An ink uniformity emulsion liquid for ink gradation enhancement of calligraphy and painting paper, a preparation method and an application method

Abstract

This invention discloses a water-based ink-level enhancement latex for calligraphy and painting paper, its preparation method, and its application method. The latex comprises, by weight, 15 to 25 parts calcined kaolin, 8 to 15 parts rutile titanium dioxide, 25 to 35 parts heavy calcium carbonate, 3 to 8 parts organically modified bentonite, 1 to 3 parts sulfonated castor oil, 25 to 35 parts styrene-acrylic emulsion, 80 to 120 parts quaternary ammonium cationic plant starch, and additives. A multi-level porous structure is constructed using gradient particle size mineral fillers. The electrostatic adsorption of cationic starch and carbon black particles achieves gradient deposition of ink levels. The styrene-acrylic emulsion film network imparts water resistance and durability to the coating. After coating, the ink diffusion uniformity coefficient of the calligraphy and painting paper is greater than 0.85, the ink level distinguishability is greater than 5 levels, and the coating wet abrasion resistance is greater than 25 times.

Description

Technical Field

[0001] This invention belongs to the field of papermaking chemicals technology, specifically relating to a latex composition suitable for coating the surface of calligraphy and painting paper, which can achieve uniform diffusion of ink and enhance the expressive power of ink and water layers, as well as the preparation method of the latex and its application method in coating calligraphy and painting paper. Background Technology

[0002] Painting and calligraphy paper is an indispensable medium in traditional Chinese calligraphy and painting. High-quality painting and calligraphy paper should possess excellent ink-absorbing properties, allowing the ink to spread evenly and clearly, presenting rich variations in ink color, such as dark, light, dry, wet, and burnt. This characteristic is known in the field of calligraphy and painting as the "five colors of ink." However, existing painting and calligraphy papers have many shortcomings in practical use.

[0003] First, there is the problem of uneven ink penetration. The irregular fiber structure of traditional calligraphy and painting paper leads to inconsistent ink diffusion rates and directions on the paper surface. This results in some areas being excessively dark while adjacent areas are lighter, severely affecting the visual expressiveness of the artwork. This uneven penetration is particularly noticeable when artists apply large-area washes or use splashed ink techniques.

[0004] Secondly, there is the problem of unreasonable coating formulation design. Existing coatings for calligraphy and painting papers mostly use simple mixtures of mineral pigments and natural adhesives, such as kaolin and calcium carbonate as fillers, and starch or polyvinyl alcohol as binders. While these coatings can improve the whiteness and smoothness of the paper surface, they lack the ability to precisely control the diffusion behavior of ink. Specifically, the uniform particle size distribution of mineral pigments makes it impossible to construct an effective gradient pore structure in the coating to guide the capillary penetration process of the ink.

[0005] Third, there is the problem of insufficient ink tonal gradation. High-quality calligraphy and painting paper should allow the ink marks after writing or painting to show clear transitions in shade and a three-dimensional sense of gradation. However, in the existing coating system, the interfacial interaction between mineral fillers and binders is weak, and the hydrophilic-hydrophobic balance of the coating surface is difficult to control precisely. This causes the ink to either quickly penetrate into the deep layers of the paper base (manifested as ink leakage) or spread excessively on the surface without penetrating (manifested as floating ink), neither of which can achieve the ideal ink tonal gradation effect.

[0006] Fourth, there are issues regarding the durability and preservation of the coating. Some existing technologies use pure water-soluble adhesives as the coating film-forming substance. Although the coating process is simple, the resulting coating is prone to absorbing moisture, softening, or even dissolving and peeling off in environments with large humidity changes. This leads to deterioration of calligraphy and painting works, such as discoloration and peeling, during long-term preservation.

[0007] Chinese patent CN1261646C discloses a water-writing paper and its preparation method. This method involves coating the surface of black base paper with a water-soluble polymer composite coating composed of carboxymethyl cellulose, methyl cellulose, silica, and kaolin. While this technology achieves a water-writing color-changing effect, its coating system is entirely based on water-soluble polymers and lacks water-resistant emulsion components, making it unsuitable for calligraphy and painting applications requiring ink wash painting. Chinese patent CN102134821B discloses a water-removable hot-press mounting paper. Its coating contains mineral pigments such as kaolin, calcium carbonate, and diatomaceous earth, along with natural or synthetic adhesives. However, this method focuses on mounting and unmounting performance and does not address the control of ink diffusion uniformity. International patent WO2016151511A1 discloses an inkjet ink receiving coating containing esterified or etherified starch and inorganic minerals. It uses modified starch combined with kaolin or silicate pigments to improve ink absorption density. However, this method is designed for inkjet printing, and its formulation design logic differs fundamentally from traditional ink wash calligraphy and painting paper.

[0008] In summary, current technologies have not yet proposed a solution that can precisely control the uniform diffusion of ink on the surface of calligraphy and painting paper and enhance the tonal gradation through coating composition design. In particular, significant technological gaps remain in areas such as filler particle size gradient design, synergistic combination of cationic modified starch and acrylic emulsion, and directional control of surface wettability. Summary of the Invention

[0009] The purpose of this invention is to overcome the technical defects of existing technologies, such as uneven ink penetration, insufficient ink color gradation, and poor coating durability in calligraphy and painting paper, and to provide an ink-level enhancement latex composition for calligraphy and painting paper. This latex, through the synergistic effect of a gradient particle size mineral filler system and a cationic modified starch-acrylate emulsion composite binder system, constructs a microporous coating structure with directional capillary penetration function on the surface of calligraphy and painting paper, thereby achieving uniform ink diffusion and enhanced color gradation.

