A pre-filter depth filter paperboard, its preparation method, filtration system, and its usage.

Abstract

This application relates to the field of filter paperboard, specifically to a pre-filtered deep filter paperboard, its preparation method, filtration system, and usage method. The deep filter paperboard exhibits the following IvIg protein adsorption performance: a 0.5 g / L IvIg protein solution is supplied to the deep filter paperboard via a feed surface, and the deep filter paperboard captures the IvIg protein, achieving a filtration rate of 100 L / m³. 2 When measuring the filtered 1vIg protein solution, the concentration decreased by 5% to 70%; the hydrophobicity of the deep filter paperboard gradually increases from the feed surface to the discharge surface in the thickness direction; the density of the deep filter paperboard gradually increases from the feed surface to the discharge surface in the thickness direction. This application has the advantages of taking into account good retention effect on protein aggregates, retention efficiency, filtration speed, and low impurity shedding.

Description

Technical Field

[0001] This invention relates to the field of depth filter paperboard, and more specifically, to a pre-filtered depth filter paperboard, a method of preparation, a filtration system, and a method of use. Background Technology

[0002] Plasma-derived protein solutions, such as immunoglobulins (IgG) and other proteins (natural or recombinant) such as monoclonal antibodies, often contain protein aggregates, including protein trimers or higher polymers. Before administering this solution to a patient, these aggregates must first be removed to avoid toxic reactions. When using conventional filtration processes, virus clearance filters become rapidly clogged with aggregates, even at low concentrations of 0.01–0.1%. Therefore, expensive gel chromatography or size exclusion chromatography must be used to achieve selective aggregate removal.

[0003] US Patent No. US7465397B2 from EMD Millipore discloses a method for removing protein aggregates and viruses from a protein solution. It provides a process for selectively removing protein aggregates from a protein solution during normal flow (NFF) filtration. In the first step, the protein solution is filtered in NFF mode through one or more adsorption depth filters, charged or surface-modified microporous membranes, or small chromatography media beds to create a free flow of protein aggregates. The protein flow is then filtered through one or more ultrafiltration membranes to retain virus particles at a retention level of at least 3 LRV while allowing the passage of an aggregate-free and virus-free protein solution.

[0004] In other words, depth filters can be used to filter solutions containing protein aggregates. EMD Millipore's Chinese invention patent, authorized in publication number CN105492101A, discloses a high-capacity composite depth filter medium with low extractability, comprising one or more of the following media components: synthetic nonwoven fabric or microfibers, fibrillated polymeric fibers, synthetic filter aids, and wet-strength resins. This depth filter medium exhibits better binding capacity for soluble impurities such as DNA and host cell proteins from biological / cell culture feed streams during secondary clarification. Therefore, current depth filters are typically used for clarification filtration of biological / cell culture feed streams, employing exclusion and adsorption through hydrophobic, ionic, and other interactions.

[0005] However, through continuous exploration, we have found that not all depth filters are suitable for filtering protein aggregates. This is because filtering solutions containing protein aggregates, compared to clarification filtration, aims to prevent protein aggregates from clogging the virus removal filter. Since protein aggregates are smaller than the cellular proteins filtered in clarification filtration, directly applying a depth filter designed for clarification filtration to solutions containing protein aggregates inevitably leads to problems such as low flux, premature saturation, rapid flow decay, and excessive impurity shedding.

[0006] Therefore, it is desirable to provide a depth filter that reduces impurity desorption while maintaining good performance in all aspects, which can be used to filter protein aggregates. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of this invention is to provide a pre-filtered deep filter paperboard, a preparation method, a filtration system, and a method of use.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A pre-filtering depth filter paperboard includes fibers and an adhesive for bonding the fibers, the depth filter paperboard including a feed surface for receiving the liquid to be filtered and an outlet surface for discharging the permeate.

[0010] The depth filter paperboard has the following IvIg protein adsorption performance: A 0.5 g / L IvIg protein solution is supplied to the depth filter paperboard from the feed side, and the depth filter paperboard captures the IvIg protein, achieving a filtration rate of 100 L / m³. 2 When measuring the filtered IvIg protein solution, the concentration decreased by 5% to 70%;

[0011] The hydrophobicity of the deep filter paperboard gradually increases from the feed surface to the discharge surface in the thickness direction;

[0012] The density of the deep filter paperboard gradually increases from the feed surface to the discharge surface in the thickness direction.

[0013] By employing the above technical solution, when the IvIg protein passes through the deep-filtration paperboard, it is retained by the paperboard through non-specific hydrophobic interactions between the hydrophobic groups in the paperboard and the hydrophobic groups on the IvIg protein. Of course, the paperboard also retains the IvIg protein through some physical retention, but since the difference in pore size between the paperboard and the protein diameter is on the order of magnitude, this effect is negligible. Therefore, the paperboard primarily adsorbs the IvIg protein through hydrophobic interactions.

[0014] After the deep filter paperboard of this application is filtered with 0.5 g / L IvIg protein solution, the IvIg protein concentration in the downstream filtrate decreases by 5% to 70%, which can indirectly demonstrate the overall hydrophobic adsorption capacity of the deep filter paperboard.

[0015] Antibody monomers are weakly hydrophobic, but when they aggregate, the hydrophobic groups converge, significantly increasing the hydrophobicity of the aggregates. Therefore, when a depth filter paperboard meeting these conditions is used for pre-filtration before virus removal, the antibody aggregates will interact hydrophobically with the filter paperboard and be adsorbed and retained. The antibody monomers will not be affected by the hydrophobic interaction, thus removing the antibody aggregates from the fluid and preventing them from clogging subsequent virus removal filtration. Since the filtered fluid is typically an aqueous solution, excessively hydrophobic depth filter paperboard will hinder filtration, causing a significant loss of filtration flow rate. Conversely, if the hydrophobicity of the depth filter paperboard is too low, it may easily reach saturation, resulting in low loading capacity. Furthermore, it may not be able to stably retain and adsorb protein aggregates, allowing smaller aggregates to easily detach and re-enter the subsequent virus removal process, causing clogging of the virus removal membrane.

[0016] Secondly, the hydrophobicity of the deep filter paper increases in a gradient from the feed surface to the discharge surface along the thickness direction. This means that the area of ​​the deep filter paper near the feed surface is only used to provide pre-filtration of antibody aggregates, while the area of ​​the deep filter paper near the discharge surface is used to ensure complete filtration of antibody aggregates. This allows the deep filter paper to balance a large filtration speed, a better antibody aggregate filtration efficiency, and a larger antibody aggregate retention capacity.

[0017] To ensure the strength of the depth filter paperboard, its density should not be too low. Excessive density, however, makes it prone to clogging by various impurities, causing a rapid decline in throughput. In this application, the density of the depth filter paperboard maintains a gradient increase along the thickness direction from the feed surface to the discharge surface. This allows the area near the feed surface to retain a large amount of physically intercepted impurities, providing a pre-filtration effect and ensuring the depth filter paperboard can maintain a high throughput for a longer period.

