Method for reducing silicon precipitation amount of glass fiber

Abstract

The invention discloses a method for reducing silicon precipitation of a glass fiber, the glass fiber with low silicon precipitation amount obtained by the method, a filter material prepared from the glass fiber with low silicon precipitation amount and application of the filter material. The method for reducing silicon precipitation of the glass fiber comprises the following steps: S1, soaking the glass fiber in dilute sulphuric acid with the volume percent concentration of 1%-5% at 60-90 DEG C for 8-24 hours, and then washing with water; and S2, immediately drying the cleaned glass fiber obtained in the step S1 at 100-150 DEG C for 2-3 hours, then placing the dried glass fiber at 500-650 DEG C for heat treatment for 0.5-1.5 hours, and naturally cooling. The filter material with low silicon precipitation amount provided by the invention has the advantages of high silica content, stable performance and longer service life, solves the problems caused by silicon precipitation of a nuclear-grade water filter element, and can ensure the normal operation of a nuclear power system.

Description

Technical Field

[0001] The invention belongs to the technical field of glass fiber and papermaking, and particularly relates to a method for reducing silicon precipitation amount of glass fiber. Background Art

[0002] With the rapid development of nuclear energy technology, the performance of water filters used in nuclear facilities is also constantly improving. Glass fiber filter materials are widely used as filter element materials in nuclear-grade water filtration due to their good physical properties and excellent filtration performance. However, it is found that in the long-term operation of nuclear power plants, the silicon element in the glass fiber will continue to precipitate from the material. The released silicon element will affect the normal operation of the device in various forms in the pipeline, especially attached to the nuclear fuel cladding and fuel rods, seriously affecting the thermal conductivity efficiency of the components, increasing the risk of stress corrosion of reactor materials, and even endangering the safe operation of the nuclear power system, bringing great safety hazards to nuclear power plants.

[0003] Glass fiber is mainly composed of a three-dimensional network structure of SiO2 tetrahedrons and other metal ions. After long-term immersion in boric acid-containing water, the Si-O-Si bond is easily affected by the highly active H + The attack breaks off to form silanol groups, which increases the hydrophilicity of the glass and further reacts to form silicate substances dispersed in water; at the same time, H + It also penetrates deep into the glass fiber to exchange with alkali metal and alkaline earth metal ions, causing them to escape to the surface and react with hydroxide ions (OH — ) generates soluble salt products, which promotes the forward progress of the silicon precipitation reaction, significantly increases the dissolution rate of the glass fiber, and significantly reduces its performance.

[0004] Therefore, in order to solve the problems of material performance degradation and damage to the functions of nuclear power components caused by silicon precipitation during the use of glass fiber filter materials, researchers have tried to study and develop methods to reduce the amount of silicon precipitation in glass fibers from multiple angles and directions. For example, the Chinese utility model patent with announcement number CN217430924U discloses a water filter system with a backwashing function; the Chinese utility model patent with announcement number CN204875374U discloses a nuclear-grade composite water filter paper with a protective layer to prevent the precipitation of silicon dioxide in the inner layer of glass fiber; and the Chinese invention patent application with publication number CN112370865A improves the silicon precipitation of the filter material by adding an appropriate amount of aramid fiber in the preparation of glass fiber. The above methods are all for the post-processing of the already formed glass fiber or filter. The inventor took a different approach and carried out a series of treatments on the glass fiber based on the structure of the fiber itself, which unexpectedly achieved the purpose of reducing the amount of silicon precipitation in the fiber body. Summary of the invention

[0005] The invention provides a method for reducing the amount of silicon precipitation in glass fiber. The method is simple to operate, low in cost and suitable for industrial production.

[0006] To this end, the present invention adopts the following technical solution:

[0007] A method for reducing silicon precipitation in glass fiber comprises the following steps:

[0008] S1. Soak the glass fiber in dilute sulfuric acid at a volume percentage concentration of 1%-5% at 60-90°C for 8-24 hours, and then wash with water;

[0009] S2. Immediately dry the cleaned glass fiber obtained in step S1 at 100-150°C for 2-3h, then heat treat the dried glass fiber at 500-650°C for 0.5-1.5h, and cool naturally.

[0010] Preferably, the glass fiber is selected from glass fiber wool and / or alkali-free chopped strands, and has an average fiber diameter of 0.1-10 μm.

