JPH10151330A - Porous double-layer plastic filter and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the filter grain from falling off and to provide high fine grain collecting efficiency and low pressure drop performance. SOLUTION: This filter has a porous plastic substrate and at least one porous layer integrated with the surface, and the substrate is obtained by sintering and compacting the grain of a thermoplastic material having a relatively large average diameter and has a large pore diameter. The porous layer is obtained by sintering and compacting the grain of a cross-linked polyolefin resin having a relatively small average diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous plastic filter for separating and filtering fine particles contained in a fluid such as a liquid and a gas, and a method for producing the same.

[0002]

2. Description of the Related Art Hitherto, a large number of porous plastic filters for separating and filtering fine particles contained in a fluid such as liquid or gas have been known. Among them, filters having different pore sizes on the inflow side and the outflow side of the fluid, for example, one of the inflow side and the outflow side is formed from particles of a plastic material having a relatively large average particle diameter to obtain a large pore diameter, and the other is averaged. A porous multilayer filter formed from particles of a plastic material having a relatively small particle size and having a small pore size is desirable in terms of improving filtration accuracy, high collection efficiency of fine particles, and low pressure loss. A thermoplastic material with a relatively large average particle size, for example polyethylene,
Polytetrafluoroethylene (hereinafter referred to as "PTFE") having an average particle size relatively smaller than the plastic material on the surface of a porous plastic substrate obtained by sintering polypropylene, polysulfone, polyether sulfone, polyphenylene sulfide, etc. A porous multi-layer filter has been proposed in which the pore size of the porous layer is made different between the outer surface of the porous plastic substrate and the inner surface thereof by directly applying the same together with an adhesive.

[0003]

However, in such a porous multilayer filter, since the PTFE used has poor adhesive properties, the porous plastic base material and the PTFE are not used.
The adhesion at the interface with E becomes insufficient, and PTFE particles fall off from the porous plastic substrate during filtration or backwashing,
As a result, there is no difference in the hole diameter, or there is a partial difference, leading to a decrease in the filtering performance of the filter,
Alternatively, there has been a problem that the dropped PTFE particles are mixed into the collected fine particles.

In addition, the surface of a porous plastic substrate is made of PTFE having a pore size smaller than that of the porous plastic substrate.
Although a method of coating with a porous film made of has been proposed,
Similar to the above, there was a problem that the adhesion to the base material was insufficient, and there was a problem that the production cost was high because the porous PTFE film itself was expensive. Furthermore, a method has been proposed in which the surface of a sintered and molded porous plastic substrate is pressed and compressed so that the hole diameter of the pressed and compressed surface portion is smaller than that of the other portions. It is difficult to control the compression, and it is difficult to form a small pore size uniformly on the surface.

[0005]

SUMMARY OF THE INVENTION The present invention has found a plastic filter and a method for producing the same, which can solve the above-mentioned problems. The gist of the present invention is as follows. It has at least one porous layer integrated on its surface, and the porous plastic substrate has a large pore size obtained by sintering and molding particles of a thermoplastic material having a relatively large average particle size. Wherein the porous layer has a small pore size obtained by sintering and molding particles of a crosslinked polyolefin-based resin material having a relatively small average particle size. And (2) sintering the particles of thermoplastic material to form a porous plastic substrate, preferably the porous plastic substrate In a state in which the surface is previously provided with conductivity, the particles of the radiation-crosslinked polyolefin-based resin material having compatibility with the plastic, after imparting conductivity to the porous plastic base material, the surface of the base material. A porous multi-layer plastic filter, characterized in that the coated particles and the surface of the base material are heated and sintered and integrated to form at least one porous layer. It is in.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The porous multi-layer plastic filter of the present invention is characterized in that particles of a crosslinked polyolefin-based resin material are coated on the surface of a porous plastic substrate formed by sintering particles of a thermoplastic material. It is preferably obtained by forming at least one porous layer by sintering and integrating after electrostatic coating, and a thermoplastic resin having a different average particle size from the surface of the porous plastic base material. It has a multi-layer structure in which particles of a plastic material are sintered and laminated and integrated.

