PROCESS FOR PRODUCING A SELF-ADHESIVE COMPOSITION LAYER FOAMED WITH MICROBALLOONS

Abstract

The present invention relates to a method for producing a layer of self-adhesive composition at least partially foamed with microballoons, wherein a foamable layer of self-adhesive composition comprising expandable microballoons and disposed between (i) two liners, (ii) a liner and a carrier, or (iii) a liner and a further layer of self-adhesive composition which (a) is not foamable or (b) is foamable and typically comprises expandable microballoons,
is heat-treated at a temperature suitable for foaming for a period such that after the subsequent cooling of the layer the desired degree of foaming is attained, characterized in that
the two liners or the liner during the foaming remain or remains adhering substantially completely on the respective surface of the foamable layer of self-adhesive composition on which they or it are or is disposed.

Claims

1. Method for producing a layer of self-adhesive composition at least partially foamed with microballoons, said method comprising heat-treating a foamable layer of self-adhesive composition comprising expandable microballoons and disposed between (i) two liners, (ii) a liner and a carrier, or (iii) a liner and a further layer of self-adhesive composition which (a) is not foamable or (b) is foamable and typically comprises expandable microballoons, by suitable energy input at a temperature suitable for foaming for a period such that after subsequent cooling of the layer the desired degree of foaming is attained, wherein the two liners or the liner during the foaming remain or remains adhering substantially completely on the respective surface of the foamable layer of self-adhesive composition on which they or it are or is disposed.

2. Method according to claim 1, wherein the foamable layer of self-adhesive composition is disposed between (i) two liners, (ii) a liner and a carrier, or (iii) a liner and a further layer of self-adhesive composition, by application of a self-adhesive composition comprising expandable microballoons from a solution to a liner or carrier and drying thereof below the foaming temperature, and a liner, a carrier or a further layer of self-adhesive composition, optionally applied to a liner or carrier, is laminated onto that surface of the dried layer of self-adhesive composition that is opposite the liner or carrier.

3. Method according to claim 1, wherein the foamable layer of self-adhesive composition is disposed between (i) two liners, (ii) a liner and a carrier, or (iii) a liner and a further layer of self-adhesive composition, by (i) the two liners, (ii) the liner and the carrier, or (iii) the liner and the further layer of self-adhesive composition, typically applied to a liner or carrier, being laminated onto the foamable layer of self-adhesive composition.

4. Method according to claim 1, wherein the two liners independently of one another or the liner during foaming are or is weight-stable.

5. Method according to claim 1, wherein the shrinkage of the two liners independently of one another or of the liner during foaming both in transverse direction and in longitudinal direction is less than 2%.

6. Method according to claim 1, wherein the liners or the liner during foaming consistently adopt a flat lie.

7. Method according to claim 1, wherein the foamable layer of self-adhesive composition is fully foamed.

8. Method according to claim 1, wherein the degree of foaming is at least 20% and less than 100%.

9. Method according to claim 1, wherein the energy needed for foaming is transferred by convection, radiation, or by heat conduction to the assembly composed of foamable layer of self-adhesive composition, liner and optionally carrier and/or further layer of self-adhesive composition.

10. Method according to claim 9, wherein the energy needed for foaming is transferred to the assembly uniformly by heat conduction over the web width.

11. Method according to claim 9, wherein the assembly is foamed in a drying tunnel.

12. Method according to claim 10, wherein the temperature difference of the assembly over the web width is at most 5 K.

13. Method according to claim 1, wherein the two liners independently of one another or the liner are or is (a) polyester liner(s).

14. Method according to claim 13, wherein the two liners or the liner have or has a thickness of more than 12 μm and up to 200 μm.

15. Method according to claim 1, wherein the carrier is a stretchable film carrier.

16. Method according to claim 1, wherein the carrier is a non-stretchable film carrier.

17. Method according to claim 1, wherein the foamable layer of self-adhesive composition is based on a vinylaromatic block copolymer composition and/or an acrylate composition.

18. Method according to claim 1, wherein the assembly made up of foamable layer of self-adhesive composition, liner and optionally carrier and/or further layer of self-adhesive composition is a transfer tape, a single-sided adhesive tape or a double-sided, carrier-containing adhesive tape.

19. Method according to claim 1, wherein the at least partially foamed layer of self-adhesive composition has a surface roughness R.sub.a of less than 3 μm.

20. Adhesive tape which comprises at least one layer of self-adhesive composition at least partially foamed with microballoons and obtained by a method according to claim 1.

21. Method comprising bonding a component with an adhesive tape according to claim 20.

22. Method according to claim 21, wherein the component is selected from rechargeable batteries, electronic devices, mobile devices, and mobile phones.

