DETACHABLE ADHESIVE STRIP

Abstract

The invention relates to an adhesive strip which can be detached substantially on the adhesion plane in a residue-free and nondestructive manner by stretching, said strip consisting of one or more adhesive material layers and optionally one or more intermediate carrier layers, at least one of the adhesive materials layers containing at least one filler, the primary particles of which can be individually separated, wherein the primary particles (i) are substantially spherical and (ii) have an average diameter d(0.5) of less than 10 μm, and the ratio of the average diameter d(0.5) of the primary particles to the thickness of the adhesive material layer in which the primary particles are contained is less than 1:2. The invention also relates to the production and use of said adhesive strip.

Claims

1. A pressure-sensitive adhesive strip (PSA strip) which is redetachable, without residue or destruction, by extensive stretching substantially in the bond plane, comprising one or more layers of pressure-sensitive adhesive (PSA layers) and optionally one or more intermediate carrier layers, where at least one of the PSA layers comprises at least one filler which can be separated into its primary particles, the primary particles (i) being spherical, and (ii) having a median diameter d(0.5) of less than 10 μm, and where the ratio of the median diameter d(0.5) of the primary particles to the thickness of the PSA layer containing the primary particles is less than 1:2.

2. The PSA strip as claimed in claim 1, wherein the primary particles have a median diameter d(0.5) of 10 μm.

3. The PSA strip as claimed in claim 1, wherein the primary particles have a median diameter d(0.5) of 100 nm to less than 10 μm.

4. The PSA strip as claimed in claim 1, wherein the ratio of the median diameter d(0.5) of the primary particles to the thickness of the PSA layer containing the primary particles is less than 1:5.

5. The PSA strip as claimed in claim 1, wherein the particles of the filler are inorganic particles.

6. The PSA strip as claimed in claim 1, wherein the filler is present in the PSA layer at up to 50 wt % basded on the total weight of the PSA layer.

7. The PSA strip as claimed in claim 1, wherein at least one PSA layer is based on vinyl aromatic block copolymer, where the vinyl aromatic block copolymer comprises (i) polymer blocks predominantly formed by polymerization of vinyl aromatics (A blocks), and at the same time (ii) polymer blocks predominantly formed by polymerization of conjugated dienes having 4 to 18 carbon atoms and/or isobutylene (B blocks), where the B blocks are optionally at least partly hydrogenated.

8. The PSA strip as claimed in claim 7, wherein the vinyl aromatic block copolymer of the PSA layer comprises triblock copolymer A-B-A and/or multiblock copolymer, and optionally, further, diblock copolymer A-B.

9. The PSA strip as claimed in claim 8, wherein the vinyl aromatic block copolymer consists to an extent of at least 90 wt % of diblock copolymer A-B and triblock copolymer A-B-A.

10. The PSA strip as claimed in claim 8, wherein the vinyl aromatic block copolymer comprises radial block copolymer (A-B)nX or (A-B-A)nX, in which in each case X is the radical of a coupling reagent or initiator and n is an integer ≥3, where the fraction of the radial block copolymer in relation to the total block copolymer content is more than 10 wt %.

11. The PSA strip as claimed in claim 8, wherein the fraction of diblock copolymer in relation to the total block copolymer content is 10 to 65 wt %.

12. The PSA strip as claimed in claim 1, wherein one or more layers are syntactic or nonsyntactic foams, where the layers optionally comprise hollow glass beads, hollow polymer beads, hollow ceramic beads, at least partially expanded microballoons, or a mixture thereof.

13. The PSA strip as claimed in claim 1, wherein one or more PSA layers, containing the filler which can be separated into its primary particles, comprise at least one further filler.

14. The PSA strip as claimed in claim 1, wherein the PSA strip consists of a single PSA layer.

15. The PSA strip as claimed in claim 1, wherein the PSA strip consists of at least two layers.

16. The PSA strip as claimed in claim 15, wherein at least one layer has/have a thickness of less than 50 μm, and optionally at least one further layer has a thickness of more than 30 μm.

17. The PSA strip as claimed in claim 1, wherein the PSA strip has a thickness of less than 3000 μm.

18. The PSA strip as claimed in claim 1, wherein the peel adhesion of the PSA strip on at least one side is less than 29 N/cm.

19. The PSA strip as claimed in claim 1, wherein the PSA strip is transparent.

20. A method for producing a PSA strip as claimed in claim 1, where the PSA strip is produced by means of a solvent-based coating method or hotmelt coating method.

21. Method of using at least one pressure-sensitive adhesive (PSA) which comprises at least one filler which can be separated into its primary particles, the primary particles (i) being spherical, and (ii) having a median diameter d(0.5) of less than 10 μm, in a pressure-sensitive adhesive strip (PSA strip) which is redetachable, without residue or destruction, by extensive stretching substantially in the bond plane, comprising one or more layers of pressure-sensitive adhesive (PSA layers) and optionally one or more intermediate carrier layers, where the ratio of the median diameter d(0.5) of the primary particles to the thickness of the PSA layer containing the primary particles is less than 1:2.

