JP2011240311A - Filtering medium for air filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filtering medium for an air filter of low pressure loss and high collection efficiency, reduced and uniformized in a dispersion of a pore size distribution, and having a sufficient strength required in practical use.SOLUTION: The problem to be solved in the present invention is solved by containing, as a glass fiber constituting the filter medium, a submicron glass fiber of less than 1 μm in the average fiber diameter in which a value of a ratio (Mg+Ca/Si) of total mass of magnesium and calcium existing in a glass fiber measured by a fundamental parameter method using fluorescent X-ray analysis, to a mass of silicon, is 0.10 or less, and by depositing a binder and a fluoro surfactant onto the glass fiber constituting the filtering medium.

Description

  The present invention is a filter medium for air filters, in particular, clean rooms and clean benches used in the fields of semiconductors, liquid crystals, nanotechnology, biotechnology, foods, pharmaceuticals, medicines, etc., air filters used for air filters for buildings, air cleaners, etc. The present invention relates to a filter medium.

  In order to efficiently collect submicron or micron particles in the air, an air filter collection technique is used. Air filters are roughly classified into coarse dust filters, medium performance filters, quasi-high performance filters, high performance filters (HEPA filters, ULPA filters), etc., depending on the target particle size and collection efficiency. Among these, as high-performance filters mainly used for clean room applications and the like, filter media for air filters made of glass fiber wet nonwoven fabric are widely used. Generally, the glass fiber constituting the air filter medium has an average fiber diameter of 0. 0. Glass fibers having a diameter of several μm to less than 1 μm (hereinafter referred to as submicron glass fibers) and glass fibers having an average fiber diameter of about 1 μm to several tens of μm (hereinafter referred to as micron glass fibers) are used. ing.

Major required characteristics of the filter medium for air filter include pressure loss indicating the ventilation resistance of the filter medium in addition to the collection efficiency. In order to increase the collection efficiency of the filter medium, it is necessary to increase the blending of fine submicron glass fibers having a large surface area, but at the same time, the pressure loss of the filter medium also increases. A high pressure loss increases the operating load of the intake fan and causes an increase in power consumption, which is undesirable from the viewpoints of both energy saving and running cost reduction. Therefore, a filter medium for air filter having both low pressure loss and high collection efficiency is required. As an index value of the level of low pressure loss and high collection efficiency of the air filter medium, there is a PF value defined by the equation (1). The high PF value indicates that the filter medium for air filter has low pressure loss and high collection efficiency. The transmittance [%] = 100−the collection efficiency [%].

In response to the problems of low pressure loss and high collection efficiency of an air filter, a method of making paper by adjusting the pH to about 6 to 9 by adding a pH adjuster in a head box after the glass fiber slurry is prepared acidic. Has been proposed (see, for example, Patent Document 1). However, in this embodiment of the method, since no binder is used during the production of the filter medium, it is easy for the filter medium obtained here to not have sufficient strength required for actual use. Presumed. On the other hand, the present inventors have proposed a method of preventing fiber breakage by controlling the disaggregation conditions when preparing the glass fiber slurry, and setting the sedimentation volume of the slurry to 450 cm ³ / g or more (for example, (See Patent Document 2). However, even in this method, when the binder is used, a decrease in the PF value is observed as compared with the case of no binder.

  The glass fibers that make up the filter medium for air filters have almost no self-adhesive strength, so that they can be processed as an air filter unit, or to give the filter medium strength that is required when actually ventilated and used. It is necessary to bond glass fibers with a binder. However, if the binder is attached to the glass fiber, the binder film clogs the pores of the filter medium, causing an increase in pressure loss, or the glass fiber is buried in the binder film, resulting in a decrease in collection efficiency. Cause a decrease in the PF value. Therefore, achieving both a high PF value and sufficient filter medium strength is a major problem in producing a practical filter medium.

  In order to solve this problem, the present inventors attach a fluorosurfactant having a minimum surface tension of 20 dyne / cm or less when added to a glass fiber constituting a filter medium in a binder and 25 ° C. pure water. (See, for example, Patent Document 3), a method of attaching a binder and an acetylene-based surfactant to glass fibers constituting a filter medium (see, for example, Patent Document 4), a glass fiber constituting a filter medium, and a binder. Proposals have been made on methods for attaching ether type nonionic surfactants (see, for example, Patent Document 5). By using these methods, air filters can be obtained by preventing clogging of pores due to a binder film. It was shown that low pressure loss and high collection efficiency can be achieved.

