WO2023222200A1

WO2023222200A1 - Adhesive tape

Info

Publication number: WO2023222200A1
Application number: PCT/EP2022/063325
Authority: WO
Inventors: Vincent Leon; Victoria RITTER; Ruben FRIEDLAND
Original assignee: Lohmann Gmbh & Co.Kg
Priority date: 2022-05-17
Filing date: 2022-05-17
Publication date: 2023-11-23

Abstract

The invention relates to an adhesive tape (10) comprising at least one carrier (12) and at least one adhesive layer (14), wherein the adhesive layer (14) comprises fillers. To improve flexibility, it is proposed that the fillers are embodied as magnetisable fillers configured to be repeatedly magnetised and de-magnetised by an external magnetic field, wherein an adhesion peel strength of the adhesive layer (14) on stainless steel differs by at least 2 N/25 mm between a non-magnetised state and a magnetised state of the magnetisable fillers.

Description

Adhesive tape

The invention relates to an adhesive tape according to the preamble of claim 1, a system for debonding on demand according to claim 7 and a method for controlled debonding of an adhesive tape according to claim 9.

There is a strong demand for adhesive tapes able to combine a high adhesion to a substrate with being easily repositionable and/or removable. In many applications, parts which must be fixed strongly to a support need to be readjusted until the proper positioning is obtained. However, high adhesion reduces the ability to reposition and/or remove the adhesive tape, making a balancing of these two attributes necessary. Additionally, most adhesive tapes with high adhesion strength cannot be removed from the substrate without leaving any residual adhesive or other unwanted residues.

It is known to disperse magnetic fillers within an adhesive to make a repositioning and/or a fixation of the adhesive easier. US 5,985,435 Al discloses a hot melt patch comprising strontium ferrite particles to hold the patch in place until the hot melt adhesive is heated to form a seal. This is especially useful for patching up automotive vehicle bodies, since they comprise metallic structures for the magnetic fillers to adhere to. A similar application of a magnetic sealant is disclosed in the earlier patent application US 4,693,775 Al, using a hot melt adhesive and magnetic fillers, typically ferrites with a size of at least 150 pm.

US 2011/0014463 Al discloses a removable sheet comprising a hot melt adhesive with a magnetic powder dispersed in it. Similar to US 5,985,435 Al, the magnetic fillers allow to place and reposition the removable sheet easily without any residue. In addition, the hot melt adhesive is easily removable by heating. This solution allows for both easy repositioning and/or removal and a good adhesion, however, it is only suitable for metallic substrates, and the lack of tackiness before heating can make a proper positioning difficult.

In view of this state of the art, the objective of the invention is, in particular, to provide an adhesive tape with improved flexibility compared to adhesive tapes known in the state of the art. This objective is achieved, according to the invention, by the features of claims 1, 7 and 9, while advantageous implementations and further developments of the invention may be gathered from the dependent claims.

The invention is based on an adhesive tape comprising at least one carrier and at least one adhesive layer, wherein the adhesive layer comprises fillers.

It is proposed that the fillers are embodied as magnetisable fillers configured to be repeatedly magnetised and de-magnetised by an external magnetic field, wherein an adhesion peel strength of the adhesive layer on stainless steel differs by at least 2 N/25 mm between a non-magnetised state and a magnetised state of the magnetisable fillers. This way, it is possible to repeatedly switch between the magnetised state of the magnetisable fillers, in which the adhesive tape provides a strong adhesion, and the nonmagnetised state of the magnetisable fillers, in which it is easy to reposition and/or remove the adhesive tape. Advantageously, it is possible to use any type of adhesive for the adhesive layer since the switching of the states is only dependent on the magnetisable fillers.

The adhesive tape could be embodied as a transfer tape and comprise two removable carriers, wherein the adhesive layer is positioned in between the removable carriers. Alternatively, the adhesive tape could be embodied as a one-sided adhesive tape or double-sided adhesive tape and comprise a permanent carrier and one or two adhesive layers. The adhesive tape may be embodied in the form of an adhesive tape roll, alternatively the adhesive tape could be embodied in the form of a sheet, a foil and/or a stamped part.

