SILICONE ELASTOMER COMPOSITIONS

Abstract

Curable silicone elastomer compositions having enhanced adhesive properties with respect to a wide variety of substrates are described. The compositions described herein are provided with a phenylmethylpolysiloxane based additive which comprises at least one, alternatively at least two Si—H groups per molecule and at least one, alternatively at least two epoxide functional groups per molecule. Said phenylmethylpolysiloxane based additives provide resulting elastomers with improved heat-humidity stabilization.

Claims

1. A curable silicone elastomer composition that can achieve adhesion on plastic/thermoplastic/resin material substrates, the curable silicone elastomer composition comprising: (A) one or more organopolysiloxanes containing at least 2 alkenyl and/or alkynyl groups per molecule and having a viscosity in a range of 1,000 to 500,000 mPa.Math.s at 25° C.; (B) a curing agent comprising (B)(i) an organic peroxide radical initiator; or (B)(ii) a hydrosilylation cure catalyst package comprising a hydrosilylation catalyst and an organosilicon compound having at least 2, optionally at least 3 Si—H groups per molecule; (C) at least one reinforcing filler and optionally one or more non-reinforcing fillers; and (D) an organopolysiloxane based additive which comprises at least one, optionally at least two Si—H groups per molecule and which comprises at least one, optionally at least two epoxide functional groups per molecule.

2. The A-curable silicone elastomer composition in accordance with claim 1, wherein the organopolysiloxane based additive (D) is of the following formula
D-O—[Y]-D in which each D group is a cyclic siloxane of the structure
[(O—Si(−)R.sup.3)(OSiR.sup.3H).sub.m(OSiR.sup.3X).sub.a] wherein each R.sup.3 group is an alkyl group containing from 1 to 6 carbons and each X is an epoxide containing group in which m is an integer of at least 1 and a is an integer of at least 1; and [Y] is a linear siloxane group of the structure [SiPhR.sup.3O].sub.n or [SiPh.sub.2O].sub.n wherein Ph is a phenyl group and n is an integer of from 2 to 20.

3. The curable silicone elastomer composition in accordance with claim 2, wherein the organopolysiloxane based additive (D) is or comprises a compound selected from either: a compound where [Y] is a polymethylphenylsiloxane chain, e is 1, d is zero, m is 2, a is 1 and the value of n is an average between 4 and 10; or a compound where [Y] is a polymethylphenylsiloxane chain, e is 1, d is zero, m is 1, a is 2 and the value of n is an average between 4 and 10.

4. The curable silicone elastomer composition in accordance with claim 1, wherein component (D) is added to the composition in an amount of from 0.5 to 5% by weight of the total composition of the other components.

5. The curable silicone elastomer composition in accordance with claim 1, wherein the composition comprises a cure inhibitor.

6. The curable silicone elastomer composition in accordance with claim 1, stored before use in at least 2 separate parts.

7. A process for preparing an article or a composite part of an article, the process comprising: a) forming a mixture of the curable silicone elastomer composition according to claim 1; b) applying the mixture onto a surface of a substrate; and c) curing the mixture at a temperature of from 80 to 250° C.

8. The process in accordance with claim 7, wherein the substrate is a polycarbonate.

9. An article cured from the curable silicone elastomer composition according to claim 1.

10. The article in accordance with claim 9, containing silicone elastomer cured from the curable silicone elastomer composition adhered to a plastic substrate.

11. The article in accordance with claim 9, containing silicone elastomer cured from the curable silicone elastomer composition adhered to on a thermoplastic substrate, an organic resin substrate, or a thermoplastic and organic resin substrate.

12. The article in accordance with claim 9, selected from housings with a silicone seal or gasket, plugs and connectors, components of sensors, membranes, diaphragms, climate venting components, personal electronic equipment, mobile phone cover seals, mobile phone accessories, precision electronic equipment, electrical switches and switch covers, watches and wristbands, or wearable electronic devices.

