JPH09286609A - Method for producing composite particles of titania and silica - Google Patents

Abstract

(57) Abstract: A method for producing TiO ₂ / SiO ₂ composite particles for imparting excellent post-printing opacity to paper. SOLUTION: The temperature of the alkaline silicate solution is 20 to 55.
The first mineral acid was added at ℃, the secondary particles of silica were generated while the temperature was raised to 65 to 95 ℃, and then the crystalline titanium dioxide was added at a ratio of TiO ₂ / total SiO ₂ of 2. ~ 2
After adding 5% by weight, an additional alkaline silicate aqueous solution is added in an amount of 2 to 40% by weight based on the weight of silica contained in the alkaline silicate aqueous solution at the start of the reaction, and then a mineral acid is further added. The pH of the obtained slurry was adjusted to 3 to 6.5.
And then pulverizing and / or classifying in a wet manner, the method for producing composite particles of titania and silica.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the production of composite particles of titania and silica, which are used as a filler for paper during papermaking and impart excellent whiteness and opacity to the paper, especially outstanding post-printing opacity. Regarding the method.

[0002]

2. Description of the Related Art In recent years, paper has tended to be reduced in weight.
Especially when the weight of the printing paper is reduced, the opacity when printed on the paper decreases, and the problem that the print looks transparent from the opposite side of the paper occurs, which is not desirable, so it prevents the decrease in opacity after printing on the paper. To do this, it is common practice to add various fillers to the paper. In addition, various inorganic and organic fillers are being researched and developed for the purpose of improving opacity, and even now, those that are still inexpensive and have a sufficient effect of improving opacity are being developed. It has not been done. In addition, recently, there is a strong tendency to further reduce the weight, so in addition to the ability to improve the opacity after printing by suppressing the permeation of oil components in the ink when printing, the opacity of white paper The advent of fillers with the ability to improve oil is strongly desired.

Among the above-mentioned various fillers, like titanium dioxide, the opacity of white paper is improved, but the ability to suppress penetration of ink is inferior, and further, in the range of particle diameter that can maximize light scattering ability. , Which is very uneconomical in yield when added to pulp to make paper with a paper machine,
Alternatively, it is generally known that an organic urea-formalin resin has both the ability to improve opacity after printing and the opacity of blank paper, but lacks the absolute ability to improve each. Also, like hydrous silicic acid,
It is cheaper than other types of fillers, and when added to pulp to make paper, it also has the effect of giving opacity after printing on paper, but it has reached a sufficiently satisfactory level including the effect on white paper opacity. Some are not known.

Japanese Patent Publication No. 6-45451 discloses a composite of titania and silica in order to overcome the drawbacks of the filler. However, this complex is obtained by spending at least 30 minutes or more of an acidic solution of titanium in an alkaline silicate aqueous solution in the presence or absence of titanium oxide so that the pH of the aqueous solution is 1 to 7. Is added and heated to a temperature in the range of 80 ° C. to the boiling point of the aqueous solution, and the resulting composite has a single product in which the titania and silica contained in the composite are bonded to each other. It is an amorphous substance that has a structure of forming a compound, a microblend, or a mixture of both forms. Such titania is an optimal crystalline substance from the viewpoint of light scattering ability. It has the disadvantage of not having a structure.

That is, even if crystalline titanium dioxide is added during the neutralization reaction, most of it is covered with the composite of titania and silica. For this reason, the titania and titanium oxide contained in the composite have not fully utilized their potential scattering ability. Further, the above-mentioned publication does not specifically describe the degree of the effect on the opacity after printing and the opacity of white paper when this composite is added as a filler for paper, and the composite is solid. Since it is obtained as a substance, it has poor handleability, labor is required for crushing and handling, and it is extremely difficult to produce it efficiently.

In order to solve the drawbacks of the prior art, the present inventors add mineral acid to an aqueous solution of alkali silicate to form secondary particles of silica, and then add crystalline titanium dioxide to
H7 or more, and then the resulting slurry is further neutralized with a mineral acid to be neutralized, and the average particle size is 3 to 25 μm and 1 to 30.
A composite particle of titania and silica composed of titanium dioxide and secondary particles of silica, containing 80% by weight or more of particles having a particle diameter of μm, and a method for producing the same were proposed. The whiteness of the paper obtained by internally adding pulp to the composite particles of titania and silica produced by this method, the opacity of white paper and the opacity after printing are improved, but when producing the composite particles Not all of the titanium dioxide used in this step was complexed with the secondary particles of silica, and when the slurry of the obtained composite particles was wet-milled, part of the titanium dioxide already complexed was removed. Apart from that, it does not contribute to improving the opacity of the paper, and the expensive titanium dioxide used is wasted, and there is room for improvement in the method for producing the composite particles.

