A digital printing process for all-cotton

Abstract

This invention discloses a digital printing process for all-cotton fabrics, belonging to the field of digital printing technology. The process includes the following steps: preparing a pretreatment paste → sizing the fabric → drying I → digital printing → drying II → steaming → washing I → soaping → washing II → drying III. The pretreatment paste, by mass percentage, comprises the following components: sodium alginate 1-4%, modified cellulose 0.5%-2%, urea 6-12%, sodium sulfate 2-8%, sodium bicarbonate 2-6%, anti-dyeing salt 0-1%, and the remainder being water. This invention provides a digital printing process for all-cotton fabrics by adding cationic and amphoteric modified cellulose to the pretreatment paste. This allows the pretreatment paste to maintain a positively charged environment under alkaline conditions, improving the adsorption capacity between the pretreatment paste and reactive dyes. The anions in the pretreatment paste also promote dye uptake, resulting in digitally printed all-cotton fabrics with high dye uptake, high clarity, good uniformity, and high color fastness.

Description

Technical Field

[0001] This invention belongs to the field of digital textile printing technology, specifically relating to a digital printing process for all-cotton fabrics. Background Technology

[0002] In recent years, with the development of technologies such as computers, materials, information, and precision machinery manufacturing, digital printing technology, hailed as "a revolution in textile printing technology," has gradually entered the market. This product of the combination of traditional printing and dyeing techniques with digital technology boasts advantages such as no need for plate making, rich and detailed color reproduction, unrestricted small-batch customization, water conservation, low pollution, and low labor intensity. Digital printing technology originates from digital inkjet printing technology, a printing technology that directly jets ink onto printing paper. Similar to digital inkjet printing, digital printing technology for textiles uses a printhead to repeatedly emit micro-droplets of different colors onto the surface of the textile substrate. Under the control of a computer system, large amounts of data are rapidly processed to print a variety of colorful patterns. However, due to the specific purity and conductivity requirements of inkjet printing, traditional printing chemicals cannot be directly added to the ink formulation. Therefore, before the digital printing stage, appropriate pretreatment processes are usually selected based on the type of textile fabric. This provides the necessary chemical environment for ink to dye the fibers and controls the interaction between ink droplets and the fabric. Sodium alginate, due to its good solubility and excellent stability even after high-temperature fixing, is often used as a thickener in the pretreatment printing paste for reactive dye digital inkjet printing. However, sodium alginate has very little interaction with cotton fabrics and reactive dyes, resulting in poor clarity and colorfastness in digital printing. Considering the mechanism of reactive dye printing, some researchers have replaced sodium alginate with amino-containing chitosan in the pretreatment paste for cotton fabrics. The results showed that the clarity and colorfastness of digital printing on chitosan-treated cotton fabrics were improved, but the dye uptake rate decreased by 30% compared to sodium alginate. Therefore, a fully cotton digital printing process still needs to be developed to address the issues of clarity, colorfastness, and dye uptake rate in fully cotton digital printing. Summary of the Invention

[0003] To overcome the shortcomings of the prior art, the present invention provides a whole cotton digital printing process. By adding modified cellulose to the pretreatment paste, wherein the modified cellulose is surface modified by zwitterions and cations, the pretreatment paste maintains a positive charge environment under alkaline conditions, thereby improving the adsorption capacity of the pretreatment paste to reactive dyes. The anions it carries also have the effect of promoting dye uptake, which is beneficial to producing whole cotton digital printed fabrics with high dye uptake, high clarity, good uniformity and high color fastness.

[0004] The technical solution for achieving the objective of this invention is as follows:

[0005] A digital printing process for all-cotton fabrics includes the following steps:

[0006] Pretreatment paste preparation → Fabric sizing → Drying I → Digital printing → Drying II → Steaming → Washing I → Soap washing → Washing II → Drying III;

[0007] The pretreated slurry, by mass percentage, comprises the following components: sodium alginate 1-4%, modified cellulose 0.5%-2%, urea 6-12%, sodium sulfate 2-8%, sodium bicarbonate 2-6%, anti-dyeing salt 0-1%, and the balance being water;

[0008] The modified cellulose is a cellulose with cationic and zwitterionic surface modification, which is prepared by reacting allylated cellulose with zwitterionic ligands with thiol groups and cationic ligands with thiol groups via a UV-initiated thiol-ene click reaction.

