Method for producing porous resin body

Abstract

To form micropores.SOLUTION: In a production method of a resin porous body, (a) a polymer solution is formed by mixing an olefinic resin, a first solvent and a block copolymer in a pressure vessel, (b) mixed fluid is formed by mixing a high-pressure fluid of carbon dioxide and the polymer solution in the pressure vessel, (c) the mixed fluid is cooled thereby causing phase separation of the mixed fluid, and (d) a resin porous body is formed by releasing the pressure in the pressure vessel, after the phase separation.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for producing a porous resin body, and a porous resin body. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2016-176061 (Patent Document 1) discloses forming a resin porous body by press-molding polyethylene particles into a sheet and heating the sheet. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-176061 A Summary of the Invention [Problem to be solved by the invention]

[0004] Porous resin bodies are used in various applications. For example, there is a need for porous resin bodies having micropores. Thus, the present disclosure has an object to form micropores. [Means for solving the problem]

[0005] 1. A method for producing a resin porous body includes the following steps (a) to (d): (a) In a pressure vessel, an olefin resin, a first solvent, and a block copolymer are mixed to form a polymer solution. (b) A mixed fluid is formed by mixing a high-pressure fluid of carbon dioxide with a polymer solution in a pressure vessel. (c) The mixed fluid is cooled to cause phase separation of the mixed fluid. (d) After the phase separation, the pressure in the pressure vessel is released to form a resin porous body. The block copolymer comprises a first block and a second block, the first block comprising an olefinic component, and the second block comprising a non-olefinic component.

[0006] Conventionally, methods such as a method of sintering and molding a resin powder and a method of stretching a resin sheet have been proposed as methods for producing a resin porous body.

[0007] As a method for producing a resin porous body, high-pressure carbon dioxide (CO 2 Phase separation methods using a pore-like structure called a pore-like structure (Polyurethane) have also been investigated. In this method, for example, a unique three-dimensional network structure in which multiple bubble-like pores are interconnected can be formed. However, the pore size tends to be large, making it unsuitable for applications requiring micropores.

[0008] The three-dimensional mesh-like resin skeleton is formed by mixing a polymer solution with high-pressure CO 2 The block copolymer is formed by phase separation between the first block and the second block. Relatively large first pores are formed in the gaps between the resin skeleton. In the present disclosure, a block copolymer is added to a polymer solution. The block copolymer includes a first block and a second block. The first block includes an olefin component. The second component includes a non-olefin component. It is considered that the first block has high affinity with the olefin resin. Therefore, the block copolymer as a whole is compatible with the olefin resin. On the other hand, it is considered that the second block has low affinity with the olefin resin compared to the first block. Since the polymer compatible contains the second block, it is possible to obtain a high-pressure CO 2 It is believed that the stable phase state is lost when high pressure CO is added. 2 It is believed that the phase separation between the olefin resin and the block copolymer causes microphase separation, resulting in the formation of secondary pores (micropores) in the resin skeleton.

[0009] 2. The method for producing a resin porous body described in the above "1" may further include the following (e): (e) At least a portion of the block copolymer is separated from the resin porous body by dissolving the block copolymer in a second solvent. The block copolymer has a second solubility in the second solvent that is higher than a first solubility in the first solvent.

[0010] The block copolymer may be soluble in the first solvent. Therefore, a portion of the block copolymer may be dissolved in the first solvent and high pressure CO. 2 The block copolymer may be discharged from the system together with the first solvent. However, a part of the block copolymer may remain in the resin porous body (resin skeleton). The block copolymer may be eluted from the resin skeleton by a second solvent having a higher dissolving power than the first solvent. By eluting the block copolymer from the resin skeleton, further micropores may be formed in the resin skeleton.

[0011] 3. In the method for producing a resin porous body described in the above "2", the first solvent may contain, for example, n-pentane, and the second solvent may contain, for example, cyclohexane.

[0012] n-Pentane can dissolve olefin resins, and cyclohexane can have a higher dissolving power than n-pentane.

[0013] 4. In the method for producing a resin porous body according to any one of the above items "1" to "3", the olefin resin may contain at least one selected from the group consisting of polyethylene and polypropylene. The first block contains a first repeating unit. The second block contains a second repeating unit. The first repeating unit may be derived from at least one selected from the group consisting of ethylene, butylene, and butadiene. The second repeating unit may be derived from styrene.

