JPWO2019168117A1 - Hydrophilized polyvinylidene fluoride microporous membrane - Google Patents

Abstract

［化２］

選択図 なしSummary Task Hydrophilization of polyvinylidene fluoride-based microporous membranes.
SOLUTION: The surface of a polyvinylidene fluoride-based microporous membrane containing N, N-dimethylacrylamide represented by the following formula (1) and a trifunctional acrylate compound represented by the following formula (2) as a polymerizable monomer. A coating composition used for hydrophilization, and a hydrophilized polyvinylidene fluoride-based microporous membrane produced using this coating composition.
[Chemical 1]

[Chemical 2]

No selection diagram

Description

The present invention relates to a novel hydrophilic agent for application to the surface of a polyvinylidene fluoride-based microporous membrane, and a novel polyvinylidene fluoride microporous membrane hydrophilized by the hydrophilic agent.

Since the microporous membrane (PVDF-based microporous membrane) mainly composed of polyvinylidene fluoride (PVDF) has excellent chemical resistance and heat resistance, separation and fixation of biochemical substances, wastewater treatment, gas treatment, dust treatment, and precision It is used as various filters for filtration and as an electrolyte membrane. As a method for producing a microporous membrane of PVDF, a non-solvent-induced phase separation method (a solution in which a polymer is dissolved in a good solvent thereof is prepared, and this solution is thinly applied to a glass plate or the like and immersed in a non-solvent is used. A method of inducing phase separation to obtain a microporous membrane) and the like. The applicant has already succeeded in producing a PVDF-based microporous membrane having an asymmetric three-dimensional structure in which relatively uniform pores are formed by a unique method (Patent Document 1).

On the other hand, hydrophobic PVDF has a low affinity for aqueous fluids and biological substances, so PVDF-based microporous membranes with a hydrophilic surface are used as liquid filters, biochemical / pharmaceutical separation membranes, and electrolyte membranes. Used. As an initial method of hydrophilization, surface coating with polyvinyl alcohol (PVA) and surface treatment with ethanol were used, but these methods had problems in the stability and durability of the hydrophilic surface. Therefore, the applicant proposed in Patent Document 2 a method of coating the surface of the PVDF-based microporous film with a SiO ₂ glass layer, but in this case as well, there is a problem in the adhesion between the glass layer and the PVDF-based microporous film. It was.

As another method for hydrophilizing the hydrophobic surface of the microporous membrane, a method of coating the surface of the microporous membrane with a crosslinked polymer has been proposed. As such crosslinked polymers, a large number of nitrogen-containing crosslinked polymers (Patent Document 3), acrylamide-based polymers (Patent Document 4), fluorine-containing crosslinked polymers (Patent Document 5), and the like have been proposed. However, the compatibility between the surface coating made of these crosslinked polymers and the individual microporous membranes varies, and it is difficult to say that the compatibility with the PVDF-based microporous membranes having an asymmetric three-dimensional structure devised by the applicant in particular is optimal. ..

International Publication No. 2014/054658 Pamphlet International Publication No. 2015/01333364 Pamphlet U.S. Pat. No. 5,629,084 Special Table 2004-532724 Japanese Unexamined Patent Publication No. 2016-9733

An object of the present invention is to provide a surface coating agent suitable for hydrophilization of a PVDF-based microporous membrane having an asymmetric three-dimensional structure.

The present inventors screened an effective monomer as a raw material for surface coating from a huge number of raw material candidates, and surprisingly, a PVDF-based microporous membrane that is attracting attention as a surface coating agent obtained by cross-linking and polymerizing only two kinds of monomers. It has been found to function as an excellent hydrophilic agent for. That is, the present invention is as follows.

[Invention 1] Contains a polymerizable monomer, a photopolymerization initiator, and a solvent.
As the polymerizable monomer, N, N-dimethylacrylamide represented by the following formula (1), which is more than 0.75% by mass and 3.0% by mass or less, and more than 0.25% by mass and 1.5% by mass or less. A coating composition used for hydrophilizing a microporous film, which comprises a trifunctional acrylate compound represented by the following formula (2).

[Invention 2] The coating composition of [Invention 1], wherein the microporous membrane is a fluoropolymer-based microporous membrane.

[Invention 3] The coating composition of [Invention 1], wherein the microporous membrane is a polyvinylidene fluoride-based microporous membrane.

[Invention 4] A polyvinylidene fluoride-based microporous membrane comprises a base material and a microporous membrane layer.
The microporous membrane layer is an asymmetric membrane made of PVDF resin, and is
The asymmetric film includes a skin layer in which micropores are formed and a support layer in which pores larger than the micropores constituting the skin layer are formed.
The skin layer has a plurality of spheres, and a plurality of linear binders extend in a three-dimensional direction from each of the spheres, and the adjacent spheres are connected to each other by the linear binders. To form a three-dimensional network structure with the spherical bodies as intersections.
The mode Lm (μm) of the pore diameter measured by the gas permeation method of the polyvinylidene fluoride-based microporous membrane satisfies (Condition 1): 0.10 ≦ Lm ≦ 0.20.
95% or more of the total pores of the polyvinylidene fluoride-based microporous membrane have a pore diameter L (μm) satisfying (Condition 2): (Lm × 0.85) ≦ L ≦ (Lm × 1.15).
The coating composition of [Invention 3].

[Invention 5] A hydrophilized microporous membrane composed of a crosslinked polymer layer and a microporous membrane.
The crosslinked polymer is composed of a unit derived from N, N-dimethylacrylamide represented by the following formula (1) and a unit derived from a trifunctional acrylate compound represented by the following formula (2).
In the crosslinked polymer, the unit derived from N, N-dimethylacrylamide is present in the range of 3.3 mol or more and 79 mol or less with respect to 1 mol of the unit derived from the trifunctional acrylate compound, and the microporous. The film consists of a base material and a microporous film layer,
Hydrophilized microporous membrane.

[Invention 6] The hydrophilized microporous membrane of [Invention 5], wherein the microporous membrane is a fluoropolymer-based microporous membrane.

[Invention 7] The hydrophilized microporous membrane of [Invention 5], wherein the microporous membrane is a polyvinylidene fluoride-based microporous membrane.

