JP2014218563A - Base material for liquid filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyolefin microporous film preferable as a base material for liquid filter in which the film has both excellent capturing performance and liquid permeability and has high degree of freedom in filter design.SOLUTION: A base material for liquid filter consists of a polyolefin microporous film in which a thickness of the polyolefin microporous film is 4 to 16 μm and a bubble point of the polyolefin microporous film is 0.40 MPa or more and 0.80 MPa or less.

Description

  The present invention relates to a liquid filter substrate.

  In recent years, electronic devices have been increasingly reduced in size and performance. In particular, personal computers, digital devices represented by smartphones, and mobile terminals have undergone dramatic evolution. It is a well-known fact that technological innovation in the semiconductor industry plays a major role among the various technologies that lead and support it. In the semiconductor industry, the wiring pattern dimension, which is an important characteristic indicated by the technology roadmap, is a development race in a region below 20 nm, and each company is rushing to build a state-of-the-art manufacturing line.

The lithography process is a process for forming patterns in the manufacture of semiconductor components. In addition to the recent miniaturization of patterns, not only the properties of the chemicals used but also the handling of chemicals until they are applied on the wafer are required. It has come to be.
Highly prepared chemicals are filtered through a precise filter immediately before application onto a wafer in order to remove particles that greatly affect pattern formation and yield. In the pattern formation below the latest 20 nm, it is required that particles of around 10 nm can be collected, and filter manufacturers are energetically developing them.

  Further, in a region having a wiring pattern dimension exceeding 20 nm (for example, 30 nm to 100 nm), which is a conventional tip region, as a request for a chemical solution necessary for forming a wiring pattern, a conventional minute foreign matter from outside In addition to the elimination of chemicals, there has been a demand for elimination of gel-like substances due to gelation accompanying the high reactivity of the chemicals themselves and maintenance of the purity of the chemicals purified to a high purity, that is, prevention of contamination of the chemicals. In the manufacture of semiconductors having such various wiring pattern dimensions, there is a need to remove particles having a size of several nm to 100 nm.

  Filters are generally sold and used after being processed into a cartridge shape using a porous film made of a resin such as polyethylene, polytetrafluoroethylene, nylon, or polypropylene as a base material. Substrates are selected and used in semiconductor component manufacturing plants from the viewpoints of compatibility with chemical solutions, collection performance of each porous structure, processing capability, life, and the like. Recently, emphasis has been placed on reducing the eluate derived from the base material, and the use of polyethylene filters that are superior in terms of collection performance and low elution is increasing in the most advanced region of the base material.

  A typical method for producing a base material for a polyethylene filter is a phase separation method, which is a technique for forming pores by a phase separation phenomenon of a polymer solution. There are heat-induced phase separation, in which phase separation is induced by heat, and non-solvent-induced phase separation using the solubility characteristics of polymers in solvents. There are techniques for increasing variations in size and the like.

  For example, as disclosed in Patent Document 1, a thermal phase inversion method is a method in which a liquid in which polyethylene is dispersed in a good solvent is heated, heated to evaporate the solvent, and immersed in a poor solvent to cause phase transformation, and applied to a sheet. This is a method of forming a film. For example, as described in Patent Documents 2 and 3, a stretching method is performed by using a combination of stretching conditions such as speed, magnification, and temperature for a polyethylene sheet formed into a sheet shape by some method. This is a method of forming micropores between lamellar layers while stretching the crystalline portion and forming microfibrils.

JP-A-2-251545 JP 2010-053245 A JP 2010-202828 A

However, when trying to efficiently collect particles of several nm to 100 nm, the liquid permeability tends to deteriorate. That is, the collection performance and liquid permeability are in a trade-off relationship.
On the other hand, it is also required to obtain a larger filtration area in a filter cartridge of a predetermined size and to increase the degree of freedom in designing the flow rate and structure of the filter when processing the polyolefin microporous membrane. For this purpose, it is conceivable to form a thin polyolefin microporous membrane. However, since the thickness of the polyolefin microporous membrane also affects the collection performance and liquid permeability, it is necessary to consider the balance with these various characteristics. is there.

However, in the conventional techniques such as Patent Documents 1 to 3, a proposal has been made to improve the collection performance and liquid permeability with respect to particles of about 5 nm to 100 nm, and also realize a high degree of freedom in filter design. Not.
Therefore, in the present invention, in order to solve the above-described problems, a polyolefin microporous membrane suitable for a liquid filter substrate having both excellent collection performance and liquid permeability and having a high degree of freedom in filter design is provided. For the purpose.

The present invention adopts the following configuration in order to solve the above problems.
1. A substrate for a liquid filter comprising a polyolefin microporous membrane, wherein the polyolefin microporous membrane has a thickness of 4 to 16 μm, and a bubble point of the polyolefin microporous membrane is 0.40 MPa or more and 0.80 MPa or less, Base material for liquid filters.
2. 2. The liquid filter substrate according to 1 above, wherein the polyolefin microporous membrane has a heat shrinkage in the width direction of 20% or more after heat treatment at 130 ° C. for 1 hour.
3. 3. The liquid filter substrate according to 1 or 2 above, wherein the polyolefin microporous membrane has a pore closing temperature higher than 140 ° C.
4). 4. The liquid filter substrate according to any one of 1 to 3 above, wherein the polyolefin microporous membrane has a compressibility of less than 15%.
5. 5. The liquid filter substrate according to any one of 1 to 4 above, wherein the porosity of the polyolefin microporous membrane is 46 to 60%.
6). The liquid filter substrate according to any one of 1 to 5 above, wherein the water permeability of the polyolefin microporous membrane is 0.10 to 2.90 ml / min · cm ^2.

