Preparation method of computer-to-plate protective coating

Abstract

The invention relates to a preparation method of a computer-to-plate protective coating, and belongs to the technical field of printing plate manufacturing. The problems that an existing protective coating is insufficient in antibacterial performance, short in antibacterial time and poor in wear resistance are solved. The key points of the technical scheme are as follows: the protective coating comprises a water-soluble polymer, a functional component and a solvent, the functional component comprises an antibacterial agent, the antibacterial agent is prepared by mixing carboxylated polyvinyl alcohol, acetalated glucan and chitosan, the carboxylated polyvinyl alcohol is prepared by reacting polyvinyl alcohol with maleic anhydride, and the acetalated glucan is prepared by reacting the acetalated glucan with the chitosan. The acetalated dextran is prepared by reacting dextran with vinyl butyl ether; optionally, the functional component also comprises a reinforcing agent, and the reinforcing agent is prepared by mixing polyquaternium and polycarbonate; the protective coating forms a single-layer or double-layer structure on the aluminum plate base supporting body through coating liquid; according to the present invention, the antibacterial effect can be significantly improved, the antibacterial durability can be prolonged, the wear resistance can be improved, and the method can be used for computer-to-plate so as to enhance the antibacterial property and the durability.

Description

Technical Field

[0001] This invention relates to the field of computer-to-plate (CT) printing, and more specifically to a method for preparing a protective coating for CT printing. Background Technology

[0002] Computer-to-Plate (CTP) is a printing plate material that uses lasers to directly expose digital graphic information onto a photosensitive plate using computer-to-plate equipment, eliminating the need for traditional film as an intermediary. It is a key consumable in the digital printing process, replacing traditional film exposure technology.

[0003] Anhui Qiangbang New Material Co., Ltd. applied for a Chinese patent on August 30, 2022, entitled "A Process-Free CTP Plate with a Wear-Resistant Protective Layer," with authorization announcement number CN114953802B. The CTP plate in this application is coated with a wear-resistant protective layer, and the wear-resistant layer contains an antibacterial component made of epoxy quaternary ammonium salt and gelatin. However, the antibacterial performance of this antibacterial component cannot meet the requirements of high-end computer-to-plate (CTP) printing, especially against Gram-negative bacteria with an outer membrane structure around the cell wall, where the antibacterial effect has not reached the ideal level. In addition, there are technical problems such as short antibacterial time and insufficient wear resistance of the protective layer. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a protective coating for computer-to-plate (CTP) printing. The protective coating contains an antibacterial agent, and the method for preparing the antibacterial agent includes a technical solution of mixing carboxylated polyvinyl alcohol, acetalized dextran, and chitosan through specific steps. This solves the technical problems of insufficient antibacterial performance and short antibacterial time in existing CTP protective coatings, and produces the beneficial effects of significantly improving antibacterial effect and prolonging antibacterial durability.

[0005] To achieve the aforementioned objectives, the technical solution adopted by the present invention is as follows: A method for preparing a protective coating for computer-to-plate (CT) printing, the protective coating comprising a water-soluble polymer, a functional component, and a solvent, wherein the functional component includes an antibacterial agent, and the method for preparing the antibacterial agent includes: S1.1: Dissolve polyvinyl alcohol to obtain a polyvinyl alcohol solution; add maleic anhydride to the polyvinyl alcohol solution to obtain a carboxylated polyvinyl alcohol solution; precipitate the carboxylated polyvinyl alcohol solution in a poor solvent and dry it to obtain carboxylated polyvinyl alcohol; S1.2: Dextran is dissolved in dimethyl sulfoxide to obtain a dimethyl sulfoxide solution of dextran; vinyl butyl ether is added to the dimethyl sulfoxide solution of dextran to obtain an acetalized dextran solution; the acetalized dextran solution is precipitated in a poor solvent and dried to obtain acetalized dextran. S1.3: Dissolve chitosan, carboxylated polyvinyl alcohol, and acetalized dextran separately to obtain chitosan solution, carboxylated polyvinyl alcohol solution, and acetalized dextran solution; mix the chitosan solution, carboxylated polyvinyl alcohol solution, and acetalized dextran solution to obtain an antibacterial agent.

