Abstract: Color difference between dyeing samples is the most important problem that plagues dyeing production. An important factor in the inconsistency between large and small dyeing samples is the inconsistency of the dyeing process conditions for large and small samples. This article specifically introduces how to obtain good reproducibility from laboratory small samples to large sample production, and ultimately achieve the purpose of reducing the color difference between large and small sample dyeing.
Keywords: pretreatment dye auxiliary technology
Foreword
The printing and dyeing industry is an important part of my country’s textile industry. Since 2000, my country’s printing and dyeing industry has fully grasped the capital flow of global textile economic integration. , technology transfer, and production capacity transfer opportunities, it has achieved rapid, sustained, and stable development, and has now become the world’s largest producer, exporter, and consumer of printed and dyed fabrics.
However, with the development of the national economy, the economic growth mode of the printing and dyeing industry, which has long been characterized by the development of natural resources and free use of the environment, has become increasingly consistent with sustainable development. contradiction. The textile printing and dyeing industry has always been a high-energy-consuming, high-pollution industry. The water consumption in the printing and dyeing process accounts for about 70% of the water used in the entire textile industry. It ranks fifth in the total emissions of manufacturing enterprises in the country and provides national energy conservation and emission reduction opportunities. Key industries.
Solving the color difference between large and small dyeing samples and improving the first-time success rate of setting out is the best way for our dyeing and finishing enterprises to achieve the goals of “energy saving, emission reduction, consumption reduction, and high efficiency” method. This article discusses how to reduce the color difference of large and small dyeing samples from aspects such as pre-treatment of gray fabrics, reasonable selection of dyes and auxiliaries, and dyeing processes.
1 Pre-treatment of gray fabric
The pre-treatment of gray fabric is very important , if the pre-processing is well controlled, half of the dyeing will be completed once the dyeing is successful, so the gray fabrics we make for proofing must be consistent with the gray fabrics produced for mass production. Nowadays, many proofing gray fabrics are generally made on small prototype machines. The pre-treatment effect is often different from the large-scale production results, which will affect the accuracy of proofing. Especially now, many fabrics have to go through pre-shrinking, pre-shaping, and alkali reduction. Pre-treatment, pre-setting temperature and alkali reduction directly affect the depth of dyeing. For the same formula, the higher the alkali dosage rate, the lighter the color obtained. The sampler should use the gray fabric with good alkali content produced in the workshop to duplicate the previous formula. This should be paid attention to in actual production.
2 The selection of dyes must be appropriate
By testing customer samples Careful review and research to understand the fiber composition, dye fastness grade requirements, color light source, appearance quality requirements and post-processing requirements (such as coating, white coating, silver coating, bright PU, oil surface calendering) of the customer’s sample gray fabric etc.) to select the most suitable dye. The principle of selecting dyes is to use dyes with high one-time success rate and low cost as much as possible on the basis of meeting customer requirements.
2.1 Different fibers are dyed with different dyes
Generally, polyester fabrics are dyed with disperse dyes, nylon fabrics are dyed with acid dyes, cotton fabrics are dyed with reactive dyes or direct dyes, etc. Therefore, before we make a sample, we must first understand the fiber composition of the sample and choose the most reasonable one. dye.
2.2 There is an implementation standard issue for dye fastness
Each Each country has its own standards: GB is the Chinese national standard, ISO is the international organization standard, CEN is the European Committee for Standardization standard, AATCC is the American Association of Chemists and Colorists standard, and ATTS is the Japanese Textile Products Technology Association standard. Different standards have different detection methods and expression methods, and the results will naturally be different, even quite different. Therefore, the customer’s fastness standards and grade requirements must be clear and clear. We need to choose different dyes according to different fastness requirements. If the customer requires sun-drying, we will use a dye combination with high sun exposure. If the customer requires high water-washing, we will use a dye combination with high water-washing, etc.
2.3 Consider whether metamerism
Choose a light-hopping one For formula proofing, the color will be different under different light sources or at different time periods, which is difficult for customers to confirm. Therefore, on the premise of meeting customer requirements, it is best to choose a formula that jumps in color synchronously with the customer’s original color.
2.4 The dyes used for small samples in the laboratory must be consistent with the dyes used for large sample production in the workshop
The dye strength of each batch will be slightly different. If the dye is left for a long time, it will also cause changes in weight. Therefore, when making laboratory samples, you must use dyes used in mass production. Proofing to improve its accuracy and reduce the difference between large and small samples.
