Pressure-sensitive adhesive strip

Abstract

The invention relates to a pressure-sensitive adhesive strip comprising at least one layer SK1, preferably exactly one layer SK1, of a self-adhesive composition based on a vinylaromatic block copolymer composition foamed with microballoons, where the mean diameter of the voids formed by the microballoons in the self-adhesive composition layer SK1 is 45 to 110 m.

Claims

1. A pressure-sensitive adhesive strip comprising a layer SK1, of a self-adhesive composition based on a vinylaromatic block copolymer composition foamed with microballoons, where voids formed by the microballoons in layer SK1 have a mean diameter of 45 to 110 m.

2. The pressure-sensitive adhesive strip as claimed in claim 1, consisting of layer SK1.

3. The pressure-sensitive adhesive strip as claimed in claim 2, wherein layer SK1 has a thickness of 45 to 5000 m.

4. The pressure-sensitive adhesive strip as claimed in claim 1, further comprising a layer F of a film carrier, where layer SK1 is arranged on a surfaces of layer F.

5. The pressure-sensitive adhesive strip as claimed in claim 4, further comprising a layer SK2 composed of a self-adhesive composition based on a vinylaromatic block copolymer composition arranged on an opposite surface of layer F from the layer SK1.

6. The pressure-sensitive adhesive strip as claimed in claim 4, wherein the film carrier layer has a thickness between 5 and 125 m. and layer SK1 and layer SK2, when present, independently have a thickness between 45 and 1000 m.

7. The pressure-sensitive adhesive strip as claimed in claim 5, having a symmetric construction with respect to-layer composition, in that the foamed vinylaromatic block copolymer compositions of layers SK1 and SK2 are chemically identical.

8. The pressure-sensitive adhesive strip as claimed in claim 5, having a structurally symmetric construction, in that layers SK1 and SK2 are of the same thickness and/or have the same density.

9. The pressure-sensitive adhesive strip as claimed in claim 1, wherein layer SK1 is based on vinylaromatic block copolymers comprising polymer blocks (i) predominantly formed from vinylaromatics (A blocks), and (ii) predominantly formed by polymerization of 1,3-dienes (B blocks).

10. The pressure-sensitive adhesive strip as claimed in claim 1, wherein the vinylaromatic block copolymer 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 A blocks are independently a polymer formed by polymerization of at least one vinylaromatic, B blocks are independently a polymer formed by polymerization of conjugated dienes having 4 to 18 carbon atoms, or a partly hydrogenated derivative of such a polymer, X is the radical of a coupling reagent or initiator, and n is an integer 2.

11. The pressure-sensitive adhesive strip as claimed in claim 9, wherein the vinylaromatics for formation of the A block include styrene, -methylstyrene and/or styrene derivatives.

12. The pressure-sensitive adhesive strip as claimed in claim 9, wherein monomer for forming the B block is selected from the group consisting of butadiene, isoprene, ethylbutadiene, phenylbutadiene, piperylene, pentadiene, hexadiene, ethylhexadiene, dimethylbutadiene, and a mixture thereof.

13. The pressure-sensitive adhesive strip as claimed in claim 1, wherein proportion of the vinylaromatic block copolymers, based on overall self-adhesive composition layer SK1, totals at least 20% by weight, and at most 75% by weight.

14. The pressure-sensitive adhesive strip as claimed in claim 1, wherein layer SK1 is formed on basis of vinylaromatic block copolymer and tackifying resin.

15. The pressure-sensitive adhesive strip as claimed in claim 14, wherein layer SK1 includes 20% to 60% by weight of tackifying resin, based on the total weight of the self-adhesive composition layer.

16. The pressure-sensitive adhesive strip as claimed in claim 14, wherein the tackifying resin, to an extent of at least 75% by weight, is hydrocarbon resin or terpene resin or a mixture thereof.

17. The pressure-sensitive adhesive strip as claimed in claim 1, wherein proportion of the microballoons in the foamed layer SK1 is up to 12% by weight, based on overall composition of layer SK1.

18. The pressure-sensitive adhesive strip as claimed in claim 1, wherein mean diameter of the voids formed by the microballoons in the foamed layer SK1 is 60 to 100 m.

19. The pressure-sensitive adhesive strip as claimed in claim 1, wherein layer SK1 consists of the following composition: TABLE-US-00007 vinylaromatic block copolymers 20% to 75% by weight, tackifying resins 24.6% to 60% by weight, microballoons 0.2% to 10% by weight, and additives 0.2% to 10% by weight.

