DE102020207470A1 - OPTICALLY TRANSPARENT HIGHLY FLEXIBLE ADHESIVE TAPE AND ITS USE FOR BONDING OPTICAL COMPONENTS - Google Patents

Abstract

The present invention relates to an adhesive tape comprising at least one first pressure-sensitive adhesive (K1), at least one second pressure-sensitive adhesive (K2) and at least one carrier material (T), which is arranged between the two pressure-sensitive adhesives (K1) and (K2), the pressure-sensitive adhesives ( K1) and (K2) and the carrier material (T) are each optically transparent and the carrier material (T) has a 100% modulus of 0 to 5 N, measured according to the 100% modulus test method, with a layer thickness of 10 μm. The present invention also relates to the use of an adhesive tape according to the invention for bonding components, preferably flexible displays, in electronic devices, in particular in mobile electronic devices, preferably tablets, cell phones or smart watches.

Description

The present invention relates to an adhesive tape comprising at least one first pressure-sensitive adhesive (K1), at least one second pressure-sensitive adhesive (K2) and at least one carrier material (T), which is arranged between the two pressure-sensitive adhesives (K1) and (K2), the pressure-sensitive adhesives ( K1) and (K2) and the carrier material (T) are each optically transparent and the carrier material (T) has a 100% modulus of 0 to 5 N at a layer thickness of 10 μm, measured according to test method 1.8 "Determination of the modulus" given below 100% ”(hereinafter referred to as“ Modulus 100% test method ”). The present invention also relates to the use of an adhesive tape according to the invention for bonding components, in particular flexible displays, in electronic devices, preferably in mobile electronic devices, preferably tablets, cell phones or smart watches.

State of the art

A common use of pressure sensitive adhesives in industry today is in the manufacture of various displays, such as computer monitors, televisions, cell phones, and small displays (in cars, appliances, wearables, electronic devices, etc.). Flexible electronic displays, in which the display can be freely bent without tearing or breaking, are an emerging area of technology for the manufacture of electronic devices using, for example, flexible plastic substrates. This technology enables electronic functions to be integrated into non-planar objects, conformance with the desired design, and flexibility during use, which results in a multitude of new applications.

With the advent of flexible electronic displays, there is an increasing need for adhesives and in particular for optically transparent adhesives (OCA) and OCA adhesive tapes, which are used as a mounting layer or gap filling layer between an outer cover lens or film (e.g. based on glass, PET, PC, PMMA, Polyimide, PEN, cyclic olefin copolymer etc.) and an underlying display module for electronic display arrangements. The presence of OCA improves the performance of the display by increasing brightness and contrast while at the same time structurally supporting the assembly. In the case of a flexible assembly, the OCA or the OCA tape also serves as a mounting layer, which in addition to the typical OCA functions can also absorb most of the stress caused by bending in order to prevent damage to the fragile components of the display and the electronic To protect components from breaking due to the bending. The OCA layer or the OCA adhesive tape can also be used to position the neutral bending axis on or at least in the vicinity of the fragile components of the display, such as the barrier layers, the control electrodes or the thin-film transistors of an organic light-emitting display (OLED) and fix.

Typical OCAs are inherently viscoelastic and are designed to provide durability under various environmental conditions and high frequency loads. In such cases, a high degree of adhesion and some balance of viscoelastic properties are maintained in order to achieve good pressure-sensitive behavior and to incorporate damping properties into the OCA.

Due to the vastly different mechanical requirements for flexible display assemblies, new types of adhesives and adhesive tapes have to be developed for use in this new technology area. OCAs and OCA adhesive tapes for flexible displays are exposed to tension depending on their position in the display. Bending the display can reduce or increase the tension. Many prior art OCA adhesive tapes react to these stresses with delamination or folds.

There is therefore a need for OCA adhesive tapes which, on the one hand, have high elasticity with little application of force, in order to avoid delamination and folds when the display is bent. On the other hand, however, these adhesive tapes must also have a high adhesive strength with little application of force in order to ensure permanent and stable bonding of the display without the risk of damage during bonding.

Object of the invention

The object of the present invention was accordingly to provide an optically clear adhesive tape (OCA adhesive tape) which, on the one hand, is extremely elastic in order to avoid delamination and wrinkling during bending of the display, and, on the other hand, a high bond strength with a low adhesive strength Has the action of force in order to ensure reliable and permanent bonding without the use of high pressures, which can lead to damage to the electronic components of the display. In addition, an object of the present invention was the use of an optically clear adhesive tape for bonding components, in particular flexible displays, in electronic devices, preferably in mobile electronic devices, preferably tablets, cell phones or smart watches.

Solution of the task

• - wobei die Haftklebemassen (K1) und (K2) sowie das Trägermaterial (T) jeweils einen HAZE-Wert von 0 % bis weniger als 1 % sowie eine Transmission von mehr als 99 bis 100 %, jeweils gemessen gemäß ASTM D1003-13, aufweisen und
• - wobei die Differenz zwischen dem Brechungsindex des Trägermaterials (T) und dem Brechungsindex der mindestens zwei Haftklebemassen (K1) und (K2) jeweils 0 bis 0,1 beträgt,

dadurch gekennzeichnet, dass
das Trägermaterial (T) bei einer Schichtdicke von 10 µm einen Modulus 100 % von 0 bis 5 N, gemessen gemäß Prüfmethode Modulus 100 %, aufweist.The object is achieved by an adhesive tape comprising at least one first pressure-sensitive adhesive (K1), at least one second pressure-sensitive adhesive (K2) and at least one carrier material (T) which is arranged between the two pressure-sensitive adhesives (K1) and (K2),

• - The PSAs (K1) and (K2) and the carrier material (T) each having a HAZE value of 0% to less than 1% and a transmission of more than 99 to 100%, each measured in accordance with ASTM D1003-13 and
• - wherein the difference between the refractive index of the carrier material (T) and the refractive index of the at least two PSAs (K1) and (K2) is in each case 0 to 0.1,

characterized in that
the carrier material (T) with a layer thickness of 10 μm has a modulus 100% of 0 to 5 N, measured according to the test method modulus 100%.

The object is also achieved by using an adhesive tape according to the invention for bonding components, in particular flexible displays, in electronic devices, preferably in mobile electronic devices, preferably tablets, cell phones or smart watches.

The invention is based on the knowledge that the elasticity or flexibility of optically clear adhesive tapes can be increased if an optically clear carrier material which has a high elasticity or a 100% modulus of 0 to 5 N is used between two OCA PSAs . Such OCA adhesive tapes have a high elasticity and a high bond strength with little pressure. This ensures stable and permanent bonding of flexible displays without delamination or wrinkles occurring when the display is bent. In addition, high pressure does not have to be applied in the production of the displays in order to achieve a high bond strength of the adhesive tape according to the invention. In this way, damage to the electronic components of the display is avoided during bonding.

Detailed description of the invention

Adhesive tape according to the invention:

The adhesive tape of the invention is an optically clear adhesive tape (OCA adhesive tape) which comprises at least two pressure-sensitive adhesives (K1) and (K2) and a carrier material (T) between these pressure-sensitive adhesives. In order for an optically clear adhesive tape to result from this layer composite, both the PSAs (K1) and (K2) and the carrier material (T) must be optically clear, i.e. have a HAZE value of 0% to less than 1%, a high transmission of 99 to 100% and a difference in the refractive indices of 0 to 0.1. In addition, the adhesive tape according to the invention is highly flexible. This is achieved according to the invention in that the adhesive tape contains a highly flexible carrier material (T). The combination of optically clear pressure-sensitive adhesives (K1) and (K2) and highly transparent and highly flexible carrier material (T) thus results in an optically clear and highly flexible adhesive tape in which no delamination or creasing occurs when under tension.

