Heat-Curable Aqueous Inkjet Inks to Prevent Printhead Blockage
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Solution Overview
Problem
Existing aqueous inkjet printing technologies face issues with viscosity changes at elevated temperatures and potential printhead blockage due to crosslinking at ambient or low temperatures, using conventional crosslinkers that are hazardous and ineffective with acid-functional resins.
Innovation Solution
Aqueous inkjet compositions using an acid-functional resin and a hydroxyl-functional material, such as hydroxyl-functional polyurethane dispersion or organically modified colloidal silica, thermally cured at elevated temperatures to achieve stable and resoluble inks without low molecular weight crosslinkers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional crosslinkers (keto-hydrazide, keto-amine, acid-carbodiimide, acid-oxazoline, acid-aziridine) are used to crosslink acid-functional resins, then crosslinking efficiency is improved, but crosslinking occurs at room temperature causing printhead blockage
Solution Approach 1:
The patent changes the temperature parameter for crosslinking by using blocked isocyanates that require elevated temperatures (above 60°C, preferably above 80°C) to activate. This prevents premature crosslinking at room temperature during inkjet printing operations while enabling effective crosslinking during the thermal curing process, thus resolving the contradiction between crosslinking efficiency and printhead blockage risk
Solution Approach 2:
The patent introduces a blocking agent as an intermediary substance that temporarily prevents the isocyanate groups from reacting at low temperatures. The blocking agent (such as water, alcohols, or carboxylic acids) forms a reversible adduct with the isocyanate, preventing premature crosslinking during printing, and releases the active isocyanate groups during thermal curing to enable crosslinking
2Strength
If amino resins (melamine-formaldehyde, urea-formaldehyde) or blocked isocyanates with molecular weight <1000 Daltons are used for thermal curing, then crosslinking effectiveness is improved, but health and safety concerns arise
Solution Approach 1:
The patent uses polymer-grade isocyanates with molecular weights greater than 1000 Daltons as a safer alternative to low molecular weight crosslinkers. These higher molecular weight isocyanates provide sufficient crosslinking effectiveness while reducing health and safety concerns associated with volatile low molecular weight compounds. The isocyanate-functional polymers serve as both the resin component and the crosslinking agent
Solution Approach 2:
The patent creates a composite inkjet composition combining acid-functional polymer dispersions (first component) with isocyanate-functional polymer dispersions (second component). This composite approach enables crosslinking between the two different polymer types, achieving effective crosslinking while using safer, higher molecular weight materials that reduce health and safety risks
3Productivity
If conventional crosslinkers are used in aqueous inkjet printing, then crosslinking speed is improved, but viscosity stability at elevated temperatures deteriorates
Solution Approach 1:
The patent changes the temperature parameter to control the timing of crosslinking. By using blocked isocyanates that require elevated temperatures (above 60°C, preferably above 80°C) to activate, the patent ensures that crosslinking only occurs during the thermal curing process after printing. This maintains viscosity stability during storage and printing while enabling rapid crosslinking during curing, resolving the contradiction between crosslinking speed and viscosity stability
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 compositions exhibit excellent stability and resolubility, minimizing printhead blockage risks and maintaining ink quality at temperatures up to 50°C, suitable for applications like textiles and metal decoration.
Implementation Method 1
thermally cured at elevated temperatures to achieve stable and resoluble inks
Implementation Method 2
The acid-functional resin and the hydroxyl-functional material crosslink upon heating
Data Source
AI summary
A method of preparing a printed substrate comprising printing an aqueous inkjet ink composition to a substrate and thermally curing the printed ink by heating at a temperature of at least 80°C, wherein the aqueous inkjet ink composition comprises an acid-functional water-soluble or water-dispersible resin and a hydroxyl-functional material with the proviso that if the hydroxyl-functional material is a hydroxyl-functional polyurethane dispersion said hydroxyl-functional polyurethane dispersion has a hydroxyl value of ≥ 25 mgKOH/g (based on the dry polymer weight); and thermally curable aqueous inkjet compositions suitable for use in said method.