2.5 In terms of color matching
Light colors such as light gray, For light apricot, khaki, etc., most of the three primary colors of light colors are used for color matching, while for dark colors, the single color closest to the color sampled by the customer is mostly used as the main color, and dyes of other colors are used to adjust the color light. In order to reduce the color deviation in large sample production, dyes with similar dye uptake rates and good compatibility should be used for color matching. Moreover, the fewer the number of dyes used, the better. The more the number of dyes, the greater the error.
2.6 For orders processed after customer requirements
For customer requirements For post-processing orders (such as coating, white coating, silver coating, bright PU, oil surface calendering, etc.), when making small samples, post-processing must also be carried out before color matching, otherwise it will be very easy to set out.��, for water-soluble dyes such as reactive dyes, acid dyes, direct dyes, etc., because the dyes will hydrolyze in water, the impact of the liquor ratio is considerable. Even for water-insoluble disperse dyes, when printing dark colors At this time, the influence of liquor ratio is also quite obvious. Therefore, before making a small sample, you must first calculate the bath ratio in the large vat production based on the meter and gram weight of the gray fabric the customer has invested. Then use this bath ratio to make a small sample. According to the formula requirements, first add the amount of dye and auxiliary solution. After adding up, calculate the amount of water that needs to be added, then use a measuring cylinder to take water, add it to the dyeing cup to reach the formula liquor ratio, and then proceed to dyeing and proofing.
Nowadays, most of our factories use automatic dripping systems. The instrument will automatically add the required water according to the amount of dye or additive added to reach the set total bath volume, with high accuracy. High, the error is small, and there is no operating error between different operators. When the liquor ratio is designed to be small or the area of the sample fabric is large, the fabric is not evenly immersed in the dyeing solution, and it is easy to have sample color flowers. Once the sample color flowers are produced, it is difficult to formulate a dyeing formula, and the success rate of dyeing is reduced. Therefore, to ensure the uniformity of the sample, you can cut the sample into several small pieces and then add the dye cup to improve the uniformity of the sample.
4.4 Heating rate and holding time
The heating rate is 1- 2℃/min is appropriate. If the speed is too fast, it will easily cause the temperature gradient in the tank to be too large, resulting in uneven dyeing and color blooming; if the speed is too low, it will affect production efficiency. The holding time is divided according to the color depth. Light colors are generally kept warm for 30 minutes, medium and dark colors are generally kept warm for 45-60 minutes. After the heat preservation is completed, the temperature is lowered to normal temperature, and the first water wash after dyeing is carried out to fully wash away the residual liquid and floating color remaining on the cloth surface. Raising or cooling the temperature too quickly can easily cause defects such as stains and creases, which will directly affect the first-time success rate of repairs. When making samples, the holding time should also be consistent with that in the workshop. No matter how compatible the dyes are, their dyeing temperatures and times are different. The colors after dyeing with different holding times will be slightly different. For example, the light dye we most commonly use Among the three primary dyes, 2BLN blue, E-GL yellow, and 3B red, the shorter the holding time, the worse the coloring of 3B red. Therefore, controlling the uniformity of the heating rate and holding time is also an important point in reducing the color difference between large and small samples.
In addition to the above points, the reasons for color difference between large and small samples include the degree of automation and accuracy of dyeing and finishing equipment, the accuracy of the number of barrel meters, and the correctness of proofing operations. properties, the vehicle speed and temperature during post-processing and shaping, the drying method of the sample cloth, the color light source, etc. will all cause color differences. Therefore, we must also implement standardization and refined management, formulate detailed and complete operating standards, and strictly Check the standardized operations and continuously introduce advanced automation equipment (computerized color measurement and matching system, fully automatic feeding system, automatic sample dripping system, etc.) to ensure that our first process is correct to reduce the color difference between large and small samples. Improve the one-time success rate of dyeing.
5 Conclusions
There are many reasons for the color difference between large and small samples , it not only involves different processes such as pre-treatment, dyeing, and finishing, but is also closely related to equipment, management, operating factors, and the selection of dyes and chemicals, so we must carefully control every link and detail in the production process. And master the changing rules, reduce the difference between large and small samples, and improve the one-time success rate of dyeing. </p
