Optically clear carriers for adhesive tapes

Abstract

The present invention relates to optically clear carriers for adhesive tapes, a process for producing the carrier and adhesive tapes comprising the carrier.

Description

[0001] The present invention relates to optically clear carriers for adhesive tapes, a process for producing the carrier, and adhesive tapes comprising the carrier.

[0002] Electronic devices such as touch panels, displays, and other display devices have become indispensable parts of our lives. In many of these devices, the individual layers are bonded together. This not only creates a sustainable bond, but the bonded construction also contributes to improving the optical performance of the devices, for example, by improving the contrast ratio or increasing durability by reducing the amount of reflected light.

[0003] In order to be suitable for such optical applications, the adhesives and adhesive tapes used must meet high requirements, such as high transparency, low turbidity, temperature and UV resistance, and high resistance to brightening and yellowing.

[0004] A number of adhesive tapes are known in the state of the art that could be used for optical bonding.

[0005] For example, WO 2012 / 087804 A1 describes an optical composite layer comprising an optical film and a liquid, optically clear adhesive disposed adjacent to the optical film, wherein the composite layer has a light transmittance of at least 75%.

[0006] WO 2009 / 089137 A1 discloses an optically clear, stretch-removable, pressure-sensitive adhesive film comprising a pressure-sensitive silicone adhesive composition and a sticky tab.

[0007] EP 1 418 212 A1 provides a transparent pressure-sensitive adhesive strip comprising at least three layers which can be removed again by stretching essentially in the bonding plane without leaving residues or being destroyed, wherein the two outer layers each consist of a transparent adhesive composition based on hydrogenated vinyl aromatic block copolymers and adhesive resins, at least one layer is present between the two outer layers which is composed of a transparent adhesive composition based on vinyl aromatic block copolymers and which has a higher elongation at break than the two outer layers.

[0008] To achieve greater flexibility during bonding and, for example, to correct defects such as air pockets, it is desirable for the bonded substrates to be removable, i.e., the adhesive tape used for attachment must be removable. In particular, the adhesive tape should be mechanically removable, eliminating the need for alternative methods such as heat or chemical solvents.

[0009] Stretch-removable adhesive tapes are well known. These typically contain an elastic carrier, for example, based on polyurethane. Transparent, optically clear carriers based on polyurethane, produced by extrusion, so-called TPUs, are also commercially available. However, these carriers are unsuitable for use in removable adhesive tapes, as only higher Shore hardnesses can be used for gel- and speck-free production. Especially for thinner layer thicknesses in the range of 75 µm, only TPUs with a higher Shore hardness of greater than 95 Shore A are currently available.

[0010] A higher Shore hardness generally results in a higher 100% modulus and thus lower elongation. Excessive Shore hardness or a high 100% modulus generates high forces during the peeling process caused by stretching, causing the adhesive tape to either fail during removal or damage or even destroy the bonded component being separated. Furthermore, at higher Shore hardnesses, the backing's elongation is generally insufficient to ensure smooth, tear-free removal.

[0011] It has been shown that with TPU carriers with a Shore hardness of up to 85 Shore A or a 100% modulus of up to 12 MPa (determined according to DIN 53504 with a feed rate of 800 mm / min), in isolated cases a sufficiently good detachment can be achieved without tearing of the carrier or damage to the component, but the carrier does not meet the optical requirements and cannot be produced by extrusion without gel or specks in the required layer thickness of 30 to 50 µm.

[0012] There is therefore still a need for optically clear carriers for removable adhesive tapes that allow the adhesive tape to be removed without leaving residue or being damaged, without tearing the carrier.

[0013] The present invention seeks to meet this need and to provide appropriate supports.

[0014] The object is surprisingly achieved by a carrier as defined in claim 1. Preferred embodiments of the present invention are set out in the subclaims.

[0015] It has surprisingly been shown that the use of polyurethane produced by means of dispersion, so-called PUD, allows the production of carriers that have a high extensibility and low modulus of elasticity (100% modulus) and that allow non-destructive removal with little effort and at the same time have the required optical properties, so that an application such as in display bonding in electronic devices or in the bonding of individual components of components is possible.

[0016] The measurement methods used to determine the specified parameters are described in the "Measurement Methods" section. Unless otherwise stated, all corresponding data refer to wt.%.

