A halogen-free base paper for laminated boards, its preparation method and application

Abstract

The present invention discloses a halogen-free laminated board base paper, its preparation method and application, specifically belonging to the technical field of base paper for copper clad laminate substrates. The raw materials for preparing the halogen-free laminated board base paper include plant fibers, a composite wet strength agent and a composite flame retardant; the plant fibers include softwood fibers, hardwood fibers, cotton fibers and peanut shell fibers; the composite wet strength agent includes JH-1225 wet strength agent and polyethyleneimine resin; the composite flame retardant includes components of cardanol-modified phenolic resin and ammonium polyphosphate flame retardant. The laminated board base paper provided by the present invention is prepared from plant fibers with a specific composition, a composite wet strength agent with a specific composition and a composite flame retardant with a specific composition. The plant fibers, the composite wet strength agent and the composite flame retardant form a rich and stable chemical cross-linking network, making the laminated board base paper have excellent impregnation property, flame retardancy, heat resistance, mechanical strength, flexibility and processability at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of base paper for copper clad laminate substrates, and particularly relates to a halogen-free laminated board base paper and its preparation method and application. Background Art

[0002] In the current electronics industry, as the core material of printed circuit boards (PCBs), the performance of laminated board base paper is directly related to the reliability, safety, and service life of electronic products. With the continuous miniaturization and integration of electronic products and the continuous expansion of application fields, the performance requirements for laminated board base paper are also increasing day by day. Halogen-free laminated board base paper has deficiencies in flame retardancy, flexibility, mechanical properties, and heat resistance, making it difficult to meet the high standards of the modern electronics industry.

[0003] Traditional laminated board base paper often uses halogen compounds as flame retardants to improve its flame retardant performance. However, halogen compounds will produce toxic and harmful gases during combustion, causing serious harm to the environment and human health. With the increasing global awareness of environmental protection, the demand for halogen-free, non-toxic, and environmentally friendly laminated board base paper is becoming increasingly urgent. Therefore, the development of halogen-free laminated board base paper with high flame retardancy has become one of the current research hotspots.

[0004] During the manufacturing process of electronic products, laminated board base paper needs to undergo multiple processing processes such as bending, folding, and cutting. Therefore, good flexibility is one of the essential properties of laminated board base paper. However, traditional laminated board base paper often has deficiencies in flexibility, and is prone to problems such as fracture and delamination, affecting the overall performance and reliability of the product.

[0005] The mechanical properties of laminated board base paper, including tensile strength, tear strength, impact strength, etc., are directly related to its service life and reliability in electronic products. Traditional laminated board base paper often has deficiencies in mechanical properties, making it difficult to meet the requirements of modern electronic products for high-strength and high-toughness materials.

[0006] During the operation of electronic products, laminated board base paper needs to withstand the thermal stress in a high-temperature environment. Therefore, good heat resistance is one of the essential properties of laminated board base paper. However, traditional laminated board base paper is prone to problems such as deformation and softening in a high-temperature environment, affecting the overall performance and reliability of the product.

[0007] In view of the problems existing in the existing halogen-free laminated board base paper in terms of wet strength, toughness, impact strength, flame retardancy, and flexibility, it is urgent to develop a new type of halogen-free laminated board base paper to meet the market demand for high-performance and high-reliability electronic products. Summary of the Invention

[0008] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a halogen-free laminated board base paper with high flame retardancy, good flexibility, good mechanical properties, and high heat resistance, as well as its preparation method and application. The present invention aims to improve the flame retardancy, flexibility, mechanical properties, and heat resistance of the laminated board base paper by optimizing the material ratio and preparation process to meet the requirements of modern electronic industry for high-performance and high-reliability materials.

