Crosslinker-accelerator system for polyacrylates

Abstract

Crosslinker-accelerator system for the thermal crosslinking of polyacrylates having functional groups capable of entering into linking reactions with epoxide groups, comprising at least one substance having at least one epoxide group as crosslinker and at least one substance of the formula
R.sup.1.sub.2NCR.sup.2R.sup.3CR.sup.4R.sup.5(CR.sup.6R.sup.7).sub.nX
in which the R.sup.1 independently represent hydrogen, a substituted or unsubstituted alkyl or cycloalkyl radical or together with the nitrogen atom form a 5-7-membered ring;
R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6 and R.sup.7 independently represent hydrogen or an alkyl radical having 1 to 8 carbon atoms or form a 5-7-membered cycloalkylene group;
n=0; and
X represents OH, OR, SH, SR and PR.sub.2, in which R independently represents C.sub.1-C.sub.18 alkyl radical, C.sub.2-C.sub.18 alkenyl radical or C.sub.2-C.sub.18 alkynyl radical, an aryl group or an aliphatic or aromatic heterocycle, as accelerator.

Claims

1. A crosslinker-accelerator system for the thermal crosslinking of polyacrylates having functional groups capable of entering into linking reactions with epoxide groups, comprising at least one substance comprising at least two epoxide groups as crosslinker and at least one substance of the formula (I) as accelerator:
R.sup.1.sub.2NCR.sup.2R.sup.3CR.sup.4R.sup.5X(I) in which the radicals R.sup.1 independently of one another are a hydrogen atom or a substituted or unsubstituted alkyl or cycloalkyl radical having 1 to 8 carbon atoms or together with the nitrogen atom form a 5-7-membered ring which comprises at least 4 carbon atoms and not more than one further heteroatom as ring atoms; the radicals R.sup.2, R.sup.3, R.sup.4, and R.sup.5 independently of one another are a hydrogen atom or an alkyl radical having 1 to 8 carbon atoms or form a 5-7-membered cycloalkylene group; and X is a group selected from the group consisting of OH, OR, SH, SR and PR.sub.2, in which the radicals R independently of one another are a C.sub.1-C.sub.18 alkyl radical, C.sub.2-C.sub.18 alkenyl radical or C.sub.2-C.sub.18 alkynyl radical which is in each case linear or branched and unsubstituted or substituted, or an unsubstituted or substituted aryl group or an aliphatic or aromatic heterocycle.

2. The crosslinker-accelerator system according to claim 1, wherein X is a group selected from the group consisting of OH, OR and PR.sub.2.

3. The crosslinker-accelerator system according to claim 2, wherein X is OH or OR.

4. The crosslinker-accelerator system according to claim 3, wherein R is an optionally substituted alkylaminoalkyl radical.

5. The crosslinker-accelerator system according to claim 1, wherein at least one of the radicals R.sup.1 is a substituted or unsubstituted alkyl or cycloalkyl radical having 1 to 8 carbon atoms.

6. The crosslinker-accelerator system according to claim 5, wherein both radicals R.sup.1 independently of one another are a substituted or unsubstituted alkyl or cycloalkyl radical having 1 to 8 carbon atoms.

7. The crosslinker-accelerator system according to claim 6, wherein the two radicals R.sup.1 are each a methyl group.

8. The crosslinker-accelerator system according to claim 1, wherein the ratio of the number of all the substituted and unsubstituted amino and phosphine groups in the accelerator to the number of epoxide groups in the crosslinker is from 0.2:1 to 4:1.

9. A thermally crosslinkable composition comprising: at least one polyacrylate having functional groups capable of entering into linking reactions with epoxide groups; and a crosslinker-accelerator system according to claim 1.

10. The thermally crosslinkable composition according to claim 9, wherein the ratio of the total number of epoxide groups in the crosslinker to the number of functional groups in the polyacrylate that are capable of entering into linking reactions with epoxide groups is in the range from 0.01:1 to 1:1.

11. The thermally crosslinkable composition according to claim 9, wherein the total fraction of crosslinker is 0.1%-5% by weight and the total fraction of accelerator is 0.05%-5% by weight, based on the pure polyacrylate to be crosslinked.

12. A crosslinked polyacrylate obtained by thermal crosslinking of a thermally crosslinkable composition according to claim 9.

13. Method for the thermal crosslinking of polyacrylates having functional groups capable of entering into linking reactions with epoxide groups, comprising carrying out the thermal crosslinking with the crosslinker-accelerator system according to claim 1.

14. Method for producing thermally crosslinked polyacrylates which comprises carrying out thermally crosslinking said polyacrylates with the crosslinker-accelerator system of claim 1.

15. A pressure-sensitive adhesive comprising a thermally crosslinked polyacrylate produced by thermally crosslinking the thermally crosslinkable composition of claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a continuous process for the compounding and coating operation,

(2) FIG. 2 illustrates the effect of epoxide group concentration on the degree of crosslinking,

(3) FIG. 3 illustrates the relationship between crosslinking time and accelerator concentration,

(4) FIG. 4 illustrates microshear travel as a function of storage time.

(5) 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 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 are heated in the compounder until the melt state is reached. At the first feed point, together with the polymer, the epoxide-containing compounds are advantageously introduced into the compounder.

