Adhesive Strips

Abstract

The invention relates to adhesive strips consisting of at least four, particularly precisely four layers, comprising: a layer A having an upper side and a lower side consisting of a foamed adhesive substance containing a self-adhesive acrylate substance; a layer B consisting of a film carrier, layer B being arranged on the lower side of layer A, at least the main surface which faces layer A, preferably both main surfaces of the film carrier, being etched, the surface of layer A and the surface of layer B being in direct contact with each other; a layer C consisting of a self-adhesive substance, arranged on the upper side of layer A and containing a self-adhesive acrylate substance; and a layer D consisting of a self-adhesive substance, arranged on the side of layer B opposite layer A and containing a self-adhesive acrylate substance.

Claims

1. A pressure-sensitive adhesive strip composed of at least four comprising a layer A having a top side and a bottom side composed of a foamed adhesive composition based on a self-adhesive acrylate composition, a layer B composed of a film carrier, where layer B is arranged on the bottom side of layer A, where at least the main face facing layer A and preferably both main faces of the film carrier have been etched, where the surface of layer A and the surface of layer B are in direct contact with one another, a layer C composed of a self-adhesive composition which is arranged on the top side of layer A and is based on a self-adhesive acrylate composition, a layer that D composed of a self-adhesive composition which is arranged on the opposite side of layer B from layer A and is based on a self-adhesive acrylate composition.

2. The pressure-sensitive adhesive strip of claim 1, characterized in that: the film carrier is non-extensible.

3. The pressure-sensitive adhesive strip of claim 1, characterized in that: the film carrier has a tensile strength of greater than 100 N/mm.sup.2, in longitudinal direction, and greater than 100 N/mm.sup.2 in transverse direction.

4. The pressure-sensitive adhesive strip of claim 1, characterized in that: the film carrier has an elongation at break of less than 300% in longitudinal direction, and of less than 300% in transverse direction.

5. The pressure-sensitive adhesive of claim 1, characterized in that: the pressure-sensitive adhesive compositions used for layers A, C and/or D are acrylate-based adhesive compositions.

6. The pressure-sensitive adhesive strip of claim 1, characterized in that: the acrylate-based adhesive composition is formed using a polyacrylate which can be derived from the following monomer composition: a) acrylic ester and/or methacrylic ester of the following formula:
CH.sub.2C(R.sub.1)(COOR.sub.2) b) where R.sub.1H or CH.sub.3 and R.sub.2H or linear, branched or cyclic, saturated or unsaturated alkyl radicals having 1 to 30 and especially having 4 to 18 carbon atoms, c) olefinically unsaturated monomers having functional groups of the type already defined for reactivity with epoxy groups, d) optionally further acrylates and/or methacrylates and/or olefinically unsaturated monomers copolymerizable with component (a).

7. The pressure-sensitive adhesive strip of claim 1, characterized in that: a second, elastomer-based polymer component essentially immiscible with the polyacrylate component, especially a synthetic rubber (called elastomer component hereinafter), has been mixed into the pressure-sensitive adhesive compositions for layers A, C and/or D.

8. The pressure-sensitive adhesive strip of claim 1, characterized in that: the pressure-sensitive adhesive compositions for layers A, C and/or D comprise at least the following two components: 60% by weight to 90% by weight of the adhesive composition of a first, polyacrylate-based polymer component, 10% by weight to 40% by weigh of the adhesive composition of a second, elastomer-based polymer component essentially immiscible with the polyacrylate component.

9. The pressure-sensitive adhesive strip of claim 1, characterized in that: the adhesive composition of layer A is a crosslinkable adhesive composition consisting of: (a) at least one first base component comprising: (a1) as the first polymer component a base polymer component (also referred to hereinafter as base polymer for short) composed of a homopolymer, a copolymer or a homogeneous mixture of two or more homopolymers, two or more copolymers or one or more homopolymers with one or more copolymers, where at least one of the homopolymers or at least one of the copolymers in the base polymer component have groups that are functional in respect of the crosslinking, (a2) optionally, further constituents that are homogeneously miscible with or soluble in the base polymer component, (b) optionally, a second component comprising: (b1) as a further polymer component polymers that are essentially not homogeneously miscible with the base polymer, (b2) optionally, further constituents that are essentially not homogeneously miscible with and insoluble in the base polymer where component (f) is especially wholly or partly homogeneously miscible with the further polymer component (b) optionally present; (c) crosslinkers, selected from: (c1) at least one covalent crosslinker, (c2) at least one coordinative crosslinker, and (d) optionally, solvents or solvent residues.

