Ceramic inkjet printing has become a trend, but the color of ink is still not as good as ordinary pigments. Therefore, how to improve the color performance of products is a problem that every factory wants to overcome. Ink quality and printing quality are key factors determining ink color, but the influence of ceramic production process on ink color is crucial and cannot be ignored. Here, we analyze the impact of the following process factors on ink coloring.

1. The Color Development Mechanism of Inkjet Ink

The color stability of pigments mainly depends on the type of pigment, the temperature range of coloring, the firing atmosphere, and the composition of the matching base glaze.
The chemical composition of the base glaze has a significant impact on the coloring of pigments. For example, some pigments require the base glaze to contain higher levels of zinc or lead, resulting in more beautiful colors. For example, Fe Cr Zn spinel brown pigments (which require a high content of zinc) require the base glaze to contain small amounts of zinc and magnesium; A few colorants require no zinc or magnesium in the base glaze, resulting in a more beautiful glaze color.
1) Rice yellow, yellow brown (Fe Cr Zn Al), red brown, zirconium iron red (Zr Si Fe), and deep brown (Fe Cr Zn Al) have strong adaptability to glazes and produce better color on zirconium opaque glazes. The stability of color saturation with changes in firing temperature is average. Glazes with high levels of zinc, boron, and barium are prone to a yellowish color tone. 2) Yellow and praseodymium yellow (Zr Si Pr) have strong adaptability to glazes, and they appear better in zirconium opaque glazes with a wider temperature range. 3) Blue, cobalt blue (Co Al Zn) or deep blue (Co Si), cobalt blue (Co Al Sn Zn) have strong adaptability to glazes, and the color saturation is relatively stable with changes in firing temperature. However, excessive zinc and magnesium content in the glaze should be avoided to prevent the color tone from turning purple. 4) Pink and chrome tin red (Sn Cr Ca Si) have poor adaptability to glazes, and their color saturation changes significantly with temperature. Zinc containing glazes can easily cause significant color fading; Higher calcium content is beneficial for pink the color.
5) Green and chromium green (Cr Al) have general adaptability to glazes, and their color saturation is relatively stable with changes in firing temperature. It is better to color on transparent glaze. 6) Black and cobalt black (Fe Cr Co Mn) have poor adaptability to glazes, mainly due to the easy variation of color tones with changes in glaze composition; The stability of color saturation with changes in firing temperature is generally average. Zinc and magnesium in glaze can easily cause color tone changes. Calcium and barium in the glaze are beneficial for the development of black color, while they appear lighter on zirconium opaque glaze.

2. The influence of glaze preparation and glaze application process on the color

The influencing factors of glaze preparation on ink coloring are mainly reflected in the fineness and water retention performance of the glaze. The coarser the fineness of the glaze, the lower the packing density of the glaze surface after glaze drying. When inkjet printing, the ink penetrates more and deeper into the glaze layer, and the reaction with the glaze is more complete during firing. However, the specific changes in color saturation and hue may vary depending on the amount of ink used in the inkjet, the firing process, and the color characteristics of the pigment. Meanwhile, theoretically, the difference in fineness of glaze can also lead to a difference in the maturation temperature of glaze, thereby affecting the color development of ink.
The uniformity of water spraying and glazing in the glazing process mainly affects the uniformity of ink color on the glaze surface. Its essence is due to uneven spraying and glazing, resulting in uneven water content on the glaze surface during printing, which leads to uneven penetration and adhesion of ink on the glaze surface, ultimately affecting the uniformity of ink color. Similarly, fluctuations in water spray and glaze application can also cause fluctuations in ink color.
The water retention performance of glaze mainly affects the penetration and adhesion of ink on the glaze surface after inkjet printing by affecting the dryness and wetness of the glaze surface during inkjet printing, thereby affecting the final color of the ink. The better the water retention performance, the greater the water content on the glaze surface during inkjet printing, and the shallower the degree of ink penetration into the glaze. The less complete the reaction with the glaze during firing. However, the specific impact on the final color of the ink may vary depending on the amount of ink used, the firing process, and the color characteristics of the pigment.

3. The influence of the chemical composition of glaze on the color

The chemical composition of glaze has different effects on the color development of different pigments. The commonly used fluxes in architectural ceramic glazes, such as magnesium oxide, zinc oxide, boron oxide, etc., are detrimental to the color development of most ink pigments and should generally be considered to be used sparingly. Relatively speaking, potassium oxide, sodium oxide, calcium oxide, and barium oxide have a relatively small impact.
Usually, base glazes with high zirconia content will have significantly better color development than other zirconium free pigments such as praseodymium yellow and zirconium iron red, which also contain zirconia. In basic glazes with high zinc content, iron containing pigments such as golden yellow, beige, and reddish brown have relatively better coloration. For bright black and cobalt black in the black series, the zinc oxide and zirconium oxide in the base glaze are not conducive to color development. The same pink the color is also very sensitive to the content of zinc oxide. Generally, when the zinc oxide content exceeds 1%, the the color of pink ink begins to significantly weaken. The differences in the effects of different components on the color development of different pigments need to be balanced in the actual formulation, taking into account the glaze effect, ink color development requirements, and the mainstream color tone of the product.

