JP4846193B2 - Easily dispersible precipitated silica cake and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel precipitated silica cake made of precipitated silica obtained by a precipitation method (wet method), and a precipitated silica dispersion in which the precipitated silica cake is dispersed in a polar solvent. Specifically, the present invention provides a precipitated silica cake that is remarkably excellent in dispersibility when dispersed in a polar solvent such as water in spite of a small primary particle diameter, and a precipitated silica dispersion in which the precipitated silica cake is dispersed.
[0002]
[Prior art]
Silica dispersions include various coating agents, semiconductor wafers, and IC insulating films for imparting gas barrier properties, corrosion resistance, hydrophilicity, glossiness, liquid absorption, etc. to paper, film, resin, glass, etc., including inkjet recording sheets. Used as a polishing agent, an emulsion stabilizer, and the like.
[0003]
Conventionally, colloidal silica has been representative as a silica dispersion suitably used for the above applications. Colloidal silica is manufactured in a process in which sodium silicate solution is used as a raw material, desodiumized with an ion exchange resin, etc., concentrated appropriately, and then stabilized by adjusting the pH with ammonia or the like. A dispersed silica dispersion can be prepared.
[0004]
However, with the recent increase in demand for silica dispersions, it has become desirable to develop a method for producing a highly productive silica dispersion to replace colloidal silica with low productivity.
[0005]
Further, in the inkjet recording sheet which is one of the uses of the silica dispersion described above, the silica dispersion 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. Yes. In general, the characteristics required of the ink absorbing layer of an ink jet recording sheet include high transparency and liquid absorption. However, the ink absorbing layer using the above-mentioned colloidal silica as a coating liquid raw material has a problem that the liquid absorbing property is low although the transparency is high.
[0006]
In response to such a demand, precipitated silica produced by the so-called “precipitation method”, in which silica particles are precipitated by reacting an alkali silicate aqueous solution with an acid, is excellent in productivity and liquid absorption. Attention is being paid.
[0007]
In order to produce a highly transparent dispersion in which the silica particles are highly dispersed using the precipitated silica, it is necessary to use silica particles having a small primary particle size, that is, a high specific surface area. is there. However, since precipitated silica has a strong cohesive force, the aggregated structure of aggregated particles becomes hard, especially when precipitated silica with a high specific surface area is used. It is difficult to make it.
[0008]
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 reducing the cohesiveness, and the precipitated silica particles are polarized in the state of the cake. Attempts have been made and proposed to improve dispersibility by dispersing in a solvent (see, for example, Patent Document 1).
[0009]
However, even when the above method is used for precipitated silica having a high specific surface area, it is industrially difficult to obtain a precipitated silica cake having high dispersibility, and a dispersion in which precipitated silica is highly dispersed is obtained. Therefore, not only a great deal of time and labor is required, but a satisfactory dispersion state has not yet been achieved.
[0010]
[Patent Document 1]
Japanese Patent Laid-Open No. 9-142827
[0011]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a precipitated silica cake having significantly improved dispersibility in a polar solvent despite the fact that it is a precipitated silica having a high specific surface area, and the precipitated silica is highly dispersed by dispersing the precipitated silica cake. It is to provide a precipitated silica dispersion.
[0012]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present inventors have limited the reaction of precipitated silica to a certain condition, so that the aggregate structure is weak despite the fine silica primary particle size. The present inventors have succeeded in obtaining a silica cake that can be easily dispersed, and completed the present invention.
[0013]
That is, the present invention provides an electrolyte. (Excluding basic substances) or While maintaining the pH of the reaction solution at a constant value in the range of 7.5 to 11.5 and maintaining the reaction temperature at 92 to 98 ° C. with respect to the initial reaction solution to which no mineral acid has been added, An alkali silicate and a mineral acid are simultaneously added to the reaction solution to form precipitated silica so that the silica solid content concentration in the reaction mixture at the end of the reaction is 50 g / L or less, and the precipitated silica is added to the reaction solution. Produced by separation in a more wet state, the BET specific surface area is 220 m ² / G or more of an aqueous cake of precipitated silica, dispersed in ion-exchanged water so as to be an aqueous dispersion having a silica concentration of 5% by weight, and then diluted such that the silica concentration becomes 1.5% by weight It is an easily dispersible precipitated silica cake (hereinafter, also simply referred to as “silica cake”) characterized in that the light scattering index (n value) of the liquid is 2 or more.
[0014]
The present invention also provides a method for producing the above-described easily dispersible precipitated silica cake.
[0015]
That is, according to the present invention, the electrolyte (Excluding basic substances) or While maintaining the pH of the reaction solution at a constant value in the range of 7.5 to 11.5 and maintaining the reaction temperature at 92 to 98 ° C. with respect to the initial reaction solution to which no mineral acid has been added, An alkali silicate and a mineral acid are simultaneously added to the reaction solution to form precipitated silica so that the silica solid content concentration in the reaction mixture at the end of the reaction is 50 g / L or less, and the precipitated silica is added to the reaction solution. Provided is a method for producing a readily dispersible precipitated silica cake characterized by separation in a more wet state.
[0016]
Furthermore, the present invention also provides a precipitated silica dispersion prepared by using the above-described easily dispersible precipitated silica cake, in which precipitated silica is highly dispersed.
[0017]
That is, according to the present invention, a dispersion in which the above-described easily dispersible precipitated silica is dispersed in a polar solvent, and the average particle diameter of the silica particles in the dispersion is 300 nm or less and 500 nm or more. A precipitated silica dispersion is provided in which the proportion of aggregated particles is 5% by volume or less.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, precipitated silica is a general term for silica produced by a precipitation method.
[0019]
In general, in the precipitation method, an aqueous silica silicate solution and a mineral acid are reacted to precipitate silica in the reaction solution. Subsequently, the precipitated silica cake is recovered by filtering and washing the precipitated silica. In the present invention, the water-containing solid matter of precipitated silica recovered by reaction, filtration, and washing in this way, which remains wet without being dried, is referred to as “aqueous cake” or “cake”.
