Removable adhesive bond

Abstract

The present invention relates to a removable adhesive bond, in particular a removable adhesive tape which comprises a layer made of an adhesive resin-containing polyurethane, as well as to a method for the production thereof and to an article produced by means of the adhesive bond.

Description

[0001] Late registration

[0002] Removable adhesive bond

[0003] The present invention relates to a removable adhesive bond, in particular a removable adhesive tape comprising a layer of polyurethane containing adhesive resin, as well as a method for its production and an article produced by means of the adhesive bond.

[0004] The term "adhesive tape" is generally used as a collective term for strip-shaped carrier materials coated on one or both sides with pressure-sensitive adhesives. These carrier materials can include, for example, plastic films, paper, metal foils, or textile fabrics. In industrial manufacturing, so-called transfer adhesive tapes are also used; these are thin, carrier-free films of pressure-sensitive adhesive that are covered on both sides with waxed or siliconized release paper before processing.

[0005] With the further development of adhesive tapes beyond their classic use in the home and office, a number of technical fields have opened up in which adhesive tapes are increasingly replacing conventional joining methods such as welding or screwing, for example in the automotive industry and in the manufacture of electrical, electronic, optical, or precision mechanical components. In this respect, removable adhesive tapes have proven particularly advantageous; that is, tapes that can be removed by stretching them, leaving as little residue as possible and without damaging the component.

[0006] Removable adhesive tapes have long been established in the market and are well known to experts.

[0007] EP 4 151 693 A1 describes an adhesive tape that can be removed by stretching and comprises at least one carrier based on a cross-linked polyurethane and at least one adhesive layer based on vinyl aromatic block copolymers.

[0008] DE 10 2006 033 796 A1 describes an adhesive made of a resin-modified polyurethane.

[0009] EP 3 957 697 A1 discloses an adhesive tape with at least one carrier having a thickness of 20 to 250 pm, which contains at least one layer (i) based on thermoplastic polyurethane produced by extrusion, wherein the polyurethane is based on aromatic polyisocyanate or (ii) based on polyurethane produced from a dispersion, wherein at least one adhesive layer is arranged on the carrier.DE 10 2020 210 503 A1 relates to an adhesive tape with a thickness of 40 to 300 µm, which can be removed without leaving residue or causing damage by stretching, essentially in the adhesive plane, wherein the adhesive tape comprises a carrier with a thickness of 10 to 150 µm, which contains at least one layer typically produced by extrusion based on thermoplastic polyurethane, having a Shore A hardness of at most 87, wherein the carrier has a ratio of the force at 400% elongation F400% to the breaking force Fßr. UC The adhesive tape has a maximum thickness of 45% and a surface on at least one side with an adhesive layer. The tape has a stripping force (Fstripp) to breaking force (Fßruch) ratio of less than 60%.

[0010] Due to ongoing developments, particularly in the field of electrical, electronic and optical devices, which are becoming ever smaller or thinner but at the same time more compact, the need is growing for the thinnest possible adhesive tapes that can be used to mount the corresponding components, for example in mobile communications technology, but at the same time offer the advantage of being removable.

[0011] Against this background, the present invention aims to provide a thin-layer adhesive tape that can be removed by stretching and pulling, leaving as little residue and causing damage as possible.

[0012] It was surprisingly found that this problem is solved by an adhesive tape according to claim 1. Preferred embodiments of the adhesive tape according to the invention are described in the dependent claims.

[0013] Within the scope of the present invention, it has surprisingly been shown that the adhesive layers and the carrier, which are arranged in a three-layer structure in conventional double-sided adhesive tapes, can advantageously be combined into a single-layer structure in which an adhesive-containing polyurethane is used.

[0014] Therefore, a first object of the present invention is a removable adhesive tape comprising at least one layer of an adhesive resin-containing polyurethane produced from dispersion.

[0015] While conventional adhesive tapes consist of a layer mixed with adhesive resin applied to a backing material as the adhesive component, the adhesive tape according to the invention is distinguished by the fact that the adhesive component is incorporated into the backing material, thus combining the backing and adhesive properties in a single layer. Besides a low layer thickness, this combination offers the advantage of avoiding the formation of interfaces, which are often a weak point, especially in removable adhesive tapes. Surprisingly, concerns that the combination of adhesive resin and backing material could impair the backing material's elasticity, which is crucial for the tape's removability, have not been borne out.

[0016] Generally, two methods are available to those skilled in the art for producing the polyurethane layers commonly used as carriers in adhesive tapes. The carrier can be obtained either from a thermoplastic polyurethane (TPII) by extrusion or from a polyurethane dispersion (PUD). Within the scope of the present invention, it has surprisingly been found that carriers produced in particular from a polyurethane dispersion can be combined with adhesive resin particularly advantageously. Therefore, an embodiment is preferred in which the polyurethane is obtained from a mixture of an adhesive resin dispersion and a polyurethane dispersion (PUD).

[0017] Furthermore, an embodiment is preferred in which the proportion of adhesive resin in the mixture is 10 to 60 wt.%, preferably 15 to 50 wt.%, in each case based on the total weight of the mixture.

