Photochromic printing paste for denim discharge and method of making same

Abstract

This invention discloses a photochromic printing paste for denim discharge dyeing and its preparation method, belonging to the field of textile processing technology. The paste uses a deep eutectic solvent as the continuous phase, compounded with polymerizable photochromic functional monomers, inorganic persulfate, and multifunctional crosslinking agents. By controlling the free radical reaction environment and low water activity through the deep eutectic solvent, the storage stability, rheological stability, and printing adaptability of the persulfate and functional monomers are significantly improved. After printing on indigo denim, a one-step dry heat baking process allows the persulfate to perform both oxidative discharge dyeing and free radical initiation, enabling controlled and synergistic discharge dyeing and in-situ polymerization fixation. Without additional fixation, a photochromic three-dimensional crosslinked network pattern with excellent wash resistance and durability can be constructed in the discharge area.

Description

Technical Field

[0001] This invention belongs to the field of textile processing technology, and particularly relates to a photochromic printing paste for denim discharge dyeing and its preparation method. Background Technology

[0002] Denim apparel occupies a significant share of the textile industry. To give it richer visual layers and a more personalized appearance, discharge printing technology, which uses chemical reagents to locally disrupt the conjugated structure of indigo dye on the fabric surface, has been widely applied. With the development of smart textiles, introducing photochromic technology into the surface of denim apparel, enabling reversible color changes under sunlight or ultraviolet light, has become an important research and development direction for enhancing the added value of denim products. However, combining denim discharge printing with photochromic printing faces significant technical bottlenecks within the existing denim processing system.

[0003] Current denim discharge dyeing processes primarily rely on aqueous printing pastes, with discharge agents typically categorized into reducing discharge agents (such as thiourea dioxide and chloroform) and strong oxidizing discharge agents. These discharge agents readily dissociate in the presence of moisture, releasing strongly reducing or oxidizing active ingredients during subsequent high-temperature steaming or baking to chemically degrade the base color, indigo. This extreme chemical environment is highly detrimental to photochromic materials. Photochromic compounds (such as spiroxazine and naphthopyran dyes) rely on photoisomerization of sensitive conjugated systems within their molecules to achieve color switching. This intricate organic structure is extremely sensitive to surrounding redox environments and pH levels, making it highly susceptible to attack and inactivation by discharge agents.

[0004] Due to the aforementioned chemical conflicts, traditional processing methods typically employ a two-step process: first, the denim fabric is partially decolored using discharge dye, followed by high-temperature steaming and multiple consecutive washes to remove residual chemicals, and then dried. A second printing process involving the application of a dye-containing paste with photochromic dyes and water-based binders is then performed and the color is fixed. This process is lengthy and inefficient. Furthermore, the denim fabric is prone to uncontrollable shrinkage and deformation after the initial discharge dyeing and multiple washes and dryers, making screen registration extremely difficult during the second printing process. This results in ghosting or white areas at the edges of the pattern, severely impacting the yield. In addition, repeated washing and drying lead to high energy and water consumption, as well as significant wastewater discharge.

[0005] To overcome the drawbacks of the two-step method, the industry has attempted to develop "one-step" printing pastes that directly mix discharge agents with photochromic components, but these efforts have failed to achieve industrialization due to unresolved stability issues. In conventional aqueous media, traditional discharge agents exhibit high activity at room temperature, readily reacting with coexisting photochromic molecules in non-targeted reactions, leading to oxidation or reduction deactivation of the color-changing monomers during storage. Even if room temperature stability is maintained, the active free radicals or ions released from the discharge agent during subsequent high-temperature heat treatment indiscriminately attack the chemical framework of the photochromic dyes, causing them to completely lose their photochromic activity. Furthermore, the high concentration of electrolytes in traditional discharge systems easily triggers demulsification and gelation of conventional aqueous adhesive emulsions, resulting in deterioration of the paste's rheological properties and failing to meet the wash fastness and color-changing durability requirements for wearable applications.

[0006] Therefore, how to construct a new printing paste system, regulate the dynamic boundary of discharge dyeing and functional molecule fixation, and complete the local discharge dyeing and in-situ photochromic construction of denim substrates in one step without damaging the activity of photochromic molecules, while maintaining the excellent storage and rheological characteristics of the paste, is a technical problem that urgently needs to be solved in the denim printing and processing field. Summary of the Invention

[0007] The purpose of this invention is to provide a photochromic printing paste, which, by weight, comprises the following components: Deep eutectic solvent, 60.0-85.0 parts; Polymerizable photochromic functional monomers, 1.0-5.0 parts; Inorganic persulfate, 3.0-10.0 parts; Multifunctional crosslinking agent, 0.5-2.0 parts; The deep eutectic solvent is composed of choline chloride and a hydrogen bond donor in a molar ratio of 1:1.5-2.5; the hydrogen bond donor is an aliphatic polyol or an aliphatic amide. The polymerizable photochromic functional monomer is a photochromic dye substituted with unsaturated groups that have free radical polymerization activity; The multifunctional crosslinking agent is a (meth)acrylate crosslinking agent containing 2 or 3 (meth)acryloyloxy groups in its structure.

