Reactive Leather Dyeing for High Wetfastness at Deep Shades
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Solution Overview
Problem
Existing processes for dyeing leather with reactive dyes fail to achieve high wet- and perspirationfastness, especially at medium to high depths of shade, due to inadequate fixation yields and leather damage from alkaline conditions.
Innovation Solution
Using anionic polyazo dyes with at least three azo groups and an alkaline-activable group in an aqueous float at pH 8 or higher, allowing for rapid dyeing and fixation within 4 hours with a high fixation yield of 85% or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional acidic dyes are used to dye leather, then the dyeing process is simple, but high color intensities and high color stabilities (wet- and perspirationfastness) cannot be achieved
Solution Approach 1:
The patent changes the chemical parameters of the dyeing system by introducing reactive dyes with specific functional groups (vinyl sulfone, dichlorotriazine, isocyanate) that form covalent bonds with leather amino groups. The process optimizes pH (8.5-10.5), temperature (20-40°C), and time (30-120 min) parameters to achieve high fixation yields while maintaining process feasibility.
Solution Approach 2:
The invention uses composite dye molecules combining chromophore groups (azo, anthraquinone, triphenylmethane) with reactive functional groups. This composite structure enables both coloration and covalent bonding capabilities in a single dye molecule, achieving high fastness without complex multi-step processes.
2Reliability
If cationic complexing agents are used to improve wet- and perspirationfastness, then some fastness improvement is achieved, but the fastnesses remain inadequate for intensive shades and leather articles mark off in use
Solution Approach 1:
The patent replaces physical/ionic bonding mechanisms (complexing agents, ionic interactions) with chemical covalent bonding mechanisms. Reactive dye groups form permanent chemical bonds with leather amino groups, substituting the weaker ionic complexing mechanism with stronger covalent attachment, eliminating marking off and achieving excellent rubfastness.
3Reliability
If multiple process steps with separate float changes are used to achieve desired fastnesses, then color stability is improved, but the process becomes complex, longwinded, and costly with more wastewater
Solution Approach 1:
The patent combines multiple functions (dyeing, fixation, and fastness development) into a single integrated reactive dyeing process. The reactive dye simultaneously provides coloration and forms covalent bonds during one float treatment, eliminating the need for separate complexing agent treatments and multiple float changes, thereby reducing process complexity and wastewater.
4Reliability
If existing reactive dyes with dichlorotriazine groups are used, then some fixation is achieved, but fixation yields are only moderate (70-75%) and the technique is limited to chrome-tanned leather
Solution Approach 1:
The patent develops reactive dyes with multiple reactive group types (vinyl sulfone, dichlorotriazine, isocyanate) that can bond with amino groups present in various leather types including chrome-tanned, vegetable-tanned, and synthetic polymer-tanned leathers. This universal reactivity mechanism expands applicability beyond chrome-tanned leather while achieving high fixation yields (85-95%).
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 process achieves excellent rubfastness, washfastness, and migrationfastness even at high depths of shade, with minimal leather damage and no staining of contact materials, demonstrating improved color intensity and stability.
Implementation Method 1
Reactive dyeing refers to the use of dyes which have functional groups capable of forming a covalent chemical bond with the functional groups of leather
Implementation Method 2
using anionic polyazo dyes with at least three azo groups and an alkaline-activable group in an aqueous float at pH 8 or higher, allowing for rapid dyeing and fixation within 4 hours
Data Source
AI summary
The present invention relates to a process for dyeing leather with at least one dye F which has at least one alkaline-activable group of the formula A;where- - - - denotes the bond to the rest of the dye molecule;X is halogen, C1-C4-alkyl or C1-C4-alkoxy,k is 0, 1, 2 or 3,n is 0 or 1 andB is a CH═CH2 group or a CH2—CH2-Q group, where Q is an alkaline-detachable group,which comprises treating the leather with an aqueous float comprising at least one dye F at a pH of not less than 8, generally in the region of 8 to 11.