[0018] Suitable polyurethanes and adhesive resins for use in the adhesive tape according to the invention are described in more detail below. a) Polyurethane

[0019] The polyurethane dispersions used in the present invention can be, in particular, the following dispersions, optionally in combination: a) anionically stabilized aliphatic polyester-polyurethane dispersions (dispersions based on polyester and aliphatic anionic isocyanate polyurethane). These include the following products marketed by Covestro AG: Impranil® LP RSC 1380, DL 1537 XP, DL 1554 XP, Witcobond 373-04 from Lanxess, or PERMUTEX® RU-92-410 from Stahl; b) anionically stabilized aliphatic polyether-polyurethane dispersions. These include the following products, which are distributed by Covestro AG: Impranil® 25 LP DSB 1069 or by Lanxess Witcobond 386-53 c) anionically stabilized aliphatic polycarbonate-polyester-polyurethane dispersions.These include the following products distributed by Covestro AG: Impranil® DLU or, from Stahl, Permutex® EX-RU-92-600 d) anionically stabilized polycarbonate-polyurethane dispersions. These include the following products distributed by Covestro AG: Impranil® DL 2288 XP.

[0020] These are polyurethane dispersions with a high solids content of preferably 30 to 60 wt.%, particularly preferably 50 to 60 wt.%. All products mentioned above under a) to d) are typically free of organic co-solvents.

[0021] The polyurethane dispersions of the present invention are aqueous. Preferably they are free of organic solvents, but they may optionally contain organic solvents.

[0022] The polyurethane dispersion can also contain a thickening agent. For example, Borchi® Gel 0625 can be used. Polyether urethane solutions such as Ortegol PV301 from Evonik Industries are also suitable as thickening agents. A thickening agent ensures stability, particularly during coating and drying.

[0023] Both polyether-, polycarbonate- and polyester-based polyurethanes are suitable, but an embodiment in which the polyurethane is a polyether-based polyurethane is preferred.

[0024] Within the scope of the present invention, both crosslinked and uncrosslinked polyurethanes can be used. According to prevailing opinion, the tensile strength of a polyurethane-based carrier increases while simultaneously reducing its maximum elongation. This would preclude non-destructive removal of the adhesive tape. However, within the scope of the present invention, it has surprisingly been shown that, contrary to prevailing opinion, only the breaking strength increases, while the maximum elongation remains virtually unchanged. This has a beneficial effect on the removability of the adhesive tape according to the invention. Furthermore, no negative interaction between the crosslinker and the adhesive resin also present in the mixture was observed.

[0025] Crosslinkers can react in essentially two different ways: by reacting with a polymer or by reacting with themselves to form a so-called interpenetrating network, which creates a much denser network and thus improves many properties, such as strength, abrasion resistance, hydrolysis resistance, and chemical resistance. Crosslinkers used in the present invention are particularly preferred those based on aziridine, carbodiimide (polycarbodiimide), melamine, oxazoline, radical-forming substances such as organic peroxides, sulfur, and isocyanate. In a preferred embodiment, the crosslinker is an isocyanate, preferably a blocked polyisocyanate, and in particular a blocked aliphatic polyisocyanate.

[0026] Polyisocyanates can react with functional groups such as amino or hydroxyl groups. The polyfunctionality of this type of crosslinker results in a 3D-crosslinked network. Polyisocyanates also react with water, which in turn causes a reaction of the polyisocyanate molecules with themselves, resulting in a network consisting of a combination of a classic 3D polymer-crosslinked network and an interpenetrating network caused by the reactivity of multiple polyisocyanate molecules with themselves.

[0027] In the case of an isocyanate crosslinker, it is preferably obtained from a dispersion comprising a polyisocyanate, an isocyanate group blocking agent, and water. In a preferred embodiment, the dispersion for obtaining the crosslinker further comprises a polyamine, preferably one with at least one carboxyl and / or carboxylate group.

[0028] For the purposes of this invention, polyisocyanates are defined as compounds containing NCO groups. The polyisocyanate can have a number-average molecular weight of 140 to 1500 g / mol, and preferably of 168 to 700 g / mol. According to a preferred embodiment of the invention, the polyisocyanate has an isocyanate functionality of > 2 and < 6, preferably > 3 and < 5, and particularly preferably > 3 and < 4.

[0029] The polyisocyanate preferably has an NCO group content of 15 to 30 wt.%, more preferably of 18 to 25 wt.% and particularly preferably of 20 to 24 wt.%, based on the number-average molecular weight of the polyisocyanate.

[0030] Suitable polyisocyanates include, for example, hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 4,4'-diisocyanatodicyclohexylmethane (Hi₂MDI), 1,4-butane diisocyanate, hexahydrodiisocyanatotoluene, 1,3-bishydroxymethylcyclohexane, hexahydrodiisocyanatoxylol, and nonane triisocyanate. The use of isophorone diisocyanate, hexamethylene diisocyanate, and / or 4,4-diisocyanatodicyclohexylmethane is particularly preferred. Aliphatic polyisocyanates, preferably hexamethylene diisocyanate and especially trimers of hexamethylene diisocyanate, are particularly preferred. It is also advantageous if the aqueous blocked polyurethane urea dispersion is exclusively anionically hydrophilized. This means that the polyurethane urea dispersion is not cationically and / or nonionically hydrophilized, i.e., it does not possess any corresponding groups.

