JP2014198649A - Method for manufacturing silica sol - Google Patents
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本発明は、珪素アルコキシドの加水分解による金属不純物を含まない高純度球状シリカゾルの製造方法の改良に関する。特に本発明は、窒素吸着法による平均粒子径が５〜１００ｎｍの球状であり、内部細孔の少ない耐吸湿性に優れたシリカのゾルを製造するのに好適である。 The present invention relates to an improvement in a method for producing a high purity spherical silica sol containing no metal impurities by hydrolysis of silicon alkoxide. In particular, the present invention is suitable for producing a silica sol having a spherical shape with an average particle diameter of 5 to 100 nm by the nitrogen adsorption method and having few internal pores and excellent moisture absorption resistance.
水ガラスを原料として中和又はイオン交換によりシリカゾルを得る方法は、古くより知られている。また、四塩化珪素の熱分解法によりシリカ微粉末が得られることも知られている。高純度のシリカゾルの製法として、塩基性触媒を含有するアルコール−水溶液中で珪素アルコキシドを加水分解させる方法も知られている。例えば、数モル／リットルのアンモニア及び数モル／リットル〜１５モル／リットルの水を含むアルコール溶液に、０．２８モル／リットルのテトラエチルシリケートを添加して加水分解することにより、５０〜９００ｎｍのシリカ粒子が得られることも報告されている（例えば、非特許文献１参照）。 A method of obtaining silica sol by neutralization or ion exchange using water glass as a raw material has been known for a long time. It is also known that fine silica powder can be obtained by thermal decomposition of silicon tetrachloride. As a method for producing a high-purity silica sol, a method of hydrolyzing silicon alkoxide in an alcohol-water solution containing a basic catalyst is also known. For example, by adding 0.28 mol / liter of tetraethyl silicate to an alcohol solution containing several mol / liter of ammonia and water of several mol / liter to 15 mol / liter and hydrolyzing it, silica of 50 to 900 nm It has also been reported that particles can be obtained (for example, see Non-Patent Document 1).
また、平均粒子径が１００ｎｍ以下のシリカ粒子を得る方法として、アンモニア等のアルカリ性触媒をアルコキシシランに対し０．５〜１０のモル比に、そして水を５〜２０モル／リットルの濃度に含有するアルコール溶液中で、アルコキシシランを３０℃以上の温度で加水分解する方法が開示されている（例えば、特許文献１参照）。 As a method for obtaining silica particles having an average particle diameter of 100 nm or less, an alkaline catalyst such as ammonia is contained in a molar ratio of 0.5 to 10 with respect to alkoxysilane, and water is contained in a concentration of 5 to 20 mol / liter. A method of hydrolyzing alkoxysilane at a temperature of 30 ° C. or higher in an alcohol solution is disclosed (for example, see Patent Document 1).
また、無孔性シリカの製法として、珪素アルコキシドを加水分解して得たシリカ粒子を表面処理後６５０℃以上の高温で焼成した後に解砕する方法が開示されている（例えば、特許文献２参照）。 Further, as a method for producing nonporous silica, a method is disclosed in which silica particles obtained by hydrolyzing silicon alkoxide are subjected to surface treatment and then baked at a high temperature of 650 ° C. or higher and then crushed (see, for example, Patent Document 2). ).
また、平均粒子径が３〜１００ｎｍの粒子径を有するコロイダルシリカの製造方法として、反応媒体を、その１リットル当たり０．００２〜０．１モルのアルカリ濃度と３０モル以上の水濃度に保ちながら、この反応媒体に上記アルカリ１モルに対してＳｉ原子として７〜８０モルとなる量のアルキルシリケートを加え、４５℃〜この反応媒体の沸点以下の温度でこのアルキルシリケートを加水分解させると共に、この加水分解によって生じた珪酸の重合を進行させる方法が開示されている（例えば、特許文献３参照）。 Further, as a method for producing colloidal silica having an average particle size of 3 to 100 nm, while maintaining the reaction medium at an alkali concentration of 0.002 to 0.1 mol per liter and a water concentration of 30 mol or more. Then, an alkyl silicate in an amount of 7 to 80 mol as Si atoms is added to 1 mol of the alkali to the reaction medium, and the alkyl silicate is hydrolyzed at a temperature of 45 ° C. to the boiling point of the reaction medium. A method of proceeding polymerization of silicic acid produced by hydrolysis is disclosed (for example, see Patent Document 3).
しかしながら、水ガラスを原料として中和又はイオン交換によりシリカゾルを得る方法では、金属や遊離アニオン等の不純物を完全に除去することができない。また、四塩化珪素の熱分解法で得られるシリカ微粉末は凝集粒子であり、水に分散しても単分散のゾルを得ることができない。 However, in the method of obtaining silica sol by neutralization or ion exchange using water glass as a raw material, impurities such as metals and free anions cannot be completely removed. Moreover, the silica fine powder obtained by the thermal decomposition method of silicon tetrachloride is an agglomerated particle, and even when dispersed in water, a monodispersed sol cannot be obtained.
また、非特許文献１や特許文献１に記載の方法では、シリカ粒子は粒子内部に未加水分解のアルコキシ基が多く残存し、加熱又は加水分解によってアルコールの脱離が起きる。また、加水分解により内部アルコキシを脱離させた後に内部に細孔やシラノール基が残存し、水分、塩基触媒、アルコールなどが吸着して残る。これらはシリカを樹脂のフィラーとして用いた際に樹脂の特性を損ねる可能性がある。 In addition, in the methods described in Non-Patent Document 1 and Patent Document 1, silica particles have many unhydrolyzed alkoxy groups remaining inside the particles, and alcohol is eliminated by heating or hydrolysis. Further, after internal alkoxy is eliminated by hydrolysis, pores and silanol groups remain in the interior, and moisture, base catalyst, alcohol, etc. remain adsorbed. These may impair the properties of the resin when silica is used as the resin filler.
また、特許文献２に記載の方法では、焼成時に粒子間の焼結が起きるため実際には１００ｎｍ以下の小粒子では凝集傾向が強く、解砕を行っても１次粒子まで分散させることは困難である。また解砕時に装置やメディアからのコンタミネーションも起きやすく、純度も低下しやすい。 In addition, in the method described in Patent Document 2, sintering between particles occurs at the time of firing. In fact, small particles of 100 nm or less have a strong tendency to agglomerate, and it is difficult to disperse to primary particles even after pulverization. It is. In addition, contamination from equipment and media tends to occur at the time of crushing, and the purity tends to decrease.
さらに、特許文献３に記載の方法では、球状の小粒子ゾルを得ることができ、塩基性触媒としてアンモニアやアミンを用いれば金属不純物の少ないゾルが得られる。しかし触媒としてアンモニアを用いた場合、微小粒子が多く生成することがあり、粒子成長が抑制される課題があった。 Furthermore, in the method described in Patent Document 3, a spherical small particle sol can be obtained. If ammonia or amine is used as a basic catalyst, a sol with few metal impurities can be obtained. However, when ammonia is used as a catalyst, a large amount of fine particles may be generated, and there is a problem that particle growth is suppressed.
本発明はこのような事情に鑑み、平均粒子径が５〜１００ｎｍの球状であり、内部細孔の少ない耐吸湿性に優れた高純度シリカゾルを製造可能なシリカゾルの製造方法を提供することを目的とする。 In view of such circumstances, an object of the present invention is to provide a method for producing a silica sol that can produce a high-purity silica sol having a spherical shape with an average particle diameter of 5 to 100 nm and having few internal pores and excellent moisture absorption resistance. And
上記課題を解決する本発明の態様は、加水分解触媒としてアンモニア又は沸点が１００℃以下のアルキルアミンを用い、前記加水分解触媒の初期濃度を反応媒体１リットル当たり０．０２〜１．０モルとし、前記反応媒体を８０モル％以上の水濃度に保ちながら、加水分解触媒が珪素の総添加量に対してモル比（加水分解触媒／珪素）で０．１５以上となる前記珪素アルコキシドを反応媒体に添加し、６０℃以上、かつ前記反応媒体の沸点未満の温度で、前記珪素アルコキシドを加水分解させることを特徴とする。 The embodiment of the present invention that solves the above problems uses ammonia or an alkylamine having a boiling point of 100 ° C. or lower as the hydrolysis catalyst, and the initial concentration of the hydrolysis catalyst is 0.02 to 1.0 mol per liter of the reaction medium. The silicon alkoxide having a hydrolysis ratio of 0.15 or more in terms of molar ratio (hydrolysis catalyst / silicon) with respect to the total amount of silicon added while maintaining the reaction medium at a water concentration of 80 mol% or more is used as the reaction medium. And the silicon alkoxide is hydrolyzed at a temperature of 60 ° C. or higher and lower than the boiling point of the reaction medium.
