KR20070031330A - Hollow-fiber porous water filtration membrane of vinylidene fluoride resin and process for producing the same - Google Patents

Abstract

The present invention provides a hollow fiber membrane-like melt extrudate of a composition obtained by mixing a vinylidene fluoride-based resin having a relatively large weight average molecular weight of 300,000 or more with a plasticizer and a good solvent of a vinylidene fluoride-based resin from the outer side. Highly crystallized vinylide fluoride represented by crystal melting enthalpy of 58 J / g or more by excessively crystallizing the vinylidene fluoride-based resin in the process of contacting and cooling the inert cooling liquid with respect to the vinylidene fluoride-based resin and solidifying A den-based resin hollow fiber porous membrane is prepared. The hollow fiber porous membrane obtained in the present invention is excellent in mechanical strength represented by tensile strength and breaking elongation, is excellent in chemical resistance, and is effectively used as a microfiltration membrane.

Vinylidene fluoride resin hollow fiber porous filter membrane, high crystallinity, chemical resistance, microfiltration membrane

Description

Polyvinylidene fluoride resin hollow fiber porous filtration membrane and its manufacturing method {HOLLOW-FIBER POROUS WATER FILTRATION MEMBRANE OF VINYLIDENE FLUORIDE RESIN AND PROCESS FOR PRODUCING THE SAME}

TECHNICAL FIELD The present invention relates to a porous membrane used as a microfiltration membrane for water treatment, and more particularly, to a vinylidene fluoride resin hollow fiber porous filtration membrane having excellent mechanical strength and excellent chemical resistance, and a method for producing the same.

Since vinylidene fluoride resin is excellent in chemical resistance, heat resistance, and mechanical strength, application to a porous membrane for separation has been studied. When used for water treatment applications, in particular for constant water production or sewage treatment applications, hollow fiber porous membranes are easy to use to increase the membrane area per volume of the filtration device.

For this reason, the porous membrane has a certain degree of tensile strength and elongation at break so that the seal is not broken by physical cleaning such as back washing or air bubbling, which is performed not only during the filtration operation but also to remove the clogging of the membrane over time. Required.

In addition, since physical cleaning is insufficient in cleaning effect for clogging with organic substances, backwashing or periodical chemical cleaning with water containing sodium hypochlorite or ozone is performed. In addition, filtration may be performed by adding sodium hypochlorite or ozone to raw water (supply water). Accordingly, the porous membrane is required to have high chemical resistance so that mechanical strength (tensile strength, elongation at break) is not lowered by these chemicals over a long period of time.

Regarding the improvement in the mechanical strength and chemical resistance of the vinylidene fluoride resin porous film, Japanese Unexamined Patent Application Publication No. Hei 11-152366 discloses that a porous film using a vinylidene fluoride homopolymer is a weak film. In the case where a copolymer is used, the mechanical strength is insufficient unless the content of the vinylidene fluoride monomer unit is significantly reduced, but in this case, the chemical resistance is described as inferior.

Japanese Unexamined Patent Publication No. 2000-218267 discloses that a porous film having excellent ozone oxidation resistance is a film having a maximum peak temperature (of melting point) of 160 ° C. or more obtained by DSC, and the higher the highest peak temperature, the more ozone oxidation. It is described as having excellent resistance. In addition, the porous membrane made of PVDF resin having a weight average molecular weight of less than 100,000 is described as having an extremely low tensile elongation at break.

In these documents, it is suggested that the vinylidene fluoride resin porous film has (1) higher crystallinity, superior chemical resistance, and (2) mechanical strength is improved by using a high molecular weight polymer.

The research group of the inventors of the present invention relates to a method for producing a vinylidene fluoride-based resin porous membrane. A method of melt extruding, preferably with a good solvent, cooling one side with a chill roll having a temperature of 150 ° C. or lower, forming the other side by air cooling, and then extracting the plasticizer (Japan Patent Publication No. 7-173323). However, the higher the molecular weight, the lower the fluidity of the molecular chain at the time of crystallization and the lower the crystallinity tends to be. Therefore, a sufficient high crystallinity porous film was not obtained.

Therefore, it is a fact that the vinylidene fluoride resin porous film excellent in both mechanical strength and chemical resistance through high molecular weight and high crystallinity is not obtained.

The main object of the present invention is to use a vinylidene fluoride resin hollow fiber porous filtration membrane which is excellent in both mechanical strength and chemical resistance by using a high molecular weight vinylidene fluoride resin and to increase the crystallinity as much as possible. It is to offer.

The present inventors have studied for the above-mentioned purposes, and as a result, even if a high molecular weight vinylidene fluoride-based resin which is essential for improving the mechanical strength of the resulting hollow fiber porous filtration membrane is used, the high molecular weight vinyl fluoride after the hollow fiber film formation When appropriate cooling conditions are given in a state in which the mobility of the molecular chain of the lithium resin is improved, the degree of crystallinity can be improved, and the vinylidene fluoride resin hollow fiber porous water that satisfies both excellent mechanical strength and chemical resistance can be achieved. It was found that a filtration membrane was obtained and the present invention was reached.