[0008] Preferably, the polymerizable photochromic functional monomer is a spiroxazine dye or a naphthopyran dye substituted with an unsaturated group having free radical polymerization activity.

[0009] Preferably, the free water content in the photochromic printing paste is ≤1.0wt%, and its yield stress at 25°C is 50–200Pa. The apparent pH value of the photochromic printing paste diluted with deionized water at a mass ratio of 1:10 is 6.5–8.0.

[0010] Preferably, the average particle size D50 of the inorganic persulfate is 1-10 μm.

[0011] Preferably, the multifunctional crosslinking agent has a boiling point ≥250°C at one atmosphere and a mass loss rate ≤1.0% after exposure at 150°C for 5 min.

[0012] Preferably, the aforementioned photochromic printing paste, by weight, further includes the following components: Free radical thermal inhibitor, 0.01-0.1 parts; Thixotropic rheology modifier, 0.2-2.5 parts; Non-aqueous phase defoamer, 0.07-1.0 parts.

[0013] Preferably, the free radical thermal inhibitor is a hindered phenolic compound.

[0014] Preferably, the thixotropic rheology modifier is fumed silica, and the drying weight loss of the fumed silica itself is ≤0.5wt%.

[0015] A second objective of this invention is to provide a method for preparing the aforementioned photochromic printing paste, comprising the following steps: S1 matrix preparation: Choline chloride is mixed with the hydrogen bond donor and stirred under heating conditions until a uniform and transparent liquid is formed to obtain a deep eutectic solvent; S2 component compounding: After cooling the deep eutectic solvent obtained in step S1, add the remaining raw materials to it and stir to mix evenly; S3 Homogeneous Dispersion: The mixture obtained in step S2 is subjected to shear dispersion or grinding treatment so that the inorganic persulfate is uniformly suspended and dispersed in the deep eutectic solvent in the form of solid particles, thereby obtaining the photochromic printing paste.

[0016] The photochromic printing paste provided by this invention uses a deep eutectic solvent as the continuous phase. Compared with traditional aqueous printing pastes, it can synergistically regulate the generation, mass transfer and consumption behavior of the free radical system during paste storage, baking reaction and fixation, thereby achieving one-step completion of oxidative discharge and photochromic functional fixation.

[0017] During the paste preparation and room temperature storage stages, the deep eutectic solvent, with its low water activity, reduces the non-target decomposition rate of inorganic persulfate during storage, thereby improving the storage stability of the oxidation initiator. Simultaneously, the hydrogen-bonded network and higher viscosity formed by the deep eutectic solvent reduce the diffusion rate of each component in the system, ensuring a lower probability of direct contact between the polymerizable photochromic functional monomer and the inorganic persulfate, thus reducing the possibility of oxidation of the photochromic functional monomer during storage. In the preferred embodiment, the use of thermosensitively coated inorganic persulfate particles further delays the contact between the oxidation initiator and the system, improving the paste's storage stability. The thixotropic rheological structure in the paste ensures uniform suspension of solid particles and meets the rheological properties required for screen printing.

[0018] After the printed denim enters the baking stage, as the temperature rises, the molecular motion of the deep eutectic solvent system is enhanced, and the wetting and penetration ability of the sizing agent on the surface of the cotton fiber is improved, which is conducive to the migration of the sizing agent to the fiber surface and the shallow amorphous region. At the same time, the inorganic persulfate gradually decomposes to generate sulfate free radicals, which trigger oxidative discharge reaction and free radical polymerization reaction.

[0019] In the initial baking stage, due to the large amount of indigo dye still concentrated in the patterned area, free radicals preferentially participate in the oxidative decolorization reaction of the indigo dye, disrupting the conjugated structure of the indigo molecules and achieving in-situ whitening of the patterned area. As the discharge reaction proceeds, the base dye gradually decreases, and the proportion of free radicals participating in the polymerization reaction of polymerizable photochromic functional monomers and multifunctional crosslinking agents gradually increases. The two undergo free radical crosslinking copolymerization, forming a three-dimensional crosslinked polymerization network on the fiber surface and in the shallow amorphous region. Because the deep eutectic solvent system can weaken the inhibitory effect of oxygen on free radical polymerization, the polymerization reaction can proceed more fully, stabilizing the photochromic groups in the whitened area and improving the wash fastness and cyclic color change stability of the pattern.