Description

FIGURES

[0247] On the basis of the figures described below, particularly advantageous embodiments of the invention are elucidated in more detail, without the intention thereby to subject the invention to unnecessary limitation.

[0248] FIG. 1 shows the schematic construction of a double-sided, carrier-containing adhesive tape of the invention, in cross section.

[0249] The adhesive tape comprises a carrier 1. On the top side and on the bottom side of the carrier 1 there are two self-adhesive composition layers 2, 3 at least partially foamed with microballoons. The self-adhesive composition layers 2, 3 are in turn each lined with a liner 4, 5 suitable for use in the method of the invention such as, for example, with a double-sidedly siliconized PET liner in a thickness of 75 μm.

[0250] FIG. 2, furthermore, shows the schematic construction of a transfer tape of the invention, in cross section.

[0251] The adhesive tape (transfer tape) comprises a self-adhesive composition layer 2 at least partially foamed with microballoons. The self-adhesive composition layer 2 is lined on both sides with a liner 4, 5 suitable for use in the method of the invention, such as, for example, with a double-sidedly siliconized PET liner in a thickness of 75 μm.

[0252] FIG. 3 shows the schematic construction of a further transfer tape of the invention, in cross section.

[0253] The adhesive tape (transfer tape) comprises two self-adhesive composition layers 2 and 3 at least partially foamed with microballoons, the layers being preferably identical in chemical nature, and being disposed one above the other, i.e. in direct contact with one another. On the open side, the self-adhesive layers 2 and 3 are each lined with a liner 4, 5 suitable for use in the method of the invention, such as, for example, with a double-sidedly siliconized PET liner in a thickness of 75 μm.

[0254] FIG. 4 shows the schematic construction of a further transfer tape of the invention, in cross section.

[0255] The adhesive tape (transfer tape) comprises one self-adhesive composition layer 2 at least partially foamed with microballoons, and one unfoamed self-adhesive composition layer 6, these layers being disposed one above the other, i.e. in direct contact with one another. On the open side, the self-adhesive composition layers 2 and 6 are each lined with a liner 4, 5 suitable for use in the method of the invention, such as, for example, with a double-sidedly siliconized PET liner in a thickness of 75 μm.

[0256] FIG. 5 shows a SEM micrograph (300-fold magnification) of a cryofracture edge of the polyacrylate-based self-adhesive composition layer from Example 1, foamed in accordance with the invention between two double-sidedly siliconized PET liners each with a thickness of 75 μm. The surface of the self-adhesive composition layer is smooth. In particular, no foamed microballoons are projecting from the self-adhesive composition layer. During foaming, therefore, the microballoons remain in the self-adhesive composition layer, i.e. are not pressed out of this layer.

[0257] FIG. 6 shows an SEM micrograph (300-fold magnification) of a cryofracture edge of the polyacrylate-based self-adhesive composition layer from comparative Example 4, foamed between two liners in the form of release papers with a thickness of 77 μm each. During foaming in the drying oven, the release paper lifted on one side from the self-adhesive composition layer (and is consequently no longer visible in the micrograph). On the then open side of the self-adhesive composition layer, the expanding microballoons were subsequently pressed out of the composition. Accordingly, foamed microballoons which project from the self-adhesive composition layer are visible, and which make the open side of the self-adhesive composition layer uneven.

[0258] FIG. 7 shows an SEM micrograph (50-fold magnification) of a cryofracture edge of the polyacrylate-based self-adhesive composition layer from comparative Example 5, foamed between two HDPE liners each with a thickness of 100 μm. During the foaming of the self-adhesive composition layer in the drying oven, the HDPE liners were not temperature-stable. One of the HDPE liners took on a wave shape, in other words lost its flat lie. Thereupon the self-adhesive composition layer detached, partially at any rate, from the respective liner on both sides. As can additionally be seen from the micrograph, the self-adhesive composition layer after foaming is uneven and occasionally in fact wavy.

[0259] FIG. 8 shows an exemplary web pathway for foaming by roll contact. It employs a sequence of five heated rolls 7. The assembly 8, made up of foamable self-adhesive composition layer, liner and optionally carrier and/or further self-adhesive composition layer, is guided over the rolls 7 in such a way that the surfaces of the assembly 8 are in reciprocal contact with the roll surfaces.

[0260] The invention is elucidated in more detail below by means of a number of examples. Particularly advantageous embodiments of the invention are elucidated in more detail using the examples described below, without thereby wishing to subject the invention to any unnecessary limitation.

