A method for multilayered making of fluff pulp by a cylinder mould paper machine and products thereof

Abstract

This invention provides a method and product for multi-layer fabrication of fluff pulp using a cylinder paper machine, relating to the field of fluff pulp. The method uses bleached sulfate softwood pulp and bleached sulfate hardwood pulp as raw materials. After pulping and debonding treatment, the pulp is fabricated using a cylinder paper machine with at least six layers to produce a multi-layer composite wet paper web. This web is then pressed and dried to obtain fluff pulp. This method for multi-layer fabrication of fluff pulp using a cylinder paper machine allows for effective control of fiber morphology within the raw pulp, effectively overcoming the hardening defects of bleached wood pulp fibers and restoring fiber swelling, water absorption, softness, and pore structure. It also effectively eliminates the contradiction between interlayer separation and abnormal fiber debonding, solving the problems of easy stratification and strength imbalance in multi-layer fabricated fluff pulp. Furthermore, this method is adaptable to cylinder paper machines, enabling the production of fluff pulp products with uniform performance even under conditions of limited equipment precision, reducing dependence on scarce long-fiber softwood raw materials.

Description

Technical Field

[0001] This invention relates to the field of fluff pulp, and in particular to a method for producing fluff pulp in multiple layers using a cylinder paper machine and the product thereof. Background Technology

[0002] The core consumable products of fluff pulp are personal care and medical products, including baby diapers, adult incontinence products, feminine hygiene products and medical dressings. Its core functional requirements are high absorbency, fast absorption rate and good fluffy elasticity. At the same time, it must meet the requirements of skin contact safety and biodegradability. Different products have different requirements for parameters such as liquid absorption and liquid retention.

[0003] The current mainstream raw material for preparing fluff pulp is coniferous wood, which has prominent limitations: First, there is a lack of stable supply of high-quality raw materials in China. The sources of imported raw materials such as radiata pine and southern pine are unstable, and the output of domestic Yunnan silk pine is limited. Second, alternative raw materials such as bamboo pulp have many impurities and strong fiber binding force, making it difficult to form a fluffy structure and resulting in insufficient fluffing performance.

[0004] Currently, in order to meet domestic production capacity demand, some manufacturers are modifying old-fashioned rotary paper machines without supporting pulping workshops to produce fluff pulp using bleached commercial wood pulp boards as raw materials through multi-layer papermaking. However, due to the limitations of the material characteristics of the bleached commercial wood pulp boards themselves, the following key technical bottlenecks will inevitably exist in the production of fluff pulp: First, it is difficult to control and balance the interlayer fiber bonding force and burst strength, which can easily lead to delamination or abnormal fiber disintegration due to high burst strength; Second, the bleached commercial wood pulp boards (softwood / broadwood) have already undergone primary drying, resulting in hardened cell walls, which will significantly increase the difficulty of controlling fiber morphology during the production process when used to produce fluff pulp.

[0005] The above-mentioned technical bottlenecks directly lead to the following defects in the process of preparing fluff pulp using bleached commercial wood pulp boards: (1) Insufficient fiber swelling and high defibering energy result in a high degree of fiber fibrillation, and the average fiber length is relatively short and the proportion of fine fibers is relatively high. After drying, the fibers have poor softness and strong rigidity, and the fiber pore structure is insufficient after molding. (2) Poor fiber morphology will lead to a significant decrease in the fluffiness of fluff pulp, a slower water absorption rate, and a reduced liquid absorption. At the same time, the fiber bonding force is abnormally high, and the excessive burst strength will make it difficult to defiber during the processing of finished products. In order to adjust the burst strength, the amount of debonding agent used in the production process must be increased to reduce the amount of fiber bonding. However, excessive weakening of the hydrogen bond between fibers will cause problems such as stratification, increased lint shedding rate of finished products, and poor water absorption, which cannot meet the core functional requirements of personal care and medical products.

[0006] Furthermore, using old-style rotary paper machines to process bleached commercial wood pulp boards in multiple layers will further exacerbate the following problems on the basis of the aforementioned technical defects: (1) The difficulty of controlling interlayer bonding force and burst strength will be further increased: old paper machines have low equipment precision and fewer layers, and the range of process parameter adjustment is limited. It is impossible to accurately control the parameters of key processes such as wire forming and pressing, which will easily lead to either excessively low interlayer bonding force causing direct delamination or excessively high burst strength, exacerbating the problem of abnormal fiber disintegration; (2) Poor stability of finished fluff pulp indicators: old paper machines have low equipment operation stability and process parameters are prone to fluctuation. The high basis weight of fluff pulp will amplify this trend, resulting in large differences in core indicators such as fiber uniformity, compactness, and bulkiness between batches of fluff pulp, and poor product uniformity. Summary of the Invention

[0007] To address the technical problems existing in the prior art, this invention provides a method for multi-layer fly mulching using a cylinder paper machine. This method effectively controls the fiber morphology within the raw pulp, effectively overcomes the hardening defects of bleached wood pulp fiber, and restores the fiber's swelling properties, water absorption, softness, and pore structure. It also effectively eliminates the contradiction between interlayer separation and abnormal fiber disintegration, solving the problems of easy stratification and strength imbalance in multi-layer fly mulching. Furthermore, this method is adaptable to cylinder paper machines and can produce fly mulching products with uniform performance even under conditions of limited equipment precision, reducing dependence on scarce long-fiber coniferous wood as raw material.

[0008] The present invention also provides fluff pulp prepared by the aforementioned preparation method.

[0009] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for producing fluff pulp through multiple layers of a cylinder paper machine includes the following steps: pulping, debonding, forming on a paper machine, pressing, and drying. The pulping process involves mixing bleached sulfate softwood pulp, bleached sulfate hardwood pulp, and white water, adjusting the pH to 8.0-9.0, and then pulping the mixture to obtain disintegrated pulp. The method for debonding is to mix the debonding slurry with the debonding agent evenly to obtain the debonding slurry; The unbonding agent is composed of sodium fatty alcohol polyoxyethylene ether sulfate, alkyl glycoside, trisodium citrate and deionized water; The method for forming the paper web is as follows: after diluting the debonding pulp to an oven-dry fiber content of 0.2-0.5%, it is formed using a rotary paper machine with no less than 6 layers, and the fibers are spread on the surface of each rotary paper machine to form a wet paper web; during the paper web forming process, white water is sprayed between two adjacent rotary paper machines on each layer of wet paper web; and the layers of wet paper web are combined to form a multi-layer composite wet paper web. The multi-layer composite wet paper web is pressed and dried to obtain fluff pulp.

[0010] Preferably, in the pulping process, the oven-dry weight ratio of bleached sulfate softwood pulp to bleached sulfate hardwood pulp is 85-95:5-15. Bleached sulfate softwood pulp has an ISO brightness of ≥85%, an oven-dry fiber content of ≥90wt%, an average fiber width of ≥30μm, and a moisture content of ≤10wt%; bleached sulfate hardwood pulp has an ISO brightness of ≥85%, an oven-dry fiber content of ≥90wt%, an average fiber width of ≥20μm, and a moisture content of ≤10wt%.

[0011] Preferably, in the pulping process, the white water temperature is controlled at 50-70℃, the pulp concentration is 10-15%, the pulping speed is 800-1000 rpm, and the pulping time is 20-30 min; The beating degree of the pulp is 12-17°SR.

[0012] Preferably, in the debonding treatment, the weight ratio of sodium fatty alcohol polyoxyethylene ether sulfate, alkyl glycoside, trisodium citrate, and deionized water in the debonding agent is 60-70:20-25:5-10:5. Based on the weight of oven-dry fibers in the broken pulp, the amount of debonding agent added should be controlled at 1.0-1.5 kg / ton of oven-dry pulp.

[0013] Preferably, in the web forming process, the vacuum degree of the web section is controlled to be 0.02-0.04MPa, the synchronous web speed is 30-70m / min, and the composite pressure is 50-80kPa; The dryness of the multilayer composite wet paper web is 21-25 wt%, and the basis weight is 730-770 g / m². 2 .

[0014] Preferably, in the net forming process, the temperature of the sprayed white water is controlled to be 40-50℃, the pressure of the sprayed white water is 0.1-0.15MPa, and the angle of the sprayed white water is 45-60°. The dosage of white water for spraying single-layer wet paper webs is 50-80 g / m². 2 .

[0015] Preferably, in the web forming process, the sprayed white water has a pH of 7.0-8.0, a conductivity of ≤500μS / cm, and a suspended solids content of ≤50mg / L.

[0016] Furthermore, the pressing method involves controlling the wet end pressure to 250-600 kPa and pressing the multi-layer composite wet paper web to obtain a pressed wet paper web with a dryness of 40-45%. The drying method involves sequentially subjecting the pressed wet paper web to low-temperature drying, medium-temperature drying, and high-temperature drying, followed by equilibrium drying until the moisture content reaches 8-10%, thereby obtaining fluff pulp.

[0017] Preferably, in the drying process, the temperature for low-temperature drying is controlled at 33-36°C, and the drying is maintained at this temperature until the moisture content is 35-38%. The temperature for medium-temperature drying is controlled at 83-86℃, and the drying is maintained at this temperature until the moisture content is 20-25%. The high-temperature drying temperature is controlled at 108-112℃, and the drying is maintained at this temperature until the moisture content is 10-13%. The temperature for balanced drying should be controlled at 68-72℃.

[0018] A fluff pulp is prepared using the aforementioned method.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The method of making fluff pulp by multiple layers of cylinder paper machine of the present invention uses bleached sulfate softwood pulp and bleached sulfate hardwood pulp as raw materials for pulping treatment, and then uses a debonding agent of specific components to debond them. Then, it is made by cylinder paper machine with no less than 6 layers. The fibers are spread on the surface of each layer of cylinder paper to form a wet paper web. During the papermaking process, white water is sprayed between two adjacent cylinders on each layer of wet paper web. The layers of wet paper web are combined to make a multi-layer composite wet paper web. The multi-layer composite wet paper web is pressed and dried to obtain fluff. The aforementioned technical methods work together synergistically to effectively control the fiber morphology within the raw pulp, effectively overcome the hardening defects of bleached wood pulp board fibers, and restore the fiber's swelling properties, water absorption, softness, and pore structure. They also effectively eliminate the contradiction between interlayer separation and abnormal fiber debonding, and solve the problems of easy stratification and strength imbalance in multilayer papermaking fluff pulp. Furthermore, this method is adaptable to cylinder paper machines and can produce fluff pulp products with uniform performance under conditions of limited equipment precision, reducing dependence on scarce long-fiber coniferous wood as raw material.

[0020] (2) The method of multi-layer papermaking of fluff pulp by a cylinder paper machine of the present invention effectively solves the core technical contradiction of multi-layer papermaking and improves the stability of product quality. Specifically, through comprehensive and systematic optimization of raw material ratio, pulping process, debonding agent addition, composite moisture control of the wire section and pulping process, the technical bottleneck of easy delamination and difficulty in balancing strength performance that are common in existing multi-layer papermaking fluff pulp is effectively solved. The structural uniformity and strength stability of the prepared fluff pulp product are significantly improved, providing reliable technical support for the large-scale production of high-quality fluff pulp.

[0021] (3) The method of producing fluff pulp through multiple layers of cylinder paper machines in this invention effectively expands the compatibility range of raw materials and cylinder paper machines, and can be adapted to the transformation of old cylinder paper machine production lines, thus lowering the threshold for production transformation. Specifically, this invention directly uses softwood / broadwood bleached wood pulp board as the production raw material, and through process optimization, the finished fluff pulp achieves excellent fiber morphology and physical performance indicators. The average fiber length of the fluff pulp is ≥2.3mm, the average fiber width is ≥28.0μm, the proportion of fine fibers is ≤15.0%, the density is ≤0.65g / cm³, and the bursting strength is 900-1100kPa. At the same time, this technical solution has strong compatibility with production equipment, providing a flexible and feasible technical choice for the transformation of old paper machines or different types of paper machines to produce fluff pulp, greatly reducing the equipment investment cost for enterprises to transform to produce fluff pulp, and broadening the applicable scenarios of the technology.

[0022] (4) The present invention achieves efficient recycling of resources by using a multi-layer papermaking machine to produce fluff pulp, taking into account both economic and ecological benefits. Specifically, it effectively integrates the fiber performance advantages of both coniferous and broad-leaved wood. Under the premise of fully meeting the performance requirements of downstream customers for fluff pulp, it can effectively reduce the amount of coniferous wood raw materials used, improve economic and ecological benefits, and reduce production costs. Detailed Implementation

[0023] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific embodiments are now described. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, "first," "second," etc., are used to distinguish similar objects and are not used to describe a particular order or sequence. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0025] This invention provides a method for producing fluff pulp through multiple layers using a cylinder paper machine, comprising the following steps: S1. Raw material preparation: Place the bleached sulfate softwood pulp (NBKP) and bleached sulfate hardwood pulp (LBKP) on the chain plate of the chain conveyor and wait for feeding, according to the oven-dry weight ratio of 85-95:5-15.

[0026] Among them, bleached sulfate softwood pulp has a brightness of ≥85% ISO, an oven-dry fiber content of ≥90wt%, an average fiber width of ≥30μm, and a moisture content of ≤10wt%; bleached sulfate hardwood pulp has a brightness of ≥85% ISO, an oven-dry fiber content of ≥90wt%, an average fiber width of ≥20μm, and a moisture content of ≤10wt%.

[0027] S2. Pulping Treatment: The aforementioned proportioned bleached sulfate softwood pulp and bleached sulfate hardwood pulp are fed into the pulper via a chain conveyor. White water recovered from the papermaking system is added. To fully swell the fibers and improve their water conductivity, a 10-20 wt% sodium hydroxide solution is used to adjust the pH to 8.0-9.0. The white water temperature is controlled at 50-70℃, the pulp concentration at 10-15%, and the pulping speed at 800-1000 rpm. The pulping treatment lasts for 20-30 minutes to obtain a freeness of 12-17°SR and a pulp temperature of 50-70℃.

[0028] In this embodiment of the invention, the beating degree of the pulp is controlled to be 12-17°SR. The purpose is to avoid excessive fiber cutting due to excessive beating degree, or insufficient fiber bonding due to excessive beating degree, which would exacerbate stratification. The core purposes of adding white water are: (1) to adjust the pulp concentration so that the pulp reaches a suitable pulping concentration; (2) to provide a medium for fiber swelling so that the fiber can fully absorb water and swell, thereby improving the fiber morphology; and (3) to serve as process circulating water to reduce production water consumption and realize the recycling of water resources. Adjusting the pulp concentration is one of the main purposes of white water.

[0029] S3. Debonding treatment: The broken pulp is pumped into the pulping tank, and a debonding agent is added by adding it after the pump. The debonding agent is mixed with the broken pulp and continuously stirred in the pulping tank to obtain a debonded pulp, which is ready for subsequent wire forming.

[0030] The unbonding agent is composed of sodium fatty alcohol polyoxyethylene ether sulfate (AES), alkyl glycoside (APG), trisodium citrate, and deionized water; the weight ratio of sodium fatty alcohol polyoxyethylene ether sulfate, alkyl glycoside, trisodium citrate, and deionized water is 60-70:20-25:5-10:5. In this embodiment of the invention, sodium fatty alcohol polyoxyethylene ether sulfate is selected as the core unbonding component, which moderately weakens the hydrogen bonds between fibers; alkyl glycoside is an auxiliary unbonding component, which improves the wettability of the sizing agent and improves the fiber morphology; trisodium citrate is used to adjust the stability of the sizing system, prevent the unbonding agent from failing, and protect the fibers; deionized water is used to adjust the consistency of the unbonding agent, making it easy to add and mix; at the same time, all components of the unbonding agent used are food-grade and meet the requirements for skin contact safety.

[0031] The amount of debonding agent added is controlled at 1.0-1.5 kg / ton of oven-dry pulp, based on the weight of the oven-dry fibers in the broken pulp. Under this addition amount, an effective balance between burst strength and interlayer bonding strength can be achieved.

[0032] S4. Paper Forming: A multi-layer (6-8 layers) cylinder papermaking process is employed. The bond-resolving pulp supplied from the pulping tank is formed into a wet paper web with uniform basis weight and strong interlayer bonding on the cylinder wire. Specifically: the bond-resolving pulp supplied from the pulping tank is diluted to 0.2-0.5% (octane-dry fiber weight / total pulp weight) and then evenly distributed into each cylinder wire slot of the cylinder paper machine. The vacuum degree of the wire section is controlled at 0.02-0.04 MPa, and the synchronous wire speed is 30-70 m / min. After the fibers are spread and formed on each layer of the cylinder wire, they are compounded under a pressure of 50-80 kPa to obtain a paper web with a dryness of 21-25 wt% and a basis weight of 730-770 g / m². 2 Multi-layer composite wet paper web.

[0033] Meanwhile, during the web forming process, to improve the interlayer bonding of the fluff pulp and prevent delamination by downstream customers, water spraying devices are installed between adjacent rotary screens (7 water spraying devices are installed between 8 rotary screens) to increase the interlayer moisture content and improve the interlayer bonding. Specifically, before each layer of wet paper web is laminated at the laminating roller, white water is sprayed onto the surface of each layer of wet paper web through the water spraying devices. The water spraying temperature is controlled at 40-50℃, the water spraying pressure at 0.1-0.15MPa, the water spraying angle at 45-60°, the spraying distance at 15-20cm, and the water spraying amount per layer at 50-80g / m². 2 To increase interlayer moisture and improve interlayer bonding strength.

[0034] In this embodiment of the invention, controlling the on-grid concentration of multi-wire papermaking to 0.2-0.5% can ensure uniform forming of the pulp in the cylindrical wire section, allowing the fibers to spread fully in the wire section, improving the uniformity of the wet paper web, and laying the foundation for subsequent interlayer water spraying and lamination, while avoiding excessive on-grid concentration that leads to fiber clumping and uneven forming.

[0035] In this embodiment of the invention, the white water used is the white water recovered from the papermaking system and filtered to remove fiber impurities; its specific specifications are: pH 7.0-8.0 (matching the pH value of the pulping to avoid acid-base imbalance that could damage the fiber morphology); conductivity ≤500μS / cm (ensuring the purity of the white water and preventing impurities from affecting interlayer bonding); suspended solids content ≤50mg / L (no obvious fiber impurities to prevent nozzle clogging and affecting the uniformity of the wet paper web).

[0036] In this embodiment of the invention, the spray angle is controlled at 45-60°, and the water is sprayed at an angle to make the white water evenly cover the surface of the wet paper web, thereby improving the water replenishment effect; the spray distance is controlled at 15-20cm (vertical distance from the nozzle to the wet paper web) to avoid damaging the wet paper web if the distance is too close, or causing water loss if the distance is too far; the spray pressure is controlled at 0.1-0.15MPa to ensure the atomization effect and the spray coverage area, and to avoid damaging the wet paper web if the pressure is too high.

[0037] In this embodiment of the invention, the synchronous wire speed (rotary wire speed) is controlled at 30-70 m / min, and the rotation speed of each layer of the rotary wire is controlled to be consistent to ensure that the forming speed of each layer of wet paper web is matched and to avoid interlayer stretching misalignment; the wet paper web lamination pressure is controlled at 50-80 kPa to ensure that the wet paper webs between layers are tightly bonded and to improve the bonding force, while avoiding excessive pressure and paper surface embossing caused by rapid dehydration; the wire section vacuum degree is controlled at 0.02-0.04 MPa to regulate the dryness of the wet paper web exiting the wire and to avoid excessively high or low dryness affecting interlayer lamination.

[0038] S5. Pressing: Controlling the wet end pressure at 250-600 kPa, the multi-layer composite wet paper web is pressed to obtain a pressed wet paper web with a dryness of 40-45%. Controlling the dryness of the pressed wet paper web to 40-45% ensures sufficient dehydration while avoiding excessive pressing pressure that could over-compress the fibers and damage the fluffy structure of the pulp. This also reduces energy consumption in subsequent drying processes, balancing product performance and production efficiency.

[0039] S6. Drying: In multiple drying cylinders, the pressed wet paper web is sequentially dried at low temperature, medium temperature, and high temperature, and then balanced until the moisture content is 8-10% to obtain fluff pulp. Specifically, the pressed wet paper web is placed in the drying cylinders, and the low-temperature drying temperature is controlled at 33-36℃ and held until the moisture content is 35-38%; the medium-temperature drying temperature is controlled at 83-86℃ and held until the moisture content is 20-25%; the high-temperature drying temperature is controlled at 108-112℃ and held until the moisture content is 10-13%; the balanced drying temperature is controlled at 68-72℃ and held until the moisture content is 8-10% to obtain fluff pulp.

[0040] In this embodiment of the invention, the wet paper web still contains a large amount of moisture after pressing. The purpose of pre-drying (low temperature drying, medium temperature drying, high temperature drying) is to remove some of the moisture and reduce the paper moisture content to 10-13%. Then, post-drying (balanced drying) is performed to adjust the paper moisture content to 8-10%. In this way, multi-stage drying is used to avoid bubbling and delamination caused by severe interlayer bonding of fluff pulp due to rapid evaporation of moisture at high local temperatures.

[0041] S7. Post-processing: After the fluff pulp is rolled into rolls using a rolling device, it is slit into rolls with a width of 480mm and a roll diameter of 1200-1500mm. After coding, it is wrapped with 5 layers of stretch film and stored in the warehouse.

[0042] The present invention also provides fluff pulp prepared by the aforementioned method.

[0043] Furthermore, the process parameters in the preparation process of multi-layer fabrication of fluff pulp using a cylinder paper machine according to embodiments of the present invention are analyzed and optimized: 1. The effects of pH and white water temperature on fluff pulp properties during pulping. Because the raw materials NBKP and LBKP suffer from severe keratinization due to dehydration and shrinkage of fiber cell walls during drying, pH value and pulping white water temperature are crucial factors affecting fiber swelling during pulping treatment. These factors directly impact the bulkiness and water absorption time of the fluff pulp. Optimization experiments were conducted by changing the pH value and pulping white water temperature, while keeping other process conditions, chemical additive dosages, and paper machine parameters constant. Details are shown in the table below.

[0044] As can be seen from the table above, when the pH is 8.5 and the pulping water temperature is 60℃, the raw material fibers can be treated better, resulting in better fluffiness and water absorption time of the fluff pulp.

[0045] 2. Optimal ratio selection of raw materials NBKP and LBKP Fiber length is a key factor affecting the application of fluff pulp. A suitable length (preferably 2.3-4 mm) balances liquid absorption, bulkiness, and structural strength; excessively short fibers easily clog pores, resulting in poor liquid absorption and lint shedding. Optimization experiments were conducted on the ratio and specifications of the raw materials NBKP and LBKP. Details are shown in the table below:

[0046] As can be seen from the table above, when bleached sulfate softwood pulp (NBKP) accounts for 90%, its average fiber length can reach more than 2.3mm, which can meet the market demand for the production of mid-to-high-end products such as adult diapers and nursing pads. At the same time, it reduces the amount of NBKP used, resulting in significant economic benefits.

[0047] 3. Effect of chemical debonding agent dosage on the burst strength and interlayer bond strength of fluff pulp Flocking pulp produced through a multi-layer rotary screen forming and composite process exhibits significant uniformity advantages compared to products from traditional pulping machines. However, this process places higher demands on the dosage of chemical debonding agents in each layer. Excessive dosage can lead to insufficient interlayer bonding strength, while insufficient dosage can result in low burst strength, ultimately causing quality problems in the finished product and affecting its overall quality. Optimization experiments were conducted to optimize the amount of debonding agent added. Details are shown in the table below:

[0048] As can be seen from the table above, when the dosage of the debonding agent is in the range of 1.0-1.5 kg / ton of slurry, the burst strength is ≤1100 kPa and the interlayer bond strength is ≥50 J / m², which can meet the requirements of moderate burst strength and no delamination during use.

[0049] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described below in conjunction with some specific embodiments.

[0050] Example 1 This embodiment describes the trial production of a product on a paper machine, based on optimized raw material ratios, pulp pH, white water temperature, chemical debonding agent dosage, and optimal process application conditions. All steps were performed according to requirements, with strict control over the product's process application conditions and standardized operation. The specific steps are as follows: S1. Raw material preparation: Bleached sulfate softwood pulp (NBKP) and bleached sulfate hardwood pulp (LBKP) are placed on the chain plate of the chain conveyor and await feeding, with an oven-dry weight ratio of 90:10.

[0051] The bleached sulfate softwood pulp had a brightness of 85% ISO, an oven-dry fiber content of 90 wt%, and a moisture content of 9 wt%; the bleached sulfate hardwood pulp had a brightness of 86% ISO, an oven-dry fiber content of 91 wt%, and a moisture content of 10 wt%. The average fiber length of both bleached sulfate softwood pulp (NBKP) and bleached sulfate hardwood pulp (LBKP) was 2.31 mm, the average fiber width was 27.4 μm, and the proportion of fine fibers was 14.7%.

[0052] S2. Pulping treatment: The aforementioned proportioned bleached sulfate softwood pulp and bleached sulfate hardwood pulp are fed into the pulper via a chain conveyor. White water recovered from the papermaking system is added, and the pH is adjusted to 8.5 using a 15wt% sodium hydroxide solution. The white water temperature is controlled at 60℃, the pulp concentration at 10%, and the pulping speed at 1000rpm. The pulping process is carried out for 20 minutes to obtain a pulp with a freeness of 13°SR and a pulp temperature of 60℃.

[0053] S3, Dekeying Processing The broken pulp is pumped into the pulping tank, and the debonding agent is added by post-pumping. The debonding agent is mixed with the broken pulp and enters the pulping tank. The mixture is continuously stirred at 60 rpm to obtain the debonding treated pulp, which is ready for subsequent wire bonding.

[0054] The debonding agent is composed of sodium fatty alcohol polyoxyethylene ether sulfate (AES), alkyl glycoside (APG), trisodium citrate and deionized water; the weight ratio of sodium fatty alcohol polyoxyethylene ether sulfate, alkyl glycoside, trisodium citrate and deionized water is 65:22:8:5.

[0055] The amount of debonding agent added is calculated based on the oven-dry fiber weight of the broken pulp, and the addition amount is controlled at 1.2 kg / ton of oven-dry pulp. S4, Internet connection formed An 8-layer cylinder papermaking process is employed. The bond-resolving pulp supplied from the pulping tank is diluted to 0.3% (octane-dry fiber weight / total pulp weight) and then evenly distributed into each cylinder slot of the cylinder paper machine. The vacuum level of the wire section is controlled at 0.03 MPa, and the synchronous wire speed at 60 m / min. After the fibers are spread and formed on each layer of the cylinder wire, they are laminated under a pressure of 70 kPa to produce a multi-layer composite wet paper web with a dryness of 24 wt%. Furthermore, the basis weight of each layer is controlled at 94 g / m² during the web forming process. 2 To ensure that the total basis weight of the wet paper web reaches 750 g / m² 2 .

[0056] During the paper forming process, water spraying devices are installed between two adjacent rotary screens (7 water spraying devices are installed between 8 rotary screens). Before each layer of wet paper web is bonded at the composite roller, white water (pH 7.5, conductivity 350 μS / cm, suspended solids content 30 mg / L) is sprayed onto the surface of each layer of wet paper web through the water spraying devices. The water spraying temperature is controlled at 45℃, the water spraying pressure at 0.15 MPa, the water spraying angle at 50°, the spraying distance at 18 cm, and the water spraying amount per layer at 60 g / m². 2 .

[0057] S5, pressing By controlling the wet end pressure at 330 kPa, the multi-layer composite wet paper web was pressed to obtain a pressed wet paper web with a dryness of 43.5%.

[0058] S6, Drying After pressing, the wet paper web is placed in a drying cylinder. The temperature for low-temperature drying is controlled at 35°C and kept at this temperature until the moisture content is 37%. The temperature for medium-temperature drying is controlled at 85°C and kept at this temperature until the moisture content is 24%. The temperature for high-temperature drying is controlled at 110°C and kept at this temperature until the moisture content is 12%. The temperature for equilibrium drying is controlled at 70°C and kept at this temperature until the moisture content is 8.5%, thus obtaining fluff pulp.

[0059] S7, Post-processing After the fluff pulp is rolled into rolls using a rolling device, it is slit into rolls with a width of 480mm and a diameter of 1500mm. After being coded, it is wrapped in 5 layers of stretch film and stored in the warehouse.

[0060] Testing showed that all indicators of the fluff pulp prepared in this embodiment met the requirements of the national standard GB / T 21331-2021 "Fluff Pulp". The test results are shown in the table below:

[0061] Example 2 This embodiment provides a method for producing fluff pulp through multiple layers using a cylinder paper machine, specifically: S1. Raw material preparation: Bleached sulfate softwood pulp (NBKP) and bleached sulfate hardwood pulp (LBKP) are placed on the chain plate of the chain conveyor and await feeding, with an oven-dry weight ratio of 85:15.

[0062] The bleached sulfate softwood pulp has a brightness of 85% ISO, an oven-dry fiber content of 90 wt%, and a moisture content of 9 wt%; the bleached sulfate hardwood pulp has a brightness of 86% ISO, an oven-dry fiber content of 91 wt%, and a moisture content of 10 wt%.

[0063] S2. Pulping treatment: The aforementioned proportioned bleached sulfate softwood pulp and bleached sulfate hardwood pulp are fed into the pulper via a chain conveyor. White water recovered from the papermaking system is added, and the pH is adjusted to 8 using a 12wt% sodium hydroxide solution. The white water temperature is controlled at 50℃, the pulp concentration at 12%, and the pulping speed at 800rpm. The pulping process is carried out for 22 minutes to obtain a pulp with a freeness of 12°SR and a pulp temperature of 50℃.

[0064] S3, Dekeying Processing The broken pulp is pumped into the pulping tank, and the debonding agent is added by post-pumping. The debonding agent is mixed with the broken pulp and enters the pulping tank. The mixture is continuously stirred at 50 rpm to obtain the debonding treated pulp, which is ready for subsequent wire bonding.

[0065] The debonding agent is composed of sodium fatty alcohol polyoxyethylene ether sulfate (AES), alkyl glycoside (APG), trisodium citrate and deionized water; the weight ratio of sodium fatty alcohol polyoxyethylene ether sulfate, alkyl glycoside, trisodium citrate and deionized water is 60:25:10:5.

[0066] The amount of debonding agent added is calculated based on the oven-dry fiber weight of the broken pulp, and the addition amount is controlled at 1.2 kg / ton of oven-dry pulp. S4, Internet connection formed An 8-layer cylinder papermaking process is employed. The bond-debonding pulp supplied from the pulping tank is diluted to 0.2% (octane-dry fiber weight / total pulp weight) and then evenly distributed into each cylinder slot of the cylinder paper machine. The vacuum level of the wire section is controlled at 0.02 MPa, and the synchronous wire speed is 60 m / min. After the fibers are spread and formed on each layer of the cylinder wire, they are laminated under a pressure of 50 kPa to produce a multi-layer composite wet paper web with a dryness of 21 wt%. Furthermore, the basis weight of each layer is controlled at 91 g / m² during the web forming process. 2 To ensure that the total basis weight of the wet paper web reaches 730 g / m² 2 .

[0067] During the paper forming process, water spraying devices are installed between two adjacent rotary screens (7 water spraying devices are installed between 8 rotary screens). Before each layer of wet paper web is bonded at the composite roller, white water (pH 7.0, conductivity 500 μS / cm, suspended solids content 50 mg / L) is sprayed onto the surface of each layer of wet paper web through the water spraying devices. The water spraying temperature is controlled at 40℃, the water spraying pressure at 0.1 MPa, the water spraying angle at 50°, the spraying distance at 18 cm, and the water spraying amount per layer at 50 g / m². 2 .

[0068] S5, pressing By controlling the wet end pressure at 250 kPa, the multi-layer composite wet paper web is pressed to obtain a pressed wet paper web with a dryness of 40%.

[0069] S6, Drying After pressing, the wet paper web is placed in a drying cylinder. The temperature for low-temperature drying is controlled at 35°C and kept at this temperature until the moisture content is 37%. The temperature for medium-temperature drying is controlled at 85°C and kept at this temperature until the moisture content is 24%. The temperature for high-temperature drying is controlled at 110°C and kept at this temperature until the moisture content is 12%. The temperature for equilibrium drying is controlled at 70°C and kept at this temperature until the moisture content is 8.5%, thus obtaining fluff pulp.

[0070] S7, Post-processing After the fluff pulp is rolled into rolls using a rolling device, it is slit into rolls with a width of 480mm and a diameter of 1500mm. After being coded, it is wrapped in 5 layers of stretch film and stored in the warehouse.

[0071] The quantitative indicators of the fluff pulp prepared in this embodiment were determined by testing to be:

[0072] Example 3 This embodiment provides a method for producing fluff pulp through multiple layers using a cylinder paper machine, specifically: S1. Raw material preparation: Bleached sulfate softwood pulp (NBKP) and bleached sulfate hardwood pulp (LBKP) are placed on the chain plate of the chain conveyor and await feeding, with an oven-dry weight ratio of 95:5.

[0073] The bleached sulfate softwood pulp has a brightness of 85% ISO, an oven-dry fiber content of 90 wt%, and a moisture content of 9 wt%; the bleached sulfate hardwood pulp has a brightness of 86% ISO, an oven-dry fiber content of 91 wt%, and a moisture content of 10 wt%.

[0074] S2. Pulping treatment: The aforementioned proportioned bleached sulfate softwood pulp and bleached sulfate hardwood pulp are fed into the pulper via a chain conveyor. White water recovered from the papermaking system is added, and the pH is adjusted to 9 using a 17wt% sodium hydroxide solution. The white water temperature is controlled at 70℃, the pulp concentration at 12%, and the pulping speed at 900rpm. The pulping process is carried out for 25 minutes to obtain a pulp with a freeness of 14°SR and a pulp temperature of 70℃.

[0075] S3, Dekeying Processing The broken pulp is pumped into the pulping tank, and a debonding agent is added by post-pumping. The debonding agent is mixed with the broken pulp and enters the pulping tank. The mixture is continuously stirred at 80 rpm to obtain a debonding treated pulp, which is ready for subsequent wire bonding.

[0076] The debonding agent is composed of sodium fatty alcohol polyoxyethylene ether sulfate (AES), alkyl glycoside (APG), trisodium citrate and deionized water; the weight ratio of sodium fatty alcohol polyoxyethylene ether sulfate, alkyl glycoside, trisodium citrate and deionized water is 70:20:5:5.

[0077] The amount of debonding agent added is calculated based on the oven-dry fiber weight of the broken pulp, and the addition amount is controlled at 1.5 kg / ton of oven-dry pulp. S4, Internet connection formed An 8-layer cylinder papermaking process is employed. The bond-resolving pulp supplied from the pulping tank is diluted to 0.5% (octane-dry fiber weight / total pulp weight) and then evenly distributed into each cylinder slot of the cylinder paper machine. The vacuum level of the wire section is controlled at 0.04 MPa, and the synchronous wire speed is 70 m / min. After the fibers are spread and formed on each layer of the cylinder wire, they are laminated under a pressure of 80 kPa to produce a multi-layer composite wet paper web with a dryness of 25 wt%. Furthermore, the basis weight of each layer is controlled at 96 g / m² during the web forming process. 2 To ensure that the total basis weight of the wet paper web reaches 770 g / m² 2 .

[0078] During the paper forming process, water spraying devices are installed between two adjacent rotary screens (7 water spraying devices are installed between 8 rotary screens). Before each layer of wet paper web is bonded at the composite roller, white water (pH 8.0, conductivity 300 μS / cm, suspended solids content 30 mg / L) is sprayed onto the surface of each layer of wet paper web through the water spraying devices. The water spraying temperature is controlled at 50℃, the water spraying pressure at 0.15 MPa, the water spraying angle at 50°, the spraying distance at 18 cm, and the water spraying amount per layer at 80 g / m². 2 .

[0079] S5, pressing By controlling the wet end pressure at 450 kPa, the multi-layer composite wet paper web is pressed to obtain a pressed wet paper web with a dryness of 45%.

[0080] S6, Drying After pressing, the wet paper web is placed in a drying cylinder. The temperature for low-temperature drying is controlled at 35°C and kept at this temperature until the moisture content is 37%. The temperature for medium-temperature drying is controlled at 85°C and kept at this temperature until the moisture content is 24%. The temperature for high-temperature drying is controlled at 110°C and kept at this temperature until the moisture content is 12%. The temperature for equilibrium drying is controlled at 70°C and kept at this temperature until the moisture content is 8.5%, thus obtaining fluff pulp.

[0081] S7, Post-processing After the fluff pulp is rolled into rolls using a rolling device, it is slit into rolls with a width of 480mm and a diameter of 1500mm. After being coded, it is wrapped in 5 layers of stretch film and stored in the warehouse.

[0082] The quantitative indicators of the fluff pulp prepared in this embodiment were determined by testing to be:

[0083] Based on the test results of Examples 1-3, compared with existing commercially available fluff pulp (average fiber length 2.13-2.38 mm, average fiber width 26.6-29.1 μm, fine fiber content 13.9-16.5%, density 0.58-0.63 g / cm), the results showed that the pulp had the following properties: average fiber length 2.13-2.38 mm, average fiber width 26.6-29.1 μm, fine fiber content 13.9-16.5%, and density 0.58-0.63 g / cm. 3 Bursting strength 969-1177 kPa, bulk density 21.3-24.9 cm. 3 Compared to existing commercially available fluff pulp (with a water absorption time of 4.4-4.9s), the fluff pulp prepared by this invention using NBKP and LBKP as raw materials through a cylinder paper machine exhibits fiber properties and physical properties that are generally close to or superior to those of commercially available fluff pulp. This process not only enriches the technical pathways for fluff pulp production and provides strong case support for multi-layer fabrication of fluff pulp on cylinder paper machines, but it is also adaptable to the transformation of old-style cylinder paper machine production lines and is suitable for widespread industrial application.

[0084] Comparative Example 1 Comparative Example 1 adopts the technical solution of Example 1, but the difference is: (1) The three-layer rotary screen forming process is adopted in the screen forming step, and no interlayer water spraying is performed; the total basis weight of the multi-layer composite wet paper web is still controlled at 750g / m. 2 The quantitative distribution for each layer is 250g / m³. 2 (Bottom layer), 250g / m 2 (Middle layer), 250g / m 2 (Surface layer). Due to the thickness of the single layer of slurry in the screen section, the dewatering pressure increases sharply, the dewatering volume of the screen exit roller is large, obvious embossing phenomenon occurs, uniformity decreases significantly, slurry clumps are obvious, and the moisture content in the screen exit section reaches 50%. In order to ensure the dryness after pressing, the shoe pressing line pressure is stabilized at 600kN / m, and the density increases significantly.

[0085] (2) In the debonding process, only sodium fatty alcohol polyoxyethylene ether sulfate is used as the debonding agent. Due to its high burst strength, its addition amount is controlled at 1.5 kg / ton of oven-dry pulp.

[0086] The quantitative indicators of the fluff pulp prepared in this comparative example were tested and found to be:

[0087] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0088] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing fluff pulp through multiple layers using a cylinder paper machine, characterized in that, The process includes the following steps: pulping, debonding, wire mesh forming, pressing, and drying; The pulping process involves mixing bleached sulfate softwood pulp, bleached sulfate hardwood pulp, and white water, adjusting the pH to 8.0-9.0, and then pulping the mixture to obtain disintegrated pulp. The method for debonding is to mix the debonding slurry with the debonding agent evenly to obtain the debonding slurry; The unbonding agent is composed of sodium fatty alcohol polyoxyethylene ether sulfate, alkyl glycoside, trisodium citrate and deionized water; The method for forming the paper web is as follows: after diluting the debonding pulp to an oven-dry fiber content of 0.2-0.5%, it is formed using a rotary paper machine with no less than 6 layers, and the fibers are spread on the surface of each layer of rotary paper machine to form a wet paper web; and during the paper web forming process, white water is sprayed between two adjacent rotary paper machines on each layer of wet paper web. By laminating the wet paper webs of each layer, a multi-layer composite wet paper web is produced. The multi-layer composite wet paper web is pressed and dried to obtain fluff pulp.

2. The method for producing fluff pulp through multiple layers of a cylinder paper machine according to claim 1, characterized in that, In the pulping process, the oven-dry weight ratio of bleached sulfate softwood pulp to bleached sulfate hardwood pulp is 85-95:5-15. Bleached sulfate softwood pulp has an ISO brightness of ≥85%, an oven-dry fiber content of ≥90wt%, an average fiber width of ≥30μm, and a moisture content of ≤10wt%. Bleached sulfate hardwood pulp has an ISO brightness of ≥85%, an oven-dry fiber content of ≥90wt%, an average fiber width of ≥20μm, and a moisture content of ≤10wt%.

3. The method for producing fluff pulp through multiple layers using a cylinder paper machine according to claim 1, characterized in that, In the pulping process, the white water temperature is controlled at 50-70℃, the pulp concentration is 10-15%, the pulping speed is 800-1000 rpm, and the pulping time is 20-30 min. The beating degree of the pulp is 12-17°SR.

4. The method for producing fluff pulp through multiple layers using a cylinder paper machine according to claim 1, characterized in that, In the debonding process, the weight ratio of sodium fatty alcohol polyoxyethylene ether sulfate, alkyl glycoside, trisodium citrate, and deionized water in the debonding agent is 60-70:20-25:5-10:

5. Based on the weight of oven-dry fibers in the broken pulp, the amount of debonding agent added should be controlled at 1.0-1.5 kg / ton of oven-dry pulp.

5. The method for producing fluff pulp through multiple layers using a cylinder paper machine according to claim 1, characterized in that, In the web forming process, the vacuum degree of the web section is controlled at 0.02-0.04MPa, the synchronous web speed is 30-70m / min, and the composite pressure is 50-80kPa; The dryness of the multilayer composite wet paper web is 21-25 wt%, and the basis weight is 730-770 g / m². 2 .

6. The method for producing fluff pulp through multiple layers of a cylinder paper machine according to claim 1, characterized in that, In the web forming process, the temperature of the sprayed white water is controlled at 40-50℃, the pressure of the sprayed white water is 0.1-0.15MPa, and the angle of the sprayed white water is 45-60°. The dosage of white water for spraying single-layer wet paper webs is 50-80 g / m². 2 .

7. The method for producing fluff pulp through multiple layers of a cylinder paper machine according to claim 1, characterized in that, In the web forming process, the sprayed white water has a pH of 7.0-8.0, a conductivity of ≤500μS / cm, and a suspended solids content of ≤50mg / L.

8. The method for producing fluff pulp through multiple layers of a cylinder paper machine according to claim 1, characterized in that, The pressing method involves controlling the wet end pressure to 250-600 kPa and pressing the multi-layer composite wet paper web to obtain a pressed wet paper web with a dryness of 40-45%. The drying method involves sequentially subjecting the pressed wet paper web to low-temperature drying, medium-temperature drying, and high-temperature drying, followed by equilibrium drying until the moisture content reaches 8-10%, thereby obtaining fluff pulp.

9. The method for producing fluff pulp through multiple layers of a cylinder paper machine according to claim 8, characterized in that, During the drying process, the temperature for low-temperature drying is controlled at 33-36℃, and the drying is maintained at this temperature until the moisture content is 35-38%. The temperature for medium-temperature drying is controlled at 83-86℃, and the drying is maintained at this temperature until the moisture content is 20-25%. The high-temperature drying temperature is controlled at 108-112℃, and the drying is carried out until the moisture content is 10-13%. The temperature for balanced drying should be controlled at 68-72℃.

10. A fluff pulp, characterized in that, It is prepared by the method described in any one of claims 1-9.

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