Preparation method of high-air-permeability CTP plate lining paper

Abstract

The invention discloses a preparation method of high-air-permeability CTP plate lining paper. The high-air-permeability CTP plate lining paper is prepared through the processes of differentiated pretreatment of softwood pulp and hardwood pulp, segmented pulping, addition of a composite air-permeable auxiliary agent and nano cellulose, papermaking by a fourdrinier, gradient drying, low-temperature calendaring and the like. By optimizing a fiber structure and constructing a stable ventilation channel, the air permeability is improved, the paper strength, surface flatness and antistatic property are guaranteed, the problem that the air permeability and strength of traditional lining paper are difficult to balance is solved, and the lining paper is suitable for protection of CTP plates, adhesion and pollution are avoided, and the storage and transportation requirements are met.

Description

Technical Field

[0001] This invention relates to the field of CTP plate backing paper preparation technology, specifically to a method for preparing high-permeability CTP plate backing paper. Background Technology

[0002] During storage, transportation, and use, CTP plates require backing paper to protect their photosensitive layer from scratches, contamination, and electrostatic damage. Traditional backing paper suffers from insufficient air permeability, making it prone to adhesion between the plate and backing paper due to changes in environmental humidity, or allowing residual volatile substances to accumulate, affecting plate performance. Furthermore, traditional manufacturing processes often sacrifice paper strength in pursuit of air permeability, or result in unstable air permeability due to improper additives, making it difficult to meet the comprehensive requirements of CTP plates for backing paper: "high air permeability, high strength, low static electricity, and a smooth surface." Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing high-permeability CTP plate backing paper to solve the technical problem of poor air permeability of traditional backing paper.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for preparing a high-permeability CTP plate backing paper includes the following steps:

[0006] S1. Raw material pretreatment: Softwood pulp and hardwood pulp are mixed at a mass ratio of 3:1 to 5:1. The softwood pulp is steam softened at a temperature of 120℃ to 130℃ for 30 to 40 minutes. The hardwood pulp is microwave treated at a power of 800W to 1000W for 5 to 8 minutes.

[0007] S2. Segmented pulping: The pretreated softwood pulp is first pulped in a pulper to control the freeness to 20°SR~25°SR. Then, 0.5%~1% of nanocellulose suspension is added to the total mass of the mixed pulp for the second pulping to achieve a freeness of 30°SR~35°SR. The pretreated hardwood pulp is pulped separately to achieve a freeness of 15°SR~20°SR.

[0008] S3. Slurry mixing: Mix the two slurries obtained in step S2, and add a composite air-permeable agent accounting for 0.3% to 0.8% of the oven-dry weight of the mixed slurry. The composite air-permeable agent is composed of alkyl ketene dimer and nano-silica in a mass ratio of 2:1. Stir evenly.

[0009] S4. Forming: The mixed pulp is fed into a fourdrinier paper machine for forming. The dewatering pressure in the wire section is controlled at 0.1MPa to 0.15MPa, the linear pressure in the press section is 150kN / m to 200kN / m, and the drying section adopts a gradient temperature increase, with the temperature gradually increasing from 80℃ to 120℃, until the moisture content is 5% to 8%.

[0010] S5. Post-processing: The dried paper is calendered at a low temperature of 40℃~50℃ and a linear pressure of 80kN / m~100kN / m to obtain CTP backing paper with a basis weight of 40g / m²~60g / m² and an air permeability ≥100CU.

[0011] The above technical solution improves the connectivity and uniformity of the internal pore structure of the paper by using differentiated pretreatment of softwood pulp and hardwood pulp, segmented pulping process, combined with the addition of composite air-permeable additives and gradient drying and low-temperature calendering. This significantly improves air permeability while ensuring basic physical strength. Furthermore, by matching process parameters, a balance between air permeability and other properties is achieved, meeting the comprehensive requirements of CTP liner paper for air permeability, protection and adaptability.

[0012] In a preferred embodiment of the present invention, the softwood pulp in step S1 is bleached sulfate Masson pine pulp, and the hardwood pulp is bleached sulfate eucalyptus pulp. By limiting the specific type of bleached sulfate pulp, the skeletal support of the long fibers of Masson pine pulp and the filling characteristics of the short fibers of eucalyptus pulp are utilized to optimize the interfiber bonding state, thereby enhancing the structural stability of the paper and providing a suitable fiber morphological basis for the formation of air permeable channels.