EXAMPLES

[0261] Described below are exemplary methods for producing a layer of self-adhesive composition foamed with microballoons, for which the foaming takes place in each case between two liners.

Inventive Example 1

[0262] In the first step, the base polymer P1, i.e. the polyacrylate (Ac), envisaged for use in the self-adhesive composition was prepared via a free radical polymerization in solution. A reactor conventional for radical polymerizations was charged here with 60 kg of 2-ethylhexyl acrylate, 33 kg of n-butyl acrylate, 7 kg of acrylic acid and 66 kg of benzine/acetone (70/30). After nitrogen gas had been passed through the reactor for 45 minutes with stirring, the reactor was heated up to 58° C. and 50 g of AIBN were added. Thereafter the external heating bath was heated to 75° C. and the reaction was carried out constantly at this external temperature. After 1 hour a further 50 g of AIBN were added and after 4 hours dilution took place with 20 kg of benzine/acetone mixture. After 5.5 hours and again after 7 hours, reinitiation took place with in each case 150 g of bis(4-tert-butylcyclohexyl) peroxydicarbonate. After a reaction time of 22 hours, the polymerization was terminated and cooling took place to room temperature (20° C.). The polyacrylate has an average molecular weight of M.sub.w=450 000 g/mol and a polydispersity PD (M.sub.w/M.sub.n)=7.8.

[0263] Subsequently, the foamable self-adhesive composition was prepared. For this purpose, 100 wt % of the base polymer P1 were adjusted by the addition of benzine and acetone (in a weight ratio of 1:1) to a solids content of 35 wt %. Thereafter 2.5 wt % of unexpanded microballoons of type Expancel 920 DU20 were added to the composition as a mixture in benzine/acetone (weight ratio 1:1) at room temperature (20° C.) and with stirring. The weight fractions of the microballoons in the examples are based in each case on the dry weight of the solution to which they were added (i.e. the dry weight of the solution used is set as 100%). The mixture was stirred for 15 minutes, after which 0.075 wt % of the covalent crosslinker Erysis GA 240 (N,N,N′,N′-tetrakis(2,3-epoxypropyl)-m-xylene-a,a′-diamine) from Emerald Performance Materials was added with stirring, based on the weight of the base polymer used. The mixture was stirred for a further 15 minutes.

[0264] The resulting mixture was then mixed continuously with a stirrer, pumped through a 50 μm filter, again mixed using a static mixer, and finally conveyed to the coating table, where a comma bar was used for application, at a web speed of 15 m/min to a PET liner (Inventive Example 1) 75 μm thick and furnished on each side with a releasing silicone (silicone coatweight: 1 g/m.sup.2 on both sides), of a layer whose thickness was such as to give a coatweight of 85 g/m.sup.2 following subsequent evaporation of the solvent at 100° C. for 15 minutes in a drying oven and hence drying of the layer of composition.

[0265] A second, identical PET liner was then laminated onto the free surface of the layer of self-adhesive composition produced and dried, and the self-adhesive composition layer was subsequently foamed between the two liners in a drying oven at 163° C. for 30 seconds and then cooled at room temperature (20° C.).

[0266] During foaming, the liners remained adhering completely to the respective surface of the foamable self-adhesive composition layer on which they were disposed. The shrinkage of the liners during foaming was 0% in both longitudinal and transverse directions; in other words, there was no shrinkage found either in transverse or in longitudinal direction. Furthermore, during foaming, the liners were weight-stable, i.e. did not lose weight. Moreover, during the foaming, the liners consistently adopted a flat lie.

[0267] As shown by the SEM micrograph from FIG. 5, the surface of the self-adhesive composition layer is smooth. In particular, no foamed microballoons project from the self-adhesive composition layer. Accordingly, the microballoons remained in the self-adhesive composition layer during foaming, i.e. were not pressed out of this layer. The surface roughness R.sub.a of the foamed self-adhesive composition layer is 2.5 μm.

Inventive Example 2

[0268] The method for producing a self-adhesive composition layer foamed with microballoons corresponds to Inventive Example 1, with the two double-sidedly siliconized PET liners used having a thickness of only 50 μm.

[0269] During foaming, the liners remained adhering completely to the respective surface of the foamable self-adhesive composition layer on which they were disposed. The shrinkage of the liners during foaming was 0% in both longitudinal and transverse directions; in other words, there was no shrinkage found either in transverse or in longitudinal direction. Furthermore, during foaming, the liners were weight-stable, i.e. did not lose weight. Moreover, during the foaming, the liners consistently adopted a flat lie.

