Pad printing refers to the irregular surface of the substrate, using copper or steel gravure, and casting a hemispherical pad printing head through silicone rubber, which is pressed against the layout to transfer the ink to the substrate to complete the transfer printing way.
What is Pad Printing Technology?
Pad printing technology can print text, graphics, and images on the surface of irregular objects, such as text and patterns on the surface of mobile phones, computer keyboards, instruments, meters, and many other electronic products, all using pad printing technology.
The Principle of Pad Printing Technology:
The pad printing process is simple. Steel (or copper, thermoplastic) gravure is used, and a curved pad printing head made of silicone rubber material is used to dip the ink on the gravure onto the surface of the pad printing head, and then press the surface of the object.
The Development of the Pad Printing Process:
The pad printing process is a special printing technology developed in the 1980s. Because of its advantages in printing on products with small areas and concave and convex surfaces, it makes up for the shortcomings of the screen-printing process, so it develops very quickly. In the early 1990s, with the opening of the China market, more and more foreign-funded enterprises in traditional industries. Such electronics, plastics, gifts, and toys entered the China market, and pad printing technology and screen-printing technology were widely used as the main decoration methods develop.
Application Areas of Pad Printing Technology:
Pad printing is widely used in daily necessities, toys, pens, electronics, electrical appliances, plastics, leather, metal, glass, light industry, food packaging, and other industries, toys, daily necessities, gifts, and other hardware and plastic products, pattern text printing.
The ability of the transfer head to absorb ink and its influence factors on printing quality:
- The shape of the transfer head: The basic shape of the transfer head tends to be round, rectangular, or square. These shapes are suitable for rolling the pattern when the surface of the transfer head is in contact with the etched plate first, and then in contact with the printed object. The size and shape of the pattern and the strength of the rolling determine which transfer head is used.
- The hardness of the transfer head: The harder the transfer head, the better the ink transfer effect. While the hardness depends on the amount of silicone oil added to the rubber, very little silicone oil is needed to use solvent-based inks.
- A Surface condition of the transfer head: Ideally, the surface of the transfer head is very smooth and matt; carefully wiping the transfer head with a solvent-saturated gauze can produce good results. If the transfer head shows signs of wear, the transfer head should be replaced, taking care not to damage the surface of the transfer head.
- Materials for making the transfer head
How to Choose Ink?
Silicone transfer head printing sheet requires ink with high pigment content, fast-drying resin, and fast solvent evaporation. The ability of the ink to become tacky quickly will determine whether the ink can be effectively transferred to the surface of the substrate. At the same time, to adjust the printability and performance of the ink, in addition to adding solvents and catalysts, it is also possible to use any additives, such as viscosity modifiers, antistatic agents, rheology agents, etc. However, the use of additives will have a great impact on the printing performance of the ink, so be careful when using them.
Due to the wide range of materials that can be printed using this process, a variety of inks are available. Silicone transfer head printing ink is expensive due to its small amount. The screen-printing ink is not suitable for transfer head printing because it does not dry fast enough and the pigment content is only 5%.
Pad printing workflow:
- One-component ink:
One-component inks are dried by solvent evaporation, and catalysts are not necessarily added to this ink. One-component inks are available in glossy and non-glossy types, and they are mainly used for printing on plastic substrates.
- Two-component ink (chemically reactive ink):
Before printing, a catalyst must be added, and the catalyst reacts with the resin in the ink to achieve the purpose of drying the ink through the polymerization reaction. When two-component inks are used in pad printing, it is necessary to add a certain ratio of catalyst, usually measured by weight. The addition ratio of the catalyst must be strictly controlled. Improper mixing ratios of ink and catalyst can lead to printed product defects such as uneven ink adhesion and insufficient durability of the printed image.
- Bake dry ink:
Bake-drying inks can be divided into two types, one is based on standard two-component inks with additional catalysts; the other is specially formulated for substrates such as glass, ceramics, and metals. Bake-drying inks must be warmed and dried at a certain temperature. When using this ink, the drying time should be calculated. The higher the temperature, the shorter the drying time. However, if the drying temperature is too high, the ink film will become brittle, so the ink should be dried at a temperature that can maintain its flexibility of the ink.
- Oxidized ink:
Oxidation ink absorbs oxygen in the surrounding environment to polymerize to form an ink film without adding a catalyst. Typical applications for oxidizing inks are flexible packaging substrates and substrates of synthetic materials such as rubber products or keyboards. Due to the slow drying speed and a long time of oxidation ink, the relative usage is limited.
- UV pad printing ink:
UV inks are rapidly cured and dried under UV energy. When UV light penetrates the ink, the photosensitive molecules in the ink interact with neighboring molecules, and the whole process is completed in seconds or milliseconds. It has the environmental protection features of friction resistance, acid and alkali resistance, and no volatile matter.
- The ink is evenly covered on the steel plate by the brush
- Scrape off excess ink with a scraping steel knife
- The ink in the pattern is smeared from the print head down to the steel plate
- Cover the pattern from the displacement of the print head to the product
- Drying, testing, and packing
What is the Difference Between Pad Printing and Silk Screen Printing?
- Pad printing is a type of screen printing. Pad printing can print curved surfaces and flat surfaces, while the general screen-printing process refers to flat screen printing. Pad printing is to corrode the pattern on the steel plate and then transfer it to the substrate through the glue head. The advantage of pad printing technology is that it is suitable for large and small products, as well as a variety of strange-shaped products. The disadvantage is that the ink layer is relatively thin.
- Silkscreen printing is to print the pattern on the substrate through the screen plate. The advantages of silk screen printing are that it has a hand feel and can be screen printed on a large plane. The disadvantage is that it is not suitable for special-shaped products, and the ink layer of the silk-screen printing process is relatively thick.
Features of Pad Printing Technology:
- Process cost: Single piece cost, low labor cost, because most of the processes are completed by machining.
- Application products: Used for surface printing of 3C electronic products, vehicles, interiors, sports equipment, etc.
- The output is suitable: Single pieces to large batches are available, a single piece can be simply made into ordinary steel plate printing, and large batches can be done by machine.
- Quality: Sharp print details are achieved, even on uneven surfaces.
- Speed: A single printing time is about 1-5 seconds, completed by the machine.