JP2000317280A - Filter using ultrahigh molecular weight polyethylene porous membrane as filter medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive filter capable of use even in a electronics filed, that an elution component does not substantially exsist, and a problem of the disposal is not caused. SOLUTION: The filter using an ultrahigh molecular weight polyethylene porous membrane as a filter medium, is produced by gelatinizing a >=4×105 ultrahigh molecular weight polyethylene solution to make a film, removing a solvent and then stretching to at least one direction to make porous. the polyethylene porous membrane having 10-300 μm thickness, a 30-90% void ratio, a 0.03-5.0 μm average pore size, and >=10 MPa tensile strength at least in one direction, is laminated in a nonwoven fabric state due to fibrillation at a stretching time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter using an ultra-high molecular weight polyethylene porous membrane as a filtration medium, and more particularly to performing a plasma hydrophilization process as a physical process in an atmosphere near atmospheric pressure. A hydrophilic filter.

[0002]

2. Description of the Related Art Porous membranes have been conventionally used as filtration media for filters. In the field of electronics, especially in the field of semiconductors, PTF
Filters using a fluorine-based porous membrane such as E (polytetrafluoroethylene) have been widely used. However, regarding the fluorine-based membrane, there has recently been a problem of disposal related to ozone layer destruction. In particular, when ISO14000 is acquired, it is required to specify the disposal method, and the use of fluorine-based membranes, which are difficult to incinerate, is being avoided. Environmental problems due to incineration are much less with polyethylene membranes than with fluorine-based membranes. The cleanliness that the products after incineration are carbon dioxide and water has come to be regarded as a use advantage. Also, the price of polyethylene films is lower than that of fluorine-based films, and there is a great demand for expanded use in this respect as well.

However, a polyethylene membrane is basically a lipophilic membrane, and can be used without any pretreatment in the case of filtration in a solvent-based solution because of its lipophilicity. In the case of use, for example, pretreatment such as wetting with an aqueous solution of a hydrophilic organic solvent such as alcohols or ketones before use is necessary. Various methods of hydrophilization for solving this inconvenience have been tried.

There are three main methods for imparting hydrophilicity to a hydrophobic film. 1) A method of treating a membrane with a hydrophilizing agent or surfactant to make it hydrophilic, 2) A method of coating and filling a hydrophilic material on the membrane surface, inside of pores, etc., 3) Making the surface hydrophilic by physical processing There are three ways to do this. Examples of the hydrophilizing agent and the surfactant include a sulfonating agent and a fluorine-based surfactant. For the coating and filling of a hydrophilic material, there are methods such as graft polymerization of a monomer having a hydrophilic functional group on the surface by irradiation with radiation or ultraviolet light, and a method of immersing in a solution of a hydrophilic cellulose-based or amide-based resin and then drying. . In physical processing, surface processing by contact of ozone gas and fluorine gas,
Examples include surface treatment by applying a high pressure in water to make the surface hydrophilic, corona discharge and plasma processing.

[0005] When the ultrahigh molecular weight polyethylene porous membrane after hydrophilization is used as a filter filtration medium, elution of other components from the filter is not preferred. In particular, when the purpose is to substitute a filter of a fluorine-based membrane, it is required that the amount of eluted substances is small. In the industry where precision filters are used, such as in the electronics field, when the amount of eluted substances from the filter is large, it also affects the product yield, and the concentration of the eluted metal component is on the order of ppb.
Therefore, a method in which the hydrophilizing agent is easily released cannot be used in the field of precision filters for electronics.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an inexpensive filter which can be used in the field of electronics and has substantially no eluted components and does not cause disposal problems.

[0007]

Means for Solving the Problems In view of the above-mentioned objects, as a result of intensive studies, the present inventors have found that ultra-high molecular weight polyethylene porous material forming a nonwoven fabric laminate by fibrillation during stretching after film formation. The present inventors have found that a porous membrane can be efficiently treated by performing hydrophilic processing by plasma processing, which is physical processing, and arrived at the present invention.

