Optically clear backings for adhesive tapes

Abstract

The present invention relates to optically clear backings for adhesive tapes, to a method for producing the backing, and to adhesive tapes comprising the backing.

Description

[0001] Optically clear carriers for adhesive tapes

[0002] The present invention relates to optically clear carriers for adhesive tapes, a process for producing the carrier, and adhesive tapes comprising the carrier.

[0003] 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.

[0004] 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.

[0005] A number of adhesive tapes are known in the state of the art that could be used for optical bonding.

[0006] 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%.

[0007] 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.

[0008] 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 damage. The two outer layers each consist of a transparent adhesive based on hydrogenated vinylaromatic block copolymers and adhesive resins. At least one layer is present between the two outer layers, which is composed of a transparent adhesive based on vinylaromatic block copolymers and has a higher elongation at break than the two outer layers. In order to achieve greater flexibility during bonding and, for example, to be able to correct defects such as air inclusions, it is desirable for the bonded substrates to be removable from one another, i.e., for the adhesive tape used for attachment to be removable.In particular, there is a desire for the adhesive tape to be mechanically removable and for alternative methods such as heat or chemical solvents to be dispensed with.

[0009] Adhesive tapes that can be removed by stretching are well known. These usually 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 pm.

[0012] There is therefore still a need for optically clear backings for removable adhesive tapes that allow for residue-free and non-destructive removal of the adhesive tape without tearing the backing. The present invention seeks to meet this need and provide suitable backings.

[0013] 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.

[0014] 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.

[0015] 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.%.

[0016] 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.

[0017] 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.

[0018] In optics, the haze parameter describes the scattering behavior of a material. In the case of carriers designed for adhesive tapes in the field of optical applications, low scattering behavior is desirable in order not to negatively influence the optical properties of the subsequent component, such as a display. Accordingly, in a further preferred embodiment, the carrier according to the invention has a haze of less than 1.5, determined according to ASTM D1003-13. Many materials tend to age over time. This aging process is usually accompanied by yellowing, i.e. the development of a yellow tinge. In the context of the present invention, it has surprisingly been found that this yellowing was not observed, or only slightly, in the case of the carrier according to the invention, but that the carrier is characterized by high light and UV resistance.A 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 substrate according to the invention preferably has a b-value of less than 1.5, determined using ASTM D2244-096 and DIN 6174.

[0019] The carrier is primarily designed for removable adhesive tapes. As described above, it has proven advantageous here if the carrier does not 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 by 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.

[0020] It has surprisingly been shown that the use of dispersion-produced polyurethanes allows the production of supports that are optically clear and gel- and particle-free. 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 support therefore has a thickness of 15 to 100 μm, preferably 30 to 50 μm.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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 lmprafix®2794 from Covestro AG.

[0027] 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.

[0028] 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. The PU dispersion is preferably applied to the temporary substrate under cleanroom conditions, using various application tools such as doctor blades, nozzles, or distribution channels. In this respect, application by nozzle is preferred, as this allows the highest quality optical properties to be achieved.

[0029] The drying of the applied PU dispersion is preferably carried out by supplying heat, in particular in a drying channel with different heating zones.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] The present invention further provides an adhesive tape comprising the carrier according to the invention. The adhesive tape is preferably optically clear and removable.

[0035] The adhesive tape according to the invention is coated on one or both sides with a pressure-sensitive adhesive. Depending on the application, it may be advantageous to use different pressure-sensitive adhesives in a double-sided adhesive structure. The present invention is explained in more detail with the help of the following examples, which are in no way to be understood as limiting the scope of the invention.

[0036] Examples

[0037] 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.

[0038] carrier

[0039] The following raw materials were used to produce the supports according to the invention:

[0040] Table 1 :

[0041] The recipes for the production of the carriers are summarized in Table 2.

[0042] Table 2:

[0043] Adhesive:

[0044] The carriers were each combined with an adhesive to form an adhesive tape. The adhesive was prepared as follows.

