JP2000351618A - Production of hydrous silicic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably and readily producing hydrous silicic acid having an excellently improved preventing effect on strike-through of ink after printing even by wet grinding. SOLUTION: This method for producing a hydrous silicic acid comprises adding a mineral acid to an aqueous solution of an alkali silicate which is an aqueous solution of the alkali silicate and an alkali metal salt except the alkali silicate and has 9-12% alkali silicate concentration calculated as SiO2 concentration and 0.5-3.0% concentration of the alkali metal salt except the alkali silicate so as to make 20-40% neutralization degree at <=50 deg.C, then heating the solution to 80-95 deg.C and adding the mineral acid at the temperature continuously for 45-90 minutes until the pH reaches 3-6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing hydrous silicic acid suitable as a filler for paper. More specifically, the present invention relates to a method for producing hydrous silicic acid, which can be used as a filler at the time of papermaking to prevent the strike-through of the ink and to improve the strength of the paper.

[0002]

2. Description of the Related Art Conventionally, paper, especially newsprint, has tended to be reduced in weight.
The tendency for printing ink to strike through increases. To prevent this, hydrated silica is usually used as a filler. Specifically, a method is generally used in which a predetermined amount of hydrous silicic acid is added to a pulp slurry in a papermaking process to make paper.

[0003] On the other hand, inorganic and organic materials other than hydrous silicic acid have also been studied as fillers for this purpose, but no filler which is inexpensive and has the desired effect has not yet been found. .

[0004] Further, it is considered that the function of preventing print-through of print ink due to hydrous silicic acid is caused by the oil absorbing properties of hydrous silicic acid. That is, when the printing ink printed on the paper surface penetrates into the paper surface, it is considered that the printing ink is adsorbed into the pores of the hydrous silica to prevent strikethrough.

Therefore, as a method of improving the above strike-through effect, a method of increasing the amount of hydrous silicic acid added to paper is conceivable. If the amount of addition is increased, the strike-through effect is increased. In addition, an increase in the amount of hydrous silicic acid causes problems such as generation of paper dust and reduction in paper strength. for that reason,
How to increase oil absorption without increasing the amount of hydrous silicic acid,
That is, a method using hydrated silicic acid having a large pore volume is being studied.

[0006] Usually, as a method of adding hydrated silicic acid to paper, a method of adding hydrated silicic acid in the form of a slurry is employed, but the hydrated silicate slurry obtained from the reaction between alkali silicate and mineral acid is used in the papermaking process. However, in the case of the method of adding as it is to the pulp slurry, many projections are generated on the surface of the paper due to the influence of the coarse particles present in the hydrous silica slurry, which causes many problems such as generation of paper powder.

For this reason, for example, Japanese Patent Application Laid-Open No. Sho 61-1741
In order to reduce the amount of coarse particles in hydrous silica,
A method of wet-grinding the obtained hydrous silicic acid is provided. However, in this method, even if hydrous silicic acid having a large pore volume is obtained by the reaction, the pore volume is reduced by pulverization, and the effect of preventing strike-through is reduced.

On the other hand, regarding the method for producing hydrous silicic acid,
Many more methods have been disclosed. For example, Japanese Patent Publication No. 38-17651 discloses that alkali silicate is neutralized in a first stage of neutralization at a ratio of 50% or less, then the temperature is raised, and the remaining alkali silicate is further added by acid addition in a second stage. A method for neutralization is described. JP-A-53-80397 describes a method in which an alkali metal salt obtained from a reaction mother liquor is allowed to react with a mineral acid in a solution of an alkali silicate. JP-A-59-141416 discloses that an alkali metal salt concentration of 0.1.
An aqueous sodium silicate solution having a concentration of 6 to 0.8% and an SiO ₂ concentration of 5.8 to 9% is neutralized with an acid at a temperature of 60 ° C. or lower at 25 to 35%, and then heated for 80 to 100 minutes. A method for adding and neutralizing residual acid is described.

However, in the above-mentioned method, since the obtained hydrated silica slurry contains coarse particles, it is necessary to carry out wet grinding. However, it is necessary to prevent a decrease in the pore volume of the hydrated silica after the wet grinding. Therefore, although it is effective in improving the properties of the paper surface, the effect of preventing the strike-through effect of the printing ink cannot be obtained sufficiently and the solution is insufficient.

[0010]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for stably and easily producing hydrous silicic acid, which is excellent in improving the effect of preventing strike-through of ink after printing, even when wet pulverized. To provide a manufacturing method.