10. The pressure-sensitive adhesive strip of claim 1, characterized in that: 15 to 100 parts by weight of tackifier have been added to the pressure-sensitive adhesive compositions of layers A, C and/or D.

11. The pressure-sensitive adhesive strip of claim 1, characterized in that: the pressure-sensitive adhesives that form layer A and/or C and/or D comprise a polymer mixture of acrylates and synthetic rubbers, where one or more crosslinkers and tackifiers have been mixed into the polymer mixture.

12. The pressure-sensitive adhesive strip of claim 1, characterized in that: at least 75% by weight of the tackifying resins are hydrocarbon resins or terpene resins or a mixture thereof.

13. The pressure-sensitive adhesive strip of claim 1, characterized in that: layer C and layer D have the same composition, and preferably layer A (apart from the microballoons added in layer A, any other crosslinking system and any dyes additionally added), layer C and layer D have an identical composition.

14. The pressure-sensitive adhesive strip of claim 1, characterized in that: a different crosslinking system is used in layer A than for layers C and/or D.

15. The pressure-sensitive adhesive strip of claim 1, characterized in that: the thickness of layers C and D is between 10 and 120 m, and the thickness of layer A is between 20 and 5000 m.

16. The pressure-sensitive adhesive strip of claim 1, characterized in that: microballoons are used for foaming of the polymer matrix of step A.

17. The pressure-sensitive adhesive strip of claim 1, characterized in that: microballoons, which have optionally been pre-expanded only slightly, are incorporated in the polymer matrix of layer A and the microballoons are expanded only after having been incorporated.

18. The pressure-sensitive adhesive strip of claim 1, characterized in that: the microballoons for the layer are chosen such that the ratio of the density of the polymer matrix of layer A to the density of the (non-pre-expanded or only slightly pre-expanded) microballoons to be incorporated into the polymer matrix of layer A is between 1 and 1:6.

19. As accumulator, or electronic device, or a cellphone comprising pressure-sensitive adhesive strip of claim 1.

20. The pressure-sensitive adhesive strip according to claim 1, consisting of: a layer A having a top side and a bottom side composed of a foamed adhesive composition based on a self-adhesive acrylate composition, a layer B composed of a film carrier, where layer B is arranged on the bottom side of layer A, where at least the main face facing layer A and preferably both main faces of the film carrier have been etched, where the surface of layer A and the surface of layer B are in direct contact with one another, a layer C composed of a self-adhesive composition which is arranged on the top side of layer A and is based on a self-adhesive acrylate composition, a layer that D composed of a self-adhesive composition which is arranged on the opposite side of layer B from layer A and is based on a self-adhesive acrylate composition.

Description

EXAMPLES

[0332] The preparation of the starting polymer is described hereinafter. The polymers examined are prepared conventionally via a free-radical polymerization in solution.

Base Polymer P1

[0333] A conventional reactor for free-radical polymerizations was charged with 47.5 kg of 2-ethylhexyl acrylate, 47.5 kg of n-butyl acrylate, 5 kg of acrylic acid and 66 kg of benzine/acetone (70/30). After passing nitrogen gas through for 45 minutes with stirring, the reactor was heated up to 58 C. and 50 g of AIBN were added. Subsequently, the external heating bath was heated to 75 C. and the reaction was conducted constantly at this external temperature. After 1 h, another 50 g of AIBN were added and, after 4 h, the mixture was diluted with 20 kg of benzine/acetone mixture.

[0334] After 5.5 and after 7 h, 150 g each time of further bis(4-tert-butylcyclohexyl) peroxydicarbonate initiator were added. After a reaction time of 22 h, the polymerization was stopped and the mixture was cooled to room temperature. The polyacrylate has an average molecular weight of M.sub.w=386 000 g/mol, polydispersity PD (Mw/Mn)=7.6.