That is, the present invention provides: 1) an ultra-high molecular weight polyethylene having a molecular weight of 4 × 10 ⁵ or more, which is formed into a laminated non-woven fabric by forming a gel film, stretching the solvent in at least one direction after removing the solvent, The thickness is 10 to 300 μm, the porosity is 30 to 90%,
The average pore diameter is 0.03 to 5.0 μm, a tensile strength is a filter using a ultra-high-molecular-weight polyethylene porous membrane having a tensile strength of at least 10 MPa or more in at least one direction as a filtration medium, preferably at least the ultra-high-molecular-weight polyethylene porous membrane One side is laminated with a reinforcing material made of a polyolefin-based woven or nonwoven fabric. More preferably, the ultra-high molecular weight polyethylene porous membrane has a contact angle with water of 45.
° or less, desirably 40 ° or less, or the time required for water to penetrate into the interior and discolor when contacted with water.
It is a porous ultrahigh molecular weight polyethylene membrane having hydrophilicity expressed within 0 seconds, preferably within 30 seconds.

The present invention also relates to 2) a porous ultra-high molecular weight polyethylene membrane having a molecular weight of 4 × 10 ⁵ or more, wherein the membrane is fibrillated into a laminated nonwoven fabric, and has a thickness of 10 to 300 μm and a porosity. Is 3
0 to 90%, an average pore diameter of 0.03 to 5.0 μm, and a tensile strength of 10 MPa or more in at least one direction. A filter using a ultrahigh molecular weight polyethylene porous membrane as a filtration medium. The molecular weight polyethylene porous membrane has a contact angle with water of 45 ° or less, preferably 40 °.
The time required for water to penetrate into the inside and discolor when contacted with the water surface is 60 seconds or less, preferably 30 seconds or less.
It is an ultra-high molecular weight polyethylene porous membrane having hydrophilicity expressed within seconds.

[0010] The filter of the present invention comprises a porogen (an aliphatic or cyclic hydrocarbon represented by nonane, decane, undecane, dodecane, decalin and paraffin oil) which is a solvent capable of sufficiently dissolving ultra-high molecular weight polyethylene. Mineral oil fraction with similar boiling point)
And heated to form a solution consisting of a porogen and a polymer, extruded from a very wide slit-shaped die into a film, cooled to a point where the film gelled, and the solvent was removed by evaporation. At least one later
A microporous nonwoven-like film fibrillated by stretching in the direction is used. This film can be used for desired filtration depending on the film thickness, porosity, and pore size controlled according to the shape of the extrusion slit, the amount of the supplied solution, the evaporation conditions of the solvent, the stretching conditions, and the like. For use as a filtration medium, it is desirable that the thickness is 10 to 300 μm, the porosity is 30 to 90%, the average pore diameter is 0.03 to 5.0 μm, and the tensile strength is 10 MPa or more in at least one direction. Further, since the raw material ultrahigh molecular weight polyethylene can be molded without adding an additive such as a plasticizer, the film is essentially very clean and has little impurities eluted during filtration.

However, ultra-high molecular weight polyethylene is essentially hydrophobic. In the filtration of the organic solvent-based liquid, the ultrahigh molecular weight polyethylene filter membrane can be used as it is. As an example of filtration for a liquid having this property, there is, for example, filtration of a photoresist liquid used for wiring a semiconductor. In this case, since the liquid is an organic solvent system, the hydrophobic ultra-high molecular weight polyethylene membrane has a strong affinity, and problems such as the occurrence of air pockets at the time of liquid filling can be sufficiently avoided by ordinary caution. . However, even in the semiconductor field, the etching solution after exposing the photoresist, the developing solution and the removing solution used in the photoresist removing step are often aqueous solutions, and these solutions are used as they are of the present invention. A filter using an ultrahigh molecular weight polyethylene porous membrane cannot be used, and some hydrophilic treatment is required. There are three conventional methods for hydrophilizing a hydrophobic membrane: 1) using a hydrophilizing agent, 2) coating and filling with a hydrophilic material, and 3) physically hydrophilizing.
Among them, examples of the use of the hydrophilizing agent include a method of wetting the surface with a hydrophilic liquid such as a surfactant, a sulfonic acid-based hydrophilizing agent, or an alcohol, and then introducing water.
The treatment of the alcoholic solution before use requires much time and effort for the person in charge, and there remains a problem in use. Examples of the surface coating with a hydrophilic material include graft polymerization of a hydrophilic group-containing monomer on the surface by irradiation with radiation or ultraviolet light, and hydrophilicization by impregnating with a solution of a hydrophilic material and drying. Examples of the method of physical hydrophilization include a corona discharge treatment, a plasma treatment, and a contact treatment with a gas containing ozone gas or fluorine gas. As mentioned earlier, the electronics field,
In particular, when used in the semiconductor field, contamination by impurities, particularly metal components, is one of the important management items that must be avoided from the viewpoint of securing product quality and improving yield. Even when a hydrophilic ultra-high molecular weight polyethylene film is used, it is necessary to maintain a material that does not cause contamination by impurities. From this point, it is difficult to use the surface hydrophilization by a surfactant or a sulfonic acid compound because the possibility of elution of the hydrophilizing agent itself is strong. Similarly, if the surface is coated with a hydrophilic substance, a strong bond that does not elute during filtration is required. In the physical treatment, the possibility of elution of the third component is reduced, but there is a decrease in hydrophilicity over time.

