JP3533800B2 - Air filter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air filter. More specifically, the present invention relates to an air filter comprising a porous film of para-oriented aromatic polyamide (hereinafter, may be referred to as para-aramid). 2. Description of the Related Art Air filters for air conditioning, which are used particularly in electronics-related factories, pharmaceutical factories and medical institutions that require a high degree of cleanliness, are used to remove fine particles and microorganisms of 0.1 μm or less. is necessary. As a raw material of a conventional air filter used for such a purpose, a nonwoven fabric made of ultrafine glass fiber is mainly used. However, in the case of a glass nonwoven fabric air filter, the organic substance used as a binder is
In electronics-related factories, the problem is that air cleanliness deteriorates. For this reason, materials replacing glass nonwoven fabrics have been sought, but no suitable materials have been found so far. On the other hand, with respect to para-aramid, a para-aramid film has been developed for magnetic tapes, taking advantage of the features of high heat resistance, high rigidity, and high strength. Specifically, Japanese Patent Publication No. 3-79175, Japanese Patent Application Laid-Open No. 3-237135, and the like disclose a para-aramid film for a magnetic tape and a method for producing the same. However, a porous film of para-aramid is not known. Japanese Patent Application Laid-Open No. 6-41298 discloses that
In a polar amide solvent, the intrinsic viscosity is 1.0 to 2.5 dl.
/ G of para-oriented aromatic polyamide of 4 to 10% by weight
And a low polymerization degree para-aramid dope containing 2 to 10% by weight of an alkali metal or alkaline earth metal chloride. It is described that the para-aramid dope having a low degree of polymerization has optical anisotropy and is a raw material for industrially useful fibers and pulp. SUMMARY OF THE INVENTION An object of the present invention is to provide an air filter used for air conditioning or the like, and particularly useful for air conditioning in an electronics-related factory, a pharmaceutical factory, a medical institution, or the like where cleanliness is required. An object of the present invention is to provide an air filter which is suitable for removing fine particles and microorganisms of 0.1 μm or less and has excellent air permeability. Specifically, an object of the present invention is to provide an air filter made of a para-aramid porous film that satisfies the above-mentioned requirements while utilizing the properties of para-aramid such as high heat resistance, high rigidity, and high strength. According to the present invention, a porosity of 70% is used.
% Or more, and 90% or more of the holes on one side have a pore size of 0.1 to 5 μm.
m, 90% or more of the holes on the opposite surface have a hole diameter of 0.5 to 2
The present invention relates to an air filter comprising a porous film of para-oriented aromatic polyamide having a thickness of 0 μm. The air filter of the present invention has the following (a) to
It can be manufactured by the step (c). (A) 1 to 10% by weight of a para-oriented aromatic polyamide having an intrinsic viscosity of 1.0 to 2.5 dl / g in a polar amide-based solvent or a polar urea-based solvent and a chloride of an alkali metal or an alkaline earth metal Forming a solution containing 1 to 10% by weight of (B) a step of immersing the film in a coagulation solution of ketones containing 0 to 70% by weight of a polar amide solvent or a polar urea solvent to precipitate para-oriented aromatic polyamide into a film. (C) a step of removing a solvent and a chloride of an alkali metal or an alkaline earth metal from the film, followed by drying. Hereinafter, the present invention will be described in detail. BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a para-oriented aromatic polyamide (para-aramid) is obtained by condensation polymerization of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide. Para-position of the aromatic ring or an orientation similar thereto (for example, an orientation extending coaxially or parallel to the opposite direction such as 4,4'-biphenylene, 1,5-naphthalene, 2,6-naphthalene, etc.)
Is essentially composed of repeating units linked by Specifically, poly (paraphenylene terephthalamide), poly (parabenzamide, poly (4,
4'-benzanilide terephthalamide), poly (paraphenylene-4,4'-biphenylenedicarboxylic amide), poly (paraphenylene-2,6-naphthalenedicarboxylic amide), poly (2-chloro-paraphenylene terephthalamide) ), Para-aramid having a para-oriented type or a structure similar to the para-oriented type, such as paraphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide copolymer. The para-aramid solution containing para-aramid and an alkali metal or alkaline earth metal chloride used in the present invention can be produced as follows. That is, the chloride of an alkali metal or an alkaline earth metal is
In a polar amide solvent or a polar urea solvent dissolved in 10 to 10% by weight, para-oriented aromatic dicarboxylic acid halide is 0.94 to 1.00 mol of para-oriented aromatic diamine.
