WO2025163191A1

WO2025163191A1 - Redetachable, optically clear adhesive tape

Info

Publication number: WO2025163191A1
Application number: PCT/EP2025/052636
Authority: WO
Inventors: Mathias Hanisch; Franziska Czerwonatis; Niko LÜBBERT
Original assignee: Tesa SE
Current assignee: Tesa SE
Priority date: 2024-02-02
Filing date: 2025-02-03
Publication date: 2025-08-07
Anticipated expiration: 2026-08-02
Also published as: DE102024103015A1

Abstract

The present invention relates to redetachable, optically clear adhesive tapes, to a process for producing them, to their use and also to components produced with the adhesive tapes.

Description

Redetachable, optically clear adhesive tape

Redetachable adhesive tapes are long-established and are employed primarily for the fastening of articles of light to medium weight in the home, work and office sectors, where they are used as replacements for conventional fastening means such as nails and screws.

EP 1 418 212 describes a transparent pressure-sensitive adhesive strip composed of at least three layers which can be redetached without residue or destruction by extensive stretching substantially in the bond plane, where the two outer layers each consist of a transparent adhesive constructed on the basis of hydrogenated vinylaromatic block copolymers and tackifier resins, and between the two outer layers there is at least one layer which is constructed of a transparent adhesive based on vinylaromatic block copolymers and which has a higher elongation at break than the two outer layers.

EP 0 761 793 relates to the multiple use of an adhesive film laminate for bonds which can be undone again without residue by pulling on the laminate in the direction of the bond plane, where the laminate used is composed of a) an elastic carrier having a resilience of at least 50% and b) as a coating on at least one side a solvent-based or acrylate hotmelt-based or dispersion-based pressure-sensitive adhesive.

US 2017/158919 provides a pressure-sensitive adhesive film for wearable electronic devices, where the adhesive film has a bond strength under shear of 0.5 MPa or more, a tear strength of 10 MPa or more and an elongation at break of 300% or more.

US 2017/0158918 discloses an adhesive tape which is redetachable by pulling and which has an adhesive strength under shear of 0.5 MPa or more, a tensile strength of 10 MPa or more and an elongation at break of 300% or more.

Whereas in the initial phase the use of redetachable adhesive tapes was limited to simple fastening tasks, the technical fields in which they are employed are nowadays much more diverse, and so the requirements imposed on the adhesive tapes themselves are also rising. One application which has come under the spotlight in particular in the electronics and automotive industries is the use of such adhesive tapes for the bonding of electronic devices, especially displays. Correspondingly, the spectrum of properties of the adhesive tapes is no longer confined only to their mechanical properties, but instead also embraces optical properties, such as transparency, for example. Hence products with a high degree of transparency and UV resistance and with little haze are needed for the lamination of displays and touchscreens.

Furthermore, in the case of display production, the display panel or the touch layer and the cover glass must be optically connected using a material having an extremely similar refractive index, so as to avoid reflections and hence to maximize the light yield and brightness of the display. For this procedure, optically clear adhesives (OCA) are employed, which in turn may take the form of liquids (liquid OCA - LOCA) or adhesive transfer tape (ATT). Where large, curved and complex displays are employed, these substrates are very expensive and sensitive.

WO 2012/087804 discloses an optical connection layer which has an optical film and a liquid, optically clear adhesive (LOCA) positioned adjacent to the optical film, where the optical connection layer has a light transmissibility of at least 75%. The connection layer is said to be redetachable by stretching.

There are, however, disadvantages to using LOCA. For example, the curing may result in stresses in the assembly, and this in turn may lead to detachment or to what is called a Mura effect (shadow-like compromising of the display). Moreover, the procedure for curing a LOCA is time-consuming, with disadvantages in turn for procedural efficiency.

WO 2009/089137 relates to a stretch-releasable adhesive tape with a pressure-sensitive adhesive comprising a silicone polymer and a tacky tab.

A disadvantage affecting silicone-based OCAs is the relatively low refractive index as compared with acrylates, resulting in a lower light yield (increased reflection). Moreover, silicone-based OCAs are weaker in bond strength and robustness by comparison with acrylate- based OCAs.

Although initial approaches to optically clear, redetachable adhesive tapes already exist, they often exhibit the disadvantages described above. This problem is especially pronounced in connection with the bonding of larger displays, of the kind used in the automotive industry, for example.

In particular, bonding is accompanied again and again by optical defects in the adhesive bond, such as air bubbles or detachment after the curing procedure. As a result of this, the expensive components must either be disposed of or separated manually, which is laborious. With regard to said separation, methods employed include those using a cutting wire, or attempts are made to undo the adhesive bond mechanically after freezing at very low temperatures (-80°C down to -140°C). Both methods carry a great risk of destroying the display components. It is therefore desirable to have a simple mechanism available for the parting of already joined display components during production.

It is therefore the object of the present invention to provide an optically clear adhesive tape which can be detached again without residue or destruction even from fairly large areas, so as to enable simple correction of defective lamination of displays, for example.

The object is achieved by an adhesive tape according to Claim 1. Preferred configurations of the adhesive tape of the invention are set out in the dependent claims.

A first subject of the present invention, therefore, is a redetachable, optically clear adhesive tape comprising:

• an elastic carrier, the carrier having an elongation of at least 300% and a maximum tensile force at 200% elongation of 20 MPa, determined according to DIN 53504; and

• an optically clear, acrylate-based pressure-sensitive adhesive applied to both sides of the carrier, wherein the pressure-sensitive adhesive has a microshear travel of less than 2 mm, determined according to method “Microshear travel” with a load of 200 g for 15 minutes, a layer thickness of 100 pm and a temperature of 40°C.

Within the present invention it has surprisingly emerged that in particular the combination of the physical properties of the carrier and the microshear travel of the pressure-sensitive adhesive affords an adhesive tape having the stated profile of properties, the tape not only forming a stable assembly but also being easy to detach from the substrate again without damaging it, even if used for laminating relatively large areas. Defects which come about in the course of lamination, such as air inclusions, for example, can therefore be easily eliminated without any need for the display to be thrown away.

Unless otherwise indicated, all quantitative data refer to % by weight.

The adhesive tape of the invention is characterized in particular by the microshear travel of its pressure-sensitive adhesive. In one preferred embodiment, said travel is less than 1 mm, more preferably less than 0.5 mm.

For the determination of the microshear travel, the adhesive can be applied to a dimensionally stable carrier of defined width and adhered by the free adhesive side onto a steel test substrate. A defined weight is suspended from the carrier beneath the bond and the vertical deflection of the test element over a certain time is captured as the microshear travel. A detailed description of the determination method is found in the "Test methods" section of the present application and is additionally described in EP 1 674 544, paragraph [0048] ff. To enable detachment of the adhesive tape by pulling, the carrier used in the invention preferentially has an elongation of at least 300%, preferably of more than 500%, and a maximum tensile force at 200% elongation of 20 MPa. In one particularly preferred embodiment, the carrier has a maximum tensile force at 200% elongation of less than 10 MPa, more preferably less than 5 MPa. A low tensile force at 200% elongation ensures that the force Fstrip required for extraction is as far as possible not more than 15 N/cm, since otherwise the forces acting on the sensitive display components become too great and may damage these components. The stripping force may be determined as described in the "Test methods" section.