[0006] Preferably, the functional component further includes a reinforcing agent, and the method for preparing the reinforcing agent includes: S2.1: Methacryloxyethyltrimethylammonium chloride, butyl acrylate and glycidyl methacrylate are dissolved in anhydrous ethanol in an inert atmosphere, and azobisisobutyronitrile is added to react and synthesize a polyquaternary ammonium salt solution; the polyquaternary ammonium salt solution is precipitated in a poor solvent and dried to obtain a high molecular weight quaternary ammonium salt. S2.2: The reinforcing agent is obtained by mixing polyquaternary ammonium salt and polycarbonate using a mixer.

[0007] Preferably, the method for preparing the protective coating includes: S3.1: Dissolve the reinforcing agent and mix it with water-soluble polymer, antibacterial agent and solvent to obtain a coating liquid; the weight percentage of each component of the coating liquid is 20-30% water-soluble polymer, 2-3% antibacterial agent, 40-50% reinforcing agent, and the balance is solvent; S3.2: Apply the coating liquid onto the aluminum plate substrate support, and form a protective coating after cooling and drying; Alternatively, the methods for preparing the protective coating include: S4.1: Mix water-soluble polymer, antibacterial agent and solvent to obtain coating liquid; the weight percentage of each component of the coating liquid is 25-40% water-soluble polymer, 2-4% antibacterial agent, and the remainder is solvent; S4.2: Apply the coating liquid onto the aluminum plate substrate support, and after drying, form a base coating; S4.3: Dissolve the reinforcing agent, apply it to the base coating, and allow it to cool and dry to form a surface coating; the surface coating and the base coating together form a protective coating; the weight of the surface coating after cooling and drying is less than 1 g / m³. 2 .

[0008] Preferably, in S1.1, the molar ratio of polyvinyl alcohol to maleic anhydride is 2.5–3.5:1; and / or, In S1.2, the concentration of dextran in the dimethyl sulfoxide solution is 60–70 g / L; the weight ratio of the dextran dimethyl sulfoxide solution to vinyl butyl ether is 1.8–2.2:1; and / or, In S1.3, an antibacterial agent is obtained by mixing 2.5 wt% chitosan aqueous solution, 10 wt% carboxylated polyvinyl alcohol aqueous solution and 6 wt% acetalized dextran aqueous solution in a volume ratio of 5:5:1.

[0009] Preferably, in S2.1, the weight ratio of methacryloyloxyethyltrimethylammonium chloride, butyl acrylate, glycidyl methacrylate, and azobisisobutyronitrile added to anhydrous ethanol is 10:7:3:0.5; and / or, In S2.2, the weight ratio of the polymeric quaternary ammonium salt and polycarbonate fed into the mixing mill is 1:1.3 to 1.7.

[0010] Preferably, in S1.1, a p-toluenesulfonic acid catalyst is added to the reaction between the polyvinyl alcohol solution and maleic anhydride; and / or, In S1.2, p-toluenesulfonic acid catalyst is added during the reaction of dextran in dimethyl sulfoxide solution and vinyl butyl ether.

[0011] Preferably, in step S1.1, polyvinyl alcohol and deionized water are mixed and stirred at a temperature of 75–95°C until the polyvinyl alcohol is completely dissolved to obtain a polyvinyl alcohol solution; after the polyvinyl alcohol solution cools to below 45°C, maleic anhydride is added, and the mixture is stirred at room temperature for 4 hours to obtain a carboxylated polyvinyl alcohol solution; and / or, In S1.2, a dimethyl sulfoxide solution of dextran and vinyl butyl ether are mixed and stirred at room temperature for 12 hours to obtain an acetalized dextran solution; and / or, In step S1.3, chitosan solution, carboxylated polyvinyl alcohol solution and acetalized dextran solution are mixed and stirred for 10 minutes at a temperature of 35-40°C to obtain a gel-like antibacterial agent.

