JP2004331881A - Porous molded product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a porous molded product with a porous structure of an unsymmetrical pattern that has a precise pore structure at the outermost surface and a rough void structure in the inside. <P>SOLUTION: The method for manufacturing the porous molded product comprises a step of melt-blending a resin composition containing a thermoplastic resin and a pore forming agent and then molding it, a step of dipping the thermoplastic resin molding into a solvent S<SB>1</SB>capable of dissolving the thermoplastic resin and swelling the molding, and a step of removing the molding from the solvent S<SB>1</SB>and then dipping the molding into a solvent S<SB>2</SB>that can not dissolve the resin but can dissolve the pore forming agent. According to the method, the porous molded product with the porous structure of the unsymmetrical pattern that has the precise pore structure at the surface and the rough void structure in the inside is obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００５２】
実施例１〜４では、外表面の孔径（Ｄ_２）、内部の孔径（Ｄ_１）、機械強度において申し分ない性能を有する多孔成形体が得られた。
【００５３】
比較例１は、溶媒への浸漬時間が長すぎたため、熱可塑性樹脂が溶媒中に溶解、拡散してしまい、結果として多孔成形体の外観、形状を損なってしまった。また、多孔成形体表面に繊維状の熱可塑性樹脂が付着した状態となり、その後の利用は不可能と判断した。
【００５４】
比較例２〜４の多孔成形体は、機械強度は良好なものの、全体が均一孔を有するスポンジ構造となり、最表面に緻密な孔構造を形成させることができなかった。
【００５５】
比較例５、６の多孔体は、湿式相転換法で作成された多孔体であるため、機械強度が非常に小さかった。
【００５６】
【発明の効果】
本発明の製造方法によれば、表面に緻密な孔構造を有し、内部は粗大なボイド構造を有する非対称型の多孔構造を有する多孔成形体を得ることができる。
【図面の簡単な説明】
【図１】実施例１で得られた多孔体の最表面の電子顕微鏡写真（４０００倍）。
【図２】実施例１で得られた多孔体の内部構造の電子顕微鏡写真（５００倍）。
【図３】比較例１で得られた多孔体の最表面の電子顕微鏡写真（２０００倍）。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a porous molded body that can be used as a solid-liquid separation membrane, and a method for producing a porous molded body suitable for producing the same.
[0002]
[Prior art]
Conventionally, a wet phase inversion method has been employed as a method for producing a porous body having continuous pores, and a dense pore structure is formed on the outermost surface by selecting a resin, both solvents, a poor solvent, or film forming conditions. However, it is known that an asymmetric type porous structure having a coarse void structure inside can be obtained.
[0003]
However, in this method, since the resin is precipitated from the state of the dope solution in which the resin is dissolved in the good solvent to form the porous body, the density of the resin in the resin portion in the porous body becomes coarse, and the resulting result is obtained. There is a problem that the mechanical strength of the porous body is very weak, and only a brittle porous body can be obtained.
[0004]
On the other hand, although there are very few applications as a separation membrane, a porous material is obtained by mixing a resin with a pore-forming agent, kneading and molding, and removing only the pore-forming agent with a solvent or the like to obtain a porous body. It has been known.
[0005]
Japanese Patent Application Laid-Open No. 2001-2825 discloses a method of using a polyhydric alcohol which becomes a molten state at a processing temperature as a pore-forming agent to obtain a highly porous continuous porous material. In this method, since the structure is formed after the resin is once in a molten state, the entanglement of the resin molecules can be sufficiently secured, and the density of the resin can be increased. It is much higher than that obtained by the phase inversion method.
[0006]
On the other hand, however, it was not possible to obtain an asymmetric porous structure having a dense pore structure on the outermost surface and a coarse void structure inside as in a separation membrane obtained by a wet phase inversion method.
[0007]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2001-2825
[Problems to be solved by the invention]
The present invention provides a molded article having the same porous structure as that obtained by applying the wet phase inversion method using a pore-forming agent, and provides a porous molded article having the above-described porous structure and a method for producing the same. Is the subject.
[0009]
[Means for Solving the Problems]
The present invention is a porous molded article containing a thermoplastic resin and a pore-forming agent, wherein the content of the pore-forming agent is 5% by mass or less of the initially used amount of the pore-forming agent. The porous molded body having an average pore diameter D ₁ of 1/10 or more inside and an average pore diameter D _{2 of the} surface satisfying a relationship represented by the following formula (I): D ₁ > 2 × D ₂ (I) I will provide a.