[0011] More preferably, the glass fiber is selected from one or more of the following:

[0012] 1) 59°SR glass wool fiber, average fiber diameter 0.35-0.4 μm, more preferably 0.37 μm,

[0013] 2) 19° SR glass wool, with an average fiber diameter of 1.2-2.0 μm, more preferably 1.59 μm, and

[0014] 3)Φ6μm alkali-free glass fiber chopped strands.

[0015] Preferably, in step S1, the total volume of the glass fibers does not exceed 1 / 5 of the volume of the dilute sulfuric acid, and the glass fibers are stirred until the fibers are evenly distributed and no obvious fiber flocculation clusters are present in the immersion container.

[0016] Preferably, in step S1, the temperature of the dilute sulfuric acid soaking treatment is 75-85°C; more preferably 80°C.

[0017] Preferably, in step S1, the dilute sulfuric acid soaking treatment time is 12h-24h, more preferably 12-15h.

[0018] Preferably, in step S1, the glass fiber is rinsed with running water until the pH value on the fiber surface is ≥5.

[0019] Preferably, in step S1, the soaking liquid for soaking the glass fiber and the washing liquid for washing the glass fiber are combined to recover the B 3+ and Na + .

[0020] Preferably, in step S2, the cleaned glass fiber obtained in step S1 is immediately transferred to a drying environment, and there is no other volatile substance in the drying environment.

[0021] Preferably, in step S2, the heat treatment temperature is 550-650°C.

[0022] Preferably, in step S2, the heat treatment time is 1-1.5 h.

[0023] Another object of the present invention is to provide a glass fiber with low silicon precipitation prepared by the above method; compared with untreated glass fiber, the glass fiber with low silicon precipitation is immersed in a mixed solution of boric acid and lithium hydroxide at 50°C for 72 hours, and the silicon concentration in the immersion solution is reduced by at least 60%, preferably by 65% ​​to 70%; wherein the concentration of boric acid in the mixed solution of boric acid and lithium hydroxide is 200ppm, and the concentration of lithium hydroxide is 1.24ppm.

[0024] Another object of the present invention is to provide a filter material prepared from the glass fiber with low silicon precipitation amount of the present invention.

[0025] Preferably, the filter material is formed by wet-coating the glass fiber with low silicon precipitation amount described in the present invention.

[0026] Also preferably, the filter material is prepared from the resin-reinforced glass fiber with low silicon precipitation amount of the present invention.

[0027] Further preferably, the filter material is prepared by wet-process papermaking of the resin-reinforced glass fiber with low silicon precipitation amount described in the present invention.

[0028] The present invention also provides application of the filter material in nuclear-grade water filtration.

[0029] The present invention adopts the acid soaking method, and the alkali metal and alkaline earth metal on the surface of the glass fiber are continuously replaced, the proportion of silicon element is significantly increased, and a microporous silicon skeleton structure is formed on the surface of the glass fiber. In this process, the specific surface area of ​​the glass fiber is significantly increased. Therefore, in the drying process, it is necessary to ensure that there are no volatile substances in the environment, such as ammonia water, halogenated hydrocarbons, liquid bromine and other volatile substances, to prevent impurities from being adsorbed into the glass structure through the microporous channels.

[0030] The essence of the heat sintering treatment used in the present invention is to make the microporous silicon skeleton of the glass fiber dense. After the heat sintering treatment, the silanol on the surface of the glass fiber undergoes a condensation reaction, and the non-bridging oxygen is converted into bridging oxygen. The number of chain structures of the molecular network on the fiber surface is also greatly reduced, and it mainly becomes a frame structure that can increase the strength of the glass fiber. As the number of non-bridging oxygen decreases, the number of bridging oxygen increases, making the surface of the glass fiber resistant to H in water. +The attacking ability is stronger and the amount of silicon precipitation is effectively reduced.

[0031] In summary, the glass fiber treated by the method of the present invention has a very low amount of silicon precipitation during the use of nuclear-grade water filtration, and the glass fiber has good strength and high silicon oxygen content. In addition, the glass fiber itself has high temperature resistance, corrosion resistance, and radiation resistance. Therefore, the prepared filter material has good and stable filtration performance and a longer service life, which solves the problem caused by silicon precipitation in nuclear-grade water filter elements and greatly guarantees the normal operation of nuclear power systems.

