Method for producing polysiloxane from which salts have been removed

Abstract

The present invention provides a method for producing polysiloxane with reduced concentrations of salts, etc., by removing salts contained as impurities in polysiloxane with activated carbon. The present invention is applicable to semiconductor-related fields. [Solution] A method for producing a polysiloxane from which salts have been removed includes step (1) of contacting a polysiloxane with activated carbon in an organic solvent, followed by step (2) of separating the polysiloxane. The polysiloxane can be applied in a proportion of 20 to 90 mass% based on the total mass of the polysiloxane and the organic solvent, and the activated carbon can be applied in a proportion of 3 to 100 mass% based on the mass of the polysiloxane. In step (1), the temperature for contact with the activated carbon can be adjusted to a range of 5 to 50°C. The organic solvent can be a nonpolar organic solvent, and aromatic hydrocarbons include benzene, toluene, xylene, mesitylene, etc., and aliphatic hydrocarbons include octane, nonane, decane, undecane, dodecane, etc. The activated carbon can have an average particle size of 3 to 200 micrometers.

Description

Technical Field

[0001] The present invention relates to a method for producing a polysiloxane from which salts have been removed. Specifically, the present invention relates to a method for removing salts incorporated into a polysiloxane by bringing the polysiloxane into contact with activated carbon in an organic solvent.

Background Art

[0002] Polysiloxanes are used in various fields such as electricity, machinery, and food. Depending on the application, there are fields where the incorporation of impurities into polysiloxanes is not desired. For example, in the electrical field, particularly in the semiconductor-related field, salts contained in polysiloxanes may have an adverse effect on electrical properties, and it is desired that the salt content be extremely low.

[0003] Polysiloxanes are typically produced by hydrolysis and polycondensation of halogenated silanes. That is, when the halosilyl group of a halogenated silane is hydrolyzed to generate silanol, and chlorosilane is used as the halogenated silane, hydrochloric acid is by-produced during hydrolysis. Therefore, by using this hydrochloric acid as an acid catalyst to polycondense silanol, polysiloxane is generated. At this time, an alkali (e.g., sodium hydroxide) is used to neutralize the by-produced hydrochloric acid, but salts such as sodium chloride generated by the neutralization are incorporated as impurities into the produced polysiloxane, which may cause the above-mentioned problems. Polysiloxanes generally tend to be hydrophobic depending on the type of substituent bonded to silicon, while salts are hydrophilic. Removing hydrophilic substances (salts) incorporated into hydrophobic substances (polysiloxanes) is also difficult in terms of process.

[0004] Conventionally, there has been a purification technique using activated carbon for removing impurities. For example, there is an invention that uses a gas adsorbent containing activated carbon and the like in a calcium-containing composition using shells, eggshells, etc. for adsorbing formalin and the like (see Patent Document 1). There is an invention for a method of producing high-purity pyrroloquinoline quinones that includes a step of contacting an aqueous medium containing pyrroloquinoline quinones with activated carbon (see Patent Document 2). Furthermore, an adsorbent that removes metals from organic solvents using activated carbon has been disclosed (see Patent Document 3). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2014-005195 [Patent Document 2] Japanese Patent Publication No. 2014-193838 [Patent Document 3] Japanese Patent Publication No. 2017-177047 [Overview of the project] [Problems that the invention aims to solve]

[0006] When polysiloxane and activated carbon are brought into contact in an aqueous medium, as mentioned above, polysiloxane generally tends to be hydrophobic, so the aqueous medium does not penetrate into the interior of the polysiloxane, making it difficult for activated carbon to reach the interior of the polysiloxane. Furthermore, in the areas on the surface of the polysiloxane where the aqueous medium has penetrated, the salts are ionized by the aqueous medium to form cations and anions, and it is thought that these ionic forms are difficult for activated carbon to adsorb. Furthermore, methods such as liquid-liquid separation or removal using ion exchange resins make it difficult to achieve purification to the extremely low levels of salts required in the semiconductor field (e.g., 10 ppm or less).

