Coextruded Double-Layer Coating for Disposable Board Containers
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Solution Overview
Problem
Existing disposable board containers, such as microwave-ovenable cups and trays, face inadequate sealing between the mantle and bottom due to poor heat conductivity of fibrous boards and suboptimal melting points of polymer coatings, leading to leakages.
Innovation Solution
A coextruded double-layer coating comprising a blend of polyethylene (PE) and polypropylene (PP) as the inner layer and a polypropylene-olefin copolymer (PP-c) as the outer layer, providing improved adhesion and heat-sealability, with the inner layer acting as a tie layer between the fibrous board and the outer heat-seal layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer PE+PP blend coating is used, then the coating provides basic liquid barrier properties, but the heat-sealing quality is inadequate due to poor heat conductivity of fibrous board and suboptimal melting point
Solution Approach 1:
The coating is segmented into two distinct layers: an inner layer (PE+PP blend) for adhesion to the fibrous board and an outer layer (PP-copolymer) for heat-sealing. This segmentation allows each layer to be optimized for its specific function, resolving the contradiction between sealing quality and coating complexity.
Solution Approach 2:
The patent uses a composite coating structure combining two different polymer blends with complementary properties. The inner layer provides adhesion to the low heat-conductivity fibrous board, while the outer layer provides adequate heat-sealing at microwave-compatible temperatures, achieving reliable sealing without excessive complexity.
2Temperature
If LDPE coating is used, then the coating has excellent extrusion and heat-sealing properties, but the melting point is too low for microwave-oven use
Solution Approach 1:
The coating is divided into two layers with distinct temperature functions: the inner layer uses PE+PP blend with lower melting point for good heat-sealability during manufacturing, while the outer layer uses PP-copolymer with higher melting point for microwave-oven compatibility, thus resolving the temperature-ease of manufacture contradiction.
Solution Approach 2:
The patent changes the polymer composition parameters by using a copolymer structure (PP-c) instead of homopolymer, which adjusts the melting point to be sufficiently high for microwave use while maintaining adequate heat-sealing properties through the blended inner layer.
3Reliability
If PE+PP blend coating is used for microwave-ovenability, then the melting point is sufficient, but the heat-sealing between mantle and bottom is inadequate due to poor heat conductivity of fibrous board
Solution Approach 1:
The inner layer acts as an intermediary between the low heat-conductivity fibrous board and the outer heat-seal layer. It provides a thermal bridge that facilitates heat transfer from the sealing jaws through the board layers to the polymeric seals, improving sealing quality despite the poor heat conductivity of the fibrous substrate.
Solution Approach 2:
The composite coating structure with PE+PP inner layer specifically addresses the heat conductivity issue by providing a polymer matrix with better thermal properties than the fibrous board, enabling adequate heat transfer for reliable sealing while maintaining microwave-ovenability.
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 solution achieves a significantly better heat-seal quality and lower melting point, ensuring leak-free microwave-ovenable containers with improved runnability in extrusion coating and compatibility with fibrous substrates, allowing for efficient microwave oven use.
Implementation Method 1
the lower edge of the mantle is bent and heat-sealed by the coating polymer against the circumferential rim surrounding the bottom. The seals secure liquid-tightness for the cup.
Implementation Method 2
The material for a disposable board cup is fibrous board, which on one or both sides is extrusion-coated with a heat-sealable liquid-barrier polymer.
Data Source
Figure 1~6
AI summary
The invention relates to a disposable container of fibrous board comprising a bottom (3) and an upward mantle (2) heat-sealed thereto. The material for both the bottom and the mantle is a polymer coated fibrous board, in which the coating covers at least the inner surfaces of the container. According to the invention the material comprises a fibrous board base (8) such as paperboard or cardboard, an extruded inner coating layer (9) of a blend of polyethylene (PE) and polypropylene (PP), and an extruded outer coating layer (10) of polypropylene-olefin copolymer (PP-c). The inner coating layer (9) secures adhesion with the board base (8) and the outer coating layer (10) is for liquid-proof heat-sealing between the bottom (3) and the mantle (2) of the container. The container is in particular a microwave ovenable cup or food tray.