Printing inks are products tailored to meet specific printing technology and end-user demands. To meet those demands, more than 1 million individual ink formulas are used today.
These formulas are used in the different printing and / or coating processes such as flexography, rotogravure, offset, screen printing, letterpress printing, non-impact printing and roller coating; Depending on the process, they can be solvents, water, oleo-resinous or energy-curing mixtures (UV rays or electrons).
Because a single formulation meets all possible end-use and technology requirements, printing ink manufacturers have formulated solutions for almost all known ink requirements, for example, an ink that meets the requirements for printing a newspaper on very high speed presses, it will not be suitable for printing on plastic bags.
History of ink
The ink is as old as the pen. The Chinese knew about ink in the 23rd century BC. C. They created vegetable, animal and mineral inks and used it to paint on silk and paper. The best ink they used was made from pine sap from trees that were 50 to 100 years old. They also built ink with a mixture of skin glue, carbon black, and black bone pigment mixed in mortar. In India, the ink was built from the 4th century BC. This ink called “masi” was a mixture of burned bones, tar and pitch. The Greeks and Romans developed ink with soot, glue, and water (so-called “carbon inks”). The “iron gall ink” was known from the 5th to the 19th century and was a mixture of iron salts and tannic acids. The only problem with this ink is that it is corrosive and damages the paper it is on. In 12th century Europe, ink was made from hawthorn branches that were cut in the spring and allowed to dry, then the bark from the branches was peeled off and allowed to soak for about eight days. That water was cooked until it was thick and black, but while it was boiling, wine was added to it. The thick black liquid was bagged and allowed to dry in the sun. The result was ready-to-use ink.
The main characteristics of the inks are described below:
Viscosity is a measure of a liquid’s ability to resist flow. A thick liquid that does not flow easily has high viscosity; a thin liquid that flows easily has low viscosity. The viscosity of the ink directly influences the performance on the press and is ultimately transferred to the sheet.
Optimizing print adhesion can be challenging due to the number of process variables that need to be controlled such as: ink chemistry, substrate quality, surface treatment, and ink transfer method.
Virtually all surfaces require preparation to ensure minimum adhesion requirements. This task is known as pre-treatment and post-treatment, and it is influenced by the surface receptivity of the base material of the ink layer.
The thixotropic ink
It is a property of fluids, which describes their “false body” or a consistency, thickness and viscosity that decreases with the application of stresses or other forces. Certain inks, such as offset inks, are stiff and thick when in their containers, but when used they become thinner and more fluid, this due to an unstable structure formed by solid particles within the ink that break down when force is applied. . Thixotropy is also called shear thinning. Some inks also exhibit the opposite property, swelling, in which viscosity increases when stresses are applied.
Drying is the process that, for a solvent or water-based ink, stands between the landing of the drop on the substrate and any final curing, fixing or post-treatment process. The ideal drying process removes moisture and / or solvent from the surface, promotes proper adhesion of ink to the surface and low penetration into the surface, as well as good fastness to rubbing and other degradation mechanisms.
What is the ink made of?
The fundamental components of ink are pigments and dyes. Pigments can be developed organically and artificially, particles that are insoluble and are not affected by any chemical present in the element with which they are being incorporated, and are only absorbed in selective areas. In contrast, dyes are soluble and when incorporated with a medium such as ink, they produce color through chemicals.
Ink made with color usually includes the following ingredients: petroleum distillate solvent, linseed oil, some form of organic pigments, and soybean oil. For black ink, the ingredients are white pigments that are usually made from titanium dioxide along with carbon black. The ink may also contain additives such as wax, oils, and some form of drying agent to enhance printing or custom design. If an ink is linseed oil based, it will oxidatively dry in air. When alcohol is present, the ink will evaporate dry.
How is the ink made?
