A paper waterproof and oil-proof emulsion and a preparation method thereof

Abstract

The present application relates to papermaking chemicals technical field, disclose a kind of paper waterproof and oil-proof emulsion and its preparation method, preparation method includes: with rosin and hydroxyethyl acrylate esterification preparation rosin acid acrylate monomer;With linseed oil and maleic anhydride reaction preparation maleated linseed oil;In anhydrous ethanol medium with maleated linseed oil and cardanol double-layer modification sepiolite and attapulgite;With rosin acid acrylate monomer and acrylate monomer emulsion copolymerization;Double-layer modified mineral is introduced and glycerol borate crosslinking agent is added, adjust pH, obtain waterproof and oil-proof emulsion.The present application uses bio-based rosin, linseed oil and cardanol as core raw material, coating film is continuously oxidized and solidified after making protective performance continuously enhanced, double-layer modified mineral systematically inhibits interface microcrack initiation, borate dynamic crosslinking gives coating self-repairing ability, and waterproof and oil-proof performance is excellent and long-acting durable.

Description

Technical Field

[0001] This invention relates to the field of papermaking chemicals, and more specifically, to a paper waterproof and oil-resistant emulsion and its preparation method. Background Technology

[0002] Waterproof and oil-repellent emulsions for paper are widely used in food packaging paper, catering paper, and industrial protective paper. Their protective performance directly determines the paper's barrier effect against moisture and grease. Existing waterproof and oil-repellent emulsions mainly fall into two technical categories: the first is a fluorinated system, using perfluorinated or long-chain fluorocarbon compounds as active functional components. While offering excellent oil-repellent properties, these compounds are persistent organic pollutants with bioaccumulation potential, and many countries and regions, including the EU and the US, have successively restricted their use in food contact materials. The second category is petroleum-based acrylate synthetic resin emulsions, which have low bio-based content and poor renewability. Furthermore, the oil-repellent performance of this type of coating mainly relies on the physical barrier of the polymer matrix after film formation, resulting in limited cross-linking density and a decline in protective performance over time. To further improve the barrier performance of the coating, the industry incorporates fibrous minerals such as sepiolite and attapulgite into the emulsion to construct an inorganic barrier.

[0003] However, there is a problem of insufficient interfacial compatibility between inorganic mineral fibers and organic polymer matrices: during the drying and film formation of the coating, the organic polymer matrix shrinks due to moisture evaporation, while the rigid inorganic mineral fibers do not shrink with the matrix. This difference in shrinkage causes interfacial tearing stress concentration at the ends of the mineral fibers. Under repeated humid-heat-drying cycles, the interfacial stress accumulates, leading to the initiation of microcracks at the fiber ends and their extension into the matrix, eventually forming through-hole penetration channels that allow grease and moisture to penetrate the coating, accelerating the failure of the barrier effect. In addition, existing mineral fiber modification usually relies on physical mixing or surfactant coating, resulting in a lack of covalent bonds between the mineral fibers and the organic polymer network. In humid and hot environments, the mineral fibers are prone to detaching from the matrix, leading to instability of the barrier structure and accelerated failure of the coating's protective performance. Summary of the Invention

[0004] This invention provides a paper waterproof and oil-resistant emulsion and its preparation method to solve the technical problems in related technologies, such as excessive reliance on fluorinated raw materials or petroleum-based synthetic resins, low bio-based content, insufficient crosslinking density after coating film formation leading to degradation of protective performance over time, insufficient interfacial compatibility between inorganic mineral fibers and organic polymer matrix leading to the initiation of microcracks at the ends of mineral fibers causing barrier structure failure, and the inability of the coating to spontaneously recover after local damage.

[0005] This invention provides a method for preparing a paper waterproof and oil-resistant emulsion, comprising the following steps: (1) Rosin and hydroxyethyl acrylate are refluxed at 110-120°C for 4-6 hours under acid catalysis at a carboxyl to hydroxyl molar ratio of 1:1 to obtain rosin acid acrylate monomer. (2) Flaxseed oil and maleic anhydride are reacted in a closed reflux apparatus at 220°C for 3-4 hours at a mass ratio of (4-6):1 to obtain maleicized flaxseed oil; (3) Mix sepiolite and attapulgite in a mass ratio of (3-5):1, add 10-20% of the total mineral mass of maleic linseed oil in anhydrous ethanol medium, covalently esterify and graft at 70-78℃ for 2 hours, then add 5-10% of the total mineral mass of cardanol, stir and adsorb at room temperature for 1 hour, and dry at low temperature to obtain cardanol / maleic linseed oil double-layer modified mineral. (4) Prepare a mixed monomer by mixing rosin acid acrylate monomer, butyl acrylate and hydroxyethyl acrylate in a mass ratio of (20-30): (60-70): (5-10), and carry out emulsion free radical copolymerization with composite emulsifier and ammonium persulfate at 70-85℃ to obtain a copolymer emulsion; (5) After dispersing the double-layer modified mineral in water, add the copolymer emulsion. The amount of mineral is 10-20% of the solid content of the copolymer emulsion. Add the glycerol borate ester crosslinking agent. The amount is 2-5% of the solid content of the emulsion. Adjust the pH to 6.5-7.5 to obtain a paper waterproof and oil-proof emulsion.

[0006] Preferably, in step (1), p-toluenesulfonic acid is used as a catalyst, with an amount of 0.5-1.0% of the total mass of the reactants; p-methoxyphenol is used as a polymerization inhibitor, with an amount of 0.1-0.3% of the total mass of the reactants; and toluene is used as an aqueous solvent. After the reaction is completed, the organic phase is washed with saturated sodium carbonate aqueous solution until the pH is neutral, dried with anhydrous sodium sulfate and filtered, and toluene is removed by vacuum distillation to obtain rosin acid acrylate monomer.

[0007] Preferably, in step (2), the closed reflux device is equipped with a reflux condenser to condense and reflux the maleic anhydride vapor volatilized in the reaction system back into the reaction system, ensuring that the amount of maleic anhydride actually participating in the reaction is consistent with the feed ratio; step (2) is carried out under nitrogen protection.

[0008] Preferably, in step (3), covalent esterification grafting is carried out in anhydrous ethanol medium. The anhydride groups of maleic linseed oil undergo esterification ring-opening reaction with the silanol groups on the surface of mineral fibers under anhydrous conditions. One end of the ester bond is covalently connected to the silicon oxygen atoms on the mineral surface, and the other end retains a free carboxyl group, thereby anchoring the polyunsaturated fatty acid segments of maleic linseed oil to the surface of mineral fibers by covalent ester bonds.

