DE102019208714A1 - Adhesive tape with a microporous polyurethane membrane - Google Patents

Abstract

The aim is to provide adhesive tapes with a small thickness, sufficient adhesive strength and good shock absorption. This is achieved with an adhesive tape which comprises at least one outer pressure-sensitive adhesive layer and furthermore at least one microporous polyurethane membrane. The invention also relates to the use of a microporous polyurethane membrane as a carrier layer in an adhesive tape and the use of an adhesive tape according to the invention for producing bonds in electronic devices or as a damping layer in electronic devices.

Description

The invention lies in the technical field of adhesive tapes, as they are used in a variety of ways for producing temporary and permanent bonds. More specifically, the invention proposes a layer structure which comprises a microporous membrane and thus allows the provision of very thin adhesive tapes with good shock absorption capacity.

In many areas of technology, adhesive tapes are used to connect two (joining) parts to one another or to apply functional layers to certain substrates. Due to the increasing miniaturization, especially in the field of electronics, there is a high demand for thin, yet high-performance adhesive tapes. Such adhesive tapes are used, for example, to attach protective strips for sealing and shock absorption to electronic devices or their components such as smartphones, computer drives or liquid crystal displays, or to produce adhesive bonds within devices.

EP 2 860 028 A1 describes a polymer tape which comprises a polyurethane core with certain mechanical properties and at least one functional layer, which can be a pressure-sensitive adhesive, among other things. The tape is intended for installation in electronic devices.

Foamed adhesive tapes are often used to achieve the required shock absorption. These adhesive tapes can consist of only one layer of a foamed pressure-sensitive adhesive, or they comprise a foamed carrier material and one or two layers of a pressure-sensitive adhesive. Poly (meth) acrylates, polyolefins or polyurethanes are usually used as the polymer base of the foamed carrier material.

WO 2015/123007 A1 describes, for example, an adhesive tape with a polyurethane foam core to which an anchoring layer is applied, and layers of pressure-sensitive adhesive applied to both sides.

Microporous membranes are known in particular for their use as a water-repellent yet breathable layer in functional clothing and shoes.

U.S. 4,560,611 For example, describes a moisture-permeable, waterproof fabric that comprises a microporous layer of polyurethane which, in addition to the micropores, is equipped with larger cavities than these.

Microporous membranes can be obtained by so-called wet coagulation processes in which essentially water-soluble salts are washed out of the freshly coated membrane matrix.

Such a process is the subject of U.S. 3,714,307 , according to which an inorganic salt is dispersed in a film-forming polyester-polyurethane and the dispersion applied is washed out with a solution of the same salt, the concentration of which in the washing solution is below two thirds of the saturation concentration.

Also DE 1 925 997 describes a process for the production of porous flat structures in which a thermoplastic polyurethane elastomer is processed on calenders in the presence of sodium hydrogen carbonate and an aliphatic carboxylic acid and the resulting films are then freed from salt in a soaking process.

There is a continuing need for the thinnest possible adhesive tapes with good shock absorption properties. Foam layer thicknesses of at least 20 μm occasionally described in the prior art are rarely achieved in practice. The object of the invention was therefore to provide an adhesive tape with a small thickness, adequate adhesive strength and good shock absorption. In particular, double-sided adhesive tapes with a total thickness of less than 150 μm, which have good shock-absorbing properties, should be provided, if possible.

A first and general object of the invention is an adhesive tape which comprises at least one outer pressure sensitive adhesive layer and is characterized in that the adhesive tape further comprises at least one microporous polyurethane membrane.

According to the invention, a pressure-sensitive adhesive or a pressure-sensitive adhesive is understood, as is customary in common parlance, to be a substance which is permanently tacky and tacky at least at room temperature. A characteristic of a pressure-sensitive adhesive is that it can be applied to a substrate by pressure and remains adhered there, the pressure to be applied and the duration of this pressure being not defined in more detail. In general, but basically depending on the exact type of pressure-sensitive adhesive as well as the substrate, the temperature and the air humidity, the application of a short-term, minimal pressure, which does not go beyond a light touch for a short moment, is sufficient to achieve the adhesive effect in other cases a longer period of exposure to a higher pressure may be necessary.

Pressure-sensitive adhesives have special, characteristic viscoelastic properties which lead to permanent tack 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. With regard to their respective proportions, the two processes have a certain relationship to one another, depending both on the exact composition, the structure and the degree of crosslinking of the PSA and on the speed and duration of the deformation and on the temperature.
The proportionate viscous flow is necessary to achieve adhesion. Only the viscous components, often caused by macromolecules with a relatively high mobility, enable good wetting and good flow onto the substrate to be bonded. A high proportion of viscous flow leads to high pressure-sensitive tack (also referred to as tack or surface tack) and thus often also to high adhesion. Strongly crosslinked systems, crystalline or glass-like solidified polymers are generally not or at least only slightly tacky 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 strongly tangled macromolecules, as well as by physically or chemically cross-linked macromolecules, and enable the forces acting on an adhesive bond to be transmitted. They mean that an adhesive bond can withstand a permanent load acting on it, for example in the form of permanent shear stress, to a sufficient extent over a longer period of time.

The storage modulus (G ') and loss modulus (G ") that can be determined by means of dynamic mechanical analysis (DMA) are used for a more precise description and quantification of the degree of elastic and viscous components and the relationship between the components.

G 'is a measure of the elastic part, G "is a measure of the viscous part of a substance. Both quantities depend on the deformation frequency and the temperature.

The sizes can be determined with the aid of a rheometer. The material to be examined is exposed to a sinusoidally oscillating shear stress in a plate-plate arrangement, for example. In the case of devices controlled by shear stress, the deformation is measured as a function of time and the time offset of this deformation with respect to the introduction of the shear stress. This time 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).

In particular, a mass is considered a pressure-sensitive adhesive and is defined as such within the meaning of the invention, if at 23 ° C in the deformation frequency range of 10 ° to 10 ¹ rad / sec both G 'and G ″ are at least partially in the range of 10 ³ up to 10 ⁷ Pa. "In part" means that at least a section of the G 'curve lies within the window, which is defined by the deformation frequency range from 10 ° up to and including 10 ¹ rad / sec (abscissa) and the range of G' Values from 10 ³ to 10 ⁷ Pa inclusive (ordinate) are spanned, and if at least a section of the G "curve is also within the corresponding window.

An “outer layer” is understood to mean a layer which closes off the layer structure of the adhesive tape on the outside.

In principle, the nature of the outer pressure-sensitive adhesive layer is uncritical provided it is compatible with the microporous membrane in the structure of the adhesive tape of the invention or interacts with it in the manner of an adhesive tape. The selection of a suitable pressure-sensitive adhesive can depend in particular on the substrate to be bonded and the conditions to which the bond to be produced is exposed.
The polymer base of the outer pressure-sensitive adhesive layer preferably consists of one or more polymers selected from the group consisting of poly (meth) acrylates, synthetic rubbers, natural rubbers, polyolefins and silicones. “Polymer base” is understood to mean that the polymer in question or the entirety of the polymers in question is contained therein to a total of at least 30% by weight, preferably a total of at least 50% by weight, based on the total weight of the pressure-sensitive adhesive layer.

