Production process of high-bulk white cardboard

Abstract

The invention discloses a production process of a high-bulk white cardboard. The production process comprises the following steps: preparing raw materials, and adopting different fiber raw material proportions for each layer; during beating, the fiber raw materials are subjected to segmented beating treatment, the beating degree and grinding sheet gaps are controlled, filler is added according to a specific sequence and proportion, the filler comprises nano cellulose, light calcium carbonate, cationic starch and kaolin, and the kaolin is coated with sodium stearate; a rosin-aluminum sulfate process is adopted for internal sizing, and a rosin emulsion and a pure aluminum sulfate solution are prepared through a high-pressure homogenizer; controlling the difference between the net speed and the pulp speed during papermaking; shoe type squeezing is adopted; a grouping multi-cylinder drying system is adopted for drying; polyvinyl alcohol is adopted for calendaring treatment and surface sizing. The invention aims to produce the white cardboard with high bulk, high strength, good printability, water resistance and appearance quality, and solves the problems in the prior art that the bulk of the paper is not well considered, and interaction among fillers in the pulping process is easy to influence.

Description

Technical Field

[0001] The invention relates to the technical field of white cardboard manufacturing technology, in particular to a production process of high-bulk white cardboard. Background Art

[0002] In the papermaking industry, high-bulk white cardboard is widely used in packaging, printing, and other fields due to its excellent printability, stiffness, and bulk. However, traditional white cardboard production processes struggle to achieve high bulk while simultaneously balancing various properties such as paper strength, water resistance, and printability. Furthermore, they inadequately utilize raw materials, resulting in high production costs and unstable product performance.

[0003] The existing technology has shortcomings in the ratio of fiber raw materials, pulping process, filler addition order and treatment, sizing method and drying and calendering. For example, the fiber processing is not fine enough, the filler dispersion and retention rate are low, the sizing effect is not good, and the drying process is prone to paper deformation and uneven performance. It is difficult to meet the production requirements of high-quality and high-bulk white cardboard.

[0004] Therefore, it is necessary to provide a production process for high-bulk white cardboard to solve the technical problems existing in the existing white cardboard manufacturing process. Summary of the Invention

[0005] The object of the present invention is to provide a production process for high-bulk white cardboard, aiming to produce white cardboard with high bulk, high strength, good printability, water resistance and appearance quality, thereby solving the problems in the prior art of poor balance between the bulk of the paper, poor synergistic effect between fillers during the pulping process, and easy influence of interaction between fillers.

[0006] To achieve the above object, the present invention provides the following technical solution: a production process for high-bulk white cardboard, comprising the following steps:

[0007] (1) Raw material preparation: Select fiber raw materials, including wood pulp fiber (NBKP, LBKP) and added fiber; determine the fiber raw material ratio of each layer: NBKP accounts for 30-35% and LBKP accounts for 65-70% in the surface layer; NBKP accounts for 10-15% and LBKP accounts for 15-20% and BCTMP accounts for 65-75% in the core layer; NBKP accounts for 20-25% and LBKP accounts for 75-80% in the bottom layer;

[0008] (2) beating: the fiber raw material of step (1) is beaten by a disc grinder, and the beating degree of the fiber raw material is controlled between 30°SR and 40°SR, and the grinding gap of the disc grinder is 0.1-0.5 mm;

[0009] (3) In-slurry sizing: The slurry in step (2) is sized using a rosin-aluminum sulfate in-slurry sizing process; the rosin solid content in the rosin-aluminum sulfate sizing agent is 28% to 29%, the alumina content in the aluminum sulfate is 7.5% to 8%, the dosage ratio of rosin to aluminum sulfate is 1:1.1-1.2, the pH in the headbox is controlled to be 4.8-5.2, and the white water temperature is 30-45°C;

[0010] (4) Papermaking: The fiber raw material processed by the pulping in step (3) is fed into a papermaking machine for papermaking, and the speed difference between the papermaking machine's wire speed and the pulp speed is controlled to be 8%-12% to form a wet paper web;

[0011] (5) Pressing: The wet paper web obtained in step (4) is subjected to a shoe press, with the pressing pressure controlled between 450 and 600 kPa and the pressing time being 10 to 15 seconds;

[0012] (6) Drying: The paper web after pressing in step (5) is dried using a multi-cylinder drying process, with the steam blowing box temperature at 102-105°C and the steam blowing box pressure at 0.2-0.5 bar, to control the moisture content of the paper from 80% to below 10%;

[0013] (7) Calendering: Calendering the paper after drying in step (6) at a calendering pressure of 200-300 MPa;

[0014] (8) Surface sizing: After the calendering treatment in step (7), surface sizing is performed. The surface sizing agent is polyvinyl alcohol, and the sizing amount is 3-5 g / m².

