As is known to all, leather is a material prone to color migration. Color migration will not only affect the inherent color of leather, but also affect the color of the object in contact with it, leading to obvious product quality defects.In practice, the product quality problems and trade disputes caused by the color transfer of leather itself are quite common.

In essence, color transfer belongs to the category of color fastness (the ability to resist external action without changing color), but compared with the color fastness to friction, water stain, heat and light, color transfer is a more complex process.Many literatures have been published on the transfer of color in textiles, and the factors that may affect the transfer of color, such as the binding force of dye, solvent, auxiliary agent, solubility of pigment and resin, were discussed.However, there are few reports on the internal color migration of leather.In this paper, based on the content of ISO 15701, the color migration of automobile leather, furniture leather and shoe upper leather in China was tested, and the degree of color migration was compared and analyzed. At the same time, the color migration was compared with the results of wet rubbing fastness, and the correlation between the results of the two kinds of color fastness was analyzed.

Experiment

Instruments and materials

PVC film (white), the sample test rack is consistent with the test rack for color fastness to sweat stains, in which the weight of the hammer is 4.5kg and the bottom size is 11.5cm×6cm.Glass plate size 8cm×5cm, smooth surface.The oven is conventional and can control the temperature (50±2).Leather rubbing color fastness tester: UTS international co., LTD.

Leather rubbing color fastness tester leather rubbing color fastness test

The leather samples tested were divided into automobile leather, furniture leather and uppers leather by use, each with 10 pieces.All samples were placed in the standard air environment for more than 24 hours before the experiment.

The experimental method

1. Determination of leather color migration

Currently, ISO 15701 and ASTM D5552 are available for testing color migration in leather.Among them, ISO 15701 USES PVC film as sticky material, while ASTM D5552 USES white cotton cloth lining as sticky material, which requires distilled water soaking before use.In comparison, ISO 15701 is simpler to operate and is widely adopted by tanning enterprises.This experiment adopts this method standard.The operation process is as follows:

With die cut samples (20 mm x 30 mm), and then sent the samples to be tested in polyvinyl chloride (PVC) film stick on a chip (hereinafter referred to as PVC, 50 mm x 30 mm), placed the tested and face down, place the sample in the center between the two pieces of stripping plate position, place the board into the device and on a heavy weight of 4.5 kg, in keeping the pressure under the condition of rotating device, carefully moving weights to keep the sample during the test an average of 750 g/cm2 pressure, put the device into the oven, oven temperature should be within the scope of the (50 + 2), placed 16 h.Remove the sample from the unit and leave to cool at room temperature. Then separate the sample from the PVC sheet and evaluate the coloring of the PVC sheet with the gray sample card.

The grading results of sticky color are given according to the requirements of GB/T 251, which are divided into five grades. Among them, grade 5 indicates that there is no sticky color and no color migration, and grade 1 indicates that there is serious stained color and obvious color migration.

2. Determination of color fastness of leather to wet rubbing

The determination of leather's color fastness to wet rubbing was carried out according to the requirements of QB/T 2537. The operation was as follows: fix the white felt after deionized water soaking and water extrusion on the test head of the friction color fastness tester (500g), then fix the leather sample on the test table of the instrument, smooth surface up, and stretch 10% along the friction direction;Put down the test head with felt, start the instrument, stop after 250 times, remove the felt, and grade the sticky color of the felt according to GB/T 251.

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