Flexographic printing paper and preparation method thereof

Abstract

The invention provides flexographic printing paper and a preparation method thereof. The preparation method comprises the following steps: providing uncoated raw paper; coating the surface of the raw paper with a coating to form a reinforcing layer; wherein the coating of the reinforcing layer comprises 2%-20% of an adhesive and 80%-98% of a solvent, and the adhesive comprises any one of cationic corn starch, carboxymethyl cellulose, polyvinyl alcohol and chitosan. According to the preparation method of the flexographic printing paper provided by the embodiment of the invention, the surface of the body paper is pre-coated with a layer of non-toxic and harmless coating liquid, and the surface smoothness of the paper is improved on the premise that the bulk of the paper is not affected through the two aspects of the bonding effect and the coating film-forming property. Meanwhile, pigments in the printing ink are fixed on the surface of a coating due to an adhesive effect, so that partial influence on the printing quality caused by overhigh pH value of the printing ink is counteracted, and the aim of improving the paper printing adaptability is fulfilled.

Description

Technical Field

[0001] This application relates to the technical field of papermaking, specifically to a flexographic printing paper and its preparation method. Background Technology

[0002] With increasing global environmental awareness and the innovation of printing technology, water-based inks, due to their low volatile organic compound (VOC) emissions, non-toxicity, and ease of cleaning, have gradually replaced traditional solvent-based inks, becoming the mainstream choice in the printing industry. However, the print quality of flexographic printing is highly dependent on factors such as inks, printing equipment, and the environment. This drawback is particularly prominent in high-speed printing, low basis weight paper, and specialty coated paper, becoming a key technical bottleneck restricting printing efficiency and quality. Compared to improving printing equipment and water-based inks, improving the adaptability of paper for flexographic printing has become a more convenient path. Therefore, there is an urgent need to develop a method to improve the adaptability of paper for flexographic printing. Summary of the Invention

[0003] The first aspect of this application provides a method for preparing flexographic printing paper, the method comprising:

[0004] Provide uncoated base paper;

[0005] A coating is applied to the surface of the base paper to form a reinforcing layer; wherein the coating of the reinforcing layer comprises 2% to 20% binder and 80% to 98% solvent, and the binder comprises any one of cationic corn starch, carboxymethyl cellulose, polyvinyl alcohol and chitosan.

[0006] In some optional embodiments, the degree of substitution of the cationic corn starch is 0.04 to 0.05, the solvent is water, and the viscosity of the mixed coating is 50 to 100 mPa·s.

[0007] In some optional embodiments, the degree of substitution of the carboxymethyl cellulose is 0.6 to 1.2, the solvent is water, and the viscosity of the mixed coating is 100 to 300 mPa·s.

[0008] In some optional embodiments, the degree of polymerization of the polyvinyl alcohol is 1500-2500, the degree of alcoholysis is 95%-99%, the solvent is water, and the viscosity of the mixed coating is 100-300 mPa·s.

[0009] In some optional embodiments, the degree of deacetylation of the chitosan is ≥60%, the solvent is an acetic acid solution, and the viscosity of the mixed coating is 100-300 mPa·s.

[0010] In some optional embodiments, in the step of coating the base paper surface to form a reinforcing layer, the coating amount is 1.0 g / m². 2~5.0g / m 2 .

[0011] In some optional embodiments, the solid content of the reinforcing layer coating is 2% to 25%.

[0012] In some optional embodiments, the drying temperature in the step of coating the base paper surface to form a reinforcing layer is 80°C to 120°C.

[0013] In some optional embodiments, the preparation method further includes coating the surface of the reinforcing layer with an ink layer.

[0014] Secondly, embodiments of this application provide a flexographic printing paper, which is prepared using the preparation method described in the above embodiments.

