Multilayer adhesive tape with resin-modified pressure-sensitive adhesive and its use

Abstract

Adhesive tape comprising a) a carrier layer containing at least one poly(meth)acrylate; and b) an outer pressure-sensitive adhesive layer containing b1) at least one poly(meth)acrylate and b2) at least one (meth)acrylate oligomer; wherein the totality of the poly(meth)acrylates b1) forms a higher molecular weight mode and the totality of the (meth)acrylate oligomers b2) forms a low molecular weight mode within the outer pressure-sensitive adhesive layer b); wherein the difference between the Hansen solubility parameters Zb1 / b2 of the low molecular weight and the higher molecular weight mode of the outer pressure-sensitive adhesive layer b) is < 1; and the difference in the Hansen solubility parameters Za / b2 of the low molecular weight mode of the outer pressure-sensitive adhesive layer b) and the totality of the poly(meth)acrylates of the carrier layer a) is > 1, wherein the at least one (meth)acrylate oligomer of the outer pressure-sensitive adhesive layer is an oligomer having a weight-average molecular weight Mw, measured according to measurement method 1a described herein, of 1.500 to 5,000 g / mol and a polydispersity D of ≤ 2, the structure of which is attributable to a monomer composition consisting of- at least 50 wt.%, based on the total weight of the monomer composition, of a mixture ofMonO1) methyl methacrylateMonO2) cyclohexyl methacrylate; and- MonO3) one or more further radically polymerizable monomersand at least one compound containing an -SH group,characterized in that the carrier layer is foamed.

Description

[0001] The invention relates to the technical field of adhesive tapes, as they are widely used in industry for the temporary or permanent bonding of substrates. More specifically, the invention relates to poly(meth)acrylate-based pressure-sensitive adhesive tapes having a foamed carrier layer and at least one outer pressure-sensitive adhesive layer comprising a low-molecular-weight (meth)acrylate component.

[0002] For various applications, such as the construction sector, the industrial production of technical products, or for assembly purposes, there is an increasing demand for thick, yet highly adhesive adhesive tapes (so-called "assembly adhesive tapes"). Since bonding often takes place outdoors and the bonded products are exposed to external weathering, expectations for the properties of such adhesive tapes are often high. The bond should be strong, durable, and weather-resistant; high resistance to moisture, heat, and humid heat is often required. Furthermore, the adhesive tapes should wet quickly, compensate for unevenness in the bonding joint or on the substrates to be bonded, and exhibit high adhesive strengths right from the start (initial bond strengths).When using non-foamed adhesive tapes, good wetting offers the additional advantage of enabling the bonding of transparent materials without optical defects. This is increasingly desired for thick adhesive tapes, for example, when bonding transparent materials such as glass or transparent plastics.

[0003] The adhesive tapes used for the purposes described above are usually equipped with adhesives whose technical properties must be very precisely coordinated. Cohesion, tack, flow behavior, and other properties must be precisely adjusted. Since the technical formulations of the pressure-sensitive adhesives that influence these properties often have opposing effects on the individual properties, coordination is usually difficult, or compromises must be accepted.

[0004] Especially for thicker adhesive tapes, it is often difficult to achieve a homogeneous property profile; due to processing, such adhesive tapes are often not homogeneous throughout the individual layers. This is usually undesirable, as the adhesive tapes are intended to have well-defined properties regardless of their layer thickness and manufacturing method.

[0005] Materials with viscoelastic properties suitable for pressure-sensitive adhesive applications are generally based on polymers and are characterized by both viscous flow and elastic recovery upon mechanical deformation. The respective proportions of both processes are in a certain relationship to each other, depending on the molecular weight distribution of the polymers, the precise composition, structure, and degree of crosslinking of the material, as well as the speed and duration of deformation and the temperature.

[0006] The viscous flow component is necessary to achieve adhesion. Only the viscous components, caused by macromolecules with relatively high mobility, enable good wetting and flow onto the substrate to be bonded. A high proportion of viscous flow leads to high inherent tack (also referred to as pressure-sensitive adhesion or tack) and thus often also to high adhesive strength. Highly cross-linked systems, crystalline or glass-like solidified polymers, or very high-molecular-weight polymers are generally not inherently tacky due to the lack of flowable components.

[0007] The proportional elastic restoring forces are necessary to achieve cohesion. They are caused, for example, by very long-chain and highly entangled macromolecules, as well as by physically or chemically cross-linked macromolecules, and enable the transfer of forces acting on an adhesive bond. They ensure that an adhesive bond can sufficiently withstand continuous loading, for example, in the form of permanent shear stress, over an extended period of time.

[0008] In foamed, multilayer adhesive tapes, continuous stress can lead to uneven stress distribution. If the forces exceed the adhesion of the pressure-sensitive adhesive layer to the surface, this can result in partial detachment of the pressure-sensitive adhesive layer. The proportion of the wetted surface then decreases.

[0009] To prevent the pressure-sensitive adhesives from flowing off the substrate and to ensure sufficient stability of the pressure-sensitive adhesive in the adhesive bond, sufficient cohesion of the pressure-sensitive adhesives is required. However, for good adhesion properties, the pressure-sensitive adhesives must be able to flow onto the substrate, develop sufficient interactions with the surface in the boundary layer, and guarantee good and permanent wetting of the substrate surface. To avoid cracks within the bond line (within the pressure-sensitive adhesive layer), a certain degree of elasticity of the pressure-sensitive adhesive is also required.

[0010] To achieve sufficient cohesion, pressure-sensitive adhesives are usually crosslinked, meaning individual macromolecules are linked together through bridge bonds. Crosslinking can occur in various ways, including physical and chemical (thermal) crosslinking methods.

[0011] To produce homogeneous adhesive tapes, it is advantageous to thermally crosslink the polymers: It is easily possible to supply even thick layers with thermal energy evenly. Compound layers crosslinked by actinic radiation (e.g., ultraviolet radiation, electron beams), on the other hand, exhibit a crosslinking profile through the crosslinked layer. This crosslinking profile results from the fact that the rays only penetrate the layer to a limited depth, with the intensity of the radiation decreasing with the penetration depth due to absorption processes. Therefore, the outer regions of a radiation-chemically crosslinked compound layer are more strongly crosslinked than the regions further inside, with the crosslinking intensity decreasing overall towards the inside. This effect is particularly significant for thick layers.

[0012] EP 2 305 389 A2 and EP 2 617 789 A1 describe thermally crosslinked assembly tapes with good adhesive and cohesive properties. However, these tapes exhibit weaknesses in bonding to plastic substrates with a medium surface energy, such as ABS or polycarbonate (PC).

[0013] US 2008 / 0 278 672 A1 teaches a stable optical film consisting of a transparent base film, a layer of discotic liquid crystals, and an outer pressure-sensitive adhesive layer. The base film can be made of poly(meth)acrylate, e.g., PMMA. The pressure-sensitive adhesive layer is composed of a high-molecular-weight (meth)acrylate polymer and a low-molecular-weight (meth)acrylate oligomer.

[0014] EP 2 100 933 A1 discloses a double-sided pressure-sensitive adhesive tape with a thin pressure-sensitive adhesive layer that exhibits excellent smoothing properties and thickness uniformity. The adhesive layer contains an acrylic polymer and an acrylic oligomer to achieve excellent adhesion to glass and transparent plastics while ensuring foaming / peeling resistance and transparency.

[0015] DE 60 2005 004 680 T2 discloses a transparent, double-sided adhesive tape or pressure-sensitive film for touch panels that exhibits excellent transparency, lift / peel properties, and anti-curl properties. The adhesive layer contains a composition of acrylic polymer and acrylic oligomer, where the oligomer may contain the monomers cyclohexyl methacrylate, methyl methacrylate, and carboxyl-containing monomers.

[0016] Further pressure-sensitive adhesives and adhesive tapes are disclosed in the prior art in EP 1 574 557 A1 and WO 2012 / 128 294 A1.

[0017] It is generally state of the art to add tackifiers to pressure-sensitive adhesives to increase bond strength and improve wetting. Common tackifier resins for polyacrylate pressure-sensitive adhesives include, in particular, terpene phenol resins and (non-, partially, and / or fully hydrogenated) rosin resins. However, (non-, partially, and / or fully hydrogenated) hydrocarbon resins or low-molecular-weight poly(meth)acrylates can also be used, provided they are compatible. The latter are described, for example, in US Pat. No. 6,657,011 B2.

[0018] In general, the use of adhesive resins in multilayer pressure-sensitive adhesive tapes carries the risk that over time and / or at elevated temperatures, the resin, if compatible with the other layers, will diffuse into them and a phase equilibrium will develop. According to EP 0 286 420 A2, resins, including a poly(isobornyl methacrylate) resin, are described as components of an acid-free polyacrylate pressure-sensitive adhesive used in combination with a polyacrylate foam carrier for the permanent fixation of components in the automotive industry. The solubility parameters of the adhesive resins range between 7 and 9.5 (cal / m³). 3). The document does not provide any information on the storage and / or aging stability of the adhesive tapes. Due to their low solubility parameters, the adhesive resins in the document should have the disadvantage of being more suitable for use in non-polar pressure-sensitive adhesives. However, acrylic acid or other polar comonomers are often used, particularly in polyacrylate pressure-sensitive adhesives, to increase adhesive strength.

[0019] The object of the invention was to provide high-performance adhesive tapes for polar and non-polar surfaces with good wetting behavior and high aging stability.

[0020] A first and general object of the invention with which this object is achieved is an adhesive tape which a) a carrier layer containing at least one poly(meth)acrylate; and b) an outer pressure-sensitive adhesive layer, which b1) at least one poly(meth)acrylate and b2) contains at least one (meth)acrylate oligomer; wherein the totality of the poly(meth)acrylates b1) forms a higher molecular weight mode and the totality of the (meth)acrylate oligomers b2) forms a low molecular weight mode within the outer pressure-sensitive adhesive layer b); where the difference in the Hansen solubility parameters Z b1 / b2 the low molecular weight and the higher molecular weight mode of the outer pressure-sensitive adhesive layer b) is < 1; and the difference in the Hansen solubility parameters Z a / b2 the low molecular weight mode of the outer pressure-sensitive adhesive layer b) and the total of the poly(meth)acrylates of the carrier layer a) is > 1, wherein the at least one (meth)acrylate oligomer of the outer pressure-sensitive adhesive layer is an oligomer having a weight-average molecular weight Mw, measured according to the measurement method 1a described herein, of 1,500 to 5,000 g / mol and a polydispersity D of ≤ 2, the structure of which is based on a monomer composition consisting of - at least 50% by weight, based on the total weight of the monomer composition, of a mixture of MonO1) Methyl methacrylate MonO2) Cyclohexyl methacrylate; and - MonO3) one or more other radically polymerizable monomers as well as at least one compound containing an -SH group, characterized in that the carrier layer is foamed.

