Backing made of foamed thermoplastic polyurethane, and adhesive tape comprising the foamed backing

Abstract

The present invention relates to a backing for an adhesive tape, which backing comprises at least one layer based on foamed thermoplastic polyurethane and is characterized by the particular compressive strength thereof, to an adhesive tape comprising the backing, to a method for producing the adhesive tape, and to the use thereof.

Description

[0001] Carrier made of foamed thermoplastic polyurethane and adhesive tape comprising the foamed carrier

[0002] The present invention relates to a carrier for an adhesive tape which comprises at least one layer based on foamed thermoplastic polyurethane and is characterized by its particular compression strength, an adhesive tape comprising the carrier, a process for producing the adhesive tape and its use.

[0003] Adhesive tapes have long been known and continue to enjoy immense popularity. Their applications extend beyond household and office use, extending from the construction industry to the automotive and electrical industries. Adhesive tapes are increasingly being used in the electrical industry, especially, to bond electronic devices. However, the challenge here is finding a balance between sufficient adhesive strength and the ability of the adhesive tape to be removed again to avoid damage to the sometimes sensitive components when the tape is removed.

[0004] WO 2015 / 135134 A1 describes a stretch-removable adhesive tape comprising a carrier and a first layer of a pressure-sensitive adhesive applied to at least one surface of the carrier. The adhesive tape has a thickness between 0.05 and 0.1 mm and a longitudinal elongation of 850 to 2200%. The adhesive tape can be firmly bonded to a substrate and detached therefrom by being peeled off at an angle of 90° or more from the surface of the substrate without tearing and without leaving a significant residue on the substrate. The pressure-sensitive adhesive is formed from an acrylate copolymer containing terminal polyurethane functional groups. The adhesive tape is also intended to be applicable in electronic devices.

[0005] EP 3757 157 A1 discloses a formulation comprising at least one aqueous dispersion of an elastomer and expandable or expanded microballoons, as well as an adhesive tape comprising a carrier produced from the dispersion. The foams produced from the dispersion are said to have an impact strength comparable to that of PE foams, in particular those of the tesa® 668 series (see https: / / www.tesa.com / en / industry / electronics / solutions / pe-foam-tapes). Particularly good results are said to be achieved with a formulation comprising a mixture of two polyether-based polyurethane dispersions. In addition to the adhesive components of an adhesive tape, the properties of an adhesive tape are also largely determined by its non-adhesive components.Particularly with regard to mechanical properties, high demands are usually placed on the carrier of the adhesive tape, which must not only be compatible with the pressure-sensitive adhesive but must also provide it with the necessary strength and stability.

[0006] The difficulty here, particularly when using adhesive tapes in sensitive devices, is to provide a carrier that has appropriate damping properties to protect the installed components from vibrations.

[0007] Adhesive tapes with a polyolefin foam backing are available in a wide variety of designs and densities and are known for their good damping properties. However, they have the disadvantage of low strength, making them generally unsuitable for removable products, for example.

[0008] Against this background, the present invention seeks to provide a carrier for adhesive tapes, in particular removable adhesive tapes, which has a corresponding property profile to meet the aforementioned requirements and which is characterized in particular by good damping properties. This object is achieved according to the invention by a carrier according to the main claim. Preferred developments of the carrier according to the invention are set out in the subclaims.

[0009] A first subject of the present invention is therefore a carrier comprising at least one closed-cell layer foamed with microballoons based on thermoplastic polyurethane, wherein the carrier has a compression hardness of at least 50% at a maximum force of 140 N / cm 2 , preferably at a maximum force of 120 N / cm 2 , particularly preferably at a maximum force of 100 N / cm 2determined according to DIN EN ISO 3386-2 (2010-09).

[0010] Compressive hardness describes the strength of foamed materials and indicates how much force is required to compress the material in the z-direction by a certain percentage from its initial state. The higher the value, the harder the material.

[0011] The production of multi-layer structures usually requires complex pretreatment to generate a sufficiently stable bond between adhesives or outer layers in order to withstand high shock loads without failure at the interfaces.

[0012] These disadvantages can be avoided by using the microballoon-foamed carriers according to the invention. High-performance adhesive tapes with a multilayer structure can be produced without complex surface pretreatment, which simultaneously withstand high shock loads and are easily removable.

[0013] Furthermore, it has surprisingly been found that the supports according to the invention have a significantly improved softness compared to conventional polyethylene-based supports, whereby advantageous damping properties can be achieved.

[0014] Within the scope of the present invention, it was surprisingly found that polyurethane foam as a carrier material in combination with the specified compression provides very good damping capacity and is therefore particularly suitable for the production of electronic components.

[0015] Without being bound to any particular theory, it is assumed that the observed damping properties of the carrier according to the invention can be further improved by a corresponding density of the carrier. In a preferred embodiment, the carrier therefore has a density of 300 to 1200 kg / m 3 , preferably 400 to 900 kg / m 3 , particularly preferably 500 to 800 kg / m 3 on.

[0016] The polyurethane used as carrier material is preferably selected from the group consisting of aromatic polyurethanes, aliphatic polyurethanes, polyester-polyol-based polyurethanes, polyether-polyol-based polyurethanes, polycarbonate-based polyurethanes and hybrids and mixtures thereof.

[0017] The polyurethane can be cross-linked or non-cross-linked.

[0018] The thickness of the support can vary depending on the application. For example, in some applications, supports with a small thickness are preferred, while in others, for example, as spacers, supports with a greater thickness are used. Within the scope of the present invention, the support preferably has a thickness of 20 to 2500 μm, particularly preferably 50 to 1000 μm. In certain cases, a support thickness of 150 to 1000 μm is preferred.

[0019] The carrier according to the invention is characterized, among other things, by its good damping capacity. In this context, an embodiment is preferred in which the carrier has a breakdown strength of at least 0.3 J, determined by the DuPont test.

[0020] In a first embodiment, the carrier contains at least one, preferably precisely one, layer based on thermoplastic polyurethane, which is typically produced by extrusion. Such a layer based on thermoplastic polyurethane typically means a layer whose proportion of thermoplastic polyurethane is at least 50% by weight. Preferably, the proportion of thermoplastic polyurethane in the layer is at least 90% by weight; in particular, the layer consists essentially of thermoplastic polyurethane.

[0021] The thermoplastic polyurethane of the at least one carrier layer is preferably polyester polyol-based, but can alternatively also be polyether polyol-based, such as poly-THF as the polyol. The thermoplastic polyurethane based on polyester polyol or polyether polyol is typically thermoplastic polyurethane based on aliphatic polyester polyol or aliphatic polyether polyol.

[0022] The polyurethane used can have two or more glass transition temperatures, one of which is preferably between -20 °C and 40 °C and the other is preferably between 60 °C and 110 °C. The glass transition temperature can be determined, for example, using DSC according to DIN 53765.

[0023] The thermoplastic polyurethane typically has a tear strength of over 10 MPa, preferably over 20 MPa. In a further preferred embodiment, the Shore A hardness is between 45 and 95, such as in particular between 60 and 85. In an alternatively preferred embodiment, the Shore A hardness is between 70 and 85. The Shore A hardness can be determined according to ASTM D2240.

[0024] The thermoplastic polyurethane is preferably a reaction product of a reaction mixture containing at least one diisocyanate, at least one polyester polyol (or polyether polyol) and optionally at least one chain extender, wherein the polyester polyol or polyether polyol typically has a melting temperature of at least 30 °C, such as at least 100 °C or at least 200 °C.

[0025] Chain extenders can be, for example, 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 2,3-butanediol, propylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, hydroquinone dihydroxyethyl ether, ethanolamine, N-phenyldiethanolamine, or m-phenylenediamine. Chain extenders are low-molecular-weight, difunctional compounds that are reactive toward isocyanates.

[0026] Monofunctional substances that are reactive toward isocyanates, such as monools, can also be used. They act as chain terminators and can thus be used to control chain length.

[0027] The proportion of diisocyanate in the reaction mixture is preferably 0.5 to 47 wt.%, more preferably 1 to 40 wt.%, and especially 10 to 25 wt.%. The amount of diisocyanate in the reaction mixture can also be expressed as the ratio of NCO to OH groups (isocyanate index). An isocyanate index is generally understood to refer to the ratio of the equivalent amount of functional isocyanate groups used to the equivalent amount of functional hydroxy groups. The isocyanate index of the reaction mixture is preferably in a range from 0.99 to 1.20, more preferably from 1.00 to 1.10.

