JPS6117415A - Preparation of hydrated silicic acid - Google Patents

Abstract

PURPOSE:To obtain a hydrated silicic acid having low content of coarse particle and having excellent oil absorptivity, by adding an acid dividedly to an aqueous solution of an alkali metal silicate to effect the precipitation of a hydrated silicic acid, and subjecting the silicic acid to wet pulverization. CONSTITUTION:An aqueous solution of an alkali metal silicate having an alkali metal salt content of 0.13-0.17mol/l, an SiO2 concentration of 0.9-1.4mol/l and an SiO2/M2O molar ratio of 3-3.2 (M is alkali metal) is heated at <=60 deg.C, added with an acid (e.g. hydrochloric acid) of an amount corresponding to 25-70% of the acid necessary to neutralize the alkali silicate, spending 8-10min, and heated to 85-95 deg.C at a heating rate of 1.5-2.5 deg.C/min. When the solution viscosity of the reaction system reaches its peak, the residual acid is added to the system spending 80-100min until the pH of the system reaches 4-6. A hydrous silicic acid is precipitated by this process to obtain a slurry of the hydrous silicic acid having a concentration of 6-15%. The slurry is pulverized in wet state until the residue on the 250 mesh sieve becomes <=1wt%.

Description

[Detailed description of the invention]