[0009] Preferably, the cardanol used in step (3) is an industrial-grade decarboxylated distilled cashew shell liquid product with a cardanol content of not less than 85%, and the main components are phenol homologues containing phenolic hydroxyl groups and C15 unsaturated alkyl side chains; the phenolic hydroxyl groups of cardanol form hydrogen bonds with the residual silanol groups on the surface of mineral fibers, and the C15 unsaturated alkyl side chains form a flexible organic coating layer on the outside of the maleic linseed oil covalent graft layer, which absorbs and dissipates the interfacial tearing stress at the ends of mineral fibers when the coating shrinks during film formation.

[0010] Preferably, the low-temperature drying temperature in step (3) is below 60°C, which preserves the integrity of the unsaturated double bonds on the grafted segments of flaxseed oil and the C15 side chain of cardanol, so that the coating can continue to undergo oxidation, curing and crosslinking in the air after film formation.

[0011] Preferably, in step (4), the composite emulsifier is a mixture of sodium dodecyl sulfate and fatty alcohol polyoxyethylene ether in a mass ratio of 1:1, and the amount used is 2 to 4% of the total mass of the mixed monomers; the amount of ammonium persulfate is 0.3 to 0.8% of the total mass of the mixed monomers; the monomer emulsion is added dropwise in a semi-continuous manner for copolymerization to obtain a copolymer emulsion with a solid content of 40 to 50%.

[0012] Preferably: In step (5), when the bilayer modified mineral is dispersed in deionized water, the pH of the dispersion is adjusted to 7.0-8.0 with ammonia water so that the free carboxyl groups on the surface of the mineral fibers are ionized into carboxylate ions, giving the surface of the mineral fibers a negative charge. After the mineral fibers are uniformly dispersed in water by electrostatic repulsion, the mineral dispersion is added to the copolymer emulsion.

[0013] Preferably, in step (5), the glycerol borate ester is formed by the primary hydroxyl groups (1,3-diol) at the C1 and C3 positions of glycerol and boric acid to form a six-membered ring borate ester structure. Its BOC bond has reversible dissociation and recombination characteristics under neutral conditions at room temperature. When the coating is formed, the borate ester group forms an initial dynamic crosslinking network with the free hydroxyl groups of the copolymer side chain and the phenolic hydroxyl groups of cardanol. After the film is formed, the newly generated hydroxyl groups produced by the oxidative crosslinking of the unsaturated double bonds of maleic linseed oil and cardanol further form BOC crosslinks with the remaining borate ester groups. The crosslinking density of the coating continues to increase after the film is formed. When the local BOC bond breaks, the free borate ester group and the adjacent free hydroxyl group reform BOC bonds at room temperature, giving the coating self-healing ability.

[0014] The present invention also provides a paper waterproof and oil-resistant emulsion, which is prepared by the above preparation method.

[0015] The beneficial effects of this invention are as follows: (1) The protective performance of the coating is continuously enhanced after film formation: the polyunsaturated fatty acid segments and the C15 unsaturated side chain of cardanol in the Malaysian linseed oil continue to be oxidized, cured and crosslinked after film formation. The crosslinking density of the coating continues to increase over time, and the protective performance has the characteristics of "film formation first, followed by continuous densification", which is fundamentally different from the existing acrylic emulsions' characteristics of "film formation and shaping". (2) Systematically eliminate microcracks at the ends of mineral fibers: the flexible organic layer of cardanol absorbs and dissipates shrinkage stress at the interface level, the covalent ester bond of flaxseed oil anchors the mineral fibers to the cross-linked network of organic polymers at the bonding level, and the short rods of attapulgite release macroscopic stress by micro-displacement in the fiber gaps at the structural level. The three work together at different levels to systematically inhibit the initiation and expansion of microcracks at the ends of mineral fibers during film shrinkage and repeated wet and hot cycles. (3) Long-term stability of inorganic mineral barrier structure: The dual interface binding mode of covalent ester bond anchoring of flaxseed oil and hydrogen bond adsorption of cardanol and subsequent covalent incorporation enables the mineral fiber to maintain stable binding with the organic matrix during repeated humid heat cycles, effectively solving the problem that existing minerals rely solely on physical encapsulation and are prone to debonding under humid heat conditions. (4) The binary mineral system forms an efficient barrier network: the binary combination of sepiolite long fibers and attapulgite short rods forms a dense three-dimensional barrier network in the coating with long rods / short rods filling each other, which significantly extends the penetration path of oils and water compared with the single mineral system. (5) The dynamic cross-linking network of borate esters endows the coating with self-healing ability: The dynamic reversible cross-linking network of borate esters (BOC) increases the overall cross-linking density of the coating and endows the coating with the ability to achieve a certain degree of self-healing through spontaneous recombination of BOC bonds after local damage, effectively delaying the overall degradation of protective performance. (6) High bio-based content, green and renewable: The three core functional raw materials, rosin acid (derived from pine resin), linseed oil (derived from flax plants), and cardanol (derived from cashew shell liquid), are all derived from renewable plant resources, which greatly reduces the dependence on fluorinated compounds and petroleum-based synthetic resins, and conforms to the trend of green and sustainable development of food contact materials.

[0016] In summary, this invention enhances the density of the polymer matrix through the rigid framework of rosin acid polycyclic terpenes, continuously increases the crosslinking density of the coating through the oxidative curing of maleic linseed oil after film formation, and synergistically inhibits the initiation of microcracks at the ends of inorganic mineral fibers by the covalent anchoring of maleic linseed oil and the flexible organic layer of cardanol. The binary mineral network of sepiolite and attapulgite strengthens the barrier, and the dynamic crosslinking of borate esters endows the coating with self-healing ability, significantly improving the protection level and long-term durability of the paper waterproof and oil-proof coating. Attached Figure Description

[0017] Figure 1This is a comparison chart of the Kit values ​​of S1 and SE coatings under different placement times in Experiment 1 of this invention; Figure 2 This is a comparison chart of the water contact angle (WCA) of S1 and SE coatings under different placement times in Experiment 1 of this invention; Figure 3 This refers to the Cobb coatings S1 and SE under different placement times in Experiment 1 of this invention. 60 A comparison chart of values ​​changing over time; Figure 4 This is a comparison chart of the crack density of each sample after 5 cycles of wet heat and drying in Experiment 2 of this invention; Figure 5 This is a comparison chart of the maximum crack width of each sample after 5 cycles of wet heat and drying in Experiment 2 of this invention; Figure 6 This is a comparison chart of the oil resistance rating (Kit value) of each sample after 5 cycles of wet heat-drying in Experiment 2 of this invention; Figure 7 This refers to the water contact angle (WCA) after the S1 and SD coatings were scratched in Experiment 3 of this invention. Figure 8 This is a comparison graph showing the change of WCA recovery rate over time after scratching of S1 and SD coatings in Experiment 3 of this invention. Detailed Implementation