[0021] As has been shown, high initial adhesive strengths can be achieved on various polar substrates using adhesive tapes according to the invention, which are maintained even after prolonged storage.

[0022] According to the invention, the carrier layer is understood to be that layer of a multilayer adhesive tape which essentially determines the mechanical and physical properties of the adhesive tape, such as tear resistance, extensibility, insulation or resilience. The carrier layer of the adhesive tape according to the invention can itself be pressure-sensitively adhesive or non-pressure-sensitively adhesive; preferably, it is pressure-sensitively adhesive. An adhesive tape according to the invention can therefore also be a double-sided adhesive tape in an embodiment in which it consists exclusively of the carrier layer and the outer pressure-sensitive adhesive layer. However, the pressure-sensitive adhesive layer preferably has a higher adhesive strength than the pressure-sensitive adhesive carrier layer. The carrier layer preferably has a composition which differs from that of the outer pressure-sensitive adhesive layer(s). The carrier layer is particularly preferably free of (meth)acrylate oligomers.

[0023] Likewise preferably, the carrier layer is thicker than the outer pressure-sensitive adhesive layer or - in the case of two outer pressure-sensitive adhesive layers - than each of the outer pressure-sensitive adhesive layers.

[0024] According to the invention, the carrier layer contains at least one poly(meth)acrylate.

[0025] A "poly(meth)acrylate" is understood to mean a polymer whose monomer base consists of at least 70 wt.% acrylic acid, methacrylic acid, acrylic esters, and / or methacrylic esters, with acrylic esters and / or methacrylic esters being present in an amount of at least 50 wt.%, based in each case on the total monomer composition of the polymer in question. Poly(meth)acrylates are generally obtainable by free-radical polymerization of acrylic and / or methacrylic monomers and, if appropriate, other copolymerizable monomers. According to the invention, the term "poly(meth)acrylate" encompasses polymers based on acrylic acid and derivatives thereof, as well as those based on acrylic acid and methacrylic acid and derivatives thereof, and those based on methacrylic acid and derivatives thereof.

[0026] The carrier layer may contain one (single) or multiple poly(meth)acrylates. Preferably, the carrier layer contains poly(meth)acrylates in a total amount of at least 50 wt.%, based on the total weight of the carrier layer. This also includes the carrier layer containing only a single poly(meth)acrylate, which then constitutes at least 50 wt.%, based on the total weight of the carrier layer.

[0027] In particular, the carrier layer contains at least 50% by weight, based on the total weight of the carrier layer, of at least one polyacrylate which is attributable to the following monomer composition: 65 to 97 wt.% ethylhexyl acrylate and / or butyl acrylate, 0 to 30 wt.% methyl acrylate, 3 to 15 wt% acrylic acid.

[0028] The poly(meth)acrylate(s) of the carrier layer preferably have a weight-average molecular weight M wof at least 500,000 g / mol, particularly preferably at least 700,000 g / mol. Likewise preferably, the poly(meth)acrylate(s) of the carrier layer have a weight-average molecular weight M w of a maximum of 1,700,000 g / mol. The polydispersity PD, i.e. the width of the molar mass distribution, which is defined as the quotient of the weight-average molecular weight M w and the number average molecular weight M n is determined, for the polymers contained in the foamed carrier is preferably 10 ≤ PD ≤ 100, particularly preferably 20 ≤ PD ≤ 80.

[0029] In one embodiment, the carrier layer contains, in addition to the at least one poly(meth)acrylate, at least one further polymer selected from the group consisting of rubbers, in particular natural rubbers, polyurethanes, and aromatic block copolymers, as well as blends of the aforementioned polymers. Preferably, the carrier layer contains, in addition to the at least one poly(meth)acrylate, at least one aromatic block copolymer.

[0030] The carrier layer preferably contains one or more aromatic block copolymers in a total of 15 to 50 wt.%, more preferably in a total of 20 to 40 wt.%, in each case based on the total weight of the carrier layer.

[0031] The aromatic block copolymer is preferably a block copolymer having a structure AB, AB-A, (AB)n, (AB)nX or (ABA)nX, wherein - the blocks A independently represent a polymer formed by polymerization of at least one vinyl aromatic compound; - the blocks B independently represent a polymer formed by polymerisation of conjugated dienes having 4 to 18 carbon atoms and / or isobutylene, or a partially or fully hydrogenated derivative of such a polymer; - X is the residue of a coupling reagent or initiator and - n stands for an integer ≥ 2.

[0032] In particular, if multiple aromatic block copolymers are present, all aromatic block copolymers of the carrier layer are block copolymers with a structure as described above. The carrier layer can thus also contain mixtures of different block copolymers with a structure as described above.

[0033] The preferred vinylaromatic block copolymers thus comprise one or more rubbery blocks B (soft blocks) and one or more glassy blocks A (hard blocks). The aromatic block copolymer of the carrier layer is particularly preferably a block copolymer having a structure AB, ABA, (AB)3X, or (AB)4X, where A, B, and X are as defined above. Most preferably, all aromatic block copolymers of the carrier layer are—where appropriate—block copolymers having a structure AB, ABA, (AB)3X, or (AB)4X, where A, B, and X are as defined above. In particular, the carrier layer contains a mixture of block copolymers having a structure AB, ABA, (AB)3X, or (AB)4X, which preferably contains at least diblock copolymers AB and / or triblock copolymers ABA.

[0034] Block A is, in particular, a glassy block with a preferred glass transition temperature (Tg) above room temperature. The Tg of the glassy block is particularly preferably at least 40°C, in particular at least 60°C, very particularly preferably at least 80°C, and extremely preferably at least 100°C. The proportion of vinylaromatic blocks A in the total aromatic block copolymers is preferably 10 to 40% by weight, particularly preferably 20 to 33% by weight. Vinylaromatics for constructing block A preferably include styrene and α-methylstyrene. Block A can thus be present as a homopolymer or copolymer. Block A is particularly preferably a polystyrene.

[0035] Block B is, in particular, a rubber-like block or soft block with a preferred Tg of less than room temperature. The Tg of the soft block is particularly preferably less than 0°C, in particular less than -10°C, for example less than -40°C, and most preferably less than -60°C.

[0036] Preferred conjugated dienes as monomers for soft block B are selected in particular from the group consisting of butadiene, isoprene, ethylbutadiene, phenylbutadiene, piperylene, pentadiene, hexadiene, ethylhexadiene, dimethylbutadiene, and the farnesene isomers, as well as any desired mixtures of these monomers. Block B can also be present as a homopolymer or as a copolymer.

[0037] Particularly preferably, the conjugated dienes used as monomers for soft block B are selected from butadiene and isoprene. For example, soft block B is a polyisoprene, a polybutadiene, or a partially or fully hydrogenated derivative of one of these two polymers, such as, in particular, polybutylenebutadiene; or a polymer made from a mixture of butadiene and isoprene. Block B is most preferably a polybutadiene.

[0038] The aromatic block copolymer of the carrier layer is preferably dispersed in the poly(meth)acrylate. Accordingly, the poly(meth)acrylate and aromatic block copolymer are preferably each homogeneous phases. The poly(meth)acrylates and aromatic block copolymers contained in the carrier layer are preferably selected such that they are not miscible with one another to the point of homogeneity at 23°C. The carrier layer thus preferably has at least a two-phase morphology, at least microscopically and at least at room temperature. Particularly preferably, the poly(meth)acrylate(s) and aromatic block copolymer(s) are not homogeneously miscible with one another in a temperature range from 0°C to 50°C, in particular from -30°C to 80°C, so that the carrier layer has at least a two-phase morphology, at least microscopically, in these temperature ranges.

[0039] For the purposes of this document, components are defined as "not homogeneously miscible with one another" if, even after intimate mixing, the formation of at least two stable phases can be physically and / or chemically verified, at least microscopically, with one phase being rich in one component and the second phase being rich in the other component. The presence of negligible amounts of one component in the other, which does not preclude the formation of multiphases, is considered irrelevant. Thus, small amounts of aromatic block copolymer and / or small amounts of poly(meth)acrylate component may be present in the poly(meth)acrylate phase, provided these are not significant amounts that affect phase separation.

[0040] Phase separation can be realized, in particular, in such a way that discrete regions ("domains") rich in aromatic block copolymer—i.e., essentially formed from aromatic block copolymer(s)—are present in a continuous matrix rich in poly(meth)acrylate—i.e., essentially formed from poly(meth)acrylate. A suitable analysis system for phase separation is, for example, scanning electron microscopy. However, phase separation can also be detected, for example, by the different phases exhibiting two independent glass transition temperatures in differential scanning calorimetry (DSC) or dynamic mechanical analysis (DMA). According to the invention, phase separation is present if it can be clearly demonstrated by at least one of the analysis methods.

[0041] Within the aromatic block copolymer-rich domains, additional multiphasic fine structure may also be present, with the A blocks forming one phase and the B blocks forming a second phase.

[0042] The carrier layer preferably contains 40 - 70 wt.% of at least one poly(meth)acrylate and 15 - 50 wt.%, each based on the total weight of the carrier layer, of at least one aromatic block copolymer.

[0043] The carrier layer of the adhesive tape according to the invention is a foamed carrier layer. Such a foamed layer or foam is understood to be a structure of gas-filled, spherical or polyhedral cells, which are bounded by liquid, semi-liquid, higher-viscosity, or solid cell webs and which are present in such a proportion that the density of the foam is reduced compared to the density of the matrix material, i.e., the totality of the non-gaseous materials from which the respective layer is constructed.The foaming of the matrix material of the carrier layer can, in principle, be carried out in any known manner, for example with expandable or pre-expanded microballoons; with other hollow microspheres such as hollow polymer spheres, hollow glass spheres or hollow ceramic spheres; with solid spheres such as solid polymer spheres, solid glass spheres, solid ceramic spheres or solid carbon spheres; chemically by substances that react with gas release or physically by introducing a propellant or propellant gas.

[0044] The foamed carrier layer preferably contains at least partially expanded microballoons. "Microballoons" are understood to be elastic and thus expandable hollow microspheres that have a thermoplastic polymer shell. These spheres are filled with low-boiling liquids or liquefied gas. Polyacrylonitrile, PVDC, PVC, or polyacrylates are particularly used as shell materials. Hydrocarbons of the lower alkanes, such as isobutane or isopentane, are particularly commonly used as low-boiling liquids, which are enclosed in the polymer shell as a liquefied gas under pressure.

