Adhesive system made of a multiplicity of pressure-sensitive adhesive layers

Abstract

The intention is to provide an adhesive system which is stable in storage and which when used permits precise positioning of the adhesive, and which can be crosslinked without exceeding moderate temperatures. The said system is moreover intended to provide strong adhesive bonds that attain high performance levels. This is achieved via a kit containing at least two pressure-sensitive adhesive layers A and B, where the two pressure-sensitive adhesive layers A and B mutually independently respectively comprise at least one polymer containing a multiplicity of carboxy groups; in the pressure-sensitive adhesive layer A a portion of the carboxy groups of the polymer containing these has been activated by reaction with an activator AA; and—the pressure-sensitive adhesive layer A—at least one crosslinking agent V.sub.A which can enter into a crosslinking reaction with the carboxy groups of the polymer containing these of the pressure-sensitive adhesive layers A and B, but which in the pressure-sensitive adhesive layer A is not significantly reactive; —the pressure-sensitive adhesive layer B—at least one crosslinking agent V.sub.B which can accelerate the crosslinking reaction of the carboxy groups of the polymer containing these of the pressure-sensitive adhesive layer B with the crosslinking agent V.sub.A and which can permit and accelerate the crosslinking reaction of the carboxy groups of the polymer containing these of the pressure-sensitive adhesive layer A with the crosslinking agent V.sub.A and can enter into a crosslinking reaction with the activated carboxy groups of the polymer containing these of the pressure-sensitive adhesive layer A. The invention moreover also relates to an adhesive tape which is obtainable via contact between the pressure-sensitive adhesive layers of the kit, and to a process for producing said adhesive tape.

Claims

1. A kit comprising at least two pressure-sensitive adhesive layers A and B, where the two pressure-sensitive adhesive layers A and B independently of one another each comprise at least one polymer containing two or more carboxyl groups; in the pressure-sensitive adhesive layer A, some of the carboxyl groups of the polymer containing them are activated as a result of reaction with an activator A.sub.A; and, the pressure-sensitive adhesive layer A comprises: at least one crosslinker V.sub.A which is suitable for a crosslinking reaction with the carboxyl groups of the polymers comprising them in the pressure-sensitive adhesive layers A and B, but is not substantially reactive in the pressure-sensitive adhesive layer A when said layer A is not in contact with layer B; the pressure-sensitive adhesive layer B comprises: at least crosslinker V.sub.B which is suitable for accelerating the crosslinking reaction of the carboxyl groups of the polymer containing them in the pressure-sensitive adhesive layer B with the crosslinker V.sub.A, and enabling and accelerating the crosslinking reaction of the carboxyl groups of the polymer comprising them in the pressure-sensitive adhesive layer A with the crosslinker V.sub.A, and for the crosslinking reaction with the activated carboxyl groups of the polymer comprising them in the pressure-sensitive adhesive layer A.

2. The kit according to claim 1, wherein the polymer comprising two or more carboxyl groups in the pressure-sensitive adhesive layer A is poly(meth)acrylate.

3. The kit according to claim 1, wherein the polymer comprising two or more carboxyl groups in the pressure-sensitive adhesive layer B is a poly(meth)acrylate.

4. The kit according to claim 1 wherein the activator A.sub.A is selected from the group consisting of: carbodiimides, benzotriazolyl-N-oxyphosphonium compounds, azabenzotriazolyl-N-oxyphosponium compounds, O-(benzotriazole-1-yl)uranium compounds, O-(7-azabenzotriasol-1-ykl)uranium compounds, N-uronium-substituted cyclic imides, thiophosphinic chlorides, thiophosphinic azides, triazyl esters and α-halopyridinum salts.

5. The kit according to claim 1 wherein the crosslinker V.sub.A is a polyfunctional epoxide.

6. The kit according to claim 1 wherein the crosslinker V.sub.B is selected from the group consisting of: polyester polyols, polyfunctional amines and polyfunctional alcohols.