[0032] The method of the invention has a simple and easy process, has no special requirements on equipment, has strong operability, is low in cost, and has good development prospects.

[0033] In the specification, unless otherwise specified, the "water" or "running water" mentioned herein refers to "tap water". DETAILED DESCRIPTION

[0034] The present invention is described below with reference to specific examples. It will be appreciated by those skilled in the art that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention in any way.

[0035] The experimental methods in the following examples are conventional methods unless otherwise specified. The medicinal materials, reagents, etc. used in the following examples are commercially available products unless otherwise specified.

[0036] Study Example 1 Investigation on the process parameters of acid soaking

[0037] The following test was conducted to investigate the effects of the concentration, temperature and immersion time of dilute sulfuric acid on the replacement of alkali metals and alkaline earth metals on the surface of glass fibers.

[0038] 1.1 Dilute sulfuric acid concentration and temperature

[0039] The soaking time was 24 hours, and the 475 type 19°SR glass fiber wool was soaked in dilute sulfuric acid according to the conditions shown in Table 1. After soaking, the glass fiber wool was washed with running water until the surface pH = 6.5, and the washed glass fiber wool was immediately transferred to a clean environment (without volatile pollutants) and dried at 100°C for 30 minutes; then the sample was subjected to EDS energy spectrum analysis to determine the content of elements such as O, Al, Si, and Ca. The results are shown in Table 1.

[0040] Table 1 Experimental design for investigation of dilute sulfuric acid concentration and temperature and EDS spectrum analysis results

[0041] serial number Acid concentration / %v / v Temperature / ℃ O Al Si Ca Other Elements Unprocessed — — 54.1％ 8.3％ 20.2％ 12.2％ 5.2％ 1 0.05 40 53.6％ 8.1％ 21.2％ 12.1％ 5.0％ 2 0.05 60 52％ 7.9％ 22.1％ 13.1％ 4.9％ 3 0.05 80 51.7％ 7.7％ 23.4％ 11.8％ 5.4％ 4 0.05 95 52.3％ 7.3％ 23.7％ 12.4％ 4.3％ 5 1 40 51.2％ 6.2％ 26.2％ 13.4％ 3％ 6 1 60 50.5％ 6.3％ 28.1％ 12.6％ 2.5％ 7 1 80 51.6％ 5.2％ 28.2％ 11.9％ 3.1％ 8 1 95 52.6％ 7.1％ 27.2％ 10.5％ 2.6％ 9 5 40 53.7％ 6.2％ 24.2％ 13.6％ 2.3％ 10 5 60 49.8％ 5.2％ 30.1％ 12.1％ 2.8％ 11 5 80 49.4％ 5.4％ 33.2％ 11.2％ 1.8％ 12 5 95 51％ 5.6％ 30.1％ 11.2％ 2.1％ 13 10 40 54.1％ 7.2％ 23.2％ 12.3％ 3.2％ 14 10 60 51％ 7.6％ 25.2％ 12.8％ 3.4％ 15 10 80 52.4％ 7.3％ 24.2％ 12.9％ 3.2％ 16 10 95 52.1％ 7.2％ 25.3％ 12.8％ 2.6％

[0042] Since alkali metal and alkaline earth metal ions are replaced during acid soaking, the silicon content increases. The effect of acid soaking is examined using the silicon content as an indicator. The data in Table 1 show that compared with untreated glass fiber wool, the silicon content of glass fiber wool treated under various acid soaking conditions increases, especially under the conditions of 1% and 5% dilute sulfuric acid concentrations, especially No. 10 (5% v / v, 60°C), 11 (5% v / v, 80°C), and No. 12 (5% v / v, 95°C), among which No. 11 is the best.

[0043] Therefore, the concentration of dilute sulfuric acid is preferably 1%-5%, and the temperature is preferably 60-90°C; considering production cost issues such as energy consumption, the dilute sulfuric acid soaking temperature is more preferably 75-85°C, and most preferably 80°C.

