I. Introduction For many years, the iridescent pearlescent effect has been loved by people, and the field of application has become more and more extensive. But so far, most printing inks and paint coatings have always contained high concentrations of volatile organic solvents. In recent years, environmental protection by the steam gradually become the focus of modern industry, various governments have issued relevant regulations (such as the United States RULE 66 and Germany's AT-LUFT), requiring substantial reduction in the content of organic solvents in industrial products . This makes the majority of industrialized countries must consider how to improve the existing process to meet environmental protection requirements. The printing inks and coatings industry in the Western countries is one hundred countries to the above standards, and the measures taken are to replace the existing organic solvent systems with water-based systems.
After rapid development in recent years, this technology has reached a fairly mature application stage. Many ink production companies have begun to provide high-quality cement system products for various printing companies.
Below we will mainly introduce the application of pearlescent pigments in water-based ink systems, and how to deal with some related issues.
Second, the use of pearlescent pigments Titanium pearlescent pigments can be used in water-based ink system surface pearl interference type gloss or metallic luster, and will not produce technical problems.
Such pearlescent pigments consist mainly of platelet-shaped mother particles and a thin layer of metal oxide coated on them. The metal oxide film has a high optical refractive index (Np=2.5-3.0), and mica optics. The refractive index is relatively low (Np = 1.5) (Fig. 1 is abbreviated).
As shown in Figure 1, the incident light is split into two paths on the surface of the pearlescent pigment, and the mirror-reflexive imported vehicle is refracted all the way to the interior of the pigment. The light has a different refractive index in the process of passing through the front material. Reflection and refraction occur at the interfaces between the two substances. It is this multiple reflection phenomenon that has led to the pearl-like iridescent luster.
From a productive point of view, there are three basic ways to create splendid, well-crafted colors:
One is to control the thickness of the transparent titanium dioxide coating deposited on the mica substrate. In this way, the part of the light reflected from each of the boundary cloths will have optical interference with each other due to the different optical paths. The color of the interference light we observe is determined by the thickness of the titanium dioxide coating.
The use of additional, optically absorptive metal oxides (such as ferric oxide or chromium oxide) in combination with the original interference layer results in correspondingly golden and green pearlescent effects.
The third is to deposit a high optical index and an optically absorptive metal oxide (such as ferric oxide) directly on the mica flakes and to control the thickness of the coating. The pigment thus obtained can perfectly and simultaneously surface optical interference and optical absorption effects, so that non-metallic pigments create the luster of metallic pigments.
It should be mentioned that pearlescent pigments can be supplied in different particle sizes, which is of great importance to the user of the product color. The reason for this is that the different particle sizes of the pigments determine the light and color effects of the product, from delicate matt effects to pearlescent luster, to flickering luster. In addition, the particle size determines how pearlescent light can be obtained. Han Ze. Fine pearlescent pigments have better hiding power than particles.
Pearlescent pigment is an inorganic pigment that is non-flammable, non-explosive, and electrically insulating. Even for diluted acid, salty solutions. Pearlescent pigments are also stable. Neither the organic solvent nor the water (which is particularly important here) has no effect on the pearlescent pigments. Like in polymer systems, pearlescent pigments can be easily dispersed in the two above-mentioned fractions.
The maximum temperature that the pearlescent pigment can withstand is 800 degrees Celsius, and it can meet the general requirements of ink making and printing drying. Its chemical inertness and extremely low heavy metal content make it very safe for the environment.
Because the interferential multiple reflection is an important light and color representation of pearlescent pigments, it is fundamentally different from conventional absorption/scattering pigments or totally reflective metal pigments, so it is defined as a third pigment.
Third, in the combined use of pearlescent pigments in water-based ink systems, there are two basic rules to note:
1. It is very important for the transparency of the ink binder system. Because of the basic characteristics of transparency, pearlescent pigments can produce pearl luster. The ink connecting material working medium should also have good transparency, otherwise the pearl luster will be significantly weakened even if it is not completely covered.