[0028] Preferably, the diisocyanate is a diisocyanate having the structure according to formula I

[0029] O=C=NRN=C=O (Formula I), wherein R is selected from substituted or unsubstituted (Ci-C4o)-alkylene, (C2-C0)-alkenylene, (C4-C2o)-arylene, (C4-C2o)-arylene-(Ci-C4o)-alkylene-(C4-C2o)-arylene, (C4-C20)-cycloalkylene, and (C4-C2o)-aralkylene. In further examples, the diisocyanate is selected from dicyclohexylmethane-4,4'-diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate,

[0030] 1,4-phenylene diisocyanate, 1,3-phenylene diisocyanate, m-xylylene diisocyanate, toluene 2,4-diisocyanate, toluene 2,4-diisocyanate, toluene 2,6-diisocyanate, poly (hexamethylene diisocyanate),

[0031] 1,4-cyclohexylene diisocyanate, 4-chloro-6-methyl-1,3-phenylene diisocyanate,

[0032] Hexamethylene diisocyanate, diphenylmethane-4,4'-diisocyanate, 1,4-diisocyanatobutane, 1,8-diisocyanatooctane, 2,6-toluene diisocyanate, 2,5-toluene diisocyanate, 2,4-toluene diisocyanate, m-phenylene diisocyanate, p-Phenylene diisocyanate, methylene bis(o-chlorophenyl diisocyanate), methylene diphenylene 4,4'-diisocyanate, (4,4'-diisocyanato-3,3',5,5'-tetraethyl)diphenylmethane, 4,4'-diisocyanato-3,3'-dimethoxy-biphenyl(o-dianisidine diisocyanate), 5-chloro-2,4-toluene diisocyanate, 1-chloromethyl-2,4-diisocyanato-benzene, tetramethyl-m-xylylene diisocyanate, 1,6-diisocyanatohexane, 1, 12-Diisocyanatododecane, 2-methyl-1,5-diisocyanatopentane, methylenedicyclohexylene-4,4'-diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate, 2,2,4-trimethylhexyl diisocyanate or a mixture thereof.

[0033] Particularly preferred diisocyanates are diphenylmethane-4,4'-diisocyanate (MDI), hexane diisocyanate (HDI), isophorone diisocyanate (IPDI) or hexamethylene diisocyanate (HMDI).

[0034] The proportion of polyester polyol or polyether polyol in the reaction mixture is preferably in the range of 43 wt% to 70 wt%, more preferably in the range of 50 wt% to 60 wt%.

[0035] The polyester polyol preferably contains two hydroxyl groups, so that the polyester polyol is a polyester diol. The polyester polyol may also contain any suitable number of hydroxyl groups; depending on the concentration of this polyester polyol and the isocyanate index, it may also contain a different number of polyester polyols.

[0036] The polyester polyol can also be a polycaprolactone polyol.

[0037] In examples where the polyester polyol is prepared according to a condensation reaction, the reaction may take place between one or more carboxylic acids and one or more polyols. Examples of suitable carboxylic acids include carboxylic acids according to formula IIa (dicarboxylic acids) and IIb (hydroxycarboxylic acids) with the structures:

[0038] OO

[0039] HO - U - R 1 - U - 0H

[0040] (Formula lla)

[0041] In formula lla, R 1 typically selected from substituted or unsubstituted (Ci-C4o)alkylene, (C2-C4o)alkenylene, (C4-C2o)arylene, (C4-C2o)cycloalkylene and (C4-C20)aralkylene.

[0042] 0 HO - R 2 - H - OH

[0043] (Formula llb)

[0044] In formula llb, R 2typically selected from substituted or unsubstituted (Ci-C4o)alkylene, (C2-C4o)alkenylene, (C4-C2o)cycloalkylene and (C4-C20)aralkylene.

[0045] Examples of suitable carboxylic acids include lactic acid (2-hydroxypropanoic acid), succinic acid (butanedioic acid), 3-hydroxybutanoic acid, 3-hydroxypentanoic acid, terephthalic acid (benzene-1,4-dicarboxylic acid), naphthalenedicarboxylic acid,

[0046] 4-Hydroxybenzoic acid, 6-Hydroxynaphthalene-2-carboxylic acid, oxalic acid, malonic acid (propanedioic acid), adipic acid (hexanedioic acid), pimelic acid (heptanedioic acid), ethonic acid, suberic acid (octanedioic acid), azelaic acid (nonanedioic acid), sebacic acid (decanedioic acid), glutaric acid (pentanedioic acid), dodecanedioic acid, brassylic acid, thapsinic acid, maleic acid, fumaric acid, glutaconic acid, 2-decenoic acid, muconic acid, glutic acid, citraconic acid, mesaconic acid, itaconic acid, malic acid (2-hydroxybutanedioic acid), aspartic acid (2-aminobutanedioic acid), glutamic acid (2-aminopentanedioic acid), tartaric acid, tartaric acid (2,3-dihydroxybutanedioic acid), diaminopimelic acid, saccharic acid, mesoxalic acid, oxaloacetic acid, acetonicarboxylic acid (3-oxopentanedioic acid), arbinaric acid, phthalic acid, isophtic acid, 2,6-naphthalenedicarboxylic acid, or a mixture thereof. Adipic acid and caprolactone are particularly preferred.

[0047] An example of a suitable polyol includes a polyol according to formula III having the structure:

[0048] HO - R 2 - OH (Formula III)

[0049] In Formula III, R 2selected from substituted or unsubstituted (Ci-C4o) alkylene, (C2-C4o) alkenylene, (C4-C2o) arylene, (Ci-C4o) acylene, (C4-C2o) cycloalkylene, (C4-C2o) aralkylene, and (Ci-C4o) alkoxylene. For example, the diol may have a number-average molecular weight in a range of 30 g / mol to 600 g / mol, preferably 50 g / mol to 350 g / mol. The diol component may contain any suitable number of carbons. For example, the diol may have a number-average number of 2 carbons to 500 carbons, preferably 3 carbons to 140 carbons. Examples of suitable diols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 1,4-cyclohexane-dimethanol or a mixture thereof.

[0050] Particularly preferred polyester polyols are polyalkylene adipates.

[0051] Traditionally, the blown film process, which involves multiple layers, is used for film production. Here, a PE layer (i.e., polyethylene layer) and the actual TPU layer are produced as a coextruded film in the blown film process (i.e., the PE layer acts as a support carrier, giving the extrudate the necessary mechanical stability). The PE support carrier is therefore removed before or during the production of the adhesive tape, i.e., it represents a temporary carrier. However, numerous additives are required to produce such blown film, such as antiblocking agents (e.g., silicate particles), which ensure controlled release of the support carrier, and lubricating waxes as processing aids. Both of these factors have a negative impact on the mechanical properties.Both the silicate particles in the film (= defects) and the crystalline superstructure (= hard, inflexible domains) lead to reduced stretchability and, above all, to a higher tendency to tear during application, i.e., during stretching. Due to migration of the waxes to the PSA surface, i.e., the surface of the pressure-sensitive adhesive, the waxes also lead to problems with reduced adhesive strength and difficulties in anchoring the PSA to the film. A high molecular weight of the PU polymer, which increases the toughness of the film, is also advantageous for high stretchability and low tear tendency.

[0052] Therefore, the TPU-based carrier layer is preferably free of additives such as antiblocking agents and waxes. Furthermore, the polyurethane preferably does not exhibit a crystalline superstructure, as manifested by a DSC peak > 210 °C.

[0053] In a preferred embodiment, the polyurethane used to produce the carrier is crosslinked.

[0054] Crosslinkers can essentially react in two different ways: by reacting with a polymer or by reacting with themselves to form a so-called interpenetrating network, which creates a much denser network and thus improves many properties, such as strength, abrasion resistance, hydrolysis and chemical resistance.

[0055] Crosslinkers based on aziridine, carbodiimide (polycarbodiimide), melamine, radical-forming substances such as organic peroxides, sulfur, and isocyanate are particularly preferred as crosslinkers within the scope of the present invention. In a preferred embodiment, the crosslinker is an isocyanate, preferably a blocked polyisocyanate, in particular a blocked aliphatic polyisocyanate.