[0018] The density of the depth filter paperboard increases gradually along its thickness. This allows the denser lower layer to effectively trap and retain impurities that may detach from the upper layer during filtration. Higher density results in more complex and convoluted flow channels within the paperboard, with smaller pores. This leads to tighter fiber density and stronger inter-fiber forces, making it less prone to impurity shedding. Furthermore, the denser areas can trap impurities that might detach from the less dense areas, preventing them from ultimately entering the filtered fluid.

[0019] Secondly, the increased density gradient can reduce the pore size and increase the porosity in this region. When a solution containing protein aggregates passes through this region, the hydrophobic fibers have a larger contact area with the solution, and the flow rate is slower, resulting in a longer contact time with the hydrophobic fibers. This increases the probability that the hydrophobic fibers will contact and adsorb the protein aggregates, thus more effectively removing the protein aggregates from the solution.

[0020] This application further specifies that the deep filter paperboard is horizontally divided at equal intervals along its thickness direction from the feed surface to the discharge surface into a first sub-filter paperboard, a second sub-filter paperboard, and a third sub-filter paperboard. A 0.5 g / L IvIg protein solution is supplied to each of the first, second, and third sub-filter paperboards, achieving a filtration rate of 100 L / m³. 2 The decrease values ​​of IvIg protein concentration K1, K2, and K3 in the downstream filtrate of the first sub-filter paperboard, the second sub-filter paperboard, and the third paper filter paperboard were measured, where K1∶K2∶K3=1∶1.05~2.5∶1.1~4.

[0021] By employing the above technical solution, the deep filter paperboard is divided into three equal parts along its thickness direction. After fabricating filters from each part, the IvIg protein adsorption capacity of the three components is tested, indirectly revealing the relative hydrophobicity of the three filter paperboards. By controlling the degree of hydrophobicity variation along the thickness direction and maintaining the gradient rate within a certain range, the deep filter paperboard can better balance flow rate and protein aggregate adsorption and retention efficiency. If the gradient of hydrophobicity along the thickness direction is too large, the fluid flow rate within the deep filter paperboard will be significantly affected, resulting in excessive impact on the area near the feed surface. This could cause deformation or other changes in the structure between the fibers and diatomaceous earth in this area, leading to a significant reduction in the retention effect of the deep filter paperboard. Conversely, if the gradient of hydrophobicity along the thickness direction is too small, the overall filtration flow rate improvement will be insignificant, resulting in low filtration efficiency.

[0022] This application further specifies that the reduction value of IvIg protein concentration in the first sub-filter paperboard is K1 = 10-30%, the reduction value of IvIg protein concentration in the second sub-filter paperboard is K2 = 15-45%, and the reduction value of IvIg protein concentration in the third sub-filter paperboard is K3 = 20-60%.

[0023] By adopting the above technical solution, the reduction value of IvIg protein concentration of the three sub-filter paperboards should meet the above range. If the reduction value of IvIg protein concentration is too low, the overall retention effect on protein aggregates will not be high, and the overall loading capacity will be low. If the reduction value of IvIg protein concentration is too high, the difference in hydrophobicity between the three sub-filter paperboards cannot reach a better range, and the hydrophobicity of the sub-filter paperboard on the discharge side will not play a role, resulting in a waste of performance.

[0024] This application further specifies that the compactness from one-third thickness of the feed surface is t1, the compactness from one-third thickness of the feed surface to one-third thickness of the discharge surface is t2, the compactness from one-third thickness of the discharge surface is t3, and the ratio of t1:t2:t3 is 1:1.1 to 1.8:1.2 to 3.

[0025] By employing the above technical solution, the deep filter paperboard is divided into three equal parts along the thickness direction, and the density strength of each of the three sub-filter paperboards is tested. By controlling the degree of variation in the density of the deep filter paperboard along the thickness direction, and controlling the gradient rate of density change within a certain range, the deep filter paperboard can better retain protein aggregates without excessively affecting the overall flow rate of the deep filter paperboard.

[0026] This application further specifies that the compactness of one-third of the thickness of the self-feeding surface is t1 = 0.2~0.5 g / cm. 3 The density from one-third of the thickness of the feed surface to one-third of the thickness of the discharge surface is t2 = 0.25~0.55 g / cm. 3 The density of the material at one-third of its thickness is t3 = 0.3–0.6 g / cm³. 3 .

[0027] By adopting the above technical solution, when the density is controlled within the specific range mentioned above, the time the solution spends in different density regions is more suitable for the protein aggregates to interact with the region when the deep filter paperboard filters a solution containing protein aggregates, thereby improving the retention capacity of the deep filter paperboard for protein aggregates.

[0028] This application further specifies that the deep filter paperboard also includes filter aid particles with a mass percentage of 30-80%; the content of the filter aid particles gradually increases in the thickness direction of the deep filter paperboard; and the deep filter paperboard is divided into three equal parts from the feed surface to the discharge surface, namely the upper layer, the middle layer and the lower layer, with the mass ratio of the filter aid particles in the upper layer, the middle layer and the lower layer being 1:1.3-2:1.8-3.

[0029] By adopting the above technical solution, the filter aid has abundant internal micropores and a large specific surface area, which can form countless intricate microchannels within the deep filter paperboard. During filtration, as the liquid passes through the filter aid particles, large suspended particles are trapped on the surface of the filter aid particles near the feed surface, while smaller impurities enter the filter aid particles and are trapped in the tortuous, intricate channels. When the deep filter paperboard of this application is used for pre-filtration of viruses, protein monomers (antibodies) can pass smoothly through the pores of the filter aid particles, while large protein aggregates are trapped by the pores of the filter aid.

[0030] The higher density of the deep filter paperboard near the discharge surface indicates a more compact fiber arrangement in this region. When fluid flows through this area, the flow rate decreases more rapidly. Increasing the pressure drop to improve flow rate can easily lead to protein aggregates penetrating, resulting in poorer retention. This application addresses this by gradually increasing the content of the filter aid along the thickness of the deep filter paperboard, thereby increasing the concentration of diatomaceous earth particles in the region near the discharge surface. This filter aid significantly improves the flow rate in this area.

[0031] Secondly, because the density of the deep filter paperboard is higher near the discharge surface, the fibers are more tightly packed, resulting in a smaller contact area between the protein aggregates and the hydrophobic fibers. This leads to lower adsorption efficiency of the hydrophobic fibers for the protein aggregates in this area. However, due to its porous structure, when the filter aid is more dispersed in the area near the discharge surface of the deep filter paperboard, it can help increase the contact area between the hydrophobic fibers and the protein aggregates, thereby improving the adsorption efficiency of the hydrophobic fibers for the protein aggregates and significantly enhancing the retention effect of the protein aggregates.

