A wire-wound filter cartridge and a method of making the same

Abstract

This invention provides a wound filter element with a three-layer structure: a surface flake-like layer, a middle fluffy layer, and an inner high-density fine filtration layer. The surface flake-like layer is composed of high-shrinkage core-sheath composite yarns with different heat shrinkage rates. The high-shrinkage core-sheath composite yarns use high-shrinkage polyester filaments as the core yarn and polypropylene filaments as the covering yarn. After heat treatment, the difference in shrinkage rates forms a flake-like protruding structure on the surface. The middle fluffy layer is formed by winding low-twist polypropylene yarns to create a fluffy structure. The inner high-density fine filtration layer is composed of ultra-fine polypropylene filament fibers. This invention employs a three-layer gradient structure and a surface hydrophobic flake-modified wound filter element. While ensuring ultra-high particle retention accuracy, it also possesses excellent water flow rate, strong anti-fouling ability, and high cleaning and regeneration rate, making it suitable for long-term application in high-standard filtration conditions such as drinking water purification, food and pharmaceutical filtration, and electronic ultrapure water preparation.

Description

Technical Field

[0001] This invention relates to the field of filter elements, and more specifically to a wound filter element and its preparation method. Background Technology

[0002] As one of the most widely used filter elements in the field of depth filtration, wound filter cartridges form a filter medium with a three-dimensional pore structure through the continuous winding of yarns on a porous framework. The tortuous channels between the fibers enable the interception and separation of suspended particles in the fluid. Compared to non-woven filter materials such as meltblown and spunbond, wound filter cartridges have significant advantages such as large dirt-holding capacity, controllable filtration accuracy, good chemical stability, and strong customizability. They are widely used in drinking water purification, industrial liquid filtration, food and beverage processing, pharmaceutical preparation impurity removal, and electronic ultrapure water preparation.

[0003] Existing wound filter cartridges typically use yarn of a single material or structure wound at a constant angle and density onto a central skeleton, forming a gradient filtration structure with density gradually increasing from the outside to the inside. The design concept of this structure is to utilize the relatively loose pores of the outer layer to pre-filter large particles, while the denser pores of the inner layer achieve fine filtration, thereby extending the filter cartridge's lifespan and improving filtration efficiency. However, with the expansion of application areas and the continuous improvement of filtration requirements, existing wound filter cartridges have revealed two key technical defects that limit their performance during actual use: the problem of blind pores inside the filter cartridge and the problem of surface clogging.

[0004] The presence of blind holes has multiple negative impacts: First, blind holes occupy the effective filtration space of the filter element, resulting in the actual porosity participating in filtration being far lower than the theoretical design value, thus reducing the dirt-holding capacity per unit volume of the filter element; second, the particles trapped in the blind holes become a breeding ground for bacteria, posing hygiene and safety hazards in food, beverage, and pharmaceutical filtration applications; third, localized blockage in the blind hole area causes uneven flow field distribution inside the filter element, forming preferential flow channels that cause some filter layers to penetrate prematurely, shortening the overall service life of the filter element; finally, particles accumulated in the blind holes are difficult to remove effectively during backwashing or chemical cleaning, resulting in low filter element regeneration efficiency and increased operating costs.

[0005] The surface layer of wound filter cartridges is typically composed of coarser fibers or yarns, serving as a pre-filter and support. In traditional designs, the surface fibers are smooth or randomly protruding, lacking a guiding structure for fluid flow. In feed solutions containing high concentrations of particulate matter or viscous impurities, the surface fibers are easily covered or embedded by particles, forming a dense filter cake layer, leading to a sharp increase in pressure differential and a rapid decline in effective flux.

[0006] Surface clogging not only shortens the filter replacement cycle but also forces the inner high-precision filtration zone to withstand high pressure differentials prematurely, causing irreversible fiber deformation or breakage. While methods exist to adjust surface materials or add coatings, these often affect filtration throughput or increase manufacturing costs, and are unlikely to simultaneously solve the blind pore problem.

[0007] In summary, there is an urgent need to provide a novel wire-wound filter element structure and its preparation method that can eliminate internal blind holes and delay surface clogging, so as to improve filtration efficiency and service life. Summary of the Invention

[0008] Technical problem to be solved: The purpose of this invention is to provide a wire-wound filter element and its preparation method, which achieves low blind pore rate, improved anti-clogging and service life.

