Curable pressure-sensitive adhesive strip based on vinylaromatic block copolymer

Abstract

The invention relates to a pressure-sensitive adhesive strip containing at least one layer SK1 of a self-adhesive composition based on vinylaromatic block copolymer and containing tackifying resin, wherein the vinylaromatic block copolymer contains at least one polymer block A formed predominantly by polymerization of vinylaromatics, and simultaneously contains at least one polymer block B formed predominantly by polymerization of conjugated dienes, where the proportion of 1,2-bonded conjugated diene in the B block is less than 30% by weight, preferably less than 20% by weight.

The invention also relates to a pressure-sensitive adhesive strip of this kind, in which at least layer SK1 has been subjected to irradiation with electrons.

Claims

1. A pressure-sensitive adhesive strip containing at least one layer SK1 of a self-adhesive composition based on vinylaromatic block copolymer and containing tackifying resin, wherein the vinylaromatic block copolymer contains at least one polymer block A formed predominantly by polymerization of vinylaromatics, and simultaneously contains at least one polymer block B formed predominantly by polymerization of conjugated dienes, where the proportion of 1,2-bonded conjugated diene in the B block is less than 30% by weight.

2. The pressure-sensitive adhesive strip according to claim 1, wherein, at least the layer SK1 has been subjected to irradiation with electrons, where the layer SK1 after the irradiation preferably has a gel value of 0%.

3. The pressure-sensitive adhesive strip according to claim 1, wherein the self-adhesive composition of layer SK1 is foamed.

4. The pressure-sensitive adhesive strip of claim 2, wherein the absolute density of the self-adhesive composition layer SK1 is 400 to 990 kg/m.sup.3.

5. The pressure-sensitive adhesive strip according to claim 1, wherein the vinylaromatic block copolymer is a mixture of linear block copolymers which comprise a mixture of diblock copolymers (A-B) and triblock copolymers (A-B-A), where the vinylaromatic block copolymer has a diblock copolymer content of 30% to 60% by weight.

6. The pressure-sensitive adhesive strip according to claim 1, wherein the tackifying resin of layer SK1 comprises, to an extent of at least 75% by weight, hydrocarbon resin or terpene resin or a mixture of thereof.

7. The pressure-sensitive adhesive strip according to according to claim 3, wherein the foamed layer SK1 comprises microballons in an amount of up to 12% by weight, based on the overall composition of the layer.

8. A process of producing the pressure-sensitive adhesive strip of claim 1, wherein the self-adhesive composition is processed from solution or from the melt to produce layer SK1, and optionally, wherein the layer SK1 is subjected to irradiation with electrons.

9. The process of claim 8, wherein the self-adhesive composition is processed from the melt to give layer SK1 using at least one first continuous compounding unit.

10. A process of producing a pressure-sensitive adhesive composition according to claim 1, based on block copolymers with hard block-soft block architecture, where the hard blocks are softenable or meltable at a temperature T (measured by means of DSC), wherein the process is conducted in a planetary roll extruder, and wherein the planetary roll extruder, downstream of the addition of the components of the adhesive composition, has a degassing apparatus in the form of a gas-permeable side-arm extruder.

11. A method of bonding surfaces having a surface energy of 50 mN/m or less, the method comprising the step of: utilizing the pressure-sensitive adhesive strip of claim 1 in bonding said surfaces.

12. A method of bonding two surfaces, where one of the surfaces has a surface energy of 50 mN/m or less, and the other surface has a surface energy of 35 mN/m or more, the method comprising the step of: utilizing the pressure-sensitive adhesive strip of claim 1 in bonding said surfaces.

13. A method of bonding two components, the method comprising the step of: utilizing the pressure-sensitive adhesive strip of claim 1 to bond the two components, wherein the said pressure-sensitive adhesive strip is double-sided, and bonding takes place at a temperature of not more than 10 C.

14. A method of bonding components utilizing the pressure-sensitive adhesive strip of claim 1, wherein the components are simultaneously mechanically bonded, and are also adhesively-bonded with the pressure-sensitive adhesive strip.