The porous plastic substrate constituting the porous multilayer filter of the present invention has low pressure loss and high strength, and the thermoplastic plastic material constituting the substrate is made of ultra-high molecular weight polyethylene, Polyolefin resins such as polyethylene and polypropylene such as high-density polyethylene, polyester resins such as polyvinyl chloride resin and polyarylate, polyamide resins, polystyrene resins, acrylic resins, polysulfone resins, polyether sulfone resins, and polyethylene sulfide Resins and the like can be used, and usually, the average particle size is 100 to
The material is not particularly limited as long as it is a thermoplastic material from which a porous body can be obtained by sintering in a range of 1,000 μm, preferably 150 to 600 μm.

In particular, the melt flow rate (hereinafter referred to as "MF
R ”), specifically, MFR of 1.0
It is preferable to use the following materials in order to obtain a base material layer having a uniform pore size. For example, the average particle size is 100 to 20.
0 μm and a bulk density of 0.35 to 0.45 g / cm ³
The grape cluster-shaped ultrahigh molecular weight polyethylene is more suitable for mechanical strength and the like. The average particle size is 1.000.
If it exceeds 0 μm, the mechanical strength of the porous multilayer filter becomes insufficient, which is not preferable.
If the thickness is less than 0 μm, the meaning of forming the porous multilayer filter into a multilayer becomes weak.

The porous layer coated and welded on the surface of the porous plastic substrate of the present invention is for separating and filtering fine particles, and the crosslinked polyolefin resin material constituting the porous layer is low in density. Polyethylene resins such as polyethylene, medium-density polyethylene, and high-density polyethylene, and polyolefin resins such as polypropylene are irradiated with ionizing radiation such as γ-rays and X-rays, or as inorganic crosslinking agents such as aluminum chloride and nitrogen fluoride. Compounds, t-
Chemically cross-linked using an organic peroxide such as butyl-cumyl-peroxide, dicumyl-peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, and acetylene peroxide. The cross-linked polyolefin resin material whose cross-linking degree is 10% or more, and which can obtain a porous layer by sintering usually having an average particle size of 5 to 90 μm, preferably 10 to 60 μm. It is not particularly limited. When the degree of crosslinking of the polyolefin-based resin material is 10% or less, the cross-linking effect is unlikely to occur due to less decrease in the fluidity at the time of melting when the crosslinked polyolefin-based resin material is heated. In addition, radiation crosslinking is preferable in comparison with chemical crosslinking in that there is no residual cross-linking agent, that the time required for addition can be reduced, and that the crosslinking is uniform, but it is disadvantageous in that a special device is required. is there.

It is to be noted that a porous multi-layer plastic filter has an antistatic property to a porous plastic substrate, a thermoplastic plastic material constituting a porous layer coated and welded on the surface thereof, and a crosslinked polyolefin resin material. In order to apply, for example, a conductive agent such as carbon black, carbon fiber, metal powder, or potassium titanate having a surface coated with a metal or the like is added in an amount of 1 to 5% by weight according to the purpose, usually 1 to It may be added in an amount in the range of 2% by weight.

[0011] The porous multi-layer plastic filter of the present invention has a porous plastic substrate formed by sintering particles of a thermoplastic material, the average particle size of which is different from that of the substrate, and the surface of the porous plastic substrate is crosslinked. It is characterized in that it has a multilayer structure in which at least one porous layer of particles of a polyolefin-based resin material is coated and welded, preferably electrostatically coated, sintered and laminated and integrated. As described above, the porous plastic substrate has a large pore size obtained by sintering a thermoplastic material having a relatively large average particle size, as described above, and further has a surface of the porous plastic substrate. The porous layer to be coated and welded has a small pore diameter obtained by applying a crosslinked polyolefin resin material having a relatively small average particle diameter, preferably by electrostatic coating and sinter molding, as described above.

The thickness composition of the porous multilayer plastic filter is such that the thickness ratio of the porous plastic substrate having a large pore diameter is in the range of 30% or more and less than 100% of the total thickness of the porous multilayer filter. Is preferred.
If the thickness ratio of the porous plastic substrate is less than 30%, the pressure loss increases, which is not preferable in terms of filter performance.

The porous multi-layer plastic filter of the present invention has a multi-layer structure of a porous plastic substrate having a large pore size and a porous layer having a small pore size coated and welded to the surface thereof. The position and number of the layers to be coated and welded are not limited, and it is possible to have two or more coated and deposited porous layers whose average particle diameters are changed according to the required quality.

