PROCESSES FOR PRODUCING VISCOUS EPOXY SYRUPS AND EPOXY SYRUPS OBTAINABLE THEREBY

Abstract

A process for producing a viscous epoxy syrup from at least one liquid multifunctional epoxy, comprising the steps of: adding an initiator selected from the group consisting of electron-poor monoisocyanate, photoinitiator and thermal initiator to at least one liquid multifunctional epoxy; mixing the components; polymerizing the multifunctional epoxy such that the viscosity of the resulting epoxy syrup is at least twice as high, preferably at least four times as high and in particular at least ten times as high as the viscosity of the employed epoxy in the unreacted state
makes it possible to produce epoxy adhesives having pressure-sensitive properties.

Claims

1-21. (canceled)

22. Epoxy adhesive obtained by a process comprising: providing an at least one liquid multifunctional epoxy; adding to the at least one liquid multifunctional epoxy an initiator selected from the group consisting of an electron-poor monoisocyanate, a photoinitiator, and a thermal initiator; mixing the at least one liquid multifunctional epoxy and the initiator; cationically polymerizing the at least one liquid multifunctional epoxy, thereby forming an epoxy syrup comprising an at least one uncrosslinked polyepoxy; and mixing the epoxy syrup with further components to form an epoxy adhesive, wherein: a viscosity of the epoxy syrup is at least twice as high as a viscosity of the at least one liquid multifunctional epoxy before the addition of the initiator; and the cationic polymerization is stopped upon reaching a desired viscosity by the addition of an initiator scavenger.

23. Epoxy adhesive according to claim 22, wherein the at least one liquid multifunctional epoxy is a bisepoxy.

24. Epoxy adhesive according to claim 22, wherein the at least one liquid multifunctional epoxy is a bisepoxycyclohexyl derivative or a bisepoxy based on bisphenol A, bisphenol S, or bisphenol F.

25. Epoxy adhesive according to claim 22, wherein: the initiator is selected from the group consisting of a photoinitiator and a thermal initiator; and the initiator is present in an amount of not more than 0.1 wt %.

26. Epoxy adhesive according to claim 22, wherein: the initiator is an electron-poor monoisocyanate; and the initiator is present in an amount of not more than 10 wt %.

27. Epoxy adhesive according to claim 26, wherein the initiator is selected from the group consisting of a p-tolyl isocyanate, an o-tolyl isocyanate, and a sulphonyl isocyanate.

28. Epoxy adhesive according to claim 26, wherein the process is carried out at a temperature between 20° C. and 120° C.

29. Epoxy adhesive according to claim 22, wherein the initiator scavenger comprises a mixture of water and acetone, a solution comprising an alkali metal hydroxide, a solution comprising an alkaline earth metal hydroxide, a solution comprising an alkali metal hydroxide, or a solution comprising an alkaline earth metal alkoxide.

30. Epoxy adhesive according to claim 22, wherein the epoxy syrup has a polydispersity D of at least 3.

31. Epoxy adhesive according to claim 22, wherein: the at least one liquid multifunctional epoxy is 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate; and the viscosity of the epoxy syrup is at least 1 Pa s (1000 mPs).

32. Adhesive tape comprising an epoxy adhesive according to claim 22.

33. Epoxy adhesive according to claim 22, wherein: the at least one liquid multifunctional epoxy comprises a plurality of original epoxy groups; and at least 65% of the plurality of original epoxy groups are present in the epoxy syrup.

34. Epoxy adhesive according to claim 22, wherein the viscosity of the epoxy syrup is at least 10 Pa s.

35. Epoxy adhesive according to claim 22, wherein the epoxy syrup has a weight-average molecular weight Mw in the range of 5,100 to 78,400 g/mol.

36. Epoxy adhesive according to claim 22, wherein the at least one uncrosslinked polyepoxy has a molecular weight of from 2,000 to 300,000 g/mol.