0.99 mol is added, and the mixture is subjected to condensation polymerization at a temperature of -20 ° C to 50 ° C to produce a para-aramid solution having a para-aramid concentration of 1 to 10% by weight. The range of the amount of the alkali metal or alkaline earth metal chloride in the para-aramid solution is determined with respect to the amount of para-aramid (more precisely, the amide group in para-aramid) as described later. In general, when the alkali metal or alkaline earth metal chloride is less than 1% by weight, the solubility of para-aramid is insufficient, and
When the concentration exceeds the above, chlorides of alkali metals or alkaline earth metals are not dissolved in polar amide solvents or polar urea solvents. When the concentration of para-aramid is less than 1% by weight, productivity is remarkably reduced and industrially disadvantageous. If the amount of para-aramid exceeds 10% by weight, para-aramid precipitates and a stable para-aramid solution cannot be obtained. The para-aramid used in the present invention is expressed in terms of intrinsic viscosity (in the present invention, the intrinsic viscosity is defined below), and is 1.0 to 2.5 dl / g, preferably 1.5 to 2 dl / g. Refers to para-aramid exhibiting a value of 0.3 dl / g. If the intrinsic viscosity is less than 1.0 dl / g, sufficient film strength cannot be obtained. If the intrinsic viscosity exceeds 2.5 dl / g, it becomes difficult to obtain a stable para-aramid solution, and para-aramid precipitates, making it difficult to form a film. Examples of the para-oriented aromatic diamine used in the condensation polymerization of para-aramid in the present invention include para-phenylenediamine, 4,4'-diaminobiphenyl,
2-methyl-paraphenylenediamine, 2-chloro-paraphenylenediamine, 2,6-dichloro-paraphenylenediamine, 2,6,6-naphthalenediamine, 1,
Examples thereof include 5-naphthalenediamine, 4,4'-diaminobenzanilide, and 3,4'-diaminodiphenyl ether. The para-oriented aromatic diamine may be used alone or in combination of two or more for the condensation polymerization. Examples of the para-oriented aromatic dicarboxylic acid halide used in the condensation polymerization of para-aramid in the present invention include terephthalic acid chloride, biphenyl-4,
4'-dicarboxylic acid chloride, 2-chloroterephthalic acid chloride, 2,5-dichloroterephthalic acid chloride, 2-methylterephthalic acid chloride, 2,6-naphthalenedicarboxylic acid chloride, 1,5-naphthalenedicarboxylic acid chloride and the like are exemplified. be able to. The para-oriented aromatic diamine may be used alone or in combination of two or more for the condensation polymerization. In the present invention, the condensation polymerization of para-aramid is carried out in a polar amide solvent or a polar urea solvent. As these solvents, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-
Examples include, but are not limited to, 2-pyrrolidone or tetramethylurea. In the present invention, an alkali metal or alkaline earth metal chloride is suitably used for the purpose of improving the solubility of para-aramid in a solvent. Specific examples include, but are not limited to, lithium chloride or calcium chloride. The amount of the alkali metal or alkaline earth metal chloride to be added to the polymerization system is preferably in the range of 0.5 to 6.0 mol per 1.0 mol of the amide group formed by the condensation polymerization. A range of 7 to 4.0 mol is more preferred. When the amount of the chloride is less than 0.5 mol, the solubility of the generated para-aramid becomes insufficient. When the amount exceeds 6.0 mol, the amount of chloride substantially dissolved in the solvent is not preferable. As the coagulating solution used in the step (b), a ketone solvent which does not dissolve para-aramid or a ketone solution containing a polar amide solvent or a polar urea solvent in a proportion of 70% by weight or less is used. If the concentration of the polar amide-based solvent or polar urea-based solvent exceeds 70% by weight, it takes a long time for coagulation, and it is difficult to maintain the form of the film until para-aramid precipitates, which is not preferable. As a solvent for ketones, acetone and methyl ethyl ketone are preferable. By using such a coagulating liquid, the porosity is 70% or more, 90% or more of the pores on one side