JP7616192B2 - Method for producing porous body - Google Patents

Description

This disclosure relates to a method for producing a porous body.

Polymer porous bodies (hereinafter simply referred to as "porous bodies") are used, for example, in foams (e.g., cushioning materials, etc.), separation membranes (e.g., water treatment, etc.), porous membranes (e.g., battery separators, etc.), and reflective substrates (e.g., lighting fixtures, etc.).

Patent Document 1 discloses a method for forming a porous body. In the method disclosed in Patent Document 1, a composition containing a binder resin, a photosensitive compound, and a photopolymerization initiator is applied onto a substrate to form a coating film. Next, the coating film is irradiated with ultraviolet light according to the desired pattern using an ultra-high pressure mercury lamp. Next, the coating film is immersed in a poor solvent for the binder resin. Next, the poor solvent that has penetrated into the coating film is volatilized. This results in a porous body.

JP 2004-143427 A

However, Patent Document 1 does not disclose a method for controlling the pore size of the porous body. Depending on the application of the porous body (e.g., separation membrane, porous membrane, etc.), a porous body with a pore size of 1000 nm or less is required.

The present disclosure has been made in consideration of the above circumstances.
An object of one embodiment of the present disclosure is to provide a method for producing a porous body capable of producing a porous body having a pore size of 1000 nm or less.

As a result of intensive research into the above problem, the inventors have experimentally discovered that the pore size of the resulting porous body can be controlled by using a polymerizable monomer whose functional group concentration, which is one of the factors that affect the polymerization rate, is within a specific range. Based on this knowledge, the inventors have completed the present invention.

Means for solving the above problems include the following embodiments.
<1> preparing a solution containing a polymerizable monomer having a functional group concentration of 3.0 mmol/g to 12.5 mmol/g, a polymerization initiator, and a solvent;
activating the polymerization initiator contained in the solution to polymerize the polymerizable monomer, thereby forming a phase-separated product containing a porous body and the solvent from the solution;
and vaporizing the solvent contained in the phase-separated product.
<2> The method for producing a porous body according to <1>, wherein the solution is adjusted so that the functional group concentration is 5.0 mmol/g or more.
<3> The method for producing a porous body according to <1> or <2>, wherein in adjusting the solution, a content of the polymerizable monomer is 14% by mass to 44% by mass with respect to a total amount of the solution.
<4> The method for producing a porous body according to any one of <1> to <3>, wherein in preparing the solution, the content of the polymerization initiator is 0.01% by mass to 3.00% by mass with respect to the total amount of the solution.
<5> The method for producing a porous body according to any one of <1> to <4>, wherein the pore size of the porous body is 500 nm or less.

The present disclosure provides a method for producing a porous body that can produce a porous body with a pore size of 1000 nm or less.

1 is a scanning electron microscope (SEM) photograph (magnification: 50,000 times) of the surface of the porous body of the example. 1A is Comparative Example 1 (functional group concentration: 2.9 mmol/g), 1B is Example 1 (functional group concentration: 6.7 mmol/g), and 1C is Example 2 (functional group concentration: 7.0 mmol/g). 2 is a SEM photograph (magnification: 50,000 times) of the surface of the porous body of the example. 2A is Example 3 (functional group concentration: 8.6 mmol/g), 2B is Example 4 (functional group concentration: 10.5 mmol/g), and 2C is Example 5 (functional group concentration: 11.5 mmol/g). FIG. 3 is an SEM photograph (magnification: 50,000 times) of the surface of the porous body of Example 6 (functional group concentration: 11.8 mmol/g). 4 is an SEM photograph (magnification: 50,000 times) of the surface of the porous body of the example. 4A is Example 4 (solvent: diethylene glycol diethyl ether), and 4B is Example 7 (solvent: 2-ethoxyethanol). 5 is a SEM photograph (magnification: 50,000 times) of the surface of the porous body of the example. 5A is Example 8 (monomer concentration: 9 mass%), 5B is Example 9 (monomer concentration: 19 mass%), 5C is Example 1 (monomer concentration: 29 mass%), and 5D is Example 10 (monomer concentration: 39 mass%). 6 is an SEM photograph (magnification: 50,000 times) of the surface of the porous body of the example. 6A is Example 11 (polymerization initiator concentration: 0.01 mass%), 6B is Example 1 (polymerization initiator concentration: 1 mass%), and 6C is Example 12 (polymerization initiator concentration: 5 mass%).

