UV-curable silicone composition

Abstract

The present invention relates to a composition comprising a) one or more compounds of Formula 1: b) polyorganosiloxane functionalized with at least two alkenyl groups; c) an alkylthiol functionalized polyorganosiloxane; d) tetraethyl orthosilicate; e) a condensation catalyst; and f) a photoinitiator; where X is a double bond and / or -CH2CH2-Si(CH3)2OSi(CH3)2-CH2CH2-Si(OCH3)3. The composition of the present invention is useful for forming fast cure UV-curable coatings with excellent adhesive strength.

Description

[0001] UV-Curable Silicone Composition

[0002] Background of the Invention

[0003] The present invention relates to a UV-curable silicone composition, more particularly a polyorganosiloxane composition containing adhesion promoters. The fast curing of silicones at room temperature is desirable and has been achieved by photoinitiator promoted UV cure alkylthiol functionalized polyorganosiloxanes. It has been observed, however, that the UV cured films of these polyorganosiloxanes exhibit poor adhesion (i.e., adhesive failure), or require long times to achieve acceptable adhesion (i.e., cohesive failure). It would therefore be desirable in the field of UV-curable silicone compositions to develop a fast curable composition with excellent adhesion.

[0004] Summary of the Invention

[0005] The present invention addresses a need in the art by providing a composition comprising: a) one or more compounds of Formula 1 :

[0006] Formula 1 b) a polyorganosiloxane functionalized with at least two alkenyl groups; c) an alkylthiol functionalized polyorganosiloxane; d) a tetra-Ci-C4-alkyl orthosilicate; e) a condensation catalyst; and f) a photoinitiator; where X is a double bond and / or -CH2CH2-Si(CH3)2OSi(CH3)2-CH2CH2-Si(OCH3)3.

[0007] The composition of the present invention provides a UV fast cure coating with excellent adhesive strength.

[0008] Detailed Description of the Invention

[0009] The present invention is a composition comprising: a) one or more compounds of Formula 1 :

[0010] Formula 1 b) a polyorganosiloxane functionalized with at least two alkenyl groups; c) an alkydthiol functionalized polyorganosiloxane; d) a tetra-Ci-C4-alkyl orthosilicate; e) a condensation catalyst; and f) a photoinitiator; where X is a double bond and / or -CH2CH2-Si(CH3)2OSi(CH3)2-CH2CH2-Si(OCH3)3- The compound of Formula 1 is typically used as a mixture of compounds of Formula la and

[0011] Formula lb:

[0012] Formula la Formula lb

[0013] The concentration of the one or more compounds of Formula 1 is preferably in the range of from 0.1 or from 0.2 or from 0.3 weight percent, to 5 or to 2 or to 1 weight percent, based on the weight of the composition.

[0014] The alkenyl groups may be endcapped or attached to the polymer backbone or both. An example of a preferred class of polyorganosiloxanes functionalized with at least two alkenyl groups is a divinyl polydimethylsiloxane of Formula 2:

[0015] Formula 2 where n is from 2 or from 10 or from 20 or from 50 or from 100, to 1000. The concentration of the dialkenyl functionalized polyorganosiloxane is preferably in the range of from 40 or from 50 or from 55 weight percent, to 80 or to 70 or to 65 weight percent, based on the weight of the composition. The alkylthiol functionalized polyorganosiloxane is a polyorganosiloxane functionalized with one or more alkyl thiol groups. A preferred class of alkylthiol functionalized polyorganosiloxanes is one or compounds of the following structure:

[0016] Formula 3 where R is a C3-Ci2-alkylthiol group; m is from 0 to 500 or to 100; and p is from 2 to 200 or to 100 or to 50 or to 20.

[0017] The concentration of the alkylthiol functionalized polyorganosiloxane is preferably in the range of from 1 or from 2 or from 3 weight percent to 20 or to 15 or to 10 weight percent, based on the weight of the composition.

[0018] The concentration of c, preferably tetraethylorthosilicate (TEOS) is preferably in the range of from 0.1 or from 0.2 or from 0.3 weight percent, to 5 or to 3 or to 1 weight percent, based on the weight of the composition. The composition of Formula 1 and TEOS in combination have been found to be effective adhesion promoters.

[0019] The condensation catalyst is used to accelerate cure speed. Examples of suitable condensation catalysts include titanium, zirconium, and tin condensation catalysts such as tetra(isopropoxy)titanium, tetra(n-butoxy)titanium, tetra(t-butoxy)titanium, di(isopropoxy)bis(ethylacetoacetate)titanium, di(isopropoxy)bis(methylacetoacetate)titanium, and di(isopropoxy)bis(acetylacetonate)titanium, tetra(isopropoxy)zirconium, tetra(n- butoxy)zirconium, tetrai / -butoxy )zirconium, di(isopropoxy)bis(ethylacetoacetate)zirconium, di(isopropoxy)bis(methylacetoacetate)zirconium, di(isopropoxy)bis(acetylacetonate)zirconium, dimethyltin dineodecanoate, dibutyltin dilaurate, and dibutyltin dioctoate.

