Pressure-sensitive adhesive tape

Applicant: Novatech International NV
Inventor(s): Kristof Van Havenbergh; Ken Meerbergen; Gunther Dreezen
Patent number: EP4372061
Publication date: 2024-05-22
 

Novatech International NV patented a pressure-sensitive adhesive tape based on an adhesive composition that is cured by exposure to UV and is still moisture-curable. The patent also describes its production method and the bonding of substrates using this innovative adhesive tape.

There is a wide range of high-performance adhesives available, with varying properties and applications across a number of industries, including automotive, aerospace, construction and biomedical.
Pressure-sensitive adhesives (PSAs) are adhesives that form a bond when pressure is applied. PSAs are frequently employed in the form of mounting tapes, which are commonly referred to as PSA tapes. These tapes typically exhibit a high immediate tack, allowing objects to be mounted immediately without the need for a further curing period. This is made possible by the formation of a physical connection (i.e. physisorption) caused by electrostatic forces such as hydrogen bonds or electromagnetic forces such as van der Waals forces. Applying the tape at a high pressure will result in a closer contact and a better wetting of the surface, which will improve the physical connection. It should be noted that a chemical reaction does not typically occur between the mounting tape and the objects.

One significant drawback of current PSA tapes is that the bond is less robust and often less permanent. This makes a mounting tape less suitable for mounting heavy objects or in outdoor applications where it is exposed to moisture, temperature, and UV radiation. It is important to note that connections made with mounting tape are typically subject to aging and become less strong with time. In extreme cases, this can result in the detached object. Consequently, mounting tapes are never used to mount heavy objects without a secondary fixation mechanism.

Liquid adhesives bond objects together through a chemical reaction. This process involves the adhesive transforming from a liquid to a solid state under the influence of moisture, temperature, UV light or other mechanisms (chemisorption). As a result of the time required for the chemical reaction to proceed, a mounting adhesive has a limited immediate tack, which makes it less user-friendly. The adhesive must be applied to the surface of the object(s) in a short timeframe, and the objects must be attached together before the chemical reaction has proceeded too far. It is only after a specified curing period that the adhesive will be able to support the weight of the object. During the curing period, it is essential to provide support for the object using a tape or mechanical fixation. Once fully cured, this adhesive offers a number of advantages. Its high adhesion strength allows it to withstand outdoor conditions for over 10 years, making it an ideal choice for long-term applications.

Dual-curable pressure-sensitive adhesives combine the advantages of PSAs and liquid adhesives, offering users the benefits of both. They often demonstrate high adhesion strengths and ease of application. The majority of dual-curable PSAs combine UV irradiation and thermal curing processes. Examples of known dual-curable PSAs include combinations of acrylics and epoxies. One advantage of dual-curable PSAs is that it is possible to advance the adhesive to a strong pressure-sensitive state sequentially. Once the adhesive has been coated on a substrate, UV energy is applied to advance the cross-linking process. This can then be further advanced by thermal means after the bond is made. The main disadvantage of these dual-curable PSAs is that they require additional energy or temperature to be added before curing is completed. The necessity for additional energy or heat significantly reduces both the user-friendliness and the application potential of the product.

There is a continuing need to provide alternative adhesive compositions with a high initial tack as well as permanent, durable and long-term adhesion. There is a need for an adhesive composition that is dual-curable in a user-friendly way, meaning that for the secondary cure no further energy or heating is required. Furthermore, there is a continuing need for such a composition that can be applied as an adhesive tape with pressure-sensitive properties.

The invention provides a pressure sensitive adhesive tape, obtainable by UV-curing of an adhesive composition. Furthermore, the invention concerns a method for the production of such an adhesive tape and a process for the bonding of substrates using said adhesive tape. The adhesive compositions on which the pressure-sensitive adhesive tape of the present invention is based are UV-curable and moisture-curable. The compositions must be cured sequentially, first by UV-curing and then by moisture-curing.

A dual-cured adhesive composition provides excellent initial tack and a permanent chemical connection after full cure by subsequent reaction with atmospheric moisture. Both curing mechanisms are necessary to obtain the desired final properties of the material. It is further essential that the UV-curing is executed before the moisture-curing. Immediate adhesion can only be achieved by activating the UV-curing system, whereas the secondary moisture curing is crucial to increase the adhesion strength and achieve a permanent bond.

The invention is based on an adhesive composition comprising both UV-active components and moisture-curable components. The adhesive composition exhibits chemical reactivity (crosslinking) upon UV light irradiation, a phenomenon that is attributed to the presence of monomers and, optionally, oligomers with a (meth)acrylate functionality. The immediate adhesion can only be achieved by activating the UV-cure system. Moreover, the composition permits the formation of an adhesive film following UV curing, thereby enabling the separation of the initial UV cure and subsequent moisture cure mechanism in terms of both time and point of use. Furthermore, the adhesive composition comprises polymers containing reactive silyl groups, which permit the reaction with atmospheric moisture. For this second cure, no additional heat or energy is required. The secondary moisture cure is of paramount importance in order to enhance the adhesion strength and achieve a permanent bond. It is therefore of paramount importance that the UV-cure is executed prior to the moisture cure.