[0010] The second objective of this invention is to provide a method for preparing the aforementioned latex solution, which is simple in process, mild in conditions, and suitable for industrial production.

[0011] The third objective of this invention is to provide a method for applying the aforementioned latex liquid to the coating of calligraphy and painting paper, thereby achieving the best ink-water layer enhancement effect by optimizing the coating amount and drying conditions.

[0012] To achieve the above objectives, the present invention provides the following technical solution: The present invention discloses an ink-leveling and ink-leveling latex for calligraphy and painting paper, comprising, by weight, the following components: 15 to 25 parts calcined kaolin, 8 to 15 parts rutile titanium dioxide, 25 to 35 parts heavy calcium carbonate, 3 to 8 parts organically modified bentonite, 1 to 3 parts sulfonated castor oil, 25 to 35 parts styrene-acrylic emulsion, 80 to 120 parts quaternary ammonium cationic plant starch, 0.5 to 1.5 parts sodium hexametaphosphate dispersant, 0.3 to 0.8 parts hydroxyethyl cellulose thickener, and 368.5 to 430 parts deionized water.

[0013] The preparation method of the above-mentioned latex liquid includes the following steps: First, cationic plant starch and deionized water are gelatinized at 85°C to 95°C for 30 to 45 minutes to form a uniform starch paste, and then the temperature is lowered to 45°C to 55°C; Sodium hexametaphosphate dispersant is dissolved in an appropriate amount of deionized water, and then calcined kaolin, rutile titanium dioxide and heavy calcium carbonate are added in sequence, and dispersed at a high speed of 1000 r / min to 1500 r / min for 20 to 30 minutes to form a mineral filler dispersion; Organically modified bentonite is pre-swollen with deionized water for 12 to 24 hours to form bentonite gel; The mineral filler dispersion is slowly added to the starch paste, and stirred and mixed at a speed of 500 r / min to 800 r / min for 15 to 20 minutes; Bentonite gel and sulfonated castor oil are added, and stirring is continued for 10 to 15 minutes; Finally, styrene-acrylic emulsion and hydroxyethyl cellulose thickener are added, and the mixture is stirred at 300... Mix thoroughly at a low speed of 500 r / min to 500 r / min, and adjust the pH of the system to 7.5 to 8.5 to obtain a water-based ink layering enhancement latex for calligraphy and painting paper.

[0014] The application method of the above-mentioned latex solution in the coating of calligraphy and painting paper includes: applying the prepared latex solution to the surface of the calligraphy and painting paper base paper using an air knife coating method, with the coating amount on one side controlled at 8 g / m². 2 Up to 15 g / m 2 (On a dry weight basis), the coating speed is 50 m / min to 120 m / min; after coating, it is dried in an infrared oven at 100°C to 130°C for 10 s to 30 s; finally, it is surface-finished by a soft calender under an online pressure of 30 kN / m to 80 kN / m to obtain a finished calligraphy and painting paper with enhanced ink and water layering effect.

[0015] Compared with existing technologies, this invention has the following advantages: A gradient particle size system is formed by calcining kaolin (flaky, D50 1.5 μm to 2.5 μm), rutile titanium dioxide (spherical, D50 0.2 μm to 0.4 μm), and heavy calcium carbonate (irregular, D50 3 μm to 5 μm), which self-assembles into a multi-level porous structure in the coating. Quaternary ammonium cationic plant starch undergoes electrostatic adsorption with the anionic dispersant on the surface of carbon black particles in the ink, causing the carbon black particles to undergo gradient deposition along the penetration path, forming a concentration decreasing distribution from the penetration center to the edge. The styrene-acrylic emulsion forms a flexible polymer film network, with its hydrophobic polymer segments and hydrophilic starch matrix alternately distributed to form hydrophilic and hydrophobic microregions. Organically modified bentonite acts as a microscopic flow guide and has a water-retaining and slow-release function. Sulfonated castor oil and cationic starch form an ion-pairing complex, constructing a dynamic wetting gradient. Testing revealed that the calligraphy and painting paper coated with the latex liquid of this invention exhibits an ink diffusion uniformity coefficient of over 0.85, an ink color gradient distinguishability of over 5 levels, and a coating wet abrasion resistance of over 25 times. Attached Figure Description

[0016] Figure 1 This is a scanning electron microscope (SEM) image of the gradient particle size mineral filler system in the latex coating of the present invention. The scale bar is 2 μm.

[0017] Figure 2 This is a scanning electron microscope (SEM) image of the cross-section of the latex coating of the present invention. The scale bar is 5 μm and the magnification is 2000x, showing a three-level gradient pore structure of macropores, mesopores and micropores.

[0018] Figure 3 This is an atomic force microscope (AFM) three-dimensional topography image of the coating surface in Example 1, with a scanning range of 10 μm by 10 μm and a scale bar of 2 μm.

[0019] Figure 4 The bar charts show the comparison of ink diffusion uniformity coefficient and ink color gradient distinguishability of coated calligraphy and painting paper in Example 1 and Comparative Examples 1 to 5.

[0020] Figure 5 The graphs show the water contact angle of the coated calligraphy and painting paper in Example 1 and Comparative Examples 1 to 5 as a function of time, with test times ranging from 0 s to 30 s. Detailed Implementation

[0021] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. All raw materials used in the embodiments are commercially available analytical grade or industrial grade products, and unless otherwise specified, the experimental conditions are at room temperature and pressure.