[0018] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples. Example

[0019] This embodiment discloses a method for preparing a waterproof and oil-resistant paper emulsion, which includes the following steps: Step (1) Weigh 300 g of rosin (acid value 165 mg KOH / g) and 102 g of hydroxyethyl acrylate (the molar ratio of carboxyl and hydroxyl groups in both is 1:1, and the mass ratio of rosin to hydroxyethyl acrylate is 2.94:1). Add 3.2 g of p-toluenesulfonic acid (0.8% of the total mass of 402 g of reactants), 0.8 g of p-methoxyphenol (0.2%), and 161 g of toluene (40%). Equip the mixture with a water separator and a reflux condenser, and reflux the esterification reaction at 115℃ for 5 hours. Continuously separate the generated water using the water separator. Cool to room temperature, wash the organic phase twice with saturated sodium carbonate aqueous solution, and then wash with deionized water until the pH of the washing solution is neutral. Dry the organic phase with anhydrous sodium sulfate and filter. Remove toluene by vacuum distillation to obtain rosin acid acrylate monomer (RHA monomer).

[0020] Step (2) Mix 500 g of linseed oil with 100 g of maleic anhydride (mass ratio 5:1) evenly, heat to 220°C in a nitrogen-protected sealed device (equipped with a reflux condenser), react at a constant temperature for 3.5 hours, and cool to room temperature to obtain maleic linseed oil (MLO).

[0021] Step (3) Add 400 g of sepiolite and 100 g of attapulgite (mass ratio 4:1, total 500 g) to anhydrous ethanol, disperse with ultrasonication at 300 W for 20 minutes, add 75 g of MLO (15% of the total mineral mass), heat and stir at 75℃ for 2 hours to complete the covalent esterification grafting of MLO onto the mineral surface; add 35 g of cardanol (industrial grade decarboxylated distilled cashew nut shell liquid product, cardanol content ≥85%, accounting for 7% of the total mineral mass) to the above ethanol dispersion, stir at room temperature for 1 hour, filter, wash with a small amount of anhydrous ethanol to remove unadsorbed free cardanol, dry at 55℃ to obtain cardanol / MLO bilayer modified mineral.

[0022] Step (4) Prepare a mixed monomer mixture (mass ratio 25:65:10, total 1000 g) by mixing 250 g of RHA monomer, 650 g of butyl acrylate, and 100 g of hydroxyethyl acrylate obtained in step (1). Use 15 g of sodium dodecyl sulfate and 15 g of fatty alcohol polyoxyethylene ether (AEO-9) (1:1 compound, total 30 g, accounting for 3.0% of the total monomer mass) as a composite emulsifier, and use 5 g of ammonium persulfate. g (0.5%) was used as the initiator. An appropriate amount of deionized water was added to make the final solid content of the system 45%. Copolymerization was carried out at 80℃ using the following semi-continuous process: 1 / 3 of the composite emulsifier was dissolved in an appropriate amount of deionized water. After heating to 80℃, 1 / 3 of the ammonium persulfate and 5% of the total monomer were added. The mixture was kept at this temperature for 15 minutes to prepare a seed emulsion. The remaining monomer was pre-emulsified with 1 / 3 of the composite emulsifier and an appropriate amount of deionized water. The pre-emulsion was then added dropwise with 1 / 3 of the ammonium persulfate aqueous solution, and the dropwise addition time was controlled to be 3.5 hours. After the dropwise addition was completed, the remaining 1 / 3 of the ammonium persulfate was added. The mixture was kept at 80℃ for 1 hour, cooled, and the pH was adjusted to 7.5 with ammonia water. The mixture was then filtered to obtain a copolymer emulsion with a solid content of 45%.

[0023] Step (5): Based on the solid content of the above copolymer emulsion of 1000 g, disperse 150 g of cardanol / MLO bilayer modified mineral in 600 g of deionized water (solid content 20%), adjust the pH to 7.5 with ammonia, and ultrasonically disperse at 300 W for 15 minutes; add the entire mineral dispersion to the copolymer emulsion (mineral amount is 15% of the emulsion solid content), and stir at 400 rpm for 30 minutes; add 30 g of glyceryl borate ester (3.0% of the emulsion solid content), adjust the pH to 7.0 with ammonia, and stir at 300 rpm for 20 minutes to obtain a paper waterproof and oil-proof emulsion. Example

[0024] This embodiment discloses a method for preparing a waterproof and oil-resistant paper emulsion. Compared with Embodiment 1, this method uses lower parameter values ​​for each step, and includes the following steps: Step (1) Weigh 300 g of rosin (acid value 175 mg KOH / g) and 109 g of hydroxyethyl acrylate (carboxyl to hydroxyl molar ratio 1:1, mass ratio 2.75:1), add 2.0 g of p-toluenesulfonic acid (0.5% of the total mass of 409 g of reactants), 0.4 g of p-methoxyphenol (0.1%), and 123 g of toluene (30%). Equip with a water separator and a reflux condenser, and reflux esterify at 110℃ for 4 hours. Wash the organic phase with saturated sodium carbonate aqueous solution until neutral, dry with anhydrous sodium sulfate, filter, and remove toluene by vacuum distillation to obtain RHA monomer.

[0025] Step (2) 400 g of linseed oil and 100 g of maleic anhydride (mass ratio 4:1) were reacted at 220°C for 3 hours in a nitrogen-protected closed reflux apparatus, and then cooled to obtain MLO.

[0026] Step (3) 300 g of sepiolite and 100 g of attapulgite (mass ratio 3:1, total 400 g) were added to anhydrous ethanol and ultrasonically dispersed at 300 W for 15 minutes. 40 g of MLO (10% of the total mineral mass) was added and stirred at 70℃ for 2 hours. 20 g of cardanol (industrial grade decarboxylated distilled cashew nut shell liquid product, cardanol content ≥85%, accounting for 5% of the total mineral mass) was added and stirred at room temperature for 1 hour. The mixture was filtered, washed with a small amount of anhydrous ethanol, and dried at 50℃ to obtain a double-layer modified mineral.

