DE102022131231A1 - Removable adhesive tape - Google Patents

Abstract

The invention relates to a pressure-sensitive adhesive tape that can be removed by stretching and to the use of the pressure-sensitive adhesive tape for bonding components in electronic devices, automobiles, medical devices and dental devices.The pressure-sensitive adhesive tape comprises:a) at least one carrier with an elongation at break of at least 200%, the carrier having at least a first side and a second side, andb) at least one first pressure-sensitive adhesive layer which has at least a first phase (i) containing at least one poly(meth)acrylate and at least a second phase (ii) containing at least one vinylaromatic block copolymer, such as in particular styrene block copolymer, the first pressure-sensitive adhesive layer being arranged at least on the first side of the carrier.

Description

The invention relates to a pressure-sensitive adhesive tape that can be removed by stretching and to the use of the pressure-sensitive adhesive tape for bonding components in electronic devices, automobiles, medical devices and dental devices.

Removable adhesive tapes have long been established on the market and are well known to experts.

EN 10 2012 223 670 A1 discloses a pressure-sensitive adhesive film strip made of at least two, in particular three layers, which can be removed again by stretching essentially in the bonding plane without leaving residues and without destruction, with a carrier on which a first, external adhesive layer is present on at least one side, wherein the adhesive layer consists of an adhesive based on vinyl aromatic block copolymers and adhesive resins, wherein at least 75% (based on the total resin content) of a resin is selected with a DACP (diacetone alcohol cloud point) of greater than -20 °C, preferably greater than 0 °C, and the carrier has at least one layer consisting of a polyurethane with an elongation at break of at least 100% and a resilience of more than 50%.

WO 2015135134 A1 describes a stretch-releasable adhesive tape comprising a backing having a first surface and a second surface, the backing being made of crosslinked thermoplastic polyurethane, and pressure-sensitive adhesive disposed on at least one of the first and second surfaces, the pressure-sensitive adhesive being formed from an acrylate copolymer comprising a functional group-terminated polyurethane, the adhesive tape having a thickness in the range between 0.05 and 0.10 mm and a longitudinal extensibility between 850% and 2200%, the adhesive tape being capable of being firmly bonded to a substrate and thereafter removed therefrom after being stretched at an angle of 90° or more degrees from the surface of the substrate without breaking the backing prior to removal of the adhesive tape from the substrate and without leaving substantial residues of the pressure-sensitive adhesive on the substrate.

Shock resistance is often important for the use of adhesive tapes in electronic components, as the bonded components must not come loose even if the mobile device falls.

In order to increase the shock resistance of the adhesive tapes, the adhesives are often foamed, especially by adding expandable microballoons.

The EN 10 2015 206 076 A1 and the EP 30 75 772 A1 each with a pressure-sensitive adhesive strip which can be removed again by stretching essentially in the bonding plane without leaving residues and without being destroyed, and whose adhesive layers are foamed with microballoons.

US2017121573 A1 discloses an adhesive formulation comprising 50 to 99% adhesive component, 0 to 3% crosslinker, 0 to 3% antioxidant and 0.1 to 10% expandable microspheres dispersed in the formulation.

The aforementioned documents mainly disclose vinyl aromatic or styrene block copolymers or acrylates as base elastomers for the adhesives.

The JP6265734 B2 describes the use of blends of acrylates and styrene block copolymers as a carrier layer for use in adhesive tapes that can be removed by stretching. The adhesive on the carrier can be selected differently.

However, it has been shown that the increase in the shock resistance of an adhesive and the adhesive tapes made from it is limited, especially when styrene block copolymers are used in the adhesive. It is therefore not possible to produce adhesive tapes of any thickness with excellent shock resistance.
When using acrylates in the adhesive, there is often the problem that residues remain on the substrate after removal, which then have to be laboriously removed.
In addition, there is still a problem in that the adhesive tapes tend to tear, especially when stretched at a large angle to the bonding surface.

The present invention is therefore based on the object of providing a pressure-sensitive adhesive tape which can be removed by stretching, which can be removed without leaving residue and without destruction and which has excellent shock resistance (impact strength) and can be removed again as tear-free as possible.

1. a) mindestens einen Träger mit einer Reißdehnung gemäß EN ISO 527 von mindestens 200 %, wobei der Träger wenigstens eine erste Seite und eine zweite Seite aufweist, und
2. b) mindestens eine erste Haftklebemasseschicht, die wenigstens eine erste Phase (i) enthaltend wenigstens ein Poly(meth)acrylat und wenigstens eine zweite Phase (ii) enthaltend wenigstens ein Vinylaromatenblockcopolymer, wie insbesondere Styrolblockcopolymer, aufweist,
3. wobei die erste Haftklebemasseschicht wenigstens auf der ersten Seite des Trägers angeordnet ist.

The object is achieved by a pressure-sensitive adhesive tape according to claim 1, ie by a pressure-sensitive adhesive tape removable by stretching comprising

1. a) at least one carrier having an elongation at break according to EN ISO 527 of at least 200 %, the carrier having at least a first side and a second side, and
2. b) at least one first pressure-sensitive adhesive layer which comprises at least one first phase (i) containing at least one poly(meth)acrylate and at least one second phase (ii) containing at least one vinylaromatic block copolymer, such as in particular styrene block copolymer,
3. wherein the first pressure-sensitive adhesive layer is arranged at least on the first side of the carrier.

Surprisingly, it has been found that a further increase in the shock resistance of the pressure-sensitive adhesive tape according to the invention can be achieved by an adhesive composition comprising the two phases (i) and (ii), namely based on poly(meth)acrylates or vinyl aromatic block copolymers.
The term “phases” already indicates that phases (i) and (ii) are present separately from one another in the pressure-sensitive adhesive layer.
At the same time, if the removal force is sufficiently high, the pressure-sensitive adhesive tape can surprisingly be removed without leaving any residue or causing any damage.
In addition, the blend of phases (i) and (ii) in the pressure-sensitive adhesive results in a higher temperature resistance than compositions based solely on vinyl aromatic block copolymers. This enables the pressure-sensitive adhesive tape according to the invention to be used in automobiles.

Such embodiments, which are referred to below as preferred, are combined in particularly preferred embodiments with features of other embodiments referred to as preferred or advantageous. Combinations of two or more of the embodiments referred to below as particularly preferred are therefore particularly preferred. Also preferred are embodiments in which a feature of an embodiment referred to as preferred to some extent is combined with one or more further features of other embodiments referred to as preferred to some extent.

The pressure-sensitive adhesive tape according to the invention can be removed by stretching or stretching. For this purpose, the pressure-sensitive adhesive tape has at least one carrier with an elongation at break of at least 200% and thus an extensible and tear-resistant carrier, which ensures sufficient tear resistance.

Since the pressure-sensitive adhesive tape according to the invention contains at least one pressure-sensitive adhesive, it is referred to as a pressure-sensitive adhesive tape. For the sake of simplicity, it is also referred to here as "adhesive tape" for short.

Instead of the term pressure-sensitive adhesive layer, the term “adhesive layer” is used in the context of the present invention for the sake of simplicity.

In the following, the properties and components of the pressure-sensitive adhesive layer, abbreviated to “pressure-sensitive adhesive” or, for the sake of simplicity, also “adhesive”, of the pressure-sensitive adhesive tape according to the invention are explained in more detail.

In the present invention, a pressure-sensitive adhesive is understood, as is generally the case, to mean a substance that is permanently tacky and adhesive, particularly at room temperature. A characteristic of a pressure-sensitive adhesive is that it can be applied to a substrate by pressure and remains adhered to there, whereby the pressure to be applied and the duration of this pressure are not defined in more detail. In some cases, depending on the exact type of pressure-sensitive adhesive, the temperature and humidity, and the substrate, the application of a short-term, minimal pressure, which does not go beyond a light touch for a brief moment, is sufficient to achieve the adhesive effect; in other cases, a longer-term exposure to high pressure may also be necessary.

Pressure-sensitive adhesives have special, characteristic viscoelastic properties that lead to permanent stickiness and adhesiveness. They are characterized by the fact that when they are mechanically deformed, both viscous flow processes and the build-up of elastic restoring forces occur. Both processes are in a certain relationship to one another in terms of their respective proportions, depending on the exact composition, structure and degree of cross-linking of the pressure-sensitive adhesive as well as on the speed and duration of the deformation and on the temperature.

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

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 the forces acting on an adhesive bond. They mean that an adhesive bond can withstand a permanent load acting on it, for example in the form of a permanent shear load, to a sufficient extent over a longer period of time.

For a more precise description and quantification of the degree of elastic and viscous components and the ratio of the components to one another, the storage modulus (G') and loss modulus (G'') can be determined using Dynamic Mechanical Analysis (DMA, according to DIN EN ISO 6721). G' is a measure of the elastic component, G'' a measure of the viscous component of a material. Both values depend on the deformation frequency and the temperature.

The values can be determined using a rheometer. The material to be tested is subjected to a sinusoidal oscillating shear stress in a plate-plate arrangement, for example. In shear stress-controlled devices, the deformation is measured as a function of time and the temporal offset of this deformation compared to the introduction of the shear stress. This temporal offset is referred to as the phase angle δ.

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).

A substance is generally considered to be pressure-sensitively adhesive and is defined as pressure-sensitively adhesive in the sense of the invention if, at room temperature, here by definition at 23°C, in the deformation frequency range from 10° to 10 ¹ rad/sec, G' is at least partly in the range from 10 ³ to 10 ⁷ Pa and if G'' is also at least partly in this range. "Partly" means that at least one section of the G' curve is within the window spanned by the deformation frequency range from 10° to 10 ¹ rad/sec (abscissa) and the range of G' values from 10 ³ to 10 ⁷ Pa (ordinate). This applies accordingly to G''.

Preferably, the pressure-sensitive adhesive has a storage modulus G' and a loss modulus G'' in the range from 10 ³ to 10 ⁷ Pa, determined in accordance with DIN EN ISO 6721, in the deformation frequency range from 10 ⁰ to ¹⁰ 1 rad/sec at 23 °C.

To achieve the viscoelastic properties, the monomers on which the polymers underlying the PSA are based, as well as any other components of the PSA that may be present, are selected in such a way that the PSA has a glass transition temperature (according to DIN 53765) below the application temperature (i.e. usually below room temperature (23 °C)). By using suitable cohesion-enhancing measures, such as crosslinking reactions (formation of bridge-forming links between the macromolecules), the temperature range in which a polymer mass has pressure-sensitive adhesive properties can be increased and/or shifted. The application range of the PSA can thus be optimized by adjusting the flowability and cohesion of the mass.