37. Viscous epoxy syrup comprising an at least one multifunctional epoxy monomer and an at least one uncrosslinked multifunctional polyepoxy prepared from the at least one multifunctional polyepoxy monomer by cationic polymerization, wherein: a viscosity of the viscous epoxy syrup is at least twice as high as a viscosity of a syrup of the at least one multifunctional epoxy monomer; and the cationic polymerization was stopped upon reaching a desired viscosity.

38. The viscous epoxy syrup according to claim 37, wherein the viscosity of the viscous epoxy syrup is at least 10 Pa s.

39. The viscous epoxy syrup according to claim 37, wherein the viscous epoxy syrup has a weight-average molecular weight Mw in the range of 5,100 to 78,400 g/mol.

40. The viscous epoxy syrup according to claim 37, wherein the at least one uncrosslinked multifunctional polyepoxy has a molecular weight of from 2,000 to 300,000 g/mol.

41. Process for producing an epoxy adhesive comprising: providing an at least one liquid multifunctional epoxy; adding to the at least one liquid multifunctional epoxy an initiator selected from the group consisting of an electron-poor monoisocyanate, a photoinitiator, and a thermal initiator; mixing the at least one liquid multifunctional epoxy and the initiator; cationically polymerizing the at least one liquid multifunctional epoxy, thereby forming an epoxy syrup comprising an at least one uncrosslinked polyepoxy; and mixing the epoxy syrup with further components to form an epoxy adhesive, wherein: a viscosity of the epoxy syrup is at least twice as high as a viscosity of the at least one liquid multifunctional epoxy before the addition of the initiator; and the cationic polymerization is stopped upon reaching a desired viscosity by the reduction of the temperature at which the epoxy syrup is formed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG. 1 shows the molecular weight distribution of Uvacure syrups polymerized over time periods of different durations.

[0045] FIG. 2 shows that even at 80° C. virtually no further polymerization still takes place while without addition of an initiation scavenger the polymerization proceeds vigorously.

EXAMPLES

[0046] Methods of Measurement

[0047] Viscosity Measurement:

[0048] Dynamic viscosity is a measure for the flowability of the fluid coating material. Dynamic viscosity may be determined according to DIN 53019. A viscosity of less than 10.sup.8 Pa.Math.s is described as a fluid. Viscosity is measured in a cylindrical rotational viscometer with a standard geometry according to DIN 53019-1 at a measurement temperature of 23° C. and a shear rate of 1 s.sup.−1.

[0049] Molecular Weight Distribution:

[0050] The molecular weight determinations for the number-average molecular weights M.sub.n and the weight-average molecular weights M.sub.w were effected by means of gel permeation chromatography (GPC). The eluent employed was THF (tetrahydrofuran) comprising 0.1 vol % of trifluoroacetic acid. The measurement was effected at 25° C. A PSS-SDV 10μ ID 8.0 mm×50 mm precolumn was employed. PSS-SDV 10μ ID 8.0 mm×300 mm columns were used for separation. The sample concentration was 1.5 g/l and the flow rate was 0.5 ml per minute. Measurements were performed against poly(methyl methacrylate) standards.

[0051] The values reported in this document for the number-average molar mass M.sub.n, the weight-average molar mass M.sub.w and the polydispersity relate to the determination by gel permeation chromatography (GPC)/the evaluation of such measurements.

[0052] Materials Employed:

TABLE-US-00001 Uvacure 1500 cycloaliphatic bisepoxy from Cytec ((3,4-epoxycyclohexane) methyl 3,4-epoxycyclohexylcarboxylate) Epon Resin 828 difunctional bisphenol-A/epichlorohydrin liquid epoxy having a weight per epoxy of 185-192 g/eq from Momentive. p-toluenesulphonyl electron-poor monoisocyanate isocyanate (TSI) TAG-2678 ammonium blocked trifluoromethanesulphonic acid from King Industries. triarylsulphonium cationic photoinitiator from hexafluoroantimonate Sigma-Aldrich The photoinitiator has an absorption maximum in the range from 320 nm to 360 nm and was provided as a 50 wt % solution in propylene carbonate

Example 1: Initiation with Electron-Poor Monoisocyanates

[0053] In a 21 polymerization reactor 1 kg of Uvacure 1500 was heated to 85° C. under a nitrogen atmosphere. The Uvacure 1500 has a viscosity of 0.25 Pa s. The initiator was added in countercurrent with nitrogen and the solution was stirred slowly.