[0022] The detailed specifications of the raw materials used are as follows. The calcined kaolin is from Suzhou Kaolin Company, calcined at 1250°C, with a D50 of 2.0 μm and a specific surface area of ​​12 m². 2 / g to 16 m 2 The rutile titanium dioxide used has a whiteness (ISO) greater than 92% and an oil absorption value of 55 mL / 100 g to 65 mL / 100 g. The selected rutile titanium dioxide is Chemours R-706, with a D50 of 0.3 μm and a hiding power greater than 240 g / m². 2 The titanium dioxide content is greater than 93%. Heavy calcium carbonate is selected from Jiande Calcium Industry, with a D50 of 4.0 μm, whiteness (ISO) greater than 95%, and calcium carbonate content greater than 98%. Organically modified bentonite is selected from Zhejiang Fenghong New Material Co., Ltd.'s DK-1 model, modified with octadecyltrimethylammonium chloride, with an interlayer spacing of 2.5 nm to 3.5 nm and a swelling ratio greater than 25 mL / 2 g. Sulfonated castor oil (also known as Taikoo oil) is selected from Shanghai Shenguang Chemical Co., Ltd., with an active ingredient content greater than 50% and a sulfonation degree greater than 4.5%. The styrene-acrylic emulsion (styrene-acrylate copolymer emulsion) is selected from BASF's Acronal S 728 model, with a solid content of 50%, a Tg of 10°C, a latex particle size of 100 nm, a minimum film-forming temperature of 5°C, and a pH value of 7.5 to 8.5. The quaternary ammonium cationic plant starch was selected from the Hi-Cat series products of National Starch Company, prepared from corn starch through quaternization modification with 2,3-epoxypropyltrimethylammonium chloride (GTA), with a degree of substitution (DS) of 0.035 to 0.045 and a nitrogen content of 0.25% to 0.35%. Sodium hexametaphosphate was analytical grade with a content greater than 98%. Hydroxyethyl cellulose was selected from Dow Chemical's Natrosol 250HHR, with a viscosity grade of 50,000 mPa·s (2% aqueous solution, 25°C). Example 1

[0023] This embodiment provides a method for preparing a water-based ink layering enhancement type ink-leveling latex liquid for calligraphy and painting paper. The specific steps are as follows.

[0024] Step 1: Preparation of Starch Paste. Take 100 parts of quaternary ammonium cationic plant starch and add 300 parts of deionized water to a stainless steel reactor. Turn on the anchor-type stirrer and stir at 200 r / min. Under stirring conditions, heat to 90°C at a rate of 3°C / min, and maintain this temperature for 40 min to allow the starch granules to fully gelatinize and expand, forming a uniform and transparent starch paste. During gelatinization, a sharp increase in viscosity can be observed in the starch slurry within the range of 65°C to 75°C. This is a typical characteristic of starch granules absorbing water, swelling, and breaking down, and the dissolution of amylose. After gelatinization, cool the starch paste to 50°C while stirring using a jacketed cooling water circulation system. The Brookfield viscosity of the starch paste (measured at 60 r / min, 25°C) should be controlled within the range of 800 mPa·s to 1200 mPa·s. If the viscosity is too high, add deionized water as needed to adjust it; if the viscosity is too low, it indicates insufficient gelatinization and the holding time needs to be extended. The solid content of the starch paste is controlled at around 25%, and the pH value is between 6.5 and 7.5.

[0025] Step 2: Preparation of the mineral filler dispersion. Dissolve 1.0 part of sodium hexametaphosphate in 50 parts of deionized water and stir at room temperature for 5 minutes until completely dissolved. Then, add 20 parts of calcined kaolin, 10 parts of rutile titanium dioxide, and 30 parts of heavy calcium carbonate in sequence. The order of addition must not be reversed: first add kaolin to fully wet it under the protection of the dispersant, then add titanium dioxide to fill the gaps between the kaolin layers with its small particle size, and finally add heavy calcium carbonate to form the framework structure. Disperse the above mixture in a high-speed disperser (60 mm diameter toothed disc) at 1200 r / min for 25 minutes, controlling the dispersion temperature to not exceed 45°C (cooling with a water bath if necessary) to prevent excessive heating that could lead to the hydrolysis and inactivation of sodium hexametaphosphate. After dispersion, the mineral filler dispersion should be a uniform milky white slurry without any visible agglomerates. The fineness of the dispersion (measured by a scraper fineness meter) was controlled to be less than 25 μm, the solid content was approximately 55%, and the pH value was approximately 7.0. The zeta potential of the dispersion was approximately -35 mV to -45 mV, indicating that the mineral particles had an electrical double layer formed by the adsorption of sodium hexametaphosphate, resulting in good dispersion stability.

[0026] like Figure 1 As shown, the microstructure of the mineral filler dispersion after drying and forming a film can be clearly observed under a scanning electron microscope: three different morphologies of mineral fillers, namely, flaky calcined kaolin particles (aspect ratio greater than 10, with clear edges), near-spherical titanium dioxide nanoparticles (particle size of about 300 nm) and irregular calcite-like heavy calcium carbonate particles (particle size of about 4 μm), are uniformly dispersed, and no obvious agglomeration phenomenon was observed.

[0027] Step 3: Preparation of Bentonite Gel. Take 5 parts of organically modified bentonite and add it to a beaker containing 45 parts of deionized water. Stir initially with a glass rod to fully impregnate the bentonite powder, then allow it to swell for 18 hours until a uniform, translucent gel is formed. The thixotropic index of the gel (viscosity ratio at 6 r / min to 60 r / min) should be greater than 3.0, indicating the formation of a good layered network structure. If swelling is insufficient (particulate matter remains in the gel), the swelling time should be extended to 24 hours. The solid content of the bentonite gel is approximately 10%.

