Adhesive for paper bonding

Description

[0001] The invention relates to the technical field of pressure-sensitive adhesives, which are widely used in industry for the temporary and permanent bonding of substrates. More specifically, the invention proposes a pressure-sensitive adhesive based on a special poly(meth)acrylate, which is particularly suitable for bonding paper and also for producing washable bonds.

[0002] Adhesive compounds are widely used in both the production and use of paper. Key applications include, for example, roll changes during the processing of large paper rolls; here, adhesive compounds are used in so-called... Splicing-Tapes are used to enable a simple, ideally seamless, changeover from one roll to the next, thus ensuring a continuous process. Permanent splices, which remain in the paper temporarily or permanently, are also common. Often, the paper is glued to the core of the roll at the beginning of the winding process (so-called splicing). core starting ), or the outer layer of paper rolls is fixed with adhesive tape during storage or transport (so-called end tabbing ) .

[0003] High demands are placed on the adhesives used in paper production and processing. For example, these adhesives are often required to have a high initial tackiness – consider, for instance, the short contact time between the outgoing and the incoming roll, where the brief contact time must be sufficient to create an adhesion between the two paper webs that withstands the shear forces present at the web speed and is ultimately stronger than the splitting force required to open the roll closure (slit labels, so-called butterflies) or the splitting system integrated into the adhesive tape.

[0004] Naturally, pressure-sensitive adhesives should also exhibit generally high adhesive strength, which develops on both polar and less polar papers. Particularly for permanent bonds, high aging stability is also required, which manifests itself, for example, in high resistance to migrating calcium ions from white-coated or CaCO3-filled paper. From a sustainability perspective, the adhesives often need to be removable from the paper substrate, at least in water (repulpability).

[0005] The aspect of the removability of an adhesive from the substrate to be bonded is also of particular interest in technical fields outside the paper industry; for example, this is also an increasingly common requirement for bonding batteries or accumulators in electronic devices such as mobile phones, etc.

[0006] Therefore, there has been no shortage of attempts to provide pressure-sensitive adhesives that meet the described requirements profile.

[0007] WO 2014 / 001096 A1 describes an adhesive compound comprising at least one polymer component based on a monomer mixture containing at least the following monomers: ia) 50 to 89.5 wt% at least one acrylic ester and / or methacrylic ester with the following formula: CH₂ = C(R₁)(COOR₂), where R₁ = H or R₂ is a linear alkyl group with 2 to 10 carbon atoms or a branched, non-cyclic alkyl group with at least 4 carbon atoms, and / or R₁ = CH₃ and R₂ is a linear alkyl group with 8 to 10 carbon atoms or a branched, non-cyclic alkyl group with at least 10 carbon atoms; ib) 5 to 20 wt% at least one N-alkyl-substituted acrylamide; ic) 5 to 25 wt% at least one acrylic ester and / or methacrylic ester with the following formula: CH₂ = C(R₃)(COOR₄), where R₃ = H or CH₃ and R₄ is a linear alkyl group with at least 12 carbon atoms; id) 0.5 to 5 wt% acrylic acid and / or methacrylic acid, where the quantities given refer to the monomer mixture and this adhesive is intended for bonding flexible printing plates.

[0008] WO 95 / 14746 A2 concerns a water-soluble or water-dispersible pressure-sensitive adhesive compound comprising a normally tacky copolymer of a water-soluble base monomer and a water-dispersible macromer.

[0009] EP 0 699 726 A2 discloses a water-soluble adhesive compound containing 100 parts by weight of a water-soluble copolymer consisting of a) 65-95 wt% of a vinylcarboxylic acid, b) 5-35 wt% of an alkyl(meth)acrylic acid ester with 1-12 carbon atoms in the alkyl group, and c) 0.05-5.0 wt% of a polymerizable photoinitiator and 30 to 150 wt% of a water-soluble plasticizer with a molar mass up to 4,000 Daltons.

[0010] EP 1 489 153 A1 describes a repulpable pressure-sensitive adhesive which comprises at least one block copolymer based on polyacrylate.

