JPH0465008B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel method for producing hydrated silicic acid. For more details, please refer to the production process of hydrated silicic acid, drying and
This is 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 a pulverization process. 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 large content of coarse particles of hydrated silicic acid compared to the slurry obtained by re-slurrying the hydrated silicic acid obtained through the above drying and pulverization process. There are many Therefore, when paper is made by adding the hydrated silicic acid slurry obtained from the hydrated silicic acid generation process to the pulp slurry in the paper-making process, many protrusions due to coarse particles of hydrated silicic acid occur on the surface of the resulting paper, which significantly reduces its commercial value. This causes the problem of deterioration. The present inventors have conducted extensive research in order to solve the above-mentioned problem caused by coarse particles in the slurry obtained from the step of producing hydrated silicic acid. As a result, by wet-pulverizing hydrated silicic acid obtained by reacting an alkali silicate and a mineral acid under specific conditions in a slurry state, hydrated silicic acid with an extremely low content of coarse particles can be obtained in a slurry state. They discovered this and completed the present invention. In the present invention, 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 amount is This method of producing hydrated silicic acid is characterized by continuously adding an acid to precipitate hydrated silicic acid, and wet-pulverizing the obtained hydrated silicic acid 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 in which the agglomeration of primary particles has developed excessively. We obtained the knowledge that the cohesive energy of particles 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. By specifying the conditions for the two-stage addition of acid to the alkali silicate as necessary, the resulting hydrated silicic acid can be imparted with excellent oil absorption properties and can be effectively used as a paper filler. 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, it contains an alkali metal salt of 0.13 to 0.17 mol/, preferably 0.14 to 0.15 mol/, and the SiO ₂ concentration is 0.9 to 0.15 mol/.
1.4 mol/, preferably 0.95 to 1.25 mol/,
SiO ₂ /M ₂ O molar ratio (M is an alkali metal)
Alkali silicates with a . That is, the amount of alkali metal salt present, the SiO ₂ concentration, and
Hydrous silicic acid produced from an alkali silicate having a SiO ₂ /M ₂ O molar ratio within the above range exhibits small drying shrinkage of paper obtained using the hydrated silicic acid and good dimensional stability. In addition, the oil absorption properties of the hydrated silicic acid can be further improved, and the oil absorption properties of the printing ink of paper obtained using the same are further improved, and the strike-through prevention properties are 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 acid, if 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
This is carried out by continuous addition of acid in an amount of .about.70%, preferably 25-35%. The temperature at the time of addition of the acid is 60°C or less, preferably 40 to 55°C to improve the oil absorption properties of the hydrous silicic acid obtained, and improve the print ink print-through property of the paper obtained using this. It is possible and preferable. 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 The effect of preventing printing ink from bleed through cannot be obtained. 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 in wet pulverization, which will be described later, will be lowered.
Further, it is preferable to continuously add the acid in the above amount over a period of 8 to 10 minutes, since this results in a hydrous silicic acid that can maintain high dimensional stability of the paper to which the hydrated 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 above temperature increase is
It is preferable to carry out the heating at a heating rate of 1.5 to 2.5°C/min. In addition, the heating temperature is 85 to 95℃, preferably 90 to 95℃.
95℃ is preferable. By raising 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 impart sufficient printing ink strike-through prevention properties 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, which significantly increases the viscosity of the solution as the amount increases, so it is easy to tell whether the seed precipitation has finished or not. can be identified. In the present invention,
In this state, that is, in the vicinity (including the point at which the solution viscosity reaches the maximum) of the reaction system, the remaining mineral acid is further added to completely precipitate the hydrous silicic acid. Adding the acid in a slight excess so that the pH of the solution is 4 to 6, and adding it over a period of 80 to 100 minutes not only improves the filterability of the precipitated hydrous silicic acid, but also improves the It is preferable because it improves the oil-absorbing properties of the hydrous silicic acid and further improves the strike-through prevention properties of printing ink on paper using the same. The acid for neutralizing the raw material alkali silicate used in the present invention is sulfuric acid, which is generally known as a method for producing hydrated silicic acid.
Mineral acids such as hydrochloric acid and nitric acid, carbon dioxide gas, etc. can be used without particular limitation, but when used as a filler for paper, sulfuric acid is generally the most suitable in consideration of the influence on the papermaking process. Also, the concentration of the above acid is 2g/
It is preferable to use one in the range of 100 c.c. to 40 g/100 c.c. The hydrated silicic acid slurry obtained by reacting an alkali silicate with an acid by the above-mentioned method generally contains coarse particles in a proportion of 20 to 30% of the 250 mesh residue. In the present invention, the hydrated silicic acid containing coarse particles can be wet-milled in a slurry state to reduce the coarse particles to 1% by weight or less. The above effects can only be achieved by producing hydrous silicic acid through two-stage addition of acid. That is, hydrated silicic acid produced by other methods, for example, the so-called one-step method in which acid and alkali silicate are simultaneously added, has a small proportion of coarse particles of about 20%, but compared to the hydrated silicic acid. Even if the wet pulverization is performed, it is extremely difficult to reduce the amount 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, a slurry having a concentration of hydrated silicic acid of 6 to 15% by weight, preferably 8 to 13% by weight is suitable because it provides good grinding efficiency. Moreover, 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 is, a mode in which the slurry is concentrated and then carried out, and a mode in which the hydrated silicic acid is filtered, in some cases washed with water, and then fluidized again to form a slurry. Wet pulverization of hydrated silicic acid is carried out until the particle size of the 250 mesh residue is 1% by weight or less, preferably 0.5% by weight or less. When hydrated silicic acid is used as a filler in the papermaking process, the surface of the resulting paper This is preferable because it can prevent the formation of protrusions due to coarse particles. 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, in the hydrous silicic acid slurry after wet pulverization, the alkali contained in the coarse particles dissolves, resulting in an increase in pH and, accordingly, a significant increase in slurry viscosity. In this case, adding acid to the slurry after wet pulverization and adjusting the pH to 3 to 7, preferably 4 to 6, can reduce the viscosity of the slurry and reduce piping resistance during transportation of the slurry. It's good to be able to do it. 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 in the vicinity of the temperature where the hydrated silicic acid becomes, 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 processing temperature and processing time of the slurry are not particularly limited as long as they are within the above ranges, but when carried out industrially, the processing temperature is generally lower than the temperature at which hydrated silicic acid is precipitated in the above reaction.
The temperature is 10-30°C, preferably 12-15°C higher, and the treatment time is 2-10 hours, preferably 4-7 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 product to the process without drying and pulverizing processes. 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 has excellent ink strike-through prevention effects and dimensional stability effects. 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 amount of hydrated silicic acid used is 0.5 to 10% by weight based on the pulp.
Preferably, 1 to 3% by weight is appropriate. In addition to the above-mentioned hydrated silicic acid, known paper additives may 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) Basis weight: The weight (g) per m ² was measured at 20°C and 64R.H. (2) Oil absorption: Measured according to JIS P130. (3) Whiteness after printing: Indicates the quality of the printing ink's print-through prevention effect ^.
It was applied uniformly over the entire surface, and the whiteness of the printed side and the opposite side was shown. 4 Surface smoothness test 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 (xg) required at that time was measured, using the formula below. calculated and expressed as surface smoothness. Surface smoothness = x/200 Example Aqueous solution of sodium silicate (molar ratio 3.02) containing mirabilite (Na ₂ SO ₄ ) at a concentration of 0.2 mol/and SiO ₂ concentration of 1.3 mol/at a temperature of 40°C. Sulfuric acid was added over 10 minutes with stirring so that the acid addition rate was 28%. Then, the temperature of the reaction solution was increased to 85℃.
After raising the temperature at 2.2°C/min, while continuing stirring, sulfuric acid was added for 80 minutes so that the pH of the solution was between 5 and 6 when the viscosity of the solution reached its maximum. It was precipitated. 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. The pH of the slurry increased due to grinding, and the viscosity of the slurry increased accordingly, so sulfuric acid was added to
was added so that the amount was 5. The viscosity at that time is the first
Shown in the table. In addition, No. 5 shows the viscosity (*) when sulfuric acid is not added. On the other hand, the pulp is mechanical pulp, GP20% by weight, RGP56% by weight, and chemical pulp.
A mixed pulp consisting of 24% by weight of NBKP and a semi-chemical pulp in which 33 parts by weight of CGP was added to 100 parts by weight of the above mixed pulp were used. Add water to the above pulp and fully decompose it,
After adding the wet-pulverized slurry to the mixed pulp so that the amount of hydrated silicic acid was 1.5% by weight,
Add 1 part by weight of sulfuric acid band [Al ₂ (SO ₄ ) _{3.8H 2} O] to 100 parts by weight of the above pulp (absolutely dry) as an aqueous solution, stir evenly, and prepare according to JISP8209 "Hand-sheeted paper for pulp testing". The paper was made according to "Adjustment method". The various properties of the obtained paper are shown in Table 1.