In the method for forming a porous multilayer plastic filter of the present invention, first, particles having a predetermined average particle diameter of a thermoplastic material are sintered and formed to form a porous plastic substrate. The particles of the crosslinked polyolefin-based resin material are coated and welded on the surface of the base material and sintered and formed to integrate the porous layer.

The molding of the porous plastic substrate is performed by a static molding method or a dynamic molding method. The former static molding method is a so-called in-mold sintering method, for example, a molding metal comprising 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. In this method, a plastic material is filled into a cavity formed in a gap between an inner surface of an outer mold and an outer surface of an inner mold, and then the molding dies are heated together.

The latter dynamic molding method uses (1) a ram-type extruder that incorporates a piston (also called a plunger) that reciprocates in a temperature-adjustable cylinder having a molding die at the tip. Ram extrusion method, (2) injection molding method using an injection molding machine with a screw built in a temperature-adjustable cylinder with a mold at the tip, (3) temperature adjustment with a mold at the tip Extrusion molding method using an extruder that incorporates a screw in a cylinder that can be used. (4) Using a molding die consisting of a female die and a male die inserted in the inner diameter of the female die, Compression molding method using a compression molding machine that heats the molding die after filling the raw material into the formed cavity, (5) Composed of a pair of upper and lower movable belts or lower movable belt at the tip Temperature-adjustable cylinder with a shaped mold And the like continuous pressing method carried out using a continuous press for extruding the raw material into the mold.

[0017] From the methods such as the static molding method and the dynamic molding method, it can be appropriately selected according to the required quality such as the final shape of the porous multilayer plastic filter of the present invention. Also, the final shape of the porous multilayer filter is
The cross-section is appropriately selected depending on the use, such as a hollow cylindrical body such as a circle, an ellipse, a rectangle, a polygon, and a star, a plate-like body, a rod-like body, a bottomed cylindrical body, or a dish-like body.

Next, on this porous plastic substrate,
A porous layer coated and welded with particles of the crosslinked polyolefin resin material, which is smaller than the average particle size of the thermoplastic resin material constituting the base material of the crosslinked polyolefin resin material, is sintered and formed. .

The method of coating welding includes the above-described in-mold sintering method, electrostatic coating method, and the like. A gap is provided in a cylindrical outer mold having an inner diameter of a larger diameter by a predetermined amount, and then the space is filled with particles of a crosslinked polyolefin-based resin material. This is a method in which sinter molding is performed by heating only for a certain time. When the porous plastic substrate is molded by the in-mold sintering method, the particles of the crosslinked polyolefin-based resin material are successively sintered and molded in the same manner as described above, and the porous plastic substrate is porous. The material layer can also be integrated by coating and welding.

The electrostatic coating method is a method in which particles of a crosslinked polyolefin resin material are ejected from a nozzle to which a high voltage is applied, and the particles are electrostatically applied. It imparts conductivity to the surface of the porous plastic substrate. The conductivity may be imparted by, for example, mixing the above-described conductive agent, for example, carbon black, carbon fiber, or metal powder into the substrate when molding the porous plastic substrate, or forming the porous plastic substrate after molding. On the surface of the surface, such as a method of applying a surfactant,
There is no particular limitation as long as it can impart conductivity to at least the surface of the porous plastic substrate.

Subsequently, from the nozzle to which the high voltage is applied, the average particle diameter is larger than the particles of the plastic material which is compatible with the surface of the porous plastic substrate and constitutes the porous plastic substrate. Particles of a crosslinked polyolefin resin material having a small diameter are ejected, electrostatically applied, and coated and laminated on the surface of a porous plastic substrate. Next, the porous plastic substrate on which the particles of the crosslinked polyolefin-based resin material are adhered and laminated is heated in a heating furnace or the like set at a predetermined temperature, and is heated and sintered. The coating is welded to the surface of the material and integrated.

