A deep filter medium and a method for making the same

Abstract

The application discloses a kind of deep filtration medium and preparation method thereof, it is related to the field of deep filtration medium, including filter medium body, for filter medium body including fiber and filter aid, fiber includes coarse fiber and superfine nanofiber, the diameter of superfine nanofiber is 5-150nm;The diameter ratio between coarse fiber and superfine nanofiber is 200-50;The diameter ratio of superfine nanofiber and the average particle size D50 of filter aid is 1:10-1000, the present application is adopted coarse fiber and superfine nanofiber collocation, using superfine nanofiber can greatly increase the filtering precision of filter medium body, so that filter medium body can be retained and adsorbed smaller impurities of particle size, while superfine nanofiber can be wrapped filter aid and form net-like package, to form net-like structure outside filter aid, filter aid can be firmly " grabbed " by the net-like package coarse fiber, prevent from falling off from filter medium body.

Description

Technical Field

[0001] This invention relates to the field of depth filtration media, and in particular to a depth filtration media and its preparation method. Background Technology

[0002] After a long period of development, cell culture technology has become an important technical means for protein production. In the field of cell culture, commonly used cell harvesting methods include flocculation, sedimentation, centrifugation, and deep filtration. Among these, deep filtration media are usually composed of fibers, filter aids, and binders, and can perform filtration at various depths. Typically, cell harvesting fluid contains a large number of intact cells, cell debris, and the desired target proteins and other biological components. In order to separate the desired target proteins and other biological components, downstream purification filtration steps such as clarification filtration, ultrafiltration, and chromatography are required. Clarification filtration is the first step in downstream purification in biopharmaceutical processes to remove cell debris, large particulate residues, colloids or precipitates, polysaccharides, pigments, host cell proteins (HCPs), and biological macromolecules such as DNA. This reduces membrane fouling during subsequent filtration, increases flux, extends cleaning cycles and service life, reduces operating costs, and improves production efficiency.

[0003] During the filtration of cell harvest fluid through a deep filtration medium, larger biological components such as intact cells or cell debris can be retained by the deep filtration medium, while DNA and HCP can be adsorbed and separated by the deep filtration medium through charge adsorption. Therefore, the target protein can be separated from intact cells, cell debris, DNA and HCP through the deep filtration medium, thus achieving the collection of the target protein.

[0004] Before using deep filtration media, it is necessary to pre-filter and rinse the media with water or buffer solution to remove easily detached fibers or filter aids. However, in the existing technology, the shedding of internal fibers or filter aids, especially the filter aids near the outlet surface of the deep filtration media, is quite serious during the pre-filtration and rinsing process. The shedding of filter aids can easily cause the deep filtration media to deviate from its original filtration precision, resulting in relatively small impurities such as cell debris, DNA, and HCP not being filtered well, thus affecting the entire clarification filtration process of the cell harvest fluid. At the same time, during the clarification filtration process, as the pores inside the deep filtration media are gradually filled with impurities, the pressure on it gradually increases. The gradually increasing pressure is more likely to cause the filter aids inside the deep filtration media to detach, thus affecting the purity of the protein collection fluid after filtration. Summary of the Invention

[0005] The purpose of this invention is to provide a deep filtration medium with stable accuracy that prevents fiber and filter aid from falling off, and a method for preparing the same.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A depth filtration medium includes a filter medium body comprising fibers and a filter aid, the filter medium body having a first side for receiving the liquid to be filtered and a second side for discharging the permeate.

[0008] The fibers include coarse fibers and ultrafine nanofibers, wherein the diameter of the ultrafine nanofibers is 5-150 nm.

[0009] In this process, coarse fibers are stacked and entangled to form the filter medium body skeleton, and ultrafine nanofibers are wrapped around the outside of the filter aid to form a mesh-like wrapping part. The mesh-like wrapping part and the filter aid form a dispersion that is dispersed in the pores of the filter medium body skeleton.

[0010] The diameter ratio between the coarse fibers and the ultrafine nanofibers is 200-50;

[0011] The ratio of the diameter of the ultrafine nanofibers to the average particle size D50 of the filter aid is 1:10-1000.

[0012] In this invention, coarse fibers are stacked and wound to form a filter medium body skeleton, and the filter aid and the wrapped ultrafine nanofibers together form a dispersion that fills the pores of the filter medium body skeleton. This invention employs ultrafine nanofibers in the filter medium body. On one hand, the use of ultrafine nanofibers can greatly increase the filtration accuracy of the filter medium body, enabling it to trap and adsorb impurities with smaller particle sizes, such as small-diameter cell debris, or undesirable protein components, such as DNA and HCP. More importantly, the use of ultrafine nanofibers can entangle the filter aid to form a mesh-like encapsulation, thereby forming a mesh structure on the outside of the filter aid. On the one hand, the mesh-like encapsulation can make the filter aid more uniform during dispersion and stirring. On the other hand, some of the ultrafine nanofibers in the mesh-like encapsulation can also entangle with ultrafine nanofibers on other dispersions or with coarse fibers. Thus, the dispersions are not completely independent of each other and are connected through the ultrafine nanofibers on the mesh-like encapsulation. The dispersions can also firmly "grab" the coarse fibers through the mesh-like encapsulation, increasing the bonding strength between the filter aid and the filter medium body skeleton. This allows the mesh-like encapsulation to firmly hold the filter aid when subjected to fluid impact, preventing its loss.

[0013] The ratio between the diameter of the ultrafine nanofibers and the average particle size of the filter aid directly affects the encapsulation of the filter aid by the ultrafine nanofibers. If the diameter of the ultrafine nanofibers is too large, they cannot effectively encapsulate the filter aid, resulting in the ultrafine nanofibers failing to form a mesh-like encapsulation or the filter aid easily detaching from the mesh-like encapsulation formed by the ultrafine nanofibers. Conversely, if the diameter of the ultrafine nanofibers is too small, they are not easy to hold the filter aid during mixing and stirring, which also easily leads to the ultrafine nanofibers failing to encapsulate the filter aid effectively. At the same time, the ratio between the diameters of coarse fibers and ultrafine nanofibers affects the overall precision. If the diameter of the ultrafine nanofibers is too large, the precision in the filter medium body is too low, while if the diameter of the ultrafine nanofibers is too small, it is easy to result in excessive precision and excessive pressure difference during filtration.

[0014] Preferably, the fiber comprises 20-40 wt% coarse fiber and 60-80 wt% ultrafine nanofiber.

[0015] The content of coarse fibers and ultrafine nanofibers is also used to adjust the proportion and precision of the dispersion in the filter medium body. If the coarse fiber content is too high, it will easily lead to more voids and fewer dispersions in the filter medium body skeleton formed by coarse fibers, resulting in too low filtration precision. If the coarse fiber content is too low, it will easily lead to fewer voids in the filter medium body skeleton and insufficient dirt-holding space.

[0016] Preferably, the length of the ultrafine nanofiber is 0.5-9 mm, and the ratio of the length of the ultrafine nanofiber to the average particle size D50 of the filter aid is 50-5000.

[0017] When the length of the ultrafine nanofibers in this invention is within a limited range, it can achieve a better encapsulation effect on the filter aid and provide a good precision adjustment effect. At the same time, the ratio between the length of the ultrafine nanofibers and the particle size of the filter aid also affects the encapsulation of the filter aid by the ultrafine nanofibers. If the length of the ultrafine nanofibers is too short, it is easy for the ultrafine nanofibers to fail to form a network encapsulation part or for the filter aid to easily fall off from the network encapsulation part formed by the ultrafine nanofibers. At the same time, it is also difficult for the ultrafine nanofibers in the network encapsulation part to entangle with the coarse fibers, which can easily cause them to fall off. On the other hand, if the length of the ultrafine nanofibers is too long, it is easy to affect the dispersibility of the dispersion.

[0018] Preferably, the diameter of the coarse fiber is 1-50 μm.

[0019] The coarse fibers are mainly used for stacking and winding to form the skeleton of the filter medium body. The diameter is within the range of this invention, which makes the deep filter medium of this invention have good strength.

[0020] Preferably, the filter aid has an average particle size D50 of 0.05-80 μm.

[0021] The filter aid of this invention can effectively adsorb and filter impurities such as DNA in cell harvest fluid through hydrophobic interactions. By adjusting the average particle size D50 of the filter aid, the precision and adsorption effect of the deep filtration medium can be adjusted.

[0022] Preferably, the particle size distribution dispersion of the filter aid is 0.5-4.

[0023] The filter aid particle size distribution used in this invention has a certain degree of dispersion, which is calculated as (D90-D10) / D50. During the dispersion formation and deep filtration media preparation process, the filter aid with smaller particle size can fill the gaps between the filter aid with larger particle size, thereby increasing the specific surface area of ​​the filter aid in the deep filtration media, improving the adsorption of substances such as DNA, and preventing the filtration and adsorption effect of the deep filtration media from decreasing due to excessive voids. At the same time, the particle size distribution dispersion can be well adjusted to meet the required precision of the deep filtration media in this invention.

[0024] Preferably, the Canadian fraction of the coarse fiber is 450-800 ml; and the Canadian fraction of the ultrafine nanofiber is 25-325 ml.

[0025] When the free carbon content of coarse fibers and ultrafine nanofibers is too high, the degree of fibrillation is too low, and there are few exposed active groups such as hydroxyl and carboxyl groups, making it difficult to combine with adhesives or charge additives. At the same time, it can easily lead to insufficient strength of the deep filter media and easy shrinkage during the drying process. Conversely, when the free carbon content is too low, the degree of fibrillation is too high, which can easily lead to a decrease in the water permeability of the deep filter media, resulting in an excessively large filtration pressure differential during use.

[0026] As a preferred option

[0027] The tightness of the first side to the second side exhibits a continuously increasing gradient change;

[0028] Furthermore, at least on the second side, the ultrafine nanofibers on the outer periphery of the mesh-like wrapping portion are entangled with the filter medium body skeleton to prevent the filter aid from detaching.

