JP5093765B2 - Ceramic raw material particles, slurry, sintered body and method for producing the same - Google Patents

Description

  The present invention relates to ceramic raw material particles and slurry / molded body / sintered body / inorganic / organic composite material comprising the ceramic raw material particles. Specifically, it has a structure in which a dispersing agent composed of an organic atomic group is directly chemically bonded to the surface, and is manufactured using ceramic raw material particles that can be dispersed uniformly and at a high concentration in a solvent, and the ceramic raw material particles. The present invention relates to a slurry, a molded body, a sintered body, and an inorganic / organic composite material.

  Ceramics are used in various applications such as structural materials, electrical / electronic materials, etc., because they are superior in mechanical / thermal / electromagnetic properties compared to metals and plastics. In the manufacturing process, the raw material particles are generally formed into a desired shape, and the formed body is heated to be densified (sintered).

  As a method for producing such a molded body, for example, an aggregate particle (ceramic powder or the like), a dispersion medium (water or the like), an organic binder, or the like is mixed to obtain a slurry, and the slurry is made of a porous material. A manufacturing method is disclosed in which a ceramic sintered body is obtained by pouring into a mold, drying the slurry, and then firing (casting molding method: see, for example, Non-Patent Document 1).

  Also, aggregate particles (ceramic powder, etc.), dispersion medium (water, etc.), gelling agent (monomer, prepolymer, etc.), etc. are mixed to obtain a slurry. A manufacturing method is disclosed in which a gelling agent is gelled by addition of an initiator or the like to solidify a slurry and then degreased to obtain an inorganic material molded body (gel casting method: see, for example, Patent Document 1). .

  In addition, after mixing aggregate particles (ceramics powder, etc.) with resin, etc. and imparting fluidity by heating and melting, injection molding into a mold at high pressure, cooling to solidify, and then degreasing to make inorganic material A method for obtaining a molded body is disclosed (injection molding method: see, for example, Non-Patent Document 1).

  The cast molding method does not require the use of a large amount of organic solvent or resin, so it has a low environmental impact and has few dangers such as fire, and is currently widely used. By the way, in the slurry of ceramic particles used in this method, it has been found that the use of fine particles can be expected to improve the function, lower the firing temperature, and form a near net shape. However, when preparing an aqueous / non-aqueous ceramic slurry in which such ceramic particles are dispersed, there is a drawback in that the viscosity rapidly increases and is not suitable for practical use, and thus it has been necessary to solve this problem.

JP 2002-179468 A Edited by the Ceramic Society of Japan, Ceramics Engineering Handbook, 2nd edition, Gihodo Publishing, 2002, p. 176-178

  In view of such circumstances, the present invention provides a ceramic slurry that has excellent dispersion stability and suppresses undesirable phenomena such as an increase in viscosity in a slurry containing fine ceramic particles having an average particle diameter of less than 1 μm. It was made for the purpose of doing.

  As a result of investigating the cause of the viscosity increase of the slurry containing fine ceramic particles, the present inventors fixed the organic molecules used as the dispersant on the surface of the ceramic particles, so that the particles between the particles due to the dispersant remaining in the solvent. The present inventors have found that the crosslinking can be completely prevented, the dispersibility of the particles can be improved, and the increase in viscosity can be suppressed, and the present invention has been completed based on this finding. Specifically, the present invention provides a slurry comprising the following ceramic raw material particles and a method for producing the same, and a method for producing a ceramic sintered body and an inorganic / organic composite material using the slurry.

[1] A silane coupling agent having an amino group (—NH ₂ ) is chemically bonded to the surface of silica particles having an average particle diameter of less than 1 μm, and oxyethylene (—C ₂ H ₄ O is further bonded to the amino group. -) Ceramic raw material particles having a hydrophilic oxyethylene structure chemically bonded to the surface by chemically bonding organic molecules having a structure.

[2] ceramic slurry of ceramic raw material particles according dispersed in an aqueous solvent before SL [1].

[ 3 ] Applying a wet forming method to the ceramic slurry according to [ 2 ] to obtain a ceramic formed body having a desired shape,
A method for producing a ceramic sintered body, wherein the ceramic molded body is fired to obtain a ceramic sintered body.

[ 4 ] An inorganic / organic composite material in which the ceramic raw material particles according to [ 1 ] are dispersed in an organic polymer.

