Sealing mass based on mercapto-terminated base polymer/epoxy compound and method for hardening by means of a photolatent catalyst

Abstract

The present invention relates to a sealing compound for coating a substrate, which is a mixture of a predominantly uncured base mass and a curing agent containing at least one epoxy composition, wherein the base mass contains a mercapto-terminated base polymer based on polyether, polythioether, polythioethersulfide, polysulfide, copolymers thereof and/or mixtures thereof, wherein the base mass, the curing agent or both contain at least one photoinitiator based on a sterically hindered nitrogen-containing organic base, and, through the effects of high-energy actinic radiation, the at least one photoinitiator dissociates at least one radical per molecule based on a nitrogen-containing organic base, from which a nitrogen-containing organic base having a pKa value of the conjugated acid in the region of 6 to 30 is formed, which acts as an active catalyst for the curing of the base mass. The present invention also relates to a corresponding method for coating a substrate with a sealing compound.

Claims

1. A sealing compound for coating a substrate, comprising a mixture of a predominantly uncured base mass and a curing agent comprising at least one epoxy composition, the base mass comprises a mercapto-terminated base polymer, based on polyether, polythioether, polythioethersulfide, polysulfide, copolymers thereof or mixtures thereof, the base mass, the curing agent or both comprises at least one photoinitiator based on a sterically hindered nitrogen-containing organic base, wherein a molar excess of epoxy composition in the range from 1.05 to 2 with respect to 1 mole of reactive SH-groups relative to the total content of mercapto-terminated base polymer is present, and, through the effects of high-energy actinic radiation, the at least one photoinitiator cleaves at least one radical per molecule based on a nitrogen-containing organic base, from which a nitrogen-containing organic base having a pKa value of the conjugated acid in the region of 6 to 30 is formed, which acts as an active catalyst for the curing of the base mass.

2. The sealing compound of claim 1, characterized in that it has a tack-free time, according to DIN 65262-1, in the range from 0.01 to 10 minutes after starting a high-energy actinic irradiation.

3. The sealing compound of claim 1, characterized in that the base mass is essentially based on at least one liquid polyether composition, which carries at the ends of molecules one respective mercapto-group, and which, optionally, contains up to about 50 mol % of disulfide groups within the molecule (polythioethersulfide).

4. The sealing compound of claim 3, characterized in that the base mass contains, in addition to the at least one liquid polythioether composition, at least one disulfide-containing composition with a percentage on base mass of up to 80 wt.% .

5. The sealing compound of claim 1, characterized in that the base polymer comprises mercapto-terminated polysulfide polymers, mercapto-terminated polythioether, mercapto-terminated polythioethersulfide, or combinations thereof, which comprise long-chain polymers with a molecular weight in particular in the range from 2500 to 6000 g/mol and short chain polymers with a molecular weight in particular in the range from 500 to 2500 g/mol, wherein the ratio of the long-chain polymers to the short chain polymers is from 25:1 to 0.5:1.

6. The sealing compound of claim 1, characterized in that the base polymer comprises a proportion of mercaptan related to reactive SH-groups with respect to the total base polymer in the range from 0.5 to 10 wt.% , a total sulfur content in the range from 1 to 50 wt.%, and an average functionality of reactive end groups of mercapto-groups per molecule in the range from 1.5 to 2.5.

7. The sealing compound of claim 1 , characterized in that the at least one epoxy composition is based on epoxy novolac resins, bisphenol A-epoxy resins, bisphenol F-epoxy resins or combinations thereof.

8. The sealing compound of claim 7, characterized in that the at least one epoxy composition is based on bisphenol A-epoxy resins with an epoxy equivalent weight in the range from 170 to 200 g/eq, based on bisphenol F-resin with an epoxy equivalent weight in the range from 150 to 180 g/eq, based on epoxy novolac resins with an epoxy equivalent weight in the range from 160 to 220 g/eq or a combination thereof.

9. The sealing compound of claim 1, characterized in that the at least one epoxy composition comprises 1,4-butandiol-diglycidyl ether, 2-ethyl-hexyl-glycidether, 1,6-hexandioldiglycidyl ether (reactive thinner) or a combination thereof.

10. The sealing compound of claim 1, characterized in that the pKa value of the conjugated acid of the nitrogen-containing organic base, lies in the range from 7 to 280.

11. The sealing compound of claim 1, characterized in that the at least one photoinitiator is a sterically hindered tertiary amine, a sterically hindered amidine, a sterically hindered guanidine, or a combination thereof.

12. The sealing compound of claim 11, characterized in that the at least one photoinitiator is added in a quantity which corresponds to a proportion of 0.05 to 5 wt.% with respect to the sealing compound.

