JP2007099586A - Method for producing silica particulate-dispersed liquid, silica particulate-dispersed liquid and ink jet recording sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing silica particulate-dispersed liquid where a silica particulate-dispersed liquid free from the intrusion of gel components and coarse particles can be produced with high efficiency. <P>SOLUTION: The production method comprises a filtering stage where a silica particle-dispersed liquid comprising silica particulates with the average secondary particle diameter of ≤1 μm is filtered with a precoat filter obtained by precoating a filter body with a filtering assistant. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a silica fine particle dispersion, and more particularly to a method for producing a silica fine particle dispersion having an average secondary particle diameter of 1 μm (1000 nm) or less.

  Inkjet printers have many recording methods because of their low noise, ease of multicolor printing, high-speed recording, small size and low cost compared to other recording methods. Widely used in the direction. In recent years, printing of color images has become common with the spread of personal computers, digital cameras, and the like. With the development of such full-color and high-resolution techniques, ink-jet recording sheets are also required to have high ink absorbency and glossiness.

As a method for increasing ink absorbability, an ink jet recording sheet provided with a pigment-based ink receiving layer has been proposed. Silica or the like is used as the pigment, and those forming secondary particles in which primary particles are aggregated are preferably used. The ink absorbability is improved by the action of the voids between the primary particles and the secondary particles.
In addition, in order to give the recording sheet surface high glossiness, a pigment having a small particle diameter is selected.
That is, as a technique for achieving both ink absorptivity and glossiness, many recording sheets provided with a receiving layer containing a silica pigment that is a porous secondary particle having a small particle diameter have been proposed.

In order to form such a receiving layer, the present inventor is obtained by colloidally dispersing fine secondary particles formed by three-dimensional aggregation of primary silica particles in water. Proposed a silica fine particle dispersion capable of forming a porous and highly transparent coating film by the method and a method for producing the same (see Patent Document 1).
Since 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, as an ink receiving layer in the production of the inkjet recording sheet. It can be used suitably.
JP 2001-354408 A

However, in the method described in Patent Document 1, gel content and silica large particles sometimes occur, but the cause is not clear.
When such a coating liquid containing this silica fine particle dispersion is used in the ink receiving layer of an ink jet recording sheet, the smoothness of the surface may be lowered, and the gloss may be lowered. In addition, when an ink jet recording sheet coating solution containing a dispersion liquid containing even a small amount of coarse silica fine particles is coated on a support to form an ink jet recording sheet, fine spots occur on the coated surface. (See FIG. 5). When printing is performed on such an ink jet recording sheet, there is a problem that the printing quality is extremely low.
In order to obtain an ink jet recording sheet having excellent gloss, it has become clear that it is necessary to remove particles of at least 5 μm or more from the silica fine particle dispersion.

It is conceivable to use a filter in order to remove the gel and coarse particles as described above from the silica fine particle dispersion.
However, as a result of studies by the present inventors, it has been found that when a colloidal silica solution is applied to a normal filter, the filter medium life is remarkably shortened due to clogging of the filter, resulting in poor productivity. It was also found that the coarse particles could not be removed sufficiently even after filtering.

  The present invention has been made in view of the above circumstances, and is a method for producing a silica fine particle dispersion capable of efficiently producing a silica fine particle dispersion free from the incorporation of gel or coarse particles, and silica obtained thereby. It is an object of the present invention to provide a fine particle dispersion and an ink jet recording sheet which is excellent in smoothness and glossiness and free from defects such as spots using the dispersion.

As a result of intensive studies, the present inventors have found that these problems can be solved by filtering the silica fine particle dispersion with a filter pre-coated with a filter aid, thereby completing the present invention. It was.
The present invention includes the following embodiments.
[1] A silica fine particle dispersion characterized by having a filtration step of filtering a silica fine particle dispersion containing silica fine particles having an average secondary particle diameter of 1 μm or less with a precoat filter having a filter body precoated with a filter aid. Manufacturing method.
[2] The method for producing a silica fine particle dispersion according to [1], wherein the filter aid is added to the silica fine particle dispersion, and then filtered through the precoat filter.
[3] The silica fine particle dispersion of [1] or [2], wherein the maximum differential pressure between the inlet pressure and the outlet pressure of the precoat filter when the silica fine particle dispersion is filtered through the precoat filter is 0.05 MPa or less. Liquid manufacturing method.
[4] The method for producing a silica fine particle dispersion of [1] to [3], wherein the filter aid pre-coated on the precoat filter and the filter aid added to the silica fine particle dispersion are both cellulose fibers. .
[5] The method for producing a silica fine particle dispersion according to [1] to [4], wherein a pore volume of the silica fine particles by a nitrogen gas adsorption method is 0.4 mL / g to 2.0 mL / g.
[6] the method for producing a silica fine particle dispersion of the specific surface area of the silica fine particles is ^{50m 2 / g~400m 2 / g [} 1] ~ [5].
[7] The method for producing a silica fine particle dispersion according to [1] to [6], including a silica synthesis step for obtaining the silica fine particle dispersion by condensation of active silicic acid.
[8] A seed solution generating step in which the silica synthesis step generates a seed solution by supplying activated silicic acid and heating, and an aggregation stopping step of adding alkali to the seed solution to stop the aggregation of silica fine particles. A method for producing a silica fine particle dispersion according to [1] to [7], further comprising a growth step of growing silica fine particles by adding active silicic acid to the seed solution.
[9] A silica fine particle dispersion produced by the production method of [1] to [8].
[10] The silica fine particle dispersion of [9], wherein the limit of the secondary particle diameter of the silica fine particles by the dynamic light scattering method is less than 5 μm.
[11] An ink jet recording sheet obtained by applying an ink jet recording sheet coating liquid containing the silica fine particle dispersion of [9] or [10].

According to the method for producing a silica fine particle dispersion of the present invention, gel components and coarse particles can be removed and the filter is not clogged with the above-described configuration.
Therefore, a uniform silica fine particle dispersion containing no coarse particles can be efficiently produced.
Also, according to the ink jet recording sheet in which the coating liquid for ink jet recording sheet containing the silica fine particle dispersion of the present invention is coated on the support, the coating surface is beautiful because the coating film has excellent smoothness and gloss. , Printing quality can be improved.

<Manufacturing method>
Hereinafter, the method for producing a silica fine particle dispersion of the present invention will be described by taking, as an example, a method of producing a silica fine particle dispersion produced in the silica synthesis step using an active silicic acid aqueous solution by filtering with a precoat filter.
Each step will be described below in order.

[Silicic acid production process]
First, an active silicic acid aqueous solution for producing a silica fine particle dispersion is produced.
The active silicic acid aqueous solution can be obtained, for example, by a method of subjecting an alkali metal silicate aqueous solution to an ion exchange treatment using a hydrogen type cation exchange resin.
The alkali metal silicate used for the generation of the active silicic acid aqueous solution may be a commercially available industrial product, and has a SiO ₂ / M ₂ O (where M represents an alkali metal atom) molar ratio of about 2 to 4. Sodium water glass is preferably used.