International Publication No. 2004/094038 International Publication No. 2009/119054 Japanese Patent No. 3874038 JP 2003-71219 A JP 2006-167491 A

  However, even if these methods are used, a filter medium for air filter that has a very high level and low pressure loss and high collection efficiency, for example, a target particle diameter of 0.10 to 0.15 μm, and a surface wind speed of 5.3 cm / sec. It is very difficult to stably produce a filter medium for glass fiber air filters having a PF value of 11.0 or more, and further improvement is required. Therefore, an object of the present invention is to provide a filter material for an air filter that has a low pressure loss and a high collection efficiency, has a small variation in pore size distribution, is uniform, and has sufficient strength required for practical use. Is to provide.

This problem is the ratio of the sum of the mass of magnesium and calcium present in the glass fiber measured by the fundamental parameter method using fluorescent X-ray analysis and the mass of silicon as the glass fiber constituting the filter medium ((Mg + Ca) / Si) is contained by sub-micron glass fibers having an average fiber diameter of less than 0.10 μm and an average fiber diameter of less than 1 μm, and a binder and a fluorosurfactant are adhered to the glass fibers constituting the filter medium. Solved. In addition, the content of silicon oxide (SiO ₂ ) in the glass fibers constituting the filter medium is 50 to 70% by mass, and further preferably borosilicate glass fibers.

  By using the method of the present invention, while having sufficient strength required for practical use, the variation in the pore size distribution is small and uniform, and the low pressure loss and high collection efficiency at a higher level than ever before. An air filter medium made of glass fiber wet nonwoven fabric can be obtained.

It is the graph which compared the PF value of the Example and the comparative example.

The submicron glass fiber used in the present invention is a glass fiber having an average fiber diameter of less than 1 μm. The submicron glass fiber having an average fiber diameter of less than 1 μm is a ratio of the mass sum of magnesium and calcium present in the glass fiber measured by the fundamental parameter method using fluorescent X-ray analysis and the mass of silicon ( Hereinafter, it is a fiber whose value of “mass ratio (Mg + Ca) / Si” is 0.10 or less. Glass fibers specially designed to fall within this range may be used, or commercially available glass fibers may be selected and used. The content of silicon oxide (SiO ₂ ) in the glass fiber may be 40 to 80% by mass, preferably 50 to 70% by mass. Moreover, it is mainly preferable to select a borosilicate glass fiber. This is because borosilicate glass fibers are excellent in chemical resistance and heat resistance required in the production and use of filter media. The content of silicon oxide (SiO ₂ ) in the borosilicate glass fiber is 40 to 80% by mass, preferably 50 to 70% by mass, and more preferably 55 to 65% by mass. Further, the content of boron oxide (B ₂ O ₃ ) is 0.5 to 40% by mass, preferably 1 to 20% by mass, and more preferably 7.5 to 15% by mass. For example, it is a borosilicate glass fiber containing 55 to 65% by mass of silicon oxide (SiO ₂ ) and 8 to 11% by mass of boron oxide (B ₂ O ₃ ).

  In the present invention, the reason why a high PF value can be achieved by keeping the value of the mass ratio (Mg + Ca) / Si of the submicron glass fiber low is estimated as follows.

  Of the components constituting the filter medium for an air filter made of a glass fiber wet nonwoven fabric, the most important component for achieving a high collection efficiency is a fine submicron glass fiber. Dust particles that have entered the filter medium together with the airflow are collected by adhering to the fiber surface in the filter medium. Therefore, it is possible to form a fine network that prevents the passage of dust particles, and the submicron glass fiber having a large surface area that increases the collision probability of dust particles is greatly increased in terms of collection efficiency. Contribute. In order to enhance the effect of such submicron glass fibers, it is important that each of the fibers is uniformly arranged in the filter medium without being unevenly distributed.