(6) Shortly before coating takes place, the accelerators are added at a second feed point (1.2). The outcome of this is that the accelerators are added to the epoxide-containing polymers not until shortly before coating, and the reaction time in the melt is low.

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

(8) Immediately after coatingpreferably by means of roll application or by means of an extrusion diethe polymer is only slightly crosslinked, but not yet sufficiently crosslinked. The crosslinking reaction preferably proceeds predominantly on the carrier.

(9) Crosslinking raises the cohesion of the polymer and hence also the shear strength. The links are very stable. This allows very ageing-stable and heat-resistant products to be produced, such as adhesive tapes, viscoelastic carrier materials or shaped articles.

(10) The physical properties of the end product, especially its viscosity, bond strength 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 this process. The most important influencing variables are the amounts (concentrations and proportions relative to one another), the chemical nature of the crosslinkers and the accelerators, the operating and coating temperatures, the residence time in the compounder (more particularly extruder) and in the coating assembly, the fraction of functional groups, more particularly acid groups and/or hydroxyl groups, in the polymer, and also the average molecular weight of the polyacrylate.

(11) The crosslinker-accelerator system of the invention, in processes for the crosslinking of polyacrylates, offers the advantage that a stable crosslinking process for polyacrylates can be offered, and one with outstanding control facility in relation to the crosslinking pattern, by virtue of substantial decoupling of degree of crosslinking and reactivity (reaction kinetics), more particularly the reaction kinetics at low temperatures. The amount of crosslinker (amount of epoxide) added here largely influences the degree of crosslinking of the product, the chemical nature and the concentration of the accelerator largely control the reactivity.

(12) Surprisingly it has been observed that through the amount of epoxide-containing substances added it has been possible to preselect the degree of crosslinking, and to do so largely independently of the process parameters that typically require additional selection: temperature and amount of added crosslinker.

(13) The effect of epoxide group concentration on the degree of crosslinking for a given amount of accelerator and a given temperature is shown schematically by FIG. 2. Here, the accelerator concentration rises from the concentration A (top curve; low concentration) via the concentrations B (second-lowest concentration) and C (second-highest concentration) to the concentration D (bottom curve; highest concentration). As can be seen, the final value of the degree of crosslinkingrepresented here by increasingly smaller values for the microshear travelgoes up as the epoxide concentration increases, whereas the reaction kinetics remain virtually unaffected.

(14) It has also been found that the amount of accelerator added has a direct influence on the crosslinking rate, and hence also on the point in time at which the final degree of crosslinking is achieved, but without influencing it absolutely. The reactivity of the crosslinking reaction here may be selected such that the crosslinking also during storage of the completed product under the conditions customary therein (room temperature) leads within a few weeks to the desired degree of crosslinking, more particularly without any need for thermal energy to be (actively) supplied or for the product to be treated further.

(15) The relationship between crosslinking time and accelerator concentration for a given temperature (in this case room temperature) and with a constant amount of epoxide is reproduced schematically in FIG. 3. Here, the accelerator concentration rises from the concentration 1 (top curve; low concentration) via the concentrations 2 (second-lowest concentration) and 3 (second-highest concentration) to the concentration 4 (bottom curve; highest concentration). Here it is found that the final value of the degree of crosslinking remains virtually constant (in the case of the lowest reaction, this value has not yet been reached); with high concentrations of accelerator, however, this value is reached more quickly than at low concentrations of accelerator.

(16) In addition to the aforementioned parameters, the reactivity of the crosslinking reaction can also be influenced by varying the temperature, if desired, especially in those cases where the advantage of inherent crosslinking in the course of storage under standard conditions has no part to play. At constant crosslinker concentration, an increase in the operating temperature leads to a reduced viscosity, which enhances the coatability of the composition but reduces the processing life.

(17) An increase in the processing life is acquired by a reduction in the accelerator concentration, reduction in molecular weight, reduction in the concentration of functional groups in the addition polymer, reduction of the acid fraction in the addition polymer, use of less-reactive crosslinkers (epoxides) or of less-reactive crosslinker-accelerator systems, and reduction in operating temperature.

(18) 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 processing life. At constant accelerator concentration, it also possible to raise the molecular weight of the polyacrylate, which is possibly more efficient. In the sense of the invention it is advantageous in any case to raise the concentration of crosslinker (substances containing epoxide groups). 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.

(19) A further subject of the invention is the use of a crosslinker-accelerator system of the invention for producing thermally crosslinked polyacrylates.

(20) Inventively crosslinked polyacrylates can be used for a broad range of applications. Below, a number of particularly advantageous fields of use are set out by way of example.

(21) A polyacrylate crosslinked with the crosslinker-accelerator system of the invention is used in particular as a pressure-sensitive adhesive (PSA), preferably as a PSA for an adhesive tape, where the acrylate PSA is in the form of a single-sided or double-sided film on a carrier sheet. These polyacrylates are especially suitable when a high coat weight in one coat is required, since with this coating technique it is possible to achieve an almost arbitrarily high coat weight, preferably more than 100 g/m.sup.2, more preferably more than 200 g/m.sup.2, and to do so in particular at the same time as homogeneous crosslinking through the coat. Examples of favourable applications are technical adhesive tapes, more especially for use in construction, examples being insulating tapes, corrosion control tapes, adhesive aluminium tapes, fabric-reinforced film-backed adhesive tapes (duct tapes), special-purpose adhesive construction tapes, such as vapour barriers, adhesive assembly tapes, cable wrapping tapes, self-adhesive sheets and/or paper labels.

