Amorphous Polyamide Multilayer Sheets for Clear Aligner Durability
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Solution Overview
Problem
Existing clear aligner materials face issues with stress retention, abrasion resistance, surface damage, and mechanical performance, particularly when using multilayer structures, which affect the efficiency and comfort of orthodontic treatment.
Innovation Solution
A multilayer polymer sheet comprising an A-layer polymer made of amorphous polyamide and a B-layer polymer selected from TPU, EVA copolymer, or copolyester, with specific molecular compositions and laminated through in-mold co-extrusion, providing improved stress retention, abrasion resistance, and low surface friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a soft PU outer layer is used in multilayer clear aligners, then ease of operation and wearing comfort are improved, but the outer layer becomes easily damaged and stained, affecting function and aesthetics
Solution Approach 1:
The patent divides the clear aligner into multiple functional layers: a soft inner layer (50-150 μm) for comfort and ease of operation, and a hard outer layer (100-500 μm) for durability and stain resistance. Each layer performs its specific function independently, resolving the contradiction between softness for comfort and hardness for durability.
Solution Approach 2:
The patent uses composite material structure combining different polymer properties - the inner layer uses soft polymers (Shore A 40-80) for comfort, while the outer layer uses hard polymers (Shore D 60-85) for durability. This composite approach allows the aligner to simultaneously achieve ease of operation and resistance to damage/staining.
2Reliability
If copolyester outer layers are used to avoid staining, then surface durability is improved, but the outer layer is prone to crazing and fracturing under stress due to poor mechanical performance
Solution Approach 1:
The patent segregates the functions of stain resistance and mechanical strength into different layers. The outer hard layer provides stain resistance while the inner soft layer provides mechanical flexibility and stress absorption, preventing crazing and fracturing that would occur in a single-layer copolyester structure.
Solution Approach 2:
The patent applies different material properties to different regions/layers of the aligner. The outer layer has hard, stain-resistant properties, while the inner layer has soft, flexible properties that prevent stress concentration and cracking. This local differentiation of material quality resolves the contradiction between stain resistance and fracture resistance.
3Ease of manufacture
If single-layer thermoplastic polymer sheets are used, then manufacturing simplicity is maintained, but stress retention performance and resistance to bite impact are insufficient
Solution Approach 1:
The patent employs composite multilayer materials combining hard and soft polymer layers, each contributing different mechanical properties. The hard outer layer provides bite impact resistance while the soft inner layer maintains stress retention, achieving superior overall performance compared to single-layer sheets while using standardized manufacturing processes.
Data Source
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AI summary
The present disclosure discloses a multilayer polymer sheet and a dental appliance. The multilayer polymer sheet includes an A-layer polymer and a B-layer polymer. The A-layer polymer is polyamide (PA), including the following groups: (1) 36 mol% to 40 mol% of 4,4-methylenebis(2-methylcyclohexylamine); (2) 36 mol% to 40 mol% of an aromatic dicarboxylic acid, which is 1,3-benzenedicarboxylic acid (IPA) and/or 1,4-benzenedicarboxylic acid (TPA); and (3) 20 mol% to 28 mol% of an alicyclic or aliphatic amino acid or lactam. The B-layer polymer is located between two layers of the A-layer polymer. The B-layer polymer is at least one selected from the group consisting of a thermoplastic polyurethane (TPU), an ethylene-vinyl acetate (EVA) copolymer, and a copolyester.