Polysiloxane Polycarbonate Copolymer for Low-Temperature Ductility
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Solution Overview
Problem
Existing polycarbonate materials struggle to achieve high flow and ductility simultaneously, leading to compromised mechanical and optical properties in thin-wall and complex injection molded parts, particularly at low temperatures, due to thermal degradation and residual stress issues.
Innovation Solution
A thermoplastic composition combining polysiloxane-polycarbonate and poly(aliphatic ester)-polycarbonate copolymers with soft block ester units, which maintains high melt flow rates and ductility retention down to -40°C, ensuring complete mold-filling capabilities without sacrificing optical and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If low molecular weight polycarbonates with higher degree of branching are used to achieve high flow properties, then mold-filling capability is improved, but impact strength and mechanical properties are compromised
Solution Approach 1:
The patent uses a composite material system consisting of polysiloxane-polycarbonate copolymer (providing flow and low-temperature ductility) combined with poly(aliphatic ester)-polycarbonate copolymer (providing high flow and flexibility). This composite approach allows achieving high mold-filling capability while maintaining impact strength through synergistic interaction of the two copolymers.
Solution Approach 2:
The patent changes the chemical composition parameters by incorporating specific soft block ester units (formula 8a) with controlled chain lengths (m=4-18) and siloxane content (1-6 wt%). These parameter adjustments enable high flow properties and low-temperature ductility without sacrificing mechanical strength.
2Productivity
If high mold temperatures are used to enable complete mold-filling of thin-wall parts, then flow properties are improved, but thermal degradation occurs and optical properties are lost
Solution Approach 1:
The patent changes the material's flow characteristics by incorporating poly(aliphatic ester)-polycarbonate with soft block units that provide high flow at lower temperatures. This allows complete mold-filling of thin-wall parts without requiring excessive temperatures that would cause thermal degradation and optical property loss.
3Ease of manufacture
If conventional polycarbonate materials are used for thin-wall injection molding, then manufacturing simplicity is maintained, but residual stress and low temperature ductility are compromised
Solution Approach 1:
The patent employs a composite of two specialized copolymers where polysiloxane-polycarbonate provides low-temperature ductility through siloxane chain flexibility, while poly(aliphatic ester)-polycarbonate contributes to overall processability. This composite maintains ease of injection molding while achieving superior low-temperature ductility (100% ductile fracture at -40°C).
Data Source
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AI summary
Disclosed herein is a thermoplastic composition comprising a combination of: a polysiloxane-polycarbonate copolymer and a poly(aliphatic ester)-polycarbonate copolymer comprising soft block ester units of the formula (8a); wherein m is 4 to 18, wherein the thermoplastic composition has a melt volume rate of 14 cc/10 min to 22 cc/10 min at 300°C and under a load of 1.2 Kg and a dwell time of 6 minutes, according to ASTM D1238-04, wherein an article molded from the thermoplastic composition and having a thickness of 3.2 mm has a percent transmittance of greater than 85% according to ASTM D1003-00, and wherein 100% of a set of five test articles each having a thickness of 3.2 mm and molded from the thermoplastic composition exhibit ductile fracture at -40°C when measured for notched Izod Impact according to ASTM D256-04. An article comprising the thermoplastic composition is also disclosed.