SILICONE RUBBER COMPOSITION

Abstract

A silicone based composition comprises a blend of a non-fluorinated polydiorganosiloxane polymer and a fluorinated polydiorganosiloxane polymer. The composition is useful in the manufacture of insulators for high voltage direct current (HVDC) applications and accessories such as cable joints, cable terminal applications, and connectors. In general, the composition is a curable silicone elastomer composition comprising: (A) a combination of (A)(i) and (A)(ii), where (A)(i) is a non-fluorinated polydiorganosiloxane in an amount of from 50 to 99.5% by weight of component (A) and (A)(ii) is a fluorinated polydiorganosiloxane polymer in an amount of from 0.5 to 50% by weight of component (A); (B) at least one reinforcing filler; and at least one of (C) or (D), where (C) is at least one organohydrogenpolysiloxane (C)(i), at least one hydrosilylation catalyst (C)(ii), and optionally at least one cure inhibitor (C)(iii); or (D) at least one peroxide catalyst.

Claims

1. A curable silicone elastomer composition, the composition comprising: (A) a combination of (A)(i) and (A)(ii), wherein (A)(i) is a non-fluorinated polydiorganosiloxane present in an amount of from 50 to 99.5% by weight of component (A) and (A)(ii) is a fluorinated polydiorganosiloxane polymer present in an amount of from 0.5 to 50% by weight of component (A); (B) at least one reinforcing filler; and at least one of (C) or (D) wherein (C) is at least one organohydrogenpolysiloxane (C)(i), at least one hydrosilylation catalyst (C)(ii), and optionally at least one cure inhibitor (C)(iii); or (D) at least one peroxide catalyst; wherein the composition contains less than or equal to 0.1% by weight of the composition of conductive filler or semi conductive filler or a mixture thereof.

2. The curable silicone elastomer composition in accordance with claim 1, wherein the composition contains zero % by weight of conductive filler.

3. The curable silicone elastomer composition in accordance with claim 1, wherein component (C) is present in the composition, and component (A)(i) and optionally component (A)(ii) contain at least two alkenyl or alkynyl groups per molecule.

4. The curable silicone elastomer composition in accordance with claim 1, wherein component (B) is surface treated with a treating agent selected from the group consisting of organosilanes, polydiorganosiloxanes, organosilazanes, hexaalkyl disilazanes, short chain siloxane diols, fatty acids, fatty acid esters, and combinations thereof, to render the filler(s) hydrophobic.

5. The curable silicone elastomer composition in accordance with claim 1, wherein component (C)(i) is present and selected from the group consisting of: (i) trimethylsiloxy-terminated methylhydrogenpolysiloxane; (ii) trimethylsiloxy-terminated polydimethylsiloxane-methylhydrogensiloxanes; (iii) dimethylhydrogensiloxy-terminated dimethylsiloxane-methylhydrogensiloxane copolymers; (iv) dimethylsiloxane-methylhydrogensiloxane cyclic copolymers; (v) copolymers composed of (CH.sub.3).sub.2HSiO.sub.1/2 units and SiO.sub.4/2 units; (vi) copolymers composed of (CH.sub.3).sub.3SiO.sub.1/2 units, (CH.sub.3).sub.2HSiO.sub.1/2 units, and SiO.sub.4/2 units; (vii) copolymers containing (CH.sub.3).sub.2HSiO.sub.1/2 units and (R.sup.2Z).sub.d(R.sup.3).sub.eSiO.sub.(4-d-e)/2; and (viii) combinations thereof; wherein each R.sup.2 is the same or different and denotes a branched or linear fluoroalkyl group having from 1 to 8 carbon atoms; wherein each Z is the same or different and denotes a divalent alkylene group containing at least two carbon atoms, a hydrocarbon ether or a hydrocarbon thioether; wherein each R.sup.3 is the same or different and denotes an optionally substituted saturated or unsaturated silicon-bonded, monovalent hydrocarbon group; and wherein d=0 to 2, e=0 to 2, and when d is 0 at least one R.sup.3 group per unit contains one or more carbon-fluorine bonds.

