Pad printing is a printing process that can transfer a 2-D image onto a 3-D object. This is accomplished using an indirect offset (gravure) printing process that involves an image being transferred from the printing plate (cliché) via a silicone pad onto a substrate (surface to be printed). Pad printing is used for printing on otherwise impossible products in many industries including medical, automotive, promotional, apparel, electronics, appliances, sports equipment and toys. It can also be used to deposit functional materials such as conductive inks, adhesives, dyes and lubricants.

Physical changes within the ink film both on the cliché and on the pad allow it leave the etched image area in favor of adhering to the pad, and to subsequently release from the pad in favor of adhering to the substrate (material being printed).

The unique properties of the silicone pad enable it to pick the image up from a flat plane and transfer it to a variety of surface (i.e. flat, cylindrical, spherical, compound angles, textures, concave surfaces, convex surfaces).

Pad printing cycle

1. From the home position, the sealed ink cup (an inverted cup containing ink) sits over the etched artwork area of the printing plate, covering the image and filling it with ink.
2. The sealed ink cup moves away from the etched artwork area, taking all excess ink and exposing the etched image, which is filled with ink. The top layer of ink becomes tacky as soon as it is exposed to the air, that is how the ink adheres to the transfer pad and later to the substrate.
3. The transfer pad presses down onto the printing plate momentarily. As the pad is compressed, it pushes air outward and causes the ink to lift (transfer) from the etched artwork area onto the pad.
4. As the transfer pad lifts away, the tacky ink film inside the etched artwork area is picked up on the pad. A small amount of ink remains in the printing plate.
5. As the transfer pad moves forward, the ink cup also moves to cover the etched artwork area on the printing plate. The ink cup again fills the etched artwork image on the plate with ink in preparation for the next cycle.
6. The transfer pad compresses down onto the substrate, transferring the ink layer picked up from the printing plate to the substrate surface. Then, it lifts off the substrate, returning to the home position, which completes one print cycle.

Printing plate makingThere are two main techniques used to create a printing plate. The traditional technique requires a UV exposure unit and involves photo exposure with film positives and chemical etching of a photopolymer plate. A newer technique known as “computer to plate” requires a laser engraver and involves laser etching of a steel or specialized polymer plate. The latter technique provides several advantages over the former; among them:

• Print quality is improved due to minimized loss of resolution. With photo exposure, the image is first transferred on film positive and only them, on the plate. Thus the image on the plate is second generation. With laser etching, the image is transferred on the plate directly from a digital file. Thus the image is first generation and better quality.

• The image on the plate is easily duplicated. Unlike chemical etching that involves several steps with many variables and manual work, laser etching is a simple, easily repeatable procedure with stable results. Plates can be made the same every time.

• Laser etching enables “combination etching” - using halftones for bold areas and open etch for fine graphics.

• With laser etched plate, ink lay down is improved. Laser engraved steel and polymer plates have a straight walled etching and more precise inkwell than photopolymer, thin or thick steel plates.

• Laser etching saves time. Chemical etching usually takes 15-20 minutes for a plate; laser etching takes about 1-5 minutes per plate.

• Laser etching is “greener.” Laser etching does not involve chemicals and thus eliminates hazardous waste.