[0015] The method for preparing flexographic printing paper provided in this application involves pre-coating the surface of the base paper with a non-toxic and harmless coating liquid. Through both adhesion and film-forming properties, the surface smoothness of the paper is improved without affecting its bulk. Simultaneously, the adhesion fixes the pigments in the ink to the coating surface, partially offsetting the impact of excessively high ink pH on printing quality, thus improving the paper's printability. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart of an embodiment of the method for preparing flexographic printing paper according to this application;

[0018] Figure 2 This is a schematic diagram of the laminated structure of an embodiment of the flexographic printing paper of this application;

[0019] Figure 3 This is a schematic flowchart of another embodiment of the method for preparing flexographic printing paper according to this application;

[0020] Figure 4 This is a schematic diagram of the stacked structure of another embodiment of the flexographic printing paper of this application. Detailed Implementation

[0021] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the application. Similarly, the following embodiments are only some, not all, embodiments of the present application, and all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present application.

[0022] The terms "first," "second," and "third" used in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationships and movement of components in a specific posture (as shown in the figures). If the specific posture changes, the directional indication will also change accordingly. The terms "comprising" and "having," and any variations thereof, in the embodiments of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or components inherent to these processes, methods, products, or devices.

[0023] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0024] Traditional technical approaches to improving paper printing quality have significant drawbacks:

[0025] 1. Adjusting the pH value of water-based inks: Due to the influence of printing environment and climate, increasing the pH value of water-based inks during printing (generally controlled between 8.5 and 9.5) can reduce the drying speed of the ink and prevent ink accumulation on the printing plate and anilox roller. However, when the pH value exceeds 9.5, the solubility of the resin in the ink increases, the ink film softens easily, scratch resistance decreases, gloss is damaged, and the adhesion of the ink to the paper surface also decreases.

[0026] 2. Environmental Paradox: While some additives (such as ethylene glycol) can significantly improve the flowability and uniformity of water-based inks—by reducing the surface tension of the ink and allowing pigments and resins to disperse evenly, thus avoiding problems such as poor ink transfer, dripping, or foaming caused by excessive viscosity—they introduce new volatile substances, contradicting the original intention of water-based inks to be low in volatility.

[0027] 3. Improving paper surface smoothness through calendering: Soft calendering or supercalendering can improve the smoothness of the paper surface, thereby improving print quality. However, the calendering process can easily cause a loss of paper thickness, and if the paper bulk is too low after calendering, ink penetration will be difficult, resulting in a decrease in print quality.

[0028] In view of this, the present application provides a method for preparing flexographic printing paper, which solves the obvious defects of traditional improvement schemes such as low process compatibility and poor environmental protection, and improves printing quality in a high-efficiency and low-emission manner, which is the technical problem to be solved by the present invention.

[0029] Please see Figure 1 , Figure 1 This is a schematic flowchart of an embodiment of the preparation method of flexographic printing paper of this application, wherein the preparation method includes, but is not limited to, the following steps.

[0030] Step S100: Provide uncoated base paper.

[0031] The preparation method in this application embodiment has low requirements for the basic printability of the base paper. There is no need to improve the paper surface smoothness through calendering. Flexographic printing typically recommends a minimum BEKK smoothness of 80s for low-basis-weight paper; below 80s, ink can easily accumulate in the recesses of the paper surface, leading to a decrease in print quality. In this invention, the reinforcing layer forms a film on the paper surface to improve paper smoothness, and can be used for base paper with a smoothness ≥50s.

[0032] Step S200: Apply coating to the surface of the base paper to form a reinforcing layer.

[0033] Please see Figure 2 , Figure 2 This is a schematic diagram of the laminated structure of an embodiment of the flexographic printing paper of this application, wherein 110 represents the base paper and 120 represents the reinforcing layer.

[0034] The coating of the reinforcing layer 120 in this embodiment includes 2% to 20% binder and 80% to 98% solvent, wherein the binder includes any one of cationic corn starch, carboxymethyl cellulose, polyvinyl alcohol and chitosan.

[0035] The method of improving the adaptability of paper to flexographic printing by means of reinforcing layer 120 is to improve the smoothness of the paper surface and improve the printing quality by means of the film-forming principle of reinforcing layer 120; by means of the adhesive function of reinforcing layer 120, the pigments in water-based inks are adhered to the paper surface, thereby improving the bonding between paper and water-based inks.

