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A broad and novel array of UV-curable pressure-sensitive adhesives from Henkel now combine many of the virtues of familiar water- and solvent-based adhesives formulations plus the advantages of hotmelts.
The principle of UV curing has been known since the Seventies. However, it was not until the
introduction of new raw materials, in the mid-Nineties, that the commercial use for intensive UVinduced crosslinking of macromolecules became possible. The ingenious feature of the new Liotron adhesives is the possibility to obtain different adhesive properties by precisely defining the curing window. For more than 10 years, UV curable pressure sensitive adhesives have been available to the market, for different applications. The customers have found many benefits from using this technology, for example
- No need to remove & regain solvents
- High line speeds
- Improved ageing resistance
- Good water stability
- Chemical resistance
- Temperature resistance
Today there are 4 major chemistries used for UV curable pressure sensitive coatings. These products are characterized as
- Hot Melt UVPSA
- Warm Melt UV PSA
- LowMeItUVPSA
- Liquid UVPSA
Due to only a limited range of raw materials being available for a couple of years, the number of
suitable formulations has also been quite limited. Today, together with innovative coating technologies and advanced additives the situation has changed: There are amazing new possibilities available to meet the markets demands. Adhesive formulators like Henkel use these tools to fulfil the markets demands by
- converting existing raw materials
- developing special solutions for high demand
- opening new market opportunities by innovation
The tailor-made development of PSA has several different facettes. Due to the variations of the end users requirements, there is still an urgent need for specialities in PSA formulations. A real challenge in the past was not only the formulation of removable pressure sensitive adhesive, but also for them to be based on UV curable technology. These products have to fulfil some very important properties
- Moderate adhesion: Peel strength of 1.5— 5 N/inch (FTM 1)
- No increase or decrease of peel strength during storage
- No interaction with face stock or substrate and no adhesive transfer during removal
- Good anchorage to face stock
Compared to the conventional technology the UV curable PSA match most of the necessary
requirements:
- Acrylic dispersions had a lot of advantages and have been the technology of choice for
removable applications by special formulation but one of the drawbacks is the limited water
resistance.
- Conventional HMPSA can overcome this problem but they are sensitive against ageing,
temperature, solvents and UV and also have some drawbacks regarding die-cuttability.
• UV curable PSA combine the benefits of the acrylic chemistry with the attractiveness of
HMPSA and can be optimized by a new degree of freedom, the curing level.
In the past, the industry tried to achieve those goals by adding soft raw materials to the basic polymer which had a permanent character. Bleeding and creep independent of the curing level occurred and made products like that unsuitable, especially for non-primered paper labels.
By using
- the right curing level
- improved formulations
- the right application technology
Henkel has managed to overcome these limitations.