The carrier used in the adhesive tape of the invention may be produced from a series of materials. In one preferred embodiment, the carrier material is selected from the group consisting of styrene block copolymers, natural rubber, polyisoprene, polybutadiene, polychloroprene rubber, butyl rubber, EPDM rubber, ethylene-propylene copolymers, polyurethanes, vinyl copolymers, ethylene-vinyl acetate copolymers, vinyl chloride-acrylate copolymers, polyetheresters, polyetheramides, polyesteramides, polyether-amide block copolymers, polycarbonate-polyester copolymers, ethylene-acrylate copolymers, ABS copolymers and also mixtures and blends thereof.

Carriers composed of polyurethane have proved particularly advantageous, with preference being given especially to thermoplastic polyurethanes (TPU) and dispersion polyurethanes (PUD), aromatic polyurethanes, aliphatic polyurethanes, polyester-polyol-based polyurethanes, polyether-polyol-based polyurethanes, polycarbonate-based polyurethanes, urethane-based (meth)acrylates and also hybrids and mixtures thereof. The polyurethane may be crosslinked or non-crosslinked.

Preference is given to using optically clear carriers, which preferably have an optical transparency of at least 95%, determined via transmission measurement.

The adhesive tape of the invention uses an optically clear pressure-sensitive adhesive. For the purposes of the present invention, an optically clear pressure-sensitive adhesive refers to a pressure-sensitive adhesive which has an optical transparency of at least 95%, determined via transmission measurement.

According to one preferred embodiment, the pressure-sensitive adhesive of the invention is prepared by polymerizing a mixture in solvent, preferably in ethyl acetate with a regulating solvent component, comprising: a) monomers whose homopolymers have a glass transition temperature, determined by DSC, of less than, equal to or greater than 0°C; and b) 5% to 30% by weight of hydroxy-containing monomers, based on the total mass of the monomer composition; and c) 0.01 % to 5% by weight of polymerization initiator, preferably an azo-based radical initiator which for a half-life of 10 h has a maximum temperature of 80°C, based on the total mass of the monomer composition, wherein the monomer content at the start of polymerization is 35% to 55% by weight, based on the total mass of the monomer composition. The polymerized mixture is crosslinked with 0.02% to 0.5% by weight of crosslinkers, based on the solid polymer fraction. Optionally, the polymerized mixture is crosslinked with further reactive monomers in a fraction of in total not more than 10% by weight, based on the solid polymer fraction.

According to yet another preferred embodiment, the pressure-sensitive adhesive is prepared by polymerizing a mixture in solvent, preferably in ethyl acetate with a regulating solvent component, comprising: a) at least 50% by weight of monomers whose homopolymers have a glass transition temperature, determined by DSC, of at least 0°C, based on the total mass of the monomer composition; and b) 5% to 30% by weight of hydroxy-containing monomers, based on the total mass of the monomer composition; and c) 0.01 % to 5% by weight of polymerization initiator, preferably an azo-based radical initiator which for a half-life of 10 h has a maximum temperature of 80°C, based on the total mass of the monomer composition, wherein the monomer content at the start of polymerization is 35% to 55% by weight, based on the total mass of the monomer composition. Optionally, the polymerized mixture is crosslinked with 0.02% to 0.5% by weight of crosslinkers, based on the solid polymer fraction. Optionally, the polymerized mixture is crosslinked with further reactive monomers in a fraction of in total not more than 10% by weight, based on the solid polymer fraction.

According to a further preferred embodiment, the pressure-sensitive adhesive is prepared by polymerizing a mixture comprising: a) at least 5% by weight of hydroxy-containing monomers, based on the total mass of the monomer composition; and b) less than 0.5% by weight of photoinitiator, based on the total mass of the monomer composition; and one of the following: c) more than 10% by weight of monomers whose homopolymers have a glass transition temperature, determined by DSC, of greater than 0°C, based on the total mass of the monomer composition; or d) at least 0.01% by weight of a crosslinking component, preferably at least 0.03%, more preferably at least 0.05% by weight, based on the solid polymer fraction; or e) more than 10% by weight of a monomer mixture which as a homopolymer has a glass transition of greater than 0°C and at least 0.01 % by weight of a crosslinking component, preferably at least 0.03%, more preferably at least 0.05% by weight, based on the solid polymer fraction.

The adhesive component used in the adhesive tape of the invention is an acrylate-based pressure-sensitive adhesive. It is preferably selected from the group consisting of solvent- containing and solvent-free acrylate adhesives, especially copolymers based on acrylic acid/methacrylic acid and esters thereof having C1 to C25 atoms, maleic, fumaric and itaconic acid and esters thereof, substituted (meth)acrylamides, further vinyl compounds, such as vinyl esters, vinyl acetate, vinyl alcohol and/or esters thereof, compounds of acrylate copolymers and resins, and compounds of different acrylate copolymers.

In the invention, copolymers of acrylic acid and non-acrylate monomers can be used. It has proved advantageous here to limit the content of free acrylic acid in the pressure-sensitive adhesive so as to prevent damage to the display by the acid. An embodiment is therefore preferred in which the pressure-sensitive adhesive is free from free acrylic acid. In this connection, preference is given in particular to a fraction of less than 5 ppm, more preferably less than 1 ppm and especially a fraction of less than 0.1 ppm.

The pressure-sensitive adhesive used in the adhesive tape of the invention may be selected and adapted according to desired application. Accordingly, especially preferred monomers whose homopolymers, as a basis of the pressure-sensitive adhesive, are those having a glass transition temperature below 0°C, whereas for other applications monomers having a glass transition temperature of above 0°C are preferred. In yet other applications, the use of hydroxycontaining monomers is advised. Furthermore, mixtures of these monomers may be used for obtaining the pressure-sensitive adhesive.

For good technical adhesive properties, such as good wetting of the substrates and flow-on of the adhesive, for surrounding of edges which are formed by applied black print at the margin of the display glasses (black display frame), and for high suitability of the adhesive for flexible, foldable and rollable displays, the pressure-sensitive adhesive is preferably obtained from monomers whose homopolymers have a glass transition temperature of not more than 0°C; the glass transition temperature may be determined via DSC. The lower this specific glass transition temperature, the greater the positive effect on the technical adhesive properties stated above. From the group of the monomers having a glass transition temperature of not more than 0°C, particular preference is given to 2-ethylhexyl acrylate, n-butyl acrylate, propylheptyl acrylate, lauryl acrylate, isodecyl acrylate, isooctyl acrylate, n-octyl acrylate, stearyl acrylate, isostearyl acrylate, iso-C17 acrylate, ethylene diglycol acrylate, 2-ethylhexyl diglycol acrylate, 2-(2-ethoxyethoxy)ethyl acrylate and also mixtures.