20. The pressure-sensitive adhesive strip as claimed in claim 1, wherein layer SK1 consists of the following composition: TABLE-US-00008 vinylaromatic block copolymers 35% to 65% by weight, tackifying resins 34.6% to 45% by weight, microballoons 0.2% to 10% by weight, and additives 0.2% to 10% by weight.

21. The pressure-sensitive adhesive strip as claimed in claim 1, wherein layer SK1 consists of the following composition: TABLE-US-00009 vinylaromatic block copolymers 30% to 75% by weight, tackifying resins 24.8% to 60% by weight, and microballoons 0.2% to 10% by weight.

22. The pressure-sensitive adhesive strip as claimed in claim 1, wherein layer SK1 has an absolute density of 400 to 990 kg/m.sup.3, and/or a relative density of 0.35 to 0.99.

23. The pressure-sensitive adhesive strip as claimed in claim 4, wherein the film carrier is non-extensible.

24. The pressure-sensitive adhesive strip as claimed in claim 4, wherein the film carrier is extensible.

25. A method for bonding components of accumulators or electronic devices, the method comprising application of a pressure-sensitive adhesive strip according to claim 1 to a substrate.

Description

FIGURES

[0211] With reference to the figures described hereinafter, particularly advantageous embodiments of the invention will be elucidated in detail, without any intention to unnecessarily restrict the invention thereby.

[0212] FIG. 1 shows the schematic construction of a three-layer pressure-sensitive adhesive strip of the invention, composed of three layers 1, 2, 3 in cross section.

[0213] The strip comprises a non-extensible film carrier 1 (layer F) in the form of a PET film that has been etched on both sides. On the top side and on the bottom side of the PET film 1 there are two outer self-adhesive composition layers 2, 3 (layer SK1 and layer SK2). The self-adhesive composition layers 2, 3 (layers SK1 and SK2) are covered in turn by a liner 4, 5 on each side in the illustrative embodiment shown.

[0214] FIG. 2, moreover, shows the schematic construction of a one-layer pressure-sensitive adhesive strip of the invention, consisting of one layer 2 in cross section.

[0215] The strip comprises a self-adhesive composition layer 2 (layer SK1). The self-adhesive composition layer 2 (layer SK1) is covered by a liner 4, 5 on each side in the illustrative embodiment shown.

[0216] In addition, the invention encompasses a process for producing a self-adhesive composition layer of the invention (see FIG. 3), wherein [0217] the constituents for formation of an adhesive composition, such as polymers, resins or fillers and non-expanded microballoons, are mixed in a first mixing unit and heated to expansion temperature under elevated pressure, [0218] the microballoons are expanded on exit from the mixing unit, [0219] the adhesive composition mixture along with the expanded microballoons is formed to a layer in a roll applicator, [0220] the adhesive composition mixture along with the expanded microballoons is optionally applied to a carrier or release material in sheet form.

[0221] In addition, the invention encompasses a process for producing a self-adhesive composition layer of the invention (likewise see FIG. 3), wherein [0222] the constituents for formation of an adhesive composition, such as polymers, resins or fillers and non-expanded microballoons, are mixed in a first mixing unit and heated to expansion temperature, [0223] the microballoons expand at least partly during mixing, and are preferably expanded fully, [0224] the adhesive composition mixture along with the expanded microballoons is formed to a layer in a roll applicator, [0225] the adhesive composition mixture along with the expanded microballoons is optionally applied to a carrier or release material in sheet form.

[0226] The invention likewise encompasses a process for producing a self-adhesive composition layer of the invention (see FIG. 4), wherein [0227] the constituents for formation of an adhesive composition, such as polymers, resins or fillers, together with non-expanded microballoons, are mixed in a first mixing unit under elevated pressure and heated to a temperature below the expansion temperature of the microballoons, [0228] the mixed, especially homogeneous adhesive composition from the first mixing unit is transferred into a second unit and heated to expansion temperature, [0229] the microballoons are expanded in the second unit or on exit from the second unit, [0230] the adhesive composition mixture along with the expanded microballoons is formed to a layer in a roll applicator, [0231] the adhesive composition mixture along with the expanded microballoons is optionally applied to a carrier or release material in sheet form.

[0232] The invention likewise relates to a process for producing a self-adhesive composition layer of the invention (see FIG. 5), wherein [0233] the constituents for formation of an adhesive composition, such as polymers, resins or fillers, are mixed in a first mixing unit, [0234] the mixed, especially homogeneous adhesive composition from the first mixing unit is transferred into a second mixing unit, into which the non-expanded microballoons are also introduced, [0235] the microballoons are expanded in the second mixing unit or on exit from the second mixing unit, [0236] the adhesive composition mixture along with the expanded microballoons is formed to a layer in a roll applicator, [0237] the adhesive composition mixture along with the expanded microballoons is optionally applied to a carrier or release material in sheet form.