[Invention 8] A polyvinylidene fluoride-based microporous membrane comprises a base material and a microporous membrane layer.
The microporous membrane layer is an asymmetric membrane made of a polyvinylidene fluoride-based resin, and the asymmetric membrane has a skin layer in which micropores are formed and pores larger than the micropores constituting the skin layer. With a support layer
The skin layer has a plurality of spheres, and a plurality of linear binders extend in a three-dimensional direction from each of the spheres, and the adjacent spheres are connected to each other by the linear binders. To form a three-dimensional network structure with the spherical bodies as intersections.
The mode Lm (μm) of the pore diameter measured by the gas permeation method of the polyvinylidene fluoride-based microporous membrane satisfies (Condition 1): 0.10 ≦ Lm ≦ 0.20.
95% or more of the total pores of the polyvinylidene fluoride-based microporous membrane have a pore diameter L (μm) satisfying (Condition 2): (Lm × 0.85) ≦ L ≦ (Lm × 1.15).
The hydrophilized microporous membrane of [Invention 7].

The hydrophilized PVDF-based microporous membrane of the present invention is a novel industrial material having high surface hydrophilicity and high permeation efficiency.

The cross section of the PVDF-based microporous membrane 1 manufactured in the reference example is shown. The cross section of the PVDF-based microporous membrane used in the present invention is schematically shown. A scanning electron micrograph of the skin layer of the PVDF-based microporous membrane 1 manufactured in the reference example. A scanning electron micrograph of the skin layer of the PVDF-based microporous membrane 1 manufactured in the reference example. The relationship between the shear rate (1 / s) (x) and the reciprocal of the viscosity (1 / mPa · s) (y) of the raw material liquid used in the PVDF-based microporous membrane 2 of the reference example is shown. The graph which shows the pore diameter distribution of PVDF-based microporous membrane 2 of a reference example.

[Coating composition]
The coating composition of the present invention contains N, N-dimethylacrylamide represented by the following formula (1) and a trifunctional acrylate compound represented by the following formula (2) as a polymerizable monomer.

The total concentration of the polymerizable monomer contained in the coating composition of the present invention is adjusted within a range in which the surface of the PVDF-based microporous membrane can be sufficiently hydrophilized and the pores of the PVDF-based microporous membrane are not blocked. .. The N, N-dimethylacrylamide and the trifunctional acrylate compound are contained in the coating composition of the present invention in a state of being diluted with a solvent so that such a polymerization monomer concentration is achieved. The preferred solvent is ultrapure water.

That is, in the coating composition of the present invention, the N, N-dimethylacrylamide is contained in a concentration of more than 0.75% by mass and 3.0% by mass or less, preferably 1.5% by mass or more and 2.0% by mass or less. The above trifunctional acrylate compound is present at a concentration of more than 0.25% by mass and 1.5% by mass or less, preferably 0.50% by mass or more and 1.0% by mass or less.

That is, the coating composition of the present invention contains 3.3 mol or more and 79 mol or less, preferably 9.8 mol or more and 26 mol or less of the above N, N-dimethylacrylamide with respect to 1 mol of the trifunctional acrylate compound. Exists. The amount ratio of such a polymerizable monomer is the repeating unit ratio of the crosslinked polymer produced by photocuring of the coating composition of the present invention, that is, the unit derived from N, N-dimethylacrylamide constituting the crosslinked polymer and the above 3 The ratio with the unit derived from the functional acrylate compound is determined. By adjusting the amount ratio of the polymerizable monomer contained in the coating composition of the present invention in this way, the crosslinked polymer produced by curing the coating composition of the present invention appropriately maintains the permeability of the PVDF-based microporous film. The surface of the PVDF-based microporous film can be made hydrophilic in this state.

The coating composition of the present invention contains a photopolymerization initiator in addition to the above-mentioned polymerizable monomer and solvent. The photopolymerization initiator is not particularly limited. The IRGACURE® series provided by BASF can be used as such a photopolymerization initiator. Among them, the preferred photopolymerization initiator is an alkylphenone-based photopolymerization initiator such as the product "IRGACURE2959".

The coating composition of the present invention can further contain additives such as antioxidants and stabilizers in normal concentrations.

The method of mixing the polymerizable monomer with the solvent, the photopolymerization initiator, and any additive is not limited. Usually, the coating composition of the present invention is obtained by adding a polymerization initiator and an arbitrary additive to a polymerizable monomer solution dissolved in a solvent at a temperature of 15 ° C. or higher and 35 ° C. or lower and stirring the mixture.

[PVDF-based microporous membrane]
The coating composition is applied to the surface of a microporous membrane. The coating composition is cured on the surface of the microporous membrane, and the crosslinked polymer produced makes the surface of the microporous membrane hydrophilic. Such hydrophilicity can be expressed by any of general microporous membranes, but it is hydrophobic as an application target of the coating composition of the present invention, and positive hydrophilicization is desirable and necessary in practical use. Microporous membrane can be selected. As such a microporous membrane, one having a microporous membrane layer made of a fluorine-containing resin generally called "fluoropolymer" (referred to as "fluoropolymer-based microporous membrane" in the present invention) is preferable, and PVDF-based microporous membrane is particularly preferable. Membranes are preferred.

The preferable PVDF-based microporous membrane used in the present invention is composed of a base material and a microporous membrane layer, and the microporous membrane layer is an asymmetric membrane made of a PVDF-based resin. The asymmetric film includes a skin layer in which micropores are formed and a support layer in which pores larger than the micropores constituting the skin layer are formed. The skin layer has a plurality of spheres, and a plurality of linear binders extend in a three-dimensional direction from each of the spheres. The adjacent spheres are connected to each other by the linear binder to form a three-dimensional network structure with the spheres as intersections.

The "skin layer" refers to a layer having a thickness from the surface to the generation of macrovoids in the cross section of the microporous membrane, and the "support layer" is a value obtained by subtracting the thickness of the skin layer from the thickness of the entire microporous membrane. A layer of thickness. "Macrovoid" refers to a huge cavity that occurs in the support layer of a microporous membrane and has a minimum size of several μm and a maximum size approximately the same as the thickness of the support layer. The "sphere" is a sphere formed at the intersection of the three-dimensional network structure of the present invention, and is not limited to a perfect sphere, but also includes a substantially sphere.

A typical example of such an asymmetric three-dimensional structure can be visually understood with reference to the drawings.

