SILICONE ELASTOMER COMPOSITIONS

Abstract

The present disclosure relates to curable silicone elastomer compositions having enhanced adhesive properties with respect to a wide variety of substrates (hereafter referred to as curable silicone elastomer compositions). Elastomers made by curing the curable silicone elastomer compositions may be adhered to a wide variety of substrates to form composites comprising the elastomers and the substrates. Processes for adhering the elastomers made by curing the curable silicone elastomer compositions to the substrates are also provided. An adhesion promoter, component (D), is provided to enhance adhesion. Component (D) is a polyorganosiloxane having (i) at least one unsaturated group per molecule selected from alkenyl groups and alkynyl groups and (ii) an anhydride functionality and an aromatic functionality, wherein a carbon of the aromatic functionality is separated from a carbon of a carbonyl group of the anhydride by a carbon chain of from 1 to 3 non-aromatic carbon atoms inclusive.

Claims

1. A curable silicone elastomer composition that can achieve adhesion on suitable material substrates, the composition comprising: (A) one or more organopolysiloxanes containing at least two unsaturated groups per molecule selected from alkenyl groups and alkynyl groups and having a viscosity in a range of 1,000 mPa.Math.s to 500,000 mPa.Math.s at 25?, but which contains no anhydride functionality; (B) a curing agent comprising: (B)(i) an organic peroxide radical initiator; or (B)(ii) a hydrosilylation cure catalyst package comprising: a) an organosilicon compound having at least two, optionally at least three, SiH groups per molecule; and b) a hydrosilylation catalyst; (C) at least one reinforcing filler, and optionally one or more non-reinforcing fillers; and (D) a polyorganosiloxane having; (i) at least one unsaturated group per molecule selected from alkenyl groups and alkynyl groups; and (ii) an anhydride functionality and an aromatic functionality, wherein a carbon of the aromatic functionality is separated from a carbon of a carbonyl group of the anhydride by a carbon chain of from 1 to 3 non-aromatic carbon atoms inclusive.

2. The curable silicone elastomer composition in accordance with claim 1, wherein component (D) comprises a monofunctionalized polyorganosiloxane of the formula ViR.sup.4.sub.2SiO(R.sup.5.sub.2SiO).sub.mSiR.sup.4.sub.2A or the formula AR.sup.4.sub.2SiO(R.sup.5.sub.2SiO).sub.mSiR.sup.4.sub.2A where each R.sup.4 is an alkyl group, each R.sup.5 is an alkyl group, an alkenyl group, an alkynyl group or A and where A is: ##STR00004## with X being an aromatic group and wherein each molecule comprises at least one alkenyl or alkynyl group.

3. The curable silicone elastomer composition in accordance with claim 2, wherein in component (D), X is a benzoyl group, a tolyl group or a xylyl group.

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 ingredients.

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, which is 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 polycarbonate.

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

10. An article comprising a silicone elastomer cured from the curable silicone elastomer composition in accordance with claim 1 adhered to a plastic substrate.

11. An article comprising a silicone elastomer cured from the curable silicone elastomer composition in accordance with claim 1 adhered to a thermoplastic substrate, an organic resin substrate or a thermoplastic and an 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 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 apparatuses and/or wearable electronic devices, parts of mobile phones, mobile telecommunications equipment, gaming machines, clocks, image receivers, DVD equipment, MD equipment, CD equipment, precision electronic 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, OA equipment, connector seals, spark plug caps, components of sensors, and automobile components.

15. The curable silicone elastomer composition in accordance with claim 1, wherein component (C) comprises reinforcing filler and non-reinforcing filler.