[0029] In this invention, the density gradient increases from the first side to the second side. Therefore, the density is lower near the first side, resulting in a relatively large dirt-holding space, while the density is higher near the first side, which is more conducive to precise adsorption. At the same time, the ultrafine nanofibers on the outer periphery of the mesh-like wrapping part at the second side where the permeate is discharged are entangled with the filter medium body skeleton, resulting in greater density. Therefore, during the pre-rinsing or filtration process of the deep filter medium, it can be ensured that the filter aid cannot be detached from the second side, thereby preventing the detachment of the filter aid in the entire deep filter medium.

[0030] As a preferred option

[0031] The first region is defined as the area from the first side where the thickness of the filter medium body is 0-33%.

[0032] The second region is located at 33-66% of the thickness of the filter medium body from the first side.

[0033] The third region is located at 66-100% of the thickness of the filter medium body from the first side.

[0034] The ratio between the standard deviation and the average value of the filter aid content in each region is 0.01-0.08.

[0035] In this invention, a small ratio between the standard deviation and the average value of the filter aid content in each region indicates a uniform distribution of filter aid content in each region. Compared to deep filtration media with uneven filter aid distribution, this invention can eliminate the phenomenon of stratification and sedimentation, that is, it prevents impurities that can be adsorbed or retained by the filter aid from settling in areas with high filter aid content, making the adsorption or retention of the filter aid more uniform and less prone to clogging. At the same time, if the filter aid content is relatively low in a certain region, it means that there are more gaps in the filter media skeleton in that region that are not filled. Therefore, the adsorption and retention effect in that region is low, making it easy for impurities to penetrate. At the same time, due to the lower filtration resistance at that point, the cell harvesting fluid can also penetrate more easily from that point, resulting in low utilization of the deep filtration media in other regions and affecting the overall filtration performance of the deep filtration media.

[0036] Preferably, the standard deviation of the filter aid content in each region is 0.005-0.04.

[0037] As a preferred option

[0038] The filter medium body is positively charged, and the amount of charge changes in a gradient that increases continuously from the first side to the second side.

[0039] Take the filter media body and feed a 20 ppm yellow soap dye solution to the first side at a constant rate of 5 ml / min. When the transmittance of the permeate at 430 nm drops to 95%, the permeate amount of the yellow soap dye solution is 300-6500 μg / cm³. 3 ;

[0040] in:

[0041] The permeation rate from the first side in the first region, which is 0-33% of the thickness of the filter medium body, is L1.

[0042] The permeability from the first side in the third region, which is 66-100% of the thickness of the filter medium body, is L2.

[0043] The ratio of L1:L2 is 1:1.2-3;

[0044] L1 is 120-2200 μg / cm³ 3 L2 is 150-4200 μg / cm 3 .

[0045] The coarse fibers form a framework that encapsulates the filter aid, creating a deep filtration medium. Simultaneously, positively charged adhesives or additives can impart a positive charge to the deep filtration medium. During use, the pores between the fibers trap and remove large-particle impurities such as cells and larger cell debris. The hydrophobicity of the filter aid, the positive charge from the charged adhesive or additives, and the ability to adsorb smaller cell debris or unwanted protein components such as DNA and HCP are all beneficial. Therefore, after the cell harvest fluid passes through the deep filtration medium, unwanted biological components are removed through trapping or adsorption, resulting in a cell harvest fluid containing desired biological components such as antibodies and viruses.

[0046] The invention team discovered during filtration that when using existing deep filtration media, the rated pressure difference is easily reached, meaning the deep filtration media clogs quickly. The reason for this is that the cell harvest fluid contains a high content of cell debris in non-required biological components, and the cell debris has a wide diameter distribution. With a relatively high charge in the upper layer of the deep filtration media, the relatively small cell debris, which is mainly removed by adsorption, easily fills the contaminant-holding space in the upper layer of the deep filtration media too quickly, along with large cell debris and cells. This leads to a decrease in the utilization rate of the lower layer of the deep filtration media, which is detrimental to overall filtration.

[0047] In the deep filtration medium of this invention, the density of the medium from the first side to the second side exhibits a continuously increasing gradient, and the charge also exhibits a continuously increasing gradient from the first side to the second side. The density and charge content are lower on the first side, resulting in a larger dirt-holding space near the first side. This allows for the trapping and accommodating of more cells and larger cell debris. The main function here is to trap and accommodate larger impurities such as cells and cell debris. Meanwhile, relatively smaller cell debris passes through more easily due to weaker charge adsorption, without occupying excessive dirt-holding space. However, as the medium approaches the second side… The deep filter medium has a higher density and fewer pores, resulting in a narrower and more tortuous flow path. This allows for greater contact between the cell harvest fluid and the fibers during filtration, and also a higher charge content. Consequently, it can effectively remove fine cell debris through adsorption (and due to the increased density, the precision is higher, allowing some fine cell debris to be filtered through interception; and because the cell debris is small in diameter, it does not cause blockage even with the small contaminant holding space). At the same time, it can also effectively adsorb unwanted proteins such as HCP and DNA, resulting in lower turbidity in the filtered cell harvest fluid.

[0048] Therefore, when using the deep filtration medium of this invention to filter cell harvest fluid, a large number of intact cells and large cell fragments are first retained in the cell harvest fluid, while relatively small cell fragments are less adsorbed due to the relatively weaker charge adsorption at this point. This allows the contaminant-holding space near the first side of the deep filtration medium to accommodate more intact cells and large cell fragments, preventing excessive clogging. When the cell harvest fluid passes near the second side, the density is higher, the flow path is narrower and more tortuous, and the cell harvest fluid can more easily fill the entire plane, making more thorough contact with the fibers and more likely to undergo charge adsorption. Combined with the higher charge content at this point, it can better adsorb and remove small cell fragments and unwanted proteins such as HCP and DNA. Therefore, compared to deep filtration media with more uniform charge content, the deep filtration medium of this invention is less prone to excessive clogging, has a higher utilization rate, lower turbidity of the filtrate, and relatively lower HCP and DNA residues.

[0049] As a preferred option

[0050] The density of the first region located on the first side, within 0-33% of the thickness of the filter medium body, is t1.

[0051] The density of the third region, which is 66-100% of the thickness of the filter medium body from the first side, is t2.

[0052] The ratio of t1:t2 is 1:1.1-1.7;

[0053] The density of the filter medium body is 0.2-0.38 g / cm³. 3 t1 is 0.15-0.35 g / cm³. 3 t2 is 0.23-0.40 g / cm³ 3 .

[0054] In this invention, the first region has a lower density and a larger contaminant-holding space, while the third region has a higher density, which is conducive to precise adsorption. When the density is set within the above range, it is suitable for various types of cell harvesting fluids.

[0055] Preferably, the filter medium body contains:

[0056] The porosity of the first region located on the first side, within 0-33% of the thickness of the filter medium body, is n1.

[0057] The porosity of the third region, located on the first side and within 66-100% of the filter media body thickness, is n2.

[0058] The ratio of n1:n2 is 1.1-5:1;

[0059] Among them, n1 is 25-70%, and n2 is 5-60%.

[0060] In this invention, the first region has a relatively large porosity and a large contaminant-holding space, while the third region has a relatively low porosity, which is conducive to precise adsorption. When the compactness and porosity are set within the above range, it is suitable for various types of cell harvesting fluids.

[0061] Preferably, the fiber content in the filter medium body is 10-85 wt%, and the filter aid content is 15-90 wt%.

[0062] Preferably, the fiber includes one or more of cellulose fiber, polyacrylonitrile fiber, polyester fiber, and polypropylene fiber.

[0063] Preferably, the filter aid includes one or more of diatomaceous earth, silica, and activated carbon.

[0064] Preferably, the permeability of the filter aid is between 0.05 and 6 dracy.

[0065] Preferably, the filter media body further includes an adhesive, the adhesive content being 1-10 wt%; the adhesive includes one or more of melamine-formaldehyde resin, polyamide-epoxychlorohydrin resin, and glyoxal-polyacrylamide.

[0066] Preferably, the filter medium body further includes a charge additive, wherein the charge additive accounts for 1-10 wt% of the total binder content in the filter medium body.

[0067] Preferably, the charge additive includes one or more of triethylenediamine, tetraethylenepentamine, and chitosan.

[0068] Preferably, the wet strength of the filter medium body is between 150-400 kPa.

[0069] A method for preparing a depth filtration medium, characterized by comprising the following steps:

[0070] S1: Pulping, coarse fibers and ultrafine nanofibers are selected and mixed with water to pulverize, resulting in coarse fiber slurry and ultrafine nanofiber slurry;

[0071] S2: Mixing, the ultrafine nanofiber slurry and filter aid are mixed and pre-stirred to prepare a dispersion, which is then added to the coarse fiber slurry and stirred to form a dispersion with uniform concentration;

[0072] S3: Molding, the stirred dispersion is placed on the upper surface of the screen, and a vacuum is drawn from the lower surface of the screen to form a negative pressure, forming the initial product;

[0073] S4: Drying, shaping and drying the initial finished product;

[0074] S5: Punching, cutting the initial product into the finished product.

[0075] In preparing the deep filtration medium, this invention first selects coarse fibers and ultrafine nanofibers according to a ratio and pulps them separately to obtain slurries. Then, the ultrafine nanofiber slurry and filter aid are pre-stirred to obtain a dispersion. Next, coarse fiber slurry is added and stirred evenly to form a dispersion liquid. In this invention, after the dispersion liquid is placed on the upper surface of a screen, a vacuum is drawn only from the lower surface of the screen to form a negative pressure, and the water in the slurry is removed to form a preliminary product. During this process, the suction force is greater closer to the screen, so the density of the deep filtration medium is higher in the area closer to the screen. Furthermore, the fibers of this invention are composed of coarse fibers and ultrafine nanofibers. Among them, the fine fibers are more likely to gather near the screen under suction force than the coarse fibers. Moreover, the ultrafine nanofibers have a small diameter, lower degree of free hydroxyl groups, and a high degree of fibrillation, so they expose more hydroxyl groups and generate more negative charges. Compared with coarse fibers, they are more likely to attract the attachment of charge modifiers. Therefore, the charge amount of the deep filtration medium prepared by this invention shows a continuous increasing gradient change from the first side to the second side.

