SILICONE RUBBER COMPOSITIONS

Abstract

A curable silicone rubber composition of the type referred to in industry as “self-adhesive” or as having “selective adhesion” (hereafter referred to as “curable self-adhesive silicone rubber compositions”). The curable self-adhesive silicone rubber compositions comprise: (A) one or more organopolysiloxanes containing at least 2 alkenyl groups and/or alkynyl groups per molecule and having a viscosity in a range of 1000 mPa.Math.s to 200,000 mPa.Math.s at 25° C.; (B) an organopolysiloxane containing at least 2 or 3 silicon-bonded hydrogen atoms per molecule; (C) at least one hydrosilylation catalyst; (D) at least one reinforcing and optionally one or more non-reinforcing fillers; (E) an adhesion promoter; and (F) an oligomer which has been found to surprisingly provide heat-humidity stabilization.

Claims

1. A self-adhesive curable silicone elastomer composition that can achieve adhesion on plastic/thermoplastic/resin material substrates, the self-adhesive curable silicone elastomer composition comprising: (A) one or more organopolysiloxanes containing at least 2 alkenyl groups and/or alkynyl groups per molecule and having a viscosity in a range of 1,000 to 200,000 mPa.Math.s at 25° C.; (B) an organopolysiloxane containing at least 2 or 3 silicon-bonded hydrogen atoms per molecule; (C) at least one hydrosilylation catalyst; (D) at least one reinforcing filler and optionally one or more non-reinforcing fillers; (E) an adhesion promoter; and (F) an oligomer of the formula;
(R.sup.3O).sub.3Si—X—(SiR.sup.3.sub.2—O).sub.y(SiR.sup.3.sub.2—X).sub.n—(SiR.sup.3.sub.2—O).sub.z—Y—(O—SiR.sup.3.sub.2).sub.z(XSiR.sup.3.sub.2).sub.n(O—SiR.sup.3.sub.2).sub.y—X—Si(O R.sup.3).sub.3 wherein Y is —SiR.sup.1.sub.2—, —SiR.sup.1R.sup.2— or —Si R.sup.3R.sup.1—O—R.sup.3R.sup.1Si—; each R.sup.3 may be the same or different and is an alkyl group having 1 to 6 carbons; each X may be the same or different and is an alkylene group having from 1 to 6 carbons; each R.sup.1 is a phenyl group; each R.sup.2 is —(O—Si R.sup.3.sub.2).sub.z(XSi R.sup.3.sub.2).sub.n(O—Si R.sup.3.sub.2).sub.y—X—Si(OR.sup.3).sub.3; and y is zero or an integer up to 6, n is 0 or 1, and z is 0 or 1; with the proviso that z is 0 when n is 0 and y is greater than zero.

2. The self-adhesive curable silicone elastomer composition in accordance with claim 1, wherein the adhesion promoter (E) is selected from the group of diacrylates, triacrylates, tetraacrylates, pentaacrylates, and hexaacrylates.

3. The self-adhesive curable silicone elastomer composition in accordance with claim 1, wherein the oligomer (F) is selected from: (MeO).sub.3—Si—(CH.sub.2).sub.2—SiPhMe-O—SiPhMe-(CH.sub.2).sub.2—Si(OMe).sub.3 (MeO).sub.3—Si—(CH.sub.2).sub.2—Si(CH.sub.3).sub.2—O—Si(CH.sub.3).sub.2—(CH.sub.2).sub.2—SiPhMe-O—SiPhMe-(CH.sub.2).sub.2—Si(CH.sub.3).sub.2—O—Si(CH.sub.3).sub.2—(CH.sub.2).sub.2—Si(OMe).sub.3 Si(Ph).sub.2 (—O—Si(CH.sub.3).sub.2—(CH.sub.2).sub.2—Si(CH.sub.3).sub.2—O Si(CH.sub.3).sub.2—(CH.sub.2).sub.2—Si(OMe).sub.3).sub.2 Si(Ph).sub.2 (—O—Si(CH.sub.3).sub.2—(CH.sub.2).sub.2—Si(OMe).sub.3).sub.2 Si(Ph).sub.2 ((CH.sub.2).sub.2—Si(OMe).sub.3).sub.2 Si(Ph)-(O—Si(CH.sub.3).sub.2—(CH.sub.2).sub.2—Si(CH.sub.3).sub.2—O Si(CH.sub.3).sub.2—(CH.sub.2).sub.2—Si(OMe).sub.3).sub.3 Si(Ph)-(O—Si(CH.sub.3).sub.2—(CH.sub.2).sub.2—Si(OMe).sub.3).sub.3 Si(Ph)-((CH.sub.2).sub.2—Si(OMe).sub.3).sub.3, or a mixture of two or more thereof.