22. Method of using a PSA strip as claimed in claim 1 for bonding electronic components.

Description

EXAMPLES

[0151] Commercially available chemicals used (see table 1 below)

TABLE-US-00001 TABLE 1 Trade Chemical compound name Manufacturer CAS No. Radial styrene-butadiene block Kraton Kraton 9003-55-8 copolymer; with 16 wt % D1116 Polymers diblock; block polystyrene content: 23 wt % Linear Kraton Kraton 9003-55-8 styrene-butadiene-styrene D1118 Polymers triblock copolymer; with 78 wt % diblock; block polystyrene content: 33 wt % Linear Kraton Kraton 9003-55-8 styrene-butadiene-styrene D1152 Polymers triblock copolymer; with 15 wt % diblock; block polystyrene content: 29 wt % Solid α-pinene tackifier resin Piccolyte Pinova 31393-98-3 with a ring and ball A115 softening temperature of 112 to 118° C. and a DACP of 27° C. Liquid hydrocarbon resin Wingtack Cray Valley 26813-14-9 10 Pentaerythritol Irganox BASF SE 6683-19-8 tetrakis[3-(3,5-di-tert-butyl-4- 1010 hydroxyphenyl)propionate] Tris(2,4-di-tert-butylphenyl) Irgafos BASF SE 31570-04-4 phosphite 168 FF Microballoons (unexpanded Expancel Expancel microspheres) 920 DU Nobel 20 Industries Spherical amorphous silicon Sidistar Elkem 69012-64-2 dioxide (96-99% SiO.sub.2); BET T120U surface area 20 m.sup.2/g; median diameter d(0.5) = 150 nm SiLibeads glass beads, polished SiLiBeads Sigmund 65997-17-3 circular solid glass beads of soda- 0-20 μm Lindner lime glass; median diameter (Article GmbH, d(0.5) = 7 μm; bulk density number Germany 0.7 kg/dm.sup.3; sphericity >= 0.89 5209) (ratio of width to length) SiLibeads glass beads, polished SiLiBeads Sigmund 65997-17-3 circular solid glass beads of soda- 40-70 μm Lindner lime glass; bulk density (Article GmbH, 0.7 kg/dm.sup.3; sphericity >= 0.89 number Germany (ratio of width to length) 5211) SiLibeads glass beads, polished SiLiBeads Sigmund 65997-17-3 circular solid glass beads of soda- 90-150 μm Lindner lime glass; bulk density (Article GmbH, 0.7 kg/dm.sup.3; sphericity >= 0.89 number Germany (ratio of width to length) 5213) Spherical TiO.sub.2 particles, TiO.sub.2 Kronos Kronos 13463-67-7 content >= 90.5%, median 2360 diameter d(0.5) = 600 nm Hydrophilic fumed silica, specific Aerosil ® Aerosil ® 112945-52-5 surface area = 170 to 210 m.sup.2/g, 200 7631-86-9 SiO.sub.2 content (based on calcined substance) >= 99.8%, diameter (primary particles) by SEM (cryofracture edge) about 12 nm, diameter (secondary particles, i.e., aggregates, not separable into primary particles) by SEM (cryofracture edge) in the order of magnitude of 100 nm Fumed silica aftertreated with Aerosil ® Aerosil ® 199876-45-4 hexadecyl silane, specific surface R816 area = 200 m.sup.2/g, SiO.sub.2 content (based on calcined substance) >99.8%, diameter (primary particles) by SEM (cryofracture edge) about 12 nm, diameter (secondary particles, i.e., aggregates, not separable into primary particles) by SEM (cryofracture edge) in the order of magnitude of 100 nm Phyllosilicate, i.e., in layer form Garamite Byk 68953-58-2 rather than spherical 1958 Additives and Instruments

[0152] Test methods

[0153] Unless otherwise indicated, all measurements were conducted at 23° C. and 50% relative humidity. The mechanical and technical adhesive data were ascertained as follows:

[0154] Test Method 1: Glass transition temperature (T.sub.g)

[0155] Glass transition points—referred to synonymously as glass transition temperatures—are reported as the result of measurements by dynamic 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 (see DIN 53 765; section 7.1; note 1). The initial sample mass is 20 mg.

[0156] Test Method 2: median particle diameter d(0.5)

[0157] The median diameter d(0.5) of primary particles is determined by laser diffraction on a suspension of the particles in deionized water, on the basis of the distribution curve of proportional volume plotted over the particle size. If the primary particles in the suspension are not separate from the outset, they can be separated prior to the measurement by the action of shear on the suspension. Here, d(0.5) is defined as the particle size value for which the summated volume fractions reach 0.5, i.e., 50%. The median diameter d(0.5) is therefore a volume-averaged diameter. The median diameter is determined by laser diffraction with a darkening of 17±1%. Using the specified technique, the median diameter may be determined using commercially customary instruments intended for this purpose, for example using the “Mastersizer” line from Malvern (e.g., Mastersizer 2000, Mastersizer 3000).