[0009] Specifically, the zwitterionic ligand with a thiol group has the structure shown in Formula 1.

[0010]

[0011] Specifically, the thiol-containing cationic ligand has the structure shown in Formula 2:

[0012]

[0013] Specifically, the zwitterionic ligand is prepared by reacting cystamine with iodomethane to obtain bis(2-dimethylaminoethyl) disulfide, reacting bis(2-dimethylaminoethyl) disulfide with vinyl sulfate in a ring-opening reaction to obtain sulfanilamide disulfide, and then reducing sulfanilamide disulfide under the action of triphenylphosphine to obtain the zwitterionic ligand. The reaction process is shown in Formula 3.

[0014]

[0015] Specifically, the cationic ligand is obtained by reacting (3-bromopropyl)trimethylammonium bromide with sodium thiosulfate, followed by reduction with sulfuric acid and triphenylphosphine, as shown in Formula 4:

[0016]

[0017] Preferably, the pretreated slurry is prepared by: first adding urea, sodium bicarbonate, sodium sulfate and anti-dyeing salt to deionized water and stirring thoroughly; then adding sodium alginate and modified cellulose and stirring evenly.

[0018] Preferably, the anti-dyeing salt is anti-dyeing salt S.

[0019] Preferably, the mass ratio of the cationic ligand to the zwitterionic ligand is (1-4):(1-4).

[0020] Preferably, the fabric sizing step is as follows: the cotton fabric is completely immersed in the sizing agent, and after a period of time, the cotton fabric is taken out and the excess sizing agent is removed by a rolling mill. The process is carried out by two dips and two rollings. After rolling, the fabric is dried and shaped immediately, and then placed in a sealed bag for storage.

[0021] Preferably, the drying temperature I is 80–120°C; the drying temperature II is 65–105°C; the drying temperature III is 100–120°C; the steaming temperature is 100–105°C, the state is atmospheric pressure saturated steam, and the time is 8–20 min.

[0022] Preferably, the soap washing uses standard soap flakes at a concentration of 1-2 g / L, a temperature of 90-100℃, and a washing time of 8-12 minutes; the water washing I is a 4-6 minute wash in warm water at 35-45℃; the water washing II is a 4-6 minute wash in warm water at 35-45℃ followed by a 4-6 minute wash in cold water; and the water bath ratio for the soap washing, water washing I, and water washing II is 40:1-20:1.

[0023] Preferably, the allylated cellulose is prepared by reacting cellulose with allyl bromide or allyl chloride under alkaline conditions.

[0024] Preferably, the thiol-ene click reaction is prepared by reacting allylated cellulose, zwitterionic ligands and cationic ligands under photoinitiator and ultraviolet light irradiation.

[0025] Preferably, the cellulose is at least one of hydroxyethyl cellulose (HEC), hydroxypropyl methylcellulose (HPMC), or hydroxyethyl methylcellulose (HEMC).

[0026] Beneficial effects

[0027] The present invention has the following beneficial effects:

[0028] This invention provides a digital printing process for all-cotton fabrics. Modified cellulose is added to the pretreatment paste, and cations and zwitterions are introduced through cellulose surface modification. Compared to grafting, this method allows for a more uniform distribution of cations and zwitterions on the cellulose surface, maintaining a uniform and effective positive charge environment in the pretreatment paste under alkaline conditions. This improves the bonding force between the pretreatment paste and the negatively charged cotton fabric. Furthermore, the positively charged quaternary ammonium groups in the pretreatment paste bind to the negatively charged reactive dyes through electrostatic attraction, ensuring uniform dispersion of dye molecules and enhancing the adsorption force between the pretreatment paste and the reactive dyes. This guarantees the clarity, uniformity, and colorfastness of the digitally printed all-cotton fabrics. Simultaneously, the anionic groups in the pretreatment paste exhibit electrostatic repulsion with the reactive dye molecules, promoting dye uptake and ensuring a high dye uptake rate for digital printing. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Unless otherwise specified, the experimental methods used in the embodiments are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0031] The raw materials and equipment used in the embodiments and comparative examples are described below:

[0032] Belt-type digital printing machine: Model DTBS-1638, purchased from Chengdu Jinzhida Digital Technology Co., Ltd.;

[0033] Cotton fabric: Pure cotton plain weave fabric, warp density is 40 count, weft density is 40 count;

[0034] Standard soap flakes: International standard soap powder, purchased from Standard Group Limited;

[0035] Sodium alginate: Purity: 99%, Jiangsu Dongju Biotechnology Co., Ltd.;

[0036] Cellulose: Hydroxyethyl cellulose, viscosity 1500-2500 mPa·s, 25℃, Guangdong Wengjiang Chemical Reagent Co., Ltd.

[0037] Cystamine dihydrochloride: CAS: 56-17-7, Shanghai Tongyuan Chemical Co., Ltd.;

[0038] Modified cellulose 1: The preparation method is as follows. All reactions sensitive to air and moisture were carried out in flame-dried glassware under an inert argon atmosphere:

[0039] S1. Preparation of allyl cellulose: Under an argon atmosphere, 5.5 g of cellulose was dissolved in 60 ml of tetrahydrofuran and stirred to disperse. Then, 5.5 g of sodium hydroxide was dissolved in 4 ml of deionized water and added to the cellulose solution. The mixture was stirred continuously, and 6.5 g of allyl bromide was slowly added. The temperature was set to 65 °C and the reaction was stirred for 48 hours. After that, 0.1 M hydrochloric acid was added to terminate the reaction. The resulting precipitate was placed on a rotary evaporator to remove the solvent. The resulting solid was washed with water and then dried under vacuum to obtain allyl cellulose.

[0040] S2. Preparation of zwitterionic ligands: Under an argon atmosphere, 0.01 mol of cystamine dihydrochloride was dissolved in 25 ml of deionized water, and the pH was adjusted to 6.5 by adding 1 M sodium hydroxide solvent to obtain a cystamine solution. 0.02 mol of iodomethane was dissolved in 610 ml of deionized water, and the cystamine solution was slowly added to the iodomethane solution. The mixture was stirred at room temperature for 3 hours, and the crude product was obtained by vacuum distillation. The crude product was further recrystallized to obtain bis(2-dimethylaminoethyl) disulfide. 0.01 mol of bis(2-dimethylaminoethyl) disulfide was dissolved in 15 ml of anhydrous acetone and cooled to 0°C in an ice bath. 0.22 mol of vinyl sulfate was dissolved in 20 ml of anhydrous acetone. The solution was added dropwise to a cooled bis(2-dimethylaminoethyl) disulfide solution using a syringe. The mixture was stirred continuously at 0°C for 1 hour, then left to stand overnight at room temperature to obtain a white precipitate. The precipitate was filtered, thoroughly washed with acetone, and dried under vacuum to obtain sulfanilamide disulfide. 0.05 mol of sulfanilamide disulfide and 0.5 mol of triphenylphosphine were dissolved in a mixed solvent of 200 ml of dichloromethane, trifluoroethanol, and water (volume ratio 1:1:1). The mixture was stirred and reduced at room temperature for 48 hours. The aqueous phase was separated, and trifluoroethanol was removed from the aqueous phase by rotary evaporation. The remaining aqueous phase was freeze-dried to obtain zwitterionic ligands, which were stored under an inert gas atmosphere. The reaction process is shown below.

[0041]

[0042] S3. Preparation of cationic ligands: Under an argon atmosphere, 0.022 mol of sodium thiosulfate pentahydrate was dissolved in 20 ml of deionized water and mixed with 0.2 mol of (3-bromopropyl)trimethylammonium bromide. The mixture was heated to 100 °C and stirred under reflux for 12 hours. The Bunte salt intermediate was generated without separation. Concentrated sulfuric acid was added directly to make the final acid concentration reach 1 M. The mixture was stirred under reflux for another 24 hours. The reaction was neutralized by adding 1 M sodium hydroxide aqueous solution. The crude product was separated by freeze drying. The crude product was dissolved in methanol and then filtered. The filtrate was concentrated under vacuum and freeze-dried to obtain disulfide. 0.05 mol of disulfide and 0.5 mol of triphenylphosphine were dissolved in 200 ml of a mixed solvent of dichloromethane, trifluoroethanol and water (volume ratio 1:1:1). The mixture was stirred and reduced at room temperature for 48 hours to obtain cationic ligands. The reaction process is shown below.