[0036] Film formation principle and coating adhesion function:

[0037] 1. Adhesive function

[0038] In cationic starch solution, the positively charged amino groups and the negatively charged (carboxyl / phenolic hydroxyl groups) of the fiber combine through electrostatic adsorption, resulting in a strong bond between the coating and the fiber. In chitosan solution, the protonated amino groups form ionic bonds with the negatively charged fiber, creating a stable interfacial layer. The hydroxyl groups in carboxymethyl cellulose, polyvinyl alcohol, and chitosan solutions form multiple hydrogen bonds with the hydroxyl groups of the fiber (each hydroxyl group can participate in 2-3 hydrogen bonds), ensuring the coating adheres firmly to the paper surface. Simultaneously, the interfacial bonding also facilitates the adhesion of pigments in water-based inks. The core logic: Polymer chains are fixed to the fiber surface through intermolecular forces, forming a stable interfacial layer.

[0039] 2. Film formation

[0040] During the drying process, the polymer chains in starch solution, carboxymethyl cellulose solution, polyvinyl alcohol solution, and chitosan solution become entangled, forming a "fishing net"-like structure. This structure not only forms a film but also imparts strength and toughness to the film. The core logic is that the polymer molecular chains form a network through physical entanglement, giving the film mechanical strength.

[0041] 3. Improved smoothness

[0042] The membrane material is prepared in a solution state, and the molecular chains can be highly uniformly distributed to form a dense, non-porous structure, resulting in a high degree of surface smoothness.

[0043] Optionally, the solid content of the reinforcing layer coating in this embodiment is 2% to 25%.

[0044] The degree of substitution of cationic corn starch is 0.04–0.05. Too high a substitution rate results in an excessively high positive charge density on the paper surface, affecting the paper's absorbency and air permeability. Too low a substitution rate leads to insufficient bonding between the solution-formed coating and the fibers, failing to provide adhesion. Therefore, the viscosity of the cationic corn starch solution should be controlled between 50 and 100 mPa·s to achieve the expected production plan.

[0045] The degree of substitution (DOS) of carboxymethyl cellulose (CMC) powder ranges from 0.6 to 1.2, directly affecting its solubility. When the DOS is between 0.6 and 0.7, CMC exhibits good emulsifying properties; when the DOS is greater than 0.8, its acid and salt resistance is significantly enhanced. Simultaneously, the CMC aqueous solution shows optimal transparency within the DOS range of 0.7 to 1.2, which is beneficial for forming a uniform and transparent coating on the paper surface, improving printing quality. Therefore, the viscosity of the cation-modified CMC solution should be controlled between 100 and 300 mPa·s to achieve the expected production plan.

[0046] Polyvinyl alcohol (PVA) with a degree of polymerization of 1500–2500 exhibits good adhesion to hydrophilic fibers (such as paper fibers), enhancing the bonding force between the coating and paper, preventing coating peeling, and ensuring stable adhesion of printing inks to the paper surface. Higher degree PVA molecules have longer chains and stronger hydrogen bonding with fibers, thus improving adhesion. PVA with a degree of alcoholysis of 95%–99% is completely soluble in water at 95°C. Complete alcoholysis requires heating to above 90°C for dissolution. This alcoholysis range satisfies the process temperature requirements while avoiding uneven coating due to insufficient solubility. Therefore, the viscosity of the cation-modified PVA solution should be controlled between 100 and 300 mPa·s to achieve the expected production plan.

[0047] The degree of deacetylation of the chitosan (powder) is ≥60%. Chitosan with a degree of deacetylation of 85%-95% can be completely dissolved in a 1% acetic acid solution to form a transparent and uniform coating solution, meeting the process requirements for dissolution temperature (room temperature) and operating time (short-term stirring). This deacetylation range avoids the uneven coating solution caused by insufficient solubility of low-deacetylated chitosan, and the risk of coating brittleness caused by excessive solubility of high-deacetylated chitosan. Therefore, the viscosity of the polyvinyl alcohol solution should be controlled between 100 and 300 mPa·s to achieve the expected production plan.

