Method for manufacturing porous silicone rubber

Abstract

To provide a manufacturing method of a silicone rubber porous body which suppresses formation of a skin layer and has good air permeability, by press molding.SOLUTION: A manufacturing method of a silicone rubber porous body includes a mixing step of mixing a liquid silicone rubber and a pore forming material, and producing an uncrosslinked silicone rubber composition, a molding step of crosslinking the silicone rubber composition by press molding, and producing a silicone rubber molding, and an extraction step of bringing the silicone rubber molding into contact with water, and extracting the pore forming material from the silicone rubber molding, wherein the pore forming material is one or more selected from polyethylene glycol and polyether-modified silicone oil, and has a water-soluble organic matter having an HLB value of 9.5 or more and a water-soluble inorganic matter.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a method for producing a silicone rubber porous body having a continuous cell structure.

Background Art

[0002] As a method for producing a polymer porous body, after blending a pore-forming material with a polymer material such as a resin or an elastomer and molding, the pore-forming material is removed from the molded body using a solvent, and pores (voids) are formed in the portion where the pore-forming material was present. An extraction method is known. For example, Patent Document 1 describes a method for producing a silicone porous body having a step of kneading a silicone raw material and a water-soluble bubble-forming material to obtain a mixture, a step of crosslinking the obtained mixture after molding to obtain a silicone molded body, and a step of bringing the obtained silicone molded body into contact with water to extract the bubble-forming material. Patent Document 1 lists, as the bubble-forming material, a water-soluble organic substance composed of an alkyl ether represented by the chemical formula R1O(CH2CH2O) n R2 (R1 is a hydrocarbon group, R2 is hydrogen or a hydrocarbon group), and water-soluble inorganic substances such as NaCl and KCl. And in the examples, it is described that a mixture of a silicone raw material and a bubble-forming material is extruded and molded by a twin-screw roll.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When using porous silicone rubber materials in microfluidic devices that contain samples in fine grooves and pores for various operations, high precision is required in their shape and dimensions. In this case, press molding using a mold is a suitable method for molding the raw material silicone rubber composition. However, some alkyl ethers, listed as water-soluble organic materials for bubble-forming materials in Patent Document 1, are highly evaporative. Therefore, if press molding is performed at a relatively high temperature of, for example, 130°C, the alkyl ether evaporates during molding, generating a large amount of gas. Thus, when using highly evaporative alkyl ethers, press molding is difficult as a molding method. Furthermore, incorporating water-soluble organic materials can be expected to suppress the formation of a skin layer on the surface of the silicone rubber molded body during press molding. However, if the water-soluble organic material evaporates during molding, this effect cannot be obtained, and even if press molding is possible, a skin layer will be formed on the surface. In this case, in order to ensure breathability, the skin layer must be removed from the resulting porous silicone rubber material. Removing the skin layer is an extremely difficult task when the porous material is thin. In addition, the water-soluble organic material exists around the other pore-forming material, the water-soluble inorganic material, and plays a role in increasing the elution rate of the water-soluble inorganic material in the subsequent extraction process. Therefore, if water-soluble organic matter evaporates during molding, water-soluble inorganic matter will exist independently within the silicone rubber molded body, reducing the elution rate of water-soluble inorganic matter and decreasing the pore connectivity.

[0005] This disclosure has been made in view of the above circumstances, and aims to provide a method for producing a porous silicone rubber body with good breathability by suppressing the formation of a skin layer through press molding. [Means for solving the problem]

[0006] (1) In order to solve the above problems, the method for manufacturing a porous silicone rubber body of the present disclosure comprises a mixing step of mixing liquid silicone rubber and a pore-forming material to produce an uncrosslinked silicone rubber composition; a molding step of press-molding the silicone rubber composition to crosslink it and produce a molded silicone rubber body; and an extraction step of bringing the molded silicone rubber body into contact with water to extract the pore-forming material from the molded silicone rubber body, wherein the pore-forming material is one or more selected from polyethylene glycol and polyether-modified silicone oil, and comprises a water-soluble organic substance with an HLB value of 9.5 or higher and a water-soluble inorganic substance.