That is, the vinylidene fluoride resin hollow fiber porous filtration membrane of the present invention is composed of a vinylidene fluoride resin having a weight average molecular weight of 300,000 or more, and has a crystal melting enthalpy of 58 J measured by differential scanning thermal analysis (DSC). It is characterized by having a high degree of crystallinity represented by / g or more.

Moreover, the manufacturing method of the vinylidene fluoride resin hollow fiber porous filtration film of this invention is a total amount of the good solvent of a plasticizer and a vinylidene fluoride resin with respect to 100 weight part of vinylidene fluoride resins whose weight average molecular weight is 300,000 or more. The composition obtained by adding so that the ratio of the good solvent of vinylidene fluoride-type resin to 100-300 weight part and also the total amount (100 weight%) of the good solvent of a plasticizer and vinylidene fluoride system resin will be 8 to 22 weight%. Is melt-extruded into a film form, and it cools with the liquid inactive with respect to vinylidene fluoride system resin from the outer surface, and solidifies and forms a film, and then extracts and removes a plasticizer and a good solvent.

In the manufacturing method of the vinylidene fluoride resin hollow fiber porous filtration membrane of this invention, the crystallinity degree of the vinylidene fluoride-type resin in the product hollow fiber porous film obtained is improved, using the high molecular weight vinylidene fluoride system resin. Since the vinylidene fluoride resin coexists with the good solvent and the plasticizer in a specific ratio in the hollow fiber membrane-like material after melt extrusion, the high mobility of vinylidene fluoride resin polymer molecules necessary to provide high crystallinity by rearrangement It is believed that the reason is that a moderately gentle cooling condition suitable for rearrangement crystallization was given by contact with a liquid cooling medium (cooling liquid) inert to the vinylidene fluoride resin from the outer surface of the hollow fiber membrane in that state. do.

Best Mode for Carrying Out the Invention

Hereinafter, the vinylidene fluoride resin hollow fiber porous filtration membrane of this invention is demonstrated in order according to the manufacturing method of this invention which is its preferable manufacturing method.

(Vinylidene fluoride resin)

In the present invention, a vinylidene fluoride resin having a weight average molecular weight (Mw) of 300,000 or more is used as the main film raw material. It is preferable that Mw is 300,000-600,000. If Mw is less than 300,000, the mechanical strength of the porous film obtained will become small. Moreover, when Mw exceeds 600,000, the phase separation structure of vinylidene fluoride system resin and a plasticizer will become excessively fine, and there exists a tendency for the water permeation amount at the time of using the obtained hollow fiber porous membrane as a precision receiving membrane.

In the present invention, as the vinylidene fluoride resin, a homopolymer of vinylidene fluoride, that is, a polyvinylidene fluoride, a copolymer with another copolymerizable monomer, or a mixture thereof is used. As a monomer copolymerizable with vinylidene fluoride-type resin, 1 type, or 2 or more types, such as tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, trifluoroethylene, and vinyl fluoride, can be used. It is preferable that vinylidene fluoride system resin contains 70 mol% or more of vinylidene fluoride as a structural unit. Especially, since mechanical strength and chemical-resistance are high, it is preferable to use the homopolymer which consists of 100 mol% of vinylidene fluoride.

The relatively high molecular weight vinylidene fluoride resin as described above is preferably obtained by emulsion polymerization or suspension polymerization, particularly preferably by suspension polymerization.

The vinylidene fluoride resin which forms the hollow fiber porous filtration membrane of the present invention has a relatively large molecular weight of 300,000 or more as described above, and has a relatively large molecular weight as well as the original melting point of resin Tm 2 (° C.) by DSC measurement. It is preferable that the difference Tm2-Tc between the crystallization temperature and Tc (° C) has good crystal properties represented by 32 ° C or less, more preferably 30 ° C or less.

Here, resin original melting point Tm2 (degreeC) is distinguished from melting | fusing point Tm1 (degreeC) measured by adding obtained sample resin or resin which forms a porous film as it is to the temperature rising process by DSC as it is. That is, the generally obtained vinylidene fluoride-based resin exhibits a melting point Tm1 (° C) different from the resin's original melting point Tm2 (° C) by thermal and mechanical histories received during the production process or the heat molding process thereof. The original melting point Tm2 (° C) of the resin is the melting point (endothermic peak due to crystal melting) that is found again in the DSC temperature rising process after the obtained sample resin is first subjected to a predetermined elevated temperature cycle to remove heat and mechanical history. Temperature), and the detail of the measuring method is described before describing the Example mentioned later.

Although the conditions of Tm2-Tc≤32 ° C representing the crystallization characteristics of the vinylidene fluoride-based resin preferably used in the present invention can be achieved by, for example, lowering Tm2 by copolymerization, in this case, it is produced. The tendency for the chemical resistance of sclera to fall is recognized. More preferably, 70-98 weight% of vinylidene fluoride-type resins whose weight average molecular weights (Mw) are 200,000-600,000 are made into matrix (main body) resin, On the other hand, Mw is 1.8 times or more, Preferably it is 2 times or more It is achieved by using the vinylidene fluoride resin mixture obtained by adding 2-30 weight% of high molecular weight vinylidene fluoride resins for crystal characteristic modification of 1.2 million or less. According to this method, the crystallization temperature Tc can be raised significantly without changing the crystal melting point of the matrix resin alone (preferably represented by Tm2 in the range of 170 to 180 ° C). More specifically, by raising Tc, it is possible to accelerate the solidification of the vinylidene fluoride-based resin from the inside of the membrane to the inside of the membrane at the time of preferential cooling at the inside and the outside of the membrane, which is slower than the membrane surface. Can suppress growth. Tc becomes like this. Preferably it is 143 degreeC or more.