13. The sealing compound of claim 11 , characterized in that the at least one photoinitiator is a photolatent 1 ,5-diazabicyclo[4.3.0]non-5-en (DBN), a photolatent 1,8-diazabicyclo[5.4.0]undec-7-en (DBU), a photolatent TMG (tetramethylguanidine), a photolatent triethylendiamine (1 ,4-diazabicyclo[2.2.2]octane), or a combination thereof.

14. The sealing compound of claim 1, further comprising an additional, free catalyst, which is a free nitrogen-containing organic base with a pKa value of the conjugated acid in the range from 6 to 30 and said additional free catalyst is a free tertiary amine, a free amidine, a free guanidine, or a combination thereof.

15. The sealing compound of claim 14, characterized in that the free catalyst is selected from the group consisting of 1,4-dimethylpiperazine, N-methylmorpholine, 2,2-dimorpholinodiethylether, tris-(dimethylaminomethyl-phenol), triethylendiamine, and TMG.

16. The sealing compound of claim 1, further comprising a photosensitizer.

17. A method for coating a substrate with a sealing compound, said method comprising coating a substrate with the sealing compound of claim 1, irradiating said sealing compound with high energy actinic radiation, and curing said sealing compound thereby coating said substrate.

18. The method of claim 17, characterized in that the high-energy actinic radiation has a wavelength in the range from 315 to 600 nm.

19. The method of claim 17, characterized in that the curing is performed at a temperature of from 10 to 40 C.

20. An aircraft containing components which are sealed with a sealing compound of claim 1.

21. The sealing compound of claim 1, wherein said substrate is a component, for construction and/or maintenance of aerospace vehicles, for cars and railway vehicles, in shipbuilding, in the mechanical industry, in the civil building industry, for casting resin or for production of cast resins for the electric and electronic industry.

22. The method of claim 17, wherein said substrate is a component in the transportation industry, in the automobile industry, in the railway vehicle construction sector, in shipbuilding, in the construction of aircraft or in the spacecraft industry, in the mechanical sector, in the civil building industry or for the manufacturing of furniture.

Description

EXAMPLES AND COMPARATIVE EXAMPLES

(1) The object of the invention is explained in the following by means of exemplary embodiments.

(2) General Production and Testing Specifications for the Inventive Sealing Compounds:

(3) The basic composition of the invention was prepared by first mixing polysulfide polymers such as Thiokol LP 12, Thioplast G 10 and/or Thioplast G131, and/or polythioether polymers and/or polythioethersulfide polymers and/or polyetherpolymers, at least one photoinitiator based on hindered tertiary amine and/or amidine and/or guanidine, at least one photosensitizer, based on benzophenone and/or isopropyl, a thixotropic agent, such as on the basis of sepiolite, and an adhesion promoter such as based on a phenol resin or based on organofunctional alkoxysilane, for 10 minutes under vacuum of <50 mbar and under cooling of a planetary dissolver with cooling water at a speed of about 2000 rpm. Subsequently, the remaining fillers, such as those based on magnesium silicate hydrates, aluminum silicates, calcium silicates, polyamides and/or polyethylene waxes, and antioxidants, such as those based on phosphorous acid ester, were added for a further 10 to 20 minutes under vacuum of <50 mbar by planetary dissolver, dispersed at a speed of about 2000 rpm. The polysulfide, polythioethers, polythioethersulfides, polyether copolymers and their copolymers were always mercapto-terminated.

(4) For good dispersion of the base mass, in particular speed ranges from 1800 to 2200 rpm and times of 30 to 40 minutes depending on the composition, rheological properties and on apparatus equipment are suitable.

(5) The curing agent according to the invention was prepared by mixing the epoxy compounds with the thixotropic agent on the basis of fumed silica Aerosil R202 under vacuum of <50 mbar using a planetary dissolver at a speed of about 2000 rpm.

(6) For compaction, filling and/or coating of structural parts and for the manufacture of test specimens, the base mass and curing agent were mixed at a ratio of 100:5 to 100:7, and then activated by high-energy actinic radiation. The sealing compounds of the invention were cured even without high-energy actinic radiation, wherein, depending on layer thickness, a curing time in the range from 24 to 168 hours with layer thicknesses in the range from 0.2 to 6 mm was required.

(7) The mechanical properties of sealing compounds, such as Shore A hardness determined according to ISO 7619-1, tensile strength and elongation determined according to ISO 37 were determined after the sealing compound had been stored for 7 days in air at an ambient air temperature of 23 C. and relative humidity of 50%. After mixing of the base mass with the curing agent, the sealing compound was immediately applied on a substrate with the curing agent in air, the sealing compound on a substrate and then immediately irradiated with high-energy actinic radiation. From then on, it was stored in air.