[0007] In the method for producing a porous silicone rubber body according to this disclosure, a water-soluble organic substance and a water-soluble inorganic substance are used as pore-forming materials. The water-soluble organic substance is one or more compounds selected from polyethylene glycol and polyether-modified silicone oil, and has an HLB value of 9.5 or higher. The polyether-modified silicone oil has a structure in which polyether groups are introduced into a linear silicone polymer. The polyether groups may be introduced into the side chains of the linear polymer, or into one or both ends.

[0008] As a result of the inventors' extensive research, it was found that polyethylene glycol and polyether-modified silicone oil do not evaporate easily under press molding conditions. Therefore, by using one or more of these as water-soluble organic substances, the evaporation of the water-soluble organic substances during press molding can be suppressed. This makes it possible to manufacture a porous silicone rubber body with high accuracy in shape and dimensions by press molding a silicone rubber composition containing water-soluble organic substances. Furthermore, the presence of water-soluble organic substances during press molding suppresses the formation of a skin layer on the surface of the silicone rubber molded body. Therefore, breathability can be ensured without the need for a separate skin layer removal process. In addition, because the evaporation of water-soluble organic substances is suppressed during press molding, and the water-soluble organic substances are present around the water-soluble inorganic substances, the elution of water-soluble inorganic substances is facilitated in the extraction process, making it possible to manufacture a porous silicone rubber body with an open-cell structure and excellent breathability.

[0009] The HLB (Hydrophile-Lipophile Balance) value is an indicator of the balance between hydrophilicity and lipophilicity; a higher HLB value indicates higher hydrophilicity. By increasing the HLB value of water-soluble organic matter to 9.5 or higher to enhance hydrophilicity, the mixing process can maintain a sea-island state where the liquid silicone rubber is in the sea phase and the water-soluble inorganic matter is in the island phase. As a result, the moldability of the silicone rubber composition can be improved. Furthermore, after extracting the pore-forming material, the water-soluble organic matter with hydrophilic components remains in the porous silicone rubber body, making it easy to hydrophilize the surface of the porous silicone rubber body.

[0010] (2) In the above configuration, the melting point of the water-soluble organic substance may be 10°C or lower. With this configuration, since the water-soluble organic substance is liquid at room temperature, the water-soluble inorganic substance can be dispersed without heating in the mixing process and without reducing the fluidity of the silicone rubber composition. In addition, the water-soluble organic substance does not solidify easily even when it returns to room temperature after the molding process. Therefore, aggregation of the water-soluble organic substance can be suppressed in the crosslinked silicone rubber molded article, and the water-soluble organic substance can be easily eluted in the extraction process.

[0011] (3) In any of the above configurations, the polyethylene glycol (HO[CH2-CH2-O] n The weight-average molecular weight of H) may be set to be between 400 and 600. In polyethylene glycol, the larger the number of repeating units n, the higher the hydrophilicity. With this configuration, both hydrophilicity and being in a liquid state at room temperature can be satisfied.

[0012] (4) In any of the above configurations, the water-soluble inorganic substance may be in particulate form, and the particle size of the water-soluble inorganic substance may be 5 μm or more and 600 μm or less. This configuration improves the dispersibility of the water-soluble inorganic substance in the silicone rubber composition, making it possible to obtain a homogeneous silicone rubber molded article. Furthermore, it is possible to form pores of a desired size after the water-soluble inorganic substance has been eluted.

[0013] (5) In any of the above configurations, the water-soluble inorganic substance may be one or more selected from sodium chloride, potassium chloride, calcium chloride, and calcium carbonate. The water-soluble inorganic substance in this configuration is relatively inexpensive, readily available, and highly safe.

[0014] (6) In any of the above configurations, the press forming may be carried out at a temperature of 100°C to 130°C. This configuration allows for a relatively short molding time (crosslinking time), resulting in high productivity. In addition, evaporation of water-soluble organic matter is suppressed during press forming.

[0015] (7) In any of the above configurations, a hydrophilization treatment step may be provided after the extraction step, in which a treatment is performed to impart hydrophilicity to the surface of the obtained porous silicone rubber.