[0027] Step (4) 200 g of RHA monomer, 700 g of butyl acrylate, and 100 g of hydroxyethyl acrylate (mass ratio 20:70:10, total 1000 g); composite emulsifier: 10 g of sodium dodecyl sulfate and 10 g of AEO-9 (total 20 g, 2.0%); 3 g of ammonium persulfate (0.3%); final solid content of the system: 40%; copolymerize at 70℃ using a semi-continuous process: dissolve 1 / 3 of the emulsifier in an appropriate amount of water, add 1 / 3 of the ammonium persulfate and 5% of the monomer at 70℃, and keep warm for 15 minutes to prepare a seed emulsion; pre-emulsify the remaining monomer with 1 / 3 of the emulsifier and an appropriate amount of water, and add dropwise with 1 / 3 of the ammonium persulfate aqueous solution for 3 hours; add the remaining 1 / 3 of the ammonium persulfate, keep warm at 70℃ for 1 hour, cool, adjust pH to 7.5 with ammonia water to obtain a copolymer emulsion with a solid content of 40%.

[0028] Step (5) Based on a copolymer emulsion solid content of 1000 g, disperse 100 g of the bilayer modified mineral in 567 g of deionized water (solid content 15%), adjust the pH to 7.0 with ammonia, and ultrasonically disperse for 15 minutes at 300 W; add the mineral dispersion to the copolymer emulsion (mineral amount is 10% of the emulsion solid content), and stir for 30 minutes; add 20 g of glyceryl borate ester (2.0%), adjust the pH to 6.5 with ammonia, and stir evenly to obtain a waterproof and oil-resistant emulsion. Example

[0029] This embodiment discloses a method for preparing a waterproof and oil-resistant emulsion for paper. Compared with Embodiment 1, this method uses higher parameter values ​​for each step, including the following steps: Step (1) Weigh 300 g of rosin (acid value 185 mg KOH / g) and 115 g of hydroxyethyl acrylate (carboxyl to hydroxyl molar ratio 1:1, mass ratio 2.61:1), add 4.15 g of p-toluenesulfonic acid (1.0% of the total mass of 415 g of reactants), 1.25 g of p-methoxyphenol (0.3%), and 207.5 g of toluene (50%). Esterify the mixture under reflux at 120 °C for 6 hours with a water separator and reflux condenser. Wash the organic phase with saturated sodium carbonate aqueous solution until neutral, dry with anhydrous sodium sulfate, filter, and remove toluene by vacuum distillation to obtain RHA monomer.

[0030] Step (2) 600 g of linseed oil and 100 g of maleic anhydride (mass ratio 6:1) were reacted at 220°C for 4 hours in a nitrogen-protected closed reflux apparatus, and then cooled to obtain MLO.

[0031] Step (3) 500 g of sepiolite and 100 g of attapulgite (mass ratio 5:1, total 600 g) were added to anhydrous ethanol and ultrasonically dispersed at 500 W for 30 minutes. 120 g of MLO (20% of the total mineral mass) was added and stirred at 78°C for 2 hours. 60 g of cardanol (industrial grade decarboxylated distilled cashew nut shell liquid product, cardanol content ≥85%, accounting for 10% of the total mineral mass) was added and stirred at room temperature for 1 hour. The mixture was filtered, washed with a small amount of anhydrous ethanol, and dried at 58°C to obtain a double-layer modified mineral.

[0032] Step (4) 300 g of RHA monomer, 650 g of butyl acrylate, and 50 g of hydroxyethyl acrylate (mass ratio 30:65:5, total 1000 g); composite emulsifier: 20 g of sodium dodecyl sulfate and 20 g of AEO-9 (total 40 g, 4.0%); 8 g of ammonium persulfate (0.8%); final solid content of the system: 50%; copolymerize at 85℃ using a semi-continuous process: dissolve 1 / 3 of the emulsifier in an appropriate amount of water, add 1 / 3 of the ammonium persulfate and 5% of the monomer at 85℃, keep warm for 15 minutes to prepare a seed emulsion; pre-emulsify the remaining monomer with 1 / 3 of the emulsifier and an appropriate amount of water, and add dropwise with 1 / 3 of the ammonium persulfate aqueous solution for 4 hours; add the remaining 1 / 3 of the ammonium persulfate, keep warm at 85℃ for 1 hour, cool, adjust pH to 7.5 with ammonia water to obtain a copolymer emulsion with a solid content of 50%.

[0033] Step (5) Based on a copolymer emulsion solid content of 1000 g, disperse 200 g of bilayer modified minerals in 800 g of deionized water (solid content 20%), adjust the pH to 8.0 with ammonia, and ultrasonically disperse for 20 minutes at 500 W; add the mineral dispersion to the copolymer emulsion (mineral amount is 20% of the emulsion solid content), and stir for 30 minutes; add 50 g (5.0%) of glyceryl borate, adjust the pH to 7.5 with ammonia, and stir evenly to obtain a waterproof and oil-proof emulsion. Example

[0034] This embodiment discloses a method for preparing a waterproof and oil-resistant paper emulsion. The method uses a combination of medium and high-value mixed parameters and includes the following steps: Step (1) Weigh 300 g of rosin (acid value 170 mg KOH / g) and 106 g of hydroxyethyl acrylate (carboxyl to hydroxyl molar ratio 1:1, mass ratio 2.83:1), add 3.2 g of p-toluenesulfonic acid (0.8% of the total mass of 406 g of reactants), 0.8 g of p-methoxyphenol (0.2%), and 162 g of toluene (40%). Esterify the mixture under reflux at 115 °C for 5 hours with a water separator and reflux condenser. Wash the organic phase with saturated sodium carbonate aqueous solution until neutral, dry with anhydrous sodium sulfate, filter, and remove toluene by vacuum distillation to obtain RHA monomer.

[0035] Step (2) 450 g of linseed oil and 100 g of maleic anhydride (mass ratio 4.5:1) were reacted at 220°C for 3 hours in a nitrogen-protected closed reflux apparatus, and then cooled to obtain MLO.

[0036] Step (3) 450 g of sepiolite and 100 g of attapulgite (mass ratio 4.5:1, total 550 g) were added to anhydrous ethanol and ultrasonically dispersed at 400 W for 20 minutes. 66 g of MLO (12% of the total mineral mass) was added and stirred at 73°C for 2 hours. 44 g of cardanol (industrial grade decarboxylated distilled cashew nut shell liquid product, cardanol content ≥85%, accounting for 8% of the total mineral mass) was added and stirred at room temperature for 1 hour. The mixture was filtered, washed with a small amount of anhydrous ethanol, and dried at 55°C to obtain a double-layer modified mineral.

