JP6005552B2 - Porous material and method for producing the same - Google Patents

Description

  The present invention relates to a porous body having fine bubbles, a low relative dielectric constant, and excellent heat resistance, and a method for producing the same. The porous body of the present invention is useful, for example, as an insulating sheet incorporated in an automobile or industrial motor with inverter control.

  Conventionally, since a plastic film has high insulating properties, it is used for components or members that require reliability, for example, electrical devices such as circuit boards or motors or electronic components. Recently, motors and industrial motors are widely used that have a structure in which inverter control can be performed at a high voltage as electronic and electric devices become smaller and have higher performance.

  However, since the high surge voltage generated from the inverter affects the motor, the insulator is required to have high reliability.

  As countermeasures against surge voltage, in addition to improving the reliability of insulation, lowering the dielectric constant of the insulator can be mentioned.

  In general, since the relative dielectric constant of a plastic material is determined by its molecular skeleton, a method of modifying the molecular skeleton can be considered as an attempt to lower the relative dielectric constant. However, there is a limit to reducing the dielectric constant even if the molecular skeleton is modified.

  As other attempts to lower the dielectric constant, various methods have been proposed in which the relative permittivity of air is utilized, the plastic material is made porous, and the relative permittivity is controlled by the porosity.

  Conventional methods for producing a porous body include a dry method and a wet method, and the dry method includes a physical method and a chemical method. A general physical method is to form bubbles by dispersing a low boiling point liquid (foaming agent) such as chlorofluorocarbons and hydrocarbons in a polymer and then volatilizing the foaming agent by heating. In the chemical method, a porous material is obtained by forming a cell with a gas generated by adding a foaming agent to a polymer and thermally decomposing the foaming agent.

  Further, in recent years, as a porous body having a small cell diameter and high cell density, a gas such as nitrogen and carbon dioxide is dissolved in the polymer at high pressure, and then the pressure is released, so that the glass transition temperature or softening point of the polymer. There has been proposed a method of forming bubbles by heating to the vicinity. In this foaming method, nuclei are formed from a thermodynamically unstable state, and bubbles are formed by expanding and growing the nuclei, and an unprecedented microporous porous body can be obtained. There are advantages.

  For example, Patent Document 1 proposes a method for producing a foam having a low density and a high mechanical strength by applying the foaming method to polyetherimide.

  Also, for example, in Patent Document 2, the foaming method is applied to a styrene resin having a syndiotactic structure to obtain a foam having a cell size of 0.1 to 20 μm, and this is used as an insulator for an electric circuit board. It has been proposed.

  Further, for example, Patent Document 3 proposes a low dielectric constant plastic insulating film including a porous plastic having a porosity of 10 vol% or more, a heat resistant temperature of 100 ° C. or more, and a dielectric constant of 2.5 or less. Has been.

  Further, for example, in Patent Document 4, a component constituting the discontinuous phase is selected from evaporation and decomposition from a polymer composition having a microphase separation structure in which a discontinuous phase having an average diameter of less than 10 μm is dispersed in the continuous phase of the polymer. In addition, a method for producing a porous body is proposed, which is removed by at least one kind of operation and an extraction operation to make it porous.

  However, the method of removing the additive by heating or solvent extraction has a problem that the additive cannot be removed sufficiently. When the porous body contains impurities such as additives, there is a problem that the glass transition temperature of the porous body is lowered and the heat resistance of the material cannot be utilized.

JP-A-6-322168 JP 10-45936 A Japanese Patent Application Laid-Open No. 9-130033 JP 2001-81225 A

  The present invention has been made in view of the above problems, and is to provide a porous body excellent in heat resistance, having a fine cell structure, and having a low relative dielectric constant, and a method for producing the same. The present invention also provides a heat-resistant porous material that suppresses a decrease in heat-resistant temperature by effectively removing the residue of additives that cannot be removed by conventional methods such as solvent extraction, and a method for producing the same. For the purpose.

  In the present invention, a polymer composition containing a polymer, a phase separation agent and an organic solvent is applied on a substrate and dried to produce a polymer sheet having a microphase separation structure, and a carbon dioxide fluid is used as an extraction solvent. The present invention also relates to a method for producing a porous body including a step of producing a porous polymer sheet by extracting and removing a phase separation agent from the polymer sheet while increasing the temperature of the carbon dioxide fluid.

