JP2000096487A - Production of silica-based loading material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply and efficiently obtain silica-based loading material having many voids by neutralizing an aqueous silicic acid alkali solution containing a surfactant with a mineral acid in the presence of fine bubbles to deposit silica. SOLUTION: A surfactant in an amount of 0.1-30 wt.% based on solid content expressed in terms of silica is added to an aqueous solution of silicic acid alkali, e.g. sodium silicate and the solution is mechanically stirred to generate fine bubbles having 0.1-10 μm average diameter in an amount of 10-100% based on volume of aqueous sodium silicate solution as total volume and then, the solution is neutralized and silica is deposited by adding a mineral acid such as sulfuric acid thereto to provide the objective silica-based loading material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a silica-based filler. In particular, the present invention relates to a method for producing a silica-based filler having voids, which is suitable for use as a filler for papermaking.

[0002]

2. Description of the Related Art In recent years, paper has tended to be reduced in weight by reducing its thickness. In particular, when the weight of printing paper is reduced, opacity when printed on paper (hereinafter referred to as opacity after printing).
Is reduced, and the print appears transparent from the opposite side of the paper. It is common practice to add various fillers to the paper to improve the opacity of the paper, including post-print opacity. Various inorganic and organic fillers have been researched and developed for the purpose of improving the opacity, but even now, those that are inexpensive and have a sufficient opacity improving effect are still being developed. Not reached.
Further, recently, since there is a strong tendency to further reduce the weight, there is a strong demand for a filler having an ability to further improve the opacity of the existing filler.

[0003] Among the opacity improving fillers currently used, titanium oxide improves the opacity of white paper.
If the opacity after printing is not expected to be improved due to the poor ability to suppress ink penetration, and the light scattering ability can be maximized, the yield when adding to pulp and making paper with a paper machine can be reduced. Very bad and uneconomical. Although organic urea-formalin resins have both the ability to improve opacity after printing and the opacity of blank paper, their absolute abilities are insufficient. Also, hydrous silicic acid is less expensive than other types of fillers, and when added to pulp to make paper, it has the effect of imparting opacity after printing by suppressing the penetration of ink. Has not yet reached a satisfactory level, including the effects on

With hydrous silicic acid, the amount of oil absorption, which is an index of the ability to suppress the penetration of ink, which greatly contributes to the improvement in opacity after printing, increases in proportion to the specific surface area of hydrous silicic acid. It is known that it can be controlled by acid synthesis conditions. However, if the specific surface area is made larger than the hydrated silicic acid currently used, when dried under the same conditions as during papermaking, the filler itself shrinks, so the oil absorption decreases, The improvement in opacity after printing is small. Amorphous silica disclosed in Japanese Patent Publication No. 9-264316 is an amorphous silica particle having a high oil absorption and a small specific surface area. The effect is not much different from the hydrated silica commonly used at present.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to propose a method for easily and efficiently producing a silica-based filler having many pores by using inexpensive sodium silicate or the like as a raw material. Another object of the present invention is to provide a silica filler capable of imparting excellent opacity after printing to paper containing the filler.

[0006]

In order to solve the above problems, the present invention employs the following constitution. That is, the present invention relates to a method for producing a silica-based filler which precipitates silica by adding a mineral acid to an aqueous alkali silicate solution to neutralize the silica-based filler, wherein the silica is dispersed in the presence of fine bubbles having an average diameter of 0.1 to 10 μm. A process for producing a silica-based filler, characterized in that In the present invention, the total volume of the fine bubbles is 10 to 1 with respect to the volume of the aqueous alkali silicate solution.
Desirably, it is 00%.

In the present invention, a method of generating fine bubbles by mechanically stirring an aqueous alkali silicate solution is recommended. Further, at that time, it is preferable that the aqueous solution of the alkali silicate contains a surfactant in an amount of 0.1 to 30% by weight based on the solid content in terms of silica.

[0008]

DETAILED DESCRIPTION OF THE INVENTION A feature of the present invention is that fine bubbles are generated in an aqueous solution of an alkali silicate before or during the addition of a mineral acid to the aqueous solution of an alkali silicate, and silicate is formed in the presence of the air bubbles. This is where silica is deposited by neutralizing the alkali. Therefore, the generation of bubbles is completed before the silica starts to precipitate.

