Reversible Drying Aqueous Polyurethane Ink Resins
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Solution Overview
Problem
Water-based inks for inkjet applications face challenges such as clogging due to pigment flocculation, dye crystallization, and irreversible drying, which affect printing quality and reliability, and existing polyurethane polymers struggle to balance re-solubility with water and solvent resistance.
Innovation Solution
Aqueous resin compositions comprising a polymerizable ethylenically unsaturated polyurethane polymer with a weight average molecular weight of less than 15,000 Daltons, incorporating specific weight ratios of polyisocyanate, hydrophilic compounds, and copolymerizable ethylenically unsaturated compounds, along with a non-volatile neutralizing agent, allowing for controlled crosslinking and re-dispersibility in water.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If water dispersible polyurethane polymers are used to form continuous films after drying, then film formation is achieved, but irreversible drying occurs causing nozzle clogging and printing process interruption
Solution Approach 1:
The patent applies dynamics by making the drying process reversible rather than irreversible. The polymer composition dynamically changes from a dried film state back to a dispersible state upon contact with water, allowing the printing process to continue without interruption. This is achieved through specific polymer architecture and hydrophilic character that enable redispersion.
Solution Approach 2:
The patent implements discarding and recovering by allowing the polymer to be discarded as a dried film during printing, then recovered by redispersion in water for reuse. The polymer particles can be redeposited onto the substrate or collected and reused, preventing waste and maintaining productivity.
2Reliability
If polymer crosslinking density is increased to ensure water and solvent resistance, then chemical resistance is improved, but pot-life is limited and premature crosslinking occurs
Solution Approach 1:
The patent applies preliminary action by preparing the polymer composition with all necessary components for crosslinking (polymerizable groups, crosslinking agents) but delaying the actual crosslinking reaction until the printing process is complete. The composition remains stable and non-crosslinked during storage and printing, then crosslinks after application to achieve the desired chemical resistance.
Solution Approach 2:
The patent uses parameter changes by controlling the reaction conditions (temperature, catalyst presence, moisture) to prevent premature crosslinking during storage. The polymer composition is formulated with parameters that maintain stability at storage conditions but enable crosslinking under processing conditions, extending pot-life while ensuring final chemical resistance.
3Adaptability or versatility
If polymer molecular weight is decreased to improve re-solubility, then re-dispersibility is enhanced, but water and solvent resistance deteriorates
Solution Approach 1:
The patent applies composite materials by combining low molecular weight polymer segments with crosslinking structures. The low molecular weight provides re-dispersibility and processability, while the crosslinking networks (formed after printing) provide the necessary water and solvent resistance. This composite structure resolves the contradiction between processability and performance.
Solution Approach 2:
The patent implements local quality by having different regions of the polymer composition with different properties. The polymer chains themselves are low molecular weight for re-dispersibility, while the crosslinked network regions provide chemical resistance. This local differentiation allows simultaneous achievement of both properties.
4Reliability
If thermal curing is used to crosslink the polymer, then crosslinking is achieved, but gels or coagulation occur due to uncontrolled reaction
Solution Approach 1:
The patent replaces the thermal curing mechanism with a controlled chemical or photo-initiated crosslinking system. Instead of relying on heat to drive the crosslinking reaction (which causes uncontrolled gelling), the invention uses specific initiators or catalysts that enable gradual and controlled crosslinking under milder conditions, preventing defects while achieving the desired network structure.
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 provides stable, water- and solvent-resistant ink compositions with improved re-dispersibility, flexibility, and optical properties, preventing nozzle clogging and ensuring robust printing processes with extended shelf-life and high crosslinking density.
Implementation Method 1
Radiation curable aqueous compositions with reversible drying
Implementation Method 2
an improved re-solubility (re-dispersibility) of the polymers can be obtained with a sufficiently hydrophilic character
Data Source
AI summary
The present invention relates to an aqueous resin composition (I) comprising at least one polymerizable ethylenically unsaturated polyurethane polymer (A), optionally, at least one polymerizable ethylenically unsaturated compound (B) different from (A), and optionally, at least one neutralizing agent (C); wherein the polyurethane polymer (A) has a weight average molecular weight of less than 15.000 Daltons and is obtained from the reaction of: at least one polyisocyanate (i); at least one hydrophilic compound (ii) containing at least one reactive group capable to react with isocyanate groups and at least one group which is capable to render the polyurethane polymer dispersible or soluble in aqueous medium either directly or after reaction with a neutralizing agent (C) to provide a salt; at least one compound (iii) containing essentially one reactive group capable to react with isocyanate groups and at least one copolymerizable ethylenically unsaturated group; at least one compound (iv) containing at least two reactive groups capable to react with isocyanate groups; and, optionally, at least one chain extender (v) containing at least two reactive groups capable to react with isocyanate groups, which chain extender is different from compounds (iv); and wherein the non-volatile components of the resin composition (I) after drying are re-dispersible or re-soluble in water at 25°C. The present invention further relates to radiation curable compositions comprising a resin composition of the invention for use in coating applications or graphic art applications.