[0270] In SEM micrographs, a smooth surface can be seen for the self-adhesive composition layer. In particular, no foamed microballoons project from the self-adhesive composition layer. Accordingly, the microballoons remained in the self-adhesive composition layer during foaming, i.e. were not pressed out of this layer (not shown). The surface roughness R.sub.a of the foamed self-adhesive composition layer is 1.8 μm.

Comparative Example 3

[0271] The method for producing a self-adhesive composition layer foamed with microballoons corresponds to Inventive Example 1, with the two double-sidedly siliconized PET liners used having a thickness of only 12 μm.

[0272] During foaming, the liners lost their flat lie. The foaming operation led to shrinkage of the liners by in each case 2% in longitudinal and transverse directions. During the foaming, therefore, the liners did not remain adhering completely to the respective surface of the foamable self-adhesive composition layer on which they were disposed. The suitability of a liner for the method of the invention is therefore dependent not merely on the liner material but also on the liner thickness. At those locations where the liners lifted, microballoons emerged from the surface of the adhesive composition, and the surface of the adhesive composition was matt and rough.

Comparative Example 4

[0273] The method for producing a layer of self-adhesive composition foamed with microballoons corresponds to Inventive Example 1, with the two liners used each comprising a release paper (TP) with a thickness of 77 μm in each case.

[0274] During foaming, the liners were not weight-stable, instead losing around 2 wt % through loss of moisture. One of the release papers lifted from the self-adhesive composition layer during foaming in the drying oven. On the then open side of the self-adhesive composition layer, the expanding microballoons were subsequently pressed out of the composition. In an SEM micrograph, accordingly, foamed microballoons are visible, projecting from the self-adhesive composition layer, which make the open side of the self-adhesive composition layer uneven (see FIG. 6). Moreover, foaming resulted in shrinkage of the liners by 1% in the longitudinal direction and 0% in the transverse direction.

Comparative Example 5

[0275] The method for producing a layer of self-adhesive composition foamed with microballoons corresponds to Example 1, with the two liners used each comprising an HDPE liner with a thickness of 100 μm.

[0276] During the foaming of the self-adhesive composition layer, the liners melted, owing to the low melting temperature of polyethylene. As can be seen from the SEM micrograph from FIG. 7, one of the HDPE liners adopted a wavy shape, i.e. lost its flat lie (additionally, the liner shrank by 74% in the longitudinal direction and 0% in the transverse direction). Thereafter the self-adhesive composition layer underwent at least partial detachment from the respective liner on both sides. As can also be seen from the micrograph, the self-adhesive composition layer after foaming is uneven and occasionally in fact is wavy.

Comparative Example 6

[0277] The method for producing a layer of self-adhesive composition foamed with microballoons corresponds to Example 1, with the two liners used each comprising paper (TP) coated double-sidedly with polyethylene (PE).

[0278] During the foaming of the self-adhesive composition layer, the polyethylene layers of the liners melted, owing to the low melting temperature of polyethylene. When viewed with the naked eye after foaming, therefore, the liners appeared blistery and matt. One of the liners adopted a wavy shape during foaming, i.e. lost its flat lie (additionally, the liner shrank by 1% in the longitudinal direction and 0% in the transverse direction). Thereafter the self-adhesive composition layer underwent at least partial detachment from the liner on both sides. After foaming, the self-adhesive composition layer was uneven and occasionally in fact was wavy.

Inventive Example 7

[0279] An inventive pressure-sensitive adhesive strip was produced on the basis of a styrene block copolymer (SBC) composition.

[0280] For this purpose, first, a 40 wt % strength adhesive solution in benzine/toluene/acetone was prepared from 48.0 wt % of Kraton D1102AS, 48.0 wt % of Piccolyte A115, 3.5 wt % of Wingtack 10 and 0.5 wt % of ageing inhibitor Irganox 1010 (also called adhesive solution 1). The weight fractions of the dissolved constituents here are based in each case on the dry weight of the resulting solution. The stated constituents of the adhesive are characterized as follows: [0281] Kraton D1102AS: styrene-butadiene-styrene triblock copolymer from Kraton Polymers with 17 wt % diblock, block polystyrene content: 30 wt % [0282] Piccolyte A115: solid α-pinene tackifying resin having a Ring & Ball softening temperature of 115° C. [0283] Wingtack 10: liquid hydrocarbon resin from Cray Valley [0284] Irganox 1010: pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxy-phenyl)propionate) from BASF SE

[0285] The solution was subsequently admixed with 3.3 wt % of Expancel 920 DU20 unexpanded microballoons, the microballoons being used in the form of a suspension in benzine. The weight fractions of the microballoons in the examples are based in each case on the dry weight of the solution used to which they were added (i.e. the dry weight of the solution used is set as 100%). The resulting mixture was then applied with a coating bar to a 75 μm PET liner as defined in Example 1, in a layer thickness such as to result in a coatweight of 75 g/m.sup.2 following subsequent evaporation of the solvent at 100° C. for 15 minutes and therefore drying of the layer of composition.