[0048] The solvents for cationic corn starch, carboxymethyl cellulose powder, and polyvinyl alcohol powder are water, while the solvent for chitosan powder is acetic acid solution (solution concentration 0%–5% (v / v)).

[0049] Optionally, in this embodiment, the coating amount of the reinforcing layer 120 is 1.0 g / m². 2 ~5.0g / m 2 The coating method is rod coating, and the drying method is infrared drying or hot air drying. The drying temperature is 80℃~120℃, and the solution is dried until it forms a film on the paper surface.

[0050] The method for preparing flexographic printing paper in this embodiment involves pre-coating the surface of the base paper with a non-toxic and harmless coating liquid. Through adhesion and film-forming properties, the surface smoothness of the paper is improved without affecting its bulk. Simultaneously, the adhesion fixes the pigments in the ink to the coating surface, partially offsetting the impact of excessively high ink pH on printing quality, thus improving the paper's printability.

[0051] Please see Figure 3 , Figure 3 This is a schematic flowchart of another embodiment of the preparation method of flexographic printing paper of this application, wherein the preparation method includes, but is not limited to, the following steps.

[0052] Step S100: Provide uncoated base paper.

[0053] The preparation method in this application embodiment has low requirements for the basic printability of the base paper. There is no need to improve the paper surface smoothness through calendering. Flexographic printing typically recommends a minimum BEKK smoothness of 80s for low-basis-weight paper; below 80s, ink can easily accumulate in the recesses of the paper surface, leading to a decrease in print quality. In this invention, the reinforcing layer forms a film on the paper surface to improve paper smoothness, and can be used for base paper with a smoothness ≥50s.

[0054] Step S200: Apply coating to the surface of the base paper to form a reinforcing layer.

[0055] Please see Figure 4 , Figure 4 This is a schematic diagram of the laminated structure of another embodiment of the flexographic printing paper of this application, wherein 110 in the figure represents the base paper and 120 represents the reinforcing layer.

[0056] The coating of the reinforcing layer 120 in this embodiment includes 2% to 20% binder and 80% to 98% solvent, wherein the binder includes any one of cationic corn starch, carboxymethyl cellulose, polyvinyl alcohol and chitosan.

[0057] The method of improving the adaptability of paper to flexographic printing by means of reinforcing layer 120 is to improve the smoothness of the paper surface and improve the printing quality by means of the film-forming principle of reinforcing layer 120; by means of the adhesive function of reinforcing layer 120, the pigments in water-based inks are adhered to the paper surface, thereby improving the bonding between paper and water-based inks.

[0058] Film formation principle and coating adhesion function:

[0059] 1. Adhesive function

[0060] In cationic starch solution, the positively charged amino groups and the negatively charged (carboxyl / phenolic hydroxyl groups) of the fiber combine through electrostatic adsorption, resulting in a strong bond between the coating and the fiber. In chitosan solution, the protonated amino groups form ionic bonds with the negatively charged fiber, creating a stable interfacial layer. The hydroxyl groups in carboxymethyl cellulose, polyvinyl alcohol, and chitosan solutions form multiple hydrogen bonds with the hydroxyl groups of the fiber (each hydroxyl group can participate in 2-3 hydrogen bonds), ensuring the coating adheres firmly to the paper surface. Simultaneously, the interfacial bonding also facilitates the adhesion of pigments in water-based inks. The core logic: Polymer chains are fixed to the fiber surface through intermolecular forces, forming a stable interfacial layer.

[0061] 2. Film formation

[0062] During the drying process, the polymer chains in starch solution, carboxymethyl cellulose solution, polyvinyl alcohol solution, and chitosan solution become entangled, forming a "fishing net"-like structure. This structure not only forms a film but also imparts strength and toughness to the film. The core logic is that the polymer molecular chains form a network through physical entanglement, giving the film mechanical strength.

