JP2015085250A - Filter medium for air filter and production method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter medium for an air filter having a high PF value in the filter medium for the air filter using a fluorine-based surfactant.SOLUTION: In a filter medium for an air filter mainly containing glass fiber, a mixture of a binder resin and a fluorine-based surfactant containing a perfluoroalkyl compound is adhered to the glass fiber. The perfluoroalkyl compound is a compound having a perfluoroalkyl group having the number of carbon atoms of 6 or less.

Description

  The present invention relates to a filter medium for an air filter. More specifically, the present invention relates to a filter medium for an air filter used in a clean room, a clean bench, an air filter for building air conditioning, an air purifier, and the like used in the fields of semiconductors, liquid crystals, bio / food, pharmaceuticals, medicine and the like.

  In order to collect submicron to micron dust particles in the air, an air filter collection technique is used. Air filters are broadly classified into coarse dust filters, medium performance filters, high performance filters (HEPA filters, ULPA filters), etc., depending on the target particle size and collection efficiency. Among these, high-performance filters are mainly used for clean room applications and the like, and air filter media made of glass fiber wet nonwoven fabric are widely used as air filter media.

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 small diameter 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 air filter media, glass fibers having an average fiber diameter on the order of several to several tens of micrometers are usually used as main components. Since glass fiber has almost no self-adhesive force, it is processed as an air filter unit, and in order to give the filter medium strength required when actually ventilating and using the glass fiber, the glass fibers are bonded together with a binder resin. Need to be glued. However, if a binder resin is attached to the glass fiber, the binder film clogs the pores of the filter medium, causing an increase in pressure loss, and further, the glass fiber is buried in the binder film, so that the collection efficiency is increased. May 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, a method has been proposed in which a fluorosurfactant having a minimum surface tension of 20 mN / m or less when added to glass fiber constituting the filter medium in a binder resin and 25 ° C. pure water has been proposed. (For example, refer to Patent Document 1) It has been shown that by using this method, pore clogging due to the binder film can be prevented, and the air filter medium can have a high PF value.

JP-A-10-156116

  The fluorosurfactant contains a perfluoroalkyl group having 7 or more carbon atoms because the effect of preventing clogging of pores due to the binder film described above increases as the number of carbon atoms of the perfluoroalkyl group contained increases. It is considered preferable.

  However, when a fluorosurfactant is used, the wettability of the filter medium itself is increased and the water repellency of the filter medium is decreased. When the water repellency of the filter medium is lowered, there arises a problem that the sealing agent used when the filter medium is processed is soaked. In addition, when used in an air filter unit, water droplets may adhere to the filter medium due to moisture condensation due to changes in temperature and humidity or ventilation of air with high humidity. At this time, if the water repellency of the filter medium is low, there is a problem that these water droplets block the pores of the filter medium (hereinafter referred to as a problem due to low water repellency). The present invention has been made in view of such problems, and an object of the present invention is to provide an air filter medium having a high PF value in an air filter medium using a fluorosurfactant. It is in.

  The present inventors have found that the above problem can be solved by adhering a mixed liquid of a fluorosurfactant containing a binder resin and a perfluoroalkyl group having 6 or less carbon atoms to the glass fiber constituting the filter medium. I found it. That is, the air filter medium according to the present invention is an air filter medium mainly composed of glass fibers, wherein a mixture of a binder resin and a fluorosurfactant containing a perfluoroalkyl compound adheres to the glass fibers. The perfluoroalkyl compound is a compound having a perfluoroalkyl group having 6 or less carbon atoms.

  Moreover, in the filter material for air filters which concerns on this invention, it is preferable that the minimum surface tension when the said fluorosurfactant is added in 25 degreeC pure water is 20 mN / m or less. A filter medium having a higher PF value can be obtained.

  In the air filter medium according to the present invention, the mixture further contains a water repellent, and the amount of the water repellent added to the binder resin is 100 parts by mass in terms of solid content. On the other hand, it is preferable that the said water repellent is 1-40 mass parts. It is possible to obtain a filter medium having a water resistance while having a high PF value and no problem due to low water repellency.

