Calcium carbonate wrapping agent for papermaking and preparation method thereof

Abstract

The invention discloses a calcium carbonate wrapping agent for papermaking and a preparation method thereof. The preparation method comprises the following steps: stirring and mixing deionized water, acrylamide and (3-acrylamide propyl) trimethyl ammonium chloride in advance to prepare a monomer solution; the preparation method comprises the following steps: pre-stirring and mixing acrylate-terminated polysiloxane and a cationic gemini emulsifier to prepare an intermediate, wherein the stirring time is not less than 30 minutes; stirring and dissolving an initiator and deionized water in advance to prepare an initiator solution; deionized water, acrylamide, itaconic acid, EDTA and a reaction type emulsifier are stirred and dissolved to be uniform to serve as a base material, and in the inert atmosphere, an initiator, the monomer solution and the intermediate are dropwise added for a reaction; and adjusting the pH value to 5-7 by using a regulator, and cooling to below 40 DEG C to obtain the calcium carbonate wrapping agent for papermaking. When the calcium carbonate wrapping agent for papermaking is applied to paper making, the utilization rate of calcium carbonate can be increased, and the tensile strength, the internal bonding strength and the surface strength of paper can be maintained or improved.

Description

Technical Field

[0001] The present invention relates to the field of preparation of fillers for papermaking, in particular to a calcium carbonate coating agent for papermaking and a preparation method thereof. Background Art

[0002] With the shift in papermaking from acidic to neutral and alkaline papermaking, the use of calcium carbonate in the papermaking industry has increased significantly. Calcium carbonate, with its high whiteness and fine particle size, is an indispensable inorganic filler and pigment in the papermaking industry. It significantly enhances the printing and optical properties of paper, not only improving ink absorption but also resulting in paper with high whiteness, high opacity, and a dense, glossy finish. Due to its numerous advantages and low cost, calcium carbonate addition effectively conserves paper fiber raw materials and reduces fiber costs, the papermaking industry is moving toward higher addition rates. However, increased calcium carbonate use often leads to other adverse effects, such as reduced calcium carbonate retention during water filtration and sizing issues on paper machines. During the papermaking process, calcium carbonate also disrupts fiber bonds, reducing paper strength. The higher the calcium carbonate content in the paper, the greater the impact on fiber bonds and the more pronounced the decrease in strength. Excessive calcium carbonate content also reduces the surface strength of the paper, leading to dusting and linting, which compromises printing quality. Traditional direct addition techniques based on calcium carbonate have limitations, which restrict the amount of calcium carbonate that can be added. Therefore, under the premise of increasing the amount of calcium carbonate added, it is of great significance to overcome and reduce the negative effects of addition.

[0003] In order to solve the problem that increasing the ash content of paper affects the strength of paper, one way is to modify the calcium carbonate through encapsulation to form a composite material with calcium carbonate as the core and the encapsulation material as the shell. The encapsulation layer is used as a medium to achieve an indirect bonding effect between calcium carbonate and fiber, thereby improving the negative effects caused by the addition of calcium carbonate.

[0004] In the existing technical solutions, there are two main processes for coating and modifying calcium carbonate. One is to mix the coating agent with calcium carbonate, coat it, dry it, and grind it to obtain the coated and modified calcium carbonate filler, which is then used as a filler in papermaking. For example, Lu Dongdong et al. (Preparation of starch-coated calcium carbonate filler and its application in papermaking, Paper Science and Technology, 2015, 34(3):42-48) and Zheng Bin et al. (Study on starch-modified calcium carbonate filler to improve the performance of copy paper, Paper and Papermaking, 2016, 35(2):23-28) prepared starch-coated modified calcium carbonate filler by mixing starch and calcium carbonate, gelatinizing and swelling them, and then drying and grinding them. However, this preparation process consumes a lot of energy and is too costly.