The adhesive tape according to the invention has two side surfaces, a front side and a rear side. The terms front and back relate to the two surfaces of the adhesive tape parallel to its main extent (surface area, main expansion plane) and are only used to distinguish between these two surfaces arranged on opposite sides of the adhesive tape, without the absolute spatial arrangement of the both surfaces is fixed; consequently, the front side can also represent the side surface of the adhesive tape that is spatially rearward, namely if the rear side accordingly forms its side surface that is spatially forward. The general expression "adhesive tape" in the context of this invention accordingly includes all flat structures such as films or film sections extended in two dimensions, tapes with extended length and limited width, Tape sections, diecuts, labels and the like. The adhesive tape can be produced in the form of a roll, that is to say rolled up on itself in the form of an Archimedean spiral.

Pressure-sensitive adhesives (PSA) are, in particular, polymeric compositions which - if necessary through suitable additives with other components, such as adhesive resins - are permanently tacky and permanently adhesive at the application temperature (unless otherwise defined, at room temperature) and adhere to a large number of surfaces upon contact, in particular adhere immediately (have a so-called "tack"). They are able to wet a substrate to be bonded sufficiently at the application temperature without activation by solvents or by heat - but usually by the influence of a more or less high pressure - so that there is sufficient adhesion between the mass and the substrate be able to develop sufficient interactions. The main influencing parameters for this are pressure and contact time. The special properties of the PSAs are due, inter alia, in particular to their viscoelastic properties.

Pressure-sensitive adhesives comprise at least one or more polymers (in the context of this document the polymers are referred to collectively as the “polymer component” of the pressure-sensitive adhesive), which can be homopolymers and / or comonomers composed of various monomers polymerizable with one another. The polymer component can already have pressure-sensitively adhesive properties, or they can only acquire these after suitable additives, for example with resins.

The polymer component can in principle be produced on the basis of polymers of different chemical nature. The pressure-sensitive adhesive properties can be influenced, inter alia, by the type and proportions of the monomers used in the polymerization of the polymers on which the pressure-sensitive adhesive is based, their average molecular weight and molecular weight distribution, and by the type and amount of additives in the pressure-sensitive adhesive, such as tackifier resins, plasticizers and the like.

Resins for the purposes of this document are oligomeric and polymeric compounds with a number average molecular weight M _n of not more than 10,000 g / mol; these are not included in the polymer component.

To achieve the viscoelastic properties, the monomers on which the polymers on which the PSA is based are based, and any further components of the PSA that may be present, are selected in particular such that the PSA has a glass transition temperature (measured according to DIN 53765: 1994-03 ) below the application temperature (i.e. usually below room temperature).

Suitable measures to increase cohesion, such as crosslinking reactions (formation of bridging links between the macromolecules), can increase and / or shift the temperature range in which a polymer composition has pressure-sensitive adhesive properties. The area of application of the PSAs can thus be optimized by adjusting between flowability and cohesion of the composition.

The adhesive tape of the invention can contain two identical or two different PSAs. It is therefore preferred according to the invention if the PSAs (K1) and (K2) are identical or different, preferably identical.

All pressure-sensitive adhesives known to the person skilled in the art can be used as PSAs (K1) and (K2), e.g. those based on acrylates and / or methacrylates, polyurethanes, natural rubbers, synthetic rubbers, styrene block copolymer compositions with an elastomer block composed of unsaturated or hydrogenated polydiene blocks (polybutadiene, polyisoprene, copolymers of both and other elastomer blocks familiar to those skilled in the art), polyolefins, fluoropolymers and / or silicones. This also includes other materials which have pressure-sensitive adhesive properties in accordance with the “Handbook of Pressure Sensitive Adhesive Technology” by Donatas Satas (Satas & Associates, Warwick 1999).

According to a first preferred embodiment of the first subject matter of the invention, however, the pressure-sensitive adhesive (K1) and / or the pressure-sensitive adhesive (K2) is an acrylate-based pressure-sensitive adhesive.

In the context of the present invention, “acrylate-based PSAs” are understood as meaning PSAs in which the properties of the PSAs or polymer mixture at least are can be largely determined by the basic properties of the (meth) acrylate polymer (the so-called “base polymer”), although it is of course not excluded that these are additionally influenced by the use of modifying auxiliaries or additives or other polymers in the composition. In particular, this can mean that the proportion of the base polymer in the total mass of the polymeric phase is more than 50% by weight. (Meth) acrylate polymers are to be understood as meaning polymers based on acrylates, methacrylates and mixtures thereof.

1. a) 5 bis 35 Gew.-% eines oder mehrerer hydroxygruppenhaltiger Monomere mit copolymerisierbarer Doppelbindung,
2. b) 0 bis 50 Gew.-% eines oder mehrerer Acrylat- und/oder Methacrylatmonomere mit jeweils zumindest einer Amidgruppe, Urethangruppe, Harnstoffgruppe, Carbonsäureanhydrideinheit und/oder Ethylenglykoleinheit,
3. c) 15 bis 95 Gew.-% eines Alkyl(meth)acrylates, wobei der Alkylrest eines bis 14 Kohlenstoffatome aufweist,

wobei der Haftklebemasse zumindest ein 2-(2H-Benzotriazol-2-yl)derivat (im Folgenden auch als „Additiv 1“ bezeichnet) beigemischt ist, und zwar bevorzugt in einer solchen Menge, dass das Produkt aus Dicke der Acrylathaftklebemassenschicht und der Menge des zugemischten Additivs 1 je 100 g der Polymerkomponente, im Bereich von 75 bis 200 g*µm (1 g*µm = 10^-9 kg*m) liegt.Acrylate-based PSAs (K1) and / or (K2) which are preferably used are PSAs whose polymer component is formed from one or more copolymers which are each attributable to the following monomers:

1. a) 5 to 35% by weight of one or more monomers containing hydroxyl groups with a copolymerizable double bond,
2. b) 0 to 50% by weight of one or more acrylate and / or methacrylate monomers each with at least one amide group, urethane group, urea group, carboxylic acid anhydride unit and / or ethylene glycol unit,
3. c) 15 to 95% by weight of an alkyl (meth) acrylate, the alkyl radical having one to 14 carbon atoms,

wherein at least one 2- (2H-benzotriazol-2-yl) derivative (hereinafter also referred to as “additive 1”) is admixed with the PSA, preferably in an amount such that the product of the thickness of the acrylate PSA layer and the amount of admixed additive 1 per 100 g of the polymer component is in the range from 75 to 200 g * µm (1 g * µm = 10 ^-9 kg * m).

Suitable monomers (a) are, for example, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 2-hydroxyethyl acrylamide, N-hydroxypropyl acrylamide and mixtures thereof. In addition to hydroxymonomers with acrylamide groups, it is also possible to use hydroxymonomers with ethylene glycol units. An example of this is hydroxy-terminated propylene glycol acrylate.

Optionally, up to 50% by weight of one or more acrylate and / or methacrylate monomers, each of which carries at least one polar protic or basic group, are contained as component b). These groups can in particular be carboxylic acid groups, carboxylic acid anhydride groups, amide groups, amino groups, urethane groups or urea units. If two or more of these functional groups are present, they can be identical or be selected independently of one another from the functional groups mentioned. Examples of these which are very suitable according to the invention are acrylic acid or methacrylic acid, N-vinylcaprolactam, N-vinylpyrrolidone, acrylamide, methacrylamide, N-alkyl acrylamide, such as e.g. N-methylacrylamide, N-alkyl methacrylamides, e.g. N-methyl methacrylamide, N, N-dialkyl acrylamides, e.g. N, N-dimethylacrylamide, diacetone acrylamide and N, N-alkyl methacrylamides, e.g. N, N-dimethyl methacrylamide. Further examples are 4-vinylpyridine, N-vinylphthalimide, N-vinylformamide. Also very suitable monomers in the sense of monomer group (b) are monomers with (poly) ethylene glycol segments, at least two ethylene glycol units being present in the monomer. The corresponding monomers can in particular be hydroxy-terminated and / or methoxylated.