[0017] A first subject matter of the present invention is accordingly a carrier for removable adhesive tapes which comprises at least one layer based on a polyurethane produced by means of dispersion, wherein the carrier has a transmission of at least 94%, preferably at least 97%, determined by transmission measurement according to ASTM D1003-13.

[0018] To achieve optimal performance of a display or similar electronic device, it has proven advantageous for the display to have low reflection. This not only increases the contrast ratio but also improves the operating time, since the device requires less backlight. Therefore, an embodiment is preferred in which the carrier according to the invention has a refractive index nD of 1.45 to 1.57, preferably 1.45 to 1.50. The refractive index can be determined, for example, using a conventional refractometer.

[0019] In optics, the haze parameter describes the scattering behavior of a material. In the case of backings designed for adhesive tapes in optical applications, low scattering behavior is desirable to avoid negatively affecting the optical properties of the final component, such as a display. Accordingly, in a further preferred embodiment, the backing according to the invention has a haze of less than 1.5, determined according to ASTM D1003-13.

[0020] Many materials tend to age over time. This aging process is usually accompanied by yellowing, i.e., the development of a yellow tinge. Within the scope of the present invention, it has surprisingly been found that this yellowing was not observed, or only slightly, in the carrier according to the invention; rather, the carrier is characterized by high light and UV resistance. One measure of yellowing is the so-called b-value, which describes the blue or yellow component of a color in the Lab color space, with negative values representing blue and positive values representing yellow. The carrier according to the invention preferably has a b-value of less than 1.5, determined using ASTM D2244-096 and DIN 6174.

[0021] The carrier is primarily designed for removable adhesive tapes. As described above, it has proven advantageous for the carrier not to exceed a certain Shore hardness in order to ensure residue-free and non-destructive removal without tearing of the carrier. In a preferred embodiment, the carrier therefore has a maximum Shore hardness of 85 Shore A, preferably a maximum of 80 Shore A, determined using ASTM D2240. Alternatively and / or further preferably, the carrier according to the invention has a 100% modulus of preferably a maximum of 12 MPa, particularly preferably a maximum of 9 MPa, determined according to DIN 53504 (at a feed rate of 800 mm / min). The combination of maximum Shore hardness and 100% modulus ensures that the carrier does not tear during redetachment.

[0022] It has surprisingly been shown that the use of dispersion-produced polyurethanes allows the production of carriers that are optically clear and free of gel and particles. They also exhibit the required lower 100% modulus of less than 12 MPa, determined according to DIN 53504 (at a feed rate of 800 mm / min), and are also available in the required layer thicknesses. In a preferred embodiment, the carrier therefore has a thickness of 15 to 100 µm, preferably 30 to 50 µm.

[0023] To minimize the risk of the carrier tearing during the detachment process, it is desirable for the carrier to have sufficiently high elongation. Surprisingly, it has been shown that this requirement is also met by the carrier according to the invention. Therefore, an embodiment in which the carrier has an elongation at break of more than 300%, determined according to DIN 53504, is preferred.

[0024] Particularly for applications in which the adhesive tape must be removable without damaging the component, care must be taken to ensure that the maximum tensile strength of the carrier, i.e., the maximum achievable tensile force, is not too high. In this regard, an embodiment of the carrier according to the invention is preferred in which the maximum tensile strength of the carrier, determined according to the test method description for tensile testing using a tensile testing machine, is no more than 50 MPa, preferably no more than 40 MPa, and particularly preferably no more than 35 MPa.

[0025] A variety of polyurethane dispersions can be used to produce the carrier. The polyurethane of the dispersion is preferably selected from the group consisting of polycarbonate-based polyurethanes, polyether-based polyurethanes, polyester-based polyurethanes, or mixtures thereof. The polyurethane is preferably a polyether polyurethane and / or a polyester polyurethane. Particular preference is given to using aliphatic polyurethanes, in particular aliphatic polyether polyurethane and / or polycarbonate ester polyether polyurethane.

[0026] The PU dispersion used to produce the carrier according to the invention may contain, in addition to the polyurethane, other components such as thickeners and / or other additives. A preferred embodiment of the carrier according to the invention is one in which thickeners and optionally other additives are first predispersed and then added to the polyurethane dispersion in portions.

