Polylactic Acid Hollow Articles Heat Resistance
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Solution Overview
Problem
Polylactic acid-based biodegradable resin containers lack heat resistance, making them unsuitable for applications involving hot water, microwave ovens, and high-temperature treatments, and they often deform or adhere to molds during injection molding due to insufficient rigidity and contraction, limiting the production of hollow articles like bowls and cups.
Innovation Solution
A process for producing heat-resistant hollow articles using a biodegradable resin composition with at least 50% polylactic acid and 1-28% nanocomposite inorganic filler, involving a mold with a stripper plate and an infrared temperature sensor to control crystallization and release, ensuring accurate timing for mold opening and minimizing deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If polylactic acid is used to make food containers, then biodegradability is achieved, but heat resistance deteriorates
Solution Approach 1:
The patent uses a composite material system consisting of polylactic acid (50-95 mass%) combined with inorganic fillers (5-40 mass%, including calcium carbonate, magnesium oxide, or silica) and a specific nucleating agent (0.1-5 mass%). This composite structure allows the material to maintain biodegradability while achieving heat resistance through enhanced crystallization properties, enabling the containers to withstand temperatures up to 100°C or higher.
Solution Approach 2:
The patent changes the crystallization parameters of polylactic acid by adding a nucleating agent that promotes rapid crystallization at lower temperatures. This parameter change allows the material to achieve its crystalline structure and heat resistance before final cooling, enabling the food containers to maintain structural integrity at high temperatures while remaining biodegradable.
2Manufacturing precision
If the mold is cooled to solidify the injected resin, then the hollow article is formed, but the article adheres to the male mold portion due to contraction
Solution Approach 1:
The patent changes the thermal parameters by heating the mold surface to a specific temperature range (80-120°C) before injection. This temperature control prevents excessive contraction and adhesion to the male mold portion, while still allowing solidification to occur. The nucleating agent also accelerates crystallization, enabling timely release before complete contraction occurs.
Solution Approach 2:
The patent applies preliminary heating to the mold surface before injection to create a temperature gradient that prevents adhesion. Additionally, the nucleating agent is pre-added to the resin composition to ensure rapid crystallization occurs during cooling, creating a timing window for easy mold release before excessive contraction sets in.
3Ease of manufacture
If the resin is cooled insufficiently, then the article can be released from the mold, but deformation occurs due to insufficient rigidity
Solution Approach 1:
The patent changes the crystallization kinetics by adding a nucleating agent that promotes rapid crystal formation at temperatures above 100°C. This allows the resin to develop sufficient rigidity and structural stability at higher temperatures, enabling mold release before complete cooling, while preventing deformation that would occur with insufficient cooling in conventional systems.
Solution Approach 2:
The patent creates local quality differences through the nucleating agent, which promotes crystallization in specific regions and orientations within the resin. This localized crystalline structure development provides enhanced rigidity in critical areas, allowing the article to maintain its shape during early release from the mold while still achieving complete solidification later.
4Ease of manufacture
If polymer-alloyed resin is used to prevent adhesion, then mold release is improved, but biodegradability deteriorates due to synthetic resin content
Solution Approach 1:
The patent uses a composite material system combining polylactic acid with inorganic fillers (calcium carbonate, magnesium oxide, or silica) and a nucleating agent, avoiding petroleum-based synthetic resins entirely. This biodegradable composite achieves mold release through controlled crystallization and temperature management rather than through synthetic resin blending, maintaining full biodegradability while improving manufacturing ease.
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
The process enables the production of heat-resistant, biodegradable hollow articles that can withstand high temperatures and are easily released from molds, allowing for the creation of complex shapes like bowls and cups without deformation, while maintaining environmental sustainability.
Implementation Method 1
Excellent heat resistance can be imparted to the above-described biodegradable resin compositions by crystallization at temperatures near 110° C.
Implementation Method 2
when a temperature T (° C.) of the polylactic acid containing resin injected into the cavity which is detected by an infrared temperature sensor provided in a position which is housed in the convexity of the male mold portion or in the concavity of the female mold portion
Data Source
AI summary
A process for production of a heat-resistant hollow article made of a polylactic acid containing resin by using a mold which includes a female mold portion having a concavity, a male mold portion having a convexity and a stripper plate having an edge-forming part. The surface of the mold facing the cavity is heated to a temperature corresponding to a crystallization temperature of the polylactic acid containing resin. The male mold portion and the stripper plate are moved away from the female mold portion when a temperature T(° C.) of the resin detected by an infrared temperature sensor is in the range of T=(t+3.5)±1.5 (t(° C.) is the surface temperature of the mold). Gas is introduced between an inner surface of the hollow article and the male mold portion, and the hollow article is taken out of the mold by advancing the stripper plate toward the hollow article.