Lightweight waterproof and oil-proof plant parchment paper and papermaking process thereof

Abstract

This invention relates to the field of papermaking technology, and discloses a lightweight, waterproof, and oil-resistant vegetable parchment paper and its papermaking process. The parchment paper is made of a base paper substrate, sizing components, and a plasticizer. Polyamide epichlorohydrin resin penetrates into the internal pores of the base paper, while inorganic aluminum salt, alkyl ketone dimer, and cationic dispersed rosin are loaded onto the surface of the substrate. The surface loading structure is formed by sequential spraying of an aqueous solution of inorganic aluminum salt and a mixture of the latter two through a spatially and temporally delayed process. The papermaking process includes mixed acid impregnation and gelation of the base paper, multi-stage washing, resin pressing and penetration, delayed sequential surface spraying, plasticizer impregnation, and segmented drying, and also includes the concentration, crystallization, purification, and recovery of waste mixed acid solution. This invention, through its internal and external layering and delayed surface application design, effectively avoids salt precipitation and demulsification during the sizing process, achieving a balance between the paper's internal wet strength and surface impermeability.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, specifically to a lightweight, waterproof, and oil-resistant vegetable parchment paper and its papermaking process. Background Technology

[0002] Vegetable parchment paper is typically made by impregnating and gelling base paper in concentrated acid, causing the fibers to hydrolyze and produce a gel that fills the pores. It is commonly used in packaging applications requiring high oil and water resistance. With the trend towards lightweight packaging materials, low-grammage lightweight parchment paper is gradually becoming a production focus. However, in actual processing, the lightweight base paper itself is quite thin, and simultaneously ensuring its internal wet strength (without tearing when wet) and its surface oil and water resistance presents significant processing challenges.

[0003] In existing sizing processes, factories typically introduce wet-strength resins and water- and oil-resistant sizing emulsions to improve the overall performance of paper. However, due to the lack of effective spatial barriers, these chemical additives are prone to disordered penetration into the thinner paper base. If a large amount of the surface-applied water- and oil-resistant emulsion seeps into the deeper layers of the paper, not only is the effective ingredient wasted, resulting in low retention on the press, but it also interferes with the bonding between the internal reinforcing resin and cellulose. Conversely, if the internal reinforcing agents are unevenly distributed, the paper's basic wet strength will fail to meet standards. This creates a situation where the paper's internal strength and surface impermeability are often at odds and difficult to balance.

[0004] Another prominent engineering problem is salting-out demulsification of sizing agents. To ensure the sizing emulsion adheres firmly to the negatively charged paper fibers, inorganic aluminum salts must be added to provide a positive charge. Under conventional application methods, high concentrations of inorganic salt ions often directly mix with or come into continuous contact with sizing emulsions such as alkyl ketone dimers or rosin gum for short periods. This high-salt environment rapidly disrupts the charge repulsion balance on the outer layer of the emulsion particles, directly leading to demulsification and clumping. Premature demulsification of the sizing agent not only prevents it from spreading evenly on the outermost layer of the paper to form a uniform anti-fluid barrier but also easily causes glue buildup on the equipment. Therefore, how to fix the reinforcing agent and surface anti-seepage agent in their proper positions on a lightweight paper production line while preventing demulsification during sizing is a pressing technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a lightweight, waterproof, and oil-resistant vegetable parchment paper and its papermaking process. The technical problem it solves is that existing lightweight parchment paper suffers from issues such as easy demulsification of the sizing agent emulsion, low effective retention rate, and difficulty in simultaneously achieving both internal wet strength and surface water and oil resistance during the sizing process.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a lightweight, waterproof, and oil-resistant vegetable parchment paper, employing the following technical solution: A lightweight, waterproof, and oil-resistant vegetable parchment paper, wherein the parchment paper is made of a base paper substrate and sizing components and plasticizers loaded on the base paper substrate; Based on the oven-dry weight of the base paper substrate as 100%, the sizing component contains the following raw materials by oven-dry weight percentage: Polyamide epichlorohydrin resin 0.5-1.0%; inorganic aluminum salt, calculated as aluminum oxide 0.1-0.5%; alkyl ketone dimer 0.5-1.5%; cationic dispersed rosin 0.3-1.0%; polyamide epichlorohydrin resin is permeated and loaded into the internal pores of the base paper substrate; inorganic aluminum salt, alkyl ketone dimer and cationic dispersed rosin are loaded on the surface of the base paper substrate; the loading structure on the surface of the base paper substrate is formed by the sequential spraying of an aqueous solution of inorganic aluminum salt and a mixture of alkyl ketone dimer and cationic dispersed rosin with a spatial and temporal delay.

[0007] By employing the above technical solution, the use of polyamide epichlorohydrin resin to penetrate into the internal pores, combined with a surface sequential loading structure with spatial and temporal delay, achieves the effect of improving both internal wet strength and surface resistance to fluid penetration. The problem of simultaneously achieving both internal wet strength and surface resistance to penetration is solved through spatial layering and sequential application over time. The polyamide epichlorohydrin resin primarily penetrates into the internal pores of the paper along with residual moisture. During the subsequent heat drying stage, the highly reactive nitrogen-containing heterocyclic butyl groups within the resin molecules undergo ring-opening addition with the free hydroxyl groups of cellulose. This forms stable covalent carbon-oxygen bonds between the cellulose and the resin matrix, solidifying the originally relatively loose fibrous network structure and providing the paper with a basic wet strength that prevents it from dispersing when wet. In constructing the paper surface properties, setting the time interval between the two spraying processes is crucial. After contacting the paper surface, the inorganic aluminum salt aqueous solution spontaneously hydrolyzes in the microenvironment, transforming into a positively charged polynuclear hydroxyl aluminum polycationic complex, which is then adsorbed onto the negatively charged fiber surface by electrostatic attraction. This buffer period prevents the high-concentration salt solution from directly mixing with the subsequent sizing emulsion, thus preventing salt precipitation and demulsification during the production process. After the paper web has traveled a certain distance, the mixture of alkyl ketone dimer and cationic rosin covers the paper surface. At this point, the pre-anchored aluminum complex acts as a surface anchoring and retention node, fixing rosin particles through complexation, interfacial adsorption, and the shallow barrier effect of the paper sheet. During the final curing period, the four-membered lactone rings in the alkyl ketone dimer structure open successively and combine with the cellulose hydroxyl groups; the outwardly oriented hydrophobic long chains match the rosin acid components, together constructing a dense water- and oil-resistant barrier on the outside of the paper.

[0008] Preferably, the cationic dispersed rosin gum is a dispersion obtained by high-temperature melting, high-speed shearing primary emulsification and high-pressure homogenization of rosin and a positively charged cationic polymer aqueous solution; the positively charged cationic polymer is selected from polydimethyldiallylammonium chloride and cationic starch with a degree of substitution of 0.030 to 0.035, and the solid content of the cationic dispersed rosin gum is 30 to 35 wt%.

[0009] By employing the above-mentioned technical solution, during the preparation of dispersed rosin gum, solid rosin is initially dispersed into micron-sized droplets under the dual effects of high-temperature melting and high-speed shearing. The subsequent high-pressure homogenization process further refines the droplets through intense physical extrusion and shear collision. In this dispersion system, cationic starch or polydimethyldiallyl ammonium chloride with a specific degree of substitution adsorbs and coats the surface of the refined rosin particles. Due to the same positive charge on the polymer coating layer, the particles generate significant electrostatic repulsion when they approach each other. This repulsive force allows the entire emulsion system to maintain a stable, non-agglomerated, and non-stratified state even at a relatively high solids content of 30–35 wt%.