[0286] Subsequently a second such PET liner was laminated onto the free surface of the layer of adhesive composition produced and dried, after which the layer of adhesive composition was foamed between the two liners in the oven at 163° C. for 30 seconds and then cooled at room temperature (20° C.).

[0287] During foaming, the liners remained adhering completely to the respective surface of the foamable self-adhesive composition layer on which they were disposed. The shrinkage of the liners during foaming was 0% in both longitudinal and transverse directions; in other words, there was no shrinkage found either in transverse or in longitudinal direction. Furthermore, during foaming, the liners were weight-stable, i.e. did not lose weight. Moreover, during the foaming, the liners consistently adopted a flat lie.

[0288] The surface of the self-adhesive composition layer is smooth. In particular, no foamed microballoons project from the self-adhesive composition layer. Accordingly, the microballoons remained in the self-adhesive composition layer during foaming, i.e. were not pressed out of this layer. The surface roughness R.sub.a of the foamed self-adhesive composition layer is 2.1 μm.

Inventive Example 8

[0289] An inventive pressure-sensitive adhesive strip was produced on the basis of a polyacrylate (Ac)-styrene block copolymer (SBC) blend.

[0290] For this purpose a mixture was prepared comprising 42.425 wt % of base polymer P1 as described above in Inventive Example 1, 37.5 wt % of Dertophene T resin and also 20 wt % of Kraton D 1118. Dertophene T is a terpene-phenolic resin (softening point 110° C.; M.sub.w=500 to 800 g/mol; PD=1.50) from DRT resins. Kraton 1118 is a styrene-butadiene-styrene block copolymer from Kraton Polymers with 78 wt % of 3-block, 22 wt % of 2-block, a block polystyrene content of 33 wt %, and a molecular weight M.sub.w of 150 000 g/mol for the 3-block fraction. Benzine was added to set a solids content of 38 wt %. The mixture of polymer and resin was stirred until the resin had visibly dissolved entirely. Then 0.075 wt % of the covalent crosslinker Erysis GA 240 (N,N,N′,N′-tetrakis(2,3-epoxypropyl)-m-xylene-a,a′-diamine) from Emerald Performance Materials was added. The weight fractions of the dissolved constituents are based in each case on the dry weight of the resulting solution. The mixture was stirred for 15 minutes with addition of 0.8 wt % of Expancel 920 DU20 unexpanded microballoons at room temperature (20° C.). The resulting mixture was then applied with a coating bar to a 75 μm PET liner as defined in Example 1, in a layer thickness such as to result in a coatweight of 130 g/m.sup.2 following subsequent evaporation of the solvent at 100° C. for 15 minutes and therefore drying of the layer of composition.

[0291] Subsequently a second such PET liner was laminated onto the free surface of the layer of adhesive composition produced and dried, after which the layer of adhesive composition was foamed between the two liners in the oven at 163° C. for 30 seconds and then cooled at room temperature (20° C.).

[0292] During foaming, the liners remained adhering completely to the respective surface of the foamable self-adhesive composition layer on which they were disposed. The shrinkage of the liners during foaming was 0% in both longitudinal and transverse directions; in other words, there was no shrinkage found either in transverse or in longitudinal direction. Furthermore, during foaming, the liners were weight-stable, i.e. did not lose weight. Moreover, during the foaming, the liners consistently adopted a flat lie.

[0293] The surface of the self-adhesive composition layer is smooth. In particular, no foamed microballoons project from the self-adhesive composition layer. Accordingly, the microballoons remained in the self-adhesive composition layer during foaming, i.e. were not pressed out of this layer. The surface roughness R.sub.a of the foamed self-adhesive composition layer is 2.9 μm.

[0294] Table 1 shows various properties of the microballoon-foamed self-adhesive composition layers from the inventive examples and comparative examples.

TABLE-US-00001 Liner Peel type and Base Thickness* Density* adhesion* Dupont z* Example thickness polymer [μm] [kg/m.sup.3] R.sub.a* [μm] [N/cm] [J] 1 PET, Ac 130 650 2.5 7 0.7 75 μm 2 PET, Ac 130 650 1.8 7 0.7 50 μm C3 PET, Ac 130 650 8 4 0.21 12 μm C4 TP, Ac 130 650 11 4 0.15 77 μm C5 HDPE, Ac 130 650 not not not 77 μm measurable, measurable measurable i.e. >75 μm C6 PE TP, Ac 130 650 not not not 100 μm measurable, measurable measurable i.e. >75 μm 7 PET, SBC 145 520 2.1 8 0.62 75 μm 8 PET, Ac/SBC 150 880 2.9 11 0.8 75 μm *pertains to the foamed self-adhesive composition layer.

