JP4962643B2 - Porous material and method for producing the same - Google Patents

Description

  The present invention is based on polymethyl methacrylate, which can be usefully used as a separation membrane and an adsorbent, and can be structurally controlled from nanometer order to micrometer order, taking advantage of excellent structural uniformity and high surface porosity. The present invention relates to a porous body and a method for producing the same, a separation membrane made of the porous body, and an adsorbent made of the porous body.

  The porous body is used as a separation membrane, an adsorbent, a fuel cell separator, a low dielectric constant material, a catalyst carrier, and the like. Among these, separation membranes are used in a wide range of applications including medical fields such as artificial kidneys and plasma separation membranes, and environmental energy fields such as water treatment and carbon dioxide separation. In addition, since the membrane separation process does not involve a phase transition from a liquid to a gas or the like, the membrane separation process has attracted attention as a separation process with a smaller energy load compared to distillation or the like. Adsorbents are also used in a wide range of fields including medical materials such as blood purification columns, water treatment, petroleum refining, deodorization, and decolorization.

  Polymethyl methacrylate can be suitably used for an optical device because of its high light transmittance. On the other hand, it can be suitably used as a separation membrane as an artificial kidney composed of a polymethylmethacrylate hollow fiber membrane by utilizing high biocompatibility and specific protein adsorption. This polymethylmethacrylate separation membrane is produced using a stereocomplex of polymethylmethacrylate.

  For example, in Patent Document 1, a stock solution in which isotactic polymethyl methacrylate and syndiotactic polymethyl methacrylate are dissolved in an organic solvent capable of forming a stereocomplex such as dimethyl sulfoxide and dimethylformamide is used as a poor solvent from a die having an appropriate shape. A technique that can be obtained by discharging the ink inside is described.

  Patent Document 2 describes a melt film-forming method in which a crystalline polymer such as polyethylene is melted by heating, and is discharged from a die and stretched. This melt film-forming method is a method of tearing and opening an amorphous portion of a polymer, and is also referred to as a stretch hole-opening method, and can increase the film-forming speed.

  Patent Document 3 describes another melt film-forming method in which a polymer is partially removed from a polymer alloy obtained by melt-kneading two or more types of polymers to obtain a porous separation membrane. .

  Non-Patent Document 1 reports that polymethyl methacrylate forms a stereocomplex even during melt-kneading and has a melting point of 200 ° C. or higher.

JP-A-49-37879 JP 58-163490 A JP 2003-64214 A

E.L.Feitsma., A.de.Boer., G.Challa., 1975, Polymer Vol.16, pp.515-519

  However, the method described in Patent Document 1 is so-called solution casting, and the porosity of the membrane surface is lower than the porosity inside the membrane, and as a result, the membrane surface is a material-permeating bottleneck. Therefore, there was a limit to improving the material permeation efficiency. This decrease in the porosity in solution casting is due to the extremely high mobility of polymer molecules in the solution compared to the mobility in the molten polymer. That is, the phase separation of the polymethyl methacrylate solution (stock solution) discharged from the spinneret starts from the interface with a gas such as air or a liquid such as a coagulation liquid. At this time, since the phase separation rapidly proceeds in the vicinity of the interface, polymethyl methacrylate molecules having high mobility aggregate and a polymethyl methacrylate-rich layer called a skin layer is formed on the film surface. Since this skin layer has a lower porosity than the inside of the membrane, the surface porosity of the separation membrane produced by solution casting tends to be lower than that of the inside of the membrane. It is conceivable to remove the skin layer in order to increase the porosity of the membrane surface, but the thickness of the skin layer is several microns or less, and it is technically difficult to remove only the skin layer, Furthermore, it was not practical to remove the skin layer in continuous production such as solution casting.

  Further, the melt film forming method of Patent Document 2 can increase the film forming speed as compared with the solution film forming, and can increase the film forming speed to nearly 100 times that of the solution film forming. However, the polymers to which the stretch opening method can be applied are limited to some of the crystalline polymers such as polyethylene and polypropylene, and are difficult to apply to amorphous polymers such as polymethyl methacrylate. Further, since the holes are opened by tearing, it is difficult to control the hole diameter, and it is difficult to make fine and uniform holes.

  In another melt film-forming method of Patent Document 3, a porous body is obtained from an alloy having a fine and uniform continuous structure obtained by spinodal decomposition, and a fine and uniform opening is possible. Since it is used, the film forming speed is also high. However, for melt-kneaded polymer alloy by spinodal decomposition, selection of a polymer alloy system, that is, a combination of polymers is important. In particular, when producing a porous body, it is necessary to select a polymer alloy system in consideration of the removal of the polymer. For example, when removing a polymer using a solvent, the base material polymer of the porous body does not dissolve and the polymer to be removed Only a solvent that selectively dissolves is required, and the selection range of the polymer alloy system becomes very narrow. Although some combinations are described in Patent Document 3 as an alloy system of polymethylmethacrylate, an alloy system capable of easily removing a polymer is not described.

  Further, as described above, Non-Patent Document 1 reports that polymethyl methacrylate forms a stereocomplex even during melt-kneading and has a melting point of 200 ° C. or higher. Therefore, a stereocomplex is formed. As a result, not only melt kneading becomes difficult, but also an unmelted part is partially generated, and a uniform melt kneading alloy cannot be obtained. It goes without saying that a uniform porous body cannot be obtained from such a non-uniform alloy.

  Under such circumstances, there has been a demand for a method for obtaining a polymethyl methacrylate porous body having a high surface porosity and high productivity.