[0005] Another method is to use multiple coating agents to mix calcium carbonate slurry online, and then add it to the paper machine Loeb mixer to enter the paper machine system. For example, Chinese patent CN119531180A uses two coating agents to modify calcium carbonate based on the papermaking filling method of calcium carbonate coating. Chen Zicheng et al. (Modification of precipitated calcium carbonate filler for papermaking with cationic chitosan and carboxymethyl cellulose, Silicate Bulletin, 2016, 35(5):1602-1605) first added cationic chitosan solution to precipitated calcium carbonate (PCC) slurry, and then added carboxymethyl cellulose to blend to obtain coated modified PCC. Compared with unmodified PCC, the modified PCC has a higher retention rate in paper and has a smaller negative impact on the paper tensile index. However, cationic chitosan is expensive and has low economic efficiency, making it difficult to use in production practice. Chinese patent 116752374A, a paper product, papermaking filler and its coated pre-flocculation modification method, proposes the use of two cationic coating agents to modify calcium carbonate. The application effect has a good effect on the ash retention rate and internal bonding strength of the paper, but the effect on the surface strength of the paper is not obvious. Summary of the Invention

[0006] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the object of the present invention is to provide a method for preparing a calcium carbonate coating agent for papermaking, during which acrylate-terminated polysiloxane is introduced into the polymerization reaction to significantly increase the surface strength of the paper.

[0007] Another object of the present invention is to provide a calcium carbonate packaging agent for papermaking.

[0008] Another object of the present invention is to provide a method for preparing a coated modified calcium carbonate filler. The prepared calcium carbonate coating agent is mixed online with a calcium carbonate suspension, which can rapidly adsorb calcium carbonate particles and form a dense polymer film on the surface of the calcium carbonate particles. This changes the surface properties of the calcium carbonate particles, creates a "bridging" effect between the calcium carbonate particles, and forms a network structure (producing micro-flocculation, with floc sizes of 5 to 25 μm, preferably 10 to 20 μm). The calcium carbonate suspension modified by the coating agent is then added to paper pulp. The active groups of the coating agent form hydrogen bonds and covalent bonds with the fibers, significantly enhancing the bonding strength and bonding area between the calcium carbonate particles and the pulp fibers / fines. The calcium carbonate flocs are fixed to the fibers, forming dense flocs with enhanced shear resistance and reduced water content, making them easier to dehydrate in the press section. In addition, the retention of the calcium carbonate particles is significantly improved, thereby improving the utilization rate of the calcium carbonate and maintaining or improving the tensile strength, internal bonding strength, and surface strength properties of the paper.

[0009] Another object of the present invention is to provide cultural paper.

[0010] The purpose of the present invention is achieved through the following technical solutions:

[0011] The present invention provides a method for preparing a calcium carbonate coating agent for papermaking, comprising the following steps:

[0012] S1: pre-stir and mix deionized water, acrylamide, and (3-acrylamidopropyl)trimethylammonium chloride to prepare a monomer solution;

[0013] The acrylate-terminated polysiloxane and the cationic gemini emulsifier are pre-stirred and mixed for not less than 30 minutes to obtain an intermediate;

[0014] Stir and dissolve the initiator and deionized water in advance to prepare an initiator solution;

[0015] S2: Deionized water, acrylamide, itaconic acid, EDTA and reactive emulsifier are stirred and dissolved uniformly as a base material. Under an inert atmosphere, the temperature is uniformly raised to 65-70°C, and the initiator solution is started to be added dropwise. The reaction temperature is controlled at 80-85°C. After the reaction is carried out for 15-20 minutes, the monomer solution is started to be added dropwise. After 2 / 3 of the monomer solution has been added dropwise, the intermediate is added to the remaining monomer solution to obtain a mixed solution of the intermediate and the monomer. The mixed solution of the intermediate and the monomer is added dropwise, and the addition time is controlled to be 3-3.5 hours. During the process of adding the monomer solution and the mixed solution of the monomer and the intermediate, the initiator solution is continuously added dropwise. After the addition of the mixed solution of the monomer and the intermediate is completed, the initiator solution is continued to be added dropwise for 15-20 minutes, and the mixture is kept at 80-85°C for 45-60 minutes, and the material is cooled to below 50°C.