[0011] JP 2018 159018 A discloses an adhesive compound containing a copolymer comprising 61 to 93 wt.% alkoxyalkyl(meth)acrylate, 6 to 19 wt.% of a nitrogen-containing monomer and 1 to 20 wt.-7% of a crosslinking functional group, and describes the production of an adhesive compound containing a polymer of 2-methoxyethyl acrylate, dimetheylacrylamide and 2-hydroxyethyl acrylate.

[0012] The use of pressure-sensitive adhesives for the production of water-soluble bonds is described in WO 95 / 14746 A2, JP H11 323292 and US 4 388 432 A.

[0013] There is a continuing need for adhesive tapes with a good property profile for bonding paper. The object of the invention was to provide a repulpable pressure-sensitive adhesive that can be used effectively on both polar and non-polar papers and is stable during storage.

[0014] The solution to the problem is based on the idea of ​​using a poly(meth)acrylate with a specific underlying monomer composition in an adhesive pressure-sensitive material. A first and general object of the invention is therefore an adhesive pressure-sensitive material containing at least one polymer whose underlying monomer composition a) 10 to 30 wt.% of at least one compound according to formula (I) CH₂=CH-C(O)NR₁<R₂< (I), wherein R₁< represents an unsubstituted alkyl group, a hydroxyalkyl group, or an acetonyl group, and R₂< represents a hydrogen atom, an unsubstituted alkyl group, a hydroxyalkyl group, an acetonyl group, or an aminoalkyl group; b) 60 to 80 wt.% ethyl diglycol acrylate; and c) 0.5 to 10 wt.% of at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, and (C₂-C₄-hydroxyalkyl)(meth)acrylates. As has been shown, such pressure-sensitive adhesives exhibit good repulpability, high tack, high adhesive strength on various papers, and good shear strength. Furthermore, they show a low tendency to migrate into paper and have proven to be resistant to the migration of calcium ions.

[0015] According to the invention, an adhesive compound or pressure-sensitive adhesive is understood, as is common in general usage, to be a substance that is permanently sticky and adhesive, at least at room temperature. A characteristic of a pressure-sensitive adhesive is that it can be applied to a substrate by pressure and adheres there, whereby the pressure to be applied and the duration of this pressure are not defined in detail. Generally, however, depending on the exact type of pressure-sensitive adhesive and the substrate, as well as the temperature and humidity, the application of a short-term, minimal pressure, not exceeding a light touch for a brief moment, is sufficient to achieve the adhesive effect; in other cases, a longer duration of higher pressure may be necessary.

[0016] Pressure-sensitive adhesives possess special, characteristic viscoelastic properties that result in their permanent tackiness and bonding strength. A defining characteristic is that when mechanically deformed, both viscous flow processes and the development of elastic restoring forces occur. The relative proportions of these two processes depend on the precise composition, structure, and degree of cross-linking of the pressure-sensitive adhesive, as well as the rate and duration of deformation and the temperature.

[0017] The proportion of viscous flow is necessary to achieve adhesion. Only the viscous components, often caused by macromolecules with relatively high mobility, enable good wetting and flow onto the substrate to be bonded. A high proportion of viscous flow leads to high tack (also known as surface tack) and thus often also to high adhesion. Highly cross-linked systems, crystalline or glassy polymers, are generally not tacky or at least only slightly tacky due to a lack of flowable components.

[0018] The elastic restoring forces are necessary to achieve cohesion. They are generated, for example, by very long-chain and highly entangled macromolecules, as well as by physically or chemically cross-linked macromolecules, and enable the transmission of forces acting on an adhesive bond. This allows an adhesive bond to withstand a sustained load, such as continuous shear stress, to a sufficient degree over an extended period.

[0019] To describe and quantify the degree of elastic and viscous components, as well as their ratio, the storage modulus (G') and loss modulus (G"), which can be determined using Dynamic Mechanical Analysis (DMA), are employed. G' is a measure of the elastic component, and G'' is a measure of the viscous component of a material. Both quantities depend on the deformation frequency and the temperature.

[0020] The parameters can be determined using a rheometer. The material under investigation is subjected, for example, to a sinusoidally oscillating shear stress in a plate-plate arrangement. In shear-stress controlled devices, the deformation is measured as a function of time, along with the time lag of this deformation relative to the application of the shear stress. This time lag is called the phase angle δ.