  The present invention utilizes a high surface porosity and a fine and uniform porous structure, and can be usefully used as an adsorbent for blood component separation membranes such as artificial kidneys and blood purification columns. It is an object of the present invention to provide a porous body mainly composed of polymethylmethacrylate whose pore diameter can be controlled in order and a method for producing the same.

In order to solve the above problems, the porous body of the present invention has the following configuration.
1. A porous body mainly composed of polymethyl methacrylate having continuous pores, the pore diameter of the continuous pores being 0.001 μm or more and 500 μm or less, and the porosity of at least one surface being 10% or more and 80% or less. The ratio of isotactic polymethyl methacrylate in the polymethyl methacrylate was less than 10% by weight, and was photographed with a square field of view having a length of 10 to 100 times the pore diameter of the porous body as one side. In a graph curve obtained by Fourier transforming a microscope image, the horizontal axis is the wave number and the vertical axis is the intensity, the peak half-value width (a) and the peak maximum wavelength (b) are 0 <(a) / (b) A porous body satisfying ≦ 1.2.
2 . Porous shapes thickness 1μm or more 5mm or less of the sheet, or thickness 1μm or more 5mm or less hollow fiber or outer diameter 1μm or more 5mm or less fibrous or 1 in diameter 10μm 5mm or more or less particulate, The porous body described.
3 . A separation membrane comprising the porous material according to any one of 1 to 2 .
4 . 4. The separation membrane according to 3 , wherein the substance to be separated is a biological component.
5 . 5. The separation membrane according to 4 , wherein the biological component is blood or a part thereof.
6 . An adsorbent comprising the porous material according to any one of 1 to 2 .
7 . The adsorbent according to 6 , wherein the adsorption symmetric substance is a biological component.
8 . 8. The adsorbent according to 7 , wherein the biological component is blood or a part thereof.
9 . 4. The method for producing a porous body according to any one of 1 to 3, wherein the aliphatic polyester is removed from the polymer alloy molded article obtained from the polymethyl methacrylate and the aliphatic polyester , wherein the proportion of isotactic polymethyl methacrylate is less than 10% by weight. .
10 . 10. The method for producing a porous body according to 9 , wherein the aliphatic polyester is polylactic acid.
11 . The method for producing a porous body according to any one of 9 to 10 , wherein the aliphatic polyester is removed by hydrolysis.
12 . The method for producing a porous body according to any one of 9 to 11 , wherein the polymer alloy is obtained by melt kneading.
13 . The method for producing a porous body according to any one of 9 to 12 , wherein the polymer alloy is obtained by phase separation by spinodal decomposition.

  According to the present invention, by removing aliphatic polyester from a polymer alloy obtained by phase separation by spinodal decomposition from polymethyl methacrylate and aliphatic polyester by hydrolysis or the like, the surface porosity is 10% or more and 80% or less. In addition, a porous body having continuous pores whose pore diameter is controlled to be 0.001 μm or more and 500 μm or less can be obtained.

  Since the porous body obtained by the method of the present invention has a fine and uniform porous structure whose pore diameter can be controlled from the nanometer order to the micrometer order, it can be used as a separation membrane or adsorbent such as a blood component separation membrane such as an artificial kidney. It can be usefully used.

1 is an electron microscope image of the surface of the porous sheet of Example 1. FIG. FIG. 2 is an image obtained by binarizing the image of FIG. 1 with image analysis software. FIG. 3 is an electron microscope image of the surface of the porous sheet of Example 2. FIG. 4 is an image obtained by binarizing the image of FIG. 3 with image analysis software. FIG. 5 is an electron microscope image of the hollow fiber inner surface of Comparative Example 3. FIG. 6 is an image obtained by binarizing the image of FIG. 5 with image analysis software.

  The present invention is described in further detail below.

  The porous body in the present invention refers to a porous body having continuous pores, and can be used as a separation membrane by utilizing the continuous pores as a sieve. A continuous hole is a hole that penetrates continuously. In the present invention, a hole having a length of 5 times or more the hole diameter is defined as a continuous hole. The separation membrane has a continuous pore diameter, that is, a desired pore size can be set depending on the size of the substance to be separated. In the porous body of the present invention, the pore diameter of the continuous pore is 0.001 μm or more and 500 μm or less. If the pore diameter of the continuous pores is less than 0.001 μm, not only the pressure required for separation is increased, but also there is a problem that it takes a long time for separation, and if it exceeds 500 μm, the strength of the porous body is reduced, and the separation membrane There are problems such as difficulty in use.

  The pore diameter of the continuous holes is preferably 0.002 μm to 100 μm, and more preferably 0.003 μm to 50 μm. The method for measuring the pore diameter is as follows. First, the porous body is cooled with liquid nitrogen, and stress is applied to cleave it. Next, the cross section is observed with an electron microscope, the obtained electron microscope image is Fourier transformed, the maximum wave number is obtained when the wave number is plotted on the horizontal axis and the intensity is plotted on the vertical axis, and the pore diameter is obtained from the reciprocal thereof. To do. At this time, the image size of the electron microscope image is a square having one side with a length of 5 to 100 times the hole diameter.