[0007]

DISCLOSURE OF THE INVENTION In view of the above situation, the inventors of the present invention have conducted extensive studies and as a result, when an alkaline silicate aqueous solution was neutralized with a mineral acid and secondary particles of silica began to precipitate. Alternatively, after the formation of the secondary particles, crystalline titanium dioxide is added, and the pH of the resulting slurry is adjusted to a specific range to produce a composite particle of titania and silica. Before the secondary particles are generated and titanium dioxide is added, or when the secondary particles are added, the secondary particles of silica are dispersed by a high shearing force, if necessary.
By adding titanium dioxide or dispersing the titanium dioxide by high shearing force and then adding a small amount of alkali silicate additionally, the amount of titanium dioxide fixed on the silica secondary particles can be increased. In addition, titanium dioxide can be prevented from desorbing from the secondary particles of silica, and when the titania-silica composite particles obtained by this method are added together with pulp during papermaking, the whiteness of the paper and The inventors have found that there is an excellent effect that the transparency, especially the opacity after printing is remarkably improved, and completed the present invention.

The object of the present invention is to prepare a composite particle of titania and silica, which can be added together with a pulp raw material in papermaking and used to impart extremely excellent whiteness and opacity to the paper. By reducing the amount of titanium dioxide not supported on the particles, it is possible to significantly improve the whiteness and opacity of the paper, especially the opacity after printing when the composite particles are added to the pulp to make paper. It is to provide a method for producing composite particles of titania and silica.

[0009]

The first aspect of the present invention is to add a mineral acid to an aqueous alkali silicate solution to form secondary particles of silica, then add titanium dioxide, and further add a mineral acid. In the method of producing a composite particle of titania and silica composed of secondary particles of titanium dioxide and silicon dioxide by neutralization, a first mineral acid is added to an aqueous alkali silicate solution at a temperature of 20 to 55 ° C. Secondary particles of silica were generated during the temperature rise to 65 to 95 ° C., and then crystalline titanium dioxide was added to the ratio of TiO ₂ / total SiO ₂ , that is, finally adjusted to pH 3 to 6.5 with mineral acid. TiO relative to the amount of total silica (SiO ₂ ) contained in the conditioned slurry
₂ to 40% by weight based on the weight of silica contained in the aqueous alkali silicate solution at the start of the reaction after addition of 2 to 2 to 25% by weight.
Of the titania-silica composite particles, characterized in that the pH of the slurry obtained by adding and then adding the mineral acid is adjusted to the range of 3 to 6.5, and then pulverized and / or classified by a wet method. Is the way.

In the second aspect of the present invention, at least 1 is added between the start of the formation of the secondary particles of silica and the addition of the mineral acid for adjusting the pH of the slurry to the range of 3 to 6.5. The method for producing composite particles of titania and silica according to claim 1, wherein a high shearing force is applied to the slurry to disperse the slurry.

A third aspect of the present invention is that after the secondary particles of silica are precipitated, mineral acid is added to adjust the pH to the range of 8 to 12, and then crystalline titanium dioxide is added. The method for producing composite particles of titania and silica according to the first or second aspect of the present invention is characterized by:

In a fourth aspect of the present invention, when a mineral acid is added to an alkali silicate aqueous solution to form secondary particles of silica, the amount of the mineral acid required to neutralize the alkali silicate aqueous solution is 30 to 7.
The method for producing composite particles of titania and silica according to any one of the first to third aspects of the present invention is characterized in that 0% by weight of mineral acid is added.

The fifth aspect of the present invention is to apply a high shearing force to silica 2
Any one of the first to fourth aspects of the present invention, wherein the secondary particle diameter of silica by a laser diffraction type particle size distribution measuring device after being applied to a slurry containing secondary particles and dispersed therein is in the range of 3 to 40 μm. The method for producing composite particles of titania and silica according to any one of the above.

The sixth aspect of the present invention is that the composite particles of titania and silica after wet pulverization and / or classification have an average particle size of 3 to 30 μm by the particle size measuring device, and 1 to 30 μm.
The titania-silica composite particles according to any one of the first to fifth aspects of the present invention.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing composite particles of titania and silica, which is to be provided by the present invention, comprises adding a specific amount of a mineral acid to an aqueous solution of alkali silicate, and then raising the temperature to obtain a silica of 2
After the secondary particles start to precipitate, or after the secondary particles of the silica have precipitated, a mineral acid is added if necessary, and finally a slurry whose pH is adjusted to 3 to 6.5 by the mineral acid is prepared. The ratio of crystalline titanium dioxide to the weight of total silica (SiO ₂ ) contained (TiO ₂ / total SiO ₂ ) is 2 to 25.
Crystalline titanium dioxide is added so that the weight% becomes
Subsequently, an additional aqueous solution of alkali silicate is added so as to be 2 to 40% by weight based on the weight of silica contained in the aqueous solution of alkali silicate at the start of the neutralization reaction.
At this time, if necessary, a high shearing force is applied to the secondary particle slurry of silica in the aqueous alkali silicate solution, or to the slurry composed of the secondary particles of silica and the particles of titanium dioxide to sufficiently disperse, and further The pH of the slurry obtained by the acid is adjusted to 3 to 6.5, and the resulting composite particles of titania and silica are wet-ground and / or classified.