[0063] 3. Improved smoothness

[0064] The membrane material is prepared in a solution state, and the molecular chains can be highly uniformly distributed to form a dense, non-porous structure, resulting in a high degree of surface smoothness.

[0065] Optionally, the solid content of the reinforcing layer coating in this embodiment is 2% to 25%.

[0066] The degree of substitution of cationic corn starch is 0.04–0.05. Too high a substitution rate results in an excessively high positive charge density on the paper surface, affecting the paper's absorbency and air permeability. Too low a substitution rate leads to insufficient bonding between the solution-formed coating and the fibers, failing to provide adhesion. Therefore, the viscosity of the cationic corn starch solution should be controlled between 50 and 100 mPa·s to achieve the expected production plan.

[0067] The degree of substitution (DOS) of carboxymethyl cellulose (CMC) powder ranges from 0.6 to 1.2, directly affecting its solubility. When the DOS is between 0.6 and 0.7, CMC exhibits good emulsifying properties; when the DOS is greater than 0.8, its acid and salt resistance is significantly enhanced. Simultaneously, the CMC aqueous solution shows optimal transparency within the DOS range of 0.7 to 1.2, which is beneficial for forming a uniform and transparent coating on the paper surface, improving printing quality. Therefore, the viscosity of the cation-modified CMC solution should be controlled between 100 and 300 mPa·s to achieve the expected production plan.

[0068] Polyvinyl alcohol (PVA) with a degree of polymerization of 1500–2500 exhibits good adhesion to hydrophilic fibers (such as paper fibers), enhancing the bonding force between the coating and paper, preventing coating peeling, and ensuring stable adhesion of printing inks to the paper surface. Higher degree PVA molecules have longer chains and stronger hydrogen bonding with fibers, thus improving adhesion. PVA with a degree of alcoholysis of 95%–99% is completely soluble in water at 95°C. Complete alcoholysis requires heating to above 90°C for dissolution. This alcoholysis range satisfies the process temperature requirements while avoiding uneven coating due to insufficient solubility. Therefore, the viscosity of the cation-modified PVA solution should be controlled between 100 and 300 mPa·s to achieve the expected production plan.

[0069] The degree of deacetylation of the chitosan (powder) is ≥60%. Chitosan with a degree of deacetylation of 85%-95% can be completely dissolved in a 1% acetic acid solution to form a transparent and uniform coating solution, meeting the process requirements for dissolution temperature (room temperature) and operating time (short-term stirring). This deacetylation range avoids the uneven coating solution caused by insufficient solubility of low-deacetylated chitosan, and the risk of coating brittleness caused by excessive solubility of high-deacetylated chitosan. Therefore, the viscosity of the polyvinyl alcohol solution should be controlled between 100 and 300 mPa·s to achieve the expected production plan.

[0070] The solvents for cationic corn starch, carboxymethyl cellulose powder, and polyvinyl alcohol powder are water, while the solvent for chitosan powder is acetic acid solution (solution concentration 0%–5% (v / v)).

[0071] Optionally, in this embodiment, the coating amount of the reinforcing layer 120 is 1.0 g / m². 2 ~5.0g / m 2 The coating method is rod coating, and the drying method is infrared drying or hot air drying. The drying temperature is 80℃~120℃, and the solution is dried until it forms a film on the paper surface.

[0072] Please continue reading. Figure 3 Unlike the previous embodiments, the preparation method in this embodiment further includes step S300, which involves coating an ink layer on the surface of the reinforcing layer.

[0073] Please continue reading. Figure 4 The ink layer 130 is disposed on the reinforcing layer 120. The ink adhesion is enhanced by the adhesive function of the reinforcing layer 120.

[0074] The ink layer 130 can be made of water-based ink.