[0013] As a preferred embodiment of the present invention, the concentration of the nanocellulose suspension in step S2 is 1wt% to 2wt%, its length is 100 to 500 nm, and its diameter is 5 to 20 nm. By controlling the size and concentration of nanocellulose, a nanoscale bridging structure is formed between the fibers, which improves the fiber bonding strength while avoiding excessive clogging of pores, thereby achieving synergistic optimization of paper strength and air permeability.

[0014] As a preferred embodiment of the present invention, in step S3, the particle size of the nano-silica is 50nm to 100nm and the specific surface area is ≥150m² / g. By limiting the particle size and specific surface area of ​​the nano-silica, it can be uniformly dispersed in the fiber gaps. Its porous structure characteristics are used to construct additional air-permeable channels, while enhancing the interfacial bonding between the additives and the fibers, thereby improving the stability of the air permeability performance.

[0015] As a preferred embodiment of the present invention, in step S4, the wire speed of the long wire paper machine is 300m / min to 400m / min, and the wire density is 0.8wt% to 1.2wt%, which ensures that the pulp is evenly spread on the wire, reduces fiber flocculation, and forms a more regular pore distribution, laying the foundation for the preservation of the pore structure in the subsequent drying process.

[0016] As a preferred embodiment of the present invention, the gradient heating rate of the drying section in step S4 is 5°C / section to 10°C / section, and a total of 5 to 8 drying sections are set. By using the gradient heating drying method, premature hardening of the paper surface caused by rapid drying is avoided, and the collapse of pores formed when internal moisture evaporates is reduced, which is conducive to maintaining the loose internal structure of the paper and ensuring air permeability.

[0017] As a preferred embodiment of the present invention, step S3 further includes adding cationic starch at a dry weight of 0.1% to 0.3% of the mixed pulp as a dry strength agent, with a degree of substitution of 0.05 to 0.1. Adding cationic starch as a dry strength agent enhances the interfiber bonding force through its adsorption with the fibers, thereby improving the paper's resistance to breakage and durability during use without significantly reducing air permeability.

[0018] As a preferred embodiment of the present invention, the pretreated softwood pulp and hardwood pulp in step S1 need to be screened. The screening equipment is a 200-mesh pressure screen with a screening residue rate of ≤0.5%. Screening can remove coarse impurities and insufficiently treated fiber bundles from the pulp, reduce the blockage of the paper pore structure, ensure the unobstructed air passage, and improve the uniformity of the paper surface.

[0019] As a preferred embodiment of the present invention, after low-temperature calendering in step S5, an antistatic treatment is performed. A quaternary ammonium salt antistatic agent with a mass concentration of 0.5% to 1% is applied by spraying, and the application amount is 0.1 g / m² to 0.3 g / m. The antistatic treatment reduces the accumulation of static electricity on the paper surface, reduces the risk of dust adhesion and plate contamination caused by static adsorption, improves the protective effect of the backing paper on the CTP plate, and does not affect the air permeability structure of the paper.

[0020] As a preferred embodiment of the present invention, the basis weight deviation of the CTP plate liner paper is ≤ ±2g / m², the bursting strength is ≥1.5kPa·m² / g, and the surface roughness (PPS) is ≤2.0μm. By controlling the basis weight stability, bursting strength and surface roughness, the liner paper is ensured to have uniform thickness and is not easily damaged during use, and the risk of scratches can be reduced when it comes into contact with the CTP plate surface, taking into account both air permeability and adaptability in practical applications.

[0021] Compared with existing technologies, the method for preparing a high-permeability CTP plate backing paper of the present invention has the following beneficial effects:

[0022] This invention achieves a comprehensive performance improvement in CTP plate liner paper through the synergistic effects of raw material pretreatment, segmented pulping, addition of composite additives, gradient process control, and post-processing optimization. Specifically, after differentiated pretreatment and precise pulping, the fibers form a uniform and interconnected pore structure; the combination of composite air-permeable additives and nanocellulose enhances fiber bonding strength while constructing stable air-permeable channels, significantly improving the paper's air permeability; gradient drying and low-temperature calendering processes reduce pore collapse, ensuring the integrity of the air-permeable structure; and post-processing measures such as screening and antistatic treatment further optimize the unobstructed air-permeable channels, reducing usage risks. The final product, while highly air-permeable, also possesses good physical strength, surface smoothness, and antistatic properties, effectively protecting the CTP plate and adapting to its storage and usage environment. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only examples of embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart of an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0026] In the description of the embodiments of the present invention, it should be understood that the terms "upper", "lower", "front", "rear", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0027] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation", "connection" and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, an integral connection, or a detachable connection; they can refer to the internal connection of two components; they can refer to a direct connection or an indirect connection through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present invention should be understood according to the specific circumstances.