[0076] Preferably, the concentration of the coarse fiber slurry in step S1 is 4-6 wt%; the concentration of the ultrafine nanofiber slurry is 1-3 wt%.

[0077] Preferably, the pre-stirring in step S2 includes the following stages:

[0078] S21 stretching stage: Stir at 10-50 rpm for 1-1.5 hours at 35-50℃;

[0079] S22 encapsulation stage: Stir at 50-200 rpm for 1-1.5 hours at 35-50℃;

[0080] S23 shaping stage: Stir at 10-50 rpm for 0.5-1 h at 20-35℃.

[0081] In the preparation of this invention, the pre-stirring is divided into three stages: the spreading stage, in which the ultrafine nanofibers are spread out by stirring at a higher temperature and a lower speed; the encapsulation stage, in which the speed is increased so that the ultrafine nanofibers can well encapsulate the filter aid to form a dispersion; and finally, the temperature and speed are reduced so that the structure of the dispersion is stabilized.

[0082] Preferably, in step S2, the fiber content is 10-70 wt% and the filter aid content is 30-90 wt%. Preferably, in step S2, an adhesive is also added, and the adhesive content is 1-10 wt%.

[0083] Preferably, a charge additive is also added in step S2, wherein the charge additive accounts for 1-10 wt% of the total content of the adhesive in the filter medium body.

[0084] Preferably, the vacuum forming step in step S3 is as follows:

[0085] S31: Vacuum level is -10 to -60 kPa;

[0086] S32: The vacuum level is -50 to -100 kPa.

[0087] Preferably, in step S3, vacuuming is performed until the moisture content of the initial product is less than 100%.

[0088] Preferably, the sieve in step S3 is double-layered, with one layer having a mesh size of 20-120 mesh and the other layer having a mesh size of 80-500 mesh, and the mesh size of the layer closer to the dispersion is smaller than that of the layer farther away from the dispersion.

[0089] Preferably, the drying in step S4 continues until the moisture content is below 10%.

[0090] Preferably, the drying temperature is 60-200℃ and the drying time is 3-8h.

[0091] The deep filtration medium of this invention uses a combination of coarse fibers and ultrafine nanofibers. The use of ultrafine nanofibers can greatly increase the filtration accuracy of the filter medium itself, thereby enabling the filter medium to trap and adsorb impurities with smaller particle sizes. At the same time, the ultrafine nanofibers can wrap around the filter aid to form a mesh-like encapsulation part, thereby forming a mesh structure on the outside of the filter aid. The filter aid can firmly "grab" the coarse fibers through this mesh-like encapsulation part, preventing them from falling off from the filter medium itself. Attached Figure Description

[0092] The present invention will be further described below with reference to the accompanying drawings:

[0093] Figure 1 This is a SEM image of the liquid outlet side of the deep filtration medium in Embodiment 2-2 of the present invention; Detailed Implementation

[0094] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0095] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0096] Example 1-1:

[0097] A depth filtration medium includes a filter medium body comprising fibers, a filter aid, and an adhesive, wherein the fibers are bonded together by the adhesive, and the filter medium body has a first side for receiving the liquid to be filtered and a second side for discharging the permeate.

[0098] The fiber is cellulose fiber. The coarse fiber is stacked and entangled to form the filter medium body skeleton. The ultrafine nanofiber is wrapped around the outside of the filter aid to form a mesh-like wrapping part. The mesh-like wrapping part and the filter aid form a dispersion in the pores of the filter medium body skeleton.

[0099] The composition of each component is as follows: coarse fiber 14 wt%, ultrafine nanofiber 46 wt%, filter aid 32 wt%, binder 8 wt%; among which:

[0100] The diameter of the coarse fibers is 5-10μm, and the freeness in Canada is 450ml;

[0101] The diameter of the ultrafine nanofibers is 15-25nm, the freeness is 80ml, and the length is 1-2mm.

[0102] The filter aid is diatomaceous earth with an average particle size D50 of 3 μm, a particle size distribution dispersion of 3.3, and a permeability of 0.1 dracy;

[0103] The wet strength of the deep filter medium is 375 kPa and the accuracy is 0.8 μm. The filter medium body is positively charged, and the amount of charge shows a gradient change that increases continuously from the first side to the second side.

[0104] Take the filter media body and feed a 20 ppm yellow soap dye solution to the first side at a constant rate of 5 ml / min. When the transmittance of the permeate at 430 nm drops to 95%, the permeate amount of the yellow soap dye solution is 6378 μg / cm³. 3 ;

[0105] in:

[0106] The permeability from the first side in the first region, which is 0-33% of the thickness of the filter medium body, is 1035 μg / cm². 3 The density is 33g / cm. 3 The porosity is 23%.

[0107] The permeability from the first side to the third region, which is 66-100% of the thickness of the filter medium body, is 2238 μg / cm³. 3 The density is 0.39 g / cm. 3 The porosity is 8%.

[0108] Method for testing the permeability of yellow soap dye: Take a deep filter paperboard of a specific thickness and diameter, and feed a yellow soap dye solution with a concentration of 20 ppm to the first side at a constant rate of 5 ml / min. When the transmittance of the permeate at 430 nm drops to 95%, calculate the mass of yellow soap dye solution that has passed through, thus obtaining the permeability of the yellow soap dye solution. Meanwhile, since measuring the entire layer of deep filter paperboard in separate layers results in a relatively low overall utilization rate, the total charge of the separate layers is lower than that of the entire layer.

[0109] In this invention, the morphology of the deep filtration medium structure can be characterized using a scanning electron microscope (SEM), followed by measurements of fiber diameter and filter aid particle size using computer software (such as Matlab, NIS-Elements, etc.) or manual measurement. This allows for the measurement of the average diameter or particle size of the fibers and filter aids actually used in this invention. During the preparation of the deep filtration medium, its characteristics, such as fiber distribution and filter aid distribution, remain largely consistent in the direction perpendicular to the thickness of the deep filtration medium, i.e., in the plane direction of the deep filtration medium. Therefore, the overall level of the plane can be reflected by the average fiber diameter or filter aid particle size in a certain area of ​​the corresponding plane. In actual measurement, the membrane surface can be characterized first using an electron microscope to obtain the corresponding SEM image. Since the surface distribution is roughly uniform, a certain area, such as 1 μm, can be selected. 2 (1μm x 1μm) or 10mm 2 (100μm by 100μm), etc. The specific area size depends on the actual situation. Then, the average fiber diameter or filter aid particle size on this area is measured by corresponding computer software or manually to represent the average value of the surface. Of course, those skilled in the art can also obtain the above parameters by other measurement methods. The above measurement methods are for reference only.

[0110] Filter aid content test method: Place the sample paperboard in a muffle furnace and ignite it to constant weight (temperature should be sufficient to ignite the fibers, varying depending on the type of fiber, e.g., 575±25℃ for cellulose fibers, 800-1000℃ for polyacrylonitrile fibers), and weigh it as m. The filter aid ratio is calculated according to the following formula:

[0111] B = 100% × m / M

[0112] Where M is the total weight of the sample cardboard.

[0113] The wet strength test method refers to GB / T 465.1-2008.

[0114] Accuracy test method: Take an appropriate amount of ISO 12103-1A4 standard particles and place them in pure water to prepare a 5 mg / L suspension. After wetting the deep filter paper, pass the suspension through at a rate of 10 L / min and calculate the retention efficiency. Retention efficiency = (1 - number of downstream particles larger than diameter X / number of upstream particles larger than diameter X) × 100%. The particle size with a retention efficiency ≥ 95% is the accuracy.

[0115] The preparation method of depth filtration media includes the following preparation steps:

[0116] S1: Pulping, coarse fibers and ultrafine nanofibers are selected and mixed with water to obtain 4wt% coarse fiber slurry and 1wt% ultrafine nanofiber slurry;

[0117] S2: Mixing, pre-stir the ultrafine nanofiber slurry and filter aid, then add it to the coarse fiber slurry, add the binder, and stir to form a dispersion with uniform concentration;

[0118] The pre-mixing process includes the following stages:

[0119] S21 stretching stage: Stir at 30 rpm for 1.2 hours at 45℃;

[0120] S22 encapsulation stage: Stir at 200 rpm for 1.5 hours at 45°C;

[0121] S23 Shaping Stage: Stir at 30 rpm for 0.8 h at 30℃;

[0122] S3: Molding, the stirred dispersion is placed on the upper surface of the screen, and a vacuum is drawn from the lower surface of the screen to form a negative pressure until the moisture content of the initial product is less than 100%, thus forming the initial product;

[0123] The vacuum forming process is as follows:

[0124] S31: The vacuum level is -40 kPa;

[0125] S32: Vacuum level is -80KPa;

[0126] The sieve is double-layered, with one layer having a mesh size of 110 mesh and the other layer having a mesh size of 400 mesh. The mesh size of the layer closer to the dispersion is smaller than that of the layer farther away from the dispersion.

[0127] S4: Drying, the initial finished product is shaped and dried at 170℃ for 5 hours until the moisture content is less than 10%;

[0128] S5: Punching, cutting the initial product into the finished product.

[0129] Examples 1-2:

[0130] A depth filtration medium includes a filter medium body comprising fibers, a filter aid, and an adhesive, wherein the fibers are bonded together by the adhesive, and the filter medium body has a first side for receiving the liquid to be filtered and a second side for discharging the permeate.

[0131] The fiber is cellulose fiber. The coarse fiber is stacked and entangled to form the filter medium body skeleton. The ultrafine nanofiber is wrapped around the outside of the filter aid to form a mesh-like wrapping part. The mesh-like wrapping part and the filter aid form a dispersion in the pores of the filter medium body skeleton.