また、前記珪素アルコキシドが、テトラメチルシリケート（ＴＭＯＳ）であることが好ましい。 The silicon alkoxide is preferably tetramethyl silicate (TMOS).
また、前記反応媒体に前記珪素アルコキシドを添加する速度が、前記反応媒体１リットル当たり毎時０．０５〜１．５モルであることが好ましい。 Moreover, it is preferable that the rate at which the silicon alkoxide is added to the reaction medium is 0.05 to 1.5 mol per hour per liter of the reaction medium.
また、前記反応媒体の水濃度が８０モル％未満となる前に、前記珪素アルコキシドの添加を中断し、前記珪素アルコキシドの加水分解によって生じるアルコールを前記反応媒体から除去すると共に、前記反応媒体の前記加水分解触媒の濃度を調整した後、前記珪素アルコキシドの添加を再開する工程を含むことが好ましい。 Further, before the water concentration of the reaction medium becomes less than 80 mol%, the addition of the silicon alkoxide is interrupted, alcohol generated by hydrolysis of the silicon alkoxide is removed from the reaction medium, and the reaction medium It is preferable to include a step of restarting the addition of the silicon alkoxide after adjusting the concentration of the hydrolysis catalyst.
また、前記珪素アルコキシドを添加する前に、核となるシリカ粒子を前記反応媒体に予め添加しておくことが好ましい。 Moreover, before adding the silicon alkoxide, it is preferable to add silica particles serving as a nucleus to the reaction medium in advance.
本発明によれば、加水分解触媒としてのアンモニア又は沸点が１００℃以下のアルキルアミンによって、珪素アルコキシドを加水分解させることができ、さらに、加水分解によって生成する活性珪酸の重合速度を大きくすることができる。また、粒子生成後に加水分解触媒としてのアンモニア又は沸点が１００℃以下のアルキルアミンを、蒸留等により容易に除去することができる。よって、平均粒子径が５〜１００ｎｍの球状であり、内部細孔の少ない耐吸湿性に優れた高純度シリカのゾルを製造することができる。 According to the present invention, silicon alkoxide can be hydrolyzed with ammonia as a hydrolysis catalyst or an alkylamine having a boiling point of 100 ° C. or lower, and the polymerization rate of active silicic acid produced by hydrolysis can be increased. it can. In addition, ammonia as a hydrolysis catalyst or an alkylamine having a boiling point of 100 ° C. or lower can be easily removed by distillation or the like after the particles are formed. Therefore, it is possible to produce a high-purity silica sol having a spherical shape with an average particle diameter of 5 to 100 nm and having few internal pores and excellent moisture absorption resistance.
本実施形態のシリカゾルの製造方法は、加水分解触媒としてアンモニア又は沸点が１００℃以下のアルキルアミンを用い、加水分解触媒の初期濃度を反応媒体１リットル当たり０．０２〜１．０モルとし、反応媒体を８０モル％以上の水濃度に保ちながら、加水分解触媒が珪素の総添加量に対してモル比（加水分解触媒／珪素）で０．１５以上となる珪素アルコキシドを反応媒体に添加し、６０℃以上、かつ反応媒体の沸点未満の温度で、珪素アルコキシドを加水分解させるものである。以下、本発明の実施形態に係るシリカゾルの製造方法について詳述する。 In the method for producing a silica sol of this embodiment, ammonia or an alkylamine having a boiling point of 100 ° C. or lower is used as a hydrolysis catalyst, the initial concentration of the hydrolysis catalyst is 0.02 to 1.0 mol per liter of the reaction medium, and the reaction While maintaining the medium at a water concentration of 80 mol% or more, silicon alkoxide in which the hydrolysis catalyst is 0.15 or more in molar ratio (hydrolysis catalyst / silicon) with respect to the total amount of silicon added is added to the reaction medium, The silicon alkoxide is hydrolyzed at a temperature of 60 ° C. or higher and lower than the boiling point of the reaction medium. Hereinafter, the manufacturing method of the silica sol which concerns on embodiment of this invention is explained in full detail.
まず、本実施形態の反応媒体は８０モル％以上の水濃度を有する。ここで使用される水としては、イオン交換水、限外濾過水、逆浸透水、蒸留水等の純水又は超純水を用いることができる。また、本明細書において、水濃度は、加水分解触媒を含む反応媒体のうち、加水分解触媒を除いた反応媒体中の水濃度（モル％）である。 First, the reaction medium of this embodiment has a water concentration of 80 mol% or more. As water used here, pure water or ultrapure water such as ion exchange water, ultrafiltration water, reverse osmosis water, and distilled water can be used. Moreover, in this specification, water concentration is water concentration (mol%) in the reaction medium except a hydrolysis catalyst among the reaction media containing a hydrolysis catalyst.
反応媒体を８０モル％以上の水濃度で維持することで、珪素アルコキシドを好適に加水分解させることができ、粒子内に残存する未反応のアルコキシ基を減少させることができる。さらに反応温度を６０℃以上とすることで加水分解によって生じた活性珪酸の重合を促進し、内部細孔の少ない粒子を製造できる。一方、珪素アルコキシドの加水分解によってアルコールが生成するため、加水分解反応の進行と共に、反応媒体の水濃度が徐々に減少する。反応媒体の水濃度を８０モル％以上で維持するには、生成したアルコールの反応媒体の濃度が高くならないように、例えば珪素アルコキシドの添加速度を制御するか、アルコール濃度が高くなる前に生成したアルコールの一部を蒸留等によって系外に排出することが好ましい。 By maintaining the reaction medium at a water concentration of 80 mol% or more, silicon alkoxide can be suitably hydrolyzed, and unreacted alkoxy groups remaining in the particles can be reduced. Furthermore, by setting the reaction temperature to 60 ° C. or higher, polymerization of active silicic acid generated by hydrolysis can be promoted, and particles having few internal pores can be produced. On the other hand, since alcohol is generated by hydrolysis of silicon alkoxide, the water concentration of the reaction medium gradually decreases as the hydrolysis reaction proceeds. In order to maintain the water concentration of the reaction medium at 80 mol% or more, for example, the addition rate of silicon alkoxide is controlled or the alcohol is generated before the alcohol concentration becomes high so that the concentration of the reaction medium of the generated alcohol does not increase. It is preferable to discharge a part of the alcohol out of the system by distillation or the like.
次に、加水分解触媒の初期濃度は、反応媒体１リットル当たり０．０２〜１.０モルである。加水分解触媒の初期濃度が上記範囲より小さくなると、珪素アルコキシドの加水分解によって生成する活性珪酸の重合速度が小さくなり、耐吸湿性に優れたシリカゾルを製造できない。一方、加水分解触媒の初期濃度が上記範囲より大きくなると、加水分解反応の速度を制御することが困難となり、やはり、耐吸湿性に優れたシリカ粒子のゾルを製造できない。 Next, the initial concentration of hydrolysis catalyst is 0.02 to 1.0 mole per liter of reaction medium. When the initial concentration of the hydrolysis catalyst is smaller than the above range, the polymerization rate of the active silicic acid produced by the hydrolysis of the silicon alkoxide is reduced, and a silica sol excellent in moisture absorption resistance cannot be produced. On the other hand, when the initial concentration of the hydrolysis catalyst is larger than the above range, it becomes difficult to control the rate of the hydrolysis reaction, and it is impossible to produce a sol of silica particles having excellent moisture absorption resistance.