15. A method of bonding oil-contaminated substrates, the method comprising the step of: utilizing the pressure-sensitive adhesive strip of claim 1 in bonding the oil-contaminated substrates.

16. The pressure-sensitive adhesive strip, where the proportion of 1,2-bonded conjugated diene in the B block is less than 20% by weight.

17. The pressure-sensitive adhesive strip of claim 4, wherein the absolute density of the self-adhesive composition layer SK1 is 450 to 800 kg/m.sup.3.

18. The pressure-sensitive adhesive strip of claim 17, wherein the absolute density of the self-adhesive composition layer SK1 is 500 to 700 kg/m.sup.3.

Description

FIGURE

[0214] With reference to the FIGURE described hereinafter, a particularly advantageous execution of the invention will be elucidated in detail, without any intention to unnecessarily restrict the invention thereby.

[0215] FIG. 1 shows the schematic construction of a single-layer pressure-sensitive adhesive strip of the invention, consisting of one layer 2 in cross section.

[0216] The strip comprises a self-adhesive composition layer 2 (layer SK1). The self-adhesive composition layer 2 (layer SK1) is covered by a liner 4, 5 on each side in the illustrative embodiment shown.

[0217] The invention is elucidated in detail hereinafter by examples. With reference to the examples described hereinafter, particularly advantageous executions of the invention will be elucidated in detail, without any intention to unnecessarily restrict the invention thereby.

EXAMPLES

[0218] The raw materials used are characterized as follows: [0219] Kraton D1101: styrene-butadiene-styrene triblock copolymer from Kraton Polymers with 16% by weight of diblock, block polystyrene content: 31% by weight, proportion of 1,2-bonded conjugated diene in the butadiene block: 10% by weight [0220] Kraton D1118: styrene-butadiene-styrene triblock copolymer from Kraton Polymers with 78% by weight of diblock, block polystyrene content: 33% by weight, proportion of 1,2-bonded conjugated diene in the butadiene block: 10% by weight [0221] Dercolyte A115: solid -pinene tackifying resin with a ring and ball softening temperature of 115 C. and a DACP of 35 C. [0222] Piccolyte A25: polyterpene resin based on -pinene with a ring and ball softening temperature of 22 to 28 C. [0223] Escorez 2203: hydrocarbon resin based on C5 and C9 with low aromatics content, softening point (ring & ball) 95 C. [0224] Expancel 920 DU40, Expancel 920 DU80: unexpanded microballoons. [0225] Ebecryl 140: di(tnmethylolpropane) tetraacrylate

[0226] Table 1 shows the composition of the adhesive composition formulations used.

TABLE-US-00003 TABLE 1 Composition of the adhesive composition formulations used (figures in parts by weight). R1 R2 R3 R4 Kraton D 1101 25 25 20 20 Kraton D 1118 25 25 30 30 Escorez 2203 50 Dercolyte A115 50 48 50 Piccolyte A25 2 Expancel 920DU40 3 3 Expancel 920DU80 3 3

Process V1 (Solution Process):

[0227] For this purpose, first of all, a 40% by weight adhesive solution of the formulation specified in each case in benzine/toluene/acetone was prepared. The proportions by weight of the dissolved constituents are each based on the dry weight of the resulting solution.

[0228] The solution was subsequently admixed if required with unexpanded microballoons, using the microballoons in the form of a suspension in benzine. The proportion by weight of the microballoons is based on the dry weight of the solution used to which they have been added (i.e. the dry weight of the solution used is fixed at 100%). The mixture obtained was then coated with a coating bar onto a PET liner provided with a silicone release agent in the desired layer thickness, then the solvent was evaporated off at 100 C. for 15 min and so the composition layer was dried. Thereafter, a second PET liner of this kind was laminated onto the free surface of the dried adhesive composition layer produced and the adhesive composition layer was then foamed between the two liners in an oven at 150 C. for 5 min, so as to obtain a pressure-sensitive adhesive strip of the invention of thickness about 100 m. If required, the target thickness was established by multiple lamination of this layer. Die-cutting gave the desired dimensions.

