Pressure-sensitive adhesive and method for producing same

Abstract

The invention relates to a photopolymerized pressure-sensitive adhesive comprising at least one first base polymer component having one or more functional groups suitable for coordinative crosslinking, one or more photoinitiators, and one or more crosslinkers, wherein at least one of the crosslinkers is a coordinative crosslinker.

Description

[0001] Late registration

[0002] 1

[0003] Pressure-sensitive adhesive and its manufacturing process

[0004] The invention relates to an adhesive compound, in particular a photopolymerized adhesive compound having a coordinative crosslinking system, and to a method for producing the adhesive compound.

[0005] Pressure-sensitive adhesives, such as polyacrylate pressure-sensitive adhesives, are generally produced in solution via free-radical polymerization. The polyacrylates are typically coated in solution onto the substrate using a coating bar and then dried. To increase cohesion, the polymer is crosslinked. Curing is achieved thermally, by UV crosslinking, or by electron beam curing (ES). Prior art for solution-based polyacrylate pressure-sensitive adhesives includes those using a single covalent crosslinker, a single coordinative crosslinker, or a combination of these crosslinkers. The use of coordinative crosslinkers for producing polyacrylate pressure-sensitive adhesives typically requires monomers with acid functionality, such as acrylic acid, in high proportions by weight.

[0006] EP3417005B1 discloses the solvent polymerization of poly(meth)acrylates in which 5 wt% acrylic acid, based on the total mass of the monomers to be polymerized, is used. A preferred embodiment discloses a maximum acrylic acid content of 12.5 wt% of the total mass of the monomers to be polymerized. The described pressure-sensitive adhesive has both coordinative and covalent crosslinking agents.

[0007] Solvent-based processes for the production of pressure-sensitive adhesives have several disadvantages, including high environmental impacts from emissions of volatile organic compounds (VOCs), increased production costs due to the purchase, handling, and disposal of solvents, and safety risks for workers from fire and chemical exposure. Therefore, there is a need for solvent-free processes for the polymerization of pressure-sensitive adhesives.

[0008] Photopolymerization, particularly syrup polymerization, is a substantially solvent-free polymerization of poly(meth)acrylates. The monomer mixtures used for polymerizing poly(meth)acrylates typically have a viscosity too low to be efficiently processed without additional processing steps, for example, to be applied to a support material. To increase the viscosity, the monomer mixture is prepolymerized to a syrupy consistency, advantageously up to a conversion of 2–20%. This results in a syrup that can be readily coated onto a support material. UV light with a wavelength of 280–450 nm is preferably used to initiate the prepolymerization.

[0009] US Patent 4,303,485 describes a process for producing partially polymerized (meth)acrylate syrup using photopolymerization techniques. The syrup is partially polymerized to a spreadable viscosity. In producing the spreadable syrup, (meth)acrylate monomer is irradiated with ultraviolet radiation for less than one minute in the presence of a photoinitiator, resulting in a (meth)acrylate syrup with a viscosity of 0.3–10 pascal-seconds (300–10,000 centipoise) at ordinary room temperature. The spreadable syrup can be stored for subsequent coating and ultraviolet irradiation to convert the coating into its desired end use (e.g., an adhesive).

[0010] The use of covalent crosslinkers, particularly diacrylates or higher-functionality monomers, in syrup polymerization is known in the prior art. These crosslinkers are generally added to the monomers to be polymerized during the polymerization process and polymerized into the forming polymer. This means that the covalent crosslinkers become part of the polymer structure and form chemical bonds with the monomers during polymerization to create a rigid (“covalent”) network. WO2016089805 discloses the production of poly(meth)acrylate pressure-sensitive adhesives in which the covalent crosslinker hexamethylene diacrylate (HDDA) or allyl acrylate (AIA) is added to a (meth)acrylate syrup produced in two steps. Covalently crosslinked polymer systems often exhibit limitations regarding their flexibility, repairability, and processing temperatures.

[0011] Coordinatively cross-linked pressure-sensitive adhesives offer numerous advantages over covalently cross-linked adhesives, including the reversibility of the bonds, which enables improved processability and repairability, as well as the ability to self-heal small cracks or damage, which increases the service life and reliability of the adhesives (see Benedek, I., & Feldstein, MM (Eds.); 2009; Handbook of Pressure-Sensitive Adhesives and Products: Technology of Pressure-Sensitive Adhesives and Products. CRC Press, Taylor & Francis Group; Chapter 5.3.2.3.1 Oragnometallic Cross-Linkers). Furthermore, these systems offer increased flexibility and elongation, which is particularly advantageous under dynamic loads.The properties of pressure-sensitive adhesives can be precisely tailored by selecting specific metal ions or ligands, and they can be processed at lower temperatures, offering energy savings and reduced thermal stress on sensitive substrates. As in solvent polymerization, the use of coordinative crosslinkers in syrup-polymer technology requires a high proportion of monomers with acid functionality, such as acrylic acid. However, the use of coordinative crosslinkers is severely limited, as even small proportions of monomers with acid functionality lead to gel formation, resulting in poorer adhesive properties and limitations in the further processing of the syrup.

[0012] German patent applications DE 10 2013 219 495 A1 and DE 10 2013 219 491 A1 disclose pressure-sensitive adhesives based on polyacrylate, which are produced by polymerizing a monomer mixture and subsequent crosslinking. The described processes involve first polymerizing a monomer mixture to form a polyacrylate (process step B). Only then is a crosslinker, for example, a metal chelate as a coordinative crosslinker, added to the polyacrylate already formed (process step C), before the mixture is finally crosslinked (process step D). This approach, in which the crosslinker is added to the finished polymer after the polymer has been formed, is typical for solvent-based production processes in batch reactors. Long polymer chains are thus linked together.However, if one were to attempt to add the coordinative crosslinker at the beginning of the described process, i.e., during the polymerization of the monomers, this would lead to premature and uncontrolled gel formation. The coordinative bonds would form uncontrollably between the monomers and the growing polymer chains, resulting in a drastic increase in viscosity and gelation of the entire reaction mixture. The mass would then no longer be processable. Under these conditions, the production of a functional, coordinatively crosslinked pressure-sensitive adhesive would not be possible.

[0013] The technical object of the present invention is to provide an adhesive compound which is produced by a substantially solvent-free photopolymerization.

[0014] Furthermore, improved adhesion, flexibility, and self-healing properties are to be achieved. The aim is to develop an adhesive compound that remains stable under dynamic loads, has a longer service life, and can be processed at lower temperatures.

[0015] Furthermore, the pressure-sensitive adhesive is intended to exhibit reversible cross-linking, enabling easy repair and reuse, thereby increasing efficiency and sustainability in various applications. A first and general object of the invention is a photopolymerized pressure-sensitive adhesive comprising: a) at least one base polymer component with one or more functional groups suitable for coordinative cross-linking; b) one or more photoinitiators; c) one or more coordinative cross-linkers.

[0016] In a preferred embodiment, the photopolymerized pressure-sensitive adhesive is characterized in that it is produced by a web polymerization process, wherein the coordinative crosslinkers are present in the syrup and are photopolymerized together with the syrup. Due to the presence of one or more coordinative crosslinkers in the syrup during photopolymerization, these crosslinkers are actively integrated into the forming polymer network under light irradiation. This results in a particularly homogeneous crosslinking density and a finer, more uniform network structure of the polymer.In addition to the aforementioned improved recoil resistance and good cohesion at elevated temperatures, the direct technical advantages of this unique microstructure include significantly reduced creep (improved creep resistance), increased long-term stability and durability, and improved resistance to dynamic loads. These properties contribute significantly to the increased reliability and service life of the pressure-sensitive adhesive, especially compared to products where crosslinking is subsequently introduced into a pre-molded polymer.

[0017] In a further embodiment, the photopolymerized pressure-sensitive adhesive according to the invention is characterized in that the at least one base polymer component has a distribution of its polymer composition which consists of at least a first (K1 ) and a second component (K2), wherein the components differ from each other in that: a) the first component (K1 ) has a higher molecular weight and a lower content of functional groups, and b) the second component (K2) has a lower molecular weight and a higher content of functional groups.

[0018] In this embodiment, the base polymer component has a polymer composition distribution consisting of at least one first component (K1) and one second component (K2). These components differ characteristically in their molecular weight and their content of functional groups suitable for coordinate crosslinking. The first component (K1) is typically characterized by a higher molecular weight. The first component (K1) may already exist as a polymer, which is photopolymerized with further monomers to form the base polymer. Alternatively, component (K1) may be formed during an initial syrup polymerization. In this phase, a monomer mixture with a deliberately lower content of functional groups is polymerized to ensure processability and prevent gelation. The second component (K2) has a lower molecular weight in comparison.It is primarily formed in the second phase of the manufacturing process, in which further monomers with functional groups are added and partially polymerized to achieve the higher concentration of functional groups necessary for the final coordinate crosslinking. Consequently, this second component (K2) is characterized by a higher content of functional groups.

[0019] In one embodiment, the first component (K1) is produced by syrup polymerization.

[0020] In an alternative embodiment, the first component K1 is already present as a polymer. In this embodiment, the photopolymerized pressure-sensitive adhesive is formed by adding further monomers, one or more photoinitiators, and one or more coordinative crosslinkers, followed by photopolymerization, in particular web polymerization.

[0021] The phrase "at least one first and one second component" means that the base polymer component according to the invention consists primarily of these two characteristically distinct polymer populations. However, it is not excluded that the overall distribution may also contain minor amounts of other polymer fractions or monomer residues, as long as the defining features of the first and second components, as described above, are dominant and detectable and do not impair the inventive step. The crucial property is the presence of these two populations with their specific, mutually complementary properties.

[0022] The distinction between "higher" and "lower" molecular weight, as well as "lower" and "higher" functional group content, is always relative and refers to a comparison of the first component with the second component within the overall distribution of the base polymer component. The first component thus exhibits a molecular weight and functional group content that differ significantly from those of the second component, and vice versa. The existence and characterization of this polymer composition distribution, particularly with regard to the molecular weight and functional group content of the individual components, can be demonstrated using established analytical methods. These include, for example, gel permeation chromatography (GPC) or size exclusion chromatography (SEC) in combination with suitable detectors.In particular, detectors such as a refractive index (RI) detector can be used to determine the molecular weight, and an infrared (IR) spectrometer or a UV detector (if the functional groups are UV-active) can be used to determine the chemical composition along the molecular weight distribution. Such a chromatogram would indicate the presence of at least two overlapping or separate polymer populations (components) that differ significantly in their average molecular weights and / or the concentration of their functional groups.