  ADVANTAGE OF THE INVENTION According to this invention, the base material for liquid filters which has the outstanding collection performance and liquid permeability, and has a high freedom degree of filter design can be provided.

  Embodiments of the present invention will be sequentially described below. However, these descriptions and examples illustrate the present invention and do not limit the scope of the present invention. In addition, in the whole specification, when “to” is used in a numerical range, each numerical range includes an upper limit value and a lower limit value. Regarding the polyolefin microporous membrane, the “longitudinal direction” means the longitudinal direction of the polyolefin microporous membrane produced in a long shape, and the “width direction” is orthogonal to the longitudinal direction of the polyolefin microporous membrane. It means the direction to do. Hereinafter, the “width direction” is also referred to as “TD”, and the “longitudinal direction” is also referred to as “MD”.

[Substrate for liquid filter]
The substrate for a liquid filter of the present invention is a substrate for a liquid filter comprising a polyolefin microporous membrane, the polyolefin microporous membrane has a thickness of 4 to 16 μm, and the bubble point of the polyolefin microporous membrane is 0. It is 40 MPa or more and 0.80 MPa or less.
According to the present invention as described above, it is possible to provide a liquid filter substrate having both excellent collection performance and liquid permeability and having a high degree of freedom in filter design. Details of each component will be described below.

(Bubble point)
The polyolefin microporous membrane that is the substrate for a liquid filter of the present invention is characterized by highly collecting fine particles. The bubble point of the polyolefin microporous membrane is 0.40 MPa or more and 0.80 MPa or less, more preferably 0.40 to 0.75 MPa, and 0.42 to 0.75 MPa. Further preferred. In the present invention, when the bubble point of the polyolefin microporous membrane is lower than 0.40 MPa, the fine particles as described above cannot be sufficiently collected and sufficient collection performance is not exhibited. On the other hand, when the bubble point of the polyolefin microporous membrane is higher than 0.80 MPa, the liquid permeation performance is remarkably insufficient although the very excellent collection performance is exhibited. For example, the polyolefin microporous membrane is used as a base material. Problems such as instable liquid feeding through the filter. As a method for improving the liquid passing performance, for example, the liquid feeding pressure can be increased. However, this may cause problems such as a reduction in filter life and leakage of filtrate.

(Thickness)
The polyolefin microporous membrane, which is the substrate for a liquid filter of the present invention, is characterized in that the degree of freedom in filter design is increased without impairing the collection performance and liquid permeability. The thickness of the polyolefin microporous membrane is 4 to 16 μm, more preferably 5 to 15 μm. When the film thickness of the polyolefin microporous membrane is less than 4 μm, the fine particles as described above cannot be sufficiently collected, the mechanical strength is low, and there is a problem in handling during processing of the polyolefin microporous membrane, This may cause a problem that the durability of the filter cartridge is insufficient during long-term use. On the other hand, when the thickness exceeds 16 μm, high mechanical strength can be obtained, but the liquid permeation performance (liquid permeation amount) is lowered, and the liquid permeation performance is insufficient.

  The polyolefin microporous membrane that is the substrate for a liquid filter of the present invention is characterized in that the film thickness is thin, and it becomes easier to obtain a larger filtration area in a filter cartridge of a predetermined size. It is easy to design the flow rate and structure of the filter during machining.

  For example, when it is assumed that the filter cartridge is housed in a housing of the same size, the filter medium area can be increased as the thickness of the filter medium (the entire constituent material including the filter base material) is thinner, which is preferable as a liquid filter. High flow and low filtration pressure can be designed. That is, the liquid filter can be designed such that the filtration pressure is low when the same flow rate is desired to be maintained, and the flow rate is high when the same filtration pressure is desired. In particular, there is a probability that the foreign matter once collected by the filtration pressure is lowered and continuously exposed to the filtration pressure inside the filter medium, so that it is pushed out together with the filtrate from the inside of the filter medium and leaks over time. It is possible to expect favorable effects such as a significant decrease in the probability that the gas dissolved in the liquid to be filtered will appear as fine bubbles due to the pressure difference before and after filtration (pressure drop after filtration). It can be expected that the filtration yield of the filtration object such as a chemical solution is improved and that the quality of the product is maintained at a high level for a long time.

  On the other hand, the thinner the filter media, the greater the degree of freedom in design, but the strength and durability of the filter media decrease. For example, if possible in the filter design, adjust the durability and flow rate design while reinforcing by combining with a coarse high-strength support (for example, by superimposing and folding) Is also possible.

  In the present invention, it is necessary to adjust the above-described film thickness and bubble point to appropriate ranges. The method for controlling these physical properties is not particularly limited. For example, the average molecular weight of the polyolefin resin, when a mixture of a plurality of polyolefin resins is used, the mixing ratio, the concentration of the polyolefin resin in the raw material, When mixing a plurality of solvents, the mixing ratio, the heating temperature for squeezing out the solvent inside the extruded sheet, the pressing force, the stretching ratio, the heat treatment (heat setting) temperature after stretching, the extraction solvent For example, adjustment of production conditions such as immersion time may be mentioned.

(Heat shrinkage)
The polyolefin microporous membrane that is the substrate for a liquid filter of the present invention preferably has a shrinkage ratio in the width direction (TD) of 20% or more after standing at a temperature of 130 ° C. for 1 hour, more preferably 20%. ˜35%, particularly preferably 22˜32%. When the thermal shrinkage of the polyolefin microporous membrane is 20% or more, it is preferable because good transportability can be easily obtained without occurrence of slack in the conveyance under the condition of undergoing a heat treatment in the processing of the polyolefin microporous membrane. . On the other hand, when the polyolefin microporous membrane has a heat shrinkage rate of 35% or less, it is easy to obtain good transportability without causing meandering and wrinkles in transport under the condition of being subjected to heat treatment during processing of the polyolefin microporous membrane. Therefore, it is preferable.