[0016] S3 adds a pH regulator to adjust the pH to 5-7, and cools the temperature to below 40° C. to obtain a calcium carbonate coating agent for papermaking.

[0017] Preferably, in the monomer solution, acrylamide accounts for 90-95% of the total mass of acrylamide and (3-acrylamidopropyl)trimethylammonium chloride, and (3-acrylamidopropyl)trimethylammonium chloride accounts for 5-10% of the total mass of acrylamide and (3-acrylamidopropyl)trimethylammonium chloride; and the amount of deionized water added is 1.2-1.5 times the total mass of acrylamide and (3-acrylamidopropyl)trimethylammonium chloride;

[0018] The mass ratio of the gemini emulsifier to the acrylate-terminated polysiloxane in the intermediate is (8-12):100;

[0019] In the initiator solution, the mass ratio of initiator to deionized water is (1.0-1.5):100.

[0020] Preferably, in the base material, acrylamide accounts for 90-96% of the total mass of acrylamide and itaconic acid, itaconic acid accounts for 4-10% of the total mass of acrylamide and itaconic acid, the added amount of EDTA is 0.03-0.06% of the total mass of acrylamide and itaconic acid, the added amount of reactive emulsifier is 25-35% of the total mass of acrylamide and itaconic acid, and the added amount of deionized water is 1.4-1.8 times the total mass of acrylamide and itaconic acid.

[0021] Preferably, the acrylate-terminated polysiloxane is a monoacrylate-terminated polysiloxane with a molecular weight of 400-5000; more preferably, the molecular weight is 1000-4000.

[0022] Preferably, the mass of the acrylate-terminated polysiloxane is 5-9% of the total mass of the acrylamide in the monomer solution and the acrylamide in the primer.

[0023] Preferably, the mass ratio of acrylamide in the monomer solution to acrylamide in the primer is (1.6-1.8):1.

[0024] Preferably, the cationic gemini emulsifier used is at least one of octadecylamine polyoxyethylene ether diquaternary ammonium salt, tetradecylamine polyoxyethylene ether diquaternary ammonium salt, and asymmetric C8-14 ethoxy diquaternary ammonium salt; further, asymmetric C8-14 ethoxy diquaternary ammonium salt is more preferred.

[0025] Preferably, the initiator is one of persulfates (such as potassium salt, sodium salt or ammonium salt), more preferably ammonium persulfate.

[0026] Preferably, the reactive emulsifier is one or a combination of 3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt and 2-acrylamido-2-methylpropanesulfonic acid sodium salt.

[0027] Preferably, the pH regulator is sulfuric acid with a mass concentration of 30%, ammonia water with a mass concentration of 15%, or liquid alkali with a mass concentration of 20%.

[0028] Preferably, step S3 further includes the following steps: adding deionized water to adjust the solid content to 25-30%.

[0029] The present invention also provides a calcium carbonate coating agent for papermaking, which is prepared by the preparation method of the calcium carbonate coating agent for papermaking.

[0030] The present invention also provides a preparation method of a coated modified calcium carbonate filler, comprising diluting the calcium carbonate coating agent for papermaking with clean water, adding the diluted solution to a calcium carbonate suspension, and stirring the solution to obtain the coated modified calcium carbonate filler; the amount of the calcium carbonate coating agent for papermaking is 1 to 5 kg / t of calcium carbonate.

[0031] Preferably, the average size of the calcium carbonate flocs in the wrapped modified calcium carbonate filler is 2 to 25 μm.

[0032] Preferably, in the coated modified calcium carbonate filler, the amount of the calcium carbonate coating agent for papermaking is 2.8 to 3.2 kg / t calcium carbonate.

[0033] The present invention provides cultural paper, comprising the wrapped modified calcium carbonate filler prepared by the preparation method of the wrapped modified calcium carbonate filler.