[0158] Test Method 3: Thickness

[0159] The thickness of a layer or of a PSA strip may be ascertained using commercially customary thickness gauges (sensor test instruments) with accuracies of less than 1 μm deviation. If fluctuations of thickness are found, the average value of measurements at not less than three representative sites is reported—that is, in particular, not including measurement at wrinkles, creases, nibs and the like.

[0160] Test Method 4: Density

[0161] The density of layers is ascertained by forming the ratio of weight per unit area and thickness of the layer. The thickness of the layer is determined according to Test Method 3.

[0162] Test Method 5: Elongation at break, tensile strength and strain at 50% elongation

[0163] The elongation at break, the tensile strength and the strain at 50% elongation are measured in a method based on DIN 53504 using S3-size dumbbell specimens at a separation velocity of 300 mm per minute. The test conditions are 23° C. and 50% relative humidity.

[0164] Test Method 6: Resilience or elasticity

[0165] Resilience is measured by elongating the test specimen by 100%, holding it in this elongation for 30 s, and then releasing it. After a waiting time of 1 min, the length is measured again.

[0166] The resilience is then calculated as follows: RS=((L.sub.100-L.sub.end)/L.sub.0).Math.100, where RS=resilience in %

[0167] L.sub.100: length of adhesive strip after elongation by 100%

[0168] L.sub.0: length of adhesive strip before elongation

[0169] Lend: length of adhesive strip after relaxation for 1 min.

[0170] The resilience here corresponds to the elasticity.

[0171] Test Method 7: Solids content

[0172] The solids content is a measure of the fraction of non-vaporizable constituents in a PSA. It is determined gravimetrically, with the PSA being weighed, then the vaporizable fractions being evaporated off in a drying cabinet at 120° C. for two hours, and the residue being weighed again.

[0173] Test Method 8: Coat weight

[0174] The coat weight of a PSA layer in g/m.sup.2 can be determined by determining the mass of a section of such an adhesive layer applied to a carrier or liner, the section being of defined length and defined width, minus the (known or separately ascertainable) mass of a section of the carrier or liner used that has the same dimensions. Any solvents present are disregarded in this measurement.

[0175] Test Method 9: Tear susceptibility 100 strips 10 mm in width and 40 mm long are punched from the PSA strip under investigation. These strips are bonded over a length of 30 mm to a PC plate cleaned with ethanol, to form a finger tab 10 mm long. A second PC plate is bonded to the second side of the bonded strips, specifically in such a way that the two PC plates lie flush over one another. The assembly is rolled over ten times using a 4 kg roller (five times back and forward). After a peel adhesion time of 24 h, the 100 strips are stripped from the bond line manually, using the finger tab, at a peel angle of

[0176] a) about 45° with respect to the bond plane, or alternatively

[0177] b) about 90° with respect to the bond plane, or alternatively

[0178] c) about 0° with respect to the bond plane, i.e., substantially in the bond plane.

[0179] An assessment is made of how many of the 100 specimens tear on stripping at the selected angle, the result being reported in %.

[0180] Test Method 10: Tack (probe tack)

[0181] With the probe tack method, the bonding behavior of a double-sided adhesive tape, i.e., PSA strip, is characterized using a “Texture Analyser TA.XT2i” from Stable Micro Systems.

[0182] In the method, a probe with a cylindrical steel die is moved vertically onto the adhesive at a specified test velocity up to a defined pressing force, and, after a defined contact time, is removed again, the velocity likewise being specified. During this operation, the force applied for the pressing and the detachment, respectively, is recorded as a function of the travel distance. [0183] Instrument: [0184] Texture Analyser TA.XT2i from SMS (Stable Micro Systems Ltd.) or [0185] Texture Analyser TA.XT plus from SMS (Stable Micro Systems Ltd.) measuring head/force probe: 5 kg with measuring range: 0.001 to 50 N [0186] Tack die:

[0187] Standard: cylinder (stainless steel): 0 2 mm [0188] Test conditions:

[0189] Standard: 23±1° C./50±5% relative humidity

[0190] The sample for measurement is bonded to a steel plate without bubbles and in a defined manner, by rolling a 2 kg roller back and forward over it at 150 mm/s. The steel die is cleaned in acetone and conditioned at RT for 30 min. The release paper is not removed from the adhesive strip until immediately before the measurement.

[0191] The steel plate is screwed firmly in the sample bench and adjusted beneath the die.

[0192] The test parameters for selection are as follows: [0193] Tack die: cylinder (stainless steel): ∅2 mm [0194] Pre-test speed: 0.1 mm/s [0195] Test speed: 0.1 mm/s [0196] Trigger force: 0.05 N [0197] Post-test speed: 1.5 mm/s [0198] Contact time: 0.01 sec [0199] Pressing force: 1 N

[0200] Before each individual measurement, it is necessary to position the sample bench beneath the probe and secure it by screwing. The distance between the measurement locations is three times the diameter of the die.