The carrier may comprise a plastic, a cellulose and/or a metal. The carrier may comprise a woven material, a foam material and/or a sheet material.

The adhesive layer could be embodied as a layer with a constant thickness throughout. Alternatively, the adhesive layer could comprise at least one protrusion, indentation and/or gap. Furthermore, a thickness of the adhesive layer may vary locally, for example, the adhesive layer could have a wedge-like shape. The adhesive layer may be applied to the carrier with any method known in the art. For example, the adhesive layer may be applied using a two-dimensional coating method, such as curtain coating, roller coating or blanket coating. Alternatively, the adhesive layer may be applied using an additive manufacturing method, such as liquid additive manufacturing, 3D screen printing, stereolithography or polyjet modelling. The adhesive layer could comprise any type of adhesive known in the art. For example, the adhesive layer could comprise an adhesive based on polyurethane and/or epoxy resin and/or a hot-melt adhesive. Preferably, the adhesive layer is tacky at a temperature of 24°C and comprises an adhesive based on acrylate, synthetic rubber, natural rubber and/or silicone. Of course, the adhesive layer could also comprise a blend of any of the types of adhesives mentioned.

Advantageously, the magnetisable fillers lose at least 50 %, preferably at least 70 % of their maximum flux density when switching from the magnetised state to the nonmagnetised state. The switch between these two states is preferably triggered by deactivation and re-activation of the external magnetic field. Alternatively or additionally, the external magnetic field could be changed in order to trigger a switch of the magnetisable fillers from the magnetised state to the non-magnetised state. Advantageously, the magnetisable fillers comprise at least one magnetically soft material. It could be possible that the magnetisable fillers are slightly magnetic even in their non-magnetised state and provide a maximum flux density of at least 10’⁴ T. Preferably, the magnetisable fillers provide a maximum flux density of below 10’⁴ T in their non-magnetised state and an adhesion of the adhesive tape is only dependent on the tackiness of the adhesive. It is also possible that the magnetisable fillers comprise a mix of magnetically hard and magnetically soft materials. The amount of magnetically hard and magnetically soft materials may depend on the tackiness of the used adhesive, a desired ratio of magnetisable fillers to adhesive, as well as a desired adhesion peel strength in the non-magnetised state and the magnetised state.

Furthermore, the magnetisable fillers may have a cuboid or amorphous shape. Preferably, the magnetisable fillers have a spherical shape.

It is possible that the adhesive tape is configured to be applied to a metallic substrate, in which case the magnetisable fillers could be switched between the two states even while the adhesive tape is separate from the substrate. Preferably, the external magnetic field is shaped in a way that the magnetisable fillers are pulled towards a substrate on which the adhesive tape is applied in the magnetised state. This way, the adhesive tape may be applied to any type of substrate.

The adhesion peel strength on stainless steel is based on the norm DIN EN 1939:2003- 12 and refers to a procedure in which the adhesive tape is applied on different identical substrates with a width of 25 mm. The substrates may consist of stainless steel, aluminum, acrylonitrile butadiene styrene, polyethylene, polypropylene or polycarbonate. The back of the substrates is supported by a polyester foil, preventing stretching of the substrates. Before use, the substrates are wiped with a petrol ether- soaked cloth and left until the petrol ether has evaporated from the surface of the substrates. The adhesive tape is applied to the substrates and then adhered by rolling over the adhesive tape using a 5 kg roller at a speed of 5 m/min. The substrates with the applied adhesive tapes are then stored for 24 hours at a norm climate, which is 23 °C and 50 % humidity. After storage, the adhesive tapes are peeled off at a 180° angle at a speed of 300 mm/min. The force needed to peel the adhesive tapes is measured in N/25 mm.

