Transfer pad printing, commonly known as pad printing, is an “indirect offset gravure” printing process directly related to a process invented several hundred years ago in Europe.It was originally used in the watchmaking industry in Switzerland to decorate watch faces. It has now developed to a point where it is one of the major methods for printing and decorating the surfaces of objects, particularly plastic.
GENERAL INDUSTRY
The founder of the Tampoprint Company in Germany built the first automatic machines used in general industry in the early 1960′s. He had seen small hand operated machines that lent themselves to automation. The printing pads on these machines were made of gelatine. This was a major limiting factor in the use of the process in automatic applications. The gelatine’s lack of elasticity and susceptibility to ambient changes meant that the process did not really take off in general industry until the invention of silicone rubber transfer pads.
POTTERY INDUSTRY
Before this time the Pottery Industry in Stoke on Trent had been using the same process for decorating their ceramic ware. It was generally single colour work on both flatware (plates, saucers, etc) and hollowware (cups, jugs, etc). The process was faster than applying transfers was but limited to one colour. Originally the transfer pads used by the potteries were made from an inflated pig’s bladder. This was then replaced by gelatine. These pads were much bigger than those used in general industry, as they had to cover the area of a dinner plate.
The original flatware machines were developed in the late 1940′s, and it was not until the 1960′s that the hollowware machines were produced. These used a rotary pad and cylinder. The printing plates were hand engraved onto copper and then chromium plated. The depth of engraving was varied to give different densities of colour. Inks were thermoplastic; that is, in normal ambient conditions they were wax like and had to be heated up for printing. This meant that the ink trough, plate and sometimes the pad were kept at a temperature of approximately 60o centigrade. The very nature of the process meant that high levels of skills were required to maintain constant production.
The next change in the potteries came when etched steel plates that had been developed for use in general industry were used. At the same time silicone pads took over from gelatine and inks were formulated that also used solvent evaporation to enable the transfer mechanism. At the same time the ability to use four colour process to print onto ceramics was achieved.