Aqueous Ink Microspheres with Internal Dye for Rubfastness
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Solution Overview
Problem
Existing aqueous ink compositions for writing instruments face challenges in achieving desired hiding power, water resistance, and rubfastness, particularly when using dyes, and initial writability and writing feel when used on paper.
Innovation Solution
An aqueous ink composition containing microspheres with a polymer matrix and a water-insoluble dye, where the dye is densely present within the matrix rather than on its surface, with specific circularity and compressive strength properties, and optionally using multiple types of microspheres with different dyes to achieve desired color and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If water-soluble dye is used for coloring, then the ink is easy to apply and flow smoothly, but the characters and drawn lines become smeared or removed by perspiration or water
Solution Approach 1:
The patent embeds water-insoluble dye molecules within the interior of hydrophobic resin microspheres. The microspheres serve as protective containers that hold the dye inside, preventing direct contact with water while allowing the dye to function. This nested structure resolves the contradiction by protecting the water-sensitive dye from water exposure while maintaining its coloring function.
Solution Approach 2:
The patent creates a composite structure combining hydrophobic resin microspheres with water-insoluble dye. This composite material integrates the water-resistant properties of the resin matrix with the coloring function of the dye, achieving both ease of application and water resistance simultaneously.
2Reliability
If pigment is used instead of dye, then water resistance and light resistance are improved, but different dispersion treatment is required for each pigment due to differences in material, size or specific gravity
Solution Approach 1:
The patent controls the particle size of the microspheres to be 1 μm to 10 μm and adjusts the resin composition and crosslinking degree to achieve uniform dispersion properties. By standardizing these parameters across different dye types, the patent eliminates the need for separate dispersion treatments for each pigment, reducing complexity while maintaining water and light resistance.
3Reliability
If colored resin particles are used, then water resistance is improved, but the desired hiding power cannot be realized and water-soluble dye may seep into water
Solution Approach 1:
The patent concentrates the water-insoluble dye specifically within the interior region of the hydrophobic resin microspheres, creating a local high-concentration dye zone. This localized dye distribution maximizes the hiding power (color force) in the critical interior region while the outer resin shell maintains water resistance. The circularity coefficient of 0.6 to 1.0 ensures proper spherical geometry for optimal performance.
Solution Approach 2:
The patent specifies that the microspheres should have a circularity coefficient of 0.6 to 1.0, indicating nearly perfect spherical shapes. This sphericity optimizes the surface-area-to-volume ratio, ensuring uniform dye distribution throughout the interior while maintaining compact size for effective hiding power and proper ink flow characteristics.
4Stability of the object's composition
If the microsphere 10% strength is too high, then the ink flow is stable, but the initial writability and writing feel on paper are impaired
Solution Approach 1:
The patent optimizes the crosslinking degree of the hydrophobic resin to achieve a balanced 10% strength value between 5 MPa and 30 MPa. This parameter optimization allows the microspheres to maintain structural integrity for stable ink flow while being sufficiently soft to deform properly on paper contact, ensuring good initial writability and writing feel. The circularity coefficient of 0.6 to 1.0 also contributes to this balanced mechanical behavior.
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 ink composition achieves desired color force, initial writability, and superior rubfastness when written on paper, with balanced initial writability and rubfastness, and stable ink flow due to optimized microsphere properties.
Implementation Method 1
the water-insoluble dye is more densely present within the matrix than on the surface of the matrix
Data Source
Figure 1
AI summary
Provided is aqueous ink composition for a writing instrument, which contains water and microspheres having a water-insoluble dye and a matrix constituted from a polymer wherein the water-insoluble dye is higher densely present in the inner part of the matrix than at the surface of the matrix, and at least one of the following (a) and (b) is satisfied: (a) the circularity coefficient of the microspheres, as measured by image analysis, is 0.6-1.0, and (b) the 10% strength of the microspheres, as determined in a micro-compression test, is 5-30 MPa.