The present invention provides a novel method for producing hydrated silicic acid. Specifically, a method for producing hydrated silicic acid for obtaining hydrated silicic acid in a slurry state, which has an extremely low content of coarse particles and has excellent oil absorption properties, without going through the drying and pulverization steps from the generation process of hydrated silicic acid. It is. Conventionally, in the process of using hydrated silicic acid in a slurry state, for example, in the papermaking process using hydrated silicic acid as a filler, in order to reduce the manufacturing cost of hydrated silicic acid, the hydrated silicic acid slurry obtained from the hydrated silicic acid generation process is dried and There was a desire for a method that could be used directly without going through the pulverization process. However, the slurry obtained by the reaction between an alkali silicate and a mineral acid has an extremely high content of coarse particles of hydrous silicic acid compared to the slurry obtained by re-slurrying the hydrous silicic acid obtained through the above drying and pulverization process. . Therefore, when paper is made by adding the hydrated silicic acid slurry obtained from the hydrated silicic acid generation process to the valve slurry in the papermaking process, many coarse particles of hydrated silicic acid (protrusions) are formed on the surface of the resulting paper, and the product The inventors of the present invention have conducted extensive research to solve the above-mentioned problem caused by coarse particles in the slurry obtained from the process of producing hydrous silicic acid.As a result, they have found that alkali silicate and mineral acid The present inventors have discovered that hydrous silicic acid with an extremely low content of coarse particles can be obtained in a slurry state by wet-pulverizing the hydrated silicic acid obtained by reacting the hydrated silicic acid under specific conditions in a slurry state, and have completed the present invention. In the present invention, after adding to an aqueous alkali silicate solution 25 to 70% of the acid required to neutralize the alkali silicate, the solution viscosity of the reaction system is at its maximum.
The method for producing hydrated silicic acid is characterized in that the remaining acid is continuously added to precipitate hydrated silicic acid, and the obtained hydrated silicic acid is wet-pulverized in a slurry state. The feature of the present invention is the combination of a step of adding an acid to an alkali silicate in two stages to produce hydrated silicic acid, and a step of wet-pulverizing the hydrated silicic acid in a slurry state. That is, all hydrated silicic acid produced by the reaction between an alkali silicate and an acid contains a large amount of coarse particles with excessively developed agglomeration. We gained the knowledge that energy changes. As a result of further research, among the many reaction conditions for alkali silicate and acid, the method of adding acid to alkali silicate in two stages significantly reduced the cohesive energy of coarse particles compared to other methods. I discovered something small. By combining the above method for producing hydrated silicic acid with wet grinding, they succeeded in obtaining a hydrated silicic acid slurry with extremely few coarse particles. Furthermore, by specifying the conditions for two-stage addition of acid to alkali silicate as necessary, it is possible to impart excellent oil absorption properties to the resulting hydrated silicic acid, and it is effectively used as a filler for paper. In the present invention, the aqueous alkali silicate solution is not particularly limited, and those conventionally used in the production of hydrous silicic acid are generally used. Among them, 0.13 to 0.17 mol/? of alkali metal salts? L preferably 0.14-0
．． Contains 15 mol/7 and has a concentration of 0.9 to 1.4 as SiO
Mol/? X, preferably 0.95 to 1.25 mol/h,
Alkali silicates having a S i O1/M, 0 molar ratio (where M is an alkali metal) of 3 to 3.2 are advantageous when the resulting hydrated silicic acid is used as a paper filler. That is, the abundance of alkali metal salt, S j O, 11 degrees, and S
i02/M. Hydrous silicic acid produced from an alkali silicate having a molar ratio of 0 within the above range has a small drying shrinkage of paper obtained using the hydrated silicic acid.
Shows good dimensional stability. Further, the oil absorption properties of the hydrated silicic acid can be further improved, and the oil absorption performance of the printing ink of the paper obtained using this is further improved, and the strike-through prevention property is improved. In the present invention, sodium silicate is generally used as the alkali silicate, but potassium silicate can also be used. As the alkali metal salt, sulfates, hydrochlorides, and nitrates of sodium, potassium, etc. are generally used. In particular, salts of the same type as the acids described below are preferably used. In the present invention, the specific aqueous alkali silicate solution is neutralized with an acid to precipitate hydrous silicic acid. For neutralization with an acid, when the amount of acid required to neutralize all the alkalis in the aqueous alkali silicate solution is 1, the ratio of acid to this (hereinafter referred to as acid addition rate) is 25 to 70, preferably 25-35%
This is done by continuously adding an amount of acid. The temperature at the time of adding the acid is 60°C or less, preferably 40°C or less.
Setting the temperature to 55° C. improves the oil absorption properties of the hydrous silicic acid obtained, and improves the ability to prevent printing in from printing on paper obtained using the same. In addition, if the acid addition rate is lower than the above range, the particle size of particles other than coarse particles will become significantly smaller, resulting in increased dusting when paper is made using the obtained hydrated silicic acid, and the oil absorption properties will also decrease, resulting in insufficient No effect can be obtained to prevent printing ink from bleeding out. On the other hand, if the acid addition rate is higher than the above range, not only the oil absorption properties will be lowered, but also the reduction rate of coarse particles during wet grinding, which will be described later, will be lowered. Furthermore, it is preferable to continuously add the acid in the above amount for a period of 8 to 10 minutes, since this results in a hydrous silicic acid that can maintain high dimensional stability of the resulting paper to which the hydrous silicic acid is added. In the present invention, in the aqueous alkali silicate solution, after the above-mentioned acid addition is completed, seeds of hydrated silicic acid begin to gradually precipitate. In this case, it is preferable to raise the temperature of the aqueous solution to a specific temperature because the seeds can be effectively precipitated. The temperature increase is preferably performed at a temperature increase rate of 1.5 to 2.6° C./min. In addition, the heating temperature is 85-95℃,
The temperature is preferably 90 to 95°C. By increasing the temperature to the above-mentioned temperature, the oil-absorbing properties of the hydrated silicic acid obtained can be increased, and it is also possible to provide sufficient prevention of print ink strike-through to paper produced using the same. Seed precipitation is initially a sol that cannot be seen with the naked eye, but it eventually becomes a feather-like precipitate, and the viscosity of the solution increases significantly depending on the amount, so it is easy to tell whether seed precipitation has finished or not. . In the present invention, in this state, that is, in the vicinity of the maximum solution viscosity of the reaction system (including the point at which it reaches the maximum), the remaining mineral acid is further added to completely precipitate the hydrous silicic acid. Adding the nucleic acid in a slight excess so that the p)I of the solution is 4 to 6, and adding the nucleic acid over a period of 80 to 100 minutes not only improves the filterability of the precipitated hydrous silicic acid, but also It is preferable to improve the oil absorption properties of the obtained hydrated silicic acid, and to use the same to remove printing ink from paper, which further improves the IE resistance. As the acid for neutralizing the raw material alkali silicate used in the present invention, mineral acids such as sulfuric acid, hydrochloric acid, and nitric acid, carbon dioxide gas, etc., which are generally known for the production of hydrated silicic acid, can be used without particular restriction, but they can be used as fillers for paper. In this case, sulfuric acid is generally the most suitable in consideration of the influence on the papermaking process. In addition, the concentration of the above acid is 2 g/100c, c, ~40 g/100c,
It is preferable to use one in the range c. The hydrated silicic acid slurry obtained by reacting an alkali silicate with an acid by the method described above generally contains coarse particles at a ratio of 20 to 30% of the 250 mesh residue.