[0010]
In this porous molded body, a pore-forming agent in a residual state defined by the following definition is always present, and the remaining pore-forming agent is added at the time of production and then removed. Part of the material that remains without being removed. "Surface" means an outer surface when the porous molded body is planar or the like, and means an outer surface and an inner surface when the porous molded body is tubular or the like.
[0011]
Further, the present invention is a step of melt-kneading a resin composition containing a thermoplastic resin and a pore-forming agent, and molding and processing.
Process was immersed in a solvent S ₁ for dissolving the thermoplastic resin to swell the thermoplastic resin molded article,
After removal of the thermoplastic resin molded article, the process thermoplastic resin is not dissolved, the pore forming agent is immersed in a solvent S ₂ to be dissolved,
The present invention provides a method for producing a porous molded body comprising:
[0012]
The porous compact obtained by applying this production method includes both a porous molded body in which no pore forming agent remains and a porous molded body in which the pore forming agent remains. Whether or not the pore forming agent remains or not can be confirmed by the following method. That is, the obtained porous molded body is dissolved in a solvent in which both the thermoplastic resin component and the pore forming agent are soluble, and the amount of the pore forming agent is quantified by ¹ H-NMR.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
First, a method for producing a porous molded article suitable for producing the porous molded article of the present invention will be described step by step. In addition to the steps described below, steps commonly performed by those skilled in the art can be added.
[0014]
In the first step, a resin composition containing a thermoplastic resin and a pore-forming agent is melt-kneaded and molded. Note that a cooling step can be provided before moving to the next step.
[0015]
The shape and size of the molded article are appropriately determined according to the use of the finally obtained porous molded article and the like.
[0016]
The melt-kneading method can be performed using a single-screw or twin-screw extruder, a kneader, a calender roll, or another device. Prior to melt kneading, the thermoplastic resin may be preliminarily processed into a powdery state by a freeze grinder or the like, or may be preliminarily kneaded by a Henschel mixer, a tumble mixer, a ball mill, or the like.
[0017]
Examples of the molding method include injection molding, extrusion molding, blow molding, calender molding, and the like. Injection molding and extrusion molding are preferred from the viewpoint of productivity and ease of processing. Also, in the process of extrusion molding or injection molding, or in the process of an additional step such as heat fusion, it can be molded as a laminate with another substrate.
[0018]
The molding temperature is set according to the type of the thermoplastic resin, the mixing ratio of the thermoplastic resin and the pore-forming agent, and the molding method.
[0019]
The combination of the thermoplastic resin and the pore-forming agent is determined in relation to the types of the solvents S ₁ and S ₂ used in the subsequent processes.
[0020]
The thermoplastic resin is not particularly limited, and styrene resins such as polystyrene (PS) and high-impact polystyrene (HIPS); olefin resins such as polypropylene (PP) and polyethylene (PE); polyethylene terephthalate (PET); Polyester resins such as polybutylene terephthalate (PBT); polycarbonate resins (PC), polymethyl methacrylate (PMMA), cellulose acetate (CA), cellulose acetate propionate (CAP), cellulose acetate butyrate (CAB), etc. Cellulose derivative resins; halogen resins such as polyvinyl chloride (PVC) and polyvinylidene fluoride (PVDF); ethylene vinyl alcohol copolymer resin (EVOH), ethylene vinyl acetate copolymer resin (EVA), styrene resin Diene copolymer resin (SB, SBS), include copolymer resins, styrene-acrylonitrile copolymer resin (AS). These resins may be used alone or as a mixture of two or more.
[0021]
The pore-forming agent is not limited as long as it is soluble in a solvent, but is preferably a water-soluble one, and examples thereof include oligosaccharides and polyhydric alcohols that are solid at room temperature.
[0022]
Oligosaccharides (or small sugars) include disaccharides (maltose, isomaltose, palatinose, cellobiose, lactose, sucrose, trehalose, gentibinose, cozybiose, laminaribiose, melibiose, nigerose, sophorose, etc.), and trisaccharides (Maltotriose, meletitose, raffinose, etc.), tetrasaccharides (stachyose, cellotetraose, etc.), pentasaccharides, hexasaccharides, etc. are preferred. The oligosaccharide may be in a reduced form or a non-reduced form, but the reduced form is more preferable in consideration of applying heat. As the polyhydric alcohol, those which are solid at room temperature and do not cause a sharp decrease in viscosity upon melting are desirable, and pentaerythritol is preferred from that viewpoint. These pore-forming agents may be used alone or in a mixture of two or more. In addition, other water-soluble polyhydric alcohols or water-soluble monosaccharides may be added for the purpose of adjusting the viscosity of the pore-forming agent.