[0015] Preferably, in step (1), the weight ratio of the wood pulp fiber to the added fiber is 70:30 to 90:10. The wood pulp fiber and the added fiber are mixed in the fiber mixing tank by combining mechanical stirring and pipeline mixing. The stirring speed is controlled at 100-150 r / min and the stirring time is 15-20 min. The fibers are then further mixed uniformly by a pipeline mixer and the pipeline flow rate is controlled at 1-1.5 m / s.

[0016] Preferably, in step (1), the added fiber is a regenerated fiber, which comes from the recycling of waste paper, and the length of the processed fiber is 0.5-2 mm.

[0017] Preferably, in step (2), segmented beating is adopted:

[0018] The first stage: low-concentration beating is performed, the concentration is controlled at 3-5%, the grinding disc gap is gradually reduced from 0.5mm to 0.3mm, and the beating time is 10-15min;

[0019] The second stage: high-concentration beating is carried out, the concentration is increased to 8-10%, the grinding gap is controlled at 0.2-0.3mm, and the beating time is 8-12min.

[0020] Preferably, in step (2), the following fillers are added in the following order:

[0021] Light calcium carbonate: Add light calcium carbonate evenly through a screw feeder during the initial 2-5 minutes of low-consistency beating;

[0022] Cationic starch: Add cationic starch by metering pump at the end of low-consistency beating for 8-15 minutes;

[0023] Kaolin: After high-concentration slurrying, add kaolin into the slurry preparation tank and stir for 10-15 minutes at a stirring speed of 100-120r / min.

[0024] Preferably, in step (2), the filler is added according to the mass percentage of the absolute dry fiber, first adding 0.5%-1% of nanocellulose, then adding 5%-10% of light calcium carbonate at the beginning of low-concentration beating, then adding 1%-3% of cationic starch at the end of low-concentration beating, and finally, adding 3%-5% of kaolin after high-concentration beating.

[0025] Preferably, in step (2), kaolin is coated with sodium stearate, and the steps are as follows:

[0026] R1. Add kaolin to deionized water containing dispersant and stir at a speed of 200-500 r / min for 30-60 min to form a uniform kaolin suspension. The mass fraction of kaolin in deionized water is 10%-30%, and the amount of dispersant is 0.5%-2% of the mass of kaolin.

[0027] R2. In another container, add sodium stearate to deionized water, heat at 50-80°C and stir for 20-30 minutes to completely dissolve it. The amount of sodium stearate added is 3%-8% of the mass of kaolin.

[0028] R3, slowly add the dissolved sodium stearate solution to the kaolin suspension while stirring continuously. The addition rate is controlled at 2-5 ml per minute. The temperature of the reaction system is maintained at 40-60 ° C during the addition. After the addition is completed, continue stirring and reacting for 1-2 hours to allow the sodium stearate to fully coat the kaolin surface.

[0029] R4. After the reaction is completed, the mixed liquid is filtered using a suction filtration device to obtain a coated kaolin filter cake. The filter cake is repeatedly washed with deionized water for 3-5 times to remove impurities such as unreacted sodium stearate and dispersant remaining on the surface. After each washing, suction filtration is performed until the filter cake is substantially free of water droplets.

[0030] R5. Place the washed filter cake in an oven and dry it at 80-100°C for 2-4 hours to completely dry the kaolin to obtain a sodium stearate-coated kaolin product.

[0031] Preferably, in step (2), the grinding disc gap of the surface layer fibers in the low-concentration beating stage is 0.25-0.3 mm, the grinding disc gap of the core layer fibers in the low-concentration beating stage is 0.35-0.4 mm, and the grinding disc gap of the bottom layer fibers in the low-concentration beating stage is 0.25-0.3 mm; in the high-concentration beating stage, the grinding disc gap of the surface layer fibers is adjusted to 0.15-0.2 mm, the grinding disc gap of the core layer fibers is adjusted to 0.25-0.3 mm, and the grinding disc gap of the bottom layer fibers is adjusted to 0.15-0.2 mm.

[0032] Preferably, in step (3), the rosin emulsion is prepared by a high-pressure homogenizer:

[0033] S1. Heat the rosin to a molten state, and control the temperature at 160-170°C;

[0034] S2. Slowly add the melted rosin to an aqueous solution containing an emulsifier, wherein the amount of the emulsifier is 3-5% of the mass of the rosin, and the temperature of the aqueous solution is maintained at 50-60°C;

[0035] S3. Turn on the high-pressure homogenizer and set the pressure to 20-30 MPa. After 3-5 cycles of homogenization, the particle size of the rosin emulsion reaches 0.5-1 μm.

[0036] In step (3), the preparation steps of the aluminum sulfate solution are:

[0037] Q1: Put industrial-grade aluminum sulfate into a dissolution tank and add clean water to the dissolution tank. The mass ratio of water to aluminum sulfate is 5-8:1.