[0007] The present invention provides a method for producing polysiloxane in which salts contained as impurities in the polysiloxane are removed by activated carbon, thereby reducing the concentration of salts and other impurities. [Means for solving the problem]

[0008] The present invention, in first view, provides a method for producing polysiloxane from which salts have been removed, comprising the steps of (1) contacting polysiloxane with activated carbon in an organic solvent, and (2) separating the polysiloxane thereafter. From a second perspective, the polysiloxane is applied in a proportion of 20 to 90% by mass based on the total mass of the polysiloxane and the organic solvent, as described in the first perspective. As a third point, the activated carbon is applied in a proportion of 3 to 100% by mass based on the mass of the polysiloxane, according to the manufacturing method described in the first or second point. As a fourth point of view, in step (1), the contact temperature with activated carbon is adjusted to a range of 5 to 50°C, the manufacturing method according to any one of the first to third points of view. As a fifth point, the manufacturing method described in any one of the first to fourth points, wherein the organic solvent is a nonpolar organic solvent, As a sixth point, the activated carbon has an average particle size of 3 to 200 micrometers and is manufactured according to any one of the first to fifth points. [Effects of the Invention]

[0009] In the present invention, salts in polysiloxane are removed by contacting the polysiloxane with activated carbon in an organic solvent, thereby obtaining polysiloxane from which the salts have been removed. When polysiloxane is brought into contact with activated carbon in an organic solvent, unlike polysiloxane in an aqueous medium, the organic solvent penetrates into the interior of the polysiloxane, or the polysiloxane dissolves in the organic solvent, allowing the salts in the polysiloxane to exist as particulate salts without being ionized. It is thought that the salts in the polysiloxane can be removed by adsorbing these minute particulate salts onto activated carbon and then separating the polysiloxane from the activated carbon on which the salts have been adsorbed. [Modes for carrying out the invention]

[0010] The present invention relates to a method for producing polysiloxane from which salts have been removed, comprising the steps of (1) contacting polysiloxane with activated carbon in an organic solvent, and (2) separating the polysiloxane thereafter.

[0011] The polysiloxane used as a raw material in step (1) of the present invention is not particularly limited, and polysiloxanes obtained by various manufacturing methods and having various functional groups can be used. For example, when producing polysiloxane by hydrolysis and polycondensation of chlorosilane with hydrochloric acid, the resulting hydrochloric acid can be neutralized with an aqueous alkali (e.g., sodium hydroxide) solution to obtain the polysiloxane used in step (1). Examples of alkalis used for neutralization include sodium hydroxide, potassium hydroxide, and ammonia. Furthermore, the polysiloxane mentioned above can be a polysiloxane obtained by hydrolyzing and polycondensing a chlorosilane containing an organic functional group. The organic functional group referred to here typically means an organic group other than a chlorine atom, and examples include alkyl groups such as methyl and ethyl groups, alkenyl groups such as vinyl groups, and aryl groups such as phenyl and 1-naphthyl groups.

[0012] Chlorosilanes are classified into tetrafunctional, trifunctional, difunctional, and monofunctional types depending on the number of chlorine atoms bonded to the silicon atom, and the present invention can use chlorosilanes of any functional number. Here, "functional number" refers to the number of chlorine atoms bonded to the silicon atom. Tetrachlorosilane is an example of a tetrafunctional silane. Examples of trifunctional silanes include trichlorosilane, alkyltrichlorosilane, alkenyltrichlorosilane, and aryltrichlorosilane. Examples of difunctional silanes include dichlorosilane, dialkyldichlorosilane, diaryldichlorosilane, diaryldichlorosilane, alkylalkenyldichlorosilane, alkylaryldichlorosilane, and alkenylaryldichlorosilane. Examples of monofunctional silanes include chlorosilane, trialkylchlorosilane, triarylkenylchlorosilane, triarylchlorosilane, dialkylalkenylchlorosilane, dialkylarylchlorosilane, diarylkenylalkylchlorosilane, diarylkenylarylchlorosilane, diarylalkylchlorosilane, and diarylalkenylchlorosilane.