The pressure-sensitive adhesive preferably has a glass transition temperature of ≤ 23 °C, determined according to DIN 53765.

In contrast to pressure-sensitive adhesives, hot melt adhesives, e.g. based on polyamides, polyurethanes or modified polyethylenes, do not exhibit any tack at room temperature (23 °C), even in hot melt adhesive compositions.

The adhesive tape according to the invention comprises at least one first pressure-sensitive adhesive layer which has at least one first phase (i) containing at least one poly(meth)acrylate and at least one second phase (ii) containing at least one vinylaromatic block copolymer, such as in particular styrene block copolymer.

As stated above, (i) and (ii) are separate phases. Poly(meth)acrylate and vinylaromatic block copolymer are each present in the pressure-sensitive adhesive layer of the adhesive tape according to the invention in their own phases, which surround one another. In particular, the vinylaromatic block copolymer can be dispersed in the poly(meth)acrylate and thus form domains in the poly(meth)acrylate matrix, or conversely, the poly(meth)acrylate can be present in the vinylaromatic block copolymer and thus form domains in the vinylaromatic block copolymer matrix. The above statements apply analogously to the case where more than one poly(meth)acrylate, in particular two or more poly(meth)acrylates, and/or more than one vinylaromatic block copolymer, in particular two or more vinylaromatic block copolymers, are present in phase (i).

In particular, the presence of 1.) domains of phase (i) in phase (ii) or 2.) of phase (ii) in phase (i) results in a particularly high shock resistance of the pressure-sensitive adhesive.

Preferably, the poly(meth)acrylates and vinylaromatic block copolymers contained in the pressure-sensitive adhesive are therefore not miscible with one another to the point of homogeneity at 23°C. The pressure-sensitive adhesive of the adhesive tape according to the invention is therefore preferably present in at least a two-phase morphology, at least microscopically and at least at room temperature. Particularly preferably, poly(meth)acrylate(s) and vinylaromatic block copolymer(s) are not homogeneously miscible with one another in a temperature range from -20°C to 90°C, in particular from 0°C to 60°C, so that the pressure-sensitive adhesive is present in at least a two-phase morphology, at least microscopically, in these temperature ranges.

Components are defined in this document 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 demonstrated 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 prevent the formation of multiphases, is considered irrelevant. For example, small amounts of vinyl aromatic block copolymer and/or small amounts of poly(meth)acrylate component may be present in the poly(meth)acrylate phase, which are not significant amounts that affect phase separation.

As explained above, the phase separation can be realized in particular in such a way that discrete regions ("domains") which are rich in vinylaromatic block copolymer - i.e. are essentially formed from vinylaromatic block copolymer - are present in a continuous matrix which is rich in poly(meth)acrylate - i.e. is essentially formed from poly(meth)acrylate.

A suitable analysis system for phase separation is, for example, scanning electron microscopy. Phase separation can also be recognized, for example, by the fact that the different phases have two independent glass transition temperatures in dynamic differential scanning calorimetry (DSC) or dynamic mechanical analysis (DMA). According to the invention, phase separation is present in particular when it can be clearly demonstrated by at least one of the analysis methods.

Within the vinylaromatic block copolymer-rich domains, an additional multiphase fine structure may also be present, whereby the vinylaromatic block copolymer typically has A and B blocks and thus the A blocks form a first phase and the B blocks a second phase.

The pressure-sensitive adhesive layer preferably contains 40 to 90 parts by weight, preferably 50 to 80 parts by weight, of poly(meth)acrylate, and 10 to 60 parts by weight, preferably 20 to 50 parts by weight, of vinyl aromatic block copolymer, the two parts by weight adding up to 100% and further additives are therefore not taken into account here.

As a result, the problem underlying the invention is solved particularly well.

Preferably, phase (i) contains 90 to 99.5 wt. % (weight percent) of poly(meth)acrylates based on the total mass of phase (i).

Preferably, phase (ii) contains 40 to 60 wt. % of vinylaromatic block copolymers based on the total mass of phase (ii).

The total amount of poly(meth)acrylates and vinylaromatic block copolymers in the pressure-sensitive adhesive is preferably 60 to 95% by weight, particularly preferably 63 to 87% by weight, in each case based on the total mass of the pressure-sensitive adhesive.

With the above-mentioned preferred amounts of the polymers in the individual phases or the total amount in the pressure-sensitive adhesive, the object underlying the invention is achieved particularly well.

A "poly(meth)acrylate" is understood to mean a polymer which is obtainable by radical polymerization of acrylic and/or methacrylic monomers and optionally other copolymerizable monomers. In particular, a "poly(meth)acrylate" is understood to mean a polymer whose monomer base consists of at least 50% by weight of acrylic acid, methacrylic acid, acrylic esters and/or methacrylic esters, with acrylic esters and/or methacrylic esters being present at least in proportion, preferably at least 30% by weight, based on the total monomer base of the polymer in question.

The glass transition temperature (according to DIN 53765) of the poly(meth)acrylate of the pressure-sensitive adhesive according to the invention is preferably < 0 °C (less than zero degrees Celsius), particularly preferably between -20 and -50 °C (between minus twenty degrees and minus fifty degrees Celsius). With such a glass transition temperature of the poly(meth)acrylate, a particularly optimal shock resistance is achieved with very good tackiness. If the glass transition temperature of the poly(meth)acrylate is 0 °C or more than 0 °C, a lower shock resistance is achieved. With a glass transition temperature of the poly(meth)acrylate of < -20 °C, the shock resistance is further optimized. If the glass transition temperature of the poly(meth)acrylate is significantly less than -50 °C, the pressure-sensitive adhesive is too soft overall and the tackiness is less pronounced.

The glass transition temperature of the poly(meth)acrylate is determined in particular by the selection of the monomers.

The poly(meth)acrylate of the pressure-sensitive adhesive layer preferably contains at least a portion of polymerized functional monomers, particularly preferably monomers of at least one type with at least one functional group selected from the group consisting of carboxylic acid groups, sulfonic acid groups, phosphonic acid groups, hydroxyl groups, acid anhydride groups, epoxy groups and amino groups.

The groups mentioned, with the exception of epoxy groups, exhibit reactivity with epoxy groups, whereby the poly(meth)acrylate is advantageously accessible to thermal crosslinking with introduced epoxides.

The poly(meth)acrylate of the pressure-sensitive adhesive layer very particularly preferably contains at least a proportion of polymerized functional monomers, particularly preferably monomers of at least one type with at least one functional group selected from the group consisting of carboxylic acid groups and epoxy groups; in particular it contains at least one carboxylic acid group.

According to particularly advantageous embodiments, the poly(meth)acrylate of the pressure-sensitive adhesive contains proportionately polymerized acrylic acid and/or methacrylic acid. As a result, the poly(meth)acrylate has a reactivity with epoxy groups due to the carboxylic acid groups, whereby the poly(meth)acrylate is advantageously accessible to thermal crosslinking with introduced epoxides.

1. a) mindestens ein Acrylsäureester und/oder Methacrylsäureester der folgenden Formel (1) CH₂=C(R^I)(COOR^II) (1), worin R¹ = H oder CH₃ und R'' ein Alkylrest mit 4 bis 18 C-Atomen ist;
2. b) mindestens ein olefinisch ungesättigtes Monomer mit mindestens einer funktionellen Gruppe ausgewählt aus der Gruppe bestehend aus Carbonsäuregruppen, Sulfonsäuregruppen, Phosphonsäuregruppen, Hydroxygruppen, Säureanhydridgruppen, Epoxidgruppen und Aminogruppen;
3. c) optional weitere Acrylsäureester und/oder Methacrylsäureester und/oder olefinisch ungesättigte Monomere, die mit der Komponente (a) copolymerisierbar sind.

The poly(meth)acrylate of the pressure-sensitive adhesive can preferably be traced back to the following monomer composition:

1. a) at least one acrylic acid ester and/or methacrylic acid ester of the following formula (1) CH ₂ =C(R ^I )(COOR ^II ) (1), wherein R ¹ = H or CH ₃ and R'' is an alkyl radical having 4 to 18 C atoms;
2. b) at least one olefinically unsaturated monomer having at least one functional group selected from the group consisting of carboxylic acid groups, sulfonic acid groups, phosphonic acid groups, hydroxyl groups, acid anhydride groups, epoxy groups and amino groups;
3. c) optionally further acrylic acid esters and/or methacrylic acid esters and/or olefinically unsaturated monomers which are copolymerizable with component (a).

According to advantageous embodiments, the poly(meth)acrylate is based on a monomer composition which contains monomers of group a) in a proportion of 45 to 99 wt. %, particularly preferably 80 to 99 wt. %, and monomers of group b) in a proportion of 1 to 15 wt. %, particularly preferably 1 to 7 wt. %, and optionally monomers of group c) in a proportion of 0 to 40 wt. %, wherein the information relates to the monomer mixture for the polymer without addition of any additives such as resins, etc.

With such a poly(meth)acrylate in the pressure-sensitive adhesive layer of the adhesive tape according to the invention, a particularly good property profile is achieved comprising stickiness, shock resistance and residue-free removability.

According to a particularly advantageous embodiment, the poly(meth)acrylate is based on a monomer composition which contains monomers of group a) in a proportion of 93 to 99 wt.% and monomers of group b) in a proportion of 1 to 7 wt.%, and monomers of group c) in a proportion of 0 wt.%.

With such a poly(meth)acrylate in the pressure-sensitive adhesive layer of the pressure-sensitive adhesive tape according to the invention, a particularly good property profile is achieved comprising stickiness, shock resistance and residue-free removability.

The monomers of component a) are generally plasticizing, rather non-polar monomers. R'' in the monomers a) is particularly preferably an alkyl radical with 4 to 10 C atoms. The monomers of formula (1) are in particular selected 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, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-propylheptyl acrylate and 2-propylheptyl methacrylate.

Particularly preferably, the monomers of formula (1) or group a) are selected from the group consisting of butyl acrylate, n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate and 2-propylheptyl acrylate.

With these comparatively non-polar monomers, phase separation between phases (i) and (ii) is produced particularly well. This results in a particularly high shock resistance of the pressure-sensitive adhesive composition and thus of the pressure-sensitive adhesive tape according to the invention.

