Adhesives, UV-crosslinkable PSAs and bonding agents with UV-crosslinked PSAs

Abstract

Adhesives and pressure-sensitive adhesives comprising polymerization products of acrylates, the adhesives being meltable and comprising polymerization products of esters of (meth)acrylic acid and (meth)acrylic acid, the polymerization product having a molecular weight Mn of greater than 50 000 g/mol and Mw of greater than 500 000 g/mol.

Claims

1. Adhesive comprising polymerization products of acrylates, the adhesive being meltable, wherein it comprises at least one polymerization product synthesized from a) 75 to 99.9 wt % of esters of (meth)acrylic acid of the general formula I, ##STR00007## wherein R.sub.1H or CH.sub.3 and R.sub.2 is a linear, branched or cyclic alkyl chain having 2 to 20 C atoms, b) 0.1 to 25 wt % of (meth)acrylic acid of the formula II, ##STR00008## where R.sub.3H or CH.sub.3, and the sum of all the components used makes 100 wt % of the polymerization product, the polymerization product having a molecular weight Mn greater than 50 000 g/mol and Mw greater than 500 000 g/mol, and wherein tan , the ratio of loss modulus G to storage modulus G, is between 0.45tan 0.50 for a measuring frequency of 0.1 rad/s.

2. Adhesive according to claim 1, wherein it further comprises c) olefinically unsaturated monomers having functional groups and/or d) olefinically unsaturated monomers which are copolymerizable with component (a) and/or (b).

3. Adhesive according to claim 1, wherein the polymerization product has a static glass transition temperature (T.sub.g) of less than or equal to 0 C.

4. Adhesive according to claim 1, wherein the polymerization product comprises (a) 80 to 99.9 wt % of esters of (meth)acrylic acid of the general formula I, (b) 0.1 to 20 wt % of (meth)acrylic acid of the formula II, (c) 0 to 10 wt % of olefinically unsaturated monomers having functional groups, (d) 0 to 10 wt % of olefinically unsaturated monomers, the sum of all of the components used making 100 wt %.

5. Adhesive according to claim 1, wherein the polymerization product has a residual monomer content of less than or equal to 1 wt % in respect of the overall composition of the adhesive.

6. Adhesive according to claim 1, wherein the K value is greater than or equal to 40.

7. Adhesive according to claim 1, wherein the polydispersity Q of the polymerization product, where Q=Mw/Mn, is greater than or equal to 5.

8. Pressure-sensitive adhesive wherein the pressure-sensitive adhesive is UV-crosslinkable and meltable and comprises a) an adhesive according to claim 1, and b) at least one photoinitiator selected from the group consisting of -cleavers, benzophenone derivatives and thioxanthone derivatives.

9. Pressure-sensitive adhesive according to claim 8, wherein the -cleaver is selected from the group consisting of -hydroxy ketones and derivatives thereof.

10. Pressure-sensitive adhesive according to claim 9, wherein a) the -cleaver is selected from the group consisting of oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone], 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl) phenoxy]phenyl}-2-methyl-propan-1-one, 2,4,6-trimethylbenzophenone and also mixtures comprising at least two of the aforesaid -cleavers.

11. Pressure-sensitive adhesive according to claim 10, wherein the amount of at least one -cleaver in the overall composition of the adhesive is 0.25 to 0.75 wt %.

12. Process for preparing the pressure-sensitive adhesive according to claim 8, by mixing (i) an adhesive comprising at least one polymerization product synthesized from (a) 75 to 99.9 wt % of esters of (meth)acrylic acid of the formula I, ##STR00009## where R.sub.1H or CH.sub.3 and R.sub.2 is an alkyl chain having 2 to 20 C atoms and (b) 0.1 to 25 wt % of (meth)acrylic acid of the formula II, ##STR00010## where R.sub.3H or CH.sub.3, and the sum of all the components used makes 100 wt % of the polymerization product, the polymerization product having a molecular weight Mn of greater than 50.000 g/mol and Mw of greater than 500 000 g/mol, with (ii) at least one photoinitiator selected from the group consisting of -cleavers and benzophenone derivatives.