  The method for producing a ceramic slurry according to the present invention has an advantageous effect compared to the conventional production method that can suppress an increase in viscosity due to the refinement of ceramic particles and can be used for firing a high-density molded body. It is.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the inorganic material molded body and the method for producing the same of the present invention will be specifically described below. However, the present invention is a ceramic slurry, an inorganic material molded body, an inorganic material sintered body based on the idea that an organic atomic group serving as a dispersant is chemically bonded directly to the surface of inorganic material particles and then dispersed in a solvent. In addition, the present invention broadly encompasses inorganic / organic composite materials and methods for producing the same, and should not be interpreted as being limited to the embodiments described below.

  One aspect of the present invention is a ceramic raw material particle comprising inorganic material particles and a dispersant composed of an organic atomic group as constituent elements, and having a structure in which the dispersant is directly chemically bonded to the surface of the inorganic material particles. Is a method for obtaining an inorganic material molded body, an inorganic material sintered body, and an inorganic / organic composite material.

[1] First Step The first step of the production method of the present invention is a step for obtaining ceramic raw material particles by directly chemically bonding a dispersant composed of an organic atomic group to the surface of the inorganic material particles.

  The inorganic material particles are particles that are the main constituent components of the molded body, and when the inorganic material molded body is manufactured, inorganic material particles made of an inorganic material are used. And in the manufacturing method of this invention, it is necessary to use the inorganic material particle by which the organic atom group with high affinity with the solvent which disperse | distributes inorganic material particle was chemically bonded on the surface. “Organic atomic group” means an atomic group containing a carbon atom as a constituent atom, and the other structure is not particularly limited.

As a dispersant composed of an organic atomic group, when used for dispersion in an aqueous solvent, a nonionic hydrophilic structure such as oxyethylene (—C ₂ H ₄ O—) or a hydroxyl group (—OH), a carboxyl group (—COOH) , Anionic hydrophilic structures such as sulfonyl group (—SO ₃ H), hydrogen sulfate group (—OSO ₃ OH), phosphate group (—PO ₄ H ₂ ), and their salts, amino groups (—NH ₂ ), Examples include those containing at least one structure selected from the group consisting of a cationic hydrophilic structure such as a quaternary ammonium group (N ^+. (CH ₃ ) ₃ .Cl ⁻ ) and each salt.

  Examples of the dispersant composed of an organic atomic group include those having a lipophilic structure containing a hydrocarbon chain when used for dispersion in a non-aqueous solvent.

  As the “inorganic material particles”, those made of an inorganic material having a binding site (such as a hydroxyl group) capable of forming a covalent bond with a dispersant made of an organic atomic group are preferably used. Particles made of ceramics can be suitably used. Also, particles made of non-oxide ceramics or metals can be used as “inorganic material particles” because oxide ceramics are inevitably formed on the surface by air oxidation (surface oxide film). That is, in the production method of the present invention, it is preferable to use inorganic material particles made of at least one inorganic material selected from the group of oxide ceramics, non-oxide ceramics, and metals.

  Examples of the oxide ceramic include metal oxides such as barrier, ceria, zinc oxide, germanium oxide, indium oxide, tin oxide, and antimony oxide, in addition to general-purpose ceramics such as silica, alumina, zirconia, and titania. These oxide ceramics have a surface hydroxyl group as a binding site, and are preferable in that chemical bonding of a dispersant composed of an organic atomic group is easy. Examples of non-oxide ceramics include silicon carbide and silicon nitride. Examples of metals include silicon, aluminum, zirconium, titanium, barium, cerium, zinc, germanium, indium, tin, and antimony.

  The average particle diameter of the inorganic material particles is preferably in the range of 1 nm to 1 μm, and more preferably in the range of 10 to 500 nm. If it is less than the above range, the specific surface area of the inorganic material particles becomes excessive, and the proportion of the dispersing agent per unit mass of the inorganic material particles may become too large, which is not preferable. On the other hand, when the above range is exceeded, the diameter of the ceramic particles becomes coarse, and it becomes impossible to provide a slurry containing fine ceramic particles, which is an object of the present invention.

  There is no particular limitation on the method of chemically bonding the dispersant composed of an organic atomic group to the surface of the inorganic material particle, and a conventionally known chemical modification method can be used. For example, a method of fixing organic molecules by a coupling agent, a method of fixing organic molecules by an autoclave method, a method using surface modification by corona discharge, a method using surface modification by ozone, a reaction in supercritical water And the like. Among them, it is preferable to use a method of fixing organic molecules with a coupling agent because it is possible to easily form a strong bond.