[0028] Reference Figure 1 The present invention provides specific embodiments.

[0029] Example 1:

[0030] Preparation method: Bleached sulfate pine pulp was selected as the softwood pulp, and bleached sulfate eucalyptus pulp was selected as the hardwood pulp, mixed at a mass ratio of 3:1. The softwood pulp was steamed at 120℃ for 30 min, and the hardwood pulp was microwaved at 800W for 5 min. The softwood pulp was first pulped to 20°SR, and then 1% of 1wt% nanocellulose suspension (length 100-500nm, diameter 5-20nm) was added before pulping to 30°SR; the hardwood pulp was pulped to 15°SR. 0.3% of a composite air-permeable agent consisting of alkyl ketene dimers (mass ratio 2:1) and nano-silica with a particle size of 50-100nm and a specific surface area ≥150m² / g, and 0.1% of cationic starch with a degree of substitution of 0.05 were added to the mixed pulp. The paper is produced on a long-wire paper machine with a wire speed of 300 m / min, a wire density of 0.8 wt%, a wire dewatering pressure of 0.1 MPa, a press linear pressure of 150 kN / m, and a drying section where the temperature is gradually increased from 80°C to 120°C at a rate of 5°C per stage, for a total of 5 stages. After drying, the paper is calendered at a low temperature of 40°C with a linear pressure of 80 kN / m.

[0031] Technical effects: Through specific raw material pretreatment and pulping processes, the fibers form a suitable porous structure, composite air-permeable additives construct and stabilize air-permeable channels, and cationic starch enhances fiber bonding. All these processes work together to improve the air permeability of the paper while ensuring that the paper has a certain physical strength, thus meeting the air permeability and protection requirements of CTP plate liner paper.

[0032] Working principle: Steam softens softwood pulp fibers, making them easier to break down; microwave treatment of hardwood pulp improves fiber surface properties. Nanocellulose forms bridges between fibers, increasing bonding strength without clogging pores. Alkyl ketone dimers in the composite air-permeable agent improve fiber wettability, while the porous structure of nano-silica increases air permeability channels. Cationic starch adsorbs onto the fibers, enhancing the overall strength of the paper. Gradient drying prevents premature hardening of the paper surface, and low-temperature calendering maintains the internal structure of the paper.

[0033] Experimental data: The finished paper has a basis weight of 40 g / m², an air permeability of 105 CU, a burst strength of 1.6 kPa·m² / g, a surface roughness (PPS) of 1.8 μm, and a basis weight deviation within ±2 g / m².

[0034] Example 2:

[0035] Preparation method: The mass ratio of softwood pulp to hardwood pulp is 4:1. The softwood pulp is steamed at 125℃ for 35 min, and the hardwood pulp is microwave-treated at 900W for 6 min. The softwood pulp is first-stage beaten to 22°SR, then second-stage beaten to 32°SR after adding 0.7% of a 1.5wt% nanocellulose suspension; the hardwood pulp is beaten to 17°SR. 0.5% of a composite air-permeable agent and 0.2% cationic starch are added to the mixed pulp. The pulp is formed on a four-wire paper machine with a wire speed of 350 m / min, a wire density of 1.0 wt%, a wire dewatering pressure of 0.12 MPa, a press linear pressure of 175 kN / m, and a drying section that heats from 80℃ to 120℃ at a rate of 7℃ / section, for a total of 6 sections. After drying, the pulp is calendered at 50℃ with a linear pressure of 90 kN / m. Technical effects: The optimized process parameters make the internal pore distribution of the paper more uniform, further improve the air permeability, and achieve a good balance between the paper's strength and surface quality, making it better suited to the CTP plate's usage environment.

[0036] Working principle: Appropriately increasing the intensity of steaming and microwave treatment promotes improved fiber properties. Adjusting the concentration and amount of nanocellulose optimizes the bonding between fibers. The composite air-permeability additive works synergistically with cationic starch to enhance air permeability while maintaining paper strength. Moderate papermaking and drying parameters facilitate the formation of an ideal paper structure, and low-temperature calendering stabilizes paper properties.

[0037] Experimental data: Paper basis weight 50 g / m², air permeability 110 CU, burst strength 1.7 kPa·m² / g, surface roughness (PPS) 1.6 μm, basis weight deviation ≤ ±2 g / m².