If the Mw of the high molecular weight vinylidene fluoride resin is less than 1.8 times the Mw of the matrix resin, it is difficult to sufficiently suppress the formation of the spherical particle structure, while if it is 1.2 million or more, it is difficult to disperse uniformly in the matrix resin.

If the amount of the high molecular weight vinylidene fluoride resin is less than 2% by weight, the effect of suppressing the formation of the spherical particle structure is insufficient. On the other hand, if the content exceeds 30% by weight, the phase separation structure of the vinylidene fluoride resin and the plasticizer is excessive. It tends to become fine and the water permeability of the film tends to be lowered.

According to the present invention, a plasticizer and a good solvent of vinylidene fluoride-based resin are added to the vinylidene fluoride-based resin to form a raw material composition for film formation.

(Plasticizer)

As a plasticizer, Aliphatic polyester which consists of dibasic acid and glycol generally, For example, Adipic acid type-polyesters, such as adipic acid- propylene glycol type | system | group, adipic acid-1, 3- butylene glycol type | system | group; Sebacic acid polyester, such as sebacic-propylene glycol type | system | group; Azelaic-acid polyester, such as azelaic acid propylene glycol system and azelaic acid- 1, 3- butylene glycol system, etc. are used.

(Good solvent)

Moreover, as a good solvent of vinylidene fluoride system resin, the solvent which can melt | dissolve vinylidene fluoride system resin in the temperature range of 20-250 degreeC is used, For example, N-methylpyrrolidone, dimethylformamide, dimethyl Acetamide, dimethyl sulfoxide, methyl ethyl ketone, acetone, tetrahydrofuran, dioxane, ethyl acetate, propylene carbonate, cyclohexane, methyl isobutyl ketone, dimethyl phthalate, and mixed solvents thereof. Especially, N-methylpyrrolidone (NMP) is preferable from stability at high temperature.

(Composition)

The raw material composition for forming the hollow fiber membrane is preferably 100 to 300 parts by weight in total amount of the good solvent of the plasticizer and vinylidene fluoride resin as described above with respect to 100 parts by weight of vinylidene fluoride resin. It is obtained by addition-mixing so that the ratio of the good solvent to the total amount (100 weight%) of a good solvent may be 8-22 weight%.

When there are too few plasticizers, since the porosity will become low, the water permeation amount of the hollow fiber filtered membrane obtained will fall. In addition, when too much, the porosity becomes too large, and mechanical strength falls.

When there are too few good solvents, polyvinylidene fluoride system resin and a plasticizer cannot be mixed uniformly, or time will be required for mixing. In addition, when excess, the porosity suitable for the addition amount of a plasticizer is not obtained. In other words, efficient pore formation is inhibited by extraction of the plasticizer.

Both the plasticizer and the good solvent have an effect of reducing the viscosity of the melt extrusion composition, and generally act to some extent.

(Mixing, melting extrusion)

The melt extrusion composition is generally extruded from a hollow nozzle into a hollow fiber membrane at a temperature of 140 to 270 ° C, preferably 150 to 200 ° C. Therefore, as long as a homogeneous composition in the above temperature range is finally obtained, the mixing and melting forms of the vinylidene fluoride resin, the plasticizer and the good solvent are arbitrary. According to one of the preferred embodiments for obtaining such a composition, a twin screw kneading extruder is used, vinylidene fluoride resin is fed upstream of the extruder, a mixture of plasticizer and good solvent is fed downstream, and passed through an extruder To a homogeneous mixture until discharged. This twin-screw extruder can be divided into a plurality of blocks along its longitudinal axis direction to enable independent temperature control, and appropriate temperature control is achieved by the contents of the passages in each site.

(Cooling)

According to the method of the present invention, the melt-extruded hollow fiber membrane-like material is cooled and solidified from its outer surface side by a liquid (cooling liquid) inert to the vinylidene fluoride resin. As the cooling liquid, any liquid inert to the vinylidene fluoride resin (ie, non-reactive and non-solvent) is used, but water is preferably used. Cooling is performed by passing a hollow fiber membrane extruded from a nozzle in the cooling liquid bath. The temperature of the cooling liquid is 5 to 120 ° C., which can be selected in a fairly wide temperature range, but is preferably in the range of 10 to 100 ° C., particularly preferably 30 to 80 ° C.

(extraction)

The cooled and solidified hollow fiber membrane-like substance is then introduced into the extraction liquid bath, and the plasticizer and the good solvent are extracted and removed. The extract is not particularly limited as long as the plasticizer and the good solvent can be dissolved without dissolving the vinylidene fluoride resin. For example, a polar solvent having a boiling point of about 30 to 100 ° C. such as dichloromethane and 1,1,1-trichloroethane is suitable for chlorinated hydrocarbons such as methanol and isopropyl alcohol as alcohols.