For the filler, rheological additives, etc. should also have the same phase requirements. There are circumstances in which pearlescent inks need to be mixed with colorants to express color. Of course, it should be noted that the colorants here should have good transparency.
2. The morphology of the pigment The thickness of the pearlescent pigment is approximately 0.4 μm, and the size of the front surface of the pigment is 2 μm. Therefore, its overall shape is a very thin platelet-like structure. In addition to the transparency of the pigment, this ruthenium structure is another basis for the expression of pearl luster, but from another perspective, it is very sensitive to the shearing action, and the large shearing motion destroys the pearlescent effect. Therefore, in the process of ink production, we require that pearlescent pigments be blended in a gentle manner, and three-roll mills, high-speed dispersers, and other equipment that may damage the pigment morphology should be avoided.
In some cases, pearlescent pigments need to be mixed with other pigments. At this point, the pigment is first dispersed and stirred separately with a high shearing force and shear rate. After that, the pearlescent pigment is slowly added and dispersed at a low speed and gently dispersed in the pigment because the pearl pigment is easy to be used. Scattered, so this can be done very easily.
If pearlescent pigments need to be braked into inks that have already been dispersed, practice has shown that pearlescent pigments are first “pre-moistened†with water so that they can receive the best results. In aqueous printing ink systems, pearlescent pigments are usually added at a concentration of 20% to 30%.
In order to improve the anti-settling ability of pearlescent pigments in aqueous inks, thixotropic thickeners should be used. This additive helps the pigment to be suspended in the emulsified aqueous system.
However, the facts show that different types of thickeners should be selected for the different order of pearlescent pigments in the different ink manufacturing processes. For example, before and after the pearlescent pigment is added to the ink, the PH value of the ink dispersion will change, and it should be adjusted.
In water-based ink systems, pH is a very important factor, but whether it is acidic or alkaline, it will not affect the stability of the pearlescent pigments. Relative to aluminum powder pigments, this is an advantage of pearlescent pigments in water-soluble systems. In addition, a factor influencing the pearlescent effect of printed products is the distribution of pearlescent pigments in the ink layer. If the pearlescent pigment particles can be arranged in the same direction on the surface of the substrate (as shown in FIG. 2 ), the light reflected by the pearlescent pigments is also reflected. Spread in a single direction, you can achieve the best luster, otherwise (as shown in Figure 3) refracted light is diffusely reflected, its effect is greatly reduced. Practice shows that choosing the right type of thixotropic additives can optimize the directional arrangement of pearlescent pigments.
The directionality of the pearlescent pigment arrangement influences the DOI value (image characteristic value), and the DOI value represents the smoothness of the image surface.
4. Application of Pearlescent Pigments in Waterborne Systems In Europe, pearlescent pigments have been used in waterborne systems in the gravure wallpaper industry and are still the most widely used field. Other areas of celebration include the printing of labels, boxes and special decorative papers and gift wraps.
In terms of coating, a common method is an air knife coating method, and other methods include roll coating, curtain coating, and the like. In addition to ordinary silver-white pearlescent pigments, iridescent interference pigments, pearlescent gold pigments and bronze pearlescent pigments can also be used to express special pearlescent effects.
Due to the fact that it is dead and transparent, it is often overprinted/coated on a variety of backgrounds so that it can acquire unique color effects.
Special effects can also be achieved by adding transparent pigments to aqueous pearlescent inks, such as carbon black or different types of transparent organic dyes or pigments. The use of pearlescent inks can exhibit metallic luster. One of the commonly used techniques is the incorporation of a small amount of carbon black into the silvery pearlescent ink. The original transparent pearlescent ink of Song will show the metallic silver color, with the addition of carbon black. With the increase, the silver can gradually turn from soft to strong metal.