Process V2 (Hotmelt Process):

[0229] The elastomer components were added in the intake of the PRE (planetary roll extruder), which comprised an intake region and two process parts. The run-in rings had increasing diameter in process direction. Even though different spindle fittings were suitable, preference was given to fittings that were at least % of the maximum fitting number in the first process part. The resin components were melted and added in the second process part of the PRE. A particularly suitable means of production of homogeneous mixtures was a resin split in which one portion of the resin was added in the first process part and the rest downstream in the second process part. A particularly suitable means of addition of the two components was in liquid form via a side feed or run-in rings, where the first portion is about 10% of the total amount of resin, and the process was executed in such a way unless stated otherwise. Another suitable option would have been the addition of the first resin component in solid form in the intake of the PRE or via the side feed in the first process part. The compounded composition was transferred into the twin-screw extruder by a heated hose. Microballoons were added via a side feed in the first third of the TSE (twin-screw extruder) and foamed therein, such that the foaming had essentially ended before exit from the unit. As a result of heat of friction, the melt temperature in the TSE was always above the wall temperatures set. At the end of the TSE, a vacuum was applied at a suitable point. The melt exit temperature was about 130 C. The melt was then transferred via a pre-distribution nozzle (coathanger nozzle) into a two-roll calender and formed between two double-sidedly siliconized 50 m PET films. This advantageous process always achieved roughnesses R.sub.a<5 m (measured by means of white light interferometry).

[0230] Table 2 shows the parameters of the hotmelt process.

TABLE-US-00004 TABLE 2 Parameters of the hotmelt process (L/D = length/diameter). Total throughput of elastomer components 20 kg/h Roll cylinder diameter 70 mm PRE central spindle temp. 50 C. PRE zone temps 90 C./90 C./90 C./90 C. PRE speed 100/min Diameter of TSE screws and L/D 42 mm, 36 L/D TSE zone temps 20 C./50 C./80 C./80 C. TSE speed 100/min TSE vacuum 200 mbar Calendering roll temps 120 C./120 C.

[0231] There follows a description of the production of a pressure-sensitive adhesive strip of the invention which consists of a single foamed self-adhesive composition layer SK1 (transfer tape) based on vinylaromatic block copolymer foamed with microballoons. The self-adhesive composition layer SK1 can be produced without use of a soft resin (Example B1), or with use of such a resin (Example B2). Example B3 corresponds to Example B2, but produced by the hotmelt process V2. Example B4 corresponds to B3, but with Escorez 2203 resin and another elastomer mixture. Example B5 corresponds to B3, but with another elastomer mixture; see also the remarks below.

[0232] Table 3 gives an overview of examples B1 to B5 as a combination of different formulations and processes.

TABLE-US-00005 TABLE 3 Overview of the formulations and production processes used in Examples B1 to B5. Example Formulation Process B1 R1 V1 B2 R2 V1 B3 R2 V2 B4 R3 V2 B5 R4

[0233] In each case, as described, the self-adhesive composition layer SK1 was subsequently irradiated with electrons.

Example B1

[0234] The pressure-sensitive adhesive strip was produced by process V1 using formulation R1, in such a way that it has a thickness of about 1000 m. The thickness is always based on the pressure-sensitive adhesive strip without PET liner.

Example B2

[0235] The production of the pressure-sensitive adhesive strip from Example B2 differs from the production of the pressure-sensitive adhesive strip from Example B1 merely in that the 40% by weight adhesive solution used also contains 2% by weight of Piccolyte A25, based on the dry weight of the resulting solution.

Examples B3-B5

[0236] Example B3 was produced with the formulation of B2, but by the hotmelt process V2. Examples B4 and B5 were produced like B3, but with the formulations as specified in Table 3.

Irradiation with Electrons of Examples B1 to B5:

[0237] The self-adhesive composition layer SK1 of the pressure-sensitive adhesive strip from Example B1-B5 was subsequently subjected to electron beam curing, using a system from ELECTRON CROSSLINKING AB (Halmstad, Sweden). The acceleration voltage was 220 keV. The dose was varied in each case within the range from 10 to 100 kGy in steps of 10 kGy. The self-adhesive composition layer was subjected here to irradiation with electrons from both sides, i.e. symmetrically, in order to assure homogeneous curing. Prior to the irradiation, the liner was removed on the side to be irradiated in each case. An unirradiated reference specimen was always also produced.

