A paper strength improver, high-strength base paper and preparation method thereof

Abstract

The present invention belongs to the technical field of papermaking, and in particular relates to a paper strength improver, high-strength base paper and a preparation method thereof. The paper strength improver comprises the following raw materials in parts by weight: 20 to 50 parts of calcium oxide, 40 to 80 parts of rubber, 10 to 30 parts of a surfactant, an appropriate amount of an organic solvent, and an appropriate amount of water. The paper strength improver of the present invention can effectively improve the strength performance of paper, and can be used in paper products to prepare base paper with excellent strength performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of papermaking, and in particular relates to a paper strength improver, high-strength base paper and a preparation method thereof. Background Art

[0002] In the papermaking process, a variety of additives are commonly used to improve production efficiency, enhance paper quality, reduce waste, and conserve raw material consumption. These additives can be categorized into two main categories: process additives and functional additives, depending on their function. Process additives primarily improve the wet-end handling of paper stock, ensuring smooth papermaking. Commonly used include retention and drainage aids, such as cationic starch, polyacrylamide, and polyethyleneimine. These enhance the retention of fine fibers and fillers, reduce waste, and improve the drainage properties of paper stock, thereby increasing production efficiency. Other additives include dispersants, defoamers, preservatives, and flocculants. Functional additives, on the other hand, are primarily used to impart special properties or improve certain characteristics of paper. Commonly used additives include internal sizing agents, surface sizing agents, dry strength additives, wet strength additives, softeners, water repellents, and brighteners. A wide variety of additives are used in the papermaking process, and their rational use is crucial for increasing production efficiency, improving paper quality, and reducing production costs.

[0003] Paper strength improvers, also known as paper enhancers, are important chemical additives in the papermaking process. They are comprehensive additives that combine the properties of one or more of the aforementioned additives, such as internal sizing agents, surface sizing agents, dry strength agents, wet strength agents, and softeners. Through their unique chemical structure and mechanism of action, they can enhance paper strength, improve fiber bonding and distribution, and thereby improve various strength properties such as tensile strength, tear strength, and bursting strength, while also enhancing the paper's uniformity and printability. Currently, paper strength improvers are widely used in the production of various types of paper, particularly decorative paper, cultural paper, offset paper, household paper, wrapping paper, map paper, napkin paper, and paper bag paper, which require enhanced performance.

[0004] In the prior art, polyacrylamide mixtures and starch mixtures are often used to improve the strength properties of paper. In comparison, the price of polyacrylamide mixtures is higher than that of starch, but their fixation on paper pulp is higher than that of starch. They are currently the most commonly used paper strength improvers. Polyacrylamide mixtures mainly include anionic polyacrylamide, cationic polyacrylamide and amphoteric polyacrylamide, among which amphoteric polyacrylamide has the best comprehensive effect. On this basis, those skilled in the art have also proposed methods for improving paper strength by combining polyacrylamide polymers and water-soluble polysaccharides. However, in these methods, the improvement of paper strength by starch mixtures is limited; amphoteric polyacrylamide mixtures have problems such as a relatively narrow applicable pH system range, a disordered distribution of anionic and cationic monomers, uncontrollable interactions between anionic and cationic charges, and large batch performance differences caused by unstable binding effects with pulp fibers; the dispersibility of the mixed solution of anionic water-soluble polysaccharides and ionic polyacrylamide is still a problem, and it cannot be used stably. As a result, the above methods have limited improvement in paper strength.

[0005] In view of this, providing a new type of paper strength improver that can effectively improve the strength properties of paper and a preparation method thereof, and further preparing base paper with excellent strength performance, is one of the technical problems that technical personnel in this field urgently need to solve. Summary of the Invention

[0006] The purpose of the present invention is to provide a paper strength improver, high-strength base paper and a preparation method thereof in response to the above-mentioned technical problems.

[0007] In view of this, the present invention provides a paper improving agent, comprising the following raw materials in parts by weight:

[0008] 20~50 parts of calcium oxide,

[0009] 40~80 parts of rubber,

[0010] 10~30 parts of surfactant,

[0011] Appropriate amount of organic solvent,

[0012] Appropriate amount of water.

