REMOVABLE CONTACT-ADHESIVE TAPE

Abstract

The invention relates to a contact-adhesive tape which can be removed damage-free and residue-free by stretching the tape substantially within the adhesion plane and which consists of one or more adhesive substance layers, all made of a contact-adhesive substance expanded with micro-balloons, and one or two optional intermediate backings. The disclosed contact-adhesive tape consists exclusively of the aforementioned adhesive substance layers and optional intermediate backings, and the one external upper surface as well as the one external lower surface of the contact-adhesive tape are formed by said adhesive substance layer or layers.

Claims

1. A pressure-sensitive adhesive strip which is redetachable without residue or destruction by extensive stretching substantially within the bond plane, comprising one or more layers of adhesive, all of which consist of a pressure-sensitive adhesive foamed with microballoons, and optionally comprising one or more intermediate carrier layers, wherein the pressure-sensitive adhesive strip consists exclusively of the stated layers of adhesive and optional intermediate carrier layers present, and an outer upper face and an outer lower face of the pressure-sensitive adhesive strip are formed by the stated layer or layers of adhesive.

2. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the pressure-sensitive adhesive strip consists of a single layer of adhesive.

3. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the pressure-sensitive adhesive strip consists of a layer of adhesive which has a single intermediate carrier composed more particularly of a polymer film.

4. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the pressure-sensitive adhesive is constructed on the basis of vinylaromatic block copolymers and tackifying resins, with selection to an extent of at least 75% by weight (based on the total resin content) of a resin having a DACP (diacetone alcohol cloud point) of greater than 20 C., and a softening temperature (ring & ball) of not less than 70 C.

5. The pressure-sensitive adhesive strip as claimed in claim 1, wherein pressure-sensitive adhesives used are adhesives based on block copolymers comprising polymer blocks predominantly formed from vinylaromatics (A blocks), preferably styrene, and blocks predominantly formed by polymerization of 1,3-dienes (B blocks) such as, for example, butadiene and isoprene or a copolymer of the two.

6. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the vinylaromatic block copolymer used is at least one synthetic rubber in the form of a block copolymer having an A-B, A-B-A, (A-B).sub.n, (A-B).sub.nX or (A-B-A).sub.nX structure, in which the A blocks are independently a polymer formed by polymerization of at least one vinylaromatic; the B blocks are independently a polymer formed by polymerization of conjugated dienes having 4 to 18 carbon atoms and/or isobutylene, or a partly or fully hydrogenated derivative of such a polymer; X is the radical of a coupling reagent or initiator; and n is an integer 2.

7. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the vinylaromatics for construction of the A block comprise styrene, -methylstyrene and/or other styrene derivatives.

8. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the monomer for the B block is selected from the group consisting of butadiene, isoprene, ethylbutadiene, phenylbutadiene, piperylene, pentadiene, hexadiene, ethylhexadiene and dimethylbutadiene, and any desired mixtures of these monomers.

9. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the proportion of the vinylaromatic block copolymers, especially styrene block copolymers, in total, based on the overall pressure-sensitive adhesive, is at least 20% by weight, and at the same time at most 75% by weight.

10. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the pressure-sensitive adhesive includes 20% to 60% by weight of tackifying resin, based on the total weight of the pressure-sensitive adhesive.

11. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the tackifying resins to an extent of at least 75% by weight are hydrocarbon resins or terpene resins or a mixture of the same.

12. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the adhesive consists of the following composition: TABLE-US-00008 vinylaromatic block copolymers 20% to 75% by weight tackifying resins 24.6% to 60% by weight microballoons 0.2% to 10% by weight additives 0.2% to 10% by weight.

13. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the adhesive consists of the following composition: TABLE-US-00009 vinylaromatic block copolymers 35% to 65% by weight tackifying resins 34.6% to 45% by weight microballoons 0.2% to 10% by weight additives 0.2% to 10% by weight.

14. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the adhesive consists of the following composition: TABLE-US-00010 vinylaromatic block copolymers 30% to 75% by weight tackifying resins 24.8% to 60% by weight microballoons 0.2% to 10% by weight.

15. The pressure-sensitive adhesive strip as claimed in claim 1, wherein between greater than 0% and 10% by weight of microballoons are included in the adhesive, based in each case on the overall composition of the adhesive.

16. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the absolute density of the foamed pressure-sensitive adhesive is 350 to 990 kg/m.sup.3, and/or the relative density is 0.35 to 0.99.

17. The pressure-sensitive adhesive strip as claimed in claim 1, wherein if the pressure-sensitive adhesive has an intermediate carrier, the absolute density of the foamed pressure-sensitive adhesive is between 220 to 990 kg/m.sup.3, and/or the relative density is between 0.20 to 0.99.

18. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the pressure-sensitive adhesive strip is of single-layer implementation, with the thickness of the pressure-sensitive adhesive strip being preferably from 20 m to 2000 m.