[0020]
The precipitated silica constituting the silica cake of the present invention has a BET specific surface area of 220 m. ² / G or more, preferably 240 to 400 m ² / G, more preferably 250 to 350 m. ² / G.
[0021]
The BET specific surface area is 220m ² Although the silica cake made of precipitated silica of less than / g is relatively easy to disperse, with a particle diameter corresponding to the BET specific surface area, a highly transparent precipitated silica dispersion is used as shown in the examples described later. It is difficult to manufacture.
[0022]
The BET specific surface area is S.I. Brunaure, P.M. H. Emmett, E.M. J. Teller. Am. Chem. Soc. , 60, 309 (1938), which is a specific surface area measured by applying the multi-layer adsorption theory and is considered to correspond to the average primary particle diameter of silica. For example, as described in the Powder Engineering Society et al., “Revised Supplemental Powder Physical Properties” (1985), assuming that the primary particles are spherical, the specific surface area and the average diameter of the primary particles are expressed by the following formula (1). There is a relationship, and the larger the specific surface area, the smaller the average primary particle size.
[0023]
D = 6 / (S · ρ) (1)
(Here, D is the average primary particle size, S is the specific surface area, and ρ is the density of the particles.)
The silica cake of the present invention is characterized by exhibiting extremely good dispersibility when dispersed in a polar solvent while having the above-described relatively large BET specific surface area.
[0024]
That is, the silica cake of the present invention is dispersed in ion-exchanged water so as to become an aqueous dispersion having a silica concentration of 5% by weight by the method described later, and then diluted so that the silica concentration becomes 1.5% by weight. The light scattering index (n value) of the liquid is 2 or more, preferably 2.1 or more, and more preferably 2.2 or more.
[0025]
The n value is an index representing the dispersion state of silica in the dispersion, and this value increases as the dispersibility improves. Therefore, it can be considered that the larger the n value is, the finer the dispersion state becomes, so that it becomes an index of the fragility of the aggregate structure of the silica cake.
[0026]
The n value is a value measured according to the method described in Journal of Ceramic Society of Japan, 101 [6], 707-712 (1993). That is, using a commercially available spectrophotometer, the absorbance (τ) is obtained by measuring the spectrum of the dispersion having a light wavelength (λ) in the range of 460 nm to 700 nm, and log (λ) τ) is plotted, and the slope (−n) of the straight line is obtained by the least square method using the following equation (2).
[0027]
τ = αλ ^-N (2)
(Where τ is absorbance, α is a constant, λ is the wavelength of light, and n is the light scattering index.)
In addition, in the measurement of the n value, an aqueous dispersion having a silica concentration of 5% by weight prepared from an aqueous cake of precipitated silica is added with ion-exchanged water so that the silica concentration becomes the above-mentioned silica concentration, and stirred with a propeller mixer. Then, preliminary dispersion was carried out, and the obtained slurry was obtained by subjecting it to atomization by treating it once at a treatment pressure of 78 MPa using a high-pressure homogenizer.
[0028]
As described above, in order to improve the transparency of the precipitated silica dispersion, it is necessary to use precipitated silica having a high specific surface area. As described above, the specific surface area is 220 m. ² / G or more of precipitated silica has very high primary particle agglomeration. In conventional silica cake, the n value is at most about 1.6 due to insufficient dispersibility.
[0029]
On the other hand, the n value of the silica cake of the present invention exhibits an extremely high dispersibility of 2 or more. And when it disperses | distributes to a polar solvent with this silica cake which shows such a high n value, the highly stable and stable silica dispersion liquid can be obtained.
[0030]
Although the other structure of the silica cake of the present invention is not particularly limited, when the silica dispersion is produced, it is easier to disperse in a polar solvent when the water content is in the range of 83 to 93% by weight. preferable. More preferably, it is 85 to 92% by weight.
[0031]
Furthermore, when the silica cake is dispersed in water to give a 5% by weight dispersion, a pH value in the range of 3 to 7 is preferable because the dispersibility of the silica cake can be further improved. More preferably, the pH is 3.5 to 6.5.
[0032]
Although the manufacturing method of the silica cake of this invention is not restrict | limited in particular, If the typical manufacturing method is illustrated, the following method will be mentioned.
[0033]
That is, according to the present invention, the electrolyte (Excluding basic substances) or While maintaining the pH of the reaction solution at a constant value in the range of 7.5 to 11.5 and maintaining the reaction temperature at 92 to 98 ° C. with respect to the initial reaction solution to which no mineral acid has been added, An alkali silicate and a mineral acid are simultaneously added to the reaction solution to form precipitated silica so that the silica solid content concentration in the reaction mixture at the end of the reaction is 50 g / L or less, and the precipitated silica is added to the reaction solution. Provided is a method for producing a readily dispersible precipitated silica cake characterized by separation in a more wet state.
[0034]
In the above production method, sodium silicate, potassium silicate and the like can be used as the alkali silicate, but sodium silicate is generally used as an industrial raw material. In addition, the chemical formula of alkali silicate is generally expressed as M, where M is an alkali metal (Na or K). ₂ O · xSiO ₂ It is written. x is SiO ₂ / M ₂ It is the molar ratio of O.
[0035]
SiO of alkali silicate used in the method for producing silica cake of the present invention ₂ / M ₂ The molar ratio x of O is not particularly limited, but generally a molar ratio of 2 to 4, preferably 3.0 to 3.5 can be suitably used. Moreover, the concentration at the time of use of the alkali silicate is not particularly limited, and those available for industrial use can be added to the reaction solution as they are, or they can be used after being appropriately diluted. SiO in use in alkali silicate ₂ A concentration of 50 to 300 g / L is a general standard.
[0036]
As the mineral acid, sulfuric acid, hydrochloric acid, nitric acid and the like can be used, but for industrial use, sulfuric acid is generally used. The concentration of the mineral acid is not particularly limited, and those available for industrial use can be added to the reaction solution as they are, or can be used after appropriately diluted.
[0037]
Below, the manufacturing method of the silica cake of this invention is demonstrated in detail. In the following, the reaction liquid before the alkali silicate and the mineral acid are added simultaneously is referred to as an initial reaction liquid.
