SELF-ADHESIVE SILICONE ELASTOMER

Abstract

Provided herein are self-adhesive curable silicone rubber compositions. When cured, the curable silicone rubber compositions generally achieve significant adhesion to plastic/thermoplastic/resin material substrates, and especially adhesion to polycarbonate materials. Also provided herein is a process for preparing plastic/thermoplastic/resin materials, especially polycarbonate/cured silicone elastomer materials, and articles and composite parts made from such curable silicone rubber compositions. The silicone rubber compositions generally comprise one or more organopolysiloxanes containing at least 2 alkenyl groups per molecule and having a viscosity of greater than 1,000,000 mPa.Math.s at 25 C.; an organopolysiloxane containing at least 2 silicon-bonded hydrogen atoms per molecule; a platinum group catalyst; reinforcing and/or non-reinforcing fillers; and one or more rubber modified epoxy resins.

Claims

1. A self-adhesive curable silicone elastomer composition comprising: (A) 5-95% by weight of one or more organopolysiloxanes containing at least 2 alkenyl groups per molecule and having a viscosity of greater than 1,000,000 mPa.Math.s at 25 C.; (B) 0.1-40% by weight of an organopolysiloxane containing at least 2 silicon-bonded hydrogen atoms per molecule; (C) 0.01-10% by weight of a platinum group catalyst; (D) 1-80% by weight of reinforcing and/or non-reinforcing fillers; and (E) 0.1-50% by weight of one or more rubber modified epoxy resins; wherein component (E) is selected from the group consisting of carboxyl-terminated butadiene acrylonitrile (CTBN) modified epoxy resin, hydroxyl-terminated butadiene acrylonitrile (HTBN) modified epoxy resin, -amido-terminated butadiene acrylonitrile (ATBN) modified epoxy resin-, epoxy-terminated butadiene acrylonitrile (ETBN) modified epoxy resin, vinyl-terminated butadiene acrylonitrile (VTBN) modified epoxy resin, and combinations thereof; and wherein the total weight (wt.) % of the composition is 100%.

2. The self-adhesive curable silicone elastomer composition in accordance with claim 1, wherein component (E) comprises, or consists of, carboxyl-terminated butadiene acrylonitrile (CTBN) modified epoxy resin.

3. The self-adhesive curable silicone elastomer composition in accordance with claim 1, wherein component (A) is a silicone gum.

4. The self-adhesive curable silicone elastomer composition in accordance with claim 1, further comprising a cure inhibitor containing at least one unsaturated bond and selected from the group consisting of acetylenic alcohols and their derivatives.

5. The self-adhesive curable silicone elastomer composition in accordance with claim 1, wherein the ratio of silicon-bonded hydrogen atoms in component (B)/alkenyl groups in component (A) ranges from (0.7:1.0) to (5.0:1.0).

6. The self-adhesive curable silicone elastomer composition in accordance with claim 1, comprising at least 2 separate parts.

7. A process for preparing an article or a composite part of an article, said 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 polycarbonate.

9. An article cured from the self-adhesive curable silicone elastomer composition in accordance with claim 1.

10. The article in accordance with claim 9, containing silicone elastomer cured from the self-adhesive curable silicone elastomer composition and adhered to a substrate selected from the group consisting of plastic materials, thermoplastic materials, resin materials, and combinations thereof.

11. The article in accordance with claim 10, wherein the substrate is a polycarbonate substrate.

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

13. A composite part comprising a silicone elastomer cured from the curable silicone elastomer composition in accordance with claim 1 on a substrate selected from the group of plastic materials, thermoplastic materials, resin materials, and combinations thereof.

14. The composite part in accordance with claim 13, selected from the group consisting of housings with a silicone seal or gasket, plugs, connectors, sensor components, membranes, diaphragms, climate venting components, personal electronic equipment, mobile phone cover seals, mobile phone accessories, precision electronic equipment, electrical switches, switch covers, watches, wristbands, wearable apparatuses, 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, OA equipment, connector seals, spark plug caps, and automobile components.