[0034] The principle of the present invention is:

[0035] The coating agent of the present invention can be adsorbed by coupling with the surface of calcium carbonate particles through metal ion bonds (calcium ions are present in the calcium carbonate suspension). This coupling forms ion pairs or ion bridges, which facilitate the adsorption and expansion of the coating agent's molecular chains on the surfaces of fibers and calcium carbonate particles. The coating agent molecules contain a large number of active functional groups such as carboxyl, hydroxyl, and amide groups. The surfaces of both calcium carbonate particles and pulp fibers contain hydroxyl groups, which serve as hydrogen bonding sites and can form intermolecular hydrogen bonds in the form of —OH┄NH2 and —OH┄OH.

[0036] The coating agent of the present invention first acts on the surface of the calcium carbonate particles to form a dense polymer film on the surface of the calcium carbonate particles, changing the surface properties of the calcium carbonate particles. Due to the adsorption and bridging effect between the polymers (the calcium carbonate particles can simultaneously adsorb two or more polymer chains through charge neutralization, ionic bonds, and hydrogen bonds, these polymer chains act as adsorption and bridging between the particles to connect multiple particles together, and the polymer chains are coated on the surface of the particles, thereby increasing the volume of the particles), and the charge and compression of the double layer (charge neutralization and double layer compression weaken the electrostatic repulsion between the particles, thereby promoting mutual collision between the particles and aggregation to form flocs), micro-flocculation (micro-flocculation) is generated. When the coated calcium carbonate particles are added to paper pulp, the polymer film formed by the coating agent is conducive to the bonding between the calcium carbonate and the pulp fibers, thereby increasing the strength of the paper. The micro-flocculation is also conducive to the retention of the calcium carbonate.

[0037] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0038] (1) The preparation method of the calcium carbonate coating agent for papermaking of the present invention introduces acrylate-terminated polysiloxane into the polymerization reaction, which significantly increases the surface strength of the paper; and the acrylate-terminated polysiloxane and the gemini emulsifier are pre-stirred and evenly mixed, and then added at the rear end of the polymerization reaction. This process can avoid the problem of easy slag generation in the system when directly adding the bulk.

[0039] (2) The preparation method of the calcium carbonate coating for papermaking of the present invention greatly reduces the residual small molecule emulsifier in the system through raw material and process optimization, thereby reducing the adverse effects on the environment and product performance. The unique molecular chain structure makes the calcium carbonate coating excellent in hydrolysis resistance and temperature resistance. It can also provide more reactive sites than conventional coatings (such as starch, carboxymethyl cellulose, etc.), forming hydrogen bonds and covalent bonds with the hydroxyl groups on the pulp fibers, thereby improving the tensile index, internal bonding strength, and surface strength of the paper.

[0040] (3) The calcium carbonate coating agent for papermaking of the present invention is a polymer with an ultra-high branched and highly reactive zwitterionic amine basic structure. The polymer chain segments contain both anionic and cationic groups, showing a significant "anti-polyelectrolyte effect". It can adapt to the weakly alkaline environment of the calcium carbonate suspension, has both charge neutralization and adsorption bridging effects, and has a "wrapping" coating effect, and is particularly suitable for chemical coating treatment of calcium carbonate. DETAILED DESCRIPTION

[0041] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

[0042] All raw materials used in the examples are conventional raw materials and commercially available products. "%" refers to mass percentage.

[0043] Example 1:

[0044] S1: 238 kg of deionized water, 156 kg of acrylamide, and 14 kg of (3-acrylamidopropyl)trimethylammonium chloride (effective content 75%, unless otherwise specified, effective content is taken as 100%, the same below) are pre-stirred and mixed to prepare a monomer solution; 18.6 kg of monoacrylate-terminated polysiloxane (molecular weight 1250) and 1.9 kg of asymmetric C8-14 ethoxydiquaternary ammonium salt are pre-stirred and mixed for not less than 30 minutes to prepare an intermediate; 0.85 kg of ammonium persulfate and 80 kg of deionized water are pre-stirred and dissolved to prepare an initiator solution.

