Technical Highlights of Color Printing for Special Ink Printing

This article mainly introduces the technical points of color decoration and some troubleshooting methods.

First, the technical point of color decoration

There are mainly the following aspects

1, gold and silver

In order to ensure the purity of the ink, when printing the gold and silver inks lastly, first wet the mesh with a washing solution 783, clean the surface, wait for the solvent to evaporate completely, and then re-ink the ink, because the gold and silver inks will react when they encounter the solvent. , causing ink discoloration. Because of the poor mobility of gold and silver inks, it is often necessary to add a varnish or a slow-drying agent to increase the fluidity of the ink, and to prevent the formation of an oxide film that can cause darkening of the ink film without adding a small amount of yellow ink. . To bring out the gloss of gold/silver foil, add some slow drying agent as appropriate.

2, pearl ink

Pearlescent pigments can be combined with transparent pigments or dyes to give unique pearlescent effects, but should avoid mixing with opaque pigments, and should avoid mixing pigments with complementary color pearlescent pigments. When using silver white pearlescent pigments, a small amount of carbon black or blue pulp should be added to enhance its pearlescent effect. The pearlescent pigments have a good dispersion and should avoid the long-term effects of strong shear forces. This kind of ink will precipitate in the low viscosity varnish, and should be stirred gently before use, and it will not affect the use effect.

3, luminous ink

Adding a certain proportion of light-storing material in transparent varnish can be formulated as a light-emitting ink. The particle size of the light-storing material should be controlled within the range of 45 to 65 μm so that a useful light-emitting ink can be formulated. Note on the use of luminescent ink: The viscosity of the processed luminescent ink is slightly thicker at about 300-500 Pa·s. When printing, according to the printing speed, the viscosity of the ink is adjusted with thinner to meet the printing needs. When printing patterns and logos with luminescent inks, polyester screens with a size of less than 150 mesh are generally selected. In order to obtain the best luminescent effect, 80-120 mesh screens may be used. The luminescent ink is printed on a white substrate, which can increase the brightness and afterglow time of the printed pattern or logo. When the coating thickness of the printed luminescent ink is controlled at 130-150 μm, the luminescent effect is the best. If it is printed twice with a 80-mesh screen, this thickness can be achieved.

4, fluorescent ink

Fluorescent inks are suitable for screens and high-tension screens up to 300 mesh. When the printing ink on the substrate is transferred at 50 to 60 g/m2, the hair color and light resistance are ideal. Glossy processing will slightly reduce the fluorescence effect, so use a good transparency oil. When the substrate is a transparent object, the white ink must be printed before printing the fluorescent ink, which can improve the fluorescence effect. Can also be printed on paper with high whiteness, the higher the whiteness of the paper, the better the printing effect. When using a fluorescent ink to print the background color, the color will be better and the light resistance will be improved if the same color printing is used. For four-color printing, if you print red, yellow, you can get bright prints. Pay attention to the printing sequence to improve the printing effect.

The range of UV ink color choice is very wide, and the ink with strong coloring power is selected, the amount is less; the greater the pigment dispersion, the stronger the coloring power; the smaller the pigment particles, the greater the hiding power. Color mixing ink generally uses primary colors. For example, on electronic elements, silver and black background colors are generally used. The contrast should not be too large. Do not mix white, black and blue colors. Specific colors interfere with the absorption of light energy, resulting in difficulty in curing. The proportion of the colorant should not be too large, and it must be precisely controlled. Otherwise, the UV curing of the ink may be affected, because the greater the specific gravity of the colorant contained in the UV ink layer, the greater the UV blocking effect of the ink layer. It takes much time to completely cure the ink layer, and if the ink layer is not completely cured, the print has poor wear resistance, solvent resistance, and the like. Screen printing crystal glue or UV crystal glue, can not see a significant effect, sprinkled with colorful glitter, like a greeting card as gorgeous.

