Classification and Importance of Inkjet Digital Printing Inks
Inkjet printing relies on a specialized ink that has the right viscosity to ensure smooth operation. This ink is non-toxic, stable, and designed to prevent nozzle clogging. It also retains moisture and offers excellent jetting performance while being non-corrosive to metal components of the printer. Most inkjet inks today are dye-based, but they must have sufficient surface tension to avoid splattering when sprayed. Additionally, fast-drying properties are essential to prevent smearing on paper, making the ink itself a key factor in determining print quality. Choosing the right ink and adjusting printing parameters are crucial for achieving optimal results.
Ink plays a vital role in the inkjet printing process. The evolution of inkjet inks has closely followed the development of inkjet technology, as the ink not only affects image quality but also influences droplet formation and system reliability. Typically, inkjet inks consist of colorants, binders, and additives. The binder, which can be water, oil, solvent, or resin, determines the ink’s dynamic behavior and makes up 40% to 90% of the formulation. Colorants contribute to color development, usually accounting for 1% to 10%, while additives enhance properties like viscosity, adhesion, thermal stability, light resistance, and surface tension.
There are numerous types of inks used in inkjet printing, and classification methods vary depending on the properties of the ink. A common approach is to categorize them based on the binder type, resulting in water-based, oil-based, solvent-based, and thermosetting inks. Water-based inks are widely used on porous materials such as paperboard and paper, and are popular in commercial printing applications like direct mail. They can also be divided into pigment-based and dye-based inks. Pigment inks are insoluble in water and need to be finely ground to prevent clogging. Ideally, particles should be smaller than 30 microns for better performance, especially at high resolutions. Pigments offer good weather resistance, lightfastness, and durability, whereas dyes provide vibrant colors and good solubility but tend to fade more easily.
Oil-based inks are ideal for printing on porous materials because they dry through absorption. They are often formulated with vegetable or mineral oils and are commonly used in cardboard packaging. However, they are not suitable for office environments due to potential air pollution. These inks can also be classified into pigment and dye types, with oil-soluble inks known for their quick drying time, making them popular in industrial settings.
Solvent-based inks are versatile and widely used in applications ranging from signage to barcodes and outdoor advertising. They are cost-effective, fast-drying, and compatible with various materials, including uncoated surfaces like vinyl, wire mesh, glass, and paper. Their ability to adhere well to different substrates makes them a preferred choice in many industries.
UV/EB inks are particularly useful for high-quality prints on both soft and rigid materials, such as corrugated cardboard and metal foil. These inks cure rapidly under UV light, offering superior durability and long-lasting results. They are ideal for DOD (Drop On Demand) applications, such as retail display ads, business cards, credit cards, and frequently used shopping cards.
In addition to classifications based on binding agents, there are other ways to categorize inks. For instance, they can be divided into organic dye inks, polymer dye inks, and pigment inks based on the color material. By drying mechanism, inks can be classified as volatile or polymeric. Water-based and non-aqueous inks use water or solvents as binders and dry through absorption by the substrate. This can reduce color density and sharpness, especially on regular paper. Thermosetting inks remain solid at room temperature and melt when ejected, then solidify quickly upon contact with the substrate. This prevents ink from spreading or penetrating the material, ensuring consistent print quality.
Selecting the right ink is essential for achieving high-quality results in inkjet printing. While modern inkjet printers deliver impressive color performance and image quality, the process is still relatively slow, and the requirements for paper are quite strict. Although there are many specialty papers available for inkjet printing, they are often expensive, limiting their accessibility for home users and students. To make inkjet technology more widely applicable, developing inks that work effectively on a broader range of paper types is a key area of current research. Instead of producing costly special papers, creating new ink formulations is a more practical and efficient solution.
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