Another widely used field for pearlescent pigments is the printing/printing of textiles, especially pearlescent inks for aqueous systems, the main component of which is butadiene or acrylic resins. In the past, pearl ink was once considered to be inappropriate for rotary screen printing of fabrics. Through years of research and development in the industry, especially with the technical cooperation of pigment suppliers, Pearl Light has been able to maturely apply this field.
After rapid development in recent years, this technology has reached a fairly mature application stage. Many ink production companies have begun to provide high-quality cement system products for various printing companies.
Below we will mainly introduce the application of pearlescent pigments in water-based ink systems, and how to deal with some related issues.
Second, the use of pearlescent pigments Titanium pearlescent pigments can be used in water-based ink system surface pearl interference type gloss or metallic luster, and will not produce technical problems.
Such pearlescent pigments consist mainly of platelet-shaped mother particles and a thin layer of metal oxide coated on them. The metal oxide film has a high optical refractive index (Np=2.5-3.0), and mica optics. The refractive index is relatively low (Np = 1.5) (Fig. 1 is abbreviated).
As shown in Figure 1, the incident light is split into two paths on the surface of the pearlescent pigment, and the mirror-reflexive imported vehicle is refracted all the way to the interior of the pigment. The light has a different refractive index in the process of passing through the front material. Reflection and refraction occur at the interfaces between the two substances. It is this multiple reflection phenomenon that has led to the pearl-like iridescent luster.
From a productive point of view, there are three basic ways to create splendid, well-crafted colors:
One is to control the thickness of the transparent titanium dioxide coating deposited on the mica substrate. In this way, the part of the light reflected from each of the boundary cloths will have optical interference with each other due to the different optical paths. The color of the interference light we observe is determined by the thickness of the titanium dioxide coating.
The use of additional, optically absorptive metal oxides (such as ferric oxide or chromium oxide) in combination with the original interference layer results in correspondingly golden and green pearlescent effects.
The third is to deposit a high optical index and an optically absorptive metal oxide (such as ferric oxide) directly on the mica flakes and to control the thickness of the coating. The pigment thus obtained can perfectly and simultaneously surface optical interference and optical absorption effects, so that non-metallic pigments create the luster of metallic pigments.
It should be mentioned that pearlescent pigments can be supplied in different particle sizes, which is of great importance to the user of the product color. The reason for this is that the different particle sizes of the pigments determine the light and color effects of the product, from delicate matt effects to pearlescent luster, to flickering luster. In addition, the particle size determines how pearlescent light can be obtained. Han Ze. Fine pearlescent pigments have better hiding power than particles.
Pearlescent pigment is an inorganic pigment that is non-flammable, non-explosive, and electrically insulating. Even for diluted acid, salty solutions. Pearlescent pigments are also stable. Neither the organic solvent nor the water (which is particularly important here) has no effect on the pearlescent pigments. Like in polymer systems, pearlescent pigments can be easily dispersed in the two above-mentioned fractions.
The maximum temperature that the pearlescent pigment can withstand is 800 degrees Celsius, and it can meet the general requirements of ink making and printing drying. Its chemical inertness and extremely low heavy metal content make it very safe for the environment.
Because the interferential multiple reflection is an important light and color representation of pearlescent pigments, it is fundamentally different from conventional absorption/scattering pigments or totally reflective metal pigments, so it is defined as a third pigment.
Third, in the combined use of pearlescent pigments in water-based ink systems, there are two basic rules to note:
1. It is very important for the transparency of the ink binder system. Because of the basic characteristics of transparency, pearlescent pigments can produce pearl luster. The ink connecting material working medium should also have good transparency, otherwise the pearl luster will be significantly weakened even if it is not completely covered.
For the filler, rheological additives, etc. should also have the same phase requirements. There are circumstances in which pearlescent inks need to be mixed with colorants to express color. Of course, it should be noted that the colorants here should have good transparency.
