Thermoplastic elastomer compounds exhibiting low compression set properties

Abstract

A tackifier to modify the Tan Delta of midblock segments of a hydrogenated styrenic block copolymer in a thermoplastic elastomer compounds aids in rendering the HSBC TPE more effective as an overmolding compound having a low percentage compression set value when measured at the high temperature compression set standard. The HSBC TPE can overmold effectively upon polar polymeric substrates depending on the bonding agent chosen.

Claims

1. A thermoplastic elastomer compound, comprising: (a) hydrogenated styrenic block copolymer; (b) oil; (c) more than 30 parts of a midblock tackifier per one hundred parts of the copolymer; (d) bonding agent for overmolding of the thermoplastic elastomer compound to a polar polymeric substrate, wherein the compound has a compression set of less than about 50% when tested at 70° C. for 22 hours using ASTM D395 Test Method B; and wherein the tackifier raises the Tan Delta of the midblock, resulting in a reduction of viscosity as compared with a midblock which is not tackified.

2. The compound of claim 1, wherein the copolymer has a midblock and the tackifier modifies the property of the midblock.

3. The compound of claim 1, wherein the bonding agent is selected from the group comprises thermoplastic polyurethane if the polar polymeric substrate is selected from the group consisting of polycarbonate (PC), a blend of polycarbonate and acrylonitrile butadiene styrene (PC/ABS), and a blend of polycarbonate and polybutadiene terephthalate (PC/PBT); and wherein the bonding agent comprises a copolyester elastomer if the polar polymeric substrate comprises polyamide.

4. The compound of claim 1, wherein the hydrogenated styrenic block copolymer is selected from the group consisting of styrene-ethylene-butylene-styrene (SEBS); styrene-ethylene-ethylene-propylene-styrene (SEEPS) styrene-isoprene/butadiene-styrene (SIBS); styrene-ethylene-propylene-styrene (SEPS); styrene-isoprene-styrene (SIPS); and combinations thereof.

5. The compound of claim 4, wherein the hydrogenated styrenic block copolymer has a high vinyl content.

6. The compound of claim 1, wherein the hydrogenated styrenic block copolymer has a weight average molecular weight of 300,000 and above.

7. The compound of claim 1, wherein the tackifier is an amorphous, low-molecular-weight hydrocarbon resin derived from aromatic petrochemical feedstocks and is fully hydrogenated to a saturated cyclo-aliphatic structure that is highly compatible with polyolefin polymers.

8. The compound of claim 1, wherein the compound further comprises hardness adjusters, waxes, and antioxidants.

9. The compound of claim 1, wherein the compound has the following parts per one hundred parts of hydrogenated styrenic block copolymer: TABLE-US-00012 Midblock Tackifier 30-130 Oil 30-130 Bonding agent for overmolding 60-200 Hardness Modifier 0-60 Wax 0-3  Anti-oxidant 0-3. 

10. An overmolded molded article, comprising the thermoplastic elastomer compound of claim 1 as an overmolding layer and the polar polymeric substrate as the overmolded layer; wherein the polar polymeric substrate is selected from the group consisting of polycarbonate (PC), a blend of polycarbonate and acrylonitrile butadiene styrene (PC/ABS), and a blend of polycarbonate and polybutadiene terephthalate (PC/PBT) if the bonding agent comprises thermoplastic polyurethane; and wherein the polar polymeric substrate comprises polyamide if the bonding agent comprises a copolyester elastomer.

11. The article of claim 10, wherein the article is in the shape of a consumer electronic product.

12. The article of claim 10 wherein the overmolding layer does not cover the entire overmolded layer.

13. A method of using the compound of claim 1, wherein the method comprises the step of overmolding the thermoplastic elastomer compound on to the polar polymeric substrate.

Description

EXAMPLES

(1) Table 4 shows the ingredients for all Examples 1-20 and Comparative Examples A-K, including the composition of the substrates for the testing of overmolding. Table 5 shows the test methods.

(2) Tables 6-11 report the formulations, the processing of the formulations, and the results of experimentation.