[0028] Step 4: Latex Solution Compounding and Preparation. In a stainless steel reactor equipped with an anchor-type stirrer, the mineral filler dispersion prepared in Step 2 is slowly added to the starch paste prepared in Step 1 over 15 minutes using a peristaltic pump at a stirring speed of 500 r / min. The purpose of slow addition is to prevent excessively high local concentrations that could cause flocculation of the starch and mineral particles. After the addition is complete, stirring continues for 15 minutes until the system is macroscopically homogeneous. At this point, the system is a milky white slurry with a viscosity of approximately 1000 mPa·s to 1500 mPa·s. Then, the total amount of bentonite gel prepared in Step 3 and 2 parts of sulfonated castor oil are added, and the stirring speed is adjusted to 600 r / min, continuing to stir for 12 minutes. The addition of bentonite gel will slightly increase the viscosity of the system and make it thixotropic, while the addition of sulfonated castor oil will slightly reduce the surface tension of the system. Finally, add 30 parts of styrene-acrylic emulsion and 0.5 parts of hydroxyethyl cellulose (pre-swelled in 5 times the volume of deionized water for 2 hours to form a homogeneous solution). Reduce the stirring speed to 300 to 500 r / min and stir at low speed for 15 minutes to ensure thorough mixing of all components. The stirring speed should not be too high to avoid introducing excessive air bubbles and compromising the stability of the emulsion particles. After thorough mixing, adjust the pH of the system to 8.0 dropwise with a 10% sodium hydroxide solution. This yields a finished ink-leveling emulsion for calligraphy and painting paper.

[0029] The main technical indicators of the finished latex solution are: solid content of 38% to 42%, Brookfield viscosity (60 r / min, 25°C) of 1500 mPa·s to 2500 mPa·s, pH value of 7.5 to 8.5, fineness of less than 20 μm, and qualified coating stability (no obvious stratification after standing for 72 h). The latex solution can be stored in a sealed container at 5°C to 35°C for more than 6 months without stratification or deterioration.

[0030] Step 5, Coating Application. Take a dosage of 60 g / m³. 2The calligraphy and painting paper base paper (made from a mixture of 40% sandalwood bark pulp and 60% rice straw pulp, with a beating degree of 35°SR to 45°SR and a sizing degree greater than 1.0 mm) was coated with the aforementioned latex solution on one side of the base paper using a laboratory air knife coating machine. The air knife pressure was adjusted to 3 kPa to 5 kPa, the distance between the air knife and the paper surface was 5 mm to 10 mm, and the dry coating amount was controlled at 12 g / m². 2 The coating speed was 80 m / min. The coated wet paper was dried in an infrared oven at 110°C for 15 s, with residual moisture content controlled at 6% to 8%. Then, it underwent surface finishing at an online pressure of 50 kN / m using a soft calender (elastic rollers with a Shore D hardness of 88 to 92, and chrome-plated steel rollers) to obtain the finished ink-uniform calligraphy and painting paper. The finished paper has a smooth feel, moderate whiteness, and when written with a brush dipped in standard ink, the ink spreads evenly and clearly, exhibiting excellent suitability for calligraphy and painting creation. Example 2

[0031] The difference between this embodiment and Example 1 lies in the adjustment of the component ratio, aiming to obtain a more water-resistant coating for calligraphy and painting paper. 120 parts of quaternary ammonium cationic plant starch (DS = 0.030 to 0.040) and 360 parts of deionized water were used to prepare a starch paste according to step one of Example 1, with a gelatinization temperature of 88°C and a holding time of 45 min. 1.2 parts of sodium hexametaphosphate, 15 parts of calcined kaolin, 8 parts of rutile titanium dioxide, 25 parts of heavy calcium carbonate, and 40 parts of deionized water were used to prepare a mineral filler dispersion according to step two of Example 1, with a dispersion speed of 1000 r / min and a dispersion time of 30 min. 3 parts of organically modified bentonite and 27 parts of deionized water were used to prepare a bentonite gel according to step three of Example 1, with a swelling time of 24 h. During the compound preparation, 1.5 parts of sulfonated castor oil, 35 parts of styrene-acrylic emulsion, and 0.6 parts of hydroxyethyl cellulose were added, and the remaining steps were the same as in Example 1, adjusting the pH value to 7.8. The finished latex has a liquid solids content of 36% to 40% and a viscosity of 1800 mPa·s to 2800 mPa·s. The dry coating amount should be controlled at 10 g / m² during application. 2 The coating speed was 100 m / min, the drying temperature was 120°C, the drying time was 12 s, and the pressure of the soft pressing light was 40 kN / m.

[0032] This embodiment increases the emulsion dosage to 35 parts and reduces the total filler content to 48 parts (compared to 60 parts in Example 1), resulting in a more continuous and dense polymer film network in the coating. This makes it suitable for high-quality calligraphy and painting papers with higher requirements for water resistance and long-term preservation. Due to the increased proportion of styrene-acrylic emulsion, the latex particles fuse more fully during the drying and film-forming process, resulting in a higher coverage of the polymer network and effectively preventing moisture from penetrating the paper base through the coating. However, the reduced proportion of mineral filler decreases the porosity of the coating, slightly lowering the initial ink absorption rate, which needs to be compensated for by appropriately reducing the coating amount. Example 3

