Anti-fading Huizhou ink and preparation method thereof

Abstract

The invention belongs to the technical field of Huizhou ink, and particularly relates to anti-fading Huizhou ink and a preparation method thereof. According to the invention, dopamine is introduced as a potential cross-linking agent, so that breakthrough improvement of the Huizhou ink performance is realized. The formula is unique in that in the preparation process, the dopamine and the gelatin are not subjected to cross-linking reaction, and the traditional processing characteristics of the ink ingot are kept; after writing, dopamine in the ink marks is slowly crosslinked under natural conditions to form a stable three-dimensional network structure, degradation of gelatin in the ink marks is remarkably delayed, the effect of curing the ink marks is achieved, accordingly, the water resistance and fading resistance of the ink marks are remarkably improved, and the ink is particularly suitable for art works and literatures needing to be stored for a long time.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of seal ink, and particularly relates to a kind of anti-fading seal ink and a preparation method thereof. BACKGROUND

[0002] Seal ink is the culmination of traditional Chinese ink-making technology, and is named after its origin in Huizhou, Anhui Province. It is not only a writing and drawing material, but also an artistic product that condenses culture, skill, and aesthetics. The origin of seal ink can be traced back to the Tang Dynasty, and its maturity and heyday were in the Song, Ming, and Qing Dynasties. Since ancient times, seal ink has been renowned for its rich color, long-lasting fragrance, smooth writing, and non-fading properties, and has been hailed as the first of the "Four Treasures of the Study". Seal ink is not only a companion for scholars and artists, but also a outstanding representative of the combination of science and art in ancient China.

[0003] Seal ink has a long history. According to the Records of Geography in the New Tang Book, Shexian County (now around Huangshan, Anhui Province) was already famous for its ink-making in the Tang Dynasty. The famous ink-makers, the father and son of Xi Chao, were considered to be the founders of seal ink. Xi Chao used pine smoke as the material, and added precious spices such as musk and camphor to make ink that was "smooth as lacquer and fragrant as a person", which was deeply loved by scholars and officials. From the Five Dynasties to the Song Dynasty, the ink-making industry in Huizhou gradually developed, and together with Huizhou paper, Huizhou inkstone, and Huizhou brush, it was known as the "Four Treasures of Huizhou". During the Ming and Qing Dynasties, seal ink reached its peak, and famous ink merchants and families such as Cao Sugong, Wang Jinsheng, and Hu Kaiwen emerged. In particular, the "Dragon Fragrance Ink" and "Five Color Ink" produced by Hu Kaiwen's ink shop were sold as far as Southeast Asia and Japan, and became the tribute and overseas treasures of the time.

[0004] The production method of seal ink is complex and ingenious, with dozens of processes, and condenses the experience and aesthetics of traditional craftsmen. The main raw materials are smoke, glue, water, and spices. The "smoke" of seal ink comes from the carbon black obtained by burning pine or oil, and can be divided into "pine smoke ink" and "oil smoke ink" according to the fuel. Pine smoke is taken from the dry branches or roots of pine trees, and after roasting, the smoke dust particles are larger, the ink color is soft and greenish, and it is suitable for calligraphy. Oil smoke is obtained by burning tung oil, sesame oil, or soybean oil, and the particles are even finer, the ink color is dark and shiny, and it is suitable for painting. The glue is mostly taken from cowhide glue, which can not only stick the smoke powder, but also determine the hardness, gloss, and ink-releasing properties of the ink. The quality of water is crucial, and ancient people often take mountain spring water or well water to avoid impurities affecting the quality of the ink. In terms of spices, seal ink is unique in that musk, camphor, borneol, clove, sandalwood, and agarwood are added, making the ink fragrant without being irritating, and having the functions of preventing corrosion and mildew.

[0005] The main process of making Huizhou ink includes taking soot, refining glue, mixing, kneading, beating, molding, drying, and polishing. The soot is first sieved and cleaned to ensure uniformity. The temperature and concentration of the glue need to be controlled. If the glue is too thick, the ink will be brittle; if it is too thin, the ink will not form. The soot and glue are mixed at an appropriate temperature. The craftsman judges the temperature by the feel, color, and smell of the mixture to form a smooth "ink paste". The mixture is often beaten repeatedly to ensure that the soot and glue are fully combined, a process that can take several days. The ink paste is then pressed into a wooden mold, which is often carved with dragon and phoenix, landscape, poetry, or flower and bird patterns. The mold is both practical and artistic. After molding, the ink is naturally dried and must not be exposed to sunlight, as this can cause the ink to crack. Finally, the ink is decorated with gold, polished, and sealed with wax to make the surface shiny and the patterns clear and elegant.

[0006] The chemical composition of Huizhou ink is relatively simple but very sophisticated. The main components are carbon (from soot) and protein-based glue (animal glue), as well as a small amount of inorganic salts, spice oil, plant extracts, and metal elements. The particle structure of the soot determines the ink's covering power and gloss, while the animal glue affects the ink's flow, adhesion, and durability. When the ink is ground, the glue dissolves in water to form a colloidal solution, and the soot is evenly dispersed in it. After the water evaporates when the ink is applied to rice paper, a dense carbon film is formed. The uniform structure of this carbon-glue film gives Huizhou ink its deep, glossy, and long-lasting properties.