[0013] Furthermore, the paper strength improving agent comprises the following raw materials in parts by weight:

[0014] 20~30 parts of calcium oxide,

[0015] 50~60 parts of rubber,

[0016] 15-25 parts of surfactant,

[0017] Appropriate amount of organic solvent,

[0018] Appropriate amount of water.

[0019] Furthermore, the rubber is selected from one or more of natural rubber, nitrile rubber, and polyurethane rubber.

[0020] Furthermore, the surfactant is selected from polyol nonionic surfactants and / or polyoxyethylene anionic surfactants.

[0021] A method for preparing a paper strength improving agent, the method is used to prepare the above-mentioned paper strength improving agent, and the method for preparing the paper strength improving agent comprises the steps of:

[0022] S1, preparing a calcium hydroxide suspension: dissolving a formulated amount of calcium oxide in water, stirring thoroughly to prepare a calcium hydroxide suspension with a solid content of 3-10 wt%;

[0023] S2, preparing a rubber solution: dissolving a formulated amount of rubber in an appropriate amount of an organic solvent to prepare a rubber solution having a rubber content of 1 to 6 wt%;

[0024] S3, preparing a surfactant aqueous solution: dissolving a formulated amount of surfactant in water to prepare a surfactant aqueous solution having a surfactant content of 0.1 to 0.5 wt %;

[0025] S4, preparing a mixed solution a: slowly adding the rubber solution obtained in step S2 to the calcium hydroxide suspension obtained in step S1 under stirring, and stirring thoroughly to mix uniformly to obtain a mixed solution a; then slowly pouring the mixed solution a into the surfactant aqueous solution under stirring to obtain a mixed solution b;

[0026] S5, preparing a paper improving agent: heating the mixed solution b obtained in step S4 to 100-130° C. and distilling off the organic solvent therein to obtain the paper improving agent.

[0027] A high-strength base paper comprises the following raw materials in parts by weight: 60-100 parts of hardwood pulp, 20-40 parts of softwood pulp, 10-20 parts of bast pulp, 15-25 parts of calcium carbonate, 3-5 parts of polyvinyl alcohol, 3-5 parts of aluminum sulfate, 20-30 parts of cross-linked starch, 3-8 parts of microfibrillated cellulose, 0.3-0.5 parts of a dispersant, 0.1-0.3 parts of citric acid, and 60-300 parts of the above-mentioned paper strength improver.

[0028] Furthermore, the calcium carbonate is modified calcium carbonate that has undergone modification treatment.

[0029] Furthermore, the preparation process of the modified calcium carbonate is as follows:

[0030] First, 10-20 parts by weight of calcium carbonate are dispersed in an organic solvent, stirred to make it uniformly dispersed, heated to 50-70°C, and 3-5 parts by weight of 1-aminopropane are slowly added under stirring. After continuing to stir and react at 50-70°C for 5-10 minutes, 5-10 parts by weight of silane are slowly added dropwise. After continuing to stir and react at 50-70°C for 1-2 hours, the modified calcium carbonate is obtained by filtering, washing, and drying.

[0031] A method for preparing high-strength base paper, the method is used to prepare the above-mentioned high-strength base paper, the method comprising the steps of:

[0032] (I) beating: dry pulp of hardwood pulp, softwood pulp and bast pulp is mixed according to a weight ratio and added to a hydraulic pulper for disintegration, the pulping concentration is controlled to be 5-10 wt% and the disintegration time is 30-60 min, and then the pulp obtained after disintegration is poured into a pulper for beating to obtain a pulp with a beating degree of 30-45°SR and a mass concentration of 4-7 wt%;

[0033] (II) Slurry preparation: adding a formulated amount of calcium carbonate, polyvinyl alcohol, aluminum sulfate, cross-linked starch, microfibrillated cellulose, a dispersant, and citric acid to the slurry obtained in step (I), diluting with water until the concentration of the mixed wood pulp fibers in the slurry is 0.2-0.5 wt%, adding a formulated amount of a paper strength improver, and stirring uniformly to obtain a prepared slurry;

[0034] (III) Forming on the web: feeding the slurry prepared in step (II) into a papermaking machine, distributing it through a headbox and forming it on the web to obtain wet paper sheets;

[0035] (IV) Carbonization treatment: The wet paper is first placed in an inert gas at a temperature of 100-130°C for 30-60 seconds, and then placed in a mixed gas containing carbon dioxide at a temperature of 60-90°C for 5-10 minutes;

[0036] (V) Pressing, drying, calendering and rolling: The carbonized paper sheets are pressed, dried, calendered and rolled to obtain high-strength base paper.