[0201] 10 individual measurements are carried out on each sample in order to calculate the average. The die is generally not cleaned between individual measurements, unless there are deposits on the die, or the measurement series shows a significant trend. The measurements performed are averaged.

[0202] From the measurement curve (graph of the force [N] as a function of the travel distance [mm]), a determination is made of the maximum force: this figure is referred to as the probe tack.

[0203] Test Method 11: 180° peel adhesion test

[0204] The peel strength (peel adhesion) is tested in a method based on PSTC-1. A strip 1 cm wide of an adhesive tape consisting of (i) a PET film 23 μm thick and (ii) a PSA strip applied thereon in the form of a double-sided adhesive tape as described in the present specification is adhered on the test substrate in the form of an ASTM steel plate, the surface of the latter having been cleaned with acetone beforehand, by rolling over back and forth five times using a 4 kg roller. The plate is clamped in and the adhesive tape is peeled from the plate via its free end on a tensile test machine, with a velocity of 300 mm/min and at a peel angle of 180°, and the force needed to achieve this is ascertained. The results of the measurement are reported in N/cm (i.e., standardized to the width of the adhesive tape) and are averaged from three measurements.

[0205] Test Method 12: Transverse impact strength (DuPont test in the x,y plane)

[0206] A square sample in the shape of a frame was cut from the PSA strip under investigation (external dimensions 33 mm×33 mm; border width 2.0 mm; internal dimensions (window cutout) 29 mm×29 mm). This sample is adhered 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). On the other side of the PSA strip a PC window of 35 mm×35 mm is adhered. PC frame, adhesive tape frame and PC window are bonded such that the geometric centers and the diagonals each lay over one another (corner to corner). The bond area is 248 mm.sup.2. The bond is pressed at 248 N for 5 s and stored under conditions of 23° C./50% relative humidity for 24 hours.

[0207] Directly after storage, the bonded assembly consisting of PC frame, PSA strip and PC pane is clamped by the protruding edges of the PC frame into a sample holder in such a way that the assembly is aligned vertically. The sample holder is then inserted centrally into the designated holder of the DuPont Impact Tester. The impact head, weighing 150 g, is inserted in such a way that the rectangular impact geometry with dimensions of 20 mm×3 mm impacts centrally and flush on the upwardly directed end face of the PC window.

[0208] A weight having a mass of 150° g guided on two guide rods is dropped vertically from a height of 5 cm onto the assembly arranged in this way and composed of sample holder, sample and impact head (measuring conditions 23° C., 50% relative humidity).

[0209] The height of the dropped weight is increased in 5 cm steps until the impact energy introduced destroys the sample as a result of the transverse impact load, and the PC window parts from the PC frame.

[0210] In order to be able to compare experiments with different samples, the energy is calculated as follows:

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

[0211] Five samples per product are tested and the mean energy value is reported as the index of the transverse impact strength.

[0212] Test Method 13: Penetrative impact strength (DuPont test in the z plane)

[0213] A square sample in the shape of a frame was cut from the PSA strip under investigation (external dimensions 33 mm×33 mm; border width 2.0 mm; internal dimensions (window cutout) 29 mm×29 mm). This sample is adhered to a polycarbonate (PC) frame (external dimensions 45 mm×45 mm; border width 10 mm; internal dimensions (window cutout) 25° mm×25 mm; thickness 3 mm). On the other side of the PSA strip a PC window of 35 mm×35 mm is adhered. PC frame, adhesive tape frame and PC window are bonded such that the geometric centers and the diagonals each lay over one another (corner to corner). The bond area is 248 mm.sup.2. The bond is pressed at 248 N for 5 s and stored under conditions of 23° C./50% relative humidity for 24 hours.

[0214] Directly after storage, the bonded assembly consisting of PC frame, PSA strip and PC pane is clamped by the protruding edges of the PC frame into a sample holder in such a way that the assembly is aligned horizontally. The PC frame here lies flat at the protruding edges on the sample holder, so that the PC window is in free suspension (held by the adhesive tape specimen) below the PC frame. The sample holder is then inserted centrally into the designated holder of the DuPont Impact Tester. The impact head, weighing 150 g, is inserted in such a way that the circular impact geometry with a diameter of 24 mm impacts centrally and flush on the face of the PC window that is freely accessible from above.

[0215] A weight having a mass of 150 g guided on two guide rods is dropped vertically from a height of 5 cm onto the assembly arranged in this way and composed of sample holder, sample and impact head (measuring conditions 23° C., 50% relative humidity).

[0216] The height of the dropped weight is increased in 5 cm steps until the impact energy introduced destroys the sample as a result of the penetrative impact load, and the PC window parts from the PC frame.

[0217] In order to be able to compare experiments with different samples, the energy is calculated as follows:

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

[0218] Five samples per product are tested and the mean energy value is reported as the index of the penetrative impact strength.

[0219] Test Method 14: Surface roughness R.sub.a

[0220] The surface roughness R.sub.a is determined by laser triangulations. The PRIMOS system used consists of an illumination unit and a recording unit. The illumination unit projects lines onto the surface with the aid of a digital micro-mirror projector. These projected parallel lines are deflected or modulated by the surface structure. For the registration of the modulated lines, a CCD camera arranged at a particular angle, called the triangulation angle, is used.