2. The morphology of the pigment The thickness of the pearlescent pigment is approximately 0.4 μm, and the size of the front surface of the pigment is 2 μm. Therefore, its overall shape is a very thin platelet-like structure. In addition to the transparency of the pigment, this ruthenium structure is another basis for the expression of pearl luster, but from another perspective, it is very sensitive to the shearing action, and the large shearing motion destroys the pearlescent effect. Therefore, in the process of ink production, we require that pearlescent pigments be blended in a gentle manner, and three-roll mills, high-speed dispersers, and other equipment that may damage the pigment morphology should be avoided.
In some cases, pearlescent pigments need to be mixed with other pigments. At this point, the pigment is first dispersed and stirred separately with a high shearing force and shear rate. After that, the pearlescent pigment is slowly added and dispersed at a low speed and gently dispersed in the pigment because the pearl pigment is easy to be used. Scattered, so this can be done very easily.
If pearlescent pigments need to be braked into inks that have already been dispersed, practice has shown that pearlescent pigments are first “pre-moistened†with water so that they can receive the best results. In aqueous printing ink systems, pearlescent pigments are usually added at a concentration of 20% to 30%.
In order to improve the anti-settling ability of pearlescent pigments in aqueous inks, thixotropic thickeners should be used. This additive helps the pigment to be suspended in the emulsified aqueous system.
However, the facts show that different types of thickeners should be selected for the different order of pearlescent pigments in the different ink manufacturing processes. For example, before and after the pearlescent pigment is added to the ink, the PH value of the ink dispersion will change, and it should be adjusted.
In water-based ink systems, pH is a very important factor, but whether it is acidic or alkaline, it will not affect the stability of the pearlescent pigments. Relative to aluminum powder pigments, this is an advantage of pearlescent pigments in water-soluble systems. In addition, a factor influencing the pearlescent effect of printed products is the distribution of pearlescent pigments in the ink layer. If the pearlescent pigment particles can be arranged in the same direction on the surface of the substrate (as shown in FIG. 2 ), the light reflected by the pearlescent pigments is also reflected. Spread in a single direction, you can achieve the best luster, otherwise (as shown in Figure 3) refracted light is diffusely reflected, its effect is greatly reduced. Practice shows that choosing the right type of thixotropic additives can optimize the directional arrangement of pearlescent pigments.
The directionality of the pearlescent pigment arrangement influences the DOI value (image characteristic value), and the DOI value represents the smoothness of the image surface.
4. Application of Pearlescent Pigments in Waterborne Systems In Europe, pearlescent pigments have been used in waterborne systems in the gravure wallpaper industry and are still the most widely used field. Other areas of celebration include the printing of labels, boxes and special decorative papers and gift wraps.
In terms of coating, a common method is an air knife coating method, and other methods include roll coating, curtain coating, and the like. In addition to ordinary silver-white pearlescent pigments, iridescent interference pigments, pearlescent gold pigments and bronze pearlescent pigments can also be used to express special pearlescent effects.
Due to the fact that it is dead and transparent, it is often overprinted/coated on a variety of backgrounds so that it can acquire unique color effects.
Special effects can also be achieved by adding transparent pigments to aqueous pearlescent inks, such as carbon black or different types of transparent organic dyes or pigments. The use of pearlescent inks can exhibit metallic luster. One of the commonly used techniques is the incorporation of a small amount of carbon black into the silvery pearlescent ink. The original transparent pearlescent ink of Song will show the metallic silver color, with the addition of carbon black. With the increase, the silver can gradually turn from soft to strong metal.
Another widely used field for pearlescent pigments is the printing/printing of textiles, especially pearlescent inks for aqueous systems, the main component of which is butadiene or acrylic resins. In the past, pearl ink was once considered to be inappropriate for rotary screen printing of fabrics. Through years of research and development in the industry, especially with the technical cooperation of pigment suppliers, Pearl Light has been able to maturely apply this field.
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