CROSS-LINKABLE ADHESIVE COMPOUND

Abstract

Pressure sensitive adhesive (PSA) compositions and methods are provided and may comprise a) at least one crosslinkable polymer constructed at least of (i) at least two monomers selected from monomer A, monomer B, and monomer C, wherein each monomer, independently of one another, comprises an olefinically unsaturated aliphatic or cycloaliphatic hydrocarbon, and (ii) at least one comonomer D comprising an olefinically unsaturated monomer having at least one carboxylic acid group and/or carboxylic anhydride group. The PSA compositions and methods may also comprise b) at least one organosilane and c) at least one tackifier resin.

Claims

1. A pressure sensitive adhesive composition comprising: a) at least one crosslinkable polymer constructed at least of (i) at least two monomers selected from monomer A, monomer B, and monomer C, wherein each monomer, independently of one another, comprises an olefinically unsaturated aliphatic or cycloaliphatic hydrocarbon, and (ii) at least one comonomer D comprising an olefinically unsaturated monomer having at least one carboxylic acid group and/or carboxylic anhydride group; b) at least one organosilane conforming to the formula (1)
R.sup.1Si(OR.sup.2).sub.nR.sup.3.sub.m(1), wherein R.sup.1 is a radical able to enter into a chemical bond with a carboxylic acid group or with a carboxylic anhydride group, the radicals R.sup.2 independently of one another are each a hydrogen, an alkyl, a cycloalkyl, an aryl or an acyl radical, R.sup.3 is a hydrogen, an alkyl, a cycloalkyl or an aryl radical, n is 2 or 3, and m is the number resulting from 3-n; and c) at least one tackifier resin.

2. The pressure sensitive adhesive composition of claim 1, wherein the at least two monomers are -olefins having 2 to 8 carbon atoms selected from ethylene, propylene, 1-hexene, 1-octene, 5 ethylidene-2-norbornene, dicyclopentadiene, and 5-vinyl-2-norbornene.

3. The pressure sensitive adhesive composition of claim 2, wherein the monomer A is ethylene, the monomer B is propylene, and the monomer C, if present, is a diene selected from 5-ethylidene-2-norbornene, dicyclopentadiene, and 5-vinyl-2-norbornene.

4. The pressure sensitive adhesive composition of claim 3, wherein the diene is 5-ethylidene-2-norbornene.

5. The pressure sensitive adhesive composition of claim 1, wherein the comonomer D is acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, fumaric anhydride, methylmaleic acid, methylfumaric acid, itaconic acid, crotonic acid, crotonic anhydride, 4-methylcyclohex-4-ene-1,2-dicarboxylic anhydride, bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride, bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, bicyclo[2.2.2]oct-5-ene-2,3-dicarboxylic acid, bicyclo[2.2.2]oct-5-ene-2,3-dicarboxylic anhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic anhydride, 5-norbornene-2,3-dicarboxylic acid, norborn-5-ene-2,3-dicarboxylic anhydride, tetrahydrophthalic acid, and tetrahydrophthalic anhydride.

6. The pressure sensitive adhesive composition of claim 1, wherein the crosslinkable polymer is obtainable by copolymerization at least of the at least two monomers to give a polymer, and grafting of the comonomer D onto the polymer.

7. The pressure sensitive adhesive composition of claim 1, wherein the crosslinkable polymer is obtainable by copolymerization at least of the at least two monomers with the comonomer D.

8. The pressure sensitive adhesive composition of claim 1, wherein the crosslinkable polymer has a Mooney viscosity (ML 1+4/125 C.), measured according to DIN 53523, of more than 25.

9. The pressure sensitive adhesive composition of claim 1, wherein the radicals R.sup.2 of the organosilane of the formula (1) independently of one another are each an alkyl group or acetyl group.

10. The pressure sensitive adhesive composition of claim 1, wherein the radical R.sup.3 of the organosilane of formula (1), if present, is an alkyl group selected from a methyl group, an ethyl group, a propyl group, and an isopropyl group.

11. The pressure sensitive adhesive composition of claim 1, wherein the radical R.sup.1 of the organosilane of the formula (1) is at least one hydroxyl group, at least one thio group, at least one amino group NHR.sup.4, wherein R.sup.4 is a hydrogen, alkyl, cycloalkyl or aryl radical, or a mixture thereof, and, if R.sup.4 is an alkyl or cycloalkyl radical, this radical optionally comprises at least one further amino group NHR.sup.4, at least one hydroxyl group, at least one thio group, or a mixture thereof.

12. The pressure sensitive adhesive composition of claim 11, wherein the radical R.sup.1 comprises at least one amino group NHR.sup.4.

13. The pressure sensitive adhesive composition of claim 12, wherein the radical R.sup.1 is an X(CH.sub.2)(CH.sub.2).sub.p radical where X is a hydroxyl group, a thio group or an amino group NHR.sup.4, wherein R.sup.4 is a hydrogen, alkyl, cycloalkyl or aryl radical, and p is an integer from 0 to 10, and, if R.sup.4 is an alkyl or cycloalkyl radical, this radical optionally comprises at least one further amino group NHR.sup.4, at least one hydroxyl group, at least one thio group, or a mixture thereof.

14. The pressure sensitive adhesive composition of claim 13, wherein the organosilane of the formula (1) is N-cyclohexyl-3-aminopropyltrimethoxysilane, N-cyclohexylaminomethyl-triethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-(2-aminomethylamino)propyltriethoxysilane, or a mixture thereof.

15. The pressure sensitive adhesive composition of claim 11, wherein the radical R.sup.1 of the organosilane of the formula (1) is a radical comprising at least one cyclic ether function.

16. The pressure sensitive adhesive composition of claim 15, wherein R.sup.1 comprises at least one epoxide group, at least one oxetane group, or a mixture thereof.

17. The pressure sensitive adhesive composition of claim 16, wherein R.sup.1 comprises at least one glycidyloxy group, at least one epoxycyclohexyl group, at least one epoxyhexyl group, at least one oxetanylmethoxy group, or a mixture thereof.

18. The pressure sensitive adhesive composition of claim 17, wherein R.sup.1 is a Y(CH.sub.2)(CH.sub.2).sub.q radical, where Y is a group as defined in claim 17 and q is an integer from 0 to 10.

