JPH05178606A - Production of hydrated silicic acid for paper making - Google Patents

Abstract

PURPOSE:To attain stable operations on production because of low viscosity of slurry of hydrated silicic acid, to prevent the obtained hydrated silicic acid from dropping down from paper on paper making and to improve oppacity of printed paper as well as white paper and whiteness. CONSTITUTION:The amount of sulfuric acid corresponding to 35-45% of the total one required to neutralize sodium silicate is added in the 1st stage to obtain a water solution by neutralization. At that time, sodium sulfate is previously replenished to make adjustment so that the obtained water solution may have a silicon dioxide concentration of 6.8-8.0g/100ml and a sodiun sulfate concentration of 3.5-4.1g/100ml. Then the water solution is heated to a temp. of 85-95 deg.C while stirring and the balance sulfuric is added to complete neutralization. Hydrated silicic acid is deposited and separated from the water solution to form slurry again. The slurry is wet-crushed and/or wet-classified to make it include particles of 3-10mum average particle diameter of hydrated silicic acid and also include particles of 1-300mum particle diameter by at least 80%.

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 hydrated silicic acid used as a filler for paper during papermaking. More specifically, the present invention provides a hydrated material which, when used as a filler for papermaking, has a good yield on paper and is effective for improving the opacity and whiteness of printed paper and of white paper. The present invention relates to a method for producing silicic acid.

[0002]

2. Description of the Related Art In recent years, the weight of paper tends to be reduced,
When the paper is made lighter, the opacity of the paper after printing is lowered when printed on the paper, which is not preferable.Therefore, a filler is generally added to the paper in order to prevent the opacity of the paper after printing from being lowered. Has been.

For this purpose, various inorganic and organic fillers have been researched and developed, but at present, inexpensive and sufficiently effective fillers have not yet been developed. In addition, recently, there is a strong tendency toward further weight reduction, so in addition to the ability to improve the opacity after printing by suppressing the permeation of the oil component in the ink during printing, the opacity of blank paper is also positively improved. A filler that has the ability to do so is desired.

Among the above-mentioned various fillers, those having the ability to increase the opacity of white paper but have a poor ability to suppress the penetration of ink, such as titanium dioxide, or those having the above two capabilities, such as an organic urea-formalin resin, are used. It is generally known that they have a combination but lack the ability of each. On the other hand, hydrated silicic acid as a filler is cheaper than other types and has a great effect of imparting opacity after printing on paper, but in that effect, or in the effect on white paper opacity. Not enough to provide.

Regarding the method for producing hydrated silicic acid, for example, in Japanese Examined Patent Publication (Kokoku) No. 38-17651, the acid addition in the first step is 50% or less when neutralizing sodium silicate with acid, and then the temperature is raised. After that, it is described that the acid addition in the second step is performed, and Japanese Patent Publication No. 49-36877 describes a method for producing hydrated silicic acid as a filler for paper. JP-B-52-28755 and JP-B-52-28755 disclose that the concentration of alkali silicate converted to silica is 2 to 9.5 g / cc and the acid concentration is 2 to 40 g / 1.
A production method is described in which the addition rate of mineral acid when 00 ml of mineral acid is added is expressed as a function value of the formation rate of silica and is kept within an appropriate range.

Further, as a technique for producing finely powdered silicic acid, Japanese Patent Application Laid-Open No. 53-80397 discloses reacting an alkali silicate with a mineral acid in the presence of an alkali metal salt. It is described that the mother liquor obtained when the silicic acid is deposited and then filtered and separated is used. Further, Japanese Patent Laid-Open No. 55-113611 discloses that the above-mentioned techniques are collected and the addition ratio (A) of the first stage acid is 20 to 50%, and Silica concentration (C) of 2 ~ 6g / 100ml
And that the reaction temperature (T) is within the range of 70 to 100 ° C. and the value X obtained from the relational expression of these A, C and T is limited within a specific range. However, this is a technique for increasing the oil absorption rate of hydrated silicic acid powder, that is, it is possible to increase the oil absorption rate of boil oil by setting the pore volume with a pore radius of 50 to 150 to 0.5 to 0.9 cm3 / g. It is described, and it is not mentioned whether it can be used as a filler for papermaking.

However, when the hydrated silicic acid produced by the above-mentioned production method is added to the paper, the ability to improve the opacity of white paper is extremely small, and the ability to improve the opacity after printing is not sufficient, and the production conditions described above are used. Even in the range of 10, the above-mentioned performance of the hydrated silicic acid obtained by varying the conditions remarkably fluctuates, and it is difficult to obtain a product of stable quality. Furthermore, when adding products made by these manufacturing methods to make paper, the filler falls off during paper making and adheres to instruments such as the moisture meter and thickness meter of the paper machine, and when the paper product made from paper is printed. There is a serious drawback that the filler comes off during printing and adheres to the plate of the printing machine, which shortens the life of the plate.

As an improved technique thereafter, a technique in which an operation of wet-milling hydrated silicic acid is added is described in JP-A-61-17415, and further, JP-A-61-41415 proposed by the present inventors. -141767, it is possible to improve the ink receptivity and the opacity after printing by adjusting the average particle size and particle size distribution of hydrated silicic acid to a specific ratio by performing wet grinding and classification. A method is disclosed.

[0009] However, the above-mentioned improved technique relating to wet pulverization has been able to improve the drawback of the dropping of the filler from the surface of the paper among the techniques for producing hydrated silicic acid for papermaking, but has the effect of improving the opacity after printing. In particular, the effect of improving white paper opacity was not sufficiently improved. In the additional test results after that, although the loss problem of the filler was significantly improved, sometimes the slight loss problem still occurred and it was not completely solved yet.