19. The pressure-sensitive adhesive strip as claimed in claim 1, wherein, the intermediate carrier has a thickness of between 20 and 60 m, and the optionally identical layers of adhesive on the intermediate carrier each have a thickness of between 20 and 60 m.

20. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the intermediate carrier layer is 10 to 200 m thick.

21. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the intermediate carrier has an elongation at break of at least 100%, and optionally a resilience of more than 50%.

22. Method of using a pressure-sensitive adhesive strip as claimed in claim 1 for bonding of components.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0178] In the drawings

[0179] FIG. 1 shows a three-layer pressure-sensitive adhesive strip of the invention,

[0180] FIG. 2 shows a three-layer pressure-sensitive adhesive strip of the invention in an alternative embodiment, and

[0181] FIG. 3 shows a one-layer pressure-sensitive adhesive strip of the invention.

[0182] FIG. 4 the process with one mixing unit, wherein the microballoons are added directly in the first mixing unit,

[0183] FIG. 5 the process with two mixing units, wherein the microballoons are added in the first mixing unit, and

[0184] FIG. 6 the process with two mixing units, wherein the microballoons are added only in the second mixing unit.

[0185] FIG. 7 shows a lateral section through a specimen according to example 5.

[0186] FIG. 8 shows a lateral section through a specimen according to example 8.

[0187] FIG. 1 shows the pressure-sensitive adhesive strip of the invention composed of three layers 1, 2, 3, which is redetachable without residue or destruction by extensive stretching substantially within the bond plane.

[0188] The strip consists of an intermediate carrier 1, the intermediate carrier 1 being of one-layer embodiment.

[0189] On the intermediate carrier there are external inventive adhesive layers 2, 3 on either side.

[0190] The protruding end of the intermediate carrier 1 may serve as a grip tab, but is not mandatorily present.

[0191] In FIG. 2, the pressure-sensitive adhesive strip of the invention is shown in a variant. The strip consists of three layers 1, 2, 3 which are arranged congruently one above another.

[0192] In order to produce a grip tab for pulling, to achieve the extensive stretching particularly in the bond plane, one end of the adhesive film strip is made non-adhesive on both sides, by the application of preferably siliconized pieces of film or of paper 6.

[0193] FIG. 3 shows a single-layer pressure-sensitive adhesive strip 1 which has a grip tab composed of siliconized film or paper pieces 6 applied to both sides of the adhesive strip 1.

[0194] Furthermore, the invention encompasses a method for producing an adhesive of the invention which comprises expanded microballoonssee FIG. 4wherein [0195] the constituents for forming the adhesive such as polymers, resins or fillers and unexpanded microballoons are mixed in a first mixing unit and heated to expansion temperature under elevated pressure, [0196] the microballoons are expanded on exit from the mixing unit, [0197] the adhesive composition mixture along with the expanded microballoons is formed into a layer in a roll applicator, [0198] the adhesive composition mixture along with the expanded microballoons is optionally applied to a carrier or release material in web form.

[0199] Furthermore, the invention encompasses a method for producing an adhesive of the invention which comprises expanded microballoonssee FIG. 5wherein [0200] the constituents for forming the adhesive such as polymers, resins or fillers and unexpanded microballoons are mixed in a first mixing unit under elevated pressure and are heated to a temperature below the expansion temperature of the microballoons, [0201] the mixed, more particularly homogeneous adhesive is transferred from the first mixing unit into a second unit and is heated to expansion temperature under elevated temperature, [0202] the microballoons are expanded in the second unit or on exit from the second unit, [0203] the adhesive composition mixture along with the expanded microballoons is formed into a layer in a roll applicator, [0204] the adhesive composition mixture along with the expanded microballoons is optionally applied to a carrier or release material in web form.

[0205] Furthermore, the invention encompasses a method for producing an adhesive of the invention which comprises expanded microballoonssee FIG. 6wherein [0206] the constituents for forming the adhesive such as polymers, resins or fillers are mixed in a first mixing unit, [0207] the mixed, more particularly homogeneous adhesive is transferred from the first mixing unit into a second mixing unit, which is supplied simultaneously with the unexpanded microballoons, [0208] the microballoons are expanded in the second mixing unit or on exit from the second mixing unit, [0209] the adhesive composition mixture along with the expanded microballoons is formed into a layer in a roll applicator, [0210] the adhesive composition mixture along with the expanded microballoons is optionally applied to a carrier or release material in web form.

[0211] According to one preferred embodiment of the invention, the adhesive is shaped in a roll applicator and applied to the carrier material.

[0212] There is generally no need to degas compositions foamed with microballoons prior to coating in order to obtain a homogeneous, continuous coating. The expanded microballoons displace the air incorporated into the adhesive composition during compounding. In the case of high throughputs, it is nevertheless advisable to degas the compositions prior to coating in order to obtain a homogeneous feed of composition in the roll gap. The degassing is ideally effected directly upstream of the roll applicator at mixing temperature and with a pressure differential from ambient pressure of at least 200 mbar.

