Melamine-Formaldehyde Microcapsules with Calcium Hydroxide
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Solution Overview
Problem
Existing microcapsule dispersions based on melamine-formaldehyde resins contain residual formaldehyde, which is undesirable for environmental and occupational health reasons, and current methods to reduce formaldehyde content, such as using formaldehyde scavengers, often compromise the stability and viscosity of the dispersions.
Innovation Solution
Incorporating calcium salts, particularly calcium hydroxide, during and after the curing process of microcapsule formation, to reduce formaldehyde emissions and achieve low-viscosity, high-solids-content dispersions suitable for printing inks and paper coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If formaldehyde scavengers (ammonia, urea, ethylene urea, or melamine) are added to microcapsule dispersions to reduce formaldehyde content, then the formaldehyde content is reduced, but the stability and viscosity of the dispersion are adversely affected
Solution Approach 1:
The patent introduces a specific intermediary substance (polymer containing carboxyl groups with specific molecular weight and carboxyl content) that acts as a mediator between the formaldehyde-scavenging function and the dispersion stability. This intermediary binds formaldehyde while maintaining colloidal stability, unlike conventional scavengers that directly compromise the dispersion system.
Solution Approach 2:
The invention changes the chemical parameters of the dispersion system by introducing a polymer with specific functional groups (carboxyl groups) and specific physical parameters (molecular weight 10,000-1,000,000, carboxyl content 0.1-10 mmol/g). These parameter changes enable formaldehyde binding while maintaining the colloidal properties of the dispersion.
2Object-generated harmful factors
If conventional formaldehyde scavengers are added to reduce formaldehyde emissions, then environmental and occupational health requirements are improved, but the processing properties (viscosity) of the microcapsule dispersion deteriorate
Solution Approach 1:
The polymer with carboxyl groups serves as an intermediary that reduces formaldehyde emissions through chemical binding while simultaneously acting as a protective colloid that maintains or improves the flow properties of the dispersion, unlike conventional scavengers that increase viscosity and impair processing.
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 use of calcium salts effectively lowers the formaldehyde content in coated papers and maintains the stability and viscosity of microcapsule dispersions, achieving a balance between low formaldehyde levels and favorable processing properties.
Implementation Method 1
The use of calcium salts effectively lowers the formaldehyde content in coated papers
Data Source
AI summary
The calcium salt is calcium hydroxide of 0.5-15 wt.% in melamine-formaldehyde-resin. The microcapsules are made from condensation of methylated melamine-formaldehyde-resins with molar ratio of melamine:formaldehyde:methanol is 1:3.0:2.0-1:6.0:4.0 in water. The water insoluble capsule core plastic material is dispersed in presence of protective colloids at pH 3-6.5. The microcapsules are formed at 20-50[deg] C and hardening of capsule wall at 50-100[deg] C. One calcium salt is added after hardening of capsule wall.