PRESSURE-SENSITIVE ADHESIVE STRIP

Abstract

The invention relates to a pressure-sensitive adhesive strip composed of three layers, comprising an inner layer F composed of a nonextensible film carrier, a layer SK1 composed of a self-adhesive composition arranged on one of the surfaces of the film carrier layer F and based on a foamed acrylate composition, a layer SK2 composed of a self-adhesive composition arranged on the opposite surface of the film carrier layer F from layer SK1 and based on a foamed acrylate composition.

Claims

1. A pressure-sensitive adhesive strip composed of three layers, comprising (i) an inner layer F composed of a film carrier, (ii) a layer SK1 composed of a self-adhesive composition arranged on one of the surfaces of the film carrier layer F and based on a foamed acrylate composition, (iii) a layer SK2 composed of a self-adhesive composition arranged on the opposite surface of the film carrier layer F from layer SK1 and based on a foamed acrylate composition.

2. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the film carrier is nonextensible.

3. The pressure-sensitive adhesive strip as claim 1, wherein the film carrier has a tensile strength of in each case more than 100 N/mm.sup.2, in longitudinal direction and in transverse direction.

4. The pressure-sensitive adhesive strip as claimed in claim 1, having: a symmetric construction in relation to the composition of the layers, in that the foamed self-adhesive acrylate compositions of the two self-adhesive composition layers SK and SK2 are chemically identical, and/or a structurally symmetric construction, that the two self-adhesive composition layers SK1 and SK2 are of the same thickness and/or have the same density.

5. (canceled)

6. The pressure-sensitive adhesive strip as claimed in claim 1, wherein one or both surfaces of the film carrier layer F have been physically and/or chemically pretreated, wherein optionally the pretreatment is an etching operation and/or a corona treatment and/or a primer treatment.

7. (canceled)

8. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the acrylate composition for at least one of the self-adhesive composition layers SK1 and SK2 is formed using a polyacrylate that can be derived from the following monomer composition: (i) acrylic esters and/or methacrylic esters of the following formula: CH.sub.2=C(R.sup.1)(COOR.sup.2) where R.sup.1H or CH.sub.3 and R.sup.2H or linear, branched or cyclic, saturated or unsaturated alkyl radicals having 1 to 30 and especially having 4 to 18 carbon atoms, (ii) optionally olefinically unsaturated comonomers having functional groups of the type already defined for reactivity with epoxy groups, (iii) optionally further acrylates and/or methacrylates and/or olefinically unsaturated monomers copolymerizable with component (i).

9. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the pressure-sensitive adhesive compositions for at least one of the self-adhesive composition layers SK1 and SK2 comprise at least the following two components: (P) a first, polyacrylate-based polymer component, (E) a second, elastomer-based polymer component which is essentially immiscible with the polyacrylate component.

10. The pressure-sensitive adhesive strip as claimed in claim 9, wherein the polyacrylate-based polymer component (P) has a proportion of 60% by weight to 90% by weight, the elastomer-based polymer component (E) has a proportion of 10% by weight to 40% by weight, in the entirety (100%) of the two components (P) and (E).

11. The pressure-sensitive adhesive strip as claimed in claim 9, wherein the elastomer-based polymer component (C) is formed by one or more synthetic rubbers or comprises one or more synthetic rubbers.

12. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the pressure-sensitive adhesive compositions for at least one of the self-adhesive composition layers SK1 and SK2 have been admixed with crosslinkers.

13. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the adhesive composition for at least one and of the self-adhesive composition layers SK1 and SK2 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, or all the polymers, 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 wholly or partly homogeneously miscible with the further polymer component (b) optionally present; (c) crosslinkers selected from (c1) and (c2) below: (c1) at least one covalent crosslinker, (c2) at least one coordinative crosslinker, and (d) optionally solvents or solvent residues.

14. The pressure-sensitive adhesive strip as claimed claim 1, wherein 15 to 100 parts by weight of tackifier per 100 parts by weight of adhesive composition without tackifier have been added to the pressure-sensitive adhesive compositions for at least one of the self-adhesive composition layers SK1 and SK2.

15. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the tackifiers are tackifying resins.

16. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the polymer matrix of the self-adhesive composition layers SK1 and/or SK2 is foamed using microballoons.

17. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the proportion of the microballoons in the self-adhesive composition layer SK1 or the self-adhesive composition layer SK2 or in both self-adhesive composition layers SK1 and SK2 (based on the unexpanded microballoons) is up to 12% by weight, based in each case on the overall composition of the corresponding layer SK1 or SK2.

18. The pressure-sensitive adhesive strip as claimed in claim 1, wherein after foaming, at least 90% of all voids formed by microballoons in layer SK1 or layer SK2 or in both layers SK and SK2 have a maximum diameter of 7 to 200 m.

19. The pressure-sensitive adhesive strip as claimed in claim 18, wherein the elastomer component in the polyacrylate component forms domains, where the maximum diameter of at least 90% of the domains of the elastomer component is within the size range below 100 m, and the maximum diameter of the voids formed by at least 90% of all microballoons is likewise below 100 m.

20. The pressure-sensitive adhesive strip as claimed in claim 16, wherein microballoons that have been pre-expanded only slightly, if at all, are incorporated into the polymer matrix of the self-adhesive composition layers SK1 and/or SK2 and are expanded only after having been incorporated.

21. The pressure-sensitive adhesive strip as claimed in claim 16, wherein the microballoons for the foaming of the self-adhesive composition layers SK1 and/or SK2 are chosen such that the ratio of the density of the polymer matrix of the corresponding adhesive composition layers to the density of the (non-pre-expanded or only slightly pre-expanded) microballoons to be incorporated into the polymer matrix of the respective layer itself is between 1 and 1:6.

22. A method for bonding of components selected from the group consisting of accumulators and electronic devices, comprising a step of applying the pressure-sensitive adhesive strip of claim 1 to a substrate.

Description

EXAMPLES

Base Polymers, Blends

[0298] There follows a description of the preparation of the starting polymer and the blends comprising microballoons that are produced therefrom. The polymers examined are prepared conventionally via a free-radical polymerization in solution.

Base Polymer P1

[0299] 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.

[0300] 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

[0301] 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-a,a-diamine from Emerald Performance Materials, CAS NO. 63738-22-7) is added. The mixture is stirred at room temperature for 15 minutes.

[0302] During this period, for production of blends 1, 2, 3, 9 and 10, the amounts of microballoons (Expancel 920 DU20) specified in table 2 are added.

Example: Pressure-Sensitive Adhesive Composition B2

[0303] 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.

[0304] During this period, 1.25% by weight of microballoons (Expancel 920 DU20) and 3% by weight of Hostatint are added (production of blend 4).

Example: Pressure-Sensitive Adhesive Composition B3

[0305] A mixture comprising 29.925% by weight, based on the dry weight of the polymer, of the base polymer P1, 30% by weight of the resin Dertophene T and 40% 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 (a tetrafunctional epoxy resin based on meta-xylenediamine, CAS NO. 63738-22-7) are added. The mixture is stirred at room temperature for 15 minutes.

[0306] During this period, for production of blends 5 to 8, the amounts of microballoons (Expancel 920 DU20) specified in table 2 are added.

Example: Pressure-Sensitive Adhesive Composition B4

[0307] 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.

[0308] During this period, for production of blends 11 to 14, the amounts of microballoons (Expancel 920 DU20) specified in table 2 are added. [0309] 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 [0310] (molecular weight M.sub.w of the 3-block content of 150 000 g/mol) [0311] 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 [0312] Al chelate: Al(III) acetylacetonate (from Sigma Aldrich) [0313] Expancel 920 DU20 microballoons [0314] Hostatint black pigment from Clariant