[0007] However, traditional Huizhou ink also has some problems that cannot be ignored during long-term storage and use. The most notable are fading and loss of gloss. Although ancient texts claim that the ink will not fade for thousands of years, modern research shows that the ink's fading is closely related to environmental factors such as humidity, light, acidity, and oxidation of the glue. When the air humidity is too high, the animal glue in the ink film will absorb moisture and swell, causing the carbon particle structure to loosen and the ink to turn gray. Light, especially ultraviolet light, can accelerate the degradation of the glue, causing the surface to powder and turn gray. In addition, acidic air pollution or paper acidification can also cause chemical erosion of the ink layer, reducing the adhesion between carbon particles and causing the ink to flake off and lose color.

[0008] Another common problem is that the ink is prone to mold and cracking during storage. Huizhou ink contains natural animal glue and spices, and if the storage environment is humid or poorly ventilated, the glue is prone to mold and the surface may develop white spots or even an unpleasant odor. Over-drying can also cause the ink to crack due to increased internal tension, affecting its appearance and use. In addition, in modern painting and calligraphy applications, there may be compatibility issues between traditional Huizhou ink and new types of paper or chemical pigments, leading to ink bleeding, color loss, or unstable layering.

[0009] In recent years, researchers and ink makers have made improvements in various aspects to address these issues. One approach is to optimize the formula and process. By improving the purification method of animal glue, adding natural antifungal and antioxidant ingredients such as catechin, rosemary extract, and vitamin E, the aging of the glue can be slowed down. Some people also use fish glue or gelatin instead of cowhide glue to improve toughness and crack resistance. Another approach is to develop improved ink powder, such as using nanoscale carbon black or active carbon particles instead of traditional ink powder, to make the ink color more pure and stable. At the same time, surface modification technology is used to improve the dispersibility of the ink powder, thereby reducing the decrease in gloss or loss of gloss caused by the aggregation of carbon particles after exposure to light. Some research explores the use of bio-based adhesives or synthetic polymer additives to maintain the traditional texture of the ink while enhancing its weather resistance and adhesion.

[0010] An important aspect of modern seal ink protection is the scientific management of storage and use conditions. High-quality seal ink should be stored in a cool, dry, and well-ventilated environment, avoiding direct sunlight and drastic temperature changes. Traditional wooden boxes and silk bags are considered ideal storage containers due to their good air permeability and cushioning properties. For ancient ink works that have already faded or powdered, cultural heritage restoration experts often use neutral buffer paper storage, constant temperature and humidity preservation, and light filtering to slow down the aging process. Some research institutions also use infrared, Raman spectroscopy, and scanning electron microscopy to analyze the microstructure of seal ink, revealing the fading mechanism and providing a theoretical basis for restoration and replication.

[0011] The article titled "Study on the Performance of Acrylic Polyurethane for the Protection of Handwriting on Paper Relics" (MDPI Journal, 2023) explores the use of synthetic polymers to reinforce written ink to reduce fading and diffusion. The study investigates the reinforcement effect of acrylic polyurethane materials on handwritten / ink on paper, and examines the color change and diffusion behavior before and after treatment. This type of polymer reinforcement method is a common technique used in cultural heritage preservation, which can form a protective film on the ink layer / paper layer to slow down oxidation, photodegradation, and migration, thereby inhibiting fading and image blurring. It is a feasible technical route for treating faded or fragile ink.

[0012] European Patent Document (EP0969052) reports the use of ozone oxidation and other methods to treat carbon black to improve its properties as a pigment. Oxidizing the surface of carbon black or introducing functional groups can change its dispersibility, compatibility with colloidal media, and response behavior to photooxidation, thereby improving the stability of the ink layer in light, moisture, and other environments. This type of carbon black treatment process can provide a direct materials science approach to improving traditional ink powder.

[0013] The paper titled “The aging and color development of writing in paper archives” (Chemical Papers, Volume 78, pages 6553-6562, (2024)) reveals the microscopic mechanisms of ink fading, powdering, color reproduction, and other processes through artificial aging and characterization (spectroscopy, etc.), and explores the effects of dye / color development treatment and preservation environment control (constant temperature and humidity, spectral filtering, etc.) on delaying fading. Such mechanism research provides experimental basis and evaluation index for selecting appropriate antioxidants, antifungal agents, or protective coatings (such as the aforementioned polymer reinforcement) for traditional ink.

[0014] Although these patents are mainly aimed at modern inkjet and printing applications, their effects on pigment modification, dispersants, and film-forming systems (including pH control, surfactants, and auxiliaries) on light resistance and fading provide a referenceable technical route for traditional ink through material modification (such as surface-modified soot, dispersion modifier, or trace stabilizer addition).

[0015] Dopamine, with the chemical name 4-(2-ethylamino)benzene-1,2-diol, is an endogenous catecholamine. Its molecular structure contains two key parts: a catechol functional group (ortho-benzene diol) and a primary amino group. This structure determines its core physicochemical properties: high chemical reactivity and environmental instability. The chemical structure is as follows:

[0016] .

