Cationic pretreating agent and application thereof in pad dyeing process of cotton fabric

Abstract

The invention discloses a cationic pretreating agent and application thereof in a pad dyeing process of cotton fabrics. The cationic pretreating agent is prepared from the following components in percentage by mass: 1-10wt% of a cationic modifier; 0.1-1 wt% of an alkaline agent; and the balance of ultrapure water. The method comprises the following steps: (1) washing the cotton fabric with ultrapure water, and drying; (2) padding a cationic pretreatment agent; (3) baking at 100 DEG C for 2-6 minutes; (4) dyeing: performing pad dyeing on the pretreated cotton fabric with an active dye; (5) color fixation: directly putting the cotton fabric into a steamer at 100 DEG C for steaming and color fixation for 8-12 minutes without drying the cotton fabric; (6) washing: washing the cotton fabric subjected to color fixation for multiple times; and (7) drying. According to the invention, a limited amount of cationic modifier is utilized, and through the synergistic effect of the cationic modifier and sodium carbonate, the problems of large use amount of salt and alkali auxiliaries, much wastewater, low dye uptake and non-ideal fixation rate in the cotton fabric dyeing process in the prior art are fundamentally solved, and the color performance of the dyed fabric is improved; and the vacancy of a multi-factor interaction mechanism in the prior art is filled.

Description

Technical Field

[0001] The present invention belongs to the technical field of textile dyeing and finishing, and particularly relates to a cationic pretreatment agent and its application in the pad dyeing process of cotton fabrics. Background Art

[0002] Reactive dyes, also known as reactive dyes, are one of the most important dyes for the dyeing and finishing of cellulose fibers. They have one or more reactive groups in their molecular structure and can chemically react with fibers to form covalent bonds under appropriate conditions. Reactive dyes are suitable for the dyeing of cellulose fibers, protein fibers, and polyamide fibers, and have excellent wet fastness and leveling property, as well as bright colors and a complete color spectrum. When reactive dyes are used for dyeing, a large amount of salt and alkali auxiliaries are often used to improve the affinity of the dyes for cotton fabrics, as well as the dye uptake rate and fixation rate. The addition of salt and alkali auxiliaries not only increases the production cost, but also causes blockage of the channels due to caking in the dyeing equipment. Moreover, after dyeing, the high-concentration neutral salts remaining in the dyeing wastewater are difficult to remove, and will cause environmental problems such as water body salinization and soil compaction after discharge. Therefore, the development of new low-salt or salt-free dyeing methods and processes for reactive dyes is of great significance for achieving the industry development goals of energy conservation, emission reduction, ecological protection.

[0003] In view of the above problems, the existing technology mainly reduces the use of inorganic salts by cationic modification of cotton fabrics. The cationic modification process provides a new idea for improving the dye adsorption efficiency through the principle of charge neutralization. This technology reverses the surface potential of the fiber by introducing positively charged groups (such as quaternary ammonium groups) onto the surface of cotton fabrics, significantly reducing the electrostatic repulsion between the dyes and the fibers, and even forming electrostatic attraction, so as to achieve the purpose of reducing the amount of salt and alkali and improving the dye uptake rate, which is conducive to the development of the printing and dyeing industry towards the direction of green environmental protection and sustainability. However, in the existing technology, it is difficult to achieve extremely excellent dye uptake rate and fixation effect only by cationic modification.

[0004] Existing research has confirmed that modifiers such as quaternary ammonium salts (such as CHPTAC) and polyelectrolytes (such as PDADMAC) can effectively enhance the adsorption ability of reactive dyes. For example, the team of Dong Xia from Donghua University increased the dye uptake rate of reactive dyes to 95% and reduced the salt dosage by 88.8% through TEMPO oxidation pretreatment combined with PDADMAC modification. Although this patented technology improves the dye uptake rate and fixation rate of dyes, a certain amount of salt is still required to participate, and in addition to adding cationic modifiers, 2,2,6,6-tetramethylpiperidine oxide, sodium bromide, oxidants and other auxiliaries are also added. The dosage of auxiliaries is not low, and the cotton fabrics also need to be pretreated by TEMPO oxidation in advance. It can be seen that the overall dyeing process is still relatively complex and the cost is still relatively high.

[0005] In summary, how to effectively improve the dye uptake rate and fixation rate of cotton fabric dyeing, reduce production costs, while greatly shortening the process flow and improving production efficiency on the premise of reducing the dosage of auxiliaries has become a difficult problem that technicians in the field of cotton fabric dyeing urgently need to solve. Summary of the Invention

[0006] Aiming at the deficiencies of the existing technology, the technical problem to be solved by the present invention is to provide a cationic pretreatment agent that can effectively improve the dye uptake rate and fixation rate of cotton fabric dyeing, reduce production costs, while greatly shortening the process flow and improving production efficiency on the premise of reducing the dosage of auxiliaries, and its application in the pad dyeing process of cotton fabric.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is: A cationic pretreatment agent is composed of the following components in mass fraction:

[0008] Cationic modifier 1-10wt%;

[0009] Alkali agent 0.1-1wt%;

[0010] Ultra-pure water balance.

[0011] The above cationic pretreatment agent is composed of the following components in mass fraction: cationic modifier 5wt%, alkali agent 0.5wt%, and the balance is ultra-pure water.

[0012] In the above cationic pretreatment agent, the cationic modifier is poly(dimethyldiallylammonium chloride), and the alkali agent is any one of sodium carbonate, sodium silicate, and sodium phosphate.

[0013] The preparation method of the above cationic pretreatment agent includes the following steps:

[0014] (1) At room temperature, weigh a certain amount of poly(dimethyldiallylammonium chloride) aqueous solution and place it in a container, add a certain amount of ultra-pure water, and stir for 30 min to prepare a pretreatment agent aqueous solution with a concentration of 1-10wt%;

[0015] (2) At room temperature, weigh a certain amount of Na 2 CO 3 and add it to the pretreatment agent aqueous solution prepared in step (1), stir for 30 min, and prepare a cationic pretreatment agent with a concentration of poly(dimethyldiallylammonium chloride) of 1-10wt% and a concentration of Na 2 CO 3 of 0.1%-1wt%.