[0027] To further improve the mechanical properties of the support according to the invention, it can be crosslinked. Crosslinking can be carried out using at least one crosslinker. The at least one crosslinker is preferably selected from the group consisting of isocyanates, in particular selected from the group consisting of aliphatic polyisocyanates, silane isocyanates, acrylate isocyanates, and poly(propylene glycol), 2,4-tolylene diisocyanate. Polyfunctional epoxy crosslinkers such as polyglycidylamine are also suitable crosslinking reagents.

[0028] Suitable aliphatic isocyanates include, in particular, hexamethylene diisocyanate (HDI), 1,6-hexylene diisocyanate, isophorone diisocyanate (IPDI), 5-isocyanato-1-isocyanatomethyl-1,3,3-trimethylcyclohexane, and trimethyl diisocyanate (TMDI). Blocked crosslinkers are particularly preferred. A suitable aliphatic polyisocyanate is available, for example, under the trade name Imprafix. ® 2794 available from Covestro AG.

[0029] The present invention further provides a process for producing the carrier according to the invention. For this purpose, a polyurethane-based dispersion is applied to a temporary carrier or functional layer and dried.

[0030] To ensure the best possible quality and bubble-free dispersion, it is preferably degassed before application to the temporary substrate. This can be achieved, for example, using a vacuum deaerator such as a vacuum thin-film rotation system. This also eliminates the need for defoamers.

[0031] The PU dispersion is preferably applied to the temporary substrate under clean-room conditions, using various application tools such as doctor blades, nozzles, or distribution channels. Application by nozzle is preferred in this regard, as this method allows for the highest quality optical properties to be achieved.

[0032] The drying of the applied PU dispersion is preferably carried out by supplying heat, in particular in a drying channel with different heating zones.

[0033] The PU dispersion can be applied either to a temporary carrier or directly to a functional layer, such as a pressure-sensitive adhesive. After drying, a second functional layer can be laminated to the opposite side, creating a multi-layer product in a single step. This process has the advantage of allowing a multi-layer product to be manufactured particularly efficiently and improving the bond strength / anchoring between the carrier and functional layer.

[0034] To optimize tensile strength, it has proven advantageous to subject the support to a tempering process. Therefore, the process according to the invention further comprises a step in which the support is tempered. The tempering can be carried out, for example, at a temperature of 120°C or more.

[0035] In addition to the polyurethane, the PU dispersion may contain other components such as thickeners and / or other additives. To obtain a homogeneous and bubble-free dispersion, it has proven advantageous to predisperse these additional components and then add them to the PU dispersion in portions. In a preferred embodiment of the process according to the invention, this therefore comprises a step in which thickeners and / or other additives are predispersed and added to the PU dispersion in portions.

[0036] The carrier according to the invention is particularly suitable for bonding optical components. Therefore, a further subject of the present invention is the use of the carrier in optical components and / or adhesive tapes for bonding optical components, in particular displays and touch panels.

[0037] The present invention further provides an adhesive tape comprising the carrier according to the invention. The adhesive tape is preferably optically clear and removable.

[0038] The adhesive tape according to the invention is coated on one or both sides with a pressure-sensitive adhesive, whereby, depending on the application, it may be advantageous to use different pressure-sensitive adhesives in a double-sided adhesive structure.

[0039] The present invention is explained in more detail with reference to the following examples, which are in no way to be understood as a limitation of the inventive concept. Examples

[0040] Adhesive tapes with the inventive backings made from a polyurethane dispersion (PUD) were produced, and their optical and mechanical properties were measured. Adhesive tapes with a backing made from a thermoplastic polyurethane (TPU) produced by extrusion were used as comparative examples. carrier

[0041] The following raw materials were used to produce the supports according to the invention: Table 1: raw material Manufacturer / Supplier Description Alberdingk U4101 Alberdingk Boley Polyether PU made from 66 wt% polytetrahydrofuran and 34 wt% meta-tetramethylxylylene diisocyanate Impranil DL 1116 Covestro Polyester polyurethane dispersion of approximately 51 wt.% adipic acid, 29 wt.% 1,6-hexanediol, 15 wt.% neopentyl glycol and 5 wt.% hexamethylene diisocyanate (HDI Impranil DLU Covestro Aliphatic polycarbonate ester polyether polyurethane dispersion Ortegol PV 301 Evonik Non-ionic thickener for water-based coating systems Borchi Gel 0625 Borchers GmbH Non-ionic thickener for water-based coating systems Elastollan L1185 A BASF Polyurethanes GmbH Aliphatic polyether polyurethane, Shore hardness A 85 Nupro N5650M 60D 50µm NUPRO Aliphatic polycaprolactone thermoplastic polyurethane, Shore hardness D 63

