JP2005154235A - Silica minute particle dispersion and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silica minute particle dispersion containing no gel nor macro particle and useful for forming an ink reception layer for a smooth and high gloss inkjet recording sheet, and its manufacturing method. <P>SOLUTION: In this manufacturing method of a silica minute particle dispersion, an active silicate aqueous solution having total concentration of cations comprising a sodium ion, an aluminum ion, and a calcium ion of 1-20 ppm is used in a manufacturing method of a silica minute particle dispersion by forming a silica minute particle dispersion by adding an active silicate aqueous solution little by little in a hot water or by heating an active silicate aqueous solution, then adding an alkali before the dispersion forms a precipitate or gels to stabilize the minute particles, and adding the active silicate aqueous solution little by little while keeping a stable condition to grow the silica minute particles. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a silica fine particle dispersion and a method for producing the same. More specifically, since the silica fine particle dispersion does not contain gel or giant particles and forms a smooth and high gloss coating film, the silica fine particle dispersion is suitable for producing an inkjet recording sheet excellent in gloss. About.

  In recent years, inkjet recording methods have been widely spread due to the rapid progress of high image quality and high-speed printing. In producing an ink jet recording sheet, it is known to mainly apply an inorganic pigment as an ink receiving layer together with a binder in order to provide high ink absorbability. Among inorganic pigments, silica is widely used as a suitable pigment.

  Furthermore, an ink jet recording sheet for obtaining photographic image quality requires an ink receiving layer that is as transparent and glossy as possible in order to obtain a high color density and photographic texture in addition to high ink absorptivity. In order to form such a receiving layer, colloidal silica fine particles are preferably used.

  Colloidal silica is widely known as colloidal silica fine particles, but most of them are true spherical particles, and each primary particle is monodispersed without agglomeration. For this reason, in a dry state, the particles are densely packed and there are very few voids between the particles. Accordingly, a coating film obtained using monodispersed colloidal silica is inferior in ink absorbability in ink jet printing and is not suitable as an ink receiving layer.

  On the other hand, a method of linking the above monodispersed colloidal silica to agglomerate into a non-spherical shape is known, and as described in Patent Documents 1 to 5 and the like, the active silicic acid has a water solubility of 2 or more. By adding a salt and aging with heat, colloidal silica linked and aggregated in an elongated chain can be obtained.

  The colloidal silica linked and aggregated in the above chain form has a larger interparticle void in a dry state than a monodispersed general colloidal silica, and a more porous coating film can be obtained. However, the ink absorption capacity is not yet sufficient for application as an ink receiving layer in inkjet recording, and colloidal silica fine particles having a more porous aggregated structure are required.

  In view of the above requirements, the present inventors have obtained that fine secondary particles formed by three-dimensional aggregation of silica primary particles are colloidally dispersed in water, and are porous by drying. Invented and applied for a silica fine particle dispersion capable of forming a high-quality and highly transparent coating film and a method for producing the same (see Patent Document 6). The coating film obtained by drying the silica fine particle dispersion according to the present invention can absorb a large amount of ink and has high transparency and high gloss, so that the above-mentioned photographic image quality can be obtained. Can be suitably used as an ink-receiving layer.

  In the method for producing a silica fine particle dispersion disclosed in Patent Document 6, various types of colloidal silica fine particles having different particle properties such as particle diameter, specific surface area, and pore volume are synthesized by changing synthesis conditions. can do. For this reason, ink jet recording sheets prepared using silica fine particle dispersions having different particle physical properties can be various in ink absorptivity, coating film transparency, and the like.

In the method for producing a silica fine particle dispersion disclosed in Patent Document 6 above, an active silicic acid aqueous solution is added little by little in hot water or the active silicic acid aqueous solution is heated to produce a silica fine particle dispersion, Before precipitation occurs or before gelation, an alkali is added to stabilize the silica fine particles, and an aqueous silica solution is added to grow the silica fine particles while maintaining the stable state. In this method, gel particles and silica particles are sometimes generated, and when used in the ink receiving layer of an ink jet recording sheet, the smoothness of the surface is lowered and the gloss may be lowered. There wasn't.
JP-A-1-317115 Japanese Patent Laid-Open No. 4-65314 Japanese Patent Laid-Open No. 4-187512 Japanese Patent Laid-Open No. 7-118008 Japanese Patent Laid-Open No. 10-166715 JP 2001-354408 A

  An object of the present invention is to provide a silica fine particle dispersion containing no gel content or giant particles and a method for producing the same, thereby providing an inkjet recording sheet having a smooth and high gloss.

  As a result of intensive studies, the present inventors have found that the above object can be achieved by the following method. The present invention includes the following aspects.

(1) A silica fine particle dispersion is formed by adding an aqueous solution of active silicate to hot water little by little, or heating the aqueous solution of active silicate, and before the dispersion is precipitated or gelled, In the method for producing a silica fine particle dispersion in which the silica fine particles are grown by adding a small amount of an active silicic acid aqueous solution while maintaining a stable state to grow silica fine particles. An active silicic acid aqueous solution having a total concentration of cations consisting of ions, magnesium ions and calcium ions of 1 to 20 ppm is used.

(2) The method for producing a silica fine particle dispersion according to (1), wherein the concentration of sodium ions in the active silicic acid aqueous solution is 1 to 15 ppm.

