To achieve a good print result, particular attention needs to be paid to the most important parameters in rotary screen printing. The key factors influencing this printing method are the type of screen plate, the ink, the squeegee and the flow path. The article in this edition looks at the squeegee, because this is the parameter that press operators are best able to influence themselves in screen printing. The important requirements for the squeegee are to ensure the rubber is of the appropriate hardness, to print with the best possible squeegee edge and to find the optimum squeegee position.
Selecting the correct squeegee rubber
In most cases, the squeegee rubber is made of polyurethane (PU, DIN abbreviation: PUR). Polyurethanes are plastics or synthetic resins that, depending on the manufacturing method, can be hard and brittle but also soft and elastic. These different PU properties are reflected in the different hardness grades of the squeegee rubber, which are indicated using the Shore system. Squeegee rubbers with three different Shore hardness grades – 55-60, 65-70 and 70-75 – are used for rotary screen printing. The lower the Shore figure, the softer the squeegee rubber. The individual hardness grades are also identified by different colours. Shore 55-60 rubbers are yellow or white, Shore 65-70 rubbers are red and Shore 70-75 rubbers are green.
In principle, more ink is transferred by a soft squeegee rubber than a hard one, but a harder rubber is more suitable for text. The screen acts less abrasively on a hard squeegee rubber and it is therefore possible to use it for longer than a soft squeegee rubber before regrinding. The squeegee pressure should always be kept as high as necessary and as low as possible.
The different characteristics of the individual squeegee rubbers are shown in the table below.
Pengde Rubber And Plastic Products Co., Ltd. (ISO9001:2008 Certified) was established in 2004, located in Foshan, China. Specialize in researching and manufacturing high performance standard and custom mold casting polyurethane elastomer products. Moreover, we manufacture some polyurethane products that meet SGS and ROHS material specifications.
Trust us! Our engineering staff have more than 20 years' experience in polyurethane elastomer production.