[0016] Silicone rubber has low affinity for water. Therefore, when applying porous silicone rubber to microfluidic devices, it is desirable to apply a treatment to impart hydrophilicity to the surface in order to improve the flowability of hydrophilic liquids. According to this configuration, porous silicone rubber having a hydrophilic surface can be easily manufactured. Examples of treatments to impart hydrophilicity (hydrophilization treatment) include application of a coating agent and modification treatment by irradiation with high energy such as plasma. For example, if a water-soluble organic substance with a high HLB value and high hydrophilicity is left behind in the extraction process, it is possible to impart hydrophilicity by irradiation with plasma or the like without applying a coating agent. [Effects of the Invention]

[0017] According to the method for manufacturing a porous silicone rubber body of this disclosure, a porous silicone rubber body with good breathability can be manufactured by press molding, thereby suppressing the formation of a skin layer. [Modes for carrying out the invention]

[0018] The following describes embodiments of the method for manufacturing a porous silicone rubber body according to this disclosure. However, the embodiments are not limited to those described below, and can be implemented in various modified and improved forms as possible for those skilled in the art.

[0019] The method for producing a porous silicone rubber body according to this disclosure comprises a mixing step, a molding step, and an extraction step. Each step will be described below.

[0020] <Mixing process> This process involves mixing liquid silicone rubber and a pore-forming material to produce an uncrosslinked silicone rubber composition.

[0021] "Liquid silicone rubber" is a concept that includes, in addition to a polymer component (base polymer), a crosslinking agent, a catalyst, etc. for crosslinking it. As the base polymer of liquid silicone rubber, those widely known as organopolysiloxanes may be used. Organopolysiloxanes have predetermined reactive groups depending on their crosslinking mechanism (curing mechanism). Examples of the reactive groups include alkenyl groups (vinyl group, allyl group, butenyl group, pentenyl group, hexenyl group, etc.), silanol groups, and the like. The organopolysiloxane having the former alkenyl group is crosslinked by a peroxide crosslinking reaction using an organic peroxide as a crosslinking agent or an addition reaction using an organopolysiloxane having a hydrosilyl group (organohydrogenpolysiloxane) as a crosslinking agent. For the addition reaction, a hydrosilylation catalyst such as a platinum catalyst can be used in combination. The organopolysiloxane having the latter silanol group is crosslinked by a condensation reaction. For the condensation reaction, a crosslinking agent for condensation can be used in combination.

[0022] The pore-forming material has a water-soluble organic substance and a water-soluble inorganic substance. The water-soluble organic substance is one or more selected from polyethylene glycol and polyether-modified silicone oil, and is a compound having an HLB value of 9.5 or more. Polyethylene glycol and polyether-modified silicone oil are relatively inexpensive and easily available. In addition, since it has both a hydrophilic part and a hydrophobic part (lipophilic part), it is easy to mix with hydrophobic liquid silicone rubber and is also advantageous for hydrophilizing the surface of the silicone rubber porous body. The water-soluble organic substance to be used may be one kind or two or more kinds. When using polyethylene glycol, from the viewpoint of being in a liquid state at room temperature and having a desired hydrophilicity, it is desirable to select one having a weight average molecular weight of 400 or more and 600 or less.

[0023] Several calculation methods for the HLB value have been proposed depending on the type of compound, etc. For example, it can be calculated by the following formula (i). From the viewpoint of enhancing hydrophilicity, improving moldability, and facilitating the imparting of hydrophilicity, it is more preferable to set the HLB value to 12 or more. HLB value = 20 × sum of formula weights of hydrophilic parts / molecular weight ··· (i)

[0024] From the viewpoint of enhancing the fluidity of the silicone rubber composition and improving the dispersibility of the water-soluble inorganic substance, it is desirable that the water-soluble organic substance be liquid at room temperature. For example, it is desirable that the melting point of the water-soluble organic substance be 10°C or lower.

[0025] The blending amount of the water-soluble organic substance may be appropriately adjusted in consideration of the miscibility with the liquid silicone rubber, the effect of suppressing the formation of the skin layer, the elution property of the pore-forming material, etc. For example, the blending amount of the water-soluble organic substance may be 10 parts by mass or more and 360 parts by mass or less with respect to 100 parts by mass of the liquid silicone rubber. From the viewpoint of suppressing separation in the silicone rubber composition, it is preferably less than 180 parts by mass.

