Adhesion promoters for polyaddition silicone formulations

Abstract

The present invention relates to two-component (2K) silicone-based adhesive compositions comprising an adhesion promotor, as well as to the use of such compositions. Furthermore, the present invention is directed to the use of a —Si(OR.sup.a).sub.3 terminated polyorganosiloxane prepolymer, as described herein, for improving the adhesive properties of silicone-based adhesive compositions.

Claims

1. Two-component silicone-based adhesive composition comprising a first component (A) comprising at least one vinyl-terminated polysiloxane polymer and at least one hydrosilyl group-containing crosslinker; and a second component (B) comprising at least one —Si(OR.sup.a).sub.3 terminated polyorganosiloxane prepolymer, a hydrosilylation catalyst and at least one vinyl-terminated polysiloxane polymer, wherein OR.sup.a is a hydrolysable group, and the —Si(OR.sup.a).sub.3 terminated polyorganosiloxane prepolymer is the reaction product of a hydrogen-terminated polyorganosiloxane with a vinyl and —Si(OR.sup.a).sub.3 group containing silane in the presence of a catalyst, wherein the hydrogen-terminated polyorganosiloxane is used in molar excess with respect to the ratio of reactive hydrogen atoms to vinyl groups of the vinyl and —Si(OR.sup.a).sub.3 group containing silane.

2. The two-component silicone-based adhesive composition according to claim 1, wherein the —Si(OR.sup.a).sub.3 terminated polyorganosiloxane prepolymer is a —Si(OR.sup.a).sub.3 terminated poly(diorganosiloxane) prepolymer.

3. The two-component silicone-based adhesive composition according to claim 2, wherein the alkyl groups of the —Si(OR.sup.a).sub.3 terminated poly(diorganosiloxane) prepolymer are each independently selected from the group consisting of methyl and ethyl.

4. The two-component silicone-based adhesive composition according to claim 2, wherein the —Si(OR.sup.a).sub.3 terminated poly(diorganosiloxane) prepolymer is —Si(OR.sup.a).sub.3 terminated poly(dimethyl siloxane).

5. The two-component silicone-based adhesive composition according to claim 1, wherein OR.sup.a is an alkoxy or acyloxy group, the alkoxy groups selected from the group consisting of methoxy, ethoxy and propoxy.

6. The two-component silicone-based adhesive composition according to claim 1, wherein the —Si(OR.sup.a).sub.3 group is a trialkoxy silyl group or a triacetoxy silyl group.

7. The two-component silicone-based adhesive composition according to claim 1, wherein the vinyl and —Si(OR.sup.a).sub.3 group containing silane is a trialkoxy silane.

8. The two-component silicone-based adhesive composition according to claim 1, wherein the catalyst used in the formation of the at least one —Si(OR.sup.a).sub.3 terminated polyorganosiloxane prepolymer is a platinum hydrosilation catalyst.

9. The two-component silicone-based adhesive composition according to claim 1, wherein the amount of the at least one —Si(OR.sup.a).sub.3 terminated polyorganosiloxane prepolymer, is in the range of 1.5% to 30% by weight, based on the weight of the component (B) of the silicone-based adhesive composition.

10. An adhesion promoter in two- component silicone-based polyaddition curing adhesive compositions; comprising a —Si(OR.sup.a).sub.3 terminated polyorganosiloxane prepolymer, wherein OR.sup.a is a hydrolysable group, that is the reaction product of a hydrogen-terminated polyorganosiloxane with a vinyl and —Si(OR.sup.a).sub.3 group containing silane in the presence of a catalyst, wherein the hydrogen-terminated polyorganosiloxane is used in molar excess with respect to the ratio of reactive hydrogen atoms to vinyl groups.

11. The adhesion promoter according to claim 10, wherein the —Si(OR.sup.a).sub.3 terminated polyorganosiloxane prepolymer is a —Si(OR.sup.a).sub.3 terminated poly(diorganosiloxane) prepolymer.

12. The adhesion promoter according to claim 11, wherein: the alkyl groups of the —Si(OR.sup.a).sub.3 terminated polyorganosiloxane prepolymer are each independently selected from the group consisting of methyl and ethyl; and/or the OR.sup.a groups of the vinyl and —Si(OR.sup.a).sub.3 group containing silane are alkoxy groups.