The hollow fiber membrane-like material after the extraction is the most basic aspect of the improved vinylidene fluoride resin hollow fiber porous filter membrane having improved mechanical strength and chemical resistance.

(Heat treatment)

It is preferable to increase the crystallinity by heat-treating the hollow fiber membrane-like material after extraction for 1 second to 3600 seconds, preferably 3 seconds to 900 seconds at a temperature in the range of 80 to 160 ° C, preferably 100 to 140 ° C. The improvement of the crystallinity degree by this heat treatment is also preferable for the improvement of extending | stretching operability which is carried out preferably.

(Extension)

That is, it is preferable to stretch the hollow fiber membrane-like material after the extraction, to increase the porosity and the pore size and to improve the elongation. It is preferable to perform extending | stretching generally as uniaxial stretching to the longitudinal direction of a hollow fiber membrane-like substance by roller pair etc. which differ in circumferential speed. This means that in order to match the porosity and elongation of the vinylidene fluoride resin porous film of the present invention, it is preferable that a microstructure in which stretched fibrils and unstretched nodes appear alternately along the stretching direction is preferred. Because it is known. The draw ratio is appropriately 1.2 to 4.0 times, particularly about 1.4 to 3.0 times.

(Eluent treatment)

It is more preferable to apply the vinylidene fluoride resin hollow fiber porous membrane after stretching to the immersion treatment with an eluent. This is because the characteristics of the hollow fiber porous membrane of the present invention are not inherently impaired by this eluent treatment, and the water permeation rate is significantly increased. As the eluent, an alkaline liquid, an acid liquid or an extract of a plasticizer is used.

The reason why the water permeation rate of the hollow fiber porous membrane is significantly increased by the eluent treatment is not necessarily obvious, but it is assumed that the plasticizer remaining in the microporous wall enlarged by stretching is exposed and is efficiently removed by the eluent treatment. do. The alkali and the acid as the eluent are understood to have an action of promoting the elution and removal by decomposing and solubilizing the polyester used as the plasticizer of the vinylidene fluoride resin.

Therefore, as the alkaline liquid, a pH of 12 or more, more preferably 13 or more, is preferably used in water or a water / alcohol solution of a strong base such as sodium hydroxide, potassium hydroxide, calcium hydroxide or the like. On the other hand, as the acid solution, a water or water / alcohol solution of strong acid such as hydrochloric acid, sulfuric acid or phosphoric acid has a pH of 4 or less, more preferably 3 or less, particularly preferably 2 or less.

In addition, the extract of the plasticizer is not particularly limited as long as it is capable of dissolving the plasticizer without dissolving the polyvinylidene fluoride resin in the same manner as used before stretching. For example, as alcohols, a polar solvent having a boiling point of about 30 to 100 ° C such as dichloromethane and 1,1,1-trichloromethane is suitable for chlorinated hydrocarbons such as methanol and isopropyl alcohol.

The eluent treatment is performed by immersing the hollow fiber porous membrane after stretching as necessary in the eluent for 10 seconds to 6 hours at a temperature of about 5 to 100 ° C. after preliminary immersion for improving the lyophilic property. When performing an eluent process under heating, it is preferable to carry out in the state which fixed to prevent shrinkage of a hollow fiber porous membrane.

(Vinylidene fluoride resin hollow fiber porous membrane)

The vinylidene fluoride resin hollow fiber porous membrane of the present invention obtained as described above is characterized by having a high degree of crystallinity represented by a crystal melting enthalpy of 58 J / g or more measured by DSC. Crystal enthalpy of fusion is preferably 60 J / g or more. As a result, the high chemical resistance represented by 90% or more of tensile strength retention after immersion in the sodium hypochlorite aqueous solution mentioned later and 90% or more of tensile breaking elongation is obtained as a practical characteristic.

According to a preferred embodiment, according to the vinylidene fluoride resin hollow fiber porous membrane of the present invention obtained through the stretching step, the porosity is generally 55 to 90%, preferably 60 to 85%, particularly preferably 65 to A characteristic of 80%, a tensile strength of 5 MPa or more, and an elongation at break of 5% or more can be obtained, and a water permeability of 5 m 3 / m 2 · day · 100 kPa or more can be obtained at the time of use as a water permeation treatment film. The thickness is usually in the range of about 5 to 800 m, preferably 50 to 600 m, particularly preferably 150 to 500 m. The outer diameter of the hollow porous membrane is suitably about 0.3 to 3 mm, particularly about 1 to 3 mm.

In addition, the vinylidene fluoride resin porous film of the present invention obtained through stretching is characterized in that, as a fine structure, a crystal alignment portion and a crystal non-alignment portion (random alignment portion) are recognized by an X-ray diffraction method. It is understood that they correspond to the stretched fibrillated portion and the unstretched node portion, respectively.

(X-ray diffraction method)

In more detail, the X-ray-diffraction characteristic of the hollow fiber membrane described in this specification is based on the measurement result by the following measuring methods.