[0238] The processes for producing a self-adhesive composition layer of the invention that are illustrated in FIGS. 3 to 5 are thus each a process in which a pressure-sensitive adhesive strip consisting of a single self-adhesive composition layer can be provided, i.e. a transfer tape. Optionally, the self-adhesive composition layer can be covered here with release material in sheet form, i.e. a liner. Preferably, the self-adhesive composition layer is covered with a liner on both surfaces.

[0239] If, in the processes from FIGS. 3 to 5, the self-adhesive composition layer obtained is applied to a carrier material in sheet form, i.e. a film carrier F, the result is a single-sided adhesive tape. Optionally, it is then possible to cover the opposite surface of the self-adhesive composition layer from the film carrier layer F with release material in sheet form, i.e. a liner.

[0240] If, in the three-layer system composed of film carrier layer F, self-adhesive composition layer and liner, a further self-adhesive composition layer is then applied to the opposite surface of the film carrier layer F from the self-adhesive composition layer, the result is a double-sided adhesive tape of the invention with a film carrier. Optionally, it is then possible to cover the opposite surface of the self-adhesive composition layer from the film carrier layer F with release material in sheet form, i.e. a liner.

[0241] In a preferred embodiment of the invention, the adhesive composition is shaped in a roll applicator and applied to the carrier material.

[0242] 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.

[0243] In addition, it is advantageous when [0244] the first mixing unit is a continuous unit, especially a planetary roll extruder, a twin-screw extruder or a pin extruder, [0245] the first mixing unit is a batchwise unit, especially a Z kneader or an internal mixer, [0246] the second mixing unit is a planetary roll extruder, a single-screw or twin-screw extruder or a pin extruder and/or [0247] 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.

[0248] 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 components, is possible.

[0249] 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.

[0250] The figures show:

[0251] FIG. 3 the process with one mixing unit, wherein the microballoons are added directly in the first mixing unit,

[0252] FIG. 4 the process with two mixing units, wherein the microballoons are added in the first mixing unit, and

[0253] FIG. 5 the process having two mixing units, wherein the microballoons are added only in the second mixing unit.

[0254] FIG. 3 shows a particularly advantageously configured process for producing a foamed pressure-sensitive adhesive composition layer.

[0255] In a continuous mixing unit, for example a planetary roll extruder (PRE), the pressure-sensitive adhesive composition is produced.

[0256] For this purpose, the reactants E that are to form the adhesive composition are introduced into the planetary roll extruder PRE 1. At the same time, the unexpanded microballoons MB are incorporated homogeneously into the self-adhesive composition during the compounding process.

[0257] 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 at least begin to expand during mixing and preferably foam completely 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.

[0258] With a roll applicator 3 as shaping unit, this foam-like adhesive composition M is calendered and coated onto a carrier material in sheet 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.

[0259] 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. The drop in bonding force resulting from the microballoons can thus be distinctly reduced.

[0260] FIG. 4 shows a further particularly advantageously configured process for producing a foamed pressure-sensitive adhesive composition layer.

[0261] The planetary roll 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.

[0262] An example of a suitable apparatus is the planetary roll extruder from Entex in Bochum.

[0263] Subsequently, the microballoons are incorporated homogeneously into the self-adhesive composition in a second mixing unit, for example a twin-screw extruder, heated above the expansion temperature and foamed.

[0264] For this purpose, the adhesive composition K formed from the reactants E is introduced here into the twin-screw extruder TSE 2; at the same time, the microballoons MB are introduced. The twin-screw extruder TSE has a total of four heating zones over its run length 21.

[0265] An example of a suitable apparatus is a twin-screw extruder from Kiener.

[0266] During the expansion caused by the pressure drop at the nozzle exit of TSE 2, the foamed microballoons MB break through the surface of the composition.

[0267] With a roll applicator 3, this foam-like adhesive composition M is calendered and coated onto a carrier material in sheet 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.

[0268] 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. The drop in bonding force resulting from the microballoons can thus be distinctly reduced.

[0269] FIG. 5 shows a further particularly advantageously configured process for producing a foamed pressure-sensitive adhesive composition layer.

[0270] In a continuous mixing unit, for example a planetary roll extruder (PRE), the pressure-sensitive adhesive composition is produced.

[0271] Here, the reactants E that are to form the adhesive composition are introduced into the planetary roll extruder PRE 1. The planetary roll 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.