7. An adhesive tape formed by: contacting at least two pressure-sensitive adhesive layers A and B where the two pressure-sensitive adhesive layers A and B independently of one another each comprise at least one polymer containing at least one polymer containing two or more carboxyl groups; in the pressure-sensitive adhesive layer A, some of the carboxyl groups of the polymer comprising them are activated as a result of reaction with an activator A.sub.A; and, the pressure-sensitive adhesive layer A comprises: at least one crosslinker V.sub.A which is suitable for a crosslinking reaction with the carboxyl groups of the polymers comprising them in the pressure-sensitive adhesive layers A and B, but is not substantially reactive in the pressure-sensitive adhesive layer A when said layer A is not in contact with layer B; the pressure-sensitive adhesive layer B comprises: at least crosslinker V.sub.B which is suitable for accelerating the crosslinking reaction of the carboxyl groups of the polymer containing them in the pressure-sensitive adhesive layer B with the crosslinker V.sub.A, and for enabling and accelerating the crosslinking reaction of the carboxyl groups of the polymer comprising them in the pressure-sensitive adhesive layer A with the crosslinker V.sub.A, and for the crosslinking reaction with the activated carboxyl groups of the polymer comprising them in the pressure-sensitive adhesive layer A.

8. The adhesive tape according to claim 7, in that it is formed by the contacting of two or more pressure-sensitive adhesive layers A and/or B.

9. The adhesive tape according to claim 8, wherein that it has a structure of the form A-B-A or has an alternating structure A-B-A-B-A-B-A . . . and the outermost layers in each structure are formed of a pressure-sensitive adhesive layer A.

10. A method of producing an adhesive tape, comprising: contacting at least two pressure-sensitive adhesive layers A and B where the said two pressure-sensitive adhesive layers A and B independently of one other each comprise at least one polymer containing at least one polymer containing two or more carboxyl groups; in the pressure-sensitive adhesive layer A, some of the carboxyl groups of the polymer comprising them are activated as a result of reaction with an activator A.sub.A; and, the pressure-sensitive adhesive layer A comprises: at least one crosslinker V.sub.A which is suitable for a crosslinking reaction with the carboxyl groups of the polymers comprising them in the pressure-sensitive adhesive layers A and B, but is not substantially reactive in the pressure-sensitive adhesive layer A when said layer A is not in contact with layer B; the pressure-sensitive adhesive layer B comprises: at least crosslinker V.sub.B which is suitable for accelerating the crosslinking reaction of the carboxyl groups of the polymer containing them in the pressure-sensitive adhesive layer B with the crosslinker V.sub.A, and for enabling and accelerating the crosslinking reaction of the carboxyl groups of the polymer comprising them in the pressure-sensitive adhesive layer A with the crosslinker V.sub.A, and for the crosslinking reaction with the activated carboxyl groups of the polymer comprising them in the pressure-sensitive adhesive layer A.

Description

EXAMPLES

(1) Unless indicated otherwise or evident individually, the sample preparation and measurement procedures take place under standard conditions (25° C., 101 325 Pa).

(2) I. Static Glass Transition Temperature Tg

(3) The static glass transition temperature is determined via dynamic scanning calorimetry according to DIN 53765. The figures for the glass transition temperature Tg are based on the glass transformation temperature Tg according to DIN 53765:1994-03, unless otherwise indicated in a specific case.

(4) II. Molecular Weights The average molecular weights (weight average Mw and number average Mn) and the polydispersity D were determined by gel permeation chromatography (GPC). The eluent used was THF with 0.1 vol % of trifluoroacetic acid. Measurement took place at 25° C. The pre-column used was PSS-SDV, 5 μm, 10.sup.3 Å (10.sup.−7 m), ID 8.0 mm×50 mm. Separation took place using the columns PSS-SDV, 5 μm, 10.sup.3 Å (10.sup.−7 m), 10.sup.5 Å (10.sup.−5 m) and 10.sup.6 Å (10.sup.−4 m) each with ID 8.0 mm×300 mm. The sample concentration was 4 g/L, the flow rate 1.0 ml per minute. Measurement was made against PMMA standards.

(5) III. Solids Content:

(6) The solids content is a measure of the fraction of unevaporable constituents in a polymer solution. It is determined gravimetrically by weighing the solution, then evaporating off the evaporable fractions in a drying cabinet at 120° C. for 2 hours and reweighing the residue.