[0023] The advantages of this distribution are manifold and can be fully exploited, particularly in the context of solvent-free web polymerization. The first fraction of the polymer chains (higher molecular weight, lower content of functional groups) forms the cohesive backbone of the pressure-sensitive adhesive, ensuring internal strength and load-bearing capacity under mechanical stress. The second fraction (lower molecular weight, higher content of functional groups) contributes significantly to efficient crosslinking and can simultaneously improve adhesion and wetting properties by providing a higher density of reactive sites for coordinate crosslinking.

[0024] This precise combination and distribution of polymer chains is hardly achievable in known solvent-based processes, especially not in combination with the early presence of coordinative crosslinkers. In a solvent-based system, the high mobility of the polymers and monomers, combined with a high content of reactive functional groups and the presence of crosslinkers, would very quickly lead to uncontrolled gel formation. The mass would instantly lose its processability and be unusable for producing a homogeneous pressure-sensitive adhesive. The solvents would make the reactive components too mobile, resulting in uncontrolled, three-dimensional crosslinking.

[0025] The present invention overcomes this fundamental problem through the targeted use of essentially solvent-free photopolymerization, in particular web polymerization of a viscous syrup. The higher viscosity of the syrup, combined with rapid, controlled UV curing on the web, makes it possible to precisely control the reactivity of the bimodally distributed polymer chains. The coordinative crosslinkers can thus be actively and homogeneously integrated into the forming network without premature and uncontrolled gel formation. This results in an adhesive with a unique network architecture that exhibits improved homogeneity, increased long-term stability, optimized creep resistance, and high resistance to dynamic loads.The bimodal distribution of the polymer chains thus ensures an optimized balance between processability and superior end-product properties, which would not be achievable in conventional solvent-based processes.

[0026] In one embodiment, the first component (K1) is present in the base polymer component in a quantity of less than or equal to (<) 25 wt.%, preferably < 10 wt.%, particularly preferably < 8 wt.%, based on the total weight of the base polymer component.

[0027] In a further aspect, the invention relates to a reactive composition for the production of a photopolymerized pressure-sensitive adhesive, in particular by web polymerization. This composition is designed to overcome the previous problems of premature gelation that occur during the UV photopolymerization of systems with coordinative crosslinkers and functional monomers. The composition comprises: i. one or more polymers (hereinafter referred to as "component P1"), which are preferably based on (meth)acrylate monomers and optionally have functional groups suitable for coordinative crosslinking. This component P1 can be produced by various routes, for example as a syrup from a prepolymerization or as a separately produced polymer. ii.one or more photopolymerizable monomers (hereinafter referred to as "component M1") designed to form a second polymer component by polymerization and to form, together with component P1, the base polymer of the pressure-sensitive adhesive; these monomers M1 typically have functional groups suitable for coordinative crosslinking; ill. one or more photoinitiators; and iv. one or more coordinative crosslinkers.

[0028] In a particularly preferred embodiment, component P1 forms the previously mentioned component K1 in the base polymer and the photopolymerized monomer M1 forms component K2 in the base polymer.

[0029] This reactive composition is suitable for producing a photopolymerized pressure-sensitive adhesive that is UV-photopolymerized and coordinatively cross-linked without premature gelling. This enables the efficient and solvent-free production of pressure-sensitive adhesives with the desired properties, which were not achievable with conventional approaches due to gelation problems.

[0030] Photopolymerized pressure-sensitive adhesive

[0031] A photopolymerized pressure-sensitive adhesive is a pressure-sensitive adhesive comprising one or more photoinitiators. According to the understanding of those skilled in the art, a photopolymerized pressure-sensitive adhesive is produced by the action of light, in particular UV light, on a mixture of monomers and / or oligomers. This mixture contains photoinitiators that are activated by the light irradiation and initiate a polymerization reaction. This process produces polymers that give the pressure-sensitive adhesive its adhesive properties. Photopolymerization allows control over the curing time and the mechanical properties of the adhesive. For the purposes of this application, a photopolymerized pressure-sensitive adhesive is synonymous with a pressure-sensitive adhesive produced by photopolymerization.

[0032] In accordance with professional understanding, an adhesive is an adhesive that possesses pressure-sensitive properties, meaning it forms a permanent bond to a substrate even under relatively light pressure. Such adhesives or pressure-sensitive tapes are generally permanently tacky even at room temperature, meaning they exhibit a certain viscosity and tackiness, allowing them to wet the surface of a substrate even with minimal pressure. While not bound to this theory, it is often assumed that an adhesive can be considered an extremely highly viscous liquid with an elastic component, which consequently exhibits characteristic viscoelastic properties that lead to the permanent tackiness and pressure-sensitive adhesion described above.It is assumed that pressure-sensitive adhesives undergo both viscous flow processes and the development of elastic restoring forces during mechanical deformation. The viscous flow contributes to adhesion, while the elastic restoring forces are particularly necessary for cohesion. The relationships between rheology and pressure sensitivity are well-established in the art and are described, for example, in "Satas, Handbook of Pressure Sensitive Adhesives Technology," Third Edition, (1999), pages 153 to 203. The storage modulus (G') and the loss modulus (G") are typically used to characterize the degree of elastic and viscous components. These can be determined by dynamic mechanical analysis (DMA), for example, using a rheometer.Within the scope of the present invention, an adhesive compound is preferably understood to be adhesive and thus a pressure-sensitive adhesive compound if, at a temperature of 23 °C in the deformation frequency range of 10° to 10. 1 rad / sec G' and G" each at least partially in the range of 10 3 up to 10 7 Pressure-sensitive adhesives can generally be produced based on polymers of different chemical nature. The adhesive properties are influenced, among other things, by the type and proportions of the monomers used in the polymerization of the polymers underlying the pressure-sensitive adhesive, their average molar mass and molar mass distribution, as well as by the type and quantity of additives in the pressure-sensitive adhesive, such as adhesive resins, plasticizers, and the like.

[0033] To achieve viscoelastic properties, the monomers on which the polymers underlying the pressure-sensitive adhesive are based, as well as any other components of the adhesive, are selected such that the adhesive has a glass transition temperature (according to DIN 53765) below the application temperature (i.e., usually below room temperature). By means of suitable cohesion-enhancing measures, such as crosslinking reactions (formation of bridge-forming links between the macromolecules), the temperature range in which a polymer compound exhibits pressure-sensitive properties can be increased and / or shifted. The application range of the pressure-sensitive adhesive can thus be optimized by adjusting the balance between flowability and cohesion of the compound.

[0034] To achieve desired properties in an adhesive compound, for example, to ensure sufficient cohesion, the adhesive is typically crosslinked. This means that the individual macromolecules are linked together by bridging bonds. Crosslinking can occur in various ways, including physical, chemical, and thermal methods. The term "polymer crosslinking" specifically refers to a reaction in which many initially linear or branched macromolecules are linked together to form a more or less branched network through bridging. This bridging occurs primarily through the reaction of suitable chemical molecules—so-called crosslinkers or crosslinking agents—with the macromolecules, for example, with specific functional groups of the macromolecules that are particularly receptive to the respective crosslinker molecule.The sites on the crosslinking molecule that attack the macromolecules are generally referred to as "reactive centers." Crosslinking molecules can link two macromolecules together—by having the same crosslinking molecule react with two different macromolecules, meaning they must possess at least two reactive centers—or they can have more than two reactive centers, allowing a single crosslinking molecule to link three or more macromolecules. As a side reaction, intramolecular reactions can occur if the same crosslinking molecule attacks the same macromolecule with at least two of its reactive centers. For effective polymer crosslinking, such side reactions are generally undesirable. Different types of crosslinking agents can be distinguished, namely...

[0035] I. Covalent crosslinkers, namely those that attack the macromolecule to be linked covalently and thus form a covalent chemical bond between their corresponding reactive center and the site of attack – in particular the functional group – on the macromolecule. In principle, all conceivable chemical reactions that form covalent bonds are suitable for this purpose;

[0036] II. Coordinative crosslinkers, namely those that attack the macromolecule to be linked in a coordinative manner and thus form a coordinative bond between their corresponding reactive center and the site of attack – in particular the functional group – on the macromolecule. In principle, all conceivable chemical reactions that form coordinative bonds are eligible for this purpose.

[0037] Base polymer components

[0038] Suitable polymers for the at least one base polymer component a) (hereinafter also referred to as base polymer) for the present invention are polymers and polymer mixtures that can be crosslinked by coordinative crosslinkers and optionally by covalent crosslinkers. These are, in particular, polymers that have free, suitable functional groups for crosslinking, preferably acid groups.

[0039] Another criterion for the base polymer component a) is that it is based on monomers suitable for photopolymerization. Acrylic monomers such as n-butyl acrylate and 2-ethylhexyl acrylate are particularly common, as they improve the flexibility and stickiness of the resulting polymer. Methacrylic monomers such as methyl methacrylate and butyl methacrylate are also frequently used and offer increased durability and resistance to environmental influences. Additionally, vinyl monomers such as vinyl acetate can be incorporated to improve the adhesive's cohesive strength.

[0040] These monomers share several key characteristics that make them suitable for use in photopolymerization processes for the production of pressure-sensitive adhesives. Primarily, they all possess reactive double bonds, typically carbon-carbon double bonds (C=C), which enable radical polymerization upon exposure to UV light or other photoinitiation sources. This reactivity is crucial for the rapid and efficient formation of polymer networks. Furthermore, these monomers often exhibit flexible side chains that contribute to the viscoelastic properties required for effective pressure-sensitive adhesion. The presence of functional groups such as acrylate or methacrylate enhances their reactivity and allows for the formation of cross-linked structures, thus improving the adhesive's performance.Additionally, these monomers are typically soluble in a wide variety of solvents, which simplifies their formulation and application. Overall, these shared characteristics ensure that the monomers polymerize effectively and can produce pressure-sensitive adhesives with the desired balance of adhesion, cohesion, and durability.