  Another aspect of the present invention is a process for producing a polymer sheet having a microphase separation structure by applying a polymer composition containing a polymer, a phase separation agent and an organic solvent on a substrate and drying the composition, and a carbon dioxide fluid as an extraction solvent. And a method for producing a porous body including a step of producing a porous polymer sheet by extracting and removing a phase separation agent from the polymer sheet while reducing the pressure of the carbon dioxide fluid.

  The present inventors improve the extraction efficiency of the phase separation agent and the like by changing the temperature or pressure of the carbon dioxide fluid when extracting and removing the phase separation agent from the polymer sheet using the carbon dioxide fluid, It has been found that the heat resistance of the porous body can be improved thereby.

  In the said manufacturing method, it is preferable to raise the temperature of a carbon dioxide fluid 10 degreeC or more from initial temperature. By setting the difference between the initial temperature of the carbon dioxide fluid and the temperature during extraction to 10 ° C. or more, the extraction efficiency of the phase separation agent and the like can be further improved.

  In the manufacturing method, it is preferable to reduce the pressure of the carbon dioxide fluid by 5 MPa or more from the initial pressure. By making the difference between the initial pressure of the carbon dioxide fluid and the pressure during extraction 5 MPa or more, the extraction efficiency of the phase separation agent and the like can be further improved.

  Another aspect of the present invention is a process for producing a polymer sheet having a microphase separation structure by applying a polymer composition containing a polymer, a phase separation agent and an organic solvent on a substrate and drying the composition, and a carbon dioxide fluid as an extraction solvent. The present invention relates to a method for producing a porous body, which includes a step of producing a porous polymer sheet by extracting and removing a phase separation agent from a polymer sheet using a mixed fluid containing an organic solvent.

  When extracting and removing a phase separation agent from a polymer sheet using a carbon dioxide fluid, the present inventors improve the extraction efficiency of the phase separation agent and the like by adding an organic solvent as an extraction aid to the carbon dioxide fluid. It has been found that the heat resistance of the porous body can be improved.

  The organic solvent contained in the mixed fluid is preferably at least one selected from the group consisting of alcohols, ketones, aromatic hydrocarbons, polar amide solvents, and ester solvents.

The porous body of the present invention obtained by the production method has a thermal weight reduction rate represented by the following formula of 4% or less. Since the porous body of the present invention contains almost no additives such as a phase separation agent, the thermal weight reduction rate (%) is low and the heat resistance is excellent.
Thermal weight loss rate (%) = {(weight loss at 400 ° C.−weight loss at 100 ° C.) / Sample weight} × 100

  The porous body of the present invention preferably has a relative dielectric constant of 1.4 to 2.5.

  Moreover, the porous body of the present invention is suitably used as an insulating sheet for motors.

  Furthermore, the present invention relates to an insulating laminated sheet for motors having a sheet material on at least one side of the porous body.

  The porous body of the present invention is excellent in heat resistance because there is very little residual organic solvent, phase separation agent, etc., and is excellent in mechanical strength and insulation because it has a fine cell structure. In addition, the dielectric constant is low. Therefore, the porous body of the present invention is suitably used as an insulating sheet incorporated in an automobile or industrial motor with inverter control.

  As the polymer used as the material of the porous body of the present invention, that is, the polymer constituting the continuous phase of the microphase separation structure, any polymer can be used as long as it is a material excellent in heat resistance. Examples thereof include polyamide, polycarbonate, polybutylene terephthalate, polyethylene terephthalate, polyphenylene sulfide, polysulfone, polyether sulfone, polyether ether ketone, polyamide imide, polyimide, and polyether imide. These may be used alone or in combination of two or more. Of these, polyethersulfone, polyetheretherketone, polyamideimide, polyimide, and polyetherimide, which are particularly excellent in heat resistance, are preferably used, and from the viewpoint of solubility in organic solvents and cost, polyethersulfone Polyamideimide and polyetherimide are preferably used.

  The phase separation agent is a component that constitutes a discontinuous phase of a microphase separation structure and is capable of forming a microphase separation structure when the polymer is mixed and can be extracted with an extraction solvent. Not. For example, polyalkylene glycol such as polyethylene glycol and polypropylene glycol; one end or both end methyl blockade of the polyalkylene glycol, or one end or both end (meth) acrylate blockade; urethane prepolymer; phenoxy polyethylene glycol (meth) (Meth) acrylate, ε-caprolactone (meth) acrylate, trimethylolpropane tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, urethane (meth) acrylate, epoxy (meth) acrylate, oligoester (meth) acrylate, etc. ) Acrylate compounds. These may be used alone or in combination of two or more.