[0054] To enable determination of the molecular weight distributions and viscosities, samples were taken at different reaction times during the reaction and analyzed by means of GPC and viscometry.

TABLE-US-00002 TABLE 1 GPC results for inventive epoxy syrups initiated with TSI amount of TSI Mw Mn reaction time temperature [%] [g mol.sup.−1] [g mol.sup.−1] D [h] [° C.] 6 13 500 780 17.4 3.25 100 6 11 100 740 15.1 4.25 100 6 22 000 790 27.9 5.25 100 7 22 500 830 27.3 1.0 100 7 59 700 830 71.7 2.25 100 7 78 400 850 92 3.75 100 7.4   5100 630 8 0.5 100 7.4   6000 600 9.9 1 100 7.4 16 100 650 24.8 3.3 100

[0055] It is apparent that polydispersity increases with increasing reaction time. For the substances used in the example there is a reaction rate maximum at an amount of TSI of 7 wt %. The use of a greater amount of initiator does not result in higher reaction rates here.

TABLE-US-00003 TABLE 2 viscosities of inventive epoxy syrups initiated with TSI amount of TSI reaction time viscosity [%] [min] [Pa s] 6 30 10.9 6 60 40 6 90 67.2 6 130 132 6 180 203 6 230 334 7 30 39.6 7 60 115 7 90 230 7 120 420 7 190 1536 7 210 1956

[0056] It is readily apparent also from table 2 that a greater amount of initiator causes the reaction to proceed markedly more rapidly and that a viscosity increase is achieved very much more rapidly.

[0057] FIG. 1 shows the molecular weight distribution of Uvacure syrups polymerized over time periods of different durations. What is striking is the enormously broad distribution containing many molecules smaller than 1000 g/mol but also chains of in some cases up to greater than 10.sup.6 g/mol which bring about the high viscosity.

[0058] Stopping the Reaction

[0059] After the desired viscosity has been reached the reaction is stopped by adding an amount of a water-acetone mixture equal to the amount of initiator (1:1 ratio) as initiation scavenger. FIG. 2 shows that even at 80° C. virtually no further polymerization still takes place while without addition of an initiation scavenger the polymerization proceeds vigorously.

Example 2: Initiation with Highly-Dilute Photoinitiators

[0060] In a 21 glass reactor a photoinitiator (triarylsulphonium hexafluoroantimonate) was added to 1 kg of Epon Resin 828 under exclusion of light and under a nitrogen atmosphere at 23° C. with stirring (50 rpm). Initiation of the reaction was effected by 2-minute irradiation with 4 medium pressure Hg lamps positioned radially around the polymerization reactor.

[0061] To enable determination of the viscosities, samples were taken at different reaction times during the reaction and analyzed by means of GPC and viscometry.

TABLE-US-00004 TABLE 3 viscosities of inventive epoxy syrups initiated with triarylsulphonium hexafluoroantimonate amount of photoinitiator viscosity after 120 h [%] [mPa s] 0.004 500 0.01 860 0.02 1300

[0062] It is apparent that markedly smaller amounts of initiator are required and that for a given reaction time viscosities increase with increasing amount of initiator.

Example 3: Initiation with Highly-Dilute Thermal Initiators

[0063] 0.02% of TAG-2678 was added to a 30% solution of Uvacure 1500 in toluene and the mixture was heated under reflux. After the desired reaction time the cooling was deactivated and the solvent removed. As in the other examples a completely transparent colourless epoxy syrup was obtained. Even after 1 h of reaction time, viscosities more than double the viscosity of the reactant were measured.

[0064] Example 3 shows that with thermal initiators too, viscous epoxy syrups can be prepared in solution and without protective gas.