A method for preparing paper with high bulk thickness

Abstract

This invention provides a method for preparing high bulk paper, comprising the following steps: using softwood chemical pulp, hardwood chemical pulp, and bleached chemimechanical pulp as fiber raw materials, and mixing them in a specific ratio; the chemical additives added during the mixing process include: porous calcium silicate, paper machine filler, cationic acrylic resin, spherical anionic polyacrylamide, cationic starch, alkyl ketene dimer, and cationic polyacrylamide; the amount of porous calcium silicate used is 30-60 kg / ton of paper; the mixed pulp is then sized, dewatered and formed at the wire section to form a wet sheet; the wet sheet is then pressed, pre-dried, surface-sized, and post-dried to obtain the finished paper. This invention, by applying the aforementioned porous calcium silicate, can improve paper retention while significantly increasing paper bulk, as well as improving paper stiffness and opacity, meeting customer requirements for paper bulk, and reducing the amount of plant fiber used, thereby reducing production costs.

Description

Technical Field

[0001] This invention belongs to the field of papermaking technology, and particularly relates to a method for preparing paper with high bulk. Background Technology

[0002] Bulk is a crucial performance indicator for paper and paperboard. High bulk means that, for the same basis weight, paper or paperboard has greater thickness, stiffness, and opacity. At the same thickness, this allows for an effective reduction in basis weight, making the paper lighter and thus reducing fiber consumption, saving pulp costs, and reducing the consumption of forest and other fiber raw material resources. Lighter paper also reduces costs for commercial paper customers; for student paper such as textbooks, supplementary materials, and notebooks, it reduces the burden on students. For paper products requiring high stiffness, such as electrostatic copy paper and boxboard, lightweighting effectively improves stiffness performance, enhances the machine-passing performance of copy paper products, and optimizes the stiffness of cartons.

[0003] Currently, the main technologies for improving paper bulk include: adding high-yield pulp; using shoe press; employing metal belt calendering; using bulking agents; and reducing paper smoothness. Among these, improving paper bulk by adding bulking agents is a currently popular research direction.

[0004] To increase paper bulk during production, two methods are employed: adding low-density substances and increasing paper porosity. Traditional bulk additives generally have a density greater than wood fiber but less than inorganic fillers (such as calcium carbonate). In application, they can only increase bulk when replacing inorganic fillers, not directly replace wood fiber. Because these bulk additives are significantly more expensive than inorganic fillers and cannot effectively reduce the proportion of wood fiber, costs increase significantly. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a method for preparing paper with high bulk. The paper product prepared by the present invention has high bulk and other properties, and the cost is low. The method and process of the present invention can be widely applied to various types of paper that require increased bulk.

[0006] This invention provides a method for preparing high bulk paper, comprising the following steps:

[0007] The pulp is prepared using softwood chemical pulp, hardwood chemical pulp, and bleached chemimechanical pulp as fiber raw materials in a specific ratio. The chemical additives added during the pulp preparation process include: porous calcium silicate, paper machine filler, cationic acrylic resin, spherical anionic polyacrylamide, cationic starch, alkyl ketene dimer, and cationic polyacrylamide. The amount of porous calcium silicate used is 30-60 kg / ton of finished paper.

[0008] The prepared pulp is then sized, dehydrated and formed on the wire section to create wet paper;

[0009] The wet paper is pressed, pre-dried, surface sizing and post-dried to obtain finished paper; the sizing agent used for surface sizing is enzyme-converted starch gum, and the sizing amount for surface sizing is 40-60 kg per ton of finished paper.

[0010] In an embodiment of the present invention, both the softwood chemical pulp and the hardwood chemical pulp are bleached pulp boards; the bleached chemimechanical pulp is bleached hardwood chemimechanical pulp; and the mass ratio of the softwood chemical pulp, hardwood chemical pulp and bleached chemimechanical pulp is 8-25:0-65:15-92.

[0011] In embodiments of the present invention, the beating concentration of the softwood chemical pulp is 4.0-4.5%, and the freeness is 38-40°SR; the beating concentration of the hardwood chemical pulp is 4.0-4.5%, and the freeness is 40-42°SR; the pulp concentration of the bleached chemimechanical pulp is 4.0-4.5%, and the freeness is 52-56°SR.