[0038]
In the production of the silica cake of the present invention, first, the initial reaction liquid is charged into the reaction vessel, and stirred using a propeller blade or the like, external heating or internal heating by a heater, or introduction of steam, etc. (The temperature to be maintained during the reaction between the alkali silicate and the mineral acid, which will be described later).
[0039]
The initial reaction solution may be an aqueous alkali silicate solution having an appropriate concentration, or an alkaline aqueous solution whose pH is appropriately adjusted with a basic substance such as sodium hydroxide, aqueous ammonia, or amines, preferably a pH value of 7.5. It may be an aqueous alkaline solution adjusted in advance to a constant value in the range of ˜11.5 (a pH value to be maintained during the reaction between an alkali silicate and a mineral acid described later), or water. In general, a moderate concentration, eg SiO ₂ When the initial reaction liquid is an alkali silicate aqueous solution adjusted to a concentration of about 1 to 50 g / L, the pH value tends to be maintained at a constant value, and a small amount of mineral acid is used. preferable. Further, as is generally practiced in the method for producing precipitated silica by the precipitation method, an electrolyte, generally sodium sulfate, can be added to the initial reaction solution, but the electrolyte acts as a flocculant, and BET Since it is easy to reduce the specific surface area, it is preferable not to use the precipitated silica cake having a high BET specific surface area and good dispersibility as in the present invention. In addition, when the initial reaction solution is an alkali silicate aqueous solution having an appropriate concentration, it is possible to add a mineral acid for the purpose of adjusting the pH value etc. before starting to add the alkali silicate and the mineral acid simultaneously. However, when a mineral acid is added, a small amount of silica or the above-mentioned electrolyte is generated by the neutralization reaction between the alkali silicate in the initial reaction solution and the added mineral acid, and the dispersibility targeted by the present invention is good. Therefore, the initial reaction liquid is preferably an alkali silicate aqueous solution to which no mineral acid is added.
[0040]
The stirring of the reaction solution is not particularly limited as long as the uniformity can be maintained in the sense that concentration distribution of contents in the reaction solution and segregation of precipitated solids can be avoided. Dispersion of general agitators with propeller blades, turbine blades, paddle blades, high-speed rotary radial agitators such as disper mixers, high-speed rotary shear type agitators such as homogenizers, homomixers, and ultramixers, colloid mills, planetary mixers, etc. What is necessary is just to stir or mix with a machine. In addition, stirring by circulation of the reaction liquid, such as extracting a part of the reaction liquid using a pump for transporting liquid and re-injecting it from another position, can be employed.
[0041]
In the present invention, it is important to perform an operation of simultaneously adding an alkali silicate and a mineral acid to produce precipitated silica by a neutralization reaction while uniformly stirring an initial reaction liquid having a predetermined temperature and a predetermined concentration. . In this operation, it is also important to set the reaction temperature to 90 ° C. or higher and maintain the pH at a constant value within the range of 7.5 to 11.5.
[0042]
The first feature of the present invention is to maintain the reaction temperature at 90 ° C. or higher as described above. When the reaction temperature is lower than 90 ° C., the dispersibility of the resulting precipitated silica cake becomes low, and the dispersibility index (n value) described later becomes smaller than 2. In particular, the reaction temperature is preferably in the range of 92 to 98 ° C, and more preferably 93 to 97 ° C.
[0043]
The 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. If the pH value fluctuates greatly, the dispersibility of the resulting precipitated silica cake is still inferior. Nevertheless, the constant value is that some fluctuation is allowed, and the fluctuation range of pH is preferably within ± 0.3, and more preferably within ± 0.2. When the pH value of the reaction solution is less than 7.5, the reaction becomes unstable, for example, the reaction solution tends to gel, and productivity exceeding 11.5 results in a decrease in productivity. A more preferable range of the pH value is 8 to 11, and further preferably 9 to 11 in which the pH is easily maintained at a constant value.
[0044]
The third feature of the present invention is that an operation of simultaneously adding alkali silicate and mineral acid to the reaction solution is employed as means for maintaining the pH of the reaction solution at a constant value as described above. As means for maintaining the pH at a constant value, it is conceivable to introduce a buffer, an alkali such as sodium hydroxide, a mineral acid other than the mineral acid added simultaneously with the alkali silicate, and the like into the reaction solution. However, when a buffering agent is added, the residue of the buffering agent may adhere to the resulting silica cake and adversely affect as an impurity during the preparation of the silica dispersion (for example, it may be difficult to adjust the pH value, The compatibility with the other additives). In addition, the addition of an alkali or another mineral acid as described above is substantially equivalent to changing the type, concentration, molar ratio x, etc. of the alkali silicate and / or mineral acid, so the range defined by the present invention. Operation.
[0045]
In the precipitation method of synthesizing precipitated silica by neutralizing alkali silicate with mineral acid, the reaction is generally alkaline with a pH value of 7 or more from the start of the neutralization reaction until at least silica precipitation occurs. To be implemented. The reaction format at that time is roughly divided into a method of adding a mineral acid to an alkali silicate solution adjusted to an appropriate concentration (reaction format A), and an alkali silicate and mineral acid employed in the present invention are reacted under certain conditions. There are two types of methods (reaction format B), which are simultaneously added to the liquid. Among these reaction modes A and B, a precipitated silica cake having a high specific surface area and excellent dispersibility can be easily obtained. Therefore, reaction mode B, that is, alkali silicate and mineral acid are simultaneously introduced into the reaction solution under a certain condition. It is preferable to employ the method of adding.
[0046]
As described above, it is possible to use an alkali silicate solution added with a mineral acid as an initial reaction solution. However, an electrolyte is formed at the initial stage of the neutralization reaction, and it acts as a flocculant. Since it is easy to reduce the specific surface area, the addition of the mineral acid before the simultaneous addition of the alkali silicate and the mineral acid makes it possible to obtain a precipitated silica cake having a high BET specific surface area and good dispersibility. Preferred for manufacturing.