[0033] The difference between this embodiment and Example 1 lies in the optimization of the component ratio boundary, aiming to obtain a coating for ink-splashed calligraphy and painting paper with stronger ink absorption. 80 parts of quaternary ammonium cationic plant starch (DS = 0.040 to 0.050) and 240 parts of deionized water were used to prepare a starch paste according to step one of Example 1, with a gelatinization temperature of 95°C and a holding time of 30 min. 0.8 parts of sodium hexametaphosphate, 25 parts of calcined kaolin, 15 parts of rutile titanium dioxide, 35 parts of heavy calcium carbonate, and 55 parts of deionized water were used to prepare a mineral filler dispersion according to step two of Example 1, with a dispersion speed of 1500 r / min and a dispersion time of 20 min. 8 parts of organically modified bentonite and 72 parts of deionized water were used to prepare a bentonite gel according to step three of Example 1, with a swelling time of 18 h. During compound preparation, 3 parts of sulfonated castor oil, 25 parts of styrene-acrylic emulsion, and 0.3 parts of hydroxyethyl cellulose were added, and the pH was adjusted to 8.5. The finished latex has a liquid solids content of 40% to 44% and a viscosity of 1200 mPa·s to 2000 mPa·s. The dry coating amount should be controlled at 15 g / m² during application. 2 The coating speed was 60 m / min, the drying temperature was 100°C, the drying time was 25 s, and the pressure of the soft pressing light was 80 kN / m.

[0034] This embodiment increases the total filler content to 75 parts (compared to 60 parts in Example 1) and the bentonite content to 8 parts, resulting in a more developed gradient pore structure in the coating and an increase in coating porosity of approximately 15%. The higher porosity gives the coating a stronger ink absorption capacity, making it particularly suitable for freehand ink-splashing painting paper. It can withstand large-area, high-volume ink-splashing operations without ink overflow or uneven penetration. However, because the proportion of styrene-acrylic emulsion is reduced to 25 parts, the continuity of the polymer network in the coating is somewhat decreased, and the water resistance and mechanical strength of the coating are lower than in Examples 1 and 2. Another effect of increasing the bentonite content to 8 parts is a significant improvement in the thixotropic and water-retention properties of the latex, allowing the coating to maintain a moist state for a longer period during the initial drying stage, providing ample time for the natural wetting of the ink in ink-splashing techniques.

[0035] Comparative Example 1 (without cationic starch, replaced by ordinary oxidized starch) The difference between this comparative example and Example 1 is that 100 parts of ordinary oxidized starch (carboxyl content 0.1% to 0.2%, prepared by oxidation of corn starch with sodium hypochlorite) are used instead of quaternary ammonium cationic plant starch. The remaining component ratios and preparation processes are the same as in Example 1. Ordinary oxidized starch is weakly anionic in aqueous solution (Zeta potential approximately -5 mV to -15 mV), and there is a repulsive relationship between it and the anionic dispersant on the surface of carbon black particles, thus it does not have the ability to electrostatically adsorb and capture carbon black particles.

[0036] Comparative Example 2 (excluding organically modified bentonite) The difference between this comparative example and Example 1 is that: no organically modified bentonite and its corresponding swelling water are added, and 5 parts of heavy calcium carbonate are added accordingly (i.e., the total amount of heavy calcium carbonate is 35 parts). The remaining component ratios and preparation processes are the same as in Example 1.

[0037] Comparative Example 3 (without styrene-acrylic emulsion, replaced by polyvinyl alcohol) The difference between this comparative example and Example 1 is that 300 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 1700 to 1800, degree of hydrolysis 88%) were used instead of 30 parts of styrene-acrylic emulsion. The remaining component ratios and preparation processes are the same as in Example 1. The polyvinyl alcohol aqueous solution forms a continuous, transparent, hydrophilic film during the coating drying process, but this film rapidly swells and softens upon contact with water.

[0038] Comparative Example 4 (the filler is kaolin with a single particle size, without titanium dioxide and heavy calcium carbonate) The difference between this comparative example and Example 1 is that only 60 parts of calcined kaolin (D50 is 2.0 μm) were used as the mineral filler, and rutile titanium dioxide and heavy calcium carbonate were not used. The amount of sodium hexametaphosphate was adjusted to 1.5 parts to accommodate the increased filler amount. The remaining component ratios and preparation processes are the same as in Example 1.

[0039] Comparative Example 5 (without sulfonated castor oil) The difference between this comparative example and Example 1 is that sulfonated castor oil is not added, while the proportions of the remaining components and the preparation process are the same as in Example 1.

[0040] The detection method is as follows: Method for determining the uniformity coefficient of ink diffusion: Take a 5 cm x 5 cm coated calligraphy and painting paper sample and equilibrate it for 24 h under constant temperature and humidity conditions of 23°C ± 1°C and 50% ± 2% relative humidity. Using a standard brush, apply a drop of standard ink (5% solids carbon black ink with a carbon black particle size D50 of 80 nm to 120 nm) to the center of the sample, approximately 2 mm in diameter. Allow it to stand for 60 s to allow the ink to diffuse naturally and partially dry. Scan the ink image using a flatbed scanner at 1200 dpi resolution and 8-bit grayscale mode. Using ImageJ image analysis software, divide the ink area into eight 45° sector regions with the center point as the origin. Measure the average grayscale value (0 to 255 scale) of each sector region and calculate the coefficient of variation (CV) (standard deviation divided by the mean) of the eight grayscale values. The uniformity coefficient of ink diffusion, U, is equal to 1 minus CV. The closer the U value is to 1.0, the more uniform the diffusion. Each group of samples was measured 5 times, the average value was taken, and the standard deviation was calculated.

