JP2000024428A - Porous plastic filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter excellent in heat resistance and strength without lowering elasticity modulus by using a thermoplastic elastomer having a soft phase for generating entropy elasticity and a rigid phase for preventing plastic deformation in the molecule, and also showing the property of an elastomer at the normal temperature and capable of plastic deformation at high temperature. SOLUTION: As a material for porous plastic filter, the thermoplastic elastomer having the soft phase for generating entropy elasticity and the rigid phase for preventing plastic deformation and showing the property of the elastomer at the normal temperature and capable of plastic deformation at high temperatures, and showing viscoelasticity behavior having a rubber like flat part in a broad range in a high temperature range higher than m.p., is used. Preferably, the elastomer having the rubber like flat part in the temperature range over 20 deg.C is suited. Since a polyolefin base elastomer is less in elasticity modulus change at the rubber like flat part and high in flatness, the polyolefin base one is preferable selected. The fine particles to be sintered having 10-120 μm average particle size are used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a porous plastic filter for separating and filtering fine particles contained in a fluid such as a liquid or a gas.

[0002]

2. Description of the Related Art Hitherto, a large number of porous filters have been known for separating and filtering fine particles of submicron to about 10 μm contained in fluids such as liquids and gases.

For example, there is a porous filter in which fine particles of a polyolefin-based material such as polyethylene or polypropylene are filled in a mold, heated to a temperature near the melting point of the material, and only the particle surface is sintered and formed. However, since this type of material is a crystalline resin, the viscoelastic behavior is such that the elastic modulus sharply decreases above the melting point, and almost no rubber-like flat part is observed. In the case of particles, the particles flow with a slight temperature rise, and the voids between the particles are likely to be blocked by the Laplace principle, making it difficult to control the porosity and the pore diameter. Therefore, the porous filter is inevitably subjected to sinter molding with particles having a relatively large particle size, and the pore size is inevitably increased, and its use as a filter is naturally limited.

In order to solve the above-mentioned problem that it is difficult to form a porous body having a fine pore diameter, among polyethylenes, ultra-high molecular weight polyethylene is often used as a material for forming a porous filter. Ultra-high molecular weight polyethylene exhibits a unique viscoelastic behavior and a very high molecular weight of several millions, so that a rubber-like flat portion is observed in a wide temperature range of the melting point or higher regardless of the crystalline polymer material. When sintering is performed in the temperature range of this rubber-like flat part, melting of the crystal occurs, but the material itself has a certain elastic modulus,
Sinter molding of the porous body can be easily performed without blocking of the interparticle voids. However, this porous filter has a problem of insufficient heat resistance (the measurement method will be described later), which can be continuously used only in an atmosphere of about 60 ° C.

On the other hand, in order to improve heat resistance, fine particles of an amorphous resin such as polysulfone (glass transition temperature 190 ° C.) and polyether sulfone (glass transition temperature 225 ° C.) are filled in a mold. A porous filter has been proposed which is heated to a temperature of 200 to 270 ° C. near the glass transition temperature of a material and sintered and molded. Certainly, the heat resistance is 150 ° C for polysulfone and 180 ° C for polyether sulfone.
The degree is enough for the filter. However, both of the above materials have a rubber-like flat portion that is advantageous for forming a porous body,
At most 205-225 ° C (PS) and 240-26
Since it is as narrow as 0 ° C. (PES), sinter molding using particles having a relatively large particle size is inevitable, and as a porous filter, it is possible to separate fine dust and improve collection performance. A method has been adopted in which fine polytetrafluoroethylene (hereinafter referred to as "PTFE") is applied directly to the surface of sintered base particles together with an adhesive to reduce the pore diameter. .

[0006] In the porous filter obtained by such a method, the PTFE has poor tackiness, the adhesion at the interface between the porous base material and the PTFE adhered is insufficient, and filtration and backwashing are not possible. At this time, the PTFE particles are likely to fall off the porous substrate. As a result, there has been a problem in that the wiping performance is reduced, the collecting performance on the filter surface is reduced, and the dropped PTFE particles are mixed into the collected fine particles. Further, the above-mentioned material has a high glass transition temperature, and has a property that it is brittle below the glass transition temperature, and since the operating temperature of the filter such as 150 ° C. or 180 ° C. is below the glass transition temperature, it is fragile. Become.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems in a porous filter for separating fine particles obtained by sintering and molding plastic fine particles, that is, a rapid decrease in the elastic modulus near the sintering temperature. It is another object of the present invention to provide a technology that has heat resistance enough to withstand continuous use and that is not brittle or fragile in a use environment.

[0008]

Means for Solving the Problems As a result of diligent studies, the present inventor has found that a rubber-like flat portion which is advantageous for forming a porous body is wide and flexible in use environment, and for example, polypropylene as a hard phase. And a raw material for a porous filter that can be used in an environment of about 140 ° C. depending on the selection of materials, such as a polyolefin-based thermoplastic elastomer composed of ethylene-propylene rubber as a soft phase.