次に、本実施形態の珪素アルコキシドは、珪酸モノマー又は重合度２〜３の珪酸オリゴマーのアルキルエステルである。アルキル基としては、１〜２の炭素数を有するものが好ましい。好ましい珪素アルコキシドの例としては、テトラメチルシリケート、テトラエチルシリケート、トリエチルメチルシリケート等が挙げられるが、経済性等の観点から、特にテトラメチルシリケート（ＴＭＯＳ）が好ましい。尚、分子内に異なったアルキル基を有する混合エステルや、これらの混合物も用いることができる。従って、例えば珪素アルコキシドとしてテトラメチルシリケートを用いる場合、これに異なったアルキル基を有する混合エステルが含まれていても構わない。これらの珪素アルコキシドは原液として添加しても、水溶性の有機溶媒で希釈して添加しても良い。 Next, the silicon alkoxide of this embodiment is a silicic acid monomer or an alkyl ester of a silicic acid oligomer having a polymerization degree of 2 to 3. As the alkyl group, those having 1 to 2 carbon atoms are preferred. Preferred examples of the silicon alkoxide include tetramethyl silicate, tetraethyl silicate, triethylmethyl silicate and the like, and tetramethyl silicate (TMOS) is particularly preferable from the viewpoint of economy and the like. In addition, mixed ester which has a different alkyl group in a molecule | numerator, and these mixtures can also be used. Therefore, for example, when tetramethyl silicate is used as the silicon alkoxide, a mixed ester having a different alkyl group may be contained therein. These silicon alkoxides may be added as a stock solution or diluted with a water-soluble organic solvent.
また、珪素アルコキシドは、本実施形態の方法による反応の終了時点で、全反応媒体中のアルコキシドに由来するＳｉ原子として４モル／リットル以下、好ましくは０．１〜２モル／リットルの濃度となる量が用いられる。上述のように、珪素アルコキシドの加水分解によって反応媒体に生じるアルコールは、蒸留等によって系外に排出させることができる。 Further, the silicon alkoxide has a concentration of 4 mol / liter or less, preferably 0.1 to 2 mol / liter, as Si atoms derived from the alkoxide in the entire reaction medium at the end of the reaction according to the method of the present embodiment. A quantity is used. As described above, alcohol generated in the reaction medium by hydrolysis of silicon alkoxide can be discharged out of the system by distillation or the like.
また、本実施形態で用いられる加水分解触媒は、好ましくはアンモニアである。これによれば、蒸留等による除去が容易であり、加水分解触媒が残留してシリカゾルの純度に悪影響を与えることがない。さらに、加水分解触媒としてアンモニアを用いれば、加水分解によって生成した活性珪酸を速やかに重合させ、より耐吸湿性に優れたシリカ粒子のゾルを製造できるようになる。 In addition, the hydrolysis catalyst used in the present embodiment is preferably ammonia. According to this, removal by distillation or the like is easy, and the hydrolysis catalyst remains and does not adversely affect the purity of the silica sol. Furthermore, if ammonia is used as the hydrolysis catalyst, the activated silicic acid produced by hydrolysis can be rapidly polymerized to produce a silica particle sol with better moisture absorption resistance.
加水分解触媒はアンモニアに限られず、沸点が１００℃以下のアルキルアミンでもよい。沸点が１００℃以下のアルキルアミンとしては、将来的に蒸留等によってアルキルアミンを除去する必要があることを踏まえると、モノアルキルアミン、ジアルキルアミン又はトリアルキルアミンといった低沸点であるアルキルアミンが好ましい。本実施形態の方法に用いることができるアルキルアミンとしては、メチルアミン、ジメチルアミン、トリメチルアミン、エチルアミン、ジエチルアミン、トリエチルアミン、プロピルアミン、ジプロピルアミン及びトリプロピルアミン等が挙げられるが、特に、低沸点であるメチルアミン及びエチルアミンがより好ましい。尚、アンモニア溶液の沸点は、アンモニアの濃度によって変わるものの一般に１００℃以下である。 The hydrolysis catalyst is not limited to ammonia, but may be an alkylamine having a boiling point of 100 ° C. or lower. As the alkylamine having a boiling point of 100 ° C. or lower, an alkylamine having a low boiling point such as a monoalkylamine, a dialkylamine, or a trialkylamine is preferable in view of the necessity of removing the alkylamine by distillation or the like in the future. Examples of the alkylamine that can be used in the method of the present embodiment include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, and tripropylamine. Certain methylamines and ethylamines are more preferred. In addition, although the boiling point of an ammonia solution changes with the density | concentrations of ammonia, generally it is 100 degrees C or less.
加水分解触媒は、上述のアンモニア及びアルキルアミンを単独で用いてもよく、二種以上を混合して用いてもよい。また、反応媒体の加水分解触媒の濃度は、例えば反応媒体中の加水分解触媒に含まれる窒素原子のモル数によって算出される。 As the hydrolysis catalyst, the above-mentioned ammonia and alkylamine may be used alone, or two or more kinds may be mixed and used. The concentration of the hydrolysis catalyst in the reaction medium is calculated, for example, based on the number of moles of nitrogen atoms contained in the hydrolysis catalyst in the reaction medium.
ここで、本実施形態では、加水分解触媒が珪素の総添加量に対してモル比（加水分解触媒／珪素）で０．１５以上となる珪素アルコキシドを、反応媒体に添加する。これにより、珪素アルコキシドに対して十分量の加水分解触媒を反応媒体中に存在させ、加水分解により生成した活性珪酸を速やかに反応系内の粒子と結合させることができる。 Here, in this embodiment, a silicon alkoxide in which the hydrolysis catalyst has a molar ratio (hydrolysis catalyst / silicon) of 0.15 or more with respect to the total amount of silicon added is added to the reaction medium. Thereby, a sufficient amount of hydrolysis catalyst can be present in the reaction medium with respect to silicon alkoxide, and the active silicic acid produced by the hydrolysis can be quickly bonded to the particles in the reaction system.
図１は、珪素アルコキシドを所定の添加速度及び総添加量で反応媒体に添加したときの、モル比（加水分解触媒／珪素）の推移を示す。尚、縦軸はモル比（加水分解触媒／珪素）を示し、横軸は時間を示す。 FIG. 1 shows the transition of the molar ratio (hydrolysis catalyst / silicon) when silicon alkoxide is added to the reaction medium at a predetermined addition rate and total addition amount. The vertical axis represents the molar ratio (hydrolysis catalyst / silicon), and the horizontal axis represents time.
珪素アルコキシドの添加初期では、反応媒体は加水分解触媒の初期濃度にあり、モル比（加水分解触媒／珪素）が大きく、加水分解触媒が過剰状態にある。珪素アルコキシドは、加水分解触媒によって加水分解が加速され、やがて、反応媒体中にシリカの核が形成される。 In the initial stage of addition of silicon alkoxide, the reaction medium is at the initial concentration of the hydrolysis catalyst, the molar ratio (hydrolysis catalyst / silicon) is large, and the hydrolysis catalyst is in an excess state. Hydrolysis of silicon alkoxide is accelerated by the hydrolysis catalyst, and eventually a silica nucleus is formed in the reaction medium.
反応媒体中にシリカの核が形成される具体的なタイミングは、反応媒体の水濃度、加水分解触媒の濃度や種類、添加される珪素アルコキシドの種類等によって変動する。例えば、反応媒体の加水分解触媒の初期濃度が大きくなるにつれ、添加される珪素アルコキシドの加水分解速度が大きくなる一方、加水分解によって生じる活性珪酸の重合速度が大きくなり、核形成のタイミングが早められると推察される。また、反応媒体の加水分解触媒の初期濃度に応じ、形成される核の数も異なってくる。 The specific timing at which silica nuclei are formed in the reaction medium varies depending on the water concentration of the reaction medium, the concentration and type of the hydrolysis catalyst, the type of silicon alkoxide added, and the like. For example, as the initial concentration of the hydrolysis catalyst in the reaction medium increases, the hydrolysis rate of the added silicon alkoxide increases, while the polymerization rate of active silicic acid generated by hydrolysis increases, and the timing of nucleation is advanced. It is guessed. Further, the number of nuclei formed varies depending on the initial concentration of the hydrolysis catalyst in the reaction medium.
ここで、本明細書において、核は、モル比（加水分解触媒／珪素）が０．１５以上である反応媒体中に、はじめて現れるシリカの初期核である。よって、シリカの初期核が現れた後に生成する二次的な核は、本明細書の核に含まれない。 Here, in this specification, the nucleus is an initial nucleus of silica that appears for the first time in a reaction medium having a molar ratio (hydrolysis catalyst / silicon) of 0.15 or more. Therefore, secondary nuclei generated after the initial nuclei of silica appear are not included in the nuclei in this specification.
図１中、実線Ａで示す本実施形態では、反応媒体に珪素アルコキシドを添加するにつれモル比（加水分解触媒／珪素）が小さくなるが、かかるモル比は０．１５以上で維持される。 In this embodiment indicated by a solid line A in FIG. 1, the molar ratio (hydrolysis catalyst / silicon) decreases as silicon alkoxide is added to the reaction medium, but this molar ratio is maintained at 0.15 or more.