[0056] Polyisocyanates can react with functional groups such as amino or hydroxyl groups. The polyfunctionality of this type of crosslinker creates a 3D crosslinked network. Polyisocyanates also react with water, which in turn causes the polyisocyanate molecules to react with themselves, resulting in a network consisting of a combination of a classic 3D polymer crosslinked network and an interpenetrating network caused by the reactivity of several polyisocyanate molecules with themselves.

[0057] In the case of an isocyanate crosslinker, this is preferably obtained from a dispersion comprising a polyisocyanate, a blocking agent for isocyanate groups, and water. In a preferred embodiment, the dispersion for obtaining the crosslinker further comprises a polyamine, preferably one with at least one carboxyl and / or carboxylate group.

[0058] Polyisocyanates are considered herein to be compounds containing NCO groups. The polyisocyanate may have a number-average molecular weight of 140 to 1500 g / mol, and preferably of 168 to 700 g / mol. According to a preferred embodiment of the invention, the polyisocyanate has an isocyanate functionality of > 2 and < 6, preferably > 3 and < 5, and particularly preferably > 3 and < 4.

[0059] The polyisocyanate preferably has an NCO group content of 15 to 30 wt.%, preferably 18 to 25 wt.% and particularly preferably 20 to 24 wt.%, based on the number-average molecular weight of the polyisocyanate.

[0060] Suitable polyisocyanates include hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 4,4'-diisocyanatodicyclohexylmethane (Hi2MDI), 1,4-butane diisocyanate, hexahydrodiisocyanatotoluene, 1,3-bishydroxymethylcyclohexane, hexahydrodiisocyanatoxylol, and nonane triisocyanate. Particular preference is given to the use of isophorone diisocyanate, hexamethylene diisocyanate, and / or 4,4-diisocyanatodicyclohexylmethane.

[0061] Particularly preferred polyisocyanates are aliphatic polyisocyanates, preferably hexamethylene diisocyanate, and especially preferably trimers of hexamethylene diisocyanate. It is also advantageous if the aqueous blocked polyurethane urea dispersion is exclusively anionically hydrophilic. This means that the polyurethane urea dispersion is not cationically and / or nonionically hydrophilic, i.e., it does not contain any corresponding groups.

[0062] In this context, a blocking agent refers to compounds that react with an isocyanate group and can be cleaved from it again under defined conditions, for example, thermally. This process is referred to as deblocking. A low deblocking temperature has proven particularly advantageous in the context of the present invention. Therefore, an embodiment in which the deblocking temperature is less than 130°C is preferred.

[0063] Polycarbodiimides react selectively with carboxylic acid groups in polymer chains. This type of crosslinking creates a classic 3D polymer-crosslinked network. Compared to polyisocyanates, polycarbodiimides are less sensitive to water and thus achieve longer pot lives.

[0064] Melamine resins are very effective crosslinkers due to their high reactivity. They require lower addition quantities than isocyanates or carbodiimides. Melamine resins are often used in combination with hydroxy-functional polymer resins to form very hard crosslinks, but can also react with acid groups. Melamine resins require quite high crosslinking temperatures, which can be reduced by adding catalysts.

[0065] Polyaziridines are among the most reactive crosslinkers and therefore highly efficient. Polyaziridines react selectively with carboxylic acid groups in polymer chains. This type of crosslinking creates classic 3D polymer crosslinked networks. Due to their lower molecular weight, a significantly smaller amount is required compared to polyisocyanates and polycarbodiimides.

[0066] Peroxide crosslinking achieves a high degree of crosslinking with favorable processing reliability and broad applicability. However, the vulcanization times are very long.

[0067] For crosslinking with sulfur, the addition of vulcanization accelerators is usually necessary to prevent degradation at the temperatures used for crosslinking. The elasticity and cold resistance of the vulcanizates are usually lower.

[0068] Foaming:

[0069] The carrier comprises a polyurethane layer foamed by microballoons. "Microballoons" are elastic and thus expandable hollow microspheres with a thermoplastic polymer shell. These spheres are filled with low-boiling liquids or liquefied gas. Polyacrylonitrile, PVDC, PVC, or polyacrylate are particularly used as shell materials. Low-boiling liquids, such as isobutane or isopentane, are particularly suitable as low-boiling liquids, which are enclosed in the polymer shell as a liquefied gas under pressure.

[0070] When exposed to external influences, particularly heat, the outer polymer shell softens. At the same time, the liquid propellant gas contained within the shell transforms into a gaseous state. The microballoons expand irreversibly and expand three-dimensionally. The expansion is complete when the internal and external pressures equalize. Since the polymer shell remains intact, a closed-cell foam is created.

[0071] A variety of microballoon types are commercially available, which differ primarily in their size, preferably 5 to 45 μm in diameter in the unexpanded state, and the starting temperatures required for expansion, preferably 75 to 220 °C. An example of commercially available microballoons is the Expancel® DU types (DU = dry unexpanded) from Nouryon.

[0072] Unexpanded microballoon types are also available as aqueous dispersions with a solids or microballoon content of approximately 40 to 45 wt.%, and also as polymer-bound microballoons (masterbatches), for example in ethyl vinyl acetate with a microballoon concentration of approximately 50 wt.%.

[0073] According to the invention, the average diameter of the cavities formed by the microballoons in the foamed carrier is preferably from 10 to 200 μm, more preferably from 15 to 200 μm. Since the diameters of the cavities formed by the microballoons in the foamed carrier are measured here, the diameters are the diameters of the cavities formed by the expanded microballoons. The average diameter refers to the arithmetic mean of the diameters of the cavities formed by the microballoons in the pressure-sensitive adhesive layer. The average diameter of the cavities formed by the microballoons can be determined using a scanning electron microscope (SEM).The diameters of the microballoons visible in the images are determined graphically by extracting the maximum expansion in any (two-dimensional) direction from the SEM images for each individual microballoon, which is considered its diameter. According to a preferred embodiment of the invention, the proportion of microballoons in the polyurethane is between greater than 0 wt.% and 10 wt.%, in particular between 0.25 wt.% and 5 wt.%, and most particularly between 0.5 wt.% and 4 wt.%, in each case based on the total composition of the carrier. This information refers to unexpanded microballoons.

[0074] In addition to expandable hollow microspheres, the polyurethane can also contain non-expandable hollow microspheres. The only crucial factor is that almost all gas-containing cavities are sealed by a permanently sealed membrane, regardless of whether this membrane is made of an elastic and thermoplastically expandable polymer blend or of elastic and—within the range of temperatures possible in plastics processing—non-thermoplastic glass.

[0075] Also suitable - independently of other additives - are solid polymer spheres, hollow glass spheres, solid glass spheres, hollow ceramic spheres, solid ceramic spheres and / or solid carbon spheres (“carbon micro balloons”).

[0076] Additionally, the polyurethane layer can be foamed by adding a physical blowing agent. For example, the starting mixture can be foamed in the presence of a gas such as air, nitrogen, or a noble gas such as helium, neon, or argon. Blowing agents can be used individually or as a mixture of different blowing agents. Blowing agents can be selected from a large number of materials, including hydrocarbons, ethers, esters, and the like. Typical physical blowing agents have a boiling point in the range from -50°C to +100°C, and preferably from -50°C to +50°C. Preferred physical blowing agents include hydrocarbons such as n-pentane, isopentane, cyclopentane, methylene chloride, or any combination of the aforementioned compounds. Such blowing agents can preferably be used in amounts of from 5% to 50% by weight of the reaction mixture, in particular from 10% to 30% by weight.-% of the reaction mixture.

[0077] It is also possible to use a chemical blowing agent in addition. Chemical blowing agents are substances that release gas only during the processing due to a chemical reaction – usually initiated by the application of heat – and thus enable the creation of a foam structure in the polymer. The cause of the gas release can be either the thermal decomposition of the blowing agent or a chemical reaction of various substances contained in the blowing agent. The resulting gas is usually N2, CO2, or CO.

[0078] The present invention further provides an adhesive tape comprising the carrier according to the invention, which is coated on at least one side with a pressure-sensitive adhesive.

[0079] The foamed polyurethane carrier according to the invention is compatible with a number of pressure-sensitive adhesives, with preference being given to using pressure-sensitive adhesives based on vinyl aromatic block copolymers, polyacrylates, polyurethanes or combinations thereof.

[0080] In a preferred embodiment, at least one pressure-sensitive adhesive layer consists of a pressure-sensitive adhesive based on vinyl aromatic block copolymers.

