Fatigue resistant thermoplastic composition, method of making, and articles formed therefrom
A thermoplastic composition comprises a resin composition comprising a polycarbonate having a weight averaged molecular weight of greater than or equal to 30,000 as measured using gel permeation chromatography, a polysiloxane-polycarbonate comprising 1 to 50 weight percent of siloxane units; and a SAN copolymer, wherein the amounts of polycarbonate, polysiloxane-polycarbonate, and SAN copolymer are selected such that fatigue failure for the thermoplastic composition occurs at greater than or equal to 70,000 cycles at a pressure of 28.2 MPa and a frequency of 5 Hz according to ASTM D638-03 type I, and the viscosity of the thermoplastic composition is less than or equal to 112 Pa-s when measured at a shear rate of 6,000 sec −1 and at 300° C. according to ASTM D4440-01. A method of making the thermoplastic is also disclosed.
1 . A thermoplastic composition comprising a resin composition comprising:
a polycarbonate having a weight averaged molecular weight of greater than or equal to 30,000 as measured using gel permeation chromatography,
a polysiloxane-polycarbonate comprising 1 to 50 weight percent of siloxane units; and
a SAN copolymer,
wherein the amounts of polycarbonate, polysiloxane-polycarbonate, and SAN copolymer are selected such that fatigue failure for the thermoplastic composition occurs at greater than or equal to 70,000 cycles at a pressure of 28.2 MPa and a frequency of 5 Hz according to ASTM D638-03 type I, and the viscosity of the thermoplastic composition is less than or equal to 112 Pa-s when measured at a shear rate of 6,000 sec −1 and at 300° C. according to ASTM D4440-01.
2 . The thermoplastic composition of claim 1 , wherein the polycarbonate is present in the resin composition in an amount of 65 to 87 weight percent, wherein the polysiloxane-polycarbonate is present the resin composition in an amount of 3 to 15 weight percent, and the SAN copolymer is present the resin composition in an amount of 10 to 20 weight percent, and wherein the combined amounts of polycarbonate, polysiloxane-polycarbonate, and SAN copolymer is 100 weight percent of the resin composition.
3 . The thermoplastic composition of claim 1 , wherein the polycarbonate comprises greater than or equal to 90 wt % of a linear polycarbonate.
4 . The thermoplastic composition of claim 3 , wherein the linear polycarbonate is bisphenol A polycarbonate.
5 . The thermoplastic composition of claim 1 , wherein the resin composition comprises 0.6 to 3 weight percent polysiloxane as provided by the polysiloxane-polycarbonate, based on the total weight of the resin composition.
6 . The thermoplastic composition of claim 1 , wherein the polysiloxane-polycarbonate is free of Si—O—C bonds.
7 . The thermoplastic composition of claim 6 , wherein the polysiloxane-polycarbonate comprises polydimethylsiloxane units and bisphenol-A carbonate units.
8 . The thermoplastic composition of claim 1 , wherein the SAN copolymer comprises styrene and acrylonitrile in a ratio of 65:35 to 85:15.
9 . The thermoplastic composition of claim 8 , wherein the weight averaged molecular weight of the SAN copolymer is 30,000 to 150,000, as measured using gel permeation chromatography.
10 . The thermoplastic composition of claim 1 , further comprising an impact modifier, filler, antioxidant, heat stabilizer, light stabilizer, ultraviolet light absorber, plasticizer, mold release agent, lubricant, antistatic agent, pigment, dye, flame retardant, anti-drip agent, or a combination comprising at least one of these.
11 . The thermoplastic composition of claim 1 wherein the tensile strength is greater than or equal to 650 kg/cm 2 , as measured at 50 mm/min according to ASTM D638-03.
12 . The composition of claim 1 , wherein the flexural modulus is greater than or equal to about 23,000 kg/cm 2 as measured at 2.8 mm/min. according to ASTM D790-03.
13 . The thermoplastic composition of claim 1 , wherein the notched Izod impact strength is greater than or equal to 70 kg-cm/cm, as measured on 3.18 mm bars at 23° C. according to ASTM D256-04.
14 . The thermoplastic composition of claim 1 , wherein the viscosity of the thermoplastic composition is greater than or equal to 900 Pa-s when measured at a shear rate of 25 sec −1 and at 300° C. according to ASTM D4440-01.
15 . A thermoplastic composition comprising a resin composition comprising:
65 to 87 weight percent of a polycarbonate, wherein the polycarbonate comprises greater than or equal to 90 wt % of a linear polycarbonate, and wherein the polycarbonate has a weight averaged molecular weight of greater than or equal to 30,000 as measured using gel permeation chromatography, 3 to 15 weight percent of a polysiloxane-polycarbonate, wherein the polysiloxane-polycarbonate comprises 1 to 50 weight percent of siloxane units; and
10 to 20 weight percent of a SAN copolymer, wherein the resin composition comprises 0.6 to 3 weight percent polysiloxane as provided by the polysiloxane-polycarbonate, based on the total weight of the resin composition, and wherein the combined amounts of polycarbonate, polysiloxane-polycarbonate, and SAN copolymer is 100 weight percent of the resin composition.
16 . The thermoplastic composition of claim 15 wherein fatigue failure for the thermoplastic composition occurs at greater than or equal to 70,000 cycles at a pressure of 28.2 MPa and a frequency of 5 Hz according to ASTM D638-03 type I.
17 . The thermoplastic composition of claim 15 , wherein the viscosity of the thermoplastic composition is less than or equal to 112 Pa-s when measured at a shear rate of 6,000 sec −1 and 300° C. according to ASTM D4440-01.
18 . A resin composition comprising:
a polycarbonate having a weight averaged molecular weight of greater than or equal to 30,000 as measured using gel permeation chromatography,
a polysiloxane-polycarbonate comprising 1 to 50 weight percent of siloxane units; and
a SAN copolymer,
wherein the amounts of polycarbonate, polysiloxane-polycarbonate, and SAN copolymer are selected such that fatigue failure for a thermoplastic composition prepared from the resin composition occurs at greater than or equal to 70,000 cycles, at a pressure of 28.2 MPa and a frequency of 5 Hz, according to ASTM D638-03 type I, and wherein the viscosity of the thermoplastic composition is less than or equal to 112 Pa-s when measured at a shear rate of 6,000 sec −1 and at 300° C. according to ASTM D4440-01.
19 . A method of making a thermoplastic composition comprising melt blending:
a polycarbonate having a weight averaged molecular weight of greater than or equal to 30,000 as measured using gel permeation chromatography,
a polysiloxane-polycarbonate comprising 1 to 50 weight percent of siloxane units; and
a SAN copolymer,
wherein the amounts of polycarbonate, polysiloxane-polycarbonate, and SAN copolymer are selected such that fatigue failure for the thermoplastic composition occurs at greater than or equal to 70,000 cycles, at a pressure of 28.2 MPa and a frequency of 5 Hz, according to ASTM D638-03 type I, and the viscosity of the thermoplastic composition is less than or equal to 112 Pa-s when measured at a shear rate of 6,000 sec −1 and at 300° C. according to ASTM D4440-01.
20 . An article comprising the thermoplastic composition of claim 1.