[0221] Measurement field size: 14.5×23.4 mm.sup.2

[0222] Profile length: 20.0 mm

[0223] 30 area roughness: 1.0 mm away from the edge (Xm=21.4 mm; Ym=12.5 mm)

[0224] Filtering: 3.sup.rd order polynomial filter

[0225] The surface roughness R.sub.a represents the average height of the roughness, more particularly the average absolute distance from the center line (regression line) of the roughness profile within the evaluation range. In other words, R.sub.a is the arithmetic mean roughness, i.e., the arithmetic mean value of all profile values in the roughness profile.

[0226] Corresponding measuring instruments can be acquired from sources including GFMesstechnik GmbH in Teltow.

[0227] Test Method 15: Transmission

[0228] For sample preparation, the specimen under investigation, such as more particularly the PSA strip or PSA layer, is applied without bubbles to a polycarbonate film (125 μm Lexan 8010 with freshly exposed surfaces). The transmission of the specimen is determined by way of the VIS spectrum. The VIS spectrum is recorded on a UVIKON 923 from Kontron. The wavelength range of the measured spectrum embraces all wavelengths between 800 nm and 400 nm with a resolution of 1 nm. A blank channel measurement is carried out as a reference over the entire wavelength range. For the reporting of the result, the transmission measurements are averaged within the stated range. There is no correction for interfacial reflection losses.

[0229] Production of the PSA strips [0230] (a) Examples 1 to 7: single-layer PSA strips based on vinyl aromatic block copolymer (formulation 1), produced by the hotmelt process

[0231] In the noninventive example 5, 380 g of Kraton D1152, 120 g of Kraton D1118, 460 g of Piccolyte A 115, 30 g of Wingtack 10, 5.0 g of Irgafos 168 FF, 5.0 g of Irganox 1010 (formulation 1) were mixed using a hotmelt compounder at 170° C. for two hours to form a homogeneous composition, which was pressed out using a press between two PET liners 75 μm thick to a layer thickness of 150 μm, thus producing a single-layer transparent PSA strip without filler.

[0232] Inventive examples 1 to 4 differ from example 5 only in that different amounts of Sidistar T120U were added additionally to the components stated in example 5. Accordingly 2.5 wt % (example 1), 5 wt % (example 2), 7.5 wt % (example 3) and 10 wt % (example 4) of Sidistar T120U were added, with the weight fractions of Sidistar T120U here being based in each case on the total weight of the other components (i.e., the weight of the other components is set at 100%). The result in each case is a single-layer transparent PSA strip comprising filler according to the invention.

[0233] Noninventive examples 6 and 7 differ from example 5 only in that 5 wt % of Garamite 1958 (example 6) or 7.5 wt % of Aerosil® 200 were added additionally to the components stated in example 5, with the weight fractions of Garamite 1958 or Aerosil® 200 being based here in each case on the total weight of the other components (i.e., the weight of the other components is set at 100%). The result in each case is a single-layer transparent PSA strip comprising noninventive filler. [0234] (b) Examples 8-10 and 24 to 27: single-layer PSA strips based on vinyl aromatic block copolymer (formulation 3), produced by the hotmelt process

[0235] In the inventive example 9, 380 g of Kraton D1152, 120 g of Kraton D1118, 460.0 g of Piccolyte A 115, 30 g of Wingtack 10, 30.0 g of Kronos 2360, 5 g of Irgafos 1010, 5.0 g of Irgafos 168 FF (formulation 3) were mixed using a hotmelt compounder at 170° C. for two hours to form a homogeneous composition, which was pressed out using a press between two PET liners 75 μm thick to a layer thickness of 150 μm, thus producing a white single-layer PSA strip, which comprises filler according to the invention.

[0236] For comparison, examples 8 and 10 were conducted. Inventive example 8 differs from example 9 only in that rather than 30.0 g of Kronos 2360, the same amount (30 g) of Sidistar T120U was added. The end product was therefore a transparent single-layer PSA strip likewise comprising filler according to the invention. Noninventive example 10 differs from example 9 only in that 30.0 g of Kronos 2360 were omitted, i.e., no filler was used. The end product was therefore a transparent single-layer PSA strip containing no filler.