[0272] Further reactants are added to the injection ring 13, for example plasticizer or liquid resin.

[0273] An example of a suitable apparatus is the planetary roll extruder from Entex in Bochum.

[0274] 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.

[0275] For this purpose, the adhesive composition K formed from the reactants E is introduced here into the single-screw extruder TSE 2; at the same time, the microballoons MB are introduced. The single-screw extruder TSE has a total of four heating zones over its run length 21.

[0276] An example of a suitable apparatus is a single-screw extruder from Kiener.

[0277] During the expansion caused by the pressure drop at the nozzle exit of TSE 2, the microballoons MB break through the surface of the composition.

[0278] With a roll applicator 3, this foam-like adhesive composition M is calendered and coated onto a carrier material in sheet 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.

[0279] 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. The drop in bonding force resulting from the microballoons can thus be distinctly reduced.

[0280] 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. 3. FIG. 3 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.

[0281] 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.

[0282] 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 length 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.

[0283] Planetary roll 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 compounding processes that require a mode of operation with exceptional temperature control.

[0284] Planetary roll extruders exist in various designs and sizes according to the manufacturer. According to the desired throughput, the diameters of the roll cylinders are typically between 70 mm and 400 mm.

[0285] Planetary roll extruders generally have a filling section and a compounding section.

[0286] 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.

[0287] 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.

[0288] 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.

[0289] 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 roll 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 roll cylinder diameter, it is possible with a greater number of spindles to achieve better homogenization and dispersion performance, or a greater product throughput.

[0290] The maximum number of planetary spindles that can be installed between the central spindle and roll cylinder is dependent on the diameter of the roll cylinder and on the diameter of the planetary spindles used. In the case of use of greater roll diameters as necessary for achievement of throughputs on the production scale, or smaller diameters for the planetary spindles, the roll cylinders can be equipped with a greater number of planetary spindles. Typically, up to seven planetary spindles are used in the case of a roll diameter of D=70 mm, while ten planetary spindles, for example, can be used in the case of a roll diameter of D=200 mm, and 24, for example, in the case of a roll diameter of D=400 mm.

[0291] 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.

[0292] 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.

[0293] 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.

[0294] 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.

[0295] 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 sheet form are brought together.

[0296] Depending on the nature of the carrier material in sheet form which is to be coated, coating can be effected in a co-rotational or counter-rotational process.

[0297] 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.

[0298] In an alternative process for producing a self-adhesive composition layer of the invention, all constituents of the adhesive 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. For this purpose, it is possible in principle to use the known compounding and stirring units, and it should be ensured that the microballoons do not yet expand in the course of mixing. As soon as the microballoons are distributed homogeneously in the solution, the adhesive composition can be coated, for which it is again possible to use prior art coating systems. For example, the coating can be accomplished by means of a doctor blade onto a conventional PET liner. In the next step, the coating composition applied is dried at 100 C. for 15 min. In none of the aforementioned steps is there any expansion of the microballoons. After the drying, the adhesive layer is covered with a second ply of PET liner or with a film carrier and foamed in the oven within an appropriate temperature/time window, for instance at 150 C. for 5 min or at 170 C. for 1 min, specifically covered between the two liners or between the liner and the film carrier, in order to produce a particularly smooth surface.

[0299] If the dried adhesive layer is foamed between the two liners, the result is a pressure-sensitive adhesive strip of the invention that consists of the self-adhesive layer. If the self-adhesive layer is foamed between the liner and the film carrier, the result is a pressure-sensitive adhesive strip of the invention in the form of a single-sided adhesive tape.

[0300] Alternatively, prior to the foaming of the dried self-adhesive layer localized between the liner and the film carrier, it is possible to laminate a second, likewise dried microballoon-containing self-adhesive layer that has in turn been applied to a liner onto the opposite surface of the film carrier from the dried self-adhesive layer, such that it is possible to provide an unfoamed three-layer composite composed of an inner film carrier and two self-adhesive layers that are in direct contact with the film carrier and have in turn been provided with liners on their outer faces. Such a three-layer composite can also be provided by directly coating the film carrier F simultaneously or successively with the unfoamed self-adhesive compositions containing microballoons, after which the self-adhesive composition layers are dried at 100 C. for 15 min and then covered with liners. After the drying, the adhesive layers are foamed in the oven within an appropriate temperature/time window, for instance at 150 C. for 5 min or at 170 C. for 1 min, specifically covered between the two liners, in order to produce a particularly smooth surface. The result is a pressure-sensitive adhesive strip of the invention in the form of a double-sided adhesive tape with carrier.