[0075] The preparation method in this application embodiment has low requirements for the basic printability of the base paper. There is no need to improve the paper surface smoothness through calendering. Flexographic printing typically recommends a minimum BEKK smoothness of 80s for low-basis-weight paper; below 80s, ink can easily accumulate in the recesses of the paper surface, leading to a decrease in print quality. In this invention, the reinforcing layer forms a film on the paper surface, improving paper smoothness, and can be used for base paper with a smoothness ≥50s. The adhesive function of the reinforcing layer 120 enhances ink adhesion; environmental impact and printability are synergistic. All reinforcing layers in this invention achieve zero VOC emissions throughout the entire process, significantly reducing wastewater pollution. Using the coating as an interface bonding material, the adhesive function of the reinforcing layer 120 simultaneously fixes paper fibers and pigments in water-based inks onto the coating.

[0076] The following will introduce several specific embodiments for detailed explanation and data parameter comparison.

[0077] a) Example 1:

[0078] I. Preparation of modified cationic starch coating solution: 5% cationic corn starch powder (degree of substitution 0.04) and 95% water were mixed, heated to 90℃ and stirred for 30 minutes until completely gelatinized, cooled to room temperature, the solid content of the solution was 5%, and the viscosity of the solution was 100 mPa·s.

[0079] II. Paper Coating: The prepared coating solution is evenly coated onto the base paper (42 g / m²) using a rod coater. 2 The coating amount is 3g / m². 2 After coating, the paper is dried with hot air at 105℃ for 1 minute.

[0080] b) Example 2:

[0081] I. Preparation of carboxymethyl cellulose coating solution: 2% carboxymethyl cellulose powder (degree of substitution 0.8) was slowly added to 98% water while stirring. The dissolution temperature was 60℃ and the time was 4 hours. The solid content of the coating solution was 2% and the viscosity of the solution was 120 mPa·s.

[0082] II. Paper Coating: The prepared coating solution is evenly coated onto the base paper (42 g / m²) using a rod coater. 2 The coating amount is 2g / m². 2 After coating, the paper is dried with hot air at 105℃ for 3 minutes.

[0083] c) Example 3:

[0084] I. Preparation of polyvinyl alcohol coating solution: 7.5% polyvinyl alcohol powder (degree of polymerization 1799) was slowly added to 92.5% water while stirring. The dissolution temperature was 80℃ and the time was 2 hours. The solid content of the coating solution was 7.5% and the viscosity of the solution was 150 mPa·s.

[0085] II. Paper Coating: The prepared coating solution is evenly coated onto the base paper (42 g / m²) using a rod coater. 2 The coating amount is 5g / m². 2 After coating, the paper is dried with hot air at 90℃ for 5 minutes.

[0086] d) Example 4:

[0087] I. Preparation of chitosan coating solution: 98.5% acetic acid solution (concentration 1%) was slowly added to 1.5% chitosan powder (degree of deacetylation 90%) while stirring. The dissolution temperature was 60℃ and the time was 1.5 hours to ensure that the chitosan was completely dissolved and a uniform solution was formed. The solid content of the coating solution was 2% and the viscosity of the solution was 120 mPa·s.

[0088] II. Paper Coating: The prepared coating solution is evenly coated onto the base paper (42 g / m²) using a rod coater. 2 The coating amount is 3g / m². 2 After coating, the paper is dried with hot air at 80℃ for 2 minutes.

[0089] 7. Compare with case studies

[0090] e) Comparison example:

[0091] 42g / m² was used in the examples. 2 Uncoated base paper.

[0092] The paper samples from the above cases were tested for printability using an IGT-F1 printer. The same ink, test speed, anilox roller, and pressure were used during the printing tests. The printed samples were tested using an X-Rite color density meter, and the color density values ​​of the printed samples were compared. KN ink absorbency was tested according to GB / T 12911-1991. Smoothness was tested according to GB / T 456-2002.

[0093] The color density, ink absorption, and smoothness test parameters of the paper samples produced in each example are shown in the table below.

[0094]

[0095] Remark:

[0096] 1. The absorbency of KN ink was tested according to GB / T 12911-1991.

[0097] 2. Smoothness test was conducted using GB / T 456-2002.