Due to impurities from the base monomer (in particular the monomers from monomer group (c)), traces of acrylic acid can also be contained in the composition if the monomers of monomer group (b) are to be dispensed with.

Component c) contains from 15 to 95% by weight of one or more alkyl acrylates, the alkyl radical in particular having 1 to 14 carbon atoms. The hydrocarbon radical of the acrylic monomers can be branched or unbranched or cyclic, saturated or unsaturated, aliphatic or aromatic, substituted or unsubstituted. The hydrocarbon radical of the acrylic monomers can in particular be an alkyl or alkenyl group with one to 14 carbon atoms; hydrocarbon radicals with 4 to 10 carbon atoms are particularly advantageous. Advantageous examples of acrylic monomers which can be used in the sense of monomer group (c) are n-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, n-heptyl acrylate, n-octyl acrylate, n-nonyl acrylate, lauryl acrylate, stearyl acrylate, behenyl acrylate, and the like branched isomers, such as isobutyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate. Further advantageous monomers (c) which can be used are, for example, methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, isooctyl methacrylate. Further advantageous monomers (c) are monofunctional acrylates and / or methacrylates of bridged cycloalkyl alcohols which have at least 6 carbon atoms. The Cycloalkyl alcohols can also be substituted, for example by C-1-6 alkyl groups, halogen atoms or cyano groups. Advantageous examples of such monomers are cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate and 3,5-dimethyladamantyl acrylate.

wobei die Reste R unabhängig voneinander und die Reste R* unabhängig voneinander und unabhängig von den Resten R jeweils Wasserstoff oder anorganische oder organische - aliphatische oder aromatische - Reste darstellen,
wobei bevorzugt die Reste R unabhängig voneinander Wasserstoff oder lineare oder verzweigte oder cyclische, aliphatische oder aromatische, Kohlenwasserstoffreste sind, insbesondere mit bis zu 14 Kohlenstoffatomen, wobei die Kohlenwasserstoffreste auch heterosubstituiert sein können, wie ein- oder mehrfach mit Stickstoff und/oder Schwefel und/oder Sauerstoff, und
die Reste R* unabhängig voneinander Wasserstoff, Halogenidsubstituenten (insbesondere vorteilhaft Cl) oder aliphatische, lineare oder verzweigte oder cyclische Kohlenwasserstoffreste mit 1 bis 12 Kohlenstoffatomen darstellen.2- (2H-benzotriazol-2-yl) derivatives of the formula (I) are preferably contained as additive 1

where the radicals R independently of one another and the radicals R * independently of one another and independently of the radicals R each represent hydrogen or inorganic or organic - aliphatic or aromatic - radicals,
where preferably the radicals R independently of one another are hydrogen or linear or branched or cyclic, aliphatic or aromatic, hydrocarbon radicals, in particular with up to 14 carbon atoms, wherein the hydrocarbon radicals can also be heterosubstituted, such as one or more times with nitrogen and / or sulfur and / or oxygen, and
the radicals R * are independently hydrogen, halide substituents (particularly advantageously Cl) or aliphatic, linear or branched or cyclic hydrocarbon radicals having 1 to 12 carbon atoms.

If cyclic hydrocarbon radicals are mentioned at this point or elsewhere in the context of this document, this refers in particular to those radicals that contain a cyclic building block at any point - and not in the immediate vicinity of the aromatic rings - so that between them cyclic building block and the aromatic ring one or more carbon atoms and / or heteroatoms are arranged.

It can be provided to crosslink the acrylate-based pressure-sensitive adhesive in order to increase the cohesion of this pressure-sensitive adhesive. This ensures punchability and perfect bonding. In addition, the parts to be joined are prevented from sliding off during the gluing, in particular during the vertical gluing.

The acrylate-based pressure-sensitive adhesive is preferably crosslinked by thermal crosslinking and / or chemical crosslinking. In order to achieve good processability, the crosslinking should then be carried out up to a degree of crosslinking which is characterized by a loss factor (tan δ value) between 0.1 and 1.0, the loss factor being the quotient of the storage modulus G '(G '= τ / γ · cos (δ)) and the loss modulus G' '(G' '= τ / γ · sin (δ)). This loss factor can be determined by means of a rheometer in plate-on-plate configuration, based on a round sample with a sample diameter of 8 mm and a sample thickness of 1 mm at 130 ° C. and 10 rad / s.

The crosslinking is very preferably carried out using polyfunctional crosslinking substances (hereinafter referred to as crosslinking agents), which are added to the acrylate-based pressure-sensitive adhesive prior to crosslinking. Such crosslinkers can react with suitable reactive groups of the acrylate-based polymers under the respective crosslinking conditions, and thereby form bridges between the macromolecules, which creates a network.

The acrylate-based PSA is particularly preferably thermally crosslinked. To achieve the desired degree of crosslinking, isocyanate crosslinkers, epoxy-based crosslinkers, melamine-based crosslinkers, peroxide-based crosslinkers, metal chelate-based crosslinkers, metal salt-based crosslinkers, carbodiimide-based crosslinkers, oxazoline-based crosslinkers, aziridine-based crosslinkers, amine based crosslinkers, silane-based crosslinkers and mixtures thereof can be used.

When difunctional crosslinkers are used, their proportion in the acrylate-based pressure-sensitive adhesive is between 0.3 and 3 parts by weight, particularly preferably between 0.5 and 2 parts by weight, of crosslinker per 100 parts by weight of the acrylate-based pressure-sensitive adhesive. When trifunctional crosslinkers are used, their proportion is preferably added at 0.02 to 0.5 part by weight per 100 parts by weight of the acrylate-based pressure-sensitive adhesive, especially preferably 0.05 to 0.2 part by weight. However, crosslinkers with higher functionality can also be used. Furthermore, several crosslinkers can be used, which can be the same or different with regard to their functionality (for example a combination of difunctional and trifunctional crosslinkers). The amounts used should then be adjusted advantageously.

It can be provided according to the invention to add further components and / or additives to support the setting of the desired product properties, in particular those additives which are not incorporated into the acrylate-based polymer and / or do not take part in the crosslinking reaction. These compounds can be added before, during or after the polymerization, but advantageously before the crosslinking.

The presence of tackifier resins and plasticizers is preferably dispensed with in the acrylate-based pressure-sensitive adhesive which is used for the adhesive tape of the invention, so that the acrylate-based pressure-sensitive adhesive does not contain any resins and / or plasticizers, particularly advantageously neither resins nor plasticizers. Such additives often have disadvantageous effects when used for optical bonds. The resins used in accordance with the prior art as tackifier resins for acrylate-based PSAs are usually polar in nature in order to achieve compatibility with the acrylate-based polymer matrix. This usually leads to the use of aromatic tackifier resins, which discolour yellowish on prolonged storage or when exposed to light.

In order to achieve a high optical transparency of the adhesive tape of the invention, it is preferred according to the invention if the PSA (K1) and / or the PSA (K2) have a high refractive index. It is therefore advantageous according to the invention in this context if the pressure-sensitive adhesive (K1) and / or (K2), in particular the preferred acrylate-based pressure-sensitive adhesives listed above, has a refractive index of 1.40 to 1.59, in particular 1.48, where the refractive index is determined using an Abbe refractometer at 25 ° C. and a wavelength of 550 nm ± 150 nm on a 25 μm thick film of the pressure-sensitive adhesive.

In addition, it is preferred according to the invention in this connection if the pressure-sensitive adhesive (K1) and / or (K2) has a low dielectric constant. According to the invention, the PSA (K1) and / or (K2) therefore preferably has a dielectric constant of 3 to 5, in particular of 4, the dielectric constant using the capacitance method between parallel plates at a frequency of 100 kHz and a temperature of 25 ° C and 50% relative humidity is determined on a 25 μm thick film of the PSA.