[0012] Preferably, in step S2.1, methacryloyloxyethyltrimethylammonium chloride, butyl acrylate, glycidyl methacrylate, and anhydrous ethanol are mixed, azobisisobutyronitrile is added, and the mixture is stirred at 70–80°C for 6 hours. After cooling to room temperature, the anhydrous ethanol is evaporated to obtain a polyquaternary ammonium salt solution; and / or, In S2.2, the mixing temperature of the mixer is set to above 230℃.

[0013] Preferably, in S1.1, the carboxylated polyvinyl alcohol solution precipitates in ethanol; and / or, In S1.2, the acetalized dextran solution settles in deionized water; and / or, In step S1.3, chitosan, carboxylated polyvinyl alcohol, and acetalized dextran are dissolved in deionized water to obtain chitosan solution, carboxylated polyvinyl alcohol solution, and acetalized dextran solution, respectively.

[0014] Preferably, in S2.1, the polyquaternary ammonium salt solution is precipitated in diethyl ether.

[0015] The beneficial effects of this invention are: 1. Significantly improves antibacterial spectrum and antibacterial activity; by combining chitosan with carboxylated polyvinyl alcohol and acetalized dextran to form a multi-target, synergistic antibacterial system, it can enhance the inhibitory or killing effect on Gram-negative and Gram-positive bacteria, and can effectively improve antibacterial properties compared with existing technologies.

[0016] 2. Extends antibacterial durability and sustained-release capability; acetalized dextran can form a microphase or encapsulation structure in the coating, forming a gel complex with carboxylated polyvinyl alcohol and chitosan, which is conducive to the slow release and sustained effect of antibacterial active ingredients, thereby significantly extending the antibacterial duration of the coating and reducing the risk of rapid decay of antibacterial activity over time.

[0017] 3. Improve the mechanical strength and wear resistance of the coating; by mixing the polyquaternary ammonium salt obtained by copolymerizing methacryloyloxyethyltrimethylammonium chloride with polycarbonate to form a reinforcing agent, a high-strength, high-wear-resistant and antistatic coating is formed, which significantly improves the scrub resistance, scratch resistance and wear resistance of the protective coating under long-term service.

[0018] In summary, this protective coating, which combines broad-spectrum and highly effective antibacterial properties, long-lasting slow release, and high abrasion resistance, can significantly improve the hygiene and mechanical durability of computer-to-plate (CTP) during storage, assembly, and printing. This reduces the frequency of plate replacement and meets the high-end printing market's requirements for both antibacterial and abrasion-resistant performance. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of the method for preparing antibacterial agents; Figure 2 This is the infrared spectrum of the protective coating described in this invention. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The chemical reagents described in the following examples are all commercially available chemical reagents. For example: polyvinyl alcohol (PVA) was purchased from Chongqing Chuanwei Chemical Co., Ltd., a subsidiary of China Petrochemical Corporation; maleic anhydride (MA) was purchased from Mitsubishi Chemical Corporation; dextran was purchased from Mitsubishi Chemical Corporation; dimethyl sulfoxide (DMSO) was purchased from Toray Industries, Inc.; vinyl butyl ether (BVE) was purchased from Alfaesa Chemical Co., Ltd.; chitosan was purchased from Zhejiang Jinke Pharmaceutical Co., Ltd.; methacryloyloxyethyltrimethylammonium chloride (DMC) was purchased from Anhui Jucheng Fine Chemical Co., Ltd.; butyl acrylate (BA) was purchased from Mitsubishi Chemical Corporation; glycidyl methacrylate (GMA) was purchased from Shandong Runtian Chemical Technology Co., Ltd.; anhydrous ethanol was purchased from Sichuan Kangyuelai Biotechnology Co., Ltd.; azobisisobutyronitrile (AIBN) was purchased from Shandong Aowei Chemical Co., Ltd.; polycarbonate (PC) was purchased from Mitsubishi Chemical Corporation; and p-toluenesulfonic acid (PTSA) was purchased from Tokyo Chemical Industry Co., Ltd.