(22) The inventively crosslinked polyacrylate may also be made available as a PSA for a carrierless adhesive tape, in the form of what is called an adhesive transfer tape. Here as well, the possibility of setting the coat weight almost arbitrarily high in conjunction with homogeneous crosslinking through the coat is a particular advantage. Preferred weights per unit area are more than 10 g/m.sup.2 to 5000 g/m.sup.2, more preferably 100 g/m.sup.2 to 3000 g/m.sup.2.

(23) The inventively crosslinked polyacrylate may also be present in the form of a heat-sealing adhesive in adhesive transfer tapes or single-sided or double-sided adhesive tapes. Here as well, for carrier-containing pressure-sensitive adhesive tapes, the carrier may be an inventively obtained viscoelastic polyacrylate.

(24) One advantageous embodiment of the adhesive tapes obtained using an inventively crosslinked polyacrylate can be used as a strippable adhesive tape, more particularly a tape which can be detached again without residue by pulling substantially in the plane of the bond.

(25) The crosslinker-accelerator system of the invention or the crosslinker composition of the invention is also particularly suitable for producing three-dimensional shaped articles, whether they be tacky or not. A particular advantage of this process is that there is no restriction on the layer thickness of the polyacrylate to be crosslinked and shaped, in contrast to UV and EBC curing processes. In accordance with the choice of coating assembly or shaping assembly, therefore, it is possible to produce structures of any desired shape, which are then able to continue crosslinking to desired strength under mild conditions.

(26) This system or composition is also particularly suitable for the production of particularly thick layers, especially of pressure-sensitive adhesive layers or viscoelastic acrylate layers, with a thickness of more than 80 m. Layers of this kind are difficult to produce with the solvent technology, since, for example, this technology entails bubble formation and very slow coating speeds. The alternative lamination of thin layers one over another is complicated and harbours weak points.

(27) Thick pressure-sensitive adhesive layers may be present, for example, in unfilled form, as straight acrylate, or in resin-blended form or in a form filled with organic or inorganic fillers. Also possible is the production of layers foamed to a closed-cell or open-cell form in accordance with the known techniques, as well as of syntactic foams, using the crosslinker-accelerator system of the invention or the thermally crosslinkable composition of the invention. Possible methods of foaming are those of foaming via compressed gases such as nitrogen or CO.sub.2, or foaming via expandants such as hydrazines or expandable microballoons. Where expandable microballoons are used, the composition or the shaped layer is advantageously activated suitably by means of heat introduction. Foaming may take place in the extruder or after coating. It may be judicious to smooth the foamed layer by means of suitable rollers or release films. To produce foam-analogous layers it is also possible to add hollow glass beads or pre-expanded polymeric microballoons to the tacky, thermally crosslinked polyacrylate.

(28) In particular it is possible, using systems or compositions of the invention, to produce thick layers as well, which can be used as a carrier layer for double-sidedly PSA-coated adhesive tapes. With particular preference these are filled and foamed layers which can be utilized as carrier layers for foamlike adhesive tapes. With these layers as well it is sensible to add hollow glass beads, solid glass beads or expanding microballoons to the polyacrylate prior to the addition of the crosslinker-accelerator system or of the crosslinker or of the accelerator. It is possible to laminate a pressure-sensitive adhesive layer onto at least one side of a foamlike viscoelastic layer of this kind. It is preferred to laminate a corona-pretreated polyacrylate layer on both sides. Alternatively it is possible to laminate differently pretreated adhesive layers, i.e. pressure-sensitive adhesive layers and/or heat-activable layers based on polymers other than on acrylates, onto the viscoelastic layer. Suitable base polymers are adhesives based on natural rubber, synthetic rubbers, acrylate block copolymers, styrene block copolymers, EVA, certain polyolefins, specific polyurethanes, polyvinyl ethers, and silicones. Preferred compositions, however, are those which have no significant fraction of migratable constituents and whose compatibility with the polyacrylate is so good that they diffuse in significant quantities into the acrylate layer and alter the properties therein.

(29) Instead of laminating a pressure-sensitive adhesive layer onto both sides, it is also possible on at least one side to use a hotmelt-adhesive layer or thermally activable adhesive layer. Asymmetric adhesive tapes of this kind allow the bonding of critical substrates with a high bonding strength. An adhesive tape of this kind can be used, for example, to affix EPDM rubber profiles to vehicles.

(30) One particular advantage of the inventively crosslinked polyacrylates is that these layers, whether utilized as a viscoelastic carrier, as a pressure-sensitive adhesive or as a heat-sealing composition, combine an equal surface quality with no crosslinking profile through the layer (or, correspondingly, through the shaped article produced from the polyacrylates)in particular in contrast to UV-crosslinked and EBC-crosslinked layers. As a result it is possible for the balance between adhesive and cohesive properties to be controlled and set ideally for the layer as a whole through the crosslinking. In the case of radiation-crosslinked layers, in contrast, there is generally one side or one sublayer which is over- or undercrosslinked.