  The pore diameter of the continuous pores in the porous body is preferably uniform, and if the pore diameter is uneven such that there are various pore sizes, the separation characteristics may be lowered, which is not preferred. The uniformity of the hole diameter can be judged by the peak half-value width of a curve in which the hole diameter is plotted on the horizontal axis and the number of continuous holes having the hole diameter is plotted on the vertical axis. That is, in the case of a film having a uniform pore diameter, the curve forms a sharp peak and the half width is narrow. On the other hand, when the pore diameter is not uniform, the curve forms a broad peak and the half-value width becomes wide. The pore diameter uniformity evaluation based on the peak half width of the graph in which the pore diameter is plotted on the horizontal axis and the number of holes on the vertical axis is the same as the reciprocal of the pore diameter, that is, the wave number on the horizontal axis. Assume that the electron microscope image of the body is evaluated using a graph obtained by Fourier transform. Here, the electron microscope image used for the Fourier transform is the image used for the above pore diameter measurement. Also, since the peak half-value width tends to increase as the peak maximum wave number increases, the value of (a) / (b) calculated from the peak half-value width (a) and peak maximum wave number (b) It was used as an index for evaluating the uniformity of the pore diameter. In order to develop excellent separation characteristics, it is preferable that the pore diameter uniformity is high, and the value of (a) / (b) is preferably 1.2 or less, and 1.1 or less. More preferred is 1.0 or less. In addition, the uniform structure of the polymer alloy is better, so the lower limit of (a) / (b) is not particularly limited. In the present invention, the half width of the peak means that when a straight line parallel to the vertical axis of the graph is drawn from the apex of the peak (point A) and the intersection (point B) of the straight line and the baseline of the spectrum is (point A) And the width of the peak at the midpoint (point C) of the line segment connecting (point B). The peak width referred to here is a width on a straight line parallel to the base line and passing through (point C).

  When using a porous body as a separation membrane, the surface porosity is particularly important because it has a great influence on separation characteristics such as material permeation. Therefore, in the porous body of the present invention, the porosity of at least one surface is 10% or more and 80% or less. If the porosity is less than 10%, even if the porosity inside the porous body is high, there is a problem that the surface becomes a bottleneck in material permeation and desired characteristics cannot be obtained. If it exceeds, there is a problem that the strength of the porous body is lowered and there is a risk that the structure cannot be maintained eventually.

  The porosity is preferably 12% to 70%, more preferably 15% to 60%. In conventional solution casting, the porosity of the membrane surface is around 5%, and it is difficult to make it 10% or more. This is because the mobility of the polymer molecules in the solution is extremely higher than the mobility in the molten polymer as described above. That is, polymethylmethacrylate molecules are rapidly precipitated and aggregated at the gas-liquid interface between the undiluted solution and the gas such as air and the liquid-liquid interface between the undiluted solution and the coagulating solution at which phase separation starts. This is considered to form a skin phase having a low porosity. As a result of diligent investigation on the problem of the surface area ratio, the surface area ratio can be obtained by removing the aliphatic polyester from the polyalmethacrylate and the aliphatic polyester by phase separation by spinodal decomposition by hydrolysis or the like. Was 10% or more and 80% or less, and succeeded in obtaining a porous body whose pore diameter was controlled to be 0.001 μm or more and 500 μm or less. This is because polymethyl methacrylate is phase-separated in a molten state, so that the mobility of polymethyl methacrylate molecules can be suppressed as compared with phase separation in a solution state, and as a result, a skin phase having a low porosity is not formed. The surface open area ratio can be 10% or more.

  The surface porosity in the present invention refers to the ratio of the area of the aperture per unit area on at least one surface of the porous body. This surface porosity is determined by analyzing an electron microscope image on the surface of the porous body. That is, an electron microscope image observed in a square field of view with a length of 5 to 100 times the pore diameter on the surface of the porous body is opened with image analysis software (ScionImage (Scion Corporation), MatroxInspector (Matrox), etc.) And the non-opening part are distinguished by binarization, and the hole area is obtained by calculating the area of the opening part. Moreover, the porosity in this invention refers to the ratio of the volume of the void | hole part per unit volume of a porous body.

  In addition to the separation membrane, the porous body can also be used as an adsorbent by utilizing the size of its surface area. In particular, polymethyl methacrylate has high blood compatibility and has a characteristic of specifically adsorbing proteins and the like, and the porous body of the present invention is suitable for blood purification columns and the like.

  The shape of the porous body is not particularly limited, but when used as a separation membrane, a hollow fiber shape that can be used as a hollow fiber membrane, or a sheet shape that can be used as a flat membrane or a coil membrane is preferable. Among these, the hollow fiber membrane is particularly preferable because the area of the separation membrane can be increased. Moreover, when using as an adsorbent, it is preferable that it is a particulate form, such as a fiber form and a bead which can be used as a knitted fabric or a nonwoven fabric other than a sheet form or a hollow fiber form.

  When the porous body is used as a separation membrane, if the thickness is too thin, not only the separation characteristics are deteriorated but also the strength becomes insufficient, and there is a possibility that the porous body may be broken during use. Conversely, if it is too thick, it takes a long time for separation, which is not preferable. Therefore, when the porous body is in the form of a sheet or a hollow fiber, the thickness of the porous body is preferably 1 μm or more and 5 mm or less, more preferably 5 μm or more and 2 mm or less, and further preferably 10 μm or more and 1 mm or less. On the other hand, when used as an adsorbent, if the size of the fiber or particle is large, the filling rate when the fiber or particle is filled in the case is low, and the adsorption area per unit volume is low. On the other hand, if the size of the fiber or particle is too small, there is a risk that the fiber is cut or the particle leaks to the treatment liquid, which is not preferable. Therefore, when the porous body is fibrous, the outer diameter is preferably 1 μm to 5 mm, more preferably 5 μm to 1 mm, and even more preferably 10 μm to 500 μm. Moreover, when the shape of the porous body is particulate, the particle diameter is preferably 10 μm or more and 5 mm or less, more preferably 25 μm or more and 1 mm or less, and further preferably 50 μm or more and 500 μm or less.