[0021] The storage modulus G' is defined as follows: G' = (τ / γ) • cos(δ) (τ = shear stress, γ = deformation, δ = phase angle = phase shift between the shear stress and deformation vectors). The definition of the loss modulus G" is: G" = (τ / γ) • sin(δ) (τ = shear stress, γ = deformation, δ = phase angle = phase shift between the shear stress and deformation vectors).

[0022] A mass is considered an adhesive compound, and is defined as such within the meaning of the invention, particularly if, at 23 °C in the deformation frequency range of 10⁰ to 10⁻¹ rad / sec, both G' and G" lie at least partially within the range of 10⁻³ to 10⁻⁷ Pa. "Partially" means that at least a section of the G' curve lies within the window defined by the deformation frequency range from 10⁰ to 10⁻¹ rad / sec (abscissa) and the range of G' values ​​from 10⁻³ to 10⁻⁷ Pa (ordinate), and if at least a section of the G" curve also lies within the corresponding window.

[0023] According to the invention, the monomer composition of the polymer comprises 10 to 30 wt.% of at least one compound according to formula (I) CH₂=CH-C(O)NR₁<R₂< (I), wherein R₁< represents an unsubstituted alkyl group, a hydroxyalkyl group, or an acetonyl group, and R₂< represents a hydrogen atom, an unsubstituted alkyl group, a hydroxyalkyl group, an acetonyl group, or an aminoalkyl group. If several such monomers are present, the monomer composition comprises monomers a) in a total of 10 to 30 wt.%. The weight fraction range of monomers a) according to the invention ensures, in particular, good tackiness and good repulpability of the pressure-sensitive adhesive. Preferably, the monomer composition of the polymer comprises 15 to 28 wt.% of at least one compound according to formula (I). If several such monomers are included, the monomer composition comprises monomers a) preferably in a total of 15 to 28 wt.%.

[0024] Preferably the compound according to formula (I) is selected from the group consisting of N-methylacrylamide, N-ethylacrylamide, N-hydroxyethylacrylamide, diacetonylacrylamide, N-isopropylacrylamide, N-ethyl-N-aminoethylacrylamide, N-ethyl-N-hydroxyethylacrylamide, N,N-dimethylacrylamide, N,N-dihydroxymethylacrylamide, N,N-diethylacrylamide, N,N-dihydroxyethylacrylamide.

[0025] In one embodiment, R 1< and R 2< independently represent an unsubstituted alkyl group; the compound according to formula (I) N,N-dimethylacrylamide is particularly preferred.

[0026] Preferably, the monomer composition comprises at least acrylic acid or 2-hydroxyethyl acrylate as monomer c). If several monomers c) are present, the monomer composition comprises monomers c) in a total amount of 0.5 to 10 wt.%.

[0027] The monomer composition underlying the polymer of the adhesive compound according to the invention can furthermore comprise up to 10 wt.% acrylic acid alkyl esters with 1 to 4 C atoms in the alkyl group.

[0028] In one embodiment, the monomer composition underlying the polymer of the adhesive compound according to the invention comprises a) 10 to 30 wt% N,N-dimethylacrylamide; b) 60 to 80 wt% ethyl diglycol acrylate; and c) acrylic acid and / or 2-hydroxyethyl acrylate to a total of 0.5 to 10 wt%, where the weight percentages are of course based on the total weight of the monomer composition.

[0029] The polymer of the pressure-sensitive adhesive according to the invention is preferably cross-linked. Thermal cross-linking is particularly preferred. Thermal cross-linking can be carried out under significantly milder conditions than, for example, radiation-induced cross-linking, which can occasionally be destructive. According to the invention, however, it is also possible to effect cross-linking of the polyacrylate exclusively or additionally by actinic radiation, whereby optionally necessary or promoting cross-linking substances can be added, e.g., UV cross-linkers.

[0030] Preferably, the polymer of the pressure-sensitive adhesive according to the invention is thermally crosslinked, i.e., by means of substances that enable (initiate) and / or promote a crosslinking reaction under the influence of thermal energy. Preferred thermal crosslinkers are coordination crosslinkers; the polymer is particularly preferably thermally crosslinked with one or more metal chelates, in particular with at least one aluminum chelate and / or at least one titanium chelate.