[0041] Method for determining the distinguishability of ink color gradients: One drop each of carbon black ink with a concentration of 1%, 2%, 3%, 4%, 5%, 6%, 7%, and 8% (approximately 5 μL per drop) was placed on coated calligraphy and painting paper, spaced more than 10 mm apart to avoid interference. After drying at room temperature for 2 hours, the optical density value (OD value, using a D65 light source and a 2° viewing angle) was measured in the central area of ​​each ink mark using an X-Rite eXact spectrophotometer. A difference of more than 0.05 between adjacent OD values ​​was considered distinguishable. The number of distinguishable gradients was counted. A higher number of distinguishable gradients indicates a higher resolution of the coating's response to different ink concentrations, resulting in a more delicate ink color transition during calligraphy and painting creation.

[0042] Method for determining wet abrasion of coatings: Refer to the principle of GB / T 9286 with appropriate modifications. Use a PME type wet abrasion tester, placing a 10 cm² area on the coating surface. 2 A nonwoven fabric friction head was used to apply a 500 g load (equivalent to 5 kPa pressure). After wetting the friction head with deionized water, the head was used to perform reciprocating friction on the coating surface at a frequency of 40 times / min for a 1 cm stroke. The number of reciprocating friction cycles was recorded when the coating showed signs of exposure (the exposed area of ​​the paper base fiber was greater than 50% of the test area). Each group of samples was measured 3 times and the average value was taken.

[0043] Method for determining coating whiteness: The ISO whiteness of the coated paper was determined using an Elrepho whiteness meter according to the GB / T 7974 standard method under d / 0 geometric conditions, with magnesium oxide white board as the reference standard. Three points were measured on each side of each sample, and the average of the six readings was taken.

[0044] Method for determining the contact angle of the coating: A JC2000D1 contact angle meter was used with deionized water as the test liquid (droplet volume approximately 3 μL). The initial contact angle (reading within 1 s after droplet drop) and the equilibrium contact angle (reading 30 s after droplet drop) were measured on the coating surface. Five points were measured for each sample, and the average value was taken. The initial contact angle reflects the initial wettability of the coating surface, while the equilibrium contact angle reflects the dynamic wetting evolution of the coating surface during water penetration.

[0045] Table 1 summarizes the performance test results of each embodiment and comparative example.

[0046] The following conclusions can be drawn from the above data.

[0047] Comparing Example 1 and Comparative Example 1, it can be seen that after replacing ordinary oxidized starch with quaternary ammonium cationic plant starch, the ink diffusion uniformity coefficient increased from 0.62 to 0.89, an improvement of 43.5%, and the ink color level improved from 3 to 6. This significant difference is attributed to the electrostatic adsorption effect of cationic starch. Quaternary ammonium cationic starch carries a positive charge in solution (Zeta potential approximately +25 mV to +35 mV), while the carbon black particles in standard carbon black ink carry a negative charge after being stabilized by an anionic dispersant (Zeta potential approximately -30 mV to -45 mV). When the ink penetrates into the coating, electrostatic adsorption occurs between the cationic starch and the carbon black particles, causing the dispersion stability of the carbon black particles to gradually decrease along the penetration path, and the particles gradually aggregate and deposit on the pore walls. This gradual charge neutralization-deposition process results in a concentration gradient distribution of carbon black particles in the coating, i.e., the carbon black concentration is the highest (darkest ink) at the penetration center, gradually decreasing towards the edge (lighter ink), thereby producing rich ink color level variations. It is worth noting that the degree of substitution (DS) of cationic starch needs to be controlled within the range of 0.030 to 0.050. If the DS is too low (less than 0.020), the charge density will not be sufficient to effectively capture carbon black particles. If the DS is too high (greater than 0.060), excessive flocculation will occur at the penetration front, which will cause carbon black particles to accumulate on the coating surface and not penetrate deeply, resulting in the ink floating on the paper surface.

[0048] Comparing Example 1 and Comparative Example 2, it can be seen that the addition of organically modified bentonite increased the ink diffusion uniformity coefficient from 0.78 to 0.89. The layered silicate structure of bentonite acts as a microscopic guide plate in the coating. Its layers are oriented along the paper surface during coating and drying, guiding the ink to diffuse uniformly along the planar direction and preventing irregular penetration due to local defects in the coating structure (such as pinholes and cracks). Simultaneously, the slow release of water between the bentonite layers prolongs the ink's residence time in the coating, which is beneficial for the full and uniform deposition and distribution of carbon black particles under the electrostatic adsorption of cationic starch. Furthermore, the octadecyl long-chain alkyl groups of the organically modified bentonite endow the coating with a certain degree of hydrophobicity adjustment capability, complementing the hydrophilic and hydrophobic micro-region structure of the styrene-acrylic emulsion-starch system.

[0049] Comparing Example 1 and Comparative Example 3, it is evident that the styrene-acrylic emulsion has a decisive influence on the coating's durability. Replacing the styrene-acrylic emulsion with polyvinyl alcohol (PVA) drastically reduced the wet abrasion wear of the coating from 32 cycles to 10 cycles, a decrease of 68.8%. During the coating drying and film formation process, the latex particles in the styrene-acrylic emulsion fuse together above the minimum film-forming temperature (approximately 5°C) to form a continuous hydrophobic polymer network. This network has a glass transition temperature of approximately 10°C and remains in an elastic state at room temperature, exhibiting both good flexibility and sufficient mechanical strength. This network firmly bonds the mineral filler particles and starch matrix together, endowing the coating with excellent water resistance and mechanical strength. The benzene ring structure of the styrene segments provides additional interfacial adhesion through interaction with the kaolinite sheet surface. While PVA has good film-forming properties, its highly hydrophilic molecular structure (numerous hydroxyl groups) causes the coating to rapidly swell and soften under wet conditions, making it unable to withstand mechanical friction. The hydrophobic polymer membrane segment of the styrene-acrylic emulsion and the hydrophilic starch matrix form a hydrophilic-hydrophobic alternating micro-region structure in the coating. This microphase separation structure effectively regulates the penetration path of the ink in the coating, allowing the ink to preferentially penetrate along the hydrophilic channels (starch-rich areas) and slow down and change direction at the boundary of the hydrophobic micro-regions (emulsion membrane-rich areas), thereby forming a more uniform and fine diffusion pattern.