実線Ａの本実施形態においては、加水分解触媒の初期濃度が反応媒体１リットル当たり０．０２〜１．０モルとされるとともに、モル比（加水分解触媒／珪素）が０．１５以上で維持されるため、添加される珪素アルコキシドに対して、常に十分量の加水分解触媒が反応媒体中に存在する。このため、添加される珪素アルコキシドは、反応媒体中に形成された核のまわりで重合し、シリカの核成長が起きる。 In this embodiment of the solid line A, the initial concentration of the hydrolysis catalyst is 0.02 to 1.0 mol per liter of the reaction medium, and the molar ratio (hydrolysis catalyst / silicon) is maintained at 0.15 or more. Therefore, a sufficient amount of hydrolysis catalyst is always present in the reaction medium with respect to the added silicon alkoxide. For this reason, the added silicon alkoxide is polymerized around the nuclei formed in the reaction medium, and silica nucleation occurs.
尚、図１では、実線Ａに示す本実施形態のモル比（加水分解触媒／珪素）は、高いところから０．１５に近づくように推移しているが、これは一例である。本実施形態では、モル比（加水分解触媒／珪素）を０．１５以上で維持するため、珪素アルコキシドの添加を適宜中断して、反応媒体中の加水分解触媒の濃度を高めるようにしてもよい。 In FIG. 1, the molar ratio (hydrolysis catalyst / silicon) of the present embodiment indicated by a solid line A changes so as to approach 0.15 from a high point, but this is an example. In the present embodiment, in order to maintain the molar ratio (hydrolysis catalyst / silicon) at 0.15 or more, the addition of silicon alkoxide may be appropriately interrupted to increase the concentration of the hydrolysis catalyst in the reaction medium. .
また、本実施形態において、珪素アルコキシドは、連続的に添加又は間欠的に添加することが好ましい。これによれば、反応媒体の水濃度やモル比（加水分解触媒／珪素）の調整が容易となる。具体的に、珪素アルコキシドは、反応媒体の１リットル当たり毎時０．０５〜１．５モルの速さで添加することが好ましく、０．０９〜１．１モルの速さで添加することがより好ましい。上記範囲内の添加速度であれば、反応媒体の水濃度やモル比（加水分解触媒／珪素）の調整がさらに容易となる。 Moreover, in this embodiment, it is preferable to add silicon alkoxide continuously or intermittently. This facilitates adjustment of the water concentration and molar ratio (hydrolysis catalyst / silicon) of the reaction medium. Specifically, the silicon alkoxide is preferably added at a rate of 0.05 to 1.5 moles per hour per liter of the reaction medium, more preferably 0.09 to 1.1 moles. preferable. If the addition rate is within the above range, the water concentration and molar ratio (hydrolysis catalyst / silicon) of the reaction medium can be adjusted more easily.
本実施形態では、上述の加水分解触媒の初期濃度を有する反応媒体を、珪素の総添加量に対する加水分解触媒のモル比（加水分解触媒／珪素）が０．１５以上となるよう維持するため、珪素アルコキシドの添加速度が低い場合はもちろん、珪素アルコキシドの添加速度が大きい場合であったとしても、添加される珪素アルコキシドに対し、十分量の加水分解触媒を反応媒体に存在させることができる。これにより、珪素アルコキシドの加水分解によって生成する活性珪酸の重合速度を大きくし、核成長を促進させることがきる。よって、珪素の総添加量に対する加水分解触媒のモル比（加水分解触媒／珪素）を０．１５未満とし、他を同条件とした場合と比較して、平均粒子径が大きな高純度シリカゾルを製造できる。例えば平均粒子径が５〜１００ｎｍの球状である高純度シリカゾルを、珪素の総添加量に対する加水分解触媒のモル比（加水分解触媒／珪素）を０．１５未満とした場合より極めて容易に製造できるようになる。 In this embodiment, in order to maintain the reaction medium having the above initial concentration of the hydrolysis catalyst so that the molar ratio of the hydrolysis catalyst to the total amount of silicon added (hydrolysis catalyst / silicon) is 0.15 or more, Even if the addition rate of silicon alkoxide is low, even if the addition rate of silicon alkoxide is high, a sufficient amount of hydrolysis catalyst can be present in the reaction medium with respect to the added silicon alkoxide. Thereby, the polymerization rate of the active silicic acid produced | generated by hydrolysis of a silicon alkoxide can be enlarged, and a nucleus growth can be promoted. Therefore, a high-purity silica sol with a large average particle size is produced compared to the case where the molar ratio of the hydrolysis catalyst to the total amount of silicon added (hydrolysis catalyst / silicon) is less than 0.15 and the other conditions are the same. it can. For example, a high-purity silica sol having a spherical shape with an average particle diameter of 5 to 100 nm can be produced much more easily than when the molar ratio of the hydrolysis catalyst to the total amount of silicon added (hydrolysis catalyst / silicon) is less than 0.15. It becomes like this.
ここで、平均粒子径は、製造されたシリカ粒子の一次粒子径である。本明細書において、平均粒子径は、特に断りのない限り窒素吸着法（ＢＥＴ法）によって算出される平均粒子径をいい、後述する実施例に示すように、製造したシリカの乾燥粉末に基づいて測定される。 Here, the average particle diameter is the primary particle diameter of the produced silica particles. In the present specification, the average particle diameter means an average particle diameter calculated by a nitrogen adsorption method (BET method) unless otherwise specified. As shown in Examples described later, the average particle diameter is based on the produced silica dry powder. Measured.
また、本実施形態では、反応媒体中に予め核となるシリカ粒子を添加し、このシリカ粒子を成長させることもできる。これによれば、珪素アルコキシドの添加初期からシリカ粒子を成長させることができるため、反応媒体中に予め核となるシリカ粒子を添加しない場合、すなわち、反応媒体中で核を自然に発生させて核成長させる場合と比較して、平均粒子径の大きなシリカゾルを容易に製造できるようになる。反応媒体中に予め核となるシリカ粒子を添加しない条件下はもちろん、反応媒体中に予め核となるシリカ粒子を添加する条件下であっても、本実施形態では、珪素の総添加量に対する加水分解触媒のモル比（加水分解触媒／珪素）が０．１５未満となる場合と比較して、平均粒子径が大きな高純度シリカゾルを容易に製造できるようになる。 Moreover, in this embodiment, the silica particle used as a nucleus can be previously added in the reaction medium, and this silica particle can also be grown. According to this, since the silica particles can be grown from the initial stage of addition of the silicon alkoxide, when the silica particles that serve as nuclei are not added to the reaction medium in advance, that is, the nuclei are naturally generated in the reaction medium. Compared to the case of growing, a silica sol having a large average particle diameter can be easily produced. In this embodiment, the amount of water added to the total amount of silicon added is not limited to the condition in which the silica particles serving as nuclei are added to the reaction medium in advance, but also the condition in which the silica particles serving as nuclei are added to the reaction medium in advance. Compared with the case where the molar ratio of the decomposition catalyst (hydrolysis catalyst / silicon) is less than 0.15, a high-purity silica sol having a large average particle diameter can be easily produced.
また、本実施形態では、反応媒体を８０モル％以上の水濃度で維持するため、珪素アルコキシドを好適に加水分解させ、粒子内に残存する未反応のアルコキシ基を減少させることができる。これにより、内部細孔の少なく、耐吸湿性の優れたシリカ粒子のゾルを製造できるようになる。 Moreover, in this embodiment, since the reaction medium is maintained at a water concentration of 80 mol% or more, silicon alkoxide can be suitably hydrolyzed to reduce unreacted alkoxy groups remaining in the particles. As a result, it is possible to produce a sol of silica particles having few internal pores and excellent moisture absorption resistance.
また、本実施形態では、珪素アルコキシドとして、例えばテトラエチルシリケートと比べて反応性が高く反応の調節が難しいテトラメチルシリケートを用いたとしても、同様に、上述の加水分解触媒の初期濃度を有する反応媒体を、珪素の総添加量に対する加水分解触媒のモル比（加水分解触媒／珪素）が０．１５以上となるよう維持するとともに、反応媒体を８０モル％以上の水濃度で維持するため、珪素の総添加量に対する加水分解触媒のモル比（加水分解触媒／珪素）が０．１５未満となる場合と比較して、例えば平均粒子径が５〜１００ｎｍの球状であり、内部細孔の少ない耐吸湿性に優れた高純度シリカゾルを製造できるようになる。 Further, in the present embodiment, even when tetramethyl silicate having high reactivity and difficult to control the reaction is used as silicon alkoxide, for example, the reaction medium having the initial concentration of the hydrolysis catalyst described above is used. In order to maintain the molar ratio of the hydrolysis catalyst to the total amount of silicon added (hydrolysis catalyst / silicon) to be 0.15 or more and to maintain the reaction medium at a water concentration of 80 mol% or more, Compared to the case where the molar ratio of the hydrolysis catalyst to the total amount added (hydrolysis catalyst / silicon) is less than 0.15, for example, the average particle size is spherical with an average particle diameter of 5 to 100 nm and moisture absorption resistance with few internal pores. High-purity silica sol with excellent properties can be produced.
