JP6964033B2 - Filter material for air filter - Google Patents

Description

The present invention relates to a filter medium for a dust-removing air filter used for filtering impurities in the air, and more specifically, to a filter medium for an air filter which is excellent in collecting dust and the like and has a low pressure loss. ..

In recent years, with changes in the living environment and growing interest in the indoor environment at the individual level, there is a demand for cleaning the air in offices and living spaces. As a method of removing airborne dust in the air, a method using a dust removal filter is common, and various filter media for a dust removal air filter exist. Larger ones are used for system air conditioning in buildings and factories, and smaller ones are widely used in air purifiers and air conditioners. There is a demand for a filter medium for an air filter having the above.

The filter medium for an air filter is roughly classified into a coarse dust filter, a medium performance filter, a HEPA filter, a ULPA filter, and the like according to the difference in the target particle size and dust removal efficiency. Most of these air filters use filter media for fiber layer air filters such as non-woven fabric, woven fabric, and matte, and in particular, non-woven glass fiber air filter filters for medium-performance filters, HEPA filters, and ULPA filters. Is widely used.

As a method for producing a filter medium for an air filter, a method of obtaining a filter medium for an air filter by sheeting short glass fibers or organic fibers into a sheet by a wet papermaking method and then applying a binder and a water repellent agent, or a molten fiber. There is a dry method represented by the melt blown method using. Generally, glass fibers are sheeted by a wet papermaking method and formed as a filter medium.

Filter media for air filters using glass fibers have lower pressure loss and higher collection efficiency than air filters using other fibers due to the characteristics of high rigidity peculiar to glass fibers and a fine fiber diameter of 1 μm or less. High filter performance. However, there is an increasing demand for a cleaner environmental space and a reduction in the environmental load, and there is a demand for a filter medium for an air filter having high filter performance with low energy consumption and high efficiency and low pressure loss.

As such a filter medium for an air filter, less than 55% by mass of chopped strand glass fiber, less than 25% by mass of glass fiber having an average fiber diameter of less than 1 μm, and 40 to 90% by mass of glass fiber having an average fiber diameter of 1 μm or more are blended. A filter medium for an air filter has been proposed (Patent Document 1).

Further, the average fiber diameter of fibers having a small fiber diameter of less than 1.0 μm is 0.1 μm or more and less than 0.8 μm, and the average fiber diameter of fibers having a large fiber diameter of 1.0 μm or more is 1.2 μm or more and 3.0 μm. A filter medium for an air filter having a main collection layer having a volume ratio of less than 30:70 to 80:20 between the fibers having a small fiber diameter and the fibers having a large fiber diameter has been proposed (see Patent Document 2). .. However, these air filter filter media are not sufficiently energy efficient, have insufficient collection efficiency, consume less energy, are more efficient and have low pressure loss, and there is still a demand for air filter filter media. ..

Special Table 2012-518527 Gazette Japanese Unexamined Patent Publication No. 2017-35684

The present invention provides a filter medium for an air filter that consumes less energy, is highly efficient, and has a low pressure loss.

As a result of diligent studies to solve the above problem, it was found that the air filter filter medium is composed of chopped strand glass fiber and ultrafine glass fiber, and the above problem can be solved by the air filter filter medium in which the fiber diameter distribution of the glass fiber is defined. bottom.

That is, the filter medium for an air filter of the present invention is a filter medium for an air filter mainly composed of glass fibers, and the glass fibers contain chopped strand glass fibers and ultrafine glass fibers, and the fibers of the filter medium for the air filter. In the diameter distribution, the cumulative frequency in the range larger than 1.5 μm and 2.9 μm or less is 2 to 15%.

Further, the filter medium for an air filter of the present invention may have a PF value of 13.5 or more represented by the formula of Equation 1 at a target particle size of 0.3 μm and a surface wind speed of 5.3 cm / sec (sec). The PF value in the present invention is calculated based on the following formula by measuring the PAO (polyalphaolefin) transmittance of a 0.3 μm monodisperse.

According to the present invention, it is possible to provide a filter medium for an air filter having low energy consumption, high efficiency and low pressure loss.

