Silk sericin micro-nanoparticle neutral ink, preparation method and application thereof

Abstract

The present application relates to the technical field of neutral ink, and particularly relates to a sericin micro-nanoparticle neutral ink, a preparation method and application thereof, sericin micro-nanoparticles 0.05% to 20%, colorant 0.05% to 40%, additive 0.05% to 1.0%, antibacterial agent 0.05% to 1.0%, and the balance is water; the sericin micro-nanoparticles are prepared from sericin through glutamine transaminase crosslinking. The present application adopts glutamine transaminase crosslinking sericin protein to form sericin micro-nanoparticles as a film forming agent and a load stable base material, which is added into neutral ink, has a higher specific surface area, more hydrophobic groups and hydrophilic groups, so as to load and disperse biodegradable natural colorant through interface interaction, so that the neutral ink is functionalized, has higher colorant loadability, and meanwhile, the sericin micro-nanoparticles have excellent antioxidant property, can effectively protect biodegradable colorant, and improve the photo-thermal stability thereof.

Description

Technical Field

[0001] This invention relates to the technical field of neutral inks, specifically to a sericin micro / nano particle neutral ink, its preparation method, and its applications. Background Technology

[0002] Currently, traditional inks are commonly used in both domestic and international markets. However, some traditional inks contain harmful substances in their raw materials (such as heavy metals, sulfuric acid, and volatile organic compounds). These substances pose a threat to the health of ink production workers during the ink manufacturing process and also have an impact on consumers, especially young students whose curiosity may lead to accidental ingestion, posing a significant safety hazard. Furthermore, the discharge of these ink substances into the environment can cause pollution and spark controversies related to environmental protection and degradation. At the same time, the limited color options available for existing neutral inks restrict their application scenarios and hinder their potential for expanding market share. The green, environmentally friendly, safe, and harmless development of inks is based on the global trend of green development and national policies. Biodegradable neutral ink is a new type of green and environmentally friendly ink, whose components are all made from biodegradable raw materials, meeting safety, compatibility, and hygiene requirements. Currently, research on biodegradable neutral inks is relatively scarce, and the technology is not yet mature. Natural pigments, due to their excellent color rendering, biodegradability, and wide availability, can be used as colorants in the preparation of green biodegradable inks. However, natural pigments are prone to degradation and fading under light and other conditions, so the stability of the ink needs to be improved. At the same time, the writing adhesion and durability of neutral inks need to be improved in order to enhance the writing performance and applicability of neutral ink refills. Summary of the Invention

[0003] One of the objectives of this invention is to provide a neutral ink for sericin micro-nano particles, which has the advantages of high stability, good adhesion, greenness, environmental friendliness, and safety.

[0004] The second objective of this invention is to provide a method for preparing neutral ink made from sericin micro / nano particles, which is simple to operate and has low processing costs.

[0005] The third objective of this invention is to provide an application of a neutral ink containing sericin micro / nano particles.

[0006] One of the solutions adopted to achieve the objective of this invention is: a neutral ink containing sericin micro-nanoparticles, comprising, by mass percentage: 0.05%–20% sericin micro-nanoparticles, 0.05%–40% pigment, 0.05%–1.0% additives, 0.05%–1.0% antibacterial agent, and the balance being water; wherein the sericin micro-nanoparticles are obtained by cross-linking sericin with transglutaminase.

[0007] Preferably, the preparation method of the sericin micro / nano particles includes the following steps:

[0008] A1. Add silk sericin to deionized water and dissolve to obtain sericin solution;

[0009] A2. Adjust the sericin solution to a weakly acidic state;

[0010] A3. Add glutamine transaminase solution to the weakly acidic sericin solution obtained in step A2, and carry out the reaction at a certain temperature. After the reaction is completed, raise the temperature to inactivate glutamine transaminase.

[0011] A4. Adjust the pH of the reaction solution to neutral to obtain sericin micro / nano particles.

[0012] Preferably, in step A1, the dissolution temperature is 25–40°C; and in step A2, the final concentration of sericin is 0.05 wt.%–26 wt.%.

[0013] Preferably, in step A3, the concentration of the transglutaminase solution is 1–20 mg / mL, the mass ratio of sericin to transglutaminase is 0.025–260:1, the reaction temperature is 40–45 °C, and the reaction time is 1–24 h.

[0014] The enzyme is inactivated at temperatures above 80°C.