(Hole closing temperature)
The polyolefin microporous membrane that is the substrate for a liquid filter of the present invention preferably has a pore closing temperature higher than 140 ° C. When the pore closing temperature of the polyolefin microporous membrane is higher than 140 ° C., the porosity of the polyolefin microporous membrane is lost in the vicinity of the high temperature treatment part or in the vicinity of the hot body contact part in the thermal bonding process when processing the polyolefin microporous film. Therefore, the water permeation performance is maintained, and a planned filtration area can be easily obtained even after processing.

(Compression rate)
The compression ratio when the polyolefin microporous membrane, which is the substrate for a liquid filter of the present invention, is pressed at 2 MPa for 30 seconds at a temperature of 70 ° C. is preferably less than 15%, more preferably 12% or less. . When the compression ratio of the polyolefin microporous film is less than 15%, the polyolefin porous film is not crushed more than necessary in the process of heating press (adhesion) when processing into a filter, and the original porous structure is obtained. It is preferable in that it can be maintained.

(Porosity)
The porosity of the polyolefin microporous membrane that is the substrate for a liquid filter of the present invention is preferably 46 to 60%, more preferably 47% to 58%. When the porosity of the polyolefin microporous membrane is 46% or more, it is preferable in that the liquid permeation performance is good. On the other hand, when the porosity is 60% or less, the mechanical strength of the polyolefin microporous membrane is good, and this is preferable in terms of improving handling properties. Here, the porosity (ε) of the polyolefin microporous membrane is calculated by the following formula.
ε (%) = {1−Ws / (ds · t)} × 100
Ws: basis weight of polyolefin microporous membrane (g / m ² )
ds: true density of polyolefin (g / cm ³ )
t: Film thickness of microporous polyolefin membrane (μm)

(Permeability (water flow rate))
The polyolefin microporous membrane, which is the substrate for a liquid filter of the present invention, preferably has a water permeability of 0.10 to 2.90 ml / min · cm ² under a differential pressure of 90 kPa, and is preferably 0.10 to 2.40 ml / More preferably, it is min · cm ² . When the water permeability of the polyolefin microporous membrane is 0.10 ml / min · cm ² or more, not only can a sufficient water permeability be obtained as a liquid filter, but, for example, particles with a size of about 5 nm or more can be advanced. It is preferable because it is easy to collect. On the other hand, when the water permeability of the polyolefin microporous membrane is 2.90 ml / min · cm ² or less, for example, particles of about 100 nm or less can be highly easily collected. Not only is it easy to obtain sufficient performance, but also the stability of liquid feeding through the filter (for example, the stability of the power load to maintain a constant liquid feeding amount and the constant liquid feeding pressure (constant power load) ), Which is easy to obtain over the long term.

(Polyolefin)
The polyolefin microporous membrane that is the substrate for a liquid filter of the present invention is a microporous membrane configured to contain polyolefin. Here, the microporous membrane has a structure in which a large number of micropores are connected and these micropores are connected, and gas or liquid can pass from one surface to the other. Means a membrane. In the polyolefin microporous membrane, it is preferable that the polyolefin is contained in an amount of 90 parts by weight or more, and an additive such as an organic or inorganic filler or a surfactant is included as the balance so long as the effect of the present invention is not affected. Also good.

  Examples of the polyolefin include homopolymers or copolymers such as polyethylene, polypropylene, polybutylene, and polymethylpentene, or a mixture of one or more of these. Among these, polyethylene is preferable. As the polyethylene, high-density polyethylene, a mixture of high-density polyethylene and ultrahigh molecular weight polyethylene, and the like are suitable. Further, polyethylene and other components may be used in combination. Examples of components other than polyethylene include polypropylene, polybutylene, polymethylpentene, and a copolymer of polypropylene and polyethylene. Also, polyolefins having mutually different properties are used as polyolefins, that is, they are used in combination with polyolefins having poor compatibility and different degree of branching, in other words, different crystallinity, stretchability and molecular orientation. Also good.

Among the polyolefins used in the present invention, polyethylene can be particularly preferably used, and a polyethylene composition containing 5% by weight or more of ultrahigh molecular weight polyethylene having a weight average molecular weight of 900,000 or more is preferably used. Is more preferably 7% by weight or more, and particularly preferably a composition containing 13 to 80% by weight of ultrahigh molecular weight polyethylene. Further, by blending an appropriate amount of two or more kinds of polyethylene, there is an effect of forming a network network structure accompanying fibrillation at the time of stretching and increasing the generation rate of pores. The weight average molecular weight after blending two or more kinds of polyethylene is preferably 350,000 to 4.5 million. In particular, the ultra high molecular weight polyethylene having a weight average molecular weight of 900,000 or more and the high density polyethylene having a weight average molecular weight of 200,000 to 800,000 and a density of 0.92 to 0.96 g / cm ³ are mixed. In that case, the proportion of the high-density polyethylene in the polyethylene composition is preferably 95% by weight or less, more preferably 93% by weight or less, and 87 to 20% by weight. It is particularly preferred.

  The weight average molecular weight is determined by dissolving a sample of a polyolefin microporous membrane in o-dichlorobenzene by heating and using GPC (Waters Alliance GPC 2000 type, column; GMH6-HT and GMH6-HTL), column temperature of 135 ° C. It can be obtained by measuring under the condition of a flow rate of 1.0 mL / min.

[Liquid filter]
The above-described substrate for a liquid filter of the present invention can be used as a liquid filter after being processed into a cartridge shape after appropriately applying affinity treatment with a chemical solution. The liquid filter is an instrument for removing particles from a liquid to be treated that contains or may contain particles composed of organic substances and / or inorganic substances. The particles exist in a solid state or a gel state in the liquid to be treated. The present invention is suitable for removing fine particles of about 100 nm from very fine particles having a particle size of about several nm. The liquid filter can be used not only in the semiconductor manufacturing process but also in other manufacturing processes such as display manufacturing and polishing.