FIG. 1 shows a cross section of the PVDF-based microporous membrane 1 manufactured in the reference example. FIG. 2 schematically represents FIG. As shown in FIGS. 1 and 2, a support layer 2 having holes is formed on the surface of the base material 3. On the surface of the support layer 2, a very thin skin layer 1 having pores smaller than the pores of the support layer is further formed. In this way, a microporous film layer composed of the skin layer 1 and the support layer 2 is formed on the surface of the base material 3. The PVDF-based microporous membrane of the present invention is a thin film formed by integrating the base material 3 and the microporous membrane layer.

3 and 4 are enlarged views of the skin layer 1 of the PVDF-based microporous membrane 1 manufactured in the reference example. The skin layer 1 is composed of a spherical body 4 and a binder 5 that connects the spherical bodies 4 to each other. A plurality of binders 5 extend from one sphere 4 in a three-dimensional direction, and each binder 5 is connected to another sphere 4. In this way, the skin layer 1 is formed of a large number of spherical bodies 4 arranged three-dimensionally and the binder 5.

In the PVDF-based microporous membrane of the present invention, the voids between the spheres are partitioned by a linear binder, so that the voids are far greater than those of the conventional microporous membrane without spheres. There are micropores with the same shape and size, and a skin layer with excellent permeability is formed. Since the linear binder bridges the spheres and prevents the spheres from falling off, it is possible to prevent the filter medium itself from being mixed into the filtrate. Since the spheres existing at the intersections of the three-dimensional network structure prevent deformation and breakage of the three-dimensional network structure due to the pressure of the fluid during filtration, the PVDF-based microporous membrane of the present invention has high pressure resistance.

In the PVDF-based microporous membrane of the present invention, the spheres preferably have an average particle size of 0.05 μm or more and 0.5 μm or less. The thickness of the skin layer of the microporous membrane of the present invention is preferably 0.5 μm or more and 10 μm or less, and the thickness of the support layer of the microporous membrane of the present invention is preferably 20 μm or more and 500 μm or less.

The PVDF-based resin, which is the main material of the PVDF-based microporous membrane of the present invention, is mechanically, thermally, and chemically stable and suitable as a filtration membrane material. The PVDF resin is also advantageous in that it is easier to process than other fluororesins. PVDF resin is easy to perform secondary processing such as cutting after primary processing and adhesion with other materials.

The PVDF-based microporous membrane of the present invention preferably has a particularly sharp pore size distribution. That is, in a preferable PVDF-based microporous membrane, the mode of the pore diameter measured by the gas permeation method is Lm (μm) satisfying (Condition 1): 0.10 ≦ Lm ≦ 0.20, and further. 95% or more of all pores have a pore diameter L (μm) satisfying (Condition 2) (Lm × 0.85) ≦ L ≦ (Lm × 1.15).

When the PVDF-based microporous membrane of the present invention shows a more preferable pore size distribution, the mode Lm (μm) of the pore size measured by the gas permeation method is (Condition 3): 0.11 ≦ Lm. ≦ 0.18 is satisfied, and 96% or more of the total number of pores satisfies (Condition 4) :( Lm × 0.85) ≦ L ≦ (Lm × 1.15).

The gas permeation method (palm poromometry) is one of the general methods for measuring the pore size distribution, and is used for materials in which pores form through holes, such as ceramics, hollow fibers, separators, non-woven fabrics, and membrane filters. It is most often used as a pore size distribution measurement method. In this method, the size of the penetrating pore is calculated as the neck diameter by utilizing the phenomenon that the gas flow is stagnant at the neck portion (the narrowest point) of the penetrating pore when the gas passes through the penetrating pore to be measured. .. In any measuring device (palm porometer) based on the gas permeation method, air filled with an organic solvent that is easy to get wet is sent into the through pores to be measured while gradually increasing its pressure, and the pressure of the inflow air and the exhaust air are measured. The pore size distribution is calculated from the relationship of the flow rate.

[Manufacturing method of PVDF-based microporous membrane]
Such a method for producing a PVDF-based microporous film of the present invention includes a step of preparing a raw material liquid containing a PVDF-based resin, a solvent, a porosifying agent, and water, and a step of applying the raw material liquid to a base film and solidifying it. The step of washing the film after the solidification of the raw material liquid is completed is included. Usually, dimethylacetamide is used as the solvent, and polyethylene glycol is used as the porosifying agent.

The method for producing a PVDF-based microporous membrane of the present invention is characterized in that water is added to a raw material liquid to be applied on a substrate in addition to a PVDF-based resin, a solvent, and a porosifying agent. By using such a raw material solution, uniform pores can be formed by the PVDF-based microporous membrane.

In order to achieve the above-mentioned asymmetric three-dimensional structure peculiar to the PVDF-based microporous membrane of the present invention, the PVDF-based resin having an appropriate viscoelasticity is preferable.

Such a suitable PVDF-based resin can be determined by the relationship between the shear rate of the good solvent solution and the solution viscosity. For this determination, the shear rate of a solution consisting of 10 parts by weight of PVDF resin, 10 parts by weight of polyethylene glycol, and 80 parts by weight of dimethylacetamide is plotted on the horizontal axis and the reciprocal of the solution viscosity is plotted on the vertical axis. If in the case of the following areas shear rate of 40 per second is approximated by a quadratic function, for example, as shown in FIG. 5, curve a secondary factor comprises an arc having a convex upward less than -10 ^-8 is obtained, this It can be determined that the PVDF-based resin is suitable for the PVDF-based microporous film of the present invention.

[Production Example 1 of PVDF Microporous Membrane]
A preferred method for producing the PVDF-based microporous film of the present invention is (step 1) a step of preparing a raw material solution containing a PVDF-based resin, dimethylacetamide as a solvent, polyethylene glycol as a porosifying agent, and water. (Step 2) A step of applying the raw material liquid obtained in Step 1 to a base film, (Step 3) A step of immersing the film obtained in Step 2 in water to solidify the raw material liquid, (Step 4) Step. It has a step of washing the film that has passed through step 3 with water.