15-17. (canceled)

18. The self-adhesive curable silicone elastomer composition in accordance with claim 1, further comprising at least one additive selected from the group consisting of cure inhibitors, mold releasing agents, adhesion catalysts, silane crosslinkers, pigments, and combinations thereof.

19. The self-adhesive curable silicone elastomer composition in accordance with claim 1, wherein component (B) is present in an amount of from 1-5% by weight.

20. The self-adhesive curable silicone elastomer composition in accordance with claim 5, wherein the ratio of silicon-bonded hydrogen atoms in component (B)/alkenyl groups in component (A) ranges from 1.1 to 3.5.

Description

EXAMPLES

[0089] In the following examples the two part high viscosity rubber composition depicted in Table 1 was used as the basic composition.

TABLE-US-00001 TABLE 1 Standard 2 Part Composition A B dimethylvinylsiloxy-terminated polydimethyl 65.32 64.02 siloxane gum (Williams Plasticity No range 140- 165 mm/100) dimethylvinylsiloxy-terminated 5.30 5.19 dimethylmethylvinyl siloxane gum (Williams Plasticity No range 145-160 mm/100) 250 g/m.sup.2 (BET) Fumed Silica 21.18 21.10 dimethylhydroxyl terminated 7.77 7.62 polydimethylsiloxane dimethylhydroxyl terminated 0.07 0.07 polydimethylmethylvinyl siloxane 1,3-Diethenyl-1,1,3,3 -Tetramethyldisiloxane 0.35 Complexes (Platinum), 1.5% in dimethylvinylterminated, polydimethylsiloxane, having a viscosity of 500 mPa.s at 25 C. 1-Ethynyl-1-cyclohexanol 0.05 trimethyl terminated 1.95 polydimethylmethylhydrogensiloxane having a viscosity of 5 mPa.s at 25 C.
The OH polymers are provided for in situ treatment of the filler to render it hydrophobic and easier to mix with the other ingredients.

[0090] Ingredients used in addition to the composition were as follows:

CV-ZC a 1:1 composition of Zirconium Tetrakisacetylacetonate and a dimethylvinylsiloxy-terminated Dimethyl Siloxane used as adhesion catalyst;
NPEL-127 a standard bisphenol A type epoxy resin having a viscosity of from 8,000-11,000 cps, and an epoxide equivalent weight 176-184 g/eq.;
NPEL 128 a standard bisphenol A type epoxy resin having a viscosity of 12,000-15,000 cps and an epoxide equivalent weight 184-190 g/eq.;
NPER 133L a polyurethane modified BPA type epoxy resin with linear C4-C8 diol as solvent;
NPER 450 a carboxyl-terminated butadiene acrylonitrile (CTBN) modified BPA type epoxy resin in accordance with component E of the composition herein.
All NPEL and NPER products listed above were obtained from Nan Ya Plastics Corporation.

[0091] The compositions were prepared by using the standard silicone rubber gum composition depicted in Table 1 with the sole difference that an amount, typically 2 parts by weight, of the indicated additive was introduced per 100 parts by weight of the Total composition i.e. Part A+Part B.

[0092] The process undertaken was that Part A, Part B and the additive were mixed together with Part A and Part B being added in a 1:1 ratio. Compositions in the following Tables were prepared by mixing together using a Z-blade mixer or on two roll mill directly, without any additional treatment.

TABLE-US-00002 TABLE 2a Raw Comp. 1 Comp. 2 Comp. 3 Ex. 1 Ex. 2 Comp. 4 Materials A B A B A B A B A B A B Standard 100 100 100 100 100 100 100 100 100 100 100 100 (Table 1) CV-ZC M/B 2.0 NPEL 127 2.0 2.0 NPEL 128 2.0 NPER 133L 2.0 NPER 450 2.0 2.0 PC untreated N N N G G N Mixing after G G 3 days

[0093] In Table 2a, N indicates No adhesion and G indicates good adhesion. It was unexpectedly seen that only the rubber modified epoxy resin worked as an additive, in that only compositions containing NPER 450 gave good adhesion results when the prepared silicone rubber composition was applied onto an untreated polycarbonate substrate surface. Standard epoxy resins did not have a similar adhesive effect.