13. Pressure-sensitive adhesive obtained by a process according to claim 12.

14. Method for producing a bonding agent, a transfer adhesive, an adhesive transfer tape, a coated carrier, or an adhesive tape, where the meltable pressure-sensitive adhesive of claim 8 is discharged as a melt in the temperature range from 60 to 200 C. with a coatweight of 20 to 250 g/cm.sup.3 to give a layer which is optionally applied to a carrier or to a transfer medium, and the layer is crosslinked with high-energy radiation.

15. Method according to claim 14, the application of adhesive taking place in the form of a uniform layer with a layer thickness of 2 to 200 m, with optional application of the layer to a carrier or to a transfer medium.

16. Method according to claim 15, the adhesive being applied to a carrier or to a transfer medium selected from woven fabric, nonwoven fabric, film and paper.

17. Bonding agent obtained by the method of claim 14.

18. Bonding agent according to claim 17, wherein the TFT (Threshold Flagging Time) in minutes is greater than or equal to 1000 minutes.

19. Bonding agent according to claim 18, wherein it has a holding power (HP) of greater than or equal to 100 minutes under standard conditions (23 C., 55% humidity), the holding power being measured in minutes as the time taken for the adhesive tape to detach fully from the substrate.

20. Bonding agent according to claim 19 in the form of a flat bonding agent or in the form of a carrier or a transfer medium coated with a UV-crosslinked pressure-sensitive adhesive, the bonding agent being a flat bonding agent selected from the group consisting of a label, adhesive tape, cable wrapping tape, protective sheet, flat transfer adhesive and an adhesive transfer tape.

21. Flat bonding agent according to claim 19, wherein it is an adhesive tape comprising a textile carrier.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The adhesive tape will now be more particularly elucidated using several figures without any intention thereby to cause any kind of restriction.

(2) In the figures

(3) FIG. 1 shows the adhesive tape in lateral section,

(4) FIG. 2 shows a detail of a cable harness composed of a bundling of individual cables and jacketed with the adhesive tape of the invention, and

(5) FIG. 3 shows an advantageous use of the adhesive tape.

(6) FIG. 4 illustrates the TFT method for measurement of flagging resistance.

(7) FIG. 5 illustrates a test strip assembly for use in the flagging resistance test.

(8) FIG. 6 illustrates a test strip bonded to an adhesion base.

(9) FIG. 7 illustrates test samples adhered to a card core.

(10) FIG. 1 shows a section in the transverse direction (cross section) of the adhesive tape, which consists of a woven fabric carrier 1 applied on one side of which is a layer of a self-adhesive coating 2.

(11) FIG. 2 shows a detail of a cable harness which is composed of a bundling of individual cables 7 and which is jacketed with the adhesive tape 11 of the invention. The adhesive tape is guided in a helical-linear movement around the cable harness.

(12) The cable harness detail shown shows two windings I and II of the adhesive tape. Further windings would extend towards the left; they are not depicted here.

(13) In a further embodiment for jacketing, two tapes of the invention, 60 and 70, furnished with an adhesive, are laminated onto one another with their adhesives offset (preferably by 50% in each case), to produce a product as depicted in FIG. 3.

EXPERIMENTAL SECTION

(14) The exemplary experiments below are intended to elucidate the invention in more detail, without any intention that the invention should be unnecessarily restricted through the choice of examples given.

(15) Measurement Methods (General):

(16) Static Glass Transition Temperature Tg:

(17) The static glass transition temperature is determined via dynamic scanning calorimetry in accordance with DIN 53765. The figures for the glass transition temperature Tg relate to the glass transformation temperature value Tg according to DIN 53765:1994-03, unless specifically indicated otherwise.