[0047]
Specifically, the synthesis reaction of the precipitated silica cake of the present invention according to reaction mode B is carried out as follows: As the initial reaction liquid in the reaction vessel, the molar ratio x is 2 to 4, SiO 2 ₂ A sodium silicate aqueous solution adjusted to a concentration of 1 to 50 g / L is charged, and the reaction temperature is adjusted to 90 ° C. or higher while stirring uniformly. While maintaining uniform stirring and reaction temperature, the molar ratio x is 2-4 and SiO 2 ₂ Sodium silicate aqueous solution adjusted to a concentration of 50 to 300 g / L and H ₂ SO ₄ Sulfuric acid whose concentration is adjusted so that the content is about 100 to 1000 g / L is simultaneously added while adjusting the pH to be a constant value within a range of 7.5 to 11.5. After the formation of silica particles and confirmation of silica precipitation, the simultaneous addition is continued until the desired BET specific surface area is reached. Thereafter, only the sulfuric acid is added to adjust the pH to 2 to 6, thereby stabilizing the reaction solution and terminating the reaction.
[0048]
As a manufacturing method of the easily dispersible precipitated silica cake of this invention, it is required to add simultaneously an alkali silicate and a mineral acid on the conditions controlled so that pH may become a constant value. In particular, in order to obtain a precipitated silica cake with high dispersibility, it is important to follow the reaction format B until an alkali silicate and a mineral acid are simultaneously added to the initial reaction solution until silica particles are formed and at least precipitation occurs.
[0049]
Although details of the reaction mechanism are unclear, in the method for producing silica cake of the present invention, the pH is maintained at a constant value, and the alkali silicate and the mineral acid are added at the same time. It is presumed that the concentration of the remaining alkali silicate is kept at a substantially constant value, and as a result, a precipitated silica cake with high dispersibility will be formed. On the other hand, in the case of the reaction type A in which mineral acid is added to the alkali silicate solution, not only is it difficult to maintain the pH at a constant value, but the alkali silicate concentration remaining in the reaction solution without being neutralized is the mineral acid. It is estimated that precipitated silica with low dispersibility may be produced because it gradually changes (decreases) with the addition of.
[0050]
After simultaneous addition until the desired BET specific surface area is achieved, it is desirable to add only mineral acid to bring the pH to 7 or less, preferably 2 to 6 in order to stabilize the reaction solution. In order to stabilize the reaction solution, the simultaneous addition of alkali silicate and mineral acid is temporarily 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 the completion of the simultaneous addition. It is also possible to perform a so-called aging process.
[0051]
As a preferred embodiment in the method for producing silica cake of the present invention, the initial reaction liquid is added simultaneously so 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. The concentration and / or amount of alkali silicate or mineral acid is set. Setting in this way is effective for adjusting the BET specific surface area of the obtained precipitated silica to the above range.
[0052]
In the present invention, as is generally performed in the method for producing precipitated silica by the precipitation method, an electrolyte, generally sodium sulfate, can be appropriately added to the reaction solution without any limitation. However, as described above, the electrolyte acts as a flocculant and also tends to lower the BET specific surface area. Therefore, in producing a precipitated silica cake having a high BET specific surface area and good dispersibility as in the present invention. It is preferable not to use an electrolyte.
[0053]
In the present invention, the precipitated silica is further separated from the reaction solution obtained by the above reaction by filtration, and if necessary, washed with water and / or dehydrated and separated in a wet state to obtain a silica cake. Can do. As described above, the moisture content of the wet silica cake is preferably in the range of 83 to 93% by weight when the silica dispersion is produced because the dispersion becomes easier. More preferably, it is 85 to 92% by weight.
[0054]
A solid-liquid separation device such as a filter press is generally used for the filtration, washing with water and dehydration. Further, the washing with water is carried out so that a 5 wt% dispersion obtained by dispersing the obtained silica cake in water has a pH value of 3 to 7 and an electric conductivity value of 20 to 400 μS / cm. Since the dispersibility of can be improved more, it is preferable. More preferably, the pH is 3.5 to 6.5 and the conductivity value is 50 to 300 μS / cm.
[0055]
The silica cake of the present invention has very good dispersibility in polar solvents, and a silica dispersion in which precipitated silica is highly dispersed can be obtained by a simple dispersion operation. Incidentally, by dispersing the silica cake of the present invention in a polar solvent, the average particle diameter of silica in the precipitated silica dispersion is 300 nm or less, and the ratio of aggregated particles of 500 nm or more is 5% by volume or less. A highly transparent silica dispersion in which particles are highly dispersed can be obtained.
[0056]
Conventionally, there is no example of a silica dispersion obtained by dispersing precipitated silica in a polar solvent in which aggregated particles are highly dispersed as described above. The reason is estimated as follows. That is, the conventional precipitated silica has a wide primary particle size particle size distribution, so it contains a large amount of ultrafine primary particles having strong cohesive force, and as a result, settled to a highly dispersed state as in the silica dispersion of the present invention. Silica cannot be substantially dispersed. On the other hand, the precipitated silica in the silica dispersion of the present invention has a narrow primary particle size distribution by limiting the conditions under which the precipitated silica particles are generated as described above, and therefore contains ultrafine primary particles. Since the amount is small, it is presumed to have excellent dispersibility.
[0057]
Next, the precipitated silica dispersion of the present invention will be described.
[0058]
In the present invention, the average particle diameter refers to the average particle diameter of the silica agglomerated particles in the precipitated silica dispersion, and is a volume-based arithmetic average diameter D as measured with a light scattering diffraction type particle size distribution meter. ₅₀ That is.
[0059]
In the precipitated silica dispersion of the present invention, the silica concentration in the polar solvent may be a concentration required as appropriate depending on the application, but when the silica cake is dispersed in the polar solvent, it is 8 to 15% by weight, If it concentrates with the below-mentioned concentration method, it can also be 15 weight% or more.
[0060]
As a method for producing a precipitated silica dispersion using the silica cake of the present invention as a raw material, a known slurrying method can be carried out without particular limitation.