  As a substrate for a liquid filter, for example, a porous substrate such as polytetrafluoroethylene is well known. When the above-mentioned base material comprising the polyolefin microporous membrane of the present invention is used as a base material for a liquid filter, it has a good affinity for a chemical solution compared to a polytetrafluoroethylene porous base material. The process of imparting affinity to the chemical solution is easy, and when the filter cartridge is loaded in the filter housing and the chemical solution is filled in the filter, air can be trapped in the filter cartridge. In addition to the effect of improving the filtration yield of chemicals, the polyethylene resin itself does not contain halogen elements, so it is easy to handle used filter cartridges and reduce the environmental impact. .

[Production method of polyolefin microporous membrane]
The polyolefin microporous membrane which is the substrate for a liquid filter of the present invention can be preferably produced by the method shown below. That is,
(I) a step of preparing a solution containing a volatile solvent having a boiling point of less than 210 ° C. at least at atmospheric pressure in a solution containing a polyethylene composition and a solvent;
(II) melt-kneading this, extruding the resulting melt-kneaded product from a die, cooling and solidifying to obtain a gel-like molded product,
(III) a step of squeezing a part of the solvent from the gel-shaped molding in advance before stretching the gel-shaped molding in at least one direction;
(IV) a step of stretching the gel-like molded article in at least one direction;
(V) It can manufacture preferably by performing sequentially the process of extracting and washing a solvent from the inside of the stretched intermediate molded product.

In step (I), a solution containing a polyolefin composition and a solvent is prepared, but at least a solution containing a volatile solvent having a boiling point of less than 210 ° C. at atmospheric pressure is prepared. Here, the solution is preferably a thermoreversible sol-gel solution, that is, the polyolefin is dissolved in the solvent by heating to prepare a thermoreversible sol-gel solution. The volatile solvent having a boiling point of less than 210 ° C. at atmospheric pressure in step (I) is not particularly limited as long as it can sufficiently swell or dissolve polyolefin, but tetralin, ethylene glycol, decalin, toluene, xylene Liquid solvents such as diethyltriamine, ethylenediamine, dimethylsulfoxide, hexane and the like are preferable, and these may be used alone or in combination of two or more. Of these, decalin and xylene are preferred.
In addition, in the preparation of this solution, in addition to the volatile solvent having a boiling point of less than 210 ° C. at the atmospheric pressure, a non-volatile solvent having a boiling point of 210 ° C. or more such as liquid paraffin, paraffin oil, mineral oil, castor oil is included. It can also be made.

  In the solution of the step (I), from the viewpoint of controlling the liquid permeation performance of the polyolefin microporous membrane and the removal performance as a filter medium, the concentration of the polyolefin composition is preferably 10 to 45% by weight, more preferably 12 to 40% by weight is preferred. When the concentration of the polyolefin composition is lowered, the mechanical strength tends to be lowered, so that the handling property is deteriorated, and further, the frequency of occurrence of cutting in the production of the polyolefin microporous membrane tends to increase. Moreover, when the concentration of the polyolefin composition is increased, pores tend not to be formed.

  In step (II), the solution prepared in step (I) is melt-kneaded, and the obtained melt-kneaded product is extruded from a die and cooled and solidified to obtain a gel-like molded product. Preferably, an extrudate is obtained by extrusion from a die in a temperature range of the melting point of the polyolefin composition to the melting point + 65 ° C., and then the extrudate is cooled to obtain a gel-like molded product.

  The molded product is preferably shaped into a sheet. Cooling may be quenching to an aqueous solution or an organic solvent, or casting to a cooled metal roll, but generally a method by quenching to a volatile solvent used during water or sol-gel solution is used. Is done. The cooling temperature is preferably 10 to 40 ° C. In addition, it is preferable to prepare a gel-like sheet | seat, providing a water flow in the surface layer of a water bath, and preventing the mixed solvent which is discharge | released from the sheet | seat gelatinized in the water bath and floats on the water surface from adhering to a sheet | seat again.

  Step (III) is a step of pre-squeezing a part of the solvent in the gel-shaped molding before stretching the gel-shaped molding in at least one direction. The step (III) can be suitably carried out by applying pressure to the surface of the gel-like molded product by, for example, passing the gap between the upper and lower two belts or rollers. The amount of solvent to be squeezed out needs to be adjusted depending on the liquid permeation performance required for the polyolefin microporous membrane and the removal performance of the filtration target, but the adjustment is done by the pressing pressure between the upper and lower belts and rollers and the temperature of the squeezing process. , It can be adjusted to an appropriate range depending on the number of presses. In addition, it is preferable to adjust so that the pressure which a gel-shaped molding receives may be 0.1-2.0 MPa when performing with planar objects, such as a belt, and when performing with a roller etc., 2-45 kgf / m. It is preferable to carry out. The squeezing temperature is preferably 40 to 100 ° C. Moreover, since the number of times of pressing depends on the allowable space of the equipment, it can be implemented without any particular limitation. If necessary, one or more stages of preheating may be performed before squeezing out the solvent to remove a part of the volatile solvent from the sheet. In that case, the preheating temperature is preferably 50 to 100 ° C.

  Step (IV) is a step of stretching the gel-like molded product in at least one direction. Here, the stretching in step (IV) is preferably biaxial stretching, and sequential biaxial stretching in which longitudinal stretching and lateral stretching are separately performed, and simultaneous biaxial stretching in which longitudinal stretching and lateral stretching are simultaneously performed are suitable. Can be used. Also, a method of stretching a plurality of times in the longitudinal direction and then stretching in the transverse direction, a method of stretching in the longitudinal direction and stretching a plurality of times in the transverse direction, and further sequentially or biaxially stretching once or a plurality of times in the longitudinal direction and / or the transverse direction. A method of stretching is also preferred.

