Anti-yellowing rayon fabric and washing-free printing process thereof

Abstract

The invention provides an anti-yellowing rayon fabric and a washing-free printing process thereof, and relates to the technical field of textile printing and dyeing. According to the sizing agent disclosed by the invention, polyacrylic resin and cellulose ether are matched in an auxiliary agent, the dosage and the type of the cellulose ether are optimized, and sodium bicarbonate, urea and sodium thiosulfate are cooperated, so that the sizing agent has good flowability and viscosity in a printing process, and the definition and the fineness of a printed pattern are ensured; meanwhile, the film-forming property and the water-retaining property of the slurry are improved, the printing continuity, the printing stability and the printing fixation rate are improved, and printed patterns are firmer and brighter; wherein the polyacrylic resin and the hydroxyethyl cellulose cooperate to adjust the viscosity and the fluidity of the slurry and improve the film-forming property and the water-retaining property; sodium bicarbonate and urea provide an alkaline environment to promote the combination of the dye and the fiber and improve the fixation rate and the dyeing depth; sodium thiosulfate provides a reducing environment, prevents the dye from being oxidized, ensures the stability and brightness of the dye and inhibits the fabric from yellowing.

Description

Technical Field

[0001] The invention relates to the technical field of textile printing and dyeing, and in particular to an anti-yellowing rayon fabric and a water-free washing printing process thereof. Background Art

[0002] Rayon (viscose) is a common textile fabric, known for its softness, comfort, and breathability, making it widely used in the textile and apparel industry. However, in traditional digital printing, rayon is prone to yellowing during high-temperature drying, which seriously affects product quality and appearance. Traditional digital printing processes typically use water washing to remove the yellowing caused by high-temperature drying. However, this process has numerous drawbacks, including high water consumption and wastewater discharge, which increase production costs and environmental pressures. Furthermore, the washing process can affect the clarity and color vividness of printed patterns.

[0003] CN107090724A discloses a dual-nozzle digital printing process for polyester-cotton fabrics, using disperse dyes for printing polyester and reactive dyes for printing cotton. Baking soda is added to the sizing process during this process. However, no detailed description is given of the disperse dyes and reactive dyes in the alkaline environment during digital printing, nor is any explanation provided on how to achieve identical printing of the two dyes. Conventional disperse dye inks may fade or yellow due to alkalinity, and color deviation may occur when printing the same color with the two dyes. Furthermore, color fixation involves high-temperature baking and steaming, resulting in high energy consumption. Summary of the Invention

[0004] The purpose of the present invention is to provide a yellowing-resistant rayon fabric and a water-free printing process thereof. By adding a specific auxiliary agent in the pre-sizing treatment of digital printing, the yellowing problem of the prepared rayon during high-temperature drying is effectively solved, while avoiding the disadvantages of the traditional washing process, realizing water-free digital printing of rayon, reducing production costs and reducing environmental pollution.

[0005] In a first aspect, the present application provides a water-free printing process for anti-yellowing rayon fabrics:

[0006] A water-free printing process for yellowing-resistant rayon fabrics comprises the following preparation steps:

[0007] The rayon grey fabric is immersed in sizing liquid to sizing rate of 50-90%, and then dried; then it is subjected to digital printing, drying, steaming, color fixing finishing, finishing and drying to obtain anti-yellowing rayon fabric;

[0008] The temperature of the drying, steaming, color fixing and drying after finishing is less than 105°C;

[0009] The sizing liquid comprises 1wt%-5wt% of acrylic resin, 0.5wt%-4wt% of cellulose ether, 1wt%-5wt% of pH regulator, 2wt%-10wt% of urea, 1wt%-5wt% of reducing agent, and the balance is water;

[0010] The acrylic resin is polyacrylic acid resin or acrylic acid copolymer.

[0011] Further preferably, the preparation steps are as follows:

[0012] 1) Immerse the rayon fabric in the sizing solution to achieve a sizing rate of 50-90%, and then dry it at 90-110°C.

[0013] 2) Digital printing;

[0014] 3) Dry at 80-100℃ for 3-6 minutes;

[0015] 4) Steaming at 102°C for 15 minutes;

[0016] 5) Color fixation and finishing;

[0017] 6) Dry at 80-100℃ for 3-6 minutes.

[0018] The key to this invention lies in the additives used in the sizing solution. These additives utilize a polyacrylic acid resin in combination with hydroxyethyl cellulose, along with sodium bicarbonate, urea, and sodium thiosulfate, all mixed in specific proportions. As a water-soluble polymer, polyacrylic acid resin can regulate the fluidity and permeability of the ink and also acts as a cross-linking fixative to improve post-print fastness. Hydroxyethyl cellulose imparts an appropriate viscosity to the printing paste, ensuring clarity and fineness of the printed pattern. It also helps retain moisture in the printing paste, ensuring continuity and stability of the print.