[0020] Therefore, this invention utilizes a deep eutectic solvent to reconstruct the free radical reaction environment in the traditional discharge printing system, enabling the originally competing oxidative discharge reaction and polymerization fixation reaction to proceed in a controlled manner during the same baking process. This achieves the integrated completion of the whitening and photochromic functions of denim fabrics, allowing for the acquisition of photochromic patterns with excellent durability without additional color-fixing treatment.

[0021] The present invention has the following beneficial effects: (1) The present invention uses a deep eutectic solvent as a continuous phase, which improves the storage stability of inorganic persulfate and reduces the possibility of photochromic functional monomers being oxidized and deactivated during storage, thus giving the printing paste good storage stability.

[0022] (2) This invention utilizes inorganic persulfate, which has both oxidative discharge and free radical initiation functions, to achieve in-situ fixation of denim substrate whitening and photochromic functions in the same baking process, reducing process steps and improving processing efficiency.

[0023] (3) The present invention forms a cross-linking polymer network by polymerizable photochromic functional monomers and multifunctional cross-linking agents, so that photochromic molecules are stably fixed on the fiber surface and shallow amorphous area, thereby improving the wash fastness and photochromic durability of printed patterns.

[0024] (4) The printing paste obtained by the present invention has good rheological stability and printing adaptability, and can obtain denim printed products with uniform whitening, clear pattern and photochromic function.

[0025] (5) By controlling the free radical reaction environment through deep eutectic solvent, the present invention achieves controlled synergistic action of oxidative discharge reaction and free radical polymerization reaction, solves the problem that strong oxidants and photochromic molecules are difficult to coexist stably in traditional discharge system, and improves the process compatibility of the system. Attached Figure Description

[0026] Figure 1 The discoloration effects of embodiments 1, 2, 3, 8, 4, and 10 of the present invention are shown.

[0027] Figure 2 The photochromic performance of Examples 8 and 10 of the present invention is tested; the upper left side is the non-excited state (initial whitening state) of Example 8 without light; the upper right side is the ultraviolet excited state (high saturation color-changing state); and the lower side is the initial whitening state under natural sunlight light source of Example 10. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0030] In the description of this invention, the term "for example" is used to mean "used as an example, illustration, or description." Any embodiment described as "for example" in this invention is not necessarily to be construed as being more preferred or advantageous than other embodiments. The following description is provided to enable any person skilled in the art to make and use the invention. Details are set forth in the following description for purposes of explanation. It should be understood that those skilled in the art will recognize that the invention can be made without using these specific details. In other instances, well-known structures and processes will not be described in detail to avoid obscuring the description of the invention with unnecessary detail. Therefore, the invention is not intended to be limited to the embodiments shown, but is consistent with the broadest scope of the principles and features disclosed herein.

[0031] Unless otherwise specified, the experimental methods used in the specific implementation methods are all conventional methods, and the materials and reagents used are all commercially available unless otherwise specified.

[0032] In this invention, unless otherwise specified, "%" represents a percentage by mass; the raw materials and reagents used are all commercially available products.

[0033] In this invention, the aliphatic polyol is glycerol (glycerol).

[0034] In this invention, the aliphatic amide is urea.

[0035] In this invention, the multifunctional crosslinking agents are polyethylene glycol (400) diacrylate and trimethylolpropane triacrylate.

[0036] In this invention, the polymerizable photochromic functional monomers are allylspiroxazine and naphthopyran methacrylate.

[0037] Allylspiroxazine, specifically 1-allyl-3,3-dimethylspiro[indoline-2,3'-[3H]naphtho[2,1-b][1,4]oxazine], belongs to the spirooxazine class, with an allyl group introduced at the N-position.

[0038] At least 80% of the naphthopyran methacrylate is 2,2-diphenyl-5-methacryloyloxy-2H-naphtho[1,2-b]pyran.

[0039] In this invention, the inorganic persulfate is ammonium persulfate, specifically an industrial-grade ammonium persulfate solid crystalline powder with an average particle size D50 of 3.5 μm, which has been mechanically finely pulverized or air-jet milled.

[0040] In this invention, the free radical thermal inhibitor is 2,6-di-tert-butyl-p-cresol (BHT).

[0041] In this invention, the thixotropic rheology modifier is hydrophobic fumed silica with a drying weight loss rate of ≤0.3wt%.

[0042] In this invention, the non-aqueous defoamer is a silicone-free polyacrylate non-aqueous system defoamer, specifically BYK®-052 from BYK Chemicals.

[0043] This invention selects pure indigo-dyed warp yarns, fully desized (desizing rate ≥98%), and untreated with color fixing and silicone softening finishing as the base material.

[0044] Example 1: Preparation of Spiroxazine Photochromic Printing Paste 1. Reaction raw materials and their mass ratio Choline chloride: 30.1 parts; Glycerol: 29.9 parts; Allylspiroxazine: 1.0 part; Ammonium persulfate: 3.0 parts; Polyethylene glycol (400) diacrylate: 0.5 parts; Free radical thermal inhibitor: 0.01 parts; Thixotropic rheology modifier: 0.2 parts; Non-aqueous phase defoamer: 0.07 parts.