The alkali silicate aqueous solution used in the present invention is not particularly limited, but is preferably a sodium silicate aqueous solution or a potassium silicate aqueous solution. Molar concentration of aqueous alkali silicate solution in the case of sodium silicate, the molar ratio (SiO ₂ / Na ₂ O) is preferable to choose from a range of 2.0 to 3.4. As the mineral acid used for depositing silica in the present invention, known mineral acids can be used without any limitation, and these may be used alone or in combination of two or more. Specific examples of the mineral acid include hydrochloric acid, sulfuric acid, nitric acid and the like. Sulfuric acid is preferably used because it is easily available and relatively inexpensive. The concentration of the mineral acid is not particularly limited, but may be generally selected from the range of 10 to 30% by weight.

In the present invention, the mineral acid may be added to the aqueous alkali silicate solution under stirring once or may be added in two or more portions.

When the mineral acid is added at one time, the addition of the mineral acid is carried out at a temperature of the aqueous alkali silicate solution of 60 ° C. or higher and the boiling point of the aqueous solution or lower, preferably 75 ° C. or higher and the boiling point of the aqueous solution or lower. This is done in a range to produce silica particles. The addition of the mineral acid is carried out all at once or continuously. When the mineral acid is added at one time as described above, it is easy to generate bubbles before starting to add the mineral acid. However, during the addition of the mineral acid, bubbles may be generated before the silica starts to precipitate.

Mineral acid for neutralizing alkali silicate is 2
When the mineral acid is added in a plurality of times, the first addition of the mineral acid is performed at a temperature of the slurry of 20 to 60 ° C., and the total amount of the mineral acid necessary to neutralize the aqueous alkali silicate solution is added. An amount corresponding to 10 to 50% of the acid amount is added as a first time. Next, the temperature is raised to 70 ° C. or higher and lower than the boiling point of the aqueous solution, and aging is performed as necessary.
At this time, the first mineral acid is performed by adding the above-mentioned mineral acid amount to the alkali silicate aqueous solution all at once or continuously.

Thereafter, the aqueous alkali silicate solution is heated to a temperature of 70 ° C. or higher and lower than the boiling point of the aqueous solution, preferably 85 ° C. or higher and lower than the boiling point of the aqueous solution in a short time such as 10 to 30 minutes while continuously stirring. And ripen if necessary. This is followed by a second mineral acid addition. The second addition of the mineral acid is performed by adding the mineral acid all at once or continuously, neutralizing the aqueous alkali silicate solution, and then further aging as necessary. When the mineral acid is added twice in this manner, it is easy to complete the generation of bubbles before the second addition of the mineral acid.

In the present invention, as an apparatus for generating fine bubbles in an aqueous solution of alkali silicate, for example, a confectionery foaming machine having a stirring blade rotating while carrying out planetary motion, a homomixer generally used for emulsification and dispersion, etc. And a batch type stirrer such as Cowles dissolver. Further, fine bubbles can be generated with a general stirrer such as a three-one motor, but in order to obtain bubbles of an appropriate size, a long period of stirring is required. A suitable stirrer is desirable.

In these stirrers, the method of adjusting the size of bubbles generated in the aqueous alkali silicate solution includes the viscosity of the aqueous alkali silicate solution, additives (surfactant, foaming agent, foaming agent, Type and amount of viscosity modifier, etc.)
The point is to select the rotation speed, rotation continuation time, temperature during foaming, etc. of the stirrer. Amount of generated bubbles (expansion ratio)
Can also be adjusted substantially by the factors described above.

Since the alkali silicate aqueous solution itself has a weak ability to form air bubbles, the purpose is to promote the generation of air bubbles when generating air bubbles in the alkali silicate aqueous solution, and to further increase the stability of the generated air bubbles. It is preferable to appropriately select and blend a surfactant called a foaming agent or a foaming agent. Examples of such surfactants include higher fatty acids, modified higher fatty acids, and alkali salts of higher fatty acids (for example, ammonium salts), but there is no particular limitation on the selection thereof, and the amount of the surfactant is not particularly limited. However, the solid content of the surfactant is preferably from 0.1 to 30% by weight, more preferably from 1 to 10% by weight, based on the solid content (solid content in terms of silica) of the aqueous alkali silicate solution. If it is less than 0.1% by weight, the effect of generating bubbles is small, and if it exceeds 30% by weight, the effect is not improved.

The viscosity modifier is also effective in keeping the generated air bubbles stable. The viscosity modifier is also not particularly limited, and any known viscosity modifier can be used. It can be selected as appropriate within a range that does not impair the workability and impairs the flowability of the aqueous solution.However, in the present invention, by adjusting the viscosity by adjusting the concentration of the aqueous alkali silicate solution, sufficient stability of generated bubbles can be obtained In addition, a viscosity modifier is not always necessary.