[0041] The term base polymer component a) within the meaning of the present invention refers to polymers that can be produced by radical polymerization. Particularly preferably, within the meaning of the present invention, the base polymer component is a poly(meth)acrylate.

[0042] An advantageous pressure-sensitive adhesive composition according to the invention comprises as a base component (a), which is hereinafter also referred to as the polyacrylate component, 50 to 100 wt.%, preferably 60 to 90 wt.%, particularly preferably 65 wt.% to 80 wt.%, of optionally blended acrylate copolymers.

[0043] Typical examples of base polymers suitable for coordinative crosslinking with one or more functional groups are polymers derived from one or more monomers with a functionality selected from i. one or more acid functionalities, ii. one or more alcohol functionalities, ill. one or more amine functionalities, iv. one or more thiol functionalities, v. one or more carbonyl functionalities; vi. one or more imidazole functionalities; and vii. a combination of the aforementioned functionalities.

[0044] In a preferred embodiment, the functional groups suitable for coordinative crosslinking comprise ethylene-unsaturated monomer units with functional groups selected from the group consisting of acid, hydroxyl, acid anhydride, epoxide, amine, amide groups and any combinations thereof.

[0045] In a preferred embodiment, the at least one base polymer comprises a) a monomer with acid functionality, wherein the acid functionality may be an actual acid, such as a carboxylic acid, or partially a salt thereof, such as an alkali metal carboxylate. Acid-functional monomers include, among others, those selected from ethylene-unsaturated carboxylic acids, ethylene-unsaturated sulfonic acids, ethylene-unsaturated phosphonic acids, and mixtures thereof. Examples of such compounds include those selected from acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, maleic acid, oleic acid, β-carboxyethyl (meth)acrylate, 2-sulfoethyl methacrylate, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinylphosphonic acid, and mixtures thereof.

[0046] Due to their availability, acid-functional monomers of the acid-functional copolymer or base polymer are generally selected from ethylene-unsaturated carboxylic acids, i.e., (meth)acrylic acids. If even stronger acids are desired, acid-containing monomers include ethylene-unsaturated sulfonic acids and ethylene-unsaturated phosphonic acids.

[0047] The acid-functional monomer is generally used in amounts of 0.1 to 20 parts by weight, preferably 1 to 15 parts by weight, particularly preferably 3 to 13 parts by weight, based on the total mass of the base polymer component a).

[0048] In a preferred embodiment, the at least one base polymer component a) comprises functional groups suitable for coordinate crosslinking in a total weight fraction of at least 3 wt.%, preferably at least 4 wt.%, and particularly preferably at least 5 wt.%, based on the total mass of the base polymer component. These embodiments are advantageous for improving the adhesive properties on polar substrates.

[0049] Polymethylacrylate component

[0050] Poly(meth)acrylates are preferred base polymers, particularly polymers (copolymers, polymer blends) that are at least 50 wt% based on acrylic monomers. Copolymerizable monomers containing free acid groups are preferred as comonomers for introducing the crosslinking groups; acrylic acid is particularly preferred. Monomers containing acid groups, such as acrylic acid, have the property of influencing the tack-free properties of the pressure-sensitive adhesive.

[0051] The term "poly(meth)acrylates" refers – in accordance with general understanding – to polymers that are accessible through radical polymerization of acrylic and / or methylacrylic monomers and optionally other copolymerizable monomers. According to the invention, the term "poly(meth)acrylate" encompasses polymers based on acrylic acid and its derivatives, as well as those based on acrylic and methacrylic acids and their derivatives, and those based on methacrylic acid and its derivatives, wherein the polymers always contain acrylic esters, methacrylic esters, or mixtures of acrylic and methacrylic esters.

[0052] Preferably, the monomers of the poly(meth)acrylates and their quantitative composition are chosen such that, according to the so-called Fox equation (G1 )

[0053] (cf. TG Fox, Bull. Am. Phys. Soc. 1 (1956) 123) yields a glass transition temperature TG for the polymer of < 25 °C. Such a value is particularly advantageous for pressure-sensitive adhesives that are used essentially at room temperature.

[0054] In equation G1, n represents the number of iterations over the monomers used, w n the mass fraction of the respective monomer n (wt%) and Tc, n the respective glass transition temperature of the homopolymer made from the respective monomers n in Kelvin.

[0055] Preferably, the one or more poly(meth)acrylate(s) can be traced back to the following monomer composition: a) Acrylic acid esters and / or methacrylic acid esters of the formula CH2=C(R I )(COOR"), wherein R 1= H or CH3 and R" is an alkyl group with 1 to 30 C atoms, more preferably with 4 to 14 C atoms, particularly preferably with 4 to 9 C atoms; b) ethylene-unsaturated monomers with functional groups exhibiting reactivity with crosslinking substances; c) optionally further ethylene-unsaturated monomers that are copolymerizable with monomers (a) and (b).

[0056] Examples of monomers a) are methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate, n-butyl methacrylate, n-pentyl acrylate, n-hexyl acrylate, n-heptyl acrylate, n-octyl acrylate, n-octyl methacrylate, n-nonyl acrylate, lauryl acrylate, stearyl acrylate, behenyl acrylate and their branched isomers such as isobutyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, isooctyl acrylate, isooctyl methacrylate. Particularly preferably, R" represents a methyl, an n-butyl, and a 2-ethylhexyl group, especially an n-butyl and a 2-ethylhexyl group, or the monomers a) are selected from n-butyl acrylate and 2-ethylhexyl acrylate.

[0057] The monomers b) are preferably ethylene-unsaturated monomers with functional groups that can react with epoxide groups. Particularly preferably, the monomers b) each contain at least one functional group selected from the group consisting of hydroxy, carboxy, sulfonic acid and phosphonic acid groups, acid anhydride functional groups, epoxide groups and substituted or unsubstituted amino groups.

[0058] In particular, the monomers b) are selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, aconitic acid, dimethylacrylic acid, β-acrylic acid, trichloroacrylic acid, vinylacetic acid, vinylphosphonic acid, maleic anhydride, 2-hydroxyethyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl methacrylate, 6-hydroxyhexyl methacrylate, allyl alcohol, glycidyl acrylate, and glycidyl methacrylate. The monomers b) acrylic acid and / or methacrylic acid, especially acrylic acid, are particularly preferred.

[0059] In principle, all vinylically functionalized compounds that can be copolymerized with monomers a) and monomers b) are suitable as monomers c). The properties of the pressure-sensitive adhesive can be advantageously controlled by selecting and adjusting the quantity of monomers c).

[0060] The monomers c) are particularly preferably selected from the group consisting of benzyl acrylate, benzyl methacrylate, phenyl acrylate, phenyl methacrylate, tert-butyl phenyl acrylate, tert-butyl phenyl methacrylate, phenoxyethyl acrylate, 2-butoxyethyl methacrylate,

[0061] 2-Butoxyethyl acrylate, 4-cumyl-phenyl methacrylate, cyanoethyl acrylate, cyanoethyl methacrylate,

[0062] 4-biphenyl acrylate, 4-biphenyl methacrylate, 2-naphthyl acrylate, 2-naphthyl methacrylate, tetrahydrofurfuryl acrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate,

[0063] 3-Methoxyacrylic acid methyl ester, 3-methoxybutyl acrylate, phenoxyethyl acrylate, phenoxy-ethyl methacrylate, 2-phenoxyethyl methacrylate, butyl diglycol methacrylate, ethylene glycol acrylate, ethylene glycol monomethyl acrylate, methoxy polyethylene glycol methacrylate 350, methoxy polyethylene glycol methacrylate 500, propylene glycol monomethacrylate,

[0064] Butoxydiethylenglykolmethacrylat, Ethoxytriethylenglykolmethacrylat, Octafluoropentyl- acrylat, Octafluoropentylmethacrylat, 2,2,2-Trifluoroethylmethacrylat, 1 ,1 ,1 ,3,3,3-Hexa- fluoroisopropylacrylat, 1 ,1 ,1 ,3,3,3-Hexafluoroisopropylmethacrylat, 2,2,3,3,3-Pentafluoro- propylmethacrylat, 2,2,3,4,4,4-Hexafluorobutylmethacrylat, 2,2,3,3,4,4,4-Heptafluoro- butylacrylat, 2,2,3,3,4,4,4-Heptafluorobutylmethacrylat, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,8,8-

[0065] Pentadecafluorooctylmethacrylat, Dimethylaminopropylacrylamid, Dimethylaminopropylmethacrylamid, N-(1 -Methyl-undecyl)acrylamid, N-(n- Butoxymethyl)acrylamid, N-(Butoxymethyl)methacrylamid, N-(Ethoxymethyl)acrylamid, N-(n-Octadecyl)acrylamid,

[0066] N,N-Dialkyl-substituierten Amiden, insbesondere N,N-Dimethylacrylamid, N,N-Dimethylmethacrylamid, N-Benzylacrylamid, N-Isopropylacrylamid,

[0067] N-tert-butylacrylamide, N-tert-octylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide; also acrylonitrile, methacrylonitrile; vinyl ethers such as vinyl methyl ether, ethyl vinyl ether, vinyl isobutyl ether; vinyl esters such as vinyl acetate; vinyl chloride, vinyl halides, vinylidene halides, vinylpyridine, 4-vinylpyridine, N-vinylphthalimide, N-vinyllactam, N-vinylpyrrolidone, styrene, o- and p-methylstyrene, o-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, 3,4-dimethoxystyrene, 2-polystyrene ethyl methacrylate (molecular weight M w from 4,000 to 13,000 g / mol), poly(methyl methacrylate)ethyl methacrylate (M w from 2,000 to 8,000 g / mol), vinylcaprolactam, potassium acrylic acid (3-sulfopropyl) ester and ethylenediglycol acrylate.

[0068] The monomers c) can advantageously be chosen to contain functional groups that support radiation-chemical crosslinking (for example, by electron beams or UV light). Suitable copolymerizable photoinitiators are, for example, benzoin acrylate and acrylate-functionalized benzophenone derivatives. Monomers that support crosslinking by electron irradiation are, for example, tetrahydrofurfuryl acrylate, N-tert-butylacrylamide, and allyl acrylate.

[0069] In one embodiment, the poly(meth)acrylates according to the invention comprise up to 30 wt.% of one or more acrylamides, wherein the wt.% refers to the total weight of the poly(meth)acrylates.