The alkali silicate aqueous solution used in the present invention is not particularly limited, but a sodium silicate aqueous solution or a potassium silicate aqueous solution is preferable. Molar concentration of alkali silicate aqueous solution is molar ratio (SiO ₂ / Na ₂ O or K ₂ O)
Is preferably selected from the range of 2.0 to 3.4. or,
The concentration of the aqueous solution of alkali silicate is silica (S
It is selected from the range of 3 to 15% by weight in terms of iO ₂ ). If the concentration is higher than this range, the viscosity of the solution during the reaction will be high, and if the concentration is low, the amount of the reaction solution will be large and it will be inefficient. Further, it is preferable to keep the silica concentration in the reaction solution within the range of 3 to 15% by weight even during the reaction. As the mineral acid used in the present invention, known mineral acids can be used without any limitation. Specific examples of the mineral acid include hydrochloric acid, sulfuric acid, nitric acid and the like, but sulfuric acid is preferably used because it is easily available and relatively inexpensive. The concentration of the mineral acid is not particularly limited, but is generally selected from the range of 10 to 30% by weight.

In the present invention, the mineral acid is added to the aqueous solution of alkali silicate in a plurality of two or more times, and the first addition of the mineral acid is carried out when the temperature of the aqueous solution is 20 to 55 ° C. at the start of neutralization. And then the temperature is raised to 65 to 95 ° C. to generate secondary particles of silica. The amount of the mineral acid at this time is necessary to neutralize the total aqueous alkali silicate solution. An amount in the range of 35 to 70% by weight based on the total amount of the mineral acid is used as the first mineral acid at once in the aqueous solution of alkali silicate so that the pH of the aqueous solution does not fall below 7 during addition. Add continuously over a short period of time.

After the first addition of the mineral acid, the aqueous solution of alkali silicate was stirred for 65 minutes in a short time such as 10 to 30 minutes.
The temperature is raised to a temperature in the range of ˜95 ° C. to deposit and form secondary silica particles. When secondary particles of silica started to form,
Alternatively, after the formation, secondary particles of silica are aged if necessary, and then shearing force is applied at a high speed as necessary to disperse the particles, and crystalline titanium dioxide is added to this solution or slurry, Then, the second alkali silicate aqueous solution prepared in advance is added all at once or continuously, and the pH of the slurry containing titanium dioxide and secondary particles of silica produced by neutralization is adjusted to 3 to 6.5, Preferably 4-6
The mineral acid for adjusting to the above range is added all at once or continuously, and after further aging if necessary, the slurry is wet-milled and / or classified. When the crystalline titanium dioxide is added, the pH of the reaction solution is more preferably maintained in the range of 8 to 12 so that a better effect can be obtained. Is added to adjust the pH. Moreover, since the temperature of the slurry before and after the addition of the crystalline titanium dioxide is maintained in the range of 90 to 100 ° C., the composite particles of titania and silica can be provided with a more excellent effect. preferable.

In the present invention, mineral acid is added to partially neutralize the alkali silicate aqueous solution, and the temperature is raised to the above range to generate secondary particles of silica, and if necessary, sufficient aging and aging are performed. And / or a dispersion treatment by a shearing force at a high speed is performed, and then the pH is adjusted to a range of 8 to 12 by addition of a mineral acid, or without the adjustment, crystalline titanium dioxide is added, followed by addition of an additional alkali silicate. , And then the mineral acid is added again to adjust the pH of the slurry to the range of 3 to 6.5,
After that, if desired, if aging and dispersion by high shearing force are combined in combination during each unit operation, such as aging if necessary, or crushing and / or classification by the above-mentioned wet method without aging, a better performance can be obtained. Thus, composite particles of titania and silica having the above are stably obtained. In addition, an electrolyte substance such as sodium sulfate may be added in advance in order to maintain the viscosity of the slurry low and stabilize it when accelerating the formation and aging of flocs. Incidentally, aging in the present invention means that the slurry is stirred for a predetermined period of time, for example, 2 times.
Maintaining a predetermined temperature, for example, 65 to 100 ° C., for 0 to 180 minutes.

The dispersion treatment of the silica secondary particles in the present invention is carried out at any place between the start of the production of the silica secondary particles and the pH of the slurry with the mineral acid being from 3 to 6.5, that is,
From the start of the formation of the secondary particles of silica to the completion of the precipitation of the secondary particles of silica and the subsequent addition of crystalline titanium dioxide, from the start of the addition of crystalline titanium dioxide After the addition is complete, and before the addition of the additional alkali silicate, the steps from the start of the addition of the additional alkali silicate to the completion of the addition and the addition of the additional alkali silicate 3-6.
In any one of the steps up to the step of adding the mineral acid for adjusting to the range of 5, the slurry is subjected to high shearing force at least once to sufficiently disperse the slurry, whereby the secondary particles The particle size is reduced and at the same time the distribution range is narrowed. The particle size of the secondary particles without dispersion depends on the degree of stirring of the slurry, but is 10 μm.
It is in the range of ˜2 mm, and in this case, it is necessary to strengthen the pulverization and classification by the wet method after forming the composite particles.