[0009] To achieve the above purpose, the present invention discloses the following technical solutions:

[0010] In the first aspect, the present invention provides a halogen-free laminated board base paper, and the preparation raw materials of the halogen-free laminated board base paper include plant fibers, a composite wet strength agent, and a composite flame retardant;

[0011] The plant fibers include softwood fibers, hardwood fibers, cotton fibers, and peanut shell fibers;

[0012] The composite wet strength agent includes JH-1225 wet strength agent and polyethyleneimine resin;

[0013] The composite flame retardant includes cardanol-modified phenolic resin and ammonium polyphosphate flame retardant;

[0014] The preparation method of the halogen-free laminated board base paper includes the following steps:

[0015] S1-1. Mix the plant fibers with the composite wet strength agent and carry out sizing treatment, then form on the wire to obtain the base paper;

[0016] S1-2. Immerse the base paper in the composite flame retardant and then dry to obtain the halogen-free laminated board base paper.

[0017] Preferably, by mass, the plant fibers include the following components:

[0018]

[0019] Further preferably, the fiber length of the hardwood fibers is 0.6 - 1.0 mm, the fiber length of the softwood fibers is 3.1 - 3.5 mm, the fiber length of the cotton fibers is 10 - 15 mm, and the fiber length of the peanut shell fibers is 0.15 - 0.27 mm.

[0020] Preferably, by mass, the composite wet strength agent includes the following components:

[0021] JH-1225 wet strength agent 20 parts;

[0022] Polyethyleneimine resin 5 - 7 parts.

[0023] Preferably, by mass, the composite flame retardant includes the following components:

[0024] 20 - 30 parts of cardanol modified phenolic resin;

[0025] 10 parts of ammonium polyphosphate flame retardant.

[0026] Further preferably, the preparation method of the cardanol modified phenolic resin comprises the following steps:

[0027] S1. Put cardanol shell oil, phenol, and aqueous formaldehyde solution into a reaction kettle according to a mass ratio of 1:4:6, stir for 1 h at a stirring speed of 500 r / min, wherein the concentration of the aqueous formaldehyde solution is 30 wt%.

[0028] S2. Add aqueous hydrochloric acid solution to adjust the pH of the system to 2, heat the reaction kettle to 60 °C and react for 10 h to obtain a polymerization product, and let the obtained polymerization product flow to a dehydration kettle by gravity, wherein the concentration of the aqueous hydrochloric acid solution is ≥95 wt%.

[0029] S3. Heat the dehydration kettle to 130 °C, perform high-temperature dehydration on the polymerization product for 1 h, lower the temperature to 90 °C, turn on the vacuum pump for vacuum dehydration to obtain cardanol modified phenolic resin, wherein the vacuum dehydration time is 6 h and the vacuum degree is 0.09 Mpa.

[0030] Even more preferably, the cardanol shell oil contains ≥80 wt% cardanol.

[0031] Preferably, when the plant fiber is mixed with the composite wet strength agent, the addition amount of the composite wet strength agent is (10 - 13) g of the composite wet strength agent added to every 100 g of the absolutely dry plant fiber.

[0032] In a second aspect, the present invention provides a preparation method of the halogen-free laminated board base paper described in the first aspect, and the preparation method comprises the following steps:

[0033] S2 - 1. Place softwood fiber, hardwood fiber, cotton fiber, and peanut shell fiber according to the ratio in a hydrapulper for mixing and pulping, obtain pulped slurry after pulping in the hydrapulper for 12 - 20 min, convey the pulped slurry to a stock pond, and then beat it in a way of connecting a defibrator and two refiners in series to control the beating degree of the pulped slurry at (20 - 23) °SR and the wet weight of the fiber at (1.0 - 1.5) g to obtain qualified slurry;

[0034] S2 - 2. Convey the qualified slurry to a sizing pond, add the composite wet strength agent thereto, and then perform sizing, wherein (10 - 13) g of the composite wet strength agent is added to every 100 g of the absolutely dry qualified slurry to obtain sized slurry;

[0035] S2-3. Next, the sized pulp is sent to a pressure screen for screening after passing through a first-stage three-stage purification system with good pulp countercurrent, dilution in a white water tower, and pumping by a filling pump to obtain the on-machine pulp; the on-machine pulp is formed into a wet paper web at the headbox of the wire section through a flow equalizing box and a headbox, obtaining a wet paper web; the wet paper web is pressed and dried to obtain the base paper, and the moisture content of the base paper is ≤10%.