[0016] In the above cationic pretreatment agent, in step (1), the concentration of the weighed poly(dimethyldiallylammonium chloride) aqueous solution is 35wt%.

[0017] Application of a cationic pretreatment agent in the pad dyeing process of cotton fabrics, comprising the following steps:

[0018] I. Pretreatment of cotton fabrics:

[0019] (1), At room temperature, rinse the impurities on the surface of the cotton fabric with ultrapure water, and put it into a blast drying oven to dry;

[0020] (2), Pad the cotton fabric with the cationic pretreatment agent according to any one of claims 1-3, dip and pad twice, and the liquor pickup rate is 65%-70%;

[0021] (3), After padding, bake the cotton fabric at 100°C for 2-6 min;

[0022] II. Dyeing of cotton fabrics:

[0023] (4), Dyeing: Pad-dye the pretreated cotton fabric with reactive dyes, dip and pad twice, and the liquor pickup rate is 65%-70%;

[0024] (5), Fixing: Put the cotton fabric directly into a 100°C steamer without drying and steam-fix for 8-12 min;

[0025] (6), Washing: Wash the cotton fabric after fixing multiple times;

[0026] (7), Drying: Dry the washed cotton fabric.

[0027] In the application of the above-mentioned cationic pretreatment agent in the pad dyeing process of cotton fabrics, in step (3), after padding, bake the cotton fabric at 100°C for 3 min.

[0028] In the application of the above-mentioned cationic pretreatment agent in the pad dyeing process of cotton fabrics, in step (4), the reactive dye is any one of RB49, RY95, RR218, and RB5.

[0029] In the application of the above-mentioned cationic pretreatment agent in the pad dyeing process of cotton fabrics, in step (5), the steam-fixing time is 10 min.

[0030] In the application of the above-mentioned cationic pretreatment agent in the pad dyeing process of cotton fabrics, in step (6), first wash with cold water for 2 min, then wash with hot water for 2 min, wash with 2 g / L soap solution for 2 min, and finally wash with cold water for 2 min.

[0031] The advantages of the cationic pretreatment agent of the present invention and its application in the pad dyeing process of cotton fabrics are as follows: By using polydimethyldiallylammonium chloride (PDADMAC) to carry out cationic modification on cotton fabrics, the problems of low dye uptake rate and wastewater pollution caused by electrostatic repulsion in reactive dyeing are effectively solved. First, after pretreatment with PDADMAC, the surface potential of cotton fibers is significantly reversed, and the combination of dyes and fibers is enhanced through electrostatic adsorption. Second, the synergistic effect of PDADMAC-Na 2 CO 3 optimizes the alkaline reaction environment and promotes dye fixation, and the K / S value of RR218 increases by 50% (reaching 5.25). Third, the steaming and fixing process further strengthens the covalent bond between dyes and fibers, enhances the apparent color depth of the fabric, and improves the dye uptake rate. Compared with the traditional process, the present invention greatly reduces the usage of salt and alkali, and significantly reduces the wastewater pollution load. The present invention provides a green process scheme with high fixation rate and low environmental load for the reactive dyeing of cotton fabrics, and has significant potential for industrial application. Description of the Drawings

[0032] Figure 1 It is a mechanism diagram of the process of modifying cotton fabrics with the cationic pretreatment agent of the present invention;

[0033] Figure 2 It is a test diagram of the solid Zeta potential on the surface of pretreated cotton fabrics before and after adding Na 2 CO 3 under different concentrations of PDADMAC;

[0034] Figure 3 It is a comparative Fourier transform infrared spectroscopy diagram of fabrics treated with different contents of PDADMAC;

[0035] Figure 4 It is a comparison diagram of dyed fabrics with different contents of PDADMAC;

[0036] Figure 5 It is a super-depth-of-field comparison diagram of dyed fabrics with different contents of PDADMAC;

[0037] Figure 6 It is a K / S comparison diagram of dyed fabrics with different contents of PDADMAC;

[0038] Figure 7 It is a comparison diagram of dyed fabrics with different contents of PDADMAC after adding Na 2 CO 3 ;

[0039] Figure 8 It is a super-depth-of-field comparison diagram of dyed fabrics with different contents of PDADMAC after adding Na 2 CO 3 ;

[0040] Figure 9 For adding Na 2 CO 3 After that, the K / S comparison diagram of dyed fabrics with different contents of PDADMAC;

[0041] Figure 10 For adding Na 2 CO 3 Before and after adding, the KS comparison diagram of dyed fabrics with different contents of PDADMAC;

[0042] Figure 11 The K / S value comparison diagram of fabric samples with different fixing methods; Specific implementation mode

[0043] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0044] In the present invention, unless otherwise stated, the orientation terms such as "upper" and "lower" usually refer to the upper and lower in the actual use or working state of the device, specifically the drawing direction in the accompanying drawings; while "inner" and "outer" refer to the contour of the device. In addition, in the description of the present application, the term "comprising" means "including but not limited to". The terms first, second, third, etc. are only used as labels and do not impose numerical requirements or establish an order. The term "a plurality" means "two or more".

[0045] A cationic pretreatment agent is composed of the following components in mass fractions: 1-10 wt% of a cationic modifier; 0.1-1 wt% of an alkali agent; and the balance of ultrapure water. Among them, the cationic modifier is poly(dimethyldiallylammonium chloride), and the alkali agent is any one of sodium carbonate, sodium silicate, and sodium phosphate.