  The molecular weight of the phase separation agent is not particularly limited, but the weight average molecular weight is preferably 10,000 or less (for example, about 100 to 10,000), more preferably 100 to 2000, because the extraction and removal operation becomes easy. When the weight average molecular weight is less than 100, it is difficult to phase separate from the cured polymer. On the other hand, if the weight average molecular weight exceeds 10,000, the microphase separation structure becomes too large, or it is difficult to extract and remove from the polymer sheet. As the phase separation agent, an oligomer is often used.

  The addition amount of the phase separation agent can be appropriately selected according to the combination with the polymer. To produce a porous body having an average pore diameter of 0.1 to 10 μm and a volume porosity of 20 to 90%, a polymer is used. It is preferable to use 20 to 300 parts by weight with respect to 100 parts by weight, and more preferably 30 to 100 parts by weight.

  The polymer composition is prepared by mixing a polymer, a phase separation agent, and an organic solvent. Examples of the organic solvent include amides such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, and N, N-dimethylformamide. The usage-amount of an organic solvent is about 150-2000 weight part with respect to 100 weight part of polymers, Preferably it is 150-400 weight part, More preferably, it is 300-350 weight part.

  An additive other than the phase separation agent may be added to the polymer composition. Examples of additives include tackifier resins, flame retardants, antioxidants, inorganic fillers, cell nucleating agents, crystal nucleating agents, thermal stabilizers, light stabilizers, ultraviolet absorbers, plasticizers, lubricants, pigments, and crosslinking agents. , Crosslinking aids, and silane coupling agents.

  In the method for producing a porous body of the present invention, first, the polymer composition is applied onto a substrate and dried to produce a polymer sheet (including a film) having a microphase separation structure.

  The substrate is not particularly limited as long as it has a smooth surface. Examples of the continuous application method include a wire bar, kiss coat, and gravure. Examples of the batch application method include an applicator, a wire bar, and a knife coater.

  By drying the polymer composition coated on the substrate and evaporating the organic solvent, a polymer sheet in which the phase separation agent is microphase-separated can be obtained. The temperature at which the organic solvent is evaporated (dried) is not particularly limited, and may be appropriately adjusted depending on the type of the organic solvent used, but is usually 60 to 200 ° C. The microphase separation structure usually has a sea-island structure in which the polymer is the sea and the phase separation agent is the island.

  Thereafter, the phase separation agent is extracted and removed from the polymer sheet using a carbon dioxide fluid as an extraction solvent to produce a porous polymer sheet. Examples of the carbon dioxide fluid include liquefied carbon dioxide, subcritical carbon dioxide, and supercritical carbon dioxide. Since these carbon dioxide fluids easily penetrate into the polymer sheet, the phase separation agent and the like can be efficiently extracted. An organic solvent suitable as an extraction aid may be added to the carbon dioxide fluid. Thereby, the solubility of the phase separation agent in the carbon dioxide fluid can be improved, and the extraction efficiency can be increased.

  As a method for adding the extraction aid, a method in which a certain amount of the extraction aid is put together with the polymer sheet in the pressure vessel before pressurization with carbon dioxide, and the extraction aid is added to the carbon dioxide fluid using a liquid feed pump. The method of adding etc. is mentioned.

  The addition amount of the extraction aid is usually 0.1 to 20% by weight, preferably 0.5 to 10% by weight, more preferably 1 to 8% by weight in the mixed fluid containing carbon dioxide fluid. is there. When the amount of the extraction aid added is too large, the mixed fluid cannot maintain the subcritical state or the supercritical state, so that the diffusibility unique to the critical fluid is impaired. If the amount of extraction aid added is too small, it will be difficult to improve the solubility of the phase separation agent in the carbon dioxide fluid.

  The extraction aid is not particularly limited as long as it is highly compatible with the phase separation agent. For example, alcohols such as methanol, ethanol, 1-propanol, isopropanol, and butanol; ketones such as acetone and methyl ethyl ketone; Aromatic hydrocarbons such as toluene, xylene, and benzene; polar amide solvents such as N-methyl-2-pyrrolidone and dimethylacetamide; and ester solvents such as ethyl acetate. These may be used alone or in combination of two or more.

  When a carbon dioxide fluid is used as the extraction solvent, a pressure vessel is usually used. As the pressure vessel, for example, a batch type pressure vessel, a pressure vessel equipped with a pressure-resistant sheet feeding and winding device, or the like can be used. The pressure vessel is usually provided with carbon dioxide fluid supply means including a pump, piping, valves, and the like.