Example: Pressure-Sensitive Adhesive Composition B1

[0335] A mixture comprising 42.425% by weight, based on the dry weight of the polymer, of the base polymer P1, 37.5% by weight of the resin Dertophene T and 20% by weight of Kraton D 1118 is prepared. A solids content of 38% is established by the addition of benzine. The mixture of polymer and resin is stirred until the resin has visibly fully dissolved. Thereafter, 0.075% by weight of the covalent crosslinker Erysis GA 240 (N,N,N,N-tetrakis(2,3-epoxypropyl)-m-xylene-,-diamine from Emerald Performance Materials, CAS NO. 63738-22-7) is added. The mixture is stirred at room temperature for 15 minutes.

TABLE-US-00001 Kraton 1118 styrene-butadiene-styrene block copolymer from Kraton Polymers 78% by weight of 3-block, 22% by weight of 2-block; block polystyrene content: 33% by weight (molecular weight M.sub.w of the 3-block content of 150 000 g/mol) Dertophene T terpene-phenol resin (softening point 110 C.; M.sub.w = 500 to 800 g/mol; D = 1.50), DRT resins, 25359-84-6

Example: Pressure-Sensitive Adhesive Composition B2

[0336] A mixture comprising 42.34% by weight, based on the dry weight of the polymer, of the base polymer P1, 35.25% by weight of the resin Dertophene T and 17% by weight of Kraton D 1118 is prepared. A solids content of 38% is established by the addition of benzine. The mixture of polymer and resin is stirred until the resin has visibly fully dissolved. Thereafter, 0.035% by weight of the covalent crosslinker Erysis GA 240 (a tetrafunctional epoxy resin based on meta-xylenediamine, CAS NO. 63738-22-7) and 0.075% by weight of Al chelate are added. The mixture is stirred at room temperature for 15 minutes.

[0337] During this period, 2.3% by weight of microballoons (Expancel 920 DU20) and 3% by weight of Hostatint are added.

TABLE-US-00002 Al chelate: Al(III) acetylacetonate (from Sigma Aldrich) Expancel 920 DU20 microballons Hostatint black pigment from Clariant

Example 1

[0338] The four-layer pressure-sensitive adhesive strip is produced by the process outlined below:

[0339] Layer C (consisting of pressure-sensitive adhesive composition B1) is coated onto a process liner, especially at 75 g/m.sup.2, and wound up.

[0340] Layer D (consisting of pressure-sensitive adhesive composition B1) is coated onto a further liner, especially at 75 g/m.sup.2, and, after drying, a PET film (layer B) of thickness 23 m that has been etched on both sides is laminated on.

[0341] The tensile strength of the PET film chosen is 185 N/mm.sup.2 in longitudinal direction and 210 N/mm.sup.2 in transverse direction. The elongation at break of the film is 146% in longitudinal direction and 92% in transverse direction. The same PET film is used in all examples.

[0342] The microballoon-containing layer A (consisting of pressure-sensitive adhesive composition B2) is coated onto a further liner, especially at 86 g/m.sup.2, and, after drying, laminated together with layer C on the process liner.

[0343] The last step includes the foaming of layer A by the action of hot air (155 C.) for about one minute. Downstream of the drying/foaming channel, the process liner on the microballoon-containing layer A is delaminated and layer D is laminated on.

Examples 2 to 4

[0344] The following pressure-sensitive adhesive strips are produced by the same method:

Example 2

[0345] 75 g/m.sup.2 of layer C [0346] 86 g/m.sup.2 of layer A [0347] 23 m PET film etched on both sides as layer B [0348] 75 g/m.sup.2 of layer D

[0349] This results in a pressure-sensitive adhesive strip having a thickness of about 300 m.

Example 3

[0350] 30 g/m.sup.2 of layer C [0351] 46 g/m.sup.2 of layer A [0352] 23 m PET film etched on both sides as layer B [0353] 30 g/m.sup.2 of layer D

[0354] This results in a pressure-sensitive adhesive strip having a thickness of about 150 m.

[0355] In FIG. 1, example 2 and a total of seven comparative examples are compared. In this case, the impact resistance measured in z direction is compared.

[0356] Example 2 has been measured twice.

[0357] The comparative examples basically have the same construction as the pressure-sensitive adhesive strip described in example 2.

[0358] However, not an etched PET film but a PET film unetched on both sides is used.