According to the general understanding, “poly (meth) acrylates” are understood to mean polymers that are accessible by free-radical polymerization of acrylic and / or methacrylic monomers and, if appropriate, other copolymerizable monomers. According to the invention, the term “poly (meth) acrylate” encompasses both polymers based on acrylic acid and its derivatives and those based on acrylic acid and methacrylic acid and their derivatives as well as those based on methacrylic acid and its derivatives, the polymers always being acrylic acid esters, methacrylic acid esters or mixtures of acrylic and methacrylic acid esters. The poly (meth) acrylates of the outer pressure-sensitive adhesive layer preferably have a weight-average molar mass M _w of at most 2,000,000 g / mol.

(vgl. T.G. Fox, Bull. Am. Phys. Soc. 1 (1956) 123) ein TG-Wert für das Polymer von ≤ 25 °C ergibt. Ein solcher Wert ist besonders vorteilhaft für Haftklebemassen, die im Wesentlichen bei Raumtemperatur eingesetzt werden.The monomers of the poly (meth) acrylates of the outer pressure-sensitive adhesive layer and their quantitative composition are preferably selected such that, according to the so-called Fox equation (G1) $$\frac{1}{{\text{T}}_{\text{G}}}={\displaystyle \sum _{\text{n}}\frac{{\text{W.}}_{\text{n}}}{{\text{T}}_{\text{G}\text{, n}}}}$$

(cf. TG Fox, Bull. Am. Phys. Soc. 1 (1956) 123) gives a TG value for the polymer of ≤ 25 ° C. Such a value is particularly advantageous for PSAs which are used essentially at room temperature.

In equation G1, n represents the running number over the monomers used, w _n the mass fraction of the respective monomer n (% by weight) and T _{G, n} the respective glass transition temperature of the homopolymer from the respective monomers n in Kelvin.

1. a) Acrylsäureester und/oder Methacrylsäureester der Formel (F1) CH₂ = C(R^I)(COOR^II) (F1), worin R^I = H oder CH₃ und R^II ein Alkylrest mit 1 bis 30 C-Atomen, stärker bevorzugt mit 4 bis 14 C-Atomen, besonders bevorzugt mit 4 bis 9 C-Atomen, ist;
2. b) olefinisch ungesättigte Monomere mit funktionellen Gruppen, die eine Reaktivität mit Vernetzersubstanzen aufweisen;
3. c) optional weitere olefinisch ungesättigte Monomere, die mit den Monomeren (a) und (b) copolymerisierbar sind.

The outer pressure-sensitive adhesive layer preferably contains one or more poly (meth) acrylate (s) which can be attributed to the following monomer composition:

1. a) Acrylic acid esters and / or methacrylic acid esters of the formula (F1) CH ₂ = C (R ^I ) (COOR ^II ) (F1), where R ^I = H or CH ₃ and R ^{II is} an alkyl radical having 1 to 30 C atoms, more preferably 4 to 14 C atoms, particularly preferably 4 to 9 C atoms;
2. b) olefinically unsaturated monomers with functional groups which are reactive with crosslinking substances;
3. c) optionally further olefinically unsaturated monomers which are copolymerizable with the monomers (a) and (b).

Examples of monomers a) are methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate, n-butyl methacrylate, n-pentyl acrylate, n-hexyl acrylate, n-heptyl acrylate, n-octyl acrylate, n-octyl methacrylate, n-nonyl acrylate, lauryl acrylate, stearyl acrylate and behenyl acrylate their branched isomers, such as, for example, isobutyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, isooctyl acrylate, isooctyl methacrylate. R ^II particularly preferably represents a methyl, an n-butyl and a 2-ethylhexyl group, in particular an n-butyl and a 2-ethylhexyl group, or the monomers a) are selected from n-butyl acrylate and 2-ethylhexyl acrylate.

The monomers b) are preferably olefinically unsaturated monomers with functional groups which can react with epoxy groups. Particularly preferably, the monomers b) each contain at least one functional group selected from the group consisting of hydroxyl, carboxy, sulfonic acid and phosphonic acid groups, acid anhydride functions, epoxy groups and substituted or unsubstituted amino groups.
In particular, the monomers b) are 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, 2-hydroxyethyl acrylate, 3-hydroxyethyl acrylate, Hydroxyethyl methacrylate, 3-hydroxypropyl methacrylate, 6- Hydroxyhexyl methacrylate, allyl alcohol, glycidyl acrylate and glycidyl methacrylate. The monomers b) acrylic acid and / or methacrylic acid, in particular acrylic acid, are very particularly preferred.

In principle, all vinylically functionalized compounds which are copolymerizable with the monomers a) and the monomers b) are suitable as monomers c). The properties of the PSA of the invention can advantageously be regulated with the choice and amount of the monomers c).

The monomers c) are particularly preferably selected from the group consisting of methyl acrylate, ethyl acrylate, n-propyl acrylate, methyl methacrylate, ethyl methacrylate, benzyl acrylate, benzyl methacrylate, sec-butyl acrylate, tert-butyl acrylate, phenyl acrylate, phenyl methacrylate, isobornyl acrylate, isobornyl acrylate, tert-butyl phenyl acrylate, tert-butylaphenyl methacrylate, dodecyl methacrylate, isodecyl acrylate, lauryl acrylate, n-undecyl acrylate, stearyl acrylate, tridecyl acrylate, behenyl acrylate, cyclohexyl methacrylate, cyclopentyl methacrylate, phenoxyethylacrlylate, 2-butoxyethyl methacrylate, trimethyl acrylate, 3-acyl acyladoxy, 4-butoxyethyl methacrylate, 3, 3-amethylacrylate, 3,5-acyl acyladoxy, 3,3-butoxyethyl methacrylate-dimethyladoxy-acrylate, 3,3-butoxyethyl methacrylate, 3, 3, 3, 3, and 4-arylacryl. Cumyl phenyl methacrylate, cyanoethyl acrylate, cyanoethyl methacrylate, 4-biphenyl acrylate, 4-biphenyl methacrylate, 2-naphthyl acrylate, 2-naphthyl methacrylate, tetrahydrofurfuryl acrylate, diethylaminoethyl acrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, diethylaminoethyl methacrylate, diethylaminoethyl methacrylate, 3-methylamethyl methacrylate, 3-methylaminoethyl acrylate, dimethylamethyl methacrylate, 3-methoxyethyl methacrylate, 3-methoxyethyl methacrylate, 3-methoxyethyl methacrylate, 3-methoxyethyl methacrylate, 3-methoxyethyl methacrylate, 3-methylamethyl acrylate, dimethylaminoethyl acrylate, dimethylaminoethyl acrylate, 4-biphenyl methacrylate, 4-biphenyl methacrylate xybutylacrylat, Phenoxyethylacrlylat, phenoxyethyl methacrylate, 2-phenoxyethyl, Butyldiglykolmethacrylat, ethylene glycol acrylate, Ethylenglycolmonomethylacrylat, methoxy polyethylene glycol-350, polyethylene glycol methacrylate, methoxy-500, Propylenglycolmonomethacrylat, Butoxydiethylenglykolmethacrylat, ethoxytriethyleneglycol, Octafluoropentyl acrylate, octafluoropentyl methacrylate, 2,2,2-trifluoroethyl, 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, dimethylaminopropyl acrylamide, dimethylaminopropyl methacrylamide, N- (1-methyl-undecyl) acrylamide, N- (n-butoxymethyl) acrylamide, N- (butoxymethyl) methacrylamide, N- (ethoxymethyl) acrylamide, N- (n-octadecyl) acrylamide,
N, N-dialkyl-substituted amides, in particular N, N-dimethylacrylamide, N, N-dimethyl methacrylamide, N-benzylacrylamide, N-isopropylacrylamide, N-tert-butylacrylamide, N-tert-octylacrylamide, N-methylolacrylamide, N-methylol methacrylamide; further acrylonitrile, methacrylonitrile; Vinyl ethers such as vinyl methyl ether, ethyl vinyl ether, vinyl isobutyl ether; Vinyl esters such as vinyl acetate; Vinyl chloride, vinyl halides, vinylidene halides, vinyl pyridine, 4-vinyl pyridine, N-vinyl phthalimide, N-vinyl lactam, N-vinyl pyrrolidone, styrene, α- and p-methylstyrene, α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, 3 , 4-dimethoxystyrene, 2-polystyrene ethyl methacrylate (molecular weight Mw from 4000 to 13000 g / mol) and poly (methyl methacrylate) ethyl methacrylate (Mw from 2000 to 8000 g / mol). In particular, the monomer c) is methyl acrylate.