[0042] The recipes for the production of the carriers are summarized in Table 2. Table 2: Designation component raw material Portion [Wt.%] Core layer TPU 1 commercially available carrier Nupro N5650M, 63 ShD 100,00 Core layer TPU 2 TPU granules Elastollan L1185A, 85 ShA 100,00 Core layer PUD 1 PU dispersion Impranil DL 1116 97,40 Thickener Ortegol PV 301 0,60 Networker Imprafix 2794 2,00 Core layer PUD 2 PU dispersion Alberdingk U4101 97,65 Thickener Borchigel 0625 0,35 Networker Imprafix 2794 2,00 Core layer PUD 3 PU dispersion Impranil DLU 97,50 Thickener Borchi Gel 0625 0,35 Networker Imprafix 2794 2,00 Adhesive:

[0043] The carriers were each combined with an adhesive to form an adhesive tape. The adhesive was prepared as follows.

[0044] A reactor conventional for radical polymerizations was charged with 160 g of 2-ethylhexyl acrylate, 120 g of 4-hydroxybutyl acrylate, and 120 g of tert-butyl acrylate, as well as the photoinitiator Irgacure 651 at a concentration of 0.01 wt.%. After passing nitrogen gas through the reactor for 45 minutes while stirring, the reactor was sufficiently purged of oxygen. Subsequently, a (UV) LED lamp with an intensity of 3000 [mJ / cm 2 ] polymerized for 10 min.

[0045] The prepolymer was then blended with photoinitiator Irgacure 184 (0.2 wt.%) and crosslinker (0.1 wt.% HDDA), and a vacuum pump was used to create a vacuum to remove bubbles from the mixture. The blend was then coated with a thickness of 100 µm between two siliconized PET films (50 µm each). Further reaction was achieved by irradiation with a Heraeus UV-LED lamp (wavelength 365 nm) with a UV dose of 3000 mJ / cm³. 2 initiated. Production of adhesive tapes with TPU core layer TPU 1 (Comparative Example 1):

[0046] The 50 µm TPU core layer TPU 1 is coated with the adhesive layer on both sides. The adhesive layers have the same thickness, 100 µm each, on both sides of the carrier.

[0047] The entire composite of carrier and adhesive layers is subjected to a further tempering step for better anchoring.

[0048] The result is the double-sided adhesive tapes with the TPU core layer TPU 1 (see example 1). Production of the carriers and adhesive tapes with TPU core layer TPU 2 (Comparative Example 2):

[0049] All thermoplastic polyurethane granules, i.e., TPU granules, are pre-dried in a granule dryer (Somos) at 80 °C for at least 3 hours prior to processing. The granules 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 determined according to the optimal processing temperature of the respective TPU granules. After melting the granules, the extrudate is transferred via a hose into a feedblock and then into the slot die. Table 5 shows the temperature control of the ESE, including the slot die. Table 5: Temperature control of the ESE including the slot die. Extruder and slot die Move-in Heating zones single-screw extruder speed Hose Feedblock nozzle Zone 1 2 3 4 5 6 7 n 8 9 10 [°C] [°C] [°C] [°C] [°C] [°C] [°C] [rpm]* [°C] [°C] [°C] TPU 2 30 170 175 180 180 180 180 15 180 190 190 *RPM = revolutions per minute.

[0050] The preformed melt film is then deposited onto a steel roller. It has proven effective to coat it 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 TPU 2) are free of additional processing aids.

[0051] The 50 µm TPU core layer (TPU 2) is coated with an adhesive layer on both sides. The adhesive layers are the same thickness on both sides of the carrier, 100 µm each.

[0052] The entire composite of carrier and adhesive layers is subjected to a further tempering step for better anchoring.