[0132] The composition of each component is as follows: coarse fiber 8 wt%, ultrafine nanofiber 27 wt%, filter aid 62 wt%, binder 3 wt%; among which:

[0133] The diameter of the coarse fibers is 5-10 μm, and the freeness in Canada is 480 ml;

[0134] The diameter of the ultrafine nanofibers is 15-25nm, the freeness is 80ml, and the length is 1-2mm.

[0135] The filter aid is diatomaceous earth with an average particle size D50 of 6 μm, a particle size distribution dispersion of 2.8, and a permeability of 0.3 dracy.

[0136] The wet strength of the deep filter medium is 341 kPa and the accuracy is 2 μm. The filter medium body is positively charged, and the amount of charge shows a gradient change that increases continuously from the first side to the second side.

[0137] Take the filter media body and feed a 20 ppm yellow soap dye solution to the first side at a constant rate of 5 ml / min. When the transmittance of the permeate at 430 nm drops to 95%, the permeate amount of the yellow soap dye solution is 5321 μg / cm³. 3 ;

[0138] in:

[0139] The permeability from the first side in the first region, which is 0-33% of the thickness of the filter medium body, is 770 μg / cm². 3 The density is 0.32g / cm. 3 The porosity is 31%.

[0140] The permeability from the first side in the third region, which is 66-100% of the thickness of the filter medium body, is 1721 μg / cm³. 3 The density is 0.37 g / cm. 3 The porosity is 12%;

[0141] The preparation method of depth filtration media includes the following preparation steps:

[0142] S1: Pulping, coarse fibers and ultrafine nanofibers are selected and mixed with water to obtain 4wt% coarse fiber slurry and 1wt% ultrafine nanofiber slurry;

[0143] S2: Mixing, pre-stir the ultrafine nanofiber slurry and filter aid, then add it to the coarse fiber slurry, add the binder, and stir to form a dispersion with uniform concentration;

[0144] The pre-mixing process includes the following stages:

[0145] S21 stretching stage: Stir at 30 rpm for 1 hour at 50℃;

[0146] S22 encapsulation stage: Stir at 180 rpm for 1.3 hours at 45°C;

[0147] S23 Shaping Stage: Stir at 20 rpm for 0.6 hours at 25℃;

[0148] S3: Molding, the stirred dispersion is placed on the upper surface of the screen, and a vacuum is drawn from the lower surface of the screen to form a negative pressure until the moisture content of the initial product is less than 100%, thus forming the initial product;

[0149] The vacuum forming process is as follows:

[0150] S31: Vacuum level is -50Kpa;

[0151] S32: Vacuum level is -90KPa;

[0152] The sieve is double-layered, with one layer having a mesh size of 110 mesh and the other layer having a mesh size of 400 mesh. The mesh size of the layer closer to the dispersion is smaller than that of the layer farther away from the dispersion.

[0153] S4: Drying, the initial finished product is shaped and dried at 1600℃ for 4 hours until the moisture content is less than 10%;

[0154] S5: Punching, cutting the initial product into the finished product.

[0155] Examples 1-3:

[0156] A depth filtration medium includes a filter medium body comprising fibers, a filter aid, and an adhesive, wherein the fibers are bonded together by the adhesive, and the filter medium body has a first side for receiving the liquid to be filtered and a second side for discharging the permeate.

[0157] The fiber is cellulose fiber. The coarse fiber is stacked and entangled to form the filter medium body skeleton. The ultrafine nanofiber is wrapped around the outside of the filter aid to form a mesh-like wrapping part. The mesh-like wrapping part and the filter aid form a dispersion in the pores of the filter medium body skeleton.

[0158] The composition of each component is as follows: coarse fiber 10 wt%, ultrafine nanofiber 33 wt%, filter aid 47 wt%, binder 5 wt%; among which:

[0159] The diameter of the coarse fibers is 10-15μm, and the freeness in Canada is 520ml;

[0160] The diameter of the ultrafine nanofibers is 25-35μm, the freeness is 100ml, and the length is 1-2mm.

[0161] The filter aid is diatomaceous earth with an average particle size D50 of 7 μm, a particle size distribution dispersion of 3.1, and a permeability of 1 dracy.

[0162] The wet strength of the deep filter medium is 315 kPa and the accuracy is 1.5 μm. The filter medium body is positively charged, and the amount of charge shows a gradient change that increases continuously from the first side to the second side.

[0163] Take the filter media body and feed a 20 ppm yellow soap dye solution to the first side at a constant rate of 5 ml / min. When the transmittance of the permeate at 430 nm drops to 95%, the permeate amount of the yellow soap dye solution is 5736 μg / cm³. 3 ;

[0164] in:

[0165] The permeability from the first side in the first region, which is 0-33% of the thickness of the filter medium body, is 785 μg / cm². 3 The density is 0.3g / cm. 3 The porosity is 37%.

[0166] The permeability from the first side in the third region, which is 66-100% of the thickness of the filter medium body, is 1864 μg / cm³. 3 The density is 0.36 g / cm. 3 The porosity is 21%.

[0167] The preparation method of depth filtration media includes the following preparation steps:

[0168] S1: Pulping, coarse fibers and ultrafine nanofibers are selected and mixed with water to obtain 4wt% coarse fiber slurry and 1wt% ultrafine nanofiber slurry;

[0169] S2: Mixing, pre-stir the ultrafine nanofiber slurry and filter aid, then add it to the coarse fiber slurry, add the binder, and stir to form a dispersion with uniform concentration;

[0170] The pre-mixing process includes the following stages:

[0171] S21 stretching stage: Stir at 40 rpm for 1.5 hours at 40℃;

[0172] S22 encapsulation stage: Stir at 180 rpm for 1.5 h at 40℃;

[0173] S23 Shaping Stage: Stir at 30 rpm for 0.8 h at 30℃;

[0174] S3: Molding, the stirred dispersion is placed on the upper surface of the screen, and a vacuum is drawn from the lower surface of the screen to form a negative pressure until the moisture content of the initial product is less than 100%, thus forming the initial product;

[0175] The vacuum forming process is as follows:

[0176] S31: The vacuum level is -40 kPa;

[0177] S32: Vacuum level is -80KPa;

[0178] The sieve is double-layered, with one layer having a mesh size of 110 mesh and the other layer having a mesh size of 400 mesh. The mesh size of the layer closer to the dispersion is smaller than that of the layer farther away from the dispersion.

[0179] S4: Drying, the initial finished product is shaped and dried at 160℃ for 5 hours until the moisture content is less than 10%;

[0180] S5: Punching, cutting the initial product into the finished product.

[0181] Example 2-1:

[0182] A depth filtration medium includes a filter medium body comprising fibers, a filter aid, and an adhesive, wherein the fibers are bonded together by the adhesive, and the filter medium body has a first side for receiving the liquid to be filtered and a second side for discharging the permeate.

[0183] The fiber is cellulose fiber. The coarse fiber is stacked and entangled to form the filter medium body skeleton. The ultrafine nanofiber is wrapped around the outside of the filter aid to form a mesh-like wrapping part. The mesh-like wrapping part and the filter aid form a dispersion in the pores of the filter medium body skeleton.

[0184] The composition of each component is as follows: coarse fiber 17 wt%, ultrafine nanofiber 35 wt%, filter aid 41 wt%, binder 7 wt%; among which:

[0185] The diameter of the coarse fibers is 10-15μm, and the freeness in Canada is 610ml;

[0186] The diameter of the ultrafine nanofibers is 70-90nm, the freeness is 220ml, and the length is 2-3mm.

[0187] The filter aid is silica with an average particle size D50 of 28 μm and a particle size distribution dispersion of 2.5.

[0188] The wet strength of the depth filter media is 252 kPa, and the accuracy is 6 μm.

[0189] The distribution of filter aids in each area is as follows:

[0190] The thickness of the filter medium body in the first region, located on the first side at 0-33% of the first side thickness, is 40.1 wt%.

[0191] The thickness of the filter medium body in the second region, which is 33-66% from the first side, is 41.1 wt%.

[0192] The content from the first side at the third region, which is 66-100% of the thickness of the filter media body, is 41.8 wt%.

[0193] The filter medium body is positively charged, and the amount of charge changes in a gradient that increases continuously from the first side to the second side.

[0194] Take the filter media body and feed a 20 ppm yellow soap dye solution to the first side at a constant rate of 5 ml / min. When the transmittance of the permeate at 430 nm drops to 95%, the permeate amount of the yellow soap dye solution is 4365 μg / cm³. 3 ;

[0195] in:

[0196] The permeability from the first side in the first region, which is 0-33% of the thickness of the filter medium body, is 894 μg / cm². 3 The density is 0.26 g / cm. 3 The porosity is 47%.

[0197] The permeability from the first side in the third region, which is 66-100% of the thickness of the filter medium body, is 1438 μg / cm³. 3 The density is 0.34 g / cm. 3 The porosity is 28%.

[0198] The preparation method of depth filtration media includes the following preparation steps:

[0199] S1: Pulping, coarse fibers and ultrafine nanofibers are selected and mixed with water to obtain 5wt% coarse fiber slurry and 2wt% ultrafine nanofiber slurry;

[0200] S2: Mixing, pre-stir the ultrafine nanofiber slurry and filter aid, then add it to the coarse fiber slurry, add the binder, and stir to form a dispersion with uniform concentration;

[0201] The pre-mixing process includes the following stages:

[0202] S21 stretching stage: Stir at 250 rpm for 1.3 hours at 40℃;

[0203] S22 encapsulation stage: Stir at 100 rpm for 1.5 h at 380℃;

[0204] S23 Shaping Stage: Stir at 20 rpm for 0.8 hours at 29℃;

[0205] S3: Molding, the stirred dispersion is placed on the upper surface of the screen, and a vacuum is drawn from the lower surface of the screen to form a negative pressure until the moisture content of the initial product is less than 100%, thus forming the initial product;

[0206] The vacuum forming process is as follows:

[0207] S31: The vacuum level is -40 kPa;

[0208] S32: Vacuum level is -80KPa;

[0209] The sieve is double-layered, with one layer having a mesh size of 60 mesh and the other layer having a mesh size of 200 mesh. The mesh size of the layer closer to the dispersion is smaller than that of the layer farther away from the dispersion.