[0017] Dopamine is extremely unstable in aqueous solutions with neutral to alkaline pH values and will spontaneously undergo oxidative self-polymerization. Oxygen in the air first oxidizes its catechol ring to ortho-benzene quinone, which has high electrophilicity (electron deficiency). Subsequently, it undergoes complex intramolecular and intermolecular reactions, including rearrangement, cyclization, and further oxidative coupling, ultimately forming a class of black or brown polymers called polydopamine. This process is similar to the mechanism of adhesion proteins secreted by marine mussels, making polydopamine exhibit extraordinary and almost universal adhesion properties, allowing it to firmly coat the surfaces of almost all types of materials. In addition, the catechol and amino groups of dopamine molecules enable them to both chelate with metal ions and act as hydrogen bond donors and acceptors, complementing their covalent cross-linking ability.

[0018] Based on the above unique chemical properties, dopamine (more accurately, its active intermediates generated by oxidation and polydopamine) has great application potential in the field of protein cross-linking, with its main uses in the following areas:

[0019] Preparation of high-performance protein hydrogels: Traditional protein crosslinking methods (such as using glutaraldehyde) are often toxic or uncontrollable. Dopamine, as a biologically derived crosslinking agent, can be used to crosslink gelatin, collagen, silk fibroin, etc., to form hydrogels with excellent biocompatibility. Such hydrogels have broad prospects in tissue engineering scaffolds, wound dressings, and drug delivery systems. Dopamine-crosslinked protein hydrogels generally have stronger mechanical strength, better stability, and adjustable degradation rate.

[0020] Immobilization of enzymes and antibodies: In the field of biotechnology and biosensing, it is crucial to firmly and efficiently immobilize enzymes or antibodies on the surface of carriers. The active layer formed during the oxidative polymerization of dopamine can act as a "molecular glue" to covalently anchor protein molecules on various substrates. This method is simple to operate (usually by shaking in a mild pH 8.5 buffer), has high immobilization efficiency, and can well maintain the biological activity of proteins.

[0021] Improving the interfacial properties of biomaterials: By dopamine-mediated crosslinking, a firm protein coating (such as collagen coating) can be constructed on the surface of medical devices or implants, significantly improving their biocompatibility, promoting cell adhesion, proliferation, and differentiation, and reducing immune rejection.

[0022] Reaction mechanism of dopamine as a protein crosslinking agent: Essentially, the active intermediates generated by the oxidation of dopamine undergo a series of covalent reactions with the nucleophilic groups on the protein molecules. The entire process can be summarized in the following key steps:

[0023] Oxidation and activation: Under dissolved oxygen and alkaline conditions (usually Tris-HCl buffer, pH 8.5), the catechol ring of dopamine is oxidized to generate a highly reactive o-benzoquinone structure. This is the starting step of the entire crosslinking process.

[0024] Michael addition reaction: This is the main crosslinking mechanism. The generated o-benzoquinone is a strong electrophile that preferentially attacks the nucleophilic groups rich in the side chains of proteins, mainly the ε-amino group of lysine and the thiol group of cysteine. The nucleophilic attack of the nucleophilic groups of the protein on the quinone ring forms stable C-N or C-S covalent bonds, covalently linking dopamine molecules or oligomers to the protein chain.

[0025] Schiff base reaction: Aldehyde intermediates may also be generated during the oxidation of dopamine, or the amino group of dopamine molecules can condense with the quinone generated by the oxidation of proteins (such as the oxidation of tyrosine residues) or directly with the terminal amino group of proteins to form a Schiff base, further strengthening the crosslinking network.

[0026] The pi-pi stacking and hydrogen bonding: while covalent cross-linking, the aromatic rings in the polydopamine chains and the aromatic amino acid residues (such as tryptophan, tyrosine) of the protein can produce pi-pi stacking. At the same time, the phenolic hydroxyl and amino groups of dopamine and the carboxyl, amino groups of the protein form a wide hydrogen bond network. These non-covalent interactions and covalent bonds synergize to form a solid and stable three-dimensional protein network.

[0027] However, so far, there has been no report on the application of dopamine or its salt in the preparation of seal ink. SUMMARY

[0028] Applicants, as a professional seal ink research and production enterprise, have made in-depth research on the properties and composition of seal ink. In the research, it is found that the addition of a certain amount of dopamine in the seal ink can significantly improve the color fastness of the seal ink.

[0029] The present application first discloses the use of dopamine as a component for enhancing the color fastness of ink.

[0030] The present application secondly discloses a seal ink containing dopamine, which has significantly improved color fastness compared with ordinary ink. Unexpectedly, the water resistance of the ink is also improved.

[0031] The seal ink described in the present application is composed of pigment, gelatin, dopamine and pH regulator.

[0032] The pigment is one of pine smoke and oil smoke;

[0033] The gelatin is a natural protein extracted from animal connective tissue (such as pig, cow skin, bone, tendon), which is obtained by partial hydrolysis of collagen.

[0034] The dopamine refers to dopamine or its salt.

[0035] The pH regulator refers to citric acid.