[0053] The result is the double-sided adhesive tapes with the TPU core layer TPU 2 (see example 2). Production of the inventive backings and adhesive tapes based on PUD (PUD 1 to 3):

[0054] The corresponding polyurethane dispersion (PU dispersion, PUD) PUD 1, PUD 2, and PUD 3 are mixed with the crosslinker and thickener using a conventional vertical stirring apparatus equipped with a ViscoJet stirrer. The polyurethane dispersion is placed in a sufficiently large container and stirred gently. The formation of whirlpools or any incorporation of air should be avoided throughout the mixing process. The crosslinker Imprafix 2794 is added in portions while continuously stirring. Subsequently, the thickener Ortegol PV301 (25 wt.% solids) or the thickener BorchiGel 0625 (33 wt.% solids) is pre-diluted with water in a ratio of 1:1 and added in portions while continuously stirring. To achieve a homogeneous mixture, the stirring time is at least 30 minutes. The resulting thickened polyurethane dispersion is ideally prepared one day before coating.This allows any air bubbles that have been stirred in to escape. The mixed polyurethane dispersions can then be spread onto a PET carrier with a release function using a spreader with a comma spreader at the desired basis weight and dried in a standard circulating air dryer at 60 °C. The resulting PUD core layers (i.e., PUD cores 1 to 3) are free of processing aids.

[0055] The adhesive layers are then laminated on both sides. The entire composite of carrier and adhesive layers is subjected to further heat treatment for better anchoring. This results in the double-sided adhesive tapes examples 1, 2, and 3 with the PUD core layers PUD 1, PUD 2, and PUD 3. Measurement results

[0056] The carriers used in the examples have a layer thickness of 50 µm. The adhesive used in the examples has a layer thickness of 100 µm when applied on both sides, resulting in a total thickness of the three-layer structure of 250 µm. Example carrier Mechanical properties carrier Optical properties of adhesive tape Application Elongation at break High tensile strength Module at 100% Trans mission Haz e b-value Refractive index Stripping force Removable [%] [MPa] [MPa] [%] [%] [N / cm] See 1 TPU 1 342,0 52,5 22,5 99,6 0,2 7 0,02 1,472 17,5 No, component destroyed See 2 TPU 2 512,0 55,3 10,5 99,8 0,3 5 0,06 1,473 12,0 Yes, but beginning deformation 1 PUD 1 765,0 34,0 1,4 99,1 0,3 2 0,08 1,472 5,0 Yes 2 PUD 2 925,0 21,8 1,2 98,7 0,4 2 0,12 1,473 4,5 Yes 3 PUD 3 710,0 24,6 2,6 99,3 0,4 0 0,09 1,472 6,3 ia

[0057] The properties of the carrier used can directly determine its suitability as a carrier in a removable adhesive tape. If the modulus at 100% elongation is too high, the stripping force—the force required to pull the adhesive tape out of the bonded component—is also too high, leading to component deformation and even destruction.

[0058] As can be seen from the data, in addition to the optical properties, non-destructive detachment is ensured due to the low modulus at 100% elongation of less than 12 MPa in combination with sufficiently high elongation of more than 300%.

[0059] Although the adhesive bond of Comparative Example 2 can be removed again, the force required for this and the modulus at 100% are already very high at 10.5 MPa, and initial deformation of the component can be observed. Furthermore, speck- and gel-free production, as required for bonding in optical applications, is not possible in this layer thickness range. Figures: Fig. Figure 1 clearly shows the differences in the tensile-elongation properties of the beams described in the examples.

[0060] TPU 1 (solid line) is a commercially available TPU carrier (Nupro N5650M 60 Shore D) in 50 µm based on an aliphatic polycaprolactone for optically good quality with a high Shore hardness of 63 ShD.

[0061] TPU 2 (dashed line) is a TPU carrier based on an aliphatic polyether polyurethane (Elastollan L1185A) with a moderate Shore hardness of 85 ShA. Its mechanical properties, such as elongation and force distribution, are only marginally suitable for removal and are only partially suitable. The carrier causes frequent, premature tearing of the adhesive tape during the removal process or even excessive stress, even leading to the destruction of the component. Adequate optical quality cannot be achieved in thinner layers either.