Although there are several methods for hydrophilization by physical processing, effective methods are limited due to the life of the hydrophilicity and the cost of hydrophilization.

Many of the hydrophilization methods by plasma treatment involve irradiating a material to be hydrophilized with high-voltage plasma under reduced pressure, and require a batch-type process, which is not suitable for mass processing. Recently, plasma processing at near atmospheric pressure has been developed. Since the pressure is close to the atmospheric pressure, continuous processing of a roll-shaped film becomes possible, leading to cost competitiveness.

The atmosphere for the plasma treatment is often a hydrocarbon gas atmosphere in order to prolong the effect of hydrophilization. This is presumed to be due to the fact that a thin film is formed in a hydrocarbon atmosphere to prevent active sites that provide hydrophilicity generated on the surface by the plasma treatment from being deactivated due to electron transfer from the inside. I have.

A filter is made using a hydrophilic ultra-high molecular weight polyethylene porous film as a filtering material. Since the porous film alone has insufficient physical strength,
At least one side is laminated with a reinforcing material that also serves as a liquid flow path before or after filtration. As the type of reinforcing material, woven fabric such as taffeta, spun bond, non-woven fabric by melt-blowing or mesh material made of polymer resin, which has a small amount of eluted material, has sufficient strength, and can maintain the filtration area and flow rate, etc. Yes, according to the purpose of use, conditions, etc., select and use the best one from the conventional knowledge. When processing into a filter,
Depending on the required filtration area, pleating or the like may be added to the filtering material. The conditions of the filter processing can be achieved only by finely adjusting the conventional processing method and conditions using a film from the difference in the material.

[0016]

Examples of the present invention will be described below. In addition, the test method in an Example is as follows.

(1) Hydrophilicity-1: Expressed as a contact angle with pure water on the film surface after the treatment. A contact angle of 45 ° or less, desirably 40 ° or less is regarded as hydrophilic.

(2) Hydrophilicity-2: Evaluated by the time required for discoloration due to penetration when the treated film is brought into contact with the water surface. For example, a small piece of a 2 cm × 2 cm film sample is floated on water placed in a container, and the discoloration (from porous white to transparent) when water seeps from the lower surface of the film to the upper surface by capillary suction is determined. Time to change
The hydrophilicity was determined within 60 seconds, preferably within 30 seconds.

(3) Average pore size: ASTM F316-8
6. Perm-Porometer based on JIS K3832
The calculated value from the measurement of the air permeability of WET and DRY by (PMI) was adopted.

(4) Contact angle: The Wilhelmy plate method, in which a dynamic contact angle is determined from a process of suspending a sample on an electronic balance and submerging it into a liquid having a known surface tension and a process of pulling the sample up, is used. As the contact angle in the process of sinking (advance contact angle) and the contact angle in the process of lifting (receding contact angle) do not usually take the same value and cause hysteresis, the measured value this time is expressed as the average value of both. I have.

Comparative Example 1 Five parts of ultra high molecular weight polyethylene having an average molecular weight of 3.3 × 10 ⁶ (manufactured by Mitsui Chemicals, Hyzex Million, 340M) was dissolved in 95 parts of decalin by heating and stirring at 170 ° C. After extruding to form a film and removing the solvent by heating, the film was biaxially stretched three times vertically and horizontally to obtain a porous film. A spunbonded nonwoven fabric (thickness: 0.2 mm, high-density polyethylene) was laminated on the film to form a filter membrane. Table 1 shows the physical property values of the PE film used for this membrane.

Example 1 Since the ultrahigh molecular weight polyethylene porous membrane-laminated membrane of Comparative Example 1 was hydrophobic, it was hydrophilized by normal pressure plasma treatment. The conditions of the plasma treatment are a frequency of 5 KHz, an application time of 20 seconds, an atmosphere of argon containing acetone, and a pressure of normal pressure (about 0.1 Mpa).
The physical properties of the PE film of this membrane are also shown in Table 1.