[0023]
The amount of the pore-forming agent to be added can be adjusted according to the mechanical strength of the porous molded body, the separation ability when the porous molded body is applied as a separation membrane, the processing time, and the like. Regarding the amount of the pore-forming agent added, the content of the pore-forming agent is preferably 40 to 90% by mass, more preferably 50 to 80% by mass, and still more preferably 60 to 90% by mass of the total amount of the thermoplastic resin and the pore forming agent. The amount is 75% by mass.
[0024]
Further, in addition to the thermoplastic resin and the pore-forming agent, other additives may be added for the purpose of improving the mechanical strength and processability of the porous molded body, and for improving the viscosity characteristics. Further, if necessary, a heat stabilizer, a lubricant, an ultraviolet absorber, a thickener, a flame retardant, an antioxidant, an antistatic agent, and a reinforcing agent such as fiber may be contained. Such additives are preferably used in an amount of 30 parts by mass or less based on 100 parts by mass of the thermoplastic resin.
[0025]
Next, in the second step, was immersed in a solvent S ₁ for dissolving the thermoplastic resin to swell the thermoplastic resin molded article. By swelling the surface of the molded body by the treatment in this step, the pore-forming agent is easily removed in the treatment in the next step.
[0026]
The solvent _{S 1} is an organic solvent. The immersion time in the solvent S1 is preferably ₁ to 300 seconds, more preferably 10 to 180 seconds. If the immersion time in the solvent is 1 second or more, a sufficient swelling state can be created, and if it is 300 seconds or less, the thermoplastic resin dissolves and diffuses in the solvent.
[0027]
Then in the third step, after removal of the thermoplastic resin molded article, the thermoplastic resin is not dissolved, the pore forming agent is immersed in the solvent S ₂ to dissolve.
[0028]
By the treatment in the second step, the outer surface of the molded body is in a swollen state, and by the treatment in the third step, the thermoplastic resin undergoes phase transformation on the outer surface to form a fine pore structure, and at the same time, pores are formed. with the dissolution of the former to the solvent S _2, the formation of coarse pore structure is performed inside the formed body.
[0029]
Solvent _{S 2} is preferably water, more preferably hot water at 50 to 90 ° C.. Time of immersion in the solvent S ₂ is preferably more than 95 wt% of pore-forming agent contained in the molded body is a sufficient time to be removed.
[0030]
By applying the production method of the present invention, a molded article containing no pore-forming agent and a porous molded article containing the pore-forming agent can be obtained. When the porous molded article contains a pore-forming agent, the residual amount of the pore-forming agent is 5% by mass or less of the initially used amount of the pore-forming agent (the amount used in the first step).
[0031]
The porous compact obtained by applying the production method of the present invention has a composite pore structure having a coarse pore structure inside and a dense pore structure on the surface similarly to the porous body obtained by the wet phase inversion method. Have.
[0032]
Porous molded article of the present invention, the inner and the average pore diameter _{D 1} of the hole 1/10 or more to the total thickness from the surface, the average pore diameter _{D 2} of the surface, the following equation _{(I): D 1> 2} × D _{2 The} relationship shown in (I) is satisfied. When the porous molded body is applied as a separation membrane for solid-liquid separation, by satisfying the above formula (I), the separation performance (for example, the molecular weight cut off) and the liquid permeation performance (for example, water permeation rate) of the whole membrane are balanced. Can be well equipped.
[0033]
Considering the case of using the porous shaped body as a separation membrane for water purification, D ₂ in the above formula is preferably not more than 2μm, which is sufficient for the separation of cryptosporidium (protozoa).
[0034]
The porosity of the porous molded article of the present invention is preferably 40 to 90%, more preferably 50 to 80%, and still more preferably 60 to 75%.
[0035]
The porous molded product of the present invention has a tensile strength at break S (tensile test of a plastic molded product in accordance with JIS K7113) at a tensile speed of 50 mm / min of a porous molded product having a porosity of P%, where S> 40. X (100-P) / 100 (MPa) (40 MPa indicates a tensile strength at break of a molded article of a single thermoplastic resin alone at a tensile speed of 50 mm / min).