Second, bad and countermeasures

Some failures and defects are easily caused in color decoration. The following countermeasures are mainly adopted.

1. Discoloration

In the course of use, the color of the ink film changes, and its hue, lightness, and chroma greatly deviate from the standard color mark.

the reason:
(1) It is caused by the action of eyesight (mainly short-wave zone), humidity, high temperature, and corrosive gases (such as sulfur dioxide) in the air;
(2) The weatherability of the ink used is poor;
(3) The organic pigment migrates through the ink film during aging of the ink film, precipitation of the plasticizer, and the like.

Prevention:
(1) Select the appropriate ink according to the conditions of use of the substrate;
(2) Select an ink with excellent weatherability.

2. fade

During use, the color of the ink film becomes lighter.

the reason:
(1) The effects of sunlight, chemicals, and air pollution will reduce the color;
(2) The effect of heat and ultraviolet light degrades the resin;
(3) The ink used (or the pigment contained in the ink) has poor weatherability or is not suitable for outdoor use.

Prevention:
(1) Choose an ink with excellent weather resistance according to the use environment;
(2) Use indelible ink.

3. fade

When the surface of the ink layer is wiped with a cloth, the color of the ink adheres to the cloth.

the reason:
The main reason is that the pigment (especially the organic pigment) contained in the ink penetrates the surface of the ink film.

Prevention:
(1) Improve the ink formulation;
(2) Add resin or cover the selected ink.

4. Color difference

The hue, lightness, and saturation of the printed ink film are different from the standard color patches.

the reason:
(1) There is a large difference between the batches of ink used;
(2) When the color is changed, some parts are not washed;
(3) Inconsistent drying conditions, especially drying;
(4) Ink-filling causes printing stains.

Prevention:
(1) Strengthen the inspection of inks into the factory;
(2) Some parts of the color must be washed;
(3) Drying conditions (drying time, temperature) should be strictly controlled;
(4) Make up as little ink as possible or only make up the ink on the surface with a sharp dividing line.

5. Floating color, color layering

Due to the difference in size, shape, density, dispersibility, and cohesion of the pigments in the ink, the pigments on the surface and the underlying layer of the ink film are unevenly distributed, resulting in a phenomenon in which the hue of each layer is different.

the reason:
In the process of formation of floating color and ink film, the distribution of the pigment in the solvent is inconsistent, and the ink formulation and the ink distribution process are unreasonable.
(1) When the ink with two or more pigments is blended, since the solvent volatilizes in the interior of the ink layer and the surface is inconsistent, convection is likely to occur and a floating color phenomenon occurs;
(2) The density of pigments in the ink varies greatly;
(3) The operating method and equipment are not suitable for use.

Prevention:
(1) Improve the ink formulation and manufacturing process (such as selecting pigments that are not easily floatable, easily dispersible, and improving the pigment dispersion process);
(2) Adding anti-floating agents, such as silicone oil, has a significant effect on preventing floating color;
(3) Select the appropriate modulation method and equipment.

6. Color uneven (color hair flowers)

The color of the ink film is locally uneven, and the phenomenon of spot printing, stripes, and hue appears. It is generally caused by improper printing operations of the ink and the effects of ink components and certain substances.

the reason:
(1) Insufficient dispersion of the pigment in the ink or insufficient mixing of two or more color paints when mixed with each other;
(2) Insufficient solvent strength or inappropriate working viscosity of the solvent used;
(3) It is printed too thickly so that the pigment in the ink film produces "convection" in the surface;
(4) Gases (such as ammonia, sulfur dioxide, etc.) and acids, alkalis, and other substances that have come into contact with the ink film at the job site.

Prevention:
(1) Use pigments with good dispersibility and mutual solubility;
(2) Select the appropriate solvent and use printing viscosity and film thickness that meet the process requirements;
(3) The same type of ink should be used when formulating the multicolor paint, using the same type of ink produced by the same manufacturer.