[0081] Preferably, the vinylaromatic block copolymer is at least one synthetic rubber in the form of a block copolymer with a structure AB, ABA, (AB) n , (AWAY) n X or (ABA) n X, where

[0082] • the blocks A independently represent a polymer formed by polymerization of vinyl aromatics;

[0083] • the blocks B independently of one another represent a polymer formed by polymerization of conjugated dienes having 4 to 18 C atoms and / or isobutylene, or a partially or fully hydrogenated derivative of such a polymer;

[0084] • X represents the residue of a coupling reagent or initiator and

[0085] • n stands for an integer > 2.

[0086] In particular, all synthetic rubbers of the pressure-sensitive adhesive of the invention are block copolymers with a structure as described above. The pressure-sensitive adhesive of the invention can thus also contain mixtures of various block copolymers with a structure as described above.

[0087] Suitable block copolymers comprise one or more rubber-like blocks B (soft blocks) and one or more glassy blocks A (hard blocks). More preferably, at least one of the block copolymers is a block copolymer having a structure AB, ABA, (AB)3X or (AB)4X, where A, B and X are as defined above, and where at least one block copolymer contains at least two hard blocks. Most preferably, the block copolymers are those having a structure AB, AB-A, (AB)3X or (AB)4X, where A, B and X are as defined above. In particular, a mixture of block copolymers having a structure AB, ABA, (AB)3X or (AB)4X, which preferably contains at least diblock copolymers AB and / or triblock copolymers ABA, can also be used.

[0088] Also advantageous is a mixture of diblock and triblock copolymers and (AB) n or (AB)nX block copolymers with n greater than or equal to 3.

[0089] The block copolymers resulting from the A and B blocks can contain identical or different B blocks. The block copolymers can have linear ABA structures. Radial block copolymers, as well as star-shaped and linear multiblock copolymers, can also be used. AB diblock copolymers can be present as additional components. The aforementioned polymers can be used alone or in mixtures with one another, although AB diblock copolymers cannot be used alone.

[0090] In particular, block A is a glassy block with a preferred glass transition temperature (T g , DSC), which is above room temperature. Particularly preferred is the T gof the glassy block at at least 40 °C, in particular at least 60 °C, very particularly preferably at least 80 °C, and extremely preferably at least 100 °C. The proportion of vinylaromatic blocks A in the total block copolymers is preferably 10 to 40 wt. %, particularly preferably 20 to 33 wt. Vinylaromatics for constructing block A preferably include styrene and α-methylstyrene. Block A can thus be present as a homopolymer or copolymer. Block A is particularly preferably a polystyrene.

[0091] The block B is in particular a rubber-like block or soft block with a preferred T g less than room temperature. The T g 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.

[0092] Monomer units for constructing block A preferably comprise styrene, α-methylstyrene, and / or other styrene derivatives. Block A can thus be present as a homopolymer or copolymer. Block A is particularly preferably a polystyrene.

[0093] 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, and dimethylbutadiene, as well as any desired mixtures of these monomers. Block B can also be present as a homopolymer or as a copolymer. The conjugated dienes as monomers for the soft block B are particularly preferably 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 of a mixture of butadiene and isoprene. Block B is most preferably a polybutadiene.

[0094] In the context of this invention, A blocks are also referred to as "hard blocks." B blocks are correspondingly also called "soft blocks" or "elastomer blocks." This reflects the inventive selection of the blocks according to their glass transition temperatures, preferably at least 25°C, in particular at least 50°C, for A blocks, and at most 25°C, in particular at most -25°C, for B blocks. In a preferred embodiment, the proportion of vinylaromatic block copolymers, based on the total pressure-sensitive adhesive, is 15 to 60% by weight, particularly preferably 20 to 50% by weight. An excessively low proportion of vinylaromatic block copolymers results in the cohesion of the pressure-sensitive adhesive being relatively low, so that the tear strength required for stripping is too low. An excessively high proportion of vinylaromatic block copolymer, in turn, results in the pressure-sensitive adhesive being barely tacky.

[0095] In an alternative preferred embodiment, a polyacrylate-based pressure-sensitive adhesive is used.

[0096] In this application, the terms "acrylate" and "polyacrylate" are used synonymously. These terms refer to a polymer resulting from the polymerization of (meth)acrylic acid, an ester thereof, or mixtures of the aforementioned monomers, and optionally other copolymerizable monomers. The term (meth)acrylic acid also encompasses both acrylic acid and methacrylic acid. Polyacrylates are typically copolymers.

[0097] For the purposes of the invention, solvent-based, water-based, or hot-melt pressure-sensitive adhesives can be used for the polyacrylate-based pressure-sensitive adhesives, for example, an acrylate hot-melt-based adhesive, which may have a K value of at least 20, in particular greater than 30, obtainable by concentrating a solution of such a adhesive to form a system that can be processed as a hot-melt. Concentration can take place in appropriately equipped tanks or extruders; a vented extruder is preferred, particularly for the associated degassing. Such an adhesive is described in DE 43 13 008 A1, the contents of which are hereby incorporated by reference and whose contents become part of this disclosure and invention. The acrylate hot-melt-based adhesive may be chemically crosslinked.

[0098] An adhesive that has also proven to be suitable is a low-molecular acrylic hotmelt pressure-sensitive adhesive such as acResin® UV from BASF and acrylic dispersion pressure-sensitive adhesives such as those available under the trade name Acronal® from BASF.

[0099] In a further embodiment, pressure-sensitive adhesives contain copolymers of (meth)acrylic acid and its esters having 1 to 25 carbon atoms, maleic, fumaric, and / or itaconic acid and / or its esters, substituted (meth)acrylamides, maleic anhydride, and other vinyl compounds such as vinyl esters, especially vinyl acetate, vinyl alcohols, and / or vinyl ethers. The residual solvent content should be less than 1% by weight. In another preferred embodiment, a pressure-sensitive adhesive containing a polyacrylate polymer is used. This is a polymer obtainable by free-radical polymerization of acrylic monomers, which also includes methylacrylic monomers, and optionally other copolymerizable monomers.

[0100] According to the invention, it can be a polyacrylate crosslinkable with epoxy groups. Accordingly, functional monomers crosslinkable with epoxy groups are preferably used as monomers or comonomers. In particular, monomers containing acid groups (especially carboxylic acid, sulfonic acid, or phosphonic acid groups) and / or hydroxyl groups and / or acid anhydride groups and / or epoxy groups and / or amine groups are used here. Monomers containing carboxylic acid groups are preferred. It is particularly advantageous if the polyacrylate contains polymerized acrylic acid and / or methacrylic acid.Other monomers that can be used as comonomers for the polyacrylate are, for example, acrylic acid and / or methacrylic acid esters with up to 30 C atoms, vinyl esters of carboxylic acids containing up to 20 C atoms, vinyl aromatics with up to 20 C atoms, ethylenically unsaturated nitriles, vinyl halides, vinyl ethers of alcohols containing 1 to 10 C atoms, aliphatic hydrocarbons with 2 to 8 C atoms and 1 or 2 double bonds or mixtures of these monomers.

[0101] Preferably, a polyacrylate is used which can be traced back to the following monomer composition: i. Acrylic acid esters and / or methacrylic acid esters of the following formula CH2=C(R 1 )(COOR 2 ), where R 1 = H or CH3 and R 2= H or linear, branched or cyclic, saturated or unsaturated alkyl radicals having 1 to 30, in particular 4 to 18, carbon atoms, ii. olefinically unsaturated monomers having functional groups of the type already defined for reactivity with epoxy groups, iii. optionally further acrylates and / or methacrylates and / or olefinically unsaturated monomers which are copolymerizable with component (i).

[0102] Further preferably, for use of the polyacrylate as a pressure-sensitive adhesive, the proportions of the corresponding components (i), (ii), and (iii) are selected such that the polymerization product has, in particular, a glass transition temperature of less than or equal to 15 °C (determined by DSC (Differential Scanning Calorimetry) according to DIN 53765 at a heating rate of 10 K / min). For the production of pressure-sensitive adhesives, it is very advantageous to select the monomers of component (i) in a proportion of 45 to 99 wt. %, the monomers of component (ii) in a proportion of 1 to 15 wt. %, and the monomers of component (iii) in a proportion of 0 to 40 wt. % (the figures are based on the monomer mixture for the "base polymer," i.e., without the addition of any additives to the finished polymer, such as resins).