[It's here. In the present invention, the hydrated silicic acid containing coarse particles is
Coarse particles are removed by wet grinding in a slurry state.]
It can be reduced to less than % by weight. The above effects can only be achieved by producing hydrous silicic acid through two-stage addition of acid. That is, in hydrated silicic acid produced by other methods, for example, the so-called one-step method in which acid and alkali silicate are simultaneously added, the proportion of coarse particles is 20%.
Even if the hydrated silicic acid is wet-pulverized to a lesser extent, it is extremely difficult to reduce the number of coarse particles to the above range because the cohesive energy of the coarse particles is large. In the wet grinding of the present invention, the slurry state includes all states in which hydrated silicic acid exhibits fluidity with water. Generally, the concentration of hydrated silicic acid is 6 to 15% by weight, preferably 8 to 15% by weight.
A slurry with a content of 13% by weight has good grinding efficiency and is suitable. Furthermore, the timing of wet pulverization is not particularly limited. For example, examples include a mode in which a slurry in which hydrated silicic acid has been precipitated is used as it is, a mode in which the slurry is concentrated and then carried out, and a mode in which the hydrated silicic acid is filtered, or in some cases washed with water, and then fluidized again to form a slurry. In the wet grinding of hydrated silicic acid, 1 particle of 250 mesh residue
When hydrated silicic acid is used as a filler in the papermaking process, it is preferable to perform the pulverization until the concentration is 0.5% by weight or less, since this can prevent the formation of protrusions due to coarse particles on the surface of the resulting paper. . For the above-mentioned wet pulverization, any known method may be employed without particular limitation, for example, a pulverization method using a colloid mill, a pearl mill, a ball mill, a tower mill, a fluid energy mill, etc. is generally used. In the present invention, the pH of the hydrous silicic acid slurry after wet pulverization increases as the alkali contained in the coarse particles dissolves out, and the viscosity of the slurry increases accordingly. In this case, adding acid to the slurry after wet pulverization and adjusting ρ■ to 3 to 7, preferably 4 to 6 reduces the viscosity of the slurry and reduces piping resistance etc. during transportation of the slurry. This is preferable. The present invention also provides the method for producing hydrated silicic acid described above, in which the hydrated silicic acid is precipitated, and then the hydrated silicic acid is heat-treated under specific conditions and wet-pulverized to further improve the pulverization efficiency and reduce coarse particles. The present invention also provides a method for producing hydrated silicic acid that further increases silicic acid. That is, the second invention of the present invention is such that after adding an acid to an aqueous alkali silicate solution in an amount of 25 to 70% of the acid required to neutralize the alkali silicate, the solution viscosity of the reaction system reaches its maximum. After continuously adding the remaining acid to precipitate hydrated silicic acid at a temperature near the point where the hydrated silicic acid is precipitated, and maintaining the resulting hydrated silicic acid in a slurry state at a temperature at least 10°C higher than the temperature at which the hydrated silicic acid is precipitated for 2 hours or more, This is a method for producing hydrated silicic acid characterized by wet pulverization. In the above invention, if the processing temperature of the slurry is lower than the above range or the processing time is shorter than the above range, the effect of improving the grinding efficiency in the subsequent wet grinding will not be sufficiently exhibited. The treatment temperature and treatment time of the slurry are not particularly limited as long as they are within the above ranges, but in the case of industrial implementation, the treatment temperature is generally 10 to 30°C, preferably 10 to 30°C higher than the temperature at which hydrated silicic acid is precipitated in the reaction. 12-15℃ higher temperature,
The treatment time is 2 to 10 hours, preferably 4 to 7 hours. In the above treatment, the slurry may be left standing or may be appropriately stirred. As can be understood from the above explanation, the method of the present invention can directly obtain hydrous silicic acid in the form of a slurry with an extremely low content of coarse particles from the hydrous silicic acid generation process, and the hydrous silicic acid can be used in the slurry form. It becomes possible to supply the drying and pulverizing processes to the process without any problems. In particular, when the hydrated silicic acid of the present invention is supplied to the papermaking process, it is possible to obtain paper that does not generate protrusions on the surface and is excellent in preventing ink bleed-through and in dimensional stability. In this case, a known wet pulverization technique can be used as the paper making method without any particular restriction. In addition, in this case, the mackerel used for hydrated silicic acid is
0.5 to 10% by weight, preferably 1 to 3%, based on the valve
Weight % is appropriate. In addition to the above-mentioned hydrated silicic acid, known paper additives may also be used without any particular restrictions. EXAMPLES Hereinafter, Examples will be shown to further specifically explain the present invention, but the present invention is not limited thereto. In the Examples and Comparative Examples, the basis weight, oil absorption, whiteness after printing, and surface smoothness of the paper were measured by the following methods. (1) Weighing: The weight (g) per 14 was measured at 20°C, 64R, H. (2) Oil absorption: Measured according to JIS P130. (3) Whiteness after printing: The back-out of the printing ink indicates the quality of the prevention effect, and oil-based black ink was applied to the entire surface at a rate of 1.5 g/approx, and the whiteness of the printed side and the opposite side was shown. . 4. Smoothness test on both sides A weight of 200g was placed on a flat plate, and the sample paper was pulled horizontally at a pulling speed of 30mm/min, and the tensile force (χg) required at that time was measured, using the following method. calculated and expressed as surface smoothness. Sulfuric acid was added for an acid addition time of 11 minutes to precipitate hydrated silicic acid so that the pn of the solution was 5 to 6, and the S i OJ degree was 111 mol/socket. Next, the obtained hydrated silicic acid was filtered and washed with water to form a slurry having the hydrated silicic acid concentration shown in Table 1. The above slurry of hydrated silicic acid was wet-pulverized under the conditions shown in Table 1. As a result, a hydrous silicic acid slurry containing 250 mesh residue particles in the ratio shown in Table 1 was obtained. Since the pN increased due to the grinding and the viscosity of the slurry increased accordingly, sulfuric acid was added so that the pH of the slurry was 5. The viscosity at that time is shown in Table 1. Note that N15 indicates the viscosity (*) when sulfuric acid is not added. On the other hand, the valve is a mechanical valve, GP20% by weight, R
A mixing valve consisting of 56% by weight of GP and 24% by weight of NBKP was used as a chemical valve, and a semi-chemical valve in which 33 parts by weight of CGP was added to 100 parts by weight of the above mixing valve was used. The wet-pulverized slurry was added to the photolyzed cotton by adding water to the above-mentioned bulb so that the amount of hydrated silicic acid was 1.6% by weight based on the mixing bulb, and then sulfate band [A I
, (S 04)a・8Hyo0] with the above valve (absolutely dry) 1
1 part by weight was added as an aqueous solution to 00 parts by weight, stirred uniformly, and paper was made according to J I 5P8209 "Method for preparing handsheet paper for valve testing". The obtained paper properties are shown in Table 1. Example 2 NQI was carried out in the same manner as in Example 1 except that the hydrous silicic acid slurry was stirred for 3 hours at the temperature shown in Table 2 before being wet-milled. The results are shown in Table 2. Table 2 shows that the 250 mesh residue is 0.8 when the grinding time is 1 minute for N++2 and 0.2 minutes for Nti3.
% or less. Comparative Example Hydrous silicic acid was obtained by a so-called one-step method by simultaneous addition of acid and sodium silicate. That is, a sodium silicate aqueous solution and sulfuric acid having the same molar ratio as in Example 1 were continuously added to hot water kept at 80°C at a rate that maintained the pH of 8.5 to 9.0 to form hydrated silicic acid. It was precipitated. Next, this hydrated silicic acid was filtered and washed with water, water was added to make an 8% slurry, and the slurry was pulverized for 40 minutes in a tower mill. The 250 mesh residue after crushing was as high as 1.4%, and the paper obtained using this in the same papermaking method as in Example 1 had a basis material of 4B, 2 g/m, and a whiteness of 46.2% after printing. , the surface smoothness was 0.45.

