KR20050024277A - Cake of easily dispersible precipitated silica and process for producing the same - Google Patents

Abstract

There is provided a cake of silica composed of precipitated silica having a small primary particle diameter and easy dispersion, which can efficiently obtain a highly transparent silica dispersion liquid therefrom. This silica cake is a cake of precipitated silica having a BET specific surface area of 220 m ² / g or more, which is dispersed in ion-exchanged water to give an aqueous dispersion having a silica concentration of 5% by weight, and then diluted to a silica concentration of 1.5% by weight. The light scattering index (n value) of is characterized in that two or more. This silica cake produces precipitated silica by adding and reacting alkali silicate and mineral acid to the reaction solution simultaneously while maintaining the pH of the reaction solution at a constant value within the range of 7.5 to 11.5 and maintaining the temperature at 90 ° C or higher. And the precipitated silica is separated from the reaction solution in a wet state.

Description

CAKE OF EASILY DISPERSIBLE PRECIPITATED SILICA AND PROCESS FOR PRODUCING THE SAME

The present invention relates to a novel cake of precipitated silica obtained by precipitation (wet method), a precipitated silica dispersion obtained by dispersing the cake of precipitated silica in a polar solvent, and inkjet recording of the precipitated silica and a binder dispersed in a polar solvent. A coating liquid for a sheet (hereinafter, simply referred to as "coating liquid"). More specifically, in the present invention, although the primary particle size is small, the cake of precipitated silica having excellent dispersibility when dispersed in a polar solvent such as water and the precipitated silica cake is dispersed. The present invention relates to a coating liquid excellent in transparency and stability, in which a precipitated silica dispersion liquid and precipitated silica having a relatively small primary particle size are contained in an extremely high dispersion state.

Silica dispersions are used as various coating agents for imparting gas barrier properties, corrosion resistance, hydrophilicity, glossiness, liquid absorption property to paper, films, resins, glass, etc., including inkjet recording sheets, as well as semiconductor wafers and IC insulating films. It is also used as an abrasive, stabilizer of emulsion, and the like.

Conventionally, colloidal silica was typical as a silica dispersion liquid used suitably for the said use. Colloidal silica is prepared by a process of stabilizing by deionization with an ion exchange resin or the like using sodium silicate solution as a raw material, concentrating appropriately, and then adjusting the pH with ammonia or the like. Highly dispersed silica dispersions can be prepared.

By the way, in recent years, with the increase of the demand of the silica dispersion liquid, development of the manufacturing method of a high productivity silica dispersion liquid instead of the low productivity colloidal silica became desired.

In addition, in the inkjet recording sheet which is one of the uses of the above-mentioned silica dispersion liquid, the silica dispersion liquid is used as a coating liquid raw material for forming an ink absorbing layer on one side or both sides of a support such as paper. Generally, as a characteristic required for the ink absorption layer of an inkjet recording sheet, the thing with high transparency and liquid absorption is mentioned. However, the ink absorbing layer using the colloidal silica described above as a coating liquid raw material has a problem of high transparency but low liquid absorption.

Under such a demand, precipitated silica produced by a so-called "precipitation method", in which an alkali silicate aqueous solution is reacted with an acid to precipitate silica particles, has been attracting attention as a material for the dispersion liquid because of its excellent productivity and liquid absorption.

In order to produce a highly transparent dispersion liquid in which the silica particles are highly dispersed using precipitated silica, it is necessary that the silica particles have a small primary particle diameter, that is, have a large specific surface area. However, since precipitated silica has a strong cohesive force, especially when precipitated silica having a large specific surface area is used, the aggregated structure of the aggregated particles becomes hard, which makes it difficult to atomize to a fine aggregated particle state in a polar solvent.

Therefore, for the purpose of improving the dispersibility, the precipitated silica obtained through the reaction, filtration, and washing is recovered as an aqueous cake without drying, thereby relieving the cohesiveness, and dispersing the precipitated silica particles in a polar solvent in the cake state. Attempts have been made to improve acidity (Japanese Patent Application Laid-Open No. 9-142827).

However, even by this method, when precipitated silica having a large specific surface area is used, it is industrially difficult to obtain a cake of precipitated silica having high dispersibility, and in order to obtain a dispersion liquid in which precipitated silica is highly dispersed, an enormous time is required. Not only does it require effort and effort, but a satisfactory dispersion has not been achieved.

Accordingly, an object of the present invention is to produce a cake of precipitated silica, which has extremely high disintegration ability and remarkably improved dispersibility in a polar solvent, even though precipitated silica having a large specific surface area. The present invention provides a coating liquid excellent in transparency and stability, in which dispersed precipitated silica dispersion liquid and precipitated silica having a relatively small primary particle diameter are contained in an extremely high dispersion state.

The present inventors have conducted extensive studies to achieve the above object, and as a result, by restricting the production reaction of precipitated silica to a certain condition, the aggregate structure is weak and easily dispersed even though the silica primary particle size is fine. It succeeded in obtaining the cake of silica, and came to complete this invention.

In this way, according to the present invention, a cake of precipitated silica having a BET specific surface area of 220 m ² / g or more, which is dispersed in ion-exchanged water so as to form an aqueous dispersion having a silica concentration of 5% by weight, and then diluted to a silica concentration of 1.5% by weight. A cake of heterodisperse precipitated silica (hereinafter, simply referred to as a "silica cake") is characterized in that the light scattering index (n value) of the dispersion is two or more.

According to the present invention, the pH of the reaction solution is in the range of 7.5 to 11.5 in the method for producing a precipitated silica cake comprising neutralizing a alkali silicate and a mineral acid, followed by filtration, washing, and dehydration. Maintaining a constant value within the temperature and maintaining the temperature above 90 ℃, simultaneously adding alkali silicate and mineral acid to the reaction solution to produce precipitated silica, characterized in that the precipitated silica is separated from the reaction solution in a wet state A method for producing a cake of heterodisperse precipitated silica is provided.

According to the present invention, there is also provided a dispersion liquid in which the heterodisperse precipitated silica is dispersed in a polar solvent, in which the average particle diameter of the silica particles in the dispersion is 300 nm or less and the proportion of the agglomerated particles of 500 nm or more is 5% by volume or less. This is provided.

According to the present invention, there is also a coating liquid for an ink jet recording sheet comprising a polar solvent containing precipitated silica and a binder having a BET specific surface area of 220 m ² / g or more, which is measured by diluting the coating liquid to a silica concentration of 1.5% by weight. A coating liquid for an ink jet recording sheet is provided, wherein the transmittance is 20% or more.

Disclosure of the Invention

In the present invention, "precipitated silica" is a generic term for silica produced by the precipitation method.

In general, in the precipitation method, an alkali silicate aqueous solution is reacted with a photo acid to precipitate silica in the reaction solution, and subsequently, the precipitated silica cake is recovered by filtration and washing with precipitated silica. In the present invention, the water-containing solids of precipitated silica recovered and reacted, filtered and washed are called "aqueous cakes" or "cakes" while being dried and not hydrated.

Precipitated silica constituting the silica cake of the present invention, the BET specific surface area in the range of 220m ² / g or more, preferably 240~400m ² / g, and more preferably in the range of 250~350m ² / g.

Silica cakes composed of precipitated silicas having a BET specific surface area of less than 220 m ² / g are relatively easy to disperse, but as precipitated silicas having a particle size corresponding to such BET specific surface areas, as shown in Examples described later, high transparency It is difficult to produce precipitated silica dispersions.