[0012] In embodiments of the present invention, the porous calcium silicate crystals are elliptical in shape, honeycomb-like, with a median particle size of 4.8-6.2 micrometers and a density of 0.15-0.2 g / cm³. 3 The ISO whiteness is 94-96%.

[0013] In an embodiment of the present invention, the porous calcium silicate is added after the paper machine filler is added; the paper machine filler is calcium carbonate.

[0014] In an embodiment of the present invention, the prepared pulp is subjected to thick pulp screening, conditioning, rinsing, sand removal and degassing, and then sized, and after fine screening, it is dewatered and formed in the wire section to form wet paper.

[0015] In embodiments of the present invention, the amount of cationic starch used is 8-10 kg / ton of finished paper; the amount of alkyl ketene dimer used is 15-20 kg / ton of finished paper.

[0016] In an embodiment of the present invention, the alkyl ketene dimer is added at the pulp inlet to control the Cobb value of the paper at 25-30 g / m². 2 Cationic polyacrylamide is added at a dosage of 0.2-0.4 kg per ton of paper at the pulp outlet.

[0017] In an embodiment of the present invention, the basis weight of the paper is 65-80 g / m³. 2 It is lightweight paper, copy paper, or notebook paper.

[0018] In an embodiment of the present invention, the bulk of the paper is 1.4-2.0 cm.2 / g.

[0019] Compared with existing technologies, this invention uses softwood chemical pulp, hardwood chemical pulp, and bleached chemimechanical pulp as fiber raw materials, and employs a certain amount of inorganic bulking agent in the pulping system. This agent is a porous calcium silicate obtained through chemical modification, possessing characteristics such as light weight, low density, strong adsorption, and good dispersibility. It replaces part of the filler in the pulp system, and after papermaking, produces a high-bulk paper product. By applying the aforementioned porous calcium silicate, this invention can significantly increase paper bulk while improving paper retention, as well as paper stiffness and opacity, meeting customer requirements for paper bulk. Furthermore, it can reduce the amount of plant fiber used, thereby reducing production costs. The paper produced by this method increases bulk by 5-12% while maintaining its original properties, thus reducing production costs and maximizing paper profits. Detailed Implementation

[0020] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, the technical solution of the present invention will now be described in detail with reference to specific embodiments. The described embodiments are only some embodiments of the present invention, and not all embodiments.

[0021] This invention provides a method for preparing high bulk paper, comprising the following steps:

[0022] The pulp is prepared using softwood chemical pulp, hardwood chemical pulp, and bleached chemimechanical pulp as fiber raw materials in a specific ratio. The chemical additives added during the pulp preparation process include: porous calcium silicate, paper machine filler, cationic acrylic resin, spherical anionic polyacrylamide, cationic starch, alkyl ketene dimer, and cationic polyacrylamide. The amount of porous calcium silicate used is 30-60 kg / ton of finished paper.

[0023] The prepared pulp is then sized, dehydrated and formed on the wire section to create wet paper;

[0024] The wet paper is pressed, pre-dried, surface sizing and post-dried to obtain finished paper; the sizing agent used for surface sizing is enzyme-converted starch gum, and the sizing amount for surface sizing is 40-60 kg per ton of finished paper.

[0025] The paper products prepared by this invention have high bulk and other properties, and the cost is low. The method and process of this invention can be widely applied to various types of paper that require increased bulk.

[0026] To achieve the above objectives, the technical solution adopted in the embodiments of the present invention specifically includes the following process: softwood chemical pulp, hardwood chemical pulp and bleached chemimechanical pulp are used as fiber raw materials and mixed according to requirements. The mixed pulp sample is subjected to thick pulp screening, mixing, rinsing, sand and gas removal, sizing, fine screening, wire dewatering and forming, pressing, pre-drying, surface sizing, post-drying, calendering, winding and packaging to obtain the desired paper product.

[0027] Specifically, in this embodiment of the invention, the fiber raw materials are first processed into pulp: the softwood commercial pulp board and the hardwood commercial pulp board are respectively sent to hydraulic pulping and then sent to the pre-pulping tank; the bleached chemimechanical pulp is a self-produced bleached chemimechanical pulp, which is pumped to the pre-pulping tank by the pulping workshop.