[0036] The seal ink formula described in the present application is as follows in mass fraction:

[0037] Oil smoke 40-60 parts

[0038] Gelatin 25-35 parts

[0039] Dopamine hydrochloride 0.5-2.5 parts

[0040] Citric acid 1.0 part

[0041] Deionized water 17 parts

[0042] The mass ratio of the gelatin and the dopamine hydrochloride is 15-30:1.

[0043] The mass ratio of the gelatin and the dopamine hydrochloride is 20:1.

[0044] The dosage of the dopamine hydrochloride is preferably 1.5 parts;

[0045] The dosage of the dopamine hydrochloride is preferably 2.0 parts;

[0046] The badge ink can further comprise a perfume, which is one of borneol and musk.

[0047] The badge ink preparation method is as follows:

[0048] Step 1: Dissolve citric acid in deionized water, stir until completely dissolved, and adjust the pH value to 3.8-4.2 with NaOH solution;

[0049] Step 2: Slowly add gelatin to part of the acidic aqueous solution, stir to form a uniform colloid; dissolve dopamine hydrochloride in the remaining acidic aqueous solution, and stir until completely dissolved;

[0050] Step 3: First, mix the gelatin solution obtained in Step 2 with oil smoke, use a wooden stirrer to stir at low speed to form a uniform ink paste; slowly add the perfume to the obtained ink paste, continue to stir at low speed to ensure that the perfume is uniformly dispersed in the entire ink paste. Then slowly drop the dopamine hydrochloride solution obtained in Step 2 into the ink paste, continue to stir to ensure uniform distribution but avoid excessive shearing;

[0051] Step 4: Fill the mixed ink paste into a mold, lightly press it at 20-25℃, and immediately transfer it to a 15-18℃ environment for pre-solidification;

[0052] Step 5: First stage: dry at 20℃ and 60% humidity for 12 hours; second stage: dry at 25℃ and 40% humidity for 24-48 hours, and age in a sealed container at 20-25℃ for 7 days to make the moisture distribution uniform, cut into pieces, and obtain the product.

[0053] Compared with the prior art, the present application has the following beneficial effects:

[0054] The present application realizes a breakthrough improvement of the performance of the ink by introducing dopamine as a potential crosslinking agent. The unique feature of the formula is that the present application takes advantage of the highly pH-sensitive property of the oxidative crosslinking reaction of dopamine. In the preparation process, the premature crosslinking of dopamine and gelatin is effectively inhibited by strictly controlling the pH value of the system at 3.8-4.2 in the acidic condition, thereby ensuring that the ink stick can adopt the traditional processing technology. When the ink mark containing the ink of the present application is written on the rice paper and dried, the dopamine in the ink mark is exposed to the air (close to neutral conditions), thereby enabling the slow oxidative crosslinking under the action of oxygen and possible light, thereby forming a stable three-dimensional network structure, significantly delaying the degradation of gelatin in the ink mark, achieving the effect of solidifying the ink mark, thereby significantly improving the water resistance and anti-fading performance of the ink mark, and being particularly suitable for artistic works and documents that need to be preserved for a long time. DETAILED DESCRIPTION

[0055] The present application will be further described in detail by the following examples, which are illustrative of the present application, but the examples do not limit the present application in any form. Unless otherwise specified, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the technical field.

[0056] Example 1 Preparation of anti-fading ink

[0057] The present embodiment gives an innovative ink preparation method, which realizes a breakthrough improvement of the performance of the ink by introducing dopamine as a potential crosslinking agent. The unique feature of the formula is that in the preparation process, dopamine does not react with gelatin, maintaining the traditional processing characteristics of the ink stick; and after writing, the dopamine in the ink mark slowly crosslinks under natural conditions, forming a stable three-dimensional network structure, significantly delaying the degradation of gelatin in the ink mark, achieving the effect of solidifying the ink mark, thereby significantly improving the water resistance and anti-fading performance of the ink mark, and being particularly suitable for artistic works and documents that need to be preserved for a long time.

[0058] The formula composition is shown in Table 1:

[0059] The preparation method is as follows:

[0060] Step 1: Prepare an acidic aqueous solution

[0061] Dissolve 1 g of citric acid in 17 ml of deionized water, stir until completely dissolved, and adjust the pH value to 3.8-4.2 with a 0.1 M NaOH solution;

[0062] Step 2: Prepare gelatin solution and dopamine hydrochloride solution respectively

[0063] Gelatin solution: slowly add 30 g of gelatin to 12 ml of the acidic aqueous solution, gently stir in a 45°C water bath for 30 minutes, and form a uniform colloid;

[0064] Dopamine hydrochloride solution: 1.5 g of dopamine hydrochloride was dissolved in the remaining acidic aqueous solution, stirred for 5 minutes, avoiding long stirring times;

[0065] Step 3: Stepwise mixing process

[0066] The gelatin solution obtained in Step 2 was first mixed with 52 g of lampblack using a wooden stirrer at a speed of 60-80 rpm for 20 minutes, forming a homogeneous ink paste; 0.5 g of borneol was slowly added to the resulting ink paste, continuing to stir at the same low speed for 5-10 minutes, ensuring uniform dispersion of the flavoring agent throughout the ink paste. Subsequently, the dopamine hydrochloride solution obtained in Step 2 was slowly added dropwise to the ink paste, continuing to stir for 10 minutes, ensuring uniform distribution but avoiding excessive shearing;