また、本実施形態において、反応媒体に、予め核となるシリカ粒子を添加しておくこともできる。これによれば、自然に核が発生する場合とは異なり、初期の核の数と平均粒子径とを制御して、製造されるシリカゾルの平均粒子径を制御することが容易となる。すなわち、珪素アルコキシドの添加初期から、珪素アルコキシドを予め添加したシリカ粒子の核成長に用いることができるため、求める粒子径や体積まで成長させるのに必要な珪素アルコキシドの積算量を、核の量と平均粒子径とから逆算することが可能になる。 Moreover, in this embodiment, the silica particle used as a nucleus can also be previously added to the reaction medium. According to this, unlike the case where nuclei spontaneously occur, it becomes easy to control the average particle size of the silica sol produced by controlling the initial number of nuclei and the average particle size. That is, from the initial stage of addition of silicon alkoxide, it can be used for nucleation of silica particles to which silicon alkoxide has been added in advance, so that the cumulative amount of silicon alkoxide required to grow to the desired particle diameter and volume is the amount of nuclei. It becomes possible to calculate backward from the average particle diameter.
予め核となるシリカ粒子の添加量は、製造するシリカゾルの粒子径や添加する珪素アルコキシド量に応じて調節可能である。添加される珪素アルコキシドが核成長に均一に用いられるとすると、予め核となるシリカ粒子の添加量を多く（少なく）すれば、所定の粒子径まで核を成長させるのに必要な珪素アルコキシドの量は多く（少なく）なる。また、予め核となるシリカ粒子の添加量を多く（少なく）すると、所定量の珪素アルコキシドが添加されたときのシリカ粒子の成長量は小さく（大きく）なる。よって、添加する珪素アルコキシド量に対し、予め核となるシリカ粒子量の割合を小さくすれば、平均粒子径が例えば２０ｎｍ以上である比較的大きいシリカゾルの製造が容易となる。 The addition amount of silica particles as a nucleus can be adjusted in advance according to the particle size of the silica sol to be produced and the amount of silicon alkoxide to be added. Assuming that the added silicon alkoxide is uniformly used for nucleus growth, the amount of silicon alkoxide required to grow the nucleus to a predetermined particle diameter can be increased by increasing (reducing) the amount of silica particles to be the nucleus in advance. Will be more (less). Further, if the amount of silica particles added as nuclei is increased (reduced) in advance, the growth amount of silica particles when a predetermined amount of silicon alkoxide is added becomes smaller (larger). Therefore, if the ratio of the amount of silica particles serving as a nucleus is reduced in advance with respect to the amount of silicon alkoxide to be added, production of a relatively large silica sol having an average particle diameter of, for example, 20 nm or more is facilitated.
尚、核となるシリカ粒子は、本実施形態によって製造されたシリカを用いてもよいし、それ以外の方法により製造されたシリカ粒子を用いてもよい。核となるシリカ粒子の粒度分布のばらつきは、シリカ粒子の核成長に伴って相対的に小さくなるため、充分な粒子成長が行われれば製造されるシリカゾルの粒度分布に実質的に影響を及ぼさない。 In addition, the silica particle manufactured by this embodiment may be used for the silica particle used as a nucleus, and the silica particle manufactured by the method other than that may be used. The variation in the particle size distribution of the silica particles that become the core becomes relatively small as the silica particles grow, so that if the particle growth is sufficient, the particle size distribution of the manufactured silica sol is not substantially affected. .
核となるシリカ粒子を添加する方法として、反応媒体を６０℃以下とし、一部の珪素アルコキシドを添加して、加水分解により微小核を発生させる方法もある。かかる方法では、６０℃以上に昇温後、残りの珪素アルコキシドを供給して核成長させる。このような方法によっても、平均粒子径の制御が容易となる。 As a method for adding silica particles as nuclei, there is also a method in which a reaction medium is set to 60 ° C. or less, a part of silicon alkoxide is added, and micronuclei are generated by hydrolysis. In such a method, after the temperature is raised to 60 ° C. or higher, the remaining silicon alkoxide is supplied to cause nucleus growth. Such a method also makes it easy to control the average particle size.
次に、本実施形態のシリカゾルの製造方法の具体例について説明する。本実施形態では、上述の加水分解触媒の初期濃度を有する反応媒体を６０℃以上に加熱しておき、反応媒体に攪拌下で珪素アルコキシドを徐々に添加することにより、加水分解反応を進行させる。 Next, a specific example of the method for producing the silica sol of the present embodiment will be described. In the present embodiment, the reaction medium having the above initial concentration of the hydrolysis catalyst is heated to 60 ° C. or higher, and the silicon alkoxide is gradually added to the reaction medium with stirring to advance the hydrolysis reaction.
加水分解反応は、減圧、常圧、加圧のいずれの圧力下でも行うことができるが、反応温度は、特に珪酸の脱水縮合に影響を与える。反応温度が６０℃より低いと、活性珪酸の脱水縮合が不十分となり残存シラノール基が増加する。粒子内のシラノール基の残存を減少させるために、反応温度は６０℃以上が好ましく、６５℃以上がより好ましい。ただし、反応温度は、反応媒体の沸点未満の値である。 The hydrolysis reaction can be performed under any pressure of reduced pressure, normal pressure, or increased pressure, but the reaction temperature particularly affects dehydration condensation of silicic acid. When the reaction temperature is lower than 60 ° C., the dehydration condensation of the active silicic acid becomes insufficient and the residual silanol groups increase. In order to reduce the residual silanol groups in the particles, the reaction temperature is preferably 60 ° C. or higher, more preferably 65 ° C. or higher. However, the reaction temperature is a value less than the boiling point of the reaction medium.
反応媒体を攪拌することで、反応媒体中での珪素アルコキシドの加水分解が進行すると共に、その結果生成した珪酸が、重合によりシリカ粒子に一様に沈着する。不溶状態で存在していたアルキルシリケートも、攪拌によって反応媒体中に懸濁状態で維持される。その結果、反応媒体との接触による加水分解や反応媒体への溶解が円滑に進行する。 By stirring the reaction medium, the hydrolysis of the silicon alkoxide in the reaction medium proceeds, and the resulting silicic acid is uniformly deposited on the silica particles by polymerization. The alkyl silicate that was present in the insoluble state is also maintained in suspension in the reaction medium by stirring. As a result, hydrolysis due to contact with the reaction medium and dissolution in the reaction medium proceed smoothly.
珪素アルコキシドの供給は容器上方から液面に滴下してもよいが、その供給口を反応媒体に接触させ、液中に供給してもよい。これによれば、供給口近傍での加水分解によるゲルの発生や粗大粒子の発生を抑制することができる。特に、加水分解速度の速いテトラメチルシリケートについては液中への添加が好ましい。 Silicon alkoxide may be supplied to the liquid surface from above the container, but the supply port may be brought into contact with the reaction medium and supplied into the liquid. According to this, generation | occurrence | production of the gel by the hydrolysis in the vicinity of a supply port and generation | occurrence | production of a coarse particle can be suppressed. In particular, tetramethyl silicate having a high hydrolysis rate is preferably added to the liquid.