[0015] Preferably, the colorant is a biodegradable colorant, including at least one of beet yellow, phycocyanin, beet red, algal pigment, safflower yellow, safflower red, sorghum red pigment, carotenoids, shell red pigment, chlorophyll, annatto orange pigment, cochineal red pigment, grape skin red pigment, cocoa shell pigment, and red yeast rice yellow pigment.

[0016] Preferably, the additive is a biodegradable additive, including at least one of polyethylene glycol, pentose gum, pectin, dextrin, hexose gum, casein, collagen, ovalbumin, soy protein, whey protein, and myofibrillar protein.

[0017] Preferably, the antibacterial agent is an edible antibacterial agent, including at least one of aminochitosan oligosaccharide, aminochitin, and aminochitosan.

[0018] The second objective of this invention is achieved through a method for preparing the aforementioned sericin micro / nano particle neutral ink, comprising the following steps:

[0019] B1. Disperse the sericin micro-nano particles in water to obtain an aqueous solution of sericin micro-nano particles;

[0020] B2. Add the colorant to the aqueous solution of sericin micro-nano particles obtained in step B1 and mix evenly to obtain a sericin micro-nano particle-colorant mixture;

[0021] B3. Add the additives to the sericin micro-nano particles-colorant mixture obtained in step B2 and mix evenly;

[0022] B4. Add the antibacterial agent to the mixture obtained in step B3 and mix well;

[0023] B5. The mixture obtained in step B4 is ball-milled to obtain a uniformly dispersed neutral ink of sericin micro-nano particles.

[0024] Preferably, in step B1, the mass fraction of the sericin micro / nano particle aqueous solution is 0.05%-15%; in steps (B1)-(B2), the mixture is stirred and mixed evenly at a stirring speed of 100r / min-1500r / min; in steps (B3)-(B4), the mixture is stirred and mixed evenly at a stirring speed of 100r / min-2000r / min; and in step (B5), the ball milling speed is 100-1000r / min.

[0025] The preparation of steps B1 to B5 can all be carried out at room temperature.

[0026] The solution adopted to achieve the third objective of this invention is: an application of the aforementioned sericin micro-nano particle neutral ink, which is applied to the ballpoint pen refill.

[0027] Sericin is a component of the outer silk collagen and plays an adhesive role in silkworm cocoons. Sericin chains have many amino acids with long side chains, such as lysine, tryptophan, and tyrosine, as well as many polar hydrophilic groups (such as -OH, -COOH, -NH2, -NH, etc.) on the surface of polypeptide chains. These structural features endow sericin with excellent loading, moisture regulation, moisture retention, and compatibility, while also possessing excellent film-forming properties, mechanical properties, and good appearance and color. This sericin is cross-linked with transglutaminase. The cross-linking reaction mainly involves an amide group transfer reaction between the γ-amide group of glutamine residues and the ε-amino group of lysine in the sericin. This can occur intramolecularly or intermolecularly, subsequently forming an ε-(γ-glutamine)-lysine heteropeptide bond, yielding sericin micro / nano particles. These particles possess a high specific surface area and numerous hydrophobic and hydrophilic groups, allowing them to load and disperse biodegradable pigments through interfacial interactions. Furthermore, these sericin micro / nano particles exhibit excellent antioxidant properties, effectively protecting biodegradable natural pigments and improving their photothermal stability. With the aid of auxiliaries, the separation... The intertwined sub-chains form a stable core-shell structure (with the pigment stably immobilized between the core and shell); further, under the action of antibacterial agents, an overall network structure is formed, which can promote the stability of the system and facilitate the preparation and use of neutral ink. The neutral ink prepared from sericin micro / nanoparticles is simple to produce, environmentally friendly, and pollution-free. It can be used for writing with gel pens, exhibiting good color rendering on paper, smooth writing, stable and vibrant colors, clear and bright handwriting, and rich and saturated colors. This reduces concerns about the safety of ink preparation and use, especially for ink production workers and young consumers. Therefore, research on this neutral ink is of great significance. The sericin protein used is derived from silkworm cocoons, which also facilitates the high-value utilization of these cocoons.

[0028] The present invention has the following advantages and beneficial effects:

[0029] This invention utilizes transglutaminase to crosslink sericin to form sericin micro / nanoparticles as a film-forming agent and loading substrate, which are added to neutral ink. These micro / nanoparticles have a high specific surface area and numerous hydrophobic and hydrophilic groups, allowing them to load and disperse biodegradable pigments through interfacial interactions. This functionalizes the neutral ink, giving it high pigment loading capacity. Furthermore, the sericin micro / nanoparticles exhibit excellent antioxidant properties, effectively protecting the biodegradable pigments and improving their photothermal stability. Under the action of additives, the molecular chains intertwine and entangle, forming a stable core-shell structure (with the pigment stably immobilized between the core and shell). Subsequently, under the action of antibacterial agents, an overall network structure is formed, further promoting system stability and facilitating the preparation and use of neutral ink.