[0295] The foamed self-adhesive composition layers from the inventive examples, produced using in each case an inventively suitable liner, are smooth, having in each case a surface roughness R.sub.a of less than 3 μm. As the Dupont z values show, they also have high penetration toughness. In addition they possess very good peel adhesions. As shown by Examples 1, 7 and 8, this is the case for various base polymers.

[0296] The foamed self-adhesive composition layers from the comparative examples, conversely, have much higher surface roughnesses R.sub.a, and also significantly lower penetration resistance and peel adhesion on steel (or else the self-adhesive compositions are so poor in relation to the stated physical parameters that they cannot be measured). The comparative examples show that the inventive suitability of the liner is influenced not only by the nature of the liner material but also by the thickness of the liner.

Test Methods

[0297] Unless stated otherwise, all measurements were conducted at 23° C. and 50% rel. air humidity.

[0298] The mechanical and technical adhesive data were ascertained as follows:

Tensile Strength, Tear Strength (Tear Force) and Elongation at Break (Measurement Method R1)

[0299] The elongation at break, the tear strength and the tensile strength, of a film carrier, for example, were measured in accordance with DIN EN ISO 527-3:2003-07 using a sample strip, specimen type 2, having a width of 20 mm, at a separation speed of 100 mm per minute. The initial distance between the clamping jaws was 100 mm. The test conditions were 23° C. and 50% rel. air humidity.

Detachment Force

[0300] The detachment force (stripping force or stripping strain) was ascertained using a pressure-sensitive adhesive strip having dimensions of 50 mm length×20 mm width with a non-adhesive grip tab region at the upper end. The pressure-sensitive adhesive strip was adhered between two steel plates, disposed congruently to one another, having dimensions of 50 mm×30 mm, adhesion taking place with a pressing 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 set-up can be fixed for measurement in the lower clamping jaw of a tensile testing machine. The bonds were stored for a time of 24 hours at +40° C. After reconditioning to room temperature (20° C.), the pressure-sensitive adhesive strip was removed 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 operation, the required detachment force was measured, in newtons (N). The figure reported is the mean of the stripping strain values (in N per mm.sup.2), measured in the range in which the adhesive strip is detached from the steel substrates over a bond length of between 10 mm and 40 mm.

Peel Adhesion

[0301] The peel adhesion was determined (in accordance with AFERA 5001) as follows: The defined substrate used was galvanized steel plate having a thickness of 2 mm (acquired from Rocholl GmbH). The pressure-sensitive adhesive strip under investigation was cut to a width of 20 mm and a length of about 25 cm, provided with a handling section, and immediately thereafter pressed five times onto the selected substrate using a 4 kg steel roller with a rate of advance of 10 m/min. Directly after that, the adhesive strip was pulled from the substrate at an angle of 180° using a tensile testing apparatus (from Zwick) at a velocity v=300 mm/min, and a measurement was made of the force required to achieve this at room temperature (20° C.). The measurement value (in N/cm) is obtained as the mean value from three individual measurements.

Thickness

[0302] The thickness, for example, of a pressure-sensitive adhesive strip, of an adhesive composition layer or of a carrier layer can be determined by means of commercial thickness measuring instruments (calliper test instruments) with accuracies of less than 1 μm deviation. The thickness of an adhesive composition layer is ascertained typically by determining the thickness of a section, defined in terms of its length and width, of such a 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. If variations in thickness are found, the mean of measurements at not less than three representative sites is reported, i.e. more particularly not measured at creases, folds, specks and the like. In the present specification, thickness is measured using the Mod. 2000 F precision thickness measuring instrument, which has a circular probe with a diameter of 10 mm (flat). The measuring force is 4 N. The value is read off 1 s after loading.

Density

[0303] The density of an adhesive composition layer is ascertained by forming the quotient of coatweight and thickness of the adhesive composition layer applied to a carrier or liner.

[0304] The coatweight of an adhesive composition layer can be determined by determining the mass of a section, defined in terms of its length and width, of such a 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.

[0305] 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 a 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 layer can be determined by means of commercial thickness measuring instruments (calliper test instruments) with accuracies of less than 1 μm deviation. If variations in thickness are found, the mean of measurements at not less than three representative sites is reported, i.e. more particularly not measured at creases, folds, specks and the like. In the present specification, thickness is measured using the Mod. 2000 F precision thickness measuring instrument, which has a circular probe with a diameter of 10 mm (flat). The measuring force is 4 N. The value is read off 1 s after loading.

