Biaxially Oriented Polypropylene Film Surface Roughness Control
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Solution Overview
Problem
Current methods for surface roughening of biaxially orientated polypropylene film for capacitors fail to achieve sufficient roughness density and uniformity, leading to issues with oil impregnation, reliability, and recyclability, particularly at high voltage gradients and temperatures.
Innovation Solution
A biaxially orientated polypropylene film with specific surface characteristics, including a thickness of 1 to 3 μm, ten point average roughness of 50 nm to 500 nm, and controlled protrusion densities on both surfaces, along with the addition of branched polypropylene, to enhance roughness uniformity and processability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If mechanical methods such as embossing and sand blasting are used to roughen the surface, then surface roughness is improved, but roughness density and uniformity are insufficient
Solution Approach 1:
The patent changes the method of surface roughening from mechanical methods to a chemical method using a specific solvent treatment process. By controlling parameters such as solvent type, treatment time, and temperature, the invention achieves uniform surface roughness with high roughness density, resolving the contradiction between surface roughness improvement and manufacturing precision.
2Shape
If chemical etching with solvent is used to roughen the surface, then surface roughness is improved, but oil impregnation is insufficient leading to short capacitor life
Solution Approach 1:
The patent optimizes the chemical etching parameters by selecting specific solvents and controlling treatment conditions to achieve an optimal surface roughness profile. This optimized roughness structure enables sufficient oil impregnation while maintaining capacitor reliability and extending capacitor life.
3Shape
If stretching of β crystal-containing sheet is used to roughen the surface, then surface roughness is improved, but bulky protrusions are formed reducing roughness density
Solution Approach 1:
The patent replaces the mechanical stretching method with a chemical solvent treatment method. This substitution eliminates the formation of bulky protrusions that occur during mechanical stretching, achieving uniform surface roughness with high roughness density without compromising manufacturing precision.
4Ease of operation
If dissimilar polymer such as polyethylene is used for stretching to roughen surface, then slip properties are improved, but recyclability is reduced
Solution Approach 1:
The patent changes from using dissimilar polymers for surface treatment to using chemical solvent etching on the polypropylene film itself. This approach maintains the polypropylene composition throughout, preserving recyclability while achieving the desired surface roughness and slip properties through controlled chemical treatment.
5Manufacturing precision
If high melt tension polypropylene is used to improve roughness density, then uniformity of protrusions is improved, but heat resistance and withstand voltage characteristics are reduced
Solution Approach 1:
The patent replaces the approach of using high melt tension polypropylene with a chemical solvent treatment method. This substitution achieves uniform surface roughness and high roughness density through controlled chemical etching without compromising the thermal and electrical properties of the polypropylene material, thereby maintaining heat resistance and withstand voltage characteristics.
Data Source
AI summary
A biaxially orientated polypropylene film for capacitor includes protrusions on both surfaces. The biaxially orientated polypropylene film has a thickness (t1) of 1 to 3 μm, has a ten point average roughness (SRz) of 50 nm or more and less than 500 nm on both surfaces, and meets equations (1) and (2) where one surface and the other surface are referred to as a surface A and a surface B, respectively:150≦Pa≦400 (1)50≦Pb≦150 (2)wherein Pa denotes number of protrusions per 0.1 mm2 on the surface A and Pb denotes number of protrusions per 0.1 mm2 on the surface B.