In this disclosure, a numerical range indicated using "~" means a range including the numerical values before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In the numerical ranges described in this disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in an example. In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In this disclosure, the amount of each component means the total amount of the multiple substances unless otherwise specified, when there are multiple substances corresponding to each component. In this disclosure, the term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. In this disclosure, "(meth)acrylate" refers to at least one of acrylate and methacrylate, and "(meth)acryloyl group" refers to at least one of acryloyl group and methacryloyl group.

(1) Manufacturing method of a porous body The manufacturing method of a porous body of the present disclosure includes preparing a solution containing a polymerizable monomer having a functional group concentration of 3.0 mmol/g to 12.5 mmol/g (hereinafter also simply referred to as "polymerizable monomer"), a polymerization initiator, and a solvent (hereinafter also referred to as "preparation step"); activating the polymerization initiator contained in the solution and polymerizing the polymerizable monomer to form a porous body having a pore size of 1000 nm or less and a phase-separated product containing the solvent from the solution (hereinafter also referred to as "formation step"); and vaporizing the solvent contained in the phase-separated product (hereinafter also referred to as "vaporization step").

The term "polymerizable monomer" refers to a monomer containing an ethylenically unsaturated group. The term "functional group concentration" refers to a value calculated from the following formula (a).
Formula (a): Functional group concentration [mmol/g] = (average number of functional groups contained in polymerizable monomer [mol] / average molecular weight (Mw) of polymerizable monomer [g]) × 1000 [mmol/mol]
The term "average number of functional groups" refers to the average number of functional groups (i.e., ethylenically unsaturated groups) per molecule, and when three types of polymerizable monomers are included, it is the average number of the three numbers. When the polymerizable monomer is a (meth)acrylate having a (meth)acryloyl group, the functional group indicates a (meth)acryloyl group. The term "average molecular weight" refers to the average molecular weight of the entire polymerizable monomer, and is determined by arithmetic calculation. The term "activating a polymerization initiator" refers to generating active species such as radicals by irradiating the polymerization initiator with active energy rays (e.g., electromagnetic waves, radiation, etc.). The term "solution" refers to a liquid phase in which the two are homogeneously dissolved. The term "porous body" refers to a polymer (solid phase) of a polymerizable monomer.

The method for producing a porous body disclosed herein has the above configuration, and therefore can produce a porous body with a pore size of 1000 nm or less.

(1.1) Preparation Step In the preparation step, a solution containing a polymerizable monomer having a functional group concentration of 3.0 mmol/g to 12.5 mmol/g, a polymerization initiator, and a solvent is prepared.

The solution contains a polymerizable monomer. The polymerizable monomer preferably has a (meth)acryloyl group. Examples of polymerizable monomers having a functional group concentration of 3.0 mmol/g to 12.5 mmol/g include monofunctional polymerizable monomers, bifunctional polymerizable monomers, and trifunctional or higher polymerizable monomers. Examples of monofunctional polymerizable monomers include β-carboxyethyl (meth)acrylate (functional group concentration: 6.9 mmol/g), isobornyl (meth)acrylate (functional group concentration: 4.8 mmol/g), and ethoxylated phenyl (meth)acrylate (functional group concentration: 4.2 mmol/g). Examples of bifunctional polymerizable monomers include tricyclodecane dimethanol di(meth)acrylate (functional group concentration: 6.7 mmol/g), ethylene oxide (EO)-modified neopentyl glycol di(meth)acrylate (EBECRYL 150) (functional group concentration: 3.9 mmol/g), dipropylene glycol di(meth)acrylate (functional group concentration: 8.2 mmol/g), and glycerin di(meth)acrylate (functional group concentration: 10.0 mmol/g). Examples of trifunctional or higher polymerizable monomers include pentaerythritol ethoxy tetra(meth)acrylate (functional group concentration: 7.0 mmol/g), ditrimethylolpropane tetra(meth)acrylate (functional group concentration: 8.6 mmol/g), trimethylolpropane tri(meth)acrylate (functional group concentration: 10.5 mmol/g), dipentaerythritol hexa(meth)acrylate (functional group concentration: 11.5 mmol/g), and glycerin tri(meth)acrylate (functional group concentration: 11.8 mmol/g). The polymerizable monomer may be one type alone or two or more types may be used in combination. The functional group concentration in the examples of the polymerizable monomer is the functional group concentration when the (meth)acrylate is an acrylate. When the porous body is used as a separator (hereinafter simply referred to as "separator") for a lithium secondary battery using a nonaqueous electrolyte, the polymerizable monomer is preferably a polymerizable monomer that does not contain an ether bond.

