The inks you buy may not have the amount or type of solvent required for this to enable you to "fine tune" the system to suit the ambient conditions. Even in a controlled environment, different solvents may be needed depending on the application. For example, the drying speed of the ink may be influenced by whether you are doing single-color work or wet-on-wet multicolor printing. It may be necessary to use a faster-drying solvent for the first color printed, an intermediate-speed solvent for the second, and a retarded for the last.

Minor additives include plasticizers and surfactants designed to improve the ink's flexibility, flow, pigment stability, and other characteristics. These additives are essential for adequate performance. Without them, the ink would suffer such defects as brittleness, poor film strength, pigment separation, and unsatisfactory flow.

We represent

We, at Spinks India, are the importers and suppliers of various products of various companies in India. These include:-

Ink types

The ink systems currently available to the industry fall into seven different categories:

• Solvent evaporating
• Oxidation curing
• Reactive (i.e., catalyst curing, two component)
• Baking
• UV curable
• Sublimation
• Ceramic and glass

Solvent-based inks are predominant in the pad-printing industry. They dry very rapidly through solvent evaporation alone. Care must be taken when printing non-absorbent materials with these inks, as absorbency is required to give best adhesion. They are available in gloss and matte finishes and perform particularly well with many thermoplastic substrates. A simple way to tell if a solvent based ink is suitable for a particular plastic is to rub the solvent used to thin the ink onto the substrate. If the solvent melts the surface of the plastic, chances are the ink will adhere very well.

In Oxidation-drying inks, the resin absorbs oxygen from the atmosphere and undergoes a polymerization process, producing a very tough, flexible, weather-resistant ink film. They have limited uses in pad-printing applications due to their slow drying speed, but they are excellent for printing onto metal and glass.

Two-part or Reactive (catalyst curing) inks, used extensively in pad printing, also contain resins capable of polymerization. However, the required catalyst is either blended into the ink by the manufacturer or supplied separately and mixed in by the printer when required. Either way, the inks have a restricted shelf life once the catalyst is added.

Two-part inks cure very rapidly when heated. They are generally printed on difficult substrates such as metals, some plastics, and glass, and are particularly popular when good chemical and abrasion resistance is required. Particular care must be taken when mixing the base ink with the catalyst. Manufacturers specify an exact weight to be added, so you must always weigh the components when mixing - no exceptions! Inaccurate mixing can give inconsistent adhesion and product-resistance characteristics.

Another important factor to be aware of with two-component inks is that after printing and prior to complete curing, the temperature of the printed ink film must not drop below 59°F (15°C). Should this occur, the ink will cease curing and cannot be restated. This may not be a problem if the curing may nearly be complete. However, if curing takes place in storage over a period of time, the ink film is vulnerable. A dry ink film is not necessarily cured. It takes time, temperature, or combination of both to effect a complete cure. With two-component inks, curing typically takes five days at 68°F (20°C) or 10 min at 212°F (100°C). This information is available on the ink's technical data sheet, which unfortunately, most users do no bother to read.

Baking inks need a certain minimum temperature and time to cure. The cure time varies inversely with the temperature: the higher the temperature, the shorter the drying time. The flexibility of the ink film is another factor to consider with these inks. Ink films that must retain their flexibility require lower temperatures, for a higher temperature can cause brittleness.

Sublimation inks involve a special process where a solid turns into a gas when heated. When these inks are applied to an appropriate surface and then heated to the specified temperature (approximately 392°F or 200°C), dyes in the ink sublime, the surface of the material becomes porous, and the dyes pass into the material. This actually changes the color of the base material. Once the material has cooled, the ink is sealed into the surface. Pad printing is a suitable process for sublimation since the ink deposit must be kept to a minimum to prevent color bleeding. Applications include keyboards and other areas where abrasion resistance is critical. Care must be taken when selecting colors, as certain inks are sensitive to UV light and fade very quickly. The range of colors is very limited, and matching Pantone colors is almost impossible. Another limitation is that the substrate color must be lighter than that of the ink.

Ceramic and gas thermoplastic inks are used quite successfully in the pad-printing industry. These inks are similar to the ones used in screen printing in that at ambient temperatures, the ink is solid (like candle wax). It becomes fluid when raised to 176°F (80°C), which is accomplished in the ink reservoir and cliché

Post-production processes
Any post-printing steps the part must go through could affect the ink performance. In screen printing, die-cutting and thermo-forming can both be problematic with certain inks. In pad printing, clear coating is a process to watch. The underlying ink must be fully cured and impervious to any solvents in the clear coat. The clear coat won't stick to under-cured ink, and it may cause the ink to bleed if the solvents aren't compatible.

Depending on the ink system and the ambient temperatures, the ink will have to be completely replaced with a new batch in 8-10 hr. This is because a two-component ink will begin curing in the ink reservoir and its printing characteristics will change. In very high ambient temperatures, it may be necessary to change the ink more often. It's very important to estimate a two-component ink carefully, since anything not used that day should be disposed of correctly and is expensive to waste. If the job had called for a single-component ink (no catalyst), the ink wouldn't cure in the reservoir and could be used on press for a much longer period. I would still recommend changing it after 48 hr, as contaminants can build up that will alter the ink's properties. Oxidation-curing inks may also undergo chemical changes.

By the way, two-component inks are not recommended for use in sealed ink cups, as they gel if they are not agitated and will cure completely if left in the cup for extended periods. Care must also be taken when using reactive ink on screened clichés. Any trace of ink left in the etched portion of the cliché overnight will cure and be impossible to remove the next day. This applies to a greater or lesser extent with any part of the machine or jigging.

Rules of Using Ink

• Read the technical data sheets.
• Read and understand the Health and Safety Data Sheet.
• Always wear protective clothing, gloves, and goggles when mixing inks.
• Ensure that ventilation is adequate at all times.
• Stir ink and hardeners before use.
• Use only specified solvents.
• Weigh the ink, solvent, hardener, components, and mixture.
• Do not use inks or hardeners that are past their shelf life.
• Seal partly used cans of ink. Their shelf life is reduced once opened.
• Keep unused mixed ink in a closed container.
• Do not used mixed two-component ink after pot life is expired.
• Do not use two-component inks in closed-cup printing system.
• If single-component ink is used, continuously change every two days.
• Never Mix ink types to achieve a color match.
• If ink splashes onto your skin, wipe off excess with tissue or cloth and wash with soap and water or proper hand cleaner.
• Never use thinners to remove ink from skin.
• If ink or solvents enter your eye, irrigate with water for 15 min and seek medical advice immediately.
• In case of swallowing, do not induce vomiting. Seek medical advice immediately.
• In both the above cases, take the Health and Safety Data Sheet and the Technical Data Sheet to the medical authority.