[Comparative Example 2] A Solupor film (DSM Solutec, The Netherlands) was used as an ultrahigh molecular weight polyethylene porous membrane.
(manufactured by Company h) and laminated with a spunbonded nonwoven fabric for reinforcement in the same manner as in Comparative Example 1 to obtain a membrane for a filter. The physical properties of the PE film are shown in Table 1.

Example 2 The membrane of Comparative Example 2 was hydrophilized under normal pressure plasma treatment under the same conditions as in Example 1. Table 1 also shows the physical property values of the PE membrane used for the hydrophilized membrane.

[0025]

[Table 1]

Example 3 Using the membrane of Example 1, a 25 cm long filter cartridge was prototyped.
When the particle entrapment rate of this cartridge was measured, the entrapment rate of 1 μm polystyrene latex particles was 99.9% or more,
The capture rate of μm latex particles was 92%.

[Embodiment 4] A cartridge manufactured in the same manner as in Embodiment 3 was manufactured using the membrane in Embodiment 2 with the cartridge of Embodiment 4.
The capture ratio of the 0.1 μm latex particles was 99.9% or more, indicating that the particles had a sufficient particle capture ratio.

[0028]

As described in detail above, the filter of the present invention has been hydrophilized by a plasma treatment near atmospheric pressure, and is formed by laminating an ultra-high molecular weight polyethylene porous membrane originally showing hydrophobicity and a high-density polyolefin nonwoven fabric. It became clear that the contact angle of the membrane was changed by the hydrophilization treatment. As a result, a filter was completed which can be used not only in organic solvent-based liquids but also in aqueous-based developing solutions and stripping solutions without prior hydrophilic treatment. This filter is suitable for various uses in the fields of chemistry, pharmaceuticals, foods, etc., because it has a small amount of additives such as plasticizers, and is particularly suitable for electronics, particularly semiconductors, which dislike elution of impurities, particularly metal components. is there.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA02 MA03 MA06 MA22 MA24 MA31 MB06 MB09 MB16 MB20 MC22X MC88 NA03 NA32 NA66 PA01 PA02 PB08 PB12 PB14 PC01 4D019 AA03 BA13 BB08 BC13 BD01 CB06 CB08

Claims (7)

[Claims] An ultra-high-molecular-weight polyethylene having a molecular weight of 4 × 10 ⁵ or more is formed into a gel and formed into a laminated non-woven fabric by stretching in at least one direction after removing a solvent, and has a thickness of 10 to 300 μm. Porosity is 30
A filter using an ultrahigh molecular weight polyethylene porous membrane having a filtration medium of about 90%, an average pore diameter of 0.03 to 5.0 μm, and a tensile strength of 10 MPa or more in at least one direction. 2. The filter according to claim 1, wherein a reinforcing material made of a polyolefin-based woven or nonwoven fabric is laminated on at least one surface of the ultrahigh molecular weight polyethylene porous membrane. 3. The ultra high molecular weight polyethylene porous membrane,
The contact angle with water is 45 ° or less, preferably 40 ° or less, or the time required for water to penetrate into the inside and discolor when contacted with the water surface is represented within 60 seconds, preferably within 30 seconds. 3. The filter according to claim 1, which is a porous ultrahigh molecular weight polyethylene membrane having hydrophilicity. 4. The filter according to claim 3, wherein said hydrophilicity is imparted by hydrophilization by physical processing. 5. The filter according to claim 4, wherein said physical processing is plasma processing at substantially atmospheric pressure (atmospheric pressure: 0.05 to 0.2 MPa). 6. An ultra-high molecular weight polyethylene porous membrane having a molecular weight of 4 × 10 ⁵ or more, wherein the membrane is fibrillated into a laminated nonwoven fabric, and has a thickness of 10 to 300 μm.
A filter using a ultrahigh molecular weight polyethylene porous membrane having a porosity of 30 to 90%, an average pore diameter of 0.03 to 5.0 μm, and a tensile strength of at least 10 MPa in at least one direction as a filtration medium. 7. The ultra high molecular weight polyethylene porous membrane,
The contact angle with water is 45 ° or less, preferably 40 ° or less, or the time required for water to penetrate into the inside and discolor when contacted with the water surface is represented within 60 seconds, preferably within 30 seconds. 7. The filter according to claim 6, which is a porous ultrahigh molecular weight polyethylene membrane having hydrophilicity.