JP2011064435A - Method of producing powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce an Fe content in obtained powder when material slurry comprising particulates dispersed in a solvent is dried by using a vacuum dryer. <P>SOLUTION: In this method, the material slurry in which the particulates are dispersed in the solvent is dried to produce powder by using the vacuum dryer in which one end of a heating tube heated externally and maintained in a decompressed state is connected to a supply part of the material slurry and the other end is connected to a powder collecting chamber maintained in the decompressed state. The heating tube comprises straight tubes and elbows which are alternately connected. At least the inner surface layer of the heating tube is formed of SUS 316, and the average particle diameter of the powder is 1 &mu;m or larger. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a method for producing a powder having no secondary aggregation by drying a slurry in which fine particles are dispersed in a solvent, and more particularly to a method for producing a powder having a low Fe content. is there.

  Vacuum drying apparatuses have been known for a long time. For example, Patent Document 1 discloses a vacuum concentration drying apparatus having a combined structure of a long tubular heater, a vacuum evaporation chamber, and a receiver. In this device, the liquid containing solids is heated while being transferred inside the long tubular heater, and is introduced into the vacuum evaporation chamber. The liquid is instantaneously vaporized by adiabatic expansion and separated from the solids. It is configured not to heat the minute.

  Similarly, Patent Document 2 discloses a pulverization drying method in which the ratio of the diameter and length of the long tubular heating tube is 1: 100 or more. Patent Document 3 describes a particle surface treatment method in which a surface treatment is performed simultaneously with particle drying using a similar apparatus.

  The present applicant has also proposed a method for producing fine particle powder using an apparatus similar to the above (Patent Document 4).

  On the other hand, in the display display field represented by liquid crystal display elements, inorganic fine particles and organic fine particles are applied to additives (light diffusing agents, antiblocking agents, etc.) used for adding to spacer materials and optical films. Therefore, a high-purity fine particle powder that does not contain foreign substances is required. In addition, in optical film additives such as spacers, light diffusion films and antiglare films, the required level for transparent fine particles without coloring or fine particles with high whiteness is increasing.

Japanese Patent Publication No.52-38272 Japanese Patent Publication No.55-38588 Japanese Patent Publication No. 58-35736 JP-A-3-288538

  The inventors of the present application have noticed that slight coloring is observed in the powder dried using the vacuum drying apparatus, and as a result of examining the cause of the coloring, the metal component mixed in the powder in the drying process, particularly iron (Fe ). In addition, the present inventors have also found that the problem of Fe contamination is likely to occur in inorganic fine particles having an average particle diameter of 1 μm or more and organic resin fine particles having a relatively high hardness. As liquid crystal display element members such as spacers and optical films, inorganic fine particles such as silica, organic cross-linked polymer particles, or organic-inorganic composite particles are used, particularly in the semiconductor field and liquid crystal display element members. However, it is necessary to reduce impurities to 10 ppm or less, and it is becoming impossible to apply a powder using a conventional vacuum drying apparatus.

  Therefore, in the present invention, based on the application to the industrial field where demands for purity and colorlessness are increasing, it has been set as an object to reduce the coloring of the powder and the Fe content in the powder that causes the powder.

  The inventors of the present invention have studied the configuration of a vacuum drying apparatus to solve the above-mentioned problems and succeeded in suppressing the mixing of Fe that causes coloring.

  The method for producing the powder of the present invention that has solved the above problem is a powder in which one end of a heating tube that is externally heated and held at a reduced pressure is connected to a raw material slurry supply unit, and the other end is held at a reduced pressure. A method for producing a powder by drying a raw slurry in which fine particles are dispersed in a solvent using a vacuum drying apparatus connected to a collection chamber, wherein the heating pipes are alternately connected to a straight pipe And at least the inner surface layer of the heating tube is made of SUS316, and the powder has an average particle diameter of 1 μm or more.

  In the production method of the present invention, a powder having a low Fe content can be produced even using a vacuum drying apparatus.