19. The composition of claim 17, wherein the organosilane of the formula (1) is (3-glycidyloxy-propyl)trimethoxysilane, (3-glycidyloxypropyl)triethoxysilane, (3-glycidyloxypropyl)methyldimethoxysilane, (3-glycidoxypropyl)-methyldiethoxysilane, 5,6-epoxyhexyltriethoxysilane, [2-(3,4-epoxycyclo-hexyl)ethyl]trimethoxysilane, [2-(3,4-epoxycyclohexyl)ethyl]triethoxysilane, triethoxy[3-[(3-ethyl-3-oxetanyl)methoxy]propyl]silane, or a mixture thereof.

20. The pressure sensitive adhesive composition of claim 15, wherein the pressure sensitive adhesive composition comprises the one organosilane and the at least one organosilane.

21. The pressure sensitive adhesive composition of claim 1, further comprising: at least one additional polymer constructed of ethylene, propylene and optionally a diene, where the diene, if present, is 5-ethylidene-2-norbornene, dicyclopentadiene, or 5-vinyl-2-norbornene.

22. The pressure sensitive adhesive composition of claim 21, wherein the at least one additional polymer is solid or liquid, possessing a Mooney viscosity (ML 1+4/125 C.), measured according to DIN 53523, of less than 25.

23. A method comprising: thermal crosslinking the pressure sensitive adhesive composition of claim 1 to obtain a crosslinked pressure sensitive adhesive composition.

24. A method for producing an adhesive tape, the method comprising: coating a carrier with the pressure sensitive adhesive composition of claim 1; and thermally crosslinking the pressure sensitive adhesive composition to give a layer of a crosslinked pressure sensitive adhesive.

25. An adhesive tape comprising: at least one layer of the crosslinked pressure sensitive adhesive obtained by the method of claim 23.

Description

[0102] Shown by way of example in FIG. 1 of the present specification is the compounding and coating operation, on the basis of a continuous process. The polymers and tackifier resins are introduced at the first feed point 1.1 into the compounder 1.3, here for example an extruder. Either the introduction takes place already in the melt, or the polymers and tackifier resins are heated in the compounder until the melt state is reached.

[0103] Shortly before coating takes place, the organosilanes conforming to the formula (1) and, if intended, the accelerators are added at a second feed point 1.2. The success of this is that the crosslinkers and optionally accelerators are added to the polymers not until shortly before coating, and the reaction time in the melt is low.

[0104] The reaction regime may also be discontinuous. In corresponding compounders such as reactor tanks, for example, the addition of the polymers, the tackifier resins, the crosslinkers and optionally the accelerators may take place at different times and not, as shown in FIG. 1, at different locations.

[0105] The composition can then be coated using a roll applicatorrepresented in FIG. 1 by the doctor roll 2 and the coating roll 3onto a liner or other suitable carrier. The rolls used preferably independently of one another have a temperature of 100 to 150 C., and more preferably of 110 C. to 140 C. For example, the doctor roll may have a temperature of 140 C. and the coating roll a temperature of 120 C. Directly after coating application the crosslinkable polymer is only slightly crosslinked, but not yet sufficiently crosslinked. The crosslinking reaction proceeds advantageously on the carrier.

[0106] After the coating operation, the PSA cools down relatively rapidly, in fact to the storage temperature, in general to room temperature. The crosslinker or crosslinker-accelerator system of the invention is preferably suitable for allowing the crosslinking reaction to continue without the supply of further thermal energy (without heat supply).

[0107] The crosslinking reaction between the carboxylic acid or carboxylic anhydride groups of the crosslinkable polymer and the radicals R.sup.1 of the crosslinker and also between the hydrolyzable silyl groups of the crosslinker preferably proceeds completely even without heat supply under standard conditions (room temperature). Since the crosslinking occurs only when both of the above-described reactions take place, it may be of advantage for one of the two reactions to proceed at a rate such that it takes place partially or completely in the compounder itself. Generally speaking, after a storage time of no more than 5 to 14 days, crosslinking is concluded to a sufficient extent for there to be a functional product present, more particularly an adhesive tape or a functional carrier layer on the basis of the polymer. The ultimate state and thus the final cohesion of the polymer are attained, depending on the choice of polymer and of crosslinker or crosslinker-accelerator system, after a storage time of in particular 5 to 14 days, advantageously after 5 to 10 days' storage time at room temperature, andas to be expectedearlier at a higher storage temperature.

[0108] Alternatively the PSA of the invention can be provided and processedfor example, coated onto a carrierin the form of a solution, preferably having a solids content of 25 to 40 wt %, more preferably having a solids content of 30 to 35 wt %, such as of 32 wt %, for example, after which the solvent is evaporated off at an elevated temperature of preferably 100 to 150 C., such as 120 C. for example, and the PSA is crosslinked. The solution in question is preferably a solution in a mixture of benzine and isopropanol, the benzine used being especially benzine 60-95. The carrier may be a permanent or temporary carrier. At the elevated temperature of preferably 100 to 150 C., such as 120 C., for example, the crosslinking reaction proceeds preferably until the final degree of crosslinking is reached. For this purpose the PSA is subjected to the stated temperature typically over a period of 5 to 15 min, more particularly of 10 min. Alternatively the PSA, even before reaching the final degree of crosslinking, may be cooled, for example, to room temperature, and then crosslinks further until the final degree of crosslinking is reached, over a period of 5 to 14 days, for example.

[0109] Crosslinking raises the cohesion of the polymer and hence also the shear strength (under hot conditions as well). The connections are very stable. This enables very aging-stable and heat-resistant products such as adhesive tapes in particular.

[0110] The physical properties of the end product, especially its viscosity, peel adhesion and tack, can be influenced through the degree of crosslinking, and so the end product can be optimized through an appropriate choice of the reaction conditions. A variety of factors determine the operational window of the process. The most important influencing variables are the amounts (concentrations and proportions relative to one another) and the chemical natures of the crosslinkers and optionally of the accelerators, the operating temperature and coating temperature, the residence time in the compounder (especially extruder) and in the coating assembly, the fraction of functional groups, i.e., of carboxylic acid or carboxylic anhydride groups, in the crosslinkable polymer, and the average molecular weight of the crosslinkable polymer.

[0111] Described below are a number of associations related to the production of the inventively crosslinked PSA, which more closely characterize the production process.

[0112] For the dependency of the crosslinking time on the accelerator concentration at constant temperature it is found that the ultimate value of the degree of crosslinking remains virtually constant; at high accelerator concentrations, however, this value is achieved more quickly than at low accelerator concentrations.