(18) Dynamic mechanical analysis (DMA) for the determination of loss factor tan procedure: loss factor values (and also loss modulus values and storage modulus values) are determined by means of frequency sweep. All data for the purposes of this specification relate to the results of these measurements, unless specifically indicated otherwise. In DMA, use is made of the fact that the properties of viscoelastic materials subject to a sinusoidal mechanical stress are dependent on the frequency of the stress (in other words on the time) and on the temperature.

(19) DMA procedure: instrument: Rheometric Scientific RDA III; measuring head: spring-mounted with standard force; heating: heating chamber; measurement geometry: parallel plate arrangement, sample thickness 1 (0.1) mm; sample diameter 25 mm (to produce a sample 1 mm thick, five layers (each 200 m) of the adhesive tape under investigation were laminated to one another; since the PET carrier does not make any critical contribution to the rheological properties, its presence can be disregarded).

(20) In DMA, use is made of the fact that the properties of viscoelastic materials subject to a sinusoidal mechanical stress are dependent on the frequency of the stress (in other words on the time) and on the temperature. In the case of the TTS method, frequency measurements conducted at regular temperature intervals are calculated to give a frequency sweep; by this means, the range accessible through the measurements can be expanded by a number of decades downwards and upwards.

(21) All DMA procedures: measuring instrument: Rheometric Scientific RDA III; measuring head: spring-mounted with standard force; heating: heating chamber; measurement geometry: parallel plate arrangement, sample thickness 1 (0.1) mm; sample diameter 25 mm (to produce a sample 1 mm thick, five layers (each 200 m) of the adhesive tape under investigation were laminated to one another; since the PET carrier does not make any critical contribution to the rheological properties, its presence can be disregarded). Method tan (0.1 rad/s), 25 C. by means of DMA

(22) SAFTShear Adhesive Failure Temperature:

(23) This test is used for accelerated testing of the shear strength of adhesive tapes under temperature load. For the test, the adhesive tape under investigation is adhered to a heatable steel plate and loaded with a weight (50 g), and the shear travel is recorded.

(24) Sample Preparation:

(25) The adhesive tape under investigation is adhered to an aluminium foil 50 m thick. The adhesive tape thus prepared is cut to a size of 10 mm50 mm. The cut-to-size adhesive tape sample is bonded to a polished steel test plate cleaned with acetone (steel material 1.4301, DIN EN 10088-2, surface 2R, surface roughness Ra=30 to 60 nm, dimensions 50 mm13 mm1.5 mm) in such a way that the bond area of the sample is 13 mm10 mmheightwidthand the steel test plate protrudes by 2 mm at the upper edge. The bond is then fixed by rolling a 2 kg steel roller over it six times at a speed of 10 m/min. At the top the sample is reinforced flush with a stable adhesive strip which serves as a support for the travel sensor. Using the steel plate, the sample is then suspended such that the adhesive tape end with the longer overhang points vertically downwards.

(26) Measurement:

(27) The sample for measurement is loaded at the bottom end with a 50 g weight. The steel test plate with the bonded sample is heated to the end temperature of 200 C., beginning at 25 C. and at a rate of 9 C. per minute. The slip travel of the sample is observed by means of a travel sensor, as a function of temperature and time. The maximum slip travel is set at 1000 m (1 mm); if exceeded, the test is discontinued. Test conditions: room temperature 233 C., relative humidity 505%. The test is considered passed (the sample sufficiently temperature-resistant) if at 200 C. the slip travel has not exceeded the figure of 1000 m. If the test is failed, the temperature at the point of attainment of the maximum slip travel (1000 m) is reported (in C.).

(28) TFT Method (Measurement Method H4)

(29) Assessment Criteria:

(30) The present criteria for an application-compatible adhesive tape for the wrapping of cables are the bond strength to steel, the bond strength to the reverse face in combination with the unwind force at 30 m/min. Unwind force of rolls after storage at room temperature, around 23 C. over four weeks at 50% humidity.

(31) Test Procedure: unless expressly stated otherwise, the measurements are conducted under test conditions of 231 C. and 505% relative humidity.