[0210] S4: Drying, the initial finished product is shaped and dried at 150℃ for 4 hours until the moisture content is less than 10%;

[0211] S5: Punching, cutting the initial product into the finished product.

[0212] Example 2-2:

[0213] A depth filtration medium includes a filter medium body comprising fibers, a filter aid, and an adhesive, wherein the fibers are bonded together by the adhesive, and the filter medium body has a first side for receiving the liquid to be filtered and a second side for discharging the permeate.

[0214] The fiber is cellulose fiber. The coarse fiber is stacked and entangled to form the filter medium body skeleton. The ultrafine nanofiber is wrapped around the outside of the filter aid to form a mesh-like wrapping part. The mesh-like wrapping part and the filter aid form a dispersion in the pores of the filter medium body skeleton.

[0215] The composition of each component is as follows: coarse fiber 12 wt%, ultrafine nanofiber 29 wt%, filter aid 54 wt%, binder 5 wt%; among which:

[0216] The diameter of the coarse fibers is 10-20μm, and the freeness in Canada is 620ml;

[0217] The diameter of the ultrafine nanofibers is 80-90nm, the freeness is 200ml, and the length is 2-4mm.

[0218] The filter aid is silica with an average particle size D50 of 25 μm and a particle size distribution dispersion of 2.3.

[0219] The wet strength of the depth filter media is 268 kPa, and the accuracy is 8 μm.

[0220] The distribution of filter aids in each area is as follows:

[0221] The thickness of the filter medium body in the first region, located on the first side at 0-33% of the first side thickness, is 54.5 wt%.

[0222] The thickness of the filter medium body is 55.7 wt% in the second region, which is 33-66% of the thickness of the first side.

[0223] The content from the first side at the third region, which is 66-100% of the thickness of the filter media body, is 51.8 wt%.

[0224] The standard deviation of the filter aid content in each region was 0.016, and the ratio between the standard deviation and the mean was 0.03.

[0225] The filter medium body is positively charged, and the amount of charge changes in a gradient that increases continuously from the first side to the second side.

[0226] Take the filter media body and feed a 20 ppm yellow soap dye solution to the first side at a constant rate of 5 ml / min. When the transmittance of the permeate at 430 nm drops to 95%, the permeate amount of the yellow soap dye solution is 3867 μg / cm³. 3 ;

[0227] in:

[0228] The permeability from the first side in the first region, which is 0-33% of the thickness of the filter medium body, is 736 μg / cm³. 3 The density is 0.28g / cm. 3 The porosity is 51%.

[0229] The permeability from the first side in the third region, which is 66-100% of the thickness of the filter medium body, is 1252 μg / cm³. 3 The density is 0.33g / cm. 3 The porosity is 30%.

[0230] The preparation method of depth filtration media includes the following preparation steps:

[0231] S1: Pulping, coarse fibers and ultrafine nanofibers are selected and mixed with water to obtain 5wt% coarse fiber slurry and 2wt% ultrafine nanofiber slurry;

[0232] S2: Mixing, pre-stir the ultrafine nanofiber slurry and filter aid, then add it to the coarse fiber slurry, add the binder, and stir to form a dispersion with uniform concentration;

[0233] The pre-mixing process includes the following stages:

[0234] S21 stretching stage: Stir at 20 rpm for 1.5 hours at 35°C;

[0235] S22 encapsulation stage: Stir at 120 rpm for 1.2 h at 40℃;

[0236] S23 Shaping Stage: Stir at 30 rpm for 0.6 h at 30℃;

[0237] S3: Molding, the stirred dispersion is placed on the upper surface of the screen, and a vacuum is drawn from the lower surface of the screen to form a negative pressure until the moisture content of the initial product is less than 100%, thus forming the initial product;

[0238] The vacuum forming process is as follows:

[0239] S31: The vacuum level is -40 kPa;

[0240] S32: Vacuum level is -70KPa;

[0241] The sieve is double-layered, with one layer having a mesh size of 60 mesh and the other layer having a mesh size of 200 mesh. The mesh size of the layer closer to the dispersion is smaller than that of the layer farther away from the dispersion.

[0242] S4: Drying, the initial finished product is shaped and dried at 120℃ for 4 hours until the moisture content is less than 10%;

[0243] S5: Punching, cutting the initial product into the finished product.

[0244] The SEM image of the effluent surface of the deep filtration medium prepared in this embodiment is shown below. Figure 1 As shown in the figure, the ultrafine nanofibers effectively coat the silica, preventing it from detaching.

[0245] Examples 2-3:

[0246] A depth filtration medium includes a filter medium body comprising fibers, a filter aid, and an adhesive, wherein the fibers are bonded together by the adhesive, and the filter medium body has a first side for receiving the liquid to be filtered and a second side for discharging the permeate.

[0247] The fiber is cellulose fiber. The coarse fiber is stacked and entangled to form the filter medium body skeleton. The ultrafine nanofiber is wrapped around the outside of the filter aid to form a mesh-like wrapping part. The mesh-like wrapping part and the filter aid form a dispersion in the pores of the filter medium body skeleton.

[0248] The composition of each component is as follows: coarse fiber 8 wt%, ultrafine nanofiber 18 wt%, filter aid 70 wt%, binder 4 wt%; among which:

[0249] The diameter of the coarse fibers is 15-25μm, and the freeness in Canada is 670ml;

[0250] The diameter of the ultrafine nanofibers is 60-80nm, the freeness is 190ml, and the length is 2-4mm.

[0251] The filter aid is silica with an average particle size D50 of 21 μm and a particle size distribution dispersion of 2.2.

[0252] The wet strength of the depth filter media is 273 kPa, and the accuracy is 9 μm.

[0253] The distribution of filter aids in each area is as follows:

[0254] The thickness of the filter medium body in the first region, located on the first side at 0-33% of the first side thickness, is 67.3 wt%.

[0255] The content of the second region, located on the first side at a thickness of 33-66% of the filter media body, is 70.1 wt%.

[0256] The content is 72.6 wt% in the third region, which is 66-100% of the thickness of the filter medium body, from the first side.

[0257] The standard deviation of the filter aid content in each region was 0.022, and the ratio between the standard deviation and the mean was 0.03.

[0258] The filter medium body is positively charged, and the amount of charge changes in a gradient that increases continuously from the first side to the second side.

[0259] Take the filter media body and feed a 20 ppm yellow soap dye solution to the first side at a constant rate of 5 ml / min. When the transmittance of the permeate at 430 nm drops to 95%, the permeate amount of the yellow soap dye solution is 2674 μg / cm³. 3 ;

[0260] in:

[0261] The permeability from the first side in the first region, which is 0-33% of the thickness of the filter medium body, is 584 μg / cm². 3 The density is 0.25g / cm. 3 The porosity is 52%.

[0262] The permeability from the first side in the third region, which is 66-100% of the thickness of the filter media body, is 963 μg / cm³. 3 The density is 0.33g / cm. 3 The porosity is 30%.

[0263] The preparation method of depth filtration media includes the following preparation steps:

[0264] S1: Pulping, coarse fibers and ultrafine nanofibers are selected and mixed with water to obtain 5wt% coarse fiber slurry and 2wt% ultrafine nanofiber slurry;

[0265] S2: Mixing, pre-stir the ultrafine nanofiber slurry and filter aid, then add it to the coarse fiber slurry, add the binder, and stir to form a dispersion with uniform concentration;

[0266] The pre-mixing process includes the following stages:

[0267] S21 stretching stage: Stir at 30 rpm for 1.3 hours at 40℃;

[0268] S22 encapsulation stage: Stir at 80 rpm for 1.5 h at 40℃;

[0269] S23 Shaping Stage: Stir at 35 rpm for 0.8 hours at 26℃;

[0270] S3: Molding, the stirred dispersion is placed on the upper surface of the screen, and a vacuum is drawn from the lower surface of the screen to form a negative pressure until the moisture content of the initial product is less than 100%, thus forming the initial product;

[0271] The vacuum forming process is as follows:

[0272] S31: The vacuum level is -40 kPa;

[0273] S32: Vacuum level is -70KPa;

[0274] The sieve is double-layered, with one layer having a mesh size of 60 mesh and the other layer having a mesh size of 200 mesh. The mesh size of the layer closer to the dispersion is smaller than that of the layer farther away from the dispersion.

[0275] S4: Drying, the initial finished product is shaped and dried at 100℃ for 5 hours until the moisture content is less than 10%;

[0276] S5: Punching, cutting the initial product into the finished product.

[0277] Example 3-1:

[0278] A depth filtration medium includes a filter medium body comprising fibers, a filter aid, and an adhesive, wherein the fibers are bonded together by the adhesive, and the filter medium body has a first side for receiving the liquid to be filtered and a second side for discharging the permeate.

[0279] The fiber is cellulose fiber. The coarse fiber is stacked and entangled to form the filter medium body skeleton. The ultrafine nanofiber is wrapped around the outside of the filter aid to form a mesh-like wrapping part. The mesh-like wrapping part and the filter aid form a dispersion in the pores of the filter medium body skeleton.

[0280] The composition of each component is as follows: coarse fiber 19 wt%, ultrafine nanofiber 35 wt%, filter aid 40 wt%, binder 6 wt%; among which:

[0281] The diameter of the coarse fibers is 45-50μm, and the freeness in Canada is 780ml;

[0282] The diameter of the ultrafine nanofibers is 130-150nm, the freeness is 310ml, and the length is 3-5mm.

[0283] The filter aid is diatomaceous earth with an average particle size D50 of 60 μm, a particle size distribution dispersion of 1.7, and a permeability of 5.4 dracy.

[0284] The wet strength of the deep filter medium is 174 kPa and the accuracy is 29 μm; the filter medium body is positively charged, and the amount of charge shows a gradient change that increases continuously from the first side to the second side.