[0031] In this context, a blocking agent is understood to be a compound that reacts with an isocyanate group and can be cleaved from it again under defined conditions, for example, thermally. This process is called deblocking. A low deblocking temperature has proven particularly advantageous within the scope of the present invention. Therefore, an embodiment in which the deblocking temperature is less than 130 °C is preferred.

[0032] Suitable isocyanate-based crosslinkers have proven to be, for example, those available under the trade name Imprafix 2794 from Covestro, Germany.

[0033] Polycarbodiimides react selectively with carboxylic acid groups in polymer chains. This type of crosslinking produces a classic 3D polymer-crosslinked network. Compared to polyisocyanates, polycarbodiimides are less sensitive to water and therefore achieve longer pot lives.

[0034] Melamine resins are very effective crosslinkers due to their high reactivity. They require smaller quantities than isocyanates or carbodiime. Melamine resins are often used in combination with hydroxyl-functional polymer resins to form very hard networks, but they can also react with acid groups. Melamine resins require relatively high crosslinking temperatures, which can be reduced by the addition of catalysts.

[0035] Polyaziridines are among the most reactive crosslinkers and therefore highly efficient. They react selectively with carboxylic acid groups in polymer chains, producing classic 3D polymer-crosslinked networks. Due to their lower molecular weight, significantly smaller amounts are required compared to polyisocyanates and polycarbodiimides.

[0036] Peroxide crosslinking achieves a high degree of crosslinking with favorable processing reliability and broad applicability. However, vulcanization times are very long. For crosslinking with sulfur, the addition of vulcanization accelerators is usually necessary to prevent degradation at the temperatures used for crosslinking. The elasticity and cold resistance of the vulcanizates are generally lower.

[0037] The polyurethane adhesive resin layer used in the adhesive tape according to the invention is foamed in a preferred embodiment of the present invention. This allows, for example, the damping properties of the adhesive tape to be improved. The foaming can be carried out using conventional methods, such as the addition of expandable microballoons, the use of chemical blowing agents, or targeted gas injection. The various foaming techniques can also be combined.

[0038] Foaming is preferably achieved using expandable microballoons added to the polyurethane and adhesive resin mixture. The microballoons expand during the processing, for example during drying, but can also be added in an already expanded state. b) Adhesive resin

[0039] In principle, all known classes of materials are suitable as adhesive resins. Examples of adhesive resins include hydrocarbon resins (e.g., polymers based on unsaturated Cs or Cg monomers), terpene phenolic resins, polyterpene resins based on raw materials such as α- or β-pinene, aromatic resins such as coumaron-indene resins, or resins based on styrene or α-methylstyrene such as rosin and its derivatives, for example, disproportionated, dimerized, or esterified rosin, or reaction products with glycol, glycerol, or pentaerythritol, to name just a few. Resins without readily oxidizable double bonds, such as terpene phenolic resins, aromatic resins, and especially resins produced by hydrogenation, such as hydrogenated aromatic resins, hydrogenated polycyclopentadiene resins, hydrogenated rosin derivatives, or hydrogenated polyterpene resins, are preferred.

[0040] Suitable resins include those based on terpene phenols and rosin esters. Resins based on terpene phenols and rosin esters with a softening point above 100 °C according to ASTM E28-99 (2009) are particularly suitable. The resins are advantageously used in dispersion form. This allows them to be easily and finely dispersed in the polyurethane dispersion. While these adhesive resins are not excluded according to the invention, they are preferably omitted. Additionally, additives such as light stabilizers or antioxidants can be added to the formulation. Furthermore, the derivatives of rosin, especially glycerol esters, are also preferred.

[0041] The adhesive formulation can optionally be blended with light stabilizers or primary and / or secondary antioxidants. Preferably, the polyurethane pressure-sensitive adhesive according to the invention does not contain any such additives in the form of light stabilizers or primary and / or secondary antioxidants. Products based on sterically hindered phenols, phosphites, thiosynergists, sterically hindered amines, or UV absorbers can be used as antioxidants. Suitable primary antioxidants include, for example, Irganox 1010 or Irganox 254, alone or in combination with secondary antioxidants such as Irgafos TNPP or Irgafos 168. The antioxidants can be used in any combination, with mixtures of primary and secondary antioxidants in combination with light stabilizers such as Tinuvin 213 exhibiting particularly good anti-aging properties.

[0042] Antioxidants combining a primary and a secondary antioxidant in a single molecule are also suitable. These antioxidants are cresol derivatives whose aromatic ring is substituted with thioalkyl chains at any two different positions, preferably in the ortho and meta positions relative to the OH group. The sulfur atom may also be connected to the aromatic ring of the cresol building block via one or more alkyl chains. The number of carbon atoms between the aromatic ring and the sulfur atom can be between 1 and 10, preferably between 1 and 4. The number of carbon atoms in the alkyl side chain can be between 1 and 25, preferably between 6 and 16. Particularly preferred are compounds of the type 4,6-bis(dodecylthiomethyl)-o-cresol, 4,6-bis(undecylthiomethyl)-o-cresol, 4,6-bis(decylthiomethyl)-o-cresol, 4,6-bis(nonylthiomethyl)-o-cresol or 4,6-bis(octylthiomethyl)-o-cresol.Such anti-aging agents are offered, for example, by the company Ciba Geigy under the names Irganox 1726 or Irganox 1520.