(32) Measurement of the flagging resistance to LV312, or TFT method (Threshold Flagging Time): for the determination of the flagging behaviour by the TFT method, a test is employed in which an additional flexural stress is generated by the application of the test specimens, prepared in a flat format, to a 1 core. The combination of tensile load by a test weight and flexural stress causes flagging-like detachment of the adhesive tape starting from the bonded upper end, and ultimate failure by dropping of the test specimens (see FIG. 4, which also shows the schematic construction). The time in minutes before dropping is the result. The critical parameters for the holding time of the test specimens are weight and temperature, the weight being selected such as to result in values of at least 100 minutes.

(33) The cylindrically shaped test mandrel is a 1 card core with an external diameter of 422 mm, provided with a marking line 5 mm adjacent to the vertex line. The adhesion base is the adhesive tape's own reverse face. The manual roller has a weight of 2 kg. The test weight is 1 kg. The test conditions are 231 C. and 505% relative humidity, or 40 C. in a heating cabinet.

(34) Testing takes place on strips of adhesive tapes 19 mm wide. A strip with a length of 400 mm is adhered to release paper and cut to form three strips each 100 mm in length. This should be done using a fresh cutter blade. The reverse face must not be touched. A small piece of card is adhered beneath one of the ends of each strip, and the assembly is perforated (see FIG. 5). The test strips are then individually bonded centrally to strips of the broader adhesion base (adhesive tape with a width 1 times that of the adhesive tape under test), so that the small piece of card still overlaps just (2 to 3 mm) at the end (see FIG. 6). The test specimens are rolled down using the 2 kg manual roller at a speed of 10 m/min in three cycles. The finished test samples, in other words the test strips together with adhesion base, are then adhered to the card core in such a way that the upper end of the test specimen overlaps the vertex point by 5 mm (see FIG. 7). In this operation, only the adhesion base, and not the test specimen, must be pressed on. The fully prepared test specimens are left for 204 hours without weight loading in a controlled-climate chamber at 40 C.

(35) Weights with a mass of one kilogram are then hung onto the specimens, and the stopwatch is started. The measurement ends after failure of all three test specimens of one sample. The median of the three individual measurements is reported in minutes.

(36) The holding time is reported in minutes. In this context, a TFT of >1000 minutes, preferably greater than 1200 minutes, more preferably greater than 2000 minutes is considered to be a lower limit with regard to resistance towards flagging.

(37) Unwind force; measurement of the unwind force to LV312 at a take-off speed of 30 m/min.

(38) K Value (According to Fikentscher) (Measurement Method A1):

(39) The K value is a measure of the average size of molecule in high-polymer materials. For the measurement, one percent strength (1 g/100 mL) toluenic polymer solutions were prepared and their kinematic viscosities were determined using a VOGEL-OSSAG viscometer. Standardization to the viscosity of toluene produces the relative viscosity, from which the K value can be calculated by the method of Fikentscher (Polymer 1967, 8, 381 ff.)

(40) Gel Permeation Chromatography GPC (Measurement Method A2):

(41) The figures for the number-average molar mass Mn, the weight-average molecular weight M.sub.w and the polydispersity PD in this specification relate to the determination by gel permeation chromatography. The determination is made on a 100 L sample which has undergone clarifying filtration (sample concentration 4 g/L). The eluant used is tetrahydrofuran with 0.1 vol % trifluoroacetic acid. Measurement takes place at 25 C. The pre-column used is a PSS-SDV column, 5, 10.sup.3 , ID 8.0 mm50 mm. Separation takes place using the columns PSS-SDV, 5, 10.sup.3 and also 10.sup.5 and 10.sup.6 , each of ID 8.0 mm300 mm (columns from Polymer Standards Service; detection by differential refractometerShodex RI71). The flowrate is 1.0 mL per minute. Calibration takes place against PMMA standards (polymethyl methacrylate calibration).