In addition, "BET specific surface area" means S. Bruno, P. H. Emmett, this. J. Am. By S. Brunaure, P. H. Emmett, E. Teller. Chem. The specific surface area measured by applying the multi-molecular layer adsorption theory described in Soc., 60, 309 (1938) is considered to correspond to the average primary particle diameter of silica. For example, as described in the Powder Engineering Sculpture "Revision Supplementary Powder Property Sculpture" (1985), assuming that the primary particles are spherical, the following equation (a) is obtained between the specific surface area and the average diameter of the primary particles: 1), the larger the specific surface area, the smaller the average primary particle size.

D = 6 / (Sρ) (1)

(Where D is the average primary particle diameter, S is the specific surface, and ρ is the density of the particle)

The silica cake of the present invention is characterized by exhibiting extremely good dispersibility when dispersed in a polar solvent while having the relatively large BET specific surface area described above.

That is, the silica cake of the present invention is atomized in ion-exchanged water so as to be an aqueous dispersion having a silica concentration of 5% by weight by the method described below, and then the light scattering index (n value) of the dispersion diluted to a silica concentration of 1.5% by weight. Is 2 or more, preferably 2.1 or more, and more preferably 2.2 or more.

In addition, the said n value is an index which shows the dispersion state of the silica in a dispersion liquid, This value becomes large as dispersibility improves. Therefore, since it is considered that it is a fine dispersion state, so that n value is large, it becomes an index of the fragility of the aggregation structure which a silica cake has.

The said n value is the value measured according to the method of Journal of Ceramic Society of Japan, 101 [6], 707-712 (1993). That is, absorbance was calculated | required by measuring the spectrum of the dispersion liquid whose wavelength (lambda) is the range of 460 nm-700 nm using a commercially available spectrophotometer, and plots log ((tau) with respect to 1og ((lambda)), and following formula (2) Use to find the slope of the straight line (-n) using the least-squares method.

T = αλ ^-n (2)

Where τ is the absorbance, α is the integer, λ is the wavelength of light, and n is the light scattering index.

In addition, in the measurement of the value n, an aqueous dispersion having a silica concentration of 5% by weight, prepared as an aqueous cake of precipitated silica, was added to the aqueous cake by adding ion-exchanged water so as to have the silica concentration, and stirred with a propeller mixer to predisperse the dispersion. The obtained slurry was obtained by subjecting the obtained slurry to a processing pressure of 78 MPa once using a high pressure homogenizer and atomizing it.

As described above, in order to improve the transparency of the precipitated silica dispersion, it is necessary to use precipitated silica having a large specific surface area, but as described above, precipitated silica having a specific surface area of 220 m ² / g or more has extremely high cohesion of primary particles. It is high and the said n value is about 1.6 at most because of the lack of dispersibility in the conventional silica cake. If the n value is less than 2, the transparency of the precipitated silica dispersion liquid prepared as such a silica cake is low, and the transparency of the coating liquid for an ink jet recording sheet using the precipitated silica dispersion liquid is also low. In other words, when the transparency of the coating solution is low, the transparency of the ink absorbing layer is low as described above, so that the tint of the ink penetrating into the sheet becomes unclear, and the obtained image does not feel the depth of color and is satisfied. Image quality is not obtained.

On the other hand, the silica cake of this invention shows the high n value of two or more, and shows extremely high dispersibility. Moreover, with the silica cake which shows such a high n value, the stable silica dispersion liquid with extremely high transparency when it is disperse | distributed to a polar solvent can be obtained.

Although the silica cake of this invention is not restrict | limited especially by the conditions other than the above, It is preferable that it is the range whose water content rate is 83-93 weight%, since dispersion in a polar solvent is easier when manufacturing a silica dispersion liquid. More preferably, it is 85 to 92 weight%.

Moreover, since the pH value when the silica cake is disperse | distributed to water and it is set as the 5 weight% dispersion liquid is a range of 3-7, since the dispersibility of a silica cake can be improved more, it is preferable. More suitable pH values are 3.5 to 6.5.

The method for producing the silica cake of the present invention is not particularly limited, but representative examples thereof include alkali silicate and mineral acid, while maintaining the pH of the reaction solution at a constant value within the range of 7.5 to 11.5 and maintaining the temperature at 90 ° C or higher. Precipitating silica is produced by adding and reacting to this reaction liquid simultaneously, and the method which consists of separating the precipitated silica in the wet state from the said reaction liquid is mentioned.

In the above production method, sodium silicate, potassium silicate and the like can be used as alkali silicate, but sodium silicate is generally used as an industrial raw material. The alkali silicate is a formula, when the M an alkali metal (Na or K), is generally denoted by M ₂ O · xSiO _2. x is the molar ratio of SiO ₂ / M ₂ O.

The molar ratio x of the alkali silicate SiO ₂ / M ₂ O used in the production method of the silica cake of the present invention is not particularly limited, but usually 2 to 4, preferably be suitably used to a molar ratio of 3.0 to 3.5 have. Moreover, the density | concentration at the time of use of an alkali silicate is not specifically limited, either, What is available for industrial use can also be added to a reaction liquid as it is, and can also be diluted suitably. The SiO ₂ concentration at the time of using alkali silicate is 50-300 g / L in general.

Sulfuric acid, hydrochloric acid, nitric acid, and the like can be used as the mine, but sulfuric acid is generally used for industrial purposes. It does not specifically limit about the density | concentration of a mine, either what is available for industrial use can also be added to a reaction liquid as it is, and can also be diluted suitably.

Hereinafter, the manufacturing method of the silica cake of this invention is demonstrated in detail. In addition, below, the reaction liquid before an alkali silicate and a photo acid is added simultaneously is called "initial reaction liquid."

When manufacturing the silica cake of this invention, first, the initial reaction liquid is put into a reaction tank, the temperature of 90 degreeC or more by external heating, internal heating by a heater, or the introduction of steam, etc., stirring, using a propeller blade etc., and stirring. (The temperature which should be maintained at the time of reaction of alkali silicate and a photoacid mentioned later) is previously adjusted.

The initial reaction solution may be an aqueous alkali silicate solution of a suitable concentration, an alkaline aqueous solution in which pH is appropriately adjusted with a basic substance such as sodium hydroxide, aqueous ammonia, amines, or the like, preferably a pH value within a range of 7.5 to 11.5 ( The aqueous alkali solution previously adjusted to the pH value which should be maintained at the time of reaction of alkali silicate and a photoacid mentioned later, or water may be sufficient. In general, the suitable concentration, for example, better to use the alkali silicate aqueous solution which is adjusted to a concentration of about 1~5Og / L of SiO ₂ as an initial concentration of the reaction solution, and this tends to maintain the pH value at a constant value Moreover, since the mineral acid used becomes small quantity, it is preferable. In addition, as generally practiced in the method for producing precipitated silica by precipitation, an electrolyte, generally sodium sulfate, may be added to the initial reaction solution, but the electrolyte acts as a flocculant and lowers the BET specific surface area. Since it is easy, it is preferable not to use when manufacturing a silica cake with a large BET specific surface area and favorable dispersibility like this invention. In the case of using an aqueous alkali silicate solution as the initial reaction solution, before the alkali silicate and the photo acid are added simultaneously, the mine may be added for the purpose of adjusting the pH value or the like. Alkaline silicate and the neutralized reaction of the injected mine produce a small amount of silica and the above-described electrolyte, and it is difficult to produce a precipitated silica cake having good dispersibility for the purpose of the present invention. It is preferable that it is an alkali aqueous silicate solution.

Stirring of the reaction solution is not particularly limited as long as uniformity can be maintained in the sense that concentration distribution of the contents of the reaction solution and segregation of precipitated solids can be avoided. A general stirrer having a propeller blade, a turbine blade, a paddle blade, and the like; High speed rotary centrifugal radial stirrers such as dispersion mixers and the like; High speed rotary shear stirrers such as homogenizers, homo mixers, ultra mixers and the like; It is good to stir or mix using a disperser, such as a colloid mill and a planetary mixer. Moreover, stirring by circulation of the reaction liquid which removes a part of reaction liquid and re-inserts from another position using the pump etc. for liquid conveyance can also be employ | adopted.

