JP2008074983A - Method for improving fine particle dispersion, the fine particle dispersion and coated sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple method for increasing an average particle size and a pore volume, especially bringing the fine particles to be flat and a method for modifying a fine particle dispersion to enhance quality of products made by using the fine particles. <P>SOLUTION: The method for improving a fine particle dispersion is to treat a fine particle dispersion having ≤1 μm average particle size D<SB>0</SB>by dynamic light scattering to aggregate by using a wet medium mill and bring the average particle size D to be D>2D<SB>0</SB>. In the method for improving the fine particle dispersion, the wet medium mill is a wet medium-stirring mill, and furthermore, a pulverization medium is beads having a 5 g/cm<SP>3</SP>true density. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for modifying a dispersion in which solid fine particles are dispersed in a solvent. More specifically, an object of the present invention is to provide a method for causing controlled aggregation in fine particles and increasing average particle diameter, increasing pore volume, and further flattening. The fine particle dispersion produced by the present invention can be used for various applications, but can be suitably used for the production of a coated sheet provided with a coating layer on a sheet-like support. It is suitable for manufacturing.

  Regardless of organic or inorganic, fine particle dispersions are used in various fields, and are used, for example, in the production of inks, paints, toners, cosmetics, coated sheets and the like. In addition, it is used as a filler for synthetic resins to improve its mechanical strength, enhance chemical stability, and provide functions such as ultraviolet absorption. In general, the fine particles are spherical or amorphous, but a flat shape may be preferable. For example, in the case of cosmetics, if it is flat, adhesion to the skin and elongation are good, and flat mica and titanium dioxide may be used. Further, when flat fine particles are applied to the support, the smoothness, the air permeability, and the gloss become high due to the orientation of the fine particles. However, there is a restriction that the types of flat particles are very limited. In addition, it is generally preferred that the fine particles are in a monodispersed state without secondary aggregation, but depending on the application, secondary particles in which primary particles are aggregated and particles having a fine secondary particle diameter are preferable. There is a case. One such application is a coated sheet. Since the coated sheet is often printed and used as an information transmission / recording medium, it is necessary to impart printability. When printing with oil-based or water-based ink, it is necessary to quickly absorb the solvent in the ink, and a porous coating layer is often provided. In particular, the printing method using an ink jet printer is widely used in various fields because of its ease of multicolor printing, high-speed recording, and small size and low cost compared to other recording methods. However, since a large amount of ink is used, the recording sheet needs to have a particularly high ink absorbability.

  In producing an ink jet recording sheet, in addition to high ink absorbability, an ink receiving layer that is as transparent and smooth as possible is required in order to obtain high color density and photographic gloss. In order to form such a receiving layer, fine particles are used. As fine particles, silica fine particles, alumina fine particles, boehmite fine particles, aluminum hydroxide fine particles and the like are often used.

  Colloidal silica is widely known as a dispersion of silica fine particles. There are many known methods for its production, but an aqueous solution of acidic silicic acid is prepared by treating a dilute aqueous solution of sodium silicate with a cation exchange resin. By adding and stabilizing soda as an alkali to heat and polymerize, a liquid in which silica seed particles are monodispersed (seed liquid) is made, and the remaining part of the active silicic acid aqueous solution (feed liquid) is maintained while maintaining alkaline conditions. A method of gradually adding to this to polymerize silicic acid and growing seed particles to a desired size while maintaining a monodispersed state is widely used. The shape is generally spherical, and in a dry state, the particles are closely packed and have a structure with very few voids between the particles. Therefore, the pore volume of colloidal silica measured by the nitrogen adsorption method is generally less than 0.3 ml / g, and the coating film obtained using colloidal silica is inferior in ink absorbency in ink jet printing. There was a need for improvement. In addition, colloidal silica, which is industrially available at a low price, has a particle diameter of 7 nm to 100 nm and has a very small particle diameter, so that the coating film containing colloidal silica as a main component has a drawback that it is liable to crack during drying. .

  According to the examination results of the present inventors, it is effective to use secondary particles in order to increase the pore volume of colloidal silica. When the dispersion containing the secondary particles is dried, not only the gaps between the secondary particles but also the gaps between the primary particles are present, so that a structure with many voids is formed and a large amount of ink can be absorbed. However, an attempt to produce a dispersion of secondary particles with a moderately controlled particle size by adding an aggregating agent to colloidal silica is very gelling or results in precipitation of coarse aggregates. Found it difficult. Such a phenomenon is also described in Patent Document 1. In Patent Document 1, since colloidal particles such as silica are anionic, the addition of a cation resin may cause the particles to aggregate, the dispersion to thicken, fluidity may be lost, and coating may be difficult. Are listed. Therefore, in Patent Document 1, a cationic resin is added, and the fine particles that have been aggregated and thickened are redispersed using a dispersing device to form a dispersion. This method requires the addition of a cationic resin and has the disadvantage that only cationic fine particles can be produced.

In addition, in the patent document 2, the present inventors disclose a method for producing silica fine particles by condensing activated silicic acid. This method is a method in which colloidal secondary particles bonded with fine primary particles of silica are chemically directly produced from active silicic acid, and the ink absorption and transparency of the coating film are also excellent, and the ink jet recording sheet It can be preferably used for production. However, this method is suitable for producing silica fine particles having an average secondary particle diameter of 20 nm to 200 nm by the dynamic light scattering method, and it is difficult to produce silica fine particles exceeding 200 nm, and there are limitations to applications.
Japanese Patent Laid-Open No. 10-272833 JP 2001-354408 A

  The present invention provides a simple method for increasing the average particle diameter, increasing the pore volume, particularly flattening without impairing the dispersion state of the fine particle dispersion and without using chemical means, thereby The challenge is to improve the quality of products using fine particles.

  The present inventor paid attention to the agglomeration phenomenon of fine particles due to mechanical force as a method for achieving an increase in the average particle diameter of fine particles contained in the fine particle dispersion and an increase in the pore volume, regardless of the method described above. The present inventors have experienced that when colloidal silica is vigorously stirred for a long time with a rotary homogenizer or the like, a large amount of agglomerated silica particles having a large particle diameter are produced. Further, even in a wet medium stirring mill used for producing a fine particle dispersion, it is known that pulverized particles reaggregate inside the wet medium stirring mill depending on conditions.

  The wet medium agitation mill is sometimes referred to as a bead mill, and is a wet pulverizer that pulverizes, disintegrates, and disperses powders slurried with a solvent with a pulverization medium (beads) of approximately 3 mmφ or less. In the pulverization, glass beads or ceramic beads, which are pulverization media, are filled in the pulverization chamber, and the powder is slurried with a solvent and supplied thereto while stirring with a stirring disk or a stirring arm. The powder in the slurry is captured between the moving grinding media and pulverized by forces such as shear stress, shearing force, frictional force, and impact force.