[0285] Take the filter media body and feed a 20 ppm yellow soap dye solution to the first side at a constant rate of 5 ml / min. When the transmittance of the permeate at 430 nm drops to 95%, the permeate amount of the yellow soap dye solution is 1348 μg / cm³. 3 ;

[0286] in:

[0287] The permeability from the first side in the first region, which is 0-33% of the thickness of the filter medium body, is 238 μg / cm². 3 The density is 0.22g / cm. 3 The porosity is 60%.

[0288] The permeability from the first side in the third region, which is 66-100% of the thickness of the filter media body, is 437 μg / cm³. 3 The density is 0.3g / cm. 3 The porosity is 47%.

[0289] The preparation method of depth filtration media includes the following preparation steps:

[0290] S1: Pulping, coarse fibers and ultrafine nanofibers are selected and mixed with water to obtain 6wt% coarse fiber slurry and 3wt% ultrafine nanofiber slurry;

[0291] S2: Mixing, pre-stir the ultrafine nanofiber slurry and filter aid, then add it to the coarse fiber slurry, add the binder, and stir to form a dispersion with uniform concentration;

[0292] The pre-mixing process includes the following stages:

[0293] S21 stretching stage: Stir at 30 rpm for 1.5 hours at 35°C;

[0294] S22 encapsulation stage: Stir at 100 rpm for 1.5 h at 45°C;

[0295] S23 Shaping Stage: Stir at 40 rpm for 0.8 hours at 28℃;

[0296] S3: Molding, the stirred dispersion is placed on the upper surface of the screen, and a vacuum is drawn from the lower surface of the screen to form a negative pressure until the moisture content of the initial product is less than 100%, thus forming the initial product;

[0297] The vacuum forming process is as follows:

[0298] S31: The vacuum level is -10 kPa;

[0299] S32: Vacuum level is -60KPa;

[0300] The sieve is double-layered, with one layer having a mesh size of 30 mesh and the other layer having a mesh size of 100 mesh. The mesh size of the layer closer to the dispersion is smaller than that of the layer farther away from the dispersion.

[0301] S4: Drying, the initial finished product is shaped and dried at 80℃ for 8 hours until the moisture content is less than 10%;

[0302] S5: Punching, cutting the initial product into the finished product.

[0303] Example 3-2:

[0304] A depth filtration medium includes a filter medium body comprising fibers, a filter aid, and an adhesive, wherein the fibers are bonded together by the adhesive, and the filter medium body has a first side for receiving the liquid to be filtered and a second side for discharging the permeate.

[0305] The fiber is cellulose fiber. The coarse fiber is stacked and entangled to form the filter medium body skeleton. The ultrafine nanofiber is wrapped around the outside of the filter aid to form a mesh-like wrapping part. The mesh-like wrapping part and the filter aid form a dispersion in the pores of the filter medium body skeleton.

[0306] The composition of each component is as follows: coarse fiber 12 wt%, ultrafine nanofiber 20 wt%, filter aid 62 wt%, binder 6 wt%; among which:

[0307] The diameter of the coarse fibers is 40-50μm, and the freeness in Canada is 750ml;

[0308] The diameter of the ultrafine nanofibers is 140-150nm, the freeness is 320ml, and the length is 4-5mm.

[0309] The filter aid is diatomaceous earth with an average particle size D50 of 75 μm, a particle size distribution dispersion of 1.5, and a permeability of 4.4 dracy.

[0310] The wet strength of the deep filter medium is 192 kPa and the accuracy is 26 μm; the filter medium body is positively charged, and the amount of charge shows a gradient change that increases continuously from the first side to the second side.

[0311] Take the filter media body and feed a 20 ppm yellow soap dye solution to the first side at a constant rate of 5 ml / min. When the transmittance of the permeate at 430 nm drops to 95%, the permeate amount of the yellow soap dye solution is 854 μg / cm³. 3 ;

[0312] in:

[0313] The permeability from the first side in the first region, which is 0-33% of the thickness of the filter medium body, is 165 μg / cm². 3 The density is 0.21g / cm. 3 The porosity is 69%.

[0314] The permeability from the first side in the third region, which is 66-100% of the thickness of the filter medium body, is 298 μg / cm³. 3 The density is 0.3g / cm. 3 The porosity is 54%.

[0315] The preparation method of depth filtration media includes the following preparation steps:

[0316] S1: Pulping, coarse fibers and ultrafine nanofibers are selected and mixed with water to obtain 6wt% coarse fiber slurry and 3wt% ultrafine nanofiber slurry;

[0317] S2: Mixing, pre-stir the ultrafine nanofiber slurry and filter aid, then add it to the coarse fiber slurry, add the binder, and stir to form a dispersion with uniform concentration;

[0318] The pre-mixing process includes the following stages:

[0319] S21 stretching stage: Stir at 20 rpm for 1.5 hours at 40℃;

[0320] S22 encapsulation stage: Stir at 80 rpm for 1 hour at 50°C;

[0321] S23 Shaping stage: Stir at 20 rpm for 1 hour at 20℃;

[0322] S3: Molding, the stirred dispersion is placed on the upper surface of the screen, and a vacuum is drawn from the lower surface of the screen to form a negative pressure until the moisture content of the initial product is less than 100%, thus forming the initial product;

[0323] The vacuum forming process is as follows:

[0324] S31: The vacuum level is -10 kPa;

[0325] S32: Vacuum level is -60KPa;

[0326] The sieve is double-layered, with one layer having a mesh size of 30 mesh and the other layer having a mesh size of 100 mesh. The mesh size of the layer closer to the dispersion is smaller than that of the layer farther away from the dispersion.

[0327] S4: Drying, the initial finished product is shaped and dried at 120℃ for 4 hours until the moisture content is less than 10%;

[0328] S5: Punching, cutting the initial product into the finished product.

[0329] Example 3-3:

[0330] A depth filtration medium includes a filter medium body comprising fibers, a filter aid, and an adhesive, wherein the fibers are bonded together by the adhesive, and the filter medium body has a first side for receiving the liquid to be filtered and a second side for discharging the permeate.

[0331] The fiber is cellulose fiber. The coarse fiber is stacked and entangled to form the filter medium body skeleton. The ultrafine nanofiber is wrapped around the outside of the filter aid to form a mesh-like wrapping part. The mesh-like wrapping part and the filter aid form a dispersion in the pores of the filter medium body skeleton.

[0332] The composition of each component is as follows: coarse fiber 6 wt%, ultrafine nanofiber 11 wt%, filter aid 80 wt%, binder 3 wt%; among which:

[0333] The diameter of the coarse fibers is 40-45μm, and the freeness in Canada is 770ml;

[0334] The diameter of the ultrafine nanofibers is 120-130nm, the freeness is 300ml, and the length is 4-5mm.

[0335] The filter aid is diatomaceous earth with an average particle size D50 of 66 μm, a particle size distribution dispersion of 1.3, and a permeability of 4.4 dracy.

[0336] The wet strength of the deep filter medium is 178 kPa and the accuracy is 23 μm; the filter medium body is positively charged, and the amount of charge shows a gradient change that increases continuously from the first side to the second side.

[0337] Take the filter media body and feed a 20 ppm yellow soap dye solution to the first side at a constant rate of 5 ml / min. When the transmittance of the permeate at 430 nm drops to 95%, the permeate amount of the yellow soap dye solution is 489 μg / cm³. 3 ;

[0338] in:

[0339] The permeability from the first side in the first region, which is 0-33% of the thickness of the filter medium body, is 125 μg / cm². 3 The density is 0.21g / cm. 3 The porosity is 69%.

[0340] The permeability from the first side in the third region, which is 66-100% of the thickness of the filter medium body, is 188 μg / cm. 3 The density is 0.3g / cm. 3 The porosity is 54%.

[0341] The preparation method of depth filtration media includes the following preparation steps:

[0342] S1: Pulping, coarse fibers and ultrafine nanofibers are selected and mixed with water to obtain 6wt% coarse fiber slurry and 3wt% ultrafine nanofiber slurry;

[0343] S2: Mixing, pre-stir the ultrafine nanofiber slurry and filter aid, then add it to the coarse fiber slurry, add the binder, and stir to form a dispersion with uniform concentration;

[0344] The pre-mixing process includes the following stages:

[0345] S21 stretching stage: Stir at 20 rpm for 1.5 hours at 35°C;

[0346] S22 encapsulation stage: Stir at 200 rpm for 1 hour at 50°C;

[0347] S23 Shaping Stage: Stir at 30 rpm for 0.7 h at 30℃;

[0348] S3: Molding, the stirred dispersion is placed on the upper surface of the screen, and a vacuum is drawn from the lower surface of the screen to form a negative pressure until the moisture content of the initial product is less than 100%, thus forming the initial product;

[0349] The vacuum forming process is as follows:

[0350] S31: The vacuum level is -20 kPa;

[0351] S32: Vacuum level is -60KPa;

[0352] The sieve is double-layered, with one layer having a mesh size of 30 mesh and the other layer having a mesh size of 100 mesh. The mesh size of the layer closer to the dispersion is smaller than that of the layer farther away from the dispersion.

[0353] S4: Drying, the initial finished product is shaped and dried at 100℃ for 6 hours until the moisture content is less than 10%;

[0354] S5: Punching, cutting the initial product into the finished product.

[0355] Example 4-1:

[0356] A depth filtration medium includes a filter medium body comprising fibers and a filter aid, the filter medium body having a first side for receiving liquid to be filtered and a second side for discharging permeate.

[0357] The fiber is polyacrylonitrile fiber. The coarse fibers are stacked and entangled to form the filter medium body skeleton. The ultrafine nanofibers are wrapped around the outside of the filter aid to form a mesh-like wrapping part. The mesh-like wrapping part and the filter aid form a dispersion in the pores of the filter medium body skeleton.