(42) HPHolding Power (Measurement Method H2):

(43) A strip of the adhesive tape 13 mm wide and more than 20 mm long (30 mm for example) was applied to a smooth steel surface which had been cleaned three times with acetone and once with isopropanol. The bond area was 20 mm13 mm (lengthwidth), with the adhesive tape overhanging the test plate at the edge (for example by 10 mm, corresponding to the 30 mm length indicated above). The adhesive tape was then pressed four times onto the steel support, with an applied pressure corresponding to a weight of 2 kg. This sample was hung vertically, so that the protruding end of the adhesive tape points downwards.

(44) At room temperature, a 1 kg weight was fastened to the protruding end of the adhesive tape. The measurement is carried out under standard conditions (23 C., 505% humidity) and 70 C. in a thermal cabinet.

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

(46) MSTMicroshear Test (Measurement Method H3)

(47) This test is used for the accelerated testing of the shear strength of adhesive tapes under temperature load.

(48) Sample Preparation for Microshear Test:

(49) An adhesive tape (length about 50 mm, width 10 mm) cut from the respective sample specimen is adhered to a steel test plate which has been cleaned with acetone, in such a way that the steel plate protrudes beyond the adhesive tape to the right and to the left, and that the adhesive tape protrudes beyond the test plate by 2 mm at the upper edge. The bond area of the sample in terms of heightwidth=13 mm10 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.

(50) Microshear Test:

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

(52) PSA Examples: Preparation of the Starting Polymers for Examples IE1 to IE8

(53) The preparation of the starting polymers is described below. The polymers investigated are prepared conventionally via a free radical polymerization in solution.

(54) Base Polymer P1:

(55) A reactor conventional for radical polymerizations was charged with 30 kg of 2-ethylhexyl acrylate, 67 kg of n-butyl acrylate, 3 kg of acrylic acid and 66 kg of acetone/isopropanol (96:4). After nitrogen gas has been passed through the reactor for 45 minutes, with stirring, the reactor was heated to 58 C. and 50 g of 2,2-azobis(2-methylbutyronitrile) were added. The external heating bath was then heated to 75 C. and the reaction was carried out constantly at this external temperature. After one hour a further 50 g of 2,2-azobis(2-methylbutyronitrile) were added, and after four hours the batch was diluted with 20 kg of acetone/isopropanol mixture (96:4).

(56) After five hours and again after seven hours, re-initiation took place with 150 g of bis-(4-tert-butylcyclohexyl) peroxydicarbonate each time, and the batch was diluted with 23 kg of acetone/isopropanol mixture (96:4). After a reaction time of 22 hours, the polymerization was discontinued and cooling took place to room temperature. The polyacrylate has a conversion of 99.6%, a K variable of 75.1, an average molecular weight of M.sub.w=1 480 000 g/mol and a polydispersity (PD) Q=(M.sub.w/M.sub.n)=16.1.

(57) Base Polymer P2:

(58) In analogy to example P1, 68 kg of 2-ethylhexylacrylate, 25 kg of methyl acrylate and 7 kg of acrylic acid were polymerized in 66 kg of acetone/isopropanol (94:6). Initiation took place twice with 50 g of 2,2-azobis(2-methylbutyronitrile) each time, and twice with 150 g of bis-(4-tert-butylcyclohexyl) peroxydicarbonate each time, and dilution took place with 20 kg of acetone/isopropanol mixture (94:6). After a reaction time of 22 hours, the polymerization was discontinued and cooling took place to room temperature.

(59) The polyacrylate has a conversion of 99.7%, a K value of 51.3, an average molecular weight of M.sub.w=676 000 g/mol, and a polydispersity (PD) Q=(M.sub.w/M.sub.n)=9.5.

(60) Comparative examples (CE) and inventive examples (IE) 1 to 60: the inventive and comparative examples below all feature a coatweight of 50 g/m.sup.2 on an etched PET film 23 m thick.