The gist of the present invention is to have a soft phase exhibiting entropy elasticity in a molecule and a hard phase for preventing plastic deformation, exhibit the properties of an elastomer at normal temperature, and exhibit plastic deformation at high temperature. And a viscoelastic behavior having a rubber-like flat portion over a wide temperature range in a high temperature range not lower than the melting point.

Another aspect of the present invention, in addition to the above aspects, is that the particles to be sintered are made of a polyolefin-based thermoplastic elastomer, and that the average particle size of the particles to be sintered is Is 10 to 120 μm.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The material constituting the porous plastic filter of the present invention has a soft phase exhibiting entropy elasticity in a molecule and a hard phase for preventing plastic deformation. Shows, and can be plastically deformed at high temperature, showing a viscoelastic behavior having a rubber-like flat portion over a wide range in a high temperature range above the melting point, is not particularly limited as long as it is a thermoplastic elastomer, preferably Above 20 ° C., particularly preferably 4
Those having a rubber-like flat portion over a temperature range of 0 ° C. or more are suitable for forming a porous filter.

Here, the viscoelastic behavior is usually shown by a table in which the horizontal axis shows temperature and the vertical axis shows elastic modulus. FIG. 1 shows a polyolefin-based thermoplastic elastomer (melting point: 163 ° C.) shown in Example 1 described later. , A glass transition temperature of -10 ° C), and has an elastic modulus on the order of 10 ⁸ dyne / cm ² at room temperature, and slightly decreases to a temperature of 150 ° C. by increasing the temperature, but is on the order of 10 ⁷ dyne / cm ² . Keep. The elastic modulus drops sharply when the temperature exceeds 150 ° C,
Approximately 2 ×
It is constant at 10 ⁶ dyne / cm ² , and in this example, 2
It can be seen that it has a rubbery flat over a wide temperature range of about 90 ° C up to 50 ° C. In general, a flat portion (rubber-like region) is recognized as a viscoelastic behavior of rubber in a high-temperature region equal to or higher than the glass transition temperature, and thus is referred to as a rubber-like flat portion.

[0013] As a filter constituting material in the present invention,
Specific examples include thermoplastic elastomers such as polyolefin-based, polyurethane-based, polystyrene-based, polyester-based, polyamide-based, chlorinated polyethylene-based, polyvinyl chloride-based, and fluorine-based thermoplastics. be able to.

The polyolefin-based thermoplastic elastomer has a blended or alloyed polymer structure, and the hard phase includes polypropylene and polyethylene, and the soft phase includes ethylene-propylene rubber, acrylic rubber, butyl rubber, natural rubber, and the like. . Further, the polyurethane-based thermoplastic elastomer has a block polymer structure, and hard blocks include 4,4′-diphenylmethane diisocyanate and toluene diisocyanate, and soft blocks include polycaprolactone glycol and poly (ethylene 1,4 adipate). ) Glycol,
(Hexanediol 1,6 carbonate) glycol and the like.

[0015] The polystyrene-based thermoplastic elastomer is
The hard block includes a polystyrene and the like, and the soft block includes a polybutadiene, a polyisoprene, a hydrogenated polybutadiene and the like. Polyester-based thermoplastic elastomers
The hard block includes a polyester or the like, and the soft block includes a polyether or the like. Polyamide-based thermoplastic elastomer has a block polymer structure, as a hard block, there is a polyamide or the like, as a soft block,
Examples include polyester and polyether. The chlorinated polyethylene thermoplastic elastomer has a multi-block or random polymer structure, and the hard phase includes polyethylene and the like, and the soft phase includes chlorinated polyethylene and the like. The polyvinyl chloride-based thermoplastic elastomer has a polymer structure of a blend, and as a hard phase,
There is crystalline polyvinyl chloride and the like, and as the soft phase there is nitrile rubber and the like. Further, the fluorine-based thermoplastic elastomer has a block or graft polymer structure, as the hard phase, there is a fluororesin or the like, as the soft phase,
There is fluororubber and the like.

Among these various kinds of thermoplastic elastomer materials, a polyolefin-based material is selected from the viewpoint that a stable quality can be obtained because the elasticity change in the rubber-like flat portion is particularly small and the flatness is high. Is preferred. In particular, those containing polypropylene as the hard phase are preferred. It is considered that the fact that the melting point derived from the hard phase is relatively high at 150 ° C. or higher has a favorable effect on the improvement of the heat resistance of the filter.

In the porous plastic filter of the present invention, a fine particle having an average particle diameter of 10 to 120 μm yields good results. If the average particle size is less than 10 μm, there is a problem in powder handling such as difficulty in uniformly filling the particles into a molding die.
If it exceeds m, it is difficult to exhibit sufficient collection performance as a filter for separating fine particles. In practice, depending on the size of the fine particles in the fluid to be separated, the average particle size of the thermoplastic elastomer fine particles to be sintered is selected so as to have an appropriate pore size. When a uniform pore size is required, not only the average particle size of the fine particles but also a narrow particle size distribution is preferable. In order to obtain such fine particles, for example, classification or sieving of the particles may be performed.