EXAMPLES

(31) Measurement Methods (General):

(32) K Value (According to Fikentscher) (Measurement Method A1):

(33) The K value is a measure of the average molecular size of high-polymer materials. It is measured by preparing one percent strength (1 g/100 ml) toluenic polymer solutions and determining their kinematic viscosities using a Vogel-Ossag viscometer. Standardization to the viscosity of the toluene gives the relative viscosity, from which the K value can be calculated by the method of Fikentscher (Polymer 1967, 8, 381 ff.)

(34) Gel Permeation Chromatography GPC (Measurement Method A2):

(35) The figures for the weight-average molecular weight M.sub.w and the polydispersity PD in this specification relate to the determination by gel permeation chromatography. Determination is made on a 100 l sample subjected to clarifying filtration (sample concentration 4 g/l). The eluent used is tetrahydrofuran with 0.1% by volume of trifluoroacetic acid. Measurement takes place at 25 C. The preliminary column used is a column type PSS-SDV, 5, 10.sup.3 , ID 8.0 mm 50 mm. Separation is carried out using the columns of type PSS-SDV, 5, 10.sup.3 and also 10.sup.5 and 10.sup.6 each with ID 8.0 mm300 mm (columns from Polymer Standards Service; detection by means of Shodex RI71 differential refractometer). The flow rate is 1.0 ml per minute. Calibration takes place against PMMA standards (polymethyl methacrylate calibration).

(36) Solids Content (Measurement Method A3):

(37) The solids content is a measure of the fraction of non-evaporable constituents in a polymer solution. It is determined gravimetrically, by weighing the solution, then evaporating the evaporable fractions in a drying cabinet at 120 C. for 2 hours and reweighing the residue.

(38) Measurement Methods (PSAs):

(39) 180 Bond Strength Test (Measurement Method H1):

(40) A strip 20 mm wide of an acrylate PSA applied to polyester as a layer was applied to steel plates which beforehand had been washed twice with acetone and once with isopropanol. The pressure-sensitive adhesive strip was pressed onto the substrate twice with an applied pressure corresponding to a weight of 2 kg. The adhesive tape was then removed from the substrate immediately with a speed of 300 mm/min and at an angle of 180. All measurements were conducted at room temperature.

(41) The results are reported in N/cm and have been averaged from three measurements. The bond strength to polyethylene (PE) was determined analogously.

(42) Holding Power (Measurement Method H2):

(43) A strip of the adhesive tape 13 mm wide and more than 20 mm long (30 mm, for example) was applied to a smooth steel surface which had been cleaned three times with acetone and once with isopropanol. The bond area was 20 mm.Math.13 mm (length.Math.width), the adhesive tape protruding beyond the test plate at the edge (by 10 mm, for example, corresponding to aforementioned length of 30 mm). Subsequently the adhesive tape was pressed onto the steel support four times, with an applied pressure corresponding to a weight of 2 kg. This sample was suspended vertically, with the protruding end of the adhesive tape pointing downwards.

(44) At room temperature, a weight of 1 kg was affixed to the protruding end of the adhesive tape. Measurement is conducted under standard conditions (23 C., 55% humidity) and at 70 C. in a thermal cabinet.

(45) The holding power times measured (times taken for the adhesive tape to detach completely from the substrate; measurement terminated at 10 000 min) are reported in minutes and correspond to the average value from three measurements.

(46) Microshear Test (Measurement Method H3):

(47) This test serves for the accelerated testing of the shear strength of adhesive tapes under temperature load.

(48) Sample Preparation for Microshear Test:

(49) An adhesive tape (length about 50 mm, width 10 mm) cut from the respective sample specimen is adhered to a steel test plate, which has been cleaned with acetone, in such a way that the steel plate protrudes beyond the adhesive tape to the right and the left, and that the adhesive tape protrudes beyond the test plate by 2 mm at the top edge. The bond area of the sample in terms of height.Math.width=13 mm.Math.10 mm. The bond site is subsequently rolled over 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.

(50) Microshear Test:

(51) The sample specimen for measurement is loaded at the bottom end with a weight of 100 g. The test temperature is 40 C., the test duration 30 minutes (15 minutes' loading and 15 minutes' unloading). The shear travel after the predetermined test duration at constant temperature is reported as the result in m, as both the maximum value [max; maximum shear travel as a result of 15-minute loading]; and the minimum value [min; shear travel (residual deflection) 15 minutes after unloading; on unloading there is a backward movement as a result of relaxation]. Likewise reported is the elastic component in percent [elast; elastic fraction=(maxmin).Math.100/max].

(52) Measurement Methods (Three-Layer Constructions):

(53) 90 Bond Strength to SteelOpen and Lined Side (Measurement Method V1):

(54) The bond strength to steel is determined under test conditions of 23 C.+/1 C. temperature and 50%+/5% relative humidity. The specimens were cut to a width of 20 mm and adhered to a steel plate. Prior to the measurement the steel plate is cleaned and conditioned. For this purpose the plate is first wiped down with acetone and then left to stand in the air for 5 minutes to allow the solvent to evaporate. The side of the three-layer assembly facing away from the test substrate was then lined with a 50 m aluminium foil, thereby preventing the sample from expanding in the course of the measurement. This was followed by the rolling of the test specimen onto the steel substrate. For this purpose the tape was rolled over 5 times back and forth with a rolling speed of 10 m/min using a 2 kg roller. Immediately after the rolling-on operation, the steel plate was inserted into a special mount which allows the specimen to be removed at an angle of 90 vertically upwards. The measurement of bond strength was made using a Zwick tensile testing machine. When the lined side is applied to the steel plate, the open side of the three-layer assembly is first laminated to the 50 m aluminium foil, the release material is removed, and the system is adhered to the steel plate, and subjected to analogous rolling-on and measurement.