According to a second preferred embodiment of the first subject matter of the invention, the pressure-sensitive adhesive (K1) and / or the pressure-sensitive adhesive (K2) is a synthetic rubber.

Preferred synthetic rubbers are those based on block copolymers containing polymer blocks, which are predominantly vinyl aromatics (A blocks), preferably styrene, and predominantly by polymerization of 1,3-dienes (B blocks), preferably butadiene, isoprene or a mixture of both monomers , are formed. These B-blocks usually have a low polarity. Both homo- and copolymer blocks can preferably be used as B blocks.

The block copolymers resulting from the A and B blocks can contain identical or different B blocks, which can be partially, selectively or completely hydrogenated. The block copolymers can have linear A-B-A structures. Block copolymers of radial shape as well as star-shaped and linear multiblock copolymers can also be used. A-B diblock copolymers can be present as further components. All of the aforementioned polymers can be used alone or in a mixture with one another.

Instead of the preferred polystyrene blocks, polymer blocks based on other aromatic-containing homopolymers and copolymers (preferably C ₈ to C ₁₂ aromatics) with glass transition temperatures of over 75 ° C. can also be used as vinyl aromatics, such as, for example, α-methylstyrene-containing aromatic blocks. It can also contain the same or different A blocks.

It is also possible to use block copolymers which, in addition to the blocks A and B described above, contain at least one further block, e.g. A-B-C block copolymers.

It is also conceivable, but less preferred, to use the abovementioned B blocks with A blocks of a different chemical nature which have a glass transition temperature above room temperature, such as, for example, polymethyl methacrylate.

Vinyl aromatic block copolymers are commercially available, for example, under the name Kraton from Kraton, (Kraton D 1101 and 1102 as styrene-butadiene-styrene block copolymers, Kraton D 1107 or 1163 as styrene-isoprene-styrene block copolymers, or Kraton G 1652 as hydrogenated styrene Butadiene-styrene block copolymer), known under the name Europrene from Polimeri Europa (styrene block copolymers with isoprene, butadiene or their hydrogenation products) or under the name Septon from Kuraray (hydrogenated styrene-isoprene-styrene block copolymers). AB-C vinyl aromatic block copolymers are e.g. commercially available under the name SBM from Arkema.

Preferred synthetic rubbers are those which have a polyvinyl aromatic content of 10% by weight to 80% by weight, based on the total weight of the synthetic rubber. In particular, the total proportion of vinyl aromatic block copolymers, based on the synthetic rubber, is at least 20% by weight, preferably at least 30% by weight, more preferably at least 35% by weight. A proportion of less than 10% by weight of vinyl aromatic block copolymers has the consequence that the cohesion of the synthetic rubber is relatively low. In contrast, a proportion of more than 80% by weight of vinyl aromatic block copolymers means that the synthetic rubber is hardly tacky.

According to the invention, the synthetic rubber preferably contains at least one adhesive resin in order to increase the adhesion in the desired manner. The adhesive resin should be compatible with the elastomer block of the block copolymers.

For example, non-hydrogenated, partially or fully hydrogenated resins based on rosin and rosin derivatives, hydrogenated polymers of dicyclopentadiene, non-hydrogenated, partially, selectively or fully hydrogenated hydrocarbon resins based on C ₅ , C ₅ / C ₉ - Or Cg monomer streams, polyterpene resins based on α-pinene and / or ss-pinene and / or δ-limonene and hydrogenated polymers of preferably pure C ₈ and Cg aromatics are used. The abovementioned tackifier resins can be used either alone or as a mixture. Resins which are solid as well as liquid resins at room temperature can be used. In order to ensure high aging and UV stability, hydrogenated resins with a degree of hydrogenation of at least 90%, preferably of at least 95%, are preferred.

Furthermore, non-polar resins with a DACP value (diacetone alcohol cloud point) above 30 ° C and a mmAP (mixed methylcylohexane aniline point) value of greater than 50 ° C, in particular with a DACP value above 37 ° C and a mmAP value greater than 60 ° C is preferred. The DACP value and the mmAP value each indicate the solubility in a specific solvent. A particularly high permeation barrier, especially against water vapor, is achieved through the selection of these areas.

Resins with a softening temperature (ring / ball) of more than 95 ° C., in particular more than 100 ° C., are further preferred. This selection achieves a particularly high permeation barrier, in particular to oxygen.

• • Plastifizierungsmittel, wie zum Beispiel Weichmacheröle, oder niedermolekulare flüssige Polymere, wie zum Beispiel niedermolekulare Polybutene,
• • primäre Antioxidanzien, wie zum Beispiel sterisch gehinderte Phenole,
• • sekundäre Antioxidanzien, wie zum Beispiel Phosphite oder Thioether,
• • Prozessstabilisatoren, wie zum Beispiel C-Radikalfänger,
• • Lichtschutzmittel, wie zum Beispiel UV-Absorber oder sterisch gehinderte Amine,
• • Verarbeitungshilfsmittel,
• • Endblockverstärkerharze sowie
• • gegebenenfalls weitere Polymere von bevorzugt elastomerer Natur; entsprechend nutzbare Elastomere beinhalten unter anderem solche auf Basis reiner Kohlenwasserstoffe, zum Beispiel ungesättigte Polydiene wie natürliches oder synthetisch erzeugtes Polyisopren oder Polybutadien, chemisch im wesentlichen gesättigte Elastomere wie zum Beispiel gesättigte Ethylen-Propylen-Copolymere, α-Olefincopolymere, Polyisobutylen, Butylkautschuk, Ethylen-Propylenkautschuk, sowie chemisch funktionalisierte Kohlenwasserstoffe wie zum Beispiel halogenhaltige, acrylathaltige, allyl- oder vinyletherhaltige Polyolefine.

The synthetic rubbers can also contain the following additives:

• • Plasticizers, such as plasticizer oils, or low molecular weight liquid polymers such as low molecular weight polybutenes,
• • primary antioxidants, such as sterically hindered phenols,
• • secondary antioxidants, such as phosphites or thioethers,
• • Process stabilizers, such as carbon radical scavengers,
• • light stabilizers, such as UV absorbers or sterically hindered amines,
• • processing aids,
• • End block amplifier resins as well
• • optionally further polymers of preferably elastomeric nature; Correspondingly usable elastomers include, among other things, those based on pure hydrocarbons, for example unsaturated ones Polydienes such as natural or synthetically produced polyisoprene or polybutadiene, chemically essentially saturated elastomers such as saturated ethylene-propylene copolymers, α-olefin copolymers, polyisobutylene, butyl rubber, ethylene-propylene rubber, and chemically functionalized hydrocarbons such as halogen-containing, acrylate-containing, allyl or vinyl ether-containing polyolefins.

Crosslinking of the synthetic rubbers by means of thermally activatable crosslinkers is likewise preferred. For this purpose, peroxides, acid or acid anhydrides, metal chelates, bifunctional or multifunctional epoxides, bifunctional or multifunctional hydroxides and bifunctional or multifunctional isocyanates are added, such as those for acid anhydrides in EP 1311559 B1 to be discribed.

In addition to the monomeric crosslinking agents with the functional groups described, synthetic rubbers are preferably used which are functionalized with these crosslinking groups. Functionalized synthetic rubbers such as the Kraton FG series (for example Kraton FG 1901 or Kraton FG 1924), Asahi Tuftec M 1913 or Tuftec M 1943 or Septon HG252 (SEEPS-OH) are advantageously used. Further preferred synthetic rubbers are available, for example, under the name Epofriend A 1005, A 1010 or A 1020 from Daicel. By adding suitable crosslinking agents (for example polyvalent isocyanates, amines, epoxides, alcohols, thiols, phenols, guanidines, mercaptans, carboxylic acids or acid anhydrides), these synthetic rubbers can be crosslinked thermally or by radiation. A combination of acid- or acid-anhydride-modified synthetic rubbers (for example Kraton FG series) and an epoxidized synthetic rubber (for example Daicel Epofriend series) can advantageously be used. As a result, crosslinking can be achieved without a monomeric crosslinker, as a result of which no monomeric components are present in the synthetic rubber even if the crosslinking is incomplete. A mixture of the functionalized monomers or polymers can also be used.