[0070] In a further embodiment, the poly(meth)acrylates according to the invention comprise at least 50 wt.% of one or more acrylates and up to 30 wt.% of one or more acrylamides, wherein the wt.% refers to the total weight of the poly(meth)acrylates.

[0071] Particularly preferred are the one or more poly(meth)acrylates based on the monomer composition described above. In particular, the poly(meth)acrylates according to the invention are based on a monomer composition consisting of acrylic acid, n-butyl acrylate, and 2-ethylhexyl acrylate.

[0072] Poly(meth)acrylate is particularly preferred, or rather, all poly(meth)acrylates are based on the following monomer composition:

[0073] Acrylic acid 1 - 15 wt.%, 2-Ethylhexyl acrylate 30 - 85 wt.%, n-Butyl acrylate and / or Methyl acrylate 10 - 67 wt.%, the proportions of the monomers adding up to 100 wt.%.

[0074] Photoinitiator

[0075] For photopolymerization and crosslinking with light, one or more photoinitiators are added to at least one base polymer component a). In a preferred embodiment, the photoinitiators c) are UV photoinitiators, i.e., photoinitiators that are activated by irradiation with light in the ultraviolet (UV) spectral range. Useful photoinitiators that are very suitable for use include benzoin ethers, such as benzoin methyl ether and benzoin isopropyl ether; substituted acetophenones, such as 2,2-diethoxyacetophenone (available as Irgacure 651® from Ciba Geigy®); 2,2-dimethoxy-2-phenyl-1-phenylethanone; dimethoxyhydroxyacetophenone; substituted α-ketols, such as 2-methoxy-2-hydroxypropiophenone; and aromatic sulfonyl chlorides, such as... B. 2-Naphthyl sulfonyl chloride, and photoactive oximes, such as 1-Phenyl-1,2-propanedione-2-(O-ethoxycarbonyl)oxime.

[0076] The photoinitiators mentioned above, and others that can be used, including those of the Norrish I or Norrish II type, can contain the following residues: benzophenone, acetophenone, benzil, benzoin, hydroxyalkylphenone, phenylcyclohexyl ketone, anthraquinone, trimethylbenzoylphosphine oxide, methylthiophenylmorpholine ketone, aminoketone, azobenzoin, thioxanthone, hexarylbisimidazole, triazine, or fluorenone, each of which may be additionally substituted with one or more halogen atoms and / or one or more alkyloxy groups and / or one or more amino or hydroxy groups. A representative overview is given by Fouassier: "Photoinitiation, Photopolymerization and Photocuring: Fundamentals and Applications", Hanser-Verlag, Munich 1995. Carroy et al. can also be consulted. in “Chemistry and Technology of UV and EB Formulation for Coatings, Inks and Paints”, Oldring (ed.), 1994, SITA, London.

[0077] Any suitable photoinitiator known for radical polymerization reactions can be used. The initiator is typically present in an amount in the range of 0.01 to 5 wt%, 0.01 to 2 wt%, 0.01 to 1 wt%, or 0.01 to 0.5 wt% based on the total weight of the (co)polymerizable material. In principle, all common initiators familiar to those skilled in the art are suitable. Examples of radical sources include peroxides, hydroperoxides, and azo compounds, e.g., dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-tert-butyl peroxide, cyclohexylsulfonyl acetyl peroxide, diisopropyl percarbonate, tert-butyl peroctoate, and benzopinacol. In a highly preferred method, 2,2'-azobis(2-methylbutyronitrile) (Vazo® 67™ from DuPont) or 2,2'-azobis-(2-methylpropionitrile) (2,2'-azobisisobutyronitrile; AIBN; Vazo® 64™ DuPont) is used as the radical initiator.Some example photoinitiators are benzoins (e.g., benzoin methyl ether or benzoin isopropyl ether) or substituted benzoins (e.g., anisoin methyl ether). Other example photoinitiators are substituted acetophenones such as 2,2-diethoxyacetophenone or 2,2-dimethoxy-2-phenylacetophenone (commercially available under the trade name IRGACURE 651 from BASF Corp. (Florham Park, NJ) or under the trade name ESACURE KB-1 from Sartomer (Exton, PA)). Further example photoinitiators are substituted alpha-ketols such as 2-methyl-2-hydroxypropiophenone, aromatic sulfonyl chlorides such as 2-naphthalenesulfonyl chloride, and photoactive oxime compounds such as 1-phenyl-1,2-propanedione-2-(O-ethoxycarbonyl)oxime.Other suitable photoinitiators include, for example, 1-hydroxycyclohexylphenyl ketone (IRGACURE 184), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (IRGACURE 819), 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one (IRGACURE 2959), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone (IRGACURE 369), 2-methyl-1-[4-.

[0078] (methylthio)phenyl]-2-morpholinopropan-1 -one (IRGACURE 907), and 2-hydroxy-2-methyl-1-phenylpropan-1 -one (DAROCUR 1173).

[0079] In a preferred embodiment, the photopolymerized pressure-sensitive adhesive comprises, in addition to 100 wt% of the base polymer component a), a total of 0.01 - 0.50 wt% of one or more photoinitiators.

[0080] In a further preferred embodiment, the photopolymerized pressure-sensitive adhesive comprises, in addition to 100 wt.% of the base polymer component, a) b) a total of 0.01 - 0.50 wt.% of one or more photoinitiators; and c) a total of 0.03 - 0.30 wt.% of one or more coordinative crosslinkers.

[0081] The at least one base polymer a) of the adhesive compound according to the invention preferably has a weight-average molecular weight M w of more than 500,000 g / mol, particularly preferably a weight-average molecular weight M w of more than 700,000 g / mol, in particular preferably a weight-average molecular weight M wof more than 1,000,000 g / mol, wherein the weight-average molecular weight is determined by gel permeation chromatography. In a particularly preferred embodiment, the at least one base polymer a) of the adhesive compound according to the invention has a weight-average molecular weight which exceeds the detection maximum of gel permeation chromatography.

[0082] Networker

[0083] The at least one base polymer according to the invention is present in the pressure-sensitive adhesive in a coordinately cross-linked form. The cross-linked at least one base polymer according to the invention can be further cross-linked chemically or by electron beam irradiation.

[0084] Preferred coordinative crosslinkers are multivalent metal chelates. "Multivalent metal chelates" are defined as compounds in which a multivalent metal is coordinatively bonded to one or more organic compounds. Preferred multivalent metal atoms include Al(III), Zr(IV), Co(II), Cu(I), Cu(II), Fe(II), Fe(IIII), Ni(II), V(II), V(IIII), V(IV), V(V), Zn(II), In(IIII), Ca(II), Mg(II), Mn(II), Y(IIII), Ce(II), Ce(IV), St(II), Ba(II), Mo(II), Mo(IV), Mo(VI), La(IIII), Sn(II), Sn(IV), and Ti(IV), in particular Al(IIII), Zr(IV), and Ti(IV).

[0085] In principle, all known ligands can serve as ligands for coordinative crosslinkers. However, the atoms used for the coordinative bonding of the organic compound are preferably those possessing free electron pairs, such as oxygen atoms, sulfur atoms, nitrogen atoms, and the like. Preferred organic compounds include alkyl esters, alcohols, carboxylic acids, ethers, and ketones. Particularly preferred coordinative crosslinkers are titanium dipropoxide bis(acetylacetonate), titanium dibutoxide bis(octylene glycholate), titanium dipropoxide bis(ethylacetoacetate), titanium dipropoxide bis(lactate), titanium dipropoxide bis(triethanolaminate), titanium di-n-butoxide bis(triethanolaminate), titanium tri-n-butoxide monostearate, and butyl titanate dimer.

[0086] poly(titanium acetylacetonate); Aluminum diisopropoxide monoethyl acetate, aluminum di-n-butoxide monomethyl acetoacetate, aluminum di-i-butoxide monomethyl acetoacetate, aluminum di-n-butoxide monoethyl acetoacetate, aluminum disec-butoxide monoethyl acetoacetate,

[0087] Aluminium triacetylacetonate, aluminium acrylate, titanium acrylate, aluminium triacetylacetonate, aluminium monoacetylacetonate bis(ethylacetoacetonate) and zirconium tetraacetylacetonate; in particular aluminium triacetylacetonate and aluminium diisopropoxide monoethyl acetate.

[0088] In one embodiment, the crosslinking is carried out using at least one covalent crosslinker and one coordinative crosslinker.

[0089] In a preferred embodiment, the photopolymerized pressure-sensitive adhesive has at least one covalent crosslinker and at least one coordinative crosslinker. Preferred covalent crosslinkers are epoxycyclohexyl derivatives and N,N-diglycidylamines. Preferred coordinative crosslinkers are chelate compounds, in particular multivalent metal chelates. Thermal crosslinking results in homogeneous crosslinking throughout the entire layer, whereas, for example, radiation-crosslinked compounds exhibit a crosslinking profile with decreasing crosslink density towards the interior of the compound. A homogeneously crosslinked pressure-sensitive adhesive layer enables the uniform distribution of stresses that can occur when the bond is subjected to load. Adhesive and cohesive properties can be very precisely balanced for the entire layer, so that durable bonds with a predictable property profile can be obtained.

[0090] Particularly preferred thermal crosslinkers are N,N,N',N'-tetrakis(2,3-epoxypropyl)cyclohexane-1,3-dimethylamine (e.g. Syna Epoxy S610, Synasia) and N,N,N',N'-tetrakis(2,3-epoxypropyl)-m-xylene-a,a'-diamine (e.g. Erisys GA-240, CVC) as well as epoxycyclohexyl carboxylates, in particular (3,4-epoxycyclohexane)methyl-3,4-epoxycyclohexyl carboxylate and bis(3,4-epoxycyclohexylmethyl)adipate.

[0091] One or more covalent and one or more coordinative networkers can be used; each can also be used in combination with each other.

[0092] In one embodiment, the photopolymerized pressure-sensitive adhesive according to the invention comprises one or more coordinative crosslinkers as well as one or more covalent crosslinkers. This has the advantage of improving recoil resistance and simultaneously achieving good cohesion at elevated temperatures.

[0093] In a preferred embodiment, the photopolymerized pressure-sensitive adhesive comprises, in addition to 100 wt.% of the base polymer component a) ; c), a total of 0.03 - 0.30 wt.% of one or more coordinative crosslinkers.