The half divided along the longitudinal direction of the hollow fiber membrane is attached to the sample stage so that the longitudinal direction is vertical, and X-rays are incident perpendicularly to the longitudinal direction. The X-ray generator uses "Rotaplex 200RB" manufactured by Rigaku Denki Co., Ltd., and uses an X-ray source as CuKα ray that passed a Ni filter at 30 kV-100 mA. Using an imaging plate (" BAS-SR127 " manufactured by Fuji-Sashing Film Co., Ltd.), diffraction images are taken at a distance of 60 mm between the sample-imaging plates.

As a result, the mixture of the crystal alignment portion and the crystal non-alignment portion in the hollow fiber porous film of the present invention is diffracted on the meridian at the diffraction angles 2θ = 20.1 ± 1 ° and 2θ = 23.0 ± 1 ° by the X-ray diffraction method. The intensity ratio is 1.1 or more, and the half width Δβ of the azimuth intensity distribution curve peak at 2θ = 20.1 ± 1 ° is quantitatively expressed as 80 ° or less.

Hereinafter, an Example and a comparative example demonstrate this invention further more concretely. In addition to the above-described X-ray diffraction characteristics, the characteristics of the description herein are attributable to measured values by the following methods.

(Weight average molecular weight (Mw))

The temperature was 40 using a GPC apparatus "GPC-900" manufactured by Nippon Bunko Corp., "Shodex KD-806M" manufactured by Showa Denko Corporation as a column, "Shodex KD-G" as a pre-column, and NMP as a solvent. It measured by the gel permeation chromatography (GPC) method as polystyrene conversion molecular weight at ° C and flow rate 10 ml / min.

(Crystal melting point Tm1, Tm2 and crystal melting enthalpy and crystallization temperature Tc)

10 mg of the sample resin was set in the measurement cell using a differential scanning calorimeter DSC7 manufactured by Perkin Elmer, and then heated up to 250 ° C. at a temperature increase rate of 10 ° C./min at a temperature of 30 ° C. in a nitrogen gas atmosphere, followed by 250 After holding at 1 ° C for 1 minute, the temperature was lowered from 250 ° C to 30 ° C at a temperature drop rate of 10 ° C / min to obtain a DSC curve. The endothermic peak temperature in the temperature rise process in this DSC curve was made into melting | fusing point Tm1 (degreeC), and the endotherm by the endothermic peak which provided Tm1 was made into crystal melting enthalpy. In addition, the exothermic peak temperature in temperature-fall process was made into crystallization temperature Tc (degreeC). Subsequently, after hold | maintaining for 1 minute at temperature 30 degreeC, it heated up to 250 degreeC at the temperature increase rate of 10 degreeC / min from 30 degreeC again, and measured the DSC curve. The endothermic peak temperature in this reheating DSC curve was set to the original resin melting point Tm 2 (° C.).

(Public rate)

The length, width, and thickness of the porous membrane (outer diameter and inner diameter in the case of hollow fiber) were measured to calculate the external volume V (cm 2) of the porous membrane, and the weight W (g) of the porous membrane was further measured. The public rate was calculated by 1.

Porosity (%) = (1-W / (V × ρ)) × 100

ρ: specific gravity of PVDF (= 1.78 g / cm 2)

Permeability (flux)

The hollow fiber membranes were immersed in ethanol for 15 minutes, and then immersed in water for 15 minutes to be hydrophilized, and then measured at a water temperature of 25 ° C. and a pressure difference of 100 kPa. The hollow fiber porous membrane set the test length (length of the part where filtration is performed) to 800 mm, and calculated the membrane area by the following formula (2) due to the outer diameter.

Membrane area (㎡) = outer diameter × π × test length

(Average pore size)

In accordance with ASTM F316-86 and ASTM E1294-89, the average pore diameter was measured by the half-drying method using the "pumpometer CFP-200AEX" by Porous Materials, Inc .. The test solution used perfluoropolyester (brand name "Galwick").

(Maximum pore)

In accordance with ASTM F316-86 and ASTM E1294-89, the maximum pore size was measured by the bubble point method using "Pumpometer CFP-200AEX" manufactured by Porous Materials, Inc. The test solution used perfluoropolyester (brand name "Galwick").

(Tensile strength and elongation at break)

Using a tensile tester ("RTM-100" manufactured by Toyo Baldwin Co., Ltd.), the measurement was performed under conditions of an initial sample length of 100 mm and a crosshead speed of 200 mm / min in an atmosphere of a temperature of 23 ° C. and a relative humidity of 50%.

(Chemical resistance)

The hollow fiber membranes were immersed in ethanol for 15 minutes, and then immersed in pure water for 15 minutes to be hydrophilized, and then immersed in a 5 wt% sodium hypochlorite aqueous solution maintained at a temperature of 50 ° C. for 4 weeks, followed by washing with water and drying, followed by tension. Strength and elongation at break were measured. Measurement conditions are the same as those for measuring the tensile strength and the elongation at break. Tensile strength retention (%) and elongation at break (%) were calculated by the following equations (3) and (4).

Tensile strength retention (%) = (Tensile strength after dipping (MPa) / Tensile strength before dipping (MPa)) × 100

Elongation at Break (%) = (Elongation after Break (MPa) / Elongation at Break before MPa (MPa)) × 100

(Example 1)

Polyvinylidene fluoride (PVDF) (powder) having a weight average molecular weight (Mw) of 4.92 × 10 ⁵ was used as the raw material vinylidene fluoride resin.