6. The curable silicone elastomer composition in accordance with claim 1, wherein the composition further comprises at least one ingredient selected from the group consisting of compatibilizing agents, thermally conductive fillers, non-conductive fillers, pot life extenders, flame retardants, lubricants, non-reinforcing fillers, pigments coloring agents, adhesion promoters, chain extenders, silicone polyethers, mold release agents, diluents, solvents, UV light stabilizers, bactericides, wetting agents, heat stabilizers, compression set additives, plasticizers, and combinations thereof.

7. The curable silicone elastomer composition in accordance with claim 1, wherein component (C) is present, and the composition is stored prior to use, in either: (i) two parts, a Part A containing components (A), (B), and (C)(ii), and a part B containing components (A), (B), (C)(i), and (C)(iii); or (ii) four parts, a first Part A containing components (A)(i), (B), and (C)(ii), a second part A containing components (A)(ii), (B) and optionally component (C)(ii), a first part B containing components (A)(i), (B), (C)(i), and (C)(iii), and a second part B containing components (A)(ii), (B), and optionally components (C)(i) and (C)(iii).

8. The curable silicone elastomer composition in accordance with claim 7, wherein component (A)(ii) is not mixed with component (C)(i) prior to blending with component (A)(i) in Part B and/or wherein component (A)(ii) is not mixed with component (C)(ii) prior to blending with component (A)(i) in Part A.

9. A cured product of the curable silicone elastomer composition in accordance with claim 1.

10. A high voltage direct current insulator comprising, or consisting of, the cured product of claim 9.

11. A method for the manufacture of a high voltage direct current insulator, the method comprising: providing the curable silicone elastomer composition in accordance with claim 1; and mixing the composition together and curing.

12-14. (canceled)

15. The method for the manufacture of a high voltage direct current insulator in accordance with claim 11, wherein the curable silicone rubber composition is further processed by injection moulding, encapsulation moulding, press moulding, dispenser moulding, extrusion moulding, transfer moulding, press vulcanization, centrifugal casting, calendering, bead application or blow moulding.

16. The method for the manufacture of a high voltage direct current insulator in accordance with claim 11, wherein the curable silicone elastomer composition is introduced into a mold prior to cure to form a moulded silicone article.

17. The method for the manufacture of a high voltage direct current insulator in accordance with claim 11, wherein the curable silicone elastomer composition is either injection moulded to form an article or overmoulded by injection moulding around an article.

18. A high voltage direct current insulator comprising an elastomeric product of the curable silicone elastomer composition in accordance with claim 1.

19. A high voltage direct current insulator comprising an elastomeric product obtained by curing the curable silicone elastomer composition in accordance with claim 1.

20. The high voltage direct current insulator in accordance with claim 18, wherein the composition contains zero % by weight of conductive filler.

21. (canceled)

22. The A-high voltage direct current insulator in accordance with claim 18, further defined as an insulator adapted to reduce electrical stress in high voltage direct current (HVDC) applications.

23. An article or assembly comprising the high voltage direct current insulator in accordance with claim 18.

24. (canceled)

25. (canceled)

26. A cable accessory comprising the high voltage direct current insulator in accordance with claim 18.

27-29. (canceled)

Description

EXAMPLES

[0103] Several compositions using non-fluorinated polydiorganosiloxane polymer were prepared and are identified as LSR 1, LSR 2 LSR3 and HCR 1. The LSR 1, 2 and 3 compositions are prepared in two parts as they are hydrosilylation cured. The LSR compositions are shown in Table 1a and the HCR 1 composition is shown in Table 1b below. All viscosities are given at 25° C. unless otherwise indicated. Vinyl content and Si—H content of polymers was determined by quantitative IR in accordance with ASTM E168.