TABLE-US-00001 TABLE 1 PSA PSA PSA PSA compo- compo- compo- compo- sition 1 sition 2 sition 3 sition 4 Propor- Propor- Propor- Propor- Raw tion (% tion (% tion (% tion (% material by wt.) by wt.) by wt.) by wt.) Acrylate 42.425 42.39 29.925 59.925 Kraton 1118 20 20 40 Dertophene T 37.5 37.5 30 40 Erysis GA 240 0.075 0.035 0.075 0.075 AI chelate 0.075 Total 100 100 100 100

TABLE-US-00002 TABLE 2 Base composition Microballoons * Black pigment * Blend 1 PSA composition 1 2.3% by wt. Blend 2 PSA composition 1 1.25% by wt. Blend 3 PSA composition 1 0.8% by wt. Blend 4 PSA composition 2 1.25% by wt. 3% by wt. Blend 5 PSA composition 3 0.8% by wt. Blend 6 PSA composition 3 1.5% by wt. Blend 7 PSA composition 3 2.3% by wt. Blend 8 PSA composition 3 3.5% by wt. Blend 9 PSA composition 1 1.5% by wt. Blend 10 PSA composition 1 3.5% by wt. Blend 11 PSA composition 4 0.8% by wt. Blend 12 PSA composition 4 1.2% by wt. Blend 13 PSA composition 4 2.3% by wt. Blend 14 PSA composition 4 3.5% by wt. * Figures based on 100% by weight of blended adhesive composition in each case (composed of base composition, microballoons and, if present, black pigment)

Production of the Pressure-Sensitive Adhesive Strips

[0315] The respective blends for production of the microballoon-containing layer are coated at the desired basis weight (cf. table 3) onto a process liner (siliconized film). The layers thus obtained are dried (100 C. for 15 min) and used as layers SK1 and SK2 for the pressure-sensitive adhesive tapes.

[0316] Three-layer symmetric pressure-sensitive adhesive tapes (examples 1 to 28, comparative examples 3 and 4) are obtained by laminating the respective layers SK1 and SK2present on the process liner, still unfoamedby their respective exposed self-adhesive composition surfaces onto the two pretreated surfaces of a PET film (pre-treatment of the surfaces according to the details in table 3: corona therein is an abbreviation of corona pretreatment).

[0317] Thereafter, the foaming step takes place with the composite thus obtained, with simultaneous foaming of the two layers SK1 and SK2.

[0318] Four-layer comparative pressure-sensitive adhesive tapes (comparative examples 1 and 2) are obtained by laminating a dried, microballoon-containing adhesive composition layer (according to the details in table 3) by their free pressure-sensitive adhesive surface onto a PET film that has been etched on both sides. Thereafter, an optionally dried layer of the outer pressure-sensitive adhesive compositions, present on a process liner, is laminated onto each of the outer surfaces of the composite composed of PET film and microballoon-containing layer thus obtained.

[0319] The last step of the respective adhesive strip production comprises the foaming of the layers of the respective pressure-sensitive adhesive strip that are to be foamed by the action of hot air (about 170 C.) a for about one minute.

[0320] As required, one or both of the outer liners are removed again for the studies.

[0321] By the aforementioned processes, the following pressure-sensitive adhesive strips according to table are produced:

TABLE-US-00003 TABLE 3 Total thickness Example Layer sequence (after foaming) Example 1 41 g/m.sup.2 of blend 1 150 m 23 m of corona PET 41 g/m.sup.2 of blend 1 Example 2 90 g/m.sup.2 of blend 1 300 m 23 m of corona PET 90 g/m.sup.2 of blend 1 Example 3 54 g/m.sup.2 of blend 3 150 m 23 m of corona PET 54 g/m.sup.2 of blend 3 Example 4 44 g/m.sup.2 of blend 7 150 m 23 m of etched PET 44 g/m.sup.2 of blend 7 Example 5 98 g/m.sup.2 of blend 7 300 m 23 m of etched PET 98 g/m.sup.2 of blend 7 Example 6 54 g/m.sup.2 of blend 5 150 m 23 m of etched PET 54 g/m.sup.2 of blend 5 Example 7 38 g/m.sup.2 of blends 110 m 23 m of etched PET 38 g/m.sup.2 of blend 5 Example 8 33 g/m.sup.2 of blend 6 110 m 23 m of etched PET 33 g/m.sup.2 of blend 6 Example 9 30 g/m.sup.2 of blend 7 110 m 23 m of etched PET 30 g/m.sup.2 of blend 7 Example 10 25 g/m.sup.2 of blend 8 110 m 23 m of etched PET 25 g/m.sup.2 of blend 8 Example 11 94 g/m.sup.2 of blend 1 300 m 23 m of etched PET 94 g/m.sup.2 of blend 1 Example 12 43 g/m.sup.2 of blend 1 150 m 23 m of etched PET 43 g/m.sup.2 of blend 1 Example 13 56 g/m.sup.2 of blend 3 150 m 23 m of etched PET 56 g/m.sup.2 of blend 3 Example 14 94 g/m.sup.2 of blend 7 300 m 23 m of etched PET 94 g/m2 of blend 7 Example 15 43 g/m.sup.2 of blend 7 150 m 23 m of etched PET 43 g/m.sup.2 of blend 7 Example 16 56 g/m.sup.2 of blend 5 150 m 23 m of etched PET 56 g/m.sup.2 of blend 5 Example 17 51 g/m.sup.2 of blend 2 150 m 23 m of etched PET 51 g/m.sup.2 of blend 2 Example 18 100 g/m.sup.2 of blend 2 300 m 50 m of etched PET 100 g/m.sup.2 of blend 2 Example 19 51 g/m.sup.2 of blend 4 150 m 23 m of etched PET 51 g/m.sup.2 of blend 4 Example 20 100 g/m.sup.2 of blend 4 300 m 50 m of etched PET 100 g/m.sup.2 of blend 4 Example 21 40 g/m.sup.2 of blend 3 100 m 6 m of etched PET 40 g/m.sup.2 of blend 3 Example 22 36 g/m.sup.2 of blend 9 100 m 6 m of etched PET 36 g/m.sup.2 of blend 9 Example 23 30 g/m.sup.2 of blend 1 100 m 6 m of etched PET 30 g/m.sup.2 of blend 1 Example 24 27 g/m.sup.2 of blend 10 100 m 6 m of etched PET 27 g/m.sup.2 of blend 10 Example 25 40 g/m.sup.2 of blend 11 100 m 6 m of etched PET 40 g/m.sup.2 of blend 11 Example 26 36 g/m.sup.2 of blend 12 100 m 6 m of etched PET 36 g/m.sup.2 of blend 12 Example 27 30 g/m2 of blend 13 100 m 6 m of etched PET 30 g/m.sup.2 of blend 13 Example 28 27 g/m.sup.2 of blend 14 100 m 6 m of etched PET 27 g/m.sup.2 of blend 14 Comparative 30 g/m.sup.2 of PSA composition 2.sup.# 150 m example 1 23 m of etched PET 50 g/m.sup.2 of blend 1 30 g/m.sup.2 of PSA composition 2.sup.# Comparative 75 g/m.sup.2 of PSA composition 2.sup.# 300 m example 2 23 m of etched PET 86 g/m.sup.2 of blend 1 75 g/m.sup.2 of PSA composition 2.sup.# Comparative 47 g/m.sup.2 of PSA composition 4.sup.# 100 m example 3 6 m of etched PET 47 g/m.sup.2 of PSA composition 4.sup.# Comparative 47 g/m.sup.2 of PSA composition 1.sup.# 100 pm example 4 6 m of etched PET 47 g/m.sup.2 of PSA composition 1.sup.# Comparative 44 g/m.sup.2 of PSA composition 1.sup.# 110 m example 5 23 m of etched PET 44 g/m.sup.2 of PSA composition 1.sup.# .sup.#pressure-sensitive adhesive compositions without blending with microballoons

[0322] All the (etched/corona-treated) PET films used had tensile strengths in longitudinal direction of more than 180 N/mm.sup.2 and in transverse direction of more than 200 N/mm.sup.2. All PET films used additionally had elongation at break values in longitudinal direction of less than 200%, and in transverse direction of less than 120%. Tensile strengths and elongations at break were each ascertained by method R1.