[0019] Polyacrylic acid resin has good fluidity and permeability, while hydroxyethyl cellulose can significantly improve the viscosity and water retention of the slurry. A reasonable ratio of the two can jointly adjust the viscosity of the slurry, so that it has good fluidity during the printing process and maintains sufficient viscosity to ensure the clarity and fineness of the printed pattern.

[0020] As a cross-linking fixing agent, polyacrylic acid resin can undergo a cross-linking reaction with the dye to improve the dye fixation rate, making the printed pattern color more vivid and firm; the flexible film-forming property of hydroxyethyl cellulose can protect the dye molecules and prevent them from being oxidized or decomposed during the printing process, thereby improving the stability of the dye; the synergistic combination of the two and the optimal dosage can better protect the dye molecules, improve the dye fixation rate and stability, and make the printed pattern color more full and bright.

[0021] Sodium bicarbonate decomposes during steaming or drying to produce sodium carbonate, creating an alkaline environment that promotes the covalent bonding of reactive dyes to fibers, improving dye fixation and resulting in brighter, more durable printed patterns. Urea promotes the diffusion of reactive dyes into the fibers, allowing them to better penetrate the fiber molecular chains and increase the contact area between the dye and the fiber, thereby improving fixation and dye depth, resulting in richer, more vibrant colors. Sodium thiosulfate acts as a reducing agent, creating a reducing environment that renders the dye soluble and allows it to react with the fibers. This prevents oxidation and yellowing during the printing process, which can affect the dyeing effect.

[0022] Furthermore, the pH adjuster is 2wt%-4wt%.

[0023] Furthermore, the amount of urea used is 5wt%-8wt%.

[0024] Furthermore, the reducing agent includes one or a combination of sodium thiosulfate, ascorbic acid reducing agents, and sodium thiomalate.

[0025] Furthermore, the amount of the reducing agent is 2wt%-3wt%.

[0026] Use appropriate amount of urea and pH regulator to adjust the pH value. The appropriate pH value in the sizing stage ensures the stability of the reducing agent. During steaming, urea and pH regulator are used to regulate decomposition, and the alkalinity is increased to promote color fixation.

[0027] If the pH in the sizing stage is too low, the reducing agent (such as hydrosulfite) will quickly decompose and become ineffective, losing its reducing ability, and will be unable to effectively remove free oxygen or stabilize the dye structure, causing the dye to oxidize and turn yellow; if the pH in the sizing stage is too high, the reducing agent may be over-consumed due to self-reaction or side reactions with the dye, resulting in a lack of sufficient reducing agent in the subsequent steam fixation stage to maintain dye stability, ultimately leading to a decrease in the anti-yellowing effect.

[0028] Excessive reducing agent may lead to over-reduction in the steaming environment and inhibit the release of ammonia from urea. The pH value in the steaming stage is low, which indirectly reduces the color fixation efficiency.

[0029] Urea promotes fiber swelling during the steaming stage, helping dye molecules penetrate the fiber and promoting uniform dispersion of the dye. Urea indirectly enhances alkalinity to promote color fixation, and is combined with a reducing agent to offset the oxidation risk brought by the alkaline environment. The two balance color fixation efficiency and fiber protection, jointly maintaining the dyeing uniformity and brightness, and improving anti-yellowing performance.

[0030] Furthermore, the cellulose ether includes one or a combination of methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, and hydroxyethyl methyl cellulose.

[0031] Furthermore, the cellulose ether includes one or a combination of hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxyethyl methyl cellulose; the amount of the cellulose ether is 1wt%-3wt%.

[0032] Furthermore, the Mw of the cellulose ether is 50,000-1,500,000 Da.

[0033] Furthermore, the acrylic resin has a Mw of 10,000 ≤ ≤ 100,000 Da.

[0034] The molecular weights of the cellulose ether and acrylic resin are optimized to provide the acrylic resin with better fluidity, permeability and mixing uniformity. The combination of cellulose ether with an appropriate molecular weight and acrylic resin improves the uniformity of the film layer formed by the sizing liquid, thereby improving the printing uniformity, color fixation rate and firmness of the printed pattern.

[0035] Furthermore, the pH adjuster includes sodium bicarbonate and / or sodium carbonate.

[0036] Sodium bicarbonate is safer and suitable for high-precision printing.

[0037] In a second aspect, the present application provides a yellowing-resistant rayon fabric obtained by the water-free printing process of the present application.