  It is empirically that when the pulverization of, for example, titanium dioxide is advanced in a wet medium agitation mill, the average particle diameter decreases rapidly at first, but eventually hardly changes and the particle diameter may increase. Known to. The mechanism by which this phenomenon occurs is not necessarily clear, but it is known that reaggregation occurs more strongly as the disk peripheral speed of the wet medium stirring mill is increased. It is also known that it tends to occur as the average particle size decreases. This phenomenon of re-aggregation is a troublesome person for the purpose of pulverization, and technology development to avoid it by improving the structure of the mill has been carried out as disclosed in JP-A-2004-8993. However, there has been no example in which re-aggregation by mechanical force is positively applied to the modification of the fine particle dispersion.

The present inventor examined the treatment of colloidal silica having a primary particle size of 10 nm to 20 nm with a wet medium stirring mill. Under specific conditions, secondary particles were easily aggregated to increase the average particle size. It has been found that an increase in pore volume occurs. At this time, there was no adverse effect such as thickening or gelation. In addition, when the colloidal silica formed into secondary particles was coated on paper, it was found that the ink absorbability increases. Agglomeration of fine particles by wet medium agitating mill occurred most notably in silica, but is not limited to silica, and also occurs in other fine particle dispersions such as alumina, boehmite, aluminum hydroxide and other fine particle dispersions. It can be used as a fine particle dispersion modification method. Further, the inventors have found that the aggregated fine particles have a flat shape under specific conditions, and that the gloss, smoothness, and air permeability are improved when the fine particles are coated on paper.
The present invention includes the following aspects.
(1) Fine particles characterized in that a fine particle dispersion having an average particle diameter D ₀ of 1 μm or less by a dynamic light scattering method is aggregated by treating with a wet medium mill, and the average particle diameter D is D> 2D ₀ Dispersion reforming method.
(2) The method for modifying a fine particle dispersion according to (1), wherein the wet medium mill is a wet medium stirring mill.
(3) The method for modifying a fine particle dispersion according to (1) or (2), wherein the grinding medium of the wet medium mill is beads having a true specific gravity of 5 g / cm ³ or more.
(4) A fine particle dispersion produced by the method of any one of (1) to (3) and having an average particle diameter D of fine particles after the aggregation treatment of 3 μm or less.
(5) The fine particle dispersion according to (4), wherein the fine particles after the aggregation treatment have a pore volume of 0.4 to 2.0 ml / g by a nitrogen adsorption method.
(6) The fine particle dispersion according to (4) or (5), wherein the fine particles after the aggregation treatment are flat particles having an aspect ratio (average diameter / thickness) of 3 to 50.
(7) The fine particle dispersion according to any one of (4) to (6), wherein the fine particles are silica.
(8) A coated sheet produced by applying a coating liquid containing the fine particle dispersion according to any one of (4) to (7) on a support.

  The present invention provides a simple method for increasing the average particle diameter, increasing the pore volume, and flattening the fine particles in the fine particle dispersion. Increasing average particle size reduces cracks in the coating film, increasing pore volume improves ink absorption, and flattening improves coating film gloss, smoothness, air permeability, etc. It helps to improve sheet quality. In particular, when the fine particle dispersion modified according to the present invention is used in the ink receiving layer of an ink jet recording sheet, the quality can be greatly improved due to the effect of reducing cracks and increasing the amount of ink absorbed. The present invention is not only particularly useful for the production of coated sheets, but also results in an increase in average particle size, an increase in pore volume, and flattening, so that various applications in which fine particles are used, such as inks, paints, It is also useful for the production of toners, cosmetics, resin fillers and the like.

The best mode for carrying out the present invention will be described in detail.
[Fine particle dispersion]
In the present invention, a fine particle dispersion in which fine particles having an average particle diameter D ₀ of 1 μm or less are dispersed in a solvent is used. In the present invention, the average particle diameter is a value measured by a dynamic light scattering method and calculated from an analysis using a cumulant method. In the present invention, since the fine particles are combined and combined into secondary particles by mechanical force such as shear stress, shear force, friction force, impact force in the wet medium mill, the average particle diameter is 1 μm. If it exceeds, the inertial force of the particles is so large that it is difficult for the particles to be combined and coalesced, and pulverization tends to occur preferentially. A preferable average particle diameter is 5 nm to 500 nm. When the average particle diameter exceeds 1 μm, the average particle diameter may be pulverized to 1 μm or less by some means in advance.

  The type of fine particles can be either inorganic fine particles or organic fine particles. Further, it may be primary particles or secondary particles. Examples of inorganic fine particles include fine particles of silica, alumina, boehmite, pseudoboehmite, aluminum hydroxide, calcium carbonate, clay, kaolin, zeolite, titanium dioxide, calcium sulfate, barium sulfate, zinc oxide, zinc sulfide, aluminum silicate, etc. Is done. Among these inorganic fine particles, silica is preferable because it is most likely to aggregate in the wet medium mill. This is presumably because a silica surface has a silanol group, so that a siloxane bond is generated by collision between silica fine particles and it is difficult to separate.

Colloidal silica is first mentioned as the silica fine particles. As described above, as described above, a dilute aqueous solution of sodium silicate is treated with a cation exchange resin to prepare an acidic active silicate aqueous solution, and sodium silicate is added as an alkali to a part of the active silicate aqueous solution. Then, by stabilizing and heat polymerizing, a silica seed particle monodispersed liquid (seed liquid) is made, and the remaining portion of the active silicic acid aqueous solution (feed liquid) is gradually added to this while maintaining alkaline conditions. Thus, a method of polymerizing silicic acid and growing seed particles to a desired size while maintaining a monodispersed state is widely performed. In addition, non-spherical, elongated, chain-like, or necklace-shaped primary particles are commercially available. These colloidal silicas generally have an average particle diameter of 7 nm to 100 nm. Specific surface area measured by the nitrogen adsorption method is about ^{30m 2} / ^g~400m 2 / g, the primary particles a spherical pore volume is less than 0.3 ml / g.

Moreover, the silica fine particle dispersion liquid obtained by condensing active silicic acid currently disclosed by Unexamined-Japanese-Patent No. 2001-354408 can also be used preferably. Differs from the manufacturing method of the colloidal silica, a specific surface area of 300m ² / g~1000m ² / g by a nitrogen adsorption method, silica fine pore volume is 0.4ml / g~2.0ml / g This is a point in which a colloidally dispersed liquid is used as a seed liquid. As a result, a silica fine particle dispersion having a larger pore volume than colloidal silica is obtained. Silica fine particles after growing an average particle diameter of 20 nm to 200 nm, specific surface area measured by the nitrogen adsorption method 100m ² / g~400m ² / g, and a pore volume of 0.5ml / g~2.0ml / g range It is.