(3) Pellets of all Examples 1-20 and Comparative Examples A-K were molded into tensile test bars using a Boy injection molding machine, operating at 235° C. temperature and high pressure for physical property testing.

(4) The same machine was used for overmolding in Series 3-6.

(5) TABLE-US-00004 TABLE 4 Ingredient Name Chemical Purpose Source HYBRAR KL-7135 high Mw (300K) TPE Kuraray styrene block copolymer with hydrogenated high vinyl-polyisoprene midblock (Kuraray) Kraton G1651 hydrogenated high Mw TPE Kraton (300K) styrene ethylene butylene styrene (SEBS) (Kraton) Kraton MD6958 hydrogenated high TPE Kraton Mw (380K) high vinyl SEBS (Kraton) Septon 4055 high Mw (300K) styrene TPE Kuraray (ethylene ethylene propylene) styrene copolymer (SEEPS) (Kuraray) Septon 4077 high Mw (380K) SEEPS TPE Kuraray (Kuraray) Kraton G1641 hydrogenated high Mw TPE Kraton (300K) high vinyl SEBS (Kraton) Plastolyn R1140 tackifier (Eastman) Tackifier for TPE Eastman Midblock Segment 550 viscosity white mineral oil Oil Various Sclair 2908 HDPE (Nova Chemicals) Hardness Adjust Nova Sclair 2714 HDPE (Nova Chemical) Hardness Adjust Nova Dowlex D2035 LLDPE (Dow) Hardness Adjust Dow Skypel G130D copolyester elastomer Overmolding SK Chemicals (SK Chemicals) Adhesion Exxelor VA 1801 maleic polyolefin Overmolding ExxonMobil (ExxonMobil) Adhesion Vicron 25-11 calcium carbonate Filler Specialty (Specialty Minerals) Minerals Kemamide B wax (PMC/Biogenix) Mold Release PMC/Biogenix Kemamide E wax (PMC/Biogenix) Mold Release PMC/Biogenix Irganox 1010 antioxidant (BASF) Durability BASF Irgafos 168 antioxidant (BASF) Durability BASF CYCOLOY ™ Resin C2950 non- Substrate SABIC chlorinated and non-brominated flame retardant PC/ABS BASF Ultramid 8333GHI Polyamide Substrate BASF

(6) TABLE-US-00005 TABLE 5 Test Methods Name Published Standard Shore A Hardness ASTM D2240 200° C. Rheology @ 223 seconds ASTM D3835 200° C. Rheology @ 76 seconds ASTM D3835 Peel Adhesion at 90° on Overmolded ASTM D6862 Substrate (at 5.08 cm location) (Average of 2 samples) Compression Set @ 70° C. for 22 Hr. ASTM D395, Method B DMA Tan Delta Custom test method, 10 Hz

(7) The custom test method for DMA Tan Delta is based on the use of a Q800 Dynamic Mechanical Analyzer from TA Instruments of New Castle, Del. with settings at a frequency of 10 Hz, operating at a temperature range from −40° C. to 100° C. and a scan rate of 3° C./minute on a sample of 10 mm×10 mm×and 3 mm (thickness) dimensions on a shear sandwich test fixture.

(8) Table 2 presents the ingredients of the compounds in both weight percent of the entire TPE overmolding compound and PHR of the ingredients relative to the TPE ingredient(s). The six Series of experiments identify the ingredient weight percentages and PHR also. However, some uses weight percent for formulating, in fact, by understanding the use of PHR to identify variables among constants, one can determine the constancy of most of the ingredients used across the range of each Series of experiments. For that reason, the following paragraphs identify which ingredients are variable in PHR amount across each Series of experiments.

(9) Series 1 explored the variations of tackifier for the soft midblock segment of the TPE. Computing using 100 PHR of TPE, the only ingredient varied was the tackifier at 0, 30, and 60 PHR. Both of the styrenic block copolymer types having hydrogenated mid-blocks responded well to the increasing content of tackifier. No bonding agent for overmolding was used because no overmolding test was contemplated.

(10) Series 2 explored the same variations of tackifier for two different high vinyl content SEBS copolymers. Again the only variable ingredient was the tackifier at 0, 30, and 60 PHR. Again, both SEBS copolymers with hydrogenated mid-blocks responded well to the increasing content of tackifier. Again, no bonding agent for overmolding was used because no overmolding test was contemplated.

