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2021-04-19
1 Introduction
Polyester woven fabrics are widely used in apparel fabrics for their good dyeing, abrasion resistance and resistance to mold and rot. Polyester fabrics have poor hygroscopicity, are easy to carry static electricity, are prone to pilling and cause poor wearing comfort, and ultimately affect the widespread use of polyester fabrics. It is the most commonly used processing method to improve the performance of polyester woven fabrics through hygroscopic finishing agents. There are three methods for using hygroscopic finishing agents under normal circumstances. The first is the dyeing bathing method, the second is the dyeing and post-impregnation method, and the third is the dyeing and post-impregnation method. This article focuses on the advantages and disadvantages of the above different finishing methods in the processing and the effect on the moisture absorption effect of the polyester woven fabric.
2 process flow
Among the above three methods, different process methods have different process flows. The common process flow is as follows:
1 dyeing bath:
Pre-treatment --- Water --- Feeding --- Dyeing --- Post-processing --- Dehydration --- Open-width --- Stereotype --- Inspection --- Packaging --- Outbound
2 Dye impregnation:
Pre-treatment --- Water --- Feeding --- Dyeing --- Post-processing --- Impregnation --- Dehydration --- Open-width --- Stereotype --- Inspection --- Packaging --- Outbound
3 Dyeing after dyeing
Pre-treatment --- Water --- Feeding --- Dyeing --- Post-processing --- Dehydration --- Open --- Padding --- Stereotype --- Inspection --- Packaging --- Outbound
3 Process Comparison and Discussion
The above three processes are qualitatively identical after the process, and the process prior to the dyeing is not significantly different. Therefore, the focus of the discussion is naturally after dyeing and prior to shaping. In the first process, hygroscopic finishing agent and dyeing are carried out in the same bath, which requires that the moisture absorbing agent not only has high temperature resistance and weak acid resistance, but also has good stability to the anionic surfactant.
3.1 dyeing with bath
The dyeing temperature of the disperse dyestuff is 130°C, and the stability of the moisture-absorbing finish under such moist heat conditions directly affects the finishing effect. At the same time, since the pH of the dyeing solution during the dyeing process is generally weakly acidic, the moisture absorbing agent must have a weak acid stability. Since the disperse dyes are not soluble in water, they are slightly soluble in water under the action of an anionic dispersant. Therefore, in the case where the moisture-absorbing finishing agent is in the same bath as the dyeing liquid, the example of the moisture-absorbing finishing agent cannot be cationic. Can only be non-ionic or anionic. If the cationic hygroscopic finishing agent is likely to react with the anionic dispersant in the dyeing solution at a weak acid condition of 130°C, it finally affects the finishing effect of the hygroscopic finishing agent. Since this method does not require a separate process time, it is time-saving. However, the process conditions are severe, so the stability requirements for the moisture absorption finishing agent are the highest.
High temperature and high pressure jet overflow dyeing machine is the most commonly used polyester dyeing equipment, dye bath ratio is generally 1:10, fabric quality is generally about 320kg. Therefore, the total volume of dyeing solution is about 3000L. Table 1 shows the difference in moisture absorption effect of fabrics with different moisture absorption and finishing agents. In accordance with the FZ/T01071 standard test method to test the height of the liquid climbed on the sample within 30 minutes, you can compare the moisture absorption effect of the fabric. The fabric specification is 33.3tex polyester DTY low stretch plain cloth black cloth. The fabric is only dried after pretreatment, without dyeing and other finishing. Sample size 25mm × 300mm, finishing conditions are as follows: dyeing temperature 130 °C, holding time 60min, fabric dyeing washed to clear. Pre-baking temperature 110 °C, time 120s, baking temperature 170 °C, time 120s, pH value of 5 when dyeing. Table 1 shows the capillary effect of hygroscopic finishing agents on the fabrics of polyester woven fabrics after different moisture consumption.
Table 1: Effect of Different Amounts of Hygroscopic Finishing Agents on Fabric Hairiness
Finishing agent dosage (g/L)
0
1
2
3
4
5
Longitudinal hair height (cm)
4
7.3
10.6
10.7
10.9
11.1
The data in Table 1 shows that the amount of 2g/L or more and 4g/L or less can make the finishing effect of the dyeing bath method reach an ideal hygroscopic finishing effect.