[0010] Preferably, the inorganic aluminum salt is sodium aluminate or polyaluminum chloride; the plasticizer is glycerol or polyethylene glycol. By adopting the above technical solution, considering that the microenvironment of the paper surface needs to be supplemented with positive charge to neutralize the negative charge of the fiber itself, the polynuclear aluminum ions released by sodium aluminate or polyaluminum chloride under weakly acidic conditions precisely meet this chemical requirement. Glycerol or polyethylene glycol is introduced because these two plasticizers contain abundant small-molecule hydroxyl groups, which can easily penetrate into the relatively loose, non-crystalline regions of cellulose. By replacing some water molecules, they moderately weaken the hydrogen bonding forces that tightly bind cellulose segments, ensuring that the lightweight paper does not become excessively stiff after drying, thus retaining the necessary flexibility.

[0011] Preferably, the basis weight of the base paper is 25-30 g / m²; the final moisture content of the parchment paper is controlled at 6-8 wt%.

[0012] By adopting the above technical solution, limiting the basis weight of the base paper to 25-30 g / m², it is possible to ensure that the acid and resin can penetrate the entire thickness direction of the substrate under relatively low pressure, achieving full penetration. Combined with the 6-8 wt% moisture content retained during the papermaking stage, this bound water maintains the free volume within the cellulose. With an appropriate amount of moisture as a buffer, the paper can effectively avoid problems such as drying out, becoming brittle, or even breaking during subsequent storage or folding.

[0013] Secondly, the present invention provides a papermaking process for lightweight, waterproof, and oil-resistant vegetable parchment paper, employing the following technical solution: A papermaking process for lightweight, waterproof, and oil-resistant vegetable parchment paper includes the following steps: The original paper web is continuously introduced into a mixed acid solution provided by an acid mixing tank for impregnation and gelation. After exiting the acid bath, the free acid solution on the surface is initially removed to obtain a wet paper web. The wet paper web is continuously washed through a multi-stage reverse washing tank. When the wet paper web reaches the middle and later part of the washing process, it enters a low-shear impregnation shallow tank, where a polyamide epichlorohydrin resin aqueous solution is continuously applied to the wet paper web and pressed to penetrate it. Inorganic aluminum salt aqueous solution is sprayed onto the surface of the wet paper web after pressing and penetration. After the wet paper web continues to travel through a spatial and time delay, a mixture of alkyl ketone dimer emulsion and cationic dispersed rosin is sprayed onto the paper surface, followed by homogenization. The uniformly sized wet paper web is impregnated through an aqueous solution containing plasticizer, and then enters the drying section for drying, curing, and winding. The waste mixed acid liquid overflowing from the first section of the multi-stage reverse water washing tank during the aforementioned washing process is pumped into the first-stage vacuum evaporator for concentration. The concentrated liquid is transferred to the crystallizer for cooling and precipitation, and the by-product salt crystals are separated. The desalted mother liquor is pumped into the second-stage vacuum flash evaporator for deep concentration to restore the initial concentration of the mixed acid liquid and circulate it back to the acid mixing kettle.

[0014] By adopting the above technical solution, the entire production process integrates the chemical modification and strength enhancement of the base paper substrate with closed-loop wastewater recycling into a continuous process. After the base paper is immersed in the mixed acid solution, the high concentration of acidic protons rapidly breaks the hydrogen bonds between cellulose molecules, causing partial hydrolysis of the surface cellulose and generating starch-like hydrated gel. These fluid gels gradually fill the gaps between fibers, constructing a leak-proof, non-porous base for the paper. To prevent excessive degradation of the cellulose backbone, the paper web undergoes multi-stage reverse washing immediately after leaving the acid bath, using a concentration gradient to remove free acid. When the wet paper web is washed to a slightly acidic state and enters the shallow impregnation tank, resin molecules diffuse into the deeper layers of the paper with the residual water, filling the tiny pores left by the hydrolysis reaction, and are evenly distributed under the mechanical action of the pressure rollers. For the surface sizing process, the time and space-dimension isolation spraying plays a decisive role: the aluminum salt sprayed in the early stage pre-complicates and modifies the paper surface, forming an anchoring layer that facilitates retention. The alkyl ketone dimer and rosin latex sprayed subsequently achieve efficient adsorption and fixation in the shallow layer of the paper, allowing the effective components to be preferentially located on the outermost layer of the paper, avoiding waste caused by ineffective penetration into the deeper core. In addition, for the by-product salts that continuously accumulate during the production process, the system first increases the concentration of waste acid through primary vacuum evaporation, and then transfers it to a crystallizer for cooling and desalination. Utilizing the physical law that the solubility of salts decreases significantly at low temperatures, the corresponding by-products are crystallized and separated by centrifugation. The mother liquor after desalination further enters a secondary vacuum flash evaporator for deep concentration, and after supplementing the corresponding components with online concentration detection, it is recycled back to the acid preparation vessel for continued use.

[0015] Preferably, the mass fraction of the mixed acid solution is as follows, based on a total mass fraction of 100%: 65-68 wt% sulfuric acid, 4-6 wt% glacial acetic acid, 1-2 wt% anhydrous magnesium sulfate, with the balance being water. The acid bath temperature is controlled at 10-15°C, and the residence time of the original paper web in the mixed acid solution is 6-12 seconds.

[0016] By employing the above technical solution, each component in the mixed acid solution undertakes different chemical reaction requirements. 65–68 wt% sulfuric acid constructs the core hydrolysis environment, while the addition of 4–6 wt% glacial acetic acid effectively reduces the surface tension of the mixture, promoting more rapid wetting and penetration of the acid into the fiber interior. Considering the strong destructive effect of strong acids on the carbohydrate backbone, 1–2 wt% anhydrous magnesium sulfate is introduced into the formulation as a buffer medium to slow down excessive degradation. At this specific ratio, a relatively low temperature of 10–15°C and a short residence time of 6–12 seconds precisely control the degree of cellulose degradation to a critical state where gel formation on the surface is achieved while preserving the strength of the internal skeleton.

[0017] Preferably, during the washing process, when the pH of the water film in the latter part of the washing process is stabilized at 5.5 to 6.0 by online monitoring and control, the paper web enters the low-shear impregnation shallow tank; the dry weight ratio of the applied polyamide epichlorohydrin resin is 0.5 to 1.0% of the oven-dry paper weight.

[0018] By employing the above technical solution, the pH of the water film is stabilized in the slightly acidic range of 5.5–6.0 during the later stages of washing. This aims to provide a relatively inert penetration environment for the polyamide epichlorohydrin resin. Under this pH condition, the self-homogenization and curing reaction between resin molecules is significantly inhibited, thereby maintaining good flowability and penetration activity. This allows the resin to penetrate smoothly into the paper until it is fully activated and forms a large-area cross-linked network when it enters the high-temperature drying process with the paper web.

[0019] Preferably, when spraying the inorganic aluminum salt aqueous solution, the pH of the microenvironment on the paper surface is controlled at 5.0–7.0; specifically, when the inorganic aluminum salt is sodium aluminate, it is preferably controlled at 6.5–7.0; and when the inorganic aluminum salt is polyaluminum chloride, it is preferably controlled at 5.0–5.5. The fluid temperature is 45–50°C, the moisture content of the wet paper web is controlled at 60–75 wt%, and the spatial time delay is 0.5–2.0 seconds.