[0043] The amount of added oxidation inhibitor or oxidation inhibitor package should be in the range of 0.1 to 5 parts by weight based on the mass of the base polymer, preferably in the range of 0.2 to 3 parts by weight based on the mass of the base polymer, and particularly preferably in the range of 0.5 to 2 parts by weight based on the mass of the base polymer. To improve processing properties, the adhesive formulation may also be blended with conventional processing aids such as defoamers, deaerators, wetting agents, or leveling agents. Suitable concentrations are in the range of 0.1 to 5 parts by weight based on the mass of the base polymer. Preferably, the polyurethane pressure-sensitive adhesive according to the invention does not contain any such additives.

[0044] The shear viscosities of commercial dispersions are generally too low. To achieve the necessary shear viscosities for the chosen coating application process, rheology additives, also known as thickeners, are typically used.

[0045] In a preferred embodiment, a rheology additive is added to the polymer dispersion so that the polymer dispersion has a viscosity of 0.5 Pa*s to 5 Pa*s at a shear rate of 10 / s before drying.

[0046] Preferably, the polymer dispersion has a viscosity of 1.0 Pa*s to 2.0 Pa*s at a shear rate of 10 / s before drying.

[0047] According to a preferred embodiment of the invention, the adhesive compound contains between 0.1 and 5 parts by weight of thickener based on the mass of the base polymer.

[0048] A fundamental distinction is made between organic and inorganic rheology additives. Organic thickeners are further divided into two main modes of action: (i) thickening of the aqueous phase, i.e., non-associating, and (ii) association between the thickener molecule and particles, sometimes involving stabilizers (emulsifiers). Representatives of the first (i) group of substances are water-soluble polyacrylic acids and polycoacrylic acids, which form polyelectrolytes with large hydrodynamic volume in basic media. These are also referred to as alkali swellable emulsions (ASEs). They are characterized by high quiescent shear viscosities and significant shear thinning.Another class of substances are the modified polysaccharides, especially cellulose ethers such as carboxymethylcellulose, 2-hydroxyethylcellulose, carboxymethyl-2-hydroxyethylcellulose, methylcellulose, 2-hydroxyethylmethylcellulose, 2-hydroxyethylethylcellulose, 2-hydroxypropylcellulose, 2-hydroxypropylmethylcellulose, and 2-hydroxybutylmethylcellulose. This class also includes less common polysaccharides such as starch derivatives and special polyethers.

[0049] The group of (ii) associative thickeners are, in principle, block copolymers with a water-soluble central block and hydrophobic end blocks, wherein the end blocks interact with the particles or themselves, thereby forming a three-dimensional network that incorporates the particles. Typical examples are familiar to those skilled in the art as HASE (hydrophobically modified alkali swellable emulsion), HEIIR (hydrophobically modified ethyleneoxide urethane), or HMHEC (hydrophobically modified hydroxyethyl cellulose). In HASE thickeners, the central block is an ASE, and the end blocks are mostly long, hydrophobic alkyl chains coupled via polyethylene oxide bridges. In HEIIR, the water-soluble central block is a polyurethane, and in HMHEC, it is 2-hydroxyethylcellulose. The non-ionic HEIIR and HMHEC, in particular, are largely pH-insensitive.

[0050] Depending on their structure, associative thickeners exhibit more or less Newtonian (shear rate-independent) or pseudoplastic (shear-liquefying) flow behavior. Sometimes they also display thixotropic characteristics, meaning that in addition to a shear force dependence of viscosity, they also show a time dependence.

[0051] Inorganic thickeners are mostly phyllosilicates of natural or synthetic origin; examples include hectorites and smectites. Upon contact with water, the individual layers separate from one another. Due to differing charges on the surfaces and edges of the platelets, they form a space-filling, card-house-like structure at rest, resulting in high shear viscosities at rest, sometimes even reaching yield strength. Under shear, the card-house structure collapses, and a significant drop in shear viscosity is observed. Depending on the charge, concentration, and geometric dimensions of the platelets, the structure formation can take some time, so thixotropy can also be achieved with such inorganic thickeners.

[0052] The thickeners can be stirred directly into the adhesive dispersion in some cases, or are advantageously pre-diluted or pre-dispersed in water beforehand.

[0053] Suppliers of thickeners include, for example, OMG Borchers, Omya, Byk, Dow Chemical Company, Evonik, and Münzing Chemie. c) Adhesive tape

[0054] The combination of polyurethane and adhesive resin according to the invention makes it possible to produce particularly thin adhesive tapes, such as those required for the manufacture of miniature electronic components. Therefore, a preferred embodiment is one in which the adhesive tape according to the invention has a thickness of 10 to 500 pm, preferably 20 to 350 pm. In a particularly preferred embodiment, the adhesive tape according to the invention has a thickness of no more than 250 pm.