The monomers c) can advantageously also be chosen in such a way that they contain functional groups which support radiation-chemical crosslinking (for example by electron beams or UV). Suitable copolymerizable photoinitiators are e.g. Benzoin acrylate and acrylate-functionalized benzophenone derivatives. Monomers that support crosslinking by electron irradiation are e.g. Tetrahydrofurfuryl acrylate, N-tert-butyl acrylamide and allyl acrylate.

If the outer pressure-sensitive adhesive layer contains a plurality of poly (meth) acrylates, it is particularly preferred to attribute all of the poly (meth) acrylates of the outer pressure-sensitive adhesive layer to the monomer composition described above. In particular, all the poly (meth) acrylates of the outer pressure-sensitive adhesive layer are due to a monomer composition consisting of acrylic acid, n-butyl acrylate and 2-ethylhexyl acrylate.

The poly (meth) acrylate or all poly (meth) acrylates of the outer pressure-sensitive adhesive layer are very particularly preferably due to the following monomer composition: Acrylic acid 1 - 10% by weight 2-ethylhexyl acrylate 30-60% by weight, n-butyl acrylate 30-60% by weight,
the proportions of the monomers adding up to 100% by weight.

The poly (meth) acrylates can be prepared by radical polymerization of the monomers in solvents, in particular in solvents with a boiling range from 50 to 150 ° C, preferably from 60 to 120 ° C, using the usual amounts of polymerization initiators, which are generally at 0, 01 to 5, in particular 0.1 to 2% by weight (based on the total weight of the monomers) are produced.
In principle, all customary initiators familiar to the person skilled in the art are suitable. Examples of free 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, benzpinacol. In a very preferred procedure, 2,2'-azobis (2-methylbutyronitrile) or 2,2'-azobis (2-methylpropionitrile) (2,2'-azobisisobutyronitrile; AIBN) is used as the radical initiator.
Solvents for the preparation of the poly (meth) acrylates are alcohols such as methanol, ethanol, n- and iso-propanol, n- and iso-butanol, preferably isopropanol and / or isobutanol, and hydrocarbons such as toluene and, in particular, gasolines with a boiling point of 60 up to 120 ° C in question. Furthermore, ketones such as preferably acetone, methyl ethyl ketone, methyl isobutyl ketone and esters such as ethyl acetate and mixtures of solvents of the type mentioned can be used, mixtures containing isopropanol, in particular in amounts of 0.5 to 15% by weight, preferably 3 to 10% by weight. -%, based on the solvent mixture used, are preferred.

The weight-average molecular weights M _{w of} the polyacrylates are preferably 20,000 to 2,000,000 g / mol; very preferably 100,000 to 1,500,000 g / mol, extremely preferably 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.

The details of the number-average molar mass M _n and the weight-average molar mass M _w in this document relate to the known determination by gel permeation chromatography (GPC). The determination is carried out on 100 µl clear-filtered sample (sample concentration 4 g / l). Tetrahydrofuran with 0.1% by volume of trifluoroacetic acid is used as the eluent. The measurement takes place at 25 ° C.
A column type PSS-SDV, 5 µm, 10 ³ Å, 8.0 mm * 50 mm (details here and below in the order: type, particle size, porosity, inner diameter * length; 1 Å = 10-10 m) used. A combination of PSS-SDV columns, 5 µm, 10 ³ Å, 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. In the case of poly (meth) acrylates, calibration is carried out against PMMA standards (polymethyl methacrylate calibration) and otherwise (resins, elastomers) against PS standards (polystyrene calibration).

• - die Blöcke A unabhängig voneinander für ein Polymer, gebildet durch Polymerisation mindestens eines Vinylaromaten;
• - die Blöcke B unabhängig voneinander für ein Polymer, gebildet durch Polymerisation von konjugierten Dienen mit 4 bis 18 C-Atomen und/oder Isobutylen, oder für ein teil- oder vollhydriertes Derivat eines solchen Polymers;
• - X für den Rest eines Kopplungsreagenzes oder Initiators und
• - n für eine ganze Zahl ≥ 2 stehen.

The polymer base of the outer pressure-sensitive adhesive layer of the adhesive tape of the invention can, as described, comprise a synthetic rubber. One or more synthetic rubbers can be contained in the outer pressure-sensitive adhesive layer.
The synthetic rubber is preferably a block copolymer with a structure AB, ABA, (AB) _n , (AB) _n X or (ABA) _n X,
wherein

• the blocks A independently of one another for a polymer formed by polymerizing at least one vinyl aromatic;
• the blocks B, independently of one another, for a polymer formed by the polymerization of conjugated dienes with 4 to 18 carbon atoms and / or isobutylene, or for a partially or fully hydrogenated derivative of such a polymer;
• - X for the remainder of a coupling reagent or initiator and
• - n stand for an integer ≥ 2.

If a plurality of synthetic rubbers are contained in the outer pressure-sensitive adhesive layer, all synthetic rubbers of this pressure-sensitive adhesive layer are preferably block copolymers with a structure as set out above. The outer pressure-sensitive adhesive layer can thus also contain mixtures of different block copolymers with a structure as above.

The preferred synthetic rubbers, which are also referred to as vinyl aromatic block copolymers, thus comprise one or more rubber-like blocks B (soft blocks) and one or more glass-like blocks A (hard blocks). The synthetic rubber is particularly preferably a block copolymer with a structure AB, ABA, (AB) ₃ X or (AB) ₄ X, where A, B and X are as defined above. If several synthetic rubbers are contained in the outer pressure-sensitive adhesive layer, all synthetic rubbers are very particularly preferred block copolymers with a structure AB, ABA, (AB) ₃ X or (AB) ₄ X, where A, B and X are as defined above. In particular, the synthetic rubber is a Mixture of block copolymers with a structure AB, ABA, (AB) 3X or (AB) 4X, which preferably contains at least diblock copolymers AB and / or triblock copolymers ABA.