On the other hand, as a method for improving the opacity after printing, the present inventors have already disclosed in JP-A-60-65713 that the sulfuric acid in the first step while performing sufficient stirring and / or dispersion. It was proposed that the opacity after printing could be improved to the maximum by increasing the usage ratio of 45 to 50%, but this method also raises the temperature of the partially neutralized aqueous solution to precipitate hydrated silicic acid. Since the viscosity in the process and the viscosity of the obtained hydrated silicic acid slurry become high, it is important to carry out a uniform reaction when manufacturing with a large-scale apparatus, and to transfer and handle the product slurry. It has a defect.

[0011]

In view of the above situation, the inventors of the present invention have earnestly studied a method for stably and easily producing hydrated silicic acid having an excellent improving effect on opacity after printing. As a result, we focused on the pore size distribution of hydrated silicic acid, and compared the effect on opacity after printing with the pore diameter.
Pore volume obtained in the range of 11-50 nm (nanometers) is most important for imparting opacity after printing,
That is, the larger the pore volume of the hydrated silicic acid in the pore diameter range of 11 to 50 nm, the more significantly the opacity after printing is significantly improved. Surprisingly, it is also excellent in improving the opacity and whiteness of white paper. Therefore, the present invention has been completed and the present invention has been completed.

Further, the present inventors have found that the viscosity and the hydrated silicic acid obtained in the step of increasing the pore volume and heating the partially neutralized aqueous solution to precipitate hydrated silicic acid. As a condition for suppressing the viscosity of the slurry of low, when neutralizing sodium silicate with sulfuric acid in the presence of sodium sulfate, to specify the use ratio of the first stage sulfuric acid and the first stage part It was found that the concentration of sodium sulfate (Na2SO4) and the concentration of silicon dioxide (SiO2) in the aqueous solution after the neutralization reaction should be kept within the specified range.

Therefore, an object of the present invention is to eliminate the drawbacks of the prior art, improve the opacity after printing, and especially stabilize hydrated silicic acid which has an excellent effect in improving the opacity and whiteness of white paper. Another object of the present invention is to provide a method of easily manufacturing.

[0014]

The first aspect of the present invention is a method for producing hydrated silicic acid for papermaking by adding sulfuric acid to an aqueous solution of sodium silicate in two stages in the presence of sodium sulfate and neutralizing the solution. In, the amount of sulfuric acid corresponding to 35 to 45% of the total amount of sulfuric acid necessary for neutralizing the sodium silicate was added as the first-stage sulfuric acid to partially neutralize it. Sodium sulfate (SiO2) concentration of 6.0-8.0g / 100ml and sodium sulfate (Na2SO4) concentration of 3.5-4.1g / 100ml were adjusted by supplementing with sodium sulfate, and then 85-95 while stirring the aqueous solution. The temperature was raised to ℃, the remaining sulfuric acid was continuously added as the second stage sulfuric acid to complete the neutralization to precipitate hydrated silicic acid, and the obtained hydrated silicic acid was filtered and separated. Then, wet pulverization and / or wet pulverization using a slurry obtained by redispersing the hydrated silicic acid in water. A method for producing hydrated silicic acid for papermaking, characterized in that hydrated silicic acid has an average particle size of 3 to 10 μm and contains at least 80% of particles having a particle size of 1 to 30 μm by classification. ..

The second aspect of the present invention is the temperature (T ° C.) of the aqueous solution after the temperature of the aqueous solution after the partial neutralization reaction exceeds 70 ° C. and the total amount of sodium silicate added in advance. The integral value X calculated by the equation 1 with respect to the time (tc minutes) until 85% of the water is neutralized is 500-1000.
The method is described in.

[0016]

[Formula 1]

The third aspect of the present invention is that the pH of the aqueous solution after the neutralization reaction in the step of adding sulfuric acid in the second step for neutralizing sodium silicate with sulfuric acid is in the range of 5 to 8.5. The method according to the first or second aspect of the present invention is characterized in that aluminum sulfate is added in an amount of 0.1 to 0.5% based on the weight of silicon dioxide (SiO2) in terms of aluminum oxide (Al2O3).

A fourth aspect of the present invention is to add aluminum sulfate to the slurry when wet-milling the slurry.
The method according to any one of the first to third aspects of the present invention, characterized in that the slurry is adjusted to pH 4 to 5 and then wet-milled.

The fifth aspect of the present invention is that the hydrated silicic acid powder obtained by filtration, washing with water and freeze-drying has a pore volume in the range of 11 to 50 nm (nanometer) measured by mercury porosimetry. Is 0.4 to 1.0 cm3 / g, the method according to any one of the first to fourth aspects of the present invention.

The sodium silicate used in the present invention is not particularly limited, and those conventionally used for the production of hydrated silicic acid can be used. A Na2O molar ratio of 3.05 ± 0.05 is preferably used.

In the present invention, sodium silicate is first dissolved in water to form an aqueous solution, and then partially neutralized with sulfuric acid to precipitate hydrated silicic acid, and when appropriate primary particles are formed, Final neutralization is performed to form primary particle aggregates.
Although it is based on the principle of forming secondary particles, from the process in which hydrated silicic acid begins to precipitate and primary particles are formed, each primary particle aggregates into large primary particles. The reaction in the process of forming secondary particles is important.

In the present invention, the sulfuric acid for neutralization is added in two steps, and 35 to 45% of the total amount of sulfuric acid necessary for neutralizing sodium silicate in the first stage is added. It is added with stirring to an aqueous sodium silicate solution in the presence of sodium sulfate. The time for adding sulfuric acid is not particularly limited, but in order to carry out a uniform reaction, it is necessary to add 8 to 15 under normal stirring conditions.
It is preferable to add it over minutes. The higher the temperature and the higher the addition rate of sulfuric acid, the higher the precipitation rate of hydrated silicic acid. Therefore, in order to prevent localized precipitation or gelation of hydrated silicic acid, the addition time of sulfuric acid is short. In the case, it is preferably 50 ° C or lower, and when the time is long, 60 ° C or lower is preferable. The aqueous solution after the addition of the sulfuric acid in the first step is then heated to a temperature of 85 to 95 ° C with stirring, and the silicon dioxide (SiO2) concentration in this solution is 6.0 to 8.0 g / 100 ml. In addition, the amounts of sodium sulfate aqueous solution and fresh water added are adjusted so that the sodium sulfate (Na2SO4) concentration is 3.5 to 4.1 g / 100 ml.