[0036] S2-4. The composite flame retardant and the solvent are mixed at a material-liquid ratio of 1:5 g / mL to prepare an impregnating solution. The base paper is impregnated in the impregnating solution for 50 s, and then through extrusion, pressing, and drying, a halogen-free laminate base paper is obtained. The specification of the halogen-free laminate base paper is a thickness of 0.270 ± 0.02 mm and a basis weight of 140 g / m 2 ;

[0037] The solvent is a mixture of an ethanol aqueous solution with a concentration of 65 wt% and an acetone aqueous solution with a concentration of 60 wt% in a volume ratio of 1:1.

[0038] In a third aspect, the present invention provides the application of the halogen-free laminate base paper described in the first aspect or the second aspect in a copper clad laminate or a prepreg.

[0039] In the present invention:

[0040] The outer surface of the peanut shell fiber is relatively rough and contains a waxy layer, which promotes the overall water resistance and chemical resistance of the base paper. At the same time, the peanut shell fiber has a porous network structure, and the high lignin and low hemicellulose content cause the peanut shell fiber to aggregate in a tile-like structure. This structure enables it to improve the toughness and strength of the base paper and reduce its warpage degree after being compounded with hardwood fibers, softwood fibers, and cotton fibers in a specific ratio.

[0041] As a polymer containing primary amines, secondary amines, and tertiary amines and having a branched structure, polyethyleneimine resin has a high cation density. It forms hydrogen bonds with the hydroxyl groups on the fiber through cationic functional groups such as tertiary amines and primary amines, enhancing the wet strength of the paper. At the same time, JH-1225 wet strength agent is also a cationic polymer. After being compounded with polyethyleneimine resin in a specific ratio, it can significantly improve the wet strength and dry strength of the copper clad laminate base paper, and also improve the toughness and strength properties of the base paper.

[0042] Cardanol-modified phenolic resin has a higher char residue rate and better thermal stability compared to unmodified phenolic resin, and can improve the thermal stability of the substrate of copper clad laminate; ammonium polyphosphate, as an excellent non-halogen flame retardant, can generate phosphate, amino cyclide and carbon compounds during the combustion process when compounded with cardanol-modified phenolic resin. These products can form a continuous and dense protective layer, effectively preventing the exchange of heat and combustibles during the combustion process, achieving the purpose of flame retardancy; the research of the present invention finds that the compound use of cardanol-modified phenolic resin and ammonium polyphosphate produces a certain synergistic effect, which can further improve the flame retardancy and thermal stability of the substrate of copper clad laminate.

[0043] Advantages of the present invention:

[0044] The laminated board base paper provided by the present invention is prepared from plant fibers with a specific composition, a composite wet strength agent with a specific composition and a composite flame retardant with a specific composition. The plant fibers, the composite wet strength agent and the composite flame retardant form a rich and stable chemical cross-linking network, so that the laminated board base paper has excellent impregnation, flame retardancy, heat resistance, mechanical strength, flexibility and processability at the same time. Specific embodiments

[0045] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0046] The test methods used in the specific embodiments are all conventional methods unless otherwise specified; the materials, reagents, etc. used can be obtained from commercial channels unless otherwise specified; the percentages mentioned in the specific embodiments are all mass percentages unless otherwise specified.

[0047] In the present invention:

[0048] Plant fibers: including hardwood fibers, softwood fibers, cotton fibers and peanut shell fibers. Among them, the fiber length of hardwood fibers is 0.6 - 1.0 mm, the fiber length of softwood fibers is 3.1 - 3.5 mm, the fiber length of cotton fibers is 10 - 15 mm, and the fiber length of peanut shell fibers is 0.15 - 0.27 mm, purchased from Henan Huining Paper Co., Ltd.;

[0049] JH-1225 wet strength agent: model JH-1225, which is a water-soluble thermosetting resin, purchased from Qingzhou Jinhao New Materials Co., Ltd.;

[0050] Polyethyleneimine resin: model SP-003, purchased from Nippon Shokubai;

[0051] Cashew shell oil: containing ≥80 wt% cardanol, purchased from Shanghai Dayi Biological Materials Co., Ltd.;

[0052] Flame retardant: ammonium polyphosphate flame retardant, purchased from Hefei Wuran New Material Technology Co., Ltd.;

[0053] All other raw materials are commercially available.

