Choosing a Pad Printing Machine

Pad Printing Machines with Sealed Ink Cups

The diagram here shows a reciprocating cliche press, but other sealed-cup models are available. These presses are designed to contain the ink in a cup that is turned upside down and pressed firmly against the cliche, sealing in the ink. The cup holds the ink and also acts as the doctor blade. The advantage of this system is that solvent evaporation is reduced to a minimum.

This system (Figure 4) is considered by some to be the panacea of all pad-printing ills; would that it were so. What is surprisirrg is that this "new" development has actually been around for many years. A swiss manufacturer of padprinting machines for the watch-dial industw had a system 30 years ago!

The concept of these presses is to contain the ink in a cup that is turned upside down. The cup is pressed firmly against the cliche, sealing in the ink. The cup not only holds the ink but acts as a doctor blade as well; it tl-averses back and forth across the cliche, leaving ink only in the etched areas. The obvious advantage of this system is that solvent evaporation is reduced to a minimum. This allows much closer contror of ink conditions, resulting in the opportunity for reduced downtime and partially unmanned operation.

"But", you say, "the salesman told me it will run 24 hours a day, seven days a week, 52 weeks a year." Did he say what the print quality would be, how often you would have to add ink, how much the cliche would wear, or how long the cup would last? Did he mention that you can't ignore the fact that the ink does degl-ade the cliche over time, that using two-component inks is not recommended, that the cliche should be twice the size of a conventional cliche for a given image, or that it is better to keep the cliches and cups as matched pairs? That question raises another one you shou[d ask when shopping for such a system: "How much does a replacement cup cost?" The answer may be a surprise: $500 is not at all unusual. Fortunately, if the damage to the cup is very slight, it can be repaired by carefully honing the contact surface on a fine carborundum stone. Some cups can be remachined at a quarter of the replacement costs. This all means that the cups must be handled very carefully.

Ink cups come in different constructions. The simplest is machined from solid metal, normally hardened steel.

The second type has a rlbbon-steel contact surface that can be replaced when worn. The third is a metal cup with a ceramic contact surface bonded onto the metar. This provides a very good life. But is more expensive than the conventionaL cup.

To achieve maximum usage with any of these cups, apply minimum pressure and be certain that the cup is mounted on a stable bearing. Any tendency for the cup to rock will cause uneven wear and leave a film of ink on the cliche that will be transferred by the pad. Some systems use a magnet to hold the cup onto the cliche, which appears to work very well. Cliche and cup wear with a magnet can be less than in a vertical-loading al-rangement, thus allowing satisfactory change from one cliche to another with out changing the cup as a matched pair.

Figure 4 shows a reciprocating cliche press. In many sealed-cup systems today, the cliche is stationary and the cup tl-averses the plate. Mukicolour machines are now commonplace, and some manufacturers offer a choice of a sealed ink cup or open inking mechanisms on the same basic press.

There is no doubt that the sealed-cup systems are being further refined. They were available only in limited print sizes originally, but the use of larger cups is changing thb. Another interesting variation on the closed-cup press involves the use of cliches that are mounted inside the ink container vertically rather than horizontally.

The cliche rises straight up out of the container, with a doctor blade at the top scraping ink from non-image areas as well as sealing ink in the container from solvent evaporation. The pad moves horizontafly to pick up the image from the cliche and, depending on the application and the press design, rotates either 90° or 180° to deposit the image on the substrate. The Ink/solvent mixture is nearly as stable as in a closed-cup system, but larger areas can be printed as large as 5 x 18 in. (12.7 x 45.7cm). One additional benefit of sealed inking systems: They reduce the lever of solvents that are exposed in the working envil-onment and expelled into the atmosphere.

Choosing a Pad Printing Machine - Introduction

In the padprinting industry purchasing decisions are often based on asswnptions that are simply nuts - literally.

Manually Operated Pad Printing Presses

Except in cases where pad printing will be done on a very small scale, manual machines are not even entry level anymore. However, some may be useful for testing purposes.

Open Ink Trough Pad Printing Machines

In these original semiautomatic machines, the inking mechanism is mounted above the cliche. Although more modern models ha we better features, contro/lirrg ink condition fluctuations.

Partially Covered Ink Troughs

In these machines, ink is contained in a trough behind the cliche. The ink is pulled forward by a spatula mounted on a horizontal carriage with the doctor-blade assembly.

Sealed Ink Cup Pad Printing Machines

These presses are designed to contain the ink in a cup that is turned upside down and pressed firmly against the cliche, sealing in the ink.

Reciprocating Cliches Pad Printing Machines

In these models, instead of the pad moving back and forth from cliche to substrate, the cliche moves out of the way, while the pad remains stationary.

Rotary Pad Printing Presses

These presses use a rotary drum-type sllicone pad, usually in conjunction with a steel cylinder cllche into which the desfgn is etched.

Total Colour Transfer System

This technique, used almost exclusively in ceramic decoration, combines pad and screen printing.

Carousel Style Pad Printing System

This multicolour pad-printing system uses a cambination of two rotary tables and a rotating pad carousel.

Non-Horizontal Pad Printing

Machines such as this are suited for printing onto surfaces that are vertical or angled.

Computer Numeric Control (CNC)

In presses with computer numeric control (CNC), the substrate is stationary and the pads are programmed to print one image at a time onto the item.

Pad Printing Press Options

Most manufacturers provide a variety of add-ons for their presses.

How to decide what machine to buy

To enable you to judge which press to buy, you will at least need answers to all of the questions shown under Purchasing Considerations.

Pad Printing Machine Purchasing Considerations

Trying to decide which pad-printing machine to buy? Start by answering the following questions.