[0045] S2: 173 kg of deionized water, 92 kg of acrylamide, 8 kg of itaconic acid, 0.04 kg of EDTA, 20 kg of 3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt, and 10 kg of 2-acrylamido-2-methylpropanesulfonic acid sodium salt were added to the reactor in sequence, stirred and dissolved evenly as a base material, and the temperature was uniformly raised to 65-70 ° C under an inert atmosphere. The initiator solution was added dropwise, and the reaction temperature was controlled at 80-85 ° C. After 15-20 minutes, the monomer solution was added dropwise. After 2 / 3 of the monomer solution was added, the intermediate was added to the monomer solution and continued to be added dropwise. The addition time was controlled at 3-3.5 hours. After the monomer solution and the intermediate were added dropwise, the initiator solution was continued to be added dropwise for 15-20 minutes. The temperature was kept at 80-85 ° C for 45-60 minutes, and the material was cooled to below 50 ° C.

[0046] S3: adding a pH regulator to adjust the pH to 5-7, adding deionized water to adjust the solid content to 25-30%, and cooling to below 40° C. to obtain a calcium carbonate coating agent.

[0047] Example 2:

[0048] S1: 192 kg of deionized water, 144 kg of acrylamide, and 16 kg of (3-acrylamidopropyl)trimethylammonium chloride (effective content 75%) were pre-stirred and mixed to prepare a monomer solution; 18.2 kg of monoacrylate-terminated polysiloxane (molecular weight 4000) and 1.8 kg of tetradecylamine polyoxyethylene ether diquaternary ammonium salt were pre-stirred and mixed for not less than 30 minutes to prepare an intermediate; 0.8 kg of ammonium persulfate and 80 kg of deionized water were pre-stirred and dissolved to prepare an initiator solution.

[0049] S2: 140 kg of deionized water, 90 kg of acrylamide, 10 kg of itaconic acid, 0.03 kg of EDTA and 25 kg of 3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt were added to the reactor in sequence, stirred and dissolved evenly as a base material, and the temperature was uniformly raised to 65-70 ° C under an inert atmosphere. The initiator solution was started to be added dropwise. The reaction temperature was controlled at 80-85 ° C. After 15-20 minutes, the monomer solution was started to be added dropwise. After 2 / 3 of the monomer solution was added, the intermediate was added to the monomer solution and continued to be added dropwise. The addition time was controlled at 3-3.5 hours. After the monomer solution and the intermediate were added dropwise, the initiator solution was continued to be added dropwise for 15-20 minutes. The temperature was kept at 80-85 ° C for 45-60 minutes, and the material was cooled to below 50 ° C.

[0050] S3: adding a pH regulator to adjust the pH to 5-7, adding deionized water to adjust the solid content to 25-30%, and cooling to below 40° C. to obtain a calcium carbonate coating agent.

[0051] Example 3:

[0052] S1: 261 kg of deionized water, 170 kg of acrylamide, and 10 kg of (3-acrylamidopropyl)trimethylammonium chloride (effective content 75%) were pre-stirred and mixed to prepare a monomer solution; 21.2 kg of monoacrylate-terminated polysiloxane (molecular weight 4000) and 2.1 kg of asymmetric C8-14 ethoxydiquaternary ammonium salt were pre-stirred and mixed to prepare an intermediate, with the stirring time being not less than 30 minutes; 0.91 kg of ammonium persulfate and 80 kg of deionized water were pre-stirred and dissolved to prepare an initiator solution.

[0053] S2: 180 kg of deionized water, 95 kg of acrylamide, 5 kg of itaconic acid, 0.05 kg of EDTA, 20 kg of 3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt and 15 kg of 2-acrylamido-2-methylpropanesulfonic acid sodium salt were added to the reactor in sequence, stirred and dissolved evenly as a base material, and the temperature was uniformly raised to 65-70 ° C under an inert atmosphere. The initiator solution was added dropwise, and the reaction temperature was controlled at 80-85 ° C. After 15-20 minutes, the monomer solution was added dropwise. After 2 / 3 of the monomer solution was added, the intermediate was added to the monomer solution and continued to be added dropwise. The addition time was controlled at 3-3.5 hours. After the monomer solution and the intermediate were added dropwise, the initiator solution was continued to be added dropwise for 15-20 minutes. The temperature was kept at 80-85 ° C for 45-60 minutes, and the material was cooled to below 50 ° C.