[0009] Technical solution: A wound filter element, wherein the wound filter element has a three-layer structure, namely a surface scale-like layer, a middle fluffy layer, and an inner high-density fine filtration layer. The surface scale-like layer is composed of high-shrinkage core-sheath composite yarns with different heat shrinkage rates. The high-shrinkage core-sheath composite yarns use high-shrinkage polyester filaments as the core yarn and polypropylene filaments as the covering yarn. After heat treatment, the difference in shrinkage rate forms a scale-like protrusion structure on the surface. The middle fluffy layer is formed by winding low-twist polypropylene yarns to form a fluffy structure. The inner high-density fine filtration layer is composed of ultra-fine polypropylene filament fibers.

[0010] Preferably, the method for preparing the high-shrinkage core-sheath composite yarn in the surface scale-like layer is as follows: 300D~500D high-shrinkage polyester filament is selected as the core yarn, and 150D~300D polypropylene filament is selected as the covering yarn; Tetraethyl orthosilicate, water and ethanol were mixed and stirred in a volume ratio of 5:2:18. Nitric acid was then added dropwise to adjust the pH to 3. The mixture was stirred to obtain a silica sol. Dodecyltrimethoxysilane was then stirred and mixed evenly to obtain an impregnation solution. Polypropylene filaments are immersed in an impregnation solution and then dried at a low temperature of 80°C to obtain hydrophobic modified covered yarn. Spinning core-spun yarn with a core yarn ratio of 20-30% and a twist of 50-70 twists / 10cm yields a high-shrinkage core-spun yarn.

[0011] Preferably, the high-shrinkage polyester filament has a specification of 300~500D / 24~48f, and the polypropylene filament has a specification of 150~300D / 24~96f.

[0012] Preferably, the low-twist polypropylene yarn in the intermediate fluff layer is a polypropylene filament of 600~1200D / 72~144f with a twist of 5~20 twists / 10cm.

[0013] Preferably, the linear density of the ultrafine polypropylene filaments in the inner high-density fine filter layer is 30~50D / 48~72f.

[0014] Preferably, the thickness of the inner layer is 1.5~2.5mm, the thickness of the middle layer is 8~12mm, and the thickness of the outer layer is 4~5mm.

[0015] The above-mentioned method for preparing a wound filter element includes the following steps: Step 1. First, wind the ultra-fine polypropylene filament fibers onto the porous skeleton at a winding density of 400~500 turns / cm and a winding angle of 25~29° to obtain a high-density fine filter layer; Step 2. Wind 600~1200D / 72~144f low-twist polypropylene yarn onto the high-density fine filter layer at a winding density of 200~350 turns / cm and a winding angle of 30~38° to obtain a fluffy layer; Step 3. Wind high-shrinkage core-sheath composite yarn onto the fluffy layer at a winding density of 100-150 turns / cm and a winding angle of 40-50° to obtain the filter element; Step 4. Preheat the filter element obtained in Step 3 to obtain a preheated filter element; Step 5. Place the preheated filter element in a hot air circulation environment for heat treatment. The hot air penetrates along the filter element axis and is then rapidly cooled to ≤40℃ to obtain a wound filter element.

[0016] Preferably, the winding tension of the ultrafine polypropylene filament fiber is 18~25cN; the winding tension of the low-twist polypropylene yarn is 12~16cN; and the winding tension of the high-shrinkage core-sheath composite yarn is 5~10cN.

[0017] Preferably, the preheating temperature in step 4 is 75~85℃, and the treatment time is 10~15min.

[0018] Preferably, in step 5, the heat treatment temperature is 120~150℃, the wind speed is 2~4m / s, and the time is 3~5min.

[0019] Beneficial effects: This invention has the following advantages: The surface flake-like layer of this invention utilizes a high-shrinkage core-sheath composite yarn that undergoes a two-stage heat treatment. Due to the difference in heat shrinkage rates between the core yarn (high-shrinkage polyester) and the sheath yarn (polypropylene), a uniform, open flake-like protrusion structure is formed. This flake-like protrusion increases the apparent filtration area, effectively pre-retaining large particulate impurities in the fluid. In addition to designing this flake-like protrusion structure, the polypropylene-coated yarn is also hydrophobically modified to maintain a suitable hydrophobic surface. This hydrophobic surface reduces the adhesion between particles and fibers, making it easier for retained particles to be re-rolled and carried away by the fluid's shear force. This invention employs a gradient decreasing winding tension. The inner layer of ultra-fine polypropylene filaments is wound at a high density with a low tension of 15-20 cN, resulting in naturally curved and stacked fibers that automatically fill tiny gaps, preventing fiber flattening due to excessive tension or loose voids caused by insufficient tension. The middle layer of low-twist polypropylene yarn is wound with a medium tension of 10-15 cN, forming a fluffy but structurally uniform transition layer that effectively connects the inner and outer layers, preventing interlayer debonding or voids. The outer layer of high-shrinkage core-sheath composite yarn is wound with a low tension of 5-10 cN, reserving space for shrinkage during subsequent heat treatment and preventing local collapse caused by winding stress. Each layer maintains appropriate fluffiness and interlayer bonding tightness during winding, avoiding local over-compaction or interlayer peeling voids caused by uneven tension, further eliminating potential conditions for blind hole formation. The inner layer of this invention uses ultra-fine polypropylene filaments with a linear density as low as 30~50D / 48~72f, which are wound at high density to form a dense fine filter layer, enabling effective interception of submicron-sized particles. The middle loose layer uses low-twist polypropylene yarns of 600~1200D / 72~144f to form a three-dimensional network structure with large pores, providing ample space for particle containment. The surface scale layer not only resists clogging but also serves as a pre-filter layer to share some of the impurity load. The synergistic effect of these three layers allows the filter element to maintain high filtration accuracy and efficiency. Detailed Implementation