As aliphatic polyester, adipic acid polyester plasticizer ("PN-150" manufactured by Asahi Denka Kogyo Co., Ltd.), and N-methylpyrrolidone (NMP) as a solvent at room temperature in the ratio of 87.5 weight% / 12.5 weight%. The mixture B was obtained by stirring and mixing at the same time.

In the same direction rotational bite-type twin screw extruder ("BT-30" manufactured by Kogyo Kogyo Co., Ltd., screw diameter 30 mm, L / D = 48), the powder supply part installed at the position of 80 mm from the uppermost part of the cylinder is The raw material vinylidene fluoride resin (PVDF) was supplied, and the mixture B heated at a temperature of 100 ° C. in a liquid supply part installed at a position of 480 mm at the uppermost part of the cylinder was replaced at a ratio of PVDF / mixture B = 42.9 / 57.1 (wt%). The mixture was fed and kneaded at a barrel temperature of 210 ° C., and the mixture was extruded into a hollow fiber at a discharge amount of 13 g / min from a nozzle having a circular slit having an outer diameter of 7 mm and an inner diameter of 3.5 mm.

The extruded mixture is kept at 11 ° C. in the molten state and guided into a water bath having a water surface 140 mm away from the nozzle (ie, an air gap of 140 mm), cooled and solidified (retention time in the water bath: about 5 seconds). ), And was taken off at a take-up speed of 10 m / min, then this was wound up to obtain a first intermediate molded body.

Subsequently, the first intermediate molded body was immersed for 30 minutes at room temperature while vibrating in dichloromethane while being fixed so as not to shrink in the longitudinal direction, and then dichloromethane was changed to a new one and immersed under the same conditions again to give an aliphatic poly The ester and the solvent were extracted and then heated in an oven at a temperature of 120 ° C. in a fixed state for 1 hour to remove dichloromethane and heat treatment at the same time to obtain a second intermediate molded body.

Subsequently, the second intermediate molded product is stretched at a magnification of 2.0 times in the longitudinal direction at 25 ° C. of the ambient temperature, and then heated in a oven at a temperature of 100 ° C. for 1 hour to perform thermal fixation to form a polyvinylidene fluoride-based porous hollow body. Got four.

The production conditions and the physical properties of the obtained polyvinylidene fluoride-based porous hollow yarn are combined with the results of the following examples and comparative examples, and are shown in Table 1 below.

(Example 2)

A porous hollow fiber was obtained in the same manner as in Example 1 except that the air gap was 300 mm, the take-off speed after cooling and solidifying the melt-extruded product was 5 m / min, and the take-out draw ratio was 1.3 times.

(Example 3)

Principal (matrix) polyvinylidene fluoride (PVDF) (powder) having a weight average molecular weight (Mw) of 2.52 × 10 ⁵ and polyvinylidene fluoride (PVDF) (powder) for modifying crystal properties of Mw of 6.59 × 10 ⁵ , respectively. Mixing was carried out using a Henschel mixer at a ratio of 87.5 wt% and 12.5 wt%, to obtain a mixture A having a Mw of 3.03 × 10 ⁵ .

As an aliphatic polyester, adipic acid type polyester plasticizer ("PN-150" by Asahi Denka Kogyo Co., Ltd.) and N-methylpyrrolidone (NMP) are used as a solvent in the ratio of 87.5 weight% / 12.5 weight%. Mixture B was obtained by stirring at room temperature.

Mixing in a powder feed section using the same direction rotary bite-type twin screw extruder ("BT-30" manufactured by Plastic Kogyo Co., Ltd., screw diameter 30 mm, L / D = 48) at a position of 80 mm from the uppermost part of the cylinder A was supplied, and the mixture B heated to a temperature of 100 ° C. from a liquid supply installed at a position of 480 mm at the uppermost part of the cylinder was supplied at a ratio of mixture A / mixture B = 37.5 / 62.5 (wt%), and the barrel temperature was 210 ° C. The mixture was kneaded at and the mixture was extruded into a hollow fiber at a discharge amount of 13 g / min from a nozzle having a circular slit having an outer diameter of 7 mm and an inner diameter of 3.5 mm.

The extruded mixture is kept in a molten state at a temperature of 60 ° C., guided, cooled and solidified in a water bath having a water surface (ie, an air gap of 10 mm) at a position 10 mm from the nozzle (retention time in the water bath: about 10 Second), after taking at a pulling speed of 5 m / min, it was wound up to obtain a first intermediate molded body.

Subsequently, the first intermediate molded body was immersed for 30 minutes at room temperature while vibrating in dichloromethane while being fixed so as not to shrink in the longitudinal direction, and then dichloromethane was changed to a new one and immersed under the same conditions again to give an aliphatic poly The ester and the solvent were extracted and then heated in an oven at a temperature of 120 ° C. in a fixed state for 1 hour to remove dichloromethane and heat treatment at the same time to obtain a second intermediate molded body.