  The extraction of the phase separation agent may be performed by continuously supplying and discharging the carbon dioxide fluid to and from the pressure vessel containing the polymer sheet, and the pressure vessel is closed (the charged polymer sheet and the carbon dioxide fluid are separated from each other). It may be performed in a state where it does not move out of the container. When subcritical carbon dioxide or supercritical carbon dioxide is used, swelling of the polymer sheet is promoted, and the phase separation agent is efficiently removed from the polymer sheet by improving the diffusion coefficient of the insolubilized phase separation agent. The When liquefied carbon dioxide is used, the diffusion coefficient is lowered, but the permeability into the polymer sheet is improved, so that the phase separation agent is efficiently removed from the polymer sheet.

  The temperature and pressure when the phase separation agent is extracted with the carbon dioxide fluid may be any temperature and pressure at which carbon dioxide is in each state (liquid, subcritical or supercritical). It is 7.3-100 MPa, Preferably it is 25-200 degreeC and 10-50 MPa.

  The density of carbon dioxide fluid varies greatly depending on temperature or pressure. Therefore, under high-density conditions such as low temperature and high pressure, compatibility with additives such as organic solvents and phase separation agents increases, so the organic solvent and additives in the polymer sheet can be efficiently extracted. Can do.

  The polymer sheet before extraction contains many organic solvents and additives. Therefore, when the temperature of the carbon dioxide fluid is high at the beginning of extraction, the polymer sheet is plasticized and easily deforms. Therefore, extraction at low temperature and high pressure is preferable in the early stage of extraction. On the other hand, in the later stage of extraction, the polymer sheet is difficult to deform. Therefore, in the latter stage of extraction, extraction at high temperature and low pressure is preferable in order to improve the diffusion coefficient in addition to the compatibility with the organic solvent and the additive. In the present invention, the initial stage of extraction means a period until 80% of the extract contained in the polymer sheet is extracted, and the latter stage of extraction means a period after the initial stage of extraction.

  From the above viewpoint, in the method for producing a porous body of the present invention, it is preferable to extract and remove the organic solvent and the additive from the polymer sheet while increasing the temperature of the carbon dioxide fluid from a low temperature to a high temperature. Thereby, extraction of a phase-separation agent etc. can be promoted. The temperature of the carbon dioxide fluid may be continuously increased or may be increased stepwise.

  Specifically, in the high temperature condition, it is preferable to increase the temperature of the carbon dioxide fluid by 10 ° C. or more compared to the low temperature condition, more preferably 20 ° C. or more, and further preferably 30 ° C. or more.

  More specifically, the temperature of the carbon dioxide fluid under low temperature conditions is preferably 20 to 60 ° C, more preferably 25 to 55 ° C, and further preferably 30 to 50 ° C. On the other hand, the temperature of the carbon dioxide fluid under high temperature conditions is preferably 60 to 230 ° C, more preferably 70 to 200 ° C, and further preferably 80 to 150 ° C.

  In the present invention, it is preferable to perform extraction at a low temperature condition at the beginning of extraction and to perform extraction at a high temperature condition at a later stage of extraction, but after performing the temperature increasing operation at least once, the temperature decreasing operation and the temperature increasing operation are repeated. Also good. When the temperature raising operation and the temperature lowering operation are repeated, the density change of the carbon dioxide fluid accompanying the temperature change occurs, and the carbon dioxide fluid in and out of the polymer sheet is promoted and the extraction rate can be improved.

  In this invention, it is preferable that the time maintained at low temperature conditions is 40 to 300 minutes, More preferably, it is 45 to 180 minutes, More preferably, it is 50 to 150 minutes. On the other hand, the time for maintaining at high temperature is preferably 60 to 600 minutes, more preferably 90 to 500 minutes, and still more preferably 120 to 400 minutes. When the low temperature condition and the high temperature condition are repeated, the ratio of the time to be maintained (low temperature condition time / high temperature condition time) is preferably 0.06 to 5, more preferably 0.09 to 2, Preferably it is 0.12-1.25. Further, the number of times of repeating the temperature raising operation and the temperature lowering operation is usually 3 times or less, preferably 1 time or 2 times from the viewpoint of productivity.

  Moreover, in the manufacturing method of the porous body of this invention, you may extract and remove an organic solvent and an additive from a polymer sheet, reducing the pressure of a carbon dioxide fluid. Thereby, extraction of a phase-separation agent etc. can be promoted. Specifically, the change in pressure promotes the introduction and removal of the carbon dioxide fluid in the polymer sheet, and the extraction rate can be improved. The pressure of the carbon dioxide fluid may be continuously decreased or may be decreased stepwise.