[0032] This application further specifies that the deep filter paperboard is divided into three equal parts from the feed surface to the discharge surface, namely the upper layer, the middle layer and the lower layer; the mass ratio of the filter aid in the upper layer of the deep filter paperboard is B1, the mass ratio of the filter aid in the middle layer of the deep filter paperboard is B2, and the mass ratio of the filter aid in the lower layer of the deep filter paperboard is B3, where B1 < B2 < B3.

[0033] By adopting the above technical solution, since the density of the deep filter paperboard increases in the thickness direction, in order to improve the synergistic effect between the filter aid and the hydrophobic fibers, the proportion of the filter aid in the deep filter paperboard also needs to gradually increase along the thickness direction. A higher proportion means a greater content of diatomaceous earth relative to the hydrophobic fibers. Therefore, in the lower layer, the filter aid can more fully synergize with the hydrophobic fibers, improving the hydrophobicity of the fibers and thus increasing the overall hydrophobic gradient of the deep filter paperboard, thereby enhancing the adsorption effect on protein aggregates. Simultaneously, the flow rate in the lower layer can also be increased, avoiding the defect of a significant decrease in flow rate due to excessive density.

[0034] This application further specifies that the mass ratio of filter aid in the upper layer of the deep filter paperboard is B1 = 10-60%; the mass ratio of filter aid in the middle layer of the deep filter paperboard is B2 = 20-70%; and the mass ratio of filter aid in the lower layer of the deep filter paperboard is B3 = 30-80%.

[0035] By adopting the above technical solution, the diatomaceous earth content in the upper and lower layers can be obtained by tearing the deep filter paperboard into two equal parts along the thickness direction, then completely burning and decomposing the fibers in the paperboard into gas using a calcination method, and measuring the remaining ash content. By controlling the mass ratio of diatomaceous earth in the upper layer of the deep filter paperboard to 20-30% and the mass ratio in the lower layer to 40-60%, the diatomaceous earth particles contained on and around the fibers of the deep filter paperboard show an increasing trend along the thickness direction. This ensures the overall flux of the deep filter paperboard while significantly improving its adsorption and retention effect on protein aggregates.

[0036] This application further specifies that the mass ratio of filter aid in the 20% thickness region of the deep filter paperboard from the feed surface is less than 50%, and the mass ratio of filter aid in the 80% thickness region of the deep filter paperboard from the feed surface is greater than 50%.

[0037] By adopting the above technical solution, the mass ratio of filter aid in a certain thickness area of ​​the deep filter paperboard from the feed surface is less than 50%, indicating that the proportion of filter aid in this area is small. Furthermore, the area of ​​the deep filter paperboard near the feed surface in this application has low hydrophobicity and density, mainly serving a certain pre-filtration function and preventing excessively low filtration efficiency. If the thickness of the area where the proportion of filter aid is less than 20% and less than 50% indicates that the pre-filtration and flow rate compensation effects of the deep filter paperboard are not high.

[0038] This application further specifies that the fiber comprises coarse fiber with an average SEM diameter of 8 to 20 μm, the filter aid has an average SEM particle size of 1 to 80 μm, and the ratio of the average SEM particle size of the filter aid to the average SEM diameter of the coarse fiber is 0.1 to 1.

[0039] In this application, the fibers may consist only of coarse fibers, or they may be composed of both coarse and fine fibers. The average diameter of the fibers can be measured by characterizing the morphology of the paperboard structure using a scanning electron microscope, followed by measurement using computer software (such as Matlab, NIS-Elements, etc.) or by manual calculation.

[0040] During the paperboard manufacturing process, in the direction perpendicular to the thickness of the paperboard, its various characteristics, such as fiber diameter distribution, are roughly uniform and generally consistent. Therefore, the average fiber diameter of the entire plane can be reflected by the average fiber diameter of a portion of the corresponding plane. In actual measurement, the paperboard surface can be characterized using an electron microscope to obtain the corresponding SEM image. A certain area can be selected, for example, 1 μm. 2 (1μm x 1μm) or 25μm 2 The area is 5μm x 5μm, and the specific size depends on the actual situation. The diameter of the coarse fibers on this area is then measured using appropriate computer software or manually, and the average diameter of the coarse fibers on the surface is calculated. Of course, those skilled in the art can also obtain the above parameters through other measurement methods, which are for reference only. In this application, coarse fibers refer to fibers with a diameter greater than 1μm obtained by the above method. The SEM average diameter of the coarse fibers is the average of the sum of all coarse fiber measurements.

[0041] By adopting the above technical solution, the larger the ratio of the average particle size of diatomaceous earth SEM to the average diameter of fiber SEM, the larger the actual size of diatomaceous earth particles in the deep filter paperboard is compared with the fiber size. Therefore, during the preparation of the deep filter paperboard, diatomaceous earth particles are not easy to migrate to the lower layer, which easily leads to the content of diatomaceous earth particles in the lower layer being lower than that in the upper layer, resulting in a decrease in flux and a decrease in protein adsorption efficiency.

[0042] In the preparation process of the deep filter paperboard of this application, a vacuum suction step is adopted. The surface of natural fibers contains hydroxyl groups. During the vacuum suction process, the natural fibers will migrate downward due to the vacuum suction effect. On the other hand, hydrogen bonds are easily formed between natural fibers, and the natural fibers are more likely to become entangled, making it difficult for the natural fibers to migrate downward.

[0043] When the vacuum level of vacuum suction is relatively high, the hydrogen bonding between natural fibers is less than that of vacuum suction, resulting in a higher density of natural fibers in the lower layer than in the upper layer. Since diatomaceous earth particles also contain hydroxyl groups on their surface, they also form hydrogen bonds with natural fibers. Through vacuum suction, this leads to a higher content of diatomaceous earth particles in the lower layer compared to the upper layer.

[0044] When the vacuum level is relatively low, the hydrogen bonding between natural fibers is greater than the vacuum suction effect, making it difficult for natural fibers to migrate downwards, resulting in a lower density of natural fibers in the lower layer compared to the upper layer. Secondly, because diatomaceous earth particles contain a large number of hydroxyl groups on their surface, they easily form hydrogen bonds with natural fibers, hindering the downward migration of diatomaceous earth particles; vacuum suction, on the other hand, helps diatomaceous earth particles migrate downwards. Therefore, under low vacuum conditions, the hydrogen bonding between diatomaceous earth and natural fibers is stronger than the vacuum suction effect, leading to fewer or less abundant diatomaceous earth particles in the lower layer, resulting in reduced flux and protein aggregate adsorption rate in the lower layer.

