JP5148888B2 - Filter material for air filter and method for producing the same - Google Patents

Description

  The present invention relates to a filter medium for an air filter used for semiconductors, liquid crystals, bio / food industry-related clean rooms, clean benches, etc., air conditioning air filters for buildings, and air cleaners.

  Conventionally, in order to efficiently collect submicron or micron particles in the air, an air filter collecting technique is used. Air filters are roughly classified into coarse dust filters, medium performance filters, HEPA filters, ULPA filters, and the like, depending on the target particle size and dust removal efficiency. Many of these air filters use fiber layer air filter media such as non-woven fabric, woven fabric, and mat. Especially, medium performance filters, HEPA filters, and ULPA filters have non-woven glass fiber air filter media. Widely used. This is due to the high characteristics of pressure loss and collection efficiency, which are the basic performances of air filters, in addition to the non-combustibility of glass fibers. Generally, this glass fiber is formed into a sheet by a wet papermaking method and formed as a filter medium.

  The manufacturing method by the wet papermaking method is, for example, that the glass fiber constituting the filter medium is dispersed in water using a dispersing machine such as a pulper, and the slurry is formed, dehydrated and dried with a paper machine to obtain a filter medium sheet. Is the method.

  Here, since the glass fiber has almost no self-adhesive property, in most cases, a binder is added to impart practically necessary strength to the filter medium. As the binder, synthetic resins such as acrylic resins, urethane resins, and olefin resins are widely used. Generally, these binder resins in the form of an aqueous solution or an aqueous emulsion are applied to the filter medium by dipping or spraying. At the same time, a water repellent may be applied to the filter medium in order to provide water repellency that is practically required. This water repellent is also generally applied to the filter medium by dipping or spraying, like the binder resin.

  Currently, low pressure loss and high collection efficiency are strongly demanded as basic physical properties of air filter media. As a measure to achieve this low pressure loss and high efficiency, when applying a binder, various chemicals are added to the binder liquid to reduce the surface tension of the binder liquid and suppress the formation of a web-like film. Has been proposed.

  For example, Patent Document 1 proposes a method using a silicon resin for this purpose. However, when low molecular siloxanes such as cyclic siloxane contained in the silicon resin are present in the semiconductor manufacturing process, the silicon wafer and the semiconductor manufacturing process are contaminated, resulting in a decrease in product yield.

Previously, the present inventors have proposed a method using a fluorine-based surfactant in Patent Document 2 and a method using an acetylene-based surfactant in Patent Document 3. However, the use of such a surfactant has a problem of reducing the water repellency and strength of the filter medium.
Japanese Unexamined Patent Publication No. 7-185235 JP-A-10-156116 JP 2003-71219 A

  It is an object of the present invention to satisfy a low pressure drop and a high collection efficiency, and to further contaminate a semiconductor manufacturing process such as siloxane and phthalate ester, or to influence a health. It is intended to provide a filter medium for air filters that does not contain and has high strength and water repellency.

The present inventors have found that the above problem can be solved by attaching partially saponified polyvinyl alcohol having a saponification degree of up to 90% to the glass fiber surface, and have completed the present invention. That is, the filter medium for an air filter according to the present invention is made by adhering a liquid containing partially saponified polyvinyl alcohol having a saponification degree of up to 90% to a wet paper mainly composed of glass fiber and in a wet state after wet papermaking. The paper is dried to adhere the partially saponified polyvinyl alcohol to the surface of the glass fiber .

By adhering partially saponified polyvinyl alcohol having a saponification degree of up to 90% to the surface of the glass fiber constituting the filter medium, both low pressure loss and high collection efficiency are satisfied, and further, the semiconductor manufacturing process is contaminated. The effect is achieved that an air filter medium having high strength and water repellency can be provided without containing a substance that may affect health.

  The present invention is described in detail below.