In the wet nonwoven fabric manufacturing process, glass fibers are dispersed in water to prepare a glass fiber slurry. At this time, the surface charge of the glass fiber shows a high negative charge, but when the value of the mass ratio (Mg + Ca) / Si of the submicron glass fiber increases, the surface charge increases (the negative charge weakens). The inventors have found. This is because silicon oxide (SiO ₂ ) constituting most of the glass fiber shows a negative charge, while magnesium oxide (MgO) and calcium oxide (CaO) added as modifying components show a positive charge. It is thought that. When the negative charge of the glass fiber is weakened, the repulsive force acting between the fibers is weakened. Therefore, it is considered that the glass fiber works disadvantageously in order to prevent the fiber from being unevenly distributed. Further, when opposite charges are mixed on the fiber surface, the fibers are likely to aggregate, which is also considered disadvantageous for arranging the fibers uniformly. For the above reasons, keeping the mass ratio (Mg + Ca) / Si of the submicron glass fibers low increases the collection efficiency of the filter medium and improves the PF value by providing a uniform arrangement of the submicron glass fibers. Estimated. Moreover, the lower limit of the mass ratio (Mg + Ca) / Si may be 0.005 or more, and further 0.02 or more.

  In the present invention, micron glass fibers are used in combination with submicron glass fibers. The micron glass fiber may be a glass fiber having an average fiber diameter of 1 μm or more, but is preferably a micron glass fiber having a size of 1 μm or more and less than 10 μm. The micron glass fiber is not particularly limited in composition as the submicron glass fiber. This is because the micron glass fiber has little influence on the collection efficiency of the filter medium for the air filter as compared with the submicron glass fiber. The fiber diameter, fiber length, fiber form, and the like of the micron glass fiber are appropriately selected according to physical properties such as pressure loss, strength, and rigidity of the air filter medium. Furthermore, as long as it does not affect the effect of the submicron glass fibers, natural fibers, organic synthetic fibers, and the like may be blended in the glass fibers as auxiliary materials.

  The blending amount of the submicron glass fiber with respect to the total glass fiber (submicron glass fiber + micron glass fiber) mass is appropriately adjusted according to physical properties such as target pressure loss and collection efficiency, but preferably 10 to 100. %, More preferably 30 to 95%, still more preferably 40 to 85%. When the blending amount of the submicron glass fiber is less than 10%, it is difficult to obtain an effect on the PF value of the submicron glass fiber. Although the effect on the PF value can be obtained even if the blending amount of the submicron glass fiber is 100%, the design value of the blending amount should be 95% or less in order to easily control the physical properties by adjusting the blending amount at the time of manufacture. More preferably.

  The binder used in the present invention is not particularly limited as long as it is a substance that can adhere glass fibers to give practically necessary tensile strength and can be dissolved or dispersed in water or a solvent. Examples of such substances include acrylic ester resins, styrene-acrylic ester resins, ethylene-acrylic acid resins, styrene-butadiene resins, vinyl acetate resins, ethylene-vinyl acetate resins, polyolefin resins, urethane resins, and polyvinyl alcohol. Etc.

  The fluorosurfactant used in the present invention contains a hydrophobic group composed of a fluoroalkyl group in the molecule and a hydrophilic group. For example, perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, perfluoroalkyl betaines, perfluoroalkyl ammonium salts and the like can be mentioned. The addition amount of the fluorosurfactant in the liquid containing the binder, the fluorosurfactant, and other additives (hereinafter referred to as the binder liquid) is 0.1 to 0.1 in terms of a solid mass ratio with respect to the binder. 5%, preferably 0.5 to 3%. When the addition amount of the fluorosurfactant is less than 0.1% with respect to the binder, the effect of improving the PF value cannot be obtained sufficiently. In addition, if the amount of the fluorosurfactant added exceeds 5%, not only can the effect of increasing the PF value be commensurate with the increase in the amount added, but also the decrease in the tensile strength of the filter medium and the water repellent treatment. If this occurs, problems such as a decrease in water repellency are caused.

  In the present invention, the fluorosurfactant together with the binder is also an essential component constituting the filter medium. As described above, a filter medium having a high PF value can be obtained from a wet nonwoven fabric using submicron glass fibers with a low mass ratio (Mg + Ca) / Si. However, when a binder is attached here, the mass ratio (Mg + Ca) ) / Si almost disappears. However, the present inventors have found that the effect of the mass ratio (Mg + Ca) / Si is manifested again when a fluorosurfactant is attached together with the binder. The reason for this is that if a binder is attached to the glass fiber constituting the filter medium, the submicron glass fiber is buried in the water-binder-like binder film, and the effect is not exhibited. It is estimated that this is because the surface tension of the binder liquid is decreased, the water-binder-like binder film is reduced, and the effect of the submicron glass fiber is manifested again. It is also estimated that the reduction in the surface tension of the binder liquid weakens the force that pulls the fibers together when the binder liquid is dried and solidified, and as a result, it is possible to suppress changes in the uniform fiber arrangement.