Here, in the radiation irradiation method for crosslinking the polyolefin resin material, the irradiation target material is sealed in a predetermined radiation irradiation device, and the irradiation target material is exposed to the atmosphere under atmospheric pressure.
At room temperature, a predetermined dose (G
y) is irradiated for a predetermined time, whereby a radiation-crosslinked polyolefin-based resin material having a desired degree of crosslinking is obtained. Further, it is more convenient for each layer of the porous multilayer plastic filter to be formed of the same kind of plastic material when molding, and it is also preferable from the viewpoint of the interlayer adhesion of each layer.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. In addition, the performance of the porous multilayer plastic filter obtained in the following Examples and Comparative Examples was evaluated or measured by the following method, and the results were displayed.

"Presence / absence of particle detachment" At the time of wiping by backwashing, the presence / absence of filter particle detachment was visually evaluated. That is, a sample having good filter particles without dropping was rated as (○), a sample with some filter particle dropping was identified as (Δ), and a sample with considerable filter particle dropping was rated as (x). Here, the filter particles included all particles constituting the filter, regardless of whether the falling source was a porous plastic substrate or a porous layer integrated on the surface thereof.

"Particle collection performance" At the time of washing off by backwashing, the presence or absence of mixing of the washed out fine particles into the fluid outflow side was visually evaluated. That is, a sample in which fine particles were not mixed was evaluated as (○), a sample in which fine particles were slightly mixed was evaluated as (Δ), and a sample in which fine particles were substantially mixed was evaluated as (x).

"Powder wiping property" At the time of wiping by backwashing, the quality of the wiping of fine particles (powder) adhering to the filter surface on the fluid inflow side was visually evaluated. In other words, the fine particles (powder) with very good removal (◎), the fine particles (powder) with good removal (○), and the fine particle (powder) with some poor removal (Δ), and those with considerably poor removal of fine particles (powder) were rated (x).

[Pressure loss / mmAq] This is a value obtained by measuring the pressure loss on the inflow side and the outflow side when air containing no fine particles is sucked at 1 m / min, and expressed in mm of water. "Contact angle / degree of water / degree" This is a value obtained by measuring the contact angle of water on the inflow side sintered plastic with a goniometer type contact angle measuring instrument (G-1 type manufactured by Elma) and expressing the angle in degrees.

<Example 1> As a molding die, one inner die having a cylindrical outer surface and one outer die having a cylindrical inner surface are prepared. The outer diameter of the inner mold is 3 mm smaller than the inner diameter of the outer mold. First, the inner mold is inserted into the outer mold, and the inner mold is set so that a gap of 3 mm is uniformly formed between the outer mold and the inner mold. Next, ultra-high molecular weight polyethylene particles having an average particle diameter of 170 μm and a molecular weight of 4,000,000 (MFR = 0.01 or less) are filled in the gaps,
Heating was performed in a heating furnace at a temperature of 0 to 200 ° C. for 60 minutes for sinter molding to obtain a hollow cylindrical porous plastic substrate having a relatively large pore diameter and a thickness of 3 mm. continue,
After applying a surfactant to the surface of the porous plastic substrate to impart conductivity to the surface of the substrate, 200 KGy is separately added to low-density polyethylene having an average particle size of 26 μm.
Irradiated with γ-rays, crosslinked polyethylene particles having a degree of crosslinking of 77% (MFR = 0.01 or less) were used with an automatic electrostatic coating machine at a working voltage of 60 KV and an atomizing air pressure of 1.5 kg / c.
Electrostatic coating with a thickness of 70 μm on the surface of the substrate
And crosslinked low density polyethylene particles were laminated. This was further heated in a heating furnace at a temperature of 150 to 200 ° C. for 30 minutes, and sintered and molded to form a porous layer having a relatively small pore diameter on the outer layer side of the base material, that is, on the fluid inflow side. ,
A hollow cylindrical porous two-layer plastic filter having a total thickness of 3 mm was obtained.