The SiO ₂ concentration of the aqueous alkali metal silicate solution when performing the ion exchange treatment is preferably 1 to 6% by mass. When the SiO ₂ concentration exceeds 6% by mass, the viscosity of the solution in the ion exchange resin column tower becomes remarkable and the treatment becomes difficult. On the other hand, when the SiO ₂ concentration is less than 1% by mass, the amount of water in the reaction solution increases, which may reduce the production efficiency.
The active silicic acid aqueous solution is preferably 1 to 6% by mass, more preferably 2 to 5% by mass in terms of SiO ₂ concentration. Moreover, it is preferable that pH is 2-4.

[Silica synthesis process]
In the example shown in FIG. 4, the silica synthesis step includes small steps of a seed solution generation step, an aggregation stop step, and a growth step.
Below, each small process of a silica synthesis process is demonstrated.

(Seed liquid production process)
In the seed solution generation step of FIG. 4A, seed particles are generated by supplying and heating an active silicic acid aqueous solution into a vessel for silica synthesis, and a seed solution is obtained as a dispersion of seed particle aggregates.
In the seed liquid generation step, the liquid (active silicic acid aqueous solution) in the container is reacted for a predetermined time in a state of being heated to a constant temperature by a method such as circulating heating to generate and agglomerate seed particles.

The seed solution obtained by the seed solution generation step of the present invention is a dispersion in which porous seed particle aggregates obtained by agglomerating seed particles are colloidally dispersed. Seed particle agglomerates, a specific surface area by nitrogen adsorption method 300m ² / g~1000m ² / g, pore volume of 0.4mL / g~2.0mL / g, preferably 0.5 mL / g to 2. It is preferably 0 mL / g.

The average secondary particle diameter of the seed particle aggregate is not particularly limited, but is preferably 5 nm to 2000 nm, and more preferably 10 nm to 600 nm. Even if the average secondary particle diameter of the seed particles exceeds 1000 nm, the secondary particle diameter may be reduced due to alkali added in the growth process or mechanical force due to stirring, and the average secondary particles of the seed particle aggregate are not necessarily limited. The diameter need not be 1000 nm or less.
In the present invention, the average secondary particle diameter is a value measured by a dynamic light scattering method and calculated from an analysis using a cumulant method. At this time, the measurement is performed in a state where the dispersion in which the silica fine particles are dispersed is sufficiently diluted in water.

  The concentration of the seed particle aggregate is desirably 0.05 to 10.0% by mass in terms of silica. If the seed-particle aggregate concentration in terms of silica is less than 0.05% by mass, new seed particles may be generated in the process of growing the seed particle aggregate later, and the particle size distribution of the resulting particles is broad. This is not preferable. On the other hand, when the silica equivalent concentration of the seed particle aggregates exceeds 10% by mass, excessive aggregation of the particles may proceed, and in some cases, gelation may occur.

In the seed solution generation step, as a first method, there is a method in which an aqueous silicic acid solution is supplied into a reaction vessel, and this is heated by a method such as circulation heating to generate a seed solution.
In the seed solution generation step, as a second method, first, water is supplied into the reaction vessel, and this is heated by a method such as circulating heating to obtain hot water, and then the hot water in the reaction vessel is converted into hot water in the reaction vessel. There is a method of generating a seed solution by adding an activated silicic acid aqueous solution. This method is characterized in that it is easy to control the average secondary particle size of silica to a desired size and that the particle size distribution is narrow.

When the seed solution is generated using a method in which the active silicic acid aqueous solution is directly supplied into the reaction vessel and heated as in the first method described above, the reaction is performed for a certain period of time while heating to a certain temperature. The heating temperature is preferably 40 ° C. or higher, more preferably 70 to 95 ° C., and particularly preferably 86 to 93 ° C.
When the heating temperature is less than 40 ° C., the condensation rate of silicic acid is slow, and the production efficiency of the seed solution is reduced. When the heating temperature exceeds 95 ° C., the pressure in the reaction vessel may increase rapidly due to bumping.
The heating reaction time is preferably 0.5 to 4 hours, more preferably 1 to 3 hours, and particularly preferably 1.1 to 2 hours.
If the heating time is 0.5 hours or less, the condensation of silicic acid may be insufficient, and if it exceeds 4 hours, the productivity is lowered.

The progress of seed particle aggregation in the first method largely depends on the SiO ₂ equivalent concentration in the active silicic acid aqueous solution and the heating time. That is, as the concentration of the active silicic acid aqueous solution is increased and the heating time is increased, the aggregation of the seed particles can be advanced.
As the seed particles agglomerate, the average secondary particle diameter becomes larger and the pore volume increases when grown as the seed solution under the same conditions. Further, when the aggregation of the seed particles proceeds excessively, gelation of the solution is caused, and even when alkali is added in the condensation stop process described later, it cannot be stabilized as a colloid and becomes unsuitable as a seed solution. For this reason, it is preferable to set the SiO ₂ concentration and the heating time to optimum values in consideration of these points.
SiO ₂ concentration in the active silicic acid aqueous solution is preferably 1 to 6 wt%, more preferably 3 to 5 wt%.

Moreover, when producing | generating a seed liquid using the method of adding active silicic acid aqueous solution with respect to hot water like the above-mentioned 2nd method, the temperature of the hot water to which active silicic acid is added is 50 degreeC or more. It is preferable to set it as 70 degreeC or more. When the temperature of the hot water is less than 50 ° C., the condensation rate of silicic acid is slow, and the production efficiency of the seed solution is reduced.
Further, the pH of the water used by being supplied into the reaction vessel is preferably 8 or less, more preferably 3 or more and 7 or less. When the pH exceeds 8, the aggregation of seed particles caused by the condensation of silicic acid does not proceed sufficiently, and silica fine particles having a sufficient pore volume cannot be obtained when used as a seed solution. In addition, the frequency with which the added active silicic acid is used for the growth of existing seed particles without generating new seed particles increases, and the generation efficiency of the seed liquid decreases. When the pH is less than 3, the condensation rate of silicic acid is slowed and the production efficiency of seed particles is lowered.
Moreover, it is preferable not to add active silicic acid at once and to add dropwise little by little during reaction time.
The heating reaction time is preferably 0.5 hours or more, more preferably 1 to 3 hours, and particularly preferably 1.1 to 2 hours, from the viewpoint of efficiently performing the reaction.

Further, the progress of seed particle aggregation in the second method also depends greatly on the SiO ₂ solid content concentration in the solution and the heating time, as in the first method. That is, as the amount of active silicic acid to be added to hot water is increased and the pH of the solution is decreased toward the isoelectric point of silica (about pH 2.2), As the heating time is increased, seed particles agglomerate.
Further, as the seed particles agglomerate, the average secondary particle diameter becomes larger and the pore volume increases when grown in the growth step described later. In addition, if the seed particles agglomerate excessively, gelation of the solution and precipitation of the seed particle aggregates will be caused, and even if alkali is added in the aggregation stop step described later, it cannot be stabilized as a colloid. It becomes unsuitable as a seed solution. Therefore, it is preferable to set the charging ratio of the active silicic acid aqueous solution and water and the addition rate of the active silicic acid aqueous solution to the hot water to optimum values in consideration of these tendencies.