[0045] Therefore, by controlling the ratio of diatomaceous earth particle size to fiber diameter, paperboard with a higher proportion of diatomaceous earth particles in the lower layer can be produced even with a lower vacuum level and more natural fibers. The smaller the ratio of diatomaceous earth particles to natural fibers, the greater the resistance; the larger the ratio, the greater the resistance of the diatomaceous earth itself. Therefore, it is necessary to control the ratio within this range to achieve the desired effect.

[0046] Controlling the average SEM diameter of the fibers to 8–20 μm can ensure the strength of the paperboard. This is because the skeleton of the paperboard is mainly composed of fibers. If the fiber diameter is too large, the paperboard will become too brittle and will be easily damaged or broken when the paperboard is assembled into the filter. If the fiber diameter is too small, the paperboard will become too soft and will be easily bent and deformed. It will also directly affect the tightness of the fit with diatomite, leading to problems such as diatomite particles falling off.

[0047] Controlling the average particle size of diatomaceous earth in SEM to 1–5 μm ensures a tighter and more uniform bond between the diatomaceous earth and the fibers. If the particle size is too small, the diatomaceous earth particles are prone to uneven dispersion and agglomeration, resulting in significant differences in the performance of different parts of the deep filter paperboard and making the paperboard susceptible to various defects. On the other hand, if the particle size is too large, the entanglement between the fibers may not be tight enough, leading to a decrease in the wet strength of the paperboard.

[0048] This application further specifies that the filter aid has a D 50 Filter aid particles with a particle size of 1 to 50 μm, wherein the permeability of the filter aid particles is 0.01 to 0.5 darcy.

[0049] By employing the above technical solution, the pore size of diatomaceous earth particles is controlled within the range of 20–600 nm. If the pore size of the diatomaceous earth particles is too small, some antibody molecules may easily collide and aggregate, leading to a decrease in antibody yield. Conversely, if the pore size of the diatomaceous earth particles is too large, the specific surface area of ​​the diatomaceous earth will decrease, reducing the amount of hydrophobic groups exposed per unit volume of diatomaceous earth within the internal pores, thus reducing the adsorption efficiency of protein aggregates.

[0050] This application further specifies that the filter aid is selected from one or more of diatomaceous earth particles, silica, perlite, and activated carbon.

[0051] This application further specifies that the adhesive is PE, PP, PET fiber or powder.

[0052] This application further specifies that the apparent contact angle of the feed surface of the deep filter paperboard is 40 to 120 degrees, the apparent contact angle of the discharge surface is 45 to 130 degrees, and the apparent contact angle of the discharge surface is greater than the apparent contact angle of the feed surface.

[0053] By adopting the above technical solution, the feed surface of the deep filter paperboard has lower hydrophobicity, which is conducive to the fluid entering the paperboard; the discharge surface of the deep filter paperboard has higher hydrophobicity, which is conducive to improving the retention efficiency of aggregates.

[0054] This application further specifies that the deep filter paperboard is used to create an effective filter area of ​​1.3 × 10⁻⁶. -3 m 2 A filter with a thickness of bcm was flushed at room temperature with ultrapure water at a flow rate of 600 LMH. The flushing volume reached 1.4 × 10⁻⁶. - 2 L / cm 3 Then, a yellow soap dye solution with a concentration of 50 ppm was supplied to the filter at a constant rate of 5 ml / min. When the absorbance of the permeate at 418 nm increased to 0.05 Å, the permeate amount of the yellow soap dye solution was b × (14 ~ 43) ml.

[0055] This application further specifies that the dry bursting strength of the deep filter paperboard is 400-600 kPa and the wet bursting strength is 150-250 kPa.

[0056] By adopting the above technical solution, the dry bursting strength of the deep filter paperboard is controlled at 400-600 kPa, indicating that the fibers and diatomaceous earth particles in the deep filter paperboard are closely integrated, thereby improving the overall strength of the deep filter paperboard. However, the wet bursting strength is lower than the dry bursting strength because the sliding between polymer molecules after the paperboard is wetted during the test.

[0057] A method for preparing a pre-filter depth filter paperboard includes the following steps:

[0058] S1: Pulping, selecting fibers and water to mix and pulp to obtain fiber pulp; the fibers include 1-80 wt% hydrophobic fibers and 20-99% natural fibers; the degree of freeing of the fiber pulp is controlled between 30-95°SR.

[0059] S2: Mixing, add binder to fiber slurry, stir evenly to obtain mixed slurry;

[0060] S3: Molding, the mixed slurry is spread on the screen and the side of the screen without mixed slurry is vacuumed to form a pre-shaped preliminary product; the vacuum degree of vacuuming is controlled to be -40 to -100 kPa.

[0061] S4: Drying, shaping and drying the initial finished product; during the drying process, the temperature of the discharge side of the deep filter paperboard is kept higher than the temperature of the feed side;

[0062] S5: Punching, cutting the initial product into the finished product.

[0063] By adopting the above technical solutions, the addition of hydrophobic fibers, the control of vacuum degree during molding, and the control of temperature gradient during drying are combined to prepare a deep filter paperboard with a gradient distribution of density and hydrophobicity in the thickness direction.

[0064] This application further specifies that the adhesive is PE, PP, PET fiber or powder.

[0065] This application further specifies that the hydrophobic fibers are subjected to a hydrophilic pretreatment before the preparation of the deep filter layer paperboard, and the hydrophilic pretreatment includes soaking the hydrophobic fibers in a hydrophilic surfactant solution.

[0066] This application further specifies that the hydrophilic surfactant is selected from one or more of calcium dodecylbenzenesulfonate, sodium dodecyl sulfate, polyacrylamide, and ethylene oxide.

[0067] By adopting the above technical solution, hydrophobic fibers are prone to adsorption and aggregation due to mutual hydrophobic interactions when dispersed in water. However, when hydrophobic fibers are treated with hydrophilicity, they are less likely to aggregate, resulting in more uniform dispersion.

[0068] Hydrophobic fibers are generally synthetic fibers, and the surface of synthetic fibers is relatively smooth, making it difficult for most to form hydrogen bonds. Therefore, it is not easy for diatomaceous earth particles to adhere to hydrophobic fibers. However, the adhesion between hydrophobic fibers and diatomaceous earth particles is improved after hydrophilic treatment, and diatomaceous earth particles can also adhere to the surface of synthetic fibers. Therefore, hydrophilic treatment can also improve the adhesion or uniformity of distribution between diatomaceous earth particles and synthetic fibers.

[0069] This application further specifies that the hydrophobic fiber is selected from one or more of polyacrylonitrile fiber, polyolefin fiber, polyester fiber, and hydrophobically modified natural fiber.

[0070] This application further specifies that the temperature during the drying process in step S4 is controlled between 120 and 270°C, and the drying temperature on the feed side of the deep filter paperboard is lower than the drying temperature on the discharge side, with a temperature difference of 3 to 20°C between the two sides.

