JP7639802B2 - Method for producing porous resin body - Google Patents

Description

The present disclosure relates to a method for producing a resin porous body, and a resin porous body.

JP 2016-176061 A (Patent Document 1) discloses forming a resin porous body by press-molding polyethylene particles into a sheet and then heating the sheet.

JP 2016-176061 A

The purpose of this disclosure is to provide a resin porous body with small variation in pore size.

1. A method for producing a resin porous body includes the following steps (a) to (c):
(a) A mixed fluid is formed by mixing a high-pressure fluid of carbon dioxide, an olefin-based resin, insulating particles, and a solvent in a pressure vessel.
(b) Cooling the mixed fluid causes phase separation of the mixed fluid.
(c) After the phase separation, the pressure in the pressure vessel is released to form a resin porous body.

Conventionally, methods proposed for producing porous resin bodies include sintering resin powder and stretching a resin sheet.

A phase separation method using high-pressure carbon dioxide (CO ₂ ) is also being considered as a method for producing a resin porous body. In this method, for example, a unique three-dimensional network structure in which a plurality of bubble-like pores are interconnected can be formed. However, there is a tendency for the pore size to vary widely. Due to the large variation, coarse pores can also be formed. Some applications of the resin porous body require small variation in pore size and fine pores.

The three-dimensional mesh-like resin skeleton is formed by phase separation between the resin component and high-pressure CO ₂ (poor solvent). During phase separation, the temperature, pressure, and composition of the system may change in a complex manner. As a result, it is believed that pores of various sizes may be generated randomly. According to the new findings of this disclosure, during phase separation, the presence of insulating particles in the system tends to reduce the variation in pore size and to make the pores finer. Although this is merely speculation, the following mechanism is thought to be the cause.

First possible mechanism: Insulating particles can be the starting point of phase separation. By dispersing insulating particles throughout the system, phase separation can be induced uniformly throughout the system.

Second assumed mechanism: When the mixed fluid is cooled, phase separation is induced and the structure of the resin skeleton is fixed. In other words, the formation of the resin skeleton is accompanied by a large temperature change. The resin skeleton is mainly composed of olefin-based resin. The linear expansion coefficient of the insulating particles is significantly different from that of the olefin-based resin. Therefore, as the temperature of the system changes, distortion may occur at the interface between the insulating particles and the olefin-based resin. The distortion may become pores. For example, the size of the insulating particles may be a controlling factor, reducing the variation in pore size and making the pores finer.

2. In the method for producing a resin porous body described in "1" above, the insulating particles may contain at least one type selected from the group consisting of boehmite, alumina, titania, magnesia, and zirconia.

3. In the method for producing a resin porous body described in "1" or "2" above, the mass fraction of the insulating particles relative to the total mass of the olefin resin and the insulating particles may be, for example, 7.7 to 33.3%.

By having the mass fraction of insulating particles be 7.7% or more, it is expected that the variation in pore size will be reduced. By having the mass fraction of insulating particles be 33.3% or less, it is expected that the shape stability will be improved.

4. In the method for producing a resin porous body according to any one of the above items "1" to "3," the above (a) may include the following (a1) and (a2):
(a1) An olefin resin and insulating particles are mixed to form a mixture.
(a2) A mixed fluid is formed by mixing a high pressure fluid of carbon dioxide, the mixture, and a solvent in a pressure vessel.

It is believed that the dispersibility of the olefin resin and the insulating particles affects the variation in pore size. By premixing the olefin resin and the insulating particles prior to mixing with high pressure _CO2 , it is expected that the dispersibility will be improved and the variation in pore size will be reduced.

5. The resin porous body includes a resin skeleton. The resin skeleton is connected in a three-dimensional network. Pores that are connected in a three-dimensional network are formed in the gaps between the resin skeleton. The resin skeleton includes an olefin resin and insulating particles. The olefin resin forms a continuous phase. And the insulating particles form a dispersed phase.

