MOISTURE-CURING RTV SILICONE COMPOSITION WITH HOMOGENEOUS DEEP-CURE

Abstract

A moisture-curing, condensation-crosslinking silicone composition that can be used as elastic adhesives and sealants. The silicone composition shows homogeneous depth curing, such that it cures through even under movement without forming cracks. The silicone composition contains at least one polyorganosiloxane having Si(OR.sup.3).sub.3 end groups, at least one condensation catalyst and at least one crosslinker having hydrolyzable radicals, characterized in that the polymer end groups Si(OR.sup.3) have a reaction rate in the crosslinking reaction that is at least equal to and preferably higher than the hydrolyzable radicals of the at least one crosslinker.

Claims

1. A moisture-curing silicone composition comprising a) at least one crosslinkable polydiorganylsiloxane of the general formula I ##STR00007## where R.sup.1, R.sup.2 and R.sup.3 are independently monovalent hydrocarbyl groups having 1-8 carbon atoms that may be substituted by F, N, P, O and/or S, Y is a divalent hydrocarbyl group having 1-8 carbon atoms, an oxygen atom or a group of the general formula (II) ##STR00008## where R.sup.3 has the definition given above and 1=1-5, and n is chosen such that the crosslinkable polydiorganylsiloxane has a viscosity at a temperature of 25° C. of 10-500,000 mPa s, b) at least one condensation catalyst c) at least one crosslinker having hydrolyzable radicals d) optionally fillers e) optionally further ingredients, wherein polydiorganylsiloxanes of the general formula (I) account for at least 90% of the total mass of polydiorganylsiloxane present, and the polymer end groups Si(OR.sup.3) of the at least one polydiorganylsiloxane of the general formula (I) have a reaction rate in the crosslinking reaction that is at least equal to or higher than the hydrolyzable radicals of the at least one crosslinker.

2. The moisture-curing silicone composition as claimed in claim 1, wherein the crosslinkable polydiorganylsiloxane is prepared in a condensation reaction from OH-terminated polydiorganylsiloxane.

3. The moisture-curing silicone composition as claimed in claim 1, wherein the crosslinkable polydiorganylsiloxane is prepared in a condensation reaction from OH-terminated polydiorganylsiloxane and a tetraalkoxysilane.

4. The moisture-curing silicone composition as claimed in claim 1, wherein the crosslinkable polydiorganylsiloxane is prepared in a hydrosilylation reaction.

5. The moisture-curing silicone composition as claimed in claim 1, wherein the crosslinkable polydiorganylsiloxane is prepared directly in the mixing unit, and the further ingredients are metered and mixed in on conclusion of this preparation, without workup and/or intermediate storage of the crosslinkable polydiorganylsiloxane.

6. The moisture-curing silicone composition as claimed in claim 1, wherein the condensation catalyst is a compound of an element of groups 1, 2, 4, 12, 14 or 15 of the Periodic Table of the Elements.

7. The moisture-curing silicone composition as claimed in claim 1, wherein the at least one crosslinker having hydrolyzable radicals is selected from compounds of the general formula (III)
R.sup.4.sub.mSiX.sub.4-m  (III) where R.sup.4 is independently a nonhydrolyzable monovalent hydrocarbyl radical having 1-18 carbon atoms, which is saturated or unsaturated and optionally has one or more functional groups containing the elements N, P, O and/or S, m is 0, 1, 2 or 3, X is independently an OH group, a linear or branched alkoxy group having 1-8 carbon atoms or a group of the general formula IV
N(SiR.sup.4.sub.m).sub.o(R.sup.5).sub.p(R.sup.6).sub.q  (IV) where R.sup.4 and m have the definitions given above, R.sup.5 is a hydrogen atom or a monovalent hydrocarbyl group having 1-8 carbon atoms and R.sup.6 is an acyl group having 1-9 carbon atoms, and o, p, q are 0, 1 or 2, with the proviso that o+p+q=2.

8. The moisture-curing silicone composition as claimed in claim 7, wherein the at least one crosslinker is selected from hydrolysis and/or condensation products of compounds of the general formula (III).

