THERMOPLASTIC SILICONE ELASTOMERS

Abstract

Thermoplastic silicone elastomer compositions are disclosed. The thermoplastic elastomer compositions comprise a blend of an organic thermoplastic elastomer and a silicone composition. A process for forming a vulcanised thermoplastic elastomer composition is also disclosed. The thermoplastic elastomer compositions can be used to form functional and/or aesthetic automotive parts such as gear knobs, seat belt connectors, interior mats, airbag protective covers, and over-moulded skins for dash boards and armrests; to form appliance parts; to form soft-feel grips for hand held devices; and to form medical devices, sporting goods and general rubber parts. The thermoplastic elastomer compositions provide durable aesthetics, haptic and ergonomic properties along with stability to most commonly used chemicals and high mechanical performance, abrasion and scratch resistance.

Claims

1. A thermoplastic elastomer composition comprising a blend of: (A) a thermoplastic organic polymer comprising (A1) a block copolymer elastomer, and (A2) a polyolefin elastomer; (B) a silicone base comprising (B1) a diorganopolysiloxane gum having an average of at least 2 alkenyl groups per molecule, and (B2) optionally, from 1 to 50% by weight based on the diorganopolysiloxane gum (B1) of a reinforcing filler; (C) an organohydrido silicone compound which contains an average of at least 2 silicon-bonded hydrogen groups per molecule; (D) a catalyst; and (E) a coupling agent.

2. The thermoplastic elastomer composition according to claim 1, wherein the coupling agent (E) is selected from glycidyl ester functional polymers or organofunctional grafted polyolefins, polymer compositions comprising a thermoplastic polymer selected from a polyacetal and a polyolefin, and a branched block copolymer of a polysiloxane and an olefin polymer, or mixtures thereof.

3. The thermoplastic elastomer composition according to claim 1, wherein the reinforcing filler (B2) is silica and is present in the silicone base (B).

4. The thermoplastic elastomer composition according to claim 1, wherein the weight ratio of (A1) to (A2) ranges from 10:90 to 90:10.

5. The thermoplastic elastomer composition according to claim 1, wherein the weight ratio of (A)+(E) to (B)+(C)+(D) ranges from 50:50 to 85:15.

6. The thermoplastic elastomer composition according to claim 1, wherein the coupling agent (E) is present in the thermoplastic elastomer composition at a level of from 0.01 to 25% weight percent of the thermoplastic elastomer composition.

7. The thermoplastic elastomer composition according to claim 1, wherein (A) has a hardness below 45 Shore D, and optionally, a hardness below 85 Shore A.

8. The thermoplastic elastomer composition according to claim 1, having a hardness below 45 Shore D, and optionally, a hardness below 85 Shore A.

9. A part or component for automotive, appliances, electronics, portable electronic, electrical, communication, and/or medical applications wherein the part or component is formed of the thermoplastic elastomer composition according to claim 1.

10. The part or component according to claim 9, having a hardness below 45 Shore D, and optionally, a hardness below 85 Shore A.

11. A wearable item formed of the thermoplastic elastomer composition according to claim 1.

12. The wearable item according to claim 11, having a hardness below 45 Shore D, and optionally, a hardness below 85 Shore A.

13. A process for forming a vulcanised thermoplastic elastomer, said process comprising contacting: (A) a thermoplastic organic polymer comprising (A1) a block copolymer elastomer, and (A2) a polyolefin elastomer; (B) a silicone base comprising (B1) a diorganopolysiloxane gum having an average of at least 2 alkenyl groups per molecule; and (B2) optionally, from 1 to 50% by weight based on the diorganopolysiloxane gum (B1) of a reinforcing filler; (C) an organohydrido silicone compound which contains an average of at least 2 silicon-bonded hydrogen groups per molecule; (D) a hydrosilylation catalyst; and (E) a coupling agent; wherein the weight ratio of (A)+(E) to (B)+(C)+(D) ranges from 50:50 to 85:15.

14. The process according to claim 13, wherein the thermoplastic organic polymer (A), the silicone base (B), the organohydrido silicone compound (C), the hydrosilylation catalyst (D) and the coupling agent (E) are contacted at a temperature in the range of from 100° C. to 250° C.