In addition, the monomers mentioned can be polymerized particularly well and the glass transition temperature of the poly(meth)acrylate produced can be adjusted particularly well. This in turn makes it possible to achieve optimized properties in terms of flowability and stickiness, which are also adapted to the respective substrate or component to be bonded.

The monomers of formula (1) or group a) are in turn preferably selected from the group consisting of butyl acrylate, isooctyl acrylate and 2-ethylhexyl acrylate.

Butyl acrylate and 2-ethylhexyl acrylate are very particularly preferably used as monomers of formula (1) or group a).

The monomers of group b) are particularly preferably selected from the group consisting of 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,
2-Hydroxyethyl acrylate, hydroxypropyl acrylate, 3-hydroxypropyl acrylate, hydroxybutyl acrylate, 4-hydroxybutyl acrylate, hydroxyhexyl acrylate, 6-hydroxyhexyl acrylate, hydroxyethyl methacrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, hydroxybutyl methacrylate, 4-hydroxybutyl methacrylate, hydroxyhexyl methacrylate, 6-hydroxyhexyl methacrylate, allyl alcohol, glycidyl acrylate, glycidyl methacrylate.

Preferably, the monomers of group b) are selected from acrylic acid and hydroxyethyl acrylate.

Acrylic acid is particularly preferably used as monomer of group b).

• 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, Dimethylaminoethylacrylat, Dimethylaminoethylmethacrylat, 3-Methoxyacrylsäuremethylester, 3-Methoxybutylacrylat, 2-Phenoxyethylmethacrylat, Butyldiglykolmethacrylat, Ethylenglycolacrylat, Ethylenglycolmonomethylacrylat, Methoxypolyethylenglykolmethacrylat 350, Methoxypolyethylenglykolmethacrylat 500, Propylenglycolmonomethacrylat, Butoxydiethylenglykolmethacrylat, Ethoxytriethylenglykolmethacrylat, Octafluoropentylacrylat, Octafluoropentylmethacrylat, 2,2,2-Trifluorethylmethacrylat, 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; N,N-Dialkyl-substituierte Amide wie beispielsweise N,N-Dimethylacrylamid und N,N-Dimethylmethacrylamid; N-Benzylacrylamid, N-Isopropylacrylamid, N-tert-Butylacrylamid, N-tert-Octylacrylamid, N-Methylolacrylamid, N-Methylolmethacrylamid, Acrylnitril, Methacrylnitril; Vinylether wie Vinylmethylether, Ethylvinylether, Vinylisobutylether; Vinylester wie Vinylacetat; Vinylhalogenide, Vinylidenhalogenide, Vinylpyridin, 4-Vinylpyridin, N-Vinylphthalimid, N-Vinyllactam, N-Vinylpyrrolidon, Styrol, α- und p-Methylstyrol, α-Butylstyrol, 4-n-Butylstyrol, 4-n-Decylstyrol, 3,4-Dimethoxystyrol; Makromonomere wie 2-Polystyrolethylmethacrylat (gewichtsmittleres Molekulargewicht Mw, bestimmt mittels GPC, von 4000 bis 13000 g/mol), Poly(methylmethacrylat)ethylmethacrylat (Mw von 2000 bis 8000 g/mol).

Examples of monomers of component c) are:

• Methyl acrylate, ethyl acrylate, propyl acrylate, methyl methacrylate, ethyl methacrylate, benzyl acrylate, benzyl methacrylate, sec-butyl acrylate, tert-butyl acrylate, phenyl acrylate, phenyl methacrylate, isobornyl acrylate, isobornyl methacrylate, tert-butylphenyl acrylate, tert-butylaphenyl methacrylate, dodecyl methacrylate, isodecyl acrylate, lauryl acrylate, n-undecyl acrylate, stearyl acrylate, tridecyl acrylate, behenyl acrylate, cyclohexyl methacrylate, cyclopentyl methacrylate, phenoxyethyl acrylate, phenoxyethyl methacrylate, 2-butoxyethyl methacrylate, 2-butoxyethyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, 3,5-dimethyladamantyl acrylate, 4-cumylphenyl methacrylate, cyanoethyl acrylate, cyanoethyl methacrylate, 4-biphenyl acrylate, 4-biphenyl methacrylate, 2-naphthyl acrylate, 2-naphthyl methacrylate, tetrahydrofurfuryl acrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, 3-methoxyacrylic acid methyl ester, 3-methoxybutyl acrylate, 2-phenoxyethyl methacrylate, butyldiglycol methacrylate, ethylene glycol acrylate, ethylene glycol monomethyl acrylate, methoxypolyethylene glycol methacrylate 350, methoxypolyethylene glycol methacrylate 500, propylene glycol monomethacrylate, butoxydiethylene glycol methacrylate, ethoxytriethylene glycol methacrylate, octafluoropentyl acrylate, octafluoropentyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, 2,2,3,3,3-pentafluoropropyl methacrylate, 2,2,3,4,4,4-hexafluorobutyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl acrylate, 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl methacrylate, dimethylaminopropylacrylamide, dimethylaminopropylmethacrylamide, N-(1-methylundecyl)acrylamide, N-(n-butoxymethyl)acrylamide, N-(butoxymethyl)methacrylamide, N-(ethoxymethyl)acrylamide, N-(n-octadecyl)acrylamide; N,N-dialkyl-substituted amides such as N,N-dimethylacrylamide and 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, α- and p-methylstyrene, α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, 3,4-dimethoxystyrene; Macromonomers such as 2-polystyrene ethyl methacrylate (weight average molecular weight Mw, determined by GPC, from 4000 to 13000 g/mol), poly(methyl methacrylate)ethyl methacrylate (Mw from 2000 to 8000 g/mol).

Monomers of component c) can also advantageously be chosen such that they contain functional groups that support subsequent radiation-chemical crosslinking (for example by electron beams or UV radiation). Suitable copolymerizable photoinitiators are, for example, benzoin acrylate and acrylate-functionalized benzophenone derivatives. Monomers that support crosslinking by electron irradiation are, for example, tetrahydrofurfuryl acrylate, N-tert-butylacrylamide and allyl acrylate.

The poly(meth)acrylate is preferably a polyacrylate which is produced by polymerization of butyl acrylate and/or n-hexyl acrylate and/or n-octyl acrylate and/or isooctyl acrylate and/or 2-ethylhexyl acrylate and/or 2-propylheptyl acrylate and acrylic acid.

The poly(meth)acrylate is particularly preferably a polyacrylate which is produced by polymerization of butyl acrylate, 2-ethylhexyl acrylate and acrylic acid.

As a result, the pressure-sensitive adhesive tape according to the invention has a particularly high shock resistance and at the same time can be removed without leaving residue.

The poly(meth)acrylates are preferably produced by conventional radical polymerizations or controlled radical polymerizations. The poly(meth)acrylates can be produced by copolymerization of the monomers using conventional polymerization initiators and, if appropriate, regulators, with polymerization taking place at the usual temperatures in bulk, in emulsion, for example in water or liquid hydrocarbons, or in solution.

The poly(meth)acrylates are preferably prepared by copolymerizing the monomers in solvents, particularly preferably in solvents having a boiling range of 50 to 150 °C, in particular 60 to 120 °C, using 0.01 to 5% by weight, in particular 0.1 to 2% by weight, in each case based on the total weight of the monomers, of polymerization initiators.

In principle, all conventional initiators are suitable. Examples of radical sources are peroxides, hydroperoxides and azo compounds, for example dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-t-butyl peroxide, cyclohexylsulfonylacetyl peroxide, diisopropyl percarbonate, t-butyl peroctoate and benzpinacol. Preferred radical initiators are 2,2'-azobis(2-methylbutyronitrile) (Vazo® 67™ from DuPont) or 2,2'-azobis(2-methylpropionitrile) (2,2'-azobisisobutyronitrile; AIBN; Vazo® 64™ from DuPont).

Preferred solvents for the production of the poly(meth)acrylates are alcohols such as methanol, ethanol, n- and iso-propanol, n- and iso-butanol, in particular isopropanol and/or isobutanol; hydrocarbons such as toluene and in particular petroleum spirits with a boiling range of 60 to 120°C; ketones, in particular acetone, methyl ethyl ketone, methyl isobutyl ketone; esters such as ethyl acetate and mixtures of the abovementioned solvents. Particularly preferred solvents are mixtures which contain isopropanol in amounts of 2 to 15% by weight, in particular 3 to 10% by weight, in each case based on the solvent mixture used.

After the poly(meth)acrylates have been produced, they can be further processed from solution or they can be concentrated and the further processing of the poly(meth)acrylates can be carried out essentially without solvents. The concentration of the polymer can take place in the absence of crosslinking and accelerator substances. However, it is also possible to add one of these classes of compounds to the polymer before concentration, so that the concentration then takes place in the presence of this substance(s).

After the concentration step, the polymers can be transferred to a compounder. If necessary, concentration and compounding can also take place in the same reactor.

The weight-average molecular weights (weight average molecular weight distribution) Mw of the poly(meth)acrylate(s) are preferably in a range from 20,000 to 2,000,000 g/mol, particularly preferably in a range from 100,000 to 1,500,000 g/mol, very particularly preferably in a range from 150,000 to 1,000,000 g/mol. For this purpose, it can be advantageous to carry out the polymerization in the presence of suitable polymerization regulators such as thiols, halogen compounds and/or alcohols in order to set the desired average molecular weight.

With such an Mw including all preference levels of the poly(meth)acrylate(s), sufficient cohesion is achieved with good flowability and good adhesion of the pressure-sensitive adhesive, it being understood that the pressure-sensitive adhesive is optimized to a greater extent with regard to the property profile of the properties mentioned at a higher preference level.

The Mw is determined according to GPC as described under the test methods.

The poly(meth)acrylates preferably have a K value of 30 to 90, particularly preferably 40 to 70, measured in toluene (1% solution, 21 °C). The K value according to Fikentscher is a measure of the molecular weight and viscosity of polymers.

The principle of the method is based on the capillary viscometric determination of the relative solution viscosity. For this, the test substance is dissolved in toluene by shaking for 30 minutes to obtain a 1% solution. The flow time is measured in a Vogel-Ossag viscometer at 25 °C and the relative viscosity of the sample solution is determined from this in relation to the viscosity of the pure solvent. According to Fikentscher [P. E. Hinkamp, Polymer, 1967, 8, 381], the K value can be read from tables (K = 1000 k).