In the present invention, it is important to perform an operation of generating precipitated silica by neutralization reaction by simultaneously adding alkali silicate and photoacid to this while uniformly stirring the initial reaction solution maintained at a predetermined temperature. In addition, it is also important in this invention to keep reaction temperature at 90 degreeC or more, and to maintain pH at a fixed value within the range of 7.5-11.5 at the time of this operation.

The 1st characteristic of this invention is maintaining reaction temperature at 90 degreeC or more as mentioned above. When reaction temperature is lower than 90 degreeC, the dispersibility of the silica cake obtained will become low, and the index (n value) of the dispersibility mentioned later becomes smaller than two. The said reaction temperature is the temperature range suitable especially for 92-98 degreeC to implement, and 93-97 degreeC is more preferable.

A second feature of the present invention is to maintain the pH at a constant value within the range of 7.5 to 11.5 as described above. When the pH value fluctuates greatly, the dispersibility of the obtained silica cake is also inferior. Even so, some variation in pH is allowed, and the variation range is preferably within ± 0.3, and more preferably within ± 0.2. If the pH value of the reaction solution is 7.5 or less, the reaction becomes unstable and problems such as the reaction solution tends to gel easily, and if it exceeds 11.5, productivity decreases. The range of the more preferable pH value is 8-11, More preferably, it is 9-11 which is easy to maintain pH at a fixed value.

According to a third aspect of the present invention, an operation of simultaneously adding alkali silicate and photo acid to the reaction solution is employed as a means for maintaining the pH of the reaction solution at a constant value as described above. As a means for maintaining the pH at a constant value, it is conceivable to introduce a mineral such as a buffer, sodium hydroxide or the like, and a mineral acid different from the mineral acid added at the same time to the reaction liquid. However, when a buffer is added, the residue of the buffer adheres to the silica cake obtained, and it adversely affects as an impurity in the preparation of the silica dispersion (for example, it becomes difficult to adjust the pH value or with other additives). There is a fear that the phases of deterioration may be worse. Adding an alkali such as alkali hydroxide and the other photoacid is substantially the same as changing the type, concentration, molar ratio x, etc. of alkali silicate and photoacid, and therefore is an operation within the range defined by the present invention.

In the precipitation method of synthesizing precipitated silica by neutralizing alkali silicate with a photoacid, the reaction is generally carried out at an alkalinity with a pH value of 7 or more from the start of the neutralization reaction until at least silica precipitates. As a reaction type at that time, the method (reaction type A) which adds a mineral acid to the alkali silicate solution adjusted to the suitable density | concentration largely divided, and the alkali silicate and photoacid which this invention employ | adopts are simultaneously added to reaction liquid on a fixed condition. There are two types of methods (reaction type B). Among these reaction types A and B, since a silica cake with a large specific surface area and excellent dispersibility can be easily obtained, reaction type B, that is, alkali silicate and a method of adding a photo acid to the reaction solution simultaneously under constant conditions is adopted. It is preferable.

In addition, as described above, one obtained by adding a photo acid to the alkali silicate solution may be used as the initial reaction solution, but since the electrolyte is generated at the beginning of the neutralization reaction and it acts as a coagulant, it is easy to lower the BET specific surface area. It is preferable not to add a photo acid before adding an alkali and a photo acid simultaneously, in order to manufacture the silica cake with a big BET specific surface area aimed at this invention, and having favorable dispersibility.

The synthesis reaction of the silica cake of the present invention according to reaction type B is specifically carried out as follows: As an initial reaction liquid in the reactor, a concentration such that the molar ratio x is 2-4 and the SiO ₂ concentration is 1-50 g / L. An aqueous sodium silicate solution adjusted to is added thereto, and the mixture is adjusted to a reaction temperature of 90 ° C. or higher while stirring so as to be uniform. Aqueous sodium silicate adjusted to a concentration such that the molar ratio x is 2 to 4 and the SiO ₂ concentration is 50 to 300 g / L while maintaining a uniform stirring and reaction temperature, and the H ₂ SO ₄ content is about 100 to 1000 g / L. Concentrated sulfuric acid is added at the same time while adjusting so that pH may become a fixed value within the range of 7.5-11.5. After the silica particles are formed and the sedimentation of the silica is confirmed, simultaneous addition is continued until the desired BET specific surface area is achieved. Then, only sulfuric acid is added and pH is adjusted to 2-6, a reaction liquid is stabilized and reaction is complete | finished.

In the method for producing a silica cake of the present invention, it is required to simultaneously add alkali silicate and a photo acid under conditions that control the pH to a constant value. In particular, it is important to obtain a cake of precipitated silica having high dispersibility, starting with the addition of alkali silicate and a mineral acid to the initial reaction solution at the same time, until silica particles are formed and at least sedimentation occurs.

Although the details of the reaction mechanism are unclear, in the method for producing the silica cake of the present invention, since the pH is maintained at a constant value and alkali silicate and photoacid are added at the same time, the concentration of alkali silicate remaining in the reaction solution without neutralization is almost constant. It is assumed that a cake of precipitated silica having high dispersibility is formed as a result by maintaining the value. On the other hand, in the reaction type A in which the acid is added to the alkali silicate solution, it is difficult to maintain the pH at a constant value, and the alkali silicate concentration remaining in the reaction solution without neutralization gradually changes (reduces) with the addition of the mine. Therefore, it is estimated that precipitated silica with low dispersibility may be produced. After simultaneous addition of alkali silicate and mineral acid until the desired BET specific surface area is desired, in order to stabilize the reaction solution, it is desired to add only the mineral acid to adjust the pH to 7 or less, preferably 2 to 6. The stabilization of the reaction liquid may also be carried out by a so-called aging process in which simultaneous addition of alkali silicate and mineral acid is once stopped and the reaction solution is stirred for a certain time or the stirring is continued for a certain time while maintaining the temperature after completion of the simultaneous addition. have.

According to a suitable embodiment in the method for producing a silica cake of the present invention, the initial reaction solution and the alkali silicate added simultaneously are such that the silica solid content concentration in the reaction mixture at the end of the reaction is 50 g / L or less, preferably 35 to 47 g / L. And the concentration of the mine, and / or the amount. This setting is effective to adjust the BET specific surface area of the precipitated silica obtained in the above range.

In the present invention, as is generally practiced in the method for producing precipitated silica by the precipitation method, an appropriate addition of an electrolyte, generally sodium sulfate, to the reaction solution can be carried out without any limitation. However, as described above, the electrolyte acts as a flocculant and tends to lower the BET specific surface area. Therefore, in order to produce a cake of precipitated silica having a large BET specific surface area and good dispersibility as in the present invention, an electrolyte is not used. desirable.

In the present invention, the precipitated silica can be separated from the reaction solution obtained by the above reaction by filtration, washed with water and / or dehydrated as necessary, and separated into a wet state to obtain a silica cake. The moisture content of the wet silica cake is preferably in the range of 83 to 93% by weight, as described above, since dispersion becomes easier when producing the silica dispersion. More preferably, it is 85 to 92 weight%.

In general, solid-liquid separation devices such as filter presses are used for the filtration, washing with water and dehydration. In addition, water washing is performed so that the dispersion liquid which disperse | distributed the obtained silica cake to the concentration of 5 weight% in water may have a pH value of 3-7 and a conductivity value of 20-400 microS / cm, and the dispersibility of the silica cake It is preferable because it can improve. More preferably, the pH is 3.5 to 6.5 and the conductivity value is 50 to 300 µS / cm.