[0028] Furthermore, the fiber raw materials used in the pulping process are commercial bleached softwood chemical pulp boards, commercial bleached hardwood chemical pulp boards, and bleached hardwood chemimechanical pulp produced by the applicant company itself. Specifically, the specifications of the softwood chemical pulp include: brightness of 88±2% ISO, fiber length of 1.8-3.2 mm, and fiber width of 24.1-30.0 μm; the specifications of the hardwood chemical pulp include: brightness of 90±2% ISO, fiber length of 0.8-1.1 mm, and fiber width of 14.0-20.0 μm; the brightness of the bleached chemimechanical pulp can be 74-76% ISO, fiber length of 0.5-0.6 mm, and fiber width of 15-24 μm. The mass ratio of softwood chemical pulp, hardwood chemical pulp, and bleached chemimechanical pulp is 8-25:0-65:15-92. In some embodiments, the pulp is prepared with a mass ratio of softwood chemical pulp to bleached chemimechanical pulp of 8-10:90-92, which means that hardwood chemical pulp may not be used. This is to maximize the use of chemimechanical pulp to improve the bulk of the paper while ensuring the paper strength (among the three pulps, chemimechanical pulp contributes the most to the bulk, while softwood chemical pulp contributes the most to the strength).

[0029] In this embodiment of the invention, pulping is performed as follows: the loosened pulp is pumped from the pre-beating tank into the mill and pulped according to production needs. Preferably, the pulping concentration is 4.0-4.5%, and the pulp beating degree requirements are as follows: softwood chemical pulp: 38-40°SR, hardwood chemical pulp: 40-42°SR, bleached chemimechanical pulp: 52-56°SR; the pulped pulp is sent to the post-beating tank, diluted with paper machine white water, and then sent to the mixing tank.

[0030] The present invention also includes the preparation of porous calcium silicate: water is added to the preparation tank, the stirrer is turned on, and then porous calcium silicate is added. The preferred concentration is 10-15 wt%. The transfer pump is turned on to pump the stirred porous calcium silicate mixture into the storage tank. During production, in order to ensure the stability of the amount of porous calcium silicate added, the liquid level in the storage tank should be kept as stable as possible.

[0031] The porous calcium silicate described in this invention is characterized by its light weight, low density, strong adsorption, and good dispersibility; specifically, it has the following properties: elliptical crystal shape, honeycomb structure, median particle size of 4.8-6.2 micrometers, and density of 0.15-0.2 g / cm³. 3 With an ISO whiteness of 94-96%, it is suitable for commercially available products.

[0032] In a specific embodiment of the present invention, the addition of porous calcium silicate, other chemicals (including paper machine fillers, pulp starch, alkyl ketene dimer (AKD), cationic polyacrylamide retention aid, etc.) and auxiliary materials includes: adding the porous calcium silicate using a porous calcium silicate addition system at a dosage of 30-60 kg / t of paper; in addition to adding porous calcium silicate, cationic acrylic resin is also added (at a dosage of 0.5-1.5 kg / t of paper) at the pulp mixing tank, and a certain amount of spherical anionic polyacrylamide is added to the paper machine tank at a dosage of 0.1-0.5 kg / t of paper. Furthermore, paper machine filler (preferably calcium carbonate, with a filler dosage of 230-300 kg / t paper) is added to the pulp mixing box, with the addition point preceding the addition point of porous calcium silicate; cationic starch is added at the outlet of the high-level box, preferably 15-20 kg / t paper AKD is added at the inlet of the pulp pump, and cationic polyacrylamide retention aid (GPAM retention aid, with a dosage of 0.3-0.6 kg / t paper) is added at the outlet of the pulp pump.

[0033] Furthermore, the amount of cationic starch used can be 8-10 kg / ton of finished paper; the amount of AKD used is preferably 15-20 kg / ton of finished paper. The AKD is added at the pulp inlet to control the Cobb value of the finished paper at 25-30 g / m³. 2 Preferably, cationic polyacrylamide is added at the pulp outlet at a dosage of 0.2-0.4 kg per ton of paper. The specifications of the cationic acrylic resin include: solid content of 33-36%, pH value of 5-7, and anion requirement of 125-200 ueq / L; the specifications of the spherical anionic polyacrylamide include: solid content of up to 2%, and degree of polymerization of 150,000-300,000.

