Analysis Of Cotton Color Characteristics

　　 cotton Color characteristic is an important index to evaluate cotton quality. Color characteristic test is one of the core and difficult points in the reform of cotton standard. It is very important for cotton inspection to pass from sensory examination to instrumental examination. In this paper, the color characteristics and grade test data of cotton inspection in Tianjin in recent three years are analyzed, and the color characteristic test and color characteristic map of cotton in China are analyzed and discussed based on the test of color characteristics in the United States.

1 principle of color characteristic test

The color of any object can be described by three basic parameters of colorimetry, that is, lightness, hue and saturation. Classical theory holds that the tone of cotton is in the 10YR plane of Munsell color space. Therefore, in the 10YR color plane, we only use the two coordinates of lightness and saturation to characterize the color characteristics of cotton. Rd is used to describe cotton lightness index, and yellow depth (+b) is used to describe cotton saturation index.

Ripe cotton fibre Because of the high crystallinity, degree of polymerization and orientation, the fiber structure is compact and deposited. cellulose The shape is closer to the cylinder, so the reflected light is strong and the reflectivity is high. Therefore, by observing the color characteristics of cotton, the quality of cotton can be judged as a whole, which is the theoretical basis of color grading.

2 Analysis of cotton color characteristics and grade in Tianjin in recent three years

2.1. The proportion of color characteristic level detected by instrumental examination.

In the past three years, Tianjin has checked 25 thousand and 600 tons of cotton by instrumental examination. According to the distribution of color characteristic level (see Figure 1), from 2007 to 2009, the proportion of white cotton grade 2 was continuously reduced, and the level of white cotton 3 increased slightly, and the white cotton 4 increased from 45% to 70% in 08 years.

Intuitively, it seems that the color quality of cotton is decreasing, but in fact it is due to the large difference in annual inspection volume. As can be seen from Fig. 1, the proportion of white cotton grade 4 is the highest in three years, followed by white cotton grade 3. With the increasing coverage of instrumental testing, the statistics of test results will more comprehensively reflect the real situation of cotton processing quality in Tianjin.

Fig. 12007-2009 distribution of color characteristic grade of cotton in Tianjin

2.2 color characteristic level and grade relationship

From the scatter diagram of grade and color characteristics, there is a certain regularity between color characteristics and grades. Overall trend, low grade color characteristics, low grade, high grade color characteristics, but there are many samples that do not conform to this rule. As shown in figures 2 and 3, some of the lower grade cotton color characteristics are the same as those of high grade cotton, while Figure 4 shows that grade 2 grade color characteristics are not as good as those of 3 or 4 grade cotton. This shows that the characteristics of grade and color are not one-to-one, and can not be fully characterized by color characteristics.

Fig. 22007 scatter plot of grade and color characteristic grade distribution of cotton in Tianjin

Fig. 32008 scatter plot of grade and color characteristic grade distribution of cotton in Tianjin

Fig. 42009 scatter plot of grade and color characteristic grade distribution of cotton in Tianjin

3 Comparison of cotton color characteristics between China and the United States

3.1 cotton color characteristic test in China

In 2002, the cotton inspection system reform started. China began to use large capacity cotton fiber tester (HVI) to detect many indicators including cotton color characteristics. Before that, cotton inspection in China was mainly based on sensory and physical examination. Only individual units had HVI equipment or other color measuring instruments.

At present, cotton color characteristics test in China is mainly based on GB 1103 - 2007 "cotton fine wool cotton". The color characteristic map of this standard draws on the principle and application of the US cotton color characteristic map. After several years of extensive inspection and survey data, according to the distribution of cotton color characteristic value Rd and +b in China, and combining with the characteristics of the cotton quality and production, processing, inspection and utilization, the cotton color characteristics of our country are divided into 13 grades: white cotton, light yellow dyed cotton and yellow cotton three kinds. Each color feature level includes a certain range of (Rd, +b) values. It is drawn on the graph with Rd as the ordinate and +b as the abscissa, which is used for fast inspection of cotton color characteristics by HVI equipment, and has high scientific and local characteristics. But the US cotton color characteristic map has been used for more than 50 years, and the domestic color characteristic map is only a few years old, and it needs to be perfected continuously. {page_break}

3.2 cotton color test in the US

The United States is the earliest country to study and apply cotton color characteristic map. Since the 50s of last century, the characteristic level of cotton color has passed from sensory test to instrument inspection, and its cotton standard has become the universal standard in the world. The conditions for determining cotton grades in the United States are: color characteristics, leaf litter grades, and rolling mills. The grading method is equal to manual grading and instrument testing. If there is any objection, the grading organ's sensory test results will prevail. Under the condition of sensory testing, the standard of physical characteristics of cotton color is the basis for evaluating cotton color characteristics.

