Printing Inks

Printing Inks
Ink Ingredients
Ink ingredients fall into three main categories: pigment, vehicle, and modifiers/additives. Because there are so many different types of printing processes and print applications, the ingredients used in these three categories may vary widely. For example, for offset lithography, ink requires a higher degree of pigment than many other processes. This is because nearly half of the ink used in the offset process does not reach the printing surface. In direct printing methods, such as letterpress, a much higher percentage of the ink reaches the substrate.

Pigment
The ingredients that comprise the color of the ink are referred to as pigment. The pigments are formulated from substances that create a desired color when the substances are blended together in specific proportions. Some of these substances may be ingredients found in nature or they may be produced synthetically. The substances can be in the form of dyes, powders, liquid dispersions, or concentrated pastes.
Pigments for printing inks are chosen for certain characteristics that make them suitable for use on printed products. For example, it is desirable for many print applications to be printed with inks that have a high degree fade resistance (light fastness), while other applications, such as food packaging, may be printed with nontoxic ink because of the possible contact with food items.
Vehicle
The vehicle is the substance in the ink mixture which carries the pigment and binds it to the printed surface. The vehicle can be formulated from petroleum or vegetable oils, solvents, or water. The vehicle must have the ability to be in a liquid form during the printing process, but dry rapidly when it reaches the printing surface. The illustration below shows how the vehicle carries the pigment through the roller train of a press and transfers it to the paper.


Modifiers and Additives
Modifiers and additives change the properties of the ink so that it can be used properly for different types of print processes and applications. Modifiers and additives may include the following:
• Driers: speed up the ink drying process.
• Waxes: reduce the possibility of ink from the front of one sheet transferring to the back of another sheet (setoff). The wax improves slip and scuff resistance of the ink. It is not possible to apply varnish to a printed sheet that has been printed with ink containing wax additives.
• Antiskinning agents: keep the ink from drying too rapidly and skinning over in the ink fountains of the printing press.
• Extenders: increase the coverage of the pigment in the ink.
• Distillates: improve the flow of ink.

Ink Characteristics
Body
The body refers to the consistency of the ink. The consistency of the ink may vary from the beginning of a press run to the end of a press run because of external factors, such as prolonged exposure to the air and the increase in heat produced by the roller train of the press.
Tack
The tack refers to the stickiness of the ink. The tack is determined by the resistance of the ink film to "split". Splitting occurs when the ink from a printing plate is transferred to the printing blanket. During this process, only some of the ink is transferred, which splits the ink film. If the ink does not have the proper tack, the print quality will be poor because the improper quantity of ink is transferred to the printed surface.
Viscosity
Viscosity is the degree that ink resists flow when it is under force, such as in the roller train of a printing press. If ink does not flow easily, it has a high viscosity, and if it flows easily, its viscosity is low. As with body, the viscosity can change as it is used on a press, because of the friction and heat generated by the roller train. Viscosity is measured with an instrument called an inkometer.
Length
Length is the ability of ink to flow and is sometimes confused with viscosity (the degree to which ink resists flow under force). It is necessary for the ink to move properly through the roller train of the press in order to achieve the best results. The friction and heat produced by the press may change the length of the ink.
Opacity
Opacity refers to the covering power of ink. Different pigments have different degrees of opacity because of the substances used to produce the pigments. Opacity is sometimes referred to as color strength.
Tinting Strength
Tinting strength is the ability of an ink color to produce a tint with the addition of white pigment and is also referred to as coloring power.
Permanency
The degree in which printed ink resists the fading power of light is known as permanency. Inks that have a greater proportion of their volume as pigment tend to fade more slowly. The rate that an ink fades is known as the degree of lightfastness and is especially important when printed items, such as an outdoor billboard, will be exposed to a high level of light.