13. A composite part comprising a silicone elastomer cured from the curable silicone elastomer composition according to claim 1, on a plastic/thermoplastic/resin material substrate, optionally on a polycarbonate material substrate.

14. The composite part in accordance with claim 13, selected from housings with a silicone seal or gasket, plugs and connectors, components of sensors, membranes, diaphragms, climate venting components, personal electronic equipment, mobile phone cover seals, mobile phone accessories, precision electronic equipment, electrical switches and switch covers, watches and wristbands, wearable apparatus and/or wearable electronic devices, parts of mobile phones, mobile telecommunications equipment, gaming machines, clocks, image receivers, DVD equipment, MD equipment, CD equipment, microwave ovens, refrigerators, electric rice cookers, cathode ray TVs, thin displays of liquid crystal TVs and plasma TVs, home appliances, copying machines, printers, facsimile machines, and other OA equipment, connector seals, spark plug caps, and other automobile components.

15. (canceled)

Description

EXAMPLES

[0123] In the following examples all viscosities were measured using a Brookfield® rotational viscometer using Spindle (LV-4) and adapting the speed (shear rate) according to the polymer viscosity. All viscosity measurements were taken at 25° C. unless otherwise indicated.

TABLE-US-00001 TABLE 1 composition used for examples with varying Additives as indicated below Part A Part B Comp. Comp. Ingredient (wt. %) (wt. %) Masterbatch 1 50.30 50.87 dimethylvinyl-terminated Dimethyl siloxane gum 1.75 1.70 having a Williams plasticity of 156 mm/100 (ASTM D-926-08) Calcium carbonate, fatty acid treated 17.55 17.06 Quartz (average particle size 5 μm) 5.84 5.68 Dimethyl hydroxy terminated Dimethyl siloxane 1.75 1.70 viscosity of 42 mPa .Math. s Dimethylvinyl terminated Dimethyl siloxane, 12.78 9.50 viscosity of about 57,000 mPa .Math. s Karstedt's (Pt) catalyst in vinyl polymer 1.69 — dimethylvinylsiloxy-terminated Dimethyl siloxane, Ethynyl cyclohexanol (ETCH) in — 1.26 dimethylvinylsiloxy-terminated - Dimethyl, methylvinyl siloxane, dimethylvinylsiloxy-terminated Dimethyl, 7.73 3.15 methylvinyl siloxane, viscosity of about 340 mPa .Math. s trimethylsiloxy-terminated - Dimethyl, — 0.66 methylhydrogen siloxane, viscosity of about 12-13 mPa .Math. s Dimethyl siloxane, hydrogen-terminated viscosity of — 5.04 about 10 mPa .Math. s 50 wt % zirconium (IV) acetylacetonate in 50 wt % 0.60 vinyl terminated polydimethylsiloxane Additive - see below 3.38 Total (100%) (100%)

[0124] Masterbatch 1 comprises 68.7% of Dimethylvinyl terminated Dimethyl siloxane, viscosity of about 57,000 mPa.Math.s and 31.3% treated silica.

[0125] Four alternative additives were tested.

[0126] Additive 1 (Add. 1) is in accordance with the disclosure herein and was a mixture of component (D) structures prepared following the process described in PCT/US19/064350, comprising a majority of molecules (approximately e.g. 51 to 55%) having a structure wherein [Y] is a polymethylphenylsiloxane chain, e is 1, d is zero, m is 2, a is 1 and the value of n is an average between 6 and 7, and each cyclic siloxane is an 8 membered ring and it is to be understood that the epoxide group can replace any of the Si—H groups originally positioned in the ring of each cyclic siloxane so the main ingredient of the mixture maybe but is not necessarily the following structure

##STR00004##

The rest being a mixture of analogous molecules in which cyclic siloxanes in the structure were 10 membered rings (approximately 40 to 45%) and the remainder (approximately >0-5%). The total amount adding up to 100%.