[0037] Furthermore, in step (IV), the volume percentage of carbon dioxide in the mixed gas is 30-50%.

[0038] The beneficial effects of the present invention are:

[0039] The paper strength improver of the present invention can effectively improve the strength performance of paper, and can be used in paper products to prepare base paper with excellent strength performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1Schematic diagram of the working mode of the paper strength improving agent of the present invention;

[0041] The marks in the figure are:

[0042] 1. Pulp fiber, 2. Rubber particles, 3. Filler particles. DETAILED DESCRIPTION

[0043] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of this application.

[0044] It should be noted that, in the present application, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element. In addition, it should be pointed out that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in the opposite order according to the functions involved. For example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0045] A paper strength improving agent comprises the following raw materials in parts by weight:

[0046] 20~50 parts of calcium oxide,

[0047] 40~80 parts of rubber,

[0048] 10~30 parts of surfactant,

[0049] Appropriate amount of organic solvent,

[0050] Appropriate amount of water.

[0051] Preferably, the paper strength improving agent comprises the following raw materials in parts by weight:

[0052] 20~30 parts of calcium oxide,

[0053] 50~60 parts of rubber,

[0054] 15-25 parts of surfactant,

[0055] Appropriate amount of organic solvent,

[0056] Appropriate amount of water.

[0057] Preferably, the particle size of the calcium oxide is 0.1-30 μm.

[0058] As some examples of the present invention, the rubber is selected from one or more of natural rubber, nitrile rubber, and polyurethane rubber.

[0059] Preferably, the rubber is natural rubber.

[0060] Preferably, the surfactant is a nonionic surfactant and / or an anionic surfactant.

[0061] As some examples of the present invention, the surfactant is selected from polyol-type nonionic surfactants, such as sucrose fatty acid esters, sorbitan fatty acid esters, and / or polyoxyethylene-type anionic surfactants, such as fatty alcohol polyoxyethylene ether sulfate (AES).

[0062] As some examples of the present invention, the organic solvent is selected from one or more of toluene, xylene, chloroform, carbon tetrachloride, ethyl acetate, MIBK and the like.

[0063] Furthermore, the present invention also provides a method for preparing a paper strength improving agent, which is used to prepare the above-mentioned paper strength improving agent, and the preparation method comprises the steps of:

[0064] S1, preparing a calcium hydroxide suspension: dissolving a formulated amount of calcium oxide in water, stirring thoroughly to prepare a calcium hydroxide suspension with a solid content of 3-10 wt%;

[0065] S2, preparing a rubber solution: dissolving a formulated amount of rubber in an appropriate amount of an organic solvent to prepare a rubber solution having a rubber content of 1 to 6 wt%;

[0066] S3, preparing a surfactant aqueous solution: dissolving a formulated amount of surfactant in water to prepare a surfactant aqueous solution having a surfactant content of 0.1 to 0.5 wt %;

[0067] S4, preparing a mixed solution a: slowly adding the rubber solution obtained in step S2 to the calcium hydroxide suspension obtained in step S1 under stirring, and stirring thoroughly to mix uniformly to obtain a mixed solution a; then slowly pouring the mixed solution a into the surfactant aqueous solution under stirring to obtain a mixed solution b;

[0068] S5, preparing a paper improving agent: heating the mixed solution b obtained in step S4 to 100-130° C. and distilling off the organic solvent therein to obtain the paper improving agent.

[0069] Preferably, in step S4, the rubber solution obtained in step S2 is added to the calcium hydroxide suspension in batches within 5 to 10 minutes, and then stirred at a speed of 1000 to 5000 rpm for 20 to 40 minutes, and fully mixed to obtain a mixed solution a.

[0070] Specifically, the rubber solution can be divided into 5 to 10 equal parts, and one part thereof is added to the calcium hydroxide suspension every 1 minute.

[0071] Preferably, in step S4, the mixed solution a is continuously and slowly poured into the surfactant aqueous solution within 10 to 20 minutes to obtain the mixed solution b.

[0072] Specifically, the mixed solution a can be continuously added to the surfactant aqueous solution at an appropriate flow rate, wherein the continuous addition time of the mixed solution a is between 10 and 20 minutes.

