Polypropylene Sheet Thermal Sealing via Melting Point Segmentation
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Solution Overview
Problem
High-speed production of polypropylene sheets with high mechanical properties and transparency is hindered by insufficient thermal sealing between uniaxially or biaxially oriented polypropylene films, limiting their application in thicker forms.
Innovation Solution
Alternately laminating biaxially oriented polypropylene films with specific melting points and thermally sealing them using a heating element, ensuring a melting point difference of at least 8°C, to achieve a polypropylene sheet with a thickness of 0.5 to 5 mm and enhanced mechanical and transparency properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high speed forming is performed to produce polypropylene sheets with high production rate, then productivity is improved, but thermal sealing between films becomes insufficient leading to poor mechanical properties
Solution Approach 1:
The invention divides the polypropylene sheet into multiple thin films (each less than 150 μm thick) with different melting points, alternating high melting point films (Tm1) and low melting point films (Tm2). This segmentation allows each film to be processed independently at optimized temperatures, enabling high-speed production while maintaining adequate thermal sealing through the melting point difference (Tm1 - Tm2 ≥ 8°C).
Solution Approach 2:
The invention changes the melting point parameter by using polypropylene films with specifically controlled different melting points (Tm1 and Tm2 where Tm1 - Tm2 ≥ 8°C). This parameter differentiation enables the thermal sealing process to occur at temperatures that are high enough to seal the low melting point films effectively but low enough to prevent degradation during high-speed forming, thus resolving the contradiction between production rate and mechanical properties.
2Volume of moving object
If thickness of oriented film is increased to produce sheets with thickness of 0.5 to 5 mm, then application range is expanded, but thermal sealing becomes insufficient at high production rates
Solution Approach 1:
Instead of using a single thick film that cannot be adequately sealed at high production rates, the invention segments the total thickness (0.5 to 5 mm) into multiple thin films (each < 150 μm). This segmentation allows each individual film to be thermally sealed effectively even at high speeds, while the cumulative thickness achieves the desired sheet dimensions for expanded applications.
Solution Approach 2:
The invention creates a composite structure by laminating multiple polypropylene films with different melting points in an alternating pattern. This composite approach combines the benefits of thin films (easy sealing) with the advantages of thick sheets (expanded application range), achieving both reliable thermal sealing and desired thickness for various applications.
3Volume of moving object
If multiple thin films are laminated to achieve desired thickness, then sheet thickness can be controlled, but delamination occurs due to insufficient thermal sealing
Solution Approach 1:
The invention changes the thermal parameter by using films with different melting points (Tm1 and Tm2 where Tm1 - Tm2 ≥ 8°C). This melting point differentiation ensures that during thermal sealing, the low melting point films (Tm2) melt and bond to adjacent films while the high melting point films (Tm1) remain structurally intact, providing strong interlayer adhesion and preventing delamination in the final multi-layer sheet.
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 method produces polypropylene sheets with excellent transparency and mechanical properties, including high tensile modulus and cold impact resistance, while maintaining a high production rate and preventing delamination, thus expanding their application to thicker forms.
Implementation Method 1
a step 2 of bringing a heating element into contact with an outermost layer of the precursor to thermally seal layers of the film
Implementation Method 2
thermally seal layers of the film, in which Tmh−Tml≥8(° C.) where the melting point is measured by a differential scanning calorimeter
Data Source
AI summary
A method for producing a polypropylene sheet having a thickness of 0.5 to 5 mm, the method comprising;a step 1 of preparing a precursor in which a first biaxially oriented polypropylene film having a thickness of less than 0.15 mm and a melting point Tmh and a second biaxially oriented polypropylene film having a thickness of less than 0.15 mm and a melting point of Tml are alternately laminated;a step 2 of bringing a heating element into contact with an outermost layer of the precursor to thermally seal layer of the films, whereTmh−Tml≥8(° C.)where the melting point is measured by a differential scanning calorimeter (DSC) under the condition at 30° C. to 230° C. and a heating rate of 10° C./min.