[0031] The coordinative crosslinkers, in particular aluminum chelates, are preferably used in an amount of 0.1 to 1 part by weight, particularly preferably 0.2 to 0.8 parts by weight, each based on 100 parts by weight of the polymer (solvent-free). In one variant, the coordinative crosslinkers, in particular titanium chelates, are preferably used in an amount of 1 to 4 parts by weight, particularly preferably 1.7 to 3.3 parts by weight, each based on 100 parts by weight of the polymer (solvent-free).

[0032] The polymer is particularly preferred when cross-linked with aluminium acetylacetonate or titanium diisopropoxide bis(acetylacetonate).

[0033] In principle, all radical or radical-controlled polymerizations, as well as combinations of different polymerization processes, can be used to produce the polymers of the pressure-sensitive adhesive according to the invention. Besides conventional free-radical polymerization, these include, for example, ATRP, nitroxide / TEMPO-controlled polymerization, or the RAFT process. Preferred solvents for the polymerization are water, acetone, isopropanol, ethanol, and ethyl acetate, as well as any mixtures thereof.

[0034] The polymer of the adhesive compound according to the invention preferably has a weight-average molar mass M w of 300,000 to 2,000,000 g / mol.

[0035] In one embodiment, the pressure-sensitive adhesive composition according to the invention contains at least one adhesive resin. Adhesive resins, also referred to as tackifying resins, are frequently added to pressure-sensitive adhesive compositions for fine-tuning the adhesive properties.

[0036] The term "resins" refers in particular to oligo- and (low-)polymeric compounds whose number-average molar mass Mn does not exceed 5,000 g / mol. Naturally, short-chain polymerization products formed during the polymerization process for the production of the polymer of the pressure-sensitive adhesive according to the invention are not included under the term "resins".

[0037] Adhesive resins often have softening points in the range of 80 to 150 °C. The softening point (TE) values ​​for oligomeric and polymeric compounds, such as resins, refer to the ring-ball method according to DIN EN 1427:2007, provided the specifications are applied accordingly (testing the oligomer or polymer sample instead of bitumen, while otherwise maintaining the same procedure). The measurements are performed in a glycerol bath.

[0038] In one embodiment, the adhesive compound according to the invention contains at least one adhesive resin selected from the group consisting of rosin and rosin derivatives such as rosin esters, also rosin derivatives stabilized by e.g. disproportionation or hydrogenation; terpene phenol resins; acrylate resins and sugar resins.

[0039] Adhesive resins are preferably present in the pressure-sensitive adhesive composition according to the invention in a total maximum of 30% by weight. One or more adhesive resins may be included.

[0040] Preferably, the adhesive compound according to the invention is free of adhesive resins.

[0041] To optimize the properties of the adhesive compound according to the invention, it can also contain other common additives such as fillers, for example electrically conductive filler materials, thermally conductive filler materials and the like, or flame retardants, for example ammonium polyphosphate and its derivatives.

[0042] If the adhesive compound according to the invention is to be colored, it can also contain water-soluble pigments or other dyes.

[0043] The adhesive compound according to the invention can also be in a foamed form and contain appropriate blowing agents, in particular blowing gases; microbodies, in particular microhollow spheres, made of e.g. glass, ceramic or fly ash; expandable or expanded microhollow spheres with a thermoplastic polymer shell and the like.

[0044] Another object of the invention is an adhesive tape comprising an adhesive compound according to the invention.

[0045] For the purposes of this invention, the general term "adhesive tape" includes all planar structures such as films or film sections, papers or paper sections, tapes of extended length and limited width, labels, die-cuts and the like, which are extended in two dimensions and coated at least on one side and over their entire surface or partially with adhesive material.

[0046] In the simplest case, an adhesive tape according to the invention consists only of an adhesive compound according to the invention (transfer tape). In order to be able to apply the adhesive tape, which is wound onto a disc roll or cross-wound onto a spool, without it sticking to itself, the adhesive compound is preferably covered with at least one release liner.

[0047] An adhesive tape according to the invention can comprise, in addition to an adhesive compound according to the invention, at least one carrier and optionally also further layers, for example further layers of adhesive compound, further reinforcing carrier layers, etc.