[0067] Step 4: Low-temperature molding

[0068] The mixed ink paste was filled into a mold and lightly molded at 20-25 °C, immediately transferred to a 15-18 °C environment for pre-curing for 2 hours, inhibiting any possible cross-linking reactions;

[0069] Step 5: Staged drying

[0070] First stage: drying at 20 °C, 60% humidity for 12 hours; second stage: drying at 25 °C, 40% humidity for 24-48 hours, aging in a sealed container at 20-25 °C for 7 days to evenly distribute the moisture, and cutting into pieces, resulting in the final product.

[0071] Preparation of a fade-resistant ink

[0072] The formulation was basically the same as in Example 1, with the only difference being the addition of 0.5 g of dopamine hydrochloride. The specific formulation composition is shown in Table 1.

[0073] The preparation method was the same as in Example 1.

[0074] Preparation of a fade-resistant ink

[0075] The formulation was basically the same as in Example 1, with the only difference being the addition of 1.0 g of dopamine hydrochloride. The specific formulation composition is shown in Table 1.

[0076] The preparation method was the same as in Example 1.

[0077] Preparation of a fade-resistant ink

[0078] The formulation was basically the same as in Example 1, with the only difference being the addition of 2.0 g of dopamine hydrochloride. The specific formulation composition is shown in Table 1.

[0079] The preparation method was the same as in Example 1.

[0080] Preparation of a fade-resistant ink

[0081] The formulation of Example 1 was essentially the same except that 2.5 g of dopamine hydrochloride was added. The formulation is shown in Table 1.

[0082] The preparation method was the same as Example 1.

[0083] Example 6 Preparation of fade-resistant ink

[0084] The amounts of oil smoke, gelatin and dopamine hydrochloride were varied, but the mass ratio of gelatin to dopamine hydrochloride was maintained at 20:1. The formulation is shown in Table 1.

[0085] The preparation method was the same as Example 1.

[0086] Example 7 Preparation of fade-resistant ink

[0087] The amounts of oil smoke, gelatin and dopamine hydrochloride were varied, but the mass ratio of gelatin to dopamine hydrochloride was maintained at 20:1. The formulation is shown in Table 1.

[0088] The preparation method was the same as Example 1.

[0089] Comparative Example 1

[0090] The formulation of Example 1 was essentially the same except that no dopamine hydrochloride was added. The formulation is shown in Table 1.

[0091] Preparation method:

[0092] Step 1: Preparation of acidic aqueous solution

[0093] Dissolve 1 g of citric acid in 17 ml of deionized water, stir until completely dissolved, and adjust the pH to 3.8-4.2 with a 0.1 M NaOH solution;

[0094] Step 2: Preparation of gelatin solution

[0095] Gelatin solution: Slowly add 30 g of gelatin to 17 ml of the acidic aqueous solution, gently stir in a 45°C water bath for 30 minutes, and form a uniform gel;

[0096] Step 3: Stepwise mixing process

[0097] First, mix the gelatin solution obtained in Step 2 with 52 g of oil smoke, use a wooden stirrer to stir at a speed of 60-80 rpm for 20 minutes to form a uniform ink paste, and then slowly add 0.5 g of menthol to the obtained ink paste, continue to stir at the same low speed for 5-10 minutes to ensure that the flavor is evenly dispersed throughout the ink paste;

[0098] Step 4: Low-temperature molding

[0099] The mixed ink paste is filled into the mold, and is lightly pressed at 20-25℃, and is immediately transferred to a 15-18℃ environment for 2 hours of pre-curing, to inhibit any possible cross-linking reaction;

[0100] Step 5: Sectional drying

[0101] First stage: drying at 20℃, humidity 60% for 12 hours; second stage: drying at 25℃, humidity 40% for 24-48 hours, aging at 20-25℃ in a sealed container for 7 days to make the moisture distribution uniform, and cutting, to obtain the product.

[0102] Table 1 Formulation composition of Examples 1-7 and Comparative Example 1, unit: g

[0103] .

[0104] Test Example 1: Anti-fading performance test of the ink marks obtained from Examples 1-7 and Comparative Example 1

[0105] The anti-fading seal ink described in the present application is unique in that, during the preparation process, the dopamine does not cross-link with the gelatin, and the traditional processing characteristics of the ink tablet are maintained; and after writing, the dopamine in the ink mark slowly cross-links under natural conditions to form a stable three-dimensional network structure, thereby significantly improving the water resistance and anti-fading performance of the ink mark, and being particularly suitable for artistic works and documents that need to be preserved for a long time.

[0106] 1. Purpose of the test

[0107] The purpose of the test is to simulate the color change of the seal ink mark under long-term sunlight irradiation after being filtered through a window glass indoors by means of laboratory accelerated aging, to evaluate its anti-fading performance (light resistance), and to classify it into a corresponding light resistance category according to the standard, to provide a scientific basis for the durability evaluation and quality control of the seal ink.