(55) The results measured on both sides, open and lined, are reported in N/cm and are averaged from three measurements.

(56) Holding PowerOpen and Lined Side (Measurement Method V2):

(57) Specimen preparation took place under test conditions of 23 C.+/1 C. temperature and 50%+/5% relative humidity. The test specimen was cut to 13 mm and adhered to a steel plate. The bond area is 20 mm.Math.13 mm (length.Math.width). Prior to the measurement, the steel plate was cleaned and conditioned. For this purpose the plate was first wiped down with acetone and then left to stand in the air for 5 minutes to allow the solvent to evaporate. After bonding had taken place, the open side was reinforced with a 50 m aluminium foil and rolled over back and forth 2 times using a 2 kg roller. Subsequently a belt loop was attached to the protruding end of the three-layer assembly. The whole system was then suspended from a suitable device and subjected to a load of 10 N. The suspension device is such that the weight loads the sample at an angle of 179+/1. This ensures that the three-layer assembly is unable to peel from the bottom edge of the plate. The measured holding power, the time between suspension and dropping of the sample, is reported in minutes and corresponds to the average value from three measurements. To measure the lined side, the open side is first reinforced with the 50 m aluminium foil, the release material is removed, and adhesion to the test plate takes place as described. The measurement is conducted under standard conditions (23 C., 55% humidity).

(58) Commercially Available Chemicals Used

(59) TABLE-US-00001 Chemical compound Trade name Manufacturer CAS No. 2,2-Azobis(2-methylbutyronitrile) Vazo 67 DuPont 13472-08-7 2,2-Azobis(isobutyronitrile), AIBN Vazo 64 DuPont 78-67-1 Bis-(4-tert-butylcyclohexyl) Perkadox 16 Akzo Nobel 15520-11-3 peroxydicarbonate Terpene-phenolic-based tackifier Dertophene T105 DRT, France 73597-48-5 resin (softening point 105 C., hydroxyl value 30-60) Pentaerythritol tetraglycidyl ether Polypox R16 UPPC AG 3126-63-4 3,4-Epoxycyclohexylmethyl-3,4- Uvacure 1500 Cytec Industries 2386-87-0 epoxycyclohexanecarboxylate Inc. Dimethyl propanephosphonate Levagard DMPP Lanxess 18755-43-6 Bis-(2-dimethylaminoethyl) ether Jeffcat ZF-20 Huntsman 3033-62-3 trans-2-Aminocyclohexanol Sigma-Aldrich 5456-63-3 N,N,N-Trimethyl-N- Jeffcat ZF-10 Huntsman 83016-70-0 hydroxyethylbisaminoethyl ether Isophoronediamine Sigma-Aldrich 2855-13-2 N,N,N,N,N-Pentamethyl- Jeffcat ZR-40 Huntsman 3030-47-5 diethylenetriamine N-(3-(Dimethylamino)propyl)-N,N- Jeffcat Z-130 Huntsman 6711-48-4 dimethyl-1,3-propanediamine Diethylenetriamine Epikure 3223 Hexion Spec. 111-40-0 Chemicals N,N,N,N-Tetramethyl- Sigma-Aldrich 51-80-9 methanediamine Thermoplastic hollow microbeads Expancel 092 DU Akzo Nobel (particle size 10-17 m; density max. 40 0.017 g/cm.sup.3; expansion temperature 127-139 C. [start]; 164-184 C. [max. exp.]) all specification figures at 20 C.; Epikure also marketed under the tradenames Epi-Cure and Bakelite EPH

Pressure Sensitive Adhesive (PSA) Examples

Preparation of Starting Polymers for Examples B1 to B9

(60) Described below is the preparation of the starting polymers. The polymers investigated are prepared conventionally via free radical polymerization in solution.

(61) Base Polymer P1

(62) A reactor conventional for free-radical polymerizations was charged with 30 kg of 2-ethylhexyl acrylate, 67 kg of n-butyl acrylate, 3 kg of acrylic acid, 0.5 kg and 66 kg of acetone/isopropanol (96:4). After nitrogen gas had been passed through the reactor for 45 minutes with stirring, the reactor was heated to 58 C. and 50 g of 2,2-azobis(2-methylbutyronitrile) were added. Subsequently the external heating bath was heated to 75 C. and the reaction was carried out constantly at this external temperature. After 1 h a further 50 g of 2,2-azobis(2-methylbutyronitrile) were added, and after 4 h the batch was diluted with 20 kg of acetone/isopropanol mixture (96:4).

(63) After 5 h and again after 7 h, reinitiation took place with 150 g of bis(4-tert-butylcyclohexyl) peroxydicarbonate in each case. After a reaction time of 22 h the polymerization was terminated and the batch was cooled to room temperature. The polyacrylate has a conversion of 99.6%, a K value of 79.6, an average molecular weight of M.sub.w=1 557 000 g/mol, polydispersity PD (M.sub.w/M.sub.n)=12.6.