[0036]
Since the porous body obtained by the wet phase inversion method is made from a thermoplastic resin solution, the cohesive force of the thermoplastic resin in the porous body is weak, and the mechanical strength of the porous body is reduced. On the other hand, since the porous molded body obtained by applying the production method of the present invention includes a melt-kneading step, the entanglement between the molecules of the thermoplastic resin is sufficiently ensured. There is no decrease in mechanical strength.
[0037]
The porous molded article of the present invention can be formed into various types of membranes such as a flat membrane and a hollow fiber membrane.
[0038]
INDUSTRIAL APPLICABILITY The porous molded body of the present invention can be used as a membrane for solid-liquid separation, such as membrane purification of purified water, purification of industrial wastewater, sewage, and the like.
[0039]
【Example】
Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto. The details of each component used below are as follows.
[0040]
Resin-1: Ethylene vinyl alcohol copolymer resin (EP-L101B manufactured by Kuraray Co., Ltd., ethylene content 19.8% by mass)
Resin-2: Polystyrene resin (HRM63C manufactured by Toyo Styrene Co.)
Resin-3: Cellulose acetate butyrate resin (CAB171-15S manufactured by Eastman)
Pore forming agent-1: oligosaccharide (PO-10, manufactured by Towa Kasei)
Pore forming agent-2: pentaerythritol (manufactured by Wako Pure Chemical Industries)
Solvent-1: dimethyl sulfoxide DMSO (manufactured by Wako Pure Chemical Industries)
Solvent-2: tetrahydrofuran (manufactured by Wako Pure Chemical Industries).
[0041]
Examples 1-4, Comparative Example 1
(First step)
The resin composition composed of each component having the composition shown in Table 1 (indicated by mass%) was melt-kneaded at a set temperature of 200 ° C. for 5 minutes by Brabender (Labo Plastmill manufactured by Toyo Seiki). Then, after cooling to room temperature once, it was formed into a plate having a thickness of 1 mm under the conditions of 200 ° C., 20 MPa, and 3 minutes using a press machine.
[0042]
(2nd process)
The pressed molded product was immediately cooled at 30 ° C. and 20 MPa for 3 minutes, and then immersed in the solvent (S ₁ ) for the time shown in Table 1.
[0043]
(3rd step)
Then, it was immediately immersed in hot water (solvent S ₂ ) at 60 ° C. and left as it was until a mass reduction of 95% of the charged pore forming agent was confirmed, to obtain a porous molded body.
[0044]
Scanning electron micrographs of the outer surface and the inner pore structure (portion 100 μm from the surface) of the porous molded body obtained in Example 1 are shown in FIGS. 1 (outer surface; 4000 times) and 2 (inner structure; 500 times). FIG. 3 shows an electron micrograph (× 2000) of the outer surface of the porous body obtained in Comparative Example 1. The measuring method of each measured value in Table 1 is as follows.
[0045]
(1) The pore size of the porous molded body, the interior of the pore diameter D ₁ of the measuring scanning electron microscope: using (SEM manufactured by JEOL) to confirm the cross-section of the pore structure of the porous molded body. When the pores of the porous molded body have continuity, there are no independent pores (see FIG. 1). Thus, from a photograph of a cross section of a porous body taken at a magnification of 100 to 10,000, the value at which the distance between the resin phases facing each other that forms one hole is defined as the hole diameter (for example, when the hole has an elliptical shape). If there is, the length of the minor axis is the pore diameter), 100 points are randomly extracted from the cross section of 100 μm or more inside the outer surface of the porous molded body having a thickness of 1 mm, the pore diameter is measured, and displayed as the average pore diameter. did.
[0046]
(2) porous body having a pore size, in the same manner as in the measurement of the measuring hole diameter D ₁ of the hole diameter D ₂ of the outer surface was measured. When the pore structure on the surface of the porous body was composed of independent pores, the area of each pore was converted to a circle, and the diameter calculated at this time was defined as the pore diameter. 100 holes were randomly sampled and the hole diameter was measured and displayed as the average hole diameter.
[0047]
(3) Mechanical strength of the porous molded body The porous molded body was punched into a size of No. 2 dumbbell according to JIS K7113, and a tensile test was performed using a Tensilon RTA520 (manufactured by Toyo Seiki) at a tensile speed of 50 mm / min. The tensile strength at break was obtained.
[0048]
(4) Measurement of Porosity of Porous Molded Body The porous molded body was immersed in pure water at 25 ° C. and kept under reduced pressure until generation of air bubbles from inside the porous molded body was no longer observed. Thereafter, the weight of the porous molded body was measured to obtain a wet weight M _1. Then weighed after drying the porous shaped body to absolute dry state to obtain a dry weight M _2. From these measured values, the specific gravity ρ _{1 of} water, and the specific gravity ρ ₂ of the thermoplastic resin used as the raw material of the porous body, the porosity P was calculated using the following equation.