[0037] Step (4) 250 g of RHA monomer, 680 g of butyl acrylate, and 70 g of hydroxyethyl acrylate (mass ratio 25:68:7, total 1000 g); composite emulsifier: 17.5 g of sodium dodecyl sulfate and 17.5 g of AEO-9 (total 35 g, 3.5%); 6 g of ammonium persulfate (0.6%); final solid content of the system: 45%; copolymerization at 75℃ using a semi-continuous process: dissolve 1 / 3 of the emulsifier in an appropriate amount of water, add 1 / 3 of the ammonium persulfate and 5% of the monomer at 75℃, and keep warm for 15 minutes to prepare a seed emulsion; pre-emulsify the remaining monomer with 1 / 3 of the emulsifier and an appropriate amount of water, and add dropwise with 1 / 3 of the ammonium persulfate aqueous solution for 3.5 hours; add the remaining 1 / 3 of the ammonium persulfate, keep warm at 75℃ for 1 hour, cool, adjust pH to 7.5 with ammonia water, and obtain a copolymer emulsion with a solid content of 45%.

[0038] Step (5) Based on a copolymer emulsion solid content of 1000 g, disperse 120 g of bilayer modified minerals in 480 g of deionized water (solid content 20%), adjust the pH to 7.5 with ammonia, and ultrasonically disperse for 15 minutes at 400 W; add the mineral dispersion to the copolymer emulsion (mineral amount is 12% of the emulsion solid content), and stir for 30 minutes; add 35 g (3.5%) of glyceryl borate, adjust the pH to 7.0 with ammonia, and stir evenly to obtain a waterproof and oil-proof emulsion. Example

[0039] This embodiment discloses a method for preparing a waterproof and oil-resistant paper emulsion, which includes the following steps: Step (1) Preparation of rosin acid acrylate monomer Rosin (acid value 165 mg KOH / g) and hydroxyethyl acrylate (HEA) were metered at a 1:1 molar ratio of carboxyl to hydroxyl groups (the mass ratio of rosin to hydroxyethyl acrylate was approximately 2.8:1). Toluenesulfonic acid was used as a catalyst (0.8% of the total reactant mass), p-methoxyphenol (MEHQ) as a polymerization inhibitor (0.2% of the total reactant mass), and toluene as a water-removing solvent (40% of the total reactant mass). The reaction was carried out under reflux at 115°C for 5 hours, equipped with a water separator and a reflux condenser. Water generated during the reaction was continuously separated using the water separator. After the reaction, the mixture was cooled to room temperature, and the organic phase was washed with a saturated sodium carbonate aqueous solution until the pH of the washing liquid was neutral. The organic phase was dried over anhydrous sodium sulfate, filtered, and toluene was removed by vacuum distillation to obtain rosin acid acrylate monomer (RHA monomer).

[0040] Step (2) Preparation of Malayan Flaxseed Oil (MLO) Linseed oil and maleic anhydride were mixed evenly at a mass ratio of 5:1 and heated to 220°C in a closed reaction apparatus (equipped with a reflux condenser) under nitrogen protection, and reacted at a constant temperature for 3.5 hours. During the reaction, linolenic acid in linseed oil underwent thermal isomerization at high temperature, partially converting into conjugated linolenic acid containing a conjugated diene structure. The conjugated diene structure then reacted with maleic anhydride via a Diels-Alder cycloaddition reaction, attaching maleic anhydride to the linolenic acid chain segment, so that the linseed oil chain segment carries the active anhydride group. After the reaction was completed, the mixture was cooled to room temperature to obtain maleic linseed oil (MLO).

[0041] Step (3) Preparation of Cardanol / MLO bilayer modified mineral Sepiolite and attapulgite were weighed and mixed at a mass ratio of 4:1, and then added to anhydrous ethanol and ultrasonically dispersed at 300 W for 20 minutes. MLO was added at 15% of the total mineral mass, and the mixture was heated and stirred at 75°C for 2 hours. In anhydrous ethanol medium, the anhydride groups of MLO and the exposed silanol groups (Si-OH) on the surface of the mineral fibers underwent an esterification ring-opening reaction, and the polyunsaturated fatty acid segments of MLO were grafted onto the surface of the mineral fibers by covalent ester bonds to obtain MLO-grafted minerals. In the ethanol dispersion of the above-mentioned MLO-grafted minerals, cardanol (industrial-grade decarboxylated distilled cashew nut shell liquid product, cardanol content ≥85%, main components are C15 unsaturated alkylphenol homologues such as 3-(8Z,11Z,14Z-pentadecatrienyl)phenol) was added at 7% of the total mineral mass. The mixture was stirred at room temperature for 1 hour to allow the phenolic hydroxyl groups of cardanol to form hydrogen bonds with the residual silanol (-Si-OH) on the surface of the mineral fibers and the free carboxyl groups (-COOH) in the MLO grafted segments. The hydrophobic C15 long carbon chain side chains of cardanol covered the surface of the mineral fibers, forming a cardanol flexible organic layer on the outside of the MLO covalent graft layer. The mixture was filtered, washed with a small amount of anhydrous ethanol to remove unadsorbed free cardanol, and dried at low temperature at 55°C to obtain the cardanol / MLO bilayer modified mineral.

[0042] Step (4) Preparation of copolymer emulsion The RHA monomer obtained in step (1), butyl acrylate (BA), and hydroxyethyl acrylate (HEA) were mixed in a mass ratio of 25:65:10 to prepare a mixed monomer; sodium dodecyl sulfate (SDS) and fatty alcohol polyoxyethylene ether (AEO-9) were compounded in a mass ratio of 1:1 as a composite emulsifier (3% of the total monomer mass), and ammonium persulfate (APS) was used as an initiator (0.5% of the total monomer mass). Copolymerization was carried out at 80°C according to the following semi-continuous emulsion free radical polymerization process: 1 / 3 of the composite emulsifier was dissolved in deionized water (the amount of deionized water was made up to 1 / 3 of the total monomer mass). The final solid content of the system is 45%. After heating to 80℃, 1 / 3 of the APS and 5% of the total monomer are added, and the mixture is kept at this temperature for 15 minutes to prepare a seed emulsion. The remaining mixed monomers, the remaining composite emulsifier, and an appropriate amount of deionized water are mixed and pre-emulsified evenly. The pre-emulsified monomer emulsion and 1 / 3 of the APS aqueous solution are simultaneously and continuously added dropwise to the seed emulsion, with the addition time controlled at 3.5 hours. After the addition is completed, the remaining 1 / 3 of the APS is added to initiate the process, and the mixture is kept at 80℃ for 1 hour. After cooling to room temperature, the pH is adjusted to 7.5 with ammonia water, and the mixture is filtered to obtain a copolymer emulsion with a solid content of 45%.