(7) IV. K Value (According to Fikentscher):

(8) The K value is a measure of the average molecular size of high-polymer compounds. For the purpose of the measurement, one percent strength (1 g/100 ml) toluenic polymer solutions were prepared and their kinematic viscosities were determined by means of a Vogel-Ossag viscometer. Following standardization to the viscosity of the toluene, the relative viscosity is obtained, from which the K value can be computed by the method of Fikentscher (Polymer 8/1967, 381 ff.).

(9) V. Shear Strength: Static Shear Test HP

(10) A strip of the adhesive tape, 13 mm wide and 30 mm long, was applied to a smooth steel surface which had been cleaned three times with acetone and once with isopropanol. The bond area was 20 mm.Math.13 mm (length.Math.width), and so the adhesive tape overhung the test plate at the edge by 10 mm. The adhesive tape was subsequently pressed onto the steel support four times with an applied pressure corresponding to a weight of 2 kg. This sample was suspended vertically so that the protruding end of the adhesive tape pointed downward.

(11) At room temperature a weight of 1 kg was affixed to the protruding end of the adhesive tape. The measurement was conducted under standard conditions (23° C.+/−1° C., 55%+/−5% atmospheric humidity) and at 70° C. in a heating cabinet, the sample for this measurement having been loaded with a weight of 0.5 kg.

(12) The holding powers measured (times taken for the adhesive tape to detach completely from the substrate; measurement terminated at 10 000 minutes) are reported in minutes and correspond to the average from three measurements.

(13) VI. Peel Strength (Peel Adhesion) PA

(14) A strip of the adhesive tape under investigation is bonded in a defined width (standard: 20 mm) to a sanded steel plate (stainless steel 302 according to ASTM A 666; 50 mm×125 mm×1.1 mm; bright annealed surface; surface roughness Ra=50±25 nm average arithmetic deviation from the baseline) by being rolled down ten times with a 4 kg steel roller. Double-sided adhesive tapes are reinforced on the reverse with an unplasticized PVC film 36 μm thick. Identical samples are produced and are alternatively provided for immediate measurement, stored for 7 days and then measured, or stored for 14 days and then measured.

(15) The prepared plate is clamped (fixed) into the testing apparatus, and the adhesive strip is peeled from the plate via its free end in a tensile testing machine at a peel angle of 180° and at a speed of 300 mm/min in the longitudinal direction of the adhesive tape. The force necessary for performing this operation is recorded. The results of the measurements are reported in N/cm (force standardized to the particular distance of bond parted) and are averaged over three measurements. All of the measurements are carried out in a conditioned chamber at 23° C. and 50% relative humidity.

(16) VII. Microshear Test

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

(18) Sample Preparation for Microshear Test:

(19) An adhesive tape (length 50 mm, width 10 mm) cut from the respective sample specimen is bonded to a steel test plate cleaned with acetone, so that the steel plate protrudes beyond the adhesive tape to the right and left, and so that the adhesive tape protrudes beyond the test plate by 2 mm at the top edge. The bond area of the sample in terms of height.Math.width=13 mm.Math.10 mm. The bond site is subsequently rolled down six times with a 2 kg steel roller at a speed of 10 m/min. The adhesive tape is reinforced flush with a stable adhesive strip which serves as a support for the travel sensor. The sample is suspended vertically by means of the test plate.

(20) Microshear Test:

(21) The sample specimen under measurement is loaded at the bottom end with a 100 g weight. The test temperature is 40° C., the test time 30 minutes (15 minutes of loading and 15 minutes of unloading). The shear travel after the specified test duration at constant temperature is reported as the result, in μm, as both the maximum value [“max”; maximum shear travel as a result of 15-minute loading] and the minimum value [“min”; shear travel (“residual deflection”) 15 minutes after unloading; on unloading there is a backward movement as a result of relaxation]. Likewise reported is the elastic component in percent [“elast”; elastic component=(max−min).Math.100/max].

(22) VIII. Dynamic Shear Strength:

(23) A square of adhesive transfer tape with an edge length of 25 mm is bonded between two steel plates and the bond is pressed down at 0.9 kN (force P) for 1 minute. Following storage for 24 hours, the assembly is parted in a tensile testing machine from Zwick, at 50 mm/min and at 23° C. and 50% relative humidity, in such a way that the two steel plates are pulled apart at an angle of 180°. The maximum force is ascertained, in N/cm.sup.2.