7. Bad gloss

The ink layer did not reach the desired gloss after drying, and the ink layer showed a drop in gloss soon after printing.

the reason:
(1) Improper choice of pigment, poor miscibility of the resin, improper solvent selection;
(2) The surface of the printing ink absorption, uneven;
(3) The surface of printing is rough and uneven;
(4) Insufficient ventilation during drying of the ink layer;
(5) Printing under high temperature, high humidity, or extremely low temperature.

Prevention:
(1) Select the appropriate ink and solvent through the test;
(2) Printing primer ink to improve the roughness of the surface of the printing surface, ie roughness;
(3) Strictly control the ink layer drying conditions, and the ventilation in the drying room should be appropriate;
(4) Pay attention to the control of the printing process to ensure uniform thickness of the ink layer;
(5) Polishing after the ink layer has dried and matured;
(6) Control the environmental conditions of the printing job.

8. Uneven metallic luster

When printing metallic decorative inks, due to the uneven thickness of the printing, the solvent and the ink used do not match to cause uneven distribution and orientation of the metal powder, resulting in uneven appearance of the coating film.

the reason:
(1) Improper ink formulation (eg, low metal powder content, high solvent concentration, low molecular weight of resin, slow drying of resin, etc.);
(2) Improper selection of printing viscosity (too low or too high);
(3) The ink layer is too thick or the film thickness is not uniform, and the operation is not skilled;
(4) The interval between the ink primer and the cover varnish process is too short;
(5) The ambient temperature is low.

Prevention:
(1) Improve the ink formulation and use slow-evaporating solvents;
(2) The viscosity of the ink should be appropriate;
(3) The background color of the ink and the varnish must be properly dried and dried with hot air of 60-80°C;
(4) The ambient temperature of printing is adjusted to a suitable range.

9. Pan-copper light

The copper film on the surface of the film shows a purple color, and it suddenly glows in the sunlight.

the reason:
(1) Affected by sunlight, ultraviolet rays or affected by high temperature;
(2) Caused by the migration of red, blue, etc. pigments, especially when the pigment particles are less than 0.1 μm.

Prevention:
Use inks with good weather resistance and use suitable pigments for color matching.

10. Uncovered, poorly covered

The phenomenon that the surface of the printing surface is not printed with ink is called exposed bottom (commonly known as lack of ink). The thin printing ink layer or poor hiding power of the ink does not cover the bottom surface (background color), which is called poor coverage.

the reason:
(1) The ink itself has a low pigment content or the ink is not stirred evenly before use;
(2) The printing ten inks have low viscosity and the ink layer is too thin;
(3) The substrate is complex in shape and missed;
(4) The color difference between the background color and the surface ink color is too large, such as printing a high-brightness light color ink on a deep background.

Prevention:
(1) Choose strong ink with strong hiding power. The ink should be fully stirred before use and during printing;
(2) Appropriately increase the viscosity of the ink; the thickness of the ink layer should be reached at each printing operation;
(3) Improve the proficiency of operations;
(4) The background color is as close as possible to the surface ink layer.

11. White ink

The surface of the ink layer during printing and printing is milky white, resulting in cloud-like whitish loss of light. Occurs when printing volatile inks. When they are severe, they will completely lose their luster. Microvoids will appear on the ink layer and the adhesion will decrease.

the reason:
(1) The air humidity in the workplace is too high;
(2) The organic solvent used has a low boiling point and is too volatile;
(3) The humidity of the substrate is too high;
(4) Water in the ink and thinner;
(5) The solvent and diluent do not match, causing the resin to appear white on the surface of the ink layer.
The first three conditions cause water vapor in the air to condense on the surface of the substrate and penetrate into the ink layer causing whitening.

Prevention:
(1) The ambient temperature of the work site is preferably 15 to 25°C and the relative humidity is not higher than 70%;
(2) Selection