[0020] By adopting the above technical solution, under fluid temperature conditions of 45–50°C, when the inorganic aluminum salt is sodium aluminate, the pH of the microenvironment on the paper surface is controlled at 6.5–7.0; when the inorganic aluminum salt is polyaluminum chloride, the pH of the microenvironment on the paper surface is controlled at 5.0–5.5. These conditions are conducive to the formation of positively charged polynuclear aluminum hydroxy complexes by the inorganic aluminum salt in the paper surface microenvironment, thereby increasing the positive charge density on the paper substrate surface. The 60–75 wt% moisture content maintained by the paper web at this time provides the necessary liquid-phase channel for ion migration and adsorption. Furthermore, the set spatial time delay of 0.5–2.0 seconds is a buffer period matched to the papermaking speed and the aluminum salt reaction and adsorption rate; ensuring that the aluminum salt fully reacts and adheres to the paper surface before applying the subsequent emulsion, thus ensuring the stable progress of the surface fixation reaction.

[0021] Preferably, the mass fraction of the aqueous solution containing plasticizer is 5-8 wt%, and the immersion time is 2-5 seconds; the surface temperature of the front drying cylinder of the drying section is set to 90-100°C, and the temperature of the rear section is controlled at 105-110°C.

[0022] By employing the above technical solution and limiting the concentration and impregnation time of the plasticizer solution, small molecules can fully penetrate into the gaps between cellulose chain segments. After the paper web enters the drying section, segmented temperature settings are crucial: the first drying cylinder is controlled at a relatively mild condition of 90–100°C, allowing the moisture in the paper base to evaporate and dissipate smoothly, preventing the internal moisture from expanding violently and causing the dense paper layer to rupture and bubble. As a large amount of moisture is removed, the paper web transitions to the second drying cylinder at 105–110°C; at this point, the higher heat energy reserve is released in a concentrated manner, strongly driving the esterification and ring-opening of the ester ring in the alkyl ketone dimer, and promoting the final rigid curing of the resin network that has penetrated inside.

[0023] Preferably, the waste mixed acid solution is concentrated to a sulfuric acid mass fraction of 30-35 wt% in a primary vacuum evaporator; the temperature is slowly lowered to 0-5°C and held for 1-2 hours in a crystallizer; and the concentration is carried out in a secondary vacuum flash evaporator at a temperature of 70-90°C and a vacuum degree of -0.08 to -0.09 MPa.

[0024] By adopting the above technical solution, the waste liquid recovery process gradually separates salts from excess water by changing the temperature and pressure of the system. The main purpose of the first-stage concentration is to remove some water, bringing the waste liquid to a supersaturated concentration range where crystallization is easy. Subsequently, the waste acid is transferred to a crystallizer and kept at 0-5°C for 1-2 hours. This process provides sufficient space for crystal nuclei to form and grow, allowing the salts to gradually grow into distinct inorganic salt crystals (mainly magnesium sulfate crystals), thereby improving the desalination efficiency of subsequent centrifugal separation. The desalinated mother liquor, from which salt crystals have been removed, is then introduced into a second-stage vacuum flash evaporator. Utilizing the principle that high vacuum significantly lowers the boiling point of water, the purification process only requires a moderate temperature of 70-90°C to complete the deep dehydration of the mixed sulfuric acid system, restoring it to the initial acid concentration.

[0025] This invention provides a lightweight, waterproof, and oil-resistant vegetable parchment paper and its papermaking process. It has the following beneficial effects: 1. This invention achieves internal curing by allowing polyamide epichlorohydrin resin to penetrate deep into the pores of the paper base, and then applies a spatially and temporally delayed sequential spraying method to the paper surface. First, inorganic aluminum salt is applied for pre-modification, followed by the spraying of alkyl ketone dimers and cationic dispersed rosin after a certain time interval. This layered structure with delayed surface application ensures that the resin independently cross-links into a network within the paper to provide basic wet strength, while the time difference prevents direct mixing of high-concentration salt ions with the sizing emulsion, physically eliminating the risk of salt precipitation and demulsification. This results in a stable and dense water- and oil-resistant barrier being constructed on the outside of the paper.

[0026] 2. In the preparation of the sizing emulsion, the solid rosin resin undergoes high-temperature melting, high-shear, and high-pressure homogenization, and is then coated with a positively charged cationic polymer to refine the microparticles. The electrostatic repulsion between like charges ensures that the emulsion does not separate during long-term storage at a high solids content of 30-35 wt%. During the application stage, aluminum complexes are pre-deposited on the paper surface, forming a surface anchoring structure that promotes retention. When the mixed emulsion is applied, interfacial adsorption, complexation, and the paper surface retention effect promote efficient anchoring of rosin microparticles and alkyl ketone dimers, which are directly retained on the outermost layer of the paper, reducing ineffective penetration and waste of active ingredients into the paper core.

[0027] 3. This invention first removes some water through a primary vacuum evaporation process to achieve a supersaturated concentration in the waste acid. The acid is then transferred to a crystallizer and kept at a low temperature of 0–5°C. Utilizing the difference in solubility, the separated salts grow into large inorganic salt crystals (such as magnesium sulfate hydrate), which are then separated by centrifugation. The mother liquor, after impurity removal, undergoes deep dehydration in a secondary vacuum flash evaporator under high negative pressure and a medium temperature of 70–90°C. This process avoids the dangers of conventional high-temperature acid boiling, safely and stably restoring the mixed acid to its initial concentration for reuse in production. Attached Figure Description

[0028] Figure 1 This is a tensile stress-strain evolution diagram of the wet paper web of the present invention after extrusion deacidification; Figure 2 This is a concentration distribution diagram of the leached substances in the sizing process solution of the present invention, wherein, Figure 2 (a) is a diagram showing the actual turbidity distribution of the free liquid. Figure 2 (b) is a distribution diagram of total solids content. Figure 2 (c) is a distribution map of total organic carbon concentration; Figure 3 This is a diagram showing the desalination efficiency of the waste acid freeze-crystallization process of the present invention, wherein... Figure 3 (a) is a comparison chart of residual magnesium ion concentrations in the mother liquor after freeze centrifugation. Figure 3 (b) is a chart showing the actual desalination rate of the waste acid system; Figure 4 The figures shown are test results of the liquid resistance and oil resistance properties of the various groups of parchment paper products of the present invention. Figure 4 (a) is a distribution diagram of Kit oil resistance level on the sample surface. Figure 4 (b) is a graph showing the difference in water absorption of Cobb60 over a standard time period; Figure 5 The diagram shows the physical and mechanical properties of the parchment paper product of the present invention, wherein... Figure 5 (a) is a distribution diagram of the dry tensile index under normal dry conditions. Figure 5 (b) is a graph showing the wet tensile strength retention rate after 24 hours of water immersion; Figure 6 The figures show the operational stability of each test group in continuous production according to the present invention. Figure 6 (a) is a graph showing the frequency of paper breaks in the wet section during the 100-kilometer papermaking process. Figure 6 (b) is a statistical chart of the continuous operation cycle of the anti-fouling evaporator in the secondary evaporator. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0031] Insulating base paper is made from 100% bleached sulfate softwood pulp with a basis weight of 25-30 g / m³. 2It has not undergone any surface adhesive treatment.

[0032] Concentrated sulfuric acid has a mass fraction of 98%. Glacial acetic acid has a purity greater than 99.5%. Anhydrous magnesium sulfate has a purity greater than 99.0%. Glycerol has a purity greater than 99.0%. Sodium aluminate has an alumina mass fraction greater than 50%. Polyaluminum chloride has an alumina mass fraction of 28-30% and a basicity of 45-85%.

[0033] Polyethylene glycol is a homopolymer with a number average molecular weight of 400, a hydroxyl value of 255-285 mgKOH / g, and CAS number 25322-68-3.

[0034] The softening point of rosin is 76℃, and its acid value is 166mgKOH / g.

[0035] The cationic starch is a quaternary ammonium type cationic modified starch prepared with 2,3-epoxypropyltrimethylammonium chloride as an etherifying agent, with a degree of substitution of 0.035; a similar cationic starch with a degree of substitution of 0.030 is also available for comparison.

