Printing inks reviewed

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  • Date March 14th, 2011 12:42
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  • We're starting a review on the chemistry of inks - more specifically on the different pigments that are commonly used and how these end up being an ink. The idea is to describe how the pigments are made and applied for them to become a printing ink, and what the manufacturing aspects are of this procedure. Then when pigments are understood, we'll do the same for the binders, oils and additives that are used by printers in their process of ink making. Why do all that? As print oriented designers, ink is one of the more impacting materials used. While it is often the easiest to have your printer deal with all the finer aspects of ink selection and quality control, a designer needs to also understand the suitability and character of a color and ink. Having knowledge on the constitution and methods of manufacture of these materials helps to better guide your projects through the mazes of sustainable design. Yes, the title sounds heavy, but we're not devoting any space to doing chemical analysis of finished inks. From a designer point of view there is nothing to be learned by such an analysis. Having said that, there are terms and lingo that are used, which may need some explanation. So part one here is to help describe some technical terms that could be used in either description, value proposition, quality or application of an ink. Keep the list in mind when reading up on the pigment descriptions, as these terms come back quite a few times, and some are a constant as to summarize pigment properties. Hue - When spectrum colors merge into each other, there are conditions where one color has a slight mixture of another in it, and that mixture gives to the predominant color an additional hue. Think a red that has a violet kind of shine to it. That would then be a red of violet hue. A green that has a blue hue (because its mixture of yellow and blue will have had a predominant blue proportion). Tint - When we use a color or a hue, and mix it with white, there is a gradation of that color. It's lighter in its original appearance - and is a tint of its original color. For pigments; this would be lightening the pigment powered by an admixture of a white pigment. Shade - This is the opposite of tint; a color or hue is mixed with a small amount of black, or its complementary color, so that you get a darker gradation of the original. It's often misused or misunderstood as a hue. Top Hue and Under Hue - very printer jargon, but one of importance for any print designer. We print on different materials, and each medium has or offers different thicknesses. In a few cases, there are different amounts of color absorption related to the different thickness of a medium. That causes a variation in the color or the hue of the ink that was applied on to it. So miss the mark here and your magenta is a pink or has a blue hue, or became a deep dark red. Color Strength - by that it is describing the actual amount of color present in a pigment. It's measured by its tinting power when mixed with white. It is to measure the power a pigment has to impart its hue or color to another pigment. Has to do with the crystalline character of a pigment, where the more amorphous ones always have to higher color strength. Abrasive Quality - when a pigment has hard material in it, it will have an abrasive effect on plates, forms and cuts. Hence it will wear down these, which can result in a loss of sharpness and definition. Important factor; it determines the duration of a usable print plate or cut, and can risk increase of waste when the quality of work has been compromised. Fineness - to be understood for what it actually means; how fine is the powder. And heads up; a material can be quite fine in its powder, but still be abrasive. Pigments by default need to have a high rate of fineness. And it influences the inks ability to print fine lines and delicate tonal effects. Oil Absorption - The physical structure of pigments will see the need for different amounts of oil to be needed in order to make them into a paste. The measure of this is called the oil absorption of a pigment. Not to be confused with the oil used in ink; the pigment is made into a paste, which is going to get prepared into an ink later. Livering - When an ink thickens to a rubber-like mass, it is said to liver. This happens basically when the oils in the paste or ink start oxidizing. The faster a pigment livers, the less ideal or suitable that pigment is. Shortness - this gets hands on now; when a pigment is mixed with large quantities of oil, and it still remains stiff or cannot be drawn out between the fingers (it breaks) it is said to be short. These could have some print applications, but the rule of thumb is the shorter a pigment the less suitable the ink of these will be. Flow and Length - another print jargon. Flow is the property of a pigment to combine with another property, and have the ability to run and feed well on the press. Inks that do this well are the ones that can be drawn out into a string between the fingers; and that is called Length. In other words; each includes and suggest the other. Another word used for this is Viscosity. These are essential ink properties, and pigments that do not measure up to an extent should be avoided. Tack and softness - Tack can best be described as the pulling power of an ink against another surface. When there is very little cohesion between ink and tack is absent, an ink is rated to be soft. Body color - that is the color of the pigment itself, before it is mixed with a vehicle (oil) to be a paste. Adding that vehicle to the pigment will almost always influence and change that body color. Transparency - is used in the general sense of the word; the degree with which an ink or pigment allows color or light from another source to pass through it. Opacity - gets confused with transparency but is different. It is the property of absolute stopping the transmission of light or color from another source. So, a transparent color can be made more or less opaque by adding a base to it. Many opaque pigments can be made transparent (to some extent) if printed in a thin film. The opacity and its covering power will vary (as will the color strength) depending on the crystalline character of a pigment. Body - the measure of the density of a pigment is called the body of that pigment. It is more a slang or work floor term over a genuine chemical term, and it is used to convey the amount of covering power an ink has. The denser the more covering it does. We'll use the term Body as a measure of the consistency and density of an ink. As in a stiff ink that stands well will have a 'good body', while an ink that is soft and runny is going to be having 'lack of body'. Incompatibility - for various reasons (chemically and or physically) certain pigments cannot be used with others. Or certain pigments can not be used with certain vehicles under certain circumstances. Lead based pigments cannot be used with others that have sulphur particles. Colors affected by alkalies are bit to be used for printing labels for soap. Bleeding - not to be confused with the bleed setting in your DTP software. Certain pigments when mixed with water or oil or other print vehicles are partially soluble and this solubility is called Bleeding. Some pigments bleed easily, while in other cases the bleeding is cause because the pigment paste has not been properly made. Fastness to light - to be understood for what it means; the degree of resistance the color has to the changing action of ordinary light. Atmospheric Influences - it is related to the fading of colors - sometimes attributed to it. Physical and or chemical changes in the color due to the influence of the atmosphere. Oxidation, solvent actions of gases, acid radical present in the air, dryness or moisture, temperature variable. Those are the terms and variants that will be covered and discussed for all ranges of colors and pigments. First up; the blacks. sources: The Printing Ink Manual Analysis and Deformulation of Polymeric Materials: Paints, Plastics, Adhesives, and Inks (Topics in Applied Chemistry)
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