1.The stability of ceramic ink

   Ceramic ink is a dispersion system obtained by dispersing colorants in a dispersion medium, and this system is relatively stable. The stability of dispersion needs to take into account that it does not aggregate or precipitate after being left for a certain period of time. Aggregation refers to the mutual aggregation between inorganic pigments, which is related to the dispersion effect between pigment particles. Precipitation refers to the continuous aggregation of inorganic pigment particles until they sink to the bottom of the dispersion system. The influencing factors include the density, particle size distribution, and composition of the dispersion system of the inorganic pigment. At the same time, the dispersion system requires the selection of appropriate dispersion media, dispersants, binders, and other organic compounds, requiring ink to maintain good chemical stability and not undergo chemical reaction changes even after long-term storage. Inorganic ceramic pigments have a high specific gravity. After ceramic ink is left for a certain period of time, the pigments in the ceramic ink settle. As long as stirring is applied, the ceramic ink will once again become a uniform dispersion system, which is a recoverable process. Ceramic ink circulates in inkjet printers and nozzles, and its recoverability is particularly important.

   The factors that affect the stability of ink include Brownian motion, gravitational settling, and particle agglomeration of colored particles. Brownian motion mainly depends on ink temperature, viscosity, and ink particles. The higher the temperature, the stronger the Brownian motion, the larger the viscosity and particles, the weaker the Brownian motion, and the less likely the particles are to aggregate. Because the pigment particles are relatively large and have a high density, the settling speed of ink mainly depends on the density difference between the pigment and the solvent. The larger the density difference, the faster the settling speed. The settling speed is directly proportional to the square of particle size. The larger the particle, the greater the settling speed, the higher the viscosity of the ink, and the slower the settling speed. There are two stabilization mechanisms for ink particle dispersion: steric hindrance and electrostatic stabilization. Spatial hindrance refers to the encapsulation of polymer microcapsules on the surface of ink particles to prevent adhesion between particles in space. At present, this mechanism is widely used in the ceramic ink industry, but it has the disadvantage of affecting ink viscosity, resulting in a decreasing trend of ink viscosity over time, which affects the stability of ink. Electrostatic stability, using small molecule dispersants, suitable for water and polar diluents, but currently most ceramic inks use non-polar diluents.

2.Viscosity

   Appropriate viscosity can ensure smooth circulation of ink in the ink path, which is beneficial for the ink to be ejected from the nozzle and the uniform formation of ink droplets. The viscosity is too low, the frictional force inside the ink is small, and the liquid droplets form a crescent shape, causing damping oscillation and affecting the spraying speed; Excessive viscosity, poor ink fluidity, and difficulty in forming small droplets. In addition, ink spraying is also very sensitive to its viscosity changes, and even small shear thickening phenomena can make printing impossible due to a sharp increase in viscosity. Xaar introduces on its official website that the Xaar 1001 GS12 nozzle is suitable for ceramic ink with a viscosity range of 7-50mPa · s (which can be understood as adjusting the ink temperature to adjust the viscosity during spraying to 7-20mPa · s, but high or low ink viscosity can affect the nozzle’s service life). The technical parameter manual of Dimatix Fujifilm StarFireTM SG-1024/M-C introduces that the nozzle can be used for ceramic ink with a viscosity range of 8-20mPa · s, and the recommended range is 10-14mPa · s.

3.surface tension

   Appropriate surface tension can ensure the uniform formation of ink droplets and non stick nozzle, which helps to maintain long-term stability in inkjet printing. The surface tension of ceramic ink is too high, which easily leads to the phenomenon of ink droplets dragging tail; If the surface tension is too small, ink droplets are prone to diffusion and satellite shaped ink droplets are generated, which can reduce the clarity and layering of the pattern. At the same time, the surface tension of ink will decrease with the increase of ink temperature. The temperature control system of the nozzle can be used to adjust the surface tension of ceramic ink. At present, the surface tension of commercialized ceramic ink at inkjet temperature is about 20-35mN · m-1.

4.Particle size distribution

   Due to the limitations of the nozzle aperture and ink path system, the pigment particles in the ink must be small enough to ensure smooth inkjet. Starting from avoiding particle precipitation during storage and use, it is also required that the particles of the colorant be small. The particle size distribution in ceramic ink should be as narrow as possible to avoid the phenomenon of uneven color development caused by too coarse colorants (uneven packing density of colorants on ceramic products) and weakening caused by too fine particles (colorants melting in glaze). At present, the D50 of commercialized ceramic ink is about 200-350nm, and the D90 is less than 850nm.

5.solids

   Solid content refers to the mass percentage of inorganic ceramic pigments and related solid phase additives in ceramic ink, with the main component being inorganic ceramic pigments. The higher the solid content, the higher the pigment content per unit mass of ink, which can improve the color intensity and color range of ceramic inkjet, reduce the amount of ceramic ink used, and thus reduce the cost of ceramic production enterprises. In terms of expressive power of design drafts, the effect of increasing ink solid content is better than the effect of stacking ink dots by repeatedly printing at the same position. This is because repeated printing at the same position can easily cause ink dots to deviate from the target position, reducing clarity. Increasing the solid content can also lead to an increase in the viscosity of ceramic ink.