The concentration of silicon dioxide (SiO 2) in this aqueous solution is
If the amount is less than 6.0 g / 100 ml, the primary particles of the hydrated silicic acid collide relatively little with each other, the aggregation may be insufficient, and the obtained hydrated silicic acid does not impart desired paper opacity after printing. Conversely, if the silicon dioxide concentration exceeds 8.0 g / 100 ml,
Agglomeration of particles is promoted, the chemical reaction inside the agglomerated particles becomes insufficient, and a non-uniform reaction occurs, so that the desired effect cannot be obtained in the same manner as described above.

Although the viscosity of the step of precipitating hydrated silicic acid and the viscosity of the resulting hydrated silicic acid slurry can be lowered by raising the temperature of the partially neutralized aqueous solution by the addition of sodium sulfate, If the concentration of sodium sulfate in the aqueous solution is less than 3.5 g / 100 ml, the decrease in viscosity will be insufficient and, in addition, the growth and aggregation of hydrated silicate particles will tend to decrease. The desired effect of the present invention cannot be obtained from the acid. Moreover, in this case,
The viscosity of the slurry in the subsequent step of wet pulverization and / or wet classification increases, resulting in a decrease in processing capacity, which is not preferable.

On the other hand, the concentration of sodium sulfate is 4.1 g / 100 ml
When it exceeds, the primary particle diameter becomes large, and further, the distribution of the pore diameter deviates from the desirable range, and thus the hydrated silicic acid accompanied by the change in the physical properties does not exhibit the desired effect. Moreover, although the reason is unknown, despite the fact that coarse particles in the obtained hydrated silicic acid are removed by classification for use in papermaking, there is a drawback that the amount of filler dropped from the paper increases. This in turn causes serious troubles such as sticking to instruments of a paper machine and sticking to a blanket or a plate of a printing machine.

As described above, in the present invention, the concentration of sodium sulfate in the aqueous solution during the temperature rise to a predetermined temperature after the partial neutralization of sodium silicate is completed by adding the first stage sulfuric acid. Is extremely important and is an essential requirement of the present invention.

As described above, according to the present invention, it is essential to specify the concentrations of sodium sulfate and silicon dioxide in the partially neutralized aqueous solution before the addition of the sulfuric acid in the second stage. As a requirement, these adjustments are
For example, in the case of sodium sulphate, the amount of sodium sulphate initially charged, the amount of fresh water initially charged, the amount of sodium sulphate generated by the addition of sulfuric acid in the first step or the partially neutralized aqueous solution is raised. When steam is directly blown in for warming, careful consideration should be given to the fact that it will be diluted due to the generated drain.

In the present invention, it is essential that the use ratio of the sulfuric acid in the first stage is within the range of 35 to 45% of the total amount of used sulfuric acid. Hydrated silicic acid is generally an aggregate of single particles of hydrated silicic acid having a particle size of 10 to 50 nm, and the size of the pore size formed inside the aggregate depends on the size of the particle size of this single particle. It is known that the number of particles and the number of particles change, that is, the pore volume changes.
It is preferably ˜40 nm, and therefore it is important to maintain the sulfuric acid ratio in the first stage within the above range.

When the proportion of sulfuric acid used in the first step is less than 35%, the growth of primary particles is not sufficient, so that the obtained hydrated silicic acid has a sufficient pore volume in the 11 to 50 nm diameter range. The amounts are not reached, and therefore such hydrated silicic acids do not reach a satisfactory level of improvement in opacity after printing. on the other hand,
If the usage rate of sulfuric acid in the first stage is 45% or more,
Up to around 50%, an increase in the pore volume in the pore diameter of 11 to 50 nm is observed, and the effect of improving the opacity after printing tends to increase, but when the use ratio of the sulfuric acid exceeds 45%. However, the viscosity of the obtained slurry of hydrated silicic acid becomes remarkably high and the subsequent handling becomes extremely difficult, which is not suitable.

After the addition of the sulfuric acid in the first step is completed, it is preferable to raise the temperature of the aqueous solution in which the neutralization is partially finished to accelerate the precipitation rate of hydrated silicic acid particles. The temperature may be raised as early as the equipment allows, or the temperature may be raised slowly, but a certain amount of time is required for the precipitation and growth of the hydrated silicic acid particles, so the temperature rises rapidly as 3 ° C / min. If the temperature rises, the second stage of neutralization is performed after the temperature is raised.
It is desirable to perform a aging of the primary particles with a holding time of 5 to 10 minutes before shifting to the formation of secondary particles). On the other hand, when the temperature is raised slowly such as 1 ° C./minute, it is not necessary to set the above holding time. In the present invention, the first stage of neutralization with sulfuric acid is completed at 40 to 50 ° C, and then the temperature is raised to 85 to 95 ° C at a temperature rising rate of 1.5 to 2.5 ° C / min for 20 to 30 minutes. It is preferable to perform warming and then carry out the second stage of neutralization with sulfuric acid without setting a holding time because it is the easiest and most advantageous in the production operation.

During the above-mentioned temperature rise, hydrated silicic acid particles are precipitated and their primary particles are grown, and then the second stage of neutralization with sulfuric acid completely precipitates the remaining hydrated silicic acid. At the same time, the secondary particles in which the primary particles are slightly aggregated are formed. After the neutralization with sulfuric acid in the first step, if the primary particles of hydrated silicic acid grow sufficiently,
There are no particular restrictions on the conditions such as the concentration of sulfuric acid in the addition of sulfuric acid in the second step and the time required for the addition, but if the growth of primary particles is not sufficient, neutralization with sulfuric acid in the second step is not possible. It is preferable to carry out the reaction for 20 to 40 minutes to carry out a uniform neutralization reaction.