  Specifically, in the low pressure condition, it is preferable to reduce the pressure of the carbon dioxide fluid by 5 MPa or more, more preferably 10 MPa or more, and further preferably 12 MPa or more compared to the high pressure condition.

  More specifically, the pressure of the carbon dioxide fluid under high pressure conditions is preferably 15 to 100 MPa, more preferably 20 to 70 MPa, and further preferably 25 to 40 MPa. On the other hand, the pressure of the carbon dioxide fluid under the low pressure condition is preferably 7.3 to 20 MPa, more preferably 10 to 18 MPa, and further preferably 12 to 16 MPa.

  In the present invention, it is preferable to perform extraction under a high pressure condition at the beginning of extraction and to perform extraction under a low pressure condition at a later stage of extraction. However, the pressure increasing operation and the pressure decreasing operation may be repeated after performing the pressure decreasing operation at least once. . When the pressure reduction operation and the pressure increase operation are repeated, the density change of the carbon dioxide fluid accompanying the pressure change occurs, the taking in and out of the carbon dioxide fluid in the polymer sheet is promoted, and the extraction rate can be improved.

  In this invention, it is preferable that the time maintained under high pressure conditions is 40-300 minutes, More preferably, it is 45-180 minutes, More preferably, it is 50-150 minutes. On the other hand, it is preferable that the time maintained under low pressure conditions is 30 to 600 minutes, more preferably 60 to 500 minutes, and still more preferably 90 to 400 minutes. When the high pressure condition and the low pressure condition are repeated, the ratio of the time to be maintained (time of the high pressure condition / time of the low pressure condition) is preferably 0.06 to 10, more preferably 0.09 to 3, Preferably it is 0.12-1.7. Moreover, the frequency | count of repeating pressure | voltage fall operation and pressure | voltage rise operation is 10 times or less normally from a viewpoint of productivity, Preferably it is 1-5 times.

  The extraction time needs to be appropriately adjusted depending on the temperature and pressure during extraction, the blending amount of the phase separation agent, the thickness of the polymer sheet, and the like, but is usually about 30 minutes to 900 minutes, preferably 60 minutes to 500 minutes. Minutes, more preferably 100 minutes to 300 minutes. If it is less than 30 minutes, sufficient extraction is not achieved, and if it exceeds 900 minutes, the extraction time becomes too long, so that the production efficiency is lowered.

  The flow rate of the carbon dioxide fluid at the time of extraction is usually about 20 to 1000 kg / hr, preferably 30 to 900 kg / hr, more preferably 40 to 800 kg / hr. If the flow rate of the carbon dioxide fluid is less than 20 kg / hr, sufficient extraction is not achieved, and if it exceeds 1000 kg / hr, the load on the pump increases.

  The amount of carbon dioxide fluid used during extraction is usually about 70 to 1000 kg, preferably 100 to 900 kg, and more preferably 200 to 800 kg. When the use amount of the carbon dioxide fluid is less than 70 kg, sufficient extraction is not achieved, and when it exceeds 1000 kg, the extraction time becomes too long, so that the production efficiency is lowered.

  Moreover, in the manufacturing method of the porous body of this invention, you may extract and remove an organic solvent and an additive from a polymer sheet, raising the temperature of a carbon dioxide fluid, and reducing a pressure. Thereby, extraction of a phase separation agent etc. can be promoted more.

  A suitable extraction method in the method for producing a porous body of the present invention is as follows.

Case (1)
First, a carbon dioxide fluid is injected into a pressure vessel under conditions of a temperature of 30 to 50 ° C., a pressure of 25 to 40 MPa, and a flow rate of 40 to 100 kg / hr, exhausted, and a carbon dioxide fluid having a total usage amount of 70 to 150 kg is circulated. Thereafter, carbon dioxide fluid is injected into the pressure vessel under conditions of a temperature of 80 to 150 ° C., a pressure of 25 to 40 MPa, and a flow rate of 40 to 100 kg / hr, exhausted, and a carbon dioxide fluid having a total usage amount of 100 to 500 kg is circulated.

Case (2)
First, a carbon dioxide fluid is injected into a pressure vessel under conditions of a temperature of 30 to 50 ° C., a pressure of 25 to 40 MPa, and a flow rate of 40 to 100 kg / hr, exhausted, and a carbon dioxide fluid having a total usage amount of 70 to 150 kg is circulated. Thereafter, carbon dioxide fluid is injected into the pressure vessel under conditions of a temperature of 30 to 50 ° C., a pressure of 12 to 16 MPa, and a flow rate of 40 to 100 kg / hr, exhausted, and a carbon dioxide fluid having a total usage amount of 100 to 500 kg is circulated.