Results for Examples B1 to B5:

Example 1

[0238] The pressure-sensitive adhesive strip (containing no soft resin) from Example B1 that has been subjected to the specified doses of electron radiation was tested in each case for its lifetime under high-temperature shear by means of the static shear test (dimensions of the test strip: length 25 mm, width 25 mm, measurement temperature: 80 C., load 500 g). Without electron irradiation the lifetime under high-temperature shear was already more than 2000 min, at a radiation dose of 40 or 60 kGy it was about 2600 min, at a radiation dose of 80 kGy it was about 8000 min, and at a radiation dose of 100 kGy the sample strip still had not yet sheared off even after 10 000 min. It was thus possible to increase the lifetime under high-temperature shear with increasing radiation intensity; the result (even without additional crosslinking promoter) was very good lifetimes under high-temperature shear. The gel content of the self-adhesive composition layer SK1 at all irradiation intensities was found in each case to be 0% by weight, meaning that no macroscopic crosslinking could be observed.

[0239] The bonding force of the unirradiated pressure-sensitive adhesive strip was about 28 N/cm. The bonding force (and also the tensile strength) of the pressure-sensitive adhesive strip also remained essentially unchanged on irradiation with electrons (different dose).

Example 2

[0240] The pressure-sensitive adhesive strip (containing Piccolyte A25 as soft resin) from Example B2 that has been subjected to the specified doses of electron radiation was likewise tested in each case for its lifetime under high-temperature shear by means of the static shear test (dimensions of the test strip: length 13 mm, width 20 mm, measurement temperature: 70 C., load 500 g). Without electron irradiation, the lifetime under high-temperature shear was already about 3400 min. Even from a radiation dose of 10 kGy (and up to a radiation dose of 100 kGy), the sample strip still had not sheared off even after 10 000 min. The slip travel of the test specimen after 10 000 min was, for example, at radiation doses of 10 kGy, 20 kGy, 30 kGy and 40 kGy, 4.8 mm, 2.8 mm, 2.7 mm and 2.0 mm respectively. In the case of a pressure-sensitive adhesive strip comprising soft resin, it was thus possible to increase heat resistance with increasing irradiation intensity, and the result (even without additional crosslinking promoter) was very good heat resistances. The gel content of the self-adhesive composition layer SK1 was found in each case to be 0% by weight; in other words, no macroscopic crosslinking was observed. The use of soft resin is therefore not a barrier to the achievement of high heat resistances.

[0241] The bonding force of the unirradiated pressure-sensitive adhesive strip was about 34 N/cm; in other words, it was increased by the use of soft resin. The bonding force (and also the tensile strength) of the pressure-sensitive adhesive strip also remained essentially unchanged on irradiation with electrons (different dose).

Example B3

[0242] Example B3 was tested in the same way as Example B2. The gel content even after EBC irradiation at the doses specified was found to be 0% by weight in each case. Without EBC irradiation, the lifetime under high-temperature shear in the static shear test at 70 C. was 4000 min. Over and above a dose of 20 kGy, the lifetime under shear was >10 000 min.

Example B4

[0243] Example B4 was tested in the same way as Example B2. The gel content even after EBC irradiation at the doses specified was found to be 0% by weight in each case. Without EBC irradiation, the lifetime under high-temperature shear in the static shear test at 70 C. was 1200 min. Over and above a dose of 20 kGy, the lifetime under shear was >10 000 min.

Example B5

[0244] Example B5 was tested in the same way as Example B2. The gel content even after EBC irradiation at the doses specified was found to be 0% by weight in each case. Without EBC irradiation, the lifetime under high-temperature shear in the static shear test at 70 C. was 5400 min. Over and above a dose of 20 kGy, the lifetime under shear was >10 000 min.

Examples 6 to 8 (Including Results)

[0245] There follows a description of the production of a foamed self-adhesive composition layer SK1 of the invention of about 500 m in thickness, which was produced in Examples B6-B8 with formulation R1 by the hotmelt process V2. These examples contained the proportion of Ebecryl 140 crosslinking promoter specified in each case in Table 4. Examples B6-B8 were each produced with and without irradiation with electrons, as specified in Table 4.