TABLE-US-00001 TABLE 1a Wt. % of Each Ingredient in LSR 1 and 2 LSR 1 LSR 1 LSR 2 LSR 2 LSR3 LSR3 Pt A Pt B Pt A Pt B Pt A Pt B Dimethylvinyl-terminated dimethyl 65.9 63.1 38.1 40.5 59.2 52.9 siloxane viscosity approximately 55 Pa.s Dimethylvinyl-terminated dimethyl 27.0 21.9 7.8 10.3 siloxane viscosity approximately 2 Pa.s Dimethylvinyl-terminated dimethyl 4.4 4.9 methylvinyl siloxane-viscosity 370 mPa.s, 1.16% vinyl Treated Fumed silica surface area 29.1 28.4 17.2 18.6 16.8 18.5 300m.sup.2/g (BET) with vinyl functionalization of about 0.15 mmol/g Dimethylhydroxy terminated 0.6 0.6 polydimethyl siloxane viscosity 21 mPa.s Dimethylhydrogensiloxy modified 0.0 2.8 silica having 0.97 wt. % H as Si—H and a viscosity of 25 mPa.s 1-Ethynylcyclohexanol 0.00 0.18 0.00 0.09 0.00 0.10 Karstedt's catalyst (Platinum, 1,3- 0.08 0.00 0.48 0.00 0.47 0.00 diethenyl-1,1,3,3- tetramethyldisiloxane complexes) diluted in dimethyl vinyl terminated siloxanes to give approximately 0.54% by weight of Pt Dimethylvinylated and trimethylated 17.3 14.7 silica Dimethyl, methylhydrogen siloxane 0 4.2 0 4.6 with methyl silsesquioxane having 0.81 wt. % H as SiH and a viscosity of 15 mPa.s

TABLE-US-00002 TABLE 1b Wt. % of Each Ingredient in HCR 1 HCR 1 Dimethylvinyl-terminated dimethyl Siloxane gum having 48.7 Williams plasticity of about 154 mm/100 having a vinyl content of 0.014% wt. Dimethylvinyl-terminated dimethyl methylvinyl Siloxane gum 17.7 having Williams plasticity of about 155 mm/100 having a vinyl content of 0.067% wt Treated Fumed silica surface area 300 m.sup.2/g (BET) - vinyl 33.6 functionalization of about 0.051 mmol/g

[0104] HCR 1 was cured using a peroxide catalyst, hereafter referred to as peroxide 1 which was a 45% paste of 2,5-Dimethyl-2,5-di(tert.butylperoxy)hexane in silicone. This is available commercially under a range of trade names such as DHBP-45-PSI (United Initiators). Peroxide 1 was added to the composition in an amount of 1 part per hundred parts of HCR 1.

[0105] Several compositions using fluorinated polydiorganosiloxane polymer were prepared and are identified as F-LSR 1, F-LSR 2 and FSR 1. F-LSR 1 was prepared in two parts as it is hydrosilylation cured. The compositions of F-LSR 1, F-LSR 2 are provided in Table 2a, the compositions of F-LSR 3 and F-LSR 4 are provided in Table 2b and, and the composition of FSR-1 is shown in Table 2c.

TABLE-US-00003 TABLE 2a Wt. % of Each Ingredient in F-LSR 1 and 2 F-LSR F-LSR F- 1 Pt A 1 Pt B LSR-2 dimethylvinyl-terminated Trifluoropropylmethyl 72.0 71.0 siloxane, viscosity 59 Pa .Math. s Dimethylvinylsiloxy-terminated dimethyl, 68.8 Trifluoropropylmethyl Siloxane (40 mol % trifluoropropylmethyl siloxane groups) - viscosity of 25 Pa .Math. s Treated Fumed silica 26.0 26.8 Treated Fumed silica surface area 300 m.sup.2/g 31.2 (BET) - with vinyl functionalization of about 0.16 mmol/g Cerium Hydrate 1.0 Unreactive silicone resin containing a mixture 1.0 of dimethylsiloxane units and phenylsilsesqui- oxane units, having a glass transition tempera- ture of about 65° C. Karstedt catalyst (Platinum, 1,3-diethenyl- 0.03 1,1,3,3-tetramethyldisiloxane complexes) diluted in dimethyl vinyl terminated siloxanes to give approximately 0.54% by weight of Pt Trifluoropropyl Silsesquioxane, Dimethylhydro-  2.1 gensiloxy-terminated containing 0.57% SiH as H Methyl-3-butyn-2-ol  0.1