TABLE-US-00003 TABLE 2b Raw Comp. 5 Comp. 6 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Materials A B A B A B A B A B A B Standard 100 100 100 100 100 100 100 100 100 100 100 100 (Table 1) CV-ZC M/B 2.0 2.0 2.0 2.0 NPEL 128 2.0 NPER 133L 2.0 NPER 450 2.0 2.0 1.0 3.0 PC untreated N N G G G G Mixing after P N 3 days HH aging P G 85 C./ 85% RH

[0094] In Table 2b N indicates No adhesion, P indicates poor adhesion and G indicates good adhesion. It can be seen that the introduction of CV-ZC (a 1:1 masterbatch of zirconium tetrakisacetylacetonate and dimethylvinylsiloxy-terminated Dimethyl Siloxane) which is used as an adhesion catalyst in some liquid silicone rubber compositions had no positive effect on adhesion and indeed may have given worse results when samples were aged for 3 days before mixing in Ex. 3. It was found that addition of 1 part by weight of NPER 450 gave good results at normal room temperature (Ex. 5) but adhesion was not as good after high heat aging at 85 C. and 85% relative humidity (RH) for a period of 2 weeks.

TABLE-US-00004 TABLE 2c Raw Ex. 7 Comp. 7 Comp. 8 Comp. 9 Comp. 10 Materials A B A B A B A B A B Standard 100 100 (Table 1) LSR 1 100 100 LSR 2 100 100 LSR 3 100 100 100 100 NPER 450 5.0 2.0 2.0 2.0 2.0 PC untreated G N N N N HH aging G 85 C./85% RH

[0095] In Table 2c, N indicates No adhesion and G indicates good adhesion. It was unexpectedly seen that the rubber modified epoxy resin only worked as an adhesion additive with high viscosity silicone rubber (gum) materials, e.g. the standard formulation of Table 1. Examples using 3 alternative liquid silicone rubber compositions did not generate adhesion on the polycarbonate substrate surfaces to which they were applied.

[0096] In Table 3 the cure profile and physical properties are compared between the standard formulation indicated in Table 1 and the same composition with 2 parts by weight of NPER 450 added per 100 parts by weight of the total composition of the standard composition. For the avoidance of doubt tx % is the time to reach x % of maximum cure and such measurements were taken with a Moving Die Rheometer MDR 2000 from Monsanto Instruments Co., Akron, Ohio US and were based on ASTM D5289-92.

TABLE-US-00005 TABLE 3 Ex. 8 Comp. 11 100 parts by weight of Standard Standard Formulation + formulation 2 parts by wt. of (Table 1) NPER 450 Cure Conditions 120 C. for 6 minutes t02 (Seconds (s)) 14.4 18.6 (ASTM D5289-92) t10% (s) (ASTM D5289-92) 18.6 23.4 t20% (s) (ASTM D5289-92) 20.4 25.8 t50% (s) (ASTM D5289-92) 24.0 30.6 t90% (s) (ASTM D5289-92) 30.0 47.4 Press Cure 120 C. for 10 minutes Durometer, Shore A 39.1 36.7 (ASTM D2240) Tensile Strength (MPa) 9.1 9.8 (ASTM D412- 16) Elongation at Break (%) 1200 1302 (ASTM D412- 16) Modulus 100% (MPa) 0.92 0.80 (ASTM D412- 16) Modulus 200% (MPa) 1.46 1.27 (ASTM D412- 16) Modulus 300% (MPa) 1.79 1.59 (ASTM D412- 16) Tear Strength Die C kN/m 35.44 31.84 (ASTM D624-00 (2012))

[0097] Whilst it was found that the presence of the NPER 450 seemed to result in a slower cure speed and lower hardness generally there was little change to the physical properties of the silicone rubber.