  As the coupling agent, for example, a silane coupling agent, a titanate coupling agent, an aluminum coupling agent, a chromium coupling agent, or the like can be used.

  Examples of the chemical bonding method using a silane coupling agent include the following methods.

  First, a silanol residue acts on the inorganic material particles by causing a silane coupling agent to act on the inorganic material particles and causing a condensation reaction between the inorganic material particles and the silane coupling agent. Silanol-bonded inorganic material particles having a structure bonded by covalent bonds are obtained.

For example, as shown in the following general formula (1), a silane coupling agent (II) is allowed to act on the inorganic material particles (I), and the surface hydroxyl groups (OH) of the inorganic material particles (I) and the silane system By causing a condensation reaction with the hydrolyzable functional groups (Hy ₁ , Hy ₂ , Hy ₃ ) of the coupling agent (II), silanol residues are bonded to the inorganic material particles by covalent bonds. Silanol-bound inorganic material particles (III) having the above structure are obtained.
(However, Hy ₁ , Hy ₂ , Hy ₃ : Hydrolyzable functional group, A: Organic atomic group, Re ₁ : Reactive functional group, Pi: Inorganic material particles)

Examples of the hydrolyzable functional group (Hy ₁ , Hy ₂ , Hy ₃ ) include an alkoxy group (RO—: R is an alkyl group). Each functional group may be the same functional group or a different functional group. In the case of an alkoxy group, it is hydrolyzed by the presence of water to produce a silanol group (—SiO—), and the silanol group is adsorbed on the surface hydroxyl group of the inorganic material particles by a hydrogen bond. By heating this at a high temperature, the silanol group and the surface hydroxyl group undergo dehydration condensation, and the silanol residue is bonded to the inorganic material particles by a covalent bond.

Next, an organic compound having a high affinity with the solvent is allowed to act on the reactive functional group Re ₁ on the surface of the silanol-bonded inorganic material particle to cause a bond formation reaction between the silanol-bonded inorganic material particle and the organic compound. By doing so, inorganic material particles in which the dispersant is chemically bonded to the surface are obtained. Alternatively, the organic atomic group A and the reactive functional group Re ₁ may be organic atomic groups having high affinity with the solvent.

[2] Second Step The second step of the production method of the present invention is a step of dispersing ceramic raw material particles in a solvent to obtain a ceramic slurry, and using this to form a formed body.

  The method for dispersing the ceramic raw material particles in the solvent is not particularly limited, and can be arbitrarily selected from conventionally known dispersion methods as long as the performance of the dispersant of the present invention is not impaired. For example, a method using an ultrasonic bath, a method using a homogenizer, a method using stirring, a method using a ball mill, and the like can be suitably used.

  There is no restriction | limiting in particular about the shaping | molding method, What is necessary is just to select suitably from conventionally well-known shaping | molding methods. For example, a wet molding method in which aggregate particles are packed in a dense state, such as casting molding, centrifugal molding, extrusion molding, electrophoresis method, filtration method, magnetic field press, sheet molding, and tape molding, can be suitably used.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. However, since the following examples show only some embodiments of the present invention, the present invention should not be construed as being limited to these examples.

Example 1
Silica particles are used as the inorganic material particles, and a silane coupling agent having an amino group (—NH ₂ ) is chemically bonded to the surface of the silica particles, and oxyethylene (—C ₂ H ₄ O— is further bonded to the amino group. ) By chemically bonding organic molecules having a structure, silica particles having a hydrophilic oxyethylene structure chemically bonded to the surface were obtained.

First, as shown in the following formula (2), 3-aminopropyltriethoxysilane (II-a: NH ₂ C ₃ H ₆ Si (II-a), which is a silane coupling agent, is applied to the silica particles (Ia). OC ₂ H ₅ ) ₃ ) was allowed to act to obtain silanol-bonding silica particles (III-a) having an amino group on the surface.

  Specifically, 1.0 g of 3-aminopropyltriethoxysilane was dissolved in 100 ml of pure water to prepare an aqueous solution of a silane coupling agent, and an average particle diameter of 270 nm obtained by a sol-gel method was obtained in the aqueous solution. After dispersing 5.0 g of the silica particles and stirring for 1 hour, 3-aminopropyltriethoxysilane was adsorbed on the surface of the silica particles, and free 3-aminopropyltriethoxysilane was removed by centrifugal washing. Silanol-bonded silica particles having a structure in which silanol residues are covalently bonded to the silica particles by causing a condensation reaction between the silica particles and 3-aminopropyltriethoxysilane by heating and drying at ° C. Got.