Also, a dry process silica dispersed in water can be used. Dry silica is a particulate silica produced by a method in which a volatile silicon compound such as silicon tetrachloride is decomposed at high temperature in a flame, and various types having different specific surface areas are commercially available. Dry silica is a very bulky powder and can easily be made into an aqueous dispersion. The average particle size of the aqueous dispersion varies depending on the method for producing the dispersion, but is in the range of about 100 nm to 900 nm. When the aqueous dispersion was dried to measure the specific surface area and pore volume by the nitrogen adsorption method is about a specific surface area of ^{50m 2} / ^g~400m 2 / g, a pore volume of 0.6ml / g~1.8ml / G.

More recently, dispersions of amorphous silica produced by a wet method are also commercially available and can be used in the present invention. The wet method is obtained by mixing an acid with a water-soluble silicate aqueous solution such as sodium silicate. For example, there is a method (precipitation method) of obtaining hydrous silicic acid amorphous silica having a pore volume of 0.5 ml / g or more by adding acid in two stages to an aqueous sodium silicate solution and precipitating silica. Has been done. In addition, a method (gel method) for producing porous, hydrous amorphous silica by adding an acid to an aqueous sodium silicate solution to gelate the entire mixture, followed by pulverization, washing, and drying is also performed. . The average particle diameter of silica in the dispersion can be changed depending on the production conditions of the dispersion, and a silica having an average particle diameter of 1 μm or less may be selected for use in the present invention. When the dispersion dried to measure the specific surface area and pore volume by the nitrogen adsorption method is about a specific surface area of ^{50m 2} / ^g~500m 2 / g, a pore volume of 0.4ml / g~1.8ml / The range of g.

  Organic fine particles include acrylic or methacrylic resins, vinyl chloride resins, vinyl acetate resins, polyester resins, styrene-acrylic resins, styrene-butadiene resins, styrene-isoprene resins, polycarbonate resins, silicone resins. Examples thereof include fine particles of resin, urea resin, melamine resin, epoxy resin, phenol resin, diallyl phthalate resin, and the like.

  The fine particle grinding medium is preferably water from the viewpoint of safety and ease of handling, but may be an organic solvent or a mixture thereof.

[Wet medium mill]
The wet medium mill is a general term for an apparatus for finely pulverizing particles slurried with a solvent using a pulverizing medium. The wet medium mill is classified into a wet medium stirring mill and a wet container drive medium mill. The wet medium agitation mill is sometimes called a bead mill, and is a wet pulverizer that pulverizes, disintegrates, and disperses particles slurried with a solvent with a pulverization medium (beads) of approximately 3 mmφ or less. In the pulverization, glass beads or ceramic beads, which are pulverization media, are filled in the pulverization chamber, and the particles are slurried with a solvent and supplied thereto while stirring with a stirring disk or a stirring arm. Particles in the slurry are trapped between the moving grinding media and given a force such as shear stress, shear force, friction force, impact force and the like. Various types of equipment are manufactured, tower mill, flow pipe mill (sand grinder, pearl mill is this type), stirred tank mill (attritor, aquamizer is this type), annular type mill, annular type stirred tank mill And micros type.

  The container drive medium mill is an apparatus that performs pulverization by rotating a pulverization chamber filled with a pulverization medium and slurry or by applying vibration. Types such as a ball mill, a vibration mill, a medium planetary mill, and a CF mill (centrifugal fluidized ball mill) are known.

  Any of the above-mentioned wet medium mills can be used in the present invention. In particular, the wet medium stirring mill can move the grinding medium at a high speed and can give a strong force to the fine particles. Is particularly excellent. In addition, it is easy to remove a large amount of heat generated by continuous processing and operation by cooling, which is suitable for the present invention.

  Since the grinding chamber is easily worn by collision with the grinding media, a material with high wear resistance is selected. For example, carbon steel, stainless steel, hard chrome plating, zirconia, alumina, zirconia reinforced alumina, silicon nitride, rubber, polyurethane, plastics (cast nylon, ultrahigh molecular weight polyethylene) and the like are used.

The grinding media used for grinding are glass beads, special glass beads (low alkali, no alkali, high specific gravity), zirconia-silica ceramic beads, alumina beads, zirconia beads, silicon nitride beads, titania beads, steel beads. Yes. In the present invention, beads having a higher true specific gravity are preferable because they have a higher effect of promoting aggregation of the fine particle dispersion. In particular, when a grinding medium having a true specific gravity of 5 g / cm ³ or more is selected, the aggregation promoting effect is particularly high. Compared with beads having the same particle diameter, the kinetic energy of the beads is proportional to the true specific gravity of the beads, and therefore it is interpreted that the effect of promoting aggregation is high. Zirconia beads are most preferable because they have a true specific gravity of about 6 g / cm ³ and excellent wear resistance. The bead particle size of 0.05 mmφ to 3 mmφ is most used. The larger the particle size, the higher the effect of promoting the aggregation of the fine particle dispersion, but at the same time the particle size after aggregation tends to increase, so it is necessary to select according to the purpose.

  The pulverization treatment by the wet medium mill is performed by a batch method, a pass method, or a circulation method. The batch method is a method in which a pulverizing chamber and a slurry are filled in a pulverizing chamber like a ball mill and the operation is continuously performed until a desired particle size is obtained. The pass system is a system in which raw material slurry is pumped from a tank to a wet medium mill and the pulverized slurry is collected in a tank different from the raw material tank. If the desired particle size is not reached in a single treatment, pulverization is repeated a plurality of times. In this case, a single mill may be used, or a plurality of mills may be connected in series for operation. The circulation system is a system in which the pulverized slurry is returned to the raw material tank and the operation is continued until a desired particle diameter is obtained. However, in this case, it is necessary to increase the circulation amount of the slurry so that the particle diameter does not become non-uniform.

  Since there are many types of wet media mills, the operating conditions cannot be described uniformly, but the agglomeration is more likely to occur in the operating conditions where the movement speed of the grinding media is faster. In the case of a wet medium agitation mill, agglomeration occurs in a shorter time as the number of revolutions of the agitation disk and agitation arm is increased. As an index of the speed of movement of the grinding medium, when expressed by the peripheral speed of the stirring disk or stirring arm, aggregation becomes remarkable at 8 m / second or more. Of course, the longer the slurry residence time in the grinding chamber, the stronger the aggregation. The required residence time varies depending on the peripheral speed of the stirring disk and the stirring arm, but is, for example, about 1 to 20 minutes in the case of 8 m / sec. However, as described above, the aggregation promoting effect on the fine particle dispersion also changes depending on the true specific gravity of the beads and the particle size of the beads. Therefore, if the desired modification effect is obtained by combining these and operating conditions such as the peripheral speed. good.