[0011]

The present inventors have studied in view of the present situation and found that the absorption of printing ink by hydrous silicic acid has a pore radius of 100 to 1000 ° and 3000 nm.
It was found that it was well absorbed in the pore portion of ２０20000 °.

[0012] Then, even after the wet pulverization, a intensive study on a method for producing hydrous silicic acid having an excellent effect of preventing strike-through of a printing ink after printing without substantially reducing the pore volume of the above-mentioned pore radius. As a result, they have found that the use of hydrous silicic acid obtained under specific conditions hardly reduces the pore volume even when wet pulverization is performed, and completed the present invention.

That is, the present invention relates to an aqueous solution containing an alkali silicate and an alkali metal salt other than the alkali silicate, wherein the alkali silicate concentration is 9 to 12 in terms of SiO ₂ concentration.
%, Alkali metal salt concentration other than alkali silicate is 0.5 to
Mineral acid is added to an aqueous alkali silicate solution of 3.0% at a temperature of 50 ° C. or less so that the degree of neutralization is 20 to 40%.
Then, the temperature is raised to 80 to 95 ° C., and a mineral acid is continuously added for 45 to 90 minutes until the pH at the temperature becomes 3 to 6;

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The aqueous solution of alkali silicate used in the present invention can be used without any particular limitation as long as it is within the range specified by the present invention as described below.

That is, the aqueous alkali silicate solution can be used without any limitation as long as it is an aqueous solution containing an alkali silicate and an alkali metal salt other than the alkali silicate.

Specific examples of the above alkali silicate include:
One type or a mixture of two or more types such as sodium silicate and potassium silicate is exemplified. Among them, sodium silicate is preferable.

The alkali metal salts other than the above-mentioned alkali silicate include one or a mixture of two or more of sodium sulfate, sodium chloride and the like. Among them, sodium sulfate is preferred.

The concentration of the alkali metal salt other than the alkali silicate in the aqueous alkali silicate solution needs to be 0.5 to 3.0, preferably 0.7 to 2.5. When the concentration of the alkali metal silicate is less than 0.5, the timing of the aggregation is delayed, and loose aggregates are generated. When wet milling is performed, pores are broken due to shear during the milling. It is not desirable because the volume is reduced,
When the concentration is more than 3.0, the timing of aggregation is advanced, and aggregation is started when the primary particles are still small, so that an aggregate having an original small pore volume is not preferable.

The concentration of the alkali silicate in the aqueous solution of alkali silicate must be 9 to 12%, preferably 9 to 11 as the concentration of SiO ₂ . When the SiO ₂ concentration is lower than 9%, the amount of primary silica particles generated during the reaction is small, so that the aggregation becomes loose and the aggregation breaks during wet pulverization, resulting in a phenomenon of pore volume. On the other hand, if the SiO ₂ concentration exceeds 12%, the aggregation of the particles is promoted, the pores of the particles become small, and the desired effect cannot be obtained.

The molar ratio of alkali silicate to SiO ₂ / M ₂ O (where M is an alkali metal) in the aqueous alkali silicate solution is not particularly limited, but the molar ratio is 3.0 to 3.4.
It is preferred that

The method for producing the aqueous alkali silicate solution is not particularly limited. For example, a method of adding an alkali metal salt other than the alkali silicate to an aqueous solution containing only the above-mentioned alkali silicate so as to have a predetermined concentration. Adopt it. As described above, in the production method of the present invention, it is important that an alkali metal salt other than alkali silicate is previously contained in an aqueous solution of alkali silicate before being reacted with a mineral acid.

The mineral acid used in the present invention is not particularly limited, and a known acid can be used. Specific examples include one or a mixture of two or more of sulfuric acid, hydrochloric acid, nitric acid and the like, and among them, sulfuric acid is preferred.

In the method for producing hydrous silicic acid of the present invention, it is necessary to employ a two-stage reaction in which a mineral acid is added in two portions. Conversely, in the case of a one-stage reaction in which a mineral acid is added only once, aggregation is promoted and the pore volume is reduced, which is not preferable.

First, in the first-stage reaction, it is necessary to use 20 to 40% of a mineral acid necessary for neutralizing all alkali silicates, and preferably 25 to 35% of a mineral acid. It is preferred to carry out the reaction using

In the first-stage reaction, the temperature during the reaction needs to be 50 ° C. or lower, and preferably 40 ° C. or lower. When the temperature during the reaction exceeds 50 ° C., aggregation of nuclei starts, and as a result, the pore volume becomes small, which is not preferable.