[0026] The water-soluble inorganic substance is preferably particulate because it is easy to control the pore diameter to be formed, etc. The water-soluble inorganic substance may be of one kind or two or more kinds. For example, salts of alkali metals such as sodium chloride, potassium chloride, calcium chloride, sodium nitrate, potassium nitrate, calcium nitrate, sodium sulfate, potassium sulfate, calcium sulfate, sodium carbonate, potassium carbonate, calcium carbonate, etc. may be mentioned. Among them, sodium chloride, potassium chloride, calcium chloride, and calcium carbonate are suitable because they are relatively inexpensive and available.

[0027] The particle diameter of the water-soluble inorganic substance is not particularly limited, but in consideration of the pore diameter to be formed, etc., it is desirable that it be 5 μm or more and 600 μm or less. When the particle diameter is less than 5 μm, the pore diameter to be formed may become small, and there is a risk that the air permeability of the silicone rubber porous body will decrease. On the contrary, when the particle diameter becomes larger than 600 μm, in addition to the decrease in the dispersibility of the water-soluble inorganic substance in the silicone rubber composition, there is a risk that the pore diameter to be formed will become large and the mechanical strength of the silicone porous body will decrease. In this specification, as the particle diameter of the water-soluble inorganic substance, the maximum length when the particles are observed with a microscope is adopted.

[0028] The amount of water-soluble inorganic material added should be adjusted appropriately according to the particle size of the water-soluble inorganic material, taking into consideration the air permeability and moldability of the porous silicone rubber. For example, if the particle size of the water-soluble inorganic material is 5 μm or more and 600 μm or less, the amount added should be 100 parts by mass or more and 650 parts by mass or less per 100 parts by mass of liquid silicone rubber. From the viewpoint of improving the moldability of the porous silicone rubber, it is preferable to use 300 parts by mass or less.

[0029] The liquid silicone rubber and pore-forming material can be mixed using a mixer such as a planetary mixer, homomixer, homogenizer, or disperser. The mixing temperature can be room temperature, and heating is not necessary. However, this does not preclude heating to the extent that the crosslinking reaction of the liquid silicone rubber does not proceed. It is preferable not to add water during mixing. If water is present in the silicone rubber composition, it may inhibit the crosslinking reaction in the next molding process, and the desired pores may not be formed due to the evaporation of water. Mixing should be done by first adding a water-soluble inorganic substance to the liquid silicone rubber and stirring, and then adding a water-soluble organic substance and stirring. This suppresses the separation of the liquid silicone rubber and the water-soluble organic substance, and the dispersion is improved as the water-soluble organic substance coordinates around the water-soluble inorganic substance.

[0030] <Forming process> This process involves press molding the silicone rubber composition produced in the previous process to crosslink it and produce a silicone rubber molded article. The press molding temperature should be determined appropriately, taking into consideration the crosslinking temperature of the liquid silicone rubber, productivity, etc. For example, from the viewpoint of improving productivity while suppressing the evaporation of water-soluble organic matter, it is desirable to perform the process at a temperature of 100°C to 130°C. The molding time should be set to allow the crosslinking reaction to proceed sufficiently, depending on the molding temperature. For example, if the molding temperature is 100°C to 130°C, the molding time can be set to 5 minutes to 20 minutes.

[0031] It is desirable that silicone rubber molded articles manufactured by press molding do not have a skin layer. The size and shape of the silicone rubber molded article should be appropriately determined according to the application of the porous silicone rubber article. For example, when used in microfluidic devices, it is acceptable to mold it into thin films with thicknesses of 1 μm or more, 15 μm or more, 300 μm or more, or thin plates of 1 mm or more. When used in microfluidic devices for optical inspection using a microscope, the thickness should be 2 mm or less, 1 mm or less, 750 μm or less, or 500 μm or less. Silicone rubber molded articles may be in the form of a sheet, container, tube, or other shapes.

[0032] <Extraction process> This process involves contacting the silicone rubber molded body produced in the previous process with water to extract the pore-forming material from the silicone rubber molded body. The method of contact between the silicone rubber molded body and water is not particularly limited. For example, it can be done by immersing the silicone rubber molded body in water or by spraying water onto the silicone rubber molded body. The water temperature can be room temperature, but from the viewpoint of shortening the extraction time of the pore-forming material and increasing the dissolution rate, warm water of about 30 to 70°C may be used. The extraction time can be appropriately determined according to the ease with which the pore-forming material dissolves, for example, it can be about 10 to 48 hours.