The poly(meth)acrylate of the pressure-sensitive adhesive preferably has a polydispersity PD < 4 and thus a relatively narrow molecular weight distribution. Despite a relatively low molecular weight, compositions based on this have a particularly good shear strength after crosslinking. In addition, the lower polydispersity enables easier processing from the melt, since the flow viscosity is lower than that of a more broadly distributed poly(meth)acrylate with largely the same application properties. Narrowly distributed poly(meth)acrylates can be advantageously polymerized by anionic polymerization or by controlled radical polymerization. cal polymerization methods, the latter being particularly suitable. Corresponding poly(meth)acrylates can also be produced via N-oxyls. Atom Transfer Radical Polymerization (ATRP) can also be used advantageously to synthesize narrowly distributed poly(meth)acrylates, with monofunctional or difunctional secondary or tertiary halides preferably being used as initiators and Cu, Ni, Fe, Pd, Pt, Ru, Os, Rh, Co, Ir, Ag or Au complexes being used to abstract the halides. RAFT polymerization is also suitable.

The poly(meth)acrylates of the pressure-sensitive adhesive according to the invention are preferably crosslinked by linking reactions - in particular in the sense of addition or substitution reactions - of functional groups contained in them, such as in particular carboxylic acid groups, with thermal crosslinkers. This results in the advantage that the pressure-sensitive adhesive is not too soft and does not have too high a cold flow. This has a beneficial effect on the cohesion of the pressure-sensitive adhesive as well as the storage and processability of the pressure-sensitive adhesive.

• - sowohl eine ausreichend lange Verarbeitungszeit gewährleisten, sodass es nicht zu einer Vergelung während des Verarbeitungsprozesses, insbesondere des Extrusionsprozesses, kommt,
• - als auch zu einer schnellen Nachvernetzung des Polymers auf den gewünschten Vernetzungsgrad bei niedrigeren Temperaturen als der Verarbeitungstemperatur, insbesondere bei Raumtemperatur, führen.

All thermal crosslinkers can be used that

• - ensure a sufficiently long processing time so that gelling does not occur during the processing process, in particular the extrusion process,
• - as well as rapid post-crosslinking of the polymer to the desired degree of crosslinking at temperatures lower than the processing temperature, especially at room temperature.

For example, a combination of polymers containing carboxy (carboxylic acid), amino and/or hydroxy groups and isocyanates, in particular aliphatic or blocked isocyanates, for example trimerized isocyanates deactivated with amines, as crosslinkers is possible. Suitable isocyanates are in particular trimerized derivatives of MDI [4,4-methylenedi(phenyl isocyanate)], HDI [hexamethylene diisocyanate, 1,6-hexylene diisocyanate] and IPDI [isophorone diisocyanate, 5-isocyanato-1-isocyanatomethyl-1,3,3-trimethylcyclohexane].

Thermal crosslinkers are preferably used at 0.1 to 5 wt.%, in particular at 0.2 to 1 wt.%, based on the total amount of the polymer to be crosslinked.

Cross-linking via complexing agents, also known as chelates, is also possible. A preferred complexing agent is, for example, aluminum acetylacetonate.

Preferably, the poly(meth)acrylates of the pressure-sensitive adhesive are crosslinked using epoxy(s) or one or more substances containing epoxy groups. This ensures permanent, non-reversible crosslinking.

The substances containing epoxy groups are in particular multifunctional epoxides, i.e. those with at least two epoxy groups; accordingly, there is an indirect link between the building blocks of the poly(meth)acrylates that carry the functional groups. The substances containing epoxy groups can be both aromatic and aliphatic compounds.

Excellently suitable multifunctional epoxides are oligomers of epichlorohydrin, epoxy ethers of polyhydric alcohols, in particular ethylene, propylene and butylene glycols, polyglycols, thiodiglycols, glycerin, pentaerythritol, sorbitol, polyvinyl alcohol, polyallyl alcohol and the like; Epoxy ethers of polyhydric phenols, in particular resorcinol, hydroquinone, bis-(4-hydroxyphenyl)-methane, bis-(4-hydroxy-3-methylphenyl)-methane, bis-(4-hydroxy-3,5-dibromophenyl)-methane, bis-(4-hydroxy-3,5-difluorophenyl)-methane, 1,1-bis-(4-hydroxyphenyl)ethane, 2,2-bis-(4-hydroxyphenyl)propane, 2,2-bis-(4-hydroxyphenyl)propane, 2,2-bis-(4-hydroxy-3-methylphenyl)propane, 2,2-bis-(4-hydroxy-3-chlorophenyl)propane, 2,2-bis-(4-hydroxy-3,5-dichlorophenyl)propane, bis-(4-hydroxyphenyl)phenylmethane, bis-(4-hydroxyphenyl)phenylmethane, bis-(4-hydroxyphenyl)diphenylmethane, bis (4-hydroxyphenyl)-4'-methylphenylmethane, 1,1-bis-(4-hydroxyphenyl)-2,2,2-trichloroethane, bis-(4-hydroxyphenyl)-(4-chlorophenyl)-methane, 1,1-bis-(4-hydroxyphenyl)-cyclohexane, bis-(4-hydroxyphenyl)-cyclohexylmethane, 4,4'-dihydroxydiphenyl, 2,2'-dihydroxydiphenyl, 4,4'-dihydroxydiphenylsulfone and their hydroxyethyl ethers; phenol-formaldehyde condensation products such as phenol alcohols and phenolaldehyde resins; S- and N-containing epoxides, for example N,N-diglycidylaniline, N,N'-dimethyldiglycidyl-4,4-diaminodiphenylmethane, tetraglycidyl-meta-xylenediamines; and epoxides which have been prepared by conventional processes from polyunsaturated carboxylic acids or monounsaturated carboxylic acid esters of unsaturated alcohols; glycidyl esters; polyglycidyl esters which can be obtained by polymerisation or copolymerisation of glycidyl esters of unsaturated acids or from other acidic compounds, for example from cyanuric acid, diglycidyl sulfide or cyclic trimethylenetrisulfone or its derivatives.

Very suitable ethers are, for example, 1,4-butanediol diglycidyl ether, polyglycerol-3-glycidyl ether, cyclohexanedimethanol diglycidyl ether, glycerol triglycidyl ether, neopentyl glycol diglycidyl ether, pentaerythritol tetraglycidyl ether, 1,6-hexanediol diglycidyl ether, polypropylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, bisphenol A diglycidyl ether and bisphenol F diglycidyl ether.

Other preferred epoxides are cycloaliphatic epoxides such as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (UVACure1500).

Tetraglycidyl-meta-xylenediamine is particularly preferred as a crosslinking agent.

According to preferred embodiments, the poly(meth)acrylates are crosslinked by means of a crosslinker-accelerator system (“crosslinking system”) in order to obtain better control over the processing time, the crosslinking kinetics and the degree of crosslinking. The crosslinker-accelerator system preferably comprises at least one substance containing epoxy groups as a crosslinker and at least one substance that accelerates crosslinking reactions using compounds containing epoxy groups at a temperature below the melting temperature of the polymer to be crosslinked as an accelerator.

According to the invention, amines are particularly preferably used as accelerators. These are formally to be understood as substitution products of ammonia; the substituents include in particular alkyl and/or aryl radicals. Particularly preferred are those amines which react little or not at all with the polymers to be crosslinked.

In principle, primary (NRH ₂ ), secondary (NR ₂ H) and tertiary amines (NR ₃ ) can be selected as accelerators, including, of course, those which have several primary and/or secondary and/or tertiary amino groups. Particularly preferred accelerators are tertiary amines such as triethylamine, triethylenediamine, benzyldimethylamine, dimethylaminomethylphenol, 2,4,6-tris-(N,N-dimethylaminomethyl)phenol, N,N'-bis(3-(dimethylamino)propyl)urea. Other preferred accelerators are multifunctional amines such as diamines, triamines and/or tetramines, for example diethylenetriamine, triethylenetetramine, trimethylhexamethylenediamine.

Further preferred accelerators are amino alcohols, in particular secondary and/or tertiary amino alcohols, wherein in the case of several amino functionalities per molecule, preferably at least one, particularly preferably all amino functionalities are secondary and/or tertiary. Particularly preferred accelerators of this type are triethanolamine, N,N-bis(2-hydroxypropyl)ethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, 2-aminocyclohexanol, bis(2-hydroxycyclohexyl)methylamine, 2-(diisopropylamino)ethanol, 2-(dibutylamino)ethanol, N-butyldiethanolamine, N-butylethanolamine, 2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)-1,3-propanediol, 1-[bis(2-hydroxyethyl)amino]-2-propanol, triisopropanolamine, 2-(dimethylamino)ethanol, 2-(diethylamino)ethanol,
2-(2-dimethylaminoethoxy)ethanol, N,N,N'-trimethyl-N'-hydroxyethylbisaminoethyl ether, N,N,N'-trimethylaminoethylethanolamine and N,N,N'-trimethylaminopropylethanolamine.

Other suitable accelerators are pyridine, imidazoles such as 2-methylimidazole and 1,8-diazabicyclo[5.4.0]undec-7-ene. Cycloaliphatic polyamines can also be used as accelerators. Phosphorus-based accelerators such as phosphines and/or phosphonium compounds, for example triphenylphosphine or tetraphenylphosphonium tetraphenylborate, are also suitable.

Quaternary ammonium compounds can also be used as accelerators; examples are tetrabutylammonium hydroxide, cetyltrimethylammonium bromide and benzalkonium chloride.

The vinylaromatic block copolymer(s) may in principle be any type known to the person skilled in the art.

The vinylaromatic block copolymers preferably have the structure AB, ABA and/or (AB) _n X, where X is a residue of a coupling reagent or initiator and n is greater than or equal to 2.

Particularly preferably, the vinylaromatic block copolymer(s) have the structure A-B-A, optionally in admixture with portions of A-B, the latter representing the diblock portion.

Most preferably, the vinylaromatic block copolymer(s) are present as a mixture of polymers of structure ABA with polymers of structure AB.

The A blocks represent the blocks made from vinyl aromatic monomers.

Preferably, the blocks A are produced from a polymerization mixture containing at least styrene and α-methylstyrene, preferably produced from a polymerization mixture containing at least styrene. Most preferably, the blocks A are blocks produced from styrene and thus polystyrene blocks.

The blocks B represent the remaining blocks of the block copolymer. The blocks B are preferably produced from a polymerization mixture containing monomers of 1,3-dienes and isobutylene, more preferably produced from a polymerization mixture containing butadiene and/or isoprene. The blocks B are very particularly preferably blocks produced from butadiene and thus polybutadiene blocks.