[0013] Furthermore, when producing polysiloxanes, the raw material silane may be a single silane or a combination of multiple silanes. When using a single silane, for example, the above-mentioned tetrafunctional silane, trifunctional silane, difunctional silane, and monofunctional silane may be used individually. Furthermore, when using multiple silanes in combination, for example, silanes resulting from the above-mentioned combinations of tetrafunctional silane and monofunctional silane, trifunctional silane and monofunctional silane, difunctional silane and monofunctional silane, tetrafunctional silane, trifunctional silane and monofunctional silane, trifunctional silane, difunctional silane and monofunctional silane, or tetrafunctional silane, trifunctional silane, difunctional silane and monofunctional silane can be used.

[0014] Examples of alkyl groups included in the silanes exemplified above include alkyl groups having 1 to 10 carbon atoms, such as methyl, ethyl, propyl, i-propyl, butyl, pentyl, and octyl groups. Examples of alkenyl groups contained in the above-mentioned silane include alkenyl groups with 2 to 10 carbon atoms, such as vinyl groups and propenyl (allyl) groups. Examples of aryl groups included in the above-mentioned silanes include aryl groups with 6 to 40 carbon atoms, such as phenyl groups, naphthyl groups, and anthyl groups. These alkyl, alkenyl, and aryl groups can also be used in combination. Furthermore, alkyl, alkenyl, and aryl groups may be substituted with halogen groups, hydroxyl groups, nitro groups, sulfone groups, amino groups, etc.

[0015] As the above polysiloxane, a polysiloxane in a state where all the silanol groups (-Si-OH) in the silane are condensed into siloxane bonds (-Si-O-Si-), a state where some or all of the silanol groups are present as silanol groups without condensation, or a state where these are mixed can be used. In addition, the above polysiloxane may have a crosslinked structure in its structure.

[0016] The molecular weight of the polysiloxane used in step (1) is not particularly defined, but for example, a polysiloxane having a weight average molecular weight in the range of 100 to 1,000,000, or 1,000 to 100,000 can be used. The weight average molecular weight can be measured, for example, using a GPC device (EcoSEC, HLC-8320GPC manufactured by Tosoh Corporation) and GPC columns (Shodex (registered trademark), KF-803L, KF-802, and KF-801 manufactured by Showa Denko K.K.), setting the column temperature at 40°C, using tetrahydrofuran as the eluent (elution solvent), setting the flow rate (flow velocity) at 1.0 mL / min, and using polystyrene (manufactured by Sigma-Aldrich) as the standard sample.

[0017] The content of salts contained in the polysiloxane used in step (1) is not particularly defined, but usually, it contains 100 ppm or more, or 200 ppm or more, or 400 ppm or more as cations such as sodium, and 100 ppm or more, or 200 ppm or more, or 400 ppm as anions such as chlorine, and those can be used. Of course, polysiloxanes containing salts in other ranges may also be used. Usually, the upper limit suitable for treatment is about 1000 ppm. Note that these ions counted as the salt content do not include ions present in a free state, but include ions (salts) taken into the polysiloxane by adsorption or the like and cannot be removed by washing or the like.

[0018] The activated carbon used in the present invention can be in powder or granular form. The particle size of the activated carbon can be in the range of 3 to 400 micrometers or 3 to 200 micrometers in terms of average particle diameter. The average particle diameter referred to here is the value obtained by measuring a dispersion of activated carbon in water using a laser diffraction / scattering particle size distribution analyzer LA-920 manufactured by Horiba, Ltd. Commercially available activated carbon can be used. Examples include products from Osaka Gas Chemical Co., Ltd., such as "Tokusei Shirasagi," and products from Ajinomoto Co., Inc., such as "SD."

[0019] The organic solvent used in the present invention is preferably a solvent that has affinity for the raw material (i.e., unrefined or insufficiently refined) polysiloxane used in step (1), or a solvent that dissolves polysiloxane. Among these, the organic solvent is preferably a nonpolar organic solvent. As the above-mentioned organic solvent, aromatic or aliphatic hydrocarbons, or siloxane-based solvents can be used. Examples of aromatic hydrocarbons include benzene, toluene, xylene, and mesitylene. Examples of aliphatic hydrocarbons include saturated hydrocarbons such as octane, nonane, decane, undecane, and dodecane. Hexamethyldisiloxane can be given as an example of a siloxane-based solvent.