(11) Series 3 explored the reduced (10 PHR) but constant amount of Sclair 2714 HDPE hardness modifier, the addition (100 PHR) but constant amount of the Skypel G130D copolyester elastomer bonding agent, and same variations of tackifier for the same two TPEs as used in Series 2. Series 3 also explored overmolding capabilities, with more than 30 PHR of tackifier being required to have the desired cohesive failure mode.

(12) Series 4 explored the same formulations as Series 3, except that the amount of Skypel G130D was increased to 145 PHR but held constant for all six experiments. Viewed from the perspective of PHR of tackifier, more than 30 PHR was needed, with the results of Comparative Example J and Example 13 using 30 PHR was inconclusive.

(13) Series 5 explored the same formulation as in Series 4, except that Septon 4055 SEEPS was used in place of Kraton G1641H and Kraton MD 6958 SEBS. More than 30 PHR of tackifier was required, as seen in the use of 60 PHR of tackifier as the only example and resulting cohesive failure.

(14) Series 6 explored several variations, with the most prominent being the replacement of Skypel G130D copolyester elastomer bonding agent with Exxolor VA1801 maleic polyolefin for overmolding bonding. Dowlex 2035 HDPE for hardness adjustment replaced the Sclair HDPE. Vicron 25-11 filler was added for the first time in the experiments. The first four experiments of the Series 6 used a 3:1 ratio of SEBS:SEEPS blend for the 100 PHR of resin. The latter two experiments explored a 3:1 ratio of high vinyl SEPS:SEEPS blend. The amount of tackifier in each experiment of the Series 6 used 50 PHR or more, and all of Series 6 resulted in desired cohesive failure.

(15) TABLE-US-00006 TABLE 6 Series 1 Series 1A 1B 1C 1D 1E 1F Example A 1 2 3 4 B Weight Percent (%) or PHR % PHR % PHR % PHR % PHR % PHR % PHR Kraton G1651 45.25 100 39.84 100 35.59 100 0 0 0 0 0 0 Septon 4077 0 0 0 0 0 0 35.59 100 39.84 100 45.25 100 550 viscosity oil 36.2 80 31.87 80 28.47 80 28.47 80 31.87 80 36.2 80 Plastolyn R1140 0 0 11.95 30 21.35 60 21.35 60 11.95 30 0 0 Scilair 2908 18.1 40 15.94 40 14.23 40 14.23 40 15.94 40 18.1 40 Kemamide E 0.23 0.5 0.2 0.5 0.18 0.5 0.18 0.5 0.2 0.5 0.23 0.5 Irganox 1010 0.23 0.5 0.2 0.5 0.18 0.5 0.18 0.5 0.2 0.5 0.23 0.5 Total 100 221 100 251 100 281 100 281 100 251 100 221 Mixing Equipment Twin extruder Mixing Temp. 204° C. (400° F.) Mixing Speed 500 RPM Order of Addition of Ingredients All together Form of Product After Mixing Pellet Hardness, Shore A 62 57 51 54 58 62 200° C. Rheology viscosity @ 223/sec 550 490 415 410 540 620 viscosity @ 67/sec 1310 1185 1010 1010 1320 1530 Tan Delta, temperature, ° C. <−40 −40 3 −10 -40 <−40 Tan Delta, peak height N/A 0.18 0.37 0.27 0.28 N/A Compression Set at 70° C. (%) 35 35 31 26 26 32