The vinylaromatic block copolymer(s) are particularly preferably styrene block copolymer(s), in turn preferably styrene-butadiene block copolymers of the structure A-B-A and optional proportions of A-B.

Hereby, the problem underlying the invention is solved particularly well.

According to particularly advantageous embodiments, the pressure-sensitive adhesive layer comprises a mixture of at least two styrene-butadiene block copolymers as vinylaromatic block copolymer, wherein a first block copolymer has a diblock proportion A-B of 50 to 85% and a second block copolymer has a diblock proportion A-B of 5 to 35%.

Hereby, the problem underlying the invention is solved particularly well.

The diblock content is determined by GPC and, as is known to those skilled in the art, can be specifically adjusted by choosing suitable manufacturing processes.

Preferably, the weight average molecular weight distribution Mw (according to GPC) of the A-B-A polymer strands of the vinylaromatic block copolymer(s) present is from 50,000 g/mol to 300,000 g/mol, particularly preferably from 80,000 to 180,000 g/mol.

The pressure-sensitive adhesive layer preferably comprises at least one adhesive resin, wherein the adhesive resin is preferably contained in phase (ii).

This increases the tack of the pressure-sensitive adhesive, in particular phase (ii), without undermining the object underlying the invention. The pressure-sensitive adhesive tape according to the invention can therefore still be removed without residue by stretching.

According to the understanding of the person skilled in the art, an “adhesive resin” is understood to mean an oligomeric or polymeric resin which increases the adhesion (the tack, the inherent stickiness) of the pressure-sensitive adhesive layer in comparison to the pressure-sensitive adhesive layer which does not contain an adhesive resin but is otherwise identical.

The at least one adhesive resin preferably has a weight-average molecular weight M _w of 400 to 15,000 g/mol, particularly preferably 400 to 5,000 g/mol, very particularly preferably 500 to 2,000 g/mol.

Preferably, the at least one adhesive resin is selected from the group consisting of non-hydrogenated, partially or fully hydrogenated resins based on rosin or rosin derivatives, hydrogenated polymers of dicyclopentadiene, non-hydrogenated, partially, selectively or fully hydrogenated hydrocarbon resins based on C-5, C-5/C-9 or C-9 monomer mixtures and polyterpene resins based on α-pinene and/or β-pinene and/or δ-limonene.

It is clear to the person skilled in the art that he can choose such an adhesive resin which can be mixed homogeneously with the vinylaromatic block copolymer(s) and is thus present in phase (ii) and at the same time is not compatible with the poly(meth)acrylate, so that no adhesive resin is required in the pressure-sensitive adhesive tape according to the invention. or only minor, insignificant amounts of adhesive resin are contained in phase (i) of the pressure-sensitive adhesive layer.

• Beim Verstrecken muss die Klebrigkeit der Klebebänder deutlich sinken. Je niedriger die Klebleistung im verstreckten Zustand ist, umso weniger stark wird der Untergrund beim Ablösen beschädigt. Besonders deutlich ist diese Eigenschaft bei Klebemassen auf Basis von Vinylaromatenblockcopolymeren zu erkennen, bei denen in der Nähe der Streckgrenze die Klebrigkeit (engl. „tack“) auf unter 10 % sinkt. Im Gegensatz dazu ist der Verlust der Klebrigkeit bei der Verwendung von Acrylatklebemassen in der Regel sehr viel geringer und beträgt meistens nur 50 %.

In order for adhesive tapes that can be removed by stretching to be easy and residue-free, they must have certain adhesive properties:

• When stretched, the adhesive tape's tack must drop significantly. The lower the adhesive performance in the stretched state, the less damage the substrate will suffer when it is removed. This property is particularly evident in adhesives based on vinyl aromatic block copolymers, where the tack drops to less than 10% near the yield point. In contrast, the loss of tack when using acrylic adhesives is usually much lower and is usually only 50%.

It is all the more surprising that the reduction in tackiness by the present blend pressure-sensitive adhesive composition according to the invention comprising at least phases (i) and (ii) is significantly higher and that the tackiness can also fall to below 20%.

In order for adhesive tapes that can be removed by stretching to be easy to remove without leaving residue, they must have certain mechanical properties in addition to the adhesive properties described above.

Particularly advantageously, the ratio of the tear force to the detachment force is greater than two, preferably greater than three.

The removal force is the force that must be applied to remove an adhesive tape from an adhesive joint by pulling parallel in the direction of the bonding plane. This removal force is made up of the force that is required to remove the adhesive tape from the bonding substrate and the force that must be applied to deform the adhesive tape. The force required to deform the adhesive tape depends on the thickness of the adhesive tape. The force required to remove the tape, however, is independent of the thickness of the adhesive tape in the considered thickness range of the adhesive tape (30 µm to 800 µm).

The present invention relates to an adhesive tape which can be in any form, with adhesive tape rolls being preferred. The adhesive tape, in particular in web form, can be produced either in the form of a roll, i.e. rolled up on itself in the form of an Archimedean spiral, or as an adhesive strip, such as is obtained in the form of die-cut pieces, for example.

The adhesive tape according to the invention is in particular in web form. A web is understood to mean an object whose length (extension in the x-direction) is many times greater than its width (extension in the y-direction) and the width is preferably approximately exactly the same along the entire length.

The general term “adhesive tape”, also synonymously called “adhesive strip”, includes in the sense of this invention all flat structures, such as films or film sections extended in two dimensions, tapes with extended length and limited width, tape sections and the like, and ultimately also die-cuts or labels.

In addition to the longitudinal dimension (x-direction) and width dimension (y-direction), the adhesive tape also has a thickness (z-direction) that runs perpendicular to both dimensions, with the width dimension and longitudinal dimension being many times greater than the thickness. The thickness is as uniform as possible, preferably exactly the same, across the entire surface area of the adhesive tape, determined by the length and width.

The statements apply analogously to the carrier, which, as an integral and shaping component of the adhesive tape, forms a layer in the x and y directions. It is understood that the top and bottom of the carrier face each other along the z direction.

The “first side” and the “second side” of the carrier refer in particular to the sides opposite each other in the z-direction.

According to the invention, the pressure-sensitive adhesive layer described in more detail comprising phases (i) and (ii) is arranged at least on the first side and thus at least on one side of the carrier. This is achieved in particular by means of methods known to those skilled in the art. The carrier is thus coated with the pressure-sensitive adhesive at least on the first side.

The outer, exposed surfaces of the pressure-sensitive adhesive layer(s) of the adhesive tape according to the invention can advantageously be equipped with anti-adhesive materials such as a release paper or a release film, also called a liner. A liner can also be a material that is anti-adhesively coated on at least one side, preferably on both sides, such as material that is siliconized on both sides. A liner, or more generally a temporary carrier, is not a component of an adhesive tape, but only an aid for its production, storage and/or for further processing by punching. Furthermore, in contrast to a permanent carrier, a liner is not firmly connected to an adhesive layer, but rather functions as a temporary carrier, i.e. as a carrier that can be removed from the adhesive layer. In the present application, "permanent carriers" are synonymously also referred to simply as "carriers".

As described, the adhesive tape according to the invention can be removed again by stretching without leaving any residue or causing any damage. According to the invention, “residue-free removal” of the adhesive tape means that when it is removed, it leaves no adhesive residue on the bonded surfaces of the components. Furthermore, according to the invention, “non-destructive removal” of the adhesive tape means that when it is removed, it does not damage the bonded surfaces of the components and in particular does not destroy them.

As described, the carrier is coated with the pressure-sensitive adhesive on at least one side. The adhesive tape can therefore be a single-sided adhesive tape.

According to advantageous embodiments, the carrier of the adhesive tape according to the invention is provided with at least a second pressure-sensitive adhesive layer on the second side. This is a double-sided pressure-sensitive adhesive tape.

According to advantageous embodiments, the second pressure-sensitive adhesive layer has a composition identical to that of the first pressure-sensitive adhesive layer. As a result, the advantage achieved with the invention is particularly effective and the adhesive tape can be produced in a simple manner without further increasing the complexity.

According to further advantageous embodiments, the second pressure-sensitive adhesive layer has a different composition to that of the first pressure-sensitive adhesive layer. As a result, the pressure-sensitive adhesive tape can be flexibly designed for bonding different substrates or components and pressure-sensitive adhesives adapted to the respective substrate can be used.

Preferably, the second pressure-sensitive adhesive layer likewise comprises at least a first phase (i) comprising at least one poly(meth)acrylate and at least a second phase (ii) comprising at least one vinylaromatic block copolymer, such as in particular styrene block copolymer.

As a result, the problem underlying the invention is solved to a particularly high degree.

Preferably, at least one pressure-sensitive adhesive layer, preferably at least the first pressure-sensitive adhesive layer, is foamed. This further improves the shock resistance of the pressure-sensitive adhesive tape according to the invention.
Preferably, the foaming is produced by expanding expandable microballoons. “Microballoons” are understood to mean elastic hollow microspheres that are expandable in their basic state and have a thermoplastic polymer shell. These spheres are filled with low-boiling liquids or liquefied gas. Polyacrylonitrile, PVDC, PVC or polyacrylates are used in particular as shell material. Hydrocarbons of the lower alkanes, for example isobutane or isopentane, are particularly suitable as low-boiling liquids or as gases, which are enclosed in the polymer shell as liquefied gas under pressure, with isopentane being particularly preferred.

When the microballoons are exposed to heat, the outer polymer shell softens. At the same time, the liquid propellant gas in the shell changes into its gaseous state. The microballoons expand irreversibly and three-dimensionally. Expansion is complete when the internal and external pressure equalize. Since the polymer shell remains intact, a closed-cell foam is achieved.

A variety of microballoon types are commercially available, which differ essentially in their size (6 to 45 µm diameter in the unexpanded state) and the starting temperatures required for expansion (75 to 220 °C). An example of commercially available microballoons are the Expancel® DU types (DU = dry unexpanded) from Nuryon.

Unexpanded microballoon types are also available as an aqueous dispersion with a solids or microballoon content of approx. 40 to 45% by weight, and also as polymer-bound microballoons (masterbatches), for example in ethyl vinyl acetate with a microballoon concentration of approx. 65% by weight. Both the microballoon dispersions and the masterbatches, like the DU types, are suitable for producing a foamed pressure-sensitive adhesive.