[0038] Example 3:

[0039] Preparation method: A 5:1 mass ratio of softwood pulp to hardwood pulp was used. The softwood pulp was steamed at 130℃ for 40 min, and the hardwood pulp was microwave-treated at 1000W for 8 min. The softwood pulp was first beaten to 25°SR, and after adding 0.5% of a 2wt% nanocellulose suspension, it was beaten to 35°SR in the second stage. The hardwood pulp was beaten to 20°SR. 0.8% of a composite air-permeable agent and 0.3% cationic starch were added to the mixed pulp. The pulp was formed on a fourdrinier paper machine with a wire speed of 400 m / min, a wire density of 1.2 wt%, a wire dewatering pressure of 0.15 MPa, a press linear pressure of 200 kN / m, and a drying section that heated from 80℃ to 120℃ at a rate of 10℃ / section for a total of 8 sections. After drying, the pulp was calendered at 45℃ with a linear pressure of 100 kN / m.

[0040] Technical effects: The enhanced pretreatment and pulping process, combined with a high proportion of composite air-permeable additives, greatly improves the air permeability of the paper. At the same time, cationic starch and subsequent processes ensure that the paper is not easily damaged under high-intensity use, and has a smooth and flat surface, meeting the stringent performance requirements of CTP plate liner paper.

[0041] Working principle: High-temperature steaming and high-power microwaves thoroughly treat the fibers, allowing nanocellulose to better exert its reinforcing and porosity-optimizing effects at high concentrations. Numerous composite air-permeable additives create abundant air-permeable channels, while cationic starch significantly enhances fiber bonding. High-speed papermaking, high-pressure dehydration, and rapid gradient temperature drying form a dense and breathable paper structure, while low-temperature calendering stabilizes the paper's properties.

[0042] Experimental data: The basis weight of the finished paper is 60 g / m², the air permeability is 120 CU, the bursting strength is 1.8 kPa·m² / g, the surface roughness (PPS) is 1.5 μm, and the basis weight deviation is controlled within ±2 g / m².

[0043] Example 4:

[0044] Preparation method: Softwood pulp and hardwood pulp were mixed in a 4:1 ratio. The softwood pulp was steamed at 122℃ for 32 minutes, and the hardwood pulp was microwaved at 850W for 7 minutes. The softwood pulp was first beaten to 21°SR, and then a second beating was performed after adding 0.6% of a 1.2wt% nanocellulose suspension to 31°SR. The hardwood pulp was beaten to 16°SR. 0.4% of a composite air-permeable agent and 0.15% cationic starch were added to the mixed pulp. The pulp was screened through a 200-mesh pressure sieve, with a residue rate ≤0.5%. The pulp was formed on a long-wire paper machine with a wire speed of 320 m / min, a wire density of 0.9 wt%, a wire dewatering pressure of 0.11 MPa, a press linear pressure of 160 kN / m, and a drying section that increased the temperature from 80℃ to 120℃ at a rate of 6℃ / section for a total of 7 sections. After drying, the product is calendered at a low temperature of 42℃ with a linear pressure of 85kN / m. Then, it undergoes antistatic treatment by spraying 0.5% quaternary ammonium salt type antistatic agent at an application rate of 0.1g / m².

[0045] Technical benefits: The screening process removes impurities, ensuring unobstructed airflow channels; the antistatic treatment reduces the hazards of static electricity; and while improving air permeability and strength, it enhances the paper's protective effect on the CTP plate, comprehensively improving the practicality of the liner paper.

[0046] Working principle: Screening removes coarse impurities and untreated fiber bundles, preventing clogging of pores. An antistatic agent forms a conductive layer on the paper surface, reducing static electricity buildup. Other processes work synergistically to optimize paper structure and improve air permeability and strength.

[0047] Experimental data: Paper basis weight 45 g / m², air permeability 108 CU, burst strength 1.65 kPa·m² / g, surface roughness (PPS) 1.7 μm, basis weight deviation ±1.8 g / m², electrostatic voltage significantly reduced, meeting the requirements for actual use.