Next, using an organic compound (water-soluble polycarbodiimide) (IV) having a molecular weight of about 2000 having a structure in which an oxyethylene structure and a carbodiimide group (—N═C═N—) are linked at a ratio of 10: 1, the following formula ( As shown in 3), the carbodiimide group in the structure was bonded to the amino group on the surface of the silanol-bonding silica particles.
(However, (IV) is a random copolymer of B block and -N = C = N-block, B: oxyethylene group)

Specifically, 2.5 g of the silanol-binding silica particles and 0.55 g of water-soluble polycarbodiimide are added to 25 ml of pure water, and the mixture is stirred for 2 hours while being heated to 55 ° C., and then the particles are washed with pure water. Unreacted water-soluble polycarbodiimide was removed and lyophilized to obtain oxyethylene-bonded silica particles. The silica particles before treatment, the silanol-bonding silica particles, and the oxyethylene-bonded silica particles were analyzed by infrared spectroscopy. As shown in the IR chart of FIG. 1, the silica particles and silanol bonds before treatment were analyzed. The absorption peak (2120 / cm ⁻¹ ) due to the carbodiimide group that is not observed in the porous silica particles was observed only in the oxyethylene-bonded silica particles, indicating that the water-soluble polycarbodiimide was fixed on the silica particle surface.

  An aqueous slurry in which the oxyethylene-bonded silica particles were dispersed was prepared. This ceramic slurry was subjected to a casting method to obtain a ceramic molded body.

  Specifically, 6.63 g of the oxyethylene-bonded silica particles were added to 7 ml of pure water and dispersed by an ultrasonic bath to obtain a high-concentration slurry in which the particles accounted for 30% by volume. The ceramic slurry was cast into a gypsum mold.

(Comparative Example 1)
A ceramic slurry and a ceramic molded body were obtained in the same manner as in Example 1 except that the same amount of untreated silica particles was used without using the oxyethylene-bonded silica particles.

(Evaluation)
The ceramic slurry made of oxyethylene-bonded silica particles produced in Example 1 and the ceramic slurry made of untreated silica particles produced in Comparative Example 1 were subjected to viscosity measurement using a rotational viscometer. When the pH of the ceramic slurry was measured in advance, the ceramic slurry of Example 1 was pH = 8.7, and the ceramic slurry of Comparative Example 1 was pH = 4.1, both of which were near the isoelectric point. . As shown in FIG. 2, it was shown that the ceramic slurry composed of the oxyethylene-bonded silica particles of Example 1 has a very low viscosity as compared with Comparative Example 1.

  Further, the ceramic slurry made of oxyethylene-bonded silica particles produced in Example 1 and the ceramic slurry made of untreated silica particles produced in Comparative Example 1 were subjected to casting. When the density of each molded body was measured by the Archimedes method, the density of the molded body of Example 1 was 58% by volume. In comparison, the density of the molded body of Comparative Example 1 was 53% by volume, and an effect was also observed in improving the density of the molded body.

  The method for producing an inorganic material molded body of the present invention includes various ceramic and metal molded bodies, ceramic sintered bodies, and inorganic / organic composite materials used in various applications such as structural materials and electrical / electronic materials. It is suitably used for production.

It is IR chart which shows the result of having analyzed the silica particle, the silanol bond silica particle, and the oxyethylene bond silica particle by infrared spectroscopy. It is a chart which shows the rotational viscometer measurement result of the ceramic slurry which contains 30 volume% of a silica particle and an oxyethylene bondable silica particle respectively.

Claims (4)

A silane coupling agent having an amino group (—NH ₂ ) is chemically bonded to the surface of silica particles having an average particle size of less than 1 μm , and the amino group has an oxyethylene (—C ₂ H ₄ O—) structure. Ceramic raw material particles having a hydrophilic oxyethylene structure chemically bonded to the surface by chemically bonding organic molecules having a surface. A ceramic slurry in which the ceramic raw material particles according to claim 1 are dispersed in an aqueous solvent. Applying a wet forming method to the ceramic slurry according to claim 2 to obtain a ceramic formed body having a desired shape,
A method for producing a ceramic sintered body, wherein the ceramic molded body is fired to obtain a ceramic sintered body.   An inorganic / organic composite material comprising the ceramic raw material particles according to claim 1 dispersed in an organic polymer.