Foamed pressure-sensitive adhesive layers can also be produced using so-called pre-expanded microballoons. With pre-expanded microballoons, expansion takes place before they are mixed into the polymer matrix. Pre-expanded microballoons are commercially available, for example, under the name Dualite® or with the type designation Expancel xxx DE yy (Dry Expanded) from Nuryon. ''xxx'' stands for the composition of the microballoon mixture. "yy" stands for the size of the microballoons in the expanded state. When processing microballoons that have already been expanded, it can happen that the microballoons have a tendency to flotation due to their low density in the polymer matrix into which they are to be incorporated, i.e. they float "upwards" in the polymer matrix during processing. This leads to an uneven distribution of the microballoons in the layer. There are more microballoons in the upper area of the layer (z-direction) than in the lower area of the layer, creating a density gradient across the layer thickness.

In order to largely or almost completely prevent such a density gradient, according to the invention, preferably not or only slightly pre-expanded microballoons are incorporated into the polymer matrix of the pressure-sensitive adhesive layers. The microballoons are only expanded after they have been incorporated into the layer. This results in a more uniform distribution of the microballoons in the polymer matrix.

Preferably, the microballoons are selected such that the ratio of the density of the polymer matrix to the density of the microballoons to be incorporated into the polymer matrix (not or only slightly pre-expanded) is between 1 and 1.6, i.e.: (density of the polymer matrix)/(density of the microballoons to be incorporated) = 1 to 1.6.

Expansion only takes place after or immediately after incorporation. In the case of solvent-containing masses, the microballoons are preferably only expanded after incorporation, coating and drying (solvent evaporation). According to the invention, DU types are therefore preferably used.

The average diameter of the cavities formed by the microballoons in the foamed PSA layer(s) is preferably 10 to 200 µm, particularly preferably 15 to 200 µm, very particularly preferably 15 to 150 µm, again preferably 20 to 100 µm, again particularly preferably 25 to 70 µm. Particularly good shock resistance is achieved with the preferred and particularly preferred size ranges mentioned. At the same time, the sizes are adapted with regard to the layer thicknesses of the PSA layer(s).

Since the diameters of the cavities formed by the microballoons in the foamed PSA layer(s) are measured here, the diameters are the diameters of the cavities formed by the expanded microballoons. The mean diameter is the arithmetic mean of the diameters of the cavities formed by the microballoons in the PSA layer. The mean diameter of the cavities formed by the microballoons in a PSA layer is determined using 5 different cryo-fracture edges of the adhesive tape in a scanning electron microscope (SEM) at 500x magnification. The diameters of the microballoons visible in the images are determined graphically in such a way that the maximum extension in any (two-dimensional) direction is taken from the SEM images for each individual microballoon of the PSA layer to be examined and is regarded as its diameter.

If foaming is carried out using microballoons, the microballoons can be added to the formulation as a batch, paste or as an unblended or blended powder. Furthermore, they can be Solvents are suspended.
According to preferred embodiments of the invention, the proportion of microballoons in the pressure-sensitive adhesive layers is between greater than 0% by weight and 12% by weight, particularly preferably between 0.25% by weight and 5% by weight, very particularly preferably between 0.5% and 3% by weight, in each case based on the total composition (including mixed-in microballoons) of the corresponding layer. The figures refer in each case to unexpanded microballoons.

The quantities mentioned above resolve the conflicting objectives of the properties of stickiness, flow behaviour and foaming particularly well.

A polymer mass of the pressure-sensitive adhesive layer(s) containing expandable hollow microspheres may also contain non-expandable hollow microspheres. The only decisive factor is that almost all gas-containing caverns are closed by a permanently sealed membrane, regardless of whether this membrane consists of an elastic and thermoplastically stretchable polymer mixture or of elastic and - within the range of temperatures possible in plastics processing - non-thermoplastic glass. Also suitable for the pressure-sensitive adhesive layers - independently of other additives - are solid polymer spheres such as PMMA spheres, hollow glass spheres, solid glass spheres, phenolic resin spheres, ceramic hollow spheres, ceramic solid spheres and/or solid carbon spheres ("carbon micro balloons").

The absolute density of the foamed PSA layer(s) is preferably 350 to 950 kg/m ³ , particularly preferably 450 to 930 kg/m ³ , very particularly preferably 570 to 880 kg/m ³ . The relative density describes the ratio of the density of the respective foamed layer to the density of the corresponding unfoamed layer of identical formulation. The relative density of the PSA layer(s) is preferably 0.35 to 0.99, more preferably 0.45 to 0.97, in particular 0.50 to 0.90.

According to particularly advantageous embodiments, the first and the second pressure-sensitive adhesive layer have an identical composition, wherein preferably both layers are foamed, preferably by means of expanding expandable microballoons.

According to advantageous embodiments of the invention, one or both surfaces of the pressure-sensitive adhesive layers are physically and/or chemically pretreated. Such pretreatment can be carried out, for example, by plasma pretreatment. If both surfaces of the pressure-sensitive adhesive layers are pretreated, the pretreatment of each surface can be carried out differently or, in particular, both surfaces can be pretreated in the same way.

Plasma treatment - particularly low-pressure plasma treatment - is a well-known process for surface pretreatment of adhesives. The plasma activates the surface to increase its reactivity. This leads to chemical changes in the surface, which can, for example, influence the behavior of the adhesive towards polar and non-polar surfaces. This pretreatment essentially involves surface phenomena.

The thickness of the individual pressure-sensitive adhesive layer(s) (in the z-direction) is preferably from 15 to 150 µm, particularly preferably from 20 to 100 µm, very particularly preferably from 25 to 70 µm.

Basically, all carriers that have an elongation of at least 200% before they tear are suitable as the carrier of the adhesive tape according to the invention, which can be removed by stretching. Carriers with an elongation at break of at least 400% are preferred, and those with an elongation at break of over 500% are particularly preferred.

The supports can be either mainly elastic or plastically deformable.

Elastic beams are those beams that remain stretched less than 100% after being stretched by 200% and then relaxed. If the subsequent stretching after relaxation is more than 100% of the initial value, the beams are plastically deformable.

Elastically deformable supports can be based on polyurethane, for example, as used in DE 102012223670 A1 are disclosed.

Polyurethanes made from dispersion or from the melt can be used. Particularly preferred is polyurethane, aliphatic polyester polyurethane or aliphatic cal polyether polyurethane, i.e. the polyurethane in this case is based on aliphatic polyester or aliphatic polyether.

In principle, polyurethanes made from dispersion can be cross-linked or uncross-linked, with isocyanates often being used in cross-linked polyurethanes. These cross-linked polyurethanes have the disadvantage that cross-linking is often very slow and the final properties of the adhesive tapes can only be achieved after a long period of storage. In addition, the isocyanates used are often harmful to health. However, due to cross-linking, the tear resistance of the carriers is generally higher than with uncross-linked polyurethanes.

Many other films can be used as additional carriers. Examples of raw materials on which the stretchable carrier material is based include thermoplastic polyolefins, polyvinyl chloride, polyvinyl acetate, polyamides, polystyrenes, polyacrylates, polyesters, rubbers (synthetic and natural) and silicones. Preferred raw materials are polyolefins such as ethylene vinyl acetate (EVA), ethylene acrylate (EA), ethylene methacrylate (EMA), low density polyethylene (PE-LD), linear low density polyethylene (PE-LLD), very low density linear polyethylene (PE-VLD), polypropylene homopolymer (PP-H), polypropylene copolymer (PP-C) (impact or random). Other examples of raw materials from which the stretchable carrier material can be constructed include thermoplastic elastomers based on polyolefins TPO, polyamides TPA, TPU, styrene block copolymers TPS and polyesters TPC. Preferred raw materials are polyolefin copolymers such as ethylene-vinyl acetate EVA, ethylene acrylate EA, soft polyethylene elastomers such as Affinity™, Engage™, Exact™, Tafmer™, soft polypropylene copolymers such as Vistamaxx™, Versify™ which have a low melting point due to their random structure, and elastomers heterophasic polyolefins (for example with a block structure) such as Infuse™, Hifax™, Adflex™ or Softell™. Examples of styrene elastomers are Kraton™, Hybrar™, Septon™, Cariflex™, Vector™ and Styroflex™.

Again, non-cross-linked carriers are preferred.

The carrier preferably has a thickness of 10 to 150 µm, particularly preferably 20 to 100 µm, most preferably 25 to 70 µm.

This gives the pressure-sensitive adhesive tape according to the invention sufficient stability without being too thick.

The thickness of the pressure-sensitive adhesive tape can be selected depending on the application. According to preferred embodiments, the pressure-sensitive adhesive tape has a thickness of 30 to 350 µm, preferably 30 to 250 µm, and particularly preferably 50 to 200 µm.

Another object of the present invention is a process for producing the pressure-sensitive adhesive tape according to the invention.

The PSAs can be produced and processed either from solution or from the melt. The PSAs can be applied to the carrier layer by direct coating or by lamination, particularly hot lamination.

Preferably, the pressure-sensitive adhesives are manufactured from the melt in a solvent-free and thus environmentally friendly manner.

Another object of the invention is the use of the pressure-sensitive adhesive tape according to the invention for bonding components in electronic devices, automobiles, medical devices and dental devices.

Test methods

• Reißertest mittels Zugprüfmaschine, Zwick

Unless otherwise stated, all measurements are carried out at 23 °C and 50 % relative humidity. The mechanical and adhesive data were determined as follows:

• Tear test using tensile testing machine, Zwick

In the tear test, a first test plate made of polyethylene and a second test plate made of steel are used. The first test plate made of polyethylene is wrapped with a double-sided adhesive tape tesa® 67215, onto which a “battery foil” is then applied. The adhesive tape tesa® 67215 is 150 µm thick in total and contains a polyurethane carrier on which a foamed pressure-sensitive adhesive layer based on vinyl aromatic block copolymer is arranged on both sides. The "battery foil" is a polymer foil laminated with aluminum and 88 µm thick from the manufacturer DNP - the foil is typically used to manufacture lithium polymer batteries.

Test pieces 8 mm wide and 60 mm long are punched or lasered out of the adhesive tape to be tested. These test pieces are glued to the first polyethylene test plate, which is wrapped in battery foil as described above, over a length of 50 mm, so that a 10 mm long handle protrudes. The handle is covered on both sides with 36 µm PET. The second steel test plate is cleaned with acetone and preconditioned for 1 to a maximum of 10 minutes at 23 °C and 50% relative humidity and glued to the opposite side of the glued strip (i.e. test piece) in such a way that the two test plates lie flush, i.e. congruent, on top of each other. The composite is rolled over the back of the steel plate 10 times with a 4 kg roller (five times back and forth). After a minimum of 4 hours of application at 23 °C and 50% relative humidity, the strips on the handle are removed from the adhesive joint using a tensile testing machine (from Zwick) at a constant speed of 800 mm/min at an angle of 90° over the edge of the first polyethylene test plate wrapped in battery foil. The test specimen is fixed with an angle-adjustable adapter and the handle is clamped vertically in the middle of the clamping jaws.