(64) Base Polymer P2

(65) A reactor conventional for free-radical polymerizations was charged with 47.5 kg of 2-ethylhexyl acrylate, 47.5 kg of n-butyl acrylate, 5 kg of acrylic acid, 150 g of dibenzoyl trithiocarbonate and 66 kg of acetone. After nitrogen gas had been passed through the reactor for 45 minutes with stirring, the reactor was heated to 58 C. and 50 g of AIBN were added. Subsequently the external heating bath was heated to 75 C. and the reaction was carried out constantly at this external temperature. After 1 hour a further 50 g of AIBN were added. After 4 h the batch was diluted with 10 kg of acetone. After 5 h and again after 7 h, 150 g each time of bis(4-tert-butylcyclohexyl) peroxydicarbonate were added. After a reaction time of 22 h the polymerization was terminated and the batch was cooled to room temperature.

(66) The polyacrylate has a conversion of 99.5%, a K value of 41.9 and an average molecular weight of M.sub.w=367 000 g/mol, polydispersity PD (M.sub.w/M.sub.n)=2.8.

(67) Base Polymer P3

(68) In the same way as for Example P1, 30 kg of 2-ethylhexyl acrylate, 67 kg of n-butyl acrylate and 3 kg of acrylic acid were polymerized in 66 kg of acetone/isopropanol (96:4). Initiation was carried out twice with 50 g each time of 2,2-azobis(2-methylbutyronitrile), twice with in each case 150 g of bis(4-tert-butylcyclohexyl) peroxydicarbonate, and dilution with 23 kg of acetone/isopropanol mixture (96:4). After a reaction time of 22 h the polymerization was terminated and the batch was cooled to room temperature.

(69) The polyacrylate has a conversion of 99.6%, a K value of 75.1 and an average molecular weight of M.sub.w=1 480 000 g/mol, polydispersity PD (M.sub.w/M.sub.n)=16.1.

(70) Base Polymer P4 (Viscoelastic Carrier)

(71) In the same way as in Example P1, 68 kg of 2-ethylhexyl acrylate, 25 kg of methyl acrylate and 7 kg of acrylic acid were polymerized in 66 kg of acetone/isopropanol (94:6). Initiation was carried out twice with 50 g of 2,2-azobis(2-methylbutyronitrile) in each case, twice with 150 g of bis(4-tert-butylcyclohexyl) peroxydicarbonate in each case, and dilution was carried out with 20 kg of acetone/isopropanol mixture (94:6). After a reaction time of 22 h the polymerization was terminated and the batch was cooled to room temperature.

(72) The polyacrylate has a conversion of 99.7%, a K value of 51.3 and an average molecular weight of M.sub.w=676 000 g/mol, polydispersity PD (M.sub.w/M.sub.n)=9.5.

(73) Process 1: Concentration/Preparation of the Hotmelt PSAs:

(74) The acrylate copolymers (base polymers P1 to P4) are very largely freed from the solvent by means of a single-screw extruder (concentrating extruder, Berstorff GmbH, Germany) (residual solvent content 0.3% by weight; cf. the individual examples). The parameters given here by way of example are those for the concentration of base polymer P1. The screw speed was 150 rpm, the motor current 15 A, and a throughput of 58.0 kg liquid/h was realized. For concentration, a vacuum was applied at 3 different domes. The reduced pressures were, respectively, between 20 mbar and 300 mbar. The exit temperature of the concentrated hotmelt is approximately 115 C. The solids content after this concentration step was 99.8%.

(75) Process 2: Preparation of the Modified Hotmelt PSAs and Viscoelastic Carriers:

(76) The acrylate hotmelt PSAs prepared in accordance with Process 1 as elucidated above were conveyed directly into a downstream Welding twin-screw extruder (Welding Engineers, Orlando, USA; model 30 mm DWD; screw diameter 30 mm, length of screw 1=1258 mm; length of screw 2=1081 mm; 3 zones). Via a solids metering system, the resin Dertophene T105 was metered in zone 1 and mixed in homogeneously. In the case of the composition for Examples MT 1, no resin was metered in; instead, the hollow thermoplastic microbeads, mixed to a paste with Levagard DMPP beforehand, were metered in via the solids metering system. The parameters given here by way of example are those for resin compounding with base polymer P1. The speed was 451 rpm, the motor current 42 A, and a throughput of 30.1 kg/h was realized. The temperatures of zones 1 and 2 were each 105 C., the melt temperature in zone 1 was 117 C., and the composition temperature on exit (zone 3) was 100 C.