15. The process according to claim 13, wherein the thermoplastic organic polymer (A), the silicone base (B), the organohydrido silicone compound (C), the hydrosilylation catalyst (D) and the coupling agent (E) are blended in an extruder.

16. The process according to claim 13, further defined as a process for forming a wearable item intended to be in contact with a wearer's skin when in use.

17. The process according to claim 13, further defined as a process for forming a part or component for automotive, appliances, electronics, portable electronic, electrical, communication, and/or medical applications.

18. The process according to claim 17, wherein the part or component is overmoulded with the vulcanised thermoplastic elastomer.

19. The wearable item according to claim 11, further defined as a bracelet or a support pad for sunglasses, reading glasses or wearable electronics.

Description

EXAMPLES

[0107] The invention is illustrated by the following examples, in which parts and percentages are by weight unless otherwise stated.

[0108] The materials used in the Examples were [0109] Si-Rubber 1: Uncatalysed Silicone Rubber Base comprising a vinyl-terminated diorganopolysilxane gum of 70 Shore A hardness with a silica content of 35% [0110] Cat.: Dow corning ‘Syl-Off 4000’ Platinum Catalyst having a Pt content of 0.40% [0111] XL: Dimethyl, Methylhydrogen Siloxane copolymer, Trimethylsiloxy-terminated of Si-bonded hydrogen content 1.6% [0112] PPH: polypropylene homopolymer, Total PPH 7060 [0113] PPC: polypropylene copolymer, Total PP 108 MF 10, [0114] TPO 1: polypropylene copolymer, Exxon VISTAMAXX® 6202 [0115] SBC 1: Styrene block Copolymer 1: DYNASOL CALPRENE® H6174 [0116] SBC 2: Styrene block Copolymer 2: DYNASOL CALPRENE® H6171 [0117] COUPLING AGENT 1: random terpolymer of ethylene, acrylic ester and glycidyl methacrylate, ARKEMA LOTADER® AH8900 [0118] COUPLING AGENT 2: Polypopylene grafted anhydride maleic: ARKEMA OREVAC® CA100 [0119] FILLER: Calcium Carbonate, OMYA OMYACARB® 5 AV [0120] SiMB: Dow Corning® Siloxane Masterbatch MB50001 [0121] AO: BASF Irganox® 1010, tetrakis(methylene(3,5-di-tert-butyl-4-hydroxy-hydrociannate)methane [0122] UV Additive: Oligomeric Hindered Amine Light stabilizer (HALS), CIBA TINUVIN® 622 [0123] BLACK COLOR MASTERBATCH: Carbon black concentrates in Polyethylene (PE), A. Schulman Plastics BVBA POLYBLAK BLACK 1423

[0124] Thermoplastic elastomers were prepared by the process of the invention. The mixing of components and vulcanisation was carried out using a twin screw extruder, 25 mm of diameter and 48 L/D. The processing section was heated in a range from 180° C. up to 220° C. the screw speed was 200 rpm and the throughput rate was 15 kg/hour. Si-Rubber 1 was added to organic thermoplastic preblend (PPH, PPC, TPO, SBC, additives and coupling agent) within the two first sections of the extruder. The organohydridopolysiloxane XL is added into the blend to achieve a good dispersion of these two silicone components in the thermoplastic before addition of the catalyst, which initiates the vulcanization of the silicone composition within the thermoplastic matrix. Feeding zones for each component are fixed and located within the first half of the twin screw extruder barrel. The proportions of materials used are shown in Tables 1 and 2 below.

[0125] Test specimens for mechanical and scratch resistance testing were prepared by injection moulding. Heating temperature for injection moulding was set at 180° C. to 220° C. and mold temperature set at 40° C. The mechanical properties were tested according to international standards as set out in Tables 1 and 2.