(16) TABLE-US-00007 TABLE 7 Series 2 Series 2A 2B 2C 2D 2E 2F Example 5 6 C D 7 8 Weight Percent (%) or PHR % PHR % PHR % PHR % PHR % PHR % PHR Kraton MD 6958 45.25 100 39.84 100 35.59 100 0 0 0 0 0 0 Kraton G1641H 0 0 0 0 0 0 35.59 100 39.84 100 45.25 100 550 viscosity oil 36.2 80 31.87 80 28.47 80 28.47 80 31.87 80 36.2 80 Plastolyn R1140 0 0 11.95 30 21.35 60 21.35 60 11.95 30 0 0 Scilair 2908 18.1 40 15.94 40 14.23 40 14.23 40 15.94 40 18.1 40 Kemamide E 0.23 0.5 0.2 0.5 0.18 0.5 0.18 0.5 0.2 0.5 0.23 0.5 Irganox 1010 0.23 0.5 0.2 0.5 0.18 0.5 0.18 0.5 0.2 0.5 0.23 0.5 Total 100 221 100 251 100 281 100 281 100 251 100 221 Mixing Equipment Twin extruder Mixing Temp. 204° C. (400° F.) Mixing Speed 500 RPM Order of Addition of Ingredients All together Form of Product After Mixing Pellets Hardness, Shore A 52 45 38 39 45 53 200° C. Rheology viscosity @ 223/sec 340 310 240 250 290 335 viscosity @ 67/sec 780 710 660 580 700 755 Tan Delta, temperature, ° C. −40 −30 4 8 −30 −40 Tan Delta, peak height 0.27 0.48 0.45 0.5 0.43 0.3 Compression Set at 70° C. (%) 34 31 31 29 33 35

(17) TABLE-US-00008 TABLE 8 Series 3 Series 3A 3B 3C 3D 3E 3F Examples E F 9 10 G H Weight Percent (%) or PHR % PHR % PHR % PHR % PHR % PHR % PHR Kraton G1641H 34.19 100 31.01 100 28.37 100 0 0 0 0 0 0 Kraton MD 6958 0 0 0 0 0 0 28.37 100 31.01 100 34.19 100 550 viscosity oil 27.35 80 24.81 80 22.7 80 22.7 80 24.81 80 27.35 80 Plastolyn R1140 0 0 9.3 30 17.02 60 17.02 60 9.3 30 0 0 Scilair 2714 3.42 10 3.1 10 2.84 10 2.84 10 3.1 10 3.42 10 Skypel G130D 34.19 100 31.01 100 28.37 100 28.37 100 31.01 100 34.19 100 Kemamide B 0.65 1.9 0.59 1.9 0.54 1.9 0.54 1.9 0.59 1.9 0.65 1.9 Irganox 1010 0.21 0.6 0.19 0.6 0.17 0.6 0.17 0.6 0.19 0.6 0.21 0.6 Total 100 292.5 100 322.5 100 352.5 100 352.5 100 322.5 100 292.5 Mixing Equipment Twin extruder Mixing Temp. 193° C. (380° F.) Mixing Speed 500 RPM Order of Addition of Ingredients All together Form of Product After Mixing Pellets Hardness, Shore A 51 45 41 40 43 48 200° C. Rheology viscosity @ 223/sec 340 290 250 240 285 320 viscosity @ 67/sec 705 615 590 550 600 740 Compression Set at 70° C. (%) 46 45 45 44 42 44 Substrate SABIC Cycoloy C2950 PC/ABS Barrel temperature, ° C. 215 Thicknesses of TPE and Substrate Substrate 1.5 mm, OM TPE 1.5 mm, total 3 mm Peel force measured location 5.08 cm (2 inches) Force (Newtons/m) (lb/in) 1051 (6) 1401 (8) 1576 (9) 2452 (14) 2102 (12) 1051 (6) Failure mode Adhesive Adhesive Cohesive Cohesive Adhesive Adhesive

