Paper strength improving agent, high-strength base paper and preparation method of high-strength base paper

Abstract

The invention belongs to the technical field of papermaking, and particularly relates to a paper strength improving agent, high-strength base paper and a preparation method thereof.The paper strength improving agent is prepared from, by weight, 20-50 parts of calcium oxide, 40-80 parts of rubber, 10-30 parts of a surfactant, a proper amount of an organic solvent and a proper amount of water.The paper strength improving agent can effectively improve the strength performance of paper, and the paper strength is improved. And the base paper with excellent strength performance can be prepared by applying the modified starch to paper products.

Description

Technical Field

[0001] The 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, in order to improve production efficiency, improve paper quality, reduce loss and save raw material consumption, a variety of additives are usually used. These additives can be divided into two categories according to their functions: process additives and functional additives. Among them, process additives are mainly used to improve the operating performance of paper materials in the wet end to ensure the smooth progress of the papermaking process. Commonly used ones are retention and drainage aids, such as cationic starch, polyacrylamide, polyethyleneimine and other retention and drainage aids. They can improve the retention rate of fine fibers and fillers, reduce loss, and improve the water filtration performance of paper materials and improve production efficiency; there are also dispersants, defoamers, preservatives, flocculants, etc. Functional additives are mainly used to give paper special properties or improve certain characteristics of paper. Commonly used ones are internal sizing agents, surface sizing agents, dry strength agents, wet strength agents, softeners, waterproofing agents, brighteners, etc. There are many types of additives used in the papermaking process. The rational use of additives is of great significance to improving production efficiency, improving paper quality, and reducing production costs.

[0003] Paper strength improver, also known as paper strength enhancer, is an important chemical additive in the papermaking process. It is a comprehensive additive that combines the performance of one or more of the above additives such as internal sizing agent, surface sizing agent, dry strength agent, wet strength agent, softener, etc. Through its unique chemical structure and mechanism of action, it can enhance paper strength, improve fiber bonding and distribution, and thus improve the tensile strength, tear strength, bursting strength and other strength properties of paper, and improve the uniformity and printability of paper. At present, paper strength improver has been widely used in the production of various types of paper, especially in decorative paper, cultural paper, offset paper, household paper, packaging paper, map paper, napkin paper, paper bag paper and other paper types that require enhanced performance.

[0004] In the prior art, the strength properties of paper are often improved by polyacrylamide mixtures and starch mixtures. In comparison, the price of polyacrylamide mixtures is higher than starch, but its fixation on pulp is higher than starch. It is currently the most commonly used paper strength improver. 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 a method of 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 the problems of relatively narrow applicable pH system range, disordered distribution of anionic and cationic monomers, uncontrollable interaction between anionic and cationic charges, and large batch performance differences caused by unstable binding effect 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, resulting in the above methods having limited improvement on 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 improving agent, high-strength base paper and a preparation method thereof in view of the above-mentioned technical problems.

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

[0008]

[0009]

[0010] Furthermore, the paper strength improving agent comprises the following raw materials in parts by weight:

[0011]

[0012] Furthermore, the rubber is selected from one or more of natural rubber, nitrile rubber, and polyurethane rubber.

[0013] Furthermore, the surfactant is selected from polyol type nonionic surfactant and / or polyoxyethylene type anionic surfactant.

[0014] A method for preparing a paper strength improving agent, the method for preparing the above-mentioned paper strength improving agent, the method for preparing the paper strength improving agent comprising the steps of:

[0015] S1, preparing a calcium hydroxide suspension: dissolving a formulated amount of calcium oxide in water, and stirring thoroughly to prepare a calcium hydroxide suspension having a solid content of 3 to 10 wt %;

[0016] 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 %;

[0017] 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 %;

[0018] 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 make the mixture uniform, thereby obtaining a mixed solution a; then slowly pouring the mixed solution a into the surfactant aqueous solution under stirring, thereby obtaining a mixed solution b;

[0019] S5, preparing a paper strength improving agent: heating the mixed solution b obtained in step S4 to 100-130° C., and evaporating the organic solvent therein to obtain the paper strength improving agent.

[0020] 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 dispersant, 0.1-0.3 parts of citric acid, and 60-300 parts of the paper strength improver described in any one of claims 1 to 4.