Below, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present embodiment") are described. However, the present embodiment and the present embodiment do not limit the technical scope of the present disclosure. The present embodiment and the present embodiment are illustrative in all respects. The present embodiment and the present embodiment are non-restrictive. The technical scope of the present disclosure includes all modifications within the meaning and scope equivalent to the description of the claims. For example, it is originally intended that any configuration may be extracted from the present embodiment and the present embodiment, and that they may be combined in any manner.

FIG. 1 is a schematic flow chart of a method for producing a resin porous body in this embodiment. FIG. 2 is a conceptual diagram showing an example of a manufacturing apparatus according to this embodiment. FIG. 3 shows SEM images of Nos. 0, 1, 2, and 7.

<Method of manufacturing resin porous body>
Fig. 1 is a schematic flow chart of the method for producing a resin porous body in this embodiment. Hereinafter, "the method for producing a resin porous body in this embodiment" may be abbreviated as "the present production method". The present production method includes "(a) formation of a mixed fluid", "(b) phase separation", and "(c) release of pressure".

Manufacturing Equipment
2 is a conceptual diagram showing an example of a manufacturing apparatus in this embodiment. The manufacturing method can be implemented in, for example, a manufacturing apparatus 100. The manufacturing apparatus 100 includes a gas cylinder 1, a drying tube 2, a cooling device 3, a filter 4, a compression device 5, a first pressure gauge 6, a first safety valve 7, a temperature adjustment device 8, a check valve 9, a pressure vessel 10, an agitation device 11, a heating device 12, a second pressure gauge 13, a second safety valve 14, and a wet gas flow meter 15. The manufacturing apparatus 100 further includes a back pressure valve 21, a first valve 22, a second valve 23, and a third valve 24. The first valve 22 to the third valve 24 can each independently open and close the flow path.

(a) Formation of mixed fluid
The manufacturing method includes forming a mixed fluid by mixing a high-pressure fluid of carbon dioxide, an olefin resin, insulating particles, and a solvent in a pressure vessel. A "pressure vessel" refers to a sealed vessel that receives pressure from at least one of the inside and outside of the vessel. The pressure vessel may be configured to withstand a pressure of, for example, 0.2 to 50 MPa. In this specification, a numerical range such as "m to n%" includes an upper limit and a lower limit unless otherwise specified. In other words, "m to n%" indicates a numerical range of "m% or more and n% or less". "m% or more and n% or less" includes "more than m% and less than n%".

For example, all materials may be mixed together in a pressure vessel. For example, prior to mixing in the pressure vessel, premixing of the olefin resin and insulating particles may be performed outside the pressure vessel. That is, the present manufacturing method may include "(a1) premixing" and "(a2) adding high-pressure CO _2" . In the premixing, the olefin resin and insulating particles are mixed to form a mixture. Next, in the pressure vessel, the mixture, high-pressure CO ₂ , and a solvent may be mixed to form a mixed fluid.

By carrying out premixing, the dispersibility of the olefin resin and the insulating particles can be improved. As a result, it is expected that the variation in pore size will be reduced. In premixing, a melt of the olefin resin and the insulating particles may be mixed. Premixing may be carried out, for example, by a twin-screw kneader (twin-screw extruder) or the like. A solvent may be used in premixing.

(Olefin resin)
The olefin resin may be, for example, in the form of a powder or pellets. The olefin resin refers to a polymeric material synthesized from a monomer containing an alkene. The olefin resin may be a homopolymer or a copolymer. The olefin resin may contain, for example, at least one selected from the group consisting of low-density polyethylene (LDPE), high-density polyethylene (HDPE), ultra-high molecular weight polyethylene (UHMW), polypropylene (PP), polymethylpentene (PMP), and ethylene-vinyl acetate copolymer (EVA). For example, LDPE manufactured by Tosoh Corporation (product name "Petrothene (registered trademark) 353"), PP manufactured by Prime Polymer Co., Ltd. (product name "Prime Polypro (registered trademark) J137G"), etc. may be used.