  In the method for producing a powder of the present invention, a vacuum drying apparatus in which one end of a heating tube to be externally heated is connected to a raw material slurry supply unit and the other end is connected to a powder collecting chamber held under reduced pressure. Use. The raw slurry is heated while it is transported through the heating tube held at a reduced pressure, and part or all of the solvent of the slurry is volatilized, and the powder is collected in a powder collecting chamber held at a reduced pressure. If the solvent remains, it is further dried.

  In the vacuum drying apparatus used in the present invention, the heating tube is composed of alternately connected straight tubes and elbows, and at least the inner surface layer of the heating tube is composed of SUS316. Since the heating tube is usually made of stainless steel, it is considered that this heating tube is an Fe source, but it was found that the heating tube using SUS316 can reduce the amount of Fe contamination compared to SUS304. In the present invention, at least the inner surface layer of the heating tube in contact with the powder is made of SUS316. Moreover, also in other members which comprise vacuum drying apparatuses, such as a powder collection chamber, it is preferable that the inner surface which powder contacts is made from SUS316.

  That at least the inner surface layer of the heating tube is made of SUS316 means that the entire heating tube is made of SUS316, only the inner surface layer of the heating tube is SUS316, and the other outer peripheral side is made of a different alloy other than SUS316. It is also meant to include heating tubes with a certain laminated connection structure. As the dissimilar alloy, SUS304 is preferable.

  The number of straight pipes constituting the heating pipe is preferably 2 to 10, more preferably 2 to 4. The number of elbows used is preferably n-1 when the number of straight pipes is n. If the heating tube is composed only of a straight tube, the external heating means for heating the heating tube must also be lengthened, but by connecting the straight tube and the elbow alternately to form a serpentine heating tube, a vacuum can be obtained. The drying device can be made compact. The end of the elbow may be extended in a straight tube shape.

  The ratio (length / inner diameter) of the length (mm) of the heating tube to the inner diameter (mm) of the heating tube is preferably suppressed to 1200 times or less. This is because if the length exceeds 1200 times the inner diameter of the heating tube, the Fe content of the powder tends to increase. The length / inner diameter is more preferably 400 times or less, further preferably 300 times or less, and particularly preferably 250 times or less. The lower limit of the length / inner diameter is not particularly limited, but is preferably 100 times or more from the viewpoint of heating efficiency. Specifically, for example, when using a heating tube with a diameter of 8 mm, it is preferable that the total length of the heating tube is 800 mm or more and 9600 mm or less. Note that the length of the inner wall on the outer peripheral side is adopted as the length of the elbow.

  Although the length of one straight pipe which comprises a heating pipe is not specifically limited, 400-1500 mm is preferable and 600-1200 mm is more preferable. If it is shorter than 400 mm, solvent evaporation in the heating tube becomes insufficient, and there is a possibility that the anti-aggregation effect, which is an advantage for drying in a stationary state (drying in the collection chamber), will be insufficient. On the other hand, when the length exceeds 1500 mm, when the aggregation of the fine particles proceeds in the straight pipe, the cohesion force between the particles is increased, so that the primary particles may not be crushed by the crushing force due to the collision at the elbow portion. is there.

  When the number of straight pipes constituting the heating tube is 10 or less and the number of elbows is 9 or less, the overall length of the heating tube is shortened, and the probability that the powder collides with the inner wall of the heating tube or the elbow part decreases. The Fe content of the powder can be further reduced, which is a preferred embodiment of the present invention. The heating tube is more preferably composed of three or less straight tubes and two or less elbows, and most preferably composed of two straight tubes and one elbow.

  The straight pipe and the elbow in the heating pipe are connected to the straight pipe and elbow with a flange with a threaded hole, and the flanges are fixed with bolts and nuts. , A method of fixing with a joint and a nut, a method of connecting and fixing a coupler type joint at the end of a straight pipe and an elbow, and the like.