[0108] 2. Test standard

[0109] Test method D in ASTM D4303-10 “Standard Test Method for Light Resistance of Pigments Used in Paints” — exposing the sample to simulated sunlight filtered through a window glass in a controlled humidity xenon arc lamp device.

[0110] 3. Test principle

[0111] The prepared seal ink mark sample is placed in a controllable xenon arc lamp aging test box. The test box is equipped with a window glass filter to filter out short-wave ultraviolet light, to simulate the working condition of sunlight passing through a glass. Under the conditions of controlling temperature, relative humidity and irradiance, the sample is continuously exposed to light for a period of time. By comparing the color change of the sample before and after exposure (using CIELab color difference ΔEab), the light resistance grade of the seal ink mark is determined.

[0112] 4. Instruments and Materials

[0113] Xenon arc lamp weathering apparatus: an apparatus that meets the requirements of ASTM G 155 and is capable of controlling the relative humidity within the chamber.

[0114] Spectrophotometer: with specular exclusion, using D65 illuminant and 10° observer of 1964.

[0115] Sample substrate: rice paper.

[0116] Window glass filter: used in the xenon arc lamp apparatus to simulate the spectrum of sunlight transmitted through glass.

[0117] Standard black panel thermometer: used to monitor the temperature of the non-insulated black panel.

[0118] 5. Test Procedure

[0119] 5.1 Sample Preparation

[0120] Prepare the ink samples from Examples 1-7 and Comparative Example 1 to be applied to the selected rice paper in a uniform and consistent manner, ensuring that the sample surface is flat and free of significant defects. Prepare two application samples for each ink sample.

[0121] Cut the samples to a size appropriate for exposure to the holder and spectrophotometer measurement port.

[0122] 5.2 Initial Color Measurement

[0123] Immediately prior to the start of the exposure test, measure the color of all samples (including those to be exposed and retained) using the spectrophotometer. Record the CIELAB values (L ,a ,b ) for each sample. Note the following when measuring:

[0124] Mark the measurement points to ensure that the same points are measured after exposure. Maintain the same orientation of the rice paper fiber grain when measuring.

[0125] 5.3 Xenon Arc Lamp Exposure Test (Test Method D)

[0126] Apparatus Settings:

[0127] Filter system: configure with filters to simulate sunlight filtered through window glass (e.g., "S" type borosilicate internal filter and soda-lime external filter).

[0128] Irradiance: control point of 0.35 W / (m²·nm) at 340 nm wavelength.

[0129] Black panel temperature: 63 ± 2 °C (non-insulated black panel).

[0130] Relative humidity: Control point 55 ± 5%.

[0131] Air temperature in the chamber: 43 ± 2°C.

[0132] Sample installation: The sample to be tested was installed on a sample holder without backing. To avoid the influence of thermal radiation, the empty spaces in the exposed area were filled with blank metal plates.

[0133] Exposure period:

[0134] The sample was continuously exposed under 100% illumination until the total radiation exposure at 340 nm reached 510 kJ / (m2·nm). This radiation amount was reached after about 410.5 hours.

[0135] 5.4 Final color measurement and evaluation

[0136] After the end of the exposure, the sample was removed from the device as soon as possible.

[0137] The sample surface was checked for the presence of severe streaks, spots or exposure of the substrate. If this was the case, the ink sample was immediately classified as lightfastness class V (worst class).

[0138] For samples that were not classified as class V, a color measurement was again carried out under exactly the same conditions as the initial measurement (same instrument, same point, same direction) and the CIELAB values after exposure were recorded. The change before and after exposure was calculated according to the following formula.

[0139]

[0140] The test results are shown in the following table:

[0141] Table 2 Test results before and after light exposure of ink-applied samples of examples 1-7 and comparative example 1

[0142] .

[0143] The present application realizes that the ink maintains the traditional processing characteristics during preparation, and improves the durability by slow crosslinking after use, which is suitable for artistic works that need to be preserved for a long time.

[0144] As shown in the above table data, the ∆Eab of all examples and comparative example 1 is less than 4.0, and according to the standard ASTM D4303-10, the lightfastness belongs to class I (best), but the ∆Eab of comparative example 1 is higher (3.39), which is significantly higher than that of examples 1-7, indicating that the addition of dopamine indeed improves the anti-fading performance.

[0145] As can be seen from the data in table 2, the addition of dopamine significantly reduces the ∆Eab, i.e. improves the lightfastness and anti-fading performance of the ink. The specific trend is as follows:

[0146] No dopamine (Comparative Example 1): AEab = 3.39, relatively large color change.

[0147] As the amount of dopamine added increases, AEab first decreases and then slightly increases:

[0148] Dopamine 0.5 g (Example 2): AEab = 2.62

[0149] Dopamine 1.0 g (Example 3): AEab = 2.52

[0150] When the amount of dopamine added is 1.5 g - 2.0 g (Examples 1 and 4): AEab reaches a minimum value (1.32 and 1.31), indicating that the anti-fading performance is optimal in this range.

[0151] Further increase in the amount of dopamine added (Example 5, 2.5 g): AEab slightly increases to 1.52, but is still better than Comparative Example 1.