[0023] Computer-to-plate (CTP) typically includes an aluminum substrate support, a photosensitive layer coated on its surface, and a protective coating coated on the outermost surface. The protective coating usually comprises a water-soluble polymer, a functional component, and a solvent. The preparation method of the water-soluble polymer is disclosed in Chinese patent document CN114953802B, and will not be elaborated further here. However, the preparation method of the water-soluble polymer should not be limited to the method disclosed in CN114953802B. Furthermore, the method of preparing a protective coating by mixing the water-soluble polymer, functional component, and solvent and coating it onto the aluminum substrate support is also disclosed in Chinese patent document CN114953802B, and will not be elaborated further here. Meanwhile, the functional component disclosed in Chinese patent document CN114953802B also includes an antibacterial agent. In summary, the preparation methods of this invention are similar to those of the prior art, and will not be elaborated further here. This invention further improves the composition and preparation method of the functional component.

[0024] Example 1

[0025] The preparation method of the antibacterial agent in the functional components of the computer-to-plate protective coating has been improved as follows: The preparation method of the antibacterial agent includes: S1.1: Polyvinyl alcohol is dissolved to obtain a polyvinyl alcohol solution. The preferred solvent for dissolving polyvinyl alcohol is deionized water. Specifically, polyvinyl alcohol and deionized water can be mixed and stirred at a temperature of 75-95°C until the polyvinyl alcohol is completely dissolved, to obtain a polyvinyl alcohol aqueous solution with a weight percentage preferably of 10 wt%. After cooling, maleic anhydride is added to the polyvinyl alcohol solution at a temperature not exceeding 45°C. The molar ratio of polyvinyl alcohol to maleic anhydride is preferably 2.5-3.5:1. To accelerate the reaction rate between the polyvinyl alcohol solution and maleic anhydride, 2 wt% toluenesulfonic acid catalyst can also be added. The mixture is stirred at room temperature for more than 4 hours to obtain a carboxylated polyvinyl alcohol solution. The carboxylated polyvinyl alcohol solution is precipitated in a poor solvent and dried to obtain carboxylated polyvinyl alcohol. Anhydrous ethanol can be selected as the poor solvent here.

[0026] S1.2: Dextran is dissolved in dimethyl sulfoxide to obtain a dimethyl sulfoxide solution of dextran, the concentration of which is preferably 60-70 g / L; vinyl butyl ether is added to the dimethyl sulfoxide solution of dextran, the weight ratio of which is preferably 1.8-2.2:1, to obtain an acetalized dextran solution; to accelerate the reaction rate of the dimethyl sulfoxide solution of dextran and vinyl butyl ether, 1 wt% toluenesulfonic acid catalyst can also be added, but it is best to place the toluenesulfonic acid catalyst into the reaction vessel first, and then add the dimethyl sulfoxide solution of dextran and vinyl butyl ether to the reaction vessel in sequence; the acetalized dextran solution is precipitated in a poor solvent and dried to obtain acetalized dextran, the poor solvent being deionized water.

[0027] S1.3: Chitosan, carboxylated polyvinyl alcohol, and acetalized dextran are dissolved in water to obtain a 2.5 wt% chitosan aqueous solution, a 10 wt% carboxylated polyvinyl alcohol aqueous solution, and a 6 wt% acetalized dextran aqueous solution. To increase the solubility of chitosan in water, 1 wt% acetic acid can be added to deionized water. The chitosan solution, carboxylated polyvinyl alcohol solution, and acetalized dextran solution are preferably mixed in a volume ratio of 5:5:1 and stirred for 10 minutes at a temperature of 35-40°C to obtain a gel-like antibacterial agent.

[0028] Antibacterial agent, water-soluble polymer and solvent are prepared according to existing technology, coated on aluminum plate substrate support, and dried to obtain protective coating.

[0029] Example 2 Based on Example 1 above, a reinforcing agent was added to the functional components of the computer-to-plate protective coating. The preparation method of the reinforcing agent includes: S2.1: Dissolve methacryloyloxyethyltrimethylammonium chloride, butyl acrylate, and glycidyl methacrylate in anhydrous ethanol under an inert atmosphere, add azobisisobutyronitrile, stir at 70-80°C for 6 hours, cool to room temperature, and evaporate the anhydrous ethanol using a rotary evaporator to obtain a polyquaternary ammonium salt solution. The preferred weight ratio of methacryloyloxyethyltrimethylammonium chloride, butyl acrylate, glycidyl methacrylate, and azobisisobutyronitrile is 10:7:3:0.5. Precipitate the polyquaternary ammonium salt solution in a poor solvent and dry to obtain a high molecular weight quaternary ammonium salt. Diethyl ether can be selected as the poor solvent here.