  The binder and the fluorosurfactant used in the present invention are simultaneously applied in the state of a binder liquid. Depending on the physical properties required for the filter material for the air filter, this binder liquid has a water repellent and a crosslinker. Additives such as agents and flame retardants can be added as appropriate within a range that does not impair the effects of the present invention. In particular, in most uses of air filter media, water repellent is used in most cases because water repellent of a certain level or more is required. Examples of the water repellent include a fluorine water repellent, a silicone water repellent, a wax water repellent, and an alkyl ketene dimer. The addition amount of additives such as water repellents is 0 to 40%, preferably 1 to 30% in terms of the solid mass ratio with respect to the binder. More preferably, it is 2 to 25%.

The solid content of the binder, the fluorosurfactant and other additives (hereinafter referred to as the binder composition) contained in the binder liquid is 1 to 15%, preferably 2 based on the total mass of the filter medium. -10%, more preferably 3-8%. If the adhesion amount is less than 1%, it is difficult to obtain the tensile strength required for practical use. On the other hand, when the adhesion amount exceeds 15%, the pressure loss increases to fill the voids in the filter medium, and the PF value decreases.

  The filter medium for an air filter of the present invention is produced by a wet papermaking method. Here, first, glass fibers are dispersed in water, and then the obtained glass fiber slurry is laminated on a wire and dehydrated to make a paper (sheet). The paper machine used at this time is not particularly limited, but one that can make paper as uniformly as possible is selected. The water used for dispersion and papermaking is preferably adjusted to a pH of about 2 to 4 by adding an acid in order to make the fiber dispersion uniform.

  As a method for applying the binder liquid to the wet paper-made sheet, methods such as impregnation, roll coating, spray coating, curtain coating and the like are used. In order to prevent the filter medium from being clogged by the binder film, it is preferable to remove the excessively applied binder liquid by negative pressure suction or the like. Thereafter, the wet sheet to which the binder liquid has been applied is dried using a hot air dryer, a rotary dryer, or the like to obtain a final air filter filter medium.

  Next, an Example is given and this invention is demonstrated more concretely.

Submicron glass fiber made of borosilicate glass having an average fiber diameter of about 0.65 μm and a mass ratio (Mg + Ca) / Si value of 0.076 measured using X-ray fluorescence analysis (silicon oxide content: 58 mass%) 65% by mass of micron glass fiber (B-26-R, manufactured by Lauscha) with an average fiber diameter of about 2.70 μm, and a sulfuric acid acidic pH 2.5 tap water with a solid content concentration of 0.5% by mass Water was added and disaggregated using a pulper to obtain a glass fiber slurry. Next, the obtained slurry was made using a hand-making cylinder to obtain a wet paper. Next, an acrylic resin binder (Boncoat AN-1190, manufactured by DIC Corporation), a fluorosurfactant (Factent 110, manufactured by Neos Co., Ltd.), and a fluorine water repellent (NK Guard S-02, Japan) Hana Kagaku Co., Ltd.) and the binder liquid blended so that the solid content mass ratio is 100/1/5 impregnated the wet paper, and then dried with a hot air dryer at 130 ° C., A filter medium for an air filter having a basis weight of 70 g / m ² and a binder composition solid content of 5.5% by mass relative to the total mass of the filter medium was obtained.

Submicron glass fiber made of borosilicate glass having an average fiber diameter of about 0.65 μm and a mass ratio (Mg + Ca) / Si value of 0.099 measured using X-ray fluorescence analysis (silicon oxide content: 58 mass%) 65% by mass of micron glass fiber (B-26-R, manufactured by Lauscha) with an average fiber diameter of about 2.70 μm, and a sulfuric acid acidic pH 2.5 tap water with a solid content concentration of 0.5% by mass Water was added and disaggregated using a pulper to obtain a glass fiber slurry. Thereafter, by the same method as in Example 1, a filter medium for an air filter having a basis weight of 70 g / m ² and a binder composition solid content adhesion amount of 5.4% by mass was obtained.