(77) Process 3: Production of the Inventive Adhesive Tapes, Blending with the Crosslinker-Accelerator System for Thermal Crosslinking, and Coating:

(78) The acrylate hotmelt PSAs prepared by Processes 1-2 were melted in a feeder extruder (single-screw conveying extruder from Troester GmbH & Co. KG, Germany) and using this extruder were conveyed as a polymer melt into a twin-screw extruder (Leistritz, Germany, ref. LSM 30/34). The assembly is heated electrically from the outside and is air-cooled by a number of fans, and is designed such that, with effective distribution of the crosslinker-accelerator system in the polymer matrix, there is at the same time a short residence time ensured for the adhesive in the extruder. For this purpose the mixing shafts of the twin-screw extruder were arranged in such a way that conveying elements are in alternation with mixing elements. The addition of the respective crosslinkers and accelerators is made with suitable metering equipment, where appropriate at two or more points (FIG. 1: metering points 1.1 and 1.2) and, where appropriate, with the use of metering assistants into the unpressurized conveying zones of the twin-screw extruder. Following exit of the ready-compounded adhesive, i.e. of the adhesive blended with the crosslinker-accelerator system, from the twin-screw extruder (exit: circular die, 5 mm diameter), coating takes place in accordance with FIG. 1 onto a carrier material in web form.

(79) The time between metered addition of the crosslinker-accelerator system and the shaping or coating procedure is termed the processing life. The processing life indicates the period within which the adhesive, blended with the crosslinker-accelerator system, or the viscoelastic carrier layer, can be coated with a visually good appearance (gel-free, speck-free). Coating takes place with web speeds between 1 m/min and 20 m/min; the doctor roll of the 2-roll applicator is not driven.

(80) In the examples below and in Tables 1 and 3 to 4, the formulations employed, the production parameters and the properties obtained are each described in more detail.

Examples B1 to B4

(81) The base polymers P1 to P4 were polymerized in accordance with the polymerization process described, concentrated in accordance with Process 1 (solids content 99.8%) and then blended with the Dertophene T105 resin in accordance with Process 2. These resin-modified acrylate hotmelt compositions were then compounded in accordance with Process 3 continuously with the crosslinker-accelerator system consisting of a Pentaerythritol tetraglycidyl ether, in this case Polypox R16 from UPPC AG (epoxide)
and a Bis(2-dimethylaminoethyl) ether, In this case Jeffcat ZF-20 from HUNTSMAN (amine accelerator).

(82) Detailed description: In the twin-screw extruder described in Process 3, a total mass flow consisting of 70 parts of one of the polymers P1 to P4 and 30 parts each of Dertophene T105 resin of 533.3 g/min (corresponding to 373 grams of the pure polymer per minute) was blended with 0.70 g/min of the epoxide crosslinker pentaerythritol tetraglycidyl ether (corresponding to 0.19% by weight based on polymer) and with 3.71 g/min of the amine accelerator bis(2-dimethylaminoethyl) ether (corresponding to 1.0% by weight based on polymer). The epoxide was metered via a peristaltic pump at metering point 1.1, and the amine was metered separately via a peristaltic pump at metering point 1.2 (see FIG. 1). To improve meterability and the quality of mixing achievable, the crosslinker system used was diluted with the liquid dimethyl propylphosphonate Levagard DMPP from Lanxess (ratio of the crosslinker 0.5:1). The operational parameters are summarized in Table 3. The processing life of the completed compounded formulations was more than 7 minutes with an average composition temperature of 125 C. after departure from the Leistritz twin-screw extruder. Coating took place on a 2-roll applicator in accordance with FIG. 1, at roll surface temperatures of 100 C. in each case and with a coat weight each of 100 g/m.sup.2 onto 23 m PET film. On the adhesive tapes thus produced, measurements were made of the bond strength to steel at room temperature and microshear travel at 40 C. as a function of the storage time. After 14 days of room-temperature storage, the maximum microshear travel is not significantly different. The technical adhesive data of Examples B1 to B5 are summarized in Table 4. These examples show that very high-performance adhesive tapes can be produced, featuring, among other qualities, high bond strengths to polar and apolar substrates (steel and polyethylene) and good cohesive properties even under the influence of temperature.

(83) TABLE-US-00002 TABLE 1 Composition-specific details Compounding by Process 2 Substances and quantities % by weight Polymer K Value Crosslinker based on Example I base [ ] Polymer and adjuvants Accelerator polymer B1 P1 79.6 70 parts polymer P1 + Polypox R16 0.19 30 parts resin DT 105 Jeffcat ZF-20 1.0 B2 P2 41.9 70 parts polymer P2 + Polypox R20 0.19 30 parts resin DT 105 Jeffcat ZF-20 1.0 B3 P3 75.1 70 parts polymer P3 + Polypox R16 0.19 30 parts resin DT 105 Jeffcat ZF-20 1.0 B4 P4 51.3 70 parts polymer P4 + Polypox R16 0.19 30 parts resin DT 105 Jeffcat ZF-20 1.0 K value = measurement method A1 DT 105 = Dertophene T105
Comparison of the Room Temperature Kinetics of Various Accelerators (Examples B5 to B9)

(84) The following examples were carried out in each case with the polymer P3, with the epoxide crosslinker pentaerythritol tetraglycidyl ether (Polypox R 16 from UPPC, 0.19% by weight based on polymer) and with the resin Dertophene T105 (from DRT, 32% by weight based on polymer). The amount of accelerator was selected such that the number of activating basic groups is constant (see Table 2). Because of the different number of functionalities per molecule, there is therefore variation in the amount-of-substance concentration, based on the polyacrylate.

