Silicone elastomer compositions

Abstract

There is provided curable silicone elastomer compositions having enhanced adhesive properties with respect to a wide variety of substrates. The curable silicone elastomer compositions described herein are provided with a phenylmethylpolysiloxane based additive which comprises at least one, alternatively at least two SiH groups per molecule and at least one, alternatively at least two anhydride 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 SiH groups per molecule, optionally at least 3 SiH 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 SiH group per molecule, optionally at least two SiH groups per molecule and which comprises at least two anhydride functional groups per molecule, wherein the organopolysiloxane based additive (D) is of the following formula [(XR.sup.3SiO).sub.a(HR.sup.3SiO).sub.m(SiR.sup.3O)]OY[(SiR.sup.3O)(OSiR.sup.3H).sub.m(OSiR.sup.3X).sub.a] wherein, repeating units in [ ] brackets have a cyclic siloxane structure with the silicon atom in (SiR.sup.3O) connecting the cyclic siloxane structure to the rest of the molecule, each R.sup.3 group is an alkyl group containing from 1 to 6 carbons, each X is an anhydride containing group, m is an integer of at least 1, optionally at least 2, a is an integer of at least 1; Y is a linear siloxane group of the structure (SiPhR.sup.3O).sub.n or (SiPh.sub.2O).sub.n; Ph is a phenyl group and n is an integer of from 2 to 20.

2. The curable silicone elastomer composition in accordance with claim 1, wherein m is 2, a is 1, and the average value of n is between 4 and 10.

3. The curable silicone elastomer composition in accordance with claim 1, wherein the organopolysiloxane based additive (D) is added to the composition in an amount of from 0.5 to 5% by weight of the total composition.

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

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

6. 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.

7. The process in accordance with claim 6, wherein the substrate is a polycarbonate.

8. An article containing a silicone elastomer cured from the curable silicone elastomer composition according to claim 1.

9. The article in accordance with claim 8, wherein the silicone elastomer is adhered to a plastic substrate.

10. The article in accordance with claim 8, wherein the silicone elastomer is adhered to a thermoplastic substrate, an organic resin substrate, or a thermoplastic and organic resin substrate.

11. The article in accordance with claim 8, 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.

12. 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.

13. The composite part in accordance with claim 12, 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, 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-media device and mini-disk 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 office automation equipment, connector seals, spark plug caps, and automobile components.

Description

EXAMPLES

(1) 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.

(2) TABLE-US-00001 TABLE 1 curable silicone elastomer 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 having a 1.75 1.70 Williams plasticity of 156 mm/100 (ASTM D-926-08) Calcium carbonate, fatty acid treated 17.55 17.06 Quartz (average particle size 5 m) 5.84 5.68 Dimethyl hydroxy terminated Dimethyl siloxane 1.75 1.70 viscosity of about 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 Dimethyl 1.69 siloxane, dimethylvinylsiloxy-terminated Ethynyl cyclohexanol (ETCH) in 1.26 Dimethyl, methylvinyl siloxane, dimethylvinylsiloxy-terminated Dimethyl, methylvinyl siloxane, dimethylvinylsiloxy- 7.73 3.15 terminated viscosity of about 340 mPa .Math. s Dimethyl, methylhydrogen siloxane, trimethylsiloxy- 0.66 terminated viscosity of about 12-13 mPa .Math. s Dimethyl siloxane, hydrogen-terminated 5.04 viscosity of about 10 mPa .Math. s 50 wt % zirconium (IV) acetylacetonate in 0.60 50 wt % vinyl terminated polydimethylsiloxane Additive-see below 3.38 Total (100%) (100%)

(3) Masterbatch 1 comprises 68.7% of Dimethylvinyl terminated Dimethyl siloxane, viscosity of about 57,000 mPa.Math.s and 31.3% treated silica.

(4) Three alternative additives were tested.

(5) Additive 1 (Add. 1) was in accordance with the disclosure herein and was a mixture of component (D) structures prepared following the process described in PCT/US Ser. No. 19/064,350, comprising a majority of molecules (approximately 51 to 55%) 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, each cyclic siloxane is an 8 membered ring and it is to be understood that the X group can replace any of the SiH groups originally positioned in the ring so may be but is not necessarily the following structure. A possible structure for the main ingredient of Additive 1 may be:

(6) ##STR00004##
The rest being a mixture of analogous molecules in which cyclic siloxanes D in the structure were 10 membered rings (approximately 40 to 45%) and the remainder (approximately >0-5%) had cyclic siloxanes D made of 12 membered rings. The total amount adding up to 100%

(7) Comparative additive 1 (Comp. Add. 1) below is a comparative mixture of oligomers prepared in accordance with the method described in U.S. Pat. No. 7,429,636 comprising a majority of molecules (approximately e.g. 57.5 to 62%) where the number of silicon atoms in the linear chain (n+2 in the above structure) is an average about 7, and each cyclic siloxane is an 8 membered ring. The epoxide group may be linked directly to any of the silicon atoms forming part of the cyclic siloxane and it should be appreciated that the following is merely a representation of one of the options of the main ingredient of Comp. Add. 1

(8) ##STR00005##
The rest being a mixture of analogous molecules in which each cyclic siloxane cyclic siloxane was a 10 membered ring (approximately 35 to 40%) and the remainder (approximately >0-5%) had cyclic siloxanes made of 12 membered rings. The total amount adding up to 100%

(9) Comparative additive 2 was a mixture similar to Add.1 and prepared in accordance with the process described in PCT/US19/064350 but which has terminal epoxy groups as opposed to anhydride groups comprising a majority of molecules (approximately 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 it is to be understood that the X group can replace any of the SiH groups originally positioned in the ring of each cyclic siloxane so the main ingredient of Comparative additive 2 maybe but is not necessarily the following structure

(10) ##STR00006##
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%.