[0045] When exposed to external influences, particularly heat, the outer polymer shell softens. At the same time, the liquid propellant gas contained within the shell transforms into a gaseous state. The microballoons expand irreversibly and expand three-dimensionally. The expansion is complete when the internal and external pressures equalize. Since the polymer shell remains intact, a closed-cell foam is created.

[0046] A variety of microballoon types are commercially available, differing primarily in their size (6 to 45 µm diameter in the unexpanded state) and the initial temperatures required for expansion (75 to 220 °C). Unexpanded microballoon types are also available as aqueous dispersions with a solids or microballoon content of approximately 40 to 45 wt.%, and also as polymer-bound microballoons (masterbatches), for example, in ethylene-vinyl acetate with a microballoon concentration of approximately 65 wt.%. Both the microballoon dispersions and the masterbatches, like the unexpanded microballoons, are suitable for foaming the carrier layer.

[0047] The foamed carrier layer can also be produced using so-called pre-expanded microballoons. In this group, the expansion takes place before mixing into the polymer matrix. The carrier layer preferably contains at least partially expanded microballoons, regardless of the manufacturing method and the initial shape of the microballoons used.

[0048] The term "at least partially expanded microballoons" is understood to mean that the microballoons are expanded at least to the extent that this results in a reduction in the density of the carrier layer to a technically reasonable extent compared to the same layer with the unexpanded microballoons. This means that the microballoons do not necessarily have to be fully expanded. Preferably, the "at least partially expanded microballoons" are each expanded to at least twice their maximum dimension in the unexpanded state.

[0049] The term "at least partially expanded" refers to the state of expansion of the individual microballoons and is not intended to imply that only a portion of the microballoons in question must be partially expanded. Therefore, if "at least partially expanded microballoons" are included in the carrier layer, this means that all of these "at least partially expanded microballoons" are at least partially expanded in the above sense, and unexpanded microballoons are not included in the "at least partially expanded microballoons."

[0050] The foamed carrier layer preferably contains silica, particularly preferably precipitated silica surface-modified with dimethyldichlorosilane. This is advantageous because it allows the thermal shear strength of the carrier layer to be adjusted, and in particular increased. Silicas are also excellent for use in transparent carrier layers. Silica is preferably present in the foamed carrier layer in quantities of up to 15% by weight, based on the total amount of all polymers contained in the foamed carrier layer.

[0051] Other components of the foamed carrier layer as well as the carrier layer in general can be, for example, plasticizers, anti-aging agents, fillers and / or flame retardants.

[0052] The thickness of the foamed carrier layer is preferably 300 to 2,500 µm, more preferably 400 to 2,400 µm.

[0053] For the purposes of the invention, a pressure-sensitive adhesive is understood, as is common parlance, to be a substance that is permanently tacky and adhesive, at least at room temperature. A characteristic of a pressure-sensitive adhesive is that it can be applied to a substrate by pressure and remains adhered there, whereby the pressure to be applied and the duration of this pressure are not defined in more detail. In general, however, depending on the exact type of pressure-sensitive adhesive and the substrate, the temperature, and the humidity, the application of short-term, minimal pressure, which does not go beyond a light touch for a brief moment, is sufficient to achieve the adhesion effect; in other cases, a longer exposure period of higher pressure may be necessary.

[0054] Pressure-sensitive adhesives have special, characteristic viscoelastic properties that lead to their permanent tack and adhesive strength. They are characterized by the fact that, when mechanically deformed, both viscous flow processes and the development of elastic restoring forces occur. The respective proportions of both processes are in a specific relationship to each other, depending on the precise composition, structure, and degree of crosslinking of the pressure-sensitive adhesive, as well as the speed and duration of the deformation and the temperature.

[0055] The viscous flow component is necessary to achieve adhesion. Only the viscous components, often caused by macromolecules with relatively high mobility, enable good wetting and flow onto the substrate to be bonded. A high proportion of viscous flow leads to high pressure-sensitive adhesion (also referred to as tack or surface stickiness) and thus often to high adhesion. Highly cross-linked systems, crystalline, or glass-like polymers, are generally not or at least only slightly pressure-sensitive due to the lack of flowable components.

[0056] The proportional elastic restoring forces are necessary to achieve cohesion. They are caused, for example, by very long-chain and highly entangled macromolecules, as well as by physically or chemically cross-linked macromolecules, and enable the transfer of forces acting on an adhesive bond. They ensure that an adhesive bond can sufficiently withstand continuous loading, for example, in the form of permanent shear stress, over an extended period of time.

[0057] To more precisely describe and quantify the degree of elastic and viscous components, as well as the relationship between the components, the storage modulus (G') and loss modulus (G''), which can be determined using Dynamic Mechanical Analysis (DMA), are used. G' is a measure of the elastic component, while G'' is a measure of the viscous component of a material. Both parameters depend on the deformation frequency and the temperature.

[0058] These parameters can be determined using a rheometer. The material under test is subjected to sinusoidal oscillating shear stress, for example, in a plate-on-plate arrangement. Shear stress-controlled devices measure the deformation as a function of time and the temporal offset of this deformation relative to the application of the shear stress. This temporal offset is referred to as the phase angle δ.

[0059] The storage modulus G' is defined as follows: G' = (τ / γ) · cos(δ) (τ = shear stress, γ = deformation, δ = phase angle = phase shift between shear stress and deformation vector). The definition of the loss modulus G'' is: G'' = (τ / γ) · sin(δ) (τ = shear stress, γ = deformation, δ = phase angle = phase shift between shear stress and deformation vector).

[0060] A mass is considered to be a pressure-sensitive adhesive and is defined as such in the sense of the invention in particular if at 23 °C in the deformation frequency range from 10° to 10 1 rad / sec both G' and G'' are at least partly in the range of 10 3 up to 10 7 Pa. “Partially” means that at least a section of the G' curve lies within the window defined by the deformation frequency range of 10 0 up to and including 10 1 rad / sec (abscissa) and the range of G' values from 10 3 up to and including 10 7 Pa (ordinate) and if at least one section of the G'' curve also lies within the corresponding window.

[0061] The at least one poly(meth)acrylate of the outer pressure-sensitive adhesive layer can preferably be traced back to the following monomer composition: Mon1) at least one acrylic acid ester and / or methacrylic acid ester of the following formula (1) CH2 = C(R I )(COOR II ) (1), where R I = H or CH3 and R II is an alkyl radical with 4 to 14 C atoms, Mon2) at least one olefinically unsaturated monomer having functional groups suitable for chemically or physically crosslinking the polymer and Mon3) optionally further acrylates and / or methacrylates and / or olefinically unsaturated monomers which are copolymerizable with the monomers Mon1 and Mon2.

[0062] The proportions of the monomers Mon1, Mon2 and Mon3 are preferably selected such that the polymerization product has a glass transition temperature ≤ 15 °C (DMA at low frequencies).

[0063] The monomers Mon1 are preferably present in the poly(meth)acrylate in a proportion of 45 to 99 wt.%, the monomers Mon2 in a proportion of 1 to 20 wt.% and the monomers Mon3 in a proportion of 0 to 40 wt.%, in each case based on the total monomer mixture without taking into account additives that may be added to the finished polymer.

[0064] The monomers Mon1 are, in particular, plasticizing and / or nonpolar monomers. They are preferably selected from acrylic and methacrylic acid esters with alkyl groups in the alcohol component, which contain 4 to 14 carbon atoms, particularly preferably 4 to 9 carbon atoms, in particular from the group consisting of n-butyl acrylate, n-butyl methacrylate, n-pentyl acrylate, n-pentyl methacrylate, n-amyl acrylate, n-hexyl acrylate, n-hexyl methacrylate, n-heptyl acrylate, n-octyl acrylate, n-octyl methacrylate, n-nonyl acrylate, isobutyl acrylate, isooctyl acrylate, isooctyl methacrylate, and their branched isomers, in particular 2-ethylhexyl acrylate and 2-ethylhexyl methacrylate.

[0065] The monomers Mon2 are in particular olefinically unsaturated monomers with functional groups that can react with epoxy groups.

[0066] They preferably contain functional groups selected from hydroxy, carboxy, amino, sulfonic acid, phosphonic acid, acid anhydride and epoxide groups.

[0067] Particularly preferred examples of monomers Mon2 are acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, aconitic acid, dimethylacrylic acid, β-acryloyloxypropionic acid, trichloroacrylic acid, vinylacetic acid, vinylphosphonic acid, maleic anhydride, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, 6-hydroxyhexyl methacrylate, allyl alcohol, glycidyl acrylate and glycidyl methacrylate.

[0068] In principle, all vinyl-functionalized compounds that are copolymerizable with the monomers Mon1 and Mon2 can be used as monomers Mon3. The monomers Mon3 can be used to adjust the properties of the pressure-sensitive adhesive.

[0069] The monomers Mon3 are preferably selected from the following monomers: Methylacrylat, Ethylacrylat, Propylacrylat, Methylmethacrylat, Ethylmethacrylat, Benzylacrylat, Benzylmethacrylat, sec-Butylacrylat, tert-Butylacrylat, Phenylacrylat, Phenylmethacrylat, Isobornylacrylat, Isobornylmethacrylat, tert-Butylphenylacrylat, tert-Butylaphenylmethacrylat, Dodecylmethacrylat, Isodecylacrylat, Laurylacrylat, n-Undecylacrylat, Stearylacrylat, Tridecylacrylat, Behenylacrylat, Cyclohexylmethacrylat, Cyclopentylmethacrylat, Phenoxyethylacrlylat, Phenoxyethylmethacrylat, 2-Butoxyethylmethacrylat, 2-Butoxyethylacrylat, 3,3,5-Trimethylcyclohexylacrylat, 3,5-Dimethyladamantylacrylat, 4-Cumylphenylmethacrylat, Cyanoethylacrylat, Cyanoethylmethacrylat, 4-Biphenylacrylat, 4-Biphenylmethacrylat, 2-Naphthylacrylat, 2-Naphthylmethacrylat, Tetrahydrofufurylacrylat, Diethylaminoethylacrylat, Diethylaminoethylmethacrylat, Dimethylaminoethyl-acrylat, Dimethylaminoethylmethacrylat, 2-Butoxyethylacrylat, 2-Butoxyethylmethacrylat, 3-Methoxyacrylsäuremethylester, 3-Methoxybutylacrylat,Phenoxyethylacrlylat, Phenoxyethylmethacrylat, 2-Phenoxyethylmethacrylat, Butyldiglykolmethacrylat, Ethylenglycolacrylat, Ethylenglycolmonomethylacrylat, Methoxy Polyethylenglykolmethacrylat 350, Methoxy Polyethylenglykolmethacrylat 500, Propylenglycolmonomethacrylat, Butoxydiethylenglykolmethacrylat, Ethoxytriethylenglykolmethacrylat, Octafluoropentylacrylat, Octafluoropentylmethacrylat, 2,2,2-Trifluoroethylmethacrylat, 1,1,1,3,3,3-Hexafluoroisopropylacrylat, 1,1,1,3,3,3-Hexafluoroisopropylmethacrylat, 2,2,3,3,3-Pentafluoropropylmethacrylat, 2,2,3,4,4,4-Hexafluorobutylmethacrylat, 2,2,3,3,4,4,4-Heptafluorobutylacrylat, 2,2,3,3,4,4,4-Heptafluorobutylmethacrylat, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-Pentadecafluorooctylmethacrylat, Dimethylaminopropylacrylamid, Dimethylaminopropylmethacrylamid, N-(1-Methylundecyl)acrylamid, N-(n-Butoxymethyl)acrylamid, N-(Butoxymethyl)methacrylamid, N-(Ethoxymethyl)acrylamid, N-(n-Octadecyl)acrylamid; weiterhin N,N-dialkyl-substituted amides such as N,N-dimethylacrylamide, N,N-dimethylmethacrylamide; N-benzylacrylamide, N-isopropylacrylamide, N-tert-butylacrylamide, N-tert-octylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, acrylonitrile, methacrylonitrile; vinyl ethers such as vinyl methyl ether, ethyl vinyl ether, vinyl isobutyl ether; vinyl esters such as vinyl acetate; vinyl halides, vinylidene halides, vinylpyridine, 4-vinylpyridine, N-vinylphthalimide, N-vinyllactam, N-vinylpyrrolidone, styrene, o- and p-methylstyrene, o-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, 3,4-dimethoxystyrene; Macromonomers such as 2-polystyrene ethyl methacrylate (molecular weight Mw from 4000 to 13000 g / mol) and poly(methyl methacrylate) ethyl methacrylate (Mw from 2000 to 8000 g / mol).