[0046] The preparation method of the cationic pretreatment agent of the present invention includes the following steps:

[0047] (1) At room temperature, weigh a certain amount of an aqueous solution of poly(dimethyldiallylammonium chloride) with a concentration of 35 wt% and place it in a container, add a certain amount of ultrapure water, and stir for 30 min to prepare a pretreatment agent aqueous solution with a concentration of 1-10 wt%;

[0048] (2) At room temperature, weigh a certain amount of Na 2 CO 3 And add it to the pretreatment agent aqueous solution prepared in step (1), stir for 30 min, and prepare a cationic pretreatment agent with a concentration of poly(dimethyldiallylammonium chloride) of 1-10 wt% and a concentration of Na 2 CO 3 Of 0.1%-1 wt%.

[0049] Application of a cationic pretreatment agent in the pad dyeing process of cotton fabrics, comprising the following steps:

[0050] I. Pretreatment of cotton fabrics:

[0051] (1) At room temperature, rinse the impurities on the surface of the cotton fabric with ultrapure water and put it into a blast drying oven for drying;

[0052] (2) Pad the cotton fabric with the cationic pretreatment agent described in any one of claims 1-3, dip and pad twice, and the liquor ratio is 65%-70%;

[0053] (3) After padding, bake the cotton fabric at 100°C for 2-6 minutes;

[0054] II. Dyeing of cotton fabrics:

[0055] (4) Dyeing: Pad-dye the pretreated cotton fabric with reactive dyes, dip and pad twice, and the liquor ratio is 65%-70%;

[0056] (5) Fixing: Put the cotton fabric directly into a 100°C steamer for steaming and fixing for 8-12 minutes without drying;

[0057] (6) Washing: Wash the fixed cotton fabric several times;

[0058] (7) Drying: Put the washed cotton fabric into a blast drying oven and dry it at 60°C.

[0059] Among them, the reactive dye can be any one of RB49, RY95, RR218, and RB5. In step (6), first wash with cold water for 2 minutes, then wash with hot water for 2 minutes, wash with 2 g / L soap solution for 2 minutes, and finally wash with cold water for 2 minutes.

[0060] As Figure 1 shown, in the PDADMAC-Na 2 CO 3 synergistic modification system for cotton fabric dyeing, the mechanisms of the dyeing and fixing stages are as follows:

[0061] As is well known, the basic principle of reactive dyeing of cotton fabrics mainly includes three processes: dye adsorption, diffusion, and fixation. Reactive dyes are adsorbed from the dye liquor onto the fiber, uniformly diffuse on the fiber, and finally chemically react with the fiber to form covalent bonds, thus achieving dyeing. Adsorption process: Reactive dyes are first adsorbed onto the fiber surface during the dyeing process. The adsorption process depends on the interaction forces between the dye and the fiber, including van der Waals forces, hydrogen bonds, and electrostatic attraction, etc. Diffusion process: The dye adsorbed on the fiber surface further diffuses into the fiber interior. Fixation process: When the dye reaches a saturated state in the fiber interior, the fixation process begins. Fixation is achieved by the chemical reaction between the dye and the fiber to form covalent bonds, thereby firmly fixing the dye on the fiber.

[0062] Currently, in order to improve the dye uptake rate of reactive dyes on the surface of cotton fabrics, in the field of reactive dyeing of cotton fabrics, the conventional practice is to utilize the principle of charge neutralization. By introducing a positively charged group (such as a quaternary ammonium group) onto the surface of the cotton fabric, the surface potential of the fiber is reversed, significantly reducing the electrostatic repulsion between the dye and the fiber, and even forming electrostatic attraction, so as to achieve the purpose of reducing the usage of salts and alkalis and enhancing the dye uptake rate.

[0063] However, relying solely on cationic modifiers cannot further improve the dye uptake rate. This is because although the quaternary ammonium salt group undergoes hydrolysis reaction in water, generating positively charged quaternary ammonium ions and anionic parts, the quaternary ammonium ions adsorb and covalently bond with the cellulose negative ions (-O-), which can neutralize the negative charges on the fiber surface and reduce the repulsion between dye ions and the fiber. However, the ionization of the quaternary ammonium salt group in water is reversible. Part of the quaternary ammonium salt will ionize into quaternary ammonium ions and anions, but at the same time, it will also recombine into quaternary ammonium salt molecules, so it cannot be completely ionized. This also leads to a limited state of fiber surface potential reversal and cannot neutralize the charges on the fiber surface to the greatest extent. The electrostatic repulsion between dye ions and the fiber surface still affects the further adsorption of the dye.

[0064] Moreover, although cationic modifiers can reduce the usage of salts and alkalis during the dyeing process and promote the improvement of the dye uptake rate to a certain extent, if too much cationic modifier is added, the excessive cationic modifier will significantly increase the density of cationic groups on the surface of cotton fibers, resulting in too fast an electrostatic binding rate between the dye and the fiber. At this time, dye molecules rapidly accumulate on the fiber surface, but the internal diffusion and penetration ability are insufficient, forming a "ring dyeing" phenomenon where the surface is dyed too deeply while the inside is not penetrated. High-concentration modifiers will also cause excessive swelling of cotton fibers, resulting in a significant difference in the penetration rate of the dye in different regions, which is instead not conducive to level dyeing. For example, the difference in the modification degree between the crystalline region and the non-crystalline region of the fiber will exacerbate the uneven distribution of the dye. At the same time, since the binding between cationic dyes and fibers is mainly based on strong ionic bonds, excessive modifiers will further strengthen this binding force. Once the dye molecules are fixed, even if the dyeing time is extended or the temperature is increased, it is difficult to achieve level dyeing through dye migration. Too many modifiers will hinder the effective binding between the dye and the fiber, resulting in a decrease in the dye uptake rate. That is to say, increasing the dosage of cationic modifiers cannot fundamentally solve the problem of low dye uptake rate, and uneven dyeing will also occur.