[0021] Furthermore, the calcium carbonate is modified calcium carbonate that has been subjected to modification treatment.

[0022] Furthermore, the preparation process of the modified calcium carbonate is as follows:

[0023] First, 10 to 20 parts by weight of calcium carbonate are dispersed in an organic solvent, stirred to make it uniformly dispersed, heated to 50 to 70° C., and 3 to 5 parts by weight of 1-aminopropane are slowly added under stirring, and the reaction is continued at 50 to 70° C. for 5 to 10 minutes, and then 5 to 10 parts by weight of silane are slowly added dropwise, and the reaction is continued at 50 to 70° C. for 1 to 2 hours, and then filtered, washed, and dried to obtain modified calcium carbonate.

[0024] 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:

[0025] (I) beating: mixing dry pulp of hardwood pulp, softwood pulp and bast pulp in a weight ratio and adding the mixture to a hydraulic pulper for beating, controlling the concentration of the pulp to be 5-10 wt% and the beating time to be 30-60 min, then pouring the pulp obtained after the pulping into a pulper for beating, and obtaining a pulp with a beating degree of 30-45° SR and a mass concentration of 4-7 wt%;

[0026] (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 mixed wood pulp fibers in the slurry is 0.2 to 0.5 wt%, adding a formulated amount of a paper strength improver, and stirring to obtain a prepared slurry;

[0027] (III) forming on the screen: feeding the slurry prepared in step (II) into a papermaking machine, distributing it through a headbox and forming it on the screen to obtain a wet paper sheet;

[0028] (IV) Carbonization treatment: The wet paper is first placed in an inert gas at a temperature of 100 to 130°C for 30 to 60 seconds, and then the paper is placed in a mixed gas containing carbon dioxide at a temperature of 60 to 90°C for carbonization treatment for 5 to 10 minutes;

[0029] (V) Pressing, drying, calendering and rolling: The carbonized paper sheets are pressed, dried, calendered and rolled to obtain high-strength base paper.

[0030] Furthermore, in step (IV), the volume percentage of carbon dioxide in the mixed gas is 30-50%.

[0031] The beneficial effects of the present invention are:

[0032] The paper strength improving agent 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

[0033] Figure 1 Schematic diagram of the working mode of the paper strength improving agent of the present invention;

[0034] The symbols in the figure are:

[0035] 1. Pulp fibers, 2. Rubber particles, 3. Filler particles. DETAILED DESCRIPTION

[0036] The following will be combined with the 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, rather than all the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments in the present application belong to the scope of protection of this application.

[0037] It should be noted that, in the present application, the terms "comprise", "include" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including 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 sentence "comprises one..." does not exclude the presence of other identical elements in the process, method, article or device including the element. In addition, it should be noted that the scope of the method and device in the embodiment 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 reverse 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.

[0038] A paper strength improving agent comprises the following raw materials in parts by weight:

[0039]

[0040] Preferably, the paper strength improving agent comprises the following raw materials in parts by weight:

[0041]

[0042] Preferably, the particle size of the calcium oxide is 0.1 to 30 um.

[0043] As some examples of the present invention, the rubber is selected from one or more of natural rubber, nitrile rubber, and polyurethane rubber.

[0044] Preferably, the rubber is natural rubber.

[0045] Preferably, the surfactant is a nonionic surfactant and / or an anionic surfactant.

[0046] 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 sodium sulfate (AES) and the like.

[0047] 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.

[0048] 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:

[0049] S1, preparing a calcium hydroxide suspension: dissolving a formulated amount of calcium oxide in water, and stirring thoroughly to prepare a calcium hydroxide suspension having a solid content of 3 to 10 wt %;

[0050] 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 %;

[0051] 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 %;

[0052] 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 make the mixture uniform, thereby obtaining a mixed solution a; then slowly pouring the mixed solution a into the surfactant aqueous solution under stirring, thereby obtaining a mixed solution b;

[0053] S5, preparing a paper strength improving agent: heating the mixed solution b obtained in step S4 to 100-130° C., and evaporating the organic solvent therein to obtain the paper strength improving agent.

[0054] 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 after being fully mixed, a mixed solution a is obtained.

[0055] Specifically, the rubber solution can be divided into 5 to 10 equal parts, and one part of the parts is added to the calcium hydroxide suspension every 1 minute.