[0020] While it is preferable that the above organic solvent contains as little water as possible, it is possible for it to contain less than 5.0% by volume of water. The reason why it is preferable to use a nonpolar organic solvent (e.g., hydrophobic hydrocarbon) as the organic solvent and to avoid moisture is that the salts contained in polysiloxane become ionized in the presence of hydrophilic solvents or water, making them difficult to remove with activated carbon.

[0021] In step (1), the polysiloxane can be applied in an amount of 5 to 95% by mass, 20 to 90% by mass, 40 to 90% by mass, or 50 to 80% by mass, based on the total mass of the polysiloxane and the organic solvent. That is, the polysiloxane can be dispersed or dissolved at the above concentrations in a liquid consisting of the polysiloxane and the organic solvent. Furthermore, activated carbon can be applied in amounts of 1-200% by mass, 1.5-175% by mass, 2.0-150% by mass, 1.5-125% by mass, or 3-100% by mass, based on the mass of the polysiloxane. Of course, it is possible to apply activated carbon in amounts exceeding these limits, but this would require more time for the separation of the activated carbon in the subsequent step (2), making it inefficient. Moreover, by applying activated carbon within these ranges, highly purified polysiloxane can be obtained with good reproducibility.

[0022] In step (1), the contact temperature of the polysiloxane with the activated carbon in the organic solvent can be adjusted to, for example, typically within the range of 5 to 50°C or 10 to 40°C. It is also possible to adjust the contact temperature outside this range, but the melting point, boiling point, and vapor pressure of the organic solvent used must be taken into consideration. The contact time of polysiloxane with activated carbon in an organic solvent is preferably adjusted to approximately 0.001 to 20 hours, or 0.1 to 10 hours. Contact between polysiloxane and activated carbon can be carried out in either a batch or continuous manner. In the batch method, a container equipped with a stirring device is used, and the polysiloxane can be brought into contact with activated carbon in an organic solvent.

[0023] Step (2) is a step to separate the polysiloxane. First, activated carbon is separated by filtration or the like to obtain an organic solvent solution of polysiloxane. Then, the organic solvent is further separated by distillation or the like to produce polysiloxane from which salts have been removed.

[0024] To separate activated carbon and obtain an organic solvent solution of polysiloxane, an effective method is to pass the solution through a filter equipped with filter paper or a membrane filter with a pore size of 1 μm or less. This method leaves activated carbon on the filter paper, allowing the organic solvent solution of polysiloxane to be separated as a filtrate. While the organic solvent solution can pass through by gravity, it can also be passed through by pressurizing it with air or an inert gas (e.g., nitrogen gas). It is preferable to use an inert gas if there is a possibility that the polysiloxane may denature upon contact with air.

[0025] After separating the activated carbon, the polysiloxane can be recovered by removing the organic solvent from the polysiloxane organic solvent solution by distillation or other methods. Depending on the organic solvent used, the organic solvent can be removed under atmospheric pressure or reduced pressure (e.g., 50 Pa).

[0026] The polysiloxane obtained by the present invention has a reduced salt content, in which the content of cations such as sodium in the polysiloxane is 10 ppm or less, for example in the range of 0.1 to 10 ppm, and the content of anions such as chlorine is 10 ppm or less, for example in the range of 0.1 to 10 ppm.

[0027] As described above, the present invention demonstrates the reduction of sodium chloride as an example of salts, but it is also possible to remove salts that form particulate matter in organic solvents, such as metal halides, metal sulfides, and metal hydroxides. Examples of these metals include silver, cobalt, chromium, copper, lithium, manganese, nickel, lead, potassium, platinum, tin, aluminum, calcium, iron, manganese, and zinc.

[0028] In this invention, salts are removed using activated carbon. However, for salts that are ionized for some reason and cannot be removed by activated carbon, it is possible to further reduce the salts by alternately contacting a cation exchange resin and an anion exchange resin after the activated carbon treatment. [Examples]

[0029] <Analysis Method for Salts (Cations, Anions) in Polysiloxanes> Cations were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). Anions were measured using ion chromatography.

