Learning points │4 key points that you must know to do a good job in the production technology management of printing and dyeing factories [Dyeing Factory Management]

1 Order review and sample review

Correct review of orders and samples is the prerequisite for correct formulation of production processes.

1.1 Order Review

The so-called “order review” means to carefully “interpret” the legally valid production contract or arrangement agreement signed by the enterprise and the merchant before formulating the production process. Every clause and even every word in the contract or agreement must be carefully studied, and one must understand it accurately and thoroughly. If the “order review” is wrong, the production process must be wrong. Once the wrong production process is implemented, it will definitely cause a major accident.

There are examples to prove:

A certain company mistook the nylon-cotton fabric for polyester-cotton fabric due to sloppy “order review” and adopted the high-temperature and high-pressure (130°C) method for coloring. As a result, all three cylinders of fabric (5,000 meters) were scrapped. ,lost heavily.

Everyone understands. Although polyester and nylon are both synthetic fibers, their coloring properties are completely different. Polyester, because its macromolecular chain is relatively straight and has no side chains, it has a good linear state and the macromolecules can easily move closer together. Therefore, it has good alignment, good crystallinity and tight structure. In addition, polyester macromolecules have no strong hydrophilic groups and are highly hydrophobic (moisture absorption rate is only 0.4%). Therefore, polyester fiber is difficult to swell (Tg=75℃), and it must be dyed under high temperature (125-135℃) conditions when the polyester swells significantly.

Nylon is different from polyester. The structure of nylon is much looser than polyester, and its molecular structure also contains many -NH and -COOH (hygroscopic centers), so the hygroscopicity of nylon is higher than that of polyester. 10 times larger (4%). The glass transition temperature is also much lower (nylon 6 Tg=35-50 ℃), so the nylon fibers are easy to swell and only need to be colored at 100 ℃. If 130°C is used for coloring, the temperature is too high and has approached or reached the “viscous flow” temperature of nylon, so the nylon fabric will become “papery” (elasticity, strength reduction, stiffness, yellowing) and thus lose use. value. (Note: Testing shows that the upper limit of high heat resistance of nylon 6 is l20 ℃, and it will obviously become paper when it is greater than 120 ℃).

Practical experience tells us that the following points must also be paid attention to when “reviewing orders”.

(1) Merchants pay special attention to the intrinsic quality (color fastness) of the product, so they will clearly state the dye fastness grade requirements in the order, but do not indicate the applicable fastness. standard. Whether the fastness standards implemented by merchants are GB Chinese national standards or IS0 organization standards; whether they are CEN European Standardization Committee standards or AATCC American Association of Fabric Chemists and Colorists standards; whether they are ATTS Japanese Fiber Products Technology Association standards or ASAC Asian Standardization Advisory Committee standards. Because different standards, detection methods and expression methods are different, the results will naturally be different, even quite different. Therefore, the fastness standards implemented by merchants must be clarified. Otherwise, it is very likely that due to different implementation standards, disagreements with customers will occur, and delivery will not be possible on time.

For example, domestic fastness usually follows the LS0 international standard (equivalent to the GB Chinese standard), but some merchants follow the AATCC American standard. The IS0 international standard is an eight-level system. One level is better than eight levels. The AATCC American standard is a five-level system, with one level being worse and five being better. That is, the AATCC standard level 1 is equivalent to the IS0 standard level 1.6.

If the customer’s requirement for fastness is 3+ (level 3 or above) and the implemented standard is lS0 standard, it means that the requirement is moderate and can be met. If the AATCC standard is implemented (level 3+ is equivalent to IS0 standard level 5), the requirements are too high, and it will be very difficult to produce deep and rich colors that meet the standards.

There are two reasons:

First, the darker the color, the better the fastness, and the lighter the color, the worse the fastness.

Second, more than 95% of reactive dyes have poor fastness (especially for light colors). Only a few dyes have good fastness, and light colors can reach IS0 standard 5. Level or so. For example, Huntsman’s three primary colors for dip dyeing: reactive yellow FN-2R, reactive red FN-2BL, and reactive blue FN-R; Taiwan Yongwan Company’s three primary colors for pad dyeing: reactive yellow C-GL, reactive red C-3B, and reactive Lan C-BB et al.

Therefore, for the fastness in the contract or agreement, the implementation standards must be clarified and must not be taken for granted. Because once the ISO standard is regarded as the AATCC standard, improper selection of dyes will lead to unqualified fastness, which will lead to a big mistake.

(2) Complete fastness includesPrinciples”:

(1) Natural cotton fabrics of different tissue specifications cannot be mixed.

(2) Natural cotton fabrics with the same tissue specifications but different manufacturers cannot be mixed.

(3) Natural cotton fabrics with the same organizational specifications and the same manufacturer but produced in different batches cannot be mixed.

The reason is that different origins, different brands, and different batches of natural cotton fabrics often use different fabric fibers with different coloring properties. After coloring, it is easy to produce differences in color (color finish, color depth) .

For example: cotton fiber. Due to different cotton varieties, different planting environments (such as temperature, finishing, rain, fertilization, soil, etc.), as well as different maturity levels, the amount of impurities (natural companions) and cellulose content of cotton will be different. Different, even the crystallinity of cotton fiber will have certain differences. These all make the coloring properties of cotton different.

Polyester fiber. Differences in process factors during the manufacturing process of polyester fiber. It will cause differences in the crystallinity of polyester fibers, resulting in differences in color absorption. According to testing, domestic polyester can produce 5-10% color differences due to different crystallinity levels. The quality of imported polyester is relatively good, and the difference in crystallinity is small, so the range of color differences that can occur is usually ≤5%.

Nylon fiber. The difference in coloring performance of different brands and different batches of nylon is much greater than that of polyester. This is due to differences in process factors during the manufacturing process of nylon. For example: differences in process conditions in monomer polymerization projects will result in different polymer molecular weights and different amino acid contents. During the spinning process, the differences in stretching uniformity and stretching ratio between single filaments will cause differences in microstructures such as orientation and crystallinity of nylon. Differences in process parameters of heat treatment (such as steam setting) of virgin silk will also significantly affect the orientation and crystallinity of nylon. Differences in the microstructure of nylon will inevitably lead to differences in coloring properties (such as the speed of color absorption, the level of equilibrium adsorption value, and the size of color absorption capacity (dyeing depth)). This is the reason for the large difference in coloring performance of nylon yarn. Currently, there are two types of nylon filaments used for fabrics, namely nylon 6 and nylon 66. Although nylon 6 and nylon 66 are both polyamide fibers and have similar structures, the amide amide in the structure of nylon 66 can generate hydrogen bonds, and its hydrogen bond density is much higher than that of nylon 6. Therefore, the arrangement of macromolecular chains is much closer, and the amino content of nylon 66 is more than twice lower than that of nylon 6, so the difference in color absorption performance between the two is very obvious. For example, the color absorption rate of nylon 66 is much slower than that of nylon 6, and the color absorption capacity (dye depth) of nylon 66 is much lower than that of nylon 6.

Obviously, if fabrics made from fibers (or silk) of different brands, different specifications or different batches are mixed and colored together, significant color differences and batch differences are inevitable. . Because of this, the “three no’s principles” must be implemented in the management of natural cotton at the production site. Moreover, dyeing the same color sheet must be produced using the same brand, the same specifications, the same manufacturer, and the same batch of natural cotton fabrics, and they must not be mixed. If it is necessary to mix hair, be sure to conduct parallel experiments on coloring in advance to confirm that there is no obvious color difference before combining the hair blanks.

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