[0043] Step (5) Add glycerol borate ester crosslinking agent to obtain waterproof and oil-resistant emulsion. The cardanol / MLO bilayer modified mineral obtained in step (3) was dispersed in deionized water (mineral solid content 20%), and the pH of the dispersion was adjusted to 7.5 with ammonia. The dispersion was then ultrasonically dispersed (300 W, 15 minutes) to obtain a mineral dispersion. The mineral dispersion was added to the copolymer emulsion obtained in step (4), with the amount of mineral being 15% of the solid content of the copolymer emulsion. The mixture was stirred thoroughly (400 rpm, 30 minutes). A glycerol borate ester crosslinking agent was added to the above composite emulsion, with the amount being 3% of the solid content of the emulsion. The pH of the emulsion was adjusted to 7.0 with ammonia and stirred thoroughly (300 rpm, 20 minutes) to obtain the paper waterproof and oil-proof emulsion of the present invention.

[0044] The above emulsion is applied to the paper surface by scraping, dipping, or sizing, and dried at 80–100°C to form a film, resulting in a waterproof and oil-resistant coated paper. After film formation, the MLO grafted segments and the unsaturated double bonds of the cardanol side chains continue to undergo oxidative curing and cross-linking in air. The cross-linking density of the coating continuously increases with the storage time (usually increasing significantly within 1–7 days after film formation), and the protective performance shows a continuous improvement after film formation.

[0045] Experimental verification This section selects the three most innovative technical effects of the present invention and verifies them through comparative experiments: (1) Oxidation curing after film formation continuously enhances the protective performance of the coating; (2) Cardanol / MLO double-layer modification systematically inhibits microcracks at the ends of mineral fibers; (3) Dynamic crosslinking of glycerol borate ester gives the coating self-healing ability.

[0046] Experiment 1: Verification of the continuous enhancement effect of oxidative curing after film formation on the protective performance of the coating. 1.1 Experimental Objective The study verified that the MLO grafted segments and the unsaturated C15 side chains of cardanol continued to oxidize and cure after the coating was formed, which significantly improved the waterproof and oil-proof properties of the coating with the time of placement, forming a clear difference from the control sample of pure acrylic emulsion without oxidation curing mechanism.

[0047] 1.2 Sample Preparation S1 (Example 1 of the present invention): A waterproof and oil-resistant emulsion was prepared according to the entire process of Example 1. It was coated on the surface of 80 g / m² kraft paper by a blade coating method (wire bar coating, wet film thickness 100 μm). The film was dried at 90℃ for 3 minutes and then placed in a standard environment of 23±2℃ and 50±5% RH. Samples were taken and tested on day 0, day 1, day 3, day 7 and day 14 after film formation.

[0048] SE (control sample): Using 650 g of butyl acrylate (BA), 250 g of methyl methacrylate (MMA), and 100 g of hydroxyethyl acrylate (HEA) (mass ratio 65:25:10) as monomers, and the same emulsifier system (SDS / AEO-9=1:1, 3%) and ammonium persulfate (0.5%) as initiators, a pure acrylate emulsion (solid content 45%) was prepared at 80℃ using the same semi-continuous emulsion polymerization process. Glyceryl borate ester (3%) and the same amount of unmodified minerals (total mineral mass 15%) were added, and the pH was adjusted to 7.0. The emulsion was free of MLO, cardanol, and RHA monomers. The emulsion was coated and placed using the same process, and samples were taken for testing at the same time points.

[0049] 1.3 Test Conditions Oil resistance rating (Kit value): Refer to the TAPPI T 559 cm-12 standard. Use test solutions Kit 1 to 12 (castor oil / n-heptane / toluene mixture, the higher the Kit value, the better the oil resistance) to observe the penetration after 15 seconds on the paper surface. Record the highest non-penetrating Kit value. Take the average value of 3 parallel samples for each group.

[0050] Water resistance (Cobb value): The Cobb value is measured after 60 seconds according to GB / T 1540—2002 standard. (Unit: g / m², lower value indicates better waterproofing).

[0051] Contact angle (WCA): The static contact angle of the coating surface with deionized water (5 μL) was measured using an optical contact angle meter. The average value of 5 measurement points was taken for each group.

[0052] 1.4 Experimental Results Table 1 Comparison of protective performance of S1 and SE coatings at different placement times

[0053] 1.5 Results Analysis From Table 1 (and Figure 1-3 As can be seen, the Kit value of the S1 coating (in this invention) is 6 on day 0 of film formation. The concentration was 38.2 g / m²; as the storage time increased, the Kit value rose to 9 on the 7th day. It dropped to 23.2 g / m², and the Kit value reached 10 on day 14. The concentration decreased to 19.8 g / m², while the protective performance showed a continuous improvement trend. This change is due to the continuous auto-oxidative crosslinking of the MLO grafted segments and the unsaturated C15 side chains of cardanol with oxygen in the air after film formation. The crosslinking density of the coating increases over time, and the penetration pathway of oils and moisture is further extended.

[0054] The control sample SE (pure acrylate, free of MLO / cardanol / RHA monomers) showed that its Kit value and WCA remained basically unchanged or decreased slightly after film formation. It increases slowly over time, exhibiting the characteristics of "film formation and fixation, with protective performance slowly declining over time," which contrasts sharply with S1.

[0055] Experimental results demonstrate that the oxidation curing mechanism introduced by MLO and cardanol in this invention endows the coating with the unique characteristic of "continuous densification after film formation," with the Kit value increasing by 4 levels after 14 days compared to the initial stage of film formation. It reduces the coating size by approximately 48%, and its protective performance is significantly better than that of existing pure acrylic emulsion coatings.

[0056] Experiment 2: Verification of the inhibitory effect of cardanol / MLO bilayer modification on microcracks at the ends of mineral fibers. 2.1 Experimental Objective The effect of the cardanol / MLO bilayer modification system on systematically inhibiting the initiation of microcracks at the ends of mineral fibers under repeated humid heat-drying cycles was verified. The results were compared with unmodified mineral samples and samples modified with only MLO monolayer to demonstrate the necessity of the bilayer structure design.

[0057] 2.2 Sample Preparation S1 (Example 1 of the present invention): Prepared according to the entire process of Example 1, containing cardanol / MLO double-layer modified mineral (sepiolite / attapulgite = 4:1).

[0058] SB (Unmodified mineral control): Except for step (3), which is to directly disperse sepiolite and attapulgite (4:1) in deionized water (without MLO grafting and cardanol treatment) and add them to the copolymer emulsion, the other steps are exactly the same as in Example 1; the amount of mineral used is the same as in S1 (15% of the emulsion solid content).

[0059] SC (MLO monolayer modification control only): MLO covalent esterification grafting was performed according to step (3) of Example 1, omitting the cardanol adsorption treatment, and MLO monolayer modified mineral was obtained by direct low-temperature drying. The remaining steps were exactly the same as in Example 1.