9. The moisture-curing silicone composition as claimed in claim 1, wherein fillers are selected from natural, ground or precipitated calcium carbonates or chalks, silicas, hydroxide, carbon black, barium sulfate, dolomite, siliceous earths, kaolin, hollow beads, quartz, calcined aluminum oxides, aluminum silicates, magnesium aluminum silicates, zirconium silicates, cristobalite flour, diatomaceous earth, mica, titanium oxide, zirconium oxide, gypsum, graphite, zeolites, ground glass, carbon fibers, polymer fibers or glass fibers, and have optionally been surface-modified.

10. The moisture-curing silicone composition as claimed in claim 1, wherein further comprising at least one component selected from the group consisting of OH-terminated polydimethylsiloxanes, plasticizers, adhesion promoters, curing accelerators, OH scavengers, desiccants, wetting aids, rheology modifiers, thixotropic agents, processing aids, biocides, UV stabilizers, heat stabilizers, flame retardants, color pigments, odorants, antistats, and emulsifiers.

11. The moisture-curing silicone composition as claimed in claim 1, wherein the composition is a one-component silicone composition.

12. A two-component silicone composition comprising (i) a component A that includes a) the at least one crosslinkable polydiorganylsiloxane of the general formula I ##STR00009## where R.sup.1, R.sup.2 and R.sup.3 are independently monovalent hydrocarbyl groups having 1-8 carbon atoms that may be substituted by F, N, P, O and/or S, Y is a divalent hydrocarbyl group having 1-8 carbon atoms, an oxygen atom or a group of the general formula (II) ##STR00010## where R.sup.3 has the definition given above and 1=1-5, and n is chosen such that the crosslinkable polydiorganylsiloxane has a viscosity at a temperature of 25° C. of 10-500,000 mPa s, b) optionally fillers c) optionally further ingredients and (ii) a component B that includes e) the at least one condensation catalyst f) the at least one crosslinker having hydrolyzable radicals g) optionally fillers h) optionally further ingredients.

13. (canceled)

14. A method of bonding or joining substrates with the two-component silicone composition claimed in claim 12, comprising: a) mixing component B into component A in order to obtain a mixture, b) applying the mixture to a substrate and contacting the mixture applied to the substrate with a further substrate in order to obtain an adhesive bond between the substrates, or introducing the mixture into a joint between two substrates in order to obtain a joint between the substrates, and c) curing the mixture.

15. A bonded or joined substrate obtainable by a method as claimed in claim 14.

16. A method of bonding or joining substrates with the moisture-curing silicone composition as claimed in claim 1, comprising: a) applying the composition to a substrate and contacting the composition applied to the substrate with a further substrate in order to obtain an adhesive bond between the substrates, or introducing the composition into a joint between two substrates in order to obtain a joint between the substrates, and c) curing the composition.

Description

EXAMPLES

[0103] Specific embodiments of the invention are described hereinbelow, but are not intended to limit the scope of the invention. The amounts are stated in phr (parts per hundred rubber) and are each based on 100 parts by mass of the polydiorganylsiloxane. All tests were conducted at 23° C. and 50% RH (relative humidity).

[0104] The proportions of the constituents for the silicone compositions given in the tables below were weighed out successively and mixed on a Hauschild SpeedMixer at 23° C. and 50% RH for 20 s at 2000 rpm with application of reduced pressure. The compositions obtained were sealed airtight, stored at 23° C. for 24 h and then tested.

[0105] In order to determine skin times (ST), the composition to be tested was painted on over an area of about 20 cm.sup.2 with a thickness of about 1 cm. It was ensured that the surface was smooth. The time of painting marked the commencement of the measurement. A PE pipette was used to touch the surface of the curing composition. The skin time was attained when the PE pipette was removable without any visible adhesion.

[0106] The through-curing time was determined using a Teflon wedge. This wedge was produced from a piece of Teflon of mass 340×30×30 mm. For this purpose, a wedge of mass 300×10 mm was machined out of the surface of this piece of Teflon, this wedge having a depth of 20 mm at one end—the deep end—and tapering to the surface of the piece of Teflon at the other—the flat end. The slope in the wedge is constant from one into the other. From the deep end, this wedge was filled with the composition to be tested. The surface was smoothed with a spatula. Through-curing was tested by pulling out the hardened composition from the flat end of the wedge until adhering material became visible on the base and/or walls of the wedge. The depth of through-curing was determined after 24 h, 3 d, 7 d.