  After producing the porous polymer sheet by extracting and removing the phase separation agent, a drying treatment or the like may be performed.

  The porous body obtained by the production method of the present invention is characterized by excellent heat resistance, extremely small average pore diameter, and extremely low relative dielectric constant. Specifically, the average pore diameter of the porous body is about 0.1 to 10 μm (0.1 to 5 μm, more preferably 0.1 to 3 μm from the viewpoint of insulation), and the volume porosity is about 20 to 90%. (Preferably 30 to 80%, more preferably 35 to 70%), and the relative dielectric constant is about 1.4 to 2.5 (preferably 1.4 to 1.8).

  Further, the porous body obtained by the production method of the present invention has few impurities because the phase separation agent and the like are efficiently extracted and removed. If impurities are present in the porous body, the glass transition point of the polymer used as the material is lowered, so that the thermal characteristics of the material cannot be fully utilized, and the heat resistance is lowered.

The amount of impurities in the porous body can be evaluated by the thermal weight reduction rate represented by the following formula. The smaller the amount of impurities in the porous body, the smaller the value of the thermal weight reduction rate. The porous body of the present invention has a thermal weight loss rate of 4% or less, preferably 3.5% or less, more preferably 3% or less.
Thermal weight loss rate (%) = {(weight loss at 400 ° C.−weight loss at 100 ° C.) / Sample weight} × 100

  Although the shape of a porous body can be suitably changed according to a use, in the case of a sheet form or a film form, thickness is usually 1-500 micrometers, preferably 10-250 micrometers, more preferably 30-200 micrometers.

  The porous body of the present invention is suitably used as an insulating sheet for motors.

  The insulating laminated sheet for motors of the present invention has a sheet material on at least one side of the insulating sheet for motors which is the porous body.

  The shape of the motor insulating laminated sheet is not particularly limited, and may be a sheet shape or a tape shape, may be punched into a necessary shape, or may be three-dimensionally bent.

  By providing the sheet material, the strength and slipperiness of the insulating laminated sheet for motor are improved.

  Examples of the sheet material include a nonwoven fabric, paper, or a film. In order to improve the heat resistance of the insulating laminated sheet for motors, it is preferable to use a nonwoven fabric, paper, or a film having heat resistance.

  The thickness of the sheet material is not particularly limited, but is usually 5 to 100 μm, preferably 5 to 50 μm. If the thickness of the sheet material is less than 5 μm, it will be difficult to impart strength to the insulating laminated sheet for motors. If the sheet material exceeds 100 μm, the number of turns of the coil wire will decrease and the motor output will decrease, or the motor insulation It becomes difficult to reduce the relative dielectric constant of the conductive laminated sheet.

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

[Measurement and evaluation method]
(Relative permittivity)
The relative dielectric constant at a frequency of 1 GHz was measured by the cavity resonator contact method. Measurement was performed using a cylindrical cavity resonator (“Network Analyzer N5230C” manufactured by Agilent Technologies, “Cavity Resonator 1 GHz” manufactured by Kanto Electronics Application Development Co., Ltd.) using a sample size φ2 mm × 70 mm length.

(Average bubble diameter)
The porous body was cooled with liquid nitrogen and cut perpendicularly to the sheet surface using a blade to produce an evaluation sample. The cut surface of the sample was subjected to Pd—Pt deposition treatment, and the cut surface was observed with a scanning electron microscope (SEM) (“JSM-6510LV” manufactured by JEOL Ltd.). The image was binarized with image processing software (“NanoHunter NS2K-Lt” manufactured by Nanosystem), separated into a bubble portion and a resin portion, and the maximum horizontal chord length of the bubbles was measured. The average value was taken for 40 bubbles from the larger bubble diameter, and the value was taken as the average bubble diameter.

