The compatibility between digital inkjet ink and substrates is one of the key factors affecting the printing effect. This compatibility is reflected in multiple aspects such as physical action, chemical action and process adaptability. They are interrelated and work together to determine whether the ink can stably adhere to the surface of the substrate, present ideal colors and maintain long-term performance.
From the perspective of physical adhesion, the surface tension matching between digital inkjet ink and substrate is crucial. If the surface tension of the ink is higher than the surface tension of the substrate, it is difficult for the ink droplets to spread evenly after falling on the substrate. They may gather into small droplets or even rebound and splash, resulting in uneven distribution of ink dots and blurred images; on the contrary, if the surface tension of the ink is too low, it may spread excessively on the surface of the substrate, causing edge bleeding and loss of details. For example, when printing on a smooth plastic film surface, due to the low surface energy of such materials, ordinary water-based inks are often difficult to adhere and are prone to ink film shedding. Solvent-based or UV-curable inks that are specially formulated to reduce surface tension can better wet the surface and form a uniform ink layer.
In terms of chemical compatibility, the composition of digital inkjet ink and the chemical properties of the substrate need to adapt to each other. The water in water-based ink may affect some highly hygroscopic substrates such as paper and wood, causing the material to swell and deform, thereby affecting the printing accuracy and pattern stability; the organic solvent in solvent-based ink may swell with some plastic substrates, destroy the surface structure of the substrate, and affect the performance of the ink after drying, such as glossiness and wear resistance. In addition, the acidity and alkalinity of the ink may also react chemically with the substrate. For example, acidic ink may corrode the oxide film on the surface of the metal substrate and affect the adhesion, while alkaline ink may react with some coating materials to neutralize, resulting in color changes or coating failure.
In terms of color performance, the ink absorbency and whiteness of the substrate are directly related to the color rendering effect of the ink. For substrates with strong ink absorption, such as uncoated paper, the ink penetrates quickly and the pigment particles can be quickly fixed inside the material, but the color vividness may decrease due to excessive penetration, especially for transparent ink or light-colored ink, excessive penetration will make the color appear dull; for substrates with weak ink absorption, such as coated paper or synthetic materials, the ink mainly adheres to the surface and has strong color expression, but if the ink dries slowly, it is easy to accumulate on the surface, forming ink droplets or causing smudges. The whiteness of the substrate affects the contrast and vividness of the color. Substrates with high whiteness can better reflect light and make the ink color brighter, while substrates with a base color may cause an offset in the ink color, which needs to be corrected through the color management system.
The drying method of the ink also needs to match the heat resistance and chemical resistance of the substrate. UV curing ink requires ultraviolet irradiation to dry and cure quickly, which requires that the substrate can withstand ultraviolet irradiation without performance changes. Some plastic or rubber materials may age and turn yellow under long-term ultraviolet irradiation, affecting the appearance and service life of the printed product; solvent-based ink dries by solvent evaporation. If the substrate is sensitive to the solvent, it may shrink or become brittle during the drying process; water-based ink dries by water evaporation. For water-intolerant substrates, such as some metal plating or coating, the plating may peel off or the coating may fail due to water penetration during the drying process.
The process parameters during the printing process will also be adjusted according to the characteristics of the substrate, which will affect the compatibility and printing effect. For example, for substrates with rough surfaces, it may be necessary to increase the injection pressure of the print head to ensure that the ink can adhere smoothly, but if the pressure is too high, it may cause excessive diffusion of the ink; for substrates with uneven thickness, it is necessary to adjust the distance between the print head and the substrate. If the distance is too close, the nozzle may scratch the substrate, and if the distance is too far, the ink will be affected by air disturbance during flight, resulting in reduced positioning accuracy. In addition, in the multi-pass printing process, the degree of drying of the previous ink and the surface state of the substrate will affect the adhesion of the subsequent ink. If the previous ink is not completely dry, it may be re-dissolved or lifted during the subsequent printing, causing color mixing or pattern damage.
In terms of long-term performance, the compatibility of digital inkjet ink with substrates is also reflected in weather resistance and wear resistance. In outdoor application scenarios, the ink needs to resist the influence of environmental factors such as ultraviolet rays, rain, and temperature changes together with the substrate. If the compatibility between the two is poor, problems such as ink fading and substrate cracking may occur, resulting in premature failure of the printed content. For example, in the printing of outdoor billboards, using UV-curing ink on PVC sheets with good UV resistance can keep the colors bright for a long time, while if ordinary water-based ink is used on non-water-resistant paper, it will lose its visual effect in a short period of time due to rain erosion and ultraviolet radiation.
In practical applications, in order to improve the compatibility of digital inkjet ink with substrates, it is often necessary to pre-treat the substrate or adjust the ink formula. For example, corona treatment and coating of substrates before printing can change their surface tension and chemical properties and improve ink adhesion; ink manufacturers will also develop special inks according to different substrates, and optimize the performance of ink on specific substrates by adjusting the pigment particle size, solvent composition, additive types, etc. Only by fully considering the compatibility of ink and substrates at all levels can stable ink droplet deposition, ideal color reproduction, strong adhesion effect and long-lasting performance be achieved in actual printing, ensuring that the printed work has both visual beauty and meets the functional requirements of actual applications.