The measurement is taken at an angle of 90° and the force that is continuously required to remove/strip the sample is recorded by the tensile testing machine - the so-called stripping force F _stripp . The measurement is finished as soon as the sample has been completely removed from between the two test plates or the sample has torn during the measurement. At least 10 measurements are carried out per sample. The test climate is 23 °C and 50% relative humidity.

• Reißer 90° - der Test gilt als bestanden, wenn während des Ablösevorgangs weniger als 50 % der Prüflinge reißen.
• F_stripp 90° [N/cm] - benötigte Kraft, um den Prüfling aus der Klebefuge zu abzulösen (zu strippen) bei einem Winkel von 90° (Ablösekraft)

Indication of results:

• Tear 90° - the test is considered passed if less than 50% of the test pieces tear during the detachment process.
• F _stripp 90° [N/cm] - force required to detach (strip) the test specimen from the adhesive joint at an angle of 90° (detachment force)

The adhesive residues on both the steel plate and the battery foil are examined.

Tensile test using a tensile testing machine, Zwick, including elongation at break in accordance with EN ISO 527. From the sample to be tested (adhesive tape, i.e. preferably a carrier coated with adhesive on both sides, or just the carrier as a raw carrier), 15 mm wide strips with a length of approx. 150 mm are cut lengthwise using a strip cutter or razor blade knife. The sample, which has been preconditioned in the test climate for 24 hours, is clamped vertically in the middle of the clamping jaws with a clamping length of 10 mm and stretched at a speed of 800 mm/min until it tears. The tear should occur somewhat in the middle of the strip. If the tear occurs near the jaws (closer than 1 cm), the value should be discarded and another strip should be tested instead. 5 measurements are carried out for each sample variant. The test climate is 23 °C and 50% relative humidity.

The measurements are carried out according to EN ISO 527.

F_Bruch [N/cm], [N/mm²] - Kraft bei Riss/ Bruch der Probe (d.h. Reißfestigkeit)
RD [%] - Reißdehnung, d.h. prozentuale Dehnung bei Riss/ Bruch der ProbeIndication of results: $${\text{F}}_{\text{x}\%}\left[\text{N}/\text{cm}\right],\left[\text{N}/{\text{mm}}^2\right]-\text{Force at x}\%\text{strain}$$

F _break [N/cm], [N/mm ² ] - force at tear/break of the sample (ie tear strength)
RD [%] - Elongation at break, ie percentage elongation at tear/break of the sample

Dielectric strength, i.e. DuPont test in z-plane

A square, frame-shaped sample is cut out of the adhesive tape to be tested (external dimensions 33 mm × 33 mm, web width 2.0 mm, internal dimensions (window cutout) 29 mm × 29 mm). This sample is glued to a polycarbonate (PC) frame (external dimensions 45 mm × 45 mm, web width 10 mm, internal dimensions (window cutout) 25 mm × 25 mm; thickness 3 mm). On the other side of the double-sided A PC window measuring 35 mm × 35 mm is glued using the adhesive tape. The PC frame, adhesive tape frame and PC window are bonded in such a way that the geometric centers and diagonals are on top of each other (corner to corner). The bonding area is 248 mm ² . The bond is pressed for 5 s with 248 N and stored conditioned for 24 hours at 23 °C / 50 % relative humidity.

Immediately after storage, the adhesive bond made of PC frame, adhesive tape and PC window is clamped into a sample holder with the protruding edges of the PC frame in such a way that the bond is aligned horizontally. The PC frame lies flat on the sample holder at the protruding edges so that the PC window is floating freely below the PC frame (held in place by the adhesive tape pattern). The sample holder is then inserted centrally into the designated holder of the "DuPont Impact Tester". The 150 g impact head is inserted in such a way that the circular impact geometry with a diameter of 24 mm lies centrally and flush on the surface of the PC window that is freely accessible from above.

A weight with a mass of 150 g guided by two guide rods is dropped vertically from a height of 5 cm onto the assembly of sample holder, sample and impact head arranged in this way (measurement conditions 23 °C, 50 % relative humidity). The height of the falling weight is increased in 5 cm increments until the impact energy introduced destroys the sample through the breakdown load and the PC window detaches from the PC frame.

In order to compare experiments with different samples, the energy is calculated as follows: $$\text{Energy E}\left[\text{J}\right]=\text{H}\ddot{\text{O}}\text{he}\left[\text{m}\right]*\text{mass weight}\left[\text{kg}\right]*9.81\text{kg}/\text{m}*{\text{s}}^2$$

Five samples per product are tested and the average energy value is given as an indicator for the breakdown strength as a measure of shock resistance.

thickness

The thickness of an adhesive layer can be determined by determining the thickness of a section of such an adhesive layer applied to a liner, defined in terms of its length and width, minus the (known or separately ascertainable) thickness of a section of the same dimensions of the liner used. The thickness of the adhesive layer can be determined using commercially available thickness measuring devices (probe testers) with an accuracy of less than 1 µm deviation. If thickness fluctuations are determined, the average value of measurements at at least three representative locations is given, i.e. in particular not measured at creases, folds, spots and the like.

Just like the thickness of an adhesive layer, the thickness of an adhesive tape (adhesive strip) or a carrier can be determined analogously using commercially available thickness measuring devices (probe testers) with an accuracy of less than 1 µm deviation. If thickness fluctuations are detected, the average value of measurements at at least three representative points is given, i.e. in particular not measured at creases, folds, spots and the like.

density

The density of the unfoamed and foamed adhesive layers is determined by calculating the quotient of the mass application and the thickness of the adhesive layer applied to a liner.

The mass application can be determined by determining the mass of a section of such an adhesive layer applied to a liner, defined in terms of its length and width, minus the (known or separately determinable) mass of a section of the same dimensions of the liner used.

The density of a carrier can be determined analogously.

Molecular weight M _n , M _w

The information on the number-average molecular weight M _n or weight-average molecular weight M _w in this document refers to the determination by gel permeation chromatography (GPC). The Determination is carried out on 100 µl of clear-filtered sample (sample concentration 4 g/l). Tetrahydrofuran with 0.1 vol.% trifluoroacetic acid is used as the eluent. The measurement is carried out at 25 °C. A column type PSS-SDV, 5 µm, 10 ³ Å, 8.0 mm * 50 mm (information here and below in the order: type, particle size, porosity, internal diameter * length; 1 Å = 10 ^-10 m) is used as the pre-column. A combination of columns type PSS-SDV, 5 µm, 10 ³ Å as well as 10 ⁵ Å and 10 ⁶ Å, each with 8.0 mm * 300 mm, is used for separation (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer). The flow rate is 1.0 ml per minute. For polar molecules such as the starting materials of polyurethane, calibration is carried out against PMMA standards (polymethyl methacrylate calibration) and otherwise against PS standards (polystyrene calibration).

Adhesive resin softening temperature

The adhesive resin softening temperature is carried out according to the relevant methodology known as Ring & Ball and standardized according to ASTM E28.

Some examples are described below to further illustrate the invention.

Examples according to the invention

• Die in den Beispielen jeweils eingesetzte Haftklebemasseschicht enthält ein Ausgangspolymer auf Acrylatbasis, das im Folgenden Basispolymer P1 genannt wird, sowie ein Vinylaromatenblockcopolymer.

Production of the pressure-sensitive adhesive layer used in the adhesive tapes:

• The pressure-sensitive adhesive layer used in the examples contains an acrylate-based starting polymer, which is referred to below as base polymer P1, and a vinyl aromatic block copolymer.

The base polymer P1 is produced as follows: A conventional reactor for radical polymerization is filled with 47.5 kg 2-ethylhexyl acrylate, 47.5 kg n-butyl acrylate, 5 kg acrylic acid and 66 kg petrol/acetone (70/30). After passing nitrogen gas through the reactor for 45 minutes while stirring, the reactor is heated to 58 °C and 50 g AIBN is added. The external heating bath is then heated to 75 °C and the reaction is carried out at a constant external temperature. After 1 h, another 50 g AIBN is added and after 4 h, the mixture is diluted with 20 kg petrol/acetone mixture. After 5.5 and after 7 h, the reaction is reinitiated with 150 g bis-(4-tert-butylcyclohexyl)peroxydicarbonate. After a reaction time of 22 h, the polymerization is stopped and cooled to room temperature. The polyacrylate has an average molecular weight of Mw = 386,000 g/mol, polydispersity PD (Mw/Mn) = 3.6.

• Es wird eine Mischung hergestellt aus dem Basispolymer P1, einem Klebharz Piccolyte A115 sowie einer Mischung aus zwei Styrolbutadienstyrol-Blockcopolymeren (Kraton D1118 und Kraton D1102 im Verhältnis 2:1). Durch die Zugabe von Benzin wird ein Feststoffgehalt von 38 Gew.-% eingestellt. Die Mischung aus Polymer und Klebharz wird solange gerührt, bis sich das Klebharz sichtbar vollständig gelöst hat. Im Anschluss werden 0,1 Gew. % bezogen auf den Anteil an Basispolymer P1 des kovalenten Vernetzers Erysis GA 240 zugegeben. Die Mischung wird für 15 Minuten bei Raumtemperatur gerührt. Die Gewichtsanteile (siehe nachfolgende Tabelle) der gelösten Bestandteile beziehen sich dabei jeweils auf das Trockengewicht der resultierenden Lösung. Währenddessen werden 0,8 Teile unexpandierte Mikroballons (Expancel 920 DU20) hinzugefügt, wobei die Mikroballons als Anschlämmung in Benzin eingesetzt werden. Die Gewichtsanteile der Mikroballons beziehen sich auf das Trockengewicht der eingesetzten Lösung, zu der sie gegeben werden (d.h. das Trockengewicht der eingesetzten Lösung wird als 100 Teile festgesetzt).