[0301] The surface of the self-adhesive layer thus produced has a roughness R.sub.a of less than 15 m, more preferably less than 10 m, most preferably less than 3 m.

[0302] 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. In other words, R.sub.a is the arithmetic mean roughness, i.e. the arithmetic mean of all profile values in the roughness profile. R.sub.a is measured by means of laser triangulation.

[0303] The expansion temperature chosen is especially higher than the drying temperature in order to avoid the expansion of the microballoons in the course of drying.

[0304] The invention is elucidated in detail hereinafter by a few examples. With reference to the examples described hereinafter, particularly advantageous embodiments of the invention will be elucidated in detail, without any intention to unnecessarily restrict the invention thereby.

EXAMPLES

[0305] There follows a description of the production of pressure-sensitive adhesive strips of the invention, each of which consists of a single self-adhesive composition layer SK1 based on a vinylaromatic block copolymer composition foamed with Expancel 920 DU80 microballoons. The microballoon content of Expancel 920 DU80 was varied.

[0306] For this purpose, first of all, a 40% by weight adhesive solution in benzine/toluene/acetone was produced from 50.0% by weight of Kraton D1102AS, 45.0% by weight of Dercolyte A115, 4.5% by weight of Wingtack 10 and 0.5% by weight of Irganox 1010 aging stabilizer (also called adhesive solution 1). The proportions by weight of the dissolved constituents are each based on the dry weight of the resulting solution. Said constituents of the adhesive composition are characterized as follows:

TABLE-US-00004 Kraton D1102AS: styrene-butadiene-styrene triblock copolymer from Kraton Polymers with 17% by weight of diblock, block polystyrene content: 30% by weight Dercolyte A115: solid -pinene tackifying resin with a ring and ball softening temperature of 115 C. and a DACP of 35 C. Wingtack 10: liquid hydrocarbon resin from Cray Valley Irganox 1010: pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate) from BASF SE

[0307] The solution was subsequently admixed with 2% by weight or 3% by weight of unexpanded Expancel 920 DU80 microballoons, using the microballoons in the form of a slurry in benzine. The proportions by weight of the microballoons are based here in each case on the dry weight of the solution used to which they have been added (i.e. the dry weight of the solution used is fixed at 100%). The mixture obtained was then coated with a coating bar onto a PET liner provided with a silicone release agent in the desired layer thickness, then the solvent was evaporated off at 100 C. for 15 min and so the composition layer was dried.

[0308] Thereafter, a second PET liner was laminated in each case onto the free surface of the dried adhesive composition layer produced and the adhesive composition layer was then foamed between the two liners in an oven at 150 C. for 5 min. Through the foaming between two liners, products having particularly smooth surfaces are obtainable (with R.sub.a values less than 15 m). By die-cutting, pressure-sensitive adhesive strips of the invention with the desired dimensions were obtained (examples 1 and 2). The pressure-sensitive adhesive strips were produced such that they had a thickness of about 150 m. The thickness is based on the pressure-sensitive adhesive strips without PET liner.

[0309] In comparative experiments, the production of the pressure-sensitive adhesive strips was repeated in the same way, except using unexpanded microballoons of the Expancel 920 DU20, Expancel 920 DU40 or Expancel 920 DU120 types in place of unexpanded Expancel 920 DU80 microballoons. The proportions by weight of the microballoons chosen, in the case of use of Expancel 920 DU20 or Expancel 920 DU40, were again 2% by weight and 3% by weight, and in the case of use of Expancel 920 DU120 were 0.9% by weight and 2% by weight, based in each case on the dry weight of the adhesive solution used (comparative examples 1 to 6). The pressure-sensitive adhesive strips were likewise produced such that they had a thickness of about 150 m. The thickness is based on the pressure-sensitive adhesive strips without PET liner.

[0310] There also follows a description of the production of a pressure-sensitive adhesive strip of the invention which consists of a single self-adhesive composition layer SK1 likewise based on a vinylaromatic block copolymer composition foamed with Expancel 920 DU80 microballoons. However, a different adhesive solution was used (also called adhesive solution 2).