have a pore size of 0.1 to 5 μm, and 90% or more of the pores on the opposite side have a pore size of 90% or more. Is 0.5 to 20 μm, and the para-aramid porous film suitable for the purpose of the present invention, in which the pore diameter or the shape of the pores differs in the thickness direction, can be produced. In the air filter of the present invention, a para-aramid solution is formed into a film and then immersed in a coagulation solution which is a ketone solution containing 70% by weight or less of a polar amide-based solvent or a polar urea-based solvent. Is produced by producing a para-aramid porous film by a simple method of precipitating and coagulating. The film comprising coagulated para-aramid is washed with water, alcohol, an aqueous solution or an alcohol-based solution to remove the solvent and the chloride of the alkali metal or alkaline earth metal, and then dried. A porous film suitable for the purpose of (1) can be obtained. The drying method is not particularly limited, and various known methods can be used. The para-aramid porous film produced by the above method is excellent in heat resistance, rigidity and strength, has a porosity of 70% or more, and has a pore size of 0.1% or more on one side.
５5 μm, and 90% or more of the holes on the opposite surface have a hole diameter of 0.
5 to 20 μm. That is, the porous film of the para-oriented aromatic polyamide of the present invention has a feature that the pore diameter is relatively small on one side of the porous film and large on the opposite side, that is, the pore diameter has a structure different in the thickness direction of the film. . Such a porous film is an air filter for air conditioning, and is particularly suitable as an air filter for a clean room such as an electronics-related factory, a pharmaceutical factory, and a medical institution where cleanliness is required. The air filter of the present invention can be constituted by the para-aramid porous film produced by the above method alone or, if necessary, overlaid on a support. The support is not particularly limited and can be appropriately selected depending on the mode in which the air filter is used. The present invention will be described below in detail with reference to examples. Test / evaluation methods or criteria in Examples and Comparative Examples are as follows. (1) Intrinsic Viscosity In the present invention, the intrinsic viscosity is defined by the following measuring method. For a solution in which 0.5 g of the para-aramid polymer was dissolved in 100 ml of 96-98% sulfuric acid and for a 96-98% sulfuric acid, the flow time was measured at 30 ° C. using a capillary viscometer, and the following equation was obtained from the ratio of the flow times obtained. Was used to determine the intrinsic viscosity. Intrinsic viscosity = ln (T / T ₀ ) / C [unit: dl /
g] Here, T and T ₀ are the flow times of the para-aramid sulfate solution and sulfuric acid, respectively, and C indicates the para-aramid concentration (dl / g) in the para-aramid sulfate solution. (2) The porosity film is cut into a square shape, and the length of one side (Lc
m), weight (Wg), and thickness (Dcm) were measured. Assuming that the true specific gravity of para-aramid was 1.45 g / cm ³ , the porosity (% by volume) was determined from the following equation. Porosity = 100-100 × (W / 1.45) / (L ² ×
D) Example 1 1. Polymerization of poly (paraphenyleneterephthalamide) Using a 5 l separable flask having a stirring blade, a thermometer, a nitrogen inlet tube and a powder addition port, poly (paraphenyleneterephthalamide). ) (Hereinafter sometimes referred to as PPTA). The flask was sufficiently dried, 4200 g of N-methyl-2-pyrrolidone (hereinafter, sometimes referred to as NMP) was charged, 272.7 g of calcium chloride dried at 200 ° C. for 2 hours was added, and the temperature was raised to 100 ° C. After the calcium chloride is completely dissolved, return to room temperature,
132.9 g of paraphenylenediamine (hereinafter sometimes referred to as PPD) was added and completely dissolved. While keeping this solution at 20 ° C. ± 2 ° C., 243.3 g of terephthalic acid chloride (hereinafter sometimes referred to as TPC) was added to 10
Add in portions about every 5 minutes. The solution is then cooled to 20 ° C ±