As described above, when a high shearing force is applied to the slurry to sufficiently disperse it, the degree of dispersion is determined by the average particle size of secondary particles of silica measured by a laser diffraction type particle size distribution measuring device being 3 -40 μm, preferably 5-30 μm
It is adjusted to be within the range. Average particle size is 40 μm
In the case of silica secondary particles exceeding the above range, in order to achieve an average particle size of 3 to 30 μm in the range of 80 to 99% by weight, the subsequent wet pulverization treatment, as in the case without dispersion. Since it is necessary to considerably strengthen the titanium dioxide, the titanium dioxide may be desorbed by the pulverization treatment, which is not preferable. By carrying out the dispersion treatment, the ability of the composite particles obtained to improve the opacity of paper is improved, but the surface area of the silica particles is increased by the dispersion treatment of the secondary particles of silica, and titanium dioxide It is presumed that this is because more is adsorbed, the yield of titanium dioxide on the silica particles is increased, and titanium dioxide is more uniformly compounded on the silica surface. As a device that can obtain a high shearing force used for the dispersion treatment of the present invention,
Known ones such as a continuous homomixer, a homogenizer, an inline mixer, a disc refiner, and a sand grinder are mentioned, and they are appropriately selected and used.

In the composite particles of titania and silica of the present invention, crystalline titanium dioxide is contained in an amount of 2 to 2 based on the total weight of silica.
It is contained in the range of 25% by weight, preferably 5 to 20% by weight. If the content of titanium dioxide is less than 2% by weight, the resulting composite particles cannot impart desired opacity after printing and white paper opacity to the paper, and if it exceeds 25% by weight, excellent whiteness and opacity are not obtained. Although the improvement effect can be obtained, the tendency of the improvement reaches a ceiling and the manufacturing cost of the composite particles is increased due to the expensive titanium oxide, which is not economically suitable.

The crystalline titanium dioxide used for the composite particles of titania and silica of the present invention is not particularly limited, and the crystalline type may be either rutile type or anatase type.
It may be surface-treated with silica, alumina, etc.,
Its average particle size is 50 to 400 nm, preferably 100.
Is in the range of up to 300 nm. If the average particle size is larger or smaller than this range, the light scattering ability will be low, which is not suitable.

In the composite particles of titania and silica obtained by the present invention, the crystal peak of titanium dioxide can be confirmed by X-ray diffraction measurement, and the particles of titanium dioxide are supported on the surface of silica by observation with a scanning electron microscope. Can be confirmed to exist. Furthermore, a laser diffraction type particle size distribution measuring device (model: SALD-1100, manufactured by Shimadzu Corporation) was used to mix the crystalline titanium dioxide and silica alone in the same ratio as in the case of the composite particles. The particle size distribution of the composite particles produced without adding the second alkaline aqueous solution of alkali silicate after the titanium dioxide addition, or the particle size distribution of the composite particles according to the present invention, when compared with the particle size distribution of the composite particles without the dispersion treatment In the case of the composite particles of the present invention, it was found that the peak of the particle size distribution derived from titanium dioxide is considerably reduced. From these facts, the composite particles have the silica particles forming the secondary particles as cores. It was presumed that the titanium dioxide particles formed particles which were fixed in the surface area.

When the titania-silica composite particles of the present invention are produced, a part of the mineral acid necessary for neutralization of the aqueous alkali silicate solution (35 to 70% of the mineral acid necessary for neutralization) is partially removed. Add the temperature at 55 ° C or lower as the first time, then adjust the temperature to 65 to 9
The temperature is raised to 5 ° C., and crystalline titanium dioxide is added at a pH of 7 or more, preferably in the range of 8 to 12 after the formation of secondary particles of silica or after the formation of the secondary particles. . Therefore, if necessary, the pH of the aqueous solution can be adjusted within the above range by adding the mineral acid after the first addition of the mineral acid and before the addition of the crystalline titanium dioxide. Be seen. The secondary particles of silica may be aged before the addition of crystalline titanium dioxide, or both before and after the addition.

In the present invention, after the addition of titanium dioxide, the second aqueous alkali silicate solution is added in an amount of 2 to 40% by weight, preferably 5 to 40% by weight, based on the silica content in the first aqueous alkali silicate solution at the start of the reaction. 30% by weight, partially neutralized, added to the slurry to which crystalline titanium dioxide has been added. If the addition amount of this alkaline silicate aqueous solution as the silica content is less than 2% by weight with respect to the silica content of the initial alkaline silicate aqueous solution at the start of the reaction, the fixation of titanium dioxide becomes insufficient and 40% by weight If the amount is larger than that, the titanium dioxide is covered, and the performance of improving the opacity and whiteness as a filler becomes insufficient, which is not preferable. The temperature of the slurry when the second alkaline silicate aqueous solution is added is not particularly limited, but it is preferable from the viewpoint of efficiency that the temperature is the same as the temperature set before and after this step.

Although the mechanism by which the composite particles of titania and silica according to the present invention are used by adding them to a pulp raw material at the time of papermaking to give high opacity to the obtained paper, it is not clear that they are crystalline. By adding an aqueous solution of alkali silicate after adding titanium dioxide, crystalline titanium dioxide is already supported and fixed more uniformly on the surface area of the silica particles by using the secondary particles of silica as nuclei. As a result of newly adhering titanium dioxide that is not bonded to the silica secondary particles, titanium dioxide becomes difficult to desorb during wet pulverization or classification, and at the same time, titanium dioxide becomes silica secondary particles. Since the fixing amount of TiO2 also increases, the characteristics of titanium dioxide can be more efficiently expressed, and the synergistic effect of this makes it possible for the composite particles themselves to form on paper. Chromaticity and opacity, considered more ability to further remarkably improved has been granted.
Further, the composite particles of the present invention, because the crystalline titanium dioxide is complexed with the silica particles, the titanium dioxide and silica are mixed with each other or added separately to the paper, compared with the papermaking, papermaking In that case, there is also an effect that the yield of titanium dioxide is improved.