(11) 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).

(12) TABLE-US-00002 TABLE 2 Physical Properties for compositions containing the respective additives Add. 1 Comp. Add. 1 Comp. Add. 2 Elongation (%) 900 742 892 Modulus at 100% 0.4 0.94 0.63 elongation (MPa) Modulus at 150% 0.61 1.28 0.84 elongation (MPa) Young's Modulus (MPa) 0.41 0.86 0.5 Tensile Strength (MPa) 3.23 4.84 4.20 Shore A Hardness 24 40 33
Adhesion Testing

(13) Laminates of 470 dtex polyester and nylon 66 (420 denier, 4646 thread count) 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.

(14) 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 mm10 in). The part A and part B compositions were mixed in a 1:1 weight ratio in a speedmixer.

(15) 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.

(16) 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.

(17) 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.

(18) 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.

(19) 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.

(20) 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 210 grid (4 mm4 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.

(21) The respective results for 470 dtex polyester substrates and nylon 66 substrates are depicted in Tables 3a-d and 4a-c respectively.

(22) 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 470 dtex polyester substrate. H&H Peak Load/Width Cohesive Adhesion Promoter Treatment aging (kN/m) failure (%) None Plasma No 0.3 0

(23) It will be seen that without the additives, although plasma treated minimal adhesion is achieved. The results were so poor that no aging was undertaken.

(24) TABLE-US-00004 TABLE 3b Adhesion test using formulation defined in Table 1 containing Comp. Add. 1 on a 470 dtex polyester substrate. Adhesion H&H Peak Load/Width Cohesive Promoter Treatment aging (kN/m) failure (%) Comp. Add. 1 Plasma No 5.8 72 Comp. Add. 1 Plasma Yes 2.3 5

(25) It can be seen that adhesion was not achieved after aging using comp. Add. 1 even subsequent to plasma treating the substrate surface.

(26) TABLE-US-00005 TABLE 3c Adhesion test using formulation defined in Table 1 containing Comp. Add. 2 on a 470 dtex polyester substrate. Adhesion H&H Peak Load/Width Cohesive Promoter Treatment aging (kN/m) failure (%) Comp. Add. 2 Plasma No 4.8 98 Comp. Add. 2 Plasma Yes 2.1 3 Comp. Add. 2 None No 4.9 86 Comp. Add. 2 None Yes 2.5 14

(27) Likewise, it can be seen that adhesion was not achieved after aging using comp. Add. 2 either when not plasma treated or subsequent to plasma treating the substrate surface.

(28) TABLE-US-00006 TABLE 3d Adhesion test using formulation defined in Table 1 containing Add.1 on a 470 dtex polyester substrate. Adhesion H&H Peak Load/Width Cohesive Promoter Treatment aging (kN/m) failure (%) Additive 1 Plasma No 5.9 100 Additive 1 Plasma Yes 4.9 99 Additive 1 None No 5.7 100 Additive 1 None Yes 0.6 0

(29) It can be seen that adhesion was achieved with Additive 1 without plasma treatment although adhesion was lost after the aging process. However, unlike the comparatives above adhesion was retained with respect to substrates subsequent to plasma treating the substrate surface.

(30) TABLE-US-00007 TABLE 4a 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 Promoter Treatment aging (kN/m) failure (%) None Plasma No 0.3 0

(31) It will be seen that without the additives, although plasma treated minimal adhesion is achieved. The results were so poor that no aging was undertaken.

(32) TABLE-US-00008 TABLE 4b 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 Plasma No 5.0 68 Comp. Add. 1 Plasma Yes 4.9 93

(33) A good level of adhesion was retained to plasma treated nylon 66 substrate.

(34) TABLE-US-00009 TABLE 4c 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 Plasma No 5.9 98 Additive 1 Plasma Yes 4.6 98 Additive 1 None No 5.0 98 Additive 1 None Yes 3.9 73

(35) It can be seen that adhesion was achieved with Additive 1 without plasma treatment although adhesion and was substantially retained even after aging. However, unlike the comparatives above adhesion was retained with respect to substrates subsequent to plasma treating the substrate surface.

(36) Adhesion Method and Analysis

(37) 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]

(38) TABLE-US-00010 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 2024T3 ALCLAD-(aluminium sheet)

(39) TABLE-US-00011 TABLE 5b Adhesion test using formulation defined in Table 1 containing Additive 1 Substrate Adhesion Lexan 121R (polycarbonate)-Sabic + Ultramid B3EG6 (Nylon 6)-BASF + Ultramid A3EG6 (Nylon 66)-BASF + Ultradur B4300 G4 (Polybutylene terephthlate)-BASF + 2024T3 ALCLAD-(aluminium sheet) +