The mixture was aged for 1 hour while maintaining at 2 ° C., and stirred for 30 minutes under reduced pressure to remove bubbles. The obtained polymerization liquid (polymer dope) showed optical anisotropy. A part of the polymerization solution was sampled, reprecipitated with water, taken out as a polymer, and the resulting PP
When the intrinsic viscosity of TA was measured, it was 1.98 dl / g. 2. Production of Porous Film (Air Filter) The polymerization solution obtained by the polymerization in the above item 1 was used as it was as a PPTA solution for producing a porous film. A PPTA solution was formed into a film on a glass plate using a bar coater (film thickness: 0.60 mm) manufactured by Tester Sangyo KK and immersed in an acetone solution containing 1% by weight of NMP. After 10 minutes, the film was peeled off from the glass plate. The deposited film was taken out of the acetone solution and immersed in ion exchanged water for about 15 hours. Next, the film was taken out of the water, free water was wiped off, and then sandwiched between filter papers, and further sandwiched between glass cloths. With the film sandwiched between filter paper and glass cloth, place it on an aluminum plate and cover it with a nylon film,
The nylon film and the aluminum plate were sealed with gum, and a conduit for decompression was provided. Put the whole in a heat oven 12
The film was dried under reduced pressure at 0 ° C. The obtained film has a thickness of 264 μm,
The porosity was 86.8%. 1 and 2 show the results of observation with a scanning electron microscope. The obtained porous film is a nonwoven fabric made of fibrils having a diameter of 0.2 to 1 μm, and 90% or more of the pores observed on the glass plate side of the porous film have a pore diameter of about 1%. ~ 1
It was 0 μm. Also, the holes observed on the opposite side are:
90% or more thereof was about 0.5 μm. That is, the porous film of the para-oriented aromatic polyamide of the present invention,
The porous film is characterized in that it has a structure in which the pore size is relatively small on one side and large on the opposite side, that is, the porous film has a structure different in the thickness direction of the film. 3. Measurement of Air Permeability In order to use the obtained para-aramid porous film as an air filter, a Porous Material Co., Ltd. palm-porometer (porous material automatic pore measurement system)
Was measured for air permeability. The air flow rate of the porous film was 40 cc / sec at a gauge pressure of 1 kg / cm ² and ² kg / cm ^2.
In cm ² 90cc / sec., at 3kg / cm ² 160cc /
240 cc / sec at 4 kg / cm ² for 5 kg / cm ²
At 320 cc / sec and 6 kg / cm ² at 410 cc / sec, and had an air permeability usable as an air filter. Further, the air filter of the para-aramid porous film had a strength such that it was not damaged even when pressurized to 6 kg / cm ^{2 as} described above. The air filter comprising the porous film of the para-oriented aromatic polyamide of the present invention is excellent in heat resistance, rigidity and strength, in addition to the properties of the para-oriented aromatic polyamide, and has a thickness of 0.1 μm or less. It has a pore size suitable for removing fine particles and microorganisms and has high air permeability, so it is used for air filters for air conditioning, especially in clean rooms such as electronics-related factories, pharmaceutical factories, and medical institutions where cleanliness is required. Particularly useful as an air filter.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the structure of the surface on the glass plate side of the air filter obtained in Example 1. A photo (magnification 1000)
Magnification scanning electron micrograph). FIG. 2 shows the structure of the surface on the coagulating liquid side of the air filter obtained in Example 1. A photograph instead of a drawing (a scanning electron microscope photograph at a magnification of 5,000).

──────────────────────────────────────────────────続 き Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 53/22 B01D 61/00-71/82 B01D 39/00-41/04

Claims (1)

(57) [Claims 1] A porosity of 70% or more and 90% of holes on one side
The above is a hole diameter of 0.1-5 μm, and 90% of the hole on the opposite surface.
% Or more of which has a pore diameter of 0.5 to 20 μm, wherein the air filter comprises a porous film of para-oriented aromatic polyamide.