[0127] Additive 2 (Add. 2) was also a mixture of component (D) structures prepared following the process described in PCT/US19/064350, comprising a majority of molecules (approximately e.g. 51 to 55%) of the equivalent same structure as additive 1 with one difference m is 1, a is 2 and as such it contained 4 epoxy groups as opposed to 2 in Additive 1 so the main ingredient of the mixture maybe but is not necessarily the following structure:—

##STR00005##

The rest of Additive 4 being a mixture of analogous molecules in which cyclic siloxanes in the structure were 10 membered rings (approximately 40 to 45%) and the remainder (approximately >0-5%). The total amount adding up to 100%.

[0128] Comparative additive 1 (Comp. Add. 1) below was a mixture of component (D) structures prepared following the method described in U.S. Pat. No. 7,429,636, comprising a majority of molecules (approximately e.g. 57.5 to 62%) having a structure wherein [Y] is a polydimethylsiloxane chain, d is 1, e is zero, m is 2, a is 1, the number of silicons in the linear chain (n+2 in the following structure) is an average about 7 and each cyclic siloxane is an eight membered ring, and it is to be understood that the X group can replace any of the Si—H groups originally positioned in the ring of each cyclic siloxane so the main ingredient of the mixture maybe but is not necessarily the following structure:—.

##STR00006##

The rest being a mixture of analogous molecules in which cyclic siloxanes in the structure were 10 membered rings (approximately 35 to 40%) and the remainder (approximately >0-5%). The total amount adding up to 100%.

[0129] A further comparative additive, Comp. Add. 2, was tested. This was also a mixture of structures, comprising a majority of molecules (approximately e.g. 51 to 55%) having a structure wherein [Y] is a polymethylphenylsiloxane chain, and the value of n is an average between 6 and 7, but this had no epoxy functionality. Each cyclic siloxane of the main ingredient is an 8 membered ring so the main ingredient of the mixture has the following structure but this had no epoxy functionality:—

##STR00007##

The rest being a mixture of analogous molecules in which cyclic siloxanes in the structure were 10 membered rings (approximately 40 to 45%) and the remainder (approximately >0-5%). The total amount adding up to 100%

[0130] The respective Part A and part B for compositions as depicted in Table 1 above mixed in a 1:1 weight ratio using a speedmixer an slabs of each sample were prepared and then cured at 150° C. for 5 minutes. The physical properties were then determined as depicted in table 2 below. Elongation and Modulus results cured test pieces (ASTM D412-98A) using DIN S2 die and Shore A hardness was determined in accordance with (ASTM D2240-97).

TABLE-US-00002 TABLE 2 Physical Properties for compositions containing the respective additives Comp. Comp. Add. 1 Add. 2 Add. 1 Add. 2 Elongation (%) 892 1238 742 774 Modulus at 100% elongation (MPa) 0.63 0.36 0.94 0.91 Modulus at 150% elongation (MPa) 0.84 0.48 1.28 1.24 Young's Modulus (MPa) 0.5 0.31 0.86 0.82 Tensile Strength (MPa) 4.2 3.5 4.8 4.7 Shore A Hardness 33 22 40 39

Adhesion Testing

[0131] Laminates of nylon 66 having a 46×46 thread count, 420 denier were prepared using the composition as herein before described in Table 1 including the additives discussed above with a view to assessing the Peak adhesion strength with tearing by peeling the laminate apart at one hundred eighty degrees. As well as the peak adhesion strength, an estimation of the percent cohesive failure is reported which was determined by examining the freshly exposed surface at the completion of the test and estimating the percent cohesive failure. The methodology used was based on ASTM D 413-98 with the following differences machine rate, sample width and sample thickness.

[0132] The fabric was cut along the weft direction (˜12 in) and then in the warp direction (˜16 in) to provide substrate sheets (dimensions 12 in (30.48 cm)×16 in (40.64 cm)). All substrates used were pre-dried at 150° C. for one minute in an oven. The fabric was then removed and placed on a workbench. A chase mold was aligned so that it was positioned straight across the fabric in the weft direction (chase used in this study had a 1.16 mm depth [leads to ˜1 mm thick adhesive line]; all internal dimensions are 10 mm×10 in). The part A and part B compositions were mixed in a 1:1 weight ratio in a speedmixer. A plastic spatula was used to fill the chase with the adhesive. The chase was removed, and a second piece of the respective substrate was placed on top of the sample bead. A Styrofoam roller was then used to gently wet-out the bead. The sample was then cured in the oven at 150° C. for 5 minutes.