[0094] In a further development of this embodiment, the photopolymerized pressure-sensitive adhesive comprises, in addition to 100 wt.% of the base polymer component a); c), a total of 0.03–0.30 wt.% of one or more coordinative crosslinkers and a total of 0.015–0.15 wt.% of one or more covalent crosslinkers. Crosslinking accelerators can also be used; however, preferably the pressure-sensitive adhesive layer contains neither externally added nor polymerized accelerators, and in particular, it contains no accelerators at all.

[0095] Photopolymerization

[0096] Photopolymerization can, in principle, be carried out in any manner. Preferably, photopolymerization is performed as syrup polymerization in a reactor, particularly in a reactor designed for processing highly viscous materials.

[0097] In a preferred embodiment, the base polymer according to the invention, preferably the poly(meth)acrylate, is produced by polymerization with little solvent, essentially solvent-free or with no solvent.

[0098] In the present application, “low solvent” means that the polymerization contains less than 5 wt% solvent, based on the total mass of reaction substrate used.

[0099] In the present application, “essentially solvent-free” means that the polymerization contains less than 2 wt.%, preferably less than or equal to (<) 1 wt.%, or even no solvent at all, based on the total mass of reaction substrate used.

[0100] In a preferred embodiment, the base polymer according to the invention, preferably the poly(meth)acrylate, is produced by a substance polymerization, in particular syrup polymerization. The polymerization can thus take place, for example, in a reactor which allows light irradiation, in particular UV irradiation.

[0101] In a particularly preferred embodiment, the photopolymerized pressure-sensitive adhesive is produced by a two-stage photopolymerization process. According to the general understanding of those skilled in the art, a two-stage photopolymerization process corresponds to the production of the pressure-sensitive adhesive by two separate photopolymerization steps. This is particularly the case if, first, a syrup polymerization takes place, preferably in a reactor, followed by a web polymerization.

[0102] Syrup polymerization

[0103] In one embodiment, the pressure-sensitive adhesive is produced by syrup polymerization. The term syrup, or monomer syrup, is used for solutions of polymers or oligomers in monomers (see Benedek, I., & Feldstein, MM (Eds.); 2009; Handbook of Pressure-Sensitive Adhesives and Products: Technology of Pressure-Sensitive Adhesives and Products. CRC Press, Taylor & Francis Group; Chapter 5.4.4.2 Monomer Syrups). The monomer mixtures used for polymerization typically have a viscosity that is too low to be easily handled at the beginning of the polymerization process. To increase the viscosity, the monomer mixture is prepolymerized to a syrupy consistency; this can be done to a conversion of 1 to 20%, preferably 2 to 15%, and particularly preferably 3 to 10%. In this way, a syrup is formed that can be easily coated onto a carrier material.UV light with a wavelength of 280 - 450 nm is preferably used to initiate the prepolymerization.

[0104] Furthermore, the monomers are optionally mixed with resins after or preferably before prepolymerization. Before complete polymerization, additional monomers can be added to or mixed into the syrup.

[0105] After coating in syrup form, the second stage of polymerization takes place in the already coated form under anaerobic conditions until the desired reaction is achieved on the syrup-coated web by further irradiation with UV light. The result of this second stage of the polymerization reaction on the web is determined by parameters known to those skilled in the art, such as web speed, number of lamps, UV wavelength, light intensity, and cooling power.

[0106] The inventive method is particularly advantageous for the production of, for example, adhesive tapes, since the prepolymer can be coated onto a substrate as a syrup.

[0107] In one embodiment, the photopolymerized adhesive is produced by UV polymerization of a syrup, preferably a (meth)acrylate syrup, in the presence of one or more coordinative crosslinking agents.

[0108] In a further embodiment of this embodiment, the (meth)acrylate syrup comprises one or more poly(meth)acrylate prepolymers, which together contain a maximum of 4 wt% monomers with one or more functional groups suitable for coordinate crosslinking.

[0109] Polymerization in a reactor

[0110] Various polymerization reactors are known to those skilled in the art for bulk polymerization, such as kneading reactors. Alternative polymerization reactors include stirred tank reactors, tubular reactors, and batch reactors. In a bulk polymerization reactor, the liquid monomers are typically introduced into the reactor first. An initiator is then added to start the polymerization. The reaction is carried out under controlled conditions, with temperature and pressure regulated to achieve the desired reaction rate and polymer structure. For highly viscous reactions, as are common in bulk polymerization, intensive mixing is required to ensure a uniform distribution of the reactants. Since polymerization is exothermic, the heat generated must be efficiently dissipated to prevent overheating and product degradation.During polymerization, the monomers combine to form polymer chains, with the viscosity of the mixture continuously increasing. Once the desired polymerization stage is reached, the reaction is stopped, for example by adding an inhibitor or by cooling.

[0111] Web polymerization

[0112] Another object of the invention is a method for producing an adhesive compound according to the invention by web polymerization of a syrup, preferably a (meth)acrylate syrup.

[0113] Adhesives can be produced from compositions comprising (meth)acrylate monomer and any other types of monomers and desired components in a resulting adhesive using batch or continuous processes. Known continuous methods for producing web-polymerized adhesives include coating partially polymerized syrup onto a movable support material, as described in IIS patents 4,181,752; 4,303,485; 4,421,822; and 5,462,977. In the continuous production of (meth)acrylate-based web-polymerized adhesives, it is common to form a syrup with a spreadable viscosity based on (meth)acrylate monomer. As described in IIS patent no. 4,303,485, this syrup can be partially polymerized conventionally by the application of ultraviolet radiation to a container containing (meth)acrylate monomer.The partial photopolymerization step can be easily stopped at any time by switching off the ultraviolet radiation. This syrup can then be stored, if needed, until it is used to produce an adhesive. In adhesive production, the syrup can, for example, be applied to a movable substrate where further polymerization can be initiated to form the adhesive.

[0114] A movable carrier material within the meaning of the present invention can be either a permanent or a temporary carrier. Permanent carriers are those that remain permanently bonded to the adhesive and are part of the final product, such as films, nonwovens, or foams.

[0115] Temporary carriers, also known as liners or release materials, serve to protect or transport the adhesive and are removed before final application. These can be, for example, siliconized papers or films.

[0116] In a preferred embodiment, the syrup is applied to a movable carrier material, wherein the movable carrier material is a liner.

[0117] In a further preferred embodiment, the syrup is located between two liners during web polymerization.

[0118] One aspect of the invention relates to a process for producing an adhesive compound comprising the process steps: a) providing a syrup, preferably a (meth)acrylate syrup, which in its entirety comprises a maximum of 4 wt.% of its total mass monomers with one or more functional groups suitable for coordinative crosslinking; b) adding one or more further monomers to the syrup from step a); c) adding one or more coordinative crosslinkers to the syrup from step b); d) polymerizing the syrup from step c) by light irradiation, preferably UV irradiation.

[0119] In one embodiment, process step b) comprises process step b1) adding one or more monomers with one or more functional groups suitable for coordinative crosslinking.

[0120] In one embodiment, process step a) comprises process steps a1) providing a monomer composition comprising a maximum of 4 wt% of monomers with one or more functional groups suitable for coordinate crosslinking; a2) polymerizing the monomer composition from a1) to a reaction conversion of 1 to 20%, preferably 2 to 15%, particularly preferably 3 to 10%, by light irradiation, preferably UV irradiation.

[0121] In one embodiment of the method, the syrup, before the addition of one or more coordinative crosslinkers in step c), essentially comprises no, preferably no, coordinative crosslinker. Adhesive-enhancing resins

[0122] The term "adhesive-enhancing resin," synonymous with "adhesive resin" as defined in the present disclosure, is understood, according to the general understanding of those skilled in the art, to be an oligomeric or polymeric resin that increases the autoadhesion (the tack, the inherent stickiness) of the pressure-sensitive adhesive compared to an otherwise identical pressure-sensitive adhesive that does not contain an adhesive-enhancing resin. Furthermore, adhesive-enhancing resins can advantageously also improve the wetting properties of the pressure-sensitive adhesive with respect to the substrate to be bonded, its flow behavior, and / or its adhesion.

[0123] The pressure-sensitive adhesive according to the invention can further comprise at least one adhesive-strengthening resin. According to the general understanding of those skilled in the art, this is understood to be an oligomeric or polymeric resin that increases the self-adhesion (the tack, the inherent stickiness) of the pressure-sensitive adhesive compared to an otherwise identical pressure-sensitive adhesive without an adhesive-strengthening resin. Furthermore, adhesive-strengthening resins can advantageously also improve the wetting properties of the pressure-sensitive adhesive with respect to the substrate to be bonded, its release behavior, and / or its adhesion.

[0124] The one or more adhesive-enhancing resins can, in principle, be any adhesive resin compatible with the pressure-sensitive adhesive and, in particular, with copolymer A or copolymers A of the pressure-sensitive adhesive.

[0125] The at least one adhesive-strengthening resin of the pressure-sensitive adhesive according to the invention can, in principle, be any adhesive resin compatible with the pressure-sensitive adhesive and, in particular, with the copolymer(s) of the pressure-sensitive adhesive. In one embodiment, the adhesive-strengthening resin is selected from the group consisting of aliphatic, aromatic, and alkylaromatic hydrocarbon resins; hydrocarbon resins based on pure monomers; hydrogenated hydrocarbon resins; functional hydrocarbon resins; and optionally, derivatized natural resins. Preferably, the adhesive resin is selected from the group consisting of pinene, indene, and rosin resins, their disproportionated, hydrogenated, polymerized, esterified derivatives and salts; aliphatic and aromatic hydrocarbon resins; terpene resins and terpenephenolic resins; as well as C5, C9, and other hydrocarbon resins.The adhesive compound according to the invention can in principle comprise one (single) or several adhesive-strengthening resins.

[0126] Particularly preferred is at least one adhesive-strengthening resin selected from rosin resins and polyterpene-based resins. Rosin resins are understood to be a group of resins containing their disproportionate, hydrogenated, polymerized, modified derivatives, and salts.

[0127] Modified derivatives of rosin resin include esterified derivatives and / or further substituted derivatives such as maleate resin (CAS: 68038-41-5).