[0045] 2. Preparation steps Preparation of S1 matrix: Anhydrous choline chloride and dried glycerol (with the total initial water content of the mixture controlled to ≤0.1 wt%) were added to a reaction vessel. Stirring was started, and the stirring speed was adjusted to 300–400 rpm. The temperature was raised to 75°C and stirred for 1.5 h. The reaction continued until the system had completely reacted and formed a colorless, clear, homogeneous, and transparent liquid, yielding a deep eutectic solvent. The system was then cooled to 30°C for later use.

[0046] S2 component compound: Under light-protected conditions, allyl spirooxazine monomer, polyethylene glycol (400) diacrylate crosslinking agent, free radical thermal inhibitor, and non-aqueous defoamer were sequentially added to the cooled deep eutectic solvent. The stirring speed was increased to 600 rpm, and the mixture was stirred at high speed for 30 min at 35°C in the dark to ensure that the polymerizable functional monomer, crosslinking agent, and organic additives were completely dissolved and microscopically uniformly dispersed, thus forming a liquid pre-dispersed phase.

[0047] S3 homogeneous dispersion: Add a thixotropic rheology modifier and 3.0 parts of solid ammonium persulfate particles with an average particle size D50 of 3.5 μm to the liquid pre-dispersed phase obtained in step S2. Transfer the mixture to a high-shear homogenizer and perform high-speed shearing and cold grinding at 4500 rpm for 20 min under conditions of light protection and cooling circulating water (material temperature controlled ≤40°C). This allows the solid ammonium persulfate particles and the rheology modifier to form a highly micro-nano suspension in the non-aqueous matrix, ultimately obtaining a rheologically stable photochromic printing paste.

[0048] 3. Finished product performance test results Free water content detection: The free water mass fraction in the slurry of this embodiment was 0.32 wt% as determined by the Karl Fischer coulometric method.

[0049] Yield stress test: Shear stress scanning was performed using a rotational rheometer at 25°C, and the yield stress of the slurry was measured to be 68 Pa.

[0050] Apparent pH value test: The printing paste prepared in this embodiment was mixed with deionized water at a mass ratio of 1:10 and diluted evenly. The apparent pH value was measured to be 6.95 using a potentiometric pH meter.

[0051] Crosslinking agent thermal stability test: The polyethylene glycol (400) diacrylate crosslinking agent used in this example has a boiling point greater than 250°C at one atmosphere. After the sample was exposed in a 150°C oven for 5 minutes, its heat loss rate was measured to be 0.45 wt%.

[0052] Example 2: Preparation of Naphthopyran Photochromic Printing Paste 1. Reaction raw materials and their mass ratio Choline chloride: 36.50 parts; Urea: 23.50 parts; Naphthopyran methacrylate: 1.0 part; Ammonium persulfate: 3.0 parts; Trimethylolpropane triacrylate: 0.5 parts; Free radical thermal inhibitor: 0.01 parts; Thixotropic rheology modifier: 0.2 parts; Non-aqueous phase defoamer: 0.07 parts.

[0053] 2. Preparation steps Preparation of S1 matrix: Anhydrous choline chloride and dried urea were added to a reaction vessel, stirred at 350 rpm and heated to 80°C. The mixture was stirred at a constant temperature for 1.0 h until a colorless and clear liquid was formed, thus obtaining a deep eutectic solvent. The solvent was then cooled to 30°C for later use.

[0054] S2 component compound: Under light-protected conditions, naphthopyran methacrylate, trimethylolpropane triacrylate, free radical thermal inhibitor, and non-aqueous defoamer were sequentially added to the above-mentioned deep eutectic solvent. The mixture was stirred at a high speed of 600 rpm for 25 min to completely dissolve all organic components and construct a liquid predispersed phase.

[0055] S3 homogeneous dispersion: Thixotropic rheology modifier and solid ammonium persulfate particles are added to the pre-dispersed phase in step S2. The material is placed in a high-shear homogenizer and homogenized at a high speed of 5000 rpm for 15 minutes under conditions of light protection and cooling circulating water (material temperature ≤40°C) to uniformly suspend the solid particles, and finally obtain a rheologically stable photochromic printing paste.

[0056] 3. Finished product performance test results Free water content: The free water mass fraction in the slurry was 0.25 wt%, as determined by the Karl Fischer method.

[0057] Yield stress: The yield stress of the slurry was measured to be 72 Pa at 25°C.

[0058] Apparent pH value: After the slurry was diluted with deionized water at a mass ratio of 1:10, its apparent pH value was measured to be 7.12.

