A method for increasing the bulk of pulp fibers by localized heat treatment

Abstract

The application discloses a method for improving the bulkiness of paper pulp fibers by local heat treatment, and relates to the technical field of pulping and papermaking; step 1: dispersing or laying the paper pulp fibers; step 2: performing local heat bulk treatment on the paper pulp fibers; step 3: performing shaping on the paper pulp fibers after the bulk treatment by spraying a film forming agent on the surfaces of the fibers; and step 4: reducing the temperature of the shaped paper pulp fibers to room temperature by air cooling; the application can improve the bulkiness of the paper pulp and the bulkiness of paper.

Description

Technical Field

[0001] This invention discloses a method for improving the bulkiness of pulp fibers by using local heat treatment, which relates to the field of pulp and paper technology. Background Technology

[0002] Pulp is a fiber extracted from plant raw materials, with cellulose as its main chemical component. Modern pulping and papermaking primarily uses wood, resulting in pulp fibers that are long and spindle-shaped. For example, softwood pulp fibers are 2-4 mm long, 30-55 μm thick, and have an aspect ratio of 40-140; hardwood pulp fibers are 0.8-1.2 mm long, 15-30 μm thick, and have an aspect ratio of 25-80. Pulp extracted from wood is relatively soft and generally straight without external processing. Under mechanical pulping, the fibers will break down, but remain relatively straight overall. This wet-process papermaking, followed by pressing, dewatering, and calendering, results in paper with good smoothness.

[0003] In certain sectors, soft, flexible, and fluffy pulp is required. For example, fluff pulp is used in disposable hygiene products. High-end fluff pulp is a type of softwood pulp produced through a chemical process, involving bleaching and removal of extracts using organic solvents. It is primarily used as the absorbent medium in sanitary napkins, diapers, and other hygiene products, possessing long fibers and high strength, and meeting requirements for rapid absorption and other hygiene standards. Similarly, in the packaging and printing industries, some paper types require high bulk, such as food-grade coated white cardboard, kraft paper, lightweight printing paper, lightweight paper (Munken paper), and toilet paper.

[0004] Existing technologies using high-consistency refining can cause pulp fibers to bend to a certain extent. Refining changes the shape of fibers through mechanical action, achieving fiber bending and softening. However, it also significantly leads to fiber breakage, reduced fiber length, and uneven fiber distribution during papermaking, making it difficult to ensure the uniformity of the finished paper. Summary of the Invention

[0005] This invention addresses the problems of existing technologies by providing a method for improving the bulkiness of pulp fibers through localized heat treatment, thereby increasing the dry bulkiness of fluff pulp and the thickness of paper.

[0006] The specific solution proposed in this invention is as follows: This invention provides a method for improving the bulkiness of pulp fibers using localized heat treatment, comprising: Step 1: Disperse or spread the pulp fibers: Use airflow to drive the pulp fibers through the air duct, where the pulp fibers are dispersed; or form the pulp fibers into a loose, low-basis-weight pulp board with a basis weight of 15~40g / m³. 2 The fibers on the pulp board are laid flat. Step 2: Fluffing treatment of pulp fibers by localized heating: Local heating of dispersed pulp fibers in the air duct using a laser array: First, the pulp fibers are humidified and the humidity is adjusted to the range of 15-35%. Then, the airflow drives the pulp fibers to the laser array in the air duct. The laser irradiates and heats the moving pulp fibers locally. The power of the laser is adjusted to the highest local temperature of 160-200 °C for the pulp fibers. For the pulp fiber board in a flat state, a metal heating roller is used to locally heat the pulp fiber board: First, the pulp fiber is humidified and the humidity is adjusted to the range of 15~35%. The pulp board is rolled and locally heated by a metal heating roller and a drive roller. The surface of the metal heating roller has heating protrusions. By controlling the temperature of the heating protrusions of the metal heating roller and the speed at which the drive roller moves the pulp board, the maximum local temperature of the pulp fiber is made to be 160-200 °C. Step 3: After fluffing, the pulp fibers are fixed by spraying a film-forming agent onto the fiber surface; Step 4: Cool the shaped pulp fibers to room temperature using air cooling.

[0007] Furthermore, in step 2 of the method for improving the bulkiness of pulp fibers using local heat treatment, the laser spot size is set to 1.5-2.5 times the thickness of the pulp fiber, or less than 1 / 20-1 / 4 of the pulp fiber length, and the laser spot spacing is set to an integer multiple of the average length of the pulp fiber.

[0008] Furthermore, in step 2 of the method for improving the bulkiness of pulp fibers using local heat treatment, the width of the heated protrusion is 5-25 times the thickness of the pulp fiber, or 1 / 20-1 / 4 of the length of the pulp fiber.

[0009] Furthermore, in step 2 of the method for improving the bulkiness of pulp fibers by using local heat treatment, multiple heating protrusions are arranged on the surface of the metal heating roller, and their shape is a continuous thread, a continuous cylinder, a square column or other shape. Steam or heat transfer oil is used to provide heat to the metal heating roller.

[0010] Furthermore, in step 2 of the method for improving the bulkiness of pulp fibers by using local heat treatment, the metal heating roller and the drive roller are arranged to be parallel to each other, with equal diameters and the same rotational angular velocity. The pulp plate passes through the middle of the metal heating roller and the drive roller. The metal heating roller has square columnar heating protrusions with a spacing of 0.2 mm between the columns.

[0011] Furthermore, in step 3 of the method for improving the bulkiness of pulp fibers using local heat treatment, the film-forming agent includes one or more of polyquaternium-46, vinylpyrrolidone and vinyl acetate copolymer, and polyvinyl alcohol. The film-forming agent is prepared into an aqueous solution and sprayed, with the spray amount of film-forming agent being 0.01~0.5% of the mass of the pulp fibers. The pulp fibers are then sent into a hot air system for drying and shaping.

[0012] The present invention describes a method for improving the bulkiness of pulp fibers by using local heat treatment. The method involves using a laser array to perform local heat treatment on coniferous chemimechanical pulp to obtain pulp fibers with improved bulkiness, which can be used to manufacture lightweight offset paper, copy paper, office paper, kraft paper, white cardboard, and toilet paper.

[0013] The present invention describes a method for improving the bulkiness of pulp fibers by using local heat treatment. This method involves local heat treatment of commercial fluff pulp with a metal heating roller to obtain pulp fibers with improved bulkiness, which can be used to manufacture disposable hygiene products.

[0014] The advantages of this invention are: This invention utilizes localized heating to increase the bulkiness of pulp fibers, concentrating energy and avoiding the prolonged mechanical kneading of the entire fiber pulp as in a refiner. The efficiency of converting electrical energy into heat is high, and the energy is applied only to the areas requiring deformation, thus avoiding the significant mechanical wear and heat loss associated with large-scale operation of heavy-duty grinding discs.

[0015] This invention simplifies the process flow. The treated slurry does not require a complicated anti-submersion process and can be directly used for papermaking, thereby simplifying the process flow and saving equipment investment and time costs.

[0016] This invention allows for precise control, enabling bending without damaging the pulp fibers. It can be set to heat only the parts that need bending, and the degree of bending can be controlled by changing the laser intensity or the shape of the heating protrusions on the metal heating roller, thereby improving the conversion efficiency of bulkiness.

[0017] The method of this invention is green and environmentally friendly, with no chemical additives or chemical auxiliaries, reducing costs and making the product purer and safer. It can be used to produce high-end absorbent hygiene products that are sensitive to chemicals, such as baby diapers and sanitary napkins. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, some simple figures will be drawn below to describe the sample data characterization process in the implementation of the present invention.

[0019] Figure 1 This is a schematic diagram of localized heating of pulp fibers using laser technology and the addition of a film-forming agent.

[0020] Figure 2 This is a schematic diagram of localized heating of pulp fiberboard and addition of film-forming agent using a metal heating roller method.

[0021] Figure 3 This is a schematic diagram before and after the local heating and fluffing treatment in Example 1.

[0022] Figure 4 This is a schematic diagram before and after the local heating and fluffing treatment in Example 2. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0024] The national standard GB / T21331-2021 for fluff pulp specifies the dry bulk index, which refers to the volume of pulp per unit weight, measured in cm³. 3 / g. High dry bulk indicates a relatively fluffy pulp with good air permeability and water absorption. In the packaging and printing industries, some paper types require high bulk. Paper bulk is an indicator of paper density, referring to the volume occupied by a unit weight of paper, measured in cm³. 3 / g. For the same weight, high bulk paper has a greater thickness and a more substantial feel. High bulk paper is generally used for food-grade coated white cardboard, kraft paper, lightweight printing paper, lightweight paper (Munken paper), and toilet paper. Its specifications are stipulated in relevant national standards such as "GB / T24328.2-2020 Toilet paper and its products Part 2: Determination of thickness, laminate thickness, apparent laminate density and bulk" and "Lightweight printing paper" (GB / T 26705-2023). Example

[0025] The method of this invention is used to process pulp fibers for making high bulk unbleached kraft paper. The pulp fibers are softwood chemimechanical pulp, which has been beaten to 25 °SR. This process may include: Step 1: Dispersing the pulp fibers: Using airflow to drive the pulp fibers through the air duct, the dryness reaches 78%, and the pulp fibers are dispersed in the air duct. (Refer to...) Figure 3 The state of pulp fibers in section a.

[0026] Step 2: Fluffing treatment of pulp fibers by localized heating: Local heating of dispersed pulp fibers in the air duct using a laser array; the deployment within the air duct can be referenced. Figure 1 : First, the pulp fibers are humidified and the humidity is adjusted to the range of 15-35%. The humidity is the mass ratio of water content in the pulp fibers. Then, the airflow drives the pulp fibers to the laser array in the air duct. The laser locally irradiates and heats the moving pulp fibers. The laser spot size is set to 100 μm, the distance between the spots is 4 mm, and the laser power is adjusted to the highest local heating temperature of 180 °C for the pulp fibers. Step 3: The fluffed pulp fibers are fixed by spraying a film-forming agent onto the fiber surface, using 1% polyvinyl alcohol as the fixing agent, with a polyvinyl alcohol content of 0.05%. The pulp fibers are dried with hot air at 60°C to a dryness of 89%, and then cooled with room temperature air.

[0027] Step 4: Cool the shaped pulp fibers to room temperature using air cooling. See below for the appearance of the cooled pulp sample. Figure 3 On the right, significant fiber bending is visible. After the above treatment, the thickness of the kraft paper made from the pulp increased from 2.8 cm before treatment. 3 / g increased to 3.5 cm 3 / g. Example

[0028] The method of the present invention is used to process pulp fibers for disposable hygiene products, wherein the pulp fibers are commercial fluff pulp, and the process is as follows: Step 1: Form the pulp fibers into loose, low-basis-weight pulp boards, with a basis weight of 15-40 g / m³. 2 The fibers on the pulp board are laid flat, for reference. Figure 4 c; Step 2: Fluffing treatment of pulp fibers by localized heating: For pulp fiber boards laid flat, localized heating of the pulp fiber boards is achieved using metal heating rollers: First, the pulp fibers are humidified to approximately 30% humidity. Then, the pulp boards are rolled and locally heated using metal heating rollers and drive rollers. (Refer to...) Figure 2 The layout is as follows: The surface of the metal heating roller has heating protrusions, which are square pillars. The heated surface of each pillar is 1.0 mm wide and 2 mm high, with a spacing of 0.2 mm between the pillars. The metal heating roller and the drive roller are parallel to each other and rotate at the same angular velocity. The pulp sheet passes between the two heating rollers. When the two rollers rotate, high-temperature steam flows through the inside of the metal double rollers. The square pillars on the rollers locally heat the pulp fibers, raising the local temperature of the fibers to 190 °C. The square pillars also exert a certain mechanical force on the fibers, promoting fiber bending.

[0029] Step 3: The fluffed pulp fibers are then fixed by spraying a film-forming agent onto the fiber surface. A 2% concentration of vinylpyrrolidone and vinyl acetate copolymer is used as the fixing agent, with a dosage of 0.1%. The pulp fibers are dried with hot air at 60°C to 88% dryness, and then cooled with room temperature air to obtain a flexed fluff pulp. (Refer to...) Figure 4 d.

[0030] Step 4: Cool the shaped pulp fibers to room temperature using air cooling. Measure the dry bulk of the fluff pulp according to national standard GB / T21331-2021. The dry bulk of the fluff pulp before treatment is 15.2 cm. 3 / g increased to 19.7 cm 3 / g.

[0031] The above are preferred embodiments of the present invention. Within the scope of the technical solution of the present invention, the effects produced by the present invention can be obtained by adjusting the type and amount of reagents according to the actual situation.

[0032] Unless otherwise specified, all reagents used in the method of this invention were purchased or obtained through legitimate channels.

[0033] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for improving the bulkiness of pulp fibers using localized heat treatment, characterized in that: include: Step 1: Disperse or spread the pulp fibers: Use airflow to drive the pulp fibers through the air duct, in which the pulp fibers are dispersed; Alternatively, the pulp fibers can be formed into loose, low-basis-weight pulp boards with a basis weight of 15-40 g / m³. 2 The fibers on the pulp board are laid flat. Step 2: Fluffing treatment of pulp fibers by localized heating: Local heating of dispersed pulp fibers in the air duct using a laser array: First, the pulp fibers are humidified and the humidity is adjusted to the range of 15-35%. Then, the airflow drives the pulp fibers to the laser array in the air duct. The laser irradiates and heats the moving pulp fibers locally. The power of the laser is adjusted to the highest local temperature of 160-200 °C for the pulp fibers. For the pulp fiber board in a flat state, a metal heating roller is used to locally heat the pulp fiber board: First, the pulp fiber is humidified and the humidity is adjusted to the range of 15~35%. The pulp board is rolled and locally heated by a metal heating roller and a drive roller. The surface of the metal heating roller has heating protrusions. By controlling the temperature of the heating protrusions of the metal heating roller and the speed at which the drive roller moves the pulp board, the maximum local temperature of the pulp fiber is made to be 160-200 °C. Step 3: After fluffing, the pulp fibers are fixed by spraying a film-forming agent onto the fiber surface; Step 4: Cool the shaped pulp fibers to room temperature using air cooling.

2. The method for improving the bulkiness of pulp fibers using localized heat treatment according to claim 1, characterized in that: In step 2, the laser spot size is set to 1.5-2.5 times the thickness of the pulp fiber, or less than 1 / 20-1 / 4 of the pulp fiber length, and the laser spot spacing is set to an integer multiple of the average length of the pulp fiber.

3. The method for improving the bulkiness of pulp fibers using localized heat treatment according to claim 2, characterized in that: In step 2, the width of the heated protrusion is 5-25 times the thickness of the pulp fiber, or 1 / 20-1 / 4 of the length of the pulp fiber.

4. The method for improving the bulkiness of pulp fibers by using localized heat treatment according to claim 1, characterized in that: In step 2, multiple heating protrusions are arranged on the surface of the metal heating roller. The protrusions are continuous threads, continuous cylinders, square columns or other shapes. Steam or heat transfer oil is used to provide heat to the metal heating roller.

5. A method for improving the bulkiness of pulp fibers using localized heat treatment according to claim 1, characterized in that: In step 2, the metal heating roller and the drive roller are configured to be parallel to each other, have the same diameter, and have the same rotational angular velocity. The slurry plate passes through the middle of the metal heating roller and the drive roller. The metal heating roller has square column heating protrusions with a spacing of 0.2 mm between the columns.

6. A method for improving the bulkiness of pulp fibers using localized heat treatment according to claim 1, characterized in that: In step 3, the film-forming agent includes one or more of polyquaternium-46, vinylpyrrolidone and vinyl acetate copolymer, and polyvinyl alcohol. The film-forming agent is prepared into an aqueous solution and sprayed. The amount of film-forming agent sprayed is 0.01~0.5% of the mass of the pulp fiber. The pulp fiber is sent into a hot air system for drying and shaping.

7. A method for improving the bulkiness of pulp fibers by using local heat treatment according to claim 1 or 2, wherein a laser array is used to perform local heat treatment on coniferous chemimechanical pulp to obtain pulp fibers with improved bulkiness after treatment, which are used for making lightweight offset paper, copy paper, office paper, kraft paper, white cardboard, and toilet paper.

8. A method for improving the bulkiness of pulp fibers by means of local heat treatment according to any one of claims 1, 3-6, wherein commercial fluff pulp is subjected to local heat treatment with a metal heating roller to obtain pulp fibers with improved bulkiness after treatment, for use in the manufacture of disposable hygiene products.

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