[0128] Rosin resins are advantageous because they can be largely, and in particular entirely, produced or obtained from renewable raw materials. These adhesive resins can be produced from renewable raw materials and have proven particularly suitable for significantly improving the adhesive properties of the pressure-sensitive adhesive compound according to the invention.

[0129] A fully hydrogenated rosin resin is particularly preferred as the adhesive-enhancing resin. This is especially advantageous because these resins have a comparatively low softening temperature and thus contribute favorably to the development of adhesive properties. Furthermore, they exhibit particularly good aging stability.

[0130] Preferably, the adhesive compound according to the invention comprises one or more adhesive-enhancing resins in a total of 5 to 50 wt.%, more preferably in a total of 7 to 45 wt.%, in particular in a total of 9 to 35 wt.%, and most preferably in a total of 10 to 32 wt.%, in each case based on the total weight of the adhesive compound.

[0131] Other components

[0132] The adhesive compound according to the invention can further comprise additional components, e.g. plasticizers; fillers, in particular fibers, carbon black, zinc oxide, titanium dioxide, spinels, dyes, pigments, chalk, solid or hollow glass spheres, microspheres made of other materials, e.g. polymeric microspheres, silica and / or silicates; nucleating agents; blowing agents; compounding agents; stabilizers and / or anti-aging agents, e.g. primary and / or secondary antioxidants and / or light stabilizers.

[0133] As experts in the field of pressure-sensitive adhesive formulation know, the pressure-sensitive adhesive composition can contain one or more conventional, but optional, additives, depending on the desired properties of the resulting pressure-sensitive adhesive. Examples of additional additives include, but are not limited to, one or more plasticizers, UV stabilizers, antistatic agents, dyes, antioxidants, fungicides, bactericides, organic and / or inorganic filler particles, pigments, colorants, and combinations thereof. Advantageously, the additional additives used here are non-polymerizable.

[0134] The adhesive layer can optionally be foamed, resulting in advantageous further developments of the invention. In other advantageous embodiments of the invention, however, the adhesive is unfoamed. Whether or not foaming is used depends, for example, on the intended application of the adhesive. For instance, foamed adhesives can increase the shock absorption effect, enabling the adhesive to absorb or dissipate impact energy within the adhesive film.

[0135] Foaming can be achieved using any chemical and / or physical methods. However, a foamed pressure-sensitive adhesive compound according to the invention is preferably obtained by introducing and subsequently expanding microballoons. "Microballoons" are defined as elastic, and therefore expandable in their ground state, hollow microspheres that have a thermoplastic polymer shell. These spheres are filled with low-boiling liquids or liquefied gas. Polyacrylonitrile, PVDC, PVC, or polyacrylates are particularly suitable as shell materials. Suitable low-boiling liquids include hydrocarbons of the lower alkanes, for example, isobutane or isopentane, which are enclosed as a liquefied gas under pressure within the polymer shell.

[0136] When the microballoons are subjected to stress, particularly heat, the outer polymer shell softens. Simultaneously, the liquid propellant gas inside the shell transitions into a gaseous state. This causes the microballoons to expand irreversibly and three-dimensionally. The expansion ceases when the internal and external pressures equalize. Because the polymer shell remains intact, this process results in a closed-cell foam.

[0137] A wide variety of microballoon types are commercially available, differing primarily in their size (6 to 45 pm diameter in the unexpanded state) and the initial expansion temperatures required (75 to 220 °C). An example of commercially available microballoons are the Expancel® DU types (DU = dry unexpanded) from Akzo Nobel. Unexpanded microballoon types are also available as aqueous dispersions with a solids or microballoon content of approximately 40 to 45 wt.%, and also as polymer-bonded microballoons (masterbatch), for example, in ethyl vinyl acetate with a microballoon concentration of approximately 65 wt.%. Both the microballoon dispersions and the masterbatch, like the DU types, are suitable for producing a foamed pressure-sensitive adhesive according to the invention.

[0138] A foamed pressure-sensitive adhesive according to the invention can also be produced using so-called pre-expanded microballoons. With this group, the expansion takes place before the microballoons are mixed into the polymer matrix. Pre-expanded microballoons are commercially available, for example, under the name Dualite® or with the type designation DE (Dry Expanded). The density of the adhesive films in the case of foamed adhesive layers is preferably between 200 kg / m³. 3 and 1000 kg / m² 3 , preferably between 500 kg / m² 3 and 980 kg / m² 3 , preferably between 700 kg / m 3 and 950 kg / m² 3 .

[0139] Preferably, the poly(meth)acrylates are crosslinked with a crosslinker-accelerator system.

[0140] A particularly preferred crosslinker-accelerator system comprises at least one epoxy group-containing substance as a crosslinker and at least one accelerator substance that accelerates the crosslinking reaction at temperatures below the melting point of the poly(meth)acrylate. The system requires that the polymers contain functional groups capable of crosslinking with epoxy groups. Suitable epoxy group-containing substances include multifunctional epoxides, especially bifunctional or trifunctional epoxides (i.e., those with two or three epoxy groups, respectively), but also higher-functional epoxides or mixtures of differently functional epoxides. Preferably, amines (formally considered as substitution products of ammonia), for example primary and / or secondary amines; in particular tertiary and / or multifunctional amines, can be used as accelerators.Substances containing multiple amine groups can also be used, whereby these amine groups can be primary, secondary, and / or tertiary, particularly diamines, triamines, and / or tetraamines. Amines that exhibit no or only minimal reactions with the polymer building blocks are especially favored. Phosphorus-based compounds, such as phosphines and / or phosphonium compounds, can also be used as accelerators.

[0141] Suitable functional groups for the poly(meth)acrylate to be crosslinked include acid groups (e.g., carboxylic acid, sulfonic acid, and / or phosphonic acid groups), hydroxyl groups, acid anhydride groups, epoxy groups, and / or amine groups. The polymer particularly preferably contains incorporated acrylic acid and / or methacrylic acid.

[0142] However, it can also be advantageous to forgo accelerators, as these can, for example, tend to yellow (especially nitrogen-containing substances). Epoxycyclohexyl derivatives are suitable crosslinkers that do not require the addition of accelerators, particularly when carboxylic acid groups are present in the poly(meth)acrylate to be crosslinked. This can be achieved, for example, by incorporating at least 5 wt% acrylic acid into the polymer. It is particularly advantageous that the polymer to be crosslinked does not contain proton acceptors, electron pair donors (Lewis bases), and / or electron pair acceptors (Lewis acids). The absence of these substances refers in particular to externally added accelerators, i.e., those not incorporated into the polymer backbone; however, it is especially preferred that neither externally added nor incorporated accelerators, and in particular no accelerators at all, are present.The crosslinking agent is particularly preferred as an epoxycyclohexyl carboxylate, especially (3,4-epoxycyclohexane)methyl-3,4-epoxycyclohexyl carboxylate (Uvacure® 1500).

[0143] Applications

[0144] Another aspect of the invention is the use of the adhesive compound according to the invention in an adhesive tape, which is also referred to as adhesive tape and also includes transfer adhesive tapes.

[0145] The adhesive products according to the invention find a wide variety of applications, for example in the construction industry, the electronics industry, the DIY sector, the automotive industry, shipbuilding, boatbuilding and railway construction, for household appliances, furniture and the like. Advantageous applications include, for example, the bonding of strips and emblems in the aforementioned areas, the bonding of stiffening profiles in elevators, the bonding of components and products in the solar industry, frame bonding in consumer electronics such as televisions and the like, and bonding in sign manufacturing.

[0146] The adhesive composition according to the invention and its use in adhesive tapes are ideally suited for bonding flexible printing plates to curved surfaces. In flexographic printing, flexible printing plates (also known as clichés) are bonded to printing cylinders or printing tubes. Such clichés consist, for example, of a polyethylene terephthalate film (PET film) onto which a layer of a photopolymer is applied, into which the corresponding printing relief can be introduced by exposure to light. The cliché is then bonded to the printing cylinder or printing tube via the PET film.

[0147] The adhesive tapes according to the invention excellently fulfill the very high requirements in this area. For the printing process, the adhesive tape must have a certain hardness as well as a certain elasticity. In addition, the adhesive strength should be sufficient to prevent the printing plate from detaching from the double-sided adhesive tape or the adhesive tape from the cylinder or sleeve. This also applies, for example, at elevated temperatures of 40 to 60 °C and at higher printing speeds. In addition to this property, the adhesive compound should also possess reversible adhesive properties so that the printing plates can be removed again after the printing process (in this respect, both the adhesive bond of the adhesive tape to the printing cylinder or sleeve and the bond to the printing plate must be removable without leaving any residue in order to ensure the reusability of both components).This removability should be maintained even after prolonged bonding (up to 6 months). Furthermore, it is desirable that the adhesive tape, and especially the printing plate, can be removed without damage, i.e., without significant force, since the printing plates are generally reused multiple times. Additionally, no residue should remain on the printing plate or on the cylinder or sleeve. In summary, very high demands are placed on the double-sided adhesive tapes suitable for this application, demands which are excellently met by the adhesive compound according to the invention.

[0148] The adhesive can be advantageously used to bond components of precision mechanical, optical, electrical, and / or electronic devices, for example, during their manufacture, repair, decoration, or similar applications. Materials such as plastics, glass, metals, and the like can be bonded using this method.

[0149] The adhesive is particularly suitable for the permanent bonding of flexible materials, especially in the production of flexible displays. Such displays are becoming increasingly important.

[0150] Advantageously, the adhesive can be used for bonding windows or lenses in the housings of precision mechanical, optical, and / or electronic devices (so-called "lens mounting"). At least one of the rigid or flexible substrates is transparent or translucent. The transparent or translucent substrate can, for example, be a window or an optical lens for the purpose of protecting sensitive components located beneath it—such components can be, for example, liquid crystal displays (LCDs), light-emitting diodes (LEDs), or organic light-emitting diodes (OLEDs) in displays, but also printed circuits or other sensitive electronic components; this plays a significant role, for example, in applications for touch-sensitive displays—and / or for producing optical effects for the device's function—for example, refraction, focusing, attenuation, amplification, etc.- be.

[0151] The transparent substrate is very advantageously selected to have a haze value of at most 50%, preferably not more than 10%, and very preferably not more than 5% (measured according to ASTM D 1003). The second substrate is preferably also a component of a precision mechanical, optical, and / or electronic device. In particular, housings for such devices or mounts for windows or lenses as described above are suitable.