Moreover, for particularly advantageous microshear travel and a corresponding suitability of the adhesive for re-extraction from a laminated display, it is advantageous to use monomers whose homopolymers have a glass transition temperature of at least 0°C. The higher this specific glass transition temperature, the greater the positive effect on the mechanical properties according to the invention. From this group of monomers, particular preference is given to dihydrodicyclopentadienyl acrylates, isobornyl (meth)acrylate, methyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, stearyl methacrylate, tert-butyl (meth)acrylate, cyclohexyl methacrylate, 4-tert-butylcyclohexyl (meth)acrylate, ethyl methacrylate, N-vinylpyrrolidone, N-vinylcaprolactam, dimethylacrylamide, diethylacrylamide, 4-acryloylmorpholine, phenoxybenzyl (meth)acrylate and also mixtures.

For the production of optically transparent adhesive tapes with OCA requirements, it may be advantageous to use hydroxy-containing monomers. Firstly, this increases the adhesion to the usually polar substrates, such as glass, polycarbonate (PC), polymethyl methacrylate (PMMA) or polarizers. Secondly, by increasing the polarity of the OCA, penetrating moisture is absorbed better at high temperatures and does not result in hazing of the OCA. Preferred monomers include 2-hydroxyethyl (meth) acrylates, 2-hydroxypropyl (meth) acrylates, 3-hydroxypropyl (meth) acrylates, 2-hydroxybutyl (meth) acrylates, 4-hydroxybutyl (meth) acrylates, 6- hydroxyhexyl (meth) acrylates, 1 ,4-cyclohexanedimethanol mono(meth)acrylates, 1 -glycerol (meth) acrylates, 2-hydroxyethyl(meth)acrylamides, N-hydroxypropyl(meth)acrylamides, vinyl alcohol and allyl alcohol and also mixtures thereof.

Corresponding monomer mixtures may be used to achieve an advantageous combination of the properties of the adhesive.

The pressure-sensitive adhesive is obtained preferably by polymerization of a corresponding monomer mixture. The polymerization may take place according to the commonplace processes, especially by conventional radical polymerizations or controlled radical polymerizations. The polymers and/or oligomers may be prepared by copolymerization of the monomeric components, using the customary polymerization initiators and also, optionally, chain transfer agents; polymerization may be carried out at the customary temperatures in bulk or in solution, for example.

Preference is given to polymerization in solvents, more preferably in solvents having a boiling temperature in the range from 50 to 150°C, more preferably in the range from 60 to 120°C, using the customary amounts of polymerization initiators, wherein the polymerization initiators are added to the monomer composition in general in a fraction of about 0.01% to 5% by weight, more particularly of 0.05% to 2% by weight, based on the mass of the monomer composition.

Examples of suitable polymerization initiators are radical sources such as peroxides, hydroperoxides and azo compounds, e.g. dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-t-butyl peroxide, cyclohexylsulfonyl acetyl peroxide, diisopropyl percarbonate, t-butyl peroctoate or benzopinacol.

A particularly preferred radical initiator used is 2,2'-azobis(2-methylbutyronitrile), which is available for example under the trade name Vazo67 from Nouryon, or 2,2-azobis(2,4- dimethylvaleronitrile), which is available for example under the trade name Vazo52 from Nouryon. The temperature of the reaction mixture here is preferably less than 70°C. The lower the polymerization temperature, the better the microshear travel performance of the resulting polymer and hence its suitability for the extraction of the adhesive tape.

Candidate solvents include, in particular, alcohols such as methanol, ethanol, n- and isopropanol, n- and isobutanol, preferably isopropanol and/or isobutanol, and also hydrocarbons such as toluene and, in particular, benzines having a boiling temperature in the range from 60 to 120°C. Use may be made in particular of ketones, such as acetone, methyl ethyl ketone and methyl isobutyl ketone, and esters, such as ethyl acetate, for example, and also mixtures of these solvents. One function of solvents is the regulating effect on the polymerization, meaning that the polymerization does not lead to high molar masses and ultimately to gelling. Certain solvents have a more strongly regulating effect than others, meaning that the risk of gelling is prevented particularly effectively. The use of the alcohols described in particular has a strongly regulating effect, and consequently they are preferably used at not more than 5% by weight in the solvent mixture. Ketones, and also toluene, also have a regulating effect, albeit less strongly, and for that reason preference is given here to a concentration of not more than 40% by weight. If the polymerization is regulated excessively, there is in turn a prolongation of the microshear travel and such copolymers are accordingly unsuitable for an inventive embodiment of the pressure-sensitive adhesive.

At the start of the polymerization, monomer concentrations are established of preferably 35% to 55% by weight, more preferably of 40% to 50% by weight. Similarly to excessive regulation, too low a monomer concentration has the effect of reducing the microshear travel of the copolymer. In the event of too high a monomer concentration, in turn, the risk of gelling goes up.

To improve the properties of the pressure-sensitive adhesive used in the adhesive tape of the invention, this adhesive may be crosslinked. The crosslinking here may take place via at least one crosslinker, preferably selected from the group consisting of isocyanates, more particularly selected from the group consisting of aliphatic polyisocyanates, silane isocyanates, acrylate isocyanates and polypropylene glycol) 2,4-tolylene diisocyanate. Polyfunctional epoxy crosslinkers as well such as polyglycidylamine are suitable crosslinking reagents.

Suitable aliphatic isocyanates are, in particular, hexamethylene diisocyanate (HDI), 1 ,6- hexylene diisocyanate, isophorone diisocyanate (IPDI), 5-isocyanato-1-isocyanatomethyl- 1 ,3,3-trimethylcyclohexane and trimethyl diisocyanate (TMDI). A suitable aliphatic polyisocyanate is available for example under the trade name Desmodur ® N75 BA from Covestro AG. A suitable silane isocyanate is for example 3-isocyanatopropyltrimethoxysilane, under the trade name VESTANAT® EP*-IPMS from Evonik Operations. A suitable acrylate isocyanate is available for example under the trade name VESTANAT® EP*- DC 1241 from Evonik Operations. For this the adhesive in the non-crosslinked state preferably contains 0.02% to 0.5%, preferably 0.05% to 0.3%, more preferably 0.1 % to 0.2% by weight of crosslinkers.

Too low an amount of crosslinkers may be deleterious to the microshear travel and accordingly to the suitability of the adhesive in accordance with the invention. The degree of crosslinking is reflected in the microshear travel of the pressure-sensitive adhesive. The lower the degree of crosslinking, the longer the microshear travel.