  Conventional methods of low pressure loss and high collection efficiency reduce the surface tension of the binder liquid, reduce the pressure loss by suppressing the formation of a web-like binder film, and further, fibers involved in particle collection This is based on the idea that the collection efficiency can be increased without being coated with a binder film, and as a result, the PF value, which is an index value of the filter performance expressed by the following equation, can be increased.

  The higher the PF value obtained by this equation, the lower the pressure loss and the higher the collection efficiency.

  Unlike the conventional method, the method of increasing the pressure loss and the high collection efficiency according to the present invention makes the glass fiber surface in the filter medium more uniform by appropriately hydrophobizing the surface of the glass fiber. Based on the idea that the fibers involved in particle collection are efficiently arranged and the collection efficiency can be increased.

  The glass fiber filter medium is in the form of wet paper containing a large amount of moisture during the period from when the binder liquid is applied to the glass fiber filter medium formed into a sheet by the wet papermaking method until drying. At this time, if the surface of the glass fiber is appropriately hydrophobized, the fibers repel each other in the wet paper to prevent agglomeration, and the dispersibility is increased, and the glass fiber array in the filter medium after drying is more uniform. Can be. The substance that moderately hydrophobizes the glass fiber surface needs to have not only hydrophobicity but also moderate hydrophilicity in order to adhere to the hydrophilic glass fiber surface.

The present inventors have found that partially saponified polyvinyl alcohol having a saponification degree of up to 90% is suitable as such a substance. When partially saponified polyvinyl alcohol is attached to a wet glass fiber filter medium after wet papermaking, the fibers are moderately hydrophobized, the dispersibility of the fibers is improved, and the arrangement of the glass fibers in the filter medium becomes uniform. As a result, a filter medium for an air filter having a low pressure loss and a high collection efficiency can be obtained.

  Polyvinyl alcohol is produced from polyvinyl acetate as a raw material by saponifying a carboxyl group in polyvinyl acetate, that is, converting it to a hydroxyl group by alkaline hydrolysis. Here, the ratio of the carboxyl group converted into a hydroxyl group is particularly called the degree of saponification. The partially saponified polyvinyl alcohol used in the present invention is a polyvinyl alcohol in which a part of the carboxyl groups is left unsaponified, and compared with a completely saponified polyvinyl alcohol in which almost all (about 98% or more) carboxyl groups are saponified to hydroxyl groups. High hydrophobicity. Moreover, the partially saponified polyvinyl alcohol can adjust the hydrophobicity of the molecule by changing the saponification degree. The lower the saponification degree, the higher the hydrophobicity.

Here, the degree of saponification (%) = {m / (m + n)} × 100
When partially saponified polyvinyl alcohol is adhered to a glass fiber filter medium in a wet state, as the degree of saponification decreases, the glass fiber arrangement in the filter medium becomes uniform due to the hydrophobic effect of the glass fiber surface described above. PF value increases. When fully saponified polyvinyl alcohol is used, the hydrophilicity of the molecule is too strong, so that a sufficient hydrophobizing effect cannot be obtained, so the increase in the PF value is very small.

  The degree of saponification of the partially saponified polyvinyl alcohol used in the present invention is in the range of up to 90%, preferably 20% to 90%, particularly preferably 30% to 90%, particularly preferably from the viewpoint of harmony of hydrophobicity and affinity. Is selected from 40% to 90%. If the degree of saponification is too low, the solubility in water will be low and it will not be possible to adhere well to the glass fiber surface. On the other hand, if the degree of saponification is too high, as described above, a sufficient hydrophobizing effect cannot be obtained, so that the increase in the PF value is small. For these reasons, saponification degrees in the range of 40% to 80%, 40% to 70%, in particular 40 to 60%, are particularly advantageous.

  The amount of partially saponified polyvinyl alcohol attached to the glass fiber is effective if the partially saponified polyvinyl alcohol sufficiently covers the surface of the glass fiber, and is not particularly limited in the present invention. % Or more, particularly 0.1% by mass or more is preferable.