  In the seed liquid generation process, the progress of seed particle aggregation is not linear with respect to the reaction time, but tends to progress exponentially. May cause gelation or precipitation. This phenomenon can be reduced by adding an antigelling agent. As an anti-gelling agent, a water-soluble organic solvent is known, but alcohol is most easy to use and is preferable. Any alcohol can be used as long as it has high water solubility, for example, methanol, ethanol, isopropyl alcohol, n-propyl alcohol, n-butanol, isobutanol, tert-butanol, ethylene glycol, propylene glycol. However, it is preferable to use methanol, ethanol, isopropyl alcohol, or n-propyl alcohol, which has a low boiling point, can be easily removed from the silica fine particle dispersion, and is inexpensive.

As a method for adding alcohol, of the two methods for producing seed solution described above, in the second method in which the water supplied to the reaction vessel is heated and the aqueous active silicic acid solution is dropped little by little, it is added in advance to hot water. However, in order to produce a silica fine particle dispersion having a large pore volume, seed particles can be agglomerated. Since it is necessary, it is preferably added immediately before shifting to the growth step. The same applies to the first method in which the active silicic acid aqueous solution is supplied to the reaction vessel as it is and heated, and may be added in advance to the active silicic acid, or may be added before shifting to the growth step described later. Although it is good, in order to produce a silica fine particle dispersion having a large pore volume, it is preferably added immediately before shifting to the growth step.
Moreover, as for the addition rate of alcohol, it is desirable that it is 10-300 mass parts with respect to the silica solid content in a solution.

In the seed liquid production step, it is preferable to add an alkylammonium salt. This has the advantage that the seed particle agglomeration is promoted and the production time of the seed liquid is shortened, and the stability of the fine particle dispersion is increased.
When the alkylammonium salt is not added, there is a problem that the viscosity rapidly increases as the concentration of the finally obtained silica fine particle dispersion increases, and gelation occurs in a short time. However, by adding an alkyl ammonium salt to prepare a silica fine particle dispersion, the above phenomenon can be greatly reduced.

  The alkylammonium salt to be added is not particularly limited. For example, monoammonium salt such as methylammonium salt, ethylammonium salt, propylammonium salt, butylammonium salt, laurylammonium salt, stearylammonium salt, dimethylammonium salt, diethylammonium salt Dialkylammonium salts such as salts, trialkylammonium salts such as trimethylammonium salts and triethylammonium salts, tetramethylammonium salts, tetraethylammonium salts, lauryltrimethylammonium salts, stearyltrimethylammonium salts, distearyldimethylammonium salts, alkylbenzyldimethylammonium salts And tetraalkylammonium salts such as salts. Of these alkylammonium salts, tetraalkylammonium salts are preferred because of the high effects described above, and tetramethylammonium salts are particularly preferred. When a tetramethylammonium salt is used, the effect of promoting the aggregation of seed particles can be obtained by adding a small amount, and the effect of improving the stability of the finally produced silica fine particle dispersion can also be obtained.

As the addition amount of the alkylammonium salt, it is preferable to add an amount of 0.05 to 1% with respect to the SiO ₂ equivalent mass contained in the active silicic acid aqueous solution used when the seed solution is generated.
In addition, as a method for adding the alkylammonium salt, in the first method described above, a method of adding in advance to hot water, and in a second method, a method of adding in advance to an aqueous solution of active silicic acid. preferable.

(Aggregation stop process)
In the aggregation stopping step of FIG. 4B, the seed solution is circulated and heated while adding a necessary amount of alkali to the seed solution in the reaction vessel, thereby stopping further aggregation of the seed particle aggregates in the seed solution. . The alkali added in the aggregation stopping step also acts as a condensation catalyst for active silicic acid added to the seed solution.
In this aggregation stopping step, it is preferable to heat the seed solution so that the temperature of the seed solution is 40 ° C. or higher, more preferably in the range of 70 to 95 ° C. By keeping the temperature of the seed solution in the above range, seed particles can be efficiently stopped from agglomeration.

In the present invention, the alkali used for stopping the aggregation of the seed solution includes, for example, ammonia water, hydroxide of an alkali metal element such as sodium hydroxide, potassium hydroxide, lithium hydroxide, alkaline earth metal hydroxide, Nitrogen compounds such as alkali metal silicates, quaternary ammonium hydroxides and amines can be used, and these alkalis can be used alone or in combination.
Among these alkalis, it is most preferable to use ammonia water because it is easy to control the pH of the solution and can be easily volatilized when producing a dry coating film. Moreover, when ammonia water is used for stopping the aggregation, the transparency of the coating film becomes good when a dry coating film made of silica and a binder is prepared.

The amount of alkali added is not particularly limited, but the amount of alkali necessary to make the pH of the solution 6.5 or more, more preferably pH 8 or more, more specifically, 1 mol of silica component (SiO ₂ ) in the seed particle aggregate. The amount of alkali is preferably 1 × 10 ^{−3 to} 1.0 mol, more preferably 0.01 to 0.1 mol. In addition, as the amount of alkali increases, that is, as the pH value of the solution increases, the surface charge amount of the silica seed particles increases and the repulsive force between the particles increases. When the growth is performed under the same conditions, the average secondary particle diameter of the silica fine particles becomes small, and the mixing of coarse silica can be prevented.

The alkali addition method is a method of adding at a time to the seed solution after completion of the seed solution generation step, a method of adding a small amount together with active silicic acid to be added to the seed solution during the growth step, or a growth step. In the method, a method of mixing with activated silicic acid and adding a small amount thereof or a method using these in combination can be used.
When the alkali is mixed with the active silicic acid and added to the seed solution, it is desirable to mix the alkali in such an amount that the pH of the active silicic acid aqueous solution becomes 7 or more. When the pH of the active silicic acid aqueous solution is less than 7, the active silicic acid aqueous solution may gel in a short time.

(Growth process)
In the growth step of FIG. 4C, an active silicic acid aqueous solution is added to the seed solution in the reaction vessel, and this liquid is heated in the same manner as in the seed solution generation step to grow seed particles (primary particles).
In this growth step, the seed solution is reacted for a certain time while being heated to a certain temperature. The heating temperature is preferably 60 ° C. or higher, more preferably 80 to 95 ° C., and particularly preferably 86 to 93 ° C.
If the heating temperature is less than 60 ° C., the seed particles grow slowly, reducing the production efficiency of the seed solution. If the heating temperature exceeds 95 ° C., the pressure in the reaction vessel may rise rapidly due to bumping.
The heating reaction time is preferably 1 to 8 hours, more preferably 2 to 6 hours, and particularly preferably 3 to 5 hours.
If the heating time is 1 hour or less, the seed particles may be insufficiently grown, and if it exceeds 8 hours, the productivity is lowered.

The method for adding active silicic acid is not particularly limited, but it is preferable to perform continuous addition at a constant rate.
Further, during the addition of active silicic acid, a necessary amount of alkali may be added as needed to prevent aggregation and precipitation of silica fine particles due to a decrease in pH of the solution.

