Coated White Paper Fluorescence Intensity and Printability
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Solution Overview
Problem
Existing coated sheets face challenges in achieving high fluorescence intensity while maintaining offset-printability, as fluorescent whitening agents are poorly fixed by coat components, leading to 'greening' and mottling issues, especially when using high quantities of support substances.
Innovation Solution
A coated sheet with a surface coat comprising at least 1% dry weight fluorescent whitening agent and over 2% dry weight support substance, applied using a curtain coating process to ensure a regular coat thickness, allowing for high fluorescence intensity and preventing mottling during offset-printing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If high quantity of fluorescent whitening agent is used to increase fluorescence intensity, then fluorescence intensity is improved, but greening effect occurs causing shade change from blue towards green
Solution Approach 1:
A support substance acts as an intermediary between the fluorescent whitening agent and the coat components. This mediator improves the fixation of the whitening agent, allowing higher quantities to be used without causing greening, thus enabling fluorescence intensity improvement while maintaining shade control.
Solution Approach 2:
The invention changes the chemical and physical parameters of the coat composition by introducing specific support substances and optimizing the ratio of whitening agent to support substance. This parameter change enables the system to accommodate higher whitening agent concentrations without adverse shade effects.
2Reliability
If high quantity of support substance is used to fix fluorescent whitening agent, then fixation is improved, but mottling occurs during offset-printing
Solution Approach 1:
The invention optimizes the quantity parameter of support substance to a specific range (0.5-5% relative to whitening agent) and adjusts the molecular weight parameters of the support substance. These parameter changes achieve reliable fixation while preventing mottling during offset-printing.
Solution Approach 2:
The coat composition is formulated as a composite material system combining fluorescent whitening agent, support substance, and binder in specific proportions. This composite approach ensures both reliable fixation of the whitening agent and uniform printing performance without mottling.
3Ease of manufacture
If thick coat is applied to improve offset-printability, then printability is improved, but UV filtering effect increases reducing fluorescence intensity
Solution Approach 1:
The invention changes the composition parameters of the coat, specifically the ratio of binder to pigment and the type of support substance used. These parameter changes allow the coat to maintain adequate thickness for good offset-printability while minimizing UV filtering effects that would reduce fluorescence intensity.
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 achieves a high fluorescence intensity of over 55, measured by ISO 11475 standards, while maintaining offset-printability without substantial mottling, even with air-drying inks, by ensuring a homogeneous coat composition and regular thickness.
Implementation Method 1
fluorescent whitening agents have been used which act by absorbing natural light in the ultraviolet and in the near-visible below 420 nm then re-emitting the light by fluorescence at about 440 nm
Data Source
AI summary
The invention concerns a coated white sheet having a fluorescence intensity of more than 55, measured in accordance with international standard ISO 11475: 2004, by the difference between the value for the CIE whiteness under D65 illuminant and the value for this same CIE whiteness after interposing a filter that eliminates wavelengths shorter than 420 nm, and being offset-printable with no mottling, said coated sheet comprising at least one base sheet and a printable white surface coat having a pigmented composition which comprises: —at least some white coating pigments and at least one coating binder; —at least one fluorescent whitening agent in a total quantity of 1% dry weight or more with respect to the dry weight of said pigments; —at least one support substance for said whitening agent in a total quantity of dry weight of more than 2% with respect to the dry weight of said pigments. The invention also concerns a method for producing said coated sheet by curtain coating said pigmented composition.