The functional group concentration of the polymerizable monomer is preferably 0.50 or more. This results in a porous body with a pore diameter of 10 nm to 500 nm and a porosity of 40% or more. When the porosity is 40% or more, the porous body functions as a separator (hereinafter also simply referred to as "separator") for a lithium secondary battery using a non-aqueous electrolyte. Therefore, the resulting porous body is suitable for use as a separator. From the viewpoint of making the pore diameter smaller, the functional group concentration of the polymerizable monomer is more preferably 0.75 to 1.25, and even more preferably 0.95 to 1.25.

The content of the polymerizable monomer is not particularly limited, but is preferably 14% by mass to 44% by mass relative to the total amount of the solution. This will produce a porous body suitable for a separator. From the viewpoint of maintaining a small pore diameter and high porosity, the content of the polymerizable monomer is more preferably 24% by mass to 39% by mass.

The solution contains a polymerization initiator. Examples of the polymerization initiator include a photopolymerization initiator that generates active species such as radicals by irradiation with active energy rays (e.g., electromagnetic waves, radiation, etc.) and a thermal polymerization initiator that generates active species such as radicals by application of heat, and a photopolymerization initiator is preferable. Examples of the photopolymerization initiator include acetophenone-based compounds (e.g., 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-1,2-diphenylethan-1-one, etc.), benzophenone-based compounds (e.g., benzophenone, 4-phenylbenzophenone, etc.), and the like. The polymerization initiator may be a single type alone or a combination of two or more types.

The content of the polymerization initiator is not particularly limited, and is preferably 0.01% by mass to 3.00% by mass with respect to the total amount of the solution. This results in a porous body with a pore diameter of 10 nm to 500 nm and a porosity of 50% or more. If the porosity is 50% or more, the battery performance of the nonaqueous electrolyte secondary battery becomes less dependent on the porosity. In other words, the battery performance of the nonaqueous electrolyte secondary battery is improved.

The solution contains a solvent. Examples of the solvent include ether solvents (e.g., diethylene glycol dimethyl ether, diethylene glycol diethyl ether, 2-methoxyethanol, 2-ethoxyethanol, ethyl ether, n-butyl ether, n-hexyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, 1,4-dioxane, etc.), polyhydric alcohol solvents (e.g., ethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol, 2,4-pentanediol, 1,2-hexanediol, etc.), ester solvents (e.g., diethyl carbonate, methyl acetate, ethyl acetate, etc.), etc. The solvent may be used alone or in combination of two or more kinds.

Among them, the solvent preferably contains an ether-based solvent, and more preferably consists of an ether-based solvent, so that the structure of the obtained porous body tends to be a structure in which each of the multiple particulate materials is connected to each other.
Furthermore, when the solvent contains an ether solvent, the polymerizable monomer having a functional group concentration of 3.0 mmol/g to 12.5 mmol/g preferably contains a di- or higher functional polymerizable monomer, which allows a porous body having a smaller pore size to be obtained.

The solution may or may not contain additives. Examples of additives include dispersants, adhesion promoters such as silane coupling agents, antioxidants, anti-aggregation agents, defoamers, and surfactants.

(1.2) Forming Step In the forming step, the polymerization initiator contained in the solution is activated to polymerize the polymerizable monomer, thereby forming a phase-separated product containing a porous body and the solvent from the solution.

The method for activating the polymerization initiator is not particularly limited, and examples thereof include a method of irradiating the solution with electromagnetic waves (far ultraviolet rays, ultraviolet rays, near ultraviolet rays, etc.) and radiation (for example, electron beams, X-rays, gamma rays, etc.). Among these, the method for activating the polymerization initiator is preferably irradiation with ultraviolet rays. The intensity of the ultraviolet rays is preferably 5 mW/cm ² to 800 mW/cm ² , more preferably 30 mW/cm ² to 250 mW/cm ^2. The temperature of the solution during irradiation with ultraviolet rays is preferably 25° C. to 120° C., more preferably 25° C. to 60° C. When activating the polymerization initiator, the solution may be in the form of a coating film applied on the surface of the substrate.

(1.3) Vaporization Step In the vaporization step, the solvent contained in the phase-separated product is vaporized.