[0038] Beneficial effects:

[0039] 1. The sizing solution of the present invention adopts polyacrylic acid resin and cellulose ether as auxiliary agents, preferably the amount and type of cellulose ether, and cooperates with sodium bicarbonate, urea and sodium thiosulfate to make the slurry have good fluidity and viscosity during the printing process, ensuring the clarity and fineness of the printed pattern; at the same time, the film-forming property and water retention of the slurry are improved, ensuring the continuity and stability of the printing, and improving the color fixation rate of the dye, making the printed pattern more firm and bright; wherein, the polyacrylic acid resin and hydroxyethyl cellulose cooperate to adjust the viscosity and fluidity of the slurry, improve the film-forming property and water retention; sodium bicarbonate and urea provide an alkaline environment, promote the combination of the dye and the fiber, improve the color fixation rate and the depth of dyeing; sodium thiosulfate provides a reducing environment, prevents the oxidation of the dye, ensures the stability and brightness of the dye, and inhibits the yellowing of the fabric.

[0040] 2. The dosage of urea, pH regulator and reducing agent is optimized, so that the film layer formed by the sizing liquid on the grey cloth is more stable at high temperature, so that urea, pH regulator and reducing agent can play a better role, weaken the side reactions that affect each other, improve the printing uniformity, improve the color fixation rate and the firmness of the printed pattern.

[0041] 3. Environmental advantages: The water-free digital printing process of the present invention completely abandons the traditional water washing process, greatly reduces the consumption of water resources and the discharge of wastewater, meets environmental protection requirements, and is conducive to sustainable development.

[0042] Quality improvement: By adding auxiliaries in the early stage, the yellowing problem of rayon caused by high-temperature drying is effectively solved. In addition, since no water washing is performed during the entire printing process, the printed patterns of the anti-yellowing rayon fabric obtained are clear, the colors are vivid, the color fastness is significantly improved, and the product quality is better.

[0043] Cost reduction: eliminating the water washing process, reducing the investment and operating costs of water washing equipment, while saving manpower and material resources consumed by water washing, and reducing the cost of the entire production process. DETAILED DESCRIPTION

[0044] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to specific embodiments.

[0045] Example 1, a water-free printing process for yellowing-resistant rayon fabric, comprising the following preparation steps:

[0046] 1) The rayon fabric was dipped and rolled in a sizing solution (specific components are shown in Table 1) with a liquid rate of 50%; then dried at 100°C.

[0047] 2) Digital direct printing (reactive ink);

[0048] 3) Drying (100°C, 4 min);

[0049] 4) Steaming at 102°C for 15 minutes;

[0050] 5) After drying, the fabric is passed through a setting machine and then dipped and padded in an impregnation finishing solution (using 3 wt% of a formaldehyde-free color fixing agent; in other embodiments, a formaldehyde-free color fixing agent at a concentration of 2-4 wt% may be used), followed by drying (100° C., 4 min) to obtain a yellowing-resistant rayon fabric.

[0051] Example 2 and Example 5 are a water-free printing process for yellowing-resistant rayon fabrics. The difference from Example 1 is that the components and dosage of the sizing treatment liquid and the process parameter settings of the water-free printing process are different, as shown in Table 1.

[0052] Table 1. Components and dosage of the sizing solution used in the water-free printing process of Examples 1 to 5 and process parameter settings of the water-free printing process

[0053]

[0054] Example 6, a water-free printing process for yellowing-resistant rayon fabric, differs from Example 1 in that an equal amount of carboxymethyl cellulose (50,000 Da) is used in the sizing treatment liquid to replace hydroxyethyl cellulose (50,000 Da).

[0055] Example 7, a water-free printing process for yellowing-resistant rayon fabric, differs from Example 1 in that ethyl cellulose (50,000 Da) is used in an equal amount to replace hydroxyethyl cellulose (50,000 Da) in the sizing treatment liquid.

[0056] Example 8, a water-free printing process for yellowing-resistant rayon fabric, differs from Example 1 in that 2 million Da hydroxyethyl cellulose and 300,000 Da polyacrylic acid resin are used in the sizing treatment liquid.

[0057] Example 9, a water-free printing process for yellowing-resistant rayon fabric, differs from Example 1 in that 4 wt % of hydroxyethyl cellulose is used.

[0058] Comparative Example 1 is a water-free printing process for yellowing-resistant rayon fabrics, which differs from Example 1 in that hydroxyethyl cellulose is not used in the sizing solution.

[0059] Comparative Example 2 is a water-free printing process for yellowing-resistant rayon fabrics, which differs from Example 1 in that no reducing agent is used in the sizing solution.

