Non-Ionic Polyurethane Varnish for Reliable Wet-on-Wet Jetting
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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
1Productivity
If latex-based over-print varnish compositions are used for wet-on-wet printing on absorbing substrates, then productivity is improved by enabling in-line printing without separate drying steps, but manufacturing precision deteriorates due to inability to achieve high gloss levels and acceptable coalescence
Solution Approach 1:
The patent modifies the chemical composition parameters of the over-print varnish by incorporating specific polymers (acrylic, vinyl, or styrene-based) with controlled molecular weights and glass transition temperatures. This allows the formulation to achieve proper coalescence and gloss when printed wet-on-wet on absorbing substrates, resolving the manufacturing precision issue while maintaining productivity
Solution Approach 2:
The invention creates a composite varnish formulation combining multiple polymer types (acrylic, vinyl, styrene) with complementary properties. This composite approach enables the varnish to simultaneously achieve adhesion to absorbing substrates, proper coalescence, and high gloss finish in a single formulation, resolving the contradiction between productivity and manufacturing precision
2Manufacturing precision
If non-ionic polyurethane dispersions are used, then manufacturing precision is improved by providing acceptable coalescence, but reliability deteriorates due to thixotropic rheology causing unreliable jetting
Solution Approach 1:
The patent changes the rheological parameters of the formulation by selecting polymers with specific glass transition temperatures and molecular weights that provide Newtonian flow characteristics. This ensures consistent jetting behavior and droplet formation while maintaining the coalescence properties needed for proper film formation, thus resolving the reliability issue without sacrificing manufacturing precision
3Productivity
If wet-on-wet printing is implemented, then productivity is improved by eliminating separate drying steps, but manufacturing precision deteriorates due to difficulty achieving high gloss levels
Solution Approach 1:
The invention adjusts key formulation parameters including polymer glass transition temperature (50-150°C range), molecular weight, and composition ratios to enable proper coalescence and gloss development during wet-on-wet printing. The modified formulation achieves high surface finish quality without requiring separate drying steps, thus maintaining both productivity and manufacturing precision
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 enables in-line printing with excellent gloss levels and acceptable coalescence on absorbing substrates, eliminating the need for a separate drying step and ensuring reliable jetting.
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... which exhibits Newtonian-like rheology
Implementation Method 3
applying an over-print varnish formulation onto the ink composition
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.