[0034] In the pulps described in this invention embodiment, the lower the ratio of chemimechanical pulp, the more significant the effect of porous calcium silicate, mainly because chemimechanical pulp has a higher bulk compared to chemical pulp. The principle by which porous calcium silicate increases paper bulk in the process of this invention embodiment includes: cationic acrylic resin first encapsulates the porous calcium silicate, forming positively charged particles, which then undergo electrostatic adsorption with negatively charged spherical polyacrylamide. Because the spherical polyacrylamide has numerous cationic tentacles, it can effectively encapsulate both calcium silicate and cationic acrylic resin, thereby increasing the retention rate of calcium silicate and ensuring it remains in the paper as much as possible. Therefore, if the amount of cationic acrylic resin and spherical polyacrylamide is too low, it can easily lead to incomplete encapsulation of calcium silicate, resulting in a decreased retention rate and ultimately reducing the effect of calcium silicate on increasing bulk.

[0035] After pulp preparation, the pulp in this embodiment of the invention is fed onto the paperboard via the sizing system and then sequentially undergoes wet papermaking, forming, pre-drying, surface sizing, post-drying, and winding. The surface sizing process includes: an enzyme-converted starch gum concentration of 10%-15% (room temperature viscosity of 5-20 mPa·s), and a sizing amount of 40-60 kg / ton of paper (sizing amount at 5-6 g / m²). 2 control).

[0036] This invention does not impose special limitations on other process conditions. For example, the pulp concentration can be 0.75-1.03%, the pH value 7.0-8.5, and the pulp-to-mesh speed ratio 1.02-1.03. The dewatering method involved is pressing, specifically double-shoe pressing, with a first press pressure of 700 N / m and a second press pressure of 900 N / m, resulting in a pressing moisture content of 48-52%. The surface sizing compound has a mass concentration of 10-15%, and the application rate is 5-6 g / m³. 2 Control; the pre- and post-drying temperatures are usually 50-110℃, there are 5 groups of drying cylinders, and the speed difference of each group can be 0-4m / min; the moisture content before drying is preferably 5-7%, and the moisture content after drying is preferably 6-8%.

[0037] The paper produced according to the above process in this embodiment of the invention has a basis weight of 65-80 g / m³. 2 The performance meets the basic requirements of lightweight paper, copy paper, or notebook paper, with a significant improvement in bulk, for example, the bulk of the finished paper ranges from 1.4 to 2.0 cm. 2 / g. In some specific embodiments, the amount of chemimechanical pulp in the copy paper formulation is small, generally only 0-15%; while in other embodiments, the amount of chemimechanical pulp in the notebook paper formulation is larger, generally reaching 20-92%, with other papermaking processes being roughly the same.

[0038] To further understand the present invention, the method and process for preparing paper provided by the present invention will be described in detail below with reference to embodiments. The scope of protection of the present invention is not limited to the following embodiments. In the embodiments, all original reagents and materials are commercially available, and experimental methods without specific experimental conditions are conventional methods and conditions well known in the art.

[0039] The pulps used are commercially available bleached softwood chemical pulp board, commercially available bleached hardwood chemical pulp board, and bleached hardwood chemimechanical pulp produced by the company itself, with specific parameters as described above. The specific indicators of the porous calcium silicate involved are: elliptical crystal shape, honeycomb structure, median particle size 4.8-6.2 micrometers, density 0.15-0.2 g / cm³, ISO whiteness 94-96%; the preparation is as follows: add clean water to the mixing tank, turn on the stirrer, then add the inorganic thickening agent porous calcium silicate to prepare a concentration of 10-15%, turn on the transfer pump, and pump the stirred porous calcium silicate mixture into the storage tank.

[0040] The specifications of the cationic acrylic resin include: solid content of 33-36%, pH value of 5-7, and anion requirement of 125-200ueq / L; the specifications of the spherical anionic polyacrylamide include: solid content of 2% and degree of polymerization of 150,000-300,000.

