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 opportunities of capital flow, technology transfer, and capacity transfer in the global textile economic integration, and has achieved rapid, continuous and stable development. It 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 the free use of the environment, has become increasingly contradictory to sustainable development. The textile printing and dyeing industry has always been a high-energy consumption and high-pollution industry. The water consumption in the printing and dyeing process accounts for about 70% of the total water consumption of the textile industry. It ranks fifth in the total emissions of manufacturing enterprises nationwide and is a key industry for national energy conservation and emission reduction.

Solving the color difference between dyeing samples and improving the one-time success rate of sample placement is a good way for our dyeing and finishing enterprises to achieve the goal of "energy saving, emission reduction, consumption reduction, and high efficiency". Now we will explore how to reduce the color difference of dyeing samples from the aspects of pre-treatment of grey fabrics, reasonable selection of dyes and auxiliaries, and dyeing technology.

1. Pretreatment of grey fabric

Pretreatment of grey fabric is very important. If the pretreatment is well controlled, dyeing is half done in one go. Therefore, the grey fabric we sample should be consistent with the grey fabric produced in large quantities. Nowadays, many sample grey fabrics are generally made on small sample machines. The pretreatment effect is often different from the results of large-scale production, which will affect the accuracy of the sample. In particular, many fabrics now have to undergo pre-shrinking, pre-setting, alkali reduction and other pre-treatments. The pre-setting temperature and the level of alkali reduction directly affect the depth of dyeing. For the same formula, the higher the alkali rate, the lighter the color. The sampler should use the grey fabric with good alkali content in the workshop to duplicate the previous formula. This should be taken seriously in actual production.

2. The dye selection must be appropriate

Through careful review and research of customer samples, understand the fiber composition, dyeing 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, etc.) of the customer sample grey fabric, so as to select the most suitable dye. The principle of dye selection is to select dyes with high one-time success rate and low cost as much as possible on the basis of meeting customer requirements.

2.1. Use different dyes for different fibers

Generally, we use disperse dyes to dye polyester fabrics, acid dyes to dye nylon fabrics, reactive dyes or direct dyes to dye cotton fabrics, etc., so we must first understand the fiber composition of the sample before making samples, so as to choose the most reasonable dye.

2. 2 There is an implementation standard problem for dye fastness

Each country has its own standards. Different standards have different detection methods and expression methods, and the results are naturally different, even with large differences. Therefore, the fastness standards and grade requirements for customers must be clear and clear. We must choose different dyes according to different fastness requirements. If the customer requires sun exposure, we use a high sun exposure dye combination. If the customer requires high water washing, we use a high water washing dye combination, etc.

2.3 Consider whether it is the same color but different spectrum

Choose a light-jumping formula for proofing. The color will be different under different light sources or different time periods. It is difficult for customers to confirm. Therefore, we must choose the best formula that jumps the color synchronously with the customer's original sample on the premise of meeting customer requirements.

2.4 The dyes used in the laboratory for small samples must be consistent with the dyes used in the workshop for large sample production

The strength of each batch of dyes will be slightly different, and the dyes will also cause changes in weight if they are placed for a long time. Therefore, when making samples in the laboratory, the dyes used in large production must be used for 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, light apricot, khaki, etc. are mostly matched with light primary colors, while dark colors are mostly matched with the single color closest to the customer's sample color as the main color, and then other colors of dyes are used to adjust the color. In order to reduce the color deviation in large sample production, dyes with similar dyeing rates and good compatibility should be used for color matching as much as possible. Moreover, the fewer dyes used, the better, and the more dyes, the greater the error.

2.6 For orders that require post-processing by customers

For orders that require post-processing by customers (such as coating, white coating, silver coating, bright PU, oil surface calendering, etc.), post-processing must be carried out before color matching when making small samples, otherwise it is very easy to return to the cylinder to add color during sample placement, which affects the success rate of sample placement in one time.

3. Use auxiliaries appropriately

As we all know, adding an appropriate amount of dyeing auxiliaries to the dye bath can effectively improve the dyeing quality. For example, when dyeing nylon fabrics, adding 1-1.5g/L nylon leveling agent to the dye bath can significantly improve the covering ability of neutral dyes or acid dyes on nylon defects and prevent the formation of warp and weft files. The same auxiliaries such as leveling agents, acids, and color fixers used in large sample production must also be used for small samples. Because these auxiliaries, such as leveling agents, have an impact on color light, so when making small samples, the temperature, pressure and other conditions in large sample production should be simulated at the same time, and leveling agents should be used at the same time, and they should be reduced in proportion, and the amount should be the same to ensure the consistency of the dye bath components of the small sample and the large sample.

It is worth noting that the amount of leveling agent should not be too much, because the leveling agent not only plays a leveling effect in the dyeing process, but also has a dye-blocking effect on the dye. When the amount of leveling agent is appropriate, the leveling agent inhibits the dyeing speed of the dye, so that the dye will not cause color flower phenomenon due to too fast dyeing; but if the amount of leveling agent is too large, it will reduce the dyeing rate of the dye, increase the concentration of the dyeing residual liquid, waste the dye, and increase the cost. Generally speaking, the amount of leveling agent is larger when dyeing light colors; when dyeing dark colors, the amount of leveling agent is less. Since each leveling agent has different concentrations and component contents, the amount of various leveling agents should be determined based on actual experimental comparisons.

Considering that the amount of small samples is very small, it is easy to cause weighing errors, so the auxiliary agents used should be dissolved in advance to a standard solution with a concentration of 20g/L and then added according to the amount.