[0065] Poly(dimethyldiallylammonium chloride) (PDADMAC) is a cationic polymer. Quaternary ammonium salt groups are carried on its molecular chain. After these groups are ionized in water, quaternary ammonium ions and chloride ions with positive charges are released. Sodium carbonate is an alkaline substance, which ionizes in water to generate carbonate ions and sodium ions. The addition of sodium carbonate will significantly increase the pH value of the solution, making the hydroxyl groups on the surface of cotton fibers more easily ionized, generating more negative charges, thus increasing the charge density on the surface of cotton fibers. The alkaline environment of sodium carbonate converts some of the quaternary ammonium groups in PDADMAC into quaternary ammonium bases, resulting in a decrease in the positive charge density in the solution. On the other hand, the alkaline environment provided by sodium carbonate increases the negative charge density on the surface of cotton fibers, further weakening the positive charge effect of PDADMAC. These factors together lead to a decrease in the surface potential of the fabric.

[0066] Among them, the principle of the conversion of quaternary ammonium salt into quaternary ammonium base is as follows:

[0067] Hydrolysis of sodium carbonate:

[0068] Na 2 CO 3 +H 2 O→Na + +HCO 3 - +OH -

[0069] As a strong base and weak acid salt, sodium carbonate reacts preferentially with water to generate bicarbonate (HCO 3 - ) and hydroxide (OH - ), releasing a large amount of OH- , making the solution strongly alkaline (pH increases). (The generated carbonate ions can also undergo weak hydrolysis. Since its hydrolysis effect is small and has little impact on the experimental results, this step is ignored.)

[0070] Quaternary ammonium salt is converted into quaternary ammonium base:

[0071] R-N + (CH 3 ) 3 Cl - +OH - →R-N + (CH 3 ) 3 OH - +Cl -

[0072] In the alkaline environment provided by sodium carbonate, the quaternary ammonium salt group (in the form of chloride) in PDADMAC undergoes an ion exchange reaction with OH - .

[0073] Although the surface potential of the fabric decreases, it does not affect the dye uptake rate of the reactive dyes of the present invention. Because the formation of quaternary ammonium base increases the adsorption amount of reactive dyes on the fiber surface from another perspective, and the synergistic effect between the two improves the dye uptake rate because quaternary ammonium base can be completely ionized in water. Quaternary ammonium base is an ionic compound. The quaternary ammonium base molecule is composed of a quaternary ammonium cation (R 4 N + ) and a hydroxide ion (OH - ) bonded by an ionic bond. When it dissolves in water, it will undergo 100% ionization to form a positively charged quaternary ammonium ion and a hydroxide ion. This ionization process makes quaternary ammonium base have weak alkalinity.

[0074] The ionization process of quaternary ammonium base can be expressed as: R 4 N + OH - →R 4 N + +OH - . This ionization process makes quaternary ammonium base show alkalinity in water, although its molecular structure contains a positively charged quaternary ammonium ion.

[0075] That is to say, in the co-modification system of the present invention, in an alkaline environment, part of the quaternary ammonium salt groups can be converted into quaternary ammonium hydroxides that can be 100% ionized. At this time, the quaternary ammonium ions formed by the ionization of quaternary ammonium hydroxide can further combine with dye ions through ionic bonds. And due to the addition of sodium carbonate, the negative charge density on the surface of cotton fibers is increased, so more binding sites are provided for the positively charged quaternary ammonium ions ionized from quaternary ammonium hydroxide. At this time, the further adsorption of dye ions is achieved, and covalent bonds are firmly combined to improve the dye uptake rate. The quaternary ammonium hydroxide generated by the transformation of the present invention has weaker cationicity than the quaternary ammonium salt. When it further combines with dye ions and adsorbs onto the fiber surface, it adsorbs more uniformly on the fiber surface and is more likely to penetrate into the fiber interior, improving the dye penetration rate. Therefore, while improving the dye uptake rate, it is also more conducive to level dyeing. And compared with cationic modifiers with stronger cationicity, quaternary ammonium hydroxide can significantly reduce the hydrolysis phenomenon of dyes, enabling more unhydrolyzed dyes to combine with quaternary ammonium hydroxide, thus improving the dye uptake rate. This also solves the problem that the traditional method of only adding cationic modifiers cannot further improve the dye uptake rate.

[0076] During the fixation process, due to the stronger penetration of quaternary ammonium hydroxide, the penetration of the fabric sample is also enhanced. A higher penetration rate allows more dye molecules to enter the fabric interior, thereby increasing the depth and saturation of the dyeing. The dyes penetrate thoroughly and bind tightly to the fibers, which helps to improve the fastness of the dyeing and reduce the possibility of dye shedding. Therefore, in the steam fixation process, the covalent bond between the dye and the fiber is further strengthened, promoting dye fixation and enhancing the apparent color depth of the fabric.

[0077] The present invention pre-treats cotton fabrics by padding with a cationic pretreatment agent and then pads with reactive dyes for dyeing. The cationic pretreatment agent has an alkaline environment. While the quaternary ammonium salt groups ionize to release positively charged quaternary ammonium ions, quaternary ammonium hydroxide is also generated simultaneously, further ionizing to produce quaternary ammonium ions and simultaneously increasing the pH of the pretreatment agent. Through this PDADMAC-Na 2 CO 3 co-modification effect, when the cationic pretreatment agent contacts (pads) the cotton fibers, the alkaline environment makes the hydroxyl groups on the surface of the cotton fibers more likely to ionize, generating more negative charges, thus rapidly increasing the charge density on the surface of the cotton fibers. At this time, a large number of quaternary ammonium ions are quickly adsorbed and combined with the hydroxyl groups through ionic bonds. After all preparations are completed, reactive dyes are padded. The dye ions can quickly combine with the quaternary ammonium ions through ionic bonds in the shortest time, and at the same time, part of the dye ions are adsorbed onto the fiber surface under the action of electrostatic attraction.

[0078] That is to say, before padding with reactive dyes, the present invention has created an optimal environment for the adsorption of reactive dyes. Therefore, when the reactive dyes come into contact with the fibers during dyeing, they can quickly bind to the fiber surface and rapidly penetrate into the fibers. Compared with adding alkali agents during traditional dyeing, the adsorption efficiency and adsorption amount of the dyes are improved, the dye uptake rate is increased, and the dyeing process is shortened. At the same time, compared with the traditional method of pre-mixing a modifier, alkali liquor, and reactive dyes, the present invention shortens the mixing time of reactive dyes in an alkaline environment. The rapid dyeing process also reduces the probability of side reactions such as hydrolysis of dye reactive groups in an alkaline environment, generating hydrolyzed dyes (which cannot bind to fibers) and resulting in a decrease in the fixation rate.