The filter medium for an air filter of the present invention contains chopped strand glass fibers and ultrafine glass fibers as glass fibers. The chopped strand glass fiber refers to a glass fiber obtained by aligning a bundle of short glass fibers with an average fiber diameter of several μm to several tens of μm drawn from a spinning nozzle to a length of about 1.5 mm to 25 mm. .. The ultrafine glass fiber refers to a wool-like glass fiber having an average fiber diameter of 6.0 μm or less produced by a flame stretching method or a rotary method. By using the chopped strand glass fiber and the ultrafine glass fiber in combination, it is possible to maintain the fine fibers and voids required for particle collection, and to have the rigidity of the filter medium required for unit processing. The blending ratio of the chopped strand glass fiber and the ultrafine glass fiber is not particularly limited, but the mass (weight) ratio is preferably chopped strand glass fiber: ultrafine glass fiber = 10: 90 to 50:50. .. When the mass ratio of the chopped strand glass fibers is more than 50, the entanglement between the fibers is reduced, so that the strength is likely to decrease. For example, glass fibers containing 50 to 90% by mass, preferably 50 to 80% by mass, and chopped strand glass fibers in an amount of 10 to 50% by mass, preferably 20 to 50% by mass, based on the total glass fibers. Is preferably used as the raw material glass fiber.

The type of glass fiber is not particularly limited, but low boron glass fiber having a low boron content may be used in semiconductor factory applications where boron is disliked.

The filter medium for an air filter of the present invention may contain an auxiliary material other than glass fiber. Such auxiliary materials include binder fibers made of natural fibers and synthetic resins. Moreover, you may contain synthetic resin. In particular, it is preferable to contain a binder fiber or a non-fibrous synthetic resin binder in order to impart strength to the filter medium. The binder fiber is, for example, polyethylene fiber, modified polyester fiber, core-sheath synthetic fiber, polyvinyl alcohol fiber, or the like, and these can be used alone or in combination of two or more. The content of the binder fiber is not particularly limited, but is preferably 0 to 20 parts with respect to 100 parts by mass of the glass fiber. The non-fibrous synthetic resin binder is, for example, acrylic latex, NBR latex, vinyl acetate latex, olefin latex, or polyvinyl alcohol latex, and can be used alone or in combination of two or more. The content of the synthetic resin binder is not particularly limited, but is preferably 2 to 10 parts with respect to 100 parts by mass of the glass fiber. The non-fibrous binder resin used in the present invention may be selected from a polymer capable of adhering glass fibers to each other and imparting strength, and the glass is dissolved or dispersed in water or an organic solvent. It may be given to the fiber. Further, in the manufacturing process, the glass fibers may be mixed when they are dissociated. Alternatively, the synthetic resin binder can be applied by applying or spraying the filter medium (wet paper sheet). Further, if necessary, chemicals such as a water resistant agent, a surfactant, an antifoaming agent, and a pH adjuster can be added within a range in which sufficient strength can be obtained.

The filter medium for an air filter of the present invention may further contain a water repellent. The water repellent is not particularly limited, and examples thereof include water repellents such as silicon-based, fluorine-based, and paraffin wax-based.

The method for producing the filter medium for an air filter of the present invention is not particularly limited, but it can be obtained by forming a sheet by a wet papermaking method using a slurry in which glass fibers are dispersed in water and drying it. The paper machine used in the wet paper making method is not particularly limited, and a long net type paper machine, a short net type paper machine, a circular net type paper machine, an inclined wire type paper machine, a gap former, and a delta former can be used. .. The drying method is not particularly limited, and various methods such as a hot air method, an infrared method, a Yankee dryer, and a multi-cylinder dryer can be used.

The filter medium for an air filter of the present invention has a cumulative frequency of 2 to 15% within a range of more than 1.5 μm and 2.9 μm or less in the fiber diameter distribution of glass fibers. More preferably, it is 3 to 12%. Here, the fiber diameter distribution of the air filter filter medium is the cross section of the filter medium when the air filter filter medium is cut in the direction perpendicular to the papermaking flow direction (hereinafter referred to as the MD direction) (hereinafter referred to as the CD direction). It is the frequency distribution based on the number of fibers calculated from.

As a method for measuring the fiber diameter distribution of the filter medium for an air filter, measurement is performed using an electron micrograph or the like of a cross section of the filter medium cut in the CD direction. The magnification at that time is not particularly limited, but it is desirable that it is 3000 times or more, and it is desirable that the fiber diameters of all the fibers used in the filter medium for the air filter can be measured at the same magnification.