[0062] PUD 1 (dotted line) is a dispersion-coated carrier based on polyether polyurethane. The carrier according to the invention can be produced in both optically excellent quality and at lower layer thicknesses, particularly 30 to 50 µm. Its high elongation combined with low force allows for non-destructive and tear-free removal. Test methods

[0063] Unless otherwise stated, all measurements are conducted at 23 °C and 50% relative humidity. The mechanical and adhesive data were determined as follows: Shore hardness A, D

[0064] The Shore hardness A, D of a sample is determined according to ASTM D2240. thickness

[0065] 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, excluding measurements taken at creases, folds, spots, and the like.

[0066] Just like the thickness of an adhesive layer, the thickness of an adhesive tape (adhesive strip) or a carrier can be determined analogously using commercially available thickness gauges (touch-type thickness 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. Static glass transition temperature T g

[0067] Glass transition points – synonymously referred to as glass transition temperatures – are given as the result of measurements using Dynamic Scanning Calorimetry (DSC) according to DIN 53765, particularly sections 7.1 and 8.1, but with uniform heating and cooling rates of 10 K / min in all heating and cooling steps (see DIN 53765; section 7.1; note 1). The sample weight is 20 mg. Molecular weight M n , M w

[0068] 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) is used. For separation, a combination of columns of type PSS-SDV, 5 µm, 10 3 Å and 10 5 Å and 10 6Å columns with a diameter of 8.0 mm x 300 mm each were used (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer). The flow rate was 1.0 ml per minute. Calibration was performed against PMMA standards (polymethyl methacrylate calibration) for polar molecules, such as the starting materials for polyurethane, and against PS standards (polystyrene calibration) for other molecules. Tensile test using a tensile testing machine, Zwick

[0069] From the sample to be tested (adhesive tape, i.e., a backing preferably coated with adhesive on both sides, or just a blank backing), 15 mm wide strips with a length of approximately 150 mm are cut lengthwise using a strip cutter or razor blade knife. The sample, preconditioned for 24 hours in the test environment, is clamped vertically in the center of the clamping jaws with a clamping length of 10 mm and stretched at a speed of 800 mm / min until it tears. The tear should occur somewhat in the center of the strip. If the tear occurs near the jaws (closer than 1 cm), the value is discarded and a different strip is tested. Five measurements are performed for each sample variant. The test environment is 23 °C and 50% relative humidity. The measurements are carried out in accordance with EN ISO 527.

[0070] Indication of results: Fx%[N / cm],[N / mm2],[MPa]−Force at x% strain FBreak [N / cm], [N / mm2], [MPa] − Force at crack / break of the sample (i.e., tear strength or ultimate tensile strength) RD[%]−Elongation at break, ie percentage elongation at tear / break of the sample Modulus at x% elongation, elongation at break

[0071] The modulus at x% elongation or the elongation at break in [MPa] of a sample is determined according to DIN 53504. Detachability using a tensile testing machine, Zwick

[0072] In the removability test, the double-sided adhesive tape to be tested is bonded between two test panels made of polycarbonate and glass.

[0073] Test specimens 20 mm wide are cut from the adhesive tape to be tested. These test specimens are bonded to the first glass test plate after uncovering the first siliconized PET film over a length of 70 mm. After uncovering the second siliconized PET film, the free adhesive is covered on both sides with 36 µm PET. The second PC test plate is cleaned with isopropanol and preconditioned for 1 to a maximum of 10 minutes at 23 °C and 50% relative humidity, and then bonded to the opposite side of the bonded strip (i.e., test specimen) in such a way that the PC plate protrudes beyond the glass plate. The back of the composite is rolled over the steel plate 10 times using a 4 kg roller (five times back and forth).After at least 24 hours of application at 23 °C and 50% relative humidity, the strips are stripped from the adhesive joint at the grip using a tensile testing machine (Zwick) at a constant speed of 800 mm / min at an angle of 0°. The specimen is fixed with an angle-adjustable adapter, and the grip is clamped vertically in the center of the clamping jaws.

[0074] It is measured at an angle of 0° and during this time the force required to continuously remove / strip the sample is recorded by the tensile testing machine - the so-called stripping force F Stripp The measurement is complete when the sample has been completely removed from between the two test plates or the sample has cracked during the measurement. At least two measurements are performed per sample. The test environment is 23 °C and 50% relative humidity.

