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Cong Red (commonly referred to as Congo Red or Direct Red 28) is an anionic secondary diazo dye historically valued for its brilliant red hue and direct affinity for cellulosic fibers. Chemically designated as disodium 4-amino-3-[[4'-[[4-amino-3-(4-sulfonatonaphthalen-1-yl)diazenyl]phenyl]phenyl]diazenyl]naphthalene-1-sulfonate (CAS Number: 573-58-0), it represents a foundational chemistry in the colorant industry. Its molecular structure consists of a benzidine backbone coupled with two naphthalene sulfonic acid residues, which attributes a high degree of conjugation and a strong substantive binding capability via hydrogen bonds and van der Waals forces directly onto cellulose polymer chains.
As a leading OEM Cong Red Supplier & Factory, Tianjin Sunrise Chem Group utilizes advanced purification methodologies to ensure the dye meets strict purity standards for various vertical domains. Because Cong Red is highly sensitive to pH variations—transitioning from a deep blue/purple at pH 3.0 to a bright red at pH 5.2—its manufacturing process demands precise control over acidity, moisture levels, and inorganic salt contents to prevent premature shade shifts during formulation.
| Technical Parameter | Industrial Grade Range | Analytical / Diagnostics Grade | Testing Standard Method |
|---|---|---|---|
| Active Colorant Content (Purity) | ≥ 85.0% - 92.0% | ≥ 98.5% | UV-Vis Spectrophotometry |
| Water Insolubles | ≤ 0.5% | ≤ 0.05% | Gravimetric Method |
| Moisture Content | ≤ 5.0% | ≤ 1.5% | Karl Fischer Titration |
| pH Sensitivity Transition | 3.0 (Blue) - 5.2 (Red) | 3.0 (Blue) - 5.0 (Red) | Potentiometric Assessment |
| Heavy Metal Impurities (Pb, Cd, Hg, As) | ≤ 50 ppm total | ≤ 10 ppm total | ICP-OES Analysis |
Deploying advanced chemical processes to transition Congo Red production into a sustainable, high-precision industrial science.
Replacing high-energy batch processes with automated, continuous-flow microreactor systems. This stabilizes transient diazonium salts, reduces reaction byproducts by 85%, and guarantees an extremely consistent dye matrix from batch to batch.
By implementing membrane filtration technologies (reverse osmosis and nanofiltration) directly into our manufacturing lines, we recover and recycle up to 95% of reaction water, dramatically lowering the environmental footprint of heavy chemical processing.
Our long-term R&D focuses on using non-petrochemical, bio-based chemical intermediates to yield high-affinity direct colorants, ensuring compliance with evolving global regulations such as REACH and TSCA.
Modern colorant sourcing goes beyond simple unit costs; it is deeply rooted in supply chain stability. Our China-based chemical manufacturing facility operates on Factory 4.0 principles. We utilize integrated DCS (Distributed Control Systems) to monitor temperature, pH, pressure, and flow rates in real-time, preventing the thermal anomalies that lead to shade deviations or high salt concentrations.
Our raw materials are sourced directly through long-term partnerships with leading chemical producers, shielding our clients from market price shocks. Through optimized inventory management, automated packaging lines, and dedicated container loading systems, we maintain a consistent domestic inventory of dry powders and pre-dissolved liquid complexes. This guarantees short lead times and reliable shipping dates, even during peak global demand periods.
Tailoring Cong Red formulations to meet the specific requirements of target industries worldwide.
Optimized for cotton, viscose, and silk fibers. We control ionic strength to maximize fiber absorption, leading to deeper shades and improved wash and light fastness properties.
Delivers high affinity for bleached kraft pulp. This increases fiber retention, minimizes color runoff in wastewater, and results in a highly uniform color distribution across paper sheets.
Highly purified dye formulations with low mineral contents, specifically manufactured for histology applications. Ideal for identifying amyloid fibrillar aggregates in tissue samples.
Ensuring smooth global logistics through strict adherence to environmental regulations and compliance with chemical safety laws.
Global environmental guidelines call for the responsible elimination of hazardous substances across chemical supply chains. Our production facility is certified to ZDHC Level 3 and GOTS (Global Organic Textile Standard), certifying that our dyes and processes meet rigorous ecological requirements.
We supply safety documentation including complete SDS (Safety Data Sheets) and COA (Certificate of Analysis) reports with every batch. By working closely with local distribution hubs in North America, Europe, and Asia, we help partners comply with regional frameworks such as REACH (EU) and TSCA (US), simplifying customs clearances and supply chain management.
Decades of industrial dye synthesis experience, serving global textiles, papermaking, and scientific research.
Tianjin Sunrise Chem Group specializes in manufacturing high-quality dyestuffs. Our extensive product portfolio includes Direct dyes, Acid dyes, Basic dyes, Sulphur dyes, Solvent dyes, Liquid dyes, and Fluorescent dyes. Backed by decades of industry and export experience, we have built a reputation for reliability and excellence, serving clients from diverse sectors including denim, textile, leather, paper, and plastic.
We always maintain a strong focus on product quality and stability. Every single shipment undergoes rigorous laboratory testing before leaving the port. Our ZDHC Level 3 and GOTS certifications offer guaranteed compliance for your quality management systems.
We pride ourselves on offering customized OEM/ODM formulations. Our team of technical specialists works closely with clients to understand their unique needs and deliver tailored products. We actively seek strategic partnerships to expand our distribution reach and enhance our service offerings. Collaborate with us to explore mutual growth opportunities.
Environmental protection is the cornerstone of our innovation. We are dedicated to providing clients with eco-friendly, high-performance colorants that balance productivity with environmental harmony, driving the industry towards a more sustainable development path for a greener textile industry and a sustainable future.
Ensuring safe handling, secure packaging, and reliable global delivery for every shipment.
Addressing key technical, safety, and logistical questions for procurement managers and chemists.
Direct Red 28, commonly known as Congo Red, has the CAS Registry Number 573-58-0. It is a secondary diazo dye containing a biphenyl backbone coupled with naphthalene sulfonic acids. In aqueous solution, it forms a colloidal suspension and exhibits pH indicator properties, shifting from blue-purple at pH 3.0 to red at pH 5.2.
Our automated Factory 4.0 production line relies on continuous DCS monitoring to control reaction factors (temperature, pH, concentration). Each production batch undergoes UV-Vis spectrophotometry and HPLC verification, ensuring our batch-to-batch delta-E variation remains below 0.5.
Yes, our direct dyes are GOTS and ZDHC Level 3 certified. This verifies that our manufacturing processes limit the use of hazardous substances and align with the zero-discharge ecological requirements of the global textile and apparel sectors.
We provide standard packaging in 25kg fiber drums, multi-layer paper sacks, and large bulk bags. Through our OEM service, we can adjust active dye concentrations, optimize salt content, customize liquid dye viscosity, and print buyer-specific labeling for direct integration into commercial processes.
With our plant located close to major northern China shipping ports, standard products can typically be loaded and shipped within 10 to 15 days of order confirmation. Custom OEM formulations or specialized packaging requests generally require 20 to 30 days to process and manufacture.
Browse our supplementary range of acid, basic, direct, and inorganic colorants for diverse industrial applications.
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