The silica cake of the present invention has extremely good dispersibility in polar solvents, and a silica dispersion liquid in which precipitated silica is highly dispersed can be obtained by a simple dispersion operation. In addition, by dispersing the silica cake of the present invention in a polar solvent, a highly transparent silica dispersion liquid in which the aggregated particles are highly dispersed, wherein the average particle diameter of the silica in the precipitated silica dispersion is 300 nm or less and the proportion of the aggregated particles of 500 nm or more is 5% by volume or less. You can get it.

Conventionally, in the silica dispersion liquid obtained by disperse | distributing precipitated silica in a polar solvent, the thing which agglomerated particles highly disperse | distributed as mentioned above has not been obtained. As a reason, the following mechanism of action is estimated. That is, the conventional precipitated silica has a large particle size distribution of the primary particle diameter, and thus contains a large amount of ultrafine primary particles having a strong cohesive force, and as a result, it precipitates to a highly dispersed state as in the silica dispersion liquid of the present invention. It is practically impossible to disperse the silica. In contrast, the precipitated silica in the silica dispersion liquid of the present invention has a narrow particle size distribution of the primary particles by limiting the production conditions of the precipitated silica particles as described above, so that the content of the ultrafine primary particles is small. It is assumed to have dispersibility.

Next, the precipitated silica dispersion liquid of the present invention will be described.

In the present invention, the "average particle diameter" refers to the average particle diameter of the silica aggregated particles in the precipitated silica dispersion, and means the volume-based arithmetic mean diameter D ₅₀ as measured by a light scattering diffraction particle size distribution meter.

The silica concentration in the precipitated silica dispersion liquid of this invention can be suitably adjusted according to a use. Although it is 8 to 15 weight% normally, you may make it 15 weight% or more by concentrating by the density | concentration method mentioned later as needed.

As a method for producing the precipitated silica dispersion liquid using the silica cake of the present invention as a raw material, a known slurrying method can be carried out without particular limitation.

For example, after mixing a predetermined amount each of a silica cake and a polar solvent, the method of disperse | distributing a silica cake in a polar solvent using a disperser, a polar solvent is previously put in a dispersing tank, and gradually operating a silica cake, operating a disperser. And a method of dispersing the same. In addition, if necessary, after dispersing the silica cake in the polar solvent using the above method, a method of performing highly atomizing means for further atomizing the silica particles in the dispersion to an average particle size in a suitable range is suitably employed.

The disperser used for the dispersion is not particularly limited, but a general stirrer having a propeller blade, a turbine blade, a paddle blade, and the like; High speed rotary centrifugal radial stirrers such as dispersion mixers and the like; High speed rotary shear stirrers such as homogenizers, homo mixers, ultra mixers and the like; And dispersers such as colloid mills, planetary mixers, and the like.

Among the dispersers, a disperser having a strong shearing force is suitable. Specifically, a high speed shear type stirrer; A composite disperser combining a propeller blade and a paddle blade with a high speed shear stirrer; And a complex disperser in which a planetary mixer and a high speed rotary centrifugal stirrer or a high speed rotary shear stirrer are combined.

In the present invention, the above-mentioned high atomization method is not particularly limited, but an atomization treatment using a bead mill, a sand mill, an ultrasonic homogenizer, a high pressure homogenizer, and the like can be given. Among them, a dispersion treatment using a high pressure homogenizer is preferable.

Precipitate is made by using a high-pressure homogenizer to collide the predispersed liquid in which the silica is dispersed in the polar solvent at a processing pressure of 30 MPa or more, or to pass the orifice under conditions of 30 MPa or more at the inlet and outlet sides of the orifice. Precipitated silica dispersions in which the average particle diameter of silica in the silica dispersion is 300 nm or less and the proportion of agglomerated particles of 500 nm or more are 5% by volume or less can be obtained.

In addition, the precipitated silica dispersion liquid thus obtained can be carried out without any problem by appropriately performing an operation of diluting with a polar solvent, various concentration operations, etc. in order to achieve an appropriate concentration according to the use as described above.

The operation of concentrating the precipitated silica dispersion liquid can be carried out without particular limitation to the existing concentration method. For example, an evaporative concentration method performed by raising the temperature to the boiling point of the polar solvent, a reduced pressure evaporation method performed by lowering the boiling point of the polar solvent under reduced pressure, and further, a thin film such as polysulfone, polyacrylonitrile or cellulose is applied by applying pressure. The ultrafiltration method etc. which remove a polar solvent using are mentioned.

The polar solvent used in the present invention can be used without particular limitation as long as the silica cake is dispersed. For example, water; Alcohols such as methanol, ethanol and 2-propanol; Ethers; Ketones can be used. The dispersion medium which mixed 2 or more types of said solvents can also be used. Generally, water is used suitably.

Moreover, in order to improve the storage stability and dispersibility of a silica particle, you may add a small amount of surfactant, a preservative, etc. in the range which does not impair the effect of this invention.

Further, for the purpose of modifying the silica particles exhibiting anionicity in a polar solvent to cationic properties, the silica cake and the cationic resin of the present invention are mixed and dispersed in a polar solvent to precipitate the silica particles dispersed in the cation. A silica dispersion, that is, a cationic resin modified precipitated silica dispersion may be prepared.

When the cationic resin modified precipitated silica dispersion liquid is used as a raw material of the coating liquid for an ink jet recording sheet, ink fixability, water resistance and image density of the ink jet recording sheet coated with the coating liquid can be increased.

The cationic resin can be used without particular limitation so long as it is a resin which dissociates when dissolved in water to show cationicity. Resin having a primary to tertiary amine group or a quaternary ammonium base is suitable. Specific examples include polyethyleneimine, polyvinylpyridine, polyamine sulfone, polydialkylaminoethyl methacrylate, polydialkylaminoethyl acrylate, polydialkylaminoethyl methacrylamide, polydialkylaminoethylacrylamide, poly Polymers such as epoxyamines, polyamideamines, dicyandiamide-formalin condensates, dicyandiamidepolyalkyl-polyalkylenepolyamine condensates, polyvinylamines, polyallylamines and the like and hydrochlorides thereof; Polydiallyldimethylammonium chloride; Copolymers of diallyldimethylammonium chloride with other monomers such as acrylamide and the like; Polydiallylmethylamine hydrochloride; Polymethacrylic acid ester methyl chloride quaternary salt etc. are mentioned.

In the present invention, the blending amount of the cationic resin can be stably produced without gelation of the cationic resin modified precipitated silica dispersion during production, and the viscosity of the obtained cationic resin modified precipitated silica dispersion can be lowered. It is preferable to set it as 3-50 weight part with respect to 100 weight part of silicas especially 3-15 weight part.

When the viscosity of the cationic resin-modified precipitated silica dispersion is high, handling properties are deteriorated in subsequent production processes, which is not preferable. Since the stability of the cationic resin-modified precipitated silica dispersion liquid with respect to the amount of the cationic resin added varies depending on the type of cationic resin to be added, the optimum addition amount of which the viscosity of the dispersion liquid becomes the lowest by experiment in advance is in the above addition amount range. It is desirable to choose.

The method for producing the cationic resin modified precipitated silica dispersion by mixing and dispersing the silica cake and the cationic resin of the present invention in a polar solvent is not particularly limited, but the cationic resin is mixed and dispersed in the dispersion of the silica cake in the polar solvent. And a method of mixing and dispersing the silica cake and the cationic resin by gradually adding a silica cake to the method of mixing the cationic resin in the polar solvent. In addition, if necessary, a method of preparing a cationic resin-modified precipitated silica dispersion using the above method, and then carrying out a high atomization means in order to further atomize the silica particles in the dispersion to a suitable range of average particle diameters is suitably employed. do.