[0020] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments: High-shrinkage polyester filament, Jiangsu Hengli Chemical Fiber Co., Ltd.; Low-twist polypropylene yarn, Zhejiang Xuri Fiber Co., Ltd.; Ultrafine polypropylene filament fiber, Zhejiang Xuri Fiber Co., Ltd.; Polypropylene filament, Zhejiang Xuri Fiber Co., Ltd.; Tetraethyl orthosilicate, Sinopharm Chemical Reagent Co., Ltd.; Dodecyltrimethoxysilane, Sinopharm Chemical Reagent Co., Ltd.

[0021] Example 1 A wound filter element has a three-layer structure: a surface flake-like layer, a middle fluffy layer, and an inner high-density fine filtration layer. The surface flake-like layer is composed of high-shrinkage core-sheath composite yarns with different heat shrinkage rates. The high-shrinkage core-sheath composite yarns use high-shrinkage polyester filaments as the core yarn and polypropylene filaments as the covering yarn. After heat treatment, the difference in shrinkage rate forms a flake-like protruding structure on the surface. The middle fluffy layer is formed by winding low-twist polypropylene yarns to form a fluffy structure. The inner high-density fine filtration layer is composed of ultra-fine polypropylene filament fibers. The thickness of the inner layer is 1.5 mm, the thickness of the middle layer is 10 mm, and the thickness of the surface layer is 4 mm. The above-mentioned method for preparing a wound filter element includes the following steps: Step 1. First, wind 30D / 48f ultrafine polypropylene filaments onto a porous skeleton at a winding density of 500 turns / cm, a winding angle of 25°, and a winding tension of 18cN to obtain a high-density fine filter layer. Step 2. Wind 600D / 72f low-twist polypropylene yarn onto the high-density fine filter layer. The twist is 20 twists / 10cm, the winding density is 350 turns / cm, the winding angle is 30°, and the winding tension is 12cN to obtain a fluffy layer. Step 3. Wind high-shrinkage core-sheath composite yarn onto the fluffy layer at a winding density of 100 turns / cm, a winding angle of 50°, and a winding tension of 5cN to obtain the filter element; Step 4. Preheat the filter element obtained in Step 3 at a temperature of 75°C for 15 minutes to obtain a preheated filter element. Step 5. Place the preheated filter element in a hot air circulation environment for heat treatment. The heat treatment temperature is 120℃, the wind speed is 2m / s, and the time is 5min. The hot air penetrates along the filter element axis and then is rapidly cooled to 40℃ to obtain a wire-wound filter element. The method for preparing the high-shrinkage core-sheath composite yarn in the surface scale-like layer is as follows: 300D / 24f high-shrinkage polyester filament is selected as the core yarn, and 150D / 24f polypropylene filament is selected as the covering yarn; Tetraethyl orthosilicate, water and ethanol were mixed and stirred in a volume ratio of 5:2:18. Nitric acid was then added dropwise to adjust the pH to 3. The mixture was stirred to obtain a silica sol. Dodecyltrimethoxysilane was then stirred and mixed evenly to obtain an impregnation solution. Polypropylene filaments are immersed in an impregnation solution and then dried at a low temperature of 80°C to obtain hydrophobic modified covered yarn. Core-spun yarn with a core yarn ratio of 20% and a twist of 70 twists / 10cm is spun to obtain a high-shrinkage core-spun yarn.