[0098] The following conclusions can be drawn from the printing adaptability test, KN ink absorption test, and smoothness test:

[0099] (1) After printing with a flexographic printing adaptability tester, the higher the measured color density value, the better the paper's printability. According to the experimental data, the color density value of the example was significantly higher than that of the control example, indicating that the paper's printability was improved after coating;

[0100] (2) The KN ink absorbency test was conducted according to GB / T 12911-1991. The standard stipulates that the higher the ink absorbency value, the better the ink absorbency of the paper. The ink absorbency of the example was significantly higher than that of the control example, indicating that the ink absorbency of the coated paper was improved.

[0101] (3) Smoothness test was conducted according to GB / T 456-2002. The higher the smoothness value, the higher the smoothness. The smoothness of the sample oil was significantly higher than that of the control example, which means that the smoothness of the paper after coating was improved.

[0102] The method for preparing flexographic printing paper in this embodiment enhances the adhesion between the water-based ink and the paper, overcoming the limitations of traditional techniques that are complex and environmentally unfriendly. This solution improves the adhesion between the ink and paper interface through a coating, significantly enhancing printing quality and production efficiency, and has broad industrial application prospects.

[0103] By leveraging the film-forming and adhesive properties of the reinforcing layer, the smoothness of the paper surface is improved. Furthermore, the adhesion between the coating and paper fibers, and between the reinforcing layer and pigments in the ink, is enhanced, effectively addressing current problems encountered in flexographic printing. In this invention, all reinforcing layers achieve zero VOC emissions throughout the entire process, demonstrating excellent environmental performance. This invention can be used to improve the printing performance of paper with a smoothness ≥50s, solving the minimum requirement of 80s smoothness for low-basis-weight paper in flexographic printing.

[0104] The above description is only a part of the embodiments of this application and does not limit the scope of protection of this application. Any equivalent device or equivalent process transformation made based on the content of this application specification and drawings, or direct or indirect application in other related technical fields, are similarly included in the patent protection scope of this application.

Claims

1. A method for preparing flexographic printing paper, characterized in that, The preparation method includes: Provide uncoated base paper; A coating is applied to the surface of the base paper to form a reinforcing layer; wherein the coating of the reinforcing layer comprises 2% to 20% binder and 80% to 98% solvent, and the binder comprises any one of cationic corn starch, carboxymethyl cellulose, polyvinyl alcohol and chitosan.

2. The preparation method according to claim 1, characterized in that, The degree of substitution of the cationic corn starch is 0.04 to 0.05, the solvent is water, and the viscosity of the mixed coating is 50 to 100 mPa·s.

3. The preparation method according to claim 1, characterized in that, The degree of substitution of the carboxymethyl cellulose is 0.6 to 1.2, the solvent is water, and the viscosity of the mixed coating is 100 to 300 mPa·s.

4. The preparation method according to claim 1, characterized in that, The degree of polymerization of the polyvinyl alcohol is 1500-2500, the degree of alcoholysis is 95%-99%, the solvent is water, and the viscosity of the mixed coating is 100-300 mPa·s.

5. The preparation method according to claim 1, characterized in that, The degree of deacetylation of the chitosan is ≥60%, the solvent is acetic acid solution, and the viscosity of the mixed coating is 100-300 mPa·s.

6. The preparation method according to claim 1, characterized in that, In the step of coating the base paper surface with a coating to form a reinforcing layer, the coating amount is 1.0 g / m². 2 ~5.0g / m 2 .

7. The preparation method according to claim 1, characterized in that, The solid content of the reinforcing layer coating is 2% to 25%.

8. The preparation method according to claim 1, characterized in that, In the step of coating the base paper surface with a coating to form a reinforcing layer, the drying temperature is 80℃~120℃.

9. The preparation method according to claim 1, characterized in that, The preparation method further includes: coating the surface of the reinforcing layer with an ink layer.

10. A type of flexographic printing paper, characterized in that, The flexographic printing paper is prepared using the preparation method described in any one of claims 1-9.

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