[0311] For this purpose, first of all, a 40% by weight adhesive solution in benzine/toluene/acetone was produced from 25.0% by weight of Kraton D1101AS, 25.0% by weight of Kraton D1118ES, 45.0% by weight of Dercolyte A115, 4.5% by weight of Wingtack 10 and 0.5% by weight of Irganox 1010 aging stabilizer (called adhesive solution 2). The proportions by weight of the dissolved constituents are each based on the dry weight of the resulting solution. Said constituents of the adhesive composition are characterized as follows:

TABLE-US-00005 Kraton D1101AS: styrene-butadiene-styrene triblock copolymer from Kraton Polymers with 16% by weight of diblock, block polystyrene content: 31% by weight Kraton D1118ES: styrene-butadiene-styrene triblock copolymer from Kraton Polymers with 78% by weight of diblock, block polystyrene content: 33% by weight Dercolyte A115: solid -pinene tackifying resin with a ring and ball softening temperature of 115 C. and a DACP of 35 C. Wingtack 10: liquid hydrocarbon resin from Cray Valley Irganox 1010: pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate) from BASF SE

[0312] The solution was subsequently admixed with 2% by weight of unexpanded Expancel 920 DU80 microballoons, using the microballoons in the form of a slurry in benzine. The proportion by weight of the microballoons is based on the dry weight of the solution used to which they have been added (i.e. the dry weight of the solution used is fixed at 100%). The mixture obtained was then coated with a coating bar onto a PET liner provided with a silicone release agent in the desired layer thickness, then the solvent was evaporated off at 100 C. for 15 min and so the composition layer was dried.

[0313] Thereafter, a second PET liner was laminated onto the free surface of the dried adhesive composition layer produced and the adhesive composition layer was then foamed between the two liners in an oven at 150 C. for 5 min. Through the foaming between two liners, products having particularly smooth surfaces are obtainable (with Ra values less than 15 m). By die-cutting, an inventive pressure-sensitive adhesive strip of the desired dimensions was obtained (example 3). The pressure-sensitive adhesive strip was produced such that it has a thickness of about 150 m. The thickness is based on the pressure-sensitive adhesive strip without PET liner.

[0314] In a comparative experiment, the production of the pressure-sensitive adhesive strip was repeated in the same way, except using unexpanded microballoons of the Expancel 920 DU20 type in place of unexpanded Expancel 920 DU80 microballoons. The proportion by weight of the microballoons chosen was again 2% by weight, based on the dry weight of the adhesive solution used (comparative example 7). The pressure-sensitive adhesive strip was likewise produced such that it had a thickness of about 150 m. The thickness is based on the pressure-sensitive adhesive strip without PET liner.

[0315] Table 1 below shows the thermal shear strengths of the inventive pressure-sensitive adhesive strips (examples 1 to 3) and of the noninventive pressure-sensitive adhesive strips (comparative examples 1 to 7).

TABLE-US-00006 TABLE 1 Thermal shear strengths of inventive pressure-sensitive adhesive strips and comparative examples MB.sup.1 SACL SSS.sup.3 SSS.sup.3 Adhesive MB.sup.1 content density.sup.2 70 C./1 kg 80 C./0.5 kg SAFT.sup.4 Experiment solution type (% by wt.) (kg/m.sup.3) (min) (min) ( C.) Example 1 1 DU80 2.0 639 134 338 118.2 Example 2 1 DU80 3.0 522 147 304 118.1 Example 3 2 DU80 2.0 702 146 516 129.9 Comparative 1 DU20 2.0 651 88 84 111.2 example 1 Comparative 1 DU20 3.0 599 46 42 113.0 example 2 Comparative 1 DU40 2.0 630 104 227 111.1 example 3 Comparative 1 DU40 3.0 567 103 209 117.2 example 4 Comparative 1 DU120 0.9 667 100 95 110.7 example 5 Comparative 1 DU120 2.0 530 140 251 114.4 example 6 Comparative 2 DU20 2.0 707 89 262 122.6 example 7 .sup.1MB = microballoons; .sup.2SACL = self-adhesive composition layer; .sup.3SSS = static shear strength; .sup.4SAFT = shear adhesion failure temperature (tesa-SAFT), thermal stability.

[0316] Examples 1 to 3 show that, surprisingly, excellent static shear strengths and thermal stabilities can be achieved in pressure-sensitive adhesive strips when the self-adhesive composition layers based on vinylaromatic block copolymer are foamed with unexpanded Expancel 920 DU80 microballoons.

[0317] A comparison of the inventive pressure-sensitive adhesive strips with the pressure-sensitive adhesive strips from comparative examples, the self-adhesive composition layers of which based on vinylaromatic block copolymer are foamed with distinctly smaller microballoons or distinctly larger microballoons, shows that voids in the foamed adhesive composition layers obviously lead to distinctly improved thermal shear strengths when these have a mean diameter in the order of magnitude of about 80 m.

[0318] A comparison of examples 1 and 2 shows that similarly good thermal shear strengths can be achieved in the pressure-sensitive adhesive strips of the invention with contents of microballoons of 2% by weight or 3% by weight.