[0022] Example 2

[0023] A wound filter element has a three-layer structure: a surface flake-like layer, a middle fluffy layer, and an inner high-density fine filtration layer. The surface flake-like layer is composed of high-shrinkage core-sheath composite yarns with different heat shrinkage rates. The high-shrinkage core-sheath composite yarns use high-shrinkage polyester filaments as the core yarn and polypropylene filaments as the covering yarn. After heat treatment, the difference in shrinkage rate forms a flake-like protruding structure on the surface. The middle fluffy layer is formed by winding low-twist polypropylene yarns to form a fluffy structure. The inner high-density fine filtration layer is composed of ultra-fine polypropylene filament fibers. The thickness of the inner layer is 1.5 mm, the thickness of the middle layer is 10 mm, and the thickness of the surface layer is 4 mm. The above-mentioned method for preparing a wound filter element includes the following steps: Step 1. First, wind 50D / 72f ultrafine polypropylene filaments onto a porous skeleton at a winding density of 400 turns / cm, a winding angle of 29°, and a winding tension of 25cN to obtain a high-density fine filter layer. Step 2. Wind 1200D / 144f low-twist polypropylene yarn onto the high-density fine filter layer. The twist is 5 twists / 10cm, the winding density is 200 turns / cm, the winding angle is 38°, and the winding tension is 16cN to obtain a fluffy layer. Step 3. Wind high-shrinkage core-sheath composite yarn onto the fluffy layer at a winding density of 150 turns / cm, a winding angle of 40°, and a winding tension of 10cN to obtain the filter element; Step 4. Preheat the filter element obtained in Step 3 at a temperature of 85°C for 10 minutes to obtain a preheated filter element. Step 5. Place the preheated filter element in a hot air circulation environment for heat treatment. The heat treatment temperature is 150℃, the wind speed is 4m / s, and the time is 3min. The hot air penetrates along the filter element axis and then is rapidly cooled to 40℃ to obtain a wire-wound filter element. The method for preparing the high-shrinkage core-sheath composite yarn in the surface scale-like layer is as follows: 500D / 48f high-shrinkage polyester filament is selected as the core yarn, and 300D / 96f polypropylene filament is selected as the covering yarn; Tetraethyl orthosilicate, water and ethanol were mixed and stirred in a volume ratio of 5:2:18. Nitric acid was then added dropwise to adjust the pH to 3. The mixture was stirred to obtain a silica sol. Dodecyltrimethoxysilane was then stirred and mixed evenly to obtain an impregnation solution. Polypropylene filaments are immersed in an impregnation solution and then dried at a low temperature of 80°C to obtain hydrophobic modified covered yarn. Core-spun yarn with a core yarn ratio of 30% and a twist of 50 twists / 10cm is spun to obtain a high-shrinkage core-spun yarn.

[0024] Example 3

[0025] A wound filter element has a three-layer structure: a surface flake-like layer, a middle fluffy layer, and an inner high-density fine filtration layer. The surface flake-like layer is composed of high-shrinkage core-sheath composite yarns with different heat shrinkage rates. The high-shrinkage core-sheath composite yarns use high-shrinkage polyester filaments as the core yarn and polypropylene filaments as the covering yarn. After heat treatment, the difference in shrinkage rate forms a flake-like protruding structure on the surface. The middle fluffy layer is formed by winding low-twist polypropylene yarns to form a fluffy structure. The inner high-density fine filtration layer is composed of ultra-fine polypropylene filament fibers. The thickness of the inner layer is 1.5 mm, the thickness of the middle layer is 10 mm, and the thickness of the surface layer is 4 mm. The above-mentioned method for preparing a wound filter element includes the following steps: Step 1. First, wind 30D / 48f ultrafine polypropylene filaments onto a porous skeleton at a winding density of 420 turns / cm, a winding angle of 26°, and a winding tension of 22cN to obtain a high-density fine filter layer. Step 2. Wind 600D / 72f low-twist polypropylene yarn onto the high-density fine filter layer. The twist is 16 twists / 10cm, the winding density is 220 turns / cm, the winding angle is 36°, and the winding tension is 13cN to obtain a fluffy layer. Step 3. Wind high-shrinkage core-sheath composite yarn onto the fluffy layer at a winding density of 120 turns / cm, a winding angle of 40°, and a winding tension of 8cN to obtain the filter element; Step 4. Preheat the filter element obtained in Step 3 at a temperature of 85°C for 12 minutes to obtain a preheated filter element. Step 5. Place the preheated filter element in a hot air circulation environment for heat treatment. The heat treatment temperature is 130℃, the wind speed is 3m / s, and the time is 4min. The hot air penetrates along the filter element axis and then is rapidly cooled to 40℃ to obtain a wire-wound filter element. The method for preparing the high-shrinkage core-sheath composite yarn in the surface scale-like layer is as follows: 300D / 24f high-shrinkage polyester filament is selected as the core yarn, and 150D / 24f polypropylene filament is selected as the covering yarn; Tetraethyl orthosilicate, water and ethanol were mixed and stirred in a volume ratio of 5:2:18. Nitric acid was then added dropwise to adjust the pH to 3. The mixture was stirred to obtain a silica sol. Dodecyltrimethoxysilane was then stirred and mixed evenly to obtain an impregnation solution. Polypropylene filaments are immersed in an impregnation solution and then dried at a low temperature of 80°C to obtain hydrophobic modified covered yarn. Core-spun yarn with a core yarn ratio of 23% and a twist of 65 twists / 10cm is spun to obtain a high-shrinkage core-spun yarn.