[0033] A porous silicone rubber body is obtained by extracting the pore-forming material and then drying it to remove moisture. The pore-forming material does not necessarily have to be completely extracted. That is, some of the pore-forming material may remain in the manufactured porous silicone rubber body. For example, if some of the water-soluble organic matter remains in the porous silicone rubber body, it facilitates the hydrophilization of the surface of the porous silicone rubber body. The porous silicone rubber body has an open-cell structure, but from the viewpoint of minimizing the amount of remaining water-soluble inorganic matter, it is desirable for the permeability (porosity) of the porous silicone rubber body to be as high as possible.

[0034] <Hydrophilicization treatment process> The method for manufacturing a porous silicone rubber body according to this disclosure may consist of the three steps described above. However, if hydrophilicity of the surface of the porous silicone rubber body is required, a hydrophilization treatment step may be added after the extraction step to impart hydrophilicity to the surface of the porous silicone rubber body. The hydrophilization treatment may be applied to only a part of the surface or to the entire surface. Examples of hydrophilization treatments include film formation treatment using a coating agent and modification treatment by irradiation with high energy. Examples of film formation treatments include spray coating, dip treatment, transfer method, and plasma CVD method. Examples of modification treatments include plasma irradiation, ultraviolet (UV) irradiation such as excimer light, corona discharge, electron beam irradiation, and gamma ray irradiation. Among these, plasma treatment is preferred because it is effective in a short time and does not cause thermal damage to the porous silicone rubber body. Plasma treatment may be performed under atmospheric pressure or vacuum, and the treatment may be performed in an atmosphere containing noble gases such as argon or oxygen, and irradiated with RF plasma using a high-frequency (RF) power supply or microwave plasma using a microwave power supply. If not all of the water-soluble organic matter is extracted during the extraction process, and some remains in the porous silicone rubber body, then high hydrophilicity can be imparted simply by applying plasma treatment. [Examples]

[0035] Next, the present disclosure will be described in more detail with reference to examples.

[0036] <Sample Manufacturing> [Samples 1-6] First, sodium chloride powder, a water-soluble inorganic substance, was dried by holding it in an oven at 80°C for 24 hours. Next, a predetermined amount of the dried sodium chloride powder was added to 100 parts by mass of liquid silicone rubber ("LR3391 / 70" manufactured by Asahi Kasei Wacker Silicone Co., Ltd.), and the mixture was stirred in a planetary mixer at room temperature. Then, a predetermined amount of polyethylene glycol (PEG400, weight-average molecular weight 380-420), a water-soluble organic substance, was added, and the mixture was further stirred in the same mixer at room temperature to produce an uncrosslinked silicone rubber composition (mixing step). The liquid silicone rubber used contained an organopolysiloxane having vinyl groups, a crosslinking agent, a retarder, and a catalyst. Subsequently, the silicone rubber composition was placed in a mold and press-molded at 130°C for 5 minutes to produce a square sheet-shaped silicone rubber molded body measuring 120 mm in length, 120 mm in width, and 1 mm in thickness (molding step). Next, the silicone rubber molded body was immersed in 60°C hot water for 24 hours to dissolve the pore-forming material (sodium chloride, PEG400). The resulting porous silicone rubber body was then dried in a 60°C oven for 24 hours to obtain the sample (extraction step).

[0037] Three types of sodium chloride powder with different particle sizes were used. PEG400 has an HLB value of 20, a boiling point of 250°C, and a melting point of 8°C. The proportions of each material are shown in Table 1 below, along with the evaluation results. Sodium chloride powder a: Particle size 300 μm or more and 600 μm or less. Sodium chloride powder b: Particle size 30 μm to 60 μm. Sodium chloride powder c: Particle size 5 μm to 10 μm.

[0038] [Sample 7] Sample 7 was prepared in the same manner as Sample 2 (using sodium chloride powder a), except that the water-soluble organic substance was replaced with polyether-modified silicone oil a (KF-6011, manufactured by Shin-Etsu Chemical Co., Ltd.). The HLB value of polyether-modified silicone oil a is 12, and based on the boiling and melting points of silicone oil, the boiling point is estimated to be above 200°C and the melting point below -50°C. The manufacturing methods for Samples 1 to 7 are included in the concept of the manufacturing method for porous silicone rubber bodies of this disclosure.

