Polyester Film Surface Height Control for Battery Casing

Solution Overview

Problem

Lithium battery casings and pharmaceutical packaging require materials with improved moisture resistance, moldability, and deep drawability, as existing polyester films are insufficient in these aspects, leading to issues like warping and delamination.

Innovation Solution

A polyester film with specific surface height ranges on both surfaces, combined with a laminated structure and a sealant layer, providing enhanced warp resistance, reduced post-molding wrinkles, and improved delamination resistance, while maintaining high strength and mold conformability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If polyester film with improved deep drawability is used, then moldability is improved, but warping of molded product occurs

Engineering Contradiction:

ImprovemoldabilityVSAvoidwarping

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The invention changes the surface roughness parameters of the polyester film by controlling the maximum surface height (SRmax) within specific ranges (50-500 nm for one surface, 500-2000 nm for the other surface). This parameter optimization enables the film to achieve both improved moldability through better conformability and reduced warping through controlled surface properties.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention applies different surface roughness characteristics to different surfaces of the polyester film. One surface has SRmax of 50-500 nm while the other has SRmax of 500-2000 nm, creating local quality differences that optimize both adhesion to metal foil and resistance to warping during molding operations.

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If polyester film with improved deep drawability is used, then moldability is improved, but delamination between polyester film and metal foil occurs

Engineering Contradiction:

ImprovemoldabilityVSAvoiddelamination

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The invention applies different surface roughness characteristics to different surfaces of the polyester film. One surface has SRmax of 50-500 nm while the other has SRmax of 500-2000 nm, creating local quality differences that optimize both adhesion to metal foil and resistance to warping during molding operations.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention creates a composite structure by laminating the polyester film with metal foil, where the controlled surface roughness of the polyester film enhances interfacial adhesion. The combination of specific surface height ranges on both surfaces of the polyester film with the metal foil creates a composite material system that prevents delamination while maintaining moldability.

Inventive Principle:

Principle #40Composite materials

3Object-affected harmful factors

If polyamide film is used, then moisture resistance is improved, but stability to contents deteriorates

Engineering Contradiction:

Improvemoisture resistanceVSAvoidstability to contents

Core Design Contradiction:

Object-affected harmful factorsVSStability of the object's composition

Solution Approach 1:

The invention replaces the polyamide film (which has good moisture resistance but poor content stability) with a polyester film that, while having inherently lower moisture resistance, achieves sufficient performance through the metal foil lamination. The polyester film offers superior content stability and can be processed more easily, trading off some moisture resistance for overall system performance.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The invention creates a composite structure by laminating the polyester film with metal foil, where the controlled surface roughness of the polyester film enhances interfacial adhesion. The combination of specific surface height ranges on both surfaces of the polyester film with the metal foil creates a composite material system that prevents delamination while maintaining moldability.

Inventive Principle:

Principle #40Composite materials

Data Source

PatentUS9777110B2Polyester film, laminate including the film, and laminated assembly including the laminate and sealant layer

Publication Date: 2017.10.03 TORAY INDUSTRIES INC

AI summary

A polyester film has a maximum surface height on a surface A side (SRmaxA) of 1500 nm to 7000 nm, a maximum surface height on a surface B side (SRmaxB) of 5 nm or more but less than 7000 nm, the SRmaxA and the SRmaxB satisfying the following relation (1), and a strength at break at 25° C. of 200 MPa to 330 MPa in both the longitudinal direction and the width direction.SRmaxA>SRmaxB (1)