(3) The active silicic acid aqueous solution is prepared by treating a sodium silicate aqueous solution with an H-type strongly acidic cation exchange resin to remove cations, and the H-type strongly acidic cation exchange resin The method for producing a silica fine particle dispersion according to (1) or (2), wherein the regeneration level is 1.0 to 3.0 eq-HCl / eq-R.

(4) The active silicic acid aqueous solution is adjusted to an ion exchange capacity of 1.5 times or more with respect to the total amount of cations composed of sodium ion, aluminum ion, magnesium ion and calcium ion in the sodium silicate aqueous solution. Any of (1) to (3), wherein the H-type strongly acidic cation exchange resin is produced by treating the aqueous sodium silicate solution to remove cations. 2. A method for producing a silica fine particle dispersion according to item 1.

(5) The rate of adding the active silicic acid aqueous solution while maintaining the stable state is a rate of 0.001 to 0.1 mol / min in terms of SiO ₂ per 1 mol of SiO ₂ contained in the silica fine particles. The method for producing a silica fine particle dispersion according to any one of items (1) to (4), wherein:

(6) The pore volume of the silica fine particle dispersion a nitrogen adsorption method using a specific surface area of 300m ² / g~1000m ² / g of silica fine particles in prior to the growth and scope pore diameter less 100 nm, is 0. The method for producing a silica fine particle dispersion according to any one of items (1) to (5), wherein the amount is 2 to 2.0 ml / g.

(7) the post-growth of the silica particle dispersion liquid nitrogen adsorption method using a specific surface area of ^{50m 2} / ^g~400m 2 / g of silica fine particles in an average secondary particle diameter of 20Nm～800nm, and pore size is less 100nm The method for producing a silica fine particle dispersion according to any one of items (1) to (6), wherein the pore volume in the range is 0.4 to 2.0 ml / g.

(8) A silica fine particle dispersion produced by the method described in any one of (1) to (7).

(9) An ink jet recording sheet in which a coating liquid containing the silica fine particle dispersion described in (8) is coated on a support.

  In the said invention, the uniform silica fine particle dispersion liquid which does not contain a gel part and a huge particle can be obtained. Further, since this silica fine particle dispersion does not contain a gel content or giant particles, the coated film has high smoothness and glossiness when applied, and is suitable for producing an inkjet recording sheet.

  The method for producing silica fine particles of the present invention comprises an active silicic acid aqueous solution adjustment step, a seed solution preparation step, and a growth step. Hereafter, each process of this invention is demonstrated in order.

  First, the active silicic acid aqueous solution adjusting step will be described in detail. The active silicic acid aqueous solution in the present invention is produced by dissolving an alkali metal silicate in distilled water and treating it with an H-type strongly acidic cation exchange resin.

As the alkali metal silicate, lithium silicate, sodium silicate, and potassium silicate are available as commercial industrial products, but it is preferable to use inexpensive sodium silicate. It is convenient to use a commercially available sodium silicate in the form of an aqueous solution, and it is preferable to use a so-called sodium water glass of 2 to 4 as the SiO ₂ / Na ₂ O molar ratio.

The alkali metal silicate, particularly sodium silicate, is diluted with water, preferably with pure water, and diluted to 1 to 6% by mass, preferably 2 to 5% by mass as SiO ₂ concentration. . When the concentration is less than 1% by mass, the productivity of silica fine particle production is poor. Conversely, when the concentration exceeds 6% by mass, the column may be clogged by forming a gel when treated with an ion exchange resin.

  An ion exchange resin is a kind of synthetic resin produced by introducing an exchange group having ion exchange ability into a three-dimensional crosslinked polymer substrate. For the kind, a cation exchange resin that exchanges cations, an anion is used. There are anion exchange resins to be exchanged, chelate resins that capture chelates and capture ions, and special resins such as synthetic adsorbents that do not have exchange groups. In the present invention, a resin that exchanges cations is used. Use of strongly acidic cation exchange resins having ion exchange properties in the region is suitable for ion exchange of alkali silicates, particularly sodium silicate. Usually, strongly acidic cation exchange resins are commercially available in the form of Na salts, and are used for the production of activated silicic acid by replacing Na with protons through an acid treatment called regeneration to form H.

  The above ion exchange resin can be used repeatedly by regenerating, and there are also batch processing and a method of passing through a column (resin tower) and processing, but a batch type reversible reaction occurs, Since equilibrium is considered to be established, it is more efficient to perform the liquid flow using a column method. The regeneration is usually carried out with an aqueous hydrochloric acid solution or an aqueous sulfuric acid solution. Since strongly acidic cation exchange resins are strongly acidic, they are difficult to regenerate, and it is important to adjust the regeneration level (the amount of regenerant used). It is usual to use [eq-regenerant / eq-R] as the unit of regeneration level, which is the ratio of the equivalent of the regenerant (eq-regenerant) to the ion exchange capacity (eq-R) of the ion exchange resin. Is shown. The H-type strongly acidic cation exchange resin preferably has a regeneration level adjusted to 1.0 to 3.0 eq-regenerant / eq-R, more preferably 1.5 to 2.5 eq-regenerant / eq-R. It is. If the regeneration level is less than 1.0, it is difficult to adjust the total concentration of sodium ion, aluminum ion, magnesium ion and calcium ion in the active silicic acid to 1 to 20 ppm, and at a regeneration level exceeding 3.0, Not only has the quality of activated silicic acid almost unaffected, but the cost of the regenerant increases.