DuPont Test in the z Direction (Penetration Resistance)

[0306] A square sample in the shape of a frame was cut out of the adhesive tape (pressure-sensitive adhesive strip) to be examined (external dimensions 33 mm×33 mm; border width 2.0 mm; internal dimensions (window cut-out) 29 mm×29 mm). This sample was stuck to a PC frame (external dimensions 45 mm×45 mm; border width 10 mm; internal dimensions (window cutout) 25 mm×25 mm; thickness 3 mm). A PC window of 35 mm×35 mm was stuck to the other side of the adhesive tape. The bonding of PC frame, adhesive tape frame and PC window was carried out such that the geometric centres and the diagonals were each superimposed on one another (corner-to-corner). The bonding area was 248 mm.sup.2. The bond was subjected to a pressure of 248 N for 5 s and stored under conditions of 23° C./50% relative humidity for 24 hours. Immediately after the storage, the adhesive assembly composed of PC frame, adhesive tape and PC window was braced by the protruding edges of the PC frame in a sample holder such that the assembly was aligned horizontally and the PC window was beneath the frame. The sample holder was then inserted centrally into the intended receptacle of the DuPont Impact Tester. The impact head of weight 190 g was used in such a way that the circular impact geometry with the diameter of 20 mm impacted centrally and flush on the window side of the PC window.

[0307] A weight having a mass of 150 g, guided on two guide rods, was allowed to drop vertically from a height of 5 cm onto the assembly thus arranged and composed of sample holder, sample and impact head (measuring conditions: 23° C., 50% relative humidity). The height from which the weight dropped was increased in 5 cm steps until the impact energy introduced destroyed the sample as a result of the impact stress, and the PC window parted from the PC frame.

[0308] In order to be able to compare experiments with different samples, the energy was calculated as follows:

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

[0309] Five samples per product were tested, and the mean energy was reported as the index of penetration resistance.

Diameter

[0310] 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 SEM micrographs of five 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 five SEM 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 in any (two-dimensional) direction is inferred from the SEM micrographs for each individual microballoon in the self-adhesive composition layer to be examined, and is regarded as the diameter thereof.

Static Glass Transition Temperature T.SUB.g

[0311] Glass transition points—referred to synonymously as glass transition temperatures—are reported as the result of measurements by means of Dynamic Scanning calorimetry (DSC) in accordance with DIN 53765:1994-03, especially sections 7.1 and 8.1, but with uniform heating and cooling rates of 10 K/min in all heating and cooling steps (compare DIN 53765:1994-03; section 7.1; note 1). The sample mass is 20 mg.

DACP

[0312] 5.0 g of test substance (the tackifier resin sample to be examined) are weighed into a dry test tube, and 5.0 g of xylene (isomer mixture, CAS [1330-20-7], 98.5%, Sigma-Aldrich #320579 or comparable) are added. The test substance is dissolved at 130° C. and then cooled down to 80° C. Any xylene that escapes is made up for with fresh xylene, such that 5.0 g of xylene are present again. Subsequently, 5.0 g of diacetone alcohol (4-hydroxy-4-methyl-2-pentanone, CAS [123-42-2], 99%, Aldrich #H41544 or comparable) are added. The test tube is shaken until the test substance is 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, the temperature recorded is that at which the turbidity of the solution is 70%. The result is reported in ° C. The lower the DACP value, the higher the polarity of the test substance.

MMAP

[0313] 5.0 g of test substance (the tackifier resin sample to be examined) are weighed into a dry test tube, and 10 ml of dry aniline (CAS [62-53-3], 99.5%, Sigma-Aldrich #51788 or comparable) and 5 ml of dry methylcyclohexane (CAS [108-87-2], 99%, Sigma-Aldrich #300306 or comparable) are added. The test tube is shaken until the test substance is 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, the temperature recorded is that at which the turbidity of the solution is 70%. The result is reported in ° C. The lower the MMAP value, the higher the aromaticity of the test substance.

Softening Temperature

[0314] The determination of softening temperature, such as of tackifying resins, polymers or polymer blocks, for example, is conducted by the relevant methodology, known as Ring & Ball and standardized in ASTM E28-14.