Description

EXAMPLES

[0132] All viscosities in the following examples were measured using a All viscosities in the following examples were measured using a rheometer such as an Anton-Paar MCR-301 rheometer fitted with a 25 mm cone-and-plate fixture and operated at 25? C. unless otherwise indicated. Unless otherwise noted, viscosities are reported as zero-shear viscosities, meaning the value extrapolated to zero shear rate from the statistically significant, rate-independent Newtonian region of a viscosity vs. shear rate sweep. The wt. % of vinyl and SiH were determined using quantitative infra-red analysis in accordance with ASTM E168. In the first series of Examples, a Reference Example and 3 examples were provided using compositions containing the following ingredients:

TABLE-US-00001 TABLE 1 ingredients Ingredient Description Polymer 1 Dimethylvinylsiloxy-terminated Dimethyl Siloxane, 0.085 wt. % Vinyl (Vi), zero shear viscosity 57000 mPa .Math. s Polymer 2 Dimethylvinylsiloxy-terminated Dimethyl, Methylvinyl Siloxane, vinyl content of 1.1 wt. % and a viscosity of about 400 mPa .Math. s Polymer 3 Tetramethyltetravinylcyclotetrasiloxane Polymer 4 Dimethyl Hydroxy-terminated Dimethyl Siloxane, zero shear viscosity of viscosity 40 mPa .Math. s Treated filler In situ hydrophobically treated fumed silica Cross-linker 1 Dimethyl, Methylhydrogen Siloxane with Methyl Silsesquioxane Si-H content of 0.84, and with zero shear viscosity of 15 mPa .Math. s Cross-linker 2 Trimethylsiloxy-terminated Dimethyl, Methylhydrogen Siloxane, Si-H content of 0.776 wt. %, and viscosity of about 5 mPa .Math. s Catalyst Karstedt's (Platinum) catalyst in dimethyl siloxane, dimethylvinylsiloxy terminated (0.42 wt. % Vi, 400 mPa .Math. s Inhibitor 3.5 wt. % Ethynyl Cyclohexanol (ETCH) in Polymer 2

[0133] The treated filler was fumed silica sold under the trade name CAB-O-SIL? S-17D by the Cabot Corporation treated with hexamethyldisilazane (HMDZ) and tetramethyldivinyldisilazane.

[0134] Four alternative adhesion promoters were utilised in the following first series of examples. They were prepared in accordance with the method described in PCT/US20/044709, published as WO 2021/0260055: [0135] Adhesion Promoter 1: Reaction product of ViR.sup.4.sub.2SiO(R.sup.5.sub.2SiO).sub.mSiR.sup.4.sub.2Vi in which R.sup.4 and R.sup.5 are methyl and the average value of m is 177 with maleic anhydride (MAH) and AH and benzoyl peroxide (BPO), in m-xylene, the resulting product had an equivalent wt. of vinyl (g/mol Vi) of 9600 and an equivalent wt. of anhydride (g/mol anhydride) of 22,000. [0136] Adhesion Promoter 2 Reaction product of ViR.sup.4.sub.2SiO(R.sup.5.sub.2SiO).sub.mSiR.sup.4.sub.2Vi in which R.sup.4 and R.sup.5 are methyl and the average value of m is 46 with maleic anhydride and benzoyl peroxide (BPO), in m-xylene, the resulting product had an equivalent wt. of vinyl (g/mol Vi) of 3700 and an equivalent wt. of anhydride (g/mol anhydride) of 3900. [0137] Adhesion Promoter 3 Reaction product of ViR.sup.4.sub.2SiO(R.sup.5.sub.2SiO).sub.mSiR.sup.4.sub.2Vi in which R.sup.4 and R.sup.5 are methyl and the average value of m is 7 with maleic anhydride and benzoyl peroxide (BPO), in m-xylene, the resulting product had an equivalent wt. of vinyl (g/mol Vi) of 1000 and an equivalent wt. of anhydride (g/mol anhydride) of 860. [0138] Adhesion Promoter 4 is further example using the starting ingredients identified for Adhesion promoter 3 but using reduced ratio of MAH:Vi than was used for Additive 3. resulting with an equivalent wt. of vinyl (g/mol Vi) of 590 and an equivalent wt. of anhydride (g/mol anhydride) of 1400.
In the above the estimate of the average value of m was determined from the number average molecular weight (Mn) of the polymer peak obtained by GPC in a solvent such as toluene calibrated with polystyrene standards by using the following formula. by using the following formula:

n=[Mn?2*FW(M(R.sup.4.sub.2Vi))]/FW(D(R.sup.5.sub.2))

where FW denotes the formula weight of the structural group in brackets, with Mn, and all FW reported in g/mol. For instance, for a vinyl terminated PDMS of structure M.sup.Vi-D.sub.n-M.sup.Vi,

n=[Mn?2*(93.202)]/74.16

The equivalent weight of vinyl (EW(Vi)) is again determined from the number average molecular weight (Mn) of the polymer peak obtained by GPC in a solvent such as toluene calibrated with polystyrene standards and is determined using the following formula