[0030] S2.2: The reinforcing agent is obtained by mixing polyquaternary ammonium salt and polycarbonate using a mixer. The mixing temperature of the mixer is set to above 230°C, preferably 230-250°C, and the mixing time is 50-80 minutes. The weight ratio of the polymeric quaternary ammonium salt to polycarbonate is preferably 1:1.3-1.7. It is worth noting that the main function of the polyquaternary ammonium salt here is as an antistatic agent, while the polycarbonate is the matrix resin and plays a role in wear resistance.

[0031] Example 3 In Example 2 above, a reinforcing agent was added to the functional components of the computer-to-plate (CTP) protective coating. Therefore, based on Example 2 above, this example elaborates on the first method for preparing the protective coating: The first method for preparing a protective coating includes: S3.1: The reinforcing agent is heated and dissolved in acetone. The dissolved reinforcing agent is then mixed with a water-soluble polymer, an antibacterial agent, and a solvent to obtain a coating liquid. The weight percentage of each component in the coating liquid is 20-30% water-soluble polymer, 2-3% antibacterial agent, 40-50% reinforcing agent, and the remainder is solvent. The solvent here can be one or more of deionized water and ethanol mixed in any proportion.

[0032] S3.2: Apply the coating liquid onto the aluminum substrate support, and allow it to cool and dry to form a protective coating; the weight of the dried protective coating is 3-5 g / m². 2 ; However, the aforementioned method of mixing the melted reinforcing agent and antibacterial agent can affect the performance of the antibacterial agent to some extent. Therefore, the second preparation method will be described here.

[0033] The second method for preparing the protective coating includes: S4.1: Mix water-soluble polymer, antibacterial agent and solvent to obtain coating liquid; the weight percentage of each component of the coating liquid is 25-40% water-soluble polymer, 2-4% antibacterial agent, and the balance is solvent, which can be one or more of deionized water and ethanol mixed in any proportion.

[0034] S4.2: Apply the coating liquid onto the aluminum substrate support, and after drying, form a base coating; the weight of the dried base coating is 2-4 g / m². 2 .

[0035] S4.3: The reinforcing agent is dissolved in acetone by heating, applied to the base coating, cooled and dried, and the solvent evaporates to form a surface coating; the surface coating and the base coating together form a protective coating; the coating weight of the surface coating after cooling and drying is less than 1 g / m². 2 .

[0036] The protective coatings prepared in Example 1 and the protective coatings prepared by the second preparation method in Example 3 were respectively analyzed using the potassium bromide pellet method and measured using a Bio-Rad Life Sciences Win-IR infrared spectrometer. The results are as follows: Figure 2 The infrared spectra shown are as follows: (A) is the protective coating prepared in Example 1, and (B) is the protective coating prepared in Example 3.

[0037] Comparative Example 1 Based on Example 1, the method for preparing the antibacterial agent is modified as follows, while the other preparation methods remain unchanged: N,N-diethyl ethanethiol hydrochloride and tert-butanol were mixed, and an aqueous sodium hydroxide solution was added. The mixture was stirred at 20°C for 20 min, then perfluorobutyl ethyl iodide was added, and the temperature was raised to 80°C and stirred for 12 h. The solvent was then removed by rotary evaporation, and the mixture was extracted three times with an aqueous solution, washed three times with saturated brine, and evaporated to dryness to obtain the fluorinated monomer. The molar ratio of N,N-diethyl ethanethiol hydrochloride to perfluorobutyl ethyl iodide was 1:1; the molar ratio of sodium hydroxide to N,N-diethyl ethanethiol hydrochloride in the aqueous sodium hydroxide solution was 2.1:1. Under nitrogen protection, fluorinated monomers and ethanol were mixed and heated to 40°C. Epichlorohydrin was added dropwise, and the temperature was kept constant after the addition was complete. The mixture was stirred for 2 hours, cooled to room temperature, and the solvent was removed by rotary evaporation. The mixture was washed with anhydrous diethyl ether and then dried under vacuum to obtain the epoxy quaternary ammonium salt. The mass ratio of fluorinated monomers to epichlorohydrin was 3:1.