TABLE-US-00006 TABLE 4 Overview of Examples 6 to 8 (including results). EBC Base Cross- dose LSS BF 90 formu- linking Production [kGy, at 70 C. ASTM Gel lation promoter process 170 kV] [min] [N/cm] value B6 R1 0% V2 0 4592 22.7 0% B6 R1 0% V2 50 10 000 17.3 0% B7 R1 1% V2 0 3564 20.8 0% B7 R1 1% V2 50 10 000 13.0 15% B8 R1 3% V2 0 460 18.6 0% B8 R1 3% V2 50 10 000 11.2 11% LSS = lifetime under shear stress. BF = bonding force.

[0246] The table shows that a high lifetime under shear stress can be achieved at 70 C. by means of EBC even without crosslinking promoter, and, furthermore, the use of the crosslinking promoter is disadvantageous since the bonding force is noticeably lowered even at low gel values (11% or less). The pressure-sensitive adhesive compositions of the invention thus preferably have a gel value of 0% after EBC treatment. More particularly, in the EBC treatment of the invention without crosslinking promoter, the bonding force after EBC treatment reaches at least 75% of the original value without EBC treatment, and/or the dose of the EBC treatment is selected such that the bonding force after EBC treatment reaches at least 75% of the original value without EBC treatment.

Bonding on Oiled Substrates:

[0247] For testing of suitability for bonding on oiled substrates, the adhesive tapes, as specified in Table 5, were bonded to steel sheets having 4 g/m.sup.2 of oil (Quaker 61AUS). Comparative adhesive tape 1 is a double-sided acrylate adhesive tape of 500 m in thickness, produced according to Example MT15 from DE 10 2009 048036 A1. Comparative adhesive tape 2 is the commercially available product Tesa 4954, i.e. a double-sided adhesive tape of about 430 m in thickness with natural rubber adhesives.

[0248] It can be seen that the an adhesive tape of the invention according to Example B6 (but produced with irradiation intensity 20 kGy) has excellent bonding force on the oiled substrate.

TABLE-US-00007 TABLE 5 Bonding force on oiled substrate. 90 bonding force [N/cm] Comparative Comparative Attachment time adhesive adhesive B6 with [min] tape 1 tape 2 EBC 20 kGy 2 0.02 0.23 0.80 60 0.05 0.77 3.85 240 0.24 1.30 9.23

Bonding at Low Temperatures:

[0249] For testing of suitability for bonding at low temperatures, the adhesive tapes, as specified in Table 6, were bonded to ASTM steel at 0. Comparative adhesive tape 1 is a double-sided acrylate adhesive tape of 500 m in thickness, produced according to Example MT15 from DE 10 2009 048036 A1. The bonding forces were measured as described in the test methods, except that the attachment time and measurement were each effected at 0 C.

[0250] It can be seen that the adhesive tape of the invention according to example B5 has excellent bonding force at 0 C.

TABLE-US-00008 TABLE 6 Bonding at 0 C. Bonding force 90 [N/cm], measured at 0 C. Comparative Attachment time adhesive B5 with at 0 C. tape 1 EBC 20 kGy 2 min 1 31 24 h 19 37

Test Methods

[0251] Unless stated otherwise, all measurements were conducted at 23 C. and 50% rel. air humidity.

[0252] The mechanical and adhesive data were ascertained as follows:

DACP

[0253] 5.0 g of test substance (the tackifier resin sample to be examined) are weighed into a dry test tube, and 5.0 g of xylene (isomer mixture, CAS [1330-20-7], 98.5%, Sigma-Aldrich #320579 or comparable) are added. The test substance is dissolved at 130 C. and then cooled down to 80 C. Any xylene that escapes is made up for with fresh xylene, such that 5.0 g of xylene are present again. Subsequently, 5.0 g of diacetone alcohol (4-hydroxy-4-methyl-2-pentanone, CAS [123-42-2], 99%, Aldrich #H41544 or comparable) are added. The test tube is shaken until the test substance has dissolved completely. For this purpose, the solution is heated to 100 C. The test tube containing the resin solution is then introduced into a Novomatics Chemotronic Cool cloud point measuring instrument and heated therein to 110 C. It is cooled down at a cooling rate of 1.0 K/min. The cloud point is detected optically. For this purpose, that temperature at which the turbidity of the solution is 70% is registered. The result is reported in C. The lower the DACP value, the higher the polarity of the test substance.