[0020] The concentration of the condensation catalyst is preferably in the range of from 0.05 or from 0.1 or from 0.2 weight percent to 1 or to 0.5 weight percent, based on the weight of the composition. A photoinitiator refers to a compound that create reactive free radicals upon exposure to U V light. Examples of suitable photoinitiators include 2-hydroxy-2-methylpropiophenone, diethoxyacetophenone, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, diethoxyxanthone, chlorothioxanthone, azobisisobutyronitril, N-methyl diethanolaminebenzophenone 4,4'-bis(dimethylamino)benzophenone, diethoxyacetophenone, 2,2-dimethoxy- 1 ,2-diphenylethan- 1 -one, 1 -hydroxycyclohexyl-phenylketone, 2-hydroxy-2- methyl- 1 -phenylpropan- 1 -one, 2-methyl- 1 - [4-(methylthio)phenyl] -2-morpholinopropan- 1 -one, 1 - [4-(2-hydroxyethoxy)phenyl]2-morpholinopropan- 1 -one, 2-benzyl-2-dimethylamino- 1 -(4- morpholinophenyl)butan-l-one, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

[0021] The concentration of the photoinitiator is preferably in the range of from 0. 1 or from 0.2 or from 0.5 or from 0.8 weight percent, to 3 or to 2 or to 1 weight percent, based on the weight of the composition.

[0022] The composition of the present invention may include other additives such as treated fumed silica, typically at a concentration in the range of from 5 or from 10 or from 20 or from 25 weight percent, to 40 or to 35 or to 30 weight percent, based on the composition.

[0023] A preferred formulation can be advantageously prepared by mixing the dialkenyl functionalized polyorganosiloxane, the alkylthiol functionalized polyorganosiloxane, and fumed silica, then contacting this mixture with the photoinitiator, the compound of Formula 1, and TEOS, with continued mixing, then contacting this mixture with the condensation catalyst.

[0024] This formulation can then be applied to a substrate such as an aluminum substrate and cured by UV irradiation. Curing is typically completed within seconds at room temperature. The cured coating has been observed to have excellent adhesive strength.

[0025] Examples

[0026] Intermediate Example 1 - Preparation of Compounds of Formula la and lb l,3,5-Triallyl-l,3,5-triazine-2,4,6(lH,3H,5H)-trione (TTT, 37.4 g) was added to an oven-dried 250 mL 3 -neck round bottom flask containing a magnetic stir bar and equipped with an addition funnel, thermocouple, and glass stopper. l,l,3,3-Tetramethyl-l-(2-

[0027] ( trimethoxy silyl)ethyl)disiloxane (TTDS, 31.8 g) was added to the addition funnel, and the flask was heated to 60 °C with stirring. Once the contents of the flask reached 58 °C, addition of TTDS was added over 2 min with concomitant addition of Karstedt's catalyst (5 ppm). The mixture was allowed to stir with heating for 45 min. Next, TTDS (31.8 g) was added to the addition funnel; this material was added to the flask over 3 min with concomitant addition of Karstedt’s catalyst (5 ppm). The reaction was allowed to stir with heating for 30 min. Next, the temperature was increased to 80 °C, and the reaction allowed to stir with heating for 18 h. The material was collected as a colorless, transparent liquid.13C NMR and29Si NMR spectroscopic data were consistent with the formation of structures of Formulas la and lb. Prep HPLC was used to verify the product distribution: Formula la - 38.0 wt%; Formula lb = 38.5 wt%, TTT = 6.6 wt%; and tri-TTDS functionalized isocyanurate = 16.9 wt%.

[0028] Example 1 - Preparation of Polyorganosiloxane composition with Dual Adhesion Promoters

[0029] An alkylthiol functionalized polyorganosiloxane (5.8 pbw, compound of Formula 3, R = -zi-propyl-SH, m = 43, p =5), a first divinyl polydimethylsiloxane (DVPDS1, 29.8 pbw, compound of Formula 2, n = 766), a second di vinyl polydimethylsiloxane (DVPDS2, 31.8 pbw, compound of Formula 2, n = 158), Cabot TS-30 hexamethyldisilazane treated fumed silica (26.4 pbw) were added to a 100-mL dental cup and blended at 1000 rpm for 20 s, then further blended at 2000 rpm for 45 s to form a blended master batch. This master batch was then added to a 30-cc PDF UV stable adhesive dispensing tube along with Darocur 1173 photoinitiator (0.94 pbw), TEOS (1 pbw), and Intermediate Example 1 (0.5 pbw, 75 wt% active).

[0030] Tyzor PITA-SM Di(isopropoxy)bis(ethylacetoacetate)titanium Catalyst (0.25 pbw) was then added with mixing at 3500 rpm for 45 s.