[0036] Aqueous solution of polydimethyldiallylammonium chloride (PDADMAC) with a mass fraction of 20%, a weight-average molecular weight of 100,000-200,000, and CAS number 26062-79-3.

[0037] Polyamide epichlorohydrin resin is a water-soluble thermosetting resin prepared by polycondensation and crosslinking reaction of adipic acid, diethylenetriamine and epichlorohydrin. The main chain is a polyamide amine structure and the side chain contains azacyclobutane cationic active groups. The resin aqueous solution has a solid content of 12.5 wt%, a pH value of 4.0-4.5, and a weight average molecular weight of 300,000-500,000.

[0038] The active ingredient of the alkyl ketone dimer emulsion is a reactive sizing agent with a four-membered lactone ring structure, synthesized from higher fatty acid acyl chlorides with carbon chain lengths of C16 to C18 via a dehydrochlorination reaction. The emulsion has a solid content of 15.0 wt%, a pH value of 3.0–4.0, and a zeta potential greater than +20 mV.

[0039] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a method for preparing cationic dispersed rosin gum with a solid content of 32 wt%, including the following steps: 100g of rosin was weighed and added to a reaction vessel equipped with a heating jacket, and heated to 140℃ until it was completely melted into a liquid state for later use. Separately, 15g of cationic starch with a degree of substitution of 0.035 was dissolved in 200g of deionized water, stirred until completely gelatinized and dissolved, and the pH of the aqueous solution was adjusted to 3.5 using 10% hydrochloric acid. The solution was then heated to 90℃ to obtain the aqueous phase. The aqueous phase was placed in a stainless steel container equipped with a high-speed shear emulsifier, and the shearing speed was set to 8000 r / min. The molten rosin at 140℃ was slowly poured into the aqueous phase, and shearing was continued for 15 minutes for primary emulsification to obtain a crude emulsion. The crude emulsion was immediately pumped into a high-pressure homogenizer and homogenized twice at a pressure of 25 MPa. The homogenized emulsion was then rapidly cooled to room temperature using a cold water bath. Deionized water was added to adjust the solid content to 32 wt%, yielding a positively charged cationic dispersed rosin gum.

[0040] Preparation Example 2: This preparation example provides a method for preparing a cationic dispersion rosin gum with a solid content of 30 wt%, including the following steps: 100g of rosin was weighed and added to a reaction vessel equipped with a heating jacket, and heated to 130℃ until it was completely melted into a liquid state for later use. Separately, 12g of cationic starch with a degree of substitution of 0.030 was dissolved in 220g of deionized water, stirred until completely gelatinized and dissolved, and the pH of the aqueous solution was adjusted to 4.0 using 10% hydrochloric acid. The solution was then heated and kept at 85℃ to obtain the aqueous phase. The aqueous phase was placed in a stainless steel container equipped with a high-speed shear emulsifier, and the shearing speed was set to 6000 r / min. The molten rosin at 130℃ was slowly poured into the aqueous phase, and shearing was continued for 10 minutes for primary emulsification to obtain a crude emulsion. The crude emulsion was immediately pumped into a high-pressure homogenizer and homogenized twice under a pressure of 20 MPa, followed by rapid cooling to room temperature via a cold water bath. Deionized water was added to adjust the solid content to 30 wt%, yielding a positively charged cationic dispersed rosin gum.

[0041] Preparation Example 3: This preparation example provides a method for preparing cationic dispersed rosin gum with a solid content of 35 wt%, including the following steps: 100g of rosin was weighed and added to a reaction vessel equipped with a heating jacket, and heated to 150℃ until it was completely melted into a liquid state for later use. Separately, 80g of a 20% (w / w) aqueous solution of polydimethyldiallylammonium chloride was added to 120g of deionized water and mixed thoroughly. The pH of this aqueous solution was adjusted to 3.0 using 10% (w / w) dilute hydrochloric acid, and the mixture was heated and kept at 95℃ to obtain the aqueous phase. The aqueous phase was placed in a stainless steel container equipped with a high-speed shear emulsifier, and the shearing speed was set to 10000 r / min. The molten rosin at 150℃ was slowly poured into the aqueous phase, and shearing was continued for 20 minutes for primary emulsification to obtain a crude emulsion. The crude emulsion was immediately pumped into a high-pressure homogenizer and homogenized twice under a pressure of 30 MPa, followed by rapid cooling to room temperature via a cold water bath. Deionized water was added to adjust the solid content to 35 wt%, yielding a positively charged cationic dispersed rosin gum.

[0042] Examples 1-5: Example 1:

[0043] This embodiment provides a papermaking process for lightweight, waterproof, and oil-resistant vegetable parchment paper, including the following steps: (1) Controlled gelation: Prepare a mixed acid solution in an acid mixing tank with the following mass fractions: sulfuric acid 66.5 wt%, glacial acetic acid 5.0 wt%, anhydrous magnesium sulfate 1.5 wt%, and the remainder being water. Turn on the external jacket heat exchange system of the tank and control the acid bath temperature at 12℃. The amount of water is 28 g / m³. 2 The raw paper web is continuously introduced into the mixing acid bath through guide rollers at a constant tension, and the operating speed is controlled to ensure that the paper web's residence time in the acid solution is 9 seconds. Immediately after exiting the acid bath, the paper web passes through a pair of rubber squeeze rollers to initially remove free acid from the surface.

[0044] (2) Reverse washing and retention of polyamide epichlorohydrin resin: The extruded paper web continuously passes through a 5-stage reverse washing tank. When the paper web reaches the later stage of the washing process and the pH of the water film in this stage is stabilized at 5.8 by online monitoring and control, the paper web is separated from the violently disturbed bulk washing liquid and enters a separate low-shear impregnation shallow tank, where a polyamide epichlorohydrin resin aqueous solution is continuously and uniformly applied at a dry weight ratio of 0.75% of the oven-dry paper weight. Subsequently, the paper web is gently pressed to allow the resin to penetrate into the pores of the wet paper web.

[0045] (3) In-situ sequential spraying and sizing of the paper web: After the paper web travels to the last section of the reverse washing squeeze roll, the pH of the microenvironment on the paper surface is controlled at 6.8, the fluid temperature at 48℃, and the moisture content of the wet paper web is controlled at 68wt%. A 2wt% sodium aluminate aqueous solution is uniformly sprayed onto the surface of the wet paper web through a double-sided spraying system, with the amount applied being equivalent to 0.3% of the oven-dry paper weight (calculated as Al2O3). The paper web continues to travel, and after a spatial time delay of 1.0s, it reaches the second set of spraying devices to spray a mixture of alkyl ketone dimer emulsion and the cationic dispersed rosin obtained in Preparation Example 1 onto the paper surface. The amount applied is equivalent to: the oven-dry amount of alkyl ketone dimer accounts for 1.0% of the oven-dry paper weight, and the oven-dry amount of cationic rosin accounts for 0.6% of the oven-dry paper weight. After sizing, the paper web is homogenized by a vacuum descaling box.

[0046] (4) Plasticization and drying curing: The homogenized paper web is passed through an impregnation tank containing a 6.5 wt% glycerol aqueous solution for 3 seconds. The paper web enters the drying section, with the surface temperature of the front drying cylinder set at 95°C and the rear cylinder at 108°C. The final paper moisture content is controlled at 7 wt% before winding.