[0060] Comparative Example 3, a water-free printing process for yellowing-resistant rayon fabric, differs from Example 1 in that no reducing agent is used in the sizing solution; after the post-fixing step, a reducing cleaning solution is used for reduction cleaning, followed by setting and drying.

[0061] The reducing cleaning solution includes 2 g / L of sodium thiosulfate and 1 g / L of caustic soda.

[0062] Reduction cleaning process: Place the baked and colored polyester in an overflow dyeing machine, heat it to 70°C at 2°C / min, keep warm and wash for 20 minutes, then wash it in hot water at 60°C for 10 minutes, and then wash it in room temperature water until it becomes neutral.

[0063] Performance testing

[0064] 1. Crockmeter Test: Take a 14 cm × 5 cm specimen and secure it to the base of the crockmeter. Select a dark or easily discolored area for testing. Thoroughly wet the rubbing cloth (humidity controlled at 95%-100%). Remove the cloth and gently squeeze it to reach the standard moisture content (AATCC standard: 65 ± 5%). Secure the rubbing head with a pressure of approximately 9 N, ISO standard. Set the number of rubbing cycles to 10 (20 back-and-forth rubs). Rub the rubbing head back and forth in a straight line across the specimen surface. Maintain close contact between the specimen and the rubbing cloth during the test to avoid slippage. Visually evaluate the test using the ISO 105-A02 gray scale, 1-5, with 5 being the best. The test results are shown in Table 2.

[0065] 2. Anti-yellowing Performance Test: Using a colorimeter, randomly measure eight points on the specimen while measuring whiteness. Calculate the average value, which is recorded as the initial whiteness. A UV weathering tester is used, using a D65 light source, for 10 hours each cycle, repeated 10 times. After aging, use a colorimeter to randomly measure eight points in the same manner, calculate the average value, and record it as the test whiteness. Calculate the difference between the test whiteness and the initial whiteness to assess anti-yellowing performance. Lower color difference values indicate greater anti-yellowing performance. Test results are shown in Table 2.

[0066] Table 2. Test results of friction fastness and anti-yellowing performance of Examples 1 to 9 and Comparative Examples 1 to 3

[0067]

[0068] As can be seen from Table 1, the wet friction fastness of the yellowing-resistant rayon obtained by the water-free printing process of the present application is ≥ level 3, and the color difference is <1. The obtained yellowing-resistant rayon has high resistance to discoloration and yellowing and has high quality. At the same time, the traditional water washing process is eliminated in the preparation process, which reduces production costs and reduces environmental pollution.

[0069] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A water-free printing process for anti-yellowing rayon fabrics, characterized in that: The method comprises the following preparation steps: The rayon grey fabric is immersed in sizing liquid to sizing rate of 50-90%, and then dried; then it is subjected to digital printing, drying, steaming, color fixing finishing, finishing and drying to obtain anti-yellowing rayon fabric; The temperature of the drying, steaming, color fixing and drying after finishing is less than 105°C; The sizing liquid comprises 1wt%-5wt% of acrylic resin, 0.5wt%-4wt% of cellulose ether, 1wt%-5wt% of pH regulator, 2wt%-10wt% of urea, 1wt%-5wt% of reducing agent, and the balance is water; The acrylic resin is polyacrylic acid resin or acrylic acid copolymer.

2. The water-free printing process for anti-yellowing rayon fabric according to claim 1, characterized in that: The pH value regulator is 2wt%-4wt%.

3. The water-free printing process for anti-yellowing rayon fabric according to claim 2, characterized in that: The amount of urea used is 5wt%-8wt%.

4. The water-free printing process for anti-yellowing rayon fabric according to claim 1, characterized in that: The reducing agent includes one or a combination of sodium thiosulfate, ascorbic acid reducing agent, and sodium thiomalate.

5. The water-free printing process for anti-yellowing rayon fabric according to claim 1, characterized in that: The amount of the reducing agent is 2wt%-3wt%.

6. The water-free printing process for anti-yellowing rayon fabric according to claim 1, characterized in that: The cellulose ether includes one or a combination of methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, and hydroxyethyl methyl cellulose.

7. The water-free printing process for anti-yellowing rayon fabric according to claim 6, characterized in that: The cellulose ether includes one or a combination of hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxyethyl methyl cellulose; the amount of the cellulose ether is 1 wt % to 3 wt %.

8. The water-free printing process for anti-yellowing rayon fabric according to claim 7, characterized in that: The Mw of the cellulose ether is 50,000-1,500,000 Da.

9. The water-free printing process for anti-yellowing rayon fabric according to claim 1, characterized in that: The pH adjuster includes sodium bicarbonate and / or sodium carbonate.

10. A yellowing-resistant rayon fabric obtained by the water-free printing process according to any one of claims 1 to 9.

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