A preferable method for obtaining a porous body mainly composed of polymethyl methacrylate having such a structure is obtained by phase separation by spinodal decomposition from polymethyl methacrylate having a ratio of isotactic polymethyl methacrylate of less than 10% by weight and aliphatic polyester. It can be obtained by removing aliphatic polyester from the polymer alloy obtained by hydrolysis or the like.

  In the present invention, the porous body composed mainly of polymethyl methacrylate means that 50% by weight or more of the total weight of the porous body after removing the aliphatic polyester is composed of polymethyl methacrylate.

There are three types of polymethyl methacrylate, isotactic polymethyl methacrylate, syndiotactic polymethyl methacrylate, and atactic polymethyl methacrylate, because of the difference in the configuration of their side chains. Among these, when isotactic polymethyl methacrylate and syndiotactic polymethyl methacrylate are mixed, a stereo complex having a melting point of 200 ° C. or higher is formed. When this stereocomplex is formed, not only melt kneading becomes difficult, but also an unmelted portion is partially generated, and a problem that a uniform melt kneading alloy cannot be obtained arises. It goes without saying that a uniform porous body cannot be obtained from such a non-uniform alloy. In addition, isotactic polymethyl methacrylate is relatively expensive because it is difficult to synthesize by ordinary radical polymerization, so it is not preferable to use a large amount economically unless there is a special reason. Therefore, in the porous body of the present invention, the proportion of isotactic polymethyl methacrylate in polymethyl methacrylate is preferably less than 10% by weight, more preferably 9% by weight or less, and even more preferably 8% by weight or less.

In the present invention, the proportion of isotactic polymethyl methacrylate in the polymethyl methacrylate is measured by proton nuclear magnetic resonance spectrum. The porous material is dissolved in deuterated chloroform, tetramethylsilane is added as an internal standard substance, and the proton nuclear magnetic resonance spectrum is measured. Here, in the chemical shift based on the signal of tetramethylsilane, the signal of 1.33 ppm out of the three kinds of peaks of 1.33 ppm, 1.21 ppm and 1.10 ppm as the signal of α-methyl proton is isotactic poly It is derived from methyl methacrylate. Therefore, the ratio of isotactic polymethyl methacrylate in polymethyl methacrylate is obtained by the following formula.
W = X / (X + Y + Z) × 100

Here, W, X, Y, and Z mean the following.
W:% by weight of isotactic polymethyl methacrylate in polymethyl methacrylate
X: 1.33 ppm peak area in proton nuclear magnetic resonance spectrum Y: 1.21 ppm peak area in proton nuclear magnetic resonance spectrum Z: 1.10 ppm peak area in proton nuclear magnetic resonance spectrum

  The molecular weight of polymethyl methacrylate is not particularly limited. However, if the molecular weight is too low, the strength of the porous body is low, and it is not preferable because it cannot be used for a separation membrane. On the other hand, if the molecular weight is too high, the viscosity at the time of melting becomes high and it becomes difficult to form a melt film. Therefore, the weight average molecular weight is preferably 10,000 to 2,000,000, more preferably 20,000 to 1,500,000, more preferably 30,000 to 100. Even less than 10,000 is more preferable.

  The porous body mainly composed of polymethyl methacrylate of the present invention can be obtained by removing aliphatic polyester from a polymer alloy (precursor of porous body) composed of polymethyl methacrylate and aliphatic polyester. Therefore, in order to form fine and uniform continuous holes, the structure of the polymer alloy needs to be fine and uniform. In order to obtain a fine and uniform polymer alloy, alloying by phase separation by spinodal decomposition is effective.

  Next, spinodal decomposition will be described.

  In general, polymer alloys composed of two-component resins are compatible with these compositions in a practical system where the glass transition temperature is higher than the thermal decomposition temperature or lower, and vice versa. There is a non-compatible system that dissolves and a partially compatible system that is compatible in one region and in a phase separated state in another region. In this partially compatible system, phase separation is performed by spinodal decomposition depending on the conditions of the phase separated state. Some are phase separated by nucleation and growth.

  Phase separation by spinodal decomposition refers to phase separation that occurs in an unstable state inside the spinodal curve in phase diagrams for different two-component resin compositions and temperatures, and phase separation by nucleation and growth refers to the phase separation. In the figure, it refers to phase separation that occurs in the metastable state inside the binodal curve and outside the spinodal curve.

  The spinodal curve refers to the difference (ΔGmix) between the free energy when compatibilized and the sum of the free energies in the two phases that are not compatible (ΔGmix) when mixing two different resin components with respect to the composition and temperature. φ) is a curve in which the partial differential of twice (∂2ΔGmix / ∂φ2) is 0, and inside the spinodal curve is an unstable state where ∂2ΔGmix / 不 安定 φ2 <0, and outside is ∂ 2ΔGmix / ∂φ2> 0.

  The binodal curve is a boundary curve between the region where the system is compatible and the region where the system is separated with respect to the composition and temperature.

