PAD PRINTING

Pad printing, also known 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. Printing machines range in style depending on the number of colors and the size of the image. Typical applications for this printing method include industrial, automotive, medical, promotional, and textiles.

To successfully pad print, you will need ink, an ink cup or a doctor blade for open ink well machines, a printing plate (cliche), a silicone pad, and a pad printing machine.

THE PRINTING PROCESS

To successfully pad print, you need a printing machine. This printing machine requires four components to perfectly print onto a part. These components are the printing plate, the ink cup, the silicone pad, and printing ink. We will review each of these pad printing supplies below.

An image gets 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 and cross-links with the substrate.

PAD PRINTING STEPS

Lets review the printing steps in detail:

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

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, which becomes sticky (tacky) immediately when exposed to air. This is how the ink sticks to the printing pad. Once the silicone pad picks up the ink, the exposed opposite side becomes sticky as well. Then the silicone pad stamps the object (which has a higher surface energy than a silicone pad), and 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 gets 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 is an older method of pad printing. These printing machines use an ink trough (ink well) for the printing ink supply. The ink well is behind the printing plate. A flood bar, which is similar to a squeegee, pushed a pool of ink over the plate. It is this blade that 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 containers which act as the ink supply. The ink cups have a sharp ceramic ring or carbide ring that acts as a flood bar to supply the image with ink. Additionally, the doctor blade removes 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 from silicone rubber. Their function is to pick up the printing ink from the printing plate and transfer it to the substrate.
 
The pads, also known as tampons, vary in shape, size, and hardness depending on the application. The most common types 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. An ink cup has a doctor ring 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.

The cup assembly has several components. The main components are the ring and the cup housing. The ring floods and cleans excess ink from the plate. Additionally, it ensures that the etch has the right amount of ink.
As mentioned, zirconia or carbide are the common materials used to make the cup rings. Ceramic is typically the best material. As a result, it will not scratch the plate. Additionally, it is strong enough to handle the constant motion of the pad printer.

The other components of the cup are the vent plug, which lets the cup vent. And lastly, the drive pin. Other machines have clumps. This pin drives the cup back and forth.

PAD PRINTING PLATES (CLICHÉS)

A pad printing plate, also known as a cliche, holds the image to be printed. The image for printing gets etched on the printing plate. There are two types of printing plates. These are photopolymer and laser plates.

Photopolymer Plate-making

 
Photopolymer plates are light-sensitive. A UV exposure unit is used to etch these plates. Using a film positive or a line screen, the plate gets exposed several times. Plate exposure is cost-effective and gives very high detail compared to laser. It takes about 30–40 minutes to make good printing plates.

Laser Plate-making

Laser plate-making is the process of etching a plate with a laser. There are two types of lasers: a fiber laser and a CO2 laser. These laser marking and etching systems allow for complete repeatability without concern for variation in etch depth, dot pattern, or image quality. Laser plate-making is fast, and takes about 6 minutes per printing plate.

 

 

 
 
laser pad printing plates - Boston Industrial Solutions, Inc

WHAT IS AN INK CUP?

Pad printing machines use supplies to complete the print process. These pad printing supplies are inks, solvents, hardeners, and printing primers. Please note that silicone inks use catalyst and not hardener. Mix the right amount of ink, solvent, and hardener depending on the application. In cases where the ink adhesion is not optimum, use printing primers to improve ink adhesion.
pad printing ink - 2

PAD PRINTING INK

Printing ink is an important component of the pad printing process. A wide variety of ink series are available for different substrates. To achieve the desired ink adhesion, you must use the correct ink. Different pad printing inks work for different types of materials, like glass, metal, plastic, silicone, and more.
 
The Natron inks for pad printing are available in a wide variety of colors. Standard colors such as black and white are always available. And if you want a non-standard, we can make it for you within 24 hours. Boston Industrial Solutions’ inks are formulated to allow custom color matching.
 

INK SOLVENT

Solvent is a component of pad printing ink that aids in ink transfer.
The solvent once mixed withe ink evaporates during the printing process. This evaporation not only helps in the transfer of image but also helps in drying of the ink.
 
There are many different types of solvent.
Some solvents only work with certain series of ink.
Other solvents work with more than one series of ink and vary in how fast they evaporate (speed).
The rate at which the ink evaporates is important. Some factors that might affect the choice of the solvent are the substrate, humidity, and desired printing speed.
TPV ink Thinner