[0113] In addition, the reactivity of the crosslinking reaction can also be influenced by varying the temperature, if desired, especially if the advantage of inherent crosslinking in the course of storage under standard conditions has no part to play. At constant crosslinker and optionally accelerator concentration, an increase in the operating temperature leads to a reduced viscosity, which enhances the coatability of the composition but reduces the working time.

[0114] An increase in the working time is acquired by a reduction in the accelerator concentration, reduction in polymer molecular weight, reduction in the concentration of functional groups (i.e., carboxylic acid/anhydride groups) in the polymer, use of less-reactive crosslinkers or of less-reactive crosslinker-accelerator systems, and/or reduction in operating temperature.

[0115] An improvement in the cohesion of the composition can be obtained by a variety of pathways. In one, the accelerator concentration is increased, which reduces the working time. At constant accelerator concentration, it is also possible to raise the molecular weight of the polymer used, moreover. In the sense of the invention it is advantageous in any case to raise the concentration of crosslinker.

[0116] Depending on the desired requirements profile of the composition or of the product it is necessary to adapt the abovementioned parameters in a suitable way.

[0117] The PSA of the invention can be used particularly for producing an adhesive tape. The expression adhesive tape in the sense of this invention encompasses all sheetlike structures such as two-dimensionally extended films or film sections, tapes with extended length and limited width, tape sections, diecuts, labels and the like. The adhesive tape is preferably in the form of a continuous web, as a roll, and not in the form of a diecut or label. The adhesive tape can be produced for example in the form of a roll, in other words in the form of an Archimedean spiral rolled up onto itself. For the purposes of the present invention a temporary carrier, in contrast to a permanent carrier, is not considered a constituent of an adhesive tape, but merely as an aid to its production (process liner) or as a means for its lining.

[0118] In the use of the PSA of the invention for producing an adhesive tape, a carrier is coated with the PSA and the PSA is crosslinked thermally to give a layer of a crosslinked PSA of the invention. The carrier may be a permanent carrier or a temporary carrier. Coating a carrier with a PSA in the context of the present patent application means in particular that the ready-made carrier is coated with the PSA. It may, however, also refer to the PSA being coextruded with the carrier. Coating a carrier with a PSA may also mean, in the present patent application, that the PSA is brought into direct contact with one surface of the carrier, i.e. is disposed directly on one surface of the carrier. Alternatively, however, it may also mean that the PSA is not brought directly into contact with a surface of the carrier, but instead at least one further layer is disposed between the carrier and the PSA when the carrier is being coated with the PSA. Preferably, for coating a carrier with a PSA, the PSA is brought into direct contact with one surface of the carrier. The carrier may selectively be coated on one side or on both sides with a PSA of the invention, and the PSA or PSAs of the invention are further thermally crosslinked. If the carrier is coated on both sides with a PSA of the invention, the two sides of the carrier may be coated either with PSAs of the invention that are identical in composition, or else with PSAs of the invention that differ in their composition; preferably, the PSAs of the invention are identical in composition. As already elucidated in more detail above, depending on the process for producing the adhesive tape, the thermal crosslinking of the PSA of the invention may take place only after the carrier has been coated with the PSA, or may commence even before, or during, the coating of the carrier with the PSA.

[0119] The PSA of the invention may be applied to a carrier material in a variety of processes. Depending on the equipment present, the target coat weight, reaction rate of the crosslinking, and solubility of the crosslinkable polymer, the PSA may be produced and coated from solution or from the melt, and alternatively by coating onto or coextrusion with the carrier.

[0120] The PSA of the invention is used preferably in the form of a melt. PSA layers with a thickness of more than around 80 m are difficult to produce by the solvent technique, owing to problems which occur such as blistering, very low coating speed, problematic lamination of thin layers one above another, and weak points in the layered assembly. Suitable production procedures for a melt include both batch processes and continuous processes.

[0121] Alternatively, the PSA of the invention can be used in the form of a solution, preferably in a mixture of benzine and isopropanol, the benzine used being preferably benzine 60-95.

[0122] If the PSA of the invention is to be coated from a solution, the solution is produced beforehand by the processes known in the prior art. In particular, for example, the polymers are digested in a first portion of the solvent, and preswollen, in a suitable kneader (for example, a double-sigma kneader). Subsequently, the rest of the adjuvants are added simultaneously or with a staggering in terms of time, and at the end the desired solids content of the homogeneous mixture is established. The organosilanes and optionally accelerators that are added to the PSA of the invention are not incorporated homogeneously until shortly before the coating operation, in order to prevent premature crosslinking. Coating must then take place within the pot life or open timethat is, before the crosslinking has advanced to a point where uniform coating even in thin coat weights is no longer possible.

[0123] A solvent-containing PSA of the invention may be used for coating by the customary methods. In particular, the PSA may be applied to the carrier by means of a comma bar or Meyer bar or by means of an engraved roll. Alternatively, a nozzle may be used for coating, or the PSA is applied by spraying or in a screen printing process. Thereafter the solvent is removed in a suitable drying tunnel. The crosslinking of the PSA of the invention is typically accomplished largely during the drying operation itself, but may also take place separately and, for example, at the end of the drying tunnel, by means of infrared irradiation.

[0124] In the production of an adhesive tape of the invention it is possible optionally, besides at least one PSA of the invention, to use at least one further, arbitrary PSA as well. The further PSA may optionally in particular be thermally crosslinkable. It may further comprise one or more additives. Preferred additives are those also preferably present in a PSA of the invention. The statements made regarding preferred additives of the PSAs of the invention are therefore valid analogously for the further PSAs. If at least one further PSA is used in the production of an adhesive tape of the invention, the carrier is preferably coated on one side with a PSA of the invention, and this PSA is thermally crosslinked, and the carrier is coated with the further PSA on the side opposite the PSA of the invention, and this further PSA is crosslinked, if it is a crosslinkable PSA.

[0125] The PSA of the invention is used in particular for producing an adhesive tape in the form of a transfer tape, single-sided adhesive tape or a double-sided adhesive tape, and more particularly a double-sided adhesive tape.

[0126] A transfer tape of the invention refers to a single-layer crosslinked PSA of the invention. It therefore constitutes a single-layer, double-sidedly self-adhesive tape. The transfer tape is typically coated on one or both sides with a temporary carrier, i.e., with a liner. According to the present invention, a transfer tape is preferably produced by coating a temporary carrier with a PSA of the invention, thermally crosslinking the PSA, and optionally applying a further temporary carrier on the surface of the PSA layer opposite the temporary carrier.