The size of the fine bubbles generated in the alkali silicate aqueous solution in this manner can be measured with an image analyzer by photographing a part of the alkali silicate aqueous solution containing the bubbles with an optical microscope. It is possible.

A feature of the present invention is that fine bubbles are generated in an aqueous solution of an alkali silicate, silica is precipitated around these bubbles, and finally aggregates of silica particles containing fine bubbles are formed. It is in. Therefore, the size of the bubbles greatly affects the performance of the resulting silica-based filler. JP-A-5-301707 discloses that a silica filler having a pore diameter of 10 μm or less works effectively for absorbing ink components. In the present invention, it is suitable that the average diameter of bubbles generated in the aqueous alkali silicate solution is not more than 10 μm. However, too small bubbles require a great deal of labor for mechanical stirring for generation thereof, and Since a large amount of an additive such as a foaming agent is required, it cannot be said that it is preferable from the viewpoint of workability and economy. Conversely, if the air bubbles are too large, not only is the ink absorbency poor, but also the strength of the aggregates of silica particles is significantly reduced, and the aggregates of silica particles are destroyed at the time of reaction generation. The size of the bubbles to be generated is preferably in the range of 0.1 to 10 μm, more preferably in the range of 0.2 to 5 μm.

If the amount of generated bubbles is too small, the pore size of the silica-based filler becomes insufficient, and the performance as the filler is insufficient. Conversely, if the amount is too large, the strength of the aggregate of silica particles decreases. Because it is remarkably reduced, it is in the range of 10 to 100% with respect to the volume of the aqueous alkali silicate solution before the generation of bubbles,
More preferably, it is in the range of 30 to 80%.

The paper obtained by adding the silica-based filler according to the present invention to a pulp raw material and making the paper has high opacity, particularly opacity after printing. The reason is,
It is considered that the ability to suppress the penetration of ink printed on paper was increased by increasing the amount of voids inside the particles and increasing the amount of oil absorption.

The silica-based filler according to the present invention can be obtained in the form of a slurry, and its transportation and storage can be carried out using known equipment. When the silica-based filler obtained in the present invention is added to paper, it is used after wet pulverization and / or wet classification if necessary. Examples of the wet pulverization include a known continuous homomixer, colloid mill, disc refiner, sand grinder, ball mill, rod mill, and the like.In the case of pulverization and further classification, the silica-based filler is used as a known vibrating screen. It is used after performing wet classification with an appropriate classifier to remove coarse particles exceeding 70 to 75 μm. The silica-based particles obtained by such a treatment have an average particle diameter of 3 to 30 μm, preferably 6 to 25 μm.
m. Of course, when the particle size after generation is in this range, wet pulverization and wet classification do not have to be performed.

The silica-based particles obtained according to the present invention have a specific surface area of 30 to 200 m ² / mer as measured by a mercury intrusion method.
g, preferably in the range of 60 to 180 m ² / g. Further, the oil absorption according to JIS K5101 is 250 to
500ml / 100g, preferably 300-450ml
/ 100 g. Specific surface area is 30m ² /
If it is smaller than g, it is difficult to increase the oil absorption to 250 or more. If the specific surface area exceeds 200 m ² / g, the properties will approach that of a gel, and the shrinkage during drying will increase, resulting in a low oil absorption. If the oil absorption is less than 250 ml / 100 g, the ability to suppress ink penetration is insufficient.
The desired post-print opacity cannot be imparted to the paper.

The silica-based filler obtained according to the present invention may be used as a filler dispersed in raw pulp fibers of an acid paper,
It can be used in either neutral papermaking or alkaline papermaking, and can also be used as a pigment for a surface coating agent. The silica-based filler produced by the above method can be mixed with a raw material of paper in a slurry state, and paper can be produced by a known wet paper machine. It can be stored as a body and redispersed in water when it is mixed with the raw material of paper. As the pulp raw material used for the paper filled with the silica filler in the present invention, a commonly used known papermaking pulp can be used. Specifically, wood pulp such as chemical pulp such as sulfite pulp, kraft pulp and soda pulp, semi-chemical pulp and mechanical pulp, or non-wood pulp such as mulberry, mitsumata and hemp may be used. These pulp may be unbleached pulp or bleached pulp, and may be unbeaten or beaten. Further, these may be used alone or in combination of two or more.

The silica-filled paper according to the present invention includes:
Additives usually used in papermaking, such as sizing agents, defoamers, slime control agents, dyes, coloring pigments, fluorescent dyes, dry paper strength agents, wet paper strength agents, drainage improvers,
And a retention aid and the like can be used as needed. In addition, starch, polyvinyl alcohol, polyacrylamide, various surface sizing agents, and the like can be applied to the surface of the silica-based filler-filled paper of the present invention.