Claims (6)

[Claims] (1) After adding an amount of acid that is 25 to 70% of the acid required to neutralize the alkali silicate to an aqueous alkali silicate solution, the remaining acid is 1. A method for producing hydrated silicic acid, which comprises continuously adding hydrated silicic acid to precipitate hydrated silicic acid, and wet-pulverizing the obtained hydrated silicic acid in a slurry state. (2) The concentration of the slurry to be wet-milled is 6 to 15% by weight.
The method according to claim 1. (3) 1% by weight of 250 mesh residue particles of hydrated silicic acid
The method according to claim 1, wherein wet pulverization is carried out as follows. (4) After adding an amount of acid that is 25 to 70% of the acid required to neutralize the alkali silicate to the aqueous alkali silicate solution, the remaining acid is continuously added to precipitate hydrated silicic acid, and the resulting hydrated silicic acid is maintained in a slurry state at a temperature at least 10°C higher than the temperature at which the hydrated silicic acid is precipitated for 2 hours or more, and then wet-pulverized. A method for producing hydrated silicic acid. (5) The method according to claim 4, wherein the slurry to be wet-milled has a concentration of 6 to 15% by weight. (6) Wet pulverization is performed so that the 250 mesh residue particles in the hydrated silicic acid are 1% by weight or less.
How to describe the section.