[0070] The Mon3 monomers can also contain functional groups that support subsequent radiation-chemical crosslinking (e.g., by electron beam or UV). Such copolymerizable photoinitiators include benzoin acrylate and acrylate-functionalized benzophenone derivatives. Monomers that support crosslinking by electron irradiation include tetrahydrofurfuryl acrylate, N-tert-butylacrylamide, and allyl acrylate.

[0071] The weight-average molecular weight M w of the poly(meth)acrylate of the outer pressure-sensitive adhesive layer is preferably 20,000 to 2,000,000 g / mol, particularly preferably 100,000 to 1,500,000 g / mol, in particular 200,000 to 1,200,000 g / mol [the data for the average molecular weight M wand the polydispersity PD in this document refer to the determination by gel permeation chromatography (see measurement methods 1a and 1b; experimental section). Furthermore, the poly(meth)acrylate of the outer pressure-sensitive adhesive layer preferably has a K value of 30 to 90, particularly preferably 50 to 80, measured in toluene (1% solution, 21°C). The Fikentscher K value is a measure of the molecular weight and viscosity of a polymer.

[0072] Particularly preferably, all poly(meth)acrylates of the outer pressure-sensitive adhesive layer b) optionally have a weight-average molecular weight according to the above.

[0073] The at least one (meth)acrylate oligomer of the outer pressure-sensitive adhesive layer is, according to the invention, an oligomer having a weight-average molecular weight Mw, measured according to the measurement method 1a described herein, of 1,500 to 5,000 g / mol and a polydispersity D of ≤ 2, the structure of which is based on a monomer composition consisting of - at least 50% by weight, based on the total weight of the monomer composition, of a mixture of MonO1) Methyl methacrylate MonO2) Cyclohexyl methacrylate; and - optional MonO3) one or more other radically polymerizable monomers as well as at least one compound containing an -SH group.

[0074] As has been shown, such methacrylate resins exhibit a high compatibility with a wide range of (meth)acrylate-based pressure-sensitive adhesives and contribute to the development of a balanced property profile of these materials.

[0075] According to the general understanding of the person skilled in the art, the polydispersity D is the ratio between the weight-average molecular weight M w and number average molecular weight M n understood: D = M w / M n .

[0076] Methyl methacrylate is preferably present in the monomer composition underlying the preferred (meth)acrylate oligomer at 40 to 90 wt.%, based on the total weight of the monomer composition.

[0077] Cyclohexyl methacrylate is preferably present in the monomer composition underlying the preferred (meth)acrylate oligomer in an amount of 10 to 60 wt.%, based on the total weight of the monomer composition.

[0078] A mixture of methyl methacrylate and cyclohexyl methacrylate is present in the monomer composition underlying the (meth)acrylate oligomer according to the invention at a concentration of at least 50% by weight. Preferably, the mixture of methyl methacrylate and cyclohexyl methacrylate is present in the monomer composition underlying the preferred (meth)acrylate oligomer at a concentration of at least 60% by weight, particularly preferably at least 65% by weight, and in particular at least 70% by weight.

[0079] The further radically polymerizable monomers optionally contained in the monomer composition underlying the preferred (meth)acrylate oligomer are preferably selected from the group consisting of acrylic acid esters, methacrylic acid esters, acrylamides, vinyl esters, vinyl ethers, and vinyl aromatics. More preferably, the further radically polymerizable monomers are selected from acrylic acid esters and methacrylic acid esters, in particular from methacrylic acid esters. Very particularly preferably, isobutyl methacrylate is contained as a further radically polymerizable monomer in the monomer composition underlying the preferred (meth)acrylate oligomer. For example, the monomer composition underlying the preferred (meth)acrylate oligomer consists of at least 50 wt. %, based on the total weight of the monomer composition, of a mixture of a) Methyl methacrylate and b) cyclohexyl methacrylate; as well as from c) Isobutyl methacrylate.

[0080] In addition to the monomer composition, at least one compound containing an -SH group is involved in the synthesis of the (meth)acrylate oligomer according to the invention. Preferably, one or more compounds containing an -SH group are present in this total in a total amount of 1 to 15 mol%, more preferably 3 to 12 mol%, in particular 5 to 9 mol%, based in each case on the totality of the substances involved in the synthesis of the (meth)acrylate oligomer. The compounds containing an -SH group are not included in the monomer composition underlying the (meth)acrylate oligomer; rather, these compounds are intended as chain transfer agents and / or polymerization regulators.

[0081] The compound containing an -SH group according to the invention is preferably selected from alkylthiols and hydroxycarboxylic acids. For example, the compound containing an -SH group is dodecanethiol (lauryl mercaptan), 2-mercaptopropionic acid, or thioglycolic acid (mercaptoacetic acid). The compound containing an -SH group preferably contains no carboxyl group and no thiocarboxy group. Therefore, the compound containing an -SH group is particularly preferably dodecanethiol. One or more compounds containing an -SH group can be present in the totality of the substances involved in the construction of the preferred (meth)acrylate oligomer; preferably, a single compound containing an -SH group is present.

[0082] The weight-average molecular weight M w of the preferred (meth)acrylate oligomer is preferably 2,000 to 4,500 g / mol, particularly preferably 2,500 to 4,000 g / mol. The polydispersity D is preferably ≤ 1.8.

[0083] Furthermore, the preferred (meth)acrylate oligomer preferably has a glass transition temperature, determined according to the method described herein, of ≤ 100 °C, in particular of ≤ 80 °C, most preferably of ≤ 65 °C.

[0084] The preferred (meth)acrylate oligomer preferably has an iodine number, measured according to DIN EN ISO 3961, of ≤ 0.3. More preferably, the preferred (meth)acrylate oligomer has an iodine number, measured according to DIN EN ISO 3961, of ≤ 0.2, in particular ≤ 0.1. The iodine number is a measure of the degree of unsaturation of a chemical compound.

[0085] To determine this, halogen compounds are added to the double bonds. The iodine number indicates the ratio of the mass of halogen, calculated as iodine, bound by the sample material under test conditions to the mass of the sample material.

[0086] The low double bond content of the preferred (meth)acrylate oligomer indicates high aging stability and low yellowing tendency.

[0087] The outer pressure-sensitive adhesive layer of the adhesive tape according to the invention can contain one or more poly(meth)acrylate(s) and one or more (meth)acrylate oligomer(s). When reference is made to the "totality of the poly(meth)acrylates b1)" and the "totality of the (meth)acrylate oligomers b2)" according to the invention, this includes both a pressure-sensitive adhesive containing only one (single) poly(meth)acrylate and / or only one (single) (meth)acrylate oligomer and a pressure-sensitive adhesive containing multiple poly(meth)acrylate(s) and / or multiple (meth)acrylate oligomers. This also applies accordingly to the "totality of the poly(meth)acrylates of the carrier layer a)".

[0088] The outer pressure-sensitive adhesive layer preferably contains at least one plasticizer. The plasticizer is preferably selected from the group consisting of (meth)acrylate oligomers, phthalates, cyclohexanedicarboxylic acid esters (e.g., Hexamoll® DINCH, BASF, CAS 166412-78-8), water-soluble plasticizers, plastic resins, phosphates (e.g., Levagard® DMPP, Lanxess, CAS 18755-43-6), and polyphosphates.

[0089] The thickness of the outer pressure-sensitive adhesive layer is preferably 40 to 150 µm, particularly preferably 50 to 100 µm.

[0090] According to the invention, the totality of the poly(meth)acrylates b1) forms a higher molecular mode and the totality of the (meth)acrylate oligomers b2) forms a low molecular mode within the outer pressure-sensitive adhesive layer b).

[0091] According to the invention, the difference of the Hansen solubility parameters Z b1 / b2 the low molecular and the higher molecular mode of the outer pressure-sensitive adhesive layer b) < 1; and the difference in the Hansen solubility parameters Z a / b2 the low molecular weight mode of the outer pressure-sensitive adhesive layer b) and the totality of the poly(meth)acrylates of the carrier layer a) > 1.

[0092] A well-known description of solubility parameters in the literature is the one-dimensional Hildebrand parameter (δ). However, these one-dimensional δ values are subject to errors, which are usually large for polar compounds such as acrylates or those that can form hydrogen bonds, such as acrylic acid. Because the one-dimensional Hildebrand solubility parameter model has only limited application, it was further developed by Hansen (Hansen Solubility Parameters: A User's Handbook, 2nd Edition; Ch. M. Hansen; 2007 CRC Press; ISBN 9780849372483).