[0041] Example 1:

[0042] First, the softwood chemical pulp board is sent to a hydraulic pulping plant for pulping, and then to a pre-beating tank. The bleached chemimechanical pulp is pumped from the self-produced bleached chemimechanical pulp workshop to the pre-beating tank. Then, the pre-beating tank pumps the pulp to the corresponding mills for beating. The beating concentration of the softwood chemical pulp is controlled at 4.0-4.5%, and the beating degree is controlled at 38-40°SR. The beating concentration of the bleached chemimechanical pulp is controlled at 4.0-4.5%, and the beating degree is controlled at 52-56°SR. The beating pulp is then sent to a post-beating tank.

[0043] The pulp is then diluted with white water and sent to the mixing tank, where it is mixed at a ratio of softwood chemical pulp to chemimechanical pulp of 8:92. In the mixing tank, calcium carbonate filler is added at a rate of 285 kg / t paper, porous calcium silicate at a rate of 65 kg / t paper, and cationic acrylic resin at a rate of 1.0 kg / t paper. Simultaneously, 0.3 kg / t paper spherical anionic polyacrylamide is added to the paper machine tank, 10 kg / t paper cationic starch is added to the outlet of the high-level box, and AKD is added at a rate of 15 kg / t paper at the inlet of the pulp pump. The Cobb value of the finished paper is controlled at 25-30 g / m³. 2 The pulp is pumped to the deslagging device by the slurry pump and then sent to the slurry system by the slurry pump. 0.3 kg / t of paper cationic polyacrylamide retention aid (GPAM retention aid) is added at the outlet of the slurry pump.

[0044] After the slurry is fed into the slurry system, it is then formed, shaped, and surface-sized (sizing amount is 5-6 g / m). 2 The process involves control, drying, and winding to obtain paper. The enzyme-converted starch gum has a mass concentration of 15% (room temperature viscosity can be 15-20 mPa·s).

[0045] The paper produced using the above process is lightweight paper, and its main indicators include: basis weight 76.1 g / m³. 2 Thickness 152.3μm, loose thickness 2.00cm 3 / g, Cobb value 21.5g / m 2 Longitudinal tear length 3.58km, transverse tear length 2.28km, longitudinal stiffness 111.0mN, transverse stiffness 73.1mN, whiteness 77.9% ISO, moisture content 6.6%, surface fuzzing coefficient 4.7, smoothness controlled at 7-10s, and no paper fuzz.

[0046] Furthermore, compared with the paper without the addition of porous calcium silicate, see Table 1. The first pass retention of the present invention was increased by 8.8%; the paper bulk was increased by 5.3%, the longitudinal stiffness was increased by 6.7%, and the ash content of the finished paper was increased by 6.9%, while other indicators remained largely unchanged, all of which meet the basic requirements of existing lightweight paper.

[0047] Example 2:

[0048] First, the softwood and hardwood chemical pulp boards are sent to the hydraulic pulping and then to their respective pre-beating tanks. The bleached chemimechanical pulp is pumped from the self-produced bleached chemimechanical pulp workshop to the pre-beating tank. From the pre-beating tank, the pulp is then pumped to the corresponding mills for beating. The beating concentration of the softwood chemical pulp is controlled at 4.0-4.2%, and the beating degree is beaten to 38°SR; the beating concentration of the hardwood chemical pulp is controlled at 4.0-4.3%, and the beating degree is beaten to 41°SR; the beating concentration of the chemimechanical pulp is controlled at 4.1%, and the beating degree is controlled at 53°SR. The beaten pulp is then sent to the post-beating tank.

[0049] The pulp is then prepared according to a ratio of softwood chemical pulp: hardwood chemical pulp: chemimechanical pulp = 20:65:15. In the pulping tank, calcium carbonate filler is added at a rate of 300 kg / t paper, porous calcium silicate at a rate of 50 kg / t paper, and cationic acrylic resin at a rate of 0.8 kg / t paper. Simultaneously, 0.4 kg / t paper spherical anionic polyacrylamide is added to the paper machine tank, 9 kg / t paper cationic starch is added at the outlet of the high-level box, and AKD is added at a rate of 20 kg / t paper at the inlet of the pulp pump. The Cobb value of the finished paper is controlled at 25-30 g / m³. 2 The pulp is pumped to the deslagging device by the slurry pump and then sent to the slurry system by the slurry pump. 0.3 kg / t of paper cationic polyacrylamide retention aid (GPAM retention aid) is added at the outlet of the slurry pump.