[0213] In addition, it is advantageous when [0214] the first mixing unit is a continuous unit, especially a planetary roller extruder, a twin-screw extruder or a pin extruder, [0215] the first mixing unit is a batchwise unit, especially a Z kneader or an internal mixer, [0216] the second mixing unit is a planetary roll extruder, a single-screw or twin-screw extruder or a pin extruder and/or [0217] the shaping unit in which the adhesive composition along with the expanded microballoons is shaped to give a carrier layer is a calender, a roll applicator or a gap formed by a roll and a fixed doctor.

[0218] With the processes of the invention, solvent-free processing of all previously known components of adhesive compositions and those described in the literature, especially self-adhesive compositions, is possible.

[0219] The above-described processes within the concept of the invention in variants of particularly excellent configuration are illustrated hereinafter, without any intention to impose unnecessary restriction through the choice of the figures depicted.

[0220] FIG. 4 shows a particularly advantageously configured process for producing a foamed pressure-sensitive adhesive strip.

[0221] In a continuous mixing unit, for example a planetary roller extruder (PRE), the pressure-sensitive adhesive composition is produced.

[0222] For this purpose, the reactants E that are to form the adhesive composition are introduced into the planetary roller extruder PRE 1. At the same time, the unexpanded microballoons MB are incorporated homogeneously under elevated pressure into the self-adhesive composition during the compounding process.

[0223] The temperatures required for homogeneous production of the self-adhesive composition and for expansion of the microballoons are adjusted with respect to one another such that the microballoons foam up in the self-adhesive composition M on exit from the PRE 1 as a result of the pressure drop on exit from the die, and in so doing break through the surface of the composition.

[0224] With a roll applicator 3 as shaping unit, this foam-like adhesive composition M is calendered and coated onto a carrier material in web form, for example release paper TP; in some cases, further foaming can still take place in the roll gap. The roll applicator 3 consists of a doctor roll 31 and a coating roll 32. The release paper TP is guided onto the latter via a pick-up roll 33, such that the release paper TP takes up the adhesive composition K from the coating roll 32.

[0225] At the same time, the expanded microballoons MB are forced back into the polymer matrix of the adhesive composition K, and hence a smooth surface is generated.

[0226] FIG. 5 shows a further particularly advantageously configured process for producing a foamed pressure-sensitive adhesive strip.

[0227] The planetary roller extruder PRE 1 has two successive mixing zones 11, 12 in which a central spindle rotates. In addition, there are six planetary spindles per heating zone. Further reactants are added to the injection ring 13, for example plasticizer or liquid resin. An example of a suitable apparatus is the planetary roller extruder from Entex in Bochum.

[0228] Subsequently, the microballoons are incorporated under elevated pressure homogeneously into the self-adhesive composition in a second mixing unit, for example a single-screw extruder, heated above the expansion temperature and foamed on exit.

[0229] For this purpose, the adhesive composition K formed from the reactants E is introduced here into the single-screw extruder SSE 2; at the same time, the microballoons MB are introduced. The single-screw extruder SSE has a total of four heating zones over its run length 21.

[0230] An example of a suitable apparatus is a single-screw extruder from Kiener.

[0231] During the expansion caused by the pressure drop at the die exit of SSE 2, the microballoons MB break through the surface of the composition.

[0232] With a roll applicator 3, this foam-like adhesive composition M is calendered and coated onto a carrier material in web form, for example release paper TP; in some cases, further foaming can still take place in the roll gap. The roll applicator 3 consists of a doctor roll 31 and a coating roll 32. The release paper TP is guided onto the latter via a pick-up roll 33, such that the release paper TP takes up the adhesive composition K from the coating roll 32.

[0233] At the same time, the expanded microballoons MB are forced back into the polymer matrix of the adhesive composition K, and hence a smooth surface is generated.

[0234] FIG. 6 shows a further particularly advantageously configured process for producing a foamed pressure-sensitive adhesive strip.

[0235] In a continuous mixing unit, for example a planetary roller extruder (PRE), the pressure-sensitive adhesive composition is produced.

[0236] Here, the reactants E that are to form the adhesive composition are introduced into the planetary roller extruder PRE 1. The planetary roller extruder PRE 1 has two successive mixing zones 11, 12 in which a central spindle rotates. In addition, there are 6 planetary spindles per heating zone.

[0237] Further reactants are added to the injection ring 13, for example plasticizer or liquid resin. An example of a suitable apparatus is the planetary roller extruder from Entex in Bochum.

[0238] Subsequently, the microballoons are incorporated homogeneously under elevated pressure into the self-adhesive composition in a second mixing unit, for example a single-screw extruder, heated above the expansion temperature and foamed on exit.

[0239] For this purpose, the adhesive composition K formed from the reactants E is introduced here into the single-screw extruder SSE 2; at the same time, the microballoons MB are introduced. The single-screw extruder SSE has a total of four heating zones over its run length 21.

[0240] An example of a suitable apparatus is a single-screw extruder from Kiener.

[0241] During the expansion caused by the pressure drop at the die exit of SSE 2, the microballoons MB break through the surface of the composition.