[0093] The Hansen solubility parameters, which are therefore widely used today, are three-dimensional solubility parameters. They consist of a disperse part (δ d ), a portion from polar interactions (δ p ) and a portion for the hydrogen bonds (δ H ). They are related to the Hildebrand parameter δ as follows: δ2=δd2+δp2+δH2 δ d , δ p and δ H cannot be determined directly experimentally for poly(meth)acrylates, but can be calculated using incremental systems. A common method—also used in the present invention—is the method according to Stefanis / Panayiotou (E. Stefanis, C. Panayiotou, Int. J. Thermophys. 2008, 29, 568):

[0094] To determine the Hansen solubility parameters for poly(meth)acrylates, the solubility parameters of the building blocks in the polymers attributable to the individual monomers, i.e., those of the repeating unit in a polymer chain (without the polymerizable double bond, which is replaced by a covalent sigma bond, as present in the polymer chain), are calculated according to the procedure in the cited document. For each group in the building block, a specific value for the dispersed fraction (δ d ), the polar interactions (δ p ) and the hydrogen bonding fraction (δ H ) tabulated, see Int. J. Thermophys. 2008, Tables 3 to 6, pages 578 to 582.

[0095] The following examples should clarify these calculations: Polyacrylic acid contains the repeating unit -[-CH2-CHCOOH-] n - ; According to the increment system of Stefanis / Panayiotou, the Hansen solubility parameters (one CH2 group, one CH group and one COOH group) for the corresponding building block are δ d = 17.7; δ p = 8.6 and δ H = 11.1. Polybutylacrylate contains the repeating unit -[-CH2-CHCOO(CH2)3CH3-] n - ; with four CH2 groups, one CH group, one COO group and one CH3 group, the Hansen solubility parameters for the corresponding building block are δ d = 17.1; δ p = 8.6 and δ H = 6.5.

[0096] The Hansen solubility parameter calculations presented here as examples are based on the "first-order or group contribution" increment values according to Table 3 of the aforementioned Stefanis / Panayiotou paper (W = 0), which are applied to relatively simple structural elements. If the Hansen solubility parameters are to be determined for more complex monomer building blocks that contain structural elements as listed in Tables 4 and 6 of the Stefanis / Panayiotou paper ("second-order group contribution" increment values; W = 1), the values listed there should be used.

[0097] After calculating the Hansen solubility parameters of the monomer building blocks, the corresponding Hansen solubility parameters of the poly(meth)acrylates (copolymers) or (meth)acrylate oligomers can be determined. The solubility parameters (δ d , δ p , δ H) for (meth)acrylate copolymers or cooligomers are determined from the molar proportion of the individual monomers (building blocks) of which the poly(meth)acrylate is composed, whereby the respective values of the solubility parameters are multiplied by the molar proportion of the monomer building block in the copolymer and then the proportional parameters (δ d , δ p , δ H for each monomer).

[0098] This is illustrated by the example of a poly(meth)acrylate consisting of 97 wt% butyl acrylate and 3 wt% acrylic acid, corresponding to a molar composition of 94.8 mol% butyl acrylate and 5.2 mol% acrylic acid (Table 1). Table 1: Example calculation of Hansen solubility parameters of an acrylate copolymer d d d p d H Butyl acrylate (δ d = 17.1, δ p = 8.6 and δ H = 6.5) 0,948 × 17,1 = 16,2 0,948 × 8,6 = 8,2 0,948 × 6,5 = 6,1 Acrylic acid (δ d = 17.7, δ p = 8.6 and δ H = 11.1) 0,052 × 17,7= 0,9 0,052 × 8,6 = 0,4 0,052 × 11,1 = 0,6 + Polyacrylate 17,1 8,6 6,7

[0099] For homogeneously miscible polymer mixtures, the following procedure is followed: The Hansen solubility parameters of each polymer are multiplied by the molar fraction of this polymer in the polymer mixture and the proportional values are then added together to obtain the respective parameter of the polymer mixture.

[0100] The difference in the Hansen solubility parameters of two polymer components (for clarification, two polymer components 1 and 2 below) is given by the parameter Z.

[0101] Of the parameters δ d1 δ p1 and δ H1 of polymer component 1, the corresponding parameters δ d2 , δ p2 and δ H2of polymer component 2 is subtracted and the difference is squared. The squares of the differences are added, with the difference in the dispersed fractions of the solubility parameters being weighted by a factor of 4 (see Int. J. Thermophys. 2008, 29, formula (5), page 570). The square root of the sum is calculated, which then yields the difference in the Hansen solubility parameters: Z=4∗(δd1−δd2)2+(δp1−δp2)2+(δH1−δH2)2

[0102] For a number of monomers which are very suitable for the invention, the respective Hansen solubility parameters are listed in Table 2, so that the above values for polymer components with polymers formed therefrom can be easily determined. Table 2: Hansen solubility parameters of (meth)acrylate monomers suitable according to the invention Monomer δ d [MPa 1 / 2 ] δ p [MPa 1 / 2 ] δ H [MPa 1 / 2 ] Methyl methacrylate MMA 16,8 9,3 7,2 Cyclohexyl methacrylate CHMA 17,9 6,4 5,8 Isobornyl methacrylate IBOMA 17,3 5,9 3,6 4-tert-Butylcyclohexyl methacrylate TBCHMA 15,6 3,6 3,3 Acrylic acid AS 17,7 8,6 11,1 2-Ethylhexylacrylate EHA 16,7 7,0 4,7 n-Butyl acrylate BA 17,1 8,6 6,5 Isobornyl acrylate IBOA 17,6 6,1 4,1

[0103] According to the invention, the difference Z is b1 / b2between the Hansen solubility parameters of the low molecular weight and the higher molecular weight mode of the outer pressure-sensitive adhesive layer b) < 1.

[0104] The Difference Z a / b2 between the Hansen solubility parameters of the low molecular weight mode of the outer pressure-sensitive adhesive layer b) and the totality of the poly(meth)acrylates of the carrier layer a) is, according to the invention, > 1, preferably > 1.2 and particularly preferably > 1.5.

[0105] Preferably, the quotient of the difference Z is b1 / b2 and diversity Za / b2 Zb1 / b2 / Za / b2≤0.9.

[0106] The difference between the disperse fractions of the Hansen solubility parameters of the higher and lower molecular weight modes within the outer pressure-sensitive adhesive layer is preferably less than 1, more preferably less than 0.5, and in particular less than 0.2. The difference between the polar fractions of the solubility parameters of the higher and lower molecular weight modes within the outer pressure-sensitive adhesive layer is preferably less than 1, more preferably less than 0.8, and in particular less than 0.6. The difference between the hydrogen bond fractions of the solubility parameters of the higher and lower molecular weight modes within the outer pressure-sensitive adhesive layer is preferably less than 1, more preferably less than 0.7, and in particular less than or equal to 0.5. Likewise preferably, the difference between just one Hansen solubility parameter of the higher and lower molecular weight modes within the outer pressure-sensitive adhesive layer is < 1, and all other Hansen solubility parameters are identical.

[0107] The poly(meth)acrylates and (meth)acrylate oligomers of the invention can be prepared by conventional processes, in particular by conventional radical polymerizations or controlled radical polymerizations. The polymers or oligomers can be prepared by copolymerization of the monomer components using conventional polymerization initiators and, if appropriate, regulators, polymerization being carried out at conventional temperatures in bulk, in emulsion, e.g., in water or liquid hydrocarbons, or in solution.

[0108] The poly(meth)acrylates and (meth)acrylate oligomers are preferably prepared by polymerization in solvents, preferably in solvents having a boiling range of 50 to 150 °C, particularly preferably 60 to 120 °C, using the usual amounts of polymerization initiators, which are generally from 0.01 to 5, in particular from 0.1 to 2 wt.% (based on the total weight of the monomers).

[0109] In principle, all initiators commonly used for acrylates are suitable. Examples of radical sources include peroxides, hydroperoxides, and azo compounds, e.g., dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-t-butyl peroxide, cyclohexylsulfonyl acetyl peroxide, diisopropyl percarbonate, t-butyl peroctoate, and benzpinacol. 2,2'-azobis(2-methylbutyronitrile) (Vazo® 67™ from DuPont) or 2,2'-azobis(2-methylpropionitrile) (2,2'-azobisisobutyronitrile; AIBN; Vazo® 64™ from DuPont) are very preferred radical initiators.

[0110] Suitable solvents include, in particular, alcohols such as methanol, ethanol, n- and isopropanol, n- and isobutanol, preferably isopropanol and / or isobutanol; as well as hydrocarbons such as toluene and, in particular, gasolines with a boiling range of 60 to 120 °C. In particular, ketones such as, preferably, acetone, methyl ethyl ketone, and methyl isobutyl ketone; and esters such as ethyl acetate, as well as mixtures of solvents of the type mentioned, can be used. Among the mixtures, those containing isopropanol, in particular in amounts of 2 to 15 wt. %, preferably 3 to 10 wt. %, based on the solvent mixture used, are most preferred.

[0111] The poly(meth)acrylates of the pressure-sensitive adhesive layer of the adhesive tape of the invention are preferably thermally crosslinked using at least one covalent crosslinker or using a combination of at least one covalent crosslinker with at least one coordinative crosslinker. Preferred covalent crosslinkers are epoxycyclohexyl derivatives and N,N-diglycidylamines. Preferred coordinative crosslinkers are chelate compounds, in particular polyvalent metal chelate compounds. Thermal crosslinking results in homogeneous crosslinking throughout the entire layer of the adhesive, whereas, for example, with radiation-crosslinked compounds, a crosslinking profile with decreasing crosslinking density toward the center of the compound is observed. A homogeneously crosslinked pressure-sensitive adhesive layer enables the uniform distribution of stresses such as those that may occur when the bond is subjected to stress.Adhesive and cohesive properties can be balanced very precisely for the entire layer, so that resilient bonds with a predictable property profile can be obtained.

[0112] Particularly preferred thermal crosslinkers are N,N,N',N'-tetrakis(2,3-epoxypropyl)cyclohexane-1,3-dimethylamine (e.g. Syna Epoxy S610, Synasia) and N,N,N',N'-tetrakis(2,3-epoxypropyl)-m-xylene-a,a'-diamine (e.g. Erisys GA-240, CVC) as well as epoxycyclohexylcarboxylates, in particular (3,4-epoxycyclohexane)methyl-3,4-epoxycyclohexylcarboxylate and bis(3,4-epoxycyclohexylmethyl)adipate.

[0113] Preferred coordinative crosslinkers are polyvalent metal chelate compounds. “Polyvalent metal chelate compounds” are understood to be compounds in which a polyvalent metal is coordinately bonded to one or more organic compounds. Preferred polyvalent metal atoms are Al(III), Zr(IV), Co(II), Cu(I), Cu(II), Fe(II), Fe(III), Ni(II), V(II), V(III), V(IV), V(V), Zn(II), In(III), Ca(II), Mg(II), Mn(II), Y(III), Ce(II), Ce(IV), St(II), Ba(II), Mo(II), Mo(IV), Mo(VI), La(III), Sn(II), Sn(IV), and Ti(IV), in particular Al(III), Zr(IV), and Ti(IV).