[0048] Example 5:

[0049] Preparation method: The mass ratio of softwood pulp to hardwood pulp is 3.5:1. The softwood pulp is steamed at 128℃ for 38 min, and the hardwood pulp is microwave-treated at 950W for 7 min. The softwood pulp is first beaten to 23°SR, then after adding 0.8% of a 1.8wt% nanocellulose suspension, it is beaten to 33°SR in the second stage; the hardwood pulp is beaten to 18°SR. The mixed pulp is then mixed with 0.6% of a composite air-permeable agent and 0.25% of cationic starch, and screened through a 200-mesh pressure sieve. The paper is produced on a fourdrinier paper machine with a wire speed of 380 m / min, a wire density of 1.1 wt%, a wire dewatering pressure of 0.13 MPa, a press linear pressure of 180 kN / m, and a drying section that heats from 80℃ to 120℃ at a rate of 8℃ / section, for a total of 7 sections. After drying, the material is calendered at a low temperature of 48℃ with a linear pressure of 95 kN / m. Antistatic treatment is performed using a 1% quaternary ammonium salt antistatic agent, applied at a rate of 0.2 g / m. 2 .

[0050] Technical benefits: The comprehensive and optimized process, from raw material processing to post-processing, fully improves paper performance, resulting in high air permeability, good strength, and excellent antistatic properties, providing better protection and compatibility for CTP plates.

[0051] Working principle: Appropriate pretreatment and pulping parameters, combined with suitable additives and screening processes, result in a good internal paper structure. Antistatic treatment effectively reduces static electricity, ensuring the safety and stability of CTP plates during use and storage.

[0052] Experimental data: basis weight 55 g / m², air permeability 115 CU, burst strength 1.75 kPa·m² / g, surface roughness (PPS) 1.65 μm, basis weight deviation ≤ ±1.5 g / m², good electrostatic properties, and all indicators meet the high standard requirements of CTP plate backing paper.

[0053] Working principle of this invention:

[0054] 1. Raw material optimization: Softwood pulp (long fiber) provides skeletal support, while hardwood pulp (short fiber) fills the gaps, forming a suitable fiber network structure through mass ratio control; steam softening of softwood pulp promotes fiber fibrillation, while microwave treatment of hardwood pulp improves fiber surface activity and enhances interfiber bonding efficiency.

[0055] 2. Structural control: Segmented pulping controls the degree of fiber fibrillation and avoids excessive pulping that clogs pores; nanocellulose forms nanobridges between fibers, enhancing the bonding strength without damaging the pore structure; in the composite breathable additive, alkyl ketene dimers optimize fiber wettability, and nano silica utilizes its porous properties to construct additional breathable channels, with the two working together to improve breathability stability.

[0056] 3. Process assurance: Gradient temperature drying avoids the collapse of pores caused by hardening of the paper surface, preserving the loose internal structure; low-temperature calendering improves surface smoothness without significantly compressing pores; screening removes impurities to prevent pore blockage; antistatic agent forms a conductive layer to reduce the impact of static electricity on the printing plate.

[0057] 4. Performance balance: Cationic starch enhances fiber bonding through adsorption, compensating for the strength loss that may be caused by the breathable structure, and achieving synergistic optimization of air permeability and strength.

[0058] How to use this invention:

[0059] 1. Cutting and Adaptation: Cut the prepared backing paper to the corresponding size according to the size of the CTP plate, ensuring that the edge of the backing paper is aligned with the edge of the plate to avoid insufficient protection in some areas due to size deviation.

[0060] 2. Lamination Operation: In a clean environment, smoothly cover the CTP plate surface with the backing paper, ensuring no wrinkles or air bubbles, and make the backing paper in close contact with the plate surface without applying additional pressure to prevent scratching the photosensitive layer.

[0061] 3. Stacking and storage: When stacking CTP plates with backing paper, control the stacking height to avoid heavy pressure that could compress the pore structure of the backing paper and affect its breathability; the storage environment should be kept ventilated and dry to balance local humidity by utilizing the breathability of the backing paper.

[0062] 4. Precautions for handling: Avoid direct contact with the bonding surface of the backing paper and the printing plate during handling to prevent fingerprint and dust contamination; if the backing paper needs to be reused (if it is not contaminated), its surface must be kept clean to ensure the protective effect when bonding again.

[0063] In summary, this invention achieves a comprehensive performance improvement in CTP plate liner paper through the synergistic effects of raw material pretreatment, segmented pulping, addition of composite additives, gradient process control, and post-processing optimization. Specifically, after differentiated pretreatment and precise pulping, the fibers form a uniform and interconnected pore structure; the combination of composite air-permeable additives and nanocellulose enhances fiber bonding strength while constructing stable air-permeable channels, significantly improving the paper's air permeability; gradient drying and low-temperature calendering processes reduce pore collapse, ensuring the integrity of the air-permeable structure; and post-processing measures such as screening and antistatic treatment further optimize the unobstructed air-permeable channels, reducing usage risks. The final product, while exhibiting high air permeability, also possesses good physical strength, surface smoothness, and antistatic properties, effectively protecting the CTP plate and adapting to its storage and usage environment.