  The glass fiber used as the main fiber in the present invention is freely selected from ultrafine glass fibers and / or chopped glass fibers having various fiber diameters and fiber lengths according to the required filtration performance and other physical properties. I can do it. In particular, the ultrafine glass fiber is a woolen glass fiber produced by a flame drawing method or a rotary method, and is an essential component for maintaining the pressure loss of the filter medium at a predetermined value and achieving an appropriate collection efficiency. As the fiber diameter becomes smaller, the collection efficiency becomes higher. Therefore, in order to obtain a high-performance filter medium, it is necessary to blend ultrafine glass fibers having a fine average fiber diameter. However, since the pressure loss may increase excessively when the fiber diameter is reduced, an appropriate fiber diameter should be selected within this range. In addition, you may blend and mix the thing of several types of fiber diameters. Moreover, low boron glass fiber, silica glass fiber, etc. can also be used for the purpose of preventing boron contamination of a silicon wafer in semiconductor process applications. Furthermore, natural fibers, organic synthetic fibers, and the like may be blended in the glass fiber as a secondary material within a range that does not affect the effects of the present invention.

  In the present invention, in order to give the filter medium strength sufficient to withstand secondary processing such as pleating, it is preferable to apply a binder resin on the glass fiber substrate of the filter medium for air filter. Examples of the binder resin to be used include acrylic resins, vinyl acetate resins, epoxy resins, and urethane resins. However, the binder resins are not limited to these as long as they do not inhibit the purpose. The application rate of the binder resin to the filter medium base material is desirably 1 to 10% by mass, and if the application rate is less than 1% by mass, the filter medium strength that can withstand filter media processing and actual use does not come out. Since clogging occurs, the pressure loss increases and the filtration performance decreases. Moreover, when there is much binder amount which is a combustible material, the flame retardance of a filter medium will be deteriorated.

  Examples of the production method of the present invention include a method by which the air filter medium of the present invention can be obtained by the production method described below. That is, the glass fibers constituting the filter medium are dispersed in water using a dispersing machine such as a pulper, and the resulting slurry is wet-made by a paper machine to obtain a wet paper. In order to improve the dispersibility in the raw fiber dispersion step, a method of adjusting the pH within a range of 2 to 4 with sulfuric acid acid is used, but a neutral surfactant such as a dispersant may be used. Next, the binder is attached to the aforementioned wet paper, and this is dried with a dryer. Examples of the method for attaching the binder include a method in which the wet paper is once dried and the binder is applied again and dried, or a method in which the binder is mixed with the raw material slurry in advance. The method for applying the wet paper is not particularly limited. However, the wet paper or dry paper is immersed in the adhering liquid, the wet paper or dry paper is sprayed on the wet paper, and the wet liquid is attached to the roll. Examples thereof include a method of transferring to paper or dry paper. In order to impart water repellency, flame retardancy, etc., it is also possible to add a water repellent, a flame retardant, etc. to the binder liquid within the scope of the object of the present invention. About these provision methods, the optimal method with which the effect of this invention is acquired is selected.

  As a method of adhering partially saponified polyvinyl alcohol to the glass fiber filter medium, there is a method of mixing the filter medium with raw material slurry before forming the sheet with wet papermaking, but immersing the partially saponified polyvinyl alcohol in the wet paper after forming the wet papermaking sheet. A method of attaching by spraying is more preferable from the viewpoint of adhesion efficiency. However, partially saponified polyvinyl alcohol needs to be attached to the wet paper in a wet state before the wet papermaking sheet is dried. This is because once the glass fiber filter medium is dried, the effect of changing the fiber arrangement is weakened. In particular, in order to improve the dispersibility of the glass fiber, when paper is made under acidic conditions, the glass is dried after drying. Since the fibers are fixed by acid adhesion, it is difficult to change the fiber arrangement.

  As a form when attaching partially saponified polyvinyl alcohol, it may be attached in either a mixed solution of a binder resin and a water repellent or an aqueous solution of a partially saponified polyvinyl alcohol alone, When used in admixture, care must be taken so that the adhesion of partially saponified polyvinyl alcohol to the glass fibers is not hindered by interactions with other components.