The block A is in particular a vitreous block with a preferred glass transition temperature (Tg, DSC) which is above room temperature. The Tg of the glass-like block is particularly preferably at least 40 ° C, in particular at least 60 ° C, very particularly preferably at least 80 ° C and extremely preferably at least 100 ° C. The proportion of vinyl aromatic blocks A in the total of the block copolymers is preferably 10 to 40% by weight, particularly preferably 20 to 33% by weight. Vinyl aromatics for building up the A block preferably include styrene and α-methylstyrene. The block A can thus be present as a homo- or copolymer. Block A is particularly preferably a polystyrene.

The block B is in particular a rubber-like block or soft block with a preferred Tg of less than room temperature. The Tg of the soft block is particularly preferably less than 0 ° C, in particular less than -10 ° C, for example less than -40 ° C and very particularly preferably less than -60 ° C.
Preferred conjugated dienes as monomers for the soft block B are in particular selected from the group consisting of butadiene, isoprene, ethylbutadiene, phenylbutadiene, piperylene, pentadiene, hexadiene, ethylhexadiene, dimethylbutadiene and the Farnese isomers and any mixtures of these monomers. Block B can also be present as a homopolymer or as a copolymer.
The conjugated dienes are particularly preferred as monomers for the soft block B selected from butadiene and isoprene. For example, the soft block B is a polyisoprene, a polybutadiene or a partially or fully hydrogenated derivative of one of these two polymers, such as in particular polybutylenebutadiene; or a polymer made from a mixture of butadiene and isoprene. Block B is very particularly preferably a polybutadiene.

In one embodiment, the outer pressure-sensitive adhesive layer comprises a poly (meth) acrylate synthetic rubber blend. This poly (meth) acrylate synthetic rubber blend preferably contains at least one poly (meth) acrylate and at least one synthetic rubber as described above.
In the poly (meth) acrylate synthetic rubber blend, the synthetic rubber is preferably present in dispersed form in the poly (meth) acrylate. Accordingly, poly (meth) acrylate and synthetic rubber are preferably each homogeneous phase. The poly (meth) acrylates and synthetic rubbers contained in the blend are preferably selected in such a way that they cannot be mixed with one another to the point of homogeneity at 23 ° C. In this case, the outer pressure-sensitive adhesive layer is therefore present at least microscopically and at least at room temperature in at least two-phase morphology. Poly (meth) acrylate (s) and synthetic rubber (s) are particularly preferably not homogeneously miscible with one another in a temperature range from 0 ° C. to 50 ° C., in particular from -30 ° C. to 80 ° C., so that the outer pressure-sensitive adhesive layer therein Temperature ranges is present at least microscopically in at least two phases.

Components are defined as “not homogeneously miscible with one another” if, even after intimate mixing, the formation of at least two stable phases can be physically and / or chemically demonstrated at least microscopically, one phase rich in one component and the second phase rich in the other component is. The presence of negligibly small amounts of one component in the other, which does not prevent the formation of multiphase, is regarded as negligible. Thus, small amounts of synthetic rubber can be present in the poly (meth) acrylate phase and / or small amounts of poly (meth) acrylate component can be present in the synthetic rubber phase, provided that the amounts involved are not substantial, which influence the phase separation.
The phase separation can in particular be implemented in such a way that discrete areas (“domains”) that are rich in synthetic rubber - that is, essentially formed from synthetic rubber - are in a continuous matrix that is rich in poly (meth) acrylate - that is, essentially is formed from poly (meth) acrylate - are present. 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 mutually independent glass transition temperatures in dynamic differential calorimetry (DDK, DSC) or dynamic-mechanical analysis (DMA). According to the invention, phase separation is present if it can be clearly demonstrated by at least one of the analytical methods.
Within the domains rich in synthetic rubber, there can also be additional multiphase as a fine structure, with the A blocks forming one phase and the B blocks forming a second phase.

The outer pressure-sensitive adhesive layer preferably contains 25-60% by weight of at least one poly (meth) acrylate and 5-35% by weight, based in each case on the total weight of the outer pressure-sensitive adhesive layer, of at least one synthetic rubber. This outer pressure-sensitive adhesive layer likewise preferably contains at least one bond strength-enhancing resin, in particular a terpene-phenolic resin; are adhesive strength-enhancing resins in this outer pressure-sensitive adhesive layer, preferably a total of 15-55% by weight, based on the total weight of the pressure-sensitive adhesive layer.

In one embodiment, the polymer base of the outer pressure-sensitive adhesive layer comprises natural rubber. Natural rubber is an elastic polymer that is based on plant products such as milk juice (latex) in particular. As an essential raw material, natural rubber is processed into natural rubber adhesives.
In one embodiment, the outer pressure-sensitive adhesive layer contains a mixture which contains natural rubber and tackifier resins, the proportion of tackifier resins being from 40 to 250 phr, preferably from 100 to 210 phr, in particular from 70 to 130 phr. As a result, particularly good adhesion and cohesion values can typically be achieved at the same time. The indication “phr” means “parts by weight of the component in question based on 100 parts by weight of all rubber-polymer components of the outer pressure-sensitive adhesive layer (solid / solid)”, that is to say on the natural rubber component and thus, for example, without taking into account the (polymeric) adhesive resins.

Liquid rubbers are distinguished from solid rubbers in that they have a softening point T _E of less than 40.degree. Solid rubbers are thus characterized in that they do not have a softening point T _E of less than 40 ° C. The natural rubber contained in the outer pressure-sensitive adhesive layer is preferably at least 75% by weight solid natural rubber, more preferably at least 90% by weight. In particular, the natural rubber contained in the outer pressure-sensitive adhesive layer is exclusively solid natural rubber.

The natural rubber or natural rubbers can basically be selected from all available qualities such as crepe, RSS, ADS, TSR or CV types, depending on the required purity and viscosity level.
In order to improve the processability, thermoplastic elastomers, such as synthetic rubbers, are preferably added to the natural rubber in a proportion of up to 5% by weight. The particularly compatible styrene-isoprene-styrene (SIS) and styrene-butadiene-styrene (SBS) types should be mentioned here as representatives.

The adhesive resin is preferably selected from hydrogenated and non-hydrogenated hydrocarbon resins and polyterpene resins. Particularly suitable are, inter alia, hydrogenated polymers of dicyclopentadiene (for example Escorez 5300 series; Exxon Chemicals), hydrogenated polymers of preferably C8 and C9 aromatics (for example Regalite and Regalrez series; Eastman Inc. or Arkon P series; Arakawa). These can flow out of pure aromatic streams by hydrogenation of polymers or else they can be based on mixtures of different aromatics by hydrogenation of polymers. Partially hydrogenated polymers of C8 and C9 aromatics (for example Regalite and Regalrez series; Eastman Inc. or Arkon M; Arakawa), hydrogenated polyterpene resins (for example Clearon M; Yasuhara), hydrogenated C5 / C9 polymers (for example ECR-373; Exxon Chemicals) and aromatic-modified, selectively hydrogenated dicyclopentadiene derivatives (for example Escorez 5600 series; Exxon Chemicals). The aforementioned adhesive resins can be used either alone or in a mixture.
Other non-hydrogenated hydrocarbon resins or non-hydrogenated analogs of the hydrogenated resins described above can also be used.