[0079] This is also the important reason why, compared with adding cationic modifiers or a large amount of saline-alkali auxiliaries in the traditional cotton fabric dyeing process, adding a small amount of Na 2 CO 3 to form a synergistic modification system with PDADMAC can significantly improve the dye uptake rate and fixation rate of cotton fabrics.

[0080] The following specific examples are used to specifically illustrate the present application. The following examples are only partial examples of the present application and do not limit the present application.

[0081] Example 1

[0082] A cationic pretreatment agent is composed of the following components by mass fraction: polydimethyldiallylammonium chloride 1 wt%; sodium carbonate 0.1 wt%; the balance is ultrapure water. Its preparation method includes the following steps:

[0083] (1), At room temperature, weigh 2.86 g of an aqueous solution of polydimethyldiallylammonium chloride with a concentration of 35 wt% and place it in a container. Add a certain amount of ultrapure water to prepare a 100 g solution, and stir for 30 min to prepare a pretreatment agent aqueous solution with a concentration of 1 wt%.

[0084] (2), At room temperature, weigh a certain amount of the pretreatment agent aqueous solution prepared in step (1) and set it aside.

[0085] (3), Weigh 0.1 g of Na 2 CO 3 and add it to the pretreatment agent aqueous solution prepared in step (1) to prepare a 100 g solution, and stir for 30 min to prepare a cationic pretreatment agent with a polydimethyldiallylammonium chloride concentration of 1 wt% and a Na 2 CO 3 concentration of 0.1 wt%.

[0086] The application of the cationic pretreatment agent of the present invention in the pad dyeing process of cotton fabrics includes the following steps:

[0087] I. Pretreatment of cotton fabric:

[0088] (1) At room temperature, rinse the impurities on the surface of the cotton fabric with ultrapure water, and then put it into a blast drying oven to dry.

[0089] (2) Immerse and pad the cotton fabric with a cationic pretreatment agent, two dips and two pads, and the liquor pickup is 65%.

[0090] (3) After padding, bake the cotton fabric at 100 °C for 2 min.

[0091] II. Dyeing of cotton fabric:

[0092] (4) Dyeing: Pad-dye the pretreated cotton fabric with reactive dye RB49, two dips and two pads, and the liquor pickup is 65%.

[0093] (5) Fixing: Put the cotton fabric directly into a 100 °C steaming pot without drying for 8 min for steaming and fixing.

[0094] (6) Washing: First wash the fixed cotton fabric with cold water for 2 min, then wash it with hot water for 2 min, wash it with 2 g / L soap solution for 2 min, and finally wash it with cold water for 2 min.

[0095] (7) Drying: Put the washed cotton fabric into a blast drying oven and dry it at 60 °C.

[0096] Example 2

[0097] A cationic pretreatment agent is composed of the following components by mass fraction: polydimethyldiallylammonium chloride 3 wt%; sodium carbonate 0.5 wt%; the balance is ultrapure water. Its preparation method includes the following steps:

[0098] (1) At room temperature, weigh 8.58 g of an aqueous solution of polydimethyldiallylammonium chloride with a concentration of 35 wt% and place it in a container, add a certain amount of ultrapure water to prepare a 100 g solution, stir for 30 min to prepare an aqueous pretreatment agent solution with a concentration of 3 wt%.

[0099] (2) At room temperature, weigh a certain amount of the pretreatment agent aqueous solution prepared in step (1) for standby.

[0100] (3) Weigh 0.1 g of Na 2 CO 3 and add it to the pretreatment agent aqueous solution prepared in step (1) to prepare a 100 g solution, stir for 30 min to prepare a cationic pretreatment agent with a polydimethyldiallylammonium chloride concentration of 3 wt% and a Na 2 CO 3 concentration of 0.1 wt%.

[0101] Application of the cationic pretreatment agent in the pad dyeing process of cotton fabrics, comprising the following steps:

[0102] I. Pretreatment of cotton fabrics:

[0103] (1) At room temperature, rinse the impurities on the surface of the cotton fabric with ultrapure water, and put it into a blast drying oven to dry.

[0104] (2) Pad the cotton fabric with the cationic pretreatment agent, two-bath two-padding, and the liquor ratio is 68%.

[0105] (3) After padding, bake the cotton fabric at 100 °C for 2 min.

[0106] II. Dyeing of cotton fabrics:

[0107] (4) Dyeing: Pad the pretreated cotton fabric with the reactive dye RY95, two-bath two-padding, and the liquor ratio is 68%.

[0108] (5) Fixing: Put the cotton fabric directly into a 100 °C steamer without drying and steam-fix for 10 min.

[0109] (6) Washing: First wash the fixed cotton fabric with cold water for 2 min, then wash it with hot water for 2 min, wash it with a 2 g / L soap solution for 2 min, and finally wash it with cold water for 2 min.

[0110] (7) Drying: Put the washed cotton fabric into a blast drying oven and dry it at 60 °C.

[0111] Example 3

[0112] A cationic pretreatment agent, composed of the following components by mass fraction: 5 wt% of polydimethyldiallylammonium chloride; 0.5 wt% of sodium carbonate; the balance is ultrapure water. Its preparation method includes the following steps:

[0113] (1) At room temperature, weigh 14.29 g of an aqueous solution of polydimethyldiallylammonium chloride with a concentration of 35 wt% and place it in a container, add a certain amount of ultrapure water, prepare a 100 g solution, stir for 30 min, and prepare an aqueous pretreatment agent solution with a concentration of 5 wt%.

[0114] (2) At room temperature, weigh a certain amount of the pretreatment agent aqueous solution prepared in step (1) and set it aside.