Methods for vaporizing the solvent are not particularly limited, and examples thereof include heat drying, vacuum drying, and freeze drying. In heat drying, if the heating temperature is equal to or lower than the glass transition temperature of the polymerizable monomer or its polymer, the solvent can be removed from the phase-separated product without destroying the porous structure of the porous body. Examples of heat drying include radiant heat drying using an infrared heater and air drying using a blower.

(1.4) Porous Body The porous body obtained by the method for producing a porous body according to the present disclosure has a porosity of 1000 μm or less.

The size of the porous body is not particularly limited and is appropriately selected depending on the application of the porous body. The porous body is preferably used, for example, as a foam (e.g., cushioning material, etc.), a separation membrane (e.g., water treatment, etc.), a porous membrane (e.g., separator, etc.), and a reflective substrate (e.g., lighting fixture, etc.).

The pore diameter of the porous body is preferably 500 nm or less. This makes the porous body suitable for use as a separator.

The present disclosure will be explained in more detail below with reference to examples, but the invention of the present disclosure is not limited to these examples.

[1] Porous membrane [1.1] Example 1
[1.1.1] Preparation process Tricyclodecane dimethanol diacrylate was prepared as a polymerizable monomer. From the values listed in the catalog of the polymerizable monomer (number of functional groups: 2, average molecular weight (Mw): 300), the functional group concentration of the polymerizable monomer was 6.7 mmol/g. Diethylene glycol diethyl ether was prepared as a solvent. 1-Hydroxycyclohexyl phenyl ketone was prepared as a polymerization initiator.
29 parts by mass of the polymerizable monomer was placed in a sample bottle, and then 70 parts by mass of the solvent and 1 part by mass of the polymerization initiator were added thereto. The mixture was stirred until the polymerizable monomer and the polymerization initiator were completely dissolved in the solvent to obtain a solution.

[1.1.2] Formation step The inside of the glove box was purged with nitrogen gas ( _N2 ). The oxygen gas concentration in the glove box was 0%. In this glove box, the solution was applied by casting onto a copper foil to form a coating film. The thickness of the coating film was 120 μm.
The coating film was irradiated with ultraviolet (UV) rays to obtain an irradiated coating film. A UV irradiation device was used for the irradiation of ultraviolet rays. The irradiation time of UV irradiation was 60 seconds, and the intensity of UV irradiation was 50 mW/ ^cm2 . The temperature of the coating film during UV irradiation was 25°C.

[1.1.3] Vaporization step The copper foil on which the irradiated coating film was formed was placed on a hot plate. The hot plate was set to a temperature of 120° C., and the irradiated coating film was heated at 120° C. for 5 minutes to volatilize and remove the solvent from the irradiated coating film. This resulted in a polymer film.

The surface of the polymer film was observed using a scanning electron microscope (SEM) (magnification: 10,000 or 50,000 times). Figure 1 shows an SEM image of the polymer film of Example 1.

[1.2] Examples 2 to 6 and Comparative Example 1
Polymer films were obtained in the same manner as in Example 1, except that the type of polymerizable monomer was changed as shown in Table 1. Figure 1 shows SEM images of the polymer films of Examples 2 to 6 and Comparative Example 1. The functional group concentrations of the polymerizable monomers were calculated using the values listed in the catalogs of the polymerizable monomers, as in Example 1. Figures 1 to 3 show SEM images of the polymer films of Examples 2 to 6.

[1.3] Example 7
Polymer membranes were obtained in the same manner as in Example 4, except that the type of solvent was changed as shown in Table 1. Fig. 4 shows SEM images (magnification: 50,000 times) of the polymer membranes of Examples 4 and 7.

[1.4] Examples 8 to 10
Polymer films were obtained in the same manner as in Example 1, except that the content of the polymerizable monomer was changed as shown in Table 1. Fig. 5 shows SEM images (magnification: 50,000 times) of the polymer films of Examples 1 and 8 to 10.

[1.5] Examples 11 and 12
Polymer films were obtained in the same manner as in Example 1, except that the content of the polymerization initiator was changed as shown in Table 1. Fig. 6 shows SEM images (magnification: 50,000 times) of the polymer films of Examples 1, 11, and 12.