[0237] Inventive example 24 differs from example 9 only in that additionally 5 wt % of Sidistar T120U were added, with the weight fraction of Sidistar T120U being based on the total weight of the other components (i.e., the weight of the other components is set at 100%). The end product is therefore a white single-layer PSA strip likewise comprising filler according to the invention. Examples 25 (inventive) and 26 to 27 (noninventive) differ from example 9 only in that additionally 5 wt % of SiLibeads, 0-20 μm (example 25), 5 wt % of SiLibeads, 40-70 μm (example 26) or 5 wt % of SiLibeads, 90-150 μm (example 27) were added, with the weight fraction of the SiLibeads being based in each case on the total weight of the other components (i.e., the weight of the other components is set at 100%). The result in each case is a white single-layer PSA strip comprising filler. [0238] (c) Examples 11 to 17: single-layer PSA strips based on vinyl aromatic block copolymer (formulation 2), produced by the solvent process

[0239] In noninventive example 14 first a 40 to 55 wt % strength adhesive solution in a solvent mixture of benzine/toluene/acetone (in which the solvents were used in the stated sequence in a weight ratio of 69 : 20 : 11) was produced from 380 g of Kraton D1152, 120 g of Kraton D1118, 460 g of Piccolyte A 115, 30 g of Wingtack 10, 5.0 g of Irgafos 168 FF and 5.0 g of Irganox 1010 (formulation 2). The adhesive solution obtained was then coated out in the desired layer thickness, using a coating bar, onto a PET liner furnished with a silicone release, after which the solvent was removed by evaporation at 100° C. for 15 min to dry the layer of composition. This produced a transparent PSA layer containing no filler. The coat weight was selected such that the PSA layer had a thickness of 75 μm. Then two such PSA layers were laminated one atop the other to produce a transparent single-layer PSA strip having a thickness of 150 μm and containing no filler.

[0240] Inventive examples 11 to 13 differ from example 14 only in that different amounts of Sidistar T120U were added additionally to the components stated in example 14. Accordingly 2.5 wt % (example 11), 5 wt % (example 12) or 7.5 wt % (example 13) of Sidistar T120U were added, with the weight fractions of Sidistar T120U here being based in each case on the total weight of the other components (without taking account of the solvent mixture, i.e., the dry weight of the other components is set at 100%). The result in each case is a transparent single-layer PSA strip having a thickness of 150 μm and comprising filler according to the invention.

[0241] Noninventive examples 15 to 17 differ from example 14 only in that different amounts of Aerosil® R816 were added additionally to the components stated in example 14. Accordingly 2.5 wt % (example 15), 5 wt % (example 16) or 7.5 wt % (example 17) of Aerosil® R816 were added, with the weight fractions of Aerosil® R816 here being based in each case on the total weight of the other components (without taking account of the solvent mixture, i.e., the dry weight of the other components is set at 100%). The result in each case is a transparent single-layer PSA strip having a thickness of 150 μm and comprising noninventive filler. [0242] (d) Examples 18 to 23: three-layer PSA strips based on vinyl aromatic block copolymer

[0243] In noninventive example 20, 500.0 g of Kraton D1152, 485.0 g of Piccolyte A 115, 5.0 g of Irganox 1010 and 5.0 g of Irgafos 168 FF (formulation 4) were mixed to form a homogeneous composition using a hotmelt compounder at 170° C. for two hours and the mixture was pressed out using a press to a layer thickness of 100 μm between two PET liners 75 μm thick, to produce a transparent PSA layer containing no filler.

[0244] Furthermore, a 36 wt % strength adhesive solution in a solvent mixture of benzine/toluene/acetone (in which the solvents were used in the stated sequence in a weight ratio of 65 : 25 : 10) was produced from 200 g of Kraton D1116, 300 g of Kraton D1118, 490 g of Piccolyte A 115, 5 g of Irgafos 168 FF and 5 g of Irganox 1010 (formulation 6). The adhesive solution obtained was subsequently admixed with 15 g of unexpanded Expancel 920 DU20 microballoons, the microballoons being used in the form of a slurry in acetone. The mixture obtained was then coated out using a coating bar at a coat weight of 17 g/m.sup.2 (solvents disregarded), onto a PET liner furnished with a silicone release, after which the solvent was removed by evaporation at 100° C. for 15 min to dry the layer of composition. The product was a PSA layer which comprises unexpanded microballoons.

[0245] The above-described transparent PSA layer containing no filler was laminated onto the free surface of the PSA layer thus produced, containing unexpanded microballoons. Atop the second surface of the transparent PSA layer, the free surface of a second PSA layer containing unexpanded microballoons, produced as described above, was laminated, resulting in an unfoamed symmetrical three-layer assembly composed of the inner transparent PSA layer containing no filler, and of two PSA layers provided with liners and containing unexpanded microballoons.

[0246] After drying, the three-layer construction was foamed in an oven at 170° C. for 30 s between the two liners, resulting in outer PSA layers having thicknesses each of about 25 μm. As a result of the foaming between two liners, products having particularly smooth surfaces are obtainable (surface roughness R.sub.a less than 15 μm).

[0247] Inventive examples 18 and 19 differ from example 20 only in that, in the production of the transparent PSA layer, different amounts of Sidistar T120U were added additionally to the stated components. Hence 2.5 wt % (example 18) or 5 wt % (example 19) of Sidistar T120U were added, with the weight fractions of Sidistar T120U here being based in each case on the total weight of the other components (i.e., the weight of the other components is set at 100%). The product in each case is a three-layer PSA strip whose inner PSA layer comprises filler according to the invention and whose outer PSA layers are foamed.