[0359] The tensile strength of the films unetched on both sides that are used in the comparative examples is greater than 180 N/mm.sup.2 in longitudinal direction and greater than 200 N/mm.sup.2 in transverse direction. The elongation at break of the films is less than 300% in longitudinal direction and less than 300% in transverse direction.

Comparative Examples 1 to 7

[0360] 75 g/m.sup.2 of layer C [0361] 86 g/m.sup.2 of layer A [0362] 23 m PET film as layer B [0363] 75 g/m.sup.2 of layer D

[0364] This results in each case in a pressure-sensitive adhesive strip having a thickness of about 300 m.

[0365] The person skilled in the art is aware of different ways of enhancing the adhesion between the PET film and the foamed layer.

[0366] A corona pretreatment is used in the first four comparative examples (first four bars in FIG. 1), subjecting the surface of the PET film and the surface of the foamed layer that are laminated to one another at a later stage to said corona pretreatment prior to lamination. During the corona pretreatment, (as well as the usual air) it is possible to use different process gases such as nitrogen that form a protective gas atmosphere or promote the corona pretreatment.

[0367] In comparative example 1, the PET film surface and the surface of the foamed layer are corona-pretreated under air.

[0368] In comparative example 2, the PET film surface is corona-pretreated under nitrogen and the surface of the foamed layer likewise under nitrogen.

[0369] In comparative example 3, the PET film surface is corona-pretreated under nitrogen and the surface of the foamed layer under air.

[0370] In comparative example 4, the PET film surface is corona-pretreated under air and the surface of the foamed layer under nitrogen.

[0371] Another way of enhancing the adhesion which is known to the person skilled in the art is to use primers between two surfaces.

[0372] In comparative examples 5 and 6 (fifth and sixth bars in FIG. 1), both surfaces are treated with two commercial primers based on an aqueous crosslinking acrylate before these surfaces are laminated together.

[0373] In comparative example 7 (seventh bar in FIG. 1), an untreated 23 m-thick PET film (i.e. neither primed nor corona-pretreated) is laminated onto the bonding surface of the foamed layer.

[0374] The bonding force tests as shown in tabular form in FIG. 2 show that the use of an etched PET film offers no advantages over the known measures; all results are comparable within the scope of measurement accuracy.

[0375] PA initial steel (foam side) means immediate bonding force on steel, the pressure-sensitive adhesive strip having been bonded such that the foamed layer is between the substrate and PET film.

[0376] PA initial steel (PET side) means immediate bonding force on steel, the pressure-sensitive adhesive strip having been bonded such that the PET film is between the substrate and foamed layer.

[0377] PA initial PC (foam side) means immediate bonding force on polycarbonate, the pressure-sensitive adhesive strip having been bonded such that the foamed layer is between the substrate and PET film.

[0378] PA 3d steel (foam side) means bonding force on steel after storage for three days, the pressure-sensitive adhesive strip having been bonded such that the foamed layer is between the substrate and PET film.

[0379] The other conditions in the bonding force measurement arise correspondingly.

[0380] The use of an etched PET film does not show any significant effect either in terms of immediate bonding force or in terms of bonding force after three days on steel or polycarbonate.

[0381] In the push-out test, by contrast, and also in terms of impact resistance in z direction and in x,y direction, a significant improvement can be seen in properties resulting from the use of an etched PET film compared to a corona pretreatment, to priming, especially to priming with aqueous, crosslinked acrylate-based primers, or to nontreatment of the PET film surface.

[0382] Under shock stress, the use of an etched PET film leads to a distinctly improved pressure-sensitive adhesive strip.

[0383] The pressure-sensitive adhesive strips of the invention are very impact-resistant. This can be seen in that they especially fulfill the following conditions (i) and (ii): [0384] (i) push-out resistance 120 N, preferably 150 N [0385] (ii) impact resistance, z direction 0.45 J, preferably 0.5 J, very preferably 0.6 J

Test Methods

[0386] Unless stated otherwise, all measurements were conducted at 23 C. and 50% rel. air humidity.

[0387] The mechanical and adhesive data were ascertained as follows:

Elongation at Break and Tensile Strength (R1 Method)

[0388] Elongation at break and tensile strength were measured in accordance with DIN 53504 using dumbbell specimens of size S3 at a separation speed of 300 mm per min. The test conditions were 23 C. and 50% rel. air humidity.