  The higher the concentration of the fine particles during the treatment, the easier the aggregation of the fine particles occurs. However, the higher the concentration, the higher the viscosity of the dispersion liquid, and thus the treatment with the wet medium mill becomes difficult. Further, if the concentration is too low, it is difficult to agglomerate, and the energy efficiency is poor, so 5 mass% to 50 mass% may be performed.

In order to substantially change the quality of the fine particle dispersion by the above method, it is necessary to set the average particle diameter (D) after the treatment to a value exceeding twice the average particle diameter (D ₀ ) before the treatment. It is. Preferably they are 3 times or more and less than 100 times.

  When the average particle diameter (D) of the fine particles modified by the above method is 3 μm or less, the glossiness of the coated sheet is preferably high. The reduction to 3 μm or less can be achieved by a combination of the average particle size of the fine particles before aggregation, the true bead specific gravity, the bead particle size, and the wet medium mill operating conditions. Preferably it is 0.05 micrometer or more. Moreover, when the pore volume by the nitrogen adsorption method of the fine particles after the aggregation treatment is 0.4 to 2.0 ml / g, a coating film having high ink absorbability can be obtained, and such a coating film is formed on the support. The provided one can be suitably used as an ink jet recording sheet. Setting the pore volume in the range of 0.4 to 2.0 ml / g can be achieved by a combination of the true specific gravity of the beads, the bead particle size, the wet medium mill operating conditions, and the selection of fine particles. Especially when silica is selected, the above pore volume can be easily achieved.

  In the method for modifying a fine particle dispersion of the present invention, the aggregated particles after modification may have a flat shape. Although the mechanism is not clear, it seems that the fine particles are flattened because they are sandwiched between two grinding media and united by impact force. In order to promote flattening, it is first important to select fine particles. In particular, silica is easily flattened. Further, as beads, zirconia beads having a large true specific gravity promote flattening. Furthermore, the aspect ratio tends to increase as the particle size increases. When flat particles having an aspect ratio (particle diameter / thickness) of 3 to 50 are coated on a support, there are preferable effects such as improvement in gloss, increase in air permeability and smoothness.

[Support]
Hereinafter, a method for producing a coated sheet using the fine particle dispersion of the present invention will be described. First, the support is not particularly limited, and paper, resin-coated paper, synthetic paper, synthetic resin film, metal foil, and the like can be used.
Paper made from various types of chemical pulp, semi-chemical pulp, mechanical pulp, recycled pulp (waste paper pulp), non-wood pulp such as hemp, jute, kenaf, synthetic pulp, synthetic fiber short fiber, etc. Can be used. Also, chlorine-free pulp such as so-called ECF and TCF pulp can be preferably used. These pulps can be adjusted in the beating degree by a beating machine in order to adjust paper strength, smoothness, papermaking suitability, and the like. The beating degree is not particularly limited, but generally about 50 to 550 ml (CSF: JIS-P-8121) is a preferable range. If necessary, a filler can be internally added, and talc, calcium carbonate, clay, kaolin, calcined kaolin, silica, zeolite, titanium dioxide, barium sulfate, organic filler and the like are preferably used. By adding the filler, the opacity and smoothness can be increased. However, if excessively added, the paper strength may be lowered, and the internal amount of the filler is preferably about 1 to 30% by mass with respect to the wood pulp.

  The resin-coated paper is a paper whose surface is coated with a synthetic resin. Particularly, a paper whose surface is coated with polyethylene kneaded with titanium oxide is also used for silver salt photographic printing paper and glossy inkjet recording sheets. . 3-50 micrometers is preferable and, as for the thickness of a polyethylene coating layer, 5-30 micrometers is more preferable. When the thickness of the polyethylene coating layer is less than 3 μm, defects such as holes in the polyethylene resin tend to increase during resin coating, and there are many cases where it is difficult to control the thickness, and smoothness is difficult to obtain. Conversely, if it exceeds 50 μm, the effect obtained is small and uneconomical for an increase in cost. In order to enhance the adhesion to the ink receiving layer, it is preferable to subject the surface of the resin layer to corona discharge treatment or to provide a subcoat layer such as gelatin or polyvinyl alcohol.

  As synthetic paper, YUPO (manufactured by YUPO Corporation) in which polypropylene with internal pigments is biaxially stretched, and polyester film that has been specially processed to give a paper-like texture and printability are commercially available. .

  Examples of the synthetic resin film include films of polyethylene terephthalate, polyvinyl chloride, polycarbonate, polyimide, cellulose triacetate, cellulose diacetate, polyethylene, polypropylene, and the like. These synthetic resin films can be applied with a subcoat layer or various easy adhesion treatments such as corona discharge treatment when the adhesive strength with the ink receiving layer formed on the surface thereof is insufficient.

  Although there is no restriction | limiting in particular in the thickness of a support body, in the case of inkjet recording sheet manufacture, it is 50-500 micrometers normally in consideration of the paper permeability of a printer. In addition, a back layer can be provided for curling suppression and improving transportability in a printer.

[Coating fluid]
The coating liquid contains the binder resin as an essential component in the fine particle dispersion of the present invention, other pigments if necessary, and various additives and solvent for concentration adjustment as necessary. Prepared.

  The binder resin is not particularly limited. For example, proteins such as casein and gelatin; various starches such as starch, oxidized starch and processed starch; carboxymethylcellulose, hydroxyethylcellulose, methylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose and the like Cellulose derivatives: polyethylene oxide, polyalkylene oxide, polyvinyl pyrrolidone, water-soluble polyvinyl acetal, poly-N-vinylacetamide, polyacrylamide, polyacryloylmorpholine, polyhydroxyalkyl acrylate, polyacrylic acid, fully saponified polyvinyl alcohol, partially saponified polyvinyl Synthetic water-soluble resins such as alcohol; styrene-butadiene resin, methyl methacrylate-butadiene copolymer Conjugated diene resin latex: Acrylic resin latex that is a polymer or copolymer of acrylic acid, methacrylic acid, acrylic ester, methacrylic ester, etc .; Vinyl resin latex such as ethylene-vinyl acetate copolymer, etc. Can be mentioned. These binder resins may be used alone or in combination of two or more.

  The blending amount of the binder resin is preferably about 5 to 100 parts by mass with respect to 100 parts by mass in total of the fine particles of the present invention and other pigments added as necessary. When preparing a coating liquid for an ink jet recording sheet, specifically select the pore volume of the fine particles of the present invention and add as necessary so that the dried coating film becomes porous. The pore volume of the coating film may be adjusted to be in the range of 0.2 to 2.0 ml / g by appropriately selecting the pore volume of the other pigments and appropriately adjusting the addition amount of the binder resin. . In addition, the pore volume here is measured by a nitrogen adsorption method and is the total pore volume of pores having a pore diameter of 100 nm or less.