[0073] In the paper strength improver of the present invention, a rubber solution is slowly added to a calcium hydroxide suspension. After sufficient stirring, the rubber latex is dispersed in water and coats the calcium hydroxide particles, forming a core-shell structure in which the shell layer is the rubber solution and the core layer is the calcium hydroxide particles dispersed in water. On this basis, when the rubber solution is dispersed in an aqueous surfactant solution, the core-shell structure in which the shell layer is the rubber solution and the core layer is the calcium hydroxide particles can be further fixed and its morphology can be stably maintained under the cross-linking and fixing effect of the surfactant, so that the final paper strength improver contains a core-shell structure in which the shell layer is the rubber solution and the core layer is the calcium hydroxide particles, which can be stably dispersed in the aqueous phase.

[0074] In the papermaking process, people have long desired to add rubber as an additive to paper products, hoping to utilize rubber's unique properties to enhance the strength, elasticity, and flexibility of paper products, as well as improve properties such as abrasion resistance and tear resistance. However, due to the significant differences in the chemical and physical properties of rubber and paper fibers, their compatibility is poor, making it difficult to evenly disperse the rubber in paper, ultimately affecting the uniformity and overall performance of the paper. As described in U.S. Patent Publication No. US1799217A, how to evenly disperse rubber in paper products is a technical challenge in this field. In the prior art, a common practice is to emulsify rubber into a rubber latex and add it to paper products. While this can improve the uniformity of rubber dispersion in paper products to a certain extent, the rubber latex easily agglomerates during the stirring process during papermaking, reducing the uniformity of rubber dispersion. Furthermore, the addition of the rubber latex can adversely affect the fluidity and filterability of the paper pulp. Another common practice is to add rubber powder to paper products. However, the rubber powder added in this way is difficult to form a good combination with other components in the paper products, such as fibers, inorganic fillers, etc., so the effect on improving the performance of paper products is also very limited.

[0075] The paper strength improver of the present invention forms a core-shell structure capable of being stably present in an aqueous phase by compounding rubber with calcium hydroxide particles under the action of a surfactant. The core-shell structure is not easily agglomerated into blocks during the papermaking stirring process. The final paper strength improver can not only achieve uniform and stable dispersion of the rubber, but also has high fluidity, and will not significantly affect the fluidity and filtration performance of the pulp. More importantly, the paper strength improver can also play the role of a paper strength improver and improve the strength performance of the paper.

[0076] Furthermore, the present invention also provides a high-strength base paper, comprising the following raw materials in parts by weight:

[0077] 60~100 parts of hardwood pulp,

[0078] 20~40 parts of softwood pulp,

[0079] 10~20 parts of bast pulp,

[0080] 15-25 parts of calcium carbonate,

[0081] 3-5 parts of polyvinyl alcohol,

[0082] 3~5 parts of aluminum sulfate,

[0083] 20-30 parts of cross-linked starch,

[0084] 3-8 parts of microfibrillated cellulose,

[0085] 0.3~0.5 parts of dispersant,

[0086] 0.1~0.3 parts of citric acid,

[0087] And, 60-300 parts of the above-mentioned paper strength improving agent.

[0088] Preferably, the calcium carbonate is modified calcium carbonate that has been subjected to modification treatment.

[0089] Specifically, the preparation process of the modified calcium carbonate is as follows:

[0090] First, 10-20 parts by weight of calcium carbonate are dispersed in an organic solvent, stirred to make it uniformly dispersed, heated to 50-70°C, and 3-5 parts by weight of 1-aminopropane are slowly added under stirring. After continuing to stir and react at 50-70°C for 5-10 minutes, 5-10 parts by weight of silane are slowly added dropwise. After continuing to stir and react at 50-70°C for 1-2 hours, the modified calcium carbonate is obtained by filtering, washing, and drying.

[0091] Preferably, the 1-aminopropane is added within 3 to 5 minutes, and the silane is added dropwise within 5 to 10 minutes.

[0092] As some examples of the present invention, the organic solvent for preparing the modified calcium carbonate is selected from one or more of cyclohexane, n-hexane, n-heptane, toluene, xylene, ethyl acetate, and the like.