TABLE-US-00004 TABLE 2b Wt % of Each Ingredient in F-LSR 3 and 4 F-LSR F-LSR F-LSR 3 Pt A 3 Pt B 4 dimethylvinyl-terminated Trifluoropropylmethyl 67.1 65.1 66.4 siloxane, viscosity 59 Pa .Math. s Treated Fumed silica 32.0 32.9 33.6 Unreactive silicone resin containing a mixture 0.9 of dimethylsiloxane units and phenylsilsesqui- oxane units, having a glass transition tempera- ture of about 65° C. Karstedt catalyst (Platinum, 1,3-diethenyl- 0.03 1,1,3,3-tetramethyldisiloxane complexes) diluted in dimethyl vinyl terminated siloxanes to give approximately 0.54% by weight of Pt Trifluoropropyl Silsesquioxane, Dimethylhydro- 1.9 gensiloxy-terminated containing 0.57% SiH as H Methyl-3-butyn-2-ol 0.06

TABLE-US-00005 TABLE 2c Wt % of Each Ingredient in FSR 1 FSR 1 Dimethylhydroxy terminated methylvinyl, trifluoropropyl- 49.05 methyl siloxane gum having a Williams plasticity of about 300 mm/100 Fumed silica surface area 300 m.sup.2/g (BET) treated with 33.9 dimethylhydroxyl terminated trifluoropropylsiloxanes (no vinyl content) Dimethylhydroxy terminated Trifluoropropylmethyl siloxane 16.4 gum having a Williams plasticity of about 300 mm/100 Dimethylvinyl terminated dimethylmethylvinyl siloxane 0.65 having a viscosity of about 14,500 mPa .Math. s at 25° C. and about 7.5 wt. % vinyl content groups

Cured Sheets

[0106] Cured sheets were prepared at 0.5 mm or 1 mm thickness using compression molds, a hydraulic press set at 300 psi (2.068 MPa) and a temperature of 170° C. The sheets were cured for a period of 10 minutes. If desired cured sheets were suspended in vented ovens and post cured for up to 4 hours at 200° C.

[0107] Example 1—Blends of F-LSR 1 and LSR 1 were prepared using the parts by weight as shown, cured sheets prepared as described above and the volume resistivity of each cured sheet was measured. In this case sheets were not post cured.

[0108] All required part A materials were mixed together first, all required part B materials were similarly mixed together before the resulting intermediate mixtures were combined to give the final overall formulation. The blends used are indicated in Table 3a and the resulting volume resistivity results are depicted in Table 3b below.

TABLE-US-00006 TABLE 3a Blends used in Example 1 Parts by Weight F-LSR 1 F-LSR 1 Example LSR 1 Part A Part A LSR 1 Part B Part B Comparative 1 100 0 100 0 Example 1-1 99 1 99 1 Example 1-2 97 3 97 3 Example 1-3 95 5 95 5 Example 1-3 95 5 95 5 Example 1-5 90 10 90 10 Example 1-6 80 20 80 20 Example 1-7 80 20 80 20 Example 1-8 70 30 70 30 Example 1-9 60 40 60 40 Comparative 2 0 100 0 100

[0109] Volume Resistivity (VR) Testing Volume resistivity was measured in accordance with ASTM D257-14 Standard Test Methods for DC Resistance or Conductance of Insulating Materials on cured sheets ranging in thickness from 0.5 to 2 mm using a Keithley® 8009 test cell coupled with a Keithley® 5½-digit Model 6517B Electrometer/High Resistance Meter, controlled with Model 6524 High Resistance Measurement Software. D257.

[0110] Within the Model 6524 High Resistance Measurement Software an alternating polarity test was implemented as an “Hi-R” test to minimise the effects of background currents. This is described in detail in Keithley White Paper “Improving the Repeatability of Ultra-High Resistance and Resistivity Measurements” by Adam Daire.

[0111] The Hi-R alternating polarity test was used to minimise effects of background current. This method is designed to improve high resistance/resistivity measurements which are prone to large errors due to background currents.