The two main ingredients to create the ink are a dye, and the chosen pigment that must be ground before adding it so that it mixes well and does not settle to the bottom or separate and form pigment pockets. The combinations of colorants and pigments along with the other ingredients will vary depending on how the ink will be used. After the combination of the dyes and pigments is complete, they will be combined with water, possibly alcohol or linseed oil, and other chemical ingredients depending on the ink being manufactured. All ingredients are placed in a large, hot bowl until properly mixed and appear in a smooth liquid form. Some manufacturers filter the ink mixture to ensure that no ingredient deposits remain that can impede the rest of the printing process when the ink is used.
Types of printing inks for paper
When we talk about color printing inks, different types of ink are used. Each of these inks has its own unique characteristics that offer benefits in some areas and disadvantages in others. In large format printing, the types of inks used are too important to build the exact type of design that is desired.
Below we will describe the five most common types of color printing ink used and the differences between them.
1. Aqueous Inks
They are water-based printing inks that have two varieties called: dye (Dye) and UV inks. The former combine with water when applied and then the water evaporates to leave the ink, they have the advantage of offering bright colors, but they fade very quickly under the sun’s rays and they are not waterproof, so it is recommended for interiors and for short-term promotional work.
UV inks are similar to chalk dust suspended in water. When the water evaporates, they leave the chalk as small dots that later form the image. They are very resistant to UV rays and will last longer. However, they do not have the brightness of the color of dye inks.
2. Dry sublimation inks
You can select between the aqueous type used for desktop and wide format printing and the solvent type used in large format printing devices. It is not exactly an inkjet print, but it is a type that is often mistaken for such.
3. Solvent inks
They are pigment printing inks that contain colorants, but do not use water. Instead, they use volatile organic compounds that are cheaper and very flexible on certain types of surfaces. Solvent inks are waterproof, durable in all conditions, UV resistant and provide very bright colors. Its main disadvantage is that it uses toxic chemicals in its preparation, for which special care must be taken.
4. UV cured inks
They are printing inks that “cure” when exposed to strong ultraviolet light, dry quickly, which makes them quite attractive to printers and can be used on different surfaces. Their disadvantage is that they are quite expensive.
5. Latex inks
They are new printing inks on the market that can be used on different surfaces, even on vinyl. They act similar to solvent inks but without the dangerous toxic chemicals. However, chemicals are used that are not totally environmentally friendly either. For many, these types of inks are still new, but they offer a lot of promise.
Flexographic ink: composition
Printing inks are mixtures developed starting from combinations of colorants (pigments, colorants), binders, solvents and additives. A wide variety of raw materials is essential for this great variety of formulas, and this is especially true for additives that, although used in small quantities, are essential for the ink to meet the required conversion properties. It is in this matter that the specific knowledge and intellectual property of individual ink manufacturers lie.
Raw materials can be individual chemicals, but are typically mixtures of different substances, resulting in inks that contain 20 to 60 unique chemical compounds.
The Flexographic Ink Composition comprises: about 10 to 30 weight percent resinous binder, about 5 to 10 weight percent coloring agent, about 4 to 7 weight percent wax, about 3 to 12 percent by weight weight percent chlorinated polyolefin, and about 55 to 75 weight percent solvent.
Flexographic ink viscosity
The main components of the ink are pigments, additives and solvents. Any change in composition or impure raw materials results in various chemical and physical properties of the ink that can negatively affect the printing process. Knowing the density and viscosity of ink is of paramount importance to ink producers because these physical properties generate vital information about the quality and usability of the raw material and the final product.
Offset printing inks
The ink used for lithographic offset presses is a paste, rather than a fluid. That means it is thick and sticky. Usually it is distributed in cans.
Web offset inks are generally more fluid and have less tack than sheet-fed lithographic inks. Most offset inks dry quickly without the need for additional equipment, but there are also inks optimized for infrared, ultraviolet, or electron curing. All offset inks contain water repellent materials, which are necessary because offset lithography relies on the fact that oil and water do not mix.
Types of inks pdf
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