  Other pigments used in combination with the fine particles of the present invention as necessary include silica, alumina, boehmite, pseudo-boehmite, aluminum hydroxide, heavy calcium carbonate, precipitated calcium carbonate (light calcium carbonate), clay, kaolin, calcined Inorganic pigments such as kaolin, zeolite, titanium dioxide, calcium sulfate, barium sulfate, zinc oxide, zinc sulfide, aluminum silicate, diatomaceous earth; acrylic or methacrylic resins, vinyl chloride resins, vinyl acetate resins, polyester resins, styrene Organics composed of resins such as acrylic resins, styrene-butadiene resins, styrene-isoprene resins, polycarbonate resins, silicone resins, urea resins, melamine resins, epoxy resins, phenol resins, diallyl phthalate resins Pigments. Et pigments may be irregular in spherical, or may be porous even non-porous. These pigments may be used alone or in combination of two or more.

  When preparing a coating liquid for an ink jet recording sheet, it is necessary to add an ink fixing agent. As the ink fixing agent, a cationic resin, a polyvalent metal salt, a cationic surfactant, or the like is used. Typical cationic resins include polyalkylene polyamines such as polyethylene polyamine and polypropylene polyamine or derivatives thereof, polymers of (meth) acrylates having primary to tertiary amino groups or quaternary ammonium groups, ~ (Meth) acrylamide derivative polymer having tertiary amino group or quaternary ammonium group, vinylamine polymer or derivative thereof, allylamine polymer or derivative thereof, diallylamine polymer, diallylmethylamine polymer, diallyldimethylammonium Chloride polymer, diallylamine-sulfur dioxide copolymer, diallyldimethylammonium chloride-sulfur dioxide copolymer, acrylamide-diallylamine copolymer, acrylamide-diallyldimethylammonium chloride copolymer, dicyan Dicyan-based cationic resin represented by amide-formalin polycondensate, polyamine-based cationic resin represented by dicyandiamide-diethylenetriamine polycondensate, epichlorohydrin-dimethylamine addition polymer, acrylonitrile and N-vinylformamide copolymer Cationic resins such as hydrolysates and polyvinylamidine resins can be exemplified, and they may be used alone or in combination of several kinds. The blending amount of the cationic resin is preferably about 5 to 30 parts by mass with respect to 100 parts by mass in total of the fine particles of the present invention and other pigments added as necessary.

As the polyvalent metal salt, a water-soluble zirconium compound and a water-soluble aluminum compound are excellent in fixing effect. Here, water solubility means that 1 g or more is dissolved in 100 g of water at 20 ° C. Among the water-soluble zirconium compounds, zirconyl acetate, zirconyl nitrate, zirconyl lactate, zirconium oxychloride and basic zirconyl chloride are preferable, and a compound in which a plurality of zirconium ions are combined to form a polymer is preferable. Basic zirconyl chloride is known. The water-soluble aluminum compound is preferably aluminum chloride, aluminum sulfate, aluminum nitrate, aluminum lactate, basic aluminum chloride, basic aluminum sulfate, or basic aluminum sulfate silicate. Such compounds are preferably basic aluminum chloride, basic aluminum sulfate, basic aluminum sulfate silicate and the like. The blending amount in the coating liquid is ₂ to 30 parts by mass in terms of oxide (Al ₂ O ₃ or ZrO ₂ ) with respect to a total of 100 parts by mass of the fine particles of the present invention and other pigments added as necessary. The degree is preferred.

  In order to improve the fixability of the ink, a method of treating the pigment with a cationic silane coupling agent can be used. In particular, since silica is anionic, surface treatment with a cationic silane coupling agent is preferred. Examples of cationic silane coupling agents include those having a primary, secondary, tertiary amino group, or quaternary ammonium group in the molecular structure, and specific examples thereof include N-β (aminoethyl) γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, γ-aminopropyltrimethoxysilane, γ- [bis (β-hydroxyethyl)] Aminopropyltriethoxysilane, hexamethyldisilazane, γ-anilinopropyltrimethoxysilane, octadecyldimethyl [3- (trimethoxysilyl) propyl] ammonium chloride, N-β- (N-vinylbenzylaminoethyl) -γ -Aminopropyltrimethoxysilane hydrochloride, SH-6026, SZ-6050 (Torayda Special aminosilane or the like, which is commercially available under the trade name of Corning), and the like.

  Other optional components include thickeners, antifoaming agents, wetting agents, surfactants, colorants, antistatic agents, light resistance improvement aids, UV absorbers and antioxidants used in general recording sheet production. Various assistants such as an agent, a gas resistance improving aid, an antiblocking agent, and an antiseptic are added as appropriate.

  As the surfactant, any of an anionic surfactant, a cationic surfactant, and a nonionic surfactant may be used. Examples of anionic surfactants include sulfate ester salts, sulfonate salts, phosphate ester salts, and the like. Examples of the cationic surfactant include amine salt type and quaternary ammonium salt type. Nonionic surfactants include, for example, acetylene glycols, polyethylene glycols (higher alcohol ethylene oxide adducts, fatty acid ethylene oxide adducts, alkylphenol ethylene oxide adducts, polypropylene glycol ethylene oxide adducts, higher aliphatic amines and fatty acids. Amide ethylene oxide adducts), polyhydric alcohols (fatty acid esters of glycerin and pentaerythritol, fatty acid esters of sorbitol and sorbitan, fatty acid esters of sucrose, ethylene oxide adducts of polyhydric alcohols, fatty acid alkanolamides, etc.) Can be mentioned.

[Coating method]
The coating can be formed by various known coating apparatuses such as a blade coater, an air knife coater, a roll coater, a bar coater, a gravure coater, a rod blade coater, a lip coater, a curtain coater, and a die coater. After coating, the gloss, thickness, density, and the like may be adjusted using a calendar such as a machine calendar, super calendar, soft calendar, gloss calendar, shoe nip calendar.

Coating amount is preferably about 1~60g / ^{m 2} as the mass after drying, more preferably about 3 to 50 g / ^{m 2.} In the case of an inkjet recording sheet, if the coating amount is less than 1 g / m ² , ink absorption tends to be insufficient, and if it is more than 60 g / m ² , curling tends to occur and the cost increases, which is not preferable.

  Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. In the following, “%” means “mass%” except “75 ° gloss value”, and “parts” means mass parts. The measuring method of the test item described in the Example and the comparative example is as follows.

[Pore volume measurement method]
The sample dispersion was dried as it was at 105 ° C., and measured after vacuum degassing at 200 ° C. for 2 hours as a pretreatment using a nitrogen gas adsorption specific surface area / pore distribution measuring device (Coulter SA3100plus type). did. As the pore volume, the value of the total pore volume (nitrogen relative pressure 0.9814) having a pore diameter of 100 nm or less was used.