[0115] (3) Weigh 0.5 g of Na 2 CO 3 Add it to the aqueous pretreatment agent solution prepared in step (1) to prepare a 100 g solution, stir for 30 min, and prepare an aqueous solution with a polydimethyldiallylammonium chloride concentration of 5 wt% and Na 2 CO3 A cationic pretreatment agent with a concentration of 0.5 wt%.

[0116] The application of the cationic pretreatment agent of the present invention in the pad dyeing process of cotton fabrics includes the following steps:

[0117] I. Pretreatment of cotton fabrics:

[0118] (1), At room temperature, rinse the impurities on the surface of the cotton fabric with ultrapure water, and put it into a blast drying oven to dry.

[0119] (2), Pad the cotton fabric with the cationic pretreatment agent, two dips and two rolls, and the liquor pickup is 68%.

[0120] (3), After padding, bake the cotton fabric at 100 °C for 3 min.

[0121] II. Dyeing of cotton fabrics:

[0122] (4), Dyeing: Pad the pretreated cotton fabric with the reactive dye RR218, two dips and two rolls, and the liquor pickup is 68%.

[0123] (5), Fixing: Put the cotton fabric directly into a 100 °C steamer without drying and steam-fix for 10 min.

[0124] (6), Washing: First wash the fixed cotton fabric with cold water for 2 min, then wash it with hot water for 2 min, wash it with a 2 g / L soap solution for 2 min, and finally wash it with cold water for 2 min.

[0125] (7), Drying: Put the washed cotton fabric into a blast drying oven and dry it at 60 °C.

[0126] Example 4

[0127] A cationic pretreatment agent is composed of the following components by mass fraction: 10 wt% of polydimethyldiallylammonium chloride; 1 wt% of sodium carbonate; the balance is ultrapure water. Its preparation method includes the following steps:

[0128] (1), At room temperature, weigh 28.27 g of an aqueous solution of polydimethyldiallylammonium chloride with a concentration of 35 wt% and place it in a container, add a certain amount of ultrapure water, and prepare a 100 g solution, stir for 30 min to prepare an aqueous solution of the pretreatment agent with a concentration of 10 wt%.

[0129] (2), At room temperature, weigh a certain amount of the aqueous solution of the pretreatment agent prepared in step (1) and set it aside.

[0130] (3), Weigh 1 g of Na 2 CO 3It is added to the aqueous solution of the pretreatment agent prepared in step (1) to prepare 100 g of solution, and stirred for 30 min to prepare a cationic pretreatment agent with a concentration of 10 wt% of polydimethyldiallylammonium chloride and a concentration of 1 wt% of Na 2 CO 3 .

[0131] The application of the cationic pretreatment agent of the present invention in the pad dyeing process of cotton fabrics includes the following steps:

[0132] I. Pretreatment of cotton fabrics:

[0133] (1), At room temperature, the impurities on the surface of the cotton fabric are rinsed clean with ultrapure water and then placed in a blast drying oven for drying;

[0134] (2), The cotton fabric is impregnated with the cationic pretreatment agent, double-dip and double-roll, and the liquor pickup rate is 70%;

[0135] (3), After impregnation and rolling, the cotton fabric is baked at 100 °C for 6 min;

[0136] II. Dyeing of cotton fabrics:

[0137] (4), Dyeing: The pretreated cotton fabric is pad-dyed with the reactive dye RB5, double-dip and double-roll, and the liquor pickup rate is 70%;

[0138] (5), Fixing: The cotton fabric is directly put into a 100 °C steamer for steam fixing for 12 min without drying;

[0139] (6), Washing: The cotton fabric after fixing is first washed with cold water for 2 min, then with hot water for 2 min, washed with 2 g / L soap solution for 2 min, and finally with cold water for 2 min;

[0140] (7), Drying: The washed cotton fabric is put into a blast drying oven and dried at 60 °C.

[0141] The performance test results of the dyed cotton fabric obtained by using the ionic pretreatment agent of the present invention in the pad dyeing process of cotton fabrics are as follows:

[0142] As Figure 2 shown, among which, Figure 2 (a) is the test chart of the solid Zeta potential of the cotton fabric surface treated with different concentrations of PDADMAC; Figure 2 (b) is the test chart of the solid Zeta potential of the cotton fabric surface treated with different concentrations of PDADMAC + 0.5% Na 2 CO 3 . The surface potential of the fabric is an important index affecting the dyeing effect. The solid surface potential of the fabric is tested on cotton fabrics treated with five different PDADMAC concentrations. As Figure 2As shown in (a), the Zeta potential of the surface of cotton fabric without PDADMAC modification treatment is negative at different pH values, and the surface potential of the cotton fabric after PDADMAC modification treatment changes from negative to positive. The surface potential of the cotton fabric without PDADMAC modification is negative under acidic, neutral and alkaline conditions, and the potential can reach about -20 mV. The potential of the cotton fabric treated with 1% PDADMAC pretreatment agent can reach about 20 mV, and the Zeta potential of the surface of the cotton fabric treated with 5% PDADMAC pretreatment agent drops to about 17 mV. As the number of cationic polymer molecules adsorbed on the surface of the cotton fabric increases, the potential decreases. Analyzing the reason, as the concentration of the pretreatment solution increases, the number of quaternary ammonium groups adsorbed on the fabric surface also increases. The hydrophobic groups are on the outside, and the hydrophobic groups of PDADMAC gradually cover the hydrophilic cationic groups, and the number of cationic groups exposed outside decreases. Therefore, the solid Zeta of the cotton fabric surface decreases with the increase of the pretreatment agent concentration.

[0143] After adding 0.5% Na 2 CO 3 to the pretreatment agent, the solid surface potential of the treated cotton fabric decreases as a whole. As shown in Figure 2 (b), the potential of the cotton fabric treated with 1% PDADMAC + 0.5% Na 2 CO 3 is about 15 mV, and the Zeta potential of the surface of the cotton fabric treated with 3% PDADMAC + 0.5% Na 2 CO 3 drops to about 10 mV. And as the concentration of PDADMAC in the pretreatment agent increases, the solid surface potential of the treated fabric samples continues to decrease. The Zeta potential of the surface of the cotton fabric treated with 10% PDADMAC + 0.5% Na 2 CO 3 is only about 7 mV.