In the first-stage reaction, the time for adding the mineral acid is not particularly limited, but is preferably 10 to 20 minutes. If the addition time is shorter than 10 minutes, the reaction may proceed locally and hydrated silica may be precipitated. If the addition time is longer than 20 minutes, it is disadvantageous from the viewpoint of productivity.

In the above reaction, considering that the reaction proceeds uniformly, it is preferable to carry out the reaction with sufficient stirring.

In the present invention, it is necessary to raise the temperature to 80 to 95 ° C. when the addition of the mineral acid in the first-stage neutralization is completed. The time for raising the temperature from 50 ° C. or lower to 80 to 95 ° C. may be left to the restrictions on the apparatus, but it is preferable to raise the temperature in 20 to 40 minutes.

There is no particular limitation on the heating rate, but a method of slowing the heating rate or increasing the heating rate and maturing for a certain time after reaching a predetermined temperature is called floc growth. Therefore, it is preferable.
Considering that the reaction proceeds uniformly during the temperature increase, it is preferable to carry out the reaction with sufficient stirring.

In the present invention, the aforementioned 80 to 95 ° C.
After the temperature is raised to the maximum, a mineral acid is added to carry out a second-stage reaction.

In the second stage reaction, the addition time is 45
It is necessary to carry out continuously for up to 90 minutes, and it is preferred to carry out continuously for 45 to 60 minutes. If the addition time is shorter than 45 minutes, aggregation is promoted and the pore volume is reduced, which is not preferable. On the other hand, when the time is 90 minutes or longer, the effect of improving the pore volume is not improved, and there is no merit in production. If they are not added continuously, the resulting hydrous silicic acid is not preferred because the pore volume decreases greatly when wet-milled.

The reaction must be carried out until the pH reaches 3-6. If the pH is higher than 6, the formation of hydrous silicic acid is not sufficient, and a large pore volume cannot be obtained, which is not preferable. On the other hand, when the pH is less than 3, hydrous silicic acid having a larger pore volume cannot be obtained, and conversely, disadvantages in production, such as the necessity of a special device capable of withstanding strong acidity, are not preferable.

In view of the fact that the reaction proceeds uniformly, it is preferable to carry out the reaction with sufficient stirring.

The hydrous silicic acid obtained by the method of the present invention is obtained in the form of a slurry. The hydrous silicic acid obtained in the present invention is not particularly limited and can be used for various applications, but when used as a paper filler which is one of the objects of the present invention, usually,
It is processed by the following steps.

That is, the hydrated silica slurry is filtered, washed, re-slurried and pulverized by a known method.

The filtration device used at this time is not particularly limited, and a usual filter press, Oliver filter, or the like may be used. By this filtration, the hydrous silica slurry is separated into a hydrous silica cake and an aqueous solution containing impurities. Here, water is added to the obtained hydrated silicate cake to form a slurry again. This re-slurried hydrated silica slurry is wet-pulverized using a device such as a ball mill, a tower mill, and a colloid mill, and may be further subjected to wet classification in some cases. By this operation, giant particles of 63 μm or more contained in the hydrous silicic acid are reduced from about 10 to 30% to 1% or less. At this time, the average agglomerated particle diameter, which was about 20 to 30 μm at the same time, becomes about 10 μm. As a result, when paper is made, the roughness on the paper surface caused by the presence of the giant particles disappears, and problems such as reduction in paper strength do not occur.

Then, the wet-milled hydrated silica slurry obtained by the above method is added to pulp as a filler for paper by a conventionally known method, and papermaking is performed to obtain paper in which print-through of print ink is prevented. be able to.

The hydrous silicic acid produced in the present invention has a small pore volume of only 10% or less even if the giant particles are reduced to a predetermined amount by wet pulverization using a ball mill or the like as described above. It has a pore volume. Conversely, the hydrous silicic acid obtained by the conventional method reduces the pore volume by 20% or more when subjected to the above-mentioned wet pulverization.

As described above, the absorption of the printing ink by the hydrous silicic acid is well absorbed in the pores having pore radii of 100 to 1000 ° and 3000 to 20000 °. Attention was paid only to the pore volume in both regions.

[0040]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. In the following examples and comparative examples,
The measurement of the pore volume and the grindability were performed by the following methods. (1) Pore volume It was measured using a mercury porosimeter (Model 2000 manufactured by Carlo Elba). (2) Pulverizability Using Ball Mill ANZ-50S manufactured by Nitto Chemical Co., Ltd.
A crushability test was performed on a zirconia ball mill of 〜4 mm. Example 1 Commercially available sodium silicate solution (SiO ₂ / Na ₂ O molar ratio:
3.20, SiO ₂ concentration: 39.5%) 1.46 liters of water 2.24 l and sodium sulfate solution (concentration 3.31%) 2.38 liters equipped with a stirring blade reactor having an internal capacity of 10 liters Was charged. The sodium silicate concentration at the time of charging was 9.9% in terms of SiO ₂ concentration, and the concentration of sodium sulfate was 1.2%.