[0047] (5) Waste acid phase diagram control and recovery: The waste mixed acid liquid overflowing from the first-stage reverse washing tank is pumped into the first-stage vacuum evaporator and evaporated until the sulfuric acid mass fraction is concentrated to 32wt%. The concentrated liquid is transferred to the crystallizer, slowly cooled to 2℃, and kept at this temperature for 1.5h to allow a large amount of magnesium sulfate hydrate to precipitate out. The solid magnesium salt crystals are separated by centrifugation. The mother liquor after centrifugation and desalination is pumped into the second-stage vacuum flash evaporator and deeply concentrated at a temperature of 80℃ and a vacuum degree of -0.085MPa until the sulfuric acid concentration rises back to 66.5wt%. The condensate containing acetic acid secondary vapor generated during the two-stage vacuum evaporation process is collected and directly pumped back to the acid mixing kettle for circulation through the buffer tank. An appropriate amount of concentrated sulfuric acid or deionized water is added according to the online concentration detection. At the same time, by real-time monitoring of the volatile components and salt concentrations in the circulating mother liquor, glacial acetic acid and / or anhydrous magnesium sulfate are added quantitatively as needed to accurately restore the target ratio of the initial quaternary mixed acid bath and ensure the dynamic balance of the impregnation liquid composition in continuous production. Example 2:

[0048] This embodiment provides a papermaking process for lightweight, waterproof, and oil-resistant vegetable parchment paper, including the following steps: (1) Controlled gelation: Prepare a mixed acid solution in an acid mixing tank with the following mass fractions: sulfuric acid 65wt%, glacial acetic acid 4wt%, anhydrous magnesium sulfate 1wt%, and the remainder being water. Control the acid bath temperature at 10℃. The quantitative amount is 25g / m³. 2 The raw paper web is continuously introduced into the mixing acid bath, where it remains for 6 seconds. After exiting the acid bath, it undergoes preliminary removal of free acid by a squeeze roller.

[0049] (2) Reverse washing and polyamide epichlorohydrin resin retention: The paper web passes continuously through the reverse washing tank. When it reaches the middle and later part of the washing process and the pH of the water film is stable at 5.5, it enters the low shear impregnation shallow tank and continuously applies polyamide epichlorohydrin resin aqueous solution at a dry weight ratio of 0.5% of the oven-dry paper weight, followed by press impregnation.

[0050] (3) In-situ sequential spraying and sizing of the paper web: The pH of the microenvironment on the paper surface was controlled at 6.5, the fluid temperature at 45℃, and the moisture content of the wet paper web was controlled at 60wt%. A 1wt% sodium aluminate aqueous solution was sprayed onto the paper surface through a spraying system, with the application amount converted to 0.1% of the oven-dry paper weight (calculated as Al2O3). After a spatial time delay of 0.5s, a mixture of alkyl ketone dimer emulsion and the cationic dispersed rosin obtained in Preparation Example 2 was sprayed. The application amount was converted to: 0.5% of the oven-dry paper weight for alkyl ketone dimer and 0.3% of the oven-dry paper weight for cationic rosin. The paper was then uniform after sizing.

[0051] (4) Plasticization and drying curing: The paper web is passed through an impregnation tank containing a 5wt% glycerol aqueous solution for 2 seconds. The temperature of the front section of the drying section is set at 90℃, and the temperature of the rear section is controlled at 105℃. The final paper moisture content is controlled at 6wt% before winding.

[0052] (5) Waste acid phase diagram control and recovery: The waste mixed acid liquid is pumped into the primary vacuum evaporator and concentrated to a sulfuric acid mass fraction of 30 wt%. It is then transferred to a crystallizer, cooled to 0°C, kept at that temperature for 1 hour, and centrifuged to separate magnesium sulfate crystals. The mother liquor is pumped into the secondary vacuum flash evaporator and concentrated at a temperature of 70°C and a vacuum degree of -0.08 MPa until the sulfuric acid concentration rises back to 65 wt%. The condensate is pumped back to the acid mixing vessel for circulation. Example 3:

[0053] This embodiment provides a papermaking process for lightweight, waterproof, and oil-resistant vegetable parchment paper, including the following steps: (1) Controlled gelation: Prepare a mixed acid solution in an acid mixing tank with the following mass fractions: sulfuric acid 68 wt%, glacial acetic acid 6 wt%, anhydrous magnesium sulfate 2 wt%, and the remainder being water. Control the acid bath temperature at 15℃. The quantitative amount is 30 g / m³. 2 The raw paper web is continuously introduced into the mixing acid bath, where it remains for 12 seconds. After exiting the acid bath, the free acid is removed by a squeeze roller.

[0054] (2) Reverse washing and polyamide epichlorohydrin resin retention: The paper web passes continuously through the reverse washing tank. When it reaches the middle and later part of the washing process and the pH of the water film is stable at 6.0, it enters the low shear impregnation shallow tank and continuously applies polyamide epichlorohydrin resin aqueous solution at a dry weight ratio of 1.0% of the oven-dry paper weight, followed by press impregnation.

[0055] (3) In-situ sequential spraying of sizing on the paper web: The pH of the microenvironment on the paper surface was controlled at 7.0, the fluid temperature at 50°C, and the moisture content of the wet paper web was controlled at 75 wt%. A 3 wt% sodium aluminate aqueous solution was sprayed onto the paper surface through a spraying system, with the application amount converted to 0.5% of the oven-dry paper weight (calculated as Al2O3). After a spatial time delay of 2.0 s, a mixture of alkyl ketone dimer emulsion and the cationic dispersed rosin obtained in Preparation Example 3 was sprayed. The application amount was converted to: 1.5% of the oven-dry paper weight for alkyl ketone dimer and 1.0% of the oven-dry paper weight for cationic rosin. The paper was then uniform after sizing.

[0056] (4) Plasticization and drying curing: The paper web is passed through an impregnation tank containing an 8wt% glycerol aqueous solution for 5 seconds. The temperature of the front section of the drying section is set at 100℃ and the temperature of the rear section is controlled at 110℃. The final paper moisture content is controlled at 8wt% before winding.

[0057] (5) Waste acid phase diagram control and recovery: The waste mixed acid liquid is pumped into the primary vacuum evaporator and concentrated to a sulfuric acid mass fraction of 35 wt%. It is then transferred to a crystallizer, cooled to 5°C, kept at that temperature for 2 hours, and centrifuged to separate magnesium sulfate crystals. The mother liquor is pumped into the secondary vacuum flash evaporator and concentrated at a temperature of 90°C and a vacuum degree of -0.09 MPa until the sulfuric acid concentration rises back to 68 wt%. The condensate is pumped back to the acid mixing vessel for circulation. Example 4:

[0058] This embodiment provides a papermaking process for lightweight, waterproof, and oil-resistant vegetable parchment paper, including the following steps: The steps in this embodiment are basically the same as those in embodiment 1, except that some reagents are replaced: in step (3), the aluminum source agent used in the first spraying is replaced by sodium aluminate aqueous solution with a mass fraction of 2wt% polyaluminum chloride aqueous solution, and the amount applied is also converted to 0.3% of the dry paper weight (calculated as Al2O3). In order to match the action conditions of acidic polyaluminum chloride, the pH parameter of the microenvironment on the paper surface is adjusted and controlled to 5.0 to 5.5 during spraying. In step (4), the impregnation solution used in the plasticizing stage is replaced by a glycerol aqueous solution with a 6.5 wt% polyethylene glycol aqueous solution. All other operating steps and process parameters are completely consistent with those in Example 1. In the waste acid recovery process, the waste acid recovery and proportion restoration logic is completely consistent with that in Example 1, and will not be repeated here. Example 5:

[0059] This embodiment provides a papermaking process for lightweight, waterproof, and oil-resistant vegetable parchment paper, including the following steps: The steps in this embodiment are basically the same as those in Embodiment 1, except that the only difference is the time delay control between the two spraying processes in step (3): In the in-situ sequential spraying of sizing on the paper web in step (3), after spraying the sodium aluminate aqueous solution, the paper web continues to travel for a spatial time delay of 0.5s (instead of 1.0s in Embodiment 1), that is, it reaches the second set of spraying devices to spray the mixture of alkyl ketone dimer emulsion and cationic dispersed rosin onto the paper surface. The remaining operation steps, the proportions of each group, and the waste acid recovery process are completely consistent with those in Embodiment 1.