  The method for producing a filter material for an air filter according to the present invention is a method for producing a filter material for an air filter, which includes a step of forming wet paper by wet papermaking a slurry in which glass fibers are dispersed, and a step of drying the wet paper. In the method, before or after drying the wet paper, a mixture of a binder resin and a fluorosurfactant containing a compound having a perfluoroalkyl group having 6 or less carbon atoms is attached to the wet paper It is characterized by making it.

  ADVANTAGE OF THE INVENTION According to this invention, the filter medium for air filters which has a high PF value can be provided in the filter medium for air filters using a fluorine-type surfactant.

  Next, the present invention will be described in detail with reference to embodiments, but the present invention is not construed as being limited to these descriptions. As long as the effect of the present invention is exhibited, the embodiment may be variously modified.

  The filter medium for an air filter according to this embodiment is a filter medium for an air filter mainly composed of glass fibers, and a mixture of a binder resin and a fluorosurfactant containing a perfluoroalkyl compound is attached to the glass fibers. The perfluoroalkyl compound is a compound having a perfluoroalkyl group having 6 or less carbon atoms.

The fluorine-based surfactant contains a compound having a hydrophobic group and a hydrophilic group of a perfluoroalkyl group (CF ₃ -CF ₂ -CF ₂ -...) in the molecule, and the carbon of the perfluoroalkyl group The number of atoms is 6 or less, and the number of carbon atoms is more preferably 4-6.

  The filter medium (filter medium A) produced by adding a fluorosurfactant containing a perfluoroalkyl compound having 6 or less carbon atoms in the perfluoroalkyl group to the binder resin has reduced water repellency. In contrast, a filter medium (filter medium B) produced by adding a fluorosurfactant containing a perfluoroalkyl compound having a perfluoroalkyl group having 7 or more carbon atoms to a binder resin has a large decrease in water repellency. . A water repellent may be attached to the filter medium for the purpose of imparting water repellency, but the amount of water repellent attached to the filter medium is reduced because the filter medium A has a higher original water repellency than the filter medium B. It is possible to reduce the cost. On the other hand, improvement in the PF value of the filter medium is related to the minimum surface tension value of the fluorosurfactant, and is not related to the number of carbon atoms of the perfluoroalkyl group.

A perfluoroalkyl compound having a perfluoroalkyl group having 7 or more carbon atoms is perfluorooctane sulfonic acid (C ₈ F ₁₇ SO ₃ H. hereinafter abbreviated as “PFOS”) or perfluorooctanoic acid (C ₇ F ₁₅ COOH (hereinafter abbreviated as “PFOA”) and the like. A fluorosurfactant containing a perfluoroalkyl compound has a higher effect of preventing clogging of pores due to the binder film described above as the number of carbon atoms of the perfluoroalkyl group of the perfluoroalkyl compound increases. Those having 7 or more carbon atoms are widely used, but PFOS or PFOA has a problem of high accumulation in living bodies and the environment. Perfluoroalkyl compounds having 6 or less carbon atoms in the perfluoroalkyl group can not generate PFOS or PFOA due to the structure of the molecule, and the substances that can be generated have low accumulation in the living body and environment. There is also an advantage of high safety.

  Examples of the fluorosurfactant include perfluoroalkyl carboxylates, perfluoroalkyltrimethylammonium salts, perfluoroalkylbetaines, perfluoroalkylamine oxides, perfluoroalkylethylene oxide adducts, and perfluoroalkylaminosulfonic acids. Among compounds, those containing a compound having a perfluoroalkyl group having 6 or less carbon atoms can be mentioned, but the compounds are not limited to those specifically listed as long as the object of the present invention can be achieved. .

  Adding a fluorosurfactant to the binder liquid lowers the surface tension of the binder liquid and eliminates or reduces the formation of a binder web-like film between the glass fibers. Increase collection efficiency. In order to sufficiently obtain the above effect, it is necessary to use a fluorosurfactant having a minimum surface tension of 20 mN / m or less when added to 25 ° C. pure water. As for the fluorosurfactant used in the present invention, it is preferable to use a fluorosurfactant having a minimum surface tension of 20 mN / m or less in order to obtain a filter medium having a higher PF value. More preferably, a fluorosurfactant having a minimum surface tension of 10 to 18 mN / m is used.