The rate of addition of the active silicic acid aqueous solution to the heated seed solution is such that the surplus active silicic acid that generates new seed particles does not exist in the seed solution so that the SiO ₂ 1 contained in the seed particle aggregates in the seed solution. It is preferably added dropwise at a rate of 0.001 to 0.1 mol / min, more preferably 0.01 to 0.05 mol / min in terms of SiO ₂ per mole. When activated silicic acid is dropped at a rate exceeding this range, new monodispersed seed particles are generated, broadening the particle size distribution and reducing the pore volume.

In addition, the amount of active silicic acid added is based on the specific surface area (primary particle diameter) of the seed particle aggregate, and an active silicic acid solution equivalent to SiO ₂ necessary for growing the primary particle diameter to the desired specific surface area is added. To do. The active silicic acid aqueous solution to be added is desirably added at a temperature of 60 ° C. or less, preferably 40 ° C. or less so that condensation does not proceed before addition to the seed solution.

  By performing the growth process, each of the seed particles can be grown together in a state of being agglomerated and chemically bonded between the primary particles, resulting in a very strong aggregation state of primary particles that cannot be obtained by the dry method. Can be formed.

(Post-process)
The liquid after the addition of the active silicic acid aqueous solution in the growth process is sufficiently stable even if cooled as it is, but in order to complete the condensation of the silicic acid, the temperature is 70 ° C. or more in a time within the range of 1 to 24 hours. Further heat treatment is preferable in that the particle size distribution of the silica fine particles becomes narrower.

  Moreover, the surface of the obtained silica fine particles may be modified with a silane coupling agent, or various compounds such as polymers, metal oxides, metal hydroxides, cationizing agents, surfactants, amines, etc. It is also possible to modify the silica surface to give various functionalities.

Silica synthesis process described above, the specific surface area by the nitrogen adsorption method ^{50m 2} / ^g~400m 2 / g, average secondary particle diameter of 20 nm to 300 nm, and a pore volume of 0.4mL / g~2.0mL / g A silica fine particle dispersion in which the silica fine particles are dispersed in a colloidal form is obtained.

(Other methods for synthesizing silica fine particle dispersions)
The silica fine particle dispersion used in the present invention is not particularly limited as long as it is a silica fine particle dispersion containing silica fine particles having an average secondary particle diameter of 1 μm or less. For example, Japanese Patent Application No. 54-22004 Japanese Patent Application No. 5-280703, Japanese Patent Application No. 8-102494, Japanese Patent Application No. 8-328983, Japanese Patent Application No. 2-317417, Japanese Patent Application No. 1-52270, Japanese Patent Application No. 2-177835, etc. You may use what was obtained by the method.

[Filtration process]
In the method for producing a silica fine particle dispersion of the present invention, the silica fine particle dispersion is filtered in the filtration step.
When the silica fine particle dispersion produced in the silica synthesis step contains gel or coarse particles, as described above, gloss is produced when an inkjet recording sheet is produced using a coating liquid containing the silica fine particle dispersion. There is a risk that problems such as the inability to obtain a feeling may occur. For this reason, it is effective to remove these coarse particles and gel by filtering the silica fine particle dispersion.

(Filtration device)
In the method for producing a silica fine particle dispersion of the present invention, for example, a silica fine particle dispersion is produced by using a silica fine particle dispersion filtration device (hereinafter sometimes abbreviated as a filtration device) 1 as shown in FIG. be able to. The filtration device 1 includes a filter 2 that filters the silica fine particle dispersion, and a plurality of filter bodies 3 that perform filtration after pre-coating a filter aid by a method described later in the filter 2. Is arranged so that the silica fine particle dispersion stored in the container 5 can be filtered.
Further, the filtration device 1 is provided with a filter aid or an auxiliary tank 4 for storing a liquid in which the filter aid is dispersed, and supplies the filter aid to the filter 2 (filter body 3), and a container. The filter aid can be supplied to and added to the silica fine particle dispersion of No. 5.

As shown in FIG. 2, the filter body 3 includes a cylindrical element 31 in which a wire made of a metal such as stainless steel is spirally wound at regular intervals. A connecting pipe 32 is disposed at one end of the element 31 and a lid 36 is disposed at the other end. The filter body 3 is configured such that the solution enters from the outside of the cylindrical element 31 toward the internal space 37, and the filtered solution flows out from the outlet 33 of the connection pipe 32.
As the filter body 3, for example, “MS filter (trade name: manufactured by Tokyo Special Electric Cable Co., Ltd.)” can be used.

As shown in FIG. 3, the element 31 is formed with a uniform and strong slit 34 having a width of the slit width A between the wires.
As a result of investigations by the present inventors, it has been found that, in the production method of the present invention, when the slit width A is in the range of 5 μm to 100 μm, it is possible to efficiently perform filtration.
If the slit width A is less than 5 μm, clogging frequently occurs and there is a possibility that the filtration process cannot be performed efficiently. If the slit width A exceeds 100 μm, the filter aid cannot be held (attached) outside the slit, and the filter aid may be mixed into the silica fine particle dispersion after filtration.

  In addition, as a water-permeable base material used as the element 31, in the present invention, an element made of a metal wire as described above is used from the viewpoint of strength, durability, etc., but filter paper, mesh or the like may be used. it can.

(Precoat layer formation)
In the production method of the present invention, a precoat filter 3a is formed by previously forming a precoat layer 35 precoated with a filter aid on the surface of the element 31 of the filter body 3, and the precoat filter 3a is filtered through a silica fine particle dispersion. . Thereby, even if the particle G (see FIG. 3) captured by the precoat filter 3a is a particle having a smaller diameter than the interval of the slit width A (see FIG. 3) of the slit 34, it can be easily captured and filtered. it can.
The precoat layer 35 allows the filter aid to adhere to the outside of the element 31 (slit 34) by repeatedly passing the liquid in which the filter aid is dispersed in advance through the element 31 before filtering the silica fine particle dispersion. Form. Specifically, as shown in FIG. 1, the liquid in which the filter aid in the aid tank 4 is dispersed is circulated in the direction of arrow B, introduced into the filter 2, and passed through the element 31 of the filter body 3. Then, the filter aid dispersion liquid is passed through the element 21 repeatedly by flowing in the direction of arrow C and returning to the aid tank 4 again.

  Even if the average fiber length and average particle diameter of the filter aid are smaller than the slit width A, the filter aid having a larger fiber length and particle diameter is gradually captured outside the element 31 (slit 34). As a result, a precoat layer 35 is formed so that the filter aid does not leak inside the element 31 (slit 34).

The precoat layer 35 is preferably formed so that the amount of the filter aid to be precoated on the surface of the element 31 is 2 kg / m ² or less.
When the amount of the filter aid exceeds ² kg / m ² , it is necessary to increase the filtration pressure when filtering the silica fine particle dispersion. As a result, since shear force is applied to the particles, the fine particles sometimes aggregate. There is a risk of it.