[Comparative Example 1]
65% by mass of submicron glass fiber (B-06-F, manufactured by Lauscha) having an average fiber diameter of about 0.65 μm and a mass ratio (Mg + Ca) / Si value of 0.168 measured using X-ray fluorescence analysis Then, tap water having a sulfuric acid pH of 2.5 is added to 35% by mass of micron glass fiber (B-26-R, manufactured by Lauscha) having an average fiber diameter of about 2.70 μm so that the solid content concentration is 0.5% by mass. The glass fiber slurry was obtained by disaggregation using a pulper. Thereafter, by the same method as in Example 1, a filter medium for an air filter having a basis weight of 70 g / m ² and a binder composition solid content adhesion amount of 5.5% by mass was obtained.

[Comparative Example 2]
Glass fiber slurry obtained by the same method as in Example 1, acrylic resin binder (Boncoat AN-1190, manufactured by DIC Corporation) and fluorine-based water repellent (NK Guard S-02, manufactured by Nikka Chemical Co., Ltd.) ) And a binder liquid blended so that the solid content mass ratio is 100/5, the basis weight is 70 g / m ² and the binder composition solid content is 5.4 mass by the same method as in Example 1. % Of filter medium for air filter was obtained.

[Comparative Example 3]
Glass fiber slurry obtained by the same method as in Example 2, acrylic resin binder (Boncoat AN-1190, manufactured by DIC Corporation), and fluorine-based water repellent (NK Guard S-02, manufactured by Nikka Chemical Co., Ltd.) ) With a basis weight of 70 g / m ² and a binder composition solid content adhesion amount of 5.6 mass by the same method as in Example 1 using a binder solution in which the solid mass ratio is 100/5. % Of filter medium for air filter was obtained.

[Comparative Example 4]
Glass fiber slurry obtained by the same method as Comparative Example 1, an acrylic resin binder (Boncoat AN-1190, manufactured by DIC Corporation), and a fluorine-based water repellent (NK Guard S-02, manufactured by Nikka Chemical Co., Ltd.) ) And a binder liquid formulated so that the solid content mass ratio is 100/5, and the basis weight is 70 g / m ² and the binder composition solid content adhesion amount is 5.5 mass by the same method as in Example 1. % Of filter medium for air filter was obtained.

[Comparative Example 5]
Wet paper obtained by papermaking the glass fiber slurry obtained by the same method as in Example 1 using a hand-made cylinder is dried as it is with a hot air dryer at 130 ° C. without being impregnated with a binder, and the basis weight is 70 g. / m ² , a no-binder air filter medium was obtained.

[Comparative Example 6]
Wet paper obtained by papermaking the glass fiber slurry obtained by the same method as in Example 2 using a hand-made cylinder was dried as it was with a hot air dryer at 130 ° C. without being impregnated with a binder, and the basis weight was 70 g. / m ² , a no-binder air filter medium was obtained.

[Comparative Example 7]
A wet paper obtained by papermaking a glass fiber slurry obtained by the same method as in Comparative Example 1 using a hand-making cylinder was dried as it was with a hot air dryer at 130 ° C. without being impregnated with a binder, and a basis weight of 70 g. / m ² , a no-binder air filter medium was obtained.

  The filter media obtained in Examples and Comparative Examples were evaluated using the following method.

  The value of the mass ratio (Mg + Ca) / Si present in the submicron glass fiber is determined by using a fluorescent X-ray analyzer (SEA2210A, manufactured by SII Nanotechnology) for the submicron glass fiber before disaggregation. The abundance (mass%) of magnesium, calcium and silicon were measured by the fundamental parameter method, and calculated from the measured values.

  The zeta potential of the submicron glass fiber is a glass fiber slurry obtained by adding tap acid having a sulfuric acid pH of 2.5 to a submicron glass fiber so as to have a solid content concentration of 0.5% by mass, and separating using a pulper. Was measured using a zeta potentiometer (SZP06, manufactured by Mutech Co., Ltd.) by the streaming potential method.

