Discussion on the Cause of DTY Stiffness

In DTY processing, stiff silk often affects the first grade product rate and appearance degradation of DTY dyeing in varying degrees, thus affecting the final first grade product rate, qualified product rate and unit consumption of DTY, especially when POY quality is unstable. Stiff wire also has a great impact on the processing quality of the next process, often causing quality feedback from users. Based on years of production experience, this paper starts with the phenomenon of stiff silk, analyzes its morphological characteristics and causes, so as to minimize the stiff silk in production.

1. Morphological characteristics of stiff filament

In actual production, DTY stiff silk shows that DTY packages have different length and non bulky spots (1~5cm) in appearance, which are reflected in dark dots or stripes on the test sock tube. The specific forms are as follows:

1.1 Monofilament adhesive dark dot type (stiff filament length is less than 1cm and appears dark dot on sock tube)

If the sock tube is cut open, when the corresponding DTY silk strip is carefully drawn out, it will be found that the DTY single fiber at the dark spot is in an adhesive state and cannot be separated. The formation of this kind of stiff filament mainly occurs in the process of heating. A weak link in the fiber (that is, the strength of intermolecular force, the rigidity of macromolecular chain, and the regularity of monomer unit position are lower than normal) has a low melting point. When heated, the monofilaments are fused together. Even after untwisting, the fibers cannot be separated, and the dyeing stiff spots are dark.

1.2 Dark dot type without adhesion of monofilament (stiff filament length less than 1cm)

If the sock tube is cut open and the corresponding DTY silk strip is carefully drawn out, it will be found that the DTY silk strip at the dark spots has poor bulkiness. The single fibers are twisted together in the shape of network knots. Hold both ends of the silk strip with a certain force. The single fibers at the dark spots are loosened. The single fibers have obvious loops and braids. Unlike 1.1, the DTY single fibers are not bonded together, which is caused by the single fibers being twisted together and not smoothly untwisted. When the filament is deformed by heat, due to the influence of adverse factors, the twist transmission is uneven, and the filament is subject to uneven torque in the migration process, forming a special point. After untwisting, the effect of the special torque causes the multifilament to wind together, resulting in poor looseness. When dyeing, these bad parts react as dark spots on the sock tube.

1.3 Dark stripes of different lengths

On the test sock tube, they showed dark stripes of different lengths and thin. After the silk strips were drawn out, the observation was not much different from that of type 1.2, except that the single fiber entanglement at the color difference was slightly longer (1~5cm) or there was continuous dot stiff silk within a range of tens of centimeters, which indicated that the adverse factors were not changed much, unlike that of type 1.2, the adverse factors were not changed much.

1.4 Regular dark stripes

The regular dark stripes are displayed on the test sock tube. After the silk strips are drawn out, the observation is not much different from the 1.2 type, but the length of the silk strips with color difference is the same, which is more regular, indicating that the adverse factor is a fixed factor.

1.5 Sock tube transparent color depth

On the test hose tube, the whole hose tube basically keeps the style of raw silk, the fabric surface is shiny, and the fabric is very thin when touched by hand When placed in front of the light source, it is more transparent than normal silk. This kind of silk is generally caused by insufficient deformation or insufficient twist during deformation processing. Therefore, it still has the style of precursor, which is reduced to substandard in the inspection judgment.

From the above description, it can be seen that stiff silk is a kind of silk with many types and different shapes, which can not be generalized. Only by focusing on the problem, can we find the cause of the problem. There are many reasons for stiff silk, and the phenomenon of category 1.1 is special, Under normal production conditions, the false twist deformation temperature is controlled within the critical temperature range, which is rarely produced; 1.4. Category 1.5 in normal production is generally caused by mechanical problems of single spindle position in post processing, which will not be discussed here. This article mainly analyzes the 1.2 and 1.3 phenomena that are common and difficult to eliminate in production.

2. Main factors for production of stiff silk

There are many reasons for tight spots in DTY processing, which are ultimately reflected in the fluctuations of twisting tension, untwisting tension and their ratios in post-processing. There are many factors affecting the twisting tension and untwisting tension, mainly including uneven oiling of POY, the characteristics of POY oil, the internal quality of POY, improper selection of DTY processing technology, etc., which cause the imbalance of twist balance or melting adhesion, and then cause DTY yarn to produce necking or untwisted stiff yarn. These factors are discussed below.

2.1 POY oil

POY finishes affect the balance of the yarn. If the smoothness is poor, the twisting tension will decrease, the untwisting tension will increase, and the false twisting tension will lose its stability, resulting in partial uneven twist and melting adhesion between monofilaments under high temperature, resulting in stiff yarn. The oiling uniformity of the sliver will affect the friction coefficient and evenness of the sliver. At the same time, the characteristics of the finish also play a key role in the viscosity of the white powder, and will affect the contact performance between the sliver and the friction disc surface. These factors all affect the twisting tension, untwisting tension and their ratios, resulting in tight point stiff yarn.

2.3 Post processing process parameters

In actual production, if the post-processing process parameters (such as the setting of the drawing ratio) are properly selected, some POY defects can be covered, otherwise a large number of stiff filaments or wools will be caused, or even stiff filaments and wools will coexist.

When the draw ratio is within a certain range, the dyeing is relatively stable, but when the draw ratio is less than a certain value, with the decrease of the draw ratio, the percentage of the first grade dyed products decreases seriously. This is because with the reduction of the drawing ratio, the twisting tension decreases, and the twisting effect is good, but the processing is unstable, and it is easy to form a balloon in the first hot box. The heating is uneven, and the twist distribution on the filament is uneven. After untwisting, it is easy to form a stiff tight point.

3. Discussion on the cause of stiff filament

The causes of stiff filament are described from the macro indicators above, mainly due to uneven twist transmission. But how do the monofilaments in the multifilament wind together to form stiff filament? When the multifilament is heated and stretched, the monofilament transfers in the radial direction. The wavelength transferred from the monofilament and the spectrogram show that: in the cooling zone, there is generally a peak value. Even if the tension changes, the wavelength transferred does not change significantly; The transfer wavelength decreases with the increase of twist; After passing through the heater, the monofilament transfer is more complicated One, two or even three peaks appear on the transfer wave. At this time, the influence of some unfavorable factors (spinning oil, POY internal quality, post-processing process parameters, etc.) will cause uneven tension and twist of the filament, which will cause uneven distribution of spiral crimp wavelength and wave height on the length of the monofilament, and show some characteristics different from the normal crimp. When the monofilament is heated, untwisted and loosened, the braid and loop are formed with the special point of crimp as the center. The monofilament with coil and braid is mixed with the normal crimped monofilament in the multifilament to form the stiff filament shape as shown in Figure 3. If there are regular special points, regular tight points will be formed, otherwise, stiff filament tight points with different lengths will be formed.

4. Conclusion

1. There are many types of stiff wires in production, and the causes are different. Different measures should be taken for different reasons.

2. In normal production, the main cause of stiff filament is that the filament is affected by uneven twist and tension when it is transferred during heating and stretching deformation, which causes uneven distribution of spiral crimp wavelength and wave height on the length of the filament, and some special points different from the normal crimp appear. When the filament is untwisted and loosened, the braid and coil are formed around the specific point of crimp, and they are intertwined with the normal crimp filament, Form tight points of different lengths.