Furthermore, rosin-based resins (for example Foral, Foralyn) can be used. These include natural rosin, polymerized rosin, partially hydrogenated rosin, fully hydrogenated rosin, esterified products of these rosins such as glycerol esters, pentaerythritol esters, ethylene glycol esters and methyl esters, and rosin derivatives such as disproportionation rosin, rosin modified with fumaric acid and lime modified rosin.
The adhesive resin is very particularly preferably a terpene-phenolic resin, in particular exclusively one or more terpene-phenolic resins, without further types of resin being used.

To stabilize a natural rubber-based external pressure-sensitive adhesive layer, preference is given to adding primary antioxidants such as sterically hindered phenols, secondary antioxidants such as phosphites or thioethers and / or carbon radical scavengers. Such an outer pressure-sensitive adhesive layer can furthermore contain additives such as fillers, dyes or anti-aging agents (antiozonants, light stabilizers, etc.) for setting optical and technical adhesive properties.

In one embodiment, the polymer base of the outer pressure-sensitive adhesive layer comprises at least one polyolefin, in particular an ethylene polymer. The person skilled in the art did not consider ethylene polymers to be suitable for high-quality PSAs. Nevertheless, ethylene polymers with a density between 0.86 and 0, 89 g / cm ³ , preferably between 0.86 and 0.88 g / cm ³ , particularly preferably between 0.86 and 0.87 g / cm ³ , and a crystallite melting point of at least 105 ° C., preferably at least 115 ° C., pressure-sensitive adhesives can be produced with high bond strength and shear strength as well as good tack, which are particularly suitable for coating porous adhesive tape backings.

The ethylene polymer preferably has a melt index of less than 6 g / 10 min, particularly preferably less than 1.5 g / 10 min. The flexural modulus of the ethylene polymer is preferably less than 26 MPa, particularly preferably less than 17 MPa.
The ethylene polymer preferably contains a C3 to C10 olefin, in particular 1-octene, as a comonomer. The ethylene polymer preferably has a structure of crystalline polyethylene blocks and substantially amorphous blocks of ethylene and a C3 to C10 olefin.
The density of the ethylene polymer is determined according to ISO 1183 and expressed in g / cm ³ . The melt index is tested according to ISO 1133 at 190 ° C. and 2.16 kg and expressed in g / 10 min.

The crystallite melting point (Tcr) is determined using DSC at a heating rate of 10 ° C./min according to ISO 3146. The flexural modulus is to be determined according to ASTM D 790 (secant modulus at 2% elongation).

The ethylene polymer can be combined with the elastomers known from rubber compounds, such as natural rubber or synthetic rubbers. Unsaturated elastomers such as natural rubber, SBR, NBR or unsaturated styrene block copolymers are preferably used only in small amounts or, particularly preferably, not at all. Synthetic rubbers saturated in the main chain, such as polyisobutylene, butyl rubber, EPM, HNBR, EPDM or hydrogenated styrene block copolymers, are preferred for the case of a desired modification.

It turned out that the tack and bond strength of a polyethylene-based adhesive, in contrast to conventional rubber compounds, are heavily dependent on the polydispersity of the resin. The polydispersity is the ratio of weight average to number average of the molar mass distribution and can be determined by gel permeation chromatography. The adhesive resin used is therefore those with a polydispersity of less than 2.1, preferably less than 1.8, particularly preferably less than 1.6. The highest tack can be achieved with resins with a polydispersity of 1.0 to 1.4.

The adhesive resin for an outer pressure-sensitive adhesive layer containing an ethylene polymer is preferably a resin based on rosin (for example balsam resin) or rosin derivatives (for example disproportionated, dimerized or esterified rosin), preferably partially or fully hydrogenated. Of all adhesive resins, these have the highest tack (stickiness, grip). Terpene-phenolic resins are also suitable; they lead to only moderate tack, but very good shear strength and aging resistance.
Hydrocarbon resins are also preferred, for example aromatic resins such as coumarone-indene resins or resins based on styrene or α-methylstyrene or cycloaliphatic hydrocarbon resins from the polymerization of C5 monomers such as piperylene or from the C5 or C9 fraction of crackers, or Terpenes such as β-pinene or δ-limonene or combinations thereof, preferably partially or fully hydrogenated, and hydrocarbon resins obtained by hydrogenation of aromatic hydrocarbon resins or cyclopentadiene polymers.

The amount of adhesive resin is preferably 130 to 350 phr, particularly preferably 200 to 240 phr (phr means parts by weight based on 100 parts by weight of rubber, that is to say here ethylene polymer).

The PSA containing an ethylene polymer preferably also contains a liquid plasticizer such as aliphatic (paraffinic or branched), cycloaliphatic (naphthenic) and aromatic mineral oils, esters of phthalic, trimellitic, citric or adipic acid, wool wax, liquid rubbers (for example low molecular weight nitrile -, butadiene or polyisoprene rubbers), liquid polymers made from isobutene homopolymer and / or isobutene-butene copolymer, liquid and soft resins with a melting point below 40 ° C based on the raw materials of adhesive resins, in particular the classes of adhesive resin listed above. Particularly preferred plasticizers are liquid polymers composed of isobutene and / or butene and esters of phthalic, trimellitic, citric or adipic acid, in particular their esters of branched octanols and nonanols.

Instead of a liquid plasticizer, a very soft and hardly crystalline ethylene polymer can also be used. This is preferably a copolymer of ethylene and butene- (1), hexene- (1) or Octene (1), or a terpolymer of ethylene, propylene and butene (1), hexene (1) or octene (1), the flexural modulus preferably being below 10 MPa and the crystallite melting point preferably below 50 ° C. Further preferred ethylene polymers are oil-free EPM or EPDM, i.e. copolymers or terpolymers of ethylene and propylene and optionally a diene such as ethylidenenorbornene, preferably with an ethylene content of 40 to 70% by weight, a Mooney viscosity (conditions 1 + 4, 125 ° C) below 50 and / or a density below 0.88 g / cm ³ , particularly preferably below 0.87 g / cm ³ . Since such ethylene polymers are indeed very soft - compared to a liquid plasticizer - the amount should be very high in relation to the ethylene polymer according to the invention, that is to say well over 100 phr.

To optimize the properties, the pressure-sensitive adhesive comprising an ethylene polymer can be mixed with further additives such as fillers, flame retardants, pigments, UV absorbers, antiozonants, metal deactivators, light stabilizers, flame and / or photoinitiators, crosslinking agents or crosslinking promoters. Suitable fillers and pigments are, for example, carbon black, titanium dioxide, calcium carbonate, zinc carbonate, zinc oxide, silicates or silicic acid.
Such PSAs can be produced and processed from solution or from the melt. Preferred manufacturing and processing methods are carried out from the melt.

For the latter case, suitable manufacturing processes include both batch processes and continuous processes. Particularly preferred is the continuous production of the pressure-sensitive adhesive with the aid of an extruder and subsequent coating directly onto the substrate to be coated at a correspondingly high temperature of the adhesive. The preferred coating methods are extrusion coating with slot dies and calender coating.
The mass application (coating thickness) is preferably between 30 and 120 g / m ² , particularly preferably between 50 and 70 g / m ² .