[0045] 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.

[0046] 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 remove any bubbles from the mixture. The blend was then coated with a thickness of 100 μm between two siliconized PET films (each 50 μm thick). 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.

[0047] Production of adhesive tapes with TPU core layer TPU 1 (Comparative Example 1):

[0048] 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.

[0049] The entire composite of carrier and adhesive layers is subjected to a further tempering step for better anchoring.

[0050] The result is the double-sided adhesive tapes with the TPU core layer TPU 1 (see example 1)-

[0051] Production of the carriers and adhesive tapes with TPU core layer TPU 2 (comparison example 2):

[0052] 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.

[0053] Table 5: Temperature control of the ESE including the slot die.

[0054] *RPM = revolutions per minute.

[0055] 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.

[0056] The 50 μm TPU core layer, TPU 2, is coated with the adhesive layer on both sides. The adhesive layers have the same thickness on both sides of the carrier, each 100 μm.

[0057] The entire composite of carrier and adhesive layers is subjected to a further tempering step for better anchoring.

[0058] The result is the double-sided adhesive tapes with the TPU core layer TPU 2 (see example 2).

[0059] Production of the inventive carriers and adhesive tapes based on PUD (PUD 1 to 3):

[0060] 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 vortexes or any incorporation of air should be avoided throughout the entire mixing process. The crosslinker Imprafix 2794 is added in portions while stirring continuously. The thickener Ortegol PV301 (25 wt.% solids content) or the thickener BorchiGel 0625 (33 wt.% solids content) is then pre-diluted with water in a ratio of 1:1 and added in portions while stirring continuously. To achieve a homogeneous mixture, the stirring time is at least 30 minutes. The thickened polyurethane dispersion thus prepared 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 commercially available circulating air dryer at 60 °C. The resulting PUD core layers (i.e., PUD cores 1 to 3) are free of processing aids.

[0061] 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.

[0062] Measurement results

[0063] 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 to both sides, resulting in a total thickness of the three-layer structure of 250 μm.

[0064] The suitability of the carrier as a carrier in a removable adhesive tape can be directly determined from the properties profile of the carrier used. 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. As can be seen from the data, in addition to the optical properties, the low modulus at 100% elongation of less than 12 MPa, combined with a sufficiently high elongation of more than 300%, ensures non-destructive removal.

[0065] 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.

[0066] Figures:

[0067] Figure 1 clearly shows the differences in the tensile-elongation properties of the beams described in the examples.

[0068] TPU 1 (solid line) is a commercially available TPU carrier (Nupro N5650M 60 Shore D) in 50 pm based on an aliphatic polycaprolactone for optically good quality with a high Shore hardness of 63 ShD.

[0069] TPU 2 (dashed line) is a TPU carrier based on an aliphatic polyether polyurethane (Elastollan L1 185A) 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.

[0070] 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 the same time in thinner layer thicknesses, particularly 30 to 50 μm. Its high elongation combined with low force enables non-destructive and tear-free removal.

[0071] Test methods

[0072] Unless otherwise stated, all measurements are conducted at 23 °C and 50% relative humidity. The mechanical and adhesive properties were determined as follows: Shore hardness A, D

[0073] The Shore hardness A, D of a sample is determined according to ASTM D2240.

[0074] thickness

[0075] The thickness of an adhesive layer can be determined by determining the thickness of a section of such an adhesive layer applied to a liner, defined in terms of its length and width, minus the (known or separately determinable) thickness of a section of the same dimensions of the liner used. The thickness of the adhesive layer can be determined using commercially available thickness gauges (touch-type testers) with an accuracy of less than 1 pm. If thickness variations are detected, the average value of measurements taken at at least three representative locations is given, thus, in particular, not measured at creases, folds, spots, and the like.

[0076] Just as the thickness of an adhesive layer can be determined, the thickness of an adhesive tape (adhesive strip) or a carrier can be determined analogously using commercially available thickness gauges (touch gauges) with an accuracy of less than 1 pm. 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.