[0030] The production equipment used in this invention are all commonly used and readily available mechanical equipment, with controllable costs and simple operation, which is beneficial for realizing the large-scale industrial production of neutral ink and its practical application in filling ballpoint pen refills.

[0031] The neutral ink of this invention has all its components in the formula being biodegradable (biodegradable film-forming agent, biodegradable natural pigment, biodegradable additive, biodegradable antibacterial agent), and is green, low-carbon, biodegradable, environmentally friendly, safe, sustainable, and environmentally friendly, avoiding the potential threats to human health (such as ink production workers and ink consumers) posed by traditional inks.

[0032] The biodegradable neutral ink of the present invention can be used for writing after filling ballpoint pen refills. It has good color rendering, strong adhesion, and stable color, and has good market application prospects. Attached Figure Description

[0033] Figure 1 This invention relates to the dispersion mechanism and writing effect of glutamine transaminase crosslinking induced sericin micro / nano particle neutral ink (a) and uncrosslinked sericin neutral ink (b);

[0034] Figure 2 These are liquid dispersion micrographs of the glutamine transaminase crosslinking induced sericin micro / nanoparticle neutral ink (a) and the uncrosslinked sericin neutral ink (b) of the present invention.

[0035] Figure 3 The UV light stability diagrams show the results of the neutral ink and the uncrosslinked sericin neutral ink with glutamine transaminase crosslinking induced sericin micro / nano particles of the present invention.

[0036] Figure 4 The thermal stability diagrams are shown for the neutral ink and the uncrosslinked sericin neutral ink of the glutamine transaminase crosslinking induced sericin micro / nano particles of the present invention.

[0037] Figure 5 The images show the neutral ink (left) and uncrosslinked sericin neutral ink (right) of the glutamine transaminase crosslinking induced sericin micro / nano particles of the present invention after being heated at 100°C for 5 hours.

[0038] Figure 6 The stability diagrams of neutral ink and uncrosslinked sericin neutral ink induced by glutamine transaminase crosslinking of the present invention after one year of storage are shown.

[0039] Figure 7 The diagram shows the abrasion resistance and adhesion properties of neutral ink and uncrosslinked sericin neutral ink after writing with glutamine transaminase crosslinking-induced sericin micro / nano particles, as described in this invention. Detailed Implementation

[0040] To better understand the present invention, the following embodiments are further illustrations of the present invention, but the content of the present invention is not limited to the following embodiments.

[0041] The sericin is obtained from silkworm cocoons. The obtained sericin is treated with a microwave-alkali process to obtain sericin with a stable molecular weight distribution of 10kDa-65kDa.

[0042] The preparation of sericin includes the following steps:

[0043] (1) After processing the silkworm cocoons into small pieces and washing them, they were then processed under microwave. During the processing, the silkworm cocoons were gently kneaded at regular intervals to ensure that the samples were processed evenly during the microwave process.

[0044] (2) Add the microwave-treated sample to a 0.5% Na2CO3 (w / v) solution and heat to boiling for a certain time;

[0045] (3) Filter to remove undissolved substances and centrifuge to collect the supernatant;

[0046] (4) The collected supernatant was dialyzed to obtain sericin with a molecular weight distribution range of 10kDa-65kDa.

[0047] Specifically, the preparation of sericin includes the following steps:

[0048] (1) Weigh out silkworm cocoons, cut them into small pieces, wash them four times with ultrapure water, put them into a cooking bag, and then microwave them at 350W for 15min-420min. During the process, gently knead the cooking bag every 30min to ensure that the sample is processed evenly during the microwave process.

[0049] (2) Add 0.5% Na2CO3 (w / v) solution and heat to boiling for 1 hour;

[0050] (3) Filter to remove undissolved substances, centrifuge at 5000 rpm for 10 min, and collect the supernatant;

[0051] (4) Transfer the collected supernatant into a dialysis bag (1500 Da) and dialyze at room temperature for 36 hours, changing the ultrapure water every 6 hours; the molecular weight distribution range is 10 kDa-65 kDa.

