Curable Aqueous Composition for Flexible Substrates
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Solution Overview
Problem
Conventional curable aqueous compositions used to strengthen flexible substrates often release formaldehyde, which is environmentally harmful, and do not provide adequate tensile strength, especially in wet or IPA-immersed conditions.
Innovation Solution
A curable aqueous composition comprising a (co)polymer with ethylenically unsaturated acidic monomers and an aliphatic epoxy crosslinker with reactive oxirane groups, which is applied to a flexible substrate and heated to enhance crosslinking and tensile strength without releasing formaldehyde.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional crosslinking agents such as copolymerized N-methylol acrylamide and added urea/formaldehyde resins are used, then crosslinking and tensile strength are improved, but formaldehyde release occurs which is harmful to the environment
Solution Approach 1:
The patent changes the chemical parameters of the crosslinking system by replacing formaldehyde-based crosslinking agents with isocyanate-based crosslinking agents. This substitution fundamentally alters the chemical reaction pathway, eliminating formaldehyde release while maintaining effective crosslinking functionality. The specific parameter change involves using compounds containing isocyanate groups (NCO) as the crosslinking mechanism instead of formaldehyde-based mechanisms.
Solution Approach 2:
The patent converts the harmful formaldehyde release issue into a benefit by selecting isocyanate-based crosslinking agents that not only eliminate formaldehyde but also provide enhanced crosslinking efficiency. The isocyanate groups react with hydroxyl groups in the polymer to form urea linkages, creating a crosslinked network that improves tensile strength while being environmentally benign.
2Ease of operation
If the curable aqueous composition is present in a substantially thermoplastic or substantially uncrosslinked state, then flow, penetration and film formation occur easily, but tensile strength and crack resistance are insufficient
Solution Approach 1:
The patent applies preliminary action by incorporating the crosslinking agent into the aqueous composition before application to the substrate. This allows the composition to remain in a flowable, uncrosslinked state during application and penetration phases, then undergo crosslinking after reaching the final location. The crosslinking can occur during drying or through subsequent heating, transforming the material from a soft, penetrable state to a strong, resistant state.
Solution Approach 2:
The patent employs dynamics by creating a time-dependent transformation of the material properties. The composition starts as a thermoplastic, flowable state that enables easy application and penetration, then transitions dynamically to a crosslinked, high-strength state after application. This dynamic property change allows the material to satisfy both requirements: ease of operation during application and high strength in the final state.
3Strength
If crosslinking is effected once the curable aqueous composition has reached its final location, then tensile strength is improved, but the composition must remain stable during transport and application
Solution Approach 1:
The patent uses an intermediary approach by selecting isocyanate-based crosslinking agents that remain stable in the aqueous composition during storage and application but become active under specific conditions. The isocyanate groups can be stabilized at lower temperatures and only become reactive when heated or when moisture is present after application. This intermediary stability allows the composition to be transported and applied without premature crosslinking, then crosslinks effectively when needed.
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 composition achieves improved tensile strength in dry, wet, and IPA conditions, providing enhanced resiliency and crack resistance while being environmentally friendly by avoiding formaldehyde release.
Implementation Method 1
the curable aqueous composition has reached its final location, or concurrently with the drying process. Many of the conventional crosslinking agents
Implementation Method 2
heating the curable aqueous composition at a temperature of from 80°C to 250°C
Data Source
AI summary
The present invention provides a curable aqueous composition comprising a (co)polymer and an epoxy crosslinker. The (co)polymer comprises, as (co)polymerized units, from 0.05％ to 10％ by dry weight, based on total monomers of the (co)polymer, ethylenically unsaturated acidic monomers having at least two carboxylic acid groups, and the epoxy crosslinker is an aliphatic compound having at least two reactive oxirane groups. It further provides a method for forming a treated substrate and a substrate formed by the method.