[0112] An Alternating Polarity stimulus voltage was used with a view to isolating stimulated currents from background currents. When the Alternating Polarity method is used, the Voltage Source output of the electrometer alternates between two voltages: Offset Voltage+Alternating V, and Offset Voltage—Alternating V, at timed intervals (the Measure Time).

[0113] A current measurement (Imeas) is performed at the end of each alternation. After four Imeas values are collected, a current reading is calculated (Icalc). Icalc is the binomially weighted average of the last four current measurements (Imeas1 through Imeas4):

Icalc=(1*Imeas1−3*Imeas2+3*Imeas3−1*Imeas4)/8

The signs used for the four terms are the polarities of the alternating portion of the voltages generating the respective currents. This calculation of the stimulated current is unaffected by background current level, slope, or curvature, effectively isolating the stimulated current from the background current. The result is a repeatable value for the stimulated current and resistance or resistivity that are calculated from it. The time dependence of the stimulated current is a material property. That is, different results will be obtained when using different Measure Times, due to material characteristics.

[0114] A Measure Time of 60 seconds was used with 3 voltage cycles typically of +1000V then −1000V. From the 6 resulting measured currents the software obtains 3 Icalc values, the 1.sup.st of these are rejected and then the subsequent 2 values used to calculate VR from

VR=(V.sub.max−V.sub.min)×area/(2×Icalc×Sample Thickness)

The two resulting VR values were averaged to give a final value.
For the polymer blends shown in the examples a weighted average VR was calculated based on

Calculated Blend VR=(% Mass Component A×VR component A)+(% Mass Component B×VR component B)

TABLE-US-00007 TABLE 3b volume resistivity results of Example 1 Measured Volume Example Resistivity Ω .Math. cm Calculated Blend VR Comparative 1 1.69 × 10.sup.16 1.69 × 10.sup.16 Example 1-1 1.14 × 10.sup.15 1.67 × 10.sup.16 Example 1-2 4.25 × 10.sup.14 1.64 × 10.sup.16 Example 1-3 2.24 × 10.sup.14 1.61 × 10.sup.16 Example 1-3 3.17 × 10.sup.14 1.61 × 10.sup.16 Example 1-5 2.36 × 10.sup.14 1.52 × 10.sup.16 Example 1-6 2.41 × 10.sup.14 1.35 × 10.sup.16 Example 1-7 2.58 × 10.sup.14 1.35 × 10.sup.16 Example 1-8 3.61 × 10.sup.14 1.18 × 10.sup.16 Example 1-9 2.55 × 10.sup.14 1.01 × 10.sup.16 Comparative 2 1.33 × 10.sup.12 1.33 × 10.sup.12

[0115] It is clear that in all examples the achieved change in VR is much greater than would be predicted from the calculated blend VR.

[0116] For examples 1-2 and 1-3 a number of duplicates were measured, and the results analyzed statistically using a Student's t-test. This clearly showed that the measured difference between the means was non-zero at the 99% confidence level and thus that the volume resistivity could be well controlled within a desired range. These results are depicted in Table 3c below

TABLE-US-00008 TABLE 3c Example 1-2 Number of Duplicates  4 Mean 4.36 × 10.sup.14 Std Dev 2.62 × 10.sup.13 Example 1-3 Number of Duplicates 12 Mean 2.65 × 10.sup.14 Std Dev 5.30 × 10.sup.13

[0117] Example 2—Blends of F-LSR 1 and LSR 2 were prepared using the parts by weight as shown in Table 4a below.

TABLE-US-00009 TABLE 4a blends used in Example 2 Parts by Weight F-LSR 1 F-LSR 1 Example LSR 2 Part A Part A LSR 2 Part B Part B Comparative 3 100 0 100 0 Example 2-1 100 0  94 6 Example 2-2  97 5  97 5

[0118] Cured sheets of the blends were prepared as described above and the VR was measured for each sheet using the method and equipment previously described.