[0052] The sericin protein solution was freeze-dried for 24 hours and stored for later use.

[0053] The preparation method of sericin micro / nano particles in this invention includes the following steps:

[0054] A1. Add silk sericin to deionized water and dissolve to obtain sericin solution;

[0055] A2. Adjust the sericin solution to a weakly acidic state;

[0056] A3. Add glutamine transaminase solution to the weakly acidic sericin solution obtained in step A2, and carry out the reaction at a certain temperature. After the reaction is completed, raise the temperature to inactivate glutamine transaminase.

[0057] A4. Adjust the pH of the reaction solution to neutral to obtain sericin micro / nano particles.

[0058] In step A1, the dissolution temperature is 25–40°C.

[0059] In step A2, the final concentration of sericin is 0.05 wt.% to 26 wt.%.

[0060] In step A3, the concentration of the transglutaminase solution is 1–20 mg / mL, the mass ratio of sericin to transglutaminase is 0.025–260:1, the reaction temperature is 40–45 °C, the reaction time is 1–24 h, and the inactivation temperature is above 80 °C.

[0061] Example 1

[0062] A method for preparing a neutral ink of sericin micro / nanoparticles induced by transglutaminase crosslinking includes the following steps: dispersing the sericin micro / nanoparticle system in water, adjusting the concentration with distilled water, and stirring at 45°C for 500 r / min for 0.5 h; adding biodegradable phycocyanin to obtain a sericin micro / nanoparticle-phycocyanin mixture, and stirring at 45°C for 1000 r / min for 1 h; adding the biodegradable dextrin to the sericin micro / nanoparticle-phycocyanin mixture, and stirring at 45°C for 1500 r / min for 1 h; adding the antibacterial agent aminated chitosan to the sericin micro / nanoparticle-phycocyanin mixture, and stirring at 45°C for 1000 r / min for 1 h; and ball milling the mixture (500 r / min for 4 h) to obtain a uniformly dispersed neutral ink of sericin micro / nanoparticles. Sericin micro-nano particles, phycocyanin, dextrin, and aminochitosan account for 1.0%, 10.0%, 0.3%, and 0.3% of the mass of neutral ink, respectively, with the remainder being water, thus obtaining a glutamine transaminase crosslinking-induced sericin micro-nano particle neutral ink.

[0063] Example 2

[0064] A method for preparing a neutral ink of sericin micro / nanoparticles induced by transglutaminase crosslinking includes the following steps: dispersing the sericin micro / nanoparticle system in water, adjusting the concentration with distilled water, and stirring at 45°C for 1000 r / min for 0.5 h; adding biodegradable safflower yellow to obtain a mixture of sericin micro / nanoparticles and safflower yellow, and stirring at 45°C for 1500 r / min for 1 h; adding the biodegradable auxiliary agent polyethylene glycol to the mixture of sericin micro / nanoparticles and safflower yellow, and stirring at 45°C for 1400 r / min for 1 h; adding the antibacterial agent aminated chitosan to the mixture of sericin micro / nanoparticles and safflower yellow, and stirring at 45°C for 1000 r / min for 1 h; and ball milling the mixture (1000 r / min for 2 h) to obtain a uniformly dispersed neutral ink of sericin micro / nanoparticles. Sericin micro-nano particles, safflower yellow, polyethylene glycol, and amino-modified chitosan account for 20%, 10.0%, 0.05%, and 0.05% of the mass of neutral ink, respectively, with the balance being water, thus obtaining a glutamine transaminase crosslinking-induced sericin micro-nano particle neutral ink.

[0065] Example 3

[0066] A method for preparing a neutral ink of sericin micro / nanoparticles induced by transglutaminase crosslinking includes the following steps: dispersing the sericin micro / nanoparticle system in water, adjusting the concentration with distilled water, and stirring at 45°C for 100 r / min for 0.5 h; adding biodegradable safflower yellow to obtain a sericin micro / nanoparticle-chlorophyll mixture, and stirring at 45°C for 1500 r / min for 1 h; adding the biodegradable auxiliary agent polyethylene glycol to the sericin micro / nanoparticle-chlorophyll mixture, and stirring at 45°C for 2000 r / min for 1 h; adding the antibacterial agent aminated chitosan to the sericin micro / nanoparticle-chlorophyll mixture, and stirring at 45°C for 2000 r / min for 1 h; and ball milling the mixture (100 r / min for 8 h) to obtain a uniformly dispersed neutral ink of sericin micro / nanoparticles. Sericin micro-nano particles, chlorophyll, polyethylene glycol, and amino-modified chitosan oligosaccharides account for 0.05%, 40%, 1.0%, and 1.0% of the mass of the neutral ink, respectively, with the remainder being water, thus obtaining a glutamine transaminase crosslinking-induced sericin micro-nano particle neutral ink.