[0075] Indication of results: FStripp [N / cm] - force required to strip the test specimen from the adhesive joint at an angle of 0° (stripping force) transmission

[0076] The transmittance of the adhesive tape is determined according to ASTM D1003-13 (Procedure A (BYK Gardner Haze Gard Plus), standard illuminant D65). A correction for interfacial reflection losses is made. The transmittance of other layers is determined analogously and refers to the actual thickness of the layer. Haze

[0077] The haze of the entire assembly is determined as described in ASTM D1003-13 using a BYK Gardner Haze Gard Plus. The haze value describes the proportion of transmitted light that is scattered forward at a large angle by the sample being irradiated. Thus, the haze value quantifies material defects in the surface or structure that impair clear visibility. The standard requires the measurement of four transmission measurements. The light transmittance is calculated for each transmission measurement. The four transmittances are added together to determine the percentage haze value. The haze of other coatings is determined analogously and refers to the actual thickness of the coating. b-value

[0078] The b-value is a measure of discoloration on a yellow-blue color scale and, together with the L-value (brightness) and the a-value (red-green color scale), provides an objective determination of color perception. The so-called Lab values are determined using the Spectro-Guide-Sphere-Gloss device from BYK Gardner in accordance with ASTM D2244-096 and DIN 6174. First, a triple background measurement is performed on a known reference substrate. The adhesive tape is then measured on this reference substrate, also at three different locations. To determine the b-value, the average of the three individual values is calculated and the average of the reference value is subtracted. refractive index

[0079] An Abbemat 350 refractometer (Anton Parr) is used to determine the refractive index. First, a test measurement is performed against air or water to verify functionality. The adhesive tape or individual components are then applied to the measuring window, and the measurement is started. The measurement is performed at 20 °C. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2012 / 087804 A1

[0005] WO 2009 / 089137 A1

[0006] EP 1 418 212 A1

[0007]

Claims

[1] A carrier for removable adhesive tapes comprising at least one layer based on a dispersion-produced polyurethane, the carrier having a transmittance of at least 94%, preferably at least 97%, determined by ASTM D1003-13 (Procedure A (BYK Gardner Haze Gard Plus), standard illuminant D65). [2] Carrier according to claim 1, characterized by that the carrier has a refractive index n D from 1.45 to 1.57, preferably 1.45 to 1.

50. [3] Carrier according to at least one of the preceding claims, characterized by that the carrier has a haze of less than 1.5, determined according to ASTM D1003-13. [4] Carrier according to at least one of the preceding claims, characterized by that the beam has a b-value of less than 1.5, determined according to ASTM D2244-096 and DIN 6174. [5] Carrier according to at least one of the preceding claims, characterized bythat the carrier has a maximum Shore hardness of 85 Shore A, determined by ASTM D2240, and / or a 100% modulus of maximum 12 MPa, determined according to DIN 53504 (at 800 mm / min). [6] Carrier according to at least one of the preceding claims, characterized by that the carrier has a thickness of 15 to 100 µm, preferably 30 to 50 µm. [7] A process for producing an adhesive tape according to at least one of claims 1 to 6, in which a dispersion based on polyurethane (i) is applied to a temporary support and dried or (ii) is applied to a functional layer and dried. [8] Method according to claim 7, characterized by that the polyurethane dispersion is degassed before being applied to the temporary carrier. [9] Method according to at least one of claims 7 to 8, characterized by that the dispersion is applied to the temporary carrier by means of a nozzle. [10] Method according to at least one of claims 7 to 9, characterized by that drying is carried out by means of heat. [11] Method according to at least one of claims 7 to 10, characterized by that the method further comprises a step in which the carrier is tempered. [12] Method according to at least one of claims 7 to 11, characterized by that the polyurethane is selected from the group consisting of polycarbonate-based polyurethanes, polyether-based polyurethanes and polyester-based polyurethanes or mixtures thereof. [13] Use of a carrier according to at least one of claims 1 to 6 in optical components and / or in adhesive tapes for bonding optical components, in particular displays and touch panels. [14] Adhesive tape comprising the carrier according to the invention. [15] Adhesive tape according to claim 14, characterized by that the adhesive tape is optically clear and removable.

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