A method and apparatus for making high-strength kraft linerboard

Abstract

The application discloses a kind of preparation method and device of high-strength kraft paperboard, it is related to papermaking technical field.Method includes: fiber grading pretreatment, multistage screening, stratified forming, glue spraying and press drying.Long fiber is divided into three categories, long fiber is used for surface layer and bottom layer, middle fiber and short fiber are used for core layer and short fiber is located in the middle of core layer, and modified starch and nano microfilament mixed emulsion are sprayed between layers, finally, finished product is obtained by boot pressing and hot air penetration drying.The device includes composite fiber grading device, glue spraying device, boot pressing device and hot air penetration drying device.The grading device adopts conical two-stage screening structure and automatic discharging and feeding mechanism, which can realize continuous grading and stable discharging.The application significantly improves the ring compression strength and interlayer bonding force of the paperboard by combining fiber grading, stratification and interlayer reinforcement.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, and more specifically, to a method and apparatus for preparing high-strength kraft paperboard. Background Technology

[0002] Kraft linerboard, as a high-strength packaging material, is widely used in the production of corrugated boxes, express delivery packaging, and outer packaging for heavy goods due to its excellent compression resistance and bursting strength. With the rapid development of e-commerce and logistics industries, the market's performance requirements for packaging materials are increasing. Kraft linerboard is required not only to have higher ring crush strength and interlayer bond strength, but also to have good surface flatness and uniformity to adapt to high-speed printing and automated packaging lines.

[0003] In traditional kraft paperboard manufacturing processes, waste paper or virgin pulp fiber raw materials are typically directly pulped and fed into the paper machine for forming. However, fibers of different lengths play different roles in paperboard: long fibers mainly provide strength and toughness, suitable for the surface and bottom layers; medium fibers provide filling and some strength, suitable for the core layer; and short fibers mainly act as fillers, improving uniformity and surface properties. If fibers of different lengths are mixed and directly formed, it can easily lead to problems such as a rough surface layer, insufficient core layer strength, and poor interlayer bonding, limiting the improvement of the overall performance of the paperboard. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for preparing high-strength kraft paperboard, which solves the problems of rough surface layer, insufficient core layer strength, and poor interlayer bonding in some existing kraft paperboards.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing high-strength kraft paperboard boxes includes the following steps:

[0007] S1: Fiber grading pretreatment: The raw materials are fed into a fiber pretreatment device for crushing and modification to obtain fiber material;

[0008] S2: Multi-stage screening: The modified fiber material is fed into a composite fiber grading device to classify the fibers into long fiber material, medium fiber material and short fiber material.

[0009] S3: Layered forming: Long fiber material is conveyed to the bottom and top layers, and medium and short fiber material is conveyed to the core layer, with the short fiber material located in the middle of the core layer;

[0010] S4: Spray adhesive: During the lamination process, a composite reinforcing agent is sprayed onto the interlayer surface;

[0011] S5: Press drying: The composite wet paper web is processed by a boot press and a hot air penetration drying device to obtain the finished product.

[0012] In the above method, the composite reinforcing agent in step S4 is a mixed emulsion of modified starch and nanofibers, wherein the solid content ratio of modified starch to nanofibers is 5:1 to 10:1. During the spraying process, the moving speed of the fiber material is 0.1-0.5 m / s, the spraying angle of the nozzle used for spraying is 60-90 degrees, and the spraying pressure is 1.5-3.0 MPa.

[0013] Mechanism explanation of the method of the present invention:

[0014] This invention achieves a significant improvement in cardboard strength through a "grading-layering-adhesive spraying" process, the specific mechanism of which is as follows:

[0015] (1) Synergistic reinforcement mechanism of fiber grading and layered arrangement: Long fibers have a high aspect ratio and hydrogen bonding ability. When arranged in the surface and bottom layers, they can form a dense fiber network skeleton, providing the main tensile strength and ring crush strength. Medium and short fibers are arranged in the core layer, with short fibers located in the middle of the core layer, which can fill the gaps in the medium fiber network and improve the uniformity of the core layer. This gradient structure of "long fiber wrapping - medium fiber support - short fiber filling" allows the stress to be effectively transferred from the outer layer to the inner layer and dispersed and absorbed when the paperboard is subjected to external force, avoiding interlayer delamination caused by stress concentration.

[0016] (2) Interlayer bridging and bonding reinforcement mechanism of composite reinforcing agents: Modified starch has excellent film-forming and adhesive properties. After being sprayed onto the core layer surface, it can penetrate into the fiber gaps between the surface layer and the core layer, and between the sublayers of the core layer, during subsequent pressing and drying. Meanwhile, nanofibers have extremely high aspect ratios and abundant surface hydroxyl groups. When modified starch is mixed with nanofibers, the nanofibers form a three-dimensional network structure in the starch emulsion. On the one hand, they bond with the fiber surface through physical entanglement; on the other hand, the hydroxyl groups on the nanofibers form numerous hydrogen bonds with the hydroxyl groups on the fiber surface, thus establishing a multi-layer bridging structure of "fiber-nanofiber-starch film-fiber". This structure significantly increases the interlayer bonding area and bonding strength, effectively resisting interlayer shear stress.

[0017] (3) Spray adhesive mechanism: Controlling the fiber material movement speed to 0.1-0.5 m / s ensures that the sprayed droplets have sufficient time to spread and penetrate the fiber surface, while avoiding excessive local application of adhesive due to slow speed. The nozzle spray angle of 60-90 degrees ensures that the spray coverage can uniformly cover the entire width of the core layer. The spray pressure of 1.5-3.0 MPa enables the composite reinforcing agent to be sprayed into the fiber layer in the form of tiny droplets rather than just remaining on the surface, thus achieving the effect of internal reinforcement rather than just surface application of adhesive.

[0018] The present invention also provides an apparatus for preparing high-strength kraft paperboard for implementing the above method, comprising:

[0019] A composite fiber grading device is used to perform multi-stage screening in step S2;

[0020] A glue spraying device is used to perform step S4;

[0021] A boot press device is used to perform the boot press in step S5;

[0022] A hot air penetration drying device is used to perform hot air penetration drying in step S5.

[0023] Furthermore, the composite fiber grading device includes a fixed support, a screening device, and a feeding device. The screening device is mounted on the fixed support, and the feeding device is fixedly mounted on the fixed support and located below the screening device. The screening device is a conical screening device, and two sets are symmetrically arranged. The screening device includes a fixed cylinder, a first screening cylinder, a second screening cylinder, a rotating shaft, and a drive motor. The fixed cylinder is fixedly mounted on the fixed support, and the rotating shaft is rotatably mounted on the fixed support and extends into the fixed cylinder. The first screening cylinder is fixedly mounted on the rotating shaft and located inside the fixed cylinder, and the second screening cylinder is fixedly mounted on the rotating shaft and located inside the first screening cylinder. Screening channels are respectively provided between the fixed cylinder and the first screening cylinder, and between the first screening cylinder and the second screening cylinder. An arc-shaped receiving plate is inclinedly arranged at the lower part of the second screening cylinder. The lower inner end of the screening channel and the lower inner end of the second screening cylinder are respectively provided with discharge ports, and the discharge port corresponding to the second screening cylinder corresponds to the lower end of the arc-shaped receiving plate. The drive motor is fixedly mounted on the fixed bracket and is connected to the rotating shaft for transmission. A feed inlet is fixedly provided on the upper part of the fixed cylinder, corresponding to the position of the screening channel between the fixed cylinder and the first screening cylinder.

[0024] In the above-mentioned device, front and rear baffles are provided on both sides of the upper part of the screening channel to prevent the screening material from being directly carried to the bottom of the screening channel by the rotation of the first screening cylinder or the second screening cylinder, and to force the screening material to enter the lower part of the screening channel from between the outer end of the fixed cylinder and the outer end of the first screening cylinder and between the outer end of the first screening cylinder and the second screening cylinder.

[0025] Furthermore, the feeding device includes a set of short fiber feeding cylinders, two sets of medium fiber feeding cylinders, two sets of long fiber feeding cylinders, and an automatic feeding and replenishing mechanism. The short fiber feeding cylinders are located below the two sets of screening devices. The two sets of medium fiber feeding cylinders are symmetrically arranged on both sides of the short fiber feeding cylinders, and the two sets of long fiber feeding cylinders are symmetrically arranged on both sides of the short fiber feeding cylinders and located outside the medium fiber feeding cylinders. The upper end of the short fiber feeding cylinder corresponds to the outlet of the second screening cylinder of the two sets of screening devices. The upper ends of the two sets of medium fiber feeding cylinders respectively correspond to the discharge ports of the screening channels between the first and second screening cylinders of the two sets of screening devices. The upper ends of the two sets of long fiber feeding cylinders respectively correspond to the discharge ports of the screening channels between the fixed cylinder and the first screening cylinder of the two sets of screening devices. The cross-section of the short fiber feeding cylinders, medium fiber feeding cylinders, and long fiber feeding cylinders is square. The automatic feeding and replenishing mechanism is installed on the short fiber feeding cylinders, medium fiber feeding cylinders, and long fiber feeding cylinders.

[0026] Furthermore, the automatic feeding and replenishing mechanism includes sliders that are slidably disposed on both sides of the short fiber feeding cylinder, the medium fiber feeding cylinder, and the long fiber feeding cylinder, respectively. A feeding roller is rotatably disposed between the sliders, and a feeding motor is mounted on each slider to drive the feeding roller. The outer ends of the roller shafts of the medium fiber and long fiber feeding cylinders are disposed within a first long groove of a first crank, and the outer ends of the roller shafts of the short fiber feeding cylinder are disposed within a second long groove of a second crank. A sliding block is hinged to the middle of the first crank, and the sliding block is slidably disposed between the medium fiber and long fiber feeding cylinders. Fixed blocks are respectively disposed between the medium fiber and long fiber feeding cylinders, above and below the sliding blocks, and a spring is disposed between the sliding blocks and the fixed blocks. The end of the second crank away from the feeding roller of the short fiber feeding cylinder is hinged to the middle of the first crank, and the middle of the second crank is hinged between the short fiber and medium fiber feeding cylinders. Push rods are vertically fixed on the sliders corresponding to the short fiber feeding cylinder, medium fiber feeding cylinder, and long fiber feeding cylinder, and U-shaped push plates are provided on the upper side of the push rods. Feeding switch mechanisms are respectively provided on the outer side of the short fiber feeding cylinder, medium fiber feeding cylinder, and long fiber feeding cylinder, corresponding to the positions of the U-shaped push plates, and these feeding switch mechanisms are connected to an external feeding bin.

[0027] The feeding switch mechanism includes a feeding channel, with a rotating plate rotatably mounted on the outside of the feeding channel. The rotating plate is located on both sides of the short fiber feeding cylinder, medium fiber feeding cylinder, and long fiber feeding cylinder. A switch plate is fixedly mounted between the rotating plates via a fixing rod, and the switch plate is located inside the short fiber feeding cylinder, medium fiber feeding cylinder, and long fiber feeding cylinder. The fixing rod is slidably connected to the outer wall of the feeding channel. The feeding channel has a feeding port, and the switch plate cooperates with the feeding port. The feeding port communicates with the interior of the short fiber feeding cylinder, medium fiber feeding cylinder, and long fiber feeding cylinder. The middle part of the rotating plate is connected to one end of a tension spring, and the other end of the tension spring is fixedly mounted on a spring fixing block on the outer side of the rotating plate. A stop shaft is fixedly mounted on the outer side of the inner end of the rotating plate, and a U-shaped push plate cooperates with the stop shaft.

[0028] The short fiber feeding cylinder, medium fiber feeding cylinder, long fiber feeding cylinder, and the chute on the feeding channel are each equipped with a cover plate fixed to the slider or fixed block to prevent the fiber material from leaking during the unloading process.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention employs a "grading-layering-spraying" process, using long fibers for the face / bottom layer and medium / short fibers for the core layer to form a gradient structure, significantly improving ring crush strength and interlayer bonding. Spraying a mixed emulsion of modified starch and nanofibers creates a multi-bridged structure between layers: "fiber-nanofiber-starch film-fiber," greatly increasing the bonding area and strength. A conical double-stage screening device, with two symmetrically arranged sets, continuously and stably separates fibers into long, medium, and short categories, ensuring the accuracy of raw materials for layered forming. The feeding device, through the linkage of a slider, crank, and spring, automatically triggers a replenishment switch based on the material level, achieving continuous and stable feeding and avoiding fluctuations in paper web basis weight. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the composite fiber grading device of the present invention;

[0032] Figure 2 This is a partial structural schematic diagram of the composite fiber grading device of the present invention.

[0033] Figure 3 This is a cross-sectional view of the screening device of the present invention;

[0034] Figure 4 This is a schematic diagram of the automatic feeding and replenishing mechanism of the present invention;

[0035] Figure 5 This is a cross-sectional view of the feeding switch mechanism when the feeding port is closed according to the present invention;

[0036] Figure 6This is a cross-sectional view of the feeding switch mechanism when the feeding port of the present invention is opened.

[0037] In the diagram: 1-Composite fiber grading device; 11-Fixed bracket; 12-Screening device; 13-Feeding device; 121-Fixed cylinder; 122-First screening cylinder; 123-Second screening cylinder; 124-Rotating shaft; 125-Drive motor; 126-Screening channel; 127-Outlet; 128-Inlet; 129-Front and rear baffles; 1210-Arc plate; 13-Feeding device; 131-Short fiber feeding cylinder; 132-Medium fiber feeding cylinder; 133-Long fiber feeding cylinder; 134-Automatic feeding and replenishing mechanism; 1341-Slider; 1 342 - Feeding roller; 1344 - First crank; 1345 - First long groove; 1346 - Second crank; 1347 - Second long groove; 1348 - Upper and lower sliding blocks; 1349 - Fixed block; 13410 - Spring; 13411 - Push rod; 13412 - U-shaped push plate; 135 - Feeding switch mechanism; 1351 - Feeding channel; 1352 - Rotating plate; 1353 - Fixed rod; 1354 - Switch plate; 1355 - Feeding port; 1356 - Tension spring; 1357 - Spring fixing block; 1358 - Stop shaft; 13413 - Cover plate Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] A method for preparing high-strength kraft paperboard boxes includes the following steps:

[0040] S1: Fiber Grading Pretreatment: The raw materials are fed into a fiber pretreatment device for crushing and modification to obtain fiber material. Modification includes adding appropriate amounts of water, caustic soda, and surfactants for dispersing and swelling, so that the fibers are fully dispersed and their subsequent bonding ability is improved.

[0041] S2: Multi-stage screening: The modified fiber material is fed into the composite fiber grading device 1, which classifies the fibers into long fiber material, medium fiber material, and short fiber material. The specific grading standards are as follows: Long fiber material is the fiber that remains outside the first screening cylinder 122, with an average length of 2.2-3.5 mm; medium fiber material is the fiber that passes through the first screening cylinder 122 but is intercepted by the second screening cylinder 123, with an average length of 1.0-2.0 mm; short fiber material is the fiber that passes through the second screening cylinder 123, with an average length of 0.3-0.8 mm.

[0042] S3: Layered forming: Long fiber material is conveyed to the bottom and top layers, and medium and short fiber material is conveyed to the core layer, with the short fiber material located in the middle of the core layer.

[0043] S4: Spraying Adhesive: During the lamination process, spraying devices are installed between the middle layer of the short fiber core layer and the upper and lower medium fiber core layers to spray the composite reinforcing agent onto the core layer surface. The composite reinforcing agent is a mixed emulsion of modified starch (using oxidized starch) and nanofibers, wherein the solid content ratio of modified starch to nanofibers is 5:1. The fiber material moving speed during spraying is 0.3 m / s, the spraying nozzle angle is 75 degrees, and the spraying pressure is 2.2 MPa. The amount of adhesive sprayed is controlled at 8-12 g per square meter of core layer surface (based on solid content).

[0044] The specific mechanism of the above-mentioned spraying process is as follows: When the composite reinforcing agent is sprayed from a 75-degree angle nozzle at a pressure of 2.2 MPa, it forms tiny droplets with a diameter of approximately 50-100 micrometers. At a fiber material movement speed of 0.3 m / s, the droplets have sufficient time to spread and penetrate the fiber surface. The nanofibers form a three-dimensional thixotropic network in the modified starch emulsion, ensuring both uniform spraying and the formation of "microbridge" structures between the fibers during the subsequent drying process.

[0045] S5: Press Drying: The composite wet paper web is press-dried using a shoe press (press line pressure 800 kN / m, pressing time approximately 0.5 seconds), and then processed by a hot air penetration drying device (hot air temperature 160℃, air velocity 25 m / s, drying time approximately 3 seconds) to obtain the finished product. The total basis weight of the finished kraft linerboard is 160 g / m². 2 The thickness is 0.25 mm.

[0046] II. Preparation Apparatus

[0047] The apparatus for preparing high-strength kraft paperboard using the above method includes a composite fiber grading device 1, a glue spraying device, a shoe press device, and a hot air penetration drying device. The glue spraying device, shoe press device, and hot air penetration drying device all use existing, relatively conventional devices, which will not be described in detail here.

[0048] The composite fiber grading device 1 is used to perform multi-stage screening in step S2. The adhesive spraying device, which includes multiple nozzles spaced 100 mm apart and evenly distributed between the lower ends of each feeding cylinder, is used to perform the spraying of the composite reinforcing agent in step S4. The shoe press device is used to perform shoe pressing in step S5. The hot air penetration drying device is used to perform hot air penetration drying in step S5.

[0049] (I) Specific Structure of Composite Fiber Grading Device

[0050] like Figures 1 to 3 As shown, the composite fiber grading device 1 includes a fixed support 11, a screening device 12, and a feeding device 13. The screening device 12 is mounted on the fixed support 11, and the feeding device 13 is fixedly mounted on the fixed support 11 and located below the screening device 12.

[0051] The screening device 12 is a conical screening device, and two sets are symmetrically arranged, one on the left and one on the right. Each set of screening devices 12 includes a fixed cylinder 121, a first screening cylinder 122, a second screening cylinder 123, a rotating shaft 124, and a drive motor 125. The fixed cylinder 121 is fixedly mounted on a fixed support 11. The rotating shaft 124 is rotatably mounted on the fixed support 11 via bearings and extends horizontally to the inner center of the fixed cylinder 121. The first screening cylinder 122 is a conical screen cylinder, fixedly mounted on the rotating shaft 124 and located inside the fixed cylinder 121. The second screening cylinder 123 is a finer conical screen cylinder, fixedly mounted on the rotating shaft 124 and located inside the first screening cylinder 122. Annular screening channels 126 are formed between the fixed cylinder 121 and the first screening cylinder 122, and between the first screening cylinder 122 and the second screening cylinder 123, respectively. An arc-shaped receiving plate 1210 is inclinedly arranged at the lower part of the second screening cylinder 123. A discharge port 127 is respectively provided on the lower inner end side of the screening channel 126 and the lower inner end side of the second screening cylinder 123. The discharge port of the second screening cylinder 123 corresponds to the lower end of the arc-shaped receiving plate 1210. The drive motor 125 is fixedly mounted on the fixed bracket 11, and its output shaft is connected to the rotating shaft 124 via a belt. A feed inlet 128 is fixedly arranged on the upper part of the fixed cylinder 121, corresponding to the position of the screening channel 126 between the fixed cylinder 121 and the first screening cylinder 122.

[0052] Front and rear baffles 129 are provided on both sides of the upper part of each screening channel 126. The front and rear baffles 129 are installed on the inner wall of the fixed cylinder 121 and the outer wall of the first screening cylinder 122 along the circumferential direction. Their function is to prevent the screened material from being directly carried to the lower area of ​​the screening channel 126 by the centrifugal force of the rotation of the first screening cylinder 122 or the second screening cylinder 123. This forces the material to slowly fall into the lower part of the screening channel 126 from the outer end of the fixed cylinder 121 and the first screening cylinder 122 and the outer end of the first screening cylinder 122 and the second screening cylinder 123 (i.e., the small end edge of the conical screen), thus ensuring the grading effect.

[0053] (II) Specific structure of the feeding device

[0054] The feeding device 13 includes a short fiber feeding cylinder 131, two medium fiber feeding cylinders 132, two long fiber feeding cylinders 133, and an automatic feeding and replenishing mechanism 134. The short fiber feeding cylinder 131 is located directly below the two sets of screening devices 12, and the two sets of screening devices 12 share one short fiber feeding cylinder 131. The two medium fiber feeding cylinders 132 are symmetrically arranged on the left and right sides of the short fiber feeding cylinder 131. The two long fiber feeding cylinders 133 are symmetrically arranged on the left and right sides of the short fiber feeding cylinder 131 and located outside the medium fiber feeding cylinders 132, that is, from left to right, they are: long fiber feeding cylinder 133, medium fiber feeding cylinder 132, short fiber feeding cylinder 131, medium fiber feeding cylinder 132, and long fiber feeding cylinder 133.

[0055] The upper end of the short fiber feeding cylinder 131 corresponds to the outlet 127 of the second screening cylinder 123 of the left and right sets of screening devices 12, and is used to receive the shortest fibers discharged from inside the second screening cylinder 123. The upper ends of the two medium fiber feeding cylinders 132 correspond to the discharge ports of the screening channels 126 between the first screening cylinder 122 and the second screening cylinder 123 of the left and right sets of screening devices 12, respectively, and are used to receive medium-length fibers. The upper ends of the two long fiber feeding cylinders 133 correspond to the discharge ports of the screening channels 126 between the fixed cylinder 121 and the first screening cylinder 122 of the left and right sets of screening devices 12, respectively, and are used to receive the longest fibers. This material receiving layout from one side to the other places the medium and short fiber materials in the middle area and the long fiber materials on both sides, which facilitates the direct connection of the feeding cylinders to each layer of the forming device during subsequent layer forming. The forming material receiving device at this point can be a conveyor belt.

[0056] The short fiber feeding cylinder 131, medium fiber feeding cylinder 132, and long fiber feeding cylinder 133 all have square cross-sections. An automatic feeding and replenishing mechanism 134 is installed on the short fiber feeding cylinder 131, medium fiber feeding cylinder 132, and long fiber feeding cylinder 133.

[0057] (III) Specific structure of the automatic feeding and replenishing mechanism

[0058] like Figure 2 and Figure 4 As shown, the automatic feeding and replenishing mechanism 134 includes sliders 1341 that are respectively slidably disposed on the front and rear side walls of the short fiber feeding cylinder 131, the medium fiber feeding cylinder 132, and the long fiber feeding cylinder 133. Feeding rollers 1342 are rotatably mounted between the sliders 1341 via bearings. The surface of the feeding rollers 1342 has toothed grooves or feed channels to facilitate forced and stable feeding. A feeding motor (not shown) is mounted on the sliders 1341 to drive the feeding rollers 1342 to rotate.

[0059] The outer ends (i.e., the front and rear ends) of the roller shafts of the feeding rollers 1342 of the medium fiber feeding cylinder 132 and the long fiber feeding cylinder 133 are located in the first long groove 1345 of the first crank 1344, and can slide along the first long groove 1345. The outer ends of the roller shafts of the feeding rollers 1342 of the short fiber feeding cylinder 131 are located in the second long groove 1347 of the second crank 1346.

[0060] A sliding block 1348 is hinged to the middle of the first crank 1344. The sliding block 1348 is slidably mounted on a vertical slide rail between the medium fiber feed cylinder 132 and the long fiber feed cylinder 133. Fixing blocks 1349 are respectively installed between the medium fiber feed cylinder 132 and the long fiber feed cylinder 133, above and below the sliding block 1348. Springs 13410 (one at the top and one at the bottom) are sleeved between the sliding block 1348 and the fixing blocks 1349.

[0061] One end of the second crank 1346 away from the feeding roller 1342 of the short fiber feeding cylinder 131 is hinged to the middle of the first crank 1344, and the middle of the second crank 1346 is hinged to the fixed fulcrum between the short fiber feeding cylinder 131 and the medium fiber feeding cylinder 132.

[0062] Each short fiber feeding cylinder 131, medium fiber feeding cylinder 132, and long fiber feeding cylinder 133 has a vertically fixed push rod 1341 on its corresponding slider 1341. A U-shaped push plate 13412 is fixedly installed on the upper side of the push rod 13411. A replenishment switch mechanism 135 is respectively installed on the outer wall of the short fiber feeding cylinder 131, medium fiber feeding cylinder 132, and long fiber feeding cylinder 133 at the position corresponding to the U-shaped push plate 13412. The replenishment switch mechanism 135 is connected to the external replenishment bin.

[0063] (iv) Specific structure of the feeding switch mechanism

[0064] like Figure 5 and Figure 6 As shown, the feeding switch mechanism 135 includes a feeding channel 1351. A rotating plate 1352 is rotatably mounted on the outer end of the feeding channel 1351 via a bracket. The rotating plate 1352 is located on both sides of the short fiber feeding cylinder 131, the medium fiber feeding cylinder 132, and the long fiber feeding cylinder 133. A switch plate 1354 is fixedly mounted between the two rotating plates 1352 via a fixing rod 1353. The switch plate 1354 is located inside the short fiber feeding cylinder 131, the medium fiber feeding cylinder 132, and the long fiber feeding cylinder 133. The fixing rod 1353 is slidably connected to a groove on the outer wall of the feeding channel 1351, allowing the switch plate 1354 to move with the fixing rod 1363.

[0065] The feeding channel 1351 is provided with a feeding port 1355. One side of the switch plate 1354 cooperates with the feeding port 1355 to open or close it. The feeding port 1355 communicates with the interior of the short fiber feeding cylinder 131, the medium fiber feeding cylinder 132, and the long fiber feeding cylinder 133. The middle part of the rotating plate 1352 is connected to one end of the tension spring 1356. The other end of the tension spring 1356 is fixedly mounted on the spring fixing block 1357 on the outer side of the outer end of the rotating plate 1352. The tension spring 1356 always pulls the outer end of the rotating plate 1352 outward. The switch plate 1354 is controlled by the fixing rod 1353 to seal the feeding port 1355. A stop shaft 1358 is fixedly mounted on the outer side of the inner end of the rotating plate 1352. The opening of the U-shaped push plate 13412 faces the stop shaft 1358 and cooperates with it.

[0066] (v) Sealing structure

[0067] The short fiber feeding cylinder 131, the medium fiber feeding cylinder 132, the long fiber feeding cylinder 133, and the feeding channel 1351 are respectively provided with telescopic cover plates 13413 fixed to the slider 1341 or the fixing block 1349. The cover plates 13413 are made of flexible rubber material or metal sheet structure and are used to always cover the opening of the chute when the slider 1341 or the upper and lower sliding blocks 1348 move, so as to prevent the fiber material from leaking from the chute during the unloading process.

[0068] III. Working Process and Principle of the Device

[0069] (I) Fiber grading process

[0070] like Figures 1 to 3 As shown, during operation, the fiber raw material, after pretreatment, is fed into the screening channel 126 between the fixed cylinder 121 and the first screening cylinder 122 through the feed inlet 128. The drive motor 125 drives the rotating shaft 124, the first screening cylinder 122, and the second screening cylinder 123 to rotate together at a speed of 80 rpm. Long fibers (diameter > 1.8 mm equivalent aperture) cannot pass through the first screening cylinder 122 and remain between the fixed cylinder 121 and the first screening cylinder 122; medium fibers (diameter 0.8-1.8 mm) pass through the first screening cylinder 122 and enter between the first screening cylinder 122 and the second screening cylinder 123; short fibers (diameter < 0.8 mm) pass through the second screening cylinder 123 and enter its interior. Under the forced guidance of the front and rear baffles 129, fibers of each grade do not fall directly into the discharge port 127, but instead descend along the screening channel 126, bypassing the edge of the small end of the conical cylinder before reaching the lower discharge port 127, thus ensuring grading accuracy.

[0071] After grading, long fibers fall from the discharge port 127 between the fixed cylinder 121 and the first screening cylinder 122 into the long fiber feeding cylinder 133 on the corresponding side; medium fibers fall from the discharge port 127 between the first screening cylinder 122 and the second screening cylinder 123 into the medium fiber feeding cylinder 132 on the corresponding side; and short fibers fall from the discharge port 127 at the bottom of the second screening cylinder 123 into the middle short fiber feeding cylinder 131.

[0072] (ii) Automatic feeding and replenishment process

[0073] As shown in the figure Figure 4 and Figure 6 As shown, during the feeding process, the feeding motor drives the feeding roller 1342 to rotate, and the fiber material is forced to be discharged from the bottom of the feeding cylinder to supply the subsequent layering forming process.

[0074] The working principle of the automatic feeding and replenishing mechanism 134 is as follows: When the feeding speed is greater than the feeding speed, the material level in the feeding cylinder drops, and the total weight of the fiber material in the feeding cylinder is reduced. Since the feeding during screening is quantitative and stable, it is unlikely that the short fiber feeding cylinder 131, medium fiber feeding cylinder 132, and long fiber feeding cylinder 133 will have insufficient material at the same time. Therefore, it is common for one feeding cylinder to have insufficient material speed, while the other feeding cylinders have sufficient material. Therefore, at this time, the middle part of the crank is hinged. Under the action of the crank, the slider 1341 corresponding to the feeding cylinder with insufficient material speed will rise, and the slider 1341 corresponding to the feeding cylinder with sufficient material speed will fall. The rising slider 1341 will drive the corresponding push rod 13411 to rise. For example, when the long fiber feeding cylinder 133 is short of material, but the medium fiber feeding cylinder 132 is full, the corresponding slider 1341 of the long fiber feeding cylinder 133 moves upward, causing the feeding roller 1342 to move upward. At the same time, the push rod 13411 moves upward with the slider 1341, causing the U-shaped push plate 13412 to move upward, triggering the feeding switch mechanism 13 to open and begin feeding material into the long fiber feeding cylinder 133. The principle is the same when other feeding cylinders are short of material. It should be noted that even if both the long fiber feeding cylinder 133 and the medium fiber feeding cylinder 132 are short, the short fiber feeding cylinder 131 will necessarily be full. In this case, the corresponding slider 1341 of the short fiber feeding cylinder 131 will lower, while the corresponding sliders 1341 of the fiber feeding cylinder 133 and the medium fiber feeding cylinder 132 will rise simultaneously, and the automatic feeding of the fiber feeding cylinder 133 and the medium fiber feeding cylinder 132 can still be controlled.

[0075] When the U-shaped push plate 13412 moves to a certain position, the lower part of the U-shaped push plate 13412 will push the stop shaft 1358 upward, causing the rotating plate 1352 to rotate against the force of the tension spring 1356. When the tension spring 1356 and the rotating plate 1352 are on the same straight line, the tension of the tension spring 1356 is at its maximum. When the tension spring 1356 passes the same straight line as the rotating plate 1352, the tension spring 1356 will pull the inner end of the rotating plate 1352 to rotate upward until the stop shaft 1358 is blocked by the upper part of the U-shaped push plate 13412. At the same time, the rotating plate 1352 drives the switch plate 1354 to move through the fixed rod 1353, opening the feeding port 1355. Since the tension spring 1356 is pulling the rotating plate 1352 at this time, the switch plate 1354 will remain open, and the fiber material in the external feeding bin will be automatically fed into the feeding cylinder under the action of gravity.

[0076] As the material level rises, the weight of the fiber material in the feed cylinder, which was previously insufficient, increases. Under gravity, slider 1341 moves downwards, and U-shaped push plate 13412 moves downwards. The upper side of U-shaped push plate 13412 pushes the stop shaft 1358 downwards. After the tension spring 1356 passes through a point aligned with rotating plate 1352, it pulls the inner end of rotating plate 1352 downwards, causing switch plate 1354 to close the feeding port 1355 and stop feeding. This achieves automatic feeding with a self-stabilizing material level, preventing material shortage in the feed cylinder.

[0077] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-strength kraft paperboard, characterized in that... This includes the following steps: S1: Fiber grading pretreatment: The raw materials are fed into a fiber pretreatment device for crushing and modification to obtain fiber material; S2: Multi-stage screening: The modified fiber material is fed into a composite fiber grading device (1) to classify the fiber into long fiber material, medium fiber material and short fiber material; S3: Layered forming: Long fiber material is conveyed to the bottom layer and the top layer, and medium fiber material and short fiber material are conveyed to the core layer, with the short fiber material located in the middle of the core layer; S4: Spray adhesive: During the lamination process, a composite reinforcing agent is sprayed onto the interlayer surface; S5: Press drying: The composite wet paper web is processed by a boot press and a hot air penetration drying device to obtain the finished product.

2. The method according to claim 1, characterized in that, The composite reinforcing agent in step S4 is a mixed emulsion of modified starch and nanofibers, wherein the solid content ratio of modified starch to nanofibers is 5:1 to 10:

1.

3. The method according to claim 1, characterized in that, The fiber material moving speed during the adhesive spraying process is 0.1-0.5 m / s, the spraying angle of the nozzle used for adhesive spraying is 60-90 degrees, and the spraying pressure is 1.5-3.0 MPa.

4. The apparatus for preparing high-strength kraft paperboard according to claim 1, characterized in that, include A composite fiber grading device (1) is used to perform step S2; A glue spraying device is used to perform step S4; A boot press device is used to perform the boot press in step S5; A hot air penetration drying device is used to perform hot air penetration drying in step S5.

5. The apparatus for preparing high-strength kraft paperboard according to claim 4, characterized in that, The composite fiber grading device (1) includes a fixed support (11), a screening device (12) and a feeding device (13). The screening device (12) is mounted on the fixed support (11), and the feeding device (13) is fixedly mounted on the fixed support (11) and located below the screening device (12). The screening device (12) is a conical screening device with two sets symmetrically arranged. The screening device (12) includes a fixed cylinder (121), a first screening cylinder (122), a second screening cylinder (123), a rotating shaft (124), and a drive motor (125). The fixed cylinder (121) is fixedly mounted on a fixed support (11). The rotating shaft (124) is rotatably mounted on the fixed support (11) and extends into the fixed cylinder (121). The first screening cylinder (122) is fixedly mounted on the rotating shaft (124) and located inside the fixed cylinder (121). The second screening cylinder (123) is fixedly mounted on the rotating shaft (124) and located inside the first screening cylinder (122). The fixed cylinder (121) and the first screening cylinder (122) are... Screening channels (126) are provided between the first screening cylinder (122) and the second screening cylinder (123). An arc-shaped receiving plate (1210) is inclinedly provided at the lower part of the second screening cylinder (123). A discharge port (127) is provided at the lower inner end of the screening channel (126) and the lower inner end of the second screening cylinder (123). The discharge port of the second screening cylinder (123) corresponds to the lower end of the arc-shaped receiving plate (1210). The drive motor (125) is fixedly mounted on the fixed bracket (11) and is connected to the rotating shaft (124). A feed inlet (128) is fixedly provided at the upper part of the fixed cylinder (121) and at the position of the screening channel (126) between the fixed cylinder (121) and the first screening cylinder (122).

6. The apparatus for preparing high-strength kraft paperboard according to claim 5, characterized in that, The upper sides of the screening channel (126) are provided with front and rear baffles (129) to prevent the screening material from being directly carried to the bottom of the screening channel (126) by the rotation of the first screening cylinder (122) or the second screening cylinder (123), and to force the screening material to enter the lower part of the screening channel (126) from between the outer end of the fixed cylinder (121) and the outer end of the first screening cylinder (122) and between the outer end of the first screening cylinder (122) and the second screening cylinder (123).

7. The apparatus for preparing high-strength kraft paperboard according to claim 5, characterized in that, The feeding device (13) includes a set of short fiber feeding cylinders (131), two sets of medium fiber feeding cylinders (132), two sets of long fiber feeding cylinders (133), and an automatic feeding and replenishing mechanism (134). The short fiber feeding cylinders (131) are located below the two sets of screening devices (12). The two sets of medium fiber feeding cylinders (132) are symmetrically arranged on both sides of the short fiber feeding cylinders (131). The two sets of long fiber feeding cylinders (133) are symmetrically arranged on both sides of the short fiber feeding cylinders (131) and located outside the medium fiber feeding cylinders (132). The upper end of the short fiber feeding cylinders (131) corresponds to the discharge port (127) of the second screening cylinder (123) of the two sets of screening devices (12). The upper end of the medium fiber feeding cylinder (132) corresponds to the feeding port of the screening channel (126) between the first screening cylinder (122) and the second screening cylinder (123) of the two sets of screening devices (12). The upper ends of the two sets of long fiber feeding cylinders (133) correspond to the feeding ports of the screening channel (126) between the fixed cylinder (121) and the first screening cylinder (122) of the two sets of screening devices (12). The cross-section of the short fiber feeding cylinder (131), the medium fiber feeding cylinder (132), and the long fiber feeding cylinder (133) is square. The automatic feeding and replenishing mechanism (134) is set on the short fiber feeding cylinder (131), the medium fiber feeding cylinder (132), and the long fiber feeding cylinder (133).

8. The apparatus for preparing high-strength kraft paperboard according to claim 7, characterized in that, The automatic feeding and replenishing mechanism (134) includes sliders (1341) that are respectively slidably disposed on both sides of the short fiber feeding cylinder (131), the medium fiber feeding cylinder (132), and the long fiber feeding cylinder (133). A feeding roller (1342) is rotatably disposed between the sliders (1341). A feeding motor that drives the feeding roller (1342) to rotate is disposed on the sliders (1341). The outer end of the roller shaft of the feeding roller (1342) of the medium fiber feeding cylinder (132) and the long fiber feeding cylinder (133) is disposed on the first Within the first long groove (1345) of the crank (1344), the outer end of the roller shaft of the feed roller (1342) of the short fiber feed cylinder (131) is disposed within the second long groove (1347) of the second crank (1346). A sliding block (1348) is hinged to the middle of the first crank (1344). The sliding block (1348) slides vertically between the medium fiber feed cylinder (132) and the long fiber feed cylinder (133). Fixed blocks (1349) are respectively provided above and below the upper and lower sliding blocks (1348). A spring (13410) is provided between the upper and lower sliding blocks (1348) and the fixed blocks (1349). One end of the second crank (1346) away from the feeding roller (1342) of the short fiber feeding cylinder (131) is hinged to the middle of the first crank (1344). The middle of the second crank (1346) is hinged between the short fiber feeding cylinder (131) and the medium fiber feeding cylinder (132). The short fiber feeding cylinder (1344) 1) A push rod (13411) is vertically fixed on the slider (1341) corresponding to the medium fiber feed cylinder (132) and the long fiber feed cylinder (133). A U-shaped push plate (13412) is provided on the upper side of the push rod (13411). A feeding switch mechanism (135) is provided on the outer side of the short fiber feed cylinder (131), the medium fiber feed cylinder (132), and the long fiber feed cylinder (133) and at the position corresponding to the U-shaped push plate (13412). The feeding switch mechanism (135) is connected to the external feeding bin.

9. The apparatus for preparing high-strength kraft paperboard according to claim 8, characterized in that, The feeding switch mechanism (135) includes a feeding channel (1351). A rotating plate (1352) is rotatably mounted on the outside of the feeding channel (1351). The rotating plate (1352) is located on both sides of the short fiber feeding cylinder (131), the medium fiber feeding cylinder (132), and the long fiber feeding cylinder (133). A switch plate (1354) is fixedly mounted between the rotating plates (1352) by a fixing rod (1353). The switch plate (1354) is located inside the short fiber feeding cylinder (131), the medium fiber feeding cylinder (132), and the long fiber feeding cylinder (133). The fixing rod (1353) is slidably connected to the outer wall of the feeding channel (1351). The feeding channel (1351) is provided with a feeding port (1355). The switch plate (1354) cooperates with the feeding port (1355). The feeding port (1355) communicates with the interior of the short fiber feeding cylinder (131), the medium fiber feeding cylinder (132), and the long fiber feeding cylinder (133). The middle part of the rotating plate (1352) is connected to one end of the tension spring (1356). The other end of the tension spring (1356) is fixedly installed on the spring fixing block (1357) outside the outer end of the rotating plate (1352). A stop shaft (1358) is fixedly installed on the outer side of the inner end of the rotating plate (1352). The U-shaped push plate (13412) cooperates with the stop shaft (1358).

10. The apparatus for preparing high-strength kraft paperboard according to claim 8, characterized in that, The short fiber feeding cylinder (131), medium fiber feeding cylinder (132), long fiber feeding cylinder (133) and the feeding channel (1351) are respectively provided with a cover plate (13413) fixed on the slider (1341) or the fixing block (1349) to prevent the fiber material from leaking during the unloading process.

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