The sintering of the thermoplastic elastomer fine particles is carried out in a certain range of the elastic modulus in a high temperature range higher than the melting point of the material, that is, at a temperature in the rubber-like flat portion. Preferably, the elastic modulus in the rubber-like flat portion is 10 ⁶ to 1
0 ⁸ good that is in the range of dyne / cm ^2. This is because if the elastic modulus of the material at the time of sintering is too high, fusion between the particles is not performed, and if it is too low, the particles flow and the fused particles block the pores.

The method of sintering and molding the porous plastic filter of the present invention is not particularly limited, and is usually a so-called in-mold sintering method. That is, using a molding die consisting of an outer mold having an inner surface shape such as a cylindrical shape and an inner mold having a similar outer surface shape inserted therein, the gap between the inner surface of the outer mold and the outer surface of the inner mold is used. After filling the formed cavity with the thermoplastic elastomer microparticles, the molding die is heated together with the molding die. In addition to (1) a temperature-adjustable cylinder having a molding die at the tip end A ram extrusion method using a ram type extruder with a reciprocating piston (also called a plunger), (2) an injection molding machine with a molding die at the tip and a screw inside a temperature-adjustable cylinder And (3) a dynamic molding method such as an extrusion molding method using an extruder having a screw inside a temperature-adjustable cylinder having a molding die at the tip.

From the methods such as the static molding method and the dynamic molding method, the shape of the final porous body may be appropriately selected according to requirements.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. The measurement of physical properties of the materials used in the examples was performed as follows.

[Example] Polypropylene (hard phase) 40
wt% and ethylene-propylene rubber (soft phase) 25 wt%
%, And other components (lubricant etc.) 35 wt% of a polyolefin thermoplastic elastomer pellet (melting point 16
(3 ° C., glass transition temperature −10 ° C.) was mechanically pulverized to obtain fine particles for a porous filter having an average particle diameter of 98 μm. The mold is a combination of an inner mold and an outer mold having a cylindrical surface, and the gap between the two molds is vibration-filled with the above-mentioned fine particles, and the mold filled with the particles is heated at a temperature of 160 to 200 ° C. for 30 to 60 minutes. Then, sinter molding is performed according to the so-called in-mold sintering method, and the
m, a cylindrical porous filter having an outer diameter of 56 mm and a length of 1200 mm were obtained.

[Evaluation of Filter] Heat resistance at -110 ° C. The tubular porous body obtained in the above example was placed in a dust collector, and 25 g of calcium carbonate (average particle size: 5 μm) was placed.
Feeding a 110 ° C. air containing dust, including / m ^3, filtered wind speed 1
The system was operated continuously at m / min for one week, and the differential pressure during operation, the dust concentration after passing through the porous filter, and the deformation state of the filter were observed. The results are shown in the table below. In addition, as a method of removing dust accumulated on the surface of the porous filter, a normal backwashing method was used.

[0024]

As shown in the above table, in the case of the embodiment, the differential pressure during operation was 200 mmAq or less and the dust concentration was 0.1 m
g / m ³ or less, a good result was obtained, and no trouble such as breakage of the porous filter occurred during continuous operation.

Comparative Example A porous filter was obtained in the same manner as in the above example, except that ultrahigh molecular weight polyethylene (melting point 140 ° C.) was used instead of the polyolefin-based thermoplastic elastomer. When the heat resistance of the filter was evaluated in the same manner as in the example, after operating for one week, a large deformation occurred, and the filter was not practical.

[0027]

According to the present invention, a rubber-like flat portion which is advantageous for molding can be formed over a wide temperature range and, depending on the material selection, can be reduced to one.
Since a thermoplastic elastomer material that can be used continuously in an environment of about 40 ° C. is used, particles to be sintered are 10
Even if the particles are fine particles of up to 120 μm, it is possible to easily form a porous body having a desired pore diameter and porosity by sintering. It is possible to provide a porous plastic filter having high performance of collecting fine particles.

[Brief description of the drawings]

FIG. 1 is a chart showing the viscoelastic behavior of a material.

Claims (4)

[Claims] 1. It has a soft phase exhibiting entropy elasticity in a molecule and a hard phase for preventing plastic deformation, exhibits the properties of an elastomer at room temperature, enables plastic deformation at high temperature, and enables high temperature above melting point. A porous plastic filter for separating fine particles, comprising sintering and molding particles of a thermoplastic elastomer exhibiting viscoelastic behavior having a rubber-like flat portion over a wide temperature range in a region. 2. The porous plastic filter for separating fine particles according to claim 1, wherein the particles to be sintered are made of a thermoplastic elastomer having a rubber-like flat portion over a temperature range exceeding 20 ° C. . 3. The porous plastic filter for separating fine particles according to claim 1, wherein the particles to be sintered are made of a polyolefin-based thermoplastic elastomer. 4. The sintered particles have an average particle size of 10 to 120.
The porous plastic filter for separating fine particles according to claim 1, wherein the thickness of the porous plastic filter is μm.