[0056] 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 a mixed solution b.

[0057] 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.

[0058] In the paper strength improving agent described in the present invention, the rubber solution is slowly added to the calcium hydroxide suspension. After sufficient stirring, the rubber latex is dispersed in water and covers the calcium hydroxide particles to form 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 it is dispersed in an aqueous surfactant solution, under the cross-linking and fixing effect of the surfactant, 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, so that the final paper strength improving agent has a core-shell structure in which the shell layer is the rubber solution and the core layer is the calcium hydroxide particles that can be stably dispersed in the aqueous phase.

[0059] In the process of papermaking, people have always hoped to add rubber as an additive to paper products, in order to utilize the unique properties of rubber to improve the strength, elasticity and flexibility of paper products, and improve the wear resistance and tear resistance of paper. However, due to the large difference between the chemical and physical properties of rubber and paper fibers, their compatibility is poor, making it difficult for rubber to be evenly dispersed in paper, which ultimately affects the uniformity and overall performance of the paper. As described in the U.S. patent with the publication number of US1799217A, how to evenly disperse rubber in paper products is a technical problem in this field. In the prior art, a common practice is to emulsify rubber into rubber emulsion and add it to paper products. Although this can improve the uniformity of rubber dispersion in paper products to a certain extent, the rubber emulsion is easy to agglomerate into blocks during the stirring process during papermaking, which reduces the uniformity of rubber dispersion. At the same time, the addition of rubber emulsion will also have an adverse effect on pulp fluidity, filtration performance, etc. Another common practice is to add rubber powder to paper products, but the rubber powder added in this way is difficult to form a good combination with other components in paper products, such as fibers, inorganic fillers, etc., so the effect on improving the performance of paper products is also very limited.

[0060] The paper strength improver of the present invention forms a core-shell structure that can stably exist in an aqueous phase by compounding rubber with calcium hydroxide particles under the action of a surfactant. The core-shell structure is not easy to agglomerate into blocks during the papermaking stirring process, so that the finally formed paper strength improver can not only achieve uniform and stable dispersion of the rubber, but also has high fluidity, and will not have a significant effect on the fluidity and filtration performance of the pulp. More importantly, it can also play the role of the paper strength improver to improve the strength performance of the paper.

[0061] Furthermore, the present invention also provides a high-strength base paper, comprising the following raw materials in parts by weight:

[0062]

[0063]

[0064] Preferably, the calcium carbonate is modified calcium carbonate that has been subjected to modification treatment.

[0065] Specifically, the preparation process of the modified calcium carbonate is as follows:

[0066] First, 10 to 20 parts by weight of calcium carbonate are dispersed in an organic solvent, stirred to make it uniformly dispersed, heated to 50 to 70° C., and 3 to 5 parts by weight of 1-aminopropane are slowly added under stirring, and the reaction is continued at 50 to 70° C. for 5 to 10 minutes, and then 5 to 10 parts by weight of silane are slowly added dropwise, and the reaction is continued at 50 to 70° C. for 1 to 2 hours, and then filtered, washed, and dried to obtain modified calcium carbonate.

[0067] Preferably, the 1-aminopropane is added within 3 to 5 minutes, and the silane is added dropwise within 5 to 10 minutes.

[0068] 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.

[0069] As some examples of the present invention, the silane used for preparing the modified calcium carbonate is selected from one or more of trimethylbutyl peroxysilane, 3-aminopropyltriethoxysilane (APTES), vinyltri(2-methoxyethoxy)silane, and the like.

[0070] In the modification process of the calcium carbonate, 1-aminopropane is an organic amine compound, and the amino group (-NH2) in its molecule can react with the hydroxyl group (-OH) on the surface of the nano inorganic filler, and the amino group is introduced on the surface of the calcium carbonate, and these amino groups can be used as active sites for subsequent reactions. Further, in the subsequent silanization reaction, the silane molecule can further modify the surface of the nano inorganic filler, and the silicon oxygen bond (Si-O) in the silane molecule can react with the remaining hydroxyl group or the introduced amino group on the surface of the calcium carbonate to form a more solid chemical bond connection. The surface of the calcium carbonate after the modification is coated with a substance with a double bond, which helps to reduce the agglomeration phenomenon between the calcium carbonate particles, making it more dispersible, and with other components in the paper, especially the interface bonding strength of the organic phase is higher, so that the retention rate of the filler and the physical strength of the paper, such as tensile strength, tear strength, etc., can be improved, and at the same time, it helps to improve the burst resistance and folding resistance of the paper.