[0026] Example 4

[0027] A wound filter element has a three-layer structure: a surface flake-like layer, a middle fluffy layer, and an inner high-density fine filtration layer. The surface flake-like layer is composed of high-shrinkage core-sheath composite yarns with different heat shrinkage rates. The high-shrinkage core-sheath composite yarns use high-shrinkage polyester filaments as the core yarn and polypropylene filaments as the covering yarn. After heat treatment, the difference in shrinkage rate forms a flake-like protruding structure on the surface. The middle fluffy layer is formed by winding low-twist polypropylene yarns to form a fluffy structure. The inner high-density fine filtration layer is composed of ultra-fine polypropylene filament fibers. The thickness of the inner layer is 1.5 mm, the thickness of the middle layer is 10 mm, and the thickness of the surface layer is 4 mm. The above-mentioned method for preparing a wound filter element includes the following steps: Step 1. First, wind 50D / 72f ultrafine polypropylene filaments onto a porous skeleton at a winding density of 4700 turns / cm, a winding angle of 28°, and a winding tension of 20cN to obtain a high-density fine filter layer. Step 2. Wind 1200D / 144f low-twist polypropylene yarn onto the high-density fine filter layer. The twist is 8 twists / 10cm, the winding density is 320 turns / cm, the winding angle is 32°, and the winding tension is 15cN to obtain a fluffy layer. Step 3. Wind high-shrinkage core-sheath composite yarn onto the fluffy layer at a winding density of 140 turns / cm, a winding angle of 50°, and a winding tension of 9cN to obtain the filter element; Step 4. Preheat the filter element obtained in Step 3 at a temperature of 75°C for 15 minutes to obtain a preheated filter element. Step 5. Place the preheated filter element in a hot air circulation environment for heat treatment. The heat treatment temperature is 130℃, the wind speed is 4m / s, and the time is 3.5min. The hot air penetrates along the filter element axis and then is rapidly cooled to 40℃ to obtain a wire-wound filter element. The method for preparing the high-shrinkage core-sheath composite yarn in the surface scale-like layer is as follows: 500D / 48f high-shrinkage polyester filament is selected as the core yarn, and 300D / 96f polypropylene filament is selected as the covering yarn; Tetraethyl orthosilicate, water and ethanol were mixed and stirred in a volume ratio of 5:2:18. Nitric acid was then added dropwise to adjust the pH to 3. The mixture was stirred to obtain a silica sol. Dodecyltrimethoxysilane was then stirred and mixed evenly to obtain an impregnation solution. Polypropylene filaments are immersed in an impregnation solution and then dried at a low temperature of 80°C to obtain hydrophobic modified covered yarn. Core-spun yarn with a core yarn ratio of 28% and a twist of 55 twists / 10cm is spun to obtain a high-shrinkage core-spun yarn.

[0028] Example 5

[0029] A wound filter element has a three-layer structure: a surface flake-like layer, a middle fluffy layer, and an inner high-density fine filtration layer. The surface flake-like layer is composed of high-shrinkage core-sheath composite yarns with different heat shrinkage rates. The high-shrinkage core-sheath composite yarns use high-shrinkage polyester filaments as the core yarn and polypropylene filaments as the covering yarn. After heat treatment, the difference in shrinkage rate forms a flake-like protruding structure on the surface. The middle fluffy layer is formed by winding low-twist polypropylene yarns to form a fluffy structure. The inner high-density fine filtration layer is composed of ultra-fine polypropylene filament fibers. The thickness of the inner layer is 1.5 mm, the thickness of the middle layer is 10 mm, and the thickness of the surface layer is 4 mm. The above-mentioned method for preparing a wound filter element includes the following steps: Step 1. First, wind 50D / 72f ultrafine polypropylene filaments onto a porous skeleton at a winding density of 450 turns / cm, a winding angle of 28°, and a winding tension of 20cN to obtain a high-density fine filter layer. Step 2. Wind 800D / 96f low-twist polypropylene yarn onto the high-density fine filter layer. The twist is 10 twists / 10cm, the winding density is 250 turns / cm, the winding angle is 35°, and the winding tension is 15cN to obtain a fluffy layer. Step 3. Wind high-shrinkage core-sheath composite yarn onto the fluffy layer at a winding density of 120 turns / cm, a winding angle of 45°, and a winding tension of 8cN to obtain the filter element; Step 4. Preheat the filter element obtained in Step 3 at a temperature of 80°C for 12 minutes to obtain a preheated filter element. Step 5. Place the preheated filter element in a hot air circulation environment for heat treatment. The heat treatment temperature is 140℃, the wind speed is 3m / s, and the time is 4min. The hot air penetrates along the filter element axis and then is rapidly cooled to 40℃ to obtain a wire-wound filter element. The method for preparing the high-shrinkage core-sheath composite yarn in the surface scale-like layer is as follows: 400D / 36f high-shrinkage polyester filament is selected as the core yarn, and 250D / 48f polypropylene filament is selected as the covering yarn; Tetraethyl orthosilicate, water and ethanol were mixed and stirred in a volume ratio of 5:2:18. Nitric acid was then added dropwise to adjust the pH to 3. The mixture was stirred to obtain a silica sol. Dodecyltrimethoxysilane was then stirred and mixed evenly to obtain an impregnation solution. Polypropylene filaments are immersed in an impregnation solution and then dried at a low temperature of 80°C to obtain hydrophobic modified covered yarn. Core-spun yarn with a core yarn ratio of 25% and a twist of 60 twists / 10cm is spun to obtain a high-shrinkage core-spun yarn.

[0030] Comparative Example 1 The difference between Comparative Example 1 and Example 5 is that the filter element does not contain a surface flake-like layer.

[0031] Comparative Example 2 The difference between Comparative Example 2 and Example 5 is that the surface flake layer in the filter element is a normal surface layer and does not use high-shrinkage core-sheath composite yarn, but is replaced with 800D / 48f polypropylene filament.

[0032] Comparative Example 3 The difference between Comparative Example 3 and Example 5 is that the winding tension in step 3 is 20cN.

[0033] Comparative Example 4 The difference between Comparative Example 4 and Example 5 is that the polypropylene filaments are not hydrophobically modified during the preparation of the high-shrinkage core-sheath composite yarn.

[0034] Comparative Example 5 The difference between Comparative Example 5 and Example 5 is that the winding angle of each layer is different; A wound filter element has a three-layer structure: a surface flake-like layer, a middle fluffy layer, and an inner high-density fine filtration layer. The surface flake-like layer is composed of high-shrinkage core-sheath composite yarns with different heat shrinkage rates. The high-shrinkage core-sheath composite yarns use high-shrinkage polyester filaments as the core yarn and polypropylene filaments as the covering yarn. After heat treatment, the difference in shrinkage rate forms a flake-like protruding structure on the surface. The middle fluffy layer is formed by winding low-twist polypropylene yarns to form a fluffy structure. The inner high-density fine filtration layer is composed of ultra-fine polypropylene filament fibers. The thickness of the inner layer is 1.5 mm, the thickness of the middle layer is 10 mm, and the thickness of the surface layer is 4 mm. The above-mentioned method for preparing a wound filter element includes the following steps: Step 1. First, wind 50D / 72f ultrafine polypropylene filaments onto a porous skeleton at a winding density of 450 turns / cm, a winding angle of 45°, and a winding tension of 20cN to obtain a high-density fine filter layer. Step 2. Wind 800D / 96f low-twist polypropylene yarn onto the high-density fine filter layer. The twist is 10 twists / 10cm, the winding density is 250 turns / cm, the winding angle is 45°, and the winding tension is 15cN to obtain a fluffy layer. Step 3. Wind high-shrinkage core-sheath composite yarn onto the fluffy layer at a winding density of 120 turns / cm, a winding angle of 45°, and a winding tension of 8cN to obtain the filter element; Step 4. Preheat the filter element obtained in Step 3 at a temperature of 80°C for 12 minutes to obtain a preheated filter element. Step 5. Place the preheated filter element in a hot air circulation environment for heat treatment. The heat treatment temperature is 140℃, the wind speed is 3m / s, and the time is 4min. The hot air penetrates along the filter element axis and then is rapidly cooled to 40℃ to obtain a wire-wound filter element. The method for preparing the high-shrinkage core-sheath composite yarn in the surface scale-like layer is as follows: 400D / 36f high-shrinkage polyester filament is selected as the core yarn, and 250D / 48f polypropylene filament is selected as the covering yarn; Tetraethyl orthosilicate, water and ethanol were mixed and stirred in a volume ratio of 5:2:18. Nitric acid was then added dropwise to adjust the pH to 3. The mixture was stirred to obtain a silica sol. Dodecyltrimethoxysilane was then stirred and mixed evenly to obtain an impregnation solution. Polypropylene filaments are immersed in an impregnation solution and then dried at a low temperature of 80°C to obtain hydrophobic modified covered yarn. Core-spun yarn with a core yarn ratio of 25% and a twist of 60 twists / 10cm is spun to obtain a high-shrinkage core-spun yarn.

[0035] Comparative Example 6 The difference between Comparative Example 6 and Example 5 is that the low-twist polypropylene yarn in the fluffy layer is replaced with a twist of 120 twists / 10cm.

[0036] Comparative Example 7 The difference between Comparative Example 7 and Example 5 is that Comparative Example 7 does not contain an intermediate fluffy layer.

[0037] Comparative Example 8 The difference between Comparative Example 8 and Example 5 is that the winding density of each layer is the same; A wound filter element has a three-layer structure: a surface flake-like layer, a middle fluffy layer, and an inner high-density fine filtration layer. The surface flake-like layer is composed of high-shrinkage core-sheath composite yarns with different heat shrinkage rates. The high-shrinkage core-sheath composite yarns use high-shrinkage polyester filaments as the core yarn and polypropylene filaments as the covering yarn. After heat treatment, the difference in shrinkage rate forms a flake-like protruding structure on the surface. The middle fluffy layer is formed by winding low-twist polypropylene yarns to form a fluffy structure. The inner high-density fine filtration layer is composed of ultra-fine polypropylene filament fibers. The thickness of the inner layer is 1.5 mm, the thickness of the middle layer is 10 mm, and the thickness of the surface layer is 4 mm. The above-mentioned method for preparing a wound filter element includes the following steps: Step 1. First, wind 50D / 72f ultrafine polypropylene filaments onto a porous skeleton at a winding density of 250 turns / cm, a winding angle of 28°, and a winding tension of 20cN to obtain a high-density fine filter layer. Step 2. Wind 800D / 96f low-twist polypropylene yarn onto the high-density fine filter layer. The twist is 10 twists / 10cm, the winding density is 250 turns / cm, the winding angle is 35°, and the winding tension is 15cN to obtain a fluffy layer. Step 3. Wind high-shrinkage core-sheath composite yarn onto the fluffy layer at a winding density of 250 turns / cm, a winding angle of 45°, and a winding tension of 8cN to obtain the filter element; Step 4. Preheat the filter element obtained in Step 3 at a temperature of 80°C for 12 minutes to obtain a preheated filter element. Step 5. Place the preheated filter element in a hot air circulation environment for heat treatment. The heat treatment temperature is 140℃, the wind speed is 3m / s, and the time is 4min. The hot air penetrates along the filter element axis and then is rapidly cooled to 40℃ to obtain a wire-wound filter element. The method for preparing the high-shrinkage core-sheath composite yarn in the surface scale-like layer is as follows: 400D / 36f high-shrinkage polyester filament is selected as the core yarn, and 250D / 48f polypropylene filament is selected as the covering yarn; Tetraethyl orthosilicate, water and ethanol were mixed and stirred in a volume ratio of 5:2:18. Nitric acid was then added dropwise to adjust the pH to 3. The mixture was stirred to obtain a silica sol. Dodecyltrimethoxysilane was then stirred and mixed evenly to obtain an impregnation solution. Polypropylene filaments are immersed in an impregnation solution and then dried at a low temperature of 80°C to obtain hydrophobic modified covered yarn. Core-spun yarn with a core yarn ratio of 25% and a twist of 60 twists / 10cm is spun to obtain a high-shrinkage core-spun yarn.

[0038] Performance testing: Pure water flux test: Under a temperature of 25℃, the filter element was completely immersed in deionized water for 20 minutes, followed by filtration with deionized water. After the outflow water stabilized, the pure water flux was calculated using the formula J=V / (A×t×P), where J is the pure water flux, V is the outflow rate (L), and A is the effective surface area of ​​the membrane (m²). 2 ), t is the filtration time (h), and P is the transmembrane pressure (bar); Water flux test after contamination: ISO 12103-1 A2 dust was added to water to obtain a contaminated aqueous solution with a concentration of 2.5 wt%. The water flux was then tested using the contaminated aqueous solution.

[0039] As can be seen from the table above, the pure water flux of Comparative Examples 1, 7, and 8 is significantly higher. This is because after eliminating the surface flake layer, the intermediate loose layer, and uniformly winding density, the overall pores of the filter element are large and the structure is loose, resulting in minimal fluid flow resistance. Comparative Example 4 did not undergo hydrophobic modification, which clearly shows that hydrophobic modification of the silane system is a key process for delaying surface clogging. Without modification, dust easily adheres and accumulates, quickly forming a dense filter cake that suppresses flux. Comparative Example 6 uses high-twist yarn instead of low-twist loose yarn. Although the flux is higher after contamination, the structure is compact with no space for dirt to accumulate, allowing impurities to quickly accumulate and penetrate, resulting in extremely poor anti-contamination durability. Comparative Example 2 uses a common polypropylene surface without a flake-like flow-guiding structure, resulting in a compacted and solidified surface filter cake that is difficult to remove during cleaning. Comparative Examples 3 and 5... The significantly low pure water flux is due to excessive surface winding tension and an unreasonable winding angle, which causes excessive fiber compaction, squeezing and clogging of internal pores, narrowing of the flow channel, and directly reducing the original water flux.

[0040] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A spin-on filter cartridge, characterized by: The wound filter element has a three-layer structure: a surface scaly layer, a middle fluffy layer, and an inner high-density fine filtration layer. The surface scaly layer is composed of high-shrinkage core-sheath composite yarns with different heat shrinkage rates. The high-shrinkage core-sheath composite yarns use high-shrinkage polyester filaments as the core yarn and polypropylene filaments as the covering yarn. After heat treatment, the difference in shrinkage rate forms a scaly protrusion structure on the surface. The middle fluffy layer is formed by winding low-twist polypropylene yarns to form a fluffy structure. The inner high-density fine filtration layer is composed of ultra-fine polypropylene filament fibers.

2. The spin-on filter cartridge of claim 1, wherein: The preparation method of the high-shrinkage core-sheath composite yarn in the surface scaly layer is as follows: 300D~500D high-shrinkage polyester filament is selected as the core yarn, and 150D~300D polypropylene filament is selected as the covering yarn; Tetraethyl orthosilicate, water and ethanol were mixed and stirred in a volume ratio of 5:2:

18. Nitric acid was then added dropwise to adjust the pH to 3. The mixture was stirred to obtain a silica sol. Dodecyltrimethoxysilane was then stirred and mixed evenly to obtain an impregnation solution. Polypropylene filaments are immersed in an impregnation solution and then dried at a low temperature of 80°C to obtain hydrophobic modified covered yarn. Spinning core-spun yarn with a core yarn ratio of 20-30% and a twist of 50-70 twists / 10cm yields a high-shrinkage core-spun yarn.

3. The spin-on filter cartridge of claim 1, wherein: The high-shrinkage polyester filament has a specification of 300~500D / 24~48f, and the polypropylene filament has a specification of 150~300D / 24~96f.

4. The spin-on filter of claim 1, wherein: The intermediate fluffy layer contains low-twist polypropylene yarns of 600~1200D / 72~144f polypropylene filaments with a twist of 5~20 twists / 10cm.

5. The spin-on filter cartridge of claim 1, wherein: The linear density of the ultrafine polypropylene filaments in the inner high-density fine filter layer is 30~50D / 48~72f.

6. The spin-on filter of claim 1, wherein: The inner layer has a thickness of 1.5~2.5mm, the middle layer has a thickness of 8~12mm, and the outer layer has a thickness of 4~5mm.

7. The method of claim 1, wherein Includes the following steps: Step 1. First, wind the ultra-fine polypropylene filament fibers onto the porous skeleton at a winding density of 400~500 turns / cm and a winding angle of 25~29° to obtain a high-density fine filter layer; Step 2. Wind 600~1200D / 72~144f low-twist polypropylene yarn onto the high-density fine filter layer at a winding density of 200~350 turns / cm and a winding angle of 30~38° to obtain a fluffy layer; Step 3. Wind high-shrinkage core-sheath composite yarn onto the fluffy layer at a winding density of 100-150 turns / cm and a winding angle of 40-50° to obtain the filter element; Step 4. Preheat the filter element obtained in Step 3 to obtain a preheated filter element; Step 5. Place the preheated filter element in a hot air circulation environment for heat treatment. The hot air penetrates along the filter element axis and is then rapidly cooled to ≤40℃ to obtain a wound filter element.

8. The method of claim 7, wherein: The winding tension of the ultrafine polypropylene filament fiber is 18~25cN; the winding tension of the low-twist polypropylene yarn is 12~16cN; and the winding tension of the high-shrinkage core-sheath composite yarn is 5~10cN.

9. The method of claim 7, wherein: The preheating temperature in step 4 is 75~85℃, and the treatment time is 10~15min.

10. The method of claim 7, wherein: In step 5, the heat treatment temperature is 120~150℃, the wind speed is 2~4m / s, and the time is 3~5min.

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