  In the production method of the present invention, the raw slurry is supplied from the supply unit to the heating tube. The supply rate is preferably in the range of 1 to 50 L / hr, more preferably 10 to 30 L / hr. If the supply rate is less than 1 L / hr, the drying process is inefficient, and if it exceeds 50 L / hr, the impact when the particles collide with the inner wall of the heating tube increases. There is a risk that the effect of reducing the content is insufficient. The supply of the raw material slurry may be performed using a known means such as a pump.

  The heating tube is preferably heated to about 150 to 200 ° C. by an external heating means such as a jacket through which heating steam or a heat medium can pass. As the heating medium, superheated steam is preferred. In addition, what is necessary is just to change heating temperature suitably according to the boiling point of the solvent of raw material slurry.

  The pressure (degree of reduced pressure) inside the heating tube and inside the powder collection chamber is preferably about 6 kPa to 27 kPa (gauge pressure). By reducing the pressure, the solvent having a high boiling point at normal pressure also evaporates at a low temperature, so that drying proceeds efficiently. For example, it is preferable to incorporate a bag filter powder collecting means in the powder collecting chamber to separate the gas generated by evaporation of the solvent from the target powder. The temperature of the powder collection chamber is not particularly limited, but is preferably heated to about 150 to 200 ° C. by an external heating means in the same manner as in the case of the heating tube in order to remove the residual solvent.

  The fine particles in the slurry as the raw material of the powder are not particularly limited as long as the average particle diameter is 1 μm or more. In the present invention, it is assumed that primary particles (powder) in a dry state are obtained using a vacuum drying apparatus, so there is no substantial difference between the particle size of the fine particles in the slurry and the particle size of the powder. Here, the fine particles (powder) having an average particle diameter of 1 μm or more are limited to fine particles having an average particle diameter of less than 1 μm because the Fe content is very small as 5 ppm or less even when a heating tube made of SUS304 is used. It is. This is probably because fine particles (powder) with a small average particle diameter have a small energy when colliding with the inside of the heating tube, and therefore the amount of scraping off Fe is extremely small.

  As described above, considering that the contact between the particles (powder) and the heating tube is a factor of Fe contamination, the method for reducing the Fe content according to the present invention is effective for particles harder than soft particles. . Accordingly, inorganic particles such as metal oxides such as alumina, titania, zirconia, zinc oxide and cerium oxide; metal nitrides; metal sulfides; metal carbides; metal salts such as metal sulfates and metal carbonates; In terms of increasing the degree, white pigments such as titania, zinc oxide, silica, and barium sulfate are more preferable. Among them, metal oxide fine particles, particularly metal oxide fine particles obtained by hydrolytic condensation of metal alkoxide, particularly amorphous silica, have a small particle size distribution and a uniform particle size. Application is more preferable in that particles having excellent monodispersibility can be obtained.

  Organic crosslinked polymer particles and the like are also hard particles and are preferably used. Organic cross-linked polymer particles include, for example, vinyl cross-linked polymer particles obtained by copolymerizing a vinyl polyfunctional monomer with a monofunctional monomer (a vinyl polyfunctional monomer and a monofunctional monomer are also referred to as vinyl monomers). Is mentioned. Such vinyl-based crosslinked polymer particles can be produced by emulsion polymerization, suspension polymerization, seed polymerization method, etc., and after polymerization, any dispersion using an aqueous medium as a dispersion medium (also called an aqueous dispersion). This aqueous dispersion can be used as a raw material slurry as it is. Among these, seed polymerization is preferable because the particle size distribution can be reduced. The composition of the particles can be confirmed by GC-MS or the like.