[0114] In principle, any known ligand can serve as ligands for the coordinative crosslinkers. However, the atoms used for the coordination bond of the organic compound are preferably those that have free electron pairs, such as oxygen atoms, sulfur atoms, nitrogen atoms, and the like. Preferred organic atoms are alkyl esters, alcohol compounds, carboxylic acid compounds, ether compounds, and ketone compounds.Particularly preferred coordinative crosslinkers are titanium dipropoxide bis(acetylacetonate), titanium dibutoxide bis(octylene glycolate), titanium dipropoxide bis(ethyl acetoacetate), titanium dipropoxide bis(lactate), titanium dipropoxide bis(triethanolaminate), titanium di-n-butoxide bis(triethanolaminate), titanium tri-n-butoxide monostearate, butyl titanate dimer, poly(titanium acetylacetonate); aluminum diisopropoxide monoethyl acetate, aluminum di-n-butoxide monomethyl acetoacetate, aluminum di-i-butoxide monomethyl acetoacetate, aluminum di-n-butoxide monoethyl acetoacetate, aluminum disec-butoxide monoethyl acetoacetate, aluminum triacetylacetonate, aluminum triacetylacetonate, aluminum monoacetylacetonate bis(ethyl acetoacetonate) and zirconium tetraacetylacetonate; in particular aluminum triacetylacetonate and aluminum diisopropoxide monoethyl acetate.

[0115] One or more covalent and one or more coordinative crosslinkers can be used, also in combination with each other.

[0116] Crosslinking accelerators may be used; however, the pressure-sensitive adhesive layer preferably contains neither externally added nor polymerized accelerators, and in particular it contains no accelerators at all.

[0117] Preferably, covalent crosslinkers and coordinative crosslinkers are used in such a way that the functional groups of the covalent crosslinkers are present in molar excess relative to the binding sites of the coordinative crosslinkers. Preferably, the crosslinkers are used in such a way that the molar ratio of the functional groups of the covalent crosslinkers to the binding sites of the coordinative crosslinkers - i.e., the ratio of the amount of substance used n kov the functional groups of the covalent crosslinkers to the amount of substance used n koord the binding sites of the coordinative crosslinkers - is in the range from 3 : 1 to 9 : 1, particularly preferably from 4.5 : 1 to 8.5 : 1.

[0118] The poly(meth)acrylates or poly(meth)acrylate of the foamed carrier layer are also preferably thermally crosslinked. The poly(meth)acrylates of the carrier layer are particularly preferably thermally crosslinked by at least one glycidyl ether, in particular at least one polyglycidyl ether, very preferably at least by pentaerythritol tetraglycidyl ether (CAS 3126-63-4). The crosslinking of the poly(meth)acrylates of a foamed carrier layer is preferably carried out in combination with an amine, particularly preferably with isophoronediamine (CAS 2855-13-2), as an accelerator. The total proportion of crosslinkers in the carrier layer is preferably up to 1.0 wt. %, more preferably up to 0.8 wt. %, based in each case on the total amount of polymers to be crosslinked. Particularly preferred amounts of crosslinker are, for example, in the range from 0.05 to 0.6, in particular from 0.10 to 0.5 wt.%, in each case based on the total amount of the polymers to be crosslinked.

[0119] The accelerator(s) is / are preferably present in an amount of 0.1 to 1.5 wt.%, more preferably 0.15 to 1.2 wt.%, in each case based on the total amount of the polymers to be crosslinked.

[0120] The presence of an amine accelerator in a foamed carrier layer is uncritical, particularly in three- or multi-layer structures, since in these cases the carrier layer is largely shielded from the influence of oxidizing substances such as atmospheric oxygen by the outer adhesive or pressure-sensitive adhesive layers.

[0121] The (meth)acrylate oligomers of the pressure-sensitive adhesive layer can be crosslinked—particularly in accordance with the statements regarding the crosslinking of the poly(meth)acrylates of this layer. This requires that they contain functional groups suitable for crosslinking. The (meth)acrylate oligomers of the pressure-sensitive adhesive layer are preferably uncrosslinked.

[0122] The production of adhesive tapes according to the invention is preferably carried out according to the process aspects described below.

[0123] The carrier layer is preferably obtained by first converting the poly(meth)acrylate into the melt state. At least one thermal crosslinker is added to the melt, preferably under precise temperature and time control. The poly(meth)acrylate provided with the crosslinker is conveyed to a coating unit, particularly preferably using an extruder, in particular the same compounding extruder in which the crosslinker was already added and in which the concentration of the poly(meth)acrylate may have already taken place. At the end of the extrusion process, the material is formed into a layer, for example, using a suitable die.

[0124] The crosslinking of the poly(meth)acrylates applied in this way preferably takes place in the applied layer, particularly at least partially after the application of the pressure-sensitive adhesive layer(s). This allows the respective thermal crosslinkers to react across layer boundaries with the poly(meth)acrylates of the adjacent layer. This achieves good anchoring of the carrier layer and the pressure-sensitive adhesive layer(s).

[0125] The time from the addition of the crosslinking system in the compounding unit until the carrier layer is formed is referred to as the processing time. Within this time, the now crosslinked layer can be coated gel-free and with a visually good coating pattern. Crosslinking then occurs primarily after coating on the web under mild conditions that damage neither the layer nor the liner, thus, particularly advantageously, without the influence of actinic radiation such as UV radiation or electron beams. This results in a homogeneously crosslinked layer, meaning it exhibits no crosslinking profile throughout the layer.

[0126] The extruders used according to the above are preferably twin-screw extruders and / or planetary roller extruders. The spindles of the respective extruder are particularly preferably temperature-controlled, in particular coolable. The addition of the crosslinkers and, if appropriate, further constituents of the respective layer can take place at one or more points in the extruder; preferably, it takes place in pressure-free zones. The thermally reactive crosslinker substances are particularly preferably added to the polymers in finely distributed form, for example as an aerosol, in fine droplets, or diluted in a suitable diluent such as a polymer-compatible plasticizer. The temperature of the poly(meth)acrylate of the carrier layer during the addition of the thermal crosslinker is preferably between 60°C and 120°C, particularly preferably between 70°C and 100°C.

[0127] The introduction of expandable, but not yet expanded, microballoons into the mass system of a carrier layer to be foamed can be achieved, in particular, by mixing the microballoons with the other components required to form the mass system. However, the microballoons can also be added to the already melted mass system.

[0128] During this phase of the process, components of the crosslinking system can be added that do not yet react thermally, for example, because another component of the system is not yet present. For example, it is possible to add crosslinking agents during this phase that only react to a significant extent in the presence of accelerators.

[0129] The components for producing the compounding system can be introduced into an extruder and, in particular, melted. It is also possible to introduce prefabricated solvent-free compound using a conveyor extruder, such as a single-screw extruder, or through a drum melt by injection, and then meter in the microballoons in the feed area of the compounding extruder, such as a planetary roller extruder.

[0130] Compounds foamed with microballoons generally do not require degassing prior to coating to achieve a uniform, continuous coating. The expanding microballoons displace the air trapped in the adhesive during compounding. However, at high throughputs, it is advisable to degas the compounds prior to coating to ensure a uniform composition in the roller gap. Ideally, degassing should then take place immediately upstream of the roller applicator at mixing temperature and a pressure differential to ambient pressure of at least 200 mbar.

[0131] It is possible to cool the mass system after the expansion of the microballoons and to add heat-sensitive substances of the crosslinking system in the same mixing unit in which the mass system was mixed with the not yet expanded microballoons. However, this process can also take place in a second mixing unit.

[0132] A possible process for producing a foamed carrier layer of the adhesive tape according to the invention could comprise the following steps: - Firstly, introducing expandable microballoons and, if necessary, further additives into the mass system in a first mixing unit; - heating the mass system containing the microballoons - in particular under excess pressure to a temperature which is at least equal to the expansion temperature of the microballoons at normal pressure, preferably higher than this, - Expansion of the microballoons upon exiting the first mixing unit, - introducing the mass system into a second mixing unit, wherein in this second mixing unit the mass system is at a temperature which is below the expansion temperature of the microballoons, - Addition of the thermally sensitive substances of the crosslinking system in the second mixing unit, - Formation of the mass system mixed in this way.

[0133] The cooling of the mass system to a temperature below the expansion temperature of the microballoons takes place during and / or after the transfer of the mass system to the second mixing unit. Accordingly, the addition of the sensitive crosslinking substances takes place during and / or after the cooling of the mass system, especially after cooling.

[0134] Another possible method for producing a foamed carrier layer of the adhesive tape according to the invention could comprise the following steps: - Firstly, introducing expandable microballoons and, if necessary, further additives into the mass system in a first mixing unit; - heating the mass system containing the microballoons - in particular under excess pressure within a first mixing zone of the mixing unit to a temperature which corresponds at least to the expansion temperature of the microballoons at normal pressure, advantageously higher than this, - transferring the mass system from the first mixing zone into a second mixing zone of the first mixing unit, wherein in this second mixing zone the mass system is at a temperature which is below the expansion temperature of the microballoons, - Addition of thermally sensitive substances during and / or after transfer of the mass system into the second mixing zone, - Formation of the mass system mixed in this way.

[0135] The cooling of the mass system to a temperature below the expansion temperature of the microballoons takes place during and / or after the transfer of the mass system to the second mixing zone. Accordingly, the addition of the sensitive crosslinking substances takes place during and / or after the cooling of the mass system, especially after cooling.

[0136] At or after the coating unit, the resulting carrier layer is coated on one or both sides with the preferably pretreated, especially corona-pretreated, outer pressure-sensitive adhesive layer(s). The pressure-sensitive adhesive layer is preferably applied directly to the carrier layer from solution or from the melt, for example, directly from a nozzle, possibly with parallel application of the carrier and pressure-sensitive adhesive layers (coextrusion).

[0137] Alternatively, the pressure-sensitive adhesive layer can first be applied to a temporary carrier material after its production. This temporary carrier material can be, for example, a film, a foam, a fabric, a paper, a nonwoven, or a release liner; preferably, the temporary carrier material is a release liner, in particular a siliconized release film or siliconized release paper. The coating or lamination from a temporary carrier material is preferably carried out using a roller applicator.

[0138] The basis weight of the outer pressure-sensitive adhesive layer - if necessary after removal of solvent - is preferably 40 to 3,000 g / m 2 . Especially for mass applications ≥ 150 g / m 2 Coating by hotmelt extrusion is preferred.