[0014] 5. The resin porous body includes a resin skeleton. The resin skeleton is connected in a three-dimensional network. First pores that are connected in a three-dimensional network are formed in the gaps of the resin skeleton. Second pores are formed in the resin skeleton. The first pores have a first maximum Feret diameter of 10 μm or more. The second pores have a second maximum Feret diameter of 1 μm or less. The resin skeleton includes an olefin resin and a block copolymer. The block copolymer includes a first block and a second block. The first block includes an olefin component. The second block includes a non-olefin component.

[0015] Hereinafter, 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") will be 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 encompasses 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 arbitrarily combined. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic flow chart of the method for producing a porous resin body in this embodiment. [Diagram 2] FIG. 2 is a conceptual diagram showing an example of a manufacturing apparatus in this embodiment. [Diagram 3] Figure 3 is an SEM image of No. 0-1. [Figure 4] Figure 4 shows SEM images of No. 2-1 and 2-2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] <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 polymer solution", "(b) formation of a mixed fluid", "(c) phase separation", and "(d) release of pressure". The present production method may further include "(e) washing".

[0018] 《Manufacturing equipment》 2 is a conceptual diagram showing an example of a manufacturing apparatus in this embodiment. This 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 agitator 11, a heater 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.

[0019] 《(a) Polymer solution》 This manufacturing method includes forming a polymer solution by mixing an olefin resin, a first solvent, and a block copolymer in a pressure vessel 10. The "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. An agitator 11 may mix the materials in the pressure vessel 10.

[0020] In general, olefin resins tend to be difficult to dissolve in a solvent. To promote the formation of a solution, for example, the materials may be mixed in a high-temperature environment. For example, the materials may be mixed in a high-temperature and high-pressure environment. For example, the heating device 12 may heat the pressure vessel 10. The heating temperature may be, for example, the melting point of the olefin resin ±20°C. The heating temperature may be, for example, 90 to 160°C. For example, the olefin resin and the block copolymer may be dissolved in the first solvent to form a polymer solution. For example, the melt of the olefin resin and the block copolymer may be mixed with the first solvent to form a polymer solution. The "melting point" refers to the peak top temperature of the melting peak (endothermic peak) in a DSC (Differential Scanning Calorimetry) curve. The DSC curve may be measured in accordance with "JIS K 7121".

[0021] (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 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 (product name "Prime Polypro (registered trademark) J137G"), etc. may be used.

[0022] (First Solvent) The first solvent may be, for example, a good solvent for the olefin resin, and may contain, for example, n-pentane.

[0023] (Block copolymer) The block copolymer may be, for example, in the form of a powder or pellet. The block copolymer may be compatible with an olefin resin. The block copolymer includes a first block and a second block. The block copolymer may include a plurality of first blocks and a plurality of second blocks. The block copolymer may include, for example, 1 to 5 first blocks and 1 to 5 second blocks. The block copolymer may include, for example, 1 to 3 first blocks and 1 to 3 second blocks. The total number of the first blocks and the second blocks may be, for example, 2 to 10, 3 to 5, or 3 to 4. The first block includes an olefin component. The first block includes a first repeating unit. The first repeating unit may be derived from at least one selected from the group consisting of ethylene, butylene, and butadiene. The second block includes a non-olefin component. The second block includes a second repeating unit. The second repeating unit may be derived from, for example, styrene. The first block and the second block may each independently include a graft chain.

[0024] The block copolymer may include at least one selected from the group consisting of, for example, polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene (SEBS), polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene-graft-maleic anhydride (SEBSM), polystyrene-block-polybutadiene-block-polystyrene (SBS), and polystyrene-block-poly(ethylene-co-butylene)-block-polyethylene (SEBE). Note that "-co-" indicates an unspecified type. "-co- (unspecified type)" includes "-stat- (statistical type)", "-ran- (random type)", "-alt- (alternating type)", "-per- (periodic type)", "-block- (block type)" and "-graft- (graft type)". The block copolymer may have a relatively low molecular weight. The block copolymer may have, for example, a mass average molecular weight (Mw) of 10,000 to 100,000. The "mass average molecular weight" can be measured by GPC (Gel Permeation Chromatography).

[0025] The mass fraction of the block copolymer relative to the total amount of the olefin resin and the block copolymer may be, for example, 1% or more, 2.44% or more, 8% or more, or 10% or more. The mass fraction may be, for example, 50% or less, 30% or less, 20% or less, or 12% or less. When the mass fraction is 12% or less, the shape stability of the resin porous body tends to be good.

[0026] The mass ratio of the first solvent to the total amount of the olefin resin and the block copolymer may be, for example, 50 to 150 or 50 to 100. Numerical ranges such as "m to n%" include upper and lower limits 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%."