In a further embodiment, the polymer base of the outer pressure-sensitive adhesive layer comprises at least one silicone. According to the general understanding, a "silicone" is a synthetic polymer compound in which silicon atoms are linked in a chain-like or network-like manner via oxygen atoms and the remaining valences of the silicon are linked by hydrocarbon residues (mostly methyl groups, more rarely ethyl groups, Propyl groups, phenyl groups, etc.) are saturated. Systematically, silicones are generally referred to as organopolysiloxanes. Usually the organopolysiloxanes are crosslinked, i. At least parts of the silicone macromolecules are linked to one another through the formation of bridge bonds between them. This presupposes the presence of an initially crosslinkable silicone system from which the crosslinked silicone system is obtained by any kind of initiation of the crosslinking reaction. The crosslinkable silicone systems include, for example, mixtures of crosslinking catalysts and so-called thermally curable, condensation or addition crosslinking polysiloxanes.

• - ein alkenyliertes Polydiorganosiloxan (insbesondere lineare Polymere mit endständigen Alkenylgruppen),

ein Polyorganowasserstoffsiloxan-Vernetzungsmittel sowie
einen Hydrosilylierungskatalysator.
Als Katalysatoren für additionsvernetzende Silikonsysteme (Hydrosilylierungs-katalysatoren) haben sich beispielsweise Platin oder Platinverbindungen, wie zum Beispiel der Karstedt-Katalysator (eine Pt(0)-Komplexverbindung) durchgesetzt.In one embodiment, the pressure-sensitive adhesive contains a silicone which can be traced back to an addition-crosslinkable silicone system. Silicone systems based on addition curing can be hardened by hydrosilylation. They usually include the following components:

• - an alkenylated polydiorganosiloxane (especially linear polymers with terminal alkenyl groups),

a polyorganohydrogensiloxane crosslinking agent and
a hydrosilation catalyst.
As catalysts for addition-crosslinking silicone systems (hydrosilylation catalysts), for example, platinum or platinum compounds, such as the Karstedt catalyst (a Pt (0) complex compound), have become established.

In a further embodiment, the pressure-sensitive adhesive contains a silicone which can be traced back to a free-radically crosslinkable silicone system. This is usually an organopolysiloxane that has alkyl substituents in the chain and has no vinyl functions. These organopolysiloxanes are frequently OH-terminated. The radical crosslinking takes place preferably with peroxides, in particular with BPO or chlorinated BPOs, and proceeds via the alkyl groups. The alkyl groups are preferably methyl groups.

In a further embodiment, the pressure-sensitive adhesive contains a silicone which can be traced back to a silicone system which can be crosslinked by radiation. For example, photoactive catalysts, so-called photoinitiators, in combination with UV-curable, cationically crosslinking siloxanes based on epoxy and / or vinyl ether or UV-curable, free-radical crosslinking siloxanes such as acrylate-modified siloxanes can be used as such. Likewise, the use of electron beam curable Silicone acrylates possible. Corresponding systems can also contain other additives such as stabilizers or flow control agents.

The PSA containing a silicone preferably further comprises at least one silicone resin. The at least one silicone resin is preferably selected from MQ, MTQ, TQ, MT and MDT resins. Mixtures of different silicone resins can also be contained in the pressure-sensitive adhesive, in particular mixtures of the aforementioned silicone resins. The at least one silicone resin is particularly preferably an MQ resin. MQ silicone resins are readily available and are characterized by very good stability. If several silicone resins are contained in the composition according to the invention, all silicone resins of the pressure-sensitive adhesive MQ-Harze are very particularly preferred.
The weight-average molar mass Mw of the at least one silicone resin is preferably 500 to <30,000 g / mol. The resin can contain alkenyl groups.

The adhesive tape according to the invention further comprises a microporous polyurethane membrane. A “microporous membrane” is understood to mean a flat material with a cell structure and high cell density. The microporous membrane can have an open, a closed or also a mixed cell structure, preferably it has a closed-cell structure. The microporous membrane of the adhesive tape according to the invention particularly preferably has a cell density, determined using imaging methods such as scanning electron microscopy (SEM recordings) or computed tomography and counting with suitable software, of at least 10 ⁶ cells / cm ³ and an average cell diameter, also determined using imaging methods such as scanning electron microscopy (SEM recordings) or computed tomography and, if necessary, evaluation with suitable software, of a maximum of 20 µm, in particular a maximum of 12 µm, very particularly preferably a maximum of 8 µm. Such a preferred microporous membrane can also be referred to as a microcellular plastic foam.

The thickness of the microporous membrane of the adhesive tape according to the invention is preferably 10 to 70 μm, more preferably 11 to 60 μm, in particular 12 to 55 μm.

The microporous membrane of the adhesive tape according to the invention is preferably produced by a wet coagulation process. First of all, water-soluble salts are introduced into a coating solution - in the present case a polyurethane coating solution. The microporosity is then achieved by washing out these salts by treating the applied coating with water. With certain additives in the coating solution, special additional effects can be achieved in the microporous membrane. For example, the pores can be made water-repellent by adding water-repellent substances and nonionic surfactants. This can be further intensified by treating the coated membrane with water-repellent substances. For polyurethane membranes, it was possible to achieve higher water vapor permeability and water resistance by adding approx. 1% by weight of an inorganic filler, for example silica or magnesium oxide with a particle size of <0.1 μm, to the polyurethane resin.
With wet coagulation processes, ultra-fine pores with diameters of <1 µm can be achieved.

The micropores of the microporous polyurethane membrane preferably have no orientation. Conventional foamed carrier materials with a small layer thickness are often produced by means of continuous processes at high web speeds. As a result, their foam cells are usually strongly oriented. The wet coagulation process for producing the microporous polyurethane membrane of the adhesive tape according to the invention, on the other hand, enables extremely thin layers to be obtained without orienting the cells.
Likewise preferably there is no continuous channel between the top and bottom of the membrane within the cell network of the microporous membrane.

An adhesive tape according to the invention preferably has a total thickness of 50 to 170 μm, particularly preferably 80 to 160 μm.
An inventive adhesive tape can (precisely) have an outer pressure-sensitive adhesive layer; it preferably has an outer pressure-sensitive adhesive layer on both sides. The two outer pressure-sensitive adhesive layers can be identical or different; they are preferably identical. A particularly preferred adhesive tape has two identical outer pressure-sensitive adhesive layers, the polymer base of which consists of a blend of a poly (meth) acrylate and a synthetic rubber, in particular a styrene-butadiene block copolymer.

In one embodiment, the outer pressure-sensitive adhesive layer or the outer pressure-sensitive adhesive layers of the adhesive tape of the invention are foamed. Under a "foamed Pressure-sensitive adhesive layer ”is understood to be a pressure-sensitive adhesive layer which comprises a pressure-sensitive adhesive matrix material and a plurality of gas-filled cavities, so that the density of this pressure-sensitive adhesive is reduced compared to the mere matrix material without cavities.