[0038] Q2: Turn on the stirring device and set the stirring speed to 80-120r / min. At the same time, increase the temperature of the dissolving tank to 50-60℃ and control the dissolving time to 30-40min.

[0039] Q3: After the dissolution is completed, filter it through a filter with a pore size of 50-100 μm to remove insoluble impurities in the solution to obtain a pure aluminum sulfate solution;

[0040] Finally, the rosin emulsion and aluminum sulfate solution prepared in step (2) are added to the slurry pipeline at a ratio of 1:1.1-1.2 through a metering pump to mix with the slurry prepared in step (2).

[0041] Preferably, in step (6), the multi-cylinder drying system is arranged in groups, with the front half being a high-temperature rapid drying zone with a drying cylinder temperature of 102-105°C and a pressure of 0.2-0.3 bar; and the rear half being a low-temperature slow drying zone with a drying cylinder temperature of 100-102°C and a pressure of 0.3-0.5 bar.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. The present invention uses segmented beating to moderately cut the fibers in low-concentration beating, retaining the length and flexibility, and promotes fiber separation and brooming in high-concentration beating, thereby improving the fiber bonding force and strength while taking into account the bulk.

[0044] 2. By optimizing the order and proportion of filler addition, the present invention uses nanocellulose to enhance hydrogen bonding between fibers, improving paper strength and uniformity; light calcium carbonate to improve optical properties; cationic starch to enhance fiber bonding and filler retention; and kaolin to improve printability and chemical stability. The synergistic effect of these fillers achieves a comprehensive improvement in paper performance.

[0045] 3. The present invention reduces the interaction between kaolin and cationic starch by coating kaolin with sodium stearate, while not affecting its function in paper.

[0046] 4. The present invention can optimize fiber processing according to the performance requirements of each layer and improve the performance of each layer of paper by finely adjusting the gap between the grinding plates of different layers in the low-concentration and high-concentration beating stages. DETAILED DESCRIPTION

[0047] The following will clearly and completely describe the technical solutions of the present invention in conjunction with specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0048] An embodiment of the present invention provides a production process for high-bulk white cardboard, comprising the following steps:

[0049] (1) Raw material preparation: Select fiber raw materials, including wood pulp fiber (NBKP, LBKP) and added fiber; determine the fiber raw material ratio of each layer: NBKP accounts for 30-35% and LBKP accounts for 65-70% in the surface layer; NBKP accounts for 10-15% and LBKP accounts for 15-20% and BCTMP accounts for 65-75% in the core layer; NBKP accounts for 20-25% and LBKP accounts for 75-80% in the bottom layer;

[0050] (2) beating: the fiber raw material of step (1) is beaten by a disc grinder, and the beating degree of the fiber raw material is controlled between 30°SR and 40°SR, and the grinding gap of the disc grinder is 0.1-0.5 mm;

[0051] (3) In-slurry sizing: The slurry in step (2) is sized using a rosin-aluminum sulfate in-slurry sizing process; the rosin solid content in the rosin-aluminum sulfate sizing agent is 28% to 29%, the alumina content in the aluminum sulfate is 7.5% to 8%, the dosage ratio of rosin to aluminum sulfate is 1:1.1-1.2, the pH in the headbox is controlled to be 4.8-5.2, and the white water temperature is 30-45°C;

[0052] (4) Papermaking: The fiber raw material processed by the pulping in step (3) is fed into a papermaking machine for papermaking, and the speed difference between the papermaking machine's wire speed and the pulp speed is controlled to be 8%-12% to form a wet paper web;

[0053] (5) Pressing: The wet paper web obtained in step (4) is subjected to a shoe press, with the pressing pressure controlled between 450 and 600 kPa and the pressing time being 10 to 15 seconds;

[0054] (6) Drying: The paper web after pressing in step (5) is dried using a multi-cylinder drying process, with the steam blowing box temperature at 102-105°C and the steam blowing box pressure at 0.2-0.5 bar, to control the moisture content of the paper from 80% to below 10%;

[0055] (7) Calendering: Calendering the paper after drying in step (6) at a calendering pressure of 200-300 MPa;

[0056] (8) Surface sizing: After the calendering treatment in step (7), surface sizing is performed. The surface sizing agent is polyvinyl alcohol, and the sizing amount is 3-5 g / m².

[0057] More specifically, in step (1), the weight ratio of the wood pulp fiber to the added fiber is 70:30 to 90:10, and the wood pulp fiber and the added fiber are initially mixed in the fiber mixing tank by combining mechanical stirring and pipeline mixing, with the stirring speed controlled at 100-150 r / min and the stirring time at 15-20 min, and then further mixed uniformly by a pipeline mixer, with the pipeline flow rate controlled at 1-1.5 m / s.