[0064] The foregoing has shown and described the basic principles of the present invention. The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. The above embodiments and descriptions in the specification are only illustrative of the principles of the present invention. Any modifications, equivalent substitutions, and improvements made within the scope of the present invention without departing from the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-permeability CTP plate backing paper, characterized in that... Includes the following steps: S1. Raw material pretreatment: Softwood pulp and hardwood pulp are mixed at a mass ratio of 3:1 to 5:

1. The softwood pulp is steam softened at a temperature of 120℃ to 130℃ for 30 to 40 minutes. The hardwood pulp is microwave treated at a power of 800W to 1000W for 5 to 8 minutes. S2. Segmented pulping: The pretreated softwood pulp is first pulped in a pulper to control the freeness to 20°SR~25°SR. Then, 0.5%~1% of nanocellulose suspension is added to the total mass of the mixed pulp for the second pulping to achieve a freeness of 30°SR~35°SR. The pretreated hardwood pulp is pulped separately to achieve a freeness of 15°SR~20°SR. S3. Slurry mixing: Mix the two slurries obtained in step S2, and add a composite air-permeable agent accounting for 0.3% to 0.8% of the oven-dry weight of the mixed slurry. The composite air-permeable agent is composed of alkyl ketene dimer and nano-silica in a mass ratio of 2:

1. Stir evenly. S4. Forming: The mixed pulp is fed into a fourdrinier paper machine for forming. The dewatering pressure in the wire section is controlled at 0.1MPa to 0.15MPa, the linear pressure in the press section is 150kN / m to 200kN / m, and the drying section adopts a gradient temperature increase, with the temperature gradually increasing from 80℃ to 120℃, until the moisture content is 5% to 8%. S5. Post-processing: The dried paper is calendered at a low temperature of 40℃~50℃ and a linear pressure of 80kN / m~100kN / m to obtain CTP backing paper with a basis weight of 40g / m²~60g / m² and an air permeability ≥100CU.

2. The method for preparing a high-permeability CTP plate backing paper according to claim 1, characterized in that: In step S1, the softwood pulp is bleached sulfate pine pulp, and the hardwood pulp is bleached sulfate eucalyptus pulp.

3. The method for preparing a high-permeability CTP plate backing paper according to claim 1, characterized in that: In step S2, the concentration of the nanocellulose suspension is 1wt% to 2wt%, its length is 100 to 500 nm, and its diameter is 5 to 20 nm.

4. The method for preparing a high-permeability CTP plate backing paper according to claim 1, characterized in that: In step S3, the particle size of the nano-silica is 50nm to 100nm, and the specific surface area is ≥150m² / g.

5. The method for preparing a high-permeability CTP plate backing paper according to claim 1, characterized in that: In step S4, the wire speed of the long wire paper machine is 300m / min to 400m / min, and the wire density is 0.8wt% to 1.2wt%.

6. The method for preparing a high-permeability CTP plate backing paper according to claim 1, characterized in that: In step S4, the gradient heating rate of the drying section is 5℃ / section to 10℃ / section, and a total of 5 to 8 drying sections are set.

7. The method for preparing a high-permeability CTP plate backing paper according to claim 1, characterized in that: Step S3 also includes adding cationic starch at a dry strength of 0.1% to 0.3% of the oven-dry weight of the mixed slurry as a dry strength agent, with a degree of substitution of 0.05 to 0.1 for the cationic starch.

8. The method for preparing a high-permeability CTP plate backing paper according to claim 1, characterized in that: The pretreated softwood pulp and hardwood pulp in step S1 still need to be screened. The screening equipment is a 200-mesh pressure screen with a screening residue rate of ≤0.5%.

9. The method for preparing a high-permeability CTP plate backing paper according to claim 1, characterized in that: In step S5, after low-temperature calendering, an antistatic treatment is also performed by spraying a quaternary ammonium salt type antistatic agent with a mass concentration of 0.5% to 1% at a rate of 0.1 g / m² to 0.3 g / m².

10. A method for preparing a high-permeability CTP plate backing paper according to any one of claims 1-9, characterized in that: The basis weight deviation of CTP backing paper is ≤ ±2g / m², the burst strength is ≥1.5kPa·m² / g, and the surface roughness (PPS) is ≤2.0μm.

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