As a result of a more quantitative understanding of the above facts, the present inventors found that the temperature (T ° C.) after the temperature of the partially neutralized aqueous solution exceeded 70 ° C. and 85% of sodium silicate were Integral value X shown in Equation 1 regarding the time until neutralization (tc minutes)
It has been found that is preferably in the range of 500 to 1000. The concentration of sulfuric acid used for neutralization is not particularly limited, but a concentration of 20 to 30% by weight is preferable from the viewpoint of increasing the amount of liquid and easiness of handling.

The hydrated silicic acid slurry obtained by the above-mentioned method has a silicon dioxide (SiO2) concentration of 5.5 to 6.5 g / 100.
Although it is in the range of ml, this slurry is a belt filter,
It is separated into a filtrate containing sodium sulfate and a cake of hydrated silicic acid in a filter device such as a filter press or a screw press. Then, fresh water is added to the obtained cake and mixed and stirred to obtain a slurry having a hydrated silicic acid concentration of 8 to 12 g / 100 ml. This slurry contains sodium sulphate which could not be separated from the hydrated silicic acid, which can also be removed repeatedly by washing with water at the cake stage. When filtering the slurry, set the slurry temperature to 40-60
It is important that the temperature is kept above ℃, the filtration rate is not deteriorated, and the basic physical properties of hydrated silicic acid are not changed.

In the slurry having a hydrated silicic acid concentration of 8 to 12 g / 100 ml, coarse particles of 70 μm or more are usually contained in the total amount of 5 to 20.
Since it is contained in the range of%, the slurry is processed by a wet homogenizer such as a continuous homomixer, a colloid mill, a disc refiner, a sand grinder, a ball mill and a rod mill, and then passed through a classifier such as a vibrating screen, Removes hydrated silicic acid with coarse particles of 70 μm or more,
Finally, the content of coarse particles of 70 μm or more is 0.05% by weight of the whole.
The following is done: As the processing conditions of the wet crusher, it is necessary to consider that coarse particles of hydrated silicic acid of 70 μm or more are selectively crushed, but particles of 30 μm or less, especially 10 μm or less are not crushed. That is,
When selecting the type and conditions of the wet pulverizer, it is desirable to select so as to minimize the decrease in the average particle size of the hydrated silicic acid particles, and to remove only the coarse particles remaining in the classifier.

A decrease in the average particle size of the hydrated silicic acid particles causes a decrease in the yield when hydrated silicic acid is added during papermaking, and at the same time, the reason is unknown, but a pore volume of 11 to 50 nm is also present. As a result, the effect on post-printing as well as on white paper opacity is reduced, and the intended purpose of the present invention is not achieved. The particle size distribution of the hydrated silicic acid according to the present invention has an average particle size of 3 to 10 μm, and the particle ratio of the particle size 1 to 30 μm is at least 80% or more. The larger the value, the greater the effect.

On the other hand, in wet pulverizing hydrated silicic acid and classifying it, the concentration and viscosity of the slurry of hydrated silicic acid are very important factors from the viewpoint of the processing capacity of the equipment and operation. After printing and in order to further increase the effects of white paper opacity, etc., it is better to increase the use ratio of sulfuric acid in the first stage to around 45%, but in this case, the viscosity of the slurry tends to increase at the same time. Therefore, the use ratio of the sulfuric acid cannot be increased unnecessarily in terms of processing capacity and operation. In the present invention, in view of this, the pH of the slurry obtained by redispersing the deliquored cake after neutralization is adjusted to the range of 4 to 5 by adding aluminum sulfate (Al2 (SO4) 3). Adjusting to 50% can reduce the viscosity of the slurry to 50-80% compared to the case where aluminum sulfate is not added, so even if the 5% increase in the first stage sulfuric acid ratio from 37% to 42%, Wet grinding and classification can be performed quickly without reducing the capacity.

Further, in the present invention, as described in JP-A-60-65713, sodium aluminate (NaAlO2) is added to an aqueous solution of sodium silicate, or instead of sulfuric acid during neutralization. Aluminum sulphate (sulfuric acid band: Al2 (SO4) 3) can also be used to reduce the viscosity of the hydrated silicic acid slurry. However, when more than 0.5% of aluminum compound is present during the neutralization reaction of sodium silicate, SiO2-Al
2O3 type compounds or composites are produced, and the resulting pore size distribution of hydrated silicic acid may be affected, and the effect of improving the opacity of white paper after printing may be impaired, so conversion to aluminum oxide (Al2O3) Therefore, only a very small amount such as 0.5% or less of the weight of hydrated silicic acid can be used. However, if the amount is less than 0.1%, the desired viscosity cannot be lowered, which is not preferable. Also, when used in the latter half of the neutralization reaction with sulfuric acid instead of adding an aluminum compound at the start of the neutralization reaction, the reaction does not reach the inside of the secondary particles, and therefore the slurry viscosity is changed without changing the pore size distribution. It can be lowered, which is convenient.

For the above reason, it is preferable to add aluminum sulfate at pH 8.5 or less, and conversely, if the aluminum sulfate is added at pH less than 5, the neutralization reaction is completed. Not only the reactivity with the hydrated silicic acid particles is poor and the yield is poor, but when the filtrate after separating the hydrated silicic acid is used for circulation for the next neutralization reaction, aluminum compounds are contained in the filtrate. It is not preferable because it becomes too large and adversely affects the subsequent neutralization reaction.

While studying the effect of improving the opacity of the paper after printing and the characteristics of the filler, the present inventors have found that the pore volume of the filler, especially the pore diameter in the range of 11 to 50 nm. We found that the pore volume was important. Moreover, in the case of hydrated silicic acid, when the pore volume is simply dried, innumerable silanol groups (-SiOH) are condensed to each other on the surface of the hydrated silicic acid particles, and a siloxane bond group (-Si-O- It was found that Si-) blocks the pores and does not show the correct pore size distribution.