TABLE-US-00010 TABLE 4b Volume resistivity results for the blends in Example 2 Measured Volume Resistivity Ω .Math. cm Calculated Blend VR Comparative 3 1.30 × 10.sup.15 1.30 × 10.sup.15 Example 2-1 3.67 × 10.sup.14 1.27 × 10.sup.14 Example 2-2 2.75 × 10.sup.14 1.24 × 10.sup.14

[0119] The physical properties of Example 2-1 were also determined and compared with those of Comparative as can be seen in Table 4c below.

TABLE-US-00011 TABLE 4c Mechanical properties were also measured for example 2-1 and Comparative 3 Example 2-1 Comparative 3 Shore A (ASTM D2240) 40 40 Modulus.sub.100 MPa (ASTM D412 Die C) 1.27 0.82 Tensile Strength MPa (ASTM D412 6.4 7.1 Die C) Elongation at Break % (ASTM D412 424 562 Die C) Tear Die B kN/m (ASTM D624 B) 20.6 24.0

[0120] Modulus.sub.100 means the modulus value at 100% elongation. Example 2-1 shows that it is not necessary to add the F-LSR equally to both parts of the formulation to achieve the desired VR modification. Example 2.1 also shows that good mechanical properties can be maintained whilst achieving the desired modification of VR. Example 2-2 shows that further modification of VR can be achieved depending on formulation.

[0121] Example 3—Blends of F-LSR 2 and LSR 2 were prepared using the parts by weight as shown in Table 5a below.

TABLE-US-00012 TABLE 5a blends used in Example 3 Parts by Weight F-LSR 2 F-LSR 2 Example LSR 2 Part A Part A LSR 2 Part B Part B Comparative 3 100 0 100 0 Example 3-1 97.5 2.5 97.5 2.5 Example 3-2 92.5 7.5 92.5 7.5 Example 3-3 92.5 7.5 92.5 7.5 Example 3-4 87.5 12.5 87.5 12.5 Example 3-5 80 20 80 20 Comparative 4 100 100

[0122] Cured sheets of the blends were prepared as described above and the VR was measured for each sheet using the method and equipment previously described.

TABLE-US-00013 TABLE 5b Volume Resistivity results from the Blends in Example 3 Measured Volume Resistivity Ω .Math. cm Calculated Blend VR Comparative 3 1.17 × 10.sup.15 1.17 × 10.sup.15 Example 3-1 6.29 × 10.sup.14 1.14 × 10.sup.15 Example 3-2 6.90 × 10.sup.14 1.08 × 10.sup.15 Example 3-3 6.75 × 10.sup.14 1.08 × 10.sup.15 Example 3-4 7.93 × 10.sup.14 1.03 × 10.sup.15 Example 3-5 6.70 × 10.sup.14 9.50 × 10.sup.14 Comparative 4 9.05 × 10.sup.13 9.05 × 10.sup.13

[0123] It is clear that in all examples the achieved change in VR is much greater than would be predicted from the calculated blend VR. In the case of Examples 3-1 to 3-3 the measured VR is notably lower than for Example 3-4 with the lowest VR unexpectedly being observed for Example 3-1 which has the lowest level of F-LSR 2.

[0124] Mechanical properties were also measured for example 3-3 and Comparative 3 as depicted in Table 5c below.

TABLE-US-00014 TABLE 5c Physical property results from Example 3 Example 3-1 Comparative 3 Shore A (ASTM D2240) 49 40 M.sub.100 MPa (ASTM D412 Die C) 2.42 0.82 Tensile Strength MPa (ASTM D412 6.1 7.1 Die C) EB % (ASTM D412 Die C) 307 562 Tear Die B kN/m (ASTM D624 B) 33.2 24.0 Dielectric Strength (AC) kV/mm 35.5 30.0 (IEC 60243)

[0125] EB means elongation at break. Example 3-3 shows good physicals with tear strength and dielectric strength actually improved over Comparative 3.

[0126] Example 4—Blends of HCR 1 and FSR 1 were prepared using the parts by weight as shown in Table 6a below. Peroxide 1 was used as the curing catalyst, 0.5 mm thick cured sheets prepared and post cured for 1 h @ 200° C. The Volume Resistivity of the resulting sheets was then measured and the results also depicted in Table 6a below.