The pressure-sensitive adhesive used may additionally be post-crosslinkable through use of crosslinkable reactive monomers, referred to as polyfunctional monomers. In one such embodiment of the invention, the adhesive is post-crosslinkable via polyfunctional monomers and by means of a photoinitiator, with the adhesive for this purpose including the corresponding polyfunctional monomers as a constituent. The polyfunctional monomers here are preferably selected from the group consisting of difunctional (meth)acrylates, for example 1 ,10- decanediol di(meth)acrylate, 1 ,6-hexanediol di(meth)acrylate, 1 ,4-butanediol di(meth)acrylate, tricyclodecanedimethylol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate and pentaerythritol di(meth)acrylates, and also trifunctional or higher polyfunctional (meth)acrylates as for example pentaerythritol tri(meth)acrylate, di pentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate and tetramethylolmethane tri (meth) acrylate; allyl (meth)acrylates, vinyl (meth)acrylates, divinylbenzene, epoxy acrylates, polyester acrylates, urethane acrylates, and also consisting of the group of the silanes and also further related building blocks. The silanes here may have constructions with differing functionality. The silanes may have only an alkoxy substitution. Alternatively, the silanes may have both an alkyl substitution and an alkoxy substitution on the Si atom. Examples of these silanes are, for instance, vinyltrimethoxysilane, vinyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilanes, 3- glycidoxypropyltrimethoxysilanes, 3-glycidoxypropylmethyldiethoxysilanes, 3- glycidoxypropyltriethoxysilanes, p-styryltrimethoxysilanes, 3- methacryloxypropylmethyldimethoxysilanes, 3-methacryloxypropyltrimethoxysilanes, 3- methacryloxypropylmethyldiethoxysilanes, 3-methacryloxypropyltriethoxysilanes, 3- acryloxypropyltrimethoxysilanes and further related building blocks. The polyfunctional monomers may be employed individually and in combination of two or more monomers. This leads to advantages for the technical adhesive properties of the adhesive, such as to a greater assembly strength. The use of polyfunctional monomers, however, may adversely affect the properties in accordance with the invention and the microshear travel.

As is apparent from the possibilities set out, the skilled person has a range of alternatives available for obtaining a pressure-sensitive adhesive which can be used in accordance with the invention, with corresponding microshear travel. Hence instead of the use of polyfunctional acrylates or a crosslinker, for example, a lower polymerization temperature and/or fraction of monomers whose homopolymers have a glass transition temperature of more than 0°C may be used to obtain pressure-sensitive adhesives having a microshear travel as claimed in accordance with the invention.

The pressure-sensitive adhesive used in the adhesive tape of the invention is obtained with particular preference through the solvent-free polymerization by means of UV syrup technology, as particularly cohesive pressure-sensitive adhesives are obtainable in this way. In this case, a prepolymer (5% to 10% conversion) is produced first from a monomer mixture and a suitable photoinitiator (e.g. Irgacure 651). Next, the final formulation is established, optionally using further monomers and/or further photoinitiators, and is coated between two siliconized PET films. The final curing takes place under UV light, preferably with a radiation dose of up to 10 J/cm². Additional crosslinking may be achieved, moreover, by means of difunctional and polyfunctional acrylates such as, for example, hexanediol diacrylate or polyurethane acrylate-based crosslinkers (e.g. Miramer PU2562NT from Miwon), bearing in mind that there is preferably no free acrylic acid present. Suitable photoinitiators include hydroxycyclohexyl phenyl ketone (Irgacure 184), 2,2-dimethoxy-1 ,2-diphenylethan-1-one (Irgacure 651), ethyl 2,4,6-trimethylbenzoylphenylphosphinate (TPO-L), 2,4,6- trimethylphenyldiphenylphosphine oxide (TPO) or phenylbis(2,4,6-trimethylbenzoyl)- phosphine oxide (Irgacure 819).

The adhesive tape of the invention is developed particularly for the production of optical components such as displays, for example. In this sector, stringent requirements are imposed not only on the technical adhesive properties of the adhesive tapes but also on their optical properties. Within the present invention, it has surprisingly become apparent that it is possible with the adhesive tape of the invention also to fulfil the stringent quality requirements imposed in this respect by the automotive industry. In one preferred embodiment, therefore, the adhesive tape of the invention has at least one, preferably two or more and more particularly all, of the following properties:

• a transmission of at least 95%, determined according to "method Transmission"

• a b-value of less than 1 .5, determined according to "method b-value"

• a haze of less than 1.5, determined according to "method Haze"

• a refractive index nD of 1.45 to 1.53, determined according to "method Refractive index".

The adhesive tape of the invention is coated on both sides with a pressure-sensitive adhesive; depending on application, it may be advantageous to use different pressure-sensitive adhesives. An embodiment is therefore preferred in which the pressure-sensitive adhesives are identical or different.

In one preferred embodiment, the adhesive tape of the invention has a thickness of 100 to 500 pm.

As well as its optical properties, the adhesive tape of the invention is notable for its redetachability, achieved by way of properties including the elongation at break of the adhesive tape. This elongation is preferably 300% to 800% as determined according to DIN 53504.

A further subject of the present invention is a process for producing the adhesive tape of the invention. For this, an assembly is formed from carrier and pressure-sensitive adhesive, with the carrier disposed between two layers of pressure-sensitive adhesive. The carrier for this purpose may be coated or laminated on both sides with the pressure-sensitive adhesive. Additionally, the carrier may be subjected to a corona pretreatment, for example under air at 120 W min/m². In this way, the assembly between carrier and pressure-sensitive adhesive can be strengthened, so preventing delamination of the pressure-sensitive adhesive should the adhesive tape have to be removed.

A series of different pressure-sensitive adhesives may be used for producing the adhesive tape of the invention, with the process of the invention being adapted correspondingly in each case.

In one preferred embodiment, the adhesive tape of the invention is produced such that the pressure-sensitive adhesive comprising a mixture of monomers with a glass transition temperature of less than, equal to or greater than 0°C and 5% to 30% by weight of hydroxycontaining acrylates, based on the monomer mixture, preferably at a temperature of less than 70°C and a monomer content at the start of polymerization of 35% to 55% by weight is polymerized

• in ethyl acetate with a regulating solvent component, preferably 20% to 40% by weight of MEK,

• by means of an azo-based radical initiator which for a half-life of 10 h has a maximum temperature of 80°C, blended

• with more than 0.02% by weight of isocyanate-based crosslinker, based on the solid polymer fraction,

• and optionally with further reactive monomers in a fraction of in total not more than 10% by weight, based on the solid polymer fraction, coated on a siliconized liner film, dried and then used to generate an assembly with the carrier.

In one alternatively preferred embodiment, the adhesive tape of the invention is produced such that a pressure-sensitive adhesive comprising 5% to 30% by weight of hydroxy-containing acrylates and at least 50% by weight of monomers whose homopolymer has a glass transition temperature of at least 0°C, based on the monomer mixture, preferably at a temperature of less than 70°C and a monomer content at the start of polymerization of 35% to 55% by weight is polymerized

• optionally with further reactive monomers in a fraction of in total not more than 10% by weight, based on the solid polymer fraction,

• and optionally with more than 0.02% by weight of isocyanate-based crosslinker, based on the solid polymer fraction, coated on a siliconized liner film, dried and then used to generate an assembly with the carrier.