(Filtration method)
After forming the precoat layer 35, the silica fine particle dispersion in the container 5 can be circulated in the direction of arrow D (FIG. 1), introduced into the filter 2 as it is, and filtered by the precoat filter 3a.
Alternatively, the filter aid dispersion liquid in the aid tank 4 is circulated in the direction of arrow E (FIG. 1), the filter aid is added to the silica fine particle dispersion in the reaction vessel 5, and the silica fine particles containing the filter aid are added. It is good also as the method of distribute | circulating a dispersion liquid to the direction of arrow D, supplying to the filter 2, and performing filtration.
A filter aid precoat layer 35 is formed on the element 31 of the filter body 3 to form a precoat filter 3a, and then a filter aid is added to the silica fine particle dispersion (body feed) to perform filtration. The filtration process can be efficiently performed while reliably removing coarse particles.
As shown in FIG. 3, the gel content and coarse particles (G in FIG. 3) contained in the silica fine particle dispersion are captured by the precoat layer 35, and only the silica fine particle dispersion containing only fine fine particles is contained in the precoat layer 35. And passes through a slit 34 formed in the element 31.

The addition amount of the filter aid to the silica fine particle dispersion is preferably 0.5 to 5% by mass with respect to the silica fine particle dispersion.
If the amount of added filter aid exceeds 5%, the amount of filter aid stacked on the element increases as filtration proceeds, and the pressure required for filtration must be increased. May occur, which is not preferable. Also, using a large amount of filter aid is not preferable from the viewpoint of cost.
Moreover, when the addition amount of the filter aid is less than 0.5%, the effect of adding the filter aid to the silica fine particle dispersion cannot be obtained.

(Filter aid)
As a filter aid used for the above-mentioned precoat layer formation and silica fine particle dispersion addition, it is preferable to use a cellulose fiber, diatomaceous earth, etc., and it is especially preferable to use a cellulose fiber. As the cellulose fiber, one having an average fiber length of 50 μm to 300 μm is preferably used. Moreover, as diatomaceous earth, it is preferable to use a thing with an average particle diameter of 10 micrometers-40 micrometers, and diatomaceous earth and a cellulose fiber can also be mixed and used.

(Differential pressure during filtration)
The maximum differential pressure between the pressure (MPa) on the inlet side and outlet side of the precoat filter 3a in the filtration step is preferably 0.05 MPa or less. By setting the maximum differential pressure within the above-mentioned range, gel content and coarse particles in the silica fine particle dispersion can be reliably removed.
When the maximum differential pressure exceeds 0.05 MPa, silica fine particles are condensed, and coarse particles may be mixed into the silica fine particle dispersion after filtration.
According to the applicant's research, when filtration is performed in a state where the maximum differential pressure between the inlet side and the outlet side of the filter is increased, the silica fine particles are aggregated by the shearing force generated between the silica fine particles and the filter. On the contrary, it has been found that new coarse particles are produced.
It has been clarified that by setting the maximum differential pressure within the above range, it is possible to reliably prevent coarse particles from being mixed into the silica fine particle dispersion after filtration.
In the present invention, by using the precoat filter 3a, filtration at a differential pressure of 0.05 MPa or less can be stably performed for a long time.

  The silica fine particle dispersion from which the gel and coarse particles have been removed by the filtration process in the filtration step is sent to the outside of the filter 2 and conveyed to the next step, as shown by an arrow F (FIG. 1).

(Processing after filtration)
The filter 2 of the present invention is a backwash process in which water or compressed air is caused to flow backward from the connecting pipe 32 (inlet 33) side into the precoat filter 3a after the filtration process is completed. It can be set as the structure which performs. This makes it possible to easily remove the precoat layer 35 from the surface of the element 31 every time it is used for filtration, and to flow it out of the filter 2 for disposal.
In this case, the replacement work is simpler than the conventional filter that needs to be replaced every time clogging, such as a filter that uses a fixed filtration layer for filtration. In addition, the cost merit increases.

<Silica fine particle dispersion>
Silica fine particle dispersion of the present invention obtained by the manufacturing method described above, as before filtration, specific surface area measured by the nitrogen adsorption method ^{50m 2} / ^g~400m 2 / g, average secondary particle diameter of 20nm~300nm and Silica fine particles having a pore volume of 0.4 mL / g to 2.0 mL / g are preferably colloidally dispersed.
According to the method for producing a silica fine particle dispersion of the present invention, it is possible to purify by removing coarse particles while maintaining such excellent characteristics.

<Coating liquid for inkjet recording sheet>
In addition to the silica fine particle dispersion of the present invention, the coating liquid for inkjet recording sheets of the present invention includes other known additives such as adhesives and ink fixing agents that are generally used for ink receiving layers. Ingredients can be included.
Other fine particles contained in the coating solution are not particularly limited, and for example, light calcium carbonate, heavy calcium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, carbonate Inorganic pigments such as zinc, satin white, aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, aluminum hydroxide, alumina, boehmite, pseudoboehmite, lithopone, zeolite, hydrous halloysite, magnesium carbonate, magnesium hydroxide; acrylic or methacrylic resin , Vinyl chloride resin, vinyl acetate resin, polyester resin, styrene-acrylic resin, styrene-butadiene resin, styrene-isoprene resin, polycarbonate resin, silicone resin, urea resin, melamine Fat, epoxy resins, phenolic resins, organic pigment can be mentioned made of a resin or diallyl phthalate resin, these fine particles may be irregular in spherical, may be porous even non-porous. These fine particles may be used alone or in combination of two or more.

  The adhesive is not particularly limited, and examples thereof include proteins such as casein, soybean protein, and synthetic protein; various starches such as starch and oxidized starch; polyvinyl alcohol and derivatives thereof; cellulose such as carboxymethylcellulose and methylcellulose. Derivatives; Conjugated diene resins such as styrene-butadiene resins and methyl methacrylate-butadiene copolymers; Acrylic resins that are polymers or copolymers of acrylic acid, methacrylic acid, acrylic esters, methacrylic esters, etc .; ethylene Examples thereof include vinyl resins such as vinyl acetate copolymers. Among them, in particular, polyvinyl alcohol and its derivatives soft aggregate with water-soluble salts in the silica slurry, so that the drying load in the coating process is reduced, and the crack resistance and high ink absorbency are improved to improve productivity. Since it expresses, it is preferably selected. These adhesives may be used alone or in combination of two or more.

The fixing agent is not particularly limited, and examples thereof include cationic polymers and water-soluble polyvalent metal salts.
Examples of the cationic polymer include polyalkylene polyamines such as polyethylene polyamine and polypropylene polyamine or derivatives thereof, secondary amino groups, acrylic polymers having tertiary amino groups and quaternary ammonium groups, polyvinyl amines, polyvinylamidine, 5-membered ring amidines, dimethylamine - epichlorohydrin copolymer, diallyldimethylammonium -SO ₂ copolymer, diallylamine salt -SO ₂ copolymer, dimethyl diallyl ammonium chloride polymer, polymer of allylamine salt, a dialkyl Examples include aminoethyl (meth) acrylate quaternary salt copolymer, acrylamide-diallylamine copolymer, ternary copolymer, etc. The copolymer may be a block copolymer or a random copolymer. May be.
Examples of water-soluble polyvalent metal salts include water-soluble salts of aluminum (nitrates, chlorides, acetates, sulfates, lactates, etc.), water-soluble salts of magnesium (chlorides, sulfates, nitrates, acetates, And commercially available products such as water-soluble salts of zirconium (chlorides, sulfates, etc.), water-soluble salts of zinc (chlorides, sulfates, nitrates, acetates, lactates, etc.). .
These ink fixing agents may be used alone or in combination of two or more.