  The binder resin used in the present invention can be freely selected from resins that can bond glass fibers to each other to give filter media strength that is practically required and that can be dissolved or dispersed in water or a solvent. . Examples of such resins include acrylic ester resins, styrene-acrylic ester resins, styrene-butadiene resins, vinyl acetate resins, ethylene-vinyl acetate resins, polyolefin resins, polyurethane resins, and polyvinyl alcohol.

  The compounding amount of the fluorosurfactant with respect to the binder resin is 0.1 to 5 parts by mass, preferably 0.5 to 2 parts by mass with respect to 100 parts by mass of the binder resin in terms of solid content. To do. When the blending amount of the fluorosurfactant is less than 0.1 parts by mass, it is difficult to obtain a sufficient PF value improving effect, and when it exceeds 5 parts by mass, the strength of the filter medium and the water repellency may be greatly reduced.

  The glass fibers constituting the filter medium are freely selected from ultrafine glass fibers and chopped glass fibers having various fiber diameters and fiber lengths depending on the required filtration performance and other physical properties. It is preferably composed of two or more kinds of glass fibers including an ultrafine glass fiber of 0.70 μm or less and an ultrafine glass fiber having an average fiber diameter of 1.0 μm or more and 6.0 μm or less. Further, depending on the purpose, it is possible to blend thick organic fibers or inorganic fibers. The filter medium is mainly composed of glass fibers, but the mass ratio of the glass fibers in all fibers is 70% or more, preferably 80% or more, more preferably 90% or more. Examples of fibers other than glass fibers that can be blended in the filter medium include polyolefin fibers, polyester fibers, vinylon fibers, acrylic fibers, cellulose fibers, quartz fibers, and alumina fibers.

  The filter medium for an air filter of the present invention can be obtained by the following production method. That is, the glass fibers constituting the filter medium are dispersed in water using a pulper or the like to form a slurry, and the slurry is wet-made by a paper machine to obtain a wet paper. Next, this wet paper is a method in which a binder liquid obtained by mixing the above-mentioned fluorosurfactant and binder resin is adhered and then dried. Moreover, the effect is not changed even if the binder liquid is applied after the wet paper is dried. The adhesion amount of the binder liquid to the glass fiber is 1 to 10% by mass, preferably 4 to 7% by mass in terms of solid content. When the amount of the binder liquid attached is less than 1% by mass, it is difficult to obtain a sufficient filter medium strength. When the amount exceeds 10% by mass, an excessive binder liquid adheres to form a film due to excess binder resin. There is a risk of lowering the PF value.

  In the step of dispersing the glass fiber, in order to improve the dispersibility of the glass fiber, a method of dispersing the glass fiber in water adjusted to pH 2 to 4 with sulfuric acid is taken, but if a dispersant is added, the pH is 6 to It is also possible to disperse the glass fibers in water in the neutral range of 8. The binder resin and the fluorosurfactant are attached to the glass fiber as a binder liquid obtained by mixing them. By doing so, it is possible to reduce the film of excess binder resin and improve the PF value. The reason is not clear, but when the binder resin and the fluorosurfactant are attached separately, a film of the binder resin is likely to be formed, and even if high water repellency is obtained, a high PF value cannot be obtained. When the resin and the fluorosurfactant are attached in a mixed state, a film due to an excessive binder resin is hardly formed, so that the PF value is high and the water repellency is also high. In order to impart water resistance or flame retardancy to the filter medium, a water repellent and a flame retardant can be further added to the binder liquid. When the water repellent is used, the problem due to the low water repellency can be effectively solved. Fluorine-based, silicon-based, and wax-based types are available as the water repellent, but the use of a fluorine-based water repellent is preferable because water repellency is improved with a small amount of water repellent. As described above, in the present embodiment, since the filter medium A has higher original water repellency than the filter medium B, it is possible to reduce the amount of the water repellent adhered to the filter medium. Therefore, when using a water repellent, the compounding amount of the water repellent with respect to the binder resin is 1 to 40 parts by weight, preferably 2 to 30 parts by weight of the water repellent with respect to 100 parts by weight of the binder resin in terms of solid content. Part. When the blending amount of the water repellent is less than 1 part by mass, the water resistance of the filter medium may be insufficient, and when it exceeds 40 parts by mass, the strength of the filter medium may be reduced.