[0048] In one embodiment, the adhesive tape comprises a carrier and a layer of an adhesive compound according to the invention. The carrier material is preferably selected from the group consisting of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and paper. In particular, the carrier material is paper.

[0049] In the embodiment with a carrier, the adhesive tape according to the invention can be designed as a single-sided or double-sided adhesive tape. Furthermore, the adhesive tape according to the invention can also be designed as a slittable adhesive tape.

[0050] Even in the carrier-based embodiment, at least one adhesive layer of the adhesive tape is preferably covered with a release liner to facilitate trouble-free unwinding and to protect the adhesive layer(s) from contamination. Release liners typically consist of a single- or double-sided siliconized plastic film (e.g., PET or PP) or a siliconized paper carrier. They are not considered part of the adhesive tape itself but are only temporarily attached to it as an auxiliary component.

[0051] Particularly preferably in an adhesive tape according to the invention, the adhesive compound according to the invention is covered with a repulpable release liner.

[0052] A further aspect of the invention is the use of an adhesive compound and / or an adhesive tape according to the invention for producing water-soluble bonds. "Water-soluble bonds" are defined as bonds in which the bonded substrates can be separated from each other with a manageable and technically reasonable expenditure of time and equipment under the influence of water. This term does not imply that the adhesive compound or the adhesive tape can be removed from the substrate without leaving any residue. Preferably, however, the adhesive compound according to the invention can be removed without leaving any residue from a substrate to which it is bonded. Preferred substrates in this context are papers and components of battery cells.

[0053] Another object of the invention is the use of an adhesive compound and / or an adhesive tape according to the invention for the production of repulpable bonds.

[0054] The uses according to the invention preferably include the use of an adhesive compound and / or an adhesive tape according to the invention for producing bonds, wherein at least one of the substrates to be bonded is paper. It is particularly preferred that both substrates to be bonded are paper. Preferred bonds in this context include, for example, the bonding of papers that can be split in the z-direction to paper rolls, which serve in particular for temporary roll closure; the production of permanent splices between two paper rolls; the bonding of white-coated paper or paper filled with calcium carbonate; and the gluing of paper to a roll core ( core starting ) and fixing the outer paper layer of a paper roll ( end tabbing ) . Examples Measurement methods Gel permeation chromatography (GPC, measurement method A):

[0055] The number-mean and weight-mean molecular weights M n , M w given in this document refer to the determination by gel permeation chromatography.

[0056] The determination is performed on 100 µL of clear-filtered sample (sample concentration 0.5 g / L). Tetrahydrofuran with 0.1 vol% trifluoroacetic acid is used as the eluent. The measurement is performed at 25 °C. A PSS-SDV column, 10 µm, ID 8.0 mm × 50 mm, is used as the guard column. For the separation, PSS-SDV columns, 5 µm, 10³ < Å (SN9090201) and 5 µm, 10² < Å (SN9090200), each with an ID of 8.0 mm × 300 mm, are used (columns from Polymer Standards Service; detection is performed using a PSS-SECurity 1260 RID differential refractometer). The flow rate is 0.5 mL per minute. Calibration is performed against PMMA standards (polymethyl methacrylate calibration). Determination of repulpability according to Tappi UM 213 (measurement method B):

[0057] The test paper was used "fluffed pulp"(Co. Machery-Nagel MN 270, 270 g / m 2< ) used.

[0058] A three-layer composite was created by bonding the test paper to both sides with the adhesive under investigation, covering the entire surface. The samples prepared in this way were cut into 13 x 13 mm pieces and filled with test paper pieces of the same size in a beaker up to a weight of 15 g.

[0059] The samples were placed in a blender (Waring Blender Model 34BL47) with 500 ml of tap water.

[0060] The mixture was then blended for 20 seconds at approximately 15,000 rpm. The mixer was then stopped, and paper residue from the edges of the mixer was rinsed back into the pulp with tap water. This process was repeated twice, resulting in a total blending time of 60 seconds. The resulting pulp was designated Pulp 1.