[0060] 2.3 Humid-heat-drying cycle test conditions Each sample coated paper (coating preparation conditions were the same as in Experiment 1) was placed in the following humid-heat-drying cycle environment: each cycle consisted of: 4 hours in a 70℃, 90% RH constant temperature and humidity chamber (humid heat stage) → 1 hour in a 105℃ drying oven (drying stage), for a total of 5 cycles (25 hours in total), simulating the repeated humid-heat-drying stress experienced by the coating during use. After 5 cycles, the cross-section of the coating of each sample was characterized by SEM, and the Kit value of the coating after the cycle was measured.

[0061] 2.4 SEM Characterization Methods The coated paper sample after the wet heat-drying cycle was prepared by liquid nitrogen brittle fracture, and after gold sputtering, it was observed in two stages under a scanning electron microscope (SEM, accelerating voltage 10 kV, working distance 10 mm): (1) Low magnification statistical stage (magnification 200 to 500 times, single field area of ​​about 0.27 mm² (200 times) to 0.043 mm² (500 times)), 10 fields of view were randomly selected for each sample, and the total number of visible cracks in the field of view was counted and converted into crack density per unit area (cracks / mm²) and maximum crack width (μm); (2) High magnification morphology observation stage (magnification 2000 to 10000 times), used to characterize the micromorphology and crack orientation of the interface area between the mineral fiber end and the organic matrix.

[0062] 2.5 Experimental Results Table 2. Statistical analysis of microcracks and protective performance of each sample after 5 cycles of damp heat-drying.

[0063] 2.6 Results Analysis From Table 2 (and Figure 4-6 As can be seen, after five cycles of wet heat and drying, the crack density of the SB (unmodified mineral) coating reached as high as 12.5 cracks / mm², with a maximum crack width of 2.8 μm and a Kit value of only 4. This indicates that the unmodified mineral fibers underwent a large number of microcracks under the repeated stress of organic-inorganic shrinkage mismatch, resulting in severe damage to the barrier structure. The crack density of the SC (MLO monolayer modified) coating decreased to 5.2 cracks / mm², with a maximum crack width of 1.4 μm and a Kit value of 6. This indicates that after the MLO covalent graft layer covalently connects the mineral fibers to the organic matrix, it significantly reduces cracks caused by debonding instability. However, stress concentration at the fiber ends still exists. Due to the lack of absorption and dissipation of end stress by the cardanol flexible organic layer, the crack suppression effect is still incomplete.

[0064] The S1 (cardanol / MLO dual-layer modified) coating has a crack density of only 0.8 cracks / mm² and a maximum crack width of 0.3 μm. After 5 cycles, the Kit value is still 9, indicating that the covalent anchoring of MLO (eliminating the root cause of debonding) and the flexible organic layer of cardanol (absorbing end stress) work synergistically to reduce the microcrack initiation rate at the ends of mineral fibers to a negligible level. The inorganic barrier maintains high integrity after repeated humid heat cycling.

[0065] Experimental results demonstrate that the bilayer structure design of the cardanol / MLO bilayer modification is indispensable for systematically suppressing microcracks at the ends of mineral fibers: the inner MLO layer solves the debonding problem, and the outer cardanol layer solves the end stress concentration problem. Both are indispensable. The bilayer structure makes the barrier performance of the coating after cycling (Kit value 9) far superior to that of the single-layer modified (Kit value 6) and unmodified (Kit value 4) systems.

[0066] Verification of the self-healing ability of coatings imparted by dynamic crosslinking of triglyceride borate. 3.1 Experimental Objective The study verified that the dynamic reversible cross-linking network of glycerol borate ester (BOC) could restore the waterproof performance of the coating to a certain extent through spontaneous recombination of BOC bonds after the coating was subjected to local mechanical scratches, while the control coating without borate ester cross-linking agent did not have the above self-healing ability.

[0067] 3.2 Sample Preparation S1 (Example 1 of the present invention): Prepared according to the entire process of Example 1, containing a dynamic cross-linked network of glycerol borate ester (3% dosage).

[0068] SD (no crosslinking agent control): Except for step (5) where glycerol borate is not added, the other steps are exactly the same as in Example 1; adjust the pH to 7.0 with ammonia to obtain a control emulsion without borate crosslinking agent, coat it into a film using the same process, and place it in a standard environment for 7 days (after sufficient oxidation and curing) to perform a scratch self-healing test.

[0069] 3.3 Test Methods The following scratch self-healing test was conducted on each sample coating 7 days after film formation (after full oxidation curing): A steel needle (100 μm tip diameter, 5 N normal force applied) is used to scratch the coating surface at a constant speed to create standardized linear scratches on the coating surface. Immediately after scratching, the water contact angle (WCA) of the scratched area (scratch width 100-200 μm) is measured with an optical contact angle meter and recorded as the "immediate value after scratching". The scratched sample was placed in a constant temperature environment of 40℃ (relative humidity of 50%), and the WCA was measured in the same scratched area at 2 hours, 4 hours, 8 hours and 24 hours after scratching. The WCA recovery status at each time point was recorded. Based on the WCA before the scratch, the WCA recovery rate (%) at each time point is calculated as follows: (Measured value - Immediate value after scratch) / (Value before scratch - Immediate value after scratch) × 100%.

[0070] 3.4 Experimental Results Table 3. Recovery of WCA over time after S1 and SD scratches.

[0071] Note: WCA recovery rate =

[0072] 3.5 Results Analysis From Table 3 (and Figure 7 and 8As can be seen, the WCA of the S1 (containing glycerol borate ester dynamic cross-linked network) coating dropped sharply from 91.6° to 51.8° immediately after being scratched, indicating that the scratch damaged the coating structure. After being placed in a 40°C environment for 2 hours, the WCA recovered to 65.2° (recovery rate 33.5%), after 8 hours it recovered to 83.4° (recovery rate 79.0%), and after 24 hours it recovered to 88.6° (recovery rate 92.0%), close to the level before the scratch, showing obvious self-healing ability.

[0073] Immediately after scratching, the WCA of the control sample SD (without glycerol borate) dropped from 91.4° to 50.3°. After being placed at 40°C for 24 hours, the WCA only recovered to 58.4° (a recovery rate of only 19.8%), indicating virtually no self-healing ability. The slight recovery of WCA in SD is due to the thermal relaxation of organic polymer chains in the coating under 40°C conditions and the rearrangement of surface hydrophobic groups to the coating-air interface, which is a physical process rather than chemical repair of the cross-linked network. This slight physical recovery will be difficult to maintain when the coating is subjected to more severe or repeated damage, and the recovery rate tends to stagnate over time (WCA only increased from 57.2° to 58.4° between 8 and 24 hours), lacking the sustainability of chemical self-healing.