(61) TABLE-US-00001 TABLE 1a Adhesive data for base polymer P1 with UV crosslinker Esacure KIP 150 (oligo[2- hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone], CAS no. 163702-01-0) Concen- MST Elast. Exam- Cross- tration Dose HP RT max. comp. SAFT TFT ple linker [wt %] [mJ/cm.sup.2] [min] Fract. [m] [%] [ C.] [m] [min] CE1 Esacure 0.10 60 <10 C 890 23 <100 180 CE2 KIP 150 80 <10 C 800 33 <100 260 CE3 120 <10 C 740 38 <100 62 IE4 0.25 60 16 C 406 50 123 1260 IE5 80 42 M 294 57 148 2800 IE6 120 177 A 228 66 173 2960 IE7 0.50 60 17 C 234 58 149 4520 IE8 80 131 M 180 67 185 5030 IE9 120 102 A 101 74 186 5400 CE10 0.80 60 560 M 123 67 188 196 CE11 80 760 M 98 85 196 251 CE12 120 920 M 67 92 200 560 26

(62) TABLE-US-00002 TABLE 2 Adhesive data for base polymer P1 with UV crosslinker Esacure KIP 160 (2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)phenoxy]phenyl}-2- methylpropan-1-one, CAS No. 71868-15-0) Concen- MST Elast. Exam- Cross- tration Dose HP RT max. comp. SAFT TFT ple linker [wt %] [mJ/cm.sup.2] [min] Fract. [m] [%] [ C.] [m] [min] CE13 Esacure 0.10 60 <10 K 900 13 <100 80 CE14 KIP 160 80 <10 K 820 23 <100 160 CE15 120 <10 K 780 28 <100 62 IE16 0.25 60 85 M 217 62 170 4805 IE17 80 125 A 187 63 179 4280 IE18 120 161 A 184 79 182 1620 IE19 0.50 60 23 M 178 59 181 3895 IE20 80 50 M 146 51 189 4204 IE21 120 140 A 79 85 200 542 1510 CE22 0.80 60 660 A 120 67 188 96 CE23 80 1760 A 88 86 199 51 CE24 120 2920 A 62 94 200 460 26

(63) TABLE-US-00003 TABLE 3 Adhesive data for base polymer P1 with UV crosslinker Esacure KT 55 (mixture of 50 wt % Esacure KIP 150, 40 wt % 2,4,6-trimethylbenzophenone (CAS No. 954-16-5) and 10 wt % 4-methylbenzophenone (CAS No. 134-84-9)) Concen- MST Elast. Exam- Cross- tration Dose HP RT max. comp. SAFT TFT ple linker [wt %] [mJ/cm.sup.2] [min] Fract. [m] [%] [ C.] [m] [min] CE25 Esacure 0.10 60 <10 K 780 26 <100 80 CE26 KT 55 80 <10 K 620 34 <100 78 CE27 120 <10 K 600 38 <100 62 IE28 0.25 60 14 M 221 58 154 805 CE29 80 54 M 128 71 200 825 280 CE30 120 45 A 56 83 200 332 62 IE31 0.50 60 <10 K 394 28 107 1023 CE32 80 <10 M 352 36 114 756 CE33 120 17 A 106 64 200 569 152 CE34 0.80 60 160 M 120 67 188 196 CE35 80 170 A 98 76 200 542 151 CE36 120 172 A 92 77 200 457 26

(64) TABLE-US-00004 TABLE 4 Adhesive data for base polymer P2 with UV crosslinker Esacure KIP 160 (2-Hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)phenoxy]phenyl}-2- methyl-propan-1-one, CAS No. 71868-15-0) Concen- MST Elast. Exam- Cross- tration Dose HP RT max. comp. SAFT TFT ple linker [wt %] [mJ/cm.sup.2] [min] Fract. [m] [%] [ C.] [m] [min] CE37 Esacure 0.10 60 <10 K 810 24 <100 120 CE38 KIP 160 80 <10 K 720 27 <100 280 CE39 120 <10 K 680 31 <100 162 IE40 0.25 60 85 M 187 54 180 4608 IE41 80 115 A 126 62 189 5280 IE42 120 141 A 84 63 192 1620 IE43 0.50 60 23 M 158 51 181 4895 IE44 80 54 M 116 59 189 4204 IE45 120 129 A 79 65 200 448 1120 CE46 0.80 60 260 A 120 67 188 96 CE47 80 276 A 88 86 199 51 CE48 120 292 A 62 94 200 360 26