[0027] (b) Formation of a mixed fluid In this production method, CO 2and mixing the high pressure fluid with a polymer solution to form a mixed fluid.

[0028] "High pressure fluid" refers to a fluid at or above the critical pressure. High pressure fluids include supercritical fluids. "Supercritical fluid" refers to a fluid at or above the critical pressure and above the critical temperature. For example, CO 2 Gas cylinder 1 filled with CO (gas) is prepared. 2 Supply CO 2 The CO is supplied to the compressor 5 via the drying tube 2 and the cooling device 3. 2 A high pressure fluid can be formed by compressing the liquid above its critical pressure.

[0029] 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. For example, 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 becomes equal to or higher than 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.

[0030] 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 7.38 MPa (CO 2 The pressure in the pressure vessel 10 is adjusted to be equal to or higher than the critical pressure of CO 2 . The pressure in the pressure vessel 10 may be adjusted to, for example, 10 to 20 MPa. In the pressure vessel 10, the high-pressure fluid and the polymer solution are mixed to form a mixed fluid. For example, the mixed fluid may be stirred by a stirring device 11. In the mixed fluid, the high-pressure fluid (CO 2 2 ) is a poor solvent.

[0031] 《(c) Phase separation》 This 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.

[0032] (d) Release of Pressure The present manufacturing method includes forming a resin porous body by releasing the pressure in the pressure vessel 10 after the phase separation. By releasing the pressure, the first solvent and the CO 2 The first solvent and CO may evaporate from the system. 2 The first solvent and CO evaporate, leaving the resin skeleton (porous resin body). At this time, part of the block copolymer also evaporates. 2 It is considered that the residual liquid may be discharged to the outside of the system together with the liquid. For example, the heating device 12 may heat the pressure vessel 10 to 40 to 60°C before the pressure is released. By heating the pressure vessel 10 before the pressure is released, the generation of dry ice may be reduced. If dry ice is generated, the pore structure may be damaged.

[0033] After the pressure vessel 10 is heated, the pressure inside the pressure vessel 10 is gradually reduced. The pressure reduction time may be, for example, 10 to 30 minutes. During the pressure reduction process, the first solvent and CO 2 The resin porous body is formed by the evaporation of the resin. 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).

[0034] (e) Cleaning The present production method may include washing the resin porous body with a second solvent. The washing may dissolve the block copolymer remaining in the resin skeleton. The block copolymer may be removed in its entirety or in part. That is, the present production method may include separating at least a part of the block copolymer from the resin porous body by dissolving the block copolymer in the second solvent. The block copolymer may remain in the resin porous body after washing.

[0035] The second solvent has a higher dissolving power than the first solvent. That is, the second solubility of the block copolymer in the second solvent is higher than the first solubility of the block copolymer in the first solvent. "Solubility" refers to the limit mass of a solute that can be dissolved in 100 g of a solvent at 25°C. The second solvent may contain, for example, cyclohexane.

[0036] <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.

[0037] The resin porous matrix includes a resin skeleton. The resin skeleton includes an olefin resin. The resin skeleton may further include a block copolymer. The resin skeleton is connected in a three-dimensional network. First pores that are interconnected in a three-dimensional network are formed in the gaps of the resin skeleton. The first pores may be formed by interconnecting a plurality of bubble-like pores. The resin skeleton itself is porous. That is, second pores (micropores) are formed in the resin skeleton.

[0038] The first pores have a first maximum Feret diameter of 10 μm or more. The first maximum Feret diameter may be, for example, 10 to 200 μm. The second pores have a second maximum Feret diameter of 1 μm or less. The second maximum Feret diameter may be, for example, 0.01 to 1 μm. The "maximum Feret diameter" is measured in a SEM (Scanning Electron Microscope) image of the cross section (or side) of the resin porous body. The maximum Feret diameter indicates the maximum diameter of the opening. The maximum Feret diameter is measured for each of 10 randomly extracted first pores (openings). The arithmetic average of the 10 is adopted. The second pores are similarly measured. However, the magnification of the image may be adjusted according to the size of the first pores and the second pores. The first maximum Feret diameter may be measured, for example, in an image with a magnification of about 100 times. The second maximum Feret diameter may be measured, for example, in an image with a magnification of about 2000 times. EXAMPLES

[0039] <Production of Porous Resin Body> No.1-1 The following materials were prepared: Olefin resin: LDPE "Petrocene 353" manufactured by Tosoh Corporation First solvent: n-pentane (CAS No. 109-66-0) Block copolymer: SEBS

[0040] A manufacturing apparatus 100 was prepared (see FIG. 2). 4.5 g of n-pentane, PE, and SEBS were charged into a pressure vessel 10. The total amount of PE and SEBS was 0.05 g. The mass fraction of SEBS relative to the total amount of PE and SEBS was 2.44%. The heating device 12 heated the pressure vessel 10 to 95° C.