[0059] Thermal stability of the crosslinking agent: The trimethylolpropane triacrylate crosslinking agent used in this embodiment has a boiling point greater than 390°C at one atmosphere, and its heat loss rate after exposure to 150°C for 5 minutes is only 0.35 wt%. Example 3: Preparation of High Load Limit Photochromic Printing Paste 1. Reaction raw materials and their mass ratio Choline chloride: 32.10 parts; Glycerol: 52.90 parts; Allylspiroxazine: 5.0 parts; Ammonium persulfate: 10.0 parts; Polyethylene glycol (400) diacrylate: 2.0 parts; Free radical thermal polymerization inhibitor: 0.1 parts; Thixotropic rheology modifier: 2.5 parts; Non-aqueous phase defoamer: 1.0 part.

[0060] 2. Preparation steps S1: Choline chloride and glycerol were placed in a reaction vessel and stirred at 80°C for 2.0 h at a rate of 400 rpm until completely transparent to obtain the DES matrix. The temperature was then lowered to 30°C.

[0061] S2: Under light-protected conditions, add allyl spiroxazine, crosslinking agent, free radical thermal inhibitor, and non-aqueous phase defoamer to the DES matrix, and stir at a high speed of 600 rpm for 30 min.

[0062] S3: Continue to add thixotropic rheology modifier and solid ammonium persulfate, transfer to a high-shear homogenizer, and shear at a high speed of 5000 rpm for 20 minutes under conditions of light protection and temperature control ≤40°C to obtain the finished slurry.

[0063] 3. Finished product performance test results Free water content: 0.45 wt%.

[0064] Yield stress (25°C): 185 Pa.

[0065] Apparent pH (1:10 dilution): 7.25.

[0066] Example 4: Preparation of Comparative Printing Paste without Functional Additives 1. Reaction raw materials and their mass ratio Except for the absence of free radical thermal inhibitors, thixotropic rheology modifiers, and non-aqueous defoamers, the other raw materials and proportions are exactly the same as in Example 1: 2. Preparation steps The method of Example 1 was followed, but the addition of relevant additives was omitted in steps S2 and S3, and the ammonium persulfate solid particles were directly homogenously dispersed in the DES matrix containing monomers and crosslinking agents.

[0067] 3. Results and Explanation The yield stress of the finished slurry at 25°C is only 8 Pa.

[0068] Example 5: Preparation of Comparative Printing Paste for Non-eutectic Non-aqueous Media 1. Reaction raw materials and their mass ratio Replace the hydrogen bond donor glycerol in the formulation of Example 1 with an equal amount of a monohydric fatty alcohol (n-octanol): The types and mass fractions of the remaining functional monomers, persulfates, crosslinking agents, and additives are exactly the same as in Example 1.

[0069] 2. Preparation steps An attempt was made to mix choline chloride and n-octanol at 75°C using the method described in step S1. Because n-octanol is an insoluble, hydrogen-bonded solvent for choline chloride, the system exhibited severe solid insolubility and oil phase separation. Forced cooling was followed by the addition of the remaining components and high-shear homogenization, which barely resulted in an unstable suspension.

[0070] 3. Results Explanation Unmet requirements: Due to the severe stratification and anisotropy of the system, it is impossible to measure stable yield stress and apparent pH value.

[0071] Example 6: Preparation of printing paste with high volatile crosslinking agent in proportion 1. Reaction raw materials and their mass ratio The crosslinking agent in Example 1 was replaced in equal amounts with low molecular weight diol diacrylate: Low molecular weight diol diacrylate crosslinking agent: specifically 1,6-hexanediol diacrylate (HDDA, molecular weight 226.27): 0.5 parts; The remaining components are exactly the same as in Example 1.

[0072] 2. Preparation steps The process flow, mixing rate, and temperature control are exactly the same as in Example 1.

[0073] 3. Results The crosslinking agent exhibited a mass loss rate of 8.5% after exposure at 150°C for 5 minutes.

[0074] Example 7: Preparation of Comparative Printing Paste with Non-Reactive Functional Monomers 1. Reaction raw materials and their mass ratio Replace the polymerizable color-changing monomer in Example 1 with an equal amount of unmodified standard spiroxazine: The unmodified standard spiroxazine is specifically: 1,3,3-trimethylspiro[indoline-2,3'-[3H]naphtho[2,1-b][1,4]oxazine]; The remaining components are exactly the same as in Example 1.

[0075] 2. Preparation steps The process flow, mixing rate, and temperature control are exactly the same as in Example 1.

[0076] 3. Results The physical properties of the finished slurry are: yield stress 68 Pa, apparent pH 6.98, and free water 0.33 wt%.