[0039] [Sample 8] Sample 8 was prepared in the same manner as Sample 2, except that the water-soluble organic substance was changed to polyoxyethylene dodecyl ether (Pegnol® L-4, manufactured by Toho Chemical Industry Co., Ltd.) and the amount of sodium chloride powder a was changed to 325 parts by mass. The HLB value of the polyoxyethylene dodecyl ether used was 9.7, and as a reference value, polyoxyethylene dodecyl ether (C), which has a similar structure, was used. 12 The boiling point of EO6 is 230°C and the melting point is 26°C.

[0040] [Sample 9] Sample 9 was prepared in the same manner as Sample 2, except that the water-soluble organic substance was replaced with polyether-modified silicone oil b (KF-6015, manufactured by Shin-Etsu Chemical Co., Ltd.). The HLB value of polyether-modified silicone oil b is 5, and based on the boiling and melting points of silicone oil, the boiling point is estimated to be above 200°C and the melting point below -50°C.

[0041] [Sample 10] Sample 10 was prepared in the same manner as Samples 3 and 4 (using sodium chloride powder b), except that it did not contain water-soluble organic matter.

[0042] [Sample 11] Sample 11 was prepared in the same manner as Samples 5 and 6 (using sodium chloride powder c), except that it did not contain water-soluble organic matter.

[0043] <Evaluation Method> [Loss in weight when heated] The water-soluble organic material used was heated, and the weight loss rate was determined based on the mass before and after heating. A larger weight loss rate indicates that more components evaporate during heating. First, 5.2 g of the water-soluble organic material was placed in a cylindrical, lidless aluminum cup (50 mm in diameter, 15 mm thick), and the total mass including the cup (W0) was measured. Next, the cup was placed on a hot plate maintained at 130°C and left to stand for 1 hour. Then, the cup was removed from the hot plate and allowed to cool to room temperature, after which the total mass including the cup (W1) was measured. The weight loss rate was then calculated using the following formula (ii). Heating loss rate (%)=(W0-W1) / W0×100 (ii) [W0: Mass before heating, W1: Mass after heating]

[0044] [State of silicone rubber composition] The uncrosslinked silicone rubber composition produced during the mixing process was visually inspected to check for separation.

[0045] [Moldability] The appearance of the silicone rubber molded articles produced during the molding process was visually observed, and if the sheet shape was maintained, it was evaluated as having good moldability (indicated by a circle in Table 1 below), and if it was not maintained, it was evaluated as having poor moldability (indicated by a cross in the same table).

[0046] [Leaching rate of porosity-forming materials] The elution rate of the pore-forming material in the sample silicone rubber porous body was calculated using the following formula (iii). Elution rate of pore-forming material [mass %] = (Mass of silicone rubber molded body (mass before extraction) [g] - Mass of porous silicone rubber (mass after extraction and drying) [g]) / Theoretical amount of pore-forming material [g] × 100 ... (iii)

[0047] [Presence or absence of skin layer] The surface of the sample silicone rubber porous material was imaged using a scanning electron microscope (SEM) at 30x or 300x magnification. If pores were visible at either magnification, it was determined that there was no skin layer; if no pores were visible at either magnification, it was determined that there was a skin layer.

[0048] [Pore diameter] The cross-section of the porous silicone rubber sample in the thickness direction was imaged using a scanning electron microscope (SEM) at 30x or 300x magnification, and the pore size was measured.

[0049] [Breathability] The sample silicone rubber porous material was placed to act as a partition between an atmospheric pressure chamber and a vacuum chamber (pressure approximately 1000 Pa), and the pressure change in the vacuum chamber was measured after 60 seconds. If the pressure change in the vacuum chamber was 25000 Pa or more, the permeability was considered extremely high (indicated by ◎ in Table 1 below); if it was between 5000 Pa and 25000 Pa, the permeability was considered good (indicated by ○ in the same table); and if it was less than 5000 Pa, the permeability was considered poor (indicated by × in the same table).