[0358] The composition of each component is as follows: crude fiber 18 wt%, ultrafine nanofiber 64 wt%, and filter aid 18 wt%; among which:

[0359] The diameter of the coarse fibers is 10-15μm, and the freeness in Canada is 630ml;

[0360] The diameter of the ultrafine nanofibers is 85-95nm, the freeness is 210ml, and the length is 2-4mm.

[0361] The filter aid is silica with an average particle size D50 of 22 μm and a particle size distribution dispersion of 2.4.

[0362] The wet strength of the depth filter media is 221 kPa, and the accuracy is 9 μm.

[0363] in:

[0364] The density of the first region, located on the first side and within 0-33% of the filter media body thickness, is 0.16 g / cm. 3 The porosity is 70%.

[0365] The density of the third region, located on the first side and within 66-100% of the filter media body thickness, is 0.24 g / cm². 3 The porosity is 58%.

[0366] The preparation method of depth filtration media includes the following preparation steps:

[0367] S1: Pulping, coarse fibers and ultrafine nanofibers are selected and mixed with water to obtain 5wt% coarse fiber slurry and 2wt% ultrafine nanofiber slurry;

[0368] S2: Mixing, pre-stir the ultrafine nanofiber slurry and filter aid, then add them to the coarse fiber slurry and stir to form a uniformly concentrated dispersion;

[0369] The pre-mixing process includes the following stages:

[0370] S21 stretching stage: Stir at 25 rpm for 1.4 hours at 35°C;

[0371] S22 encapsulation stage: Stir at 130 rpm for 1.3 h at 40℃;

[0372] S23 Shaping Stage: Stir at 25 rpm for 0.7 h at 30℃;

[0373] S3: Molding, the stirred dispersion is placed on the upper surface of the screen, and a vacuum is drawn from the lower surface of the screen to form a negative pressure until the moisture content of the initial product is less than 100%, thus forming the initial product;

[0374] The vacuum forming process is as follows:

[0375] S31: Vacuum level is -45Kpa;

[0376] S32: Vacuum level is -80KPa;

[0377] The sieve is double-layered, with one layer having a mesh size of 60 mesh and the other layer having a mesh size of 200 mesh. The mesh size of the layer closer to the dispersion is smaller than that of the layer farther away from the dispersion.

[0378] S4: Drying, the initial finished product is shaped and dried at 120℃ for 4 hours until the moisture content is less than 10%;

[0379] S5: Punching, cutting the initial product into the finished product.

[0380] Example 4-2:

[0381] A depth filtration medium includes a filter medium body comprising fibers and a filter aid, the filter medium body having a first side for receiving liquid to be filtered and a second side for discharging permeate.

[0382] The fiber is polyacrylonitrile fiber. The coarse fibers are stacked and entangled to form the filter medium body skeleton. The ultrafine nanofibers are wrapped around the outside of the filter aid to form a mesh-like wrapping part. The mesh-like wrapping part and the filter aid form a dispersion in the pores of the filter medium body skeleton.

[0383] The composition of each component is as follows: coarse fiber 21 wt%, ultrafine nanofiber 45 wt%, and filter aid 35 wt%; among which:

[0384] The diameter of the coarse fibers is 15-20μm, and the freeness in Canada is 650ml;

[0385] The diameter of the ultrafine nanofibers is 85-95nm, the freeness is 200ml, and the length is 2-4mm.

[0386] The filter aid is silica with an average particle size D50 of 25 μm and a particle size distribution dispersion of 2.7.

[0387] The wet strength of the depth filter media is 245 kPa, and the accuracy is 6 μm.

[0388] in:

[0389] The density of the first region, located on the first side and within 0-33% of the filter media body thickness, is 0.21 g / cm². 3 The porosity is 66%.

[0390] The density of the third region, located on the first side and within 66-100% of the filter media body thickness, is 0.28 g / cm². 3 The porosity is 49%;

[0391] The preparation method of depth filtration media includes the following preparation steps:

[0392] S1: Pulping, coarse fibers and ultrafine nanofibers are selected and mixed with water to obtain 5wt% coarse fiber slurry and 2wt% ultrafine nanofiber slurry;

[0393] S2: Mixing, pre-stir the ultrafine nanofiber slurry and filter aid, then add them to the coarse fiber slurry and stir to form a uniformly concentrated dispersion;

[0394] The pre-mixing process includes the following stages:

[0395] S21 stretching stage: Stir at 20 rpm for 1.5 hours at 35°C;

[0396] S22 encapsulation stage: Stir at 150 rpm for 1.2 h at 40℃;

[0397] S23 Shaping Stage: Stir at 35 rpm for 0.8 hours at 30℃;

[0398] S3: Molding, the stirred dispersion is placed on the upper surface of the screen, and a vacuum is drawn from the lower surface of the screen to form a negative pressure until the moisture content of the initial product is less than 100%, thus forming the initial product;

[0399] The vacuum forming process is as follows:

[0400] S31: The vacuum level is -55 kPa;

[0401] S32: Vacuum level is -85KPa;

[0402] The sieve is double-layered, with one layer having a mesh size of 60 mesh and the other layer having a mesh size of 200 mesh. The mesh size of the layer closer to the dispersion is smaller than that of the layer farther away from the dispersion.

[0403] S4: Drying, the initial finished product is shaped and dried at 120℃ for 4 hours until the moisture content is less than 10%;

[0404] S5: Punching, cutting the initial product into the finished product.

[0405] Example 4-3:

[0406] A depth filtration medium includes a filter medium body comprising fibers and a filter aid, the filter medium body having a first side for receiving liquid to be filtered and a second side for discharging permeate.

[0407] The fiber is polyacrylonitrile fiber. The coarse fibers are stacked and entangled to form the filter medium body skeleton. The ultrafine nanofibers are wrapped around the outside of the filter aid to form a mesh-like wrapping part. The mesh-like wrapping part and the filter aid form a dispersion in the pores of the filter medium body skeleton.

[0408] The composition of each component is as follows: crude fiber 18 wt%, ultrafine nanofiber 30 wt%, and filter aid 52 wt%; among which:

[0409] The diameter of the coarse fibers is 15-20μm, and the freeness in Canada is 690ml;

[0410] The diameter of the ultrafine nanofibers is 80-90nm, the freeness is 200ml, and the length is 3-4mm.

[0411] The filter aid is silica, with an average particle size D50 of 29 μm and a particle size distribution dispersion of 2.5.

[0412] The wet strength of the depth filter media is 34 kPa, and the accuracy is 4 μm.

[0413] in:

[0414] The density of the first region, located on the first side and within 0-33% of the filter media body thickness, is 0.23 g / cm². 3 The porosity is 62%.

[0415] The density of the third region, located on the first side and within 66-100% of the filter media body thickness, is 0.32 g / cm². 3 The porosity is 41%.

[0416] The preparation method of depth filtration media includes the following preparation steps:

[0417] S1: Pulping, coarse fibers and ultrafine nanofibers are selected and mixed with water to obtain 5wt% coarse fiber slurry and 2wt% ultrafine nanofiber slurry;

[0418] S2: Mixing, pre-stir the ultrafine nanofiber slurry and filter aid, then add them to the coarse fiber slurry and stir to form a uniformly concentrated dispersion;

[0419] The pre-mixing process includes the following stages:

[0420] S21 stretching stage: Stir at 20 rpm for 1.5 hours at 40℃;

[0421] S22 encapsulation stage: Stir at 130 rpm for 1.2 h at 45℃;

[0422] S23 Shaping Stage: Stir at 20 rpm for 0.8 hours at 30℃;

[0423] S3: Molding, the stirred dispersion is placed on the upper surface of the screen, and a vacuum is drawn from the lower surface of the screen to form a negative pressure until the moisture content of the initial product is less than 100%, thus forming the initial product;

[0424] The vacuum forming process is as follows:

[0425] S31: Vacuum level is -45Kpa;

[0426] S32: Vacuum level is -70KPa;

[0427] The sieve is double-layered, with one layer having a mesh size of 60 mesh and the other layer having a mesh size of 200 mesh. The mesh size of the layer closer to the dispersion is smaller than that of the layer farther away from the dispersion.

[0428] S4: Drying, the initial finished product is shaped and dried at 120℃ for 4 hours until the moisture content is less than 10%;

[0429] S5: Punching, cutting the initial product into the finished product.

[0430] Comparative Example 1: The difference from Examples 2-2 is that the diameter of the coarse fiber is 15-20 μm, and the diameter of the ultrafine nanofiber is 1-5 nm.

[0431] Comparative Example 2: The difference from Example 2-2 is that the diameter of the ultrafine nanofibers is 550-600 nm and the diameter of the filter aid is 5 μm.

[0432] Comparative Example 3: The difference from Examples 2-2 is that the length of the ultrafine nanofibers is 0.5-0.8 mm.

[0433] Comparative Example 4: The difference from Examples 2-2 is that the mixing in step S2 during the preparation of the deep filtration media is as follows: coarse fiber slurry and ultrafine nanofiber slurry are mixed, and then filter aid and binder are added, and stirred at 40°C and 50 rpm for 2 hours.

[0434] The distribution of filter aids in each area is as follows:

[0435] The thickness of the filter medium body in the first region, located on the first side at 0-33% of the first side thickness, is 47.3 wt%.

[0436] The thickness of the filter medium body in the second region, which is 33-66% from the first side, is 56.9 wt%.

[0437] The content from the first side at the third region, which is 66-100% of the thickness of the filter media body, is 57.8 wt%.

[0438] The standard deviation of the filter aid content in each region was 0.04, and the ratio between the standard deviation and the mean was 0.08.

[0439] The deep filter media prepared in Examples 1-2, 2-2, 3-2 and Comparative Examples 1-4 before and after pre-rinsing were compared in terms of cell harvesting fluid filtration. The method was as follows: 15 layers of deep filter media with the same area and a thickness of 4 mm were stacked to obtain a deep filter. The cell density was 25*10⁻⁶. 6 400L of cell harvest medium containing cells / ml, cell viability of 90%, and turbidity of 2376 NTU was used at a flow rate of 130L / ml. 2 Filtration was performed at a flow rate of / hr, and the turbidity of the filtrate and the differential pressure of filtration were tested upon completion. Pre-rinsing was conducted at a flow rate of 10L / m³. 2 Pre-rinsing was performed underwater at a rate of 1000 rpm until no impurities were rinsed out. The results are shown in the table below.