In one alternatively preferred embodiment, the adhesive tape of the invention is produced such that a pressure-sensitive adhesive comprising at least 5% by weight of hydroxy-containing acrylates, a fraction of photoinitiator of less than 0.5% by weight and also alternatively

• more than 10% by weight of monomers whose homopolymers have a glass transition of greater than 0°C, or

• using a crosslinking component having a content of at least 0.01%, preferably at least 0.03%, more preferably at least 0.05% by weight, based on the solid polymer fraction, or

• more than 10% by weight of monomers whose homopolymers have a glass transition of greater than 0°C and using a crosslinking component having a content of at least 0.01 %, preferably at least 0.03%, more preferably at least 0.05% by weight, based on the solid polymer fraction, is coated by way of a UV syrup procedure between two siliconized liners, polymerized under UV light, preferably with a UV dose of 3000 mJ/cm² or less, and then used to generate an assembly with the carrier. A further subject of the present invention is an optical display comprising the adhesive tape of the invention. The display of the invention may for example be used in electronic devices such as mobile phones, tablets, laptops and the like.

A further subject of the present invention is the use of the adhesive tape of the invention for producing optical components, especially displays.

The invention is elucidated in more detail with the following examples, which, however, should in no way be understood as limiting the concept of the invention. i) Test methods

All measurements were conducted, unless otherwise indicated, at 23°C and 50% relative air humidity.

Thickness

The thickness of a layer of adhesive can be determined by determining the thickness of a section, defined in terms of its length and width, of such an adhesive layer applied to a liner, minus the (known or separately ascertainable) thickness of a section of the same dimensions of the liner used. The thickness of the adhesive layer can be ascertained with accuracies of less than 1 pm deviation using commercially available thickness gauges (sensor test devices). If thickness fluctuations are detected, the mean value of measurements at not less than three representative locations is reported, thus in particular not measured at pinches, folds, specks and the like.

Redetachment by stretching

In the test for redetachability, the adhesive tape under investigation, furnished with adhesive on both sides, is bonded between two test plates. Test plates of polycarbonate and glass are used.

Specimens of width 20 mm are cut out of the adhesive tape under investigation. After removal of the first siliconized PET film, these specimens are stuck over a length of 70 mm onto the first test plate of glass. The free adhesive following removal of the second siliconized PET film is covered on either side with 36 pm of PET. The second test plate of PC, after cleaning with isopropanol and preconditioning for 1 to not more than 10 min at 23°C and 50% relative air humidity, is stuck onto the reverse side of the bonded strip (i.e. specimen) such that the PC plate projects beyond the glass plate. A 4 kg roller is run 10 times over the assembly on the reverse side of the steel plate (back and forth five times). After an attachment time of at least 24 h at 23°C and 50% relative air humidity, the strips are stripped out of the adhesive join using the tab by means of a tensile tester (from Zwick) at a constant speed of 800 mm/min at an angle of 0°. The test specimen is fixed here with an angle-adjustable adapter, and the tab is clamped perpendicularly into the middle of the clamping jaws.

Measurement is made at an angle of 0°, during which the force required for extracting/stripping the sample is recorded continuously by the tensile tester - called the stripping force F_stri_P. The measurement is at an end as soon as the sample has been stripped out completely between the two test plates or the sample has torn during the measurement. At least 2 measurements per specimen are conducted. The test conditions are 23°C and 50% rel. air humidity.

Reporting of results:

Fstrip [N/cm] - force required to strip the specimen out of the adhesive join at angle 0° (stripping force)

Tensile test by means of tensile tester, Zwick

Strips of width 15 mm having a length of around 150 mm are cut out of the sample under investigation (adhesive tape, i.e. carrier provided with adhesive preferably on both sides, or plain carrier only) in longitudinal direction by means of a strip cutter or razor blade knife. The sample, preconditioned under the test conditions for 24 h, is clamped perpendicularly into the middle of the clamping jaws with a clamped length of 10 mm and stretched at a speed of 800 mm/min until it tears. The tear is supposed to occur in about the middle of the strip. If the tear is close to the jaws (closer than 1 cm), the value should be rejected and a further strip should be tested instead. 5 measurements are conducted per sample variant. The test conditions are 23°C and 50% rel. air humidity. The measurements are made in accordance with EN ISO 527.

Reporting of results:

F_x% [N/cm], [N/mm²] - force at x% elongation

Fbreak [N/cm], [N/mm²] - force at sample tear/break (i.e. tear strength)

EB [%] - elongation at break, i.e. percentage elongation at sample tear/break

Modulus atx% elongation, elongation at break

The modulus at x% elongation and the elongation at break of a sample are determined according to DIN 53504. Microshear travel

This test serves for accelerated testing of the shear strength of adhesive tapes under temperature load.

Sample preparation for microshear travel

The pressure-sensitive adhesive (PSA) specimen, with a double lining of siliconized PET film, is first freed of its liner on one side and laminated to an etched PET film (e.g. in 50 pm). A cutout adhesive strip (length around 50 mm, width 10 mm) is subsequently bonded to a steel plate, cleaned with acetone, in such a way that the steel plate projects right and left beyond the adhesive tape and the adhesive strip protrudes 2 mm over the test plate at the upper margin. The bond area of the sample in height x width amounts to 13 mm x 10 mm. A steel roller weighing 2 kg is subsequently rolled over the bond site six times at a speed of 10 m/min. The adhesive tape is reinforced flush with a stable adhesive strip which serves as a carrier for the travel sensor. The sample is suspended perpendicularly by means of the test plate.

Microshear travel measurement

The test element for measurement is loaded at the lower end with a weight of 200 g. The test temperature is 40°C, the test duration 15 minutes.

Glass transition temperature T_g

The glass transition temperature of polymers may be determined by means of dynamic scanning calorimetry (DSC). For this test, about 5 mg of the untreated polymer samples are weighed out into an aluminium crucible (volume 25 pl) and closed with a perforated lid. For the measurement, a DSC 204 F1 from Netzsch is used and is operated under nitrogen for inerting. The sample is first cooled to -150°C, then heated to +150°C at a heating rate of 10 K/min, and cooled again to -150°C. The subsequent second heating curve is run again at 10 K/min, and the change in the heat capacity is recorded. Glass transitions are characterized as steps in the thermogram. The glass transition temperature is determined as follows: a tangent is applied in each case to the baseline of the thermogram before the step. In the region of the step, a line of best fit is placed parallel to the ordinate in such a way that it intersects the two tangents, specifically such as to form two areas of equal content (between each tangent, the line of best fit, and the measurement plot). The point of intersection of the lines of best fit positioned accordingly and the measurement plot gives the glass transition temperature.

Transmission

The transmission of the adhesive tape is determined according to ASTM D1003-13 (Procedure A (BYK Gardner HazeGard Plus), standard illuminant D65). A correction is made for interfacial reflection losses. The transmission of different layers is determined analogously and refers to the actual thickness of the layer.