[0055] Within the scope of the present invention, it has surprisingly been found that the use of a carrier in which the adhesive component is embedded has no negative impact on either the adhesive strength or the elongation properties of the adhesive tape. Contrary to the expectations of those skilled in the art, who might expect that the mixture of polyurethane and adhesive resin could impair the adhesive strength or the mechanical properties such as elongation, the adhesive tape according to the invention exhibits excellent adhesive properties and good removability.

[0056] The adhesive tape according to the invention can be used on a variety of substrates, and it has surprisingly been found that the tape exhibits advantageous long-term adhesive strength. In this context, the adhesive tape according to the invention, for example, exhibits an adhesive strength of at least 1.5 N / cm, preferably at least 3.0 N / cm, and particularly preferably at least 5 N / cm on ASTM substrate, with a further increase in adhesive strength being observed after three days of application. The adhesive strength then reaches values ​​of at least 3.0 N / cm, preferably at least 5.0 N / cm. The adhesive strength can be determined according to AFERA ​​5001, as described in the section "Test Methods".

[0057] The combination of a polyethylene-based polyurethane composition consisting of polytetrahydrofuran and meta-tetramethylxylylene diisocyanate (mTMXDI) and a glycerol ester-based adhesive resin dispersion has proven to be particularly suitable within the scope of the present invention and achieved high adhesive strengths on ASTM greater than 5 N / cm after three days of application.

[0058] In a further preferred embodiment, the adhesive tape according to the invention has an elongation at break of at least 400%, preferably 400 to 1000%, particularly preferably 600 to 800%, determined in accordance with DIN EN ISO 527-3:2019-02, as described in the section "Test methods".

[0059] To ensure that the adhesive tape can be removed again, the adhesive tape according to the invention has a breaking strength of at least 5 N / mm². 2 , preferably 5 to 30 N / mm 2The test is performed in accordance with DIN EN ISO 527-3:2019-02, as described in the section "Test methods". Without being bound to any specific theory, it is assumed that, in particular, the combination of elongation at break and breaking strength in the stressed area allows for residue-free removal of the adhesive tape without damaging the bonded substrate.

[0060] In addition to the layer of polyurethane containing adhesive resin, which combines the function of the adhesive tape's backing with its adhesive properties, the adhesive tape according to the invention can comprise further layers. Preferably, however, the adhesive tape according to the invention is single-layered, so that no further adhesive layers are present besides the adhesive polyurethane layer. For transport and storage purposes, the adhesive polyurethane layer can be covered with a protective film, which, however, does not change the single-layer structure according to the invention. This protective film (also referred to as release liner or release material) is wound up together with the adhesive polyurethane layer. Such release liners are known to those skilled in the art under the names release liner or liner. A liner (release paper, release film) is not a component of an adhesive tape, but merely an aid for its manufacture, storage, or further processing by die-cutting.Furthermore, unlike an adhesive tape backing, a liner is not firmly bonded to an adhesive layer.

[0061] The single-layer structure of the adhesive tape, achieved through the inventive combination of polyurethane as the carrier material and adhesive resin as the adhesive component, has the advantage that interfaces between the carrier and the adhesive layer, as occur in conventional adhesive tapes, are avoided, thus preventing the adhesive layer from detaching from the carrier, for example, when the adhesive tape is removed. The anchorage failure between the adhesive layer and the carrier, which frequently occurs under shock loads, is also avoided by the single-layer structure of the adhesive tape according to the invention. d) Method

[0062] In addition to the adhesive tape according to the invention, a further object of the present application is a method for its production, in which a mixture of a dispersion based on a polyurethane and an adhesive resin dispersion is provided and this mixture is coated onto a temporary carrier, so that a layer of adhesive polyurethane is formed.

[0063] For the production of a homogeneous, bubble-free dispersion mixture, mixing equipment suitable for dispersions is recommended. The adhesive resin dispersion and other additives, such as crosslinkers, thickeners, and / or other additives, are preferably pre-dispersed with water and then added in portions to the polyurethane-based dispersion while stirring continuously and carefully.

[0064] During the stirring process, turbulence or excessively high speeds should be avoided to prevent the unintentional incorporation of air. It is advisable to prepare the mixture several hours before coating to allow any incorporated air bubbles to escape. For the best possible air-bubble-free dispersion quality, it is preferably degassed before application to the temporary substrate. This can be achieved, for example, using a vacuum deaerator such as a vacuum thin-film rotary coating system. This also eliminates the need for defoaming agents.

[0065] The coating can be applied to a liner using various application devices, such as a doctor blade, nozzle, or distribution channels. The applied layer of adhesive polyurethane is preferably dried by applying heat in a drying tunnel with different heating zones. If the coated liner does not have a stepped release system, a second liner is preferably laminated on top after drying and before winding. The resulting composite is then preferably wound into a bale.

[0066] For an embodiment in which the adhesive polyurethane layer is foamed, expandable microballoons can be added to the polyurethane dispersion. For this purpose, the unexpanded microballoons are preferably pre-dispersed with water and then added to the PU dispersion in portions while stirring continuously and carefully. During the stirring process, turbulence or excessively high speeds should be avoided to prevent the unintentional incorporation of air. It is advisable to prepare the mixture several hours before coating to allow any incorporated air bubbles to escape.