The pressure loss was measured using a manometer as a differential pressure when air passed through a filter medium having an effective area of 100 cm ^{2 at} a surface wind speed of 5.3 cm / sec.

The transmittance (also referred to as particle transmittance) is obtained when air containing polydispersed dioctyl phthalate (DOP) particles generated by a Ruskin nozzle passes through a filter medium having an effective area of 100 cm ^{2 at} a surface wind speed of 5.3 cm / sec. The number of upstream and downstream DOP particles was measured using a laser particle counter (KC-18, manufactured by Rion Co., Ltd.) and calculated from the number value. The target particle diameter was 0.10 to 0.15 μm.

  The PF value was calculated from the value of pressure loss and particle transmittance using the equation shown in Equation 1. The target particle diameter was 0.10 to 0.15 μm.

  Tensile strength is in accordance with JIS P 8113: 2006 “Paper and paperboard—Test method for tensile properties—Part 2: Low-speed extension method” (Strograph M1, manufactured by Toyo Seiki Seisakusho Co., Ltd.) It measured using.

  The water repellency was measured using a self-made water repellency tester according to MIL-STD-282.

  The average pore diameter and the maximum pore diameter were measured using a porous material automatic pore diameter measuring device (Palm Porometer, manufactured by PMI), and the ratio (maximum pore diameter / average pore diameter) was calculated and obtained. In addition, Fluorinert FC-40 (Sumitomo 3M Co., Ltd.) was used for the test solution.

  The evaluation results of Examples and Comparative Examples are shown in Table 1. A graph of PF value comparison is shown in FIG.

  Looking at the zeta potential, the smaller the value of the mass ratio (Mg + Ca) / Si, the smaller the micron glass fiber, the lower the zeta potential value (the larger the absolute value), that is, the greater the repulsive force acting between the fibers. Is shown.

  Looking at the PF value, in the case of the no binder filter medium (Comparative Examples 5 to 7), the PF value is high when the mass ratio (Mg + Ca) / Si value is 0.10 or less, but the binder and the water repellent are adhered. In the case of the filter medium (Comparative Examples 2 to 4), the PF values are almost the same, and the effect of the mass ratio (Mg + Ca) / Si is lost. However, in the case of the filter medium (Examples 1 and 2 and Comparative Example 1) to which a fluorosurfactant is attached, a high PF value is obtained again when the mass ratio (Mg + Ca) / Si value is 0.10 or less. Furthermore, the degree of increase in the PF value due to the attachment of the fluorosurfactant is also large. From these data, it is clear that the effect on the PF value intended by the present invention can be sufficiently obtained by suppressing the mass ratio (Mg + Ca) / Si value of the submicron glass fiber to at least 0.10 or less. .

The value of the ratio (maximum pore diameter / average pore diameter) indicates the uniformity of the pore size distribution of the filter medium, and the smaller this value, the smaller the variation in the pore size distribution and the more uniform. The smaller the value of the mass ratio (Mg + Ca) / Si, the smaller the ratio (maximum pore diameter / average pore diameter) value, indicating a more uniform pore size distribution. This indicates that in the filter medium of submicron glass fibers. This suggests that the arrangement in is more uniform.

Claims (5)

  As a glass fiber constituting the filter medium, a ratio ((Mg + Ca) / Si) of the mass sum of magnesium and calcium present in the glass fiber measured by the fundamental parameter method using fluorescent X-ray analysis and the mass of silicon The value is 0.10 or less, including an average fiber diameter of submicron glass fibers of less than 1 μm, and characterized in that a binder and a fluorosurfactant are attached to the glass fibers constituting the filter medium, Air filter media. The filter medium for an air filter according to claim 1, wherein the content of silicon oxide (SiO ₂ ) in the glass fiber constituting the filter medium is 50 to 70 mass%.   The filter medium for an air filter according to claim 1 or 2, wherein the glass fibers constituting the filter medium are borosilicate glass fibers.   The filter medium for an air filter according to any one of claims 1 to 3, wherein a ratio of a maximum pore diameter to an average pore diameter (maximum pore diameter / average pore diameter) of the filter medium is 2.4 or less. . The PF value defined by the formula (1) at an object particle size of 0.10 to 0.15 μm and a surface wind speed of 5.3 cm / sec is 11.0 or more. Item 1. A filter medium for an air filter according to item 1.