反応の進行とともに、反応媒体の水濃度やモル比（加水分解触媒／珪素）が変化するが、反応の終了まで、８０モル％以上の水濃度と、０．１５以上のモル比（加水分解触媒／珪素）とが維持される。アルコールを蒸留により除去する際には、珪素アルコキシドの添加を中断し、珪素アルコキシドの加水分解によって生じるアルコールを反応媒体から除去すると共に、反応媒体の加水分解触媒の濃度を調整した後、珪素アルコキシドの添加を再開することが好ましい。これにより、アルコールを除去する際に同時に除去される加水分解触媒を適宜補いながらモル比（加水分解触媒／珪素）を調節し、シリカゾルを好適に製造することができる。 As the reaction proceeds, the water concentration and molar ratio of the reaction medium (hydrolysis catalyst / silicon) change, but until the end of the reaction, the water concentration of 80 mol% or more and the molar ratio of 0.15 or more (hydrolysis catalyst). / Silicon). When removing the alcohol by distillation, the addition of the silicon alkoxide is interrupted, the alcohol produced by the hydrolysis of the silicon alkoxide is removed from the reaction medium, and the concentration of the hydrolysis catalyst in the reaction medium is adjusted. It is preferred to resume the addition. Thus, the silica sol can be suitably produced by adjusting the molar ratio (hydrolysis catalyst / silicon) while appropriately supplementing the hydrolysis catalyst that is simultaneously removed when removing the alcohol.
粒子生成後の反応液には高濃度の加水分解触媒のため活性な珪酸が含まれており、濃縮後のゾルの安定性や、耐吸湿性に悪影響を与える。このため、活性珪酸の減少のために加水分解触媒の一部を除去もしくは酸で中和した後に７０℃以上の加温熟成を行うことができる。 The reaction solution after particle formation contains active silicic acid due to a high concentration of hydrolysis catalyst, which adversely affects the stability of the sol after concentration and the moisture absorption resistance. For this reason, in order to reduce the active silicic acid, a part of the hydrolysis catalyst is removed or neutralized with an acid, and then the heating and aging at 70 ° C. or more can be performed.
アンモニアの除去方法としては蒸留法、イオン交換法、限外ろ過法等が挙げられる。酸による中和は無機酸、有機酸を添加する。加水分解触媒の除去、中和後の好ましいｐＨは７〜１０．８である。酸の添加は多量であると、反応媒体の電解質濃度が高くなり、かえってシリカゾルの安定性を疎外する場合があるため、加水分解触媒を除去する方法がより好ましい。もっとも簡便で好ましい方法は、加熱蒸留により加水分解触媒の除去と熟成を同時に行う方法である。 Examples of the ammonia removal method include a distillation method, an ion exchange method, and an ultrafiltration method. Neutralization with an acid adds an inorganic acid or an organic acid. The preferable pH after removal and neutralization of the hydrolysis catalyst is 7 to 10.8. If the acid is added in a large amount, the electrolyte concentration of the reaction medium becomes high, and the stability of the silica sol may be excluded, so the method of removing the hydrolysis catalyst is more preferable. The simplest and preferred method is a method in which the hydrolysis catalyst is removed and aged at the same time by heating distillation.
以下、実施例に基づいてさらに詳述するが、本発明はこの実施例により何ら限定されるものではない。 Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the examples.
〔実施例１〕
実施例１のシリカゾルを以下のように作製した。攪拌機及びコンデンサー付き３リットルのステンレス製反応容器に、純水２２２０ｇと２８質量％のアンモニア水２６．９ｇを仕込み、アンモニアの初期濃度を、反応媒体１リットル当たり０．２０モルとした。そして、オイルバスにより容器内液温を８０℃に保った。次いで、攪拌下のこの容器内に、２５３ｇの市販テトラメチルシリケート（ＴＭＯＳ）を、３時間かけて液中に連続的に供給した。珪素の総添加量に対するアンモニアのモル比（アンモニア／珪素）は０．２７であった。
[Example 1]
The silica sol of Example 1 was prepared as follows. A 3 liter stainless steel reaction vessel equipped with a stirrer and a condenser was charged with 2220 g of pure water and 26.9 g of 28 mass% ammonia water, and the initial concentration of ammonia was 0.20 mol per liter of reaction medium. And the liquid temperature in a container was kept at 80 degreeC with the oil bath. Next, 253 g of commercially available tetramethyl silicate (TMOS) was continuously fed into the liquid over 3 hours in this vessel under stirring. The molar ratio of ammonia to the total amount of silicon added (ammonia / silicon) was 0.27.
この供給の終了後、容器内液温を８０℃で１時間保った後、９０℃まで上昇させ、この温度で１時間攪拌を続けた。次いで、容器につけたコンデンサーを枝付き管につけ替え、枝付き管の先に冷却管をつけてから反応液の温度を沸点まで上昇させ、容器内の液を蒸発させ、蒸気を器外に排出させることにより、液温が９９℃になるまで濃縮した。次いで、容器内の液全量を器外に取り出し、これをロータリーエバポレーターにより１００Ｔｏｒｒの減圧下に３３０ｇまで濃縮したところ、ＳｉＯ2３０．４質量％、ｐＨ６．７、Ｂ型粘度計で２５℃において測定した粘度６．９ｍＰａ・ｓ、動的散乱法粒子径１７．７ｎｍを有するシリカゾル（実施例１）を得た。得られたゾルの透過型電子顕微鏡での観察結果では、球状の均一な粒子が観察された。 After the completion of the supply, the liquid temperature in the container was kept at 80 ° C. for 1 hour, then increased to 90 ° C., and stirring was continued at this temperature for 1 hour. Next, replace the condenser attached to the container with a branch pipe, attach a cooling pipe to the end of the branch pipe, raise the temperature of the reaction liquid to the boiling point, evaporate the liquid in the container, and discharge the steam to the outside. This was concentrated until the liquid temperature reached 99 ° C. Next, the entire amount of the liquid in the container was taken out of the vessel and concentrated to 330 g under a reduced pressure of 100 Torr using a rotary evaporator. SiO 2 30.4% by mass, pH 6.7, measured at 25 ° C. with a B-type viscometer A silica sol (Example 1) having a viscosity of 6.9 mPa · s and a dynamic scattering particle diameter of 17.7 nm was obtained. As a result of observation of the obtained sol with a transmission electron microscope, spherical uniform particles were observed.
〔実施例２〕
実施例１と同じ反応容器に、純水２２１４ｇと２８質量％のアンモニア水２５．３ｇを仕込み、アンモニアの初期濃度を、反応媒体１リットル当たり０．１９モルとした。そして、オイルバスにより容器内液温を８０℃に保った。次いで、攪拌下のこの容器内に、２６０．５ｇの市販テトラエチルシリケート（ＴＥＯＳ）を、３時間かけて液中に連続的に供給した。珪素の総添加量に対するアンモニアのモル比（アンモニア／珪素）は０．３３であった。
[Example 2]
In the same reaction vessel as in Example 1, 2214 g of pure water and 25.3 g of 28 mass% ammonia water were charged, and the initial concentration of ammonia was 0.19 mol per liter of reaction medium. And the liquid temperature in a container was kept at 80 degreeC with the oil bath. Next, 260.5 g of commercially available tetraethyl silicate (TEOS) was continuously fed into the liquid over 3 hours in this stirred vessel. The molar ratio of ammonia to the total amount of silicon added (ammonia / silicon) was 0.33.
この供給の終了後、容器内液温を８０℃で１時間保った後、９０℃まで上昇させ、この温度で１時間攪拌を続けた。次いで実施例１と同様に容器内の液を蒸発させ、蒸気を器外に排出させることにより、液温が９９℃になるまで濃縮した。次いで、容器内の液全量を器外に取り出し、これをロータリーエバポレーターにより１００Ｔｏｒｒの減圧下に３７５ｇまで濃縮したところ、ＳｉＯ2２０．０質量％、ｐＨ７．３、Ｂ型粘度計で２５℃において測定した粘度８．９ｍＰａ・ｓ、動的散乱法粒子径１８．６ｎｍを有するシリカゾル（実施例２）を得た。 After the completion of the supply, the liquid temperature in the container was kept at 80 ° C. for 1 hour, then increased to 90 ° C., and stirring was continued at this temperature for 1 hour. Next, the liquid in the container was evaporated in the same manner as in Example 1, and the liquid was concentrated to 99 ° C. by discharging the vapor outside the vessel. Next, the entire amount of the liquid in the container was taken out of the vessel and concentrated to 375 g under a reduced pressure of 100 Torr using a rotary evaporator. SiO 2 20.0 mass%, pH 7.3, measured at 25 ° C. with a B-type viscometer. A silica sol (Example 2) having a viscosity of 8.9 mPa · s and a dynamic scattering particle diameter of 18.6 nm was obtained.
〔比較例１〕
仕込みのアンモニアの初期濃度を表１のように変更した他は実施例１と同じ操作で比較例１のシリカゾルを製造した。得られたゾルの透過型電子顕微鏡での観察結果では、微小粒子が発生していた。
[Comparative Example 1]
A silica sol of Comparative Example 1 was produced in the same manner as in Example 1 except that the initial ammonia concentration was changed as shown in Table 1. As a result of observation of the obtained sol with a transmission electron microscope, fine particles were generated.