[0054] S3: adding a pH regulator to adjust the pH to 5-7, adding deionized water to adjust the solid content to 25-30%, and cooling to below 40° C. to obtain a calcium carbonate coating agent.

[0055] Example 4:

[0056] S1: 236 kg of deionized water, 160 kg of acrylamide, and 12 kg of (3-acrylamidopropyl)trimethylammonium chloride (effective content 75%, unless otherwise specified, effective content is taken as 100%, the same below) are pre-stirred and mixed to prepare a monomer solution; 17.7 kg of monoacrylate-terminated polysiloxane (molecular weight 1250), 0.8 kg of octadecylamine polyoxyethylene ether diquaternary ammonium salt, and 1.0 kg of asymmetric C8-14 ethoxy diquaternary ammonium salt are pre-stirred and mixed to prepare an intermediate, with the stirring time being not less than 30 minutes; 0.88 kg of ammonium persulfate and 80 kg of deionized water are pre-stirred and dissolved to prepare an initiator solution.

[0057] S2: 166 kg of deionized water, 91 kg of acrylamide, 9 kg of itaconic acid, 0.04 kg of EDTA and 28 kg of 2-acrylamido-2-methylpropanesulfonic acid sodium salt were added to the reactor in sequence, stirred and dissolved evenly as a base material, and the temperature was uniformly raised to 65-70 ° C under an inert atmosphere. The initiator solution was added dropwise, and the reaction temperature was controlled at 80-85 ° C. After 15-20 minutes, the monomer solution was added dropwise. After 2 / 3 of the monomer solution was added, the intermediate was added to the monomer solution and continued to be added dropwise. The addition time was controlled at 3-3.5 hours. After the monomer solution and the intermediate were added dropwise, the initiator solution was continued to be added dropwise for 15-20 minutes. The temperature was kept at 80-85 ° C for 45-60 minutes, and the material was cooled to below 50 ° C.

[0058] S3: adding a pH regulator to adjust the pH to 5-7, adding deionized water to adjust the solid content to 25-30%, and cooling to below 40° C. to obtain a calcium carbonate coating agent.

[0059] Comparative Example 1:

[0060] The method of Example 1 was followed, except that no intermediate was added.

[0061] Comparative Example 2:

[0062] The raw material ratio is the same as that of Example 1, except that the gemini emulsifier in step S1 is not used, and the monoacrylate-terminated polysiloxane is directly added dropwise to the monomer solution in a conventional manner. The result is that the product shows water-oil separation and slag.

[0063] Comparative Example 3:

[0064] The raw material ratio was the same as in Example 1, except that the intermediate and monomer solution were added dropwise at the same time.

[0065] Application examples:

[0066] The calcium carbonate coating agents prepared in Examples 1-4 and Comparative Example 1 were applied to the production of cultural paper.

[0067] At 80g / m 2Application test on offset paper: dilute the calcium carbonate coating agent 10-20 times with clean water and add it to the calcium carbonate suspension (PCC:GCC=1:3, concentration 25%) at a dosage of 1-5kg / t of calcium carbonate. After stirring evenly, the coated modified calcium carbonate filler is obtained, and the size of the calcium carbonate flocs is tested. In order to objectively reflect the application effect, other process conditions are kept unchanged as much as possible. The starch dosage is 7kg / t of absolute dry pulp, the pulp ratio is coniferous pulp:broadleaf pulp:chemical pulp=20:40:40, the retention aid dosage is 350g / t of absolute dry pulp + 250g / t of absolute dry pulp of micropolymer + 3.0kg / t of absolute dry pulp of solid retention aid, and the calcium carbonate filler dosage is 850kg / t of absolute dry pulp. When using, weigh a certain weight of pulp, add starch, calcium carbonate filler and retention aid in sequence at a speed of 800rpm, and make paper sheets.