When the cross section of the glass fiber that can be confirmed from the cross section of the filter medium is elliptical, its minor axis is defined as the fiber diameter. In the thickness direction of the cross section of the filter medium, an electron micrograph of the total thickness of the filter medium from the surface of the filter medium to the back surface of the filter medium is taken, and the fiber diameter (Di) at that time is measured. The total number of measured fibers is 400 or more. If the total measured fiber diameter is less than 400, an electron micrograph of the total filter medium thickness in a row is further taken to measure the fiber diameter. The number of fibers (Ni) of each fiber diameter is calculated from the fiber diameter measured by the above method in increments of 0.2 μm from 0.1 μm, and the fiber diameter distribution ratio is calculated by the following calculation method.
Fiber diameter: Di (μm)
Number of fibers: Ni (pieces)

In the fiber diameter distribution by the above calculation method, it was found that the PF value, which is an index of filter performance, is improved when the cumulative frequency in the range larger than 1.5 μm and 2.9 μm or less is in the range of 2 to 15%. Although the reason is not clear, if the cumulative frequency in the fiber diameter distribution larger than 1.5 μm and 2.9 μm or less is greater than 15%, it will not be effective for collection efficiency. Ultra-fine fibers with a small aspect ratio are used as filter media. It is estimated that it becomes easier to stay inside, closes the voids in the filter medium, and increases only the pressure loss. Further, if the cumulative frequency in the range larger than 1.5 μm and 2.9 μm or less is less than 2%, the ultrafine glass fibers effective for the collection efficiency become difficult to stay in the filter medium, and the collection efficiency is lowered. presume. Further, preferably, the filter medium for an air filter of the present invention has a PF value of 13.5 or more, preferably 14 at a target particle size of 0.3 μm and a surface wind speed of 5.3 cm / sec (sec). It may be 0.0 or more. The higher the PF value, the higher the collection efficiency with the same pressure loss.

In order to set the cumulative frequency in the range of 2.9 μm or more, which is larger than 1.5 μm in the fiber diameter distribution of the filter medium for air filters, to the range of 2 to 15%, the average fiber diameter is 1.5 to 2.9 μm as a raw material. It is preferable to reduce the blending ratio of the glass fiber of. Specifically, as the glass fiber used as a raw material, the amount of ultrafine glass fiber having an average fiber diameter of 1.5 to 2.9 μm is set to less than 10% by mass, preferably less than 5% by mass, of all the glass fibers. It is preferable to do so. However, since the filter medium for an air filter of the present invention uses both a large-diameter chopped strand glass fiber and a small-diameter ultrafine glass fiber, the diameter is smaller than that of the large-diameter chopped strand glass fiber especially in wet papermaking. The yield of ultrafine glass fiber is poor. Since the yield of the ultrafine glass fibers to be blended changes depending on the fiber diameter and the blending ratio to be blended, the mixing ratio at the raw material stage and the fiber diameter distribution ratio at the filter medium stage for the air filter do not match. In addition, since ultrafine glass fibers have a broad fiber diameter distribution due to the origin of the manufacturing method, the average fiber diameter is in the range of 2.9 μm or more, which is larger than 1.5 even if glass fibers having an average fiber diameter of 1.5 to 2.9 μm are not mixed. The cumulative frequency of the included classes may be 15% or more. The average fiber diameter of from greater 2.9μm than 1.5μm when the average fiber diameter and ultrafine glass fiber of less than 1.0 micron m is a combination of extreme fiber diameter as 6.0μm greater than chopped strand glass fibers The cumulative frequency of the range may be less than 2.0%. In order to increase the PF value of the air filter filter medium, the fiber diameter distribution in the air filter filter medium is important. In order to obtain a filter medium for an air filter having such a specific fiber diameter distribution, in addition to the above, the average fiber diameter of the glass fiber used as a raw material may be specified. For example, the use of ultrafine glass fibers having an average fiber diameter of 1.5 μm to 2.9 μm may be suppressed within a certain range. For example, ultrafine glass fibers having an average fiber diameter of 1.5 μm to 2.9 μm are used in the raw material of the filter medium in an amount of 5 to 15% by mass, 5 to 12% by mass, and further, less than 0 to 15% by mass, 0 to 12% by mass. %, Further preferably 0 to 5% by mass and 0% by mass. Further, for example, a certain amount of ultrafine glass fibers having an average fiber diameter larger than 2.9 μm and 6.0 μm or less may be used. For example, it is preferable that the ultrafine glass fiber having an average fiber diameter of more than 2.9 μm and 6.0 μm or less is 20 to 70% by mass, more preferably 50 to 70% by mass in the raw material of the filter medium. Further, a certain amount of chopped strand glass fiber having an average fiber diameter larger than 6.0 μm may be used. For example, it is preferable that the chopped strand glass fiber having an average fiber diameter larger than 6.0 μm is 20 to 50% by mass in the raw material of the filter medium. Further, for example, it is preferable that the chopped strand glass fiber having an average fiber diameter larger than 6.0 μm is 20 to 40% by mass in the raw material of the filter medium. Further, a certain amount of ultrafine glass fibers having an average fiber diameter of less than 1.5 μm may be used. For example, it is preferable that the ultrafine glass fiber having an average fiber diameter of less than 1.5 μm is 3 to 50% by mass and further 4 to 30% by mass in the raw material of the filter medium. Therefore, in the method for producing a filter medium for an air filter of the present invention, it is preferable to use glass fiber having the above composition as a raw material. For example, in the method for producing a filter medium for an air filter of the present invention, at least one or more chopped strand glass fibers having a specific average fiber diameter and at least one or more ultrafine glass fibers having a specific average fiber diameter are shown above. It is blended in a ratio, and after decoupling with acidic water containing sulfuric acid or the like having a pH of 2 to 4 with a pulper, paper is made and paper is made with a hand paper making device to obtain wet paper. Then, for example, a binder liquid containing a non-fibrous synthetic resin binder such as acrylic latex, a water repellent such as a fluorine-based water repellent, and a surfactant such as an acetylene-based surfactant is used for moistening. Paper may be impregnated with a binder solution to prepare a filter medium for an air filter.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to these examples.