[0242] With a roll applicator 3, this foam-like adhesive composition M is calendered and coated onto a carrier material in web form, for example release paper TP; in some cases, further foaming can still take place in the roll gap. The roll applicator 3 consists of a doctor roll 31 and a coating roll 32. The release paper TP is guided onto the latter via a pick-up roll 33, such that the release paper TP takes up the adhesive composition K from the coating roll 32.

[0243] At the same time, the expanded microballoons MB are forced back into the polymer matrix of the adhesive composition K, and hence a smooth surface is generated.

[0244] With falling gap pressure in the roll gap, there is a decrease in the bonding areas of the coated foamed self-adhesive compositions, since the microballoons are then forced back to a lesser degree, as can be inferred from FIG. 4. FIG. 4 shows the bonding areas as a function of the coating process or parameter. The gap pressure required is highly dependent on the composition system used; the higher the viscosity, the greater the gap pressure should be, depending on the layer thickness desired and the coating speed chosen. In practice, a gap pressure of greater than 4 N/mm has been found to be useful; with exceptionally high coating speeds greater than 50 m/min, with low applications of composition (basis weights less than 70 g/m.sup.2) and high-viscosity compositions (50 000 Pa*s at 0.1 rad and 110 C.), gap pressures greater than 50 N/mm may even be required.

[0245] It has been found to be useful to adjust the temperature of the rolls to the expansion temperature of the microballoons. Ideally, the roll temperature of the first rolls is above the expansion temperature of the microballoons in order to enable further foaming of the microballoons without destroying them. The last roll should have a temperature equal to or below the expansion temperature in order that the microballoon shell can solidify and the smooth surface of the invention forms.

[0246] Many units for continuous production and processing of solvent-free polymer systems are known. Usually, screw machines such as single-screw and twin-screw extruders of different processing lengths and with different equipment are used. Alternatively, continuous kneaders of a wide variety of different designs, for example including combinations of kneaders and screw machines, or else planetary roller extruders, are used for this task.

[0247] Planetary roller extruders have been known for some time and were first used in the processing of thermoplastics, for example PVC, where they were used mainly for charging of the downstream units, for example calenders or roll systems. Their advantage of high surface renewal for material and heat exchange, with which the energy introduced via friction can be removed rapidly and effectively, and of short residence time and narrow residence time spectrum, has allowed their field of use to be broadened recently, inter alia, to embrace compounding processes that require a mode of operation with exceptional temperature control.

[0248] Planetary roller extruders exist in various designs and sizes according to the manufacturer. According to the desired throughput, the diameters of the roller cylinders are typically between 70 mm and 400 mm.

[0249] Planetary roller extruders generally have a filling section and a compounding section. The filling section consists of a conveying screw, into which all solid components are metered continuously. The conveying screw then transfers the material to the compounding section. The region of the filling section with the screw is preferably cooled in order to avoid caking of material on the screw. But there are also embodiments without a screw section, in which the material is applied directly between central and planetary spindles. However, this is of no significance for the efficacy of the process of the invention.

[0250] The compounding section consists of a driven central spindle and several planetary spindles that rotate around the central spindle within one or more roll cylinders having internal helical gearing. The speed of the central spindle and hence the peripheral velocity of the planetary spindles can be varied and is thus an important parameter for control of the compounding process.

[0251] The materials are circulated between the central and planetary spindles, i.e. between planetary spindles and the helical gearing of the roll section, such that the materials can be dispersed under the influence of shear energy and external temperature control to give a homogeneous compound.

[0252] The number of planetary spindles that rotate in each roll cylinder can be varied and hence adapted to the demands of the process. The number of spindles affects the free volume within the planetary roller extruder and the residence time of the material in the process, and additionally determines the size of the area for heat and material exchange. The number of planetary spindles affects the compounding outcome via the shear energy introduced. Given a constant roller cylinder diameter, it is possible with a greater number of spindles to achieve better homogenization and dispersion performance, or a greater product throughput.

[0253] The maximum number of planetary spindles that can be installed between the central spindle and roller cylinder is dependent on the diameter of the roller cylinder and on the diameter of the planetary spindles used. In the case of use of greater roller diameters as necessary for achievement of throughputs on the production scale, or smaller diameters for the planetary spindles, the roller cylinders can be equipped with a greater number of planetary spindles. Typically, up to seven planetary spindles are used in the case of a roller diameter of D=70 mm, while ten planetary spindles, for example, can be used in the case of a roller diameter of D=200 mm, and 24, for example, in the case of a roller diameter of D=400 mm.

[0254] It is proposed in accordance with the invention that the coating of the foamed adhesive compositions be conducted in a solvent-free manner with a multiroll applicator system. These may be applicator systems consisting of at least two rolls with at least one roll gap up to five rolls with three roll gaps.

[0255] Also conceivable are coating systems such as calenders (I,F,L calenders), such that the foamed adhesive composition is shaped to the desired thickness as it passes through one or more roll gaps.