[0054] Preparation of cardanol-modified phenolic resin:

[0055] S1. Put cardanol shell oil, phenol, and aqueous formaldehyde solution into the reaction kettle according to the mass ratio of 1:4:6, and stir for 1 h at a stirring speed of 500 r / min. Among them, the concentration of the aqueous formaldehyde solution is 30 wt%.

[0056] S2. Add aqueous hydrochloric acid solution to adjust the pH of the system to 2, heat the reaction kettle to 60 °C and react for 10 h to obtain a polymerization product, and let the obtained polymerization product flow into the dehydration kettle by itself. Among them, the concentration of the aqueous hydrochloric acid solution is ≥95 wt%.

[0057] S3. Heat the dehydration kettle to 130 °C, perform high-temperature dehydration on the polymerization product for 1 h, lower the temperature to 90 °C, and turn on the vacuum pump for vacuum dehydration to obtain cardanol-modified phenolic resin. Among them, the vacuum dehydration time is 6 h and the vacuum degree is 0.09 Mpa.

[0058] Preparation of composite wet strength agent:

[0059] Compound the JH-1225 wet strength agent and polyethyleneimine resin according to the mass ratio of 20:(5-7) and mix them evenly to obtain a composite wet strength agent.

[0060] Preparation of composite flame retardant:

[0061] Take an aqueous ethanol solution of 65 wt% and an aqueous acetone solution of 60 wt% and mix them according to the volume ratio of 1:1 to obtain a solvent. Take cardanol-modified phenolic resin and ammonium polyphosphate flame retardant according to the mass ratio of (2-3):1 and put them into the reaction kettle, add the solvent, and the material-liquid ratio is 1:5 g / mL. Mix and stir evenly at a rotation speed of 1000 r / min to obtain a composite flame retardant.

[0062] Preparation of halogen-free laminated board base paper:

[0063] 1. Preparation steps of the example

[0064] Step (1): Place softwood fiber, hardwood fiber, cotton fiber, and peanut shell fiber in a hydraulic pulper according to a mass ratio of 1:(1.5 - 2):(0.5 - 0.7):(0.2 - 0.5) for mixing and pulping. After pulping in the hydraulic pulper for 12 - 20 minutes, obtain pulped slurry. Transport the pulped slurry to a storage tank, and then beat it through a combination of a defiberizer and two refiners in series to control the freeness of the pulped slurry at (20 - 23)°SR and the wet weight of the fiber at (1.0 - 1.5) g to obtain qualified slurry.

[0065] Step (2): Transport the qualified slurry to a sizing tank, and add the above-prepared composite wet strength agent for sizing. Add (10 - 13) g of the composite wet strength agent to every 100 g of the qualified slurry (dry weight: the mass of the fiber after removing moisture) to obtain sized slurry.

[0066] Step (3): Then, send the sized slurry through a first-stage three-stage purification system with good pulp countercurrent, dilution in a white water tower, and pumping through a filling pump to a pressure screen for screening to obtain the on-machine stock. The on-machine stock passes through a headbox stabilizer and a headbox and forms a wet paper web at the wet paper forming section in front of the wire section. Press and dry the wet paper web to obtain the base paper, and the moisture content of the base paper is ≤10%.

[0067] Step (4): Use the above-prepared composite flame retardant as the impregnating solution. Immerse the base paper in the impregnating solution for 50 s, and then through extrusion, pressing, and drying, obtain a halogen-free laminate base paper. The specifications of the halogen-free laminate base paper are a thickness of 0.270 ± 0.02 mm and a basis weight of 140 g / m 2 。

[0068] 2. Corresponding parameters of specific examples

[0069] The specific parameters are shown in Table 1 below.