Nanoscale and / or transparent fillers are preferably used as fillers. In the present case, a filler is referred to as nanoscale if it has a maximum dimension of approximately 100 nm, preferably approximately 10 nm, in at least one dimension. It is particularly preferable to use those fillers which are transparent in the mass and have a platelet-shaped crystallite structure and a high aspect ratio with homogeneous distribution. The fillers with a platelet-like crystallite structure and aspect ratios well over 100 are generally only a few nm thick, but the length or width of the crystallites can be up to a few μm. Such fillers are also referred to as nanoparticles. The particulate design of the fillers with small dimensions is also particularly advantageous for a transparent design of the synthetic rubber.

In order to achieve a high optical transparency of the adhesive tape of the invention, it is preferred according to the invention if the PSA (K1) and / or the PSA (K2) have a high refractive index. It is therefore advantageous according to the invention if the pressure-sensitive adhesive (K1) and / or (K2) has a refractive index of 1.45 to 1.59, in particular 1.52, the refractive index being measured at 25 ° C. and using an Abbe refractometer a wavelength of 550 nm ± 150 nm is determined on a 25 μm thick film of the pressure-sensitive adhesive.

In addition, it is preferred according to the invention in this connection if the pressure-sensitive adhesive (K1) and / or (K2) has a low dielectric constant. According to the invention, the PSA (K1) and / or (K2) therefore preferably has a dielectric constant of 1 to 3, in particular 2.4, the dielectric constant using the capacitance method between parallel plates at a frequency of 100 kHz, one temperature of 25 ° C. and 50% relative humidity is determined on a 25 μm thick film of the pressure-sensitive adhesive.

According to the invention, the PSAs are advantageously used in a certain thickness. The PSA (K1) and (K2) therefore preferably each have a thickness of 5 to 100 μm, preferably 5 to 75 μm, more preferably 10 to 50 μm, in particular 10 μm.

The difference between the refractive index of the backing material (T) and the refractive index of the at least two pressure-sensitive adhesives (K1) and (K2), in particular of all pressure-sensitive adhesives contained in the adhesive tape, is 0 to 0.1 in order to ensure high optical transparency. However, it can also be preferred that the difference between the refractive index of the carrier material (T) and the refractive index of the at least two PSAs (K1) and (K2) is in each case from 0 to 0.08, preferably from 0 to 0.05, preferably from 0 to 0.03, more preferably 0 to 0.02, in particular 0 to 0.01.

The carrier material (T) of the adhesive tape according to the invention is preferably selected from the group of polyethylene, polypropylene, polycarbonate or polyurethane, in particular polyurethane.

In addition, it is advantageous according to the invention if the carrier material (T) has a certain thickness. It is therefore preferred according to the invention if the carrier material (T) has a thickness of 5 to 100 μm, preferably 5 to 75 μm, more preferably 10 to 50 μm, in particular 10 μm.

In order to ensure high elasticity of the adhesive tape according to the invention, the carrier material (T) must have high elasticity with a low stretching force, in particular at 5N. It is therefore particularly advantageous in accordance with the invention if the carrier material (T) has an elasticity of greater than 90 to 100%, the elasticity on a 25 µm thick carrier material according to the formula elasticity E = ((L ₁₀₀ -L _end ) / L ₀ ) * 100 with L ₁₀₀ = length of carrier material after stretching by 100%, L ₀ = length of carrier material before stretching, L _end = length of carrier material after relaxation of 1 minute.

The adhesive tape according to the invention is preferably used for bonding optical components. For this reason, the adhesive tape should have the smallest possible overall thickness. It is therefore preferred if the adhesive tape has a total thickness of 25 to 200 μm, in particular 30 μm.

The adhesive tapes of the invention can be produced by applying the PSAs (K1) and (K2) from solution or from the melt. The advantage of processing the PSAs (K1) and (K2) from solution lies in the possibility of being able to achieve very small layer thicknesses (mass applications). Preferred manufacturing and processing methods are therefore carried out from solution. For the latter case, suitable manufacturing processes include both batch processes and continuous processes. Particularly preferred is the continuous application of the PSAs (K1) and (K2) directly to the carrier material (T) and subsequent removal of the solvent and, if appropriate, crosslinking of the PSAs.

For use, the double-sided pressure-sensitive adhesive tapes can be covered with one or two release films or release papers. In a preferred version, siliconized or fluorinated films or papers, such as, for example, glassine, HPDE or LDPE coated papers, are used, which in turn are provided with a release layer based on silicone or fluorinated polymers.

The adhesive tape according to the invention is particularly suitable for permanent bonds, that is to say, in particular, bonds in which the adhesive bond is to be maintained permanently. The bonds can also be carried out over a large area and can also be subjected to high temperatures. Higher permanent temperature loads can result from external influences (solar radiation) or from heat produced in the electronic device. This generally increases as the processor performance continues to increase and the components have less and less space available in the housing due to slimmer designs. Furthermore, even after storage conditions of 1 month at 70 ° C. or 1000 h at 85 ° C. and 85% r.h. no significant yellowing. Furthermore, through the use of the adhesive tape of the invention, yellowing of the electronic components of the display and an increase in the electrical resistance of the electronic component, which leads to an undesirable reduction in the touch sensitivity of the display, can be reduced or avoided.

A second subject matter of the present invention is therefore the use of an adhesive tape according to the invention for bonding components, in particular flexible displays, in electronic devices, preferably in mobile electronic devices, preferably tablets, cell phones or smart watches.

Because of the high bond strength and the excellent elasticity of the adhesive tape according to the invention, it is outstandingly suitable for bonding flexible displays in electronic devices in which the adhesive tape is exposed to high mechanical stress. Due to their high elasticity, the adhesive tapes according to the invention do not lead to delamination or folds when the flexible displays are bent, and they also have a sufficiently high bond strength with little force to ensure permanent adhesion without damaging the display.

With regard to further preferred embodiments of the use according to the invention, in particular with regard to the adhesive tape used, what has been said about the adhesive tape according to the invention applies mutatis mutandis.

• Gemäß einer ersten Ausführungsform betrifft die vorliegende Erfindung ein Klebeband, umfassend mindestens eine erste Haftklebemasse (K1), mindestens eine zweite Haftklebemasse (K2) sowie mindestens ein Trägermaterial (T), welches zwischen den beiden Haftklebemassen (K1) und (K2) angeordnet ist,
  • - wobei die Haftklebemassen (K1) und (K2) sowie das Trägermaterial (T) jeweils einen HAZE-Wert von 0 % bis weniger als 1 % sowie eine Transmission von mehr als 99 bis 100 %, jeweils gemessen gemäß ASTM D1003-13, aufweisen und
  • - wobei die Differenz zwischen dem Brechungsindex des Trägermaterials (T) und dem Brechungsindex der mindestens zwei Haftklebemassen (K1) und (K2) jeweils 0 bis 0,1 beträgt,

dadurch gekennzeichnet, dass das Trägermaterial (T) bei einer Schichtdicke von 10 µm einen Modulus 100 % von 0 bis 5 N, gemessen gemäß Prüfmethode Modulus 100 %, aufweist.The invention relates in particular to the following embodiments:

• According to a first embodiment, the present invention relates to an adhesive tape comprising at least one first pressure-sensitive adhesive (K1), at least one second pressure-sensitive adhesive (K2) and at least one carrier material (T) which is arranged between the two pressure-sensitive adhesives (K1) and (K2),
  • - The PSAs (K1) and (K2) and the carrier material (T) each having a HAZE value of 0% to less than 1% and a transmission of more than 99 to 100%, each measured in accordance with ASTM D1003-13 and
  • - wherein the difference between the refractive index of the carrier material (T) and the refractive index of the at least two PSAs (K1) and (K2) is in each case 0 to 0.1,

characterized in that the carrier material (T) with a layer thickness of 10 µm has a modulus 100% of 0 to 5 N, measured according to the test method modulus 100%.