[0071] In addition, the present invention also provides a method for preparing high-strength base paper, which comprises the steps of:

[0072] (I) beating: mixing dry pulp of hardwood pulp, softwood pulp and bast pulp in a weight ratio and adding the mixture to a hydraulic pulper for beating, controlling the concentration of the pulp to be 5-10 wt% and the beating time to be 30-60 min, then pouring the pulp obtained after the pulping into a pulper for beating, and obtaining a pulp with a beating degree of 30-45° SR and a mass concentration of 4-7 wt%;

[0073] (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 mixed wood pulp fibers in the slurry is 0.2 to 0.5 wt%, adding a formulated amount of a paper strength improver, and stirring to obtain a prepared slurry;

[0074] (III) forming on the screen: feeding the slurry prepared in step (II) into a papermaking machine, distributing it through a headbox and forming it on the screen to obtain a wet paper sheet;

[0075] (IV) Carbonization treatment: The wet paper is first placed in an inert gas at a temperature of 100 to 130°C for 30 to 60 seconds, and then the paper is placed in a mixed gas containing carbon dioxide at a temperature of 60 to 90°C for carbonization treatment for 5 to 10 minutes;

[0076] (V) Pressing, drying, calendering and rolling: The carbonized paper sheets are pressed, dried, calendered and rolled to obtain high-strength base paper.

[0077] Preferably, in step (IV), the volume percentage of carbon dioxide in the mixed gas is 30-50%.

[0078] In the process of preparing the high-strength base paper of the present invention, by adding a certain amount of coniferous rice pulp and bast pulp, the fibers of coniferous wood pulp are slender and have fewer foreign cells, so that the prepared paper has good flexibility, high folding resistance and good tensile strength; the bast fibers are slender and strong, which helps to improve the performance indicators of the base paper such as tensile strength and tear resistance. Polyvinyl alcohol, cross-linked starch and microfibrillated cellulose can enhance the bonding force between fibers, thereby improving the strength of the paper.

[0079] On this basis, the strength performance of paper can be further improved by compounding the paper strength improving agent of the present invention. Figure 1As shown, the working process of the paper strength improver of the present invention is as follows: in the preparation process of base paper, the wet paper sheet is first placed in a high temperature environment formed by an inert gas. Under the dual effects of water loss and high temperature, the surfactant in the paper strength improver loses the cross-linking and fixing effect on the rubber shell layer, and the rubber shell of the outer layer of the core-shell structure gradually breaks, unfolds, and adheres to the pulp fiber 1 and filler particles 3 in the paper. The filler particles 3 include calcium carbonate particles directly added to the papermaking raw material 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 the filler particles 3 in the paper, which not only realizes the uniform and good dispersion of the rubber, but also forms bonding points with the rubber particles 2 as the core, which can not only enhance the interaction force between the rubber particles 2, the pulp fibers 1 and the filler particles 3, thereby improving the overall strength of the paper, including tensile strength, bursting resistance and tear resistance, etc., but also the adhesion of the rubber particles 2 can make the surface of the paper smoother and more uniform, which is beneficial to the improvement of the printing quality and image clarity of the paper. Afterwards, through the high-temperature carbon dioxide gas, the reaction between carbon dioxide and calcium hydroxide can be utilized to generate a layer of calcium carbonate in situ on the surface of the calcium hydroxide, so that the calcium hydroxide forms a composite particle with an outer layer of calcium carbonate and an inner layer of calcium hydroxide, and the calcium carbonate in the composite particle can be fixed on the surface of the calcium hydroxide by heterogeneous nucleation, in-situ generation, etc., and attached to the pulp fiber 1 through a deposition reaction, so that the composite particle can finally form a stable connection with the rubber particles 2, the pulp fiber 1, etc., and is not easy to be lost. At the same time, the composite particle can form a more uniform and tight filling between the paper fibers 1, thereby improving the gloss, smoothness and strength of the paper. In addition, compared with the traditional calcium carbonate inorganic filler, the structure of the composite particle can improve the whiteness, opacity and ink absorption performance of the filler through its unique double-layer structure, thereby improving the whiteness, opacity and printing performance of the paper.