[0031] Preparation and Curing of Coated Al substrate

[0032] A 2024 T3 Alcald Aluminum substrate (12 cm x 7.5 cm x 1 mm) was cleaned with acetone and isopropanol, then dried with air. A 1-cm wide PTFE tape was applied to cover one edge of the substrate. Then, each formulation was cast onto the substrate and tape (across the substrate and transverse to the tape) at a 2.5 + 0.2 mm thickness. The samples were then cured using a Model DRS-10 UV oven and VPS / I600 lamp system at a dosage of 4 J / cm2. The cured samples were loaded onto Texture Technologies Corp TA XT Plus 100 Texture Analyzer equipped with a 90° peel rig. This rig allows for the samples to be peeled at 90°. Each sample was loaded by peeling the adhesive sample edge over the Teflon tape and loading it in the instrument's gripper. The samples were then peeled using the peel test method included in the software package. The test speed was 1 ,5” / s for 3.5 inches triggered manually. This test was repeated for each replicate on the substrate.

[0033] A coating that peeled from the Alcald Al substrate without residue was deemed to be an adhesive failure (AF). A coating that stuck to the substrate while peeling off and breaking was deemed to be a cohesive failure (CF). The peel testing data is summarized in Table 1.

[0034] Comparative Examples 1-4 were prepared substantially as described in Example 1, except for differences shown in the table. Thiol-PDMS refers to the alkylthiol functionalized polyorganosiloxane; DV-PDMS1 refers to the first divinyl poly dimethylsiloxane; DV-PDMS2 refers to the second divinyl polydimethylsiloxane; AF refers to adhesive failure; and CF refers to cohesive failure.

[0035] Table 1 - Results of Peel Testing

[0036] The results illustrate that a combination of TEOS, Intermediate 1, and the moisture catalyst are needed to achieve the desired cohesive failure and adhesion.

Claims

Claims:

1. A composition comprising: a) one or more compounds of Formula 1 :Formula 1 b) polyorganosiloxane functionalized with at least two alkenyl groups; c) an alky lthiol functionalized polyorganosiloxane; d) a tetra-Ci-C4-alkyl orthosilicate; e) a condensation catalyst; and f) a photoinitiator; where X is a double bond and / or -CH2CH2-Si(CH3)2OSi(CHs)2-CH2CH2-Si(OCH3)3.

2. The composition of Claim 2 wherein, based on the weight of the composition, the concentration of the one or more compounds of Formula 1 is in the range of from 0.1 to 5 weight percent; the concentration of the polyorganosiloxane functionalized with at least two alkenyl groups is in the range of from 40 to 80 weight percent; the concentration of the alkylthiol functionalized polyorganosiloxane is in the range of from 1 to 20 weight percent; the concentration of tetra-Ci-C4-alkyl orthosilicate is in the range of from 0.1 to 5 weight percent; the concentration of the condensation catalyst is in the range of from 0.05 to 1 weight percent; and the concentration of the photoinitiator is in the range of from 0.2 to 3 weight percent.

3. The composition of Claim 2 which further comprises from 5 to 40 weight percent of a fumed silica.

4. The composition of any of Claims 1 to 3 wherein the one or more compounds of Formula 1 is a mixture of compounds of Formula la and Formula lb:Formula la Formula lb where the dialkenyl functionalized polyorganosiloxane is one or more compounds of Formula 2:Formula 2 where n is from 2 to 1000; the alkylthiol functionalized polyorganosiloxane is one or more compounds of Formula 3:Formula 3 where R is a Ca-Cn-alkylthiol group; m is from 0 to 500; and p is from 2 to 200;the tetra-Ci-C4-alkyl orthosilicate is tetraethyl orthosilocate; and the condensation catalyst is a titanium condensation catalyst.

5. The composition of Claim 4 wherein, based on the weight of the composition, the concentration of the mixture of compounds of Formula la and Formula lb is in the range of from 0.2 to 2 weight percent; the concentration of the one or more compounds of Formula 2 is in the range of from 50 to 70 weight percent; the concentration of the compound of Formula 3 is in the range of from 2 to 15 weight percent, and p is from 2 to 15; the concentration of tetraethyl orthosilicate is in the range of from 0.2 to 3 weight percent; the concentration of the titanium condensation catalyst is in the range of from 0. 1 to 0.5 weight percent; the concentration of the photoinitiator is in the range of from 0.1 to 2 weight percent; and the concentration of the fumed silica is in the range of from 20 to 35 weight percent.

6. The composition of Claim 5 wherein the photoinitiator is selected from the group consisting of 2-hydroxy-2-methylpropiophenone, diethoxyacetophenone, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, diethoxyxanthone, chlorothioxanthone, azobisisobutyronitril, N-methyl diethanolaminebenzophenone 4,4'- bis(dimethylamino)benzophenone, diethoxyacetophenone, 2,2-dimethoxy- 1,2-diphenylethan-l- one,l-hydroxycyclohexyl-phenylketone, 2-hydroxy-2-methyl-l-phenylpropan-l-one, 2-methyl- l-[4-(methylthio)phenyl]-2-morpholinopropan-l-one, l-[4-(2-hydroxyethoxy)phenyl]2- morpholinopropan- 1 -one, 2-benzyl-2-dimethy lamino- 1 -(4-morpholinophenyl)butan- 1 -one, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide; and the titanium condensation catalyst is a di(isopropoxy)bis(ethylacetoacetate)titanium.

7. The composition of Claim 6 wherein the photoinitiator is 2-hydroxy-2-methylpropiophenone.

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