[0050] [Hydrophilic properties] A porous silicone rubber sample was subjected to plasma treatment on one surface in the thickness direction, followed by a film deposition process. Plasma treatment was performed by irradiating the sample with microwave plasma under a vacuum of 9.0 Pa in an argon gas and oxygen gas atmosphere. The argon gas supply rate was 30 cc / min, and the oxygen gas supply rate was 150 cc / min. The microwave frequency was 2.45 GHz, the output power was 0.3 kW, and the treatment time was 2 seconds. Film deposition was performed using a coating agent made by diluting polyethersilane (Shin-Etsu Chemical Co., Ltd. "X-12-641") with pure water to 50%. First, the plasma-treated sample was immersed in the coating agent for 1 minute. Next, the same sample was immersed in pure water for 1 minute, and then air-dried for 24 hours. Then, 2 μL of water was dropped onto the plasma and film-deposited surfaces of the samples. If the water soaked in, it was evaluated as hydrophilicity could be imparted (indicated by a circle in Table 1 below), and if the water did not soak in, it was evaluated as hydrophilicity could not be imparted (indicated by a cross in the same table).

[0051] <Evaluation Results> Table 1 summarizes the material proportions and evaluation results for each sample. [Table 1]

[0052] As shown in Table 1, in samples 1 to 7 produced by the silicone rubber porous body manufacturing method of this disclosure, no skin layer was formed even after press molding, and the breathability was good. Furthermore, the elution rate of the pore-forming material was high in all samples, exceeding 70%. Here, the heat loss rate of PEG400 used in samples 1 to 6 was 1.9%, and the heat loss rate of polyether-modified silicone oil a used in sample 7 was 0.0%. Comparing samples 1 and 2, 3 and 4, and 5 and 6, it can be seen that increasing the amount of water-soluble organic matter increases the elution rate of the pore-forming material. In addition, hydrophilicity could be imparted to the surface of all samples by applying plasma treatment and film deposition treatment. Separation was observed in the silicone rubber composition during the manufacturing process of sample 2, but this did not affect the moldability.

[0053] In contrast, in sample 8, which used polyoxyethylene dodecyl ether as the water-soluble organic substance with a large heating loss rate of 5.8%, a large amount of gas was generated during press molding, making molding impossible. Furthermore, in sample 9, which used polyether-modified silicone oil b with an HLB value of 5, the liquid silicone rubber formed island phases during the mixing process, preventing sufficient dispersion of the water-soluble inorganic substance (sodium chloride powder), thus preventing sheet molding. While press molding was possible for samples 10 and 11, which did not contain water-soluble organic substances, a skin layer formed on the resulting silicone rubber molded body, resulting in low permeability of the porous silicone rubber body. Additionally, the elution rate of the pore-forming material was low, and hydrophilicity could not be imparted to the surface. [Industrial applicability]

[0054] The porous silicone rubber obtained by the manufacturing method of this disclosure can be used in microfluidic devices, filters, cushioning materials, heat insulating materials, and the like.

Claims

1. A mixing step to produce an uncrosslinked silicone rubber composition by mixing liquid silicone rubber and a pore-forming material, A molding process for producing a silicone rubber molded article by press molding the silicone rubber composition and crosslinking it, An extraction step of bringing the silicone rubber molded body into contact with water to extract the pore-forming material from the silicone rubber molded body, It has, A method for producing a porous silicone rubber body, characterized in that the pore-forming material is one or more selected from polyethylene glycol with a weight-average molecular weight of 400 to 600 and polyether-modified silicone oil, and comprises a water-soluble organic substance with an HLB value of 9.5 or higher and a water-soluble inorganic substance.

2. The method for producing a porous silicone rubber body according to claim 1, wherein the melting point of the water-soluble organic substance is 10°C or lower.

3. The aforementioned water-soluble inorganic substance exhibits particulate matter, A method for producing a porous silicone rubber body according to claim 1, wherein the particle size of the water-soluble inorganic substance is 5 μm or more and 600 μm or less.

4. The method for producing a porous silicone rubber body according to claim 1, wherein the water-soluble inorganic substance is one or more selected from sodium chloride, potassium chloride, calcium chloride, and calcium carbonate.

5. The method for producing a porous silicone rubber body according to claim 1, wherein the press molding is performed at a temperature of 100°C or higher and 130°C or lower.

6. A method for producing a silicone rubber porous body according to claim 1, further comprising a hydrophilization treatment step of applying a treatment to the surface of the obtained silicone rubber porous body to impart hydrophilicity after the extraction step.

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