Haze

The haze of the overall construction is determined as described in ASTM D1003-13 using a BYK Gardner Haze Gard Plus. The haze value describes the fraction of transmitted light which is scattered forwards at large angles by the irradiated sample. The haze value therefore quantifies material defects in the surface or the structure that disrupt the clear sight through the sample. The standard requires the measurement of four transmission measurements. For each transition measurement, the light transmittance is calculated. The fourtransmittances are used to compute the percentage haze value. The haze of other layers is determined analogously and refers to the actual thickness of the layer. b-value

The b-value is a measure of discoloration on a yellow-blue colour scale and, together with the L-value (lightness) and the a-value (red-green colour scale), produces an objective determination of the perceived colour. The values referred to as Lab values are determined using the Spectro-Guide Sphere Gloss instrument from BYK Gardner according to ASTM D2244-096 and DIN 6174. To start with, a 3-fold background measurement is carried out on a known reference ground. The adhesive tape is then measured on this reference ground, likewise at three different points. To determine the b-value, the mean value is then formed from the three individual values and the mean value of the reference is subtracted.

Refractive index

The refractive index is determined using an Abbemat 350 refractometer (Anton Paar). To start with, the sample is measured against air and against water in order to verify the functionality. The adhesive tape or the individual components are then applied to the measuring window and the measurement is started. The measurement is carried out at 20°C. ii) Examples

Solvent-based production processes

Example A1

A reactor conventional for radical polymerizations is charged with 140 g of 2-ethylhexyl acrylate, 180 g of isobornyl acrylate, 80 g of 4-hydroxybutyl acrylate and 400 g of ethyl acetate/2-butanone (70/30). After nitrogen gas has been passed through the reactor for 45 minutes with stirring, the reactor is heated up to 70°C and 0.27 g of Vazo52 is added. The external heating bath is subsequently regulated such that the reaction mixture is held constantly at 40°C. After 2 h, a further 0.27 g of Vazo52 is added and after 4.5 h and 6 h, the mixture is diluted with 80 g of ethyl acetate/2-butanone mixture each time. After 7 h, reinitiation is performed with 0.21 g of Vazo67 and the reaction temperature is raised to 80°C. After a reaction time of 18 h, the polymerization is discontinued and the product is cooled to room temperature. The polymer solution is subsequently diluted to a solids content of around 30% with ethyl acetate and, using a coating knife, it is coated on siliconized PET liner such that the adhesive film obtained after the evaporation of the solvent for 30 minutes has a thickness of 100 pm. This film is also dried in an oven at 120°C for 15 minutes, lined with a second siliconized PET liner and stored at room temperature for 6 days until ultimate crosslinking is attained.

Example A2

A reactor conventional for radical polymerizations is charged with 160 g of n-butyl acrylate, 80 g of lauryl acrylate, 48 g of 4-hydroxybutyl acrylate, 112 g of 2-propylheptyl acrylate and 489 g of ethyl acetate/2-butanone (70/30). After nitrogen gas has been passed through the reactor for 45 minutes with stirring, the reactor is heated up to 70°C and 0.31 g of Vazo52 is added. The external heating bath is subsequently regulated such that the reaction mixture is held constantly at 40°C. After 1 h, a further 0.31 g of Vazo52 is added and after 2.5 h, 3 h, 3.5 h, 4.75 h and 6.5 h, the mixture is diluted with 80 g of ethyl acetate/2-butanone mixture each time. After 10 h, reinitiation is performed with 0.24 g of Vazo67 and the reaction temperature is raised to 80°C. After a reaction time of 18 h, the polymerization is discontinued and the product is cooled to room temperature. The polymer solution is subsequently diluted to a solids content of around 30% with ethyl acetate and, using a coating knife, it is coated on siliconized PET liner such that the adhesive film obtained after the evaporation of the solvent for 30 minutes has a thickness of 100 pm. This film is also dried in an oven at 120°C for 15 minutes, lined with a second siliconized PET liner and stored at room temperature for 6 days until ultimate crosslinking is attained.

Example A3

A reactor conventional for radical polymerizations is charged with 108 g of n-butyl acrylate, 100 g of methyl acrylate, 80 g of 4-hydroxybutyl acrylate, 112 g of tert-butyl acrylate and 600 g of ethyl acetate/2-butanone (70/30). After nitrogen gas has been passed through the reactor for 45 minutes with stirring, the reactor is heated up to 70°C and 0.62 g of Vazo52 is added. The external heating bath is subsequently regulated such that the reaction mixture is held constantly at 65°C. After 3.65 h and 6.75 h, the mixture is diluted with 80 g of ethyl acetate/2- butanone mixture each time. After 10 h, the reaction temperature is raised to 80°C. After a reaction time of 18 h, the polymerization is discontinued and the product is cooled to room temperature. The polymer solution is subsequently admixed with 6%, based on the solids content of the polymer, of ethoxylated trimethylolpropane triacrylate, 2% of vinyltrimethoxysilane and 2% of TPO-L, diluted to a solids content of around 30% with ethyl acetate and, using a coating knife, coated on siliconized PET liner such that the adhesive film obtained after the evaporation of the solvent for 30 minutes has a thickness of 100 pm. This film is also dried in an oven at 120°C for 15 minutes, lined with a second siliconized PET liner and stored at room temperature for 6 days until ultimate crosslinking is attained.

Comparative example C1

A reactor conventional for radical polymerizations is charged with 228 g of n-butyl acrylate, 80 g of methyl acrylate, 40 g of 4-hydroxybutyl acrylate, 52 g of tert-butyl acrylate and 600 g of ethyl acetate/2-butanone (70/30). After nitrogen gas has been passed through the reactor for 45 minutes with stirring, the reactor is heated up to 70°C and 0.62 g of Vazo52 is added. The external heating bath is subsequently regulated such that the reaction mixture is held constantly at 65°C. After 10 h, the reaction temperature is raised to 80°C. After a reaction time of 18 h, the polymerization is discontinued and the product is cooled to room temperature. The polymer solution is subsequently admixed with 6%, based on the solids content of the polymer, of ethoxylated trimethylolpropane triacrylate, 2% of vinyltrimethoxysilane and 2% of TPO-L, diluted to a solids content of around 30% with ethyl acetate and, using a coating knife, coated on siliconized PET liner such that the adhesive film obtained after the evaporation of the solvent for 30 minutes has a thickness of 100 pm. This film is also dried in an oven at 120°C for 15 minutes, lined with a second siliconized PET liner and stored at room temperature for 6 days until ultimate crosslinking is attained.

UV syrup technology

Example A4

A reactor conventional for radical polymerizations is charged with 160 g of 2-ethylhexyl acrylate, 120 g of 4-hydroxybutyl acrylate and 120 g of tert-butyl acrylate and with the photoinitiator Irgacure 651 with a fraction of 0.01% by weight. After nitrogen gas has been passed through the reactor for 45 minutes with stirring, the reactor is sufficiently freed from oxygen. The reaction is subsequently initiated with a (UV) LED lamp having an intensity of 3000 [mJ/cm²] for 10 min until a monomer-polymer mixture of defined viscosity is present. Subsequently, the prepolymer is blended with photoinitiator Irgacure 184 (0.2% by weight and crosslinker (0.1 % by weight of HDDA) and, using a vacuum pump, a reduced pressure is applied so as to free the mixture from bubbles. The blend is subsequently coated in a thickness of 100 pm between two siliconized PET films (each 50 pm). The further reaction through to 100% polymer is initiated by irradiation with a Heraeus UV LED lamp (wavelength 365 nm) with a UV dose of 3000 mJ/cm².