The titania-silica composite particles obtained by the method of the present invention are obtained in the form of a slurry, and the known equipment can be used as it is for the transportation and storage thereof. When the composite particles obtained in the present invention are used as a filler for paper, they are used by wet pulverization and / or wet classification in advance. Examples of the apparatus for wet pulverization include known continuous homomixers, colloid mills, disc refiners, sand grinders, ball mills, rod mills, and the like. In the case of further classification, the composite is subjected to wet classification with a classifier such as a known vibrating screen to remove coarse particles exceeding 70 to 75 μm of the composite and used as a filler. The composite obtained by such treatment has an average particle size of 3 to 30 μm, preferably 6 by a laser diffraction type particle size distribution measuring device.
To 25 μm, the particle size of 1 to 30 μm is contained in the range of 80 to 99% by weight, and the specific surface area by BET method by nitrogen gas adsorption is 90 to 140 m ² / g.
Oil absorption according to JIS K 5101 is 200-350g
/ 100 g range. In order to obtain a value of particles having a particle size of 1 to 30 μm exceeding 99% by weight, it is necessary to reduce the addition rate of titanium dioxide and to make the pulverizing conditions severe.

As explained above, in the composite particles of titania and silica obtained by the production method of the present invention, the crystalline titanium dioxide having the secondary particles of silica as the core is more uniformly distributed on the surface region of the silica particles. When carried and used as a filler in papermaking, it can impart excellent whiteness and opacity to the paper, and particularly excellent post-printing opacity.

[0030]

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.

Example 1 240 g of a commercially available aqueous solution of sodium silicate No. 3 (manufactured by Tokuyama Soda, solid content concentration 30%) was diluted to 1000 g with pure water to obtain a silica (silicon dioxide) concentration of 72 g / kg and 2 liters. Place in a stainless beaker, add 17.9 g of anhydrous sodium sulfate at a temperature of 50 ° C., and continuously add 72 g of sulfuric acid (concentration 20%) (40% of mineral acid necessary for neutralization) over 15 minutes while stirring with a three-one motor. Was added to. After the first addition of mineral acid, stir 1
The temperature was raised to 95 ° C in 5 minutes and titanium dioxide (JA
-2, average particle diameter 250 nm, manufactured by Teika) 8.4 g was added. Then, the silica concentration obtained by dilution is 72
350 g of a g / kg sodium silicate aqueous solution was added to the slurry liquid, and subsequently, a second 90 g of sulfuric acid was continuously added for 15 minutes in order to neutralize the residual alkali and make it weaker acidic. The pH of the slurry at this time was 5.3. Weight ratio of titanium dioxide to total silica weight,%
(100 × TiO ₂ / SiO ₂ ) is 10%, the weight ratio of the second silica to the weight of the first silica,% (100
× Second time SiO ₂ / first time SiO ₂ ) was 5%.

Next, 1500 g of glass beads having a diameter of 2.0 to 2.6 mm were added to the slurry containing this reaction product, and the mixture was heated at 50 ° C. while being heated by a three-one motor to 4 times.
The mixture was stirred at 50 rpm for 9 minutes and pulverized, and the slurry was passed through a JIS 200 mesh standard sieve.
The residue that did not pass through the sieve was removed. The average particle diameter of the composite particles was 8.86 μm as measured by the laser diffraction type particle size distribution measuring device, and 85.4% of the composite particles were in the range of 1 to 30 μm. The composite particle slurry that passed through the sieve was filtered with a Buchner funnel to obtain cake-like composite particles, which were dispersed in water, stirred, and re-slurried to adjust the slurry concentration to 8%.

Next, bleached softwood kraft pulp (NBK
P) 15%, thermomechanical pulp (TMP) 34
%, Mechanical pulp (GP) 11%, and newspaper deinked waste paper pulp (DIP) 40%, 25 g of an absolutely dried mixed pulp is dispersed in tap water and diluted to 2 liters to obtain a 1.25% concentration pulp slurry. In this, the composite particle slurry,
The pulp was added so as to have a composite particle content of 3% per dry weight, and after stirring for 2 minutes, a sulfuric acid band (Al ₂ (SO ₄ ) ₃
18H ₂ O) was added to the pulp at a dry weight of 1%, the whole was diluted to 12.5 liters by stirring for 2 minutes, and thoroughly mixed, and then the basis weight was 40.0 using a TAPPI standard square sheet machine.
Paper of g / m ² was made and dried.