EW(Vi)=Mn/(v+y)

The equivalent weight of anhydride (EW(anh)) is given as follows: EW(anh)=Mn/(x+z)

[0139] The seven different compositions assessed were prepared by making the part A compositions and then the part B compositions and subsequently mixing the part A and part B compositions in a 1:1 weight ratio.

TABLE-US-00002 TABLE 2 Part A composition (wt. %) Component Ref. Ex. 1 Ex. 2 Ex. 3 Polymer 1 67.00 53.53 64.30 64.30 Polymer 2 3.53 2.82 3.38 3.38 Polymer 3 0.15 0.12 0.15 0.15 Polymer 4 1.07 0.85 1.02 1.02 Treated filler 27.90 22.30 26.78 26.78 Catalyst 0.36 0.28 0.34 0.34 Adhesion Promoter 1 Adhesion Promoter 2 20.09 Adhesion Promoter 3 4.02 Adhesion Promoter 4 4.02

[0140] Adhesion promoters 1 and 2 were added directly into Part A. Adhesion promoters 3 and 4 were found to be solids and were therefore solubilized in an equivalent of acetone, which was then mixed into the Part A composition. The acetone was then allowed to evaporate.

[0141] The part A composition was prepared using a Flacktek Speedmixer? the ingredients were added into a polypropylene dental cup and then the mixture was mixed at 2000 rpm for 20 seconds, followed by hand scraping and mixing. The sample was mixed at 2000 rpm for a further 20 seconds, followed by hand scraping and mixing and then for a final mixing at 2000 rpm for 20 seconds.

TABLE-US-00003 TABLE 3 Part B composition (wt. %) Component Ref. 1 Ex. 1 Ex. 2 Ex. 3 Polymer 1 61.23 60.55 60.80 60.48 Polymer 2 1.53 1.51 1.52 1.51 Cross-linker 1 1.99 1.97 1.98 1.97 Cross-linker 2 1.10 0.69 1.22 Polymer 4 1.02 1.01 1.01 1.00 Treated filler 31.89 31.54 31.67 31.50 Inhibitor 2.34 2.32 2.33 2.31

[0142] A similar mixing protocol was employed for mixing Part B, as was used for the part A composition. Subsequently Parts A and B were mixed together in a 1:1 weight ratio.

[0143] The different compositions prepared once the part A and part B compositions had been mixed together were applied onto two substrates. [0144] Substrate 1 (S. 1) was a polybutylene terephthalate (PBT) sold under the tradename Ultradur? B4300G4 by BASF (20% glass fibers); and

[0145] In each instance the respective substrate was wiped with isopropyl alcohol (IPA) and air-dried prior to application of the prepared composition. In each case the prepared composition was then applied onto the substrate at a thickness of 25 mils (0.0635 cm). Subsequently, the silicone composition was cured in a forced air oven at 150? C. for 1 hour. Using a razor blade, two perpendicular lines separated by roughly the width of the 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 material between the cuts by the spatula held down at approximately an angle of 30? from the substrate surface. Adhesion (or lack of adhesion) was then subjectively assessed.

TABLE-US-00004 TABLE 4 Tested Property Results. Mmol anhydride/100 g Mmol anhydride/100 g Adhesion of total formulation of total matrix on S. 1 Ref. 1 ? Ex. 1 2.56 3.53 + Ex. 2 2.32 3.30 + Ex. 3 1.43 2.02 +

[0146] For the avoidance of doubt in the above and following tables etc., when referring to the total composition this is relative to everything shown in the ingredients table. When referring to the matrix we are discussing the unfilled composition (total composition minus treated filler).

[0147] In Table 4 the indication (?) poor adhesion=adhesive failure (separation from the substrate) and +) moderate to good adhesion=mixed mode failure [cohesive failure (tear in the elastomer) and adhesive failure].