[0067] Here too, a subsequent degassing of the PU dispersion mixed with microballoons can be carried out with the help of a vacuum deaerator such as a vacuum thin-film rotary principle.

[0068] The expansion of the microballoons is preferably initiated by the application of heat. To prevent the surface of the applied layer from rupturing, it can be covered with a temporary support such as an auxiliary liner. Foaming with microballoons produces a closed-cell polyurethane foam.

[0069] In another embodiment, the PU dispersion can be mixed with pre-expanded microballoons.

[0070] PU foam can also be produced by deliberately incorporating air, a process known as "frothing." Here, the incorporation of air is controlled and induced using suitable stirring equipment and specific stirring conditions.

[0071] The adhesive tape according to the invention is based on a layer of adhesive polyurethane that combines the function of the carrier and the function of the adhesive component. Therefore, a further object of the present invention is the use of a mixture containing a polyurethane and an adhesive resin for the production of a removable adhesive tape.

[0072] The adhesive tape according to the invention is particularly intended for the production of complex components. Therefore, a further object of the present invention is an article comprising at least two substrates which are joined by means of the adhesive tape according to the invention.

[0073] The adhesive tape according to the invention is characterized, in addition to its low thickness, by the fact that it can be removed without leaving any residue or causing damage, requiring relatively little force. This combination of properties makes it particularly suitable for the manufacture of electronic components. Therefore, an embodiment in which the article is an electronic component is preferred.

[0074] The present invention is explained in more detail by means of the following examples, which are in no way to be understood as a limitation of the inventive concept.

[0075] Examples:

[0076] Table 1 shows the formulations of the adhesive tapes according to the invention, as well as those produced for reference purposes. The values ​​are given in weight percent based on the total weight of the composition.

[0077] The following materials were used:

[0078] Polyurethane in examples 1 to 6 and comparative examples:

[0079] Alberdingk U4101 (aqueous anionic dispersion of an aliphatic polyether polyurethane with a solids content of 39 to 41%; Alberdingk Boley; polytetrahydrofuran and approx. 34% meta-tetramethylxylylene diisocyanate (mTMXDI)).

[0080] Polyurethane in examples 7 to 10:

[0081] Impranil DL1068 (aqueous, anionic dispersion of an aliphatic polyether polyurethane with a solids content of 48 to 52%, Covestro; polytetrahydrofuran (PolyTHF) and approx. 6% hexamethylene diisocyanate (HDI)).

[0082] Adhesive resin: Snowtack 100G (water-based adhesive resin dispersion based on glycerol esters with a solids content of 57%, Lawter)

[0083] Thickener: Rheobyk-T 1000 (VOC-free associative thickener, Byk)

[0084] Crosslinker: Imprafix 2794 (Blocked aliphatic water-based polyisocyanate, Covestro) Microballoons: Expancel 920DU20 (expandable microspheres, Nouryon)

[0085] Table 1: Composition

[0086] The additives, which were pre-dispersed in water for improved processability, and the adhesive resin dispersion were carefully incorporated into the polyurethane dispersion. The resulting mixture was applied to a temporary support and allowed to dry.

[0087] The manufactured adhesive tapes were measured as described in the "Test Methods" section. The results of the adhesive strength tests are summarized in Table 2, those of the mechanical properties such as tensile elongation properties in Table 3, and those of the removability in Table 5.

[0088] Table 2: Adhesive strength Table 3: Tensile elongation properties

[0089] Table 4: Shear test

[0090] Table 5: Removability / Tear test

[0091] “+++” = less than 20% of the candidates fail

[0092] “++” = less than 35% of the test takers fail

[0093] “+” = less than 50% of the candidates fail

[0094] Testing methods

[0095] Unless otherwise stated, all measurements are performed at 23 °C and 50% relative humidity. The mechanical and adhesive properties were determined as follows:

[0096] Adhesive strength

[0097] The determination of adhesive strength (according to AFERA ​​5001) is carried out as follows. ASTM, polycarbonate, or polyethylene sheets are used as defined substrates. The bondable surface element to be tested is cut to a width of 20 mm and a length of approximately 25 cm, provided with a handling section and, if necessary, with a reinforcing film, and immediately thereafter pressed five times onto the chosen substrate using a 4 kg steel roller at a feed rate of 10 m / min. Immediately afterwards, the bondable surface element is peeled off the substrate at an angle of 180° using a tensile testing device (Zwick) at a speed of v = 300 mm / min, and the force required for this is measured under standard climatic conditions (23 ± 1 °C, 50 ± 5% relative humidity). The measured value (in N / cm) is calculated as the average of at least three individual measurements.Furthermore, the application behavior of the tested adhesive tapes was examined (adhesive strength fresh and after three days, three days of application).

[0098] To determine the application behavior, the adhesive tape under test was cut to a width of 20 mm and a length of 25 cm, provided with a handling section, and immediately afterwards pressed five times onto the chosen substrate using a 4 kg steel roller at a feed rate of 10 m / min. The sheets were then stored for three days under standard climatic conditions (23 ± 1 °C, 50 ± 5% relative humidity). Following this, the pull-off force after application was determined using a tensile testing machine, analogous to the adhesive strength test described above, and the arithmetic mean (in N / cm) of the three individual measurements was calculated.