[0133] As will be seen below some substrate samples were plasma treated before use. Plasma treatment took place after the substrate sheets had been oven treated. For plasma treated samples, a mark was made on the fabric at the center of the plasma treating line; albeit the marks were not made where the adhesive was going to be applied. The bottom piece of fabric was plasma treated using an FG3001 plasma generator from Plasmatreat; speed set to 125 mm/s. The robot coordinates were set with x=82.24 mm, y=13.76 mm, z=117 mm; these coordinates lead to a 7 mm gap from plasma treating head to fabric). After treatment the samples were applied following the process above. The second substrate sheet was plasma treated and applied with the plasma treated surface toward the sealant bead. Samples were then cured as described above.

[0134] Samples were allowed to sit at room temperature for about 20 hours until analysis was performed. Four samples were cut from each specimen, which consisted of a 10 in seam. The outer 1 in (2.54 cm) of specimen was discarded and four 2 in (5.08 cm) samples were cut. The length of the fabric was then cut to approximately 6 in (15.24 cm) for each sample. The thickness of each sample was measured. This was done by subtracting the width of two pieces of fabric from the width of the overall sample construction.

[0135] Peak adhesion strength with tearing by peeling the laminate apart at one hundred eighty degrees. As well as the peak adhesion strength, an estimation of the percent cohesive failure is reported which was determined by examining the freshly exposed surface at the completion of the test and estimating the percent cohesive failure. These were undertaken shortly after cure as discussed above and also after heat and humidity (H & H) aging for 17 days, at 70° C. at 95% relative humidity.

[0136] In the case of Peak Load/Width samples were test using an MTS Alliance RF/100 tensile tester. The adhesion specimen was placed in the sample holder crosshead speed was set to 8 in/min (200 mm/min) and the Peak Load/Width was determined. Results provided in the Tables below were an average of four data points.

[0137] In the case of the cohesive failure measurement this was achieved by analyzing samples pulled Peak Load/Width for percent cohesive failure. A template that contained a 2×10 grid (4 mm×4 mm squares) was placed at the center of the pulled seam, neglecting approximately 5 mm on each side and 2 mm on the top and bottom of the seam. Each square represents a 5% area. The percent cohesive failure was determined for each sample, and then the average was taken of each of the four replicates.

[0138] The results for nylon 66 substrates are depicted in Tables 3a-d.

TABLE-US-00003 TABLE 3a Ref. Adhesion test using formulation defined in Table 1 in the absence of any additive as discussed above on a Nylon 66 substrate. Adhesion H&H Peak Load/Width Cohesive failure Promoter Treatment aging (kN/m) (%) None none No 0.3 0

TABLE-US-00004 TABLE 3b Adhesion test using formulation defined in Table 1 containing Add.1 on a Nylon 66 substrate. Adhesion H&H Peak Load/Width Cohesive Promoter Treatment aging (kN/m) failure (%) Additive 1 None No 4.2 99 Additive 1 None Yes 3.5 100

[0139] It can be seen that adhesion was achieved with Additive 1 without plasma treatment although adhesion and was substantially retained even after aging.

TABLE-US-00005 TABLE 3c Adhesion test using formulation defined in Table 1 containing Add.2 on a Nylon 66 substrate. Adhesion H&H Peak Load/Width Cohesive Promoter Treatment aging (kN/m) failure (%) Add. 2 Plasma No 5.2 99 Add. 2 Plasma Yes 4.9 100

[0140] Inventive example: Adhesion is retained on substrate when SiH and epoxy functionalized component/additive (D) is used.