[0071] This application further specifies that a filter aid is added to the fiber slurry in step S2, wherein the filter aid is selected from one or more of diatomaceous earth particles, silica, perlite, graphite powder, magnesium oxide, gypsum, and activated carbon.

[0072] By employing the above technical solution, controlling the temperature difference between the feed side and the discharge side during the drying process in step S4, and combining this with vacuum control during vacuum suction, the density and hydrophobicity distribution in the thickness direction of the deep filter paperboard can be controlled. At higher vacuum levels, fibers and filter aids migrate more easily towards the discharge side. Controlling the temperature difference during drying allows for different degrees of decomposition or volatilization of hydrophilic surfactants on the hydrophilic-treated hydrophobic fibers on the feed and discharge sides, thereby controlling the variation in hydrophobicity intensity in the thickness direction of the deep filter paperboard. The filter aid is affected by both vacuum level and hydrophilic surfactants. Therefore, this application can produce paperboards with different density gradients and different hydrophobicity gradients.

[0073] A virus filtration system using the aforementioned pre-filtered deep filter paperboard includes a deep filter and a virus removal filter assembled sequentially along the filtration direction of the system; the deep filter paperboard serves as the filter medium for the deep filter.

[0074] This application further specifies that a nylon membrane is disposed between the deep filter and the virus removal filter, wherein the nylon membrane has a pore size of 0.1 to 0.4 μm and a thickness of 100 to 300 μm.

[0075] A method using the aforementioned deep filter paperboard to remove protein aggregates and viruses from a fluid includes the following steps:

[0076] A1: Rinse the deep filter paperboard with ultrapure water at room temperature, with a rinsing volume of at least 100L / m2;

[0077] A2: Filtering fluids containing protein aggregates and / or viruses using a deep filter paperboard that has been treated by at least one step A1;

[0078] A3: The filtrate from step A2 is then passed through at least one virus filter with a molecular weight cutoff of 50-150 kD;

[0079] Before proceeding to step A1, the viral load in the fluid must not exceed 0.1%.

[0080] In summary, the present invention has the following beneficial effects:

[0081] First, the deep filter paperboard of this application controls the density and hydrophobicity to vary in a gradient in the thickness direction, so as to take into account the good retention effect of protein aggregates, retention efficiency, filtration speed and low amount of impurities falling off.

[0082] Secondly, this application achieves the effect of further improving the retention effect, retention efficiency, filtration speed and lower impurity shedding by specifically setting the hydrophobicity distribution in the thickness direction of the deep filter paperboard and the distribution of the filter aid. Attached Figure Description

[0083] Figure 1 These are bar charts of Vmax for Examples 1-10 and Comparative Examples 1-4;

[0084] Figure 2 This is a bar chart of Vmax from Examples 11 to 26. Detailed Implementation

[0085] The present invention will be further described in detail below with reference to the embodiments.

[0086] Example

[0087] Example 1

[0088] A method for preparing a depth filter paperboard includes the following steps:

[0089] S1: Pulping, which is a process of mixing 41 wt% hydrophobic fibers and 59% natural fibers with water to obtain fiber pulp;

[0090] Among them, the hydrophobic fiber is polyacrylonitrile fiber; the natural fiber is cotton fiber;

[0091] Hydrophobic fibers are hydrophilicized by soaking in an aqueous solution of sodium dodecyl sulfate (5% by mass) as a hydrophilic surfactant.

[0092] The beating degree of the fiber pulp is controlled at 80°SR.

[0093] S2: Mixing: Add epichlorohydrin binder to the fiber slurry and stir until homogeneous to obtain a mixed slurry;

[0094] The fiber and epichlorohydrin binder content is: 98% fiber and 2% epichlorohydrin binder.

[0095] S3: Shaping, spreading the mixed slurry on a screen and using vacuum suction to remove the side of the screen from which the mixed slurry is not spread, forming a pre-shaped initial product;

[0096] The vacuum degree of vacuum suction is -55 kPa;

[0097] S4: Drying, shaping and drying the initial finished product;

[0098] The temperature on the feed side is controlled at 130℃, and the temperature on the discharge side is controlled at 133℃.

[0099] S5: Punching, cutting the initial product into the finished product.

[0100] Example 1 also discloses a virus filtration system using a deep filter paperboard, comprising a deep filter and a virus removal filter assembled sequentially along the filtration direction of the system; the filter medium of the deep filter is the filter paperboard prepared above.

[0101] Example 1 also discloses a method for removing protein aggregates and viruses from fluids using a deep filter paperboard, comprising the following steps:

[0102] A1: Select 100L / m deep filter paper rinsed with ultrapure water. 2 The fluid containing protein aggregates and / or viruses is then filtered; the pressure is 30 psi and the temperature is 25°C. The viral load in the fluid does not exceed 0.1%.

[0103] A2: The filtrate filtered in step A2 is then passed through a virus filter with a molecular weight cutoff of 150kD.

[0104] The differences between Examples 2-10 and Comparative Examples 1-3 and Example 1 lie in the ratio of hydrophobic fibers to natural fibers and the different process parameters, as shown in the table below:

[0105] Table 1

[0106]

[0107]

[0108] Comparative Example 4 is a conventional cellulose / diatomite deep filter, Millistak X0HC.

[0109] In Comparative Examples 2 and 3, the molding process in step S3 is extrusion molding, and the extrusion pressure is 10 kPa.

[0110] In Comparative Example 1 and Example 2, the temperatures on the feeding and discharging sides of the drying process were kept consistent.

[0111] Segmentation test:

[0112] The deep filter paperboard was cut into three equal parts along the thickness direction, and then divided into upper, middle and lower layers from the feed surface to the discharge surface; the density and IvIg protein retention capacity of the upper, middle and lower layers were tested respectively.

[0113] Tightness is calculated using the following formula:

[0114]

[0115] Where G is the mass of the sample tested by instruments such as an electronic precision balance, d is the thickness of the sample tested by an electric thickness gauge, and S is the cross-sectional area of ​​the sample.

[0116] The IvIg protein retention capacity can be calculated using the following formula:

[0117]

[0118] The IvIg protein retention capacity was tested using the following method:

[0119] Prepare a 0.5 g / L IVIg protein solution, and use a clamp to hold a sample with a cross-sectional area of ​​13 cm². 2 A circular sheet of paperboard is fed with an 1vIg protein solution from the feed side, with a filtration rate of 120 L / m³ and a filtration rate of 100 L / m³. 2 Then, the concentration C of the IvIg protein solution in the filtrate was measured.

[0120] Table 2

[0121]

[0122] Performance testing:

[0123] (1) Contact angle test: After placing the deep filter paperboard in an environment with a temperature of (20±2℃) and a relative humidity of (65±4)% for 30h, the apparent contact angle of the feed surface and the discharge surface of the deep filter paperboard is tested with an apparent contact angle tester and the readings are recorded.