Ink Types
Nearly all types of ink can be placed into one of two main categories:
1. Standard Printing Inks: web offset ink (heatset and non-heatset), sheet-fed ink, soybean based ink, process ink for color printing, and others.
2. Specialty Inks: metallic, fluorescent, security, phosphorescent, and others.
Standard Ink Types
Web Offset Non-Heatset Ink
The non-heatset variety of web offset printing ink is a common type of ink used on web presses for newspaper and business forms printing. Non-Heatset ink is printed on absorbent, uncoated paper stock. Coated stocks should not be used with this type of ink because the paper will not completely absorb the ink, resulting in excess smudging and smearing.
Web Offset Heatset Ink
The heatset variety of web offset ink contains special varnishes that help the ink dry when heat is applied. Heatset presses are equipped with drier units for this purpose. Due to the varnishes, the ink printed on the paper is highly flammable, so the drying units must be specially built and properly maintained to avoid potential hazards. The main advantage of heatset ink is a printed product with a higher degree of quality.
Quickset Ink
Quickset ink contains a special varnish to speed the drying process. Unlike heatset ink, quickset ink does not require a heat source for proper drying and curing. The ink will not dry out on the press, but will dry quickly after it has been printed onto the substrate.
The are four basic processes that allows quickset ink to dry depending on the formulation: evaporation, absorption, oxidation, and polymerization. Newer types of quickset ink have a greater proportion of antioxidants and higher boiling-point distillates, which evaporate more slowly, so the absorption process plays a greater role with the newer inks. All four processes share equally in the ink curing process with older ink types.
Uncoated paper stocks are best suited for quickset ink. This is because the low viscosity distillates and antioxidants are quickly absorbed by the substrate, which leaves the remaining pigment and vehicle to dry quickly on the surface.
Sheet-fed Ink
Sheet-fed ink is manufactured specifically for sheet-fed presses and usually has a higher tack than web offset inks. The reason for this is that most sheet-fed presses run at slower speeds than web presses and a higher tack is necessary to provide the necessary quality.
Rubber-base Ink
Ink formulated with a rubber base is a good choice when flexibility in the printing process is important. Rubber-base ink can be printed on coated and uncoated paper and it dries quickly. It is most often used on small sheet-fed presses.
Soybean-base Ink
Soybean-base ink is becoming a popular alternative to petroleum-base ink because of the ease in which it is used and because it is environmentally friendly. Soy-base ink prints and handles similar to petroleum-base ink, but it is much less toxic because of the soybean oil. The soybean ink is biodegradable, meaning that it is eventually broken down and is much less hazardous to the environment. Some soy inks may contain petroleum additives, so if a client requires 100% soy-based ink for a print application, it is important to be fully informed on the type of soy ink that is used.
Water-base Ink
Water-base ink has been around for awhile, but it is still not as popular as other ink types. The usage of water-base ink may increase as environmental laws get tougher on the acceptable VOC (Volatile Organic Compounds) emissions generated from petroleum-base ink. Water-base ink emits no VOC's. It is safe to work with and the print quality is comparable to other ink types. Water-base ink is used mainly in flexography and gravure printing. It is a good choice for printers and customers who want their projects manufactured with nontoxic materials.
Laser Ink
Laser ink is specially formulated to withstand the extreme heat of the laser printer. If conventional ink is used for the preprinted portion of a document (such as an invoice or statement), the ink will melt in a laser printer because of the excessive heat produced by the laser printer. This results in damage to the preprinted document and possible damage to the laser printer because of ink adhering to the internal parts of the printer.
UV (Ultraviolet) Ink
Ultraviolet ink is formulated to cure and dry when exposed to a UV light source, unlike conventional ink, which dries through evaporation and absorption. Instead of being absorbed into the paper, the UV ink remains on the surface until it is exposed to the UV rays, which instantaneously transforms the ink into a hard film. UV ink can be applied to many types of substrates including paper, metal, vinyl, and glass.
Process Ink Colors
Process ink colors are used in Four Color Process Printing. Cyan, magenta, yellow, and black are the colors necessary for this process and are formulated differently for different types of printing processes.
High-Fidelity Ink Colors
High-fidelity ink colors are use in an advanced form of color printing, combining the standard four process colors of cyan, magenta, yellow, and black, with two more colors - usually orange and green. This allows for a greater color range, increased subtlety in the gradations of color, and additional vibrancy.