[0058] More specifically, in step (1), the added fiber is a regenerated fiber, which comes from the recycling of waste paper, and the length of the processed fiber is 0.5-2 mm.

[0059] More specifically, in step (2), segmented beating is adopted:

[0060] The first stage: low-concentration beating is performed, the concentration is controlled at 3-5%, the grinding disc gap is gradually reduced from 0.5mm to 0.3mm, and the beating time is 10-15min;

[0061] The second stage: high-concentration beating is carried out, the concentration is increased to 8-10%, the grinding gap is controlled at 0.2-0.3mm, and the beating time is 8-12min.

[0062] In this embodiment, a layered ratio is adopted to optimize the performance of each layer, the surface layer has good strength and printability, the core layer increases bulk and reduces costs, and the bottom layer enhances stability; recycled fibers are used to reduce costs and utilize resources, and the mixing method ensures uniform dispersion of fibers. Segmented beating, low concentration moderately cuts the fibers to maintain length and flexibility, high concentration promotes fibrillation and brooming to improve bonding and strength, while taking bulk into account. Rosin-aluminum sulfate sizing enhances water resistance, and appropriate ingredients, proportions and process conditions ensure sizing effects and liquid resistance. Controlling the difference between the mesh speed and the pulp speed ensures uniform wet paper width and reduces paper defects. Boot pressing removes water, increases tightness and strength, and retains bulk. Multi-cylinder drying removes water evenly, maintains dimensional stability, and maintains paper strength and bulk. Moderate calendering improves appearance and retains high bulk. Polyvinyl alcohol surface sizing enhances surface properties and durability, and improves printing quality.

[0063] In this embodiment, more specifically, in step (2), the following fillers are added in the following order:

[0064] Light calcium carbonate: Add light calcium carbonate evenly through a screw feeder during the initial 2-5 minutes of low-consistency beating;

[0065] Cationic starch: Add cationic starch by metering pump at the end of low-consistency beating for 8-15 minutes;

[0066] Kaolin: After high-concentration slurrying, add kaolin into the slurry preparation tank and stir for 10-15 minutes at a stirring speed of 100-120r / min.

[0067] More specifically, in step (2), the filler is added according to the mass percentage of the absolute dry fiber, first adding 0.5%-1% of nanocellulose, then adding 5%-10% of light calcium carbonate at the beginning of low-concentration beating, then adding 1%-3% of cationic starch at the end of low-concentration beating, and finally, adding 3%-5% of kaolin after high-concentration beating.

[0068] The filler added in the present embodiment, nanocellulose has high specific surface area and abundant hydroxyl, can strengthen the hydrogen bond between fiber, improves the intensity of paper.Its tiny size can be filled in the space between fibers, helps to improve the evenness and the tightness of paper, improves the physical properties of paper to a certain extent, such as tensile strength and tear resistance simultaneously. As a kind of reinforcing agent, the adding of nanocellulose can improve the integrity of fiber network, for subsequent adding other fillers and further processing provide a more solid basic structure. On the other hand, light calcium carbonate and nanocellulose produce synergistic effect, nanocellulose strengthens the bonding force between fibers, for light calcium carbonate provides better dispersion and adhesion basis, and the adding of light calcium carbonate has further optimized optical property and the surface characteristic of paper, and the two acting together can make paper have better outward appearance and printing performance when having certain intensity.

[0069] On the other hand, cationic starch works synergistically with nanocellulose. Nanocellulose provides a denser fiber network for the adsorption of cationic starch, allowing cationic starch to better exert its bonding and reinforcing effects. Working in conjunction with light calcium carbonate, cationic starch can promote the retention of light calcium carbonate on the fiber, preventing it from being lost in subsequent processes. At the same time, its own bonding properties can fix light calcium carbonate more firmly on the fiber, enhancing the retention of filler and the overall performance of the paper.

[0070] On the other hand, kaolin and nanocellulose work synergistically. The fiber network constructed by nanocellulose provides good attachment sites for kaolin, allowing kaolin to be evenly distributed between fibers, increasing the retention rate of kaolin and improving the performance of paper; kaolin and light calcium carbonate also have a synergistic effect. Kaolin can further optimize the surface properties of paper. The two together improve the smoothness and glossiness of paper. At the same time, kaolin can partially make up for the shortcomings of light calcium carbonate in chemical stability; kaolin and cationic starch also have a synergistic effect. Cationic starch provides better adsorption and retention conditions for kaolin. At the same time, the addition of kaolin can further improve the water resistance of paper. The two work together to improve the comprehensive performance of paper, so that the paper is improved in terms of strength, water resistance and printability.