[0061] The entire pulp 1 was placed in a disperser containing 2 ml of tap water. It was rinsed with tap water to ensure the pulp 1 was completely removed. The disperser was then filled to 5 ml with tap water. Dispersion was carried out for 1 minute, after which five beakers, each containing 770 ml of the diluted pulp 1, were filled. The first, third, and fifth beakers were used to prepare test sheets.

[0062] For this purpose, the contents of a beaker were placed in a cylinder and filled to 7 mm with tap water. Air was then blown through for 20 seconds, followed by a 20-second waiting period to allow the foam to settle and the fibers to self-orient. The water was then drawn off through a sieve embedded in the bottom of the cylinder, and a vacuum was subsequently applied for 1 minute.

[0063] The freshly formed sheet was covered with a coverboard (chromoly replacement board, 240 mm diameter, Estanit) (smooth side down) and rolled over with a 2 kg steel roller. The resulting composite was removed and the exposed side covered with a release paper (paper B13-c, 205 mm diameter, Estanit). This composite was then dried for approximately 5 minutes in a dryer at 100 °C under vacuum.

[0064] After drying, the top carton sheets were carefully removed and the test sheet examined for fiber pull-out. Fiber pull-out indicates residual tackiness caused by insufficient repulpability of the adhesive. Ideally, the top carton sheets should be removable without any problems, and the test sheet should have two completely smooth sides. Minor fiber pull-out was considered acceptable.

[0065] The test sheet was further examined for particles (specks) in both transmitted and reflected light. To pass the test, no particles could be visible on the test sheet.

[0066] The test result recorded was "Repulpable yes / no". Adhesive strength (measurement method C):

[0067] The adhesive strength was determined at a temperature of 23 °C + / - 1 °C and a relative humidity of 50 % + / - 5 %.

[0068] The paper substrates used were previously stored continuously in the test climate.

[0069] The following paper substrates were used: Label paper Raflatac 1600.9, glued to a flat PE board; CaCO3-containing paper: MediaPrint Silk 250 g, Stora Enso Uetersen, 100% CaCO3 in the coating; fixed to a PE board with tesa® 4965; Wallpaper topsheet 44540, 90 g / m², Koehler SE; fixed to a PE board with tesa® 4965.

[0070] A 20 mm wide and 250 mm long strip of the adhesive under investigation was applied to the paper in question. The adhesive strip was pressed onto the substrate twice with a pressure equivalent to a weight of 2 kg. The adhesive under investigation was then immediately and, when measuring on CaCO3-containing paper, additionally after storage of the adhesive for 3 days at 40 °C / 80% relative humidity and subsequently for 20 hours in the test climate The paper was pulled from the substrate at a speed of 300 mm / min and at an angle of 180°. The force required was measured using a tensile testing machine. The measurement results are given in N / cm and are averaged from three measurements. Splitting force (measurement method D):

[0071] This test determines the splitting strength of a paper in the z-direction. The splitting strength, or splitting force, is the force required to split the paper in the z-direction.

[0072] The adhesive to be tested was applied to both sides of a split paper (splittable in the z-direction, 69 µm, 73 g / m², splitting work < 30 cN / cm) by initially smoothing it with a finger to avoid air inclusions and then rolling over it twice with a hand roller. This bond was created so that on one side the ends of the adhesive strip extended beyond the test specimen and could be folded and glued together to form a handle. The measurements were immediately and after storing the test specimen for 1 month at 40 °C and 80% relative humidity carried out.

[0073] Using a steel ruler, 15 mm wide strips, 20 cm long, were cut from the composite material. The tabs were pulled apart by hand until the paper began to split.

[0074] The test specimen was clamped into a tensile testing machine by its handles, hanging freely at the top and bottom, and the strip was pulled apart at a speed of 300 mm / min (measurement climate 23 °C, 50% relative humidity).

[0075] The force required for this was measured and is given in Table 2 as the average of five measurements. Tack - Rolling Ball - Test (Measurement Method E):

[0076] In this test, a steel ball weighing 5.6 g rolled from a 65 mm high ramp onto a horizontal strip of the adhesive being tested. The distance traveled until the ball came to a stop was measured (test climate 23 °C, 50% relative humidity).

[0077] The spheres were cleaned with cellulose and acetone before measurement and conditioned in the test climate for 30 minutes.