  The amount of H-type strongly acidic cation exchange resin when passing through an alkali metal silicate aqueous solution, particularly a sodium silicate aqueous solution, is 1.5 times the total cation amount in the silicate aqueous solution. It is preferable to adjust so that it may become above.

  Furthermore, the volume velocity is preferably 2 to 10 when the aqueous silicate solution is passed through the H-type strongly acidic cation exchange resin column.

  The total concentration of sodium ions, aluminum ions, magnesium ions and calcium ions in the activated silicic acid can be adjusted to 1 to 20 ppm by adjusting the regeneration level of the ion exchange resin and the amount of the ion exchange resin within the above range. . When sodium water glass is used as the silicate, the cation in the active silicic acid is mostly sodium ions, so the concentration is preferably adjusted to 1 to 15 ppm. The purpose can be achieved by adjusting the resin regeneration level and the amount of ion exchange resin within the above ranges. When the total concentration exceeds 20 ppm, it is recognized by the naked eye that gel particles and coarse particles are mixed in the silica fine particle dispersion, and even when used in the ink receiving layer of an ink jet recording sheet, the surface is not smooth and glossy. Also decreases. Sodium ions, aluminum ions, magnesium ions, and calcium ions in activated silicic acid have the effect of promoting the aggregation of silica fine particles. When 20 ppm or more is present, the aggregation of silica fine particles occurs rapidly, resulting in gel and coarse particles. Presumed to be generated. However, if the concentration is less than 1 ppm, the silica fine particles are not sufficiently aggregated and the pore volume of the silica fine particles becomes small, and the ink absorbability tends to be lowered.

Next, the seed solution adjustment step will be described in detail. The seed liquid in the present invention is a liquid in which secondary agglomerated particles formed by agglomeration of fine silica primary particles are colloidally dispersed, and the physical properties of the secondary agglomerated particles are the ratio by the nitrogen adsorption method. surface area is desirably 300m ² / g~1000m ² / g, pore volume is 0.4ml / g~2.0ml / g. When the pore volume is smaller than this, the pore volume of the silica fine particles finally obtained and the ink absorptivity of the coating film using the dispersion liquid are lowered, making it unsuitable as an ink receiving layer.

The active silicic acid aqueous solution preferably has a SiO ₂ concentration of 1 to 6% by mass, more preferably 2 to 5% by mass and a pH of 2 to 4. When the pH of the activated silicic acid is greater than 4, gelation of the activated silicic acid aqueous solution may proceed in a short time.

  The seed solution is produced using the above-mentioned active silicic acid aqueous solution as a raw material, and there are two types of methods. The first method is to add the active silicic acid aqueous solution little by little to heated water (hot water). Is the method.

  The heating temperature of the water to which the active silicic acid aqueous solution is added is 60 ° C. or higher, preferably 80 ° C. or higher. When the pressure is applied at atmospheric pressure or higher, it is possible to set the temperature to 100 ° C. or higher. The lower the temperature, the slower the condensation rate of the active silicic acid, and lowers the production efficiency of the seed solution. Moreover, the pH of water is 2-8, More preferably, it is 4-7. When the pH is less than 2 or exceeds 8, the secondary particles of the primary particles generated by the condensation of active silicic acid do not proceed sufficiently, and the silica fine particles have a sufficient pore volume when used as a seed solution. May not be obtained.

  Although there is no restriction | limiting in particular in the addition method to hot water of active silicic acid aqueous solution, It is preferable to perform continuous addition at a fixed rate. Although not limited, the amount of hot water is preferably 0.2 to 5 times, more preferably 0.5 to 2.5 times the mass of the active silicic acid aqueous solution for producing the seed solution. . The addition rate of the active silicic acid aqueous solution is preferably 0.001 to 0.1 kg / min with respect to 1 kg of hot water.

The activated silicic acid condenses in hot water to first produce fine silica primary particles, which then aggregate to produce silica secondary agglomerated particles. The progress of the aggregation of the primary particles greatly depends on the SiO ₂ concentration and pH of the solution and the heating time. That is, as the amount of active silicic acid added to the hot water increases and the pH of the solution decreases toward the isoelectric point of silica (about pH 2.2), addition of the active silicic acid aqueous solution begins. As the heating time from time increases, secondary aggregation proceeds. Therefore, the charged ratio of the active silicic acid aqueous solution and hot water to be added and the addition rate of the active silicic acid aqueous solution to the hot water are set to optimum values in consideration of these tendencies.

  The progress of secondary aggregation can be easily visually recognized as a change in turbidity or a change in viscosity of the reaction solution. As the secondary aggregation progresses, the transparent reaction solution gradually becomes bluish. Further, as the aggregation proceeds, the turbidity and viscosity of the solution increase.

