Because the testing process of these items is special, the instruments and equipment involved are special, and the environmental control requirements are high, among which color fastness, fuzzing and pilling still use manual rating methods. These test characteristics greatly increase the uncertainty of test results. At present, CNAS and other official institutions provide few capability verification plans for these projects, and textile testing institutions are actively seeking capability verification plans for these projects
1. test items and requirements
The seven test items involved in this ability verification plan are: (1) color fastness to water, according to GB/T 5713-1997 "Color fastness of textiles"; (2) Color fastness to perspiration, according to GB/T 3922-1995 "Test Method for Color Fastness to Sweat of Textiles"; (3) Color fastness to rubbing, according to GB/T 3920-2008 "Color fastness to rubbing of textiles"; (4) Color fastness to saliva, according to GB/T 18886-2002 "Color fastness of textiles"; (5) Dimensional stability after washing and drying, according to GB/T 8628-2001 "Preparation and determination of samples when measuring dimensional changes of fabrics", GB/T 8629-2001 "Household washing procedures used in textile tests", and GB/T 8630-2002 "Measurement of dimensional changes of textiles during washing and drying"; (6) Tearing strength, according to GB/T 3917.1-2009 "Tearing Properties of Textiles-Part 1: Determination of Tearing Strength"; (7) Anti-pilling, according to GB/T 4802.2-2008 "Determination of fuzzing and pilling properties of textiles-Part 2: Modified martindale method". At the same time of sending samples to participating laboratories, a Confirmation Form of Acceptance Status of Proficiency Verification Samples, a Proficiency Verification Operation Instruction and a Proficiency Verification Test Record Form are attached, requiring each laboratory to conduct tests according to the requirements of the operation instruction and submit test results within the prescribed time limit.
2. sample preparation, uniformity and stability inspection
Purchase samples with stable quality, uniform appearance and properties meeting the test requirements from well-known fabric manufacturers, and cut them into certain pieces. Among them, the color fastness to rubbing project uses solid samples to avoid possible differences between colors. Color fastness to perspiration, color fastness to water and color fastness to saliva. The main purpose of choosing printed fabrics is to assess the sample preparation ability of participating laboratories.
Before the samples are distributed, the uniformity and stability of the samples are tested according to CNAS-GL03: 2006 Evaluation Guide for Uniformity and Stability of Ability Verification Samples [1]. The results show that the samples are uniform and stable, which can meet the requirements of the capability verification plan. The results of capability verification feedback can also prove that the samples sent this time have stable properties.
3. statistical methods
There are seven capability verification plans involved in this capability verification. Statistical analysis and result evaluation are mainly divided into two ways: 5 capability verifications such as water fastness, perspiration fastness, rubbing fastness, saliva fastness and anti-pilling are carried out according to 1.3.1, and 2 capability verifications such as dimensional stability and tear strength after washing and drying are carried out according to 1.3.2.
3.1 result evaluation of color fastness to water, perspiration, rubbing, saliva and pilling
Take the value specified by experts as the specified value, compare the laboratory results with the specified value, and evaluate the laboratory results according to the following principles, that is, the difference between the final evaluation results of the laboratory and the specified value does not exceed 0.5, which is satisfactory; The difference between the final evaluation result of the laboratory and the specified value exceeds 0.5 grade, which is considered as unsatisfactory.
3.2 Evaluation of dimensional stability and tear strength after washing and drying
In this capability verification plan, the specified value and standard deviation of capability assessment are determined by Robust statistics, that is, the median value of robust statistics is used as the specified value, and the standardized quartile distance (NIQR) is used as the standard deviation of capability assessment.
The z value (z ratio score) is calculated according to the following formula for the test results of the laboratory of this capability verification plan:
In which: x is the laboratory test result; X is the specified value; σ is the standard deviation of ability evaluation.
In this plan, the Z-score of each participating laboratory is used to evaluate the detection ability of the laboratory. The z score is close to 0, which indicates that the data is in good agreement with the overall sample. If the absolute value of z ratio score is less than or equal to 2, the test result of the laboratory is satisfactory; If the absolute value of z ratio score is 2 ~ 3, the test result of this laboratory is suspicious; If the absolute value of Z score is ≥3, the test result of this laboratory is an outlier result. That is, |Z|≤2 is a satisfactory result; 2 < | z | < 3, which is the result with problems; |Z|≥3 is an outlier, which is an unsatisfactory result.