[0093] As some examples of the present invention, the silane used to prepare the modified calcium carbonate is selected from one or more of trimethylbutyl peroxysilane, 3-aminopropyltriethoxysilane (APTES), vinyltris(2-methoxyethoxy)silane, and the like.

[0094] During the modification process of the calcium carbonate, 1-aminopropane, as an organic amine compound, has amino groups (-NH2) in its molecules that react with hydroxyl groups (-OH) on the surface of the nano-inorganic filler, introducing amino groups on the surface of the calcium carbonate. These amino groups can serve as active sites for subsequent reactions. Furthermore, in the subsequent silanization reaction, the silane molecules can further modify the surface of the nano-inorganic filler. The silicon-oxygen bonds (Si-O) in the silane molecules can react with the remaining hydroxyl groups or introduced amino groups on the surface of the calcium carbonate to form a stronger chemical bond. The surface of the modified calcium carbonate is coated with a substance with double bonds, which helps to reduce the agglomeration of calcium carbonate particles, making it more dispersible and having a higher interfacial bonding strength with other components in the paper, especially the organic phase. This can improve the retention rate of the filler and the physical strength of the paper, such as tensile strength and tear strength, while also helping to improve the paper's burst resistance and folding resistance.

[0095] In addition, the present invention also provides a method for preparing high-strength base paper, which comprises the steps of:

[0096] (I) beating: dry pulp of hardwood pulp, softwood pulp and bast pulp is mixed according to a weight ratio and added to a hydraulic pulper for disintegration, the pulping concentration is controlled to be 5-10 wt% and the disintegration time is 30-60 min, and then the pulp obtained after disintegration is poured into a pulper for beating to obtain a pulp with a beating degree of 30-45°SR and a mass concentration of 4-7 wt%;

[0097] (II) Slurry preparation: adding a formulated amount of calcium carbonate, polyvinyl alcohol, aluminum sulfate, cross-linked starch, microfibrillated cellulose, a dispersant, and citric acid to the slurry obtained in step (I), diluting with water until the concentration of the mixed wood pulp fibers in the slurry is 0.2-0.5 wt%, adding a formulated amount of a paper strength improver, and stirring uniformly to obtain a prepared slurry;

[0098] (III) Forming on the web: feeding the slurry prepared in step (II) into a papermaking machine, distributing it through a headbox and forming it on the web to obtain wet paper sheets;

[0099] (IV) Carbonization treatment: The wet paper is first placed in an inert gas at a temperature of 100-130°C for 30-60 seconds, and then placed in a mixed gas containing carbon dioxide at a temperature of 60-90°C for 5-10 minutes;

[0100] (V) Pressing, drying, calendering and rolling: The carbonized paper sheets are pressed, dried, calendered and rolled to obtain high-strength base paper.

[0101] Preferably, in step (IV), the volume percentage of carbon dioxide in the mixed gas is 30-50%.

[0102] During the preparation of the high-strength base paper described herein, the addition of a certain amount of softwood rice pulp and bast pulp increases the slender fibers and reduced cell content of the softwood pulp, resulting in paper with excellent flexibility, high folding resistance, and good tensile strength. The slender and strong bast fibers contribute to improved performance indicators such as tensile strength and tear resistance of the base paper. Polyvinyl alcohol, cross-linked starch, and microfibrillated cellulose enhance interfiber adhesion, thereby increasing the strength of the paper.