[0067] Comparative Example 1

[0068] A method for preparing a sericin neutral ink includes the following steps: dispersing the uncrosslinked sericin system obtained from the above extraction in water, adjusting the concentration with distilled water, and stirring at 45°C for 500 r / min for 0.5 h; adding biodegradable safflower yellow to obtain a sericin-safflower yellow mixture, and stirring at 45°C for 1200 r / min for 1 h; adding the biodegradable dextrin to the sericin-safflower yellow mixture, and stirring at 45°C for 1400 r / min for 1 h; adding the antibacterial agent aminated chitosan to the sericin-safflower yellow-aminated chitosan mixture, and stirring at 45°C for 1000 r / min for 1 h; and ball milling the mixture (500 r / min for 4 h) to obtain a uniformly dispersed sericin neutral ink. The sericin, safflower yellow, dextrin, and aminated chitosan account for 1.4%, 8.0%, 0.2%, and 0.5% of the mass of the neutral ink, respectively, with the remainder being water, thus obtaining a non-sericite neutral ink.

[0069] contrast Figure 1 a (glutamine transaminase crosslinking induced sericin micro / nanoparticle neutral ink, Example 2) and Figure 1 b (Uncrosslinked sericin neutral ink). It can be seen that the former, crosslinked sericin neutral ink, remained uniformly dispersed and stable after one month of storage; after being filled with a ballpoint pen, the ink wrote smoothly, adhered well, and produced good color. However, the latter, uncrosslinked neutral ink, exhibited sedimentation, layering, and flocculation after one month of storage; after being filled with a ballpoint pen, the ink was prone to ink breakage, had poor adhesion, and produced discontinuous color during writing.

[0070] contrast Figure 2 a (glutamine transaminase crosslinking induced sericin micro / nanoparticle neutral ink, Example 2) and Figure 2 b (uncrosslinked sericin neutral ink): Crosslinked ink has a micro-nano structure and is uniformly dispersed; while the microstructure of uncrosslinked sericin ink has larger aggregated particles with varying dispersion sizes.

[0071] contrast Figure 3 Stability of neutral and uncrosslinked sericin inks induced by transglutaminase crosslinking (Example 2): After UV irradiation for 48 h and 96 h, the color retention rate of the crosslinked sericin neutral ink was nearly 100%, and the color retention rate was unaffected. However, the color retention rate of the uncrosslinked sericin neutral ink was low after UV irradiation, and the color retention rate continued to decrease with the extension of irradiation time. After UV irradiation for 48 h, the color retention rate was only about 65%, and after UV irradiation for 96 h, the color retention rate was only about 55%.

[0072] Depend on Figure 4It can be seen that after being heated at 100°C for 1 hour (Example 2), the color retention rate of the cross-linked sericin neutral ink is still high (up to 99%), while the color retention rate of the uncross-linked sericin neutral ink is only about 65%. Even after 5 hours, the color retention rate of the cross-linked sericin neutral ink is still high. Figure 4 ), and the yellow color remains good ( Figure 5 The color retention rate of non-crosslinked inks is significantly reduced. Figure 4 ), and the yellow color became noticeably lighter ( Figure 5 Within one year of storage, the rheological viscosity recovery rate of cross-linked sericin neutral ink is relatively high. Figure 6 In contrast, the rheological viscosity recovery rate of uncrosslinked sericin neutral inks decreases rapidly with prolonged storage time. On one hand, in uncrosslinked sericin inks, sericin can act as a coating agent, and other additives and antibacterial agents can assist in loading pigments onto the sericin. However, the network structure is weak, and with prolonged storage, the system experiences instability phenomena such as flocculation and precipitation. Simultaneously, under UV irradiation and 100℃ high-temperature treatment, the system cannot effectively protect safflower yellow, and the safflower yellow structure undergoes photothermal degradation, thus affecting the color of the ink system. On the other hand, cross-linked sericin micro / nano particles, incorporating transglutaminase-crosslinked sericin protein micro / nano particles as film-forming agents and loading substrates into neutral ink systems, possess a high specific surface area and numerous hydrophobic and hydrophilic groups. These particles can thus load and disperse biodegradable safflower yellow through interfacial interactions, functionalizing the neutral ink and providing high pigment loading capacity. Simultaneously, these sericin micro / nano particles effectively protect the biodegradable pigment, improving its photothermal stability. Under the action of additives, molecular chains intertwine and entangle, forming a stable core-shell structure (pigment stably immobilized between the core and shell). Subsequently, under the action of antibacterial agents, an overall network structure is formed, further promoting the system's UV light, heat, and storage stability, and also facilitating the practical application of this cross-linked sericin neutral ink. Therefore, even after one year of storage, cross-linked sericin ink still exhibits higher ink fastness than non-crosslinked sericin ink. Figure 7 )