[0127] A single-sided adhesive tape of the invention is an adhesive tape wherein a permanent carrier is coated on one of its surfaces with a crosslinked PSA of the invention. Preferably the single-sided adhesive tape consists exclusively of the permanent carrier and of the crosslinked PSA layer of the invention. Optionally there is a temporary carrier applied on the surface of the crosslinked PSA layer opposite the permanent carrier.

[0128] According to the present invention, a single-sided adhesive tape is produced preferably by

(i) coating a permanent carrier with a PSA of the invention, thermally crosslinking the PSA, and optionally applying a temporary carrier on the surface of the resultant crosslinked PSA layer opposite the permanent carrier, or
(ii) coating a temporary carrier with the PSA, thermally crosslinking the PSA, and applying a permanent carrier on the surface of the resultant crosslinked PSA layer opposite the temporary carrier.

[0129] A double-sided adhesive tape of the invention is an adhesive tape wherein a permanent carrier is coated on both of its surfaces with a PSA, and at least one of the two PSAs is a crosslinked PSA of the invention. With preference both PSAs and crosslinked PSAs of the invention. In the latter case the crosslinked PSAs may be identical or different in their composition; preferably they are identical in their composition. Also preferably, the double-sided adhesive tape consists exclusively of the permanent carrier and of the two PSA layers. Optionally in each case a temporary carrier is applied on the surfaces of the PSA layers opposite the permanent carrier.

[0130] According to one embodiment of a double-sided adhesive tape of the invention, a permanent carrier is coated on one of its two surfaces with a crosslinked PSA of the invention, and on the other of its two surfaces is coated with any other PSA. This other PSA may likewise be crosslinked, especially thermally. It may further comprise one or more additives. Preferred additives in that case are those also preferably present in a PSA of the invention. The statements made regarding preferred additives of the PSAs of the invention are therefore valid analogously for the other PSAs.

[0131] According to the present invention, a double-sided adhesive tape of the invention is produced preferably by coating two temporary carriers each independently of one another with a PSA of the invention, thermally crosslinking the PSAs, and additionally applying the surfaces of the resultant crosslinked PSA layers that are opposite the temporary carriers to the two surfaces of a permanent carrier. The two PSAs of the invention used may be identical or different in their composition, and preferably have an identical composition. An alternative embodiment of the production process may differ in that one of the two PSAs used is an arbitrary other PSA rather than a PSA of the invention. If the other PSA is likewise crosslinkablethermally, for examplethen it is also crosslinked during the production of the adhesive tape.

[0132] The coat weight of a PSA layer of the invention in the production of the adhesive tapes of the invention is preferably 10 to 5000 g/m.sup.2, more preferably 15 to 3000 g/m.sup.2, more preferably still 20 to 75 g/m.sup.2, and especially about 50 g/m.sup.2 (based in each case on the crosslinked PSA layer ultimately produced). On account in particular of the high shear strength after crosslinking, the PSAs of the invention are also suitable for use in adhesive tapes with a high coat weight of more than 100 g/m.sup.2, such as, for example, more than 200 g/m.sup.2. Even with such a high coat weight of PSA layer, it is possible in accordance with the process of the invention to achieve homogeneous crosslinking right through the layer. Examples of specific applications include industrial adhesive tapes, especially for use in the construction industry, examples being insulating tapes, anticorrosion tapes, aluminum bonding tapes, fabric-reinforced film adhesive tapes (duct tapes), special-purpose construction adhesive tapes, e.g., vapor barriers, adhesive assembly tapes, cable wrapping tapes; self-adhesive films and/or paper labels.

[0133] The present invention therefore also relates to an adhesive tape comprising at least one layer of a crosslinked PSA of the invention, i.e., of a PSA obtainable by thermal crosslinking of a PSA of the invention. The adhesive tape of the invention preferably comprises a permanent carrier coated with at least one layer of a crosslinked PSA of the invention. A carrier coated with a PSA means in accordance with the invention in particular that the ready-made carrier has been coated with the PSA. It may also be used, however, to mean that the PSA has been coextruded with the carrier. In accordance with the invention, furthermore, a carrier coated with a PSA may mean in one case that the PSA layer is in direct contact with one surface of the carrier, i.e., is disposed directly on one surface of the carrier. Alternatively in accordance with the invention, however, it may also mean that the PSA layer is not in contact directly with a surface of the carrier, but instead that there is at least one further layer disposed between the PSA layer and the carrier. In the case of a carrier coated with a PSA, preferably, the PSA layer is in direct contact with one surface of the carrier, i.e., it is preferably disposed directly on one surface of the carrier. The permanent carrier may selectively be coated on one or both sides with a crosslinked PSA of the invention. If the carrier is coated on both sides with a crosslinked PSA of the invention, then the two sides of the carrier may be coated either with crosslinked PSAs of the invention that are identical in their composition or else with crosslinked PSAs of the invention which differ in their composition; preferably the crosslinked PSAs of the invention are identical in their composition.

[0134] An adhesive tape of the invention may optionally comprise at least one further arbitrary PSA layer as well as at least one crosslinked PSA layer of the invention. The further PSA layer may optionally in particular be a thermally crosslinked PSA layer. It may further comprise one or more additives. Preferred additives in that case are those also preferably present in a crosslinked PSA layer of the invention. The statements made regarding preferred additives of the crosslinked PSAs of the invention are therefore valid analogously for the further PSAs. If an adhesive tape of the invention comprises at least one further PSA layer, the carrier is preferably coated on one side with a crosslinked PSA of the invention, and is coated with the further PSA on the side opposite the crosslinked PSA layer of the invention, with the further PSA optionally being a PSA which, in particular, is crosslinked thermally.

[0135] The adhesive tape of the invention is typically a transfer tape, a single-sided adhesive tape or a double-sided adhesive tape, with particular preference a double-sided adhesive tape. The transfer tape, the single-sided adhesive tape, and the double-sided adhesive tape in this case are defined as above.

[0136] In an adhesive tape of the invention, the coat weight of the at least one crosslinked PSA layer of the invention that is present therein, independently of one another, is 10 to 5000 g/m.sup.2, preferably 15 to 3000 g/m.sup.2, more preferably 20 to 75 g/m.sup.2, and especially about 50 g/m.sup.2.