[0099] Static shear test

[0100] The double-sided adhesive tape to be tested is bonded between two steel plates with a bonding area of ​​20 x 13 mm and subjected to a force of 100 N / cm² for 1 minute. 2 The specimens are pressed together. Three test specimens per sample are tested. After the specified curing time of 3 days at room temperature, the static test begins by hanging the prepared test specimens at the designated measuring stations and loading them with the appropriate weights (1 kg at room temperature and 500 g at 40 °C). For testing in a heating chamber, the test specimens are first hung in the chamber. After a preheating time of 15 to 20 minutes, the weights are attached.

[0101] The test is completed when the specified minimum holding time of 10,000 minutes has been reached or all test specimens have fallen off.

[0102] The median of the three individual results is determined.

[0103] The result is the holding time in minutes [min],

[0104] Tear test using a tensile testing machine, Zwick

[0105] In the tear test, a first test plate made of polyethylene and a second test plate made of steel are used. The first polyethylene test plate is wrapped with tesa® 67215 double-sided adhesive tape, onto which a "battery foil" is subsequently applied. The tesa® 67215 adhesive tape is 150 µm thick and contains a polyurethane carrier, on which a foamed adhesive layer based on vinyl aromatic block copolymer is applied to both sides. The "battery foil" is an aluminum-laminated polymer film with a thickness of 88 µm from the manufacturer DNP – this film is typically used in the production of lithium-polymer batteries.

[0106] Test specimens 8 mm wide and 60 mm long are punched or laser-cut from the adhesive tape to be tested. These specimens are glued over a length of 50 mm onto the first polyethylene test plate, which has been wrapped with battery foil as described above, leaving a 10 mm long tab protruding. The tab is covered on both sides with 36 µm PET. The second steel test plate, after cleaning with acetone and preconditioning for 1 to a maximum of 10 minutes at 23 °C and 50% relative humidity, is glued to the opposite side of the glued strip (i.e., the test specimen) in such a way that the two test plates are flush, i.e., perfectly aligned. The back of the assembly is then rolled over the steel plate ten times with a 4 kg roller (five passes in each direction).After a minimum of 4 hours of curing time at 23 °C and 50% relative humidity, the strips are stripped from the adhesive joint over the edge of the first polyethylene test plate wrapped with battery foil at a constant speed of 800 mm / min using a tensile testing machine (Zwick). The strips are pulled at a 45° angle over the edge. The specimen is fixed with an angle-adjustable adapter, and the handle is clamped vertically in the center of the clamping jaws.

[0107] The measurement is taken at an angle of 45°, and the force continuously required to strip the sample is recorded by the tensile testing machine – the so-called stripping force Fstripp. The measurement ends as soon as the sample has been completely stripped out from between the two test plates or if the sample breaks during the measurement. At least six measurements are performed per sample. The test climate is 23°C and 50% relative humidity.

[0108] Results are presented as follows:

[0109] Tear 45°: “+++” = less than 20% of the test subjects tear

[0110] “++” = less than 35% of the test takers fail

[0111] “+” = less than 50% of the candidates fail

[0112] Tensile test using a tensile testing machine, Zwick

[0113] Strips approximately 15 mm long and 150 mm wide are cut longitudinally from the sample to be tested using a strip cutter or razor blade. The sample, preconditioned for 24 hours in the test climate, is clamped vertically in the center of the jaws with a clamping length of 10 mm and stretched at a speed of 800 mm / min until it tears. The tear should occur slightly in the middle of the strip. If the tear occurs near the jaws (closer than 1 cm), the result must be discarded and another strip tested. Five measurements are performed for each sample variant. The test climate is 23 °C and 50% relative humidity. The measurements are performed in accordance with DIN EN ISO 527-3:2019-02 / 2 / 800.

[0114] Results are presented as follows:

[0115] F x % [N / cm], [N / mm 2 ], [MPa]- Force at x % elongation

[0116] Ff [N / cm], [N / mm 2], [MPa] - Force at crack / breakage of the sample (that is, tensile strength)

[0117] RD [%] - Elongation at break, that is, the percentage elongation at break of the sample.

[0118] Shore hardness A

[0119] The Shore A hardness of a sample is determined according to ASTM D2240-15 (2021).

[0120] Module at x% elongation, elongation at break

[0121] The modulus at x% elongation or the elongation at break of a sample are determined according to DIN 53504-2017-03.

[0122] thickness

[0123] The thickness of the adhesive tape can be determined using commercially available thickness gauges (touch-type testers) with accuracies of less than 1 pm deviation. If thickness variations are detected, the mean value of measurements taken at at least three representative locations is given, specifically excluding measurements taken at creases, folds, spots, and the like.