Chopped strand glass fiber and ultrafine glass fiber are mixed in the ratio shown in Table 1, and after disintegration at a concentration of 0.5% by mass using sulfuric acid-acidic water with a pH of 3.0 in a pulper, papermaking is performed and a hand-paper machine is used. Paper was made at the site to obtain wet paper. Next, the binder liquid composition is acrylic latex (trade name: Boncoat AN-155, manufacturer: Dainippon Ink and Chemicals Co., Ltd.) and fluorine-based water repellent (trade name: NK-Guard N-07, manufacturer: Japan). Hua Chemical Co., Ltd.) and acetylene-based surfactant (trade name: Dynol 604, manufacturing company: Nissin Chemical Industry Co., Ltd.) mixed with a binder solution so as to have a solid content ratio of 100/20/2. Paper was impregnated with a binder solution and dried with a rotary dryer at 130 ° C. to prepare filter media for air filters of each Example and Comparative Example. The content of all the binders in the filter medium was 5.0% by mass except for Examples 3, 9 and 12, and was 6.0% by mass in Examples 3, 9 and 12. The blending ratio of the chopped strand glass fiber and the ultrafine glass fiber is, for example, in Example 1, 11 parts of the ultrafine glass fiber having an average fiber diameter of 0.59 μm and an average fiber diameter of 2.3 μm. It shows that 10 parts of the fiberglass, 54 parts of the fiberglass having an average fiber diameter of 4.0 μm, and 25 parts of the chopped strand glass fiber having an average fiber diameter of 6.3 μm were blended. Further, in Examples 3, 9 and 12, when the chopped strand glass fiber and the ultrafine glass fiber were dissociated with a pulper, one part of a PVA binder (particulate) was blended. Since the PVA binder melts in the process of producing the filter medium for the air filter (it is melted by heating after containing water), it is not counted as a fiber constituting the filter medium for the air filter in the calculation of the fiber diameter distribution.

(Test method)
(1) Pressure loss A ^{filter medium for an air filter having an effective area of 100 cm 2 and} a differential pressure when air was ventilated at a surface wind speed of 5.3 cm / sec were measured with a micro differential pressure gauge.

(2) PAO transmittance PAO when air containing polydisperse PAO (polyalphaolefin) particles generated by a Ruskin nozzle ^{is ventilated through a filter medium for an air filter having an effective area of 100 cm 2} at a surface wind speed of 5.3 cm / sec. The collection efficiency of the particles was measured using a laser particle counter manufactured by Rion. For the particle size of 0.3 μm monodisperse to be measured, the geometric mean of the PAO transmittances of 0.2 to 0.3 μm and 0.3 to 0.4 μm was taken as the transmittance of 0.3 μm monodisperse. The PAO collection efficiency was determined from the formula of 100- (PAO transmittance). The PAO generation concentration on the upstream side was about 1 × 10 ⁹ / ft ³ at 0.1 μm or less.

(3) PF value The PF value, which is an index of the filter performance of the filter paper, was obtained from the following equation based on the measurements of (1) and (2). The higher the PF value, the higher the collection efficiency with the same pressure loss.