In this invention, the coating liquid for inkjet recording sheets which consists of a polar solvent containing precipitated silica particle and binder which have a BET specific surface area of 220 m <^2> / g or more in a polar solvent by using the above-mentioned silica cake of this invention, The coating liquid The coating liquid for inkjet recording sheets can be easily obtained, which is diluted to have a silica concentration of 1.5% by weight and has a transmittance of 20% or more.

The coating liquid of the present invention is characterized in that the silica particles are extremely highly dispersed regardless of the presence of precipitated silica having a relatively large BET specific surface area. That is, the coating liquid of the present invention is characterized in that the transmittance of the liquid diluted so that the silica concentration is 1.5% by weight is 20% or more, particularly 25% or more. The transmittance is an index indicating the transparency of the coating liquid. If the transmittance is less than 20%, the transparency of the ink absorbing layer obtained by applying the coating liquid is low, and the color of the obtained image becomes unclear due to unclearness of the ink penetrating into the sheet. Depth is not felt, and it becomes impossible to realize picture quality.

In addition, in this invention, the transmittance | permeability of the said coating liquid is made into the absorbance (tau) of the measurement wavelength of 589 nm (NaD line | wire) of the coating liquid diluted so that the silica concentration might be 1.5 weight% using the same polar solvent as the coating liquid. It is the value which measured with the spectrophotometer and calculated | required transmittance | permeability (T) by following formula (3).

T (%) = 10 ^(2-τ) (3)

In the coating liquid obtained using the precipitated silica particle whose specific surface area is 22Om <^2> / g or more, as mentioned above, high transparency is an example of the conventional coating liquid, and it is an effect achieved by using the silica cake of this invention.

As a binder used in this invention, the well-known various binder used for manufacture of a coating liquid can be used. As a specific example of a typical binder, polyvinyl alcohol and its derivative (s), casein, starch, carboxymethylcellulose, etc. are mentioned. Of these, polyvinyl alcohol or derivatives thereof are most effectively used in view of dispersion suitability and paint stability. As said polyvinyl alcohol derivative, cation modified polyvinyl alcohol or nonionic modified polyvinyl alcohol is mentioned. Moreover, the binder which mixed two or more types of said binders can also be used.

In the present invention, the mixing ratio of the binder with respect to the precipitated silica is generally employed without particular limitation in the known coating liquid. For example, it is 10-100 weight part with respect to 100 weight part of precipitated silicas, Preferably it is the ratio of 30-60 weight part.

In the present invention, the precipitated silica concentration in the coating liquid is determined by the precipitated silica concentration of the precipitated silica dispersion liquid as a raw material, but is 5 to 30% by weight, preferably 5 to 20% by weight.

It is preferable that the coating liquid of this invention contains a cationic resin further. By containing cationic resin, the ink fixing property, water resistance, and image density of the inkjet recording sheet coated with the coating liquid can be increased.

As the cationic resin, the same resin as the cationic resin in the above cationic resin modified precipitated silica dispersion can be used.

In addition, the compounding quantity of cationic resin can be manufactured stably without gelling a coating liquid in the middle of manufacture, and also 3-50 weight part with respect to 100 weight part of precipitated silica particles so that the viscosity of the obtained coating liquid can be made low. It is preferable to set it as 3-15 weight part especially.

The coating solution of the present invention can be produced by dispersing precipitated silica and a binder having a BET specific surface area of 220 m ² / g or more in a polar solvent.

Although the method of disperse | distributing a precipitated silica and a binder in a polar solvent is not specifically limited, Generally, the method of adding a binder to the precipitated silica dispersion liquid obtained by disperse | distributing a precipitated silica in a polar solvent is suitable.

When the silica cake of the present invention is used as precipitated silica, it is possible to easily obtain a highly transparent coating liquid which is extremely suitable for use of the inkjet recording sheet. Therefore, it is preferable to use what disperse | distributed the silica cake of this invention in polar solvent as a precipitated silica dispersion liquid. When manufacturing the coating liquid containing cationic resin, the said cationic resin modified precipitated silica dispersion liquid may be used.

A well-known method is employ | adopted without a restriction | limiting in particular as a method of mixing the said precipitated silica dispersion liquid which disperse | distributed the silica cake of this invention in a polar solvent, or a cationic resin modified precipitated silica dispersion liquid, and a binder. For example, a precipitated silica dispersion or a cationic resin-modified precipitated silica dispersion and a binder are introduced into a mixing tank equipped with a general stirrer having a propeller blade, a turbine blade, or the like, or a high speed rotary shear stirrer such as a homogenizer or a homo mixer. In general, a method of mixing is common.

The coating liquid of this invention can be mix | blended with well-known arbitrary additives, unless the effect of this invention is remarkably reduced. Representative additives include water resistance enhancers such as cationic resins, ultraviolet absorbers, fluorescent brighteners, surfactants, pH adjusters, antifoaming agents, and flavoring agents.

There is no restriction | limiting in particular in the addition method to the coating liquid of the said arbitrary additive, When manufacturing the coating liquid mentioned above, it can add by a well-known method. For example, the method of adding to the mixture of a precipitated silica dispersion liquid and a binder, the method previously added to a binder, the method previously added to the precipitated silica dispersion liquid, etc. are mentioned. Alternatively, in order to produce a precipitated silica dispersion, the silica cake may be added in advance when dispersed in a polar solvent.

The support for the inkjet recording sheet produced using the coating solution of the present invention is not particularly limited, and a transparent or opaque support can be suitably used. Films of plastic such as polyethylene, polypropylene, polyvinyl chloride, polyester and the like; Papers such as quality paper, art paper, polyethylene laminated paper, and the like; Synthetic paper is an example.

Best Mode for Carrying Out the Invention

In order to demonstrate this invention concretely below, an Example and a comparative example are shown, but this invention is not limited only to these Examples.

The measuring method regarding a silica cake and a silica dispersion liquid is as follows.

[BET specific surface area]

After putting a silica cake into a dryer (120 degreeC) for 24 hours or more, nitrogen adsorption amount was measured using Asaphart 2010 made from Micromeritics, and the value of the one-point method in 0.2 of relative pressure was employ | adopted.

[Moisture Content of Silica Cake]

3-10 g of silica cakes were chewed in a weighing bottle, and it put in the drier heated at 105 degreeC for 12 hours or more, and computed from the weight before and behind water drying.

PH and Conductivity of 5 wt% Silica Dispersion

The silica cake and the ion-exchanged water which measured the water content in advance are mix | blended so that a silica concentration may be 5 weight%, the mixture is stirred and mixed with a propeller mixer, and it is made into a slurry, and is the value at 25 degreeC using a commercial pH meter and a conductivity meter. Was measured.

[n value]

Ion-exchange water was added to the silica cake which measured the water content in advance so that a silica concentration might be 5 weight%, and it premixed by stirring with a propeller mixer, and it slurryed.

The obtained slurry was processed once using the high pressure homogenizer (nanomizer; nanomizer, LA-31) at the process pressure of 78 MPa, and the silica dispersion liquid was produced. Next, the visible light absorption spectrum of this silica dispersion liquid was measured using the spectrophotometer (Japanese spectrometer, Ubest-35 type | mold).

First, ion-exchanged water was filled in the reference cell and the sample cell, respectively, using a cell having an optical path length of 10 mm, and zero calibration was performed over the full-wavelength range. Next, it diluted with ion-exchange water so that the silica concentration of the silica dispersion might be 1.5 weight%, and put into the sample cell, and the absorbance (tau) of wavelength (lambda) 460-760 nm was measured. 1og (λ) and 1og (τ) were plotted and the slope (-n) of the straight line was obtained by the least square method using the above equation (2).