It is possible to use only a very small amount of magnetisable fillers and compensate by applying a stronger external magnetic field. Preferably, the adhesive layer comprises at least 40, most preferably at least 50 parts of magnetisable fillers for 100 parts of adhesive matrix. Usually, using a high amount of fillers in an adhesive layer is not recommended, since this reduces the adhesion peel strength of the adhesive. However, since the adhesion peel strength of the adhesive layer is comprised of the adhesion of the adhesive as well as the adhesion of the magnetisable fillers, using a high amount of fillers can provide a surprising advantage. The reduction of the adhesion of the adhesive allows for even easier reposition and/or removal of the adhesive tape in the nonmagnetised state of the magnetisable fillers, while the increased adhesion of the magnetisable fillers still allows for a high adhesion peel strength of the adhesive tape in the magnetised state of the magnetisable fillers.

The magnetisable fillers preferably comprise at least one ferromagnetic material. For example, the magnetisable fillers could comprise any type of ferrite, iron oxide, any alloy based on iron, cobalt and/or nickel or any powder, particles or granulate containing iron, cobalt and/or nickel. To further improve the adhesive tape, it is proposed that the magnetisable fillers comprise carbonyl iron. Through experimentation, carbonyl iron has been determined as the most consistent choice for the magnetisable fillers, since carbonyl iron powder exhibits a low size disparity and a high chemical purity, which in turn minimises a deviation of the adhesion peel strength.

It is possible to use magnetisable fillers with a diameter up to a thickness of the adhesive layer. To further improve the adhesive tape, it is proposed that an average particle diameter of the magnetisable fillers is less than 10 pm. This way, an even distribution of the magnetisable fillers within the adhesive layer can be provided.

Further, adhesive failures due to the magnetisable fillers contacting a surface of the adhesive layer can be prevented.

Additionally, it is proposed that a weight area of the adhesive layer is between 50 and 200 g/m². Adhesive layers which are too thin cause adhesion failures due to not providing enough space for the magnetisable fillers. Adhesive layers which are too thick on the other hand may cause cohesion failures. Experiments have shown that within this range of weight area, a good balance between adhesion and cohesion can be achieved.

It is possible that the tackiness of the adhesive layer could be very low for even easier repositioning or very high to prevent any accidental reposition or removal of the adhesive tape. However, a tackiness that is too low can result in unwanted shifting of the adhesive tape, while a tackiness that is too high might cause residue to remain on the substrate after the repositioning or removal of the adhesive tape. In order to further improve the adhesive tape, it is proposed that the adhesion peel strength of the adhesive layer on stainless steel is between 2 and 5 N/25 mm without application of the external magnetic field. This way, a repeatable repositioning of the adhesive tape in the nonmagnetised state of the magnetisable fillers can be provided without the risk of leaving residue on the substrate.

The invention further relates to a system for debonding on demand, comprising the adhesive tape as well as a device for generating the external magnetic field. This way, it is possible to repeatedly switch between the magnetised state of the magnetisable fillers, in which the adhesive tape provides a strong adhesion, and the non-magnetised state of the magnetisable fillers, in which it is easy to reposition and/or remove the adhesive tape.

Preferably, the adhesive tape is configured to be used with the device. In particular, different kinds of adhesive tapes according to the invention may be used with different types of devices according to the invention. Advantageously, the adhesive tape is embodied as a piece of equipment which may be purchased, replaced and/or exchanged independently of the device.

Preferably, the device is at least partially positioned behind, most preferably directly behind, a substrate the adhesive tape is applied on. Advantageously, the device comprises the substrate. This way, the required maximum flux density of the external field in order to switch the magnetisable fillers to the magnetised state can be reduced.

Furthermore, a compact and efficient construction of the system can be achieved.