  Further, when the secondary agglomeration progresses, when used as a seed solution and grown under the same conditions, the average secondary particle diameter (silica fine particle aggregate diameter) of the final silica fine particle becomes a large particle diameter, resulting in pores. The volume tends to increase. The average secondary particle diameter of the secondary agglomerated particles in the seed solution is preferably 5 nm to 2000 nm, and more preferably 10 nm to 800 nm. Even if the average secondary particle diameter exceeds 2000 nm, the secondary particle diameter may be reduced due to alkali added in the growth step or mechanical force due to stirring, and it is not always necessary to make the average secondary particle diameter 2000 nm or less. Absent.

  However, if secondary aggregation in the seed solution proceeds excessively, gelation of the solution and precipitation of secondary aggregated particles may occur, and it becomes difficult to stabilize as a colloid even if alkali is added in the subsequent growth process. There is also a fear.

The second method for producing the seed solution is a method of heating the active silicic acid aqueous solution. The active silicic acid aqueous solution is preferably 1 to 6% by mass as SiO ₂ concentration, more preferably 2 to 5% by mass and an active silicic acid aqueous solution having a pH of 2 to 4.

  The heating temperature of the activated silicic acid aqueous solution is preferably 40 ° C. or higher. If it is less than 40 ° C., the condensation rate of silicic acid is slow, which may reduce the production efficiency of the seed solution. When the pressure is applied at atmospheric pressure or higher, it is possible to set the temperature to 100 ° C. or higher.

In the method of the present invention, the progress of secondary aggregation of the silica primary particles greatly depends on the SiO ₂ concentration of the active silicic acid aqueous solution and the heating temperature. That is, the higher the concentration of the active silicic acid aqueous solution and the higher the heating temperature, the faster the secondary aggregation proceeds. As secondary agglomeration progresses, when used as a seed solution and grown under the same conditions, the average secondary particle diameter tends to be larger and the pore volume tends to increase. The average secondary particle diameter of the secondary agglomerated particles in the seed solution is preferably 5 nm to 2000 nm, and more preferably 10 nm to 800 nm. Even if the average secondary particle diameter exceeds 2000 nm, the secondary particle diameter may be reduced due to the alkali added in the growth step or mechanical force due to stirring, and the average secondary particle diameter need not necessarily be 2000 nm or less. Absent.

  However, if secondary aggregation proceeds excessively, gelation of the solution is caused, and it may be difficult to stabilize the secondary aggregated particles as a colloid even if alkali is added in a later growth step.

  As described above, the seed solution can be manufactured by the above-described first and second methods. However, the seed solution can also be manufactured by a combination of the first and second methods. A method of dropping an acid aqueous solution is also possible. In addition, when precipitation or gelation occurs during the seed solution production, it can be re-dispersed with a strong mechanical share to obtain a seed solution, but the number of steps increases and the production cost increases. It is preferable to move to a secondary growth step before gelation occurs.

  Next, the growth process will be described in detail. The seed solution is an acidic solution immediately after production, and preferably has a pH of 4 or less. And even if it complete | finishes heating, it gelatinizes in a short time and is unstable. For this reason, alkali is added to make the seed solution an alkaline atmosphere, and the secondary aggregated particles of silica contained in the seed solution are stabilized as a colloid. Further, this alkali also acts as a catalyst for growing the primary silica particles constituting the secondary aggregated particles in the growth step of the present invention.

  The alkali used is not particularly limited, but hydroxides of alkali metal elements such as sodium hydroxide, potassium hydroxide and lithium hydroxide, alkaline earth metal hydroxides, alkali metal silicates, ammonia, quaternary Nitrogen compounds such as ammonium hydroxide and amines can be mentioned, and these alkalis are used alone or in combination.

The amount of alkali added is not particularly limited, but the amount of alkali necessary for adjusting the pH of the seed solution to 6.5 or more, more preferably pH 7 or more and pH 11 or less is desirable. More specifically, the alkali amount is preferably 0.001 to 1.0 mol, more preferably 0.01 to 0.1 mol, per 1 mol of silica (SiO ₂ ) contained in the seed solution. When the pH of the seed solution is less than 6.5, the condensation reaction of silicic acid is slow, and the production efficiency during the growth operation is lowered. On the other hand, when the pH of the solution exceeds 11, the silica is eluted in the solution, so that the yield of the silica content decreases.

  The alkali can be added to the seed solution at a time, or added in small amounts together with the active silicic acid aqueous solution added to the seed solution during the growth process, or mixed with the active silicic acid aqueous solution and added in small portions. And a method comprising a combination thereof. When an alkali is mixed with the active silicic acid aqueous solution and added to the seed solution, it is desirable to mix an alkali amount so that the pH of the active silicic acid aqueous solution becomes 7 or more. When the pH of the activated silicic acid aqueous solution is less than 7, the activated silicic acid aqueous solution may gel in a short time.

  In the growth process of the present invention, the seed solution is desirably heated to 60 ° C. or higher, preferably 80 ° C. or higher. When the temperature is low, the condensation rate of silicic acid is slow and the production efficiency is lowered.