[0041] Gas cylinder 1 is CO 2 Compressor 5 supplies CO 2 A high-pressure fluid was formed by compressing the high-pressure fluid. The temperature of the high-pressure fluid was adjusted to 100° C. by the temperature adjustment device 8. 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.

[0042] 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.

[0043] 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.

[0044] An SEM image of the cross section (or side surface) of the resin porous body was obtained. In the SEM image, the presence or absence of the first pores and the second pores was confirmed.

[0045] No.1-2 The resin porous body obtained in No.1-1 was washed by shaking in cyclohexane. After shaking for 24 hours, the resin porous body was dried. After drying, the shape stability of the resin porous body was evaluated and SEM images were taken. That is, No.1-1 is the sample before washing, and No.1-2 is the sample after washing.

[0046] No.2-1~No.6-2 Except for the mass fraction of the block copolymer relative to the total amount of the olefin resin and the block copolymer being changed, resin porous bodies were produced in the same manner as in No. 1-1 and 1-2 (see Table 1 below). For example, No. 2-1 is a sample before washing, and No. 2-2 is a sample after washing, in the same manner as in No. 1-1 and 1-2.

[0047] No.0-2 A resin porous body was produced in the same manner as in No. 1-1, except that no block copolymer was used.

[0048] No.0-1 A resin porous body was produced in the same manner as in No. 0-2, except that the amounts of PE and n-pentane used were changed.

[0049] [Table 1]

[0050] <Result> By mixing the block copolymer into the polymer solution, the resin skeleton becomes porous, and secondary pores (micropores) tend to form (comparison of No. 0-1, 0-2 with other samples).

[0051] FIG. 3 is an SEM image of No. 0-1. In No. 0-1, a resin skeleton that is connected in a three-dimensional network is formed. First pores that are interconnected in a three-dimensional network are formed in the gaps of the resin skeleton. The first pores are formed by a plurality of bubble-like pores that are interconnected. The first pores have a first maximum Feret diameter of 10 μm or more. The resin skeleton is non-porous. No micropores are formed in the resin skeleton.

[0052] Figure 4 shows SEM images of No. 2-1 and 2-2. In No. 2-1, secondary pores (micropores) are formed in the inner walls (resin skeleton) of the primary pores. The secondary pores have a second maximum Feret diameter of 1 μm or less. No. 2-2 is a sample obtained by washing No. 2-1. There is a tendency for the porosity of the resin skeleton to increase by washing. This is thought to be due to the elution of the block copolymer remaining in the resin skeleton.

[0053] The higher the mass fraction of the block copolymer, the lower the shape stability tends to be (No. 5-1 to 7-1). It is believed that the strength of the resin skeleton decreases due to the increase in porosity of the resin skeleton. Samples with low shape stability may be damaged during washing (for example, compare No. 5-1 with No. 5-2). [Explanation of symbols]

[0054] Reference Signs List 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 agitation 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 equipment.

Claims

1. (a) combining an olefinic resin, a first solvent, and a block copolymer in a pressure vessel to form a polymer solution; (b) forming a mixed fluid by mixing a high pressure fluid of carbon dioxide and the polymer solution in the pressure vessel; (c) cooling the mixed fluid to cause phase separation of the mixed fluid; and (d) after the phase separation, releasing the pressure in the pressure vessel to form a resin porous body; Including, The block copolymer comprises a first block and a second block, the first block comprises an olefinic component; the second block comprises a non-olefinic component; a mass fraction of the block copolymer relative to the total amount of the olefin resin and the block copolymer is 2.44% or more and 12% or less; A method for producing a resin porous body.

2. (e) separating at least a portion of the block copolymer from the resin porous body by dissolving the block copolymer in a second solvent; Further comprising: a second solubility of the block copolymer in the second solvent is higher than a first solubility of the block copolymer in the first solvent; The method for producing the resin porous body according to claim 1 .

3. the first solvent comprises n-pentane; and The second solvent comprises cyclohexane. The method for producing the resin porous body according to claim 2 .

4. The olefin resin includes at least one selected from the group consisting of polyethylene and polypropylene, the first block comprises a first repeat unit, the second block comprises a second repeat unit, The first repeat unit is derived from at least one selected from the group consisting of ethylene, butylene, and butadiene; and The second repeat unit is derived from styrene. The method for producing a resin porous body according to any one of claims 1 to 3.

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