Gel Permeation Chromatography (GPC)

[0315] M.sub.n, M.sub.w, PD: the data for number-average molar mass M.sub.n, for weight-average molecular weight M.sub.w and the polydispersity PD are based on determination by gel permeation chromatography. The determination is made on 100 μL of sample having undergone clarifying filtration (sample concentration 1 g/L). The eluent used is tetrahydrofuran with 0.1% by volume of trifluoroacetic acid. Measurement takes place at 25° C. The pre-column used is a column type PSS-SDV, 5μ, 10.sup.3 Å, ID 8.0 mm×50 mm. Separation takes place using the columns of type PSS-SDV, 5μ, 10.sup.3 Å and also 10.sup.5 Å and 10.sup.6 Å each of ID 8.0 mm×300 mm (columns from Polymer Standards Service; detection using Shodex RI71 differential refractometer). The flow rate is 1.0 ml per minute. Calibration takes place against PMMA standard (polymethyl methacrylate calibration) and/or against polystyrene in the case of (synthetic) rubbers.

Resilience or Elasticity

[0316] To measure the resilience, the film carriers 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.

[0317] The resilience is then calculated as follows:

R=((L.sub.100−L.sub.end)/L.sub.0)*100

where R=resilience in %
L.sub.100: Length of the film carrier after extension by 100%
L.sub.0: Length of the film carrier prior to extension
L.sub.end: Length of the film carrier after relaxation for 1 min.

[0318] The resilience here corresponds to the elasticity.

Modulus of Elasticity

[0319] The modulus of elasticity indicates the mechanical resistance that a material offers to elastic deformation. It is determined as the ratio of the strain σ required to the elongation c achieved, where c is the quotient of the change in length ΔL and the length L.sub.0 in Hooke's regime of deformation of the test specimen. The definition of the modulus of elasticity is elucidated, for example, in Taschenbuch der Physik (H. Stöcker (ed.), Taschenbuch der Physik, 2nd edn., 1994, Verlag Harri Deutsch, Frankfurt, pp. 102-110).

[0320] To determine the modulus of elasticity of a film, the tensile strain characteristics were ascertained using a type 2 specimen (rectangular film test strip of length 150 mm and width 15 mm) according to DIN EN ISO 527-3:2003-07 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 using sharp blades. A Zwick tensile testing machine (model Z010) was employed. 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. The 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 behaviour in respect of Hooke's law, and was reported in GPa.

Surface Roughness R.SUB.a

[0321] The surface roughness R.sub.a was determined by laser triangulation.

[0322] The PRI MOS system used consists of an illumination unit and a recording unit. The illumination unit, with the aid of a digital micro-mirror projector, projects lines onto the surface. These projected parallel lines are diverted or modulated by the surface structure. The modulated lines are recorded using a CCD camera arranged at a defined angle, referred to as the triangulation angle.

[0323] Size of measuring field: 14.5×23.4 mm.sup.2

[0324] Profile length: 20.0 mm

[0325] Areal roughness: 1.0 mm from the edge (Xm=21.4 mm; Ym=12.5 mm)

[0326] Filtering: 3rd-order polynomial filter

[0327] The surface roughness R.sub.a represents the average height of the roughness, more particularly the average absolute distance from the centre line (regression line) of the roughness profile within the region under evaluation. Expressed alternatively, R.sub.a is the arithmetic mean roughness, i.e. the arithmetic mean value of all profile values of the roughness profile.

[0328] Corresponding instruments can be acquired from companies including GFMesstechnik GmbH of Teltow, Germany.

Shrinkage

[0329] To determine the shrinkage of a liner under the conditions prevailing during the foaming of a self-adhesive composition layer in accordance with the method of the invention, test strips of the liner are stored at the foaming temperature and for the foaming time used in the method. Specimens employed here are typically a swatch or roll specimen of the liner. Ater the removal of the first three turns, test strips in original width and with a length of 15 cm each are taken from the roll under test. The test strips are then accommodated in free suspension (holder: paperclip) in the preheated air-circulation cabinet, for the intended time (foaming time) at the specified testing temperature (foaming temperature) and, after this exposure, are cooled. Before and after storage, the dimensions of the strips in longitudinal and transverse directions are ascertained. To determine the dimensions, a steel rule (0.5 mm divisions) is used in each case. The shrinkage (in longitudinal and transverse directions) is calculated in % relative to the original dimensions of the test strips. The mean of the individual results from the measurement of three test strips is calculated, in both longitudinal and transverse directions.

Weight Loss

[0330] To determine the weight loss of a liner under the conditions of the kind prevailing during the foaming of a self-adhesive composition layer in accordance with the method of the invention, test strips of the liner are stored at the foaming temperature and for the foaming time employed in the method and are subsequently cooled. Before and after the storage, the weight of the test strip is ascertained. The weight loss in % is calculated by reference to the original weight. The mean value of the individual results from three measurements on different test strips is used.