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Leather color fastness test analysis of leather color fastness test
As we all know, leather is a substance prone to color migration. Color migration will not only affect the inherent color of leather, but also affect the color of objects in contact with it, resulting in obvious product quality defects. In practice, product quality problems and trade disputes caused by the color migration of leather are common. In essence, color migration belongs to the category of color fastness (the ability to resist external effects without discoloration), but compared with color fastness such as friction resistance, water stain resistance, heat resistance, and light resistance, color migration is a more complicated process. Leather rubbing color fastness tester is a test instrument for testing the performance of leather color fastness to rubbing. In addition, based on the content of the standard ISO 15701, the R&D engineers tested the current color migration of domestic automotive leather, furniture leather and shoe upper leather, and compared the degree of color migration with the results of wet rubbing fastness. The correlation of the two color fastness results was analyzed. 1. Experimental part Instruments and materials Polyvinyl chloride film (white), the sample test frame is the same as the perspiration color fastness test sample frame, in which the weight of the weight is 4.5kg, and the bottom size is 11.5cm×6cm. Glass plate size 8cm×5cm, the surface is flat. The oven is conventional and can control the temperature (50±2) °C. Leather rubbing color fastness tester: Shanghai Qianshi Precision Electromechanical Technology Co., Ltd. The tested leather samples are divided into automotive leather, furniture leather and shoe upper leather according to their uses, with 10 pieces for each type. All samples were placed in a standard air environment for more than 24h before the experiment. Experimental methods 1. Determination of leather color migration At present, the detection methods for color migration in leather are ISO 15701 and ASTM D5552. Among them, ISO 15701 uses polyvinyl chloride film as the sticky material, while ASTM D5552 uses white cotton lining as the sticky material, which needs to be soaked in distilled water before use. Comparatively speaking, ISO 15701 is simpler to operate and is also commonly used by tannery companies. This experimental operation adopts this method standard. The operation process is as follows: Use a die to cut the sample (20mm×30mm), and then stick the tested surface of the sample on the polyvinyl chloride film (referred to as PVC, 50mm×30mm), place the side to be tested face down, place the sample in the center between the two peel-off plates, put the plate into the device and place a 4.5kg weight on it, turn the device carefully while maintaining the pressure , move the weight to keep the sample at an average pressure of 750g/cm2 during the test, put the device into the oven, the oven temperature should be at (50±2) Within the range of ℃, place for 16h. The sample was removed from the device and left to cool at room temperature, then the sample and the PVC sheet were separated, and the coloration of the PVC sheet was evaluated with a gray sample card. The rating results of sticky color are given in accordance with the requirements of GB/T 251, and are divided into 5 grades, of which grade 5 indicates no stickiness and no color migration, and grade 1 indicates serious staining and obvious color migration. 2. Determination of color fastness to wet rubbing of leather The determination of color fastness to wet rubbing of leather is carried out in accordance with the requirements of QB/T 2537. The operation is as follows: the white felt after soaking and squeezing in deionized water is fixed in the rubbing color fastness measurement. Put the leather sample on the test head of the instrument (500g), then fix the leather sample on the test table of the instrument, with the smooth side up, and stretch it by 10% in the friction direction; put down the test head with felt, start the instrument, stop after 250 times, take Under the felt, according to the requirements of GB/T 251, grade the sticky color of the felt. 2. Results and discussion 1. Measurement results of color migration Analysis of the data in Table 1 shows that the average color migration grade of the tested shoe upper leather is 3, indicating that the color migration in the samples is obvious, and the color migration of individual samples is serious (such as A02). The data in Table 2 shows that the average color migration grade of the tested furniture leather is between 4, indicating that there is a slight color migration in the sample. The data in Table 3 shows that the color migration grade of the tested automotive leather is basically between 4 and 5, indicating that the color in the sample has basically no migration. The comparison of the data in the three tables shows that the color migration results of leather for different purposes are quite different, which is related to the processing technology and quality requirements of the products. Generally speaking, the color fastness index of automobile leather is the highest, because automobile manufacturers have a complete quality index system for leather-like fabrics, which puts forward the requirements for the processing technology of the tannery, the dyes, pigment pastes and auxiliaries used in the tannery. Strict requirements to prevent color migration in leather fibers and coatings, so of the three types of leather tested, automotive leather has the least color migration.
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