[0124] Molecular weight M n , M w

[0125] The data on the numerical mean molecular weight M n or weight-average molecular weight M w In this document, the results refer to the determination by gel permeation chromatography (GPC). The determination is performed on a 100 pl clear-filtered sample (sample concentration 4 g / l). Tetrahydrofuran with 0.1 vol.% trifluoroacetic acid is used as the eluent. The measurement is performed at 25 °C. A PSS-SDV type column, 5 pm, 103 Å, 8.0 mm x 50 mm, is used as the guard column (specifications here and in the following are in the order: type, particle size, porosity, inner diameter x length; 1 Å = 10 -10 m) is used. For separation, a combination of columns of type PSS-SDV, 5 pm, 10 is used. 3 Ä and 10 5 A and 10 6Columns measuring 8.0 mm x 300 mm (Polymer Standards Service; detection via Shodex RI71 differential refractometer) were used. The flow rate was 1.0 ml per minute. Calibration was performed against PMMA standards (polymethyl methacrylate calibration) for polar molecules such as polyurethane starting materials and against PS standards (polystyrene calibration) for other materials.

[0126] Adhesive resin softening temperature

[0127] The adhesive resin softening temperature is determined according to the relevant methodology known as Ring & Ball, which is standardized according to ASTM E28-99 (2009).

[0128] Viscosity measurement

[0129] Viscosity measurement is performed using an ARES (Rheometric Scientific) type rheometer at room temperature and at a shear rate of 10 s⁻¹. -1 carried out using a cone-plate system with a diameter of 50 mm.

[0130] DACP

[0131] Weigh 5.0 g of the test substance (the adhesive resin sample to be examined) into a dry vial and add 5.0 g of xylene (isomer mixture, CAS [1330-20-7], > 98.5%, Sigma-Aldrich #320579 or equivalent). Dissolve the test substance at 130 °C and then cool to 80 °C. Any evaporated xylene is replenished with more xylene to restore the total amount to 5.0 g. Next, add 5.0 g of diacetone alcohol (4-hydroxy-4-methyl-2-pentanone, CAS [123-42-2], 99%, Aldrich #H41544 or equivalent). Shake the vial until the test substance is completely dissolved. To achieve this, heat the solution to 100 °C. The sample vial containing the resin solution is then placed in a Novomatics Chemotronic Cool cloud point meter and heated to 110 °C. Cooling is performed at a rate of 1.0 K / min. The cloud point is then detected optically.The temperature at which the solution's turbidity reaches 70% is recorded. The result is given in °C. The lower the DACP value, the higher the polarity of the test substance.

[0132] Static glass transition temperature T g

[0133] Glass transition points – also known as glass transition temperatures – are determined by measurements using Dynamic Scanning Calorimetry (DSC) according to DIN 53765-1994-03, in particular sections 7.1 and 8.1, but with uniform heating and cooling rates of 10 K / min in all heating and cooling steps (see DIN 53765-1994-03; section 7.1; note 1). The sample weight is 20 mg.

Claims

Patent claims 1. Removable adhesive tape, characterized in that the adhesive tape comprises at least one layer of an adhesive resin-containing polyurethane produced from dispersion.

2. Adhesive tape according to claim 1, characterized in that the polyurethane is obtained from a polyurethane dispersion containing adhesive resin, wherein the proportion of adhesive resin is preferably 10 to 60 wt.%, based on the total weight of the dispersion.

3. Adhesive tape according to at least one of the preceding claims, characterized in that the polyurethane is a polyether-based polyurethane.

4. Adhesive tape according to at least one of the preceding claims, characterized in that the polyurethane is cross-linked or uncross-linked.

5. Adhesive tape according to claim 4, characterized in that the crosslinker is selected from the group consisting of aziridine, carbodiimide (polycarbodiimide), melamine, oxazoline, radical-forming substances such as organic peroxides, sulfur and isocyanate.

6. Adhesive tape according to at least one of the preceding claims, characterized in that the layer of adhesive resin-containing polyurethane is foamed, preferably by means of expanding microballoons, chemical blowing agents and / or targeted gas injection.

7. Adhesive tape according to at least one of the preceding claims, characterized in that it is a resin based on terpene phenols and / or rosin esters, preferably with a softening point above 100 °C, determined according to ASTM E28-99 (2009) 8. Adhesive tape according to at least one of the preceding claims, characterized in that the adhesive tape has a thickness of 10 to 500 pm, preferably 20 to 350 pm.

9. Adhesive tape according to at least one of the preceding claims, characterized in that the adhesive tape has an elongation at break of at least 400%. preferably 400 to 1000%, particularly preferably 600 to 800%, determined according to J0PCM001.

10. Adhesive tape according to at least one of the preceding claims, characterized in that the adhesive tape has a tensile strength of at least 5 N / mm². 2 , preferably 5 to 30 N / mm 2 exhibits, determined according to DIN EN ISO 527-3:2019- 02 / 2 / 800.

1. Adhesive tape according to at least one of the preceding claims, characterized in that the adhesive tape is formed in a single layer.

12. Method for producing an adhesive tape according to any one of claims 1 to 1 1 , wherein a mixture of a polyurethane-based dispersion and an adhesive resin dispersion is provided and coated onto a temporary carrier and dried so that a film is formed.

13. Use of a mixture comprising a mixture containing a polyurethane and an adhesive resin for the manufacture of a removable adhesive tape.

14. Article, characterized in that the article comprises at least two substrates which are joined by means of an adhesive tape according to at least one of claims 1 to 1.

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