PAD PRINTING

Pad Printing also know as tampography or tampo printing is the process of transferring a 2-D image onto a 3-D part. It is an indirect offset (gravure) printing process where a silicon pad picks up ink (image) from an etched plate (also known as cliche) and transfers it onto a 3D object. This printing process prints odd shaped parts such as curved (convex), hollow (concave), cylindrical, spherical, compound angles, textures, etc. which are not possible with traditional printing methods like inkjet. This printing process requires printing equipment. The Pad printing machines range in style depending on the number of colors and the size of the image. Tampo printing operations are used in a wide range applications and industries, most prominently: industrial, automotive, medical, promotional, and textiles.

Here are the necessary components to successfully pad print;  pad print ink, pad print ink cup, pad print plate (with image), pad print pad, and a pad printer machine

THE PRINTING PROCESS

To successfully pad print, you need a printing machine. The printing machines need 4 components to successfully deliver a perfect print onto a substrate (part or object). These components are: the printing plate, the ink cup, the silicone pad, and printing ink. We will review each of these pad printing supplies components below.

An image is etched onto a printing plate. The ink cup holds the ink. Each cup has a ceramic ring for doctoring (sliding) over the etched image on the plate. As the cup slides over the image, it leaves ink in the etch. This ink is then picked up by the printing pad and transferred onto the substrate.

The solvent evaporates, and the ink hardens / cross-links with the substrate.

PAD PRINTING STEPS

Lets review the printing steps in detail:

1: Home position: The ink cup also known as sealed ink cup sits over the  artwork engraved on the printing plate. The cup floods the image pad printing ink.

2: Image pick up: The closed ink cup moves away from the engraved artwork area. As it moves away, the ink cup removes all the excess ink. This exposes the inked engraved image. The exposed ink becomes sticky (tacky) as soon as it is exposed to air.  This is how the ink sticks to the printing pad. Once the ink is picked up, the exposed opposite side becomes sticky as well. When the pad stamps the object (which has a higher surface energy, than silicone pad); the ink sticks to the object.

3: Image pick up:  The silicone printing pad compressed down onto the printing plate.  This pushes the air outward, which in turn causes the ink to lift from the engraved artwork area onto the pad.

4: Image transfer: The sticky ink film inside the engraved artwork area lifts from the engraved artwork area. Please note that not all ink is lifted from the etched printing plate. A small amount of ink is left on the etched plate.

5: Image flooding: The printing pad moves forward.  At the same time the ink cup also moves back to the home position to cover the engraved artwork area on the printing plate. The ink cup again fills the engraved artwork in preparation for the next cycle.

6: Image transfer: The transfer printing pad compresses down onto the product. This transfers the ink layer picked up from the printing plate onto the product.Then, it lifts off the substrate and returns to the home position, thus completing one print cycle.

Pad printing process
pad printing consumables

PLATE AND INK INTERFACE TECHNOLOGIES

Open inkwell system

Open ink well printing equipment are an older method of pad printing. These printing machines use ink trough (ink well) for the printing ink supply. The ink well is located behind the printing plate. A flood bar similar to a squeegee pushed a pool of ink over the plate. Then a doctor blade removes the excess ink from the plate surface, leaving ink on the etched artwork area ready for the pad to pick up.

Sealed ink cup system

Sealed ink cup systems are also known as closed ink cup printing machines. These printing machines use sealed container which act as the ink supply. The ink cups/ sealed ink cups have a sharp ceramic ring or carbide ring with act as the flood bar to supply the image and remove the excess ink from the plate. A pad printing ceramic ring with a highly polished working edge provides the seal against the printing plate.

There are pros and cons for both types of systems.  We will cover this later.

PRINTING PADS

Printing Pads are three-dimensional and are molded mostly form silicone rubber. Their function is to pick up the printing ink from the printing plate and transfer it to the part (substrate).

The pads also known as tampon vary in shape, size, and hardness depending on the application. The most common type of pads are round, square, and rectangular. However, for unique applications, there are specialty pads made for custom applications.

 

pad printing consumables

WHAT IS AN INK CUP?

The ink cup component is the housing for the ink. The ink cup has a doctor ring. The ring is made of carbine or Zirconia. The cup slides front and back across the plate over the etched image. This leaves only a small amount of ink in the etch. This back and forth movement is called doctoring.

The cup assembly is made of several components. The main components are the ring and the cup. The ring is used for doctoring the plate. Additionally, it ensures that only ink is left in the etched artwork on the plate. Rings are made of carbide metal, or zirconia also known as ceramic. Ceramic is typically the best material. The reason is because it is gentle enough not to scratch the plate and strong enough to handle the constant motion of the pad printer.

The other components of the cup are the vent plug which lets the ink vent. And the Drive pin – this is used to drive the cup back and forth.