(insulating particles)
The insulating particles have insulating properties. The insulating particles may have a volume resistivity of, for example, 1×10 ¹⁰ Ω·cm or more, or 1×10 ¹⁵ Ω·cm or more. The insulating particles may include, for example, a ceramic material or the like. The insulating particles may include, for example, a metal oxide or the like. The insulating particles may include, for example, at least one selected from the group consisting of boehmite, alumina, titania, magnesia, and zirconia. The insulating particles may have any shape. The insulating particles may be, for example, spherical, ellipsoidal, rod-like, plate-like, or the like. The insulating particles may have an aspect ratio of, for example, 1 to 20 or 5 to 15. The "aspect ratio" refers to the ratio of the major axis diameter to the minor axis diameter. In this specification, elements expressed in the singular form also include the plural form unless otherwise specified. For example, "particle" can mean not only "one particle" but also "an aggregate of particles (powder, powder, particle group)". The insulating particles may have an average particle size of, for example, 10 nm to 5 μm, 10 nm to 1 μm, or 0.5 to 2 μm. The "average particle size" is measured by microscopy. The average particle size refers to the arithmetic mean of the maximum Feret diameters of 100 particles. The "maximum Feret diameter" refers to the distance between the two most distant points on the contour of a particle. The 100 particles are randomly selected.

The olefin resin has a first linear expansion coefficient. The insulating particles have a second linear expansion coefficient. The insulating particles may have a linear expansion coefficient smaller than that of the olefin resin. For example, the ratio of the second linear expansion coefficient to the first linear expansion coefficient may be 0.01 to 0.5, or 0.05 to 0.1. The first linear expansion coefficient may be, for example, 50 to 200×10 ⁶ /K. The first linear expansion coefficient may be measured in accordance with "JIS K7197-1991". The second linear expansion coefficient may be, for example, 2×10 ⁶ to 20×10 ⁶ /K, or 5×10 ⁶ to 10×10 ⁶ /K. The second linear expansion coefficient may be measured in accordance with "JIS R1618:2022".

The mass fraction of the insulating particles relative to the total of the olefin resin and the insulating particles may be, for example, 7.7 to 33.3%. When the mass fraction of the insulating particles is 7.7% or more, it is expected that the variation in pore size will be reduced. The mass fraction of the insulating particles may be, for example, 7.8% or more, or 10% or more. When the mass fraction of the insulating particles is 33.3% or less, it is expected that the shape stability (strength) will be improved. The mass fraction of the insulating particles may be, for example, 30% or less, or 20% or less.

(solvent)
The solvent may be, for example, a good solvent for the olefin resin, and may include, for example, n-pentane, cyclohexane, etc.

(High Pressure _CO2 )
In the pressure vessel, the mixture is mixed with a high-pressure fluid of _CO2 to form a mixed fluid. The high-pressure fluid of _CO2 is also referred to as "high-pressure _CO2 ". In the mixed fluid, the high-pressure _CO2 is a poor solvent. "High-pressure fluid" refers to a fluid at or above the critical pressure. The high-pressure fluid includes a supercritical fluid. "Supercritical fluid" refers to a fluid at or above the critical pressure and above the critical temperature. For example, a gas cylinder 1 filled with _CO2 (gas) is prepared. The gas cylinder 1 supplies _CO2 . _{The CO2} is supplied to a compressor 5 via a drying tube 2 and a cooling device 3. The compressor 5 compresses the _CO2 to or above the critical pressure, so that a high-pressure fluid can be formed.

For example, the temperature adjustment device 8 may heat the high-pressure fluid. The temperature adjustment device 8 may include, for example, a preheating tube or the like. The temperature of the high-pressure fluid may be, for example, 20°C or more, 30°C or more, 40°C or more, or 50°C or more. When the temperature of the high-pressure fluid reaches or exceeds the critical temperature (31°C), a supercritical fluid may be formed. The temperature of the high-pressure fluid may be, for example, 200°C or less, 150°C or less, or 100°C or less.

The pressure vessel 10 is pressurized by introducing the high-pressure fluid into the pressure vessel 10. The pressure inside the pressure vessel 10 is adjusted to 7.38 MPa (critical pressure of _CO2 ) or higher. The pressure inside the pressure vessel 10 may be adjusted to, for example, 10 to 20 MPa. In the pressure vessel 10, a stirring device 11 may stir the mixed fluid.