[0137] The crosslinked PSA of the invention and an adhesive tape comprising at least one layer of a crosslinked PSA of this kind are very suitable for the bonding of low-energy surfaces such as, for example, apolar coatings, printing plates, polyethylene, polypropylene or EPDM, in other words, for example, for the closing or strapping of polyolefin bags or for the fastening of parts made of olefinic plastics or elastomers, and especially of plastic parts, to motor vehicles. They are therefore ideal for labels on cosmetics packaging (for example, for body lotion bottles or shampoo bottles), since they are highly transparent, adhere well to plastic bottles, and are water-resistant and stable to aging. In the context of security labels such as magnetic alarm labels or data carriers such as Holospot (tesa Holospot is a self-adheive polymer label containing an information field just a few square millimeters in size; the label adheres firmly to the product and contains various overt and covert security features, which are written into the information field beforehand using a high-resolution laser), they solve the problem of the poor adhesion of conventional adhesives to apolar substrates. They are additionally suitable for bonding to skin and to rough substrates in the construction sector, as adhesive packaging tape, and for wrapping applications. Examples of applications on skin are plasters in roll and individual form, diecuts for the bonding of colostomy bags and electrodes, active ingredient patches (transdermal patches), and bandages. On account of the aging stability, they offer the possibility for avoiding substances causing skin irritation or having other chemical actions. Consequently they are also suitable for the construction of hygiene products such as diaper closures, infant diapers or sanitary towels; furthermore, they adhere in particular to the polyolefin film and polyolefin nonwoven materials used in these contexts, and have lower costs and higher heat resistance than conventional compositions comprising hydrogenated styrene block copolymers. Examples of wrapping applications are electrical insulation and the production of automobile cable harnesses. The crosslinked PSA of the invention and the adhesive tape of the invention are also compatible at high temperatures with PP, PE and PVC wire insulation. In construction applications as plastering tape, for the bonding of roof insulation films (water vapor or liquid water barrier films) and as bitumen adhesive tape for sealing applications, and other outdoor applications, they are notable for effective bonding behavior under low-temperature conditions and for relatively good UV stability. Further applications are as adhesive splicing tapes for the continuous bonding of printed or unprinted film webs, and as adhesive barrier tape with respect to diffusion of moisture and oxygen in photovoltaic modules or electronic components.

[0138] The PSA layers in the adhesive tapes of the invention may for example be filled with organic or inorganic fillers. Also possible are layers foamed in open-cell or closed-cell form by known processes. A possible foaming method is that of foaming using compressed gases such as nitrogen or CO.sub.2, or foaming using expandants such as hydrazines or expandable microballoons. Where expanding microballoons are used, the PSA or the shaped layer is advantageously activated suitably by means of introduction of heat. Foaming may take place in the extruder or after coating. It may be useful to smoothen the foamed layer using suitable rolls or release films. For producing foam-analogous layers, hollow glass spheres or already expanded polymeric microballoons may also be added to the PSA of the invention. The PSA layers of the adhesive tapes of the invention may also not be foamed.

EXAMPLES

Commercially Available Chemicals Used

[0139]

TABLE-US-00001 Chemical compound Trade name Manufacturer EPDM (ethylene content 55 wt %, ENB Vistalon 6602 Exxon Mobil content 5.2 wt %) Maleic anhydride-grafted EPDM (ethylene Keltan 1519r Lanxess content: 49 wt %, maleic anhydride content (grafted): 1.9 wt %, Mooney viscosity (ML 1 + 4/125 C.): 65) White oil (paraffinic-naphthenic mineral oil) Ondina 933 Shell Liquid EPDM (ethylene/propylene weight Trilene 67 Lion ratio 46:54, ENB content: 9.5 wt %) Copolymers Hydrogenated hydrocarbon resin (softening Regalite R1100 Eastman temperature: 100 C.) Alkylphenol resin based on octylphenol SP 1045 SI-Group (softening temperature: 60-70 C.) Zinc resinate (zinc complex of rosin) Bremazit 3050 Robert Kramer Trimethylol propane triacrylate (TMPTA) Sigma- Aldrich Dibenzoyl peroxide (BPO) Sigma- Aldrich (3-Glycidyloxypropyl)triethoxysilane Dynasylan GLYEO Evonik 3-Aminopropyltriethoxysilane Dynasylan AMEO Evonik Benzine 60-95 Exxsol DSP 60/95 SH Exxon Mobil Isopropanol Helm AG Ethanol Helm AG Acetone Helm AG

Production of the PSAs and their Properties

[0140] Inventive examples 1 to 3 describe the production of PSAs of the invention based on maleic anhydride-grafted EPDM in the form of a solution, the coating of said solution onto a carrier from the solution, and the crosslinking of the PSAs to give crosslinked PSA layers of the invention.

[0141] Comparative example 4 describes the production of a crosslinker-free PSA based on maleic anhydride-grafted EPDM in the form of a solution and also the coating of that solution onto a carrier from the solution.

[0142] Inventive examples 5 and 6 describe the production of resole-containing PSAs based on EPDM in the form of a solution, the coating of that solution onto a carrier from the solution, and the crosslinking of the PSAs to give crosslinked PSA layers.

[0143] Inventive examples 7 and 8 describe the production of peroxide-containing PSAs based on EPDM in the form of a solution, the coating of that solution onto a carrier from the solution, and the crosslinking of the PSAs to give crosslinked PSA layers.

Inventive Example 1

[0144] 120 g of Keltan 1519r, 242 g of benzine 60-95 and 13 g of isopropanol were combined, preswollen at 23 C. for 24 hours, and then kneaded in a kneader with double-sigma kneading hook at 35 rpm for 15 minutes. Then 133.2 g of Regalite R1100 were added and the composition obtained was kneaded at 35 rpm for 60 minutes. Thereafter 45 g of Ondina 933 were added and the resulting composition was kneaded at 35 rpm for 10 minutes. Subsequently 364 g of benzine 60-95 and 19 g of isopropanol were added and the resulting composition was kneaded at 35 rpm for 30 minutes. Then a solution of 1.3 g of 3-aminopropyltriethoxysilane in 42 g of benzine 60-95 was added and stirring was carried out for 1 minute. Thereupon a solution of 0.5 g of 3-glycidyloxypropyltriethoxysilane in 16 g of benzine 60-95 was added and stirring was carried out for 1 minute.

