Dissymmetric Azomethine Direct Dyes for Keratin Fibre Fastness
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Solution Overview
Problem
Conventional direct dyes for keratin fibers, such as hair, result in temporary or semi-permanent colorations due to weak binding interactions, lack stability against light and washing, and require multiple dyes to achieve desired shades, leading to unsatisfactory color persistence and fading.
Innovation Solution
Development of azomethine direct dyes of specific formulas and their leuco forms, which can be used alone to achieve intense, stable colorations resistant to light, washing, and perspiration, and are compatible with chemical oxidizing agents for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional direct dyes are used for keratin fibres, then the dyeing process is simple, but the colour fastness and stability are poor
Solution Approach 1:
The patent uses composite dye molecules containing both direct dye moieties (for affinity binding to keratin fibres) and reactive dye moieties (for covalent bonding). This composite structure enables the dye to exhibit properties of both direct and reactive dyes, achieving superior colour fastness while maintaining ease of application.
Solution Approach 2:
The invention changes the chemical structure parameters of the dye molecules by introducing reactive groups (such as vinyl sulfone, halogen, or epoxide groups) alongside direct dye chromophores. This structural modification allows the dye to form stable covalent bonds with keratin fibres, dramatically improving colour persistence without complicating the overall dyeing process.
2Stability of the object's composition
If conventional direct dyes are used, then the application is easy, but the stability towards light and washing is insufficient
Solution Approach 1:
The patent employs composite dye molecules that integrate direct dye structures (providing ease of application and fibre affinity) with reactive dye structures (providing light and wash stability through covalent bonding). This dual-function composite design achieves both stability and operational simplicity.
Solution Approach 2:
The reactive groups in the composite dye molecules act as intermediaries that form covalent bridges between the dye and keratin fibres. This intermediary bonding mechanism provides enhanced stability towards light and washing while maintaining the simplicity of the dyeing application process.
3Adaptability or versatility
If multiple dyes are combined to achieve desired shades, then colour variety is improved, but colour persistence and fastness deteriorate
Solution Approach 1:
The patent uses single composite dye molecules that contain multiple chromophoric units or auxochromes within one molecular structure. This intramolecular diversity provides colour variety while ensuring that all colour components are bonded to the fibre through the same reactive group, maintaining colour persistence and preventing the fading issues associated with multiple separate dyes.
Solution Approach 2:
The invention merges multiple colour-generating functional groups and chromophores into a single composite dye molecule. This consolidation ensures that all colour components behave uniformly during dyeing and bonding, achieving both colour variety and persistent fastness without the problems of differential fading that occur with multiple separate dyes.
4Strength
If conventional direct dyes are used, then the dyeing process is straightforward, but the binding strength to keratin fibres is weak
Solution Approach 1:
The patent employs composite dye molecules that combine direct dye chromophores (for initial fibre affinity) with reactive groups (for strong covalent bonding). This composite structure provides both straightforward application and strong binding strength, as the direct dye portion facilitates initial adsorption while the reactive portion forms durable covalent bonds with keratin fibres.
Solution Approach 2:
The direct dye portion of the composite molecule performs preliminary action by providing initial affinity and adsorption to the keratin fibre surface. This preliminary binding positions the reactive groups optimally for subsequent covalent bond formation, achieving strong overall binding without excessive molecular complexity.
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 azomethine direct dyes provide persistent, chromatic colorations on keratin fibers, specifically achieving natural shades like brown and black without the need for multiple dyes, while maintaining stability and compatibility with lightening processes.
Implementation Method 1
The process conventionally used in direct dyeing consists in applying to keratin fibres one or more direct dyes, or colouring molecules, which have affinity for said fibres
Implementation Method 2
compatible with chemical oxidizing agents for enhanced performance
Data Source
AI summary
The present invention relates to dissymmetric azomethine direct dyes of formula (I) and the leuco forms thereof of formula (II), and also to the use thereof for dyeing keratin fibres, in particular human keratin fibres such as the hair:in which formula (I) or (II) R1, R2, R3, R4, R5, R6, n and n′ are as defined in the description.The compounds of formula (I) or (II) according to the invention can give powerful, chromatic and sparingly selective colourings with good colour build-up, which are resistant to the various attacking factors to which keratin fibres may be subjected, such as inclement weather, light, washing and perspiration.