(8) To activate the sealing compound, normally, a UV surface emitter with a Fe-doped Hg lamp was used at a power of 400 W. Herein, for curing of the actinically activated coatings, all commercially available UV light sources, including ultraviolet light-emitting diodes and fluorescent lamps, or electron beam sources are suitable. The sealing compounds can be cured at a wavelength in the range 315 to 600 nm, such as with UVA and/or UV/VIS.

(9) The formulations listed in Table 4 of the inventive examples were prepared in order to determine the influence of three different photoinitiators on the processing properties of the uncured base mass and on the curing sealing compound, as well as on the mechanical properties of the sealing compound. The basic compositions of the invention and the curing agent compositions were prepared as in all the other examples according to the prescriptions. Both partial mixtures were homogeneously mixed in a mass ratio of 100:5 with a layer thickness of 2 mm on sheets of aluminum alloy by extrusion from a mixer cartridge, applied at about 23 C. and subsequently irradiated with an Fe-doped UV surface radiator at wavelengths in the range from 300 to 600 nm, with a UV dose of about 10 J/cm.sup.2 and with a UV intensity of 0.3 W/cm.sup.2 at a distance of 10 cm for over 40 s. Here, the curable coating warmed slightly, though it didn't reach 60 C.

(10) Subsequently, the cured sealing compounds were removed from the test mold and stored for 7 days at 232 C. at 505% relative humidity in air, before the mechanical properties such as hardness, elongation and tensile strength were determined. After storage in air, subsequently a storage in various other media took place, see Table 7 below.

(11) As a photoinitiator 1, 2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one was used. As a photoinitiator 2, 2-benzyl-2-dimethyl-amino-1-(4-morpholinophenyl)-butanone-1 was used. As photoinitiator 3, a sterically hindered DBN was used. As an additional catalyst, triethylene diamine was used. As the curing agent, a mixture of a bisphenol A epoxy resin having an epoxy equivalent weight of 180-195 g/eq and a viscosity of 10-15 Pas (available as Epikote 828 or DER 331) and reactive diluent based on 1,4-butanediol diglycidyl ether were used. The mixture ratio of bisphenol A epoxy resin and reactive diluent was 4:1. The measured properties of the examples are listed in Table 5 below.

(12) Comparative Example 1 (CE1) does not contain a photoinitiator, and was prepared for better comparison of the effects of the individual photoinitiators. The comparative examples 2 and 3 (CE2 and CE3) contain, as photoinitiators, sterically hindered tertiary amines, which, however, after activation with UV light, have a too low basicity to initiate and/or accelerate the curing reaction. Therefore, here, no advantage can be seen in comparison to VB1. Surprisingly, Example 1 (B1) shows a significantly accelerated reaction due to the use of the sterically hindered DBN. Accordingly, the sterically hindered DBN seems to have sufficiently high basicity to catalyze the reaction between the SH-groups and the epoxy groups.

(13) TABLE-US-00004 TABLE 4 Composition of VB1 to VB3 and B1 example Content (wt.-%) VB1 VB2 VB3 B1 Base mass Polythioethersulfide 1 71.6 69.7 69.7 69.7 (3500-4400 g/mol) Photoinitiator 1 1 Photoinitiator 2 1 Photoinitiator 3 1 1,4-dimethylpiperazine 0.4 0.4 0.4 0.4 Photosensitizer: benzophenone 0.9 0.9 0.9 Filler aluminum silicate 22.0 22.0 22.0 20.2 Adhesion promoter 1.0 1.0 1.0 1.0 mercaptopropyl trimethoxysilane Thixotropic agent; sepiolite 3.0 3.0 3.0 3.0 Anti-ageing agent phosphorous 2.0 2.0 2.0 2.0 acid ester Sum 100 100 100 100 Curing agent Bisphenol A-epoxy resin 78.4 78.4 78.4 78.4 1,4-butandioldiglycidyl ether 19.6 19.6 19.6 19.6 Fumed silica 2 2 2 2 Sum 100 100 100 100 Mixing ratio base mass/curing 100:5 100:5 100:5 100:5 agent

(14) TABLE-US-00005 TABLE 5 Properties of VB1 to VB3 as well as B1 example Properties VB1 VB2 VB3 B1 Processing time (min) 120 120 120 60 Tack-free time (min) 405 415 410 5 Through-hardening time for 535 540 535 90 initial hardness Shore A 30 (min) Shore A hardness after 48 49 48 47 7 days RT Tensile resistance (MPa) 1.85 1.89 1.83 1.92 after 7 days RT Elongation (%) after 7 days 398 391 401 397 RT

(15) In the following example 2 (B2) and in the comparative example 4 (VB4) an inventive formulation with the conventional manganese-dioxide curing sealing compound MC-780 B-1/2 is compared, which is commercially available. B2 is once activated by UV light, and a second time it is not activated by UV light. Table 6 shows the composition of these formulations. Table 7 shows properties of these sealing compounds. It can be clearly seen that both sealing compounds have the same processing time. Surprisingly, the inventive sealing compound reaches the tack-free state in a much shorter time as well as the initial hardness of 30 Shore A, with respect to MC-780 B-1/2, if it was previously activated by UV light. Otherwise, the sealing compound still reaches its end properties, although after a much longer time. The inventive sealing compound surprisingly has good mechanical properties even after storage in various mediums and higher temperatures, such as in case of storage in water at 35 C. or in fuel at 60 C. or 100 C.

