Analysis of Causes for Dye Transfer in Polyester Coated Fabrics

1 Introduction
With the development of the textile industry, various coated fabrics have emerged, with varying quality. Coated fabric is a fabric treated by a special process. Using solvents or water to dissolve films into a viscous state, then uniformly coating the fabric by some method (rotary screen, scraper, or roller), followed by fixation at a certain temperature in an oven, forming a uniform layer of coating on the fabric surface to achieve waterproof, windproof, and breathable functions. In actual production, garments composed of multiple colored parts sometimes experience dye transfer from one area to another during storage, usually from darker to lighter colors. This phenomenon differs from sublimation because it occurs at temperatures below the dye's sublimation temperature and with non-sublimable dyes. When garments are folded with different colors in close contact, dye transfer occurs. Usually, dye transfer increases under humid conditions, so the problem worsens in hot and humid weather or when clothes are stored immediately after steaming. Storing in plastic bags can maintain the initial relative humidity of the garment environment; whether this aggravates or alleviates dye transfer depends on the conditions when the garment is bagged. These phenomena are especially evident in polyester coated fabrics. To address this issue, testing and analysis can be conducted using AATCC 163-2007 "Colorfastness: Transfer of Dye in Storage Fabric to Fabric" method.

2 Difference Between Dye Transfer and Dry Heat Colorfastness

Dye transfer refers to the phenomenon where garments with more than one color sometimes experience dye moving from one area to another during storage, usually from darker to lighter colors. This differs from sublimation in that dye transfer occurs at temperatures below the dye's sublimation temperature and with dyes that cannot sublimate. Dye transfer is related to the molecular structure of the dye itself and has no absolute relation to the dye's sublimation fastness because the mechanisms differ. Conversely, dyes with good dry heat fastness may not have good dye transfer resistance.

3 Causes of Dye Transfer

3.1 Dyeing Causes

Polyester is generally dyed with disperse dyes under high temperature and high pressure, with leveling agents and other auxiliaries added during dyeing. Due to the effect of auxiliaries, disperse dyes can exhibit migration, which may also occur during long-term storage of dyed goods. The widespread use of auxiliaries (non-ionic surfactants) during dyeing is the main cause of disperse dye migration. Since both polyester fibers and disperse dyes are non-ionic, the abundant non-ionic surfactants act as a second solvent for disperse dyes, causing partial or complete dissolution of disperse dyes, preventing them from aggregating into complexes, instead solubilizing them within micelle cores. Due to the lack of polarity, they freely move within polyester fiber capillaries, accelerating dye migration from fiber interior to surface, causing fastness reduction. To address this, disperse dyes resistant to dye transfer have been gradually developed, and hydrophilic amino silicone softeners have been introduced. Using such amino silicone softeners, which do not contain non-ionic surfactants, can solve dye migration issues. Therefore, using heat migration-resistant disperse dyes and non-ionic surfactant-free formulations can better solve heat migration of disperse dyes in polyester dyeing.

3.2 Finishing Causes

3.2.1 Setting Process Factors: During setting, dyes do not sublimate to the fabric surface at high temperature; dye migration caused by environmental changes during later processing leads to reduced colorfastness.

3.2.2 Reductive Washing Factors: If the fabric is not washed after setting, reductive washing aims to remove surface loose dyes to improve rubbing fastness, washing fastness, sublimation fastness, and dye transfer fastness.

3.2.3 Coating Process Factors:

3.2.3.1 Calendaring: To save glue or make the fabric surface smooth after coating, calendaring is done before coating, usually at 150–180°C. After calendaring, dyes may sublimate, causing surface loose dyes.

3.2.3.2 Additives: To improve coating adhesion, certain additives are added to the glue, usually non-ionic, which can dissolve disperse dyes to some extent.

3.2.3.3 Color Paste: Due to glue and color paste quality issues, colorfastness decreases after coating and calendaring.

3.2.3.4 Glue Material: Coating fabric glue materials mainly include PVC glue, PU glue, and semi-PU glue. Color migration mainly occurs in PVC products. For PVC coated fabrics, PVC particles disperse in plasticizers; upon heating, resin absorbs plasticizers, crosslinks, and cures, forming a PVC film firmly bonded to fiber molecules on the fabric surface. When plasticizer and pigment content increases, molecular spacing enlarges, structure loosens, and poor pigment dispersion easily causes migration in the sol. Therefore, during coated fabric production, it is important to minimize plasticizer and pigment addition and improve dispersion.

3.2.3.4 Other Causes: If the fabric is not fully dried after coating and is directly packaged, residual solvents (toluene, methyl ethyl ketone, or water) on the fabric surface may affect colorfastness.

3.3 Garment Processing and Storage Causes

3.3.1 In fabric storage, the warehouse environment is too hot or humid.

3.3.2 During garment making, residual moisture remains on clothes after steam ironing; stacking semi-finished products together in a hot and stuffy workshop causes dye transfer.

3.3.3 Finished products are ironed and packaged before moisture is completely dried, which is also a factor causing dye transfer. Therefore, packaging should be done after drying, preferably with a small packet of desiccant added inside the packaging bag.