[0077] Example 8 Preparation of Composite Photochromic Printing Paste 1. Reaction raw materials and their mass ratio Choline chloride: 30.2 parts; Glycerol: 39.8 parts; Allylspiroxazine: 1.5 parts; Naphthopyran methacrylate: 1.5 parts; Ammonium persulfate: 6.0 parts; Polyethylene glycol (400) diacrylate: 0.6 parts; Trimethylolpropane triacrylate: 0.6 parts; Free radical thermal inhibitor: 0.05 parts; Thixotropic rheology modifier: 1.2 parts; Non-aqueous phase defoamer: 0.5 parts.

[0078] 2. Preparation steps S1 matrix preparation: Choline chloride and glycerol were added to a reaction vessel and stirred at 350 rpm at 75°C for 1.5 h until completely transparent to obtain liquid DES matrix, which was then cooled to 30°C.

[0079] S2 component compounding: Under light-protected conditions, allyl spirooxazine, naphthopyran methacrylate, polyethylene glycol (400) diacrylate, trimethylolpropane triacrylate, free radical thermal inhibitor, and non-aqueous phase defoamer are added sequentially to the DES matrix, and the mixture is stirred at a high speed of 600 rpm for 30 min to ensure complete dissolution.

[0080] S3 Homogenization and Dispersion: Continue to add thixotropic rheology modifier and ammonium persulfate, transfer to a high-shear homogenizer, and homogenize at a high speed of 5000 rpm for 20 minutes under conditions of light protection and temperature control ≤40°C to obtain the finished slurry.

[0081] 3. Finished product performance testing and technical effects The free water content of the slurry was measured to be 0.28 wt%; the yield stress at 25°C was 112 Pa; the apparent pH value after dilution with 1:10 water was 7.02; and the mass loss rate of the crosslinking agent after exposure at 150°C for 5 min was 0.40 wt%.

[0082] Example 9: Preparation of High Free Water Comparative Printing Paste 1. Reaction raw materials and their mass ratio In this embodiment, except for the active introduction of deionized water to disrupt the low water activity confined environment, the other raw materials and proportions are exactly the same as in Example 1: 2. Preparation steps After DES is prepared in step S1, in the compounding stage of step S2, 3.0 parts of deionized water are mixed together with the monomer and crosslinking agent. The remaining mechanical stirring and shearing homogenization processes are exactly the same as in Example 1.

[0083] 3. Results The free water content in the finished slurry reached 3.22 wt%; the yield stress at 5°C collapsed to 32 Pa.

[0084] Example 10: Preparation of Strongly Alkaline Comparative Printing Paste 1. Reaction raw materials and their mass ratio In this embodiment, except for the addition of an organic strong base additive to artificially raise the pH value of the system, the other raw materials and proportions are exactly the same as in Example 1: 2. Preparation steps In step S2, during component compounding, 1.2 parts of triethylamine are added along with the monomer and crosslinking agent to utilize its bridging properties. The remaining mixing and shear homogenization processes are exactly the same as in Example 1.

[0085] 3. Results The finished slurry was diluted with deionized water at a mass ratio of 1:10, and its apparent pH value was measured to be 9.65.

[0086] Example 11: Preparation of Large Particle Size Persulfate Comparative Printing Paste 1. Reaction raw materials and their mass ratio In this embodiment, except for the replacement of the particle size distribution of ammonium persulfate, the other raw materials and proportions are exactly the same as in Example 1: Large particle size inorganic persulfate (substitute: commercially available coarse ammonium persulfate powder that has not been air-jet milled, with an average particle size D50 of 45 μm) The remaining components are exactly the same as in Example 1.

[0087] 2. Preparation steps In step S3, coarse ammonium persulfate powder of 45 μm is directly added. Although it also undergoes high-speed shearing at 4500 rpm, the coarse crystals cannot be sheared to the micro-nano level in a short time in the high-viscosity DES because it has not undergone pre-fine airflow pulverization.

[0088] 3. Results The average particle size D50 of the solid particles in the dispersed phase was measured to be 38.5 μm by a laser particle size analyzer.

[0089] Test Example 1: Discharge Processing and Performance Testing of Printing Paste 1. Specific operating steps for discharge printing This test example uniformly uses pure indigo-dyed cotton denim (K / S value of 18) with warp yarns, fully desized (desizing rate ≥98%), and without color fixing or silicone softening treatment as the test substrate. The photochromic printing pastes prepared in Examples 1–11 were subjected to discharge printing. The specific operation process is as follows: Step A: Screen Printing The cotton denim fabric to be tested was laid flat on the printing table. A 140-mesh polyester screen printing stencil was used, with the squeegee angle set to 75°. The photochromic printing paste described in any one of Examples 1–11 was squeegeed onto the denim surface using a flat screen printing method, controlling the wet paste coating amount to be 120–150 g / m². 2 This process yields wet-printed fabrics with preset patterns.

[0090] Step B: Pre-baking Place the wet printed fabric in an oven and pre-dry it at 80°C for 3 minutes to allow the paste to be initially set on the fabric surface.

