Thermoplastic elastomer compounds exhibiting low compression set properties
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.
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:
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.