Subsequently, the second intermediate molded product is stretched at a magnification of 1.6 times in the longitudinal direction at 25 ° C. of the ambient temperature, and then heated in a oven at a temperature of 100 ° C. for 1 hour to perform thermal fixation to form a polyvinylidene fluoride-based porous hollow body. Got four.

(Example 4)

The porous hollow fiber obtained in Example 3 was immersed in ethanol for 15 minutes in a state of being fixed so as not to shrink in the longitudinal direction, and then immersed in pure water for 15 minutes to be hydrophilized, followed by 20% caustic soda maintained at a temperature of 70 ° C. It was immersed in an aqueous solution (pH 14) for 1 hour, and then washed with water, and then dried for 1 hour in a warm air oven maintained at a temperature of 60 ℃.

(Example 5)

A porous hollow fiber was obtained in the same manner as in Example 3 except that the cooling water bath temperature for cooling the melt extrudate was changed to 11 ° C. and the draw ratio was changed to 1.8 times.

(Example 6)

A porous hollow fiber was obtained in the same manner as in Example 5 except that the mixture A obtained by changing the mixing ratio of the main PVDF and the reforming PVDF to 50/50 (% by weight) was used to increase the air gap to 140 mm. .

(Example 7)

75% by weight of main polyvinylidene fluoride (PVDF) (powder) with a weight average molecular weight (Mw) of 2.52 × 10 ⁵ and polyvinylidene fluoride (PVDF) (powder) for crystal characteristic modification with a Mw of 6.91 × 10 ⁵ , respectively. And by using a Henschel mixer at a ratio of 25% by weight, to obtain a mixture A having a Mw of 3.67 × 10 ⁵ .

As the aliphatic polyester, adipic acid polyester plasticizer ("PN-150" manufactured by Asahi Denka Kogyo Co., Ltd.) and N-methylpyrrolidone (NMP) as solvents are respectively 87.5% by weight and 12.5% by weight. Mixture B was stirred and mixed at room temperature in proportion to obtain a mixture B.

From the powder feed part installed at the position of 80 mm in the uppermost part of a cylinder using the same direction rotary bite-type twin-screw extruder ("BT-30" by Plastic Kogyo Co., Ltd., screw diameter 30mm, L / D = 48) The mixture A was supplied, and the mixture B heated at a temperature of 100 ° C. in a liquid supply installed at a position of 480 mm at the uppermost part of the cylinder was supplied at a ratio of mixture A / mixture B = 40/60 (wt%), and the barrel The mixture was kneaded at a temperature of 220 ° C., and the mixture was extruded into a hollow fiber at a discharge amount of 9.8 g / min from a nozzle having a circular slit having an outer diameter of 7 mm and an inner diameter of 5 mm. At this time, air was injected into the hollow part of the chamber at a flow rate of 6.2 ml / minute from the vent provided at the nozzle center part.

The extruded mixture is kept in a molten state at a temperature of 60 ° C., guided, cooled and solidified in a water bath having a water surface (ie, an air gap of 30 mm) at a distance of 30 mm from the nozzle (retention time in the water bath: about 10 Second), after being taken out at a take-up speed of 5 m / min, this was wound up to obtain a first intermediate molded body. The inner diameter of this first intermediate molded body was 1.462 mm, and the outer diameter was 2.051 mm.

Subsequently, the first intermediate molded body was immersed for 30 minutes at room temperature while vibrating in dichloromethane while being fixed so as not to shrink in the longitudinal direction, and then dichloromethane was changed to a new one and immersed under the same conditions again to give an aliphatic poly The ester and the solvent were extracted and then heated in an oven at a temperature of 120 ° C. in a fixed state for 1 hour to remove dichloromethane and heat treatment at the same time to obtain a second intermediate molded body.

Subsequently, this 2nd intermediate | mold molded object is extended | stretched at the magnification of 1.8 times in the longitudinal direction at 25 degreeC of atmospheric temperature, and then immersed for 30 minutes at room temperature, applying vibration in dichloromethane in the state fixed so as not to shrink | contract in the longitudinal direction, Subsequently, dichloromethane was changed to a new one and immersed again under the same conditions, followed by heating in an oven at a temperature of 150 ° C. for 1 hour in a fixed state to remove dichloromethane and thermally fixing at the same time, thereby performing polyvinylidene fluoride-based porous hollow Got four.

(Example 8)

The main PVDF is changed to PVDF (powder) with Mw of 4.12 × 10 ⁵ and the modified PVDF is changed to PVDF (powder) with Mw of 9.36 × 10 ⁵ , and the mixing ratio of the main PVDF and the modified PVDF is 95/5 (weight % Using the mixture A obtained by using the mixture A obtained by changing the mixing ratio of the plasticizer and the good solvent to 82.5 / 17.5 (% by weight), and the feed ratio of the mixture A and the mixture B was 35.7 / 64.3 (weight %) And the porous hollow fiber was obtained like Example 7 except having changed the air gap to 150 mm and the draw ratio to 1.7 times.

(Example 9)

A porous hollow fiber was obtained in the same manner as in Example 8 except for changing the nozzle outer diameter to 5 mm, the nozzle inner diameter to 3.5 mm, and the air gap to 170 mm.