The device preferably comprises at least one electromagnet. The switching of the states of the adhesive tape could, for example, comprise an activation and deactivation of a power supply of the device. Alternatively or additionally, the device could comprise at least one permanent magnet. Furthermore, the switching of the states of the adhesive tape could also comprise a manual and/or automatic movement of the device towards and away from the adhesive tape. Preferably, the device provides a maximum flux density between 1 mT and 2 T, most preferably between 0,5 T and 1,5 T.

Furthermore, it is proposed that the device is embodied as an electric motor comprising at least one rotor and at least one stator. Preferably, the rotor and the stator are both fixed on a shaft. The rotor could be positioned inside the stator, advantageously, the stator is positioned inside the rotor. These kinds of electric motors are commonly referred to as outrunner motors. This way, there is no need for a manual switching of the states of the adhesive tape, since the rotation of the rotor not only generates rotational forces, which require a strong adhesion of the adhesive tape to the rotor, but also generates the external magnetic field providing the strong adhesion.

Advantageously, during maintenance or replacements, when the rotor is static, there is no external magnetic field and therefore an easy replacement of the adhesive tape is made possible. This is especially advantageous in machines which already require a rotation of a cylinder in order to function. For example, the device may be embodied as a printing cylinder of a printing machine, wherein the rotor is a jacket of the printing cylinder, and the stator is located on the inside of the printing cylinder.

The invention lastly relates to a method for debonding on demand of the adhesive tape, wherein the external magnetic field is applied after an application of the adhesive tape and deactivated prior to a repositioning and/or removal of the adhesive tape. This way, it is possible to repeatedly switch between the magnetised state of the magnetisable fillers, in which the adhesive tape provides a strong adhesion, and the non-magnetised state of the magnetisable fillers, in which it is easy to reposition and/or remove the adhesive tape.

Further advantages may become apparent from the following description of the drawings. In the drawings an exemplary embodiment of the invention is shown. The drawings, the description and the claims contain a plurality of features in combination. If there is more than one specimen of a certain object, only one of these is given a reference numeral in the figures and in the description. The description of this specimen may be correspondingly transferred to the other specimens of that object.

Fig. 1 a schematic view of an adhesive tape,

Fig. 2 a schematic view of a system for debonding on demand comprising the adhesive tape and a device for generating an external magnetic field and

Fig. 3 a schematic chart of a method for debonding on demand of the adhesive tape

Figure 1 shows an adhesive tape 10. The adhesive tape 10 is embodied as a doublesided adhesive tape. Alternatively, the adhesive tape 10 may also be embodied as a transfer tape or a one-sided adhesive tape. The adhesive tape 10 comprises a carrier 12. The carrier 12 is embodied as a plastic foam carrier. Alternatively, the carrier 12 may for example be embodied as a sheet carrier or a woven carrier and comprise paper, cardboard and/or metal foil. The adhesive tape 10 comprises an adhesive layer 14. The adhesive layer 14 is permanently adhered to a first side of the carrier 12. The adhesive tape 10 comprises a release liner 20. The release liner 20 is removably adhered to a side of the adhesive layer 14 opposite to the carrier 12. The adhesive tape 10 comprises an additional adhesive layer 22. The additional adhesive layer 22 is permanently adhered to a second side of the carrier 12 opposite to the adhesive layer 14.

A weight area of the adhesive layer 14 is about 60 g/m². An adhesion peel strength of the adhesive layer 14 on stainless steel is about 4 N/25 mm. The adhesive layer 14 comprises magnetisable fillers. The adhesive layer 14 comprises 50 parts of magnetisable fillers for 100 parts of adhesive matrix. The magnetisable fillers are in a non-magnetised state. An adhesion peel strength of the adhesive layer 14 on stainless steel is about 3,5 N/25 mm.

The magnetisable fillers comprise carbonyl iron. The magnetisable fillers are embodied as a carbonyl iron powder (97% Fe, 3-4 pm, BASF SE). A particle diameter of the magnetisable fillers is about 5 pm.