4. The self-adhesive curable silicone elastomer composition in accordance with claim 1, wherein component (F) 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 self-adhesive curable silicone elastomer composition in accordance with claim 1, wherein the composition comprises a cure inhibitor.

6. The self-adhesive 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 self-adhesive 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 self-adhesive curable silicone elastomer composition according to claim 1.

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

11. The article in accordance with claim 9, containing silicone elastomer cured from the self-adhesive 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, 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)

16. A method of forming a three-dimensional (3D) article, the method comprising: i) printing a first heat-curable silicone composition with a 3D printer to form a layer; ii) heating the layer to form an at least partially cured layer; iii) printing a second heat-curable silicone composition on the at least partially cured layer with the 3D printer to form a subsequent layer; iv) heating the subsequent layer to form an at least partially cured subsequent layer; and, v) optionally, repeating steps iii) and iv) with independently selected heat-curable silicone composition(s) for any additional layer(s) to form the 3D article; wherein at least one of the heat-curable silicone compositions is the self-adhesive curable silicone elastomer composition according to claim 1.

Description

EXAMPLES

[0182] In the following examples all viscosities were measured using a Brookfield® rotational viscometer using Spindle (LV 1 to LV-4) or (RV-7) and adapting the speed (shear rate) according to the polymer viscosity. Two different 2-pa liquid silicone rubber (LSR) compositions were utilised as the basis for the examples. One of the LSR compositions was a self-adhesive curable silicone rubber “composition designed to able to adhere during cure to substrates made from thermoplastic materials, organic resin based materials or both thermoplastic materials and organic resin based materials with which they are placed in direct contact prior to or during the cure process but which remain non-adhesive towards metallic substrates such as molds and is referred to as the A-comp. The second composition is non-adhesive to said thermoplastic materials and is referred to as the N-comp.

[0183] The A-comp and N-comp compositions are provided in Tables 1a and 1b below. In use the part A and part B compositions were mixed on a 1:1 basis by weight.

TABLE-US-00001 TABLE 1a Self-Adhesive composition (A-Comp) used in Examples A-Comp A-Comp Ingredients Part A Part B Masterbatch 1 90.29 4.50 Masterbatch 2 80.39 vinyldimethyl terminated polydimethylsiloxane 3.00 6.38 having a viscosity of 53,000 mPa .Math. s at 25° C. Vinyl terminal poly(dimethylsiloxane-co- 4.76 5.44 methylvinylsiloxane) having a viscosity of 370 mPa .Math. s at 25° C. Karstedt catalyst 0.005 Phenyltris(dimethylsiloxy)silane 1.00 trimethyl terminated polymethylhydrogen 1.70 dimethylsiloxane having a viscosity of 30 mPa .Math. s at 25° C. hydroxydimethyl terminated polydimethylsiloxane 0.60 0.60 having viscosity of approximately 21 mPa .Math. s ethynyl cyclohexanol (ETCH) 0.08 Di(trimethylolpropane)tetraacrylate 1 100.00 100.00