[0070] Table 1 Preparation parameters of Examples 1 - 4

[0071]

[0072]

[0073] 3. Preparation of comparative examples

[0074] To prove the necessity of the raw materials provided by the present invention, default or substitution comparative experiments are carried out. Based on Example 3, defaults or substitutions are made in the raw materials. The specific operations are as follows:

[0075] Comparative Example 1: Adjust the mass ratio of the plant fibers softwood fiber, hardwood fiber, and cotton fiber in Step (1) to 1:4:0.7 (conventional ratio on the market), lacking peanut shell fiber, and the rest is the same as in Example 3;

[0076] Comparative Example 2: Adjust the mass ratio of the plant fibers, i.e., softwood fibers, hardwood fibers, and cotton fibers, in step (1) to 1:1.8:0.6, lacking peanut shell fibers, and the rest is the same as in Example 3;

[0077] Comparative Example 3: Replace the polyethyleneimine resin in the composite wet strength agent in step (2) with polyurethane resin. The model of the polyurethane resin is PU-D201, purchased from Hefei Huayue New Material Technology Co., Ltd. The mass ratio of JH-1225 wet strength agent and polyurethane resin in the composite wet strength agent is 20:6, and the rest is the same as in Example 3;

[0078] Comparative Example 4: Replace the composite wet strength agent in step (2) with the sole use of JH-1225 wet strength agent, and the rest is the same as in Example 3;

[0079] Comparative Example 5: Replace the composite wet strength agent in step (2) with the sole use of polyethyleneimine resin, and the rest is the same as in Example 3;

[0080] Comparative Example 6: Adjust the mass ratio of JH-1225 wet strength agent and polyethyleneimine resin in the composite wet strength agent in step (2) to 20:3, and the rest is the same as in Example 3;

[0081] Comparative Example 7: Adjust the mass ratio of JH-1225 wet strength agent and polyethyleneimine resin in the composite wet strength agent in step (2) to 20:9, and the rest is the same as in Example 3;

[0082] Comparative Example 8: Replace the cardanol-modified phenolic resin in the composite flame retardant in step (4) with phenolic resin. The phenolic resin is purchased from Shandong Yonghui New Material Co., Ltd. The mass ratio of phenolic resin and ammonium polyphosphate flame retardant is 2.5:1, and the rest is the same as in Example 3;

[0083] Comparative Example 9: Adjust the mass ratio of cardanol-modified phenolic resin and ammonium polyphosphate flame retardant in the composite flame retardant in step (4) to 1:1, and the rest is the same as in Example 3;

[0084] Comparative Example 10: Adjust the mass ratio of cardanol-modified phenolic resin and ammonium polyphosphate flame retardant in the composite flame retardant in step (4) to 4:1, and the rest is the same as in Example 3;

[0085] Comparative Example 11: Replace the ammonium polyphosphate flame retardant in the composite flame retardant in step (4) with hexaphenoxycyclotriphosphazene flame retardant. The hexaphenoxycyclotriphosphazene flame retardant is purchased from Qingdao Zhenguang Functional Materials Technology Co., Ltd. The mass ratio of cardanol-modified phenolic resin and hexaphenoxycyclotriphosphazene flame retardant is 2.5:1, and the rest is the same as in Example 3.

[0086] Performance Test of Laminated Board Base Paper

[0087] The laminated board base paper prepared above is used as the core material to prepare a paper-based copper clad laminate for performance testing. The specific method is as follows:

[0088] (1) The laminated board base paper is impregnated with an adhesive to obtain a pre-impregnated body. The pre-impregnated body is heated in an oven at 130 °C for 4 minutes to obtain a semi-cured sheet. The semi-cured sheet is pressed at 0.7 ± 0.2 MPa for 6 minutes, and then cut into the required size to make a paper-based semi-cured sheet;

[0089] (2) Five paper-based semi-cured sheets and one coated copper foil prepared are stacked and pressed by a hot press to control the temperature and pressure. The hot press is pressed for 90 minutes. The pressing conditions are as follows: from 0 MPa to 4 MPa in the first 5 minutes, and then gradually from 4 MPa to 8.5 MPa. The hot pressing temperature is 127 °C to obtain a 1.6 mm thick paper-based copper clad laminate.