[0050] Comparing Example 1 and Comparative Example 4, it is evident that the gradient particle size filler system has a crucial influence on ink diffusion behavior. When using only single-size kaolin (D50 of 2.0 μm), the pore size and distribution formed by particle accumulation in the coating are uniform, lacking multi-level pore control capability. As a result, the ink penetration process in the coating exhibits an all-or-nothing characteristic, either rapid overall penetration (after the coating becomes water-saturated) or complete impermeability (when the coating is dry), lacking fine-grained control of the penetration rate gradient, resulting in an ink diffusion uniformity coefficient of only 0.65 and a hierarchical gradient distinguishability of only 3 levels. This invention employs a compound of three mineral fillers with different particle sizes and morphologies: calcined kaolin (D50 approximately 2.0 μm, flake-like, aspect ratio greater than 10), titanium dioxide (D50 approximately 0.3 μm, nearly spherical), and heavy calcium carbonate (D50 approximately 4.0 μm, irregular calcite). During the coating drying process, these three fillers self-assemble to form a multi-level porous structure due to differences in particle size and morphology: large-diameter heavy calcium carbonate particles stack together to form macropores with a diameter of about 2 μm to 5 μm (based on the random sphere packing theory, the packing porosity is about 26% to 36%), serving as the initial penetration channels for ink; the gaps between medium-diameter kaolin sheets form mesopores with a diameter of about 0.5 μm to 2 μm. Based on the parallel stacking geometry of the sheet-like particles, these mesopores mainly extend along the parallel direction of the paper surface, effectively controlling the lateral diffusion rate of the ink; small-diameter titanium dioxide particles fill the gaps between macropores and mesopores, forming micropores with a diameter of about 0.1 μm to 0.5 μm, serving as locking termination sites for carbon black particles (with a diameter of about 80 nm to 120 nm) in the ink. The synergistic effect of the three-level pore structure enables the ink to undergo a graded permeation process in the coating: rapid penetration into macropores (low capillary pressure, high permeation rate) → uniform lateral expansion of mesopores (medium capillary pressure, moderate permeation rate) → termination by micropore locking (high capillary pressure, carbon black particles are physically trapped).

[0051] like Figure 2 As shown, the scanning electron microscope image of the coating cross-section visually reveals this three-level gradient pore structure: the upper part of the coating (closer to the paper surface) is dominated by macropores, the middle part by mesopores, and the bottom part (closer to the paper substrate) by micropores, forming a gradient distribution with decreasing pore size from top to bottom. Figure 3 As shown, the three-dimensional morphology image of the coating surface in Example 1 obtained by atomic force microscopy shows that the surface roughness Ra of the coating is about 0.8 μm to 1.2 μm, the surface micro-undulations are uniform, and there are no obvious large-area protrusions or depressions, which proves that the mineral filler is uniformly distributed in the coating.

[0052] Comparing Example 1 and Comparative Example 5, it is evident that sulfonated castor oil, as a wetting agent, plays a crucial regulatory role in the initial wetting behavior of the coating. Without sulfonated castor oil, the initial contact angle of the coating surface is as high as 72°, resulting in a slow initial spreading rate of the ink on the coating surface. This leads to excessive ink accumulation in the central region and insufficient diffusion to the edges, with a diffusion uniformity coefficient of only 0.74. After adding sulfonated castor oil, the initial contact angle decreases to 62°, and the equilibrium contact angle decreases from 40° to 28°, indicating that sulfonated castor oil significantly improves the dynamic wetting performance of the coating. The castor oil sulfonate structure of sulfonated castor oil possesses both lipophilic long chains and hydrophilic sulfonic acid groups, which are oriented and arranged on the coating surface, reducing the surface free energy. More importantly, the sulfonic acid groups (anions) of sulfonated castor oil and the quaternary ammonium groups (cations) of cationic starch form ion-paired complexes through Coulomb attraction. During the coating drying process, these complexes tend to accumulate on the coating surface (because moisture evaporates from the surface during drying, and solutes migrate and accumulate there), creating a wettability gradient from the surface inwards: the highest concentration of ion-pairing complexes and the strongest hydrophilicity are found on the outermost surface of the coating (facilitating rapid ink spread); the concentration of complexes gradually decreases and the hydrophilicity weakens inside the coating (facilitating gradual, slower ink penetration). This wettability gradient achieves spatiotemporal coordinated control of ink diffusion—spreading first and then penetrating in the time dimension, and faster at the surface and slower inside in the spatial dimension.

[0053] like Figure 4 As shown, the ink diffusion uniformity coefficients of Examples 1 to 3 are all greater than 0.85, and the distinguishability of ink color gradients all reach level 5 or higher, significantly better than all comparative examples. Figure 5 As shown, the water contact angle of the coating in Example 1 smoothly decreased from an initial 62° to 28° within 30 seconds, exhibiting an ideal dynamic wetting curve; while the initial contact angle of Comparative Example 5 (without sulfonated castor oil) was as high as 72° and the equilibrium contact angle was still 40°, and the initial contact angle of Comparative Example 3 (with polyvinyl alcohol replacing styrene-acrylic emulsion) was only 42° and the equilibrium contact angle was as low as 12°, both of which deviated from the optimal wetting window.