[0050] After the slurry is fed into the slurry system, it is then formed, shaped, and surface-sized (sizing amount is 5-6 g / m). 2 The process involves control, drying, and winding to obtain the finished paper. The mass concentration of the enzyme-converted starch gum is 12%.

[0051] The paper produced using the above process is copy paper, and its main specifications include: basis weight 80g / m³. 2 Thickness 116μm, loose thickness 1.45cm 3 / g, Cobb value 25.6g / m 2 Longitudinal fracture length 4.68km, transverse fracture length 2.51km, longitudinal stiffness 138mN, transverse stiffness 68.2mN, whiteness 105.9% ISO, moisture content 6.6%, surface fuzzing coefficient 5.5, smoothness 36s, no paper fuzz.

[0052] Furthermore, compared with the paper without porous calcium silicate, see Table 1. The first pass retention of the present invention is improved by 8.5%; the paper bulk is improved by 7.4%, the longitudinal stiffness is improved by 9.5%, and the ash content of the finished paper is improved by 4.4%, which can meet the basic requirements of copier paper for all-in-one machines.

[0053] Example 3:

[0054] First, the softwood and hardwood chemical pulp boards are sent to hydraulic pulping and then to their respective pre-beating tanks. The bleached chemimechanical pulp is pumped from the self-produced bleached chemimechanical pulp workshop to the pre-beating tank. From the pre-beating tank, the pulp is then pumped to the corresponding mills for beating. The beating concentration of the softwood chemical pulp is controlled at 4.0-4.5%, with a beating degree of 38-40°SR; the beating concentration of the hardwood chemical pulp is controlled at 4.2%, with a beating degree of 40-42°SR; and the beating concentration of the chemimechanical pulp is controlled at 4.0-4.5%, with a beating degree of 54°SR. The beated pulp is then sent to the post-beating tank.

[0055] The pulp is diluted with white water and sent to the mixing tank, where it is mixed according to the ratio of softwood chemical pulp: hardwood chemical pulp: chemimechanical pulp = 24:33:43. In the mixing tank, calcium carbonate filler is added at a ratio of 300 kg / t paper, porous calcium silicate at a ratio of 50 kg / t paper, and cationic acrylic resin at a ratio of 1.0 kg / t paper. Simultaneously, 0.4 kg / t paper spherical anionic polyacrylamide is added to the paper machine tank, 10 kg / t paper cationic starch is added at the outlet of the high-level box, and AKD is added at a ratio of 20 kg / t paper at the inlet of the pulp pump. The Cobb value of the finished paper is controlled at 25-30 g / m³. 2 The pulp is pumped to the deslagging device by the slurry pump and then sent to the slurry system by the slurry pump. 0.3 kg / t of paper cationic polyacrylamide retention aid (GPAM retention aid) is added at the outlet of the slurry pump.

[0056] After the slurry is fed into the slurry system, it is then formed, shaped, and surface-sized (sizing amount is 5-6 g / m). 2 The process involves control, drying, and winding to obtain the paper. The mass concentration of the enzyme-converted starch gum is 12%. Furthermore, in Examples 1-3, the web pulp concentration is 0.75-1.03%, the pH value is 7.0-8.5, and the pulp-to-web speed ratio is 1.02-1.03. The dewatering method involved is a pressing process, a double-shoe pressing, with a first press pressure of 700 N / m and a second press pressure of 900 N / m, resulting in a pressing moisture content of 48-52%. The pre- and post-drying temperatures are typically 50-110℃, with a total of 5 drying cylinders, each with a speed difference of 0-4 m / min; the pre-drying moisture content is 5-7%, and the post-drying moisture content is 6-8%.