(65) TABLE-US-00005 TABLE 5 Adhesive data for base polymer P1 with UV crosslinker Esacure 1001 M (1-[4-(4- benzoylphenylsulfanyl)phenyl]-2-methyl-2-(4-methylphenylsulfonyl)propan-1-one) Concen- MST Elast. Exam- Cross- tration Dose HP RT max. comp. SAFT TFT ple linker [wt %] [mJ/cm.sup.2] [min] Fract. [m] [%] [ C.] [m] [min] CE49 Esacure 0.10 60 <10 K >2000 <100 <10 CE50 1001 M 80 <10 K >2000 <100 <10 CE51 120 <10 K >2000 <100 <10 CE52 0.25 60 <10 K >2000 <100 <10 CE53 80 <10 K >2000 <100 <10 CE54 120 <10 K >2000 <100 <10 CE55 0.50 60 <10 K >2000 <100 <10 CE56 80 <10 K >2000 <100 <10 CE57 120 <10 K >2000 <100 <10 CE58 0.80 60 <10 K >2000 <100 <10 CE59 80 <10 K >2000 <100 <10 CE60 120 <10 K >2000 <100 <10 The UV crosslinker Esacure 1001 M ((1-[4-(4-benzoylphenylsulfanyl)phenyl]-2-methyl-2- (4-methylphenylsulfonyl)propan-1-one, CAS No. 272460-97-6) is not suitable for the crosslinking of the acrylate-based pressure-sensitive adhesives.

(66) TABLE-US-00006 TABLE 6 tan values for the inventive and comparative examples 1 to 60, measured by means of dynamic mechanical analysis (frequency sweep) at = 0.1 rad/s and 25 C. Example tan .sup.1 CE1 0.62 CE2 0.61 CE3 0.60 IE4 0.50 IE5 0.49 IE6 0.49 IE7 0.49 IE8 0.48 IE9 0.47 CE10 0.44 CE11 0.44 CE12 0.43 CE13 0.58 CE14 0.56 CE15 0.52 IE16 0.49 IE17 0.47 IE18 0.45 IE19 0.48 IE20 0.46 IE21 0.45 CE22 0.44 CE23 0.42 CE24 0.41 CE25 0.53 CE26 0.52 CE27 0.51 IE28 0.46 CE29 0.44 CE30 0.43 IE31 0.47 CE32 0.44 CE33 0.42 CE34 0.44 CE35 0.43 CE36 0.42 CE37 0.54 CE38 0.54 CE39 0.53 IE40 0.50 IE41 0.48 IE42 0.46 IE43 0.49 IE44 0.47 IE45 0.45 CE46 0.44 CE47 0.42 CE48 0.42 CE49 0.65 CE50 0.64 CE51 0.63 CE52 0.63 CE53 0.62 CE54 0.61 CE55 0.59 CE56 0.57 CE57 0.56 CE58 0.56 CE59 0.55 CE60 0.53 .sup.1= measured by means of dynamic mechanical analysis (frequency sweep) at 25 C. and = 0.1 rad/s, stress 2500 Pa

(67) Surprisingly, and not obviously for the skilled person, adhesives having good flagging properties (measurable through the TFT test) can be obtained using photoinitiators (i.e. UV crosslinkers) having at least two photoactive groups per molecule, if a balanced ratio is set between cohesion and adhesion. This is evident in particular from the rheological properties and specifically the tan (the ratio of G to G, in other words the ratio of loss modulus to storage modulus), which with a measuring frequency of 0.1 rad/s (corresponding approximately to the timescale of the flagging process) adopts values, with particular preference, of between 0.45tan 0.50 (see Table 6). The aforesaid bonding agents are particularly suitable for the adhesive bonding of cylindrical surfaces.