[0038] Gelatin and a buffer solution with a pH of 10 were mixed and stirred at 50°C for 1 hour. Then, an epoxy quaternary ammonium salt was added, and the mixture was stirred for another 6 hours while maintaining the temperature. The mixture was then freeze-dried at low temperature. Excess epoxy quaternary ammonium salt was removed with ethanol, and the mixture was washed with deionized water to remove ethanol. Finally, the mixture was freeze-dried again to obtain the antibacterial component. The mass ratio of gelatin to epoxy quaternary ammonium salt was 8:1.

[0039] Comparative Example 2 In Example 3, a protective coating was prepared according to the first method for preparing a protective coating.

[0040] Comparative Example 3 In Example 3, a protective coating was prepared according to the second preparation method of the protective coating.

[0041] The protective coatings prepared by the methods described in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were used as samples. The prepared samples were heated and humidified in a 50°C, 80% humid heat aging chamber. The antibacterial rate of each sample was measured over time, and the average value of 5 data points was taken to obtain Table 1.

[0042] Table 1

[0043] As can be seen from Table 1, the antibacterial agent preparation method of Example 1 has excellent durability and stability, and can effectively resist degradation caused by damp heat aging; Comparative Examples 2 and 3 show better long-term antibacterial durability than Example 1.

[0044] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a protective coating for computer-to-plate (CTP) printing, the protective coating comprising a water-soluble polymer, a functional component, and a solvent, wherein the functional component comprises an antibacterial agent, characterized in that: Methods for preparing antibacterial agents include: S1.1: Dissolve polyvinyl alcohol to obtain a polyvinyl alcohol solution; add maleic anhydride to the polyvinyl alcohol solution to obtain a carboxylated polyvinyl alcohol solution; precipitate the carboxylated polyvinyl alcohol solution in a poor solvent and dry it to obtain carboxylated polyvinyl alcohol; S1.2: Dextran is dissolved in dimethyl sulfoxide to obtain a dimethyl sulfoxide solution of dextran; vinyl butyl ether is added to the dimethyl sulfoxide solution of dextran to obtain an acetalized dextran solution; the acetalized dextran solution is precipitated in a poor solvent and dried to obtain acetalized dextran. S1.3: Dissolve chitosan, carboxylated polyvinyl alcohol, and acetalized dextran separately to obtain chitosan solution, carboxylated polyvinyl alcohol solution, and acetalized dextran solution; mix the chitosan solution, carboxylated polyvinyl alcohol solution, and acetalized dextran solution to obtain an antibacterial agent.

2. The method for preparing a computer-to-plate (CTP) protective coating as described in claim 1, characterized in that: The functional components also include reinforcing agents, which are prepared by methods including: S2.1: Methacryloxyethyltrimethylammonium chloride, butyl acrylate and glycidyl methacrylate are dissolved in anhydrous ethanol in an inert atmosphere, and azobisisobutyronitrile is added to react and synthesize a polyquaternary ammonium salt solution; the polyquaternary ammonium salt solution is precipitated in a poor solvent and dried to obtain a high molecular weight quaternary ammonium salt. S2.2: The reinforcing agent is obtained by mixing polyquaternary ammonium salt and polycarbonate using a mixer.

3. The method for preparing a computer-to-plate (CTP) protective coating as described in claim 2, characterized in that: Methods for preparing protective coatings include: S3.1: Dissolve the reinforcing agent and mix it with water-soluble polymer, antibacterial agent and solvent to obtain a coating liquid; the weight percentage of each component of the coating liquid is 20-30% water-soluble polymer, 2-3% antibacterial agent, 40-50% reinforcing agent, and the balance is solvent; S3.2: Apply the coating liquid onto the aluminum plate substrate support, and form a protective coating after cooling and drying; Alternatively, the methods for preparing the protective coating include: S4.1: Mix water-soluble polymer, antibacterial agent and solvent to obtain coating liquid; the weight percentage of each component of the coating liquid is 25-40% water-soluble polymer, 2-4% antibacterial agent, and the remainder is solvent; S4.2: Apply the coating liquid onto the aluminum plate substrate support, and form a base coating after drying; S4.3: Dissolve the reinforcing agent, apply it to the base coating, and allow it to cool and dry to form a surface coating; the surface coating and the base coating together form a protective coating; the weight of the surface coating after cooling and drying is less than 1 g / m³. 2 .