  Furthermore, organic-inorganic composite particles are also hard particles and are preferably used. The organic / inorganic composite particles are particles comprising an organic part derived from a vinyl polymer and an inorganic part. As an aspect of the organic-inorganic composite particles, composite particles in which inorganic fine particles such as metal oxides such as silica, alumina and titania, metal nitrides, metal sulfides, metal carbides are dispersed and contained in vinyl polymer particles Polysilsesquioxane particles obtained by hydrolytic condensation of trifunctional alkoxysilanes such as methyltrimethoxysilane and phenyltrimethoxysilane; polymerizable unsaturated groups such as vinyltrimethoxysilane and methacryloxypropyltrimethoxysilane Particles obtained by radical polymerization of polymerizable unsaturated groups of the polymerizable polysiloxane particles obtained by hydrolytic condensation of the alkoxysilanes possessed, and the polymerizable polysiloxane particles absorb vinyl monomers, and then radical copolymerization Including particles such as polysiloxane skeleton and vinyl polymer skeleton Etc. If particles, and the like. This composite particle containing a polysiloxane skeleton and a vinyl polymer skeleton can control the hardness of the particle by changing the content ratio of the polysiloxane skeleton and the vinyl polymer skeleton and the type of vinyl monomer used, and the particle size distribution Can be preferably applied to the production method of the present invention in that small particles can be easily obtained.

  Also, inorganic coated organic particles having the surface of the organic polymer particles coated with an inorganic material such as a ceramic layer such as a metal layer or a metal oxide are highly effective and can be suitably used. Inorganic coated organic particles, for example, coating by plating such as electroless plating, displacement plating, etc .; coating using a paste obtained by mixing inorganic fine powder alone or in a binder; vacuum deposition, ion plating, ion sputtering The organic polymer particles (preferably vinyl-based crosslinked polymer particles and the like) are coated with an inorganic material by a coating method such as physical vapor deposition. Among these methods for forming a metal layer and the like, the electroless plating method does not require a large-scale apparatus and can easily form the metal layer and the like.

  As described above, particles having a high effect of reducing the Fe content by employing the present invention are particles having an average particle diameter of 1 μm or more. The upper limit of the average particle diameter is preferably 20 μm and more preferably 10 μm. In addition, the above-mentioned average particle diameter can measure the diameter of 100 arbitrary particles, for example with a scanning electron microscope (SEM), and can employ | adopt the average particle diameter of the number reference | standard.

  Among the above various particles, the metal oxide fine particles, organic-inorganic composite particles, and vinyl-based crosslinked polymer particles are highly effective from the viewpoint of high industrial value as liquid crystal display element members and optical film additives. preferable. Among metal oxide fine particles, metal oxide fine particles obtained by hydrolyzing metal alkoxide are preferable because high purity (low Fe content) metal oxide fine particles can be easily obtained. preferable. Among the silica fine particles, amorphous silica fine particles are preferable, and amorphous silica fine particles having an average particle diameter of 1 to 5 μm obtained by hydrolysis condensation reaction of silicon alkoxide are particularly preferable.

  Of the organic / inorganic composite particles, polysilsesquioxane particles and composite particles containing the polysiloxane skeleton and the vinyl polymer skeleton are preferred. A preferable average particle size of the organic-inorganic composite particles is 1 to 20 μm.

  Among vinyl-based crosslinked polymer particles, (co) polymers of (meth) acrylic monomers, (co) polymers of styrene monomers, and copolymers of (meth) acrylic monomers and styrene monomers are preferred. . The vinyl polyfunctional monomer for crosslinking is preferably used in an amount of 5% by mass or more, more preferably 10% by mass or more, out of 100% by mass of the total amount of vinyl monomers. A preferable average particle diameter of the vinyl-based crosslinked polymer particles is 1 to 50 μm, and more preferably 1 to 20 μm.