13. The adhesion promoter according to claim 11, wherein: the —Si(OR.sup.a).sub.3 terminated polyorganosiloxane prepolymer is —Si(OR.sup.a).sub.3 terminated poly(dimethyl siloxane); and/or the vinyl and —Si(OR.sup.a).sub.3 group containing silane is a trialkoxy silane.

Description

EXAMPLES

Example 1: Prepolymer Preparation

(1) TABLE-US-00001 TABLE 1 Prepolymer 1 Prepolymer 2 SiH-terminated polydimethyl siloxane 52.14 80.95 (Modifier 715) (wt. %) Allyltrimethoxy silane (ATMO) (wt. %) 47.83 19 Pt catalyst (Catalyst 512) (wt. %) 0.03 0.05 SiH mmol 151.21 234.76 Vi mmol 295.25 117.28 mmol/g SiH residue 0.00 1.17 mmol/g Vi residue 1.44 — SiH residue mmol — 117.47

(2) The ingredients are mixed and reacted at room temperature. The reaction is exothermic (until 80° C.).

Example 2

(3) Each Part B according to Table 2 was mixed with Part A1 according to Table 3 and thus obtained 2K formulations were tested. The results are shown in Table 4.

(4) TABLE-US-00002 TABLE 2 Part B formulations B1 B2 B3 Vinyl-terminated polydimethylsiloxane 30.83 28.83 26.83 (Polymer VS 5000 (Evonik Industries)) (wt. %) vinyl content: 0.06 mmol/g Vinyl-terminated polydimethylsiloxane 20 20 20 (Polymer VS 20000 (Evonik Industries)) (wt. %) vinyl content: 0.04 mmol/g Vinyl-QM resin (VQM 803) (wt. %) 5 5 5 Carbon black filler (Raven 1020) (wt. %) 0.1 0.1 0.1 Surface modified filler (Silbond 8000 TS) (wt. %) 40 40 40 Hydrophilic fumed silica filler (Aerosil 200) (wt. %) 4 4 4 MVC 1% in VS 2000 (wt. %) 0.03 0.03 0.03 (methylvinylcyclosiloxane) Pt Catalyst (wt. %) 0.04 0.04 0.04 Allyltrimethoxy silane (wt. %) 2 Prepolymer 2 (according to Example 1) (wt. %) 4

(5) TABLE-US-00003 TABLE 3 Part A formulation A1 Vinyl-terminated polydimethylsiloxane (Polymer VS 5000) 23 (wt. %) vinyl content: 0.06 mmol/g Vinyl-terminated polydimethylsiloxane (Polymer VS 20000) 22.82 (wt. %) vinyl content: 0.04 mmol/g Vinyl-QM resin (VQM 803) (wt. %) 5 Surface modified filler (Silbond 8000 TS) (wt. %) 40 Hydrophillic fumed silica filler (Aerosil 200) (wt. %) 4.1 hydrosilylation crosslinking agent (Crosslinker 200) (wt. %) 4 SiH-terminated polydimethyl siloxane (Modifier 715) (wt. %) 1.08

(6) TABLE-US-00004 TABLE 4 Results Formulation 1 Formulation 2 (A1 + B1) (A1 + B2) Formulation 3 (Comparative) (Comparative) (A1 + B3) Alu/Alu 7 d (N/mm.sup.2) 0.27 0.55 1.78 MEK Tensile strength 4.5 3.42 2.3 (N/mm.sup.2) Elongation % 279 248 391 Modulus (N/mm.sup.2) 1.48 1.17 0.62

Example 3

(7) Each Part B according to Table 5 was mixed with Part A2 according to Table 6 and thus obtained 2K formulations were tested. The results are shown in Table 7.