[0148] The tables above show the pronounced effect of the anhydride-grafted additives in the compositions of this invention relative to those which don't have adequate levels of anhydride functionality. Note additives that have low anhydride content (or higher equivalent weight of anhydride EWanh) will require commensurately higher concentrations in wt. % to be effective. For example, adhesion promoter 1 (EWanh=22,000 g/mol) will requires far higher concentrations (beyond what was tested) in the LSR formulation than adhesion promoter 2 (EWanh=3900 g/mol) and adhesion promoter 3 (EWanh=860 g/mol) to be effective as an adhesion promoter in this formulation.

[0149] A second series of examples were produced using alternative compositions. Components not previously identified are shown in Table 5 below and the compositions per se are depicted in Table 6.

TABLE-US-00005 TABLE 5 Additional ingredients not used in previous examples Component Description Filler 1 RA-0127 Silver Flake from Metalor Technologies, a 3.97 ?m average (D50) particle size Filler 2 Conduct-O-Fil? SA300S20 silver-coated aluminum granules from Potters Industries, 40 ?m average particle size (diameter) Filler 3 Conduct-O-Fil? S2429-S silver-coated solid glass spheres from Potters Industries average diameter 89 ?m average particle size (diameter) Polymer 5 Vinyl MQ resin in dimethylvinylsiloxy terminated dimethyl siloxane having an average viscosity of about 5,400 mPa .Math. s Polymer 6 Vinyldimethyl terminated polydimethylsiloxane having a viscosity of about 1949 mPa .Math. s Silane 1 Reaction product of 3-glycidoxypropyltrimethoxysilane and an oligomeric random copolymer diol of poly(methylvinylsiloxane-dimethylsiloxane) with a post-reacted vinyl content of 6 wt. % Vi and a zero-shear viscosity of 15 mPa-s at 25? C. Silane 2 1,6-bis(trimethoxysilyl) hexane Platinum 1,3,-diethyl-1,1,3,3-tetramethyldisiloxane platinum complex (2 wt. % Pt). Catalyst 2 Inhibitor A solution of 10% of polymer 3 diluted in Polymer 4. solution 1 Catalyst A solution of 10% Platinum Catalyst 2 diluted in Polymer 4. Solution 1

[0150] In this case adhesion promoter 1 as described above was utilised as adhesion promoter and was compared with the corresponding polymeric starting material for making adhesion promoter 1, namely ViMe.sub.2SiO[Me.sub.2SiO].sub.177SiMe.sub.2Vi having a viscosity of about 443 mPa.Math.s, referred to below as Anhydride-free additive. The particle size information regarding fillers 1, 2 and 3 is taken from the supplier datasheets.

[0151] The tables below list the sample formulations for Part I showing grams (g) of each component (table 3) and the calculated anhydride mmol concentration per 100 g of total formulation and matrix component (table 4).

TABLE-US-00006 TABLE 6 Formulations for the electrically conductive formulations Ref. 2, C. 1, 2 and Ex. 4 to 7. Ref. 2 C. 1 C. 2 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Adhesion Promoter (AP) None 2 1 1 1 1 1 AP (g) 0 0.4 0.04 0.2 0.4 0.6 0.8 AP (wt. %) 0 1.0 0.1 0.5 1.0 1.5 2.0 Polymer 1 (g) 5.11 4.858 5.084 4.984 4.858 4.732 4.607 Polymer 2 (g) 1.278 1.215 1.271 1.246 1.215 1.183 1.152 Silane 1 (g) 0.406 0.386 0.404 0.396 0.386 0.376 0.366 Silane 2 (g) 0.041 0.039 0.041 0.04 0.039 0.038 0.037 Cross-linker (g) 0.573 0.545 0.57 0.559 0.545 0.531 0.516 Inhibitor (g) 0.445 0.423 0.443 0.434 0.423 0.412 0.401 Catalyst (g) 0.276 0.262 0.275 0.269 0.262 0.256 0.249 Filler 1 (g) 3.822 3.822 3.822 3.822 3.822 3.822 3.822 Filler 2 (g) 19.11 19.11 19.11 19.11 19.11 19.11 19.11 Filler 3 (g) 8.941 8.941 8.941 8.941 8.941 8.941 8.941

[0152] Preparation of Samples. In a dental cup, prepare the inhibitor solution 1 and catalyst solution 1 shown below:

Inhibitor Solution 1

[0153] Prepare samples of the Inhibitor Solution 1 in a dental cup by first adding 2.00 g of Inhibitor 1, followed by 18.00 g of Polymer 2. The added components were then mixed at 2000 revolutions per minute (rpm) for 30 seconds.

