Thermoplastic Polyurethane 3D Printing With Extended Pot Life
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Solution Overview
Problem
Conventional dual-cure systems for 3D printing face limitations in pot life, making it difficult to reuse unused build material and limiting planned build times, especially due to the reactivity of NCO groups and catalysts.
Innovation Solution
A method involving a free-radically crosslinkable thermoplastic polyurethane with a urethane group content of ≥5% by weight, combined with photoinitiators, is used in additive manufacturing. The method includes layer deposition and irradiation with near-IR to near-UV light, followed by heating above the melting point to form layers, and optional further chemical reactions to enhance mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional dual-cure systems with NCO groups and catalysts are used, then mechanical strength is improved, but pot life is limited
Solution Approach 1:
The patent divides the curing process into two independent stages: UV photopolymerization for initial crosslinking and mechanical strength, followed by thermal crosslinking for enhanced pot life extension. This segmentation allows each curing mechanism to operate independently without interfering with the other, resolving the contradiction between achieving mechanical strength and maintaining pot life.
Solution Approach 2:
The patent changes the chemical parameters of the build material by incorporating specific functional groups (isocyanate, hydroxyl, carboxyl) that can undergo both UV-induced and thermal crosslinking reactions. This dual-reactivity capability allows the material to achieve mechanical strength through UV curing while maintaining extended pot life through controlled thermal crosslinking, directly addressing the contradiction.
2Productivity
If build times are extended beyond pot life, then productivity is improved, but material reusability deteriorates
Solution Approach 1:
The patent segments the curing process into UV photopolymerization for immediate layer bonding and delayed thermal crosslinking for final property development. This allows build operations to proceed beyond traditional pot life limits since the UV-cured layers maintain structural integrity while the thermal crosslinking can occur later, enabling material reuse and extended build schedules without compromising reliability.
Solution Approach 2:
The patent performs preliminary UV photopolymerization to establish immediate mechanical strength and layer adhesion during the build process, deferring the complete crosslinking reaction to a subsequent thermal treatment step. This preliminary action allows the material to remain workable and reusable during extended build times while ensuring final product reliability through the later thermal crosslinking stage.
3Speed
If UV curing alone is used, then build speed is improved, but mechanical strength in shadow regions deteriorates
Solution Approach 1:
The patent extracts the limitation of UV penetration by introducing a thermal crosslinking mechanism that operates independently of light exposure. The thermal crosslinking step compensates for shadow regions where UV light cannot reach, ensuring uniform mechanical strength throughout the printed object while maintaining the fast build speeds enabled by UV curing of accessible areas.
Solution Approach 2:
The patent creates a composite curing system combining UV photopolymerization and thermal crosslinking mechanisms. The UV component provides rapid initial curing for speed, while the thermal component ensures complete crosslinking in shadow regions, delivering uniform mechanical strength throughout the object. This composite approach resolves the contradiction between build speed and shadow region strength.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for the production of mechanically durable articles with extended pot life, enabling efficient reuse of build material and flexible build times, while maintaining shape integrity and adhesion between layers.
Implementation Method 1
a free-radically crosslinkable build material which comprises a thermoplastic free-radically crosslinkable polyurethane and a photoinitiator
Implementation Method 2
the build material is heated above its melting point for layer deposition and subsequent curing
Data Source
AI summary
The present invention relates to a method for producing an object in an additive manufacturing process from a precursor and comprises the following steps: I) depositing a layer of a radically cross-linkable construction material, which corresponds to a first selected cross-section of the precursor, on a carrier; II) depositing a layer of a radically cross-linkable construction material, which corresponds to a further selected cross-section of the precursor, on a previously applied layer of the radically cross-linked construction material; III) repeating step II) until the precursor is formed. The radically cross-linkable construction material comprises a thermoplastic radically cross-linkable polyurethane with a urethane group content of ≥5% by weight and a photoinitiator. The radically cross-linkable construction material is also heated to a processing temperature that is greater than the melting point of the radically cross-linkable polyurethane. After step III) the precursor having a temperature of 20° C. is defined as the object, or step IV) is performed: IV) performing a chemical reaction in the precursor obtained after step III) so that the object is obtained.