〔比較例２〕
仕込みのアンモニアの初期濃度を表１のように変更した他は実施例１と同じ操作を行ったが、テトラメチルシリケートの供給の途中でチャージ管の先端が目詰まりして供給が行えなくなったため、テトラメチルシリケートを１０４ｇ添加した時点で供給を中止した。以後の加温操作は実施例１と同様に行った。得られたゾルの透過型電子顕微鏡での観察結果では、形状が歪な粒子が多く、また微小粒子も多く認められた。
[Comparative Example 2]
The same operation as in Example 1 was performed except that the initial ammonia concentration was changed as shown in Table 1, but the tip of the charge tube was clogged during the supply of tetramethyl silicate, so that the supply could not be performed. The supply was stopped when 104 g of tetramethyl silicate was added. The subsequent heating operation was performed in the same manner as in Example 1. As a result of observing the obtained sol with a transmission electron microscope, many particles having a distorted shape and many fine particles were observed.
〔比較例３〕
仕込みのアンモニアの初期濃度を表１のように変更した他は実施例２と同じ操作で比較例３のシリカゾルを製造した。
[Comparative Example 3]
A silica sol of Comparative Example 3 was produced in the same manner as in Example 2 except that the initial ammonia concentration was changed as shown in Table 1.
〔比較例４〕
先行技術文献として掲げた特許文献１に記載の方法で、比較例４のシリカゾルを作製した。すなわち、攪拌機及びコンデンサー付き１リットルの反応容器に水７２．６ｇと、メタノール１８７．１ｇと、２８質量％のアンモニア水１９．３ｇとを仕込み、攪拌しながら容器内液温を４０℃に保った。次いで、攪拌下のこの容器内に、３０．４ｇの市販テトラメチルシリケート（ＴＭＯＳ）を、４７．５ｇのメタノールに溶解した溶液を３０分かけて連続的に供給した。珪素の総添加量に対する加水分解触媒のモル比（加水分解触媒／珪素）は、１．５９となった。この供給の終了後、さらに４０℃で２０分間エージングを行った。
[Comparative Example 4]
A silica sol of Comparative Example 4 was produced by the method described in Patent Document 1 listed as the prior art document. That is, 72.6 g of water, 187.1 g of methanol, and 19.3 g of 28% by mass of ammonia water were charged in a 1 liter reaction vessel equipped with a stirrer and a condenser, and the liquid temperature in the vessel was kept at 40 ° C. while stirring. . Next, a solution prepared by dissolving 30.4 g of commercially available tetramethyl silicate (TMOS) in 47.5 g of methanol was continuously fed into this vessel under stirring over 30 minutes. The molar ratio of the hydrolysis catalyst to the total amount of silicon added (hydrolysis catalyst / silicon) was 1.59. After completion of this supply, aging was further performed at 40 ° C. for 20 minutes.
反応液をロータリーエバポレーターを用い１００Ｔｏｒｒの減圧下で７３ｇとなるまで濃縮したところ、ＳｉＯ2１５．８質量％、ｐＨ９．０、動的散乱法粒子径３２．９ｎｍを有するシリカゾル（比較例４）を得た。得られたゾルの透過型電子顕微鏡での観察結果では、形状が歪であり、融着した粒子が多く観察された。 When the reaction solution was concentrated to 73 g under a reduced pressure of 100 Torr using a rotary evaporator, a silica sol having a SiO 2 of 15.8 mass%, a pH of 9.0, and a dynamic scattering method particle diameter of 32.9 nm (Comparative Example 4) was obtained. Obtained. According to the observation result of the obtained sol with a transmission electron microscope, the shape was distorted, and many fused particles were observed.
〔比表面積および平均粒子径〕
実施例１〜２及び比較例１〜４のシリカゾルにつき、以下のように窒素吸着法（ＢＥＴ法）により平均粒子径を測定した。すなわち、シリカゾルを８０℃真空乾燥器で乾燥して得られたシリカゲルを乳鉢で粉砕した後、さらに１８０℃で３時間乾燥してシリカ乾燥粉末を得た。この粉末の窒素吸着法による比表面積(ｍ2／ｇ)を測定し、平均粒子径は以下の式（１）で求めた。尚、測定結果は表１に示す。
[Specific surface area and average particle size]
About the silica sol of Examples 1-2 and Comparative Examples 1-4, the average particle diameter was measured by the nitrogen adsorption method (BET method) as follows. That is, the silica gel obtained by drying the silica sol in an 80 ° C. vacuum dryer was pulverized in a mortar and further dried at 180 ° C. for 3 hours to obtain a silica dry powder. The specific surface area (m 2 / g) of this powder by the nitrogen adsorption method was measured, and the average particle size was determined by the following formula (1). The measurement results are shown in Table 1.
［式１］
平均粒子径（ｎｍ）＝２７２０／比表面積(ｍ2／ｇ) （１）
[Formula 1]
Average particle diameter (nm) = 2720 / specific surface area (m 2 / g) (1)
〔個数平均粒子径及び粒度分布〕
実施例１〜２及び比較例１〜４のシリカゾルにつき、以下のように個数平均粒子径及び粒度分布を測定した。すなわち、シリカゾルを水で希釈してカーボンメッシュ上にサンプリングし、透過型電子顕微鏡で粒子画像を撮影した。撮影した画像を画像解析装置により解析し、等価円直径の個数平均粒子径とこの粒子径の標準偏差を求めた。粒度分布の指標として、以下の式（２）よりＣｖ値を求めた。尚、測定結果は表１に示す。
[Number average particle size and particle size distribution]
For the silica sols of Examples 1-2 and Comparative Examples 1-4, the number average particle size and particle size distribution were measured as follows. That is, silica sol was diluted with water, sampled on a carbon mesh, and a particle image was taken with a transmission electron microscope. The photographed image was analyzed by an image analyzer, and the number average particle diameter of the equivalent circular diameter and the standard deviation of the particle diameter were obtained. As an index of the particle size distribution, the Cv value was obtained from the following formula (2). The measurement results are shown in Table 1.
［式２］
Ｃｖ（％）＝標準偏差／平均粒子径 （２）
[Formula 2]
Cv (%) = standard deviation / average particle diameter (2)
〔吸湿性〕
実施例１〜２及び比較例１〜４のシリカゾルにつき、以下のように吸湿性を測定した。すなわち、比表面積の測定に用いたものと同じ１８０℃乾燥粉を各０．２ｇ秤量瓶に採取し、重量を測定した。この瓶を蓋を開けた状態で２３℃相対湿度５０％の雰囲気下に４８時間静置した後、蓋をして再び重量を測定した。そして、以下の式（３）より吸湿率を求めた。またＢＥＴ法比表面積を基に、以下の式（４）より、比表面積あたりの吸湿量を計算した。尚、測定結果は表１に示す。
[Hygroscopicity]
The hygroscopicity of the silica sols of Examples 1-2 and Comparative Examples 1-4 was measured as follows. That is, the same 180 g dry powder as that used for measurement of the specific surface area was collected in 0.2 g weighing bottles, and the weight was measured. The bottle was allowed to stand for 48 hours in an atmosphere of 23 ° C. and 50% relative humidity with the lid open, and then the lid was capped and the weight was measured again. And the moisture absorption was calculated | required from the following formula | equation (3). Moreover, the moisture absorption per specific surface area was calculated from the following formula (4) based on the BET specific surface area. The measurement results are shown in Table 1.