[0152] There is an optimal range for the amount of dopamine added (1.5 g - 2.0 g), and excessive addition (such as 2.5 g) slightly reduces the performance. However, overall, the addition of dopamine has a positive effect on reducing AEab.

[0153] Examples 6 and 7 specifically control the mass ratio of dopamine to gelatin to be 20:1 (i.e., dopamine: gelatin = 1:20) to study the effect of the ratio on performance:

[0154] Example 6 (gelatin 25 g, dopamine 1.25 g): AEab = 1.43

[0155] Example 7 (gelatin 35 g, dopamine 1.75 g): AEab = 1.40

[0156] Example 1 (gelatin 30 g, dopamine 1.5 g, ratio 20:1): AEab = 1.32

[0157] Comparative Examples 1-5 (ratio not fixed): When the ratio is close to 20:1 (such as Examples 1 and 4), AEab is low (1.32 and 1.31). While Examples 2 and 3 (ratios of 60:1 and 30:1, respectively) have higher AEab (2.62 and 2.52), indicating that the ratio is critical.

[0158] Conclusion: When the mass ratio of dopamine to gelatin is maintained at 20:1, AEab is generally small (1.32-1.43), indicating that this ratio can effectively improve the anti-fading performance. Dopamine, as a crosslinking agent, forms a stable three-dimensional network structure with gelatin after writing, thereby inhibiting color change.

[0159] In summary, the amount of dopamine added is the key factor affecting ΔEab. Adding dopamine can significantly reduce color difference, but it needs to be controlled within a certain range (1.5g-2.0g) to avoid performance degradation.

[0160] When the ratio is fixed at 20:1, the ink shows the best anti-fading performance. This may be due to the covalent cross-linking (such as Michael addition reaction) between the catechol functional group of dopamine and the amino acid residues of gelatin, forming a dense film layer and enhancing light resistance.

[0161] The amount of oil fume as pigment has little effect on ΔEab (Examples 6 and 7), as long as the dopamine-gelatin ratio is optimized.

[0162] Through the above analysis, it can be seen that the amount of dopamine added and the dopamine-gelatin ratio are the core parameters for controlling ΔEab. In practical applications, it is recommended to control the amount of dopamine added to 1.5g-2.0g (relative to the total formulation) and maintain the mass ratio of dopamine to gelatin at 20:1 to achieve the best anti-fading effect.

[0163] Test Example 2 Properties of Ink Samples of Examples 1-7 and Comparative Example 1

[0164] According to the current standard for ink DB34 / T 1379-2020 (Anhui Provincial Standard), other important parameters were tested, and the results are shown in the following table.

[0165] Table 3 Test Results of Other Parameters of Ink Samples of Examples 1-7 and Comparative Example 1

[0166] .

[0167] Ink yield (g / min): refers to the amount of ink ground from the ink stick per unit time. A standard of ≥0.015g / min reflects the efficiency of ink grinding, and a higher value indicates faster ink flow during grinding, providing sufficient ink for writing and drawing.

[0168] Table 3 data shows that after adding dopamine, the ink yield is slightly improved (all examples are ≥0.016 g / min, while comparative example 1 is 0.016 g / min). This indicates that the addition of dopamine has a slight positive effect on ink yield, possibly due to the improved uniformity and dispersion of the ink paste, making the grinding process smoother. However, the change is small, indicating that dopamine is not the main factor affecting ink yield, but it maintains the grinding characteristics of traditional ink.

[0169] Ink color (D): is an indicator of ink color darkness, ≥1.15 indicates that the ink color is dark enough. High ink color darkness can produce a rich and layered black effect during writing and drawing, which is an important manifestation of the "ink as lacquer" feature of traditional ink.

[0170] Table 3 data show that the addition of dopamine significantly improves the blackness of ink (all examples ≥ 1.15, and most higher than Comparative Example 1). This may be due to the oxidation and polymerization of dopamine after writing to form polydopamine, which is a dark polymer, thereby enhancing the darkness of the ink. For example, Example 1 (1.5 g of dopamine) and Example 7 (1.75 g of dopamine) both reach 1.23, which is better than 1.17 of Comparative Example 1. The addition amount of dopamine is 1.5 g-2.0 g, and the ink color is optimal (such as Examples 1 and 4), but excessive (such as Example 5, 2.5 g) may decrease slightly (1.21), indicating that there is an optimal range.

[0171] Viscosity (Pa s): It represents the degree of viscosity of the ink, ranging between 0.002-0.010 Pa s. The appropriate viscosity can make the ink smooth and not lag when writing, while ensuring the performance of the ink on paper, such as tonal changes, etc.

[0172] Table 3 data show that the addition of dopamine slightly increases the viscosity (0.007-0.008 for Examples 1-5, while 0.006 for Comparative Example 1). This may be due to the potential cross-linking effect of dopamine and gelatin, increasing the cohesion of the ink. But all values are within the standard range, indicating that the addition of dopamine does not cause abnormal viscosity, maintaining the smoothness when writing.