[0139] The pressure-sensitive adhesive layers can generally be pretreated using any known physical or chemical process to improve anchoring. For example, the application of a primer layer, which can be applied to the pressure-sensitive adhesive layer from either solution or dispersion, is an option. Preferred physical methods are flame treatment, corona pretreatment, atmospheric plasma pretreatment, or vacuum plasma treatment. Corona pretreatment of the pressure-sensitive adhesive layers is particularly preferred directly before lamination of the carrier layer, which is still reactive in terms of crosslinking.

[0140] An adhesive tape according to the invention preferably comprises two outer pressure-sensitive adhesive layers b) as defined above. Particularly preferably, the two outer pressure-sensitive adhesive layers b) are identical in composition.

[0141] Adhesive tapes according to the invention are particularly suitable for applications on low-energy surfaces, for high-temperature applications and for applications where the aging stability of the adhesive tape is particularly important.

[0142] The invention further relates to the use of an adhesive tape according to the invention for bonding components to the body of a vehicle, in particular trim strips, emblems, and bumpers. The surfaces to be bonded can be treated with a primer prior to bonding to further increase the bond strength.

[0143] Further areas of use for adhesive tapes according to the invention include, for example, building construction and interior design, building equipment and the architectural sector, both indoors and outdoors; the DIY sector, model making, furniture manufacturing, shipbuilding and aircraft construction; the electronics and electrical industries, for example entertainment electronics, white goods, brown goods, and, due to their good heat resistance, also red goods; and road traffic, for example road signage and the like. Example part: General measurement methods:

[0144] Gel permeation chromatography GPC (measurement method 1a and 1b): The number-average and weight-average molecular weights M n , M w and M z and the polydispersity PD in this document refer to the determination by gel permeation chromatography.

[0145] The determination is carried out on 100 µl of a clear-filtered sample (sample concentration 0.5 g / l). Tetrahydrofuran with 0.1 vol.% trifluoroacetic acid is used as the eluent. The measurement is carried out at 25 °C. A PSS-SDV column, 10 µm, ID 8.0 mm - 50 mm, is used as the pre-column. for 1a) the columns of type PSS-SDV, 5 µm, 10 3 Å (SN9090201) and 5 µm, 10 2 Å (SN9090200) with ID 8.0 mm · 300 mm and for 1b) a column of type PSS-SDV, 10 µm linear one (SN2071901) with ID 8.0 mm x 300 mm (columns from Polymer Standards Service; detection using a PSS-SECurity 1260 RID differential refractometer). The flow rate is 0.5 ml per minute. Calibration was performed using the commercially available ReadyCal Poly(styrene) high kit from PSS Polymer Standard Service GmbH, Mainz. The results were universally converted to polymethyl methacrylate (PMMA) using the Mark-Houwink parameters K and alpha, so that the data are expressed in PMMA mass equivalents. K-value (according to FIKENTSCHER) (measurement method 2):

[0146] The K value is a measure of the average molecular size of high-polymer materials. For the measurement, 1% (1 g / 100 ml) toluene polymer solutions were prepared, and their kinematic viscosities were determined using a Vogel-Ossag viscometer. After normalization to the viscosity of toluene, the relative viscosity is obtained, from which the K value can be calculated according to Fikentscher (Polymer 1967, 8, 381 ff.). Solids content (measurement method 3):

[0147] The solids content is a measure of the proportion of non-evaporable components in a polymer solution. It is determined gravimetrically by weighing the solution, then evaporating the evaporable components in a drying oven at 120 °C for 2 hours, and reweighing the residue. Glass transition temperature Tg (measurement method 4):

[0148] The static glass transition temperature is determined using differential scanning calorimetry according to DIN EN ISO 11357-2. The glass transition temperature Tg values refer to the glass transition temperature Tg according to DIN 53765:1994-03, unless otherwise specified in individual cases. Density determination via mass application and layer thickness (measurement method 5):

[0149] The density ρ of a coated self-adhesive is determined by the ratio of the basis weight to the respective layer thickness: ρ=mV=MAd [ρ]=[kg][m2]⋅[m]=[kgm3] MA Mass application / area weight (without liner weight) in [kg / m 2 ] d layer thickness (without liner thickness) in [m]

[0150] This process yields the bulk density.

[0151] This density determination is particularly suitable for determining the total density of finished, even multi-layer, products. Special measuring methods (pressure-sensitive adhesives): 90° adhesive strength steel - (measurement method M1):

[0152] The bond strength to steel was determined under conditions of 23 °C + / - 1 °C and 50% + / - 5% relative humidity. The samples were cut to a width of 20 mm and bonded to a steel plate. The steel plate was cleaned and conditioned prior to testing. The plate was first wiped with acetone and then left to air for 5 minutes to allow the solvent to evaporate.

[0153] The side of the three-layer composite facing away from the test substrate was then covered with a 50 µm aluminum foil, which prevented the sample from stretching during the measurement. The test sample was then rolled onto the steel substrate. To do this, the tape was rolled back and forth five times with a 2 kg roll at a roll-up speed of 10 m / min. Immediately after rolling, the steel plate was pushed into a special holder that allowed the sample to be pulled upwards at a 90° angle. The adhesive strength was measured using a Zwick tensile testing machine.

[0154] The measurement results are given in N / cm and are averaged from three measurements. Shear strength (SSZ, measurement method M2):

[0155] The sample was prepared in a test environment of 23 °C + / - 1 °C and 50% + / - 5% relative humidity. The test sample was cut to 13 mm and bonded to a steel plate. The bonding area was 20 mm x 13 mm (length x width). Before measurement, the steel plate was cleaned and conditioned. To do this, the plate was first wiped with acetone and then left to air for 5 minutes to allow the solvent to evaporate. After bonding, the side facing away from the substrate was reinforced with 50 µm aluminum foil and rolled back and forth twice with a 2 kg roller. A belt loop was then attached to the protruding end of the three-layer composite. The entire assembly was then suspended from a suitable fixture and loaded with a weight of 1 kg (10 N). The suspension fixture was designed so that the weight applied an angle of 179° + / - 1° to the sample.This ensured that the three-layer composite could not peel off the bottom edge of the panel. The measured shear strength, the time between hanging and falling off the sample, is given in minutes and corresponds to the average of three measurements. The measurement was conducted under standard conditions (23 °C, 55% humidity). Raw materials Table 3: Commercially available chemicals used Chemical compound Trade name Manufacturer CAS No. Methyl methacrylate MMA Visiomer® MMA Evonik 80-62-6 Cyclohexyl methacrylate CHMA Visiomer® c-HMA Evonik 101-43-9 Isobornyl methacrylate IBOMA Sigma-Aldrich 7534-94-3 4-tert-Butylcyclohexyl methacrylate TBCHMA Nourycryl MC110 Akzo Nobel 46729-07-01 Lauryl mercaptan 1-Dodecanethiol Dr. Spiess Chemical Factory 112-55-0 Acrylic acid AS Sigma-Aldrich 79-10-7 2-Ethylhexylacrylate EHA BASF 103-11-7 n-Butyl acrylate BA BASF 141-32-2 Isobornyl acrylate IBOA Visiomer® IBOA Evonik 5888-33-5 2,2-Azobis(2-methylbutyronitrile) Vazo® 67 Akzo Nobel 13472-08-7 Bis-(4-tert-butylcyclo-hexyl)peroxydicarbonate Perkadox® 16 Akzo Nobel 15520-11-3 Tetraglycidyl-metaxyloldiamine Erisys™ GA240 IMCD 63738-22-7 Pentaerythritol tetraglycidyl ether DERTM 749 DOW 3126-63-4 Isophoronediamine Vestamin® IPD Evonik 2855-13-2 Microballoons (MB) (dry-unexpanded microspheres, diameter 9 - 15 µm, expansion start temperature 106 - 111 °C, TMA density ≤ 25 kg / m3) Expancel® 051 DU 40 Expancel Nobel Industries Production of polymers for pressure-sensitive adhesives: Polymer A1

[0156] A reactor conventional for radical polymerizations was charged with 42.5 kg of 2-ethylhexyl acrylate, 42.5 kg of n-butyl acrylate, 4 kg of acrylic acid, and 11 kg of isobornyl acrylate in 72.4 kg of acetone / petrol (50:50). After 45 minutes of nitrogen gas flow with stirring, the reactor was heated to 58 °C, and 50 g of 2,2'-azobis(2-methylbutyronitrile) was added. The external heating bath was then heated to 70 °C, and the reaction was carried out at a constant external temperature. After 1 h, another 50 g of 2,2'-azobis(2-methylbutyronitrile) was added; after 2, 3, and 4 h, the reaction mixture was diluted with 15 kg of acetone / petrol mixture (50:50).

[0157] After 5.5 h and after 7 h, the reaction was reinitiated with 150 g of bis(4-tert-butylcyclohexyl) peroxydicarbonate. After a reaction time of 22 h, the polymerization was terminated and cooled to room temperature. A conversion of 99.6% was achieved. The resulting polyacrylate had a K value of 70 and an average molecular weight (measurement method 1b) of M w = 1,030,000 g / mol, polydispersity PD (M w / M n ) = 58. Polymer A2

[0158] A reactor conventional for radical polymerizations was charged with 48 kg of 2-ethylhexyl acrylate, 29 kg of n-butyl acrylate, 17 kg of isobornyl acrylate, and 6 kg of acrylic acid in 72.4 kg of acetone / petrol (50:50). After 45 minutes of nitrogen gas flow with stirring, the reactor was heated to 58 °C, and 50 g of 2,2'-azobis(2-methylbutyronitrile) was added. The internal temperature was then regulated to 70 °C over 5 h, after which the external heating bath was heated to 70 °C, and the reaction was carried out at a constant external temperature. One hour after the first addition of initiator, another 50 g of 2,2'-azobis(2-methylbutyronitrile) was added; after 2, 3, and 4 h, the reaction mixture was diluted with 15 kg of acetone / petrol mixture (50:50). After 5.5 h and 7 h, the reaction mixture was reinitiated with 150 g of bis(4-tert-butylcyclohexyl) peroxydicarbonate, and after 8 h, the mixture was diluted with 15 kg of a 50:50 acetone / benzine mixture. After a reaction time of 22 h, the polymerization was terminated and cooled to room temperature.