[0126] Scratch performance measurement relies on a test protocol specifically developed to characterize scratch resistance of soft elastomeric products corresponding to typical hardness of 40 Shore A to 45 Shore D defined according to ISO 868 standard for elastomer and rubber material. Scratch resistance protocol used relies on a quantitative measurement of the aspect change of a moulded specimen caused by scratch lines. The aspect change is a translation of both chromatic aberration measurement and gloss change before and after scratch is performed onto the specimen. For comparison purpose and to increase testing consistency and robustness a calibrated hardness scratch tester 430 PII supplied by Erichsen has been used. Scratch hardness tester is set to perform a scratch pattern composed of 80 parallel line spaced 0.5 mm apart using a ball shape scratch tip of 0.5 mm of diameter on which a constant loading of 10N is applied. The results of scratch performance presented in Table 1 are calculations representative of the residual aspect of the surface, after the impact of scratch, compared to the undamaged surface. The lower the value, the higher the scratch resistance is.

[0127] Cohesive adhesion is assessed by peel test according to Renault D41 1916 Standard. Cohesion is defined as the internal strength of an adhesive as a result of a variety of interactions within the adhesive. Adhesion is the bonding of one material to another, namely of an adhesive to a substrate, due to a variety of possible interactions. The cohesive adhesion is assessed by measuring the applied peeling force. The peeling action may result in a tearing within the elastomer (cohesive failure), causing some amount (layer) of elastomer to remain on the rigid support after testing; or may result in a total or partial removal of the elastomer from the rigid support (adhesive failure). In the present case, the test allows for the characterization of the adhesion of overmoulded thermoplastic elastomers on rigid supports (here polypropylene) by measuring the force required to pull the overmoulded thermoplastic elastomers off of the rigid support, using a Zwick mechanical tester with a test speed of 100 mm/minute, at an angle of 90°. Typically, the present overmoulded thermoplastic elastomers show cohesive adhesion to the rigid polypropylene support, that is, the overmoulded thermoplastic elastomer remain adhered to the rigid polypropylene support as the thermoplastic elastomer is torn upon peeling.

Example 1 and Comparative Examples 1 and 2

[0128] Comparative example 1, a silicone free thermoplastic elastomer, Comparative example 2, a silicone based thermoplastic elastomer free of coupling agent, and Example 1, per the present invention, a silicone based thermoplastic elastomer comprising a coupling agent, were prepared as presented in Table 1, and compared for standard properties and scratch resistance, as presented in Table 2.

[0129] Comparative example 1 shows the properties of a silicone free material, that is a, a silicone free thermoplastic elastomer, also designated as TPE-S. The material, containing a plasticizer oil, has a hardness in the same range as Comparative example 2 and Example 1. The formulation of Comparative example 1 shows a low surface performance (Scratch and abrasion) comparatively to Example 1 according to the invention.

[0130] Comparative example 2, a silicone based thermoplastic elastomer, has a hardness in the same range as Comparative example 1 and Example 1. The absence of coupling agent dramatically impacts the surface resistance as shown by a loss of color and a loss of gloss 3 times higher, comparatively to Example 1.

[0131] Example 1 containing components A, B, C D and E shows the highest surface properties performance per the scratch and abrasion tests, that is, a low color loss and low gloss loss, together with acceptable volume loss. Cohesive adhesion to polypropylene is significantly improved over Comparative examples 1 and 2.

TABLE-US-00001 TABLE 1 Comparative Comparative Ingredient example 1 example 2 Example 1 XL 0.61% 0.84% CAT 0.29% 0.40% Black color Masterbatch 2.00% 2.00% 2.00% A0 & UV additive 0.60% 0.60% 0.60% COUPLING AGENT 1 5.00% Si RUBBER, 20.69% 28.70% PPC 10.00% 10.00% PPH 1 20.00% PLASTICIZER OIL 45.00% 6.33% 5.46% SBC 1, 25.00% 9.85% 8.50% SBC 2 9.85% 8.50% Filler 7.40% TPO 1 39.50% 30.00%

