Application of Special Luster Pigments in Packaging Printing

For many print users, special gloss pigments are a relatively unfamiliar concept, but if you talk about pearlescent pigments and pearlescent effects, the printing industry is much more familiar, such as the Merck series. The traditional “pearlescent pigment” is semantically very limited, and it is easy to mistake that the effect of this pigment is like pearl: white, translucent, soft and elegant. In actual fact, even if the series has a variety of changes, such as the S-grade (10 ~ 100μm) pigments, the particles are relatively coarse, and the texture and soft pearls are completely different. For example, iron oxide pigments of the 300 and 500 series show no metallic luster in the pearl.

Therefore, products with a layered structure that expresses luster on the refraction/interference principle are represented by "special luster pigments" that are more accurate or more representative.

At present, in the domestic packaging field, the application of special luster pigments is more and more common, not only because of unique luster effect, but also because it is easy to use, flexible, and more economical and environmentally friendly. For most high-end consumer goods packaging, such as cigarettes, alcohol, candy and cosmetics, this method of decoration is more reasonable.

The following is the author's new procedure for testing special gloss pigments in packaging printing for reference.

A sheet of paper gravure printing process

Most users have used the method of engraving and gravure printing. This is because the particle size of the pigment is relatively large. It is necessary to transfer a certain amount of pigment to the packaging material by using the method of large-scale transmission of ink so that the printing can achieve an ideal gloss effect. .

However, the cost of traditional gravure printing is still high in the paper-making production. The main reasons are: First, the production cost of the printing plate cylinder is high; second, the amount of waste in the roll paper feeding method is large. On the other hand, the cost pressure of packaging customers is getting bigger and bigger, and the packaging style changes very quickly, and there are more and more short-run jobs. In this way, printers have to adopt alternative methods, such as sheet-fed gravure printing is an effective solution.

Sheet-fed gravure printing can be combined with offset printing. Unnecessary gravure printing can be accomplished using offset printing, which greatly reduces the cost, and the amount of wasted paper is much smaller, but for special large-grained shiny pigments, Gravure can be used to form an effective ink layer thickness to achieve satisfactory results.

Special gloss inks are used more as a base color in the packaging design, and the production of a plate cylinder in the field can cope with the use of different special gloss inks on a plurality of live meters, thus saving a lot of expenses from the printing plate.

Another advantage is that it can be used to print proofs, a small amount of waste, and the effect is basically the same as the product. It is very effective for pearlescent special glossy proofs, and is more conducive to packaging customers to communicate.

However, it should be noted that the printing speed and the printing pressure of the sheet-fed gravure printing are different from those of the traditional web gravure printing, and sometimes the performance of the ink needs to be adjusted accordingly to ensure the effect.

Second, offset online / offline glazing process

If you do not use sheetfed gravure, another method that can be combined with offset printing to use a special gloss effect is to polish. Glossing, also known as “oiling” or “lighting,” is traditionally a type of post-printing process that protects the ink layer from dirt, bruises, and provides extra shine. To say “glazing” is actually to use the process to “print” and transfer special glossy inks, because the offset printing ink layer is very thin and does not produce a good gloss effect, so this is a kind of “glossy coating”. ".

According to need, this type of coating can be arranged after other inks are printed, or it can be arranged before it is used as a primer.

There are several types of coating methods used in packaging and printing. The author's suggestion is to use water-based or solvent-based coating of specialized glazing mechanisms instead of offset printing in the offset printing presses. The viscosity of the latter is too high. And large-particle pigments have poor transferability.

In recent years, the glazing development equipment has adopted a “closed scraper type” mechanism and uses anilox rollers to transfer the varnish through a rubber plate or photosensitive resin plate. In addition to saving the amount of varnish, this mechanism has the greatest advantage of being able to perform local glazing and unique decorative effects. This is very important for the application of special glossy materials. In fact, it is also a flexographic printing unit, where the anilox roller has a great influence on the transferability of the pigment. The too thin screen number cannot guarantee effective transmission, and it is too thick to bring about the problem of drying.

The old "double roller" mechanism can also be used for the construction of special gloss pigments, but it is not possible to perform a precise local glazing. If you use water-based coating, you must pay attention to the drying problem. On the one hand, the water-based gloss oil is relatively slow to dry. If you want to increase the printing speed, you must adjust the gloss parameters. On the other hand, once the water-based gloss oil is dried on the plate roller, it is difficult to remove it. For a little longer, you must clean the plate roller carefully. Considering that customers use in different ink systems, different pearl pigments are produced for water, solvent, and curability, respectively, which are denoted by the abbreviations W, S, and UV in the pigment names, respectively.

Hubei Tongshan Shancheng Printing Machinery Co., Ltd. launched a new type of offset press equipment with multiple scraper type “glazing” units, some before the offset printing group and some at the end, for the printing of decorative elements.

Source: Guangdong Printing Wang Nengyou