. Excessive shear forces can cause the deformation of the metallic pigment particles or the formation of many fine particles, making the final product optical. The performance is degraded. Figure 3 shows the effect of shear force on the metal pigment particles. So use some smoother material to stir while avoiding high speed stirring. It should be emphasized that many printers are accustomed to mixing ink with hard-edged metal tools, which is highly undesirable.

3. Chemical properties

Since the materials used to make metallic inks are all active metal materials, the chemical properties of metallic inks are also very unstable. They must be tightly sealed during use and storage, and should avoid absorbing too much moisture and direct light for a long period of time. Recycled metallic inks are also not suitable for storage for too long.

The advantages of metallic ink

In order to achieve a good metallic luster, the content of the metallic pigment in the metallic ink is generally 2 to 4 times that of the pigment in the ordinary ink, so the metallic ink has a higher price than the ordinary ink. In spite of this, because its unique expressive ability can enhance the competitiveness of products and attract more consumers' attention, metal ink printing is still welcomed by the packaging and printing industry. Metal ink printing has many advantages compared with other processes such as hot stamping and aluminized printing that can also achieve metal effects.

(1) It is easy to use, does not require equipment modification, and does not require more investment.
(2) Can be printed like normal ink, improving production efficiency.
(3) Save costs.

Precautions when using

(1) Due to the high density of metallic pigments, metal pigment inks are easier to precipitate than ordinary inks, and must be fully stirred before use. Before printing on the machine, check whether there is sediment at the bottom of the ink tank. Evenly, the hue and gloss of prints are quite different.
(2) In the printing process, the viscosity of the metallic ink will gradually increase with the constant volatilization of the solvent. In order to ensure the stable and good fluidity and transferability of the metallic ink, the viscosity of the ink is measured regularly and the solvent is appropriately added to make the ink. Viscosity is maintained within a stable range.
(3) Many printing companies often achieve color metallic effects by adding colorants or toners to metallic inks. It should be noted that due to the particularity of metallic pigments, some colorants or toners may cause the ink to thicken or change its properties. Therefore, it must be tested before use. Generally, metal ink manufacturers have their own colorants for customers to choose. .
(4) Metal inks are prone to gas generation, especially silver ink. During the transportation or storage process, a lot of gas may accumulate in the ink tank. Therefore, be careful when opening the packaging barrel to prevent the lid from bouncing off when the ink tank is vigorously opened. people.
(5) Since the price of metallic ink is much higher than that of ordinary inks, the gloss of recycled metallic inks will be significantly reduced. Therefore, under the premise of satisfying continuous operation, metallic inks should be added as little as possible in the printing process. You can recreate special ink tanks.

Conclusion

As a new type of printing ink, metal ink has expanded the creative space for packaging designers, opened up new ideas for the packaging industry, and applied them in cigarette packs, wine labels, industrial packaging, daily chemical product labels, and flexible packaging. Very extensive. However, we must also see that there are many imperfections in metallic inks, especially the quality of the mirrored silver ink series is not yet stable. In addition, many users do not understand the performance of metallic inks and improperly controlled production processes, which also discounts the printing effect of metallic inks.

The author believes that with the improvement of metal ink manufacturing technology and the deepening of the understanding of the printing industry, the use of metal ink will become more and more widespread. In particular, with the continuous introduction of environmental protection laws and regulations, metal ink will become the new darling of the packaging industry.

Reprinted from: Ink Information

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