Multilayer Film Winding Defect Suppression via Surface Roughness
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Solution Overview
Problem
Multilayer films used in display devices often develop defects like gauge bands and winding wrinkles during winding, leading to optical defects and reduced product value, despite protective films being used to minimize these issues.
Innovation Solution
The surface roughness and elastic modulus of both the optical film and the protective film, along with their ratios, are set within specific ranges to prevent defects such as gauge bands and winding wrinkles, and to avoid unwanted concavo-convex shapes on the optical film surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a protective film with low elastic modulus and high surface roughness is used to suppress winding defects, then the amount of air involved during winding is decreased and defects such as gauge bands and winding wrinkles are suppressed, but an undesired concavo-convex shape is formed on the surface of the optical film due to transfer of the concavo-convex shape from the protective film
Solution Approach 1:
The patent changes the physical parameters of the protective film by setting its elastic modulus to 100 MPa or more (higher than conventional values) and controlling the surface roughness ratio between the protective film and optical film to be 0.1 or more and 10 or less. This parameter optimization resolves the contradiction by finding a balance point where winding defects are suppressed while preventing excessive concavo-convex transfer to the optical film surface.
Solution Approach 2:
The patent creates a composite structure by bonding the protective film to the optical film, where the protective film serves dual functions: suppressing winding defects through controlled air involvement while maintaining optical film surface quality through optimized elastic modulus and surface roughness characteristics. The composite system achieves both winding defect suppression and surface flatness preservation simultaneously.
2Ease of operation
If a protective film with very low elastic modulus is used to allow easy deformation during winding, then winding defects are suppressed, but the concavo-convex shape transfers more easily to the optical film surface causing optical defects
Solution Approach 1:
The patent optimizes the elastic modulus parameter of the protective film to be 100 MPa or more, which is higher than conventional protective films. This parameter change allows the film to maintain sufficient deformability for smooth winding while reducing excessive deformation that would cause concavo-convex shape transfer to the optical film, thereby resolving the contradiction between ease of operation and harmful factor reduction.
3Manufacturing precision
If the surface roughness of the protective film is increased to reduce air involvement during winding, then gauge bands and winding wrinkles are suppressed, but the concavo-convex shape on the protective film surface transfers to the optical film
Solution Approach 1:
The patent optimizes the surface roughness parameter by controlling the ratio between the surface roughness of the protective film and the optical film to be 0.1 or more and 10 or less. This parameter optimization allows the protective film to have sufficient surface roughness to reduce air involvement during winding (suppressing gauge bands and wrinkles) while preventing excessive surface irregularity that would transfer as concavo-convex shapes to the optical film.
Solution Approach 2:
The bonded composite structure of protective film and optical film with optimized surface roughness ratio creates a system where the protective film's surface characteristics are harmonized with the optical film, allowing the protective film to provide winding defect suppression through controlled roughness while preventing harmful surface pattern transfer to the optical film.
Data Source
AI summary
The present invention provides a long-length multilayer film including a long-length optical film and a long-length protective, film that is releasable from the long-length optical film, wherein a three-dimensional center-line average roughness R1 of a surface of the optical film opposite to a surface on a side of the protective film, a three-dimensional center-line average roughness R2 of a surface of the protective film opposite to a surface on a side of the optical film, a tensile elastic modulus M1 in a lengthwise direction of the optical film, and a tensile elastic modulus M2 in a lengthwise direction of the protective film satisfy predetermined relationships: and a wound body of the multilayer film.