(Step 1)
Step 1 is a step of preparing a raw material liquid containing a PVDF resin, a solvent, a porosifying agent, and water. The PVDF resin used here is a material for a microporous membrane. As the PVDF-based resin used in step 1, one or more kinds of vinylidene fluoride homopolymers, one or more kinds of vinylidene fluoride copolymers, and any mixture thereof are used. Generally, vinylidene fluoride copolymers are copolymers of vinylidene fluoride monomers and other fluoromonomers, such as vinyl fluoride, ethylene tetrafluoride, propylene hexafluoride, and ethylene trifluoride. A copolymer of one or more kinds of fluorine-based monomers selected from the above and vinylidene fluoride is used. The preferred resin as the PVDF-based resin used in step 1 is a vinylidene fluoride homopolymer, and it is desirable that the vinylidene fluoride homopolymer accounts for 50% by weight of the total PVDF-based resin. Further, a plurality of types of vinylidene fluoride homopolymers having different viscosities, molecular weights and the like can also be used.

In order to form a uniform coating film of the raw material liquid in which the raw material liquid is not absorbed by the base film in step 2 described later, generally, the weight average molecular weight (Mw) of such a PVDF resin is high. Those of 600,000 to 1.2 million are preferable.

The solvent used in step 1 is an organic solvent in which the PVDF resin can be dissolved to the extent that the PVDF resin can be dissolved in the solvent and the step 2 described later can be performed, and the solvent is mixed with water. means. Such solvents include polar solvents such as N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide, N, N-dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), methylethylketone, acetone, tetrahydrofuran. , Tetramethylurea, lower alkyl ketones such as trimethyl phosphate, esters, amides and the like can be used. These solvents may be mixed and used, and other organic solvents may be contained as long as the effects of the present invention are not impaired. Among such solvents, N-methyl-2-pyrrolidone, N, N-dimethylacetamide and N, N-dimethylformamide are preferable.

The porosifying agent used in step 1 is an organic medium that is soluble in the above solvent and soluble in water. In steps 3 and 4 described later, the porosifying agent and the solvent are transferred from the raw material liquid to water. On the other hand, since the PVDF resin is insoluble in water, it remains as a solid on the base film through steps 3 and 4, and finally forms a porous layer on the base film.

As the porosifying agent used in step 1, a water-soluble polymer such as polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinyl acetate, polyvinylpyrrolidone, or polyacrylic acid is used. The preferred porosifying agent is polyethylene glycol or polyvinylpyrrolidone, and the more preferable porosifying agent is polyethylene glycol. The most preferable porosifying agent has a weight average molecular weight in view of the pore shape of the obtained vinylidene fluoride microporous membrane. 200-1000 polyethylene glycol.

The amount ratio of the PVDF resin, the solvent, and the porosifying agent described above is generally 5 parts by weight to 20 parts by weight for the PVDF resin and 70 parts by weight for the solvent with respect to 100 parts by weight of the total amount thereof. It is adjusted so that 90 parts by weight and the porosifying agent occupy 0.5 parts by weight to 40 parts by weight.

In the present invention, it is an essential condition that water is used as a raw material for the raw material liquid in step 1 in addition to the PVDF resin, the solvent, and the porosifying agent. The water used in step 1 is preferably high-purity water, and generally water that can be obtained as pure water or ultrapure water is desirable. The amount of water added to the raw material liquid is generally 6.5% by weight or less, preferably 2% by weight to 6.5% by weight, more preferably 3% by weight to 5% by weight, based on the total amount of the raw material liquid. Adjusted to range.

The method of mixing the PVDF resin, solvent, porosifying agent, and water in step 1 is not particularly limited. For example, the temperature at which they are mixed may be any temperature as long as they are liquid and completely miscible, and is generally a temperature of room temperature or higher and 100 ° C. or lower. The raw material liquid thus obtained is used in the following step 2.

(Step 2)
Step 2 is a step of applying the raw material liquid obtained in Step 1 to the base film. The base film is required to have a function of promoting pore formation inside the raw material liquid in step 3 described later and further reinforcing the obtained PVDF-based microporous film. Therefore, as the base film, any material that is chemically stable, has mechanical strength, and has excellent affinity and adhesion to a raw material liquid, particularly a PVDF-based resin, can be used without limitation. As such a base film, for example, non-woven fabric, woven fabric, porous board or the like obtained by paper making, spunbond method, melt blow method or the like can be used, and the materials thereof are polyester, polyolefin, ceramic, cellulose and the like. Etc. are used. Among these base films, polypropylene spunbonded non-woven fabric is preferable because it has an excellent balance of flexibility, light weight, strength, heat resistance and the like. When a non-woven fabric is used, the basis weight is ^{preferably in the range of 15 g / m 2} or more and 150 g / m ² or less, and more preferably in the range of 30 g / m ² or more and 70 g / m ² or less. When the basis weight ^{exceeds 15 g / m 2} , the effect of providing the base material layer can be sufficiently obtained. Further, when the basis weight is less ^{than 150 g / m 2} , post-processing such as bending and heat bonding becomes easy.

The method of applying the raw material liquid to the base film is limited as long as the raw material liquid can be uniformly applied onto the base film in an amount that finally produces a PVDF-based microporous film having a thickness of 10 μm or more and 500 μm or less. Instead, for example, various coating devices such as a roll coater, a die coater, and a lip coater, and various film applicators are selected and used according to the area and length of the base film. Step 2 is generally performed at room temperature.

When the base film is a small piece, place the base film on a smooth coating table, fix it with an appropriate tool, and apply the raw material solution uniformly on the film. In this case, the raw material liquid is applied to each base film, and the base film coated with the raw material liquid is immediately transferred to the container for which step 3 described later is performed.

When the base film is long and typically takes the form of being wound into a roll, the wound base film is pulled out from the end and unfolded, and the unfolded base film is obtained. It is carried into a place where step 2 is performed under a constant tension or a constant speed by a transport mechanism such as a roll. The coated portion is maintained flat, and the raw material liquid is uniformly coated on the surface of the base film that continuously passes through the coated portion by various coating devices. The base film coated with the raw material liquid, which is carried out from the coating portion, is immediately transported to a place where step 3 described later is performed.