6.Color appears after firing

    The main factors that affect the color of ceramic inkjet include the type of pigment, crystal structure, purity, pigment content in ink, and particle size distribution; The composition of the body and glaze; Temperature, atmosphere system, and so on. Compared to ordinary pigments, ink pigments require good coloring ability in the state of ultrafine particles. The selected pigments are required to react completely during the preparation process, have well-developed color crystals, good high-temperature stability, and resist glaze erosion. This requires the selection of high-purity, uniform particle size, and high activity raw materials for colorants. In terms of process, it is required to have a longer firing time to ensure more complete crystal growth and structural integrity. The solid content of ink also affects the color, and the higher the solid content, the darker the color. Due to the high solid content affecting the stability of the ink, the solid content of different colored inks should be adjusted according to the situation. The larger the particle size, the closer it is to the color of the pigment. After the pigment is finely ground, some colors such as yellow and red will become lighter or even have no color. The color tone of brown and orange ink will change, so the particle size affects the color tone and color depth. Due to the decrease in particle size, the melting point of ink colorants is much lower than that of ordinary colorants. Therefore, after a large temperature fluctuation, the colorants may completely melt, and after melting, they are not crystals but molten bodies, leading to color differences and even fading. For example, the coloring performance of cobalt blue pigment depends on the coordination field splitting energy. Different splitting energies result in different absorbed wavelengths, and the pigment will exhibit a series of colors. Co2+(3d2) absorbs orange, yellow, and some green light, presenting a purplish blue color; Co3+(3d3) absorbs colored light other than green, strongly reflecting green and appearing green. Cobalt blue ceramic ink is mainly colored by Co2+in CoAl2O4 pigment. If CoAl2O4 crystals become molten at high temperatures, Co2+(3d2) may be oxidized to Co3+(3d3), causing color difference.

7.Adaptability to body glaze

   When other factors are the same, the composition of the body and glaze may differ greatly, and the effect of inkjet printing may vary greatly. Related studies have shown that various metal oxides in the composition of glaze, such as lithium oxide, boron oxide, zinc oxide, magnesium oxide, and antimony oxide, can affect the color of ink and should be avoided and reduced in use. The adverse effect of potassium oxide on the color of ceramic ink exceeds that of sodium peroxide. Calcium oxide and barium oxide do not seriously affect the color of ceramic ink and can be used to replace substances such as lithium oxide and boron oxide. Tin oxide can promote red hair color, but it can cause the product to turn red. Titanium oxide can promote red and yellow hair color, but it can make the product turn yellow and weaken black hair color.

8.Dryness

   If the drying time is too slow, excessive diffusion of ceramic ink will cause color changes and blurred patterns; If the drying time is too fast, insufficient diffusion of ceramic ink can cause blank filling areas, ink droplet expansion and capillary action can also lead to burr effects. The main way for ceramic ink to dry on the surface of the body is through the diffusion of ink droplets on the body, and the secondary way is through the evaporation of ink droplets in the air. The diffusion rate depends on the moisture on the surface of the green body, the porosity of the green body, as well as the composition of the ink and the surfactant. The drying time depends on the diffusion coefficient of the ink, and the drying time of the ink is linearly related to the ink coverage density. High resolution inkjet drying is easier.
   A certain amount of alcohol solvents can be added to the process of ceramic ink to increase volatility; A small amount of dispersant (such as polyol alkyl ether and other organic compounds) can also be added to meet the requirements of inkjet printing. In order to prevent ceramic ink from evaporating too quickly at room temperature, causing interruption of spraying and nozzle blockage, it is necessary to add some high boiling and non volatile moisturizing agents during the preparation process. Colorobia stated on the website of the Ceramic Research Center that it added DEG (diethylene glycol, with a boiling point of 245 ℃) to its ceramic ink to avoid its volatilization; And it is mentioned in its European patent EP 1840178 A1 that the boiling point of the dispersion medium must exceed 200 ℃. In order to prevent color difference caused by the different diffusion rates of ink droplets from the center to the edge of water-based ink on the body, and to avoid the generation of a large amount of water vapor, currently ceramic ink mainly uses an oil-based (organic) dispersion system. Among them, Xaar 1001 GS12 and Dimatix Fujifilm StarFireTM SG-1024/M-C nozzles require the use of Oil based ceramic inks in their parameter introduction book.

9.Other performance indicators

In addition to the above aspects, the compatibility between ceramic ink and the nozzle (whether it will severely wear the nozzle, whether it will clog the nozzle, whether it will affect the injection of other nozzles on the nozzle base due to excessive expansion of ceramic ink, whether it can run smoothly under the appropriate voltage pulse waveform equation, whether the injection speed and ink droplet capacity are reasonable, whether the ink droplet drop point is accurate, etc.), compatibility with ceramic inkjet printers (pH value, whether it will corrode, dissolve the ink path system, etc.), and other performance indicators (conductivity, etc.) also need to meet the requirements of ceramic inkjet printing to a certain extent.

If you want to consult our products, welcome to ask price, sent email to us: lemsun002@126.com.