(24) TABLE-US-00001 TABLE 1 Raw materials used: Chemical compound Trade name Manufacturer CAS No. Bis(4-tert-butylcyclohexyl) Perkadox ® 16 Akzo Nobel 15520-11-3 peroxydicarbonate 2,2′-Azobis(2-methylbutyronitrile) Vazo ® 67 DuPont 13472-08-7 Benzotriazol-1-yl- PyBOP ® Merck Millipore 128625-52-5 oxytripyrrolidinophosphonium hexafluorophosphate 2-Bromo-1-ethylpyridinium BEP ® Sigma-Aldrich 878-23-9 tetrafluoroborate Dicyclohexylcarbodiimide DCC ® Sigma-Aldrich 538-75-0 2,4-Dichloro-6-methoxy-1,3,5- DCMT ® Sigma-Aldrich 3638-04-8 triazine 5-Amino-1,3,3- Isophoronediamine Sigma Aldrich 2855-13-2 trimethylcyclohexanemethylamine (IPDA) Ethylene glycol EG Sigma-Aldrich 40771-26-4 Pentaerythritol polyglycidyl ether Polypox R16 DOW Chemical 30973-88-7 Acrylic acid n-butyl ester n-Butyl acrylate Rohm & Haas 141-32-2 Acrylic acid Acrylic acid, pure BASF 79-10-7 2-Ethylhexyl acrylate Brenntag 103-11-7

(25) Preparation of Base Polymer Ac1

(26) A reactor conventional for radical polymerizations was charged with 30.0 kg of 2-ethylhexyl acrylate, 67.0 kg of butyl acrylate, 3.0 kg of acrylic acid and 66.7 kg of acetone/isopropanol (96:4). After nitrogen gas had been passed through the reactor for 45 minutes with stirring, the reactor was heated up to 58° C. and 50 g of Vazo 67 in solution in 500 g of acetone were added. The external heating bath was subsequently heated to 70° C. and the reaction was carried out constantly at this external temperature. After 1 hour a further 50 g of Vazo 67 in solution in 500 g of acetone were added, and after 2 hours the batch was diluted with 10 kg of acetone/isopropanol mixture (96:4). After 5.5 hours, 150 g of bis-(4-tert-butylcyclohexyl)eroxydicarbonate in solution in 500 g of acetone were added; after 6 hours 30 minutes, the batch was again diluted with 10 kg of acetone/isopropanol mixture (96:4). After 7 hours, a further 150 g of bis-(4-tert-butylcyclohexyl)peroxydicarbonate in solution in 500 g of acetone were added, and the heating bath was set to a temperature of 60° C.

(27) After a reaction time of 22 hours, the polymerization was discontinued and the batch was cooled to room temperature. The product had a solids content of 50.2%. The resulting polyacrylate had a K value of 75.2, a weight-average molecular weight Mw of 1370000 g/mol, a polydispersity D (Mw/Mn) of 17.13 and a static glass transition temperature Tg of −38.0° C.

(28) Preparation of Base Polymer Ac2

(29) A reactor conventional for radical polymerizations was charged with 47.0 kg of 2-ethylhexyl acrylate, 47.0 kg of butyl acrylate, 9.0 kg of acrylic acid and 72.4 kg of acetone/benzine (50:50). After nitrogen gas had been passed through the reactor for 45 minutes with stirring, the reactor was heated up to 58° C. and 50 g of Vazo 67 in solution in 500 g of acetone were added. The external heating bath was subsequently heated to 70° C. and the reaction was carried out constantly at this external temperature. After 1 hour a further 50 g of Vazo 67 in solution in 500 g of acetone were added, and after 2 hours the batch was diluted with 10 kg of acetone/isopropanol mixture (96:4). After 5.5 hours, 150 g of bis-(4-tert-butylcyclohexyl)peroxydicarbonate in solution in 500 g of acetone were added; after 6 hours 15 minutes, the batch was again diluted with 10 kg of acetone/benzine mixture (50:50). After 7 hours, a further 150 g of bis-(4-tert-butylcyclohexyl)peroxydicarbonate in solution in 500 g of acetone were added, and the heating bath was set to a temperature of 60° C.

(30) After a reaction time of 22 hours, the polymerization was discontinued and the batch was cooled to room temperature. The product had a solids content of 39.7%. The resulting polyacrylate had a K value of 64.2, a weight-average molecular weight Mw of 946000 g/mol, a polydispersity D (Mw/Mn) of 68.69 and a static glass transition temperature Tg of −47.0° C.