[0077] Static glass transition temperature T g

[0078] 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.

[0079] Molecular weight M n , M w

[0080] 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 = 1 O -10 m). For separation, a combination of columns of type PSS-SDV, 5 pm, 10 3 Ä and 10 5 Ä and 10 6Ä with 8.0 mm x 300 mm each (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer). The flow rate is 1.0 ml per minute. Calibration is performed for polar molecules, such as the starting materials of polyurethane, against PMMA standards (polymethyl methacrylate calibration) and otherwise against PS standards (polystyrene calibration).

[0081] Tensile test using a tensile testing machine, Zwick

[0082] 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.

[0083] Indication of results:

[0084] F x % [N / cm], [N / mm 2 ], [MPa] - force at x % strain

[0085] Foot pressure [N / cm], [N / mm 2 ], [MPa] - force at tear / break of the sample (i.e. tear strength or ultimate tensile force)

[0086] RD [%] - Elongation at break, ie percentage elongation at tear / break of the sample

[0087] Modulus at x% elongation, elongation at break

[0088] The modulus at x% elongation or the elongation at break in [MPa] of a sample are determined according to DIN 53504.

[0089] Detachability using a tensile testing machine, Zwick

[0090] In the removability test, the adhesive tape to be tested, which is coated with adhesive on both sides, is bonded between two test panels. Test panels made of polycarbonate and glass are used. Test specimens 20 mm wide are cut from the adhesive tape to be tested. These test specimens are then bonded to the first glass test panel over a length of 70 mm after the first siliconized PET film has been removed. The free adhesive is then covered on both sides with 36 μm PET after the second siliconized PET film has been removed. The second PC test panel 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 panel protrudes beyond the glass panel. The back of the composite is rolled over the steel panel 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.

[0091] The measurement is taken at an angle of 0°, while the force required to continuously remove / strip the sample is recorded by the tensile testing machine – the so-called stripping force Fstrip. The measurement is completed as soon as the sample has been completely stripped from between the two test plates or the sample breaks during the measurement. At least two measurements are taken per sample. The test environment is 23°C and 50% relative humidity.

[0092] Indication of results:

[0093] Fstripp [N / cm] - force required to strip the test specimen from the adhesive joint at an angle of 0° (stripping force)

[0094] transmission

[0095] 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.

[0096] Haze

[0097] 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. For each transmission measurement, the light transmittance is calculated. The four transmittances are added together to determine the percentage haze value. The haze of other layers is determined analogously and refers to the actual thickness of the layer.

[0098] 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 ß-fold 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.

[0099] refractive index

[0100] 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 measurement window, and the measurement is started. The measurement is performed at 20 °C.

Claims

Patent 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. A carrier according to claim 1, characterized in that the carrier has a refractive index no of 1.45 to 1.57, preferably 1.45 to 1.

50.

3. A carrier according to at least one of the preceding claims, characterized in 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 in that the carrier 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 in that the carrier has a maximum Shore hardness of 85 Shore A, determined by means of ASTM D2240, and / or a 100% modulus of maximum 12 MPa, determined according to DIN 53504 (at 800 mm / min).

6. A carrier according to at least one of the preceding claims, characterized in that the carrier has a thickness of 15 to 100 pm, preferably 30 to 50 pm.

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. The method according to claim 7, characterized in that the polyurethane dispersion is degassed before being applied to the temporary carrier.

9. The method according to at least one of claims 7 to 8, characterized in that the dispersion is applied to the temporary carrier by means of a nozzle.

10. A process according to at least one of claims 7 to 9, characterized in that the drying is carried out by means of heat supply.

11. A method according to at least one of claims 7 to 10, characterized in that the method further comprises a step in which the carrier is tempered.

12. The method according to at least one of claims 7 to 11, characterized in 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 in that the adhesive tape is optically clear and removable.

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