[0057] The paper produced according to the process in Example 3 above is a thin paper, and its main indicators include: basis weight 65.8 g / m³. 2 Thickness 112.8μm, loose thickness 1.71cm 3 / g, Cobb value 24.1g / m 2 The longitudinal tear length is 3.60 km, the transverse tear length is 1.72 km, the longitudinal stiffness is 60 mN, the transverse stiffness is 27 mN, the whiteness is 76.9% ISO, the moisture content is 6.5%, the surface fuzzing coefficient is 2.2 on the front and 1.8 on the back, the smoothness is controlled at 20s, and there is no paper fuzz. Furthermore, compared with the paper without porous calcium silicate (see Table 1), the first pass retention of this embodiment is improved by 8.8%; the paper bulk is improved by 11.8%, the longitudinal stiffness by 9.1%, and the ash content of the finished paper by 6.7%, while other indicators remain largely unchanged, all meeting the basic requirements of existing high-bulk thin paper.

[0058] Table 1. Paper quality testing results with different amounts of porous calcium silicate added.

[0059]

[0060] As can be seen from the above embodiments, the application of specifically chemically modified porous calcium silicate in this invention can significantly increase paper bulk while improving paper retention, as well as paper stiffness and opacity, meeting customer requirements for paper bulk. Furthermore, it can reduce the amount of plant fiber used (reduced fiber usage but increased paper ash content), thereby lowering production costs. The paper produced by this method increases bulk by 5-12% while maintaining its original properties, and at a lower production cost.

[0061] The above examples are only used to illustrate the technical features and implementation process of the present invention, and are not intended to limit the technical solutions of the present invention. It should be noted that those skilled in the art can still make modifications or equivalent substitutions to the present invention without departing from the principle of the present invention, and all such modifications or substitutions are covered by the protection of the present invention.

Claims

1. A method for preparing paper with high bulk, characterized in that, Includes the following steps: The pulp is prepared by mixing softwood chemical pulp, hardwood chemical pulp and bleached chemimechanical pulp as fiber raw materials in a certain proportion. The chemical additives added in the pulp preparation process include: porous calcium silicate, calcium carbonate paper machine filler, cationic acrylic resin, spherical anionic polyacrylamide, cationic starch, alkyl ketone dimer and cationic polyacrylamide. The prepared pulp is then sized, dehydrated and formed on the wire section to create wet paper; The wet paper is pressed, pre-dried, surface sizing and post-dried to obtain finished paper; the surface sizing agent is enzyme-converted starch gum, and the sizing amount is 40-60 kg / ton of finished paper; The mass ratio of the softwood chemical pulp, hardwood chemical pulp, and bleached chemimechanical pulp is 8~25:0~65:15~92; the pulp preparation process specifically includes: In the pulp mixing tank, add calcium carbonate paper machine filler at 230-300 kg / t of paper and porous calcium silicate at 30-60 kg / t or 65 kg / t of paper, as well as 0.5-1.5 kg / t of cationic acrylic resin; simultaneously, add 0.1-0.5 kg / t of spherical anionic polyacrylamide in the paper machine tank, add 8-10 kg / t of cationic starch at the outlet of the high-level tank, add alkyl ketene dimer at 15-20 kg / t of paper at the inlet of the pulp pump, and add 0.2-0.4 kg / t of cationic polyacrylamide at the outlet of the pulping pump. The porous calcium silicate is added after the calcium carbonate paper machine filler; the porous calcium silicate crystals are elliptical, honeycomb-shaped, with a median particle size of 4.8-6.2 micrometers and a density of 0.15-0.2 g / cm³. 3 The ISO whiteness is 94-96%.

2. The method according to claim 1, characterized in that, Both the softwood chemical pulp and the hardwood chemical pulp are bleached pulp boards; the bleached chemimechanical pulp is bleached hardwood chemimechanical pulp.

3. The method according to claim 2, characterized in that, The beating concentration of the softwood chemical pulp is 4.0-4.5%, and the freeness is 38-40°SR; the beating concentration of the hardwood chemical pulp is 4.0-4.5%, and the freeness is 40-42°SR; the pulp concentration of the bleached chemimechanical pulp is 4.0-4.5%, and the freeness is 52-56°SR.

4. The method according to any one of claims 1-3, characterized in that, The alkyl ketene dimer is added at the pulp inlet to control the Cobb value of the finished paper at 25-30 g / m². 2 .

5. The method according to any one of claims 1-3, characterized in that, The basis weight of the finished paper is 65-80 g / m³. 2 The finished paper is lightweight paper, copy paper, or notebook paper.

6. The method according to claim 5, characterized in that, The bulk of the finished paper is 1.4-2.0 cm. 2 / g.

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