(Porosity)
The specific gravity of the porous body and the specific gravity of the non-porous body were measured using an electronic hydrometer (manufactured by Alpha Mirage, MD-300S), and the porosity was calculated by the following formula.
Porosity (%) = {1− (specific gravity of porous body) / specific gravity of nonporous body} × 100

(Thermal weight reduction rate)
A sample was obtained by finely pulverizing the porous body. Weight of sample at 100 ° C. and 400 ° C. under conditions of temperature range: room temperature to 480 ° C., temperature increase rate: 10 ° C./min using a thermogravimetric analyzer (manufactured by Bruker AXS, TGA-DTA2000SA) The amount of decrease was measured, and the thermogravimetric decrease rate was calculated by the following formula.
Thermal weight loss rate (%) = {(weight loss at 400 ° C.−weight loss at 100 ° C.) / Sample weight} × 100

(Glass-transition temperature)
The heat resistance of the porous body was evaluated by the glass transition temperature. The porous body was cut into a strip of 5 mm × 80 mm to obtain a sample. Using a viscoelasticity tester (ARES 2KFRTN1-TCO, manufactured by Rheometrix Co., Ltd.), frequency of 1 Hz, geometry: fiber / film fixture, temperature region 70-230 ° C., temperature increase rate 5 ° C./min. The elasticity was measured, and the peak top temperature of the loss tangent tan δ was defined as the glass transition temperature.

Example 1
To a 1000 ml four-necked flask, 666.7 g of N-methyl-2-pyrrolidone (NMP) was added and heated to 70 ° C. Thereto, 250 g of a polyetherimide (PEI) resin (manufactured by SABIC Innovative Plastics, UIItem 1000-1000) was added and stirred for 5 hours to obtain a PEI resin solution.

  To the obtained PEI resin solution, 35 parts by weight of propylene glycol having a weight average molecular weight of 400 was added with respect to 100 parts by weight of the PEI resin and stirred to obtain a transparent uniform PEI resin composition. The PEI resin composition was applied onto a PET film by a comma direct method, and then dried at 130 ° C. for 8 minutes to evaporate and remove NMP, thereby producing a PEI resin sheet having a microphase separation structure. The PEI resin sheet was put in a 30 L pressure vessel, carbon dioxide was injected in an atmosphere at 45 ° C., and the pressure was increased to 30 MPa. Thereafter, while maintaining the pressure, carbon dioxide fluid was injected and discharged at a flow rate of about 40 kg / hr until the total usage amount reached 70 kg, and the remaining solvent and polypropylene glycol were extracted. Thereafter, while the ambient temperature was set to 85 ° C. and the temperature of the carbon dioxide fluid was raised, 160 kg of carbon dioxide fluid was further injected and discharged to perform an extraction process, thereby obtaining a porous PEI resin sheet.

Example 2
A PEI resin sheet was produced in the same manner as in Example 1. The PEI resin sheet was put in a 30 L pressure vessel, carbon dioxide was injected in an atmosphere at 45 ° C., and the pressure was increased to 30 MPa. Thereafter, while maintaining the pressure, carbon dioxide was injected and discharged at a flow rate of about 40 kg / hr until the total amount used reached 70 kg, and the remaining solvent and polypropylene glycol were extracted. Thereafter, the pressure was reduced to 15 MPa, and the carbon dioxide fluid was injected and discharged while maintaining the pressure for 30 minutes. Thereafter, the pressure was again increased to 30 MPa, and the carbon dioxide fluid was injected and discharged while maintaining the pressure for 30 minutes. Thereafter, the carbon dioxide fluid was injected and discharged while repeating decompression and pressurization twice by the same method, and an extraction treatment was performed to obtain a porous PEI resin sheet.

Example 3
A PEI resin sheet was produced in the same manner as in Example 1. The PEI resin sheet was put in a 30 L pressure vessel, carbon dioxide was injected in an atmosphere at 45 ° C., and the pressure was increased to 30 MPa. Thereafter, while maintaining the pressure, carbon dioxide was injected and discharged at a flow rate of about 40 kg / hr until the total amount used reached 70 kg, and the remaining solvent and polypropylene glycol were extracted. However, the temperature in the pressure vessel was raised from 45 ° C. to 85 ° C. 100 minutes after starting the extraction operation. Thereafter, the pressure was reduced to 15 MPa, and the carbon dioxide fluid was injected and discharged while maintaining the pressure for 30 minutes. Thereafter, the pressure was again increased to 30 MPa, and the carbon dioxide fluid was injected and discharged while maintaining the pressure for 30 minutes. Thereafter, the carbon dioxide fluid was injected and discharged while repeating decompression and pressurization twice by the same method, and an extraction treatment was performed to obtain a porous PEI resin sheet.

Example 4
A PEI resin sheet was produced in the same manner as in Example 1. The PEI resin sheet was put in a 30 L pressure vessel, carbon dioxide was injected in an atmosphere at 45 ° C., and the pressure was increased to 30 MPa. Thereafter, the flow of carbon dioxide was stopped and held for 60 minutes. Subsequently, carbon dioxide was injected and discharged at a flow rate of about 85 kg / hr while maintaining the pressure until the total amount used reached 140 kg, and the remaining solvent and polypropylene glycol were extracted. Then, while setting the atmospheric temperature to 85 ° C. and raising the temperature of the carbon dioxide fluid, 360 kg of carbon dioxide was further injected and discharged to perform an extraction process, thereby obtaining a porous PEI resin sheet.