[0061]
For example, after blending a predetermined amount each of silica cake and polar solvent, using a disperser, a method of dispersing silica cake in a polar solvent, after pre-charging the polar solvent in a dispersion tank, and operating the disperser, Examples of the method include gradually adding and dispersing silica cake. In addition, if necessary, an advanced atomization means for further atomizing the silica particles in the dispersion to an average particle diameter in a suitable range after dispersing the silica cake in a polar solvent using the above method. The applying method is preferably employed.
[0062]
The disperser used for the above dispersion is not particularly limited, but a high-speed rotation such as a general stirrer having propeller blades, turbine blades, paddle blades, a high-speed centrifugal radial stirrer such as a disper mixer, a high-speed rotation such as a homogenizer, a homomixer, or an ultramixer. Dispersers such as a shearing stirrer, a colloid mill, and a planetary mixer can be used.
[0063]
Among the above dispersers, a disperser having a strong shearing force is suitable. Specifically, a high-speed shearing stirrer, a composite disperser in which a high-speed shearing stirrer is further combined with a propeller blade and a paddle blade, a planetary mixer and a high-speed rotating centrifugal radiation stirrer, or a high-speed rotating shearing stirrer And a composite type disperser combining the above.
[0064]
In the present invention, the above-described advanced atomization method is not particularly limited, and examples thereof include atomization treatment using a bead mill, a sand mill, an ultrasonic homogenizer, a high-pressure homogenizer, and the like. Among these, a dispersion treatment using a high-pressure homogenizer is preferable.
[0065]
Using a high-pressure homogenizer, a pre-dispersion liquid in which silica is dispersed in a polar solvent is caused to collide oppositely at a treatment pressure of 30 MPa or more, or is passed through the orifice under a condition where the differential pressure between the inlet side and the outlet side of the orifice is 30 MPa or more. Thus, a precipitated silica dispersion in which the average particle diameter of silica in the precipitated silica dispersion is 300 nm or less and the ratio of aggregated particles of 500 nm or more is 5% by volume or less can be obtained.
[0066]
In addition, since the precipitated silica dispersion obtained in this manner has an appropriate concentration according to the use as described above, it is not a problem to perform an operation of diluting with a polar solvent or various concentration operations as appropriate. Can be implemented.
[0067]
The operation of concentrating the precipitated silica dispersion can be carried out without any particular limitation using a known concentration method. For example, evaporative concentration method in which the boiling point of the polar solvent is raised, reduced pressure evaporation method in which the boiling point of the polar solvent is lowered under reduced pressure, and organic thin films such as polysulfone, polyacrylonitrile, cellulose, etc. are applied under pressure. And an ultrafiltration method for removing the polar solvent.
[0068]
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. A dispersion medium in which two or more of the above solvents are mixed can also be used. In general, water is preferably used.
[0069]
In addition, in order to improve the storage stability and dispersibility of the silica particles, a small amount of a surfactant, an antifungal agent or the like may be added within a range not impairing the effects of the present invention.
[0070]
In addition, in order to modify the anionic silica particles into a cationic solvent in a polar solvent, the easily dispersible silica cake of the present invention and a cationic resin are mixed and dispersed in a polar solvent, thereby performing a cation modification. A precipitated silica dispersion in which the silica particles are dispersed, that is, a cationic resin-modified precipitated silica dispersion can also be produced.
[0071]
When the cationic resin-modified precipitated silica dispersion is used as a raw material for a coating liquid for an inkjet recording sheet, which is one of the uses of the precipitated silica dispersion, the ink fixability of the inkjet recording sheet coated with the coating liquid, Water resistance and image density can be increased.
[0072]
Any cationic resin can be used without particular limitation as long as it is a resin that dissociates and becomes cationic when dissolved in water. Resins having primary to tertiary amine groups or quaternary ammonium bases are preferred. Specific examples include polyethyleneimine, polyvinyl pyridine, polyamine sulfone, polydialkylaminoethyl methacrylate, polydialkylaminoethyl acrylate, polydialkylaminoethyl methacrylamide, polydialkylaminoethyl acrylamide, polyepoxyamine, polyamidoamine, dicyandiamide. -Formalin condensate, dicyandiamide polyalkyl-polyalkylene polyamine condensate, compounds such as polyvinylamine, polyallylamine and their hydrochlorides, further polydiallyldimethylammonium chloride and copolymers thereof such as acrylamide, polydiallylmethylamine hydrochloride And polymethacrylic acid ester methyl chloride quaternary salt.
[0073]
In the present invention, the amount of the cationic resin is such that the cationic resin-modified precipitated silica dispersion can be stably produced without gelation during the production, and the viscosity of the obtained cationic resin-modified precipitated silica dispersion is In order to make it low, it is preferable to set it as 3-50 weight part with respect to 100 weight part of silica, especially 3-15 weight part.
[0074]
Moreover, it is not preferable that the viscosity of the cationic resin-modified precipitated silica dispersion is increased because the handling property is lowered in the subsequent production process. The stability of the cationic resin-modified precipitated silica dispersion with respect to the addition amount of the cationic resin differs depending on the type of the cationic resin to be added. It is preferable to select from the added amount.
[0075]
The method for producing a cationic resin-modified precipitated silica dispersion by mixing and dispersing the easily dispersible silica cake and the cationic resin in a polar solvent is not particularly limited, but the silica cake is dispersed in the polar solvent. After mixing the cationic resin and dispersing, after mixing the cationic resin in the polar solvent, gradually add the silica cake, while dispersing the silica cake, the silica cake and the cationic resin are mixed. Examples include a method of dispersing. In addition, if necessary, after preparing a cationic resin-modified precipitated silica dispersion using the above technique, advanced fine particles for further atomizing the silica particles in the dispersion to an average particle diameter in a suitable range. A method of applying the adjusting means is preferably employed.
[0076]
【Example】
In the following, examples and comparative examples are shown to specifically describe the present invention, but the present invention is not limited to these examples.
[0077]
The measuring method regarding the silica cake and the silica dispersion is as follows.
[0078]
(BET specific surface area)
After the silica cake is put in a dryer (120 ° C.) for 24 hours or more and dried, the amount of nitrogen adsorption is measured using Asap 2010 manufactured by Micromeritics, and the value of the one-point method at a relative pressure of 0.2 Adopted.