[0078] The adhesive was conditioned in the test climate for one day before measurement. Production of the adhesives:

[0079] A conventional 300 L reactor for radical polymerizations was filled with a total of 100 kg of the monomers listed in Table 1, according to the composition also specified therein, and 72.4 kg of ethanol / water (70:30). After 45 minutes of nitrogen gas purging with stirring, the reactor was heated to 58 °C and 50 g of Vazo®< 67 was added. The jacket temperature was then increased to 80 °C and the reaction was carried out at a constant jacket temperature of 70 °C. After 1 h of reaction time, another 50 g of Vazo®< 67 was added. To reduce the residual initiators, a further 50 g of Vazo®< 67 was added after 6 h. The reaction was stopped after 24 h and the reactor cooled to room temperature. The solution was adjusted to a solids content of 30 wt%. The specified crosslinker was then stirred in.

[0080] The resulting composition was coated in solution onto a siliconized PET film using a comma-squeegee. The solvent was removed in a drying tunnel (20 min, 80 °C). The mass thus obtained was laminated as the adhesive under investigation onto a backing material specified in the respective test methods; the coating weight was 50 g / cm². Table 1: Composition of the adhesives Nr. Monomers (wt%, based on the monomer composition) Crosslinker (wt%, based on polymer) Acrylic acid 2-Hydroxyethyl acrylate N,N-Dimethylacrylamide Ethyl diglycol acrylate n-Butyl acrylate Aluminum acetylacetonate Titanium diisopropoxide bis(acetyl acetonate) 1* 5 95 0,33 2* 10 90 0,33 3* 22 28 35 15 0,33 4 5 20 75 0,33 5 5 30 65 0,33 6 10 10 80 0,33 7* 10 90 2 8* 20 80 2 9 1 30 69 2 10 3 20 77 2 11 5 30 65 3 12 10 10 80 3 * - Comparative example Table 2: Test results Nr. Repulpability Adhesive strength (N / cm) Rolling Ball (mm) Splitting force Label paper CaCO3 paper (immediately / after storage) Wallpaper top sheet immediately after storage (1 month at 40 °C / 80 % relative humidity) 1* No 2* No 3* Yes 7,7 6,42 / 3,73 6,2 208 not determined not determined 4 Yes 7,8 7,0 / 7,0 8,2 56 29 27,2 5 Yes 8 6,5 / 6,0 7,95 78 29,2 27,5 6 Yes 8,4 6,5 83 29,2 28,1 7* No 8* No 9 Yes 7,2 7,7 41 26,9 44,1 10 Yes 7 7,2 9 30,2 37,6 11 Yes 7,3 8,5 / 7,9 8,8 80 29,3 33,8 12 Yes 6,3 6,9 34 29,3 33,6 * - Comparative example

Claims

1. Pressure-sensitive adhesive comprising at least one polymer whose parent monomer composition comprises a) 10 to 30 wt% of at least one compound of the formula (I)         CH2=CH-C(O)NR1R2     (I), in which R1 is an unsubstituted alkyl group, a hydroxyalkyl group or an acetonyl radical and R2 is a hydrogen atom, an unsubstituted alkyl group, a hydroxyalkyl group, an acetyl radical or an aminoalkyl group; b) 60 to 80 wt% of ethyl diglycol acrylate; and c) 0.5 to 10 wt% of at least one monomer selected from the group consisting of acrylic acid, methacrylic acid and (C2-C4-hydroxyalkyl) acrylates.

2. Pressure-sensitive adhesive according to Claim 1, characterized in that R1 and R2 independently of one another are an unsubstituted alkyl group.

3. Pressure-sensitive adhesive according to any of the preceding claims, characterized in that the monomer composition comprises as monomer c) at least acrylic acid or 2-hydroxyethylacrylate.

4. Pressure-sensitive adhesive according to any of the preceding claims, characterized in that the polymer is thermally crosslinked.

5. Adhesive tape comprising a pressure-sensitive adhesive according to any of the preceding claims.

6. Use of a pressure-sensitive adhesive according to any of Claims1 to 4 and / or of an adhesive tape according to Claim 5 for producing water-soluble bonds.