[0030] <Materials used> PS1: Polysiloxane material 1 (commercially available silicone resin, component is polydimethylsiloxane, weight-average molecular weight 9,000, containing 130 ppm Na and 220 ppm Cl) PS2: Polysiloxane material 2 (commercially available silicone resin, component is polydimethylsiloxane, weight-average molecular weight 7,300, containing 250 ppm Na and 400 ppm Cl)

[0031] AC1: Activated carbon 1 (manufactured by Osaka Gas Chemical Co., Ltd., product name: Special White Heron, average particle size 72 μm) AC2: Activated carbon 2 (manufactured by Ajinomoto Co., Inc., product name: SD, average particle size 75 μm) AC3: Activated carbon 3 (manufactured by Ajinomoto Co., Inc., product name: ZN, average particle size 75 μm) AC4: Activated carbon 4 (manufactured by Futamura Chemical Co., Ltd., product name: Taiko Y, average particle size 35 μm) AC5: Activated carbon 5 (manufactured by Futamura Chemical Co., Ltd., product name: Taiko K, average particle size 35 μm)

[0032] S1: Solvent 1 (toluene, commercially available) S2: Solvent 2 (manufactured by ExxonMobil, trade name Isopar-E, main component is a mixture of octane and nonane) S3: Solvent 3 (Hexamethyldisiloxane, commercially available) S4: Solvent 4 (methylbutylcarbinol, commercially available)

[0033] (Example 1) According to the materials and concentrations shown in Table 1, a predetermined amount of polysiloxane material and an organic solvent were added to a 300 ml beaker to prepare a polysiloxane solution. Activated carbon was then added, and the mixture was stirred with a stirrer at a predetermined temperature and for a predetermined time. Subsequently, the activated carbon was filtered through filter paper (pore size: 0.5 μm), and the organic solvent was removed from the polysiloxane solution after activated carbon filtration by distillation to obtain polysiloxane. The salt content (cations and anions) in the obtained polysiloxane (residual Na and Cl content) was analyzed. The results are shown in Table 2.

[0034] (Examples 2-18, Example 19) Similar to Example 1, Examples 2-18 and Example 19 were carried out using the materials shown in Table 1, and the salt (cation, anion) content (residual Na amount, residual Cl amount) in the obtained polysiloxane was analyzed. The results are shown in Table 2.

[0035] In Table 1, the "Type" column in the "Polysiloxane Material" section refers to one of the two types of polysiloxane material (PS1 or PS2) mentioned above, and the "Concentration" indicates the concentration (mass%) of the polysiloxane material relative to the total mass of the polysiloxane material and the organic solvent. "Organic solvent" refers to one of the above solvent types 1-3 (S1, S2, or S3). In the "Activated Carbon" column, "Type" refers to one of the five types of activated carbon listed above (AC1, AC2, AC3, AC4, or AC5), and "Amount Added" is the amount added (mass%) relative to the polysiloxane material (mass). The temperature and time refer to the temperature (°C) and time (h) at which the polysiloxane material is brought into contact with activated carbon in an organic solvent.

[0036] [Table 1]

[0037] [Table 2]

[0038] (Comparative Example 1: Operation using liquid-liquid separatory treatment (1)) The above polysiloxane material 1 (PS1) and toluene (S1) were mixed to prepare a 50% by mass polysiloxane solution, which was added to a 300 ml separatory funnel. Subsequently, a 10% by mass sulfuric acid aqueous solution was added to the separatory funnel in a mass ratio of polysiloxane solution:sulfuric acid aqueous solution = 50:50, and the polysiloxane solution was recovered after separation. This procedure (addition of sulfuric acid aqueous solution and separation) was repeated five times. After five operations, the organic solvent was removed from the obtained polysiloxane solution by distillation to obtain polysiloxane, and the salt content (residual Na amount, residual Cl amount) in the polysiloxane was analyzed. The results are shown in Table 3.

[0039] (Comparative Example 2: Operation using liquid-liquid separatory treatment (2)) The liquid-liquid separation procedure (addition of sulfuric acid aqueous solution and liquid-liquid separation) of Comparative Example 1 was repeated 10 times. After 10 operations, the organic solvent was removed from the obtained polysiloxane solution by distillation to obtain polysiloxane, and the salt content (residual Na amount, residual Cl amount) in the polysiloxane was analyzed. The results are shown in Table 3.