[0060] Comparative Examples 1-5: Comparative Example 1: Compared with Example 1, the difference is that in the controlled gelation step (1), glacial acetic acid and anhydrous magnesium sulfate are not added to the acid mixing tank. Instead, concentrated sulfuric acid is directly diluted with pure water to the same sulfuric acid mass fraction as in Example 1 (i.e., a pure sulfuric acid aqueous solution with a mass fraction of 66.5 wt%). All other aspects are the same.

[0061] Comparative Example 2: Compared with Example 1, the difference is that in step (2) reverse washing and polyamide epichlorohydrin resin retention, the independent low-shear impregnation shallow tank and the control of water film pH stabilization at 5.8 are cancelled. Instead, the corresponding dose of polyamide epichlorohydrin resin aqueous solution is directly and continuously added to the front-end strongly acidic reverse water washing main tank phase. All other aspects are the same.

[0062] Comparative Example 3: Compared with Example 1, the difference is that in step (3), the in-situ sequential spraying and sizing process of paper web is cancelled, and the corresponding dose of sodium aluminate aqueous solution, alkyl ketone dimer emulsion and cationic dispersed rosin are directly mixed and continuously added to the water phase of the washing tank before the last extrusion roller of the reverse washing for in-tank sizing. The rest are the same.

[0063] Comparative Example 4: Compared with Example 1, the difference is that in step (3), the spatial time delay between the two sprayings is eliminated, and the corresponding doses of sodium aluminate aqueous solution, alkyl ketone dimer emulsion and cationic dispersed rosin are premixed into one agent and sprayed onto the wet paper surface simultaneously through the same set of spraying devices. All other aspects are the same.

[0064] Comparative Example 5: Compared with Example 1, the difference is that in step (5) waste acid recovery, the waste mixed acid liquid overflowing from the first stage reverse washing tank does not go through the pre-concentration of the first-stage vacuum evaporator, but is directly pumped into the crystallizer to slowly cool down to 2°C for freezing and desalting. The mother liquor after centrifugation then enters the evaporator for concentration. The rest are the same.

[0065] Test Examples 1-6: Test Example 1: Mechanical Properties of Wet Paper Web During the Gelation Stage (1) Sampling stage: During the continuous operation of the production line, the wet paper web that has been impregnated in the mixed acid bath and squeezed by the first rubber roller is selected as the test object. In order to prevent the residual acid from continuing to degrade the fiber after sampling, the sample is immediately immersed in a deionized ice water bath at 0°C to quench it, wash away the free mixed acid to terminate the reaction, and then use absorbent filter paper to dry the surface moisture.

[0066] (2) Sample preparation: At room temperature, use a standard paper cutter to longitudinally cut the quenched wet paper web into test strips that are 15 mm wide and 150 mm long, avoiding areas with holes or edge burrs during the operation.

[0067] (3) On-machine testing: An electronic tensile testing machine equipped with PTFE anti-corrosion clamps and a 100N sensor was used. The specimen was clamped and fixed, the initial gauge length was set to 100mm, and it was stretched at a constant speed of 20mm / min until fracture. The instantaneous moisture content, initial wet tensile strength and elongation at break were recorded during the test. Eight parallel experiments were conducted for each group, and the average value was taken after excluding data with large deviations.

[0068] Table 1. Test data of mechanical properties of wet paper web at the gelation stage

[0069] like Figure 1 As shown in Table 1, the tensile stress-strain evolution of the wet paper web after extrusion and deacidification is illustrated. Different geometric markings in the figure indicate the points where the corresponding samples fractured. In actual operation, Comparative Example 1, impregnated with pure sulfuric acid, showed poor stability. The wet paper web immediately after leaving the extrusion roll was semi-transparent and pasty, easily sticking to the roll. Test data showed that its initial wet tensile strength was only 0.215 kN / m, and its elongation at break was only 1.28%, making it prone to fracture under stress. This is mainly because the single high-concentration strong acid caused excessive swelling and degradation of cellulose, leading to a decrease in the degree of polymerization of the fiber backbone and the disintegration of the original interwoven network. The example group introduced a mixed solvent system. The wet tensile strength of Examples 1 to 3 remained above 0.772 kN / m, and the elongation at break was all above 3.8%, indicating that the paper strip had a certain deformation space during stretching. This is because glacial acetic acid reduced the dielectric constant of the liquid phase, slowing down the penetration rate of acid into the fiber interior; at the same time, magnesium ions generated an osmotic pressure gradient, causing the swelling effect of the acid to concentrate on the fiber surface. This results in a gel network forming on the paper web surface, while the internal skeleton fibers remain relatively intact. After liquid absorption, the internal skeleton layer still provides mechanical support, thereby reducing paper breaks caused by tension fluctuations during production.

[0070] Test Example 2: In-situ sizing retention effect and physicochemical properties analysis of free liquid on paper (1) Sampling preparation: The adhesive application and setting sections of Example 1, Comparative Example 3 and Comparative Example 4, which are in continuous operation, were selected as test nodes.

[0071] (2) Collection of free liquid: Use a wide-mouth sampling bottle to continuously collect the removed free liquid at the white water collection tray below the vacuum suction box and the squeezing roller. Maintain a constant speed of the production line during sampling, and the collection time is 10 minutes.

[0072] (3) Turbidity determination: After shaking the free liquid sample well, inject it into the cuvette of the scattering turbidity meter and measure the actual turbidity.

[0073] (4) Solid content analysis: Take 100 mL of the shaken free liquid and place it in an evaporating dish with constant weight. Bake it in an oven at 105℃ until constant weight. Calculate the total solid content based on the mass difference.

[0074] (5) Organic matter detection: A portion of the free liquid was filtered through a 200-mesh nylon screen to remove free fibers. The filtrate was then injected into a total organic carbon analyzer to determine the total organic carbon (TOC) concentration. Each test item was performed in parallel five times, and the average value was taken.

[0075] Table 2. Test data of physicochemical properties of the free liquid after sizing

[0076] like Figure 2 As shown in (a), (b), and (c), combined with the data in Table 2, the concentration distribution of various loss indicators in the sizing process effluent is presented. Sampling observation revealed that the effluent from Comparative Example 3 was milky white and turbid. Its free liquid turbidity was 876.3 NTU, total organic carbon concentration was 812.6 mg / L, and total solids content was as high as 1542.7 mg / L. This is because when the sizing agent was directly mixed and added in the washing tank, the rosin gum and alkyl ketone dimers failed to be fully adsorbed onto the fibers, and some were lost with the water into the white water circulation system and coagulated. Compared to the traditional in-tank mixing method, Example 1, using in-situ spraying on the paper surface, significantly reduced the concentration of various loss indicators in the effluent, with a turbidity of only 12.4 NTU, improving the retention rate of the sizing agent. Comparative Example 4 also used in-situ spraying, but the spraying time interval was eliminated; its free liquid total solids content was 689.1 mg / L, indicating a decrease in retention. The hydrolysis of inorganic aluminum salt into polymers requires a certain amount of time. When sprayed simultaneously without a time difference, the inorganic aluminum has not yet formed a microscopic network structure, and the hydrophobic colloidal particles arriving at the same time can easily penetrate the paper and be washed away by the water. Example 1 maintains a 1.0s time interval, providing sufficient time for the inorganic salt to hydrolyze, allowing it to form a network on the paper surface, thereby intercepting colloidal particles and reducing permeation loss.