[0091] Step C: Dry heat baking The fabric was transferred to a tenter frame oven and dried at 140°C for 3 minutes to fix the color.

[0092] Step D: Post-treatment water washing Immediately after baking, the fabric is rinsed in cold water for 1 minute, then transferred to a soap bath containing 2g / L of standard detergent and washed at 60°C for 5 minutes to thoroughly remove residual deep eutectic solvent, unreacted monomers, crosslinking agents and indigo decomposition products. Finally, it is rinsed clean with water.

[0093] Step E: Drying The washed cotton denim is dried in an 80°C oven until it reaches a constant weight, resulting in the final photochromic discharge printed denim fabric.

[0094] 2. Performance Test Items and Evaluation Methods The following dimensions were used to precisely quantify and evaluate the finished denim fabrics processed with the sizing agents of Examples 1–11, as well as the physical stability of the sizing agents themselves: ① Evaluation of discharge effect (whitening rate test) Test method: The reflectance spectrum of the discharge area of ​​the printed fabric (in the unexcited color change state) was measured using a computer colorimeter (Datacolor 800), and its K / S value was calculated according to the Kubelka-Munk formula.

[0095] Whitening rate (%). The formula is: Whitening rate = [(18 - K / S)] 拔染后 The result is calculated as [(18)] × 100%. A higher whitening rate indicates more thorough destruction of the indigo and a whiter base color.

[0096] ② Photochromic performance test Test method: A UVLED ultraviolet light source with a power of 500W and a center wavelength of 365nm was used to vertically irradiate the printed discharge area at a distance of 10cm from the fabric surface to induce a color change reaction.

[0097] Test items: Static color difference (ΔE) * The total color difference ΔE (CIE L*a*b*) between the state before ultraviolet irradiation (whitening state) and the state after irradiation to equilibrium (color change state) is measured using a colorimeter to evaluate the color change sensitivity.

[0098] Light response time (T)90 : Record the time (in seconds) required for the color-changing area to reach 90% of the maximum color-changing depth.

[0099] Light fatigue resistance (light fatigue resistance): The discolored fabric is placed in a light resistance tester (xenon arc lamp, conforming to GB / T8427 standard) for continuous exposure for 24 hours, and the retention rate (%) of the maximum color difference before and after exposure is tested.

[0100] ③ Evaluation of wash fastness and functional durability Test method: The test shall be conducted in strict accordance with the "Test C(3)" standard in GB / T 3921-2008 "Textiles - Tests for color fastness to washing".

[0101] Test items: Standard color fastness: The staining grade and discharge grade of the all-cotton white lining fabric are assessed using the staining grey scale and the discoloration grey scale (grades 1–5).

[0102] Color-changing function retention rate: After 20 and 50 cycles of standard soap washing, the color difference ΔE under UV irradiation was retested. * After washing, calculate the light intensity retention rate = (ΔE) * After washing / ΔE * (Before washing) × 100%, used to evaluate the strength of the covalent bond network of the color-changing dye.

[0103] The results are shown in Table 1.

[0104] Table 1 ; Partial discharge effect, such as Figure 1 As shown. The photochromic performance test is as follows. Figure 2 As shown, Example 8 exhibits a pure white state with sharp edges in the absence of light. After ultraviolet excitation, the two monomers respond in situ in a synergistic manner, presenting a composite purplish-red color with uniform spatial distribution. However, Example 10, due to irreversible ring-opening deadlock caused by strong base, produces an uneven burnt yellow residual color and severe edge burrs and color bleeding even before excitation.

[0105] As shown in Table 1, the formulation system of this invention exhibits a decolorizing effect in the indigo discharge dyeing of all-cotton denim. The non-aqueous reaction medium constructed mainly with a deep eutectic solvent exhibits penetration and mass transfer properties under dry heat baking conditions. It can swell the amorphous regions of cotton fibers and transport the encapsulated inorganic persulfate into the fiber interior, thereby causing in-situ oxidation and destruction of the conjugated color-forming structure of indigo dye, achieving a high whitening rate.

[0106] In the comparative examples, when a monohydric alcohol (Example 5) was used instead of a polyhydric alcohol, the system was prone to solid insolubility and phase separation because a deep eutectic solvent network with hydrogen bonding could not be formed. During the baking stage, the monohydric alcohol volatilized before reaching the reaction temperature, hindering the swelling and penetration of the oxidant into the inner layer of the fiber, thus limiting the discharge function. In the comparative example (Example 9) where free water was actively introduced, the discharge rate decreased after sealed storage. This is because the presence of free water increased the water activity in the system, causing the solid persulfate, which was in a protected state, to undergo non-target hydrolysis and premature decomposition during storage, consuming the active free radicals required for discharge.