3.2 Dyeing after dyeing
The impregnation process conditions for dyeing are generally dehydration after approximately 30 minutes of rope running in the dyeing tank at room temperature. The process conditions are moderated, so the requirements for the stability of moisture absorbing finishes are lower. However, this method consumes process time and affects the production efficiency. If dyeing is performed in the dyeing tank by impregnation after per-cylinder dyeing, it takes about 30 minutes longer and the amount of water is larger. If the impregnation method is applied to the fabric of each cylinder by using a fixed dyeing machine alone, the water can be saved and the moisture absorbing agent can be saved. However, the time for the fabric to be taken out and put into the cylinder can also affect the production efficiency. If there are many equipments in the dyeing factory and the production task is not particularly busy, the stability of the hygroscopic finishing agent can not meet the basic requirements of the dyeing bathing method, then the polyester woven fabrics can be hygroscopically finished by the dyeing impregnation method. The use of the impregnation method for hygroscopic finishing requires that the fabric be dehydrated without taking too long, so that the moisture-absorbing finish removes more moisture-absorbing finish from the surface of the fabric as the centrifugal dewatering method leaves too much moisture, and finally affects the hygroscopic finishing effect. Therefore, due to the fact that the fabric is in the final shape, there is a need to properly reduce the final speed of the car due to the fact that there is a lot of water. Table 2 shows the effects of different impregnation methods on the water absorption properties of fabrics. The fabric size and sample size are the same as in Table 1. The immersion time was 30 minutes, the immersion temperature was 40°C, and the working fluid had a pH of 5.
Table 2: Effect of Different Dosages of Soaking Finishing Agent on Fabric Hairiness
Finishing agent dosage (g/L)
0
1
2
3
4
5
Longitudinal hair height (cm)
4
6.1
9.3
9.6
9.7
9.9
The data in Table 2 shows that the amount of moisture absorbing finishing agent used for the impregnation method is between 2g/L and 4g/L, which can give the fabric a significant moisture absorption effect.
3.3 Dyeing after dyeing
Dyeing and padding method is the most commonly used finishing method, continuous production, high production efficiency, saving water, saving finishing agent, convenient control of process conditions, high temperature stability requirements for moisture absorbing finishing agent. Any hygroscopic finishing agent that satisfies the requirement of dyeing and bathing can meet the basic requirements of dyeing after padding. If there is less water on the fabric prior to finishing the fabric, more finishing fluid will be absorbed when the hygroscopic finish is added. The effect of finishing will be more obvious. However, the excessive adsorption of the finishing agent tends to cause uneven finishing effects. This requires special attention during processing.
The optimum amount of hygroscopic finishing agent is discussed based on the speed of water absorption after fabric finishing. The rate of water absorption was measured as follows: A drop of water was placed on the fabric using a pipette and the time required for the water to completely spread out was measured. The fabric specifications are the same as in Table 1, and the sample size is 10cm x 10cm. Test conditions: one dip and one roll, rolling point pressure 0.32MPa, pre-baking temperature 110°C, time 120s; baking temperature 170°C, time 120s, working fluid pH value 5. Table 3 shows the changes in the water absorption time for different dosage finishes.
Table 3: Effect of Moisture Absorbent Finishing Agent on the Water Absorption Rate of Fabrics
Finishing agent dosage (g/L)
0
1
2
4
8
16
Fabric water absorption speed (s)
14
4
2
1
0
0
Finishing agent dosage (g/L)
3
5
6
7
9
10
Fabric water absorption speed (s)
2
1
0
0
0
0
Because the process conditions of the dyeing and bathing process are relatively violent and the process time is the longest, special attention should be paid to the chemical material process and the material-drawing process when the moisture-absorbing agent is used. It is better not to directly pour the dyeing acid into the finishing agent barrel to finish the process. The agent should be added separately from the disperse dye into the dyeing tank. What kind of process method and process is chosen is not only related to the basic properties of the hygroscopic finishing agent, but also related to the processing of the fabric and the specifications of the fabric.
The more polar the active groups of the finishing agents, the more pronounced the effect of moisture absorption. At the same time, in order to maintain the durability of the finishing effect, the molecules of the finishing agent must have groups that are relatively tightly bound to the macromolecules of the polyester. Therefore, the molecular weight of the polyester hygroscopic finishing agent must be composed of two parts, one is a hydrophilic group and the other is a hydrophobic group. The hydrophilic group ensures the hydrophilic properties of the finishing agent, and the hydrophobic group ensures the close combination of the finishing agent and the polyester macromolecule. Because the polyester molecule is hydrophobic, the structure of the hydrophobic group molecular chain segment in the polyester hygroscopic finishing agent can be similar to the structure of the polyester molecule according to the similar compatibility principle. The extent of the combination of the segment and the polyester macromolecular structure is The more closely. Because the backbone of the polyester macromolecular structure is p-xylylene glycol, a structure similar to this must be an aromatic ring segment. In summary, finishing agents with both hydrophilic and lyophilic groups can have good hygroscopic finishing effects on polyester fabrics. The effect of reducing and washing with disperse dyes and dyeing polyester on the moisture absorption finishing effect of the same bath method is negligible.
4 Discussion
Dyeing and finishing process conditions mainly include process formulation, process temperature, process time and pH. In this paper, the hygroscopic finishing agent Liweilong-N produced by Hangzhou Meigaohua Chemical Co., Ltd. is taken as an example to discuss the effect of process conditions on the effect of moisture absorption and finishing of polyester woven fabrics. In the discussion process, the changes in the hygroscopicity of the fabrics before and after comparison and finishing were the main factors, and the influence of certain factors in the actual production on the finishing effect was discussed.