(Step 3)
Step 3 is a step of immersing the film obtained in Step 2 in water to solidify the raw material liquid. This solidification reaction starts when the raw material liquid on the film obtained in step 2 comes into contact with water, and the water-soluble component in the raw material liquid, that is, the fraction mainly composed of the solvent and the porosifying agent becomes water. The transition completes the process by leaving and fixing the water-insoluble PVDF resin on the base film. As described above, the raw material liquid is generally 6.5% by weight or less, preferably 2% by weight or more and 6.5% by weight or less, and more preferably 3% by weight or more and 5% by weight or less with respect to the total amount of the raw material liquid. The water present inside also naturally elutes out of the film. With the transfer of the solvent and the porosifying agent into water, the PVDF-based resin solidifies while forming voids inside. This step 3 can also be called a porosity step or a phase transition step in the formation of the PVDF-based microporous membrane. The water used in step 3 is preferably of high purity, and generally water that can be obtained as pure water or ultrapure water is desirable.

In such a step 3, naturally, a container containing water is required to bring the film obtained in the step 2 into contact with water, but in the present invention, such a container containing water is used as a solidification tank. Called. As the solidification progresses in the solidification tank, water-soluble components, that is, fractions mainly composed of the above-mentioned solvent and porosifying agent, are transferred from the raw material liquid to the water in the solidification tank. Such an increase in the concentration of the water-soluble transition component or a rapid fluctuation may hinder the stable progress of the solidification reaction in step 3 and the repetition of step 3 with good reproducibility. Therefore, it is desirable to provide an appropriate means for maintaining the purity of the water in the solidification tank according to the scale of the solidification tank or the amount of water in the solidification tank.

When a PVDF-based microporous film having a thickness of 10 μm or more and 500 μm or less is formed on the above-mentioned base film, the time (solidification time) for immersing the base film coated with the raw material liquid in water is 30 seconds or more. It is preferably 1 minute or more and 10 minutes or less, and more preferably 2 minutes or more and 5 minutes or less. In order to generate as uniform pores as possible inside the PVDF resin, it is desirable to suppress the physical irritation on the surface of the film obtained in step 2 as much as possible during immersion in water. Therefore, in step 3, it is not preferable to stir or foam the water in the solidification tank. The water temperature at the time of performing the step 3 may be any temperature at which the solidification proceeds, and is generally room temperature.

When the film obtained in step 2 is a small piece, step 3 can be performed in a batch manner. Specifically, the film obtained in step 2 is allowed to stand in a state where the entire film is in contact with water in the solidification tank during the solidification time. The solidifying tank used in this case may be appropriately selected according to the shape of the film, and at the laboratory level, a stainless steel vat or a flat glass bowl is used. If the water is replaced for each batch of the solidification operation so that the purity of the water in the solidification tank does not fluctuate significantly depending on the components transferred from the raw material liquid, solidification can be performed with good reproducibility in each step 3.

When the raw material liquid is applied to a long base film in step 2, in step 3, the film obtained in step 2 is first continuously carried into a solidification tank using a transport means such as a roll, and then. During the solidification time, the film is passed through the water in the solidification tank so that the film comes into contact with water, and then the film is discharged from the solidification tank. In this way, solidification of the raw material liquid applied to the long film obtained in step 2 starts, progresses, and is completed. Appropriate drainage and water supply mechanisms can be attached to the solidification tank so that the purity of the water in the solidification tank does not fluctuate significantly. As such a mechanism, a sensor, a drainage pump, a water supply pump, or the like usually used in a chemical plant can be appropriately combined.

The film on which the surface raw material liquid has been solidified in step 3 is immediately transferred to a place where step 4 described later is performed.

(Step 4)
Step 4 is a step of washing the film that has undergone step 3 in water. The water used here is preferably of high purity as in step 3, and generally water that can be obtained as pure water or ultrapure water is desirable.

In such a step 4, naturally, a container filled with water for introducing the film that has undergone the step 3 is required, but in the present invention, such a container is called a washing tank. In order to enhance the cleaning effect, in the present invention, the film can be washed a plurality of times by using a plurality of washing tanks or by replacing the water in the washing tanks. Further, in the present invention, it is possible to attach a device for generating a water stream or air bubbles to the washing tank to wash the film while giving an appropriate stimulus. In this case, the water flow generating means can be designed by appropriately combining known drainage, water supply mechanism and stirring mechanism. Further, the bubble generator in this case is appropriately selected from means generally called an air diffuser or the like according to the scale of the washing tank. The strength of the water flow and bubbles is adjusted to such a strength that the PVDF resin pores on the surface of the film to be washed are not deformed. The flow path of the water flow and the density of the bubbles are adjusted so that the water flow and the bubbles come into uniform and continuous contact with the film in the washing tank. Also in step 4, in order to improve the cleaning efficiency, it is possible to make an appropriate means for maintaining the purity of the water in the cleaning tank.

In step 4, the temperature of the water in the washing tank may be any temperature as long as it can be washed without damaging the film, and is generally room temperature.

When processing a small piece of film in step 4, step 4 can be performed in a batch manner. Specifically, the film obtained in step 3 is allowed to stand in contact with water and bubbles in the washing tank during the washing time (bubble washing). The washing tank used in this case may be appropriately selected according to the shape of the film, and at the laboratory level, a stainless steel vat or a glass flat bowl is used. If the water is replaced for each washing batch so that the purity of the water in the washing tank does not fluctuate significantly depending on the components transferred from the film surface, the film can be washed with good reproducibility in each step 4.

When processing a long film in step 4, in step 4, the film discharged from the solidifying tank in step 3 is first continuously carried into the washing tank using a transport means such as a roll, and then. During the washing time, the film is passed through the water in the washing tank so that the film comes into contact with water and bubbles, and then the film is discharged from the washing tank (bubble washing). In this way, the water-soluble components remaining on the long film in the process of step 3 are efficiently removed. An appropriate water supply / drainage mechanism can be attached to the washing tank so that the purity of the water in the washing tank does not fluctuate significantly. As such a mechanism, a sensor, a drainage pump, a water supply pump, or the like usually used in a chemical plant can be appropriately combined.

The film that has completed step 4 is dried, wound, cut, and packed according to a conventional method and, if necessary. In this way, a PVDF-based microporous membrane that can be used as a filtration membrane or a separation membrane is completed.

[Production Example 2 of PVDF Microporous Membrane]
Instead of the step 4 of the above-mentioned production example 1, the step of cleaning the film through the step (step 4-1) step 3 in water and the step of cleaning the film through the step (step 4-2) step 4-1 in alcohol. The steps may be performed in this order.