TABLE-US-00002 TABLE 1b Non-Adhesive Composition (N-Comp) used in Examples N-Comp N-Comp Ingredients Part A Part B Masterbatch 1 90.29 4.50 Masterbatch 2 80.39 vinyldimethyl terminated polydimethylsiloxane 4.00 7.73 having a viscosity of 53,000 mPa .Math. s at 25° C. Vinyl terminal poly(dimethylsiloxane-co- 4.76 5.44 methylvinylsiloxane) having a viscosity of 370 mPa .Math. s at 25° C. Karstedt catalyst 0.005 trimethyl terminated polymethylhydrogen 1.35 dimethylsiloxane having a viscosity of 30 mPa .Math. s at 25° C. hydroxydimethyl terminated polydimethylsiloxane 0.60 0.60 having a viscosity of approximately 21 mPa .Math. s ethynyl cyclohexanol (ETCH) 0.08 100.00 100.00

[0184] In the above compositions: [0185] Masterbatch 1 contains 70.8 parts of a dimethylvinylsiloxy terminated polydimethylsiloxane having a viscosity of about 53,000 mPa.Math.s at 25° C., and 22.4 parts of a fumed silica filler having a surface area of approximately 300 m.sup.2/g. The silica is hydrophobized and contains no vinyl functionalization; and [0186] Masterbatch 2 contains 66.6 parts of a dimethylvinylsiloxy terminated polydimethylsiloxane having a viscosity of about 55 Pa.Math.s at 25° C., and 25.8 parts of a fumed silica filler having a surface area of approximately 300 m.sup.2/g. The silica is hydrophobized and has a vinyl functionalization of approximately 0.178 mmol/g.

[0187] The physical properties of A-comp or N-comp compositions were analysed, either with no further additive present or after mixing with an additional additive, e.g. oligomer (F) or an alternative. The amount of additive introduced was determined by weight and was per the complete mixed composition of the A-comp composition or N-comp composition. The additive may be introduced into the part A composition, the part B composition or alternatively may be added into the final mixture after the part A composition and the part B composition have been mixed together.

TABLE-US-00003 TABLE 1c C1 C2 EX1 C3 C4 C5 C6 LSR type A-Comp N-Comp A-Comp N-Comp N-Comp A-Comp A-Comp Additive type — — (F) (F) (F) Add-1 Add-2 wt. % added — — 1 1 2 0.52 0.36 mmol added — — 1.59 1.59 3.18 1.59 1.59

[0188] Wherein (F) is,

##STR00003## [0189] Add-1 is 1,6-bis(trimethylsilyl)hexane and [0190] Add-2 is 1,6-hexanediol diacrylate (HDDA)

[0191] The resulting compositions were Cure parameters were tested using a Premier MDR from Alpha Technologies. Test parameter 10 min 120° C.

[0192] Table 2a shows the point in cure time when 2% (TC2), 10% (TC10), 60% (TC60), or 90% (TC90) of cure occurred.

TABLE-US-00004 TABLE 2a MDR-measurement Cure Parameters (10 min @ 120° C.) C1 C2 EX1 C3 C4 C5 C6 TC2 (s) 34 24 38 36 33 36 38 TC10 (s) 41 35 43 40 37 42 55 TC60 (s) 59 44 56 52 46 56 94 TC90 (s) 91 61 77 75 63 81 162

[0193] Samples were tested for initial adhesion and after 7 days at 85° C. and 85% relative humidity to provide an indication of long-term heat-humidity stability to assess if the peel (adhesive) strength is maintained after aging. Adhesion was tested in a 900 “floating roller peel test” using a floating roller device designed for e.g. DIN EN 1372 (“Adhesives—Test method for adhesives for floor and wall coverings”).

[0194] Three commercially available thermoplastic substrate materials were used as indicated in Table 2 b below. They were [0195] Ultradur® B 4300 G4 polybutylene terephthalate (PBT) from BASF [0196] Ultramid® A3EG6 polyamide (PA) from BASF; and [0197] LEXAN™ Resin 121 polycarbonate (PC) from SABIC.

[0198] The thermoplastic substrates had the dimensions: 25 mm×100 mm (3 mm thickness) and were cleaned with isopropanol and dried according to the following conditions: [0199] PBT: 18 hours at 120° C. [0200] PA-66:18 hours at 80° C. [0201] PC: 18 hours at 120° C.