[0256] It has been found to be particularly advantageous to choose the temperature regime for the individual rolls such that controlled further foaming can take place if appropriate, in such a way that transferring rolls can have a temperature above or equal to the foaming temperature of the microballoon type chosen, whereas receiving rolls should have a temperature below or equal to the foaming temperature, in order to prevent uncontrolled foaming, and where all rolls can be set individually to temperatures of 30 to 220 C.

[0257] In order to improve the transfer characteristics of the shaped composition layer from one roll to another, it is also possible to use anti-adhesively finished rolls or patterned rolls. In order to produce a sufficiently precisely shaped adhesive film, the peripheral speeds of the rolls may have differences.

[0258] The preferred 4-roll applicator is formed by a metering roll, a doctor roll, which determines the thickness of the layer on the carrier material and is arranged parallel to the metering roll, and a transfer roll disposed beneath the metering roll. At the lay-on roll, which together with the transfer roll forms a second roll gap, the composition and the material in web form are brought together.

[0259] Depending on the nature of the carrier material in web form which is to be coated, coating can be effected in a co-rotational or counter-rotational process.

[0260] The shaping system may also be formed by a gap formed between a roll and a fixed doctor. The fixed doctor may be a knife-type doctor or else a stationary (half-)roll.

[0261] In an alternative process for producing an adhesive composition, all constituents of said composition are dissolved in a solvent mixture (benzine/toluene/acetone). The microballoons are converted to a slurry in benzine and stirred into the dissolved adhesive composition. As soon as the microballoons are distributed homogeneously in the solution, the adhesive composition can be coated; for example, the coating can be accomplished by means of a doctor blade onto a conventional PET liner.

[0262] In the first step, the coated adhesive is dried exposed at 100 C. for 15 min. After the drying, the adhesive layer is covered with a second ply of PET liner and foamed in the oven at 150 C. for 5 min, specifically covered between two liners, in order to produce a particularly smooth surface.

[0263] The surface thus produced has a roughness R.sub.a of less than 15 m, more preferably less than 10 m.

[0264] The surface roughness R.sub.a is a unit for the industrial standard for the quality of the final surface processing and constitutes the average height of the roughness, especially the average absolute distance from the center line of the roughness profile within the range of evaluation. R.sub.a is measured by means of laser triangulation.

[0265] The expansion temperature is usually always higher than the drying temperature.

[0266] FIGS. 7 and 8 show an adhesive composition of the invention in lateral section. As a result of the foaming of the adhesive composition using microballoons, technical bonding and performance properties are improved.

[0267] This reduction in the drop in peel adhesion is promoted by the high surface quality, produced as a result of the pressing of the expanded microballoons back into the polymer matrix during the coating operation.

[0268] Furthermore, relative to the unfoamed composition with the same polymer basis, the foamed PSA gains additional performance features such as, for example, an improved impact resistance at low temperatures, boosted peel adhesion on rough substrates, greater damping and/or sealing properties, or conformance of the foam adhesive to uneven substrates, a more favorable crushing/hardness behavior, and enhanced compression capacity.

[0269] Further elucidation of the characteristic properties and additional functions of the pressure-sensitive adhesive compositions of the invention is accomplished in part in the examples.

[0270] The invention is elucidated in more detail below by means of a number of examples.

[0271] In these examples, the constituents of the PSAs were dissolved at 40% in benzine/toluene/acetone, admixed with a benzine slurry of the microballoons, and coated out in the desired film thickness, using a coating bar, onto a PET film equipped with a silicone release, followed by evaporation of the solvent at 100 C. for 15 min so as to dry the layer of composition.

[0272] After drying, the adhesive layer was lined with a second ply of PET liner, free from any air inclusions, and was foamed in an oven between the two liners at 150 C. for 5 min. By foaming between two liners, products are obtainable that have particularly smooth surfaces. All of the examples given feature an RA value of less than 15 m.

[0273] Pressure-sensitive adhesive strips with the desired dimensions were obtained by diecutting.

EXAMPLES

Examples 1 to 3

[0274]

TABLE-US-00001 Comparative example Example 1 Example 2 Example 3 Raw material Fraction (wt %) Fraction (wt %) Fraction (wt %) Fraction (wt %) Kraton 1102 50 48.6 48.1 47.40 Dercolyte A115 45 46.4 46.0 45.5 Wingtack 10 4.5 3.0 2.9 2.9 Aging inhibitor 0.5 0.5 0.5 0.5 Expancel 920 DU20 0 1.5 2.5 3.5 Total 100.00 100.0 100.0 100.0 Constituents of the adhesive: Kraton 1102 styrene-butadiene-styrene block copolymer from Kraton polymers, 83 wt % 3-block, 17 wt % 2-block; block polystyrene content: 30 wt % Dercolyte A 115 solid -pinene tackifying resin having a ring and ball softening temperature of 115 C. and a DACP of 35 C. Wingtack 10 liquid hydrocarbon resin from Cray Valley Expancel 920 DU20 microballoons

[0275] Aging inhibitors used include Irganox 1010 (phenolic antioxidant).