[0248] In noninventive example 23, 380 g of Kraton D1152, 120 g of Kraton D1118, 460 g of Piccolyte A 115, 30 g of Wingtack 10, 5.0 g of Irgafos 168 FF and 5.0 g of Irganox 1010 (formulation 1) were mixed to form a homogeneous composition using a hotmelt compounder at 170° C. for two hours and the mixture was pressed out using a press to a layer thickness of 100 μm between two PET liners 75 μm thick, to produce a transparent PSA layer containing no filler.

[0249] Furthermore, a 36 wt % strength adhesive solution in a solvent mixture of benzine/toluene/acetone (in which the solvents were used in the stated sequence in a weight ratio of 65 : 25 : 10) was produced from 200 g of Kraton D1116, 300 g of Kraton D1118, 490 g of Piccolyte A 115, 5 g of Irgafos 168 FF and 5 g of Irganox 1010 (formulation 6). The adhesive solution obtained was subsequently admixed with 15 g of unexpanded Expancel 920 DU20 microballoons, the microballoons being used in the form of a slurry in acetone. The mixture obtained was then coated out using a coating bar at a coat weight of 17 g/m.sup.2 (solvents disregarded), onto a PET liner furnished with a silicone release, after which the solvent was removed by evaporation at 100° C. for 15 min to dry the layer of composition. The product was a PSA layer which comprises unexpanded microballoons.

[0250] The above-described transparent PSA layer containing no filler was laminated onto the free surface of the PSA layer thus produced, containing unexpanded microballoons. Atop the second surface of the transparent PSA layer, the free surface of a second PSA layer containing unexpanded microballoons, produced as described above, was laminated, resulting in an unfoamed symmetrical three-layer assembly composed of the inner transparent PSA layer containing no filler, and of two PSA layers provided with liners and containing unexpanded microballoons.

[0251] After drying, the three-layer construction was foamed in an oven at 170° C. for 30 s between the two liners, resulting in outer PSA layers having thicknesses each of about 25 μm. As a result of the foaming between two liners, products having particularly smooth surfaces are obtainable (surface roughness Ra less than 15 μm).

[0252] Inventive examples 21 and 22 differ from example 23 only in that, in the production of the transparent PSA layer, different amounts of Sidistar T120U were added additionally to the stated components. Hence 2.5 wt % (example 21) or 5 wt % (example 22) of Sidistar T120U were added, with the weight fractions of Sidistar T120U here being based in each case on the total weight of the other components (i.e., the weight of the other components is set at 100%). The product in each case is a three-layer PSA strip whose inner PSA layer comprises filler according to the invention and whose outer PSA layers are foamed.

[0253] Experimental Results

[0254] The PSA strips referred to as inventive can be redetached, without residue or destruction, by extensive stretching substantially in the bond plane, i.e., at a peel angle of about 0° .

[0255] Table 2 shows mechanical and technical adhesive properties of the single-layer PSA strips based on vinyl aromatic block copolymer (formulation 1), produced by the hotmelt process.

TABLE-US-00002 TABLE 2 Tearing Tearing Peel susceptibility susceptibility Tack adhesion DuPont DuPont Example (45°) [%] (90°) [%] [N] [N/cm] x, y [J] z [J] 1 25 79 3.7 17.3 0.9 0.5 2 13 54 3.4 16.6 0.9 0.5 3 8 29 3.9 16.7 0.9 0.6 4 0 13 4.2 17.0 0.9 0.6 5 79 98 3.7 16.4 1.0 0.6 6 33 25 1.1 11.4 0.7 0.2 7 96 100 2.6 14.2

[0256] A comparison of examples 1 to 4 with example 5 shows that the inventive spherical filler particles of Sidistar T120U significantly reduce the tearing susceptibility of the PSA strip, at peel angles both of 45° and of 90° . Moreover, there is no substantial adverse effect on the technical adhesive properties such as the tack and the peel adhesion. The same is true of the shock resistance. Examples 1 to 4 also show that the tearing susceptibility can be adjusted via the filler content as well.

[0257] Example 6 also shows that the Garamite 1959 phyllosilicate which accordingly is not spherical does lower the tearing susceptibility, but leads to unacceptable technical adhesive properties (tack, peel adhesion) for the PSA strip.

[0258] Example 7 shows that Aerosil® 200, and hence a filler not separable into its primary particles, has the effect in particular that the PSA strip becomes brittle. The tearing susceptibility is in fact higher than without filler. Moreover, a significant deterioration in tack and peel adhesion is apparent. Because of these inadequate values, the specimens were not investigated further (shock resistance).

[0259] (b) Tables 3a and 3b show mechanical and technical adhesive properties of the single-layer PSA strips based on vinyl aromatic block copolymer (formulation 3), produced by the hotmelt process.

TABLE-US-00003 TABLE 3a Tearing susceptibility Tearing susceptibility Example (45°) [%] (90°) [%] 8 17 67 9 49 100 10 78 100

[0260] A comparison of example 9 with example 10 shows that with different spherical filler particles as well, such as the Kronos 2360 titanium dioxide, for example, the tearing susceptibility can be reduced. A comparison of example 9 with example 8 also shows that replacing the Kronos 2360 titanium dioxide with the same amount of Sidistar T120U again produces a substantial reduction in the tearing susceptibility.