[0145] The resulting PSA was coated on a standard commercial laboratory coating bench (for example, from Sondermaschinen Oschersleben GmbH) with the aid of a coating knife onto a PET film 23 m thick which had been etched with trichloroacetic acid. The solvent was evaporated off in a forced air drying cabinet at 120 C. for 10 minutes, during which the PSA began to crosslink. The slot width during coating was set so that the coat weight achieved following evaporation of the solvent was 50 g/m.sup.2. The result was a crosslinked PSA layer.

Inventive Example 2

[0146] A crosslinked PSA layer was produced as described in example 1, but adding 47 g of Trilene 67 rather than 45 g of Ondina 933.

Inventive Example 3

[0147] A crosslinked PSA layer was produced as described in example 1, but adding 47 g of Trilene 67 rather than 45 g of Ondina 933. In a further departure from example 1, no (3-glycidyloxypropyl)triethoxysilane crosslinker was used, but only 3-aminopropyl-triethoxysilane. For this purpose, a solution of 2.1 g of 3-aminopropyltriethoxysilane in 68 g of benzine 60-95 was added and stirring was carried out for 1 minute.

Comparative Example 4

[0148] 120 g of Keltan 1519r, 242 g of benzine 60-95 and 13 g of isopropanol were combined, preswollen at 23 C. for 24 hours, and then kneaded in a kneader with double-sigma kneading hook at 35 rpm for 15 minutes. Then 133.2 g of Regalite R1100 were added and the composition obtained was kneaded at 35 rpm for 60 minutes. Thereafter 45 g of Ondina 933 were added and the resulting composition was kneaded at 35 rpm for 10 minutes. Subsequently 364 g of benzine 60-95 and 19 g of isopropanol were added and the resulting composition was kneaded at 35 rpm for 30 minutes. kneaded. Then a solution of 1.3 g of 3-aminopropyltriethoxysilane in 42 g of benzine 60-95 was added and stirring was carried out for 1 minute. Thereupon a solution of 0.5 g of 3-glycidyloxy-propyltriethoxysilane in 16 g of benzine 60-95 was added and stirring was carried out for 1 minute.

[0149] The resulting PSA was coated on a standard commercial laboratory coating bench (for example, from Sondermaschinen Oschersleben GmbH) with the aid of a coating knife onto a PET film 23 m thick which had been etched with trichloroacetic acid. The solvent was evaporated off in a forced air drying cabinet at 120 C. for 10 minutes, and so the resultant PSA layer is substantially free of solvent. The slot width during coating was set so that the coat weight achieved following evaporation of the solvent was 50 g/m.sup.2.

Comparative Example 5

[0150] 115.5 g of Vistalon 6602 and 213 g of benzine 60-95 were combined, preswollen at 23 C. for 48 hours, and then kneaded in a kneader with double-sigma kneading hook at 35 rpm for 15 minutes. Then 125.4 g of Regalite R1100 were added and the composition obtained was kneaded at 35 rpm for 60 minutes. Thereafter 39 g of Ondina 933 were added and the resulting composition was kneaded at 35 rpm for 10 minutes. 14.1 g of SP 1045 (crosslinker resin) and 5.9 g of Bremazit 3050 (zinc resinate) were dissolved in 20 g of ethanol, added together with a first diluent amount of 192 g of benzine 60-95, and the resulting composition was kneaded at 35 rpm for 20 minutes. Thereafter a second diluent amount of 213 g of benzine 60-95 was added and was incorporated by kneading at 35 rpm for 30 minutes.

[0151] The resulting PSA was coated on a standard commercial laboratory coating bench (for example, from Sondermaschinen Oschersleben GmbH) with the aid of a coating knife onto a PET film 23 m thick which had been etched with trichloroacetic acid. The solvent was evaporated off in a forced air drying cabinet at 105 C. for 10 minutes. The slot width during coating was set so that the coat weight achieved following evaporation of the solvent was 50 g/m.sup.2. Subsequently the film freed of the solvent was crosslinked at 180 C. for 40 minutes. The result was a resole-crosslinked PSA layer.

Comparative Example 6

[0152] 87.3 g of Vistalon 6602 and 213 g of benzine 60-95 were combined, preswollen at 23 C. for 48 hours, and then kneaded in a kneader with double-sigma kneading hook at 35 rpm for 15 minutes. Then 132.6 g of Regalite R1100 were added and the composition obtained was kneaded at 35 rpm for 60 minutes. Thereafter 60 g of Trilene 67 were added and the resulting composition was kneaded at 35 rpm for 10 minutes. 14.1 g of SP 1045 (crosslinker resin) and 5.9 g of Bremazit 3050 (zinc resinate) were dissolved in 20 g of ethanol, added together with a first diluent amount of 192 g of benzine 60-95, and the resulting composition was kneaded at 35 rpm for 20 minutes. Thereafter a second diluent amount of 213 g of benzine 60-95 was added and was incorporated by kneading at 35 rpm for 30 minutes.

[0153] The resulting PSA was coated on a standard commercial laboratory coating bench (for example, from Sondermaschinen Oschersleben GmbH) with the aid of a coating knife onto a PET film 23 m thick which had been etched with trichloroacetic acid. The solvent was evaporated off in a forced air drying cabinet at 105 C. for 10 minutes. The slot width during coating was set so that the coat weight achieved following evaporation of the solvent was 50 g/m.sup.2. Subsequently the film freed of the solvent was crosslinked at 180 C. for 40 minutes. The result was a resole-crosslinked PSA layer.

Comparative Example 7

[0154] 121.2 g of Vistalone 6602 and 213 g of benzine 60-95 were combined and preswollen at 23 C. for 48 hours. Then 127.2 g of Regalite R1100 were added and the composition obtained was kneaded at 35 rpm for 60 minutes. Thereafter 39.9 g of Ondina 933 were added and the resulting composition was kneaded at 35 rpm for 10 minutes. A first dilution was carried out with 212 g of benzine 60-95, which was incorporated by kneading at 35 rpm for 20 minutes. Together with a second dilution of 213 g of benzine 60-95, 2.9 g of TMPTA were added and the resulting composition was kneaded at 35 rpm for 30 minutes. Shortly before coating, 8.7 g of BPO as a 10 wt % strength solution in acetone were added and incorporated by kneading for 20 minutes.