[0440]

[0441] As can be seen from the above data, the filtration accuracy of the deep filter media prepared in the embodiments of the present invention remains basically unchanged before and after pre-rinsing. In Comparative Example 1, the diameter of the ultrafine nanofibers is too small, making it difficult to bind the filter aid during mixing and stirring; the diameter of the ultrafine nanofibers is too large, making it easy for the filter aid to fall off from the network encapsulation part; the length of the ultrafine nanofibers is too short, which also fails to achieve a good encapsulation effect on the filter aid. Therefore, the filtration performance decreases after pre-rinsing.

[0442] Meanwhile, the deep filtration media prepared in Examples 1-1, 2-1 and 3-1 were compared with commercially available deep filtration media with similar formulations and charge amounts, but with unevenly distributed charge content, through cell harvesting liquid filtration. The results are shown in the table below.

[0443] Example 1-1 5-15 0.5 Commercially available 1 (X0HC) 15-25 0.8 Example 2-1 45-55 1.1 Commercially available 2 (C0HC) 100-120 1.5 Example 3-1 120-200 1.1 Commercially available 3 (D0HC) 200-400 1.2

[0444] As shown in the table above, after filtering the same volume of cell harvest fluid, the present invention exhibits lower turbidity and pressure difference compared to commercially available products, indicating that the deep filtration medium prepared by the present invention has a higher utilization rate.

[0445] The preferred embodiments of the present invention have been described in detail above. However, it should be understood that after reading the above teachings, those skilled in the art can make various alterations or modifications to the present invention. These equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A depth filtration medium, comprising a filter medium body, wherein the filter medium body includes fibers and a filter aid, the filter medium body having a first side for receiving the liquid to be filtered and a second side for discharging the permeate, characterized in that: The fibers include coarse fibers and ultrafine nanofibers, the ultrafine nanofibers having a diameter of 5-150 nm; wherein, the coarse fibers are stacked and entangled to form the filter medium body skeleton, the ultrafine nanofibers are wrapped around the outside of the filter aid to form a mesh-like wrapping part, and the dispersion formed by the mesh-like wrapping part and the filter aid is dispersed in the pores of the filter medium body skeleton. The diameter ratio between the coarse fibers and the ultrafine nanofibers is 200-50; The ratio of the diameter of the ultrafine nanofibers to the average particle size D50 of the filter aid is 1:10-1000.

2. The depth filtration medium according to claim 1, characterized in that, The fiber comprises 20-40 wt% coarse fiber and 60-80 wt% ultrafine nanofiber.

3. The depth filtration medium according to claim 1, characterized in that, The length of the ultrafine nanofibers is 0.5-9 mm; the ratio of the length of the ultrafine nanofibers to the average particle size D50 of the filter aid is 50-5000.

4. The depth filtration medium according to claim 1, characterized in that, The diameter of the coarse fibers is 1-50 μm.

5. The depth filtration medium according to claim 1, characterized in that, The average particle size D50 of the filter aid is 0.05-80 μm.

6. The depth filtration medium according to claim 5, characterized in that, The particle size distribution of the filter aid has a dispersion of 0.5-4.

7. The depth filtration medium according to claim 1, characterized in that, The Canadian freeness of the coarse fiber is 450-800 ml; the Canadian freeness of the ultrafine nanofiber is 25-325 ml.

8. The depth filtration medium according to claim 1, characterized in that, The tightness of the first side to the second side exhibits a continuously increasing gradient change; Furthermore, at least on the second side, the ultrafine nanofibers on the outer periphery of the mesh-like wrapping portion are entangled with the filter medium body skeleton to prevent the filter aid from detaching.

9. The depth filtration medium according to claim 1, characterized in that, The first region is defined as the area from the first side where the thickness of the filter medium body is 0-33%. The second region is located at 33-66% of the thickness of the filter medium body from the first side. The third region is located at 66-100% of the thickness of the filter medium body from the first side. The ratio between the standard deviation and the average value of the filter aid content in each region is 0.01-0.

08.

10. The depth filtration medium according to claim 9, characterized in that, The standard deviation of the filter aid content in each region is 0.005-0.

04.

11. The depth filtration medium according to claim 1, characterized in that, The filter medium body is positively charged, and the amount of charge changes in a gradient that increases continuously from the first side to the second side. Take the filter media body and feed a 20 ppm yellow soap dye solution to the first side at a constant rate of 5 ml / min. When the transmittance of the permeate at 430 nm drops to 95%, the permeate amount of the yellow soap dye solution is 300-6500 μg / cm³. 3 ; in: The permeation rate from the first side in the first region, which is 0-33% of the thickness of the filter medium body, is L1. The permeability from the first side in the third region, which is 66-100% of the thickness of the filter medium body, is L2. The ratio of L1:L2 is 1:1.2-3; L1 is 120-2200 μg / cm³ 3 L2 is 150-4200 μg / cm 3 .

12. The depth filtration medium according to claim 1, characterized in that, The density of the first region located on the first side, within 0-33% of the thickness of the filter medium body, is t1. The density of the third region, which is 66-100% of the thickness of the filter medium body from the first side, is t2. The ratio of t1:t2 is 1:1.1-1.7; The density of the filter medium body is 0.2-0.38 g / cm³. 3 t1 is 0.15-0.35 g / cm³. 3 t2 is 0.23-0.40 g / cm³ 3 .

13. The depth filtration medium according to claim 1, characterized in that, In the filter media body: The porosity of the first region located on the first side, within 0-33% of the thickness of the filter medium body, is n1. The porosity of the third region, located on the first side and within 66-100% of the filter media body thickness, is n2. The ratio of n1:n2 is 1.1-5:1; Among them, n1 is 25-70%, and n2 is 5-60%.

14. The depth filtration medium according to claim 1, characterized in that, The fiber content in the filter medium body is 10-85 wt%, and the filter aid content is 15-90 wt%.

15. The depth filtration medium according to claim 1, characterized in that, The fibers include one or more of cellulose fibers, polyacrylonitrile fibers, polyester fibers, and polypropylene fibers.

16. The depth filtration medium according to claim 1, characterized in that, The filter aid includes one or more of diatomaceous earth, silica, and activated carbon.

17. The depth filtration medium according to claim 1, characterized in that, The filter media body also includes an adhesive, the adhesive content being 1-10 wt%; the adhesive includes one or more of melamine-formaldehyde resin, polyamide-epoxychlorohydrin resin, and glyoxal-polyacrylamide.

18. The depth filtration medium according to claim 17, characterized in that, The filter medium body also includes a charge additive, which accounts for 1-10 wt% of the total binder content in the filter medium body.

19. The depth filtration medium according to claim 18, characterized in that, The charge additive includes one or more of triethylenediamine, tetraethylenepentamine, and chitosan.

20. The depth filtration medium according to claim 1, characterized in that, The wet strength of the filter medium body is between 150-400 kPa.

21. A method for preparing a depth filtration medium as described in any one of claims 1-20, characterized in that, The preparation steps include the following: S1: Pulping, coarse fibers and ultrafine nanofibers are selected and mixed with water to pulverize, resulting in coarse fiber slurry and ultrafine nanofiber slurry; S2: Mixing, the ultrafine nanofiber slurry and filter aid are mixed and pre-stirred to prepare a dispersion, which is then added to the coarse fiber slurry and stirred to form a dispersion with uniform concentration; S3: Molding, the stirred dispersion is placed on the upper surface of the screen, and a vacuum is drawn from the lower surface of the screen to form a negative pressure, forming the initial product; S4: Drying, shaping and drying the initial product; S5: Cutting, cutting the initial product into finished products.

22. The method for preparing a depth filtration medium according to claim 21, characterized in that, In step S1, the concentration of coarse fiber slurry is 4-6 wt%; the concentration of ultrafine nanofiber slurry is 1-3 wt%.

23. The method for preparing a depth filtration medium according to claim 21, characterized in that, The pre-stirring in step S2 includes the following stages: S21 stretching stage: Stir at 10-50 rpm for 1-1.5 hours at 35-50℃; S22 encapsulation stage: Stir at 50-200 rpm for 1-1.5 hours at 35-50℃; S23 shaping stage: Stir at 10-50 rpm for 0.5-1 h at 20-35℃.

24. The method for preparing a depth filter medium according to claim 21, characterized in that, In step S2, the fiber content is 10-70 wt% and the filter aid content is 30-90 wt%.

25. The method for preparing a depth filter medium according to claim 24, characterized in that, In step S2, an adhesive is also added, with an adhesive content of 1-10 wt%.

26. The method for preparing a depth filtration medium according to claim 21, characterized in that, In step S2, a charge additive is also added, and the charge additive accounts for 1-10 wt% of the total adhesive content in the filter medium body.

27. The method for preparing a depth filtration medium according to claim 21, characterized in that, The vacuum forming step described in step S3 is as follows: S31: Vacuum level is -10 to -60 kPa; S32: Vacuum level is -50 to -100 kPa.

28. The method for preparing a depth filter medium according to claim 21, characterized in that, In step S3, vacuum is applied until the moisture content of the initial product is less than 100%.

29. The method for preparing a depth filtration medium according to claim 21, characterized in that, The sieve mentioned in step S3 is double-layered, with one layer having a mesh size of 20-120 mesh and the other layer having a mesh size of 80-500 mesh, and the mesh size of the layer closer to the dispersion liquid is smaller than that of the layer farther away from the dispersion liquid.

30. The method for preparing a depth filtration medium according to claim 21, characterized in that, The drying process described in step S4 continues until the moisture content is below 10%.

31. The method for preparing a depth filtration medium according to claim 21 or 30, characterized in that, The drying temperature is 60-200℃, and the drying time is 3-8 hours.

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