4.1 Li Weilong-N Introduction
The hygroscopic finishing agent Liweilong-N is a non-ionic high-molecular polymer with white or light yellow emulsion and is easily soluble in water. The pH value of 10% aqueous solution is between 5 and 7, which is from the date of shipment. Closed containers and room temperature can be stored for 6 months. The size of the package must not only take into account the amount of dyeing plant, but also consider the convenience of loading and unloading.
With the naked eye, it is necessary to change the test method when it is determined that the speed of absorption of the fabric after a certain amount of moisture absorption is adjusted. The optimum amount of finishing agent can be determined by measuring the diffusion diameter of water droplets on the surface of the dripping fabric after finishing. Table 4 shows the variation in the diffusion diameter of water droplets on the surface of the fabric at different dosages of the hygroscopic finishing agent. Fabric specifications, sample size, and sample conditions are in Table 3. The dripping height of the burette was 2 cm, one drop of water droplet was dropped each time, and the data was measured after 30 s.
Table 4: Effect of the amount of hygroscopic finishing agent on the diffusion diameter of water droplets on the fabric surface
Finishing agent dosage (g/L)
0
5
6
7
8
9
10
20
Water droplet diffusion diameter (cm)
0.9
4.6
4.8
4.9
5.1
5.2
5.3
5.6
Based on the data in Table 3 in Table 3, the most commonly used padding method for hygroscopic finishing after the test agent exceeds 10 g/L, the moisture absorption effect is not significantly increased; the moisture absorbing agent dosage is less than 5 g/L, and the moisture absorption effect is not obvious.
4.2 Pad Milling Process
The padding process is the key stage for fabrics to absorb the finishing agent before entering the setting machine. The factors that can affect the hygroscopic finishing effect are the following: the leveling of the fabric, the degree of weft, the pressure of the nip, the level of the rolling mill, and the finishing agent And feeding, liquid level control and so on.
The degree of flatness of the fabric prior to the hygroscopic finishing mainly depends on the tension bar of the setting machine head and the wrap angle of various guide rollers and fabrics. The larger the wrap angle, the greater the friction, the greater the tension, and the more obvious the flatness of the fabric surface. If the fabric is not even, it will affect the uniformity of the padding when it passes through the rolling mill, thereby affecting the effect of moisture absorption and finishing. Whether the fabric has hysteresis or whether the weft angle exceeds the standard after the hygroscopic finishing is mainly related to whether the fabric joint is flush or not, and the method of sewing the head after tearing the head is effective. It is the best way to reduce the weft of the fabric by passing the fabric through the electro-optic weft-setting device before setting it after padding.
The smoothness and smoothness of the surface of the Rubber Roller of the rolling mill have a great influence on the moisture absorption and finishing of the fabric. If the surface of the rubber roller is cracked or uneven, or if it wears out after a long period of use, it is necessary to perform necessary maintenance on the rubber roller. Using a feeler gauge to check the gap width between two rubber rollers at both ends of the roller is the key to ensure the level of the roller. If necessary, the homogeneity of the two rubber roller press fabrics can be checked by rolling the carbon paper in the newspaper. The size of the nip pressure selected during hygroscopic finishing is mainly related to the performance of the rolling mill. The greater the pressure applied at both ends, the greater the pressure at the nip, and the more pronounced the elastic deformation of the entire roll. The long-term accumulation of this elastic deformation will destroy the horizontal flatness of the rubber roller core. Thickness of the rubber layer also has a significant effect on the uniformity of the rolling mill. When the thickness of the rubber is thin, the rubber roller of the rolling mill should be replaced in time. Table 5 shows the influence of the change of the nip pressure on the hygroscopic effect during the padding method. The fabric specifications are the same as in Table 1, the finishing agent dosage is 5g/L, and the sample size is 10cm x 10cm. Pre-baking temperature 110 °C, time 120s; baking temperature 170 °C, time 120s.
Table 5: Effect of Different Rolling Point Pressure on Finishing Effect
Rolling point pressure (MPa)
0.15
0.2
0.25
0.3
0.35
0.4
0.45
Longitudinal hair height (cm)
11.4
10.1
9.9
9.8
9.8
9.7
9.6
Rolling point pressure is too large, the fabric hair efficiency declines. When the nip pressure is too small, the fabric's effect increases. However, the rolling point rolling pressure is too large and the deformation of the rolling mill is significant, which affects the service life of the rolling mill. If the nip pressure is too small and the fabric is too much water, the liquid level in the holding tank will fall too fast, affecting the uniformity of the fabric finishing, increasing the drying pressure of the setting machine, causing the vehicle speed to decrease and the production efficiency to decline. The data in Table 5 shows that the rolling point pressure is between 0.2 MPa and 0.4 MPa, which can guarantee the good moisture absorption and finishing effect of the fabric.
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