On the other hand, the pore volume when the pore size distribution is measured using freeze-dried hydrated silicic acid powder is such that the above-mentioned polycondensation is unlikely to occur, and the silanol groups remain in a large amount. As a result, it is possible to obtain accurate values with less pores. On the other hand, the hydrated silicic acid added when paper is made into paper is drawn into the paper while being entangled with pulp fibers and dried. In the range of 5.0%, the hydrated silicic acid particles are less likely to be in close contact with each other, and thus the probability that the pores are blocked is considered to be small.

On the other hand, regarding the pore volume measured in this way, a pore diameter of 11 to 50 nm does not have a critical meaning, but in the region where the pore diameter is small, the ability to retain the oil component in the ink is the most. These values were considered to be excellent and were selected for the convenience of handling the measured data.
The reason for this is that the smaller the pore size, the stronger the suction force based on the capillary phenomenon, and therefore the oil component contained in the larger size is eventually absorbed by the adjacent small size pores. However, the oil component is a mixture of many kinds of hydrocarbons, and it is considered that the oil component cannot penetrate if the diameter is too small.

Therefore, hydrated silicic acid having a large pore volume of 0.4 cm3 / g or more in the range of 11 to 50 nm according to the above measurement results has an excellent ability to improve opacity after printing.
On the contrary, when trying to obtain a pore volume of 1.0 cm3 / g, it is necessary to reselect manufacturing conditions such as increasing the use ratio of sulfuric acid in the first stage to 45% or more within a special range. It becomes difficult to stably produce hydrated silicic acid.

As described above, according to the present invention, in the production of hydrated silicic acid as a filler for papermaking, unit operations such as stirring, separation, transfer, pulverization and classification become extremely easy, and the obtained hydrated silicic acid is obtained. When an acid is used in papermaking, it has an effect that the yield on the paper is good and it contributes to the improvement of the opacity and whiteness of the white paper after printing.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these.

[0045]

【Example】

Example 1 Sodium silicate aqueous solution (Si
O2 / Na2O molar ratio = 3.05, SiO2 concentration = 187g / l) 80.2 liters and sodium sulfate (Na2SO4) aqueous solution (concentration = 60.0g / l)
62 liters and 44.2 liters of fresh water were supplied to an internal heating type reaction vessel with an internal volume of 300 liters equipped with a stirrer. Next, the temperature of the aqueous solution was adjusted to 45 ° C. by steam heating, and 13.0 liters of 20 wt% (228 g / l) sulfuric acid was added over 10 minutes while stirring. At this time, the addition ratio of the sulfuric acid in the first stage to the total amount of added sulfuric acid was 37%.

At this time, the content of the contents is increased by adding a steam drain.
Since it reached 206 liters, the silicon dioxide (SiO2) concentration was 7.2 g / 100 ml, and sodium sulfate was 4.3 K in the first stage of neutralization.
As a result, the concentration of sodium sulfate (Na2SO4) in the partially neutralized aqueous solution was 3.9 g / 100 ml. Steam was blown into this partially neutralized aqueous solution while further stirring, and the temperature was raised to 95 ° C. in 20 minutes. Further, while continuing stirring, of 22.3 liters of sulfuric acid in the second stage,
Add 16.9 liters over 30 minutes to obtain 85% total sodium silicate.
%, And then the remaining 5.4 liters of sulfuric acid was added over 10 minutes to complete the neutralization. The pH of the hydrated silicic acid slurry obtained at this time was 5.0, and the integral value X calculated by the formula 1 was 87.
It was 5.

20 liters of the obtained hydrated silicic acid slurry was placed in a bucket type centrifugal dehydrator covered with a filter cloth for dewatering to obtain 6 kg of cake-like hydrated silicic acid. Next, the cake-like hydrated silicic acid was taken out, water was added to this, and the mixture was stirred to form a slurry again, and the concentration of the hydrated silicic acid was adjusted to 100 g / l.
Take 1 liter of this slurry and put it in a stainless beaker with an internal volume of 2 liters along with 1 liter of glass beads with a diameter of 2.0 to 2.6 mm.While keeping the temperature at 50 ° C, stir for 3 minutes at 480 rpm with a YAMATURABO stirrer and pulverize. After the treatment, this slurry was sieved with a JIS 200 mesh standard sieve to remove the residue. The pH of the slurry after this pulverization and classification treatment is 6.3, the viscosity by a B-type viscometer is 500 cp, the average particle size of hydrated silicic acid is 7.2 μm, and the particle ratio of 1 to 30 μm is 86.
%, And the lyophilized powder of this slurry which had been filtered, washed with water, and then freeze-dried had a pore volume of 0.42 cm3 / g in the range of 11 to 50 nm in diameter measured by mercury porosimetry.

Using 10.0 ml of this slurry, 2 liters of pulp slurry of 25 g / l of mixed pulp for newsprint consisting of 13% bleached softwood kraft pulp, 19% thermomechanical pulp, 38% ground pulp and 30% deinked waste paper pulp , Add hydrated silicic acid to 2% by weight of bone-dry pulp, stir for 2 minutes, and then add sulfuric acid band (Al2 (SO4) 3-
18H2O) at 1% based on absolute dry pulp weight, stir for an additional 2 minutes, dilute by adding water to a total volume of 16 liters, mix well, and then use a TAPPI standard square sheet machine to weigh 42.5 g. Paper of g / m2 was made and dried.

This handmade sheet was conditioned in a room at 20 ° C. and 65% relative humidity, and then a machine calender with a linear pressure of 40 kg / cm was used.
After passing twice, the Oken type smoothness was adjusted within the range of 50 to 60 seconds, and then the paper quality test such as whiteness and opacity and the printing test were conducted and evaluated.