  The draw ratio (the product of the longitudinal draw ratio and the transverse draw ratio) is preferably 40 to 120 times, more preferably 50 to, from the viewpoint of controlling the liquid permeation performance of the polyolefin microporous membrane and the removal performance of the filtration target. 100 times. Increasing the draw ratio tends to increase the frequency of cutting in the production of a polyolefin microporous membrane. Moreover, when the draw ratio is lowered, the thickness unevenness tends to increase. As described above, the stretching is preferably carried out with the solvent remaining in a suitable state. The stretching temperature is preferably 80 to 125 ° C.

  Further, a heat setting treatment may be performed after the stretching step (IV). The heat setting temperature is preferably 110 to 143 ° C. from the viewpoint of controlling the liquid permeation performance of the polyolefin microporous membrane and the removal performance of the filtration target. When the heat setting temperature is increased, the removal performance of the filtration object of the polyolefin microporous membrane tends to be remarkably deteriorated, and when the heat setting temperature is lowered, the liquid permeation performance tends to be significantly decreased.

Step (V) is a step of extracting and washing the solvent from the inside of the stretched intermediate molded product. Here, in order to extract the solvent from the inside of the stretched intermediate molded product (stretched film), the step (V) is preferably washed with a halogenated hydrocarbon such as methylene chloride or a hydrocarbon solvent such as hexane. . In the case of washing by immersing in a tank in which a solvent is stored, it is preferable to take 20 to 150 seconds to obtain a polyolefin microporous membrane with a small amount of elution, more preferably 30 to 150 seconds. Especially preferably, it is 30 to 120 seconds. Furthermore, in order to further increase the effect of washing, the tank is divided into several stages, the washing solvent is poured from the downstream side of the polyolefin microporous film conveyance process, and the washing solvent is flowed toward the upstream side of the process conveyance, It is preferable that the purity of the cleaning solvent in the downstream tank is higher than that in the upstream layer. Further, depending on the required performance of the polyolefin microporous film, heat setting may be performed by annealing. In addition, it is preferable to implement annealing processing at 50-150 degreeC from viewpoints, such as the conveyance property in a process, and 50-140 degreeC is further more preferable.
By this production method, it is possible to provide a polyolefin microporous membrane having both excellent liquid permeation performance and excellent filtration target removal performance and low elution.

  Examples of the present invention, comparative examples, and various measurement methods will be described below, but the present invention is not limited to these examples.

[Measuring method]
(thickness)
The film thickness of the polyolefin microporous film was measured at 20 points with a contact-type film thickness meter (manufactured by Mitutoyo Corporation), and the average value was obtained. Here, the contact terminal used was a cylindrical one having a bottom surface of 0.5 cm in diameter. The measurement pressure was 0.1N.

(Bubble point)
The bubble point of the polyolefin microporous membrane was measured using ethanol as a measurement solvent in accordance with ASTM E-128-61.

(Heat shrinkage)
The width after the polyolefin microporous membrane is cut into a size of 100 mm square so that each side is parallel to the longitudinal direction (MD) and the width direction (TD) and left in an oven adjusted to a temperature of 130 ° C. for 1 hour. The shrinkage rate (dimensional change rate) in the direction (TD) was calculated by the following formula.
Thermal shrinkage (%) = (| Dimension before heat treatment−Dimension after heat treatment | / Dimension before heat treatment) × 100

(Hole closing temperature)
The polyolefin microporous membrane substrate cut out in a methanol solution in which 3% by weight of a nonionic surfactant (manufactured by Kao Corporation; Emulgen 210P) was dissolved was immersed and air-dried. The air-dried sample was sandwiched between SUS plates of a predetermined size and impregnated with 1M LiBF ₄ propylene carbonate / ethylene carbonate (1/1 weight ratio) as an electrolyte. This was enclosed in a 2032 type coin cell. Take the lead from the coin cell, put it in an oven with a thermocouple, and increase the resistance of the cell at an amplitude of 10 mV and a frequency of 100 kHz by the AC impedance method while raising the temperature at a rate of temperature rise of 1.6 ° C / min. It was measured. The temperature when the resistance value reached 1000 Ω · cm ² was defined as the hole closing temperature.

(Compression rate (Change rate of film thickness before and after pressing))
A sample microporous polyolefin membrane was cut into 47 mm × 100 mm and pressed at 2 MPa for 30 seconds under a temperature condition of 70 ° C. Measure the film thickness (before t) of the sample before pressing, measure the film thickness (after t) of the sample left at 25 ° C. for 30 minutes after pressing, and calculate the compression rate from the following formula from these film thicknesses did. In addition, the film thickness of the sample was measured at an ambient temperature of 24 ± 2 ° C. using a contact-type film thickness meter (Mitutoyo Corporation terminal diameter: 0.5 cm, terminal shape: cylinder, measurement pressure: 0.1 N).
Compression rate = {(before t−after t) / before t} × 100 (%)

(Porosity)
The porosity (ε) of the polyolefin microporous membrane was calculated by the following formula.
ε (%) = {1−Ws / (ds · t)} × 100
Ws: basis weight of polyolefin microporous membrane (g / m ² )
ds: true density of polyolefin (g / cm ³ )
t: Film thickness of microporous polyolefin membrane (μm)
The basis weight of the polyolefin microporous membrane was obtained by cutting a sample into 10 cm × 10 cm, measuring its mass, and dividing the mass by the area.