[0098] The results in Table 4 depict levels of adhesion after different press cure times using a cure temperature of 120 C. Heat and humidity (HH) aging and high temperature were undertaken in both instances for a period of two weeks. The composition was cured by compression molding to form samples of the size 100 mm*25 mm*2 mm. These were adhered to polycarbonate plates obtained from Suzhou Aomei. Heat aging was undertaken on samples at 100 C. for a period of four weeks. Heat & humidity aging was undertaken at 85 C. and 85% relative humidity for a period of two weeks. The level of adhesion was tested immediately after the termination of the aging experiments using the 180 degree peel adhesion testing method described in method of ASTM C 794-10, Good results were obtained as indicated in Table 4 below (CF means cohesive failure, AF means adhesive failure, the number after that represents for the percentage of CF or AF).

TABLE-US-00006 TABLE 4 Ex. 9 Ex. 10 Ex. 11 Standard formulation parts 100 100 100 (Table 1) Curing NPER 450 parts 1 3 5 120 C./ Initial Average Force 49.72 [8706] 58.46 65.14 10 min (lbf/in) [N/m] [10236] [11406] Failure Model CF100 CF100 CF100 HH aging Average Force 26.28 [4999] 29.07 53.13 85 C./85% RH, 2W (lbf/in) [N/m] [5087] [9307] Failure Model CF20AF80 CF100 CF100 aging 100 C., 4W Average Force 59.65 [10444] 56.43 69.03 (lbf/in) [N/m] [9880] [12087] Failure Model CF100 CF100 CF100 120 C./ Initial Average Force 43.18 [7560] 62.33 58.26 8 min (lbf/in) [N/m] [10913] [10201] Failure Model CF100 CF100 CF100 HH aging 85 C./ Average Force 28.61 [5009] 30.74 21.42 85% RH, 2W (lbf/in) [N/m] [5382] [3750] Failure Model AF100 CF80AF20 CF100 aging 100 C., 4W Average Force 42.54 [7448] 54.89 47.21 (lbf/in) [N/m] [9611] [8266] Failure Model CF100 CF100 CF100 120 C./ Initial Average Force 45.63 [7989] 55.61 59.2 6 min (lbf/in) [N/m] [9737] [10365] Failure Model CF100 CF100 CF100 HH aging 85 C./ Average Force 15.3 [2679] 34.54 22.52 85% RH, 2W (lbf/in) [N/m] [6047] [3943] Failure Model AF100 CF70AF30 CF90AF10 aging 100 C., 4W Average Force 50.1 [8772] 61.83 49.61 (lbf/in) [N/m] [10832] [8686] Failure Model CF100 CF100 CF100 120 C./ Initial Average Force 34.27 [6000] 57.39 62.58 4 min (lbf/in) [N/m] [10048] [10957] Failure Model CF50AF50 CF100 CF100 HH aging 85 C./ Average Force 12.45 [2179] 21.63 23.39 85% RH, 2W (lbf/in) [N/m] [3787] [4095] Failure Model AF100 CF50AF50 CF90AF10 aging 100 C., 4W Average Force 55.2 [9665] 57.12 63.98 (lbf/in) [N/m] [10001] [11202] Failure Model CF100 CF100 CF100 120 C./ Initial Average Force 21.03 [3682] 48.99 60.32 2 min (lbf/in) [N/m] [8578] [10562] Failure Model CF50AF50 CF100 CF100 HH aging 85 C./ Average Force 0 21.3 34.45 85% RH, 2W (lbf/in) [N/m] [3729] [6032] Failure Model AF100 CF50AF50 CF100 aging 100 C., 4W Average Force 50.2 [8790] 53.08 62.26 (lbf/in) [N/m] [9294] [10901] Failure Model CF100 CF100 CF100