The test method used is as follows. 1) Particle size distribution Particles with a particle size of 44 μm (325 mesh) or more were placed on a JIS standard sieve and measured by a water sieving method in which water was passed from the top while vibrating on a shaker. Particles of 44 μm or less were measured using a Shimadzu centrifugal sedimentation type degree distribution measuring device (SA-CP2 type). The average particle size is shown by the median cumulative value (median size).

2) Slurry viscosity Using a B-type viscometer manufactured by Tokyo Keiki Co., No. 1-at 20 ° C. and 60 rpm
It measured using the rotor of 3.

3) Pore Volume Pore volume is 2000 type mercury porosimeter (DILATOMETER type CD-3P, manufactured by CARLOERBA), CAPILLARRY: 3 mmφ, 0.070
65 cm2). The pore volume is 11 to 50n in diameter.
It was expressed as the volume of m.

4) Opacity after printing Solid printing with a size of 13.9 × 18 cm was carried out with a Miyakoshi M-3 printing machine, and the opacity Y (%) after printing was defined by equation 2. Since the opacity after printing varies by 0.2 to 0.3% depending on the lot of raw pulp used in the test, the opacity after printing of sheets without hydrated silicic acid 88.7% and as a standard substance are commercially available. 2 hydrated silicic acid powders per absolute dry pulp weight
Opacity after printing of the sheet added so as to become 9% 91.4
The value was corrected based on%.

[0054]

[Formula 2]

5) White paper opacity A backing plate having a reflectance of 89.5% was measured according to JIS P 8138.

6) Whiteness Measured according to JIS P 8123.

Example 2 Using 66.3 liters of an aqueous solution of hydrated sodium silicate, 63.9 liters of an aqueous solution of sodium sulfate and 58 liters of clear water, the addition amount of sulfuric acid in the first step was 10.2 liters and the addition amount of sulfuric acid in the second step was Hydrated silicic acid was produced in the same manner as in Example 1 except that the amount was 18.9 liters. At this time, the ratio of sulfuric acid used in the first step was 35%, and the silicon dioxide (SiO2) concentration at the start of temperature rise was 6.
0g / 100ml, sodium sulfate (Na2SO4) concentration 3.5g / 100ml
Met.

The hydrated silicic acid thus obtained was treated in the same manner as in Example 1 and crushed to obtain JIS 20
The pH of the hydrated silicic acid slurry after removing the residue with a 0-mesh standard sieve was 6.0, the proportion of particles of 1 to 30 μm was 91%, and the pore volume was 0.40 cm 3 / g. Further, a handmade sheet was prepared from this slurry in the same manner as in Example 1 and evaluated.

Examples 3 and 4 Table 1 shows the use ratio of the first stage sulfuric acid, the concentration of silicon dioxide (SiO2) and the concentration of sodium sulfate (Na2SO4) at the start of heating.
In the same manner as in Example 1, two types of hydrated silicic acid and sheets containing the same were produced and evaluated.

Example 5 Under the same reaction conditions as in Example 1, hydrated silicic acid was produced in a commercial-scale apparatus, and wet-milled and vibrated. That is, an aqueous solution of sodium silicate (SiO2 / Na2O molar ratio =
3.05, SiO2 concentration 187g / l) 9.62m3, sodium sulfate aqueous solution (concentration 60g / l) 7.53m3 and clear water 5.82m3 were supplied to an internally heated reaction layer with an agitator with an effective volume of 30m3, and then 20% by weight of sulfuric acid 1.52m3. Was added with stirring over 12 minutes. At this time, the use ratio of sulfuric acid in the first step was 36%, the silicon dioxide concentration was 7.35 g / 100 ml, and the sodium sulfate concentration was 3.9 g / 100 ml. After that, blow steam with stirring,
The temperature was raised from 45 ℃ to 91 ℃ in 2.0 minutes, and 2.08m3 of 85% of the total amount of sulfuric acid required for complete neutralization out of 2.71m3 of sulfuric acid added in the second step was immediately added for 25 minutes. Then, the remaining 0.63 m3 of sulfuric acid was added over 21 minutes to terminate the precipitation reaction of hydrated silicic acid.

The hydrated silicic acid slurry having a concentration of 6.1 g / 100 ml obtained by this reaction was then made into a cake shape with a belt filter, and fresh water was added thereto and stirred to obtain a slurry of 10.5 g / 100 ml. Next, Oji Kogyo's sand grinder (internal volume
It was treated with 100 liters, 60 kg of beads of 2.0 to 2.3 mmφ) at a slurry supply rate of 60 l / min, and then treated with a 200 mesh vibrating screen (Tsukishima Kikai Co., Ltd .: Bolton 48 type). The viscosity of the hydrated silicic acid slurry was 400 cp, and the average particle size of the hydrated silicic acid was 6.0 μm.

Using this hydrated silicic acid slurry, a finished raw material for a twin wire paper machine exclusively for newsprint (compounding: 13% softwood bleached kraft pulp, 19 thermomechanical pulp)
%, Ground pulp 38%, deinked waste paper pulp 30%)
Was added to 2.5% of the absolute dry raw material, and newsprint having an absolute dry weight of 42.5 g / m2 was produced at 1200 m / min, and the obtained paper was evaluated.

Comparative Examples 1 to 4 Using the same operation as in Example 1, the use ratio of the sulfuric acid in the first stage shown in Table 1 and the silicon dioxide (SiO 2
2) Hydrated silicic acid slurries were produced at concentrations and sodium sulfate (Na2SO4) concentrations, and using this, handmade sheets were obtained and evaluated.

Comparative Example 5 A hydrated silicic acid slurry was produced in the same manner as in Example 5, except that the sodium sulfate concentration at the start of heating was 4.2 g / 100 ml.
Using this, paper was obtained and evaluated.

The results obtained in Examples 1 to 5 are shown in Table 1.

