Before testing the relevant properties of textiles, they should be placed in a standard atmosphere for humidity control. This is because the humidity in the atmosphere has a great impact on the physical and mechanical properties of textiles.
Why do textiles need humidity testing?
Before testing the relevant properties of textiles, they should be placed in a standard atmosphere for humidity control. This is because the humidity in the atmosphere has a great impact on the physical and mechanical properties of textiles. Influence.
When the humidity is high, the moisture content of textiles increases, the mass increases, the size shrinks, becomes thicker and stiffer, and the strength and stretch will also change greatly.
Since textiles have moisture absorption and release characteristics, the humidity control process of textiles is to make the humidity of textiles balance with the humidity of the standard atmosphere. During the humidity control process, the equilibrium state can only be considered to be reached when the continuous weighing step change every 2 hours does not exceed 0.25%.
According to the standard GB6529-86, the standard atmosphere used for testing is: the temperature in temperate areas is 20°C and the relative humidity is 65%; the temperature in tropical areas is 27°C and the relative humidity is 65%. The relative humidity of air refers to the ratio of the actual water vapor pressure of the atmosphere to the saturated water vapor pressure at the same temperature.
The standard atmospheric pressure stipulated in our country is one standard atmospheric pressure (i.e. 101.3kPa or 760mmHg column). Table 1 shows the standard classification of atmospheres for textile testing.
Table 1 Standard classification of atmosphere for textile testing
Since textiles also have hygroscopic hysteresis, when the sample is wet, it is considered that it is not easy to reach a hygroscopic equilibrium state , the sample should be placed in an atmosphere with a relative humidity of 10%~25% and a temperature of 40~50℃ for pre-humidity treatment, or the sample should be dried in an oven at a lower temperature to reduce the moisture content. below the actual moisture regain, and then absorb moisture under the standard atmosphere to reach the equilibrium moisture regain. This can reduce the error caused by the moisture absorption hysteresis of the fiber. Therefore, when testing textiles, all samples taken from laboratory samples should undergo standard atmospheric humidity conditioning.
Normal moisture regain and public quality of textile materials
From the above, it is known that the moisture content of textiles changes with the changes in the surrounding atmospheric conditions. Variety. The moisture content of textiles generally uses the moisture regain index, and some also use the moisture content index.
The moisture regain of textile materials refers to the percentage of the difference between the actual mass (wet weight) and the drying quality (dry weight) of the material to the dry weight, which is called the actual moisture regain (W). Quality is also called visual quality. The actual moisture content (M) of textile materials is as follows.
The moisture regain of textile materials when they reach moisture absorption equilibrium under standard atmospheric conditions is called the equilibrium moisture regain under standard conditions, or standard moisture regain. It is not numerically equivalent to the actual moisture regain of textile materials. Table 2 shows the moisture regain values of several commonly used fibers measured under standard atmospheric conditions.
Table 2 Moisture regain values of several commonly used fibers measured under standard atmospheric conditions
What is the official moisture regain? This is entirely for the purpose of trade and to meet the needs of weight measurement and price verification, so that textiles under different conditions can be compared. The agreed value is uniformly stipulated by the state. The agreed value is relatively close to the actual moisture regain of the variety. .
Table 3 shows the official moisture regain rates of several major textile materials specified in GB/9994-1988.
Table 3 Official moisture regain rates of several major textile materials. What is the official quality? The quality of textile materials measured when the moisture regain is determined is called the stated quality. The formula for calculating the public mass when the dry weight of the material is known and the public mass when the actual moisture regain of the material is known is as follows.
Standard sample cards for textile testing
In various aspects of testing textiles When it comes to performance indicators, most indicators can be expressed quantitatively by data, such as yarn density, fabric density, breaking strength and elongation of textiles, number of wear resistance, and number of defects.
There are also many indicators that can only be expressed qualitatively or by comparison with standard sample photos and sample cards, such as the gray sample card for dyeing fastness, the blue wool standard for light fastness, and the physical cotton grade standard. , wool physical standards, cotton yarn evenness blackboard sample photos, etc. Among them, some have period validity and need to be replaced after a certain period, while others are relatively stable.
The following introduces the dyeing gray sample card and blue wool standard respectively.
Dye fastness gray sample card
Gray sample card is also called gray grading card, including color change sample card and staining sample card Sample card.
