Pad printing

The pad printing is a relatively young reproduction process. It consists of a metal or plastic plate, coated with a photosensitive emulsion, where the image is recorded by a process chemical, forming a gravure, this plate is covered with ink and swept by a blade, later a silicone pad presses on the engraving of the plate collecting the ink from the gravure and transporting it over the piece that will be printed by contact. This system is currently widely used for marking industrial parts and advertising.

Physical changes in the ink film on both the cliché and the platform allow leaving the area of the engraved image in favor of adhesion to the platform, and later the release of the platform in favor of adhesion to the substrate (material being printed).

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

History

Although certain forms of pad printing had existed for centuries, it was not until the 20th century that this technology became suitable for widespread use. It first established itself in the watch industry after World War II, and in the late 1960s and early 1970s new developments such as silicone pads and more advanced equipment made the printing method much more practical. The ability to print on previously unprintable surfaces caught the fancy of engineers and designers, and as a result pad printing exploded onto the mass-produced market.

Today, pad printing is a well-established technology that spans a wide spectrum of industries and applications.

Processes

Print Cycle

1. From the start position, the sealed ink cup (an inverted cup containing ink) is placed on the work area of the printing plate, covering the image (design to be transferred) and filling it with ink.
2. The ink cup is removed from the work area, removing excess ink and exposing the engraved image, which is now filled with ink. The top layer of the ink becomes sticky as soon as it is exposed to the air, so the ink attaches to the transfer pad and then to the substrate.
3. The transfer pad is pushed over the printing plate momentarily. While the pad is compressed, air is injected, causing the ink to rise (transfer) from the work area to the pad.
4. As the pad rises, the ink inside the design rises along with the pad. A small amount of ink remains on the printing plate.
5. As the pad is removed a little further, the ink cup again covers the work area on the printing plate, refilling the ink design by preparing the mechanism for the next cycle.
6. The pad is placed on the substrate, transferring the ink layer to the final surface. The pad is finally lifted from the substratum, returning to its initial position and leaving the mechanism ready for the next cycle.

Open inkwell system (old technology)

Open inkwell system is the use of a channel (inkwell) for the supply of ink, which is located behind the printing plate. A flood bar pushes the ink onto the plate, and a palette (known as a Ductor Blade or Doctor Blade in English) removes excess ink from the surface of the plate, leaving only the design ink ready for the pad to pick up..

Sealed ink cup system (Latest technology)

Sealed ink cup systems use a sealed container (ink cup) or (ink cup), which acts as the ink supply, replacing the ink supply channel and vane (Ductor Blade). A ceramic ring with a highly polished edge acts as a seal against the printing plate.

Impression Pads

Impression pads are three-dimensional objects typically molded from silicone rubber. They function as a transfer vehicle, picking up the ink from the printing plate, and transferring it to the final surface (substrate). They vary in shape and hardness depending on the application.

There are three main groups of shapes: "round pads", elongated pads called "Bar Pads", and various shapes (square, rectangular, etc) called "Bar Pads" of bread". Within each group there are three size categories: small, medium, and large. Pads can also be custom designed to meet special requirements.

Image Plates

Image plates are used to contain the "image" of the design engraved on its surface. Its function is to hold the ink in this etched cavity, allowing the pad to pick up the ink in the shape of the design, and then transfer it to the substrate.

There are two types of printing plate materials: photopolymer and steel. Photopolymer plates are the most popular, as they are the easiest to use. These are typically used in small and medium scale productions. Steel plates come in two options: thin steel for medium and large scale production, and thick steel for very large scale production. Both types of steel plate are generally processed by the plate supplier, as it involves the use of specialized equipment.

Printing Ink

The ink is used to mark or decorate the pieces. It comes in different chemistries to match the type of media to be printed (see media compatibility chart for selection).

Printing inks are "solvent based" and they require to be mixed with additives to use them. It usually dries to the touch in seconds, although full drying (curing) can take a much longer period of time. There are many more options, such as inks that are cured through the use of ultraviolet light (UV inks), which are suitable for certain applications. UV inks are not fully cured until UV light is applied to the ink. The advantage of these inks is that they can be cleaned off the substrate in case a mistake is made (before UV light is applied). It can be cured with UV light in as little as 1 second of light exposure. This depends on the ink, the substrate and the power of the light and spectrum. UV inks can be reused and their useful life is high as long as the ink is kept clean, without exposure to UV light and has not broken down from the session. This same characteristic makes it easier to clean than some solvents and epoxy resins, as a component part of two inks. There are also too-heat curable inks, which work much like UV in that there is a 'trigger' to the UV. to heal at your convenience. Two part inks typically have a pot life of only a few hours or less. They must be removed when they cannot be revived (by means of retarders, etc.) Ink options are available in many convenient and time-saving forms, but for some substrates you will need to use the type of ink that best adheres to the surface...l.

Weather conditions significantly affect the performance of any pad printing ink, especially ink and open style printers. Too dry can lead to rapid evaporation of solvents causing the ink to thicken prematurely and excessive moisture can lead to ink 'clumping' problems. or something like that. Also the weather can affect other aspects of the printing process such as ink pick up and release from plate to pad on the substrate, as well as polymer plate to blade chatter or binding, due to humidity. Keep this in mind when planning the location of the pad printer. Use any necessary heater, air conditioner, humidifier, or dehumidifier as needed. Always consult Federal, state and local authorities regarding handling, storage and disposal of inks.

Substrate

Substrate is the technical name used to address the parts or materials to be printed, and it is critical to match the substrates and ink series in terms of their chemical compatibility. Please refer to the media compatibility chart for proper ink selection. An "accessory" to hold and support your substrate in order to ensure a good quality print. Accessories vary in materials and complexity depending on the application. One of the most interesting examples of accessory creativity is the use of Lego for short-term printing. This started in a eureka moment of inspiration when Cliff Rowell, a small print shop owner and his grandfather's in Calgary, Canada, was playing with his grandson. This innovation has begun to make its way through the industry in recent years and saves the time and cost of building custom job specific fixtures. Note that substrates must be clean and free of surface contamination to allow proper ink adhesion.

Processes and techniques

There are two main techniques used to create a printing plate. The traditional technique requires a UV unit and involves exposing photos with film positives and etching chemicals on a photopolymer plate. A second technique known as "Computer to Plate" requires a laser engraver and laser engraving consists of a specialized polymer plate. Although the latter technique is suitable for short-term printing it has several disadvantages compared to the former.

Laser plate making is a process that requires the use of a very soft plate, coated with low-quality polymer. Thus, the standard life cycle that can be expected from a laser engraved plate is quite low (10,000 impressions on the high end). By comparison, a hardened steel plate can easily last for over 1 million impressions.

Examples

• Advertising articles
• Medical devices (surgical instruments, etc.)

& * Implantable in the body of medical items (catheters, contact lenses, etc)

• Golf Ball Logos / Graphics
• Decorative designs or graphics appearing in Hot Wheels, Matchbox

or scale cars

• Car parts (in turn signal indicators, panel controls, etc.)
• Cards of computer keyboards and calculator keys
• TV and computer monitors
• Identification tags and serial numbers for many applications