Tackifying Resin Softening Temperature

[0389] The tackifying resin softening temperature is carried out in accordance with the relevant methodology, which is known as Ring & Ball and is standardized according to ASTM E28.

Gel Permeation Chromatography GPC

[0390] The figures for number-average molar mass Mn, weight-average molecular weight M.sub.w and polydispersity PD are based on determination by gel permeation chromatography. The determination is carried out using a clear-filtered 100 L sample (sample concentration 1 g/L). The eluent used is THF with 0.1% by volume of trifluoroacetic acid. The measurement is made at 25 C. The precolumn used is a column of the PSS-SDV type, 5, 10.sup.3 , ID 8.0 mm50 mm. For the separation, the columns of the PSS-SDV type, 5, 10.sup.3 , and also 105 and 106 , each with ID 8.0 mm300 mm (columns from Polymer Standards Service; detection by means of Shodex RI71 differential refractometer), are used. The flow rate is 1.0 mL per minute.

[0391] Calibration is effected against PMMA standards (polymethylmethacrylate calibration) or, in the case of (synthetic) rubbers, against polystyrene.

DACP

[0392] The DACP is the diacetone cloud point and is determined by cooling a heated solution of 5 g of resin, 5 g of xylene and 5 g of diacetone alcohol to the point at which the solution turns cloudy.

Ball Drop Test (Impact Resistance)

[0393] A square sample in the shape of a frame was cut out of the adhesive tape to be examined (external dimensions 33 mm33 mm; border width 3.0 mm; internal dimensions (window cut-out) 27 mm27 mm). This sample was stuck to an ABS frame (external dimensions 45 mm45 mm; border width 10 mm; internal dimensions (window cut-out) 25 mm25 mm; thickness 3 mm). A PMMA window of 35 mm35 mm was stuck to the other side of the double-sided adhesive tape. The bonding of ABS frame, adhesive tape frame and PMMA window was effected such that the geometric centers and the diagonals were each superimposed on one another (corner-to-corner). The bonding area was 360 mm.sup.2. The bond was subjected to a pressure of 10 bar for 5 s and stored under conditions of 23 C./50% relative humidity for 24 hours.

[0394] Immediately after the storage, the adhesive composite composed of ABS frame, adhesive tape and PMMA sheet was placed by the protruding edges of the ABS frame onto a framework (sample holder) such that the composite was aligned horizontally and the PMMA sheet faced downward in a freely suspended manner. A steel ball of the weight specified in each case was allowed to drop vertically from a height of up to 250 cm (through the window of the ABS frame) onto the sample thus arranged, centered onto the PMMA sheet (test conditions 23 C., 50% relative humidity). Three tests were conducted with each sample, if the PMMA sheet had not become detached beforehand.

[0395] The ball drop test is considered to have been passed if the bond did not part in any of the three tests.

[0396] In order to be able to compare experiments with different ball weights, the energy was calculated as follows:

E=height [m]*ball weight [kg]*9.81 m/s.sup.2

Push-Out Resistance (z Plane)

[0397] By means of the push-out test, it is possible to obtain conclusions as to how high the stability of a bond of a component is in a frame-like body, for example a window in a housing.

[0398] A rectangular sample in the shape of a frame was cut out of the adhesive tape to be examined (external dimensions 43 mm33 mm; border width in each case 2.0 mm; internal dimensions (window cut-out) 39 mm29 mm, bond area on the top and bottom side 288 mm.sup.2 in each case). This sample was bonded to a rectangular ABS polymer frame (ABS=acrylonitrile-butadiene-styrene copolymers) (external dimensions 50 mm40 mm, border width of each of the long borders 8 mm; border width of each of the short borders 10 mm; internal dimensions (window cut-out) 30 mm24 mm; thickness 3 mm). A rectangular PMMA sheet (PMMA=polymethylmethacrylate) with dimensions of 45 mm35 mm was bonded to the other side of the sample of the double-sided adhesive tape. The full available bonding area of the adhesive tape was utilized. The bonding of ABS frame, adhesive tape sample and PMMA window was effected such that the geometric centers, the angle bisectors of the acute diagonal angles and the angle bisectors of the obtuse diagonal angles of the rectangles were each superimposed on one another (corner-to-corner, long sides on long sides, short sides on short sides). The bonding area was 288 mm.sup.2. The bond was subjected to a pressure of 10 bar for 5 s and stored under conditions of 23 C./50% relative humidity for 24 hours.