[0173] Diffusion rate (%): ≥70% reflects the diffusion performance of the ink on paper. Moderate diffusion rate can make the ink edge clear and not lose the charm, which helps to achieve the artistic effect of "five colors of ink".

[0174] Table 3 data show that the addition of dopamine significantly improves the diffusion rate (all examples ≥ 78.7%, while Comparative Example 1 is only 75.1%). This may be due to the hydrophilicity and cross-linking network of dopamine promoting the uniform diffusion of the ink on paper. Examples 6 and 7 (dopamine to gelatin ratio 20:1) have the highest diffusion rate (80.9% and 80.2%), indicating that dopamine optimizes the fluidity and permeability of the ink, which helps to achieve the artistic effect of "five colors of ink".

[0175] Water resistance (D): ≤0.4 indicates the water resistance of the ink, i.e. the ability of the ink to resist blurring and fading after being exposed to water. Good water resistance of the ink can be long-lasting, not easily damaged by water immersion, which embodies the characteristics of the ink "eternal truth".

[0176] The data in Table 3 show that the water resistance is slightly improved after the addition of dopamine (0.20 for Example 1, better than 0.22 for Comparative Example 1). This verifies the statement in the summary that dopamine improves water resistance. The dopamine forms a stable three-dimensional network structure after writing, solidifying the ink mark, thus reducing bleeding and fading when exposed to water. Although the change is not large, all values are much better than the standard, indicating that the addition of dopamine enhances the durability of the ink mark.

[0177] As can be seen from the above data, the addition of dopamine has a full-area effect on the performance of the ink. In the optimal range (1.5g-2.0g, corresponding to a mass ratio of gelatin to dopamine of 20:1), the ink color darkness and spreading rate are significantly improved, the ink yield and viscosity are good, and the water resistance is slightly improved. Excessive addition of dopamine (such as 2.5g) can cause a slight decrease in performance, but overall it is still better than the comparative example without dopamine.

[0178] The dopamine remains stable during preparation and does not crosslink with the gelatin, ensuring traditional processing characteristics; after writing, the dopamine slowly oxidizes and crosslinks under natural conditions to form a polydopamine network, thus solidifying the ink mark and improving the resistance to fading and water. In order to obtain the best performance, it is recommended to control the amount of dopamine added to 1.5g-2.0g (or a mass ratio of gelatin to dopamine of 20:1), which can significantly enhance the durability and artistic expression of the ink while maintaining the traditional texture of the ink.

[0179] The above summary and examples describe the basic principles and main features of the present patent application and the advantages of the present patent application. Those skilled in the art should understand that the present patent application is not limited by the above examples, and the above examples and descriptions in the specification are only the best technical solutions of the present patent application. Without departing from the spirit and scope of the present patent application, various changes and improvements can be made to the present patent application, all of which fall within the scope of the present patent application. The scope of protection of the present patent application is defined by the appended claims and their equivalents.

Claims

1. A fade resistant ink comprising soot, gelatin, dopamine hydrochloride, citric acid and deionized water, characterized in that, The anti-fading ink formula, the mass ratio is as follows: Oil smoke 40-60 parts Gelatin 25-35 parts Dopamine hydrochloride 0.5-2.5 parts Citric acid 1.0 part Deionized water 17 parts.

2. The fade-resistant ink of claim 1 wherein, The mass ratio of the gelatin and the dopamine hydrochloride is 15-30:

1.

3. The fade-resistant ink of claim 1 wherein, The mass ratio of the gelatin and the dopamine hydrochloride is 20:

1.

4. The fade-resistant ink of claim 1 wherein, The preferred amount of the dopamine hydrochloride is 1.5 parts.

5. The fade-resistant ink of claim 1 wherein, The preferred amount of the dopamine hydrochloride is 2.0 parts.

6. The fade-resistant ink of claim 1 wherein, The anti-fading ink further comprises a fragrance, which is one of borneol and musk.

7. A process for the preparation of a fade resistant ink according to any one of claims 1 to 6, characterised in that, The preparation method comprises the following steps: Step 1: Dissolve citric acid in deionized water, stir until completely dissolved, and adjust the pH value to 3.8-4.2 with NaOH solution; Step 2: Slowly add gelatin to part of the acidic aqueous solution, stir to form a uniform colloid; Dissolve dopamine hydrochloride in the remaining acidic aqueous solution, stir until completely dissolved; Step 3: First, mix the gelatin solution obtained in step 2 with oil smoke, use a wooden stirrer to stir at low speed to form a uniform ink paste; slowly add the fragrance to the obtained ink paste, continue to stir at low speed to ensure that the fragrance is uniformly dispersed in the entire ink paste, then slowly drop the dopamine hydrochloride solution obtained in step 2 into the ink paste, continue to stir to ensure uniform distribution but avoid excessive shearing; Step 4: Fill the mixed ink paste into a mold, lightly press and shape at 20-25℃, and immediately transfer to a 15-18℃ environment for pre-curing; Step 5: First stage: dry at 20℃ and 60% humidity for 12 hours; second stage: dry at 25℃ and 40% humidity for 24-48 hours, age in a sealed container at 20-25℃ for 7 days to evenly distribute the moisture, cut into pieces, and obtain the product.