[0319] Examples 1 to 3 also show that excellent thermal shear strengths are to be expected over a broad absolute density range from about 500 to 750 kg/m.sup.3 of the self-adhesive compositions in the pressure-sensitive adhesive strips of the invention.

[0320] A comparison of examples 1 and 3 also shows that the thermal shear strengths in pressure-sensitive adhesive strips of the invention can also be improved further via suitable selection of the vinylaromatic block copolymer composition.

Test Methods

[0321] Unless stated otherwise, all measurements were conducted at 23 C. and 50% rel. air humidity.

[0322] The mechanical and adhesive data were ascertained as follows:

Resilience/Elasticity

[0323] 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.

[0324] The resilience is then calculated as follows:

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

[0325] with R=resilience in %

[0326] L.sub.100: length of the adhesive strip after extension by 100%

[0327] L.sub.0: length of the adhesive strip prior to extension

[0328] L.sub.end: length of the adhesive strip after relaxation for 1 min.

[0329] The resilience corresponds here to the elasticity.

Tensile Strength and Elongation at Break (Test Method R1)

[0330] Tensile strength and elongation at break 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.

Modulus of Elasticity

[0331] Modulus of elasticity indicates the mechanical resistance that a material offers to elastic deformation. It is determined as the ratio of the strain a required to the elongation achieved, where is the quotient of the change in length L and the length L.sub.0 in Hooke's regime of deformation of the specimen. The definition of the modulus of elasticity is elucidated, for example, in the Taschenbuch der Physik [Physics Handbook] (H. Stcker (ed.), Taschenbuch der Physik, 2nd ed., 1994, Verlag Harri Deutsch, Frankfurt, p. 102-110).

[0332] To determine the modulus of elasticity of a film, the tensile strain characteristics were ascertained using a type 2 specimen (rectangular test film strip of length 150 mm and width 15 mm) according to DIN EN ISO 527-3/2/300 with a test speed of 300 mm/min, a clamping length of 100 mm and an initial force of 0.3 N/cm, the test strip for ascertainment of the data having been cut to size with sharp blades. A Zwick tensile tester (model Z010) was used. Tensile strain characteristics were measured in machine direction (MD). A 1000 N (Zwick Roell Kap-Z 066080.03.00) or 100 N (Zwick Roell Kap-Z 066110.03.00) load cell was used. Modulus of elasticity was ascertained by graphical means from the measurement curves by determining the slope of the starting region of the curve which is characteristic of the behavior in respect of Hooke's Law and is reported in GPa.

DACP

[0333] 5.0 g of test substance (the tackifying resin sample to be examined) are weighed into a dry test tube, and 5.0 g of xylene (isomer mixture, CAS [1330-20-7], 98.5%, Sigma-Aldrich #320579 or comparable) are added. The test substance is dissolved at 130 C. and then cooled down to 80 C. Any xylene that escapes is made up for with fresh xylene, such that 5.0 g of xylene are present again. Subsequently, 5.0 g of diacetone alcohol (4-hydroxy-4-methyl-2-pentanone, CAS [123-42-2], 99%, Aldrich #H41544 or comparable) are added. The test tube is shaken until the test substance has dissolved completely. For this purpose, the solution is heated to 100 C. The test tube containing the resin solution is then introduced into a Novomatics Chemotronic Cool cloud point measuring instrument and heated therein to 110 C. It is cooled down at a cooling rate of 1.0 K/min. The cloud point is detected optically. For this purpose, that temperature at which the turbidity of the solution is 70% is registered. The result is reported in C. The lower the DACP value, the higher the polarity of the test substance.

Tackifying Resin Softening Temperature

[0334] The tackifying resin softening temperature is conducted by the relevant methodology, known as ring & ball and standardized in ASTM E28.

Diameter

[0335] The mean diameter of the voids formed by the microballoons in a self-adhesive composition layer is determined using cryofracture edges of the pressure-sensitive adhesive strip in a scanning electron microscope (SEM) with 500-fold magnification. The diameter of the microballoons in the self-adhesive composition layer to be examined that are visible in scanning electron micrographs of 5 different cryofracture edges of the pressure-sensitive adhesive strip is determined in each case by graphical means, and the arithmetic mean of all the diameters ascertained in the 5 scanning electron micrographs constitutes the mean diameter of the voids formed by the microballoons in the self-adhesive composition layer in the context of the present application. The diameters of the microballoons visible in the micrographs are determined by graphical means in such a way that the maximum extent thereof in any (two-dimensional) direction is inferred from the scanning electron micrographs for each individual microballoon in the self-adhesive composition layer to be examined and regarded as the diameter thereof.