(31) Preparation of Base Polymer Ac3

(32) A reactor conventional for radical polymerizations was charged with 45.5 kg of 2-ethylhexyl acrylate, 45.5 kg of butyl acrylate, 9.0 kg of acrylic acid and 72.4 kg of acetone/benzine (50:50). After nitrogen gas had been passed through the reactor for 45 minutes with stirring, the reactor was heated up to 58° C. and 50 g of Vazo 67 in solution in 500 g of acetone were added. The external heating bath was subsequently heated to 70° C. and the reaction was carried out constantly at this external temperature. After 1 hour a further 50 g of Vazo 67 in solution in 500 g of acetone were added, and after 2 hours the batch was diluted with 10 kg of acetone/isopropanol mixture (96:4). After 5.5 hours, 150 g of bis-(4-tert-butylcyclohexyl)peroxydicarbonate in solution in 500 g of acetone were added; after 6 hours, the batch was again diluted with 10 kg of acetone/benzine mixture (50:50). After 7 hours, a further 150 g of bis-(4-tert-butylcyclohexyl)peroxydicarbonate in solution in 500 g of acetone were added, and the heating bath was set to a temperature of 60° C.

(33) After a reaction time of 22 hours, the polymerization was discontinued and the batch was cooled to room temperature. The product had a solids content of 41.3%. The resulting polyacrylate had a K value of 55.0, a weight-average molecular weight Mw of 904000 g/mol, a polydispersity D (Mw/Mn) of 44.89 and a static glass transition temperature Tg of −39° C.

(34) The base polymers Ac1, Ac2 and Ac3, present in solution, were each diluted to a solids content of 35% with acetone, then blended with a 10% strength solution of the activator and/or crosslinker in acetone, and subsequently coated from solution onto a siliconized release film (50 μm polyester) as a transfer specimen with a coating speed of 2.5 m/min. The coat weight in each case here was 50 g/m.sup.2. The specimens were dried in a drying cabinet at 80° C. for 15 minutes. Specimens KB 4 to KB 13 consisted of a plurality of layers, which after coating were in each case evaporated off likewise in a drying cabinet (80° C., 15 minutes) and, after cooling to room temperature, were laminated together, to give a coat weight of 100 g/m.sup.2 in total in the case of two-layer specimens and 150 g/m.sup.2 in the case of three-layer specimens.

(35) No measurements could be carried out with KB 14, because the specimen exhibited gelling in the glass even after blending and could no longer be coated onto the release film.

(36) Production of Adhesive Tapes KB 1 to KB 13

(37) TABLE-US-00002 TABLE 2 Adhesive-specific details Layer 1 Layer 2 Activator Crosslinker Crosslinker/activator Number fraction fraction 2.sup.nd fraction of 1.sup.st Base [n.sub.activator/n.sub.COOH; [n.sub.crosslinker/n.sub.COOH; Base Crosslinker/ [n.sub.crosslinker/n.sub.COOH; in Name layers polymer Activator in mol %] Crosslinker in mol %] polymer activator mol %] KB 1* One Ac1 — — Polypox R16 3.6 — — — KB 2* One Ac1 IPDA 28.21 Polypox R16 3.6 — — — KB 3* One Ac1 PyBOP 1.29 Polypox R16 3.6 — — — KB 4* Two Ac1 — — Polypox R16 3.6 Ac1 IPDA 28.21 KB 5* Two Ac1 PyBOP 2.77 — — Ac1 IPDA 4.23 KB 6* Two Ac1 PyBOP 2.77 — — Ac1 EG 4.39 KB 7 Two Ac1 PyBOP 2.77 Polypox R16 3.6 Ac1 IPDA 4.23 KB 8 Two Ac1 DCC 7 Polypox R16 3.6 Ac1 IPDA 4.23 KB 9 Two Ac1 DCMT 8 Polypox R16 3.6 Ac1 IPDA 4.23 KB 10 Two Ac1 BEP 5.3 Polypox R16 3.6 Ac1 IPDA 4.23 KB 11** Three Ac1 PyBOP 2.77 Polypox R16 3.6 Ac1 IPDA 4.23 KB 12** Three Ac2 PyBOP 1.38 Polypox R16 1.8 Ac2 IPDA 2.12 KB 13** Three Ac3 PyBOP 0.92 Polypox R16 1.2 Ac3 IPDA 1.41 KB 14* One Ac1 PyBOP 2.77 IPDA 4.23 — — — *Specimens KB 1-KB 6 and KB 14 serve as comparative examples. **Specimens KB 11, KB 12 and KB 13 consist of a three-layer assembly, with the two outer layers corresponding to the 1.sup.st base polymer and the middle layer to the base polymer 2.