REFERENCE METHODS

[0323] Unless stated otherwise, all measurements were conducted at 23 C. and 50% rel. air humidity.

Elongation at Break and Tensile Strength (Method R1)

[0324] 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 (Method R2)

[0325] 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 (Method R3)

[0326] 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.

[0327] Calibration is effected against PMMA standards (polymethylmethacrylate calibration) or, in the case of (synthetic) rubbers, against polystyrene.

Density (Method R4)

[0328] The density of the unfoamed and foamed adhesive composition layers is ascertained by forming the quotient of mass applied and thickness of the adhesive composition layer applied to a carrier or liner. The mass applied can 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 material used.

[0329] The thickness of the layer can be determined by means of commercial thickness measuring instruments (caliper test instruments) with accuracies of less than a 1 m deviation. 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 .(Method R5)

[0330] 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.

Micro-Shear Test

[0331] This test serves for rapid testing of the shear strength of adhesive tapes under thermal stress.

Test Sample Preparation for Micro-Shear Test:

[0332] 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 mm10 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:

[0333] 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].

Test Methods

[0334] Unless stated otherwise, all measurements were conducted at 23 C. and 50% rel. air humidity.

Ball Drop Test (Impact Resistance) (Method P1)

[0335] 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.

[0336] 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 (weight 5.6 g or 32.6 g) was allowed to drop vertically from a height of up to 250 cm (through the window of the ABS frame) centered onto the PMMA sheet in the sample thus arranged (test conditions 23 C., 50% relative humidity). Three tests were conducted with each sample, if the PMMA sheet had not become detached beforehand.

[0337] The ball drop test is considered to have been passed if the bond did not part in any of the three tests.

[0338] 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) (Method P2)

[0339] 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.

[0340] 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.

[0341] 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.

[0342] 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 (Methods P3: Steel and P4: Polycarbonate)

[0343] 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 nm 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, 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.

Impact Resistance; z Direction (Method P5)

[0344] 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.

[0345] 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 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.

[0346] 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.

[0347] 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

[0348] Five samples per product were tested, and the mean energy was reported as index for impact resistance.

Antirepulsion Test (Method P6)

[0349] The bare side of the double-sided adhesive tape to be examined was bonded to a 0.5 mm-thick aluminum plate (external dimensions 150 mm20 mm) with the aid of a rubber roller. The covered side was applied to the middle of a 3 mm-thick (external dimensions 200 mm25 mm) PC sheet. The bonding area was 3000 mm.sup.2. Thereafter, the adhesive bond composed of PC sheet, adhesive tape and aluminum plate was pressed by rolling a 4 kg hand roller back and forth five times and conditioned at 23 C./50% relative humidity for 72 hours.

[0350] Immediately after the storage, the adhesive bond was clamped by the protruding edges of the PC sheet into a circular arc-shaped sample holder with an opening angle of 33.sup.0 in such a way that the composite was aligned centrally and with the aluminum plate upward in the sample holder. The PC sheet was in full contact with the sample holder, such that the bond was also subjected to bending by the opening angle.

[0351] The composite composed of sample holder and adhesive bond in this arrangement was stored in a heating oven at a temperature of 50 C. for 48 hours.

[0352] Directly after the storage, a steel ruler was used to measure the lifting of the bond between adhesive tape and PC sheet or adhesive tape and aluminum plate in the perpendicular direction at the ends of the longitudinal sides of the adhesive bond.

[0353] In order to be able to compare experiments with different samples, the lifting was calculated for one sample by forming the average from the lifting of both sides.

Sample lifting [mm]=(lifting on the left [mm]+lifting on the right [mm])/2

[0354] Three samples per product were tested, and the average sample lifting was reported as an index for the repulsion resistance of the product. The smaller the lifting, the better the reliability of bonding with the adhesive product tested.