4 Test Methods and Conditions

Color Fastness: Dye Transfer During Storage Fabric to Fabric AATCC 163-2007, Method I, Temperature (24℃±3℃) or (50℃±3℃), Duration 48 hours, 50ml distilled water.

4.1 Scope: Color migration between different colored textiles during storage.

4.2 Principle: The treated sample is sandwiched between pre-moistened multifiber adjacent fabric and another selected fabric, placed in a perspiration stain rack at room temperature for 48 hours, then dried and rated.

4.3 Instruments and Materials: AATCC Perspiration Stain Color Fastness Tester, polyethylene zipper bags that can hold the perspiration stain rack, multifiber adjacent fabric NO.10, white fabric matching the sample components, distilled or deionized water, 50ml beaker.

4.4 Sample Preparation: 57mm × 57mm dyed fabric samples; 57mm × 57mm multifiber adjacent fabric; 57mm × 57mm white fabric samples.

4.5 Operating Procedure:

4.5.1 First, soak the multifiber adjacent fabric and selected white fabric in distilled or deionized water at 24℃±3℃. Control the fabric liquid absorption rate within 100% to 110% (generally no dripping when hanging). Do not pre-moisten the samples before the test. Then sandwich the sample between the pre-moistened multifiber adjacent fabric and selected white fabric to form a composite sample. Clamp the composite sample with the perspiration stain color fastness tester clamp, applying about 12.5kPa pressure. Place the clamp and a dish containing 50ml distilled water into a polyethylene plastic bag, seal it, and keep at room temperature 24℃±3℃ for 48 hours. Then remove the sample and adjacent fabric and dry at room temperature.

First Group of Tests:

Sample #1: A piece of black polyester fabric (with non-ionic surfactant)

Sample #2: A piece of black polyester fabric (with hydrophilic amino silicone oil)

Sample #3: A piece of black polyester fabric (PVC coating)

Sample #4: A piece of black polyester fabric (PU coating)

Second Group of Tests:

Sample #1: A piece of red polyester fabric (with non-ionic surfactant)

Sample #2: A piece of red polyester fabric (with hydrophilic amino silicone oil)

Sample #3: A piece of red polyester fabric (PVC coating)

Sample #4: A piece of red polyester fabric (PU coating)

Third Group of Tests:

Sample #1: A piece of blue polyester fabric (with non-ionic surfactant)

Sample #2: A piece of blue polyester fabric (with hydrophilic amino silicone oil)

Sample #3: A piece of blue polyester fabric (PVC coating)

Sample #4: A piece of blue polyester fabric (PU coating)
 

4.5.2 First, soak the multifiber adjacent fabric and selected white fabric in distilled or deionized water at 24℃±3℃. Control the fabric liquid absorption rate within 100% to 110% (generally no dripping when hanging). Do not pre-moisten the samples before the test. Then sandwich the sample between the pre-moistened multifiber adjacent fabric and selected white fabric to form a composite sample. Clamp the composite sample with the perspiration stain color fastness tester clamp, applying about 12.5kPa pressure. Place the clamp and a dish containing 50ml distilled water into a polyethylene plastic bag, seal it, and keep at 50℃±3℃ for 48 hours. Then remove the sample and adjacent fabric and dry at room temperature.

Fourth Group of Tests:

Sample #1: A piece of black polyester fabric (PVC coating)

Sample #2: A piece of black polyester fabric (PU coating)

Sample #3: A piece of red polyester fabric (PVC coating)

Sample #4: A piece of red polyester fabric (PU coating)

Sample #5: A piece of blue polyester fabric (PVC coating)

Sample #6: A piece of blue polyester fabric (PU coating)

4.2 Results and Analysis

Tables 1 to 4 show the test results of samples of different colors under different processing auxiliaries, coating materials, and storage environments. Based on the test results, it can be preliminarily judged that the dye transfer is influenced by the fabric composition's dyeing process, post-finishing processing, garment processing, and storage environment.

5 Conclusion
The phenomenon of color migration in textiles is caused by dye migration within the textiles. Color fastness of textiles refers to the ability of colored products to resist color change under various external influences. Color migration is not only related to the color fastness of the textiles themselves but also closely related to the material of the migrated item, relevant production processes, and environmental factors. From the results, color migration falls within the scope of textile color fastness, but compared to color fastness, color migration is a more complex process involving many factors. Therefore, the evaluation of the degree of textile color migration should be treated differently according to actual conditions, selecting appropriate methods for testing and evaluation. The test report should comprehensively describe relevant test information as much as possible. It should be ensured that the product packaging is not damaged during storage and transportation, the product is not contaminated or damp, avoid direct sunlight, prevent rain exposure, maintain cleanliness, prohibit contact with acids, alkalis, oils, and organic solvents that affect coating quality, and store in a dry and ventilated environment.

References:
[1] Cheng Lijun, Dai Jinlan. Color Migration of Textiles and Related Testing Methods [D]. Textile Guide, 2006(08)
[2] Wang Yiman. Research on Testing Methods for Dye Migration Performance on Fabrics [D]. Testing and Standards, 2009(10): 63-66
[3] AATCC163-2007 Color Fastness: Dye Transfer Between Fabrics During Storage [S]