Internal Laser Marking in Security Documents for Durable Optical Effects

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Solution Overview

Problem

Security documents, such as banknotes and passports, face challenges in maintaining the integrity of laser markings due to surface exposure, which can lead to damage and replication issues, as existing methods require the polymer layer to be absorbent to the laser wavelength and necessitate additional protective layers.

Innovation Solution

The implementation of an internal laser marking within a transparent polymer layer, using high-energy, short-pulse lasers to create a diffractive structure that is confined within the layer, eliminating the need for surface exposure and additional protective layers, and allowing for optically variable effects that are difficult to replicate.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If laser marking is applied to the surface of the polymer layer, then the marking is visible and can be applied, but the marking is exposed to damage and soiling

Engineering Contradiction:

Improvedurability of laser markingVSAvoiddamage and soiling to surface marking

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The laser marking is nested within the transparent polymer layer rather than being applied to the surface. The marking is formed internally at a depth within the layer, surrounded by the polymer material itself, which protects it from external damage and soiling while maintaining visibility through the transparent medium.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The laser marking transitions from a two-dimensional surface application to a three-dimensional internal structure within the polymer layer. By moving the marking into the depth dimension of the material, it gains protection from surface-related harmful factors while remaining optically accessible.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Ease of manufacture

If conventional laser marking is used on absorbent polymer layers, then the marking can be created, but additional protective layers are required

Engineering Contradiction:

Improvemanufacturing process simplicityVSAvoidnumber of protective layers required

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

The protective function is extracted from separate protective layers and integrated into the polymer layer itself. By forming the laser marking internally within the existing transparent polymer layer, the layer simultaneously serves as both the substrate and the protective enclosure, eliminating the need for additional protective layers.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The transparent polymer layer is given multiple functions: it serves as the substrate for the marking, provides the protective enclosure for the internal marking, and maintains optical transparency. This multi-functionality eliminates the need for separate protective layers and simplifies the overall structure.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If internal laser marking is formed in transparent polymer layer, then protection from damage is achieved, but the polymer layer must be transparent to the laser wavelength

Engineering Contradiction:

Improveprotection of laser markingVSAvoidpolymer layer material selection

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The laser parameters (wavelength, pulse duration, energy density) are adjusted to match the optical properties of transparent polymer materials. By changing these parameters, the laser can effectively mark transparent polymers without requiring them to be absorbent, enabling internal marking while maintaining material versatility.

Inventive Principle:

Principle #35Parameter changes

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

This approach enhances the durability and security of the laser markings by protecting them from damage and soiling, while simplifying manufacturing and eliminating the need for laser-absorbent additives, resulting in a more complex and difficult-to-replicate optical effect.

Implementation Method 1

irradiating a transparent polymer layer using a pulsed laser source with a pulse duration of 100 ps or less, to thereby form an internal laser marking within the transparent polymer layer

Methodology Applied

Scientific EffectLaser ablation: Laser Ablation

Implementation Method 2

the internal laser marking comprises a diffractive structure

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentEP3697623B9Security documents and methods of manufacture thereof

Publication Date: 2022.12.14 DE LA RUE INTERNATIONAL LTD

Figure 1(a)~1(c)
Figure 2(a)~4(b)
Figure 5(a)~6

AI summary

A security document is disclosed having a window region and a non-window region. The window region is of lower opacity than the non-window region. The security document comprises a transparent polymer layer at least in the window region of the security document, and the transparent polymer layer comprises therewithin an internal laser marking having an optical effect.