[0154] Catalyst Solution 1

[0155] Prepare samples of the Catalyst Solution 1 in a dental cup by first adding 2.00 g of Platinum Catalyst 1, followed by 18.00 g of Polymer 2. The added components were then mixed at 200 revolutions per minute (rpm) for 30 seconds.

[0156] Preparation of Formulations

[0157] In a dental cup, add the desired amounts of Polymer 1, Polymer 2, Additive 1 or 2 (where it applies), Silane 1, Silane 2, and Filler 1. Gently hand mix and dental mix once for 30 seconds at 1600 revolutions per minute (rpm). Add Filler 2. Gently hand mix and dental mix once for 30 seconds at 1600 revolutions per minute (rpm). Add Filler 3. Gently hand mix and dental mix for 30 seconds at 1600 revolutions per minute (rpm) twice. Add the desired amount of Inhibitor Solution 1 and Crosslinker 1. Gently hand mix and dental mix once for 30 seconds at 1600 revolutions per minute (rpm). Add the desired amount of Catalyst Solution 1. Gently hand mix and dental mix once for 30 seconds at 1600 revolutions per minute (rpm) to obtain the final sample.

TABLE-US-00007 TABLE 7 Calculated mmol of the anhydride in the overall formulation and relative to the matrix component using the calculation described below. Ref. 2 C. 5 C. 6 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Adhesion Promoter (AP) None 2 1 1 1 1 1 AP (g) 0 0.4 0.04 0.2 0.4 0.6 0.8 AP (wt. %) 0 1.0 0.1 0.5 1.0 1.5 2.0 wt. % Additive (of total composition) 0 0 0.1 0.5 1.0 1.5 2.0 mmol Anhydride/100 g NA NA 0.005 0.023 0.045 0.068 0.091 (of total composition) wt. % Additive (of total matrix) 0 4.921 0.492 2.461 4.921 7.382 9.843 mmol Anhydride/100 g total matrix NA NA 0.022 0.112 0.224 0.336 0.447 Cohesive failure to substrate ? ? ? + + + + (indicated by a +)

[0158] Description of Calculation for mmol of Anhydride: mmol anhydride was calculated by dividing the number of grams of the anhydride-grafted additive (e.g., a maleic anhydride grafted additive) in 100 g of the formulation or in 100 g of the matrix component (unfilled) itself (as shown in the table) by 22000 g/mol (for additive 1) and then multiplying this by 1000.

[0159] A filmic polyester release liner with a fluorinated coating on the other (3M? 9956 Medical Release Liner, Polyester, Fluoropolymer was used as a substrate for curing the samples in-between two sheets where the polyester side of the substrate was exposed to the sample. Each composition from Table 6 above was applied on to the substrate surface and after the sandwiched material was cured at 150? C. for 1 hour was evaluated for relative adhesion strength by determining whether cohesive failure resulted from a peel test. The results show that the control formulation with no additive 1 (reference 1), the formulation with an additive containing no anhydride functionality (additive 2, C. 1), as well as the formulation containing 0.1 wt. % additive 1 (C. 22) show adhesive failure. Formulations with between 0.5 and 2 wt. % additive 1 show cohesive failure indicating improved relative adhesion to the substrate. This surprising result prompted the previous example with the LSR demonstrating that adhesion to plastic and other substrates can be improved using component (D) as described herein. These examples demonstrate that this also is achievable using filled siloxane systems, for example electrically conductive composites.

[0160] The peel test was conducted at room temperature on the cured samples by manually peeling the two sheets apart to determine whether cohesive failure resulted.