[0152] In a preferred procedure, the transparent or translucent substrate is a substrate made of glass, polymethyl methacrylate and / or polycarbonate.

[0153] In particular, the second substrate can consist of plastics such as acrylonitrile butadiene styrene copolymers (ABS), polyamide or polycarbonate, which can also be glass fiber reinforced; or of metals such as aluminum - including anodized aluminum - or magnesium and metal alloys.

[0154] Additives such as dyes, light stabilizers, anti-aging agents, plasticizers or the like may also be added to the substrate materials, provided this is advantageous for the intended purpose; in the case of transparent or translucent materials, in particular to the extent that it does not disturb these optical properties or only to an acceptable degree.

[0155] According to the invention, the composite is thus a component of an electronic, optical or precision mechanical device.

[0156] Electronic, optical and precision mechanical devices within the meaning of this application are, in particular, devices such as those classified in Class 9 of the International Classification of Goods and Services for the Purposes of the Registration of Marks (Nice Classification); 10th Edition (NCL(10-2013)); provided they are electronic, optical or precision mechanical devices, and also watches and timekeeping devices in accordance with Class 14 (NCL(10-2013)), such as, in particular,

[0157] • Scientific, nautical, surveying, photographic, cinematographic, optical, weighing, measuring, signaling, checking, life-saving and teaching apparatus and instruments;

[0158] • Apparatus and instruments for conducting, switching, converting, storing, regulating and controlling electricity;

[0159] • Image recording, processing, transmission and playback devices, such as televisions and the like

[0160] • Acoustic recording, processing, transmission and playback devices, such as radios and the like • Computers, calculating and data processing equipment, mathematical devices and instruments, computer accessories, office equipment - such as printers, fax machines, copiers, typewriters -, data storage devices

[0161] • Remote communication and multifunctional devices with remote communication functionality, such as telephones, answering machines

[0162] • Chemical and physical measuring devices, control units and instruments, such as battery chargers, multimeters, lamps, tachometers

[0163] • Nautical equipment and instruments

[0164] • Optical devices and instruments

[0165] • Medical devices and instruments, and those for athletes

[0166] • Watches and chronometers

[0167] • Solar cell modules, such as electrochemical dye-sensitized solar cells, organic solar cells, thin-film cells,

[0168] • Fire extinguishers.

[0169] Technological development is increasingly focused on devices that are becoming ever smaller and lighter, so that they can be carried by their owners at all times and are typically carried regularly. This is usually achieved by making such devices lightweight and / or appropriately sized. In this document, such devices are also referred to as mobile devices or portable devices. This development trend involves the increasing integration of electronic components into precision mechanical and optical devices, further increasing the possibilities for miniaturization. Because mobile devices are carried around, they are subjected to increased stress, particularly mechanical stress, such as from bumping against edges, being dropped, contact with other hard objects in a pocket, and even the constant movement inherent in carrying them.Mobile devices are also exposed to greater stresses due to moisture, temperature influences, and the like than "immobile" devices that are usually installed indoors and are not, or hardly, moved. The adhesive compound used according to the invention has proven to be particularly advantageous in withstanding such disturbances and, ideally, in mitigating or compensating for them.

[0170] Below are some examples of portable devices.

[0171] • Cameras, digital cameras, photography accessories (such as light meters, flash units, apertures, camera bodies, lenses, etc.), film cameras, video cameras • Small computers (mobile computers, pocket computers, calculators), laptops, notebooks, netbooks, ultrabooks, tablet computers, handhelds, electronic calendars and organizers (so-called "Electronic Organizers" or "Personal Digital Assistants", PDAs, palmtops), modems,

[0172] • Computer accessories and control units for electronic devices, such as mice, drawing pads, graphics tablets, microphones, speakers, game consoles, gamepads, remote controls, remote controls, touchpads

[0173] • Monitors, displays, screens, touch-sensitive screens (sensor screens, "touchscreen devices"), projectors

[0174] • Reading devices for electronic books (“e-books”),

[0175] • Small television sets, pocket televisions, film players, video players

[0176] • Radios (including small and pocket radios), Walkmans, Disemons, music players for e.g. CD, DVD, Blu-ray, cassettes, USB, MP3, headphones

[0177] • Cordless phones, mobile phones, smartphones, two-way radios, hands-free devices, personal alarm devices (pagers, beepers)

[0178] • Mobile defibrillators, blood glucose meters, blood pressure monitors, pedometers, pulse monitors

[0179] • Flashlights, laser pointers

[0180] • Mobile detectors, optical magnifiers, long-range vision devices, night vision devices

[0181] • GPS devices, navigation devices, portable satellite communication interface devices

[0182] • Data storage devices (USB sticks, external hard drives, memory cards)

[0183] • Wristwatches, digital watches, pocket watches, chain watches, stopwatches.

[0184] Furthermore, the adhesive tapes equipped with the adhesive composition according to the invention are advantageously suitable for sheathing elongated goods, such as, in particular, cable sets in motor vehicles, wherein the adhesive tape can be guided around the elongated goods in a helical path or the elongated goods can be wrapped axially by the tape. Due to the excellent suitability of the adhesive tape, it can be used in a sheathing consisting of a covering in which the self-adhesive tape is present at least in one edge region of the covering, and is bonded to the covering in such a way that the adhesive tape extends over one of the longitudinal edges of the covering, preferably in an edge region that is narrow compared to the width of the covering. Such a product and optimized embodiments thereof are disclosed in EP 1 312 097 A1.Further developments for which the adhesive tape according to the invention is also very well suited are described in EP 1 300 452 A2, DE 102 29 527 A1 and WO 2006 108 871 A1. Likewise, the adhesive tape according to the invention can be used in a method as disclosed in EP 1 367 608 A2. Finally, EP 1 315 781 A1 and DE 103 29 994 A1 describe embodiments of adhesive tapes that are also possible for the adhesive tape according to the invention.

[0185] Furthermore, preferably the adhesive tape does not damage cables with PVC sheathing or polyolefin sheathing when bonded to them, provided that a combination of cables and adhesive tape according to LV 312 is stored at temperatures above 100 °C and for up to 3000 h and the cables are subsequently bent around a mandrel.

[0186] The adhesive tape according to the invention is ideally suited for wrapping cables, can be easily unwound for simple processing, shows no or only slight flaking and shows no cable embrittlement even at the high temperature classes T3 and T4 over 3000 h.

[0187] Experimental data

[0188] Measurement and testing methods:

[0189] Sales determination of the syrup

[0190] The conversion was determined gravimetrically and is expressed as a percentage of the weight of the syrup used. To isolate the polymer, it was dried in a drying oven for at least 3 hours at up to 120 °C until no further weight change of the sample was measurable over time. The weight of the polymer was weighed and divided by the weight of the syrup used. The calculated value corresponds to the percentage conversion.

[0191] Determination of the gel content

[0192] The carefully dried, solvent-free adhesive samples were sealed in 5 x 7.5 cm polyethylene (Tyvek) nonwoven pouches. The gel value was measured gravimetrically. The pouches were tared, approximately 1 g of pressure-sensitive adhesive was added, sealed, and the initial weight was determined. The samples were then stored in ethyl acetate on a shaker bench for 3 days, with the ethyl acetate being replaced daily. Finally, the samples were removed from the solvent, dried at room temperature for one day, and the final weight was determined.

[0193] Determination of the glass transition temperature To of pressure-sensitive adhesives

[0194] The static glass transition temperature of the pressure-sensitive adhesives was determined using differential scanning calorimetry (DSC). Approximately 5 mg of an untreated sample of the adhesive was weighed into an aluminum crucible (volume 25 pl) and sealed with a perforated lid. A Netzsch DSC 204 F1 was used for the measurement. The sample was inerted under nitrogen. It was first cooled to -150 °C, then heated to +150 °C at a rate of 10 K / min and cooled again to -150 °C. The subsequent second heating cycle was also performed at 10 K / min, and the change in heat capacity was recorded. Glass transitions are identified as steps in the thermogram (heat-temperature diagram).The glass transition temperature Tg is obtained as follows: The linear portions of the measurement curve before and after the step are extended in the direction of increasing (before the step) and decreasing (after the step) temperatures, respectively. Within the step, a regression line is drawn parallel to the ordinate such that it intersects the two extension lines, creating two areas of equal area (between each extension line, the regression line, and the measurement curve). The intersection of this regression line with the measurement curve yields the glass transition temperature.

[0195] Determination of molecular weight

[0196] The data on the number-average molar mass M n and the weight-average molar mass M wThis document refers to the well-known determination by gel permeation chromatography (GPC). The determination is performed on 100 µL of 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.

[0197] A PSS-SDV type column, 5 pm, 10 is used as the upstream column. 3 Ä, 8.0 mm x 50 mm (Specifications here and below in the order: type, particle size, porosity, inner diameter x length; 1 Ä = 10 -10 m) is used. For separation, a combination of columns of type PSS-SDV, 5 pm, 10 is used. 3 Ä and 10 5 A and 10 6Columns measuring 8.0 mm x 300 mm (Polymer Standards Service; detection via Shodex RI71 differential refractometer) were used. The flow rate was 1.0 ml per minute. Calibration was performed using the commercially available ReadyCal kit Poly(styrene) high from PSS Polymer Standard Service GmbH, Mainz, Germany. The values ​​were universally converted to polymethyl methacrylate (PMMA) using the Mark Houwink parameters K and alpha, so that the data were given in PMMA mass equivalents.

[0198] Glass transition temperature - Dynamic Scanning Calorimetry (DSC)

[0199] Approximately 5 mg of an untreated polymer sample is weighed into an aluminum crucible (volume 25 pL) and sealed with a perforated lid. A Netzsch DSC 204 F1 is used for the measurement. The process is carried out under nitrogen for inerting. The sample is first cooled to -150 °C, then heated to +150 °C at a rate of 10 K / min and cooled again to -150 °C. The subsequent second heating cycle is also performed at 10 K / min, and the change in heat capacity is recorded. Glass transitions are identified as steps in the thermogram as follows:

[0200] The linear portions of the measurement curve before and after the step are extended in the direction of increasing (before the step) and decreasing (after the step) temperatures, respectively. Within the step, a regression line is drawn parallel to the ordinate such that it intersects the two extension lines, creating two areas of equal area (between each extension line, the regression line, and the measurement curve). The intersection of this regression line with the measurement curve yields the glass transition temperature.