  Here, the case of being compatible in the present invention is a state in which they are uniformly mixed at the molecular level. Specifically, both phases having different two-component resins as main components are 0.001 μm or more. The case where the phase structure is not formed is indicated, and the case where the phase is incompatible is the case where the phase is not in a compatible state, that is, the phases mainly composed of two different resin components are 0.001 μm or more. It refers to the state of forming a phase structure. Whether or not they are compatible is determined by, for example, an electron microscope, a differential scanning calorimeter (DSC), or other various methods as described in Leszek A Utracki, 1990, “Polymer Alloys and Blends”, Municn: Carl Hanser Publications, pp-64. It can be judged by the method.

  According to detailed theory, in spinodal decomposition, once the temperature of a mixed system that has been uniformly mixed at the temperature of the compatible region is rapidly increased to the temperature of the unstable region, the system will rapidly phase-separate toward the coexisting composition. To start. At that time, the concentration is monochromatized to a constant wavelength, and a two-phase continuous structure is formed in which both separated phases are continuously intertwined regularly with a structure period (Λm). After the formation of the two-phase continuous structure, the process in which only the concentration difference between the two phases increases while keeping the structure period constant is called the initial process of spinodal decomposition.

Furthermore, the structural period (Λm) in the initial process of the above-mentioned spinodal decomposition has a thermodynamic relationship as shown in the following equation.
[Lambda] m- [| Ts-T | / Ts] ^-1/2
(Where Ts is the temperature on the spinodal curve)

  Here, the two-phase continuous structure referred to in the present invention refers to a structure in which both components of the resin to be mixed each form a continuous phase and are entangled three-dimensionally. A schematic diagram of this two-phase continuous structure is described, for example, in “Polymer Alloy Fundamentals and Applications (Second Edition) (Chapter 10.1)” (edited by the Society of Polymer Science: Tokyo Kagaku Dojin).

  In spinodal decomposition, after going through such an initial process, it goes through a medium-term process in which an increase in wavelength and an increase in concentration difference occur simultaneously, and a later process in which an increase in wavelength occurs in a self-similar manner after the concentration difference reaches the coexisting composition. In the present invention, the structure is fixed when the desired structure period is reached before the separation into the macroscopic two phases. Good. In addition, in the process of increasing the wavelength from the mid-stage process to the late-stage process, depending on the influence of the composition and the interfacial tension, the continuity of one phase may be interrupted and the above-described biphasic continuous structure may be changed to a dispersed structure.

  In order to realize the spinodal decomposition, it is necessary to make the resin composed of two or more components into a compatible state and then to make the unstable state inside the spinodal curve.

  First, as a method of realizing a compatible state with a resin composed of two or more components, methods such as spray-drying, freeze-drying, coagulation in a non-solvent substance, and film formation by solvent evaporation after dissolving in a common solvent And a melt casting method by melting and kneading a partially compatible system under compatible conditions. In the present invention, compared with solution casting, compatibilization by melt kneading applicable to melt casting, which is a high-speed film forming process, is preferable.

  For compatibilization by melt kneading, an ordinary extruder is used, but a twin screw extruder is preferably used. The temperature for compatibilization needs to be a condition in which the partially compatible resin is compatible.

  Next, the polymer alloy made compatible by melt-kneading is considered to be an unstable state inside the spinodal curve, and when the spinodal decomposition is performed, the temperature and other conditions for making the unstable state vary depending on the combination of the resins. However, it can be set by a simple preliminary experiment based on the phase diagram. In the present invention, as described above, it is preferable to control the structural period of the initial process to a specific range and then further develop the structure after the intermediate process to obtain a specific biphasic continuous structure defined in the present invention.

  The method for controlling the specific structural period defined in the present invention in this initial process is not particularly limited, but it is not less than the lowest temperature among the glass transition temperatures of the individual resin components constituting the polymer alloy, and is described above. Heat treatment is preferably performed at such a temperature that the structural period defined thermodynamically becomes small. Here, the glass transition temperature can be obtained from an inflection point generated at the time of temperature increase from room temperature at a temperature increase rate of 20 ° C./min with a differential scanning calorimeter (DSC).

  The method for developing the structure from this initial process is not particularly limited, but a method of heat treatment at the lowest temperature or higher among the glass transition temperatures of the individual resin components constituting the polymer alloy is usually preferably used. Furthermore, when the polymer alloy is in a compatibilized state and has a single glass transition temperature, or when the phase decomposition is in progress, the glass transition temperature in the polymer alloy is the glass transition of the individual resin components that make up the polymer alloy. When the temperature is between the temperatures, it is more preferable to perform heat treatment at a temperature equal to or higher than the lowest temperature among the glass transition temperatures in the polymer alloy. Further, when a crystalline resin is used as the individual resin component constituting the polymer alloy, it is preferable that the heat treatment temperature is equal to or higher than the crystal melting temperature of the crystalline resin, since the structural development by the heat treatment can be effectively obtained. It is preferable to set the heat treatment temperature within the crystal melting temperature of the crystalline resin within ± 20 ° C. in order to facilitate the control of the structural development, and more preferably within the crystal melting temperature within ± 10 ° C. Here, when two or more crystalline resins are used as the resin component, the heat treatment temperature is preferably within the crystal melting temperature ± 20 ° C. based on the highest temperature among the crystal melting temperatures of the crystalline resin. Furthermore, it is more preferable that the crystal melting temperature is within ± 10 ° C. However, when the heat treatment is performed at the time of stretching the sheet, the heat treatment temperature is preferably set to be equal to or lower than the temperature rising crystallization temperature of the crystalline resin. Here, the crystal melting temperature of the crystalline resin can be determined from the peak temperature of the melting curve generated at the time of temperature increase from room temperature at a temperature increase rate of 20 ° C./min with a differential scanning calorimeter (DSC). The temperature rising crystallization temperature of the fluorinated resin is a temperature rising rate of 20 ° C./min from room temperature with a differential scanning calorimeter (DSC) using a sample obtained by quenching a sample melted at a temperature higher than the crystal melting temperature. It can obtain | require from the peak temperature of the crystallization curve produced at the time of temperature rising. Moreover, as a method of immobilizing the structure product by spinodal decomposition, structure immobilization of one or both components of the phase-separated phase in a short time by rapid cooling or the like can be mentioned.

