Polyolefin Microporous Film Rolling Stability
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Solution Overview
Problem
Polyolefin microporous films used in battery separators face challenges with roll deviation and step deviation during the production and handling of long-sized electrodes, leading to instability and potential faults in battery taking-up processes.
Innovation Solution
A polyolefin microporous film with specific properties, including a compression elastic modulus of 0.1 to 1,000 kPa, a tensile elastic modulus ratio of 1.5 to 7.8, and an average pore diameter of 0.05 to 0.10 μm, combined with a hydrophilicizing treatment, to enhance rolling stability and reduce step deviation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the rolling length of separator rolls is increased to accommodate long-sized electrodes for elevated battery capacity, then the battery capacity is improved, but roll deviation and step deviation occur leading to production line instability
Solution Approach 1:
The invention changes the physical parameters of the microporous film by controlling its compression elastic modulus (0.1 to 1,000 kPa) and tensile elastic modulus ratio (1.5 to 7.8 in longitudinal to transverse direction). These parameter adjustments enable the film to maintain dimensional stability and suppress roll deviation during long-sized rolling operations, resolving the contradiction between increased productivity and maintained reliability
Solution Approach 2:
The invention applies beforehand cushioning by designing the microporous film with specific elastic modulus characteristics that inherently absorb and compensate for rolling stresses before they can cause deviation. The film's mechanical properties are pre-engineered to resist roll and step deviation during transportation and handling of long-sized rolls
2Reliability
If the microporous film is compressed to absorb thickness unevenness for better rolling stability, then the rolling stability is improved, but the compression elastic modulus must be precisely controlled within a narrow range
Solution Approach 1:
The invention defines a wide yet controlled range for compression elastic modulus (0.1 to 1,000 kPa) that balances rolling stability with manufacturing feasibility. This parameter range allows sufficient compression to absorb thickness unevenness while remaining achievable through conventional microporous film production processes
Solution Approach 2:
The invention employs composite material design by combining polyolefin base material with controlled pore structure and specific elastic modulus characteristics. This composite approach enables the film to exhibit both the compliance needed for rolling stability and the structural integrity for manufacturing consistency
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 improved taking-up stability, reduced roll deviation, and minimized step deviation, ensuring reliable battery production and handling while maintaining low air permeability and resistance.
Implementation Method 1
it is important that the microporous film itself is reasonably compressed in rolling to absorb minute thickness unevenness
Implementation Method 2
it is particularly important that a reasonable stress is developed in the film thickness directions when the microporous film is compressed
Implementation Method 3
the present inventors have further found that if the microporous film according to the present invention is further subjected to a hydrophilicizing treatment, the film resistance remarkably decreases
Data Source
AI summary
There is provided a polyolefin microporous film which is excellent in taking-up stability in a production line and a processing line of the polyolefin microporous film, and further in a line for a battery taking-up step, and hardly generates step deviation when a roll thereof has received an impact.The polyolefin microporous film has a compression elastic modulus of 0.1 to 1,000 kPa, and a ratio of a tensile elastic modulus in the longitudinal direction to a tensile elastic modulus in the transverse direction of 1.5 to 7.8.