[0044] 1.2 Dilute sulfuric acid soaking time

[0045] Based on the research in the previous section, the concentration of dilute sulfuric acid was set to 2.5%, the temperature was 80°C, and 475 type 19°SR glass fiber wool was soaked for the soaking time shown in Table 2. After soaking, the glass fiber wool was washed with running water until the surface pH = 6.3, and the washed glass fiber wool was immediately transferred to a clean environment (without volatile pollutants) and dried at 100°C for 30 minutes; then the sample was subjected to EDS energy spectrum analysis to determine the content of elements such as O, Al, Si, and Ca. The results are shown in Table 2.

[0046] Table 2 Dilute sulfuric acid immersion time investigation test design and EDS spectrum analysis results

[0047] serial number Soaking time / h O Al Si Ca Other Elements Unprocessed — 54.1％ 8.3％ 20.2％ 12.2％ 5.2％ 1 1 52.7％ 7.8％ 23.4％ 11.1％ 5.0％ 2 12 51.3％ 6.8％ 27.9％ 10.8％ 3.2％ 3 24 49.3％ 5.2％ 32.7％ 10.7％ 2.1％ 4 48 48.1％ 6.1％ 32.8％ 11.1％ 1.9％

[0048] The data in Table 2 show that under the preferred dilute sulfuric acid concentration and temperature conditions, the silicon content increases with the extension of the immersion time, and the acid immersion effect has basically reached a peak at 24 hours.

[0049] Based on the above experiments, the soaking time in dilute sulfuric acid is preferably 8-24 hours, more preferably 12-24 hours. Considering the actual production cost, the soaking time is particularly preferably 12-15 hours.

[0050] 1.3 Heat treatment parameters after drying

[0051] The dried glass fiber is subjected to high temperature heat treatment to close the micropores on the surface of the glass fiber and make the entire silicon skeleton structure denser. The following test is conducted to examine the high temperature heat treatment process parameters:

[0052] Place 475 type 19°SR glass fiber wool in dilute sulfuric acid at a temperature of 80°C and a volume percentage concentration of 1%. The volume of the glass fiber wool is 1 / 5 of the volume of 1% sulfuric acid. Stir evenly until the fiber flocculation in the container is obvious. Keep warm and soak for 12 hours. After soaking, rinse the glass fiber wool with running water until the pH on the surface of the glass fiber wool is 6.2. Immediately transfer the cleaned glass fiber wool to a clean environment (without volatile pollutants) and dry at 100°C for 2 hours. Then perform high-temperature heat treatment according to the conditions shown in Table 3. After treatment, perform silicon precipitation test on the glass fiber wool sample according to the following operations:

[0053] The sample was placed in an immersion solution at a temperature of 50°C and immersed for 72 hours. The immersion solution was a mixed aqueous solution of 200 ppm boric acid and 1.24 ppm lithium hydroxide. After the solids were filtered out of the immersion solution, the silicon concentration in the solution was determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES), and untreated glass fiber was set as a blank group for comparison.

[0054] The test results are shown in Table 3.

[0055] The data in Table 3 show that the amount of silicon precipitated from the glass fiber is related to the high-temperature heat treatment temperature. The higher the temperature, the less silicon precipitated from the treated glass fiber. In particular, high-temperature heat treatments at 550°C and 650°C can significantly reduce silicon precipitation.

[0056] In view of production practice, the high temperature heat treatment temperature of the glass fiber is preferably 500-650° C., more preferably 550-650° C.; the high temperature heat treatment time is preferably 0.5-1.5 h, more preferably 1-1.5 h.

[0057] In summary, the preferred process for glass fiber acid soaking and subsequent drying and high-temperature heat treatment is:

[0058] The volume percentage concentration of dilute sulfuric acid is 1%-5%; the soaking temperature is 60-90°C, preferably 75-85°C, and most preferably 80°C; the soaking time is 8-24h, preferably 12-24h, and more preferably 12-15h. The high-temperature heat treatment temperature after drying is preferably 500-650°C, more preferably 550-650°C; the high-temperature heat treatment time is preferably 0.5-1.5h, and more preferably 1-1.5h.