An activated silicic acid aqueous solution is added little by little to the heated seed solution in order to grow each primary particle constituting the secondary agglomerated particles. The activated silicic acid added in the growth step is polymerized with respect to each primary particle constituting the silica secondary agglomerated particles in the seed solution, and increases the particle diameter of the primary particles. A large primary particle size means a small specific surface area. In the present invention, the specific surface area is adopted as a measure of the average particle diameter of the primary particles. By reducing the specific surface area in the growth process, that is, by increasing the primary particle diameter, when a coating film is prepared by mixing with a binder, it is possible to prevent cracking of the coating film in the drying process and to withstand practical use. It becomes a silica fine particle dispersion. The preferred range of the specific surface area in the present invention ^is 50m ² / g~400m 2 / g. In the case of non-aggregated true spherical silica particles, the relationship of primary particle diameter (nm) = 2720 / specific surface area (g / m ² ) is established, but even in the case of aggregated particles, this relationship is approximately Is established.

The amount of the active silicic acid aqueous solution added depends on the specific surface area (primary particle diameter) of the silica fine particles in the seed solution to be used, and the SiO ₂ solid content necessary for growing the primary particle diameter to the desired specific surface area. The active silicic acid aqueous solution corresponding to is added. The active silicic acid aqueous solution to be added is desirably added at a temperature of 60 ° C. or lower, preferably 40 ° C. or lower so that condensation does not proceed before addition to the seed solution.

  Although there is no restriction | limiting in particular in the addition method of active silicic acid aqueous solution, It is preferable to perform continuous addition at a fixed rate. Further, during the addition of the active silicic acid aqueous solution, a necessary amount of alkali may be added at any time in order to prevent the pH of the solution from decreasing.

The addition rate of the activated silicic acid aqueous solution to the heated seed solution is 0.001 to 0.1 mol / min in terms of SiO ₂ per mol of SiO ₂ contained in the seed particle aggregate in the seed solution. It is desirable to drop at a speed. When dropping at a rate exceeding 0.1 mol / min, new monodispersed primary particles may be generated, and the pore volume may be reduced.

  After completion of the addition of the active silicic acid aqueous solution, it is sufficiently stable even if it is cooled as it is. However, in order to complete the condensation of silicic acid, it is preferable to carry out heat treatment at a temperature of 70 ° C. or more for 1 to 4 hours. .

Silica fine particles after the growth step is completed, the specific surface area of ^{50m 2} / ^g~400m 2 / g, average secondary particle diameter 20Nm～800nm, and a pore volume ranging pore diameter less 100nm is 0.4 ml / g It is preferable that it is -2.0 ml / g. If the specific surface area is less than 50 m ² / g, the transparency is low when used in the ink receiving layer, so that a high printing density cannot be obtained. If the specific surface area exceeds 400 m ² / g, cracks are likely to occur when the ink receiving layer is applied. Therefore, it is not preferable. When the pore volume is smaller than 0.4 ml / g, the ink absorbability of the ink receiving layer using the pore volume is lowered, making it unsuitable as a silica fine particle dispersion for inkjet. On the contrary, when the pore volume exceeds 2.0 ml / g, the density of the coating film is too small and the mechanical strength is inferior, cracks during coating are large, and the coating film is easily damaged. May occur. When the average secondary particle diameter exceeds 800 nm, light scattering increases, and when used in the ink receiving layer, the print density and gloss tend to decrease.

  After completion of the growth process, the silica fine particle dispersion is preferably concentrated to a desired concentration by an evaporator, ultrafiltration or the like, and usually concentrated to 5 to 30% by mass and used for producing an ink jet recording sheet.

  There is no particular limitation on the method for producing an ink jet recording sheet using the silica fine particle dispersion of the present invention. The main material other than the silica fine particle dispersion is a binder, and other secondary materials can be added.

  As the binder, a water-soluble resin can be used, such as polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, polyacrylic acid, polyhydroxyethyl acrylate, polyacryloylmorpholine, water-soluble polyvinyl acetal, poly-N-vinylacetamide, poly-N. -Vinylformamide, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, methylcellulose, hydroxyethylmethylcellulose, carboxymethylcellulose, gelatin, casein, starch and the like can be exemplified, and can be used alone or in combination. Polyvinyl alcohol is particularly preferable.

  Further, an aqueous resin emulsion may be used as a binder. For example, conjugated diene polymer latex such as styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, acrylic polymer, vinyl copolymer latex such as styrene-vinyl acetate copolymer, polyurethane latex, Commonly used aqueous emulsions such as polyester latex can be used.

  The blending amount of the binder is about 5 to 100% by mass with respect to the solid content of the silica fine particles, and preferably 10% to 50% by mass.

  As a secondary material, mix an antifoaming agent to improve workability during coating, or to add a surfactant to improve the wettability of the base material and obtain a uniform coating layer Alternatively, starch particles or synthetic resin particles may be mixed in order to prevent sticking of the coated sheet and to improve paper passing properties. Various pigments can be added to adjust the transparency and surface gloss, and light resistance improvers such as UV absorbers and light stabilizers are added to improve the storability of printed images. You can also.

  As a support, it is generally used as a coating substrate such as fine paper, medium paper, coated paper, art paper, cast coated paper, paperboard, synthetic resin laminated paper, metallized paper, synthetic paper, white film, etc. Sheets can be used, but are not limited to these. These supports may be used after undercoating and providing a coating layer. Above all, when a base sheet with a smooth surface and relatively low liquid absorbency is used, such as synthetic resin laminated paper, metal-deposited paper, synthetic paper, white film, etc., it is preferable because a high gloss coating layer is obtained. is there. A coating layer with higher gloss can also be obtained by using a film transfer method or cast coating. These supports are provided with an undercoat layer if the adhesive strength with the coating layer formed on the surface is insufficient, or various easy adhesion treatments such as corona discharge treatment, plasma treatment, and flame treatment. be able to. The thickness of the support varies greatly depending on the application, but when an ink jet recording sheet is produced, it is preferably 50 to 500 μm in consideration of the paper passing property of the printer.