(Example 10)

A vinylidene fluoride resin porous hollow fiber was obtained in the same manner as in Example 9 except that the stretching and the eluent treatment were not performed.

(Comparative Example 1)

A vinylidene fluoride resin porous film was obtained in accordance with Example 3 of JP-A-7-173323. That is, 117 parts by weight of adipic acid-based polyester plasticizer (“PN-150”) and N-methylpyrrolidone 17 with respect to 100 parts by weight of PVDF having a weight average molecular weight of 4.40 × 10 ⁵ (inherent viscosity of 1.6 dl / g) The parts by weight were mixed at room temperature, followed by melt extrusion at a temperature of 200 ° C. to pelletize. The resulting pellets were melt extruded with a T-die having a width of 350 mm and a lip clearance of 1.4 mm, melt extruded into a film having a thickness of 50 μm at a temperature of 180 ° C., and one surface was opposed by a chill roll having a temperature of 60 ° C. A continuous film was formed while cooling the surface with an air knife. The film was immersed in methylene chloride for 10 minutes at room temperature while vibrating to extract the plasticizer, and dried and heat-treated at 100 ° C. for 30 minutes while being kept in order to prevent shrinkage to obtain a vinylidene fluoride resin porous film.

The vinylidene fluoride resin porous membrane according to Example 3 of JP-A-7-173323 obtained above was stretched 2.5 times in the longitudinal direction at an ambient temperature of 25 ° C, and then in an oven at a temperature of 100 ° C for 1 hour. It heated and heat-fixed, and the vinylidene fluoride resin porous film was obtained.

(Comparative Examples 2 and 3)

Measurement of physical properties is carried out using commercially available vinylidene fluoride resin porous membrane hollow fiber ("Microser USV-3003" manufactured by Asahi Kasei Co., Ltd. and "Toray Film HFM1010-X" manufactured by Toray Industries, Ltd.). It was.

Table 1 summarizes the composition, manufacturing conditions (already known) and physical properties of the vinylidene fluoride resin porous film obtained in the above Examples and Comparative Examples.

As shown in Table 1, the vinylidene fluoride resin hollow fiber porous membrane obtained through cooling on the outer surface with a cooling liquid in the state of coexistence with a good solvent has a crystal melting enthalpy of 58 J / compared with that obtained in the comparative example. It turns out that it is larger than g and shows the outstanding chemical-resistance as represented by 90% or more of tensile strength retention after immersion of the sodium hypochlorite aqueous solution, and 90% or more of elongation at break. Therefore, it is useful as a fine filtration membrane in addition to having excellent mechanical strength represented by tensile strength and elongation at break.

Claims (10)

Polyvinylidene fluoride, comprising a vinylidene fluoride resin having a weight average molecular weight of 300,000 or more, and having a high crystallinity represented by a crystal melting enthalpy of 58 J / g or more, as measured by DSC (differential scanning thermal analysis) Den-based resin hollow fiber porous filtration membrane. The vinylidene fluoride resin according to claim 1, wherein the weight average molecular weight is 300,000 to 600,000, and the difference Tm2-Tc between the resin's original melting point Tm2 (° C) and the crystallization temperature Tc (° C) is 32 ° C or less by DSC measurement. Vinylidene fluoride resin hollow fiber porous filtration membrane which consists of. The polyvinylidene fluoride resin hollow fiber porous filter membrane according to claim 1 or 2, wherein the vinylidene fluoride resin is made of a homopolymer of vinylidene fluoride. 100 to 300 parts by weight of the total amount of the good solvent of the plasticizer and the vinylidene fluoride resin, and the total amount of the good solvent of the plasticizer and the vinylidene fluoride resin, based on 100 parts by weight of the vinylidene fluoride resin having a weight average molecular weight of 300,000 or more ( 100 wt%) of the polyvinylidene fluoride-based resin in an amount of 8 to 22 wt%, and the obtained composition is melt-extruded into a hollow fiber membrane to be inert to the vinylidene fluoride-based resin. After cooling and solidifying film-forming with a phosphorus liquid, a plasticizer and a good solvent are extracted and removed, The manufacturing method of the vinylidene fluoride-type resin hollow fiber porous filtration membrane in any one of Claims 1-3 characterized by the above-mentioned. The method for producing a vinylidene fluoride resin hollow fiber porous filtration membrane according to claim 4, wherein the inert liquid temperature for cooling is 5 to 120 ° C. The manufacturing method of the vinylidene fluoride resin hollow fiber porous filtering membrane of Claim 5 including the process of extending | stretching the vinylidene fluoride resin hollow fiber membrane after plasticizer extraction removal. The manufacturing method of the vinylidene fluoride resin hollow fiber porous filtering membrane of Claim 6 including the process of processing the hollow fiber porous membrane after extending | stretching with an eluent. The method for producing a vinylidene fluoride resin hollow fiber porous filtering membrane according to claim 7, wherein the eluent is an alkaline liquid having a pH of 12 or more. The method for producing a vinylidene fluoride resin hollow fiber porous filtering membrane according to claim 7, wherein the eluent is an acid solution having a pH of 4 or less. The method for producing a vinylidene fluoride resin hollow fiber porous filtration membrane according to claim 7, wherein the eluent is an extract of a plasticizer.