(Fiber diameter distribution in filter media)
From the field emission scanning electron micrograph, the fiber diameter was measured from the cross-sectional photograph of the filter medium for the air filter cut in the CD direction using the method of image analysis software (A image-kun; Asahi Kasei Engineering Co., Ltd.) "Particle analysis". .. As for the diameter of the fiber cross section, the minor diameter was defined as the fiber diameter (Di). The number of fibers (Ni) of each fiber diameter was calculated from the fiber diameter measured by the above method in increments of 0.2 μm from 0.1 μm, and the fiber diameter frequency distribution rate was calculated by the following calculation method, and is shown in Table 2. (In the leftmost column in Table 2 , for example, the description of "0.1" means "greater than 0.1 μm and 0.3 μm or less". The same applies to "0.3" and later.) Also, larger than 1.5 μm. The cumulative frequency in the range of 2.9 μm or less (indicated as 1.5-2.9 cumulative in Table 2) was calculated and shown in Tables 1 and 2.
Fiber diameter: Di (μm)
Number of fibers: Ni (pieces)

(Average fiber diameter of glass fiber)
Image analysis software (A image-kun; Asahi Kasei Engineering Co., Ltd.) Using the method of "particle analysis" from a cross-sectional photograph of glass fibers cut in the CD direction from a field emission scanning electron micrograph, the average fiber diameter of the glass fiber as a raw material Was measured. As for the diameter of the fiber cross section, the minor diameter was defined as the fiber diameter (Dgi). The average fiber diameter of the glass fiber was calculated by the following calculation method for the fiber diameter measured by the above method. The number of fibers (Ng) to be measured was 200 or more.
Fiber diameter: Dgi (μm)
Number of fibers: Ng (pieces)

Comparing the PF values of Examples 1 to 13 and Comparative Examples 1 to 4, the PF values of Examples 1 to 13 have a cumulative frequency of 2 to 15% in the range of 2.9 μm or less, which is larger than 1.5 μm in the fiber diameter distribution. Was a high result of 13.5 or more. On the other hand, in Comparative Examples 1 to 3 in which the cumulative frequency in the same range was more than 15%, and in Comparative Example 4 in which the cumulative frequency in the same range was less than 2%, the PF value was as low as 12.2 to 13.0. ..

Claims (7)

It is a filter medium for an air filter mainly composed of glass fibers, and the glass fibers contain chopped strand glass fibers and ultrafine glass fibers having an average fiber diameter of 6.0 μm or less, and the fibers of the filter medium for the air filter. In the diameter distribution, the cumulative frequency in the range larger than 1.5 μm and 2.9 μm or less is 2 to 15%, the pressure loss is 15 to 100 Pa , and 2 to 2 to 100 parts by mass of the glass fiber. The filter medium for an air filter, which comprises 10 parts. The filter medium for an air filter according to claim 1, wherein the PF value represented by the formula of Equation 1 is 13.5 or more at a target particle size of 0.3 μm and a surface wind speed of 5.3 cm / sec.

The filter medium for an air filter according to claim 1 or 2, wherein the synthetic resin binder is an acrylic latex, an NBR latex, a vinyl acetate latex, an olefin latex, and / or a polyvinyl alcohol latex. The method for manufacturing the filter medium for an air filter according to any one of claims 1 to 3.
The raw material contains 20 to 70% by mass of ultrafine glass fibers having an average fiber diameter of more than 2.9 μm and 6.0 μm or less.
A raw material containing 20 to 50% by mass of chopped strand glass fiber having an average fiber diameter larger than 6.0 μm is blended in the raw material, papermaking is performed to obtain a wet paper, and then the wet paper is added to a binder solution containing a synthetic resin binder. The production method, which comprises impregnating the above-mentioned production method. The method for producing an air filter filter medium according to claim 4 , wherein the raw material contains 0 to 12% by mass of ultrafine glass fibers having an average fiber diameter of 1.5 μm to 2.9 μm in the raw material. The method for producing an air filter filter medium according to claim 4 or 5 , wherein the raw material contains 3 to 50% by mass of ultrafine glass fibers having an average fiber diameter of less than 1.5 μm in the raw material. Any one of claims 4 to 6 , wherein a glass fiber containing 50 to 80% by mass of ultrafine glass fiber and 20 to 50% by mass of chopped strand glass fiber with respect to the total glass fiber is used as a raw material. The method for manufacturing a filter medium for an air filter according to the above.