In principle, the matrix material of the pressure-sensitive adhesive layer can be foamed in any desired manner.
For example, the pressure-sensitive adhesive can be foamed by means of a propellant gas introduced or released in it. CO ₂ or N ₂ , for example, can be used as the propellant gas introduced, possibly also as a supercritical fluid.
In order to release a propellant gas, the pressure-sensitive adhesive may alternatively be admixed with a propellant which decomposes thermally with the release of gas, for example NaHCO ₃ , the free acids or derivatives of citric acid, ascorbic acid, fumaric acid, gluconic acid or lactic acid or exothermic propellants such as azodicarbonamide.
Mechanical foaming (frothing) is also possible.
In one embodiment, the foamed pressure-sensitive adhesive layer contains at least partially expanded hollow microspheres. This is understood to mean at least partially expanded microspheres which in their basic state are elastic and expandable and have a thermoplastic polymer shell. These spheres are - in their basic state - filled with low-boiling liquids or liquefied gas. Polyacrylonitrile, PVDC, PVC or polyacrylates in particular are used as the shell material. Hydrocarbons of the lower alkanes, for example isobutane or isopentane, which are enclosed as a liquefied gas under pressure in the polymer shell, are particularly common as the low-boiling liquid. The term “microballoons” is also used for such microspheres.

The outer polymer shell softens when the microballoons are exposed to heat. At the same time, the liquid propellant in the envelope changes into its gaseous state. The microballoons expand irreversibly and expand three-dimensionally. The expansion is finished when the internal and external pressures equalize. Since the polymer shell is retained, a closed-cell foam is achieved.

A large number of types of microballoons are commercially available, which differ essentially in terms of their size (6 to 45 μm diameter in the unexpanded state) and the starting temperatures (75 to 220 ° C.) required for expansion. Unexpanded types of microballoons are also available as aqueous dispersions with a solids or microballoon content of approx. 40 to 45% by weight, and also as polymer-bound microballoons (masterbatches), for example in ethylene vinyl acetate with a microballoon concentration of approx. 65% by weight. Both the microballoon dispersions and the masterbatches, like the unexpanded microballoons, are suitable as such for producing the foamed pressure-sensitive adhesive.

A foamed outer pressure-sensitive adhesive layer can also be produced with so-called pre-expanded hollow microspheres. In this group, expansion takes place before it is mixed into the polymer matrix.

According to the invention, the foamed pressure-sensitive adhesive layer preferably contains at least partially expanded microspheres, irrespective of their production route and of the starting form of the hollow microspheres used. According to the invention, the term “at least partially expanded hollow microspheres” is understood to mean that the hollow microspheres are expanded at least to such an extent that the pressure-sensitive adhesive is reduced in density to a technically meaningful extent compared to the same adhesive with the unexpanded hollow microspheres. This means that the microballoons do not necessarily have to be completely expanded. The “at least partially expanded hollow microspheres” are preferably each expanded to at least twice their maximum expansion in the unexpanded state.
The expression “at least partially expanded” relates to the state of expansion of the individual hollow microspheres and is not intended to express that only some of the hollow microspheres in question need to be (partially) expanded. So if “at least partially expanded hollow microspheres” and unexpanded hollow microspheres are contained in the pressure-sensitive adhesive, this means that unexpanded (not expanded at all, including not partially expanded) hollow microspheres do not belong to the “at least partially expanded hollow microspheres”.

Another object of the invention is the use of a microporous polyurethane membrane as a carrier layer in an adhesive tape.

Adhesive tapes according to the invention are distinguished by a very good shock absorption capacity. It was found that adhesive tapes according to the invention, with similar product thicknesses, achieve shock absorption at the level of conventional adhesive tapes with PE foam-based carriers and well above the level of conventional adhesive tapes with PET film carriers.
It is also possible to make adhesive tapes according to the invention very thin. The product design of PE foam carrier-based adhesive tapes is currently characterized by a lower limit for the carrier layer alone of approx. 80 µm; for mechanically foamed, microcellular PU carriers this is approx. 100 µm. Adhesive tapes according to the invention allow total thicknesses of less than 100 μm.

The invention also relates to the use of an adhesive tape according to the invention for producing bonds in electronic devices or as a damping layer in electronic devices. For example, an adhesive tape according to the invention in one embodiment as a single-sided adhesive tape can in itself be a functional module, e.g. a damper for vibrations, knocks or noise. Electronic devices within the scope of the use according to the invention are, for example, handheld electronic devices, wearable electronic devices or car infotainment systems; also displays or display elements, CPUs, digitizers, batteries or accumulators, cameras, microphones, loudspeakers or frame elements.

Examples

Measurement methods

thickness

Thickness measurements of individual layers and the adhesive tapes were made with the precision thickness measuring device Mod. 2000 F, which has a circular probe with a diameter of 10 mm (flat). The measuring force is 4 N. The value is read 1 s after the load. If fluctuations in thickness are found, the mean value of measurements is given at at least three representative points, that is to say in particular not measured at kinks, folds, specks and the like.

Air permeability

A square, frame-shaped sample was cut out of the adhesive tape to be examined (external dimensions 33 mm × 33 mm; web width 2.0 mm; internal dimensions (window cutout) 29 mm × 29 mm). This sample was 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). A PC window of 35 mm × 35 mm was stuck on the other side of the double-sided adhesive tape. The PC frame, adhesive tape frame and PC window were glued in such a way that the geometric centers and the diagonals were each superimposed (corner-to-corner). The bond area was 248 mm ² . The bond was pressed with 248 N for 5 s and stored conditioned for 24 hours at 23 ° C / 50% relative humidity.

The composite formed in this way was placed in the measuring chamber of an Air Leakage Tester from DMC; it was hermetically sealed from above by the PC window and from below by the device, so that air could only flow through the adhesive tape in the x-y direction. An air pressure of 100 kPa was applied for 60 s and the pressure drop was measured (information on the pressure drop in%).

Water permeability

A square, frame-shaped sample was cut out of the adhesive tape to be examined (external dimensions 33 mm × 33 mm; web width 2.0 mm; internal dimensions (window cutout) 29 mm × 29 mm). This sample was glued to a polycarbonate (PC) window (external dimensions 45 mm × 45 mm; thickness 3 mm). Another PC window of 45 mm × 45 mm was glued to the other side of the double-sided tape. The PC window, adhesive tape frame and PC window were glued in such a way that the geometric centers and the diagonals were each superimposed (corner-to-corner). The bond area was 248 mm ² . The bond was pressed with 6 kg for 5 s and stored at 23 ° C. for 45 s. KMnO _{4 was} brought into the central area of the resulting network.

The composite formed in this way was placed on the bottom of a cylinder filled with water (water column of 1 m). The composite was sealed watertight from above and below by the PC window; So water could only penetrate through the adhesive tape in the xy direction into the central area of the composite. After 30 minutes of storage under water, the composite was removed and checked for discoloration of the KMnO4 examined. A discoloration indicates water permeability of the adhesive tape, no discoloration indicates impermeability to water (result “water permeable yes / no”).

Impact strength (z-direction)

A square, frame-shaped sample was cut out of the adhesive tape to be examined (external dimensions 33 mm × 33 mm; web width 2.0 mm; internal dimensions (window cutout) 29 mm × 29 mm). This sample was 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). A PC window of 35 mm × 35 mm was stuck on the other side of the double-sided adhesive tape. The PC frame, adhesive tape frame and PC window were glued in such a way that the geometric centers and the diagonals were each superimposed (corner-to-corner). The bond area was 248 mm ² . The bond was pressed with 248 N for 5 s and stored conditioned for 24 hours at 23 ° C / 50% relative humidity.
Immediately after storage, the adhesive composite of PC frame, adhesive tape and PC window with the protruding edges of the PC frame was clamped in a sample holder in such a way that the composite was aligned horizontally and the PC window was below the frame. The sample holder was then placed centrically in the intended receptacle of a "DuPont Impact Tester". The 190 g impact head was used in such a way that the circular impact geometry with a diameter of 20 mm was centered and flush on the window side of the PC window.