  Other optional components include thickeners, antifoaming agents, wetting agents, surfactants, colorants, antistatic agents, light fastness aids, UV absorbers, antioxidants used in general recording sheet production. In addition, various auxiliary agents for preservatives are appropriately added.

<Inkjet recording sheet>
The ink jet recording sheet of the present invention is obtained by applying the above-described ink jet recording sheet coating liquid on a support. In addition, you may apply | coat the same coating liquid on both surfaces of a support body. In this case, clear printing can be performed on both sides of the ink jet recording sheet.
Further, the ink receiving layer made of the coating liquid may be composed of a plurality of layers. An undercoat layer may be provided between the support and the ink receiving layer, and an overcoat layer may be formed on the ink receiving layer so as to enhance the storage stability without impairing the recordability of the ink receiving layer. Good.

  The support is not particularly limited as long as it is a support that can be used as a normal inkjet recording sheet. Fine paper, art paper, coated paper, cast coated paper, foil paper, kraft paper, baryta paper, impregnation Paper, such as paper, vapor-deposited paper, resin film, resin is uniaxially stretched or biaxially stretched to form a paper-like layer, generally called synthetic paper, and one or more layers are laminated on a substrate layer such as paper Resin-coated paper such as paper, non-woven fabric, or the like, or a resin film laminated with coated paper or high-quality paper via an adhesive, or a paper laminated with a resin is used.

The coating amount of the coating solution containing the silica fine particle dispersion obtained by the production method of the present invention is not particularly limited, but is preferably ² to 30 g / m ² as the mass after drying. More preferably, it is set to ˜20 g / m ² .
When the coating amount is 2 g / m ² or more, ink absorbability, image sharpness, and print storage stability are improved. By setting the coating amount to 30 g / m ² or less, the coating film strength and the clearness of the image are maintained.
Note that a plurality of ink receiving layers may be laminated, and in this case, the ink receiving layer composition may be different between the layers.

  The coating of the coating solution 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, finishing may be performed using a calendar such as a machine calendar, a super calendar, or a soft calendar.

  The ink jet recording sheet of the present invention can provide an ink jet recording sheet having a high transparency of the ink receiving layer by using the coating liquid for the ink receiving layer, and can print a high gloss image with high glossiness. Can be obtained.

  Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. Unless otherwise specified, “%” means mass%.

<Measurement method of each physical property>
A method for measuring each physical property in the experimental example will be described below.

[Evaluation method for presence of gel and coarse particles]
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 the following three stages.
[O]: No gel or coarse particles.
[△]: There is a small amount of gel and coarse particles.
[×]: A large amount of gel and coarse particles.

[Secondary particle size measurement method]
Using a laser particle size distribution meter (trade name: LPA3000, manufactured by Otsuka Electronics Co., Ltd.) by a dynamic light scattering method, the average secondary particle size was measured with the silica fine particle dispersion sufficiently diluted with distilled water.
The average secondary particle diameter was a volume average value.

[Specific surface area and pore volume measurement method]
The silica fine particle dispersion was dried at 105 ° C. to obtain a powder sample for measurement. This powder sample was pretreated by performing vacuum degassing at a temperature of 200 ° C. for 2 hours, and then using a nitrogen gas adsorption specific surface area / pore distribution measuring device (SA3100plus type manufactured by Coulter), the specific surface area. And the pore volume was measured. The specific surface area was measured using the BET multipoint method (5-point method), and the pore volume was a value of the total pore volume (nitrogen relative pressure 0.991) having a pore diameter of 200 nm or less.
A small specific surface area means that the primary particle diameter is large, and a large specific surface area means that the primary particle diameter is small. Since the silica fine particles of the present invention are those in which primary particles are chemically bonded to form secondary particles, it may be difficult to accurately determine the diameter of the primary particles. Therefore, in this example, the specific surface area was used as a measure of the average particle diameter of the primary particles.

[Ink absorbability evaluation method of inkjet recording sheet]
Using the inkjet recording sheet (manufactured by Seiko Epson Corporation, PM-950C) on the prepared inkjet recording sheet, 100% black solid printing is performed in a size of 30 mm × 30 mm in the recommended setting printing mode of PM photographic paper, Judgment was made according to the following criteria.
[O]: The ink was absorbed.
[△]: Ink slightly overflowed.
[×]: The ink overflows and cannot be practically used.

[Method for measuring print density of inkjet recording sheet]
Using the ink jet printer (Seiko Epson Co., Ltd., PM-950C), 100% black solid printing was performed on the produced ink jet recording sheet at a size of 30 mm × 30 mm in the recommended setting printing mode of PM photographic paper.
The print density was measured using a Macbeth reflection densitometer (Macbeth, RD-920) at the black solid print portion.

[Glossiness measuring method of inkjet recording sheet]
Using the glossiness meter (Murakami Color Research Laboratory: GM-26 PRO / AUTO) for the glossiness of the prepared inkjet recording sheet (coating amount 20 g / m ² ) at each angle of 20 ° and 75 °. , Measured based on ISO 8254-1.

[Evaluation Method for Visual Glossiness of Inkjet Recording Sheet]
The glossiness of the inkjet recording sheet formed by coating the coating liquid containing each sample of the produced silica fine particle dispersion was visually evaluated in the following five stages.
[5]: There are no spots due to coarse particles.
[4]: Spots due to coarse particles are slightly observed.
[3]: Spots due to coarse particles are slightly larger than those in [4], but are practical.
[2]: Slightly more spots due to coarse particles are observed than in [3], which is impractical.
[1]: Spots due to coarse particles are conspicuous.

[Experimental Example 1]
(Silicic acid production process)
Distilled water is mixed with a sodium silicate solution having a SiO ₂ concentration of 30% and a SiO ₂ / Na ₂ O molar ratio of 3.1 (manufactured by Tokuyama Co., Ltd., No. 3 sodium silicate), and diluted silica with a SiO ₂ concentration of 4.0% A soda aqueous solution was prepared. This aqueous solution was passed through a column packed with a strongly acidic hydrogen cation exchange resin (manufactured by Mitsubishi Chemical Corporation, Diaion SK-1BH) to prepare an active silicic acid aqueous solution.

(Silica synthesis process)
In a 5 liter glass reaction vessel equipped with a reflux, a stirrer, and a thermometer, 400 g of distilled water was heated to 95 ° C. To this hot water, hydrochloric acid was added to 3 ppm. The ionic conductivity of the hot water at this time was measured and found to be 0.05 μS / cm. While maintaining this hot water at a temperature of 95 ° C., a total of 1000 g of the above active silicic acid aqueous solution was added at a rate of 0.2 mol / min with respect to 1 mol of hot water (seed liquid generation step). Then, 0.012 mol of potassium hydroxide was added to stop and stabilize the aggregation, and heated to 100 ° C. (aggregation stopping step).
Then, a total of 584 g of the active silicic acid aqueous solution was added to the seed solution at a rate of 1 mol / min. After completion of the addition of the active silicic acid aqueous solution, the temperature of the reaction solution was kept at 95 ° C. and left to stand for 1 hour to obtain a silica fine particle dispersion with pH 8.6 (growth step).