[0054] The reason why the ink-layer enhancement latex liquid for calligraphy and painting paper of the present invention can achieve excellent ink-layer uniform diffusion and layer enhancement effect is due to the synergistic mechanism of the following five levels.

[0055] At the microstructure level of the coating, three mineral fillers with different particle sizes and morphologies form a three-tiered pore structure of macropores, mesopores, and micropores, endowing the coating with the ability to regulate the hierarchical penetration of ink, allowing the ink to undergo three stages from the paper surface to the interior of the paper substrate: rapid penetration, uniform expansion, and gradual locking. At the interfacial chemistry level, the electrostatic adsorption between quaternary ammonium cationic starch and carbon black particles in the ink constitutes the chemical driving force for the formation of ink color layers. At the polymer film-forming level, the continuous polymer network formed after the styrene-acrylic emulsion dries to form a film endows the coating with structural integrity and mechanical durability under wet conditions. At the rheological level, organically modified bentonite imparts moderate thixotropy and water retention to the latex system. At the surface wetting level, the ion-pairing complex formed by sulfonated castor oil and cationic starch constructs a wettability gradient from hydrophilic to hydrophobic on the coating surface. The synergistic effect of the five levels enables the latex liquid of the present invention to achieve both uniform ink diffusion and rich layering when coated on calligraphy and painting paper, and the coating has good durability and preservation, achieving a comprehensive effect that is significantly superior to the prior art.

[0056] The above description is only a preferred embodiment of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A water-based ink-leveling and ink-leveling latex for calligraphy and painting paper, characterized in that, The product comprises, by weight, 15 to 25 parts calcined kaolin, 8 to 15 parts rutile titanium dioxide, 25 to 35 parts heavy calcium carbonate, 3 to 8 parts organically modified bentonite, 1 to 3 parts sulfonated castor oil, 25 to 35 parts styrene-acrylic emulsion, 80 to 120 parts quaternary ammonium cationic plant starch, 0.5 to 1.5 parts sodium hexametaphosphate dispersant, 0.3 to 0.8 parts hydroxyethyl cellulose thickener, and 368.5 to 430 parts.

2. The latex liquid according to claim 1, characterized in that, The calcined kaolin is calcined at a temperature of 1200°C to 1300°C, has a particle size D50 of 1.5 μm to 2.5 μm, and a whiteness greater than 90%.

3. The latex liquid according to claim 1, characterized in that, The degree of substitution (DS) of the quaternary ammonium cationic plant starch is 0.030 to 0.050, and it is prepared by quaternization modification of corn starch or cassava starch with 2,3-epoxypropyltrimethylammonium chloride.

4. The latex liquid according to claim 1, characterized in that, The styrene-acrylic emulsion is a styrene-acrylate copolymer emulsion with a solid content of 48% to 52%, a glass transition temperature of 5°C to 15°C, and a latex particle size of 80 nm to 150 nm.

5. The latex liquid according to claim 1, characterized in that, The organically modified bentonite is modified with octadecyltrimethylammonium chloride, and the interlayer spacing is 2.5 nm to 3.5 nm.

6. A method for preparing a water-based ink-leveling enhanced ink-leveling latex liquid for calligraphy and painting paper as described in any one of claims 1 to 5, characterized in that, The process includes the following steps: Quaternary ammonium cationic plant starch is gelatinized with deionized water at 85°C to 95°C for 30 to 45 minutes to form a starch paste, then cooled to 45°C to 55°C; sodium hexametaphosphate dispersant is dissolved in deionized water, and calcined kaolin, rutile titanium dioxide, and heavy calcium carbonate are added sequentially, and dispersed at 1000 r / min to 1500 r / min for 20 to 30 minutes to form a mineral filler dispersion; organically modified bentonite is pre-swelled in deionized water for 12 to 24 hours to form a bentonite gel; the mineral filler dispersion is slowly added to the starch paste, and stirred at 500 r / min to 800 r / min for 15 to 20 minutes; the bentonite gel and sulfonated castor oil are added, and stirring continues for 10 to 15 minutes; styrene-acrylic emulsion and hydroxyethyl cellulose thickener are added, and the mixture is stirred at 300 r / min to 500 r / min. Mix thoroughly under low-speed stirring at r / min, adjust the pH value to 7.5 to 8.5, and obtain the latex solution.

7. The preparation method according to claim 6, characterized in that, The mineral filler dispersion has a fineness of less than 25 μm, and the starch paste has a Brookfield viscosity of 800 mPa·s to 1200 mPa·s.

8. A method for applying the ink-leveling enhanced ink-leveling latex liquid for calligraphy and painting paper as described in any one of claims 1 to 5 in the coating of calligraphy and painting paper, characterized in that, The latex solution was applied to the surface of the calligraphy and painting paper using an air knife coating method, with a single-sided dry coating weight of 8 g / m². 2 Up to 15 g / m 2 The coating speed is 50 m / min to 120 m / min; after coating, dry at 100°C to 130°C for 10 s to 30 s. The surface is finished by using a soft calendering machine under online pressure of 30 kN / m to 80 kN / m.

9. The application method according to claim 8, characterized in that, The basis weight of the calligraphy and painting paper is 50 g / m³. 2 Up to 70 g / m 2 It is made by mixing sandalwood pulp and rice straw pulp.

10. The application method according to claim 8, characterized in that, The ink diffusion uniformity coefficient of the coated calligraphy and painting paper is greater than 0.85, and the ink color gradient distinguishability is greater than 5 levels.

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