Figure 2 shows a system for debonding on demand. The system comprises the adhesive tape 10 of figure 1. The system comprises a device 16 for generating an external magnetic field. The adhesive tape 10 is configured to be used with the device 16. The adhesive layer 14 is releasably adhered to a printing plate (not shown). The additional adhesive layer 22 is releasably adhered to a printing cylinder. The device 16 is embodied as the printing cylinder, which serves as an outrunner electric motor at the same time. The device 16 comprises a rotor 18. The rotor 18 is embodied as a jacket of the printing cylinder, on which the adhesive tape 10 is applied. The rotor 18 is rotatably secured on a shaft 24. The device 16 comprises a stator 20. The stator 20 is positioned on the inside of the printing cylinder.

The rotor 18 comprises a plurality of permanent magnets (not shown). The permanent magnets are placed along the inner circumference of the rotor 18. The stator 20 comprised a plurality of coils 26. A rotation of the rotor 18 causes an induction current to be generated in the coils 26, which in turn generates an external magnetic field. The details of the function of the system of figure 2 can be taken from any literature about the construction and usage of state-of-the-art electric motors, in particular outrunner electric motors, and is therefore omitted in this description.

Figure 3 shows a schematic chart of a method for debonding on demand of the adhesive tape 10. In a first step 100, the adhesive tape is created by dispersing the magnetisable filler in the adhesive of the adhesive layer 14 and then coating the mixture on the carrier 14. Dispersion occurs using a SpeedMixer DAC 700.1 FVZ centrifugal mixer from Hauschild & Co. KG over 2 minutes.

The mixture is scratched out onto a siliconised polyester sheet (thickness 50 pm, Laufenberg GmbH) by means of steel blades, firstly at room temperature for 10 minutes, and then dried in a convection oven for 5 minutes at 105 °C. The thickness of the scratch was chosen so that the area weight after drying is 60 g/m². Alternatively, if the adhesive of the adhesive layer 14 is a hot-melt adhesive, the adhesive can also be filled with 35% by weight of carbonyl iron powder and coated onto a lab coater.

In a second step 110, the adhesive tape 10 is applied on a substrate, for example the rotor 18. In the second step 110, the magnetisable fillers are in the non-magnetised state. In a third step 120, the device 16 begins generating the external magnetic field, thus switching the magnetisable fillers to the magnetised state. The adhesion peel strength of the adhesive layer 14 on stainless steel in the magnetised state of the magnetisable fillers is about 10,5 N/25 mm.

In the following, an experimental setup is described, in which different transfer film samples are tested and their properties compared. Sample 1 (El):

A transfer film of 60 g/m² of an acrylic solvent-based adhesive as described in DE 10218570 Al is coated on a 50 pm PET film.

Sample 2 (E2):

Similar to sample 1 but the acrylic solvent-based adhesive is filled with 33 parts of carbonyl iron particles for 100 parts of adhesive matrix.

Sample 3 (E3):

Similar to sample 1 but the acrylic solvent-based adhesive is filled with 43 parts of carbonyl iron particles for 100 parts of adhesive matrix.

Sample 4 (E4):

Similar to sample 1 but the acrylic solvent-based adhesive is filled with 67 parts of carbonyl iron particles for 100 parts of adhesive matrix.

Sample 5 (E5):

A transfer film of 60 g/m² of a modified acrylic adhesive as described in EP 0955336 B 1 is coated on a 50 pm PET film.

Sample 6 (E6):

A transfer film of 60 g/m² of a hotmelt, being a thermoplastic rubber or a UV-cured hotmelt adhesive is coated on a 50 pm PET film.