  As the coating apparatus, a known coating apparatus such as a bar coater, a roll coater, a blade coater, an air knife coater, a gravure coater, a die coater, a lip coater, a curtain coater, and a slide bead coater can be used. Not exclusively.

Coating amount is different greatly depending on the application of the coated sheet is not particularly limited, the total coating amount of all the layers after drying is preferably from 80 g / m ² approximately as weight, more preferably It is about 3 to 60 g / m ² . If the coating amount is less than 1 g / m ² , ink absorption may be insufficient, and if it is more than 80 g / m ² , curling tends to occur and the cost increases.

  A plurality of ink receiving layers may be provided. In that case, since the silica fine particle dispersion of the present invention is difficult to crack when dried, and the coating amount per coating can be increased, the silica fine particle dispersion is applied to the ink absorption layer close to the base sheet. It can also be used to impose a role of absorbing the solvent in the ink. That is, the silica fine particle-containing layer of the present invention can be provided on a support, and a gloss developing layer can be further provided thereon.

  Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited to these examples. In addition, the measuring method of each test item described in the Example and the comparative example is as follows.

(Measurement method of Na, Al, Mg, Ca ions in active silicic acid aqueous solution)
The active silicic acid aqueous solution was measured by inductively coupled plasma emission spectroscopy (ICP-AES) [trade name CIROS120, manufactured by Rigaku Corporation].

(Measurement method of gel content and coarse particles in silica fine particle dispersion)
30 ml of a silica fine particle dispersion having a concentration of 10% by mass was placed in a glass tube having a diameter of 3.5 cm and visually judged in three stages.
○: No gel content or coarse particles Δ: Small amount of gel content or coarse particles ×: Large amount of gel content or coarse particles

(Measuring method of average secondary particle size of silica fine particles)
Using a laser particle size distribution meter (trade name UPA250, manufactured by Nikkiso Co., Ltd.) by a dynamic light scattering method, the silica fine particle dispersion was measured in a sufficiently diluted state with distilled water. The average secondary particle diameter was a volume average value.

(Specific surface area of silica fine particles, pore volume measurement method)
The silica fine particle dispersion was dried at 105 ° C., and the specific surface area and pore volume of the obtained powder sample were pretreated using a gas adsorption specific surface area / pore distribution measuring apparatus (SA3100 type manufactured by Coulter). The measurement was conducted after vacuum degassing at 200 ° C. for 2 hours. Nitrogen was used as the adsorption gas. The value obtained by the BET method was used as the specific surface area, and the value of the total pore volume of pores having a pore diameter of 100 nm or less was used as the pore volume.

(Silica fine particle coating method)
A silica fine particle dispersion having a concentration of 10% by mass is mixed with a 10% by mass aqueous solution of a completely saponified polyvinyl alcohol (Kuraray Co., Ltd., trade name: PVA-140H), and the solid content of silica: PVA solid content = 100 parts by mass: 20. A paint adjusted to mass parts was prepared. This coating material was coated on a transparent polyethylene terephthalate film having a thickness of 100 μm (trade name: Lumirror 100-Q80D, manufactured by Toray Industries, Inc.) so that the coating amount was 20 g / m ² in terms of dry mass. The sheet was dried at 120 ° C.

(Method for measuring 75 ° glossiness of silica fine particle coating)
The 75 ° glossiness of the silica fine particle coating film (coating amount 25 g / m ² ) was measured based on ISO 8254-1 using a gloss meter (GM-26 PRO / AUTO) of Murakami Color Research Laboratory.

(Method for measuring haze of silica fine particle coating film)
The haze of the silica fine particle coating film (coating amount 25 g / m ² ) was measured according to JIS standard K7105.

(Ink absorbability of silica fine particle coating)
Two types of ISO-400 images (“High-Definition Color Digital Standard”) with the recommended setting print mode for Superfine exclusive paper of an inkjet printer (manufactured by EPSON, PM-970C) on a silica fine particle coating film (coating amount 25 g / m ² ) Image data ISO / JIS-SCID ", p13, image name: fruit basket, p14, image name candle, issued by the Japanese Standards Association), and visually evaluated the image quality in the following three stages.
○: There is no overflow of ink and the solid portion is uniform.
Δ: Ink overflow is somewhat noticeable in the solid print portion.
X: Overflow of ink is conspicuous as a whole, and the image is partially broken.

Example 1
(Adjustment of sodium silicate aqueous solution)
Distilled water is mixed with a sodium silicate aqueous solution (manufactured by Tosoh Sangyo Co., Ltd., No. 3 sodium silicate) having a SiO ₂ concentration of 30% by mass and a SiO ₂ / Na ₂ O molar ratio of 3.1 to obtain a SiO ₂ concentration of 4.3. 3000 g of a mass% dilute sodium silicate aqueous solution was prepared. The cations in the dilute sodium silicate aqueous solution were analyzed by inductively coupled plasma optical emission spectrometry, as shown in Table 1.