[Average particle size measurement method]
Using a laser particle size distribution meter (FPAR1000, manufactured by Otsuka Electronics Co., Ltd.) by a dynamic light scattering method, the sample was measured in a state diluted sufficiently with distilled water. As the average particle size, a value calculated from an analysis using a cumulant method was used.

[Method for evaluating cracks in coating film]
The state of the coating layer was visually evaluated in the following three stages.
3 points: No cracks / cracks
2 points: A part of the coating layer is cracked 1 point: The entire surface of the coating layer is cracked

[Evaluation method of ink absorbency]
The sample of the ink jet recording sheet is an ISO-400 image ("high-definition color digital standard image data ISO / JIS-SCID") with the super fine paper recommended setting of the ink-jet printer PM-G820 (machine installed with dye ink) manufactured by Seiko Epson Corporation. p13, image name: fruit basket) was printed, and the image quality was visually evaluated in the following four stages.
4 points: No ink overflow 3 points: Ink overflow is somewhat noticeable in the solid print area 2 points: Ink overflow is generally noticeable 1 point: Ink is hardly absorbed and the image is completely broken

[75 degree white paper gloss measurement method]
It measured based on ISO 8254-1 using the gloss meter (GM-26 PRO / AUTO) of Murakami Color Research Laboratory.

[Measurement method of air permeability and smoothness]
Measured with Oken air permeability / smoothness measuring machine.

[Aspect ratio measurement method]
An enlarged photograph was taken with a scanning electron microscope, the average thickness of the flat particles and the average diameter in the vertical direction with respect to the thickness were measured, and the aspect ratio (average diameter / thickness) was calculated. In addition, when this value was less than 3, it indicated that it was indefinite.

Example 1
A wet medium agitating mill (LMZ-06 type manufactured by Ashizawa Finetech Co., Ltd.) with a pulverization chamber capacity of 0.6 liters is filled with 0.48 liters of 0.3 mmφ zirconia beads, and water is sent with a hose pump to pulverize. The interior was filled with water. The void (volume occupied by water) excluding beads in the pulverization chamber in this state was 0.3 liter. To a stainless steel tank equipped with a stirrer, 3.6 liters of colloidal silica (manufactured by Nissan Chemical Co., Ltd., trade name: Snowtex O, pH 3) was charged as a fine particle dispersion. After adjusting with an inverter so that the peripheral speed of the stirring blade of the wet medium stirring mill was 12 m / sec, the hose pump was operated and the fine particle dispersion was passed through the wet medium stirring mill at 1.5 liters / minute. The treatment liquid that came out of the mill was discarded in the first 0.6 liters and then returned to the stainless steel tank and processed in a circulating manner. In the circulation system, the average residence time in the pulverization chamber should be the treatment time, not the operation time of the apparatus. As will be apparent to those skilled in the art, the average residence time in the pulverization chamber of the fine particle dispersion is n minutes. To achieve this, the actual operation time of the mill may be n × 10 minutes {(3.6-0.6) /0.3=10}. Under these conditions, the aggregation treatment of the fine particle dispersion was performed with an average residence time of 2 minutes. Table 1 shows the results of measurement of the average particle diameter, pore volume, and aspect ratio before and after the aggregation treatment.

Example 2
Aggregation treatment of the fine particle dispersion was performed in the same manner as in Example 1 except that 0.5 mmφ silicon nitride beads were used as the grinding medium and the treatment time was 15 minutes. Table 1 shows the results of measurement of the average particle diameter, pore volume, and aspect ratio after the aggregation treatment.

Example 3
Aggregation treatment of the fine particle dispersion was performed in the same manner as in Example 1 except that a glass bead mixture of 0.42 mmφ to 0.6 mmφ was used as the grinding medium and the treatment time was 20 minutes. Table 1 shows the results of measurement of the average particle diameter, pore volume, and aspect ratio after the aggregation treatment.

Example 4
A ceramic pot having an internal volume of 3.1 liters was filled with 2.5 liters of 0.3 mmφ zirconia beads, and then 1 liter of colloidal silica used in Example 1 was charged. The pot was covered and attached to a vibration mill (MB-1 manufactured by Central Processing Machine Co., Ltd.) which is a kind of container drive medium mill. Next, the vibration mill was operated for 5 minutes at a vibration frequency of 1200 times / minute and an amplitude of 8 mm. After the operation was completed, the beads and the fine particle dispersion were separated with a 100 mesh stainless steel sieve to obtain a treated fine particle dispersion. Table 1 shows the results of measurement of the average particle diameter, pore volume, and aspect ratio after the aggregation treatment.

Example 5
[Production of fine particle dispersion]
Based on JP 2001-354408 A, a silica fine particle dispersion was produced as follows.
Distilled water was mixed with sodium silicate solution (No. 3 sodium silicate, manufactured by Tokuyama Corporation) having a SiO ₂ concentration of 30% and a SiO ₂ / Na ₂ O molar ratio of 3.1, and diluted with a SiO ₂ concentration of 4.0%. A sodium silicate aqueous solution was prepared. This aqueous solution is passed through a column packed with a hydrogen type cation exchange resin (manufactured by Mitsubishi Chemical Corporation, Diaion SK-1BH) to obtain an activated silicic acid having a SiO ₂ concentration of 4.0% and a pH of 2.9. Was prepared.
In a 70 liter stainless steel reaction vessel equipped with a reflux, a stirrer, and a thermometer, 11.3 kg of distilled water was heated to 90 ° C. While maintaining this hot water at 90 ° C., a total of 13.6 kg of the above active silicic acid aqueous solution was added at a rate of 13.6 kg / hour, and then heated at 90 ° C. for 30 minutes to prepare a seed solution.
To the seed solution, 0.3 kg of an aqueous ammonia solution having a concentration of 3.4% was added at a time and stabilized. While maintaining the seed solution at 90 ° C., an additional 34.8 kg of the above active silicic acid aqueous solution was added at a rate of 13.6 kg / hour. After completion of the addition, heating was performed at 90 ° C. for 1 hour to obtain 60 kg of a silica fine particle dispersion. This silica fine particle dispersion was concentrated by an ultrafiltration module (manufactured by Asahi Kasei Chemicals Corporation, Microza SLP2053) to obtain a silica fine particle dispersion having a concentration of 20% and pH 8.6.
[Agglomeration of fine particle dispersion]
3.6 liters of the fine particle dispersion was charged into a tank, and the fine particle dispersion was agglomerated in the same manner as in Example 1. Table 1 shows the results of measurement of the average particle diameter, pore volume, and aspect ratio before and after the aggregation treatment.