(b) Phase Separation
The present manufacturing method includes cooling the mixed fluid to cause phase separation of the mixed fluid. For example, the pressure vessel 10 may be cooled by a water-cooled chiller (not shown). The temperature of the pressure vessel 10 is cooled to, for example, 15 to 25°C. After the temperature of the pressure vessel 10 reaches 15 to 25°C, the temperature of 15 to 25°C is maintained for, for example, 20 to 40 minutes. This allows phase separation of the mixed fluid to proceed. The phase separation may be spinodal decomposition (liquid-liquid phase separation). The modulated structure during spinodal decomposition may form a resin skeleton that is connected in a three-dimensional network shape.

(c) Release of Pressure
The method includes forming a resin porous body by releasing the pressure in the pressure vessel 10 after phase separation. Releasing the pressure can cause the solvent and _CO2 to volatilize. The solvent and _CO2 volatilize from the system, leaving a resin skeleton (resin porous body). For example, the heating device 12 can heat the pressure vessel 10 to 40-60°C before releasing the pressure. Heating the pressure vessel 10 before releasing the pressure can reduce the generation of dry ice, which can damage the pore structure.

After the pressure vessel 10 is heated, the pressure inside the pressure vessel 10 is gradually reduced. The reduction in pressure may be, for example, 10 to 30 minutes. In the process of reduction in pressure, the solvent and _CO2 are evaporated to form a resin porous body. After the inside of the pressure vessel 10 reaches an equilibrium state, the resin porous body can be collected. For example, the resin porous body may be collected after the inside of the pressure vessel 10 reaches atmospheric pressure and room temperature (10 to 30°C).

<Porous resin body>
In this manner, a resin porous body is produced. The resin porous body may have any outer shape. The resin porous body may be, for example, in the form of a film or a plate. The resin porous body may have a thickness of, for example, 1 μm to 10 mm. The resin porous body may be used, for example, as a separator for a lithium ion battery.

The resin porous body includes a resin skeleton. The resin skeleton includes an olefin resin and insulating particles. The olefin resin forms a continuous phase. The insulating particles form a dispersed phase. The resin skeleton is connected in a three-dimensional network. Pores that are interconnected in a three-dimensional network are formed in the gaps in the resin skeleton. The pores may be formed by interconnecting a plurality of bubble-like pores.

The pore size may be, for example, 50 μm or less. The pore size may be, for example, 1 to 50 μm, or 5 to 20 μm. The "pore size" is measured in a SEM (Scanning Electron Microscope) image of the cross section (or side) of the resin porous body. The pore size indicates the arithmetic mean of the maximum Feret diameter of 10 pores. The maximum Feret diameter indicates the distance between the two most distant points on the contour line of the pore opening. The 10 pores are selected at random.

<Production of Porous Resin Body>
"No. 1"
The following materials were prepared:
Olefin resin: LDPE "Petrothene 353" manufactured by Tosoh Corporation Insulating particles: boehmite (plate-shaped particles, average particle size: 1.7 μm, aspect ratio: 10)
Solvent: n-pentane (CAS No. 109-66-0)

The olefin resin and insulating particles were premixed. That is, the olefin resin and insulating particles were mixed in a twin-screw kneader to form a mixture.

The manufacturing device 100 was prepared (see Figure 2). The mixture and solvent were sealed in the pressure vessel 10. The blending amounts of each material are shown in Table 1 below. The heating device 12 heated the pressure vessel 10 to 95°C.

The gas cylinder 1 supplied _CO2 . The compression device 5 compressed the _CO2 to form a high-pressure fluid. The temperature adjustment device 8 adjusted the temperature of the high-pressure fluid to 100°C. The high-pressure fluid after temperature adjustment was introduced into the pressure vessel 10. The high-pressure fluid was supplied so that the pressure inside the pressure vessel 10 became 15 MPa.