According to a second embodiment, the present invention relates to an adhesive tape according to embodiment 1, characterized in that the PSAs (K1) and (K2) are identical or different, preferably identical.

According to a third embodiment, the present invention relates to an adhesive tape according to one of embodiments 1 or 2, characterized in that the pressure-sensitive adhesive (K1) and / or the pressure-sensitive adhesive (K2) is an acrylate-based pressure-sensitive adhesive.

According to a fourth embodiment, the present invention relates to an adhesive tape according to embodiment 3, characterized in that the pressure-sensitive adhesive (K1) and / or (K2) has a refractive index of 1.40 to 1.59, in particular 1.48, the Refractive index is determined by means of an Abbe refractometer at 25 ° C. and a wavelength of 550 nm ± 150 nm on a 25 μm thick film of the PSA.

According to a fifth embodiment, the present invention relates to an adhesive tape according to one of embodiments 3 or 4, characterized in that the pressure-sensitive adhesive (K1) and / or (K2) has a dielectric constant of 3 to 5, in particular of 4, the dielectric constant Constant is determined by means of the capacitance method between parallel plates at a frequency of 100 kHz, a temperature of 25 ° C. and 50% relative humidity on a 25 μm thick film of the pressure-sensitive adhesive.

According to a sixth embodiment, the present invention relates to an adhesive tape according to one of embodiments 1 or 2, characterized in that the pressure-sensitive adhesive (K1) and / or the pressure-sensitive adhesive (K2) is a synthetic rubber.

According to a seventh embodiment, the present invention relates to an adhesive tape according to embodiment 6, characterized in that the pressure-sensitive adhesive (K1) and / or (K2) has a refractive index of 1.45 to 1.59, in particular 1.52, the Refractive index is determined by means of an Abbe refractometer at 25 ° C. and a wavelength of 550 nm ± 150 nm on a 25 μm thick film of the PSA.

According to an eighth embodiment, the present invention relates to an adhesive tape according to one of embodiments 6 or 7, characterized in that the pressure-sensitive adhesive (K1) and / or (K2) has a dielectric constant of 1 to 3, in particular 2.4, wherein the dielectric constant is determined by means of the capacitance method between parallel plates at a frequency of 100 kHz, a temperature of 25 ° C. and 50% relative humidity on a 25 μm thick film of the pressure-sensitive adhesive.

According to a ninth embodiment, the present invention relates to an adhesive tape according to one of the preceding embodiments, characterized in that the PSAs (K1) and (K2) each have a permeation barrier against water vapor (WVTR) of less than 10 g / (m ² * d), preferably less than 1 g / (m ² * d), based in each case on a thickness of the pressure-sensitive adhesive (K1) or (K2) of 1 mm and measured in accordance with ASTM F-1249-13 (WVTR, 38 ° C and 90% relative humidity).

According to a tenth embodiment, the present invention relates to an adhesive tape according to one of the preceding embodiments, characterized in that the pressure-sensitive adhesive (K1) and (K2) each have a thickness of 5 to 100 μm, preferably 5 to 75 μm, preferably 10 to 50 µm, in particular 10 µm.

According to an eleventh embodiment, the present invention relates to an adhesive tape according to one of the preceding embodiments, characterized in that the difference between the refractive index of the carrier material (T) and the refractive index of the at least two PSAs (K1) and (K2) is in each case 0 to 0, 08, preferably 0 to 0.05, preferably from 0 to 0.03, more preferably 0 to 0.02, in particular 0 to 0.01.

According to a twelfth embodiment, the present invention relates to an adhesive tape according to one of the preceding embodiments, characterized in that the carrier material (T) is selected from the group of polyethylene, polypropylene, polycarbonate or polyurethane, in particular polyurethane.

According to a thirteenth embodiment, the present invention relates to an adhesive tape according to one of the preceding embodiments, characterized in that the carrier material (T) has a thickness of 5 to 100 µm, preferably 5 to 75 µm, preferably 10 to 50 µm, in particular 10 µm.

According to a fourteenth embodiment, the present invention relates to an adhesive tape according to one of the preceding embodiments, characterized in that the carrier material (T) has an elasticity of greater than 90 to 100%, the elasticity on a 25 µm thick carrier material according to the formula elasticity E = ((L ₁₀₀ -L _end ) / L ₀ ) * 100 with L ₁₀₀ = length of carrier material after stretching by 100%, L ₀ = length of carrier material before stretching, L _end = length of carrier material after relaxation of 1 minute.

According to a fifteenth embodiment, the present invention relates to an adhesive tape according to one of the preceding embodiments, characterized in that the adhesive tape has a total thickness of 25 to 200 µm, in particular 30 µm.

According to a sixteenth embodiment, the present invention relates to the use of an adhesive tape according to one of embodiments 1 to 15 for gluing components, in particular flexible displays, in electronic devices, preferably in mobile electronic devices, preferably tablets, cell phones or smart watches.

The present invention is explained in more detail below on the basis of exemplary embodiments. Unless otherwise stated, all proportions of components are given based on their weight.

Examples:

Test methods

Refractive index

The refractive index of the PSA was measured in a 25 .mu.m thick film using the Optronic measuring device from Krüss at 25 ° C. and a wavelength of 550 nm ± 150 nm according to the Abbe principle. For temperature stabilization, the device was operated in conjunction with a Lauda thermostat.

Elasticity:

To measure the resilience, or the elasticity, of the PSA (K1) and (K2), it is stretched as an adhesive layer with a thickness of 25 μm by 100%, held at this stretch for 30 s and then relaxed. After a waiting time of 1 min, the length is measured again. The elasticity of the carrier material (T) is measured on a 25 μm film as described above.

The resilience is now calculated as follows: RV = ((L ₁₀₀ - L _end ) / L ₀ ) * 100 with RV = resilience in%, L ₁₀₀ : length after stretching by 100%, L ₀ : length before stretching, L _end : length after relaxation of 1 min.

Transmission:

The transmission of the PSAs (K1) and (K2) is determined using a bubble-free layer of adhesive with a thickness of 25 μm, as described in ASTM D1003-13 (Procedure A (BYK Gardner Haze Gard Plus), standard illuminant D65). The transmission of the pressure-sensitive adhesive is determined via the VIS spectrum, ie the wavelength range of the measured spectrum comprises all wavelengths between 800 nm and 400 nm with a resolution of 1 nm. An empty channel measurement is carried out as a reference over the entire wavelength range. To give the result, the transmission measurements are averaged in the specified range. Correction for interface reflection losses is made. The transmission of the carrier layer (T) is determined analogously and relates to the actual thickness of the carrier layer (T).

Haze:

The haze of the PSAs (K1) and (K2) is determined in the form of a bubble-free adhesive layer with a thickness of 25 μm as described in ASTM D1003-13 using a BYK Gardner Haze Gard Plus. The haze value describes the portion of the transmitted light that is scattered forward at a large angle by the irradiated sample. The haze value thus quantifies material defects in the surface or structure that interfere with the clear view. The standard requires the measurement of four transmission measurements. The light transmittance is calculated for each transmission measurement. The four degrees of transmission are offset against the percentage haze value. The haze of the carrier layer (T) is determined analogously and relates to the actual thickness of the carrier layer (T).

Relative dielectric constant:

The relative dielectric constant of the pressure-sensitive adhesive to be tested (K1) and (K2) is determined using an adhesive layer with a thickness of 25 µm using an Agilent E4980A LCR measuring instrument using the capacitance method between parallel plates at a frequency of 100 kHz, a temperature of 25 ° C and 50% relative humidity determined.

