Resin-Coated Metal Sheet Crystallinity Control for Can Surface Quality
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Solution Overview
Problem
The formation of appearance defects on resin coated metal sheets due to residual stress relaxation during heat treatment, which occurs when manufacturing two-piece cans with high degrees of working using steel sheets, is a challenge.
Innovation Solution
The residual stress in the resin coating layer is reduced by controlling the degree of crystallinity through specific heat quantity differences and melting point ranges, ensuring the resin coating layers are within defined parameters to prevent uneven deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If heat treatment is performed at a temperature close to the melting point of the resin coating layer to improve adhesion and laminatability, then adhesion between the resin coating layer and metal sheet is improved, but appearance defects occur due to residual stress relaxation and uneven deformation
Solution Approach 1:
The patent changes the thermal parameters of the resin coating layer by controlling its degree of crystallinity (30-80%) and setting the difference between heat quantity of crystallization and heat quantity of fusion within 0-20 J/g. This parameter optimization allows the resin to undergo controlled phase transformation during heat treatment, improving adhesion while minimizing residual stress and preventing appearance defects
Solution Approach 2:
The patent utilizes the phase transition properties of the resin coating layer during heat treatment. By controlling the degree of crystallinity and heat quantity parameters, the resin undergoes controlled melting and crystallization processes that improve adhesion between layers and between resin and metal sheet, while the controlled phase transition prevents excessive residual stress and uneven deformation that would cause appearance defects
2Quantity of substance
If a steel sheet with small sheet thickness is used to reduce cost, then manufacturing cost is reduced, but the sheet cannot withstand high degree of working processes
Solution Approach 1:
The patent creates a composite structure by coating resin layers on both sides of the steel sheet. The resin coating layer (with controlled crystallinity and heat quantity parameters) provides protective and functional properties, while the steel sheet provides structural strength. This composite structure enables the use of thinner, less expensive steel sheets while maintaining the capability to undergo high degree of working processes
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 effectively reduces the occurrence of appearance defects caused by heat treatment, maintaining the integrity and aesthetics of the resin coated metal sheets.
Implementation Method 1
the difference between a heat quantity of crystallization and a heat quantity of fusion after being laminated to the metal sheet is within a range of 0 J/g or more and 20 J/g or less
Implementation Method 2
calculating the heat quantity of crystallization from the area of the exothermic peak measured in a range of 100 to 200°C
Implementation Method 3
calculating the heat quantity of fusion from the area of the endothermic peak measured in a range of 200 to 280°C
Data Source
Figure 1~2
AI summary
A resin coated metal sheet 1 includes a metal sheet 2, a resin coating layer 3 formed on the front side of the metal sheet 2, and a resin coating layer 4 formed on the back side of the metal sheet 2. The resin coating layer 3 and the resin coating layer 4 are positioned outside and inside a metal container after forming, respectively. The resin coating layer 3 is formed of a resin material whose difference between the heat quantity of crystallization and the heat quantity of fusion after being laminated to the metal sheet is within a range of 0 J/g or more and 20 J/g or less on a unit weight basis. It is preferable that the resin coating layers 3 and 4 are formed of a resin material containing 90 mol% or more ethylene terephthalate unit and that the melting point of the resin coating layer 3 is within a range of 240°C or more and 254°C or less.