Polypropylene Film Surface Roughness Control for Capacitor Blocking
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Solution Overview
Problem
Thin polypropylene films used in capacitor fabrication are prone to wrinkling and winding shifts during the element winding process due to surface roughening, leading to blocking issues and reduced dielectric strength.
Innovation Solution
A polypropylene film with specific surface roughness parameters, including Svk and Spk values, is developed to moderate the roughening of both surfaces, reducing contact area and maintaining dielectric strength while improving conveying properties and processability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the surface of thin polypropylene film is roughened to improve slipperiness during element winding processing, then the slipperiness and ease of winding are improved, but blocking occurs and dielectric strength is reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling surface roughness parameters (Ra: 0.03-0.15 μm, Rz: 0.12-0.60 μm) to achieve optimal slipperiness while preventing blocking. This quantitative control of surface topology resolves the contradiction between improving ease of operation and maintaining reliability
Solution Approach 2:
The patent applies local quality by creating specific surface structures (protrusions and recesses) that provide slipperiness in the machine direction while controlling cross-directional properties. This localized surface modification enables differential friction characteristics that prevent blocking during winding
2Ease of manufacture
If the surface of thin polypropylene film is roughened to facilitate element winding processing, then the processability is improved, but wrinkling and winding shift occur
Solution Approach 1:
The patent uses parameter changes by optimizing surface roughness within specific ranges (Ra: 0.03-0.15 μm, Rz: 0.12-0.60 μm) to enable smooth winding without excessive friction that causes wrinkling, while maintaining enough surface texture to prevent sliding and winding shift
Solution Approach 2:
The patent applies spheroidality by creating rounded protrusions on the film surface rather than sharp irregularities. These curved surface features reduce stress concentration points that would initiate wrinkles while providing consistent friction for stable winding
3Ease of operation
If both surfaces of the polypropylene film are roughened to improve conveying properties, then the conveying property is improved, but the contact area increases leading to blocking
Solution Approach 1:
The patent applies local quality by creating anisotropic surface structures where protrusions are oriented primarily in the machine direction. This directional surface topology provides slipperiness for conveying in the machine direction while minimizing contact area in the cross direction, preventing blocking
Solution Approach 2:
The patent uses asymmetry by making the surface roughness parameters different between machine direction and cross direction. The surface structure is asymmetric such that it facilitates movement in one direction (conveying) while resisting contact and adhesion in perpendicular directions (preventing blocking)
Data Source
AI summary
A polypropylene film which is capable of suppressing blocking in a rolled polypropylene film. The polypropylene film has a first surface and a second surface, contains a polypropylene resin as a main component, and is configured such that: the Svk value (SvkA) of the first surface is 0.005 μm or more and 0.030 μm or less; the Spk value (SpkA) of the first surface is more than 0.035 μm and 0.080 μm or less; the Svk value (SvkB) of the second surface is 0.005 μm or more and 0.030 μm or less; and the Spk value (SpkB) of the second surface is 0.015 μm or more and 0.035 μm or less.