［式３］
吸湿率（％）＝増加重量／サンプル採取量×１００ （３）
[Formula 3]
Moisture absorption rate (%) = weight increase / sample collection amount × 100 (3)
［式４］
吸湿量(ｍｇ／ｍ2)＝増加重量(ｍｇ)／(サンプル量(ｇ)×比表面積(ｍ2／ｇ)) (４)
[Formula 4]
Moisture absorption (mg / m 2 ) = weight increase (mg) / (sample amount (g) × specific surface area (m 2 / g)) (4)
珪素アルコキシドとしてテトラメチルシリケートを用いた実施例１及び比較例１〜２の結果から、比較例１〜２の吸湿量は０．３０〜０．３５ｍｇ／ｍ2、吸湿率は６．０〜８．１％であったのに対し、実施例１では、吸湿量は０．２５ｍｇ／ｍ2、吸湿率は４．４％であった。尚、上記の比較例１〜２の吸湿量及び吸湿率は、先行技術文献である特許文献１に記載の比較例４よりも優れたものであると言えるが、かかる比較例１〜２に対しても、実施例１では、吸湿量及び吸湿率が少なく、耐吸湿性の向上が確認された。 From the results of Example 1 and Comparative Examples 1 and 2 using tetramethyl silicate as the silicon alkoxide, the moisture absorption of Comparative Examples 1 and 2 is 0.30 to 0.35 mg / m 2 , and the moisture absorption is 6.0 to 8 In Example 1, the moisture absorption amount was 0.25 mg / m 2 and the moisture absorption rate was 4.4%. In addition, although it can be said that the moisture absorption amount and moisture absorption rate of said Comparative Examples 1-2 are superior to the comparative example 4 of patent document 1 which is a prior art document, with respect to this comparative example 1-2. However, in Example 1, there was little moisture absorption and a moisture absorption rate, and the improvement of moisture absorption resistance was confirmed.
さらに、比較例１〜２の粒度分布（Ｃｖ）は２２〜３１％であったのに対し、実施例１の粒度分布は１２％であった。よって、実施例１は、比較例１〜２に対し、耐吸湿性に優れる上、粒度分布のばらつきが少ないことが分かった。 Furthermore, the particle size distribution (Cv) of Comparative Examples 1 and 2 was 22 to 31%, whereas the particle size distribution of Example 1 was 12%. Therefore, it was found that Example 1 was superior to Comparative Examples 1 and 2 in terms of moisture resistance and had less variation in particle size distribution.
また、珪素アルコキシドとしてテトラエチルシリケートを用いた実施例２及び比較例３の結果から、比較例３の吸湿量は０．３２ｍｇ／ｍ2、吸湿率は５．８％であったのに対し、実施例２では、吸湿量は０．２１ｍｇ／ｍ2、吸湿率は３．４％であった。すなわち、実施例２では、比較例３に対し、吸湿量及び吸湿率が少なく、耐吸湿性の向上が確認された。 Further, from the results of Example 2 and Comparative Example 3 using tetraethyl silicate as the silicon alkoxide, the moisture absorption of Comparative Example 3 was 0.32 mg / m 2 and the moisture absorption was 5.8%. In Example 2, the moisture absorption was 0.21 mg / m 2 , and the moisture absorption was 3.4%. That is, in Example 2, the moisture absorption amount and the moisture absorption rate were smaller than those in Comparative Example 3, and improvement in moisture absorption resistance was confirmed.
次に、以下の方法により、実施例３のシリカゾルを作製した。
〔製造例１（核粒子の合成）〕
実施例１と同じ反応容器に純水２２４４ｇと２８質量％のアンモア水３．４ｇを仕込み、オイルバスにより容器内液温を８０℃に保った。次いで、攪拌下のこの容器内に、２５３ｇの市販テトラメチルシリケートを、１時間かけて液中に連続的に供給した。この供給の終了後、容器内液温を８０℃で１時間保った後、９０℃まで上昇させ、この温度で１時間攪拌を続けた。次いで、容器内の液を蒸発させ、蒸気を器外に排出させることにより、液温が９９℃になるまで濃縮したところ、ＳｉＯ2４．４質量％、ＢＥＴ法平均粒子径９．７ｎｍの球状のシリカゾルが得られた。
Next, the silica sol of Example 3 was produced by the following method.
[Production Example 1 (synthesis of core particles)]
In the same reaction vessel as in Example 1, 2244 g of pure water and 3.4 g of 28% by mass ammo water were charged, and the liquid temperature in the vessel was kept at 80 ° C. by an oil bath. Then, 253 g of commercially available tetramethyl silicate was continuously supplied into the liquid over 1 hour in this container under stirring. After the completion of the supply, the liquid temperature in the container was kept at 80 ° C. for 1 hour, then increased to 90 ° C., and stirring was continued at this temperature for 1 hour. Next, the liquid in the container was evaporated and the vapor was discharged out of the vessel to concentrate it until the liquid temperature reached 99 ° C. As a result, it was 4.4% by mass of SiO 2 and a spherical shape having a BET method average particle diameter of 9.7 nm. A silica sol was obtained.
〔実施例３〕
反応容器に、予め核となるシリカ粒子を添加した以外は、基本的には実施例１と同様の仕込み組成となるよう反応液を準備した。すなわち、製造例１のシリカゾル３２５ｇと純水１９０９ｇと２８質量％のアンモア水２６．９ｇを仕込み、アンモニアの初期濃度を、反応媒体１リットル当たり０．２０モルとした。そして、オイルバスにより容器内液温を８０℃に保った。次いで、攪拌下のこの容器内に、２５３ｇの市販テトラメチルシリケートを、５時間かけて液中に連続的に供給した。珪素の総添加量に対するアンモニアのモル比（アンモニア／珪素）は０．２７であった。
Example 3
A reaction solution was prepared so as to basically have the same charged composition as in Example 1 except that silica particles serving as nuclei were previously added to the reaction vessel. That is, 325 g of silica sol of Production Example 1, 1909 g of pure water, and 26.9 g of 28 mass% ammonia water were charged, and the initial concentration of ammonia was 0.20 mol per liter of reaction medium. And the liquid temperature in a container was kept at 80 degreeC with the oil bath. Then, 253 g of commercially available tetramethyl silicate was continuously supplied into the liquid over 5 hours in this vessel under stirring. The molar ratio of ammonia to the total amount of silicon added (ammonia / silicon) was 0.27.
この供給の終了後、容器内液温を８０℃で１時間保った後、９０℃まで上昇させ、この温度で１時間攪拌を続けた。次いで、容器内の液を蒸発させ、蒸気を器外に排出させることにより、液温が９９℃になるまで濃縮した。次いで、容器内の液全量を器外に取り出し、これをロータリーエバポレーターにより１００Ｔｏｒｒの減圧下に４４７ｇまで濃縮したところ、ＳｉＯ2２５．５質量％、ｐＨ６．８、Ｂ型粘度計で２５℃において測定した粘度１１．２ｍＰａ・ｓ、動的散乱法粒子径１９．５．ｎｍを有するシリカゾル（実施例３）を得た。 After the completion of the supply, the liquid temperature in the container was kept at 80 ° C. for 1 hour, then increased to 90 ° C., and stirring was continued at this temperature for 1 hour. Next, the liquid in the container was evaporated, and the vapor was discharged outside the container to concentrate the liquid temperature to 99 ° C. Next, the entire amount of the liquid in the container was taken out of the vessel, and concentrated to 447 g under a reduced pressure of 100 Torr using a rotary evaporator. SiO 2 25.5% by mass, pH 6.8, measured at 25 ° C. with a B-type viscometer Viscosity 11.2 mPa · s, dynamic scattering particle diameter 19.5. A silica sol having a nm (Example 3) was obtained.
実施例３のシリカゾルは、上記と同様の方法により測定すると、ＢＥＴ法平均粒子径１７．０ｎｍ、比表面積あたりの吸湿量は０．２４ｍｇ／ｍ2、吸湿率は３．９％であった。かかる吸湿量及び吸湿率は、珪素アルコキシドとしてテトラメチルシリケートを用いた比較例１〜２や、先行技術文献である特許文献１に記載の比較例４よりも優れたものである。よって、実施例３の結果から、本発明とは異なる方法により得た核粒子（製造例１）を用いたとしても、それを本発明の条件下で粒子成長させることにより製造したシリカゾルは、比較例に比べ、乾燥後の吸湿量及び吸湿率が少なく、耐吸湿性に優れたものとなることが分かった。 When the silica sol of Example 3 was measured by the same method as described above, the BET method average particle size was 17.0 nm, the moisture absorption per specific surface area was 0.24 mg / m 2 , and the moisture absorption was 3.9%. Such moisture absorption and moisture absorption are superior to those of Comparative Examples 1 and 2 using tetramethyl silicate as silicon alkoxide and Comparative Example 4 described in Patent Document 1 which is a prior art document. Therefore, from the results of Example 3, even if the core particles (Production Example 1) obtained by a method different from the present invention were used, the silica sol produced by growing the particles under the conditions of the present invention was compared. It was found that the moisture absorption amount and moisture absorption rate after drying were small compared to the examples, and the moisture absorption resistance was excellent.
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| WO2019098257A1 (en) * | 2017-11-16 | 2019-05-23 | 日揮触媒化成株式会社 | Dispersion of silica particles and method for producing said dispersion |
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