[2] Evaluation method [2.1] Measurement of porosity The polymer membrane was punched to a predetermined size to prepare a sample membrane. The mass, area and thickness of this sample membrane were measured. Using the measured values of the mass, area and thickness of the sample membrane, the apparent density was calculated from the following formula (a). Using the true density of the polymer constituting the polymer membrane, the porosity of the sample membrane was calculated from the following formula (b). The calculated porosity of the sample membrane was taken as the porosity of the polymer membrane. The results are shown in Table 1.
Equation (a): Apparent density = mass of sample film / (area of sample film x film thickness of sample film)
Equation (b): Porosity of sample membrane = [1 - (apparent density / true density)] x 100

[2.2] Evaluation of porosity Based on the calculation results of the porosity, the porosity of the polymer membrane was evaluated according to the following criteria: An acceptable porosity evaluation result is "A".
"A": The porosity of the polymer membrane is 40% or more. "B": The porosity of the polymer membrane is less than 40%. "A" means that the polymer membrane is evaluated as being porous. "B" means that the polymer membrane is evaluated as not being porous. Hereinafter, a polymer membrane with a porosity evaluation result of "A" is also referred to as a "porous membrane".

[2.3] Measurement of pore size The shape of the porous membrane was observed using a field emission scanning electron microscope (FE-SEM) ("JSM-7100F" manufactured by JEOL Ltd.). In order to prevent the porous membrane from being charged, the porous membrane was coated with platinum (Pt). The cross section of the porous membrane was observed. The cross section of the porous membrane was a fracture surface of the porous membrane obtained by breaking the porous membrane using liquid nitrogen.
The diameters of a plurality of pores in the captured surface SEM image were measured. The average value of the measured diameters of the plurality of pores was taken as the pore diameter. The measurement results are shown in Table 1. The allowable range of the pore diameter is 1000 nm or less.

In Table 1, in the section on polymerizable monomers, "PEGDA" refers to PEG600 diacrylate. "TCDDA" refers to tricyclodecane dimethanol diacrylate. "PEEOTA" refers to pentaerythritol ethoxy tetraacrylate. "Di-TMPTA" refers to ditrimethylolpropane tetraacrylate. "TMPTA" refers to trimethylolpropane triacrylate. "DPHA" refers to dipentaerythritol hexaacrylate. "GLYTA" refers to glycerin triacrylate. In the section on polymerization initiators, "HPK" refers to 1-hydroxycyclohexyl phenyl ketone. In the section on solvents, "DEDE" refers to diethylene glycol diethyl ether. "DMAc" refers to dimethylacetamide. "2EE" refers to 2-ethoxyethanol.

In the manufacturing method of Comparative Example 1, the functional group concentration of the polymerizable monomer was 2.9 mmol/g, which was not within the range of 3.0 mmol/g to 1.25 mmol/g. Therefore, the porosity evaluation of Comparative Example 1 was "B." In other words, as shown in 1A in Figure 1, the polymer membrane of Comparative Example 1 was not porous. As a result, it was found that the manufacturing method of Comparative Example 1 is not a manufacturing method capable of manufacturing a porous membrane with a pore diameter of 1000 μm or less.

The manufacturing methods of Examples 1 to 12 included a preparation step, a formation step, and a vaporization step, and the functional group concentration of the polymerizable monomer was in the range of 3.0 mmol/g to 1.25 mmol/g. Therefore, the pore diameters of Examples 1 to 12 were 570 nm or less. Furthermore, as shown in 1B and 1C in FIG. 1 and in FIGS. 2 to 6, the polymer membranes of Examples 1 to 12 were porous bodies. As a result, it was found that the manufacturing methods of Examples 1 to 12 were capable of manufacturing porous membranes with pore diameters of 1000 μm or less.
Furthermore, as shown in Figs. 1B and 1C and Figs. 2 to 6, it was found that the porous bodies of Examples 1 to 12 had a structure in which a plurality of particulate materials were each connected to one another.

Claims (2)

preparing a solution containing a polymerizable monomer having a functional group concentration of 10.5 mmol/g to 12.5 mmol/g, a polymerization initiator, and a solvent;
applying the solution onto a copper foil, activating the polymerization initiator contained in the solution, and polymerizing the polymerizable monomer to form a phase-separated product containing a porous body and the solvent from the solution;
and evaporating the solvent contained in the phase separated product ;
In preparing the solution, a content of the polymerizable monomer is 14% by mass to 44% by mass, and a content of the polymerization initiator is 0.01% by mass to 3.00% by mass, based on a total amount of the solution . The method for producing a porous body according to claim 1 , wherein the pore size of the porous body is 500 nm or less.