[Particle Size Distribution and Average Particle Size]

Using a light scattering diffraction particle size distribution measuring device (Coltase, Coalta LS-230), the particle size distribution of the precipitated silica dispersion was measured under the conditions of 1.458 of the refractive index of silica and 1.332 of the refractive index of water used as the dispersion medium. The volume ratio and the volume-based arithmetic mean diameter D ₅₀ were calculated. This volumetric arithmetic mean diameter was made into the average particle diameter.

[Silica Solid Concentration in Reaction Mixture at the End of Reaction]

100 mL of the reaction mixture at the time of completion | finish of reaction was extract | collected, it filtered using No.5A filter paper, and it wash | cleaned by adding 1 L of ion-exchange water to the filtration residue. After putting this residue in the dryer (120 degreeC) for 24 hours or more, the weight was measured and it represented as the silica solid content weight (g) in unit reaction liquid quantity (1L) (unit: g / L).

In addition, the measuring method regarding a coating liquid is as follows.

[Transparency of Coating]

Dilute with ion-exchanged water so that the silica concentration of the coating solution may be 1.5% by weight, and the absorbance of the diluted coating solution is measured using a spectrophotometer (Type Ubest-35). The above formula (3) The transmittance T was calculated from the above. In the measurement, the optical path length was 10 mm and the measurement wavelength was 589 nm (NaD line).

[Stability of Coating Solution]

The coating solution was left to stand for 5 days, and the presence or absence of agglomerates in the coating solution was visually observed.

◎: no generation of aggregates

○: almost no aggregates

△: slight generation of aggregates

X: There is generation of aggregates

 [Transparency of Coating Layer]

The coating liquid was applied and dried on the surface of a PET sheet (Marynex 705, made by Eye Sea Japan) so as to have a coating amount of 20 g / m ² with a bar coder, and a coating layer was formed on the PET sheet. The measurement was performed according to the measuring method of JISK7136 using the haze meter (The Suga test company make, color computer) of the obtained sheet, and the transparency of the coating layer was evaluated on the following reference | standard.

◎: haze 50% or less

○: 50% to 60% haze

Δ: haze 60% to 70%

×: more than 70% of haze

Example 1

Sodium silicate solution (SiO ₂ concentration of 10g / L, the molar ratio x = 3.4) and put in a 6L reactor as an initial reaction mixture, while mixing with a propeller type stirring blade, heated to the temperature was raised to 95 ℃. The initial reaction solution was stirred while maintaining the temperature at 95 ° C, in which sodium silicate solution (SiO ₂ concentration 180 g / L, molar ratio x = 3.4) was further added at a rate of 32 mL / min and further sulfuric acid (concentration 221 g). / L) was added simultaneously over 50 minutes at a rate of 12 mL / min.

In the meantime, pH of the reaction liquid was 10.2-10.5. After completion | finish of simultaneous addition, stirring was continued for 40 minutes, maintaining 95 degreeC. The sulfuric acid was then added until the pH was 3.0 to obtain a reaction slurry. Silica solid content concentration was 42g / L.

The reaction slurry was filtered under reduced pressure and washed with ion exchanged water to obtain a silica cake. When the physical properties of this silica cake were measured, the water content was 89.5% by weight, the pH of the 5% dispersion was 5.1, and the conductivity was 164 µS / cm. n value was 2.4. In addition, the BET specific surface area of the silica was 276 m ² / g.

Example 2

The sodium silicate solution added in the initial reaction liquid had a SiO ₂ concentration of 27Og / L, the addition rate was 21 mL / min, and sulfuric acid was added until the pH became 4.5 after completion of the simultaneous addition. The same operation as 1 was performed.

The pH at the time of simultaneous addition was 10.4-10.6. In addition, the silica solid content concentration at the time of completion | finish of reaction was 45 g / L.

The physical properties of the silica cake obtained by filtration, washing, and dehydration from the reaction slurry were 89.0% by weight, pH of the 5% dispersion, 6.4, and conductivity of 136 µS / cm. n value was 2.5. In addition, the BET specific surface area of the silica was 265 m ² / g.

Example 3

5.9 L of 0.1 mol / L sodium hydroxide aqueous solution was put into the reactor as an initial reaction liquid, and it heated, heating at 93 degreeC, mixing with a propeller type stirring blade. In this initial reaction solution, a sodium silicate solution (SiO ₂ concentration 180 g / L, molar ratio x = 3.4) was added at a rate of 42 mL / min and sulfuric acid (concentration 221 g / L) at a rate of 12 mL / min for 40 minutes. Added over.

In the meantime, pH of the reaction liquid was 10.0-10.2. After completion | finish of simultaneous addition, stirring was continued for 20 minutes, maintaining 93 degreeC. The sulfuric acid was then added until the pH was 3.4 to obtain a reaction slurry. Silica solid content concentration was 36g / L.

The reaction slurry was filtered under reduced pressure and washed with ion exchanged water to obtain a silica cake. When the physical properties of this silica cake were measured, the water content was 89.6% by weight, the pH of the 5% dispersion was 4.6, and the conductivity was 229 µS / cm. n value was 2.9. In addition, the BET specific surface area of the silica was 316 m ² / g.

Example 4

6.3 liters of water was put into the reactor as an initial reaction liquid, and it heated and it was 93 degreeC, mixing with a propeller type stirring blade. In this initial reaction solution, sodium silicate solution (SiO ₂ concentration 270 g / L, molar ratio x = 3.4) was added at a rate of 37 mL / min and sulfuric acid (concentration 221 g / L) at a rate of 21 mL / min for 30 minutes. Added over.

In the meantime, pH of the reaction liquid was 9.3-9.6. After completion | finish of simultaneous addition, stirring was continued for 10 minutes, maintaining 93 degreeC. The sulfuric acid was then added until the pH was 3.1 to obtain a reaction slurry. Silica solid content concentration was 37g / L.

The reaction slurry was filtered under reduced pressure and washed with ion exchanged water to obtain a silica cake. When the physical properties of this silica cake were measured, the water content was 91.6 wt%, the pH of the 5% dispersion was 3.6, and the conductivity was 247 µS / cm. n value was 2.9. In addition, the BET specific surface area of the silica was 337 m ² / g.

Example 5

6.2 L of water was put into the reactor as an initial reaction liquid, and it heated, it was 94 degreeC, mixing with a propeller-type stirring blade. In this initial reaction solution, sodium silicate solution (SiO ₂ concentration 270 g / L, molar ratio x = 3.4) was added at a rate of 19 mL / min, and sulfuric acid (concentration 221 g / L) at a rate of 9.7 mL / min for 60 minutes. Added over.

In the meantime, pH of the reaction liquid was 9.5-9.8. After completion | finish of simultaneous addition, stirring was continued for 30 minutes, maintaining 94 degreeC. The sulfuric acid was then added until the pH was 3.2 to obtain a reaction slurry. Silica solid content concentration was 38g / L.

The reaction slurry was filtered under reduced pressure and washed with ion exchanged water to obtain a silica cake. When the physical properties of this silica cake were measured, the water content was 88.6% by weight, the pH of the 5% dispersion was 4.9, and the conductivity was 92 µS / cm. n value was 2.4. In addition, the BET specific surface area of the silica was 257 m ² / g.

Comparative Example 1

8 L of sodium silicate solution (SiO ₂ concentration 50 g / L, molar ratio x = 3.2) and 92 g of sodium sulfate were put into a reaction tank, and under stirring, sulfuric acid (221 g / L) was added at a rate of 31 mL / min at a temperature of 40 ° C. Added for minutes. Then, the temperature of the reaction solution was raised to 95 ° C under stirring. While maintaining at 95 ° C., the sulfuric acid was added at a rate of 5.1 mL / min until the pH of the reaction mixture reached 5.5. The produced precipitated silica was filtered and washed in the same manner as in Example 1.