TABLE-US-00002 TABLE 2 Comparative Comparative Property (method) Unit example 1 example 2 Example 1 Hardness (ISO 868) Shore 68 63.20 65.00 A Spiral flow length cm 100 33.6 27.7 (internal) Compression set % 26 29.3 29.8 24 h/23° C. Compression set % 46 79.8 80.2 24 h/70° C. Tensile strength at MPa 8 5.40 7.80 break - transversal- 500 mm/min (ISO 37) Elongation at break - % 765 744.00 831.00 transversal-500 mm/ min (ISO 37) Tear resistance (ISO 34) kN/m 26 32.00 40.10 Scratch resistance Delta −3.62 −3.06 −1.11 80 * 0.5 * 10 N (internal) color Scratch resistance Delta −1.2 −1.17 −0.47 80 * 0.5 * 10 N (internal) gloss Abrasion, Loss of mm3 103 193 97 volume (mm3) (internal) Cohesive adhesion N 32 40 54 (Renault D41 1916 Standard) - Maximum peel force

Examples 2 to 4

[0132] Examples 2 to 4 represent silicone based thermoplastic elastomers comprising a coupling agent per the present invention, where the level of said coupling agent has been varied, as presented in Table 3.

[0133] The performances of Examples 2 to 4, as presented in Table 4, indicate low color and glow loss, with good volume loss below 60 mm3. Cohesive adhesion to polypropylene is confirmed by the peel test as described above, with a maximum peeling force of 60 Newton or above.

TABLE-US-00003 TABLE 3 Ingredient Example 2 Example 3 Example 4 XL 0.84% 0.84% 0.84% CAT  0.4%  0.4%  0.4% Black color Masterbatch   2%   2%   2% A0 & UV additive  0.6%  0.6%  0.6% COUPLING AGENT 1 4.84% 3.22% 1.61% Si RUBBER, 28.7% 28.7% 28.7% PPH1 11.60 11.60 11.60 SiMB   3%   3%   3% PLASTICIZER OIL SBC 1, 10.31 10.31 10.31 SBC 2 10.31 10.31 10.31 Filler TPO 1 4.84% 4.84% 4.84% TPO2 22.56%  24.17%  25.79% 

TABLE-US-00004 TABLE 4 Exam- Exam- Exam- Property (method) Unit ple 2 ple 3 ple 4 Hardness (ISO 868) Shore A 72.8 73.3 73.5 Spiral flow length (internal) cm 32.1 32.4 33 Tensile strength at break - MPa 8.98 10.20 9.9 transversal-500 mm/min (ISO 37) Elongation at break - transversal- % 786 811 800 500 mm/min (ISO 37) Tear resistance (ISO 34) kN/m 51.75 53.15 54.34 Scratch resistance 80 * 0.5 * 10 N Delta −2.24 −1.57 −1.06 (internal) color Scratch resistance 80 * 0.5 * 10 N Delta −1.17 −0.9 −0.8 (internal) gloss Abrasion, Loss of volume (mm3) mm3 66 61 59 (internal) Cohesive adhesion (Renault D41 N 68 62 60 1916 Standard) - Maximum peel force

Examples 5 and 6

[0134] Examples 5 and 6 represent silicone based thermoplastic elastomers comprising each a different coupling agent per the present invention, as presented in Table 5. The Examples 5 and 6 start off with a higher hardness at 40 to 45 Shore D.

[0135] The performances of Examples 5 and 6, as presented in Table 6, indicate low color loss, with acceptable volume loss for the considered hardness. Cohesive adhesion to polypropylene is confirmed by the peel test as described above.

TABLE-US-00005 TABLE 5 Ingredient Example 5 Example 6 XL 0.84%   0.84%   CAT 0.4%   0.4%   Black color Masterbatch 2% 2% A0 & UV additive 0.6%   0.6%   COUPLING AGENT 1 5% 0% COUPLING AGENT 2 0% 5% Si RUBBER 28.7%   28.7%   PPH1 49.96%    49.96%    TPO2 15.50%    15.50%   

TABLE-US-00006 TABLE 6 Property (method) Unit Example 5 Example 6 Hardness (ISO 868) Shore A 43.8 44.5 Spiral flow length (internal) cm 46.9 49 Tensile strength at break - MPa 17.5 19.3 transversal-500 mm/min (ISO 37) Elongation at break - transversal- % 143.5 86.1 500 mm/min (ISO 37) Tear resistance (ISO 34) kN/m 121.2 117.2 Scratch resistance 80 * 0.5 * 10 N Delta color 0.72 1.38 (internal) Abrasion, Loss of volume (mm3) mm3 172 212 (internal)