  As a wet paper drying method, a hot air dryer, a roll dryer or the like is used, and a drying temperature of 120 ° C. or higher, preferably 140 ° C. or higher is desirable.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

60% by mass of ultrafine glass fiber with an average fiber diameter of 0.65μm, 35% by mass of ultrafine glass fiber with an average fiber diameter of 2.70μm, and 5% by mass of chopped glass fiber with an average fiber diameter of 6μm, at a concentration of 0.5% and sulfuric acid pH 2.5 The mixer disintegrated. Next, a wet paper was obtained by paper making using a hand-drawing apparatus. Next, acrylic latex (trade name: Boncoat AN-155, manufacturer: Dainippon Ink & Chemicals, Inc.), fluorine-based water repellent (product name: Lightguard T-10, manufacturer: Kyoeisha Chemical Co., Ltd.) And a partially saponified polyvinyl alcohol with a saponification degree of 48% (trade name: Gohsephimer LW-200, manufacturer: Nippon Synthetic Chemical Industry Co., Ltd.) so that the solids mass ratio is 100/5/5 and mixed. The obtained binder liquid was applied to wet paper, and then dried with a dryer at 130 ° C. to obtain a HEPA filter medium having a basis weight of 70 g / m ² and a binder composition solid content of 5.5%.

As binder liquid, acrylic latex (trade name: Boncoat AN-155, manufacturer: Dainippon Ink & Chemicals, Inc.), fluorine-based water repellent (trade name: Lightguard T-10, manufacturer: Kyoeisha Chemical Co., Ltd.) ) And partially saponified polyvinyl alcohol having a saponification degree of 55% (trade name: Goosefimmer LW-300, manufacturer: Nippon Synthetic Chemical Industry Co., Ltd.) A HEPA filter medium having a basis weight of 70 g / m ² and a binder composition solid content adhesion amount of 5.5% was obtained in the same manner as in Example 1 except that the mixed binder liquid was used.

As binder liquid, acrylic latex (trade name: Boncoat AN-155, manufacturer: Dainippon Ink & Chemicals, Inc.), fluorine-based water repellent (trade name: Lightguard T-10, manufacturer: Kyoeisha Chemical Co., Ltd.) ) And partially saponified polyvinyl alcohol (trade name: PVA-217, manufacturer: Kuraray Co., Ltd.) with a saponification degree of 88% were blended so that the solids mass ratio was 100/5/5, and a mixed binder solution was used. A HEPA filter medium having a basis weight of 70 g / m ² and a binder composition solid content adhesion amount of 5.6% was obtained in the same manner as in Example 1.

Comparative Example 1

As binder liquid, acrylic latex (trade name: Boncoat AN-155, manufacturer: Dainippon Ink & Chemicals, Inc.) and fluorine-based water repellent (product name: Lightguard T-10, manufacturer: Kyoeisha Chemical Co., Ltd.) ) Was blended so that the mass ratio of the solid content was 100/5, and the basis weight was 70 g / m ² and the binder composition solid content adhesion amount was 5.6%, except that the mixed binder liquid was used. A HEPA filter medium was obtained.

Comparative Example 2

As binder liquid, acrylic latex (trade name: Boncoat AN-155, manufacturer: Dainippon Ink & Chemicals, Inc.), fluorine-based water repellent (trade name: Lightguard T-10, manufacturer: Kyoeisha Chemical Co., Ltd.) ) And fully saponified polyvinyl alcohol (trade name: PVA-117, manufacturer: Kuraray Co., Ltd.) with a saponification degree of 99% were mixed so that the solids mass ratio was 100/5/5, and a mixed binder solution was used. A HEPA filter medium having a basis weight of 70 g / m ² and a binder composition solid content adhesion amount of 5.5% was obtained in the same manner as in Example 1.