(18) TABLE-US-00009 TABLE 9 Series 4 Series 4A 4B 4C 4D 4E 4F Examples I J 11 12 13 K Weight Percent (%) or PHR % PHR % PHR % PHR % PHR % PHR % PHR Kraton G1641H 29.71 100 27.28 100 25.21 100 0 0 0 0 0 0 Kraton MD 6958 0 0 0 0 0 0 25.21 100 27.28 100 29.71 100 550 viscosity oil 23.77 80 21.82 80 20.17 80 20.17 80 21.82 80 23.77 80 Plastolyn R1140 0 0 8.18 30 15.13 60 15.13 60 8.18 30 0 0 Scilair 2714 2.97 10 2.73 10 2.52 10 2.52 10 2.73 10 2.97 10 Skypel G130D 43.08 145 39.55 145 36.56 145 36.56 145 39.55 145 43.08 145 Kemamide B 0.3 1 0.27 1 0.25 1 0.25 1 0.27 1 0.3 1 Irganox 1010 0.18 0.6 0.16 0.6 0.15 0.6 0.15 0.6 0.16 0.6 0.18 0.6 Total 100 336.6 100 366.6 100 396.6 100 396.6 100 366.6 100 336.6 Mixing Equipment Twin extruder Mixing Temp. 193° C. (380° F.) Mixing Speed 500 RPM Order of Addition of Ingredients All together Form of Product After Mixing Pellets Hardness, Shore A 56 51 47 45 48 53 200° C. Rheology viscosity @ 223/sec 345 290 260 250 300 325 viscosity @ 67/sec 775 625 605 560 640 660 Compression Set at 70° C. (%) 47 45 44 44 45 44 Substrate SABIC Cycoloy C2950 PC/ABS Barrel temperature, ° C. 215 Thicknesses of TPE and substrate Substrate 1.5 mm, OM TPE 1.5 mm, total 3 mm Peel force measured location 5.08 cm (2 inches) Force (Newtons/m) (lb/in) 875 (5) 2102 (12) 2102 (12) 2277 (13) 2277 (13) 1401 (8) Failure mode Adhesive Adhesive Cohesive Cohesive Cohesive Adhesive

(19) TABLE-US-00010 TABLE 10 Series 5 Series 5A Example 14 Weight Percent (%) or PHR % PHR Septon 4055 24.32 100 550 viscosity oil 19.46 80 Plastolyn R1140 14.59 60 Scilair 2714 5.84 24 Skypel G130D 35.26 145 Kemamide B 0.24 1 Irgafos 168 0.15 0.6 Irganox 1010 0.15 0.6 Total 100 411.2 Mixing Equipment Twin extruder Mixing Temp. 193° C. (380° F.) Mixing Speed 500 RPM Order of Addition of Ingredients All together Form of Product After Mixing Pellets Hardness, Shore A 53 200° C. Rheology viscosity @ 223/sec 310 viscosity @ 67/sec 640 Compression Set at 70° C. (%) 38 Substrate SABIC Cycoloy C2950 PC/ABS Barrel temperature, ° C. 215 Thickness of TPE on substrate 1.5 mm Peel force measured location 5.08 cm (2 inches) Force (Newtons/m) (lb/in) 1576 (9) Failure mode Cohesive

(20) TABLE-US-00011 TABLE 11 Series 6 Series 6A 6B 6C 6D 6E 6F Example 15 16 17 18 19 20 Weight Percent (%) or PHR % PHR % PHR % PHR % PHR % PHR % PHR Septon 4055 5.7 25 5.44 25 5.29 25 5.14 25 5.11 25 5.41 25 Kraton G1641 17.11 75 16.33 75 15.88 75 15.42 75 0 0 0 0 Hybrar 7135 0 0 0 0 0 0 0 0 15.32 75 16.22 75 550 viscosity oil 18.25 80 17.41 80 16.93 80 16.45 80 16.35 80 17.3 80 Plastolyn R1140 11.41 50 13.06 60 14.82 70 16.45 80 16.35 80 12.98 60 Dowlex 2035 6.84 30 7.18 33 7.41 35 7.81 38 8.38 41 7.79 36 Exxolor VA1801 15.97 70 15.89 73 15.66 74 15.42 75 15.32 75 15.79 73 Vicron 25-11 23.95 105 23.94 110 23.29 110 22.62 110 22.48 110 23.79 110 Irganox 1010 0.16 0.7 0.15 0.7 0.15 0.7 0.14 0.7 0.14 0.7 0.15 0.7 Irgafos 168 0.11 0.5 0.11 0.5 0.11 0.5 0.1 0.5 0.1 0.5 0.11 0.5 Kemamide B 0.5 2.2 0.48 2.2 0.47 2.2 0.45 2.2 0.45 2.2 0.48 2.2 Total 100 438.4 100 459.4 100 472.4 100 486.4 100 489.4 100 462.4 Mixing Equipment Twin extruder Mixing Temp. 227° C. (440° F.) Mixing Speed 500 RPM Order of Addition of Ingredients All together Form of Product After Mixing Pellets Hardness, Shore A 50 52 52 51 49 49 200° C. Rheology viscosity @ 223/sec 740 680 630 600 480 580 viscosity @ 67/sec 1730 1570 1430 1360 1140 1310 Compression Set at 70° C. (%) 47 48 49 52 45 45 Substrate Ultramid 8333GHI PC Barrel temperature, ° C. 237 Thickness of TPE on substrate 1.5 mm TPE thickness Peel force measured location 5.08 cm (2 inches) Force (Newtons/m) (lb/in) 3503 (20) 2977 (17) 2977 (17) 2977 (17) 3853 (22) 3853 (22) Failure mode Cohesive Cohesive Cohesive Cohesive Cohesive Cohesive