【table】

[Table] Example 2 The same method as in Example 11 No. 1 was carried out except that the hydrous silicic acid slurry was stirred for 3 hours at the temperature shown in Table 2 before being wet-milled. Second result
Shown in the table.

[Table] In addition, in No. 2, the 250 mesh residue was 0.8 or less when the grinding time was 1 minute, and in No. 3, the grinding time was 0.2 minutes. 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 mixed at 80%
Hydrous silicic acid was precipitated by continuously adding it to hot water kept at ℃ at a rate maintaining the pH of 8.5 to 9.0. Next, this hydrated silicic acid was filtered and washed with water, water was added to make an 8% slurry, and the slurry was wet-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 weight of 46.2g/m ² and a whiteness after printing.
46.2%, and surface smoothness was 0.45.

Claims (1)

[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, at a point near where the solution viscosity of the reaction system reaches its maximum, A method for producing hydrated silicic acid, which comprises continuously adding the remaining acid to precipitate hydrated silicic acid, and wet-pulverizing the resulting hydrated silicic acid in a slurry state. 2. The method according to claim 1, wherein the slurry to be wet-milled has a concentration of 6 to 15% by weight. 3. The method according to claim 1, wherein wet pulverization is carried out so that the 250 mesh residue particles of hydrated silicic acid are 1% by weight or less. 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 at a point near where the solution viscosity of the reaction system reaches its maximum. The obtained hydrated silicic acid is heated in a slurry state at least 10°C above the temperature at which the hydrated silicic acid is precipitated.
1. A method for producing hydrated silicic acid, which comprises maintaining the temperature at a high temperature for 2 hours or more, followed by wet pulverization. 5 The concentration of the slurry to be wet-milled is 6 to 15% by weight.
The method according to claim 4. 6. The method according to claim 4, wherein wet pulverization is carried out so that the amount of 250 mesh residue particles in the hydrated silicic acid is 1% by weight or less.