[0040] (Comparative Example 3: Operation using liquid-liquid separation (3)) The liquid-liquid separation procedure (addition of sulfuric acid aqueous solution and liquid-liquid separation) of Comparative Example 1 was repeated 15 times. After 15 operations, the organic solvent was removed from the obtained polysiloxane solution by distillation to obtain polysiloxane, and the salt content (residual Na amount, residual Cl amount) in the polysiloxane was analyzed. The results are shown in Table 3.

[0041] (Comparative Example 4: Operation using ion exchange resin (1)) 30 g of the above polysiloxane material 1 (PS1) and 30 g of methylbutylcarbinol (S4) were added to a 200 ml beaker to prepare a 50% by mass polysiloxane solution. 6 g of cation exchange resin (manufactured by Organo Corporation, product name Amberlist 15JS-HG-Dry) was added to this mixture, and the mixture was stirred for 4 hours at 100 rpm in a mix rotor at room temperature (23°C). The cation exchange resin was separated by filtration to obtain a polysiloxane solution. 6 g of anion exchange resin (organo Corporation, trade name Amberlist B20-HG·Dry) was added to the obtained polysiloxane solution, and the mixture was stirred at 100 rpm in a mix rotor at room temperature (23°C) for 4 hours. The anion exchange resin was separated by filtration to obtain the polysiloxane solution. The organic solvent was removed from the obtained polysiloxane solution by distillation to obtain polysiloxane. The salt content (cations and anions) in the obtained polysiloxane (residual Na and Cl content) was analyzed. The results are shown in Table 3.

[0042] (Comparative Example 5: Operation using ion exchange resin (2)) In Comparative Example 4, the procedure was carried out in the same manner as in Comparative Example 4, except that the amount of cation exchange resin added was changed from 6 g to 12 g, and the amount of anion exchange resin added was changed from 6 g to 12 g. A polysiloxane was obtained, and the salt content (residual Na amount, residual Cl amount) in the polysiloxane was analyzed. The results are shown in Table 3.

[0043] [Table 3] [Industrial applicability]

[0044] Polysiloxanes are used in various fields such as electrical engineering, mechanical engineering, and food processing. Depending on the application, there are fields where the inclusion of impurities in polysiloxanes is undesirable. For example, in the electrical field, particularly in semiconductor-related fields, salts contained in polysiloxanes can adversely affect electrical properties, and extremely low concentrations are desired. This invention provides a polysiloxane suitable for applications where extremely low salt content is required.

Claims

1. A method for removing unionized particulate salts from polysiloxane, comprising the steps of: (1) contacting the polysiloxane with activated carbon in a solution in which the polysiloxane obtained by hydrolyzing and polycondensing a chlorosilane having a chlorine atom bonded to a silicon atom in advance in a solvent consisting only of a nonpolar organic solvent (excluding methylene chloride or hexane); (excluding the step of contacting the polysiloxane with activated carbon by adding activated carbon and a neutralizing base to the solution in which the polysiloxane is pre-dissolved in the solvent consisting only of the nonpolar organic solvent); and (2) separating the polysiloxane.

2. The method for removing salts according to claim 1, wherein the polysiloxane is applied in a proportion of 20 to 90% by mass based on the total mass of the polysiloxane and the organic solvent.

3. The method for removing salts according to claim 1 or claim 2, wherein activated carbon is applied in a proportion of 3 to 100% by mass based on the mass of polysiloxane.

4. The method for removing salts according to any one of claims 1 to 3, wherein in step (1), the contact temperature with activated carbon is adjusted to a range of 5 to 50°C.

5. The method for removing salts according to any one of claims 1 to 4, wherein the activated carbon has an average particle size of 3 to 200 micrometers.

6. The method for removing salts according to any one of claims 1 to 5, wherein the nonpolar organic solvent is at least one selected from the group consisting of toluene, octane, nonane, and hexamethyldisiloxane.

7. The method for removing salts according to any one of claims 1 to 6, wherein the salts are sodium chloride.

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