Then, the temperature was raised to 40 ° C., and then, as a first-stage reaction, 0.434% of 22% by weight sulfuric acid was stirred while stirring.
One liter was added over 12 minutes. The neutralization rate at this time is 3
2.5%.

After the completion of the first-stage reaction, the mixture was heated to 90 ° C. with further stirring. After heating, 0.902 liters of sulfuric acid was added over 45 minutes as a second-stage reaction while continuing stirring. The pH after the completion of the reaction is 4.
Nine.

The obtained hydrous silicic acid was filtered and dried by a filter press, and then re-slurried with water.

The obtained hydrous silicic acid slurry was wet-pulverized for 15 minutes in a 2 to 4 mm zirconia ball mill using a Ball Mill ANZ-50S manufactured by Nissin Kagaku.

Before and after the wet pulverization, the pore volume of the hydrous silica slurry was measured. Table 1 shows the results
Shown in

Further, the hydrous silicic acid slurry after the wet pulverization was added to an aqueous pulp solution of 2 g pulp / 100 cc and stirred so that the SiO 2 concentration became 3%, and the mixture was thoroughly mixed and then paper-made with a square paper machine. The paper was printed, but no strikethrough occurred. Example 2 Using the same aqueous sodium silicate solution as in Example 1, 2.84 liters of the sodium silicate solution, 2.12 liters of water and 4.89 liters of a sodium sulfate solution (3.31% concentration) were contained. The reactor was charged into a 20-liter reactor with stirring blades. The sodium silicate concentration at the time of charging was 11.2% in terms of SiO ₂ concentration, and the sodium sulfate concentration was 1.6%.

Then, the temperature was raised to 40 ° C., and then, as a first-stage reaction, 22% by weight sulfuric acid 0.78% with stirring.
One liter was added over 10 minutes. The neutralization rate at this time is 3
It was 0%.

After the completion of the first-stage reaction, the temperature was raised to 93 ° C. with further stirring. After raising the temperature, 1.79 liters of sulfuric acid was added to 60
Added over minutes. After the completion of the reaction, the pH was 5.3.

Thereafter, filtration and washing were performed in the same manner as in Example 1.
After reslurrying, wet pulverization was performed, and the pore volume of the hydrous silica slurry before and after wet pulverization was measured using the hydrous pulverized slurry. Table 1 shows the results. Example 3 Commercially available sodium silicate solution (SiO ₂ / Na ₂ O molar ratio:
3.12 SiO ₂ concentration: 28.22% Na ₂ O concentration:
313.2 liters, 124.3 liters of water and sodium sulfate solution (concentration 3.58%) 298.
4 liters were charged into a 1200 liter reactor with stirring blades. The concentration of sodium silicate when charged is S
The concentration of iO ₂ is 11.9% and the concentration of sodium sulfate is 1.
5%.

Next, the temperature was raised to 40 ° C. Then, as the first reaction, 22% by weight sulfuric acid 7 was added while stirring was continued.
3.4 liters were added over 15 minutes. The neutralization rate at this time was 35%.

After the completion of the first-stage reaction, the temperature was raised to 90 ° C. with further stirring. After the temperature was raised, 136.3 liters of sulfuric acid was added as a second-stage reaction while stirring continuously.
Added over 0 minutes. After the completion of the reaction, the pH was 5.4.

After that, filtration and washing were performed in the same manner as in Example 1.
After reslurrying, wet pulverization was performed, and the pore volume of the hydrous silica slurry before and after wet pulverization was measured using the hydrous pulverized slurry. Table 1 shows the results. Comparative Example 1 The same reaction conditions as in Example 1 were used except that 0.88 liter of aqueous sodium silicate solution and 4.62 liter of water were charged using the same sodium silicate solution as in Example 1, and sodium sulfate was not added. Then, hydrous silicic acid was produced. The concentration of sodium silicate when charged was 6.3% in terms of SiO ₂ concentration.
Met.

Thereafter, filtration and washing were performed in the same manner as in Example 1.
After re-slurrying, wet pulverization was performed, and the pore volume of the hydrous silicate slurry before and after wet pulverization was measured. Table 1 shows the results.

