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Types of Inks | Choosing an Ink | Starting Out

Types of Inks

Standard pad printing inks are made of resins, pigments, and thinners. The resin system, also referred to as the binder, is what forms the dried ink film. There are numerous resin systems for pad printing inks.

Pigments are the colorants dispersed in the resin system.

Thinners (or solvents) adjust the viscosity of the resin 1 pigment mixture, and give the ink its printing characteristics.

Catalysts (or hardeners) may be added to certain inks to make them harder, glossier, and 1 or to increase adhesion. Inks that use catalysts are referred to as "two component inks". Single component inks don't require catalyst. Some pad printing inks can be either one or two component.

Other additives that may be necessary include retarders, adhesion modifiers, matting agents, and anti-static agents.

Retarders are really just very slowly evaporating thinners that are used to slow the drying or tacking of the ink.

Adhesion modifiers are used to increase the adhesion capability of certain ink types. In some cases adhesion modifiers and catalysts can be added to ink at the same time.

Matting agents are used to lower the gloss level of ink when necessary.

Anti-static agents are added to help control static.

In addition to standard solvent based pad printing inks there are baking inks, oxidizing inks, sublimation inks, and UV cured inks that are used in pad printing.

Baking inks are usually two component inks requiring a special catalyst and sometimes-special thinner. These inks, which must be baked or flame cured, are used on glass, ceramics and some metals.

Oxidizing inks are used where weather and chemical resistance are necessary, in addition to flexibility. They cure by absorbing oxygen from the surrounding atmosphere. Their use is limited due to their slow drying nature.

Sublimation inks involve a special process whereby the substrate is heated to become porous after the ink is applied. The dyes of the ink pass into the substrate, changing the substrate's color. Once the substrate cools the ink is essentially "sealed". These inks are commonly used on items like computer keyboards, where even two-component inks can lack the necessary resistance. Sublimation inks are very difficult to color match.

UV cured ink, by design, contains no evaporative solvents, making it very difficult to transfer via pad printing. In addition to being difficult to pick up and transfer, UV ink lacks opacity, and thus doesn't work well on dark colored substrates.

Choosing an Ink

Most ink manufacturers provide technical information that recommends ink or inks for nearly any substrate you'll run across. What you need to do first is find out exactly what the material you intend to print on is made of. The more specific, the better. It doesn't help your supplier's technical people much if you tell them that you want to print on "black plastic", since there are hundred of substrates that could fall under that description.

Once you know the substrate, you'll need to find out what characteristics the ink must have. Asking your customers questions like these can do this: How well must the ink adhere? Does the ink need to meet specific abrasion, chemical and weather resistance specifications? Are there any specific concerns about the potential toxicity of the ink? What are the ink's drying and curing requirements? Can the supplier match the colors I want? Is any type of certification required?

After gathering this information you're ready to contact suppliers to discuss your project and obtain recommendations.

Most pad printing equipment and ink manufacturers have applications laboratories staffed by experienced technicians that can either recommend which ink you should use based on the information you give them, or they can test print your parts in their lab. Having your parts tested is usually no charge, unless you insist on having your image printed, in which case a nominal fee is usually applied. Even then, many manufacturers will apply the costs of testing toward the purchase of any equipment you buy as a result of the tests.

Starting Out

Once you've got your ink, make sure you read the manufacturer's technical information and carefully follow their instructions for mixing, thinning, drying and curing. All too often people fail to follow the proper procedures for mixing, and I or fail to follow drying and curing schedules, only to have their parts fail testing. Starting Out Pad printing is part art and part science. To expect to be able to purchase a machine, choose the right cliche', pads and ink, and then print successfully overnight is unrealistic. You don't need to have experience with any printing process, or be a chemist to succeed, you just need to take the time to learn the variables involved in the process, and how to control them.

The first thing to do is contact pad printing equipment manufacturers and discuss your intentions with them. In doing this you'll not only learn if your project is feasible while gaining information about the process, you'll also get a feel for which manufacturer you want to deal with.

Feeling confident with a manufacturer is more important than getting the lowest price. The costs of poor service and technical support will end up costing a lot more than you'll ever save if you allow cost to be your sole determining factor in choosing a manufacturer.

Your manufacturer should be willing to work with you from beginning to end on your project. They should be willing to test print your parts and provide you with samples to prove their machines and methods work before you agree to buy anything.

Finally, make an effort to obtain proper training by visiting the manufacturer's facility, having them make a video specific to your machine (even if it costs money), or having them come to your facility to train you and your operators there. It will prove to be well worth the costs.