[0124] (2) Protein aggregate retention performance test: Preparation of protein aggregate feed standard solution: IgG aggregate solution (SeraCare 5% human gamma globulin, purchased from SeraCare, Inc., CAT#HS-9000), phosphate buffer (10g / L Difeo FA buffer, pH 7.2, from Fisher Scientific, Cat#DF2314150) and EDTA (10mmol / L calcium disodium ethylenediaminetetraate, from Sigma Aldrich, CAT#ED2SC) were mixed to obtain the initial feed solution. The initial feed solution was passed through a PLCXK membrane (PLCXK membrane is a cellulose ultrafiltration membrane with a nominal molecular weight of 1000kDaltons, available from Millipore, Bedford, Massachusetts) to remove 90% of the protein aggregates, resulting in a protein aggregate feed solution with a concentration of 10% of the original.

[0125] Using a conventional constant-flow virus filter, without any polymer removal steps, a 13.5cm filter supplied by Millipore Corporation of Bedford, Massachusetts was used. 2 of The NFP virus filter selectively removes protein polymers from the solution during a normal flow (NFF) filtration process.

[0126] The effective filtration area assembled using the deep filter paperboards in the various embodiments and comparative examples of this application is 4.5 × 10⁻⁶. -4 m 2 A depth filter selectively removes protein aggregates from the solution during a constant flow (NFF) filtration process. Subsequently, a 13.5 cm² filter from Millipore Corporation, Bedford, Massachusetts, was used. The NFP filter performs the virus removal step.

[0127] The measured viral rejection capacity Vmax is used to measure the ability of the deep filter paperboard to remove protein aggregates; the stronger the removal capacity, the larger Vmax.

[0128] (3) Flow rate test: The deep filter paperboard was assembled into the filter to obtain a flow rate of 4.5 × 10⁻⁶. -4 m 2 A depth filter with effective filtration area; the filtration rate of each embodiment and comparative example was measured by filtering a dual-layer filter with ultrapure water at a constant pressure of 100 kPa and a temperature of 20°C.

[0129] The test results of Examples 1-10 and Comparative Examples 1-4 are as follows:

[0130] Table 3

[0131]

[0132] Conclusion: Combining Tables 2 and 3 and Figure 1 The data, obtained from Vmax of Examples 1-10 and Comparative Examples 1-4, show that when the hydrophobicity and compactness of the depth filter paperboard prepared in this application simultaneously increase in a gradient along the thickness direction of the depth filter paperboard, the retention effect on protein aggregates is significantly improved. Furthermore, a comparison between Examples 6-10 and other examples further shows that when the degree of gradient increase in hydrophobicity and compactness along the thickness direction of the depth filter paperboard meets the proportional range disclosed in this application, the protein aggregate retention effect of the depth filter paperboard is further improved. Examples 11, 12, and 13 show that when K1∶K2∶K3=1∶1.05~2.5∶1.1~4 and t1∶t2∶t3 is 1∶1.3~2∶1.8~3, the filtration effect of the depth filter paperboard on protein aggregates is even better.

[0133] Secondly, when the hydrophobicity and density of the deep filter paperboard increase in a gradient direction in the thickness direction as required by this application, the filtration speed of the deep filter paperboard is also improved.

[0134] Example 14

[0135] A method for preparing a pre-filter depth filter paperboard includes the following steps:

[0136] S1: Pulping, which is a process of mixing 70 wt% hydrophobic fibers and 30% natural fibers with water to obtain fiber pulp;

[0137] Among them, the hydrophobic fiber is polyacrylonitrile fiber; the natural fiber is cotton fiber;

[0138] Hydrophobic fibers are hydrophilicized by soaking in an aqueous solution of sodium dodecyl sulfate (5% by mass) as a hydrophilic surfactant.

[0139] The beating degree of the fiber pulp is controlled at 90°SR.

[0140] S2: Mixing: Add epichlorohydrin binder and diatomaceous earth filter aid to the fiber slurry, stir evenly to obtain a mixed slurry;

[0141] The fiber and epichlorohydrin binder content is as follows: fiber 45%, diatomaceous earth filter aid 53%, and epichlorohydrin binder 2%.

[0142] D of diatomaceous earth filter aid 50 =10μm, with a permeability of 0.35 darcy.

[0143] S3: Shaping, spreading the mixed slurry on a screen and using vacuum suction to remove the side of the screen from which the mixed slurry is not spread, forming a pre-shaped initial product;

[0144] The vacuum degree of vacuum suction is -50 kPa;

[0145] S4: Drying, shaping and drying the initial finished product;

[0146] The temperature on the feed side is controlled at 130℃, and the temperature on the discharge side is controlled at 135℃.

[0147] S5: Punching, cutting the initial product into the finished product.

[0148] Example 14 also discloses a virus filtration system using pre-filtered deep filter paperboard, comprising a deep filter and a virus removal filter assembled sequentially along the filtration direction of the system; the filter medium of the deep filter is the filter paperboard prepared above.

[0149] Example 14 also discloses a method for removing protein aggregates and viruses from fluids using pre-filtered depth filter paper, comprising the following steps:

[0150] A1: Select 100L / m deep filter paper rinsed with ultrapure water. 2 The fluid containing protein aggregates and / or viruses is then filtered; the pressure is 30 psi and the temperature is 25°C. The viral load in the fluid does not exceed 0.1%.

[0151] A2: The filtrate filtered in step A2 is then passed through a virus filter with a molecular weight cutoff of 150kD.

[0152] The difference between Examples 12-26 and Example 11 lies in the amount of diatomaceous earth filter aid added and the parameters used.

[0153] Table 4

[0154]

[0155] Examples 14–29 were tested for compactness, filter aid content, and IvIg protein retention capacity. The test results are as follows:

[0156] The filter aid content was tested using the following method:

[0157] The sample paperboard was placed in a muffle furnace at 575±25℃ and heated to constant weight (3h), and the weight was recorded as m.

[0158] The proportion of filter aid is calculated according to the following formula:

[0159]

[0160] Where M is the total weight of the sample cardboard.

[0161] Table 5

[0162]

[0163] B 20 This refers to the result of tearing off a portion of the deep filter paperboard from the feed surface to 20% of its thickness, and then conducting an ash content test. (B) 80 This refers to the result of tearing off the paperboard from the feed surface of the deep filter paperboard to 80% of its thickness from the feed surface and then conducting an ash content test.