[0059] Table 3 High temperature heat treatment process parameter settings and silicon precipitation measurement results

[0060] serial number Heat treatment time / h Heat treatment temperature / ℃ Silicon concentration in soaking solution (mg / L) blank — — 6.54 1 0.5 350 5.81 2 0.5 450 4.82 3 0.5 550 1.91 4 0.5 650 2.01 5 1 350 5.51 6 1 450 4.52 7 1 550 1.85 8 1 650 1.82 9 1.5 350 5.51 10 1.5 450 4.32 11 1.5 550 1.86 12 1.5 650 1.81 13 2 350 4.98 14 2 450 4.21 15 2 550 1.83 16 2 650 1.82

[0061] Example 1 :Method for reducing silicon precipitation of glass fiber and glass fiber with low silicon precipitation obtained by the method and filter material prepared by wet molding thereof

[0062] Take 475 type 59°SR glass fiber wool (average fiber diameter 0.37μm), 475 type 19°SR glass fiber wool (average fiber diameter 1.59μm), and Φ6μm alkali-free glass fiber chopped strands and perform the following treatments:

[0063] S1. The three types of glass fibers are treated as follows:

[0064] Put the fiber into dilute sulfuric acid at a temperature of 80°C and a concentration of 1% by volume, the volume of the glass fiber being 1 / 5 of the volume of 1% sulfuric acid, stir evenly until the fiber flocculation in the container is obvious, and soak for 12 hours; after soaking, rinse the glass fiber with running water until the pH on the surface of the glass fiber is 6.2-6.5;

[0065] S2. Immediately transfer the glass fiber washed in step S1 to a clean environment (without volatile pollutants), dry it at 105-110°C for 2 hours, and then heat treat it at 550-600°C for 1-1.5 hours to obtain glass fiber with low silicon precipitation.

[0066] According to the mass ratio shown in Table 4 (based on the total absolute dry weight of the fiber as 100%), glass fibers with low silicon precipitation were prepared, mixed with an acidic aqueous solution with pH = 2 in a fiber disperser, and stirred for 8 minutes. Subsequently, the obtained fiber dispersion was used to make wet paper webs using a paper sheet former, and then dried using a flat dryer at 105°C for 30 minutes to obtain filter materials with a basis weight of 40 g / m 2 , after cutting, the diameter is 10cm and the area is 314cm 2 Round filter media.

[0067] Table 4 Basis weight 40g / m 2 Filter fiber formula

[0068] Raw material types 475 type 59°SR glass wool 475 type 19°SR glass wool Φ6μm alkali-free chopped strands Mass percentage 32％ 53％ 15％

[0069] The amount of silicon precipitation of the prepared filter material was determined, and the specific steps were: placing the filter material in an immersion solution at a temperature of 50° C. for 72 hours, wherein the immersion solution was a mixed aqueous solution of 200 ppm boric acid and 1.24 ppm lithium hydroxide; after filtering out solids from the immersion solution, the concentration of silicon in the solution was determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES), and an untreated glass fiber filter material of the same prescription was set as a blank group for control, and the measurement was performed twice in parallel. The reduction rate of silicon precipitation of the filter material prepared in this embodiment was calculated according to the following formula, and the results are shown in Table 5.

[0070] Silicon precipitation reduction rate = (Aa) / A×100%

[0071] Where: A = average value of silicon concentration in the blank group immersion solution;

[0072] a = Silicon concentration in the immersion solution of low silicon precipitation filter media.

[0073] Table 5 Silica precipitation concentration in filter material soaking liquid

[0074]

[0075] Table 2 shows that the amount of silicon precipitated from the filter material prepared from the glass fiber treated by the method of the present invention during the soaking process is reduced by about 70% compared with the untreated sample, which proves that the method of the present invention can effectively reduce the amount of silicon precipitated from the glass fiber.

[0076] Example 2 : Resin-reinforced low silicon leaching glass fiber filter material

[0077] The glass fiber filter material obtained in Example 1 was impregnated with resin to prepare a resin-reinforced finished filter material. The resin system is an acrylic emulsion with a gel concentration of 1% by mass. The specific steps of impregnating the filter material with the resin are: first, 500 mL of acrylic glue solution is prepared at a gel concentration of 1% and placed in a glue tray, a layer of polytetrafluoroethylene mesh is placed at the bottom of the glue tray, and the glass fiber filter material of Example 1 is completely immersed in the glue solution and allowed to stand for 200 seconds. After the impregnation is completed, the filter material is taken out with a polytetrafluoroethylene mesh, and dried in a dryer at 105° C. for 30 minutes to obtain a resin-reinforced glass fiber filter material with low silicon precipitation.