[0090] 1. First, the following performance tests are carried out on the laminated board base paper:

[0091] 1.1 Limiting oxygen index LOI test: According to the standard GB / T 2406, the combustibility of the laminated board base paper is tested. The larger the index, the less likely it is to burn;

[0092] 1.2 Wet strength: Conducted according to the standard GB / T 1040.2;

[0093] 1.3 Tensile strength: Conducted according to the standard GB / T 1040.2.

[0094] 2. Then, the following performance tests are carried out on the paper-based copper clad laminate:

[0095] 2.1 Flame retardancy: Tested according to the UL-94 standard;

[0096] 2.2 Thermal stress: Conducted according to the IPC-TM-650 2.4.13.1 method;

[0097] 2.3 Maximum bending deflection: Tested according to the IPC-TM-650 2.4.4 method;

[0098] 2.4 Maximum bending load: Tested according to the IPC-TM-650 2.4.4 method;

[0099] 2.5 Water absorption rate: Determined according to the IPC-TM-650 2.6.2.1 method;

[0100] 2.6 Impact strength: Tested according to the GB / T 1843-2008 method.

[0101] The test results are shown in Table 2 below:

[0102] Table 2 Performance Test Results

[0103]

[0104] Result Analysis:

[0105] According to the performance test data in Table 2, it can be seen that the laminated board base paper provided by the present invention can effectively enhance the performance of the copper clad laminate as the core material of the copper clad laminate. Through the selection and ratio of fiber slurries in the laminated board base paper, the compounding of compound wet strength agents and the compounding of compound flame retardants, the heat resistance and flame retardancy of the copper clad laminate can be significantly improved, making the flame retardancy reach V-0 level and the thermal stress at 288 °C reach more than 50 s. At the same time, the rigidity of the laminated board base paper decreases and the flexibility improves, making the impact strength of the bending deflection of the copper clad laminate prepared by using the laminated board base paper significantly increased. The maximum bending deflection of the copper clad laminate is 3.3 - 3.6 mm, the maximum bending load is 92 - 95 N, and the impact strength is 83 - 86 kJ / m 2 , and the deflection and load are significantly higher than those of the copper clad laminate of the comparative example, and it has a lower water absorption rate (0.057 - 0.060%).

[0106] The laminated board base paper provided by the present invention is prepared from plant fibers with a specific composition, wet strength agents with a specific composition, and flame retardants with a specific composition. The plant fibers, compound wet strength agents, and compound flame retardants form a rich and stable chemical cross-linking network, making the laminated board base paper have excellent impregnation, flame retardancy, heat resistance, mechanical strength, flexibility, and processability at the same time.