(Permeability (water flow rate))
The polyolefin microporous membrane was previously immersed in ethanol and dried at room temperature. This polyolefin microporous membrane was set in a stainless steel liquid permeable cell (liquid permeable area Scm ² ) having a diameter of 37 mm. After the polyolefin microporous membrane on the liquid permeable cell is wetted with a small amount (0.5 ml) of ethanol, pure water V (100 ml) preliminarily weighed at a differential pressure of 90 kPa is permeated so that the whole amount of pure water permeates. The time Tl (min) required for the measurement was measured. From the amount of pure water and the time required for permeation of pure water, the water permeability Vs per unit time (min) and unit area (cm ² ) under a differential pressure of 90 kPa is calculated from the following formula, and this is the water permeation performance. (Ml / min · cm ² ). The measurement was performed in a temperature atmosphere at room temperature of 24 ° C.
Vs = V / (Tl × S)

(Collection performance)
100 ml of an aqueous solution containing any of the following particles (1) to (3) was filtered through a polyolefin microporous membrane at a differential pressure of 10 kPa. From the difference between the mass (M1) of 100 ml of the aqueous solution containing the particles before filtration and the mass (M2) of the filtrate that passed through the polyolefin microporous membrane, the collection rate of the particles can be calculated by the following (Formula 1) or (Formula 2). Asked. (Formula 1) is a formula for calculating the collection rate when the particles (1) are used. (Formula 2) is a calculation formula for the collection rate when the particles (2) or the particles (3) are used. The case where the collection rate was 90% or more was judged as the best (最 良), the case where it was 80% or more and less than 90% was judged as good (◯), and the case where it was less than 80% was judged as bad (×).
Particle (1) Gold colloid Average particle size 3nm Particle concentration 0.0045% by mass
Particle (2) Polystyrene particle Average particle diameter 30 nm Particle concentration 0.1% by mass
Particle (3) Polystyrene particle Average particle diameter 70 nm Particle concentration 0.1% by mass
Collection rate (%) = ((M1-M2) / (M1 × 45 × 10 ⁻⁶ )) × 100 (Formula 1)
Collection rate (%) = ((M1-M2) / (M1 × 0.1 × 10 ⁻² )) × 100 (Equation 2)

(Water permeability change rate (liquid feeding stability))
The polyolefin microporous membrane was previously immersed in ethanol and dried at room temperature. This polyolefin microporous membrane was set in a stainless steel liquid-permeable cell (liquid-permeable area Scm ² ) having a diameter of 37 mm with 5 sheets stacked at an interval of 0.5 mm, and a small amount of the polyolefin microporous membrane on the liquid-permeable cell ( After being wetted with 0.5 ml of ethanol, 200 ml of pure water was permeated under a differential pressure of 40 kPa, and the time (T1) required for the whole amount to permeate was measured. Then, the differential pressure state was immediately released. Subsequently, using the same sample, 200 ml of pure water was permeated under a differential pressure of 40 kPa, and the differential pressure was immediately released 100 times. The time (T100) required for the permeation of 200 ml of pure water at the 100th time was measured and calculated from the following equation to obtain the rate of change in water permeability (%). In addition, the case where the water permeability change rate was 10% or less was determined to be the best (◎), the case where it was more than 10% and 15% or less was good (◯), and the case where it was more than 15% was judged as bad (×).
Permeability change rate (%) = (T100−T1) / Tl × 100

(Elution resistance)
After the polyolefin microporous membrane was immersed in methylene chloride for a predetermined time, the polyolefin microporous membrane was removed, and the weight of the methylene chloride solution after immersion was measured. Separately, new methylene chloride having the same weight as the above-described measured weight was prepared, and after each methylene chloride was evaporated and the solvent was completely removed (dried), each weight was measured. Based on the weight increment after completely removing new methylene chloride, the ratio of the weight increment after drying the methylene chloride solution after immersing the polyolefin microporous membrane was calculated, and the ratio was less than 1.05 Elution resistance was judged to be good (no filtrate contamination, ◯), and when it exceeded 1.05 times, the elution resistance was judged to be poor (x).

Example 1
A polyethylene composition obtained by mixing 5 parts by weight of ultrahigh molecular weight polyethylene (PE1) having a weight average molecular weight of 4.6 million and 23 parts by weight of high density polyethylene (PE2) having a weight average molecular weight of 560,000 was used. A polyethylene solution was prepared by mixing 69 parts by weight of liquid paraffin and 3 parts by weight of decalin (decahydronaphthalene) prepared in advance so that the total concentration of the polyethylene resin was 28% by weight.
This polyethylene solution was extruded into a sheet form from a die at a temperature of 160 ° C., and then the extrudate was cooled in a water bath at 25 ° C., and a water flow was provided on the surface layer of the water bath, which was discharged from the sheet gelled in the water bath. Then, a gel-like sheet (base tape) was prepared while preventing the mixed solvent floating on the water surface from adhering to the sheet again. After the base tape was dried at 55 ° C. for 10 minutes and further at 95 ° C. for 10 minutes to remove decalin from the base tape, it was subsequently conveyed on a roller heated to 85 ° C. while applying a pressure of 20 kgf / m. Then, a part of the liquid paraffin was removed from the base tape. Thereafter, the base tape is stretched in the longitudinal direction at a temperature of 100 ° C. at a magnification of 5.8 times, subsequently stretched in the width direction at a temperature of 100 ° C. at a magnification of 14 times, and then immediately heat treated at 118 ° C. (heat setting). Went.
Next, liquid paraffin was extracted while immersing the base tape in a methylene chloride bath divided into two tanks for 30 seconds each. Note that the purity of the cleaning solvent is (low) first layer <second tank (high) when the side that starts immersion is the first tank and the side that ends immersion is the second tank. Thereafter, methylene chloride was removed by drying at 45 ° C., and a polyolefin microporous film was obtained by annealing treatment while being conveyed on a roller heated to 110 ° C.
The obtained polyolefin microporous membrane had excellent collection performance with a collection rate of colloidal gold particles having a particle size of 3 nm of 90% or more, and was excellent in liquid permeability and liquid feeding stability.
The production conditions are shown in Table 1, and the physical properties of the obtained polyolefin microporous film are shown in Table 2. The following examples and comparative examples are similarly shown in Tables 1 and 2.