[0103] The monomers of component (i) are, in particular, plasticizing and / or nonpolar monomers. Preferably, acrylic monomers comprising acrylic and methacrylic acid esters with alkyl groups consisting of 4 to 18 carbon atoms, preferably 4 to 9 carbon atoms, are used for the monomers (i). Examples of such monomers are n-butyl acrylate, n-butyl methacrylate, n-pentyl acrylate, n-pentyl methacrylate, n-amyl acrylate, n-hexyl acrylate, hexyl methacrylate, n-heptyl acrylate, n-octyl acrylate, n-octyl methacrylate, n-nonyl acrylate, isobutyl acrylate, isooctyl acrylate, isooctyl methacrylate, and their branched isomers, such as 2-ethylhexyl acrylate or 2-ethylhexyl methacrylate.

[0104] For component (ii), monomers with functional groups selected from the following list are preferably used:

[0105] Hydroxy, carboxy, sulfonic or phosphonic acid groups, acid anhydrides, epoxides, amines.

[0106] Particularly preferred examples of monomers of component (ii) are acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, aconitic acid, dimethylacrylic acid, ß-acryloyloxypropionic acid, trichloroacrylic acid, vinylacetic acid, vinylphosphonic acid, itasconic acid, maleic anhydride, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, 6-hydroxyhexyl methacrylate, allyl alcohol, glycidyl acrylate, glycidyl methacrylate.

[0107] Examples of monomers for component (iii) 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, t-butylphenyl acrylate, t-butylphenyl 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,

[0108] 3,3,5-trimethylcyclohexyl acrylate, 3,5-dimethyl adamantyl acrylate, 4-cumylphenyl methacrylate, cyanoethyl acrylate, cyanoethyl methacrylate, 4-biphenyl acrylate, 4-biphenyl methacrylate, 2-naphthyl acrylate, 2-naphthyl methacrylate, tetrahydrofufuryl acrylate,

[0109] Diethylaminoethylacrylat, Diethylaminoethylmethacrylat, Dimethyl-aminoethylacrylat, Dimethylaminoethylmethacrylat, 2-Butoxyethylacrylat, 2-Butoxyethyl-methacrylat, 3-Methoxyacrylsäuremethylester, 3- ethoxybutylacrylat, Phenoxyethylacrlylat,

[0110] Phenoxyethylmethacrylat, 2-Phenoxyethylmethacrylat, Butyldiglykolmethacrylat, Ethylen- glycolacrylat, Ethylenglycolmonomethylacrylat, Methoxy Polyethylenglykolmethacrylat, Methoxy-Polyethylenglykolmethacrylat, Propylenglycolmonomethacrylat,

[0111] Butoxydiethylenglykolmethacrylat, Ethoxytriethylenglykolmethacrylat, Octafluoropentylacrylat, Octafluoropentylmethacrylat, 2,2,2-Trifluoroethylmethacrylat, 1 ,1 , 1,3, 3, 3 Hexafluoroisopropyl- acrylat, 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, , 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 -Methyl-undecyl)- acrylamid, N-(n-Butoxymethyl)acrylamid, N-(Butoxymethyl)methacrylamid, N-(Ethoxymethyl)- acrylamid, N-(n-Octadecyl)acrylamid, weiterhin N,N-Dialkyl-substituierte Amide wie beispielsweise N,N-Dimethylacrylamid, N,N-Dimethylmethacrylamid, N- Benzylacrylamide, N-Isopropylacrylamid, N-tert.-Butylacrylamid, N-tert.Octylacrylamid, N-Methylolacrylamid, N-Methylolmethacrylamid, Acrylnitril, Methacrylnitril, Vinylether wie Vinylmethylether, Ethylvinylether, Vinylisobutylether, Vinylester wie Vinylacetat, Vinylchlorid, Vinylhalogenide, Vinylidenchlorid, Vinylidenhalogenide, Vinylpyridin, 4-Vinylpyridin, N-Vinylphthalimid, N-Vinyllactam, N-Vinylpyrrolidon, Styrol, a- und p-Methylstyrol, a-Butylstyrol, 4-n-Butylstyrol,.

[0112] 4-n-Decylstyrol, 3,4-Dimethoxystyrol, Makromonomere wie 2-Polystyrolethylmethacrylat (Molekulargewicht Mw von 4000 bis 13000 g / mol), Poly(Methylmethacrylat)ethylmethacrylat (Mw von 2000 bis 8000 g / mol).

[0113] Monomers of component (iii) can also advantageously be selected such that they contain functional groups that support subsequent radiation-chemical crosslinking (e.g., by electron beams, UV). Suitable copolymerizable photoinitiators include benzoin acrylate and acrylate-functionalized benzophenone derivatives. Monomers that support crosslinking by electron irradiation include, for example, tetrahydrofurfuryl acrylate, N-tert-butylacrylamide, and allyl acrylate, although this list is not exhaustive.

[0114] Furthermore, the composition of the polyacrylate-based pressure-sensitive adhesive (or based on an acrylate blend) often includes epoxy-based crosslinkers. As substances containing epoxy groups, multifunctional epoxides are particularly used, i.e., those that have at least two epoxy units per molecule (i.e., are at least bifunctional). These can be both aromatic and aliphatic compounds. Epoxy-based crosslinkers can also be used in oligomeric or polymeric form. The mixture of acrylates can, in turn, preferably have the following composition:

[0115] (I) 90 to 99 wt.% n-butyl acrylate and / or 2-ethylhexyl acrylate,

[0116] (II) 1 to 10 wt.% of an ethylenically unsaturated monomer having an acid or acid anhydride function, preferably (I) and (II) adding up to 100 wt.%.

[0117] Preferably, the monomer (I) forms a mixture of 2-ethylhexyl acrylate and n-butyl acrylate, more preferably in equal parts.

[0118] Advantageous monomers (II) include, for example, acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and / or maleic anhydride.

[0119] Acrylic acid or methacrylic acid are preferred, optionally a mixture of both.

[0120] In a preferred embodiment, a blend of a vinyl aromatic block copolymer and a polyacrylate can also be used as the pressure-sensitive adhesive.

[0121] In a preferred embodiment, the pressure-sensitive adhesives comprise, in addition to the at least one vinyl aromatic block copolymer, at least one adhesive resin in order to increase the adhesion in the desired manner.

[0122] According to the general understanding of those skilled in the art, an “adhesive resin” is understood to mean an oligomeric or polymeric resin that increases the adhesion (tack, inherent stickiness) of the pressure-sensitive adhesive compared to a pressure-sensitive adhesive that does not contain an adhesive resin but is otherwise identical.

[0123] In a preferred embodiment, the pressure-sensitive adhesive layer consists of a pressure-sensitive adhesive based on vinyl aromatic block copolymer and adhesive resins, wherein preferably at least 30% by weight, and preferably at least 50% by weight, in each case based on the total adhesive resin content, is selected from an adhesive resin having a DACP (diacetone alcohol cloud point) of greater than -20 °C, preferably greater than 0 °C, and a softening temperature (ring & ball) of greater than or equal to 70 °C, preferably greater than or equal to 100 °C.

[0124] Particularly preferably, at least 30% by weight, in particular at least 50% by weight, of the adhesive resins, based in each case on the total adhesive resin content, are hydrocarbon resins or terpene resins or a mixture thereof.

[0125] It has been found that particularly nonpolar hydrocarbon resins, for example hydrogenated and non-hydrogenated polymers of dicyclopentadiene, non-hydrogenated, partially, selectively, or fully hydrogenated hydrocarbon resins based on C5, C5 / C9, or C9 monomer streams, and polyterpene resins based on α-pinene and / or β-pinene and / or δ-limonene, can be advantageously used as adhesive resins for the pressure-sensitive adhesive(s). The aforementioned adhesive resins can be used alone or in mixtures. Both solid and liquid resins at room temperature can be used. Adhesive resins, hydrogenated or non-hydrogenated, which also contain oxygen can optionally be used, preferably up to a maximum proportion of 70 wt. %, based on the total mass of the resins in the adhesive.

[0126] According to a preferred variant, the proportion of resins liquid at room temperature is up to 15 wt.%, preferably up to 10 wt.%, based on the total pressure-sensitive adhesive.

[0127] The pressure-sensitive adhesive of the invention preferably contains 20 to 60 wt. %, based on the total weight of the pressure-sensitive adhesive, of at least one tackifier resin. More preferably, 30 to 50 wt. %, based on the total weight of the pressure-sensitive adhesive, contain tackifier resins.