[0107] In the comparative example introducing a strongly alkaline auxiliary agent (Example 10), the apparent environment of the system shifts towards alkalinity. During the high-temperature baking and fixation stage, the intermediate structure generated after the photochromic monomer undergoes ring-opening is susceptible to nucleophilic attack in the alkaline environment, causing structural damage or irreversible ring-opening deadlock of the photochromic molecule system. This change in chemical structure results in permanent residual color in the discharge area of ​​the fabric under dark conditions, and it no longer possesses reversible photochromic properties.

[0108] Regarding wash fastness and functional durability, the comparative example (Example 6) using a low-boiling-point, high-volatility crosslinking agent showed a significant performance decline after repeated washing. The underlying mechanism is that during the high-temperature baking process, the crosslinking agent molecules evaporate and escape from the slurry surface before complete free radical-initiated polymerization, resulting in insufficient density of the three-dimensional crosslinked network on the fiber surface and reducing the system's ability to resist surfactant washing dissolution and mechanical friction.

[0109] Similarly, in the comparative example (Example 7) using conventional color-changing dyes without polymerizable active groups, the dye molecules lack unsaturated double bonds suitable for polymerization and cannot participate in the free radical copolymerization reaction with the crosslinking agent. Therefore, they cannot be covalently anchored and embedded into the macromolecular network segments. Under the spatial confinement of relying solely on physical encapsulation or loose adsorption, the dye molecules lack inherent affinity for the cotton fibers, making them highly susceptible to interfacial desorption during post-treatment and subsequent cyclic washing stages, resulting in a rapid loss of color-changing function.

[0110] Furthermore, the comparative example (Example 11) using large-particle-size persulfate powder also showed a low whitening rate. The mechanism is that the specific surface area of ​​the coarse solid crystals is small. During the dry heat baking time, the solid-liquid heterogeneous dissolution and free radical diffusion rate lag behind the heating rate of the fabric, resulting in incomplete decolorization of the base color and the formation of uneven distribution characteristics on the fabric surface.

[0111] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A photochromic printing paste, characterized in that, Calculated by parts by weight, it includes the following components: Deep eutectic solvent, 60.0-85.0 parts; Polymerizable photochromic functional monomers, 1.0-5.0 parts; Inorganic persulfate, 3.0-10.0 parts; Multifunctional crosslinking agent, 0.5-2.0 parts; The deep eutectic solvent is composed of choline chloride and a hydrogen bond donor in a molar ratio of 1:1.5-2.5; the hydrogen bond donor is an aliphatic polyol or an aliphatic amide. The polymerizable photochromic functional monomer is a photochromic dye substituted with unsaturated groups that have free radical polymerization activity; The multifunctional crosslinking agent is a (meth)acrylate crosslinking agent containing 2 or 3 (meth)acryloyloxy groups in its structure.

2. The photochromic printing paste according to claim 1, characterized in that, The polymerizable photochromic functional monomer is a spiroxazine dye or a naphthopyran dye substituted with an unsaturated group having free radical polymerization activity.

3. The photochromic printing paste according to claim 1, characterized in that, The free water content in the photochromic printing paste is ≤1.0wt%, and its yield stress at 25°C is 50–200Pa.

4. The photochromic printing paste according to claim 1, characterized in that, The apparent pH value of the photochromic printing paste diluted with deionized water at a mass ratio of 1:10 is 6.5–8.

0.

5. The photochromic printing paste according to claim 1, characterized in that, The average particle size D50 of the inorganic persulfate is 1-10 μm.

6. The photochromic printing paste according to claim 1, characterized in that, The multifunctional crosslinking agent has a boiling point ≥250°C at one atmosphere and a mass loss rate ≤1.0% after exposure at 150°C for 5 min.

7. The photochromic printing paste according to claim 1, characterized in that, Based on parts by mass, it also includes the following components: Free radical thermal inhibitor, 0.01-0.1 parts; Thixotropic rheology modifier, 0.2-2.5 parts; Non-aqueous phase defoamer, 0.07-1.0 parts.

8. The photochromic printing paste according to claim 7, characterized in that, The free radical thermal inhibitor is a hindered phenolic compound.

9. The photochromic printing paste according to claim 7, characterized in that, The thixotropic rheology modifier is fumed silica, and the drying weight loss of the fumed silica itself is ≤0.5wt%.

10. A method for preparing a photochromic printing paste according to any one of claims 1-9, characterized in that, Includes the following steps: S1 matrix preparation: Choline chloride is mixed with the hydrogen bond donor and stirred under heating conditions until a uniform and transparent liquid is formed to obtain a deep eutectic solvent; S2 component compounding: After cooling the deep eutectic solvent obtained in step S1, add the remaining raw materials to it and stir to mix evenly; S3 Homogeneous Dispersion: The mixture obtained in step S2 is subjected to shear dispersion or grinding treatment so that the inorganic persulfate is uniformly suspended and dispersed in the deep eutectic solvent in the form of solid particles, thereby obtaining the photochromic printing paste.

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