(38) TABLE-US-00003 TABLE 3 Determination of crosslinking state from the elastic component after different storage times at room temperature Elastic Elastic Elastic Layer component component component [%] construction [%] 0dRT [%] 7dRT 14dRT KB 1* one-layer 0 0 4 KB 2* one-layer 0 14 30 KB 3* one-layer 0 0 5 KB 4* two-layer 0 0 21 KB 5* two-layer 15 30 45 KB 6* two-layer 9 25 42 KB 7 two-layer 30 49 63 KB 8 two-layer 28 39 55 KB 9 two-layer 24 36 54 KB 10 two-layer 25 33 57 KB 11** three-layer 36 52 67 KB 12** three-layer 38 57 70 KB 13** three-layer 37 59 71 *KB 1-KB 6 serve as comparative examples. **KB 11 to KB 13 are constructed as a 3-layer assembly, with the two outer layers consisting of the same base polymer.

(39) In all of the investigations for properties after different storage times at room temperature, the completed product consisting of a plurality of layers laminated together was the product stored in each case for multilayer constructions. “0dRT” means that the products were stored for half a day at room temperature in order to enable initial crosslinking particularly in the case of the multilayer products.

(40) The elastic component measurements were made according to “Microshear test”, test method VII, and they serve as a measure for determining the crosslinking state. The greater the elastic component, the further advanced the crosslinking. It is evident on the basis of table 3 that significantly accelerated crosslinking is exhibited even by the two-layer systems of the invention. Through the three-layer construction, this can be accelerated again.

(41) TABLE-US-00004 TABLE 4 Results of the peel adhesion measurements on different substrates after storage at room temperature Peel adhesion, steel at 300 mm/min Peel adhesion, PE at 300 mm/min Method [N/cm] [N/cm] Storage 0 d RT 7 dR T 14 d RT 0 d RT 7 d RT 14 d RT KB 1* 12.8 (C) 12.5 (C) 10.3 (M) 5.4 (A)   5 (A) 4.3 (A) KB 2* 12.1 (C) 11.5 (C)  9.9 (M) 4.7 (A)   4 (A) 3.7 (A) KB 3* 12.6 (C) 12.7 (C) 10.8 (M) 5.3 (A) 4.9 (A) 4.1 (A) KB 4* 12.3 (C) 11.9 (C) 11.0 (M) 5.7 (A) 5.2 (A) 4.6 (A) KB 5* 10.9 (M)  9.6 (A)  8.7 (A) 4.3 (A) 3.8 (A) 3.9 (A) KB 6* 11.4 (M) 10.1 (A)  9.2 (A) 4.8 (A) 4.2 (A) 3.9 (A) KB 7 10.7 (A)  9.4 (A)  8.3 (A) 4.6 (A) 4.3 (A) 4.2 (A) KB 8 10.6 (A)   10 (A)  8.1 (A) 4.4 (A) 4.4 (A) 4.3 (A) KB 9   11 (A) 10.3 (A)  8.5 (A) 4.4 (A) 4.5 (A) 4.3 (A) KB 10 10.8 (A)  9.7 (A)  8.8 (A) 4.5 (A) 4.6 (A) 4.3 (A) KB 11  9.7 (A)  8.8 (A)  7.6 (A) 4.3 (A) 4.1 (A) 4.1 (A) KB 12  8.9 (A)  8.2 (A)  7.7 (A) 3.3 (A) 3.9 (A) 3.4 (A) KB 13  8.5 (A)  8.1 (A)  7.4 (A) 5.9 (A) 5.8 (A) 5.5 (A) *Comparative experiments

(42) The measurement of the peel adhesion as well, carried out according to test method VI at a 180° angle and 300 mm/min on a steel or PE substrate, respectively, shows after-crosslinking of the samples. The specimens display a change in the fracture behavior from C (cohesive fracture) via M (mixed fracture) through to A (adhesive fracture). Moreover, a drop in the peel strength after prolonged storage can be recorded. This likewise suggests after-crosslinking.