(Filtration process)
“MS filter” (trade name: manufactured by Tokyo Special Electric Cable Co., Ltd .: slit width: 30 μm) as a filter body, cellulose fiber filter aid (ARBOCEL BWW40: manufactured by Toa Chemical Co., Ltd .: fiber diameter: 20 μm, fiber length: 200 μm) Was repeatedly passed through the filter body (element), and a precoat layer with a filter aid was formed in advance on the outside of the filter body until 1.0 kg / m ² to obtain a precoat filter.
Then, the cellulose fiber filter aid was added (body feed) in an amount of 1% with respect to the silica solid content in the silica fine particle dispersion. Then, a silica fine particle dispersion containing a filter aid was supplied to the precoat filter and filtered to obtain a silica fine particle dispersion from which gel and coarse particles were removed.
The flow rate of the silica fine particle dispersion during filtration was 2 liters / minute, and the filtration time was 40 minutes. Moreover, since the filter pressure at the time of filtration was 0 MPa (at the end) on both the inlet and outlet sides, the differential pressure was also 0 MPa (at the end).

[Experiment 2]
Synthetic amorphous silica (produced by Grace Devison, trade name: Silojet P612, specific surface area 290 m ² / g, primary particle size 9 nm) produced by gel method with water dispersion at a concentration of 20% The slurry whose pH was adjusted to 9.0 by adding ammonia water was repeatedly pulverized and dispersed by a horizontal bead mill (Shinmaru Enterprises Co., Ltd., Dinomill KDL-Pilot), and a 20% aqueous dispersion of silica. Manufactured.

(Filtration process)
Cellulose fiber filter aid (ARBOCEL BWW40: manufactured by Toa Chemical Co., Ltd .: fiber diameter 20 μm, fiber length 200 μm) is used as a filter aid, and a precoat layer is formed on the surface of the filter body so as to be 0.5 kg / m ² and silica. Silica was added in the same manner as in Experimental Example 1 except that it was added in an amount of 2% with respect to the silica solid content in the fine particle dispersion, the filtration flow rate was 4 liters / minute, the inlet pressure and the differential pressure were 0.015 MPa. The fine particle dispersion was filtered.

[Experiment 3]
An 11% aqueous dispersion of silica (manufactured by Nippon Aerosil Co., Ltd., trade name: AEROSIL300) having an average primary particle size of 7 nm produced by a gas phase method was dispersed three times by a hydraulic ultrahigh pressure homogenizer. At this time, the pore volume of the fine silica was 1.6 mL / g. 10 parts of an 11% aqueous solution of diallyldimethylammonium chloride / acrylamide copolymer (trade name: PAS-J-81, manufactured by Nitto Boseki Co., Ltd.), which is a cationic resin as an ink fixing agent, was added to 100 parts of this silica fine particle dispersion. Part of the gelled mixture was further dispersed using a hydraulic ultra-high pressure homogenizer to produce a silica fine particle dispersion. This silica fine particle dispersion had a solid content of 11%, a silica concentration of 10%, and a diallyldimethylammonium chloride / acrylamide copolymer concentration of 1%.

(Filtration process)
A cellulose fiber filter aid (ARBOCEL BE00: manufactured by Toa Chemical Co., Ltd.) having a fiber length of 120 μm is used as a filter aid, and a precoat layer is formed on the surface of the filter body so as to be 1.5 kg / m ^2, and a silica fine particle dispersion The silica fine particle dispersion was filtered in the same manner as in Experimental Example 1 except that it was added in an amount of 2% with respect to the silica solid content therein and the inlet pressure and the differential pressure were 0.01 MPa.

[Experimental Example 4]
A silica fine particle dispersion was produced under the same conditions as in Experimental Example 1.
As a filter aid, a cellulose fiber filter aid (ARBOCEL BE00: manufactured by Toa Chemical Co., Ltd.) having a fiber length of 120 μm is used, and a precoat layer is formed on the surface of the filter body so as to be 1.8 kg / m ^2, and silica. The silica fine particle dispersion was filtered in the same manner as in Experimental Example 1 except that it was added in an amount of 2% with respect to the silica solid content in the fine particle dispersion, and the inlet pressure and the differential pressure were 0.15 MPa.

[Experimental Example 5]
A silica fine particle dispersion was produced under the same conditions as in Experimental Example 1.
Then, a precoat layer was formed on the surface of the filter main body in the same manner as in Experimental Example 1 except that diatomaceous earth filter aid (HIACE: Hayashi Kasei Co., Ltd .: average particle size 12.8 μm) was used as the filter aid. A precoat filter was obtained.
Then, the diatomaceous earth filter aid is added to the silica fine particle dispersion in an amount of 1% with respect to the solid content in the silica fine particle dispersion, and the silica fine particle dispersion containing the filter aid is added to the filter aid. Was supplied to a filter pre-coated at 1.0 kg / m ² and filtered.
The flow rate of the silica fine particle dispersion during filtration was 2 liters / minute, and the filtration time was 3 minutes. Moreover, the inlet pressure of the filter at the time of filtration was 0.2 MPa (at the end), and the differential pressure was 0.2 MPa (at the end).

[Experimental Example 6]
A silica fine particle dispersion was obtained in the same manner as in Experimental Example 1, except that no filter aid was added to the silica fine particle dispersion and the filter inlet pressure was 0.015 MPa.

[Experimental Example 7]
A silica fine particle dispersion was produced under the same conditions as in Experimental Example 1.
In the filtration process, a “wind cartridge filter” (trade name: manufactured by Advantech Toyo Co., Ltd., pore size: 5 μm) is used as a filter, and precoat formation with a filter aid and addition of a filter aid to a silica fine particle dispersion are not performed. The silica fine particle dispersion was obtained with a filtration time of 20 minutes and an inlet pressure and a differential pressure of 0.065 MPa.
Since the differential pressure increased when the silica fine particle dispersion was filtered by about 30%, the filter was changed, and the filter was changed a total of three times to filter the entire dispersion.

<Method for producing inkjet recording sheet>
For each sample of the silica fine particle dispersion in the above experimental example, a 10% aqueous solution of fully saponified polyvinyl alcohol [manufactured by Kuraray Co., Ltd., trade name: PVA-140H] is added to a silica solid content 100 contained in each silica fine particle dispersion. An ink jet recording sheet coating solution was prepared by mixing at a ratio of 20 parts by mass with respect to parts by mass.
This coating solution was applied on a transparent polyethylene terephthalate film (trade name: Lumirror 100-Q80D, manufactured by Toray Industries, Inc.) having a thickness of 100 μm so that the coating amount was 20 g / m ² in terms of dry mass. Then, it was dried at a temperature of 120 ° C. to produce an ink jet recording sheet.

  Table 1 shows a list of production conditions and evaluation results for each experimental example.