[0128] Other additives that can typically be used include:

[0129] • Plasticizers such as plasticizer oils, or low-molecular liquid polymers, such as low-molecular polybutenes, preferably in a proportion of 0.2 to 5 wt.% based on the total weight of the pressure-sensitive adhesive

[0130] • primary antioxidants such as sterically hindered phenols, preferably in a proportion of 0.2 to 1 wt.% based on the total weight of the pressure-sensitive adhesive

[0131] • secondary antioxidants, such as phosphites or thioethers, preferably in a proportion of 0.2 to 1 wt.% based on the total weight of the pressure-sensitive adhesive

[0132] • Process stabilizers such as C radical scavengers, preferably in a proportion of 0.2 to 1 wt.% based on the total weight of the pressure-sensitive adhesive

[0133] • Light stabilizers such as UV absorbers or sterically hindered amines, preferably in a proportion of 0.2 to 1 wt.% based on the total weight of the pressure-sensitive adhesive

[0134] • Processing aids, preferably in a proportion of 0.2 to 1 wt.% based on the total weight of the pressure-sensitive adhesive

[0135] • Endblock reinforcing resins, preferably in a proportion of 0.2 to 10 wt.% based on the total weight of the pressure-sensitive adhesive and

[0136] • optionally further polymers, preferably of an elastomeric nature; correspondingly usable elastomers include, inter alia, those based on pure hydrocarbons, for example unsaturated polydienes such as natural or synthetically produced polyisoprene or polybutadiene, chemically substantially saturated elastomers such as saturated ethylene-propylene copolymers, a-olefin copolymers, polyisobutylene, butyl rubber, ethylene-propylene rubber, and chemically functionalized hydrocarbons such as halogen-containing, acrylate-containing, allyl- or vinyl ether-containing polyolefins, preferably in a proportion of 0.2 to 10 wt.% based on the total weight of the pressure-sensitive adhesive.

[0137] The type and quantity of mixing components can be selected as required.

[0138] It is also according to the invention if the adhesive mass does not contain some, preferably all, of the additives mentioned.

[0139] In one embodiment of the present invention, the pressure-sensitive adhesive contains further additives. Examples, but not limitations, include crystalline or amorphous oxides, hydroxides, carbonates, nitrides, halides, carbides, or mixed oxide / hydroxide / halide compounds of aluminum, silicon, zirconium, titanium, tin, zinc, iron, or the (alkaline earth) metals. These are essentially clays, for example, aluminum oxides, boehmite, bayerite, gibbsite, diaspore, and the like. Particularly suitable are phyllosilicates such as bentonite, montmorillonite, hydrotalcite, hectorite, kaolinite, boehmite, mica, vermiculite, or mixtures thereof. However, carbon blacks or other carbon modifications, such as carbon nanotubes, can also be used.

[0140] The adhesives can also be colored with dyes or pigments. The adhesives can be transparent, white, black, or colored.

[0141] Plasticizers that can be added include, for example, (meth)acrylate oligomers, phthalates, cyclohexanedicarboxylic acid esters, water-soluble plasticizers, plastic resins, phosphates or polyphosphates.

[0142] The addition of silicas, advantageously precipitated silica surface-modified with dimethyldichlorosilane, can be used to adjust the thermal shear strength of the pressure-sensitive adhesive.

[0143] In a preferred embodiment of the present invention, the pressure-sensitive adhesive is foamed. Foaming typically occurs by introducing and subsequently expanding microballoons, as described above.

[0144] The absolute density of a foamed pressure-sensitive adhesive is preferably 220 to 990 kg / m 3 , preferably 300 to 970 kg / m3 , more preferably 450 to 900 kg / m 3 , especially 500 to 850 kg / m 3 The relative density describes the ratio of the density of the foamed pressure-sensitive adhesive to the density of the formulation-identical, unfoamed pressure-sensitive adhesive. The relative density of a pressure-sensitive adhesive is preferably 0.20 to 0.99, more preferably 0.30 to 0.97, in particular 0.45 to 0.90, such as 0.50 to 0.85.

[0145] Within the scope of the present invention, it was surprisingly found that the adhesive tape is removable. This was unexpected, given that the carrier used in the adhesive tape is comparatively soft, so it was not expected that it would impart the adhesive tape the strength necessary for removable by stretching. Therefore, an embodiment in which the adhesive tape is removable, in particular by stretching, is preferred.

[0146] Another object of the present invention is a process for producing the adhesive tape according to the invention.

[0147] Process for producing the adhesive tape according to the invention

[0148] In a first embodiment of the process according to the invention, a mixture comprising a polyurethane and expandable microballoons

[0149] (i) extruded onto a temporary carrier and the resulting carrier is combined with at least one pressure-sensitive adhesive or

[0150] (ii) extruded directly onto a pressure-sensitive adhesive layer to form a carrier and combined with another pressure-sensitive adhesive on the opposite side.

[0151] In a preferred embodiment, the microballoons expand during the extrusion and coating process, so no subsequent heat input is necessary for the expansion of the microballoons. As described in (ii), a multilayer adhesive tape containing a foamed PU carrier can thus be produced in a single operation.

[0152] If necessary, subsequent or additional tempering of the multilayer composite can be carried out, for example to influence the foaming rate of the microballoons or to optimize the anchoring at the boundary layers.

[0153] The adhesive tape according to the invention is characterized by a unique property profile, which, in addition to residue-free removability, is characterized, among other things, by its damping capacity. These properties make the adhesive tape according to the invention particularly suitable for bonding sensitive components, such as those used in electronic devices. Therefore, a further subject of the present invention is the use of the adhesive tape according to the invention for bonding components in electronic devices.

[0154] The present invention further relates to an electronic device comprising a carrier according to the invention or an adhesive tape according to the invention. The present invention is explained in more detail with reference to the following examples and figures, which are in no way to be understood as limiting the scope of the invention.

[0155] Examples:

[0156] Table 1 shows the raw materials used in the (comparative) examples.

[0157] The following pressure-sensitive adhesives were used to produce the adhesive tapes:

[0158] Adhesive 1 (KM1):

[0159] A conventional 2 L glass reactor suitable for radical polymerizations under evaporative cooling was filled with 300 g of a reaction mixture consisting of 3 wt% acrylic acid, 67 wt% n-butyl acrylate, 30 wt% 2-ethylhexyl acrylate (M n = 64000 g / mol, M w- 1600000 g / mol), and 200 g of acetone:special boiling point spirit 60 / 95 (1:1). After 45 minutes of nitrogen gas being passed through the reactor with stirring, it was heated to 58 °C and 0.15 g of 2,2'-azodi(2-methylbutyronitrile) (Vazo 67®, DuPont), dissolved in 6 g of acetone, was added. The external heating bath was then heated to 75 °C and the reaction was carried out at a constant external temperature. After a reaction time of 1 h, another 0.15 g of VAZO 67®, dissolved in 6 g of acetone, was added. After 3 hours, the reactor was diluted with 90 g of special boiling point spirit 60 / 95.

[0160] After 5:30 hours of reaction time, 0.45 g of bis-(4-tert-butylcyclohexanyl)-

[0161] Peroxydicarbonate (Perkadox 16®, Akzo Nobel), dissolved in 9 g of acetone, was added. After a reaction time of 7 hours, a further 0.45 g of bis-(4-tert-butylcyclohexanyl)-

[0162] Peroxydicarbonate (Perkadox 16®, Akzo Nobel), dissolved in 9 g of acetone, was added. After a reaction time of 10 hours, the mixture was diluted with 90 g of special boiling point spirit 60 / 95. The reaction was stopped after 24 hours and cooled to room temperature.

[0163] The acrylate content was 45 wt.%, and the crosslinking was done with Erisys GA 240 (0.075% based on the polyacrylate). Kraton D1118 was used as the second polymer component at 20 wt.%. Sylvares TP 95 was used as the resin component at 35 wt.%.