  The method of applying the binder liquid is not particularly limited, but includes a method of immersing the wet paper in the binder liquid, a method of spraying the wet paper with a spray, a method of attaching the binder liquid to a roll and transferring it to the wet paper. It is done. As a wet paper drying method, it is preferable to dry the wet paper at 110 to 160 ° C. using a hot air dryer, a roll dryer or the like.

  Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. Further, “parts” and “%” in the examples indicate “parts by mass” and “% by mass” in terms of solid content, respectively, unless otherwise specified.

Example 1
62.5 parts by mass of ultrafine glass fiber having an average fiber diameter of 0.65 μm, 27.5 parts by mass of ultrafine glass fiber having an average fiber diameter of 2.7 μm, and 10 parts by mass of chopped glass fiber having an average fiber diameter of 6 μm are adjusted to pH 3.0 with sulfuric acid. Was dispersed in water and disaggregated using a pulper to obtain a glass fiber slurry having a solid content concentration of 0.5%. Next, using the obtained glass fiber slurry, a wet paper was obtained by making paper with a hand-made cylinder. Next, a fluorosurfactant (Surflon S) containing 100 parts of an acrylic resin emulsion (Mobile LDM7222, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) and a perfluoroalkyl compound having a perfluoroalkyl group having 6 or less carbon atoms. -211 (manufactured by AGC Seimi Chemical Co., Ltd.) was dispersed in water and impregnated with wet paper, and the excess binder liquid was removed by suction, and then heated with a 130 ° C hot air dryer. It dried and the filter medium for air filters with a basic weight of 70 g / m < ² > was obtained. The impregnation amount of the binder liquid was 3.85 g / m ² in terms of solid content.

(Example 2)
100 parts of an acrylic resin emulsion (Movinyl LDM7222, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), 7 parts of a fluorine-based water repellent (NK Guard S-09, manufactured by Nikka Chemical Co., Ltd.), and carbon of a perfluoroalkyl group A binder liquid prepared by dispersing 1 part of a fluorosurfactant (Surflon S-211, manufactured by AGC Seimi Chemical Co., Ltd.) containing a perfluoroalkyl compound having 6 or less atoms in water is used as a wet paper. A filter medium for an air filter having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that impregnation was applied. The impregnation amount of the binder liquid was 3.85 g / m ² in terms of solid content.

(Example 3)
100 parts of an acrylic resin emulsion (Molvinyl LDM7222, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), 10 parts of a fluorinated water repellent (NK Guard S-09, manufactured by Nikka Chemical Co., Ltd.), and carbon of a perfluoroalkyl group A binder liquid prepared by dispersing 1 part of a fluorosurfactant (Surflon S-211, manufactured by AGC Seimi Chemical Co., Ltd.) containing a perfluoroalkyl compound having 6 or less atoms in water is used as a wet paper. A filter medium for an air filter having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that impregnation was applied. The impregnation amount of the binder liquid was 3.85 g / m ² in terms of solid content.

Example 4
100 parts of an acrylic resin emulsion (Molvinyl LDM7222, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), 10 parts of a fluorinated water repellent (NK Guard S-09, manufactured by Nikka Chemical Co., Ltd.), and carbon of a perfluoroalkyl group A binder liquid prepared by dispersing 1 part of a fluorosurfactant (Surflon S-386, manufactured by AGC Seimi Chemical Co., Ltd.) containing a perfluoroalkyl compound having 6 or less atoms in water is used as a wet paper. A filter medium for an air filter having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that impregnation was applied. The impregnation amount of the binder liquid was 3.85 g / m ² in terms of solid content.

(Comparative Example 1)
A basis weight of 70 g in the same manner as in Example 1 except that wet paper is impregnated with a binder solution prepared by dispersing only 100 parts of an acrylic resin emulsion (Molvinyl LDM7222, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) in water. A filter medium for air filter of / m ² was obtained. The impregnation amount of the binder liquid was 3.85 g / m ² in terms of solid content.

