Curable Acrylic Adhesive Precursor Storage Stability
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Solution Overview
Problem
Curable acrylic compositions face challenges with storage stability due to self-polymerization issues, particularly in highly filled formulations with limited oxygen diffusion, and the presence of acidic monomers like acrylic acid, which can lead to core polymerization and reduced shelf life.
Innovation Solution
A curable precursor comprising C1-C32 (meth)acrylic acid ester monomers, an ethylenically unsaturated acidic compound without phosphoric acid-derived groups, a crosslinker with acid-functional groups from phosphoric acid, and a nitroxide inhibitor, which prevents core polymerization even in acidic environments, allowing for stable storage and fast curing at room temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If inhibitors are used to prevent self-polymerization during storage, then storage stability is improved, but core polymerization still occurs in highly filled compositions with limited oxygen diffusion
Solution Approach 1:
The patent introduces a base as an intermediary substance that reacts with acidic compounds to neutralize them. This base acts as a mediator between the nitroxide inhibitor and the acidic monomers, preventing the acid-catalyzed decomposition of the inhibitor and thereby maintaining its effectiveness in preventing core polymerization throughout the composition, including in regions with limited oxygen diffusion.
Solution Approach 2:
The patent changes the chemical environment parameter by adding a base to neutralize acidic compounds. This parameter change (pH adjustment) transforms the composition from acidic to neutral or basic, which stabilizes the nitroxide inhibitor and prevents its decomposition, thereby maintaining inhibition effectiveness even in highly filled systems with poor oxygen diffusion.
2Strength
If acids are added to enhance adhesive strength, then adhesion performance is improved, but storage stability deteriorates due to increased tendency for core polymerization
Solution Approach 1:
The base serves as an intermediary that separates the conflicting requirements: it allows acids to remain in the composition for adhesion enhancement while simultaneously neutralizing their destabilizing effect on the inhibitor system, thus maintaining storage stability despite the presence of acidic monomers.
Solution Approach 2:
The patent converts the harmful effect of acids (which destabilize the inhibitor and promote polymerization) into a beneficial outcome by adding a base that neutralizes the acid. This allows the acid to remain for its beneficial adhesion-enhancing effect while its harmful destabilizing effect is eliminated through neutralization.
3Quantity of substance
If large volumes of curable compositions are stored in drums, then storage capacity is improved, but oxygen diffusion becomes insufficient leading to core polymerization
Solution Approach 1:
The base acts as an intermediary that compensates for the insufficient oxygen diffusion in large storage drums. By neutralizing acidic compounds, it stabilizes the nitroxide inhibitor system, allowing the inhibitor to remain effective throughout the entire volume of the drum without requiring adequate oxygen diffusion to the core region.
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 a curable precursor with enhanced storage stability and low tendency for core polymerization, maintaining performance characteristics such as hardness, shear strength, and thermal conductivity, even in highly filled and acidic compositions, enabling storage in large volumes without significant oxygen diffusion.
Implementation Method 1
a nitroxide: wherein the C1-C32 (meth)acrylic acid ester monomers (a)(i) do not comprise functional groups other than the (meth)acrylic acid ester groups, and wherein the ethylenically unsaturated acidic compound (a)(ii) does not comprise an acid-functional group derived from phosphoric acid
Implementation Method 2
a crosslinker for the (meth)acrylate-based component, which comprises at least one acid-functional group derived from phosphoric acid and at least one radically (co)polymerizable reactive group
Implementation Method 3
a radically (co)polymerizable (meth)acrylate-based component comprising (i) C1-C32 (meth)acrylic acid ester monomers, and (ii) an ethylenically unsaturated acidic compound
Data Source
AI summary
The present disclosure relates to a curable precursor of an adhesive composition, the curable precursor comprising: (a) a radically (co) polymerizable (meth)acrylate-based component comprising (i) C1-C32 (meth)acrylic acid ester monomers; and (ii) an ethylenically unsaturated acidic compound; (b) a crosslinker for the (meth)acrylate-based component, which comprises at least one acid-functional group derived from phosphoric acid and at least one radically (co)polymerizable reactive group; and (c) a nitroxide wherein the C1-C32 (meth)acrylic acid ester monomers (a)(i) do not comprise functional groups other than the (meth)acrylic acid ester groups, and wherein the ethylenically unsaturated acidic compound (a)(ii) does not comprise an acid-functional group derived from phosphoric acid. The present disclosure further relates to a process for making a cured composition from said curable precursor and to the use of said curable precursor for adhesive applications and/or for thermal management applications in the automotive industry.