TABLE-US-00002 Comparative Example Example Example example 1 2 3 Thickness [m] 109 107 103 109 Density [g/cm.sup.3] 1 0.752 0.593 0.50 Microballoon [wt %] 1.5 2.5 3.5 Peel adhesion, [N/cm] 9 10.0 8.5 8.0 steel Peel adhesion, [N/cm] 7 6.9 6.7 6.2 PE Ball drop, [cm] 50 225 >245 (13.8 g) Ball drop, [cm] 125 185* (32.6 g) Transverse [mJ] 364 656 542 420 impact toughness Elongation at [%] 975 about 836 631 break 1000 Detachment [N/cm] 3 2.4 2.2 force

[0276] Examples 1 to 3 show the effect exerted by an increasing amount of microballoons in the adhesive, as compared with an unfoamed adhesive of equal thickness.

[0277] Result: [0278] Shock exposure in the z-plane increases with increasing microballoon content (ball drop) [0279] Shock exposure in the x,y-plane increases with increasing content of microballoons, with a maximum observable at a microballoon content of 1.5 wt % (transverse impact toughness) [0280] The detachment force falls with increasing microballoon content, in spite of increasing shock robustness

Examples 4 to 7

[0281]

TABLE-US-00003 Comparative example 2 Example 4 Example 5 Example 6 Example 7 Raw material Fraction (wt %) Fraction (wt %) Fraction (wt %) Fraction (wt %) Fraction (wt %) Kraton 1102 50 49.1 48.8 48.6 48.3 Dercolyte 44 46.2 45.9 45.7 45.5 A115 Wingtack 10 4.5 3.0 3.0 3.0 3.0 Aging 1.5 1.2 1.3 1.2 1.2 inhibitor Expancel 0 0.5 1 1.5 2 920 DU20 Total 100.00 100.0 100.0 100.0 100.0

TABLE-US-00004 Microballoon content Density Ball weight Height E (wt %) (kg/m.sup.3) (9) (cm) (J) Comparative 0 1000 32.6 25 0.9005 example Example 4 0.5 884 32.6 85 1.1124 Example 5 1 799 32.6 165 1.2272 Example 6 1.5 698 32.6 250 1.2714 Example 7 2 624 110 85 1.0948

TABLE-US-00005 Stripping force Microballoon Density F average F max content (wt %) (kg/m.sup.3) (N/cm) (N/cm) Comparative 0 1000 2.17 2.52 example Example 4 0.5 884 2.08 2.31 Example 5 1 799 1.94 2.10 Example 6 1.5 698 2.04 2.19 Example 7 2 624 1.39 1.98

[0282] Examples 4 to 7 show the influence exerted by an increasing microballoon content in the adhesive, by comparison with an unfoamed adhesive.

[0283] Result: [0284] Even at a microballoon content of 0.5 wt % there is a distinct improvement measurable in the shock robustness (ball drop) [0285] Shock robustness increases with increasing microballoon content [0286] Stripping force falls with increasing microballoon content

Examples 8 to 9

[0287] In examples 8 and 9, three-layer specimens were compared with one another.

[0288] Comparative example 2 consists of a 50 m PU film as intermediate carrier, to which on both sides an unfoamed adhesive is applied, with the composition indicated, in each case with a coat weight of 25 g/m.sup.2 and a layer thickness of 25 m on either side.

[0289] Example 8 consists of a 50 m PU film as intermediate carrier, to which on both sides an unfoamed adhesive of the composition specified is applied, in each case with a coat weight thickness of 20 g/m.sup.2 and a layer thickness of 20 m on either side. The specimen, lined on either side with PET liner, was foamed in an oven at 150 C. for 5 min to a total thickness of 100 m.

[0290] Example 9 consists of a 30 m PU film as intermediate carrier, to which on both sides an unfoamed adhesive of the composition specified is applied, in each case with a coat weight thickness of 28 g/m.sup.2 and a layer thickness of 28 m on either side. The specimen, lined on either side with PET liner, was foamed in an oven at 150 C. for 5 min to a total thickness of 100 m.

TABLE-US-00006 Comparative example 2 Examples 8 and 9 Raw material Fraction (wt %) Fraction (wt %) Kraton 1102 50 48.6 Dercolyte A115 44 45.7 Wingtack 10 4.5 3.0 Aging inhibitor 1.5 1.2 Expancel 920 DU20 0 1.5 Total 100.00 100.0

TABLE-US-00007 Comparative example 2 Example 8 Example 9 Ball drop [cm] 13.8 g 45 245 245 Ball drop [mJ] 13.8 g 60.92 331.68 331.68 Ball drop [cm] 32.6 g 145 145 Ball drop [mJ] 32.6 g 463.72 463.72 Push out [N/cm.sup.2] 32 24 31 Transverse impact toughness 270 469 [mJ] PA steel [N/cm] 7 5 6.8 PA PE [N/cm] 5 4.2 4.9 Stripping force [N/cm] 7 6 4.9 Tears [#] 180 0 0 0 Tears [#] 90 3 0 0

[0291] Examples 8 and 9 show the effect which foamed adhesives have on the peel angle of the adhesive strip.