When the physical property of the obtained silica cake was measured, pH of the water content of 88.9 weight% and the 5% dispersion was 6.0. n value was 1.6. In addition, the BET specific surface area of the precipitated silica was 280 m ² / g.

Comparative Example 2

Sodium silicate solution (SiO ₂ concentration of 10g / L, the molar ratio x = 3.4) and put in a 2.2L reaction vessel was allowed to react at 87 ℃. Among them, sodium silicate solution (SiO ₂ concentration 90 g / L, molar ratio x = 3.4) was added simultaneously over 110 minutes at a rate of 38 mL / min and sulfuric acid (concentration 221 g / L) at a rate of 6.5 mL / min. did. In the meantime, pH of the reaction liquid was 10.0-10.3. After completion | finish of simultaneous addition, stirring was continued for 10 minutes, maintaining 87 degreeC, Then, the said sulfuric acid was added until pH became 3.5, and the reaction slurry was obtained. Silica solid content concentration was 55g / L.

When the reaction slurry was filtered and the physical properties of the silica cake obtained by washing were measured, the pH of the water content of 87.3 weight% and the 5% dispersion was 5.4. n value was 0.9. Further, the silica had a BET specific surface area of 197 m ² / g.

Comparative Example 3

The silica cake obtained by the method similar to Example 1 was placed in the drier maintained at 120 degreeC for 20 hours, and it was left to stand indoors for 24 hours further. This was ground with a coffee grinder to obtain silica powder.

The water content rate of the obtained silica powder was 6.1 weight%, and the n value of the silica dispersion liquid was 0.6.

Comparative Example 4

Sodium silicate solution (SiO ₂ concentration of 10g / L, the molar ratio x = 3.4) and put in a 2.5L reaction vessel was allowed to react at 80 ℃. Among them, sodium silicate solution (SiO ₂ concentration 90 g / L, molar ratio x = 3.4) was added at a rate of 40 mL / min, and sulfuric acid (concentration 221 g / L) was simultaneously added over 115 minutes at a rate of 6.8 mL / min. did. In the meantime, pH of the reaction liquid was 10.1-10.5. After completion | finish of simultaneous addition, stirring was continued for 10 minutes, maintaining 80 degreeC, Then, the said sulfuric acid was added until pH became 3.4, and the reaction slurry was obtained. Silica solid content concentration was 55g / L.

The reaction slurry was filtered and the physical properties of the silica cake obtained by washing were measured, and the water content was 86.5 wt% and the pH of the 5% dispersion was 6.0. n value was 1.2. In addition, the BET specific surface area of the silica was 244 m ² / g.

Example 6

The silica cake obtained in Example 1 was slurried with a colloid mill (colloid mill K60, manufactured by PUC), and then diluted using a predetermined amount of ion-exchanged water to obtain a silica slurry having a silica concentration of 10% by weight. The silica slurry was atomized at a treatment pressure of 78 MPa using a high pressure homogenizer (manufacturer, nanomizer LA-31) to obtain a precipitated silica dispersion. The average particle diameter of the obtained precipitated silica dispersion liquid was 137 nm, and the ratio of the particle | grains of 500 nm or more was 0.6 volume%.

Example 7

A precipitated silica dispersion liquid was obtained in the same manner as in Example 6 except that the silica cake was changed to the silica cake obtained in Example 2. The average particle diameter of the obtained precipitated silica dispersion liquid was 133 nm, and the ratio of the particle | grains of 500 nm or more was 0.5 volume%.

Example 8

A precipitated silica dispersion liquid was obtained in the same manner as in Example 6 except that the silica cake was changed to the silica cake obtained in Example 3. The average particle diameter of the obtained precipitated silica dispersion liquid was 112 nm, and the ratio of the particle | grains of 500 nm or more was 0 volume%.

Example 9

A precipitated silica dispersion liquid was obtained in the same manner as in Example 6 except that the silica cake was changed to the silica cake obtained in Example 4. The average particle diameter of the obtained precipitated silica dispersion liquid was 100 nm, and the ratio of the particle | grains of 500 nm or more was 0 volume%.

Example 10

A precipitated silica dispersion liquid was obtained in the same manner as in Example 6 except that the silica cake was changed to the silica cake obtained in Example 5. The average particle diameter of the obtained precipitated silica dispersion liquid was 140 nm, and the ratio of the particle | grains of 500 nm or more was 0.2 volume%.

Comparative Example 5

A precipitated silica dispersion liquid was obtained in the same manner as in Example 6 except that the silica cake was changed to the silica cake obtained in Comparative Example 1. The average particle diameter of the obtained precipitated silica dispersion liquid was 380 nm, and the ratio of the particle | grains of 500 nm or more was 12.9 volume%.

Comparative Example 6

A precipitated silica dispersion liquid was obtained in the same manner as in Example 6 except that the silica cake was changed to the silica cake obtained in Comparative Example 2. The average particle diameter of the obtained precipitated silica dispersion liquid was 346 nm, and the ratio of the particle | grains of 500 nm or more was 13.1 volume%.

Comparative Example 7

A silica slurry having a silica concentration of 10% by weight was dispersed by dispersing with a homogenizer (Ikaze, Homogenizer T-25) while gradually adding 107 g (6.1% by weight of moisture) of the silica powder obtained in Comparative Example 3 to 893 g of ion-exchanged water. Got it. The silica slurry was atomized at a treatment pressure of 78 MPa using a high pressure homogenizer (manufacturer, nanomizer LA-31) to obtain a precipitated silica dispersion. The average particle diameter of the obtained precipitated silica dispersion liquid was 18.5 micrometers, and the ratio of the particle | grains of 500 nm or more was 94.5 volume%.

Comparative Example 8

A precipitated silica dispersion liquid was obtained in the same manner as in Example 6 except that the silica cake was changed to the silica cake obtained in Comparative Example 4. The average particle diameter of the obtained precipitated silica dispersion liquid was 320 nm, and the ratio of the particle | grains of 500 nm or more was 11.1 volume%.

Example 11

The silica cake obtained in Example 1 was slurried by a colloid mill (colloid mill K60 manufactured by PUC), and then diluted using a predetermined amount of ion-exchanged water to obtain a silica slurry having a silica concentration of 100% by weight. To 500 g of this silica slurry, 12.5 g of a cationic resin aqueous solution containing diallylmethylamine hydrochloride polymer at a concentration of 20% by weight was added, and mixed by using an ultra mixer (manufactured by Mitsubishi Industries Co., Ltd., Ultra Mixer LR-2). , The premixed liquid was obtained. The preliminary mixed solution was subjected to atomization treatment at a treatment pressure of 78 MPa using a high pressure homogenizer (manufacturer, nanomizer LA-31) to obtain a cationic resin-modified precipitated silica dispersion. The average particle diameter of the obtained cationic resin modified precipitated silica dispersion liquid was 193 nm, and the ratio of the particle | grains of 500 nm or more was 3.6 volume%.

Example 12

Cationic resin modified precipitated silica dispersion liquid was obtained in the same manner as in Example 11 except that the silica cake was changed to the silica cake obtained in Example 2. The average particle diameter of the obtained cationic resin modified precipitated silica dispersion liquid was 171 nm, and the ratio of the particle | grains of 500 nm or more was 2.6 volume%.

Comparative Example 9

Cationic resin modified precipitated silica dispersion liquid was obtained in the same manner as in Example 11 except that the silica cake was changed to the silica cake obtained in Comparative Example 1. The average particle diameter of the obtained cationic resin modified precipitated silica dispersion liquid was 3,584 nm, and the ratio of the particle | grains of 500 nm or more was 34.9 volume%.

