Pressure sensitive adhesives (PSAs) have a wide presence in the market, being widely used in different applications such as adhesive tapes, labels or repositionable adhesives in the food, pharmaceutical, security packaging and automotive industries. They are also commonly applied for medical purposes as they are ideal for their ease of application and adhesion to the skin.
There are different types of PSAs depending on their composition and manufacturing process: polyurethane based PSAs, acrylic PSAs, polysiloxane based PSAs, polysiloxane based PSAs, polyisobutylene based PSAs, etc.
Polyurethane based PSAs are more hydrophilic than the rest of PSAs and are biocompatible with the skin so they are preferable for medical applications. However, they present an important disadvantage as they have an inherent low tack and low peel adhesion.
In this sense, a Spanish research group has developed a process for producing a new family of PSAs based on thermoplastic polyurethanes. The new formulation has managed to solve the main drawbacks of the polyurethane PSA, i.e., its low tack at room temperature, obtaining optimum adhesion properties, without sacrificing its cohesion.
The adhesive is synthesized by the reaction of isocyanates and polyols. By controlling the synthesis, a good balance between tack, adhesion and cohesion can be achieved. The main characteristic of these adhesives is that by slightly varying the composition and synthesis conditions, specific adhesives are obtained with specific tack ratings that operate in short temperature ranges. As an example, several formulations have been optimized for specific applications in the following temperature ranges:
• Between 10ºC and 39ºC, focusing on an optimal point of adhesion at 37ºC. At temperatures below 25º its adhesion capacity drops considerably. This adhesive is ideal for use in medical and skin contact applications.
• Between 5ºC and 20ºC. This adhesive is ideal for special applications such as labelling for the transport of goods at room temperature (fresh food, beverages, etc.).
• Between -10ºC and 5ºC. This adhesive also focuses on specific applications such as labelling for the transport of refrigerated goods.
The production process has been carried out satisfactorily at laboratory level where the combination of its components and the synthesis processes have been optimised. The different adhesives obtained have been characterized and their applicability has been validated in different uses, such as biomedical or low temperature conditions.
These PSAs can be applied in the following sectors:
• Biomedical: Body temperature conditions are very stable. A number of polyurethane PSAs have been developed that operate only in these temperature ranges. This has a great applicability for example in the fixation of bandages on the skin. In addition, by slightly varying the temperature, the tack can be eliminated, avoiding patients the usual discomfort of removing the bandages.
• Labelling: There are containers and packages in all types of industries and these must be labelled and wrapped for proper treatment. Sometimes these packages must operate in very specific temperature conditions. This technology makes it possible to define optimum tack in very specific short temperature range, outside of which adhesive tack is considerably reduced. Good label condition can be a good indicator that the package has maintained the preset temperature conditions over time. It can also be useful for removing labels from products once they have fulfilled their function since they can be easily detached by slightly varying the temperature of the label.
The Spanish university looks for companies in the biomedical or labelling sector interested in patent licensing or technical cooperation agreements to scale up this process or to jointly develop R&D projects to look for new applications for these adhesives or adapt them to the necessities of the company.