Experts: Light Fastness Detection Frequently Asked Questions

Light fastness is not difficult for routine testing of textile and clothing, but in practice, various problems are often encountered.

K invited experts to ask readers questions and national standard ISO and AATCC light color.

1. What is the difference between blue wool standard sample 1-8 and L2 - L9? Is it possible to replace each other?

In GB/T 8427-2008 and ISO 105 B02: 1994, the blue wool standard samples 1-8 and L2 - L9 are described in detail. Their ingredients are all wool, and they all have 8 levels of blue label, and each higher numbered blue label is twice as light fastness as the previous one.

But they use different dyes and manufacturing processes. The blue label 1-8 is made of 8 different color fastness to light.

2, the current surface fastness tester for color fastness shows the relative humidity inside the box. Why should we calibrate it with the humidity control standard? What is the calibration process?

Most of the current color fastness tester can show the relative humidity inside the box, but in GB/T 8427-2008 and ISO 105 B02: 1994, humidity control standard is used to calibrate the humidity inside the box every day.

The reason is that the calibration of humidity control standard is not the "relative humidity" in the box. It is defined by combining the air temperature, the surface temperature of the sample and the relative humidity of the air that determines the moisture content of the sample surface during the drying process.

"Effective humidity" directly affects the test results of color fastness to humidity sensitive samples.

Therefore, the GB and ISO standards require checking the humidity inside the body every day.

The humidity control standard is a cotton fabric dyed with red azo dyes.

The following methods are used:

1) install a moisture control sample of not less than 45 mmX1Omm on the hard card with the blue wool standard sample, and place it in the middle of the sample clip as far as possible, as shown in Fig. 1.

Figure 1

2) part of the covered humidity control standard and the blue wool standard sample were also exposed to the sun until the color difference between the exposed and non exposed parts of the humidity control standard reached the grade 4 of the color change card.

3) at this time, the blue wool standard sample is used to assess the color change of the humidity control standard sample to which grade blue wool standard sample is consistent. For example, under the general conditions of European exposure conditions, the color difference between the humidity control standard sample and the non exposure part should be consistent with the color difference of the grade 5 Blue wool standard.

In case of inconsistency, the controller must be re adjusted to maintain the specified blackboard temperature and humidity.

3. what is the difference between the GB/T 3 and the GB/T 8427-2008 in the provisions of method 3? Should the GB/T 8427-2008 and ISO 105B02: 1994 method 3 be exposed to one stage or two stages? Finally, how many segments should be formed?

In the method 3 of GB/T 8427-1998, a blue wool standard sample with a minimum allowable fastness and a lower blue wool standard are selected.

Continuous exposure to the color difference between the 4 grade (first stage) and the 3 (second stage) of the Gray Wool standard is reached to the next block of blue wool standard. "

This description is not consistent with the original meaning of ISO 105 B02 1994.

In GB/T 8427-2008, "until the standard section of the next blue wool will reach the chromatic aberration of grade 4 (stage 1) and grade 3 (second stage) of grey card."

It is modified to "reach the minimum allowable fastness of the blue wool standard subsection to achieve the gray card 4 level (stage I) and the 3 stage (second stage) chromatic aberration."

This is consistent with the original intention of ISO 105 B02: 1994.

In the GB/T8427-2008 method 3, only two stages (grey grade 4 and 3 grade) of the colored samples are required to be exposed. It is not clear that several coverings should be used to cover the sample and the blue wool standard. Therefore, there are always disputes about the method 3 drying out several sections.

In fact, it is also in the two stage of drying. Using one or two covers does not affect the experimental process. But in order to facilitate the final rating comparison, it is recommended to dry out three segments.

That is to say, when covering the sample and 1/3 of the blue wool standard, when the blue wool standard surface of the lowest allowable fastness reaches the grade 4 of the gray card (stage I), it will cover 1/3 again, until the minimum allowable fastness of the blue wool standard surface reaches the 3 grade of the gray card (the second stage).

The schematic diagram of the sample and the blue mark is shown in Figure 2 (with the lowest allowable level 4).

4 in some product standards, some color fastness to light requires 3 of the selection method, and the quality requirement is intermediate level. For example, 3-4, how should we test it? {page_break}

This is true in some product standards. Some experts say this formulation is totally wrong, because the experimenters can not choose the blue wool standard.

However, because some of the existing product standards are regulated in this way, the operator suggests using the method 3 to carry out the experiment, and then refer to the rating method of 1.

For example, the standard requirement is 3-4, we will choose 4 and 3 blue wool standard method 3 requirements test, when grading, reference method 1 rating way, because there are 4 and 3 grade blue wool standard sample, in theory, we can evaluate whether the test result of the sample reaches 3-4 grade.

5 what is AFU in the US AATCC standard and what is the relationship with hourly numbers?

AFU is an energy unit. It is the abbreviation of AATCC FADINGUNIT. The Chinese meaning is "AATCC fading unit". It is defined as: 1/20 which is used to make L4 blue wool standard fade to reach 4 grade of discoloration grey card.

That is to say, the standard fading of L4 blue wool is 4 AFU, which requires 20 energy.

The AFU and radiant energy values of L2-L9 blue wool reaching 4 grade chroma are shown in the table below.

The relationship between AFU and hourly numbers can be calculated by formula. Assuming that only the lamp operates under 1.10W/m2 nm condition, the energy of L4 to 4 level chroma change is 85 kJ/m2.

85 kJ/m2= "1.10 W/m2x3.6x (hours)"

Hours = (85 kJ/m2) / (1.10W/m2x3.6) =21.5

It can be seen that when the radiant energy of xenon lamp changes, the number of hours to AFU will change. When the lamp operates at 1.10 W/m2 / nm, the energy of 20 AFU can be reached in 21.5 hours.

What is the function of the xenon reference fabric in 6. AATCC TM 16-2004? How should it be used?

Xenon Reference Fabric is a purple polyester fabric. Its function is to confirm that the temperature inside the box is correct.

The method of use is to place xenon reference fabric on the sample clip for 20 + 2 hours. If the color change of the xenon reference fabric is the same as that of the xenon reference standard or the color difference of the instrument is 20 + 1.7 CIELAB units, it is proved that the temperature inside the box is normal.