  The resin used for alloying with polymethyl methacrylate in the present invention is preferably an aliphatic polyester in consideration of polymethyl methacrylate compatibility and a removal step for making it porous, and polylactic acid is particularly preferably used with polylactic acid. From the viewpoint of excellent compatibility with.

  From the viewpoint of facilitating the formation of a continuous structure in spinodal decomposition, the aliphatic polyester ratio in the polymethyl methacrylate alloy is preferably 5% by weight or more and 95% by weight or less, more preferably 10% by weight or more and 90% by weight or less, and more preferably 20% by weight. More preferably, it is 80% by weight or less.

  When molding a polymer alloy that is a precursor of the porous body of the present invention, it is usually molded simultaneously with or after the formation of the polymer alloy and before the formation of the pores, and then the aliphatic polyester is formed. A method of removing and forming a pore is employed. The shape can be any shape, but as described above, when used as a separation membrane or adsorbent, a hollow fiber shape, a sheet shape, a fiber shape, and a particle shape are preferable.

  Examples of the molding method for molding the polymer alloy include extrusion molding, injection molding, inflation molding, blow molding, etc., among which extrusion molding is phase-dissolved during extrusion, and spinodal decomposition is performed after ejection. It can be heat-treated when the sheet is stretched and the structure can be fixed during natural cooling before winding, and can be formed into a hollow fiber, sheet, or fiber using various shapes of the die, and then hollow fiber separation membrane or flat membrane This is preferable. Also, injection molding is preferable because it can be dissolved in the plasticizing step at the time of injection, and after injection, the spinodal can be decomposed to simultaneously perform heat treatment and structural fixation in the mold.

  As a method for removing the aliphatic polyester from the polymer alloy of polymethyl methacrylate and aliphatic polyester, there are a method of dissolving and removing the aliphatic polyester using a solvent and a method of decomposing and removing the aliphatic polyester. Among these, the method by decomposition of the aliphatic polyester is preferable because it is decomposed and removed to a low molecular weight substance, and can be efficiently removed even when the pore diameter is small. The aliphatic polyester is also preferable because it can be easily decomposed and removed by hydrolysis. Since polymethyl methacrylate has high resistance to alkali, it is preferable to hydrolyze the aliphatic polyester with an alkaline aqueous solution. When the aliphatic polyester is hydrolyzed with an alkaline aqueous solution, the decomposition rate can be increased by heating. Further, in the case of continuous production such as a hollow fiber separation membrane, it is possible to make the pores online by passing an alkaline aqueous solution soot. Examples of the alkali include potassium hydroxide, sodium hydroxide, sodium carbonate, potassium carbonate and the like.

  The porous body of the present invention can be used as a separation membrane by taking advantage of its fine and uniform continuous porosity, and as an example of its use, it can be used for food components such as medical treatment and biotool treatment, water treatment, fruit juice concentration, etc. Examples of alternatives such as distillation include, but are not limited to, chemical process applications, gas separation applications, and electronic information material applications such as fuel cell separators. Moreover, the porous body of the present invention can also be used as an adsorbent, and as an example of its use, in addition to separation membranes, in addition to biological component treatment applications such as medical treatment and biotool and water treatment applications, there are also deodorization and decolorization applications. Although it is mentioned, it is not limited to these. Especially for treatment of biological components, it can be suitably used for blood purification modules by taking advantage of the excellent blood compatibility of polymethylmethacrylate. The blood purification module refers to a module having a function of removing waste and harmful substances in the blood by adsorption, filtration, dialysis, diffusion and the like when circulating blood outside the body. Such blood purification modules include artificial kidneys, plasma separation membranes, and toxin adsorption columns. In particular, by utilizing the protein-specific adsorptivity of polymethylmethacrylate, it can be expected to remove unwanted proteins in blood that cannot be removed by dialysis or filtration.

  In addition to porous separation membranes and adsorbents, it can be used as a low dielectric constant material for printed circuit boards and laminates, and can also be used for covers and seal members that prevent high-frequency component leakage current from inverters and switching power supplies. Further, it can be used for adsorbents, catalyst carriers, etc. by utilizing a large surface area.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1
Polymethylmethacrylate "UT300" manufactured by Mitsubishi Rayon Co., Ltd. as an aliphatic polyester, polylactic acid resin having a D-form weight of 1.4% and a weight average molecular weight of 260,000 in terms of PMMA by GPC measurement The melt was formed at 240 ° C. at a temperature of 240 ° C. using a twin-screw melt kneader HK-25D (manufactured by Parker Corporation) with a T-die adjusted to a lip spacing of 0.2 mm. By setting the drum temperature to 60 ° C. and adjusting the winding speed, an alloy sheet having a thickness of about 150 μm was produced.

  The sheet was cut into a 10 cm square and immersed in 100 mL of a 20 wt% aqueous potassium hydroxide solution for 3 days to hydrolyze and remove polylactic acid to make it porous. After immersing in 500 mL of ultrapure water for 1 hour and further rinsing with 200 mL of ultrapure water, the porous sheet which has polymethylmethacrylate as a main component was obtained by freeze-drying.