[0107] Shore A hardness was determined after curing on a Shore A hardness tester from Bareiss in accordance with DIN ISO 7619-1 for 7 d. For determination of Shore A hardness, round test specimens having a diameter of 42 mm and a thickness of 6 mm were produced.

[0108] Tensile strengths and elongations at break were determined to ISO 37 on S2 dumbbells using a Zwick Z010 tensile tester. For this purpose, the compositions were knife-coated to give sheets of thickness 2 mm and cured for 7 d.

[0109] Curing under movement was measured by the method that follows. The silicone compositions were applied to a joint of dimensions 120×20×20 mm in a stainless steel mold that was movable about its middle and had a PE backer rod (radius 5 mm). The substrates were not pretreated. After the surfaces had been smoothed, the silicone composition was left to cure at 23° C./50% RH for 24 h. Then the joint was stretched with a spacer, or compressed. For this purpose, the spacer was mounted 60 mm from the middle and was 30 mm wide. It followed that the maximum stretch/compression of the silicone compositions was 75%. Curing of the silicone compositions was continued at 23° C./50% RH under stretching/compression for 24 h. Then the spacer was removed and reinserted at the opposite end of the joint. The joint was thus stretched, or compressed, by the same magnitude at the opposite end. The silicone compositions were cured in the loaded state at 23° C./50% RH for a further 4 days, then the spacer was removed and, after a further 24 h at 23° C./50% RH in the unladen state, the cured silicone composition was cut out and assessed visually for cracks in the silicone.

[0110] Abbreviations of chemicals used can be found in table 1 below. All polymers are based on linear polydimethylsiloxane (PDMS). All chemicals, unless stated otherwise, are commercially available in the chemicals trade (e.g. Sigma-Aldrich).

TABLE-US-00001 TABLE 1 Name Description Polymer 1 PDMS, 20'000 mPa s, end group capped with tetraethyl orthosilicate. The end groups are oligo(ethoxysilyl). Polymer 2 PDMS, 20'000 mPa s, end group capped with tetraethyl orthosilicate. The end groups are oligo(ethoxysilyl). Polymer 3 PDMS, 65'000 mPa s, with trimethoxysilylethyl end groups. The end groups are trimethoxysilylethyl. Polymer 4 PDMS, 50'000 mPa s, end group capped (Polymer NG 410 50 T from Wacker Chemie AG). The end groups are methyldimethoxysilyl. Polymer 5 PDMS, 80'000 mPa s, end group capped with a mixture of methyl-and vinyltrimethoxysilane (Polymer Al100 from Wacker Chemie AG). The end groups are vinyldimethoxysilyl and methyldimethoxysilyl. Silicone oil PDMS, 1'000 mPa s, with trimethylsilyl end groups (AK1000 silicone oil from Wacker Chemie AG). Crosslinker 1 Methyltrimethoxysilane Crosslinker 2 2-Aminoethyl-3-aminopropyltriethoxysilane Silylurea Bis(trimethylsilyl)urea, 50% in silicone oil (Alkoxy stabilizer from Wacker Chemie AG). Silica 1 Fumed silica, BET: 150 m2/g Silica 2 Fumed silica, BET: 200 m2/g, hydrophobized with HMDS GCC Ground chalk, untreated, d50: 5 μm Catalyst 1 Dibutyltin oxide, reaction product with tetraethoxysilane (catalyst 41 from Wacker Chemie AG) Catalyst 2 Dioctyltin dilaurate

[0111] The preparation of the catalysts used for synthesis of polymer 1 and polymer 2 is described in WO 2016/207156, in WO 2013/087680, and in WO 2015/193208.

Preparation of Polymer 1

[0112] 100 g of linear OH-PDMS having a viscosity of 20'000 mPa s was mixed with 9 g of tetraethyl orthosilicate. Added to this reaction mixture were 55 mg of 1-(2-hydroxy-3-(3-triethoxysilylpropoxy)prop-1-yl)-2-methyl-1,4,5,6-tetrahydropyrimidine and 1 g of zinc(II) bis(N,N-dibutyl-3-oxoheptanamidate). The mixture was stirred at 40° C. for 14 h. Subsequently, it was no longer possible to detect any gelation on addition of a few drops of tetra-n-propyl orthotitanate to a small sample of the polymer, which indicates the completeness of the reaction. The mixture was neutralized by adding 2 mg of neodecanoic acid. The resulting polymer is storage-stable and can be used further without further workup.