Further, the hydrous silicic acid slurry after the wet pulverization was added to a 2 g pulp / 100 cc pulp aqueous solution so that the SiO 2 concentration became 3%, and the mixture was stirred and thoroughly mixed, followed by paper making with a square paper machine. Printing was performed on the paper, but strikethrough occurred. Comparative Example 2 Commercially available sodium silicate solution (SiO ₂ / Na ₂ O molar ratio:
3.15, SiO ₂ concentration: 37.22%) 0.88 liters and water 2.32 l and sodium sulfate solution (concentration 3.19%) 2.52 liters equipped with a stirring blade reactor having an internal capacity of 10 liters I charged. The sodium silicate concentration when charged was 5.7% in terms of SiO ₂ concentration, and the sodium sulfate concentration was 1.4%.

Next, the temperature was raised to 40 ° C., and then, as a first-stage reaction, 0.22% by weight of sulfuric acid of
51 liters were added over 12 minutes. At this time, the neutralization ratio was 33%.

After the completion of the first-stage reaction, the temperature was raised to 85 ° C. with further stirring. After heating, 0.51 liter of sulfuric acid was added to 45
Added over minutes. After the completion of the reaction, the pH was 5.0.

Thereafter, filtration and washing were performed in the same manner as in Example 1.
After re-slurrying, wet pulverization was performed, and the pore volume of the hydrous silicate slurry before and after wet pulverization was measured. Table 1 shows the results. Comparative Example 3 A commercially available sodium silicate solution (SiO ₂ / N
a ₂ O molar ratio: 3.20, SiO ₂ concentration: 39.5%)
1.46 liters, 2.24 liters of water, and 2.38 liters of a sodium sulfate solution (concentration: 3.31%) were charged into a 10-liter reactor equipped with stirring blades. The sodium silicate concentration at the time of charging was 9.5 in terms of SiO ₂ concentration.
% And the concentration of sodium sulfate were 1.3%.

Then, the temperature was raised to 40 ° C., and then, as a first-stage reaction, 0.6 liter of 22% by weight sulfuric acid was added over 12 minutes while stirring. The neutralization rate at this time is 45
%Met.

After the completion of the first-stage reaction, the temperature was raised to 90 ° C. with further stirring. After heating, 0.73 liters of sulfuric acid was added to 4
Added over 5 minutes. After the completion of the reaction, the pH was 5.5.

Thereafter, filtration and washing were performed in the same manner as in Example 1.
After re-slurrying, wet pulverization was performed, and the pore volume of the hydrous silicate slurry before and after wet pulverization was measured. Table 1 shows the results.

[0061]

[Table 1] As shown in Table 1, the hydrous silicic acid obtained by the method of the present invention has a sufficient pore volume and a very small decrease in the pore volume even when wet pulverized. Therefore, paper using the hydrous silicic acid obtained by the method of the present invention as a filler does not cause strikethrough of the printing ink.

On the other hand, the hydrous silicic acid obtained by a method other than the method of the present invention has insufficient pore volume, or has a remarkably large decrease in pore volume after wet pulverization. For this reason, paper using the hydrated silica obtained by a method other than the present invention as a filler causes strikethrough of the printing ink.

[0063]

As described above, the present invention provides a method for producing hydrous silicic acid which is particularly useful as a filler for paper, and the obtained hydrous silicic acid can be subjected to pulverization and classification operations. Since the reduction of the pore volume is small, the operation becomes extremely easy.Furthermore, when papermaking is performed using the obtained crushed / classified hydrous silicic acid, it is great for preventing strike-through of the printing ink without reducing the paper strength of the paper. An effect can be provided.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G072 AA28 AA35 BB05 CC04 EE01 EE02 GG03 HH21 JJ13 JJ15 LL06 LL07 MM01 MM21 MM26 PP17 RR06 SS06 TT20 UU25 4L055 AG05 AH01 EA20 EA24 EA25 EA31 EA29

Claims (1)

[Claims] An aqueous solution containing an alkali silicate and an alkali metal salt other than the alkali silicate, wherein the alkali silicate concentration is 9 to 12% in terms of SiO ₂ concentration and the alkali metal salt concentration other than the alkali silicate is 0.5%. Aqueous alkali silicate solution having a neutralization degree of 20 to 40% at a temperature of 50 ° C. or lower.
%, And then the temperature is raised to 80 to 95 ° C., and the mineral acid is continuously added at that temperature for 45 to 90 minutes until the pH becomes 3 to 6. Method for producing silicic acid.