TABLE-US-00006 TABLE 4d Adhesion test using formulation defined in Table 1 containing Comp. Add. 1 on a Nylon 66 substrate. Adhesion H&H Peak Load/Width Cohesive Promoter Treatment aging (kN/m) failure (%) Comp. Add. 1 None No 5.2 99 Comp. Add. 1 None Yes 0.2 0 Comp. Add. 1 Plasma No 2.5 0

Comparative example: Adhesion is not retained on substrate when epoxy functionalized dimethyl siloxane adhesion promoter is used Comparative example: Adhesion is better without plasma treatment

[0141]

TABLE-US-00007 TABLE 4e Adhesion test using formulation defined in Table 1 containing Comp. Add. 2 on a Nylon 66 substrate. Adhesion H&H Peak Load/Width Cohesive Promoter Treatment aging (kN/m) failure (%) Comp. Add. 2 None No 0.9 0 Comp. Add. 2 None Yes 0.1 0

[0142] It can be seen that adhesion is not achieved in the absence of the epoxy functionality. Comparative example: Adhesion is not retained on substrate when SiH and epoxy functionalized dimethyl siloxane adhesion promoter is used.

Adhesion Method and Analysis

[0143] In the follow examples depicted in Tables 5a and 5b, the respective substrate utilised was wiped with isopropyl alcohol (IPA) and then air-dried prior to application of the curable silicone elastomer composition. The curable silicone elastomer composition was applied at a thickness of 25 mils (0.635 mm). Subsequently, the curable silicone elastomer composition was cured in a forced air oven at 150° C. for 1 h. Using a razor blade, two perpendicular lines separated by roughly the width of a spatula blade were etched across the width of the substrate and through the depth of cured material down to the substrate surface. Force was applied manually to the cured elastomeric material between the cuts by the spatula held down at approximately an angle of 300 from the substrate surface. Adhesion (or lack of adhesion) was then subjectively assessed and the results are provided in Tables 5a and 5b utilising the following descriptors:

(−) poor adhesion=adhesive failure (separation from the substrate)
(+) moderate to good adhesion=mixed mode failure [cohesive failure (tear in the elastomer) and adhesive failure]

TABLE-US-00008 TABLE 5a Ref. adhesion test using formulation defined in Table 1 in the absence of any additive, and no surface treatment Substrate Adhesion Lexan ™ 121R (polycarbonate) - Sabic − Ultramid ® B3EG6 (Nylon 6) - BASF − Ultramid ® A3EG6 (Nylon 66) - BASF − Ultradur ® B4300 G4 (PBT)- BASF − Cu-Clad FR-4 (polymeric side) − 2024T3 ALCLAD - (aluminium sheet) −
Cu-Clad FR-4 is a composite material of woven fiberglass cloth with an epoxy resin binder that is flame resistant.

TABLE-US-00009 TABLE 5b Adhesion test using formulation defined in Table 1 containing Additive 1 or Additive 2 Adhesion with Adhesion with Substrate Additive 1 Additive 2 Lexan™ 121R (polycarbonate) - Sabic + + Ultramid ® B3EG6 (Nylon 6) - BASF + + Ultramid ® A3EG6 (Nylon 66) - BASF + + Ultradur ® B4300 G4 (PBT)-BASF + + Cu-Clad FR-4 (polymeric side) + + 2024T3 ALCLAD - (aluminium sheet) + +

TABLE-US-00010 TABLE 5c Adhesion test using formulation defined in Table 1 containing Additive 1 or Additive 2, after heat and humidity aging at 85° C. and 85% relative humidity (1000 hours test- for 977 hours) Adhesion with Adhesion with Substrate Additive 1 Additive 2 Lexan ™ 121R (polycarbonate) - Sabic − − Ultramid ® B3EG6 (Nylon 6) - BASF + + Ultramid ® A3EG6 (Nylon 66) - BASF + + Ultradur ® B4300 G4 (PBT)- BASF + + Cu-Clad FR-4 (polymeric side) + + 2024T3 ALCLAD - (aluminium sheet) + +