4. The method for preparing a computer-to-plate (CTP) protective coating as described in claim 1, characterized in that: In S1.1, the molar ratio of polyvinyl alcohol to maleic anhydride is 2.5–3.5:1; and / or, In S1.2, the concentration of dextran in the dimethyl sulfoxide solution is 60–70 g / L; the weight ratio of the dextran dimethyl sulfoxide solution to vinyl butyl ether is 1.8–2.2:1; and / or, In S1.3, an antibacterial agent is obtained by mixing 2.5 wt% of chitosan aqueous solution, 10 wt% of carboxylated polyvinyl alcohol aqueous solution and 6 wt% of acetalized dextran aqueous solution in a volume ratio of 5:5:

1.

5. The method for preparing a computer-to-plate (CTP) protective coating as described in claim 2, characterized in that: In S2.1, methacryloyloxyethyltrimethylammonium chloride, butyl acrylate, glycidyl methacrylate, and azobisisobutyronitrile are added to anhydrous ethanol in a weight ratio of 10:7:3:0.5; and / or, In S2.2, the weight ratio of the polymeric quaternary ammonium salt and polycarbonate fed into the mixing mill is 1:1.3 to 1.

7.

6. The method for preparing a computer-to-plate (CTP) protective coating as described in claim 1, characterized in that: In S1.1, a p-toluenesulfonic acid catalyst is added to the reaction of polyvinyl alcohol solution and maleic anhydride; and / or, In S1.2, p-toluenesulfonic acid catalyst is added during the reaction of dextran in dimethyl sulfoxide solution and vinyl butyl ether.

7. The method for preparing a computer-to-plate (CTP) protective coating as described in claim 1, characterized in that: In S1.1, polyvinyl alcohol and deionized water are mixed and stirred at a temperature of 75-95°C until the polyvinyl alcohol is completely dissolved to obtain a polyvinyl alcohol solution. After the polyvinyl alcohol solution is cooled to below 45°C, maleic anhydride is added and stirred at room temperature for 4 hours to obtain a carboxylated polyvinyl alcohol solution. And / or, In S1.2, a dimethyl sulfoxide solution of dextran and vinyl butyl ether are mixed and stirred at room temperature for 12 hours to obtain an acetalized dextran solution; and / or, In step S1.3, chitosan solution, carboxylated polyvinyl alcohol solution and acetalized dextran solution are mixed and stirred for 10 minutes at a temperature of 35-40°C to obtain a gel-like antibacterial agent.

8. The method for preparing a computer-to-plate (CTP) protective coating as described in claim 2, characterized in that: In S2.1, methacryloyloxyethyltrimethylammonium chloride, butyl acrylate, glycidyl methacrylate, and anhydrous ethanol are mixed, and azobisisobutyronitrile is added. The mixture is stirred at 70–80°C for 6 hours, cooled to room temperature, and the anhydrous ethanol is evaporated to obtain a polyquaternary ammonium salt solution; and / or, In S2.2, the mixing temperature of the mixer is set to above 230℃.

9. The method for preparing a computer-to-plate (CTP) protective coating as described in claim 1, characterized in that: In S1.1, the carboxylated polyvinyl alcohol solution precipitates in ethanol; and / or, In S1.2, the acetalized dextran solution settles in deionized water; and / or, In step S1.3, chitosan, carboxylated polyvinyl alcohol, and acetalized dextran are dissolved in deionized water to obtain chitosan aqueous solution, carboxylated polyvinyl alcohol aqueous solution, and acetalized dextran aqueous solution.

10. The method for preparing a computer-to-plate (CTP) protective coating as described in claim 2, characterized in that: In S2.1, the polyquaternary ammonium salt solution is precipitated in diethyl ether.

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