  The solvent used for the slurry as a raw material for the powder is not particularly limited. Although it may contain water, it is preferably an organic solvent having a low water content. The organic solvent is preferably hydrophilic, for example, methanol, ethanol, isopropanol, n-butanol, isobutanol, sec-butanol, t-butanol, pentanol, ethylene glycol, propylene glycol, 1,4-butanediol, etc. Alcohols; ketones such as acetone and methyl ethyl ketone; and esters such as ethyl acetate. These may be used alone or in admixture of two or more. In order to quickly remove the solvent during the drying process, it is preferable that the ratio of the organic solvent is large. Specifically, when the total amount of the solvent is 100% by mass, the amount of the organic solvent other than water is preferably 50% by mass or more, and more preferably 80% by mass or more. The organic solvent preferably has a low boiling point, specifically, an organic solvent having a boiling point of 120 ° C. or less at normal pressure is preferable, and particularly preferable is an aliphatic chain alcohol having 1 to 4 carbon atoms. . In order to efficiently distill off water that is likely to cause secondary aggregation in the drying step, it is also a preferred embodiment that an organic solvent azeotropic with water such as n-butanol coexists. In order to efficiently remove the solvent, the solid content concentration of the slurry is preferably about 0.1 to 50% by mass. More preferably, it is 5-30 mass%.

  The present invention will be described in further detail with reference to the following examples. However, the following examples are not intended to limit the present invention, and all modifications and implementations without departing from the spirit of the present invention are included in the present invention.

[Method for measuring Fe content]
Using a high frequency plasma emission spectroscopic analyzer (ICP-AES SPS3500; manufactured by Seiko Instruments Inc.), the measurement was performed by high frequency plasma emission spectroscopic analysis (ICP method). Specifically, a powder sample (5 g) was added to and mixed with a mixed solution of hydrofluoric acid and nitric acid, and nitric acid and hydrogen peroxide solution were further added to this mixed solution to make a total volume of 50 ml. It used for the measurement as a sample liquid.

Comparative Example Two straight pipes having an inner diameter of 8 mm and a length of 800 mm were connected by a 180 ° elbow having a length (length of the inner wall on the outer peripheral side) of 160 mm to form a heating pipe. This heating tube is made of SUS304. A reaction liquid obtained by hydrolytic condensation of tetramethoxysilane in water-containing methanol using ammonia as a catalyst was heated and concentrated, and 20% by mass of amorphous silica fine particles having an average particle size of 1.5 μm, 10% by mass of water, and 70% of methanol. A raw material slurry consisting of mass% was obtained. This raw material slurry was supplied to the heating tube at a supply rate of 20 L / hr from the supply unit of the vacuum dryer. It heated with the superheated steam with the external heating means so that the temperature inside a heating tube might be 175 degreeC. The collection chamber temperature was 150 ° C. The inside of the heating tube and the inside of the collection chamber were under a reduced pressure of 50 Torr (6.6 kPa).

  After drying, the Fe content of the obtained silica powder was measured by the method described above and found to be 14 ppm (mass basis). The Fe content of the powder still needs to be reduced in consideration of application to the semiconductor field and liquid crystal display element members.

Example A drying experiment of a raw material slurry containing amorphous silica particles having an average particle diameter of 1.5 μm was conducted in the same manner as in the comparative example except that a heating tube made of SUS316 was used. The obtained powder had an Fe content of 10 ppm. It can be seen that the Fe content was reduced to about 2/3 compared to the comparative example.

Reference Example A drying experiment was conducted in the same manner as in the comparative example, except that the average particle diameter of the amorphous silica particles was 0.5 μm. The Fe content of the powder was 3 ppm.

  Using the vacuum drying apparatus of the present invention in which the heating tube is made of SUS316, the raw slurry is dried to produce a powder, thereby obtaining a powder having no secondary aggregation and a very low Fe content. I was able to. Therefore, the powder obtained by the present invention can be applied to the semiconductor field, liquid crystal display devices and the like.

Claims (1)

  One end of a heating tube that is externally heated and held at a reduced pressure is connected to the raw slurry supply unit, and the other end is connected to a powder collection chamber that is held at a reduced pressure. A method for producing a powder by drying a raw material slurry in which fine particles are dispersed, wherein the heating tube is composed of alternately connected straight tubes and elbows, and at least an inner surface layer of the heating tube. Is made of SUS316, and the powder has an average particle diameter of 1 μm or more.