4. The Influence of Moisture and Temperature in Glazed Surface on Ink Coloring

The amount and uniformity of moisture on the glaze surface during inkjet printing have the same impact on the color development of ink on the glaze surface as the water retention performance of the glaze material. Its essence is that the moisture on the glaze affects the penetration and adhesion of ink on the glaze. Excessive moisture on the glaze surface during printing not only affects the color development of individual inks, but may also cause slow penetration and drying of the ink, resulting in fusion and color mixing between different ink dots, thereby reducing the level of color detail.
The temperature of the glaze body has a certain degree of influence on the viscosity of the ink sprayed onto the glaze surface and the rate of solvent evaporation in the ink. The higher the temperature of the glaze, the lower the viscosity of the ink, and the easier it is to penetrate into the glaze; At the same time, the higher the temperature of the glaze, the faster the evaporation and drying speed of the solvent in the ink, and the harder it is to penetrate into the glaze. In the case where there is a significant difference in the impact of the two on the speed of ink infiltration into the glaze, changes in the temperature of the glaze may cause changes in the color of the ink.

5. The influence of ink sorting on printing color

In commonly used ceramic inkjet inks, yellow and pink generally have lower color saturation compared to other colors. In order to maximize the actual color intensity of yellow and pink, it may be considered to arrange the printing sequence of ink by placing yellow and pink on the later channels. The overlapping areas of multiple colors during inkjet printing can slightly reduce the reaction between the glaze and the yellow and pink colors during firing, and correspondingly increase their color saturation, as the yellow and pink colors are stacked back and printed on other colored inks.

6. The influence of drying degree after printing on the color

The influence of the drying process of the glaze blank after spray printing on the ink color is mainly formed by the migration of soluble salts in the glaze to the surface of the glaze with water, thereby changing the chemical composition of the glaze surface. The process of significant influence of soluble salts on the directional migration of water in glaze is relatively slow, and it is not easy to observe this effect during the continuous production of glaze lines due to the relatively stable drying process. However, if the storage time in the kiln is too long, it can cause color differences between the stored products and the continuously produced products. In production, color mixing and plate alignment should be printed in the continuous production state for this reason and for the stability of glaze moisture.

7. The influence of firing system on ink coloring

Due to the fact that the pigments in ink are formed through high-temperature firing, there is not much variation in the firing temperature range of architectural ceramics. The influence of firing system on ink coloring is essentially formed by affecting the reaction melting performance of glaze on pigment particles at high temperatures. There are three main influencing factors: firing temperature, holding time, and firing atmosphere. Different colors have varying degrees of sensitivity to the firing process.
When the firing temperature is relatively low compared to the maturation temperature of the glaze, it is easy to cause the pigment particles in the ink to not fully react and melt with the glaze, resulting in partial firing. At this time, the ink appears as orange peel or matte on the glaze surface, with a lighter color on the surface and a darker, saturated color in the reaction area with the glaze.
When the firing temperature matches the maturation temperature of the glaze, the thickness of the pigment layer formed by the particle size of the ink pigment and the normal inkjet ink volume determines that it can be completely melted into the glaze without being excessively eroded and melted by the glaze. The ink has normal color development, high color saturation, and a gloss that is basically consistent with the glaze surface. The overall effect is the best.
When the firing temperature is relatively high compared to the maturation temperature of the glaze, due to the significantly increased melting reaction ability of the glaze, more of the pigment particles in the ink will be melted and destroyed by the glaze, and even completely melted into the glaze melt, resulting in a significant reduction or complete disappearance of residual pigment particles. During the subsequent cooling process, the structure of the original colored crystal cannot be reformed, resulting in a significant reduction or even colorless coloration. In the case where the firing temperature matches the maturation temperature of the glaze, the length of the holding time is approximately inversely proportional to the strength of the ink color. A short high-temperature insulation time may result in a small amount of pigment particles that have not melted into the glaze. When the high-temperature insulation time is between 2 and 5 minutes, the degree of reaction and melting between the pigment particles in the ink and the glaze is usually just enough to infiltrate into the glaze and retain more of the original crystals without being damaged. At this time, the ink has the best coloring effect.
In addition, a longer insulation time will increase the crystallization tendency of the glaze layer, and the existing metal oxides in the melted pigment crystals have the opportunity to form new crystals in the new melt, thereby forming new color tones; Or the crystallization formed by the glaze may alter the optical properties of the glaze, such as absorption, reflection, refraction, and transmittance of light waves, thereby changing the color of the unmelted pigment particles. In fact, under appropriate glaze composition, firing temperature, and atmosphere, colors containing iron in pigments such as red brown and black are prone to form a metallic glaze effect on the glaze surface when kept at high temperatures for a long time, and the overall color tone is also slightly different from that of normal insulation.
The different firing atmospheres also have an impact on the color of ink, partly because they affect the basic color tone of the body and glaze, thus forming a mixed color effect on the color tone of ink. On the other hand, due to the fine particle size of the pigment particles in the ink, some of them are melted and decomposed by the glaze at high temperatures, and are concentrated on the surface of the glaze layer. Compared with the oxidizing atmosphere, the reducing atmosphere has the opportunity to cause the pigment particles to be melted, and the original high valence oxide of the coloring metal is reduced to low valence oxide, thereby forming new coloring groups, ultimately affecting the actual color obtained by the ink.

Summary:
The influence of ceramic production technology on the color of inkjet printing ink is multifaceted, among which the chemical composition of the glaze, the moisture content of the glaze surface during printing, and the firing system have the most significant impact on the color of the ink during use. In addition to paying attention to understanding the impact of various process details on ink coloring during the production process, it is more important to fully recognize that inkjet printing is much more sensitive than ordinary printing due to the process characteristics of ink coloring. Strictly ensuring the stability of the production process is necessary to ensure that the ink achieves stable color development during production and use.

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