[0202] The thermoplastic substrates were preheated at 120° C. for 5 min prior to overmolding with LSR. Substrates were overmolded with 3 mm layer of LSR. compression molded at 300 bar (30 MPa) for 120° C. and cured for 5 min cure.

[0203] The resulting specimen were stored for ˜hours before performing the tests. The peel adhesion testing was carried out using floating roller peel test, at test speed of 300 mm per minute and the average force during the peel experiment was recorded (in N/mm).

[0204] Heat ageing is done in a standard ventilated oven. The heat humidity tests are Run in a Simulationsanlage Messtechnik WK3-340/70 by Weiss Umwelttechnik GmbH climate chamber.

TABLE-US-00005 TABLE 2b ADHESION (initial and after 1 week 85° C./85% relative humidity) C1 C2 EX1 C3 C4 C5 C6 initial PBT (N/25 m) 56 5 51 4 0 27 16 85/85 PBT @ 7 days (N/25 m) 7 0 47 0 0 17 6 initial PA (N/25 m) 33 0 60 0 0 23 0 85/85 PA @ 7 days (N/25 m) 2 0 33 0 0 29 0 initial PC (N/25 m) 99 0 74 0 0 90 69 85/85 PC @ 7 days (N/25 m) 13 0 50 0 0 29 20

[0205] Samples were obtained by press cure for 10 min at 120° C., at 300 bar (30 MPa). Sample thickness 2 mm. Physical properties of cured test pieces for each composition identified in Tables 1a-1c were obtained. Shore A hardness was measured following test ISO 7619-1:2010 Rubber, vulcanised or thermoplastic—Determination of indentation hardness—Part 1: Durometer method (Shore hardness) (ASTM D2240-97). The tensile strength and elongation results were obtained via ISO 37:2011 Rubber, vulcanised or thermoplastic—Determination of tensile stress-strain properties (ASTM D412-98A).

TABLE-US-00006 TABLE 2c Physical Properties (cure condition: 10 min at 120° C.) C1 C2 EX1 C3 C4 C5 C6 Shore A Hardness 33 41 30 40 39 30 40 Tensile Strength 6.4 7.2 6.2 6.9 6.8 6.3 8.6 (MPa) Elongation (%) 634 481 668 476 483 677 757

[0206] The final compositions in the examples depicted in Table 1c and the resulting elastomers cured therefrom were chosen for the following reasons: [0207] C1: self-adhesive composition with good initial adhesion, but poor heat-humidity stability; [0208] C2: non-adhesive reference composition. No adhesion; [0209] Ex1: self-adhesive composition containing oligomer (F) with good initial adhesion, and good heat-humidity stability. Furthermore, it will be appreciated that the addition of the oligomer (F) had minimal effect on physical properties and cure rates; [0210] C3: non-adhesive composition which despite containing 1% by weight oligomer (F) additive had no adhesion. It was considered surprising that oligomer (F) did not act as an adhesion promoter; [0211] C4: non adhesive composition with 2% of oligomer (F). It was even more surprising that despite increasing the amount of oligomer (F) present even at higher loadings no adhesion was apparent in the presence of oligomer (F); [0212] C5: In C5 the oligomer (F) was replaced by equimolar amounts of a known adhesion promoter for these systems, 1,6-bis(trimethylsilyl)hexane. The results showed poor adhesion and poor heat-humidity stability in the presence of 1,6-bis(trimethylsilyl)hexane which it was surmised indicated that the phenyl presence on oligomer (F) appeared to be a critical element; and [0213] C6: C6 shows that adding acrylate adhesion promoter in equimolar amounts as oligomer (F) does not improve adhesion. Furthermore, C6 shows that cure and mechanics are significantly impacted. In contrast addition of oligomer (F) does not have any impact as described before, which is good and an additional benefit for oligomer (F) as compared to other additives/adhesion promoters.

[0214] Hence, based on the above examples the addition of oligomer (F) into liquid silicone rubber compositions provides the user with three key advantages: [0215] Heat-humidity stabilization of adhesion (not only initial adhesion) [0216] Broad application range (works on PBT, polycarbonate, polyamide) [0217] Does not impact cure and physical properties.