Over-Print Varnish Formulation for Wet-on-Wet Inkjet Gloss
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Solution Overview
Problem
Existing inkjet printing methods face challenges in achieving high gloss levels, durability, and acceptable coalescence when using wet-on-wet printing with latex-based over-print varnish compositions on absorbing substrates, and non-ionic polyurethane dispersions are unsuitable for reliable jetting due to thixotropic rheologies.
Innovation Solution
An over-print varnish formulation comprising a non-ionic polyurethane dispersion, a water-soluble polymer with a molecular weight less than 55,000, a wax with a particle size of 200 nm or less, and a water-soluble solvent, which exhibits Newtonian-like rheology, allowing for effective wet-on-wet printing with improved gloss and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If latex-based over-print varnish compositions are used for wet-on-wet printing on absorbing substrates, then gloss levels and durability are improved, but coalescence becomes unacceptable
Solution Approach 1:
The patent modifies the rheological parameters of the varnish composition by selecting specific polymer types and molecular weights, and by controlling solid content and particle size distribution, to achieve Newtonian-like flow behavior that enables proper coalescence during wet-on-wet printing while maintaining durability and gloss
2Illumination intensity
If non-ionic polyurethane dispersions are used, then gloss levels are improved, but jetting reliability deteriorates due to thixotropic rheologies
Solution Approach 1:
The patent changes the rheological parameters from thixotropic to Newtonian-like by selecting specific non-ionic polyurethane dispersion types and controlling molecular weight, solid content, and particle size distribution, enabling reliable jetting while maintaining high gloss levels
3Stability of the object's composition
If a separate drying step is implemented, then coalescence is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the drying function from the printing system by formulating the varnish composition with appropriate volatility characteristics and rheological properties that enable coalescence to occur naturally during the wet-on-wet printing process itself, eliminating the need for a separate drying apparatus
Solution Approach 2:
The varnish composition is formulated to self-coalesce during the printing process through its inherent rheological properties and solvent evaporation characteristics, without requiring external drying equipment or additional processing steps
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 formulation achieves excellent gloss levels and durability while maintaining acceptable coalescence in wet-on-wet inkjet applications, eliminating the need for a separate drying step and reducing apparatus size and cost.
Implementation Method 1
a wax having a particle size (d50) 200 nm or less
Implementation Method 2
a water-soluble polymer of Mw less than 55,000
Implementation Method 3
which exhibits Newtonian-like rheology, allowing for effective wet-on-wet printing
Implementation Method 4
a water-soluble solvent
Data Source
AI summary
An over-print varnish formulation is described. The formulation comprises a non-ionic polyurethane dispersion; a water-soluble polymer of Mw less than 55,000; a wax having a particle size (d50) 200 nm or less; and a water-soluble solvent, and at least 20 wt % solids, based on the total weight of the formulation. A method of printing using the formulation, and a printed article are also described.