[0073] The above description is merely a preferred embodiment of the present invention, and should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A neutral ink containing sericin micro / nano particles, characterized in that: The composition by weight percentage includes: 0.05%~20% sericin micro-nano particles, 0.05%~40% pigment, 0.05%~1.0% additives, 0.05%~1.0% antibacterial agent, and the balance being water; the sericin micro-nano particles are obtained by cross-linking sericin with transglutaminase; The colorant is a biodegradable colorant; The additive is a biodegradable additive, including at least one of polyethylene glycol, pentose gum, pectin, dextrin, hexose gum, casein, collagen, ovalbumin, soy protein, whey protein, and myofibril protein; The antibacterial agent is an edible antibacterial agent, including at least one of aminochitosan and aminochitosan.

2. The neutral ink containing sericin micro / nanoparticles according to claim 1, characterized in that: The preparation method of the sericin micro / nano particles includes the following steps: A1. Add silk sericin to deionized water and dissolve to obtain sericin solution; A2. Adjust the sericin solution to a weakly acidic state; A3. Add glutamine transaminase solution to the weakly acidic sericin solution obtained in step A2, and carry out the reaction at a certain temperature. After the reaction is completed, raise the temperature to inactivate glutamine transaminase. A4. Adjust the pH of the reaction solution to neutral to obtain sericin micro / nano particles.

3. The sericin micro / nano particle neutral ink according to claim 2, characterized in that: In step A1, the dissolution temperature is 25~40℃; in step A2, the final concentration of the sericin solution is 0.05wt.%~26wt.%.

4. The neutral ink containing sericin micro / nanoparticles according to claim 2, characterized in that: In step A3, the concentration of the transglutaminase solution is 1-20 mg / mL, the mass ratio of sericin to transglutaminase is 0.025-260:1, the reaction temperature is 40-45℃, and the reaction time is 1-24 h.

5. The sericin micro / nano particle neutral ink according to claim 1, characterized in that: The colorant includes at least one of the following: beet yellow, phycocyanin, beet red, algal pigment, safflower yellow, safflower red, sorghum red pigment, carotenoids, shell red pigment, chlorophyll, annatto orange pigment, cochineal red pigment, grape skin red pigment, cocoa shell pigment, and red yeast rice yellow pigment.

6. A method for preparing a neutral ink containing sericin micro / nanoparticles as described in any one of claims 1 to 5, characterized in that, Includes the following steps: B1. Disperse the sericin micro-nano particles in water to obtain an aqueous solution of sericin micro-nano particles; B2. Add the colorant to the aqueous solution of sericin micro-nano particles obtained in step B1 and mix evenly to obtain a sericin micro-nano particle-colorant mixture; B3. Add the additives to the sericin micro-nano particles-colorant mixture obtained in step B2 and mix evenly; B4. Add the antibacterial agent to the mixture obtained in step B3 and mix well; B5. The mixture obtained in step B4 is ball-milled to obtain a uniformly dispersed neutral ink of sericin micro-nano particles.

7. The method for preparing the sericin micro / nanoparticle neutral ink according to claim 6, characterized in that: In step B1, the mass fraction of the sericin micro-nano particle aqueous solution is 0.05%-15%; in steps (B1)-(B2), the mixture is stirred and mixed evenly at a stirring speed of 100 r / min-1500 r / min; in steps (B3)-(B4), the mixture is stirred and mixed evenly at a stirring speed of 100 r / min-2000 r / min; in step (B5), the ball milling speed is 100-1000 r / min.

8. The application of a neutral ink containing sericin micro / nanoparticles as described in any one of claims 1 to 5, or a neutral ink prepared by the preparation method described in claim 6 or 7, characterized in that: The aforementioned sericin micro-nano particle neutral ink is applied to the refill of a ballpoint pen.

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