[0155] The resulting PSA was coated on a standard commercial laboratory coating bench (for example, from Sondermaschinen Oschersleben GmbH) with the aid of a coating knife onto a PET film 23 m thick which had been etched with trichloroacetic acid. The solvent was evaporated off in a forced air drying cabinet at 120 C. for 10 minutes, during which the PSA began to crosslink. The slot width during coating was set so that the coat weight achieved following evaporation of the solvent was 50 g/m.sup.2. The result was a peroxide-crosslinked PSA layer.

Comparative Example 8

[0156] 90 g of Vistalon 6602 and 213 g of benzine 60-95 were combined and preswollen at 23 C. for 48 hours. Then 138.3 g of Regalite R1100 were added and the composition obtained was kneaded at 35 rpm for 60 minutes. Thereafter 60 g of Trilene 67 were added and the resulting composition was kneaded at 35 rpm for 10 minutes. A first dilution was carried out with 212 g of benzine, which was incorporated by kneading at 35 rpm for 20 minutes. Together with a second dilution of 213 g of benzine 60-95, 2.9 g of TMPTA were added and the resulting composition was kneaded at 35 rpm for 30 minutes. Shortly before coating, 8.7 g of BPO as a 10 wt % strength solution in acetone were added and incorporated by kneading for 20 minutes.

[0157] The resulting PSA was coated on a standard commercial laboratory coating bench (for example, from Sondermaschinen Oschersleben GmbH) with the aid of a coating knife onto a PET film 23 m thick which had been etched with trichloroacetic acid. The solvent was evaporated off in a forced air drying cabinet at 120 C. for 10 minutes, during which the PSA began to crosslink. The slot width during coating was set so that the coat weight achieved following evaporation of the solvent was 50 g/m.sup.2. The result was a peroxide-crosslinked PSA layer.

Inventive Examples 9 to 11

[0158] Alternatively, inventive examples 1-3 were likewise produced solventlessly in an extruder by the processes described in DE19806609A1 (inventive examples 9 to 11). This was done using a planetary roll extruder from ENTEX Rust & Mitschke, with three roll cylinders. The diameter of a roll cylinder was 70 mm, and its process length was 1200 mm. The central spindle was conditioned to 18 C., the roll cylinders to 90 C. The conveying screw was operated with 75 revolutions per minute, and each roll cylinder contained 7 planetary spindles.

[0159] The solid EPDM rubbers were fed to the conveying screw via the filling port. The melted tackifier resins were added via a melt pump at the start of the second roll cylinder, while the plasticizers were fed into the thrust ring between the second and third roll cylinders. The homogeneous mixture was subsequently transferred for degassing into a degassing twin-screw extruder. In this extruder the organosilanes were added and incorporated. After the degassing, the extrudate was passed directly onto the roll applicator for the coating of the PSAs.

[0160] The properties of the specimens produced in a hotmelt process corresponded to those of the specimens from the solvent process as described above (inventive examples 1 to 3).

[0161] Results:

[0162] Table 1 provides an overview of the adhesive and mechanical properties of the crosslinked PSAs of the invention from inventive examples 1 to 3, and also those of the comparative adhesives from comparative examples 4 to 8.

TABLE-US-00002 Crosslinker system: Peel adhesion MST (200 g).sup.2 MST (1000 g).sup.3 SAFT.sup.4 Experiment EPDM type and proportion.sup.1 Plasticizer [N/cm] [m] [m] ( C.) Inventive Keltan 0.4 wt % Dynasylan AMEO Ondina 933 5.5 10 213 150 example 1 1519r 0.2 wt % Dynasylan GLYEO Inventive Keltan 0.4 wt % Dynasylan AMEO Trilene 67 8.1 19 248 142 example 2 1519r 0.2 wt % Dynasylan GLYEO Inventive Keltan 0.7 wt % Dynasylan AMEO Trilene 67 8.1 18 236 157 example 3 1519r Comparative Keltan Ondina 933 7.7 43 366 113 example 4 1519r Comparative Vistalon 4.7 wt % SP 1045 Ondina 933 2.8 613 >2000 89 example 5 6602 2.0 wt % Zn resinat Comparative Vistalon 4.7 wt % SP 1045 Trilene 67 3.4 536 >2000 92 example 6 6602 2.0 wt % Zn resinat Comparative Vistalon 2.9 wt % dibenzoyl peroxide Ondina 933 2.5 314 >2000 110 example 7 6602 1.0 wt % TMPTA Comparative Vistalon 2.9 wt % dibenzoyl peroxide Trilene 67 2.8 284 >2000 116 example 8 6602 1.0 wt % TMPTA .sup.1Proportion = proportion by weight in the PSA prior to crosslinking (in wt %, based on the solvent-free proportion); .sup.2MST (200 g) = microshear travel on loading with a weight of 200 g; .sup.3MST (1000 g) = microshear travel on loading with a weight of 1000 g; .sup.4SAFT = Shear Adhesion Failure Temperature (tesa-SAFT), heat resistance.

[0163] The organosilane-crosslinked PSAs of the invention, based on maleic anhydride-grafted EPDM, from the adhesive tapes of inventive examples 1 to 3, have much higher shear strengths, under hot conditions as well, than a corresponding noncrosslinked PSA likewise based on maleic anhydride-grafted EPDM, of the kind present in the adhesive tape from comparative example 4. They are therefore much more heat-resistant. This is evident in the microshear travel at 40 C., reduced relative to comparative example 4, even under different levels of force exposure, and also in increased SAFT temperatures (Shear Adhesion Failure Temperatures) of the adhesive tapes of the invention from inventive examples 1 to 3. The heat resistances of the adhesive tapes from inventive examples 1 to 3 additionally show that the heat resistance can be additionally adjusted through the nature of the plasticizer used and/or through the nature and amount of the organosilane crosslinker used.

[0164] Comparing the peel adhesion, i.e., the peel strength, of the adhesive tapes of the invention from inventive examples 1 to 3 with the peel adhesion of the adhesive tape from comparative example 4, it is further found that with the organosilane-crosslinked PSA layers of the invention, based on maleic anhydride-grafted EPDM, despite the crosslinking, it is possible to obtain peel adhesion comparative with that of corresponding noncrosslinked PSA layers likewise based on maleic anhydride-grafted EPDM. The comparison of the adhesive tape from inventive example 1 with the adhesive tapes from inventive examples 2 and 3 shows, furthermore, that the peel adhesion can be significantly boosted further by using liquid EPDM in the PSA. Since the peel adhesion was determined in each case relative to a polypropylene plate and hence relative to an LSE surface, it is clear, furthermore, that the organosilane-crosslinked adhesive-composition layers of the invention, like the corresponding noncrosslinked layers of adhesive composition, are outstandingly suitable for adhesive bonding, including on LSE surfaces.