[0066]

[Table 1]

Example 6 Using the same procedure as in Example 1, steam was blown into an aqueous solution partially neutralized under the conditions shown in Table 2 with stirring to a temperature of 90 ° C. in 20 minutes. The temperature was raised. further,
While continuing to stir, add 17 liters of 22.3 liters of sulfuric acid in the second stage over 23 minutes to obtain 85% of total sodium silicate.
%, And then the remaining 5.3 liters of sulfuric acid was added over 10 minutes to complete the neutralization. The pH of the hydrated silicic acid slurry obtained at this time was 5.5, and the integrated value X calculated by the equation 1 was 55.
It was 0. The obtained hydrated silicic acid slurry was treated in the same manner as in Example 1, the physical properties of the slurry were measured, and subsequently a handmade sheet was prepared and evaluated.

Example 7 Using the same procedure as in Example 1, the partially neutralized aqueous solution under the conditions shown in Table 2 was heated from 45 ° C. to 95 ° C. in 20 minutes and then stirred for 15 minutes. After that, 15.9 liters of sulfuric acid necessary to neutralize 85% of all sodium silicate in 21.4 liters of the second stage sulfuric acid was added over 20 minutes, and the remaining 5.5 liters of sulfuric acid was added for 5 minutes. Over the period of time to complete the neutralization. The pH of the hydrated silicic acid slurry obtained at this time was 5.3,
The integral value X calculated by Equation 1 was 1000. The obtained hydrated silicic acid slurry was treated in the same manner as in Example 1, the physical properties of the slurry were measured, and subsequently a handmade sheet was prepared and evaluated.

Comparative Example 6 The ultimate temperature when raising the temperature of the partially neutralized aqueous solution was 90 ° C.
To 87 ° C., a hydrated silicic acid slurry and a hand-made sheet were prepared and evaluated in the same manner as in Example 6. The integral value X calculated by Equation 1 was 460.

Comparative Example 7 Using the same procedure as in Example 1, an aqueous solution partially neutralized under the conditions shown in Table 2 was heated from 45 ° C. to 95 ° C. in 20 minutes, and stirring was continued for 20 minutes. Then, 15.3 liters of sulfuric acid necessary to neutralize 85% of all sodium silicate out of 21.0 liters of the second stage sulfuric acid was added over 20 minutes, and the rest of the sulfuric acid 5.
7 liters were added over 5 minutes to complete the neutralization. The hydrated silicic acid slurry obtained at this time had a pH of 5.5, and the integrated value X calculated by the equation 1 was 1125. The obtained hydrated silicic acid slurry was treated in the same manner as in Example 1, the physical properties of the slurry were measured, and subsequently a handmade sheet was prepared and evaluated.

Example 8 Using the same procedure as in Example 1, the neutralization of sodium silicate was completed, the cake-like hydrated silicic acid was taken out, water was added to it, and the mixture was stirred to form a slurry again to be hydrated. Concentration of silicic acid 10
Adjusted to 0 g / l. When 1 liter of this hydrated silicic acid slurry was pulverized in the same manner as in Example 1, 8.2 ml of a 10% aqueous solution of aluminum sulfate (as solid content) was added to the slurry and pulverized. The pulverized hydrated silicic acid slurry thus obtained was treated in the same manner as in Example 1, the physical properties of the slurry were measured, and subsequently a handmade sheet was prepared and evaluated.

Example 9 Using the same procedure as in Example 1, the neutralization of sodium silicate was completed under the conditions shown in Table 2, the hydrated silicic acid cake was taken out, and water was added to it and stirred. Again as a slurry,
The concentration of hydrated silicic acid was adjusted to 100 g / l. When 1 liter of this hydrated silicic acid slurry was pulverized in the same manner as in Example 1, 4.4 ml of a 10% aqueous solution of aluminum sulfate was added to the slurry and pulverized. The pulverized hydrated silicic acid slurry thus obtained was treated in the same manner as in Example 1, the physical properties of the slurry were measured, and subsequently a handmade sheet was prepared and evaluated.

Comparative Example 8 A hydrated silicified hydrate treated in the same manner as in Example 9 except that 4.4 ml of the aluminum sulfate aqueous solution added was changed to 1.1 ml of sulfuric acid having a concentration of 20% by weight when the slurry was pulverized. An acid slurry was obtained. The pH of the slurry upon completion of neutralization was the same as in Example 8, 4.8. The hydrated silicic acid slurry was treated in the same manner as in Example 1, the physical properties of the slurry were measured, and subsequently a handmade sheet was prepared and evaluated.

Example 10 Using the same procedure as in Example 1, an aqueous solution partially neutralized under the conditions shown in Table 2 was heated in 20 minutes from a temperature of 45 ° C. to 95 ° C., and then stirring was continued. While adding 17.6 liters of sulfuric acid in the second stage over 33 minutes to neutralize 90% of the total sodium silicate, then 3.9 liters of 10% aqueous solution of aluminum sulfate (this contains aluminum oxide and Al2O3 equivalent). Silicon dioxide, equivalent to 0.4% by weight of SiO2) added,
Neutralization was completed. The pH of the hydrated silicic acid slurry obtained at this time was 5.0, and the integrated value X calculated by the equation 1 was 875. The hydrated silicic acid slurry was pulverized in the same manner as in Example 1, the physical properties of the slurry were measured, and then a handmade sheet was prepared and evaluated.

Example 11 To the second stage neutralization, 17.6 liters of sulfuric acid was added, followed by 1.0 liter of a 10% aqueous solution of aluminum sulfate (this is based on the weight of silicon dioxide contained in terms of aluminum oxide).
(Corresponding to 0.1%) and a 10% aqueous solution of aluminum sulphate when grinding the hydrated silicic acid slurry.
A hydrated silicic acid slurry that had been pulverized was prepared in the same manner as in Example 10 except that 4.4 ml was added, the physical properties of the slurry were measured, and then a handmade sheet was prepared and evaluated. The pH just before adding aluminum sulfate in the second stage neutralization is 8.
5. The pH of the hydrated silicic acid slurry that had been neutralized was 5.5.