TABLE-US-00004 TABLE 3b Tearing Tearing Peel susceptibility susceptibility Tack adhesion DuPont DuPont Example (45°) [%] (90°) [%] [N] [N/cm] x, y [J] z [J] 24 8 17 4.0 12.2 0.9 0.5 25 9 25 3.9 11.8 0.9 0.5 26 22 67 3.9 11.0 0.9 0.4 27 44 89 3.6 11.0 0.8 0.3 9 52 100 4.0 13.6 0.9 0.5

[0261] The influence of filler particle size on tearing susceptibility is made clear by examples 24 to 27. It is apparent therefrom that for a given filler fraction, smaller particles are evidently able to lower the tearing susceptibility to a much greater extent than comparatively large particles. Smaller particles also influence the adhesive properties such as peel adhesion and tack, and also the shock resistance, to less of an extent than comparatively large particles.

[0262] (c) Tables 4a and 4b show mechanical and technical adhesive properties of the single-layer PSA strips based on vinyl aromatic block copolymer (formulation 2), produced by the solvent process.

TABLE-US-00005 TABLE 4a Tearing Tearing Peel susceptibility susceptibility Tack adhesion DuPont DuPont Example (45°) [%] (90°) [%] [N] [N/cm] x, y [J] z [J] 11 4 13 4.1 15.0 1.0 0.5 12 0 8 3.6 15.5 0.9 0.5 13 0 0 3.3 14.9 0.8 0.5 14 45 85 3.9 14.8 1.0 0.5

[0263] Examples 11 to 14 show that by the solvent process as well it is possible to produce PSA strips comprising spherical filler particles (Sidistar T120U) which by comparison with the filler-free PSA strip exhibit substantially reduced tearing susceptibility (at peel angles both of 45° and of)90° . Moreover, there is no substantial deterioration in the technical adhesive properties such as the tack and the peel adhesion as a result of the particles. The same is true of the shock resistance.

TABLE-US-00006 TABLE 4b Tearing Tearing Peel susceptibility susceptibility adhesion Example (45°) [%] (90°) [%] Tack [N] [N/cm] 14 45 85 3.9 14.8 15 50 88 3.7 13.8 16 46 88 3.1 12.5 17 51 81 2.9 10.4

[0264] Examples 14 to 17 show that there is no improvement in tearing susceptibility from using the hydrophobic Aerosil® R816 in different amounts, relative to the filler-free PSA strip. Moreover, a deterioration in tack and peel adhesion is apparent. On the basis of these inadequate values, no further investigation of the specimens (shock resistance) took place.

[0265] (d) Tables 5a and 5b show mechanical and technical adhesive properties of the three-layer PSA strips based on vinyl aromatic block copolymer.

TABLE-US-00007 TABLE 5a Tearing Tearing Peel susceptibility susceptibility Tack adhesion DuPont DuPont Example (45°) [%] (90°) [%] [N] [N/cm] x, y [J] z [J] 18 13 18 3.7 11.8 0.9 0.7 19 10 14 3.8 11.8 1.0 0.7 20 31 47 3.7 12.2 1.0 0.7

TABLE-US-00008 TABLE 5b Tearing Tearing Peel susceptibility susceptibility Tack adhesion DuPont DuPont Example (45°) [%] (90°) [%] [N] [N/cm] x, y [J] z [J] 21 25 74 3.9 12.1 1.1 0.8 22 21 30 3.6 12.0 1.1 0.8 23 50 88 3.7 11.8 0.9 0.7

[0266] Examples 18 to 23 show that in multilayer PSA strips as well, such as a three-layer construction, the tearing susceptibility can be significantly reduced by the incorporation of a filler according to the invention (in the present case: Sidistar T120U) into at least one layer, with the filler not leading to reduced tack, reduced peel adhesion or reduced shock resistance. In the three-layer construction as well it is possible to adjust the tearing susceptibility through the amount of filler.

[0267] Furthermore, a comparison of examples 18 to 20, whose inner layer has a comparatively low diblock fraction in the vinyl aromatic block copolymer, with examples 21 to 23, shows that a reduction in the diblock fraction in the vinyl aromatic block copolymer can bring about a lowering of the tearing susceptibility. It is presumed that in examples 18 to 20 the tearing susceptibility is also influenced positively because the inner layer (and the outer layers) in examples 18 to 20 contains no liquid resin.

[0268] A comparison of example 23, whose outer PSA layers comprise radial vinyl aromatic block copolymer in the form of Kraton D1116, with example 5 also shows that in a PSA strip based on vinyl aromatic block copolymer, the tearing susceptibility can be reduced by at any rate proportional use of radial vinyl aromatic block copolymer.

[0269] Furthermore, examples 18 to 23 show that the shock resistance of PSA strips of the invention can be increased by means of foaming, using expanded microballoons, for example.