[0079]
(Moisture content of silica cake)
3 to 10 g of silica cake was weighed in a weighing bottle, placed in a dryer kept at 105 ° C. for 12 hours or more, and calculated from the weight before and after moisture drying.
[0080]
(Measurement of pH and conductivity of dispersion with silica concentration of 5% by weight)
Mix the silica cake and the ion-exchanged water whose water content has been measured in advance so that the silica concentration is 5% by weight, stir and mix with a propeller mixer to make a slurry, and use a commercially available pH meter and conductivity meter Then, the value at 25 ° C. was measured.
[0081]
(Measurement of n value)
Ion exchange water was added to a silica cake whose moisture content was measured in advance so that the silica concentration was 5% by weight, and premixed by stirring with a propeller mixer to form a slurry.
[0082]
A silica dispersion was prepared by treating the obtained slurry once with a high pressure homogenizer (manufactured by Nanomizer; Nanomizer, LA-31) at a treatment pressure of 78 MPa. Next, the visible light absorption spectrum of this silica dispersion was measured using a spectrophotometer (manufactured by JASCO, Ubest-35 type).
[0083]
First, using a cell having an optical path length of 10 mm, the reference cell and the sample cell were each filled with ion-exchanged water, and zero point calibration was performed over the entire wavelength range. Next, the silica dispersion was diluted with ion-exchanged water so that the silica concentration was 1.5% by weight, placed in a sample cell, and the absorbance (τ) at a wavelength (λ) of 460 to 760 nm was measured. Log (λ) and log (τ) were plotted, and the slope (−n) of the straight line was determined by the least square method using the above-described equation (2).
[0084]
(Measurement of particle size distribution and average particle size)
Using a light scattering diffraction type particle size distribution measuring apparatus (Coulter, Coulter LS-230), a precipitated silica dispersion liquid under the conditions of a refractive index of 1.458 for silica and a refractive index of 1.332 for water used as a dispersion medium. The particle size distribution is measured, the volume ratio of particles of 500 nm or more, and the volume-based arithmetic average diameter D ₅₀ Was calculated. This volume-based arithmetic average diameter was taken as the average particle diameter.
[0085]
(Silica solid content concentration in the reaction mixture at the end of the reaction)
Collect 100 mL of the reaction mixture at the end of the reaction. The mixture was filtered using 5A filter paper, and washed with 1 L of ion-exchanged water added to the filtration residue. The residue was placed in a dryer (120 ° C.) for 24 hours or more and dried, and then the weight was measured and displayed as the silica solid content weight (g) in the unit reaction liquid amount (1 L) (unit: g / L). .
[0086]
Example 1
Sodium silicate solution (SiO ₂ A concentration of 10 g / L, molar ratio x = 3.4) 6 L was charged into a reaction vessel and heated to 95 ° C. while mixing with a propeller-type stirring blade. While maintaining the temperature at 95 ° C., the sodium silicate solution (SiO 2 ₂ Concentration 180 g / L, molar ratio x = 3.4) was added to the reaction vessel at a rate of 32 mL / min and sulfuric acid (concentration 221 g / L) at 12 mL / min over 50 minutes.
[0087]
During this time, the pH of the reaction solution was 10.2 to 10.5. After completion of the simultaneous addition, stirring was continued for 40 minutes while maintaining 95 ° C. Subsequently, the above-mentioned sulfuric acid was added until the pH reached 3.0 to obtain a reaction slurry. The silica solid content concentration was 42 g / L.
[0088]
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. The n value was 2.4. The BET specific surface area of the precipitated silica is 276 m. ² / G.
[0089]
Example 2
The sodium silicate solution added to the reaction solution is dissolved in SiO. ₂ The same operation as in Example 1 was performed except that the concentration was 270 g / L, the addition rate was 21 mL / min, and sulfuric acid was added until the pH reached 4.5 after the completion of the simultaneous addition.
[0090]
The pH at the time of simultaneous addition was 10.4 to 10.6. The silica solid content concentration at the end of the reaction was 45 g / L.
[0091]
The physical properties of the silica cake obtained by filtration, washing and dehydration from the reaction slurry were a water content of 89.0% by weight, a 5% dispersion having a pH of 6.4 and an electrical conductivity of 136 μS / cm. The n value was 2.5. The BET specific surface area of the precipitated silica is 265 m. ² / G.
[0092]
Example 3
5.9 L of a 0.1 mol / L sodium hydroxide aqueous solution was charged into the reaction vessel and heated to 93 ° C. while mixing with a propeller type stirring blade. To this initial reaction solution, a sodium silicate solution (SiO ₂ Concentration 180 g / L, molar ratio x = 3.4) was added to the reaction vessel at a rate of 42 mL / min and sulfuric acid (concentration 221 g / L) at 12 mL / min over 40 minutes.
[0093]
During this time, the pH of the reaction solution was 10.0 to 10.2. After completion of the simultaneous addition, stirring was continued for 20 minutes while maintaining 93 ° C. Subsequently, the above-mentioned sulfuric acid was added until the pH became 3.4 to obtain a reaction slurry. The silica solid content concentration was 36 g / L.
[0094]
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 wt%, the pH of the 5% dispersion was 4.6, and the conductivity was 229 μS / cm. The n value was 2.9. The BET specific surface area of the precipitated silica is 316 m. ² / G.
[0095]
Example 4
6.3 L of water was charged into the reaction vessel and heated to 93 ° C. while mixing with a propeller stirring blade. To this initial reaction solution, a sodium silicate solution (SiO ₂ Concentration 270 g / L, molar ratio x = 3.4) was added to the reaction vessel at 37 mL / min and sulfuric acid (concentration 221 g / L) at 21 mL / min simultaneously over 30 minutes.
[0096]
During this time, the pH of the reaction solution was 9.3 to 9.6. After completion of the simultaneous addition, stirring was continued for 10 minutes while maintaining 93 ° C. Subsequently, the above-mentioned sulfuric acid was added until the pH became 3.1 to obtain a reaction slurry. The silica solid content concentration was 37 g / L.