[0159] A conversion of 99.5% was achieved. The resulting polyacrylate had an average molecular weight (measurement method 1b) of M w = 883,000 g / mol, polydispersity PD (M w / M n ) = 81. Polymerization of the acrylate resins (B1 to B3 and comparative examples VB4 to VB6: Low molecular weight acrylate resin - Example B1

[0160] A reactor conventional for radical polymerizations was charged with 22.2 kg of methyl methacrylate, 33.3 kg of cyclohexyl methacrylate, 44.5 kg of isobornyl methacrylate, 11.1 kg of 1-dodecanethiol, and 47.6 kg of an acetone / isopropanol mixture (96:4). After 45 minutes of nitrogen gas flow with stirring, the reactor was heated to 58°C, and 444 g of Vazo 67 (5 wt.% in acetone) were added. The external heating bath was then heated to 75°C, and the reaction was carried out at a constant external temperature. After a reaction time of 7 h, another 444 g of Vazo 67 were added as a 5 wt.% solution in acetone. The reaction was stopped after 22 h and cooled to room temperature. A conversion of 98.8% was achieved. The obtained low molecular weight polymethacrylate had an average molecular weight (measurement method 1a) of M n = 2,530 g / mol, polydispersity PD (M w / M n ) = 1.6. The static glass transition temperature was 42.9°C.

[0161] Examples B2 to B3 and comparative examples VB4 to VB6 were prepared analogously to Example B1. Table 4: Methacrylate resins B2 and B3 and comparative examples VB4 to VB6 Example MMA [wt.%] CHMA [wt.%] IBOMA [wt.%] TBCHMA [wt.%] DDT [wt%] Tg [°C] M n [g / mol] PD [-] B2 25 25 15 25 10 39,4 2130 1,5 B3 30 20 10 30 10 39,3 1900 1,6 VB4 45 45 - - 10 40,6 2050 1,6 VB5 70 20 - - 10 46,2 2090 1,6 VB6 25 35 30 - 10 43,5 2120 1,5 DDT = regulator dodecanethiol

[0162] All pressure-sensitive adhesive examples were formulated by blending polyacrylate and methacrylate resin to contain 70 wt.% polymer (A1 or A2) and 30 wt.% of the low-molecular-weight methacrylate resin B (B1-B3 and VB4-VB6). Each pressure-sensitive adhesive formulation was blended with 0.05 wt.%—based on polymer A—of the crosslinker Erisys GA 240, diluted with acetone to a solids content of 30 wt.%, and then coated from solution onto a siliconized release liner (50 µm polyester). (Coating speed 2.5 m / min, drying tunnel 15 m, temperatures Zone 1: 40 °C, Zone 2: 70 °C, Zone 3: 95 °C, Zone 4: 105 °C). The application rate was 50 g / m 2. Production of the starting polymer C for the polyacrylate foam VT

[0163] A reactor conventional for radical polymerizations was charged with 30 kg of 2-ethylhexyl acrylate, 67 kg of n-butyl acrylate, 3 kg of acrylic acid, and 66 kg of acetone / isopropanol (96:4). After 45 minutes of nitrogen gas flow with stirring, the reactor was heated to 58 °C and 50 g of 2,2'-azobis(2-methylbutyronitrile) was added. The external heating bath was then heated to 75 °C, and the reaction was carried out at this constant external temperature. After 1 h, another 50 g of 2,2'-azobis(2-methylbutyronitrile) was added; after 4 h, the mixture was diluted with 20 kg of acetone / isopropanol (96:4).

[0164] After 5 and 7 hours, the reaction was reinitiated with 150 g of bis(4-tert-butylcyclohexyl) peroxydicarbonate. After a reaction time of 22 hours, the polymerization was terminated and cooled to room temperature. The conversion was 99.6%. The resulting polyacrylate had a solids content of 50.2% and average molecular weights M n = 91,900 g / mol and M w = 1,480,000 g / mol; polydispersity PD (M w / M n ) = 16.1. Production of the adhesive tape examplesProcedure 1: Concentration / Production of the polyacrylate melt

[0165] The base polymer C was largely freed of solvent using a single-screw extruder (concentration extruder, Berstorff GmbH, Germany) (residual solvent content ≤ 0.3 wt%). The parameters for the concentration of the base polymer were as follows: The screw speed was 150 rpm, the motor current was 15 A, and a liquid throughput of 58.0 kg / h was achieved. For concentration, a vacuum was applied to three different domes. The negative pressures were between 20 mbar and 300 mbar in each case. The exit temperature of the concentrated melt of polymer C was approximately 115 °C. The solids content after this concentration step was 99.8%. Process 2: Production of the polyacrylate foam, mixing with the crosslinker-accelerator system for thermal crosslinking and coating

[0166] The foaming took place in a test facility, which is similar to the one shown in Fig. 1 corresponds.

[0167] The base polymer P was melted in a feed extruder 1 according to process 1 and conveyed as a polymer melt via a heatable hose 11 into a planetary roller extruder 2 (PWE) from ENTEX (Bochum, Germany). Specifically, a PWE with four independently heatable modules T1, T2, T3, and T4 was used. Additional additives or fillers, such as color pastes, could be added via the metering opening 22. The crosslinker was added at point 23. All components were mixed to form a homogeneous polymer melt.

[0168] Using melt pump 24a and a heatable hose, the polymer melt was transferred into a twin-screw extruder 3 (BERSTORFF) (input position 33). The accelerator component was added at position 34. Subsequently, the entire mixture was freed of all gas inclusions in a vacuum dome V at a pressure of 175 mbar. A blister B was located on the screw downstream of the vacuum zone, which enabled pressure to build up in the subsequent segment S. By appropriately controlling the extruder speed and melt pump 37a, a pressure of greater than 8 bar was built up in segment S between blister B and melt pump 37a. The microballoon mixture (microballoons embedded in the dispersing agent as specified in the test series) was added at metering point 35 and homogeneously incorporated into the premix using a mixing element. The resulting melt mixture was transferred to a nozzle 5.

[0169] After leaving the nozzle 5, i.e., after the pressure drop, the incorporated microballoons expanded, resulting in low-shear cooling of the polymer mass. This resulted in a foamed pressure-sensitive adhesive, which was subsequently coated between two reusable release liners (process liners) and formed into a sheet using the roller calender 4.

[0170] In order to improve the anchoring of the pressure-sensitive adhesives on the formed polyacrylate foam, both the pressure-sensitive adhesives and the foam were pretreated using corona (corona system from VITAPHONE, Denmark, 70 W min / m 2 The process liners were then removed, and the pressure-sensitive adhesive layers were laminated to the top and bottom of the polyacrylate foam. Corona treatment resulted in improved chemical bonding of the pressure-sensitive adhesives to the polyacrylate foam carrier layer.

[0171] The web speed when passing through the laminating system was 30 m / min.

[0172] After leaving the laminating line, a siliconized release film was uncovered and the finished three-layer product was wound up with the remaining siliconized release film. Table 5: Polyacrylate foam VT Example VT Components Base polymer C Expancel 051 DU 40 Polypox R16 IPDA Reofos RDP [Wt.%] 97,8 1,5 0,139 0,144 0,41 Construction Thickness Density [µm] [kg / m 3 ] 902 749

[0173] The following examples of adhesive tapes made from the polyacrylate foam carrier VT and the pressure-sensitive adhesive layers applied on both sides are presented.

[0174] Table 6 initially lists the differences Z between the acrylic resins B and VB and the polymers A of the pressure-sensitive adhesive layers as well as the polymer C of the foam carrier.

Claims

[1] Adhesive tape, comprising a) a carrier layer containing at least one poly(meth)acrylate; and b) an outer pressure-sensitive adhesive layer containing b1) at least one poly(meth)acrylate and b2) at least one (meth)acrylate oligomer; wherein the totality of the poly(meth)acrylates b1) forms a higher molecular weight mode and the totality of the (meth)acrylate oligomers b2) forms a low molecular weight mode within the outer pressure-sensitive adhesive layer b); where the difference in the Hansen solubility parameters Z b1 / b2 the low molecular weight and the higher molecular weight mode of the outer pressure-sensitive adhesive layer b) is < 1; and the difference in the Hansen solubility parameters Z a / b2 the low molecular weight mode of the outer pressure-sensitive adhesive layer b) and the total of the poly(meth)acrylates of the carrier layer a) is > 1, wherein the at least one (meth)acrylate oligomer of the outer pressure-sensitive adhesive layer is an oligomer having a weight-average molecular weight Mw, measured according to the measurement method 1a described herein, of 1,500 to 5,000 g / mol and a polydispersity D of ≤ 2, the structure of which is based on a monomer composition consisting of - at least 50% by weight, based on the total weight of the monomer composition, of a mixture of MonO1) Methyl methacrylate MonO2) Cyclohexyl methacrylate; and - MonO3) one or more other radically polymerizable monomers as well as at least one compound containing an -SH group, characterized by that the carrier layer is foamed. [2] Adhesive tape according to claim 1, characterized by that the quotient of the difference Z b1 / b2 and the diversity Z a / b2 ≤ 0.

9. [3] Adhesive tape according to one of the preceding claims, characterized by that the weight-average molecular weight M w of the poly(meth)acrylate of the outer pressure-sensitive adhesive layer, measured according to Method 1b described herein, is 20,000 to 2,000,000 g / mol. [4] Adhesive tape according to one of the preceding claims, characterized by that the weight-average molecular weight M w of the poly(meth)acrylate of the carrier layer, measured according to Method 1b described herein, is 500,000 to 1,700,000 g / mol. [5] Adhesive tape according to one of the preceding claims, characterized by that the weight-average molecular weight M w of the (meth)acrylate oligomer of the outer pressure-sensitive adhesive layer, measured according to Method 1a described herein, is 1,500 to 5,000 g / mol. [6] Adhesive tape according to one of the preceding claims, characterized by that the adhesive tape comprises two outer pressure-sensitive adhesive layers b). [7] Adhesive tape according to claim 6, characterized by that the two outer pressure-sensitive adhesive layers b) are identical in terms of their composition. [8] Use of poly(meth)acrylates and (meth)acrylate oligomers in an adhesive tape according to one of claims 1 to 7 such that the adhesive tape a) a carrier layer containing at least one poly(meth)acrylate; and b) an outer pressure-sensitive adhesive layer containing b1) at least one poly(meth)acrylate and b2) comprises at least one (meth)acrylate oligomer; wherein the totality of the poly(meth)acrylates b1) forms a higher molecular weight mode and the totality of the (meth)acrylate oligomers b2) forms a low molecular weight mode within the outer pressure-sensitive adhesive layer b); the difference in the Hansen solubility parameters Z b1 / b2 the low molecular weight and the higher molecular weight mode of the outer pressure-sensitive adhesive layer b) is < 1; and the difference in the Hansen solubility parameters Z a / b2 the low molecular weight mode of the outer pressure-sensitive adhesive layer b) and the total of the poly(meth)acrylates of the carrier layer a) is > 1, to improve the weather and / or storage resistance of the adhesive tape.

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