[0080] The paper strength improving agent and high-strength base paper of the present invention are illustrated by specific examples below:

[0081] Embodiments 1 to 5

[0082] Preparation of paper strength improving agent: The raw material ratio of the paper strength improving agent is shown in Table 1 below:

[0083] Table 1

[0084]

[0085] The rubbers used in Examples 1 to 5 are natural rubber, nitrile rubber, natural rubber, polyurethane rubber, and nitrile rubber, respectively; the surfactants are sucrose fatty acid esters, sorbitan fatty acid esters, sodium sulfate of fatty alcohol polyoxyethylene ether, sodium sulfate of fatty alcohol polyoxyethylene ether, and sucrose fatty acid esters, respectively; and the organic solvents are a mixture of toluene and chloroform, toluene, a mixture of toluene and chloroform, acetone, and a mixture of xylene and chloroform, respectively;

[0086] 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 evaporation amount of the organic solvent is controlled to be not less than 97% of the total added amount.

[0087] Example 6

[0088] Preparation of modified calcium carbonate:

[0089] First, 15 parts by weight of calcium carbonate are dispersed in an organic solvent, stirred to make it evenly 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, 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.

[0090] Embodiments 7 to 11

[0091] Preparation of high-strength base paper: The raw material ratio of high-strength base paper is shown in Table 2 below:

[0092] Table 2

[0093]

[0094] Among them, the paper strength improvers used in Examples 7 to 11 are the paper strength improvers prepared in Examples 1 to 5, respectively; Examples 7 and 8 use the modified calcium carbonate prepared in Example 6, and Examples 9 to 11 use unmodified calcium carbonate.

[0095] The preparation process of high-strength base paper in Examples 7 to 11 is as follows:

[0096] (I) beating: dry pulp of hardwood pulp, softwood pulp and bast pulp is mixed according to weight ratio and added into hydraulic pulper for beating, the concentration of the pulp is controlled to be 5wt%, 6wt%, 8wt%, 9wt% and 10wt% in sequence, and the beating time is 30min, 40min, 45min, 50min and 60min in sequence, and then the pulp obtained after pulping is poured into the beating machine for beating, so as to obtain pulp with beating degree of 30°SR, 32°SR, 35°SR, 40°SR and 45°SR and mass concentration of 4wt%, 5wt%, 5wt%, 6wt% and 7wt%;

[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 mixed wood pulp fibers in the slurry is 0.2wt%, 0.3wt%, 0.3wt%, 0.4wt% and 0.5wt%, adding a formulated amount of a paper strength improver, stirring evenly to obtain a prepared slurry;

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

[0099] (IV) Carbonization treatment: the wet paper is first placed in an inert gas at 100°C, 110°C, 120°C, 120°C, 130°C for 30 seconds, 40 seconds, 40 seconds, 50 seconds, 60 seconds, and then the paper is placed in a mixed gas containing carbon dioxide at 60°C, 70°C, 70°C, 80°C, 90°C for carbonization treatment for 5 minutes, 7 minutes, 8 minutes, 7 minutes, 10 minutes; wherein the volume percentage of carbon dioxide in the mixed gas is 30%, 35%, 40%, 45%, 50%;

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

[0101] Comparative Example 1

[0102] Preparation of high-strength base paper:

[0103] The difference between Comparative Example 1 and the above-mentioned Example 8 is only that:

[0104] The preparation process of the modified calcium carbonate used is:

[0105] First, 15 parts by weight of calcium carbonate are dispersed in an organic solvent, stirred to make it evenly 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.

[0106] Comparative Example 2

[0107] Preparation of high-strength base paper:

[0108] The difference between Comparative Example 2 and the above-mentioned Example 8 is only that:

[0109] The preparation process of the modified calcium carbonate used is:

[0110] First, 15 parts by weight of calcium carbonate are dispersed in an organic solvent, stirred to make it evenly 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.

[0111] Comparative Example 3

[0112] Preparation of high-strength base paper:

[0113] The difference between Comparative Example 3 and the above-mentioned Example 8 is only that:

[0114] High-strength base paper is prepared by using nitrile rubber emulsion with equal nitrile rubber content instead of paper strength improver.

