Security Document Sheets with Reinforcing Watermarks
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Solution Overview
Problem
The application of surface-applied security features, such as optically variable stripes or patches, to paper sheets with corner or edge reinforcing watermarks is hindered by poor adhesion due to the variable profile of the reinforcing bars, leading to issues in cash handling machines and security document verification.
Innovation Solution
A method of forming fibrous substrates with corner or edge reinforcing watermarks by varying the grammage of fibers to create positive watermarks that increase stiffness and form raised regions, allowing for improved adhesion of surface-applied security features by creating a smooth planar surface for application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If corner or edge reinforcing watermarks are formed in the substrate, then the stiffness and resistance to folds/tears are improved, but the adhesion of surface-applied security features deteriorates due to variable profile
Solution Approach 1:
The patent applies local quality by creating a smooth planar surface specifically at the location where the security feature will be applied, while maintaining the reinforcing watermark structure elsewhere. This localized modification ensures good adhesion at the application point without compromising the overall stiffness and tear resistance provided by the reinforcing bars in other areas.
Solution Approach 2:
The patent segments the substrate into distinct functional regions: the reinforcing watermark areas that provide structural strength, and the smooth planar surface area that provides good adhesion for security features. This segmentation allows each region to optimize its specific function without interfering with the other.
2Strength
If reinforcing bars are formed to increase stiffness, then the sheet resistance to tearing is improved, but the surface uniformity for security feature application deteriorates
Solution Approach 1:
The patent creates a local smooth planar surface at the specific location where the security feature will be applied, while the reinforcing bars maintain their variable profile elsewhere. This localized smoothing approach preserves surface uniformity where needed for adhesion while maintaining the overall stiffness from the reinforcing structure.
Solution Approach 2:
The smooth planar surface is formed as a preliminary step before applying the security feature. This preliminary preparation ensures that when the security feature is applied, it will have good adhesion due to the uniform surface, while the reinforcing bars remain in place to provide structural strength.
Data Source
Figure 1
Figure 2a
Figure 2b~3b
AI summary
The invention relates to improvements in methods of making sheets for security documents having edge or corner reinforcing watermarks (13, 18) and a surface applied feature (15) and a method of making a sheet from a fibrous substrate, said sheet has corners and edges joined at said corners. The method comprises the step of forming the substrate by depositing fibres on a support surface and forming at least one reinforcing watermark (13, 18) at a predetermined position in the substrate. The reinforcing watermark (13, 18) increases the stiffness of the sheet in the watermarked region and is a positive watermark formed by varying the grammage of fibres of the substrate to form at least two adjacent bars (13a, 18a) of increased grammage relative to the mean grammage of fibres in adjacent areas of the substrate. At least one raised region (17) is formed by increasing the grammage of fibres, which joins the adjacent bars within the at least one reinforcing watermark to form a smooth planar surface. This surface is suitable for a subsequent application of a substantially planar security feature (15) to a portion of at least one surface of the substrate across the smooth planar surface.