Tackifying Resin Softening Temperature

[0254] The softening temperature of a tackifying resin is determined in accordance with the relevant methodology, which is known as ring & ball and is standardized according to ASTM E28.

Diameter

[0255] The average diameter of the voids formed by the microballoons in a self-adhesive composition layer is determined using cryofracture edges of the pressure-sensitive adhesive strip in a scanning electron microscope (SEM) with 500-fold magnification. The diameter of the microballoons in the self-adhesive composition layer to be examined that are visible in scanning electron micrographs of 5 different cryofracture edges of the pressure-sensitive adhesive strip is determined in each case by graphical means, and the arithmetic mean of all the diameters ascertained in the 5 scanning electron micrographs constitutes the mean diameter of the voids formed by the microballoons in the self-adhesive composition layer in the context of the present application. The diameters of the microballoons visible in the micrographs are determined by graphical means in such a way that the maximum extent thereof in any (two-dimensional) direction is inferred from the scanning electron micrographs for each individual microballoon in the self-adhesive composition layer to be examined and regarded as the diameter thereof.

Density

[0256] The density of a pressure-sensitive adhesive composition layer is ascertained by forming the quotient of mass applied and thickness of the adhesive composition layer applied to a carrier or liner.

[0257] The mass applied can be determined by determining the mass of a section, defined in terms of its length and width, of such an adhesive composition layer applied to a carrier or liner, minus the (known or separately determinable) mass of a section of the same dimensions of the carrier or liner used.

[0258] The thickness of an adhesive composition layer can be determined by determining the thickness of a section, defined in terms of its length and width, of such an adhesive composition layer applied to a carrier or liner, minus the (known or separately determinable) thickness of a section of the same dimensions of the carrier or liner used. The thickness of the adhesive composition layer can be determined by means of commercial thickness measuring instruments (caliper test instruments) with accuracies of less than a 1 m deviation. In the present application, the Mod. 2000 F precision thickness gauge is used, which has circular calipers having a diameter of 10 mm (planar). The measurement force is 4 N. The value is read off 1 s after applying load. If variations in thickness are found, the average of measurements at at least three representative sites is reported, i.e. more particularly not measured at creases, folds, specks and the like.

Thickness

[0259] Like the thickness for an adhesive composition layer as above, it is also possible to ascertain the thickness of a pressure-sensitive adhesive strip or a film carrier layer or liner by means of commercial thickness measuring instruments (caliper test instruments) with accuracies of less than a 1 m deviation. In the present application, the Mod. 2000 F precision thickness gauge is used, which has circular calipers having a diameter of 10 mm (planar). The measurement force is 4 N. The value is read off 1 s after applying load. If variations in thickness are found, the average of measurements at at least three representative sites is reported, i.e. more particularly not measured at creases, folds, specks and the like.

Static Glass Transition Temperature T.SUB.g., Melting Temperature, Softening Temperature

[0260] Glass transition pointsreferred to synonymously as glass transition temperaturesparticularly of polymers or polymer blocks are reported as the result of measurements by means of differential scanning calorimetry (DSC) according to DIN 53 765; especially sections 7.1 and 8.1, but with uniform heating and cooling rates of 10 K/min in all heating and cooling steps (cf. DIN 53 765; section 7.1; note 1). The sample weight is 20 mg. The melting temperature or softening temperature of polymers or polymer blocks is also determined in this way.

