PROCESS TO MANUFACTURE THICK LAYERS OF RADIATION CURED ADHESIVES

The invention relates to a process to manufacture an adhesive layer in an easy to handle process, whereby the adhesive is applied in a molten state to a substrate in an amount to form a layer of 150 to 5000 μm and the adhesive is cured by UV-radiation whereby the adhesive comprises a polyurethane bearing at least one unsaturated curable group in the chain and the radiation source is preferably an UV-LED.

EXAMPLE PROCEDURE

A reaction vessel is used comprising a stirring device, a vacuum pump and a heating bath. To this vessel all parts all components 1-7 were added and stirred under reduced pressure and 120° C. for drying. Component 8 is added and the reaction takes place at 90° C., then maintained at 120° C. Upon obtaining a pre-defined NCO-content components 9, 10, 11 are added, the reaction mixture homogenized and reacted until the NCO content has dropped below 0.1%

A PU prepolymer is prepared by reacting the following materials (the amount stated for each component is in parts by weight):

Formulations: The polymer was blended with the initiator and the crosslinker

Films are casted with a thickness of about 230 μm and irradiated for 1-2 sec. using a UV-lamp (380 nm, 200 mW/cm2)

Dumbbell shaped test specimens are cut from the cured film and tested.

A collection of about 200 sheets was bundled having a spine of about 1 cm.

The spine was coated with the adhesive at 130° C., the layer having a thickness of 300 μm

Immediately the layer was cured by UV-radiation (UV-LED, 380 nm).

Directly after curing the film a hard paper was pressed against the adhesive layer.

After 7 h the cover paper was pulled apart. Fiber tear was observed.

The book was opened, the adhesive holds the pages together.

The adhesive layer was pulled from the spine. Fiber tear was observed.