[0077] Test Example 3: Verification of the efficiency of waste acid phase diagram cryogenic desalination (1) Selection of test objects: Under continuous operation, the materials of Examples 1 to 3 and Comparative Example 5 before and after entering the crystallizer were extracted from the waste acid recovery section.

[0078] (2) Sampling and phase separation: Record the initial volume of waste acid and the mass concentration of magnesium ions in each group. After freezing crystallization and separating magnesium sulfate crystals by centrifugation, collect the discharged mother liquor and store it in a sealed container.

[0079] (3) Sample pretreatment: Use ultrapure water to dilute the mother liquor sample to prevent strong acid from corroding the instrument.

[0080] (4) Concentration determination: The diluted sample was injected into the ion chromatograph to determine the concentration of residual magnesium ions in the mother liquor.

[0081] (5) Data calculation: The actual desalination rate of the system is calculated by combining the volume change and the law of conservation of mass. The average value is taken from five independent repeated measurements.

[0082] Table 3. Test data of physicochemical properties of waste acid phase diagram cryogenic desalination

[0083] like Figure 3 As shown in (a) and (b), combined with the data in Table 3, the comparison between the residual magnesium ion concentration in the mother liquor after refrigerated centrifugation and the actual desalination rate of the waste acid system is presented. Whether the system salts can be removed affects the operating cycle of the evaporator. In Comparative Example 5, which was directly subjected to refrigerated desalination without pre-concentration, the residual magnesium ion concentration in the mother liquor was 6.45 g / L, and the desalination rate was only 24.8%. After the waste acid enters the subsequent evaporation stage, the vaporization of water causes magnesium sulfate to reach its solubility limit, which will precipitate on the heat exchange tube wall to form scale, affecting the heat transfer efficiency. The example group added a pre-concentration stage to the process. The desalination rates of Examples 1 to 3 were above 84%, and the desalination rate of Example 3 reached 89.9%, with the residual magnesium ion concentration reduced to 1.52 g / L. In the unconcentrated dilute acid system, magnesium sulfate has high water solubility, and the desalination effect of simply cooling is limited. The examples increased the sulfuric acid concentration through pre-concentration, and due to the common ion effect, the solubility of magnesium sulfate hydrate (or magnesium sulfate heptahydrate) decreased accordingly. At this temperature, cooling to 0°C to 5°C facilitates the crystallization and precipitation of magnesium sulfate. This method of adjusting concentration and temperature improves the salt removal rate and reduces the risk of scaling in subsequent processes.

[0084] Test Example 4: Comparative Test of Liquid and Oil Repellency Performance of Finished Products (1) Sample preparation: Cut parchment finished products from Examples 1 to 5 and Comparative Examples 1 to 5. Before testing, the paper samples were placed in a constant temperature and humidity room at 23°C and 50% relative humidity for 24 hours for conditioning.

[0085] (2) Oil resistance test: Cut a 100mm×100mm sample and perform the Kit oil resistance test according to the TAPPIT559 standard. Add standard reagent and observe the penetration within 15 seconds. Record the highest reagent number that the sample can resist. Randomly measure 10 points and take the average value.

[0086] (3) Surface water absorption determination: Cobb60 test was performed according to GB / T 1540 standard. 100 mL of distilled water was injected into the Cobb absorber, and the water was poured out after 60 seconds of contact. The remaining surface water was removed using a metal roller. The water absorption per unit area of ​​Cobb60 (g / m²) was calculated. 2 Five parallel tests were conducted, and the average value was taken.

[0087] Table 4. Test data on liquid and oil resistance properties of finished parchment paper

[0088] like Figure 4 As shown in (a) and (b), combined with the data in Table 4, the distribution of Kit oil resistance ratings on the surface of each group of parchment finished products and the differences in Cobb 60 water absorption over the standard time are presented. Parchment itself possesses basic physical barrier properties, but it is prone to penetration when exposed to organic solvents or prolonged contact with water. Comparative Example 3 has a Kit rating of 2.4 and a Cobb 60 water absorption of 88.7 g / m³. 2 The liquid penetrates the paper surface relatively quickly upon contact. In the washing tank mixing mode, the AKD emulsion hydrolyzes in water and transforms into fatty ketones, reducing sizing capacity and failing to effectively bind with cellulose. After adopting in-situ sizing, the Kit grades of Examples 1 to 5 were above 10.6, and the Cobb water absorption was controlled at 22.4 g / m³. 2 The following (range: 18.1~22.4g / m) 2 The paper's liquid resistance was improved. Comparative Example 4, although also using in-situ paper coating, eliminated the time interval, resulting in a Kit rating of 5.6 and a Cobb 60 water absorption rate of 59.4 g / m³. 2 The hydrolysis of aluminum salts upon contact with slightly acidic moisture is a time-consuming process. In this example, by allowing a time difference, the aluminum salts pre-constructed a colloidal network in the shallow layer of the paper, thereby trapping and fixing the subsequent polymer sizing emulsion. In Comparative Example 4, due to the lack of this time interval, the aluminum salt flocs had not yet formed, and some hydrophobic colloidal particles penetrated downwards with the water, affecting the oil and water resistance of the surface layer.

[0089] Test Example 5: Comparative Test of Physical and Mechanical Properties of Finished Products (1) Sample preparation: Cut off the parchment rolls from the machine as test objects.

[0090] (2) Conditioning: Place the paper sample in a constant temperature and humidity test chamber at 23℃ and 50% relative humidity for 24 hours to equilibrate.

[0091] (3) Dry tensile test: Cut a specimen 15 mm wide and 250 mm long. In an electronic tensile testing machine (initial gauge length 180 mm), stretch it at a constant speed of 20 mm / min until fracture. Record the fracture force and calculate the dry tensile index.

[0092] (4) Wet tensile test: Test strips of the same size were immersed in room temperature deionized water for 24 hours. After removing and drying the surface moisture, they were subjected to tensile testing. To ensure a consistent testing standard, parameters were fine-tuned during the post-treatment and drying / calendering stages of each group of samples, so that the final measured weight of the paper was controlled within the range of 27.6-28.4 g / m³. 2 Within the specified range, the wet tensile retention rate is calculated by combining the measured values ​​with the theoretical dry tensile strength. Ten tests are conducted for each item, and the average value is taken.

[0093] Table 5. Test data of physical and mechanical properties of finished parchment paper

[0094] like Figure 5 As shown in (a) and (b), combined with the data in Table 5, the dry tensile index and wet tensile retention rate after 24 hours of water immersion under normal dry conditions are reflected. The data shows that, except for Comparative Examples 1 and 3, the dry tensile index of the other groups is generally above 80 N·m / g. Comparative Example 1 has a dry tensile index of 54.3 N·m / g and a wet tensile strength of only 0.38 kN / m, indicating that single high-concentration sulfuric acid immersion damages the fiber skeleton, leading to a decrease in polymerization degree and affecting the basic strength of the paper. Comparative Example 2 achieved a dry strength of 86.5 N·m / g, but after 24 hours of water immersion, the wet tensile retention rate was only 16.2%. This is because PAE wet-strength resin was added to the front-end strong acid washing tank in the process. The active groups in the resin molecules are prone to ring-opening failure in a strong acid environment and are lost in subsequent water washing, failing to form an effective water-resistant network. The wet tensile retention rates of Examples 1 to 5 are between 35% and 42%, and the wet tensile strength remains above 0.85 kN / m. The process involves transferring PAE resin to a shallow tank in the later stage for addition, and controlling the pH within a slightly acidic range of 5.5 to 6.0 to prevent resin degradation in strong acids. Within this pH range, the anions on the surface of hemicellulose dissociate, which is beneficial for the adhesion and penetration of PAE resin. During the drying and curing stage, the resin and cellulose undergo a cross-linking reaction, improving the paper's wet strength retention.