<Example 2> As an injection mold, one inner die having a cylindrical outer surface and an outer die 2 having a cylindrical inner surface were used.
Prepare the pieces. The inner diameter of the outer mold is 2 mm and 3 mm larger than the outer diameter of the inner mold, respectively. First, the inner mold is inserted into the outer mold having the smaller inner diameter, and is installed so that a gap of 2 mm is uniformly formed between the outer mold and the inner mold. Then, ultra high molecular weight polyethylene particles having an average particle diameter of 160 μm and a molecular weight of 4,000,000 (MFR = 0.
01 or less), heated in a heating furnace at a temperature of 160 to 220 ° C. for 30 minutes, and sintered and molded to obtain a porous plastic substrate having a relatively large pore diameter. Subsequently, the inner mold is detached from the outer mold while leaving the porous plastic base material on the outer surface, and is inserted into the outer mold having a larger inner diameter, and the uniform is formed between the substrate surface and the outer mold. 1mm
It is installed so that a gap is formed. Next, as in Example 1, a low-density polyethylene having an average particle size of 26 μm was irradiated with 200 KGy γ-ray in the secondary gap, and had a degree of crosslinking of 77% (MFR = 0.01 or less). Fill the cross-linked polyethylene particles and bring them again to 160-220 ° C.
Is heated in a heating furnace at a temperature of 30 minutes, sintered and molded, and a porous layer having a relatively small pore diameter is formed on the outer layer side of the base material, that is, on the fluid inflow side. A hollow cylindrical porous two-layer plastic filter was obtained.

Comparative Example 1 The surface of a hollow cylindrical porous plastic base material having a relatively large pore diameter and a thickness of 3 mm, which was obtained by molding in exactly the same manner as in Example 1, had an average particle size of PTFE fine particles of 0.1 μm together with a binder were sprayed and sprayed to be applied and laminated to a thickness of 10 to 20 μm to obtain a hollow cylindrical porous two-layer plastic filter having a total thickness of 3 mm.

<Comparative Example 2> Whole meat was prepared in the same manner as in Example 1, except that low-density polyethylene particles having an average particle size of 26 μm before crosslinking were used instead of the crosslinked polyethylene particles. A hollow cylindrical body having a thickness of 3 mm was obtained.

[0032]

[Table 1] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Presence or Absence of Particle Falling Out ○ ○ △ Predetermined Particle Collection Performance ○ ○ △ フ Powder Removal Property ○ ○ ◎ Pressure Pressure / mmAq 13 45 25 Other water contact angle / degree 94 93 115 Reference particle size ratio 170/26 160/26 170/10 to 20 170/26 Wall thickness 3mm 3mm 3mm 3mm Shape Round Round Round Round Molding method Mold / Electrostatic mold / in-mold mold / spray mold / electrostatic

As shown in Table 1, in Examples 1 and 2, dropping of particles, mixing of fine particles into the fluid outflow side, and powder removing property are satisfactory without any problem. The pressure loss is small and there is no problem. However, Comparative Example 1
Although the contact angle with water, which is one measure for evaluating the powder removal performance, was a large value, the PTFE particles fell off, and a performance defect was recognized. In Comparative Example 2,
The low-density polyethylene deposited and laminated on the surface of the porous plastic substrate became a thin film, and could not be a predetermined porous filter.

Example 3 Ultra-high molecular weight polyethylene particles having an average particle diameter of 340 μm and a molecular weight of 3.3 million (MFR =
0.01 or less) by a ram-type extruder provided with a die having a cylindrical opening having a width necessary for obtaining a final porous plastic filter thickness of 3 mm at the tip end, and forming a relatively large A hollow cylindrical porous plastic substrate having a hole diameter of 3 mm and a thickness of 3 mm was obtained. Thereafter, the applied lamination thickness of the crosslinked low-density polyethylene particles of
Except that the thickness was changed to 0 μm, a hollow cylindrical porous two-layer plastic filter having a total thickness of 3 mm was obtained in exactly the same manner as in Example 1.

Example 4 In Example 1, the average particle size of the ultra-high molecular weight polyethylene was from 170 μm to 160 μm.
The average particle size of the low-density polyethylene is
μm, the intensity of γ-rays irradiated from 200 KGy to 100 KGy, the degree of cross-linking from 77% to 54%, and the lamination thickness of cross-linked low-density polyethylene particles of 70 μm to 1 μm.
Except that the thickness was changed to 00 μm, a hollow cylindrical porous two-layer plastic filter having a total thickness of 3 mm was obtained in exactly the same manner as in Example 1.

<Example 5> In Example 1, the average particle size of the ultrahigh molecular weight polyethylene was from 170 μm to 160 μm.
The average particle size of the low-density polyethylene is
μm, the intensity of γ-rays irradiated from 200 KGy to 50 KGy, the degree of crosslinking from 77% to 43%, and the
A hollow cylindrical porous two-layer plastic filter having a total thickness of 3 mm was obtained in exactly the same manner as in Example 1 except that the thickness was changed to μm.