(Step 4-1)
Step 4-1 is a step of cleaning the film that has undergone step 3 with air bubbles in water. In step 4-1 the water-soluble component in the raw material liquid remaining on the base film, that is, the fraction mainly composed of the solvent and the porosifying agent, is efficiently removed from the base film by applying bubble stimulation in water. To do. The water used here is preferably of high purity as in step 3, and generally water that can be obtained as pure water or ultrapure water is desirable.

In such a step 4-1 naturally, a container provided with a bubble generator for introducing the film that has undergone the step 3 and filled with water is required, but in the present invention, such a container is referred to as a first washing tank. Call. The bubble generator attached to the first cleaning tank is appropriately selected from means generally called an air diffuser or the like according to the scale of the first cleaning tank. The strength of the bubbles is adjusted to such a strength that the PVDF resin pores on the surface of the film to be washed are not deformed. The density of the bubbles is adjusted so that the bubbles are in uniform and continuous contact with the film in the first washing tank. In step 4-1 as well, in order to improve the cleaning efficiency, it is possible to make a suitable means for maintaining the purity of the water in the first cleaning tank.

In step 4-1 the temperature of the water in the first washing tank may be any temperature as long as it can be washed without damaging the film, and is generally room temperature. The time required for bubble cleaning in step 4-1, that is, the time for the film that has undergone step 3 to come into contact with water in the first cleaning tank is usually 1 minute or more, preferably 2 minutes or more and 20 minutes or less, and more preferably 4 Minutes or more and 10 minutes or less.

When processing a small piece of film in step 4-1 the process 4-1 can be performed in a batch manner. Specifically, the film obtained in step 3 is allowed to stand in a state where the entire film is in contact with water and air bubbles in the first cleaning tank during the cleaning time. The first washing tank used in this case may be appropriately selected according to the shape of the film, and at the laboratory level, a stainless steel vat or a flat glass bowl is used. If the water is replaced for each washing batch so that the purity of the water in the first washing tank does not fluctuate significantly depending on the components transferred from the film surface, the film can be washed with good reproducibility in each step 4-1. ..

When processing a long film in step 4-1 in step 4-1, first, the film discharged from the solidifying tank in step 3 is continuously transferred to the first washing tank by using a transport means such as a roll. Then, during the cleaning time, the film is passed through the water in the first cleaning tank so that the film comes into contact with water and bubbles, and then the film is discharged from the first cleaning tank. In this way, the water-soluble components remaining on the long film in the process of step 3 are efficiently removed. An appropriate water supply / drainage mechanism can be attached to the first washing tank so that the purity of the water in the first washing tank does not fluctuate significantly. As such a mechanism, a sensor, a drainage pump, a water supply pump, or the like usually used in a chemical plant can be appropriately combined.

The film that has been washed for a predetermined time in step 4-1 is immediately transferred to a place where step 4-2 described later is performed.

(Step 4-2)
Step 4-2 is a step of cleaning the film that has undergone step 4-1 with bubbles in alcohol. In step 4-2, the alcohol-soluble component in the raw material solution remaining on the base film, that is, the fraction mainly composed of the solvent and the porosifying agent, is efficiently stimulated with air bubbles in the base film. Remove from. As the alcohol used here, generally, a liquid lower alcohol having relatively high fluidity at room temperature, preferably ethanol, propanols, butanols, and most preferably isopropanol are used.

In such a step 4-2, of course, a container provided with a bubble generator for introducing the film that has undergone the step 4-1 and filled with the above alcohol is required, but in the present invention, such a container is used as a second container. It is called a washing tank. The bubble generator attached to the second cleaning tank is appropriately selected from means generally called an air diffuser or the like according to the scale of the second cleaning tank. The strength of the bubbles is adjusted to such a strength that the PVDF resin pores on the surface of the film to be washed are not deformed. The density of the bubbles is adjusted so that the bubbles are in uniform and continuous contact with the film in the second washing tank. In step 4-2 as well, in order to improve the cleaning efficiency, it is possible to make a suitable means for maintaining the purity of alcohol in the second cleaning tank.

In step 4-2, the temperature of the alcohol in the second washing tank may be a temperature that can be washed without damaging the film, and is generally room temperature. The time required for bubble cleaning in step 4-2, that is, the time for the film that has undergone step 3 to come into contact with alcohol in the second cleaning tank is usually 1 minute or more, preferably 5 minutes or more and 120 minutes or less, and more preferably 5. Minutes or more and 60 minutes or less.

When processing a small piece of film in step 4-2, step 4-2 can be performed in a batch manner. Specifically, the film obtained in step 4-1 is allowed to stand in a state where the entire film is in contact with alcohol and air bubbles in the second washing tank during the washing time. The second washing tank used in this case may be appropriately selected according to the shape of the film, and at the laboratory level, a stainless steel vat or a flat glass bowl is used. If the alcohol is replaced for each washing batch so that the purity of the alcohol in the second washing tank does not fluctuate significantly depending on the components transferred from the film surface, the film can be washed with good reproducibility in each step 4-2. ..

When processing a long film in step 4-2, in step 4-2, first, the film discharged from the first washing tank in step 4-1 is second-washed by using a conveying means such as a roll. It is continuously carried into the tank, and then, during the washing time, the film is passed through the alcohol in the second washing tank so that the film comes into contact with the alcohol and bubbles, and then this is passed from the second washing tank. Discharge. In this way, the alcohol-soluble component remaining on the long film at the end of step 4-1 is efficiently removed. An appropriate water supply / drainage mechanism can be attached to the second washing tank so that the purity of alcohol in the second washing tank does not fluctuate significantly. As such a mechanism, a sensor, a drainage pump, a water supply pump, or the like usually used in a chemical plant can be appropriately combined.

The film that has completed step 4-2 is dried, wound, cut, and packed according to a conventional method and, if necessary.

[Hydrophilicization of PVDF-based microporous membrane]
The hydrophilized PVDF-based microporous membrane of the present invention is produced by sequentially performing the following steps 5 to 7.
(Step 5) This is a step of bringing the coating composition into close contact with the surface of the PVDF-based microporous membrane. The PVDF-based microporous membrane is contacted or immersed in the coating composition in a batch or continuous manner, and the coating composition is uniformly adhered to the surface of the PVDF-based microporous membrane.