The handmade sheet was conditioned in a room at a temperature of 20 ° C. and a relative humidity of 65%, passed through a laboratory machine calender twice at a linear pressure of 40 kg / cm to adjust the smoothness, and then the whiteness and An opacity paper quality test and a printing test were conducted by the following test methods for evaluation. The test method used is as follows. (1) Whiteness It was measured according to JIS P 8123. (2) White paper opacity Measured according to JIS P 8138, reflectance 89.
A 5% backing plate was used. (3) Opacity after printing Solid printing having a size of 11 × 21 cm was performed by an RI printing tester using a newspaper offset ink, and the opacity Y (%) after printing was defined by Formula 1. Y (%) = {(reflectance of back surface after printing) / (reflectance of unprinted back surface)} × 100 (1)

Further, the manufacturing cost and comprehensive evaluation were carried out according to the following criteria. The manufacturing cost is "relatively cheap" for TiO ₂ / SiO ₂ = 5% or less, "normal" for more than 5% and 10% or less, "moderately high" for more than 10% and 25% or less.
△ ”, those exceeding 25% were displayed as“ high, x ”.
The overall judgment is that the whiteness is 53.0% or more, the white paper opacity is 84.0% or more, the opacity after printing is 86.0% or more, and the manufacturing cost is ◎, "the best, ◎", and the characteristics are "Good, good" if the manufacturing cost is △ or more, but "bad, △" if the manufacturing cost is bad,
If any one of the characteristics did not reach the above numerical value, it was displayed as "very bad, x". Manufacturing cost: ◎ ~ relatively cheap, ○ ~ normal, △ ~ moderately high, × ~ high Comprehensive evaluation: ◎ ~ best, ○ ~ good, △ bad, × ~ very bad

Example 2 240 g of a commercially available aqueous solution of sodium silicate No. 3 (manufactured by Tokuyama Soda, solid content concentration 30%) was diluted to 1000 g with pure water to obtain a silica (silicon dioxide) concentration of 72 g / kg and 2 liters. Place in a stainless beaker, add 17.9 g of anhydrous sodium sulfate at a temperature of 50 ° C., and continuously add 72 g of sulfuric acid (concentration 20%) (40% of mineral acid necessary for neutralization) over 15 minutes while stirring with a three-one motor. Was added to. After the first addition of mineral acid, stir 1
The temperature was raised to 85 ° C. in 5 minutes. Stirring is continued as it is at this temperature for aging for 60 minutes, then the temperature is raised to 95 ° C., and 36 g of sulfuric acid for the second time is continuously added to adjust the pH to 1
After setting to 0.9, 9.7 g of titanium dioxide (JA-2, average particle size 250 nm, manufactured by Teika) was added. afterwards,
To the slurry, 350 g of a sodium silicate aqueous solution having a silica concentration of 72 g / kg was added to the slurry, followed by neutralizing the remaining alkali to make the acid weaker by adding 135 g of sulfuric acid for the third time in 15 minutes. It was continuously added, and after this sulfuric acid was added, it was aged at 95 ° C. for 30 minutes. P of the slurry at this time
H was 5.7.

The weight ratio of titanium dioxide to the total silica weight,% (100 × TiO ₂ / SiO ₂ ) is 10%, the weight ratio of the second silica to the weight of the first silica,%
(100 x 2nd SiO ₂ / 1st SiO ₂ ) is 35%
Met. Then, the obtained slurry was wet-milled in the same manner as in Example 1, the slurry was passed through a JIS 200 mesh standard sieve, and the residue not passing through the sieve was removed. The average particle size of the composite particles was 7.35 μm as measured by the laser diffraction type particle size distribution measuring device,
The content in the range of 1 to 30 μm was 81.4%. Using the composite particles that passed through the sieve, a handmade paper having a basis weight of 40.0 g / m ₂ was prepared and tested in the same manner as in Example 1.
The quality was evaluated.

Example 3 The amount of crystalline titanium dioxide added was 15.1 g, the amount of the second aqueous sodium silicate solution (silica concentration 72 g / kg) was 50 g, and the third amount of sulfuric acid was added. 81
A composite particle slurry was prepared in the same manner as in Example 2 except that g was used, and the obtained composite particle slurry was evaluated in the same manner as in Example 1. Weight ratio of titanium dioxide per total silica _{weight,% (100 × TiO 2 /} SiO 2)
Is 20%, the weight ratio of the second silica to the weight of the first silica,% (100 × second SiO ₂ / first Si
O ₂ ) was 5%. The average particle size of the obtained composite particles was 7.97 μm, and the average particle size of 1 to 30 μm was 82.9%.

Example 4 In the same manner as in Example 2, the first sulfuric acid was added, the mixture was aged for 60 minutes, heated to 95 ° C., and then the second sulfuric acid 3 was added.
6 g was added. Then crystalline titanium dioxide 4.0
g was added, and the slurry was dispersed in a homomixer for 5 minutes for treatment. The average particle size of the silica particles at this time is 2
It was 4.3 μm. Subsequently, 100 g of a second sodium silicate aqueous solution (silica concentration: 72 g / kg) was added, and then a third sulfuric acid solution was added to neutralize the remaining alkali.
0 g was continuously added over 15 minutes, and after addition of sulfuric acid, the mixture was aged at 95 ° C. for 30 minutes. The pH of the aqueous solution at this time was 5.3. Then, the obtained slurry liquid was pulverized, classified, filtered and re-dispersed in the same manner as in Example 1 to obtain a slurry of composite particles. Titanium dioxide weight ratio based on total silica weight,
% (100 × TiO ₂ / SiO ₂ ) is 5%, the weight ratio of the second silica to the weight of the first silica,% (10
0 × second SiO ₂ / first SiO ₂ ) was 10%. The obtained composite particles have an average particle size of 10.56 μm,
The content of 1 to 30 μm was 95.1%. or,
Using this slurry, a handmade sheet was prepared in the same manner as in Example 1 and evaluated.