[0097]
The reaction slurry was filtered under reduced pressure and washed with ion-exchanged water to obtain a silica cake. When the physical properties of the silica cake were measured, the water content was 91.6% by weight, the pH of the 5% dispersion was 3.6, and the conductivity was 247 μS / cm. The n value was 2.9. The precipitated silica has a BET specific surface area of 337 m. ² / G.
[0098]
Example 5
6.2 L of water was charged into the reaction vessel and heated to 94 ° C. while mixing with a propeller stirring blade. To this initial reaction solution, a sodium silicate solution (SiO ₂ Concentration 270 g / L, molar ratio x = 3.4) was added to the reaction vessel simultaneously at 19 mL / min and sulfuric acid (concentration 221 g / L) at 9.7 mL / min over 60 minutes.
[0099]
During this time, the pH of the reaction solution was 9.5 to 9.8. After completion of the simultaneous addition, stirring was continued for 30 minutes while maintaining 94 ° C. Subsequently, the above-mentioned sulfuric acid was added until the pH became 3.2 to obtain a reaction slurry. The silica solid content concentration was 38 g / L.
[0100]
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. The n value was 2.4. The BET specific surface area of the precipitated silica is 257 m. ² / G.
[0101]
Comparative Example 1
Sodium silicate solution (SiO ₂ Concentration 50 g / L, molar ratio x = 3.2) 8 L and sodium sulfate 92 g were charged into the reaction vessel, the temperature was 40 ° C. with stirring, and sulfuric acid (221 g / L) was added at 31 mL / min for 15 minutes Added. Next, the temperature of the reaction solution was raised to 95 ° C. with stirring. While maintaining the temperature at 95 ° C., the above sulfuric acid was added at 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.
[0102]
Regarding the physical properties of the obtained silica cake, the water content was 88.9% by weight, the pH of the 5% dispersion was 6.0, and the n value was 1.6. The precipitated silica has a BET specific surface area of 280 m. ² / G.
[0103]
Comparative Example 2
Sodium silicate solution (SiO ₂ A reactor was charged with a concentration of 10 g / L and a molar ratio x = 3.4) of 2.2 L, and the reaction temperature was maintained at 87 ° C. Sodium silicate solution (SiO ₂ Concentration 90 g / L, molar ratio x = 3.4) was added to the reaction vessel at 38 mL / min and sulfuric acid (concentration 221 g / L) at 6.5 mL / min simultaneously over 110 minutes. During this time, the pH of the reaction solution was 10.0 to 10.3. After completion of the simultaneous addition, stirring was continued for 10 minutes while maintaining 87 ° C., and then the sulfuric acid was added until the pH reached 3.5 to obtain a reaction slurry. The silica solid content concentration was 55 g / L.
[0104]
When the physical properties of the silica cake obtained by filtering and washing the reaction slurry were measured, the water content was 87.3% by weight, the pH of the 5% dispersion was 5.4, and the n value was 0.9. The precipitated silica has a BET specific surface area of 197 m. ² / G.
[0105]
Comparative Example 3
The silica cake obtained by the same method as in Example 1 was placed in a drier kept at 120 ° C. for 20 hours, dried, and then left in the room for 24 hours. This was pulverized with a coffee mill to obtain silica powder.
[0106]
The water content of the obtained silica powder was 6.1% by weight, and the n value of the silica dispersion was 0.6.
[0107]
Comparative Example 4
Sodium silicate solution (SiO ₂ 2.5 L of concentration 10 g / L, molar ratio x = 3.4) was charged into the reaction vessel, and the reaction temperature was maintained at 80 ° C. Sodium silicate solution (SiO ₂ Concentration 90 g / L, molar ratio x = 3.4) was added to the reaction vessel at 40 mL / min and sulfuric acid (concentration 221 g / L) at 6.8 mL / min simultaneously over 115 minutes. During this time, the pH of the reaction solution was 10.1 to 10.5. After completion of the simultaneous addition, stirring was continued for 10 minutes while maintaining the temperature at 80 ° C., and then the sulfuric acid was added until the pH reached 3.4 to obtain a reaction slurry. The silica solid content concentration was 55 g / L.
[0108]
When the physical properties of the silica cake obtained by filtering and washing the reaction slurry were measured, the water content was 86.5% by weight, the pH of the 5% dispersion was 6.0, and the n value was 1.2. The BET specific surface area is 244 m. ² / G.
[0109]
Example 6
The silica cake obtained in Example 1 was slurried with a colloid mill (manufactured by PUC, colloid mill K60), and then diluted with 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 using a high-pressure homogenizer (Nanomizer LA-31, manufactured by Nanomizer) at a treatment pressure of 78 MPa to obtain a precipitated silica dispersion. The resulting precipitated silica dispersion had an average particle size of 137 nm, and the proportion of particles of 500 nm or more was 0.6% by volume.
[0110]
Example 7
A precipitated silica dispersion was obtained in the same manner as in Example 6 except that the silica cake obtained in Example 2 was used as the silica cake. The obtained precipitated silica dispersion had an average particle size of 133 nm, and the proportion of particles of 500 nm or more was 0.5% by volume.
[0111]
Example 8
A precipitated silica dispersion was obtained in the same manner as in Example 6 except that the silica cake obtained in Example 3 was used as the silica cake. The average particle diameter of the obtained precipitated silica dispersion was 112 nm, and the proportion of particles of 500 nm or more was 0% by volume.
[0112]
Example 9
A precipitated silica dispersion was obtained in the same manner as in Example 6 except that the silica cake obtained in Example 4 was used as the silica cake. The average particle diameter of the obtained precipitated silica dispersion was 100 nm, and the proportion of particles of 500 nm or more was 0% by volume.
[0113]
Example 10
A precipitated silica dispersion was obtained in the same manner as in Example 6 except that the silica cake obtained in Example 5 was used as the silica cake. The average particle diameter of the obtained precipitated silica dispersion was 140 nm, and the proportion of particles of 500 nm or more was 0.2% by volume.
