Biaxially Stretched Polypropylene Film Surface Roughness Control
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Solution Overview
Problem
Biaxially stretched polypropylene films used in capacitors face challenges with insufficient roughness density and uniformity, leading to impaired withstand voltage characteristics and preservability, especially at high electrical potential gradients, and existing methods for surface roughening result in low roughness density or coarse projections, affecting capacitor reliability and recyclability.
Innovation Solution
A biaxially stretched polypropylene film with specific surface roughness parameters, including ten-point average roughness and projection height ranges, is developed to enhance withstand voltage characteristics and processability, incorporating a branched polypropylene content for improved crystal modification and melt crystallization temperature, ensuring uniform projections and compact surface morphology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If mechanical methods (embossing, sandblasting) or chemical methods (solvent etching) are used to roughen the film surface, then the surface roughness is improved, but the roughness density becomes low resulting in insufficient impregnation property
Solution Approach 1:
The patent changes the physical-chemical parameters of the polypropylene resin by controlling the stereoregular fraction (10-85%) and using specific crystallization conditions to achieve optimal surface roughness density without mechanical or chemical treatment, resolving the contradiction between surface roughness and impregnation property
Solution Approach 2:
The patent replaces mechanical roughening methods (embossing, sandblasting) and chemical etching with a controlled crystallization process that naturally forms surface projections during film formation, achieving high roughness density without mechanical intervention
2Volume of moving object
If the film is made thinner to reduce capacitor size, then the capacitance density is improved, but the withstand voltage characteristics deteriorate
Solution Approach 1:
The patent changes the electrical parameters of the film by precisely controlling the stereoregular fraction (10-85%) and crystallization temperature to optimize the balance between film thickness and withstand voltage characteristics, enabling thinner films to maintain high breakdown voltage
Solution Approach 2:
The patent creates local quality differences within the film structure through controlled crystallization, forming surface projections that enhance electrical breakdown resistance locally, allowing the overall film to be thinner while maintaining high withstand voltage capability
3Shape
If high melt strength polypropylene resin is used to improve surface roughness, then the projection formation is improved, but the heat resistance and withstand voltage characteristics are lowered
Solution Approach 1:
The patent changes the compositional parameters by precisely controlling the stereoregular fraction (10-85%) rather than using high melt strength resins, achieving projection formation through controlled crystallization while maintaining the heat resistance and electrical properties of standard polypropylene
Solution Approach 2:
The patent creates a composite-like structure within the polypropylene film through controlled crystallization, forming a dual-phase structure with surface projections and bulk material that maintains both mechanical properties and electrical performance
4Shape
If a different polymer such as polyethylene is blended to roughen the surface, then the surface morphology is improved, but the recyclability deteriorates
Solution Approach 1:
The patent maintains homogeneity by using only polypropylene resin with controlled stereoregular fraction, avoiding blending with different polymers, thus preserving recyclability while achieving the desired surface morphology through controlled crystallization
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 film exhibits excellent withstand voltage characteristics, preservability, and processability, particularly for AC capacitors, with improved dielectric breakdown resistance and self-healing properties, maintaining capacitor lifespan and electrical insulation under varying conditions.
Implementation Method 1
a method of stretching a sheet in which β-crystals are formed
Implementation Method 2
incorporating a branched polypropylene content for improved crystal modification and melt crystallization temperature
Data Source
AI summary
Provided is a biaxially stretched polypropylene film for capacitors which has high withstand voltage characteristics when used as a dielectric for capacitors and which has highly suitable processability into elements. The biaxially stretched polypropylene film for capacitors has projections on both surfaces and has a thickness (t1, μm) of 4-20 μm. When one of the surfaces is expressed by surface A and the other by surface B, all of the following relationships are satisfied. 800≤SRzB≤1,300 (nm) 0.1≤SRzA/SRzB≤0.8 PBmin≥100 (nm) PBmax≤1,500 (nm) 0.4≤PB450-750/PB≤0.7.