[0074] The above comparison shows that the dynamic reversible crosslinking network of glycerol borate ester (BOC) is the key source of the coating's self-healing ability: after scratches cause local breakage of BOC bonds, the free borate ester groups around the breakage site spontaneously reform BOC bonds with adjacent free hydroxyl groups at room temperature (accelerated by mild heating at 40°C), causing the crosslinking network to heal locally and the coating's waterproof performance to gradually recover. After 24 hours, the WCA recovery rate of S1 reached 92%, proving that the dynamic crosslinking system of glycerol borate ester of this invention endows the coating with practical self-healing ability, effectively delaying the degradation of protective performance caused by local damage and significantly extending the coating's service life.

[0075] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A method for preparing a paper waterproof and oil-resistant emulsion, characterized in that, Includes the following steps: (1) Rosin and hydroxyethyl acrylate are refluxed at 110-120°C for 4-6 hours under acid catalysis at a carboxyl to hydroxyl molar ratio of 1:1 to obtain rosin acid acrylate monomer. (2) Flaxseed oil and maleic anhydride are reacted in a closed reflux apparatus at 220°C for 3-4 hours at a mass ratio of (4-6):1 to obtain maleicized flaxseed oil; (3) Mix sepiolite and attapulgite in a mass ratio of (3-5):1, add 10-20% of the total mineral mass of maleic linseed oil in anhydrous ethanol medium, covalently esterify and graft at 70-78℃ for 2 hours, then add 5-10% of the total mineral mass of cardanol, stir and adsorb at room temperature for 1 hour, and dry at low temperature to obtain cardanol / maleic linseed oil double-layer modified mineral. (4) Prepare a mixed monomer by mixing rosin acid acrylate monomer, butyl acrylate and hydroxyethyl acrylate in a mass ratio of (20-30): (60-70): (5-10), and carry out emulsion free radical copolymerization with composite emulsifier and ammonium persulfate at 70-85℃ to obtain a copolymer emulsion; (5) After dispersing the double-layer modified mineral in water, add the copolymer emulsion. The amount of mineral is 10-20% of the solid content of the copolymer emulsion. Add the glycerol borate ester crosslinking agent. The amount is 2-5% of the solid content of the emulsion. Adjust the pH to 6.5-7.5 to obtain a paper waterproof and oil-proof emulsion.

2. The preparation method according to claim 1, characterized in that, In step (1), p-toluenesulfonic acid is used as a catalyst, with an amount of 0.5-1.0% of the total mass of the reactants. p-Methoxyphenol is used as a polymerization inhibitor, with an amount of 0.1-0.3% of the total mass of the reactants. Toluene is used as a water-removing solvent. After the reaction is completed, the organic phase is washed with saturated sodium carbonate aqueous solution until the pH is neutral. The mixture is dried with anhydrous sodium sulfate, filtered, and toluene is removed by vacuum distillation to obtain rosin acid acrylate monomer.

3. The preparation method according to claim 1, characterized in that, In step (2), the closed reflux device is equipped with a reflux condenser to condense and reflux the maleic anhydride vapor volatilized in the reaction system back into the reaction system, ensuring that the actual amount of maleic anhydride participating in the reaction is consistent with the feed ratio; step (2) is carried out under nitrogen protection.

4. The preparation method according to claim 1, characterized in that, In step (3), covalent esterification grafting is carried out in anhydrous ethanol medium. The anhydride groups of maleic linseed oil undergo esterification ring-opening reaction with the silanol groups on the surface of mineral fibers under anhydrous conditions. One end of the ester bond is covalently connected to the silicon oxygen atoms on the mineral surface, while the other end retains a free carboxyl group. The polyunsaturated fatty acid segments of maleic linseed oil are anchored to the surface of mineral fibers by covalent ester bonds.

5. The preparation method according to claim 1, characterized in that, The cardanol used in step (3) is an industrial-grade decarboxylated distilled cashew shell liquid product with a cardanol content of not less than 85%. Its main components are phenol homologues containing phenolic hydroxyl groups and C15 unsaturated alkyl side chains. The phenolic hydroxyl groups of cardanol form hydrogen bonds with the residual silanol groups on the surface of mineral fibers. The C15 unsaturated alkyl side chains form a flexible organic coating layer on the outside of the maleic linseed oil covalent graft layer. When the coating shrinks during film formation, it absorbs and dissipates the interfacial tearing stress at the ends of the mineral fibers.

6. The preparation method according to claim 1, characterized in that, In step (3), the low-temperature drying temperature is below 60°C, which preserves the integrity of the unsaturated double bonds on the grafted segments of flaxseed oil and the C15 side chain of cardanol, so that the coating can continue to undergo oxidation, curing and crosslinking in the air after film formation.

7. The preparation method according to claim 1, characterized in that, In step (4), the composite emulsifier is a mixture of sodium dodecyl sulfate and fatty alcohol polyoxyethylene ether in a mass ratio of 1:1, and the amount used is 2 to 4% of the total mass of the mixed monomers; the amount of ammonium persulfate is 0.3 to 0.8% of the total mass of the mixed monomers; the monomer emulsion is added dropwise in a semi-continuous manner to copolymerize, and a copolymer emulsion with a solid content of 40 to 50% is obtained.

8. The preparation method according to claim 1, characterized in that, In step (5), when the bilayer modified mineral is dispersed in deionized water, the pH of the dispersion is adjusted to 7.0-8.0 with ammonia water so that the free carboxyl groups on the surface of the mineral fibers are ionized into carboxylate ions, giving the surface of the mineral fibers a negative charge. After the mineral fibers are uniformly dispersed in water by electrostatic repulsion, the mineral dispersion is added to the copolymer emulsion.

9. The preparation method according to claim 1, characterized in that, In step (5), the glycerol borate ester is formed by the primary hydroxyl groups (1,3-diol) at the C1 and C3 positions of glycerol and boric acid to form a six-membered ring borate ester structure. Its BOC bond has reversible dissociation and recombination characteristics under neutral conditions at room temperature. When the coating is formed, the borate ester group forms an initial dynamic cross-linking network with the free hydroxyl groups of the copolymer side chain and the phenolic hydroxyl groups of cardanol. After the film is formed, the newly generated hydroxyl groups generated by the oxidative cross-linking of the unsaturated double bonds of maleic linseed oil and cardanol further form BOC cross-linking with the remaining borate ester group. The cross-linking density of the coating continues to increase after the film is formed. When the local BOC bond breaks, the free borate ester group and the adjacent free hydroxyl group reform BOC bond at room temperature, giving the coating self-healing ability.

10. A paper waterproof and oil-resistant emulsion, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

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