(43) TABLE-US-00005 TABLE 5 Values of the measurement of holding power and shear strength after storage at room temperature Method Holding power [min] Dynamic shear test [N/cm.sup.2] Storage 0 d RT 7 d RT 14 d RT 0 d RT 7 d RT 14 d RT KB 1*  25 (C)  102 (C)  657 (M)  9.3 (C) 13.7 (C) 25.2 (C) KB 2*  36 (C)  89 (C)  469 (M) 10.5 (C) 18.3 (C) 29.7 (C) KB 3*  13 (C)  98 (C)  597 (M)  9.9 (C) 19.4 (C) 20.4 (C) KB 4*  37 (C)  68 (C)  479 (M) 10.7 (C) 19.3 (C) 27.5 (C) KB 5*  45 (C)  207 (C)  903 (M) 22.1 (C) 30.5 (C) 40.8 (C) KB 6*  39 (C)  198 (C)  798 (M) 23.3 (C) 31.2 (C) 38.3 (C) KB 7 214 (C)  638 (M) 4113 (A) 25.7 (C) 42.8 (C) 50.2 (M) KB 8 369 (C)  701 (M) 3997 (A) 20.8 (C) 39.1 (C) 49.8 (M) KB 9 414 (C)  540 (M) 4141 (A) 21.2 (C) 35.6 (C) 51.3 (M) KB 10 317 (C)  497 (M) 3774 (A) 19.6 (C) 28.9 (C) 47.5 (M) KB 11 588 (M) 1948 (A) 6929 (A) 27.4 (C) 45.0 (M) 60.7 (A) KB 12 573 (M) 2505 (A) 6320 (A)   30 (C) 49.2 (M) 63.9 (A) KB 13 614 (M) 1101 (A) 7493 (A) 32.5 (C) 55.7 (M) 72.1 (A) *Comparative experiments

(44) This is also made clear by the holding powers from the measurement according to test method V and from the values from the dynamic shear test according to test method VII. Apparent there over time likewise is a change in the fracture behavior of the specimens, and the shear strength increases with time as well. In the dynamic shear test, similar behavior is evident.

(45) Adhesive performance testing shows that the use of a multicomponent system with utilization of differently blended PSAs and with use of an activator affords significant advantages in relation to crosslinking time at room temperature.

(46) Further to the room temperature storage, the specimens and/or their individual layers were stored at 60° C. for a total of 4 weeks. Subsequently—and in this case, therefore, only after storage had taken place—the multilayer specimens, after cooling to room temperature, were laminated together and stored for half a day at room temperature; subsequently the microshear test was carried out on all of the samples. Here it was found that the samples KB 1, KB 2, KB 3 and KB 4 had significantly higher elastic components than in the case of the measurement after 0 days at room temperature. Conversely, the specimens KB 5 to KB 13 laminated together after 60° C. storage, but especially the specimens KB7 to KB 13, showed values comparable to or insignificantly greater than those in the case of measurement straight after coating and drying. Accordingly, the specimens of the invention exhibit storage stability even at relatively high temperatures.

(47) TABLE-US-00006 TABLE 6 Determination of crosslinking state from the elastic component after different storage times at room temperature and 60° C. Elastic Construction Elastic Elastic component [%] at component component 4 weeks measurement [%] 0dRT [%] 14dRT storage 60° C. KB 1* one-layer 0 4 60 KB 2* one-layer 0 30 85 KB 3* one-layer 0 5 7 KB 4* two-layer 0 21 45 KB 5* two-layer 15 45 42 KB 6* two-layer 9 42 46 KB 7 two-layer 30 63 63 KB 8 two-layer 28 55 60 KB 9 two-layer 24 54 59 KB 10 two-layer 25 57 57 KB 11** three-layer 36 67 73 KB 12** three-layer 38 70 71 KB 13** three-layer 37 71 73 *KB 1-KB 6 serve as comparative examples. **KB 11 to KB 13 are constructed as a 3-layer assembly, with the two outer layers consisting of the same base polymer.