1. Standard sample card for discoloration
The gray sample card for testing the degree of discoloration of textiles adopts the standard GB250-1995 “Gray Sample Card for Evaluating Discoloration”, which is consistent with IS0105/A02-1995 “Textiles, color fastness testIt is equivalent to using the gray sample card to inspect and evaluate discoloration.
The gray sample card specified in this standard is used to evaluate the color change of the sample in the textile dyeing fastness test. This card can be used as a permanent record for the purpose of making new gray cards. The composition principle of this card is a basic gray card composed of five matte gray small cards (pieces of paper or cloth). According to the distinguishable color difference, it is divided into five color fastness levels, namely 5, 4, 3, and 2 ,1.
If you add half a level between each two levels, it will be expanded to five levels and nine levels of gray cards, namely 4~5, 3~5, 2~3, 1~2. The first component of each team is neutral gray, and only the second component with a fastness level of 5 is consistent with the first component. The color of the second component of the other teams becomes lighter in sequence, and the color difference gradually increases.
The visual color difference at all levels has been tested with a colorimeter. The chromaticity regulations and the color difference regulations between the second and first components of each team are shown in Table 4. When using this gray card, the textile sample and Place each piece of the original sample side by side on the same plane and close together in the same direction. The gray card is also placed on the same plane and close to the sample and the original sample. The background is a neutral gray color, approximately between Levels 1 and 2 of this gray card. Take an equivalent light source of 6001x and above, and use the range of this gray card to visually evaluate the color difference between the sample and the original sample. When evaluating the grade difference, no progression will be made for the hue, depth or brightness of the discoloration, regardless of single or combined discoloration characteristics. Only the total color difference between the original sample and the sample is the basis for the evaluation. Table 5 provides an illustration of the characteristics of color change when evaluating the color difference levels of dyes on textiles.
Table 4 Color difference and color difference regulations (discoloration)
Table 5 Color change characteristics
2. Stain Color Standard Card
The gray sample card for testing the degree of discoloration of textiles adopts the standard GB251-1995 “Gray Sample Card for Evaluating Discoloration”, which is consistent with IS0105/A03-1993 “Textiles, Color Fastness Testing and Evaluation” The gray sample card for staining is equivalent. The gray sample card specified in this standard is used to evaluate the staining degree of the adjacent fabric in the textile dyeing fastness test. This card can be permanently recorded for the purpose of making a new gray card.
The composition principle of this card is a basic gray card composed of five pairs of matte white or gray small cards (paper or cloth). It is divided into five color fastness levels according to the distinguishable color difference. , that is, 5, 4, 3, 2, 1.
If you add half a level between each two levels, it will be expanded to five levels and nine blocks of gray cards, that is, 4~5, 3~4, 2~3, 1~2. The first component of each pair is white, and only the second component of fastness grade 5 is consistent with the first component. The chromaticity of the second component of each other pair becomes darker in turn, and the color difference gradually increases. The color difference at all levels is measured by a colorimeter. The colorimetric regulations and the color difference regulations for each pair of the second component and the first component are shown in Table 6.
When using this gray card, place an unstained lining fabric sample and a stained lining fabric sample closely side by side on the same plane. The gray card is also placed on the same plane and close to each other. The sample is as it is, the background is a neutral gray color, and it is between level 1 and level 2 of the approximate discoloration gray card. Take an equivalent light source of 6001x and above, and use the grade difference of this gray card to visually evaluate the lining fabric sample and the patch. The color difference of the lining fabric as it is.
Table 6 Chroma and color difference regulations
Two blue wool standards
To test the color fastness of colored textiles to sunlight, GB730-1998 “Textiles Color Fastness Test, Blue Wool Standard for Color Fastness to Light and Weather Resistance” is referred to as the blue standard. The blue standard specified in this standard is used to evaluate the color fastness to light and weather resistance of colored textiles in color fastness tests.
The composition principle of the blue standard is to dye wool fabrics with eight dyes of specified depths to produce eight light fastness levels. Therefore, the light fastness blue wool standard is divided into eight levels, namely level 8, level 7, level 6, level 5, level 4, level 3, level 2 and level 1, representing eight levels of color fastness to sunlight.
See Table 1-7 for the name regulations of dyes at various levels. When the blue standard is exposed to sunlight or artificial light at the same time, it can produce eight different degrees of fading. Level 1 fades the most, level 8 is the least likely to fade, level 4 takes a certain amount of time to achieve a certain degree of fading, and level 3 is about It takes half the time to fade, and at level 5 it takes twice as long.
Table 7 Regulations on the names of dyes at all levels
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