Example A5

A reactor conventional for radical polymerizations is charged with 320 g of 2-ethylhexyl acrylate, 60 g of 4-hydroxybutyl acrylate and 20 g of tert-butyl acrylate and with the photoinitiator Irgacure 651 with a fraction of 0.01% by weight. After nitrogen gas has been passed through the reactor for 45 minutes with stirring, the reactor is sufficiently freed from oxygen. The reaction is subsequently initiated with a (UV) LED lamp having an intensity of 3000 [mJ/cm²] for 10 min until a monomer-polymer mixture of defined viscosity is present.

Subsequently, the prepolymer is blended with photoinitiator Irgacure 184 (0.5% by weight) and crosslinker (0.12% by weight of HDDA) and, using a vacuum pump, a reduced pressure is applied so as to free the mixture from bubbles. The blend is subsequently coated in a thickness of 100 pm between two siliconized PET films (each 50 pm). The further reaction through to 100% polymer is initiated by irradiation with a Heraeus UV LED lamp (wavelength 365 nm) with a UV dose of 3000 mJ/cm².

Comparative example C2

A reactor conventional for radical polymerizations is charged with 320 g of 2-ethylhexyl acrylate, 60 g of 4-hydroxybutyl acrylate and 20 g of methacrylic acid and with the photoinitiator Irgacure 651 with a fraction of 0.01 % by weight. After nitrogen gas has been passed through the reactor for 45 minutes with stirring, the reactor is sufficiently freed from oxygen. The reaction is subsequently initiated with a (UV) LED lamp having an intensity of 3000 [mJ/cm²] for 10 min until a monomer-polymer mixture of defined viscosity is present.

Subsequently, the prepolymer is blended with photoinitiator Irgacure 184 (0.5% by weight) and, using a vacuum pump, a reduced pressure is applied so as to free the mixture from bubbles. The blend is subsequently coated in a thickness of 100 pm between two siliconized PET films (each 50 pm). The further reaction through to 100% polymer is initiated by irradiation with a Heraeus UV LED lamp (wavelength 365 nm) with a UV dose of 3000 mJ/cm².

The example specimens described above are each laminated onto both sides of the carrier B2. The carrier is pretreated beforehand on both sides with corona (under air at 120 W min/m²).

Example B1

The Pll dispersion Impranil DL1116 (Covestro) is admixed with 2%, based on the Pll solids content, of the crosslinker Imprafix 2794 (Covestro) and 0.6% of the thickener Ortegol PV301 (Evonik) and the mixture is homogenized by means of a beaker stirrer. Subsequently, via knife coating, a film is applied to a siliconized PET film in a manner such that the Pll film obtained after drying has a thickness of 50 pm. Following the coating operation, the product is left to evaporate at room temperature for 30 minutes to start with and then dried at 120°C for 15 minutes. After cooling, the film obtained is lined with a second siliconized PET film.

Example B2

Elastollan L1185A (BASF) was used in the form of pellets. Using an extrusion process known to the skilled person, a film 50 pm thick was produced. In addition, this film is protected on both sides with a co-extruded PE film.

Example B C1

The PU dispersion Impranil DLCF (Covestro) is admixed with 2%, based on the PU solids content, of the crosslinker Imprafix 2794 (Covestro) and 0.6% of the thickener Ortegol PV301 (Evonik) and the mixture is homogenized by means of a beaker stirrer. Subsequently, via knife coating, a film is applied to a siliconized PET film in a manner such that the PU film obtained after drying has a thickness of 50 pm. Following the coating operation, the product is left to evaporate at room temperature for 30 minutes to start with and then dried at 120°C for 15 minutes. After cooling, the film obtained is lined with a second siliconized PET film.

Example B C2

N5650M (Nupro) was used as a ready-extruded film. Abbreviations:

The compositions of the example formulations are summarized in Tables 1 and 2. Unless otherwise indicated, the data refer to % by weight. Table 1a:

Table 1b:

Table 2a

Table 2b:

Tables 3 and 4 show the optical and mechanical properties of the illustrative PSAs. Table 3

Table 4a

Table 4b:

All of the inventive adhesive tapes were redetachable without destruction, with the force F_stn_P required for extraction being in each case not more than 15 N/cm. In contrast to this, destruction-free redetachment of the adhesive tape B C2 was not possible. For the other comparative examples, the adhesive tape tore off as early as during determination of the force Fstrip required for peeling. While the non-inventive adhesive tapes did show good optical properties, it was nevertheless not possible to achieve the advantageous combination of optical properties and mechanical properties of the kind achieved by the inventive adhesive tapes.

Claims

1 . Redetachable adhesive tape comprising: o an elastic carrier, the carrier having an elongation of at least 300% and a maximum tensile force at 200% elongation of 20 MPa, determined according to DIN 53504; and o an optically clear, acrylate-based pressure-sensitive adhesive applied to both sides of the carrier, characterized in that the pressure-sensitive adhesive has a microshear travel of less than 2 mm, determined according to method MST with a load of 200 g for 15 minutes, a layer thickness of 100 pm and a temperature of 40°C.

2. Adhesive tape according to Claim 1 , characterized in that the pressure-sensitive adhesive is prepared by polymerizing a mixture in solvent, preferably in ethyl acetate with a regulating solvent component, comprising: a) monomers whose homopolymers have a glass transition temperature, determined by DSC, of less than, equal to or greater than 0°C; and b) 5% to 30% by weight of hydroxy-containing monomers, based on the total mass of the monomer composition; and c) 0.01 % to 5% by weight of polymerization initiator, preferably an azo-based radical initiator which for a half-life of 10 h has a maximum temperature of 80°C, based on the total mass of the monomer composition, wherein the polymerized mixture is crosslinked with 0.02% to 0.5% by weight of crosslinkers, based on the solid polymer fraction, and optionally with further reactive monomers in a fraction of in total not more than 10% by weight, based on the solid polymer fraction, and wherein the monomer content at the start of polymerization is 35% to 55% by weight, based on the total mass of the monomer composition.

3. Adhesive tape according to Claim 1 , characterized in that the pressure-sensitive adhesive is prepared by polymerizing a mixture in solvent, preferably in ethyl acetate with a regulating solvent component, comprising: a) at least 50% by weight of monomers whose homopolymers have a glass transition temperature, determined by DSC, of at least 0°C, based on the total mass of the monomer composition; and b) 5% to 30% by weight of hydroxy-containing monomers, based on the total mass of the monomer composition; and c) 0.01 % to 5% by weight of polymerization initiator, preferably an azo-based radical initiator which for a half-life of 10 h has a maximum temperature of 80°C, based on the total mass of the monomer composition, wherein the polymerized mixture is optionally crosslinked with 0.02% to 0.5% by weight of crosslinkers, based on the solid polymer fraction, and optionally with further reactive monomers in a fraction of in total not more than 10% by weight, based on the solid polymer fraction, and wherein the monomer content at the start of polymerization is 35% to 55% by weight, based on the total mass of the monomer composition.