  A graph in which a cross-section of the porous sheet is observed by using a transmission electron microscope at a magnification of 10,000 times, and a square image of 3 μm is obtained by Fourier transform, and the wave number is plotted on the horizontal axis and the intensity is plotted on the vertical axis. (A) / (b), which is an index of pore diameter and uniformity, was obtained from the peak wavenumber and the half-value width. Further, the sheet was dissolved in deuterated chloroform, and the proton nuclear magnetic resonance spectrum was measured to determine the ratio (% by weight) of isotactic polymethyl methacrylate in the polymethacrylate.

  The surface area of the porous sheet was observed by observing at a magnification of 100,000 using a scanning electron microscope S-5500 type (manufactured by Hitachi, Ltd.). As a pretreatment for observation, the observation sample was sputtered with platinum. The obtained observation image was trimmed into a square having a side of 500 nm, and binarization (Thereshhold) and area calculation (Analyze Particles) were executed with the image analysis software ScionImage (manufactured by Scion Corporation) to obtain the surface porosity. The microscope observation image and the image binarized with the image analysis software (the opening portion is displayed in black) are shown in FIGS.

  As shown in Table 1, the porous sheet obtained in Example 1 has a surface porosity as high as 15.61% and a film composed of a porous body mainly composed of polymethyl methacrylate having a uniform porous structure. Met.

(Example 2)
A porous sheet containing polymethyl methacrylate as a main component was obtained in the same manner as in Example 1 except that the melt kneading temperature was 200 ° C.

  A graph in which a square image of a 2 μm piece obtained by observing the cross section of the porous sheet with a transmission electron microscope at a magnification of 1,000 times is Fourier transformed, and the wave number is plotted on the horizontal axis and the intensity is plotted on the vertical axis (A) / (b), which is an index of pore diameter and uniformity, was determined from the peak wavenumber and the half-value width. Further, the sheet was dissolved in deuterated chloroform, and the proton nuclear magnetic resonance spectrum was measured to determine the ratio (% by weight) of isotactic polymethyl methacrylate in the polymethacrylate.

  Similarly to Example 1, the surface porosity of the porous sheet was observed by observing at a magnification of 10,000 using a scanning electron microscope S-5500 type (manufactured by Hitachi, Ltd.). As a pretreatment for observation, the observation sample was sputtered with platinum. The obtained observation image was trimmed into a square with a side of 5000 nm, and binarization (Thereshhold) and area calculation (Analyze Particles) were executed with image analysis software ScionImage (manufactured by Scion Corporation) to determine the surface open area ratio. FIGS. 3 and 4 show a microscope observation image and an image binarized by image analysis software (the opening portion is displayed in black).

  As shown in Table 1, the porous sheet obtained in Example 2 has a surface porosity as high as 23.63% and a film composed of a porous body mainly composed of polymethyl methacrylate having a uniform porous structure. Met.

(Comparative Example 1)
“UT300” manufactured by Mitsubishi Rayon Co., polymethyl methacrylate, isotactic polymethyl methacrylate having a weight average molecular weight of 50,000 obtained by Grignard catalyzed polymerization, aliphatic polyester, D-form weight of 1.4%, GPC A polylactic acid resin having a weight average molecular weight of 260,000 in terms of PMMA by measurement was used at a weight ratio of 30/20/50, respectively, and a twin-screw melt kneader with a T-die adjusted to 0.2 mm HK-25D (Made by Parker Corporation), and melt film formation was performed at 240 ° C. By setting the drum temperature to 60 ° C. and adjusting the winding speed, an alloy sheet having a thickness of about 150 μm was produced.

  The sheet was cut into a 10 cm square and immersed in 100 mL of a 20 wt% aqueous potassium hydroxide solution for 3 days to hydrolyze and remove polylactic acid to make it porous. After immersing in 500 mL of ultrapure water for 1 hour and further rinsing with 200 mL of ultrapure water, the porous sheet which has polymethylmethacrylate as a main component was obtained by freeze-drying.

  A graph in which a square image of a piece of 18 μm obtained by observing the cross section of the porous sheet with a transmission electron microscope at a magnification of 1,000 times is Fourier transformed, and the wave number is plotted on the horizontal axis and the intensity is plotted on the vertical axis (A) / (b), which is an index of pore diameter and uniformity, was determined from the peak wavenumber and the half-value width. Further, the sheet was dissolved in deuterated chloroform, and the proton nuclear magnetic resonance spectrum was measured to determine the ratio (% by weight) of isotactic polymethyl methacrylate in the polymethacrylate. As shown in Table 1, since the porous sheet obtained in Comparative Example 1 had a high ratio of isotactic polymethyl methacrylate, a uniform alloy could not be obtained, and as a result, a film made of a porous material having non-uniform pore sizes It became.

(Comparative Example 2)
A porous sheet containing polymethyl methacrylate as a main component was obtained in the same manner as in Comparative Example 1 except that the melt kneading temperature was 200 ° C.

  A peak of a graph in which a square image of a piece of 60 μm obtained by observing the cross section of the porous sheet with a transmission electron microscope at a magnification of 300 times is Fourier transformed, and the wave number is plotted on the horizontal axis and the intensity is plotted on the vertical axis (A) / (b), which is an index of the hole diameter and uniformity, was determined from the wave number and the half-value width. Further, the sheet was dissolved in deuterated chloroform, and the proton nuclear magnetic resonance spectrum was measured to determine the ratio (% by weight) of isotactic polymethyl methacrylate in the polymethacrylate. As shown in Table 1, since the porous sheet obtained in Comparative Example 2 had a high ratio of isotactic polymethyl methacrylate, a uniform alloy could not be obtained, and as a result, a membrane composed of a porous body having non-uniform pore sizes It became.