Comparative Example 9 15.9 liters of sulfuric acid was added for the second stage neutralization, and then 7.2 liters of a 10% aqueous solution of aluminum sulfate (this was calculated based on the weight of silicon dioxide contained in terms of aluminum oxide).
(Corresponding to 0.6%) was prepared in the same manner as in Example 10 except that it was added,
The physical properties of the slurry were measured, and subsequently a handmade sheet was prepared and evaluated. In the second-stage neutralization, the pH immediately before the addition of aluminum sulfate was 10.2, and the pH of the neutralized hydrated silicic acid slurry was 5.4.

The results obtained in Examples 6 to 9 are shown in Table 2.

[0078]

[Table 2]

As is clear from Tables 1 and 2, according to the method of the present invention, since the viscosity of the hydrated silicic acid slurry before the pulverization treatment can be maintained at a low level, the operations such as transfer and pulverization are extremely easy to obtain. Hydrated silicic acid can impart high paper opacity and whiteness after printing on paper.

On the other hand, when the concentration of silicon dioxide in the partially neutralized aqueous solution in the first stage is low, the use ratio of sulfuric acid in the first stage is low or high (Comparative Example 1 and 2)
After printing and when the opacity of white paper is poor and the addition ratio of sulfuric acid in the first stage is high, the viscosity of the slurry becomes high (Comparative Example 3), it becomes difficult to maintain stable operation, and the concentration of sodium sulfate in the aqueous solution increases. When it is low (Comparative Example 4), the slurry viscosity becomes abnormally high and the operation becomes impossible. On the contrary, when the concentration of sodium sulfate is high (Comparative Example 5), hydrated silicic acid having excellent performance can be obtained, but in use, the hydrated silicic acid falls off from the paper in the paper machine and adheres to various places or is of contact type. There was a dust problem that it became unusable because it adhered to instruments such as thickness gauges.

On the other hand, when the maximum value in raising the temperature of the partially neutralized aqueous solution is low (87 ° C.), the integrated value X is low (Comparative Example 6). The volume is too small to improve the opacity after printing, and conversely the maximum temperature is high (95 ° C) and the integrated value X becomes too high due to the long time (Comparative Example 7). Since the growth of primary particles of hydrated silicic acid proceeded, the pore volume did not increase and the effect of improving opacity after printing was poor.

When aluminum sulphate is used to grind hydrated silicic acid, the viscosity of the slurry can be reduced (comparison between Examples 1 and 3 and Examples 8 and 9), but instead of aluminum sulfate. When sulfuric acid is used, there is no effect of lowering the viscosity of the slurry (Comparative Example 8), the viscosity of the slurry becomes high, and the passability of the screen becomes poor, resulting in poor productivity, and the sulfuric acid during the second stage neutralization When a large amount of aluminum sulfate is used instead of (Comparative Example 9), the effect of improving opacity is poor.

[0083]

According to the method of the present invention, since the viscosity of the hydrated silicic acid slurry is low, stable operation can be achieved during production, the paper does not fall off during papermaking, and the opacity and whiteness of white paper after printing as well as after printing. It is possible to produce hydrated silicic acid which is effective in improving

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shigeru Yamakawa 2-1-1 Ojimachi, Tomakomai City, Hokkaido Oji Paper Co., Ltd. Tomakomai Mill

Claims (5)

[Claims] 1. A method of producing hydrated silicic acid for papermaking by adding sulfuric acid to a sodium silicate aqueous solution in two steps in the presence of sodium sulfate and neutralizing the sodium silicate. The amount of sulfuric acid corresponding to 35-45% of the total amount of sulfuric acid required for the addition of sulfuric acid as the first-stage sulfuric acid to partially neutralize the solution, and the resulting aqueous solution has a silicon dioxide (SiO2) concentration of 6.0%.
~ 8.0g / 100ml and sodium sulfate (Na2SO4) concentration 3.5 ~
Sodium sulfate was pre-supplemented and adjusted to 4.1 g / 100 ml, then the aqueous solution was heated to 85 to 95 ° C. with stirring, and the remaining sulfuric acid was continuously added as the second-stage sulfuric acid. Neutralization is completed by precipitating hydrated silicic acid, the obtained hydrated silicic acid is separated by filtration, and then the hydrated silicic acid is redispersed in water to obtain a slurry, which is wet-milled and / or Or, by wet classification, the average particle size of hydrated silicic acid is 3 ~
A method for producing a hydrated silicic acid for papermaking, which has a particle ratio of 10 μm and a particle size of 1 to 30 μm of at least 80% or more. 2. The temperature (T ° C.) of the aqueous solution after the temperature of the aqueous solution after the partial neutralization reaction exceeds 70 ° C. and 85% of the total amount of pre-added sodium silicate are medium. Integral value X calculated by equation 1 for the time until summing (tc minutes) is 500
The method of claim 1, wherein the method is ˜1000. [Formula 1] 3. In the step of adding sulfuric acid in the second step for neutralizing sodium silicate with sulfuric acid, the pH of the aqueous solution after the neutralization reaction with sulfuric acid is adjusted to the range of 5 to 8.5, and then aluminum sulfate is further added. The method according to claim 1 or 2, characterized in that is added in the range of 0.1 to 0.5% based on the weight of silicon dioxide (SiO2) in terms of aluminum oxide (Al2O3). 4. When wet pulverizing the slurry, aluminum sulphate is added to the slurry so that the pH of the slurry after wet pulverizing is 4 to 5, and then wet pulverizing. 4. The method according to any one of 3 to 3. 5. A pore diameter of 11-50 when the hydrated silicic acid powder obtained by filtration, washing with water and freeze-drying is measured by mercury porosimetry.
Pore volume obtained in the range of nm (nanometer) is 0.4 ~
The method according to any one of claims 1 to 4, wherein the method is 1.0 cm3 / g.