(85) The coat weight is 50 g/m.sup.2 in each case onto 23 m PET film. On the adhesive tapes produced in this way, measurements were made of the bond strength to steel at room temperature and microshear travel at 40 C. as a function of the storage time (selected examples of microshear travel are shown in FIG. 4). The technical adhesive data of Examples B5 to B9 are summarized in Table 4. Since operation was analogous to Example B3, the operational parameters are no longer explicitly listed.

(86) TABLE-US-00003 TABLE 2 Accelerator concentrations Amine groups/ 100 g Concentration polymer Example Accelerator [%] [mol] B5 bis(2-dimethylaminoethyl) ether 0.93 1.2 B6 trans-2-aminocyclohexanol 1.82 1.2 B7 N,N,N-trimethyl-N- 1.03 1.2 hydroxyethyl-bisaminoethyl ether Comparative diethylenetriamine 0.41 1.2 Example B8 Comparative N,N,N,N- 0.61 1.2 Example B9 tetramethylmethanediamine

(87) When the crosslinker-accelerator system of the invention is used, the crosslinking reaction proceeds to completion via the functional groups of the polyacrylate, even without supply of heat, under standard conditions (room temperature). Generally speaking, after a storage time of 7 days to 14 days, the crosslinking reaction has concluded to an extent such that an adhesive tape or carrier layer present is functional. The ultimate crosslinking state and hence the ultimate cohesion of the composition are achieved, depending on the choice of the composition/crosslinker system, after a storage time of 14 to 30 days, in advantageous form after 14 to 21 days' storage time at room temperature, expected to be earlier in the case of a higher storage temperature.

(88) As a result of the crosslinking there is an increase in the cohesion of the adhesive and hence also in the shear strength. The linking groups obtained are very stable. This allows very ageing-stable and heat-resistant self-adhesive tapes. It can be shown, moreover, that the choice of accelerator has virtually no influence on the technical adhesive properties but has a very great influence on the room-temperature kinetics (see FIG. 4 and also Table 4). Looking at Comparative Examples B8 and B9, it is apparent that within the aforementioned period of time, crosslinking is not yet concluded, and that gelling occurs in the operation beforehand unless the crosslinker-accelerator system of the invention is used.

(89) TABLE-US-00004 TABLE 3 Operational parameters Operational parameters Base polymer Target power Pressure Material K Compounding by Throughput TSE consumption at TSE temperature Coating Processing Example Polymer value Process 2 total mass speed TSE exit after TSE Doctor roll life [ ] [ ] [ ] Fraction of adjuvants TSE [kg/h] [1/min] [A] [bar] [ C.] roll DR CR [min] B1 P1 79.6 70 parts Polymer P1 + 32.0 110 15 12 125 100 100 greater 30 parts Resin DT 105 than 7 B2 P2 41.9 70 parts Polymer P2 + 32.4 110 7 5 108 100 100 greater 30 parts Resin DT 105 than 7 B3 P3 75.1 70 parts Polymer P3 + 32.0 110 15 12 125 100 100 greater 30 parts Resin DT 105 than 7 B4 P4 51.3 70 parts Polymer P4 + 33.0 110 11 13 117 100 100 greater 30 parts Resin DT 105 than 7 TSE = Twin screw extruder; DT 105 = Dertophene T105

(90) TABLE-US-00005 TABLE 4 Technical adhesive results Technical adhesive properties after specimen storage for 25 days at room temperature Base polymer Bond Bond Holding Hold K Coat strength strength power power MST 40 C./ Example Polymer value Compounding by Process 2 Carrier film weight to steel to PE 10N, 23 C. 10N, 70 C. elast. fract. [ ] [ ] [ ] Fraction of adjuvants [ ] [g/m.sup.2] [N/cm] [N/cm] [min] [min] [m]/[%] B1 P1 79.6 70 parts Polymer P1 + 23 m 100 9.8 4.2 >10.000 80 160/75 30 parts Resin DT 105 PET film B2 P2 41.9 70 parts Polymer P2 + 23 m 100 11.5 5.5 1.600 30 370/68 30 parts Resin DT 105 PET film B3 P3 75.1 70 parts Polymer P3 + 23 m 100 10.8 4.8 >10.000 680 120/67 30 parts Resin DT 105 PET film B4 P4 51.3 70 parts Polymer P4 + 23 m 100 7.4 2.9 >10.000 580 230/73 30 parts Resin DT 105 PET film B5 P3 75.1 68 parts Polymer P3 + 23 m 50 8.7 5.0 1.124 120 828/58 32 parts Resin DT 105 PET film B6 P3 75.1 68 parts Polymer P3 + 23 m 50 8.6 4.9 1.526 136 344/66 32 parts Resin DT 105 PET film B7 P3 75.1 68 parts Polymer P3 + 23 m 50 8.4 4.2 1.794 125 533/61 32 parts Resin DT 105 PET film B8 P3 75.1 68 parts Polymer P3 + 23 m 50 Tests not possible, (Comp.) 32 parts Resin DT 105 PET film formulation has gelled B9 P3 75.1 68 parts Polymer P3 + 23 m 50 Tests not possible, greater than (Comp.) 32 parts Resin DT 105 PET film formulation is not crosslinked 2000/0 Bond strength steel/PE = measurement method H1 Holding power = measurement method H2 MST = Microshear travel = measurement method H3 DT 105 = Dertophene T105 For the nature of the accelerator in Examples B5 to B9, see Table 2