Proportion of 1,2-Bonded Conjugated Diene

[0261] The proportion of 1,2-bonded conjugated diene in the B block of vinylaromatic block copolymer can be determined by means of .sup.1H NMR. The following instrument was used for spectroscopic analysis: .sup.1H NMR: Bruker AMX 500 (500.14 MHz). The standard used was the solvent signal (CHCl3)=7.24. Chemical shifts are always reported in ppm. Coupling constants J are reported in hertz [Hz]. Signal patterns are reported as follows: s (singlet), bs (broad singlet), d (doublet), dd (doublet of doublets), t (triplet), q (quintet), m (multiplet).

Surface Energies

[0262] Surface energies (surface tensions) are determined according to DIN ISO 8296. For this purpose, it is possible to use, for example, test inks from Softal. The inks are available in the range from 30 to 72 mN/m. The ink is applied to the surface with a stroke of ink at 23 C. and 50% rel. air humidity. If the stroke of ink draws together within less than 2 seconds, the measurement is repeated with ink having lower surface energy until 2 seconds are attained. If the stroke of ink remains unchanged for longer than 2 seconds, the measurement is repeated with ink having higher surface energy until 2 seconds are attained. The value specified on the appropriate bottle of ink then corresponds to the surface energy of the substrate.

Lifetime Under High-Temperature ShearStatic Shear Test SST

[0263] To determine the lifetime under high-temperature shear, also called high-temperature shear strength, a pressure-sensitive adhesive strip in a climate-controlled cabinet heated to 70 C. or 80 C. is applied to a defined rigid bonding substrate (steel here) and subjected to constant shear stress. The hold time in minutes is ascertained. The temperatures used are stated in the examples.

[0264] A double-sidedly adhesive strip of length 13 mm and width 20 mm or of length 25 mm and width 25 mm of the pressure-sensitive adhesive strip to be tested is manually applied to a polished small steel plate (test substrate) having a hole at one end. Subsequently, an identical small steel plate is manually applied in the reverse orientation. The resulting composite is compressed at 100 N/cm.sup.2 for 60 seconds (in the case of the 2013 mm geometry the force is 0.260 kN; in the case of the 2525 mm geometry the force is 0.625 kN.

[0265] The attachment time between roll-on and application of load should be 24 h, unless stated otherwise in the examples. Before applying load, the sample is subjected to heat treatment in a heated cabinet for 15 minutes. The weight is then hung on with the aid of S-shaped hooks, and was 500 g unless stated otherwise. The loads used in kPa or N/cm.sup.2 bond area are reported in the examples.

[0266] An automatic stopwatch then ascertains the juncture at which the test specimens shear off. The measurement is stopped after 10 000 min. In the case of test specimens that have still not dropped after 10 000 min, the quality of the cohesive properties at high temperature can also be quantified by determining the slip travel or the deflection without slippage of the test specimen after 10 000 min by means of a position sensor.

[0267] The average from three measurements is ascertained.

90 Bonding Force (BF)

[0268] Unless stated otherwise, the 90 bonding force is determined on steel, under controlled test conditions of temperature 23 C.+/1 C. and relative air humidity 50%+/5%. The specimens are cut to width 20 mm and bonded to the steel substrate. Unless stated otherwise, the substrate is cleaned and conditioned prior to the measurement. For this purpose, the plate is first wiped with acetone and then left to dry under air for 5 minutes in order that the solvent can evaporate off. The side of the pressure-sensitive adhesive tape remote from the test substrate is then covered with a 50 m aluminium foil, which prevents the specimen from stretching in the measurement. Thereafter, the test specimen is rolled onto the test substrate. For this purpose, a 2 kg roll is rolled over the tape five times back and forth at a rolling speed of 10 m/min. Immediately after the roll-on, the substrate is pushed into a special holder that enables the specimen to be drawn vertically upward at an angle of 90. The bonding force is measured with a Zwick tensile tester. The test results are reported in N/cm and averaged from three measurements.

Determination of Gel Content

[0269] The carefully dried solvent-free adhesive samples are welded into a small bag of polyethylene nonwoven fabric (Tyvek nonwoven). The difference in the sample weights before and after extraction by a mixture of benzine/toluene/acetone is used to determine the gel value, i.e. the proportion by weight of the polymer insoluble in the mixture. Additives that are not incorporated into the network even after EBC irradiation have to be subtracted from the total sample weight before the extraction.