TABLE-US-00015 TABLE 6a blends and volume resistivity results from Example 4 Measured Volume Example HCR 1 FSR 1 Resistivity Ω .Math. cm Calculated Blend VR Comparative 5 100  0 1.94 × 10.sup.16 1.94 × 10.sup.16 Example 4-1  90  10 1.88 × 10.sup.15 1.75 × 10.sup.16 Example 4-2  80  20 1.26 × 10.sup.15 1.55 × 10.sup.16 Comparative 6  0 100 3.86 × 10.sup.11 3.86 × 10.sup.11

[0127] The physical properties of the products of Example 4 were also determined as indicated in Table 6b below.

TABLE-US-00016 TABLE 6b physical property results from blends in Example 4 Example Example Comparative 4-1 4-2 5 Shore A (ASTM D2240) 58.3 57.6 58.9 M.sub.100 MPa (ASTM D412 Die C) 1.68 1.62 1.74 Tensile Strength MPa (ASTM D412 10.9 11.4 12.6 Die C) EB % (ASTM D412 Die C) 561 567 578 Tear Die B kN/m (ASTM D624 B) 24.1 22.7 22.1

[0128] It is clear that in all examples the achieved change in VR is much greater than would be predicted from the calculated blend VR. The examples also show that good mechanical properties can be maintained whilst achieving the desired reduction in volume resistivity.

Example 5

[0129] Blends of F-LSR 3 or F-LSR 4 and LSR 3 were prepared using the parts by weight as shown in Table 7a below. All required Part A blend ingredients were first mixed together, all required Part B blend ingredients were also mixed together. The example formulations were then prepared by mixing the Part A and Part B blends at a 1:1 ratio.

TABLE-US-00017 TABLE 7a Parts by Weight Part A Blends Part B Blends LSR 3 F-LSR 3 F-LSR LSR 3 F-LSR 3 F-LSR Example Part A Part A 4 Part B Part B 4 Example 5-1 (F-LSR with cure  90 10  90 10 package added) Example 5-2 (F-LSR without cure  80 20 100 package) Example 5-3 (F-LSR without cure  90 10  90 10 package) Example 5-4 (F-LSR without cure 100  80 20 package)

[0130] Cured sheets of the blends were prepared as described above, further sheets were post cured for 4 hours @ 200° C. as described above. The VR was measured for each sheet using the method and equipment previously described.

TABLE-US-00018 TABLE 7b Volume Resistivity results from the Blends in Example 5 Measured Volume Measured Volume Resistivity Resistivity (cured sheets) (post cured sheets) Ω .Math. cm Ω .Math. cm Example 5-1 (F-LSR with 7.61 × 10.sup.13 8.21 × 10.sup.14 cure package added) Example 5-2 (F-LSR 9.56 × 10.sup.13 1.46 × 10.sup.14 without cure package) Example 5-3 (F-LSR 5.16 × 10.sup.13 1.45 × 10.sup.14 without cure package) Example 5-4 (F-LSR 4.38 × 10.sup.13 1.60 × 10.sup.14 without cure package)

[0131] It is clear that for all materials there is some increase in volume resistivity after post cure, but the degree of increase is considerable reduced where F-LSR is used without the cure package. In the case of Example 5-2 the change in volume resistivity after post cure is especially low. Mechanical properties were also measured for examples after post cure for 4 h @ 200° C. as depicted in Table 7c below.

TABLE-US-00019 TABLE 7c Physical property results from Example 5 Example Example Example 5-1 5-3 5-4 Shore A (ASTM D2240) 47.9 49.0 48.8 M.sub.100 MPa (ASTM D412 Die C) 2.38 2.51 2.55 Tensile Strength MPa (ASTM D412 6.7 6.5 6.2 Die C) EB % (ASTM D412 Die C) 430 400 370 Tear Die B kN/m (ASTM D624 B) 25.4 20.2 25.4

[0132] Example 5-1 shows good mechanical properties where the F-LSR includes a cure package. The results for examples 5-2 to 5-4 show that the mechanical properties are not significantly degraded when an F-LSR is used without the cure package.