(Comparative Example 2)
Disperse 100 parts of acrylic resin emulsion (Molvinyl LDM7222, Nippon Synthetic Chemical Industry Co., Ltd.) and 10 parts of fluorine water repellent (NK Guard S-09, Nikka Chemical Co., Ltd.) in water. A filter medium for an air filter having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that the formed binder liquid was impregnated into wet paper. The impregnation amount of the binder liquid was 3.85 g / m ² in terms of solid content.

(Comparative Example 3)
100 parts of an acrylic resin emulsion (Molvinyl LDM7222, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), 10 parts of a fluorinated water repellent (NK Guard S-09, manufactured by Nikka Chemical Co., Ltd.), and carbon of a perfluoroalkyl group Use a binder solution prepared by dispersing 1 part of a fluorosurfactant (Megafac F-120, manufactured by DIC Corporation) containing a perfluoroalkyl compound having 7 or more atoms in water. A filter medium for an air filter having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that impregnation was applied. The impregnation amount of the binder liquid was 3.85 g / m ² in terms of solid content.

(Comparative Example 4)
100 parts of an acrylic resin emulsion (Molvinyl LDM7222, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), 10 parts of a fluorinated water repellent (NK Guard S-09, manufactured by Nikka Chemical Co., Ltd.), and carbon of a perfluoroalkyl group A binder liquid prepared by dispersing 1 part of a fluorosurfactant (Megafac F-179, manufactured by DIC Corporation) containing a perfluoroalkyl compound having 7 or more atoms in water is used as a wet paper. A filter medium for an air filter having a basis weight of 70 g / m ² was obtained in the same manner as in Example 1 except that impregnation was applied. The impregnation amount of the binder liquid was 3.85 g / m ² in terms of solid content.

  Evaluation of the filter material for air filters obtained in each example and each comparative example was performed using the following method.

The pressure loss was measured using a manometer (Manostar gauge WO81: manufactured by Kikai Seisakusho Co., Ltd.) as a differential pressure when air passes 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 determined 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 0.30 to 0.40 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 0.30 to 0.40 μm.

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

  For the surface tension, the minimum surface tension when a fluorosurfactant was added to 25 ° C. pure water was measured with a Denyu method surface tension measuring instrument manufactured by Taihei Rika Kogyo Co., Ltd.

  The evaluation results of Examples and Comparative Examples are shown in Table 1.

  As is clear from the results shown in Table 1, according to the present invention, a fluorosurfactant containing a perfluoroalkyl compound having a perfluoroalkyl group having 6 or less carbon atoms in a glass fiber together with a binder resin is used for glass fiber. By adhering, it is possible to obtain a filter material for an air filter having higher water repellency than when a conventional fluorosurfactant containing a perfluoroalkyl compound having 7 or more carbon atoms in a perfluoroalkyl group is used. It was. Further, when Example 3 and Comparative Example 3 are compared, the water repellency of Comparative Example 3 is lower, and a fluorosurfactant containing a perfluoroalkyl compound having a perfluoroalkyl group having 7 or more carbon atoms is obtained. When used, it can be seen that problems due to low water repellency are likely to occur.

Claims (4)

In air filter media mainly composed of glass fiber,
A mixture of a binder resin and a fluorosurfactant containing a perfluoroalkyl compound is attached to the glass fiber,
The filter material for an air filter, wherein the perfluoroalkyl compound is a compound having a perfluoroalkyl group having 6 or less carbon atoms.   The filter medium for an air filter according to claim 1, wherein the fluorosurfactant has a minimum surface tension of 20 mN / m or less when added to 25 ° C pure water.   The mixture further contains a water repellent, and the blending amount of the water repellent with respect to the binder resin is 1 to 40 parts by mass of the water repellent with respect to 100 parts by mass of the binder resin in terms of solid content. The filter medium for an air filter according to claim 1, wherein the filter medium is an air filter. In a method for producing a filter medium for an air filter, comprising a step of forming wet paper by wet papermaking a slurry in which glass fibers are dispersed, and a step of drying the wet paper,
Before or after drying the wet paper, a mixture of a binder resin and a fluorosurfactant containing a compound having a perfluoroalkyl group having 6 or less carbon atoms is attached to the wet paper. A method for producing a filter medium for air filter.