Example 6
Charge 200 kg of ion exchange water into a stainless steel tank, connect it to a suction disperser (Conti-TDS-4 manufactured by Ystral), and apply 20 kg of vapor phase silica (manufactured by Tokuyama, product name: Leoroseal QS-30) for about 30 minutes. Were gradually sucked in and dispersed simultaneously. At this time, the rotor of the suction disperser was performed at 3000 rpm. After completion of the suction, the operation was continued for another 30 minutes to obtain a silica fine particle dispersion. Subsequently, the aggregation treatment of the fine particle dispersion was performed in the same manner as in Example 1. Table 1 shows the results of measurement of the average particle diameter, pore volume, and aspect ratio before and after the aggregation treatment.

Example 7
Aggregation treatment was performed in the same manner as in Example 1 using a commercially available silica fine particle dispersion (produced by Grace Devison, trade name: Silojet 703A, the component was fine particles of wet silica, pH 8.3). However, the average residence time was 5 minutes. Table 1 shows the results of measurement of the average particle diameter, pore volume, and aspect ratio before and after the aggregation treatment.

Example 8
Aggregation treatment was performed in the same manner as in Example 7 except that the average residence time was 10 minutes. Table 1 shows the results of measurement of the average particle diameter, pore volume, and aspect ratio after the aggregation treatment.

Example 9
Using a commercially available alumina sol (Alumina Sol AS-3 manufactured by Catalytic Chemical Industry Co., Ltd., concentration 7.1%, pH 6.9) as it was, the aggregation treatment was performed in the same manner as in Example 1. Table 1 shows the results of measurement of the average particle diameter, pore volume, and aspect ratio before and after the aggregation treatment.

Comparative Example 1
1 liter of colloidal silica used in Example 1 was treated at 14000 rpm for 30 minutes using a high-speed rotating homomixer (Romix Fmodel, manufactured by Primix Co., Ltd., with a homomixer MARK 2-2.5 type as a stirring unit). Table 1 shows the results of measurement of the average particle diameter, pore volume, and aspect ratio after the treatment.

Comparative Example 2
One liter of colloidal silica used in Example 1 was subjected to a dispersion treatment with an ultrahigh pressure homogenizer (manufactured by Microfluidics, trade name: microfluidizer, model number: M110 / EH) once at 100 MPa. Table 1 shows the results of measurement of the average particle diameter, pore volume, and aspect ratio after the treatment.

以下に微粒子分散液を用いて塗工シートを作成した例を示す。
実施例１０
実施例１〜４で製造した凝集処理後の微粒子分散液に、完全けん化ポリビニルアルコール（クラレ社製、商品名：ＰＶＡ−１４５、重合度＝４５００、けん化度＝９９％以上）の８％水溶液と、カチオン性樹脂（センカ社製、商品名：ユニセンスＣＰ−１０３、成分：ポリジアリルジメチルアンモニウムクロライド）の１０％水溶液、及び水を加え、よく攪拌して均一な塗工液とした。配合比は固形分質量比でシリカ：ＰＶＡ：カチオン樹脂＝１００：７：６であり、全固形分濃度は１５％である。
市販のＡ４判ＰＰＣ用紙（富士ゼロックスオフィスサプライ（株）製、商品名：カラー／モノクロ兼用リサイクル用紙Ｃ２ｒ、坪量７０ｇ／ｍ^２）にこの塗工液を乾燥質量で塗工量が５ｇ／ｍ^２となるようにバー塗工を行い、１１０℃で１０分間熱風乾燥して塗工シートを得た。インクジェット記録シートとしての品質を評価するため、インク吸収量、塗膜のひび割れを測定した結果を表２に示す。

The example which created the coating sheet using the fine particle dispersion below is shown.
Example 10
An 8% aqueous solution of a fully saponified polyvinyl alcohol (manufactured by Kuraray Co., Ltd., trade name: PVA-145, polymerization degree = 4500, saponification degree = 99% or more) and the fine particle dispersion after the aggregation treatment produced in Examples 1 to 4 and Then, a 10% aqueous solution of a cationic resin (manufactured by Senka Co., Ltd., trade name: Unisense CP-103, component: polydiallyldimethylammonium chloride) and water were added and stirred well to obtain a uniform coating solution. The compounding ratio is silica: PVA: cationic resin = 100: 7: 6 in terms of solid content mass ratio, and the total solid content concentration is 15%.
This coating solution was applied to a commercially available A4 size PPC paper (manufactured by Fuji Xerox Office Supply Co., Ltd., trade name: color / monochrome recycle paper C2r, basis weight 70 g / m ² ) with a dry mass of 5 g / m. Bar coating was performed so as to be ^2, and hot air drying was performed at 110 ° C. for 10 minutes to obtain a coated sheet. Table 2 shows the results of measuring ink absorption and cracking of the coating film in order to evaluate the quality of the ink jet recording sheet.

Comparative Example 3
An ink jet recording sheet was prepared in the same manner as in Example 10 using the fine particle dispersion before agglomeration used in Examples 1 to 4, and used as Comparative Example 3.

Example 11
An 8% aqueous solution of fully saponified polyvinyl alcohol (manufactured by Kuraray Co., Ltd., trade name: PVA-145, degree of polymerization = 4500, degree of saponification = 99% or more) and a cation were added to the fine particle dispersion after the aggregation treatment produced in Example 5. A 10% aqueous solution of a water-soluble resin (manufactured by Senka Co., Ltd., trade name: Unisense CP-103, component: polydiallyldimethylammonium chloride) and water were added and stirred well to obtain a uniform coating solution. The compounding ratio was silica: PVA: cationic resin = 100: 15: 8 in terms of solid content mass ratio, and the total solid content concentration was adjusted to 15%.
Bar coating was applied to the commercially available A4 size PPC paper used in Example 10 so that the coating weight was 5 g / m ^{2 in} terms of dry mass, followed by drying with hot air at 110 ° C. for 10 minutes. A sheet was obtained.
Table 2 shows the results of measuring ink absorption and cracking of the coating film in order to evaluate the quality of the ink jet recording sheet.

Comparative Example 4
An ink jet recording sheet was prepared in the same manner as in Example 11 using the pre-aggregation fine particle dispersion used in Example 5 to obtain Comparative Example 4.