[0164] Adhesive 2 (KM2):

[0165] Production of polyacrylates

[0166] A 300 L reactor conventional for radical polymerizations was charged with a total of 100 kg of 47 wt.% n-butyl acrylate, 30 wt.% 2-phenoxyethyl acrylate, 20 wt.% methyl acrylate, 3 wt.% acrylic acid, and 72.4 kg of benzine / acetone (70:30). After 45 minutes of nitrogen gas flow with stirring, the reactor was heated to 58 °C and 50 g of Vazo® 67 were added. The jacket temperature was then increased to 75 °C and the reaction was carried out at this constant external temperature. After a reaction time of 1 h, another 50 g of Vazo® 67 were added. After 3 h, the mixture was diluted with 20 kg of benzine / acetone (70:30) and after 6 h with 10.0 kg of benzine / acetone (70:30). To reduce the residual initiators, 0.15 kg of Perkadox® 16 was added after 5.5 and 7 hours. The reaction was stopped after 24 hours and cooled to room temperature. The solution was adjusted to a solids content of 38 wt.%.If necessary, the plasticizer was then incorporated (stirred at room temperature for 24 hours). Finally, 0.075 wt.%, based on the polymer, of Erysis GA240 (epoxy crosslinker) was stirred in as a crosslinker.

[0167] The resulting composition was coated in solution onto a siliconized PET film using a comma coating machine. The solvent was removed in a drying tunnel (20 min, 80 °C). Table 2 shows the formulations of the polyurethane-based supports produced in the inventive examples. pm layer thickness.

[0168] Table 3 shows an overview of the methods used in the (comparative) examples.

[0169] Adhesive tapes:

[0170] The individual adhesive tapes were manufactured as follows:

[0171] Production of adhesive tapes with TPU core layers TPU 1

[0172] The thermoplastic polyurethane granules for the production of the carriers called TPU 1, TPU 2, and TPU 3 (i.e., cores or core layers) are pre-dried in a granule dryer (Somos) at 80 °C for at least 3 hours prior to processing. The granules of the TPU and the microballoon pre-batch, along with all other additives, are fed via a simple hopper / hopper through the feed zone of the single-screw extruder (Collin, 25D), hereinafter referred to as the ESE. The temperature control of the ESE is carried out according to the optimal processing temperature of the respective TPU granules. After melting the granules, the extrudate is transferred via a hose into a feed block and then into the slot die. Table 4 shows the temperature control of the ESE, including the slot die.

[0173] Table 4: Temperature control of the ESE including the slot die.

[0174] *RPM = revolutions per minute.

[0175] The preformed melt film is then deposited onto a steel roller. Since TPU variants with lower Shore hardness are somewhat more tacky and therefore more difficult to remove from the steel roller, it has proven effective to coat directly onto a PET carrier with a release function, i.e., a temporary carrier or liner. This is fed via an unwinder and over the take-off roller, which is half-wrapped around it, and then wound up. The resulting TPU carriers (TPU core layers) are free of processing aids and do not exhibit a crystalline superstructure.

[0176] After setting the desired layer thickness, the bale with the PET carrier with release function is exchanged for the prefabricated functional layer, i.e., the pressure-sensitive adhesive layer containing unexpanded microballoons as described above, on the unwinder. In this way, the coating is applied directly onto the functional layer. Via another unwinder, the second prefabricated pressure-sensitive adhesive layer (containing unexpanded microballoons as described above), which has the same thickness as the first pressure-sensitive adhesive layer, is laminated onto the open, upper TPU layer via the guide roller or pressure roller. This three-layer product is then wound up.

[0177] Production of adhesive tapes with PO foam comparison examples 1 and 2:

[0178] The pressure-sensitive adhesive layers on PET carrier with release function are laminated on both sides to the PO foam.

[0179] Results:

[0180] Table 5 shows the structure of the adhesive tapes of the (comparative) examples, which are formed by combining the aforementioned carriers from Table 2 with the pressure-sensitive adhesive layers KM 1 and KM 2. The adhesive tapes are each double-sided, meaning that a pressure-sensitive adhesive layer (of the same thickness) is applied to both sides of the carrier. The table also shows the mechanical and adhesive properties of the adhesive tapes.

[0181] Table 5: Structure of the adhesive tapes of the (comparative) examples and their mechanical and adhesive properties.

[0182] The adhesive tapes of all examples according to the invention meet the requirements for impact strength in the z-direction according to the DuPont test in the z- and xy-direction of at least 0.8 J each. They also each exhibit good removability (i.e., (a) essentially no tears and at most slight adhesive residues that are easily removed with ethanol, which corresponds to a value of at least 4 in our test, or even no tears and no residues and no peel angle dependence, which corresponds to a value of at least 5 in our test). Comparative Examples 1 and 2 do not exhibit sufficient removability.

[0183] The compressibility, i.e., the force required when compressing the adhesive tapes in the examples according to the invention, is particularly suitable for use in electronic components to ensure adequate shock absorption. The force required in Comparative Examples 1 and 2 is comparatively too high even at low compressions of 30%.

[0184] In addition, the examples according to the invention are each characterized by a push-out strength of at least 150 N.

[0185] Character description

[0186] Figure 1 shows the results of the compression hardness measurements of the supports produced according to the examples after one cycle (Figure 1a) and after four cycles (Figure 1b). As can be seen, the inventive supports made of foamed TPU (diamond) according to Example 1 exhibit a significantly lower hardness than conventional supports made of foamed polyethylene (circle). While the conventional supports withstand a force of up to 180 N / cm 2 While a compression force of 50% is required to achieve this, the inventive supports require significantly less force. The compressive strength of the inventive supports also exhibits a significantly more linear progression.

[0187] Surprisingly, the force increases only slightly and almost linearly with increasing compression of the carriers according to the invention compared to the PE / EVA-based adhesive tapes, so that a significantly better damping capacity of the carriers according to the invention is achieved.

[0188] Test methods

[0189] Compressive hardness according to ISO 3386

[0190] The measurement method is used for the characterization and quality control of foams.

[0191] The compression hardness is the compressive stress in N / cm determined at a specified deformation of the foam in the z-direction during the loading process 2 .

[0192] Test specimens measuring 30 x 30 mm are cut from the material to be tested and stacked to a height of 15 mm. The cut specimens must then be conditioned in the test atmosphere for 24 hours. A sample of the foam to be tested is compressed five times using a compression testing machine under specified conditions. During the final compression test, both the deformation diagram and the compressive stress at the specified deformation are recorded. If required, the force during the first compression test is also determined. Five specimens are tested per sample or product.

[0193] Push-out strength

[0194] The push-out test can be used to determine the strength of the bonding of a component in a frame-shaped body, such as a window in a housing.

[0195] A rectangular, frame-shaped sample was cut out of the adhesive tape to be tested (external dimensions 43 mm x 33 mm; web width 2.0 mm each, internal dimensions (window cutout) 39 mm x 29 mm, adhesive surface on top and bottom 288 mm each 2This sample was glued to a rectangular ABS plastic frame (ABS = acrylonitrile butadiene styrene copolymers) (external dimensions 50 mm x 40 mm, web width of the long webs 8 mm each; web width of the short webs 10 mm each; internal dimensions (window cutout) 30 mm x 24 mm; thickness 3 mm). A rectangular PMMA disc (PMMA = polymethyl methacrylate) measuring 45 mm x 35 mm was glued to the other side of the double-sided adhesive tape sample. The entire available adhesive surface of the adhesive tape was used. The ABS frame, adhesive tape sample, and PMMA window were bonded in such a way that the geometric centers, the angle bisectors of the acute diagonal angles, and the angle bisectors of the obtuse diagonal angles of the rectangles were each superimposed (corner to corner, long sides to long sides, short sides to short sides). The bonding area was 360 mm 2The bond was pressed for 5 seconds at 10 bar and stored for 24 hours at 23 °C / 50% relative humidity. Immediately after storage, the adhesive assembly consisting of ABS frame, adhesive tape, and PMMA disc was placed on a frame (sample holder) with the protruding edges of the ABS frame aligned horizontally and the PMMA disc hanging freely downwards.

[0196] A pressure stamp is then moved vertically from above through the window of the ABS frame at a constant speed of 10 mm / s so that it presses centrally onto the PMMA plate, and the respective force (determined from the respective pressure and contact area between stamp and plate) is recorded as a function of the time from the first contact of the stamp with the PMMA plate until shortly after it falls off (measurement conditions 23 °C, 50 % relative humidity).

[0197] The force acting immediately before the failure of the adhesive bond between the PMMA sheet and the ABS frame (maximum force F max The force-time diagram (in N) is recorded as the response to the push-out test. A five-fold determination is performed.