(21) The following additional observations were noted for each of the Series of experiments.

(22) In Series 1, the tackifier was effective raising Tan Delta of middle block which resulted in reduction of viscosity and improved flow. It was also effective reducing flow mark and improving plaque surface smoothness. There also was a reduction of compound viscosity which is very important for thin wall high L/D gasket design. It was also noted that the tackifier can significantly reduce hardness against a constant of 80 PHR of oil. That is very important to make soft OM grade. Oil can reduce hardness, but oil has detrimental effect on bonding. Tackifier does not have a major effect on bonding, allowing the bonding agent to do its work. Finally, the tackifier has no significant effect on 70° C. CS percentage.

(23) In Series 2, the tackifier is effective raising Tan Delta of middle block. Tackifier is effective reducing flow mark and improve plaque surface smoothness. High vinyl TPE compound has lower flow mark and better smooth surface than the equivalent formulations in Series 1. At same Mw, the difference of Tg of styrene block and Tg of midblock determine the elasticity of HSBC flow, with a small Tg difference correlating to a low elasticity and better flow. High vinyl SEBS having a high midblock Tan Delta is less elastic and has better flow than standard SEBS at the same Mw. Series 2 uses a high vinyl SEBS. At same tackifier amount, Series 2 has a lower viscosity than the corresponding formulations of Series 1 and less flow mark. High vinyl SEBS is more suitable used as base TPE for OM purposes because less viscosity is very important for thin wall high L/D gasket design.

(24) While the Series 3-6 experiments used COPE as bonding agent, it is expected to achieve the same or similar results using TPU as the bonding agent.

(25) In Series 3, 100 PHR of COPE was used. Good bonding is achieved for high L/D thin wall design.

(26) By comparison in Series 4, 145 PHR of COPE was used. Lower hardness, better bonding and better flow were obtained with tackifier as expected from prior Series experiments. The 70° C. CS was below 50%. Robust bonding was achieved for a high L/D thin wall design.

(27) In the single experiment of Series 5, no high vinyl SEBS was used. Bonding was lower and CS was better than equivalent example with high vinyl SEBS of experiment 4C.

(28) In Series 6, a high Mw high vinyl SEBS G1641 and high Mw high vinyl isoprene Hybrar 7135 were used. 70° C. CS is below 50%. Robust bonding and good flow were achieved for high L/D thin wall design.

(29) The results of the Examples demonstrated that major soft phase part of the compound is the HSBC, oil, etc. while the minor part was the hard phase of bonding agent. The use of a HSBC compound preferably uses a weight average molecular weight of at least 300,000 with a preference for at least part of the HSBC to be high vinyl, either a high vinyl SEBS or a high vinyl isoprene. The tackifier is used to raise the Tan Delta of the middle block of the styrene block copolymer. As a result, the compound has improved wetting and bonding, reduce hardness, and lower viscosity, all without compromise of compression set. A high soft point tackifier is preferred. The bonding agents to assist in overmolding efficiency can be identified as COPE or TPU or both with a polar substrate such as polycarbonate or a maleic polyolefin or SBC with a polar substrate as polyamide.

(30) The invention is not limited to the above embodiments. The claims follow.