[0201] Microshear path (MS)

[0202] A 10 mm x 50 mm strip of adhesive tape is cut from the tape under investigation. The resulting tape pattern is then adhered to a polished, temperature-controlled, 13 mm wide steel test plate (cleaned with acetone) in such a way that the longitudinal direction of the tape pattern is aligned with the transverse direction of the steel plate, the bonded area measures 13 mm x 10 mm, and the tape extends beyond the steel plate on one side by a length z = 2 mm. To fix the tape in place, it is then rolled over six times with a 2 kg steel roller at a speed of 10 m / min. On the side of the tape facing away from the steel plate, the tape is reinforced flush with the edge extending beyond the steel plate by the length z using a strong adhesive strip (dimensions 4 mm x 25 mm; carrier: 190 µm thick PET film), which serves as a support for a displacement sensor.The prepared setup is suspended vertically so that the portion of the adhesive tape pattern extending beyond the steel plate, measuring length z, points upwards. The steel test plate with the bonded sample is heated to 40 °C, and the adhesive tape pattern to be measured is clamped at its lower end with a weight of 300 g at time tO = 0. The deformation of the sample under shear is measured using a displacement sensor over a period of 15 minutes (starting at tO) at a temperature of 40 °C and a relative humidity of 50 ± 5%. The shear displacement after 15 minutes (maximum value; downward displacement of the upper edge of the sample during the measurement) is reported in pm. The shear displacement measured in this way is a quantitative measure of the internal strength (shear strength) of the sample.

[0203] The sample is then unloaded (the 300g weight is removed), and after 15 minutes, the elastic component (in percent) is determined from the residual deflection of the sample. The elastic component (in percent) is calculated as [(maximum value - minimum value) - 100 / maximum value]. The maximum value corresponds to the downward displacement of the upper edge of the sample during the measurement. The minimum value corresponds to the shear distance after 15 minutes without load. Table 1: Commercially available chemicals used

[0204] Production of prepolymers

[0205] For the preparation of the prepolymers, various approaches listed in Table 2 were prepolymerized in 1 L clear glass vials. First, 600 g of the monomer mixture of 2-ethylhexyl acrylate (2-EHA) / n-butyl acrylate (BA) / acrylic acid (AA) were blended using 0.0063 wt% Irgacure 651. The proportion of acrylic acid was selected according to Table 2. 2-EHA and BA were present in a 2:1 ratio, regardless of the acrylic acid content. The photoinitiator-containing monomer mixture was inertized for 30 min by introducing nitrogen into the liquid phase and continuously stirring. The inert mixture was polymerized under a nitrogen atmosphere in the vial by exposure to IIV-A radiation (365 nm) and stirring. The prepolymers were prepared under controlled conversion, with the conversion of the prepolymers shown in Table 2.The prepared syrups, consisting of prepolymers and unreacted monomers, were supplemented with further acrylic acid as well as 2-EHA and BA, resulting in a 2-EHA / BA / AA composition with 12 wt% AA (in the subsequent adhesive product, the pressure-sensitive adhesive). 0.24 wt% aluminum chelate was added to the composition, and the mixture was homogenized by stirring. After 16–24 hours, the Fl-FX formulations were tested for processability (see Table 2).

[0206] Example of the production of the formulation Fl

[0207] To prepare 100 g of the formulation, 78 g of the previously prepared acrylic acid-free syrup were mixed with 12 g AA, 6.7 g EHA, and 3.3 g BA in a sealable glass jar under air by stirring. During the stirring process, 0.15 wt% of the photoinitiator Irgacure 651 and 0.24 wt% of the aluminum chelate were added. The formulation was further homogenized and then stored on a rolling bench for 16–24 h.

[0208] All other formulations listed in Table 2 were produced analogously to formulation Fl.

[0209] Table 2: Processability of the formulations used Fl to FX depending on the prepolymer conversion and the acrylic acid content.

[0210] The processability of the formulations was tested by coating the formulated syrups between two 50 pm thick liners to a thickness of 100 pm using a coating calender. Processability was evaluated as follows:

[0211] - stands for a non-processable formulation;

[0212] 0 for a largely processable formulation; and

[0213] + for a processable formulation.

[0214] Processability was assessed through a qualitative evaluation by a specialist via visual inspection. Formulations were rated as "non-processable" if particulate residues accumulated on and / or in front of the coating calender and / or if visually observable particulate adhesions were present on the stirrer during formulation production. If no particulate residues or adhesions were observed, the formulation was rated "+", i.e., as processable.

[0215] Formulations were rated as “0”, i.e., as “mostly processable formulations”, if no particulate residues accumulated on and / or in front of the coating calender, but gel particles were observed after the calender.

[0216] For formulations containing less than 4 wt% monomers with one or more functional groups suitable for coordinative crosslinking, essentially gel-free processing can be observed under normal syrup production conditions.

[0217] Table 2 further shows that maintaining the processability of a formulation depends on the amount of monomers with one or more functional groups suitable for coordinate crosslinking, as well as the conversion of the prepolymers. Reaction conversions of, for example, up to 20% can thus be achieved by reducing the number of monomers with one or more functional groups suitable for coordinate crosslinking.

[0218] Patterns and measurement results

[0219] The samples were smeared at a thickness of 100 pm between two liners, each 50 pm thick, and irradiated at 365 nm with a dose of 4000 mJ / cm². 2hardened in a static system ("path speed equal to zero").

[0220] Example 1 corresponds to an adhesive compound based on formulation F-Il (acrylic acid content of 2 wt% before the final formulation).

[0221] Example 2 corresponds to an adhesive compound based on formulation Fl (with an acrylic acid content of 0 wt.% prior to the final formulation).

[0222] Table 3: Measurement results

[0223] 2 nm stands for not measurable, as the sample has been "sheared off". The measurement results in Table 3 show that, after a certain time following web polymerization, a constant state for micro-shear displacement and elastic component has been established.

[0224] The time required for this equilibrium formation of the coordinate network can be accelerated by thermal energy.

Claims

Patent claims 1. Photopolymerized pressure-sensitive adhesive comprising a) at least one base polymer component with one or more functional groups suitable for coordinative crosslinking; b) one or more photoinitiators; and c) one or more coordinative crosslinkers.

2. Photopolymerized pressure-sensitive adhesive according to claim 1, characterized in that the base polymer component has a polymer composition distribution comprising at least a first and a second component, wherein the components differ from each other in that: i. the first component has a higher molecular weight and a lower content of functional groups, and ii. the second component has a lower molecular weight and a higher content of functional groups.

3. Photopolymerized pressure-sensitive adhesive according to any of the preceding claims comprising, in addition to 100 wt.% of the base polymer component, a) b) a total of 0.01 - 0.50 wt.% of one or more photoinitiators; and c) a total of 0.03 - 0.30 wt.% of one or more coordinative crosslinkers.

4. Photopolymerized pressure-sensitive adhesive according to one of the preceding claims, characterized in that the at least one base polymer component a) comprises the functional groups suitable for coordinative crosslinking to a weight fraction of at least 3 wt.%, preferably at least 4 wt.%, particularly preferably at least 5 wt.%, based on the total mass of the base polymer component.

5. Photopolymerized pressure-sensitive adhesive according to one of the preceding claims, characterized in that the functional groups suitable for coordinative crosslinking are based on ethylene-unsaturated monomer units with functional groups selected from the group consisting of acid, hydroxyl, acid anhydride, epoxy, amine, amide groups and any combinations thereof.

6. Photopolymerized pressure-sensitive adhesive according to one of the preceding claims, characterized in that one or more coordinative crosslinkers are metal chelate compounds.

7. Photopolymerized pressure-sensitive adhesive according to one of the preceding claims, characterized in that the at least one base polymer component a) is a poly(meth)acrylate component.

8. Photopolymerized pressure-sensitive adhesive according to one of the preceding claims, characterized in that the at least one base polymer component is based on a monomer composition comprising a) one or more (meth)acrylate monomers, the alcohol component of which has 1 to 30 carbon atoms; b) ethylene-unsaturated monomer units with functional groups suitable for coordinative crosslinking; c) optionally, further ethylene-unsaturated monomer units that are copolymerizable with the monomer units a) and b).

9. Photopolymerized pressure-sensitive adhesive according to one of the preceding claims, characterized in that the photopolymerized pressure-sensitive adhesive is produced with less than 2 wt.%, preferably less than or equal to (<) 1 wt.%, or even no solvent at all.

10. Photopolymerized pressure-sensitive adhesive according to one of the preceding claims, characterized in that the photopolymerized pressure-sensitive adhesive is produced by web polymerization of a syrup in the presence of one or more coordinative crosslinkers.

11. Photopolymerized pressure-sensitive adhesive according to claim 9, characterized in that the syrup comprises one or more poly(meth)acrylate prepolymers, the total of which is attributable to a maximum of 4 wt.%, preferably a maximum of 3 wt.%, of monomers with one or more functional groups suitable for coordinative crosslinking.

12. A method for producing a photopolymerized pressure-sensitive adhesive according to any one of the preceding claims, comprising the process steps a) Provision of a syrup, preferably a (meth)acrylate syrup, which in its entirety comprises a maximum of 4 wt% of its total mass monomers with one or more functional groups suitable for coordinative crosslinking; b) Addition of one or more further monomers to the syrup from step a); c) Addition of one or more coordinative crosslinkers to the syrup from step b); d) Polymerization of the syrup from step c) by light irradiation, preferably UV irradiation.

13. Method for producing an adhesive compound according to claim 12, characterized in that process step b) comprises the addition of one or more monomers with one or more functional groups suitable for coordinative crosslinking.

14. A method for producing an adhesive compound according to claim 12 or claim 13, characterized in that process step a) comprises the process steps: a1) providing a monomer composition comprising a maximum of 4 wt.% of monomers with one or more functional groups suitable for coordinate crosslinking; a2) polymerizing the monomer composition from a1) to a reaction conversion of 1 to 20%, preferably 2 to 15%, particularly preferably 3 to 10%, by light irradiation, preferably UV irradiation.

15. Use of an adhesive compound according to any one of claims 1 to 1 1 in an adhesive tape.

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