[0198] Dielectric strength: DuPont test in z-plane and xy-plane

[0199] A square, frame-shaped sample is cut from the adhesive tape to be tested (external dimensions 33 mm x 33 mm, web width 2.0 mm, internal dimensions (window cutout) 29 mm x 29 mm). This sample is bonded to a polycarbonate (PC) frame (external dimensions 45 mm x 45 mm, web width 10 mm, internal dimensions (window cutout) 25 mm x 25 mm; thickness 3 mm). A PC window measuring 35 mm x 35 mm is bonded to the other side of the double-sided adhesive tape. The PC frame, adhesive tape frame, and PC window are bonded such that the geometric centers and diagonals overlap (corner to corner). The bonded area is 248 mm. 2The bond is pressed for 5 s with 248 N and stored for 24 hours in a conditioned condition at 23 °C / 50 % relative humidity. Immediately after storage, the adhesive composite consisting of PC frame, adhesive tape and PC window is clamped into a specimen holder in such a way that the composite is aligned horizontally for the test in the z-plane (vertical alignment of the composite for the test in the xy direction). The PC frame rests flat on the sample holder at the protruding edges so that the PC window is freely suspended 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 cuboid impact head with the impact geometry 3 mm x 20 mm is placed flush on the edge of the PC window that is freely accessible from above.

[0200] A 150 g weight, guided by two guide rods, is dropped vertically onto the assembled sample holder, sample, and impact head from a height of 5 cm (measurement conditions: 23 °C, 50% relative humidity). The height of the drop weight is increased in 5 cm increments until the impact energy destroys the sample due to the impact load and the PC window detaches from the PC frame.

[0201] To compare experiments with different samples, the energy is calculated as follows:

[0202] Energy E [J] = Height [m]*Mass Weight [kg]*9.81 kg / m*s 2

[0203] Five samples per product are tested and the average energy value is given as an indicator of the breakdown strength.

[0204] Removability - Tear test

[0205] A 10 mm wide strip sample is cut from the double-sided adhesive tape to be tested. This sample is adhered to a cleaned SUS steel plate (external dimensions 200 mm x 50 mm x 3 mm). Three individual strips are to be adhered parallel, spaced at least 1 cm apart. The backing of the double-sided tapes should not be removed. The adhesive tape ends at the edge of the substrate. The bonds are activated using a 4 kg steel roller with at least 5 double strokes at 10 m / min and conditioned for 72 hours at 85 °C / 85% relative humidity. After storage, the test specimen is cooled for two hours at room temperature, and the bond is removed manually, also at room temperature. During removal, the tester performs an assessment. Three test specimens of each sample are tested, and their removability is rated on a scale of 1 to 5. A score of 5 represents the best result.

[0206] Shore hardness A

[0207] The Shore A hardness of a sample is determined according to ASTM D 2240.

[0208] Modulus at 100% elongation

[0209] The modulus at 100% elongation of a specimen is determined according to DIN 53504.

[0210] thickness

[0211] 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 determinable) 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 gauges (touch-type testers) with an accuracy of less than 1 μm. If thickness variations are detected, the average value of measurements taken at at least three representative locations is given, thus, in particular, not measured at creases, folds, spots, and the like.

[0212] Just as with 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 gauges (touch gauges) with an accuracy of less than 1 μm. If thickness variations are detected, the average value of measurements taken at at least three representative locations is given, thus excluding creases, folds, spots, and the like.

[0213] The density of adhesive layers is determined by calculating the quotient of the mass application and the thickness of the adhesive layer applied to a liner.

[0214] 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, less the (known or separately determinable) mass of a section of the same dimensions of the liner used.

[0215] 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 determinable) 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 gauges (touch-type testers) with an accuracy of less than 1 pm. If thickness fluctuations are detected, the mean value of measurements taken at at least three representative locations is given, thus, in particular, not measured at creases, folds, spots, and the like.

[0216] The density of a carrier can be determined analogously.

[0217] Static glass transition temperature T g

[0218] The glass transition temperature of polymers can be determined using differential scanning calorimetry (DSC - Dynamic Scanning Calorimetry, according to DIN 53765). For this purpose, approximately 5 mg of the untreated polymer sample is weighed into an aluminum crucible (volume 25 μl) and sealed with a perforated lid. A Netzsch DSC 204 F1 is used for the measurement, operated under nitrogen for inerting. The sample is first cooled to -150°C, then heated to +150°C at a heating rate of 10 K / min and cooled back to -150°C. The subsequent second heating curve is run at a rate of 10 K / min, and the change in heat capacity is recorded. Glass transitions are marked as steps in the thermogram. The glass transition temperature is determined as follows: A tangent is drawn to the baseline of the thermogram before each step.In the step region, a best-fit line is placed parallel to the ordinate so that it intersects the two tangents, creating two regions of equal content (between each tangent, the best-fit line, and the measured curve). The intersection point of the best-fit line positioned in this way with the measured curve yields the glass transition temperature.

[0219] Molecular weight M n , M w

[0220] The number average molecular weight M n or weight-average molecular weight M win this document refer to the determination by gel permeation chromatography (GPC). The determination is carried out on 100 μl of a 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. The precolumn used is a PSS-SDV column, 5 μm, 103 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). For separation, a combination of columns of type PSS-SDV, 5 pm, 10 3 Ä and 10 5 Ä and 10 6Ä with 8.0 mm x 300 mm columns each (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer). The flow rate is 1.0 ml per minute. Calibration is performed for polar molecules, such as the starting materials for polyurethane or polyacrylates, against PMMA standards (polymethyl methacrylate calibration) and otherwise against PS standards (polystyrene calibration).

[0221] Adhesive resin softening temperature

[0222] The adhesive resin softening temperature is determined using the relevant methodology known as Ring & Ball, standardized according to ASTM E 28.

Claims

Patent claims 1. A carrier for an adhesive tape, wherein the carrier comprises at least one closed-cell layer foamed with microballoons based on a thermoplastic polyurethane, wherein the carrier has a compression hardness of at least 50% at a maximum force of 140 N / cm 2 , preferably at a maximum force of 120 N / cm 2 , particularly preferably at a maximum force of 100 N / cm 2 determined according to DIN EN ISO 3386-2.

2. Carrier according to claim 1, characterized in that the carrier has a density of 300 to 1200 kg / m 3 , preferably 400 to 900 kg / m 3 particularly preferably 500 to 800 kg / m 3 has.

3. Carrier according to at least one of the preceding claims, characterized in that the polyurethane is selected from the group consisting of aromatic polyurethanes, aliphatic polyurethanes, polyester-polyol-based polyurethanes, polyether-polyol-based polyurethanes, polycarbonate-based polyurethanes and hybrids and mixtures thereof.

4. A carrier according to at least one of the preceding claims, characterized in that the polyurethane is crosslinked or uncrosslinked.

5. A carrier according to at least one of the preceding claims, characterized in that the carrier has a thickness of 20 to 2500 pm, preferably 150 to 1000 pm.

6. A carrier according to at least one of the preceding claims, characterized in that the carrier has a breakdown strength of 0.3 to 1.5 J, determined by DuPont.

7. Adhesive tape comprising a carrier according to at least one of the preceding claims, wherein the carrier is coated on at least one side with a pressure-sensitive adhesive.

8. Adhesive tape according to claim 7, characterized in that it is removable.

9. Adhesive tape according to at least one of claims 7 or 8, characterized in that at least one of the pressure-sensitive adhesive layers consists of a pressure-sensitive adhesive based on vinyl aromatic block copolymer.

10. Adhesive tape according to at least one of claims 7 to 9, characterized in that at least one of the pressure-sensitive adhesive layers consists of a polyacrylate-based pressure-sensitive adhesive.

11. Adhesive tape according to at least one of claims 7 to 10, characterized in that at least one of the pressure-sensitive adhesive layers is foamed, preferably by microballoons.

12. A process for producing an adhesive tape according to at least one of claims 7 to 11, in which a mixture of a polyurethane and expandable microballoons (i) is extruded onto a temporary carrier and the resulting carrier is combined with a pressure-sensitive adhesive, or (ii) is extruded onto a pressure-sensitive adhesive layer to obtain a carrier, the carrier being combined with a further pressure-sensitive adhesive on the side opposite the pressure-sensitive adhesive layer, the carrier being foamed during or after the extrusion and / or coating process.

13. Use of an adhesive tape according to at least one of claims 7 to 11 for bonding components in electronic devices.

14. An electronic device comprising a carrier according to at least one of claims 1 to 6 and / or an adhesive tape according to at least one of claims 7 to 11.

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