A Case Study of Textile Chemical Solutions

Customer Case: Color Spots Appeared After Fluorescent Red G Dyeing

Recently, we assisted a dyeing mill in solving a quality issue encountered during fluorescent color production.

The customer was using Fluorescent Red G for dyeing. After the conventional reduction cleaning (RC) process, some areas of the fabric surface showed dark spots, dull appearance, and uneven color shade.

The problem became more obvious under the following conditions:

• Fluorescent Red G dosage around 1% or above;

• Conventional reduction cleaning process using sodium hydrosulfite and soda ash;

• Color change became more visible after high-temperature heat setting.

The customer was looking for a solution that could effectively remove floating color while maintaining the brightness and stability of the fluorescent shade.

Root Cause Analysis: The Issue Was Related to After-Treatment, Not Dye Damage

Based on the analysis of the dyeing recipe, after-treatment process, and fabric performance, we found that:

The problem was not caused by the destruction of the Fluorescent Red G dye structure.

If the fluorescent dye was damaged by excessive reduction, the typical results would be:

• Overall color fading;

• Reduced fluorescence intensity;

• General shade change.

However, the customer’s problem appeared as localized color spots, indicating that the main cause was related to:

Surface contamination caused by residues generated during the reduction cleaning process.

During high-temperature alkaline RC treatment:

• Sodium hydrosulfite decomposes rapidly and creates a strong reducing environment;

• Excessive reduction not only removes unfixed dye but may also affect residual substances on the fabric surface;

• Residual dispersants, oligomers, oils, and other impurities may form hydrophobic agglomerates;

• These substances can remain unevenly on the fabric surface and create dark spots after drying and heat setting.

Therefore, the key solution was not simply changing the dye, but:

Optimizing the after-treatment process to reduce surface contamination risks.

Comprehensive Solution: Optimizing RC Process + Mild Oxidative Cleaning

Based on the customer’s production conditions, we provided a combined solution by considering both dye performance and after-treatment requirements.

Solution 1: Reduce Sodium Hydrosulfite Dosage to Avoid Excessive Reduction

For high-brightness fluorescent dyes such as Fluorescent Red G, overly strong reduction conditions may increase the risk of staining.

Recommended adjustment:

Sodium hydrosulfite: 1–1.5 g/L

Benefits:

• Maintain sufficient floating color removal;

• Reduce formation of reduction by-products;

• Improve shade stability.

Solution 2: Proper Neutralization After RC Process

After reduction cleaning, the fabric should not directly proceed to further treatment.

The first step is acid neutralization:

Adjust pH to around 6–7

This helps to:

• Remove residual alkalinity;

• Reduce the influence of remaining reducing agents;

• Improve the efficiency of subsequent cleaning.

Solution 3: Low-Concentration Hydrogen Peroxide Cleaning

After neutralization, a mild oxidation cleaning step can be introduced:

Hydrogen peroxide: 0.5 g/L
Cold water treatment: 20 minutes

At this stage, hydrogen peroxide is not used as a bleaching agent, but as a:

mild surface-cleaning oxidant.

Its main functions are:

• Oxidizing residual reducing substances;

• Removing trace contaminants;

• Improving fabric surface cleanliness.

Because the process uses:

• Low concentration;

• Low temperature;

• Neutral conditions;

it will not affect the color development of Fluorescent Red G while helping to reduce staining problems.

Application Results

After process optimization, the customer achieved significant improvement:

✓ Fluorescent Red G staining issues were successfully reduced;
✓ Fabric shade became more uniform;
✓ Color stability after heat setting was improved;
✓ Fluorescent brightness was well maintained.

Conclusion: From Product Supply to Textile Chemical Solutions

In actual dyeing production, color problems are often caused by multiple factors rather than a single component.

Especially for fluorescent, high-brightness, and special-effect dyes, stable results require proper control of:

• Dye performance;

• After-treatment process;

• Auxiliary system;

• Production conditions.

As a textile chemical solution provider, we not only supply high-performance dyes and textile auxiliaries but also provide technical support based on practical dyeing experience.

Through our comprehensive product portfolio and application expertise, we help customers improve dyeing consistency, solve production challenges, and achieve more reliable textile performance.