The water-cooled chiller cooled the pressure vessel 10 to 20°C. After reaching 20°C, the temperature was maintained at around 20°C for 30 minutes. The heating device 12 heated the pressure vessel 10 to 50°C. After heating, the pressure vessel 10 was gradually depressurized. The depressurization time was 20 minutes. When the pressure inside the pressure vessel 10 reached atmospheric pressure and room temperature, the resin porous body was collected. The resin porous body had a membrane shape.

SEM images of the cross section (or side) of the resin porous body were taken. The SEM images were used to evaluate the pore size variation and refinement. In the "Pore size variation/refinement" section of Table 1 below, "Reference" indicates the reference. "+" indicates that the pore size variation was smaller and the pores were refined compared to the reference. "++" indicates that the pore size variation was significantly smaller and the pores were refined compared to the reference.

The shape stability of the resin porous body was evaluated. In the "shape stability" section of Table 1 below, "P (pass)" indicates that the resin porous body maintained its film shape. "F (fail)" indicates that the resin porous body was unable to maintain its film shape and collapsed.

"No. 2 to 6"
Except for the change in the blending amount of the olefin resin and the insulating particles, the resin porous body was manufactured in the same manner as in No. 1 (see Table 1 below). In No. 4, the resin porous body could not maintain the film shape and collapsed, so the variation in pore size was not evaluated.

"No. 7"
The olefin resin and the insulating particles were not premixed, and the olefin resin, the insulating particles, the solvent, and the high-pressure _CO2 were mixed in a pressure vessel. Except for this, a resin porous body was produced in the same manner as in No. 1.

"Number 0"
A resin porous body was produced in the same manner as in No. 7, except that no insulating particles were used and the blending amount of the solvent was changed.

<Results>
There is a tendency for the addition of insulating particles to reduce the variation in pore size (comparison of Nos. 1 to 7 with No. 0).

As the mass fraction of insulating particles increases, there is a tendency for shape stability (strength) to decrease (No. 4).

By carrying out premixing, there is a tendency for the variation in pore size to be reduced (comparison between No. 1 and No. 7).

Figure 3 shows SEM images of No. 0, 1, 2, and 7. No. 0 does not use insulating particles. No. 0 has a large variation in pore size and has large pores.

Nos. 1 and 2 use insulating particles. Nos. 1 and 2 have less variation in pore size compared to No. 0. Furthermore, the pores are finer in Nos. 1 and 2.

No. 7 was not premixed. Insulating particle aggregates can be seen in No. 7. No. 7 has a slightly larger variation in pore size than Nos. 1 and 2.

1 Gas cylinder, 2 Drying tube, 3 Cooling device, 4 Filter, 5 Compression device, 6 First pressure gauge, 7 First safety valve, 8 Temperature control device, 9 Check valve, 10 Pressure vessel, 11 Stirring device, 12 Heating device, 13 Second pressure gauge, 14 Second safety valve, 15 Wet gas flow meter, 21 Back pressure valve, 22 First valve, 23 Second valve, 24 Third valve, 100 Manufacturing device.

Claims (3)

(a) mixing a high-pressure fluid of carbon dioxide, an olefin-based resin, insulating particles, and a solvent in a pressure vessel to form a mixed fluid containing the high-pressure fluid of carbon dioxide, the olefin-based resin , and the solvent, and dispersing the insulating particles in the mixed fluid ;
(b) cooling the mixed fluid to cause phase separation between a resin component containing the olefin resin and the solvent and the high-pressure fluid of carbon dioxide ; and
(c) releasing the pressure in the pressure vessel after the phase separation to form a resin porous body;
Including ,
The insulating particles have electrical insulation properties,
The mass fraction of the insulating particles relative to the total mass of the olefin resin and the insulating particles is 7.7 to 33.3%.
A method for producing a resin porous body. The insulating particles include at least one selected from the group consisting of boehmite, alumina, titania, magnesia, and zirconia.
The method for producing the resin porous body according to claim 1 . The (a) is
(a1) mixing the olefin-based resin and the insulating particles to form a mixture; and
(a2) mixing the high pressure fluid of carbon dioxide, the mixture, and the solvent in the pressure vessel to form the mixed fluid in which the insulating particles are dispersed ;
Including,
The method for producing the resin porous body according to claim 1 or 2.

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