(Adjustment of active silicic acid aqueous solution)
A strong acid cation exchange resin (Amberlite IR120B Na, manufactured by Rohm and Haas Japan Co., Ltd.) having an ion exchange capacity of 2.0 meq / ml wet resin is left in pure water overnight, and then 1409 ml of this wet resin. Was packed into a 5 cm diameter glass column. The ion exchange capacity of this ion exchange column was 2,817 m equivalent, and the exchange capacity was 1.5 times that of the cation contained in the aqueous sodium silicate solution.
Next, 3.08 kg (4226 meq) of 5 mass% hydrochloric acid was passed through an ion exchange column and converted to the H form at a regeneration level of 1.5 eq-HCl / eq-R. Subsequently, the hydrochloric acid used for regeneration was removed by thoroughly washing with pure water having an electrical conductivity of 0.5 μs / cm. The aqueous sodium silicate solution was passed through the ion exchange column at a volume rate of 3 to obtain an active aqueous silicate solution. This activated silicic acid had a SiO ₂ equivalent concentration of 4.0% by mass and a pH of 2.75. Table 2 shows the metal ion concentration in the obtained active silicic acid aqueous solution.

(Adjustment of seed solution)
In a 5 liter glass reaction vessel equipped with a reflux, a stirrer, and a thermometer, 500 g of distilled water was heated to 90 ° C. While maintaining the hot water at 90 ° C., a total of 600 g of the above active silicic acid aqueous solution was added at a rate of 10.0 g / min to prepare a seed solution.

(Growth process)
In the above glass reaction vessel, 0.0146 mol of ammonia was added to 1100 g of the seed solution and stabilized. A total of 2500 g of the above active silicic acid aqueous solution was added to the stabilized seed solution at a rate of 10.0 g / min. After the addition of activated silicic acid was completed, the solution was kept as it was at 90 ° C. and left to stand for 1 hour to obtain a silica fine particle dispersion having a pH of 8.6. The measured values such as the secondary particle diameter at this time are shown in Table 2.

(Creation and evaluation of silica fine particle coating)
The silica fine particle dispersion was concentrated with an evaporator to obtain a silica fine particle dispersion having a concentration of 10% by mass. Using this, a silica fine particle coating film was prepared, and the coating film glossiness (75 °), haze value, and ink absorptivity were evaluated, and the results are shown in Table 3.

Example 2
The amount of the cation exchange resin was changed to 1314 ml (exchange capacity 1.4 times that of the cation contained in the aqueous sodium silicate solution), and in proportion to this, 2.87 kg (regeneration level) of 5% HCl for regeneration was used. 1.5 eq-HCl / eq-R). Table 2 shows the measured values of the metal ion concentration in the active silicic acid aqueous solution, the secondary particle diameter of the silica fine particle dispersion, and Table 3 shows the 75 ° glossiness, haze value, and ink absorbency of the coating film.

Example 3
The amount of cation exchange resin was changed to 1127 milliliters (exchange capacity 1.2 times that of the cation contained in the aqueous sodium silicate solution), and proportionally 5 mass% HCl for regeneration was 2.46 kg (regeneration level). 1.5 eq-HCl / eq-R). Table 2 shows the measured values of the metal ion concentration in the active silicic acid aqueous solution, the secondary particle diameter of the silica fine particle dispersion, and Table 3 shows the 75 ° glossiness, haze value, and ink absorbency of the coating film.

Comparative Example 1
The amount of the cation exchange resin was changed to 939 milliliters (1.0 times the exchange capacity of the cation contained in the sodium silicate aqueous solution), and 5 mass% HCl for regeneration was proportionally 2.05 kg (regeneration level). 1.5 eq-HCl / eq-R). Table 2 shows the measured values of the metal ion concentration in the active silicic acid aqueous solution, the secondary particle diameter of the silica fine particle dispersion, and Table 3 shows the 75 ° glossiness, haze value, and ink absorbency of the coating film.

Comparative Example 2
The amount of the cation exchange resin was changed to 751 ml (0.8 times the exchange capacity for the cation contained in the aqueous sodium silicate solution), and 5% HCl for regeneration was proportionally 1.64 kg (regeneration level). 1.5 eq-HCl / eq-R). Table 2 shows the measured values of the metal ion concentration in the active silicic acid aqueous solution, the secondary particle diameter of the silica fine particle dispersion, and Table 3 shows the 75 ° glossiness, haze value, and ink absorbency of the coating film.

Example 4
The same procedure as in Example 1 was performed, except that 5% HCl for regeneration was changed to 5.14 kg and the regeneration level was changed to 2.5 eq-HCl / eq-R. Table 2 shows the measured values of the metal ion concentration in the active silicic acid aqueous solution, the secondary particle diameter of the silica fine particle dispersion, and Table 3 shows the 75 ° glossiness, haze value, and ink absorbency of the coating film.

Example 5
The same procedure as in Example 1 was performed, except that 5% HCl for regeneration was changed to 2.06 kg and the regeneration level was changed to 1.0 eq-HCl · eq-R. Table 2 shows the measured values of the metal ion concentration in the active silicic acid aqueous solution, the secondary particle diameter of the silica fine particle dispersion, and Table 3 shows the 75 ° glossiness, haze value, and ink absorbency of the coating film.