The pressure-sensitive adhesive layer used in the (comparative) examples is produced as follows:

• A mixture is prepared from the base polymer P1, an adhesive resin Piccolyte A115 and a mixture of two styrene-butadiene-styrene block copolymers (Kraton D1118 and Kraton D1102 in a ratio of 2:1). A solids content of 38% by weight is set by adding gasoline. The mixture of polymer and adhesive resin is stirred until the adhesive resin has visibly dissolved completely. Then 0.1% by weight of the covalent crosslinker Erysis GA 240, based on the proportion of base polymer P1, is added. The mixture is stirred for 15 minutes at room temperature. The weight proportions (see table below) of the dissolved components refer to the dry weight of the resulting solution. During this time, 0.8 parts of unexpanded microballoons (Expancel 920 DU20) are added, with the microballoons being used as a slurry in gasoline. The weight proportions of the microballoons refer to the dry weight of the solution to which they are added (ie the dry weight of the solution used is set as 100 parts).

The resulting mixture is then spread with a spreader bar onto a PET liner equipped with a separating silicone, so that after drying at 110°C a layer thickness of 40 µm is created. The microballoons are still unexpanded, i.e. the pressure-sensitive adhesive layer is not yet foamed.

Depending on the carrier material and its temperature stability, the respective adhesive tape is manufactured as follows. Temperature-stable carriers such as PU films such as Platilon® U04 are first laminated on both sides with the pressure-sensitive adhesive layer containing unexpanded microballoons as described above. The two pressure-sensitive adhesive layers have the same thickness. The tape also contains two liners. The overall composite of carrier, pressure-sensitive adhesive layers and liners is used to foam the pressure-sensitive adhesive layers. subjected to a further tempering step. The wound material is heated to 170 °C for 30 s. The result is a foamed double-sided adhesive tape with a PU carrier layer.

If non-temperature-stable carriers are used, such as the carrier based on Affinity 1840, the manufacturing process is different. After the adhesive layers have been produced, the open side is covered with another liner with a lower release force. The adhesive is then foamed by heating it to 170°C for 30 seconds. The carrier is then laminated on both sides with the foamed adhesive after the liner, which is easier to release, has been removed.

After foaming, the thickness of the individual adhesive layers is 50 µm. Using a carrier with a layer thickness of 30 µm results in a total thickness of the adhesive tape of (50 + 50 + 30 =) 130 µm.

• • Kraton D1102: Styrol-Butadien-Styrol-Blockcopolymer mit dem Aufbau A-B-A und A-B im Gemisch, Styrolanteil von 30% und Diblock-Anteil (A-B) von 15 %, der Fa. Kraton
• • Kraton D1118: Styrol-Butadien-Styrol-Blockcopolymer mit dem Aufbau A-B-A und A-B im Gemisch, Styrolanteil von 31% und Diblock-Anteil (A-B) von 78 %, der Fa. Kraton
• • Klebharz Piccolyte A 115: Terpenharz aus alpha-Pinen, Erweichungspunkt 115°C, der Fa. DRT
• • Vernetzer: Erysis® GA 240: Tetraglycidyl meta-Xylenediamine der Fa. Huntsman
• • Mikroballons: Expancel® 920 DU20: Mikroballons mit einer Größe nach Expansion von ca. 20 µm, der Fa. Nuryon
• • Platilon® U04: Polyesterurethan der Fa. Epurex, Reißdehnung 650 %, Schichtdicke 30 µm
• • Affinity 1840: Polyolefin Plastomer der Fa. Dow, Reißdehnung 620 %, Schichtdicke 30 µm

Substances used:

• • Kraton D1102: Styrene-butadiene-styrene block copolymer with the structure ABA and AB in the mixture, styrene content of 30% and diblock content (AB) of 15%, from Kraton
• • Kraton D1118: Styrene-butadiene-styrene block copolymer with the structure ABA and AB in the mixture, styrene content of 31% and diblock content (AB) of 78%, from Kraton
• • Adhesive resin Piccolyte A 115: terpene resin from alpha-pinene, softening point 115°C, from DRT
• • Crosslinker: Erysis® GA 240: Tetraglycidyl meta-Xylenediamine from Huntsman
• • Microballoons: Expancel® 920 DU20: Microballoons with a size after expansion of approx. 20 µm, from Nuryon
• • Platilon® U04: Polyester urethane from Epurex, elongation at break 650%, layer thickness 30 µm
• • Affinity 1840: Polyolefin plastomer from Dow, elongation at break 620%, layer thickness 30 µm

The type of carrier and the composition of the pressure-sensitive adhesive layer of the examples according to the invention are summarized in Table 1. The proportions are given in percent by weight and add up to 100% by weight, without taking into account the microballoons and crosslinkers. Table 1 Example carrier Proportion of base polymer P1 Share Piccolyte A115 Share Kraton D1118 Share Kraton D1102 1 Platilon U04 70 15 10 5 2 Platilon U04 60 20 13.3 6.7 3 Platilon U04 50 25 16.7 8.3 4 Platilon U04 40 30 20 10 5 Platilon U04 30 35 23.3 11.7 6 Affinity 1840 60 20 13.3 6.7 7 Affinity 1840 40 30 20 10

Comparison examples

V1

In contrast to the examples, the adhesive used is an adhesive consisting only of the base polymer P1 with microballoons and crosslinker, whereby the type and amount of microballoons and crosslinker are selected as described above. This is therefore a pure acrylate mass. The carrier is again a carrier based on polyurethane, Platilon U04.

V2

In the second example, a mass of 33% Kraton D1118, 17% Kraton D1102 and 50% Piccolyte A115 is used as the adhesive. This does not contain any additional crosslinker but is mixed with microballoons, whereby the type and quantity of microballoons is as stated above (0.8 parts of unexpanded microballoons (Expancel 920 DU20) based on the dry weight of the solution used).
In this case, the mass is dissolved in a mixture of petrol and acetone (3:1) and spread onto the liner.
Platilon U04 is again used as the carrier.

Results

A tear test was carried out on all examples and comparison examples and the penetration strength was measured according to the DuPont test.
In the tear test, the proportion of tears and the detachment force were determined and the residues after re-detachment were evaluated.

The results are summarized in Table 2. Table 2 Example Detachment force in N/cm Ripper in % Residues Dielectric strength in J 1 10.5 40 No 0.91 2 10.7 0 No 0.81 3 10.3 10 No 0.76 4 10.4 20 No 0.73 5 10.6 40 No 0.71 6 12.3 20 No 0.83 7 12.5 20 No 0.79 V1 11.0 90 Clear adhesive residues 0.80 V2 10.3 70 No 0.59

It is evident from examples 1 to 7 according to the invention that very good impact strength values are achieved with blends of acrylate and vinyl aromatic block copolymer in the pressure-sensitive adhesive of the adhesive tapes according to the invention, and the adhesive tapes can still be removed without leaving any residue when peeled off. At the same time, the examples according to the invention show a low tendency to tear. In contrast, the pure acrylate mass in V1 tends to leave significant residues. V2 shows that a lower impact strength is achieved with vinyl aromatic block copolymers than with the blends.

Both the use of a pure acrylate mass and the use of a pure vinyl aromatic block copolymer mass show a significantly increased tendency to tear.

Surprisingly, only the examples according to the invention have an optimized property profile with regard to the requirements or the task underlying the invention. This was not to be expected from the examples comprising the pure polymer masses.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 102012223670 A1 [0003, 0161]
• WO 2015135134 A1 [0004]
• DE 102015206076 A1 [0007]
• EP 3075772 A1 [0007]
• US 2017121573 A1 [0008]
• JP 6265734 B2 [0010]

Claims (12)

Pressure-sensitive adhesive tape removable by stretching, comprising: a) at least one carrier with an elongation at break (according to EN ISO 527) of at least 200%, the carrier having at least a first side and a second side, and b) at least one first pressure-sensitive adhesive layer which has at least a first phase (i) containing at least one poly(meth)acrylate and at least a second phase (ii) containing at least one vinylaromatic block copolymer, such as in particular styrene block copolymer, the first pressure-sensitive adhesive layer being arranged at least on the first side of the carrier. Pressure sensitive adhesive tape Claim 1 , characterized in that the pressure-sensitive adhesive layer contains 40 to 90 parts by weight, preferably 50 to 80 parts by weight of poly(meth)acrylate, and 10 to 60 parts by weight, preferably 20 to 50 parts by weight, of vinyl aromatic block copolymer, the two parts by weight adding up to 100%. Pressure-sensitive adhesive tape according to one of the preceding claims, characterized in that the pressure-sensitive adhesive layer has a mixture of at least two styrene-butadiene block copolymers as vinyl aromatic block copolymer, a first block copolymer having a diblock content of 50 to 85% and a second block copolymer having a diblock content of 5 to 35%. Pressure-sensitive adhesive tape according to one of the preceding claims, characterized in that the glass transition temperature of the poly(meth)acrylate is < 0 °C (less than zero degrees Celsius), particularly preferably between -20 and -50 °C. Pressure-sensitive adhesive tape according to one of the preceding claims, characterized in that the pressure-sensitive adhesive layer comprises at least one adhesive resin, wherein the adhesive resin is preferably contained in phase (ii). Pressure-sensitive adhesive tape according to one of the preceding claims, characterized in that the carrier is equipped on the second side with at least one second pressure-sensitive adhesive layer, the second pressure-sensitive adhesive layer having a composition that is identical to or different from the first pressure-sensitive adhesive layer, the second pressure-sensitive adhesive layer preferably also having at least one first phase (i) containing at least one poly(meth)acrylate and at least one second phase (ii) containing at least one vinylaromatic block copolymer, such as in particular styrene block copolymer. Pressure-sensitive adhesive tape according to one of the preceding claims, characterized in that at least one pressure-sensitive adhesive layer, preferably at least the first pressure-sensitive adhesive layer, is foamed, wherein the foaming is preferably produced by expanding expandable microballoons. Pressure sensitive adhesive tape according to one of the Claims 6 or 7 , characterized in that the first and the second pressure-sensitive adhesive layer have an identical composition. Pressure sensitive adhesive tape according to one of the Claims 1 until 8th , characterized in that the carrier is an elastic carrier. Pressure sensitive adhesive tape according to one of the Claims 1 until 8th , characterized in that the carrier is a plastically deformable carrier. Pressure-sensitive adhesive tape according to one of the preceding claims, characterized in that the pressure-sensitive adhesive tape has a thickness of 30 to 350 µm, preferably 30 to 250 µm, in particular 50 to 200 µm. Use of a pressure-sensitive adhesive tape in accordance with one of the Claims 1 until 11 for bonding components in electronic devices, automobiles, medical devices and dental devices.