(Comparative Example 3)
[Production of hollow fiber membranes by solution casting]
3.5 parts by weight of isotactic polymethyl methacrylate having a weight average molecular weight of 50,000 obtained by Grignard catalyzed polymerization, 13.7 parts by weight of syndiotactic polymethyl methacrylate (“SUMIPEX” AK-150) manufactured by Sumitomo Chemical Co., Ltd. In addition to 3.8 parts dimethylsulfoxide 79 parts of Mitsubishi Rayon Co., Ltd. syndiotactic polymethylmethacrylate ("Dyanal" BR-85), it was dissolved by heating. This stock solution was sent to a spinneret part having a temperature of 110 ° C., and nitrogen as an injection gas was simultaneously discharged from the double slit tube base. At this time, the distance between the die and the coagulation bath is 190 mm, immersed in a coagulation bath made of water at 40 ° C., washed with water, wound up at a speed of 50 m / min, hollow fiber membrane having an inner diameter of 200 μm and a film thickness of 30 μm. Got. The obtained hollow fiber membrane was freeze-dried.

[Measurement of surface area ratio]
The freeze-dried hollow fiber membrane was half-cut in the longitudinal direction with a single blade razor to expose the inner surface of the hollow fiber. The porosity of the inner surface of the hollow fiber was observed at a magnification of 200,000 times using a scanning electron microscope S-5500 type (manufactured by Hitachi, Ltd.). As a pretreatment for observation, the observation sample was sputtered with platinum. The obtained observation image was trimmed to a square with a side of 250 nm, and binarization (Thereshhold) and area calculation (Analyze Particles) were executed with image analysis software ScionImage (manufactured by Scion Corporation) to determine the surface open area ratio. The surface porosity of the inner surface of the hollow fiber membrane obtained in Comparative Example 3 was a low value of 10% or less. A microscopic observation image and an image binarized by image analysis software (opened portions are displayed in black) are shown in FIGS.

[Measurement of pore diameter and (a) / (b)]
For the pore diameter, the freeze-dried hollow fiber membrane was cleaved in liquid nitrogen, and the fractured surface was observed at a magnification of 100,000 using a scanning electron microscope S-5500 type (manufactured by Hitachi, Ltd.). As a pretreatment for observation, the observation sample was sputtered with platinum. The obtained observation image was trimmed to a square with a side of 500 nm, Fourier-transformed with image analysis software ScionImage (manufactured by Scion Corporation), and the pore diameter from the peak wave number and half-value width of the graph with the wave number plotted on the horizontal axis and the intensity plotted on the vertical axis And (a) / (b), which is an index of uniformity.

  These evaluation results are shown in Table 2.

  The porous body obtained by the production method of the present invention is capable of finely and uniformly controlling the pore diameter, and as a result, the polymethyl methacrylate porous body having excellent characteristics when used as a separation membrane or an adsorbent. Can be obtained. In addition, it can be used for printed circuit substrates and laminates as a low dielectric constant material by making use of fine and uniform continuous holes, as well as covers and seal members that prevent high-frequency component leakage current from inverters and switching power supplies. Can also be used.

Claims (13)

A porous body mainly composed of polymethyl methacrylate having continuous pores, the pore diameter of the continuous pores being 0.001 μm or more and 500 μm or less, and the porosity of at least one surface being 10% or more and 80% or less. The ratio of isotactic polymethyl methacrylate in the polymethyl methacrylate was less than 10% by weight, and was photographed with a square field of view having a length of 10 to 100 times the pore diameter of the porous body as one side. In a graph curve obtained by Fourier transforming a microscope image, the horizontal axis is the wave number and the vertical axis is the intensity, the peak half-value width (a) and the peak maximum wavelength (b) are 0 <(a) / (b) A porous body satisfying ≦ 1.2. The porous body is a sheet having a thickness of 1 µm to 5 mm, a hollow fiber having a thickness of 1 µm to 5 mm, a fiber having an outer diameter of 1 µm to 5 mm, or a particle having a diameter of 10 µm to 5 mm. 2. The porous body according to 1 . Separation membrane comprising a porous body according to any one of claims 1 to 2. The separation membrane according to claim 3 , wherein the substance to be separated is a biological component. The separation membrane according to claim 4 , wherein the biological component is blood or a part thereof. Adsorbent comprising a porous body according to any one of claims 1 to 2. The adsorbent according to claim 6 , wherein the adsorption symmetric substance is a biological component. The adsorbent according to claim 7 , wherein the biological component is blood or a part thereof. 3. The porous body according to claim 1, wherein the aliphatic polyester is removed from a polymer alloy molded article obtained from the polymethyl methacrylate having a ratio of isotactic polymethyl methacrylate of less than 10% by weight and the aliphatic polyester. Production method. The method for producing a porous body according to claim 9 , wherein the aliphatic polyester is polylactic acid. The method for producing a porous body according to any one of claims 9 to 10 , wherein the aliphatic polyester is removed by hydrolysis. The method for producing a porous body according to any one of claims 9 to 11 , wherein the polymer alloy is obtained by melt kneading. The method for producing a porous body according to any one of claims 9 to 12 , wherein the polymer alloy is obtained by phase separation by spinodal decomposition.

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