[0164] Table 6

[0165]

[0166]

[0167] Protein aggregate retention performance and flow rate were tested for Examples 14-29, and the results are as follows:

[0168] Table 7

[0169]

[0170]

[0171] Conclusion: Based on Tables 5, 6, 7 and... Figure 2 It can be seen that the overall filtration speed of the depth filter paperboard was improved after adding the filter aid in this application. Data from Examples 14-29 in Tables 6 and 7 show that the addition of the filter aid, the selection of particle size, and the combination of fibers have a direct impact on the gradient structure of the depth filter paperboard. Data from Examples 14-20 shows that the density gradient structure and the hydrophobic gradient structure still have a significant impact on the retention and adsorption of protein aggregates by the depth filter paperboard. Furthermore, data from Examples 21-29 show that the gradient distribution of the filter aid in the thickness direction in the depth filter paperboard further affects its retention and adsorption of protein aggregates.

[0172] Filter aids improve the bulkiness of deep filter paperboard, resulting in a greater density gradient. They also increase the contact area between protein aggregates and hydrophobic fibers. Therefore, the selection and formulation of appropriate filter aids are crucial. Furthermore, by controlling the vacuum level and vacuuming time during the manufacturing process, the gradient structure along the thickness direction of the deep filter paperboard can achieve the optimal ratio for protein aggregate adsorption.

[0173] When the content of the filter aid increases in a gradient along the thickness direction of the deep filter paperboard, and the mass percentage of the filter aid also increases in a gradient along the thickness direction of the deep filter paperboard, the protein aggregates are better adsorbed by the deep filter paperboard, and the measured Vmax is higher.

[0174] The difference between Example 30 and Example 29 is that the adhesive used is PE powder, and the drying temperature is controlled at 220°C on the feeding side and 225°C on the discharging side.

[0175] The difference between Example 31 and Example 29 is that the adhesive used is PP powder, and the drying temperature is controlled at 160°C on the feeding side and 165°C on the discharging side.

[0176] The difference between Example 32 and Example 29 is that the adhesive used is PET powder, and the drying temperature is controlled at 270°C on the feeding side and 275°C on the discharging side.

[0177] Examples 28, 29, 30, 31, 32 and Comparative Examples 1, 2, 3, 4 were subjected to soap-yellow staining tests and protein aggregate retention tests.

[0178] Paperboard charge test: When the deep filter paperboard is assembled into the filter housing, a charge of 1.3 × 10⁻⁶ is obtained. -3 cm 2 A depth filter with an effective filtration area; using negatively charged yellow soap dye as a standard reagent, water was added to prepare a 50 ppm solution. The 50 ppm yellow soap dye solution was supplied at a constant rate of 5 ml / min. When the absorbance of the permeate at 430 nm decreased to 0.05 A, the total volume of the permeated yellow soap dye solution was measured.

[0179] Table 8

[0180]

[0181] Conclusion: As shown in the table above, when the binder is replaced with purer PE, PP, or PET powder binder, the overall charge of the deep filter paperboard decreases significantly, and the shedding of charged impurities is also reduced to a low level, while the overall protein aggregate retention capacity is not significantly affected.

[0182] The difference between Example 33 and Example 26 is that the filter aid used is silicon dioxide;

[0183] The difference between Example 34 and Example 26 is that perlite is used as the filter aid;

[0184] The difference between Example 35 and Example 26 is that the filter aid used is graphite powder;

[0185] The difference between Example 36 and Example 26 is that magnesium oxide is used as the filter aid;

[0186] The difference between Example 37 and Example 26 is that gypsum is used as the filter aid;

[0187] The difference between Example 38 and Example 26 is that activated carbon is used as the filter aid.

[0188] Table 11

[0189]

[0190] Conclusion: As shown in the table above, diatomaceous earth filter aid exhibits a certain adsorption effect on protein aggregates compared to other filter aids. Therefore, in addition to increased flow rate, the adsorption capacity of protein aggregates is also improved in depth filter paperboard with the addition of diatomaceous earth filter aid.

[0191] Bursting strength test: The test was conducted using the NPD-02 fully automatic bursting strength tester.

[0192] The paperboards prepared in Examples 1-38 have a dry bursting strength between 400 and 600 kPa and a wet bursting strength between 150 and 250 kPa, which can meet the requirements of practical applications.

[0193] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A pre-filter depth filter paperboard, comprising fibers and an adhesive for bonding the fibers, said depth filter paperboard including an inlet surface for receiving the liquid to be filtered and an outlet surface for discharging the permeate, characterized in that, The depth filter paperboard has the following hydrophobic adsorption properties for IvIg protein: A 0.5 g / L IvIg protein solution is supplied to the depth filter paperboard via the feed surface, and the IvIg protein is captured by the depth filter paperboard, achieving a filtration rate of 100 L / m³. 2 When measuring the filtered IvIg protein solution, the concentration decreased by 5% to 70%; The hydrophobicity of the deep filter paperboard gradually increases from the feed surface to the discharge surface in the thickness direction; The density of the deep filter paperboard gradually increases from the feed surface to the discharge surface in the thickness direction, and the density t is calculated according to the following formula: Where G is the mass of the sample measured by an electronic precision balance, d is the thickness of the sample measured by an electric thickness gauge, and S is the cross-sectional area of ​​the sample. The deep filter paperboard also includes filter aid particles with a mass percentage of 30-80%; the content of the filter aid particles gradually increases in the thickness direction of the deep filter paperboard; and the deep filter paperboard is divided into three equal parts from the feed surface to the discharge surface, namely the upper layer, the middle layer and the lower layer, with the mass ratio of the filter aid in the upper, middle and lower layers being 1:1.3 to 2:2 to 3.

2. The pre-filter depth filter paperboard according to claim 1, characterized in that, The deep filter paperboard is horizontally divided at equal intervals along its thickness from the feed surface to the discharge surface into a first sub-filter paperboard, a second sub-filter paperboard, and a third sub-filter paperboard. A 0.5 g / L IvIg protein solution is supplied to each of the three sub-filter paperboards, and the filtration rate is 100 L / m³. 2 The decrease values ​​of IvIg protein concentration K1, K2, and K3 in the downstream filtrate of the first, second, and third sub-filter paperboards were measured, where K1∶K2∶K3=1∶1.05~2.5∶1.1~4.

3. The pre-filter depth filter paperboard according to claim 2, characterized in that, The first sub-filter paperboard has an IvIg protein concentration reduction value K1 of 10-30%, the second sub-filter paperboard has an IvIg protein concentration reduction value K2 of 15-45%, and the third sub-filter paperboard has an IvIg protein concentration reduction value K3 of 20-60%.

4. The pre-filter depth filter paperboard according to claim 1, characterized in that, The density of the material near the feed surface (one-third of the thickness) is t1, the density from the feed surface to the discharge surface (one-third of the thickness) is t2, and the density near the discharge surface (one-third of the thickness) is t3. The ratio of t1:t2:t3 is 1:1.3 to 2:1.8 to 3.

5. The pre-filter depth filter paperboard according to claim 4, characterized in that, The density of the thickness in the third of the feed surface is t1 = 0.2~0.5 g / cm³. 3 The density from one-third of the thickness at the feed surface to one-third of the thickness at the discharge surface is t2 = 0.25~0.55g / cm². 3 The density of the thickness in the third of the material closest to the discharge surface is t3 = 0.3~0.6 g / cm³. 3 .