(8) TABLE-US-00005 TABLE 5 Part B formulations B4 B5 Vinyl-terminated polydimethylsiloxane (Polymer VS 1000) 46.86 49.86 (wt. %) vinyl content: 0.11 mmol/g Vinyl-QM resin (VQM 803) (wt. %) 3 3 Titanium dioxide filler (Kemira) (wt. %) 0.1 0.1 Surface modified filler (Silbond 8000 TS) (wt. %) 40 40 Hydrophilic fumed silica filler (Aerosil 200) (wt. %) 6 6 Pt Catalyst (wt. %) 0.04 0.04 Prepolymer 2 (according to Example 1) (wt. %) 4 1

(9) TABLE-US-00006 TABLE 6 Part A formulation A2 Vinyl-terminated polydimethylsiloxane (Polymer VS 5000) (wt. %) 26.7 vinyl content: 0.06 mmol/g Vinyl-terminated polydimethylsiloxane (Polymer VS 1000) (wt. %) 21.4 vinyl content: 0.11 mmol/g Vinyl-QM resin (VQM 803) (wt. %) 1 Surface modified filler (Silbond 8000 TS) (wt. %) 38 Hydrophillic fumed silica filler (Aerosil 200) (wt. %) 7.6 hydrosilylation crosslinking agent (Crosslinker 200) (wt. %) 4.2 SiH-terminated polydimethyl siloxane (Modifier 715) (wt. %) 1.1

(10) TABLE-US-00007 TABLE 7 Results Formulation 4 Formulation 5 (A2 + B4) (A2 + B5) Tensile strength (N/mm.sup.2) 2.43 4.38 Elongation % 227.1 175.7 Modulus (N/mm.sup.2) 1.1 2.21 Shore Hardness 33 45 Alu/Alu 7 d (N/mm.sup.2) MEK 1.54 0.37 Steel/steel 7 d (N/mm.sup.2) 1.8 0.27

(11) Tensile Shear Strength

(12) Alu/alu 7d means that two aluminum substrates were bonded and the lap shear strength was measured after 7 days. Steel/steel 7d means the same but on steel substrates. The Lap shear strength was determined according to DIN EN 1465. Lap shear specimen with the following dimensions were used: Length 100 mm, width 25 mm with and overlap of 322.6 mm2 and a gap of 1 mm.

(13) Procedure: The formulation is spread on one lap-shear specimen of sufficient quantity such that when the lap-shear specimens are mated a 322.6 mm2 (0.5 in.2) area will be completely covered. If necessary, spread the adhesive using an appropriate utensil (applicator stick, tongue depressor, etc.) so as to ensure complete coverage of the bond area. Five specimens were used for each determination. The assembled lap shear was allowed to cure under normal conditions (23+/−2° C., relative humidity 50+/−5%) for 7 days. The test was carried out under normal conditions (23+/−2° C., relative humidity 50+/−5%) and the measurement was carried out after 7 days of curing. The test specimens have to be at the same temperature at which the measurement will take place. Place the test specimen in the grips of the testing machine so that the long axis of the test specimen coincides with the direction of applied tensile force through the center line of the grip assembly. Then the lap shear specimen is stretched to <0.1 MPa with a rate of 50 mm/min. Then, the force-joint deplacement curve is recorded with a line speed of 50 mm/min.

(14) Tensile Strength/Elongation/Modulus

(15) Tensile strength and elongation at break were determined according to DIN 53504. Dumbbell specimens with the following dimensions were used: thickness 2+/−0.2 mm; bar width 10+/−0.5 mm; bar length approx. 45 mm; and total length 9 cm.

(16) Procedure: the prepolymer mixture (formulation) was spread on an even surface forming a film with a thickness of 2 mm. The film was allowed to cure under normal conditions (23+/−2° C., relative humidity 50+/−5%) for 7 days, and then the dumbbell specimen was punched out. Five specimens were used for each determination. The test was carried out under normal conditions (23+/−2° C., relative humidity 50+/−5%) and the measurement was carried out after 7 days of curing. The test specimens have to be at the same temperature at which the measurement will take place. Before the measurement, the thickness of the test specimens is determined at least at three different positions, at the middle and at the extremes, with a caliper. The mean value is introduced in the measuring software. The test specimens are clamped into the tensile tester so that the longitudinal axis coincides with the mechanical axis of the tensile tester and comprises the largest possible surface of the rod heads, without clamping the middle bar. Then the dumbbell is stretched to <0.1 MPa with a rate of 50 mm/min. Then, the force-elongation curve is recorded with a line speed of 500 mm/min.

(17) Evaluation: The following values are determined—breaking force in [N/mm.sup.2], elongation at break in [%], and modulus of elasticity in [N/mm.sup.2] at 100% elongation

(18) Shore Hardness

(19) Shore hardness was measured according to ISO 868.