[0095] Test Example 6: Stability Assessment of Continuous Industrial Operation (1) Preparation of the assessment platform: On the pilot production line, Example 1, Comparative Example 1, Comparative Example 3 and Comparative Example 5 were used as assessment objects respectively.

[0096] (2) Monitoring the stability of wet end operation: After the parameters stabilize, the machine is run at a constant speed. Based on the cumulative production of 100 kilometers of paper web, the number of non-mechanical paper breaks is counted.

[0097] (3) Determination of anti-scaling cycle of evaporator: Record the continuous running time of the secondary vacuum flash evaporator in the waste acid recovery section from clean start-up to forced shutdown for descaling when the system vacuum drops below -0.07MPa.

[0098] (4) System sediment inspection: Record the polymer adhesion on the pipe wall and guide roller surface, and summarize the operating indicators.

[0099] Table 6. Test data for continuous operation stability assessment project

[0100] like Figure 6 As shown in (a) and (b), combined with the data in Table 6, the frequency of wet-end paper breakage during the 100-kilometer papermaking process is compared with the continuous operating cycle of the secondary evaporator against scaling. In Comparative Example 1, the pure acid system experienced 17 paper breakages per 100 kilometers. Overly acidic paper webs are prone to sticking when passing through the squeeze rollers, and even slight tension fluctuations can cause tearing. In Comparative Example 3, the number of paper breakages was 9, and the evaporator operating cycle was shortened to 145.6 hours. Mixing chemicals in the tank caused unadsorbed hydrophobic colloidal particles to enter the bulk water and condense, easily accumulating on the guide roller surface and causing paper sticking and breakage. After entering the waste acid circulation with the water flow, some organic matter adhered to the evaporator tube wall, reducing heat transfer efficiency. Comparative Example 5 did not use a pre-concentration process, resulting in limited cryogenic desalination. The waste acid carried a large amount of magnesium ions into the secondary evaporator. After water vaporization, the magnesium sulfate concentration reached supersaturation, precipitating on the tube wall to form inorganic scale. The system needed to be shut down for cleaning after 42.3 hours of operation. In contrast, the number of paper breaks in Example 1 was reduced to 2, and the evaporator's continuous operating cycle reached 342.8 hours. The mixed acid bath maintained the mechanical strength of the wet paper web to some extent, reducing paper breaks; the in-situ spraying technology reduced the loss of organic matter into the water circulation system, and combined with the pre-concentration and desalination treatment in the waste acid recovery section, reduced the deposition of organic and inorganic matter in the system, thereby extending the continuous operating time of the equipment.

Claims

1. A lightweight, waterproof, and oil-resistant vegetable parchment paper, characterized in that, The parchment is made from a base paper substrate and sizing components and plasticizers loaded on the base paper substrate; Wherein, based on the oven-dry weight of the base paper substrate as 100%, the sizing component comprises the following raw materials in oven-dry weight percentages: Polyamide epichlorohydrin resin: 0.5–1.0%; Inorganic aluminum salts, calculated as Al2O3: 0.1–0.5%; Alkyl ketone dimers: 0.5–1.5%; Cationic dispersion rosin gum: 0.3–1.0%; The polyamide epichlorohydrin resin is permeated and loaded into the internal pores of the base paper substrate; the inorganic aluminum salt, the alkyl ketone dimer, and the cationic dispersed rosin are loaded on the surface of the base paper substrate; the loading structure on the surface of the base paper substrate is formed by an independent application method with spatial and temporal delay, through sequential spraying of an aqueous solution of inorganic aluminum salt, a mixture of alkyl ketone dimer and cationic dispersed rosin.

2. The parchment according to claim 1, characterized in that, The cationic dispersed rosin gum is a dispersion prepared by reacting rosin and a positively charged cationic polymer aqueous solution with high-temperature melting, high-speed shearing primary emulsification and high-pressure homogenization. The positively charged cationic polymer is selected from polydimethyldiallylammonium chloride and cationic starch with a degree of substitution of 0.030 to 0.035, and the solid content of the cationic dispersed rosin gum is 30 to 35 wt%.

3. The parchment according to claim 1, characterized in that, The inorganic aluminum salt is sodium aluminate or polyaluminum chloride; the plasticizer is glycerol or polyethylene glycol.

4. The parchment according to claim 1, characterized in that, The basis weight of the base paper is 25-30 g / m³. 2 The final moisture content of the parchment paper is controlled at 6-8 wt%.

5. A papermaking process for lightweight, waterproof, and oil-resistant vegetable parchment paper, characterized in that, The preparation of parchment as described in any one of claims 1-4 comprises the following steps: The original paper web is continuously introduced into a mixed acid solution provided by an acid mixing tank for impregnation and gelation. After exiting the acid bath, the free acid solution on the surface is initially removed to obtain a wet paper web. The wet paper web is continuously washed through a multi-stage reverse washing tank. When the wet paper web reaches the middle and later part of the washing process, it enters a low-shear impregnation shallow tank, where the polyamide epichlorohydrin resin aqueous solution is continuously applied to the wet paper web and pressed to penetrate. The inorganic aluminum salt aqueous solution is sprayed onto the surface of the wet paper web after pressing and penetration. After the wet paper web continues to travel through a spatial time delay, a mixture of alkyl ketone dimer emulsion and cationic dispersed rosin is sprayed onto the paper surface, followed by homogenization. The uniformly sized wet paper web is impregnated through an aqueous solution containing the plasticizer, and then enters the drying section for drying and curing before being wound up. The waste mixed acid liquid overflowing from the first section of the multi-stage reverse water washing tank during the aforementioned washing process is pumped into the first-stage vacuum evaporator for concentration. The concentrated liquid is transferred to the crystallizer for cooling and precipitation, and the by-product salt crystals are separated. The desalted mother liquor is pumped into the second-stage vacuum flash evaporator for deep concentration to restore the initial concentration of the mixed acid liquid and circulate it back to the acid mixing kettle.

6. The papermaking process according to claim 5, characterized in that, The mixed acid solution, with a total mass fraction of 100%, comprises: 65-68 wt% sulfuric acid, 4-6 wt% glacial acetic acid, 1-2 wt% anhydrous magnesium sulfate, and the remainder being water. The acid bath temperature is controlled at 10-15°C, and the residence time of the original paper web in the mixed acid solution is 6-12 s.

7. The papermaking process according to claim 5, characterized in that, During the washing process, when the pH of the water film in the latter part of the washing process is stabilized at 5.5 to 6.0 by online monitoring and control, the paper web enters the low-shear impregnation shallow tank; the dry weight ratio of the applied polyamide epichlorohydrin resin is 0.5 to 1.0% of the oven-dry paper weight.

8. The papermaking process according to claim 5, characterized in that, When spraying the inorganic aluminum salt aqueous solution, the pH of the microenvironment on the paper surface is controlled to be 5.0-7.0, the fluid temperature is 45-50℃, the moisture content of the wet paper web is controlled to be 60-75wt%, and the spatial time delay is 0.5-2.0s.

9. The papermaking process according to claim 5, characterized in that, The aqueous solution containing plasticizer has a mass fraction of 5-8 wt% and an immersion time of 2-5 s; the surface temperature of the front drying cylinder of the drying section is set to 90-100℃, and the rear section is controlled at 105-110℃.

10. The papermaking process according to claim 5, characterized in that, The waste mixed acid solution is concentrated to a sulfuric acid mass fraction of 30-35 wt% in the first-stage vacuum evaporator; the temperature is slowly lowered to 0-5℃ and held for 1-2 hours in the crystallizer; and the solution is concentrated in the second-stage vacuum flash evaporator at a temperature of 70-90℃ and a vacuum degree of -0.08 to -0.09 MPa.

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