[0043]

[0044] S4. Dissolve 250 mg of allylated cellulose, 125 mg of zwitterionic ligand, and 125 mg of cationic ligand in a methanol / trifluoroethanol solution. Add 34 mg of 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylphenylacetone as a photoinitiator. Stir the reaction under ultraviolet light at a wavelength of 365 nm for 45 minutes. The ultraviolet lamp used is DYMAX's BlueWave. TM A 50AS UV curing point light source lamp was used. After the reaction was completed, excess zwitterionic ligands and photoinitiators were removed by dialysis. The dialysis membrane was a cellulose dialysis membrane (molecular weight cutoff = 12500). Dialysis with deionized water was used to obtain modified cellulose 1.

[0045] Modified cellulose 2: The preparation method differs from that of modified cellulose 1 in that the amount of zwitterionic ligand and cation added in step S4 is changed to 200 mg of zwitterionic ligand and 50 mg of cation ligand.

[0046] Modified cellulose 3: The preparation method differs from that of modified cellulose 1 in that the amount of zwitterionic ligand and cation added in step S4 is changed to 50 mg of zwitterionic ligand and 200 mg of cation ligand.

[0047] Modified cellulose 4: The preparation method differs from that of modified cellulose 1 in that the amount of zwitterionic ligand and cation added in step S4 is changed to 250 mg of zwitterionic ligand and 250 mg of cation ligand.

[0048] Modified cellulose 5: The preparation method differs from that of modified cellulose 1 in that the amount of zwitterionic ligand and cation added in step S4 is changed to 0 mg zwitterionic ligand and 250 mg cation ligand.

[0049] Modified cellulose 6: The preparation method differs from that of modified cellulose 1 in that the amount of zwitterionic ligand and cation added in step S4 is changed to 250 mg of zwitterionic ligand and 0 mg of cation ligand.

[0050] Unless otherwise specified, all components and raw materials used in the embodiments and comparative examples of this invention are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0051] Example 1

[0052] A digital printing process for all-cotton fabrics includes the following steps:

[0053] Pretreatment paste preparation → Fabric sizing → Drying I → Digital printing → Drying II → Steaming → Washing I → Soaping → Washing II → Drying III; Specific steps are as follows:

[0054] Preparation of pretreated slurry: By mass percentage, the pretreated slurry comprises the following components: sodium alginate 2%, modified cellulose 1%, urea 9%, sodium sulfate 4%, sodium bicarbonate 3%, anti-dyeing salt S 1%, and the balance being water; the modified cellulose is modified cellulose 1;

[0055] The pretreated slurry is prepared as follows: first, urea, sodium bicarbonate, sodium sulfate and anti-dyeing salt are added to deionized water and stirred thoroughly; then, sodium alginate and modified cellulose are added and stirred for 2 hours.

[0056] Fabric sizing: Immerse the cotton fabric completely in the sizing agent. After 20 minutes, remove the cotton fabric and remove the excess sizing agent with a roller. Use a two-dip, two-roll method with a roll-off rate of 90%. Immediately after rolling, dry and set the fabric at 105℃ for 3 minutes. After removing the fabric, store it in a sealed bag.

[0057] Digital printing: The cotton fabric is fixed and fed into a belt-type digital printing machine. The printing is performed using Adobe Illustrator 2021 software in a single channel. The ink used is the golden yellow, red, bright blue and gray of the Shanyuansu economic light color series from Shanghai Shanyuan Dyestuff Chemical Co., Ltd.

[0058] Steaming: The printed cotton fabric enters the steamer via a guide belt. The steaming temperature is 105℃, the state is atmospheric pressure saturated steam, and the time is 10 minutes.