Known wet paper machines used in the present invention include commercially available paper machines such as a round-mesh paper machine, a short-mesh paper machine, a long-mesh paper machine, and a twin-wire machine. Used as appropriate.

As described above, the silica-based filler of the present invention increases the amount of voids inside the silica-based filler while maintaining the specific surface area such that large shrinkage does not occur even when the slurry is dried as it is. Thereby, it has high oil absorption performance and can provide excellent post-print opacity to paper when used as a filler in papermaking.

[0028]

EXAMPLES The present invention will be described more specifically with reference to examples below, but the present invention is of course not limited to these. In the following examples, all percentages are by weight.

<Amount of generated bubbles = expansion ratio> The weight of 100 ml of the aqueous alkali silicate solution (stock solution) before the foaming treatment was added to 100 m of the aqueous alkali silicate solution containing the air bubbles after the foaming treatment.
The value obtained by dividing by the weight of 1 is defined as the expansion ratio, and the amount of generated bubbles is evaluated using this value.

A part of the alkali silicate aqueous solution after the foaming treatment was sampled, photographed at a magnification of 470 times using an optical microscope (trade name: BH-2, manufactured by Olympus Corporation), and then the outline of the bubble was obtained. Is accurately drawn on a transparent film with a black pen, and a drum scanner (trade name: 260
5 Drum Scan Densitometer, Abe Design Co., Ltd.)
Then, information on the outline of the bubble was optically read, and the information was measured using an image analyzer (trade name: Luzex III, manufactured by Nicole), and the arithmetic average value was obtained as the average diameter of the bubble. The area to be measured was 0.06 mm ² (200 μm × 300 μm) in each of the examples and comparative examples. Since bubbles in the aqueous alkali silicate solution were not stable for a long time, photography with an optical microscope was performed promptly after sampling.

Example 1 240 g of a commercially available JIS No. 3 sodium silicate aqueous solution (manufactured by Tokuyama, solid content concentration: 30%) was diluted to 1000 g with pure water to obtain silica (silicon dioxide).
A concentration of 72 g / kg was placed in a 2 liter stainless beaker, and anhydrous sodium sulfate 1 was added at a temperature of 50 ° C.
7.9 g and 3.6 g of a higher fatty acid ammonium salt (trade name: F-1) as a foaming agent were added, and the mixture was stirred with a homogenizer (trade name: TK Homomixer MARKII, manufactured by Tokushu Kika Kogyo) at 5000 rpm for 5 minutes. Then, bubbles were generated in the aqueous sodium silicate solution. At this time, the expansion ratio was 1.5 and the average diameter of the bubbles was 1.8 μm.

While stirring was continued, 54 g of sulfuric acid (concentration: 20%) corresponding to 30% of the total acid required for neutralizing the sodium silicate was continuously added over 12 minutes. After the addition of sulfuric acid was completed, the temperature was raised to 90 ° C. in 25 minutes with stirring. Stirring is continued at the same temperature, aging is performed for 10 minutes, and then sulfuric acid 12
6 g was continuously added over 23 minutes. After the addition of sulfuric acid was completed, the rotation speed of the homogenizer was increased to 1200 rpm.
Aging was further performed for 20 minutes.

Next, the slurry containing the reaction product was passed through a 200-mesh sieve to remove residues. The average particle diameter of the obtained silica-based particles was 21.3 μm when measured by the laser diffraction particle size distribution analyzer. The slurry that passed through the sieve was filtered through a Buchner funnel to obtain cake-like silica-based particles, a part of which was dried at 105 ° C. overnight, the oil absorption, the specific surface area, and the pore volume were measured. Disperse, stir and adjust the concentration to 8% slurry. This is used below as a filler slurry for papermaking.

Next, softwood bleached kraft pulp 15%
Thermomechanical pulp (TMP) 34%, mechanical pulp (GP) 11%, newspaper deinked waste paper pulp (DIP) 4
25 g of absolutely dry mixed pulp consisting of 0% was dispersed in tap water and
The filler slurry was added to the slurry at a concentration of 1.25% by diluting the mixture to a liter to a concentration of 3% based on the absolute dry weight of the pulp. After stirring for 2 minutes, a sulfuric acid band (Al ₂ (SO _{4 3} ) 18H ₂ O) was added to the pulp at 1% per dry weight, stirred for 2 minutes, the whole was diluted to 12.5 liters, mixed well, and then mixed with a square sheet machine to obtain a dry weight of 40 g / m ² . The paper was made and dried.

