Pearlescent pigments used in different printing methods

Pearlescent pigments not only produce pearlescent effects in printing inks, but also maintain the original color tone, and can bring a variety of metallic luster and iridescent effects. Pearlescent pigments have been widely used in the printing industry and are commonly used in the printing of various packaging papers, magazines, advertising paintings, textiles and other items.

Usage note overview

Pearlescent pigments have excellent dispersing power and generally require only slight agitation to mix in low viscosity printing inks. Because the pearlescent pigment is a layered structure, it can only be stirred gently when mixed with the ink, to avoid rude mechanical treatment, so as not to damage the surface of the pearl powder. Pearlescent pigments are usually added during the final process of ink production. When using a disperser and a high-speed agitator, the agitation time of each batch must be the same and the shortest, which can avoid the color difference between batches of products. In the case of having to use a three-roller, the roller gap is adjusted as large as possible, and the stirring is completed in the shortest possible time so as not to damage the pigment structure and affect the gloss. Use transparent material as far as possible to avoid the use of opaque and scattered light additives to affect the pearl effect.

Judgment of the effect of ink containing pearlescent pigments, varnish, and coating is determined by the uniform distribution of the pigments on the substrate. Only the parallel alignment of the pigments with the surface of the substrate is the best. A suitable substrate can avoid the adverse effects of the printing effect, and a substrate with a smooth, flat surface can make the pigment arrangement the best gloss effect. In addition, the relationship between the number of printing plates, screens, and the particle size of the ink, the best viscosity of the ink, the printing speed, the drying conditions, the avoidance of flocculation of the pigment, and the dispersibility of the ink are also important. Pearlescent pigment anti-scratch, insulation, acid and alkali resistance.

Pearlescent pigments for flexographic printing

The printing plate used in flexo printing is made of rubber or photosensitive resin, and the ink is transferred through the emboss on the printing plate. Flexo printing inks are low-viscosity liquids, both solvent-based and water-based, and dry quickly, especially under radiation curing. Due to its physical and chemical properties, pearlescent pigments can be used in most flexographic printing inks.

Traditional pigments have the property of astigmatism, so they must be highly dispersed when mixing with pearlescent pigments and cannot exceed 3% of the ink weight. In water-based alkaline inks, basic additives should be used to adjust the surface properties of pearlescent pigments. If alkaline thixotropes are used to adjust the viscosity, pigments with acidic surfaces must be adjusted to avoid pigment flocculation and abnormal viscosity changes.

If it is necessary to improve the dispersion of pearlescent pigments in the ink, the pigments can be pre-wet and dispersed before being added to the ink. Choosing a smooth, flat surface provides the best results. Twilight and convex can increase the pearl effect.

Pearlescent pigments for offset printing

In offset printing, ink is transferred through a flat plate. Plates have a flat print area and a non-print area. Utilize the incompatibility of oil and water to color the printing area of ​​the printing plate. Offset printing currently uses thin aluminum plates that are exposed to ultraviolet light, and in most cases fountain solutions are still used to separate printed and non-printed areas.

Ordinary offset printing inks are high viscosity inks that are not suitable for pearlescent pigments. Special printing inks should be used, and ink manufacturers are required to adjust the ink composition according to the printing procedure.

Commonly used packages and labels can be printed with pearlescent pigment offset inks. The surface of the substrate is as smooth and flat as possible to optimize the pigment arrangement and achieve the desired gloss effect due to the thin ink layer in offset printing.

Pearlescent pigments for screen printing

In screen printing, the printing ink is transferred from the screen plate to the substrate. The platform of the screen printing plate is draped with a screen, and the screen information is transmitted through the screen. The ink is extruded through a screen or a squeegee and printed on the substrate. The material selection and manufacturing technology of the screens play an important role in the printing effect. The thickness of the screen determines the thickness of the ink transfer layer. Monofilaments are recommended when using pearlescent pigments to prevent the pigment from blocking the mesh holes.

Screen printing inks should have good application properties (adaptability, fluidity, and good curability), ink should not block the screen holes, and dry quickly after printing. Pearlescent pigments can be used in all screen printing ink systems, but are most suitable for use in clear ink systems. If pearlescent pigments are pre-wet and dispersed, they will mix better with the ink. The amount of pearlescent pigment added in screen printing ink is generally 8-15% of finished ink. In screen printing, due to the chemical resistance of pearlescent pigments, the post-printing process does not affect the pearlescent effect, so it is the most used in textiles.

Pearlescent pigments for gravure printing

In gravure printing, the printing result is obtained by passing ink through the corrosion of the printing plate or the engraved ink port. Intaglio printing mainly uses low-viscosity liquid ink. According to the printing and post-press processing, the pearlescent pigment is suitable for most gravure printing solvent-based or aqueous system inks. Choosing a highly transparent binder can prevent damage to the pearlescent effect. When using color inks, it is necessary to mix well-dispersed transparent colorants with pearlescent pigments. Because the pearlescent pigments only have optical effects in well-lighted ink layers, the amount of colorant should generally be within 3% of the finished ink, and the color tone should be too high. Heavy will affect the pearl effect. Suitable rheology aids should also be used to improve the surface properties of pearlescent pigments in inks. When applied to solvent-based inks, pigments are recommended to be pre-wet and dispersed. Twilight and embossing can increase the pearlescent effect.

Source: Shanghai Dongdong Pearlescent Pigment Co., Ltd.