Pad printing, also known as tampo printing, is a wet printing process used to apply ink to 3D and delicate surfaces. This technique is suitable for imprinting logos, graphics, and solid colors on a wide range of materials.
This method creates consistent prints on flat, curved, or complex surfaces. It works by using a silicone pad to apply ink to the item. When the pad touches the surface, it molds to it without distorting, allowing graphics to be applied to various surfaces without losing their shape and quality. Unlike screen printing, which applies a thicker layer of ink, pad printing puts down a very thin ink layer, usually less than 1 micron (about 0.000039 inches). For applications where backlighting or precision is essential, you might need to apply more than one layer.
Most types of materials can be printed using this method. The only materials that cannot be printed are those with a lower surface energy than silicone pads, such as polytetrafluoroethylene (PTFE). This is because the ink needs to adhere, and such materials also do not adhere well like silicone.
Some plastic materials may require surface treatment to ensure high print quality.
The pad printing process typically consists of five stages
In stage 1, the cliché is inked and wiped clean using a squeegee to ensure an even layer of ink is applied to the engraving, without covering the primary cliché. This is because the silicone pad will absorb all the ink it comes into contact with. The design on the cliché is very thin. Therefore, the ink layer is very thin and dries almost instantly.
In stage 2, the silicone pad is placed down, creating pressure on the ink layer and the cliché. The ink layer adheres to the surface of the silicone as it dries.
In stage 3, the silicone pad moves to the product. Meanwhile, the squeegee returns to the cliché, preparing to be inked again
In stage 4, the silicone pad is pressed onto the product. It adheres to the shape of the product, ensuring sufficient pressure between the surfaces to transfer the ink. Silicone has a very low surface energy, so the ink easily adheres to it.
In stage 5, the component is completed, and the silicone pad returns to the cliché, where a fresh ink layer has been applied and wiped clean. The next component is loaded, and the process begins again from the start.
The print quality is determined by the level of detail on the cliché. The smooth silicone layer will transfer the entire ink layer it absorbs onto the surface of the component. The level of detail can be very precise, going down to 0.1 mm (0.004 in.) with a spacing of 0.1 mm (0.004 in.) between lines.
Pad printing is used to decorate various products where appearance or essential information on textured or delicate surfaces is required. Keyboards on handheld devices, remote controls, and some mobile phones are printed using pad printing.
It finds extensive use in the manufacturing of consumer electronics, where decoration in inappropriate molds is necessary. Typical examples include applying logos, instructions, and images.
Sports products can have intricate shapes. For instance, golf balls are round with a surface covered in dimples. Pad printing can be used to print graphics over these contours with high detail and clean edges. Other sports balls, including soccer, baseball, and basketballs, are also printed using this method.
Pad printing and hydro transfer printing are the two primary methods suitable for applying ink directly to textured surfaces. Spray painting can be used for a similar effect, but it’s a different process that requires masking and finishing steps.
The main difference between pad printing and hydro transfer printing is that hydro transfer printing is used to cover the entire surface. Pad printing is typically more precise, faster, and used to apply fine graphic details.
Similar to other printing methods, ink is applied using either linear or rotary printing techniques. Rotary printing techniques allow for continuous printing on textured surfaces, and they can also print on cylindrical products like cosmetic packaging all around.
Pad printing can be used to apply conductive ink, thus enabling the printing of circuits on curved, concave, and convex shapes.
While it has the capability to print on flat, concave, and convex shapes, pad printing is limited in terms of how well the silicone pad can adhere to the shape. For example, it cannot print more than half the way around a cylindrical part. In such cases, rotary pad printing is used.
It is limited in printing graphic details not larger than 100 mm x 100 mm (3.94 inches). This is the maximum size that a pad can receive from the cliché.
Ink used in pad printing is often limited to solvent-based types because water-based ink will not adhere to the silicone pad.
The tooling cost is low. The cliché is typically one of the more expensive parts but is limited to a maximum size of 100 mm x 100 mm (3.94 inches). It can be cut with laser, photopolymerization, or CNC machining.
The cycle time is fast. Ink can be applied while still wet, which is an advantage for multicolor printing.
Labor costs are low as most of the process is mechanized.
This process is limited in its use of solvent-based ink, and related thinning agents may contain harmful chemicals.