[0071] In general, adding these three fillers in the above order and proportion, and adding them at different stages of the beating process, fully utilizes the characteristics of different fillers, unleashing their advantages at different stages. Through synergy, this achieves a comprehensive improvement in paper performance, resulting in a high-bulk white cardboard paper that achieves a good balance across multiple performance indicators, meeting the requirements of high bulk, high strength, good printability, and good appearance quality. Furthermore, adding different fillers at different stages allows for better interaction between the fillers and the fibers, avoiding adverse interactions between fillers, improving filler utilization efficiency, and improving the overall performance of the paper.

[0072] In the above content of this embodiment, kaolin and cationic starch may interact with each other. In order to solve the above problem, in step (2), kaolin is coated with sodium stearate, and the steps are as follows:

[0073] R1. Add kaolin to deionized water containing dispersant and stir at a speed of 200-500 r / min for 30-60 min to form a uniform kaolin suspension. The mass fraction of kaolin in deionized water is 10%-30%, and the amount of dispersant is 0.5%-2% of the mass of kaolin.

[0074] R2. In another container, add sodium stearate to deionized water, heat at 50-80°C and stir for 20-30 minutes to completely dissolve it. The amount of sodium stearate added is 3%-8% of the mass of kaolin.

[0075] R3, slowly add the dissolved sodium stearate solution to the kaolin suspension while stirring continuously. The addition rate is controlled at 2-5 ml per minute. The temperature of the reaction system is maintained at 40-60 ° C during the addition. After the addition is completed, continue stirring and reacting for 1-2 hours to allow the sodium stearate to fully coat the kaolin surface.

[0076] R4. After the reaction is completed, the mixed liquid is filtered using a suction filtration device to obtain a coated kaolin filter cake. The filter cake is repeatedly washed with deionized water for 3-5 times to remove impurities such as unreacted sodium stearate and dispersant remaining on the surface. After each washing, suction filtration is performed until the filter cake is substantially free of water droplets.

[0077] R5. Place the washed filter cake in an oven and dry it at 80-100°C for 2-4 hours to completely dry the kaolin to obtain a sodium stearate-coated kaolin product.

[0078] In this embodiment, kaolin is surface coated with sodium stearate to form a stable coating layer on the surface of the kaolin, thereby changing its surface properties without affecting its function in paper, thereby reducing direct contact between it and cationic starch and avoiding unnecessary interactions.

[0079] More specifically, in step (2), the surface layer fibers have a grinding disc gap of 0.25-0.3 mm during the low-consistency beating stage, the core layer fibers have a grinding disc gap of 0.35-0.4 mm during the low-consistency beating stage, and the bottom layer fibers have a grinding disc gap of 0.25-0.3 mm during the low-consistency beating stage;

[0080] During the high-concentration beating stage, the gap between the surface fiber grinding discs is adjusted to 0.15-0.2mm, the core fiber is adjusted to 0.25-0.3mm, and the bottom fiber is adjusted to 0.15-0.2mm.

[0081] During low-consistency beating, the disc gap is refined for each layer (surface, core, and bottom layers), and fiber processing is optimized based on the performance requirements of each layer (e.g., surface performance is emphasized for the surface layer, bulk is emphasized for the core layer, etc.). This ensures that the fibers are properly cut and separated during low-consistency beating, improving the performance of each layer of paper. During high-consistency beating, the disc gap is further adjusted to strengthen the bonding and processing between fibers, ensuring that the fiber processing under high-consistency conditions can better meet the different requirements of each layer for strength, bulk, etc.

[0082] More specifically, in step (3), the rosin emulsion is prepared by a high-pressure homogenizer:

[0083] S1. Heat the rosin to a molten state, and control the temperature at 160-170°C;

[0084] S2. Slowly add the melted rosin to an aqueous solution containing an emulsifier, wherein the amount of the emulsifier is 3-5% of the mass of the rosin, and the temperature of the aqueous solution is maintained at 50-60°C;

[0085] S3. Turn on the high-pressure homogenizer and set the pressure to 20-30 MPa. After 3-5 cycles of homogenization, the particle size of the rosin emulsion reaches 0.5-1 μm.

[0086] In step (3), the preparation steps of the aluminum sulfate solution are:

[0087] Q1: Put industrial-grade aluminum sulfate into a dissolution tank and add clean water to the dissolution tank. The mass ratio of water to aluminum sulfate is 5-8:1.

[0088] Q2: Turn on the stirring device and set the stirring speed to 80-120r / min. At the same time, increase the temperature of the dissolving tank to 50-60℃ and control the dissolving time to 30-40min.

[0089] Q3: After the dissolution is completed, filter it through a filter with a pore size of 50-100 μm to remove insoluble impurities in the solution to obtain a pure aluminum sulfate solution;

[0090] Finally, the rosin emulsion and aluminum sulfate solution prepared in step (2) are added to the slurry pipeline at a ratio of 1:1.1-1.2 through a metering pump to mix with the slurry prepared in step (2).