Comparative Example 10

Cationic resin modified precipitated silica dispersion liquid was obtained in the same manner as in Example 11 except that the silica cake was changed to the silica cake obtained in Comparative Example 2. The average particle diameter of the obtained cationic resin modified precipitated silica dispersion liquid was 433 nm, and the ratio of the particle | grains of 500 nm or more was 15.4 volume%.

Example 13

50 g of the precipitated silica dispersion liquid obtained in Example 6 and 25 g of a 10% by weight polyvinyl alcohol aqueous solution (Curarese, PVAl17) were mixed by stirring with a propeller mixer to obtain a coating solution. The physical properties of the obtained coating liquid are shown in Table 1.

Example 14

A coating solution was obtained in the same manner as in Example 13 except that the precipitated silica dispersion liquid was changed to the precipitated silica dispersion liquid obtained in Example 7. The physical properties of the obtained coating liquid are shown in Table 1.

Example 15

A coating solution was obtained in the same manner as in Example 13 except that the precipitated silica dispersion liquid was changed to the precipitated silica dispersion liquid obtained in Example 8. The physical properties of the obtained coating liquid are shown in Table 1.

Example 16

Except having changed the precipitated silica dispersion liquid into the precipitated silica dispersion liquid obtained in Example 9, it carried out similarly to Example 13, and obtained the coating liquid. The physical properties of the obtained coating liquid are shown in Table 1.

Example 17

Except having changed the precipitated silica dispersion liquid into the precipitated silica dispersion liquid obtained in Example 10, it carried out similarly to Example 13, and obtained the coating liquid. The physical properties of the obtained coating liquid are shown in Table 1.

Comparative Example 11

Except having changed the precipitated silica dispersion liquid into the precipitated silica dispersion liquid obtained by the comparative example 5, it carried out similarly to Example 13, and obtained the coating liquid. The physical properties of the obtained coating liquid are shown in Table 1.

Comparative Example 12

A coating solution was obtained in the same manner as in Example 13 except that the precipitated silica dispersion was changed to the precipitated silica dispersion obtained in Comparative Example 6. The physical properties of the obtained coating liquid are shown in Table 1.

Comparative Example 13

A coating solution was obtained in the same manner as in Example 13 except that the precipitated silica dispersion was changed to the precipitated silica dispersion obtained in Comparative Example 7. The physical properties of the obtained coating liquid are shown in Table 1.

Comparative Example 14

A coating solution was obtained in the same manner as in Example 13 except that the precipitated silica dispersion was changed to the precipitated silica dispersion obtained in Comparative Example 8. The physical properties of the obtained coating liquid are shown in Table 1.

Example 18

50 g of the cationic resin modified precipitated silica dispersion liquid obtained in Example 11 and 25 g of 10% by weight polyvinyl alcohol aqueous solution (Curarese, PVAl17) were mixed with a propeller mixer under stirring to obtain a coating solution. The physical properties of the obtained coating liquid are shown in Table 1.

Example l9

Coating liquid was obtained like Example 18 except having changed the cationic resin modified precipitated silica dispersion liquid into the cationic resin modified silica dispersion liquid obtained in Example 12. The physical properties of the obtained coating liquid are shown in Table 1.

Comparative Example 15

Coating liquid was obtained like Example 18 except having changed the cationic resin modified precipitated silica dispersion liquid into the cationic resin modified silica dispersion liquid obtained by the comparative example 9. The physical properties of the obtained coating liquid are shown in Table 1.

Comparative Example 16

A coating solution was obtained in the same manner as in Example 18 except that the cationic resin modified precipitated silica dispersion liquid was changed to the cationic resin modified silica dispersion liquid obtained in Comparative Example 10. The physical properties of the obtained coating liquid are shown in Table 1.

Table 1

Coating amount Coating layer Transmittance (%) stability Transparency Example 13 40 ○ ◎ Example 14 41 ○ ◎ Example 15 60 ○ ◎ Example 16 59 ○ ◎ Example 17 21 ○ ○ Comparative Example 11 17 ○ △ Comparative Example 12 2 ○ × Comparative Example 13 0 × × Comparative Example 14 2 ○ × Example 18 25 ◎ ○ Example 19 32 ◎ ○ Comparative Example 15 6 ◎ × Comparative Example 16 One ◎ ×

As mentioned above, the silica cake of this invention is extremely excellent in the dispersibility at the time of disperse | distributing to a polar solvent in spite of small primary particle diameter, and using this silica cake, a highly transparent silica dispersion liquid can be obtained easily. . Therefore, according to this invention, the productivity of a silica dispersion liquid can be improved significantly.

Moreover, the coating liquid for inkjet recording sheets obtained by mixing such a silica dispersion liquid and a binder has high transparency so that the transmittance of the coating liquid diluted so that a silica concentration might be 1.5 weight% is 20% or more, and for this reason, The coating layer created using the coating solution has high transparency as compared with the coating layer prepared using conventional precipitated silica. Therefore, according to the present invention, it becomes possible to manufacture an inkjet recording sheet that is optimal for obtaining photographic image quality.

Claims (12)

A cake of precipitated silica having a BET specific surface area of 220 m ² / g or more, which is dispersed in ion-exchanged water to give an aqueous dispersion having a silica concentration of 5% by weight, and then diluted to have a silica concentration of 1.5% by weight (n value) ) Is a cake of di-disperse precipitated silica, characterized in that two or more. The method of claim 1, A cake of didisperse precipitated silica having a water content of 83 to 93% by weight. As the initial reaction solution, either an alkaline silicate aqueous solution, an alkaline aqueous solution pH-adjusted with a basic substance, or water was used, and the pH of the reaction solution was maintained at a constant value within ± 0.3 within a range of 7.5 to 11.5, and the temperature was maintained. The alkali silicate and the mineral acid are added to the reaction solution at the same time while maintaining the temperature at 90 DEG C or more to produce precipitated silica, and the precipitated silica is separated from the reaction solution in a wet state. Method of preparation. The method of claim 3, The manufacturing method of the cake of di-disperse precipitated silica whose silica solid content concentration in a reaction mixture at the time of reaction completion is 50 g / L or less. A dispersion liquid in which the cake of di-disperse precipitated silica according to claim 1 is dispersed in a polar solvent, wherein the average particle diameter of the precipitated silica particles present in the dispersion is 300 nm or less and the proportion of the agglomerated particles of 500 nm or more in particle diameter is 5 vol% or less. Precipitated Silica Dispersion. The method of claim 5, Precipitated silica dispersion further disperse the cationic resin. A method of producing a precipitated silica dispersion according to claim 5, wherein the silica slurry obtained by dispersing the cake of the dispersible precipitated silica according to claim 1 in a polar solvent is atomized by a high pressure homogenizer. A pre-mixed liquid obtained by dispersing a cake of the di-disperse precipitated silica according to claim 1 and a cationic resin in a polar solvent is atomized by a high pressure homogenizer, wherein the precipitated silica dispersion according to claim 6 is produced. A coating liquid for inkjet recording sheets obtained by dispersing a cake and a binder of the di-disperse precipitated silica according to claim 1 in a polar solvent, wherein the coating liquid is diluted to a silica concentration of 1.5% by weight and has a transmittance of 20% or more. Coating liquid for inkjet recording sheets The method of claim 9, Coating liquid for inkjet recording sheets which further contain a cationic resin. A method for producing a coating liquid for an ink jet recording sheet according to claim 9, wherein the cake and binder of the heterodisperse precipitated silica according to claim 1 are dispersed in a polar solvent. A method for producing a coating liquid for an ink jet recording sheet according to claim 10, wherein the cake, cationic resin and binder of the didisperse precipitated silica according to claim 1 are dispersed in a polar solvent.