Determination of the number and weight average molecular weight:

The weight average of the molar mass distribution M _w and the number average of the molar mass distribution M _{n were} determined by gel permeation chromatography (GPC). THF with 0.1% by volume of trifluoroacetic acid was used as the eluent. The measurement was carried out at 23 ° C. PSS-SDV, 10 μ, 103 Å, ID 8.0 mm × 50 mm was used as the pre-column. The column combination PSS-SDV, 10 μ, linear-one with ID 8.0 mm × 300 mm was used for separation. The sample concentration was 1 g / l, the flow rate 0.5 ml per minute. It was measured against polystyrene standards.

Determination of the K-value

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

Determination of the modulus 100%

• Probendicke: 10 µm
• Probenlänge: 140 mm
• Prüfgeschwindigkeit: 300 mm/min

The "Modulus 100%" is a measure of the elasticity of the carrier material. The sample to be measured is stretched by 100%, the force required for this is specified in Newtons (N). The principle of the measurement is based on a tension-elongation test based on DIN EN ISO 527-1 , whereby the following different test setup was chosen:

• Sample thickness: 10 µm
• Sample length: 140 mm
• Test speed: 300 mm / min

The test specimen is clamped tension-free in a tensile testing machine (Zwick). Make sure that the length of the free film between the clamping jaws is 100 mm. Then the sample is stretched 100%. The measured force is given in Newtons.

Manufacture of adhesive tapes

Materials used

Kraton FG1924: Styrene-butadiene-styrene triblock copolymer from Kraton Polymers with 13% by weight block polystyrene content Eastotac H 1 00W: solid hydrogenated hydrocarbon resin with a ring and ball softening temperature of 100 ° C and a DACP of 82 ° C and a mmAP of 82 ° C. TerPib2600: Liquid polybutene from Ter Hell Kristalex F115: solid hydrocarbon resin with a ring and ball softening temperature of 117 ° C Al chelate Tris (2,4-pentanedionato) aluminum

Production of an inventive adhesive tape KB1 with synthetic rubber as pressure-sensitive adhesive (K1) and (K2)

For this purpose, a 20% by weight adhesive solution in gasoline / toluene / isopropanol consisting of 40.0% by weight Kraton FG 1924, 34.0% by weight Eastotac H100W, 26% by weight Terpib 2600 and 0.5 was used Wt% Al chelate. The proportions by weight of the dissolved constituents relate in each case to the dry weight of the resulting solution. This PSA has a refractive index of 1.52, an elasticity of 97%, a transmission of 99%, a haze of 0.4% and a relative dielectric constant of 2.5.

The mixture obtained was then applied with a spreader bar onto a PET liner equipped with a separating silicone, then the solvent was evaporated at 120 ° C. for 15 minutes and the layer of mass was thus dried. After drying, the adhesive has a layer thickness of 10 μm. A second PET liner was then laminated onto the free surface of the produced and dried adhesive layer.

The Easy-Liner is then removed from the pressure-sensitive adhesive (K1) and the carrier material (T) is in the form of a PU film (film thickness 25 μm, Faitgom G1122, modulus 100% = 5 N (measured according to the test method modulus 100%), refractive index = 1.55, haze = 3.1%, transmission = 93%) laminated onto the open pressure-sensitive adhesive side (K1). In the next step, the previously described pressure-sensitive adhesive (K2) is then laminated again to the opposite side of the carrier material (T). The adhesive tape of the invention consisting of PSA (K1) - backing material (T) - PSA (K2) has an elasticity of 97.5%, a haze of 0.55% and a transmission of 99%.

Production of an adhesive tape KB2 not according to the invention with synthetic rubber as the pressure-sensitive adhesive and with carrier material (T) which has a 100% modulus of greater than 5N

The adhesive tape KB2 not according to the invention was produced as described above for the adhesive tape KB1. However, instead of the PU film, a 10 μm thick PET film with a 100% modulus of greater than 5N, measured according to the 100% modulus test method, was used.

Production of an adhesive tape KB3 not according to the invention with synthetic rubber as pressure-sensitive adhesive (contains no carrier material)

To this end, a 20% by weight adhesive solution in gasoline / toluene / isopropanol consisting of 40.0% by weight Kraton FG 1924, 34.0% by weight Eastotac H100W, 26% by weight Terpib 2600 and 0.5 was used Wt% Al chelate. The proportions by weight of the dissolved constituents relate in each case to the dry weight of the resulting solution. This PSA has a refractive index of 1.52, an elasticity of 97, a transmission of 99%, a haze of 0.4% and a relative dielectric constant of 2.5.

The mixture obtained was then applied with a spreader bar onto a PET liner equipped with a separating silicone, then the solvent was evaporated off at 120 ° C. for 15 minutes and the layer of mass was thus dried. After drying, the adhesive has a layer thickness of 50 μm. A second PET liner was then laminated in each case to the free surface of the produced and dried adhesive layer.

Production of an inventive adhesive tape KB4 with acrylate-based PSA (K1) and (K2)

A 300 L reactor conventional for radical polymerizations was charged with 11.0 kg of acrylic acid, 27.0 kg of butyl acrylate (BA), 62.0 kg of 2-ethylhexyl acrylate (EHA) and 72.4 kg of acetone / isopropanol (94: 6) . 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 external heating bath was then heated 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 hours, the mixture was diluted with 20 kg of acetone / isopropanol (94: 6) and after 6 hours with 10.0 kg of acetone / isopropanol (94: 6). 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 polyacrylate obtained has a number average molecular weight M _n of 28,000 g / mol and a weight average molecular weight M _w of 1,050,000 g / mol, each determined by means of GPC (see point 1.6). The K value (see point 1.7) of the polyacrylate is 50.5. To produce the adhesive, the polyacrylate was mixed with 0.035% by weight of N, N, N ', N'-tetrakis (2,3-epoxypropyl) cyclohexane-1,3-dimethylamine (Syna-Epoxy S610 from Synasia) . This PSA has a refractive index of 1.48, an elasticity of 95, a transmission of 99%, a haze of 0.2% and a relative dielectric constant of 4.3.

The PSA obtained was diluted with acetone to a solids content of 30% and then coated from solution onto a siliconized release film (50 μm polyester) (coating speed 2.5 m / min, drying tunnel 15 m, temperatures zone 1: 40 ° C., zone 2 : 70 ° C, zone 3: 95 ° C, zone 4: 105 ° C). The mass application was 50 g / m ² .

The Easy-Liner is then peeled off the PSA and the carrier material (T) is in the form of a PU film (film thickness 25 μm, Faitgom G1122, modulus 100% = 5 N (measured according to the test method modulus 100%), refractive index = 1.55 , Haze = 3.1%, transmission = 93%) laminated onto the open pressure-sensitive adhesive side (K1). In the next step, the previously described pressure-sensitive adhesive (K2) is then laminated again to the opposite side of the carrier material (T).

Production of an adhesive tape KB5 not according to the invention with acrylate-based pressure-sensitive adhesive and carrier material (T) which has a modulus 100% of greater than 5N

The adhesive tape KB5 not according to the invention was produced as described above for the adhesive tape KB4. However, instead of the PU film, a 10 μm thick PET film with a 100% modulus of greater than 5N, measured according to the 100% modulus test method, was used.

