The benefits of UV crosslinking systems

IndPrint

Kiwo – Kissel + Wolf GmbH was founded in 1893. A family owned company, it is based in the Rhine-Neckar Metropolis and headquartered in Wiesloch near Heidelberg. Today, the company delivers its products to more than 110 countries worldwide.

As a manufacturer of chemical products, the company offers solutions in the areas of adhesives, printing form chemistry (screen printing and textile printing), cleaning agents, resists and coatings, as well as services for product development and contract manufacturing.

Die cut bonding sheets are increasingly being replaced by screen printable adhesives, because self-adhesive articles can be produced considerably cheaper with them. In adhesive printing, UV screen printable adhesives will gain more and more market share, displacing solvent and water based systems. UV screen printing pressure sensitive adhesives are characterised by very good printability. Under UV radiation they harden very quickly, are mild in odour and have a very high flash point. Furthermore, working with UV cross linking adhesives is a more environmentally friendly process. However, handling is quite complex.

Pressure sensitive adhesives have been used in screen printing for many years. Hence this is not a matter of a new technology, but a long established process. Simple solvent containing pressure sensitive adhesives are printed for ink transfers, applying the adhesive exactly on the back of the motif. The adhesive has to bond aggressively and form a smoothly flowing and even surface. For scratch resistance, a certain hardness of the adhesive is important.

Searching for further fields of application for this adhesive family, a new area was found in replacing the die cut, double sided tape. When using self-adhesive front panels and displays with double sided adhesive tape, the adhesive layer is die cut where switches and lightning are located. This process is done before laminating and can lead to serious transfer problems when working with filigree and free standing motifs, not to speak of the expensive die cutting process. Markets for this application are the automotive and electronic industries where high quality adhesives with excellent performance are being used according to given specifications.

Since the 80s specialised adhesives have been developed, partly in cooperation with customers, and have been established for series production. Alongside solvent based products, water based pressure sensitive adhesives take a high market share. They are used in the field of electronics and white goods.

Kiwo’s Kiwoprint UV 85 is a screen printable, pressure sensitive adhesive based on UV crosslinking polymers; it has excellent temperature resistance for permanent technical applications and adhesive joints in visible areas (touch panels, visual instrument panels, front panels, pressure-sensitive electrical devices).

Kiwoprint UV 92 is a UV pressure sensitive adhesive with very high tack and good shear strength for technical applications in, for example, the automotive industry and for front and control panels.

Basically UV crosslinking, pressure sensitive adhesives offer the following advantages:

• No drying on the stencil

• Very easy screen cleaning

• High build up thickness (100% system)

• Low emissions

• Fast but sophisticated UV hardening

But, what is sophisticated UV hardening? Contrary to the solvent and water based adhesives, where the evaporation of the liquid components always generate the same adhesive layer, the UV process works by polymerising only the adhesive, ie the parameters of UV crosslinking determine the bonding result.