[0399] Immediately after the storage, the adhesive composite composed of ABS frame, adhesive tape and PMMA sheet was placed by the protruding edges of the ABS frame onto a framework (sample holder) such that the composite was aligned horizontally and the PMMA sheet faced downward in a freely suspended manner.

[0400] A pressure ram is then moved vertically upward through the window of the ABS frame at a constant speed of 10 mm/min, such that it presses onto the center of the PMMA sheet, and the respective force (determined from the respective pressure and contact area between the ram and sheet) is registered as a function of the time from the first contact of the ram with the PMMA sheet until just before it drops away (test conditions: 23 C., 50% relative humidity). The force acting immediately prior to the failure of the adhesive bond between PMMA sheet and ABS frame (maximum force F.sub.max in the force-time diagram in N) is registered as the response of the push-out test.

Bonding Force

[0401] The determination of bonding force (according to AFERA 5001) is conducted as follows. The defined bonding substrate used is a polished steel sheet (302 stainless steel according to ASTM A 666; 50 mm125 mm1.1 mm; shiny annealed surface; surface roughness 5025 mm arithmetic average deviation from the baseline) or a polycarbonate. The bondable area element to be examined is cut to a width of 20 mm and a length of about 25 cm, provided with a handling section and, immediately thereafter, pressed onto the bonding substrate chosen in each case five times with a 4 kg steel roll at an advance rate of 10 m/min. Immediately thereafter or after three days had passed, the bondable area element was pulled away from the bonding substrate at an angle of 180 with a tensile tester (from Zwick) at a speed v=300 mm/min, and the force required for the purpose at room temperature was measured. The measured value (in N/cm) is obtained as the average value from three individual measurements.

Static Glass Transition Temperature T.SUB.g

[0402] Glass transition pointsreferred to synonymously as glass transition temperaturesare 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.

Impact Resistance; z Direction

[0403] A square sample in the shape of a frame was cut out of the adhesive tape to be examined (external dimensions 33 mm33 mm; border width 2.0 mm; internal dimensions (window cut-out) 29 mm29 mm). This sample was stuck to a PC frame (external dimensions 45 mm45 mm; border width 10 mm; internal dimensions (window cut-out) 25 mm25 mm; thickness 3 mm). A PC window of 35 mm35 mm was stuck to the other side of the double-sided adhesive tape. The bonding of PC frame, adhesive tape frame and PC window was effected such that the geometric centers and the diagonals were each superimposed on one another (corner-to-corner). The bonding area was 248 mm.sup.2. The bond was subjected to a pressure of 248 N for 5 s and stored under conditions of 23 C./50% relative humidity for 24 hours.

[0404] Immediately after the storage, the adhesive composite composed of PC frame, adhesive tape and PC window was braced by the protruding edges of the PC frame in a sample holder such that the composite was aligned horizontally and the PC window was beneath the frame. The sample holder was then inserted centrally in the intended receptacle of the DuPont Impact Tester. The impact head of weight 190 g was used in such a way that the circular impact geometry with a diameter of 20 mm impacted centrally and flush on the window side of the PC window.

[0405] A weight having a mass of 150 g guided on two guide rods was allowed to drop vertically from a height of 5 cm onto the composite composed of sample holder, sample and impact head thus arranged (test conditions: 23 C., 50% relative humidity). The height from which the weight dropped was increased in 5 cm steps until the impact energy introduced destroyed the sample as a result of the impact stress and the PC window parted from the PC frame.

[0406] In order to be able to compare experiments with different samples, the energy was calculated as follows:

E[J]=height [m]*mass of weight [kg]*9.81 m/s.sup.2

[0407] Five samples per product were tested, and the mean energy was reported as index for impact resistance.