Preparation of Polymer 2

[0113] 100 g of linear OH-PDMS having a viscosity of 20'000 mPa s was mixed with 9 g of tetraethyl orthosilicate. Added to this reaction mixture were 33 mg of 1,1′-(α,ω-n-propyl-poly(dimethylsiloxane))bis(2,3-dicyclohexylguanidine) and 12 mg of catalyst 1 (see table 1). The mixture was stirred at 40° C. for 20 h. Subsequently, it was no longer possible to detect any gelation on addition of a few drops of tetra-n-propyl orthotitanate to a small sample of the polymer, which indicates the completeness of the reaction. The mixture was neutralized by adding 2 mg of neodecanoic acid. The resulting polymer is storage-stable and can be used further without further workup.

Preparation of Polymer 3

[0114] To 100 g of linear, vinyl-terminated PDMS having a viscosity of 65'000 mPa s was added 0.1 g of Karstedt's catalyst (Pt complex in xylene, Pt content 2%). The mixture was heated to 60° C., and 354 mg of trimethoxysilane was added dropwise. This was followed by heating to 80° C. and stirring of the mixture at this temperature for a further 4 h. A 1H NMR spectrum indicates the disappearance of the vinyl groups and hence completeness of the reaction. The resulting polymer is storage-stable and can be used further without further workup.

[0115] Tables 2 and 3 below contain overviews of the results.

TABLE-US-00002 TABLE 2 Example 4 Example 1 Example 2 Example 3 (comp.) Polymer 1 100 Polymer 2 100 100 Polymer 5 100 Silicone oil 15 15 15 15 Crosslinker 1 3.5 3.5 0.1 3.5 Crosslinker 2 0.66 0.66 0.66 0.66 Silica 1 8.7 8.7 8.7 8.7 GCC 57 57 57 57 Catalyst 1 0.6 0.6 0.6 0.6 Results SOT [min] 46 47 >24 h 14 Through-curing in the 4.5 5 0 5 wedge (1 d) Through-curing in the 7 7 7.5 9 wedge (3 d) Through-curing in the 12 12 12 13 wedge (7 d) Shore A (7 d) 33 26 33 29 Tensile strength 1.5 1.59 1.5 1.61 Elongation at break 250 297 250 390 Curing under movement OK OK OK cracked comp.: comparative example

TABLE-US-00003 TABLE 3 Example Example Example 5 Example 7 8 Example (comp.) 6 (comp.) (comp.) 9 Polymer 1 100 Polymer 3 100 Polymer 4 100 Polymer 5 100 100 Silicone oil 15 15 15 15 15 Crosslinker 1 3.5 3.5 3 0 0.1 Crosslinker 2 0.66 0.5 0.5 0.5 0.5 Silylurea 2.5 Silica 2 8.7 10 10 10 10 GCC 57 50 50 50 50 Catalyst 2 0.6 0.2 0.2 0.2 0.2 Results SOT [min] 32 40 n.d. 37 n.d. Through-curing in the 4.5 6 n.d. 9 n.d. wedge (1 d) Through-curing in the 7.5 10 n.d. 10 n.d. wedge (3 d) Through-curing in the >10 18 >10 n.d. 8 wedge (7 d) Shore A (7 d) 30 n.d. <10 n.d. 11 Tensile strength 1.6 1.16 n.m. 0.76 0.83 Elongation at break 360 442 n.m. 678 490 Curing under cracked OK Plastically Plastically OK movement deformed deformed comp.: comparative example n.d.: not determined n.m.: not measurable

[0116] It becomes clear from the results in the above tables 2 and 3 that compositions of the invention lead to good curing under movement. The use of noninventive polydiorganylsiloxanes having exclusively dialkoxysilyl-terminated siloxane chains leads to inhomogeneous depth curing and cracking or inadequate curing under movement. Interestingly, and surprisingly to the person skilled in the art, neither the assessment of elasticity on thin samples (as utilized for determination of tensile strength and elongation at break) nor the determination of through-curing time in a wedge permits any conclusion as to the homogeneity of depth curing and hence quality of curing under movement.