[0059] Washing and drying: Washing I is a 5-minute wash in 40°C warm water; Soap washing uses standard soap flakes at 1.5g / L, at 95°C, for 10 minutes; Washing II is a 5-minute wash in 40°C warm water followed by a 5-minute wash in cold water; The water bath ratio for soap washing, washing I, and washing II is 30:1; Drying I is at 100°C; Drying II is at 85°C; Drying III is at 110°C.

[0060] Example 2

[0061] The process steps differ from those in Example 1 in that the modified cellulose 1 in the pretreated slurry is replaced with modified cellulose 2.

[0062] Example 3

[0063] The process steps differ from those in Example 1 in that the modified cellulose 1 in the pretreated slurry is replaced with modified cellulose 3.

[0064] Example 4

[0065] The process steps differ from those in Example 1 in that the modified cellulose 1 in the pretreated slurry is replaced with modified cellulose 4.

[0066] Example 5

[0067] The process steps differ from those in Example 1 in that the pretreated slurry, by mass percentage, includes the following components: sodium alginate 1%, modified cellulose 2%, urea 9%, sodium sulfate 4%, sodium bicarbonate 3%, anti-dyeing salt S 1%, and the remainder is water.

[0068] Example 6

[0069] The process steps differ from those in Example 1 in that the pretreated slurry, by mass percentage, comprises the following components: sodium alginate 2.5%, modified cellulose 0.5%, urea 9%, sodium sulfate 4%, sodium bicarbonate 3%, anti-dyeing salt S1%, and the remainder is water;

[0070] Comparative Example 1

[0071] The process steps differ from those in Example 1 in that the modified cellulose 1 in the pretreated slurry is replaced with modified cellulose 5.

[0072] Comparative Example 2

[0073] The process steps differ from those in Example 1 in that the modified cellulose 1 in the pretreated slurry is replaced with modified cellulose 6.

[0074] Comparative Example 3

[0075] The process steps differ from those in Example 1 in that the pretreated slurry, by mass percentage, comprises the following components: sodium alginate 3%, urea 9%, sodium sulfate 4%, sodium bicarbonate 3%, anti-dyeing salt S1%, and the remainder is water;

[0076] Printing quality testing for digital printing

[0077] The cotton fabrics and printing quality of Examples 1-6 and Comparative Examples 1-3 were evaluated. The digital printing content consisted of 15cm×4cm CMYK four-color blocks and 0.5mm lines. The K / S value, clarity, uniformity and color fastness of the printed fabrics were tested. The results are shown in Table 1.

[0078] (1) K / S value: Measured using a DataColor850 colorimeter, with the light source set to D65, viewing angle set to 10°, and aperture set to medium aperture (20mm). The fabric was folded twice to ensure opacity, and the total CMYK value was calculated.

[0079] (2) Clarity: The printing effect of the lines represents the ink penetration on the fabric. The obtained fabric is placed under the RH-2000 digital video optical microscope and magnified 40 times. Visual inspection is conducted to check whether the lines have unclear boundaries or penetration.

[0080] (3) Uniformity: Using a certain point on the fabric as a standard, test the color intensity value at 20 locations on the fabric, and then calculate the average absolute deviation of the values. The larger the average absolute deviation, the greater the data dispersion and the less uniform the printed fabric sample is; conversely, the smaller the average absolute deviation, the more uniform it is.

[0081] (4) Color fastness: Color fastness to rubbing was determined according to GB / T3920-2008 "Textiles - Tests for Color Fastness to Rubbing"; Color fastness to washing was determined according to GB / T3921-2008 "Textiles - Tests for Color Fastness to Rubbing: Test 1";

[0082] Table 1. Performance test results of the printed fabrics in the examples and comparative examples.

[0083]

[0084] As can be seen from the data in Table 1, the printed cotton fabrics obtained by the treatment solutions in Examples 1 to 6 have the advantages of high K / S value, high clarity, good uniformity and color fastness.