A weight of 150 g, guided on two guide rods, was 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 was increased in 5 cm steps until the impact energy destroyed the specimen by the impact load and the PC window detached from the PC frame.

In order to be able to compare tests with different samples, the energy was calculated as follows: $$\text{E.}\left[\text{J}\right]=\text{height}\left[\text{m}\right]*\text{mass weight}\left[\text{kg}\right]*9.81{\text{m / s}}^2.$$

Five samples per product were tested and the average energy value was given as an index for the impact strength.

Bond strength steel

The bond strength was determined in a test climate of 23 ° C. +/- 1 ° C. temperature and 50% +/- 5% rel. Humidity. The samples were cut to a width of 20 mm and glued onto a steel plate (SUS). The steel plate was cleaned and conditioned before the measurement. For this purpose, the plate was first wiped with solvent and then left in the air for 5 minutes so that the solvent could evaporate. The side of the adhesive tape facing away from the test substrate was then covered with 75 μm thick, etched PET film, which prevented the sample from stretching during the measurement. The test sample was then rolled onto the substrate. For this purpose, the tape was rolled back and forth five times with a 4 kg roller at a winding speed of 10 m / min. 1 min or 14 days after rolling, the plate was pushed into a special holder which enables the sample to be peeled off at a certain angle (indicated in the test results). The bond strength was measured using a Zwick tensile testing machine. The measurement results are given in N / cm and are averaged from five individual measurements.

Manufacture of adhesive tapes

A 300 L reactor conventional for radical polymerizations was filled with 5 kg of acrylic acid, 49.5 kg of 2-ethylhexyl acrylate (EHA) and 49.5 kg of n-butyl acrylate and 72.4 kg of gasoline / acetone (70:30). After nitrogen gas had been passed through for 45 minutes with stirring, the reactor was heated to 58 ° C. and 50 g of Vazo® 67 were added. The jacket temperature was then set to 75 ° C. and the reaction was carried out constantly at this external temperature. After a reaction time of 1 hour, another 50 g of Vazo® 67 were added. After 3 h, the mixture was diluted with 20 kg petrol / acetone (70:30) and after 6 h with 10.0 kg petrol / acetone (70:30). To reduce the residual initiators, 0.15 kg of Perkadox® 16 were added after 5.5 and after 7 hours. The reaction was terminated after a reaction time of 24 hours and the mixture was cooled to room temperature. The polymers obtained had weight-average molar masses M _w in the range from 1,100,000 to 1,300,000 g / mol.

Finally, the crosslinker solution (Syna Epoxy S-610, 3% by weight in acetone; 0.05 part by weight of crosslinker based on 100 parts by weight of polyacrylate), 88.2 kg of terpene phenolic resin (Dertophene T) and 47.1 kg of styrene-butadiene block copolymer (KRATON ^® D1118) incorporated into the polymer solution. The mass produced in this way was coated onto siliconized release paper by means of a doctor blade on a coating table. The coatings were then dried at 120 ° C. for 15 minutes. The layer thickness after drying is indicated in each case in Table 1 below (Hkm = pressure-sensitive adhesive).

The samples were conditioned for 14 days in a standard climate (23 ° C., 50% relative humidity) and then applied to both sides of the carrier indicated in Table 1 below by means of a steel counter-pressure roller.

carrier

• Träger 1: porelle^® microporous P355 (mikroporöse PU-Membran), Dicke 55 µm
• Träger 2: porelle^® microporous P345 (mikroporöse PU-Membran), Dicke 45 µm
• Träger 3: porelle^® microporous P330 (mikroporöse PU-Membran), Dicke 30 µm
• Träger 4: porelle^® PTFE P355, Dicke 55 µm
• Träger 5: PET-Folie, Dicke 12 µm
• Träger 6: PE-Schaum, Dicke 90 µm

Tabelle 1: Testergebnisse Nr. 1 2 3 4 (Vgl.) 5 (Vgl.) 6 (Vgl.) 7 (Vgl.) Aufbau Klebeband Schichtdicke Hkm beidseitig (µm) 50 50 50 50 50 72 30 Träger 1 2 3 4 5 5 6 Luftdurchlässigkeit (%) 0 1,4 0,4 86,8 0 0 0 Wasserdurchlässigkeit (j/n) n n n n n n n Schlagzähigkeit (J) 0,57 0,59 0,52 0,04 0,26 0,29 0,45 Klebkraft Stahl (N/cm) 13,5 13,4 12,5 0,9 11,0 12,0 7,2 Vgl. = Vergleichsversuch The following commercially available foils were used as carrier materials:

• Carrier 1: porelle ^® microporous P355 (microporous PU membrane), thickness 55 µm
• Carrier 2: porelle ^® microporous P345 (microporous PU membrane), thickness 45 µm
• Carrier 3: porelle ^® microporous P330 (microporous PU membrane), thickness 30 µm
• Carrier 4: porelle ^® PTFE P355, thickness 55 µm
• Carrier 5: PET film, thickness 12 μm
• Carrier 6: PE foam, thickness 90 μm

Table 1: Test Results No. 1 2 3 4 (cf.) 5 (cf.) 6 (cf.) 7 (cf.) Construction tape Layer thickness Hkm on both sides (µm) 50 50 50 50 50 72 30th carrier 1 2 3 4th 5 5 6th Air permeability (%) 0 1.4 0.4 86.8 0 0 0 Water permeability (y / n) n n n n n n n Impact strength (J) 0.57 0.59 0.52 0.04 0.26 0.29 0.45 Bond strength steel (N / cm) 13.5 13.4 12.5 0.9 11.0 12.0 7.2 Compare = comparison test

QUOTES INCLUDED IN THE DESCRIPTION

This list of the 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 assumes no liability for any errors or omissions.

Patent literature cited

• EP 2860028 A1 [0003]
• WO 2015/123007 A1 [0005]
• US 4560611 [0007]
• US 3714307 [0009]
• DE 1925997 [0010]

Claims (8)

Adhesive tape comprising at least one outer pressure-sensitive adhesive layer, characterized in that the adhesive tape further comprises at least one microporous polyurethane membrane. Tape according to Claim 1 , characterized in that the microporous polyurethane membrane has a thickness of 10 to 70 µm. Adhesive tape according to one of the preceding claims, characterized in that the microporous polyurethane membrane is produced by a wet coagulation process. Adhesive tape according to one of the preceding claims, characterized in that the micropores of the microporous polyurethane membrane are not oriented. Adhesive tape according to one of the preceding claims, characterized in that the polymer base of the outer pressure-sensitive adhesive layer consists of one or more polymers selected from the group consisting of poly (meth) acrylates, synthetic rubbers, natural rubbers, polyolefins and silicones. Adhesive tape according to one of the preceding claims, characterized in that the adhesive tape has a total thickness of 50 to 150 µm. Use of a microporous polyurethane membrane as a carrier layer in an adhesive tape. Use of an adhesive tape according to one of the Claims 1 to 6th for the production of bonds in electronic devices or as a damping layer in electronic devices.