[0049]
P = 100 × {[(M ₁ −M ₂ ) / ρ ₁ ] / [(M ₁ −M ₂ ) / ρ ₁ + M ₂ / ρ ₂ ]}
Comparative Examples 2 to 4
A porous molded body was obtained in the same manner as in Examples 1 to 4 and Comparative Example 1 except that a resin composition having the components shown in Table 1 (indicated by weight%) was used, and the treatment in the second step was not performed. .
[0050]
Comparative Examples 5 and 6
The thermoplastic resin was dissolved in a solvent (dimethyl sulfoxide) at the composition and temperature shown in Table 1 to obtain a raw material dope. The raw material dope was cast to a thickness of 1 mm on a glass plate kept at room temperature, left for 1 minute, and then immersed together with the glass plate in pure water at 25 ° C to obtain a porous body.
[0051]
[Table 1]

[0052]
In Examples 1-4, the diameter of the outer surface (D _2), the interior of the pore diameter (D _1), a porous molded article having a satisfactory performance in mechanical strength is obtained.
[0053]
In Comparative Example 1, since the immersion time in the solvent was too long, the thermoplastic resin was dissolved and diffused in the solvent, and as a result, the appearance and shape of the porous molded article were impaired. In addition, a fibrous thermoplastic resin was attached to the surface of the porous molded body, and it was determined that subsequent use was impossible.
[0054]
Although the porous molded bodies of Comparative Examples 2 to 4 had good mechanical strength, the whole had a sponge structure having uniform pores, and a dense pore structure could not be formed on the outermost surface.
[0055]
Since the porous bodies of Comparative Examples 5 and 6 were formed by the wet phase inversion method, the mechanical strength was very low.
[0056]
【The invention's effect】
According to the production method of the present invention, it is possible to obtain a porous molded body having an asymmetric porous structure having a dense pore structure on the surface and a coarse void structure inside.
[Brief description of the drawings]
FIG. 1 is an electron micrograph (× 4000) of the outermost surface of a porous body obtained in Example 1.
FIG. 2 is an electron micrograph (× 500) of the internal structure of the porous body obtained in Example 1.
FIG. 3 is an electron micrograph (× 2000) of the outermost surface of the porous body obtained in Comparative Example 1.

Claims (10)

A porous molded article containing a thermoplastic resin and a pore-forming agent, wherein the content of the pore-forming agent is 5% by mass or less of the used amount of the pore-forming agent, and is 1/10 or more of the total thickness from the surface. and the average pore diameter _{D 1} of the inner hole, the average pore diameter _{D 2} of the surface, the following equation _{(I): D 1> 2} × D porous molded bodies meet the relationship represented by 2 (I). Porous molded body according to claim 1, wherein D ₂ is 2μm or less. The porous molded article according to claim 1 or 2, wherein the porosity is 40 to 90%. The tensile strength at break (S: tensile test of a plastic molded article in accordance with JIS K7113) at a tensile speed of 50 mm / min of a porous molded article having a porosity of P% is S> 40 × (100−P) / 100. The porous molded product according to any one of claims 1 to 3, which satisfies (MPa). The porous molded article according to any one of claims 1 to 4, which is used as a flat membrane for solid-liquid separation. Melt-kneading a resin composition containing a thermoplastic resin and a pore-forming agent, a step of molding,
Process was immersed in a solvent S ₁ for dissolving the thermoplastic resin to swell the thermoplastic resin molded article,
After removal of the thermoplastic resin molded article, the process thermoplastic resin is not dissolved, the pore forming agent is immersed in a solvent S ₂ to be dissolved,
A method for producing a porous molded body comprising: S ₁ is an organic solvent, the production method of the porous molded body according to claim 6, wherein S ₂ is water. The method for producing a porous molded article according to claim 6 or 7, wherein the pore-forming agent is one or more selected from polyhydric alcohols and saccharides which are solid at room temperature. The method for producing a porous molded article according to any one of claims 6 to 8, wherein the amount of the pore forming agent is 40 to 90% by mass based on the total amount of the thermoplastic resin and the pore forming agent. In the step of immersion in a solvent S _2, a manufacturing method of the porous molded body according to any one of claims 6-9 to remove more than 95% by weight of the pore former contained in the porous shaped body.

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