In the batch method, the PVDF-based microporous membrane is impregnated with the coating composition and then held by a support. Specifically, the PVDF-based microporous membrane impregnated with the coating composition is overlaid on a flat support (on the side of the lid) in a closed container having a transparent lid, and then the laminate is formed. The inside of the closed container is replaced with nitrogen in a stationary state.

In the continuous method, the long PVDF-based microporous membrane is sequentially brought into contact with the coating composition. Specifically, a state in which the PVDF-based microporous membrane is carried into a container in which the coating composition is sealed by a transport mechanism including a series of rolls, and the PVDF-based microporous membrane is immersed in the coating composition. The PVDF microporous membrane is moved for a certain period of time, and then the PVDF microporous membrane is carried out of the container.

(Step 6) In a step of irradiating the coating composition with light on the surface of the PVDF-based microporous membrane to form a layer of a crosslinked polymer composed of units derived from the polymerizable monomer on the surface of the PVDF-based microporous membrane. is there. Step 6 can also be performed in batch or continuous manner as in step 5.

In the batch method, the PVDF-based microporous membrane on the support is irradiated with ultraviolet rays. Specifically, in a state where the closed container is filled with nitrogen, the surface of the PVDF-based microporous film is irradiated with ultraviolet rays from the outside of the container through a transparent lid to complete the polymerization cross-linking reaction of the polymerizable monomer.

In the continuous method, the long object of the PVDF-based microporous membrane to which the coating composition is in close contact is irradiated with ultraviolet rays. Specifically, the PVDF-based microporous membrane carried out from the container of the coating composition is carried into an ultraviolet irradiation area and moved in this area for a certain period of time. By the time the PVDF microporous membrane is carried out from the ultraviolet irradiation area, the polymerization cross-linking reaction of the polymerizable monomer is completed on the surface of the PVDF microporous membrane.

(Step 7) This is a step of drying and cleaning the surface of the PVDF-based microporous membrane that has undergone the above step 6 to remove excess components. The step 7 can also be performed in a batch system or a continuous system in the same manner as in the steps 5 and 6.

In this way, a hydrophilized PVDF-based microporous membrane composed of a crosslinked polymer layer and a PVDF-based microporous membrane (PVDF-based microporous membrane of the present invention) can be obtained. This PVDF-based microporous membrane is dried, wound, cut, and packed according to a conventional method and as necessary.

[Reference example: Production of PVDF-based microporous membrane]
A PVDF-based microporous membrane was produced through the following steps.
(Step 1) The ratios of Alchema product "Kyner HSV900" as a PVDF resin, dimethylacetamide as a solvent, polyethylene glycol having a weight average molecular weight of 400 as a porosifying agent, and ultrapure water are shown in Table 1 (raw materials). The raw material liquid was produced by uniformly mixing with (% by weight based on the total amount of the liquid).

(Step 2) As the base film, a spunbonded non-woven fabric (“Eltus P03050” manufactured by Asahi Kasei Corporation) cut into a square of 20 cm × 20 cm was used. This base film was placed on a flat glass plate, and the raw material liquid was applied to the surface of the base film using a baker applicator so as to have a thickness of 250 μm.

(Step 3) As a solidification tank, a stainless steel vat containing 2 liters of ultrapure water was used. The film obtained in step 2 was placed in this solidification tank so that the water surface did not undulate, and the raw material liquid adhered to the base film was allowed to stand in the film solidification tank for 2 minutes while the entire film was immersed in water. The solidification of the film progressed and was completed.

(Step 4-1) 2.5 liters of ultrapure water is put into a beaker into which a ceramic air stone air diffuser is inserted, dry air is supplied from an external tank to the air diffuser, and the water is uniformly dried in the ultrapure water. A bubble of air was ejected. This was used for the first washing tank. The film that had undergone step 3 was placed in this first washing tank. The film was washed for 6 minutes with the entire surface of the film in uniform contact with water and air bubbles.

(Step 4-2) Put 2.5 liters of isopropanol in a beaker into which a ceramic air stone air diffuser is inserted, supply dry air to the air diffuser from an external tank, and uniformly create bubbles of dry air in the isopropanol. It spouted. This was used for the second washing tank. The film that had undergone step 4-1 was placed in this second washing tank, and the film was washed with isopropanol and bubbles in uniform contact with the entire surface of the film. After this, the film was air-dried.

The pore diameter of the PVDF-based microporous membrane thus obtained was measured by a gas permeation method. A PMI palm polo meter supplied by Seihwa Digital Image Co., Ltd. was used as the measuring device. Table 1 shows the mode of the pore diameter of the obtained PVDF-based microporous membrane: Lm (μm) and the percentage of pores having a lumen diameter within Lm ± 15% (%). FIG. 6 shows the pore size distribution of the PVDF-based microporous membrane 2 shown in Table 1.

[Manufacturing of coating composition]
As the trifunctional acrylate compound represented by the above formula (2), "NK ester (registered trademark) A-GLY-9E" manufactured by Shin-Nakamura Chemical Industry Co., Ltd. was used. IRGACURE2959 was used as the photopolymerization initiator. N-Isopropylacrylamide and N, N'-methylenebisacrylamide were used as the monomers for the control coating composition. The materials shown in Table 2 were mixed to prepare a coating composition. The coating compositions B, C, and D shown in Table 2 are products of the present invention, and the coating compositions A, E, F, and G are control products.

[Manufacture of PVDF-based microporous membrane (hydrophilization of PVDF-based microporous membrane)]
The coating composition and the PVDF-based microporous membrane were selected in the combinations shown in Table 3. The surface of the PVDF-based microporous membrane was coated with a crosslinked polymer layer by the following method.
(Step 5) The PVDF-based microporous membrane completed in Step 4-2 was immersed in the coating composition. A PVDF-based microporous film impregnated with a non-woven fabric support and a coating composition was loaded on the bottom surface of the stainless mesh of a nitrogen gas replacement box with a quartz glass lid in this order. Nitrogen gas was circulated in the box for 2 minutes, and the inside of the box was filled with nitrogen gas. The box was kept sealed after filling.

(Step 6) The coating composition was cured by irradiating ultraviolet rays from a light source (Light Hammer 10 (product name)) outside the box through the lid of the box.

(Step 7) The PVDF-based microporous membrane was taken out from the box, washed, and dried.