(Example 2)
In Example 1, a polyethylene composition obtained by mixing 8 parts by weight of ultrahigh molecular weight polyethylene (PE1) having a weight average molecular weight of 4.6 million and 24 parts by weight of high density polyethylene (PE2) having a weight average molecular weight of 560,000 was used. The total concentration of the polyethylene resin is 32% by weight and mixed with 53 parts by weight of liquid paraffin prepared in advance and 15 parts by weight of decalin (decahydronaphthalene) to prepare a polyethylene solution and extrusion. A polyolefin microporous membrane was obtained in the same manner except that the gel-like sheet obtained by the above was stretched 4 times in the longitudinal direction and 15 times in the transverse direction.
The obtained polyolefin microporous membrane had excellent collection performance with a collection rate of colloidal gold particles having a particle size of 3 nm of 90% or more, and was excellent in liquid permeability and liquid feeding stability.

Example 3
A polyethylene composition obtained by mixing 14 parts by weight of ultrahigh molecular weight polyethylene (PE1) having a weight average molecular weight of 4.6 million and 6 parts by weight of high density polyethylene (PE2) having a weight average molecular weight of 560,000 was used. A polyethylene solution was prepared by mixing 55 parts by weight of liquid paraffin and 25 parts by weight of decalin (decahydronaphthalene) prepared in advance so that the concentration of the total amount of polyethylene resin was 20% by weight.
This polyethylene solution was extruded into a sheet form from a die at a temperature of 160 ° C., and then the extrudate was cooled in a water bath at 25 ° C., and a water flow was provided on the surface layer of the water bath, which was discharged from the sheet gelled in the water bath. Then, a gel-like sheet (base tape) was prepared while preventing the mixed solvent floating on the water surface from adhering to the sheet again. After the base tape was dried at 55 ° C. for 10 minutes and further at 95 ° C. for 10 minutes to remove decalin from the base tape, it was subsequently conveyed on a roller heated to 85 ° C. while applying a pressure of 20 kgf / m. Then, a part of the liquid paraffin was removed from the base tape. Thereafter, the base tape is stretched in the longitudinal direction at a temperature of 100 ° C. at a magnification of 5 times, subsequently stretched in the width direction at a temperature of 100 ° C. at a magnification of 14 times, and then immediately subjected to heat treatment (heat setting) at 128 ° C. It was.
Next, liquid paraffin was extracted while immersing the base tape in a methylene chloride bath divided into two tanks for 30 seconds each. Note that the purity of the cleaning solvent is (low) first layer <second tank (high) when the side that starts immersion is the first tank and the side that ends immersion is the second tank. Thereafter, methylene chloride was removed by drying at 45 ° C., and a polyolefin microporous film was obtained by annealing treatment while being conveyed on a roller heated to 110 ° C.
The resulting polyolefin microporous membrane has excellent collection performance with a collection rate of polystyrene particles having a particle size of 30 nm of 90% or more, and has excellent water permeability and liquid feeding stability (water permeability change rate 10). % Or less).

Example 4
In Example 3, using a polyethylene composition in which 20 parts by weight of ultrahigh molecular weight polyethylene (PE1) having a weight average molecular weight of 4.6 million and 5 parts by weight of high density polyethylene (PE2) having a weight average molecular weight of 560,000 were mixed. A polyethylene solution was prepared by mixing 50 parts by weight of liquid paraffin and 25 parts by weight of decalin (decahydronaphthalene) prepared in advance so that the concentration of the total amount of polyethylene resin was 25% by weight. This polyethylene solution was extruded in the same manner as in Example 3, and the resulting gel-like sheet (base tape) was heated and dried, and subsequently conveyed on a roller heated to 95 ° C. while applying a pressure of 10 kgf / m. A microporous polyolefin membrane was obtained in the same manner except that part of the liquid paraffin was removed from the sheet.
The obtained polyolefin microporous membrane has excellent collection performance with a collection rate of polystyrene particles having a particle size of 30 nm of 90% or more, and has excellent water permeability and liquid feeding stability (water permeability change rate 10%). Had the following):

(Example 5)
A polyethylene composition obtained by mixing 3 parts by weight of ultrahigh molecular weight polyethylene (PE1) having a weight average molecular weight of 4.6 million and 12 parts by weight of high density polyethylene (PE2) having a weight average molecular weight of 560,000 was used. A polyethylene solution was prepared by mixing 60 parts by weight of liquid paraffin and 25 parts by weight of decalin (decahydronaphthalene) prepared in advance so that the concentration of the total amount of polyethylene resin was 15% by weight.
This polyethylene solution was extruded into a sheet form from a die at a temperature of 160 ° C., and then the extrudate was cooled in a water bath at 25 ° C., and a water flow was provided on the surface layer of the water bath, which was discharged from the sheet gelled in the water bath. Then, a gel-like sheet (base tape) was prepared while preventing the mixed solvent floating on the water surface from adhering to the sheet again. After the base tape was dried at 55 ° C. for 10 minutes and further at 95 ° C. for 10 minutes to remove decalin from the sheet, it was continuously conveyed on a roller heated to 85 ° C. while applying a pressure of 20 kgf / m. A part of the liquid paraffin was removed from the gel sheet. Thereafter, the base tape is stretched in the longitudinal direction at a temperature of 100 ° C. at a magnification of 6 times, subsequently stretched in the width direction at a temperature of 100 ° C. at a magnification of 12 times, and then immediately subjected to heat treatment (heat setting) at 136 ° C. It was.
Next, liquid paraffin was extracted while being continuously immersed for 30 seconds in a methylene chloride bath divided into two tanks. Note that the purity of the cleaning solvent is (low) first layer <second tank (high) when the side that starts immersion is the first tank and the side that ends immersion is the second tank. Thereafter, methylene chloride was removed by drying at 45 ° C., and a polyolefin microporous film was obtained by annealing treatment while being conveyed on a roller heated to 110 ° C.
The obtained polyolefin microporous membrane has excellent collection performance with a collection rate of polystyrene particles having a particle size of 70 nm of 90% or more, and has excellent water permeability and liquid feeding stability (water permeability change rate 10). % Or less).