6. The pre-filter depth filter paperboard according to claim 1, characterized in that, The deep filter paperboard is divided into three equal parts from the feed surface to the discharge surface, namely the upper layer, the middle layer and the lower layer; the mass ratio of filter aid in the upper layer of the deep filter paperboard is B1, the mass ratio of filter aid in the middle layer of the deep filter paperboard is B2, and the mass ratio of filter aid in the lower layer of the deep filter paperboard is B3, where B1 < B2 < B3.

7. The pre-filter depth filter paperboard according to claim 6, characterized in that, The mass ratio of filter aid in the upper layer of the deep filter paperboard is B1 = 10-60%; the mass ratio of filter aid in the middle layer of the deep filter paperboard is B2 = 20-70%; and the mass ratio of filter aid in the lower layer of the deep filter paperboard is B3 = 30-80%.

8. A pre-filter depth filter paperboard according to claim 6, characterized in that, The mass ratio of filter aid in the 20% thickness area of ​​the deep filter paperboard from the feed surface is less than 50%, and the mass ratio of filter aid in the 80% thickness area of ​​the deep filter paperboard from the feed surface is greater than 50%.

9. A pre-filter depth filter paperboard according to claim 1, characterized in that, The fiber comprises coarse fibers with an average SEM diameter of 8–100 μm, the filter aid has an average SEM particle size of 1–80 μm, and the ratio of the average SEM particle size of the filter aid to the average SEM diameter of the coarse fiber is 0.1–1.

10. A pre-filter depth filter paperboard according to claim 1, characterized in that, The filter aid D 50 Filter aid particles with a particle size of 1 to 50 μm, wherein the permeability of the filter aid particles is 0.01 to 0.5 darcy.

11. A pre-filter depth filter paperboard according to claim 1, characterized in that, The filter aid is selected from one or more of diatomaceous earth particles, silica, perlite, and activated carbon.

12. The pre-filter depth filter paperboard according to claim 1, characterized in that, The adhesive is PE, PP, PET fiber or powder.

13. The pre-filter depth filter paperboard according to claim 1, characterized in that, The apparent contact angle of the feed surface of the deep filter paperboard is 40 to 120 degrees, and the apparent contact angle of the discharge surface is 45 to 130 degrees, and the apparent contact angle of the discharge surface is greater than that of the feed surface.

14. A pre-filter depth filter paperboard according to claim 1, characterized in that, The aforementioned deep filter paperboard is used to create an effective filter area of ​​1.3 × 10⁻⁶. -3 m 2 A filter with a thickness of bcm was flushed at room temperature with ultrapure water at a flow rate of 600 LMH. The flushing volume reached 1.4 × 10⁻⁶. -2 L / cm 3 Then, a yellow soap dye solution with a concentration of 50 ppm was supplied to the filter at a constant rate of 5 ml / min. When the absorbance of the permeate at 418 nm increased to 0.05 Å, the permeate amount of the yellow soap dye solution was b × (14-43) ml.

15. A pre-filter depth filter paperboard according to claim 1, characterized in that, The dry bursting strength of the deep filter paperboard is 400-600 kPa, and the wet bursting strength is 150-250 kPa.

16. A method for preparing a pre-filter depth filter paperboard according to any one of claims 1 to 15, characterized in that, Includes the following steps: S1: Pulping, selecting fibers and water to mix and pulp to obtain fiber pulp; the fibers include 1-80 wt% hydrophobic fibers and 20-99% natural fibers; the degree of freeing of the fiber pulp is controlled between 30 and 95°SR. S2: Mixing, add binder to fiber slurry, stir evenly to obtain mixed slurry; S3: Molding, the mixed slurry is spread on the screen and the side of the screen without mixed slurry is vacuumed to form a pre-shaped preliminary product; the vacuum degree of vacuuming is controlled to be -40 to -100 kPa. S4: Drying, shaping and drying the initial finished product; during the drying process, the temperature of the discharge side of the deep filter paperboard is kept higher than the temperature of the feed side; S5: Punching, cutting the initial product into the finished product.

17. The method for preparing pre-filter depth filter paperboard according to claim 16, characterized in that, The adhesive is PE, PP, PET fiber or powder.

18. The method for preparing pre-filtered deep filter paperboard according to claim 16, characterized in that, The hydrophobic fibers are subjected to hydrophilic pretreatment before the preparation of the deep filter layer paperboard. The hydrophilic pretreatment includes soaking the hydrophobic fibers in a hydrophilic surfactant solution.

19. The method for preparing pre-filtered deep filter paperboard according to claim 18, characterized in that, The hydrophilic surfactant is selected from one or more of calcium dodecylbenzenesulfonate, sodium dodecyl sulfate, polyacrylamide, and ethylene oxide.

20. The method for preparing pre-filtered deep filter paperboard according to claim 18, characterized in that, The hydrophobic fiber is selected from one or more of polyacrylonitrile fiber, polyolefin fiber, polyester fiber, and hydrophobically modified natural fiber.

21. The method for preparing pre-filtered deep filter paperboard according to claim 18, characterized in that, The temperature during the drying process in step S4 is controlled between 120 and 280°C, and the drying temperature on the feed side of the deep filter paperboard is lower than the drying temperature on the discharge side, with a temperature difference of 3 to 20°C between the two sides.

22. The method for preparing pre-filtered deep filter paperboard according to claim 16, characterized in that, In step S2, a filter aid is also added to the fiber slurry. The filter aid is selected from one or more of diatomaceous earth particles, silica, perlite, graphite powder, magnesium oxide, gypsum, and activated carbon.

23. A virus filtration system using the pre-filtered deep filter paperboard according to any one of claims 1 to 15, characterized in that, It includes a depth filter and a virus removal filter assembled sequentially along the filtration direction of the system; the depth filter paperboard serves as the filter medium of the depth filter.

24. The virus filtering system according to claim 23, characterized in that, A nylon membrane is disposed between the deep filter and the virus removal filter. The nylon membrane has a pore size of 0.1 to 0.4 μm and a thickness of 100 to 300 μm.

25. A method for using the pre-filter depth filter paperboard according to any one of claims 1 to 15, characterized in that, To remove protein aggregates and viruses from fluids, the following steps are included: A1: Rinse the depth filter paperboard with ultrapure water at room temperature, with a rinsing volume of at least 100L / m. 2 ; A2: Filtering fluids containing protein aggregates and / or viruses using a deep filter paperboard that has been treated by at least one step A1; A3: The filtrate from step A2 is then passed through at least one virus filter with a molecular weight cutoff of 50-150 kD; Before proceeding to step A1, the viral load in the fluid does not exceed 0.1%.

Images