Comparative Example 3
The same procedure as in Example 1 was performed, except that 5% by mass HCl for regeneration was changed to 1.44 kg and the regeneration level was changed to 0.7 eq-HCl / eq-R. Table 2 shows the measured values of the metal ion concentration in the active silicic acid aqueous solution, the secondary particle diameter of the silica fine particle dispersion, and Table 3 shows the 75 ° glossiness, haze value, and ink absorbency of the coating film.

Comparative Example 4
The same procedure as in Example 1 was performed, except that 5% HCl for regeneration was changed to 1.03 kg and the regeneration level was changed to 0.5 eq-HCl / eq-R. Table 2 shows the measured values of the metal ion concentration in the active silicic acid aqueous solution, the secondary particle diameter of the silica fine particle dispersion, and Table 3 shows the 75 ° glossiness, haze value, and ink absorbency of the coating film.

Comparative Example 5
The amount of the cation exchange resin was changed to 2,817 ml (exchange capacity three times that of the cation contained in the aqueous sodium silicate solution), and in proportion thereto, 10.28 kg of regeneration 5 mass% HCl (regeneration level 2. 5 eq-HCl / eq-R). Table 2 shows the measured values of the metal ion concentration in the active silicic acid aqueous solution, the secondary particle diameter of the silica fine particle dispersion, and Table 3 shows the 75 ° glossiness, haze value, and ink absorbency of the coating film.

  As shown in Table 2, by adjusting the total of specific cation concentrations in the active silicic acid to 1 to 20 ppm, a silica fine particle dispersion having no gel content or coarse particles can be obtained, and the secondary particle size can be obtained. The gloss and transparency of the coating film were excellent (Examples 1 to 5). When the total of specific cation concentrations exceeded 20 ppm, gels and coarse particles were generated, and the glossiness was significantly reduced (Comparative Examples 1 to 4). Interestingly, when the specific cation concentration was less than 1 ppm as in Comparative Example 5, the pore volume of the silica fine particles was greatly reduced, and the ink absorbability of the ink receiving layer was lowered, making it unsuitable. . Further, as shown in Table 3, an ink receiving layer using the silica fine particle dispersion produced by the method of the present invention was excellent in gloss expression and ink absorbability, and a highly transparent layer was obtained.

The silica fine particle dispersion obtained by the method of the present invention can be used for forming an ink receiving layer of an ink jet recording sheet, particularly a glossy ink jet recording sheet.

Claims (9)

Add activated silica aqueous solution little by little to hot water, or heat active silica aqueous solution to form silica fine particle dispersion, and add alkali before the dispersion precipitates or gels In the method for producing a silica fine particle dispersion in which the silica fine particles are grown by stabilizing the silica fine particles and then adding the active silicic acid aqueous solution little by little while maintaining a stable state. An active silicic acid aqueous solution having a total concentration of cations consisting of magnesium ions and calcium ions of 1 to 20 ppm is used. The method for producing a silica fine particle dispersion according to claim 1, wherein the concentration of sodium ions in the aqueous active silicic acid solution is 15 ppm or less. The active silicic acid aqueous solution is produced by treating a sodium silicate aqueous solution with an H-type strongly acidic cation exchange resin to remove cations, and the regeneration level of the H-type strongly acidic cation exchange resin is high. It is 1.0-3.0eq-HCl / eq-R, The manufacturing method of the silica fine particle dispersion liquid of Claim 1 or 2 characterized by the above-mentioned. The H-type active silicate aqueous solution is adjusted to have an ion exchange capacity of 1.5 times or more with respect to the total amount of cations composed of sodium ions, aluminum ions, magnesium ions and calcium ions in the sodium silicate aqueous solution. The silica fine particle according to any one of claims 1 to 3, wherein the silica fine particle is produced by removing the cation by treating the aqueous sodium silicate solution with a strongly acidic cation exchange resin. A method for producing a dispersion. The rate of adding the active silicic acid aqueous solution while maintaining the stable state is a rate of 0.001 to 0.1 mol / min in terms of SiO ₂ per mol of SiO ₂ contained in the silica fine particles, The method for producing a silica fine particle dispersion according to any one of claims 1 to 4. Wherein a silica fine particle dispersion a nitrogen adsorption method using a specific surface area of 300m ² / g~1000m ² / g of silica fine particles in prior to the growth, and the pore volume ranging pore diameter less 100nm is 0.2ml The method for producing a silica fine particle dispersion according to any one of claims 1 to 5, which is / g to 2.0 ml / g. Wherein a specific surface area by nitrogen adsorption method of the silica fine particles of the silica fine particle dispersion liquid after the growing ^{50m 2} / ^g~400m 2 / g, average secondary particle diameter of 20Nm～800nm, and pore size is less 100nm The method for producing a silica fine particle dispersion according to any one of claims 1 to 6, wherein the pore volume in the range is from 0.4 ml / g to 2.0 ml / g. A silica fine particle dispersion produced by the method according to any one of claims 1 to 7. An ink jet recording sheet, wherein a coating liquid containing the silica fine particle dispersion according to claim 8 is coated on a support.