Production of an adhesive tape KB6 not according to the invention with acrylic-based PSA (contains no carrier material)

A 300 L reactor conventional for radical polymerizations was charged with 11.0 kg of acrylic acid, 27.0 kg of butyl acrylate (BA), 62.0 kg of 2-ethylhexyl acrylate (EHA) and 72.4 kg of acetone / isopropanol (94: 6) . 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 external heating bath was then heated 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 hours, the mixture was diluted with 20 kg of acetone / isopropanol (94: 6) and after 6 hours with 10.0 kg of acetone / isopropanol (94: 6). 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 reaction was terminated after a reaction time of 24 hours and the mixture was cooled to room temperature. The polyacrylate obtained has a number average molecular weight M _n of 28,000 g / mol and a weight average molecular weight M _w of 1,050,000 g / mol, each determined by means of GPC (see point 1.6). The K value (see point 1.7) of the polyacrylate is 50.5. To produce the adhesive, the polyacrylate was mixed with 0.035% by weight of N, N, N ', N'-tetrakis (2,3-epoxypropyl) cyclohexane-1,3-dimethylamine (Syna-Epoxy S610 from Synasia) . This PSA has a refractive index of 1.48, an elasticity of 95, a transmission of 99%, a haze of 0.2% and a relative dielectric constant of 4.3.

The pressure-sensitive adhesive obtained was spread with a spreader bar onto a PET liner equipped with a separating silicone in a layer thickness of 50 μm, then the solvent was evaporated off at 120 ° C. for 15 min and the layer of composition was thus dried. A second PET liner was then laminated in each case to the free surface of the produced and dried adhesive layer.

Bending test

A static and a dynamic bending test is carried out on each of the adhesive tapes KB1 to KB6 produced in accordance with the test standards described below.

Static bending test

In the static bending test, the adhesive tape to be tested is bonded between 2 layers of polyimide film, the first layer having a thickness of 25 μm and the second layer having a thickness of 50 μm (asymmetrical structure). The composite is then bent by a radius r of 3 mm and then held for 72 hours. In this curved pattern, the 25 µm polyimide film is on the inside, the 50 µm polyimide film on the outside. The test is carried out both at room temperature and at elevated temperatures of 60 ° C.

The static bending test is considered to have been passed if, after the end of the test, no deformation or delamination is found on the composite by visual assessment.

Dynamic bending test

In contrast to the static bending test, the samples to be tested in the dynamic bending test are bent at a certain frequency and then relieved again. The test setup corresponds to the network described in point 3.1. The composite is bent by a radius r of 3 mm and then relieved again, the bending frequency being 60 per minute. The loading and unloading is carried out a total of 300,000 times.

The dynamic bending test is considered to have been passed if, after the end of the test, no deformation or delamination is found on the composite by visual assessment.

Results

duct tape Static bending test Dynamic bending test KB1 (according to the invention) passed passed KB2 Failed Failed KB3 Failed Failed KB4 (according to the invention) passed passed KB5 Failed Failed KB6 Failed Failed

The adhesive tapes according to the invention have high elasticity and, at the same time, high bond strength (see KB1 and KB4). On the other hand, in the absence of a carrier material, delamination or deformation occurs despite the use of the same pressure-sensitive adhesive and layer thickness of the adhesive tape (see KB3 and KB6). The use of a carrier material (T), which has a modulus of 100% of more than 5N and less elasticity, leads to delamination or deformation (see KB2 and KB5). The high elasticity with low application of force in connection with high adhesive strength is thus achieved through the use of a transparent and highly flexible carrier material (T).

The adhesive tapes of the invention are therefore particularly suitable for bonding flexible displays, since on the one hand they are extremely elastic even when the application of force is low, but on the other hand they have a high bond strength.

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 1311559 B1 [0052]

Non-patent literature cited

• DIN 53765: 1994-03 [0017]
• DIN EN ISO 527-1 [0094]

Claims (15)

Adhesive tape comprising at least one first pressure-sensitive adhesive (K1), at least one second pressure-sensitive adhesive (K2) and at least one carrier material (T), which is arranged between the two pressure-sensitive adhesives (K1) and (K2), - the pressure-sensitive adhesives (K1) and ( K2) and the carrier material (T) each have a HAZE value of 0% to less than 1% and a transmission of more than 99 to 100%, each measured in accordance with ASTM D1003-13, and - where the difference between the refractive index of the Carrier material (T) and the refractive index of the at least two pressure-sensitive adhesives (K1) and (K2) are each 0 to 0.1, characterized in that the carrier material (T) has a 100% modulus of 0 to 5 N at a layer thickness of 10 µm , measured according to the test method "Determination of the modulus 100%" in the description. Tape after Claim 1 , characterized in that the PSAs (K1) and (K2) are identical or different, preferably identical. Tape after one of the Claims 1 or 2 , characterized in that the pressure-sensitive adhesive (K1) and / or the pressure-sensitive adhesive (K2) is an acrylate-based pressure-sensitive adhesive. Tape after Claim 3 , characterized in that the pressure-sensitive adhesive (K1) and / or (K2) has a refractive index of 1.40 to 1.59, in particular of 1.48, the refractive index using an Abbe refractometer at 25 ° C and a wavelength of 550 nm ± 150 nm is determined on a 25 μm thick film of the pressure-sensitive adhesive. Tape after one of the Claims 3 or 4th , characterized in that the pressure-sensitive adhesive (K1) and / or (K2) has a dielectric constant of 3 to 5, in particular of 4, the dielectric constant using the capacitance method between parallel plates at a frequency of 100 kHz, a temperature of 25 ° C. and 50% relative atmospheric humidity is determined on a 25 μm thick film of the pressure-sensitive adhesive. Tape after one of the Claims 1 or 2 , characterized in that the pressure-sensitive adhesive (K1) and / or the pressure-sensitive adhesive (K2) is a synthetic rubber. Tape after Claim 6 , characterized in that the pressure-sensitive adhesive (K1) and / or (K2) has a refractive index of 1.45 to 1.59, in particular 1.52, the refractive index using an Abbe refractometer at 25 ° C and a wavelength of 550 nm ± 150 nm is determined on a 25 μm thick film of the pressure-sensitive adhesive. Tape after one of the Claims 6 or 7th , characterized in that the pressure-sensitive adhesive (K1) and / or (K2) has a dielectric constant of 1 to 3, in particular 2.4, the dielectric constant using the capacitance method between parallel plates at a frequency of 100 kHz, one Temperature of 25 ° C. and 50% relative atmospheric humidity is determined on a 25 μm thick film of the pressure-sensitive adhesive. Adhesive tape according to one of the preceding claims, characterized in that the pressure-sensitive adhesives (K1) and (K2) each have a permeation barrier against water vapor (WVTR) of less than 10 g / (m ² * d), preferably less than 1 g / (m ² * d), based in each case on a thickness of the PSA (K1) or (K2) of 1 mm and measured in accordance with ASTM F-1249-13 (WVTR, 38 ° C. and 90% relative humidity). Adhesive tape according to one of the preceding claims, characterized in that the pressure-sensitive adhesive (K1) and (K2) each have a thickness of 5 to 100 µm, preferably 5 to 75 µm, more preferably 10 to 50 µm, in particular 10 µm. Adhesive tape according to one of the preceding claims, characterized in that the carrier material (T) is selected from the group of polyethylene, polypropylene or polyurethane. Adhesive tape according to one of the preceding claims, characterized in that the carrier material (T) has a thickness of 5 to 100 µm, preferably 5 to 75 µm, preferably 10 to 50 µm, in particular 10 µm. Adhesive tape according to one of the preceding claims, characterized in that the carrier material (T) has an elasticity of greater than 90 to 100%, the elasticity on a 25 µm thick carrier material according to the formula elasticity E = ((L ₁₀₀ -L _end ) / L ₀ ) * 100 where L ₁₀₀ = length of carrier material after stretching by 100%, L ₀ = length of carrier material before stretching, L _end = length of carrier material after relaxation of 1 minute. Adhesive tape according to one of the preceding claims, characterized in that the adhesive tape has a total thickness of 25 to 200 µm, in particular 30 µm. Using an adhesive tape after one of the Claims 1 to 14th for bonding components, in particular flexible displays, in electronic devices, preferably in mobile electronic devices, preferably tablets, mobile phones or smart watches.