[0144] To clarify the surface chemical mechanism of PDADMAC on cotton fabric, in this study, the functional group evolution of the cotton fabric before and after modification was analyzed by Fourier transform infrared spectroscopy (FTIR), and it was confirmed that quaternary ammonium groups were successfully adsorbed on the surface of the modified cotton fabric. The results are as Figure 3 shown (a - e represent 0, 1, 3, 5, 10 wt% PDADMAC respectively). An absorption peak appears at 1455 cm -1 for the unmodified cotton fabric, which belongs to the stretching vibration of C - N in the PDDA molecule, directly proving the successful grafting of quaternary ammonium groups (—N + (CH 3 ) 3 ).

[0145] This invention aims to explore the influence of different dosages of PDADMAC on the dyeing performance of cotton fabrics. Four dyes with different colors (RB49, RY95, RR218, and RB5) were used for pad dyeing, and through comparative analysis of the dyeing effects, the internal relationship between the PDADMAC concentration and the dyeing performance was deeply studied. As Figure 4 shown, pictures of the dyed fabric samples treated with PDADMAC pretreatment agents at different concentrations are presented. It can be clearly observed from the scanned pictures that as the PDADMAC concentration increases, the dyed fabric samples of the four dyes all show a trend of gradually increasing color depth. As the PDADMAC concentration increases, the positive charge density on the fiber surface correspondingly increases, which enhances the electrostatic attraction between the fiber and the anionic dye, thereby increasing the dye uptake rate; finally, the PDADMAC molecules can also form ion pairs with the dye molecules, further promoting the fixation of the dye on the fiber.

[0146] To gain a deeper understanding of the distribution of dyes during the dyeing process, cross-sectional analysis of the dyed fabric was carried out. As Figure 5 shown, as the PDADMAC concentration in the pretreatment agent increases, the dye penetration in the cross-section of the fabric sample shows obvious improvement. This phenomenon can be explained from the following aspects: First, the PDADMAC molecules can penetrate into the amorphous region of the cotton fiber, forming cationic sites inside the fiber, providing more binding sites for the dye molecules; second, a higher concentration of PDADMAC can better open the pore structure of the fiber, reducing the resistance of the dye molecules to diffuse into the fiber; finally, the uniform distribution of the PDADMAC molecules inside the fiber helps the dye molecules to uniformly penetrate the fiber cross-section, thus obtaining better dyeing uniformity.

[0147] The color depth of the dyeing pattern is one of the important criteria for evaluating the dyeing quality of reactive dyes. As Figure 6 shown, using the undyed fabric sample without pretreatment as a reference sample, dyeing was carried out with a 1% dye solution, and the colored block patterns on the cotton fabrics pretreated with four different cation concentrations were compared. It can be seen that as the cation concentration in the pretreatment agent increases, the color depth of the fabric sample after washing also increases in turn. After soaping, the K / S value of the dyed fabric sample of the cotton fabric not treated with the cationic polymer solution is 0.27, the K / S value of the fabric sample treated with 1% PDDA is 0.97, while the K / S value of the cotton fabric pretreated with 10% PDDA can reach 5.25. Through the analysis of the color effect of the colored blocks, as the cation concentration increases, the ammonium groups bound to the active groups on the cotton fabric surface increase. During the dyeing process, the cationic groups attached to the cotton fabric surface and the dye anions are combined through electrostatic attraction.

[0148] According to the above experimental results, it can be known that increasing the concentration of PDADMAC in the pretreatment agent can improve the color performance of the fabric sample. However, the change in cation concentration still has limited effect on color improvement. Therefore, by adding a small amount of alkali to the pretreatment solution to promote the binding of ionic bonds, the color depth can be improved. In addition, adding a small amount of alkali solution can also adjust the pH of the pretreatment agent to make the dye molecules in a better dyeing state. In this experiment, 0.5wt% Na 2 CO 3 was added. As shown by the scanning diagram of the fabric sample in Figure 7 , it can be directly seen that adding a small amount of Na 2 CO 3 to the pretreatment agent improved the colors of the pad-dyed fabric samples of the four different reactive dyes to varying degrees.

[0149] To observe the penetration of the dyed fabric samples under different pretreatment conditions, cross-sectional slices of the fabric were made. As shown in Figure 8 , with the increase in the concentration of PDADMAC in the pretreatment agent, the penetration of the fabric sample cross-section also increased. After adding a small amount of Na 2 CO 3 , the penetration of the fabric sample also increased. A higher penetration rate can effectively improve the uniformity of the dyed fabric sample, which also means that more dye molecules can enter the interior of the fabric, thereby increasing the depth and saturation of the dyeing. The full penetration of the dye and its tight binding with the fiber contribute to improving the fastness of the dyeing and reducing the possibility of dye shedding.

[0150] As shown in Figure 9 , the K / S value of the fabric sample also showed a specific improvement effect. According to the color effect results, adding a small amount of Na 2 CO 3 to the pretreatment solution significantly improved the color effect, and with the increase in cation concentration, the K / S value also increased.

[0151] By adding a small amount of alkali to the pretreatment solution to improve the color depth, it not only provides conditions for the covalent reaction between the reactive dye and the fiber, but also promotes the binding of ionic bonds between PDADMAC and the reactive dye. As shown in Figure 10 (a)-(d), after adding a small amount of alkali to the treatment solution, the color performance of the fabric samples pretreated with different concentrations has been improved to varying degrees. In this experiment, 0.5% Na 2 CO 3 was added. From the results, it can be seen that adding alkali during the dyeing process not only provides conditions for the covalent reaction between the reactive dye and the fiber, but also promotes the binding of ionic bonds between PDADMAC and the reactive dye. Among them Figure 10In (c), the dyeing effect of Reactive Red 218 was improved most significantly. After alkali treatment, the K / S values of the fabric samples treated with different concentrations of the pretreatment agent increased by about 2. The dyeing effects of Reactive Blue 49, Reactive Yellow 95, and Reactive Black 5 were also moderately improved.

