Low Energy UV-Curable Offset Printing Inks for Security Documents

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Solution Overview

Problem

Conventional low energy UV-curable inks used in offset and letterpress printing for security documents suffer from poor curing efficiency and surface curing issues due to the use of conventional photoinitiators and high pigment content, leading to delays and set-off problems during the printing process.

Innovation Solution

The development of low energy radically curable offset and letterpress printing inks utilizing specific photoinitiators and (meth)acrylate compounds, along with luminescent, magnetic, or IR-absorbing materials, and fillers, which are cured using UV lamps within the 280 to 400 nm wavelength range to achieve rapid and efficient curing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by stationary object

If conventional low energy UV-curable inks are used with conventional photoinitiators, then the ink can be cured with low energy UV lamps, but the curing efficiency is poor and surface curing issues occur

Engineering Contradiction:

ImproveUV energy consumptionVSAvoidcuring efficiency

Core Design Contradiction:

Use of energy by stationary objectVSReliability

Solution Approach 1:

The patent changes the chemical parameters of the photoinitiator system by using a combination of conventional photoinitiators (acetophenone, benzophenone, alpha-aminoketone, alpha-hydroxyketone) with specific additives and co-initiators. This parameter change in the chemical composition enables efficient curing with low energy UV lamps (280-400 nm) while maintaining good surface cure properties, resolving the contradiction between low energy consumption and curing efficiency.

Inventive Principle:

Principle #35Parameter changes

2Quantity of substance

If high pigment content is used in the ink, then security features are enhanced, but curing efficiency decreases due to light absorption

Engineering Contradiction:

Improvepigment contentVSAvoidcuring efficiency

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent introduces co-initiators and additives as intermediary substances that facilitate the curing process. These intermediaries work synergistically with the photoinitiators to generate free radicals more effectively, enabling complete curing even in the presence of high pigment content that would otherwise block UV light. This resolves the contradiction between high pigment content for security features and curing efficiency.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If rapid curing is achieved to prevent set-off, then printing speed increases, but curing completeness may be compromised

Engineering Contradiction:

Improveprinting speedVSAvoidcuring completeness

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent employs a multi-component photoinitiator system that is pre-configured to provide both rapid initial curing and complete through-cure. The combination of different photoinitiators with varying activation energies and reaction kinetics ensures that surface curing occurs rapidly to prevent set-off, while the synergistic action of all components ensures complete curing throughout the ink layer, even at high printing speeds.

Inventive Principle:

Principle #10Preliminary action

4Device complexity

If conventional photoinitiators are used, then the ink formulation is simpler, but surface curing properties are insufficient

Engineering Contradiction:

Improveink formulation complexityVSAvoidsurface curing properties

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent creates a composite photoinitiator system combining multiple types of photoinitiators (acetophenone, benzophenone, alpha-aminoketone, alpha-hydroxyketone) with co-initiators and additives. This composite approach leverages the complementary strengths of each component to achieve excellent surface curing properties and through-cure, while the formulation remains practically implementable in conventional printing systems.

Inventive Principle:

Principle #40Composite materials

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 solution enables high-speed printing with excellent surface and through-cure properties, reducing set-off issues and enhancing the security features' durability on security documents.

Implementation Method 1

UV radically curable pigmented offset printing inks and UV radically curable pigmented letterpress printing inks are used in the field of the protection of security document against counterfeit and illegal reproduction

Methodology Applied

Scientific EffectPhotopolymerisation: Photopolymerisation

Implementation Method 2

curing the coating or layer with a UV lamp (280 to 400 nm) at a dose of at least 50 mJ/cm2

Methodology Applied

Scientific EffectAbsorption (EM radiation): Absorption (EM radiation)

Data Source

PatentEP3551469B1Low energy curing offset and letterpress printing inks and printing process

Publication Date: 2021.06.23 SICPA HOLDING SA

AI summary

The present invention relates to the field of low energy radically curable inks for offset or letterpress printing of security documents. In particular, the invention relates to low energy radically curable offset or letterpress printing inks for offset or letterpress printing on a substrate or security document, said low energy radically curable inks having a viscosity in the range of about 2.5 to about 25 Pa s at 40˚C and 1000 s-1 and comprising radically curable (meth)acrylate compounds, one or more one or more photoinitiators of formula (I), one or machine readable materials and one or more fillers and/or extenders.