<Embodiment 6> In Embodiment 1, the molding die was changed from one inner mold having a cylindrical outer surface and one outer mold having a cylindrical inner surface to a star-shaped corner. The inner temperature of the heating furnace was increased from 150 to 200 ° C to 160 to 220 ° C, and the heating time was increased to 60 times for one inner die having a columnar outer surface and one outer die having a prismatic inner surface having a star-shaped cross section. From 30 minutes to 30 minutes
In addition, the thickness of the cross-linked low-density polyethylene particles is 70 μm.
Except that m was changed to 200 μm, the same procedure as in Example 1 was repeated, except that a hollow prismatic porous 2
A layer plastic filter was obtained.

[0038]

[Table 2] Example 3 Example 4 Example 5 Example 6 Presence or absence of falling off of particles ○ ○ ○ ○ Performance of collecting fine particles ○ ○ ○ ○ Powder removing property ○ ○ ○ ○ Pressure loss / mmAq 920 21 11 pairs Water contact angle / degree 95 93 93 94 Reference Particle size ratio 340/26 160/10 160/10 170/26 Wall thickness 3mm 3mm 3mm 3mm Shape Round Round Round Star Molding method Mold / electrostatic mold / electrostatic metal Mold / Electrostatic Mold / Electrostatic

As shown in Table 2, in Examples 3, 4, 5, and 6 in which the average particle size of the porous plastic substrate and the plastic material to be the porous layer and the conditions of electrostatic coating were changed. It is also satisfactory without any problem regarding dropping of particles, mixing of fine particles into the fluid outflow side, and powder removal property. In addition, there is no problem in that the contact angle with water, which is one criterion for evaluating the pressure loss and the powder removing performance, is small.

[0040]

The present invention is a porous multi-layer plastic filter in which a porous layer of a cross-linked polyolefin resin material is coated and welded on the surface of a porous plastic base material to be integrated, so that a fluid can be easily formed. A porous filter having a different pore size between the inflow side and the outflow side can be provided, and the conventional PTFE particles can be prevented from falling off and being mixed into the collected fine particles. In addition, a crosslinked polyolefin-based resin material is electrostatically coated on the surface of a porous plastic base material, which is sintered and formed into a porous layer to form a porous layer having a large pore size that exhibits good air permeability. A porous layer with a small pore size that exhibits good fine particle collection performance can be easily formed on the surface of a porous plastic substrate, and the fine particle separation combines high fine particle collection efficiency and low pressure loss performance Porous filter for use.

The reason why the crosslinked polyolefin-based resin material is suitable for forming a porous layer on the surface of the porous plastic substrate is that the crosslinked polyolefin-based resin material is capable of forming a flow in a molten state having a melting point (Tm) or higher. This is because the sintering can be completed relatively easily in the state of “fusion of only the particle surface” which occurs during the process of fusion of the particle surface of the material due to the decrease in the property due to the presence of the cross-linking portion. . Therefore, instead of the ultra high molecular weight polyethylene having a small average particle size, it is possible to use a polyolefin resin material having a small average particle size, which is relatively easily available,
It is also advantageous in terms of productivity and cost.

Claims (3)

[Claims] 1. A porous plastic substrate having at least one porous layer integrated on its surface, said porous plastic substrate comprising particles of a thermoplastic material having a relatively large average particle size. The porous layer has a small pore size obtained by sintering particles of a crosslinked polyolefin-based resin material having a relatively small average particle size. A porous multi-layer plastic filter characterized by the following. 2. The porous multilayer plastic filter according to claim 1, wherein the crosslinked polyolefin resin material is a radiation crosslinked polyolefin resin material. 3. A porous plastic base material is formed by sintering and molding particles of a thermoplastic plastic material, and particles of a radiation-crosslinked polyolefin resin material compatible with the plastic are formed on the porous plastic base material. After imparting conductivity to the material, the surface of the substrate is electrostatically coated, and then the coated particles and the surface of the substrate are heated and sintered and integrated to form at least one porous layer. A method for producing a porous multi-layer plastic filter.