[0165] The organosilane-crosslinked PSAs of the invention based on maleic anhydride-grafted EPDM from inventive examples 1 to 3 are also significantly superior to the resole-crosslinked and peroxide-crosslinked PSAs based on EPDM from comparative examples 5 to 8, this superiority existing in respect both of the peel adhesion and of the heat resistance, i.e., shearing force at elevated temperature. This is evident from the microshear travel values, which are lower by a multiple factor, and also by the elevated SAFT values for the organosilane-crosslinked PSAs of the invention relative to the resole- or peroxide-crosslinked PSAs.

Measurement Methods

[0166] All of the measurements were conducted unless otherwise specified at 23 C. and 50% relative humidity. Ahead of the tests described below, the specimens were stored for 7 days at 23 C. and 50% relative humidity in order to ensure complete post-crosslinking.

[0167] The data were determined as follows:

Solids Content

[0168] The solids content is a measure of the fraction of unevaporable constituents in a PSA. It is determined gravimetrically by weighing out the PSA, then evaporating the evaporable fractions in a drying cabinet at 120 C. for 2 hours and reweighing the residue.

Thickness

[0169] The thickness of a PSA layer can be determined by determining the thickness of a section of such a layer of adhesive, applied to a carrier or liner, said section being of defined length and defined width, with subtraction of the (known or separately ascertainable) thickness of a section with the same dimensions as the carrier or liner used. The thickness of the layer of adhesive can be ascertained using commercial thickness gauges (sensor instruments) with accuracies of less than 1 m deviation. Where fluctuations in thickness are found, the value reported is the average value of measurements at not less than three representative pointsin other words, in particular, not including measurement at wrinkles, creases, specks and the like.

Coat Weight

[0170] The coat weight of a PSA layer in g/m.sup.2 can be determined by determining the mass of a section of such a layer of adhesive, applied to a carrier or liner, said section being of defined length and defined width, with subtraction of the (known or separately ascertainable) mass of a section with the same dimensions of the carrier or liner used.

Softening Point

[0171] The softening point, also called softening temperature, of a resin is carried out according to the relevant methodology, which is known as ring & ball and is standardized according to ASTM E28.

180 Peel Adhesion Test

[0172] The peel strength (peel adhesion) is tested in a method based on PSTC-1.

[0173] A single-sided adhesive tape in the form of a strip 2 cm wide is adhered to a polypropylene plate 5 mm thick, by the free PSA side, by rolling down the tape back and forth five times using a 4 kg roller. The plate is clamped in, and the adhesive tape is pulled off by its free end on a tensile testing machine at a peel angle of 180 with a velocity of 300 mm/min. The results of measurement are reported in N/cm and are averages from three measurements.

Shear Adhesion Failure Temperature (SAFT), Heat Resistance

[0174] This test is used for accelerated testing of the shear strength of adhesive tapes under temperature load. For the test, the single-sided adhesive tape under investigation is adhered by the PSA side to a heatable steel plate, loaded with a weight (50 g), and the shear travel is recorded.

[0175] Sample Preparation:

[0176] The single-sided adhesive tape is cut to a size of 10 mm*50 mm.

[0177] The adhesive tape cut to size is bonded by the free PSA side to a polished steel test plate cleaned with acetone (steel material 1.4301, DIN EN 10088-2, surface 2R, surface roughness Ra=30 to 60 nm, dimensions 50 mm*13 mm*1.5 mm) in such a way that the bond area of the sample is 13 mm*10 mmheight*widthand the steel test plate protrudes by 2 mm at the upper edge. The bond is then fixed by rolling a 2 kg steel roller over it six times at a speed of 10 m/min. At the top, the sample is reinforced flush with a stable adhesive strip which serves as a support for the travel sensor. Using the steel plate, the sample is then suspended so that the adhesive tape end with the longer overhang points vertically downward.

[0178] Measurement:

[0179] The sample for measurement is loaded at the bottom end with a 50 g weight. The steel test plate with the bonded sample is heated to the end temperature of 200 C., beginning at 30 C. and at a rate of 9 K/min.

[0180] The slip travel of the sample is observed by means of a travel sensor, as a function of temperature and time. The maximum slip travel is set at 1000 m (1 mm); if it is exceeded, the test is discontinued and the failure temperature is noted.

[0181] Test conditions: room temperature 23+/3 C., relative humidity 50+/5%.

Microshear Test

[0182] This test serves for the accelerated testing of the shear strength of adhesive tapes under temperature load.

[0183] Sample Preparation for Microshear Test:

[0184] A single-sided adhesive tape (length around 50 mm, width 10 mm) cut from the respective sample specimen is adhered by the PSA side to a steel test plate which has been cleaned with acetone, the bond being such that the steel plate protrudes beyond the adhesive tape to the right and to the left, and the adhesive tape protrudes beyond the test plate by 2 mm at the upper edge. The bond area of the sample in terms of heightwidth=13 mm10 mm. The bond site is subsequently rolled down six times with a 2 kg steel roller at a speed of 10 m/min. The adhesive tape is reinforced flush with a stable adhesive strip which serves as a support for the travel sensor. The sample is suspended vertically by means of the test plate.

[0185] Microshear Test:

[0186] The sample specimen for measurement is loaded at the bottom end with a weight of 200 g (variant 1) or 1000 g (variant 2). The test temperature is 40 C. in each case, the test load duration 15 minutes. The shear travel after the predetermined test duration at constant temperature is reported as the result in m.

Surface Energies

[0187] Surface energies (surface tensions) are determined according to DIN ISO 8296. This can be done using, for example, test inks from Softal. The inks are available in the range from 30 to 72 mN/m. The ink is applied, with a line of ink to the surface, at 23 C. and 50% relative humidity. If the line of ink contracts in less than 2 seconds, the measurement is repeated with ink of a lower surface energy until the 2 seconds are reached. If the line of ink remains unchanged for longer than 2 seconds, the measurement is repeated with ink of higher surface energy until the 2 seconds are reached. The FIGURE indicated on the corresponding ink bottle then corresponds to the surface energy of the substrate.