[0085] As can be seen from Examples 1-3 and Comparative Examples 1-2, the best dye uptake, clarity, uniformity, and color fastness of digital printing on cotton fabrics are achieved when the modified cellulose surface simultaneously carries both zwitterionic and cationic ligands. When the modified cellulose surface only contains zwitterionic ions, the total charge on the modified fiber surface is 0 under neutral conditions. Under alkaline conditions, the positively charged quaternary ammonium is partially neutralized, and the modified cellulose surface exhibits a negative charge, which electrostatically repels cotton fibers and reactive dyes, easily leading to unclear printing boundaries and bleeding. When the modified fiber surface only contains cationic ions, the electrostatic adsorption effect of the pretreatment paste on both cotton fabric and dye is good, but competitive adsorption occurs, affecting the binding between the dye and cotton fabric, thus affecting the dye uptake.

[0086] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A digital printing process for all-cotton fabrics, characterized in that, The following steps are involved: Pretreatment paste preparation → Fabric sizing → Drying I → Digital printing → Drying II → Steaming → Washing I → Soap washing → Washing II → Drying III; The pretreated slurry, by mass percentage, comprises the following components: sodium alginate 1-4%, modified cellulose 0.5%-2%, urea 6-12%, sodium sulfate 2-8%, sodium bicarbonate 2-6%, anti-dyeing salt 0-1%, and the balance being water; The modified cellulose is a cellulose with cationic and zwitterionic surface modification, which is prepared by reacting allylated cellulose with zwitterionic ligands with thiol groups and cationic ligands with thiol groups via a UV-initiated thiol-ene click reaction. The zwitterionic ligand with a thiol group has the structure shown in Formula 1, and the cationic ligand with a thiol group has the structure shown in Formula 2. The method for preparing the allylated cellulose is as follows: cellulose is reacted with allyl bromide or allyl chloride under alkaline conditions. The steps of the thiol-ene click reaction are as follows: allylated cellulose, zwitterionic ligands and cationic ligands react under photoinitiator and ultraviolet light irradiation; The cellulose is at least one of hydroxyethyl cellulose, hydroxypropyl methylcellulose, or hydroxyethyl methylcellulose.

2. The all-cotton digital printing process as described in claim 1, characterized in that, The zwitterionic ligand is prepared by reacting cystamine with iodomethane to obtain bis(2-dimethylaminoethyl) disulfide, reacting bis(2-dimethylaminoethyl) disulfide with vinyl sulfate in a ring-opening reaction to obtain sulfanilamide disulfide, and then reducing sulfanilamide disulfide under the action of triphenylphosphine to obtain the zwitterionic ligand. The reaction process is shown in Formula 3.

3. The all-cotton digital printing process as described in claim 1, characterized in that, The cationic ligand is obtained by reacting (3-bromopropyl)trimethylammonium bromide with sodium thiosulfate, followed by reduction with sulfuric acid and triphenylphosphine, as shown in Formula 4:

4. The all-cotton digital printing process as described in claim 1, characterized in that, The pretreated slurry is prepared as follows: first, add urea, sodium bicarbonate, sodium sulfate and anti-dyeing salt to deionized water and stir thoroughly; then add sodium alginate and modified cellulose and stir evenly.

5. The all-cotton digital printing process as described in claim 1, characterized in that, The mass ratio of the cationic ligand to the zwitterionic ligand is (1-4):(1-4).

6. The all-cotton digital printing process as described in claim 1, characterized in that, The fabric sizing process is as follows: the cotton fabric is completely immersed in the sizing agent, and after a period of time, the cotton fabric is taken out and the excess sizing agent is removed by a rolling mill. The process is carried out by two dips and two rollings. After rolling, the fabric is dried and shaped immediately, and then placed in a sealed bag for storage.

7. The all-cotton digital printing process as described in claim 1, characterized in that, The temperature of drying I is 80-120℃; the temperature of drying II is 65-105℃; the temperature of drying III is 100-120℃; the steam temperature is 100-105℃, the state is atmospheric pressure saturated steam, and the time is 8-20 minutes.

8. The all-cotton digital printing process as described in claim 1, characterized in that, The soap washing uses standard soap flakes at a concentration of 1-2 g / L, a temperature of 90-100℃, and a washing time of 8-12 minutes; the water washing I is a 4-6 minute wash in warm water at 35-45℃; the water washing II is a 4-6 minute wash in warm water at 35-45℃ followed by a 4-6 minute wash in cold water; the water bath ratio for the soap washing, water washing I, and water washing II is 40:1-20:1.

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