<Evaluation results>
As shown in Table 1, in Experimental Examples 1 to 3 and Experimental Example 6 in which the silica fine particle dispersion was produced by the production method of the present invention, a precoat layer was formed by using a filter aid on the filter body surface. In addition, the differential pressure between the inlet pressure and the outlet pressure of the filter is 0.05 MPa or less.

Experimental Examples 1-3, and the silica fine particle dispersion of Example 6 are both specific surface area measured by the nitrogen adsorption method ^{50m 2} / ^g~400m 2 / g, average secondary particle diameter of 20nm~1000nm and pores, The volume was in the range of 0.4 mL / g to 2.0 mL / g, and the evaluation of the presence or absence of coarse particles based on the above evaluation criteria was all good.
In addition, each of the inkjet recording sheets in which the coating liquid containing the silica fine particle dispersion liquid of Experimental Examples 1 to 3 and Experimental Example 6 was coated on the support had a 20 ° gloss of 5.0 or more and 75 °. The gloss was 45 or more and the print density was 2.3 or more. Moreover, the evaluation of the visual glossiness based on the said evaluation criteria was all in the range of 3-5.

On the other hand, in the method for producing the silica fine particle dispersion of Experimental Example 4, the inlet pressure and the differential pressure of the filter are 0.15 MPa.
The silica fine particle dispersion obtained by the production method of Experimental Example 4 has a specific surface area of 240 m ² / g, an average secondary particle diameter of 85 nm, a pore volume of 0.67 mL / g, and coarse particles. The evaluation of the presence or absence of was Δ.
In addition, the inkjet recording sheet in which the coating liquid containing the silica fine particle dispersion liquid of Experimental Example 4 was coated on the support had a 20 ° gloss of 3.5 and a 75 ° gloss of 43.5, and the print density was 2.2. Moreover, the evaluation of visual glossiness based on the above evaluation criteria was 2.

Further, in the method for producing the silica fine particle dispersion of Experimental Example 5, the inlet pressure and the differential pressure of the filter are 0.2 MPa.
The silica fine particle dispersion obtained by the production method of Experimental Example 5 has a specific surface area by a nitrogen adsorption method of 250 m ² / g, an average secondary particle diameter of 80 nm, a pore volume of 0.65 mL / g, and coarse particles Evaluation of the presence or absence of was x.
In addition, the inkjet recording sheet in which the coating liquid containing the silica fine particle dispersion of Experimental Example 5 was coated on the support had a 20 ° gloss of 1.6 and a 75 ° gloss of 40.5, and the print density was 2.1. Further, the evaluation of visual glossiness based on the above evaluation criteria was 1.

In addition, in the method for producing a silica fine particle dispersion of Experimental Example 7, filtration is performed without forming a precoat layer with a filter aid on the surface of the filter body, and without adding a filter aid to the silica fine particle dispersion. The inlet pressure and the differential pressure of the filter are 0.065 MPa.
The silica fine particle dispersion obtained by the production method of Experimental Example 7 has a specific surface area of 262 m ² / g by nitrogen adsorption method, an average secondary particle size of 200 nm, a pore volume of 0.6 mL / g, and coarse particles Evaluation of the presence or absence of was x.
Further, the inkjet recording sheet in which the coating liquid containing the silica fine particle dispersion liquid of Experimental Example 7 was coated on the support had a 20 ° gloss of 3.2 and a 75 ° gloss of 43, and a print density of 2. 25. Moreover, the evaluation of visual glossiness based on the above evaluation criteria was 2.

  Since the silica fine particle dispersions of Experimental Examples 4 to 5 and Experimental Example 7 are all mixed with a large amount of coarse particles in the dispersion liquid after the filtration treatment, an ink jet formed by applying a coating liquid containing these dispersion liquids. The evaluation of the recording sheet was low.

  Based on the above results, the silica fine particle dispersion obtained by the production method of the present invention is less mixed with gel and coarse particles. Therefore, an ink jet recording sheet coated with a coating liquid containing this dispersion has glossiness. It is clear that it is high and beautiful and has high print quality.

It is a figure explaining an example of the manufacturing method of the silica fine particle dispersion of this invention, and is the schematic of the filtration apparatus provided with the filter. It is a figure explaining an example of the manufacturing method of the silica fine particle dispersion of this invention, and is sectional drawing which shows the precoat filter inside a filter. It is a figure explaining an example of the manufacturing method of the silica fine particle dispersion of this invention, and is sectional drawing to which the principal part of the precoat filter shown in FIG. 2 was expanded. It is a figure explaining an example of the manufacturing method of the silica fine particle dispersion of this invention, and is a process figure which shows a silica synthesis process. It is an enlarged view showing the surface of an ink jet recording sheet formed by adding a silica fine particle dispersion obtained by a conventional method for producing a fine silica particle dispersion to a coating liquid and coating the support.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Silica fine particle dispersion liquid filtration apparatus, 2 ... Filter, 3 ... Filter main body, 3a ... Precoat filter, 35 ... Precoat layer, 4 ... Auxiliary tank, 5 ... Container

Claims (11)

  A method for producing a silica fine particle dispersion, comprising a filtration step of filtering a silica fine particle dispersion containing silica fine particles having an average secondary particle diameter of 1 μm or less with a precoat filter in which a filter body is precoated with a filter aid. .   The method for producing a silica fine particle dispersion according to claim 1, wherein the filter aid is added to the silica fine particle dispersion, followed by filtration with the precoat filter.   The production of the silica fine particle dispersion according to claim 1 or 2, wherein a maximum differential pressure between an inlet pressure and an outlet pressure of the precoat filter when the silica fine particle dispersion is filtered with the precoat filter is 0.05 MPa or less. Method.   The method for producing a silica fine particle dispersion according to any one of claims 1 to 3, wherein both the filter aid pre-coated on the precoat filter and the filter aid added to the silica fine particle dispersion are cellulose fibers. .   The method for producing a silica fine particle dispersion according to any one of claims 1 to 4, wherein a pore volume of the silica fine particles by a nitrogen gas adsorption method is 0.4 mL / g to 2.0 mL / g. Method for producing a silica fine particle dispersion liquid according to any one specific surface area of claims 1 to 5 is ^{50m 2} / ^g~400m 2 / g of the silica fine particles.   The method for producing a silica fine particle dispersion according to any one of claims 1 to 6, further comprising a silica synthesis step of obtaining the silica fine particle dispersion by condensation of active silicic acid.   The silica synthesis step includes a seed solution generation step of generating a seed solution by supplying and heating activated silicic acid, an aggregation stop step of adding an alkali to the seed solution to stop aggregation of silica fine particles, and the seed The method for producing a silica fine particle dispersion according to claim 1, further comprising a growth step of growing silica fine particles by adding active silicic acid to the liquid.   A silica fine particle dispersion produced by the production method according to claim 1.   The silica fine particle dispersion according to claim 9, wherein the upper limit of the secondary particle diameter of the silica fine particles by the dynamic light scattering method is less than 5 µm. An inkjet recording sheet obtained by applying a coating liquid for an inkjet recording sheet containing the silica fine particle dispersion according to claim 9 or 10.

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