The following performance was measured for the hydrophilized PVDF-based microporous membrane thus obtained. The results are shown in Table 3.
(Water contact angle)
In order to confirm the hydrophilization effect, the water contact angle (°) of the surface of the obtained hydrophilic PVDF-based microporous membrane was measured. About 2.0 μL of water droplets were applied, and the contact angle (°) 0.5 seconds later was measured as the water contact angle.

(Water permeability)
A circular sheet having a diameter of 25 mm was cut out from the obtained microporous membrane. This sheet was set in a filter sheet holder having an effective filtration area of 3.5 cm ^2. 5 mL of ultrapure water was passed through the set sheet at a filtration pressure of 50 kPa, and the time from the start to the end of the passage of the ultrapure water was measured. The flow rate (water permeation amount) per filtration area of the sheet was determined by the following formula. The results are shown in Table 2. The larger the amount of water permeation, the lower the degree of closure of the pores and the higher the liquid filtration efficiency.

Permeability ( ^10-9 m ³ / m ² / Pa / sec) = Water flow (m ³ ) ÷ Effective filtration area (m ² ) ÷ Filtration pressure (Pa) ÷ Time (sec)

(Change in permeability)
The change in water permeability due to hydrophilicity was evaluated. The rate of change in hydraulic conductivity (%) defined by the following formula was calculated. As the water permeability of the non-hydrophilic PVDF-based microporous membrane, the value measured by moistening the PVDF-based microporous membrane 1 or 2 shown in Table 1 with alcohol was used.

Permeability rate of change (%) = | (Water permeability of non-hydrophilic PVDF microporous membrane)-(Water permeability of obtained microporous membrane) | ÷ (Water permeability of non-hydrophilic PVDF microporous membrane) × 100

The balance between the hydrophilicity indicated by the water contact angle value and the fluid permeability indicated by the water permeability and the rate of change in the water permeability was determined. Table 3 shows the results by "-" (one of them is particularly inferior and unbalanced) and "+" (both are moderately prepared and well-balanced).

As shown in Table 3, in the examples using the coating compositions B, C, and D of the present invention (Examples 2, 3, and 4), the PVDF-based microporous membrane was hydrophilized without significantly impairing the water permeability. .. The hydrophilized PVDF-based microporous membranes of the present invention as in Examples 2, 3 and 4 are novel in that they have a special crosslinked polymer layer, and have a good balance of hydrophilicity and fluid filterability.

The hydrophilized PVDF-based microporous membrane of the present invention is useful as a filtration membrane or a separation membrane for handling aqueous fluids and biological substances. Further, the hydrophilized PVDF-based microporous membrane of the present invention can also be used for a chemical holding material used for adhesive plasters, a surface material for sanitary materials, a separator for a battery, a polyvinylidene fluoride sheet having a large surface area and no components falling off, and the like. it can. The PVDF-based microporous membrane of the present invention is effective for applications requiring particularly high filter selectivity.

1 Skin layer 2 Support layer 3 Base film 4 Spherical body 5 Bonding material

Claims (8)

Contains polymerizable monomers, photopolymerization initiators, and solvents
As the polymerizable monomer, N, N-dimethylacrylamide represented by the following formula (1), which is more than 0.75% by mass and 3.0% by mass or less, and more than 0.25% by mass and 1.5% by mass or less. A coating composition used for hydrophilizing a microporous film, which comprises a trifunctional acrylate compound represented by the following formula (2).

The coating composition according to claim 1, wherein the microporous membrane is a fluoropolymer-based microporous membrane. The coating composition according to claim 1, wherein the microporous membrane is a polyvinylidene fluoride-based microporous membrane. The polyvinylidene fluoride-based microporous membrane consists of a base material and a microporous membrane layer.
The microporous membrane layer is an asymmetric membrane made of PVDF resin, and is
The asymmetric film includes a skin layer in which micropores are formed and a support layer in which pores larger than the micropores constituting the skin layer are formed.
The skin layer has a plurality of spheres, and a plurality of linear binders extend in a three-dimensional direction from each of the spheres, and the adjacent spheres are connected to each other by the linear binders. To form a three-dimensional network structure with the spherical bodies as intersections.
The mode Lm (μm) of the pore diameter measured by the gas permeation method of the polyvinylidene fluoride-based microporous membrane satisfies (Condition 1): 0.10 ≦ Lm ≦ 0.20.
95% or more of the total pores of the polyvinylidene fluoride-based microporous membrane have a pore diameter L (μm) satisfying (Condition 2): (Lm × 0.85) ≦ L ≦ (Lm × 1.15).
The coating composition according to claim 3. A hydrophilized microporous membrane composed of a crosslinked polymer layer and a microporous membrane.
The crosslinked polymer is composed of a unit derived from N, N-dimethylacrylamide represented by the following formula (1) and a unit derived from a trifunctional acrylate compound represented by the following formula (2).
In the crosslinked polymer, the unit derived from N, N-dimethylacrylamide is present in the range of 3.3 mol or more and 79 mol or less with respect to 1 mol of the unit derived from the trifunctional acrylate compound.

The microporous membrane is composed of a base material and a microporous membrane layer.
Hydrophilized microporous membrane. The hydrophilic microporous membrane according to claim 5, wherein the microporous membrane is a fluoropolymer-based microporous membrane. The hydrophilic microporous membrane according to claim 5, wherein the microporous membrane is a polyvinylidene fluoride-based microporous membrane. The polyvinylidene fluoride-based microporous membrane consists of a base material and a microporous membrane layer.
The microporous membrane layer is an asymmetric membrane made of a polyvinylidene fluoride-based resin, and the asymmetric membrane has a skin layer in which micropores are formed and pores larger than the micropores constituting the skin layer. With a support layer
The skin layer has a plurality of spheres, and a plurality of linear binders extend in a three-dimensional direction from each of the spheres, and the adjacent spheres are connected to each other by the linear binders. To form a three-dimensional network structure with the spherical bodies as intersections.
The mode Lm (μm) of the pore diameter measured by the gas permeation method of the polyvinylidene fluoride-based microporous membrane satisfies (Condition 1): 0.10 ≦ Lm ≦ 0.20.
95% or more of the total pores of the polyvinylidene fluoride-based microporous membrane have a pore diameter L (μm) satisfying (Condition 2): (Lm × 0.85) ≦ L ≦ (Lm × 1.15).
The hydrophilized microporous membrane according to claim 7.

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