[0292] Result: [0293] A foamed three-layer construction still displays high shock robustness and no tears at 180 and 90 peel angles [0294] At a 90 peel angle, a foamed three-layer construction is more tear-resistant than an unfoamed three-layer construction of equal thickness

Test Methods

[0295] Unless otherwise indicated, all of the measurements were conducted at 23 C. and 50% relative humidity.

[0296] The mechanical and technical adhesive data were determined as follows:

Resilience/Elasticity

[0297] To measure the resilience, the pressure-sensitive adhesive strips were extended by 100%, kept at this extension for 30 s and then released. After a wait time of 1 min, the length was measured again.

[0298] The resilience is then calculated as follows:

R=((L.sub.100L.sub.end)/L.sub.0)*100

with R=resilience in

[0299] L.sub.100: Length of the adhesive strip after extension by 100%

[0300] L.sub.0: Length of the adhesive strip prior to extension

[0301] L.sub.end: Length of the adhesive strip after relaxation for 1 min.

[0302] The resilience corresponds here to the elasticity.

Elongation at Break, Tensile Strength and Strain at 50% Elongation

[0303] The elongation at break, the tensile strength and the strain at 50% elongation were measured in accordance with DIN 53504 using dumbbell specimens of size S3 at a separation speed of 300 mm per minute. The test conditions were 23 C. and 50% rel. air humidity.

Detachment Force

[0304] The detachment force (stripping force or stripping strain) was determined by means of a film of adhesive with dimensions of 50 mm length20 mm width having a non-adhesive grip tab region at the top end. The film of adhesive was adhered between two steel plates, arranged congruently to one another and with dimensions of 50 mm30 mm, using an applied pressure of 50 newtons in each case. At their lower end, the steel plates each have a drilled hole for accommodating an S-shaped steel hook. The lower end of the steel hook carries a further steel plate, via which the test arrangement can be fixed, for measurement, in the lower clamping jaw of a tensile testing machine. The adhesive bonds are stored at +40 C. for a time of 24 hours. After reconditioning to room temperature, the adhesive film strip is pulled apart with a pulling speed of 1000 mm per minute, parallel to the bond plane and without contact with the edge regions of the two steel plates. During this procedure, the required detachment force in newtons (N) is measured. The figure reported is the average of the stripping strain values (in N per mm.sup.2), measured in the range in which the adhesive strip underwent detachment from the steel substrates over a bonding length of between 10 mm and 40 mm.

Tearing Test

[0305] Strips 10 mm wide and 40 mm long are produced by punching from the adhesive tape under investigation. These strips are adhered over a length of 30 mm to a PC plate conditioned with ethanol, thus leaving a grip tab 10 mm long. A second PC plate is adhered to the second side of the bonded strips, in such a way that the two PC plates lie flush one above the other. The assembly is rolled down 10 times (five times back and forth) using a 4 kg roller. After a take time of 24 h, the strips are stripped from the bonded joint by the grip tab, manually, at [0306] a) a 90 angle and [0307] b) a 180 angle.

[0308] An evaluation is made of how many specimens can be redetached without residue.

Tackifying Resin Softening Temperature

[0309] The tackifying resin softening temperature is conducted by the relevant methodology, known as ring & ball and standardized in ASTM E28.

DACP

[0310] 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.

Falling Ball Test (Impact Toughness, Ball Drop)

[0311] A square sample with a frame shape was cut from the adhesive tape under investigation (external dimensions 33 mm33 mm; border width 3.0 mm; internal dimensions (window cutout) 27 mm27 mm). This sample was adhered to an ABS frame (external dimensions 50 mm50 mm; border width 12.5 mm; internal dimensions (window cutout) 25 mm25 mm; thickness 3 mm). On the other side of the double-sided adhesive tape, a PMMA window measuring 35 mm35 mm was adhered. The bonding of ABS frame, adhesive tape frame and PMMA window took place in such a way that the geometric centers and the diagonals lay in each case one above another (corner to corner). The bond area was 360 mm.sup.2. The bond was pressed under 10 bar for 5 s and stored for 24 hours with conditioning at 23 C./50% relative humidity.

[0312] Immediately after storage, the bonded assembly of ABS frame, adhesive tape and PMMA window was placed, with the protruding edges of the ABS frame, on a frame rack (sample holder) in such a way that the assembly was aligned horizontally and the PMMA window pointed downward in free suspension. A steel ball of the weight indicated in each case was dropped centrally onto the PMMA window of the sample thus arranged, the drop being vertical from a height of 250 cm (through the window of the ABS frame) (measuring conditions 23 C., 50% relative humidity). With each sample, three investigations were carried out, unless the PMMA window had already detached.

[0313] The falling ball test is passed if the bond has not parted in any of the three investigations.