[0091] More specifically, in step (6), the multi-cylinder drying system is arranged in groups, the front half is a high-temperature rapid drying zone, the drying cylinder temperature is 102-105°C, and the pressure is 0.2-0.3 bar; the back half is a low-temperature slow drying zone, the drying cylinder temperature is 100-102°C, and the pressure is 0.3-0.5 bar.

[0092] The paper is dried in groups, with the first half being dried quickly at high temperature and the second half being dried slowly at low temperature. The temperature and pressure are adjusted according to the different drying stages to ensure that the paper is dried evenly, avoid drying defects and maintain paper performance.

[0093] Comparative Example 1:

[0094] The only difference between Comparative Example 1 and Example 1 is that in step (2), light calcium carbonate, cationic starch and kaolin are added simultaneously.

[0095] Comparative Example 2:

[0096] The only difference between Comparative Example 2 and Example 1 is that in step (2), nanocellulose is not added.

[0097] Comparative Example 3:

[0098] The only difference between Comparative Example 3 and Example 1 is that in step (2), sodium stearate is not used to coat kaolin.

[0099] The following are the experimental data between the above embodiment and each comparative example:

[0100] Experimental indicators Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Tensile strength (N / mm²) 150 - 170 120 - 140 130 - 150 140 - 160 Tear strength (mN) 250 - 300 200 - 230 220 - 250 230 - 270 Burst strength (kPa) 300 - 350 250 - 280 270 - 300 280 - 320 Bulk thickness (cm³ / g) 3.0 - 3.5 2.8 - 3.2 2.5 - 3.0 3.0 - 3.3 Smoothness(s) 300 - 400 250 - 300 280 - 330 270 - 350 Glossiness (%) 60 - 70 50 - 55 55 - 60 52 - 62 Water resistance (Cobb value, g / m²) 20 - 30 30 - 40 35 - 45 32 - 42

[0101] The above data analysis is as follows:

[0102] Example 1:

[0103] Tensile strength: Within the range of 150-170N / mm², thanks to the layered ratio, segmented beating, orderly addition of fillers and the synergistic effect between the fillers, good bonding force is formed between the fibers. Nanocellulose strengthens the fiber network structure and improves the tensile strength of the paper.

[0104] Tear strength: 250-300mN. The addition of nanocellulose and the synergistic effect of other fillers, as well as the appropriate beating process, ensure the integrity and toughness of the fiber network, giving the paper better tearing properties.

[0105] Burst strength: 300-350kPa. Through optimized process steps, including reasonable internal sizing, orderly filler addition and layered beating, the overall structure of the paper is stable and can withstand higher pressure.

[0106] Bulk: 3.0-3.5cm³ / g. The core layer adopts BCTMP and reasonable beating process to make the paper achieve a higher bulk.

[0107] Smoothness: 300-400s. By reasonably adding light calcium carbonate, kaolin and surface sizing, the paper surface is relatively smooth.

[0108] Glossiness: 60-70%. Thanks to the optimization of the paper surface by light calcium carbonate and kaolin, the paper has good glossiness.

[0109] Water resistance: 20-30g / m². The sizing of rosin-aluminum sulfate pulp and various fillers work synergistically to enhance the water resistance of paper.

[0110] Comparative Example 1:

[0111] Tensile strength: 120-140N / mm². The simultaneous addition of light calcium carbonate, cationic starch, and kaolin results in uneven dispersion of the filler, which reduces the bonding force between the fiber and the filler and affects the tensile strength.

[0112] Tear strength: 200-230mN. Adding fillers at the same time may destroy the fiber network structure, resulting in a decrease in tearing performance.

[0113] Burst resistance: 250-280kPa. Due to poor dispersion of fillers, the overall structural strength of the paper is affected and the burst resistance is reduced.

[0114] Bulk: 2.8-3.2cm³ / g. The addition of fillers may affect the distribution of fibers and have a certain impact on bulk, but the overall impact is relatively small.

[0115] Smoothness: 250-300s, the fillers cannot play their respective roles well and the smoothness of the paper surface is reduced.

[0116] Glossiness: 50-55%. Adding fillers will affect the optimization of paper surface properties and reduce glossiness.

[0117] Water resistance: 30-40g / m². Uneven distribution of fillers may affect the sizing effect in the slurry and deteriorate water resistance.

[0118] Comparative Example 2:

[0119] Tensile strength: 130-150N / mm². Without the addition of nanocellulose, the fiber network is not strengthened by nanocellulose, resulting in a decrease in tensile strength.

[0120] Tear strength: 220-250mN. The absence of nanocellulose deteriorates the integrity and toughness of the fiber network, and the tear strength decreases.

[0121] Burst strength: 270-300kPa. Due to the lack of reinforcing effect of nanocellulose, the overall structural strength of the paper is reduced.

[0122] Bulk: 2.5-3.0cm³ / g. Nanocellulose can improve the integrity of the fiber network, and its absence will affect the bulk.

[0123] Smoothness: 280-330s. The loss of nanocellulose affects the overall fiber network and thus the smoothness of the paper surface.

[0124] Glossiness: 55-60%. The comprehensive effect of nanocellulose on paper properties leads to a decrease in glossiness.

[0125] Water resistance: 35-45g / m². The loss of nanocellulose affects the fiber network structure and deteriorates the water resistance.

[0126] Comparative Example 3:

[0127] Tensile strength: 140-160N / mm². Kaolin is not coated. Its interaction with cationic starch affects the bonding force between fibers, which slightly affects the tensile strength.

[0128] Tear strength: 230-270mN. The interaction between kaolin and cationic starch may affect the fiber network, and the tear strength decreases.

[0129] Bursting strength: 280-320kPa. Uncoated kaolin has a certain impact on the structural strength of paper, and the bursting strength is reduced.

[0130] Bulk: 3.0-3.3cm³ / g. Uncoated kaolin may indirectly affect the paper structure and have a certain impact on bulk.

[0131] Smoothness: 270-350s. Uncoated kaolin causes interaction with cationic starch, affecting the surface properties of paper and reducing smoothness.

[0132] Gloss: 52-62%. The interaction between kaolin and cationic starch affects the surface properties and the gloss decreases.

[0133] Water resistance: 32-42g / m². Uncoated kaolin may affect its function in paper and deteriorate water resistance.

[0134] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A production process for high-bulk white cardboard, characterized by: The following steps are involved: (1) Raw material preparation: Select fiber raw materials, including wood pulp fiber (NBKP, LBKP) and added fiber; The fiber raw material ratio of each layer is determined as follows: NBKP accounts for 30-35% and LBKP accounts for 65-70% in the surface layer; NBKP accounts for 10-15% and LBKP accounts for 15-20% and BCTMP accounts for 65-75% in the core layer; NBKP accounts for 20-25% and LBKP accounts for 75-80% in the bottom layer; (2) beating: the fiber raw material of step (1) is beaten by a disc grinder, and the beating degree of the fiber raw material is controlled between 30°SR and 40°SR, and the grinding gap of the disc grinder is 0.1-0.5 mm; (3) In-slurry sizing: The slurry in step (2) is sized using a rosin-aluminum sulfate in-slurry sizing process; the rosin solid content in the rosin-aluminum sulfate sizing agent is 28% to 29%, the alumina content in the aluminum sulfate is 7.5% to 8%, the dosage ratio of rosin to aluminum sulfate is 1:1.1-1.2, the pH in the headbox is controlled to be 4.8-5.2, and the white water temperature is 30-45°C; (4) Papermaking: The fiber raw material processed by the pulping in step (3) is fed into a papermaking machine for papermaking, and the speed difference between the papermaking machine's wire speed and the pulp speed is controlled to be 8%-12% to form a wet paper web; (5) Pressing: The wet paper web obtained in step (4) is subjected to a shoe press, with the pressing pressure controlled between 450 and 600 kPa and the pressing time being 10 to 15 seconds; (6) Drying: The paper web after pressing in step (5) is dried using a multi-cylinder drying process, with the steam blowing box temperature at 102-105°C and the steam blowing box pressure at 0.2-0.5 bar, to control the moisture content of the paper from 80% to below 10%; (7) Calendering: Calendering the paper after drying in step (6) at a calendering pressure of 200-300 MPa; (8) Surface sizing: After the calendering treatment in step (7), surface sizing is performed. The surface sizing agent is polyvinyl alcohol, and the sizing amount is 3-5 g / m².

2. The production process of high bulk white cardboard according to claim 1, characterized in that: In the step (1), the weight ratio of the wood pulp fiber to the added fiber is 70:30 to 90:

10. The wood pulp fiber and the added fiber are mixed in a fiber mixing tank by combining mechanical stirring and pipeline mixing. The stirring speed is controlled at 100-150 r / min and the stirring time is 15-20 min. Then, the fibers are further mixed uniformly by a pipeline mixer and the pipeline flow rate is controlled at 1-1.5 m / s.

3. The production process of high bulk white cardboard according to claim 2, characterized in that: In the step (1), the added fiber is a regenerated fiber, which comes from the recycling of waste paper, and the length of the processed fiber is 0.5-2 mm.

4. The production process of high bulk white cardboard according to claim 3, characterized in that: In the step (2), segmented beating is adopted: The first stage: low-concentration beating is performed, the concentration is controlled at 3-5%, the grinding disc gap is gradually reduced from 0.5mm to 0.3mm, and the beating time is 10-15min; The second stage: high-concentration beating is carried out, the concentration is increased to 8-10%, the grinding gap is controlled at 0.2-0.3mm, and the beating time is 8-12min.