[0068] The test was divided into three phases: 1) blank: adding uncoated and modified calcium carbonate filler; 2) adding coated and modified calcium carbonate filler. The physical properties of the finished paper (unsizing) were tested, including tensile index, internal bond strength, surface strength, and ash content. The results are shown in Table 1.

[0069] The determination of tensile index shall refer to GB / T 12914-2018 "Paper and paperboard - Determination of tensile strength - Constant rate of tension (20 mm / min)", and the tensile index is the tensile strength divided by the basis weight of the paper; the determination of internal bond strength shall refer to GB / T 26203-2023 "Paper and paperboard - Determination of internal bond strength (Scott type)"; the determination of surface strength shall refer to GB / T 22365-2008 "Paper and paperboard - Determination of strength of printed surface"; the determination of ash content shall refer to GB / T 742-2018 "Papermaking raw materials, pulp, paper and paperboard - Determination of ignition residue (ash) (575°C and 900°C)".

[0070] Table 1

[0071]

[0072]

[0073] As shown in Table 1, when the amount of calcium carbonate coating agent prepared in Examples 1-4 is small (1kg / t calcium carbonate), the tensile index, internal bonding strength, surface strength and ash content of the paper are not significantly increased compared with the blank; when the amount of calcium carbonate coating agent prepared in Examples 1-4 is increased to 3kg / t calcium carbonate, the tensile index, internal bonding strength, surface strength and ash content of the paper are significantly increased compared with the blank; when the amount of calcium carbonate coating agent prepared in Examples 1-4 is further increased to 5kg / t calcium carbonate, the ash content of the paper is further increased, but the tensile index, internal bonding strength and surface strength of the paper are only maintained or slightly decreased compared with the blank. Compared with the blank sample, the surface strength of the paper of the calcium carbonate coating agent prepared in Comparative Example 1 shows a downward trend as the amount of calcium carbonate coating agent added increases; and the surface strength of the paper of Example 1 increases and then decreases as the amount of calcium carbonate coating agent added increases within the range of 1 to 5kg / t calcium carbonate, but is still better than the blank sample as a whole, with an amount of 3kg / t calcium carbonate being the best.

[0074] The average particle size of unwrapped calcium carbonate was tested to be 2-3 μm; when the addition amount of calcium carbonate coating agent was 1 kg / t calcium carbonate, the average size of calcium carbonate flocs was 2-5 μm, the flocculation was too small and difficult to retain; when the addition amount of calcium carbonate coating agent was 3 kg / t calcium carbonate, the average size of calcium carbonate flocs was 10-20 μm, the flocculation was moderate, and the retention and improvement effects on the paper tensile index, internal bonding strength and surface strength were obvious; when the addition amount of calcium carbonate coating agent was 5 kg / t calcium carbonate, the average size of calcium carbonate flocs was 25-40 μm, the flocculation was too large, resulting in poor dispersion and uneven cross-section quantity, which is not conducive to the paper tensile index, internal bonding strength and surface strength.

[0075] The above test results demonstrate that the calcium carbonate coating of this embodiment can increase the surface strength of base paper. It is readily apparent that, when used in industrial paper production, the calcium carbonate coating of this embodiment can significantly improve the surface strength of paper compared to other coatings under the same surface sizing conditions. It is also readily apparent that, when paper reaches a certain surface strength (meets the required strength), the calcium carbonate coating of this embodiment can reduce the amount of surface sizing agent used. The calcium carbonate coating of this embodiment is particularly suitable for producing cultural paper.