Density

[0336] 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.

[0337] The mass applied can be determined by determining the mass of a section, defined in terms of its length and width, of such an adhesive composition layer applied to a carrier or liner, minus the (known or separately determinable) mass of a section of the same dimensions of the carrier or liner used.

[0338] The thickness of an adhesive composition layer can be determined by determining the thickness of a section, defined in terms of its length and width, of such an adhesive composition layer applied to a carrier or liner, minus the (known or separately determinable) thickness of a section of the same dimensions of the carrier or liner used. The thickness of the adhesive composition layer can be determined by means of commercial thickness measuring instruments (caliper test instruments) with accuracies of less than a 1 m deviation. If variations in thickness are found, the mean of measurements at at least three representative sites is reported, i.e. more particularly not measured at creases, folds, specks and the like.

Thickness

[0339] Like the thickness of an adhesive composition layer as above, it is also possible to ascertain the thickness of a pressure-sensitive adhesive strip or a film carrier layer 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 mean 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

[0340] 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.

Shear Adhesion Failure Temperature (SAFT), Thermal Stability

[0341] This test serves for rapid testing of the shear strength of pressure-sensitive adhesive strips under thermal stress. For this purpose, the pressure-sensitive adhesive strip to be examined is stuck to a temperature-controllable steel plate and weighted down with a weight (50 g), and the shear distance is recorded.

[0342] Test Sample Preparation:

[0343] The pressure-sensitive adhesive strip to be examined, if it is a double-sidedly adhesive pressure-sensitive adhesive strip, is stuck by one of the adhesive composition sides to an aluminum foil of thickness 50 m. The pressure-sensitive adhesive strip that has been prepared in this way if appropriate is cut to a size of 10 mm*50 mm.

[0344] The pressure-sensitive adhesive strip sample that has been cut to size is stuck by the other adhesive composition side to a polished, acetone-cleaned steel test plate (material 1.4301, DIN EN 10088-2, surface 2R, surface roughness R.sub.a=30 to 60 nm, dimensions 50 mm*13 mm*1.5 mm), in such a way that the bonding surface of the sample is height*width=13 mm*10 mm, and the steel test plate projects by 2 mm at the upper edge. Subsequently, a 2 kg steel roll is rolled over six times at a speed of 10 m/min for fixing. The sample is reinforced flush at the top with a stable adhesive strip which serves as contact point for the distance sensor. Then the sample is suspended by means of the steel plate such that the longer protruding end of the adhesive tape points vertically downward.

[0345] Measurement:

[0346] The sample to be analyzed is weighted down at the lower end with a weight of 50 g. The steel test plate bonded to the sample, commencing at 25 C., is heated at a rate of 9 K/min, to the end temperature of 200 C.

[0347] What is observed is the distance that the sample has slipped by means of the distance sensor as a function of temperature and time. The maximum slip distance is fixed at 1000 m (1 mm); if exceeded, the test is stopped and the failure temperature is noted.

[0348] Test conditions: room temperature 23+/3 C., relative air humidity 50+/5%.

Quantitative Determination of Shear Strength: Static Shear Test SST

[0349] A pressure-sensitive adhesive strip in a climate-controlled cabinet heated to 70 C. or 80 C. is applied to a defined rigid bonding substrate (steel here) and subjected to constant shear stress. The hold time in minutes is ascertained.

[0350] By means of suitable plate suspension (angle 1791), it is ensured that the pressure-sensitive adhesive strip does not peel off from the lower edge of the plate.

[0351] The test is intended primarily to give a statement as to the cohesiveness of the composition. However, this is only the case when the parameters of weight and temperature are chosen such that there is actually cohesive failure in the test.

[0352] Otherwise, the test gives information as to the adhesion to the bonding substrate or as to a combination of adhesion and cohesiveness of the composition.

[0353] A strip of width 13 mm of the pressure-sensitive adhesive strip to be tested is bonded to a polished steel plate (test substrate) over a length of 5 cm with a 2 kg roller by rolling it over 10 times. Double-sidedly adhesive pressure-sensitive adhesive strips are covered and hence reinforced with an aluminum foil of thickness 50 m on the reverse side.

[0354] Subsequently, a belt loop is attached to the lower end of the adhesive tape. Then a nut and bolt are used to secure an adapter plate to the front side of the shear test plate in order to ensure the defined angle of 1791. The maturing time between rolling-on and stress should be between 10 and 15 minutes. The weights of 500 g or 1 kg are subsequently suspended smoothly with the aid of the belt loop.

[0355] An automatic stopwatch then ascertains the juncture at which the test specimens shear off.