In Table 1, the adhesion peel strength of the six different transfer films on stainless steel is summarised. An acrylic adhesive with different amounts of carbonyl iron powder, as well as a blend adhesive and a hotmelt adhesive, exhibit very different adhesion peel strengths on stainless steel. It can be observed that in the case of the acrylic adhesive, the adhesion peel strength decreases drastically when filters are added, as can be seen in the adhesion peel strength of samples El to E4. The same effect is observed for other kinds of adhesive. It is also observed that the adhesion peel strength obtained for an acrylic adhesive without fillers (El) is too strong to allow an easy detachment from a substrate without risking leaving some residues on the substrate, or damaging the adhesive itself, excluding reusability. Contrastingly, when a large amount of fillers is introduced into the adhesive layer (E4), the adhesion peel strength becomes too low, leading to partial or complete adhesion failure. An intermediate amount of fillers (E2 and E3) reduces the adhesion peel strength just enough to prevent adhesion failure while allowing a subsequent removal without residue or damage.

With the same amount of fillers as sample (E2), adhesive blend (E5) and hot-melt adhesive (E6) exhibit a much higher adhesion peel strength, which does not allow the desired removability and repositioning. As can be seen in Table 2, this behaviour persists with different types of substrates like aluminum, ABS and polypropylene, meaning that the acrylic adhesive (E2) is the most suitable for this application.

In order to test the combination of the adhesion peel strength and the magnetic effect of the magnetisable fillers dispersed into the adhesive layer, the adhesive tape shown in figure 1 was tested. The test is similar to the setup used for measuring the adhesion peel strength on stainless steel. To determine the difference in adhesion peel strength caused by an external magnetic field, a Neodymium N45 permanent magnet (remanence B_r = 1350 mT and maximum energy product BH_max = 350 kJ/m³) is fixed under the substrates before the adhesive tape is peeled off. After removing the release liner, the adhesive layer was put in contact with a substrate and submitted for peel testing. The substrate for this test was polycarbonate. As summarised in Table 3, in the nonmagnetised state of the magnetisable fillers, a detachment of the adhesive tape could be achieved by applying a force of 50 g, which corresponds to 0.5 N/25mm (20 N/m), regardless of the amount of magnetisable fillers in the adhesive layer. However, in the magnetised state of the magnetisable fillers, an increase in adhesion peel strength of up to 300 %, corresponding to the amount of magnetisable fillers in the adhesive layer, could be measured.

Table 1:

Table 2

Table 3

Reference numbers Adhesive tape Carrier Adhesive layer Device Rotor Stator Additional adhesive layer Shaft Coil

Claims

Claims Adhesive tape (10) comprising at least one carrier (12) and at least one adhesive layer (14), wherein the adhesive layer (14) comprises fillers, characterised in that the fillers are embodied as magnetisable fillers configured to be repeatedly magnetised and de-magnetised by an external magnetic field, wherein an adhesion peel strength of the adhesive layer (14) on stainless steel differs by at least 2 N/25 mm between a non-magnetised state and a magnetised state of the magnetisable fillers. Adhesive tape (10) according to claim 1, wherein the adhesive layer (14) comprises at least 40 parts of magnetisable fillers for 100 parts of adhesive matrix. Adhesive tape (10) according to claim 1 or 2, wherein the magnetisable fillers comprise carbonyl iron. Adhesive tape (10) according to any of the preceding claims, wherein a particle diameter of the magnetisable fillers is less than 10 pm. Adhesive tape (10) according to any of the preceding claims, wherein a weight area of the adhesive layer (14) is between 50 and 200 g/m². Adhesive tape (10) according to any of the preceding claims, wherein the adhesion peel strength of the adhesive layer (14) on stainless steel is between 2 and 5 N/25 mm in the non-magnetised state of the magnetisable fillers. System for debonding on demand, comprising the adhesive tape (10) according to any of the preceding claims as well as a device (16) for generating the external magnetic field. System according to claim 7, wherein the device (16) is embodied as an electric motor comprising at least one rotor (18) and at least one stator (20). Method for debonding on demand of the adhesive tape (10) according to one of the claims 1-6, wherein an external magnetic field is applied after an application of the adhesive tape (10) and deactivated prior to a repositioning and/or removal of the adhesive tape (10).