Transverse Impact Resistance; x,y Plane

[0408] A square sample in the shape of a frame was cut out of the adhesive tape to be examined (external dimensions 33 mm33 mm; border width 2.0 mm; internal dimensions (window cut-out) 29 mm29 mm). This sample was stuck to a PC frame (external dimensions 45 mm45 mm; border width 10 mm; internal dimensions (window cut-out) 25 mm25 mm; thickness 3 mm). A PC window of 35 mm35 mm was stuck to the other side of the double-sided adhesive tape. The bonding of PC frame, adhesive tape frame and PC window was effected such that the geometric centers and the diagonals were each superimposed on one another (corner-to-corner). The bonding area was 248 mm.sup.2. The bond was subjected to a pressure of 248 N for 5 s and stored under conditions of 23 C./50% relative humidity for 24 hours.

[0409] Immediately after the storage, the adhesive composite composed of PC frame, adhesive tape and PC sheet window was braced by the protruding edges of the PC frame in a sample holder such that the composite was aligned vertically. The sample holder was then inserted centrally the intended receptacle of the DuPont Impact Tester. The impact head of weight 300 g was used in such a way that the rectangular impact geometry with dimensions of 20 mm3 mm impacted centrally and flush on the end face of the PC window facing upward.

[0410] A weight having a mass of 150 g guided on two guide rods was allowed to drop vertically from a height of 5 cm onto the composite composed of sample holder, sample and impact head thus arranged (test conditions: 23 C., 50% relative humidity). The height from which the weight dropped was increased in 5 cm steps until the impact energy introduced destroyed the sample as a result of the crosswise impact stress and the PC window parted from the PC frame.

[0411] In order to be able to compare experiments with different samples, the energy was calculated as follows:

E[J]=height [m]*mass of weight [kg]*9.81 m/s.sup.2

[0412] Five samples per product were tested, and the mean energy was reported as index for transverse impact resistance.

Micro-Shear Test

[0413] This test serves for rapid testing of the shear strength of adhesive tapes under thermal stress.

Test Sample Preparation for Micro-Shear Test:

[0414] A piece of adhesive tape cut out of the respective specimen (length about 50 mm, width 10 mm) is bonded to an acetone-cleaned steel test sheet, such that the steel plate projects beyond the adhesive tape to the right and left and that the adhesive tape projects beyond the test plate at the upper edge by 2 mm. The bonding area of the sample is height.Math.width=13 mm.Math.10 mm. A 2 kg steel roll is then rolled over the bonding site six times at a speed of 10 m/min. The adhesive tape is reinforced flush with a stable adhesive strip which serves as contact point for the distance sensor. The sample is suspended vertically by means of the test plate.

Micro-Shear Test:

[0415] The specimen to be analyzed is weighted down at the lower end with a weight of 300 g. The test temperature is 40 C., the test duration 30 minutes (15 minutes under stress and 15 minutes without stress). The shear travel after the given test duration at constant temperature is reported as the result in m, specifically as the maximum value [max; maximum shear travel resulting from stress for 15 minutes]; as the minimum value [min; shear travel (residual deflection) after removal of stress 15 min; when stress is removed, there is reverse movement as a result of relaxation]. Likewise reported is the elastic component in % [elast; elastic component=(maxmin).Math.100/max].

T-Peel Test

[0416] The laminate to be tested (total of 3 strips, about 30020 mm, or in the defined width) is pulled apart manually at one end of the specimen to form two tabs of length about 100 mm according to the material, with the aid of a suitable solvent, blade or the like, or as specified.

[0417] The T-peel test is shown in schematic form in FIG. 9.

[0418] One etched PET film 20, 30 each is laminated onto the top side and the bottom side of the pressure-sensitive adhesive strip 100, with the PET films 20, 30 protruding by 100 mm on one side of the pressure-sensitive adhesive strip 10 in order thus to form two tabs. The pressure-sensitive adhesive strip 10 has the dimensions 30020 mm.sup.2.

[0419] By bending the tabs, a T is formed. One end each is clamped in the upper and lower clamps in a Zwick tensile tester. The machine is started at the defined speed.

[0420] At a 180 pulling angle, the clamps are pulled apart at a speed of 50 mm/min and the force per unit test specimen width in N/cm at which the foam layer of the pressure-sensitive adhesive strip 10 splits (called cohesive fracture) is measured.

[0421] The measurements are triple determinations and are averaged.