Example 5
A PEI resin sheet was produced in the same manner as in Example 1. A PEI resin sheet and 1300 g of toluene were placed in a 30 L pressure vessel, carbon dioxide was injected in an atmosphere at 45 ° C., and the pressure was increased to 30 MPa. Thereafter, the flow of carbon dioxide was stopped and held for 60 minutes. Subsequently, carbon dioxide was injected and discharged at a flow rate of about 85 kg / hr while maintaining the pressure until the total amount used reached 140 kg, and the remaining solvent and polypropylene glycol were extracted. Then, while setting the atmospheric temperature to 85 ° C. and raising the temperature of the carbon dioxide fluid, 360 kg of carbon dioxide was further injected and discharged to perform an extraction process, thereby obtaining a porous PEI resin sheet.

Example 6
A PEI resin sheet was produced in the same manner as in Example 1. A PEI resin sheet and 1300 g of ethanol were placed in a 30 L pressure vessel, carbon dioxide was injected in an atmosphere at 45 ° C., and the pressure was increased to 30 MPa. Thereafter, the flow of carbon dioxide was stopped and held for 60 minutes. Subsequently, carbon dioxide was injected and discharged at a flow rate of about 85 kg / hr while maintaining the pressure until the total amount used reached 140 kg, and the remaining solvent and polypropylene glycol were extracted. Then, while setting the atmospheric temperature to 85 ° C. and raising the temperature of the carbon dioxide fluid, 360 kg of carbon dioxide was further injected and discharged to perform an extraction process, thereby obtaining a porous PEI resin sheet.

Comparative Example 1
A PEI resin sheet was produced in the same manner as in Example 1. The PEI resin sheet was put in a 30 L pressure vessel, carbon dioxide was injected in an atmosphere at 45 ° C., and the pressure was increased to 30 MPa. Thereafter, while maintaining the pressure, the carbon dioxide fluid was injected and discharged at a flow rate of about 40 kg / hr until the total amount used reached 230 kg, and the residual solvent and polypropylene glycol were extracted to remove the porous PEI resin sheet. Obtained.

Comparative Example 2
A PEI resin sheet was produced in the same manner as in Example 1. The PEI resin sheet was placed in a 30 L pressure vessel, carbon dioxide was injected in an atmosphere at 85 ° C., and the pressure was increased to 30 MPa. Thereafter, while maintaining the pressure, the carbon dioxide fluid was injected and discharged at a flow rate of about 40 kg / hr until the total amount used reached 230 kg, and the residual solvent and polypropylene glycol were extracted to remove the porous PEI resin sheet. Obtained.

Comparative Example 3
A PEI resin sheet was produced in the same manner as in Example 1. The PEI resin sheet was placed in a 30 L pressure vessel, carbon dioxide was injected in an atmosphere at 45 ° C., and the pressure was increased to 15 MPa. Thereafter, while maintaining the pressure, the carbon dioxide fluid was injected and discharged at a flow rate of about 40 kg / hr until the total amount used reached 230 kg, and the residual solvent and polypropylene glycol were extracted to remove the porous PEI resin sheet. Obtained.

  The porous body of the present invention is useful as an insulating sheet incorporated in an automobile or industrial motor with inverter control.

Claims (4)

  A step of applying a polymer composition containing a polymer, a phase separation agent and an organic solvent on a substrate and drying it to produce a polymer sheet having a microphase separation structure, and using a carbon dioxide fluid as an extraction solvent, A method for producing a porous body comprising a step of producing a porous polymer sheet by extracting and removing a phase separation agent from a polymer sheet while raising the temperature of the polymer.   The method for producing a porous body according to claim 1, wherein the temperature of the carbon dioxide fluid is increased by 10 ° C. or more from the initial temperature.   A step of applying a polymer composition containing a polymer, a phase separation agent and an organic solvent on a substrate and drying it to produce a polymer sheet having a microphase separation structure, and using a carbon dioxide fluid as an extraction solvent, A method for producing a porous body comprising a step of producing a porous polymer sheet by extracting and removing a phase separation agent from a polymer sheet while reducing the pressure.   The method for producing a porous body according to claim 3, wherein the pressure of the carbon dioxide fluid is reduced by 5 MPa or more from the initial pressure.