Example 5 In the same manner as in Example 2, the first sulfuric acid was added, the mixture was aged for 60 minutes, heated to 95 ° C., and then the second sulfuric acid 5 was added.
4 g were added. Then, the slurry was subjected to dispersion treatment with a homomixer until the average particle size of silica particles reached 10.4 μm, and then 7.6 g of crystalline titanium dioxide was added. Subsequently, 50 g of a second aqueous solution of sodium silicate (silica concentration 72 g / kg) was added, and further 63 g of sulfuric acid was continuously added for 15 minutes to neutralize the remaining alkali. Aged for 30 minutes at temperature. At this time, the pH of the slurry liquid was 5.1. Then, the obtained slurry liquid was classified, filtered, and re-dispersed to obtain a slurry of composite particles. Weight ratio of titanium dioxide per total silica _{weight,% (100 × TiO 2 /} SiO 2)
Is 10%, the weight ratio of the second silica to the weight of the first silica,% (100 × second SiO ₂ / first Si
O ₂ ) was 5%. The average particle size of the obtained composite particles was 9.40 μm, and the average particle size of 1 to 30 μm was 94.9%. Further, using this slurry, a handmade sheet was prepared in the same manner as in Example 1 and evaluated.

Example 6 In the same manner as in Example 2, the first sulfuric acid was added, the mixture was aged for 60 minutes, the temperature was raised to 95 ° C., and then the second sulfuric acid 108 g was added.
Was added continuously. After that, the slurry was dispersed and processed in a homomixer for 5 minutes. The average particle size of the silica particles at this time was 30.6 μm. Next, 7.9 g of crystalline titanium dioxide was added, 100 g of a second aqueous sodium silicate solution (silica concentration 72 g / kg) was continuously added for 15 minutes, and then 20 g of sulfuric acid for the third time was added for 3 minutes. Was continuously added. The pH of the slurry liquid at this time is 4.1.
Met. Then, the slurry liquid containing the obtained composite particles was pulverized, classified, filtered and re-dispersed in the same manner as in Example 1 to obtain a composite particle slurry. Weight ratio of titanium dioxide per total silica _{weight,% (100 × TiO 2 /} SiO 2)
Is 10%, the weight ratio of the second silica to the weight of the first silica,% (100 × second SiO ₂ / first Si
O ₂ ) was 10%. The average particle size of the composite particles is 8.
Those of 92 μm and 1 to 30 μm contained 84.2%. Further, using this slurry, a handmade sheet was prepared in the same manner as in Example 1 and evaluated.

Example 7 In the same manner as in Example 2, sulfuric acid was added for the first time and aged for 60 minutes, and then the slurry was dispersed in a homomixer for 5 minutes and treated. The average particle size of the silica particles at this time was 28.6.
μm. Next, crystalline titanium dioxide was added to 19.5.
g, and the second sodium silicate solution (silica concentration 72
g / kg) 350 g at once, and then sulfuric acid 17
1 g was continuously added over 15 minutes, and then aged for 30 minutes while stirring. Thereafter, the obtained slurry liquid was pulverized, classified, filtered and redispersed in the same manner as in Example 1 to obtain a slurry liquid of composite particles. Weight ratio of titanium dioxide per total silica _{weight,% (100 × TiO 2 /} SiO 2)
Is 20%, the weight ratio of the second silica to the weight of the first silica,% (100 × second SiO ₂ / first Si
O ₂ ) was 35%. The obtained composite particles had an average particle size of 8.37 μm, and contained 18.6 μm of 88.6%. Further, using this slurry, a handmade sheet was prepared in the same manner as in Example 1 and evaluated.

COMPARATIVE EXAMPLE 1 Except that the amount of crystalline titanium dioxide added was 7.2 g and the amount of the second aqueous sodium silicate solution (silica concentration 72 g / kg) added after titanium dioxide was 5 g. Composite particles were produced in the same manner as in Example 2, and a handmade sheet was prepared using the composite particles and evaluated. Weight ratio of titanium dioxide to total silica weight,% (100 × TiO 2
₂ / SiO ₂ ) is 10%, the weight ratio of the second silica to the weight of the first silica,% (100 × second SiO
₂ / first SiO ₂ ) was 0.5%. The average particle size of the composite particles is 7.06 μm, and that of 1 to 30 μm is 8
3.1%.

Comparative Example 2 Except that the amount of crystalline titanium dioxide added was 11.5 g and the amount of the second aqueous sodium silicate solution (silica concentration 72 g / kg) added after titanium dioxide was 600 g. Composite particles were generated in the same manner as in Example 1, and a handmade sheet was prepared using the composite particles and evaluated. Weight ratio of titanium dioxide to total silica weight,% (100 x
TiO ₂ / SiO ₂ ) was 10%, and the weight ratio of the second silica to the weight of the first silica,% (100 × second SiO ₂ / first SiO ₂ ) was 60%. The average particle size of the composite particles is 8.4 μm, and the average particle size of 1 to 30 μm is 9
3.3%.

