Choosing a Pad Printing Machine

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. Ink flows into the cliche from a trough or ducts, and a doctor blade removes excess ink. As the cylinder rotates, the s/llcone mlfer pad picks the ink out of the etching and transfers R to the substrate. One advantage of this system k speed - small items can sometimes be printed at rates of 120,000 parts/hr.

Rotary pad-printing systems (Figure 6) developed directly from gravure printing. They are very suitable for cylindrical parts and continuous flat printing.

These presses use a rotary drum type silicone pad in conjunction with a steel cylinder cliche. The design is etched into the cylindrical cliche, and the ink flows onto it from an ink trough or ducts. A doctor blade removes the excess ink. As the cylinder rotates, the silicone-rubber printing roller picks the ink out of the etching and transfers it onto the substrate.

One advantage of this system is its speed. With small components such as bottle caps and container closures, 120,000 parts/hr can be achieved. Printing these one at a time on conventional equipment, assuming a 1-in. (2.54-cm] diameter cylinder, would run at about 3000 parts/hr. Another advantage is the very fine detail that can be printed with rotary presses.

Ink deposits tend to be slightly less than in conventional pad printing, particularly a t the higher speeds that are attainable. Also, the ink must be run with high levels of solvent. Ink manufacturers recommended 20°/0 solvent, but I once used 30% on a multicolour application. Each colour may require a separate solvent mix that must be determined at the start of a job and maintained throughout and on subsequent runs. Control of the solvent balance is essential. I recommend using ink pumps to maintain the ink conditions. These will normally have solvent feeds that must be carefully set to the correct feed rate. Some pumps have viscosity-measurement devices, but I have not found them particularly successful. Remembel- that changing the colour requires purging the system and why do I not recommend rota~ysy stems for short runs.

Alternatives to steel printing cylinders are available. Steel foil and even photapolymer cliches can be mounted onto a modified cylinder, but their effectiveness is debatable because the pressure on the doctor blade causes them to wear fairly quickly. Although steel cylinders are by no means cheap, the investment is paid back by reduced downtime.

The capital cost of rotary systems is relatively high because a feeding system is almost always necessary to make full use of the technique. Output levels keep the cost per print extremely competitive. The quality should be as good as, if not better than conventional pad printing.

Although most of the major suppliers produce some variation of this equipment, availability is limited. Never accept a press without seeing it run to your specifications on the manufacturer's premises.

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.