[0076] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a calcium carbonate coating agent for papermaking, characterized in that: The following steps are involved: S1: pre-stir and mix deionized water, acrylamide, and (3-acrylamidopropyl)trimethylammonium chloride to prepare a monomer solution; The acrylate-terminated polysiloxane and the cationic gemini emulsifier are pre-stirred and mixed for a period of not less than 30 minutes to obtain an intermediate; Stir and dissolve the initiator and deionized water in advance to prepare an initiator solution; S2: Stir and dissolve deionized water, acrylamide, itaconic acid, EDTA and reactive emulsifier to form a base material. Under an inert atmosphere, uniformly heat to 65-70°C and begin to dropwise add the initiator solution. The reaction temperature is controlled at 80-85°C. After reacting for 15-20 minutes, begin to dropwise add the monomer solution. After 2 / 3 of the monomer solution has been added, the intermediate is added to the remaining monomer solution to obtain a mixture of the intermediate and the monomer; the mixture of the intermediate and the monomer is added dropwise, and the addition time is controlled within 3-3.5 hours; During the process of adding the monomer solution and the mixture of the monomer and the intermediate, the initiator solution is continuously added; After the mixture of monomer and intermediate is added dropwise, the initiator solution is added dropwise for 15-20 minutes, and then kept at 80-85°C for 45-60 minutes, and the material is cooled to below 50°C; S3 adds a pH regulator to adjust the pH to 5-7, and cools the temperature to below 40° C. to obtain a calcium carbonate coating agent for papermaking.

2. The preparation method of the calcium carbonate packaging agent for papermaking according to claim 1, wherein In the monomer solution, acrylamide accounts for 90-95% of the total mass of acrylamide and (3-acrylamidopropyl)trimethylammonium chloride; (3-acrylamidopropyl)trimethylammonium chloride accounts for 5-10% of the total mass of acrylamide and (3-acrylamidopropyl)trimethylammonium chloride; and the amount of deionized water added is 1.2-1.5 times the total mass of acrylamide and (3-acrylamidopropyl)trimethylammonium chloride; The mass ratio of the gemini emulsifier to the acrylate-terminated polysiloxane in the intermediate is (8-12):100; In the initiator solution, the mass ratio of initiator to deionized water is (1.0-1.5):

100.

3. The preparation method of the calcium carbonate packaging agent for papermaking according to claim 1, wherein In the base material, acrylamide accounts for 90-96% of the total mass of acrylamide and itaconic acid, itaconic acid accounts for 4-10% of the total mass of acrylamide and itaconic acid, the added amount of EDTA is 0.03-0.06% of the total mass of acrylamide and itaconic acid, the added amount of reactive emulsifier is 25-35% of the total mass of acrylamide and itaconic acid, and the added amount of deionized water is 1.4-1.8 times the total mass of acrylamide and itaconic acid.

4. The preparation method of the calcium carbonate packaging agent for papermaking according to claim 1, wherein The acrylate-terminated polysiloxane is a monoacrylate-terminated polysiloxane with a molecular weight of 400-5000.

5. The preparation method of the calcium carbonate packaging agent for papermaking according to claim 4, wherein The mass of the acrylate-terminated polysiloxane is 5-9% of the total mass of the acrylamide in the monomer solution and the acrylamide in the primer.

6. The preparation method of the calcium carbonate packaging agent for papermaking according to claim 1, wherein The mass ratio of acrylamide in the monomer solution to acrylamide in the primer is (1.6-1.8):

1.

7. A calcium carbonate coating agent for papermaking, prepared by the method for preparing a calcium carbonate coating agent for papermaking according to any one of claims 1 to 6.

8. A method for preparing a coated modified calcium carbonate filler, characterized in that: The calcium carbonate coating agent for papermaking is diluted with clean water, added into the calcium carbonate suspension, and stirred evenly to obtain the coated modified calcium carbonate filler; the amount of the calcium carbonate coating agent for papermaking is 1-5 kg / t calcium carbonate.

9. The method for preparing the coated modified calcium carbonate filler according to claim 8, wherein: The average size of the calcium carbonate flocs in the wrapped modified calcium carbonate filler is 2 to 25 μm.

10. A cultural paper, characterized in that: The invention relates to an encapsulated modified calcium carbonate filler prepared by the preparation method of the encapsulated modified calcium carbonate filler according to claim 8 or 9.

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