Comparative Example 3 Composite particles were produced in the same manner as in Example 4 except that the second aqueous solution of sodium silicate was not added after the dispersion treatment with a homomixer, and the composite particles were hand-made. A sheet was created and evaluated. Weight ratio of titanium dioxide to total silica weight,% (100 × TiO ₂ / Si
O ₂ ) was 5%, the weight ratio of the second silica to the weight of the first silica, and% (100 × second SiO ₂ / first SiO ₂ ) was 0%. The average particle size of the composite particles was 8.7 μm, and the average particle size of 1 to 30 μm was 85.2%.

Comparative Example 4 The amount of crystalline titanium dioxide added was 24.3 g, and the second aqueous sodium silicate solution (72 g) was added after titanium dioxide was added.
/ Kg), except that the addition amount of 250 g was set to 250 g, composite particles were produced in the same manner as in Example 4, and using this, a handmade sheet was prepared and evaluated. Weight ratio of titanium dioxide to total silica weight,% (100 × TiO ₂ /
SiO ₂ ) is 30%, the weight ratio of the second silica to the weight of the first silica,% (100 × second SiO ₂ /
The first time SiO ₂ ) was 25%. The average particle size of the obtained composite particles is 7.14 μm, and the average particle size of 1 to 30 μm is 7
It was 7.3%.

Reference Example For comparison, a handmade sheet was prepared and evaluated in the same manner as in Example 1 without using any filler. The results obtained in Examples, Comparative Examples and Reference Examples are shown in Table 1.

[0048]

[Table 1]

As is clear from Table 1, the composite particles obtained by the method of the present invention can impart high whiteness and opacity, and particularly excellent post-printing opacity to the paper in which the composite particles are internally added ( Examples 1-7). On the other hand, when the addition amount of the second sodium silicate solution after the addition of titanium dioxide is large (Comparative Example 2), the opacity after printing and the opacity of white paper cannot be sufficiently improved. This is presumably because the titanium dioxide particles were covered with secondary particles of silica due to the large amount of silica added, and the scattering ability of titanium dioxide was impaired. On the contrary, when the sodium silicate solution after addition of titanium dioxide is not added at all even after the dispersion treatment (Comparative Example 3), or when the amount of sodium silicate added is small (Comparative Example 1), It is considered that the ability to improve the opacity after printing and the opacity of white paper is insufficient due to the small amount of titanium dioxide fixed. Further, when the amount of titanium dioxide is large relative to silica (Comparative Example 4), the effect of the composite particles is high, but the production cost of the composite particles obtained is high because expensive titanium dioxide is used, which is uneconomical. .

[0050]

As described above, according to the present invention, the ratio of composite of titanium dioxide to silica particles is increased to obtain excellent whiteness and opacity, and particularly excellent opacity after printing. It is effective to provide a composite particle of titania and silica that can be applied to the above, and a method for producing the same.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kaoru Kaden 1-10-6 Shinonome, Koto-ku, Tokyo Shinoji Paper Machinery Co., Ltd. Shinonome Research Center

Claims (6)

[Claims] 1. A mineral acid is added to an alkali silicate aqueous solution,
A method for producing composite particles of titania and silica comprising secondary particles of titanium dioxide and silicon dioxide, after the secondary particles of silica are formed, titanium dioxide is added, and then mineral acid is added and neutralized. , The first mineral acid was added to the alkali silicate aqueous solution at a temperature of 20 to 55 ° C., and the temperature was adjusted to 65 to
Secondary particles of silica are generated while the temperature is raised to 95 ° C.,
Then, crystalline titanium dioxide was added so that the ratio of TiO ₂ / total SiO ₂ was 2 to 25% by weight, and then an additional alkali silicate aqueous solution was added to the silica contained in the alkali silicate aqueous solution at the start of the reaction. PH of slurry obtained by adding 2 to 40% by weight based on weight, and then adding mineral acid
In the range of 3 to 6.5, and then pulverizing and / or classifying with a wet method, and a method for producing composite particles of titania and silica. 2. From the start of the production of secondary particles of silica,
2. The high shearing force is applied to the slurry at least once before the addition of the mineral acid for adjusting the pH of the slurry to the range of 3 to 6.5, whereby the slurry is dispersed. A method for producing composite particles of titania and silica. 3. After depositing secondary particles of the silica,
The method for producing composite particles of titania and silica according to claim 1 or 2, wherein mineral acid is added to adjust the pH to a range of 8 to 12, and then crystalline titanium dioxide is added. 4. A mineral acid is added to an alkali silicate aqueous solution,
4. When forming secondary particles of silica, 30 to 70% by weight of a mineral acid necessary for neutralizing the aqueous alkali silicate solution is added, and a mineral acid is added. Item 1. A method for producing composite particles of titania and silica according to item 1. 5. A secondary particle size of silica measured by a laser diffraction type particle size distribution measuring device after applying a high shearing force to a slurry containing secondary particles of silica to disperse the slurry is 3 to 40 μm.
The method for producing composite particles of titania and silica according to any one of claims 1 to 4, wherein: 6. 80 to 99% by weight of particles having a mean particle size of 3 to 30 μm and a particle size of 1 to 30 μm measured by the particle size analyzer, of the composite particles of titania and silica after wet pulverization and / or classification. The method for producing composite particles of titania and silica according to any one of claims 1 to 5, characterized in that: