Energy-saving preparation process of non-woven fabric capable of being dispersed

Abstract

The invention discloses an energy-saving preparation process of a non-woven fabric capable of being dispersed, which comprises the steps of nano filament reinforced slurry preparation, wet forming and spunlace reinforcement, primary drying and secondary steam recovery, secondary steam fluffy treatment, secondary drying and secondary steam recovery. Secondary steam generated in the primary drying process and the secondary drying process is distributed, the first part is directly used for carrying out fluffy treatment on a primarily-dried fiber web, the fiber web is expanded through micropore injection under specific conditions, and the bulkiness of a product is improved; and the second part is converted into a thermal medium with the temperature of 70-85 DEG C through heat exchange, and the thermal medium is reused for heating and heat preservation of the front-section enzymolysis fibrillation reaction, the process realizes gradient utilization of secondary steam, waste heat recovery and product physical modification are combined, the production energy consumption is remarkably reduced, and the production cost is reduced. The technical problem that the strength, the fluffiness and the softness of the high-basis-weight dispersible non-woven fabric are difficult to consider at the same time is effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of flushable material. BACKGROUND

[0002] Flushable nonwoven fabric, as an environmentally friendly material that can quickly disperse in water and avoid sewer blockage, has been widely used in the fields of wet wipes, sanitary products and medical dressings in recent years.

[0003] Currently, there are the following problems in the preparation process of flushable nonwoven fabric: First, two contradictory performance requirements must be met at the same time: on the one hand, the product needs to have sufficient dry and wet strength to withstand high-speed processing on the production line and mechanical stress during consumer use; on the other hand, the product must be able to quickly disintegrate and disperse under the impact of toilet water flow after use to prevent pipe blockage. In addition, with the improvement of living standards, people also hope that flushable nonwoven fabric has excellent surface touch and softness.

[0004] Second, energy consumption and waste heat utilization: the production process of flushable nonwoven fabric, especially the drying link, is a high-energy-consumption process. The entire drying system usually includes multiple drying cylinders through which steam is introduced, and the wet fiber web is dried to form a dry fiber web. Currently, in order to improve steam utilization efficiency, the commonly used method is to return the used steam and condensed water to the boiler. In further improvement schemes, as shown in Chinese patent CN117073356A, by returning the secondary steam to the drying cylinders in the front section, the heat utilization efficiency can be improved to a certain extent. However, in-depth research has found that the existing drying system still has obvious deficiencies in energy utilization and product quality improvement: the existing technology mainly limits the utilization of secondary steam to heat recovery (such as reuse to drying cylinders or boiler), and does not develop a technical approach to actively modify the fiber structure using the kinetic energy and latent heat of secondary steam. This makes the potential value of a large amount of low-grade heat energy not fully tapped.

[0005] In summary, the existing technology faces the triple challenge of simultaneously achieving high strength, high dispersibility and high softness on high-basis-weight nonwoven fabric, and the production process has high energy consumption, and the waste heat is not efficiently and highly valued. Therefore, there is an urgent need in the art for an innovative technical solution that can break through the existing technical bottlenecks and achieve dual improvement of product performance and production process energy efficiency without significantly increasing costs and introducing environmental problems. SUMMARY

[0006] The present application proposes an energy-saving preparation process for flushable nonwoven fabric, comprising the following steps: S10: Nanofibril reinforced pulp preparation: Bamboo pulp is fibrillated by enzymatic treatment to generate enzymatic bamboo pulp containing nanofibrils, and the enzymatic bamboo pulp is mixed with wood pulp and hot melt adhesive fibers to form a fiber mixed slurry; S20: Wet forming and water jet reinforcement: the fiber mixed slurry is formed into a wet fiber web by wet laying, and is reinforced by a water jet process including a micro jet step; S30: Primary drying and secondary steam recovery: the wet fiber web after water jet reinforcement is subjected to primary drying to form a primary dried fiber web, and secondary steam generated in this process is recovered; S40: Secondary steam fluffing treatment: the secondary steam recovered in steps S30 and S50 is applied to the primary dried fiber web by a micro-porous jet device to fluff the fibers; S50: Secondary drying and secondary steam recovery: the fluffed web is subjected to secondary drying to obtain a finished product, and secondary steam generated in the secondary drying is recovered; Meanwhile, the method further comprises a steam distribution and circulation step: The secondary steam recovered in steps S30 and S50 is distributed, a first part of which is sent to step S40 for the fluffing treatment, the first part of the secondary steam being at a temperature of 100-105°C, and a second part of which is converted into a hot medium at 70-85°C by heat exchange and is reused in the heating or heat preservation process in the enzymatic fibrillation treatment in step S10.

[0007] After the secondary steam is recovered in steps S30 and S50, the secondary steam is subjected to steam-water separation to form condensed water, and the condensed water is heated by the second part of the secondary steam to form a hot medium at 70-85°C.

[0008] The hot medium comprises a part formed by heating the condensed water and a part formed by cooling the second part of the secondary steam, and the second part of the secondary steam is heated by the heat exchanger to cool the condensed water.

[0009] The temperature of the condensed water entering the heat exchanger is greater than or equal to 40°C.

[0010] In step S40, the secondary steam is sprayed onto the surface of the primary dried fiber web by a micro-porous jet device, the angle between the spraying direction and the surface of the primary dried fiber web is 75-105°, the spraying pressure is 200-500 Pa, and the moisture content of the secondary steam is 30-40%.

[0011] The average length of the fibers of the bamboo pulp is in the range of 1.2-2.2 mm, and the average width is in the range of 10-20 μm.

[0012] In the fiber mixed pulp, the proportions of the enzymatic bamboo pulp, the wood pulp and the hot melt adhesive fiber are: enzymatic bamboo pulp 40-60%; wood pulp 20-30%; and hot melt adhesive fiber 5-8%, and the content of nanofibril in the mixed pulp is 5-10% of the total weight of the dry fiber.

[0013] In the micro-piercing step in step S20, a micro-piercing assembly is used, which includes a micro-porous water needle plate with micro-pores of 0.08-0.1 mm, and the water pressure is 100-130 Bar.

[0014] In the enzymatic fibrillation treatment in step S10, the temperature is 55-60℃, and the time is 30-40 minutes.

[0015] The finished product has a basis weight of greater than or equal to 90 gsm and a thickness of greater than or equal to 0.75 mm.

[0016] Beneficial effects: The application discloses an energy-saving preparation process of a flushable non-woven fabric, which comprises the steps of nanofibril reinforced pulp preparation, wet forming and water jet reinforcement, primary drying and secondary steam recovery, secondary steam lofting treatment, secondary drying and secondary steam recovery. The process introduces a steam distribution and circulation step, which distributes the secondary steam generated in the primary and secondary drying processes. A first part of the secondary steam is directly used for lofting treatment of the primary dry fiber web, and the fiber network is expanded under specific conditions through micro-porous injection, so that the product thickness is improved. A second part of the secondary steam is converted into a hot medium at 70-85℃ through heat exchange, and is used for heating and heat preservation of the enzymatic fibrillation reaction in the previous step. The process realizes the cascade utilization of the secondary steam, combines waste heat recovery and product physical modification, significantly reduces the production energy consumption, and effectively solves the technical problem that the strength and lofting softness of the high-basis-weight flushable non-woven fabric are difficult to be balanced. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Schematic diagram of the device applying the energy-saving preparation process of the flushable non-woven fabric.

[0018] Explanation of the illustrated elements: Pulp preparation unit 10; enzymatic tank 101; mixed pulp tank 102; pre-coating tank 103; papermaking unit 20; water jet unit 30; first drying unit 40; lofting treatment unit 50; second drying unit 60; steam distribution and circulation unit 70; main steam pipe 71; first recovered steam pipe 721; second recovered steam pipe 722; first steam-water separator 731; second steam-water separator 732; third steam-water separator 733; heat exchanger 74; return collection pipe 740; hot medium conveying pipe 741; lofting treatment main pipe 750; first conveying pipe 751; second conveying pipe 752; third conveying pipe 753; and fourth conveying pipe 754. DETAILED DESCRIPTION

[0019] The embodiment of the present application provides a kind of energy-saving preparation process of flushable non-woven fabric, comprising the following steps: S10: nanofibril reinforced pulp preparation: bamboo pulp is treated by enzymolysis fibrillation to generate nanofibril, and the nanofibril is mixed with wood pulp and hot melt adhesive fiber to form a fiber mixed slurry; S20: wet forming and water jet reinforcement: the fiber mixed slurry is formed into a wet fiber web by wet laying, and is reinforced by a water jet process including a micro-needling step; S30: primary drying and secondary steam recovery: the wet fiber web after water jet reinforcement is subjected to primary drying to form a primary dried fiber web, and secondary steam generated in this process is recovered; S40: secondary steam lofting treatment: the secondary steam recovered in steps S30 and S50 is applied to the primary dried fiber web by a micro-porous jet device to cause fiber lofting; S50: secondary drying and secondary steam recovery: the lofted web is subjected to secondary drying to obtain a finished product, and secondary steam generated in the secondary drying is recovered.

[0020] Meanwhile, the method further comprises a steam distribution and circulation step: The secondary steam recovered in step S30 and step S50 is distributed, a first portion thereof is delivered to step S40 for the lofting treatment, the first portion of secondary steam has a temperature of 100-105°C, and a second portion thereof is converted into a hot medium at 70-85°C by heat exchange and is reused for heating or heat preservation in the enzymolysis fibrillation treatment in step S10.

[0021] For ease of understanding, please refer to the device of the energy-saving preparation process of flushable non-woven fabric in Figure 1 , and the preparation process is described in detail in combination with the device.

[0022] The device comprises a pulp preparation unit 10, a papermaking unit 20, a water jet unit 30, a first drying unit 40, a lofting treatment unit 50, a second drying unit 60, and a steam distribution and circulation unit 70.

[0023] The pulp preparation unit 10 comprises an enzymolysis tank 101, which is used for enzymolysis fibrillation treatment of bamboo pulp. In this embodiment, the enzymolysis tank 101 is a sandwich tank, which comprises an inner tank for containing bamboo pulp and a sandwich layer arranged outside the inner tank for heating and heat preservation of the inner tank. A hot medium is introduced into the sandwich layer to heat and heat preserve the inner tank. It can be understood that the hot medium can be steam, water or hot air, more specifically, a part of the secondary steam recovered in steps S30 and S50 is converted into a hot medium by heat exchange.

[0024] Specifically, the bamboo pulp can be bleached or unbleached sulfate bamboo pulp board, and the average length of the fibers of the bamboo pulp ranges from 1.2 to 2.2 mm, and the average width ranges from 10 to 20 μm. Fibers within the above ranges can be easily fibrillated during enzymatic hydrolysis, and nanoscale filaments can be peeled off. The average degree of polymerization (DP) of the bamboo pulp is 600-1200, so as to avoid insufficient fiber strength caused by too low degree of polymerization or reduced enzyme accessibility and enzyme efficiency caused by too high degree of polymerization.

[0025] Further, the content of α-cellulose in the bamboo pulp is ≥ 78%, so as to reduce the interference of impurities such as hemicellulose and lignin on the enzymatic hydrolysis process and improve the yield of nanoscale filaments.

[0026] Further, the ash content in the bamboo pulp is ≤ 0.15%, so as to reduce the inhibitory effect of inorganic matter on enzyme activity.

[0027] In the present embodiment, the heat-resistant cellulase is a complex enzyme preparation with high thermal stability, mainly containing endoglucanase and cellobiohydrolase. The endoglucanase is used to randomly cut the amorphous region of the cellulose chain to initiate fiber "fibrillation" and form nanofibers. The cellobiohydrolase is used to synergistically hydrolyze the cellulose molecules. The main meaning refers to the content of endoglucanase and cellobiohydrolase in the complex enzyme preparation being greater than 80%, and the content of endoglucanase in the complex enzyme preparation being greater than or equal to 50%.

[0028] Further, the activity of the heat-resistant cellulase is ≥ 100 FPU / g, the activity refers to enzyme activity, and the enzyme activity refers to the amount of enzyme required to release 1 μmol of glucose per minute from filter paper substrate under the conditions of pH 5.5 and temperature 60℃.

[0029] Further, the optimal temperature of the heat-resistant cellulase is 60-75℃, and the optimal pH is 4.5-6.5. Preferably, the thermal stability of the heat-resistant cellulase should reach more than 80% of the enzyme activity after being treated below 70℃ for 1 hour, so as to ensure the stability of the enzyme activity under the conditions of pH 5.5-6.0 and temperature 55-60℃ for 30-40 minutes, and to ensure that subsequent high-temperature inactivation can prevent excessive degradation. In a specific embodiment, the heat-resistant cellulase is Novozymes Cellic® CTec3 cellulase.

[0030] Through the above processing, the enzymatic bamboo pulp is obtained, and a large amount of nanofibrils peeled from the fiber surface is contained in a suspension of the enzymatic bamboo pulp, the nanofibrils have a diameter distribution range of 30-60 nm and a length distribution range of 0.5-2 μm. It can be understood that these nanofibrils will be embedded and bridged to the main fibers as key reinforcing units in the subsequent hydroentanglement and steam bulk processes, thereby significantly improving the material strength without sacrificing dispersibility.

[0031] A mixing tank 102 is further arranged downstream of the enzymatic tank 101 to mix the nanofibrils with the wood pulp and the hot melt adhesive fibers to form a fiber mixed slurry, and a headbox 103 is arranged downstream of the mixing tank 102 to provide the fiber mixed slurry to a papermaking unit 20, which includes an inclined wire former, and the inclined wire former generally includes a headbox and a forming wire having an inclined section, and the headbox is configured to accommodate the mixed slurry to pass through the inclined section of the forming wire to form a wet fiber web.

[0032] Specifically, in the fiber mixed slurry, the enzymatic bamboo pulp, the wood pulp and the hot melt adhesive fibers are mixed in a ratio of 40-60% of the enzymatic bamboo pulp, 20-30% of the wood pulp and 5-8% of the hot melt adhesive fibers, and the fiber concentration in the headbox 103 is 0.1-0.5%, and preferably, the content of the nanofibrils in the mixed slurry is 5-10% of the total weight of the dry fibers.

[0033] In addition, the wood pulp can be bleached coniferous wood kraft pulp, and the average fiber length of the wood pulp is greater than or equal to 2.2 mm, and more preferably, the average fiber length of the wood pulp is 2.5-3.5 mm. It can be understood that the longer coniferous fibers form a more continuous and stable fiber skeleton network during the hydroentanglement process, which carries the shorter bamboo fibers, and preferably, the degree of polymerization of the wood pulp is 1200-2000 to ensure the strength by the higher degree of polymerization.

[0034] In addition, the addition amount of the wood pulp is controlled to be 20-30% of the total weight of the dry fibers, and when it is less than 20%, it has a negative effect on the strength, and when it is greater than 30%, it affects the dispersion speed due to excessive interweaving of long fibers.

[0035] In addition, the hot melt adhesive fibers are used to provide hot melt adhesive points during the drying process to ensure the dry strength of the material, and the hot melt adhesive fibers are preferably ES fibers with a core-sheath structure, and specifically, the core layer is a high-melting-point polymer, which can be polyester PET or polypropylene PP, and the sheath layer is a low-melting-point polymer, which can be polyethylene PE or modified copolyester, and preferably, the melting point of the sheath layer is 110-130℃ to match the hot air drying temperature to form a fusion point.

[0036] In addition, the hot melt adhesive fiber has a fineness of 1.5-3.0 dtex, so as to ensure sufficient adhesive points and avoid the influence of thick fibers on the softness and dispersibility of the material, and has a length of 4-8 mm, so as to ensure good dispersibility of the wet fiber web and avoid flocculation.

[0037] The water jet unit 30 is configured to water jet reinforce the wet fiber web, and comprises a plurality of water jet assemblies arranged in sequence along the running direction of the wet fiber web, specifically, the plurality of water jet assemblies comprise a pre-jet assembly, a main-jet assembly and a micro-jet assembly.

[0038] The pre-jet assembly is used for preliminary compaction and entanglement of the wet fiber web, wherein the pre-jet assembly comprises 1-2 water jet heads, and the water jet pressure is 20-30 Bar, and the water jet is sprayed from top to bottom above the wet fiber web during water jet.

[0039] The main-jet assembly is used for generating intense displacement, insertion, bending and entanglement of the fibers, so as to form a main network structure, wherein the main-jet assembly comprises 3-5 water jet heads, and the water jet pressure is 50-80 Bar, and the water jet heads of the main-jet assembly can be arranged on the upper and lower sides of the wet fiber web, so as to spray from the upper and lower sides of the wet fiber web at the same time.

[0040] The micro-jet assembly is used for entanglement and arrangement of the surface and interior of the fiber web by means of ultra-high pressure and extremely fine water needles, so as to micro-adjust and surface finish the wet fiber web by means of micro-jet, and the high-pressure fine water needles of the micro-jet treatment not only play a role in entangling the fibers, but more importantly, force the nanofibrils generated in the S10 step to penetrate into the interior of the fiber network and make them firmly physically entangled and hydrogen-bonded with the skeleton fibers such as wood pulp, so as to provide strength guarantee for subsequent steam lofting and avoid network structure damage caused by the lofting process.

[0041] In the embodiment, the micro-jet assembly comprises a micro-hole water needle plate, the micro-hole water needle plate comprises micro-holes with a diameter of 0.08-0.1 mm, and the water pressure during micro-jet is 100-130 Bar, so that the high-energy fine water needles in the micro-jet process can penetrate deep into the fiber web, fix the fibers that have not been completely entangled after the main-jet, especially the fibers in the middle, firmly combine the nanofibrils generated in the S10 step on the main fiber skeleton, so as to realize the reinforcing effect of the nanofibrils, in addition, the micro-jet can eliminate the fiber fluff generated on the surface of the fiber web in the pre-jet and main-jet steps, so as to make the material surface smooth and flat, thereby improving the hand feeling and avoiding the phenomenon of fluff and powder falling, and the micro-jet can optimize the structure, i.e. optimize the lofting structure and pore structure of the fiber network, so as to balance the strength, softness and dispersibility of the material.

[0042] The first drying unit 40 is configured to dry the hydro-entangled wet web to form a primary dry web. In the present embodiment, the first drying unit 40 comprises a plurality of first drying cylinders arranged in series. It is appreciated that the first drying cylinders can be arranged in any form, such as staggered arrangement or horizontal linear arrangement. The wet web to be dried is sequentially passed through the drying cylinders to be dried.

[0043] The first drying cylinder comprises a steam inlet and a steam outlet. The steam inlet is connected to the main steam pipe 71 for supplying steam into the drying cylinder. The steam outlet is configured to discharge the steam in the drying cylinder. The steam supplied through the main steam pipe 71 is referred to as fresh steam. The steam discharged from the first drying unit 40 through the steam outlet is referred to as secondary steam.

[0044] The lofting unit 50 is configured to perform a lofting treatment on the primary dry web by the secondary steam. The lofting unit 50 comprises a micro-porous jetting device. The micro-porous jetting device comprises a jetting plate provided with jetting holes. The secondary steam is jetted to the surface of the web through the jetting holes. The jetting direction is at an angle of 75° to 105° with respect to the surface of the web. The jetting pressure is 200 to 500 Pa. The jetting direction and pressure are configured to enable the secondary steam to be jetted to the surface of the primary dry web at a near vertical angle and to penetrate the primary dry web. The jetting pressure is configured to prevent the primary dry web from being damaged. It is appreciated that the lofting treatment is performed by the jetting of the secondary steam.

[0045] Further, the temperature of the secondary steam is controlled at 100 to 105 °C and the moisture content is controlled at 30 to 40% during the lofting treatment. It is found in the research that the high-temperature steam can instantaneously heat the fibers, especially the amorphous cellulose molecular chain segments. The fiber stiffness is reduced and becomes flexible and deformable. The latent heat released by the condensation of the steam and the water further penetrate into the fibers to act as a plasticizer. The glass transition temperature of the fibers is reduced, which makes the fibers more likely to be displaced under external force. The momentum of the steam flow impacting the fiber network at the above pressure and angle provides energy for the fibers to overcome the hydrogen bonding between the fibers, which separates the fibers and expands the network structure. The process also acts on the nanofibrils to enhance their activity in the hot and humid environment. The nanofibrils have the opportunity to find new and more optimized bonding sites in the lofted network to form a more stable and lofted reinforced structure.

[0046] The second drying unit 60 is arranged downstream of the bulk treatment unit 50, and is used to perform secondary drying on the bulk-treated primary dry web. It can be understood that, due to the surface bulk treatment, the drying process inside the primary dry web can be accelerated during the secondary drying, especially for high-basis-weight and high-thickness flushable nonwoven fabrics, and more specifically, for 90 gsm and 0.75 mm or more flushable nonwoven fabrics, the treatment effect is better.

[0047] The arrangement of the second drying unit 60 can be the same as or different from the first drying unit 40. However, the second drying unit 60 also includes a plurality of second drying cylinders arranged in a certain form. The second drying cylinders can also be arranged in a staggered arrangement or a horizontal linear arrangement. The first drying cylinders also include steam inlets and exhaust outlets. The steam inlets are in communication with the main steam pipe 71, and are used to introduce steam into the second drying cylinders. The exhaust outlets are used to exhaust the steam in the drying cylinders to form secondary steam.

[0048] In the present application, a steam distribution and circulation unit 70 is also included, which is used to deliver fresh steam to the first drying unit 40 and the second drying unit 60, recover secondary steam, and distribute and reuse the secondary steam.

[0049] The steam distribution and circulation unit 70 includes a main steam pipe 71 and a steam recovery pipe. The main steam pipe 71 is configured to deliver fresh steam to the first drying unit 40 and the second drying unit 60. The steam recovery pipe includes a first recovery steam pipe 721 connected to the exhaust outlet of the first drying cylinder and a second recovery steam pipe 722 connected to the exhaust outlet of the second drying cylinder.

[0050] The steam distribution and circulation unit 70 also includes a bulk treatment main pipe 750 connected to the micro-porous jetting device and a recovery collection pipe connected to a heat exchanger 74. The bulk treatment main pipe 750 is configured to jet a first part of the secondary steam to the primary dry web through the micro-porous jetting device. The recovery collection pipe 740 is configured to deliver a second part of the secondary steam to the heat exchanger 74, and form a heat exchange medium at 70-85°C after being treated by the heat exchanger 74.

[0051] In the present embodiment, the steam distribution and circulation unit 70 further comprises a first steam-water separator 731 connected with the first recovered steam pipe 721 and configured to separate the secondary steam formed by the first drying unit 40, and a second steam-water separator 732 connected with the second recovered steam pipe 722 and configured to separate the secondary steam formed by the second drying unit 60, and further comprising a first conveying pipe 751 between the first steam-water separator 731 and the fluffing treatment main pipe 750 and a second conveying pipe 752 between the second steam-water separator 732 and the fluffing treatment main pipe 750, so as to convey the first part of the secondary steam formed by the first drying unit 40 and the second drying unit 60 to the fluffing treatment main pipe 750 respectively.

[0052] In addition, the third conveying pipe 753 is arranged between the first steam-water separator 731 and the return collection pipe 740, and the fourth conveying pipe 754 is arranged between the second steam-water separator 732 and the return collection pipe 740, so as to convey the second part of the secondary steam formed by the first drying unit 40 and the second drying unit 60 to the return collection pipe 740 respectively.

[0053] It can be understood that the steam distribution and circulation unit 70 further comprises a control system configured to adjust the amount of secondary steam conveyed by the first conveying pipe 751 and the second conveying pipe 752 to the fluffing treatment main pipe 750, so as to keep the temperature, moisture content and pressure of the secondary steam sprayed to the primary drying web stable, and to adjust the amount of secondary steam conveyed by the third conveying pipe 753 and the fourth conveying pipe 754 to the return collection pipe 740, so as to form the heat medium of a predetermined temperature in the heat exchanger 74.

[0054] Further, the control system is configured to dynamically adjust the amount of secondary steam conveyed by the first conveying pipe 751 and the second conveying pipe 752, so as to ensure that the first part of the secondary steam conveyed to the fluffing treatment unit 50 has stable temperature and dryness, and the second part of the secondary steam is conveyed to the heat exchanger 74 as a second part of the secondary steam to prepare the heat medium required in the enzymatic hydrolysis section. It can be understood that when the second part of the secondary steam is insufficient, fresh steam can be introduced for adjustment.

[0055] It can be understood that the heat exchanger 74 is configured to accept the second part of the secondary steam to form the heat medium. It can be understood that the temperature of the secondary steam is higher than 70-85℃, so that it is also a heat medium after being cooled to 70-85℃ after heating the heat medium entering the heat exchanger 74. Meanwhile, the heat medium entering the heat exchanger 74 also forms a heat medium for heating or keeping warm the enzymatic hydrolysis tank 101 after being heated by the secondary steam.

[0056] Further, the heat medium entering the heat exchanger 74 can be the condensed water formed by the first steam-water separator 731 and the second steam-water separator 732, preferably, when the condensed water temperature is greater than or equal to 40℃, the condensed water is transported to the heat exchanger 74 as the heat medium to quickly increase the temperature of the heat medium and reduce the demand for secondary steam, and in the embodiment, a heat medium conveying pipe 741 is arranged between the heat exchanger 74 and the enzymolysis tank 101 to convey the heat medium to the interlayer of the enzymolysis tank 101.

[0057] Further, the downstream of the second steam-water separator 732 is further provided with a third steam-water separator 733, the third steam-water separator 733 collects the condensed water of the first steam-water separator 731 and the second steam-water separator 732 and further separates the secondary steam and the condensed water, the secondary steam separated by the third steam-water separator 733 is collected to the fluffing treatment main pipe 750 or the return collecting pipe 740, and the condensed water is transported to the heat exchanger 74 as the heat medium.

[0058] The steam distribution and circulation unit 70 forms a water-steam-water energy closed loop through the steam distribution and circulation process, that is, on one hand, the 100-105℃ secondary steam generated in the drying process is directly used for fluffing, and the intermediate link of converting this part of heat energy into mechanical energy or electrical energy is omitted, the energy utilization efficiency is the highest, and on the other hand, part of the secondary steam is degraded into 70-85℃ heat medium and used for heating the front end 55-60℃ enzymolysis reaction, avoiding the use of fresh steam to maintain the low-temperature reaction and avoiding the waste caused by using high-temperature waste heat in low-temperature occasions, in addition, the whole heat recovery process is completed in the system, reducing the loss of heat in the transmission and conversion process, and further improving the heat recovery efficiency through steam-water separation and heat preservation pipes, and the like. It is found in practice that the integrated system can reduce the overall production energy consumption by 5-8%, in addition, through the processes of primary drying, fluffing and secondary drying, the bulkiness can be increased by 15-25% while the dry / wet strength can still be maintained at a high level, solving the contradiction between high bulkiness and high strength, and especially for the products with a basis weight of more than 90gsm, the flushable performance can still reach 99%.

[0059] The above only describes the embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent process transformation using the content of the specification and drawings of the present application, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A process for preparing energy-saving washable nonwoven fabric, characterized in that, Includes the following steps: S10: Preparation of nanofiber reinforced pulp: Bamboo pulp is enzymatically hydrolyzed to produce enzymatically hydrolyzed bamboo pulp containing nanofibers through enzymatic hydrolysis and fibrillation treatment, and the enzymatically hydrolyzed bamboo pulp is mixed with wood pulp and hot melt adhesive fibers to form a fiber mixed pulp. S20: Wet forming and hydroentangling reinforcement: The fiber mixture slurry is formed into a wet fiber web by wet forming, and reinforced by a hydroentangling process including a micro-needling step; S30: Primary drying and secondary steam recovery: The wet fiber web after hydroentanglement reinforcement is dried in one step to form a pre-dried fiber web, and the secondary steam generated in this process is recovered. S40: Secondary steam fluffing treatment: The secondary steam recovered in steps S30 and S50 is applied to the pre-dried fiber web through a micro-hole injection device to fluff the fibers. S50: Secondary drying and secondary steam recovery: The fluffed sheets are dried a second time to obtain the finished product, and the secondary steam generated during the secondary drying is recovered. The method also includes steam distribution and circulation steps: The secondary steam recovered in steps S30 and S50 is distributed, and the first part is sent to step S40 for the fluffing treatment. The temperature of the first part of the secondary steam is 100-105°C. At the same time, the second part is converted into a heat medium of 70-85°C through heat exchange and reused for heating or heat preservation in the enzymatic hydrolysis and fiberization process in step S10.

2. The energy-saving preparation process for washable nonwoven fabric as described in claim 1, characterized in that, After recovering the secondary steam in steps S30 and S50, the process further includes the step of separating the secondary steam into water to form condensate, and then heating the condensate with a second portion of secondary steam to form a heat medium at 70-85°C.

3. The energy-saving preparation process for washable nonwoven fabric as described in claim 2, characterized in that, The heat medium includes both a portion formed by heating the condensate and a portion formed by cooling the second portion of secondary steam. The second portion of secondary steam heats the condensate through a heat exchanger and cools itself.

4. The energy-saving preparation process for washable nonwoven fabric as described in claim 3, characterized in that, The temperature of the condensate entering the heat exchanger is greater than or equal to 40℃.

5. The energy-saving preparation process for washable nonwoven fabric as described in claim 4, characterized in that, In step S40, secondary steam is injected onto the surface of the pre-dried fiber web through a micro-orifice injection device. The angle between the injection direction and the surface of the pre-dried fiber web is 75° to 105°. At the same time, the injection pressure is 200 to 500 Pa, and the water content of the secondary steam is 30% to 40%.

6. The energy-saving preparation process for washable nonwoven fabric as described in claim 4, characterized in that, The average fiber length of bamboo pulp ranges from 1.2 to 2.2 mm, and the average width ranges from 10 to 20 μm.

7. The energy-saving preparation process for washable nonwoven fabric as described in claim 6, characterized in that, In the fiber mixed pulp, the ratio of enzymatically hydrolyzed bamboo pulp, wood pulp and hot melt adhesive fiber is as follows: enzymatically hydrolyzed bamboo pulp: 40-60%; wood pulp: 20-30%; hot melt adhesive fiber: 5-8%. Meanwhile, the content of nanofibers in the mixed pulp is 5-10% of the total weight of oven-dry fibers.

8. The energy-saving preparation process for washable nonwoven fabric as described in claim 6, characterized in that, In step S20, a micro-needling step is performed using a micro-needling assembly, which includes a microporous water needle plate with micropores of 0.08 to 0.1 mm and a water pressure of 100 to 130 Bar during micro-needling.

9. The energy-saving preparation process for washable nonwoven fabric as described in claim 4, characterized in that, In step S10, the enzymatic hydrolysis and fibrillation treatment is carried out at a temperature of 55–60°C for 30–40 minutes.

10. The energy-saving preparation process for washable nonwoven fabric as described in claim 4, characterized in that, The basis weight of the finished product is greater than or equal to 90 gsm, and the thickness is greater than or equal to 0.75 mm.

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