According to the standard of cotton color characteristics, the American graders carry out sensory tests, first determine the type of cotton, then decide that cotton belongs to a certain level of this type. In the process of grading, we should decide whether or not to combine with the amount of leaf litter contained in cotton samples. The cotton color characteristics of the United States are divided into five categories: white cotton, spotted cotton, spotted cotton, light yellow cotton and yellow cotton. There are 30 color classes, each containing 1 grades of cotton, 15 of which have physical standards.

Color characteristic diagram is the basis for determining the color characteristic level of the instrument. The color characteristic grade of cotton is determined by the color measuring system of the instrument. The location of the intersection points of Rd and +b is determined in the color characteristic map of the cotton in the vertical coordinates (Rd) and the Yellow depth (+b) as the abscissa, and the color characteristic grade of the cotton is determined. This method instead of the naked eye to reflect the type and grade of cotton, so as to determine the color characteristic grade of cotton, has no change in grading principle. The US cotton color characteristic map is a large number of Rd and ten b values of cotton produced in various localities and grades, and the corresponding ranges of color values and grades are drawn.

4 discussion on cotton color characteristic map

The relationship between 4.1 color characteristics and grade

The connotations of cotton color characteristics and grades are different. The grade of cotton is determined according to the maturity, color and characteristics of the cotton and the quality of the rolling mill. The color characteristic grade of cotton is determined according to the color characteristics of cotton, that is, the measured reflectivity (Rd) and yellow depth (+b). Therefore, when assessing cotton quality, the factors considered for cotton quality are more than those of cotton color. Usually when color reaches a certain level, it is degraded because of poor maturity or harmful defects. Therefore, it is not possible to take the grade color to produce the hard color characteristic level. In addition, the color characteristic standard white cotton grade 3 is based on the grade level three color characteristics. Since it is a standard class, it is necessary to increase the area in the color feature map, because at present, the grade distance of white cotton 2, 3, and 4 is increased successively, but the area is basically the same. Moreover, if the color level is set according to the grade, there will still be a problem of high grade cotton spacing.

The 4.2 part is unreasonable in color level.

From Figure 1, we can see that the number of grade 1 of contaminated cotton is very small, and 07 or 08 years do not even have this level of data. So the scope of the 1 grades of contaminated cotton may be divided. In reality, are there many cotton like grade 1 cotton with high reflectivity and high yellowness? The data show that few of them are on the map, and the range of grade 1 of stained cotton is quite large, so whether it should be adjusted should be considered.

4.3 can grade line be used in horizontal line?

At present, the type line of color characteristic map adopts the right inclined continuous line, mainly considering that the cotton grade one or two and three is basically classified as white cotton, the four or five grade cotton is classified as white cotton, the other part is divided into light yellow dyed cotton, six grade cotton is divided into yellowish dyed cotton and the other part is yellow dyed cotton. Grading line tilt is the factor that considers the rapid variation of high-grade cotton. The other reason is to consider that all cotton producing areas have first class flowers, rather than some provinces at first level, and some provinces do not.

The classification line tilting has achieved the purpose of not only reducing the grade but also reducing the type of the cotton with poor appearance. Although the grading line tilting is favorable to balance the situation, there is a problem: the color of the upper and lower two color features is compared with that of the lower right corner of the upper one. The color of cotton in the lower right corner is not as good as the cotton color in the upper left corner of the next characteristic grade area. As we all know, the grade is a comprehensive index of three factors. The so-called color characteristics should only consider the color factors, and the appearance of good cotton color characteristic level should be higher than the appearance. In some southern areas, cotton color characteristics are lower than those in the the Yellow River River Basin and the northwest inland cotton area. They are formed by varieties, production methods and natural conditions. Moreover, if the color characteristics are not regarded as indicators of settlement, it is not as important as grade. There is no need to classify the grading lines into a tilted pattern in order to have a primary flower in all places. We should refer to the internal quality indicators, such as fracture strength and length uniformity index.

4.4 the multi color characteristic chart is made, and the quality of the rolling mill is considered.

In order to make the inspection of color characteristics more practical, it is also necessary to consider that the color characteristic map should be made according to different natural conditions, main varieties, production methods, processing level and other factors, and can be divided into zones according to the grade standards. According to the scanning sample bar code automatic recognition area, the color characteristic map of the area is evaluated for grading.

At the same time, we should consider the manual evaluation of cotton mill quality. Because of the standardized processing and high management level, the quality of the mill is negligible. The quality of the cotton mill is uneven, and there are more harmful defects, which have great influence on the value of spinning. Therefore, it should be taken as an assessment index and should be abolished after the improvement of the processing level in the future.

5 Conclusion

The application of cotton color characteristics indicates that cotton inspection is moving from sensory testing to instrumental testing. How to make Chinese cotton color characteristics inspection more reasonable and effective is the common aspiration of cotton related units and inspection institutions. We should constantly improve the color feature map, promote the improvement of cotton color characteristics test in China, and make Chinese inspection recognized by the whole world.