[0114]
Comparative Example 5
A precipitated silica dispersion was obtained in the same manner as in Example 6 except that the silica cake obtained in Comparative Example 1 was used as the silica cake. The average particle size of the obtained precipitated silica dispersion was 380 nm, and the proportion of particles of 500 nm or more was 12.9% by volume.
[0115]
Comparative Example 6
A precipitated silica dispersion was obtained in the same manner as in Example 6 except that the silica cake obtained in Comparative Example 2 was used as the silica cake. The average particle diameter of the obtained precipitated silica dispersion was 346 nm, and the ratio of particles of 500 nm or more was 13.1% by volume.
[0116]
Comparative Example 7
While gradually adding 107 g of the silica powder obtained in Comparative Example 3 (moisture 6.1% by weight) to 893 g of ion-exchanged water, the silica concentration was dispersed by a homogenizer (made by Squid, homogenizer T-25) and the silica concentration was 10% by weight. A silica slurry was obtained. The silica slurry was atomized using a high-pressure homogenizer (Nanomizer LA-31, manufactured by Nanomizer) at a treatment pressure of 78 MPa to obtain a precipitated silica dispersion. A precipitated silica dispersion was obtained. The average particle diameter of the obtained precipitated silica dispersion was 18.5 μm, and the proportion of particles of 500 nm or more was 94.5% by volume.
[0117]
Comparative Example 8
A precipitated silica dispersion was obtained in the same manner as in Example 6 except that the silica cake obtained in Comparative Example 4 was used as the silica cake. The average particle size of the obtained precipitated silica dispersion was 320 nm, and the proportion of particles of 500 nm or more was 11.1% by volume.
[0118]
Example 11
The silica cake obtained in Example 1 was slurried with a colloid mill (manufactured by PUC, colloid mill K60), and then diluted with a predetermined amount of ion-exchanged water to obtain a silica slurry having a silica concentration of 10% by weight. . 500 g of this silica slurry and 12.5 g of a cationic resin aqueous solution containing diallylmethylamine hydrochloride polymer at a concentration of 20% by weight are mixed and mixed using an ultra mixer (manufactured by Mizuho Kogyo Co., Ltd., Ultra Mixer LR-2). As a result, a premixed liquid was obtained. The premixed solution was subjected to atomization treatment at a treatment pressure of 78 MPa using a high-pressure homogenizer (Nanomizer LA-31, manufactured by Nanomizer) to obtain a cationic resin-modified precipitated silica dispersion. The obtained cationic resin-modified precipitated silica dispersion had an average particle size of 193 nm, and the proportion of particles of 500 nm or more was 3.6% by volume.
[0119]
Example 12
A cationic resin-modified precipitated silica dispersion was obtained in the same manner as in Example 11 except that the silica cake obtained in Example 2 was used as the silica cake. The obtained cationic resin-modified precipitated silica dispersion had an average particle size of 171 nm, and the proportion of particles of 500 nm or more was 2.6% by volume.
[0120]
Comparative Example 9
A cationic resin-modified precipitated silica dispersion was obtained in the same manner as in Example 11 except that the silica cake obtained in Comparative Example 1 was used as the silica cake. The obtained cationic resin-modified precipitated silica dispersion had an average particle size of 3,584 nm, and the proportion of particles of 500 nm or more was 34.9% by volume.
[0121]
Comparative Example 10
A cationic resin-modified precipitated silica dispersion was obtained in the same manner as in Example 11 except that the silica cake obtained in Comparative Example 2 was used as the silica cake. The obtained cationic resin-modified precipitated silica dispersion had an average particle size of 433 nm, and the proportion of particles of 500 nm or more was 15.4% by volume.
[0122]
【The invention's effect】
As described above, the silica cake of the present invention is extremely excellent in dispersibility when dispersed in a polar solvent even though the primary particle diameter is small, and if this silica cake is used, it is easily transparent. A high silica dispersion can be obtained. Therefore, the productivity of the silica dispersion can be significantly improved.

Claims (7)

Maintain the pH of the reaction solution at a constant value within the range of 7.5 to 11.5 with respect to the initial reaction solution in which no electrolyte (excluding basic substances) or mineral acid is added, and the reaction temperature is While maintaining at 92-98 ° C., alkali silicate and mineral acid are simultaneously added to the reaction solution to produce precipitated silica so that the silica solids concentration in the reaction mixture at the end of the reaction is 50 g / L or less. And an aqueous cake of precipitated silica having a BET specific surface area of 220 m ² / g or more produced by separating the precipitated silica in a wet state from the reaction solution, After the dispersion in ion-exchanged water, the dispersion liquid diluted to have a silica concentration of 1.5% by weight has a light scattering index (n value) of 2 or more. Silica cake.   The easily dispersible precipitated silica cake according to claim 1, wherein the water content is in the range of 83 to 93% by weight. Maintain the pH of the reaction solution at a constant value within the range of 7.5 to 11.5 with respect to the initial reaction solution in which no electrolyte (excluding basic substances) or mineral acid is added, and the reaction temperature is While maintaining at 92-98 ° C., alkali silicate and mineral acid are simultaneously added to the reaction solution to produce precipitated silica so that the silica solids concentration in the reaction mixture at the end of the reaction is 50 g / L or less. The method for producing an easily dispersible precipitated silica cake according to claim 1 , wherein the precipitated silica is separated from the reaction solution in a wet state.   A dispersion obtained by dispersing the easily dispersible precipitated silica cake according to claim 1 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 particle diameter is 500 nm or more. A precipitated silica dispersion, wherein the ratio of the aggregated particles is 5% by volume or less.   The precipitated silica dispersion according to claim 4, further comprising a cationic resin dispersed therein.   5. The method for producing a precipitated silica dispersion according to claim 4, wherein the silica slurry in which the precipitated silica cake according to claim 1 is dispersed in a polar solvent is atomized by a high-pressure homogenizer.   6. The method for producing a precipitated silica dispersion according to claim 5, wherein the premixed liquid in which the precipitated silica cake according to claim 1 and the cationic resin are dispersed in a polar solvent is subjected to atomization treatment by a high-pressure homogenizer.