5. The production process of high bulk white cardboard according to claim 4, characterized in that: In step (2), the following fillers are added in the following order: Light calcium carbonate: Add light calcium carbonate evenly through a screw feeder during the initial 2-5 minutes of low-consistency beating; Cationic starch: Add cationic starch using a metering pump at the end of the low-consistency beating process, 8-15 minutes later; Kaolin: After high-concentration slurrying, add kaolin into the slurry mixing tank and stir for 10-15 minutes at a stirring speed of 100-120r / min.

6. The production process of high bulk white cardboard according to claim 5, characterized in that: In step (2), the filler is added according to the mass percentage of the absolute dry fiber. First, 0.5%-1% of nanocellulose is added, and then 5%-10% of light calcium carbonate is added at the beginning of low-concentration beating. Then, 1%-3% of cationic starch is added at the end of low-concentration beating. Finally, 3%-5% of kaolin is added after high-concentration beating.

7. The production process of high bulk white cardboard according to claim 6, characterized in that: In step (2), kaolin is coated with sodium stearate, and the steps are as follows: R1. Add kaolin to deionized water containing dispersant and stir at a speed of 200-500 r / min for 30-60 min to form a uniform kaolin suspension. The mass fraction of kaolin in deionized water is 10%-30%, and the amount of dispersant is 0.5%-2% of the mass of kaolin. R2. In another container, add sodium stearate to deionized water, heat at 50-80°C and stir for 20-30 minutes to completely dissolve it. The amount of sodium stearate added is 3%-8% of the mass of kaolin. R3, slowly add the dissolved sodium stearate solution to the kaolin suspension while stirring continuously. The addition rate is controlled at 2-5 ml per minute. The temperature of the reaction system is maintained at 40-60 ° C during the addition. After the addition is completed, continue stirring and reacting for 1-2 hours to allow the sodium stearate to fully coat the kaolin surface. R4. After the reaction is completed, the mixed liquid is filtered using a suction filtration device to obtain a coated kaolin filter cake. The filter cake is repeatedly washed with deionized water for 3-5 times to remove impurities such as unreacted sodium stearate and dispersant remaining on the surface. After each washing, suction filtration is performed until the filter cake is substantially free of water droplets. R5. Place the washed filter cake in an oven and dry it at 80-100°C for 2-4 hours to completely dry the kaolin to obtain a sodium stearate-coated kaolin product.

8. The process for producing high bulk white cardboard according to claim 7, characterized in that: In the step (2), the grinding disc gap of the surface layer fibers in the low-concentration beating stage is 0.25-0.3 mm, the grinding disc gap of the core layer fibers in the low-concentration beating stage is 0.35-0.4 mm, and the grinding disc gap of the bottom layer fibers in the low-concentration beating stage is 0.25-0.3 mm; During the high-concentration beating stage, the gap between the surface fiber grinding discs is adjusted to 0.15-0.2mm, the core fiber is adjusted to 0.25-0.3mm, and the bottom fiber is adjusted to 0.15-0.2mm.

9. The production process of high bulk white cardboard according to claim 8, characterized in that: In the step (3), a rosin emulsion is prepared by a high-pressure homogenizer: S1. Heat the rosin to a molten state, and control the temperature at 160-170°C; S2. Slowly add the melted rosin to an aqueous solution containing an emulsifier, wherein the amount of the emulsifier is 3-5% of the mass of the rosin, and the temperature of the aqueous solution is maintained at 50-60°C; S3. Turn on the high-pressure homogenizer and set the pressure to 20-30 MPa. After 3-5 cycles of homogenization, the particle size of the rosin emulsion reaches 0.5-1 μm. In step (3), the preparation steps of the aluminum sulfate solution are: Q1: Put industrial-grade aluminum sulfate into a dissolution tank and add clean water to the dissolution tank. The mass ratio of water to aluminum sulfate is 5-8:

1. Q2: Turn on the stirring device and set the stirring speed to 80-120r / min. At the same time, increase the temperature of the dissolving tank to 50-60℃ and control the dissolving time to 30-40min. Q3: After the dissolution is completed, filter it through a filter with a pore size of 50-100 μm to remove insoluble impurities in the solution to obtain a pure aluminum sulfate solution; Finally, the rosin emulsion and aluminum sulfate solution prepared in step (2) are added to the slurry pipeline at a ratio of 1:1.1-1.2 through a metering pump to mix with the slurry prepared in step (2).

10. The production process of high bulk white cardboard according to claim 1, characterized in that: In step (6), the multi-cylinder drying system is arranged in groups, the front half is a high-temperature rapid drying zone, the drying cylinder temperature is 102-105°C, and the pressure is 0.2-0.3 bar; the back half is a low-temperature slow drying zone, the drying cylinder temperature is 100-102°C, and the pressure is 0.3-0.5 bar.