[0152] To explore the effect of steaming fixation on the fabric samples treated with PDADMAC, the fabric samples dyed with four reactive dyes under the same parameter conditions were divided into three groups. During the fixation process, the fabric samples in the first group were only dried after dyeing. For the fabric samples in the second group, steaming was carried out on the basis of the first group. The fabric samples in the third group were directly steamed after dyeing. By analyzing the K / S values of the three groups of fabric samples after washing, the optimal fixation process was sought, and the mechanism of the effect of different fixation processes on the dyeing effect was explored. The results are as Figure 11 shown. The color depth of the fabric samples only dried after dyeing was much different from that of the fabric samples dried and steamed after dyeing, indicating that further fixation occurred during the steaming process of the dyed fabric samples. As mentioned above, for the pretreatment agent prepared with Na 2 CO 3 +PDADMAC, OH - would replace Cl - , and the quaternary ammonium salt became quaternary ammonium hydroxide, providing an alkaline condition that was conducive to the reaction between the dye molecules and the cotton fabric. Therefore, a part of the dyes directly reacted with the cotton fibers under the alkaline condition, and during the steaming process, this part of the dyes was more firmly bound to the cotton fibers.

[0153] In summary, the present invention utilizes a limited amount of cationic modifier. Through the synergistic effect with sodium carbonate, by using the ionized quaternary ammonium salt groups and non-ionized quaternary ammonium salt groups in the cationic modifier poly(dimethyldiallylammonium chloride) (PDADMAC), part of the unusable quaternary ammonium ions are released and fully utilized through quaternary ammonium hydroxide again, and the ionized quaternary ammonium ions continue to adsorb on the fibers, achieving the purpose of maximizing the auxiliary dyeing, fixation, and leveling of the cationic modifier. Fundamentally, it solves the problems of large consumption of saline-alkali auxiliaries, a large amount of wastewater, low dye uptake rate, and unsatisfactory fixation rate during the cotton fabric dyeing process in the prior art, and improves the color performance of the dyed fabric. The present invention utilizes the synergistic effect of multiple factors of the modifier to fill the gap in the interaction mechanism of multiple factors in the prior art. This highly efficient and environmentally friendly solution is of great significance for promoting the clean production of the printing and dyeing industry and reducing the environmental load.

[0154] Certainly, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Any changes, modifications, additions, or substitutions made by those of ordinary skill in the art within the scope of the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A cationic pretreatment agent, characterized in that It is composed of the following components by mass fraction: Cationic modifier 1-10wt%; Alkali agent 0.1-1wt%; Ultrapure water balance.

2. The cationic pretreatment agent according to claim 1, characterized in that: The composition is composed of the following components in mass fractions: 5wt% of a cationic modifier, 0.5wt% of an alkali agent, and the balance being ultrapure water.

3. The cationic pretreatment agent according to claim 1 or 2, characterized in that: The cationic modifier is polydimethyldiallylammonium chloride, and the alkali agent is any one of sodium carbonate, sodium silicate and sodium phosphate.

4. The cationic pretreatment agent according to claim 3, characterized in that: The preparation method comprises the following steps: (1) At room temperature, weigh a certain amount of polydimethyldiallylammonium chloride aqueous solution and place it in a container, add a certain amount of ultrapure water, and stir for 30 minutes to prepare a pretreatment agent aqueous solution with a concentration of 1-10wt%; (2) At room temperature, weigh a certain amount of Na2CO3 and add it to the aqueous solution of the pretreatment agent prepared in step (1), and stir for 30 minutes to prepare a cationic pretreatment agent with a polydimethyldiallylammonium chloride concentration of 1-10wt% and a Na2CO3 concentration of 0.1%-1wt%.

5. The cationic pretreatment agent according to claim 4, characterized in that: In the step (1), the concentration of the weighed polydimethyldiallylammonium chloride aqueous solution is 35 wt %.

6. Application of a cationic pretreatment agent in a cotton fabric pad dyeing process, characterized in that: The steps include:

1. Pretreatment of cotton fabrics: (1) Rinse the impurities on the surface of the cotton fabric with ultrapure water at room temperature and dry it in a blast drying oven; (2) Dipping and padding the cotton fabric with the cationic pretreatment agent according to any one of claims 1 to 3, performing two dipping and two padding, with a padding rate of 65% to 70%; (3) After padding, the cotton fabric is baked at 100°C for 2-6 minutes; 2. Dyeing of cotton fabrics: (4) Dyeing: The pre-treated cotton fabric is pad-dyed with reactive dyes, double-dipping and double-padding, with a padding rate of 65%-70%; (5) Color fixation: Put the cotton fabric directly into a steamer at 100℃ for 8-12 minutes without drying; (6) Washing: Wash the cotton fabric several times after the color fixation is completed; (7) Drying: Dry the cotton fabric after washing.

7. The use of the cationic pretreatment agent according to claim 7 in the pad dyeing process of cotton fabrics, characterized in that: In the step (3), after the padding is completed, the cotton fabric is baked at 100° C. for 3 minutes.

8. The use of the cationic pretreatment agent according to claim 7 in the pad dyeing process of cotton fabric, characterized in that: In the step (4), the reactive dye is any one of RB49, RY95, RR218 and RB5.

9. The use of the cationic pretreatment agent according to claim 7 in the pad dyeing process of cotton fabric, characterized in that: In the step (5), the steaming fixation time is 10 minutes.

10. The use of the cationic pretreatment agent according to claim 7 in the pad dyeing process of cotton fabric, characterized in that: In the step (6), first wash with cold water for 2 minutes, then wash with hot water for 2 minutes, wash with 2g / L soap solution for 2 minutes, and finally wash with cold water for 2 minutes.

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