実施例１２
実施例７及び実施例８で製造した凝集処理後の微粒子分散液に、バインダーとしてアクリル系ラテックス（ニチゴー・モビニール（株）製、商品名：モビニール７１８）、及び水を加え、よく攪拌して均一な塗工液とした。配合比は固形分質量比でシリカ：ラテックス＝１００：３０であり、全固形分濃度は１５％である。この塗工液を市販のＡ４判ＰＰＣ用紙（富士ゼロックスオフィスサプライ（株）製、商品名：カラー／モノクロ兼用リサイクル用紙Ｃ２ｒ、坪量７０ｇ／ｍ^２）に乾燥質量で塗工量が５ｇ／ｍ^２となるようにバー塗工を行い、１１０℃で１０分間熱風乾燥して塗工シートを得た。その後、金属ロールと弾性ロールで構成されたキャレンダーに線圧１４０ｋｇ/ｃｍ、ロール温度４０℃、速度１０ｍ／ｍｉｎで３回通紙して塗工面の平滑化処理を行った。印刷用紙としての品質を評価するため、７５度光沢、平滑度、透気度を測定した結果を表３に示す。

Example 12
Acrylic latex (product name: Movinyl 718, manufactured by Nichigo Movinyl Co., Ltd.) and water are added as binders to the fine particle dispersion after the aggregation treatment produced in Example 7 and Example 8, and the mixture is stirred well to be uniform. Coating solution. The mixing ratio is silica: latex = 100: 30 in terms of solid content mass ratio, and the total solid content concentration is 15%. This coating solution is applied to a commercially available A4 size PPC paper (manufactured by Fuji Xerox Office Supply Co., Ltd., trade name: color / monochrome recycle paper C2r, basis weight 70 g / m ² ) with a dry mass and a coating amount of 5 g / m. Bar coating was performed so as to be ^2, and hot air drying was performed at 110 ° C. for 10 minutes to obtain a coated sheet. Thereafter, the coated surface was smoothed by passing three times through a calender composed of a metal roll and an elastic roll at a linear pressure of 140 kg / cm, a roll temperature of 40 ° C., and a speed of 10 m / min. Table 3 shows the results of measuring the 75-degree gloss, smoothness, and air permeability in order to evaluate the quality of the printing paper.

Comparative Example 5
A coated sheet was prepared in the same manner as in Example 12 using the fine particle dispersion before aggregation treatment used in Example 7 and Example 8, and this was used as Comparative Example 5.

実施例１〜９が示しているように、各種微粒子分散液を湿式媒体ミルで処理すると、容易に平均粒子径を大きくすることができ、その大きさは使用する粉砕媒体の種類(真比重)、処理時間、媒体ミルの種類などでかなり広範囲に制御することができた。また、処理によって細孔容積の増大が起こった。一方、高速回転式ホモミキサーや高圧ホモジナイザーで微粒子分散液を処理した場合には、平均粒子径や細孔容積に違いは検出できなかった(比較例１及び比較例２)。処理により微粒子分散液の増粘やゲル化は起こらなかったので、粒子径や細孔容積を応用製品に合わせて調整することに利用できる。
詳細に見ると真比重が大きいジルコニアビーズを用いると、短時間で粒子径を大きくすることができ(実施例１)、一方真比重が小さいガラスビーズを用いた場合には凝集が比較的ゆっくり起こった（実施例３）。同一粉砕媒体を用いた場合には、容器駆動媒体ミルより、媒体攪拌ミルの方が短時間で凝集が起こった（実施例１及び実施例４）。
また、大き目の粉砕媒体を使用し、比較的長時間処理を行った試料を走査型電子顕微鏡で観察したところ、扁平な形状であることを見出した(実施例７及び実施例８)。
実施例１〜４で得られた凝集後の微粒子を用いてインクジェット記録シートを作成したところ、凝集前の微粒子と比較して、インク吸収性と塗膜のひび割れが大きく改善した（実施例１０及び比較例３）。インク吸収性は細孔容積が大きいほど良好な傾向にあり、細孔容積が元々大きい微粒子を凝集処理してインクジェット記録シートに使用するとインク吸収性はさらに改善された（実施例１１及び比較例４）。
実施例７及び実施例８で得られた扁平化した微粒子分散液を使用して、印刷用紙を製造したところ、光沢、平滑度、透気度が大幅に向上した（実施例１２及び比較例５）

As shown in Examples 1 to 9, when various fine particle dispersions are treated with a wet medium mill, the average particle diameter can be easily increased, and the size is the type of the grinding medium used (true specific gravity). It was possible to control over a wide range depending on the processing time and the type of media mill. In addition, the pore volume increased due to the treatment. On the other hand, when the fine particle dispersion was treated with a high-speed rotating homomixer or a high-pressure homogenizer, no difference was detected in the average particle diameter or pore volume (Comparative Example 1 and Comparative Example 2). Since the treatment did not cause thickening or gelation of the fine particle dispersion, it can be used to adjust the particle diameter and pore volume according to the application product.
In detail, when zirconia beads having a large true specific gravity are used, the particle diameter can be increased in a short time (Example 1). On the other hand, when glass beads having a small true specific gravity are used, aggregation occurs relatively slowly. (Example 3). When the same pulverization medium was used, the medium agitation mill agglomerated in a shorter time than the container drive medium mill (Examples 1 and 4).
Further, when a comparatively long processing sample using a large grinding medium was observed with a scanning electron microscope, it was found to have a flat shape (Examples 7 and 8).
When the ink jet recording sheet was prepared using the fine particles after aggregation obtained in Examples 1 to 4, the ink absorptivity and cracking of the coating film were greatly improved as compared with the fine particles before aggregation (Example 10 and Comparative Example 3). The larger the pore volume, the better the ink absorptivity, and the ink absorptivity was further improved when the microparticles originally having a large pore volume were agglomerated and used in an ink jet recording sheet (Example 11 and Comparative Example 4). ).
When the printing paper was manufactured using the flattened fine particle dispersion obtained in Example 7 and Example 8, the gloss, smoothness, and air permeability were greatly improved (Example 12 and Comparative Example 5). )

  The present invention can be used as a simple method for increasing the average particle diameter, increasing the pore volume, and flattening without impairing the dispersion state of the fine particle dispersion, thereby improving the quality of the product using the fine particles. Available to: For example, it can be used for the production of inks, paints, toners, cosmetics, resin fillers, coated sheets and the like.

Claims (8)

A fine particle dispersion having a mean particle diameter D ₀ of 1 μm or less by a dynamic light scattering method is agglomerated by treatment with a wet medium mill, and the mean particle diameter D is D> 2D ₀ . Modification method.   2. The method for modifying a fine particle dispersion according to claim 1, wherein the wet medium mill is a wet medium stirring mill. The method for modifying a fine particle dispersion according to claim 1 or 2, wherein the grinding medium of the wet medium mill is beads having a true specific gravity of 5 g / cm ³ or more.   A fine particle dispersion produced by the method according to any one of claims 1 to 3, wherein the fine particles after aggregation treatment have an average particle diameter D of 3 µm or less.   The fine particle dispersion according to claim 4, wherein the fine particles after the aggregation treatment have a pore volume of 0.4 to 2.0 ml / g by a nitrogen adsorption method.   The fine particle dispersion according to claim 4 or 5, wherein the fine particles after the aggregation treatment are flat particles having an aspect ratio (average diameter / thickness) of 3 to 50.   The fine particle dispersion according to any one of claims 4 to 6, wherein the fine particles are silica.   A coating sheet produced by applying a coating liquid containing the fine particle dispersion according to any one of claims 4 to 7 on a support.