Comparative Example 3

As binder liquid, acrylic latex (trade name: Boncoat AN-155, manufacturer: Dainippon Ink & Chemicals, Inc.), fluorine-based water repellent (trade name: Lightguard T-10, manufacturer: Kyoeisha Chemical Co., Ltd.) ) And a fluorosurfactant (trade name: Megafac F-142D, manufacturer: Dainippon Ink & Chemicals, Inc.) are mixed so that the solids mass ratio is 100/5/5 and mixed. A HEPA filter medium having a basis weight of 70 g / m ² and a binder composition solid content adhesion amount of 5.5% was obtained in the same manner as in Example 1 except that was used.

  Each filter medium obtained in Examples and Comparative Examples was analyzed by the following method.

  Water repellency was measured according to MIL-STD-282, “Filter Units, Protective Clothing, Gas-Mask Components and Related Products: Performance-Test Methods,” 28 May 1956.

  The tensile strength was measured in accordance with JIS P 8113: 1998 “Paper and paperboard—Test method for tensile properties”.

  The delamination strength was measured according to J.TAPPI paper pulp test method No. 18-1.

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

DOP collection efficiency is the DOP collection efficiency when air containing polydisperse DOP particles generated by Ruskin nozzle is passed through a filter medium with an effective area of 100 cm ^{2 at} a surface wind speed of 5.3 cm / sec. And measured. The target particle size was 0.3 to 0.4 μm.

  The PF value was calculated from the measured values of pressure loss and DOP collection efficiency using the above formula. The target particle size was 0.3 to 0.4 μm.

  The evaluation results of Examples 1 to 3 and Comparative Examples 1 to 3 are as shown in Table 1.

  When comparing Examples 1 to 3 in which partially saponified polyvinyl alcohol was added to the binder liquid and Comparative Example 1 in which partially saponified polyvinyl alcohol was not added, partially saponified polyvinyl alcohol was added to the binder liquid and adhered to the filter medium. As a result, the PF value was improved to 15.10 or more without decreasing the water repellency, tensile strength and delamination strength. In particular, as the degree of saponification of partially saponified polyvinyl alcohol decreases, the effect of improving the PF value increases, and when it is 60% or less, the PF value is higher than 15.5. That is, the effect intended by the present invention was obtained, and a filter medium for an air filter that satisfies both low pressure loss and high collection efficiency and has high strength and water repellency was obtained.

  In Comparative Example 2 in which fully saponified polyvinyl alcohol was added to the binder solution, the tensile strength and delamination strength were improved, but as in Comparative Example 1 without addition, the PF value was hardly improved and the pressure was not increased. The loss is as high as 304 Pa, the effects of the present invention cannot be obtained, and there is no practicality.

  In Comparative Example 3 in which a fluorosurfactant was added to the binder liquid, the PF value was 16.07 and its improvement was seen, but a large decrease in water repellency, tensile strength, and delamination strength was observed. The effect is not obtained and is not practical.

Claims (6)

In a filter medium for an air filter using glass fiber as a main fiber , a liquid containing partially saponified polyvinyl alcohol having a saponification degree of up to 90% is attached to a wet paper in a wet state after wet papermaking , and the wet paper is dried. A filter medium for an air filter , wherein the partially saponified polyvinyl alcohol is adhered to the surface of the glass fiber . The filter medium for an air filter according to claim 1, wherein the degree of saponification of the partially saponified polyvinyl alcohol is 40 to 90%. The air filter medium according to claim 1 or 2, wherein the degree of saponification of partially saponified polyvinyl alcohol is 40 to 60%. In the filter medium for an air filter glass fiber produced was mainly fiber by a wet papermaking method, a liquid containing a degree of saponification of partially saponified polyvinyl alcohol of up to 90% on the glass fiber surface of the wet paper in a wet state after the wet paper making A method for producing a filter medium for an air filter, wherein the air filter is dried after adhering. The method for producing a filter medium for an air filter according to claim 4, wherein partially saponified polyvinyl alcohol having a saponification degree of 40 to 90% is used. The method for producing a filter medium for an air filter according to claim 4 or 5, wherein partially saponified polyvinyl alcohol having a saponification degree of 40 to 60% is used.