This handmade sheet was conditioned in a room at 20 ° C. and 65% relative humidity, and then passed twice at a linear pressure of 40 kg / cm using an experimental machine calendar to adjust the smoothness. The paper quality test and the printing test of the degree and opacity were performed by the following methods, and the evaluation was performed. The test method used is as follows.

(1) Whiteness Measured in accordance with JIS P 8148 (ISO 2470).

(2) Opacity of blank paper It measured according to TAPPI 53 (ISO2471).

(3) Opacity after Printing Solid printing was performed using an offset printing ink for newspaper with an RI printing tester, and the opacity Y (%) after printing was defined by the following equation (1). Y (%) = {(reflectance of back side after printing) / (reflectance of back side without printing)} × 100
(1)

<Example 2> The time of stirring the homogenizer when forming fine bubbles in the aqueous sodium silicate solution was set to 2 hours.
A silica-based filler was obtained in the same manner as in Example 1 except that the time was set to 0 minutes. In this case, the expansion ratio was 1.7, and the average diameter of the bubbles was 1.2 μm. The silica-based particle slurry thus obtained was evaluated in the same manner as in Example 1.

<Example 3> When fine bubbles were generated in an aqueous solution of sodium silicate, the stirring speed of the homogenizer was set to 8
A silica-based filler was obtained by performing the same treatment as in Example 1 except that the rotation speed was changed to 000 rpm. In this case, the expansion ratio was 1.5, and the average diameter of the bubbles was 1.0 μm. The silica-based particle slurry thus obtained was evaluated in the same manner as in Example 1.

Example 4 A silica-based filler was obtained in the same manner as in Example 1 except that the higher fatty acid ammonium salt as a foaming agent was not added, and the stirring speed of the homogenizer was set to 8000 rpm. The expansion ratio at this time was 1.3, and the average diameter of the bubbles was 2.2 μm. The silica-based particle slurry thus obtained was evaluated in the same manner as in Example 1.

<Comparative Example 1> A silica-based filler was obtained in the same manner as in Example 1 except that the higher fatty acid ammonium salt as a foaming agent was not added. In this case, the expansion ratio was 1.0, and generation of air bubbles was not recognized. The silica filler slurry thus obtained was evaluated in the same manner as in Example 1.

Comparative Example 2 A silica-based filler was obtained by performing the same treatment as in Example 1 except that the stirring device was a three-one motor and the stirring speed was 800 rpm. The expansion ratio at this time was 2.6 times, and the average diameter of the cells was 14.5.
μm. The silica-based filler slurry thus obtained was evaluated in the same manner as in Example 1.

<Reference Example> For comparison, a handsheet was prepared and evaluated in the same manner as in Example 1 except that no filler was used. Table 1 shows the results obtained in Examples, Comparative Examples and Reference Examples.

[0045]

[Table 1]

As is clear from Table 1, the silica-based filler obtained according to the present invention can impart excellent post-print opacity to paper containing the silica-based filler (Examples 1 to 3).

[0047]

As described above, according to the present invention,
Using inexpensive sodium silicate or the like as a raw material, silica-based particles having many pores can be easily and efficiently produced.
Also, when the particles are used as a filler in papermaking,
It can impart excellent post-print opacity to paper.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Motohide Wada 1-10-6 Shinonome, Koto-ku, Tokyo Inside Oji Paper Co., Ltd. Shinonome Research Center (72) Inventor Osamu Kitao 1-10, Shinonome, Koto-ku, Tokyo No. 6 Oji Paper Co., Ltd. Shinonome Research Center F term (reference) 4G072 AA25 GG03 HH21 JJ13 JJ15 KK15 LL06 LL07 MM01 MM02 RR06 UU07 UU25 4L055 AG18 AG94 AH01 FA12

Claims (4)

[Claims] 1. A method for producing a silica-based filler in which silica is precipitated by adding a mineral acid to an aqueous solution of an alkali silicate to neutralize the silica, wherein the silica is removed in the presence of fine bubbles having an average diameter of 0.1 to 10 μm. A method for producing a silica-based filler, which is characterized in that it is precipitated. 2. The method for producing a silica-based filler according to claim 1, wherein the total volume of the fine bubbles is 10 to 100% based on the volume of the aqueous alkali silicate solution. 3. A method for producing fine bubbles by subjecting an aqueous alkali silicate solution to mechanical stirring.
The method for producing a silica-based filler according to claim 1. 4. The method for producing a silica-based filler according to claim 3, wherein the aqueous alkali silicate solution contains 0.1 to 30% by weight of a surfactant based on the solid content in terms of silica.