[0103] On this basis, by compounding the paper strength improving agent of the present invention, the strength performance of paper can be further improved. Figure 1As shown, the working process of the paper strength improver of the present invention is as follows: During the base paper preparation process, the wet paper sheet is first placed in a high-temperature environment formed by inert gas. Under the dual effects of water loss and high temperature, the surfactant in the paper strength improver loses its cross-linking and fixing effect on the rubber shell layer. The rubber shell of the outer layer of the core-shell structure gradually breaks and unfolds, and adheres to the pulp fibers 1 and filler particles 3 in the paper. The filler particles 3 include calcium carbonate particles directly added to the papermaking raw materials and calcium hydroxide particles exposed after the rubber shell layer breaks. In this way, the rubber particles 2 can be evenly distributed between the pulp fibers 1 and filler particles 3 in the paper. This not only achieves uniform and good dispersion of the rubber, but also forms bonding points with the rubber particles 2 as the core. It not only enhances the interaction between the rubber particles 2, pulp fibers 1 and filler particles 3, thereby improving the overall strength of the paper, including tensile strength, burst resistance, and tear resistance. The adhesion of the rubber particles 2 also makes the paper surface smoother and more uniform, which is beneficial to improving the printing quality and image clarity of the paper. Thereafter, high-temperature carbon dioxide gas is used to react with calcium hydroxide to in-situ generate a layer of calcium carbonate on the surface of the calcium hydroxide, forming composite particles with an outer layer of calcium carbonate and an inner layer of calcium hydroxide. The calcium carbonate in these composite particles can be fixed to the surface of the calcium hydroxide through heterogeneous nucleation and in-situ generation, and attached to the pulp fibers 1 through a deposition reaction. Ultimately, these composite particles can form a stable connection with the rubber particles 2, pulp fibers 1, etc., making them less likely to be lost. At the same time, these composite particles can form a more uniform and dense filling between the pulp fibers 1, thereby improving the gloss, smoothness, and strength of the paper. In addition, compared with traditional calcium carbonate inorganic fillers, the structure of these composite particles can improve the filler's whiteness, opacity, and ink absorption performance through its unique double-layer structure, thereby improving the whiteness, opacity, and printing performance of the paper.

[0104] The paper strength improving agent and high-strength base paper of the present invention are illustrated below by specific examples:

[0105] Examples 1 to 5

[0106] Preparation of paper strength improving agent: The raw material ratio of the paper strength improving agent is shown in Table 1 below:

[0107]

[0108] The rubbers used in Examples 1 to 5 are, in order, natural rubber, nitrile rubber, natural rubber, polyurethane rubber, and nitrile rubber; the surfactants are, in order, sucrose fatty acid esters, sorbitan fatty acid esters, sodium fatty alcohol polyoxyethylene ether sulfate, sodium fatty alcohol polyoxyethylene ether sulfate, and sucrose fatty acid esters; and the organic solvents are, in order, a mixture of toluene and chloroform, toluene, a mixture of toluene and chloroform, acetone, and a mixture of xylene and chloroform.

[0109] The preparation of the paper strength improving agent is carried out according to the process described in steps S1 to S5. In step S5, the amount of the organic solvent evaporated is controlled to be no less than 97% of the total amount added.

[0110] Example 6

[0111] Preparation of modified calcium carbonate:

[0112] First, 15 parts by weight of calcium carbonate are dispersed in an organic solvent, stirred to make it uniformly dispersed, heated to 60°C, and slowly added with stirring 4 parts by weight of 1-aminopropane. After stirring and reacting at 60°C for 8 minutes, 6 parts by weight of silane are slowly added dropwise. After stirring and reacting at 60°C for 1.5 hours, the modified calcium carbonate is obtained by filtering, washing, and drying.

[0113] Examples 7-11

[0114] Preparation of high-strength base paper: The raw material ratio of high-strength base paper is shown in Table 2 below:

[0115]

[0116] Among them, the paper strength improvers used in Examples 7 to 11 were the paper strength improvers prepared in Examples 1 to 5 above, respectively; Examples 7 and 8 used the modified calcium carbonate prepared in Example 6 above; and Examples 9 to 11 used unmodified calcium carbonate.

[0117] The preparation process of the high-strength base paper in Examples 7 to 11 is as follows:

[0118] (I) beating: dry pulp of hardwood pulp, softwood pulp and bast pulp is mixed according to a weight ratio and added to a hydraulic pulper for disintegration, the concentration of the pulp is controlled to be 5wt%, 6wt%, 8wt%, 9wt% and 10wt% in sequence, and the disintegration time is 30min, 40min, 45min, 50min and 60min in sequence, and then the pulp obtained after the disintegration is poured into a pulper for beating to obtain pulps with beating degrees of 30°SR, 32°SR, 35°SR, 40°SR and 45°SR and mass concentrations of 4wt%, 5wt%, 5wt%, 6wt% and 7wt%;

[0119] (II) Slurry preparation: adding a formulated amount of calcium carbonate, polyvinyl alcohol, aluminum sulfate, cross-linked starch, microfibrillated cellulose, a dispersant, and citric acid to the slurry obtained in step (I), diluting with water until the concentration of the mixed wood pulp fibers in the slurry is 0.2 wt%, 0.3 wt%, 0.3 wt%, 0.4 wt%, and 0.5 wt%, adding a formulated amount of a paper strength improver, and stirring uniformly to obtain a prepared slurry;