Specialty Ink Types
Non-porous Ink
Non-porous ink is used for printing on substrates, such as metal or plastic, that do not allow ink to be absorbed into the material. Because the printing surface of these materials is nonabsorbent, the ink dries solely through oxidation rather than absorption.
Metallic Ink
Metallic ink provides a distinctive look to a variety of print applications. The ink is produced by blending different types of metallic powders into the ink mixture, such as aluminum powder to create a silver appearance and bronze powder to create a gold appearance. Some metallic inks can nearly duplicate the look of foil on some applications without the need to purchase the additional equipment required for foil stamping.
Metallic ink is more challenging for the press operator to control than conventional ink. One reason for this is that the metallic powder blended into the ink mixture cannot be ground as fine as other pigments because the metallic ink will lose its luster. The larger particles create problems on the press, especially with the offset lithography process. To overcome some of the special print problems, some printers do a double hit (running the piece through the press a second time to apply another coat of ink to strengthen the coverage).
Most printers require an upcharge for the use of metallic ink on an application because the ink is more expensive to produce and makes the print job more time consuming. Metallic ink tends to have a much shorter shelf life than standard ink.
Magnetic Ink
Magnetic ink is comprised of a petroleum-base ink blended with magnetic iron oxide particles. The magnetic iron oxide particles allow documents printed with this type of ink to be read and sorted by electronic scanning equipment. Checks are an example of a document printed with magnetic ink. The MICR (Magnetic Ink Character Recognition) number at the bottom of the check is the only portion of the check printed with the magnetic ink. The remaining copy on the check is printed with standard ink to ensure that no other printed area on the check interferes with the ability of the scanner to read the magnetic MICR number.
Fluorescent Ink
Fluorescent is another type of ink that can provide a distinctive look for a variety of print applications. Fluorescent ink colors are most often printed on labels, posters, and signs that are used for alerting people to hazards or attracting their attention to advertising pieces.
There are several points to consider when using fluorescent colors. The ink tends to fade quickly, so they should be kept out of direct sunlight. Because of their tendency to fade, fluorescent inks have a short shelf life. Another point to consider is that fluorescent ink is very transparent, so it may require a double hit (a second run through the press) in order to achieve the desired results. In spite of this potential problem, fluorescent ink is a good choice for creating emphasis and increased visibility.
Phosphorescent Ink
Applications printed with phosphorescent inks acquire a "glow in the dark" property after the phosphorescent area has been exposed to light. The length of time that an application will glow in the dark depends upon the ink ingredients and the length of time that the application is exposed to light. In some cases, a 10-30 minute exposure to light can yield an afterglow of up to 12 hours. The ingredients of phosphorescent ink are nontoxic and are free of radioactive additives. It is very useful for road signs, sporting goods, exit signs, safety products, toys, and novelty items.
Pearlescent Ink
Pearlescent ink is a specialty ink that is used to add highlights and depth to the printed area of an application. It is able to provide an almost 3-dimensional effect to some applications.
Edible Ink
Edible ink is used on print applications that may come into contact with food or the ink may be part of the food product and therefore it must be made of totally nontoxic ingredients. An example where edible inks are used would be in the monogramming found on some confectionery items. Because the inks are used on food items, they are strictly regulated by the government.
Scratch and Sniff Ink
Also known as a microencapsulated ink, scratch and sniff ink releases a fragrance when the microcapsules are broken. The scratch and sniff ink is commonly used in magazines for perfume advertisements. When the consumer scratches the surface of the designated area of the ad, the capsules are broken, releasing the fragrance.
Medical Device Ink
Ink used for printing on medical devices is made of nontoxic ingredients so that direct printing on noninvasive surgical and medical disposable items is possible.
Moisture Resistant Ink
Moisture resistant ink is most often used for different types of packaging or for applications that may be used outdoors.
Security Ink
There are a variety of inks that provide added security features to print applications. Some security inks allow documents to be created that are tamper proof, while the use of other types of security inks prevent documents from being copied. Security inks include the following varieties:
• Coin Reactive
• Bleeding
• Erasable
• Heat Reactive
• Visible Infrared
• Optically Variable
• Pen Reactive
• Penetrating
• Photochromic
• Solvent/Chemical Reactive
• Thermochromic
• Water Fugitive
• UV Invisible Fluorescent
Desensitizing Ink
Desensitizing ink is a transparent ink that is applied to the face of CF (Coated Front) and/or CFB (Coated Front and Back) carbonless paper in order to deactivate the CF coating. The use of desensitizing ink is important when an application requires that handwritten or imprinted data not be transferred through the various pages of a carbonless form in specific areas.
Electronic Ink
Electronic ink can be transformed from bright white to dark and then back to bright white again with a small electrical charge. The ink consists of plastic microcapsules that contain both dark dye and white ink chips. The microcapsules are sandwiched between thin layers of flexible material, which substitutes for traditional paper. When an electrical charge is applied, some of the white chips float to the top of some capsules to create a white surface and in other capsules, the white chips remain at the bottom allowing the dark fluid to remain visible. Different characters are created by applying the electrical charge under different combinations of capsules. After the initial electrical charge is applied, no further charge is required to hold the image in place, (unlike a computer monitor, which requires a constant stream of energy in order to display an image). The content of the flexible page can be changed instantly and then be held on the page for as long as necessary. Although, this technology is still being perfected, it could be a major advancement in variable imaging and in the reduction of paper usage for some print applications.