Results

[0355] The results from the tests for the individual examples are presented in table 4 below:

TABLE-US-00004 TABLE 4 Impact Steel Polycarbonate Repulsion Total Density Push- Ball resistance bonding force bonding force resistance thickness kg/m.sup.3 out (N) drop (J) (z direction) (J) [N/cm] (N/cm) (mm) Test method (cf. table 3) R4 P2 P1 P5 P3 P4 P6 Example 1 150 m 652 108 0.53 0.57 Example 2 300 m 650 138 0.80 0.93 14.7 Example 3 150 m 857 142 0.46 1.09 12.4 Example 4 150 m 695 91 0.53 0.72 Example 5 300 m 705 66 0.46 0.54 Example 6 150 m 855 96 0.46 0.87 Example 7 110 m 880 113 0.04 0.68 Example 8 110 m 775 88 0.08 0.49 Example 9 110 m 695 77 0.14 0.46 Example 10 110 m 570 60 0.21 0.35 Example 11 300 m 665 138 0.72 0.76 10.1 Example 12 150 m 675 128 0.53 0.63 11.3 Example 13 150 m 840 143 0.46 0.96 10.1 Example 14 300 m 670 104 0.66 0.68 Example 15 150 m 700 70 0.46 0.51 Example 16 150 m 845 101 0.66 0.85 Example 17 150 m 790 129 0.59 0.79 9.8 10.1 36 Example 18 300 m 793 126 0.80 0.97 14.5 15.7 15 Example 19 150 m 805 138 0.59 0.74 10.6 10.2 10 Example 20 300 m 790 129 0.78 0.94 12.5 13.6 4 Example 21 100 m 0.47 Example 22 100 m 0.49 Example 23 100 m 0.43 Example 24 100 m 0.34 Example 25 100 m 0.28 Example 26 100 m 0.32 Example 27 100 m 0.14 Example 28 100 m 0.18 Comparative 150 m 650 180 0.40 0.37 11.4 10.4 example 1 Comparative 300 m 665 164 0.46 0.51 11.2 11.2 example 2 Comparative 100 m 0.10 example 3 Comparative 100 m 990 190 0.03 0.22 17 example 4 Comparative 110 m 999 186 0.03 0.24 example 5

[0356] A target application for characterization of the demands presented in accordance with the invention is represented by the impact resistance test (method P5). Here, for the inventive examples, good results were found throughout, which are superior to those for the non-foamed comparative examples (comparative examples 3 and 4)with corresponding product thicknesses in each case.

[0357] In addition, it is found that the impact resistance results for the three-layer products are superior with respect to four-layer products of comparable thickness (comparative examples 1 and 2).

[0358] The anti-repulsion test (method P6) shows another advantage of the bonded products that have been produced with the specific embodiment of the adhesive composition of the invention (adhesive composition 2 with coordinative and covalenti.e. dualcrosslinking) over those with polyacrylate adhesive composition layers without dual crosslinking, and so the dual-crosslinked adhesive products are especially advantageous where the repulsion properties of the adhesive product are important. In this regard, see examples 17, 18 by comparison with examples 19, 20; examples 17 and 19 are of equal thickness to 18 and 20 respectively.

[0359] However, products that do not have dual crosslinking likewise have excellent values with regard to the other parameters.

[0360] It is also possible to infer the trend from the results that the optimal proportion of microballoons in the pressure-sensitive adhesive composition is within the range between 0.5 and 3 (in this regard see, for example, examples 7 to 10 and comparative example 5 with the same thickness and based on the same base adhesive composition).

[0361] It can be inferred from a comparison of examples 21 to 24 (pressure-sensitive adhesive composition 1 based on a blend of acrylate polymers and rubber) with examples 25 to 28 (resin-blended pressure-sensitive adhesive composition 4; resin-blended acrylate adhesive composition) that the blend composition has higher impact resistance values and hence is superior to the straight acrylate composition.

[0362] The respective measurement series (variation in the proportions of the microballoons in the respective examples 21 to 24 and comparative example 4, or examples 25 to 28 and comparative example 3) confirm the optimal content of microballoons already ascertained above in the respective pressure-sensitive adhesive compositions.