(16) TABLE-US-00006 TABLE 6 Composition of B2 and VB4 example Content (wt.-%) B2 VB4 Base mass Base mass MC-780 B-1/2 100 Polythioethersulfide 1 47.3 (3500-4400 g/mol) Polythioethersulfide 2 20.5 (1500-2400 g/mol) Photoinitiator 3 1.5 1,4-dimethylpiperazine 0.6 Photosensitizer: 1.3 isopropylthioxanthone Filler feldspar 22.0 Adhesion promoter 1.5 mercaptopropyl trimethoxysilane Thixotropic agent; sepiolite 3.2 Anti-ageing agent phosphorous 2.1 acid ester Sum 100 100 Curing agent Curing agent MC-780 B-1/2 100 Bisphenol A-epoxy resin 78.4 1,4-butandioldiglycidyl ether 19.6 Fumed silica 2 Sum 100 100 Mixing ratio base mass/curing 100:7 100:10 agent

(17) TABLE-US-00007 TABLE 7 Comparison of properties of B2 and VB4 example B2 B2 with without activated activated Properties UV light UV light VB4 Processing time (min) 30 30 30 Tack-free time (min) 5 510 240 Through-hardening time for 40 970 480 initial hardness Shore A 30 (min) Shore A hardness after 7 days 53 53 50 RT Tensile resistance (MPa) after 2.20 2.18 1.5-2.2 7 days RT Elongation (%) after 7 days RT 318 323 300-400 Tensile resistance (MPa) after 2.12 2.09 1.5-2.0 168 hours at 60 C., fuel storage Elongation (%) after 168 hours 309 312 300-400 at 60 C., fuel storage Tensile resistance (MPa) after 1.85 1.87 1.5-2.0 300 hours at 100 C., fuel storage Elongation (%) after 300 hours 252 257 300-400 at 100 C., fuel storage Tensile resistance (MPa) after 1.91 1.89 1.0-1.5 1000 hours at 35 C., water storage Elongation (%) after 1000 298 295 300-400 hours at 35 C., water storage

(18) It is also possible to use an inventive sealing compound without an additional sterically not hindered catalyst in the formulation, see examples 6 and 7 (B3 and B4). Table 8 shows the composition of these examples and table 9 the measured properties. It can be clearly seen that the sealing compound curing speed is much slower without the additional sterically unhindered catalyst.

(19) In general, the highly valuable properties of conventional aircraft sealing compounds such as a high resistance to various mediums such as fuels at 60 C., measured after 168 hours and 100 C., for example, and the waterproofness at 35 C., measured after 1000 hours, the resistance to hydraulic liquids, condensed water, and anti-freeze liquid, high thermal resistance, high low temperature flexibility, high resistance to meteorological agents, high peeling resistance on different substrates, high elongation at rupture and high tensile strength may be substantially or completely achieved, in spite of the much shorter curing.

(20) TABLE-US-00008 TABLE 8 Composition of B3 and B4 example Content (wt.-%) B3 B4 Base mass Polythioethersulfide 1 50.1 49.6 (3500-4400 g/mol) Polythioethersulfide 2 15.8 15.8 (1500-2400 g/mol) Photoinitiator 3 2.3 2.3 1,4-dimethylpiperazine 0.0 0.5 Photosensitizer: benzophenone 1.0 1.0 Filler aluminum silicate 24.3 24.3 Adhesion promoter 1.6 1.6 mercaptopropyl trimethoxysilane Thixotropic agent; sepiolite 2.4 2.4 Anti-ageing agent phosphorous 2.1 2.1 acid ester Sum 100 100 Curing agent Bisphenol F-epoxy resin 80.2 80.2 1,4-butandioldiglycidyl ether 17.6 17.6 Fumed silica 2.2 2.2 Sum 100 100 Mixing ratio base mass/curing 100:6 100:6 agent

(21) TABLE-US-00009 TABLE 9 Properties of B3 and B4 example Properties B3 B4 Processing time (min) 120 20 Tack-free time (min) 5 5 Through-hardening time for 490 30 initial hardness Shore A 30 (min) Shore A hardness after 45 46 7 days RT Tensile resistance (MPa) 1.76 1.80 after 7 days RT Elongation (%) after 7 days 357 345 RT