4. Adhesive tape according to Claim 1 , characterized in that the pressure-sensitive adhesive is prepared by polymerizing a mixture comprising: a) at least 5% by weight of hydroxy-containing monomers, based on the total mass of the monomer composition; and b) less than 0.5% by weight of photoinitiator, based on the total mass of the monomer composition; and one of the following: c) more than 10% by weight of monomers whose homopolymers have a glass transition temperature, determined by DSC, of greater than 0°C, based on the total mass of the monomer composition; or d) at least 0.01% by weight of a crosslinking component, preferably at least 0.03%, more preferably at least 0.05% by weight, based on the solid polymer fraction; or e) more than 10% by weight of a monomer mixture which as a homopolymer has a glass transition of greater than 0°C and at least 0.01 % by weight of a crosslinking component, preferably at least 0.03%, more preferably at least 0.05% by weight, based on the solid polymer fraction.

5. Adhesive tape according to Claim 1 , characterized in that the carrier material is selected from the group consisting of styrene block copolymers, natural rubber, polyisoprene, polybutadiene, polychloroprene rubber, butyl rubber, EPDM rubber, ethylenepropylene copolymers, polyurethanes, vinyl copolymers, ethylene-vinyl acetate copolymers, vinyl chloride-acrylate copolymers, polyetheresters, polyetheramides, polyesteramides, polyether-amide block copolymers, polycarbonate-polyester copolymers, ethylene-acrylate copolymers, ABS copolymers and also mixtures and blends thereof.

6. Adhesive tape according to Claim 5, characterized in that the carrier material is selected from polyurethanes, especially thermoplastic polyurethanes (TPU) and dispersion polyurethanes (PUD), aromatic polyurethanes, aliphatic polyurethanes, polyester- polyol-based polyurethanes, polyether-polyol-based polyurethanes, polycarbonate- based polyurethanes and also hybrids and mixtures thereof, wherein the polyurethane may be crosslinked or non-crosslinked.

7. Adhesive tape according to at least one of the preceding claims, characterized in that the pressure-sensitive adhesive is selected from the group consisting of solventcontaining and solvent-free acrylate adhesives, especially copolymers based on acrylic acid/methacrylic acid and esters thereof having C1 to C25 atoms, maleic, fumaric and itaconic acid and esters thereof, substituted (meth)acrylamides, further vinyl compounds, such as vinyl esters, vinyl acetate, vinyl alcohol and/or esters thereof, compounds of acrylate copolymers and resins, and compounds of different acrylate copolymers.

8. Adhesive tape according to at least one of the preceding claims, characterized in that the monomers whose homopolymers having a glass transition temperature, determined by DSC, of not more than 0°C, are preferably selected from the group consisting of 2- ethylhexyl acrylate, n-butyl acrylate, propylheptyl acrylate, lauryl acrylate, isodecyl acrylate, isooctyl acrylate, n-octyl acrylate, stearyl acrylate, isostearyl acrylate, iso-C17 acrylate, ethylene diglycol acrylate, 2-ethylhexyl diglycol acrylate, 2-(2- ethoxyethoxy)ethyl acrylate and also mixtures thereof.

9. Adhesive tape according to at least one of the preceding claims, characterized in that the monomers whose homopolymers having a glass transition temperature, determined by DSC, of not less than 0°C, are preferably selected from the group consisting of dihydrodicyclopentadienyl acrylate, isobornyl (meth)acrylate, methyl (meth)acrylate, 2- phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, stearyl methacrylate, tert-butyl (meth)acrylate, cyclohexyl methacrylate, 4-tert-butylcyclohexyl (meth)acrylate, ethyl methacrylate, N-vinylpyrrolidone, N-vinylcaprolactam, dimethylacrylamide, diethylacrylamide, 4-acryloylmorpholine, phenoxybenzyl (meth)acrylate and also mixtures thereof.

10. Adhesive tape according to at least one of the preceding claims, characterized in that the hydroxy-containing monomers are preferably selected from the group consisting of 2-hydroxyethyl (meth)acrylates, 2-hydroxypropyl (meth)acrylates, 3-hydroxypropyl (meth) acrylates, 2-hydroxybutyl (meth)acrylates, 4-hydroxybutyl (meth)acrylates, 6- hydroxyhexyl (meth)acrylates, 1 ,4-cyclohexanedimethanol mono(meth)acrylates, 1- glycerol (meth)acrylates, 2-hydroxyethyl(meth)acrylamides, N- hydroxypropyl(meth)acrylamides, vinyl alcohol and allyl alcohol and also mixtures thereof.

11 . Adhesive tape according to at least one of the preceding claims, characterized in that the adhesive tape has at least one of the following properties: o a transmission of at least 95%, determined according to "method Transmission" o a b-value of less than 1 .5, determined according to "method b-value" o a haze of less than 1 .5, determined according to "method Haze" o a refractive index nD of 1.45 to 1.53, determined according to "method Refractive index"

12. Process for producing an adhesive tape according to at least one of the preceding claims, characterized in that an assembly composed of adhesive and carrier is generated, wherein the carrier is disposed between two layers of adhesive.

13. Process according to Claim 12, characterized in that a pressure-sensitive adhesive comprising acrylates with a glass transition temperature of less than, equal to or greater than 0°C and 5% to 30% by weight of hydroxy-containing acrylates and a monomer content at the start of polymerization of 35% to 55% by weight is polymerized

• in ethyl acetate with a regulating solvent component

14. Process according to Claim 12, characterized in that a pressure-sensitive adhesive comprising 5% to 30% by weight of hydroxy-containing acrylates and at least 50% by weight of monomers whose homopolymer has a glass transition temperature of at least 0°C and having a monomer content at the start of polymerization of 35% to 55% by weight is polymerized

• in ethyl acetate with a regulating solvent component

15. Process according to Claim 12, characterized in that a pressure-sensitive adhesive comprising at least 5% by weight of hydroxy-containing acrylates, a fraction of photoinitiator of less than 0.5% by weight and also alternatively

• more than 10% by weight of monomers whose homopolymers have a glass transition temperature of greater than 0°C, or

• more than 10% by weight of monomers whose homopolymers have a glass transition of greater than 0°C and using a crosslinking component having a content of at least 0.01 %, preferably at least 0.03%, more preferably at least 0.05% by weight, based on the solid polymer fraction is coated by way of a UV syrup procedure between two siliconized liners, polymerized under UV light and then used to generate an assembly with the carrier.

16. Display comprising an adhesive tape according to at least one of Claims 1 to 11.

17. Use of an adhesive tape according to at least one of Claims 1 to 11 for producing displays.