[0115] Comparative Example 4

[0116] Preparation of high-strength base paper:

[0117] The difference between Comparative Example 4 and the above-mentioned Example 8 is only that:

[0118] After step (III), step (V) is directly carried out without going through the carbonization process in step (IV).

[0119] Comparative Example 5

[0120] Preparation of high-strength base paper:

[0121] The difference between Comparative Example 5 and the above-mentioned Example 8 is only that:

[0122] The carbonization process in step (IV) 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.

[0123] The properties of the paper products prepared in the above Examples 7 to 11 and Comparative Examples 1 to 5 were tested, and the results are shown in Table 3 below:

[0124] Table 3 Paper performance test results

[0125]

[0126] The embodiments of the present application are described above in conjunction with the accompanying drawings. In the absence of conflict, the embodiments in the present application and the features in the embodiments 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 the present application, ordinary technicians in this field can also make many forms without departing from the purpose of the present application and the scope of protection of the claims, all of which are within the protection of the present application.

Claims

1. A paper strength improving agent, characterized in that: The invention comprises the following raw materials in parts by weight:

2. The paper strength improving agent according to claim 1, characterized in that: The paper strength improving agent comprises the following raw materials in parts by weight:

3. The paper strength improving agent according to claim 1, characterized in that: The rubber is selected from one or more of natural rubber, nitrile rubber and polyurethane rubber.

4. The paper strength improving agent according to claim 1, characterized in that: The surfactant is selected from polyol type nonionic surfactant and / or polyoxyethylene type anionic surfactant.

5. A method for preparing a paper strength improving agent, characterized in that: The preparation method is used to prepare the paper strength improving agent according to any one of claims 1 to 4, and 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, and stirring thoroughly to prepare a calcium hydroxide suspension having a solid content of 3 to 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 make the mixture uniform, thereby obtaining a mixed solution a; then slowly pouring the mixed solution a into the surfactant aqueous solution under stirring, thereby obtaining 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 evaporating the organic solvent therein to obtain the paper strength improving agent.

6. 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 the paper strength improver described in any one of claims 1 to 4.

7. The high-strength base paper according to claim 6, characterized in that: The calcium carbonate is modified calcium carbonate that has been subjected to modification treatment.

8. The high-strength base paper according to claim 7, characterized in that: The preparation process of the modified calcium carbonate is as follows: First, 10 to 20 parts by weight of calcium carbonate are dispersed in an organic solvent, stirred to make it uniformly dispersed, heated to 50 to 70° C., and 3 to 5 parts by weight of 1-aminopropane are slowly added under stirring, and the reaction is continued at 50 to 70° C. for 5 to 10 minutes, and then 5 to 10 parts by weight of silane are slowly added dropwise, and the reaction is continued at 50 to 70° C. for 1 to 2 hours, and then filtered, washed, and dried to obtain modified calcium carbonate.

9. A method for preparing high-strength base paper, characterized in that: The preparation method is used to prepare the high-strength base paper according to any one of claims 6 to 8, and the preparation method comprises the steps of: (I) beating: mixing dry pulp of hardwood pulp, softwood pulp and bast pulp in a weight ratio and adding the mixture to a hydraulic pulper for beating, controlling the concentration of the pulp to be 5-10 wt% and the beating time to be 30-60 min, then pouring the pulp obtained after the pulping into a pulper for beating, and obtaining 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 mixed wood pulp fibers in the slurry is 0.2 to 0.5 wt%, adding a formulated amount of a paper strength improver, and stirring to obtain a prepared slurry; (III) forming on the screen: feeding the slurry prepared in step (II) into a papermaking machine, distributing it through a headbox and forming it on the screen to obtain a wet paper sheet; (IV) Carbonization treatment: The wet paper is first placed in an inert gas at a temperature of 100 to 130°C for 30 to 60 seconds, and then the paper is placed in a mixed gas containing carbon dioxide at a temperature of 60 to 90°C for carbonization treatment for 5 to 10 minutes; (V) Pressing, drying, calendering and rolling: The carbonized paper sheets are pressed, dried, calendered and rolled to obtain high-strength base paper.

10. The method for preparing high-strength base paper according to claim 9, characterized in that: In the step (IV), the volume percentage of carbon dioxide in the mixed gas is 30-50%.

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