(Example 6)
A polyolefin microporous membrane was obtained in the same manner as in Example 5 except that the heat treatment (heat setting) temperature after biaxial stretching was 142 ° C.
The obtained polyolefin microporous membrane has excellent collection performance with a collection rate of polystyrene particles having a particle size of 70 nm of 80% or more, and has excellent water permeability and liquid feeding stability (water permeability change rate 10). % Or less).

(Example 7)
In Example 1, a polyolefin microporous film having a thickness of 5 μm was similarly prepared except that the discharge amount in the extrusion process was adjusted to approximately one half, and the heat treatment (heat setting) temperature after biaxial stretching was set to 124 ° C. Got.
The resulting polyolefin microporous membrane was a polyolefin microporous membrane having excellent collection performance with a collection rate of gold colloidal particles having a particle diameter of 3 nm of 80% or more and excellent liquid feeding stability. .

(Comparative Example 1)
In Example 5, a polyethylene composition obtained by mixing 0.5 parts by weight of ultrahigh molecular weight polyethylene (PE1) having a weight average molecular weight of 4.6 million and 4.5 parts by weight of high density polyethylene (PE2) having a weight average molecular weight of 560,000 Using a product, the total concentration of the polyethylene resin is adjusted to 5% by weight and mixed with 70 parts by weight of a liquid paraffin prepared in advance and 25 parts by weight of decalin (decahydronaphthalene). Prepared. Using this polyethylene solution, a polyolefin microporous membrane was obtained in the same manner as in Example 5 except that the heat treatment (heat setting) temperature was 144 ° C.
The obtained polyolefin microporous membrane had a low bubble point, an excessively high water permeability, a collection rate of polystyrene particles having a particle size of 70 nm was less than 80%, and the collection performance was insufficient.

(Comparative Example 2)
In Example 1, a polyethylene composition obtained by mixing 32 parts by weight of ultrahigh molecular weight polyethylene (PE1) having a weight average molecular weight of 4.6 million and 8 parts by weight of high density polyethylene (PE2) having a weight average molecular weight of 560,000 was used. The polyethylene resin is mixed with 60 parts by weight of liquid paraffin prepared in advance so that the total concentration of the polyethylene resin is 40% by weight to prepare a polyethylene solution, and the heat treatment (heat setting) temperature after stretching is 105. A polyolefin microporous membrane was obtained in the same manner except that the temperature was changed to ° C.
The obtained polyolefin microporous membrane had an excessively high bubble point and insufficient liquid feeding stability, and was not suitable as a liquid filter substrate.

(Comparative Example 3)
In Example 1, a gel sheet extruded by adjusting the discharge amount in the extrusion process to approximately one half was stretched in the longitudinal direction at a temperature of 100 ° C. at a magnification of 7 times, and subsequently in the width direction at a temperature of 100. A polyolefin microporous film having a thickness of 3 μm was obtained in the same manner as in Example 1 except that the film was stretched at a magnification of 20 times at ° C.
The obtained polyolefin microporous membrane had a collection rate of polystyrene particles having a particle diameter of 70 nm of less than 80%, and the collection performance was insufficient. Further, the handling property was poor, the film was easily broken, the liquid feeding stability was insufficient, and it was not suitable as a liquid filter substrate.

(Comparative Example 4)
In Example 1, except that the extruded sheet was stretched in the longitudinal direction at a temperature of 100 ° C. at a magnification of 4 times, and subsequently stretched in the width direction at a temperature of 100 ° C. at a magnification of 8 times, as in Example 1, A polyolefin microporous film having a thickness of 20 μm was obtained.
The obtained polyolefin microporous membrane has an excellent collection performance with a collection rate of polystyrene particles having a particle size of 70 nm of 90% or more, but on the other hand, the bubble point is excessively high and the liquid feeding stability is poor. It was sufficient and was not suitable as a substrate for a liquid filter.

Claims (6)

  A substrate for a liquid filter comprising a polyolefin microporous membrane, wherein the polyolefin microporous membrane has a thickness of 4 to 16 μm, and a bubble point of the polyolefin microporous membrane is 0.40 MPa or more and 0.80 MPa or less, Base material for liquid filters.   2. The liquid filter substrate according to claim 1, wherein the polyolefin microporous membrane has a heat shrinkage in the width direction of 20% or more after heat treatment at 130 ° C. for 1 hour.   3. The liquid filter substrate according to claim 1, wherein the polyolefin microporous membrane has a pore closing temperature higher than 140 ° C. 3.   The base material for liquid filters in any one of Claims 1-3 whose compression rate of the said polyolefin microporous film is less than 15%.   The base material for liquid filters in any one of Claims 1-4 whose porosity of the said polyolefin microporous film is 46 to 60%. The base material for liquid filters in any one of Claims 1-5 whose water permeability of the said polyolefin microporous membrane is 0.10-2.90ml / min * cm < ² >.