[0078] The silicon precipitation amount of the resin-reinforced low silicon precipitation glass fiber filter material was determined according to the same method and steps as in Example 1. An untreated glass fiber filter material impregnated with acrylic resin was also set as a blank group for control. The measurements were carried out twice in parallel, and the silicon precipitation reduction rate was calculated. The results are shown in Table 6.

[0079] Table 6 Silica precipitation concentration in resin enhanced filter material soaking liquid

[0080]

[0081] It can be seen that the glass fiber treated by the method of the present invention is prepared into a finished filter material containing a reinforced resin, and the amount of silicon precipitated during the immersion process is reduced by about 80% compared with the untreated sample.

[0082] In summary, the present invention provides a simple and easy method for reducing silicon precipitation in glass fiber, and a glass fiber with low silicon precipitation obtained by the method and a filter material prepared therefrom. The method of the present invention is particularly suitable for industrial production. The filter material with low silicon precipitation provided by the present invention has a high silicon oxygen content, stable performance, and a longer service life, which solves the problem caused by silicon precipitation in nuclear-grade water filter elements and can ensure the normal operation of nuclear power systems.

Claims

1. A method for reducing silicon precipitation in glass fiber, comprising the following steps: S1. Soak the glass fiber in dilute sulfuric acid at a volume percentage concentration of 1%-5% at 60-90°C for 8-24 hours, and then wash with water; S2. Immediately dry the cleaned glass fiber obtained in step S1 at 100-150°C for 2-3h, then heat treat the dried glass fiber at 500-650°C for 0.5-1.5h, and cool naturally.

2. The method according to claim 1, characterized in that: The glass fiber is selected from glass fiber wool and / or alkali-free chopped strands, and has an average fiber diameter of 0.1-10 μm; Preferably, the glass fiber is selected from one or more of the following: 1) 59°SR glass wool fiber, average fiber diameter 0.35-0.4 μm, more preferably 0.37 μm, 2) 19° SR glass wool, with an average fiber diameter of 1.2-2.0 μm, more preferably 1.59 μm, and 3)Φ6μm alkali-free glass fiber chopped strands.

3. The method according to claim 1 or 2, characterized in that: In the step S1, the total volume of the glass fibers does not exceed 1 / 5 of the volume of the dilute sulfuric acid, and the glass fibers are stirred until the fibers are evenly distributed and no obvious fiber flocculation clusters are present in the immersion container.

4. The method according to claim 1, characterized in that: In step S1, the temperature of the dilute sulfuric acid soaking treatment is 75-85°C; more preferably 80°C; Preferably, in step S1, the time for soaking in dilute sulfuric acid is 12h-24h; more preferably 12-15h.

5. The method according to claim 1, characterized in that In the step S1, the glass fiber is washed with running water until the pH value on the fiber surface is ≥5.

6. The method according to any one of claims 1 to 5, characterized in that: In step S1, the soaking liquid for soaking the glass fiber and the washing liquid for washing the glass fiber are combined to recover B 3+ and Na + .

7. The method according to claim 1, characterized in that In the step S2, the cleaned glass fiber obtained in the step S1 is immediately transferred to a drying environment, and there is no other volatile substances in the drying environment.

8. The method according to claim 1 or 7, characterized in that: In step S2, the heat treatment temperature is 550-650°C; Preferably, in step S2, the heat treatment time is 1-1.5 h.

9. A glass fiber with low silicon precipitation, prepared by the method according to any one of claims 1 to 8; compared with untreated glass fiber, the glass fiber with low silicon precipitation is immersed in a mixed solution of boric acid and lithium hydroxide at 50°C for 72 hours, and the silicon concentration in the immersion solution is reduced by at least 60%, preferably by 65% ​​to 70%; wherein the concentration of boric acid in the mixed solution of boric acid and lithium hydroxide is 200ppm, and the concentration of lithium hydroxide is 1.24ppm.

10. A filter material, prepared from the glass fiber with low silicon precipitation amount according to claim 9; Preferably, the filter material is formed by wet-forming the glass fiber with low silicon precipitation amount as claimed in claim 9; Also preferably, the filter material is prepared from the glass fiber with low silicon precipitation amount as claimed in claim 9 reinforced with resin; Further preferably, the filter material is prepared by wet-process papermaking of the resin-reinforced glass fiber with low silicon precipitation as claimed in claim 9.

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