[0314] 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 kg/m*s.sup.2

Push-Out Strength (z-Plane)

[0315] The push-out test provides information about the level of resistance of an adhesive bond of a component in a frame-shaped body, such as a window in a housing.

[0316] A rectangular, frame-shaped sample was cut out of the adhesive tape under investigation (external dimensions 43 mm33 mm; border width 2.0 mm in each case, internal dimensions (window cutout) 39 mm29 mm, bond area on top and bottom sides 288 mm.sup.2 in each case). This sample was adhered to a rectangular ABS polymer frame (ABS=acrylonitrile-butadiene-styrene copolymers) (external dimensions 50 mm40 mm, border width of the long borders 8 mm in each case; border width of the short borders 10 mm in each case; internal dimensions (window cutout) 30 mm24 mm; thickness 3 mm). Adhered to the other side of the sample of the double-sided adhesive tape was a rectangular PMMA sheet (PMMA=polymethyl methacrylate) with dimensions of 45 mm35 mm. The full bond area of the adhesive tape available was utilized. The ABS frame, adhesive tape sample and PMMA window were bonded in such a way that the geometric centers, the bisecting lines of the acute diagonal angles and the bisecting lines of the obtuse diagonal angles of the rectangles each lay on top of one another (corner on corner, long sides on long sides, short sides on short sides). The bond area was 360 mm.sup.2. The bond was pressed under 10 bar for 5 s and stored with conditioning at 23 C./50% relative humidity for 24 hours.

[0317] Immediately after storage, the adhesive assembly composed of ABS frame, adhesive tape and PMMA sheet was placed with the protruding edges of the ABS frame onto a frame rack (sample holder) in such a way that the assembly was oriented horizontally and the PMMA sheet pointed downwards in free suspension.

[0318] A plunger is then moved perpendicularly from above through the window of the ABS frame at a constant speed of 10 mm/s, such that it presses centrally onto the PMMA plate, and the respective force (determined from respective pressure and contact area between plunger and plate) is recorded as a function of the time between first contact of the plunger with the PMMA plate up to shortly after the PMMA plate has dropped off (measuring conditions 23 C., 50% relative humidity). The force acting immediately before failure of the adhesive bond between PMMA plate and ABS frame (maximum force F.sub.max in the force-time diagram, in N) is recorded as the outcome of the push-out test.

Transverse Impact Toughness; x,y-Plane

[0319] A square sample with a frame shape was cut from the adhesive tape under investigation (external dimensions 33 mm33 mm; border width 3.0 mm; internal dimensions (window cutout) 27 mm27 mm). This sample was adhered to an ABS frame (external dimensions 45 mm45 mm; border width 10 mm; internal dimensions (window cutout) 25 mm25 mm; thickness 3 mm). On the other side of the double-sided adhesive tape, a PMMA window measuring 35 mm35 mm was adhered. The bonding of ABS frame, adhesive tape frame and PMMA window took place in such a way that the geometric centers and the diagonals lay in each case one above another (corner to corner). The bond area was 360 mm.sup.2. The bond was pressed under 10 bar for 5 s and stored for 24 hours with conditioning at 23 C./50% relative humidity.

[0320] Immediately after storage, the bonded assembly of ABS frame, adhesive tape and PMMA window with the protruding edges of the ABS frame was clamped into a sample holder in such a way that the assembly was oriented vertically. The sample holder was subsequently inserted centrally into the intended holder of the DuPont impact tester. The impact head, weighing 300 g, was inserted such that the rectangular striking geometry with dimensions of 20 mm3 mm was central and flush against the upwardly directed end-face side of the PMMA window.

[0321] A weight with a mass of 150 g, guided on two guide rods, was dropped vertically from a height of 3 cm onto the assembly thus arranged of sample holder, sample and impact head

(measuring conditions 23 C., 50% relative humidity). The height of the falling weight was raised in steps of 3 cm until the impact energy introduced caused destruction of the sample as a result of the transverse impact load, and the PMMA window parted from the ABS frame.

[0322] In order to be able to compare experiments with different samples, the energy was calculated as follows:

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

[0323] For each product, five samples were tested, and the average energy value was reported as a characteristic number for the transverse impact toughness.

Peel Adhesion

[0324] The determination of the peel adhesion (in accordance with AFERA 5001) is carried out as follows. The defined adhesion substrate used is galvanized steel plate with a thickness of 2 mm (acquired from Rocholl GmbH) or a polyethylene block, respectively. The bondable sheetlike element under investigation is cut to a width of 20 mm and a length of about 25 cm, provided with a handling section and immediately thereafter pressed down five times using a 4 kg steel roller, at a rate of advance of 10 m/min, onto the particular adhesion substrate selected. Directly following that, the bondable sheetlike element is peeled from the substrate at an angle of 180 and a speed v=300 mm/min, using a tensile testing instrument (from Zwick), and the force required to achieve this at room temperature is recorded. The measurement value (in N/cm) is the average value resulting from three individual measurements.

Static Glass Transition Temperature Tg

[0325] 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.