[0107] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that this is only an example. The protection scope of the present invention is defined by the appended claims. Without departing from the principles and essence of the present invention, those skilled in the art can make various changes or modifications to these embodiments, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A halogen-free laminate base paper, characterized in that: The raw materials for preparing the halogen-free laminate base paper include plant fiber, composite wet strength agent and composite flame retardant; The plant fibers include softwood fibers, hardwood fibers, cotton fibers, and peanut shell fibers; The composite wet strength agent is composed of JH-1225 wet strength agent and polyethyleneimine resin; The composite flame retardant is composed of cardanol-modified phenolic resin and ammonium polyphosphate flame retardant; The method for preparing the halogen-free laminate base paper comprises the following steps: S1-1. The plant fiber is mixed with a composite wet strength agent and slurried, formed on the net, to obtain base paper; S1-2. The base paper is impregnated in a composite flame retardant and then dried to obtain the halogen-free laminate base paper; The plant fiber comprises the following components by weight: 10 parts of coniferous wood fiber; 15-20 parts of hardwood fiber; 5-7 parts of cotton fiber; 2-5 servings of peanut shell fiber; The fiber length of the hardwood fiber is 0.6-1.0 mm, the fiber length of the softwood fiber is 3.1-3.5 mm, the fiber length of the cotton fiber is 10-15 mm, and the fiber length of the peanut shell fiber is 0.15-0.27 mm; The composite wet strength agent consists of the following components in parts by mass: JH-1225 wet strength agent 20 parts; 5-7 parts of polyethyleneimine resin; The composite flame retardant is composed of the following components by mass: 20-30 parts of cardanol modified phenolic resin; 10 parts of ammonium polyphosphate flame retardant; The preparation method of the cardanol-modified phenolic resin comprises the following steps: S1. Cashew nut shell liquid, phenol and formaldehyde aqueous solution were put into a reactor in a mass ratio of 1:4:6 and stirred at a stirring speed of 500 r / min for 1 h, wherein the concentration of the formaldehyde aqueous solution was 30wt%; S2. Add hydrochloric acid aqueous solution to adjust the system pH to 2, heat the reactor to 60°C and react for 10 hours to obtain a polymer product, and flow the obtained polymer product to a dehydration reactor, wherein the concentration of the hydrochloric acid aqueous solution is ≥95wt%; S3. The dehydration kettle was heated to 130 ° C, the polymer product was dehydrated at high temperature for 1 h, the temperature was reduced to 90 ° C, and the vacuum pump was turned on for vacuum dehydration to obtain a cardanol-modified phenolic resin, wherein the vacuum dehydration time was 6 h and the vacuum degree was 0.09 MPa; When the plant fiber is mixed with the composite wet strength agent, the added amount of the composite wet strength agent is (10-13) g of the composite wet strength agent per 100 g of absolute dry weight of the plant fiber.

2. The halogen-free laminate base paper according to claim 1, characterized in that: The cashew nut shell oil contains ≥80wt% of cardanol.

3. The method for preparing the halogen-free laminate base paper according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: S2-1. Place coniferous wood fiber, hardwood wood fiber, cotton fiber and peanut shell fiber in a hydraulic pulper according to a certain ratio for mixing and crushing, obtain crushed pulp after crushing in the hydraulic pulper for 12-20 minutes, transport the crushed pulp to a pulp storage tank, and then beat it in a series of a deflaker and two disc refiners to control the beating degree of the crushed pulp to (20-23)°SR and the fiber wet weight to (1.0-1.5)g, thereby obtaining qualified pulp; S2-2. The qualified slurry is transported to a slurry mixing tank, and the composite wet strength agent is added thereto, and then the slurry is mixed, wherein (10-13) g of the composite wet strength agent is added to every 100 g of the absolute dry amount of the qualified slurry to obtain a modulated slurry; S2-3. The pulp after pulping is sent to the pressure screen for screening after passing through the first-stage three-stage purification system of good pulp countercurrent, dilution in the white water tower and pulp flushing by the pulp flushing pump to obtain the pulp on the screen; the pulp on the screen is formed into wet paper at the screen part of the front box through the stabilizing box and the head box to obtain the wet paper web; the wet paper web is pressed and dried to obtain the base paper, and the moisture content of the base paper is ≤10%; S2-4. The composite flame retardant and the solvent are mixed at a material-liquid ratio of 1:5 g / mL to prepare an impregnation solution, the base paper is immersed in the impregnation solution for 50 seconds, and then extruded, pressed and dried to obtain a halogen-free laminate base paper, the halogen-free laminate base paper having a thickness of 0.270 ± 0.02 mm and a basis weight of 140 g / m 2 ; The solvent is a mixture of 65 wt % ethanol aqueous solution and 60 wt % acetone aqueous solution in a volume ratio of 1:

1.

4. Use of the halogen-free laminate base paper according to claim 1 or 2 in copper-clad laminates or prepregs.

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