[0120] (III) Forming on the web: feeding the slurry prepared in step (II) into a papermaking machine, distributing it through a headbox and forming it on the web to obtain wet paper sheets;

[0121] (IV) Carbonization treatment: The wet paper sheets are first placed in an inert gas at temperatures of 100°C, 110°C, 120°C, 120°C, and 130°C for 30 seconds, 40 seconds, 40 seconds, 50 seconds, and 60 seconds, and then the paper sheets are placed in a mixed gas containing carbon dioxide at 60°C, 70°C, 70°C, 80°C, and 90°C for carbonization treatment for 5 minutes, 7 minutes, 8 minutes, 7 minutes, and 10 minutes; wherein the volume percentage of carbon dioxide in the mixed gas is 30%, 35%, 40%, 45%, and 50%;

[0122] (V) Pressing, drying, calendering and rolling: The carbonized paper sheets are pressed, dried, calendered and rolled to obtain high-strength base paper.

[0123] Comparative Example 1

[0124] Preparation of high-strength base paper:

[0125] The only difference between Comparative Example 1 and Example 8 is that:

[0126] The preparation process of the modified calcium carbonate used is:

[0127] First, 15 parts by weight of calcium carbonate are dispersed in an organic solvent, stirred to make it uniformly dispersed, heated to 60°C, and 4 parts by weight of 1-aminopropane are slowly added under stirring. After stirring and reacting at 60°C for 8 minutes, the modified calcium carbonate is obtained by filtering, washing, and drying.

[0128] Comparative Example 2

[0129] Preparation of high-strength base paper:

[0130] The only difference between Comparative Example 2 and Example 8 is that:

[0131] The preparation process of the modified calcium carbonate used is:

[0132] First, 15 parts by weight of calcium carbonate are dispersed in an organic solvent, stirred to make it uniformly dispersed, heated to 60°C, and 6 parts by weight of silane are slowly added dropwise under stirring. After stirring and reacting at 60°C for 1.5 hours, the modified calcium carbonate is obtained by filtering, washing, and drying.

[0133] Comparative Example 3

[0134] Preparation of high-strength base paper:

[0135] The only difference between Comparative Example 3 and Example 8 is that:

[0136] High-strength base paper is prepared by using nitrile rubber emulsion with equal nitrile rubber content instead of paper strength improver.

[0137] Comparative Example 4

[0138] Preparation of high-strength base paper:

[0139] The only difference between Comparative Example 4 and Example 8 is that:

[0140] After step (III), step (V) is directly carried out without going through the carbonization process in step (IV).

[0141] Comparative Example 5

[0142] Preparation of high-strength base paper:

[0143] The only difference between Comparative Example 5 and Example 8 is that:

[0144] In step (IV), the carbonization process is as follows: the wet paper sheet is directly placed in a mixed gas containing carbon dioxide at 60-90° C. for carbonization for 7 minutes.

[0145] The properties of the paper products prepared in Examples 7 to 11 and Comparative Examples 1 to 5 were tested, and the results are shown in Table 3 below:

[0146]

[0147] The embodiments of the present application are described above in conjunction with the accompanying drawings. Unless there is a conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of this application, ordinary technicians in this field can also make many forms without departing from the purpose of this application and the scope of protection of the claims, all of which are within the protection of this application.

Claims

1. A high-strength base paper, characterized in that: The invention comprises the following raw materials in parts by weight: 60-100 parts of hardwood pulp, 20-40 parts of softwood pulp, 10-20 parts of bast pulp, 15-25 parts of calcium carbonate, 3-5 parts of polyvinyl alcohol, 3-5 parts of aluminum sulfate, 20-30 parts of cross-linked starch, 3-8 parts of microfibrillated cellulose, 0.3-0.5 parts of dispersant, 0.1-0.3 parts of citric acid, and 60-300 parts of paper strength improver; The paper strength improving agent comprises the following raw materials in parts by weight: 20~50 parts of calcium oxide, 40~80 parts of rubber, 10~30 parts of surfactant, Appropriate amount of organic solvent, Water in moderation; The rubber is natural rubber; The preparation method of the paper strength improving agent comprises the steps of: S1, preparing a calcium hydroxide suspension: dissolving a formulated amount of calcium oxide in water, stirring thoroughly to prepare a calcium hydroxide suspension with a solid content of 3-10 wt%; S2, preparing a rubber solution: dissolving a formulated amount of rubber in an appropriate amount of an organic solvent to prepare a rubber solution having a rubber content of 1 to 6 wt%; S3, preparing a surfactant aqueous solution: dissolving a formulated amount of surfactant in water to prepare a surfactant aqueous solution having a surfactant content of 0.1 to 0.5 wt %; S4, preparing a mixed solution a: slowly adding the rubber solution obtained in step S2 to the calcium hydroxide suspension obtained in step S1 under stirring, and stirring thoroughly to mix uniformly to obtain a mixed solution a; then slowly pouring the mixed solution a into the surfactant aqueous solution under stirring to obtain a mixed solution b; S5, preparing a paper strength improving agent: heating the mixed solution b obtained in step S4 to 100-130° C. and distilling off the organic solvent therein to obtain the paper strength improving agent; The method for preparing the high-strength base paper comprises the following steps: (I) beating; (II) preparing slurry; (III) Online formation; (IV) Carbonization treatment: The wet paper is first placed in an inert gas at a temperature of 100-130°C for 30-60 seconds, and then placed in a mixed gas containing carbon dioxide at a temperature of 60-90°C for 5-10 minutes; (V) Pressing, drying, calendering and winding.

2. The high-strength base paper according to claim 1, characterized in that: The paper strength improving agent comprises the following raw materials in parts by weight: 20~30 parts of calcium oxide, 50~60 parts of rubber, 15-25 parts of surfactant, Appropriate amount of organic solvent, Appropriate amount of water.

3. The high-strength base paper according to claim 1, characterized in that: The surfactant is selected from polyol type nonionic surfactants and / or polyoxyethylene type anionic surfactants.

4. The high-strength base paper according to claim 1, characterized in that: The calcium carbonate is modified calcium carbonate that has been subjected to modification treatment.

5. The high-strength base paper according to claim 4, characterized in that: The preparation process of the modified calcium carbonate is as follows: First, 10-20 parts by weight of calcium carbonate are dispersed in an organic solvent, stirred to make it uniformly dispersed, heated to 50-70°C, and 3-5 parts by weight of 1-aminopropane are slowly added under stirring. After continuing to stir and react at 50-70°C for 5-10 minutes, 5-10 parts by weight of 3-aminopropyltriethoxysilane or vinyltris(2-methoxyethoxy)silane are slowly added dropwise. After continuing to stir and react at 50-70°C for 1-2 hours, the modified calcium carbonate is obtained by filtering, washing, and drying.

6. The high-strength base paper according to claim 1, characterized in that: The method for preparing the high-strength base paper comprises the following steps: (I) beating: dry pulp of hardwood pulp, softwood pulp and bast pulp is mixed according to a weight ratio and added to a hydraulic pulper for disintegration, the pulping concentration is controlled to be 5-10 wt% and the disintegration time is 30-60 min, and then the pulp obtained after disintegration is poured into a pulper for beating to obtain a pulp with a beating degree of 30-45°SR and a mass concentration of 4-7 wt%; (II) Slurry preparation: adding a formulated amount of calcium carbonate, polyvinyl alcohol, aluminum sulfate, cross-linked starch, microfibrillated cellulose, a dispersant, and citric acid to the slurry obtained in step (I), diluting with water until the concentration of the mixed wood pulp fibers in the slurry is 0.2-0.5 wt%, adding a formulated amount of a paper strength improver, and stirring uniformly to obtain a prepared slurry; (III) Forming on the web: feeding the slurry prepared in step (II) into a papermaking machine, distributing it through a headbox and forming it on the web to obtain wet paper sheets; (IV) Carbonization treatment: The wet paper is first placed in an inert gas at a temperature of 100-130°C for 30-60 seconds, and then placed in a mixed gas containing carbon dioxide at a temperature of 60-90°C for 5-10 minutes; (V) Pressing, drying, calendering and rolling: The carbonized paper sheets are pressed, dried, calendered and rolled to obtain high-strength base paper.

7. The high-strength base paper according to claim 6, characterized in that: In step (IV), the volume percentage of carbon dioxide in the mixed gas is 30-50%.

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